Fed-state clamp stimulates cellular mechanisms of muscle protein anabolism and modulates glucose disposal in normal men

Adegoke OA, Chevalier S, Morais JA, Gougeon R, Kimball SR, Jefferson LS, Wing SS, Marliss EB. Fed-state clamp stimulates cellular mechanisms of muscle protein anabolism and modulates glucose disposal in normal men. Am J Physiol Endocrinol Metab 296: E105-E113, 2009. First published October 28, 2008; doi: 10.1152/ajpendo.90752.2008.-Since maximum anabolism occurs postprandially, we developed a simulated fed state with clamped hyperinsulinemia, physiological hyperglycemia, and hyperaminoacidemia (Hyper-3) and explored muscle cellular mechanisms. Whole body [1-C-13]leucine and [3-H-3]glucose kinetics in healthy men were compared between hyperinsulinemic, euglycemic, isoaminoacidemic (Hyper-1, n = 10) and Hyper-3 (n = 9) clamps. In Hyper-3 vs. Hyper-1, nonoxidative leucine R-d [ rate of disappearance (synthesis)] was stimulated more (45 +/- 4 vs. 24 +/- 4 mu mol/min, P < 0.01) and endogenous R-a [ rate of appearance (breakdown)] was inhibited similarly; hence net balance increased more (86 +/- 6 vs. 49 +/- 2 mu mol/min, P < 0.001). Glucose Rd was similar; thus Hyper-3 metabolic clearance rate (331 +/- 23 vs. 557 +/- 41 ml/min, P < 0.0005) and R-d/insulin (M, 0.65 +/- 0.10 vs. 1.25 +/- 0.10 mg center dot min(-1)center dot pmol(-1)center dot l, P < 0.001) were less, despite higher insulin (798 +/- 74 vs. 450 +/- 24 pmol/l, P < 0.005). In vastus lateralis muscle biopsies, phosphorylation of Akt (P = 0.025), mammalian target of rapamycin (mTOR), ribosomal protein S6 kinase (p70(S6K1); P = 0.008), S6 (P = 0.049), and 4E-binding protein 1 (4E-BP1; P = 0.001) increased. With decreased eukaryotic initiation factor-4E (eIF4E)center dot 4E-BP1 complex (P = 0.01), these are consistent with increased mTOR complex 1 (mTORC1) signaling and translation initiation of protein synthesis. Although mRNA expression of ubiquitin, MAFbx 1, and MuRF-1 was unchanged, total ubiquitinated proteins decreased 20% (P < 0.01), consistent with proteolysis suppression. The Hyper-3 clamp increases whole body protein synthesis, net anabolism, and muscle protein translation initiation pathways and decreases protein ubiquitination. The main contribution of hyperaminoacidemia is stimulation of synthesis rather than inhibition of proteolysis, and it attenuates the expected increment of glucose disposal.