Phenotypic-genotypic analysis of CYP2C19 in the Jewish Israeli population.

OBJECTIVES: Evaluation of CYP2C19 activity and the frequency of CYP2C19 alleles in the Jewish Israeli population. METHODS: One hundred forty Jewish Israeli subjects received 100 mg racemic mephenytoin and collected urine for 8 hours. Urinary concentrations of mephenytoin enantiomers and 4'-hydroxymephenytoin were determined by gas-liquid chromatography and HPLC, respectively. CYP2C19 activity was derived from urinary S/R-ratio and 8-hour urinary excretion of 4'-hydroxymephenytoin. Mutations were identified by polymerase chain reaction and enzyme digestion with SmaI (CYP2C19*2) and BamHI (CYP2C19*3). RESULTS: Deficient mephenytoin hydroxylation was found in 4 subjects (2.9%; 95% confidence interval [CI], 0.1% to 5.7%) who were homozygous for CYP2C19*2. CYP2C19*2 was the major deactivating allele accounting for 15% (95% CI, 11% to 19%) of CYP2C19 alleles, whereas CYP2C19*3 was identified in 2 subjects (1%; 95% CI, 0% to 2%). Among 136 extensive metabolizers, 99 were homozygous for CYP2C19*1 and 37 were compound heterozygous CYP2C19*1/CYP2C19*2 (35 subjects) or CYP2C19*1/CYP2C19*3 (2 subjects). Gene dose effect was noted so that the S/R-ratio was significantly greater and urinary excretion of 4'-hydroxymephenytoin was significantly lower in compound heterozygous than in homozygous extensive metabolizers (0.310+/-0.209 versus 0.225+/-0.176, P < .04 and 48.6%+/-19.2% versus 56.3%+/-16.0%, P < .03, respectively). Female extensive metabolizers had a significantly lower excretion of 4'-hydroxymephenytoin than male extensive metabolizers (49.5%+/-17.6% versus 58.4%+/-16.7%, respectively, P < .005). CONCLUSION: The frequency of poor metabolizers of CYP2C19 and CYP2C19*2 allele in the Jewish Israeli population resembles findings in non-Asian populations. Complete concordance was noted between phenotypic and genotypic findings. CYP2C19 genotyping may enable subclassification of extensive metabolizers into subjects with high and low activity.

Markedly reduced bile acid synthesis but maintained levels of cholesterol and vitamin D metabolites in mice with disrupted sterol 27-hydroxylase gene.

Sterol 27-hydroxylase is important for the degradation of the steroid side chain in conversion of cholesterol into bile acids and has been ascribed a regulatory role in cholesterol homeostasis. Its deficiency causes the autosomal recessive disease cerebrotendinous xanthomatosis (CTX), characterized by progressive dementia, xanthomatosis, and accelerated atherosclerosis. Mice with a disrupted cyp27 (cyp27(-/-)) had normal plasma levels of cholesterol, retinol, tocopherol, and 1,25-dihydroxyvitamin D. Excretion of fecal bile acids was decreased (<20% of normal), and formation of bile acids from tritium-labeled 7alpha-hydroxycholesterol was less than 15% of normal. Compensatory up-regulation of hepatic cholesterol 7alpha-hydroxylase and hydroxymethylglutaryl-CoA reductase (9- and 2-3-fold increases in mRNA levels, respectively) was found. No CTX-related pathological abnormalities were observed. In CTX, there is an increased formation of 25-hydroxylated bile alcohols and cholestanol. In bile and feces of the cyp27(-/-) mice only traces of bile alcohols were found, and there was no cholestanol accumulation. It is evident that sterol 27-hydroxylase is more important for bile acid synthesis in mice than in humans. The results do not support the contention that 27-hydroxylated steroids are critical for maintenance of cholesterol homeostasis or levels of vitamin D metabolites in the circulation.