title: Protection against Fas receptor-mediated apoptosis in hepatocytes and nonparenchymal cells by a caspase-8 inhibitor in vivo: evidence for a postmitochondrial processing of caspase-8.
abstract: Lymphocytes can kill target cells including hepatocytes during various inflammatory diseases by Fas receptor-mediated apoptosis. Caspase-8 is activated at the receptor level, thereby initiating the processing of downstream effector caspases. The aim of this study was to investigate the time course of caspase-8 activation and to evaluate the efficacy of the caspase-8 inhibitor IETD-CHO in a model of Fas-induced apoptosis in vivo. C3Heb/FeJ mice were treated with the anti-Fas antibody Jo-2 (0.6 mg/kg). Western blot analysis demonstrated increased cytochrome c in the cytosol (20 min), which was followed by the progressive activation of caspase-3, -9 (40-120 min), and caspase-8 (120 min). At 90 and 120 min, extensive hemorrhage was observed, indicating damage to sinusoidal lining cells. In addition, high plasma ALT levels (997 +/- 316 U/L) and histological evaluation indicated severe parenchymal cell injury. Parenchymal and nonparenchymal cells showed a similar increase in caspase-3 activity and DNA fragmentation. Treatment with IETD-CHO (10 mg/kg) attenuated the increase in caspase-3 activity and DNA fragmentation by 80-90% and completely prevented hemorrhage and parenchymal cell damage. IETD-CHO also prevented the early release of mitochondrial cytochrome c and the processing of caspase-3, -8, and -9. Thus, our data support the hypothesis that Fas-mediated apoptosis is dependent on caspase-8 activation in hepatocytes and nonparenchymal cells. However, the bulk of procaspase-8 is processed late, suggesting that only a small amount of procaspase-8 may actually be activated at the Fas receptor. This initial signal may be amplified by further activation of caspase-8 by effector caspases, i.e., after mitochondrial activation. Caspase-8 is a promising therapeutic target for inhibition of Fas-mediated apoptosis.
authors.affiliation: Department of Pharmacology and Toxicology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205, USA.
authors.forename: M L
authors.initials: ML
authors.lastname: Bajt
authors.forename: J A
authors.initials: JA
authors.lastname: Lawson
authors.forename: S L
authors.initials: SL
authors.lastname: Vonderfecht
authors.forename: J S
authors.initials: JS
authors.lastname: Gujral
authors.forename: H
authors.initials: H
authors.lastname: Jaeschke
mesh_terms: D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D053181:Caspase 8; D053453:Caspase 9; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D003574:Cytochrome c Group / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D022781:Hepatocytes / Q000187:drug effects* / Q000201:enzymology / Q000473:pathology; D007728:Kupffer Cells / Q000187:drug effects* / Q000201:enzymology / Q000473:pathology; D017093:Liver Failure / Q000201:enzymology / Q000473:pathology / Q000517:prevention & control*; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D008930:Mitochondria, Liver / Q000187:drug effects / Q000201:enzymology*; D009842:Oligopeptides / Q000494:pharmacology*; D011499:Protein Processing, Post-Translational; D019014:fas Receptor / Q000378:metabolism*
chemical_list: D061945:Caspase Inhibitors; D003574:Cytochrome c Group; D004791:Enzyme Inhibitors; D009842:Oligopeptides; C401206:acetyl-isoleucyl-glutamyl-threonyl-aspartyl-aldehyde; D019014:fas Receptor; C505526:Casp8 protein, mouse; C506434:Casp9 protein, mouse; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases