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（由申请人提供）：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）， 具有深远的中枢神经系统 (CNS) 影响，并且可能对环境产生影响 原因。特别是由于接触碳等有毒物质而导致的肝损伤 四氯化物、甲苯、DDT、七氯等，以及慢性酒精中毒 以及直接接触环境氨，可引发 HE/HA 症状。 然而，该疾病对中枢神经系统产生多种影响 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最关键的疾病指标 进展。此外，啮齿动物模型的特征呈现出几个 HE/HA研究的弱点。由于我们知识上的差距，没有 实用有效的临床干预策略 预防或逆转疾病的生物标志物或症状。最近，我们有 确定了一种脊椎动物模型，即海湾蟾蜍（Opsanus beta），它既是 对氨的损害极其耐受，并且凭借其水生特性 生活方式，使得一系列在哺乳动物模型中不切实际的实验成为可能， 即快速“氨冲洗”方案。因此，我们建议测试几个 旨在利用这一新特征的这些和其他特征的假设 模型来解决 HE/HA 生物标志物和干预策略的缺乏。 特别是，我们将：（1）检验存在可逆与可逆的假设。 HE/HA 的不可逆生物标志物，并且这些可以很容易地识别和 在像蟾蜍这样的水生模型中脱颖而出； (2) 检验假设 相对于哺乳动物，蟾蜍具有极高的氨耐受性，这是由于 其生理学的一个不寻常的方面，特别是对于更强大的 大脑中的氨解毒系统，或对氨固有的不敏感 脑线粒体代谢对氨的损伤。作为对此的进一步测试 第二个假设，我们还将探讨蟾蜍具有的可能性 天然存在的氨保护剂化合物含量较高（例如， 其脑组织中的肉毒碱、氧化三甲胺等）含量高于哺乳动物。在 总而言之，这些实验将导致不容易获得的信息 来自人类和现有哺乳动物模型的作用机制 氨和细胞耐受和恢复的能力，从而达到 更好地了解 HE/HA 的原因和机制， 导致治疗策略。