Characterization of the selectivity and mechanism of cytochrome P450 inhibition by dimethyl-4,4'-dimethoxy-5,6,5',6'-dimethylenedioxybiphenyl-2,2'-dicarboxylate.
In vitro studies with human liver microsomes and cytochrome P450 (P450) prototype substrates were performed to characterize the selectivity and mechanism of inhibition of P450 by dimethyl-4,4'-dimethoxy-5,6,5',6'-dimethylenedioxybiphenyl-2,2'-dicarboxylate (DDB). DDB was found to be a strong inhibitor of testosterone 6beta-hydroxylation activity (CYP3A4) with a K(i) value of 0.27 +/- 0.21 microM. At higher concentrations, DDB marginally inhibited caffeine N(3)-demethylation (CYP1A2), diclofenac 4'-hydroxylation (CYP2C9), and dextromethorphan O-demethylation (CYP2D6) activities, but this compound had no effect on CYP2A6-, CYP2C19-, and CYP2E1-mediated reactions. Spectral analysis indicated that the formation of metabolite-P450 complex having absorbance at 456 nm was concentration-dependent; 5 to 33% of the total P450 was complexed in rat and human liver microsomes after a 5-min incubation with DDB. In addition, microsomal incubations with DDB in the presence of NADPH resulted in a loss of spectral P450 content, which was restored after adding K(3)Fe(CN)(6). This complex formation resulted in a time-dependent loss of CYP3A-catalyzed marker activity (testosterone 6beta-hydroxylation) in human liver microsomes. The inhibition was only partially restored upon dialysis. These results collectively suggest that formation of a metabolite-CYP3A complex with DDB was responsible for the CYP3A-selective time-dependent loss of catalytic function of CYP3A.
Kim
J Y
JY
Bioanalysis and Biotransformation Research Center, Korea Institute of Science and Technology, Chungryang, Seoul, Korea.
Baek
M
M
Lee
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S
Kim
S O
SO
Dong
M S
MS
Kim
B R
BR
Kim
D H
DH
D000818:Animals; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry / Q000378:metabolism; D003956:Dialysis; D004149:Dioxoles / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D008862:Microsomes, Liver / Q000378:metabolism; D051381:Rats; D013250:Steroid Hydroxylases / Q000378:metabolism; D013379:Substrate Specificity
D065607:Cytochrome P-450 Enzyme Inhibitors; D004149:Dioxoles; D004791:Enzyme Inhibitors; C041398:7,7'-dimethoxy-(4,4'-bi-1,3-benzodioxole)-5,5'-dicarboxylic acid dimethyl ester; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; C022657:steroid hormone 6-beta-hydroxylase