Short- and long-term effects of leucine and branched-chain amino acid supplementation of a protein- and energy-reduced diet on muscle protein metabolism in neonatal pigs

Authors: MANJARIN, RODRIGO - Children'S Nutrition Research Center (CNRC); COLUMBUS, DANIEL - Children'S Nutrition Research Center (CNRC); SOLIS, J - Children'S Nutrition Research Center (CNRC); HERNANDEZ-GARCIA, ADRIANA - Children'S Nutrition Research Center (CNRC); SURYAWAN, AGUS - Children'S Nutrition Research Center (CNRC); NGUYEN, HANH - Children'S Nutrition Research Center (CNRC); MCGUCKIN, MOLLY - California Polytechnic State University; JIMENEZ, RAFAEL - California Polytechnic State University; FIOROTTO, MARTA - Children'S Nutrition Research Center (CNRC); DAVIS, TERESA - Children'S Nutrition Research Center (CNRC)

Submitted to: Amino Acids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/19/2018
Publication Date: 5/4/2018
Citation: Manjarin, R., Columbus, D.A., Solis1, J., Hernandez-Garcia, A.D., Suryawan, A., Nguyen, H.V., McGuckin, M.M., Jimenez, R.T., Fiorotto, M.L., Davis, T.A. 2018. Short- and long-term effects of leucine and branched-chain amino acid supplementation of a protein- and energy-reduced diet on muscle protein metabolism in neonatal pigs. Amino Acids. 50(7):943-959. https://doi.org/10.1007/s00726-018-2572-0.
DOI: https://doi.org/10.1007/s00726-018-2572-0

Interpretive Summary: Babies born prematurely often consume less than their protein and energy requirements for growth due to feeding intolerance. In order to help these babies grow normally, we conducted experiments using piglets as a model for human infants. We have previously shown that supplementation of a complete diet with the amino acid, leucine can stimulate the synthesis of protein in skeletal muscle of newborn piglets and promote muscle growth. Leucine supplementation of diet that is low in protein but not energy can also stimulate muscle protein synthesis and growth. In this study, we tested diets that contained reduced levels of both protein and energy but were supplemented with either leucine alone or the three branched-chain amino acids, leucine, isoleucine, and valine. Our results showed that supplementation with leucine or the branched-chain amino acids stimulated the activation of intracellular signaling components that regulate protein synthesis. However, these supplements did not enhance the synthesis of muscle protein or increase muscle growth. The lack of effect of these supplements on muscle protein synthesis and growth was likely because the amount of energy that was available from the diet was not sufficient to support enhanced rates of protein synthesis and growth. This study highlights the importance of energy intake in supporting growth processes and suggests that leucine supplementation may be an effective strategy for promoting muscle growth if energy intake is adequate.

Technical Abstract: The objective of this study was to determine if enteral leucine or branched-chain amino acid (BCAA) supplementation increases muscle protein synthesis in neonates who consume less than their protein and energy requirements, and whether this increase is mediated via the upregulation of the mechanistic target of rapamycin complex 1 (mTORC1) pathway or the decrease in muscle protein degradation signaling. Neonatal pigs were fed milk replacement diets containing reduced energy and protein (R), R supplemented with BCAA (RBCAA), R supplemented with leucine (RL), or complete protein and energy (CON) at 4-h intervals for 9 (n=24) or 21 days (n=22). On days 9 and 21, post-prandial plasma amino acids and insulin were measured at intervals for 4 h; muscle protein synthesis rate and activation of mTOR-related proteins were determined at 120 min post-feeding in muscle. For all parameters measured, the effects of diet were not different between day 9 or day 21. Compared to CON and R, plasma leucine and BCAA were higher (P<=0.01) in RL- and RBCAA-fed pigs, respectively. Body weight gain, protein synthesis, and activation of S6 kinase (S6K1), 4E-binding protein (4EBP1), and eukaryotic initiation factor 4 complex (eIF4E/eIF4G) were decreased in RBCAA, RL, and R relative to CON (P<0.01). RBCAA and RL upregulated (P<=0.01) S6K1, 4EBP1, and eIF4E/eIF4G compared to R. In conclusion, when protein and energy are restricted, both leucine and BCAA supplementation increase mTOR activation, but do not enhance skeletal muscle protein synthesis and muscle growth in neonatal pigs.