FREE RADICALS AND CHOLINE DEFICIENT LIVER CARCINOGENESIS

自由基和胆碱缺乏性肝癌的发生

• 批准号: 6286902
• 负责人: ROBERT A FLOYD
• 金额: $ 33.8万
• 依托单位: OKLAHOMA MEDICAL RESEARCH FOUNDATION
• 依托单位国家: 美国
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-04-03 至 2006-01-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6286902
• 关键词: AP1 protein; apoptosis; athymic mouse; carcinogenesis inhibitor; chemical carcinogenesis; choline deficiency; epidermal growth factor; fibroblast growth factor; free radical scavengers; hepatocellular carcinoma; hydrogen peroxide; laboratory rat; mitochondrial membrane; neoplasm /cancer nutrition therapy; nonhuman therapy evaluation; nuclear factor kappa beta; nutrition aspect of cancer; nutrition related neoplasm /cancer; nutrition related tag; preneoplastic state; prostaglandin E; prostaglandin endoperoxide synthase; transforming growth factors; tumor suppressor proteins

Reactive oxygen species (ROS) have been implicated in cancer development for many years. A prime example where ROS are strongly implicated is the model system where feeding a choline deficiency (CD) diet to rats leads to hepatocellular carcinoma (HCC) development, i.e., in the complete absence of exposure to any exogenous known carcinogen. Utilizing this model, we have made novel observations that make it possible to link ROS with key signal transduction pathways that have been shown to be fundamental in cancer initiation and development. For the first time we have shown that mitochondria from CD-livers are changed such that they mediate a significantly higher yield of H202 production. Additionally, for the first time we have shown that PBN (a- phenyl-tent-butyl nitrone), a nitrone-based free radical trap, significantly reduces preneoplastic nodule development as well as inhibits hepatocellular carcinoma (HCC) formation at very low levels of the compound. PBN is the most potent anti-carcinogen ever studied in this model. To explain these observations we postulate that the CD-regimen mediates changes in mitochondrial membranes such that they produce enhanced levels of H2O2 and that PBN significantly inhibits the excess H202 production by acting at Complex 1. We further postulate that excess H202 causes an enhanced inactivation of the PTEN tumor suppressor protein, which causes a loss of its phosphatase activity and thereby mediates a shift toward the activation of the AKT-kinase pathway resulting in a decrease in apoptosis medicated processes but an increase in oncogenic events. We further propose that the cells in preneoplastic nodules that develop in CD-livers are predisposed toward oncogenesis (as opposed to apoptosis) because of the action of excess H202 and certain growth factors (most likely TGFbeta1) and that PBN alters these processes through both its inhibition of excess H202 production and also by suppression of enhanced signal transduction processes. We propose that PBN acts to cause the prenoplastic nodule cells to become predisposed toward apoptic processes thus leading to inhibition of tumor development. To test this hypothesis we have proposed 3 specific aims. Briefly they are: A) We will determine the nature of the alterations in mitochondrial membranes that cause them to produce excess H202. B) We will focus on the mechanisms of how H2O2 acts as a signaling molecule and the action of PBN in altering signal transduction processes in cell models. C) We will determine if PBN (or its metabolite 4-OH-PBN) inhibits CD-mediated HCC development and ascertain if these compounds increase apoptosis in preneoplastic cells in this model.

活性氧（ROS）与癌症的发展有关已有多年。其中ROS被强烈牵连的主要实例是模型系统，其中向大鼠喂食胆碱缺乏（CD）饮食导致肝细胞癌（HCC）发展，即，在完全没有暴露于任何外源性已知致癌物质的情况下。利用这个模型，我们进行了新的观察，使其有可能连接ROS与关键的信号转导途径，已被证明是癌症的发生和发展的基础。我们第一次表明来自CD-肝脏的线粒体被改变，使得它们介导显著更高的H2 O2产生产率。此外，我们第一次表明PBN（a-苯基-叔丁基硝酮），一种硝酮基自由基捕获剂，在非常低的化合物水平下显著减少癌前结节的发展并抑制肝细胞癌（HCC）的形成。PBN是该模型中研究过的最有效的抗癌物质。为了解释这些观察结果，我们假设CD方案介导线粒体膜的变化，使得它们产生增强水平的H2 O2，并且PBN通过作用于复合物1而显著抑制过量的H2 O2产生。我们进一步假设过量的H2 O2导致PTEN肿瘤抑制蛋白的增强的失活，这导致其磷酸酶活性的丧失，从而介导朝向AKT-激酶途径的活化的转变，导致细胞凋亡介导的过程减少，但致癌事件增加。我们进一步提出，由于过量的H2 O2和某些生长因子（最可能是TGF β 1）的作用，在CD-肝脏中发展的癌前结节中的细胞倾向于肿瘤发生（与凋亡相反），PBN通过抑制过量的H2 O2产生和抑制增强的信号转导过程来改变这些过程。我们认为PBN的作用是使癌前结节细胞倾向于增生过程，从而抑制肿瘤的发展。为了验证这一假设，我们提出了三个具体目标。简言之，它们是：A）我们将确定线粒体膜中导致它们产生过量H2 O2的改变的性质。B）我们将重点讨论H2 O2作为信号分子的作用机制以及PBN在细胞模型中改变信号转导过程的作用。C）我们将确定PBN（或其代谢物4-OH-PBN）是否抑制CD介导的HCC发展，并确定这些化合物是否在该模型中增加癌前细胞的凋亡。