Mechanisms of Sensitization to TNF hepatotoxicity in ALD

描述(申请人提供)：酒精性肝病(ALD)在美国仍然是一个重要的健康问题。肝脏蛋氨酸代谢异常是ALD后天性代谢异常，长期饮酒对肝脏蛋氨酸代谢的影响最初似乎是自相矛盾的。虽然饮酒会导致肝脏S-腺苷甲硫氨酸(SAME)不足，但它会提高肝脏同型半胱氨酸水平，这是同一代谢的产物。 同型半胱氨酸水平降低和同型半胱氨酸水平升高可能是酒精性肝损伤的原因之一。酒精对蛋氨酸代谢途径中的另一种代谢物S-同型半胱氨酸水平的影响研究较少。我们的工作假设是，肿瘤坏死因子与ALD中观察到的某些代谢异常，如甲硫氨酸/同型半胱氨酸/SAH代谢异常引起的细胞内甲基化状态的改变，在ALD肝损伤的发生发展中起病因学作用。我们推测，慢性酒精滥用导致肠道通透性增加和内毒素血症，产生活性氧中间体，Kupffer细胞NFkB激活，肿瘤坏死因子产生增加，肝细胞MAT活性降低并随后出现同样的缺陷，S-同型半胱氨酸浓度增加，转甲基化反应抑制，肝脏甲基化状态降低，对细胞内甲基化状态敏感的蛋白质表达/激活/活性增加，如caspase-8，线粒体功能障碍，增加对肝脏肿瘤坏死因子细胞毒性的易感性，以及随后的肝损伤。在这项建议中，我们将评估慢性酒精暴露对肝脏转甲基化反应的抑制作为肝脏对肿瘤坏死因子诱导的细胞毒性增敏的机制。本项目的具体目标如下：1.评价抑制肝脏转甲基化反应对肿瘤坏死因子肝毒性“增敏”的影响；2.探讨抑制转甲基化反应使肝细胞对肿瘤坏死因子肝毒性增敏的可能机制；3.评价长期饮酒(+/-相同补充)对灌胃酒精大鼠肝脏甲基化状态和对肿瘤坏死因子肝毒性增敏的影响。 这项研究将在有组织的指导支持和详细的培训计划下进行，旨在最大限度地增加我成为一名由NIH资助的独立研究员的机会。

DESCRIPTION (provided by applicant): Alcoholic liver disease (ALD) continues to be an important health problem in the United States. Abnormal hepatic methionine metabolism is an acquired metabolic abnormality in ALD and the effects of chronic alcohol intake on hepatic methionine metabolism are initially seemingly paradoxic. Whereas alcohol consumption causes hepatic deficiency of S-adenosylmethionie (SAMe), it elevates hepatic homocysteine levels, a product of SAMe metabolism. Decreased SAMe levels and elevated homocysteine levels may contribute to alcohol induced liver injury. The effect of alcohol on S-adenosylhomocysteine (SAH) levels, another metabolite in the methionine metabolism pathway, has received little investigative attention. It is our working hypothesis that tumor necrosis factor (TNF) in conjunction with certain metabolic abnormalities observed in ALD, such as altered intracellular methylation status due to abnormal methionine/SAMe/SAH metabolism play an etiologic role in the development of liver injury in ALD. We postulate that chronic alcohol abuse causes increased gut permeability and endotoxemia, generation of reactive oxygen intermediates, activation of Kupffer cell NFkB with increased TNF production, decreased hepatocyte MAT activity with subsequent SAMe deficiency, increased S-adenosylhomocysteine (SAH) concentrations, inhibition of transmethylation reactions, decreased hepatic methylation status, elevated expression/ activation/activity of proteins sensitive to intracellular methylation status such as caspase-8, mitochondrial dysfunction, increased susceptibility to hepatic TNF cytotoxicity, and subsequent liver injury. In this proposal, we will evaluate inhibition of hepatic transmethylation reactions by chronic alcohol exposure as a mechanism for hepatic sensitization to TNF-induced cytotoxicity in a relevant model of ALD. The specific objectives of this project are as follows: 1. Evaluate the effects of inhibition of hepatic transmethylation reactions on "sensitization" to TNF hepatotoxicity; 2. Investigate possible mechanisms by which inhibition of transmethylation reactions sensitizes hepatocytes to TNF hepatotoxicity; and 3. Evaluate the effects of chronic alcohol consumption (+/- SAMe supplementation) on hepatic methylation status and sensitization to TNF-hepatotoxicity in rats intragastrically fed alcohol. This research will be performed with structured mentoring support and a detailed training program designed to maximize my opportunity to become an independent NIH-funded investigator.