Cyto- and genotoxicity of ultrafine TiO2 particles in cultured human lymphoblastoid cells

In vitro cytotoxicity and genotoxicity studies of titanium dioxide (TiO2) nanoparticles in Chinese hamster lung fibroblast cells

There are increasing safety concerns about the development and abundant use of nanoparticles. The unique physical and chemical characteristics of titanium dioxide (TiO2) nanoparticles result in different chemical and biological activities compared to their larger micron-sized counterparts, and can subsequently play an important role in influencing toxicity. Therefore, our objective was to investigate the cytotoxicity and genotoxicity of commercially available TiO2 nanoparticles with respect to their selected physicochemical properties, as well as the role of surface coating of these nanoparticles. While all types of tested TiO2 samples decrease cell viability in a mass-based concentration- and size-dependent manner, the polyacrylate-coated nano-TiO2 product was only cytotoxic at higher concentrations. A similar pattern of response was observed for induction of apoptosis/necrosis, and no DNA damage was detected in the polyacrylate-coated nano-TiO2 model. Given the increasing production of TiO2 nanoparticles, toxicological studies should take into account the physiochemical properties of these nanoparticles that may help researchers to develop new nanoparticles with minimum toxicity.

Genotoxicity of metal nanoparticles: focus on in vivo studies

With increasing production and application of a variety of nanomaterials (NMs), research on their cytotoxic and genotoxic potential grows, as the exposure to these nano-sized materials may potentially result in adverse health effects. In large part, indications for potential DNA damaging effects of nanoparticles (NPs) originate from inconsistent in vitro studies. To clarify these effects, the implementation of in vivo studies has been emphasised. This paper summarises study results of genotoxic effects of NPs, which are available in the recent literature. They provide indications that some NP types cause both DNA strand breaks and chromosomal damages in experimental animals. Their genotoxic effects, however, do not depend only on particle size, surface modification (particle coating), and exposure route, but also on exposure duration. Currently available animal studies may suggest differing mechanisms (depending on the duration of exposure) by which living organisms react to NP contact. Nevertheless, due to considerable inconsistencies in the recent literature and the lack of standardised test methods - a reliable hazard assessment of NMs is still limited. Therefore, international organisations (e.g. NIOSH) suggest utmost caution when potential exposure of humans to NMs occurs, as long as evidence of their toxicological and genotoxic effect(s) is limited.

Modifications of the bacterial reverse mutation test reveals mutagenicity of TiO(2) nanoparticles and byproducts from a sunscreen TiO(2)-based nanocomposite

The bacterial reverse mutation test, recommended by the Organization for Economic Co-operation and Development (OECD) to determine genotoxicity of chemical compounds, has been recently used by several authors to investigate nanoparticles. Surprisingly, test results have been negative, whereas in vitro mammalian cell tests often give positive genotoxic responses. In the present study, we used the fluctuation test procedure with the Salmonella typhimurium strains TA97a, TA98, TA100 and TA102 to determine the mutagenic potential of TiO(2) nanoparticles (NP-TiO(2)) and showed that, when it is used conventionally, this test is not suitable for nanoparticle genotoxicity assessment. Indeed, the medium used during exposure prevents electrostatic interactions between bacterial cells and nanoparticles, leading to false-negative responses. We showed that a simple pre-exposure of bacteria to NP-TiO(2) in a low ionic strength solution (NaCl 10mM) at a pH below the nanoparticle isoelectric points (pH 5.5) can strongly improve the accuracy of the test. Thus, based on these improvements, we have demonstrated the genotoxicity of the engineered NP-TiO(2) tested and a NP-TiO(2) byproduct from a sunscreen nanocomposite. It was also shown that strain TA102 is more sensitive than the other strains, suggesting an oxidative stress-mediated mechanism of genotoxicity.

Size influences the cytotoxicity of poly (lactic-co-glycolic acid) (PLGA) and titanium dioxide (TiO(2)) nanoparticles

The aim of this study is to uncover the size influence of poly (lactic-co-glycolic acid) (PLGA) and titanium dioxide (TiO(2)) nanoparticles on their potential cytotoxicity. PLGA and TiO(2) nanoparticles of three different sizes were thoroughly characterized before in vitro cytotoxic tests which included viability, generation of reactive oxygen species (ROS), mitochondrial depolarization, integrity of plasma membrane, intracellular calcium influx and cytokine release. Size-dependent cytotoxic effect was observed in both RAW264.7 cells and BEAS-2B cells after cells were incubated with PLGA or TiO(2) nanoparticles for 24 h. Although PLGA nanoparticles did not trigger significantly lethal toxicity up to a concentration of 300 μg/ml, the TNF-α release after the stimulation of PLGA nanoparticles should not be ignored especially in clinical applications. Relatively more toxic TiO(2) nanoparticles triggered cell death, ROS generation, mitochondrial depolarization, plasma membrane damage, intracellular calcium concentration increase and size-dependent TNF-α release, especially at a concentration higher than 100 μg/ml. These cytotoxic effects could be due to the size-dependent interaction between nanoparticles and biomolecules, as smaller particles tend to adsorb more biomolecules. In summary, we demonstrated that the ability of protein adsorption could be an important paradigm to predict the in vitro cytotoxicity of nanoparticles, especially for low toxic nanomaterials such as PLGA and TiO(2) nanoparticles.

