GENETIC EFFECTS-FOLATE-DEPENDENT ONE-CARBON METABOLISM

描述：一碳（Cl）代谢包括碳的产生 用于细胞过程的装置，包括DNA合成、 甲硫氨酸（Met）从同型半胱氨酸（Hcy），以及许多生物 化合物.损害一碳代谢的疾病（如叶酸） 缺乏）与血浆Hcy水平升高和 血管疾病、某些癌症和神经管缺陷。一种常见的突变 亚甲基四氢叶酸还原酶（MTHFR），称为“不耐热”或 C677 T突变体与血浆I-Icy升高（尤其是 低叶酸状态）、血浆叶酸水平降低、红细胞分布改变 叶酸，可能增加血管疾病的风险，并降低 结肠癌C677 T突变的体内代谢效应尚未被证实。 直接决定。我们的总体假设是， 减少了从丝氨酸（C1单元的主要来源）产生甲基 在C677 T突变纯合子个体中，基因型效应 当叶酸营养不足时，我们还假设， 叶酸依赖的核苷酸（嘌呤和胸苷酸）合成速率 在叶酸缺乏时会减少，但可能会被C677 T突变增强。 拟议的研究将确定营养和遗传依赖的 Cl单位从丝氨酸（Ser）流向Met和从Ser流向核苷酸。这 协议还将允许测量同型半胱氨酸的转硫途径 在处理过量Hcy中起重要作用。具体目标。确定： (a)Ser作为甲基Cl单元供体的动力学 合成和核苷酸合成以及可能造成的损害程度 C677 T突变和/或低叶酸状态。(b)C677 T的影响 突变和叶酸状态对细胞Cl状态的影响， 红细胞中叶酸种类的分布。(C)C677 T的影响 突变和叶酸状态对同型半胱氨酸催化剂的影响。(d)的相对 胞质和线粒体代谢在Cl-生成中的作用 用于合成甲基和核苷酸的单元。(e)的意义 线粒体甘氨酸裂解产生Cl单位。方案：主要 方案中，将对营养充足的健康人类受试者（20-30岁）进行 按MTHFR基因型分类（纯合对照和纯合突变体）。 受试者最初将接受13 C-丝氨酸输注作为主要前体 并在8周的膳食消耗120 μ g/d叶酸后评估效果 营养和基因型对氯动力学的影响。这有两种变体 将进行研究，以确定线粒体的相对作用， 从丝氨酸产生Cl的胞质途径和线粒体的作用 甘氨酸裂解途径总的来说，这些研究将产生新的功能 关于叶酸缺乏的影响的数据，以及常见的 MTHFR的多态性

DESCRIPTION: One-carbon (Cl) metabolism consists of the generation of carbon units for use in cellular processes including DNA synthesis, regeneration of methionine (Met) from homocysteine (Hcy), and methylation of many biological compounds. Conditions that impair one-carbon metabolism (e.g. folate deficiency) are associated with elevation in plasma Hcy and increased risk of vascular disease, certain cancers, and neural tube defects. A common mutation of methylene-tetrahydrofolate reductase (MTHFR), known as the "thermolabile" or C677T mutant, has been associated with elevations in plasma I-Icy (especially in low folate status), lower plasma folate, altered distribution of erythrocyte folate, potentially increased risk of vascular disease, and decreased risk of colon cancer. The in vivo metabolic effects of the C677T mutation have not been determined directly. Our overall hypothesis is that the rate of acquisition and generation of methyl groups from serine (primary source of C1 units) is reduced in individuals homozygous for the C677T mutation, and that the genotypic effect is greatest when folate nutriture is inadequate. We also hypothesize that the rate of folate-dependent synthesis of nucleotides (purines and thymidylate) will be reduced in folate deficiency but may be enhanced by the C677T mutation. The proposed studies will determine nutritional and genetic dependence of the flow of Cl units from serine (Ser) to Met and from Ser to nucleotides. This protocol also will allow measurement of the transsulfuration pathway of Hcy catabolism important in disposal of excess Hcy. Specific aims. To determine: (a) The kinetics by which Ser serves as a donor of Cl units for methyl group synthesis and nucleotide synthesis and the possible degree of impairment caused by the C677T mutation and/or low folate status. (b) The influence of the C677T mutation and folate status on cellular Cl status as reflected by the distribution of folate species in erythrocytes. (C) The influence of the C677T mutation and folate status on homocysteine catabolism. (d) The relative contributions of cytosolic and mitochondrial metabolism in the generation of Cl units for synthesis of methyl groups and nucleotides. (e) The significance of mitochondrial glycine cleavage in generation of Cl units. Protocol: In the main protocol, healthy adequately nourished human subjects (20-30 yr) will be classified by MTHFR genotype, (homozygous control and homozygous mutant). Subjects will be given infusions with 13C-serine as primary precursor initially and following 8-wk dietary depletion of 120 ugld folate to evaluate the effect of nutritional and genotypic effects on Cl kinetics. Two variations of this study will be conducted to determine the relative roles of mitochondrial and cytosolic routes of Cl generation from serine and the role of the mitochondrial glycine cleavage pathway. In total, these studies will yield new functional data regarding the effects of folate deficiency, and the influence of common polymorphism of MTHFR.