SIMULTANEOUS DETERMINATION OF HOMOLOGS OF VITAMIN-E AND COENZYME-Q AND PRODUCTS OF ALPHA-TOCOPHEROL OXIDATION

A sensitive procedure is described for the simultaneous determination of vitamin E and coenzyme Q homologues and alpha-tocopherol oxidation products using two-isocratic step high pressure liquid chromatography (HPLC) and electrochemical detection in the oxidative mode. Zinc-catal yzed reduction in a post-column reactor allows the detection of alpha- tocopherolquinone, epoxy-tocopherolquinone, and ubiquinones, This tech nique was used to quantify lipophilic antioxidants in the liver tissue of rats treated or not with alpha-tocopherolquinone and in a plant oi l. alpha-Tocopherolquinone and its epoxide derivatives, formed from al pha-tocopherol during iron-catalyzed phospholipid peroxidation, were a lso determined in a liposome suspension, The high selectivity and sens itivity of the coulometric detection system enabled use of low oxidati on potentials giving little baseline noise, while a fast isolation pro cedure and quantitative recoveries of all oxidized and reduced forms m ade it possible to measure a high ubiquinol/ubiquinone ratio in Liver tissue. Administration of alpha-tocopherolquinone to rats did not alte r the antioxidant status of the liver, despite strong accumulation of both this quinone and its reduced form, alpha-tocopherolhydroquinone. These results indicate the presence of an efficient reductase and sugg est that it could contribute to the protection of cellular membranes f rom oxidative stress.