Signaling Pathways and MicroRNA Changes in Nano-TiO2 Treated Human Lung Epithelial (BEAS-2B) Cells

Brucine Entrapped Titanium Oxide Nanoparticle for Anticancer Treatment: An In Vitro Study

Backgroundand Objective. The public's health has been seriously threatened by cervical cancer during recent times. In terms of newly diagnosed cases worldwide, it ranks as the ninth most prevalent malignancy. Multiple investigations have proven that nanoparticles can effectively combat cancer due to their small dimensions and extensive surface area. In the meantime, bioactive compounds which are biocompatible are being loaded onto nanoparticles to promote cancer therapy. The current study investigates the anticancerous potential of Brucine-entrapped titanium oxide nanoparticles (TiO2 NPs) in cervical cancer cell line (HeLa). Materials and Methods. The physiochemical, structural, and morphological aspects of Brucine-entrapped TiO2 NPs were evaluated by UV-visible spectrophotometer, Fourier transform-infrared spectroscopy (FT-IR), dynamic light scattering (DLS), scanning electron microscopy (SEM), and energy dispersive X-ray (EDAX). The cytotoxic effect against the HeLa cell line was assessed using a tetrazolium-based colorimetric assay (MTT), a trypan blue exclusion (TBE) assay, phase contrast microscopic analysis, and a fluorescence assay including ROS and DAPI staining. Furthermore, estimation of antioxidant markers includes catalase (CAT), glutathione (GSH), and superoxide dismutase (SOD). Results. The UV spectrum at 266 nm revealed the formation of TiO NPs. The FT-IR peaks confirmed the effective entrapment of brucine with TiO2 NPs. The average size (100.0 nm) of Brucine-entrapped TiO2 NPs was revealed in DLS analysis. The micrograph of the SEM revealed the formation of ellipsoidal to tetragonal-shaped NPs. The Ti, O, and C signals were observed in EDAX. In MTT assay, Brucine-entrapped TiO2 NPs showed inhibition of cell proliferation in a dose-wise manner and IC50 was noticed at the concentration of 30 µg/mL. The percentage of viable cells gradually reduced in the trypan blue exclusion assay. The phase contrast microscopic analysis of Brucine-entrapped TiO2 NP-treated cells showed cell shrinkage, cell wall deterioration, and cell blebbing. The intracellular ROS level was increased in a dose-wise manner when compared to control cells in ROS staining. The condensed nuclei and apoptotic cells were increased in treated cells, as noted in DAPI staining. In treated cells, the antioxidant markers such as CAT, GSH, and SOD levels were substantially lower compared to the control cells. Conclusion. The synthesized Brucine entrapped TiO2 NPs exhibited remarkable anticancer activity against the HeLa cell line.

Differential genomic effects of four nano-sized and one micro-sized CeO2 particles on HepG2 cells

The objective of this research was to perform a genomics study of five cerium oxide particles, 4 nano and one micrometer-sized particles which have been studied previously by our group with respect to cytotoxicity, biochemistry and metabolomics. Human liver carcinoma HepG2 cells were exposed to between 0.3 to 300 ug/ml of CeO2 particles for 72 hours and then total RNA was harvested. Fatty acid accumulation was observed with W4, X5, Z7 and less with Q but not Y6. The gene expression changes in the fatty acid metabolism genes correlated the fatty acid accumulation we detected in the prior metabolomics study for the CeO2 particles named W4, Y6, Z7 and Q, but not for X5. In particular, the observed genomics effects on fatty acid uptake and fatty acid oxidation offer a possible explanation of why many CeO2 particles increase cellular free fatty acid concentrations in HepG2 cells. The major genomic changes observed in this study were sirtuin, ubiquitination signaling pathways, NRF2-mediated stress response and mitochondrial dysfunction. The sirtuin pathway was affected by many CeO2 particle treatments. Sirtuin signaling itself is sensitive to oxidative stress state of the cells and may be an important contributor in CeO2 particle induced fatty acid accumulation. Ubiquitination pathway regulates many protein functions in the cells, including sirtuin signaling, NRF2 mediated stress, and mitochondrial dysfunction pathways. NRF2-mediated stress response and mitochondrial were reported to be altered in many nanoparticles treated cells. All these pathways may contribute to the fatty acid accumulation in the CeO2 particle treated cells.

