4-isopropyl-m-cresol

Endpoint summary

Additional information

Table 7.6/1: Summary of genotoxicity tests

Test n°	Test / Guideline Reliability	Focus	Strains tested	Metabolic activation	Test concentration	Statement
1   Osaka City Institute of Public Health and Environmental Sciences, 1981	Ames Test (OECD 471) WoE, rel. 2	Gene mutation	TA 1535, TA 1537, TA 1538 TA 98, TA 100 E.coli WP2 uvrA	-S9 +S9	Up to cytotoxic concentration	-S9 : non mutagenic +S9 : non mutagenic
2   Derek KB 2014 1.0	QSAR WoE, rel.2	Mutagenicity in vitro in bacterium	Not applicable	Not applicable	Not applicable	Inactive
3   Safepharm, 2001	MLA test (OECD 476) K, rel. 1	Gene mutation	Mouse lymphoma L5178Ycells	-S9 +S9	Up to cytotoxic concentrations	-S9 : non mutagenic +S9 : non mutagenic
4   HLS, 2014	In vitro CAT (OECD 473) K, rel. 1	Chromosomal aberration	Human lymphocytes	-S9 +S9	Up to cytotoxic concentrations	-S9: positive +S9: non clastogenic
5   HLS, 2014	In vitro MN (OECD 487) K, rel. 1	Chromosomal aberration	Human lymphocytes	-S9	Up to cytotoxic concentrations	-S9 : non clastogenic

 

Gene mutation Assays (Tests n° 1 -3):

- A Bacterial Reverse mutation Assay (Ames test) was performed on Parathymol according to OECD 471 test guideline (See Table 1, Test No. 1). No significant increases in the frequency of revertant colonies were recorded for any of the bacterial strains, with any dose of the test material, either with or without metabolic activation. The test indicates that the substance does not induce gene mutations in bacteria whereas all positive control chemicals (with and without metabolic activation) induced significant increase of colonies. Since the study report was not sufficiently detailed, a QSAR prediction (DEREK, test No. 2) was used together with the study results in a weight-of-evidence approach. Parathymol is inactive according to DEREK prediction, and is within the applicability domain of the QSAR. Based on these results, Parathymol is therefore considered as non-mutagenic according to the Ames test.

- Inability to produce gene mutation was confirmed in mammals using an in vitro reverse mutation assay in mouse lymphoma TK L5178Y cells (Test No. 3). None of the treatment up to the cytotoxicity limits with Parathymol, with or without metabolic activation, induced significant mutant frequency increases in mutation tests. Parathymol does not induce forward mutations at the TK locus in L5l78Y mouse lymphoma cells under activation and non-activation conditions whereas both positive control chemicals (with and without metabolic activation) induced significant mutant frequency increases. Parathymol is therefore considered as negative for inducing forward mutations at the TK locus in L5l78Y mouse lymphoma cells under activation and non-activation conditions used in this assay. This result confirms the results of the Ames test and extends the non-mutagenic effect of Parathymol to mammalian cells.

Chromosomal aberration (Test n°4-5)

- The clastogenic potential of Parathymol was determined using an in vitro chromosome aberration test in human lymphocytes (OECD 473, Test No.4), which measures the potential of a substance to increase the incidence the of structural chromosome aberrations in cultured human lymphocytes. In the absence and presence of S9 mix following 3-hour treatment, test item caused no significant increases in the proportion of metaphase figures containing chromosomal aberrations outside of the laboratory historical control range, at any analysed concentration, when compared to the vehicle control. In the absence of S9 mix following 21-hour continuous treatment, test item caused a statistically significant increase in the proportion of metaphase figures containing chromosomal aberrations, at all concentrations analysed, when compared to the vehicle control. All statistically significant increases were outside of the laboratory historical control. However, no chromatid exchange aberrations were observed (such aberrations are highly indicative for true clastogens) and a relatively high frequency of the aberrations were chromosome break aberrations. Typically these aberrations are derived from chromatid aberrations so they are normally relatively rare events. Furthermore, two endoreduplicated cells were observed in the absence of S9 mix, 3-hour treatment group. Whilst these are not of any toxicological concern they are normally extremely rare in human lymphocyte control cultures, so they may indicate a perturbation in normal cell-cycle progression or DNA replication, as a result of toxicity rather than clastogenicity. It is concluded that in the presence of test item for 21 hours in the absence of metabolic activation, an increase in the frequency of structural chromosome aberrations was observed in this in vitro cytogenetic test system, under the experimental conditions described. However, the toxicological significance of the observed increase in the frequency of cells with aberrations is not clear.

- These results were not reproduced in an in vitro micronucleus test (Test No.5), which identifies substances that induces micronuclei in the cytoplasm of interphase cells. These micronuclei may originate from acentric fragments or whole chromosomes, and the test thus has the potential to detect both clastogenic and aneugenic chemicals. In this study, none of the dose levels, up to cytotoxicity limit, induced increase in the frequency of binucleate cells containing micronuclei, whereas the positive control chemical induced significant increases in the number of binucleate cells containing micronuclei.

Based on the whole data, Parathymol is considered non-clastogenic and non-aneugenic.

CONCLUSIONS:

This ensemble of studies investigating gene mutation both in bacteria and mammals, and mammalian chromosome aberration provide evidence that Parathymol has no mutagenicity concerns.

Justification for selection of genetic toxicity endpoint
No study was selected, since all in vitro studies and QSAR prediction performed on Parathymol were negative.

Short description of key information:
1. Ames Test, Strains: S. typhimurium TA 1535, TA 1537, TA 98, TA 100 and E.coli WP2 uvrA tested both with and without metabolic activation (S9 from rat): non mutagenic up to cytotoxic concentration (OECD 471, GLP, Rel.2);
2. QSAR prediction, Mutagenicity in vitro in bacterium: inactive (Rel.2);
3. MLA, Mouse Lymphoma TK L5178Y tested both with and without metabolic activation: non mutagenic up to cytotoxicity limit (OECD 476, GLP, Rel.1);
4. Chromosome aberration test: human lymphocytes tested both with and without metabolic activation: positive without S9. However, the toxicological significance of the observed increase in the frequency of cells with aberrations is not clear;
5. Mammalian Micronucleus Test: human lymphocytes tested without metabolic activation: non clastogenic and not aneugenic up to cytotoxicity limit (OECD 487, GLP, Rel.1).

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

Harmonized classification:

The test material has no harmonized classification for human health according to the Regulation (EC) No. 1272/2008.

Self-classification:

Based on the available data, no additional classification is proposed regarding germ cell mutagenicity according to the Annex VI of the Regulation (EC) No. 1272/2008 (CLP).