Time‐dependent bioaccumulation of distinct rod‐type TiO2 nanoparticles: Comparison by crystalline phase

A complete understanding of the interaction between nanoparticles and biological systems, including nanoparticle uptake and distribution and the biological responses, could guide the design of safer and more effective nanoparticles than those currently available. In this study, we compared the distribution in mice over time of two rod‐type titanium dioxide nanoparticles (TiNPs) that feature distinct phases, anatase (ATO) and brookite (BTO). Surface areas of BTO and ATO were estimated to be 102 and 268 m² g^–1, respectively, and negative charge on the surface of ATO was higher than that of BTO in deionized water. Both TiNPs were rapidly distributed into tissues after injection. At 4 weeks after injection, both TiNPs were maximally accumulated in the spleen, followed by the liver, but the total accumulation of ATO in tissues measured in this study was more than that of BTO. Moreover, the cellular antioxidant function was similar although the levels of Ti measured in tissues were distinct between the two TiNPs. Based on these results, we suggest that the fate of TiNPs in the body may differ according to the size and surface charge of the TiNPs even when their shape is the same. Copyright © 2014 John Wiley & Sons, Ltd.     

Comparison of toxicity between the different-type TiO2 nanowires in vivo and in vitro

In this study, we compared their toxicity in vivo and in vitro based on the physicochemical properties of three different types of TiO₂ nanowires, H₂Ti₃O₇ nanowires (1HTO), hydrothermal treatment (2HTO), and calcination (3HTO) of 1HTO. The surface of 1HTO was smooth, and the surface of 2HTO was much rougher. The negative charge on the surface increased in the order of 2HTO, 3HTO, and 1HTO, whereas the surface area increased in the order of 3HTO, 1HTO, and 2HTO. The lung is a main exposure route of nanoparticles. On day 28 after a single instillation (1 mg/kg), three nanowires induced a Th2-type inflammatory response together with the relative increase in CD4⁺ T cells, especially by 2HTO. In vitro, three TiO₂ nanowires (10 μg/ml) commonly induced the generation of cell debris in eight cell lines which may be the potential target organ of nanoparticles, especially by 2HTO. It seemed that the generation of cell debris coincides with the increase in autophagosome-like vacuoles in the cytosol. In further study using BEAS-2B cells originated from the lung, the protein amount from cells exposed to 2HTO decreased more clearly although the generation of reactive oxygen species (ROS) was less compared to 1HTO and 3HTO. Based on these results, we suggest that surface area may act as an important factor depends on the biological response by TiO₂ nanowires. Furthermore, the increase in autophagosome-like vacuoles may be an important cause of cell death by nanoparticles with ROS.     

DNA damage and repair following In vitro exposure to two different forms of titanium dioxide nanoparticles on trout erythrocyte

TiO₂ has been widely used to promote organic compounds degradation on waste aqueous solution, however, data on TiO₂ nanotoxicity to aquatic life are still limited. In this in vitro study, we compare the toxicity of two different families of TiO₂ nanoparticles on erythrocytes from Oncorhynchus mykiss trout. The crystal structure of the two TiO₂ nanoparticles was analyzed by XRD and the results indicated that one sample is composed of TiO₂ in the anatase crystal phase, while the other sample contains a mixture of both the anatase and the rutile forms of TiO₂ in a 2:8 ratio. Further characterization of the two families of TiO₂ nanoparticles was determined by SEM high resolution images and BET technique. The toxicity results indicate that both TiO₂ nanoparticles increase the hemolysis rate in a dose dependent way (1.6, 3.2, 4.8 μg mL^?1) but they do not influence superoxide anion production due to NADH addition measured by chemiluminescence. Moreover, TiO₂ nanoparticles (4.8 μg mL^?1) induce DNA damage and the entity of the damage is independent from the type of TiO₂ nanoparticles used. Modified comet assay (Endo III and Fpg) shows that TiO₂ oxidizes not only purine but also pyrimidine bases. In our experimental conditions, the exposure to TiO₂ nanoparticles does not affect the DNA repair system functionality. The data obtained contribute to better characterize the aqueous environmental risks linked to TiO₂ nanoparticles exposure. © 2011 Wiley Periodicals, Inc. Environ Toxicol 29: 117–127, 2014.     

