Title: p53 Mutagenesis by benzo[a]pyrene derived radical cations.

Authors: Sen, Sushmita; Bhojnagarwala, Pratik; Francey, Lauren; Lu, Ding; Penning, Trevor M; Field, Jeffrey

Published In Chem Res Toxicol, (2012 Oct 15)

Abstract: Benzo[a]pyrene (B[a]P), a major human carcinogen in combustion products such as cigarette smoke and diesel exhaust, is metabolically activated into DNA-reactive metabolites via three different enzymatic pathways. The pathways are the anti-(+)-benzo[a]pyrene 7,8-diol 9,10-epoxide pathway (P450/epoxide hydrolase catalyzed) (B[a]PDE), the benzo[a]pyrene o-quinone pathway (aldo ketose reductase (AKR) catalyzed) and the B[a]P radical cation pathway (P450 peroxidase catalyzed). We used a yeast p53 mutagenesis system to assess mutagenesis by B[a]P radical cations. Because radical cations are short-lived, they were generated in situ by reacting B[a]P with cumene hydroperoxide (CuOOH) and horse radish peroxidase (HRP) and then monitoring the generation of the more stable downstream products, B[a]P-1,6-dione and B[a]P-3,6-dione. On the basis of B[a]P-1,6 and 3,6-dione formation, approximately 4 μM of radical cation was generated. In the mutagenesis assays, the radical cations produced in situ showed a dose-dependent increase in mutagenicity from 0.25 μM to 10 μM B[a]P with no significant increase seen with further escalation to 50 μM B[a]P. However, mutagenesis was 200-fold less than with the AKR pathway derived B[a]P, 7-8-dione. Mutant p53 plasmids, which yield red colonies, were recovered from the yeast to study the pattern and spectrum of mutations. The mutation pattern observed was G to T (31%) > G to C (29%) > G to A (14%). The frequency of codons mutated by the B[a]P radical cations was essentially random and not enriched at known cancer hotspots. The quinone products of radical cations, B[a]P-1,6-dione and B[a]P-3,6-dione were more mutagenic than the radical cation reactions, but still less mutagenic than AKR derived B[a]P-7,8-dione. We conclude that B[a]P radical cations and their quinone products are weakly mutagenic in this yeast-based system compared to redox cycling PAH o-quinones.

PubMed ID: 22768918

MeSH Terms: Benzo(a)pyrene/metabolism; Benzo(a)pyrene/toxicity*; Cations/metabolism; Cations/toxicity; DNA Damage/drug effects; Humans; Mutagenesis*; Mutagens/metabolism; Mutagens/toxicity*; NADP/metabolism; Oxidation-Reduction; Quinones/metabolism; Quinones/toxicity; Tumor Suppressor Protein p53/genetics*; Yeasts/genetics