Nitric oxide reaction with lipid peroxyl radicals spares alpha-tocopherol during lipid peroxidation. Greater oxidant protection from the pair nitric oxide/alpha-tocopherol than alpha-tocopherol/ascorbate.
The reactions of nitric oxide ((.)NO) and alpha-tocopherol (alpha-TH) during membrane lipid oxidation were examined and compared with the pair alpha-TH/ascorbate. Nitric oxide serves as a more potent inhibitor of lipid peroxidation propagation reactions than alpha-TH and protects alpha-TH from oxidation. Mass spectrometry, oxygen and (.)NO consumption, conjugated diene analyses, and alpha-TH fluorescence determinations all demonstrated that (.)NO preferentially reacts with lipid radical species, with alpha-TH consumption not occurring until (.)NO concentrations fell below a critical level. In addition, alpha-TH and (.)NO cooperatively inhibit lipid peroxidation, exhibiting greater antioxidant capacity than the pair alpha-TH/ascorbate. Pulse radiolysis analysis showed no direct reaction between (.)NO and alpha-tocopheroxyl radical (alpha-T(.)), inferring that peroxyl radical termination reactions are the principal lipid-protective mechanism mediated by (.)NO. These observations support the concept that (.)NO is a potent chain breaking antioxidant toward peroxidizing lipids, due to facile radical-radical termination reactions with lipid radical species, thus preventing alpha-TH loss. The reduction of alpha-T(.) by ascorbate was a comparatively less efficient mechanism for preserving alpha-TH than (.)NO-mediated termination of peroxyl radicals, due to slower reaction kinetics and limited transfer of reducing equivalents from the aqueous phase. Thus, the high lipid/water partition coefficient of (.)NO, its capacity to diffuse and concentrate in lipophilic milieu, and a potent reactivity toward lipid radical species reveal how (.)NO can play a critical role in regulating membrane and lipoprotein lipid oxidation reactions.
Rubbo
H
H
Departamento de Bioquímica, Facultad de Medicina, Universidad de la República, 11800 Montevideo, Uruguay. hrubbo@fmed.edu.uy
Radi
R
R
Anselmi
D
D
Kirk
M
M
Barnes
S
S
Butler
J
J
Eiserich
J P
JP
Freeman
B A
BA
D000578:Amidines / Q000494:pharmacology; D000975:Antioxidants / Q000494:pharmacology*; D001205:Ascorbic Acid / Q000494:pharmacology*; D005609:Free Radicals; D019787:Linoleic Acid / Q000378:metabolism; D015227:Lipid Peroxidation; D009569:Nitric Oxide / Q000378:metabolism*; D010084:Oxidation-Reduction; D014810:Vitamin E / Q000494:pharmacology*
D000578:Amidines; D000975:Antioxidants; D005609:Free Radicals; D014810:Vitamin E; D009569:Nitric Oxide; C046728:2,2'-azobis(2-amidinopropane); D019787:Linoleic Acid; D001205:Ascorbic Acid