Effect of Amino Acid Derivatives and Polyphenol Supplementation on Ovine Muscle Growth In Vitro and In Vivo

Nutrient supplementation may enhance muscle growth by supporting myogenic activity and regulating metabolic pathways involved in skeletal muscle development. However, the effect of specific nutrient supplementation on satellite cell (SC) activity and muscle-related metabolic pathways remains unclear. Two experiments were conducted to investigate dietary supplements, including guanidinoacetic acid (GAA), 5-hydroxytryptophan (5-HTP), and quercetin, on SC proliferation and differentiation in vitro and on muscle growth and transcriptomics in vivo. For the in vitro study, ovine SC were cultured with different levels (0, 12.5, 25, and 50 μmol/L) of 5-HTP, GAA, or quercetin to examine SC proliferation and differentiation. SC proliferation was greater with 5-HTP and quercetin supplementation, whereas GAA increased SC differentiation. Based on these results, 5-HTP and GAA were selected for the in vivo study because they increased proliferation and differentiation, respectively, and had a wider range of dose effectiveness (12.5 and 25 μmol/L). For the in vivo study, Texel lambs (n = 15; 33 ± 6 kg) were blocked by weight and assigned to one of three treatments: control, GAA, or 5-HTP for 28 d. Supplements were administered sublingually at a dose of 2.5 mg/kg body weight daily before feeding. GAA or 5-HTP did not influence (p > 0.05) average daily gain or dry matter intake. Longissimus muscle area was greater (p < 0.05) at the end of the study compared to the start for all treatment groups. mRNA sequencing showed that GAA supplementation altered gene expression (Padj < 0.05) compared to the control or 5-HTP. However, 5-HTP did not affect (p > 0.05) gene expression compared to the control. LC-MS also showed that plasma 5-hydroxyindoleacetic acid (5-HIAA) was elevated (p < 0.05) in the 5-HTP group. The results suggest that these dietary supplements can stimulate SC proliferation or differentiation in vitro. Short-term supplementation of GAA or 5-HTP in vivo did not alter growth performance, muscle mass, or miR-133a expression; however, GAA supplementation altered the transcriptome to promote amino acid metabolism pathways that are commonly linked to muscle growth through muscle protein synthesis and energy metabolism.