Exercise and Carnosine Modulate Microbiota-Derived Metabolites, Myokines, and Cardiometabolic Profiles in Rats: A Randomized Controlled Trial

Background/Objectives: Carnosine and exercise independently improve metabolic health, yet their combined effects on myokines and microbiota-derived metabolites remain underexplored. This study evaluated the synergistic impact of carnosine supplementation and exercise intensity on microbiota-derived metabolites, as well as skeletal muscle and myocardial expression of irisin and myonectin, focusing on lipid and glycemic regulation. Methods: A randomized post-test control study was conducted using 49 male Sprague Dawley rats (9 weeks old; 250.39 ± 1.85 g), divided into 7 groups: control (C), sham (S), moderate-intensity continuous training (MICT), high-intensity continuous training (HICT), carnosine (CA), MICT with carnosine (MICT_CA), and HICT with carnosine (HICT_CA). Interventions included treadmill-based moderate or high-intensity training and carnosine supplementation (100 mg/kg/day) for 5 weeks. Blood samples were collected post-decapitation; plasma was analyzed for lipid profile, glycemic parameters, and microbiota-derived metabolites using enzymatic and ELISA methods. Irisin and myonectin levels were assessed in plasma and myocardial and skeletal muscle tissues via ELISA and immunohistochemistry. Results: The HICT_CA group showed the lowest body weight, highest HDL-C, and lowest LDL-C, TC, TG, and atherogenic index. Irisin and myonectin levels in skeletal muscle and myocardium were also highest in HICT_CA. The trimethylamine N-oxide (TMAO) was lowest and S-equol highest in HICT_CA, whereas indoxyl sulfate (IS) peaked in HICT and was lowest in the C group. Principal component analysis revealed strong positive associations between HICT_CA and cardiometabolic biomarkers. Conclusions: High-intensity training combined with carnosine may reduce weight gain, improve lipid and glycemic profiles, and enhance myokines and microbiota-derived metabolites.