Mechanobiological Analysis of Nanoparticle Toxicity

Nanoparticles (NPs) are commonly used in healthcare and nanotherapy, but their toxicity at high concentrations is well-known. Recent research has shown that NPs can also cause toxicity at low concentrations, disrupting various cellular functions and leading to altered mechanobiological behavior. While researchers have used different methods to investigate the effects of NPs on cells, including gene expression and cell adhesion assays, the use of mechanobiological tools in this context has been underutilized. This review emphasizes the importance of further exploring the mechanobiological effects of NPs, which could reveal valuable insights into the mechanisms behind NP toxicity. To investigate these effects, different methods, including the use of polydimethylsiloxane (PDMS) pillars to study cell motility, traction force production, and rigidity sensing contractions, have been employed. Understanding how NPs affect cell cytoskeletal functions through mechanobiology could have significant implications, such as developing innovative drug delivery systems and tissue engineering techniques, and could improve the safety of NPs for biomedical applications. In summary, this review highlights the significance of incorporating mechanobiology into the study of NP toxicity and demonstrates the potential of this interdisciplinary field to advance our knowledge and practical use of NPs.

The critical role of epigenetic mechanisms involved in nanotoxicology

Over the past decades, nanomaterials (NMs) have been widely applied in the cosmetic, food, engineering, and medical fields. Along with the prevalence of NMs, the toxicological characteristics exhibited by these materials on health and the environment have gradually attracted attentions. A growing number of evidences have indicated that epigenetics holds an essential role in the onset and development of various diseases. NMs could cause epigenetic alterations such as DNA methylation, noncoding RNA (ncRNA) expression, and histone modifications. NMs might alternate either global DNA methylation or the methylation of specific genes to affect the biological function. Abnormal upregulation or downregulation of ncRNAs might also be a potential mechanism for the toxic effects caused by NMs. In parallel, the phosphorylation, acetylation, and methylation of histones also take an important part in the process of NMs-induced toxicity. As the adverse effects of NMs continue to be explored, mechanisms such as chromosomal remodeling, genomic imprinting, and m⁶ A modification are also gradually coming into the limelight. Since the epigenetic alterations often occur in the early development of diseases, thus the relevant studies not only provide insight into the pathogenesis of diseases, but also screen for the prospective biomarkers for early diagnosis and prevention. This review summarizes the epigenetic alterations elicited by NMs, hoping to provide a clue for nanotoxicity studies and security evaluation of NMs. This article is categorized under: Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials.

Nanostructured Modifications of Titanium Surfaces Improve Vascular Regenerative Properties of Exosomes Derived from Mesenchymal Stem Cells: Preliminary In Vitro Results

(1) Background: Implantation of metal-based scaffolds is a common procedure for treating several diseases. However, the success of the long-term application is limited by an insufficient endothelialization of the material surface. Nanostructured modifications of metal scaffolds represent a promising approach to faster biomaterial osteointegration through increasing of endothelial commitment of the mesenchymal stem cells (MSC). (2) Methods: Three different nanotubular Ti surfaces (TNs manufactured by electrochemical anodization with diameters of 25, 80, or 140 nm) were seeded with human MSCs (hMSCs) and their exosomes were isolated and tested with human umbilical vein endothelial cells (HUVECs) to assess whether TNs can influence the secretory functions of hMSCs and whether these in turn affect endothelial and osteogenic cell activities in vitro. (3) Results: The hMSCs adhered on all TNs and significantly expressed angiogenic-related factors after 7 days of culture when compared to untreated Ti substrates. Nanomodifications of Ti surfaces significantly improved the release of hMSCs exosomes, having dimensions below 100 nm and expressing CD63 and CD81 surface markers. These hMSC-derived exosomes were efficiently internalized by HUVECs, promoting their migration and differentiation. In addition, they selectively released a panel of miRNAs directly or indirectly related to angiogenesis. (4) Conclusions: Preconditioning of hMSCs on TNs induced elevated exosomes secretion that stimulated in vitro endothelial and cell activity, which might improve in vivo angiogenesis, supporting faster scaffold integration.

