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与非酒精性脂肪性肝病（NAFLD）的发病和进展有关，仅在美国就有超过7100万人患有NAFLD。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而初始积累，也可能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，我们认为轻度脂肪变性（被认为是一种良性疾病）和脂肪性肝炎（NASH）（一种进行性和病态的NAFLD）患者之间的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、无创的、基于体内核磁共振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。使用标准的质谱技术或传统的放射性示踪剂很难或不可能进行这样的测量。本提案的第一个目的是确定胰岛素抵抗和NAFLD中观察到的糖异生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）产生的能量增加有关。我们观察到三羧酸循环中的能量生成与乳酸和丙氨酸等前体的糖异生之间存在关联，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，我们将确定从轻度脂肪变性到NASH的进展是否与线粒体功能的第二个组成部分——生酮功能的逐渐下降有关。一些报道表明，NAFLD患者肝脏中FA合成不适当地增加，这意味着线粒体FA 2氧化通过丙二酰辅酶a对肉毒碱棕榈酰转移酶的作用而受到抑制。肝2氧化的衰减可能与酮向外周的输出减少有关，有利于局部能量的产生，以支持肝细胞的细胞过程。在最后的目标中，二甲双胍（NAFLD的一种拟议疗法）增强NAFLD患者肝线粒体功能的能力将被量化。拟议研究的好处有几个方面：首先，提高对NAFLD发病和进展中的代谢紊乱的理解，将有助于更好的临床见解和集中治疗方法；其次，我们的方法可以提供一种简单的、非侵入性的方法来识别NASH患者，他们有最大的进展性肝病风险；第三，更好地了解二甲双胍治疗NAFLD的作用机制将使这种治疗能够针对最有可能获益的个体。

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.