Subchronic toxicity and genotoxicity of diiodomethyl-p-tolylsulfone (DIMPTS) in laboratory animals

These studies were conducted to determine subchronic toxicity and genotoxicity of the biocide diiodomethyl-p-tolysulfone (DIMPTS) in rats and dogs. Male and female Sprague-Dawley rats and Beagle dogs were administered DIMPTS for 90-days via the diet at 0, 5, 20, and 80 mg/kg/day to rats and via capsules at 0, 2, 10, and 60 mg/kg/day to dogs. In rats, the only treatment-related finding was squamous metaplasia of the salivary gland duct in the 80 mg/kg/day group. In dogs, female body weights in the high-dose group were significantly lower than controls. Altered clinical pathology parameters were considered secondary to inflammatory changes observed in some of the dogs. Treatment-related alterations were found in the thyroid glands, salivary glands, GI-tract in the mid- and/or high-dose groups. DIMPTS was negative in the four in vitro and one in vivo genotoxicity assays. The toxicological effects noted in the two mammalian species are consistent with the principal toxic effects of iodine, and are proposed to arise from release of iodide from the DIMPTS molecule with toxic sequelae.     

In vivo genotoxicity study of titanium dioxide nanoparticles using comet assay following intratracheal instillation in rats

Titanium dioxide (TiO₂) is widely used as a white pigment in paints, plastics, inks, paper, creams, cosmetics, drugs and foods. In the present study, the genotoxicity of anatase TiO₂ nanoparticles was evaluated in vivo using the comet assay after a single or repeated intratracheal instillation in rats. The nanoparticles were instilled intratracheally at a dosage of 1.0 or 5.0 mg/kg body weight (single instillation group) and 0.2 or 1.0 mg/kg body weight once a week for 5 weeks (repeated instillation group) into male Sprague–Dawley rats. A positive control, ethyl methanesulfonate (EMS) at 500 mg/kg, was administered orally 3 h prior to dissection. Histopathologically, macrophages and neutrophils were detected in the alveolus of the lung in the 1.0 and 5.0 mg/kg TiO₂ groups. In the comet assay, there was no increase in % tail DNA in any of the TiO₂ groups. In the EMS group, there was a significant increase in % tail DNA compared with the negative control group. TiO₂ nanoparticles in the anatase crystal phase are not genotoxic following intratracheal instillation in rats.     

Modifications of the bacterial reverse mutation test reveals mutagenicity of TiO2 nanoparticles and byproducts from a sunscreen TiO2-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 TiO₂ nanoparticles (NP-TiO₂) 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-TiO₂ in a low ionic strength solution (NaCl 10 mM) 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-TiO₂ tested and a NP-TiO₂ 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.     

Study of serum interaction with a cationic nanoparticle: Implications for in vitro endocytosis, cytotoxicity and genotoxicity

We used well-characterized and positively charged nanoparticles (NP⁺) to investigate the importance of cell culture conditions, specifically the presence of serum and proteins, on NP⁺ physicochemical characteristics, and the consequences for their endocytosis and genotoxicity in bronchial epithelial cells (16HBE14o-). NP⁺ surface charge was significantly reduced, proportionally to NP⁺/serum and NP⁺/BSA ratios, while NP⁺ size was not modified. Microscopy studies showed high endocytosis of NP⁺ in 16HBE14o-, and serum/proteins impaired this internalization in a dose-dependent manner. Toxicity studies showed no cytotoxicity, even for very high doses of NP⁺. No genotoxicity was observed with classic comet assay while primary oxidative DNA damage was observed when using the lesion-specific repair enzyme, formamidopyrimidine DNA-glycosylase (FPG). The micronucleus test showed NP⁺ genotoxicity only for very high doses that cannot be attained in vivo. The low toxicity of these NP⁺ might be explained by their high exocytosis from 16HBE14o- cells. Our results confirm the importance of serum and proteins on nanoparticles endocytosis and genotoxicity.     

Effects of Lanthanum on Human Lymphocytes Viability and DNA Strand Break

Lanthanum (La) is a rare-earth metal with applications in agriculture, industry, and medicine. Since lanthanides show a broad spectrum of applications there is an increased risk of contamination for humans. We examined the effects of lanthanum in Jurkat cells and human peripheral lymphocytes (HPL), and we found that it was cytotoxic and genotoxic on both cell lines. Additionally, HPL were more sensitive to La treatment than Jurkat cells and necrosis was the pathway by which La induced cytotoxicity. Vitamin E was able to diminish the DNA strand breaks induced suggesting that oxidative stress may be involved in the genotoxic process.     

