Therapeutic and Metabolic Responses of Citrulline vs. Arginine Supplementation

精氨酸耗竭是在败血症患者中观察到的一种现象，随着其严重程度的增加，与更高的死亡率相关。在众多其他功能中，精氨酸是信号分子一氧化氮的前体，一氧化氮在免疫、血压控制以及微循环和组织灌流的调节中发挥核心作用。尽管精氨酸耗竭和去向的机制尚未确定，但补充精氨酸已被提出以恢复精氨酸的可用性。然而，目前尚不清楚补充精氨酸是否总是有效或有益的，因为它会导致一氧化氮的过度产生，并导致感染性休克时的低血压、心源性抑郁和血管反应性低下。补充瓜氨酸可能比补充精氨酸更有效，但也可能导致过量的一氧化氮产生。瓜氨酸是内源性合成精氨酸的前体。另一种同时解决精氨酸耗竭和一氧化氮过度产生的方法是使用ADI-PEG20。这种聚乙二醇化的细菌酶催化精氨酸转化为瓜氨酸，瓜氨酸可以通过瓜氨酸“循环途径”重新利用。这一途径提供了细胞内精氨酸来维持大多数需要这种氨基酸的过程，但同时也调节了脓毒症期间一氧化氮的过度产生。我们的中心假设是，脓毒症导致精氨酸代谢失调，导致血浆精氨酸耗竭，并导致大循环和微循环衰竭，从而导致器官功能障碍。本研究的目的是阐明小儿败血症猪ARG耗竭的机制，并评价恢复ARG可用性、预防低血压和减轻组织损伤的不同策略。为了验证我们的中心假设并实现我们的目标，我们提出了以下具体目标：特定目标1：量化肝脏对精氨酸的处置速率以及在败血症猪模型中涉及的精氨酸利用途径。特异性目标2：测定补充瓜氨酸或精氨酸的脓毒症猪的精氨酸利用率及其对一氧化氮产生、血压、蛋白质合成和组织损伤标志物的影响。具体目的3：测定ADI-PEG20-精氨酸耗竭猪在脓毒症期间的精氨酸供应和心血管功能，包括血压和缺氧的组织标志物。为了实现这些目标，我们将使用耐甲氧西林金黄色葡萄球菌和致病性大肠杆菌猪的败血症引起的多器官功能障碍的模型。将使用多示踪稳定同位素方案来量化全身和肝脏的精氨酸代谢，相关酶和转运体的分析将为观察到的变化提供分子基础。分析血压、血浆代谢物、器官功能和组织损伤的标志物，以确定不同干预措施对心血管功能、组织灌注量和器官损伤的影响。

Arginine depletion is a phenomenon observed in septic patients, and is associated with greater mortality as its severity increases. Among numerous other functions, arginine is the precursor for the signaling molecule nitric oxide that plays a central role in immunity, in the control of blood pressure, and in the regulation of the microcirculation and tissue perfusion. Although the mechanism responsible for the depletion and fate of arginine has yet to be identified, arginine supplementation has been proposed to restore arginine availability. However, it is not clear if arginine supplementation is always effective or beneficial, because it can result in hyperproduction of nitric oxide and contribute to hypotension, cardio depression and vascular hyporeactivity in septic shock. Supplementing with citrulline, the precursor for the endogenous synthesis of arginine, has the potential to be more effective than arginine supplementation, but may also result in excessive nitric oxide production. An alternative approach that simultaneously addresses the depletion of arginine and hyperproduction of nitric oxide is the use of ADI-PEG 20. This pegylated bacterial enzyme catalyzes the conversion of arginine into citrulline, which can be re-utilized by the citrulline `recycling pathway'. This pathway provides intracellular arginine to sustain most processes that require this amino acid, but at the same time modulating the hyperproduction of nitric oxide during sepsis. Our central hypothesis is that sepsis causes dysregulation of arginine metabolism resulting in plasma arginine depletion and contributing to macro- and microcirculatory failure that leads to organ dysfunction. The objectives of the proposed research are to elucidate the mechanisms of ARG depletion in pediatric swine models of sepsis and evaluate different strategies to restore ARG availability, prevent hypotension and mitigate tissue injury. To test our central hypothesis and attain our objectives we propose the following specific aims: Specific Aim1: Quantify the disposal rate of arginine by the liver and the pathways involved in its utilization in swine models of sepsis. Specific Aim2: Determine arginine availability in septic pigs supplemented with citrulline or arginine and its effect on nitric oxide production, blood pressure, protein synthesis and markers of tissue injury. Specific Aim3: Determine arginine availability and cardiovascular function, including blood pressure and tissue markers of hypoxia during sepsis in ADI-PEG 20-arginine-depleted pigs. To achieve these aims we will use methicillin- resistant S. aureus and pathogenic E. Coli swine models of sepsis-induced multiple organ dysfunction. A multitracer stable isotope protocol will be used to quantify whole body and hepatic arginine metabolism, and the analysis of the relevant enzymes and transporters will provide the molecular basis for the changes observed. Blood pressure, plasma metabolites, and markers of organ function and tissue injury will be analyzed to determine the effect of the different interventions on cardiovascular function, tissue perfusion and organ injury.