Short-term dietary leucine (Leu) supplementation improves lean mass accretion in newborn pigs by acting as a building block for protein synthesis and as an anabolic agent via the mTOR pathway. However, it remains unknown whether long-term Leu inclusion in the diet upregulates protein synthesis in neonates, and thus could be used as a therapeutic protocol to improve infant growth. The objective of this study was to test whether Leu supplement coupled with 30% reduction in crude protein (CP) and metabolic energy (ME) would increase the efficiency of protein utilization for skeletal protein synthesis, and whether this increase would be correlated with the upregulation of mTOR pathway-related proteins in the skeletal muscle. Nineteen piglets were allotted into a control diet (CON), 30% reduced CP and ME diet (R), and R supplemented with Leu (RL). Piglets were fed via gastric tube into the stomach for 8 d, and euthanized to measure fractional protein synthesis rate and protein abundance (i.e. S6K1, 4EBP1, and eIF4E-4G) in skeletal muscle by using radiolabeled Phe and western blot assays, respectively. Blood samples were taken prior euthanasia for measuring glucose, insulin and Leu levels at 7 time points: 0, 30, 60, 90, 120, 180, and 240 min post-feeding. Fractional protein synthesis rate and protein abundance in skeletal muscle was measured, as well as blood glucose, insulin and Leu levels. Results showed that glucose concentration was not different at any time point between the three groups. Insulin concentration was higher for R compare to RL at 30 min and for CON compared to R and RL at 90 and 120 min. Leucine concentration was higher for RL compared to R and CON at all time points. Leucine supplementation did not increase overall piglet growth or protein synthetic activity in skeletal muscle, but increased the activation of proteins involved in mTOR pathway. Leu stimulation of protein synthesis seems to be substrate dependent, and thus it cannot be used to improve muscle growth in infants if supplemented alone in a CP and ME deficient diet.
Nguyet Minh Hoang, ’16
Ho Chi Minh City, Vietnam
Additional Authors: Rodrigo Manjarín, Daniel A. Columbus, Marta L. Fiorotto, Agus Suryawan, Adriana D. Hernandez-García, Hanh V. Nguyen, Rosemarie Almonaci, and Teresa A. Davis
Sponsor: Barbara Christie-Pope