Oxidative stress and apoptosis induced by nanosized titanium dioxide in PC12 cells

Elevated CO2 levels increase the toxicity of ZnO nanoparticles to goldfish (Carassius auratus) in a water-sediment ecosystem

Concerns about the environmental safety of metal-based nanoparticles (MNPs) in aquatic ecosystems are increasing. Simultaneously, elevated atmospheric CO₂ levels are a serious problem worldwide, making it possible for the combined exposure of MNPs and elevated CO₂ to the ecosystem. Here we studied the toxicity of nZnO to goldfish in a water-sediment ecosystem using open-top chambers flushed with ambient (400±10μL/L) or elevated (600±10μL/L) CO₂ for 30days. We measured the content of Zn in suspension and fish, and analyzed physiological and biochemical changes in fish tissues. Results showed that elevated CO₂ increased the Zn content in suspension by reducing the pH value of water and consequently enhanced the bioavailability and toxicity of nZnO. Elevated CO₂ led to higher accumulation of Zn in fish tissues (increased by 43.3%, 86.4% and 22.5% in liver, brain and muscle, respectively) when compared to ambient. Elevated CO₂ also intensified the oxidative damage to fish induced by nZnO, resulting in higher ROS intensity, greater contents of MDA and MT and lower GSH content in liver and brain. Our results suggest that more studies in natural ecosystems are needed to better understand the fate and toxicity of nanoparticles in future CO₂ levels.

Progress of in vivo studies on the systemic toxicities induced by titanium dioxide nanoparticles

Titanium dioxide nanoparticles (TiO2 NPs) are inorganic materials with a diameter of 1-100 nm. In recent years, TiO2 NPs have been used in a wide range of products, including food, toothpaste, cosmetics, medicine, paints and printing materials, due to their unique properties (high stability, anti-corrosion, and efficient photocatalysis). Following exposure via various routes including inhalation, injection, dermal deposition and gastrointestinal tract absorption, NPs can be found in various organs in the body potentially inducing toxic effects. Thus more attention to the safety of TiO2 NPs is necessary. Therefore, the present review aims to provide a comprehensive evaluation of the toxic effects induced by TiO2 NPs in the lung, liver, stomach, intestine, kidney, spleen, brain, hippocampus, heart, blood vessels, ovary and testis of mice and rats in in vivo experiments, and evaluate their potential toxic mechanisms. The findings will provide an important reference for human risk evaluation and management following TiO2 NP exposure.

Toxicity assessment of carbon black waste: A by-product from oil refineries

In Singapore, approximately 30t/day of carbon-based solid waste are produced from petrochemical processes. This carbon black waste has been shown to possess physical properties that are characteristic of a good adsorbent such as high external surface area. Therefore, there is a growing interest to reutilize and process this carbon black waste into secondary materials such as adsorbents. However, the carbon black waste obtained from petrochemical industries may contain heavy metals that are hazardous to human health and the environment, hence restricting its full potential for re-utilization. Therefore, it is important to examine the possible toxicity effects and toxicity mechanism of carbon black waste on human health. In this study, inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis showed that the heavy metals, vanadium (V), molybdenum (Mo) and nickel (Ni), were present in the carbon black waste in high concentrations. Three human cell lines (HepG2 cells, MRC-5 cells and MDA-MB-231 cells) were used to investigate the toxicity of carbon black waste extract in a variety of in vitro assays. Results from MTS assays indicated that carbon black waste extract decreased the viability of all three cell lines in a dose and time-dependent manner. Observations from confocal microscopy further confirmed this phenomenon. Flow cytometry assay also showed that carbon black waste extract induced apoptosis of human cell lines, and the level of apoptosis increased with increasing waste concentration. Results from reactive oxygen species (ROS) assay indicated that carbon black waste extract induced oxidative stress by increasing intracellular ROS generation in these three human cell lines. Moreover, induction of oxidative damage in these cells was also observed through the alteration of glutathione (GSH) and superoxide dismutase (SOD) activities. Last but not least, by treating the cells with V-spiked solution of concentration equivalent to that found in the carbon black waste extract, V was identified as the main culprit for the high toxicity of carbon black waste extract. These findings could potentially provide insight into the hazards of carbon black waste extract and its toxicity mechanism on human cell lines.

Pharmacological Tools to Activate Microglia and their Possible use to Study Neural Network Patho-physiology

BACKGROUND

Microglia are the resident immunocompetent cells of the CNS and also constitute a unique cell type that contributes to neural network homeostasis and function. Understanding microglia cell-signaling not only will reveal their diverse functions but also will help to identify pharmacological and non-pharmacological tools to modulate the activity of these cells.

METHODS

We undertook a search of bibliographic databases for peer-reviewed research literature to identify microglial activators and their cell-specificity. We also looked for their effects on neural network function and dysfunction.

RESULTS

We identified several pharmacological targets to modulate microglial function, which are more or less specific (with the proper control experiments). We also identified pharmacological targets that would require the development of new potent and specific modulators. We identified a wealth of evidence about the participation of microglia in neural network function and their alterations in pathological conditions.

CONCLUSION

The identification of specific microglia-activating signals provides experimental tools to modulate the activity of this heterogeneous cell type in order to evaluate its impact on other components of the nervous system, and it also helps to identify therapeutic approaches to ease some pathological conditions related to microglial dysfunction.

Contribution of oxidative stress to TiO2 nanoparticle-induced toxicity

With the rapid development of nanotechnology, titanium dioxide nanoparticles (TNPs) are widely used in many fields. People in such workplaces or researchers in laboratories are at a higher risk of being exposed to TNPs, so are the consumers. Moreover, increasing evidence revealed that the concentrations of TNPs are elevated in animal organs after systematic exposure and such accumulated TNPs could induce organ dysfunction. Although cellular responses such as oxidative stress, inflammatory response, apoptosis, autophagy, signaling pathways, and genotoxic effects contribute to the toxicity of TNPs, the interrelationship among them remains obscure. Given the pivotal role of oxidative stress, we summarized relevant articles covering the involvement of oxidative stress in TNPs' toxicity and found that TNP-induced oxidative stress might play a central role in toxic mechanisms. However, available data are far from being conclusive and more investigations should be performed to further confirm whether the toxicity of TNPs might be attributed in part to the cascades of oxidative stress. Tackling this uncertain issue may help us to comprehensively understand the interrelationship among toxic cellular responses induced by TNPs and might shed some light on methods to alleviate toxicity of TNPs.

Is Neurotoxicity of Metallic Nanoparticles the Cascades of Oxidative Stress?

