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Multiple activation pathways of benzene leading to products with varying genotoxic characteristics
H Glatt1, R Padykula, G A Berchtold
1Department of Toxicology, University of Mainz, Federal Republic of Germany.
Abstract:
Benzene and 13 potential metabolites were investigated for genotoxicity in Salmonella typhimurium and V79 Chinese hamster cells. In the presence of NADPH-fortified hepatic postmitochondrial fraction (S9 mix), benzene reverted his- S. typhimurium strains. The effect was strongest in strain TA1535. Among the potential metabolites, only the trans-1,2-dihydrodiol, in the presence of S9 mix, and the diol epoxides, in the presence and absence of S9 mix, proved mutagenic in this strain. The anti-diol epoxide was more potent than the syn-diastereomer. Both enantiomers of the anti-diastereomer showed similar activities. S9 mix did not appreciably affect the mutagenicity of the anti-diol epoxide. However, detoxification was observed when purified rat liver dihydrodiol dehydrogenase (EC 1.3.1.20) was used at concentrations comparable to that present in the liver. The (1S)-anti-diol epoxide was a much better substrate than the (1R)-enantiomer, as was true also for (1S)-versus (1R)-trans-1,2-dihydrodiol. The anti-diol epoxide reverted all six strains of S. typhimurium used and induced all four genotoxic effects studied in V79 cells (sister chromatid exchange greater than acquisition of 6-thioguanine resistance, acquisition of ouabain resistance, micronuclei). However, other potential benzene metabolites showed genotoxic effects in V79 cells, as well: sister chromatid exchange was induced by the syn-diol epoxide, 1,2,4-trihydroxybenzene, hydroquinone, catechol, and 1,2,3-trihydroxybenzene. Elevated frequencies of micronucleated cells were observed after treatment with hydroquinone, 1,2,4-trihydroxybenzene, catechol, phenol, 1,2,3-trihydroxybenzene, and quinone. Mutations to 6-thioguanine resistance were induced by quinone, hydroquinone, 1,2,4-trihydroxybenzene, catechol, and the trans-1,2-dihydrodiol.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Benzene and its metabolites can be genotoxic, particularly the anti-diol epoxide, which showed mutagenic activity in bacterial and mammalian cells. Detoxification by dihydrodiol dehydrogenase was observed, with specific enantiomers being better substrates.
Area of Science:
- Toxicology
- Genetics
- Biochemistry
Background:
- Benzene is a known human carcinogen, and understanding its genotoxic mechanisms is crucial for risk assessment.
- Metabolites of benzene may play a significant role in its toxicity.
- Investigating genotoxicity in various cell models provides comprehensive insights into chemical hazards.
Purpose of the Study:
- To evaluate the genotoxicity of benzene and its potential metabolites.
- To identify specific metabolites responsible for mutagenic effects.
- To explore the role of metabolic enzymes in benzene-induced genotoxicity.
Main Methods:
- Bacterial mutagenicity assays using Salmonella typhimurium strains.
- Mammalian cell genotoxicity assays using V79 Chinese hamster cells.
- In vitro metabolic studies with hepatic postmitochondrial fraction (S9 mix) and purified dihydrodiol dehydrogenase.
Main Results:
- Benzene induced mutagenicity in Salmonella typhimurium in the presence of S9 mix.
- The anti-diol epoxide metabolite was the most potent mutagen, active in both bacterial and V79 cells.
- Other metabolites like hydroquinone and catechol also exhibited genotoxic effects in V79 cells.
- Dihydrodiol dehydrogenase demonstrated a detoxification role, with specific enantiomers showing differential substrate activity.
Conclusions:
- Benzene's genotoxicity is mediated by specific metabolites, notably the anti-diol epoxide.
- Metabolic activation and detoxification pathways influence benzene's genotoxic potential.
- The study highlights the importance of considering metabolite-specific toxicity in chemical risk assessment.