Titanium dioxide induced inflammation in the small intestine

AIM

To investigate the effects of titanium dioxide (TiO₂) nanoparticles (NPTiO₂) and microparticles (MPTiO₂) on the inflammatory response in the small intestine of mice.

METHODS

Bl 57/6 male mice received distilled water suspensions containing TiO₂ (100 mg/kg body weight) as NPTiO₂ (66 nm), or MPTiO₂ (260 nm) by gavage for 10 d, once a day; the control group received only distilled water. At the end of the treatment the duodenum, jejunum and ileum were extracted for assessment of cytokines, inflammatory cells and titanium content. The cytokines interleukin (IL)-1b, IL-4, IL-6, IL-8, IL-10, IL-12, IL-13, IL-17, IL-23, tumor necrosis factor-α (TNF-α), intracellular interferon-γ (IFN-γ) and transforming growth factor-β (TGF-β) were evaluated by enzyme-linked immunosorbent assay in segments of jejunum and ileum (mucosa and underlying muscular tissue). CD4+ and CD8+ T cells, natural killer cells, and dendritic cells were evaluated in duodenum, jejunum and ileum samples fixed in 10% formalin by immunohistochemistry. The titanium content was determined by inductively coupled plasma atomic emission spectrometry.

RESULTS

We found increased levels of T CD4+ cells (cells/mm²) in duodenum: NP 1240 ± 139.4, MP 1070 ± 154.7 vs 458 ± 50.39 (P < 0.01); jejunum: NP 908.4 ± 130.3, MP 813.8 ± 103.8 vs 526.6 ± 61.43 (P < 0.05); and ileum: NP 818.60 ± 123.0, MP 640.1 ± 32.75 vs 466.9 ± 22.4 (P < 0.05). In comparison to the control group, the groups receiving TiO₂ showed a statistically significant increase in the levels of the inflammatory cytokines IL-12, IL-4, IL-23, TNF-α, IFN-γ and TGF-β. The cytokine production was more pronounced in the ileum (mean ± SE): IL-12: NP 33.98 ± 11.76, MP 74.11 ± 25.65 vs 19.06 ± 3.92 (P < 0.05); IL-4: NP 17.36 ± 9.96, MP 22.94 ± 7.47 vs 2.19 ± 0.65 (P < 0.05); IL-23: NP 157.20 ± 75.80, MP 134.50 ± 38.31 vs 22.34 ± 5.81 (P < 0.05); TNFα: NP 3.71 ± 1.33, MP 5.44 ± 1.67 vs 0.99 ± 019 (P < 0.05); IFNγ: NP 15.85 ± 9.99, MP 34.08 ± 11.44 vs 2.81 ± 0.69 (P < 0.05); and TGF-β: NP 780.70 ± 318.50, MP 1409.00 ± 502.20 vs 205.50 ± 63.93 (P < 0.05).

CONCLUSION

Our findings indicate that TiO₂ particles induce a Th1-mediated inflammatory response in the small bowel in mice.

Titanium dioxide nanoparticles activate the ATM-Chk2 DNA damage response in human dermal fibroblasts

The use of nanoparticles in consumer products increases their prevalence in the environment and the potential risk to human health. Although recent studies have shown in vivo and in vitro toxicity of titanium dioxide nanoparticles (nano-TiO2), a more detailed view of the underlying mechanisms of this response needs to be established. Here, the effects of nano-TiO2 on the DNA damage response and DNA replication dynamics were investigated in human dermal fibroblasts. Specifically, the relationship between nano-TiO2 and the DNA damage response pathways regulated by ATM/Chk2 and ATR/Chk1 was examined. The results show increased phosphorylation of H2AX, ATM, and Chk2 after exposure. In addition, nano-TiO2 inhibited the overall rate of DNA synthesis and frequency of replicon initiation events in DNA-combed fibres. Taken together, these results demonstrate that exposure to nano-TiO2 activates the ATM/Chk2 DNA damage response pathway.

The importance of a validated standard methodology to define in vitro toxicity of nano-TiO2

Several in vitro studies on the potential toxicity of nano-TiO(2) have been published and recent reviews have summarised them. Most of these reports concluded that physicochemical properties of nanoparticles are fundamental to their toxicological effects. No published review has compared in vitro tests with similar test strategies in terms of exposure duration and measured endpoints and for this reason we have attempted to assess the degree of homogeneity among in vitro tests and to assess if they afford reliable data to support risk assessment. The responses in different in vitro tests appeared to be unrelated to primary particle size. The biologically effective concentrations in different tests can be seen to differ by as many as two orders of magnitude and such differences could be explained either by different sensitivities of cell lines to nanoparticles or by effect of the test media. Our review indicates that even when the in vitro tests measure the same biomarkers with the same exposure duration and known primary particle sizes, it is insufficient merely to use such data for risk assessment. In the future, validated standard methods should include a limited number of cell lines and an obligatory selection of biomarkers. For routine purposes, it is important that assays can be easily conducted, false negatives and false positives are excluded and unbiased interpretation of results is provided. Papers published to date provide an understanding of the mode on nano-TiO(2) action but are not suitable for assessment and management of risk.

