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BY 4.0 license Open Access Published by De Gruyter November 6, 2019

Toxicity of metallic nanoparticles in the central nervous system

  • Krzysztof Sawicki EMAIL logo , Magdalena Czajka , Magdalena Matysiak-Kucharek , Berta Fal , Bartłomiej Drop , Sylwia Męczyńska-Wielgosz , Katarzyna Sikorska , Marcin Kruszewski and Lucyna Kapka-Skrzypczak
From the journal Nanotechnology Reviews


Metallic nanoparticles due to their small size and unique physico-chemical characteristics have found excellent applications in various branches of industry and medicine. Therefore, for many years a growing interest has been observed among the scientific community in the improvement of our understanding of the impact of nanoparticles on the living organisms, especially on humans. Considering the delicate structure of the central nervous systemit is one of the organs most vulnerable to the adverse effects of metallic nanoparticles. For that reason, it is important to identify the modes of exposure and understand the mechanisms of the effect of nanoparticles on neuronal tissue. In this review, an attempt is undertaken to present current knowledge about metallic nanoparticles neurotoxicity based on the selected scientific publications. The route of entry of nanoparticles is described, as well as their distribution, penetration through the cell membrane and the blood-brain barrier. In addition, a study on the neurotoxicity in vitro and in vivo is presented, as well as some of the mechanisms that may be responsible for the negative effects of metallic nanoparticles on the central nervous system.

Graphical abstract: This review summarizes the current knowledge on the toxicity of metallic NPs in the brain and central nervous system of the higher vertebrates.

1 Introduction

Nanotechnology is the design, production and application of structures, materials and devices sized at nanometre scale. It is assumed that nanoparticles (NPs) are structures having a critical dimension of less than 100 nm. Because of their size, greater surface area and volume to mass ratio, NPs present unique optical, mechanical, chemical, electrical and magnetic properties that makes them more reactive, compared to their bulk counterparts [1, 2, 3]. NPs can stimulate and affect certain cells, inducing and multiplying the desired physiological effects. On the other hand, NPs, due to their size comparable to biological molecules, can easily pass through cell membranes, penetrate cellular organelles and interfere with the normal cell physiology, and, as a result, cause damage at the cellular and sub-cellular level and/or triggering different cell/tissue responses [4, 5, 6, 7, 8].

The progress of nanotechnology has led to the development and commercialization of hundreds of products containing NPs. Nanotechnology offers many opportunities and benefits for medicine, energy production, environmental protection, the food industry, electronics, science, computer technology, cosmetics, textiles, agriculture and the defence industry [1, 3, 4, 5, 9, 10, 11]. Large scale production and use of NPs can lead, however, to unintentional human and the environmental exposure to this potentially hazardous substances [10, 12]. According to the Wilson Centre data, exposure to 45% among the 580 catalogued NPs have been classified as potentially dangerous [13]. The potential risk of exposure to toxic NPs becomes a burning issue for today’s science, despite their wide use and many beneficial applications [10]. Although to-date no human disease has been officially attributed directly to NPs, certain studies that have been conducted suggest that some NPs may cause adverse biological reactions, leading to toxic effects [9].

Humans could be exposed to metallic oxide NPs from different environmental and occupational sources. NPs can come from natural phenomena, such as volcanic activity, or as a result of industrial processes with a lot of metal fumes, e.g. cutting, grinding, melting, casting and welding. Another potential source of human exposure to metallic NPs is its intentional use in commercial products, such as vectors of drugs, sunscreens, toothpaste, cosmetics, plastic products, textiles, paints, and gasoline components [9, 14, 15, 16, 17]. Despite their origin, NPs can penetrate into the body by a number of different routes, including injection, inhalation or ingestion. Then, circling with blood, they can penetrate and accumulate in different organs and tissues including central nervous system (CNS) [9, 18, 19].

Some NPs seem to be very suitable for medical applications, such as drug delivery vectors or theranostics for therapeutic and diagnostic procedures [20]. Metal oxides are currently one of the most important tools used in the diagnosis of diseases (contrast to MRI, fluorescent dyes), drug delivery systems (photosensitizers), genes, antimicrobial substances, as well as scaffolding materials in tissue reconstruction [2, 3, 9, 18, 21]. Metallic NPs can resonate in the magnetic field, thus delivering energy directly to the target cancer cells [20]. Due to the increasing use of metallic NPs in medicine, more and more attention is paid to the safety of using NPs for CNS [22]. Numerous studies indicate inability of blood-brain barrier (BBB) to protect against NPs translocation to the brain [23]. Compared to other types of cells, nerve cells are more sensitive to toxins due to their limited ability to regenerate [24]. Thus, it is important to reliably analyze the neurotoxic impact of metallic NPs on the brain. Acquired knowledge can be used to develop safety guidelines for the potential use of NPs in industry and medicine, to minimize the negative health effects on the CNS [25].

The presented review is an attempt to summarize the current knowledge on the toxicity of metallic NPs in the brain and CNS of the higher vertebrates.

2 Modes of exposure in vivo and distribution of internalized NPs

Metallic NPs, due to their small size and specific physico-chemical properties, can penetrate into living organisms through various modes of exposure, for example, inhalation or ingestion. In general, smaller NPs show a greater accumulation in the organs and induce a higher toxicity, compared to larger NPs [26]. Thus, it is important to fully understand the mechanisms responsible for their distribution and penetration into the target organs, and the effects that they might have there [27].

Several studies support the concept that the CNS may be a potential target for inhaled NPs [28, 29]. Inhalation is one of the main route of unintentional human exposure to metallic NPs. Due to the small size, NPs efficiently bind to nose mucosa [30] or reach into bronchi and alveoli in the lung [31, 32]. From the nasal cavity, NPs are further transported by olfactory epithelium and migrate along primary olfactory neurons to the glomeruli of the olfactory bulb, olfactory nerve or trigeminal, or the blood- cerebral spinal fluid to the choroid plexus [3, 31]. Transport via the olfactory nerve, is a direct way of penetration of NPs to the brain, bypassing the BBB [33]. This has been demonstrated for several metal NPs, e.g. ultrafine silver NPs (Ag NPs) [34], CdSe/ZnS quantum dots (CdSe/ZnS QDs) [35], copper oxide NPs (CuO NPs) [36], ultrafine manganese dioxide NPs (MnO2 NPs) [37] or titanium dioxide NPs (TiO2 NPs) [38, 39].

On the other hand, inhaled metal NPs can also get into the alveoli epithelial cells and further to blood and lymph circulation, finally accumulating in potentially sensitive target sites, such as the brain, bone marrow, lymph nodes, spleen or heart [18, 40, 41]. The process was observed for aluminum oxide NPs (Al2O3 NPs) [12, 40] or lead NPs (Pb NPs) [42]. Also, it is postulated that small metal NPs are uptaken inside the alveoli by macrophages and dissolved in the phagosomes. It was shown that ions were released even from the oxidized form of NPs, which are not normally soluble. Released ions can easily penetrate BBB [14].

A digestive rout is also important way of penetration of NPs into the body. It is postulated that NPs are absorbed by epithelial cells in the digestive system, from where they can further penetrate into bloodstream and secondary organs. NPs are mainly absorbed by M cells found in Peyer’s patches through the transcytosis mechanism. It was also shown that extracellular transport through tight junctions (TJ) of epithelial cells might be involved; however, this applies only to very small NPs (d=0.5-6 nm) [43]. Loeschner et al. have shown that the digestive route constituted an important source of exposure to Ag NPs. They observed in rats after 28 days of dietary exposure to Ag NPs (14±4 nm) that Ag NPs were uptaken by the M cells and enterocytes [44]. The amount of NPs uptaken via digestive rout correlate with the size and charge of NPs. Twenty four hours after administration of different size gold NPs (Au NPs) (1.4-200 nm) with negative/positive charge, the highest accumulation in secondary organs (lung, spleen, heart) was for the smallest (1.4 nm), negatively charged NPs. In contrast, the highest accumulation in the brain was observed for NPs with a diameter of 18 nm [43].

Several studies, such as those on rats exposed to TiO2 NPs [45, 46, 47] or porcine exposed to TiO2 NPs or zinc oxide NPs (ZnO NPs) [48], demonstrated the inability of NPs to penetrate into the dermis or into the live layers of skin. This may be due to the ability of metallic NPs to form larger aggregates, as well as having a surface charge which prevents penetration to the stratum corneum (SC) and the deeper layers of the skin. Thus, it is believed that the inorganic NPs are not able to penetrate intact healthy skin. This is very important in the context of application of many metallic NPs, as a component of certain ointments and creams commonly used by people.

The CNS of vertebrates is isolated from the rest of body by BBB. Normal functioning of BBB is critical for homeostasis. BBB is responsible for the active exchange of nutrients and metabolites between the blood and brain, prevention of the xenobiotics penetration to the brain, and restricting immune cell infiltration [4]. Selective permeability is a result of the complex structure and biochemical properties of the brain capillary endothelial cells (BCEC), such as leakproof TJ connections and minimal endocytotic activity to prevent penetration of harmful substances from the blood directly to the brain [49, 50].

Nonetheless, Chen et al., showed that exposure of mice to aluminum NPs (Al NPs) caused disturbances in the normal functioning of TJ, which was associated with increased permeability of the BBB and further damage to brain tissue [4]. Moreover, high level of expression of transferrin receptor in BCEC cells may facilitate transcytosis across the BBB [51]. In line, Au NPs were capable of penetrating through the BBB and accumulating in the brain, after intravenous administration [52] or intraperitoneal administration in mice [20]. Further, the ability to penetrate the BBB and accumulation in the brain was demonstrated for many metallic NPs, such as Al NPs [53], Ag NPs [54], CuO NPs [55], manganese NPs (Mn NPs) [14] and TiO2 NPs [56]. In the brain, NPs are able to enter neurons and move along axons or dendrites to other connected neurons [57]. Transneuronal transport may occur through the synaptic connections, endocytosis or passive diffusion [58].

3 Cellular uptake

Metallic NPs can enter to the cell via interaction with components of its membrane. The main mechanism of their cellular uptake is endocytosis. During endocytosis, the absorption of NPs occurs through membrane invaginations, then their budding and pinching off to form endocytic vesicles, transported to specialized intracellular compartments [9, 59, 60, 61]. Endocytosis is classified into several types depending on molecules involved in the process. The two main classes of endocytosis are phagocytosis and pinocytosis. In addition pinocytosis can be further divided into four subclasses depending on the size of vesicles and proteins involed for their formation. On this basis, pinocytosis is differentiated into clathrin-mediated endocytosis, caveolae-dependent endocytosis, clathrin/caveolae independent endocytosis and macropinocytosis [62]. In contrast to phagocytosis, which takes place primarily in specialized phagocytes, pinocytosis are more prevalent and occurs in many kinds of cells. Interestingly, metallic NPs uptake in neurons and glial cells, also mainly based on the endocytosis process, includes all its types, even phagocytosis [61, 63, 64]. Research on astrocyte-rich primary cultures indicated endocytosis as the uptake mechanism of Ag NPs [65]. Comparable, the ZnO NPs were absorbed by neuronal cells line PC12 through endocytosis, which was required for interneuron translocation of these NPs [66]. The iron NPs (Fe NPs) coated with dimercaptosuccinic acid were also efficiently taken into astrocytes. Transmission electron microscopy showed their congregations in intracellular vesicles. Due to the negative charge, as indicated by their zeta potential, the mechanism of passive diffusion was excluded [67].

Clathrin-mediated endocytosis leads to the formation of clathrin-coated vesicles and it is the main mechanism for nutrients and membrane components cellular uptake. In contrast, another mechanism, the caveolae-dependent endocytosis, is equally important and participates in many biological processes, among others transcytosis, signaling and nutrients regulation and depends on the integral membrane protein – caveolin. Clathrin/caveolae independent endocytosis goes through other pathways, without the involvement of these proteins. The unique pinocytosis process of forming membrane extension or ruffles as a result of cytoskeleton reorganization is macropinocytosis. As a consequence of these membrane changes the large amount of extracellular fluid with dissolved molecules is collected, regardless of the presence of any specific receptors [68, 69]. Luther et al. showed that Fe NPs were successfully taken up by microglial cells chiefly through macropinocytosis and clathrin-mediated endocytosis, in the course of which absorbed particles were directed into the lysosomal compartment [70]. A predominance of endocytosis was also observed in another study on neural stem cells incubated with Ag NPs [71]. Likewise, the uptake of TiO2 NPs by glial cells was based on the mechanism of endocytosis. However, chemical immobilization of the cytoskeleton significantly reduced the entry of TiO2 NPs into the cells, suggesting macropinocytosis as the main process of their uptake [72].

In addition to various types of pinocytosis, metallic NPs may enter to the interior of the cell through the phagocytosis mechanism. Typically, the opsonization of NPs by immunoglobulins or other blood proteins precedes this process and enables recognition by the appropriate cells. This initiates a signaling cascade that allows engulfing and internalization of NPs to form so-called "phagosomes" [61]. Valentini et al. observed a characteristic phenotype of activated microglia cells caused by the presence of TiO2 NPs. Their morphological changes, such as the larger size and formation of membrane protrusions typical of phagocytosis, indicated the uptake of TiO2 NPs through this process [73].

Some studies indicated that various types of endocytosis might act simultaneously for the metallic NPs uptake by neuron- and glia-like cells. TiO2 NPs were mainly taken by astrocyte-like ALT cells and BV-2 microglia via disparate types of endocytosis: clathrin-mediated endocytosis and caveolae-dependent endocytosis in ALT cells, phagocytosis and clathrin-mediated endocytosis in BV-2 cells [74]. An analogous research of the absorption of Ag NPs showed less uptake by neuroblastoma N2a cells, as compared to ALT and BV-2 cells. In ALT cells prevailed phagocytosis and clathrin/caveolae independent endocytosis, while in BV-2 Ag NPs were taken mainly by micropinocytosis and clathrin-mediated endocytosis [75].

4 Toxicity of NPs

4.1 Toxicity in vitro

Numerous reports indicate detrimental effects of metallic NPs on neural cells in culture. In a triple coculture BBB model consisting of microvascular endothelial cells, astrocytes and pericytes exposed to Ag NPs, Xu et al. observed a severe shrinkage of mitochondria, endoplasmic reticulum expansion and vacuolations in astrocytes. An analysis of gene expression showed changes in 23 genes associated with metabolic and biosynthetic processes, cell death and response to stimuli. Another research on primary rat cortical cells showed that Ag NPs disrupted development and functioning of the nervous system. Ag NPs were toxic to nerve cells by causing abnormalities in formation of cytoskeleton, pre- and post-synaptic proteins, and functioning of the mitochondria, leading to cells death [76]. In line, Coccini et al. observed toxic effects after shortterm (4-48 h, 1-100 μg/ml) or long-term exposure (up to 10 days, 0.5-50 μg/ml), even at low doses (0.5 μg/ml) [77]. Size dependent toxicity of Ag NPs was also observed for organotypic mouse midbrain cells [78]. The mechanisms involved in Ag NPs-induced toxicity of primary cultures of rat cerebellar granule cells (CGCs) include activation of N-methyl-D-aspartate receptor, destabilization of mitochondrial function, production of free radicals [79], oxidative stress leading to caspase activation and apoptosis [80]. Apoptosis was also reported as a main cause to Ag NPs-induced death of N2A cells growing in co-culture with ALT and BV-2 cells. However, this was not a direct effect, because the NPs were effectively uptaken only by ALT and BV-2 cells. N2A cells death followed the release of toxic compounds, nitric oxide (NO) from BV-2 and hydrogen peroxide (H2O2) from ALT. These results suggested that the key factor in Ag NPs neurotoxicity may be the induction of reactive oxygen and nitrogen species by astrocytes and microglia [75]. The assessment of the effects of Ag NPs on human and rat embryonic neural stem cells (NSCs) led to similar conclusions. Apoptosis and necrosis of NSCs occurred as a result of increased mitochondrial production of reactive oxygen species (ROS) [81]. Huang et al. examined the effect of Ag NPs on the expression of genes involved in inflammation and neurodegenerative disorder on brain mouse neural cells. The study showed a significant increase in interleukin-1 beta (IL-1β) secretion, and increased expression of C-X-C motif chemokine 13, macrophage receptor with collagenous structure and glutathione synthetase (GSS). Furthermore, exposure to Ag NPs, formation of amyloid-β (Aβ) plaques responsible for Alzheimer’s disease [82].