Effects of Silver Nanoparticles and Silver Nitrate on mRNA and microRNA Expression in Human Hepatocellular Carcinoma Cells (HepG2)

In order to understand toxicity of nano silver, human hepatocellular carcinoma (HepG2) cells were treated either with silver nitrate (AgNO₃) or with nano silver capped with glutathione (Ag-S) at various concentration. Differentially expressed genelists for mRNA and microRNA were obtained through Illumina RNA sequencing and DEseq data analyses. Both treatments showed non-linear dose response relationships for mRNA and microRNA. Gene expression analysis showed signaling pathways common to both nano Ag-S and AgNO₃, such as cell cycle regulation, DNA damage response and cancer related pathways. But, nano Ag-S caused signaling pathway changes that were not altered by AgNO₃ such as NRF2-mediated oxidative stress response inflammation, cell membrane signaling, and cell proliferation. Nano Ag-S also affected p53 signaling, survival, apoptosis, tissue repair, lipid synthesis, angiogenesis, liver fibrosis and tumor development. Several of the pathways affected by nano Ag-S are hypothesized as major contributors to nanotoxicity. MicroRNA target filter analysis revealed additional affected pathways that were not reflected in the mRNA expression response alone, including DNA damage signaling, genomic stability, ROS, cell cycle, ubiquitination, DNA methylation, cell proliferation and fibrosis for AgNO₃; and cell cycle regulation, P53 signaling, cell proliferation, survival, apoptosis, tissue repair and so on for nano Ag-S. These pathways may be mediated by microRNA repression of protein translation.Our study clearly showed that the addition of microRNA profiling increased the numbers of signaling pathways discovered that affected by the treatments on HepG2 cells and gave US a better picture of the effects of these reagents in the cells.

Network-based analysis implies critical roles of microRNAs in the long-term cellular responses to gold nanoparticles

Since gold nanoparticles (AuNPs) have great potential to bring improvements to the biomedical field, their impact on biological systems should be better understood, particularly over the long term, using realistic doses of exposure. MicroRNAs (miRNAs) are small noncoding RNAs that play key roles in the regulation of biological pathways, from development to cellular stress responses. In this study, we performed genome-wide miRNA expression profiling in primary human dermal fibroblasts 20 weeks after chronic and acute (non-chronic) treatments to four AuNPs with different shapes and surface chemistries at a low dose. The exposure condition and AuNP surface chemistry had a significant impact on the modulation of miRNA levels. In addition, a network-based analysis was employed to provide a more complex, systems-level perspective of the miRNA expression changes. In response to the stress caused by AuNPs, miRNA co-expression networks perturbed in cells under non-chronic exposure to AuNPs were enriched for target genes implicated in the suppression of proliferative pathways, possibly in attempt to restore cell homeostasis, while changes in miRNA co-expression networks enriched for target genes related to activation of proliferative and suppression of apoptotic pathways were observed in cells chronically exposed to one specific type of AuNPs. In this case, miRNA dysregulation might be contributing to enforce a new cell phenotype during stress. Our findings suggest that miRNAs exert critical roles in the cellular responses to the stress provoked by a low dose of NPs in the long term and provide a fertile ground for further targeted experimental studies.

The Toxicity Phenomenon and the Related Occurrence in Metal and Metal Oxide Nanoparticles: A Brief Review From the Biomedical Perspective

Thousands of different nanoparticles (NPs) involve in our daily life with various origins from food, cosmetics, drugs, etc. It is believed that decreasing the size of materials up to nanometer levels can facilitate their unfavorable absorption since they can pass the natural barriers of live tissues and organs even, they can go across the relatively impermeable membranes. The interaction of these NPs with the biological environment disturbs the natural functions of cells and its components and cause health issues. In the lack of the detailed and comprehensive standard protocols about the toxicity of NPs materials, their control, and effects, this review study focuses on the current research literature about the related factors in toxicity of NPs such as size, concentration, etc. with an emphasis on metal and metal oxide nanoparticles. The goal of the study is to highlight their potential hazard and the advancement of green non-cytotoxic nanomaterials with safe threshold dose levels to resolve the toxicity issues. This study supports the NPs design along with minimizing the adverse effects of nanoparticles especially those used in biological treatments.

