| Background:Warfarin, a commonly prescribed oral anticoagulant in patients with mechanical heart valve prostheses exhibits large interindividual differences in the dose required for its anticoagulation effect, there is greater than 20-fold interindividual variability in the dose required to attain a therapeutic response.For reducing risk of adverse drug reactions of warfarin, Information from pharmacogenomics, the study of the interaction of an individual's genotype and drug response, can help optimize drug efficacy while minimizing adverse drug reactions. Pharmacogenetic analysis of two genes, the warfarin metabolic enzyme Cytochrome P4502C9(CYP2C9)and warfarin target enzyme, Vitamin K epoxide reductase complex 1( VKORC1), confirmed their influence on warfarin maintenance dose.Several single nucleotide polymorphisms (SNPs) in VKORC1 are associated with warfarin dose across the normal dose range. Haplotypes based on VKORC1 - 1639A /G can explain a large fraction of the interindividual variation in warfarin dose.Yet there have been no extensive and thorough studies in this field in China so far. Especially in southwestern China.Therefore, in order to study the distribution of polymorphisms of CYP2C9 and VKORC1 - 1639A /G of Han nationality in China, we chose the 100 patients with mechanical heart valve prostheses at steady state of warfarin dosing, and the correlation between CYP2C9 genotype, VKORC1-1639A/G genotype, dosage requirements, plasma concentration of warfarin at steady state were investigated., The data were assessed by statistical analysis.Clinical materials and methods:1. Clinical materials in 100 patients were collected with mechanical heart valve prostheses treated with warfarin in Chongqing aera. The sexuality, etiological factors, pathological characters, operation mode, the type of mechanical valve, body weight, postoperative cardiac rhythm were analyzed for the warfarin dosing requirement. 2. A simple HPLC method was established for the determination of warfarin in plasma to investigate the relationship between warfarin concentration and anticoagulant effect.3. A PCR-RFLP method and a restriction enzyme digestion method was developed to determine CYP2C9 genotype and VKORC1-1639A/G genotype distribution in warfarin-treated 100 patients with mechanical heart valve prostheses at steady state of warfarin dosing patients, and the relationship between this genetic polymorphisms and interindividual variation in warfarin dose was analysised.Results:1. In 100 patients with mechanical heart valve prostheses treated with warfarin in Chongqing aera, the mean warfarin dosage was (2.68±1.04mg/d), and the dosage was significantly different among the groups of age(p<0.05). The mean warfarin dosage (2.14±0.60mg/d) of people above 60 years old was much less than the dosage of people below 60 years old (p <0.05). Warfarin dosage was also significantly positively correlated with postoperative cardiac rhythm(p <0.05 ); But gender(p >0.05)and positions of heart valve prostheses (p >0.05)had no significant effect on the mean warfarin daily dosage requirements.2. Warfarin concentrations in human plasma were determined by HPLC method. The results showed that during the INR range (1.5-2.0) recommended to Chinese, the patients had a mean warfarin level at (845.48±388.16 ng/ ml). Age, postoperative cardiac rhythm, g ender and positions of heart valve had no significant effect on warfarin steady concentration (p >0.05 ).3. VKORC1 -1639A allele and VKORC1-1639G were detected in 100 patients with mechanical heart valve prostheses treated with warfarin in Chongqing aera.The frequency of A allele and G allele was 92% and 2% separately.Three genotypes have been detected too. AA was the most common genotype, with the frequency of 86%. the frequency of AG was 12% , the frequency GG was less than 2%. Patients with VKORC1-1639GG allele, required a significantly higher warfarin dose (n=2; 6.56±0.44 mg/day) than those VKORC1-1639AG allele (n=12; 3.99±0.48 mg/day) and VKORC1-1639AA allele (n=86; 2.41±0.75 mg/day) (p<0.01).4. CYP2C9*1 and CYP2C9*3 were detected in these patients too. The frequencies of CYP2C9*1 and CYP2C9 *3 were 98% and 2%, respectively. CYP2C9 *2 variant allele was not found in this study .Two genotypes CYP2C9*1/ *1and CYP2C9*1/ *3 hed been detected. There were statistically differences in warfarin concentrations in human plasma between the CYP2C9*1/*1 (n=95; 805.50±329.77ng/ml) and CYP2C9*1/*3 (n = 5; 1640.95±287.89ng/ml) (p< 0.01).5.In 100 patients with mechanical heart valve prostheses treated with warfarin in Chongqing aera,the distribution of genotypes was VKORC1-1639AA/ CYP2C9*1/*1(n=82), with the mean warfarin daily dosage(2.43±0.70mg/d) and warfarin concentration (777.72±311.31ng/ml);VKORC1-1639AG/CYP2C9*1/*1(n=12), with the mean warfarin daily dosage(4.10±0.48mg/d) and warfarin concentration(985.86±416.24 ng/ml); VKORC1- 1639AA/CYP2C9*1/*3(n=4), with the mean warfarin daily dosage(1.61±0.66 mg/d) and warfarin concentration(1323.43±155.55 ng/ml); VKORC1-1639GG/CYP2C9*1/*1 (n=1), with the mean warfarin daily dosage(6.25±0.00mg/d) and warfarin concentration (919.95±0.00ng/ml);and VKORC1-1639GG/ CYP2C9*1/*3(n=1), with the mean warfarin daily dosage(6.88±0.00mg/d) and warfarin concentration (2731.02±0.00ng/ml). There were statistically differences in warfarin doses and warfarin concentrations among these genotypes (p< 0.01).Conclusion:1. In 100 patients with mechanical heart valve prostheses treated with warfarin in Chongqing aera, the mean warfarin dosage was (2.68±1.04mg/d). Warfarin dosage requirements was significantly positively correlated with age, postoperative cardiac rhythm, but not with gender and positions of heart valve prostheses.2. VKORC1-1639A /G polymorphism had a dominant genetic influence on interindividual warfarin dosage variability than CYP2C9 polymorphism did in Chinese southwestern patients. In the present study, we found that the patients with VKORC1-1639GG allele, required a significantly higher warfarin dose (2.41±0.75 mg/d) than the patients with VKORC1-1639AG allele (3.99±0.48 mg/d) and VKORC1-1639AA allele(3.99±0.48 mg/d) did.3. CYP2C9 had a significantly role in interindividual differences in the warfarin concentrations. Patients with CYP2C9*1/*3 allele had a significantly higher warfarin concentrations (1640.95±287.89ng/ml) than patients with CYP2C9*1/*1 allele (805.50±329.77ng/ml) did. 4. The analysis of the VKORC1 - 1639A /G and CYP2C9 genotypes may be important to guide warfarin dose selection and allow personalized warfarin treatment. In 100 patients with mechanical heart valve prostheses treated with warfarin in Chongqing aera, patients with the genotype of VKORC1-1639AA/ CYP2C9*1/*3 had a significantly lower warfarin dose and higher warfarin concentration, which had the risk of major bleeding events; while patients with the genotypes of VKORC1-1639GG/CYP2C9*1/*1, VKORC1-1639AG/ CYP2C9*1/*1 and VKORC1-1639GG/CYP2C9*1/*3 had a signifcantly higher warfarin dose and lower warfarin concentrations, which had the risk of thromboembolism events. Thus, much more attention shoud be payed to patiens with this two genotypes in order to decrease the frequencies of overanticoagulation and the duration of dosage regulation.
|
PDF Full Text Request