Studies performed on astrocytes exposed to CuO NPs showed a significant decrease in viability, reduced lactate dehydrogenase activity and increased permeability of the cell membrane. Generation of ROS was point as a main cause of the CuO NPs toxicity [83]. ROS generation was also proposed as a main cause of time- and concentration-depended increase of apoptosis in CuO NPs treated HT-22 mouse hippocampal neuronal cells [84]. Impaired viability was also observed for cultured primary rat astrocytes exposed to CuO NPs. Moreover, Cu2+ ions released from CuO NPs induced nerve cells glycolytic flux, and synthesis of glutathione and metallothioneins [85]. CuO NPs and Ag NPs significantly increased release of prostaglandin E2, tumor necrosis factor (TNF), IL-1β in cells, while the Au NPs did not cause such an effect [86].

Rivet et al. studied the effect of the coating substance on the toxicity of encapsulated supermagnetic iron oxide NPs (SPION, Fe3O4 NPs). In vitro studies on cortex neuronal cells indicated that the toxicity of SPION depended on the coating substance. The polydimethyloamine coating resulted in cell death at all tested concentrations due the rapid and complete disruption of the cell membrane, whereas aminosilane coating affected cell metabolic activity at higher concentrations, leaving the cell membrane intact. Coating with dextran, even at high concentrations, did not affect the viability of the cells [87]. Toxicity of Fe3O4 NPs on brain cells was also studied by De Simone et al. They developed two types of CNS spheroids from SH-SY5Y neuron-like cells and human D384 astrocytes. After short-term (24 or 48 h, 1-100 μg/ml) and long-term (30 days,0.1-25μg/ml) exposure of 3D-spheroids to Fe3O4 NPs a cytotoxic effect was observed, more pronounced for neurons compared to astrocytes [23]. Other studies have shown that Fe3O4 NPs induced oxidative stress and activation of c-Alb tyrosine kinase, which was associated with neurotoxicity. In addition, Fe3O4 NPs caused alterations in the α-synuclein expression associated with neuronal damage, occurring among others in Parkinson’s and Alzheimer’s diseases [88].

In a study conducted by Wang et al., it was shown that Mn NPs, Ag NPs, and Cu NPs caused dopamine (DA) depletion by alteration of the expression of dopaminergic system-related genes, associated with induction of oxidative stress in PC12 cells treated for 24 h [89]. In line, a concentration-dependent decrease in the synthesis of DA by PC12 cells exposed to Mn NPs [57]. Unlike most metallic NPs, cerium dioxide NPs (CeO2 NPs) were not cytotoxic in neuronal cells and had antioxidant activity, inhibiting ROS production. Despite this results, disruption of redox balance inhibited neural stem cell differentiation [90]. Decrease in viability and increase of apoptosis were observed in primary cortical neurons after incubation with gallium trioxide NPs modified with chromium ions and hyaluronic acid (HA/Ga2O3:Cr3+ NPs). The toxicity was explained by activation of calpain and disruption autophagy signaling [91]. Also no toxicity was observed for 145 nm tungsten carbide particles (WC) in any of the cell lines tested including oligodendrocytes, rat primary neurons, rat primary astroglial cells, however, doping WC NPs with cobalt (WC – Co) resulted in an increase in the toxicity. The plausible explanation of the enhanced toxicity was increased oxidative stress and DNA damage [92].

Valdiglesias et al. compared the effects of two types of TiO2 NPs differing in crystal structure on the viability of nerve cell SH-SY5Y. The results indicate that a different structure of the NPs did not significantly impact on cells, as no decrease in cell viability was observed in neither case. Besides the NPs were efficiently taken-up by the cells, resulting in dose-dependent changes in cell cycle and genotoxicity, however not associated with formation of double-stranded breaks [93]. In contrast, low doses of TiO2 NPs caused cytotoxic effects in SH-SY5Y and glial cells D384, evidenced both after acute and prolonged exposure, and manifested as alterations of mitochondrial function and cell membrane damage [94]. In line, apoptosis associated with mitochondria-mediated and endoplasmic reticulum-mediated signaling was reported in primary cultured hippocampal neurons exposed to TiO2 NPs for 24 hours [95]. While Wu et al. observed that TiO2 NPs may directly interfere with rat PC12 neuronal function and cause damage mediated by activation of p53 and/or JNK pathway [96]. An alternative or supplementary mechanism of neurotoxicity was proposed by Xue et al. They observed a significant cytotoxicity of PC12 cells when the cells were incubated with supernatant from microglia culture exposed to TiO2 NPs and proposed that NPs-induced neurotoxicity corresponded to release of NO and pro-inflammatory factors, such as tumor necrosis factor alfa (TNFα) by the activated microglia cells [3].

Significant neurotoxicity was also observed in the rat and human neuronal cells in culture treated with ZnO NPs, however in this case toxicity was attributed rather to the action of Zn2+ than to NPs per se. ZnO NPs were uptaken via endocytosis, but low pH 5.5 in endosomes facilitated release of Zn2+ ions that penetrated to cytosol and disturbed divalent ions homeostasis, resulting in cell death [66].

The presented in vitro studies on the neurotoxicity of various metallic NPs confirmed induction of diverse adverse effects in CNS-derived cells. The vast majority of reports suggested that increased mitochondrial production of ROS and increased oxidative stress is a main mechanism of cytotoxicity of metallic NPs. This resulted in disruption of structure and function of other cell organelles, changes in gens expression, ionic imbalance and activation of apoptotic pathways. The effects of in vitro exposure to metallic NPs are summarized in Table 1.

Table 1

In vitro models for metallic nanoparticles neurotoxicity assessment.

NPsSize(nm)Surface coatingModelConcentrationExposure durationOutcomeReferences
Ag10NoneMurine astrocyte-like ALT, murine microglial BV-2 cells and murine neuroblastoma N2a cells1,3, 6 μg/ml24 h or 48 hAg NPs induced of ROS and NO production in astrocytes and microglia, which trigger apoptosis of neurons[75]
Ag20NonePrimary rat cortical cell cultures1,5,10, 50 μg/ml2,3 daysAg NPs induced toxicity in neurons, expressed as degradation of cytoskeleton components, perturbations of pre- and postsynaptic proteins expression, and mitochondrial dysfunction.[76]
Ag20NoneHuman neuronal SH-SY5Y cells and human glial D384 cells1-100 μg/ml (short-term) or 0.5-50 μg/ml (prolonged exposure)4-48 h (short-term) or up to 10 days (prolonged exposure)Ag NPs induced cytotoxic effects after short-term and prolonged exposure[77]
Ag20 and 110Citrate; polyvinylpyrrolidonePrimary organotypic mouse midbrain cells6.25,12.5, 25, 50 μg/ml24 hGreater cell susceptibility to the cytotoxic effects of smaller Ag NPs[78]
Ag<100NonePrimary rat cerebellar granule cells (CGCs)2.5-100 μg/ml24 hExcitotoxicity via activation of NMDA receptor, followed by calcium imbalance, destabilization of mitochondrial function and ROS production[79]
Ag22.1-26.2NonePrimary rat cerebellar granule cells (CGCs)0.01, 0.05, 0.1, 0.25, 0.5, 1, 2.5 μg/ml24 hAg NPs caused apoptosis based on the caspase activation-mediated signaling and oxidative stress[80]
Ag23NoneHuman and rat embryonic neural stem cells (NSCs)1, 5,10, 20 μg/ml24 hAg NPs increased mitochondrial production of ROS leading to cell apoptosis and necrosis[81]
Ag3-5NoneMurine brain astrocyte-like ALT, murine microglial BV-2 cells and murine neuroblastoma N2a cells5,10,12.5 μg/ml24 hAg NPs could alter gene and protein expressions of deposition potentially to induce AD progress in neural cells[82]
CeO210NoneNeuronal progenitor cells (C17.2)5-100 μg/ml24 and 28 hCeO2 NPs exhibited antioxidant activity and disturbed the redox balance, thus inhibiting cell differentiation[90]
Cu40,60NonePorcine brain15 μg/ml0-8 hCu NPs and Ag NPs caused[86]
Ag25, 40, 80microvesselsignificant pro-inflammatory
Au3,5endothelial cells (pBMECs)response (increased levels of PGE2, TNFa and IL-lß) that can influence the integrity of the BBB; Au NPs caused unremarkable pro-inflammatory response
CuO2,3-Primary brain10,100,1000 μM0-6 hThe CuO NP-induced toxicity was[83]
dimercaptosuccinic acidastrocytesaccompanied by an increase in the generation of ROS in the cells
CuO31NoneHT22 hippocampal cells5,10, 25 μg/ml with and without 5 μM crocetin24 hCuO NPs induced cytotoxicity in concentration- and time-dependent manner; that was associated with apoptosis and deregulation of Bax and Bcl-2 protein levels[84]
CuO52,3- dimercaptosuccinic acidPrimary rat astrocytes100 μM24 hCu2+ ions liberated from internalized CuO NPs stimulated glycolytic flux and synthesis of glutathione and metallothioneins[85]
the magnetite core diameter was 10;Aminosilane (Amine), dextran (D), poly-dimethylamine- co-epichlorhydrin-co- ethylendiamine (PEA)Primary cultured cortical neuron1,5, and 10% (v/v) of stock particle solution; The calculated mass concentrations of Amine, PEA and D particles are 39.3 mg/ml, 60.5 mg/ml and 53.1 mg/ml respectively; values supplied by the manufacturer: 25 mg/ml24 hFe3O4-PEA NPs induced cell death at all concentrations tested; aminosilane coated NPs affected metabolic activity only at higher concentrations, dextran-coated NPs partially altered viability at high concentrations[87]
1.2-20.2 and 48.7PolyvinylpyrrolidoneHuman neuronal SH-SY5Y cells and human glial D384 cells1-100 μg/ml (short-term) and 0.1-25 μg/ml (long-term exposure)24,48 h and 30 daysFe3 O4 NPs induced cytotoxic effect was more pronounced for neurons compared to astrocytes[23]
10 and 30NoneHuman neuronal SH-SY5Y cells10 μg/ml24 hFe3 O4 NPs reduced cellular dopamine content, induced alterations in the α-synuclein expression, oxidative stress and activation of c-Alb tyrosine kinase[88]
HA/Ga2O3:Cr3+125.7, 200.6 and 313.9Cysteine modified hyaluronic acid (HA)Primary cortical and SH-SY5Y neuronal cells1, 5, 25, 50,100 μg/ml12 hHA/Ga2 O3 : Cr3 + NPs induced calpain activation and disturbance of autophagy signaling[91]
Mn40NoneRat PC-12 cells1-100 μg/ml24 hMn NPs depleted DA, DOPAC, and HVA in a dose-dependent manner[57]
Mn Cu40 90NoneRat PC-12 cells10 μg/ml24 hEnzymatic alterations were involved in dopaminergic neurotoxicity induced by Mn NPs and Cu NPs[89]
TiO225NoneHuman SH-SY5Y neuronal cells20-150 μg/ml3, 6, 24 hTiO2 NP did not reduce the viability of neuronal cells but were effectively internalized by the cells and were found to induce dose-dependent cell cycle alterations, apoptosis by intrinsic pathway, and genotoxicity not related with DSB production[93]
TiO268.9-69.7NoneHuman neuronal SH-SY5Y cells and human glial D384 cells1.5-250 μg/ml (acute) and 0.05-31 μg/ml (prolonged exposure)4, 24, 48 h (acute) or 7-10 days (prolonged exposure)TiO2 NPs caused cytotoxic effects with alterations of the mitochondrial function and cell membrane damages[94]
TiO25-6NonePrimary cultured hippocampal neurons5,15, 30 μg/ml24 hHippocampal neuron apoptosis caused by TiO2 NPs may be associated with mitochondria-mediated signal pathway and endoplasmic reticulum-mediated signal pathway[95]
TiO220NoneRat PC-12 cells25, 50,100, 200 μg/ml6 and 24 hTiO2 -NPs induced damage of neurons via ROS and JNK/p53 mediated-apoptosis and caused G2/M arrest by activation of p53/p21 pathway[96]
TiO220NonePrimary microglia and rat PC-12 cells0.25, 0.5 mg/ml24 h or48 hTiO2NPs induced microglial activation and subsequently caused release of proinflammatory factors that contributed to dysfunction and cytotoxicity in PC12 cells[3]
WC (tungsten carbide), WC - Co145NoneOligodendrocyte precursor cell line OLN-93 and primary neuronal and astroglial cell cultures from cortices of Wistar rat fetuses7.5,15,30 μg/ml for WC NPs and 8.25,16.5, 33 μg/ml for WC-Co NPs3 daysDoping of WC NPs with Co noticeably increases their cytotoxic effect[92]
ZnO<50NoneRat PC-12 and human SH-SY5Y neuronal cells10,100,1000,1000024 hNewport-Green DCF-2 K+-conjugated ZnO NPs along with the membrane probe FM1-43 demonstrated endocytosis of ZnO NPs by PC12 cells; fluozin-3 measurement showed elevation of cytosolic Zn2+ concentration in cells[66]

4.2 In vivo toxicity in mammals

Neurotoxicity of metallic NPs has been confirmed in many mammalian studies. Chen et al. observed that Al NPs accumulated in the mouse brain endothelial cells, causing damage to the neurovascular system. Systemic administration of AlNPs resulted in elevated autophagy-related genes expression and autophagic activity in the brain, decreased tight-junction protein expression and increased BBB permeability [4].

The ability to cross BBB was further confirmed for Au NPs that were found in the brain of intraperitoneally administered mice, however, the concentration of gold in the brain was the lowest of all examined organs. Interestingly, no obvious toxicity to the CNS nor changes in behaviour of mice were observed [20]. In contrast, acute exposure of male Wistar rats to Au NPs resulted in a reduction of thiobarbituric acid reactive substances and carbonyl protein levels in the rats brain. In addition, suppression of catalase activity and inhibition of energy metabolism in hippocampus, striatum and cerebral cortex was observed. Interestingly, long-term exposure to Au NPs resulted only in inhibition of catalase in the brain and suppressed energy metabolism in cerebral cortex [97].