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.

Use of β-galactosidase (lacZ) gene α-complementation as a novel approach for assessment of titanium oxide nanoparticles induced mutagenesis

The mutagenic potential of titanium dioxide nanoparticles (TiO(2)-NPs) of an average size 30.6nm was investigated using β-galactosidase (lacZ) gene complementation in plasmid pUC19/lacZ(-)Escherichia coli DH5α system. Plasmid pUC19 was treated with varying concentrations of TiO(2)-NPs and allowed to transfect the CaCl(2)-induced competent DH5α cells. The data revealed loss in transformation efficiency of TiO(2)-NPs treated plasmids as compared to untreated plasmid DNA in DH5α host cells. Induction of multiple mutations in α-fragment of lacZ gene caused synthesis of non-functional β-galactosidase enzyme, which resulted in a significant number of white (mutant) colonies of transformed E. coli cells. Screening of mutant transformants based on blue:white colony assay and DNA sequence analysis of lacZ gene fragment clearly demonstrated TiO(2)-NPs induced mutagenesis. Multiple alignment of selectable marker lacZ gene sequences from randomly selected mutants and control cells provided a gene specific map of TiO(2)-NPs induced mutations. Mutational analysis suggested that all nucleotide changes were point mutations, predominantly transversions (TVs) and transitions (TSs). A total of 32 TVs and 6 TSs mutations were mapped within 296 nucleotides (nt) long partial sequence of lacZ gene. The region between 102 and 147nt within lacZ gene sequence was found to be most susceptible to mutations with nine detectable point mutations (8 TVs and 1 TSs). Guanine base was determined to be more prone to TiO(2)-NPs induced mutations. This study suggested the pUC19/E. coli DH5αlacZ gene α-complementation system, as a novel genetic approach for determining the mutagenic potential, and specificity of manufactured NPs and nanomaterials.

In vitro genotoxicity testing strategy for nanomaterials and the adaptation of current OECD guidelines

There is a pressing requirement to define a hazard identification and risk management strategy for nanomaterials due to the rapid growth in the nanotechnology industry and their promise of life-style revolutions through the development of wide-ranging nano-containing consumer products. Consequently, a battery of well defined and appropriate in vitro assays to assess a number of genotoxicity endpoints is required to minimise extensive and costly in vivo testing. However, the validity of the established protocols in current OECD recognised genotoxicity assays for nanomaterials is currently being questioned. In this report, we therefore consider the in vitro OECD genotoxicity test battery including the Ames, micronucleus and HPRT forward mutation assays, and their potential role in the safety assessment of nanomaterial induced DNA damage in vitro.

Synthesis of nanoscale TiO2 and study of the effect of their crystal structure on single cell response

To study the effect of nanoscale titanium dioxide (TiO(2)) on cell responses, we synthesized four modifications of the TiO(2) (amorphous, anatase, brookite, and rutile) capable of keeping their physicochemical characteristics in a cell culture medium. The modifications of nanoscale TiO(2) were obtained by hydrolysis of TiCl(4) and Ti(i-OC(3)H(7))(4) (TIP) upon variation of the synthesis conditions; their textural, morphological, structural, and dispersion characteristics were examined by a set of physicochemical methods: XRD, BET, SAXS, DLS, AFM, SEM, and HR-TEM. The effect of synthesis conditions (nature of precursor, pH, temperature, and addition of a complexing agent) on the structural-dispersion properties of TiO(2) nanoparticles was studied. The hydrolysis methods providing the preparation of amorphous, anatase, brookite, and rutile modifications of TiO(2) nanoparticles 3-5 nm in size were selected. Examination of different forms of TiO(2) nanoparticles interaction with MDCK cells by transmission electron microscopy of ultrathin sections revealed different cell responses after treatment with different crystalline modifications and amorphous form of TiO(2). The obtained results allowed us to conclude that direct contact of the nanoparticles with cell plasma membrane is the primary and critical step of their interaction and defines a subsequent response of the cell.

Cell membrane integrity and internalization of ingested TiO(2) nanoparticles by digestive gland cells of a terrestrial isopod

The present study was motivated by the paucity of reports on cellular internalization of ingested titanium dioxide (TiO(2)) nanoparticles (nano-TiO(2)). The model invertebrate (Porcellio scaber, Isopoda, Crustacea) was exposed to food dosed with nano-TiO(2) containing 100, 1,000, 3,000, or 5,000 µg nano-TiO(2) per gram of food. After 14 d of exposure, the amount of Ti in the entire body was analyzed by inductively coupled plasma-mass spectrometry, and elemental analyses of tissue cross sections were performed by particle induced X-ray emission. In addition, a series of toxicological markers including feeding parameters, weight change, and survival, as well as cytotoxic effects such as digestive gland cell membrane stability, were monitored. Internalization of ingested nano-TiO(2) by the isopod's digestive gland epithelial cells was shown to depend on cell membrane integrity. Cell membranes were found to be destabilized by TiO(2) particles, and at higher extracellular concentrations of nano-TiO(2), the nanoparticles were internalized.

