Measurement and stability of plasma reduced, oxidized and total coenzyme Q10 in humans.

There are findings indicating that a decreased ratio of plasma coenzyme Q10 (Q10) to LDL cholesterol could be associated with an increased risk of atherosclerosis. Furthermore, the proportion of plasma Q10H2 (reduced Q10, ubiquinol) of total Q10 has been shown to be attenuated in major diseases, such as hyperlipidemia and coronary artery disease. These observations suggest that measurement of plasma total Q10 and the proportion of plasma Q10H2 of total Q10 would be of clinical significance. However, epidemiological studies addressing this issue require large numbers of subjects, and measurements from unfrozen samples are unfeasible. For this reason, we evaluated the stability of Q10 samples during sample storage and processing. We also compared solid phase and hexane pre-treatments prior to high-performance liquid chromatographic determination of Q10. Our results indicate that samples for plasma total Q10 measurement can be pre-treated in normal laboratory lighting conditions, thawed and frozen several times, and stored deep frozen for a couple of years without changes in measured Q10 values. If purification of the samples by silica and C18 is needed, the best reproducibility tends to be achieved with powder treatment (not with cartridges). However, to measure successfully the proportion of plasma ubiquinol of total Q10, samples must be thawed, extracted, and analysed one at a time and quickly to ensure minimal ubiquinol oxidation during the measurement process.