Stable isotope evaluation of the methionine cycle in undernourished pregnancy

描述(由申请人提供)：蛋氨酸(MET)循环是发育过程中甲基化的核心(例如，基因-环境相互作用)。受损的甲基转移具有结构和代谢后果，如神经管缺陷和高同型半胱氨酸(HCYS)。基因甲基化是导致持续性表观遗传变化的基本机制。母亲营养不良和IUGR会导致胎儿组织的表观遗传学变化，包括甲基化减少，从而增加基因表达。我们建立了一种中度母体营养限制(MNR)导致IUGR的非人灵长类(NHP)模型。对照组(CTR)70%的母亲随意进食。在MNR中，胎儿维生素B12下降了22%，而叶酸没有变化。大鼠研究表明，高同型半胱氨酸血症与血浆HCYS流入和流出的增加有关。然而，由于RAT1-CC的功能不同于灵长类动物，因此需要NHP数据。我们建议在IUGR NHP模型中开发这些技术的核心是，怀孕期间的大鼠研究表明，血浆通量被低估了80%的绝对组织HCYS产生，例如很少的母体或胎儿肝脏HCYS输出到血浆。因此，血浆同型半胱氨酸不能反映主要的MET周期组织活动。因此，MET循环功能障碍并不一定会导致HCY升高，在血浆HCY正常的情况下可能会发生。B12是甲基从5-甲基四氢叶酸转移到甲基化HCYS再到MET所必需的。假设：MNR降低B12对胎儿代谢周期的利用率，减少1)总体HCYS甲基化；2)母体和胎儿组织中HCYS甲基化对血浆HCYS的贡献。方法：在妊娠0.9天的稳定同位素研究中，我们使用母体和胎儿导管在系绳系统上维持的母体和胎儿导管，在持续注入示踪剂[U-13C]MET和[1-13C]HCYS之后，我们使用启动剂量来确定在CTR和MNR妊娠中HCYS甲基化和HCYS动力学。我们的合作者在怀孕大鼠身上的方法现在正在出版中。创新：人类研究不能1)控制和匹配研究前的母体表型，2)精确控制营养摄入量，3)获得母体和胎儿组织。新奇在于 将独特的NHP模式和一个紧迫的发展问题结合在一起。R03响应性：R03机制鼓励新的、高风险的研究。这些同位素技术从未在任何早熟物种中进行过。研究人员对围产期狒狒的研究有多年的经验，并发表了大量关于NHP MNR/IUGR胎儿表型的文章。环境：我们的狒狒饲养设施是世界上唯一生产受控MNR和IUGR的设施。相关性：灵长类和啮齿类动物的MET循环代谢明显不同。识别组织甲基化的改变将提供组织中发生MET周期功能障碍并导致表观遗传学变化的证据。信息将转化为人类怀孕，以帮助诊断、预防和治疗策略。与叶酸相比，B12被忽略了。

DESCRIPTION (provided by applicant): The methionine (MET) cycle is central to methylation in developmental processes (e.g. gene-environment interactions). Impaired methyl transfers have structural and metabolic consequences e.g. neural tube defects and high homocysteine (HCYS). Gene methylation is a fundamental mechanism leading to persistent epigenetic changes. Maternal under-nutrition and IUGR results in epigenetic changes in fetal tissues, including decreased methylation that increases gene expression. We have developed a baboon non-human primate (NHP) model of moderate maternal nutrient restriction (MNR) resulting in IUGR. MNR mothers eat 70% of controls (CTR) eating ad lib. In MNR, fetal vitamin B12 is decreased 22% while folate is unchanged. Rat studies show hyperhomocysteinemia is associated with increases in both plasma HCYS inflow and outflow. However NHP data are needed since rat 1-CC function differs from primates. Central to our proposal to develop these techniques in an IUGR NHP model, rat studies in pregnancy show that plasma fluxes under- estimate by >80% absolute tissue HCYS production e.g. little maternal or fetal hepatic HCYS is exported to plasma. Thus, plasma HCYS does not reflect major MET cycle tissue activity. As a consequence, MET cycle dysfunction does not necessarily lead to elevated HCYS and can occur with normal plasma HCYS. B12 is essential for methyl group transfer from 5-methyl-tetrahydrofolate to methylate HCYS to MET. HYPOTHESIS: MNR decreases B12 availability to the fetal MET cycle decreasing 1) overall HCYS methylation 2) contribution of HCYS methylation in maternal and fetal tissues to plasma HCYS. APPROACH: In stable isotope studies at 0.9 gestation in pregnant baboons chronically instrumented with maternal and fetal catheters maintained on a tether system, we use a priming dose followed by constant infusion of the tracers [U-13C] MET and [1-13C] HCYS to determine HCYS methylation and HCYS kinetics in both CTR and MNR pregnancies. Our collaborators methods in pregnant rats are now in Press. INNOVATION: Human studies cannot 1) control and match pre-study maternal phenotype, 2) precisely control nutrient intake; 3) obtain maternal and fetal tissues. Novelty lies in combining a unique NHP model and a pressing developmental question. R03 RESPONSIVENESS: The R03 mechanism encourages novel, high-risk studies. These isotope techniques have never been performed in any precocial species. INVESTIGATORS have many years experience with perinatal baboon studies and have published extensively on this NHP MNR/IUGR fetal phenotype. ENVIRONMENT: Our baboon feeding facility is unique worldwide to produce controlled MNR and IUGR. RELEVANCE: Primate and rodent MET cycle metabolism differs markedly. Identification of alterations in tissue methylation will provide evidence of tissues in which MET cycle dysfunction occurs with resultant epigenetic changes. Information will translate to human pregnancy aiding diagnostic, preventative and therapeutic strategies. B12 has been ignored in comparison to folic acid.