Effect of Orally Administered Branched-chain Amino Acids on Protein Synthesis and Degradation in Rat Skeletal Muscle

Exercise produces changes in protein and amino acid metabolism. These changes include degradation of the branched-chain amino acids, production of alanine and glutamine, and changes in protein turnover. One of the amino acid most affected by exercise is the branched-chain amino acid leucine. Recently, there has been an increased understanding of the role of leucine in metabolic regulations and remarkable new findings about the role of leucine in intracellular signaling. Leucine appears to exert a synergistic role with insulin as a regulatory factor in the insulin/phosphatidylinositol-3 kinase (PI3-K) signal cascade. Insulin serves to activate the signal pathway, while leucine is essential to enhance or amplify the signal for protein synthesis at the level of peptide initiation. Studies feeding amino acids or leucine soon after exercise suggest that post-exercise consumption of amino acids stimulates recovery of muscle protein synthesis via translation regulations. This review focuses on the unique roles of leucine in amino acid metabolism in skeletal muscle during and after exercise. Key words: branched-chain amino acids, insulin, protein synthesis, skeletal muscle

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Does Branched-Chain Amino Acids Supplementation Modulate Skeletal Muscle Remodeling through Inflammation Modulation? Possible Mechanisms of Action

Journal of Nutrition and Metabolism ◽

10.1155/2012/136937 ◽

2012 ◽

Vol 2012 ◽

pp. 1-10 ◽

Cited By ~ 44

Author(s):

Humberto Nicastro ◽

Claudia Ribeiro da Luz ◽

Daniela Fojo Seixas Chaves ◽

Luiz Roberto Grassmann Bechara ◽

Vanessa Azevedo Voltarelli ◽

...

Keyword(s):

Skeletal Muscle ◽

Amino Acids ◽

Protein Synthesis ◽

Translation Initiation ◽

Protein Turnover ◽

Protein Translation ◽

Branched Chain Amino Acids ◽

Inflammatory Status ◽

Branched Chain ◽

Muscle Remodeling

Skeletal muscle protein turnover is modulated by intracellular signaling pathways involved in protein synthesis, degradation, and inflammation. The proinflammatory status of muscle cells, observed in pathological conditions such as cancer, aging, and sepsis, can directly modulate protein translation initiation and muscle proteolysis, contributing to negative protein turnover. In this context, branched-chain amino acids (BCAAs), especially leucine, have been described as a strong nutritional stimulus able to enhance protein translation initiation and attenuate proteolysis. Furthermore, under inflammatory conditions, BCAA can be transaminated to glutamate in order to increase glutamine synthesis, which is a substrate highly consumed by inflammatory cells such as macrophages. The present paper describes the role of inflammation on muscle remodeling and the possible metabolic and cellular effects of BCAA supplementation in the modulation of inflammatory status of skeletal muscle and the consequences on protein synthesis and degradation.

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Effect of eicosapentaenoic acid, protein and amino acids on protein synthesis and degradation in skeletal muscle of cachectic mice

British Journal of Cancer ◽

10.1038/sj.bjc.6601981 ◽

2004 ◽

Vol 91 (2) ◽

pp. 408-412 ◽

Cited By ~ 47

Author(s):

H J Smith ◽

N A Greenberg ◽

M J Tisdale

Keyword(s):

Skeletal Muscle ◽

Amino Acids ◽

Protein Synthesis ◽

Eicosapentaenoic Acid ◽

Acid Protein ◽

Protein Synthesis And Degradation ◽

Synthesis And Degradation

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Effect of plasma insulin and branched-chain amino acids on skeletal muscle protein synthesis in fasted lambs

British Journal Of Nutrition ◽

10.1079/bjn20041226 ◽

2004 ◽

Vol 92 (3) ◽

pp. 401-409 ◽

Cited By ~ 10

Author(s):

T. J. Wester ◽

G. E. Lobley ◽

L. M. Birnie ◽

L. A. Crompton ◽

S. Brown ◽

...

Keyword(s):

Skeletal Muscle ◽

Amino Acids ◽

Protein Synthesis ◽

Plasma Insulin ◽

Muscle Protein ◽

Plasma Concentrations ◽

Branched Chain Amino Acids ◽

Longissimus Dorsi ◽

Ruminant Animals ◽

Branched Chain

The increase in fractional rate of protein synthesis (Ks) in the skeletal muscle of growing rats during the transition from fasted to fed state has been explained by the synergistic action of a rise in plasma insulin and branched-chain amino acids (BCAA). Since growing lambs also exhibit an increase inKswith level of feed intake, the objective of the present study was to determine if this synergistic relationship between insulin and BCAA also occurs in ruminant animals. Six 30 kg fasted (72 h) lambs (8 months of age) received each of four treatments, which were based on continuous infusion into the jugular vein for 6 h of: (1) saline (155 mmol NaCl/l); (2) a mixture of BCAA (0·778 μmol leucine, 0·640 μmol isoleucine and 0·693 μmol valine/min·kg); (3) 18·7 μmol glucose/min·kg (to induce endogenous insulin secretion); (4) co-infusion of BCAA and glucose. Within each period all animals received the same isotope of phenylalanine (Phe) as follows: (1) l-[1-13C]Phe; (2) l-phenyl-[ring2H5]-alanine; (3) l-[15N]Phe; (4) l-[ring 2,6-3H]Phe. Blood was sampled serially during infusions to measure plasma concentrations of insulin, glucose and amino acids, and plasma free Phe isotopic activity; biopsies were taken 6 h after the beginning of infusions to determineKsinm. longissimus dorsiandvastusmuscle. Compared with control (saline-infused) lambs,Kswas increased by an average of 40 % at the end of glucose infusion, but this effect was not statistically significant in either of the muscles sampled. BCAA infusion, alone or in combination with glucose, also had no significant effect onKscompared with control sheep.Kswas approximately 60 % greater forvastusmuscle than form. longissimus dorsi(P>0·01), regardless of treatment. It is concluded that there are signals other than insulin and BCAA that are responsible for the feed-induced increase inKsin muscle of growing ruminant animals.

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