MicroRNA Response and Toxicity of Potential Pathways in Human Colon Cancer Cells Exposed to Titanium Dioxide Nanoparticles

Titanium dioxide nanoparticles (TiO₂-NPs) are widely used for biomedical and food applications, the toxicity of TiO₂-NPs in vivo and in vitro has been elucidated, but the underlying cytotoxicity of TiO₂-NPs against microRNA remains largely unknown. The purpose of this study was to analyze microRNA profiling induced by TiO₂-NPs against NCM460 and HCT116 cell lines. Comparative analysis identified 34 and 24 microRNAs were significantly altered in the TiO₂-NPs treated cells at concentrations of 3 μg/mL and 30 μg/mL, respectively. Functional classification demonstrated that a large proportion of genes involved in metabolism, human disease, and environmental information process were significantly upregulated by TiO₂-NPs. Bioinformatics analysis suggested that microRNA 378 might be an early indicator of cellular response to exogenous stimuli with apoptotic signals. Furthermore, TiO₂-NPs significantly altered the expression of microRNA 378b and 378g in HCT116 and NCM460 cell lines at different concentrations from 3 to 6 μg/mL. These concentrations elicit high-sensitivity of stimuli response in colon cancer cells when exposed to the slight doses of TiO₂-NPs. Our study indicated that microRNAs 378b and 378g may play an important role in TiO₂-NPs-mediated colonic cytotoxicity, which may provide a valuable insight into the molecular mechanisms of potential risks in colitis and colon cancer.

Irreversible disruption of the cytoskeleton as induced by non-cytotoxic exposure to titanium dioxide nanoparticles in lung epithelial cells

Exposure to TiO₂ NPs induces several cellular alterations after NPs uptake including disruption of cytoskeleton that is crucial for lung physiology but is not considered as a footprint of cell damage. We aimed to investigate cytoskeleton disturbances and the impact on cell migration induced by an acute TiO₂ NPs exposure (24 h) and the recovery capability after 6 days of NPs-free treatment, which allowed investigating if cytoskeleton damage was reversible. Exposure to TiO₂ NPs (10 μg/cm²) for 24 h induced a decrease 20.2% and 25.1% in tubulin and actin polymerization. Exposure to TiO₂ NPs (10 μg/cm²) for 24 h followed by 6 days of NPs-free had a decrease of 26.6% and 21.3% in tubulin and actin polymerization, respectively. The sustained exposure for 7 days to 1 μg/cm² and 10 μg/cm² induced a decrease of 22.4% and 30.7% of tubulin polymerization respectively, and 28.7% and 46.2% in actin polymerization. In addition, 24 h followed 6 days of NPs-free exposure of TiO₂ NPs (1 μg/cm² and 10 μg/cm²) decreased cell migration 40.7% and 59.2%, respectively. Cells exposed (10 μg/cm²) for 7 days had a decrease of 65.5% in cell migration. Ki67, protein surfactant B (SFTPB) and matrix metalloprotease 2 (MMP2) were analyzed as genes related to lung epithelial function. The results showed a 20% of Ki67 upregulation in cells exposed for 24 h to 10 μg/cm² TiO₂ NPs while a downregulation of 20% and 25.8% in cells exposed to 1 μg/cm² and 10 μg/cm² for 24 h followed by 6 days of NPs-free exposure. Exposure to 1 μg/cm² and 10 μg/cm² for 24 h and 7 days upregulates SFTPB expression in 53% and 59% respectively, MMP2 expression remain unchanged. In conclusion, exposure of TiO₂ NPs affected cytoskeleton of lung epithelial cells irreversibly but this damage was not cumulative.

Titanium Dioxide Nanoparticles Alter the Cellular Phosphoproteome in A549 Cells

TiO₂ nanoparticles (NPs) are one of the most produced NPs worldwide and are used in many consumer products. Their impact on human health, especially through inhalation, has been studied for more than two decades. TiO₂ is known for its strong affinity towards phosphates, and consequently interaction with cellular phosphates may be one of the mechanisms driving its toxicity. In the present study, we used a phosphoproteomics approach to document the interaction of TiO₂-NP with phosphoproteins from A549 human pulmonary alveolar epithelial cells. Cells were exposed to 21 nm anatase/rutile TiO₂-NPs, then their phosphopeptides were extracted and analyzed using shotgun proteomics. By comparing the phosphoprotein content, phosphorylation status and phosphorylation sites of exposed cells with that of control cells, our results show that by affecting the phosphoproteome, TiO₂-NPs affect cellular processes such as apoptosis, linked with cell cycle and the DNA damage response, TP53 being central to these pathways. Other pathways including inflammation and molecular transport are also affected. These molecular mechanisms of TiO₂-NP toxicity have been reported previously, our study shows for the first time that they may derive from phosphoproteome modulation, which could be one of their upstream regulators.

