Dijk Francina J, van Dijk Miriam, Walrand Stéphane, van Loon Luc J C, van Norren Klaske, Luiking Yvette C
Nutricia Research, Nutricia Advanced Medical Nutrition, Utrecht, The Netherlands.
Université Clermont Auvergne, INRA, UNH, Unité de Nutrition Humaine, CRNH Auvergne, F-630000 Clermont-Ferrand, France.
Clin Nutr ESPEN. 2018 Apr;24:127-133. doi: 10.1016/j.clnesp.2017.12.013. Epub 2018 Jan 11.
BACKGROUND & AIMS: It has been suggested that anabolic resistance, or a blunted protein synthetic response to anabolic stimuli, contributes to the failure of muscle mass maintenance in older adults. The amino acid leucine is one of the most prominent food-related anabolic stimuli. However, data on muscle protein synthesis (MPS) after administration of a single bolus of leucine in aged populations is lacking and long-term single leucine supplementation has not been shown to increase muscle mass. This study aimed to determine the MPS response to the administration of a single bolus of leucine or to leucine combined with whey protein, in aged mice.
Overnight fasted C57/BL6RJ mice at 25-mo of age received an oral gavage with leucine or whey-protein enriched with leucine (0.75 g/kg bodyweight total leucine in both) or 0.5 mL water (fasted control). Subsequently, mice were s.c. injected with puromycin (0.04 μmol/g bw at t = 30, 45 or 60 min) and were sacrificed 30 min thereafter. Amino acid concentrations were determined in plasma and right muscle tibialis anterior (TA). Left TA was used to analyse MPS by SUnSET method and phosphorylation rate of Akt, 4E-BP1 and p70S6k by western blot.
In aged mice, leucine administration failed to increase MPS, despite a 6-fold increase in plasma leucine and elevated muscle free leucine levels (P < 0.05). In contrast, leucine-enriched whey protein significantly stimulated MPS in aged mice at 60 min after gavage (P < 0.05). Muscle free EAA, NEAA and the phosphorylation rate of Akt, 4E-BP1 and p70S6k increased significantly (P < 0.05), only after administration of leucine-enriched whey protein.
MPS is stimulated in aged mice by leucine-enriched whey protein but not by leucine administration only. Administration of other amino acids may be required for leucine administration to stimulate muscle protein synthesis in aged mice.
有研究表明，合成代谢抵抗，即对合成代谢刺激的蛋白质合成反应减弱，是导致老年人肌肉量维持失败的原因之一。氨基酸亮氨酸是最显著的与食物相关的合成代谢刺激物之一。然而，老年人群单次注射亮氨酸后肌肉蛋白质合成（MPS）的数据尚缺乏，且长期单一补充亮氨酸尚未被证明能增加肌肉量。本研究旨在确定老年小鼠单次注射亮氨酸或亮氨酸与乳清蛋白联合使用后MPS的反应。
25月龄的C57/BL6RJ小鼠隔夜禁食后，经口灌胃给予亮氨酸或富含亮氨酸的乳清蛋白（两者总亮氨酸均为0.75 g/kg体重）或0.5 mL水（禁食对照）。随后，小鼠皮下注射嘌呤霉素（在t = 30、45或60分钟时为0.04 μmol/g体重），并在30分钟后处死。测定血浆和右侧胫前肌（TA）中的氨基酸浓度。左侧TA用于通过SUnSET法分析MPS，并通过蛋白质免疫印迹法分析Akt、4E-BP1和p70S6k的磷酸化率。
在老年小鼠中，尽管血浆亮氨酸增加了6倍且肌肉游离亮氨酸水平升高（P < 0.05），但注射亮氨酸未能增加MPS。相比之下，富含亮氨酸的乳清蛋白在灌胃后60分钟显著刺激了老年小鼠的MPS（P < 0.05）。仅在给予富含亮氨酸的乳清蛋白后，肌肉游离必需氨基酸、非必需氨基酸以及Akt、4E-BP1和p70S6k的磷酸化率显著增加（P < 0.05）。
富含亮氨酸的乳清蛋白可刺激老年小鼠的MPS，但仅注射亮氨酸则不能。在老年小鼠中，亮氨酸注射可能需要其他氨基酸的参与才能刺激肌肉蛋白质合成。
