Effect Of SLC21A6 Gene Polymorphism On Lipid-lowering Efficacy Of Simvastatin And Atorvastatin

Background and ObjectiveThe aim of pharmacogenomics is to investigate the relationship between polymorphisms on human genome and the variability of response to a specific drug in population, to achieve further insight into mechanism of a disease and mechanism of different drug responses, and eventually to guide individualized clinical practice medications. SLC21A6 gene encodes organic anion transporting polypeptide 1B1 (OATP1B1, also known as LST-1, OATP-C and OATP2), which is a drug uptake transporter located at the sinusoidal membrane of hepatocytes. Several single nucleotide polymorphisms (SNPs) have been discovered in the SLC21A6 gene, some associated with altered in vitro transport activity. Simvastatin acid (SVA) that is activity metabolite of simvastatin, atorvatatin and its activity metabolites are all transport substrates of OATP1B1. It has been hypothesized that SLC21A6 gene polymorphisms have effect on OATP1B1 transport activity, and effect on the disposition of simvastatin and atorvastatin in vivo, which may in turn influence lipid-lowering efficacy of simvastatin and atorvastatin. In a Caucasian population, the proportions of SLC21A6 gene polymorphisms have been reported as, respectively, 46.6% and 20.2% for SLC21A6 388A>G and 521T>C; However, the distribution in Chinese hyperlipidemic patients was not reported, and little is known about the relationship of SLC21A6 gene polymorphisms with lipid-lowering efficacy of simvastatin and atorvastatin. In this study, we investigated the distribution of SLC21A6 gene polymorphisms in Chinese hyperlipidemic patients, and approached the effects of SLC21A6 gene polymorphisms on lipid-lowering efficacy of simvastatin and atorvastatin. The results can provide basis for the individualized medication and the use of this genetic screening to guide selection of lipid-lowering therapy.Subjects The subjects were enrolled in the First Affiliated Hospital of ZhengzhouUniversity and Pingdingshan first municipal people's hospital from November 2005 to August 2006, including 200 hyperlipidemic patients taking simvastatin (20mg/day) and 200 hyperlipidemic patients taking atorvastatin (20mg/day). The diagnostic criteria of hyperlipemia is total cholesterol (TC) >6.0mmol/L or low-density lipoprotein cholesterol (LDL-C)>3.36 mmol/L or triglycerides (TG)>1.78 mmol/L or high-density lipoprotein cholesterol (HDL-C) <0.82 mmol/L. The blood samples were obtained for lipids testing or DNA extraction before and 15, 30 days after statins intake. Serum TG, TC, LDL-C and high-density lipoprotein cholesterol (HDL-C) levels were determined using an automated analyzer. All subjects gave written informed consent and the study was approved by the Committee on Human Research of Zhengzhou University.Genotyping DNA was extracted from peripheral blood with the method ofphenol-chloroform. SLC21A6388A>G and 521T>C gene polymorphisms were screened by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) or Allele-specificity polymerase chain reaction (AS-PCR). Several samples each different genotype were sequenced to confirm the expected sequences of each genotype.Statistical analysis Statistical analysis was performed with SPSS software (Ver12.0, SPSS Inc., 202 Chicago, IL). Chi-square test was used to verify Hardy-Weinberg equilibrium. Interethnic differences in allelic frequencies were analyzed by Chi-square test or Fisher's exact test of probabilities. Statistical comparisons of lipid levels among different genotype groups and different time intervals were performed by repeat measurement ANOVA. P<0.05 was considered to be significant.ResultsDistribution of SLC21A6 gene polymorphisms The allelic frequencies of SLC21A6 SNPs were 72.1% for 388A>G, 16.2% for 512T>C in Chinese hyperlipidemic patients. The distribution of allele and genotype was consistent with Hardy-Weinberg equilibrium. The allelic frequency of SLC21A6 388A>G in Chinese hyperlipidemic patients is similar to that reported in normal African-American(P=0.727), but higher than normal Japanese, European-American and Finnish Caucasian(P= 0.007, P=0.000, P=0.000, respectively). The allelic frequency of SLC21A6 512T>C in Chinese hyperlipidemic patients is similar to that reported in normal Japanese (P= 0.884), European-American (P=0.621), but higher than normal African-American (P=0.000), lower than normal Finnish Caucasian (P=0.036).Lipid-lowering efficacy of simvastatin and atorvastatin The levels of TG, TC and LDL-C decreased significantly 15, 30 days after intake of simvastatin or atorvastatin (20mg/day). The level of HDL-C decreased significantly after 15 days, however, there was an upward tendency after 30 days.Effects of SLC21A6 388A>G and 521T>C on lipid-lowering efficacy of simvastatin and atorvastatin For SLC21A6 521T>C, after oral intake of simvastatin 20mg daily for 15 or 30 days, the percentage change of LDL-C level in TT, TC and CC genotype groups showed a significant difference (repeated measurement ANOVA, P=0.047); There was significant difference in the percentage change of LDL-C level between patients carrying the TC and TT genotype (29.1±5.6% vs 27.1±5.4%, ANOVA, P=0.029), The comparison between the percentage change of LDL-C level patients carrying the CC and TC genotype had not no statistically difference (30.8±5.4% vs 29.1±5.6%, ANOVA, P=0.593) after oral intake of simvastatin 20mg daily for 30 days, but the percentage change of TG, TC and HDL-C levels showed no significant difference; In contrast, after oral intake of atorvastatin 20mg daily for 15 or 30 days, we found no significant difference in the percentage change of TG, TC, LDL-C and HDL-C among patients carrying the TT, TC and CC genotype. Furthermore for SLC21A6 388A>G, 521T>C constitutive haplotypes, after taking simvastatin or atorvastatin 20mg daily for 15 or 30 days, the percentage change of lipid levels (TG, TC, LDL-C and HDL-C) in AATT, Ht(Heterozygote) and GGCC genotype groups showed no significant difference.Conclusions1. The allelic frequencies of SLC21A6 SNPs are 72.1% for 388A>G, 16.2% for 512T>C in Chinese hyperlipidemic patients.2. Hyperlipidemic patients can obtain satisfactory lipid-lowering efficacy taking simvastatin or atorvastatin 20mg daily.3. SLC21A6 521T>C gene polymorphism influence lipid-lowering efficacy of simvastatin, patients carrying 521C is more prominent efficacy than non-carrying 521C; SLC21A6 521T>C gene polymorphism did not influence lipid-lowering efficacy of atorvastatin.4. Haplotypes for SLC21A63SSA>G and 521T>C do not influence lipid-lowering efficacy of simvastatin and atorvastatin.