Biology of the Nutraceutical L-Citrulline

L-瓜氨酸的生物学特性 背景资料：L-瓜氨酸（LC）是一种α-氨基酸，由L-鸟氨酸和氨基甲酰磷酸在尿素循环中通过鸟氨酸氨基甲酰转移酶合成，同时它也是一氧化氮（NO）合酶（NOS）反应的副产物，将L-精氨酸转化为LC和NO。在人类中的研究已经表明，LC可以作为一个性能增强剂，然而，LC的生物学作用，LC可以提高性能的机制已经相对不足的研究。我的目标是描述LC在骨骼肌和心肌中的生物学作用。 假设：我推测，LC通过增加过氧化物酶体增殖物激活受体γ共激活因子1a的活性，从而增强线粒体功能，从而增强运动肌肉的代谢。 方法学：我的实验室将利用一些体外/体内的方法来阐明LC在骨骼肌和心肌中的生物学作用。这包括培养新生大鼠心肌细胞（NRCM）、H9 c2心室肌细胞和C2 C12骨骼肌管。此外，小鼠将经历许多程序（即高脂肪饮食、运动），以通过间接量热法和肌肉/心脏提取物的mRNA/蛋白质表达谱确定LC处理是否影响线粒体功能和氧化代谢。最后，我们将评估分离的肌肉/心脏线粒体中的呼吸。 目的：这项研究计划将包括3个具体目标：（1）确定LC治疗后肌肉和心脏中激活的信号通路，（2）确定LC治疗是否增强肌肉和心脏中的线粒体功能，以及（3）确定LC与NO形成在NOS介导的线粒体功能增加中的相对重要性。在目标1中，我们将用LC处理培养的C2 C12肌管、H9 c2肌细胞和NRCM，并收获细胞提取物以评估mRNA/蛋白质表达谱。在目标2中，我们将从小鼠心脏和骨骼肌中分离线粒体，并确定LC处理是否增强呼吸。此外，我们将使用间接量热法来测量在饮用水中用LC处理的瘦小鼠和肥胖小鼠的O2消耗。在目标3中，我们将用LC或NO供体补充瘦的和肥胖的内皮NOS缺陷小鼠，并评估线粒体功能。 影响：我们的研究结果将深入了解LC在肌肉和心脏中的生物学作用。此外，这项研究计划的结果应该增强我们对驱动线粒体呼吸的细胞过程的理解。最后，我们的研究结果也应该提供显着的见解，什么“索赔”应该允许制造商谁市场LC作为一个非处方营养膳食补充剂，以提高运动性能。

Biology of the Nutraceutical L-Citrulline Background: L-citrulline (LC) is an a-amino acid synthesized from L-ornithine and carbamoyl phosphate in the Urea Cycle via ornithine carbamoyltransferase, while it also serves as a by-product of the nitric oxide (NO) synthase (NOS) reaction, which converts L-arginine into LC and NO. Of interest, LC can be purchased over the counter as a dietary supplement. Studies in humans have shown that LC may act as a performance enhancer, however, the biological actions of LC, and the mechanisms by which LC may enhance performance have been relatively understudied. My goal is to delineate the biological actions of LC in skeletal and cardiac muscle. Hypothesis: I hypothesize that LC enhances metabolism in exercising muscle via increasing peroxisome proliferator-activated receptor gamma coactivator 1a activity, which enhances mitochondrial function. Methodology: My laboratory will utilize a number of in vitro/in vivo approaches to elucidate the biological actions of LC in skeletal and cardiac muscle. This includes culturing of neonatal rat cardiac myocytes (NRCMs), H9c2 ventricular myocytes, and C2C12 skeletal myotubes. Furthermore, mice will be subjected to a number of procedures (i.e. high fat diet, exercise), to determine whether LC treatment influences mitochondrial function and oxidative metabolism via indirect calorimetry and mRNA/protein expression profiling of muscle/cardiac extracts. Last, we will assess respiration in isolated muscle/heart mitochondria. Aims: This research proposal will encompass 3 specific aims; (1) to determine the signaling pathways activated in muscle and heart following treatment with LC, (2) to determine whether LC treatment enhances mitochondrial function in the muscle and heart, and (3) to determine the relative importance of LC versus NO formation in NOS-mediated increases in mitochondrial function. In aim 1, we will treat cultured C2C12 myotubes, H9c2 myocytes, and NRCMs with LC and harvest cell extracts to assess mRNA/protein expression profiles. In aim 2, we will isolate mitochondria from both mouse heart and skeletal muscle and determine whether LC treatment enhances respiration. Furthermore, we will use indirect calorimetry to measure O2 consumption in lean and obese mice treated with LC in their drinking water. In aim 3, we will supplement lean and obese endothelial NOS deficient mice with either LC or a NO donor and assess mitochondrial function. Impact: Our findings will yield insight into the biological actions of LC in muscle and heart. Moreover, the results of this research program should enhance our understanding of the cellular processes that drive mitochondrial respiration. Last, our findings should also provide significant insights into what “claims” should be allowed for manufacturers who market LC as an over-the-counter nutraceutical dietary supplement to augment exercise performance.