Author(s): EGGELBUSCH, M., HAVERS, T., SING, K., OKROJEK, R., MEINHOLD, M., ARTATI, A., WITTING, M., LUTTER, D., STARKE, C., MORE, T., HILLER, K., DELA, F., SCHÖNFELDER, M., KAFKA, A., GEISLER, S., WACKERHAGE, H., Institution: TUM SCHOOL OF MEDICINE AND HEALTH, Country: GERMANY, Abstract-ID: 2317

INTRODUCTION:
To generate 1 g of dry biomass, hypertrophying skeletal muscles must take up 1 g of metabolites from the circulation. While much of this uptake is expected to consist of amino acids for protein synthesis, little is known about which of the ~200,000 metabolites detected in humans (HMDB data) are taken up or released during muscle growth. To gain insight into global metabolite exchange during skeletal muscle hypertrophy, we profiled metabolite uptake and release in IGF-1-stimulated C2C12 myotubes and in the human leg 24 h following resistance exercise compared with unstimulated controls.
METHODS:
Differentiated C2C12 myotubes were growth-stimulated with IGF-1 (100ng/ml, 24 h) or received vehicle control. To measure metabolite exchange, we analyzed fresh and spent media by GC-MS metabolomics. In a second experiment, seven untrained adults (3 males, 4 females; age 25.6 ± 3.2 years; BMI 23.8 ± 2.8 kg·m⁻²) performed single-leg hypertrophy-oriented resistance exercise, with the contralateral leg serving as control. After 24 h, we obtained femoral arterial and venous blood samples under fasting conditions and analyzed plasma by untargeted LC-MS metabolomics to quantify net muscle metabolite exchange.
RESULTS:
Compared with controls, IGF-1-treated myotubes took up more serine (log2FC = −1.73, p < 0.001), arginine (−0.58, p = 0.017), and pyridoxamine (−0.9, p = 0.017), and released more lactate into the culture medium (+0.72, p < 0.001), consistent with anabolic, Warburg-like metabolic reprogramming. Upon IGF-1 stimulation, we detected increased uptake of metabolites linked to central carbon metabolism and cofactor biosynthesis. In contrast, untargeted human arteriovenous metabolomics revealed only modest differences in global metabolite exchange between the exercised and contralateral control leg (PCA PC1 8.8%, PC2 6.3% variance explained). We observed no significant increase in essential amino acid uptake 24 h post-exercise. Nevertheless, 15 metabolites differed between legs, with the exercised muscle preferentially taking up amino acid and peptide-related metabolites (acisoga, 2-amino-4-CP), palmitic acid, and α-ketoglutarate, while releasing lipid-derived intermediates including C12:0 and C16:0 acylcarnitines. However, none of these differences persisted after FDR correction.
CONCLUSION:
IGF-1 stimulation in vitro promotes a coordinated uptake of nitrogen-rich metabolites and increased lactate release, reflecting a cancer-like metabolic reprogramming. In contrast, metabolite exchange in fasted human muscle 24 h after resistance exercise is characterized by increased peptide turnover and lipid intermediate release rather than net amino acid uptake, indicating limited substrate accumulation and net biomass accretion in the absence of exogenous nutrients.