Abstract
In overdose acetaminophen (APAP) is hepatotoxic. Toxicity occurs by metabolism to N-acetyl-p-benzoquinone imine, which depletes GSH and 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 manganese superoxide dismutase (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 wild-type (WT) mice were administered APAP (300 mg/kg). In WT mice serum alanine aminotransferase (ALT) significantly increased at 6 and 8 h, and serum aspartate aminotransferase (AST) significantly increased at 4, 6 and 8 h; however, in KO mice 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 to 2 h in WT mice and subsequently increased at 8 h. MnSOD activity was not altered at 0 to 6 h in KO mice but was significantly decreased at 8 h. There were significant increases in MnSOD nitration at 1 to 8 h in WT mice and 6 to 8 h in KO mice. Significantly more nitration occurred at 1 to 6 h in WT than in KO mice. MnSOD was the only observed nitrated protein after APAP treatment. These data indicate a role for nNOS with inactivation of MnSOD and ALT release during APAP toxicity.
Footnotes
This work was supported by the National Institutes of Health National Institute of Diabetes and Digestive and Kidney Diseases [Grants R01-DK079008, R01-DK059872, R01-DK75936].
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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ABBREVIATIONS:
- APAP
- acetaminophen
- APAP-Cys
- 3-cystein-S-yl-acetaminophen
- NAPQI
- N-acetyl-p-benzoquinone imine
- ALT
- alanine aminotransferase
- AST
- aspartate aminotransferase
- NO
- nitric oxide
- nNOS
- neuronal NO synthase (NOS1)
- iNOS
- inducible NO synthase (NOS2)
- SOD
- superoxide dismutase
- MnSOD
- manganese SOD (SOD2)
- MPT
- mitochondrial permeability transition
- WT
- wild type
- KO
- knockout
- GAPDH
- glyceraldehyde-3-phosphate dehydrogenase
- 4-HNE
- 4-hydroxynonenal
- NT
- nitrotyrosine.
- Received May 19, 2011.
- Accepted October 13, 2011.
- Copyright © 2012 by The American Society for Pharmacology and Experimental Therapeutics
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