Membrane structural changes support the involvement of mitochondria in the bile salt-induced apoptosis of rat hepatocytes

Abstract

A B S T R A C TThe accumulation of toxic bile salts within the hepatocyte plays a key role in organ injury during liver disease. Deoxycholate (DC) and glycochenodeoxycholate (GCDC) induce apoptosis in vitro and in vivo, perhaps through direct perturbation of mitochondrial membrane structure and function. In contrast, ursodeoxycholate (UDC) and its taurine-conjugated form (TUDC) appear to be protective. We show here that hydrophobic bile salts induced apoptosis in cultured rat hepatocytes, without modulating the expression of pro-apoptotic Bax protein, and caused cytochrome c release in isolated mitochondria. Co-incubation with UDC and TUDC prevented cell death and efflux of mitochondrial factors. Using spin-labelling techniques and EPR spectroscopy analysis of isolated rat liver mitochondria, we found significant structural changes at the membrane-water surface in mitochondria exposed to hydrophobic bile salts, including modified lipid polarity and fluidity, altered protein order and increased oxidative injury. UDC, TUDC and cyclosporin A almost completely abrogated DC-and GCDC-induced membrane perturbations. We conclude that the toxicity of hydrophobic bile salts to hepatocytes is mediated by cytochrome c release, through a mechanism associated with marked direct effects on mitochondrial membrane lipid polarity and fluidity, protein order and redox status, without modulation of pro-apoptotic Bax expression. UDC and TUDC can directly suppress disruption of mitochondrial membrane structure, which may represent an important mechanism of hepatoprotection by these bile salts.

Role of mitochondria in cell apoptosis during hepatic ischemia-reperfusion injury and protective effect of ischemic postconditioning

“…Under the influence of many kinds of stress factors such as ROS, Ca 2+ overloading, and toxin, mitochondrial ultrastructure and its function were easily damaged, then the active substance originally in mitochondria related to apoptosis including cytochrome C, was released into cytoplasm [14][15][16][17][18] . Recent progress in studies on apoptosis has revealed that cytochrome C is a pro-apoptotic factor.…”

Deoxycholic acid modulates cell death signaling through changes in mitochondrial membrane properties

“…4B, E ), while DCA-NBD Supplemental Material can be found at: ( 20 ). Previous studies have also identifi ed changes in average membrane fl uidity of isolated mitochondria after exposure to toxic bile acids ( 44 ). Here, we aimed to follow in real time the changes in MOM properties and correlate these changes with the onset of MPT.…”

Tauroursodeoxycholate Protects Rat Hepatocytes from Bile Acid-Induced Apoptosis via β1-Integrin- and Protein Kinase A-Dependent Mechanisms

“…recruitment of Fasassociated death domain (FADD) and caspase 8 occurs [15,16,18]. TUDC was shown to protect against bile salt-induced apoptosis and a modulation of the mitochondrial membrane permeability by TUDC [20] and activation of survival pathways, such as p38 MAPK , Erks and phosphatidylinositide 3-kinase (PI3-K) were suggested to contribute to this cytoprotective effects [21,22]. However, TUDC prevents CD95 trafficking to the plasma membrane by toxic bile acids indicating that it interferes with CD95 dependent signaling towards apoptosis at a step prior to caspase 8 activation [12].…”