Dong-Sheng Ouyang

Effect of the gene dosage of CYP2C19 on diazepam metabolism in Chinese subjects

To determine whether the gene dosage of CYP2C19 affects the metabolism of diazepam and desmethyldiazepam in healthy Chinese subjects.

Plasma caffeine metabolite ratio (17X/137X) in vivo associated with G-2964A and C734A polymorphisms of human CYP1A2

Either G-2964 or A734 in the human CYP1A2 gene was confirmed to be associated with high inducible enzyme activity in smokers, but not in nonsmokers. In this study, for the first time, we observed an association between phenotypes and genotypes of CYP1A2 with respect to the two genetic polymorphisms in 163 healthy Chinese volunteers living in Qidong. The ratio of plasma 17X/137X at 6 h after oral administration of 300 mg caffeine was employed in CYP1A2 phenotyping analysis, while genotyping analysis was carried out by polymerase chain reaction-restriction fragment length polymorphism. The allele frequencies of A at -2964 and A at 734 in 139 non-smoking subjects were 0.25 and 0.67, respectively. The A/A-2964C/C734, G/A-2964C/C734 or A/A-2964C/A734 genotype that was thought to have lower inducibility/activity of CYP1A2 than the other genotypes did not exist in the tested Chinese subjects. The ratio of 17X/137X was 0.46 +/- 0.26 in G/G-2964A/A734 genotypes (n = 22) and 0.36 +/- 0.19 in non-G/G-2964A/A734 (n = 117). In addition, there was significant difference between them (P = 0.036). A similar result was also achieved in 24 smokers. Since Qidong is a special region with particularly high incidence of hepatocellular carcinoma in China, the association of phenotypes with genotypes of CYP1A2 in the Qidong population might result from some inducible environmental factors such as those of cigarettes in smokers.

Assessment of cytochrome P450 activity by a five-drug cocktail approach

Our goal was to establish and validate a modified cocktail approach including probe drugs caffeine, chlorzoxazone, mephenytoin, metoprolol, and midazolam for simultaneous phenotyping of CYP1A2, CYP2E1, CYP2C19, CYP2D6, and CYP3A.

Meta-analysis of phenotype and genotype of NAT2 deficiency in Chinese populations.

Data on both the incidence of slow acetylator phenotype of probe drugs isoniazid, sulfadimidine or sulfamethazine, caffeine and dapsone in mainland or overseas Chinese, and the distribution of NAT2 genotypes and the frequency of NAT2 alleles in the Chinese populations were summarized and reanalysed using a meta-analysis method. Frequency of the slow acetylator phenotype in 3516 healthy Han Chinese gave an overall mean of approximately 19.9 +/- 4.0%, with the range of the combined data being between 15.8% and 25.5%. In addition, frequencies of the slow acetylator phenotype differ between the different minorities in Chinese populations and the range was between 3.2% and 50.6%, with a mean value of 20.6 +/- 12.9% in a total of 1842 individuals from 17 Chinese minorities. In addition, there was no significant heterogeneity in overseas Chinese between the probe drugs isoniazid and sulfadimidine or sulfamethazine (chi 2 = 5.97, df = 4; p > 0.05), and the mean value of slow acetylator phenotype incidence was 24.5% (119/485; 95% CI: 20.7-28.3%), consistent with that of the native Chinese. As expected, frequency of the slow acetylator genotypes in Chinese populations was 25.4% (112/441; 95% CI: 21.3-29.5%), which was in accordance with that of the slow acetylator phenotype in native or overseas Chinese. For all genotypes, *4/*4 (29.9%, 132/441), *4/*6A (27.4%, 121/441), *4/*7A (12%, 53/441) and *6A/*6A (11.3%, 50/441) occupied 80.6%, but *5A/*7A (0.2%, 1/441), *5A/*5A (1.1%, 5/441) and *7A/*7A (1.8%, 8/441) were not frequently found. From this report, the genotype frequencies of homozygous rapid acetylator, heterozygous rapid acetylator, and homozygous slow acetylator were found to be 0.299 (132/441), 0.447 (197/441) and 0.254 (112/441), respectively. Furthermore, both *4 (52.3%; 95% CI: 49-56%) and *6A (30.5%; 95% CI: 28-34%) were major NAT2 alleles, while *7A (11.2%; 95% CI: 9-13%) and *5A (6%; 95% CI: 4-8%) were uncommonly present. Frequency of the mutant alleles was observed at 0.477 (421/882 alleles). The *7A constituted 23.5% t(99/421) of slow acetylator alleles in Chinese populations, showing that this point mutation exists not only in Oriental or Asiatic, but also in Chinese populations. According to the Hardy-Weinberg equilibrium, in the phenotyped Chinese populations, the mean estimate of predicted allelic frequencies of the genotypes RR, Rr, and rr was 0.294, 0.496, and 0.210 for the Chinese, and the expected frequency of the deficient gene r was 0.458. By comparison, the predicted values are in complete agreement with the observed ones. In conclusion, this meta-analysis determined the accurate population frequencies of phenotype and genotype of the NAT2 genetic deficiency in healthy Chinese subjects.

