Effect of Alcohol on Hepatic Creatine Biosynthesis: Role of Defective Methylation

酒精对肝脏肌酸生物合成的影响：缺陷甲基化的作用

• 批准号: 8438194
• 负责人: Kusum K. Kharbanda
• 金额: --
• 依托单位: OMAHA VA MEDICAL CENTER
• 依托单位国家: 美国
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-07-01 至 2016-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8438194
• 关键词: Affect; Alcoholic Liver Diseases; Alcoholism; Alcohols; Anabolism; Apoptosis; Betaine; Biochemical; Blood Circulation; Brain; Buffers; Cells; Chronic; Combined Modality Therapy; Complement; Creatine; Defect; Development; Diet; Energy Metabolism; Equilibrium; Ethanol; Extrahepatic; Generations; Guanidinoacetate N-Methyltransferase; Hepatic; Hepatic Tissue; Hospitalization; Injury to Liver; Investigation; Kidney; Knockout Mice; Knowledge; Laboratories; Lead; Liver; Methylation; Methyltransferase; Modeling; Myocardium; Myopathy; Organ; Pathway interactions; Phosphocreatine; Phosphorylation; Plasma; Play; Production; Proteins; Rattus; Reaction; Research; Role; S-Adenosylhomocysteine; S-Adenosylmethionine; Skeletal Muscle; Source; Supplementation; Testing; Therapeutic Intervention; Tissues; Toxic effect; Veterans; alcohol effect; alcohol exposure; base; betaine-homocysteine methyltransferase; clinically relevant; cytotoxic; guanidinoacetate; insight; liver injury; meetings; methyl group; mouse model; prevent; transmethylation; uptake

DESCRIPTION (provided by applicant): In this proposal, the effect of ethanol-induced reduction in hepatocellular S-adenosylmethionine (SAM):Sadenosylhomocysteine (SAH) ratios on an important methyltransferase, guanidinoacetate methyltransferase (GAMT) will be examined. This methyltransferase catalyzes the transfer of a methyl group from SAM to guanidinoacetate (GAA) to form creatine. It has been recently established that GAA is primarily synthesized in the kidney and transported through the circulation to the liver where it is methylated to form creatine. Liver is the principa source of circulating levels of creatine for uptake by "creatine-requiring" tissues that have a hig, but variable energy demand such as skeletal and cardiac muscles Therefore, the impact of compromised GAMT function following ethanol exposure can lead to two distinct detrimental consequences: 1) It can decrease creatine availability for extra-hepatic tissues, including skeletal and cardiac muscles that rely on an intact hepatic creatine biosynthetic pathway for optimal functioning; and 2) it can cause liver injury due to the accumulation of the toxic creatine precursor, GAA. Based on these considerations, the following hypothesis has been formulated: Ethanol induced altered SAM:SAH impairs hepatic creatine synthesis via its effect on GAMT activity causing detrimental consequences in the liver as well as extra-hepatic tissues such as the skeletal and cardiac muscles. Furthermore, betaine supplementation by virtue of correcting the altered SAM:SAH ratio could normalize hepatic creatine biosynthesis and thereby prevent these detrimental effects. The specific aims to test this hypothesis are: 1) To further examine and delineate the mechanism of impaired hepatic creatine biosynthesis by chronic ethanol administration. 2) To determine the effects of ethanol and betaine on circulating creatine and GAA levels, liver creatine efflux and kidney GAA production. 3) To demonstrate the cytotoxic consequences of ethanol-induced hepatic accumulation of creatine precursor, GAA. 4) To evaluate the effects and functional consequences of altered creatine biosynthesis and availability following ethanol exposure on skeletal and cardiac muscles and to examine whether betaine and/or creatine supplementation can revert or prevent the alcohol-induced changes. The objectives of this proposal are to first determine the role of ethanol-induced reduced liver SAM: SAH ratios in regulating hepatic creatine synthesis. Then, whether betaine by correcting the SAM: SAH ratio also reverses alcohol-induced effects on the liver creatine biosynthetic pathway will be examined. Since the body's requirement for creatine is met via uptake from the circulation, the effect of ethanol and betaine treatment on plasma levels of creatine and GAA will be determined next. Further, whether kidney's ability to produce and release GAA is altered by ethanol and/or betaine will be examined. In the next specific aim the detrimental consequences of accumulation of creatine precursor, GAA in the liver will be determined. Finally, the biochemical and functional consequences of creatine shortage in the skeletal and cardiac muscles of rats consuming ethanol will be examined to determine whether these detrimental consequences could be reversed by supplementing betaine and/or creatine in the diet. Overall, completion of these studies in an ethanol model of liver injury and validated using a GAMT knockout mouse model will provide insight in to the importance of maintaining the essential methylation reaction catalyzed by GAMT in the liver in relation to hepatic and extra hepatic tissues.

描述（由申请人提供）： 在此提案中，乙醇诱导的肝细胞S-腺苷硫氨酸（SAM）的降低对萨德替糖基霍明氨酸（SAH）比对重要的甲基转移酶，鸟尼替诺乙酸甲酯甲基转移酶（GAMT）的影响。该甲基转移酶催化甲基从SAM转移到圭尼二乙酸（GAA）形成肌酸。最近已经确定，GAA主要是在肾脏中合成的，并通过循环运输到肝脏，在肝脏中甲基化形成肌酸。肝脏是通过“肌酸征用”的组织来吸收肌酸循环水平的主要来源肝肌酸生物合成途径，用于最佳功能； 2）由于有毒肌酸的积累，它可能导致肝损伤 前体，GAA。基于这些考虑，已经提出了以下假设：乙醇引起的SAM：SAH通过其对GAMT活性的影响损害了肝肌酸的合成，从而导致肝脏以及肝脏外组织（如骨骼肌和心脏肌肉）。此外，通过纠正改变的SAM：SAH比率可以使肝肌酸生物合成正常化，从而防止这些有害效应。 检验该假设的具体目的是： 1）进一步检查和描述慢性乙醇给药受损肝肌酸生物合成的机制。 2）确定乙醇和甜菜碱对循环肌酸和GAA水平的影响，肝脏肌酸外排和肾脏GAA产生。 3）证明乙醇诱导的肌酸前体肝积累的细胞毒性后果，GAA。 4）评估肌酸生物合成改变和乙醇暴露后的可用性的影响和功能后果对骨骼和心脏肌肉的影响，并检查Betaine和/或 补充肌酸可以恢复或防止酒精引起的变化。该提案的目标是首先确定乙醇诱导的肝脏SAM：SAH比在调节肝肌酸合成中的作用。然后，是否会检查Betaine是否通过校正SAM：SAH比率也逆转了酒精诱导的对肝脏肌酸生物合成途径的影响。由于人体对肌酸的需求是通过循环中的吸收来满足肌酸的，因此接下来将确定乙醇和甜菜碱治疗对肌酸和GAA血浆水平的影响。此外，还将检查肾脏生产和释放GAA的能力，并会被乙醇和/或甜菜碱改变。在下一个特定目标中，将确定肌酸前体积累的有害后果，将确定肝脏中的GAA。最后，将检查肌酸短缺在食用乙醇的大鼠的骨骼和心脏肌肉中的生化和功能后果，以确定是否可以通过补充饮食中的Betaine和/或Ceracine来逆转这些有害后果。总体而言，在肝损伤的乙醇模型中完成这些研究并使用GAMT基因敲除小鼠模型进行了验证，将洞悉维持GAMT在肝脏中与肝脏和额外肝组织有关的基本甲基化反应的重要性。