Alterations in protein and amino acid metabolism in rats fed a branched-chain amino acid- or leucine-enriched diet during postprandial and postabsorptive states.

Roman Kandar,Pavel Siman,Melita Vodenicarovova,Milan Holecek

doi:10.1186/s12986-016-0072-3

Roman Kandar, Pavel Siman + Show 2 more

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https://doi.org/10.1186/s12986-016-0072-3

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Abstract

BackgroundMany people believe in favourable effects of branched-chain amino acids (BCAAs; valine, leucine, and isoleucine), especially leucine, on muscle protein balance and consume BCAAs for many years. We determined the effects of the chronic intake of a BCAA- or leucine-enriched diet on protein and amino acid metabolism in fed and postabsorptive states.MethodsRats were fed a standard diet, a diet with a high content of valine, leucine, and isoleucine (HVLID), or a high content of leucine (HLD) for 2 months. Half of the animals in each group were sacrificed in the fed state on the last day, and the other half were sacrificed after overnight fast. Protein synthesis was assessed using the flooding dose method (L-[3,4,5-3H]phenylalanine), proteolysis on the basis of chymotrypsin-like activity (CHTLA) of proteasome and cathepsin B and L activities.ResultsChronic intake of HVLID or HLD enhanced plasma levels of urea, alanine and glutamine. HVLID also increased levels of all three BCAA and branched-chain keto acids (BCKA), HLD increased leucine, ketoisocaproate and alanine aminotransferase and decreased valine, ketovaline, isoleucine, ketoisoleucine, and LDL cholesterol. Tissue weight and protein content were lower in extensor digitorum longus muscles in the HLD group and higher in kidneys in the HVLID and HLD groups. Muscle protein synthesis in postprandial state was higher in the HVLID group, and CHTLA was lower in muscles of the HVLID and HLD groups compared to controls. Overnight starvation enhanced alanine aminotransferase activity in muscles, and decreased protein synthesis in gastrocnemius (in HVLID group) and extensor digitorum longus (in HLD group) muscles more than in controls. Effect of HVLID and HLD on CHTLA in muscles in postabsorptive state was insignificant.ConclusionsThe results failed to demonstrate positive effects of the chronic consumption of a BCAA-enriched diet on protein balance in skeletal muscle and indicate rather negative effects from a leucine-enriched diet. The primary effects of both diets are an activated catabolism of BCAAs, which leads to an enhanced production of BCKA, alanine and glutamine and their utilization in visceral tissues and an impaired protein synthesis in postabsorptive state, particularly in fast-twitch (white) muscles.

Highlights

Many people believe in favourable effects of branched-chain amino acids (BCAAs; valine, leucine, and isoleucine), especially leucine, on muscle protein balance and consume Branched-chain amino acids (BCAA) for many years
Higher values of protein synthesis were observed in the postabsorptive state in the kidneys of HVLID and High leucine diet (HLD) groups compared to controls
We conclude that the chronic intake of a BCAA- or leucineenriched diet significantly affects whole body metabolism as demonstrated by alterations in urea, alanine aminotransferase, and LDL cholesterol in blood, protein synthesis and proteolysis in various tissues, amino acid concentrations in blood and tissues, and liver and kidney weights

Summary

Introduction

Many people believe in favourable effects of branched-chain amino acids (BCAAs; valine, leucine, and isoleucine), especially leucine, on muscle protein balance and consume BCAAs for many years. The initial site for most BCAA catabolism is skeletal muscle because of the high activity of BCAA aminotransferase, which enables the transfer of the amino group of BCAAs to α-ketoglutarate to form glutamate and branched-chain keto acids (BCKA), i.e., αketoisocaproate (KIC, ketoleucine), α-keto-β-methylvalerate (KMV, ketoisoleucine) and α-ketoisovalerate (KIV, ketovaline). The enhanced availability of glutamic acid increases the flux through glutamine synthetase and alanine aminotransferase leading to enhanced synthesis of glutamine and alanine. These amino acids are released together with most of the BCKA from skeletal muscle to the blood [8,9,10]. An enhanced intake of BCAAs should lead to enhanced BCAA catabolism and the release of glutamine, alanine and BCKA from muscles to the blood stream (Fig. 1)

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