Effects Of SLC22A1 And SLC21A6 Genetic Polymorphisms On Pharmacokinetics And Pharmacodynamics Of Oral Hypoglycemic Agents

Diabetes which is gathering more and more attentions as a great disater to human physical and mental health,will be a main subject of public health problem and have a victim population of 380 million by 2025,as pointed out by the WHO.In China,the occurance ratio has reached 2%by now,and has rank in the second in the world by a victim population of 40 million,with an annual increasement of 1 million.The current recommended therapies for patients with definite diagnosis of diabetes are mainly based on the mechanism of hypoglycemic agents, such as sulfonylureas,thiazolidinediones,meglitinides,biguanides and a-glucosidase inhibitor.Among the agents mentioned above,metformin and repaglinide is the two most frequently used in practice.As proved in many studies,the clinical uses of metformin and repaglinide are accompanied with signifiant inter-individual differences in drug metabolism and drug reaction,and these differences could be led to by differences in gender, age,body weight,disease status quo and many other factors.But studies of pharmacogenetics in recent two decades suggest that it is genetic factors,the polymorphism of the genes which coding the drug metabolizing enzymes,transporters,receptors that lead to the difference in protein function,and then have a result in significiant difference in plasam drug concentration and drug sensitivity.The genetic factor of transporters is the main cause of the metformin and repaglinide drug reaction inter-individual differences,rather than drug metabolizing enzymes and drug receptors.Among frequently mentioned transporters which occupied in drug disposition,it is organic cation transporter 1(OCT1) who excuites the job of metformin transportation.The transportation of repaglinide is mainly processed by organic anion transporting polypeptide 1B1(OATP1B1, also known as LST1,OATP-C,OATP2).Both OCT1 and OATP1B1 are transporting proteins exist in the basolateral hepatocyte membrane and transport drug into hepatocytes,their coding genes are SLC22A1 and SLC21A6 respectively.SLC22A1 and SLC21A6 are the genes with polymorphisms and transporters coded by these genes will be different in function according to their polymorphisms,and as a result the tranportations of the substrates will be different.According to the knowledge we have,the mutation A388G and T521C in SLC21A6 could lead to Asn130Asp and Val174Ala amino acid residual substitutions,result in genotype *1b(Asn130Asp),*5(Val174Ala) and haplotype *15(A388G and T521C,Asn130Asp and Val174Ala) among which *15 in the mutation of SLC21A6 is commonly seen in Chinese population and has a great influence on the pharmacokinetics and pharmacodynamics of many agents with repaglinide included.The pharmacogenetic studies about SLC22A1 was launched comparatively late,but with aggressive sequencing on large volumns of samples,a series of specialized mutation was found,among which mutations C848T,C859G and C1022T which can lead to amino acid substitutions as Pro283Leu,Arg287Gly and Pro341Leu can change the transporting function of OCT1.The incidence rate and functional significance in vivo still needs further studies to figure out.Besides the direct genetic polymorphism influence of drug transporter on the pharmacokinetics and pharmacodynamics,genetic polymorphism can have its effects via drug-drug interection to influence the PK and PD process.Successive administration of rifampin can induce the OATP1B1,and the pharmacokinetics and pharmacodynamics will be affected when co-administrate with substrate repaglinide.This phenomenon is significiantly correlated with the genotype of SLC21A6, and this drug-drug interaction based on the inducement of OATP1B1 has already been included in the instruction of repaglinide.But some other studies show that rifampin could be a substrate of OATP1B1 as well,so will single does of rifampin have inhibitive influence on repaglinide via competitive binding with OATP1B1 and is this kind of interaction has something to do with SLC22A1 genetype still remain questions and needs further studies.Besides OATP1B1,rifampin can induce many drug metabolizing enzymes and drug transporters such as CYP2C9 and MDR1.According to the knowledge we got from mice,OCT1 is another drug transporter which can be induced by rifampin,so it is necessory to find out whether this kind of inducement exist in human and whether this inducement could affect the PK and PD of metformin and whether this drug-drug interaction is related with the genetype of SLC22A1.With the background of the studies mentioned above,in this study we mainly aim to find out the distribution of common mutation of SLC22A1 in population of healthy Chinese,to investgate the influence of SLC21A6 genetic polymorphism on the PK and PD process of metformin via a clinical trial specilly designed for this purpose.Our clinical trials are also specially designed for the purpose of investgating the influence of successive adminastration of rifampin on the PK and PD process of metformin,the influence of single does rifampin on the PK and PD process of repagflinide,and the correlation between these influences and the genetic polymorphism.By these studies,we hope to achieve a guide for the personalized therapy for diabetes in clinic practice.Meanwhile,it's necessory to genotype SLC22A1,SLC21A6 and many other drug related genes to carry out thisstudy and the personalized therapies for diabetes.Genotyping measures available are many,such as PCR-RFLP,PCR-SSP,manual and automatic sequencing,which all have disadvantages in common,such as inconveniance of operation,great cost of time during a test,limited samples,and comparatively uncontrollable. So its application in scientific research and clinical test is limited. Compare with these disadvantages of conventional methods,microarray chip is portable,low cost,enviroment friendly,highly automatical,fast, and needs small amount of sample or reagents.But the commom SSOP gene chip has a problem of none-specific hybridization which is unconquerable during its application.So in this study we hope to find a solution to this problem.We got the findings list as below:1.The frequencies of the SLC22A1 1022C＞T and SLC22A1 848C＞T variant alleles in Chinese population were 11.8%and 0.8%, respectively.The mutations of SLC22A1 859 C＞G was not detected in Chinese.2.The pharmacokinetics and pharmacodynamics of metformin in vivo is significantly influenced by SLC22A1 1022C＞T and SLC22A1 848C＞T genotype in healthy subjects.3.Repeated doses of 600mg rifampin had a significant effect on the pharmacodynamics of metformin.SLC22A1 1022C＞T gene polymorphism significantly influence the effect of rifampin.4.Single oral dose of 600mg rifampin had a significant effect on the pharmacokinetics and pharmacodynamics of repaglinide.SLC21A6 521T＞C gene polymorphism significantly influence the inhibition effect of rifampin on the activity of OATP1B1.5.5,A double probe microarry chip for genetic mutation test based on allele specific proliferation was created,and a microarry chip kit for SLC22A1 and SLC21A6 genotyping in the drug treatment of diabetes was invented. As far as we know,it's the first identification of Chinese SCL22A1 polymorphisms in any kind of publication,and also the study of influence of SLC22A1 polymorphism on the PK and PD process.For the first time successive adminstration of rifampin was proved to have an inductive effect over OCT1 and a single does of rifampin to have an inhibitive effect on the transporting activity of OATP1B1,and the correlation between these effects and the genetic polymorphisms was indentified.A novel method of gene mutation test based on double probe proliferation was created and with the application of this method a genotyping microarry kit was invented.The findings of this study could be a guide and tool in the avoidance of potential hazard drug-drug interaction and clinical use of metformin and repaglinide and other hypoglycemic agents.