Also prolonged exposure of rats to citrate-stabilized Ag NPs caused a severe synaptic degeneration, mainly in the hippocampal region of brain,which may consequently lead to an impairment of normal nerve function and cognitive processes [98]. In line, Ag NPs given intragastrically to adult female rats induced a slight shrinking of the hippocampus, neuron shrinkage and swelling of astrocytes after 7-day exposure. The study also showed a significant increase of interleukin-4 (IL-4) in blood. Researchers suggested that neurodegeneration after exposure to Ag NPs occurred through inflammatory effects [99]. Neurotoxicity and impaired BBB functions were also observed after intraperitoneal administration attributed to the change of level of trace element in serum and brain, reduction of antioxidant enzyme activity, apoptosis and induction of inflammatory processes and down regulated tight junction proteins expression [100]. Similarly, chronic, intragastrically exposure of rats to low doses of Ag NPs resulted in the presence of silver in various parts of the brain, including the hippocampus and impairment of hippocampal dependent memory and cognitive coordination processes [101]. In contrast Dąbrowska-Bouta et al. showed in their studies on male Wistar rats that Ag NPs administered in low concentration did not cause visible neurotoxicity in behavioral tests; however, more accurate studies showed abnormalities in the myelin sheaths and an altered expression of myelin proteins [102].

Study conducted by An et al. have shown that CuO NPs accumulated in the brain when administered via intraperitoneal injection to adult male Wistar rats, and had a toxic effect on the hippocampus, inducing learning and memory deficits. The results suggested neuronal damage, induced by an imbalance of redox homeostasis that led to the impairment of hippocampal long-term potentiation (LTP) and poor performance of animals in behaviour tests [55]. Similarly, Liu et al. examined the effect of CuO NPs after nasal instillation into mice. They observed that NPs were taken directly to the brain by the olfactory bulb, and that exposure to CuO NPs resulted in severer lesions in the mouse brain, which could be due to the induction of oxidative stress in nerve cells [36]. In line, Bai et al. observed nerve damage to astrocyte cells and abnormal neurotransmitter levels in murine after intranasally instillation of Cu NPs [103]. It was also shown that in male Wistar rats CuO NPs impaired glutamate transmission presynaptically and postsynaptically that might result in diminished LTP and other cognitive deficits [25].

In yet other studies, rats were exposed orally to cadium oxide NPs (CdO NPs) by intratracheal instillation alone, or in sequential combination with CdCl2 solution. A 3-weeks oral administration, plus 1 week delivery to the trachea, resulted in significant loss in weight of the rats and decreased open field motility. In addition, the lengthening of latency evoked potentials of sensors, and the conduction velocity of the tail nerve was decreased [16]. Similar electrophysiological effects were observed after 4-12 weeks of oral or intratracheal exposure to cadmium [17, 104]. Translocation from the lungs to the secondary organs, such as the brain,was also reported for lead oxide NP (PbO NPs) after acute or subchronic PbO NPs inhalation by female mice. Inhaled PbO NPs caused mild pathological alterations in the hippocampus area [105].

In line, intranasal administration of Fe2O3 NPs caused damage to the olfactory bulb, hippocampus and striatum, likely due to elevated levels of ROS and NO causing neurons degeneration that occurred primarily in the CA3 area of hippocampus. In addition, excessive microglial cell recruitment, proliferation and activation, especially in the olfactory bulb, was observed and proposed as an additional cause of brain injury [32]. Interestingly, no induction of DNA damage was also observed in female Wistar rats exposed to Fe2O3 NPs or Fe2O3 bulk material, suggesting that Fe2O3 NPs did not have genotoxic potential [9]. Neurotoxic were also Fe3O4 NPs when administered directly into the dorsal striatum or hippocampus of mice. Fe3O4 NPs administration reduced TH+ fiber in both dorsal striatum and hippocampus and caused motor memory deficits, attributed to activation of MAPK and JNK signalling pathways [22].

In line, MnO2 NPs instilled into the trachea of adult male rats penetrated to the brain causing damage to nerve tissue. In addition, in the open field activity, the percentage of ambulation and rearing decreased, while local activity increased. The latency of the evoked potentials was lengthened, while the conduction velocity of the tail nerve decreased [41]. Also intratracheal exposure of mice to MnO NPs caused an increase in evoked potential latency and change in cortical electrical activity to the higher frequencies. Co-exposure with Fe3O4 NPs also resulted in increase in evoked potential latency [106]. Detrimental health effects were also observed for nickel oxide NPs (NiO NPs) and Mn3O4 NPs administered intraperitoneally to rats. Mn3O4 NPs were more harmful in the most nonspecific toxicity symptoms, and caused more nerve damage in the caudate nucleus and hippocampus, as compared to NiO NPs [107].

Despite the neurotoxicity manifested in exposed adult animals, several experiments showed that exposure to metallic NPs might be detrimental also for the future generations. Intragastrically exposure to TiO2 NPs of pregnant rats resulted in significant inhibition of cell proliferation in the hippocampus of the offspring and significantly impaired their learning skills and memory [108]. A similar study by Hong et al. demonstrated that exposure to TiO2 NPs of mice during pregnancy or lactation had detrimental effects on developing CNS in offspring. TiO2 NPs were shown to negatively affect the learning and memory processes. Researchers suggested that this might be the result of down regulation of Rac 1 and Cdc42 protein expression, and upregulation of Rho A protein expression, and increased ratio of RhoA/Rac 1 proteins [24]. This was further confirmed for intraperitoneally administered TiO2 NPs. The brains of foetuses from treated mice had changes in anatomical structure linked with perivascular edema [109].

On the other end, Amara et al. showed that acute intravenous injection of ZnO NPs to adult rats caused no changes in neurotransmitter contents (norepinephrine, epinephrine, DA and serotonin), nor deterioration in locomotor activity and spatial working memory [110]. No toxicity was also observed when ZnO NP were administered intraperitoneally [111]. Similarly, Shim et al. studied the effects of 28-day oral exposure of ZnO NPs on BBB tightness in rats. In line, no damage to BBB or the brain, nor behavioural changes were observed after 28-day oral exposure of ZnO NPs [112]. In turn, de Souza et al. demonstrated that environmentally relevant concentration of ZnO NPs cause behavioral changes of male Swiss mice [113]. Also Aijie et al. reported injury in cerebral cortex and hippocampus and impaired learning and memory of rats administered with NPs ZnO and TiO2. Interestingly, in this experimental set up the NPs were administered to tongue of male Wistar rats. The experiment confirmed that NPs can enter the CNS through the taste nerve pathway [114].

As demonstrated by many in vivo studies, metallic NPs are harmful to the rodents’ CNS. NPs easily translocate and accumulate in different regions of the brain, in particular in hippocampus striatum and cerebral cortex. Damage caused by metallic NPs may result in motor deficits, and impairment of learning and memory. The effects of in vivo exposure to metallic NPs are summarized in Table 2.

Table 2

In vivo models for metallic nanoparticles neurotoxicity assessment.

NPsSize (nm)Surface coatingModelConcentrationExposure durationOutcomeReferences
Ag10±4NoneMale Wistar rats0.2 mg/kg b.w.14 days, oral exposureAg NPs caused severe synaptic degeneration, mainly in the hippocampal region of brain[98]
Ag3-30NoneSix-week-old female Sprague-Dawley rats1,10 mg/kg b.w./day14 days, intragastricallyAg NPs induced neuronal degeneration, due to inflammatory effects[99]
Ag44.13NoneMale Wistar Albino rats50 mg/kg b.w.Intraperitoneally, 3 times a week, for 30 daysAg NPs induced neurotoxicity and disrupt BBB because of perturbation of serum and brain trace elements contents, reduction of antioxidant defense, and induction of inflammation and apoptosis, along with inhibition of expression of tight junction proteins[100]
Ag20±5Bovine serum albuminMale Wistar rats30 mg/kg b.w. or 1 mg/kg b.w.Orally via gavage, for 28 daysAg NPs induced detrimental effect on memory and cognitive coordination processes[101]
Ag10±4NoneMale Wistar rats0.02 mg /ml14 days, administration via gastric tubeNo differences between treated and control animals were observed in behavioral tests, however, transmission electron microphotographs showed abnormalities in myelin sheaths and altered expression of myelin proteins[102]
Ag<100NoneNile tilapia (Oreochromis niloticus) and Redbelly tilapia (Tilapia zillii)2 and 4 mg/124,48 and 96 h, aqueous exposureAg NPs (2 mg/1) stimulated the brain antioxidant system, but inhibited it at high concentration[122]
Ag39.4Fluorescenta,b) See-througha) 1mg/1a,b) 3 days,Ag NPs shifted into the yolk and[124]
polystyrenemedaka (Oryziasb) 30 mg/1aqueous exposuregallbladder during embryonic
latipes, ST II strain) eggsc) 10 mg/1c) 7 days, aqueous exposuredevelopment; NPs were capable of penetrating BBB and reach the brain;
c) adults see-through medaka (Oryzias latipes, ST II strain)toxicity was salinity-dependent
Ag30±3Polyvinylpyrrolidone (PVP)Fathead minnow (Pimephales prometas)4.8μg/l of AgNO3 or 61.4μg/l of PVP-AgNPs96 h,aqueous exposurePVP-Ag NPs and AgNO3 affected pathways involved in Na+, K+, and H+ homeostasis and oxidative stress[125]
Ag20PolyvinylpyrrolidoneNeotropical fish (Hoplias intermedius)0.2, 2 and 20 mg/ml96 h or 40 daysAg NPs induced neurotoxicity[126]
Ag20-40NoneZebrafish (Danio rerio) embryos and larvae0.03, 0.1, 0.3,1 and 3 ppm4-120 h, aqueous exposureAg NPs caused hyperexcitability in developing embryos without mortality, significant hatching impairment or morphological abnormalities[127]
Al8-12NoneC57BL/6 mice1.25 mg/kg1 week, carotid artery surgery to deliver Al NPs directly into the cerebral circulationAl NPs caused elevation of autophagy-related genes and autophagic activity in the brain, decreased tight-junction protein expression, and elevated blood-brain barrier (BBB) permeability, increased brain infarct volume in mice subjected to a focal ischemic stroke model[4]
AI2O340NoneMozambique tilapia (Oreochromis mossambicus)120,150 and 180 ppm96 h, aqueous exposureAI2O3 NPs caused extensive histological changes in various organs, including severe necrosis of brain cells[134]
Au12.5NoneMale C57/BL6 mice40, 200, and 400 μg/kg/dayEvery day for 8 days, intraperitoneal administrationAu NPs crossed BBB and accumulated in the neural tissue; importantly, no evidence of toxicity[20]
Au10 and 30NoneAdult male Wistar rats70 μg/kg b.w.Single intraperitoneal injection or repeated injections once daily for 28 daysAcute resulted in reduction of thiobarbituric acid reactive substances and carbonyl protein levels in rats brain; inhibition of catalase activity and energy metabolism was observed in the hippocampus, striatum and cerebral cortex[97]
CdO265NoneAdult male Wistar rats0.04 mg/ kg b.w.3-4 weeks, intratracheal instillationNPs caused significant reduction of open field motility; lengthening of latency of sensory evoked potentials; conduction velocity of the tail nerve was decreased in all treated groups[16]
Cd-20NoneMale Wistar rats0.4 mg/kg3 and 6 weeks, intratracheal instillationSpontaneous cortical electrical activity was shifted to higher frequencies, the latency of sensory-evoked potentials was lengthened, and the frequency following ability of the somatosensory evoked potential was impaired, despite detectable Cd deposition in the brain[17]
Cu23.5NoneMice40 mg /kg b.w.1 week, nasal instillationCu NPs induced severe lesions of the brain with no connection to oxidative stress[36]
Cu23.5NoneCD-I (ICR) female mice1,10, 40 mg/kg b.w.21 days, intranasal instillationCu NPs entered the brain after nasal inhalation and induced damages to the CNS[103]
Cu87±27NoneJuvenile rainbow trout (Oncorhynchus mykiss)0, 20 and 100 μg/l4,10 days, semi-static aqueous exposureSignificant decrease in Na+/K+-ATPase activity in the brain; depletion of plasma and carcass ion concentrations; Cu NPs have similar types of toxic effects to CUSO4[115]
Cu87±27NoneJuvenile rainbow trout (Oncorhynchus mykiss)20 or 100 μg/l4,10 days, semi-static aqueous exposureToxicity of CuSO4 and Cu NPs was similar, but Cu NPs caused more damage in the intestine, liver and brain[132]
Cu20.3±0.9NoneJuvenile rainbow trout (Oncorhynchus mykiss)50 μg/l12 h, aqueous exposureCu NPs caused a significant increase in the ratio of oxidized to reduced glutathione in brains[133]
CuO15-90NoneMale Wistar rats0.5 mg/kg b.w.Intraperitoneal, for 14 daysCuO NPs impaired glutamate transmission presynaptically and postsynaptically, diminished LTP and caused other cognitive deficits[25]
CuO10-70NoneAdult male, specific-pathogen free (SPF) Wistar rats0.5 mg/ kgOnce a day for 14 consecutive days, intraperitoneal injectionCuO NPs impaired oxidation-antioxidation homeostasis, and hippocampal LTP, which was associated with poor performance of animals in behavior tests[55]
CuO20-40NoneJuvenile carp (Cyprinusa) 0,10, 50,100, 200,a) 96 hCholinesterase activity was inhibited[130]
carpio)300, 500,1000 mg/1 b) 100 mg/mlb) 30 daysby CuO NPs exposure, attributed to the free Cu2+ ions dissolved inside the carp body
CuO20-130NoneZebrafish (Danio rerio) embryos and larvae1, 6.25,12.5, 25 or 50 mg/L48, 72, 96 hCu NPs exposure leaded to abnormal phenotypes in zebrafish embryonic development, induced an inflammatory response and delay in retinal neurodifferentiation accompanied by reduced locomotion[145]
Fe2O330NoneAdult female Wistar rats500,1000 and 2000 mg/kg72 h, oral exposureFe2O3 NPs caused no significant DNA damage[9]
Fe3O429.78-68.09NoneC57BL/6J mice2 μl (10 μg/μl)Injection directly into the dorsal striatum and hippocampusFe3 O4 NPs reduced TH+ fiber in both dorsal striatum and hippocampus; and caused motor memory deficits in mice due to the activation of the MAPK and JNK pathways[22]
Fe2O3280±80NoneCD-ICR male mice40 mg/kg b.w.Single dose, intranasal instillationRatio of Fe (III)/Fe (II) increased in olfactory bulb and brain stem; Fe2O3 NPs were possibly transported via uptake by sensory nerve endings of the olfactory nerve and trigeminus[32]
MnO223NoneAdult male Wistar rats2.63, 5.26 mg3, 6, and 9 weeks, instilled into the tracheaMnO2 NPs translocated from airways to the brain, lengthened evoked potential latency and decreased conduction velocity of the tail nerve[41]
MnO2, Fe3O4, Cr(OH)33.6, 8.8, 13.5NoneMale Wistar rats2 mg/kg b.w., MnO2 NPs, also in 4 mg/kg b.w.Intratracheal instillation once a day, for 4 weeksMnO2 NPs caused a shift of spontaneous and evoked cortical electrical activity to higher frequencies, and lengthened evoked potential latency, which were also heavily reduced by co-exposure with Fe3O4NPs[106]
NiO Mn3O416.7±8.2 18.4±5.4NoneWhite female rats0.25, 0.50 mgIntraperitoneally 3 times a week (up to 18 injections)Both NPs negatively affected rats health; Mn3O4 NPs were more harmful in most nonspecific toxicity symptoms; Mn3 O4 NPs caused more nerve damage of the caudate nucleus and the hippocampus as compared to NiO NPs[107]
PbOFraction of 99.9% PbO NPs 7.64-120, fraction of 90% of NPs 7.64-44.5NoneAdult female mice (ICR line)Acute experiment 4.05x106 NPs/cm3, subchronic experiment 3.83x105 NPs/cm3 or 1.93xl06 NPs/cm3Whole body inhalation chambers for 4-72 h in acute experiment, for 1-11 weeks in subchronic experimentInhalted PbO NPs translocated from the lungs to secondary organs such as brain and caused mild pathological alterations in hippocampus area[105]
TiO210NonePregnant Wistar rats100 mg/kg b.w.From prenatal day 2 to day 21, orally expose (gavage)TiO2 NPs significantly reduced cell proliferation in the hippocampus, impaired learning and memory in offspring[108]
TiO26.5NonePregnant CD-I (ICR) mice1, 2,3 mg/kg b.w.Orally via gavage, from prenatal day 0 to postnatal day 21Pregnancy/lactation exposure to TiO2 NPs inhibited development of brain and decreased learning and memory in weanine mice, which was associated with down regulation of Rac 1 and Cdc42 protein expression, upregulation of Rho A protein expression and increased ratio of RhoA/Racl[24]
TiO220NonePregnant NMRI mice2 mg/mlSingle dose, intraperitoneal injectionTiO2 NPs accumulated in heart and brain fetus. Fetus and placenta sizes were lower than in control group[109]
TiO250NoneCarp (Cyprinus carpio)10, 50,100, 200 mg/18 days, aqueous exposureTiO2 NPs (100 and 200 mg/1) caused decrease in SOD, CAT and POD activities and significant increase in LPO levels in tissues, suggesting oxidative stress[116]
TiO25-6NoneZebrafish (Danio rerio)5,10, 20 and 40 μg/L45 days, aqueous exposureTiO2 NPs caused brain injury and reductions of spatial recognition memory[118]
TiO23,4±1,9NoneZebrafish (Danio rerio) larvae0,1,1,For 96 h post fertilization, aqueous exposureTiO2 NPs induced Parkinson's disease-like symptoms and faster embryos hatching[119]
TiO232.47-35.93NoneZebrafish (Danio rerio) and rainbow trout (Oncorhynchus mykiss)500 and 5000 μg/124 h and 14 days, aqueous exposureTiO2 NPs with difficulty penetrated into the brain[120]
ZnO30-40NoneMale Wistar rats25 mg/kg b.w.Every day for 14 days, intravenous injectionsZnO NPs caused no changes in neurotransmitter contents; no deterioration in locomotor activity and spatial working memory was[110]
ZnO30-40NoneMale Wistar rat25 mg/kg b.w.Single dose, intravenous injectionobserved ZnO NPs did not affect neurotransmitter contents, locomotor activity nor spatial working memory in adult rats[111]
ZnO20 and 100Citrate (for negative charge), and L-serine (for positive charge)Ratsa) 500 mg/kg, b) 0.1,10 mg/animala) 28 days, oral exposure, b) 90 days, intravenous administrationBBB was not compromised and was able to block penetration of ZnO NPs[112]
ZnO68.96±33.71NoneAdult male Swiss mice5.625x105 mg/ kg b.w., 300 mg/kg b.w.Aqueous exposureEnvironmentally relevant concentration of ZnO NPs, even for a short period of time, induced behavioral changes related to anxiety in mice[113]
ZnO30NoneCarp (Cyprinus carpio)0.5, 5, 50 mg/114 days, aqueous exposureZnO NPs (50 mg/1) caused significant decrease of several enzymatic activities; gill, liver and brain were most sensitive organs[117]
ZnO35NoneNile tilapia (Oreochromis niloticus) and Redbelly tilapia (Tilapia ziUii)500 and 2000 μg/115 days, aqueous exposureZnO NPs (500μg/l) stimulated the brain antioxidant system, but inhibited it at high concentration[121]
ZnO10-30NoneZebrafish (Danio rerio)1, 5,10, 20, 50 and 10048, 72, 96 hZnO NPs were retarded development[123]
Zn TiO250 25Noneembryos Male Wistar ratsppm 50 mg/kg b.w.aqueous exposure 30 days, NPs were tongue-instilledof nervous and vascular system NPs were deposited in the nerves and brain. The learning and memory of rats were impaired[114]

