CYP2D6-Dependent Bufuralol 1 '-Hydroxylation Assayed by Reversed-Phase Ion-Pair High-Performance Liquid Chromatography with Fluorescence Detection

CYP2D6 is an enzyme that is subject to genetic polymorphism 1. This P450 is absent in individuals with the poor metabolizer CYP2D6 phenotype 2, 3), resulting in a substantially reduced capacity to metabolize a large number of clinically useful drugs, including metoprolol, propafenone, haloperrdol, dextromethorphan and codeine (1). Quinidine competrtively inhibits CYP2D6, with a K1 of 3-30 mM (3–5). Because of its preferential inhibition of CYP2D6 (6 7), quinidine is frequently used as an inhibitory chemical probe of this polymorphically expressed P450. Diagnostic catalytic monitors of human hepatic CYP2D6 include debrisoquine 4-hydroxylase (4), dextromethorphan Odemethylase (8), and bufuralol l'-hydroxylase activities (2–4). Advantages of using bufuralol as a CYP2D6-selective substrate include the high sensitivity of the assay owing to the highly fluorescent l'-hydroxybufuralol metabohte and the fact that the use of radiolabeled substrate is not required. This chapter describes a modification of a reversed-phase ion-pair high-performance liquid chromatographic (HPLC) assay (9) with fluorescence detection for the determmation of bufuralol l'-hydroxylation activity. Methods for other CYP2D6 assays such as debrisoquine 4-hydroxylase (9) and dextromethorphan O-demethylase (9, 10) can be found in the cited references.