Hepatic gene transfer of human aquaporin‐1 improves bile salt secretory failure in rats with estrogen‐induced cholestasis

Abstract

The adenoviral gene transfer of human aquaporin-1 (hAQP1) water channels to the liver of 17a-ethinylestradiol-induced cholestatic rats improves bile flow, in part by enhancing canalicular hAQP1-mediated osmotic water secretion. To gain insight into the mechanisms of 17a-ethinylestradiol cholestasis improvement, we studied the biliary output of bile salts (BS) and the functional expression of the canalicular BS export pump (BSEP; ABCB11). Adenovector encoding hAQP1 (AdhAQP1) or control vector was administered by retrograde intrabiliary infusion. AdhAQP1-transduced cholestatic rats increased the biliary output of major endogenous BS (50%-80%, P < 0.05) as well as that of taurocholate administered in choleretic or trace radiolabel amounts (around 60%, P < 0.05). Moreover, liver transduction with AdhAQP1 normalized serum BS levels, otherwise markedly elevated in cholestatic animals. AdhAQP1 treatment was unable to improve BSEP protein expression in cholestasis; however, its transport activity, assessed by adenosine triphosphate-dependent taurocholate transport in canalicular membrane vesicles, was induced by 90% (P < 0.05). AdhAQP1 administration in noncholestatic rats induced no significant changes in either biliary BS output or BSEP activity. Canalicular BSEP, mostly present in raft (high cholesterol) microdomains in control rats, was largely found in nonraft (low cholesterol) microdomains in cholestasis. Considering that BSEP activity directly depends on canalicular membrane cholesterol content, decreased BSEP presence in rafts may contribute to BSEP activity decline in 17a-ethinylestradiol cholestasis. In AdhAQP1-transduced cholestatic rats, BSEP showed a canalicular microdomain distribution similar to that of control rats, which provides an explanation for the improved BSEP activity. Conclusion: Hepatocyte canalicular expression of hAQP1 through adenoviral gene transfer promotes biliary BS output by modulating BSEP activity in estrogen-induced cholestasis, a novel finding that might help us to better understand and treat cholestatic disorders. (HEPATOLOGY 2016;64:535-548) SEE EDITORIAL ON PAGE 344 C holestatic liver diseases result in systemic and intrahepatic accumulation of endogenous bile salts (BS) that causes liver injury, ultimately leading to fibrosis and cirrhosis. (1) The canalicular BS export pump (BSEP; ABCB11) is the primary hepatocyte transporter for biliary BS secretion, i.e., the rate-limiting step in the enterohepatic circulation of BS. (2) Impairment of expression and/or function of BSEP has been directly linked to inherited and acquired cholestatic liver diseases. (3)(4)(5) Estrogens and Abbreviations: AdhAQP1, adenovector encoding human aquaporin-1; AQP8, aquaporin-8; BS, bile salts; BSEP, bile salt export pump/ABCB11; EE, 17a-ethinylestradiol; hAQP1, human aquaporin-1; TC, taurocholate.

Aquaporin gene therapy for cholestasis

“…(1) In the setting of chronic liver disease (CLD), several studies have shown the presence of HEV infection in 3.2%-6.5% cases of decompensated CLD, mostly in patients with alcoholic CLD. (2) No differences were observed in terms of mortality between patients with and without HEV infection, but the number of HEV cases was low. To further investigate the impact of HEV in this setting, we conducted a prospective multicenter study on a French cohort of decompensated alcoholic CLD.…”

“…(1) We thank the authors for their comments in our recent studies. (2,3) Nevertheless, we believe that an analysis of the role of aquaporins (AQPs) in hepatocyte canalicular water transport and bile secretion should take into account several published contributions that were not cited in the editorial.…”

“…Nevertheless, the retrograde biliary vector administration allowed that most of the periportal hepatocytes were transduced with AQP1. (2,3) This is relevant because periportal hepatocytes are exposed to the highest blood concentrations of bile salts and thus are the primary cells involved in bile-salt-dependent bile secretion.…”

“…Nevertheless, the retrograde biliary vector administration allowed that most of the periportal hepatocytes were transduced with AQP1. (2,3) This is relevant because periportal hepatocytes are exposed to the highest blood concentrations of bile salts and thus are the primary cells involved in bile-salt-dependent bile secretion.We think it may be premature to judge whether the hepatic gene transfer of AQPs is a credible approach for treatment of cholestasis. We anticipate that further studies will clarify its impact as a novel therapeutic strategy.…”

Aquaporin-Targeted Therapeutics: State-of-the-Field

“…Though it is unlikely that AQP ‘activators’ can be identified, as the AQPs are probably already maximally active, selective transcriptional upregulators of AQP7 may reduce adipocyte hypertrophy in obesity, of AQP3 may promote wound healing, of AQP4 may have anti-epileptic activity, and of AQP5 might increase glandular fluid secretion. There is evidence that AQP gene transfer may increase epithelial water permeability, promoting saliva secretion in salivary gland disorders [2] and bile secretion in liver diseases associated with cholestasis [23]. Finally, blockers of binding of pathogenic AQP4-targeted autoantibodies to astrocyte AQP4 might prevent or reduce neuropathology and neurological deficit in neuromyelitis optica [28].…”