Anti/prooxidant activity of wine polyphenols in reactions of adrenaline auto-oxidation

Abstract

Adrenaline (epinephrine) belongs to catecholamine class. It is a neurotransmitter and both a hormone which is released by the sympathetic nervous system and adrenal medulla in response to a range of stresses in order to regulate blood pressure, cardiac stimulation, relaxation of smooth muscles and other physiological processes. Adrenaline exhibits an effective antioxidant capacity (1). However, adrenalin is capable to auto-oxidation and in this case it generates toxic reactive oxygen intermediates and adrenochrome. Under in vitro conditions, auto-oxidation of adrenaline occurs in an alkaline medium (2). The capacity of inhibition of adrenaline auto-oxidation for 38 wine polyphenols, ascorbic acid and Trolox was studied. Stock solutions of compounds in ethanol were prepared. Reaction mixtures containing 20 μL of sample, 20 µL of adrenaline solution (1mM, dissolve in distilled water) and 300 µl carbonate buffer (0.2 M, pH 10.55) were incubated at 36.6°C during 10 min. The absorbance of the resulting solution was measured at 347 nm using a BGM FLUOstar Omega plate reader. Absorbencies of samples in carbonate buffer (blank sample) and adrenaline in carbonate buffer under the same conditions were determined. Adrenaline auto-oxidation inhibition capacity (in %) was calculated as [(A-AE)/A] × 100, where A – absorbance of adrenalin in carbonate buffer, AE – difference between absorbance of the reaction mixture and absorbance of blank sample. In case when A < AE it was considered that the sample has pro-oxidant capacity. Various phenolic acids reacted quite differently. Chlorogenic acid had only a pro-oxidant action in the reactions of adrenalin auto-oxidation. Gallic acid showed the most antioxidant capacity (55.1%, in molar ratio 1:0.5, adrenaline/compound) among other tested phenolic acids. Ascorbic acid and Trolox inhibited the auto-oxidation of adrenaline to 51.4% and 8.99% respectively. Epigallocatechin and kaempferol have the most of inhibitory capacity (78.7% and 75.1%, respectively, at a molar ratio 1:0.5, adrenaline/compound) among other flavonoids aglycons. Adrenaline auto-oxidation inhibition capacity increased in the glycosylation of flavonoids. For example, the antioxidant activity of quercetin was 11.7% and rutin was 42.8%. with a molar ratio 1:1 for both. The results have shown that the antioxidant capacity decreased and prooxydant activity increased when reducing the number of hydroxy groups and increasing the amount of methyl groups in the structure of polyphenol.

References 1. Gülçin, İ. (2009) Antioxidant activity of L-adrenaline: A structure–activity insight. Chemico-Biological Interactions, 179, P. 71–80. 2. Sirota, T. V. (2011) A Novel Approach to Study the Reaction of Adrenaline Autooxidation: a Possibility for Polarographic Determination of Superoxide Dismutase Activity and Antioxidant Properties of Various Preparations. Biochemistry (Moscow) Suppl. Series B. Vol. 5 (3), P. 253–259.