An gas chromatography-electron-capture detection method has been developed for simultaneous determination of fluoxetine and p-trifluoromethylphenol (TFMP), an O-dealkylated metabolite of fluoxetine in human liver microsomes. Prior to the analysis, aliquots of alkalinized microsomal mixture were extracted with ethyl acetate solvent containing acetonitrile (10%, v/v) and the derivatizing reagent, pentafluorobenzenesulfonyl chloride (0.1%, v/v). The organ phase was retained and taken to dryness, the residue was reconstituted in methanol, and the aliquot of extracts was injected directly into a gas chromatograph equipped with an electron-capture detector. 2, 4 Dichlorophenol was added to the initial incubation mixture and carried through the procedure as the internal standard. The method provided the mean recoveries of up to 103% for fluoxetine and 104% for TFMP. Acceptable relative standard deviations were found for both within-run and day-to-day assays. The practical limit of detection (signal-to-noise ratio53) was 1.62ng/ml for TFMP and 6.92ng/ml for fluoxetine in human liver microsomes, and the limit of quantitation was 8.1 pg for TFMP and 34.6 pg for fluoxetine. The assay is rapid and sensitive and has been applied successfully to simultaneous quantification of fluoxetine and TFMP in human liver microsomes with different CYP2C19 genotypes.

Ethnic differences in drug metabolism are well documented for a number of drugs. The molecular mechanisms responsible for ethnic differences in drug metabolism have been partly clarified because of the advances in molecular biology in recent years. Gene dosage determines the drug metabolism as demonstrated for S-mephenytoin and diazepam metabolism. Genotype analysis indicates a different frequency for the mutant alleles in different ethnic populations, which results in variations in the frequency of subjects who are homozygous for the mutant allele among the extensive metabolizers in different ethnic populations. Ethnic differences in drug metabolism may result from differences in distribution of a polymorphic trait and mutations which code for enzymes with abnormal activity which occur with altered frequency in different ethnic groups.

The study was designed to define the contribution of cytochrome P450 2C19 (CYP2C19) and cytochrome P450 3A4 (CYP3A4) to citalopram N-demethylation and to evaluate the relationship between the disposition of citalopram and CYP2C19 genotype. A single oral 40mg dose of citalopram was administered to eight extensive metabolizers and five poor metabolizers recruited from 77 healthy Chinese volunteers whose genotypes and phenotypes were predetermined. The plasma concentrations of citalopram and desmethylcitalopram were N determined by high-performance liquid chromatography. It was found that the genotype of CYP2C19 had a significant effect on the N-demethylation of citalopram. Poor metabolizers with m1 mutation had higher area under the plasma concentration versus time curve (AUC03) values than did extensive metabolizers. Terminal eliminationelimination half-life (t1/2) values of citalopram in poor metabolizers were significantly higher than the values in extensive metabolizers who were either homozygous or heterozygous with CYP2C19*1. The oral clearance (CLoral) of citalopram in poor metabolizers was significantly lower than that of extensive metabolizers. The AUC03 and maximum plasma concentration (Cmax) of desmethylcitalopram in poor metabolizers were significantly lower than the values of extensive metabolizers. The results show that CYP3A4 is not the major enzyme in the N-demethylation of citalopram among extensive metabolizers. The polymorphism of CYP2C19 plays an important role in the Ndemethylation of citalopram in vivo. The extensive metabolizers and poor metabolizers of CYP2C19 had significant difference in disposition of citalopram in vivo.

