Inhibition of Peroxynitrite-Mediated Oxidation of Dopamine by Flavonoid and Phenolic Antioxidants and Their Structural Relationships

Authors

  • Nicole Kerry,

    1. Antioxidant Research Centre, Guy’s, King’s and St. Thomas’s School of Biomedical Sciences, King’s College, London, England
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  • Catherine Rice-Evans

    1. Antioxidant Research Centre, Guy’s, King’s and St. Thomas’s School of Biomedical Sciences, King’s College, London, England
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  • Lippincott Williams & Wilkins, Inc., Philadelphia

  • Abbreviations used: Rt, retention time; λmax, spectral maximum.

Address correspondence and reprint requests to Prof. C. Rice-Evans at Antioxidant Research Centre, Guy’s, King’s and St. Thomas’s School of Biomedical Sciences, Hodgkin Building, Guy’s Campus, King’s College, London SE1 9RT, U.K.

Abstract

Abstract: 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.

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