Dynamic and kinetic behavior of folate metabolism

描述（由申请人提供）：先前的研究表明，叶酸代谢的中断或缺乏会增加，叶酸补充可能会降低心血管疾病、神经管缺陷（NTDs）和癌症的风险。这种影响很大程度上与叶酸补充剂降低同型半胱氨酸（Hcy）的能力有关。近年来，一些参与叶酸代谢的酶的作用，对叶酸介导的疾病状态至关重要，已经开始被认识到。一个关键的酶是MTHFR，它催化5,10-亚甲基四氢叶酸的还原。目前对酶变异对体内叶酸代谢行为的影响的理解仍然是初级的。了解叶酸/Hcy代谢的药物基因组学的第一步是量化MTHFR和其他遗传变异背景下叶酸池的体内动力学。测试系统的功能最好使用体内示踪剂方法，具有足够的分析精度来检测正常生理条件下的差异代谢。14c标记的底物与加速器质谱（AMS）检测相结合，具有灵敏度和特异性，可以在不干扰或饱和正常酶促过程的真正示踪剂（几乎无质量）剂量下揭示差异代谢。我们的长期目标是在正常和病理条件下的遗传变异背景下，建立个体对叶酸反应（代谢表型）的基础。为了实现这一目标，我们的下一个目标是确定叶酸在个体体内对MTHFR （C677T和A1298C）、MS A2756G和蛋氨酸合成酶还原酶（MTRR） A66G的两种变体的动力学。我们的中心假设是，MTHFR 677和1298的纯合子（或复合杂合子）、MS和MTRR（或复合杂合子）的动力学行为发生了改变，从而改变了叶酸库的分布和可用于正常代谢的形式。为了实现这一应用的目标，我们将追求三个具体目标：我们将筛选和分层约400名正常绝经前女性和男性的MTHFR和MS和MTRR基因型。我们将确定痕量叶酸在血液、尿液和粪便中的体内动力学行为。然后，我们将比较不同基因型之间叶酸代谢的行为（功能终点）。

DESCRIPTION (provided by applicant): Previous studies have suggested that disruptions or deficiencies in folate metabolism increases, and that folate supplementation may reduce, the risk of cardiovascular disease, neural tube defects (NTDs), and cancer. Much of this effect is associated with the homocysteine (Hcy) lowering ability of folate supplementation. In recent years, the contribution of several enzymes involved in folate metabolism, essential to folate-mediated disease states, have begun to be recognized. A key enzyme is MTHFR, which catalyzes the reduction of 5,10-methylenetetrahyrdrofolate. Current understanding of effects of enzyme variants on the in vivo behavior of folate metabolism is still elementary. A first step in understanding the pharmacogenomics of folate/Hcy metabolism is to quantify the in vivo kinetics of folate pools in the context of MTHFR and other genetic variants. Testing system function is best accomplished using in vivo tracer methodologies that have sufficient analytical precision to detect differential metabolism under normal physiological conditions. 14C-labeled substrates coupled with Accelerator Mass Spectrometry (AMS) detection have the sensitivity and specificity to reveal differential metabolism at true tracer (nearly massless) doses that do not disturb or saturate normal enzymatic processes. Our long-range goal, is to establish the basis for the individual response (metabolic phenotyping) to folic acid in the context of genetic variants under normal and pathological conditions. As our next objective in pursuit of this goal, we propose to determine the in vivo kinetic of folic acid in individuals with respect to two variants of MTHFR (C677T & A1298C), MS A2756G, and methionine synthase reductase (MTRR) A66G. Our central hypothesis is that homozygotes for either MTHFR 677 and 1298 (or compound heterzygotes), MS and MTRR (or compound heterozygotes) display altered kinetic behavior and hence altered distribution of folate pools and forms available for normal metabolism. To accomplish the objectives of this application, we will pursue three specific aims: we will screen and stratify about 400 normal premenopausal women and men for MTHFR and MS and MTRR genotypes. We will determine the in vivo kinetic behavior of a tracer dose of folate in blood, urine, and stool. We will then compare the behavior of folate metabolism (functional endpoint) among the various genotypes.