N-Lactoyl amino acids as metabolic biomarkers differentiating low and high exercise response

Aerobic physical exercise has significant benefits for cardiovascular health; however, some individuals experience no benefit or even adverse effects. One reason for poor tolerance to aerobic exercise may be a low percentage of slow-twitch (oxidative) muscle fibers. This study aims to identify the metabolic signatures associated with low and high response to exercise by comparing the metabolic profiles of participants categorized according to their improvement of the 6-minute walking distance. In this study, pre- and postexercise intervention measurements of the 6-minute walking distance were conducted in forty-three lean and overweight young women, followed by non-targeted metabolomics analysis of 1039 known metabolites. An independent validation cohort comprising 791 individuals from the GTEx project was used to assess the gene expression of selected targets. The results indicated that a low improvement in the 6-minute walking distance (Δ 6-MWD = 27 meters) was associated with higher serum levels of N-lactoyl amino acid metabolites, particularly the exercise-inducible metabolite N-lactoyl phenylalanine (Lac-Phe) (FDR = 0.016), compared to high responders. Our results were corroborated in an independent validation cohort, which showed that the gene expression of cytosolic nonspecific dipeptidase (CNDP2), the enzyme responsible for Lac-Phe synthesis, is negatively associated with the percentage of slow-twitch muscle fibers (p < 0.0001). N-lactoyl amino acids may serve as biomarkers for rapid muscle fatigue and low response to exercise, and could be used as metabolic indicators to differentiate exercise response efficacy.