A comparison of the effects of leucine, HMB, and Vicia faba hydrolysate on activation of ERK1/2 and protein synthesis signalling in a young and aged muscle model

Research into the efficacy of dietary supplements in ageing muscle is hindered owing to the lack of reliable human cell models that capture muscle specific phenotypes through replicative ageing. Using an inducible model of human skeletal muscle to address these challenges, we compared the efficacy of L-leucine (Leu), calcium β-hydroxy-β-methylbutyrate (HMB), and Vicia faba hydrolysate (VFH) in young and aged muscle cells. VFH elicited robust activation of muscle protein synthesis (MPS) signalling, increasing phosphorylation of ribosomal S6 by 5.82-fold in young DIMs and 3.39-fold in aged DIMs, exceeding responses observed with Leu or HMB. VFH also significantly increased 4EBP1 phosphorylation in both young (2.53-fold) and aged (1.92-fold) DIMs. Kinase array and inhibitor studies identified MAPK/ERK signalling as a key mediator of VFH activity, with VFH increasing ERK1/2 phosphorylation by up to 2.25-fold. Furthermore, aged DIMs displayed reduced LAT1 expression, which appeared to impair Leu signalling, whereas VFH retained anabolic activity independent of LAT1 inhibition. Finally, combined treatment of VFH with either Leu or HMB further increased MPS signalling relative to the corresponding supplement alone, with S6 phosphorylation increasing by up to 2.91-fold and 4.4-fold in Leu- and HMB-treated aged DIMs. These findings suggest that addition of VFH to formulations containing Leu or HMB may increase anabolic signalling in ageing muscle versus individual supplements.