Cytotoxicity of different sized TiO2 nanoparticles in mouse macrophages

With large-scale production and wide application of nano-titanium oxide (TiO2), its health hazard has attracted extensive attention worldwide. In this study, mouse macrophages (Ana-1 and MH-S cells) were used to evaluate the cytotoxicity of different sized TiO2 nanoparticles. The results showed that TiO2 nanoparticles caused low toxicity, especially in MH-S cells. There was a difference in the cytotoxicity induced by different sized TiO2 particles. The 25 nm anatase particles induced the strongest cytotoxicity and oxidative stress, followed by 5 and 100 nm anatase particles; in contrast, 100 nm rutile particles induced the lowest toxicity. Although TiO2 nanoparticles induced high levels of intracellular reactive oxygen species (ROS), the determination of ROS demonstrated that the inherent oxidative capacity of TiO2 nanoparticles was lower in the absence of photoactivation. Therefore, the generation of intracellular ROS could not completely depend on inherent oxidative capacity of TiO2 nanoparticles. Toxicity of TiO2 nanoparticles could mainly depend on the structural characteristics.

The potential health risk of titania nanoparticles

Widespread use of titania nanoparticles (TNPs) has caused a significant release of TNPs into the environment, increasing human exposure to TNPs. The potential toxicity of TNPs has become an urgent concern. Various models have been used to evaluate the toxic effects of TNPs, but the relationship between TNPs' toxicity and physicochemical properties is largely unknown. This review summarizes relevant reports to support the development of better predictive toxicological models and the safe future application of TNPs.

Cytotoxicity and genotoxicity of nanosized and microsized titanium dioxide and iron oxide particles in Syrian hamster embryo cells

Potential differences in the toxicological properties of nanosized and non-nanosized particles have been notably pointed out for titanium dioxide (TiO(2)) particles, which are currently widely produced and used in many industrial areas. Nanoparticles of the iron oxides magnetite (Fe(3)O(4)) and hematite (Fe(2)O(3)) also have many industrial applications but their toxicological properties are less documented than those of TiO(2). In the present study, the in vitro cytotoxicity and genotoxicity of commercially available nanosized and microsized anatase TiO(2), rutile TiO(2), Fe(3)O(4), and Fe(2)O(3) particles were compared in Syrian hamster embryo (SHE) cells. Samples were characterized for chemical composition, primary particle size, crystal phase, shape, and specific surface area. In acellular assays, TiO(2) and iron oxide particles were able to generate reactive oxygen species (ROS). At the same mass dose, all nanoparticles produced higher levels of ROS than their microsized counterparts. Measurement of particle size in the SHE culture medium showed that primary nanoparticles and microparticles are present in the form of micrometric agglomerates of highly poly-dispersed size. Uptake of primary particles and agglomerates by SHE exposed for 24 h was observed for all samples. TiO(2) samples were found to be more cytotoxic than iron oxide samples. Concerning primary size effects, anatase TiO(2), rutile TiO(2), and Fe(2)O(3) nanoparticles induced higher cytotoxicity than their microsized counterparts after 72 h of exposure. Over this treatment time, anatase TiO(2) and Fe(2)O(3) nanoparticles also produced more intracellular ROS compared to the microsized particles. However, similar levels of DNA damage were observed in the comet assay after 24 h of exposure to anatase nanoparticles and microparticles. Rutile microparticles were found to induce more DNA damage than the nanosized particles. However, no significant increase in DNA damage was detected from nanosized and microsized iron oxides. None of the samples tested showed significant induction of micronuclei formation after 24 h of exposure. In agreement with previous size-comparison studies, we suggest that in vitro cytotoxicity and genotoxicity induced by metal oxide nanoparticles are not always higher than those induced by their bulk counterparts.

TiO₂ nanoparticles induce dysfunction and activation of human endothelial cells

Nanoparticles can reach the blood and cause inflammation, suggesting that nanoparticles-endothelial cells interactions may be pathogenically relevant. We evaluated the effect of titanium dioxide nanoparticles (TiO₂) on proliferation, death, and responses related with inflammatory processes such as monocytic adhesion and expression of adhesion molecules (E- and P-selectins, ICAM-1, VCAM-1, and PECAM-1) and with inflammatory molecules (tissue factor, angiotensin-II, VEGF, and oxidized LDL receptor-1) on human umbilical vein endothelial cells (HUVEC). We also evaluated the production of reactive oxygen species, nitric oxide production, and NF-κB pathway activation. Aggregates of TiO₂ of 300 nm or smaller and individual nanoparticles internalized into HUVEC inhibited proliferation strongly and induced apoptotic and necrotic death starting at 5 μg/cm². Besides, TiO₂ induced activation of HUVEC through an increase in adhesion and in expression of adhesion molecules and other molecules involved with the inflammatory process. These effects were associated with oxidative stress and NF-κB pathway activation. In conclusion, TiO₂ induced HUVEC activation, inhibition of cell proliferation with increased cell death, and oxidative stress.

