title: p53 Mutagenesis by benzo[a]pyrene derived radical cations.
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.
authors: Department of Pharmacology and Center of Excellence in Environmental Toxicology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors: Sushmita
authors: S
authors: Sen
authors: Pratik
authors: P
authors: Bhojnagarwala
authors: Lauren
authors: L
authors: Francey
authors: Ding
authors: D
authors: Lu
authors: Trevor M
authors: TM
authors: Penning
authors: Jeffrey
authors: J
authors: Field
mesh_terms: D001564:Benzo(a)pyrene / Q000378:metabolism / Q000633:toxicity*; D002412:Cations / Q000378:metabolism / Q000633:toxicity; D004249:DNA Damage / Q000187:drug effects; D006801:Humans; D016296:Mutagenesis; D009153:Mutagens / Q000378:metabolism / Q000633:toxicity*; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D011809:Quinones / Q000378:metabolism / Q000633:toxicity; D016159:Tumor Suppressor Protein p53 / Q000235:genetics*; D015003:Yeasts / Q000235:genetics
chemical_list: D002412:Cations; D009153:Mutagens; D011809:Quinones; D016159:Tumor Suppressor Protein p53; D001564:Benzo(a)pyrene; D009249:NADP