Lack of Effect of Ginkgo biloba on Voriconazole Pharmacokinetics in Chinese Volunteers Identified as CYP2C19 Poor and Extensive Metabolizers

Background: Ginkgo biloba is one of the most popular herbal supplements in the world. The supplement has been shown to induce the enzymatic activity of CYP2C19, the main cytochrome P450 isozyme involved in voriconazole metabolism. Because this enzyme exhibits genetic polymorphism, the inductive effect was expected to be modulated by the CYP2C19 metabolizer status. Objective: To examine the possible effects of Ginkgo biloba as an inducer of CYP2C19 on single-dose pharmacokinetics of voriconazole in Chinese volunteers genotyped as either CVP2C19 extensive or poor metabolizers. Methods: Fourteen healthy, nonsmoking volunteers–7 CYP2C19 extensive metabolizers (2C19*1/2C19*1) and 7 poor metabolizers (2C19*2/2C19*2)–were selected to participate in this study. Pharmacokinetics of oral voriconazole 200 mg after administration of Ginkgo biloba 120 mg twice daily for 12 days were determined for up to 24 hours by liquid chromatography–electrospray tandem mass spectrometry in a 2-phase randomized crossover study with 4-week washout between phases. Results: For extensive metabolizers, the median value for voriconazole area under the plasma concentration–time curve from zero to infinity (AUC0-00) was 5.17 μg•h/mL after administration of voriconazole alone and 4.28 μg•/mL after voriconazole with Ginkgo biloba (p > 0.05). The other pharmacokinetic parameters of voriconazole such as AUC0-24, time to reach maximum concentration, half-life, and apparent clearance also did not change significantly for extensive metabolizers in the presence of Ginkgo biloba. Pharmacokinetic parameters followed a similar pattern for poor metabolizers. Conclusions: The results suggest that 12 days of treatment with Ginkgo biloba did not significantly alter the single-dose pharmacokinetics of voriconazole in either CYP2C19 extensive or poor metabolizers. Therefore, the pharmacokinetic interactions between voriconazole and Ginkgo biloba may have limited clinical significance.

Effects of the CYP Oxidoreductase Ala503Val Polymorphism on CYP3A Activity In Vivo: A Randomized, Open-Label, Crossover Study in Healthy Chinese Men