Toxicity and genotoxicity of organic and inorganic nanoparticles to the bacteria Vibrio fischeri and Salmonella typhimurium

The present work aimed at evaluating the toxicity and genotoxicity of two organic (vesicles composed of sodium dodecyl sulphate/didodecyl dimethylammonium bromide—SDS/DDAB and of monoolein and sodium oelate—Mo/NaO) and four inorganic (titanium oxide—TiO₂, silicon titanium—TiSiO₄, Lumidot^™-CdSe/ZnS, and gold nanorods) nanoparticles (NP), suspended in two aqueous media (Milli Q^? water and American Society for Testing and Materials (ASTM) hardwater), to the bacteria Vibrio fischeri (Microtox^? test) and Salmonella typhimurium-his ⁻ (Ames^? test with strains TA98 and TA100). Aiming a better understanding of these biological responses physical and chemical characterization of the studied NP suspensions was carried out. Results denoted a high aggregation state of the NP in the aqueous suspensions, with the exception of SDS/DDAB and Mo/NaO vesicles, and of nanogold suspended in Milli Q water. This higher aggregation was consistent with the low values of zeta potential, revealing the instability of the suspensions. Regarding toxicity data, except for nano TiO₂, the tested NP significantly inhibited bioluminescence of V. fischeri. Genotoxic effects were only induced by SDS/DDAB and TiO₂ for the strain TA98. A wide range of toxicity responses was observed for the six tested NP, differing by more than 5 orders of magnitude, and suggesting different modes of action of the tested NP.     

Evaluation of cytotoxic,genotoxic and inflammatory response in human alveolar and bronchial epithelial cells exposed to titanium dioxide nanoparticles

The toxicity of titanium dioxide nanoparticles (TiO₂‐NPs), used in several applications, seems to be influenced by their specific physicochemical characteristics. Cyto‐genotoxic and inflammatory effects induced by a mixture of 79% anatase/21% rutile TiO₂‐NPs were investigated in human alveolar (A549) and bronchial (BEAS‐2B) cells exposed to 1–40 µg ml^–1 30 min, 2 and 24 h to assess potential pulmonary toxicity. The specific physicochemical properties such as crystallinity, NP size and shape, agglomerate size, surface charge and specific surface area (SSA) were analysed. Cytotoxic effects were studied by evaluating cell viability using the WST1 assay and membrane damage using LDH analysis. Direct/oxidative DNA damage was assessed by the Fpg‐comet assay and the inflammatory potential was evaluated as interleukin (IL)‐6, IL‐8 and tumour necrosis factor (TNF)‐α release by enzyme‐linked immunosorbant assay (ELISA). In A549 cells no significant viability reduction and moderate membrane damage, only at the highest concentration, were detected, whereas BEAS‐2B cells showed a significant viability reduction and early membrane damage starting from 10 µg ml^–1. Direct/oxidative DNA damage at 40 µg ml^–1 and increased IL‐6 release at 5 µg ml^–1 were found only in A549 cells after 2 h. The secretion of pro‐inflammatory cytokine IL‐6, involved in the early acute inflammatory response, and oxidative DNA damage indicate the promotion of early and transient oxidative‐inflammatory effects of tested TiO₂‐NPs on human alveolar cells. The findings show a higher susceptibility of normal bronchial cells to cytotoxic effects and higher responsiveness of transformed alveolar cells to genotoxic, oxidative and early inflammatory effects induced by tested TiO₂‐NPs. This different cell behaviour after TiO₂‐NPs exposure suggests the use of both cell lines and multiple end‐points to elucidate NP toxicity on the respiratory system. Copyright © 2014 John Wiley & Sons, Ltd.     

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.     

