ARGININE FLUX AND NITRIC OXIDE PRODUCTION IN SUBJECTS WITH MELAS SYNDROME

这个子项目是许多利用资源的研究子项目之一 由NIH/NCRR资助的中心拨款提供。次级项目的主要支助 而子项目的主要调查员可能是由其他来源提供的， 包括其它NIH来源。 列出的子项目总成本可能 代表子项目使用的中心基础设施的估计数量， 而不是由NCRR赠款提供给子项目或子项目工作人员的直接资金。 摘要： 线粒体肌病、脑肌病、乳酸酸中毒伴中风样发作（MELAS）综合征是一种线粒体功能障碍疾病，具有广泛的症状和不同的发病年龄。常见的表现包括运动不耐受、中风样发作、癫痫发作、粗糙的红纤维、乳酸酸中毒和痴呆，75%的病例在20岁之前出现。中风样发作的患病率接近99%。MELAS综合征是最常见的母系遗传性线粒体疾病之一，最低患病率为16.3/100，000。 中风样发作的发病机制尚不清楚。据信，上皮功能障碍可导致微血管中的一氧化氮缺乏和缺血事件。精氨酸和瓜氨酸都是一氧化氮前体。据报道，MELAS综合征受试者的血浆精氨酸和瓜氨酸水平较低，并且精氨酸给药可导致急性发作和发作间期状态的临床改善。然而，尚无临床研究评价精氨酸流量和一氧化氮生成或精氨酸或瓜氨酸给药对MELAS综合征受试者一氧化氮生成的影响。因此，我们设计了一项病例对照前瞻性研究，通过稳定同位素输注技术确定MELAS综合征受试者和对照受试者的精氨酸通量和一氧化氮生成量，两个队列将进行基线研究，不补充任何精氨酸或瓜氨酸，MELAS综合征受试者将接受精氨酸和瓜氨酸补充研究。目的是观察MELAS综合征受试者的一氧化氮产生是否较低，精氨酸和瓜氨酸补充是否会增加一氧化氮产生，以及瓜氨酸补充是否会比精氨酸补充增加一氧化氮产生，继发于精氨酸区室化。如果我们要证明MELAS综合征受试者的一氧化氮生成量低于对照受试者，并且精氨酸和/或瓜氨酸补充剂可增加一氧化氮生成量，精氨酸或瓜氨酸具有上级效果，则本临床研究的结果将确立此类补充剂在治疗和预防MELAS综合征受试者卒中样发作方面的有效性的证据。 I. 假设 假设（A）：患有MELAS综合征的受试者具有改变一氧化氮代谢的上皮功能障碍，导致一氧化氮产生减少。 假设（B）：给予L-精氨酸和L-瓜氨酸作为一氧化氮前体，将增加MELAS综合征受试者的一氧化氮产生。 假设（C）：精氨酸在精氨酸代谢发生的亚细胞区室中被区室化，因此可能不存在循环精氨酸的自由交换。相反，它依赖于当地的瓜氨酸库来补充精氨酸库，用于一氧化氮的合成。因此，补充L-瓜氨酸比补充L-精氨酸更能增加一氧化氮的产生。 二. 具体目标 具体目标（A）：确定MELAS综合征受试者是否比对照受试者产生更低的一氧化氮。 具体目的（B）：检测MELAS综合征受试者接受L-精氨酸或L-瓜氨酸给药是否会增加一氧化氮的产生。 具体目标（C）：确定补充L-瓜氨酸是否会比补充L-精氨酸更大程度地增加一氧化氮的产生。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. ABSTRACT: The Mitochondrial myopathy, Encephalomyopathy, Lactic acidosis, with Stroke-like episodes (MELAS) syndrome is a disorder of mitochondrial dysfunction that has a broad spectrum of symptoms and variable age of onset. Common manifestations include exercise intolerance, stroke-like episodes, seizures, ragged red fibers, lactic acidosis, and dementia, with 75% of cases presenting before 20 years of age. The prevalence of stroke-like episodes approaches 99%. MELAS syndrome is one of the most frequent maternally inherited mitochondrial disorders with a minimal prevalence of 16.3/100,000. The pathogenesis of the stroke-like episodes is not clear. It is believed that epithelial dysfunction may lead to nitric oxide deficiency and ischemic events in the microvasculature. Both arginine and citrulline act as nitric oxide precursors. It has been reported that plasma arginine and citrulline levels are lower in subjects with MELAS syndrome and that administration of arginine leads to clinical improvement in the acute episodes and in the interictal state. However, there are no clinical studies evaluating the arginine flux and nitric oxide production or the effect of the administration of arginine or citrulline on nitric oxide production in subjects with MELAS syndrome. Thus, we designed a case control prospective study to determine arginine flux and nitric oxide production via a stable isotope infusion technique in subjects with MELAS syndrome and control subjects, both cohorts will have a baseline study without any supplementation of arginine or citrulline, and subjects with MELAS syndrome will be studied with arginine and with citrulline supplementation. The aims are to see whether nitric oxide production is lower in subjects with MELAS syndrome, whether arginine and citrulline supplementation will increase the nitric oxide production, and whether citrulline supplementation will increase nitric oxide production more than arginine supplementation secondary to arginine compartmentalization. If we were to demonstrate that subjects with MELAS syndrome have lower nitric oxide production than control subjects and that arginine and/or citrulline supplementation increases nitric oxide production, with either arginine or citrulline having a superior effect, the outcome of this clinical research will establish evidence to the usefulness of such supplementation in the treatment and prevention of stroke-like episodes in subjects with MELAS syndrome. I. HYPOTHESIS Hypothesis (A): Subjects with MELAS syndrome have epithelial dysfunction altering the nitric oxide metabolism, leading to decreased nitric oxide production. Hypothesis (B): Administration of L-arginine and L-citrulline, as nitric oxide precursors, will increase production of nitric oxide in subjects with MELAS syndrome. Hypothesis (C): Arginine is compartmentalized in a sub-cellular compartment where arginine metabolism takes place, thus there may not be free exchange of circulating arginine. Rather it depends on the local citrulline pool to replenish the arginine pool for nitric oxide synthesis. Therefore L-citrulline supplementation will increase nitric oxide production to higher degree than L-arginine supplementation. II. SPECIFIC AIMS Specific aim (A): To determine whether subjects with MELAS syndrome have lower nitric oxide production than control subjects. Specific aim (B): To test whether administration of L-arginine or L-citrulline to subjects with MELAS Syndrome will increase nitric oxide production. Specific aim (C): To determine whether L-citrulline supplementation will increase nitric oxide production to a higher degree than L-arginine supplementation.