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 (OATP1B11a), OATP1B11b (Asn130Asp), OATP1B15 (Val174Ala) and OATP1B115 (Asn130Asp and Val174Ala). To characterize the intrinsic Vmax, observed Vmax 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 Km values for the transport of 17beta-estradiol 17beta-d-glucuronide (E217betaG), a typical substrate of OATP1B1, among these SNP variants. However, the normalized Vmax value for OATP1B115 was drastically decreased to less than 30% compared with OATP1B11a. In contrast, the transport activity of OATP1B11b (Asn130Asp) and OATP1B15 (Val 174Ala) was similar to that of OATP1B1*1a.

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.