In vitro evaluation of the toxicity and underlying molecular mechanisms of Janus Fe3O4‐TiO2 nanoparticles in human liver cells

Recent studies show that Janus Fe₃O₄‐TiO₂ nanoparticles (NPs) have potential applications as a multifunctional agent of magnetic resonance imaging (MRI) and photodynamic therapy (PDT) for the diagnosis and therapy of cancer. However, little work has been done on their biological effects. To evaluate the toxicity and underlying molecular mechanisms of Janus Fe₃O₄‐TiO₂ nanoparticles, an in vitro study using a human liver cell line HL‐7702 cells was conducted. For comparison, the Janus Fe₃O₄‐TiO₂ NPs parent material TiO₂ NPs was also evaluated. Results showed that both Fe₃O₄‐TiO₂ NPs and TiO₂ NPs decreased cell viability and ATP levels when applied in treatment, but increased malonaldehyde (MDA) and reactive oxygen species (ROS) generation. Mitochondria JC‐1 staining assay showed that mitochondrial membrane permeability injury occurred in both NPs treated cells. Cell viability analysis showed that TiO₂ NPs induced slightly higher cytotoxicity than Fe₃O₄‐TiO₂ NPs in HL7702 cells. Western blotting indicated that both TiO₂ NPs and Fe₃O₄‐TiO₂ NPs could induce apoptosis, inflammation, and carcinogenesis related signal protein alterations. Comparatively, Fe₃O₄‐TiO₂ NPs induced higher signal protein expressions than TiO₂ NPs under a high treatment dose. However, under a low dose (6.25 μg/cm²), neither NPs had any significant toxicity on HL7702 cells. In addition, our results suggest both Fe₃O₄‐TiO₂ NPs and TiO₂ NPs could induce oxidative stress and have a potential carcinogenetic effect in vitro. Further studies are needed to elaborate the detailed mechanisms of toxicity induced by a high dose of Fe₃O₄‐TiO₂ NPs.     

The effects of engineered nanoparticles on the cellular structure and growth of Saccharomyces cerevisiae

In order to study the effects of nanoparticles (NPs) with different physicochemical properties on cellular viability and structure, Saccharomyces cerevisiae were exposed to different concentrations of TiO₂-NPs (1–3 nm), ZnO-NPs (<100 nm), CuO-NPs (<50 nm), their bulk forms, Ag-NPs (10 nm) and single-walled carbon nanotubes (SWCNTs). The GreenScreen assay was used to measure cyto- and genotoxicity, and transmission electron microscopy (TEM) used to assess ultrastructure. CuO-NPs were highly cytotoxic, reducing the cell density by 80% at 9 cm²/ml, and inducing lipid droplet formation. Cells exposed to Ag-NPs (19 cm²/ml) and TiO₂-NPs (147 cm²/ml) contained dark deposits in intracellular vacuoles, the cell wall and vesicles, and reduced cell density (40 and 30%, respectively). ZnO-NPs (8 cm²/ml) caused an increase in the size of intracellular vacuoles, despite not being cytotoxic. SWCNTs did not cause cytotoxicity or significant alterations in ultrastructure, despite high oxidative potential. Two genotoxicity assays, GreenScreen and the comet assay, produced different results and the authors discuss the reasons for this discrepancy. Classical assays of toxicity may not be the most suitable for studying the effects of NPs in cellular systems, and the simultaneous assessment of other measures of the state of cells, such as TEM are highly recommended.     

Genotoxicity evaluation of titanium dioxide nanoparticles using the Ames test and Comet assay

Titanium dioxide nanoparticles (TiO₂‐NPs) are being used increasingly for various industrial and consumer products, including cosmetics and sunscreens because of their photoactive properties. Therefore, the toxicity of TiO₂‐NPs needs to be thoroughly understood. In the present study, the genotoxicity of 10nm uncoated sphere TiO₂‐NPs with an anatase crystalline structure, which has been well characterized in a previous study, was assessed using the Salmonella reverse mutation assay (Ames test) and the single‐cell gel electrophoresis (Comet) assay. For the Ames test, Salmonella strains TA102, TA100, TA1537, TA98 and TA1535 were preincubated with eight different concentrations of the TiO₂‐NPs for 4 h at 37 °C, ranging from 0 to 4915.2 µg per plate. No mutation induction was found. Analyses with transmission electron microscopy (TEM) and energy‐dispersive X‐ray spectroscopy (EDS) showed that the TiO₂‐NPs were not able to enter the bacterial cell. For the Comet assay, TK6 cells were treated with 0–200 µg ml^–1 TiO₂‐NPs for 24 h at 37 °C to detect DNA damage. Although the TK6 cells did take up TiO₂‐NPs, no significant induction of DNA breakage or oxidative DNA damage was observed in the treated cells using the standard alkaline Comet assay and the endonuclease III (EndoIII) and human 8‐hydroxyguanine DNA‐glycosylase (hOGG1)‐modified Comet assay, respectively. These results suggest that TiO₂‐NPs are not genotoxic under the conditions of the Ames test and Comet assay. Published 2012. This article is a US Government work and is in the public domain in the USA.     

