Octane-1-thiol

Endpoint summary

Additional information

In Vitro Genetic Toxicity

In Vitro Gene Mutation in Bacteria:

In a key reverse gene mutation assay in bacteria (Molinier, 1996; Klimisch score = 1), strains TA 1535, TA 1537, TA 98, TA 100 and TA 102 of S. typhimurium were exposed to octane-1-thiol in dimethylsulfoxide at concentrations of 3, 10, 30, 100, 300, 1000, or 3000 µg/plate with and without metabolic activation using the plate-incorporation method. Ocatane-1-thiol was tested up to insoluble concentrations of 1000 μg/plate. Slight oily precipitation was noted at the 1000 and 333.3 μg/plate dose levels. In the first of two mutagenicity assays, slight toxicity was observed at the highest dose-level (300 µg/plate) in the absence of metabolic activation for the four strains (TA 1535, TA 1537, TA 98, TA 100) whereas toxicity was noted for TA 102 (3000 µg/plate). Hence, the dose-levels were slightly increased or decreased for the second experiment and strains were exposed to octane-1-thiol at concentrations of 10, 30, 100, 300, or 1000 µg/plate. In the second experiment moderate to marked toxicity was observed at doses higher than 100 µg/plate in the absence of metabolic activation for strains TA1535 and TA 1537. Slight or moderate toxicity was noted at 1000 µg/plate for the TA 98, TA 100, and TA 102 strains. In the presence of metabolic activation in the second assay, Slight (TA 98, TA 102) or moderate (TA 1535, TA 100) to strong toxicity (TA 1537) was observed at the 1000 µg/plate concentration.The positive controls induced the appropriate responses in the corresponding strains. The test substance did not induce any significant increase in the number of revertants, with or without S9 mix, in any of the five strains. Since there was no evidence of induced mutant colonies over background, octane-1-thiol is considered to be negative in the bacterial reverse mutation test.

 

In another key reverse mutation assay in bacteria (MHLW, 2004; Klimisch score = 1) strains of S. typhimurium TA1535, TA1537, TA98 and TA100 and Escherichia coli WP2uvrA/pKM101 were exposed to octane-1-thiol (CAS Number 111-88-6) in dimethyl sulfoxide with and without metabolic activation using the pre-incubation method. Concentrations without activation were 0.610, 1.22, 2.44, 4.88, 9.77, 19.5 μg/plate for TA1537, TA98, TA100; 0.153, 0.305, 0.610, 1.22, 2.44, 4.88, 9.77 μg/plate for TA1535; and 0.610, 1.22, 2.44, 4.88, 9.77, 19.5, 39.1 μg/plate for WP2uvrA/pKM101. Concentrations with activation were 2.44, 4.88, 9.77, 19.5, 39.1, 78.1, 156 μg/plate for TA98, TA100, TA1535, and TA1537; 9.77, 19.5, 39.1, 78.1, 156, 313, 625 μg/plate for WP2uvrA/pKM101. A preliminary test with and without S9 mix, tested up to 5000 μg/plate showed cytotoxicity, not precipitation and negative genotoxicity. In the primary study, toxicity was noted at the two highest doses levels. The positive controls induced the appropriate responses in the corresponding strains. There was no evidence of induced mutant colonies over background and octane-1-thiol was considered to be negative in this bacterial reverse mutation test.

In a supporting reverse gene mutation assay in bacteria (Pence, 1983d; Klimisch score = 1), strains TA1535, TA1537, TA1538, TA98 and TA100 of S. typhimurium were exposed to octane-1-thiol in dimethylsulfoxide at concentrations of 0.1, 0.2, 0.5, 1.4, 4.1, 12.3, 37.0, 111.1, 333.3, and 1000 µg/plate with and without metabolic activation using the plate-incorporation method.Octane-1-thiol was tested up to insoluble concentrations of 1000 μg/plate. Slight oily precipitation was noted at the 1000 and 333.3 μg/plate dose levels.  Toxicity was noted at four of the five highest dose levels so a second assay was conducted with three doses lower than the final dose in the first mutational assay. Exposure to eight graded doses of octane-1-thiol did not increase the number of revertants in the presence and absence of metabolic activation. The positive controls induced the appropriate responses in the corresponding strains. Under the conditions of this study, octane-1-thiol was not considered to be mutagenic in the bacterial reverse mutation assay.

In Vitro Cytogenicity in Mammalian Cells:

Two key studies were identified to evaluate the in vitro cytogenicity of octane-1-thiol.

In an in vitro mammalian chromosome aberration assay (Marshall, 1997; Klimisch score = 1), duplicate human lymphocyte cultures from a male and female donor were exposed to octane-1-thiol in dimethyl sulphoxide at concentrations of 92.44, 132.1, or 188.7 μg/mL with metabolic activation by a rat liver post-mitochondrial fraction (S-9) from Aroclor 1254 induced animals, and at concentrations of 41.94, 52.43, 65.54 μg/mL without metabolic activation. Treatment in the absence of S-9 was continuous for 20 or 44 hours (20+0, 44+0). Treatment in the presence of S-9 was for 3 hours followed by a 17 or 41 hour recovery period (3+17, 3+41). Octane-1-thiol was tested dissolved in dimethyl sulphoxide and the highest dose level used (550 µg/mL) was close to the solubility limit of the test article in culture medium. The test article dose levels for chromosome analysis were selected by evaluating the effect of octane-1-thiol on mitotic index. The highest concentrations chosen for analysis, 65.54 µg/mL and 188.7 µg/mL, each induced approximately 49% mitotic inhibition (reduction in mitotic index) in the absence and presence of S-9 respectively. A small, but statistically significant increase seen at the intermediate dose at the 20 hour sampling time was considered to be not biologically significant because frequencies of aberrant cells in both replicate cultures fell within the historical negative control range. It was concluded that octane-1-thiol did not induce chromosome aberrations in cultured human peripheral blood lymphocytes when tested to its limit of toxicity in both the absence and presence of S-9.

