ARGININE FLUX AND NITRIC OXIDE PRODUCTION IN SUBJECTS WITH MELAS SYNDROME

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 线粒体肌病，脑肌病，乳酸中毒，伴卒中样发作综合征(MELAS)是一种具有广泛症状和不同发病年龄的线粒体功能障碍。常见的表现包括运动不耐受、中风样发作、癫痫发作、红色纤维粗糙、乳酸酸中毒和痴呆症，75%的病例出现在20岁之前。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，患病率最低为16.3/10万。卒中样发作的发病机制尚不清楚。据认为，上皮功能障碍可能导致一氧化氮缺乏和微血管系统的缺血事件。精氨酸和瓜氨酸都是一氧化氮的前体。据报道，MELAS综合征患者血浆精氨酸和瓜氨酸水平较低，应用精氨酸可改善急性发作和发作间歇期的临床症状。然而，还没有临床研究评估精氨酸流量和一氧化氮的产生，或者精氨酸或瓜氨酸对MELAS综合征患者一氧化氮产生的影响。因此，我们设计了一项病例对照前瞻性研究，通过稳定的同位素输注技术，在MELAS综合征患者和对照组中确定精氨酸流量和一氧化氮产生，两组都将进行基线研究，不补充精氨酸或瓜氨酸，MELAS综合征患者将接受精氨酸和瓜氨酸补充研究。这些研究的目的是了解MELAS综合征患者的一氧化氮生成是否较低，补充精氨酸和瓜氨酸是否会增加一氧化氮的生成，以及补充瓜氨酸是否会比补充精氨酸更能增加继发于精氨酸区划的一氧化氮的生成。如果我们证明MELAS综合征患者的一氧化氮生成比对照组低，补充精氨酸和/或瓜氨酸会增加一氧化氮的生成，其中精氨酸或瓜氨酸的效果更好，这项临床研究的结果将为这种补充在治疗和预防MELAS综合征患者的类中风发作方面的有效性奠定基础。 假设(A)：患有MELAS综合征的患者存在上皮功能障碍，改变了一氧化氮的代谢，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综合征患者一氧化氮的产生。假设(C)：精氨酸在发生精氨酸新陈代谢的亚细胞室中被分隔，因此循环中的精氨酸可能不会自由交换。相反，它依赖于当地的瓜氨酸池来补充精氨酸池，以合成一氧化氮。因此，补充L-瓜氨酸比补充L-精氨酸更能增加一氧化氮的生成。 具体目的(A)：确定MELAS综合征患者的一氧化氮生成量是否低于对照组。具体目的(B)：检测MELAS综合征患者应用L-精氨酸或L-瓜氨酸是否会增加一氧化氮的产生。具体目的(C)：确定补充L-瓜氨酸是否比补充L-精氨酸更能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. 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. 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. 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. 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.