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EC number: 217-614-1 | CAS number: 1908-87-8
The test item 3-Methyl-thiazolidin-2-thion, dissolved in DMSO, was assessed for its potential to induce micronuclei in human lymphocytes in vitro in the absence and presence of metabolic activation by S9 mix.
Two independent experiments were performed. In Experiment I, the exposure period was 4 hours with and without S9 mix. In Experiment II, the exposure period was 20 hours without S9 mix. The cells were prepared 40 hours after start of treatment with the test item.
In each experimental group two parallel cultures were analysed. 1000 binucleate cells per culture were scored for cytogenetic damage on coded slides. To determine a cytotoxic effect the CBPI was determined in 500 cells per culture and cytotoxicity is described as % cytostasis.
The highest treatment concentration in this study, 1332.00 μg/mL (approx. 10 mM) was chosen with regard to the molecular weight of the test item and with respect to the OECD Guideline 487 for the in vitro mammalian cell micronucleus test.
No relevant influence on osmolarity or pH value was observed.
No relevant cytotoxicity, indicated by reduced CBPI and described as cytostasis could be observed up to the highest applied concentration.
In both experiments, in the absence and presence of S9 mix, no biologically relevant increase in the number of cells carrying micronuclei was observed. The micronucleus rates of the cells after treatment with the test item (0.45 – 0.90 % micronucleated cells) did not exceed the range of the solvent control values (0.60 – 1.05 % micronucleated cells) and were within the range of the laboratory historical control data.
In both experiments, either Demecolcin (75.0 µg/mL), MMC (2.0 μg/mL) or CPA (17.5 μg/mL) were used as positive controls and showed distinct increases in cells with micronuclei.
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In a mammalian cell cytogenetics assay, an in vitro micronucleus test (OECD 487), human primary lymphocyte cultures were exposed to 3-Methyl-thiazolidin-2-thion in DMSO at concentrations of 0, 8.65, 15.14, 26.50, 46.37, 81.15, 142.02, 248.54, 434.94, 761.14, and 1332.00 µg/ml with and without metabolic activation (induced rat liver S9). In two independent experiments, cells were either exposed to the test item over 4h (±S9) or 20h (-S9).
In each experimental group two parallel cultures were analysed. Per culture 1000 binucleated cells were evaluated for cytogenetic damage. The highest applied concentration in this study (1332.0 µg/mL of the test item, approx. 10 mM) was chosen with regard to the molecular weight of the test item and with respect to the current OECD Guideline 487.
In Experiment I and II in the absence and presence of S9 mix, no cytotoxicity was observed up to the highest evaluated concentration.
In both independent experiments, neither a statistically significant nor a biologically relevant increase in the number of micronucleated cells was observed after treatment with the test item. 3-Methyl-thiazolidin-2-thion is considered to be non-mutagenic in this in vitro micronucleus test, when tested up to the highest required concentration.
Appropriate mutagens (Demecolcin (75.0 ng/mL), MMC (2.0 μg/mL) or CPA (17.5 μg/mL)) were used as positive controls. They induced statistically significant increases in cells with micronuclei.
This study is classified as acceptable. This study satisfies the requirement for an in vitro micronucleus test (OECD 487) for in vitro cytogenetic mutagenicity data.
There are all three stipulated (Annex VIII) genetic toxicity studies available, being of high quality and sufficiently reliable to assess the respective endpoints. All studies are on the registered substance itself and consistently reveal that 3-Methyl-thiazolidin-2-thion is negative for genetic toxicity, i.e. gene mutation in bacteria and mammalian cells and micronucleus induction in human lymphocytes. There is no indication given that these results are not relevant to assess the risk of genetic damage in humans, as both gene and chromosome mutation is covered and due to the addition of induced rat liver S9 mix in vivo metabolism is sufficiently mimicked. Hence, no data gaps were identified, no additional testing is required and the available data suffices to exclude the hazard of 3-Methyl-thiazolidin-2-thion towards genetic material.
All available in vitro studies on 3-Methyl-thiazolidin-2-thion covering the endpoints gene mutation in bacteria and mammalian cells and micronucleus induction in human lymphocytes gave negative results. These cover the main causes for genetic damage sufficiently and mimic due to the addition of S9 in vivo metabolism to a wide extent. Based on the available data, there is no indication given that 3-Methyl-thiazolidin-2-thion should be classified as mutagen.
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