Tauroursodeoxycholic acid protects hepatocytes from ethanol-fed rats against tumor necrosis factor-induced cell death by replenishing mitochondrial glutathione

Mitochondrial glutathione (GSH) plays a key role against tumor necrosis fac tor alpha (TNF)-induced apoptosis because its depletion is known to sensiti ze hepatocytes to TNF. The present study examined the role of tauroursodeox ycholic acid (TUDCA) administration to chronic ethanol-fed rats on mitochon drial GSH levels and kinetics, mitochondrial membrane physical properties, TNF-induced peroxide formation, and subsequent hepatocyte survival. TUDCA s electively increased the levels of GSH in mitochondria without an effect on cytosolic GSH. This outcome was accompanied by improved initial rate of GS H transport examined at low (1 mmol/L) and high (10 mmol/L) GSH concentrati ons both in intact mitochondria and mitoplasts prepared from ethanol-fed li vers. Assessment of membrane fluidity revealed an increased order parameter in mitochondria and mitoplasts from ethanol-fed rats compared with pair-fe d controls, which was prevented by TUDCA administration. Compared with hepa tocytes from pair-fed rats, TNF stimulated peroxide generation in hepatocyt es from ethanol-fed rats, preceding TNF-induced cell death. Administration of TUDCA to ethanol-fed rats prevented TNF-induced peroxide formation and c ell death, an effect that was reversed on depletion of the recovered mitoch ondrial GSH levels by (R,S)-3-hydroxy-4-pentenoate before TNF treatment. Th e protective effect of TUDCA against TNF was not because of activation of p hosphatidylinositol 3-kinase, discarding a role for a survival-dependent pa thway. Thus, these findings reveal a novel role of TUDCA in protecting hepa tocytes in long-term ethanol-fed rats through modulation of mitochondrial m embrane fluidity and subsequent normalization of mitochondrial GSH levels.