4.3 Toxicity in non-mammalian vertebrates

In water reservoirs metallic NPs are mainly present in a dispersed form or in the form of emulsion. Thus, it is believed that they may be more toxic in water, compared to the bulk counterparts, as they easier dissolved and release the metal ions [115]. Although dissolution of metallic oxide NPs is more difficult, as it must be accompanied by disruption of covalent bonding, it could be facilitated by humic acids and other chemical substances present in the water.

Studies on carp (Cyprinus carpio) showed that exposure to ZnO NPs or TiO2 NPs induced a significant increase in lipid peroxidation, oxidative stress and a decrease in the activity of antioxidant enzymes in the brain [116, 117]. Similar study conducted on zebrafish (Danio rerio) revealed that subchronic exposure to low doses of TiO2 NPs resulted in brain injury, reduction of spatial recognition memory, thus impairing behavioural response [118]. Hu et al. reported that exposure to 1 and 10 μg/ml of TiO2 NPs produced a loss of dopaminergic neurons on the level 50-70%, and induced Parkinson’s disease-like symptoms zebra fish larvae. This was confirmed in in vitro studies on PC12 cells [119]. On the contrary, Johnston et al. observed that TiO2 NPs hardly penetrated into the brain of zebrafish [120].

Effective uptake of metallic NPs from water was also noted for ZnO NPs and Ag NPs in two different fish models:Nile tilapia (Oreochromis niloticus) and redbelly tilapia (Tilapia zillii). Exposure to high concentration of ZnO NPs (2000 μg/l) and Ag NPs (4 mg/l) resulted in a destructive effect on the brain antioxidant system, while the low concentration (500 μg/l) of ZnO NPs and (2 mg/l) of Ag NPs produced completely opposite effect, supporting the antioxidant activity [121, 122]. In the study on zebrafish, ZnO NPs impaired development of the nervous and vascular system [123]. Waterborn exposure to Ag NPs resulted in the presence of NPs in the brain of medaka (Oryzias latipes) [124]. Whereas studies conducted on fathead minnow females (Pimephales promelas), revealed that Ag NPs interacts directly in the form of intact NPs and indirectly, by releasing ions from the surface of NPs, each with different pathways of neurotoxicity [125]. Also Klingelfus et al. described neurotoxic effects of Ag NPs on neotropical fish (Hoplias intermedius) [126]. A Ag NPs caused hyperexcitability in developing zebrafish was reported far below concentrations found in some aquatic environment [127].

Similarly to Ag NPs, Cu NPs suspended in water, dissolve slowly and release copper ions that might accumulate initially in the gills reflecting entry gate, and then in the other internal organs [128]. CuO NPs and ions released from the NPs penetrated into the brain and thus may be toxic to the CNS [129]. A dramatic decrease in cholinesterase activity was observed in the brains of juvenile carp exposed to CuO NPs, corresponding to a significant increase of copper concentration in the major organs of the fish, including the brain. Interestingly, cholinesterase activity returned to the control level after 10 days, most likely due to the adaptative capabilities of the fish. However, this was attributed rather to the action of the copper ions released from NPs in the fish body than to the NPs effects per se, as no CuO NPs were found in the brain tissue. A study by Zhao et al. included the effect of CuO NPs exposure on juvenile carp. Copper has a number of important characteristics in the brain of fish, including antioxidant functions in melatonin, by the modulation of the excitability of nerve cells and biological rhythms [115, 130]. Further, the NPs inhibited enzyme cholinesterase activity was important for the proper functioning of the neurotransmitter acetylcholine. The research Zhao et al. suggest that this is a consequence of the release of Cu2+ ions from CuO NPs inside the body of the carp. Thus it can be concluded that the CuO NPs have neurotoxic properties for carp. The study also showed that CuO NPs were more toxic than its copper molecular counterparts [130]. Sun et al. observed a disturbance of embryonic zebrafish development as a result of exposure to CuO NPs manifested by the delay of retinal neurodifferentiation [131]. Similarly, the study conducted by Al-Bairuty et al., where they compared the toxicity of CuO NPs and CuSO4 NPs on rainbow trout (Oncorhynchus mykiss), showed in the brain, mild changes in neuronal cell bodies in telencephalon, and some changes in the thickness of the midbrain and vasodilation in a the ventral surface of the cerebellum. Furthermore, similar toxicity was observed for Cu NPs and their molecular equivalent. However, the Cu NPs caused more damage to the brain, compared to equivalent concentrations of CuSO4. Al-Bairuty postulated that brain damage occurred indirectly as a result of gill damage and systemic hypoxia in the body of rainbow trout. The etiology of CuO NPs in the brain pathology requires further study, but it can be assumed that oxidative stress and disruption of osmotic and metal homeostasis may contribute to the pathology of the CNS [132]. Moreover, recent studies have shown that exposure of juvenile rainbow trout on Cu NPs resulted in a significant increase in the ratio of oxidized to reduced glutathione in brains of fish, which may indicate the induction of oxidative stress [133]. Also, studies on freshwater fish Mozambique tilapia (Oreochromis mossambicus) exposed to Al2O3 NPs revealed extensive histological changes in various organs, including severe necrosis of nerve tissue [134].

Although quoted studies were done only on fishes, the toxic effect of metallic NPs on non-mammalian vertebrates is clearly noticeable.Water favors a more efficient penetration of NPs into organisms enhancing their adverse effects. In larvae, metallic NPs interfere with development of embryonic brain leading to decreased vitality. Their destructive effects on nervous system of adult animals are manifested by oxidative stress, acetylcholinesterase activity disturbances, and changes in cellular signalling. The effects of in vivo exposure to metallic NPs are summarized in Table 2.

4.4 Other responses

The NPs also affect biochemical properties of the brain and iono-regulatory processes. Kumari et al. studied female albino Wistar rats after a 28-days repeated oral dose of 30 nm Fe2O3 NPs. They observed inhibition of Na+-K+, Mg2+ and Ca2+-ATP monophosphatase (ATPase) in rat brain; it was also shown that smaller Fe2O3NPs were more toxic [135]. In line, acute oral exposure of female Wistar rats to 30 nm Fe2O3 NPs resulted in more than 50% inhibition of total Na+-K+, Mg2+ and Ca2+-ATPases activity in the brain [136]. Similarly, intragastric administration of TiO2 NPs for 60 days resulted in disturbance of brain trace elements homeostasis and inhibited the activity of Na+/K+- ATPase, Ca2+ - ATPase, Ca2+/Mg2+ - ATPase [137]. Also, a 14 days exposure of rainbow trout to TiO2 NPs resulted in dose-dependent changes in the brain concentration of Cu and Zn ions and decreased in the activity of Na+/K+ - ATPase [138]. Lowering of Na+/K+ - ATPase activity in the brain was also observed in juvenile rainbow trout after waterborne exposure to Cu NPs [115]. NPs-dependent decrease in activity of AChE and increased protein oxidative damage in brain was also observed in juvenile fish Prochilodus lineatus exposured to TiO2 NPs and ZnO NPs [139]. In line Xia et al. showed that 1 mg/l of TiO2 NPs in water increased the level of AChE activity in gills (after day 5) and in digestive gland (after day 12) in the scallop (Chlamys farreri) [140]. In turn, de Oliveira et al. observed inhibition of AChE activity and a reduction in the exploratory performance in adult zebrafish exposed to SPION coated with cross-linked aminated dextran [141]. On contrary, Boyle et al. reported no accumulation of NPs neither decrease in the activity of Na+/K+ - ATPase and AChE in brain of trout exposed to TiO2 NPs for 14 days, despite a significant increase in the total glutathione pool [142]. Similarly, in a study conducted by Ramsden et al., after 14 days of aqueous exposure of zebrafish to TiO2 NPs, no changes were observed in Na+/K+ - ATPase activity in the brain [143].

Presented studies indicate that different types of metallic NPs have the ability to change the biochemical processes taking place in individual nerve cells, thus disturbing the proper functioning of the entire nervous system.

5 The role of oxidative stress in NPs-induced toxicity and DNA damage

Although molecular mechanism underlying the neurotoxicity of NPs are still obscured, generation of intracellular ROS seems to be a main cause of the toxicity. Oxidative stress is caused by an imbalance between oxidants and antioxidants in the cell. Also is considered a major cause of damage to DNA, lipids and protein.

Induction of oxidative stress by various NPs, both in vitro and in vivo, is well documented, thus is was also expected in the context of their effects on the brain. Indeed, Ag NPs and TiO2 NPs stimulated the activation of glial cells to release proinflammatory cytokines and to generate ROS and the production of NO, causing neurological inflammation [144, 145]. A decrease in antioxidant enzymes activity in neurons was also observed after exposure of rats to Ag NPs thus the level of ROS in brain tissue has increased [146]. Also exposure to Fe NPs reduced superoxide dismutase activity and an increased lipid oxidation in medaka (Oryzias latipes) embryos, however in adult animals oxidative stress was observed only at the beginning of treatment. After a certain time of exposure oxidantsantioxidants balance returned to the normal level [147]. A dose dependent, intrasynaptosomal formation of ROS was also reported for 7 nm iron particles coated ferritin [21]. Toxicity of ZnO NPs was also associated with their ability to produce ROS. Melatonin treatment, which has usually a protective effect against oxidative stress caused by external factors, was ineffective for these NPs [148].

In line, CuO NPs induced damage to hippocampal neurons and increased malonaldehyde level in Wistar rats was ascribed to increased ROS production and reduced activity of SOD and glutathione peroxidase (GSH-Px) [55]. Oxidative stress and decreased activity of antioxidant enzymes in the brain was pointed as a main cause of Au NPs-induces increase in 8-hydroxydeoxyguanosine and heat shock protein 70 level and caspase-3 activity,which might lead to cell death. In addition, the study showed a significant increase in the cerebral levels of IFN-𝛾 in the treated animals [27]. Oxidative stress was also attributed to adverse effects in brain tissue, such as increased inflammatory cytokines, DNA fragmentation and stimulation of apoptosis, in rats exposed orally for 7 days to ZnO NPs [149]. Chen et al. observed in human brain microvascular endothelial cells that oxidative stress, manifested as decreased mitochondrial potential and decreased the expression of TJ proteins, is also induced by Al NPs [18]. Also various forms of Al2O3 NPs induced ROS formation, protein oxidation, lipid peroxidation, glutathione reduction and mitochondrial dysfunction [150]. In line, oxidative stress was point as a main cause of genotoxicity observed for tungsten oxide NPs (WO3 NPs) [151], chromium oxide NPs (Cr2O3 NPs) [152] and MnO2 NPs [153]. Oxidative stress arising after treating neural stem cells with Fe3O4 NPs caused by an imbalance in the ROS formation and antioxidant cell-defence system, resulted in depleted intracellular glutathione levels, hyperpolarization of mitochondrial membrane, disturbed cell-membrane potential and DNA damages [154].