Memory effect of arsenic-induced cellular response and its influences on toxicity of titanium dioxide nanoparticle

Toxicity of arsenic (As) has been widely characterized. However, few studies focus on whether cell responses induced by As at nontoxic concentration could be inherited and further change cell tolerance to another pollutant. In this study, human A549 and HeLa cells were exposed to As at nontoxic concentrations for 10 or 15 passages, then the cells were recovered in the cell medium without As. At 25th passage, residual As in both type of cells was completely removed through the recovery process. And no abnormity in cell viability was identified in both type of cells between control and As-treated groups. Above results indicated that As exposure-recovery treatment had limited influence on phenotype of the cells. However, gene expression profiles determined by high-throughput sequencing showed that As exposure-recovery treatment induced similar expression modification of genes related to inflammation, oxidative stress and epigenetic modulation in the A549 and HeLa cells after recovery of 10 or 15 passages, indicating that As-induced cellular responses have been partially memorized at transcriptional level. The memory effect might play key roles in increased tolerance of the A549 and HeLa cells to adverse effects (cell viability, intracellular reactive oxygen species (ROS) generation and plasma membrane damage) induced by titanium dioxide nanoparticles (as representative pollutant). This study shed new lights on toxic effects induced by As at nontoxic concentration, which is useful for risk assessment of combined effects of As and other pollutants.

Induction of Apoptosis and Inhibition of Invasion in Gastric Cancer Cells by Titanium Dioxide Nanoparticles

Objectives

Nanoparticles induce oxidative stress in cells and damage them through the cell membrane and DNA damage, eventually resulting in cell death. This study aimed to evaluate the effect of titanium dioxide (TiO₂) nanoparticles on apoptosis induction and invasion of gastric cancer cell line, MKN-45.

Methods

We used the MTT assay to assess proliferation of MKN-45 gastric cancer cells after exposure to different forms of TiO₂ nanoparticles including amorph, brookite, anatase, and rutile coated with polyethylene glycol (PEG) and bovine serum albumin (BSA). Ethidium bromide and acridine orange staining were used to visualize cancer cell apoptosis, and the wound healing assay technique (migration test) was used to assay cancer cell invasion.

Results

Viability and proliferation of cancer cells in the presence of various forms of TiO₂ nanoparticles were reduced (p ≤ 0.050). This reduction in cell proliferation and viability was directly related to concentration and duration of exposure to nanoparticles. Induction of cell death was seen in all groups (p ≤ 0.050). Increased cell invasion was seen in PEG-amorph TiO₂ group compared to the control group. Cell invasion was decreased only in the brookite BSA group (p ≤ 0.050).

Conclusions

Various forms of TiO₂ nanoparticles reduced cell proliferation and induced apoptosis in cancer cells. Some forms of TiO₂ nanoparticles such as brookite BSA also inhibited cell invasion. PEG-amorph TiO₂ nanoparticles increased cell invasion. These differences seem to be due to the effects of different configurations of TiO₂ nanoparticles. TiO₂ may provide a new strategy for cancer treatment and more studies are needed.

Molecular mechanism for miR-350 in regulating of titanium dioxide nanoparticles in macrophage RAW264.7 cells

This study investigated the role of microRNA(miRNA) in regulating the cytotoxicity of TiO₂ nanoparticles (nano-TiO₂) to RAW264.7 cells. RAW264.7 cells were treated with 0 and 100 μg/ml nano-TiO₂ for 24 h (for miRNA analysis). The differentially expressed miRNAs were detected using Illumina HiSeq™ 2000 sequencing. Through the bio-informatics analysis, miR-350 was found to play an important role in multiple signaling pathways, including MAPK signaling pathway, NF-kappa B signaling pathway and Apoptosis. To characterize the miR-350 function, miR-350 mimic was transfected into RAW264.7 cells for 24 h. MTT and Flow Cytometry were performed to detect cell proliferation, apoptosis and cell cycle (repetition), respectively. QRT-PCR, Western Blot methods and Luciferase assays were applied to detect expression of putative target gene PIK3R3. The results showed that miRNA profiles were differentially dysregulated. The apoptosis rate of miR-350 mimic group was significantly higher than negative control group (p < .05). Cell proliferation and cell cycle had no significant differences between treatment and negative control group. Compared with negative control, the level of protein of PIK3R3 was significantly decreased (p < .05), and the expression of 3'UTR constructs of PIK3R3 was significantly decreased (p < .05) in miR-350 mimic group. The expression of miRNAs was changed after exposed to nano-TiO₂, and biological function and target gene results showed miR-350 may promote RAW264.7 cell apoptosis through the negative regulation of PIK3R3 gene. Our results could provide a basis for further understanding of toxicity and possible mechanisms of nano-TiO₂ exposure.

