Isobutyric anhydride

Endpoint summary

Additional information

Toxicity data has been read across primarily from isobutyric acid, which is the hydrolysis product of isobutyric anhydride. The hydrolysis is rapid, and thus the read-across is valid. A hydrolyis study is presented in section 5.1.2 of this dossier, and illustrates that at physiological pH the half life is between 5 and 10 minutes. This indicates that read-across to isobutyric acid is appropriate for all studies where water is present, as the anhydride will quickly hydrolyze to the acid.

Genetic toxicity in vitro

 

Two studies are used to assess the mutagenic potential of isobutyric acid (BASF AG 1989, Hüls 1984). Both studies are performed according or similar to OECD TG 471. Documentation for the Hüls study is only available as short abstract. Thus, reliability is low. It is used as supporting information for the study of BASF. This study is used as key study. The reliability is 2. In both studies, the result is negative.

 

A third study (Szybalski 1958) does not use a validated standard method. Thus, its reliability is low (RL3). The result of this study also is negative.

 

BASF 1989 (Ames test. key study)

 

In a valid reverse gene mutation assay in bacteria according to OECD TG 471, strains TA98, TA100, TA 1535, and TA1537 of Salmonella typhimurium were exposed to isobutyric acid (purity 99.33%) at concentrations of 0 (controls), 20, 100, 500, 2500, and 5000 µg/plate in the presence and absence of mammalian metabolic activation. Tests were performed as plate incorporation and as preincubation assays.

 

Isobutyric acid was tested up to limit concentration (5000 µg/plate). The positive controls induced the appropriate responses. There was no evidence of induced mutant colonies over background.

 

Isobutyric acid was demonstrated not to be mutagenic to Salmonella typhimurium under the conditions of this test (BASF, 1989).

 

Hüls 1984 (Ames test, supporting information)

 

Isobutyric acid was negative in a duplicate bacterial reverse gene mutation assay (Ames test, plate incorporation and preincubation method) with and without metabolic activation at concentrations from 10 to 5000 µg/plate. Because only an abstract is available, the results of this study are used as supporting information (Hüls AG, 1984).

OXEA, EASTMAN, BASF 2010 (CHO HPRT)

The study according to OECD 476 was conducted to assess the potential mutagenicity of the test material on the hypoxanthine-guanine phosphoribosyl transferase (HPRT) locus of Chinese hamster ovary (CHO) cells using 6-thioguanine (6­TG) as the selective agent. The test material did not induce any significant or dose-related increases in mutant frequency per survivor in either the presence or absence of metabolic activation in either of the two experiments. 

The test material was therefore considered to be non-mutagenic to CHO cells at the HPRT locus under the conditions of this test.

Genetic toxicity in vivo

 

For isobutyric acid, no study concerning genetic toxicity in vivo could be identified. As substitute, data for isobutanol will be used as it is oxidized to isobutyric acid in vivo.

After administration, isobutanol will rapidly be metabolized in vivo to isobutyric acid by aldehyde dehydrogenases. In the course of metabolic transformation of isobutanol, isobutyric acid is generated rapidly. Thus, it is justified to use isobutanol as supporting substance in the evaluation of the systemic in vivo effects of isobutyric acid.

 

Supporting substance: isobutanol

 

The genetic toxicity in vivo of isobutanol has been evaluated in one valid study of high reliability (GLP study) which is used as key study.

 

CMA/BASF 2000 (Mouse Micronucleus Tests, key study)

 

In a mouse bone marrow micronucleus test, 5 NMRI-mice per sex/dose were treated orally with isobutanol at doses of 0, 500, 1000, and 2000 mg/kg bw. Bone marrow cells were harvested at 24 and 48 hours post treatment. The test substance was administered orally dissolved in olive oil in single doses.

 

There were signs of toxicity during the study. Isobutanol was tested at adequate doses. The positive controls induced the appropriate responses.

 

There was no significant increase in the frequency of micronucleated polychromatic erythrocytes in bone marrow after any dose and any treatment time. Under the experimental conditions of the test, isobutanol had no chromosome damaging (clastogenic) effect nor did it lead to any impairment of chromosome distribution in the course of mitosis (CMA/BASF, 2000).

 

Transfer of result from the supporting substance to isobutyric acid

 

Based on the results for isobutanol (CMA/BASF, 2000), isobutyric acid is assessed not to exhibit a chromosome damaging (clastogenic) effect in mice in vivo.

Justification for selection of genetic toxicity endpoint
No specific endpoint was selected as there are 3 different key studies and this form only allows one selection.

Short description of key information:
Data for isobutyric anhydride was not available. Data was read-across to isobutyric acid, which is the anhydride hydrolysis product in water. A hydrolysis study in section 5 illustrates that the read-across is valid based on the short half life.


Genetic toxicity in vitro
Ames: Isobutyric acid was found not to be mutagenic in two in-vitro reverse gene mutation assays in bacteria according to Ames with and without metabolic activation (BASF AG 1989, Hüls 1984).

In Vitro Mammalian mutagenicity: Isobutyric acid was found not to be mutagenic in a CHO HPRT test (Oxea, Eastman, BASF 2010).


In Vivo chromosome aberration: In a valid mouse micronucleus test, isobutanol (read-across for isobutyric acid) did not increase the rate of micronuclei in polychromatic and normochromatic erythrocytes at the three doses tested (CMA/BASF, 2000).

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

Based on the negative results obtained in all tests for genotoxicity performed with Isobutyric acid in vitro and

with Isobutanol in vivo it is concluded that Isobutyric anhydride has not to be classified for genotoxicity according to Regulation (EC) No 1272/2008.