Influence of Hydroxylation and Conjugation of Bile Salts on Their Membrane-Damaging Properties-Studies on Isolated Hepatocytes and Lipid Membrane Vesicles†

Abstract

To characterize the relative toxicity of different bile salts, isolated hepatocytes were incubated with different concentrations of one bile salt or with identical concentrations of different bile salts and their conjugates. Incubation lasted for 1 hr; samples were taken at different intervals and studied for enzyme release, urea synthesis and stimulation by glucagon, and by electron microscopy. While the trihydroxylated bile salt, taurocholate, did not produce alterations at concentrations up to 1,500 μM, the dihydroxylated salts, chenodeoxy- and deoxycholate, caused enzyme release and membrane lysis, and inhibited urea synthesis at concentrations above 500 μM. In contrast, urso-deoxycholate was ineffective at concentrations up to 1,500 μM. Conjugation of these bile salts did not result in significant differences with the exception of deoxycholate conjugates which induced enzyme leakage more rapidly. Studies of lipid membrane vesicles revealed corresponding alterations. The monohydroxylated salt, taurolithocholate, caused cellular damage as indicated by enzyme loss and impairment of hormonal sensitivity of cells at low concentrations (30 to 100 μM). Dihydroxylated salts produced a different time course of membrane leakage, ultrastructural changes and release of volume marker and lipid in liposomes, suggesting a possible different mechanism of damage induced by this bile salt. Both systems can readily be used to study bile salt membrane interactions.