Medical Research Council-Arthritis Research United Kingdom Centre of Excellence for Musculoskeletal Ageing Research, University of Nottingham, Metabolic and Molecular Physiology, Nottingham, United Kingdom;
Am J Physiol Endocrinol Metab. 2014 Mar 1;306(5):E571-9. doi: 10.1152/ajpendo.00650.2013. Epub 2013 Dec 31.
Quantification of muscle protein synthesis (MPS) remains a cornerstone for understanding the control of muscle mass. Traditional [(13)C]amino acid tracer methodologies necessitate sustained bed rest and intravenous cannulation(s), restricting studies to 12 h, and thus cannot holistically inform on diurnal MPS. This limits insight into the regulation of habitual muscle metabolism in health, aging, and disease while querying the utility of tracer techniques to predict the long-term efficacy of anabolic/anticatabolic interventions. We tested the efficacy of the D2O tracer for quantifying MPS over a period not feasible with (13)C tracers and too short to quantify changes in mass. Eight men (22 ± 3.5 yr) undertook one-legged resistance exercise over an 8-day period (4 × 8-10 repetitions, 80% 1RM every 2nd day, to yield "nonexercised" vs. "exercise" leg comparisons), with vastus lateralis biopsies taken bilaterally at 0, 2, 4, and 8 days. After day 0 biopsies, participants consumed a D2O bolus (150 ml, 70 atom%); saliva was collected daily. Fractional synthetic rates (FSRs) of myofibrillar (MyoPS), sarcoplasmic (SPS), and collagen (CPS) protein fractions were measured by GC-pyrolysis-IRMS and TC/EA-IRMS. Body water initially enriched at 0.16-0.24 APE decayed at ~0.009%/day. In the nonexercised leg, MyoPS was 1.45 ± 0.10, 1.47 ± 0.06, and 1.35 ± 0.07%/day at 0-2, 0-4, and 0-8 days, respectively (0.05-0.06%/h). MyoPS was greater in the exercised leg (0-2 days: 1.97 ± 0.13%/day; 0-4 days: 1.96 ± 0.15%/day, P < 0.01; 0-8 days: 1.79 ± 0.12%/day, P < 0.05). CPS was slower than MyoPS but followed a similar pattern, with the exercised leg tending to yield greater FSRs (0-2 days: 1.14 ± 0.13 vs. 1.45 ± 0.15%/day; 0-4 days: 1.13 ± 0.07%/day vs. 1.47 ± 0.18%/day; 0-8 days: 1.03 ± 0.09%/day vs. 1.40 ± 0.11%/day). SPS remained unchanged. Therefore, D2O has unrivaled utility to quantify day-to-day MPS in humans and inform on short-term changes in anabolism and presumably catabolism alike.
肌肉蛋白质合成 (MPS) 的定量仍然是理解肌肉质量控制的基石。传统的 [(13)C]氨基酸示踪剂方法需要持续卧床休息和静脉插管，限制了研究时间在约 12 小时内，因此无法全面了解日间 MPS。这限制了我们对健康、衰老和疾病中习惯性肌肉代谢的调节的深入了解，同时也质疑了示踪技术预测合成代谢/抗分解代谢干预长期疗效的效用。我们测试了 D2O 示踪剂在一段时间内定量 MPS 的效果，这段时间用 (13)C 示踪剂是不可行的，而且太短，无法定量质量变化。八名男性（22 ± 3.5 岁）在 8 天的时间内进行了单腿抗阻运动（4 次×8-10 次重复，80%1RM 每 2 天一次，以产生“非运动”和“运动”腿的比较），在第 0、2、4 和 8 天分别对双侧股外侧肌进行活检。在第 0 天活检后，参与者服用 D2O 脉冲（150 ml，70 原子%）；每天收集唾液。通过 GC-热解-IRMS 和 TC/EA-IRMS 测量肌原纤维 (MyoPS)、肌浆 (SPS) 和胶原蛋白 (CPS) 蛋白分数的合成率 (FSR)。最初在 0.16-0.24 APE 处富集的体水以约 0.009%/天的速度衰减。在非运动腿中，MyoPS 分别在 0-2、0-4 和 0-8 天时为 1.45 ± 0.10、1.47 ± 0.06 和 1.35 ± 0.07%/天（约 0.05-0.06%/h）。运动腿中的 MyoPS 更高（0-2 天：1.97 ± 0.13%/天；0-4 天：1.96 ± 0.15%/天，P < 0.01；0-8 天：1.79 ± 0.12%/天，P < 0.05）。CPS 比 MyoPS 慢，但遵循相似的模式，运动腿倾向于产生更高的 FSR（0-2 天：1.14 ± 0.13 比 1.45 ± 0.15%/天；0-4 天：1.13 ± 0.07%/天比 1.47 ± 0.18%/天；0-8 天：1.03 ± 0.09%/天比 1.40 ± 0.11%/天）。SPS 保持不变。因此，D2O 具有无与伦比的效用，可以定量测定人类的日常 MPS，并提供有关短期合成代谢和分解代谢变化的信息。