With the rapid development of nanotechnology, metallic (metal or metal oxide) nanoparticles (NPs) are widely used in many fields such as cosmetics, the food and building industries, and bio-medical instruments. Widespread applications of metallic NP-based products increase the health risk associated with human exposures. Studies revealed that the brain, a critical organ that consumes substantial amounts of oxygen, is a primary target of metallic NPs once they are absorbed into the body. Oxidative stress (OS), apoptosis, and the inflammatory response are believed to be the main mechanisms underlying the neurotoxicity of metallic NPs. Other studies have disclosed that antioxidant pretreatment or co-treatment can reverse the neurotoxicity of metallic NPs by decreasing the level of reactive oxygen species, up-regulating the activities of antioxidant enzymes, decreasing the proportion of apoptotic cells, and suppressing the inflammatory response. These findings suggest that the neurotoxicity of metallic NPs might involve a cascade of events following NP-induced OS. However, additional research is needed to determine whether NP-induced OS plays a central role in the neurotoxicity of metallic NPs, to develop a comprehensive understanding of the correlations among neurotoxic mechanisms and to improve the bio-safety of metallic NP-based products.

Involvement of Programmed Cell Death in Neurotoxicity of Metallic Nanoparticles: Recent Advances and Future Perspectives

The widespread application of metallic nanoparticles (NPs) or NP-based products has increased the risk of exposure to NPs in humans. The brain is an important organ that is more susceptible to exogenous stimuli. Moreover, any impairment to the brain is irreversible. Recently, several in vivo studies have found that metallic NPs can be absorbed into the animal body and then translocated into the brain, mainly through the blood-brain barrier and olfactory pathway after systemic administration. Furthermore, metallic NPs can cross the placental barrier to accumulate in the fetal brain, causing developmental neurotoxicity on exposure during pregnancy. Therefore, metallic NPs become a big threat to the brain. However, the mechanisms underlying the neurotoxicity of metallic NPs remain unclear. Programmed cell death (PCD), which is different from necrosis, is defined as active cell death and is regulated by certain genes. PCD can be mainly classified into apoptosis, autophagy, necroptosis, and pyroptosis. It is involved in brain development, neurodegenerative disorders, psychiatric disorders, and brain injury. Given the pivotal role of PCD in neurological functions, we reviewed relevant articles and tried to summarize the recent advances and future perspectives of PCD involvement in the neurotoxicity of metallic NPs, with the purpose of comprehensively understanding the neurotoxic mechanisms of NPs.

Nano-TiO2 induces autophagy to protect against cell death through antioxidative mechanism in podocytes

Autophagy is a cellular pathway involved in degradation of damaged organelles and proteins in order to keep cellular homeostasis. It plays vital role in podocytes. Titanium dioxide nanoparticles (nano-TiO₂) are known to induce autophagy in cells, but little has been reported about the mechanism of this process in podocytes and the role of autophagy in podocyte death. In the present study, we examined how nano-TiO₂ induced authophagy. Besides that, whether autophagy could protect podocytes from the damage induced by nano-TiO₂ and its mechanism was also investigated. Western blot assay and acridine orange staining presented that nano-TiO₂ significantly enhanced autophagy flux in podocytes. In addition, AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) were involved in such process. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay indicated that upregulated level of autophagy induced by rapamycin in high concentration nano-TiO₂-treated podocytes could significantly reduce the level of oxidative stress and alleviate podocyte death. Downregulating the level of autophagy with 3-methyladenine had the opposite effects. These findings indicate that nano-TiO₂ induces autophagy through activating AMPK to inhibit mTOR in podocytes, and such autophagy plays a protecting role against oxidative stress on the cell proliferation. Changing autophagy level may become a new treatment strategy to relieve the damage induced by nano-TiO₂ in podocytes.

Engineered nanoparticles induce cell apoptosis: potential for cancer therapy

Engineered nanoparticles (ENPs) have been widely applied in industry, commodities, biology and medicine recently. The potential for many related threats to human health has been highlighted. ENPs with their sizes no larger than 100 nm are able to enter the human body and accumulate in organs such as brain, liver, lung, testes, etc, and cause toxic effects. Many references have studied ENP effects on the cells of different organs with related cell apoptosis noted. Understanding such pathways towards ENP induced apoptosis may aid in the design of effective cancer targeting ENP drugs. Such ENPs can either have a direct effect towards cancer cell apoptosis or can be used as drug delivery agents. Characteristics of ENPs, such as sizes, shape, forms, charges and surface modifications are all seen to play a role in determining their toxicity in target cells. Specific modifications of such characteristics can be applied to reduce ENP bioactivity and thus alleviate unwanted cytotoxicity, without affecting the intended function. This provides an opportunity to design ENPs with minimum toxicity to non-targeted cells.

Quantification and visualization of cellular uptake of TiO2 and Ag nanoparticles: comparison of different ICP-MS techniques

Background

Safety assessment of nanoparticles (NPs) requires techniques that are suitable to quantify tissue and cellular uptake of NPs. The most commonly applied techniques for this purpose are based on inductively coupled plasma mass spectrometry (ICP-MS). Here we apply and compare three different ICP-MS methods to investigate the cellular uptake of TiO₂ (diameter 7 or 20 nm, respectively) and Ag (diameter 50 or 75 nm, respectively) NPs into differentiated mouse neuroblastoma cells (Neuro-2a cells). Cells were incubated with different amounts of the NPs. Thereafter they were either directly analyzed by laser ablation ICP-MS (LA-ICP-MS) or were lysed and lysates were analyzed by ICP-MS and by single particle ICP-MS (SP-ICP-MS).

Results

All techniques confirmed that smaller particles were taken up to a higher extent when values were converted in an NP number-based dose metric. In contrast to ICP-MS and LA-ICP-MS, this measure is already directly provided through SP-ICP-MS. Analysis of NP size distribution in cell lysates by SP-ICP-MS indicates the formation of NP agglomerates inside cells. LA-ICP-MS imaging shows that some of the 75 nm Ag NPs seemed to be adsorbed onto the cell membranes and were not penetrating into the cells, while most of the 50 nm Ag NPs were internalized. LA-ICP-MS confirms high cell-to-cell variability for NP uptake.

Conclusions

Based on our data we propose to combine different ICP-MS techniques in order to reliably determine the average NP mass and number concentrations, NP sizes and size distribution patterns as well as cell-to-cell variations in NP uptake and intracellular localization.

Electronic supplementary material

The online version of this article (doi:10.1186/s12951-016-0203-z) contains supplementary material, which is available to authorized users.

