title: Effect of inhibitors of nitric oxide synthase on acetaminophen-induced hepatotoxicity in mice.
abstract: We recently reported that following a toxic dose of acetaminophen to mice, tyrosine nitration occurs in the protein of cells that become necrotic. Nitration of tyrosine is by peroxynitrite, a species formed from nitric oxide (NO) and superoxide. In this manuscript we studied the effects of the NO synthase inhibitors N-monomethyl-l-arginine (l-NMMA), N-nitro-l-arginine methyl ester (NAME), l-N-(1-iminoethyl)lysine (l-NIL), and aminoguanidine on acetaminophen hepatotoxicity. Acetaminophen (300 mg/kg) increased serum nitrate/nitrite and alanine aminotransferase (ALT) levels, indicating increased NO synthesis and liver necrosis, respectively. None of the NO synthase inhibitors reduced serum ALT levels. In fact, l-NMMA, l-NIL, and aminoguanidine significantly augmented acetaminophen hepatotoxicity at 4 h. A detailed time course indicated that aminoguanidine (15 mg/kg at 0 h and 15 mg/kg at 2 h) significantly increased serum ALT levels over that for acetaminophen alone at 2 and 4 h; however, at 6 and 8 h serum ALT levels in the two groups were identical. At 2 h following acetaminophen plus aminoguanidine NO synthesis was significantly increased; however, at 4, 6, and 8 h NO synthesis was significantly decreased. Aminoguanidine also decreased acetaminophen-induced nitration of tyrosine. Acetaminophen alone did not induce lipid peroxidation, but acetaminophen plus aminoguanidine significantly increased hepatic lipid peroxidation (malondialdehyde levels) at 2, 4, and 6 h. These data are consistent with NO having a critical role in controlling superoxide-mediated lipid peroxidation in acetaminophen hepatotoxicity. Thus, acetaminophen hepatotoxicity may be mediated by either lipid peroxidation or by peroxynitrite.
authors.affiliation: Department of Pharmacology and Toxicology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA. HinsonJackA@UAMS.edu
authors.forename: Jack A
authors.initials: JA
authors.lastname: Hinson
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Bucci
authors.forename: Lisa K
authors.initials: LK
authors.lastname: Irwin
authors.forename: Sherryll L
authors.initials: SL
authors.lastname: Michael
authors.forename: Philip R
authors.initials: PR
authors.lastname: Mayeux
mesh_terms: D000082:Acetaminophen / Q000633:toxicity*; D000410:Alanine Transaminase / Q000097:blood*; D018712:Analgesics, Non-Narcotic / Q000633:toxicity; D000818:Animals; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006146:Guanidines / Q000494:pharmacology; D008099:Liver / Q000166:cytology / Q000187:drug effects*; D008239:Lysine / Q000031:analogs & derivatives* / Q000494:pharmacology; D008297:Male; D051379:Mice; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000097:blood; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D019323:omega-N-Methylarginine / Q000494:pharmacology
chemical_list: D018712:Analgesics, Non-Narcotic; D004791:Enzyme Inhibitors; D006146:Guanidines; C090663:N(6)-(1-iminoethyl)lysine; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D000082:Acetaminophen; D019001:Nitric Oxide Synthase; D000410:Alanine Transaminase; D008239:Lysine; C004479:pimagedine; D019331:NG-Nitroarginine Methyl Ester