Ca(++)-activated DNA fragmentation and dimethylnitrosamine-induced hepatic necrosis: effects of Ca(++)-endonuclease and poly(ADP-ribose) polymerase inhibitors in mice.
Several hepatotoxic agents damage Ca++ regulation and produce toxic cell death in a manner consistent with a cause-and-effect relationship; however, vital targets of Ca++ remain unidentified. Recent results show that DNA may be the chief Ca++ target during apoptosis, a form of cell death considered distinct from toxic cell death or necrosis. The present studies explored whether nuclear Ca++ regulation is lost before dimethylnitrosamine-induced necrosis, whether DNA is attacked by Ca(++)-dependent endonucleases and whether inhibitors of Ca(++)-endonuclease activity and the DNA repair enzyme poly(ADP-ribose)polymerase affect necrosis. Adult male ICR mice received 100 mg/kg of dimethylnitrosamine i.p. By 2 to 4 hr, total nuclear Ca++ reached 150 to 180% of control and DNA fragmentation was 140 to 170% of control. Electrophoresis of DNA revealed a sharp decline in genomic DNA with the appearance of DNA fragments in a ladder-like pattern. Ca++ elevation and DNA fragmentation preceded toxic cell death by 4 hr or more and reached peak values at 18 to 24 hr, coincident with maximal alanine aminotransferase leakage. Aurintricarboxylic acid, a Ca(++)-endonuclease inhibitor, reduced toxicity 67%. 3-Aminobenzamide, nicotinamide adenine dinucleotide and theophylline, inhibitors of poly(ADP-ribose)polymerase-mediated DNA repair, potentiated liver damage 2-fold. These results support the hypothesis that DNA fragmentation plays a contributing role in toxic cell death induced by dimethylnitrosamine. Furthermore, the findings suggest that new opportunities may exist to moderate the toxicity of alkylating hepatotoxins by altering DNA regulation.
Ray
S D
SD
Toxicology Program, College of Pharmacy, University of New Mexico, Albuquerque 87131-1066.
Sorge
C L
CL
Kamendulis
L M
LM
Corcoran
G B
GB
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D004249:DNA Damage; D004128:Dimethylnitrosamine / Q000633:toxicity*; D004720:Endonucleases / Q000037:antagonists & inhibitors*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR
D004791:Enzyme Inhibitors; D004720:Endonucleases; D004128:Dimethylnitrosamine; D002118:Calcium