The Role of Mitochondrial Dysfunction in Non-Alcoholic Fatty Liver Disease

描述（由申请人提供）：线粒体功能障碍可能是非酒精性脂肪性肝病（NAFLD）的发病机制和进展的原因，仅在美国就有超过7100万人患有这种疾病。线粒体功能受损可能导致肝脏甘油三酯通过氧化处理减少的初始蓄积，以及由于氧化磷酸化所需的过多氧化还原反应引起的氧化应激增强而转变为脂肪性肝炎。因此，我们认为，在患有轻度脂肪变性（假定为良性疾病）和脂肪性肝炎（NASH）（NAFLD的一种进行性和病态形式）的个体之间，线粒体代谢可能存在显著差异。这项资助的目标是使用新开发的、非侵入性的、基于体内NMR的稳定同位素方法来确定肝线粒体功能障碍在NAFLD发展中的作用，以及这些改变如何与胰岛素抵抗和NASH的发展相关。使用标准质谱技术或经典放射性示踪剂难以或不可能进行这样的测量。该提案的第一个目的是确定在胰岛素抵抗和NAFLD中观察到的胰岛素生成速率的增加是否与通过柠檬酸（TCA）循环（线粒体功能的一个组成部分）增加的能量生成有关。我们已经观察到TCA循环中的能量产生与从前体如乳酸和丙氨酸发生的代谢之间的关联，表明这些过程在能量上是相关的。在本提案的第二个目标中，我们将确定从温和脂肪变性到NASH的进展是否与线粒体功能的第二组分-生酮的进行性下降相关。一些报告表明，脂肪酸合成在肝脏中不适当地增加与NAFLD的主题，这意味着线粒体脂肪酸2-氧化抑制通过影响丙二酰辅酶A对肉毒碱棕榈酰转移酶。肝脏2-氧化的减弱可能与酮向外周的输出减少有关，有利于局部能量生成，以支持肝细胞中的细胞过程。在最终目标中，将量化二甲双胍（一种拟定的NAFLD治疗方法）增强NAFLD患者肝线粒体功能的能力。拟议研究的好处有几个方面：首先，提高对NAFLD发病机制和进展中代谢紊乱的理解，将允许更好的临床洞察力和集中的治疗方法;其次，我们的方法可以提供一种简单的非侵入性方法来识别NASH个体，他们是进行性肝病的最大风险;第三，更好地理解二甲双胍治疗NAFLD的作用机制将使这种治疗针对最有可能获益的个体。 公共卫生相关性：由于肥胖和糖尿病导致的肝脏脂肪积累被称为非酒精性脂肪肝病（NAFLD），在美国有超过7100万人患有这种疾病。这种脂肪积累可能导致某些个体的炎症和进行性肝病。该提案的目标是使用基于稳定同位素示踪剂和核磁共振光谱的非侵入性技术来确定线粒体功能受损是否有助于NAFLD的发病机制和进展，这些技术有可能通过提供一种方法来识别处于进行性肝病风险中的个体来立即影响临床护理，迄今为止只有通过肝活检才有可能。

DESCRIPTION (provided by applicant): Mitochondrial dysfunction may be responsible for the pathogenesis and progression of non-alcoholic fatty liver disease (NAFLD), a condition that affects over 71 million individuals in the U.S. alone. Impaired mitochondrial function could lead to both the initial accumulation of hepatic triglycerides via decreased oxidative disposal, as well as the transition to steatohepatitis due to enhanced oxidative stress originating from the plethora of redox reactions required for oxidative phosphorylation. As a result, we believe that there may be significant differences in mitochondrial metabolism between individuals with bland steatosis, presumed to be a benign condition, and steatohepatitis (NASH), a progressive and morbid form of NAFLD. The goal of this grant will be to use newly-developed, non-invasive, in vivo NMR-based stable isotope methodologies to define the role of hepatic mitochondrial dysfunction in the development of NAFLD and how these alterations relate to the development of insulin resistance and NASH. Such measurements are difficult or impossible to do using standard mass spectrometry techniques or classic radiotracers. The first aim of this proposal seeks to determine if the increased rates of gluconeogenesis observed in insulin resistance and NAFLD are associated with increased energy generation via the citric acid (TCA) cycle, a component of mitochondrial function. We have observed an association between energy generation in the TCA cycle and gluconeogenesis occurring from precursors such as lactate and alanine, suggesting that these processes are energetically linked. In the second aim of this proposal we will determine if progression from bland steatosis to NASH is associated with a progressive decline in a second component of mitochondrial function, ketogenesis. Several reports demonstrate that FA synthesis in liver is inappropriately increased in subjects with NAFLD, implying that mitochondrial FA 2-oxidation is inhibited via the effect of malonyl-CoA on carnitine palmitoyl transferase. Attenuation of hepatic 2-oxidation may be associated with decreased export of ketones to the periphery in favor of local energy generation to support cellular processes in the hepatocyte. In the final aim, the ability of metformin, a proposed therapy for NAFLD, to augment hepatic mitochondrial function in individuals with NAFLD will be quantified. The benefits of the proposed research are several-fold: First, improved understanding of the metabolic derangements complicit in the pathogenesis and progression of NAFLD will allow better clinical insight and focused approaches to therapy; Second, our methodologies may provide a simple, non-invasive method to identify individuals with NASH, who are at greatest risk of progressive liver disease; and Third, a better understanding of the mechanism of action of metformin in the treatment of NAFLD will allow this therapy to be targeted to individuals most likely to derive benefit. PUBLIC HEALTH RELEVANCE: Accumulation of fat in the liver due to obesity and diabetes is termed non-alcoholic fatty liver disease (NAFLD), with over 71 million individuals in the USA afflicted with this disorder. Such fat accumulation can lead to inflammation and progressive liver disease in some individuals. The goal of this proposal is to determine if impaired mitochondrial function contributes to the pathogenesis and progression of NAFLD using non-invasive techniques based on stable isotope tracers and nuclear magnetic resonance spectroscopy, techniques that have the potential to immediately impact clinical care by providing a method to identify individuals at risk for progressive liver disease, heretofore only possible by liver biopsy.