Endotoxin (ET)-induced
liver failure is characterized by parenchymal cell apoptosis and
inflammation leading to liver cell
necrosis. Members of the
caspase family have been implicated in the signal transduction pathway of apoptosis. The aim of this study was to characterize ET-induced hepatic
caspase activation and apoptosis and to investigate their effect on neutrophil-mediated liver injury. Treatment of C3Heb/FeJ mice with 700 mg/kg
galactosamine (Gal) and 100 microg/kg Salmonella abortus equi ET increased
caspase 3-like
protease activity (Asp-Val-
Glu-Asp-substrate) by 1730 +/- 140% at 6 h. There was a parallel enhancement of apoptosis (assessed by DNA fragmentation ELISA and
terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay). In contrast, activity of
caspase 1 (IL-1beta-converting enzyme)-like
proteases (Tyr-Val-
Ala-Asp-substrate) did not change throughout the experiment.
Caspase 3-like
protease activity and apoptosis was not induced by Gal/ET in ET-resistant mice (C3H/HeJ). Furthermore, only murine
TNF-alpha but not IL-1alphabeta increased
caspase activity and apoptosis. Gal/ET caused neutrophil-dependent hepatocellular
necrosis at 7 h (area of
necrosis, 45 +/- 3%).
Delayed treatment with the
caspase 3-like
protease inhibitor Z-Val-Ala-Asp-CH2F (Z-VAD) (10 mg/kg at 3 h) attenuated apoptosis by 81 to 88% and prevented liver cell
necrosis (< or = 5%). Z-VAD had no effect on the initial inflammatory response, including the sequestration of neutrophils in sinusoids. However, Z-VAD prevented neutrophil transmigration and
necrosis. Our data indicate that activation of the
caspase 3 subfamily of
cysteine proteases is critical for the development of parenchymal cell apoptosis. In addition, excessive hepatocellular apoptosis can be an important signal for transmigration of primed neutrophils sequestered in sinusoids.