Characterization of the CYP2D6*29 allele commonly present in a black Tanzanian population causing reduced catalytic activity

Abstract

Debrisoquine metabolism among Tanzanians has been found to be slower than expected from the CYP2D6 genotype. In order to evaluate any genetic explanation, the coding sequence and intron-exon boundaries of the CYP2D6 gene from three Black Tanzanian volunteers with a CYP2D6*1/*1 or CYP2D6*2/*2 genotype and debrisoquine metabolic ratios (MRs) > 1 were fully sequenced to screen for new mutations. Two functional mutations, G1747 to A (causing V136I) and G3271 to A (causing V338M), were identified in the CYP2D6*2/*2 sample. Thirty-six subjects (34%) out of a total 106 subjects were heterozygous and three subjects (3%) were homozygous for the allele, yielding an allele frequency of 20%. The CYP2D6*29 allele, having also the mutations of the CYP2D6*2 allele, was subsequently expressed in yeast and mammalian COS-1 cells. No differences were seen with respect to the affinity (Km) or maximal velocity (Vmax) of the CYP2D6 substrate bufuralol between the wild-type and mutant when expression was carried out in yeast cells. By contrast, the 1'-hydroxybufuralol catalytic activity of the mutant expressed in COS-1 cells was only 26% of the wild-type (P < 0.01; Mann-Whitney U-test) and its debrisoquine hydroxylation activity was 63% of that of CYP2D6.1. The single mutants V136I and V338M had reduced capacity for bufuralol hydroxylation, but the effect was even stronger when both mutations were present together as in CYP2D6.29. Analysis of the distribution of CYP2D6*29 in subjects phenotyped for debrisoquine revealed that this allele significantly causes a reduction in the rate of debrisoquine hydroxylation in vivo. The results indicate the common existence in Tanzanians of a variant CYP2D6 form with different substrate specificity as compared to the wild-type form of the enzyme causing reduced capacity for debrisoquine metabolism.

In Vitro Functional Assessment of 22 Newly Identified CYP2D6 Allelic Variants in the Chinese Population

“…Variant CYP2D6.10 exhibited only approximately 10% of the activity of the wildtype protein. These data are in accordance with most of the previously reported results [15][16][17] and thus indicate that our CYP expression and metabolic activity analysis system is suitable for analysing the catalytic activities of the other CYP2D6 allelic variants. As shown in fig.…”

“…In the present study, we successfully expressed wild-type and 24 allelic variants of CYP2D6 proteins in 293FT cells and characterized their enzymatic activities towards two typical CYP2D6-catabolized drugs. Regarding the typical allelic variants CYP2D6.2 and CYP2D6.10, our data strongly accord with the majority of the previously reported results [15][16][17], although we have not provided the kinetic parameters of these variants. Similarly, previous reports have been revealed that the results obtained for another CYP member, CYP2C9, also are in well agreement with those from other expression systems [13]; thus, data of the present study might be constructive for the functional prediction of these newly found CYP2D6 variants.…”

A Physiologic Approach to the Pharmacogenomics of Hypertension

“…Indeed, the emphasis of this review has been on drug efficacy and agent selection. However, there is significant evidence supporting variants predicting adverse events including the hyperuricemia of thiazide use 94 , bradycardia associated with β-blockers [5][6][7][8]95,96 , and ACEI-related cough 97 .…”

Genetic polymorphisms of cytochrome P450 2D6 (CYP2D6): clinical consequences, evolutionary aspects and functional diversity

“…This creates an altered substrate specificity, 33 which is evident in vitro 33 but also when subjects of the CYP2D6*17 genotype are phenotyped in vivo. 34,35 In general, the activity of the CYP2D6.17 enzyme is lower than the wild-type enzyme.…”