Extreme Ammonia Tolerance Mechanisms: A Model Vertebrate

极端氨耐受机制：脊椎动物模型

• 批准号: 6430139
• 负责人: Patrick Joseph Walsh
• 金额: $ 15.1万
• 依托单位: UNIVERSITY OF MIAMI ROSENTEIL SCHOOL
• 依托单位国家: 美国
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-02-08 至 2004-11-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6430139
• 关键词: ammonia; astrocytes; biomarker; brain metabolism; detoxification; disease /disorder model; environmental toxicology; enzyme activity; glutamate ammonia ligase; hepatic coma /encephalopathy; hippocampus; immunocytochemistry; laboratory rat; mitochondria; model design /development; neural degeneration; neurochemistry; neuroprotectants; neurotoxicology; nicotinamide adenine dinucleotide; poisoning; sulfur aminoacid; tertiary amine; tissue /cell culture; toad; western blottings

DESCRIPTION (provided by applicant): Hepatic Encephalopathy (HE), and resultant elevated blood and tissue ammonia concentrations (i.e., hyperammonemia, HA), has profound central nervous system (CNS) effects, and can have environmental causes. In particular, liver damage due to exposure to toxicants such as carbon tetrachloride, toluene, DDT, heptachlor, etc., as well as chronic alcoholism and direct exposure to environmental ammonia, can elicit symptoms of HE/HA. However, there are such a wide variety of CNS effects produced in the disease in humans, and in rodent experimental models, that it is difficult to determine which disease biomarkers are the most critical indicators of disease progression. Furthermore, characteristics of the rodent model present several weaknesses in the study of HE/HA. Because of this gap in our knowledge, no practical and effective clinical intervention strategies are available to prevent or reverse biomarkers or symptoms of the disease. Recently, we have identified a vertebrate model, the gulf toadfish (Opsanus beta), which is both extremely tolerant of ammonia insult, and which, by virtue of its aquatic lifestyle, enables a line of experimentation not practical in mammalian models, namely rapid "ammonia washout" protocols. Therefore, we propose to test several hypotheses aimed at exploiting these and other characteristics of this new model to address the lack of biomarkers and intervention strategies for HE/HA. In particular, we will: (1) test the hypothesis that there are reversible vs. irreversible biomarkers of HE/HA, and that these can be readily identified and distinguished in an aquatic model like the toadfish; (2) test the hypotheses that extreme ammonia tolerance in the toadfish, relative to mammals, is due to an unusual aspect of its physiology, in particular, either to a more robust ammonia detoxification system in the brain, or to an inherent insensitivity of brain mitochondrial metabolism to ammonia insult. As a further test of this second hypothesis, we will also explore the possibility that the toadfish has higher levels of naturally occurring ammonia protectant compounds (e.g., carnitine, trimethylamine oxide, etc.) in its brain tissues than do mammals. In sum, these experiments will lead to information which is not readily obtainable from humans and existing mammalian models concerning the mechanisms of action of ammonia and cellular capacity for tolerance and recovery, and thus to a better understanding of the causes and mechanisms underlying HE/HA that could lead to therapeutic strategies.

描述(申请人提供)：肝性脑病(HE)及其结果 血液和组织氨浓度升高(即高氨血症，HA)， 对中枢神经系统(CNS)有深远的影响，并可能对环境产生 原因。特别是，暴露在碳等有毒物质中会对肝脏造成损害 四氯化碳、甲苯、滴滴涕、七氯等，以及慢性酒精中毒 和直接暴露在环境氨中，可引发HE/HA症状。 然而，在这种疾病中产生了如此广泛的中枢神经系统效应 在人类和啮齿动物实验模型中，很难确定 哪些疾病生物标志物是疾病最关键的指标 进步。此外，啮齿动物模型的特点表现出几个 HE/HA研究中的不足。由于我们知识上的差距，没有 实用有效的临床干预策略可用于 预防或逆转疾病的生物标志物或症状。最近，我们有 发现了一种脊椎动物模型，海湾蟾鱼(Opsanus Beta)，它既是 对氨的侮辱具有极强的耐受性，凭借其水生的 生活方式，使得一系列在哺乳动物模型中不实用的实验成为可能， 也就是快速的“氨洗出”方案。因此，我们建议测试几个 旨在利用该新技术的这些和其他特征的假设 解决缺乏生物标记物和HE/HA干预策略的模型。 特别是，我们将：(1)检验存在可逆与非可逆的假设。 不可逆的HE/HA生物标志物，这些标志物可以很容易地识别和 在像蟾鱼这样的水生模型中有所区别；(2)检验假设 与哺乳动物相比，蟾鱼对氨气的极端耐受性是由于 它生理上的一个不同寻常的方面，特别是对一个更强壮的 大脑中的氨解毒系统，或对 脑线粒体代谢对氨气的伤害。作为对这一点的进一步测试 第二个假设，我们还将探索蟾鱼是否有 更高水平的天然氨保护剂化合物(例如， 肉碱、三甲胺氧化物等)在它的脑组织中比哺乳动物更多。在……里面 总而言之，这些实验将导致不容易获得的信息 来自人类和现有的哺乳动物模型关于作用机制的 氨和细胞的耐受和恢复能力，从而达到 更好地了解HE/HA潜在的原因和机制 引出治疗策略。