Titanium dioxide induced cell damage: a proposed role of the carboxyl radical

Immunomodulatory and antioxidant effect of green synthesized titanium dioxide nanoparticles on pregnant female albino rats and their fetuses

Titanium dioxide nanoparticles (TiO2 NPs) are one of the various nanoparticles that have been increasingly commonly used in vital sectors. This study was aimed at evaluating the effects of prenatal exposure to the chemical TiO2 NPs (CHTiO2 NPs) and green-synthesized TiO2 NPs (GTiO2 NPs) on immunological and oxidative status as well as lungs and spleen. Fifty pregnant female albino rats were divided into five groups of ten rats each: control, CHTiO2 NPs-treated groups orally received 100 and 300 mg/kg CHTiO2 NPs, and GTiO2 NPs-treated groups received 100 and 300 mg/kg GTiO2 NPs, respectively, daily for 14 days. The serum level of proinflammatory cytokines IL-6, oxidative stress markers (MDA and NO), and antioxidant biomarkers (SOD and GSH-PX) were assayed. Spleen and lungs were collected from pregnant rats and fetuses for histopathological examinations. The results showed a significant increase in IL-6 levels in treated groups. In the CHTiO2 NPs-treated groups, there was a significant increase in MDA activity and a significant decrease in GSH-Px and SOD activities, revealing its oxidative effect, while GSH-Px and SOD activities significantly increased in the 300 GTiO2 NPs-treated group, confirming the antioxidant effect of green-synthesized TiO2 NPs. Histopathological findings of the spleen and lungs of the CHTiO2 NPs-treated group revealed severe congestion and thickening of the blood vessels, while those of the GTiO2 NPs-treated group revealed mild tissue alterations. It could be deduced that green synthesized titanium dioxide nanoparticles have immunomodulatory and antioxidant effects on pregnant female albino rats and their fetuses, with an ameliorated impact on the spleen and lung compared to chemical titanium dioxide nanoparticles.

A Review on Nano Ti-Based Oxides for Dark and Photocatalysis: From Photoinduced Processes to Bioimplant Applications

Catalysis on TiO₂ nanomaterials in the presence of H₂O and oxygen plays a crucial role in the advancement of many different fields, such as clean energy technologies, catalysis, disinfection, and bioimplants. Photocatalysis on TiO₂ nanomaterials is well-established and has advanced in the last decades in terms of the understanding of its underlying principles and improvement of its efficiency. Meanwhile, the increasing complexity of modern scientific challenges in disinfection and bioimplants requires a profound mechanistic understanding of both residual and dark catalysis. Here, an overview of the progress made in TiO₂ catalysis is given both in the presence and absence of light. It begins with the mechanisms involving reactive oxygen species (ROS) in TiO₂ photocatalysis. This is followed by improvements in their photocatalytic efficiency due to their nanomorphology and states by enhancing charge separation and increasing light harvesting. A subsection on black TiO₂ nanomaterials and their interesting properties and physics is also included. Progress in residual catalysis and dark catalysis on TiO₂ are then presented. Safety, microbicidal effect, and studies on Ti-oxides for bioimplants are also presented. Finally, conclusions and future perspectives in light of disinfection and bioimplant application are given.

Composition effects on photooxidative membrane destabilization by TiO2 nanoparticles

Membrane interactions and photooxidative membrane destabilization of titanium dioxide (TiO₂) nanoparticles were investigated, focusing on the effects of membrane composition, notably phospholipid headgroup charge and presence of cholesterol. For this, we employed a battery of state-of-the-art methods for studies of bilayers formed by zwitterionic palmitoyloleoylphosphatidylcholine (POPC) containing also polyunsaturated palmitoylarachidonoylphosphocholine (PAPC), as well as its mixtures with anionic palmitoyloleoylphosphatidylglycerol (POPG) and cholesterol. It was found that the TiO₂ nanoparticles display close to zero charge at pH 7.4, resulting in aggregation. At pH 3.4, in contrast, the 6 nm TiO₂ nanoparticles are well dispersed due to a strongly positive ζ-potential. Mirroring this pH dependence, TiO₂ nanoparticles were observed to bind to negatively charged lipid bilayers at pH 3.4, but much less so at pH 7.4. While nanoparticle binding has some destabilizing effect alone, illumination with ultraviolet (UV) light accentuates membrane destabilization, a result of oxidative stress caused by generated reactive oxygen species (ROS). Neutron reflectivity (NR), quartz crystal microbalance (QCM), and small-angle X-ray scattering (SAXS) results all demonstrate that membrane composition strongly influences membrane interactions and photooxidative destabilization of lipid bilayers. In particular, the presence of anionic POPG makes the bilayers more sensitive to oxidative destabilization, whereas a stabilizing effect was observed in the presence of cholesterol. Also, structural aspects of peroxidation were found to depend strongly on membrane composition, notably the presence of anionic phospholipids. The results show that membrane interactions and UV-induced ROS generation act in concert and need to be considered together to understand effects of lipid membrane composition on UV-triggered oxidative destabilization by TiO₂ nanoparticles, e.g., in the context of oxidative damage of bacteria and cells.

