Measurement of the ratio between the reduced and oxidized forms of coenzyme Q10 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 CoQ10H2 (reduced form of coenzyme Q10) is easily oxidized to CoQ10 (oxidized form of coenzyme Q10), it has been proposed that the CoQ10H2/CoQ10 ratio may be used as a possible marker of in vivo oxidative stress. However, sample preparation has an important effect on the redox status of coenzyme Q10 due to the extreme sensitivity of CoQ10H2 towards oxidation. We now report a rapid, simple isocratic HPLC procedure for the determination of CoQ10H2 and CoQ10 in plasma isopropanol extracts, and we used this method to investigate conditions by which the CoQ10H2/CoQ10 ratio can be reliably measured. Our results indicate that CoQ10H2 is unstable in whole blood, plasma, and isopropanol extracts; subsequently the CoQ10H2/CoQ10 ratio changes considerably soon after a blood sample has been obtained. The time period since blood sampling and HPLC analysis, as well as the sample pretreatment procedure, are two factors that have a profound effect on the pre-analytical variation in the determination of the CoQ10H2/CoQ10 ratio. If these two factors are properly controlled, the CoQ10H2/CoQ10 ratio may be a sensitive and practical way to measure in vivo oxidative stress. Furthermore, this indicator is independent from plasma total cholesterol concentrations, implying that groups who differ with respect to cholesterol levels may be compared directly.