Exercise Training in Standardbred Horses Alters the Skeletal Muscle Metabolome and Plasma Amino Acid Profile: Implications for the “Athlete's Paradox”
Authors: Klein Dylan J. , Mirek Emily T. , Anthony Tracy G. , McKeever Kenneth H. 
Published: June 2021

To date equine skeletal muscle metabolism has centered on a limited number of candidate metabolites. As such, there is a dearth of information regarding global changes in skeletal muscle metabolism following exercise training. Thus, the purpose of this study was to determine the effects of exercise training on skeletal muscle metabolism through changes in the skeletal muscle metabolome in healthy, untrained Standardbred horses. In addition, we aimed to determine the extent to which protein metabolism is also altered through changes in the concentrations of plasma amino acids (AA). We hypothesized that training would significantly alter the skeletal muscle metabolome, as well as protein metabolism, as reflected in changes in the plasma AA profile. Eight untrained, Standardbred horses (n=4 mares, n=4 geldings; 3–9 yrs; 485 ± 13 kg, mean ± S.E.) underwent a 12‐week training program that significantly increased VO2 and exercise capacity (p<0.05). Percutaneous needle biopsies were obtained from the M. gluteus medius in the untrained state (UT) and again following training (TR). Frozen muscle samples were submitted to Metabolon, Inc. for global metabolite profiling via UHPLC‐MS/MS. Blood obtained via jugular venipuncture was placed into EDTA tubes for the measurement of plasma AA concentrations via HPLC. For metabolomics analysis, differences between UT and TR samples were evaluated by two way‐ANOVA and Welch's t‐test for paired comparisons and considered significant at p<0.05. For plasma AAs, differences were analyzed via Student's t‐test and considered significant at p<0.05. Training resulted in significant alterations in lipid, branched‐chain amino acid (BCAA), and nucleotide metabolite classes in skeletal muscle. Of note, analysis revealed significant increases in the relative abundance of almost every identified FFA and complex lipid species in TR compared to UT muscle (p<0.05), particularly the long‐chain (LC)‐acylcarnitines and diacylglycerides (DAGs) (1.5 to 2.3‐fold increases). Further, TR muscle exhibited increased fold‐changes (1.2 to 4.2‐fold) of C4 and several C5 BCAA‐derived acylcarnitines compared to UT (p<0.05). In plasma, training caused a significant 36% increase in the concentration of total essential AAs (p<0.05), of which and interestingly there was a significant increase in total BCAAs (42%, p<0.05) and phenylalanine (27%, p<0.05). In conclusion, exercise training significantly increased blood concentrations of total EAAs and BCAAs alongside significant increases in the relative abundances of certain skeletal muscle metabolites (i.e. LC‐acylcarnitines, BCAA‐derived acylcarnitines, and DAGs) that have been shown to be elevated during obesity and are proposed to play a role in the development of insulin resistance. These data underscore the complex nature of static metabolic signatures and the role that certain metabolites play in mediating health and disease. Future research should aim to utilize other sophisticated techniques that can address issues of metabolite flux and tissue utilization.Support or Funding InformationThis research was supported by: the New Jersey Institute for Food, Nutrition and Health (IFNH), USDA NIFA (NC 1184), the Rutgers University Equine Science Center (ESC), and the New Jersey Agriculture Experiment Station (NJAES).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.