MEASUREMENT OF THE RATIO BETWEEN THE REDUCED AND OXIDIZED FORMS OF COENZYME Q(10) IN HUMAN PLASMA AS A POSSIBLE MARKER OF OXIDATIVE STRESS

It has been postulated that lipid peroxidation plays a crucial role in the pathogenesis of atherosclerosis. As CoQ(10)H(2) (reduced form of coenzyme Q(10)) is easily oxidized to CoQ(10) (oxidized form of coenzy me Q(10)), it has been pro posed that the CoQ(10)H(2)/CoQ(10) ratio ma y be used as a possible marker of in vivo oxidative stress. However, s ample preparation has an important effect on the redox status of coenz yme Q(10) due to the extreme sensitivity of CoQ(10)H(2) towards oxidat ion. We now report a rapid, simple isocratic HPLC procedure for the de termination of CoQ(10)H(2) and CoQ(10) in plasma isopropanol extracts, and we used this method to investigate conditions by which the CoQ(10 )H(2)/CoQ(10) ratio can be reliably measured. Our results indicate tha t CoQ(10)H(2) is unstable in whole blood, plasma, and isopropanol extr acts; subsequently the CoQ(10)H(2)/CoQ(10) ratio changes considerably soon after a blood sample has been obtained. The time period since blo od sampling and HPLC analysis, as well as the sample pretreatment proc edure, are two factors that have a profound effect on the pre-analytic al variation in the determination of the CoQ(10)H(2)/CoQ(10) ratio. if these two factors are properly controlled, the CoQ(10)H(2)/CoQ(10) ra tio may be a sensitive and practical way to measure in vivo oxidative stress. Furthermore, this indicator is independent from plasma total c holesterol concentrations, implying that groups who differ with respec t to cholesterol levels may be compared directly.