Holecek Milan, Siman Pavel, Vodenicarovova Melita, Kandar Roman
Department of Physiology, Faculty of Medicine in Hradec Kralove, Charles University in Prague, Simkova 870, Hradec Kralove, 500 38 Czech Republic.
Department of Biochemistry, Faculty of Medicine in Hradec Kralove, Charles University Prague, Hradec Kralove, Czech Republic.
Nutr Metab (Lond). 2016 Feb 11;13:12. doi: 10.1186/s12986-016-0072-3. eCollection 2016.
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. 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.
Rats 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-(3)H]phenylalanine), proteolysis on the basis of chymotrypsin-like activity (CHTLA) of proteasome and cathepsin B and L activities.
Chronic 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.
The 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.
许多人相信支链氨基酸（BCAAs；缬氨酸、亮氨酸和异亮氨酸），尤其是亮氨酸，对肌肉蛋白质平衡有有益作用，并已食用多年。我们测定了长期摄入富含BCAAs或亮氨酸的饮食对进食和吸收后状态下蛋白质及氨基酸代谢的影响。
将大鼠分别喂食标准饮食、高含量缬氨酸、亮氨酸和异亮氨酸的饮食（HVLID）或高含量亮氨酸的饮食（HLD），持续2个月。每组动物的一半在最后一天的进食状态下处死，另一半在禁食过夜后处死。使用灌流剂量法（L-[3,4,5-(3)H]苯丙氨酸）评估蛋白质合成，根据蛋白酶体的类胰凝乳蛋白酶活性（CHTLA）以及组织蛋白酶B和L的活性评估蛋白水解。
长期摄入HVLID或HLD可提高血浆尿素、丙氨酸和谷氨酰胺水平。HVLID还可提高所有三种BCAAs和支链酮酸（BCKA）的水平，HLD可提高亮氨酸、酮异己酸和丙氨酸转氨酶水平，并降低缬氨酸、酮缬氨酸、异亮氨酸、酮异亮氨酸和低密度脂蛋白胆固醇水平。HLD组的趾长伸肌组织重量和蛋白质含量较低，HVLID和HLD组的肾脏组织重量和蛋白质含量较高。进食后状态下，HVLID组的肌肉蛋白质合成较高，与对照组相比，HVLID和HLD组肌肉中的CHTLA较低。禁食过夜可增强肌肉中的丙氨酸转氨酶活性，并使比目鱼肌（HVLID组）和趾长伸肌（HLD组）中的蛋白质合成减少幅度大于对照组。HVLID和HLD对吸收后状态下肌肉中CHTLA的影响不显著。
结果未能证明长期食用富含BCAAs的饮食对骨骼肌蛋白质平衡有积极作用，反而表明富含亮氨酸的饮食有负面影响。两种饮食的主要作用都是激活BCAAs的分解代谢，这导致BCKA、丙氨酸和谷氨酰胺的生成增加，并在内脏组织中被利用，以及吸收后状态下蛋白质合成受损，尤其是在快肌（白肌）中。