Antagonistic cytoprotective effects of C60 fullerene nanoparticles in simultaneous exposure to benzo[a]pyrene in a molluscan animal model

The hypothesis that C₆₀ fullerene nanoparticles (C₆₀) exert an antagonistic interactive effect on the toxicity of benzo[a]pyrene (BaP) has been supported by this investigation. Mussels were exposed to BaP (5, 50 & 100μg/L) and C₆₀ (C₆₀-1mg/L) separately and in combination. Both BaP and C₆₀ were shown to co-localize in the secondary lysosomes of the hepatopancreatic digestive cells in the digestive gland where they reduced lysosomal membrane stability (LMS) or increased membrane permeability, while BaP also induced increased lysosomal lipid and lipofuscin, indicative of oxidative cell injury and autophagic dysfunction. Combinations of BaP and C₆₀ showed antagonistic effects for lysosomal stability, mTORC1 (mechanistic target of rapamycin complex 1) inhibition and intralysosomal lipid (5 & 50μg/L BaP). The biomarker data (i.e., LMS, lysosomal lipidosis and lipofuscin accumulation; lysosomal/cell volume and dephosphorylation of mTORC1) were further analysed using multivariate statistics. Principal component and cluster analysis clearly indicated that BaP on its own was more injurious than in combination with C₆₀. Use of a network model that integrated the biomarker data for the cell pathophysiological processes, indicated that there were significant antagonistic interactions in network complexity (% connectance) at all BaP concentrations for the combined treatments. Loss of lysosomal membrane stability probably causes the release of intralysosomal iron and hydrolases into the cytosol, where iron can generate harmful reactive oxygen species (ROS). It was inferred that this adverse oxidative reaction induced by BaP was ameliorated in the combination treatments by the ROS scavenging property of intralysosomal C₆₀, thus limiting the injury to the lysosomal membrane; and reducing the oxidative damage in the cytosol and to the nuclear DNA. The ROS scavenging by C₆₀, in combination with enhanced autophagic turnover of damaged cell constituents, appeared to have a cytoprotective effect against the toxic reaction to BaP in the combined treatments.

Environmental transformation of n-TiO2 in the aquatic systems and their ecotoxicity in bivalve mollusks: A systematic review

Over the past decades, titanium dioxide nanoparticles (n-TiO₂) have been extensively used in several industrial applications and the manufacture of novel consumer products. Although strict regulations have been put in place to limit their release into the aquatic environment, these nanoparticles can still be found at elevated levels within the environment, which can result in toxic effects on exposed organisms and has possible implications in term of public health. Bivalve mollusks are a unique and ideal group of shellfish for the study and monitoring the aquatic pollution by n-TiO₂ because of their filter-feeding behaviour and ability to accumulate toxicants in their tissues. In these animals, exposure to n-TiO₂ leads to oxidative stress, immunotoxicity, neurotoxicity, and genotoxicity, as well as behavioral and physiological changes. This review summarizes the uptake, accumulation, and fate of n-TiO₂ in aquatic environments and the possible interactions between n-TiO₂ and other contaminants such as heavy metals and organic pollutants. Moreover, the toxicological impacts and mechanisms of action are discussed for a wide range of bivalve mollusks. This data underlines the pressing need for additional knowledge and future research plans for the development of control strategies to mitigate the release of n-TiO₂ to the aquatic environment to prevent the toxicological impacts on bivalves and protect public health.

