Plasma ratio of ubiquinol and ubiquinone as a marker of oxidative stress.

Oxidative stress is defined as a disturbance in the prooxidant-antioxidant balance in favor of the former and has been suggested to be a relevant factor in aging as well as in different pathological conditions, such as heart attack, diabetes, and cancer. Ubiquinol is very sensitive against oxygen radicals and gives ubiquinone as an oxidation product. Therefore, the ratio of ubiquinol to ubiquinone should be a good marker of oxidative stress because of its definition. A method for the simultaneous detection of ubiquinol-10 and ubiquinone-10 in human plasma is described. Heparinized human plasma was mixed with 5 volumes of methanol and 10 volumes of hexane. After vigorous shaking and centrifugation, the hexane phase (5 microliters) was injected immediately and directly on to reverse-phase HPLC equipped with an on-line reduction column and an electrochemical detector in order to avoid the oxidation of ubiquinol to ubiquinone. It was found that the ratio of ubiquinol-10 to ubiquinone-10 was about 95/5 in human plasma from healthy donors. A significant increase in the oxidized form (ubiquinone-10) content was observed in plasmas of patients with hepatitis, cirrhosis, and hepatoma when compared with normal subjects, suggesting increased oxidative stress in these patients.