Abstract
In overdose acetaminophen (APAP) is hepatotoxic. Toxicity occurs by metabolism to N-acetyl-p-benzoquinone imine which covalently binds to proteins followed by protein nitration. Nitration can occur via the strong oxidant and nitrating agent, peroxynitrite formed from superoxide and nitric oxide (NO). In hepatocyte suspensions we reported that an inhibitor of neuronal nitric oxide synthase (nNOS; NOS1), which has been reported to be in mitochondria, inhibited toxicity and protein nitration. We recently showed that MnSOD (SOD2) was nitrated and inactivated in APAP treated mice. To understand the role of nNOS in APAP toxicity and MnSOD nitration, nNOS knockout (KO) and wildtype mice (WT) were administered APAP (300mg/kg). In WT serum ALT significantly increased at 6 and 8 h and serum AST significantly increased at 4, 6 and 8 h; however, in KO neither ALT nor AST significantly increased until 8 h. There were no significant differences in hepatic GSH depletion, APAP protein binding, hydroxynonenal covalent binding, or histopathological assessment of toxicity. The activity of hepatic MnSOD was significantly lower at 1-2 h in WT and subsequently increased at 8 h. MnSOD activity was not altered 0-6 h in KO but significantly decreased at 8 h. There were significant increases in MnSOD nitration at 1-8 h in WT and 6-8 h in KO. Significantly more nitration occurred at 1-6 h in WT than in KO. Surprisingly MnSOD was the only observed nitrated protein following APAP treatment. These data indicate a role for nNOS with inactivation of MnSOD and ALT release during APAP toxicity.
- Received May 19, 2011.
- Revision received October 12, 2011.
- Accepted October 13, 2011.
- The American Society for Pharmacology and Experimental Therapeutics