Oxidized proportion of muscle coenzyme Q10 increases with age in healthy children.

Coenzyme Q10 (CoQ10) is synthesized in most human tissues, with high concentration in the skeletal muscle. CoQ10 functions in the mitochondrial respiratory chain and serves as a potent liphophilic antioxidant in membranes. CoQ10 deficiency impairs mitochondrial ATP synthesis and increases oxidative stress. It has been suggested that plasma CoQ10 status is not a robust proxy for the diagnosis of CoQ10 deficiency.We determined the concentration and redox-status of CoQ10 in plasma and muscle tissue from 140 healthy children (0.8-15.3 y) by high-performance liquid chromatography (HPLC) with electrochemical detection.There was no correlation between CoQ10 concentration or redox status between plasma and muscle tissue. Lipid-related CoQ10 plasma concentrations showed a negative correlation with age (Spearman's, P ≤ 0.02), but there was no significant age-related correlation for muscle concentration. In muscle tissue, we found a distinct shift in the redox status in favor of the oxidized proportion with increasing age (Spearman's, P ≤ 0.00001). Reference values for muscle CoQ10 concentration (40.5 ± 12.2 pmol/mg wet tissue) and CoQ10 redox status (46.8 ± 6.8% oxidized within total) were established for healthy children.The age-related redox shift in muscle tissue suggests changes in antioxidative defense during childhood. The reference values established here provide a necessary prerequisite for diagnosing early CoQ10 deficiency.