Metal nanoparticle-induced micronuclei and oxidative DNA damage in mice

Several mechanisms regarding the adverse health effects of nanomaterials have been proposed. Among them, oxidative stress is considered to be one of the most important. Many in vitro studies have shown that nanoparticles generate reactive oxygen species, deplete endogenous antioxidants, alter mitochondrial function and produce oxidative damage in DNA. 8-Hydroxy-2'-deoxyguanosine is a major type of oxidative DNA damage, and is often analyzed as a marker of oxidative stress in human and animal studies. In this study, we focused on the in vivo toxicity of metal oxide and silver nanoparticles. In particular, we analyzed the induction of micronucleated reticulocyte formation and oxidative stress in mice treated with nanoparticles (CuO, Fe₃O₄, Fe₂O₃, TiO₂, Ag). For the micronucleus assay, peripheral blood was collected from the tail at 0, 24, 48 and 72 h after an i.p. injection of nanoparticles. Following the administration of nanoparticles by i.p. injection to mice, the urinary 8-hydroxy-2'-deoxyguanosine levels were analyzed by the HPLC-ECD method, to monitor the oxidative stress. The levels of 8-hydroxy-2'-deoxyguanosine in liver DNA were also measured. The results showed increases in the reticulocyte micronuclei formation in all nanoparticle-treated groups and in the urinary 8-hydroxy-2'-deoxyguanosine levels. The 8-hydroxy-2'-deoxyguanosine levels in the liver DNA of the CuO-treated group increased in a dose-dependent manner. In conclusion, the metal nanoparticles caused genotoxicity, and oxidative stress may be responsible for the toxicity of these metal nanoparticles.

In vitro assessment of engineered nanomaterials using a hepatocyte cell line: cytotoxicity, pro-inflammatory cytokines and functional markers

Effects on the liver C3A cell line treated with a panel of engineered nanomaterials (NMs) consisting of two zinc oxide particles (ZnO; coated 100 nm and uncoated 130 nm), two multi-walled carbon nanotubes (MWCNTs), one silver (Ag < 20 nm), one 7 nm anatase, two rutile TiO2 nanoparticles (10 and 94 nm) and two derivatives with positive and negative covalent functionalisation of the 10 nm rutile were evaluated. The silver particles elicited the greatest level of cytotoxicity (24 h LC50 - 2 µg/cm(2)). The silver was followed by the uncoated ZnO (24 h LC50 - 7.5 µg/cm(2)) and coated ZnO (24 h LC50 - 15 µg/cm(2)) particles with respect to cytotoxicity. The ZnO NMs were found to be about 50-60% soluble which could account for their toxicity. By contrast, the Ag was <1% soluble. The LC50 was not attained in the presence of any of the other engineered NMs (up to 80 µg/cm(2)). All NMs significantly increased IL-8 production. Meanwhile, no significant change in TNF-α, IL-6 or CRP was detected. Urea and albumin production were measured as indicators of hepatic function. These markers were only altered by the coated and uncoated ZnO, which significantly decreased albumin production.

Titanium dioxide in our everyday life; is it safe?

BACKGROUND

Titanium dioxide (TiO(2)) is considered as an inert and safe material and has been used in many applications for decades. However, with the development of nanotechnologies TiO(2) nanoparticles, with numerous novel and useful properties, are increasingly manufactured and used. Therefore increased human and environmental exposure can be expected, which has put TiO(2) nanoparticles under toxicological scrutiny. Mechanistic toxicological studies show that TiO(2) nanoparticles predominantly cause adverse effects via induction of oxidative stress resulting in cell damage, genotoxicity, inflammation, immune response etc. The extent and type of damage strongly depends on physical and chemical characteristics of TiO(2) nanoparticles, which govern their bioavailability and reactivity. Based on the experimental evidence from animal inhalation studies TiO(2) nanoparticles are classified as "possible carcinogenic to humans" by the International Agency for Research on Cancer and as occupational carcinogen by the National Institute for Occupational Safety and Health. The studies on dermal exposure to TiO(2) nanoparticles, which is in humans substantial through the use of sunscreens, generally indicate negligible transdermal penetration; however data are needed on long-term exposure and potential adverse effects of photo-oxidation products. Although TiO(2) is permitted as an additive (E171) in food and pharmaceutical products we do not have reliable data on its absorption, distribution, excretion and toxicity on oral exposure. TiO(2) may also enter environment, and while it exerts low acute toxicity to aquatic organisms, upon long-term exposure it induces a range of sub-lethal effects.

CONCLUSIONS

Until relevant toxicological and human exposure data that would enable reliable risk assessment are obtained, TiO(2) nanoparticles should be used with great care.

In vitro toxicity evaluation of 25-nm anatase TiO2 nanoparticles in immortalized keratinocyte cells

Titanium dioxide (TiO(2)) nanoparticles (NPs) are massively fabricated and widely used in daily life, and thus potential risk has been posed to human health. However, the mechanism of the interaction between TiO(2) NPs and cells is still unclear. In this study, the interaction of anatase TiO(2) NPs with HaCaT cells is studied in vitro with multi-techniques. The TiO(2) NPs not only insert into cells through endocytic pathway but also penetrate into the cell. The TiO(2) NPs could produce reactive oxygen species (ROS) after dispersion spontaneously. Furthermore, the interaction between TiO(2) NPs and cellular components might also generate ROS. The ROS generation could lead to cellular toxicity if the level of ROS production overwhelms the antioxidant defense. Cytoskeletal components, particularly the microfilaments and microtubules, cause modifications upon exposure to TiO(2) NPs. With all results, the toxicological effects of TiO(2) NPs on HaCaT cell can be simplified into six events.

