Influence of TiO2nanoparticles on cellular antioxidant defense and its involvement in genotoxicity in HepG2 cells

The mTOR/GCLc/GSH Pathway Mediates the Dose-Dependent Bidirectional Regulation of ROS Induced by TiO2NPs in Neurogenic Cells

Objective. The effect of TiO2NP exposure on the nervous system and the underlying mechanism remain unclear. The antioxidant effect of TiO2NPs at a low dose was newly found in our study, which was different from the effect at high dose. This study is aimed at exploring the mechanism underlying the antioxidant effects of TiO2NPs at low dose and the induction of ROS accumulation by TiO2NPs at high dose in neurogenic cell lines.Methods. We measured the changes in key molecules in the ROS regulation pathway by western blotting, flow cytometry, and commercial assay kits, and these key molecules were further evaluated to verify their interactions and roles using SH-SY5Y, U251, and SK-N-SH cell lines treated with TiO2NPs.Results. Our results showed that the weak antioxidant effect at low dose was caused by mTOR/GCLc-induced GSH overproduction and GSH-Px activity impairment. ROS accumulation at high dose was caused by a mTOR/GCLc-mediated decrease in GSH production, GSH-Px activity impairment, and dramatic ROS production. Furthermore, we found that the ROS species were mainly O2-⋅, and that SOD played a crucial role in reducing O2-⋅levels before the mTOR protein was activated.Conclusion. We revealed the mechanism underlying the bidirectional regulation of ROS induced by TiO2NPs at different doses in neurogenic cell lines. Our study emphasized the potential neurotoxic effects of NPs at low dose, which should arouse concern about their safety.

Biochemical responses of freshwater mussel Unio tumidus to titanium oxide nanoparticles, Bisphenol A, and their combination

Multiple interactions between different pollutants in the surface waters can cause unpredictable consequences. The aim of the study was to evaluate the combined effect of two widespread xenobiotics, titanium oxide nanoparticles (TiO₂) and bisphenol A (BPA), on freshwater bivalve Unio tumidus. The specimens were exposed for 14 days to TiCl₄ (Ti, 1.25 µM), TiO₂ (1.25 μM), BPA (0.88 nM), or their combination (TiO₂ + BPA). Every type of exposure resulted in a particular oxidative stress response: TiO₂ had antioxidant effect, decreasing the generation of reactive oxygen species (ROS) and phenoloxidase (PhO) activity, and doubling reduced glutathione (GSH) concentration in the digestive gland; Ti caused oxidative changes by increasing levels of ROS, PhO and superoxide dismutase; BPA decreased the GSH level by a factor of two. In the co-exposure treatment, these indices as well as lysosomal membrane stability were not affected. All Ti-containing exposures caused elevated levels of metalated metallothionein (Zn,Cu-MT), its ratio to total metallothionein protein, and lactate/pyruvate ratio. Both BPA-containing exposures decreased caspase-3 activity. All exposures, and particularly co-exposure, up-regulated CYP450-dependent oxidation, lipid peroxidation and lipofuscin accumulation, lysosomal cathepsin D and its efflux, as well as alkali-labile phosphates in gonads and caused DNA instability (except for TiO₂). To summarize, co-exposure to TiO₂ + BPA produced an overlap of certain individual responses but strengthened the damage. Development of water purification technologies using TiO₂ requires further studies of the biological effects of its mixtures. U. tumidus can serve as a sentinel organism in such studies.

Interaction of New-Developed TiO₂-Based Photocatalytic Nanoparticles with Pathogenic Microorganisms and Human Dermal and Pulmonary Fibroblasts

TiO₂-based photocatalysts were obtained during previous years in order to limit pollution and to ease human daily living conditions due to their special properties. However, obtaining biocompatible photocatalysts is still a key problem, and the mechanism of their toxicity recently received increased attention. Two types of TiO₂ nanoparticles co-doped with 1% of iron and nitrogen (TiO₂-1% Fe–N) atoms were synthesized in hydrothermal conditions at pH of 8.5 (HT1) and 5.5 (HT2), and their antimicrobial activity and cytotoxic effects exerted on human pulmonary and dermal fibroblasts were assessed. These particles exhibited significant microbicidal and anti-biofilm activity, suggesting their potential application for microbial decontamination of different environments. In addition, our results demonstrated the biocompatibility of TiO₂-1% Fe–N nanoparticles at low doses on lung and dermal cells, which may initiate oxidative stress through dose accumulation. Although no significant changes were observed between the two tested photocatalysts, the biological response was cell type specific and time- and dose-dependent; the lung cells proved to be more sensitive to nanoparticle exposure. Taken together, these experimental data provide useful information for future photocatalytic applications in the industrial, food, pharmaceutical, and medical fields.

Spectroscopic investigation of the mechanism of photocatalysis

Reaction mechanisms of various kinds of photocatalysts have been reviewed based on the recent reports, in which various spectroscopic techniques including luminol chemiluminescence photometry, fluorescence probe method, electron spin resonance (ESR), and nuclear magnetic resonance (NMR) spectroscopy were applied. The reaction mechanisms elucidated for bare and modified TiO₂ were described individually. The modified visible light responsive TiO₂ photocatalysts, i.e., Fe(III)-deposited metal-doped TiO₂ and platinum complex-deposited TiO₂, were studied by detecting paramagnetic species with ESR, •O₂⁻ (or H₂O₂) with chemiluminescence photometry, and OH radicals with a fluorescence probe method. For bare TiO₂, the difference in the oxidation mechanism for the different crystalline form was investigated by the fluorescence probe method, while the adsorption and decomposition behaviors of several amino acids and peptides were investigated by ¹H-NMR spectroscopy.

Comparative and mechanistic genotoxicity assessment of nanomaterials via a quantitative toxicogenomics approach across multiple species

This study reports a comparative and mechanistic genotoxicity assessment of four engineered nanomaterials (ENMs) across three species, including E. coli, yeast, and human cells, with the aim to reveal the distinct potential genotoxicity mechanisms among the different nanomaterials and their association with physiochemical features. Both the conventional phenotypic alkaline comet test and the newly developed quantitative toxicogenomics assay, that detects and quantifies molecular level changes in the regulation of six DNA damage repair pathways, were employed. The proposed molecular endpoints derived from the toxicogenomics assays, namely TELI (Transcriptional Effect Level Index) and PELI (Protein Effect Level Index), correlated well with the phenotypic DNA damage endpoints from comet tests, suggesting that the molecular genotoxicity assay is suitable for genotoxicity detection. Temporal altered gene or protein expression profiles revealed various potential DNA damage types and relevant genotoxic mechanisms induced by the tested ENMs. nTiO2_a induced a wide spectrum of DNA damage consistently across three species. Three carbon-based ENMs, namely carbon black, single wall carbon nanotube (SWCNT) and fullerene, exhibited distinct, species and ENM property-dependent DNA damage mechanisms. All carbon based ENMs induced relatively weak DNA damage repair response in E. coli, but more severe DNA double strand break in eukaryotes. The differences in cellular structure and defense systems among prokaryotic and eukaryotic species lead to distinct susceptibility and mechanisms for ENM uptake and, thus, varying DNA damages and repair responses. The observation suggested that eukaryotes, especially mammalian cells, are likely more susceptible to genotoxicity than prokaryotes in the ecosystem when exposed to these ENMs.