title: Inhibition of Fas receptor (CD95)-induced hepatic caspase activation and apoptosis by acetaminophen in mice.
abstract: 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-CHF2 had 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.
authors.affiliation: Department of Pharmacology, Pharmacia & Upjohn, Inc., Kalamazoo, Michigan 49007, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Lawson
authors.forename: M A
authors.initials: MA
authors.lastname: Fisher
authors.forename: C A
authors.initials: CA
authors.lastname: Simmons
authors.forename: A
authors.initials: A
authors.lastname: Farhood
authors.forename: H
authors.initials: H
authors.lastname: Jaeschke
mesh_terms: D000082:Acetaminophen / Q000633:toxicity*; D018712:Analgesics, Non-Narcotic / Q000633:toxicity*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D016227:Benzoquinones / Q000378:metabolism; D015153:Blotting, Western; D020169:Caspases / Q000378:metabolism*; D053938:DNA Fragmentation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D004797:Enzyme-Linked Immunosorbent Assay; D007097:Imines / Q000378:metabolism; D020287:In Situ Nick-End Labeling; D008099:Liver / Q000187:drug effects* / Q000201:enzymology; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D019014:fas Receptor / Q000502:physiology*
chemical_list: D018712:Analgesics, Non-Narcotic; D016227:Benzoquinones; D007097:Imines; D019014:fas Receptor; D000082:Acetaminophen; D020169:Caspases; C028473:N-acetyl-4-benzoquinoneimine