Pre-irradiation of anatase TiO2 particles with UV enhances their cytotoxic and genotoxic potential in human hepatoma HepG2 cells

Titanium dioxide (TiO(2)) is active in the UV region of the light spectra and is used as a photocatalyst in numerous applications. Photo-activated anatase TiO(2) particles promote increased production of free radicals. This is a desirable property, although the potential toxicity of such photo-activated TiO(2) particles on exposure of humans and the environment remains unknown. Therefore, we studied whether pre-irradiation of TiO(2) particles with UV influences their cytotoxic and genotoxic potential. The TiO(2) particles, as TiO(2)-A (<25 nm) and TiO(2)-B (>100 nm), were UV pre-irradiated (24h) and tested for cytotoxic and genotoxic activities in human hepatoma HepG2 cells. Non-irradiated TiO(2)-A/B at 1.0-250 μg/ml did not reduce viability of HepG2 cells, nor induce significant increases in DNA strand breaks; only TiO(2)-A induced significant increases in oxidative DNA damage. After UV pre-irradiation, both TiO(2)-A and TiO(2)-B reduced cell viability and induced significant increases in DNA strand breaks and oxidative DNA damage. This is the first study that shows that UV pre-irradiation of anatase TiO(2) particles results in increased cytotoxic and genotoxic potential. This warrants further studies as it has important implications for environmental and human health risk assessment and preventive actions to limit human exposure.

Comparison of the cytogenotoxicity induced by five different dental alloys using four in vitro assays

The purpose of present investigation was to compare the cyto-genotoxicity induced by five dental alloys in vitro. The cyto-genotoxicity induced by five dental alloy extracts on human B lymphoblast cells was assessed with neutral red uptake (NRU) , CCK-8, comet and micronucleus (CBMN) assays in vitro, respectively. The results of in vitro comet and CBMN assays indicated that DNA damage (% tail DNA) and micronucleus frequencies (MNFs) in all exposure groups did not significantly increase, as compared with the control group. However, the results of NRU and CCK-8 assays demonstrated that there were to some extent differences in the cytotoxicity among 5 dental alloy extracts in vitro. The cytotoxicity may be relevant to the Ni and Be ions released in the alloy extract.

Models for oral uptake of nanoparticles in consumer products

Presently, many consumer products contain nano-sized materials (NMs) to improve material properties, product quality and ease of use. NMs in food additives and in cosmetic articles (e.g., tooth paste) may be taken up by the oral route. As adverse effects of environmental nanoparticles, like ultrafine particles, have been reported, consumers worry about potential risks when using products containing NMs. The review focuses on metal and metal oxide NMs as common additives in tooth paste and in food industry and exposure by the oral route. Testing of NMs for oral exposure is very complex because differences in the diet, in mucus secretion and composition, in pH, in gastrointestinal transit time and in gastrointestinal flora influence NM uptake. Acellular (mucus, saliva) and epithelial layer of the orogastrointestinal barrier are described. Expected exposure doses, interaction of the NMs with mucus and permeation through the epithelium as well as in vivo data are mentioned. The role of in vitro models for the study of parameters relevant for ingested NMs is discussed.

Screening evaluation of the ecotoxicity and genotoxicity of soils contaminated with organic and inorganic nanoparticles: the role of ageing

This study aimed to evaluate the toxicity and genotoxicity of soils, and corresponding elutriates, contaminated with aqueous suspensions of two organic (vesicles of sodium dodecyl sulphate/didodecyl dimethylammonium bromide and of monoolein and sodium oleate) and five inorganic nanoparticles (NPs) (TiO(2), TiSiO(4), CdSe/ZnS quantum dots, Fe/Co magnetic fluid and gold nanorods) to Vibrio fischeri and Salmonella typhimurium (TA98 and TA100 strains). Soil samples were tested 2h and 30 days after contamination. Suspensions of NPs were characterized by Dynamic Light Scattering. Soils were highly toxic to V. fischeri, especially after 2h. After 30 days toxicity was maintained only for soils spiked with suspensions of more stable NPs (zeta potential>30 mV or <-30 mV). Elutriates were particularly toxic after 2h, except for soil spiked with Fe/Co magnetic fluid, suggesting that ageing may have contributed for degrading the organic shell of these NPs, increasing the mobility of core elements and the toxicity of elutriates. TA98 was the most sensitive strain to the mutagenic potential of soil elutriates. Only elutriates from soils spiked with gold nanorods, quantum dots (QDs) and TiSiO(4) induced mutations in both strains of S. typhimurium, suggesting more diversified mechanisms of genotoxicity.

