Modulation of hepatic content and biliary excretion of P-glycoproteins in hepatocellular and obstructive cholestasis in the rat

• Published in: Journal of hepatology 1996, Vol.25 (3), p.349-361
• Main Authors: Accatino, Luigie, Pizarro, Margarita, Solís, Nancy, Koenig, Cecilia S., Vollrath, Valeska, Chianale, José
• Format: Article
• Language: English
• Subjects: Animals; ATP Binding Cassette Transporter, Subfamily B, Member 1 - metabolism; Bile; Bile - metabolism; Biliary obstruction; Biological and medical sciences; Cell Membrane - metabolism; Cholestasis; Cholestasis - genetics; Cholestasis - metabolism; Cholestasis, Intrahepatic - chemically induced; Cholestasis, Intrahepatic - genetics; Cholestasis, Intrahepatic - metabolism; Ethinyl Estradiol; Ethynylestradiol; Gastroenterology. Liver. Pancreas. Abdomen; Gene Expression; Genes, MDR; Immunohistochemistry; Liver; Liver - metabolism; Liver - physiology; Liver. Biliary tract. Portal circulation. Exocrine pancreas; Male; mdr mRNA; Medical sciences; Other diseases. Semiology; P-glycoproteins; Rats; Rats, Wistar; Tropical medicine
• ISSN: 0168-8278; 1600-0641
• DOI: 10.1016/S0168-8278(96)80122-X

Background/Aims: Release into bile of canalicular membrane enzymes, such as alkaline phosphatase and gamma-glutamyl transpeptidase, is significantly increased in rats subjected to experimental models of hepatocellular or obstructive cholestasis. This effect appears to be related to a greater susceptibility of these membrane intrinsic proteins to the solubilizing effects of secreted bile acids. It is not known whether canalicular membrane transport proteins, such as P-glycoprotein isoforms, involved in ATP-dependent xenobiotic biliary excretion and phospholipid secretion, are excreted into bile and whether this process is modified in cholestasis. The aims of this work have been to investigate in the rat: a) whether P-glycoproteins are normally excreted into bile, b) whether their excretion is modified in two experimental models of cholestasis, i.e., hepatocellular cholestasis induced by ethynylestradiol and obstructive cholestasis, and c) whether observed changes correlate with bile acid and phospholipid secretion and enzyme release into bile and with relative P-glycoprotein content in hepatic tissue and isolated and purified canalicular membranes. Methods: P-glycoproteins in bile and hepatic tissue were identified and quantitated by Western-blotting and immunohistochemistry using the C219 MAb. Changes in total mbd mRNA were analyzed by Northern-blotting. Results: Like canalicular membrane enzymes, P-glycoproteins are normally excreted into bile. Ethylnylestradiol-induced cholestasis was associated with a 4.9-fold increase in P-glycoprotein excretion compared with controls while, in contrast, the excretion of the carrier decreased markedly in obstructive cholestasis to 2% of control values. P-glycoprotein excretion per nmol of secreted bile acids increased 4.4-fold in ethynylestradiol-induced cholestasis but decreased to 2% of control values in obstructive cholestasis. Total mdr mRNA levels in hepatic tissue were markedly increased (3.4-fold) in rats subjected to obstructive cholestasis and moderately increased (1.6-fold) in the ethynylestradiol group, compared with controls. P-glycoprotein content in isolated canalicular membranes was slightly decreased by 15% in ethynylestradiol-induced cholestasis, while it increased 4.7-fold in obstructive cholestasis. Immunohistochemistry of rat livers showed that P-glycoprotein reaction at the canalicular domain of hepatocytes at acinar zone 1 was decreased in ethynylestradiol-treated rats and markedly increased in ob