Toxicity of bile acids on the electron transport chain of isolated rat liver mitochondria

Abstract

The toxicity of hydrophilic (cholate) and lipophilic (deoxycholate, chenodeoxycholate, and lithocholate) bile acids on the function of the electron transport chain was investigated in intact and disrupted rat liver mitochondria. In intact mitochondria, lipophilic bile acids used at a concentration of 100 μmol/L (0.1 μmol/mg protein) inhibited state 3 and state 3u (dinitrophenol-uncoupled) oxidation rates for L-glutamate, succinate, duroquinol or ascorbate/N, N, N′, N′-tetramethyl-p-phenylenediamine as substrates. In contrast, state 4 oxidation rates and ADP/oxygen ratios were not significantly affected. At a bile acid concentration of 10 μmol/L (0.01 μmol/mg protein), the state 3 oxidation rate for L-glutamate was decreased in the presence of deoxycholate, chenodeoxycholate or lithocholate, whereas only lithocholate inhibited state 3 oxidation for succinate or duroquinol. In broken mitochondria, inhibition of oxidative metabolism was found for NADH or duroquinol as substrate in the presence of 100 μmol/L lithocholate (0.2 μmol/mg protein) and for duroquinol in the presence of 100 μmol/L chenodeoxycholate. Direct assessment of the activities of the enzyme complexes of the electron transport chain revealed decreased activities of complex I and complex III in the presence of 100 μmol/L deoxycholate or chenodeoxycholate or 10 μmol/L lithocholate. Inhibition of complex IV required higher bile acid concentrations (300 μmol/L for chenodeoxycholate or 30 μmol/L for lithocholate), and complex II was not affected. Both chenodeoxycholate and lithocholate were incorporated into mitochondrial membranes. The phospholipid content of mitochondrial membranes decreased in incubations containing 100 μmol/L (0.1 μmol/mg protein) chenodeoxycholate but was not affected in the presence of 100 μmol/L lithocholate. The studies show that lipophilic bile acids impair the function of the electron transport chain in isolated rat liver mitochondria. The inhibitory effect of lipophilic bile acids on the electron transport chain can be explained by an unspecific effect on the inner mitochondrial membrane of intact mitochondria at high concentrations (100 μmol/L) and by a specific impairment of complex I and complex III in broken mitochondria or in intact mitochondria incubated with low bile acid concentrations (10 μmol/L). The impairment of mitochondrial function by bile acids may be clinically relevant in patients or animals with chronic cholestasis. (Hepatology 1994;19:471-479).