Biological effect of food additive titanium dioxide nanoparticles on intestine: an in vitro study

Titanium dioxide nanoparticles (TiO₂ NPs) are widely found in food‐related consumer products. Understanding the effect of TiO₂ NPs on the intestinal barrier and absorption is essential and vital for the safety assessment of orally administrated TiO₂ NPs. In this study, the cytotoxicity and translocation of two native TiO₂ NPs, and these two TiO₂ NPs pretreated with the digestion simulation fluid or bovine serum albumin were investigated in undifferentiated Caco‐2 cells, differentiated Caco‐2 cells and Caco‐2 monolayer. TiO₂ NPs with a concentration less than 200 µg ml^–1 did not induce any toxicity in differentiated cells and Caco‐2 monolayer after 24 h exposure. However, TiO₂ NPs pretreated with digestion simulation fluids at 200 µg ml^–1 inhibited the growth of undifferentiated Caco‐2 cells. Undifferentiated Caco‐2 cells swallowed native TiO₂ NPs easily, but not pretreated NPs, implying the protein coating on NPs impeded the cellular uptake. Compared with undifferentiated cells, differentiated ones possessed much lower uptake ability of these TiO₂ NPs. Similarly, the traverse of TiO₂ NPs through the Caco‐2 monolayer was also negligible. Therefore, we infer the possibility of TiO₂ NPs traversing through the intestine of animal or human after oral intake is quite low. This study provides valuable information for the risk assessment of TiO₂ NPs in food. Copyright © 2015 John Wiley & Sons, Ltd.     

Toxicity assessment of anatase and rutile titanium dioxide nanoparticles: The role of degradation in different pH conditions and light exposure

Titanium dioxide nanoparticles (TiO₂NPs), in the two crystalline forms, rutile and anatase, have been widely used in many industrial fields, especially in cosmetics. Therefore, a lot of details about their safety issues have been discussed by the scientific community. Many studies have led to a general agreement about TiO₂NPs toxicity, in particular for anatase form, but no mechanism details have been proved yet. In this study, data confirm the different toxic potential of rutile and anatase TiO₂NPs in two cell lines up to 5 nM nanoparticles concentration. Moreover, we evaluated the role of titanium ions released by TiO₂NPs in different conditions, at pH = 4.5 (the typical lysosomal compartment pH) and at pH = 5.5 (the skin physiological pH) in conditions of darkness and light, to mimic the dermal exposure of cosmetics. Anatase nanoparticles were proner to degradation both in the acidic conditions and at skin pH. Our study demonstrates that pH and sunlight are dominant factors to induce oxidative stress, TiO₂NPs degradation and toxicity effects.     

Toxicity of nanoparticles of ZnO, CuO and TiO2 to yeast Saccharomyces cerevisiae

The aim of this study was to evaluate the toxic effect of nanosized ZnO, CuO and TiO₂ to Saccharomyces cerevisiae – a widely used unicellular eukaryotic model organisms in molecular and cell biology. The effect of metal oxide nanoparticles, their bulk forms and respective ionic forms were compared. The bioavailable Zn²⁺ and Cu²⁺ ions in the growth medium were quantified by recombinant microbial sensors.Nano and bulk TiO₂ were not toxic even at 20000 mg/l. Both, nano and bulk ZnO were of comparable toxicity (8-h EC₅₀ 121–134 mg ZnO/l and 24-h EC₅₀ 131–158 mg/l). The toxicity was explained by soluble Zn-ions as proved by the microbial sensor. However, nano CuO was about 60-fold more toxic than bulk CuO: 8-h EC₅₀ were 20.7 and 1297 mg CuO/l and 24-h EC₅₀ were 13.4 and 873 mg/l, respectively. The increase in toxicity of both CuO formulations at 24th hour of growth was due to the increased dissolution of copper ions from CuO over time. Comparison of EC₅₀ values of nano CuO, bulk CuO and Cu²⁺ with bioavailable copper concentrations in the growth medium showed that the solubilized Cu-ions explained only about 50% of the toxicity of both, nano and bulk CuO. To our knowledge, this is the first study that evaluates the toxicity of ZnO, CuO and TiO₂ nanoparticles to S. cerevisiae.     

