Hydrophobic bile salts induce hepatocyte shrinkage via NADPH oxidase activation

Hydrophobic bile salts activate NADPH oxidase through a ceramide and protein kinase Czeta-dependent pathway as an important upstream event of bile salt-induced hepatocyte apoptosis. As shown in the present study, hydrophobic bile salts such as glycochenodeoxycholate, taurochenodeoxycholate or taurolithocholylsulfate (TLCS) also induce within 30 min hepatocyte shrinkage in perfused rat liver. TLCS-induced hepatocyte shrinkage was strongly blunted in presence of desipramine, apocynin, bafilomycin and DIDS, i.e. maneuvres previously shown to inhibit TLCS-induced NADPH oxidase activation and the subsequent oxidative stress response. The antioxidant N-acetylcysteine inhibited TLCS-induced hepatocyte shrinkage. N-acetylcysteine by itself increased hepatocyte hydration, suggesting that a basal production of reactive oxygen intermediates is involved in the regulation of liver cell hydration. TLCS failed to induce shrinkage of hepatocytes from p47(phox) knock-out, but not control mice. Likewise, hepatocytes from p47(phox) knock-out mice were resistant towards TLCS-induced apoptosis and failed to activate the CD95 system. No cell shrinkage was observed in response to taurocholate and tauroursodesoxycholate, i.e. bile salts which do not induce an oxidative stress signal and apoptosis. NADPH oxidase activation also counteracts volume recovery in response to hyperosmotic hepatocyte shrinkage. The findings indicate that hydrophobic, proapoptotic bile salts induce hepatocyte shrinkage largely through NADPH oxidase-derived oxidative stress. Because cell shrinkage in turn activates NADPH oxidase, which blunts cell volume recovery, a vicious cycle ensues between oxidative stress and cell shrinkage, which propagates CD95 activation and may finally lead to apoptosis. In addition, cell shrinkage induced by proapoptotic bile salts may augment apoptosis by increasing protein breakdown and induction of cholestasis.