Cytotoxic and inflammatory responses of TiO2 nanoparticles on human peripheral blood mononuclear cells

Titanium dioxide nanoparticles (TiO2 -NPs) have been widely used in many applications. Owing to their nanoscale size, interactions between cells and NPs have been expansively investigated. With the health concerns raised regarding the adverse effects of these interactions, closer examination of whether TiO2 -NPs can induce toxicity towards human cells is greatly needed. Therefore, in this study, we investigated the cytotoxicity of TiO2 -NPs towards human blood cells (peripheral blood mononuclear cells [PBMCs]) in serum-free medium, for which there is little information regarding the cytotoxic effects of TiO2 -NPs. Our results provide evidence that PBMCs treated with TiO2 -NPs (at concentrations ≥25 μg ml(-1) ) for 24 h significantly reduced cell viability and significantly increased production of toxic mediators such as reactive oxygen species and inflammatory response cytokines such as interleukin-6 and tumor necrosis factor-α (P < 0.05). Cell apoptosis induction also occurred at these concentrations. Significant expressions of cyclooxygenase-2 and interleukin-1β were also observed in PBMCs treated with TiO2 -NPs at concentrations ≥125 μg ml(-1) . Our data presented here clearly indicate that the concentration of TiO2 -NPs (at size ~26.4 ± 1.2 nm) applied to human blood cells has a strong impact on cytotoxic induction. Copyright © 2016 John Wiley & Sons, Ltd.

Indirect effects of TiO2 nanoparticle on neuron-glial cell interactions

Although, titanium dioxide nanoparticles (TiO2NPs) are nanomaterials commonly used in consumer products, little is known about their hazardous effects, especially on central nervous systems. To examine this issue, ALT astrocyte-like, BV-2 microglia and differentiated N2a neuroblastoma cells were exposed to 6 nm of 100% anatase TiO2NPs. A lipopolysaccharide (LPS) was pre-treated to activate glial cells before NP treatment for mimicking NP exposure under brain injury. We found that ALT and BV-2 cells took up more NPs than N2a cells and caused lower cell viability. TiO2NPs induced IL-1β in the three cell lines and IL-6 in N2a. LPS-activated BV-2 took up more TiO2NPs than normal BV-2 and released more intra/extracellular reactive oxygen species (ROS), IL-1β, IL-6 and MCP-1 than did activated BV-2. Involvement of clathrin- and caveolae-dependent endocytosis in ALT and clathrin-dependent endocytosis and phagocytosis in BV-2 both had a slow NP translocation rate to lysosome, which may cause slow ROS production (after 24 h). Although TiO2NPs did not directly cause N2a viability loss, by indirect NP exposure to the bottom chamber of LPS-activated BV-2 in the Transwell system, they caused late apoptosis and loss of cell viability in the upper N2a chamber due to H2O2 and/or TNF-α release from BV-2. However, none of the adverse effects in N2a or BV-2 cells was observed when TiO2NPs were exposed to ALT-N2a or ALT-BV-2 co-culture. These results demonstrate that neuron damage can result from TiO2NP-mediated ROS and/or cytokines release from microglia, but not from astrocytes.

Short peptide based nanotubes capable of effective curcumin delivery for treating drug resistant malaria

Background

Curcumin (Ccm) has shown immense potential as an antimalarial agent; however its low solubility and less bioavailability attenuate the in vivo efficacy of this potent compound. In order to increase Ccm’s bioavailability, a number of organic/inorganic polymer based nanoparticles have been investigated. However, most of the present day nano based delivery systems pose a conundrum with respect to their complex synthesis procedures, poor in vivo stability and toxicity issues. Peptides due to their high biocompatibility could act as excellent materials for the synthesis of nanoparticulate drug delivery systems. Here, we have investigated dehydrophenylalanine (ΔPhe) di-peptide based self-assembled nanoparticles for the efficient delivery of Ccm as an antimalarial agent. The self-assembly and curcumin loading capacity of different ΔPhe dipeptides, phenylalanine–α,β-dehydrophenylalanine (FΔF), arginine-α,β-dehydrophenylalanine (RΔF), valine-α,β-dehydrophenylalanine (VΔF) and methonine-α,β-dehydrophenylalanine (MΔF) were investigated for achieving enhanced and effective delivery of the compound for potential anti-malarial therapy.

Results

FΔF, RΔF, VΔF and MΔF peptides formed different types of nanoparticles like nanotubes and nanovesicles under similar assembling conditions. Out of these, F∆F nanotubes showed maximum curcumin loading capacity of almost 68 % W/W. Ccm loaded F∆F nanotubes (Ccm-F∆F) showed comparatively higher (IC₅₀, 3.0 µM) inhibition of Plasmodium falciparum (Indo strain) as compared to free Ccm (IC₅₀, 13 µM). Ccm-F∆F nano formulation further demonstrated higher inhibition of parasite growth in malaria infected mice as compared to free Ccm. The dipeptide nanoparticles were highly biocompatible and didn’t show any toxic effect on mammalian cell lines and normal blood cells.

Conclusion

This work provides a proof of principle of using highly biocompatible short peptide based nanoparticles for entrapment and in vivo delivery of Ccm leading to an enhancement in its efficacy as an antimalarial agent.

Nanosized titanium dioxide resulted in the activation of TGF-β/Smads/p38MAPK pathway in renal inflammation and fibration of mice

Titanium dioxide nanoparticles (TiO2 NPs) have been demonstrated to damage the kidneys. However, whether chronic nephritis leads to renal fibration or the fibrosis is associated with the activation of TGF-β/Smads/p38MAPK pathway caused by TiO2 NPs exposure is not well understood. Forty male mice were separately exposed to 0, 2.5, 5, or 10 mg/kg body weight TiO2 NPs for 6 months. Renal biochemical functions and levels of TGF-β/Smads/p38MAPK pathway-related markers and extracellular matrix (ECM) expression in the kidneys were investigated. The findings showed that subchronic TiO2 NPs exposure increased levels of urinary creatisix (Cr), N-acetyl-glucosaminidase, and vanin-1, resulted in severe renal inflammation and fibration. Furthermore, TiO2 NP exposure upregulated expression of transforming growth factor-β1 (TGF-β1, 0.07- to 2.72-fold), Smad2 (0.42- to 1.63-fold), Smad3 (0.02- to 1.94-fold), ECM (0.15- to 2.75-fold), α-smooth muscle actin (0.14- to 3.06-fold), p38 mitogen-activated protein kinase (p38MAPK, 0.11- to 3.78-fold), and nuclear factor-κB (0.4- to 2.27-fold), and downregulated Smad7 (0.05- to 0.61-fold) expression in mouse kidney. Subchronic TiO2 NPs exposure induced changes of renal characteristics towards inflammation and fibration may be mediated via TGF-β/Smads/p38MAPK pathway, and the uses of TiO2 NPs should be carried out cautiously, especially in humans. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1452-1461, 2016.