Does photocatalytic activity of TiO2 nanoparticles correspond to photo-cytotoxicity? Cellular uptake of TiO2 nanoparticles is important in their photo-cytotoxicity

Titanium dioxide (TiO₂) nanoparticles are important industrial nano-objects with wide applications, including as photocatalysts and sunscreen components. Recently, the phototoxicity of TiO₂ nanoparticles has been a concern. However, phototoxicity caused by photocatalytic activity may differ between anatase and rutile nanoparticles. In the present study, we compared the phototoxicity of anatase and rutile nanoparticles. Human keratinocyte HaCaT cells were treated with stable TiO₂ nanoparticle suspensions. Without UVA irradiation, TiO₂ nanoparticles did not affect mitochondrial activity or cell membranes. However, exposure to rutile nanoparticle suspensions inhibited cell growth and induced HO-1 gene expression without UVA irradiation. These effects may be explained by the hydrophobic surface of rutile nanoparticles. Next, TiO₂-exposed cells were irradiated with UVA for 4?h and effects of TiO₂ nanoparticles on cells were examined. The rutile nanoparticles did not show any cellular effects after UVA irradiation. However, the anatase nanoparticles caused strong phototoxicity. Decreased mitochondrial activity, cell membrane damage and the induction of oxidative stress were observed in the cells exposed to anatase nanoparticles with UVA irradiation. Cellular uptake of the nanoparticles was observed in both anatase- and rutile-exposed cells. These results suggest that internalized anatase nanoparticles are important for phototoxicity. Additionally, the exposure of a 3D skin model to TiO₂ nanoparticles did not result in significant toxicity. In conclusion, rutile nanoparticles used in sunscreen did not exhibit phototoxic activity. Despite the strong phototoxic activity of anatase nanoparticles in cell cultures, they demonstrated no phototoxicity using a 3D skin model.     

Distinct toxic interactions of TiO2 nanoparticles with four coexisting organochlorine contaminants on algae

Engineered nanoparticles are increasingly discharged into the environment. After discharge, these nanoparticles can interact with co-existing organic contaminants, resulting in a phenomena referred to as ‘joint toxicity’. This study evaluated joint toxicities of TiO₂ nanoparticles (TiO₂NPs) with four different (atrazine, hexachlorobenzene, pentachlorobenzene, and 3,3′,4,4′-tetrachlorobiphenyl) organochlorine contaminants (OCs) toward algae (Chlorella pyrenoidosa). The potential mechanisms underlying the joint toxicity were discussed, including TiO₂NPs–OC interactions, effects of TiO₂NPs and OCs on biophysicochemical properties of algae and effects of TiO₂NPs and OCs on each other’s bioaccumulation in algae. The results indicate that coexposure led to a synergistic effect on the joint toxicity for TiO₂NPs–atrazine, antagonistic effect for TiO₂NPs–hexachlorobenzene and TiO₂NPs–3,3',4,4'-tetrachlorobiphenyl, and an additive effect for TiO₂NPs–pentachlorobenzene. There was nearly no adsorption of OCs by TiO₂NPs, and the physicochemical properties of TiO₂NPs were largely unaltered by the presence of OCs. However, both OCs and NPs affected the biophysicochemical properties of algal cells and thereby influenced the cell surface binding and/or internalization. TiO₂NPs significantly increased the bioaccumulation of each OC. However, with the exception of atrazine, the bioaccumulation of TiO₂NPs decreased when used with each OC. The distinct joint toxicity outcomes were a result of the balance between the increased toxicities of OCs (increased bioaccumulations) and the altered toxicity of TiO₂NPs (bioaccumulation can either increase or decrease). These results can significantly improve our understanding of the potential environmental risks associated with NPs.     

