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，例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表观遗传变化的基本机制。母亲营养不良和IUGR导致胎儿组织的表观遗传变化，包括甲基化减少，增加基因表达。我们已经建立了一个狒狒非人灵长类动物（NHP）模型，适度的母体营养限制（MNR）导致IUGR。在对照组（CTR）中，有70%的母亲吃的是即兴饮食。在MNR中，胎儿维生素B12减少22%，而叶酸保持不变。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，由于大鼠1-CC功能与灵长类动物不同，因此需要NHP数据。我们建议在IUGR NHP模型中发展这些技术的核心是，妊娠大鼠研究表明，血浆通量被低估了80 - 80%的绝对组织HCYS产生，例如很少母体或胎儿肝脏HCYS输出到血浆中。因此，血浆HCYS不能反映主要的MET循环组织活性。因此，MET周期功能障碍并不一定导致HCYS升高，也可能与正常血浆HCYS一起发生。B12对于甲基从5-甲基四氢叶酸转移到甲基化HCYS到MET至关重要。假设：MNR降低了B12对胎儿MET周期的可用性，降低了1)HCYS的总体甲基化2)母体和胎儿组织中HCYS甲基化对血浆HCYS的贡献。方法：在0.9妊娠期的稳定同位素研究中，长期使用系绳系统维持母胎导管的怀孕狒狒，我们使用启动剂量，然后持续输注示踪剂[U-13C] MET和[1-13C] HCYS，以确定CTR和MNR妊娠期间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。创新：人类研究无法1)控制和匹配研究前的母体表型，2)精确控制营养摄入；3)获取母体和胎儿组织。新奇的谎言

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.