Hardas et al. studied pro-oxidant effect of 5 nm CeO2 NPs administered peripherally to the Sprague Dawley rats. After 30 days of exposure to the CeO2 NPs, they observed elevated levels of protein carbonyls and Hsp70 protein in the hippocampus and cerebellum,while nitrotyrosine and inducible nitric oxide synthase (NOS) levels were elevated in the cortex. Whereas GSH-Px and catalase activity were decreased in the hippocampus, glutathione reductase decreased levels occurred in the cortex, and GSH-Px and cata-lase levelswere decreased in the cerebellum. The GSH: glutathione disulfide ratio, an index of cellular redox status, was decreased in the hippocampus and cerebellum. This suggests that the CeO2 NPs have a pro-oxidant potential in the rat brain [5]. On the other hand, Hardas et al. showed previously that 5nmCeO2 NPs administered intravenously to rats did not cause a significant increase in ROS, and oxidative stress was observed [31]. In turn, Hussain et al. observed an up to 10-fold increase of ROS in PC12 cells exposed to 40 nm Mn NPs that might be responsible for depleted level of DA and its metabolites, dihydroxyphenylacetic acid and homovanillic acid [57].

Significant increase in the ROS formation, oxidative stress and decreased activity of antioxidant enzymes was observed in the brain of mice treated with TiO2 NPs, ZnO NPs or Al2O3 NPs [155].

Many reports suggest that neurotoxicity of metallic NPs is associated with induction of oxidative stress in the brain by disturbing the delicate redox balance in both neurons and glial cells. This mechanism is connected with genotoxicity and activation of the apoptotic pathway.

6 Summary

During the past decade, a dynamic development of nanotechnology has been observed. Products containing metallic NPs in their composition can be found everywhere in a wide range of commercial products commonly available to virtually everyone. In addition, NPs have excellent applications in medicine, in medicaments and diagnostics. NPs, due to their small sizes, have remarkable properties which determine their widespread use and immense bioavailability in the environment.

However, the metallic NPs, in addition to their many advantages, unfortunately also have drawbacks. Figure 1 summarizes the present stage of knowledge about toxicity of metallic NPs in CNS reviewed in this work. Studies have shown a greater toxicity and reactivity of metallic NPs compared to their bulk counterparts. There are several main routes of exposure to metallic NPs, of which perhaps the most dangerous in the context of neurotoxicity NPs are those suspended in the air. It was found that NPs easily penetrate the human body, as well as rodents and aquatic organisms. In addition, researchers have observed that some of them rapidly spread throughout the body and accumulate in various organs. Numerous studies confirm that NPs can penetrate into the brain by means of a fixed route (olfactory bulb - olfactory nerve-brain), thus bypassing the BBB. On the other hand, some NPs which enter the body can pass through the BBB, and circulate in the blood vessels in the form of ions released from the surface of the NPs, as well as through damage to the integrity of the BBB which increases its permeability. Of course, it is a serious consequences to bring on the influx of unauthorized substances into the brain, and violation of the delicate homeostasis of the microenvironment. The brain, due to its sensitive structure, is particularly vulnerable to the adverse properties of metallic NPs. Numerous studies performed both in vitro and in vivo show that NPs are toxic to neuronal cells. It has also been demonstrated that NPs can penetrate into the cells, mainly through the mechanism of endocytosis, although there are other possibilities, such as transport facilitated by some membrane receptors. The primary mechanism to induce neurotoxicity can be attributed to the generation of free radicals and induction of oxidative stress, which is known to damage the cell elements (proteins, lipids, nucleic acids). In particular, oxidative damage to DNA is dangerous due to its nature and mediation of mutation in cancer formation. Although metallic NPs have not yet been directly linked to the etiology of any neurode-generative diseases, more and more studies are being conducted which provide new evidence in support of this thesis.

Figure 1 Mechanism of action of metallic nanoparticles in the central nervous system.
Figure 1

Mechanism of action of metallic nanoparticles in the central nervous system.

It is therefore important both for public health and for the environment to continue monitoring of metallic NPs and their effects in the context of the safety use of metallic NPs in medicine, especially in the CNS.

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This study was financed by the National Science Centre Fund Projects No. DEC-2013/09/B/NZ7/03934 and No. DEC-2014/15/B/NZ7/01036.





ATP monophosphatase


Blood-brain barrier


Brain capillary endothelial cells


Central nervous system




Glutathione peroxidase


Interleukin-1 beta


long-term potentiation


Nitric oxide




Reactive oxygen species


Superoxide dismutase


Supermagnetic iron oxide nanoparticles


Tight junctions


[1] Geffroy B., Ladhar C., Cambier S., Treguer-Delapierre M., Brčthes D., Bourdineaud J.P., Impact of dietary gold nanoparticles in zebrafish at very low contamination pressure: the role of size, concentration and exposure time, Nanotoxicology, 2012, 6(2), 144-60.10.3109/17435390.2011.562328Search in Google Scholar PubMed

[2] Semete B., Booysen L., Lemmer Y., Kalombo L., Katata L., Verschoor J., Swai H.S., In vivo evaluation of the biodistribution and safety of PLGA nanoparticles as drug delivery systems, Nanomedicine, 2010, 6(5), 662-71.10.1016/j.nano.2010.02.002Search in Google Scholar PubMed

[3] Xue Y., Wu J., Sun J., Four types of inorganic nanoparticles stimulate the inflammatory reaction in brain microglia and damage neurons in vitro, Toxicol. Lett., 2012, 214(2), 91-8.10.1016/j.toxlet.2012.08.009Search in Google Scholar PubMed

[4] Chen L., Zhang B., Toborek M., Autophagy is involved in nanoalumina-induced cerebrovascular toxicity, Nanomedicine, 2013, 9(2), 212-21.10.1016/j.nano.2012.05.017Search in Google Scholar PubMed PubMed Central

[5] Hardas S.S., Sultana R., Warrier G., Dan M., Florence R.L., Wu P., Grulke E.A., Tseng M.T., Unrine J.M., Graham U.M., Yokel R.A., Butter field DA. Rat brain pro-oxidant effects of peripherally administered 5 nm ceria 30 days after exposure, Neurotoxicology, 2012, 33(5), 1147-55.10.1016/j.neuro.2012.06.007Search in Google Scholar PubMed

[6] Xie Y., Wang Y., Zhang T., Ren G., Yang Z., Effects of nanoparticle zinc oxide on spatial cognition and synaptic plasticity in mice with depressive-like behaviors, J. Biomed. Sci., 2012, 19, 14.10.1186/1423-0127-19-14Search in Google Scholar PubMed PubMed Central

[7] Czajka M., Sawicki K., Sikorska K., Popek S., Kruszewski M., Kapka- Skrzypczak L., Toxicity of titanium dioxide nanoparticles in central nervous system, Toxicol In Vitro, 2015, 29(5), 1042-52.10.1016/j.tiv.2015.04.004Search in Google Scholar PubMed

[8] Matysiak M., Kapka-Skrzypczak L., Brzóska K., Gutleb A.C., Kruszewski M., Proteomic approach to nanotoxicity, J. Proteomics, 2016, 137, 35-44.10.1016/j.jprot.2015.10.025Search in Google Scholar PubMed

[9] Singh S.P., Rahman M.F., Murty U.S., Mahboob M., Grover P., Comparative study of genotoxicity and tissue distribution of nano and micron sized iron oxide in rats after acute oral treatment, Toxicol. Appl. Pharmacol., 2013, 266(1), 56-66.10.1016/j.taap.2012.10.016Search in Google Scholar PubMed

[10] Zhang L., Bai R., Liu Y., Meng L., Li B.,Wang L., Xu L., Le Guyader L., Chen C., The dose-dependent toxicological effects and potential perturbation on the neurotransmitter secretion in brain following intranasal instillation of copper nanoparticles, Nanotoxicology, 2012, 6(5), 562-75.10.3109/17435390.2011.590906Search in Google Scholar PubMed

[11] Matysiak M., Kruszewski M., Kapka-Skrzypczak L., Nanopesticides - Light or dark side of the force?, Med. Pr., 2017, 68(3), 423-432.10.13075/mp.5893.00537Search in Google Scholar PubMed

[12] Li X.B., Zheng H., Zhang Z.R., Li M., Huang Z.Y., Schluesener H.J., Li Y.Y., Xu S.Q., Glia activation induced by peripheral administration of aluminum oxide nanoparticles in rat brains, Nanomedicine, 2009, 5(4), 473-9.10.1016/j.nano.2009.01.013Search in Google Scholar PubMed

[13] Wang Z., Zhang K., Zhao J., Liu X., Xing B., Adsorption and inhibition of butyrylcholinesterase by different engineered nanoparticles, Chemosphere, 2010, 79(1), 86-92.10.1016/j.chemosphere.2009.12.051Search in Google Scholar PubMed

[14] Oszlánczi G., Vezér T., Sárközi L., Horváth E., Kónya Z., Papp A., Functional neurotoxicity of Mn-containing nanoparticles in rats, Ecotoxicol. Environ. Saf., 2010, 73(8), 2004-9.10.1016/j.ecoenv.2010.09.002Search in Google Scholar PubMed

[15] Han D., Tian Y., Zhang T., Ren G., Yang Z., Nano-zinc oxide damages spatial cognition capability via over-enhanced long-term potentiation in hippocampus of Wistar rats, Int. J. Nanomedicine, 2011, 6, 1453-61.10.2147/IJN.S18507Search in Google Scholar PubMed PubMed Central

[16] Horváth E., Oszlánczi G., Máté Z., Szabó A., Kozma G., Sápi A., Kónya Z., Paulik E., Nagymajtényi L., Papp A., Nervous system effects of dissolved and nanoparticulate cadmium in rats in subacute ex- posure, J. Appl. Toxicol., 2011, 31(5), 471-6.10.1002/jat.1664Search in Google Scholar PubMed

[17] Papp A., Oszlánczi G., Horváth E., Paulik E., Kozma G., Sápi A., Kónya Z., Szabó A., Consequences of subacute intratracheal exposure of rats to cadmiumoxide nanoparticles: Electrophysiological and toxicological effects, Toxicol. Ind. Health, 2012, 28(10), 933-41.10.1177/0748233711430973Search in Google Scholar PubMed

[18] Chen L, Yokel RA, Hennig B, Toborek M. Manufactured aluminum oxide nanoparticles decrease expression of tight junction proteins in brain vasculature, J. Neuroimmune Pharmacol., 2008, 3(4), 286-95.10.1007/s11481-008-9131-5Search in Google Scholar PubMed PubMed Central

[19] Zhao J., Xu L., Zhang T., Ren G., Yang Z., Influences of nanoparticle zinc oxide on acutely isolated rat hippocampal CA3 pyramidal neurons, Neurotoxicology, 2009, 30(2), 220-30.10.1016/j.neuro.2008.12.005Search in Google Scholar PubMed

[20] Lasagna-Reeves C., Gonzalez-Romero D., Barria M.A., Olmedo I., Clos A., Sadagopa Ramanujam V.M., Urayama A., Vergara L., Kogan M.J., Soto C., Bioaccumulation and toxicity of gold nanoparticles after repeated administration in mice, BiochemBiophys Res Commun, 2010, 393(4), 649-55.10.1016/j.bbrc.2010.02.046Search in Google Scholar PubMed

[21] Alekseenko A.V.,Waseem T.V., Fedorovich S.V., Ferritin, a protein containing iron nanoparticles, induces reactive oxygen species formation and inhibits glutamate uptake in rat brain synaptosomes, Brain Res., 2008, 1241, 193-200.10.1016/j.brainres.2008.09.012Search in Google Scholar

[22] Liu Y., Li J., Xu K., Gu J., Huang L., Zhang L., Liu N., Kong J., Xing M., Zhang L., Zhang L., Characterization of superparamagnetic iron oxide nanoparticle-induced apoptosis in PC12 cells and mousehippocampus and striatum, Toxicol. Lett., 2018, 292, 151-161.10.1016/j.toxlet.2018.04.033Search in Google Scholar

[23] De Simone U., Roccio M., Gribaldo L., Spinillo A., Caloni F., Coccini T., Human 3D Cultures as Models for Evaluating Magnetic Nanoparticle CNS Cytotoxicity after Short- and Repeated Long-Term Exposure, Int. J. Mol. Sci., 2018, 19(7), E1993.10.3390/ijms19071993Search in Google Scholar

[24] Hong F., Zhou Y., Ji J., Zhuang J., Sheng L., Wang L., Nano-TiO2 Inhibits Development of the Central Nervous System and Its Mechanism in Offspring Mice, J. Agric Food Chem, 2018, 66(44), 11767-11774.10.1021/acs.jafc.8b02952Search in Google Scholar

[25] Li X., Sun W., An L., Nano-CuO impairs spatial cognition associated with inhibiting hippocampal long-term potentiation via affecting glutamatergic neurotransmission in rats, Toxicol. Ind. Health, 2018, 34(6), 409-421.10.1177/0748233718758233Search in Google Scholar

[26] Balasubramanian S.K., Poh K.W., Ong C.N., Kreyling W.G., Ong W.Y., Yu L.E., The effect of primary particle size on biodistribution of inhaled gold nano-agglomerates, Biomaterials, 2013, 34(22), 5439-52.10.1016/j.biomaterials.2013.03.080Search in Google Scholar

[27] Siddiqi N.J., Abdelhalim M.A., El-Ansary A.K., Alhomida A.S., Ong W.Y., Identification of potential biomarkers of gold nanoparticle toxicity in rat brains, J. Neuroinflammation, 2012, 9, 123.10.1186/1742-2094-9-123Search in Google Scholar

[28] Sunderman F.W. Jr., Nasal toxicity, carcinogenicity, and olfactory uptake of metals, Ann Clin Lab Sci, 2001, 31(1),3-24.Search in Google Scholar

[29] Henriksson J., Tallkvist J., Tjälve H., Uptake of nickel into the brain via olfactory neurons in rats, Toxicol. Lett., 1997, 91(2),153-62.10.1016/S0378-4274(97)03885-XSearch in Google Scholar

[30] Liu H., Ma L., Zhao J., Liu J., Yan J., Ruan J., Hong F., Biochemical toxicity of nano-anatase TiO2 particles in mice, Biol. Trace. Elem Res., 2009, 129(1-3), 170-80.10.1007/s12011-008-8285-6Search in Google Scholar PubMed

[31] Hardas S.S., Butterfield D.A., Sultana R., Tseng M.T., Dan M., Florence R.L., Unrine J.M., Graham U.M.,Wu P., Grulke E.A., Yokel R.A., Brain dis- tribution and toxicological evaluation of a systemically delivered engineered nanoscale ceria, Toxicol. Sci., 2010, 116(2), 562-76.10.1093/toxsci/kfq137Search in Google Scholar PubMed

