Prolonged oral coenzyme Q10-β-cyclodextrin supplementation increases plasma CoQ10 concentration and skeletal muscle complex I+III activity in young, untrained healthy Thoroughbreds

Coenzyme Q10 (CoQ10) is an essential component of the mitochondrial electron transport chain (ETC). Decreased skeletal muscle CoQ10 content may result in decreased ETC activity and energy production. This study aimed to test the hypothesis that prolonged supplementation with oral CoQ10 will increase plasma CoQ10 concentrations and skeletal muscle CoQ10 content in young, healthy untrained Thoroughbreds. Nineteen Thoroughbreds (27.5±9.7 months old; 11 males, 8 females) from one farm and maintained on a grass pasture with one grain meal per day were supplemented orally once per day for 9 weeks with 1.5 mg/kg body weight of a CoQ10-β-cyclodextrin inclusion complex. Whole-blood and skeletal muscle biopsies were collected before (T0) and after (T1) 9 weeks of supplementation. Plasma CoQ10 concentrations were determined via high-performance liquid chromatography. Skeletal muscle mitochondrial ETC combined complex I+III enzyme activity (an indirect measurement of CoQ10 content) was assessed spectrophotometrically and normalised to mitochondrial abundance. Results were analysed using a paired two-tailed Students t-test with P≤0.05 significant. Horses accepted supplementation with no adverse effects. The mean change in plasma CoQ10 concentration from T0 to T1 was significantly greater than zero (0.13±0.02 vs. 0.25±0.03 μg/ml, mean difference 0.12±0.03; P=0.004), although variability in absorbance resulted in only a 58% response rate. The mean change in skeletal muscle complex I+III activity from T0 to T1 was significantly greater than zero (0.36±0.04 vs. 0.59±0.05 pmol/min/mg of muscle, mean difference 0.23±0.05; P=0.0004), although T1 values for 3/19 horses decreased on average by 23% below T0 values. In conclusion, prolonged oral supplementation of the diet of young, healthy untrained Thoroughbreds with CoQ10 increased mean plasma CoQ10 concentration by 99% and mean skeletal muscle complex I+III activity by 65% with variability in absorbance among horses. Additional research is warranted investigating training and exercise effects on skeletal muscle CoQ10 content in CoQ10 supplemented and un-supplemented Thoroughbreds.