In vitro evidence of dysregulation of blood-brain barrier function after acute and repeated/long-term exposure to TiO(2) nanoparticles

The effects of titanium dioxide nanoparticles (TiO(2) NPs) on blood-brain barrier (BBB) function are unknown. Here, we report such evidence of adverse effects after in vitro exposure of a rat primary cell-based BBB model to NPs. BBB integrity was studied by measuring the flux of sucrose through the monolayer. P-glycoprotein (P-gp) activity was assessed by measuring the passage of vinblastine. Transcription profiles of P-gp and other ABC transporters as well as of cytokines were investigated by real-time PCR. Electron microscopy and particle-induced X-ray emission measurements were performed. We compared several exposure modalities, from early to chronic, mimicking a brain-to-blood transport or a systemic contamination. In the first case, BBB integrity was preserved, but P-gp activity of endothelial cells (BECs) was reduced. In the second case, BBB integrity and P-gp function were impaired from 5 μg/mL for 24 h and expression of tight junction proteins and efflux transporters was modulated. An inflammatory response had repercussions on ABC transporter expression of glial cells. We demonstrate that NPs accumulated in BECs and crossed the cell monolayer. These findings suggest that there is an immunoregulatory loop between inflammatory components, BECs and glial cells in the dysfunction of the BBB during exposure to TiO(2) NPs.

Titanium dioxide nanoparticles exhibit genotoxicity and impair DNA repair activity in A549 cells

Titanium dioxide nanoparticles (TiO(2)-NPs) are produced in large quantities, raising concerns about their impact for human health. The aim of this study was to deeply characterize TiO(2)-NPs genotoxic potential to lung cells, and to link genotoxicity to physicochemical characteristics, e.g., size, specific surface area, crystalline phase. A549 cells were exposed to a panel of TiO(2)-NPs with diameters ranging from 12 to 140 nm, either anatase or rutile. A set of complementary techniques (comet and micronucleus assays, gamma-H2AX immunostaining, 8-oxoGuanine analysis, H2-DCFDA, glutathione content, antioxidant enzymes activities) allowed us to demonstrate that small and spherical TiO(2)-NPs, both anatase and rutile, induce single-strand breaks and oxidative lesions to DNA, together with a general oxidative stress. Additionally we show that these NPs impair cell ability to repair DNA, by inactivation of both NER and BER pathways. This study thus confirms the genotoxic potential of TiO(2)-NPs, which may preclude their mutagenicity and carcinogenicity.

Chronic exposure to nanosized, anatase titanium dioxide is not cyto- or genotoxic to Chinese hamster ovary cells

Titanium dioxide nanoparticles (nano-TiO(2) ) are widely used in cosmetics, skin care products, paints, and water treatment processes. Disagreement remains regarding the safety of nano-TiO(2) , and little epidemiological data is available to provide needed resolution. Most studies have examined effects using acute exposure experiments with relatively few studies using a chronic exposure design. We examined cyto- and genotoxicity in CHO-K1 cells following 60 days of continuous exposure to defined levels of nano-TiO(2) (0, 10, 20, or 40 μg/ml). Oxidative stress increased in a concentration-dependent manner in short- (2 days) and long-term cultures, but long-term cultures had lower levels of oxidative stress. The primary reactive oxygen species appeared to be superoxide, and ROS indicators were lowered with the addition of superoxide dismutase (SOD). No cyto- or genotoxic effects were apparent using the XTT, trypan-blue exclusion, and colony-forming assays for viability and the Comet and Hprt gene mutation assays for genotoxicity. Nano-TiO(2) increased the percentage of cells in the G2/M phase of the cell cycle, but this effect did not appear to influence cell viability or cell division. Cellular Ti content was dose-dependent, but chronically exposed cells had lower amounts than acutely exposed cells. CHO cells appear to adapt to chronic exposure to nano-TiO(2) and detoxify excess ROS possibly through upregulation of SOD in addition to reducing particle uptake.

Ameliorative effects of dimetylthiourea and N-acetylcysteine on nanoparticles induced cyto-genotoxicity in human lung cancer cells-A549

We study the ameliorative potential of dimetylthiourea (DMTU), an OH^• radical trapper and N-acetylcysteine (NAC), a glutathione precursor/H₂O₂ scavenger against titanium dioxide nanoparticles (TiO₂-NPs) and multi-walled carbon nanotubes (MWCNTs) induced cyto-genotoxicity in cultured human lung cancer cells-A549. Cytogenotoxicity was induced by exposing the cells to selected concentrations (10 and 50 µg/ml) of either of TiO₂-NPs or MWCNTs for 24 h. Anti-cytogenotoxicity effects of DMTU and NAC were studied in two groups, i.e., treatment of 30 minutes prior to toxic insult (short term exposure), while the other group received DMTU and NAC treatment during nanoparticles exposure, i.e., 24 h (long term exposure). Investigations were carried out for cell viability, generation of reactive oxygen species (ROS), micronuclei (MN), and expression of markers of oxidative stress (HSP27, CYP2E1), genotoxicity (P⁵³) and CYP2E1 dependent n- nitrosodimethylamine-demethylase (NDMA-d) activity. In general, the treatment of both DMTU and NAC was found to be effective significantly against TiO₂-NPs and MWCNTs induced cytogenotoxicity in A549 cells. Long-term treatment of DMTU and NAC during toxic insults has shown better prevention than short-term pretreatment. Although, cells responded significantly to both DMTU and NAC, but responses were chemical specific. In part, TiO_2-NPs induced toxic responses were mediated through OH^• radicals generation and reduction in the antioxidant defense system. While in the case of MWCNTs, adverse effects were primarily due to altering/hampering the enzymatic antioxidant system. Data indicate the applicability of human lung cancer cells-A549 as a pre-screening tool to identify the target specific prophylactic and therapeutic potential of drugs candidate molecules against nanoparticles induced cellular damages.

