Kinetic difference in the inhibitory activity of statins among hOATP1B1, hOATP1B3 and rOATP1B2 in MDCK cells

Abstract

Objective. Human organic anion-transporting polypeptide 1B1 (hOATP1B1) and Human organic anion transporting polypeptide 1B3 (hOATP1B3) are both selectively expressed in the liver, where they are localized to the basolateral membrane of hepatocytes. hOATP1B1 and hOATP1B3 have a single rodent orthologue, rOATP1B2. Despite the transporters was classified as the crucial transporter for screening candidates of new drugs, the specie-difference considering transport kinetics has not been systematically studied for the transporter. The objective of this study is to evaluate Ki values for commercially available statins in in vitro system expressing the OATP1B transporters. Methods. The functional expression of the transporters was determined by comparing the uptake ability of radiolabeled estradiol-17β-D-glucuronide (a standard substrate). Inhibition studies were carried out to determine the IC50 for commercially available of statins. The IC50 values were converted to absolute inhibition constant Ki using the Cheng-Prusoff equation. One way ANOVA was used to compare Ki among hOATP1B1, hOATP1B3, and rOATP1B2. Results. Among the eight statins study, four drugs were interacted with human and rat forms to a certain extent. No functional difference was found for type I statins (i.e., pravastatin, mevastatin, simvastatin, lovastatin). The inhibition constants for pravastatin were 24.06 ± 1.88, 40.14 ± 10.48, and 27.61 ± 8.16 μM in hOATP1B1, hOATP1B3 and rOATP1B2 expressing cells. The Ki values for mevastatin were 8.97 ± 4.39, 11.90 ± 2.50, and 12.29 ± 5.51 μM in hOATP1B1, hOATP1B3 and rOATP1B2 cells. The Ki values for simvastatin were 10.61 ± 4.51, 8.52 ± 3.73 and 13.69 ± 6.04 μM in hOATP1B1, hOATP1B3 and rOATP1B2 cells. The Ki values for lovastatin were 12.70 ± 6.02, 14.63 ± 3.88, and 11.99 ± 5.06 μM in hOATP1B1, hOATP1B3 and rOATP1B2 cells. All type II (i.e., fluvastatin, atorvastatin, rosuvastatin) and type III statins (pitavastatin) examined the functional difference. The Ki values for fluvastatin were 2.22 ± 0.35, 2.59 ± 0.42 and 4.15 ± 0.85 μM in hOATP1B1, hOATP1B3 and rOATP1B2 cells. The Ki values in rOATP1B2 cells was significant different from those with hOATP1B1. The Ki values for atorvastatin were 0.62 ± 0.34, 0.92 ± 0.16 and 2.05 ± 0.16 μM in hOATP1B1, hOATP1B3 and rOATP1B2 cells. The Ki value in rOATP1B2 cells was significant different from those in hOATP1B1/hOATP1B3 cells. The Ki values for rosuvastatin were 6.99 ± 3.23, 10.14 ± 0.95 and 2.98 ± 1.07 μM in hOATP1B1, hOATP1B3, rOATP1B2 cells. The Ki values in rOATP1B2 cells was significant different from those in hOATP1B3 cells. The Ki values for pitavastatin were 1.07 ± 0.16, 0.91 ± 0.36 and 2.26 ± 0.57 μM in hOATP1B1, hOATP1B3 and rOATP1B2 cells. The Ki value in rOATP1B2 cells was significant different from those in hOATP1B1/hOATP1B3 cells. Conclusion. The functional differences among hOATP1B1, hOATP1B3, and rOATP1B2 were noted for four of eight statins studied. In particular, no functional difference was found for type I statins, while all type II and III statins examined had the functional difference, suggesting that the kinetic differences among OATP1B transporters are depend on chemical structures of substrates. This aspect of OATP1B transport warrants further research.