Validation of a single biopsy approach and bolus protein feeding to determine myofibrillar protein synthesis in stable isotope tracer studies in humans.
Validation of a single biopsy approach and bolus protein feeding to determine myofibrillar protein synthesis in stable isotope tracer studies in humans.
复制标题
DOI：
10.1186/1743-7075-8-15
复制
发表时间：
2011-03-09
影响因子：
4.5
通讯作者：
Phillips, Stuart M
中科院分区：
文献类型：
--
作者：
Burd, Nicholas A;West, Daniel Wd;Phillips, Stuart M
背景技术背景：最大限度地减少肌肉活检的数量具有重要的方法学意义，并在稳定同位素氨基酸输注期间最大限度地减少受试者的不适。我们的目的是确定获得一个单一的肌肉活检的可靠性，用于计算肌肉蛋白合成率（FSR），以及在开始稳定同位素输注后获得活检所需的掺入时间（研究1）。肌肉蛋白质FSR的计算需要稳定同位素输注过程中的示踪剂稳态。因此，第二个目的是检查前体池中的稳态条件是否受到损害（血浆游离或肌肉细胞内[IC]）摄入示踪剂后富含蛋白质饮料和阻力运动后（研究2）。（23 ± 3岁; BMI = 23.8 ± 2.2 kg/m2，平均值± SD）被随机分配至研究1或研究2（n = 8，每项研究）。受试者接受预充的L-[环-13 C6]苯丙氨酸持续输注，并对股外侧肌进行肌肉活检，以测量肌原纤维蛋白合成（MPS）速率。研究2中的受试者在急性单侧阻力运动后立即喂食25 g乳清蛋白。结果：无差异（P = 0.3）在使用稳态累积乘积方程和间隔150分钟的连续活检之间的示踪剂掺入测定或使用血浆蛋白作为基线富集测定的MPS率中，前提是输注时间足够（230 ± 0.3 min）。我们还发现加入适量的示踪剂（4%富集），基于测定的蛋白质苯丙氨酸含量计算（3.5%）在饮料中，不损害稳态条件（富集曲线的斜率与零无差异）在游离血浆或更重要的IC合并液中结论：这些数据表明，单次活检方法产生的肌肉蛋白合成速率与传统的两次活检方法相当，只要利用更长的掺入时间。此外，我们还证明了用示踪剂富集含蛋白质的饮料不会干扰同位素稳态，因此两者都是确定人类MPS速率的可靠技术。
BACKGROUND: Minimizing the number of muscle biopsies has important methodological implications and minimizes subject discomfort during a stable isotope amino acid infusion. We aimed to determine the reliability of obtaining a single muscle biopsy for the calculation of muscle protein fractional synthetic rate (FSR) as well as the amount of incorporation time necessary to obtain that biopsy after initiating a stable isotope infusion (Study 1). The calculation of muscle protein FSR requires tracer steady-state during the stable isotope infusion. Therefore, a second aim was to examine if steady-state conditions are compromised in the precursor pools (plasma free or muscle intracellular [IC]) after ingestion of a tracer enriched protein drink and after resistance exercise (Study 2).METHODS: Sixteen men (23 ± 3 years; BMI = 23.8 ± 2.2 kg/m2, means ± SD) were randomized to perform Study 1 or Study 2 (n = 8, per study). Subjects received a primed, constant infusion of L-[ring-13C6]phenylalanine coupled with muscle biopsies of the vastus lateralis to measure rates of myofibrillar protein synthesis (MPS). Subjects in Study 2 were fed 25 g of whey protein immediately after an acute bout of unilateral resistance exercise.RESULTS: There was no difference (P = 0.3) in rates of MPS determined using the steady-state precursor-product equation and determination of tracer incorporation between sequential biopsies 150 min apart or using plasma protein as the baseline enrichment, provided the infusion length was sufficient (230 ± 0.3 min). We also found that adding a modest amount of tracer (4% enriched), calculated based on the measured phenylalanine content of the protein (3.5%) in the drink, did not compromise steady-state conditions (slope of the enrichment curve not different from zero) in the plasma free or, more importantly, the IC pool (both P > 0.05).CONCLUSIONS: These data demonstrate that the single biopsy approach yields comparable rates of muscle protein synthesis, provided a longer incorporation time is utilized, to that seen with a traditional two biopsy approach. In addition, we demonstrate that enriching protein-containing drinks with tracer does not disturb isotopic steady-state and thus both are reliable techniques to determine rates of MPS in humans.