In another key in vitro mammalian cell cytogenetics assay (MHLW, 2004; Klimisch score = 1), Chinese hamster CHL/IU cells were exposed to octane-1-thiol (CAS number 111-88-6) in dimethyl sulfoxide in the presence and absence of mammalian metabolic activation (S9 mix). The short-term treatment method exposed the cells to octane-1-thiol for 6 hours with an 18 hour recovery time at concentrations of 78.1, 156, 313, 625, 1250 μg/mL without metabolic activation and 625, 1250, 2500, 5000 μg/mL with metabolic activation. The continuous treatment method exposed the cells to octane-1-thiol for 24 hours with no recovery time at concentrations of 70, 80, 90, 100, 110, 120 μg/mL without metabolic activation only. The selection of concentrations for the short-term and continuous treatment method was based upon the results of a cell growth inhibition test. The two highest concentrations of each test fell above the concentration that resulted in 50% cell growth inhibition. The positive controls did induce the appropriate response.  Structural chromosomal aberrations and polyploidy was not induced at any test substance treatment groups in any procedures (less than 5%). Octane-1-thiol produced a negative result in the chromosome aberration test.  

 

Supporting data from an in vitro sister chromatid exchange (SCE) assay (Pence, 1984; Klimisch score = 1) demonstrated that exposure of Chinese Hamster Ovary (CHO) cell cultures to octane-1-thiol did not result in a positive concentration-related response in the induction of SCEs over background.

In Vitro Gene Mutation in Mammalian Cells:

One key study was identified to evaluate the in vitro gene mutation potential of octane-1-thiol in mammalian cells.

In a key mammalian cell gene mutation assay (Pence, 1983e; Klimisch score = 1), L5178Y heterozygous TK+/- mouse lymphoma cells, subline 3.7.2C, cultured in vitro were exposed to octane-1-thiol in dimethylsulfoxide at concentrations of 1.8, 2.7, 4.0, 6.0, 9.0, 13.5, 20.1, and 30.0 µg/mL in the presence and absence of mammalian metabolic activation S9 for 4 hours. Octane-1-thiol was tested up to 30 μg/mL as this concentration exhibited growth inhibition. Exposure to eight graded concentrations of n-octyl mercaptan in the presence and absence of metabolic activation did not increase the induction of forward mutations in L51781 mouse lymphoma cells at the T/K locus. The positive controls did induce the appropriate response.  Under the conditions of this study, octane-1-thiol was not considered to be mutagenic in the in vitro mammalian cell gene mutation assay.

In Vivo Genetic Toxicity

No key data are available for octane-1-thiol. However, one key read across study from dodecane-1-thiol was identified to evaluate the in vivo genetic toxicity potential of octane-1-thiol.

In a key read across in vivo bone marrow micronucleus assay (Putman, 1995; Klimisch score = 1), ICR mice (5/sex/dose) were orally administered (via gavage) dodecane-1-thiol in corn oil at singe doses of 0, 1250, 2500, or 5000 mg/kg bw. Bone marrow cells were harvested at 24, 48, and 72 hours post-treatment and examined microscopically for micronucleated polychromatic erythrocytes. No mortality occurred in male or female mice in the micronucleus study. Signs of toxicity included lethargy and diarrhea in male and female mice at all dose levels and crusty eyes in one male dosed at 5000 mg/kg bw. Slight reductions (up to 23%) in the ratio of polychromatic erythrocytes to total erythrocytes was observed in some of the test article-treated groups relative to the vehicle control groups. No significant increase in micronucleated polychromatic erythrocytes in test article-treated groups relative to the respective vehicle control group was observed in male or female mice at 24, 48 or 72 hours after dose administration (p>0.05, Kastenbaum-Bowman). Dodecane-1-thiol did not induce a significant increase in micronucleated polychromatic erythrocytes in either male or female mice. Therefore, dodecane-1-thiol was concluded to be negative in the mouse micronucleus assay.

Read Across Justification

A read across approach was used to fill data gaps for octane-1-thiol using dodecane-1-thiol as an analog. Dodecane-1-thiol has similar physiochemical properties to octane-1-thiol and thus, the toxicological properties of both these substances are also expected to be similar.

Short description of key information:
Multiple key studies were identified to evaluate the in vitro and in vivo genetic toxicity potential of octane-1-thiol. Octane-1-thiol was not observed to be mutagenic to Salmonella typhimurium in vitro and was negative in a mammalian sister chromatid exchange assay using Chinese Hamster Ovary (CHO) cells. Octane-1-thiol did not increase the induction of forward mutations in L5187Y mouse lymphoma cells at the T/K locus. In a key read-across study, dodecane-1-thiol (a close structural analog) did not induce an increase in micronucleated polychromatic erythrocytes in an in vivo mouse bone marrow micronucleus assay.

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

All in vitro genetic toxicity studies (i.e., gene mutation studies in bacteria; cytogenicity studies in mammalian cells; and gene mutation studies in mammalian cells) from octane-1-thiol showed negative results. An in vivo mouse micronucleus study with dodecane-1-thiol also produced no evidence of genotixicity. Consequently, octane-1-thiol is unlikely to be mutagenic and does not meet the criteria for classification and labelling as described in EU Dangerous Substances Directive 67/548/EEC or CLP EU Regulation 1272/2008.