No evidence of the genotoxic potential of gold,silver, zinc oxide and titanium dioxide nanoparticles in the SOS chromotest

Gold nanoparticles (Au NPs), silver nanoparticles (Ag NPs), zinc oxide nanoparticles (ZnO NPs) and titanium dioxide nanoparticles (TiO₂ NPs) are widely used in cosmetic products such as preservatives, colorants and sunscreens. This study investigated the genotoxicity of Au NPs, Ag NPs, ZnO NPs and TiO₂ NPs using the SOS chromotest with Escherichia coli PQ37. The maximum exposure concentrations for each nanoparticle were 3.23 mg l^–1 for Au NPs, 32.3 mg l^–1 for Ag NPs and 100 mg l^–1 for ZnO NPs and TiO₂ NPs. Additionally, in order to compare the genotoxicity of nanoparticles and corresponding dissolved ions, the ions were assessed in the same way as nanoparticles. The genotoxicity of the titanium ion was not assessed because of the extremely low solubility of TiO₂ NPs. Au NPs, Ag NPs, ZnO NPs, TiO₂ NPs and ions of Au, Ag and Zn, in a range of tested concentrations, exerted no effects in the SOS chromotest, evidenced by maximum IF (IFmax) values of below 1.5 for all chemicals. Owing to the results, nanosized Au NPs, Ag NPs, ZnO NPs, TiO₂ NPs and ions of Au, Ag and Zn are classified as non‐genotoxic on the basis of the SOS chromotest used in this study. To the best of our knowledge, this is the first study to evaluate the genotoxicity of Au NPs, Ag NPs, ZnO NPs and TiO₂ NPs using the SOS chromotest. Copyright © 2012 John Wiley & Sons, Ltd.     

Overview of the toxic effects of titanium dioxide nanoparticles in blood,liver, muscles,and brain of a Neotropical detritivorous fish

The toxicity of titanium dioxide nanoparticles (TiO₂‐NP) in the blood, liver, muscle, and brain of a Neotropical detritivorous fish, Prochilodus lineatus, was tested. Juvenile fish were exposed to 0, 1, 5, 10, and 50 mg L^?1 of TiO₂‐NP for 48 hours (acute exposure) or 14 days (subchronic exposure) to evaluate changes in hematology, red blood cell (RBC) genotoxicity/mutagenicity, liver function (reactive oxygen species (ROS) production, antioxidant responses, detoxification, and histopathology), acetylcholinesterase (AChE) activity in muscles and brain, and Ti bioaccumulation. TiO₂‐NP did not cause genetic damage to RBC, but acutely decreased white blood cells (WBC) and increased monocytes. Subchronically, RBC decreased, mean cell volume and hemoglobin increased, and WBC and lymphocytes decreased. Therefore, NP has the potential to affect immune system and increase energy expenditure, reducing the fish's ability to avoid predator and to resist pathogens. In the liver, acute exposure decreased ROS and increased glutathione (GSH) content, while subchronic exposure decreased superoxide dismutase activity and increased glutathione‐S‐transferase (GST) activity and GSH content. GSH and GST seem to play an essential role in metabolizing NP and ROS, likely increasing hepatocytes' metabolic rate, which may be the cause of observed cell hypertrophy, disarrangement of hepatic cords and degenerative morphological alterations. Although most studies indicate that the kidney is responsible for metabolizing and/or eliminating TiO₂‐NP, this study shows that the liver also has a main role in these processes. Nevertheless, Ti still accumulated in the liver, muscle, and brain and decreased muscular AChE activity after acute exposure, showing neurotoxic potential. More studies are needed to better understand the biochemical pathways TiO₂‐NP are metabolized and how its bioaccumulation may affect fish homeostasis and survival in the environment.     

