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).

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.

Objective: Our objective was to evaluate the relationship between the disposition of sertraline and the presence of the CYP2C19 gene and to define the contribution of cytochrome P450 2C19 (CYP2C19) to sertraline N-demethylation. Methods: A single oral 100-mg dose of sertraline was administered to 6 subjects who were extensive metabolizers and 6 subjects who were poor metabolizers recruited from 77 healthy Chinese volunteers whose genotypes were predetermined by polymerase chain reaction-based amplification, followed by restriction fragment length polymorphism analysis. Phenotypes were determined by use of the omeprazole metabolic rate. The plasma concentrations of sertraline and desmethylsertraline were determined by gas chromatography with electron-capture detection. Results: Six poor metabolizers with m1 mutation had area under the plasma concentration versus time curve (AUC0-∞) values (983.6±199.3μg·h/L versus 697.6±133.0μg·h/L; P<.05) and terminal elimination half-life values of sertraline (35.5±5.6 hours versus 23.5±4.4 hours; P<.01) that were significantly higher than the values in 6 extensive metabolizers who were either homozygous or heterozygous for CYP2C19*1. The oral clearance of sertraline in poor metabolizers (105.3±19.4L/h) was significantly lower than that of extensive metabolizers (148.4±28.6L/h). The area under the concentration-time curve from 0 to 144 hours and the maximum plasma concentration of desmethylsertraline in poor metabolizers were significantly lower than the values of extensive metabolizers (627.6±203.8μg·h/L versus 972.1±270.3μg·h/L; P<.05; and 23.6±6.5nmol/L versus 32.4±8.2nmol/L; P<.01; respectively).

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.