Inhibition of Fas Receptor (CD95)-Induced Hepatic Caspase Activation and Apoptosis by Acetaminophen in Mice

• Published in: Toxicology and applied pharmacology 1999-05, Vol.156 (3), p.179-186
• Main Authors: Lawson, Judy A., Fisher, Michael A., Simmons, Carol A., Farhood, Anwar, Jaeschke, Hartmut
• Format: Article
• Language: English
• Subjects: Acetaminophen - toxicity; acetaminophen hepatotoxicity; Analgesics, Non-Narcotic - toxicity; Animals; anti-Fas antibody Jo-2; apoptosis; Apoptosis - drug effects; Benzoquinones - metabolism; Biological and medical sciences; Blotting, Western; caspase inhibitor Z-VAD; caspases; Caspases - metabolism; CD95; DNA fragmentation; DNA Fragmentation - drug effects; Drug toxicity and drugs side effects treatment; Enzyme Activation - drug effects; Enzyme-Linked Immunosorbent Assay; Fas receptor; fas Receptor - physiology; Imines - metabolism; In Situ Nick-End Labeling; Liver - drug effects; Liver - enzymology; liver cell necrosis; Male; Medical sciences; Mice; Mice, Inbred C3H; Pharmacology. Drug treatments; Toxicity: digestive system
• ISSN: 0041-008X; 1096-0333
• DOI: 10.1006/taap.1999.8635

The mechanism of liver cell injury induced by an overdose of the analgesic acetaminophen (AAP) remains controversial. Recently, it was hypothesized that a significant number of hepatocytes die by apoptosis. Since caspases have been implicated as critical signal and effector proteases in apoptosis, we investigated their potential role in the pathophysiology of AAP-induced liver injury. Male C3Heb/FeJ mice were fasted overnight and then treated with 500 mg/kg AAP. Liver injury became apparent at 4 h and was more severe at 6 h (plasma ALT activities: 4110 ± 320 U/liter; centrilobular necrosis). DNA fragmentation increased parallel to the increase of plasma ALT values. At 6 h there was a 420% increase of DNA fragmentation and a 74-fold increase of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells located predominantly around central veins. However, the activity of the proapoptotic caspase-3 was not increased at any time after AAP. In contrast, injection of the anti-Fas antibody Jo-2 (positive control) caused a 28-fold increase of caspase-3 activity and severe DNA fragmentation before significant ALT release. Treatment with the caspase inhibitor ZVAD-CHF2had no effect on AAP toxicity but completely prevented Jo-mediated apoptosis. In contrast, Jo-induced caspase activation and apoptosis could be inhibited by AAP treatment in a time- and dose-dependent manner. We conclude that AAP-induced DNA fragmentation does not involve caspases, suggesting a direct activation of endonucleases through elevated Ca2+levels. In addition, electrophilic metabolites of AAP may inactivate caspases or their activation pathway. This indicates that AAP metabolism has the potential to inhibit signal transduction mechanisms of receptor-mediated apoptosis.