Regulation of
bilirubin glucuronide transporters during
hyperbilirubinemia in hepatic and extrahepatic tissues is not completely clear. In the present study, we evaluated the regulation of the
bilirubin glucuronide transporters,
multidrug resistance-associated proteins (MRP)2 and 3, in rats with
obstructive jaundice. Bile duct
ligation (BDL) or
sham operation was performed in Wistar rats. Liver and kidneys were removed 1, 3, and 5 days after BDL (n = 4, in each group). Serum and urine were collected to measure
bilirubin levels just before animal killing. MRP2 And MRP3
mRNA expressions were determined by real-time RT-PCR.
Protein expression of MRP2 and MRP3 was determined by Western blotting. Renal MRP2 function was evaluated by para-aminohippurate (PAH) clearance. The effect of conjugated
bilirubin, unconjugated
bilirubin, human bile, and
sulfate-conjugated
bile acid on MRP2 gene expression was also evaluated in renal and hepatocyte cell lines. Serum
bilirubin and urinary
bilirubin excretion increased significantly after BDL. In the liver, the
mRNA expression of MRP2 decreased 59, 86, and 82%, and its
protein expression decreased 25, 74, and 93% compared with
sham-operated animals after 24, 72, and 120 h of BDL, respectively. In contrast, the liver expression of MRP3
mRNA increased 138, 2,137, and 3,295%, and its
protein expression increased 560, 634, and 612% compared with
sham-operated animals after 24, 72, and 120 h of BDL, respectively. On the other hand, in the kidneys, the
mRNA expression of MRP2 increased 162, 73, and 21%, and its
protein expression increased 387, 558, and 472% compared with
sham-operated animals after 24, 72, and 120 h of BDL, respectively. PAH clearance was significantly increased after BDL. The
mRNA expression of MRP2 increased in renal proximal tubular epithelial cells
after treatment with conjugated
bilirubin,
sulfate-conjugated
bile acid or human bile. Upregulation of MRP2 in the kidneys and MRP3 in the liver may be a compensatory mechanism to improve
bilirubin clearance during
obstructive jaundice.