NEUROTOXICITY OF AMMONIA AND SHORT-CHAIN FATTY ACIDS

氨和短链脂肪酸的神经毒性

• 批准号: 3476699
• 负责人: JAMES C. LAI
• 金额: $ 11.43万
• 依托单位: WEILL MEDICAL COLL OF CORNELL UNIV
• 依托单位国家: 美国
• 财政年份: 1987
• 资助国家: 美国
• 起止时间: 1987-04-01 至 1991-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/3476699
• 关键词: Krebs' cycle; adenosinetriphosphatase; alpha ketoglutarate; ammonia; blood brain barrier; brain disorders; brain metabolism; carboxylation; citrate synthase; fatty acids; ionophores; isocitrate dehydrogenase; laboratory rat; malate dehydrogenase; membrane structure; mitochondria; neurochemistry; neurons; neurotoxins; phosphorylation; pyruvate decarboxylase; radioassay; synaptosomes

Hyperammonemia and organic acidemia are persistent features in many encephalopathies (e.g. hepatic and valproate encephalopathies, Reye's disease, Jamaican vomitting sickness). Although the evidence for ammonia and/or short-chain fatty acids (SCFA) as major toxins in these encephalopathies is not always definitive, the most effective treatments of these diseases are geared toward eliminating the hyperammonemia and organic acidemia. Moreover, administration of ammonia and SCFA induces coma in animals and the resultant neuropathologic changes show striking similarities to the brain structural abnormalities of Reye's disease, and hepatic and valproate encephalopathies. Thus, investigations of the neurotoxicity of ammonia and SCFA should help to elucidate the underlying biochemical and physiologic mechanisms and illuminate the pathophysiology and/or pathogenesis of these encephalopathies. The studies outline in this proposal aim to test our hypothesis that ammonia and SCFA exert their toxic effects by (1) interfering with tricarboxylic acid (TCA) cycle activity, and (2) altering the structure and function of the neuronal plasma membrane. Based on results of our and other studies, we further propose that these toxins could interfere with TCA cycle activity by altering the activities of key, rate-limiting and/or regulated enzymatic steps. We will further test this hypothesis by investigating the effects of ammonia and SCFA on (i) the activities of rate-limiting and/or regulated (pyruvate dehydrogenase complex (PDHC), citrate synthase, isocitrate dehydrogenase, Alpha-ketoglutarate dehydrogenase complex) and non-regulated (fumarase, malate dehydrogenase) enzymes in rat brain mitochondrial extracts, (ii) citrate-, isocitrate- and Alpha-ketoglutarate-supported oxygen uptake by metabolically competent rat brain mitochondria, and (iii) the [1-14C]pyruvate decarboxylation (i.e. flux through PDHC) by and the PDHC activation (i.e. phosphorylation) state in intact brain mitochondria. We will characterize the neuronal plasma membrane monocarboxylic acid carrier (MCC) by studying the substrate and inhibitor specificities of the MCC uptake mechanisms in rat brain synaptosomes. Then, the effects of ammonia and SCFA on synaptosomal pyruvate uptake will be investigated and the dose-effect relationships established. In addition, the toxin's effects on synaptosomal pyruvate metabolism ([1-14C]pyruvate decarboxylation) will be studied. The elucidation of these toxic mechanisms may facilitate the designs of more beneficial therapies for the encephalopathies in which hyperammonemia and organic acidemia are the persistent features.

高氨血症和有机酸血症是许多患者的持续特征， 脑病（如肝性和丙戊酸盐脑病，Reye's 牙买加呕吐病（Jamaican vomiting sickness） 虽然氨的证据 和/或短链脂肪酸（SCFA）作为这些中的主要毒素， 脑病并不总是确定的，最有效的治疗方法是 这些疾病是为了消除高氨血症和有机 酸血症 此外，氨和SCFA的给药诱导昏迷， 动物和由此产生的神经病理变化显示出惊人的 与雷氏病的大脑结构异常相似， 肝脏和丙戊酸盐脑病。 因此，对 氨和SCFA的神经毒性应有助于阐明 生化和生理机制，并阐明病理生理学 和/或这些脑病的发病机制。 这些研究概述了 该提案旨在验证我们假设，即氨和SCFA发挥其毒性 通过（1）干扰三羧酸（TCA）循环活性， 以及（2）改变神经元血浆的结构和功能 膜的 根据我们和其他研究的结果，我们进一步建议 这些毒素可以通过改变TCA循环的活性来干扰TCA循环。 关键的、限速的和/或受调节的酶促步骤的活性。 我们将 通过研究氨的影响进一步验证这一假设， SCFA对（i）限速和/或调节（丙酮酸）的活性的影响 脱氢酶复合物（PDHC），柠檬酸合酶，异柠檬酸脱氢酶， α-酮戊二酸脱氢酶复合物）和非调节（脱氢酶， 苹果酸脱氢酶）酶，（ii） 柠檬酸盐、异柠檬酸盐和α-酮戊二酸盐支持的氧摄取， 代谢能力的大鼠脑线粒体，和（iii） [1- 14 C]丙酮酸脱羧（即通过PDHC的通量）和PDHC 完整脑线粒体中的激活（即磷酸化）状态。 我们 将表征神经元质膜单羧酸载体 (MCC)通过研究MCC的底物和抑制剂特异性， 大鼠脑突触体中的摄取机制。 然后，氨的影响 和SCFA对突触体丙酮酸摄取的影响， 建立了剂量-效应关系。 此外，毒素对 突触体丙酮酸代谢（[1- 14 C]丙酮酸脱羧）将被 研究了 阐明这些毒性机制可能有助于 设计更有益的脑病治疗方法， 高氨血症和有机酸血症是持续的特征。