Is α-tocopherol a reservoir for α-tocopheryl hydroquinone

The products of oxidation of the a-tocopherol model compound, 2,2,5,7,8-pentamethyl-6-chromanol (PH) by t-butyl hydroperoxide in chloroform varied with the amount of water present. In the presence of a trace of water, the main products were the spirodimer (PSD) and spirotrimer (PST). As the content of water increased, the main product became 2-(3-hydroxy-3-methylbutyl)-3,5,6-trimethyl-1,4-benzoquinone (PQ). Oxidation ofPH in aqueous liposome suspension also producedPQ as the major product. These results suggested that, in aqueous solutions, the major oxidation product ofPH would bePQ and of α-tocopherol (TH) would be α-tocopheryl quinone (TQ). The ease of reduction ofPQ andTQ was studied in chemical and biological systems.PQ, TQ, and ubiquinone-10 (UQ) were rapidly reduced to their respective hydroquinones (PQH2,TQH2, andUQH2) atpH 7.3 by NADH plus FAD. Whole blood reducedPQ rapidly at 37°C toPQH2 but did not reduceTQ toTQH2. Human peripheral blood mononuclear cells took upTQ from a bovine serum albumin complex and reduced it to TQH2. Ingestion ofTQ (350 mg) by one of us (PSK) resulted in the formation ofTQH2 during a 5 h period. These results demonstrate that several biological systems are able to reduceTQ toTQH2 and that it is a reaction that may occur normally in vivo.