Progressive stages of mitochondrial destruction caused by cell toxic bile salts

Abstract

The cell-toxic bile salt glycochenodeoxycholic acid (GCDCA) and taurochenodeoxycholic acid (TCDCA) are responsible for hepatocyte demise in cholestatic liver diseases, while tauroursodeoxycholic acid (TUDCA) is regarded hepatoprotective. We demonstrate the direct mitochondrio-toxicity of bile salts which deplete the mitochondrial membrane potential and induce the mitochondrial permeability transition (MPT). The bile salt mediated mechanistic mode of destruction significantly differs from that of calcium, the prototype MPT inducer. Cell-toxic bile salts initially bind to the mitochondrial outer membrane. Subsequently, the structure of the inner boundary membrane disintegrates. And it is only thereafter that the MPT is induced. This progressive destruction occurs in a dose- and time-dependent way. We demonstrate that GCDCA and TCDCA, but not TUDCA, preferentially permeabilize liposomes containing the mitochondrial membrane protein ANT, a process resembling the MPT induction in whole mitochondria. This suggests that ANT is one decisive target for toxic bile salts. To our knowledge this is the first report unraveling the consecutive steps leading to mitochondrial destruction by cell-toxic bile salts.

Keywords: 4-MUP; 4-methylumbelliferyl phosphate; ANT; Bile salts; Cholestasis; Cys A; Cyt C; FCCP; GCDCA; IM; Liver; MMP; MOMP; MPT; Mitochondria; Mitochondrial permeability transition; MβCD; OD; OM; PC; ROS; Rh123; TCDCA; TUDCA; VDAC; ZE-FFE; adenine nucleotide translocator; carbonylcyanide-p-(trifluoromethoxy) phenyl-hydrazone; cyclosporine A; cytochrome C; glycochenodeoxycholic acid; inner membrane; methyl-β-cyclodextrin; mitochondrial membrane potential; mitochondrial outer membrane rupture; mitochondrial permeability transition; optical density; outer membrane; phosphatidylcholine; reactive oxygen species; rhodamine 123; taurochenodeoxycholic acid; tauroursodeoxycholic acid; voltage-dependent anion channel; zone electrophoresis in a free flow electrophoresis device.