Ca2+-calmodulin antagonist chlorpromazine and poly(ADP-Ribose) polymerase modulators 4-aminobenzamide and nicotinamide influence hepatic expression of bcl-XL and p53 and protect against acetaminophen-induced programmed and unprogrammed cell death in mice

Acetaminophen (AAP), the analgesic hepatotoxicant, is a powerful inducer of oxidative stress, DNA fragmentation, and apoptosis. The anti-apoptotic onc ogene bcl-XL, and the pro-apoptotic oncogene p53 are two key regulators of cell cycle progression and/or apoptosis subsequent to DNA damage in vitro a nd in vivo. This study investigated the effect of AAP on the expression of these oncogenes and whether agents that modulate DNA fragmentation (chlorpr omazine, CPZ) and DNA repair through poly(ADP-Ribose) polymerase (PAR-P) ac tivity (4-AB: 4-aminobenzamide) can protect against AAP-induced hepatotoxic ity by inhibiting oxidative stress, DNA fragmentation, and/or by altering t he expression of bcl-XL and p53. In addition, the protective effect of supp lemental nicotinamide (NICO), known to be depleted in cells with high PARP activity during DNA repair, is similarly evaluated. Male ICR mice (3 months old) were administered vehicle alone; nontoxic doses of 4-AB (400 mg/kg, i p), NICO (250 mg/kg, ip) or CPZ (25 mg/kg, ip), hepatotoxic dose of AAP alo ne (500 mg/kg, ip), or AA-P plus one of the protective agents 1 h later. Al l animals were sacrificed 24 h following AA-P administration. Serum alanine aminotransferase, activity (ALT), hepatic histopathology and lipid peroxid ation, DNA damage, and expression of bcl-XL and p53 (western blot analysis) were compared in various groups. All of the three agents significantly pre vented AAP-induced liver injury, lipid peroxidation, DNA damage, and associ ated apoptotic and necrotic cell deaths, 4-AB being the most effective and NICO the least. Compared to control, there was a considerable decrease in b cl-XL expression, and an increase in p53 expression in AAP-exposed livers. The effect of AAP on bcl-XL was antagonized and that on p53 was synergized by the PARP-modulator 4-AB as well as NICO, whereas the endonuclease inhibi tor CPZ was without effect on either bcl-XL or p53 expression. These result s suggest that the hepatotoxic effect of AA-P involves multiple mechanisms including oxidative stress, upregulation. of endonuclease (or cas ase-activ ated DNAse) and alteration of pro- and anti-apoptotic oncogenes. The observ ed antagonism of AAP-induced hepatocellular apoptosis and/or necrosis by mo dulators of multiple processes including DNA repair suggests the likelihood that a more effective therapy against AAP intoxication should involve a co mbination of antidotes. (C) 2001 Elsevier Science Inc.