Oxidation of Polyunsaturated Lipid Membranes by Photocatalytic Titanium Dioxide Nanoparticles: Role of pH and Salinity

In the present study, UV-induced membrane destabilization by TiO₂ (anatase) nanoparticles was investigated by neutron reflectometry (NR), small-angle X-ray scattering (SAXS), quartz crystal microbalance with dissipation (QCM-D), dynamic light scattering (DLS), and ζ-potential measurements for phospholipid bilayers formed by zwitterionic palmitoyloleoylphosphatidylcholine (POPC) containing biologically relevant polyunsaturations. TiO₂ nanoparticles displayed pH-dependent binding to such bilayers. Nanoparticle binding alone, however, has virtually no destabilizing effects on the lipid bilayers. In contrast, UV illumination in the presence of TiO₂ nanoparticles activates membrane destabilization as a result of lipid oxidation caused by the generation of reactive oxygen species (ROS), primarily ^•OH radicals. Despite the short diffusion length characterizing these, the direct bilayer attachment of TiO₂ nanoparticles was demonstrated to not be a sufficient criterion for an efficient UV-induced oxidation of bilayer lipids, the latter also depending on ROS generation in bulk solution. From SAXS and NR, minor structural changes were seen when TiO₂ was added in the absence of UV exposure, or on UV exposure in the absence of TiO₂ nanoparticles. In contrast, UV exposure in the presence of TiO₂ nanoparticles caused large-scale structural transformations, especially at high ionic strength, including gradual bilayer thinning, lateral phase separation, increases in hydration, lipid removal, and potential solubilization into aggregates. Taken together, the results demonstrate that nanoparticle-membrane interactions ROS generation at different solution conditions act in concert to induce lipid membrane destabilization on UV exposure and that both of these need to be considered for understanding the performance of UV-triggered TiO₂ nanoparticles in nanomedicine.

Suitability of human and mammalian cells of different origin for the assessment of genotoxicity of metal and polymeric engineered nanoparticles

Nanogenotoxicity is a crucial endpoint in safety testing of nanomaterials as it addresses potential mutagenicity, which has implications for risks of both genetic disease and carcinogenesis. Within the NanoTEST project, we investigated the genotoxic potential of well-characterised nanoparticles (NPs): titanium dioxide (TiO2) NPs of nominal size 20 nm, iron oxide (8 nm) both uncoated (U-Fe3O4) and oleic acid coated (OC-Fe3O4), rhodamine-labelled amorphous silica 25 (Fl-25 SiO2) and 50 nm (Fl-50 SiO) and polylactic glycolic acid polyethylene oxide polymeric NPs - as well as Endorem® as a negative control for detection of strand breaks and oxidised DNA lesions with the alkaline comet assay. Using primary cells and cell lines derived from blood (human lymphocytes and lymphoblastoid TK6 cells), vascular/central nervous system (human endothelial human cerebral endothelial cells), liver (rat hepatocytes and Kupffer cells), kidney (monkey Cos-1 and human HEK293 cells), lung (human bronchial 16HBE14o cells) and placenta (human BeWo b30), we were interested in which in vitro cell model is sufficient to detect positive (genotoxic) and negative (non-genotoxic) responses. All in vitro studies were harmonized, i.e. NPs from the same batch, and identical dispersion protocols (for TiO2 NPs, two dispersions were used), exposure time, concentration range, culture conditions and time-courses were used. The results from the statistical evaluation show that OC-Fe3O4 and TiO2 NPs are genotoxic in the experimental conditions used. When all NPs were included in the analysis, no differences were seen among cell lines - demonstrating the usefulness of the assay in all cells to identify genotoxic and non-genotoxic NPs. The TK6 cells, human lymphocytes, BeWo b30 and kidney cells seem to be the most reliable for detecting a dose-response.

Fast, Ultrasensitive Detection of Reactive Oxygen Species Using a Carbon Nanotube Based-Electrocatalytic Intracellular Sensor

Herein, we report a highly sensitive electrocatalytic sensor-cell construct that can electrochemically communicate with the internal environment of immune cells (e.g., macrophages) via the selective monitoring of a particular reactive oxygen species (ROS), hydrogen peroxide. The sensor, which is based on vertically aligned single-walled carbon nanotubes functionalized with an osmium electrocatalyst, enabled the unprecedented detection of a local intracellular "pulse" of ROS on a short second time scale in response to bacterial endotoxin (lipopolysaccharide-LPS) stimulation. Our studies have shown that this initial pulse of ROS is dependent on NADPH oxidase (NOX) and toll like receptor 4 (TLR4). The results suggest that bacteria can induce a rapid intracellular pulse of ROS in macrophages that initiates the classical innate immune response of these cells to infection.

