Abstract
trans-Resveratrol (3,5,4′-trihydroxy-trans-stilbene) has been reported to confer chemoprotection against 7,12-dimethylbenz[a]anthracene (DMBA)-induced carcinogenicity in a murine model. A potential mechanism for this effect by trans-resveratrol is inhibition of DMBA-bioactivating cytochrome P450 (CYP) enzymes such as CYP1B1, CYP1A1, and CYP1A2. In the present study, we examined in detail the in vitro inhibitory effects of trans-resveratrol on these three human CYP enzymes. trans-Resveratrol decreased 7-ethoxyresorufin O-dealkylation activity catalyzed by human recombinant CYP1B1, CYP1A1, and CYP1A2 in a concentration-dependent manner and by a mixed type of inhibition. This direct inhibition was enzyme-selective, as judged by the differences in the apparent Ki values (0.8 ± 0.1 μM, 1.2 ± 0.1 μM, and 15.5 ± 1.1 μM for CYP1B1, CYP1A1, and CYP1A2, respectively). Preincubating recombinant CYP1A2 or human liver microsomes with trans-resveratrol and NADPH prior to the initiation of substrate oxidation resulted in a time- and concentration-dependent decrease in catalytic activity. The inactivation of liver microsomal CYP1A2 bytrans-resveratrol required NADPH, was not reversible by dialysis, and was not affected by the trapping agents glutathione,N-acetylcysteine, catalase, or superoxide dismutase, but was attenuated by a CYP1A2 substrate, imipramine. Analysis of a panel of individual human liver microsomes showed intersample differences in the response to the in vitro inactivation bytrans-resveratrol. In contrast to CYP1A2, CYP1B1 was not subject to inactivation by this compound and the reduction in CYP1A1 activity was time- but not concentration-dependent. In summary,trans-resveratrol differentially inhibited human CYP1 enzymes and this occurred by two distinct mechanisms: direct inhibition (mainly CYP1B1 and CYP1A1) and mechanism-based inactivation (CYP1A2).
Footnotes
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Supported by Grant MOP-42385 (to T.K.H.C.) from the Canadian Institutes of Health Research. T.K.H.C. is the recipient of a Research Career Award in the Health Sciences from the Canadian Institutes of Health Research and Rx & D Health Research Foundation.
- Abbreviations:
- CYP
- cytochrome P450
- DMBA
- 7,12-dimethylbenz[a]anthracene
- kinactivation
- rate constant for maximal inactivation
- kobs
- pseudo-first order rate constant for inactivation
- KI
- concentration of inactivator to produce one-half the maximal inactivation
- Ki
- the equilibrium dissociation constant for the enzyme-inhibitor complex
- t1/2
- time required for half of the enzyme molecules to be inactivated
- Received July 6, 2001.
- Accepted August 28, 2001.
- The American Society for Pharmacology and Experimental Therapeutics
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