Oxidative conversion of 6-nitrocatecholamines to nitrosating products: a possible contributory factor in nitric oxide and catecholamine neurotoxicity associated with oxidative stress and acidosis.
Oxidation of 6-nitrodopamine (1) and 6-nitronorepinephrine (2), as well as of the model compounds 4-nitrocatechol and 4-methyl-5-nitrocatechol, with horseradish peroxidase (HRP)/H(2)O(2), lactoperoxidase (LPO)/H(2)O(2), Fe(2+)/H(2)O(2), Fe(2+)-EDTA/H(2)O(2) (Fenton reagent), HRP or Fe(2+)/EDTA in combination with D-glucose-glucose oxidase, or Fe(2+)/O(2), resulted in the smooth formation of yellowish-brown pigments positive to the Griess assay. In the case of 1, formation of the Griess positive pigment (GPP-1) promoted by HRP/H(2)O(2) proceeded through the intermediacy of two main dimeric species that could be isolated and identified as 3 and the isomer 4, featuring the 4-nitro-6,7-dihydroxyindole system linked to a unit of 1 through ether bonds. Spectroscopic (FAB-MS, (1)H NMR) and chemical analysis of GPP-1 indicated a mixture of oligomeric species related to 3 and 4 in which oxidative modification of the nitrocatechol moiety of 1 led to the generation of reactive nitro groups supposedly linked to sp(3) hybridized carbons. In the pH range 3-6, GPP-1 induced concentration- and pH-dependent nitrosation of 2,3-diaminonaphthalene, but very poor (up to 2%) nitration of 600 microM tyrosine. At pH 7.4, 1 exerted significant toxicity to PC12 cells, while GPP-1 proved virtually innocuous. By contrast, when assayed on Lactobacillus bulgaricus cells at pH 3.5, 1 was inactive whereas GGP-1 caused about 70% inhibition of cell growth. Overall, these results hint at novel pH-dependent mechanisms of nitrocatecholamine-induced cytotoxicity of possible relevance to ischemia- or inflammation-induced catecholaminergic neuron damage.
Palumbo
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Laboratory of Biochemistry, Zoological Station Anton Dohrn, Villa Comunale 80121 Naples, Italy.
Napolitano
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Carraturo
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Russo
G L
GL
d'Ischia
M
M
D000138:Acidosis / Q000503:physiopathology*; D002395:Catecholamines / Q000633:toxicity*; D002455:Cell Division / Q000187:drug effects; D004298:Dopamine / Q000031:analogs & derivatives* / Q000737:chemistry*; D005029:Ethylenediamines; D016166:Free Radical Scavengers / Q000737:chemistry; D006861:Hydrogen Peroxide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007778:Lactobacillus / Q000187:drug effects / Q000502:physiology; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D009569:Nitric Oxide / Q000737:chemistry*; D009638:Norepinephrine / Q000031:analogs & derivatives* / Q000737:chemistry*; D016877:Oxidants / Q000737:chemistry; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D013424:Sulfanilamides
C403895:6-nitrodopamine; C100495:6-nitronorepinephrine; D002395:Catecholamines; D005029:Ethylenediamines; D016166:Free Radical Scavengers; C095000:Griess reagent; D016877:Oxidants; D013424:Sulfanilamides; D009569:Nitric Oxide; D006861:Hydrogen Peroxide; D004298:Dopamine; D009638:Norepinephrine