Tauroursodeoxycholate counteracts hepatocellular lysis induced by tensioactive bile salts by preventing plasma membrane-micelle transition.

Ursodeoxycholic acid is widely used as a therapeutic agent for the treatment of cholestatic liver diseases. In these hepatopathies, the bile secretory failure produces accumulation of endogenous, tensioactive bile salts, leading to plasma membrane damage and, eventually, hepatocellular lysis. In the present study, we analyzed the capacity of the ursodeoxycholic acid endogenous metabolite, tauroursodeoxycholate (TUDC), to stabilize the hepatocellular plasma membrane against its transition to the micellar phase induced by the tensioactive bile salt taurochenodeoxycholate (TCDC), the main endogenous bile salt accumulated in cholestasis. The disruption of the plasma membrane was evaluated (i) in isolated hepatocytes, through the release of the enzyme lactate dehydrogenase to the incubation medium and (ii) in isolated plasma membranes, through the self-quenching assay of the membranotropic probe octadecylrhodamine B; this assay allows for detergent-induced transition from membrane bilayer to micelle to be monitored. Our results showed that isolated hepatocytes treated with TUDC are more resistant to TCDC-induced cell lysis. When this effect was evaluated in isolated plasma membranes, the TCDC concentration necessary to reach half of the transition from bilayer to micelle was increased by 22% (p<0.05). This difference remained even when TUDC was removed from the incubation medium before adding TCDC, thus indicating that TUDC exerted its effect directly on the plasma membrane. When the same experiments were carried out using the non-ionic detergent TX-100 or the cholesterol-complexing detergent digitonin, no protective effect was observed. In conclusion, TUDC prevents selectively the bilayer to micelle transition of the hepatocellular plasma membrane induced by hydrophobic bile salts that typically build up and accumulate in cholestatic processes. Our results suggest that formation of a complex between negatively charged TUDC and cholesterol in the membrane favours repulsion of negatively charged detergent bile salts, thus providing a basis for the understanding of the TUDC protective effects.