Specificity of cDNA-expressed human and rodent cytochrome P450s in the oxidative metabolism of the potent carcinogen 7,12-dimethylbenz[a]anthracene
✍ Scribed by Magang Shou; Kenneth R. Korzekwa; Kristopher W. Krausz; Jeroen T. M. Buters; James Grogan; Inna Goldfarb; James P. Hardwick; Frank J. Gonzalez; Harry V. Gelboin
- Publisher
- John Wiley and Sons
- Year
- 1996
- Tongue
- English
- Weight
- 913 KB
- Volume
- 17
- Category
- Article
- ISSN
- 0899-1987
No coin nor oath required. For personal study only.
✦ Synopsis
7,12-Dimethylbenz[a]anthracene (DMBA), a potent carcinogen, requires metabolic activation by cytochrome P450s (P450s) t o electrophilic metabolites that result in DNA modification, mutagenicity, and carcinogenicity. In this study, we used eight human forms, four rodent forms, and one rabbit form of P450 expressed from recombinant vaccinia or baculovirus vectors to define their specificity for metabolizing DMBA. Of the eight human P450s, 1Al was the most active (specific activity = 14.7 nmoVmin/nmol of P450) in total metabolism of DMBA and showed approximately 6-to 33-fold more activity than other P450s. 2B6,2C9, and 1A2 were also capable of metabolizing DMBA (2.0-2.5 nmol/min/nmol of P450), whereas 2C8, 2El. 3A4, and 3A5 exhibited relatively low activities. Among animal P450s, mouse 1Al exhibited activity similar to that of human 1Al and had 5.0-to 37-fold more activity than other rodent and rabbit P450s. In regard t o enzyme regioselectivity, most human and rodent P4505 predominantly formed the 8,9-diol, but human 2B6 and rat 2B1 preferentially formed the 5,Gdiol. In the production of monohydroxymethyl metabolites, all the enzymes yielded more 7-hydroxymethyl-12-methyl benz[a]anthracene (7HOM1 2MBA) than 12-hydroxymethyl-7-methylbenz[a]anthracene (7M1 ZHOMBA), except for human 1A1, which presented the reverse selectivity. Human liver rnicrosomes from 10 organ donors were shown t o metabolize DMBA and in most circumstances generated the metabolic profile DMBA trans-8,9dihydrodiol > 7HOM12MBA 2 DMBA trans-5,6-dihydrodiol 2 7,12-dihydroxymethylbenz[a]anthracene > 7M12HOMBA > DMBA trans-3,4-dihydrodioI. Thus, the combined activity of hepatic microsomal 2C9, 1A2, and 286 may contribute t o the metabolic activation and the metabolism of DMBA in normal human liver. 0 1996Wiley-Liss, Inc.