[32] Wang B., Feng W.Y., Wang M., Shi J.W., Zhang F., Ouyang H., Zhao Y.L., Chai Z.F., Huang Y.Y., Xie Y.N., Wang H.F., Wang J., Transport of intranasally instilled fine Fe2O3 particles into the brain: micro distribution, chemical states, and histopathological observation, Biol. Trace Elem. Res., 2007, 118(3), 233-43.10.1007/s12011-007-0028-6Search in Google Scholar PubMed

[33] Lucchini R.G., Dorman D.C., Elder A., Veronesi B., Neurological impacts from inhalation of pollutants and the nose-brain connection, Neurotoxicology, 2012, 33(4), 838-41.10.1016/j.neuro.2011.12.001Search in Google Scholar PubMed PubMed Central

[34] Takenaka S., Karg E., Roth C., Schulz H., Ziesenis A., Heinzmann U., Schramel P., Heyder J., Pulmonary and systemic distribution of inhaled ultrafine silver particles in rats, Environ. Health Perspect., 2001, 109, Suppl 4, 547-551.10.1289/ehp.01109s4547Search in Google Scholar PubMed PubMed Central

[35] Hopkins L.E., Patchin E.S., Chiu P.L., Brandenberger C., Smiley-Jewell S., Pinkerton K.E., Nose-to-brain transport of aerosolised quantum dots following acute exposure, Nanotoxicology, 2014, 8(8), 885-93.10.3109/17435390.2013.842267Search in Google Scholar PubMed PubMed Central

[36] Liu Y., Gao Y., Liu Y., Li B., Chen C., Wu G., Oxidative stress and acute changes in murine brain tissues after nasal instillation of cop per particles with different sizes, J. Nanosci. Nanotechnol., 2014, 14(6), 4534-40.10.1166/jnn.2014.8290Search in Google Scholar PubMed

[37] Elder A., Gelein R., Silva V., Feikert T., Opanashuk L., Carter J., Potter R.,Maynard A., Ito Y., Finkelstein J., Oberdörster G., Translocation of inhaled ultrafine manganese oxide particles to the central nervous system, Environ. Health Perspect, 2006, 114(8), 1172- 8.10.1289/ehp.9030Search in Google Scholar PubMed PubMed Central

[38] Wang J., Chen C., Liu Y., Jiao F., Li W., Lao F., Li Y., Li B., Ge C., Zhou G., Gao Y., Zhao Y., Chai Z., Potential neurological lesion after nasal instillation of TiO(2) nanoparticles in the anatase and rutile crystal phases, Toxicol. Lett., 2008, 183(1-3), 72-80.10.1016/j.toxlet.2008.10.001Search in Google Scholar PubMed

[39] Wang J., Liu Y., Jiao F., Lao F., Li W., Gu Y., Li Y., Ge C., Zhou G., Li B., Zhao Y., Chai Z., Chen C., Time-dependent translocation and potential impairment on central nervous system by intranasally instilled TiO(2) nanoparticles, Toxicology, 2008, 254(1-2), 82-90.10.1016/j.tox.2008.09.014Search in Google Scholar PubMed

[40] Takács S.Z., Szabó A., Oszlánczi G., Pusztai P., Sápi A., Kónya Z., Papp A., Repeated simultaneous cortical electrophysiological and behavioral recording in rats exposed to manganese-containing nanoparticles, Acta Biol. Hung., 2012, 63(4), 426-40.10.1556/ABiol.63.2012.4.2Search in Google Scholar PubMed

[41] Sárközi L., Horváth E., Kónya Z., Kiricsi I., Szalay B., Vezér T., Papp A., Subacute intratracheal exposure of rats tomanganese nanoparticles: behavioral, electrophysiological, and general toxicological effects, Inhal. Toxicol., 2009, 21 Suppl 1, 83-91.10.1080/08958370902939406Search in Google Scholar PubMed

[42] Oszlánczi G., Papp A., Szabó A., Nagymajtényi L., Sápi A., Kónya Z., Paulik E., Vezér T., Nervous system effects in rats on subacute exposure by lead-containing nanoparticles via the airways, Inhal. Toxicol., 2011, 23(4), 173-81.10.3109/08958378.2011.553248Search in Google Scholar PubMed

[43] Schleh C., Semmler-Behnke M., Lipka J., Wenk A., Hirn S., Schäffler M., Schmid G., Simon U., Kreyling W.G., Size and surface charge of gold nanoparticles determine absorption across intestinal barriers and accumulation in secondary target organs after oral administration, Nanotoxicology, 2012, 6(1), 36-46.10.3109/17435390.2011.552811Search in Google Scholar PubMed PubMed Central

[44] Loeschner K., Hadrup N., Qvortrup K., Larsen A., Gao X., Vogel U., Mortensen A., Lam H.R., Larsen E.H., Distribution of silver in rats following 28 days of repeated oral exposure to silver nanoparticles or silver acetate, Part Fibre Toxicol., 2011, 8,18.10.1186/1743-8977-8-18Search in Google Scholar PubMed PubMed Central

[45] Senzui M., Tamura T., Miura K., Ikarashi Y., Watanabe Y., Fujii M., Study on penetration of titanium dioxide (TiO(2)) nanoparticles into intact and damaged skin in vitro, J. Toxicol. Sci., 2010, 35(1), 107-13.10.2131/jts.35.107Search in Google Scholar PubMed

[46] Adachi K., Yamada N., Yoshida Y., YamamotoO., Subchronic exposure of titanium dioxide nanoparticles to hairless rat skin, Exp. Dermatol., 2013, 22(4), 278-83.10.1111/exd.12121Search in Google Scholar PubMed

[47] Unnithan J., Rehman M.U., Ahmad F.J., Samim M., Aqueous synthesis and concentration-dependent dermal toxicity of TiO2 nanoparticles in Wistar rats, Biol. Trace Elem. Res., 2011, 143(3), 1682-94.10.1007/s12011-011-9010-4Search in Google Scholar PubMed

[48] Gamer A.O., Leibold E., van Ravenzwaay B., The in vitro absorption of microfine zinc oxide and titaniumdioxide through porcine skin, Toxicol. In Vitro, 2006, 20(3), 301-7.10.1016/j.tiv.2005.08.008Search in Google Scholar PubMed

[49] Madsen S.J., Gach H.M., Hong S.J., Uzal F.A., Peng Q., Hirschberg H., Increased nanoparticle-loaded exogenous macrophage migra- tion into the brain following PDT-induced blood-brain barrier disruption, Lasers Surg. Med., 2013, 45(8), 524-32.10.1002/lsm.22172Search in Google Scholar PubMed PubMed Central

[50] Pilakka-Kanthikeel S., Atluri V.S., Sagar V., Saxena S.K., Nair M., Targeted brain derived neurotropic factors (BDNF) delivery across the blood-brain barrier for neuro-protection usingmagnetic nano carriers: an in-vitro study, PLoS One, 2013, 8(4), e62241.10.1371/journal.pone.0062241Search in Google Scholar PubMed PubMed Central

[51] Kong S.D., Lee J., Ramachandran S., Eliceiri B.P., Shubayev V.I., Lal R., Jin S., Magnetic targeting of nanoparticles across the intact blood-brain barrier, J. Control Release, 2012, 164(1), 49-57.10.1016/j.jconrel.2012.09.021Search in Google Scholar PubMed PubMed Central

[52] Sonavane G., Tomoda K., Makino K., Biodistribution of colloidal gold nanoparticles after intravenous administration: effect of particle size, Colloids Surf. B Biointerfaces, 2008, 66(2), 274-80.10.1016/j.colsurfb.2008.07.004Search in Google Scholar PubMed

[53] Kakkar V., Kaur I.P., Evaluating potential of curcumin loaded solid lipid nanoparticles in aluminium induced behavioural, biochemical and histopathological alterations in mice brain, Food Chem. Toxicol., 2011, 49(11), 2906-13.10.1016/j.fct.2011.08.006Search in Google Scholar PubMed

[54] Kruszewski M., Brzoska K., Brunborg G., Asare N., Dobrzyńska M., Dušinská M., Fjellsbř LM., Georgantzopoulou A., Gromadzka-Ostrowska J., Gutleb A.C., Lankoff A., Magdolenová Z., Pran E.R.,Rinna A., Instanes C., Sandberg W.J., Schwarze P., Stępkowski T., Wojewódzka W., Refsnes M., Toxicity of Silver Nanomaterials in Higher Eukaryotes, In: James C. Fishbein Ed., Advances in Molecular Toxicology, 2011, Vol. 5, 179-218, Amsterdam, The Netherlands.10.1016/B978-0-444-53864-2.00005-0Search in Google Scholar

[55] An L., Liu S., Yang Z., Zhang T., Cognitive impairment in rats induced by nano-CuO and its possible mechanisms, Toxicol. Lett., 2012, 213(2), 220-7.10.1016/j.toxlet.2012.07.007Search in Google Scholar PubMed

[56] Li Y., Li J., Yin J., Li W., Kang C., Huang Q., Li Q., Systematic influence induced by 3 nm titanium dioxide following intratracheal instilla- tion of mice, J. Nanosci. Nanotechnol., 2010, 10(12), 8544-9.10.1166/jnn.2010.2690Search in Google Scholar PubMed

[57] Hussain S.M., Javorina A.K., Schrand A.M., Duhart H.M., Ali S.F., Schlager J.J., The interaction of manganese nanoparticleswith PC-12 cells induces dopamine depletion, Toxicol. Sci., 2006, 92(2), 456-63.10.1093/toxsci/kfl020Search in Google Scholar PubMed

[58] Liu Z., Liu S., Ren G., Zhang T., Yang Z., Nano-CuO inhibited voltagegated sodium current of hippocampal CA1 neurons via reactive oxygen species but independent from G-proteins pathway, J. Appl. Toxicol., 2011, 31(5), 439-45.10.1002/jat.1611Search in Google Scholar PubMed

[59] Geiser M., Rothen-Rutishauser B., Kapp N., Schürch S., Kreyling W., Schulz H., Semmler M., Im Hof V., Heyder J., Gehr P., Ultrafine particles cross cellular membranes by nonphagocytic mechanisms in lungs and in cultured cells, Environ. Health Perspect, 2005, 113(11), 1555-60.10.1289/ehp.8006Search in Google Scholar PubMed PubMed Central

[60] Mühlfeld C., Mayhew T.M., Gehr P., Rothen-Rutishauser B., A novel quantitative method for analyzing the distributions of nanoparticles between different tissue and intracellular compartments, J. Aerosol. Med., 2007, 20(4), 395-407.10.1089/jam.2007.0624Search in Google Scholar PubMed

[61] Behzadi S., Serpooshan V., Tao W., Hamaly M.A., Alkawareek M.Y., Dreaden E.C., Brown D., Alkilany A.M., Farokhzad O.C.,Mahmoudi M., Cellular uptake of nanoparticles: journey inside the cell, Chem. Soc. Rev., 2017, 46(14), 4218-4244.10.1039/C6CS00636ASearch in Google Scholar

[62] Panzarini E.,Mariano S., Carata E.,Mura F., Rossi M., Dini L., Intracellular transport of silver and gold nanoparticles and biological responses: an update, Int. J. Mol. Sci., 2018, 19(5), 1305.10.3390/ijms19051305Search in Google Scholar PubMed PubMed Central

[63] Oh N., Park J.H., Endocytosis and exocytosis of nanoparticles in mammalian cells, Int J. Nanomedicine, 2014, 9(Suppl 1), 51-63.10.2147/IJN.S26592Search in Google Scholar PubMed PubMed Central

[64] Tomankova K., Horakova J., Harvanova M., Malina L., Soukupova J., Hradilova S., Kejlova K.,Malohlava J., Licman L., Dvorakova M., Jirova D., Kolarova H., Cytotoxicity, cell uptake and microscopic analysis of titanium dioxide and silver nanoparticles in vitro, Food Chem. Toxicol., 2015, 82, 106-115.10.1016/j.fct.2015.03.027Search in Google Scholar PubMed

[65] Luther E.M., Koehler Y., Diendorf J., Epple M., Dringen R., Accumula tion of silver nanoparticles by cultured primary brain astrocytes, Nanotechnology, 2011, 22(37), 37510110.1088/0957-4484/22/37/375101Search in Google Scholar PubMed

[66] Kao Y.Y., Cheng T.J., Yang D.M., Wang C.T., Chiung Y.M., Liu P.S., Demonstration of an olfactory bulb-brain translocation pathway for ZnO nanoparticles in rodent cells in vitro and in vivo, J. Mol. Neurosci., 2012, 48(2), 464-71.10.1007/s12031-012-9756-ySearch in Google Scholar PubMed

[67] Geppert M., Hohnholt M.C., Thiel K., Nürnberger S., Grunwald I., Rezwan K., Dringen R., Uptake of dimercaptosuccinate-coated magnetic iron oxide nanoparticles by cultured brain astrocytes, Nanotechnology, 2011, 22(14), 145101.10.1088/0957-4484/22/14/145101Search in Google Scholar PubMed

[68] Kaksonen M., Roux A., Mechanisms of clathrin-mediated endocytosis, Nat. Rev. Mol. Cell Biol., 2018, 19(5), 313-326.10.1038/nrm.2017.132Search in Google Scholar PubMed

[69] Stamatovic S.M., Johnson A.M., Sladojevic N., Keep R.F., And-jelkovic A.V., Endocytosis of tight junction proteins and the regulation of degradation and recycling, Ann. N. Y. Acad. Sci., 2017, 1397(1), 54-65.10.1111/nyas.13346Search in Google Scholar PubMed PubMed Central

[70] Luther E.M., Petters C., Bulcke F., Kaltz A., Thiel K., Bickmeyer U., Dringen R., Endocytotic uptake of iron oxide nanoparticles by cultured brain microglial cells, Acta Biomater., 2013, 9(9), 8454-65.10.1016/j.actbio.2013.05.022Search in Google Scholar PubMed

[71] Pongrac I.M., Ahmed L.B., Mlinarić H., Jurašin D.D., Pavičić I., Mar- janović Čermak A.M., Milić M., Gajović S., Vinković Vrček I., Surface coating affects uptake of silver nanoparticles in neural stem cells, J. Trace Elem. Med. Biol., 2018, 50, 684-692.10.1016/j.jtemb.2017.12.003Search in Google Scholar PubMed

[72] Huerta-García E., Márquez-Ramírez S.G., Ramos-Godinez M. del P., López-Saavedra A., Herrera L.A., Parra A., Alfaro-Moreno E., Gómez E.O., López-Marure R., Internalization of titanium dioxide nanoparticles by glial cells is given at short times and ismainly mediated by actin reorganization-dependent endocytosis, Neurotoxicology, 2015, 51, 27-37.10.1016/j.neuro.2015.08.013Search in Google Scholar PubMed

[73] Valentini X., Deneuflourg P., Paci P., Rugira P., Laurent S., Frau A., Stanicki D., Ris L., Nonclercq D., Morphological alterations induced by the exposure to TiO2 nanoparticles in primary cortical neuron cultures and in the brain of rats, Toxicol. Rep., 2018, 5, 878-889.10.1016/j.toxrep.2018.08.006Search in Google Scholar PubMed PubMed Central

[74] Hsiao I.L., Chang C.C.,Wu C.Y., Hsieh Y.K., Chuang C.Y.,Wang C.F., Huang Y.J., Indirect effects of TiO2 nanoparticle on neuron-glial cell interactions, Chem. Biol. Interact., 2016, 254, 34-44.10.1016/j.cbi.2016.05.024Search in Google Scholar PubMed