BACKGROUND Cytochrome P450 (CYP) oxidoreductase (POR) is the electron donor for microsomal CYP enzymes. The POR Ala503Val (POR*28 C > T) polymorphism has been reported to influence CYP3A activity in vivo in a white population. The influence of this polymorphism on CYP3A activity in vivo in the Chinese population currently unknown. OBJECTIVE This study was designed to assess the influence of the POR*28 polymorphism on the CYP3A activity in vivo in healthy Chinese men using midazolam (MID) as a probe drug. METHODS The POR*28 polymorphism was genotyped in healthy Chinese men. A randomized, 2-phase, open-label, crossover study was performed to assess in vivo CYP3A activity after both oral and intravenous MID administration, which reflect both intestinal and hepatic CYP3A or only hepatic CYP3A activity, respectively. The plasma concentrations of MID and 1-hydroxy-midazolam (1-OH-MID) were determined by liquid chromatography-tandem mass spectrometry. RESULTS A total of 73 healthy Chinese men were enrolled (CC genotype, 21 subjects; TT genotype, 11; CT genotype, 41), 22 of whom were selected for additional phenotyping of the CYP3A5*3 polymorphism (CC, 7; TT, 8; CT, 7). The mean (range) age, weight, height, and body mass index of the 22 subjects were 23 (20-28) years, 65.0 (57-75) kg, 1.74 (1.63-1.80) m, and 22.01 (19.27-24.46) kg/m(2), respectively. The frequency of the POR*28 T (503V) allele was 43.2%. No significant differences in the demographic characteristics of the subjects were observed between the POR*28 genotype groups. All of the POR*28 CC and TT homozygotes and 2 of the POR*28 CT heterozygotes carried the CYP3A5*3/*3 genotype (CYP3A5 low expressors); 6 CT heterozygotes carried the CYP3A5*1 allele (CYP3A5 expressors). The mean (SD) 1-OH-MID AUC(0-8) was significantly greater in the TT homozygotes compared with the CT heterozygotes after intravenous (86.15 [24.34] vs 53.21 [31.36] ng/mL/h; P = 0.026) but not oral (126.36 [31.60] vs 103.09 [31.00] ng/mL/h; P = 0.159) MID administration. Mean 1-OH-MID C(max) was significantly greater in the TT homozygotes (51.40 [10.72] ng/mL) compared with the CC homozygotes (31.47 [11.54] ng/mL; P = 0.002) and CT heterozygotes (30.12 [9.21] ng/mL; P = 0.001) after intravenous MID administration. After intravenous MID injection, the MID metabolic ratio was significantly greater in the TT homozygotes compared with carriers of the C allele (P = 0.031). Based on these findings, no significantly differences in overall (hepatic plus intestinal) CYP3A in vivo activity were observed between the POR*28 genotypes. CONCLUSION These findings suggest that individuals with the POR*28 C > T polymorphism underwent an increase in 1-hydroxylation of MID after intravenous MID administration, and that the polymorphism was associated with increased hepatic, but not intestinal, CYP3A activity in these healthy Chinese volunteers.

Clopidogrel Inhibits CYP2C19‐Dependent Hydroxylation of Omeprazole Related to CYP2C19 Genetic Polymorphisms

This study explores the impact of clopidogrel on the pharmacokinetics of omeprazole related to CYP2C19 genetic polymorphisms. Twelve healthy volunteers (6 CYP2C19*1/*1, 5 CYP2C19*2/*2, and 1 CYP2C19*2/*3) are enrolled in a 2‐phase randomized crossover trial. In each phase, the volunteers are administered a single oral dose of omeprazole 40 mg after pretreatment of either placebo or clopidogrel (300 mg on the first day and then 75 mg once daily for 3 consecutive days). Plasma concentrations of omeprazole and its metabolites are quantified by high‐performance liquid chromatography with UV detection. After clopidogrel treatment, the AUC0–∞ of omeprazole increases by 30.02% ± 18.03% (P = .004) and that of 5‐hydroxyomeprazole decreases by 24.30% ± 11.66% (P = .032) in CYP2C19*1/*1. The AUC0–∞ ratios of omeprazole to 5‐hydroxyomeprazole increase by 74.98% ± 35.48% (P = .001) and those of omeprazole to omeprazole sulfone do not change significantly (P = .832) in CYP2C19*1/*1. No significant alteration is observed in CYP2C19*2/*2 or *3. Clopidogrel inhibits CYP2C19‐dependent hydroxylation of omeprazole in CYP2C19*1/*1 and has no impact on CYP3A4‐catalyzed sulfoxidation of omeprazole.