Fullerene mediates proliferation and cardiomyogenic differentiation of adipose-derived stem cells via modulation of MAPK pathway and cardiac protein expression

Zero-dimensional fullerenes can modulate the biological behavior of a variety of cell lines. However, the effects and molecular mechanisms of proliferation and cardiomyogenic differentiation in brown adipose-derived stem cells (BADSCs) are still unclear. In this study, we report the initial biological effects of fullerene-C₆₀ on BADSCs at different concentrations. Results suggest that fullerene-C₆₀ has no cytotoxic effects on BADSCs even at a concentration of 100 μg/mL. Fullerene-C₆₀ improves the MAPK expression level and stem cell survival, proliferation, and cardiomyogenesis. Further, we found that the fullerene-C₆₀ modulates cardiomyogenic differentiation. Fullerene-C₆₀ improves the expression of cardiomyocyte-specific proteins (cTnT and α-sarcomeric actinin). At elevated concentration, fullerene-C₆₀ reduces the incidence of diminished spontaneous cardiac differentiation of BADSCs with time. At the genetic level, fullerene-C₆₀ (5 μg/mL) also improves the expression of cTnT. In addition, fullerene-C₆₀ promotes the formation of gap junction among cells. These findings have important implications for clinical application of fullerenes in the treatment of myocardial infarction.

Exposure to TiO2 Nanoparticles Induces Immunological Dysfunction in Mouse Testitis

Although TiO2 nanoparticles (NPs) as endocrine disruptors have been demonstrated to be able to cross the blood-testis barriers and induce reproductive toxicity in male animals, whether the reproductive toxicity of male animals due to exposure to endocrine disruptor TiO2 NPs is related to immunological dysfunction in the testis remains not well understood. This study determined whether the reproductive toxicity and immunological dysfunction induced by exposure to TiO2 NPs is associated with activation or inhibition of TAM/TLR-mediated signal pathway in mouse testis. The results showed that male mice exhibited significant reduction of fertility, infiltration of inflammatory cells, rarefaction, apoptosis, and/or necrosis of spermatogenic cells and Sertoli cells due to TiO2 NPs. Furthermore, these were associated with decreased expression of Tyro3 (-18.16 to -66.6%), Axl (-14.7 to -57.99%), Mer (-7.98 to -72.62%), and IκB (-11.25 to -63.16%), suppression of cytokine signaling (SOCS) 1 (-21.99 to -73.8%) and SOCS3 (-8.11 to -34.86%), and increased expression of Toll-like receptor (TLR)-3 (21.4-156.03%), TLR-4 (37.0-109.87%), nuclear factor-κB (14.75-69.34%), interleukin (IL)-lβ (46.15-123.08%), IL-6 (2.54-81.98%), tumor necrosis factor-α (6.95-88.39%), interferon (IFN)-α (2.54-37.25%), and IFN-β (10.19-80.56%), which are involved in the immune environment in the testis. The findings showed that reproductive toxicity of male mice induced by exposure to endocrine disruptor TiO2 NPs may be associated with biomarkers of impairment of immune environment or dysfunction of TAM/TLR3-mediated signal pathway in mouse testitis. Therefore, the potential risks to reproductive health should be attended, especially in those who are occupationally exposed to TiO2 NPs.

Drosophila melanogaster as a suitable in vivo model to determine potential side effects of nanomaterials: A review

Despite being a relatively new field, nanoscience has been in the forefront among many scientific areas. Nanoparticle materials (NM) present interesting physicochemical characteristics not necessarily found in their bulky forms, and alterations in their size or coating markedly modify their physical, chemical, and biological properties. Due to these novel properties there is a general trend to exploit these NM in several fields of science, particularly in medicine and industry. The increased presence of NM in the environment warrants evaluation of potential harmful effects in order to protect both environment and human exposed populations. Although in vitro approaches are commonly used to determine potential adverse effects of NM, in vivo studies generate data expected to be more relevant for risk assessment. As an in vivo model Drosophila melanogaster was previously found to possess reliable utility in determining the biological effects of NM, and thus its usage increased markedly over the last few years. The aims of this review are to present a comprehensive overview of all apparent studies carried out with NM and Drosophila, to attain a clear and comprehensive picture of the potential risk of NM exposure to health, and to demonstrate the advantages of using Drosophila in nanotoxicological investigations.

Unraveling the neurotoxicity of titanium dioxide nanoparticles: focusing on molecular mechanisms

Titanium dioxide nanoparticles (TiO2 NPs) possess unique characteristics and are widely used in many fields. Numerous in vivo studies, exposing experimental animals to these NPs through systematic administration, have suggested that TiO2 NPs can accumulate in the brain and induce brain dysfunction. Nevertheless, the exact mechanisms underlying the neurotoxicity of TiO2 NPs remain unclear. However, we have concluded from previous studies that these mechanisms mainly consist of oxidative stress (OS), apoptosis, inflammatory response, genotoxicity, and direct impairment of cell components. Meanwhile, other factors such as disturbed distributions of trace elements, disrupted signaling pathways, dysregulated neurotransmitters and synaptic plasticity have also been shown to contribute to neurotoxicity of TiO2 NPs. Recently, studies on autophagy and DNA methylation have shed some light on possible mechanisms of nanotoxicity. Therefore, we offer a new perspective that autophagy and DNA methylation could contribute to neurotoxicity of TiO2 NPs. Undoubtedly, more studies are needed to test this idea in the future. In short, to fully understand the health threats posed by TiO2 NPs and to improve the bio-safety of TiO2 NPs-based products, the neurotoxicity of TiO2 NPs must be investigated comprehensively through studying every possible molecular mechanism.

A review on potential neurotoxicity of titanium dioxide nanoparticles

As the rapid development of nanotechnology in the past three decades, titanium dioxide nanoparticles (TiO2 NPs), for their peculiar physicochemical properties, are widely applied in consumer products, food additives, cosmetics, drug carriers, and so on. However, little is known about their potential exposure and neurotoxic effects. Once NPs are unintentionally exposed to human beings, they could be absorbed, and then accumulated in the brain regions by passing through the blood-brain barrier (BBB) or through the nose-to-brain pathway, potentially leading to dysfunctions of central nerve system (CNS). Besides, NPs may affect the brain development of embryo by crossing the placental barrier. A few in vivo and in vitro researches have demonstrated that the morphology and function of neuronal or glial cells could be impaired by TiO2 NPs which might induce cell necrosis. Cellular components, such as mitochondrial, lysosome, and cytoskeleton, could also be influenced as well. The recognition ability, spatial memory, and learning ability of TiO2 NPs-treated rodents were significantly impaired, which meant that accumulation of TiO2 NPs in the brain could lead to neurodegeneration. However, conclusions obtained from those studies were not consistent with each other as researchers may choose different experimental parameters, including administration ways, dosage, size, and crystal structure of TiO2 NPs. Therefore, in order to fully understand the potential risks of TiO2 NPs to brain health, figure out research areas where further studies are required, and improve its bio-safety for applications in the near future, how TiO2 NPs interact with the brain is investigated in this review by summarizing the current researches on neurotoxicity induced by TiO2 NPs.

