A NOVEL ROLE FOR URSODEOXYCHOLIC ACID IN INHIBITING APOPTOSIS BY MODULATING MITOCHONDRIAL-MEMBRANE PERTURBATION

The hydrophilic bile salt ursodeoxycholic acid (UDCA) protects against the membrane-damaging effects associated with hydrophobic bile acids. This study was undertaken to (a) determine if UDCA inhibits apoptosis from deoxycholic acid (DCA), as well as from ethanol, TGF-beta 1, Fas ligand, and okadaic acid; and to (b) determine whether mitochondrial membrane perturbation is modulated by UDCA, DCA induced significant he patocyte apoptosis in vivo and in isolated hepatocytes determined by t erminal transferase-mediated dUTP-digoxigenin nick end-labeling assay and nuclear staining, respectively (P < 0.001). Apoptosis in isolated rat hepatocytes increased 12-fold after incubation with 0.5% ethanol ( P < 0.001). HuH-7 cells exhibited increased apoptosis with 1 nM TGF-be ta 1 (P < 0.001) or DCA at greater than or equal to 100 mu M (P < 0.00 1), as did Hep G2 cells after incubation with anti-Fas antibody (P < 0 .001), Finally, incubation with okadaic acid induced significant apopt osis in HuH-7, Saos-2, Cos-7, and HeLa cells. Coadministration of UDCA with each of the apoptosis-inducing agents was associated with a 50-1 00% inhibition of apoptotic changes (P < 0.001) in all the cell types. Also, UDCA reduced the mitochondrial membrane permeability transition (MPT) in isolated mitochondria associated with both DCA and phenylars ine oxide by > 40 and 50%, respectively (P < 0.001). FACS(R) analysis revealed that the apoptosis-inducing agents decreased the mitochondria l transmembrane potential and increased reactive oxygen species produc tion (P < 0.05). Coadministration of UDCA was associated with signific ant prevention of mitochondrial membrane alterations in all cell types . The results suggest that UDCA plays a central role in modulating the apoptotic threshold in both hepatocytes and non-liver cells, and inhi bition of MPT is at least one pathway by which UDCA protects against a poptosis.