TiO2nanoparticles promote the production of unsaturated fatty acids (UFAs) fighting against oxidative stress in Pichia pastoris

Since titanium dioxide (TiO₂) nanomaterials are widely implemented in various fields, their safety and toxicity receive detailed investigation.

Liver alterations in two freshwater fish species (Carassius auratus and Danio rerio) following exposure to different TiO₂ nanoparticle concentrations

The toxicity of titanium dioxide nanoparticles (TIO₂ NPs) and oxidative stress effects were studied in two freshwater fish species (Carassius auratus and Danio rerio) exposed for 21 days to different concentrations (0.01, 0.1, 1, 10, 100/mgL) of TiO₂ NPs and to a control (tap water). Additional fish were transferred to clean water for 14 days to assess the ability to recover from exposure to TiO₂ NPs. Activities of the enzyme glutathione-S-transferase (GST) and lipid peroxidation (LPO) (malondialdheyde) were measured as indicators of oxidative stress. Histological and ultra-structural changes in livers from both species of fish were evaluated by light and electron microscopy. Results show a general GST activity increase according to TiO₂ NPs concentrations, which is in agreement with data from LPO. After 21 days, GST activities decreased possibly caused by suppression of GST synthesis as a result of severe stress. Histological and ultra-structural analysis of livers from exposed fish show degeneration of the hepatic tissue and alterations in hepatocytes such as glycogen depletion and an increase in lipofucsin lysosome-like granules. After a depuration period a partial recovery for biochemical markers and cells was observed. The results suggest that TiO₂ promotes alterations in hepatic tissues compatible with oxidative stress.

Enhanced toxicity of 'bulk' titanium dioxide compared to 'fresh' and 'aged' nano-TiO2 in marine mussels (Mytilus galloprovincialis)

Marine bivalves (Mytilus galloprovincialis) were exposed to titanium dioxide (10 mg L(-1)) either as engineered nanoparticles (nTiO2; fresh, or aged under simulated sunlight for 7 days) or the bulk equivalent. Inductively coupled plasma-optical emission spectrometry analyses of mussel tissues showed higher Ti accumulation (>10-fold) in the digestive gland compared to gills. Nano-sized TiO2 showed greater accumulation than bulk, irrespective of ageing, particularly in digestive gland (>sixfold higher). Despite this, transcriptional expression of metallothionein genes, histology and histochemical analysis suggested that the bulk material was more toxic. Haemocytes showed significantly enhanced DNA damage, determined by the modified comet assay, for all treatments compared to the control, but no significant differences between the treatments. Our integrated study suggests that for this ecologically relevant organism photocatalytic ageing of nTiO2 does not significantly alter toxicity, and that bulk TiO2 may be less ecotoxicologically inert than previously assumed.

Emerging in vitro models for safety screening of high-volume production nanomaterials under environmentally relevant exposure conditions

The rising production of nanomaterial-based consumer products has raised safety concerns. Testing these with animal and other direct models is neither ethically nor economically viable, nor quick enough. This review aims to discuss the strength of in vitro testing, including the use of 2D and 3D cultures, stem cells, and tissue constructs, etc., which would give fast and repeatable answers of a highly specific nature, while remaining relevant to in vivo outcomes. These results can then be combined and the overall toxicity predicted with relative accuracy. Such in vitro models can screen potentially toxic nanomaterials which, if required, can undergo further stringent studies in animals. The cyto- and phototoxicity of some high-volume production nanomaterials, using in vitro models, is also reviewed.

Influence of humic acid on titanium dioxide nanoparticle toxicity to developing zebrafish

Titanium dioxide nanoparticle (TiO2NP) suspension stability can be altered by adsorption of dissolved organic matter (DOM). This is expected to impact their environmental fate and bioavailability. To date, the influence of DOM on the toxicity of TiO2NPs to aquatic vertebrates has not been reported. We examined the impact of Suwannee River humic acid (HA) on the toxicity of TiO2NPs to developing zebrafish (Danio rerio) in the dark and under simulated sunlight illumination. Adsorption of HA increased suspension stability and decreased TiO2NP exposure. TiO2NPs were more toxic in the presence of HA. In the absence of simulated sunlight, a small but significant increase in lethality was observed in fish exposed to TiO2NPs in the presence of HA. Under simulated sunlight illumination, photocatalytic degradation of HA reduced suspension stability. Despite the lower concentrations of Ti associated with fish in the treatments containing HA, under simulated sunlight illumination, median lethal concentrations were lower and oxidative DNA damage was elevated relative to fish exposed to TiO2NPs in the absence of HA. This study demonstrates the importance of considering environmental factors (i.e., exposure to sunlight, adsorption of DOM) when assessing the potential risks posed by engineered nanomaterials in the environment.

Free radicals generated by tantalum implants antagonize the cytotoxic effect of doxorubicin

Little is known about the interaction between antineoplastic drugs and implants in bone cancer patients. We investigated the interaction between commercially available porous tantalum (Ta) implants and the chemotherapeutic drug, Doxorubicin (DOX). DOX solutions were prepared in the presence of Ta implant. The changes in fluorescence intensity of the DOX chromophore were measured by spectrofluorometry and the efficacy of DOX was evaluated by viability of rabbit rectal tumor cells (VX2). After 5 min interaction of the DOX solution (5 μg/ml) with the Ta implant, the fluorescent intensity of the DOX solution was 85% degraded, and only 20% the drug efficacy to kill VX2 cells was retained. However, after adding a reducing agent, Dithiothreitol (DTT, 10 μg/ml), 80% of the original fluorescence and 50% of the drug efficacy were restored while UV irradiation enhanced drug degradation in the presence of Ta implant. The action of DTT and UV irradiation indicated that reactive oxygen species (ROS) were involved in the drug degradation mechanism. We detected that Ta implants in aqueous medium produced hydroxyl radicals. Cells showed higher intracellular ROS activity when culture medium was incubated with the Ta implant prior to cell culture. It is concluded that the porous Ta implant antagonizes the cytotoxicity of DOX via ROS generation of the porous Ta implant.

Oxidative DNA damage corresponds to the long term survival of human cells treated with silver nanoparticles

We examined the relation between DNA damage and the clonogenic potential of 3 human cell lines, HepG2, HT29 and A549, treated with bare 20 nm or 200 nm silver nanoparticles (AgNPs). The endpoints examined were the DNA breakage estimated by the comet assay, the oxidative base damage recognized by formamido-pyrimidine glycosylase (FPG) and estimated with the FPG+comet assay, and the frequencies of histone γH2AX foci and micronuclei. Each cell line studied had a different pattern of DNA breakage and base damage versus the NPs concentration and time of treatment. The overall pattern of DNA breakage and base damage induction corresponded to the intracellular generation of reactive oxygen species. There was no increase in the frequencies of histone γH2AX foci and micronuclei as compared to those in the untreated cells. The reported experiments suggest that only the oxidative DNA damage corresponds to the loss of the clonogenic ability of cells treated with AgNPs.

The effects of UV emission from compact fluorescent light exposure on human dermal fibroblasts and keratinocytes in vitro

Compact fluorescent light (CFL) bulbs can provide the same amount of lumens as incandescent light bulbs, using one quarter of the energy. Recently, CFL exposure was found to exacerbate existing skin conditions; however, the effects of CFL exposure on healthy skin tissue have not been thoroughly investigated. In this study, we studied the effects of exposure to CFL illumination on healthy human skin tissue cells (fibroblasts and keratinocytes). Cells exposed to CFLs exhibited a decrease in the proliferation rate, a significant increase in the production of reactive oxygen species, and a decrease in their ability to contract collagen. Measurements of UV emissions from these bulbs found significant levels of UVC and UVA (mercury [Hg] emission lines), which appeared to originate from cracks in the phosphor coatings, present in all bulbs studied. The response of the cells to the CFLs was consistent with damage from UV radiation, which was further enhanced when low dosages of TiO(2) nanoparticles (NPs), normally used for UV absorption, were added prior to exposure. No effect on cells, with or without TiO(2) NPs, was observed when they were exposed to incandescent light of the same intensity.