Oxidative stress increased hepatotoxicity induced by nano‐titanium dioxide in BRL‐3A cells and Sprague–Dawley rats

Extensive studies have shown that titanium dioxide (TiO₂) nanomaterials (NMs) can cause toxicity in vitro and in vivo under normal conditions. However, an adverse effect induced by nano‐TiO₂ in many diseased conditions, typically characterized by oxidative stress (OS), remains unknown. We investigated the toxicity of nano‐TiO₂ in rat liver cells (BRL‐3A) and Sprague–Dawley (SD) rat livers under OS conditions, which were generated using hydrogen peroxide (H₂O₂) in vitro and alloxan in vivo, respectively. In vitro results showed that cell death ratios after nano‐TiO₂ exposure were significantly enhanced (up to 2.62‐fold) in BRL‐3A cells under OS conditions, compared with normal controls. Significant interactions between OS conditions and nano‐TiO₂ resulted in the rapid G0/G1 to S phase transition and G2/M arrest, which were opposite to G0/G1 phase arrest in cells after NMs exposure only. In vivo results showed that obvious pathological changes in rat livers and the increased activities of four enzymes (i.e. aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase and alkaline phosphatase) owing to liver damage after nano‐TiO₂ exposure under OS conditions, compared with their healthy controls. In addition, compared with increased hepatotoxicity after nano‐TiO₂ exposure, micro‐TiO₂ showed no adverse effects to cells and rat livers under OS conditions. Our results suggested that OS conditions synergistically increase nano‐TiO₂ induced toxicity in vitro and in vivo, indicating that the evaluation of nanotoxicity under OS conditions is essentially needed prior to various applications of NMs in foods, cosmetics and potential treatment of diseases. Copyright © 2013 John Wiley & Sons, Ltd.     

Size of TiO2 nanoparticles influences their phototoxicity: an in vitro investigation

To uncover the size influence of TiO₂ nanoparticles on their potential toxicity, the cytotoxicity of different-sized TiO₂ nanoparticles with and without photoactivation was tested. It was demonstrated that without photoactivation, TiO₂ nanoparticles were inert up to 100 μg/ml. On the contrary, with photoactivation, the toxicity of TiO₂ nanoparticles significantly increased, which correlated well with the specific surface area of the particles. Our results also suggest that the generation of hydroxyl radicals and reactive oxygen species (ROS)-mediated damage to the surface-adsorbed biomolecules could be the two major reasons for the cytotoxicity of TiO₂ nanoparticles after photoactivation. Higher ROS generation from smaller particles was detected under both biotic and abiotic conditions. Smaller particles could adsorb more proteins, which was confirmed by thermogravimetric analysis. To further investigate the influence of the generation of hydroxyl radicals and adsorption of protein, poly (ethylene-alt-maleic anhydride) (PEMA) and chitosan were used to coat TiO₂ nanoparticles. The results confirmed that surface coating of TiO₂ nanoparticles could reduce such toxicity after photoactivation, by hindering adsorption of biomolecules and generation of hydroxyl radical (·OH) during photoactivation.     

Metabolomics reveals the perturbations in the metabolome of Caenorhabditis elegans exposed to titanium dioxide nanoparticles

Abstract

The increasing use of nanotechnology in our daily life can have many unintended effects and pose adverse impact on human health, environment and ecosystems. Wider application of engineered nanoparticles, especially TiO₂ nanoparticles (TiO₂ NP) necessitates the understanding of toxicity and mechanism of action. Metabolomics provides a unique opportunity to find out biomarkers of nanoparticles exposure, which leads to the identification of cellular pathways and their biological mechanisms. Gas chromatography mass spectrometry (GC–MS)-based metabolomics approach was used in the present study to understand the toxicity of sub-lethal concentrations (7.7 and 38.5?µg/ml) of TiO₂ NP (<25?nm) in well-known, soil nematode Caenorhabditis elegans (C. elegans). Multivariate pattern recognition analysis reflected the perturbations in the metabolism (amino acids, organic acids, sugars) of C. elegans on exposure to TiO₂ NP. The biological pathways affected due to the exposure of TiO₂ NP were identified, among them mainly affected pathways are tricarboxylic acid (TCA) cycle, arachidonic acid metabolism and glyoxalate dicarobxylate metabolism. The manifestation of differential metabolic profile in organism exposed to TiO₂ (NP or bulk particle) was witnessed as an effect on reproduction. The present study demonstrates that metabolomics can be employed as a tool to understand the potential toxicity of nanoparticles in terms of organism–environment interactions as well as in assessing the organism function at the molecular level.