p53 Mutagenesis by benzo[a]pyrene derived radical cations

Area of Science:

• Environmental Health Sciences
• Toxicology
• Molecular Biology

Background:

• Benzo[a]pyrene (B[a]P) is a potent human carcinogen found in combustion products.
• B[a]P is metabolically activated into DNA-reactive species through three distinct enzymatic pathways.
• Understanding the mutagenicity of each pathway is crucial for assessing B[a]P's carcinogenic risk.

Purpose of the Study:

• To investigate the mutagenic potential of Benzo[a]pyrene (B[a]P) radical cations using a yeast p53 mutagenesis system.
• To characterize the mutation pattern and spectrum induced by B[a]P radical cations.
• To compare the mutagenicity of B[a]P radical cations and their quinone products with other B[a]P metabolites.

Main Methods:

• Generated B[a]P radical cations in situ using horse radish peroxidase (HRP) and cumene hydroperoxide (CuOOH).
• Assessed mutagenesis by B[a]P radical cations in a yeast p53 system, monitoring dose-dependent effects.
• Analyzed mutation patterns by sequencing mutant p53 plasmids recovered from yeast.

Main Results:

• B[a]P radical cations exhibited a dose-dependent increase in mutagenicity from 0.25 to 10 μM.
• The primary mutations induced were G to T (31%), G to C (29%), and G to A (14%), with a random distribution across codons.
• The mutagenicity of B[a]P radical cations and their quinone products was significantly lower (approximately 200-fold) than that of the aldo ketose reductase (AKR) pathway metabolite, B[a]P-7,8-dione.

Conclusions:

• B[a]P radical cations and their quinone products are weakly mutagenic in the yeast p53 system.
• The mutation spectrum induced by B[a]P radical cations does not enrich known cancer hotspot codons.
• These findings suggest that other metabolic pathways of B[a]P may contribute more significantly to its carcinogenicity.