The objectives of the this study were to assess the influence of CYP3A5 genotype and sex on the variability in total CYP3A activity and to compare 4beta-hydroxycholesterol and omeprazole sulfoxidation as phenotypic markers for CYP3A activity in Ethiopians. Healthy subjects (n=150) were genotyped for CYP3A5*3, *6 and *7 using allele-specific PCR and Taqman genotyping assays. Plasma levels of 4beta-hydroxycholesterol, 3 h post-dose omeprazole and omeprazole sulfone, were determined by gas chromatography-mass spectrometry and high performance liquid chromatography, respectively. The frequency of CYP3A5*1, (*)3, (*)6 and *7 was 20.5, 67.3, 12.2 and 0%, respectively. The mean plasma 4beta-hydroxycholesterol level was 35.4 ng ml(-1). The mean 4beta-hydroxycholesterol level (P=0.0001) and the 4beta-hydroxycholesterol/cholesterol ratio (P=0.004) were higher in women than in men. CYP3A5 genotype significantly correlated with the plasma 4beta-hydroxycholesterol concentration (P=0.003) and 4beta-hydroxycholesterol/cholesterol ratio (P=0.0002). The omeprazole/omeprazole sulfone ratio was significantly correlated with 4beta-hydroxycholesterol and 4beta-hydroxycholesterol/cholesterol ratio in CYP3A5*0/*0 genotypes but not in individuals carrying the CYP3A5*1 allele. No correlation of omeprazole/omeprazole sulfone ratio with sex or CYP3A5 genotype was observed. A clear gene-dose effect implies plasma 4beta-hydroxycholesterol level as a useful endogenous biomarker for total CYP3A activity (CYP3A5 plus CYP3A4) whereas the omeprazole/omeprazole sulfone ratio reflects mainly CYP3A4 activity. Sex and CYP3A5 genotype influence total CYP3A activity. Ethiopians display high total CYP3A activity and a unique distribution of CYP3A5 variant alleles not described hitherto.The Pharmacogenomics Journal advance online publication, 16 March 2010; doi:10.1038/tpj.2010.16.
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