COMPARISON OF TWO METHODS FOR STUDYING PROTEIN METABOLISM IN HEALTHY ADULTS

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。在体内，全身蛋白质的转换和氧化通常是通过在羧基位置上标记有13C的氨基酸（例如，1-13C-亮氨酸）的血浆富集和静脉输注标记的氨基酸后呼吸13CO2来测量的。虽然这种方法对成人和年龄较大的儿童来说是非侵入性的，但通常被认为对小早产儿来说侵入性太大。因此，它在研究该人群蛋白质代谢方面的应用受到限制。理论上，应该可以通过口腔给药标记的氨基酸，并测量其在尿液中的富集程度和呼吸中13CO2的富集程度。一些针对婴儿和成人的研究表明，这两种方法在血浆和尿液中的富集程度相似，但这两种技术的所有方面从未在同一个体中进行过比较。为此，将对健康男子和未怀孕妇女（18-40岁）进行两次研究。在第一组中，他们将接受持续静脉输注1- 13c -亮氨酸或间歇性摄入13c -亮氨酸。一周后，他们将通过另一种途径接受相同剂量的1- 13c -亮氨酸。在这两种情况下，将测定血浆和尿液中亮氨酸的富集程度以及呼吸中的13CO2富集程度。这将允许将传统方法（持续静脉给药和血浆取样）与侵入性较小的方法（启动间歇肠内给药和尿液取样）以及两者的任何组合（静脉给药和尿液取样）进行比较。用两种方法计算的通量、蛋白质合成和蛋白质分解也将进行比较。所获得的数据将首次对这两种方法进行全面的评估，以研究全身蛋白质代谢，以及是否可以用侵入性较小的方法取代有创的常规方法。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In vivo whole body protein turnover and oxidation are usually measured by the plasma enrichment of an amino acid labeled in the carboxyl position with 13C (e.g., 1-13C-leucine) and breath 13CO2 following intravenous infusion of the labeled amino acid. While sufficiently non-invasive in adults and older children, this method is often considered too invasive for use in small preterm infants. Hence, its use to study protein metabolism of this population has been limited. In theory, it should be possible to administer the labeled amino acid by mouth and measure its enrichment in urine and the enrichment of 13CO2 in breath. A few studies, some in infants and some in adults, suggest that the two approaches result in similar enrichment in plasma and urine but all aspects of the two techniques have never been compared in the same individuals. To accomplish this, healthy men and non-pregnant women (age, 18-40 years) will be studied on two occasions. On the first, they will receive a primed constant intravenous infusion of 1-13C-leucine or a primed intermittent ingestion of 13C-leucine. A week later, they will receive the same dose of 1-13C-leucine by the alternative route. Plasma and urinary enrichments of leucine and breath 13CO2 enrichment will be determined on both occasions. This will permit comparison of the conventional method (constant intravenous administration and plasma sampling) with the less invasive method (primed intermittent enteral administration and urine sampling) as well as any combination of the two (intravenous administration and urine sampling). Flux, protein synthesis and protein breakdown calculated with data obtained by both approaches also will be compared. The data to be obtained will provide the first thorough evaluation of these two methods for studying whole body protein metabolism and whether the invasive conventional method can be replaced by the less invasive method.