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: 8327499
• 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/8327499
• 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; 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; 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. PUBLIC HEALTH RELEVANCE: Chronic alcoholism and alcohol-induced liver disease and its associated multi-organ involvement are common factors associated with the hospitalization of our veterans. The objectives of this proposal are to determine the mechanism of impaired hepatic creatine synthesis following ethanol exposure as well as to examine the functional consequences of this defect in hepatic and extra-hepatic tissues such as the cardiac and skeletal muscles. Further this project also seeks to determine whether these deleterious effects can be reversed by supplementing betaine or creatine in the diet or would require a combined treatment modality. This proposal is clinically relevant and complements the commitment of VA Research to acquire knowledge of the impact of alcohol on liver and other organs in hopes of developing a therapeutic intervention of using betaine and/or creatine to manage alcoholic liver injury as well as associated myopathies prevalent among veterans.

描述（由申请人提供）： 在本提案中，将检查乙醇诱导的肝细胞 S-腺苷甲硫氨酸 (SAM):腺苷高半胱氨酸 (SAH) 比例降低对重要的甲基转移酶、胍基乙酸甲基转移酶 (GAMT) 的影响。该甲基转移酶催化甲基从 SAM 转移至胍基乙酸 (GAA)，形成肌酸。最近已经确定，GAA 主要在肾脏中合成，并通过循环转运至肝脏，在肝脏中被甲基化形成肌酸。肝脏是循环肌酸水平的主要来源，供“需要肌酸”的组织摄取，这些组织具有高但可变的能量需求，例如骨骼肌和心肌因此，乙醇暴露后 GAMT 功能受损的影响可能导致两种不同的情况有害后果：1) 它会降低肝外组织的肌酸利用率，包括依赖完整的肝脏肌酸生物合成途径的骨骼肌和心肌。最佳运作； 2）由于有毒肌酸的积累，可能导致肝损伤 前体，GAA。基于这些考虑，提出了以下假设：乙醇引起的 SAM:SAH 改变通过影响 GAMT 活性来损害肝脏肌酸合成，对肝脏以及肝外组织（如骨骼肌和心肌）造成有害后果。此外，通过纠正改变的 SAM:SAH 比例补充甜菜碱可以使肝脏肌酸生物合成正常化，从而防止这些有害影响。 检验这一假设的具体目标是： 1) 进一步检查和阐明长期服用乙醇导致肝脏肌酸生物合成受损的机制。 2) 确定乙醇和甜菜碱对循环肌酸和 GAA 水平、肝脏肌酸流出和肾脏 GAA 产生的影响。 3) 证明乙醇诱导的肌酸前体 GAA 肝脏积聚的细胞毒性后果。 4) 评估乙醇暴露后肌酸生物合成和可用性改变对骨骼和心肌的影响和功能后果，并检查甜菜碱和/或 补充肌酸可以恢复或预防酒精引起的变化。该提案的目的是首先确定乙醇诱导的肝脏 SAM:SAH 比率降低在调节肝脏肌酸合成中的作用。然后，将检查甜菜碱是否可以通过纠正 SAM: SAH 比例来逆转酒精引起的对肝脏肌酸生物合成途径的影响。由于身体对肌酸的需求是通过循环摄取来满足的，因此接下来将确定乙醇和甜菜碱治疗对血浆肌酸和 GAA 水平的影响。此外，还将检查乙醇和/或甜菜碱是否改变肾脏产生和释放 GAA 的能力。在下一个具体目标中，将确定肌酸前体 GAA 在肝脏中积累的有害后果。最后，将检查消耗乙醇的大鼠骨骼和心肌中肌酸缺乏的生化和功能后果，以确定是否可以通过在饮食中补充甜菜碱和/或肌酸来逆转这些有害后果。总体而言，在肝损伤乙醇模型中完成这些研究并使用 GAMT 敲除小鼠模型进行验证，将深入了解维持肝脏中 GAMT 催化的基本甲基化反应与肝脏和肝外组织相关的重要性。 公共卫生相关性： 慢性酒精中毒和酒精引起的肝病及其相关的多器官受累是退伍军人住院的常见因素。该提案的目的是确定乙醇暴露后肝脏肌酸合成受损的机制，并检查这种缺陷在肝脏和肝外组织（例如心肌和骨骼肌）中的功能后果。此外，该项目还试图确定这些有害影响是否可以通过在饮食中补充甜菜碱或肌酸来逆转，或者是否需要联合治疗方式。该提案具有临床相关性，补充了 VA Research 的承诺，即了解酒精对肝脏和其他器官的影响，希望开发一种使用甜菜碱和/或肌酸来治疗酒精性肝损伤以及常见的相关肌病的治疗干预措施退伍军人之中。