EVALUATION OF PLASMA LOW-MOLECULAR-WEIGHT ANTIOXIDANT CAPACITY BY CYCLIC VOLTAMMETRY

The low molecular weight antioxidants (LMWA) of biological samples inc lude many compounds and contribute to the total antioxidant capacity o f the system. They act as direct chemical scavengers neutralizing, rea ctive oxygen-derived species (ROS), and contribute to the ability of t he sample to cope with oxidative stress. We propose cyclic voltammetry (CV) as a new method for evaluating the antioxidant capacity of plasm a-LMWA and the severity of oxidative stress exerted on the plasma. It is based on the reducing properties of these molecules. CV has been pr oven to be a simple, sensitive and reliable method. Its tracing does n ot change during storage of frozen plasma for up to six months. We ana lyzed the CV tracings by the oxidation potential E(1/2), and the curre nt heights Ia of its anodic wave(s). E(1/2) indicates the specific com ponent of the LMWA and its ability to donate electron(s); Ia indicates the concentration of this component. Two anodic waves have been ident ified in human plasma, at E(1/2) = 420 +/- 25 and 920 +/- 25 mV. Ascor bate (AA) and urate (UA) were identified as major LMWA components of t he first anodic wave, and were confirmed by HPLC-electrochemical detec tion. Ia was shown to depend linearly on the concentration of either o f these LMWA, both in buffer and in plasma. Oxidative stress exerted b y exposure to peroxyl radicals, copper ions and ionizing irradiation c aused marked changes in the CV tracing. These changes represent corres ponding alterations particularly in la, rather than in E(1/2). The Ia and E(1/2) values reflect the antioxidant capacity of the plasma, whil e the change of Ia value represents the severity of the oxidative stre ss induced. Copyright (C) 1996 Elsevier Science Inc.