Differential mechanism-based inhibition of CYP3A4 and CYP3A5 by verapamil.

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Wang YH, Jones DR, Hall SD

Differential mechanism-based inhibition of CYP3A4 and CYP3A5 by verapamil.

Drug Metab Dispos. 2005 May;33(5):664-71. doi: 10.1124/dmd.104.001834. Epub 2005 Feb 2.

PubMed ID

15689501 [ View in PubMed

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Abstract

The genetic basis for polymorphic expression of CYP3A5 has been recently identified, but the significance of CYP3A5 expression is unclear. The purpose of this study is to quantify the capability of verapamil, a mechanism-based inhibitor of CYP3A, and its metabolites to inhibit the activities of CYP3A4 and CYP3A5, and to determine whether CYP3A5 expression in human liver microsomes alters the inhibitory potency of verapamil. Testosterone 6beta-hydroxylation or midazolam 1'-hydroxylation was used to quantify CYP3A activity. The possibility that verapamil and its metabolites form metabolic-intermediate complex (MIC) with CYP3A was assessed using dual beam spectrophotometry. Verapamil and N-desalkylverapamil (D617) were found to have little inhibitory effect on cDNA-expressed CYP3A5 activity and did not form a MIC with cDNA-expressed CYP3A5 as indicated by the appearance of the characteristic peak at 455 nm. At 50 microM, norverapamil showed time-dependent inhibition of CYP3A5 (30%), but to a much lesser extent compared with that of CYP3A4 (80%). The estimated values of the inactivation parameters k(inact) and K(I) of norverapamil were 4.53 microM and 0.07 min(-1) for cDNA-expressed CYP3A5, and 10.3 microM and 0.30 min(-1) for cDNA-expressed CYP3A4. Human liver microsomes that expressed CYP3A5 were less inhibited by both verapamil and norverapamil. The inactivation efficiency of verapamil and norverapamil was 30 times and 45 times lower, respectively, for CYP3A5-expressing microsomes compared with CYP3A5-non-expressing microsomes. These findings indicate that the presence of variable CYP3A5/CYP3A4 expression in the liver may contribute to the interindividual variability associated with verapamil-mediated drug interactions.

DrugBank Data that Cites this Article

Drug Enzymes

Drug	Enzyme	Kind	Organism	Pharmacological Action	Actions
Verapamil	Cytochrome P450 3A4	Protein	Humans	Unknown	Substrate Inhibitor	Details
Verapamil	Cytochrome P450 3A5	Protein	Humans	Unknown	Substrate Inhibitor	Details