Trommelen Jorn, van Loon Luc J C
Department of Human Biology, NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht University Medical Center+, Maastricht, Netherlands.
Front Nutr. 2024 May 15;11:1391750. doi: 10.3389/fnut.2024.1391750. eCollection 2024.
Stable isotopes are routinely applied to determine the impact of factors such as aging, disease, exercise, and feeding on whole-body protein metabolism. The most common approaches to quantify whole-body protein synthesis, breakdown, and oxidation rates and net protein balance are based on the quantification of plasma amino acid kinetics. In the postabsorptive state, plasma amino acid kinetics can easily be assessed using a constant infusion of one or more stable isotope labeled amino acid tracers. In the postprandial state, there is an exogenous, dietary protein-derived amino acid flux that needs to be accounted for. To accurately quantify both endogenous as well as exogenous (protein-derived) amino acid release in the circulation, the continuous tracer infusion method should be accompanied by the ingestion of intrinsically labeled protein. However, the production of labeled protein is too expensive and labor intensive for use in more routine research studies. Alternative approaches have either assumed that 100% of exogenous amino acids are released in the circulation or applied an estimated percentage based on protein digestibility. However, such estimations can introduce large artifacts in the assessment of whole-body protein metabolism. The preferred estimation approach is based on the extrapolation of intrinsically labeled protein-derived plasma bioavailability data obtained in a similar experimental design setting. Here, we provide reference data on exogenous plasma amino acid release that can be applied to allow a more accurate routine assessment of postprandial protein metabolism. More work in this area is needed to provide a more extensive reference data set.
稳定同位素通常用于确定衰老、疾病、运动和饮食等因素对全身蛋白质代谢的影响。量化全身蛋白质合成、分解、氧化速率和净蛋白质平衡的最常见方法是基于血浆氨基酸动力学的量化。在吸收后状态下，使用一种或多种稳定同位素标记的氨基酸示踪剂进行持续输注，即可轻松评估血浆氨基酸动力学。在餐后状态下，存在需要考虑的外源性、源自膳食蛋白质的氨基酸通量。为了准确量化循环中内源性以及外源性（源自蛋白质）氨基酸的释放，连续示踪剂输注方法应辅以摄入内在标记的蛋白质。然而，标记蛋白质的生产成本过高且劳动强度大，无法用于更常规的研究。替代方法要么假设100%的外源性氨基酸在循环中释放，要么基于蛋白质消化率应用估计的百分比。然而，这种估计可能会在全身蛋白质代谢评估中引入较大误差。首选的估计方法是基于在类似实验设计环境中获得的内在标记的蛋白质衍生血浆生物利用度数据进行外推。在此，我们提供了关于外源性血浆氨基酸释放的参考数据，可用于更准确地常规评估餐后蛋白质代谢。该领域需要开展更多工作以提供更广泛的参考数据集。