SIMULTANEOUS ACTION OF THE FLAVONOID QUERCETIN ON CYTOCHROME P450 (CYP) 1A2, CYP2A6, N‐ACETYLTRANSFERASE AND XANTHINE OXIDASE ACTIVITY IN HEALTHY VOLUNTEERS

1 Quercetin, one of the most abundant natural flavonoids, has been reported to modulate the activity of several drug‐metabolising enzymes. The aim of the present study was to investigate the effects of quercetin on cytochrome P450 (CYP) 1A2, CYP2A6, N‐acetyltransferase (NAT2) and xanthine oxidase (XO) activity in healthy volunteers using caffeine as a probe drug. 2 Twelve unrelated, healthy volunteers were recruited to the study. There were two phases to the study; in the first phase, each subject was given a single oral dose of caffeine (one 100 mg capsule) with 150 mL water; in the second phase, each subject was give a 500 mg quercetin capsule once daily for 13 continuous days and was coadministered a 100 mg caffeine capsule on the 13th day. Urinary caffeine metabolite ratios were used as indicators of the activity of CYP1A2, CYP2A6, NAT2 and XO. The pharmacokinetics of caffeine and its metabolites were determined by HPLC. 3 In the quercetin‐treated group, CYP1A2 activity was decreased by 10.4% (95% confidence interval (CI), 1.1–29.8%; P = 0.039), whereas increases were observed in CYP2A6 (by 25.3%; 95% CI, 6.2–34.5%; P = 0.002), NAT2 (by 88.7%; 95% CI, 7.1–160.2%; P = 0.010) and XO activity (by 15.0%; 95% CI, 1.6–21.6%; P = 0.007). Plasma Cmax and the AUC(0–24 h) of 1,7‐dimethylxanthine were decreased by 17.2% (95% CI, 6.4–28.0%; P = 0.024) and 16.2% (95% CI, 3.9–28.5%; P = 0.032), respectively. The urinary excretion of 1,7‐dimethylxanthine and 1‐methylxanthine was significantly decreased by 32.4% (95% CI, 2.5–62.1%; P = 0.036) and 156.1% (95% CI, 53.3–258.9%; P = 0.004), respectively. The urinary excretion of 1,7‐dimethylurate and 1‐methylurate was increased by 82.9% (95% CI, 56.0–165.4%; P = 0.030) and 97.8% (95% CI, 12.1–183.5%; P = 0.029), respectively. No changes were observed in the urinary excretion of caffeine and 5‐acetylamino‐6‐formylamino‐3‐methyluracil between the two study phases. 4 The results of the present study indicate that quercetin inhibits CYP1A2 function, but enhances CYP2A6, NAT2 and XO activity. Simultaneously, some pharmacokinetic parameters relating to 1,7‐dimethylxanthine were affected by quercetin. Thus, we conclude that quercetin affects CYP1A2, CYP2A6, NAT2 and XO activity in vivo.

Isozyme‐specific induction of low‐dose aspirin on cytochrome P450 in healthy subjects

This study was designed to define the effect of low‐dose aspirin administration on the activity of cytochrome P450 (CYP) in normal human subjects.

Effects of lignans extracted from Eucommia ulmoides and aldose reductase inhibitor epalrestat on hypertensive vascular remodeling

AIM OF THE STUDY To investigate the effects of lignans extracted from Eucommia ulmoides and epalrestat on vascular remodeling in spontaneously hypertensive rats. MATERIALS AND METHODS Ten-week-old male spontaneously hypertensive rats were randomly divided into 3 groups (12 rats each group), and treated orally with 100 mg/kg/d of captopril (an angiotensin-converting enzyme inhibitor), 100 mg/kg/d of epalrestat (an aldose reductase inhibitor) and 300 mg/kg/d of lignans by gavage daily for 16 weeks, respectively. Sex-, age-, and number-matched spontaneously hypertensive rats and normotensive Wistar Kyoto rats, were treated with distilled water (vehicle) as controls. The rats were weighed weekly. Mean arterial blood pressure and heart rate were measured periodically by non-invasive blood pressure monitoring. They were sacrificed at the end of experiment (26-week-old). Superior mesenteric artery and aorta were isolated for determination of histomorphometry and the expression of aldose reductase by immunohistochemistry. RESULTS Captopril and lignans, but not epalrestat, decreased mean arterial blood pressure in spontaneously hypertensive rats. Vascular remodeling was improved in all three treated groups by histomorphometry. CONCLUSIONS Both lignans and epalrestat reversed hypertensive vascular remodeling. Aldose reductase played a vital role in the pathologic process of hypertensive vascular remodeling rather than elevation of blood pressure. These data suggested that aldose reductase could be a new therapeutic target for the treatment of cardiovascular diseases.