Ethanol-induced apoptosis in polarized hepatic cells possibly through regulation of the Fas pathway.
BACKGROUND
It has been noted that alcohol-related liver diseases can be associated with an increase in apoptotic hepatocellular death. Moreover, the promotion of hepatocyte apoptosis may be linked to signals emanating from death receptors, particularly Fas [CD95/apoptosis-inducing protein 1 (APO-1)]. In the present study, we utilized an in vitro hepatic culture model [hybrid of human fibroblast (WI 38) and rat hepatoma (Fao) cells, WIF-B cells] to study potential contributing mechanisms involved in hepatocellular apoptosis following ethanol administration.


METHODS
WIF-B cultures (differentiated hepatic cells that efficiently metabolize alcohol) were treated with or without ethanol and specific inhibitors of alcohol metabolism and cysteine protease activity, followed by morphological and biochemical examination of proapoptotic parameters.


RESULTS
The results of this work demonstrated that ethanol administration leads to an increase (45%-60%) in caspase-3 activity and that the induction of apoptosis was found to be linked to the metabolism of alcohol. Additionally, increases were observed in the activity of upstream initiator caspases (caspase-2 and caspase-8) that are directly related to membrane signaling events of death receptors such as Fas. Moreover, it was determined that the activation of caspase-3 could be blocked by the presence of a specific caspase-8 inhibitor, again linking death receptor-associated proteases to downstream effector caspase activity in alcohol-related death. Finally, ethanol administration was found to result in an increase in the amount of Fas protein present in the membrane fraction of the cell. The increase in membrane Fas protein indicates ligand-independent membrane targeting of Fas in the alcohol-treated cells that could potentially be a key signaling event in the induction of the proapoptotic caspase cascade.


CONCLUSIONS
The data presented here indicate that alcohol metabolism induces apoptosis in WIF-B cells that occurs, in part, by mechanisms involving signals emanating from death receptors.
McVicker
Benita L
BL
The Liver Study Unit, Department of Veterans Affairs Medical Center, 4101 Woolworth Avenue, Omaha, NE 68105, USA. bmcvicker@unmc.edu
Tuma
Dean J
DJ
Kubik
Jacy L
JL
Tuma
Pamela L
PL
Casey
Carol A
CA
D000963:Antimetabolites / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects; D002460:Cell Line; D016764:Cell Polarity / Q000187:drug effects; D003484:Cyanamide / Q000494:pharmacology; D016572:Cyclosporine / Q000494:pharmacology; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D000431:Ethanol / Q000494:pharmacology*; D022781:Hepatocytes / Q000187:drug effects*; D006801:Humans; D010084:Oxidation-Reduction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects*; D019014:fas Receptor / Q000187:drug effects / Q000502:physiology*
D000963:Antimetabolites; D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D019014:fas Receptor; D000431:Ethanol; D003484:Cyanamide; D016572:Cyclosporine; D020169:Caspases; D003546:Cysteine Endopeptidases