Antioxidant, Reactive Oxygen Species, and Coenzyme Q10 Concentrations and Expression of Electron Transfer Proteins in Thoroughbreds with Recurrent Exertional Rhabdomyolysis

In the mitochondria, complexes I and III of the electron transport system (ETS) generate reactive oxygen species (ROS) during exercise that are reduced by antioxidants to mitigate oxidative stress. Among these antioxidants are thiol-based antioxidants such as glutathione as well as coenzyme Q10 (CoQ10), which also transports electrons from complex I and II to complex III. Recurrent exertional rhabdomyolysis (RER) is associated with aberrant calcium regulation with the potential for excessive mitochondrial calcium uptake impacting mitochondria and ROS. We hypothesized that there would be a decrease in CoQ10 concentrations, as well as an increase in ROS and peptide subunits of ETS complexes in Thoroughbreds with RER. Concentrations of CoQ10 (LC/MS/MS), thiol-based antioxidants (LC/MS/MS), ROS (OxiSelect, Cell Biolabs), and citrate synthase activity (CS fluorometry) were determined in gluteal muscle biopsies from Thoroughbred mares with a history of, but not currently experiencing, rhabdomyolysis (n = 20, RER; mean ± SD age 3.3 ± 1.3 yr), compared with healthy race-trained mares at the same facility (n = 8, control; age 2.9 ± 0.8 yr). RER and control were compared by unpaired t-test. Subunit peptide components of the ETS were analyzed in 5 RER and 5 control mares using tandem mass tag proteomic analysis (FDR < 0.05). CoQ10 (P = 0.36), ROS (P = 0.36), and thiol (P = 0.99) concentrations were not significantly different between RER and controls. CS activity, a marker for mitochondrial volume density, did not differ between RER and controls (P = 0.39). ETS subunits were, however, differentially expressed in RER versus controls, with decreased expression of 11 complex I, 2 complex II, 2 complex III, 4 complex IV and 9 ATP synthase peptide subunits (P < 0.01). In conclusion, antioxidant concentrations and mitochondrial volume density did not differ in control versus RER mares between episodes of rhabdomyolysis. Expression, however, of specific peptide subunits within ETS complexes was consistently decreased in RER mares, which could be related to impacts from mitochondrial calcium buffering. Further investigation into ETS function in RER racehorses is warranted.

Henry, M., C. Fenger, J. Pagan, L. Sordillo, J. Gandy, and S. Valberg. 2021. Antioxidant, reactive oxygen species, and coenzyme Q10 concentrations and expression of electron transfer proteins in Thoroughbreds with recurrent exertional rhabdomyolysis. Journal of Equine Veterinary Science 100:103487.