[75] Hsiao I.L., Hsieh Y.K., Chuang C.Y., Wang C.F., Huang Y.J., Effects of silver nanoparticles on the interactions of neuron- and glia-like cells: toxicity, uptake mechanisms, and lysosomal tracking, Environ. Toxicol., 2017, 32(6), 1742-1753.10.1002/tox.22397Search in Google Scholar PubMed

[76] Xu F., Piett C., Farkas S., Qazzaz M., Syed N.I., Silver nanoparticles (AgNPs) cause degeneration of cytoskeleton and disrupt synaptic machinery of cultured cortical neurons,Mol. Brain, 2013, 19, 6-29.10.1186/1756-6606-6-29Search in Google Scholar PubMed PubMed Central

[77] Coccini T., Manzo L., Bellotti V., De Simone U., Assessment of cellular responses after short- and long-term exposure to sil- ver nanoparticles in human neuroblastoma (SH-SY5Y) and astrocytoma (D384) cells, Sci. World J., 2014, 13, 2014, 259765.10.1155/2014/259765Search in Google Scholar PubMed PubMed Central

[78] Weldon B.A., Park J.J., Hong S., Workman T., Dills R., Lee J.H., Griflth W.C., Kavanagh T.J., Faustman E.M., Using primary organotypicmouse midbrain cultures to examine developmental neurotoxicity of silver nanoparticles across two genetic strains, Toxicol. Appl. Pharmacol., 2018, 354, 215-224.10.1016/j.taap.2018.04.017Search in Google Scholar PubMed

[79] Ziemińska E., StafieJ. A., Strużyńska L., The role of the glutamatergic NMDA receptor in nanosilver-evoked neurotoxicity in primary cultures of cerebellar granule cells, Toxicology, 2014, 315, 38-48.10.1016/j.tox.2013.11.008Search in Google Scholar PubMed

[80] Yin N., Liu Q., Liu J., He B., Cui L., Li Z., Yun Z., Qu G., Liu S., Zhou Q., Jiang G., Silver nanoparticle exposure attenuates the viability of rat cerebellum granule cells through apoptosis coupled to oxidative stress, Small, 2013, 9(9-10), 1831-41.10.1002/smll.201202732Search in Google Scholar PubMed

[81] Liu F., Mahmood M., Xu Y., Watanabe F., Biris A.S., Hansen D.K., Inselman A., Casciano D., Patterson T.A., Paule M.G., Slikker W. Jr, Wang C., Effects of silver nanoparticles on human and rat embryonic neural stem cells, Front. Neurosci., 2015, 9, 115.10.3389/fnins.2015.00115Search in Google Scholar PubMed PubMed Central

[82] Huang C.L., Hsiao I.L., Lin H.C.,Wang C.F., Huang Y.J., Chuang C.Y., Silver nanoparticles affect on gene expression of inflammatory and neurodegenerative responses in mouse brain neural cells, Environ. Res., 2015, 136, 253-63.10.1016/j.envres.2014.11.006Search in Google Scholar PubMed

[83] Bulcke F, Thiel K, Dringen R. Uptake and toxicity of copper oxide nanoparticles in cultured primary brain astrocytes, Nanotoxicology, 2014, 8(7), 775-85.10.3109/17435390.2013.829591Search in Google Scholar PubMed

[84] Niska K., Santos-Martinez M.J., Radomski M.W., Inkielewicz-Stepniak I., CuO nanoparticles induce apoptosis by impairing the antioxidant defense and detoxification systems in the mouse hippocampal HT22 cell line: protective effect of crocetin, Toxicol. In Vitro, 2015, 29(4), 663-71.10.1016/j.tiv.2015.02.004Search in Google Scholar PubMed

[85] Bulcke F., Dringen R., Copper oxide nanoparticles stimulate glycolytic flux and increase the cellular contents of glutathione and metallothioneins in cultured astrocytes, Neurochem. Res., 2015, 40(1),15-26.10.1007/s11064-014-1458-0Search in Google Scholar PubMed

[86] Trickler W.J., Lantz-McPeak S.M., Robinson B.L., Paule M.G., Slikker W. Jr, Biris A.S., Schlager J.J., Hussain S.M., Kanungo J., Gonzalez C., Ali S.F., Porcine brain microvessel endothelial cells show proinflammatory response to the size and composition of metallic nanoparticles, Drug Metab Rev, 2014, 46(2), 224-31.10.3109/03602532.2013.873450Search in Google Scholar PubMed PubMed Central

[87] Rivet C.J., Yuan Y., Borca-Tasciuc D.A., Gilbert R.J., Altering iron oxide nanoparticle surface properties induce cortical neuron cytotoxicity, Chem. Res. Toxicol., 2012, 25(1), 153-61.10.1021/tx200369sSearch in Google Scholar PubMed PubMed Central

[88] Imam S.Z., Lantz-McPeak S.M., Cuevas E., Rosas-Hernandez H., Liachenko S., Zhang Y., Sarkar S., Ramu J., Robinson B.L., Jones Y., Gough B., Paule M.G., Ali S.F., Binienda Z.K., Iron oxide nanoparticles induce dopaminergic damage: in vitro pathways and in vivo imaging reveals mechanism of neuronal damage, Mol. Neurobiol., 2015, 52(2), 913-926.10.1007/s12035-015-9259-2Search in Google Scholar PubMed

[89] Wang J., Rahman M.F., Duhart H.M., Newport G.D., Patterson T.A., Murdock R.C., Hussain S.M., Schlager J.J., Ali S.F., Expression changes of dopaminergic system-related genes in PC12 cells induced by manganese, silver, or copper nanoparticles, Neurotoxicology, 2009, 30(6), 926-33.10.1016/j.neuro.2009.09.005Search in Google Scholar PubMed

[90] Gliga A.R., Edoff K., Caputo F., Källman T., Blom H., Karlsson H.L., Ghibelli L., Traversa E., Ceccatelli S., Fadeel B.. Cerium oxide nanoparticles inhibit differentiation of neural stem cells, Sci. Rep., 2017, 7(1), 9284.10.1038/s41598-017-09430-8Search in Google Scholar PubMed PubMed Central

[91] Lei Y., Wang C., Jiang Q., Sun X., Du Y., Zhu Y., Lu Y., Calpain activation and disturbance of autophagy are induced in cortical neurons in vitro by exposure to HA/Ga2O3:Cr3+ nanoparticles, Peer J., 2018, 6, 4365.10.7717/peerj.4365Search in Google Scholar PubMed PubMed Central

[92] Bastian S., Busch W., Kühnel D., Springer A., Meissner T., Holke R., Scholz S., Iwe M., Pompe W., Gelinsky M., Potthoff A., Richter V., Ikonomidou C., Schirmer K., Toxicity of tungsten carbide and cobalt-doped tungsten carbide nanoparticles inmammalian cells in vitro, Environ. Health Perspect, 2009, 117(4), 530-6.10.1289/ehp.0800121Search in Google Scholar PubMed PubMed Central

[93] Valdiglesias V., Costa C., Sharma V., Kiliç G., Pásaro E., Teixeira J.P., Dhawan A., Laffon B., Comparative study on effects of two different types oftitaniumdioxide nanoparticles on human neuronal cells, Food Chem. Toxicol., 2013, 57,352-61.10.1016/j.fct.2013.04.010Search in Google Scholar PubMed

[94] Coccini T., Grandi S., Lonati D., Locatelli C., De Simone U., Comparative cellular toxicity of titanium dioxide nanoparticles on human astrocyte and neuronal cells after acute and prolonged exposure, Neurotoxicology, 2015, 48, 77-89.10.1016/j.neuro.2015.03.006Search in Google Scholar PubMed

[95] Sheng L., Ze Y., Wang L., Yu X., Hong J., Zhao X., Ze X., Liu D., Xu B., Zhu Y., Long Y., Lin A., Zhang C., Zhao Y., Hong F., Mechanisms of TiO2 nanoparticle-induced neuronal apoptosis in rat primary cultured hippocampal neurons, J. Biomed. Mater. Res. A, 2015, 103(3), 1141-9.10.1002/jbm.a.35263Search in Google Scholar PubMed

[96] Wu J., Sun J., Xue Y., Involvement of JNK and P53 activation in G2/M cell cycle arrest and apoptosis induced by titanium dioxide nanoparticles in neuron cells, Toxicol. Lett., 2010, 199(3), 269-76.10.1016/j.toxlet.2010.09.009Search in Google Scholar PubMed

[97] Ferreira G.K., Cardoso E., Vuolo F.S., Galant L.S., Michels M., Gonçalves C.L., Rezin G.T., Dal-Pizzol F., Benavides R., Alonso-Núńez G., Andrade V.M., Streck E.L., da Silva Paula M.M., Effect of acute and long-term administration of gold nanoparticles on biochemical parameters in rat brain, Mater. Sci. Eng. C Mater. Biol. Appl., 2017, 79, 748-755.10.1016/j.msec.2017.05.110Search in Google Scholar PubMed

[98] Skalska J., Frontczak-Baniewicz M., Strużyńska L., Synaptic degeneration in rat brain after prolonged oral exposure to silver nanoparticles, Neurotoxicology, 2015, 46, 145-54.10.1016/j.neuro.2014.11.002Search in Google Scholar PubMed

[99] Xu L., Shao A., Zhao Y., Wang Z., Zhang C., Sun Y., Deng J., Chou L.L., Neurotoxicity of Silver Nanoparticles in Rat Brain After Intragastric Exposure, J. Nanosci. Nanotechnol., 2015, 15(6), 4215-23.10.1166/jnn.2015.9612Search in Google Scholar PubMed

[100] Lebda M.A., Sadek K.M., Tohamy H.G., Abouzed T.K., Shukry M., Umezawa M., El-Sayed Y.S., Potential role of α-lipoic acid and Ginkgo biloba against silver nanoparticles-induced neuronal apoptosis and blood-brain barrier impairments in rats, Life Sci., 2018, 212, 251-260.10.1016/j.lfs.2018.10.011Search in Google Scholar PubMed

[101] Węsierska M., Dziendzikowska K., Gromadzka-Ostrowska J., Dudek J., Polkowska-Motrenko H., Audinot J.N., Gutleb A.C., Lankoff A., Kruszewski M., Silver ions are responsible for memory im- pairment induced by oral administration of silver nanoparticles, Toxicol. Lett., 2018, 290, 133-144.10.1016/j.toxlet.2018.03.019Search in Google Scholar PubMed

[102] Dąbrowska-Bouta B., Zięba M., Orzelska-Górka J., Skalska J., Sulkowski G., Frontczak-Baniewicz M., Talarek S., Listos J., Strużyńska L., Influence of a low dose of silver nanoparticles on cerebral myelin and behavior of adult rats, Toxicology, 2016, 363-364, 29-36.10.1016/j.tox.2016.07.007Search in Google Scholar

[103] Bai R., Zhang L., Liu Y., Li B., Wang L., Wang P., Autrup H., Beer C., Chen C., Integrated analytical techniques with high sensitivity for studying brain translocation and potential impairment induced by intranasally instilled copper nanoparticles, Toxicol. Lett., 2014, 226(1), 70-80.10.1016/j.toxlet.2014.01.041Search in Google Scholar

[104] Papp A., Nagymajtényi L., Dési I., A study on electrophysiological effects of subchronic cadmium treatment in rats, Environ. Toxicol. Pharmacol., 2003, 13(3), 181-6.10.1016/S1382-6689(02)00160-6Search in Google Scholar

[105] Lebedová J., Nováková Z., Večeřa Z., Buchtová M., Dumková J., Dočekal B., Bláhová L., Mikuška P., Míšek I., Hampl A., Hilscherová K., Impact of acute and subchronic inhalation exposure to PbO nanoparticles on mice, Nanotoxicology, 2018, 12(4), 290- 304.10.1080/17435390.2018.1438679Search in Google Scholar PubMed

[106] Máté Z., Horváth E., Papp A., Kovács K., Tombácz E., Nesztor D., Szabó T., Szabó A., Paulik E., Neurotoxic effects of subchronic intratracheal Mn nanoparticle exposure alone and in combination with other welding fume metals in rats, Inhal. Toxicol., 2017, 29(5), 227-238.10.1080/08958378.2017.1350218Search in Google Scholar PubMed

[107] Katsnelson B.A., Minigaliyeva I.A., Panov V.G., Privalova L.I., Varaksin A.N., Gurvich V.B., Sutunkova M.P., Shur V.Y., Shishkina E.V., Valamina I.E., Makeyev O.H., Some patterns of metallic nanoparticles’ combined subchronic toxicity as exemplified by a combination of nickel and manganese oxide nanoparticles, Food Chem. Toxicol., 86, 351-64.10.1016/j.fct.2015.11.012Search in Google Scholar PubMed

[108] Mohammadipour A., Fazel A., Haghir H., Motejaded F., Rafatpanah H., Zabihi H., Hosseini M., Bideskan A.E., Maternal exposure to titanium dioxide nanoparticles during pregnancy; impaired memory and decreased hippocampal cell proliferation in rat offspring, Environ. Toxicol. Pharmacol., 2014, 37(2), 617-25.10.1016/j.etap.2014.01.014Search in Google Scholar PubMed

[109] Naserzadeh P., Ghanbary F., Ashtari P., Seydi E., Ashtari K., Akbari M., Biocompatibility assessment of titanium dioxide nanoparticles in mice fetoplacental unit, J. Biomed. Mater. Res. A, 2018, 106(2), 580-589.10.1002/jbm.a.36221Search in Google Scholar PubMed

[110] Amara S., Ben-Slama I., Mrad I., Rihane N., Jeljeli M., El-Mir L., Ben- Rhouma K., Rachidi W., Sčve M., Abdelmelek H., Sakly M., Acute exposure to zinc oxide nanoparticles does not affect the cognitive capacity and neurotransmitters levels in adult rats, Nanotoxicology, 2014, 8 Suppl 1, 208-15.10.3109/17435390.2013.879342Search in Google Scholar PubMed

[111] Amara S., Slama I.B., Omri K., El Ghoul J., El Mir L., Rhouma K.B., Abdelmelek H., Sakly M., Effects of nanoparticle zinc oxide on emotional behavior and trace elements homeostasis in rat brain, Toxicol. Ind. Health, 2015, 31(12), 1202-9.10.1177/0748233713491802Search in Google Scholar PubMed

[112] Shim K.H., Jeong K.H., Bae S.O., Kang M.O., Maeng E.H., Choi C.S., Kim Y.R., Hulme J., Lee E.K., Kim M.K., An S.S., Assessment of ZnO and SiO2 nanoparticle permeability through and toxicity to the blood-brain barrier using Evans blue and TEM, Int. J. Nanomedicine, 2014, 9 Suppl 2, 225-33.10.2147/IJN.S58205Search in Google Scholar

[113] de Souza J.M., Mendes B.O., Guimarăes A.T.B., Rodrigues A.S.L., Chagas T.Q., Rocha T.L., Malafaia G., Zinc oxide nanoparticles in predicted environmentally relevant concentrations leading to behavioral impairments in male swiss mice, Sci. Total. Environ., 2018, 613-614, 653-662.10.1016/j.scitotenv.2017.09.051Search in Google Scholar

