Bi-Lian Chen

Rifampicin alters atorvastatin plasma concentration on the basis of SLCO1B1 521T>C polymorphism.

BACKGROUND Both atorvastatin and rifampicin are substrates of OATP1B1 (organic anion transporting polypeptide 1B1) encoded by SLCO1B1 gene. Rifampicin is a potent inhibitor of SLCO1B1 (IC50 1.5 umol/l) and SLCO1B1 521T>C functional genetic polymorphism alters the kinetics of atorvastatin in vivo. We hypothesize that rifampicin might influence atorvastatin kinetics in a SLCO1B1 polymorphism dependent manner. METHODS Sixteen subjects with known SLCO1B1 genotypes (6 c.521TT, 6 c.521TC and 4 c.521CC) were divided into 2 groups (atorvastatin-placebo group, n=8; atorvastatin-rifampicin group, n=8) randomly. In this 2-phase crossover study, atorvastatin (40 mg single-oral dose) pharmacokinetics after co-administration of placebo and rifampicin (600 mg single-oral dose) were measured for up to 48 h by liquid chromatography-mass spectrometry (LC-MS). In the third phase, rifampicin (450 mg single-oral dose) pharmacokinetics was measured additionally. RESULTS Rifampicin increased atorvastatin plasma concentration in accordance with SLCO1B1 521T>C genotype while the increasing percentage of AUC((0-48)) among c.521TT, c.521TC and c.521CC individuals were 833+/-245% vs 468+/-233% vs 330+/-223% (P=0.007). However, SLCO1B1 521T>C exerted no impact on rifampicin pharmacokinetics (P>0.05). CONCLUSIONS These results suggested that rifampicin elevated the plasma concentration of atorvastatin depending on SLCO1B1 genotype and rifampicin pharmacokinetics were not altered by SLCO1B1 genotype.

Frequency of genetic polymorphisms of COX1, GPIIIa and P2Y1 in a Chinese population and association with attenuated response to aspirin

BACKGROUND Aspirin is a frequently prescribed drug for primary and secondary prevention of myocardial infarction, stroke and cardiovascular death. However, aspirin resistance may affect up to 45% of the population. Little is known on the role of genetic factors that contribute to resistance or augmented response to aspirin in different human populations. METHODS In a large sample of nonsmoker, medication-free healthy volunteers from mainland China (n = 323; age: 22.1 +/- 2.0 years) (mean +/- standard deviation), we determined the frequency of polymorphisms in cyclooxygenase 1 (COX1) (A-842G and C50T), glycoprotein IIIa (GPIIIa) (PLA1/A2) and purinergic receptor P2Y (P2Y1) (C893T and A1622G) genes. These candidate genes were chosen on the basis of their impact on platelet physiology and aspirin mode of action. A four panel P2Y1 genotype-stratified sample of healthy volunteers (n = 24 in total), identified from the large study sample above, prospectively received a 100 mg daily oral dose of aspirin for 7 days. We measured changes in platelet aggregation before and after aspirin treatment. As a comparison reference group, 6 out of 24 subjects in the prospective aspirin trial had the P2Y1 CT893/AG1622 genotype that displays a low frequency (<7%) in the Chinese population. RESULTS COX1 A-842G, C50T and GPIIIa PLA1/A2 genetic polymorphisms were not observed in our sample from mainland China. Allele frequencies of P2Y1 893T and 1622G were 3.5 and 30.6%, respectively. The heterozygosity for the P2Y1 A1622G polymorphism observed in the present study was different to Caucasians; Chinese displayed a higher allele frequency for the 1622G allele. After aspirin treatment, the net decrease in arachidonic acid-induced platelet aggregation was significantly larger in the P2Y1 CT893/AG1622 genotype panel (83.4 +/- 3.7%, net reduction by aspirin expressed as percentage of baseline) compared with CC893/GG1622 (68.2 +/- 13.5%), CC893/AG1622 (68.9 +/- 9.6%) and CC893/AA1622 (65.1 +/- 9.1%) genotypic groups (p = 0.012, 0.025 and 0.004, respectively; statistical power = 77%). There was no significant difference in antiplatelet effect of aspirin among the CC893/GG1622, CC893/AG1622 and CC893/AA1622 genotypes (p > 0.05). CONCLUSIONS The COX1 A-842G, C50T and GPIIIa PLA1/A2 polymorphisms are rare in Chinese. In contrast to previous studies in Caucasian populations, these candidate functional polymorphisms are unlikely to be significant contributors to aspirin pharmacodynamics in Chinese persons. Importantly, the presence of the P2Y1 893CC genotype appears to confer an attenuated antiplatelet effect during aspirin treatment in healthy Chinese volunteers. These data collectively underscore the importance of population-to-population variability in clinical pharmacogenetics research and provide a basis for further long-term studies of aspirin response and P2Y1 genetic variation in patients with cardiovascular risk.

