1,6-bis((dibenzylthiocarbamoyl)disulfanyl)hexane

Endpoint summary

Additional information

Non-human information

In vitro data

The test substance Vulcuren (purity: 99.7%) was evaluated in a Salmonella/microsome assay according to current guidelines. Vulcuren (purity: 99.7%) was considered to be non-mutagenic with and without metabolic activation in the plate incorporation as well as in the preincubation modification of the Salmonella/microsome test. No toxic effects were seen in any of the dose groups evaluated (Bayer 2000a). These findings were confirmed by a previous bacterial study, which also detected a non-mutagenic and non-toxic potential of the test substance (Hüls AG 1992d).

However, in a mammalian test system with Chinese hamster V79 cells toxic and clastogenic effects of Vulcuren (purity: 99.7%) were seen. The test substance was evaluated in the chromosome aberration assay with or without metabolic activation. In presence of metabolic activation (S9 mix) cytotoxicity was indicated at 12 µg/ml and higher. In addition, cultures of the highest dose group (18 µg/ml, with S9-mix) showed a weakly but biologically relevant and statistically significant increase in aberrant metaphases. In the absence of metabolic activation no cytotoxic and genotoxic effects were seen up to the highest concentration (128 µg/ml) evaluated (Bayer 2000b).

No data from in vitro mammalian mutation assays are available. However, data from appropriate in vivo mammalian tests are available (see below).

In vivo data

The test substance Vulcuren (purity: 99.7%) was evaluated in the in vivo micronucleus assay with male NMRI mice. The test substance was applied at concentrations of 0, 1000, 2000, 4000 mg/kg body weight. All animals from the treatment groups showed clinical signs like apathy, roughened fur, spasm and periodically stretching of the body, which demonstrated a relevant systemic exposure of males to Vulcuren (purity: 99.7%). The ratio of polychromatic to normochromatic erythrocytes in males was not biologically relevant altered by the treatment with the test substance compared to the negative control. In addition, no biologically relevant and statistically significant increase of micronucleated polychromatic erythrocytes was noted in the treated animals compared to the negative control (Bayer AG 2000e). Thus, no clastogenic effects of the test substance could be detected in the in vivo micronucleus assay.

The non-genotoxic potential of Vulcuren was confirmed in an in vivo Comet assay. Male Wistar rats were treated once via gavage with 2000 mg/kg Vulcuren (purity: 96.2%). The treated rats showed no signs of toxicity. After a single application of 2000 mg/kg test substance the tail lengths of liver cells as well the tail lengths of stomach cells were not biologically relevant increased. Based on these findings, the author concluded that Vulcuren (purity: 96.2%) is non-genotoxic in the comet assay in vivo to liver and stomach cells of male Wistar rats (Lanxess GmbH 2005).

Justification for selection of genetic toxicity endpoint
The results of 2 Ames tests, the in-vitro CA test, the in-vivo MNT and the Comet assay were considered.

Short description of key information:
Three in-vitro tests (2 Ames tests and a Chromosome Aberration test) and 2 in-vivo tests ( Mammalian erythrocyte micronucleus test and a Comet assay) are available.

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

The test substance Vulcuren was non-mutagenic in bacteria, whereas in a mammalian cell test system a weakly positive effect was detected. The increase of aberrant metaphases seen in Chinese hamster V79 cells in presence of metabolic activation was considered as biologically relevant and statistically significant. However, these clastogenic effects could not be confirmed in two additional in vivo genotoxicity assays. No clastogenic effects were detected in an in vivo micronucleus assay, beside the fact that concentrations up to 4000 mg/kg bw were evaluated and systemic toxicity was indicated. In addition, an in vivo indicator assay, the comet assay, which detects DNA damages like DNA single- and DNA double-strand breaks, which are precursor of clastogenic lesions, was negative. In conclusion, according to the results from the in vivo assay the test substance Vulcuren (purity: > 96%) is considered to be non-mutagenic and a classification is therefore not justified.