Pooling and Analysis of Published in Vitro Data: A Proof of Concept Study for the Grouping of Nanoparticles

The study aim was to test the applicability of pooling of nanomaterials-induced in vitro data for identifying the toxic capacity of specific (SiO₂, TiO₂, ZnO, CuO, CeO₂ and carbon nanotubes, [CNT]) nanoparticles (NP) and to test the usefulness for grouping purposes. Publication selection was based on specific criteria regarding experimental conditions. Two relevant biological endpoints were selected; generation of intracellular reactive oxygen species (ROS) and viability above 90%. The correlations of the ROS ratios with the NP parameters' size, concentration, and exposure time were analysed. The obtained data sets were then analysed with multiple regression analysis of variance (ANOVA) and the Tukey post-hoc test. The results show that this method is applicable for the selected metal oxide NP, but might need reconsideration and a larger data set for CNT. Several statistically significant correlations and results were obtained, thus validating the method. Furthermore, the relevance of the combination of ROS release with a cell viability test was shown. The data also show that it is advisable to compare ROS production of professional phagocytic with non-phagocytic cells. In conclusion, this is the first systematic analysis showing that pooling of available data into groups is a useful method for evaluation of data regarding NP induced toxicity in vitro.

Assessment of cytotoxicity and oxidative stress induced by titanium oxide nanoparticles on Chinook salmon cells

Titanium oxide nanoparticles (TiO2 NPs) have received wide attention in diverse application, but the potential impact of these nanomaterials on the environment, aquatic life and especially on fish cell lines is lacking. The present study aimed to investigate the cytotoxicity and oxidative stress induced by TiO2 NPs on Chinook salmon cells derived from Oncorhynchus tshawytscha embryos (CHSE-214). The The MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide] and neutral red (NR) assays in CHSE-214 cells exposed to TiO2 NPs revealed concentration-dependent cytotoxic effect in the range of 10 to 60 μg/ml for 24 h. CHSE-214 cells exposed to TiO2 NPs (10-60 μg/ml) exhibited significant decline in superoxide dismutase (SOD), catalase (CAT) glutathione (GSH) content and increased lipid peroxidation (LPO) in a concentration-dependent manner. TiO2 NPs induced cytotoxicity and oxidative stress in CHSE-214 cells which serve as a base line studies for future studies.

High content analysis at single cell level identifies different cellular responses dependent on nanomaterial concentrations

A mechanistic understanding of nanomaterial (NM) interaction with biological environments is pivotal for the safe transition from basic science to applied nanomedicine. NM exposure results in varying levels of internalized NM in different neighboring cells, due to variances in cell size, cell cycle phase and NM agglomeration. Using high-content analysis, we investigated the cytotoxic effects of fluorescent quantum dots on cultured cells, where all effects were correlated with the concentration of NMs at the single cell level. Upon binning the single cell data into different categories related to NM concentration, this study demonstrates, for the first time, that quantum dots activate both cytoprotective and cytotoxic mechanisms, resulting in a zero net result on the overall cell population, yet with significant effects in cells with higher cellular NM levels. Our results suggest that future NM cytotoxicity studies should correlate NM toxicity with cellular NM numbers on the single cell level, as conflicting mechanisms in particular cell subpopulations are commonly overlooked using classical toxicological methods.

Titanium Dioxide Nanoparticles Trigger Loss of Function and Perturbation of Mitochondrial Dynamics in Primary Hepatocytes

Titanium dioxide (TiO2) nanoparticles are one of the most highly manufactured and employed nanomaterials in the world with applications in copious industrial and consumer products. The liver is a major accumulation site for many nanoparticles, including TiO2, directly through intentional exposure or indirectly through unintentional ingestion via water, food or animals and increased environmental contamination. Growing concerns over the current usage of TiO2 coupled with the lack of mechanistic understanding of its potential health risk is the motivation for this study. Here we determined the toxic effect of three different TiO2 nanoparticles (commercially available rutile, anatase and P25) on primary rat hepatocytes. Specifically, we evaluated events related to hepatocyte functions and mitochondrial dynamics: (1) urea and albumin synthesis using colorimetric and ELISA assays, respectively; (2) redox signaling mechanisms by measuring reactive oxygen species (ROS) production, manganese superoxide dismutase (MnSOD) activity and mitochondrial membrane potential (MMP); (3) OPA1 and Mfn-1 expression that mediates the mitochondrial dynamics by PCR; and (4) mitochondrial morphology by MitoTracker Green FM staining. All three TiO2 nanoparticles induced a significant loss (p < 0.05) in hepatocyte functions even at concentrations as low as 50 ppm with commercially used P25 causing maximum damage. TiO2 nanoparticles induced a strong oxidative stress in primary hepatocytes. TiO2 nanoparticles exposure also resulted in morphological changes in mitochondria and substantial loss in the fusion process, thus impairing the mitochondrial dynamics. Although this study demonstrated that TiO2 nanoparticles exposure resulted in substantial damage to primary hepatocytes, more in vitro and in vivo studies are required to determine the complete toxicological mechanism in primary hepatocytes and subsequently liver function.

On the photocatalytic reduction of MTT tetrazolium salt on the surface of TiO2 nanoparticles: Formazan production kinetics and mechanism

HYPOTHESIS

The MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium-bromide] cell cytotoxicity indicator is photocatalytically reduced on the surface of TiO2 nanoparticles in phosphate-buffered-saline (PBS) environment. We hypothesize that specific phosphate adsorption may be used to modulate the efficiency of the TiO2-MTT reaction through colloidal and semiconductor-liquid interface processes.

EXPERIMENTS

The TiO2-MTT reaction kinetics was studied in PBS, with respect to photocatalyst and MTT concentrations and irradiation wavelength. The effects of PBS and electron scavengers (Fe(3+) ions) on reaction efficiency and the role of colloidal surface charge in the photocatalytic process were investigated. The structural and spectroscopic characteristics of relevant TiO2-formazan systems were studied by X-ray diffraction, transmission electron microscopy and IR-spectroscopy.

FINDINGS

The reaction was pseudo-first order with respect to photocatalyst and showed a negative and fractional partial order with respect to MTT. Formazan production rates were directly proportional to radiation wavelength and TiO2 concentration and inversely proportional to the MTT initial concentration. The addition of Fe(3+) ions, as well as the absence of PBS, induced strong reaction inhibition. Reaction efficiency and catalyst Zeta potential were enhanced by Na2HPO4 (PBS component) and showed a maximum around the phosphate concentration 0.005 M. Structural/spectroscopic characterization confirmed the formation of amorphous MTT-formazan on the surface of TiO2 and the TiO2-phosphate binding.