Plant polyphenol curcumin significantly affects CYP1A2 and CYP2A6 activity in healthy, male Chinese volunteers.

Background: Curcumin is a kind of plant polyphenol that is extracted from the rhizome of Curcuma longa. Studies about the effect of curcumin on the activity of drug-metabolizing enzymes in humans are lacking. Objective: To investigate the effect of curcumin on the activities of CYP1A2, CYP2A6, N-acetyltransferase (NAT2), and xanthine oxidase (XO) in vivo, using caffeine as a probe drug. Method: Sixteen unrelated, healthy Chinese men were recruited for the study. There were 2 phases in the study. In the first phase, volunteers orally received 100 mg caffeine and 0- to 12-hour blood and urine samples were collected. In the second phase, volunteers received 1000 mg curcumin once daily for 14 continuous days, and blood and urine samples were collected on day 15, following the same procedure used on the first day. Urinary caffeine metabolite ratios were used as the indicators of the activities of CYP1A2, CYP2A6, NAT2, and XO. The pharmacokinetics of caffeine and its metabolites were determined by high-performance liquid chromatography. Results: In the curcumin-treated group, CYP1A2 activity was decreased by 28.6% (95% CI 15.6 to 41.B; p < 0.000), while increases were observed in CYP2A6 (by 48.9%; 95% CI 25.3 to 72.4; p < 0.000). Plasma area under the curve from zero to 12 hours of 1,7-dimethylxanthine (17X) was decreased by 27.2% (95% CI 6.1 to 48.3; p = 0.014). The urinary excretion of 17X and 1-methylxanthine was significantly decreased by 36.4% (95% C119.4 to 53.6; p < 0.000) and 31.2% (95% CI 8.5 to 54.1; p = 0.010), respectively. The excretion of 1,7-dimethylurate (17U) was significantly increased by 77.3% (95% CI 5.6 to 148.8; p = 0.036). No significant changes were observed for caffeine, 1-methylurate, and 5-acetyiamino-6-formylamino-3-methyluracil between the 2 study phases. Conclusions: The results indicated that curcumin inhibits CYP1A2 function but enhances CYP2A6 activity. Simultaneously, some pharmacokinetic parameters relating lo 17X were affected by curcumin. If this finding is confirmed by other studies, the possibility of herb-drug interactions associated with curcumin should be considered in clinical practice,

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.

INHIBITION OF ADP-INDUCED PLATELET AGGREGATION BY CLOPIDOGREL IS RELATED TO CYP2C19 GENETIC POLYMORPHISMS

1 Clopidogrel is one of the most important antithrombotic drugs but has different efficacies in different populations. The aim of the present study was to evaluate the contribution of CYP2C19 genetic polymorphisms to the inhibition of ADP‐induced platelet aggregation by clopidogrel in healthy Chinese volunteers. 2 Eighteen healthy male volunteers (six CYP2C19*1/CYP2C19*1, six CYP2C19*1/CYP2C19*2and*3 and six CYP2C19*2/CYP2C19*2and*3) were enrolled in the study. Each subject took 300 mg clopidogrel on the first day and then 75 mg once daily for 2 consecutive days. Blood samples were taken to measure ADP‐induced platelet aggregation at baseline and 4, 24 and 72 h after administration of the first dose of clopidogrel. 3 There were significant decrease in 2 and 5 mmol/L ADP‐induced platelet aggregation at 4, 24 and 72 h after clopidogrel among the three CYP2C19 genotypes compared with baseline (P < 0.001). The change in 5 mmol/L ADP‐induced platelet aggregation in subjects with the CYP2C19*1/CYP2C19*1 genotype was greater than that in subjects with the CYP2C19*2/CYP2C19*2and*3 genotype at 4 h (49.0 ± 15.5 vs 29.7 ± 17.4%, respectively; P = 0.029), 24 h (48.7 ± 20.5 vs 25.0 ± 17.6%, respectively; P = 0.035) and 72 h (45.5 ± 15.2 vs 26.5 ± 15.8%, respectively; P = 0.030) after clopidogrel administration. 4 In conclusion, CYP2C19*2 and CYP2C19*3 genetic polymorphisms reduced clopidogrel inhibition of ADP‐induced platelet aggregation, with the degree of inhition dependent on the genetic polymorphism present.