Objectives: Our objectives were to determine whether the Gly389 polymorphism of the β1-adrenergic receptor exhibits reduced responsiveness in vivo and to test the hypothesis that the Gly389Arg polymorphism affects the blood pressure and heart rate response to metoprolol. Methods: β1-Adrenergic receptor genotype was determined by polymerase chain reaction-restriction fragment length polymorphism assay. Exercise-induced heart rate increases were compared to determine the functional significance in vivo in 8 healthy Chinese men homozygous for Gly389 and 8 homozygous for Arg389. All of the subjects were given 25, 50, or 75mg of metoprolol every 8 hours; the dosages were given in a random order, and each dosage was given for β1 day. The degree of β-blockade was measured as the reduction in resting and exercise heart rates and blood pressures. Plasma metoprolol concentrations were measured by the use of HPLC-fluorescence detection. Results: Exercise led to a workload-dependent increase in heart rate. There were no differences in exerciseinduced heart rate increases between Arg389 and Gly389 homozygotes. Oral metoprolol caused significant dose-dependent decreases in both resting and exercise heart rates in both groups. The reductions in the resting heart rate in 3 dosage levels of metoprolol were 6.3%±0.8% versus 4.1% 0.7%, 10.1%±1.0% versus 6.2%±1.1%, and 14.4%±1.4% versus 10.9%±1.3% in homozygous Arg389 subjects and Gly389 subjects, respectively (P=.008). We also found differences with respect to the exercise heart rate (8.9%±0.5%, 14.0%±0.9%, and 20.1%±1.5% in Arg389 subjects and 6.6%±0.7%, 11.7%±1.0%, and 16.4%±1.3% in Gly389 subjects; P=.017) and systolic pressure (5.9%±0.7%, 9.2%±1.0%, and 11.6% 1.2% in Arg389 subjects and 4.6%±0.5%, 6.0%±0.8%, and 9.9%±0.9% in Gly389 subjects; P=.011). However, the difference in the fall in diastolic pressure was not statistically significant (P=.442).

Aims The present study was designed to define the kinetic behaviour of sertraline N-demethylation in human liver microsomes and to identify the isoforms of cytochrome P450 involved in this metabolic pathway. Methods The kinetics of the formation of N-demethylsertraline were determined in human liver microsomes from six genotyped CYP2C19 extensive (EM) and three poor metabolisers (PM). Selective inhibitors of and specific monoclonal antibodies to various cytochrome P450 isoforms were also employed. Results The kinetics of N-demethylsertraline formation in all EM liver microsomes were fitted by a two-enzyme Michaelis-Menten equation, whereas the kinetics in all PM liver microsomes were best described by a single-enzyme Michaelis-Menten equation similar to the low-aYnity component found in EM microsomes. Mean apparent Km values for the high-and low-aYnity components were 1.9 and 88mm and V max values were 33 and 554 pmol min−1mg 1 protein, respectively, in the EM liver microsomes. Omeprazole (a CYP2C19 substrate) at high concentrations and sulphaphenazole (a selective inhibitor of CYP2C9) substantially inhibited Ndemethylsertraline formation. Of five monoclonal antibodies to various cytochrome P450 forms tested, only anti-CYP2C8/9/19 had any inhibitory eVect on this reaction. The inhibition of sertraline N-demethylation by anti CYP2C8/9/19 was greater in EM livers than in PM livers at both low and high substrate concentrations. However, anti-CYP2C8/9/19 did not abolish the formation of N-demethylsertraline in the microsomes from any of the livers. Conclusions The polymorphic enzyme CYP2C19 catalyses the high-aYnity Ndemethylation of sertraline, while CYP2C9 is one of the low-aYnity componentsof this metabolic pathway.

Aims: To investigate the incidence of the CYP2C19 polymorphism in the Chinese Dai population. Methods: One hundred and ninety-three healthy Chinese Dai volunteers were identified with respect to CYP2C19 by genotype and phenotype analyses. A polymerase chain reaction-restriction fragment length polymorphism method was performed for genotyping procedures. The 4-hydroxymephenytoin (4-OH-MP) and S/R-mephenytoin (S/R-MP) excreted in the urine were determined by high-performance liquid chromatographyand gas chromatography, respectively. Results: Eighteen subjects were identified as poor metabolisers (PMs). The frequency of PMs in the Chinese Dai subjects was 9.3% (95% confidence interval 5.2, 13.4), which is lowerthan that in the Chinese Han population (P<0.05). Chinese Dai subjects had a higher frequency of the mutant CYP2C19*2 allele (0.303) and a lowerfr equency of the mutant CYP2C19*3 allele (0.034). These two mutant alleles could explain all defi-ciencies of CYP2C19 activity in the Chinese Dai subjects. The frequency of the CYP2C193 allele is significantly lowerthan that in the Chinese Han population (P<0.05). The mean S/R ratio was lower in the homozygous extensive metabolisers (EMs) compared with that in heterozygous EMs (P<0.01), and the latter was lowerthan that in the PMs (P<0.01). Furthermore, the mean S/R ratio in CYP2C193/CYP2C192 heterozygous PMs was possibly lower than that in the CYP2C192/CYP2C19*2 homozygous PMs (P<0.05). Conclusion: The frequencies of PMs and CYP2C19*3 allele in the Chinese Dai population are significantly lowerthan those in the Han population. The CYP2C19genotype analysis is largely consistent with the mephenytoin phenotype analysis. The variability of S/R ratios in EMs and PMs shows a gene-dosage e ect.

