ICE-PROTEASE INHIBITORS BLOCK MURINE LIVER-INJURY AND APOPTOSIS CAUSED BY CD95 OR BY TNF-ALPHA

The two apoptosis receptors of mammalian cells, i.e. the 55 kDa TNF re ceptor (TNF-R1) and CD95 (Fas/APO1) are activated independently of eac h other, however, their signaling involves a variety of ICE-related pr oteases [1]. We used a cell-permeable inhibitor of ICE-like protease a ctivity to examine in vivo whether post-receptor signaling of TNF and CD95 are fully independent processes. Mice pretreated with the inhibit or, Z-VAD-fluoromethylketone (FMK) were dose-dependently protected fro m liver injury caused by CD95 activation as determined by plasma alani ne aminotransferase and also from hepatocyte apoptosis assessed by DNA fragmentation (ID50 = 0.1 mg/kg). A dose of 10 mg/kg protected mice a lso from liver injury induced by TNF-alpha. Similar results were found when apoptosis was initiated via TNF-alpha or via CD95 in primary mur ine hepatocytes (IC50 = 1.5 nM) or in various human cell lines. In add ition to prevention, an arrest of cell death by Z-VAD-FMK was demonstr ated in vivo and in vitro after stimulation of apoptosis receptors. Th ese findings show in vitro and in vivo in mammals that CD95 and the TN F-alpha receptor share a distal proteolytic apoptosis signal. (C) 1997 Elsevier Science B.V.