Merging nano-genotoxicology with eco-genotoxicology: an integrated approach to determine interactive genotoxic and sub-lethal toxic effects of C(60) fullerenes and fluoranthene in marine mussels, Mytilus sp

Whilst there is growing concern over the potential detrimental impact of engineered nanoparticles (ENPs) on the natural environment, little is known about their interactions with other contaminants. In the present study, marine mussels (Mytilus sp.) were exposed for 3 days to C(60) fullerenes (C(60); 0.10-1 mg l(-1)) and a model polycyclic aromatic hydrocarbon (PAH), fluoranthene (32-100 μg l(-1)), either alone or in combination. The first two experiments were conducted by exposing the organisms to different concentrations of C(60) and fluoranthene alone, in order to determine the effects on total glutathione levels (as a measure of generic oxidative stress), genotoxicity (DNA strand breaks using Comet assay in haemocytes), DNA adduct analyses (using (32)P-postlabelling method) in different organs, histopathological changes in different tissues (i.e. adductor muscle, digestive gland and gills) and physiological effects (feeding or clearance rate). Subsequently, in the third experiment, a combined exposure of C(60) plus fluoranthene (0.10 mg l(-1) and 32 μg l(-1), respectively) was carried out to evaluate all endpoints mentioned above. Both fluoranthene and C(60) on their own caused concentration-dependent increases in DNA strand breaks as determined by the Comet assay. Formation of DNA adducts however could not be detected for any exposure conditions. Combined exposure to C(60) and fluoranthene additively enhanced the levels of DNA strand breaks along with a 2-fold increase in the total glutathione content. In addition, significant accumulation of C(60) was observed in all organs, with highest levels in digestive gland (24.90 ± 4.91μg C(60) g(-1) ww). Interestingly, clear signs of abnormalities in adductor muscle, digestive gland and gills were observed by histopathology. Clearance rates indicated significant differences compared to the control with exposure to C(60), and C(60)/fluoranthene combined treatments, but not after fluoranthene exposure alone. This study demonstrated that at the selected concentrations, both C(60) and fluoranthene evoke toxic responses and genetic damage. The combined exposure produced enhanced damage with additive rather than synergistic effects.

Practical considerations for conducting ecotoxicity test methods with manufactured nanomaterials: what have we learnt so far?

This review paper reports the consensus of a technical workshop hosted by the European network, NanoImpactNet (NIN). The workshop aimed to review the collective experience of working at the bench with manufactured nanomaterials (MNMs), and to recommend modifications to existing experimental methods and OECD protocols. Current procedures for cleaning glassware are appropriate for most MNMs, although interference with electrodes may occur. Maintaining exposure is more difficult with MNMs compared to conventional chemicals. A metal salt control is recommended for experiments with metallic MNMs that may release free metal ions. Dispersing agents should be avoided, but if they must be used, then natural or synthetic dispersing agents are possible, and dispersion controls essential. Time constraints and technology gaps indicate that full characterisation of test media during ecotoxicity tests is currently not practical. Details of electron microscopy, dark-field microscopy, a range of spectroscopic methods (EDX, XRD, XANES, EXAFS), light scattering techniques (DLS, SLS) and chromatography are discussed. The development of user-friendly software to predict particle behaviour in test media according to DLVO theory is in progress, and simple optical methods are available to estimate the settling behaviour of suspensions during experiments. However, for soil matrices such simple approaches may not be applicable. Alternatively, a Critical Body Residue approach may be taken in which body concentrations in organisms are related to effects, and toxicity thresholds derived. For microbial assays, the cell wall is a formidable barrier to MNMs and end points that rely on the test substance penetrating the cell may be insensitive. Instead assays based on the cell envelope should be developed for MNMs. In algal growth tests, the abiotic factors that promote particle aggregation in the media (e.g. ionic strength) are also important in providing nutrients, and manipulation of the media to control the dispersion may also inhibit growth. Controls to quantify shading effects, and precise details of lighting regimes, shaking or mixing should be reported in algal tests. Photosynthesis may be more sensitive than traditional growth end points for algae and plants. Tests with invertebrates should consider non-chemical toxicity from particle adherence to the organisms. The use of semi-static exposure methods with fish can reduce the logistical issues of waste water disposal and facilitate aspects of animal husbandry relevant to MMNs. There are concerns that the existing bioaccumulation tests are conceptually flawed for MNMs and that new test(s) are required. In vitro testing strategies, as exemplified by genotoxicity assays, can be modified for MNMs, but the risk of false negatives in some assays is highlighted. In conclusion, most protocols will require some modifications and recommendations are made to aid the researcher at the bench.

