Differential metabolism of benzo[a]pyrene and benzo[a]pyrene-7,8-dihydrodiol by human CYP1A1 variants

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Item Type:	Article
Title:	Differential metabolism of benzo[a]pyrene and benzo[a]pyrene-7,8-dihydrodiol by human CYP1A1 variants
Creators Name:	Schwarz, D., Kisselev, P., Cascorbi, I., Schunck, W.H. and Roots, I.
Abstract:	Cytochrome P450 1A1 (CYP1A1) plays a key role in the metabolism of carcinogens, such as benzo[a]pyrene (B[a]P) and metabolites to ultimate carcinogens. Three human allelic variants, namely wild-type (CYP1A1.1), CYP1A1.2 (I462V) and CYP1A1.4 (T461N), were coexpressed by coinfection of baculovirus-infected insect cells with human NADPH-P450 reductase. These recombinant enzymes (in microsomal membranes) were used to analyze whether CYP1A1 polymorphisms affect catalytic activities towards B[a]P and B[a]P-7,8-dihydrodiol. The complete spectrum of phase I metabolites, including the tetrahydrotetrols resulting from hydrolysis of the ultimate carcinogen, B[a]P- 7,8-dihydrodiol-9,10-epoxide, was examined by HPLC. Wild-type enzyme showed the highest total metabolism of B[a]P, CYP1A1.2 was ∼50%, and CYP1A1.4 ∼70%. Km values for all metabolites with CYP1A1.2 were generally significantly lower than with wild-type enzyme (e.g. B[a]P-7,8-diol formation: 13.8 μM for wild-type, 3.5 μM for CYP1A1.2 and 7.7 μM for CYP1A1.4). Addition of epoxide hydrolase markedly increases the relative diol-to-phenol activities by all three variants. However, CYP1A1.4 exhibits the greatest efficiency to produce diol species. Each variant produced the diol epoxides from B[a]P-7,8-dihydrodiol. CYP1A1.1 exhibited with 10.4 pmol/min/pmol CYP1A1 the greatest total rate for 7,8-diol metabolites followed by CYP1A1.2 (7.2 pmol/min/pmol CYP1A1) and CYP1A1.4 (5.5 pmol/min/pmol CYP1A1). All enzyme variants produced about three times more diol epoxide 2-derived metabolites than diol epoxide 1-derived ones, whereby both rare allelic variants exhibited statistically significantly increased formation of diol epoxide 2. This study showed that the three CYP1A1 variants had different enzyme kinetics properties to produce both the diol metabolites from B[a]P and the ultimate mutagenic species diol epoxide 2 from B[a]P-7,8-dihydrodiol, which must be considered in the evaluation of individual susceptibility to cancer.
Keywords:	Benzo(a)pyrene, Carcinogens, Cytochrome P-450 CYP1A1, Dihydroxydihydrobenzopyrenes, High Pressure Liquid Chromatography, Spodoptera, Animals
Source:	Carcinogenesis
ISSN:	0143-3334
Publisher:	Oxford University Press
Volume:	22
Number:	3
Page Range:	453-459
Date:	1 January 2001
Official Publication:	http://carcin.oxfordjournals.org/cgi/content/abstract/22/3/453
PubMed:	View item in PubMed

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