title: Quinidine inhibition of debrisoquine S(+)-4- and 7-hydroxylations in Chinese of different CYP2D6 genotypes.
abstract: Pronounced differences in the CYP2D6 gene between Chinese and Caucasians have previously been described. There was a low frequency of detrimental mutations in the Chinese CYP2D6 gene causing the poor metabolizer (PM) phenotype. In contrast to Caucasians where the Xba I 44 kb allele is almost always associated with the PM phenotype, Chinese with the 44/44 kb RFLP pattern are extensive metabolizers (EM). In order to evaluate whether the debrisoquine hydroxylation seen in subjects with this haplotype is catalysed by a functionally similar enzyme to CYP2D6 or is catalysed by another type of P450 isozyme, product selectivity of the 4-hydroxylation was studied in 27 Chinese. The inhibition of CYP2D6 by quinidine was also investigated. In the 26 Chinese EM the S(+)-4-hydroxy enantiomer was found to be the major urinary metabolite of debrisoquine with an enantiomeric excess of 96.8-100%, which is similar to that in Caucasians. A correlation between the amount of S(+)-4-hydroxy and the minor 7-hydroxy metabolites excreted in urine (r = 0.72; p < 0.001) was seen. The amount of these two metabolites excreted was less in Chinese EM of debrisoquine with the 44/44 kb RFLP pattern, than in those with the wild type 29/29 kb pattern (p < 0.01). The stereoselectivity was very high in both groups. All Chinese homozygous for the 44 kb fragment (n = 5) were transformed to apparent PM after a single 100 mg dose of quinidine similarly to five Caucasian EM. Both the S(+)-4- and 7-hydroxylations of debrisoquine were inhibited by quinidine in both populations. This study shows that the cytochrome P450 catalysing the 4- and 7-hydroxylations of debrisoquine in Chinese EM has the same properties (product stereoselectivity and inhibition by quinidine) as the CYP2D6 in Caucasian EM.
authors.affiliation: Department of Clinical Pharmacology, Karolinska Institute, Huddinge Hospital, Sweden.
authors.forename: L
authors.initials: L
authors.lastname: Bertilsson
authors.forename: C O
authors.initials: CO
authors.lastname: Meese
authors.forename: Q Y
authors.initials: QY
authors.lastname: Yue
authors.forename: M L
authors.initials: ML
authors.lastname: Dahl
authors.forename: M
authors.initials: M
authors.lastname: Ingelman-Sundberg
authors.forename: I
authors.initials: I
authors.lastname: Johansson
authors.forename: J
authors.initials: J
authors.lastname: Säwe
authors.forename: M
authors.initials: M
authors.lastname: Eichelbaum
mesh_terms: D044466:Asian People; D019389:Cytochrome P-450 CYP2D6; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics* / Q000378:metabolism; D003647:Debrisoquin / Q000031:analogs & derivatives / Q000378:metabolism* / Q000652:urine; D005838:Genotype; D006239:Haplotypes; D006801:Humans; D006900:Hydroxylation; D008657:Metabolic Clearance Rate / Q000187:drug effects; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D012150:Polymorphism, Restriction Fragment Length; D011802:Quinidine / Q000494:pharmacology* / Q000652:urine; D013237:Stereoisomerism; D044465:White People
chemical_list: D065607:Cytochrome P-450 Enzyme Inhibitors; C012359:4-hydroxydebrisoquin; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D019389:Cytochrome P-450 CYP2D6; D011802:Quinidine; D003647:Debrisoquin