Background and aim: Eisai hyperbilirubinuria rats (EHBR) are animal models of Dubin-Johnson syndrome, which suffer from jaundice due to impaired biliary excretion of bilirubin glucuronides. In EHBR, deficiency of multidrug resistance-associated protein 2 (mrp2) causes defective biliary excretion of numerous organic anions. However, little is known about the expression of other organic anion transporters in this mrp2-deficient model. The aim of the present study was to investigate adaptive expressions of mrp1, mrp3, mrp6, organic anion transporting polypeptide 1 (oatp1) and oatp2 in liver and kidney of EHBR.
Methods: For the present study, EHBR (n = 5) were used. Hepatic and renal mRNA expression of the aforementioned transporters was determined by constructed semiquantitative reverse transcription polymerase chain reaction assay. Their protein expression was determined by western blotting. Localization of hepatic and renal mrp3 was confirmed by immunohistochemistry. Sprague-Dawley (SD) rats (n = 5) were used as normal controls.
Results: Deficiency of mrp2 protein was confirmed in EHBR. Hepatic and renal expression of mrp3 mRNA was 53.6% (P < 0.001) and 82.9% (P < 0.001), and its protein expression was 298.9% (P < 0.001) and 245.0% (P = 0.001) higher in EHBR than in SD rats, respectively. Hepatic and renal expression of mrp1 and mrp6 mRNA was not significantly different between EHBR and SD rats. The mrp1 and mrp6 proteins were expressed in very low amounts in the liver and kidney of both EHBR and SD rats. In contrast to mrp3, hepatic expression of oatp1 and oatp2 mRNA was 33.9% (P = 0. 001) and 38.6% (P < 0.001), and their protein expression was 57.4% (P < 0.05) and 51.0% (P < 0.01) lower in EHBR than in SD rats, respectively. Hepatic and renal mrp3 protein was localized at the basolateral membrane.
Conclusions: Mrp3 plays an important role in the compensation of mrp2 deficiency in liver and kidney of EHBR. Hepatic expressions of mrp3, oatp1 and oatp2 changed adaptively in this animal model. This is a compensatory mechanism for reducing injury to hepatocytes from cytotoxic materials that increase in mrp2 deficiency.