IN VIVO ARGININE METABOLISM IN IDIOPATHIC AND SECONDARY PULMONARY HYPERTENSION

这个子项目是利用资源的许多研究子项目之一。 由NIH/NCRR资助的中心拨款提供。对子项目的主要支持 子项目的首席调查员可能是由其他来源提供的， 包括美国国立卫生研究院的其他来源。为子项目列出的总成本可能 表示该子项目使用的中心基础设施的估计数量， 不是由NCRR赠款提供给次级项目或次级项目工作人员的直接资金。 摘要 肺动脉高压(PAH)是一种病因不明的疾病，其特征是肺动脉压和血管阻力增加。它可以是特发性的，也可以是其他疾病的继发性疾病，如镰状细胞病。血管扩张分子一氧化氮(NO)的减少被认为在PAH的发病机制中起重要作用，但需要对PAH患者的NO代谢进行进一步的体内研究。我们认为，PAH中存在NO缺乏，这是由于NO前体精氨酸的可获得性降低和合成NO的酶-一氧化氮合酶活性降低的综合作用所致。具体地说，我们假设，与健康对照组相比，PAH患者可用于NO合成的精氨酸将减少，这是由于精氨酸酶活性增加，精氨酸酶将精氨酸分解为尿素和鸟氨酸，并减少从头合成精氨酸。此外，它们还会增加不对称二甲基精氨酸的浓度，从而抑制一氧化氮合酶的活性。为了验证这些假说，稳定同位素示踪技术将被用来测量健康对照组、特发性PAH患者和继发性镰状细胞病PAH患者的精氨酸和一氧化氮代谢。这些测量将与血流动力学和临床参数相关联。这个项目将增加我们对精氨酸-NO途径在PAH发病机制中的作用的了解。此外，它还可能确定未来治疗试验的目标。 一、假说 在这个项目中，我们建议检验一个普遍的假设，即血管扩张分子一氧化氮(NO)的可获得性降低是肺动脉高压(PAH)发病机制的基础。NO的缺乏是由于NO前体精氨酸的可获得性降低和一氧化氮合酶活性受损所致的合成减少的结果。需要检验的具体假设如下： 1.与健康对照组相比，PAH患者体内可用于NO合成的精氨酸减少，这主要是由于a)精氨酸酶活性升高导致精氨酸转化为尿素和鸟氨酸的增加，以及2)从头合成精氨酸减少。 2.与健康对照组相比，PAH患者由于不对称二甲基精氨酸(ADMA)对一氧化氮合酶活性的抑制，导致NO合成减慢。因此，肺动脉压和疾病严重程度与NO合成率呈负相关，与血浆ADMA浓度呈正相关。 二、专项目标 为了验证上述假设，我们将利用稳定同位素示踪技术和生化方法对3组受试者：特发性肺动脉高压患者、镰状细胞病合并肺动脉高压患者和对照组进行活体测量。 1.精氨酸流量(产生率或出现率)，其血浆浓度，以及从其前体瓜氨酸合成从头合成精氨酸的速率。 2.尿素通量和鸟氨酸通量(精氨酸酶活性指标)、血浆鸟氨酸浓度以及血浆精氨酸和鸟氨酸浓度的比值 3.瓜氨酸流量、其血浆浓度以及精氨酸到瓜氨酸的转化率(NO合成的指标) 4.不对称二甲基精氨酸的血浆浓度。 这些测量将与血流动力学和临床参数相关，包括：通过超声心动图或右心导管检查的肺动脉压、右房压和心脏指数，以及6分钟步行距离。

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 Pulmonary arterial hypertension (PAH) is a disease of unknown etiology that is characterized by increased pulmonary artery pressure and vascular resistance. It can be idiopathic or secondary to other disease conditions, such as sickle cell disease. Decreased production of the vasodilatory molecule nitric oxide (NO) is believed to play an important role in the pathogenesis of PAH, but further in vivo studies of NO metabolism in patients with PAH are needed. We propose that there is a shortage of NO in PAH resulting from the combined effects of decreased availability of the NO precursor arginine and impaired activity of nitric oxide synthase, the enzyme that synthesizes NO. Specifically, we hypothesize that compared to healthy controls, patients with PAH will have less arginine available for NO synthesis secondary to increased activity of arginase, the enzyme that breaks down arginine to urea and ornithine, and decreased de novo arginine synthesis. In addition, they will have increased concentrations of asymmetric dimethylarginine, leading to inhibition of NO synthase activity. To test these hypotheses, stable isotope tracer techniques will be used to measure arginine and nitric oxide metabolism in healthy controls, patients with idiopathic PAH, and patients with PAH secondary to sickle cell disease. These measurements will be correlated with hemodynamic and clinical parameters. This project will increase our knowledge about the role of the arginine-NO pathway in the pathogenesis of PAH. In addition, it may identify future targets for therapeutic trials. I. HYPOTHESIS In this project, we propose to test the general hypothesis that decreased availability of the vasodilatory molecule nitric oxide (NO) underlies the pathogenesis of pulmonary arterial hypertension (PAH). This shortage of NO is a result of decreased synthesis due to the combined effects of the decreased availability of the NO precursor arginine and impaired nitric oxide synthase activity. Specific hypotheses to be tested are as follows: 1. Compared to healthy controls, patients with PAH have less arginine available for NO synthesis secondary to a) increased arginase activity leading to increased conversion of arginine to urea and ornithine and 2) decreased de novo arginine synthesis. 2. Compared to healthy controls, patients with PAH will have slower NO synthesis because of inhibition of nitric oxide synthase activity by asymmetric dimethylarginine (ADMA). As a consequence, pulmonary artery pressures and disease severity will be negatively correlated with the rate of NO synthesis and positively correlated with plasma ADMA concentration. II.SPECIFIC AIMS To test the above hypotheses, stable isotope tracer techniques and biochemical methods will be used to make the following measurements in vivo in 3 groups of subjects: patients with idiopathic pulmonary hypertension, patients with sickle cell disease and pulmonary hypertension, and controls. 1. Arginine flux (rate of production or rate of appearance), its plasma concentration, and the rate of de novo arginine synthesis from its precursor, citrulline. 2. Urea flux and ornithine flux (indices of arginase activity), plasma ornithine concentration, and the ratio of plasma concentration of arginine to ornithine 3. Citrulline flux, its plasma concentration, and the rate of conversion of arginine to citrulline (an index of NO synthesis) 4. Plasma concentration of asymmetric dimethylarginine. These measurements will be correlated with hemodynamic and clinical parameters, including: pulmonary artery pressures, right atrial pressure, and cardiac index by echocardiogram or right heart catheterization, and six minute walk distance.