Therapeutic and Metabolic Responses of Citrulline vs. Arginine Supplementation

精氨酸耗尽是在脓毒症患者中观察到的一种现象，随着严重程度的增加，死亡率也随之增加。在许多其他功能中，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注的调节中发挥核心作用。虽然负责精氨酸的消耗和命运的机制尚未确定，精氨酸补充剂已被提议恢复精氨酸的可用性。然而，目前尚不清楚精氨酸补充剂是否总是有效或有益的，因为它可以导致一氧化氮的过度产生，并有助于低血压，心脏抑制和血管低反应性感染性休克。补充瓜氨酸（精氨酸内源性合成的前体）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。同时解决精氨酸消耗和一氧化氮过度产生的替代方法是使用ADI-PEG 20。这种聚乙二醇化细菌酶催化精氨酸转化为瓜氨酸，瓜氨酸可通过瓜氨酸“再循环途径”再利用。该途径提供细胞内精氨酸以维持需要该氨基酸的大多数过程，但同时调节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引起精氨酸代谢失调，导致血浆精氨酸耗竭，并导致大循环和微循环衰竭，导致器官功能障碍。拟议研究的目的是阐明脓毒症儿童猪模型中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。为了检验我们的中心假设并达到我们的目标，我们提出了以下具体目标：具体目标1：量化肝脏对精氨酸的处置率及其在猪败血症模型中的利用所涉及的途径。具体目标2：确定补充瓜氨酸或精氨酸的败血症猪的精氨酸可用性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。具体目标3：测定精氨酸利用率和心血管功能，包括ADI-PEG 20-精氨酸耗竭猪败血症期间的血压和缺氧组织标志物。为了实现这些目标，我们将使用耐甲氧西林的S. aureus和致病性E.大肠杆菌感染诱导的多器官功能障碍猪模型。多示踪剂稳定同位素方案将用于量化全身和肝脏精氨酸代谢，相关酶和转运蛋白的分析将为观察到的变化提供分子基础。将分析血压、血浆代谢物以及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.