Chemical composition and cytotoxic, mutagenic and genotoxic activities of the essential oil from Piper gaudichaudianum Kunth leaves

We have investigated the chemical composition of Piper gaudichaudianum essential oil, as well as its cytotoxic, mutagenic and genotoxic effects in V79 cells. The chemical analyses showed that the major compounds are (E)-nerolidol (22.4%), α-humulene (16.5%), (E)-caryophyllene (8.9%) and bicyclogermacrene (7.4%). Dose-dependent cytotoxic effects were observed in V79 cells treated with essential oil by using clonal survival, 3-(4,5-dimethylthiazole-2-yl)-2,5-biphenyl tetrazolium bromide reduction assay (MTT) and trypan blue exclusion assay (TB), and a significant decrease in survival was observed at concentrations of 0.5 μg/mL and higher. The P. gaudichaudianum essential oil treatment caused DNA strand breaks in V79 cells at concentrations up to 2 μg/mL, as detected by the alkaline comet assay, but did not induce double-strand breaks, as verified by neutral comet assay. It induced a significant increase in the frequency of micronucleated cells at 4, 6 and 10 μg/mL. Moreover, P. gaudichaudianum essential oil significantly increased lipid peroxidation at doses of 0.5 μg/mL and higher, suggesting that the observed oxidant potential can be responsible, at least in part, for its cytotoxic and genotoxic effects.     

90-Day feeding and genotoxicity studies on a refined arachidonic acid-rich oil

The safety of a refined arachidonic acid-rich oil (RAO) was evaluated for reverse mutation, chromosome aberration and gene mutation, and in a 90-day Wistar rat feeding study with in utero exposure. The results of the genotoxicity assays were all negative. The in utero phase of the 90-day study involved dietary exposure to 0.5%, 1.5% and 5% RAO and two controls diets, a standard feed low-fat diet and a high-fat diet supplemented with 5% corn oil. This exposure covered four-weeks prior to mating, through mating, gestation and lactation until offspring (F₁) weaning. A subsequent 90-day feeding study in the F₁ rats evaluated the same test and control diets. Statistically significant effects were seen for selected histopathology, clinical chemistry and organ weight endpoints; however, other than increased absolute and relative monocytes seen in both sexes of high-dose rats, the observations were not attributed to treatment for one or more reasons. Based on these findings, no adverse treatment-related effects for RAO were seen at up to 5% in the diet, equivalent to an overall average RAO intake of 3170 mg/kg bwt/day. These and similar findings for other refined ARA-rich oils establish a strong body of evidence for the safety of this RAO.     

Effect of titanium surface modified by plasma energy source on genotoxic response in vitro

Titanium (Ti) is currently the most widely used material for the manufacture of orthopedic and dental implants. Changes in the surface of commercial pure Ti (cp Ti) can determine the functional response of cells, and is therefore a critical factor for the success of the implant. However, the genotoxicity of titanium surfaces has been poorly studied. Thus, the purpose of this study was to evaluate the genotoxic potential of a new titanium surface developed by plasma treatment using argon-ion bombardment and compare it with an untreated titanium surface. Accordingly, comet assay, analysis of chromosomal aberrations (CAs), and Cytokinesis Block Micronucleus (CBMN) assay were carried out, using CHO-K1 (Chinese hamster ovary) cells grown on both titanium surfaces. Our results show that the untreated titanium surface caused a significant increase in % tail moment, in the number of cells with CAs, tetraploidy, micronucleus frequency, and other nuclear alterations when compared with the negative control and with the plasma-treated titanium surface. This difference may be attributed to increased surface roughness and changes in titanium oxide layer thickness.     

Acute, subacute toxicity and genotoxic effect of Bio-Quinone Q10 in mice and rats

In the present study, the acute, subacute and genetic toxicity of Coenzyme Q10 (CoQ10) in the form of Bio-Quinone (Pharma Nord, Denmark) was assessed. LD(50) of CoQ10 by oral treatment was greater than 20g/kg body weight in both female and male mice. Genotoxicity was assessed in mice by Ames test in Salmonella typhimurium strains TA97, TA98, TA100 and TA102, by bone marrow micronucleus test and sperm abnormality. Thirty-day subacute toxicity was conducted with oral daily dose at 0, 0.56, 1.13 and 2.25g/kg body weight in rats. No significant changes in body weight, food intake, behavior, mortality, hematology, blood biochemistry, vital organ weight, sperm abnormality, mutagenicity and micronucleus formation were observed and no clinical signs or adverse effects were detected by administration of CoQ10. These results support the safety of CoQ10 for oral consumption.     

The transgenic mouse assay as an alternative test method for regulatory carcinogenicity studies—Implications for REACH

REACH, an EU regulation that requires the submission of safety data in support of the protection of human and environmental health, mandates that registration should be achieved with the minimum amount of animal testing possible. Under REACH, a two-year carcinogenicity assay may be required for certain chemicals produced at >1000 metric tonnes per year. In addition, some chemicals that are found to be genotoxic will also require testing. Alternative methods have been explored in an attempt to improve the predictivity of this bioassay as well as to reduce the number of animals used for such testing. This research has focused on the use of transgenic/knockout mouse models. Study results from selected models indicate that they are useful in hazard identification, even if they are not entirely suitable for risk assessment on their own. Carcinogenic hazard assessment can be greatly enhanced and animal use reduced if the traditional two-year rat bioassay is combined with a well conducted transgenic mouse assay. Importantly, the use of transgenic animals to supplement a traditional two-year carcinogenicity study may help reduce the number of false negatives, one of the unstated goals of REACH via the precautionary principle.