Hepatic aquaporin-8 (AQP8) water channels and oxidative stress are early affected during extrahepatic cholestasis in bile duct ligated (BDL) rats

Background: Interruption of bile flow during extrahepatic cholestasis may result in liver failure. Here we investigate for the first time if both AQP8-mediated osmotic water movement and oxidative stress might be early affected in an animal model of cholestasis. Materials and methods: Wistar rats underwent proximal BDL or sham operation; at days 1, 3, and 7 we measured liver histology, AQP8 (expression, subcellular localization), oxidative stress as total, oxidized glutathione (GSH, GSSG), and protein sulphydril (PSH, cytosolic/mitochondrial fractions). Results: BDL livers showed progressive intrahepatic bile duct dilatation, bile aggregates, inflammatory changes, cell degeneration, mitochondrial swelling. At day 3, intracellular but not plasma membrane AQP8 was decreased by 75% (P< 0.001). At day 7, AQP8 was decreased both intracellularly (-67%) and in plasma membranes (-56%) (P< 0.05), suggesting defective translocation or membrane insertion of AQP8. Cytosolic GSH and PSH gradually decreased while GSSG increased (P<0.01, ANOVA) after BDL. Specifically, GSH and P-SH levels declined and GSSG increased earlier in mitochondria than cytosol. Conclusions: Water transport is greatly affected by BDL; here we observed an early down-regulation of hepatocyte AQP8 protein expression which could contribute to bile secretory dysfunction of cholestatic hepatocytes. Also, early cholestatic liver shows associated remarkable changes of GSH content and redox status, especially in hepatocyte mitochondria.