EVALUATION OF THE ANTIOXIDANT CAPACITY OF UBIQUINOL AND DIHYDROLIPOICACID

Ubiquinone and alpha-lipoic acid are natural constitutents which are i nvolved in mitochondrial energy metabolism. Their bioenergetic activit ies require redox-cycling. In the case of alpha-lipoic acid redox-cycl ing leads to dihydrolipoic acid which occurs in multienzyme complexes involved in the citric acid cycle while UQ recycles through semi-and d ivalently reduced ubiquinones in the respiratory chain. We have proved the validity of the concept about the antioxidant function of these n atural compounds in their reduced form. Ubiquinol was found to interfe re with lipid peroxidation of liposomal membranes being itself degrada ted by two consecutive oxidation steps. Dihydrolipoic acid was found t o totally recycle ubiquinone to the antioxidant active divalently redu ced form. In contrast to the antioxidative derived reaction products o f ubiquinols which in turn promoted lipid peroxidation, the antioxidan t derived reaction product of dihydrolipoic acid was the unreactive tw o electron oxidation product alpha-lipoic acid. Our experiments demons trate the existence of an dihydrolipoic acid driven recycling of UQ to the antioxidative-active UQH(2). The efficiency of the antioxidative capacity of the latter was found to be diminished through prooxidant a ctivities of the antioxidant-derived metabolites.