Effects of the CYP2C9*13 allele on the pharmacokinetics of losartan in healthy male subjects

The aim of the study was to determine the pharmacokinetics of losartan in relation to the CYP2C9*13 allele. A single oral dose of 50 mg losartan was administrated to each of the 16 healthy male volunteers with a different genotype (CYP2C9*1/*1, n = 6; CYP2C9*1/*13, n = 4; and CYP2C9*1/*3, n = 6). Blood samples were collected from pre-dose up to 24 h after the drug administration. Plasma losartan and E3174 (an active metabolite of losartan) were assayed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). All the subjects finished the study without adverse drug effects. In the present study, the frequencies of CYP2C9*13 and *13 alleles were 0.6% and 2.6% in Chinese healthy volunteers, respectively, and both alleles were in Hardy–Weinberg equilibrium. Compared with the subjects in the CYP2C9*1/*1 group, individuals carrying the CYP2C9*1/*13 genotype showed significantly a longer t1/2 of losartan and E3174 and markedly increased the area under the curve (AUC) of losartan. Meanwhile, the CYP2C9*1/*3 genotype group had significant differences in t1/2 and Cmax of E3174 compared with the CYP2C9*1/*1 group. The ratio of AUCE3174/AUClosartan after losartan administration in the CYP2C9*1/*13 and CYP2C9*1/*3 groups was also statistically different from that in the CYP2C9*1/*1 group. The data indicate that the presence of the CYP2C9*13 allele results in poor metabolism of losartan after a single oral dose.

Effect of 393T>C Polymorphism of GNAS1 Gene on Dobutamine Response in Chinese Healthy Subjects

The purpose of this study was to characterize the functional consequences of the 393T>C polymorphism of the GNAS1 gene in vivo. PCR‐RFLP assays were used to identify GNAS1 and β1‐adrenoceptor genotypes. The heart rate (HR), blood pressure, left ventricular fractional shortening (LVFS), and left ventricular ejection fraction (LVEF) were determined in different genotypes through a modified dobutamine stress echocardiography protocol. Our results showed that individuals with homozygous or heterozygous C393 had an increased cardiovascular agonistic response to dobutamine, and the increases from baseline in LVFS at the 3 dosage levels of dobutamine were 19.3% ± 1.0% versus 32.0% ± 2.9%, 36.7% ± 3.1% versus 41.3% ± 4.1%, and 51.7% ± 3.3% versus 58.7% ± 2.6% in T393 homozygotes and C393 homozygotes or heterozygotes, respectively (P = .026). Significant differences were also found between these 2 groups with the increases from baseline in LVEF (P = .007) and SBP (P = .048). In addition, there were significant differences in the increases from atopine in LVFS (P = .011), LVEF (P = .004), and SBP (P = .046) between the T393 homozygotes and C393 homozygotes or heterozygotes. The change of LVEF in C393 homozygous was higher than that in T393 homozygous at the dose of 40 μg/kg/min (28.9% ± 4.0% vs 36.4% ± 2.1%; 95% CI, 18.8%‐38.9%; P = .046). These data suggested that the 393T>C polymorphism of GNAS1 was functionally relevant in vivo.

Effect of carboxylesterase 1 S75N on clopidogrel therapy among acute coronary syndrome patients

Carboxylesterase 1 (CES1) hydrolyzes the prodrug clopidogrel to an inactive carboxylic acid metabolite. The effects of CES1 S75N (rs2307240,C>T) on clopidogrel response among 851 acute coronary syndrome patients who came from the north, central and south of China were studied. The occurrence ratios of each endpoint in the CC group were significantly higher than in the CT + TT group for cerebrovascular events (14% vs 4.8%, p < 0.001, OR = 0.31), acute myocardial infarction (15.1% vs 6.1%, p < 0.001, OR = 0.37) and unstable angina (62.8% vs 37.7%, p < 0.001, OR = 0.36). The results showed that there was a significant association between CES1 S75N (rs2307240) and the outcome of clopidogrel therapy. Moreover, the frequency of the T allele of rs2307240 in acute coronary syndrome patients (MAF = 0.22) was more than four times higher than that in the general public (MAF = 0.05).

Effects of four novel genetic polymorphisms on clopidogrel efficacy in Chinese acute coronary syndromes patients

Dual antiplatelet therapy is the gold standard for the clinical treatment of coronary artery disease, especially for acute coronary syndromes patients. However, a substantial number of patients do not respond to clopidogrel despite a standardized dosage regimen, and this is directly associated with poor prognosis. Genetic polymorphisms may be one of the most important factors that contribute to this phenomenon. In this study, we aimed to detect new single nucleotide polymorphisms that can influence the efficacy of clopidogrel in 851 acute coronary syndromes (ACS) patients. Four outcomes (cerebrovascular event, Acute Myocardium Infarction, unstable angina and death) were used as endpoints among three cohorts (northern, central and southern China) of acute coronary syndromes patients. Three SNPs (rs2244923, rs2773341 and rs34428341) were significantly associated with at least one outcome in all subjects. One SNP rs16863352, may play a role in predicting unstable angina in acute coronary syndrome patients ≥75years of age.