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

BACKGROUND: 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 CoQ1 0 deficiency. METHODS: We determined the concentration and redoxstatus 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. RESULTS: 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. CONCLUSION: 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.