Determination of Coenzyme Q10 Status in Blood Mononuclear Cells, Skeletal Muscle, and Plasma by HPLC with Di-Propoxy-Coenzyme Q10 as an Internal Standard

Coenzyme Q10 (CoQ10), the predominant ubiquinone species in humans, functions as an electron carrier in the mitochondrial electron transport chain (ETC) and as an intracellular antioxidant (1). Although primary CoQ10 deficiency is rare, a profound deficiency in skeletal muscle CoQ10 has been reported in patients with multisystem mitochondrial encephalomyopathies (2)(3). Cardiovascular disease has been associated with a CoQ10 deficiency (4)(5), and it is becoming increasingly apparent that other groups of patients may become CoQ10 deficient, particularly individuals with ataxia (6) and some patients receiving statins (7).When assessing tissue CoQ10 status, we have found that the lack of a commercially available nonphysiologic internal standard (IS) is a major difficulty. Although naturally occurring ubiquinones have been used as ISs in this determination, they are not free from the influence of ubiquinones that might be present in human tissue as the result of dietary contamination (8) or synthesis by microorganisms (9)(10). There is a need, therefore, for an alternative IS that is not influenced by exogenous/endogenous ubiquinones. Di-ethoxy-CoQ10 has been suggested as a nonphysiologic IS to determine CoQ10 (11). In this study we evaluated this IS along with di-propoxy-CoQ10 for their suitability to determine tissue CoQ10. Reference intervals were established for the CoQ10 concentration of skeletal muscle, blood mononuclear cells (MNCs), and plasma. A patient with a suspected CoQ10 deficiency was subsequently identified.Reference intervals were established for the following: (a) , skeletal muscle from 26 patients [mean (SE) age, 24.5 (3.9) years; range, 0.5–59 years; ratio of males to females, 7:6] with no evidence of an ETC deficiency detected in their skeletal muscle biopsies; (b) , MNCs from 17 healthy volunteers and 13 disease controls with no clinical evidence of …