Project 4: One-Carbon Metabolism, Oxidative Stress and As Toxicity

本项目涉及该超级基金计划的生物医学研究的两个主要主题 涉及a)砷(As)的代谢和b)As诱导的氧化应激。有很大的变异性 从AS暴露到疾病的临床表现。几项研究已经导致了 假设营养状况可能是这种变异性的主要原因。无机原样 通过一碳代谢甲基化，这是一种依赖于叶酸的生物化学途径 一碳基团。我们希望扩大我们的研究，这些研究已经开始描述 一碳代谢对AS甲基化个体间变异性的营养调控。 谷胱甘肽(GSH)，主要抗氧化防御机制的关键组成部分，也是电子供体 对于As还原，是由同型半胱氨酸合成的，这种合成受一碳中间体的调节 新陈代谢。大量的基础研究，包括我们小组成员的突出工作， 这表明人们越来越相信，砷会消耗谷胱甘肽(GSH)，并诱导氧化应激。然而， 在人类中，砷暴露与氧化应激之间的关系尚未得到严格的研究 人口。 这项提议的第一个具体目标将利用由 队列研究(项目2)进行嵌套病例对照研究，以确定可改变的危险因素(例如 氧化应激和/或高同型半胱氨酸血症)与砷引起的皮肤损伤的易感性增加有关。 剩下的具体目标将利用我们研究区域的扩大(以及安装AsFree 管井)在项目3和7中招募目前暴露在砷中的375名新成年人。具体而言 目标2，我们将解决一个基本问题：尿液作为代谢物在多大程度上反映为 循环中的代谢物？在具体目标3中，我们将进行横断面研究，以测试 假设较高浓度的S-同型半胱氨酸和较低浓度的谷胱甘肽 与降低的AS甲基化有关。在具体目标4中，我们建议检查剂量反应 砷暴露与氧化应激的关系。最后，我们将检验这一假设 因为暴露在空气中可以减轻氧化压力。拟议的研究有可能a)证实 在人群中诱导氧化应激并耗尽GSH，b)AS诱导的氧化应激和/或 营养状况与砷相关的临床结局，以及c)扩大我们对其机制的理解 潜藏在这些过程中。这些发现将对确定 预防砷中毒的潜在针对性干预措施。

Two overarching themes of the biomedical research of this Superfund Program addressed in this project relate to a) the metabolism of arsenic (As) and b) As-induced oxidative stress. There is significant variability in progression from As exposure to clinical manifestations of disease. Several studies have led to the hypothesis that nutritional status may account for a substantial portion of this variability. Inorganic As is methylated via one-carbon metabolism, a biochemical pathway that is dependent on folate for recruitment of one-carbon groups. We wish to expand our studies, which have begun to characterize the impact of nutritional regulation of one-carbon metabolism on the inter-individual variability in As methylation. Glutathione (GSH), a key component of the primary antioxidant defense mechanism, and the electron donor for As reduction, is synthesized from homocysteine, and this synthesis is regulated by intermediates of onecarbon metabolism. A great deal of basic research, including salient work from members of our group, points to the growing belief that As depletes glutathione (GSH) and induces oxidative stress. However, the relationship between As exposure and oxidative stress has not been rigorously examined in human populations. The first specific aim of this proposal will utilize the repository of biological samples established by the Cohort Study (Project #2) to conduct a nested case-control study to identify modifiable risk factors (e.g. oxidative stress and/or hyperhomocysteinemia) related to increased susceptibility to As-induced skin lesions. The remaining specific aims will take advantage of the expansion of our study area (and installation of Asfree tube wells) in Projects #3 and #7 to recruit 375 new adults who are currently exposed to As. In Specific Aim 2, we will address a fundamental question: To what extent do urinary As metabolites reflect As metabolites in the circulation? In Specific Aim 3, we will conduct a cross-sectional study to test the hypotheses that higher concentrations of s-adenosylhomocysteine (SAH) and lower concentrations of GSH are associated with reduced As methylation. In Specific Aim 4, we propose to examine dose-response relationships between As exposure and oxidative stress. Finally, we will test the hypothesis that reduction of As exposure alleviates oxidative stress. The proposed studies have the potential to a) substantiate that As induces oxidative stress and depletes GSH in a human population, b) link As-induced oxidative stress and/or nutritional status to an arsenic-related clinical outcome, and c) expand our understanding of the mechanisms underlying these processes. Such findings would have significant implications for the identification of potential targeted interventions for preventing As-toxicity.