Biliary excretion of bile acid conjugates in a hyperbilirubinemic mutant sprague-dawley rat

Abstract

The hepatic transport of bile acid conjugates was studied in the Eisai hyperbilirubinuria rat, a Sprague-Dawley mutant rat with conjugated hyperbilirubinemia. Serum bile acid levels were increased, bile acid-independent bile flow was decreased and biliary glutathione concentrations were markedly decreased in the Eisai hyperbilirubinuria rat. Biliary excretion of sulfobromophthalein was markedly impaired and almost no glutathione conjugate was excreted in the bile of the Eisai hyperbilirubinuria rat. Biliary excretion of lithocholate-3-O-glucuronide and lithocholate-3-sulfate in the Eisai hyperbilirubinuria rat was markedly delayed, whereas that of lithocholate was only slightly delayed. After [14C]chenodeoxycholate infusion (1 mumol/min/100 gm for 60 min), the increases in bile flow and biliary excretion of isotope in the Eisai hyperbilirubinuria rat were not so prominent as those observed in control rats, and the glucuronide of chenodeoxycholate, which constituted about 15% of biliary chenodeoxycholate in control rats, was not observed in the Eisai hyperbilirubinuria rat. Initial uptake of lithocholate and its glucuronide and sulfate by isolated hepatocytes was not impaired in the Eisai hyperbilirubinuria rat; the profiles of cytosolic bile acid binding proteins in Eisai hyperbilirubinuria rat liver were identical to those in control liver. These data indicate that the Eisai hyperbilirubinuria rat has excretory impairment of organic anions, bile acid glucuronide and sulfate and that it has characteristics very similar to those of the hyperbilirubinemic mutant Wistar rats TR- and GY.

The emerging role of transport systems in liver function tests

“…In the human liver, the three OATPs (table 1) are excellent BSP transporters (Hagenbuch and Meier, 2004;Kullak-Ublick et al, 2001). After uptake into hepatocytes, BSP is conjugated to glutathione and excreted into bile (Combes and Stakelum, 1960) by Mrp2 in rats (Takikawa et al, 1991). Unconjugated BSP is also a substrate for MRP2 (Cui et al, 2001a) (table 1).…”

The apical conjugate efflux pump ABCC2 (MRP2)

“…Two different mutant hyperbilirubinemic rat strains, the GY/TR − rats [64] and the Eisai hyperbilirubinemic rats (EHBR) [54,163], have a hereditary defect in the secretion of anionic conjugates into bile. In consequence of the molecular identification and cloning of rat Abcc2 as the apical conjugate efflux pump [13,60,133], which is defective in these rat strains [13,60,133], both can now be considered as animal models of human Dubin-Johnson syndrome.…”

“…The function of rat Abcc2 was recognized long before its cloning by studies on the hepatobiliary elimination of organic anions in normal and transport-deficient mutant rats [54,55,64,131,163]. The loss of ATP-dependent transport across the hepatocyte canalicular membrane was identified in these mutant rats using inside-out membrane vesicles and various glutathione (GSH) S-conjugates as substrates, notably leukotriene C 4 (LTC 4 ) [57].…”

The canalicular multispecific organic anion transporter and conjugated hyperbilirubinemia in rat and man

“…TR -rats have an autosomal recessive transport defect and are characterized by mild chronic conjugated hyperbilirubinemia, which results in jaundice [11]. Apart from the TR -rat, two other transport-deficient rats were identified, the Groningen yellow rat (GY), a Wistar rat derived from the same colony as TR -rats [30], and the Eisai hyperbilirubinemic rat (EHBR), a Sprague-Dawley strain [31,32]. These animals have a defect in the hepatobiliary excretion of a broad range of organic anions, in-422 cluding bilirubin glucuronides [33,34] and other multivalent organic anions such as glutathione-S-conjugates (e.g., leukotriene C 4 [35,36]), the model organic anion dinitrophenyl glutathione (GS-DNP) [11,37], and 3-OHglucuronidated [38] and 3-OH-sulfated bile salts [30].…”