The electrostatic interactions between nano-TiO(2) and trypsin inhibit the enzyme activity and change the secondary structure of trypsin

In this work, the interaction between nano-TiO(2) and trypsin was investigated, and the mechanisms of the interaction were explored by the methods of UV-vis detection, circular dichroism (CD), and fluorescence. The results clearly demonstrated that nano-TiO(2) had an inhibitory effect on the enzyme activity. The activity was decreased to 64% of the untreated trypsin in the presence of 300 μg/ml nano-TiO(2). UV spectrometry proved that nano-TiO(2) had a strong physical absorption effect on trypsin, and the CD spectra revealed that the secondary structure of trypsin was partly destroyed while bound together with nano-TiO(2). The ratio of α-helix increased from 7.9% to 12.8% in the presence of 100 μg/ml TiO(2) while the ratio of β-sheet decreased from 48.7% to 36.4%. Furthermore, the fluorescence spectrometry indicated that nano-TiO(2) could quench the intrinsic fluorescence of trypsin through static quenching. Meanwhile, the binding constant was calculated to be 1, and the process of binding of trypsin on nano-TiO(2) was a spontaneous molecular interaction procedure in which electrostatic interaction plays a major role. Our study was to provide a useful approach for evaluating the health risk of nanomaterials on level of proteins.

Molecular mechanism of hippocampal apoptosis of mice following exposure to titanium dioxide nanoparticles

Previous studies demonstrate that the exposure to titanium dioxide nanoparticles (TiO(2) NPs) damages the central nervous system of mice; however, very little is known about the effects of TiO(2) NPs on hippocampal apoptosis or its molecular mechanism. The present study investigated the molecular mechanism associated with hippocampal apoptosis in mice induced by intragastric administration of TiO(2) NPs for consecutive 60 days. Our findings indicate that TiO(2) NPs accumulate in the mouse hippocampus, and this accumulation, in turn, led to hippocampal apoptosis and impairment in spatial recognition memory in mice. In addition, TiO(2) NPs significantly activated caspase-3 and -9, inhibited Bcl-2, and promoted the levels of Bax and cytochrome c. Furthermore, TiO(2) NPs induced accumulation of reactive oxygen species in the mouse hippocampus. These findings suggest that TiO(2) NP-induced apoptosis in the mouse hippocampus may result from an intrinsic pathway, and workers and consumers should take great caution when handling nanomaterials.

Pulmonary response to surface-coated nanotitanium dioxide particles includes induction of acute phase response genes, inflammatory cascades, and changes in microRNAs: a toxicogenomic study

Titanium dioxide nanoparticles (nanoTiO(2) ) are used in various applications including in paints. NanoTiO(2) inhalation may induce pulmonary toxicity and systemic effects. However, the underlying molecular mechanisms are poorly understood. In this study, the effects of inhaled surface-coated nanoTiO(2) on pulmonary global messenger RNA (mRNA) and microRNA (miRNA) expression in mouse were characterized to provide insight into the molecular response. Female C57BL/6BomTac mice were exposed for 1 hr daily to 42.4 ± 2.9 (SEM) mg surface-coated nanoTiO(2) /m(3) for 11 consecutive days by inhalation and were sacrificed 5 days following the last exposure. Physicochemical properties of the particles were determined. Pulmonary response to nanoTiO(2) was characterized using DNA microarrays and pathway-specific PCR arrays and related to data on pulmonary inflammation from bronchial lavages. NanoTiO(2) exposure resulted in increased levels of mRNA for acute phase markers serum amyloid A-1 (Saa1) and serum amyloid A-3 (Saa3), several C-X-C and C-C motif chemokines, and cytokine tumor necrosis factor genes. Protein analysis of Saa1 and 3 showed selective upregulation of Saa3 in lung tissues. Sixteen miRNAs were induced by more than 1.2-fold (adjusted P-value < 0.05) following exposure. Real time polymerase chain reaction confirmed the upregulation of miR-1, miR-449a and revealed dramatic induction of miR-135b (60-fold). Thus, inhalation of surface-coated nanoTiO(2) results in changes in the expression of genes associated with acute phase, inflammation and immune response 5 days post exposure with concomitant changes in several miRNAs. The role of these miRNAs in pulmonary response to inhaled particles is unknown and warrants further research.

Biodistribution and toxicity of intravenously administered silica nanoparticles in mice

As the biosafety of nanotechnology becomes a growing concern, the in vivo nanotoxicity of NPs has drawn a lot of attention. Silica nanoparticles (SiNPs) have been widely developed for biomedical use, but their biodistribution and toxicology have not been investigated extensively in vivo. Although investigations of in vivo qualitative distribution of SiNPs have been reported, the time-dependent and quantitative informations about the distribution of SiNPs are still lacking. Here we investigated the long-term (30 days) quantitative tissue distribution, and subcellular distribution, as well as potential toxicity of two sizes of intravenously administered SiNPs in mice using radiolabeling, radioactive counting, transmission electron microscopy and histological analysis. The results indicated that SiNPs accumulate mainly in lungs, liver and spleen and are retained for over 30 days in the tissues because of the endocytosis by macrophages, and could potentially cause liver injury when intravenously injected.