Functional analysis of single nucleotide polymorphisms of hepatic organic anion transporter OATP1B1 (OATP-C)

Objective: Two kinds of single nucleotide polymorphism (SNP; Asn130Asp and Val174Ala) are frequently observed in the liver specific transporter, organic anion transporting polypeptide 1B1 (OATP1B1/OATP-C) gene. Although these two SNPs occur independently in European-Americans, Val174Ala is mostly associated with Asn130Asp in Japanese. Our previous in-vivo studies in Japanese subjects indicated that the non-renal clearance of pravastatin was decreased to 13% of that in wild-type subjects (Nishizato et al. Clin Pharmacol Ther 2003;73(6):554-564). The purpose of the present study is to characterize the function of SNPs variants of OATP1B1 in cDNA transfected cells. Methods: The localization and transport activity were analyzed in HEK293 cells stably expressing wild-type OATP1B1 (OATP1B1*1a), OATP1B1*1b (Asn130Asp), OATP1B1*5 (Val174AIa) and OATP1B1*15 (Asn130Asp and Val174AIa). To characterize the intrinsic V_max, observed V_max in uptake study were normalized by the expression level estimated from Western blotting. Results: All SNP variants are predominantly located on the cell surface. No significant alteration was observed in K_m values for the transport of 17β-estradiol 17β-D-glucuronide (E₂17βG), a typical substrate of OATP1B1, among these SNP variants. However, the normalized V _max value for OATP1B1*15 was drastically decreased to less than 30% compared with OATP1B1*1a. In contrast, the transport activity of OATP1B1*1 b (Asn130Asp) and OATP1B1*5 (Val 174AIa) was similar to that of OATP1B1*1 a. Conclusions: These results are consistent with the results of our previous clinical studies. It is thus suggested that in-vivo disposition may be predicted from in-vitro results using recombinant transporters.