Characterization of synthesized silver nanoparticles and assessment of its genotoxicity potentials using the alkaline comet assay

Nano-silver (Nano-Ag) particles were synthesized and then characterized using transmission electron microscopy (TEM) and X-ray diffractometry. TEM showed that Nano-Ag were spherical in shape and their size ranged from 40 to 60nm. X-ray diffractometry indicated that the sample was crystalline and had a face centered cubic structure of pure silver. Genotoxicity of this Nano-Ag was evaluated in human peripheral blood cells using the alkaline comet assay. Results indicated that Nano-Ag (50 and 100μg/mL) caused DNA damage following a 3h treatment. Subsequently, a short treatment of 5min also showed DNA damage. In conclusion, we have shown that the synthesized Nano-Ag induced DNA damage in human peripheral blood cells as detected by the alkaline comet assay. Results further indicated that treatment of cells with Nano-Ag in the presence of hydrogen peroxide did not induce any DNA damage.

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.

Nanoparticles in dermatology

Recent advances in the field of nanotechnology have allowed the manufacturing of elaborated nanometer-sized particles for various biomedical applications. A broad spectrum of particles, extending from various lipid nanostructures such as liposomes and solid lipid nanoparticles, to metal, nanocrystalline and polymer particles have already been tested as drug delivery systems in different animal models with remarkable results, promising an extensive commercialization in the coming years. Controlled drug release to skin and skin appendages, targeting of hair follicle-specific cell populations, transcutaneous vaccination and transdermal gene therapy are only a few of these new applications. Carrier systems of the new generation take advantage of improved skin penetration properties, depot effect with sustained drug release and of surface functionalization (e.g., the binding to specific ligands) allowing specific cellular and subcellular targeting. Drug delivery to skin by means of microparticles and nanocarriers could revolutionize the treatment of several skin disorders. However, the toxicological and environmental safety of micro- and nanoparticles has to be evaluated using specific toxicological studies prior to a wider implementation of the new technology. This review aims to give an overview of the most investigated applications of transcutaneously applied particle-based formulations in the fields of cosmetics and dermatology.

Enzymatic recognition of DNA damage induced by UVB-photosensitized titanium dioxide and biological consequences in Saccharomyces cerevisiae: evidence for oxidatively DNA damage generation

Although titanium dioxide (TiO(2)) has been considered to be biologically inert, finding use in cosmetics, paints and food colorants, recent reports have demonstrated that when TiO(2) is attained by UVA radiation oxidative genotoxic and cytotoxic effects are observed in living cells. However, data concerning TiO(2)-UVB association is poor, even if UVB radiation represents a major environmental carcinogen. Herein, we investigated DNA damage, repair and mutagenesis induced by TiO(2) associated with UVB irradiation in vitro and in vivo using Saccharomyces cerevisiae model. It was found that TiO(2) plus UVB treatment in plasmid pUC18 generated, in addition to cyclobutane pyrimidine dimers (CPDs), specific damage to guanine residues, such as 8-oxo-7,8-dihydroguanine (8-oxoG) and 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyG), which are characteristic oxidatively generated lesions. In vivo experiments showed that, although the presence of TiO(2) protects yeast cells from UVB cytotoxicity, high mutation frequencies are observed in the wild-type (WT) and in an ogg1 strain (deficient in 8-oxoG and FapyG repair). Indeed, after TiO(2) plus UVB treatment, induced mutagenesis was drastically enhanced in ogg1 cells, indicating that mutagenic DNA lesions are repaired by the Ogg1 protein. This effect could be attenuated by the presence of metallic ion chelators: neocuproine or dipyridyl, which partially block oxidatively generated damage occurring via Fenton reactions. Altogether, the results indicate that TiO(2) plus UVB potentates UVB oxidatively generated damage to DNA, possibly via Fenton reactions involving the production of DNA base damage, such as 8-oxo-7,8-dihydroguanine.