Organic Anion Transporting Polypeptide 1b1 Genetic Polymorphisms On Pravastatin Pharmacokinetics,

Pravastatin is widely used in the treatment of hypercholesterolemia. The carrier- mediated hepatic uptake of this hydrophilic compound is responsible for its hepatoselective disposition and inhibition of cholesterol synthesis. However, various pharmacokinetic studies have revealed highly intersubject variabilities in blood plasma levels of pravastatin. Because OATP1B1 is thought to be the major hepatocellular uptake carrier of pravastatin, at least part of this interindividual variability was assumed to be attributed to polymorphic expression of this transport system.OATP1B1 is exclusively expressed at the basolateral membrane of hepatocytes. Various genetic polymorphisms have been identified in this gene by different groups, and most of the genetic variants could be demonstrated to significantly diminish in vitro transport of estrone-3-sulfate and estradiol-17β-glucuronide, which are specific substrates of OATP1B1, and these variants may affect the pharmacokinetic process of pravastatin. There has been no such study in China by far, so we want to gain an insight into the distribution of OATP1B1 genotypes in Han population, and the effect of the genetic polymorphism on the pharmacokinetic profile of pravastatin.In this study, a HPLC assay for the determination ofpravastatin in human plasma was developed. The method was sensitive, accurate and precise. It was suitable for the determination of pravastatin in the study of pharmacokinetics. In addition, polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and allele specific-polymerase chain reaction (AS-PCR) were used to detect the common haplotypes of OATP1BI: SLCO1B1^*1a, SLCO1B1^*1b, SLCO1B1^*5 and SLCO1B1^*15.Based on the method of the genotype analysis, 180 Han subjects (137 male, 43 female) were genotyped. The frequencies of 388A, 388G, 521T and 521C were 0.294, 0.706, 0.908 and 0.092, respectively. The frequencies of SLCO1B1^*1a, SLCO1B1^*1b and SLCO1B¹*15 were 0.294, 0.614, 0.092, respectively, however, no SLCO1B1^*5 was found. The frequencies of SLCO1B1^*1a/^*1a, SLCO1B1^*1b/^*1b, SLCO1B1^*1a/^*1b, SLCO1B1^*1a/^*15, SLCO1B1^*1b/^*15 and SLCO1B1^*15/^*15 were 0.078, 0.372, 0.372, 0.061, 0.111 and 0.006, respectively. The most common haplotype in Han population was SLCO1B1^* 1b, the frequency of SLCO1B1^*15 was high, and a SLCO1B1^*15 homozygous carrier was found.At the same time, the effect of the genetic polymorphism of OATP1B1 on the pharmacokinetic profile of pravastatin was studied. 18 healthy subjects (13 male, 5 female) with the genotypes of SLCO1B1^*1b/^*1b, SLCO1B1^*1a/^*15 SLCO1B1^*1b/^*15 or SLCO1B1^*15/^*15 were chosen and grouped according to their OATP1B1 genotypes:^*1b homozygous carriers (n=9, 7 male, 2 female), ^*15 heterozygous carriers (n=8, 5 male, 3 female) and ^*15 homozygous carrier (n=1, male). Serial blood samples were collected from an indwelling venous catheter immediately before and at 0.33h, 0.67h, 1h, 1.5h, 2h, 3h, 4h, 5h, 6h, 8h after 40mg pravastatin administration. Plasma pravastatin concentration was assayed with HPLC-UV method. The pharmacokinetic parameters of pravastatin of every subject ware analyzed. The statistical differences between SLCO1B1^*1b homozygous carriers and SLCO1B1^*15 heterozygous carriers were determined with Mann-Whitney U test. It was showed that the values of C_max in *1b homo zygous carriers and *15 heterozygous carriers were 116.06±46.22ng·mL^-1 and 173.36±36.23ng·mL^-1, respectively, with significant difference (p=0.011＜0.05). The AUC_0-8h (p=0.093＜0.05), AUC_0-∝ (p=0.370＞0.05), T_max (p=0.139＞0.05), t₁/2 (p=0.093＞0.05) and CL/F (p=0.114＞0.05) had no significant differences between two study groups. Strikingly, the C_max and AUC_0-8h in SLCO1B1*15 homozygous carrier were 401.76ng·mL^-1 and 660.05h·ng·mL^-1, respectively, the C_max was 3.46 and 2.32 times of that of SLCO1B1*1b homozygous carriers and SLCO1B1*15 heterozygous carriers, and the AUC_0-8h was 2.67 and 2.09 times of that of SLCO1B1*1b homozygous carriers and SLCO1B1*15 heterozygous carriers, respectively. The values of CL/F in SLCO1B1*15 heterozygous carriers (126.96±24.68L·h^-1) was lower than that of SLCO1B1*1b homozygous carriers (168.12±53.20L·h^-1) by 41.16L·h^-1, and the CL/F in SLCO1B1*15 homozygous carrier (59.60L·h^-1) was lowest among all subjects, which was 35.45% and 46.94% of that of SLCO1B1*1b homozygous carriers and SLCO1B1*15 heterozygous carriers.In conclusion, there was genetic polymorphism of OATP1B1 in Han population. SLCO1B1*1b was the most common haplotype, and SLCO1B1*15 was common, too. The genetic polymorphism of OATP1B1 had effect on the pharmacokinetic profile of pravastatin. The SLCO1B1*15 carriers had higher concentration after taking pravastatin, especially the SLCO1B1*15 homozygous carrier. Though the frequency of SLCO1B1*15/*15 was low (1/180), however, because of its significant effct on pravastatin pharmacokinetics, further study on the influence of SLCO1B1*15/*15 on the pharmacokinetics and pharmacodynamics of pravastatin had underlying clinical values.