Arginine and nitric oxide synthesis in the pathogenesis of ketosis-prone diabetes

描述（由申请人提供）：KPD患者代表了2型糖尿病的一个独特亚群，其中肥胖/超重患者表现为糖尿病酮症酸中毒，尽管缺乏体液或细胞β细胞自身免疫，这意味着未知的独特和深刻的β细胞功能障碍。在这个项目中，我们建议验证KPD中严重但部分可逆和间歇性的β细胞功能障碍是通过减少精氨酸合成NO的可用性来介导的，这反过来又损害了胰岛素分泌。需要检验的具体假设有：1。与健康受试者和“通常”、不容易发生酮症的T2D患者相比，KPD患者细胞内精氨酸可用性降低，原因是a)血浆精氨酸酶活性升高导致精氨酸分解代谢增加，b)精氨酸合成减少，以及肠道排出的瓜氨酸减少。2. 由于精氨酸可用性降低，KPD患者有葡萄糖刺激的胰岛素分泌受损，以及内皮功能受损；然而胰岛素对精氨酸+葡萄糖的反应是正常的。3. 细胞内精氨酸可用性的增强将导致KPD患者葡萄糖刺激胰岛素分泌的改善。然而，由于精氨酸酶的精氨酸分解代谢增加，这可以通过膳食补充瓜氨酸比膳食补充精氨酸更有效地实现。使用稳定同位素示踪方法，这些假设将在KPD患者、2型糖尿病患者和健康对照组中进行测试，实现以下目标：在基础条件下和高血糖钳夹后测量a)精氨酸通量，瓜氨酸从头合成，蛋白质分解释放，转化为鸟氨酸和一氧化氮的速率；b)鸟氨酸和瓜氨酸通量（用于计算精氨酸水解和精氨酸和NO的合成；c）苯丙氨酸通量，用于测量蛋白质分解。目标1 b。在禁食和饲喂条件下测量：谷氨酰胺在肠内转化为瓜氨酸的速率，精氨酸的内脏摄取速率，其氧化和转化为鸟氨酸的速率，作为肠内精氨酸酶活性的指标，以及体外血浆精氨酸酶活性。目标2。测量葡萄糖和精氨酸刺激的胰岛素分泌和动脉血流介导的扩张，在高血糖钳夹之前和之后。目标3。在三组KPD患者中，在补充瓜氨酸、精氨酸或等氮丙氨酸（安慰剂）之前和之后，测量精氨酸通量、瓜氨酸合成、一氧化氮合成以及Aim 2中描述的测量。这些研究产生的数据可能对了解β细胞功能障碍的原因有很大的影响，不仅在KPD中，而且在所有形式的2型糖尿病中。此外，如果补充瓜氨酸能比精氨酸更大程度地改善葡萄糖刺激的胰岛素分泌和内皮功能，它将为KPD和2型糖尿病提供一种安全、廉价的辅助治疗。

DESCRIPTION (provided by applicant): Patients with KPD represent a unique subset of type 2 diabetes in which obese/overweight patients present with diabetic ketoacidosis despite absence of humoral or cellular β cell autoimmunity, implying unique and profound β cell dysfunction of unknown. In this project we propose to test the general hypothesis that the severe but partially reversible and intermittent β cell dysfunction in KPD is mediated through diminished availability of arginine for NO synthesis, which in turn impairs insulin secretion. Specific hypotheses to be tested are: 1. Compared to healthy subjects and "usual", non-ketosis-prone T2D patients, KPD patients have decreased intracellular arginine availability due to a) increased arginine catabolism caused by elevated plasma arginase activity, and b) decreased arginine synthesis due to diminished citrulline synthesis and efflux from the intestine. 2. Due to diminished arginine availability, KPD patients have impaired glucose-stimulated insulin secretion, as well as impaired endothelial function; however the insulin response to arginine + glucose is normal. 3. Enhancement of intracellular arginine availability will result in improved glucose-stimulated insulin secretion in KPD patients. However, due to increased arginine catabolism by arginase, this can be achieved more effectively by dietary citrulline supplementation than by dietary arginine supplementation. Using stable isotope tracer methods these hypotheses will be tested in groups of KPD patients, type 2 diabetics and healthy controls by achieving the following aims: Aim 1a. Measure under basal conditions and following a hyperglycemic clamp, a) arginine flux, de novo synthesis from citrulline, release from protein breakdown, rate of conversion to ornithine and to NO; b) ornithine and citrulline fluxes (to calculate arginine hydrolysis and syntheses of arginine and NO; c) phenylalanine flux as a measure of protein breakdown. Aim 1b. Measure, under conditions of fasting and feeding: the rate of conversion of glutamine to citrulline in the intestine, the rate of splanchnic uptake of arginine, its oxidation and its conversion to ornithine as an index of arginase activity in the intestine, and in vitro plasma arginase activity. Aim 2. Measure glucose- and arginine-stimulated insulin secretion and arterial flow- mediated dilation, before and following a hyperglycemic clamp. Aim 3. In three groups of KPD patients, measure arginine flux, synthesis from citrulline, NO synthesis and the measurements described in Aim 2, before and after supplementation with citrulline, arginine or isonitrogenous alanine (placebo). Data generated from these studies could have high impact for understanding the cause of β cell dysfunction not only in KPD but also in all forms of type 2 diabetes. Further, if citrulline supplementation improves glucose- stimulated insulin secretion and endothelial function to a greater extent than arginine, it will provide a safe and inexpensive adjunct therapy for KPD and type 2 diabetes.