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Additional information

Fourteen studies were available concerning genotoxicity in vitro: Ames tests (8 studies), Gene Mutation Assay on Saccharomyces cerevisiae (1 study), Chomosomal aberrations (1 study), Sister chromatid exchange (2 studies), DNA damage and/or repair (1 study) and human pulp fibroblast (1 study).

Ames studies:

2 studies (Pool, 1982 and Haworth, 1983) were selected as key studies because they were well described (protocol and results), and 2 others (Florin, 1980 and Aeschbacher, 1989) were selected as supporting studies, because only one dose was tested and the results were not detailed. All these studies were well described and are reliability 2 according to Klimich ranking. In these studies, several strains of Salmonella typhimurium were tested, TA 98, TA 100, TA 1535, TA 1537, TA 1538, TA 102, and different doses from 0 to 11740 µg/plate were tested.

All results in these 4 studies were negative with and without metabolic activation system.

Other available studies have reliability 3 or 4 and were not taken into account for the assessment.

Chromosomal aberration:

Only one study was available (Hikiba, 2005) and was selected as a key study, because it was well described and had the reliability 2 according to Klimich ranking. In this study, Syrian Hamster Embryo cells were exposed to guaiacol at concentrations of 0 to 1000 µM in the absence of mammalian metabolic activation system.

The result with Guaiacol was positive.

The positive controls were not examined.

This study is classified as acceptable and satisfies the requirement for Test Guideline for in vitro cytogenetic mutagenicity data. 

Sister chromatid exchange:

Two studies were available, but only one was selected as a key study (Miyashi, 2005). In order to evaluate the genotoxic potential of Guaiacol used in dental practice, the abilities of this agent to induce sister-chromatid exchanges (SCEs) were examined using Syrian hamster embryo (SHE) cells (Miyachi, 2005). Statistically significant increases in the frequencies of SCEs were observed in SHE cells treated with Guaiacol, (P 0.01; Student test). Because SCE assays are used as a sensitive indicator for evaluating genetic toxicity of chemicals, the chemical agents that had a positive response in the present study are potentially genotoxic to mammalian cells.

This study is classified as acceptable and satisfies the requirement for Test Guideline for in vitro cytogenetic mutagenicity data. 

The other available study has reliability 3 and was not taken into account.

Other in vitro studies have reliability 3 or 4 and were not taking into account for assessment.

Micronucleus in vivo:

Only one study was available and was selected as key study, which summary is the following:

The study RCC, 2009 was performed to investigate the potential of Guaiacol to induce micronuclei in polychromatic erythrocytes (PCE) in the bone marrow of the mouse. The test item was formulated in corn oil, which was also used as vehicle control. The volume administered orally was 10 mL/kg b.w.. 24 h and 48 h after a single administration of the test item the bone marrow cells were collected for micronuclei analysis.

Ten animals (5 males, 5 females) per test group were evaluated for the occurrence of micronuclei. At least 2000 polychromatic erythrocytes (PCEs) per animal were scored for micronuclei. To describe a cytotoxic effect due to the treatment with the test item the ratio between polychromatic and normochromatic erythrocytes was determined in the same sample and reported as the number of PCEs per 2000 erythrocytes.

The following dose levels of the test item were investigated:

24 h preparation interval: 125, 250, and 500 mg/kg b.w..
48 h preparation interval: 500 mg/kg b.w..

The highest dose (500 mg/kg) was estimated by a pre-experiment to be suitable. In the main study 1 female (animal no. 46) died after treatment with this dose.

After treatment with the test item the number of PCEs was not substantially decreased as compared to the mean value of PCEs of the vehicle control thus indicating that Guaiacol did not exert any cytotoxic effects in the bone marrow. However, the discoloured urine of the test item treated animals indicated the systemic distribution of the test item, thus confirming the test items bioavailability.

In comparison to the corresponding vehicle controls there was no biologically relevant enhancement in the frequency of the detected micronuclei at any preparation interval after administration of the test item and with any dose level used.

40 mg/kg b.w. cyclophosphamide administered orally was used as positive control which showed a substantial increase of induced micronucleus frequency.

In conclusion, it can be stated that under the experimental conditions reported, the test item did not induce micronuclei as determined by the micronucleus test with bone marrow cells of the mouse.

Therefore, Guaiacol is considered to be non-mutagenicin this micronucleus assay.

Short description of key information:
Gaiacol is negative in Ames tests with or without metabolic activation (published data).
Negative result in micronucleus assay in vivo (study report, 2009).
Positive results observed without metabolic activation in chromosomal aberrations and SCE test with Syrian Hamster embryo (published data).

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

Based on the recentin vivomicronucleus assay, Gaiacol is not expected to be genotoxic.