Central nervous system toxicity of metallic nanoparticles

Nanomaterials (NMs) are increasingly used for the therapy, diagnosis, and monitoring of disease- or drug-induced mechanisms in the human biological system. In view of their small size, after certain modifications, NMs have the capacity to bypass or cross the blood–brain barrier. Nanotechnology is particularly advantageous in the field of neurology. Examples may include the utilization of nanoparticle (NP)-based drug carriers to readily cross the blood–brain barrier to treat central nervous system (CNS) diseases, nanoscaffolds for axonal regeneration, nanoelectromechanical systems in neurological operations, and NPs in molecular imaging and CNS imaging. However, NPs can also be potentially hazardous to the CNS in terms of nano-neurotoxicity via several possible mechanisms, such as oxidative stress, autophagy, and lysosome dysfunction, and the activation of certain signaling pathways. In this review, we discuss the dual effect of NMs on the CNS and the mechanisms involved. The limitations of the current research are also discussed.

Analysis of cytotoxic effects of silver nanoclusters on human peripheral blood mononuclear cells 'in vitro'

The antimicrobial properties of silver nanoparticles (AgNPs) have made these particles one of the most used nanomaterials in consumer products. Therefore, an understanding of the interactions (unwanted toxicity) between nanoparticles and human cells is of significant interest. The aim of this study was to assess the in vitro cytotoxicity effects of silver nanoclusters (AgNC, < 2 nm diameter) on peripheral blood mononuclear cells (PBMC). Using flow cytometry and comet assay methods, we demonstrate that exposure of PBMC to AgNC induced intracellular reactive oxygen species (ROS) generation, DNA damage and apoptosis at 3, 6 and 12 h, with a dose-dependent response (0.1, 1, 3, 5 and 30 µg ml(-1)). Advanced electron microscopy imaging of complete and ultrathin-sections of PBMC confirmed the cytotoxic effects and cell damage caused by AgNC. The present study showed that AgNC produced without coating agents induced significant cytotoxic effects on PBMC owing to their high aspect ratio and active surface area, even at much lower concentrations (<1 µg ml(-1)) than those applied in previous studies, resembling what would occur under real exposure conditions to nanosilver-functionalized consumer products.

Application of dental nanomaterials: potential toxicity to the central nervous system

Nanomaterials are defined as materials with one or more external dimensions with a size of 1-100 nm. Such materials possess typical nanostructure-dependent properties (eg, chemical, biological, optical, mechanical, and magnetic), which may differ greatly from the properties of their bulk counterparts. In recent years, nanomaterials have been widely used in the production of dental materials, particularly in light polymerization composite resins and bonding systems, coating materials for dental implants, bioceramics, endodontic sealers, and mouthwashes. However, the dental applications of nanomaterials yield not only a significant improvement in clinical treatments but also growing concerns regarding their biosecurity. The brain is well protected by the blood-brain barrier (BBB), which separates the blood from the cerebral parenchyma. However, in recent years, many studies have found that nanoparticles (NPs), including nanocarriers, can transport through the BBB and locate in the central nervous system (CNS). Because the CNS may be a potential target organ of the nanomaterials, it is essential to determine the neurotoxic effects of NPs. In this review, possible dental nanomaterials and their pathways into the CNS are discussed, as well as related neurotoxicity effects underlying the in vitro and in vivo studies. Finally, we analyze the limitations of the current testing methods on the toxicological effects of nanomaterials. This review contributes to a better understanding of the nano-related risks to the CNS as well as the further development of safety assessment systems.

Toxicity of titanium dioxide nanoparticles in central nervous system

Titanium dioxide nanoparticles (TiO2 NPs) have found many practical applications in industry and daily life. A widespread application of TiO2 NPs rises the question about safety of their use in the context of potential occupational, environmental and intentional exposure of humans and biota. TiO2 NPs easily enter the body through inhalation, cross blood-brain barrier and accumulate in the brain, especially in the cortex and hippocampus. Toxicity of these NPs and the molecular mechanisms of their action have been studied extensively in recent years. Studies showed that TiO2 NPs exposure resulted in microglia activation, reactive oxygen species production, activation of signaling pathways involved in inflammation and cell death, both in vitro and in vivo. Consequently, such action led to neuroinflammation, further brain injury. A spatial recognition memory and locomotor activity impairment has been also observed.

Comparative cellular toxicity of titanium dioxide nanoparticles on human astrocyte and neuronal cells after acute and prolonged exposure

Although in the last few decades, titanium dioxide nanoparticles (TiO₂NPs) have attracted extensive interest due to their use in wide range of applications, their influences on human health are still quite uncertain and less known. Evidence exists indicating TiO₂NPs ability to enter the brain, thus representing a realistic risk factor for both chronic and accidental exposure with the consequent needs for more detailed investigation on CNS. A rapid and effective in vitro test strategy has been applied to determine the effects of TiO₂NPs anatase isoform, on human glial (D384) and neuronal (SH-SY5Y) cell lines. Toxicity was assessed at different levels: mitochondrial function (by MTT), membrane integrity and cell morphology (by calcein AM/PI staining) after acute exposure (4-24-48 h) at doses from 1.5 to 250 μg/ml as well as growth and cell proliferation (by clonogenic test) after prolonged exposure (7-10 days) at sub-toxic concentrations (from 0.05 to 31 μg/ml). The cytotoxic effects of TiO₂NPs were compared with those caused by TiO₂ bulk counterpart treatment. Acute TiO₂NP exposure produced (i) dose- and time-dependent alterations of the mitochondrial function on D384 and SH-SY5Y cells starting at 31 and 15 μg/ml doses, respectively, after 24h exposure. SH-SY5Y were slightly more sensitive than D384 cells; and (ii) cell membrane damage occurring at 125 μg/ml after 24h exposure in both cerebral cells. Comparatively, the effects of TiO₂ bulk were less pronounced than those induced by nanoparticles in both cerebral cell lines. Prolonged exposure indicated that the proliferative capacity (colony size) was compromised at the extremely low TiO₂NP doses namely 1.5 μg/ml and 0.1 μg/ml for D384 and SH-SY5Y, respectively; cell sensitivity was still higher for SH-SY5Y compared to D384. Colony number decrease (15%) was also evidenced at ≥0.2 μg/ml TiO₂NP dose. Whereas, TiO₂ bulk treatment affected cell morphology only. TiO₂ internalization in SH-SY5Y and D384 cells was appreciated using light microscopy. These findings indicated, that (i) human cerebral SH-SY5Y and D384 cell lines exposed to TiO₂NPs were affected not only after acute but even after prolonged exposure at particularly low doses (≥ 0.1 μg/ml), (ii) these in vitro critical doses were comparable to literature brain Ti levels detected in lab animal intranasally administered with TiO₂NP and associated to neurotoxic effects. In summary, the applied cell-based screening platform seems to provide effective means to initial evaluation of TiO₂NP toxicity on CNS.

