Primary Active Transport of Provastatin Across the Liver Canalicular Membrane in Normal and Mutant Eisai Hyperbilirubinaemic Rats

Abstract

We have previously demonstrated that the HMG‐CoA reductase inhibitor pravastatin is efficiently taken up by the liver via the ‘multispecific anion transporter’ in an active manner.3 To further examine the fate of pravastatin within the liver, its biliary excretion was studied in a single‐pass liver perfusion system and isolated liver canalicular membrane vesicles (CMVs) using normal (Sprague–Dawley rats; SDRs) and mutant Eisai hyperbilirubinaemic rats (EHBRs). In the liver perfusion experiments, the outflowing drug concentration reached a steady state at 30 min and the extraction ratio was approximately 0·7 in both rat strains. Both the steady state biliary excretion rate and bile flow rate of the EHBR group were 40% of those of SDRS. At steady state, the fraction of unchanged drug in bile was 25–34% in both groups. The concentration ratios of unbound drug in cytosol versus that in sinusoid and of that in bile versus that in cytosol were, respectively, 11 and 87 in SDRs, and 13 and 94 in EHBRs. After correction for the membrane potential (−40 mV in cytosol), the ratios became 49 and 19 in SDR and 58 and 21 in EHBRs, respectively. The finding that all of these values were much larger than unity suggested that active transport occurred from liver to bile, as well as from plasma to liver, in both rat strains. Furthermore, ATP‐dependent uptake of pravastatin was clearly observed in CMVs prepared from EHBRs as well as SDRs, whereas the stimulation by ATP of DNP‐SG transport in CMVs was observed only in SDRs. It was concluded that pravastatin is excreted into bile in high concentrations and a primary active transport mechanism which is maintained in EHBRs contributes to the biliary excretion of this drug.

Intestinal Absorption of HMG-CoA Reductase Inhibitor Pravastatin Mediated by Organic Anion Transporting Polypeptide

“…However, Oat3-mediated transport does not account for the naringinsensitive pravastatin absorption observed in the present study because Oat3 is not expressed in rat intestine (35). Pravastatin is also reported to be a substrate of multidrug resistance-associated protein 2 (Mrp2) expressed in the bile canalicular membrane, based on comparative studies of biliary excretion of pravastatin in normal and Mrp2-dysfunctional Eisai hyperbilirubinemic rats (EHBR) (10,36). Therefore, Mrp2 is considered to be one of the transporters involved in the intestinal absorption process of pravastatin.…”

DISPOSITION OF ORAL AND INTRAVENOUS PRAVASTATIN IN MRP2-DEFICIENT TR–RATS

“…The origins of this variation are not completely understood. The pharmacokinetics of pravastatin in rats are characterized by a low bioavailability, selective oatp-mediated uptake by the liver, substantial biliary excretion, and enterohepatic circulation (Komai et al, 1992;Yamazaki et al, 1996bYamazaki et al, ,c, 1997Hatanaka et al, 1998;Hsiang et al, 1999;Tokui et al, 1999). Only a small amount of pravastatin is excreted unchanged in the urine, and contribution of urinary excretion to total clearance is small (Komai et al, 1992;Hatanaka et al, 1998).…”

Saturation of Multidrug-Resistant Protein 2 (Mrp2/Abcc2)-Mediated Hepatobiliary Secretion: Nonlinear Pharmacokinetics of a Heterocyclic Compound in Rats after Intravenous Bolus Administration

“…However, dose-dependent nonlinear pharmacokinetics or saturable drug exposure is not observed in these mutant rats (Yamazaki et al, 1996;Kostrubsky et al, 2001). The findings indicate that substrates could be redirected from the canalicular to the sinusoidal membrane, then back into systemic circulation, and eventually secreted into urine.…”

“…The Mrp2-deficient animals, such as transport-deficient (TRϪ) and Eisai hyperbilirubinemic rats (EHBRs), have been used in the last decade as tools to study the importance of Mrp2/Abcc2-mediated hepatobiliary elimination (Sugawara et al, 1997). For instance, Yamazaki et al (1996) reported that the biliary secretion and total clearance of pravastatin were higher in normal rats, which resulted in 2-fold reduction in steady-state plasma concentration compared with Mrp2-deficient EHBRs. Similar work further confirmed the significant increase of systemic exposure and the decrease in biliary secretion of pravastatin (Kivistö et al, 2005) or troglitazone (Kostrubsky et al, 2001) in Mrp2-deficient TRϪ rats.…”