Inhibition of peroxynitrite-mediated oxidation of dopamine by flavonoid and phenolic antioxidants and their structural relationships.
The interaction between peroxynitrite and dopamine and the inhibition of this reaction by plant-derived antioxidants have been investigated. Peroxynitrite promoted the oxidation of dopamine to 6-hydroxyindole-5-one as characterised by HPLC and photodiode array spectra, akin to the products of the tyrosinase-dopamine reaction, but no evidence of dopamine nitration was obtained. Although peroxynitrite did not cause nitration of dopamine in vitro, the catecholamine is capable of inhibiting the formation of 3-nitrotyrosine from peroxynitrite-mediated nitration of tyrosine. The plant-derived phenolic compounds, caffeic acid and catechin, inhibited peroxynitrite-mediated oxidation of dopamine. This effect is attributed to the ability of catechol-containing antioxidants to reduce peroxynitrite through electron donation, resulting in their oxidation to the corresponding o-quinones. The antioxidant effect of caffeic acid and catechin was comparable to that of the endogenous antioxidant, glutathione. In contrast, the structurally related monohydroxylated hydroxycinnamates, p-coumaric acid and ferulic acid, which inhibit tyrosine nitration through a mechanism of competitive nitration, did not inhibit peroxynitrite-induced dopamine oxidation. The findings of the present study suggest that certain plant-derived phenolics can inhibit dopamine oxidation.
Kerry
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Antioxidant Research Centre, Guy's, King's and St. Thomas's School of Biomedical Sciences, King's College, London, England, UK.
Rice-Evans
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C
D000975:Antioxidants / Q000494:pharmacology*; D002109:Caffeic Acids / Q000737:chemistry / Q000494:pharmacology; D002392:Catechin / Q000737:chemistry / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D003373:Coumaric Acids / Q000737:chemistry / Q000494:pharmacology; D004298:Dopamine / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology*; D014442:Monophenol Monooxygenase / Q000378:metabolism; D009566:Nitrates / Q000737:chemistry*; D010084:Oxidation-Reduction; D010636:Phenols / Q000494:pharmacology*; D011422:Propionates; D013329:Structure-Activity Relationship; D014443:Tyrosine / Q000737:chemistry
D000975:Antioxidants; D002109:Caffeic Acids; D003373:Coumaric Acids; D005419:Flavonoids; D009566:Nitrates; D010636:Phenols; D011422:Propionates; C039642:peroxynitric acid; D014443:Tyrosine; D002392:Catechin; C004999:ferulic acid; D014442:Monophenol Monooxygenase; C495469:p-coumaric acid; C040048:caffeic acid; D004298:Dopamine