Aims To investigate the distribution of CYP3A activity in the Chinese population, and to test for gender-related differences in CYP3A activity. Methods Using midazolam as a probe drug, CYP3A activity in 202 Chinese healthy subjects (104 men) was measured by plasma 1-hydroxymidazolam: midazolam (1-OH-MDZ: MDZ) ratio at 1 h after oral administration of 7.5mg midazolam. The different phases of the menstrual cycle including preovulatory, ovulatory and luteal phases of 66 women phenotyped with midazolam were recorded. The concentrations of 1-OH-MDZ and MDZ in plasma were measured by HPLC Results A 13-fold variation of CYP3A activity (log1-OH-MDZ: MDZ: range-0.949-0.203) was shown. The CYP3A activity was normally distributed as indicated by the frequency distribution histogram, the probit plot and the Kolmogorov-Smirnov test (P>0.05). The CYP3A activity of women was higher than that of men (median: -0.36vs-0.43, P<0.05; 95% CI for difference: -0.127,-0.012). There was a significant difference in CYP3A activity between the three phases of the menstrual cycle. The activity was highest in the preovulatory phase and decreased sequentially in the ovulatory and luteal phases (P<0.05). Conclusions A normal distribution of CYP3A activity was observed in the Chinese population. The CYP3A activity is higher in female subjects than in males. CYP3A activity differed across the phases of the menstrual cycle.

This work evaluated the kinetic behavior of fluoxetine O-dealkylation in human liver microsomes from different CYP2C19 genotypes and identified the isoenzymes of cytochrome P450 involved in this metabolic pathway. The kinetics of the -trifluoromethylphenol (TFMP) formation from fluoxetine was determined in human liver microsomes from three homozygous (wt/wt) and three heterozygous (wt/m1) extensive metabolizers (EMs) and three poor metabolizers (PMs) with m1 mutation (m1/m1) with respect to CYP2C19. The formation rate of TFMP was determined by gas chromatograph with electron-capture detection. The kinetics of TFMP formation was best described by the two-enzyme and single-enzyme Michaelis-Menten equation for liver microsomes from CYP2C19 EMs and PMs, respectively. The mean intrinsic clearance (Vmax/Km) for the high- and low-affinity component was 25.2 l/min/nmol and 3.8 l/min/nmol of cytochrome P450 in the homozygous EMs microsomes and 12.8 l/min/nmol and 2.9 l/min/nmol of cytochromecytochrome P450 in the heterozygous EMs microsomes, respectively. Omeprazole (a CYP2C19 substrate) at a high concentration and triacetyloleandomycin (a selective inhibitor of CYP3A4) substantially inhibited O-dealkylation of fluoxetine. Furthermore, fluoxetine O-dealkylation was correlated significantly with S-mephenytoin 4-hydroxylation at a low substrate concentration and midazolam 1 -hydroxylation at a high substrate concentration in liver microsomes of 11 Chinese individuals, respectively. Moreover, there were obvious differences in the O-dealkylation of fluoxetine in liver microsomes from different CYP2C19 genotypes and in microsomal fractions of different human-expressed lymphoblast P450s. The results demonstrated that polymorphic CYP2C19 and CYP3A4 enzymes were the major cytochrome P450 isoforms responsible for fluoxetine O-dealkylation, whereas CYP2C19 catalyzed the high-affinity O-dealkylation of fluoxetine, and its contribution to this metabolic reaction was gene dose-dependent.

目的：建立同时测定体外肝微粒体中氟西汀及其代谓十产物去甲氟西汀的反相高效液相色谱紫外检测法。方法：含微粒体蛋白和NADPH发生系统及氟西汀的孵育液加入冰乙腈酸终止反应后，再加入去甲替林作为内标并以，z.正己烷和乙腈的混合液进行萃取，然后以反相ODS柱分离，在226nlTl处以紫外检测器进行检测。结果：孵育体系中没有明显的干扰峰出现，氟西汀和去甲氟西汀洗脱快，分离好，线性范围均为10-800ug/L，最低检测限均为5ug/L，相对回收率为94%-104%，变异系数少于9.1%。结论：本法快速，灵敏，回收率高，且萃取过程简单，可用于体外氟西汀的代谢研究。