Nitric oxide is an environmental toxin. Surprisingly NO is a ubiquitous biological messenger. Nitric oxide itself is a weak oxidant, but it reacts with O2-. in the lung to produce peroxynitrite and peroxynitrous acid. HOONO, potent oxidants and toxins. The three specific aims of this proposal concern the mechanisms that explain the toxicity of HOONO. (#1) Peroxynitrite undergoes a pH-dependent rearrangement reaction to form nitrate, an important pathway for detoxification of HOONO. The mechanism of this reaction has been reported to involve radicals: HOONO to HO. + .NO2 to HONO2. However, our preliminary data suggest the mechanism involves a molecular (non-radical) rearrangement. HOONO exists in both cisoid and transoid forms, which calculations predict have acid pK constants that differ by about 1.3 pH units. The published analysis of the rate of HOONO disappearance versus pH proposes just one HOONO species and a single wave with an inflection point at the reported pK of HOONO, 6.8. However, preliminary experimental data are fit better by a curve with two waves, involving two species (presumed to be cis and trans) with pK values that differ by about 1.5 units. By obtaining sufficient data at about pH 7, we will be able to establish whether this detoxification reaction involves one or two HOONO species and occurs via a molecular rearrangement or via the hydroxyl radical. (#2) HOONO can oxidize biomolecules via an SN2 reaction of nucleophilic species Y:to give Y=O and HNO2. This is involved, for example, in the inactivation of methionine-containing proteins. The SN2 reaction will be studied using the oxidation of methionine to methionine sulfoxide. Reactions of methionine amide and ester also will be studied. (#3) Most inorganic and organic peroxyacids that oxidize sulfides to sulfoxides also epoxidize olefins. We will test whether HOONO can epoxidize cyclohexene, methyl oleate and 7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene. We also will ask if the ion -OO-N=O can epoxidize alpha,beta-unsaturated carbonyl compounds via a Michael addition-elimination mechanism. All three of the specific aims will be studied both in systems where trace transition metals have been removed and in systems to which chelates of redox-active transition metal ions have been added.

Agency
National Institute of Health (NIH)
Institute
National Institute of Environmental Health Sciences (NIEHS)
Type
Research Project (R01)
Project #
5R01ES006754-05
Application #
2838215
Study Section
Chemical Pathology Study Section (CPA)
Project Start
1994-09-01
Project End
2000-11-30
Budget Start
1998-12-01
Budget End
2000-11-30
Support Year
5
Fiscal Year
1999
Total Cost
Indirect Cost
Name
Louisiana State University A&M Col Baton Rouge
Department
Miscellaneous
Type
Schools of Arts and Sciences
DUNS #
075050765
City
Baton Rouge
State
LA
Country
United States
Zip Code
70803
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Zhang, H; Squadrito, G L; Uppu, R et al. (1999) Reaction of peroxynitrite with melatonin: A mechanistic study. Chem Res Toxicol 12:526-34
Bolzan, R M; Cueto, R; Squadrito, G L et al. (1999) Direct and simultaneous ultraviolet second-derivative spectrophotometric determination of nitrite and nitrate in preparations of peroxynitrite. Methods Enzymol 301:178-87
Grace, S C; Yamasaki, H; Pryor, W A (1999) Spin stabilizing approach to radical characterization of phenylpropanoid antioxidants: an ESR study of chlorogenic acid oxidation in the horseradish peroxidase, tyrosinase, and ferrylmyoglobin protein radical systems. Basic Life Sci 66:435-50
Salgo, M G; Cueto, R; Winston, G W et al. (1999) Beta carotene and its oxidation products have different effects on microsome mediated binding of benzo[a]pyrene to DNA. Free Radic Biol Med 26:162-73
Squadrito, G L; Pryor, W A (1998) The nature of reactive species in systems that produce peroxynitrite. Chem Res Toxicol 11:718-9
Uppu, R M; Lemercier, J N; Squadrito, G L et al. (1998) Nitrosation by peroxynitrite: use of phenol as a probe. Arch Biochem Biophys 358:1-16
Grace, S C; Salgo, M G; Pryor, W A (1998) Scavenging of peroxynitrite by a phenolic/peroxidase system prevents oxidative damage to DNA. FEBS Lett 426:24-8
Zhang, H; Squadrito, G L; Pryor, W A (1998) The reaction of melatonin with peroxynitrite: formation of melatonin radical cation and absence of stable nitrated products. Biochem Biophys Res Commun 251:83-7
Kafoury, R M; Pryor, W A; Squadrito, G L et al. (1998) Lipid ozonation products activate phospholipases A2, C, and D. Toxicol Appl Pharmacol 150:338-49

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