Suppression of neurite outgrowth of primary cultured hippocampal neurons is involved in impairment of glutamate metabolism and NMDA receptor function caused by nanoparticulate TiO2

Numerous studies have indicated that nano-titanium dioxide (TiO2) can induce neurotoxicity in vitro and in vivo, however, it is unclear whether nano-TiO2 affects neurite outgrowth of hippocampal neurons. In order to investigate the mechanism of neurotoxicity, rat primary cultured hippocampal neurons on the fourth day of culture were exposed to 5, 15, and 30 μg/mL nano-TiO2 for 24 h, and nano-TiO2 internalization, dendritic growth, glutamate metabolism, expression of N-methyl-D-aspartate (NMDA) receptor subunits (NR1, NR2A and NR2B), calcium homeostasis, sodium current (INa) and potassium current (IK) were examined. Our findings demonstrated that nano-TiO2 crossed the membrane into the cytoplasm or nucleus, and significantly suppressed dendritic growth of primary cultured hippocampal neurons in a concentration-dependent manner. Furthermore, nano-TiO2 induced a marked release of glutamate to the extracellular region, decreased glutamine synthetase activity and increased phosphate-activated glutaminase activity, elevated intracellular calcium ([Ca(2+)]i), down-regulated protein expression of NR1, NR2A and NR2B, and increased the amplitudes of the INa and IK. In addition, nano-TiO2 increased nitric oxide and nitrice synthase, attenuated the activities of Ca(2+)-ATPase and Na(+)/K(+)-ATPase, and increased the ADP/ATP ratio in the primary neurons. Taken together, these findings indicate that nano-TiO2 inhibits neurite outgrowth of hippocampal neurons by interfering with glutamate metabolism and impairing NMDA receptor function.

Three dimensional spheroid cell culture for nanoparticle safety testing

Nanoparticles are widely employed for many applications and the number of consumer products, incorporating nanotechnology, is constantly increasing. A novel area of nanotechnology is the application in medical implants. The widespread use of nanoparticles leads to their higher prevalence in our environment. This, in turn, raises concerns regarding potential risks to humans. Previous studies have shown possible hazardous effects of some nanoparticles on mammalian cells grown in two-dimensional (2D) cultures. However, 2D in vitro cell cultures display several disadvantages such as changes in cell shape, cell function, cell responses and lack of cell-cell contacts. For this reason, the development of better models for mimicking in vivo conditions is essential. In the present work, we cultivated A549 cells and NIH-3T3 cells in three-dimensional (3D) spheroids and investigated the effects of zinc oxide (ZnO-NP) and titanium dioxide nanoparticles (TiO2-NP). The results were compared to cultivation in 2D monolayer culture. A549 cells in 3D cell culture formed loose aggregates which were more sensitive to the toxicity of ZnO-NP in comparison to cells grown in 2D monolayers. In contrast, NIH-3T3 cells showed a compact 3D spheroid structure and no differences in the sensitivity of the NIH-3T3 cells to ZnO-NP were observed between 2D and 3D cultures. TiO2-NP were non-toxic in 2D cultures but affected cell-cell interaction during 3D spheroid formation of A549 and NIH-3T3 cells. When TiO2-NP were directly added during spheroid formation in the cultures of the two cell lines tested, several smaller spheroids were formed instead of a single spheroid. This effect was not observed if the nanoparticles were added after spheroid formation. In this case, a slight decrease in cell viability was determined only for A549 3D spheroids. The obtained results demonstrate the importance of 3D cell culture studies for nanoparticle safety testing, since some effects cannot be revealed in 2D cell culture.

Effect of titanium dioxide nanoparticles on zebrafish embryos and developing retina

AIM

To investigate the impact of titanium dioxide nanoparticles (TiO2 NPs) on embryonic development and retinal neurogenesis.

METHODS

The agglomeration and sedimentation of TiO2 NPs solutions at different dilutions were observed, and the ultraviolet-visible spectra of their supernatants were measured. Zebrafish embryos were experimentally exposed to TiO2 NPs until 72h postfertilization (hpf). The retinal neurogenesis and distribution of the microglia were analyzed by immunohistochemistry and whole mount in situ hybridization.

RESULTS

The 1 mg/L was determined to be an appropriate exposure dose. Embryos exposed to TiO2 NPs had a normal phenotype. The neurogenesis was initiated on time, and ganglion cells, cones and rods were well differentiated at 72 hpf. The expression of fms mRNA and the 4C4 antibody, which were specific to microglia in the central nervous system (CNS), closely resembled their endogenous profile.

CONCLUSION

These data demonstrate that short-term exposure to TiO2 NPs at a low dose does not lead to delayed embryonic development or retinal neurotoxicity.

Oxidative and pro-inflammatory effects of cobalt and titanium oxide nanoparticles on aortic and venous endothelial cells

Ultra-fine particles have recently been included among the risk factors for the development of endothelium inflammation and atherosclerosis, and cobalt (CoNPs) and titanium oxide nanoparticles (TiNPs) have attracted attention because of their wide range of applications. We investigated their toxicity profiles in two primary endothelial cell lines derived from human aorta (HAECs) and human umbilical vein (HUVECs) by comparing cell viability, oxidative stress, the expression of adhesion molecules and the release of chemokines during NP exposure. Both NPs were very rapidly internalised, and significantly increased adhesion molecule (ICAM-1, VCAM-1, E-selectin) mRNA and protein levels and the release of monocyte chemoattractant protein-1 (MCP-1) and interleukin 8 (IL-8). However, unlike the TiNPs, the CoNPs also induced time- and concentration-dependent metabolic impairment and oxidative stress without any evident signs of cell death or the induction of apoptosis. There were differences between the HAECs and HUVECs in terms of the extent of oxidative stress-related enzyme and vascular adhesion molecule expression, ROS production, and pro-inflammatory cytokine release despite the similar rate of NP internalisation, thus indicating endothelium heterogeneity in response to exogenous stimuli. Our data indicate that NPs can induce endothelial inflammatory responses via various pathways not involving only oxidative stress.

Molecular mechanism of DNA damage induced by titanium dioxide nanoparticles in toll-like receptor 3 or 4 expressing human hepatocarcinoma cell lines

Background

Titanium dioxide nanoparticles (TiO₂ NPs) are widely used in the biological sciences. The increasing use of TiO₂ NPs increases the risk of humans and the environment being exposed to NPs. We previously showed that toll-like receptors (TLRs) play an important role in the interactions between NPs and cells. Our previous results indicated that TLR4 increased the DNA damage response induced by TiO₂ NPs, due to enhanced NP uptake into the cytoplasm, whereas TLR3 expression decreased the DNA damage response induced by TiO₂ NPs because of NP retention in the endosome. In this study, we explored the molecular mechanism of the DNA damage response induced by TiO₂ NPs using TLR3 or TLR4 transfected cells. We examined the effect of TLR3 or TLR4 over-expression on oxidative stress and the effect of DNA damage induced by TiO₂ NPs on gene expression levels.

Results

Our results showed evidence for elevated oxidative stress, including the generation of reactive oxygen species (ROS), with increased hydrogen peroxide levels, decreased glutathione peroxidase, and reduced glutathione and activated caspase-3 levels in cells exposed for 48 h to 10 μg/ml TiO₂ NPs. These effects were enhanced by TLR4 and reduced by TLR3 over-expression. Seventeen genes related to DNA double-strand breaks and apoptosis were induced, particularly IP6K3 and ATM.

