Total and Reduced/oxidized Forms of Coenzyme Q in Fibroblasts of Patients with Mitochondrial Disease

Coenzyme Q (CoQ) is involved in ATP production through electron transfer in the mitochondrial respiratory chain complex. CoQ receives electrons from respiratory chain complex I and II to become the reduced form, and then transfers electrons at complex III to become the oxidized form. The redox state of CoQ has been reported to be a marker of the mitochondrial metabolic state, but to our knowledge, no reports have focused on the individual quantification of reduced and oxidized CoQ or the ratio of reduced to total CoQ (reduced/total CoQ) in patients with mitochondrial diseases. We measured reduced and oxidized CoQ in skin fibroblasts from 24 mitochondrial disease patients, including 5 primary CoQ deficiency patients and 10 respiratory chain complex deficiency patients, and determined the reduced/total CoQ ratio. In primary CoQ deficiency patients, total CoQ levels were significantly decreased, however, the reduced/total CoQ ratio was not changed. On the other hand, in mitochondrial disease patients other than primary CoQ deficiency patients, total CoQ levels did not decrease. However, the reduced/total CoQ ratio in patients with respiratory chain complex IV and V deficiency was higher in comparison to those with respiratory chain complex I deficiency. Measurement of CoQ in fibroblasts proved useful for the diagnosis of primary CoQ deficiency. In addition, the reduced/total CoQ ratio may reflect the metabolic status of mitochondrial disease.