[114] Aijie C., Huimin L., Jia L., Lingling O., Limin W., Junrong W., Xuan L., Xue H., Longquan S., Central neurotoxicity induced by the instillation of ZnO and TiO2 nanoparticles through the taste nerve pathway, Nanomedicine (Lond), 2017, 12(20), 2453-2470.10.2217/nnm-2017-0171Search in Google Scholar

[115] Shaw B.J., Al-Bairuty G., Handy R.D., Effects of waterborne copper nanoparticles and copper sulphate on rainbow trout, (Oncorhynchus mykiss): physiology and accumulation, Aquat. Toxicol., 2012, 116-117, 90-101.10.1016/j.aquatox.2012.02.032Search in Google Scholar

[116] Hao L., Wang Z., Xing B., Effect of sub-acute exposure to TiO2 nanoparticles on oxidative stress and histopathological changes in Juvenile Carp (Cyprinus carpio), J. Environ. Sci. (China), 2009, 21(10), 1459-66.10.1016/S1001-0742(08)62440-7Search in Google Scholar

[117] Hao L., Chen L., Oxidative stress responses in different organs of carp (Cyprinus carpio) with exposure to ZnO nanoparticles, Ecotoxicol. Environ. Saf., 2012, 80, 103-10.10.1016/j.ecoenv.2012.02.017Search in Google Scholar PubMed

[118] Sheng L.,Wang L., Su M., Zhao X., Hu R., Yu X., Hong J., Liu D., Xu B., Zhu Y., Wang H., Hong F., Mechanism of TiO2 nanoparticleinduced neurotoxicity in zebrafish (Danio rerio), Environ. Toxicol, 2016, 31(2), 163-75.10.1002/tox.22031Search in Google Scholar PubMed

[119] Hu Q., Guo F., Zhao F., Fu Z., Effects of titanium dioxide nanoparticles exposure on parkinsonism in zebrafish larvae and PC12, Chemosphere, 2017, 173,373-379.10.1016/j.chemosphere.2017.01.063Search in Google Scholar PubMed

[120] Johnston B.D., Scown T.M., Moger J., Cumberland S.A., Baalousha M., Linge K., van Aerle R., Jarvis K., Lead J.R., Tyler C.R., Bioavailability of nanoscale metal oxides TiO(2), CeO(2), and ZnO to fish, Environ Sci. Technol., 2010, 44(3), 1144-51.10.1021/es901971aSearch in Google Scholar PubMed

[121] Saddick S., Afifi M., Abu Zinada O.A., Effect of Zinc nanoparticles on oxidative stress-related genes and antioxidant enzymes activity in the brain of Oreochromis niloticus and Tilapia zillii, Saudi J. Biol. Sci., 2017, 24(7), 1672–1678.10.1016/j.sjbs.2015.10.021Search in Google Scholar PubMed PubMed Central

[122] Afifi M., Saddick S., Abu Zinada O.A., Toxicity of silver nanoparticles on the brain of Oreochromis niloticus and Tilapia zillii, Saudi J. Biol. Sci., 2016, 23(6), 754-760.10.1016/j.sjbs.2016.06.008Search in Google Scholar

[123] Kteeba S.M., El-Ghobashy A.E., El-Adawi H.I., El-RayisO.A., Sree-vidya V.S., Guo L., Svoboda K.R., Exposure to ZnO nanoparticles alters neuronal and vascular development in zebrafish: Acute and transgenerational effects mitigated with dissolved organic matter, Environ. Pollut., 2018, 242(Pt A), 433-448.10.1016/j.envpol.2018.06.030Search in Google Scholar

[124] Kashiwada S., Distribution of nanoparticles in the see-through medaka (Oryzias latipes), Environ. Health Perspect, 2006, 114(11), 1697-702.10.1289/ehp.9209Search in Google Scholar

[125] Garcia-Reyero N., Kennedy A.J., Escalon B.L., Habib T., Laird J.G., Rawat A., Wiseman S., Hecker M., Denslow N., Steevens J.A., Perkins E.J., Differential effects and potential adverse outcomes of ionic silver and silver nanoparticles in vivo and in vitro, Environ. Sci. Technol., 2014, 48(8), 4546-55.10.1021/es4042258Search in Google Scholar

[126] Klingelfus T., Lirola J.R., Oya Silva L.F., Disner G.R., Vicentini M., Nadaline M.J.B., Robles J.C.Z., Trein L.M., Voigt C.L., Silva de Assis H.C., Mela M., Leme D.M., Cestari M.M., Acute and longterm effects of trophic exposure to silver nanospheres in the central nervous system of a neotropical fish Hoplias intermedius, Neurotoxicology, 2017, 63, 146-154.10.1016/j.neuro.2017.10.003Search in Google Scholar

[127] González E.A., Carty D.R., Tran F.D., Cole A.M., Lein P.J., Developmental exposure to silver nanoparticles at environmentally relevant con centrations alters swimming behavior in zebrafish (Danio rerio), Environ. Toxicol. Chem., 2018, 37(12), 3018-3024.10.1002/etc.4275Search in Google Scholar

[128] McGeer J.C., Szebedinszky C., Gordon McDonald D., Wood C.M., Effects of chronic sublethal exposure to waterborne Cu, Cd or Zn in rainbow trout 2: tissue specific metal accumulation, Aquat. Toxicol., 2000, 50(3), 245-256.10.1016/S0166-445X(99)00106-XSearch in Google Scholar

[129] Yang Z., Liu Z.W., Allaker R.P., Reip P.,Oxford J.,Ahmad Z., Ren G., A review of nanoparticle functionality and toxicity on the central nervous system, J. R. Soc. Interface, 2010, 7 Suppl 4, S411-22.10.1007/978-94-007-1787-9_18Search in Google Scholar

[130] Zhao J., Wang Z., Liu X., Xie X., Zhang K., Xing B., Distribution of CuO nanoparticles in juvenile carp (Cyprinus carpio) and their potential toxicity, J. Hazard. Mater., 2011, 197, 304-10.10.1016/j.jhazmat.2011.09.094Search in Google Scholar PubMed

[131] Sun Y., Zhang G., He Z., Wang Y., Cui J., Li Y., Effects of copper oxide nanoparticles on developing zebrafish embryos and larvae, Int. J. Nanomedicine, 2016, 11, 905-918.10.2147/IJN.S100350Search in Google Scholar PubMed PubMed Central

[132] Al-Bairuty G.A., Shaw B.J., Handy R.D., Henry T.B., Histopathological effects of waterborne copper nanoparticles and copper sulphate on the organs of rainbow trout (Oncorhynchus mykiss), Aquat. Toxicol., 2013, 126, 104-15.10.1016/j.aquatox.2012.10.005Search in Google Scholar PubMed

[133] Sovová T., Boyle D., Sloman K.A., Vanegas Pérez C., Handy R.D., Impaired behavioural response to alarm substance in rainbow trout exposed to copper nanoparticles, Aquat. Toxicol., 2014, 152, 195- 204.10.1016/j.aquatox.2014.04.003Search in Google Scholar PubMed

[134] Murali M., Athif P., Suganthi P., Sadiq Bukhari A., Syed Mohamed H.E., Basu H., Singhal R.K., Toxicological effect of Al2O3 nanoparticles on histoarchitecture of the freshwater fish Oreochromis mossambicus, Environ. Toxicol. Pharmacol., 2018, 59,74-81.10.1016/j.etap.2018.03.004Search in Google Scholar PubMed

[135] Kumari M., Rajak S., Singh S.P., Kumari S.I., Kumar P.U., Murty U.S., Mahboob M., Grover P., Rahman M.F., Repeated oral dose toxicity of iron oxide nanoparticles: biochemical and histopathological alterations in different tissues of rats, J. Nanosci. Nanotechnol., 2012, 12(3), 2149-59.10.1166/jnn.2012.5796Search in Google Scholar PubMed

[136] Kumari M., Rajak S., Singh S.P.,Murty U.S.,Mahboob M., Grover P., Rahman M.F., Biochemical alterations induced by acute oral doses of iron oxide nanoparticles in Wistar rats, Drug Chem Toxicol, 2013, 36(3), 296-305.10.3109/01480545.2012.720988Search in Google Scholar PubMed

[137] Hu R., Gong X., Duan Y., Li N., Che Y., Cui Y., Zhou M., Liu C., Wang H., Hong F., Neurotoxicological effects and the impairment of spatial recognition memory in mice caused by exposure to TiO2 nanoparticles, Biomaterials, 2010, 31(31), 8043-50.10.1016/j.biomaterials.2010.07.011Search in Google Scholar PubMed

[138] Federici G., Shaw B.J., Handy R.D., Toxicity of titanium dioxide nanoparticles to rainbow trout (Oncorhynchusmykiss): gill injury, oxidative stress, and other physiological effects, Aquat. Toxicol., 2007, 84(4), 415-30.10.1016/j.aquatox.2007.07.009Search in Google Scholar PubMed

[139] Miranda R.R., Damaso da Silveira A.L., de Jesus I.P., Grötzner S.R., Voigt C.L., Campos S.X., Garcia J.R., Randi M.A., Ribeiro C.A., Fili- pak Neto F., Effects of realistic concentrations of TiO2, and ZnO nanoparticles in Prochilodus lineatus juvenile fish, Environ. Sci. Pollut. Res. Int., 2016, 23(6), 5179-88.10.1007/s11356-015-5732-8Search in Google Scholar PubMed

[140] Xia B., Zhu L., Han Q., Sun X., Chen B., Qu K., Effects of TiO2 nanoparticles at predicted environmental relevant concentration on the marine scallop Chlamys farreri: An integrated biomarker approach, Environ. Toxicol. Pharmacol., 2017, 50, 128-135.10.1016/j.etap.2017.01.016Search in Google Scholar PubMed

[141] de Oliveira G.M., Kist L.W., Pereira T.C., Bortolotto J.W., Paquete F.L., de Oliveira E.M., Leite C.E., Bonan C.D., de Souza Basso N.R., Papaleo R.M., Bogo M.R., Transient modulation of acetylcholinesterase activity caused by exposure to dextrancoated iron oxide nanoparticles in brain of adult zebrafish, Comp. Biochem. Physiol. C Toxicol. Pharmacol., 2014, 162,77-84.10.1016/j.cbpc.2014.03.010Search in Google Scholar PubMed

[142] Boyle D., Al-Bairuty G.A., Ramsden C.S., Sloman K.A., Henry T.B., Handy R.D., Subtle alterations in swimming speed distributions of rainbow trout exposed to titanium dioxide nanoparticles are associated with gill rather than brain injury, Aquat. Toxicol., 2013, 126, 116-27.10.1016/j.aquatox.2012.10.006Search in Google Scholar PubMed

[143] Ramsden C.S., Henry T.B., Handy R.D., Sub-lethal effects of titanium dioxide nanoparticles on the physiology and reproduction of zebrafish, Aquat. Toxicol., 2013, 126, 404-13.10.1016/j.aquatox.2012.08.021Search in Google Scholar PubMed

[144] Wu T., Tang M., The inflammatory response to silver and titanium dioxide nanoparticles in the central nervous system, Nanomedicine (Lond), 2018, 13(2), 233-249.10.2217/nnm-2017-0270Search in Google Scholar PubMed

[145] Sun C., Yin N., Wen R., Liu W., Jia Y., Hu L., Zhou Q., Jiang G., Silver nanoparticles induced neurotoxicity through oxidative stress in rat cerebral astrocytes is distinct from the effects of silver ions, Neurotoxicology, 2016, 52, 210-21.10.1016/j.neuro.2015.09.007Search in Google Scholar PubMed

[146] Skalska J., Dąbrowska-Bouta B., Strużyńska L., Oxidative stress in rat brain but not in liver following oral administration of a low dose of nanoparticulate silver, Food Chem. Toxicol., 2016, 97, 307-315.10.1016/j.fct.2016.09.026Search in Google Scholar PubMed

[147] Li H., Zhou Q., Wu Y., Fu J., Wang T., Jiang G., Effects of waterborne nano-iron on medaka (Oryzias latipes): antioxidant enzymatic activity, lipid peroxidation and histopathology, Ecotoxicol. Environ. Saf., 2009, 72(3),684-92.10.1016/j.ecoenv.2008.09.027Search in Google Scholar PubMed

[148] Sruthi S., Millot N., Mohanan P.V., Zinc oxide nanoparticles mediated cytotoxicity, mitochondrial membrane potential and level of antioxidants in presence of melatonin, Int. J. Biol. Macromol., 2017, 103, 808-818.10.1016/j.ijbiomac.2017.05.088Search in Google Scholar PubMed

[149] Attia H., Nounou H., Shalaby M., Zinc oxide nanoparticles induced oxidative DNA damage, inflammation and apoptosis in rat’s brain after oral exposure, Toxics, 2018, 6(2), E29.10.3390/toxics6020029Search in Google Scholar PubMed PubMed Central

[150] Mirshafa A., Nazari M., Jahani D., Shaki F., Size-dependent neurotoxicity of aluminum oxide particles: a comparison between nano- and micrometer size on the basis of mitochondrial oxidative damage, Biol. Trace Elem. Res., 2018, 183(2),261-269.10.1007/s12011-017-1142-8Search in Google Scholar PubMed

[151] Chinde S., Dumala N., Rahman M.F., Kamal S.S.K., Kumari S.I., Mahboob M., Grover P., Toxicological assessment of tungsten oxide nanoparticles in rats after acute oral exposure, Environ. Sci. Pollut. Res. Int., 2017, 24(15), 13576-13593.10.1007/s11356-017-8892-xSearch in Google Scholar PubMed

[152] Singh S.P., Chinde S., Kamal S.S., Rahman M.F., Mahboob M., Grover P., Genotoxic effects of chromium oxide nanoparticles and microparticles In Wistar rats after 28 days of repeated oral exposure, Environ Sci Pollut Res Int, 2016, 23(4), 3914-24.10.1007/s11356-015-5622-0Search in Google Scholar PubMed

[153] Alarifi S., Ali D., Alkahtani S., Oxidative stress-induced DNA damage bymanganese dioxide nanoparticles in human neuronal cells, Biomed. Res. Int., 2017, 2017, 5478790.10.1155/2017/5478790Search in Google Scholar PubMed PubMed Central

[154] Pongrac I.M., Pavičić I., Milić M., Brkić Ahmed L., Babič M., Horák D., Vinković Vrček I., Gajović S., Oxidative stress response in neural stem cells exposed to different superparamagnetic iron oxide nanoparticles, Int. J. Nanomedicine, 2016, 11,1701-15.10.2147/IJN.S102730Search in Google Scholar PubMed PubMed Central

[155] Shrivastava R., Raza S., Yadav A., Kushwaha P., Flora S.J., Effects of sub-acute exposure to TiO2, ZnO and Al2O3 nanoparticles on oxidative stress and histological changes in mouse liver and brain, Drug Chem. Toxicol., 2014, 37(3),336-47.10.3109/01480545.2013.866134Search in Google Scholar PubMed

Received: 2018-11-16
Accepted: 2019-07-01
Published Online: 2019-11-06

© 2019 K. Sawicki et al., published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 Public License.

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