Conclusion

Our results indicated that TiO₂ NPs induced ROS, and the above molecules are implicated in the genotoxicity induced by TiO₂ NPs.

Comparative responses to metal oxide nanoparticles in marine phytoplankton

A series of experiments was undertaken on three different marine microalgae to compare the effect of two metal oxide nanoparticles (NPs) on different physiological responses to stress: zinc oxide (ZnO), a known toxic compound for microalgae, and the never before tested yttrium oxide (Y₂O3). The effect of these potential pollutants was estimated for different physiological variables and temporal scales: Growth, carbon content, carbon-to-nitrogen (C:N) ratio, and chlorophyll fluorescence were evaluated in long-term assays, and reactive oxygen species (ROS) production was evaluated in a short-term assay. Population growth was the most susceptible variable to the acute toxic effects of both NPs as measured in terms of number of cells and of biomass. Although Phaeodactylum tricornutum and Alexandrium minutum were negatively affected by ZnO NPs, this effect was not detected in Tetraselmis suecica, in which cell growth was significantly decreased by Y₂O₃ NPs. Biomass per cell was negatively affected in the most toxic treatments in T. suecica but was positively affected in A. minutum. ZnO treatments induced a sharper decrease in chlorophyll fluorescence and higher ROS than did Y₂O₃ treatments. The pronounced differences observed in the responses between the species and the physiological variables tested highlight the importance of analyzing diverse groups of microalgae and various physiological levels to determine the potential effects of environmental pollutants.

Titanium dioxide nanoparticles induce strong oxidative stress and mitochondrial damage in glial cells

Titanium dioxide nanoparticles (TiO2 NPs) are widely used in the chemical, electrical, and electronic industries. TiO2 NPs can enter directly into the brain through the olfactory bulb and can be deposited in the hippocampus region; therefore, we determined the toxic effect of TiO2 NPs on rat and human glial cells, C6 and U373, respectively. We evaluated some events related to oxidative stress: (1) redox-signaling mechanisms by oxidation of 2',7'-dichlorodihydrofluorescein diacetate; (2) peroxidation of lipids by cis-parinaric acid; (3) antioxidant enzyme expression by PCR in real time; and (4) mitochondrial damage by MitoTracker Green FM staining and Rh123. TiO2 NPs induced a strong oxidative stress in both glial cell lines by mediating changes in the cellular redox state and lipid peroxidation associated with a rise in the expression of glutathione peroxidase, catalase, and superoxide dismutase 2. TiO2 NPs also produced morphological changes, damage of mitochondria, and an increase in mitochondrial membrane potential, indicating toxicity. TiO2 NPs had a cytotoxic effect on glial cells; however, more in vitro and in vivo studies are required to ascertain that exposure to TiO2 NPs can cause brain injury and be hazardous to health.

Mechanisms of TiO2 nanoparticle-induced neuronal apoptosis in rat primary cultured hippocampal neurons

Exposure to titanium dioxide nanoparticles (TiO2 NPs) has been demonstrated to decrease learning and memory of animals. However, whether the impacts of these NPs on the recognition function are involved in hippocamal neuron damages is poorly understood. In this study, primary cultured hippocampal neurons from one-day-old fetal Sprague-Dawley rats were exposed to 5, 15, or 30 µg/mL TiO2 NPs for 24 h, we investigated cell viability, ultrastructure, and mitochondrial membrane potential (MMP), calcium homeostasis, oxidative stress, antioxidant capacity, apoptotic signaling pathway associated with the primary cultured hippocamal neuron apoptosis. Our findings showed that TiO2 NP treatment resulted in reduction of cell viability, promoted lactate dehydrogenase release, apoptosis, and increased neuron apoptotic rate in a dose-dependent manner. Furthermore, TiO2 NPs led to [Ca(2+)]i elevation, and MMP reduction, up-regulated protein expression of cytochrome c, Bax, caspase-3, glucose-regulated protein 78, C/EBP homologous protein and caspase-12, and down-regulated bcl-2 expression in the primary cultured hippocampal neurons. These findings suggested that hippocampal neuron apoptosis caused by TiO2 NPs may be associated with mitochondria-mediated signal pathway and endoplasmic reticulum-mediated signal pathway.

ZnO nanoparticle-induced oxidative stress triggers apoptosis by activating JNK signaling pathway in cultured primary astrocytes

It has been documented in in vitro studies that zinc oxide nanoparticles (ZnO NPs) are capable of inducing oxidative stress, which plays a crucial role in ZnO NP-mediated apoptosis. However, the underlying molecular mechanism of apoptosis in neurocytes induced by ZnO NP exposure was not fully elucidated. In this study, we investigated the potential mechanisms of apoptosis provoked by ZnO NPs in cultured primary astrocytes by exploring the molecular signaling pathways triggered after ZnO NP exposure. ZnO NP exposure was found to reduce cell viability in MTT assays, increase lactate dehydrogenase (LDH) release, stimulate intracellular reactive oxygen species (ROS) generation, and elicit caspase-3 activation in a dose- and time-dependent manner. Apoptosis occurred after ZnO NP exposure as evidenced by nuclear condensation and poly(ADP-ribose) polymerase-1 (PARP) cleavage. A decrease in mitochondrial membrane potential (MMP) with a concomitant increase in the expression of Bax/Bcl-2 ratio suggested that the mitochondria also mediated the pathway involved in ZnO NP-induced apoptosis. In addition, exposure of the cultured cells to ZnO NPs led to phosphorylation of c-Jun N-terminal kinase (JNK), extracellular signal-related kinase (ERK), and p38 mitogen-activated protein kinase (p38 MAPK). Moreover, JNK inhibitor (SP600125) significantly reduced ZnO NP-induced cleaved PARP and cleaved caspase-3 expression, but not ERK inhibitor (U0126) or p38 MAPK inhibitor (SB203580), indicating that JNK signaling pathway is involved in ZnO NP-induced apoptosis in primary astrocytes.

Neurotoxicity of nanoscale materials

Nanotechnology has been applied in consumer products and commercial applications, showing a significant impact on almost all industries and all areas of society. Significant evidence indicates that manufactured nanomaterials and combustion-derived nano-materials elicit toxicity in humans exposed to these nanomaterials. The interaction of the engineered nanomaterials with the nervous system has received much attention in the nanotoxicology field. In this review, the biological effects of metal, metal oxide, and carbon-based nanomaterials on the nervous system are discussed from both in vitro and in vivo studies. The translocation of the nanoparticles through the blood–brain barrier or nose to brain via the olfactory bulb route, oxidative stress, and inflammatory mechanisms of nanomaterials are also reviewed.