Characterization of inducible nature of MRP3 in rat liver

Abstract

We found previously that expression of multidrug resistance-associated protein (MRP) 3 is induced in a mutant rat strain (Eisai hyperbilirubinemic rats) whose canalicular multispecific organic anion transporter (cMOAT/MRP2) function is hereditarily defective and in normal Sprague-Dawley (SD) rats after ligation of the common bile duct. In the present study, the inducible nature of MRP3 was examined, using Northern and Western blot analyses, in comparison with that of other secondary active [Na(+)-taurocholic acid cotransporting polypeptide (Ntcp), organic anion transporting polypeptide 1 (oatp1), and organic cation transporter (OCT1)] and primary active [P-glycoprotein (P-gp), cMOAT/MRP2, and MRP6] transporters. alpha-Naphthylisothiocyanate treatment and common bile duct ligation induced expression of P-gp and MRP3, whereas expression of Ntcp, oatp1, and OCT1 was reduced by the same treatment. Although expression of MRP3 was also induced by administration of phenobarbital, that of cMOAT/MRP2, MRP1, and MRP6 was not affected by any of these treatments. Moreover, the mRNA level of MRP3, but not that of P-gp, was increased in SD rats after administration of bilirubin and in Gunn rats whose hepatic bilirubin concentration is elevated because of a defect in the expression of UDP-glucuronosyl transferase. However, the MRP3 protein level was not affected by bilirubin administration. Although the increased MRP3 mRNA level was associated with the increased concentration of bilirubin and/or its glucuronides in mutant rats and in SD rats that had undergone common bile duct ligation or alpha-naphthylisothiocyanate treatment, we must assume that factor(s) other than these physiological substances are also involved in the increased protein level of MRP3.

Down-regulation of the organic cation transporter 1 of rat liver in obstructive cholestasis

“…A 36% reduction in Oct1 liver mRNA has been previously reported after 3 days of BDL in the rat 29 and intraperitoneal injection of lipopolysaccharide, another cholestatic experimental model, has resulted in impaired hepatic uptake of the Oct1 substrate TBuMA, 30 consistent with our findings.…”

Expression of Organic Cation Transporters OCT1 (SLC22A1) and OCT3 (SLC22A3) Is Affected by Genetic Factors and Cholestasis in Human Liver†

“…Whereas OCT1 and OCT3 expression has not yet been studied in cholestatic human liver, other hepatocellular uptake transporters such as Na ϩ /taurocholate cotransporter and organic anion transporter OATP1B1 are clearly down-regulated in patients with cholestatic liver disease. 46,47 Interestingly, obstructive and ethinylestradiol-induced cholestasis in rats significantly reduced hepatic Oct1 mRNA and protein levels, [48][49][50] which fits well with our data in humans. Further studies are warranted to elucidate, for instance, whether drug response to the OCT1 and OCT3 substrate metformin is altered in diabetic patients with cholestasis.…”

Vagaries of Impaired Transporter Function in PFIC 2 and 3 *

“…MRP3 expression was spuriously high in one very jaundiced PFIC patient (C10), but not, apparently, in the other three. This result contrasts with the uniformly marked upregulation of MRP3/Mrp3 in the liver of Gunn rats with unconjugated hyperbilirubinemia due to Ugt1a1 deficiency, 7,8 in humans with conjugated hyperbilirubinemia due to MRP2 deficiency (Dubin-Johnson Syndrome) 9 or primary biliary cirrhosis, 10 and in rats 8 and humans 11 with obstructive cholestasis. Among patients with PFIC-2 or -3, mean expression of MRP4 was strikingly elevated, and expression of OATP1B1 and OATP1B3 was moderately depressed; each alteration might engender retention of conjugated bilirubin.…”