miR-17-92基因簇在肿瘤发生发展中作用的研究进展

肿瘤是威胁全世界人类健康和影响社会经济的重要因素. 近年来, 随着经济的发展, 肿瘤的发病率呈明显上升趋势, 但是其病因尚未完全阐明. 越来越多的证据显示肿瘤的发生和遗传因素有关, 随着病理生理学和遗传学的发展, 许多学者认为生物标志物可以预测癌症甚至指导临床治疗. 微小RNA(microRNA, miRNA)是非编码小分子RNA, 在发育、生理、病理过程以及肿瘤发生等环节中起着重要的调节作用. miR-17-92基因簇是研究较为深入、最有特点的miRNA, 被认为是原癌基因miRNA的代表, 在多种肿瘤的发生发展中起着至关重要的作用. 本文就miR-17-92基因簇在肿瘤发生发展中的作用及功能进行综述.

Potential adverse effects of engineered nanomaterials commonly used in food on the miRNome

The emergence of nanotechnology has greatly impacted our daily lives. Multiple products, including cosmetics, pharmaceuticals, electronics and food, are produced with incorporation of nanomaterials (NMs). Nanotechnology has yielded many promising benefits, yet, there remains much uncertainty about the hazards of NMs to humans. Hence, it is important to ensure safety of the users. Although many in vitro and in vivo studies have been carried out on the potential toxicity generated by NMs in food, its effects on the microRNA genome (miRNome) involved in the regulation of gene expression have been poorly understood. Therefore, this review focuses on the types of commonly used NMs (containing silicon dioxide, titanium dioxide, silver or zinc oxide) in food products and their potential toxic effects, including how NMs can induce epigenetic toxicity mediated via altered miRNA expression.

Genotoxicity of TiO2 nanoparticles assessed by mini-gel comet assay and micronucleus scoring with flow cytometry

The widespread production and use of nanoparticles calls for faster and more reliable methods to assess their safety. The main aim of this study was to investigate the genotoxicity of three reference TiO₂ nanomaterials (NM) within the frame of the FP7-NANoREG project, with a particular focus on testing the applicability of mini-gel comet assay and micronucleus (MN) scoring by flow cytometry. BEAS-2B cells cultured under serum-free conditions were exposed to NM100 (anatase, 50–150nm), NM101 (anatase, 5–8nm) and NM103 (rutile, 20–28nm) for 3, 24 or 48h mainly at concentrations 1–30 μg/ml. In the mini-gel comet assay (eight gels per slide), we included analysis of (i) DNA strand breaks, (ii) oxidised bases (Fpg-sensitive sites) and (iii) light-induced DNA damage due to photocatalytic activity. Furthermore, MN assays were used and we compared the results of more high-throughput MN scoring with flow cytometry to that of cytokinesis-block MN cytome assay scored manually using a microscope. Various methods were used to assess cytotoxic effects and the results showed in general no or low effects at the doses tested. A weak genotoxic effect of the tested TiO₂ materials was observed with an induction of oxidised bases for all three materials of which NM100 was the most potent. When the comet slides were briefly exposed to lab light, a clear induction of DNA strand breaks was observed for the anatase materials, but not for the rutile. This highlights the risk of false positives when testing photocatalytically active materials if light is not properly avoided. A slight increase in MN formation for NM103 was observed in the different MN assays at the lower doses tested (1 and 5 μg/ml). We conclude that mini-gel comet assay and MN scoring using flow cytometry successfully can be used to efficiently study cytotoxic and genotoxic properties of nanoparticles.