Laboratoire de Biologie de la Nutrition EA4466, Faculté de Pharmacie, Paris Sorbonne Cité, Université Paris Descartes, 4 avenue de l'observatoire, 75270, Paris Cedex 06, France,
Amino Acids. 2013 Nov;45(5):1123-31. doi: 10.1007/s00726-013-1564-3. Epub 2013 Aug 3.
Low calorie diets are designed to reduce body weight and fat mass, but they also lead to a detrimental loss of lean body mass, which is an important problem for overweight people trying to lose weight. In this context, a specific dietary intervention that preserves muscle mass in people following a slimming regime would be of great benefit. Leucine (LEU) and Citrulline (CIT) are known to stimulate muscle protein synthesis (MPS) in post-prandial and post-absorptive state, respectively. This makes them interesting bioactive components to test in the context of dietary restriction. We tested the concept of combining LEU and CIT in adult female rats. We postulated that the sequential administration of LEU (mixed in chow) and CIT (given in drinking water before a rest period) could be beneficial for preservation of muscle function during food restriction. Sixty female rats (22 weeks old) were randomized into six groups: one group fed ad libitum with a standard diet (C) and five food-restricted groups (60 % of spontaneous intake for 2 weeks) receiving a standard diet (R group), a CIT-supplemented diet (0.2 or 1 g/kg/day, CIT0.2 group and CIT1 group, respectively), a LEU-supplemented diet (1.0 g/kg/day) or a CIT + LEU-supplemented diet (CIT + LEU 1.0 g/kg/day each). At the end of the experiment, body composition, muscle contractile properties and muscle protein synthesis (MPS) rate were studied in the tibialis anterior muscle. Dietary restriction tended to decrease MPS (R: 2.5 ± 0.2 vs. C: 3.4 ± 0.4 %/day, p = 0.06) and decrease muscle strength (R: 3,045 ± 663 vs. C: 5,650 ± 661 A.U., p = 0.03). Only CIT administration (1 g/kg) was able to restore MPS (CIT1: 3.4 ± 0.3 vs. R: 2.5 ± 0.2 %/day, p = 0.05) and increase muscle maximum tetanic force (CIT1: 441 ± 15 vs. R: 392 ± 22 g, p = 0.05) and muscle strength (CIT1: 4,259 ± 478 vs. R: 3,045 ± 663 A.U., p = 0.05). LEU had no effect and CIT + LEU supplementation had few effects, limited to adipose mass and fatigue force. The results of this study highlight the ability of CIT alone to preserve muscle function during dietary restriction. Surprisingly, LEU antagonized some effects of CIT. The mechanisms involved in this antagonistic effect warrant further study.
低热量饮食旨在减轻体重和脂肪量，但也会导致瘦体重的不利损失，这对于超重人群来说是一个重要问题，因为他们试图减肥。在这种情况下，对于遵循减肥计划的人来说，有一种特殊的饮食干预措施可以保留肌肉质量，这将是非常有益的。亮氨酸（LEU）和瓜氨酸（CIT）分别已知在餐后和吸收后状态下刺激肌肉蛋白质合成（MPS）。这使得它们成为在饮食限制的背景下测试的有趣的生物活性成分。我们测试了在成年雌性大鼠中结合 LEU 和 CIT 的概念。我们假设 LEU（混合在饲料中）和 CIT（在休息期前饮水中给予）的顺序给药可能有益于在食物限制期间保留肌肉功能。60 只雌性大鼠（22 周龄）被随机分为六组：一组自由喂食标准饮食（C），五组进行食物限制（2 周内摄入自发摄入量的 60%），分别接受标准饮食（R 组）、CIT 补充饮食（0.2 或 1 g/kg/天，CIT0.2 组和 CIT1 组）、LEU 补充饮食（1.0 g/kg/天）或 CIT+LEU 补充饮食（CIT+LEU 各 1.0 g/kg/天）。在实验结束时，研究了前胫骨肌肉的身体成分、肌肉收缩特性和肌肉蛋白质合成（MPS）率。饮食限制倾向于降低 MPS（R：2.5±0.2%/天，C：3.4±0.4%/天，p=0.06）和降低肌肉力量（R：3045±663 AU，C：5650±661 AU，p=0.03）。只有 CIT 给药（1 g/kg）能够恢复 MPS（CIT1：3.4±0.3%/天，R：2.5±0.2%/天，p=0.05）并增加肌肉最大强直力（CIT1：441±15 g，R：392±22 g，p=0.05）和肌肉力量（CIT1：4259±478 AU，R：3045±663 AU，p=0.05）。LEU 没有作用，而 CIT+LEU 补充剂的作用有限，仅限于脂肪量和疲劳力。这项研究的结果强调了 CIT 单独在饮食限制期间保持肌肉功能的能力。令人惊讶的是，LEU 拮抗了 CIT 的一些作用。需要进一步研究这种拮抗作用的机制。
