Received for publication January 28, 2008.
Revised June 9, 2008.
Accepted for publication June 10, 2008.

UTILITY OF THE OATP1B2 KNOCKOUT MOUSE MODEL FOR EVALUATING THE ROLE OF OATP1B2 IN THE HEPATIC UPTAKE OF MODEL COMPOUNDS

Abstract

We generated the organic anion transporting polypepetide (Oatp) 1b2 knockout (KO) mouse model and assessed its utility to study hepatic uptake using model compounds (cerivastatin, lovastatin acid, pravastatin, simvastatin acid, rifampicin, and rifamycin SV) that are known to interact with OATP1B1. A selective panel of liver P450s (Cyp3a11, 13, 16; 2c29 and 39) and transporters (Oatp 1b2, 1a1, 1a4, 1a5; Oat1, Oat2, Oat3; Mdr1a, 1b; Bsep, Mrp2, Mrp3; Bcrp) were measured by RT-PCR in both KO and wild-type (WT) male mice. Male KO and WT mice received each model compound subcutaneously at 3 mg/kg. Blood and liver samples were obtained at 0, 0.5, and 2 h post dose and analyzed using LC/MS/MS. Liver/plasma concentration ratio (K_p,liver) was calculated. Student's t-test was used to compare the mRNA and K_p,liver between the KO and WT mice. A similar mRNA expression was observed between the KO and WT for the selected P450s and transporters, except for Oatp1b2 for which the level was negligible in the KO but prominent in the WT mice with P<0.0001. The in vivo results demonstrated a differential effect of Oatp1b2 on hepatic uptake of the model compounds, indicating that Oatp1b2 plays a more significant role in the hepatobiliary disposition of rifampicin and lovastatin acid than the other compounds tested. This study suggests a potential species difference in substrate specificity between Oatp1b2 and OATP1B1 and highlights the Oatp1b2 mouse as a useful in vivo tool to understand drug targeting and disposition in the liver.

Key words: ABC transporters, active transport, hepatic uptake, hepatobiliary disposition, hepatobiliary transport, organic anion transport, pharmacokinetics, transgenic models