CARNITINE-DEPENDENT METABOLISM AND AMMONIA TOXICITY

肝硬变是一种常见的疾病，在这种疾病中，肝脏血流灌注 受损的实质细胞会逐渐受损，最终 被毁了。 随着肝功能的丧失，严重的中枢神经紊乱 神经系统(CNS)也可发生(肝性脑病)。可用的治疗方法有 局限性，且远期预后较差。中枢神经系统的影响被认为 用通常被除去的化合物来表示大脑的中毒 来自肝脏的血浆。尽管许多化合物可能会对 观察到的脑病，有大量证据表明氨是一种主要的 毒素。S.Grisolia等人。最近有报道称，氨的含量要低得多 L-卡尼汀对小鼠的毒性作用--线粒体转运 长链脂肪酸的载体。其保护机制尚不清楚。 L肉碱保护作用的生化基础研究 将重点放在两个问题上：(1)L-卡尼汀，给人一种保护性的 剂量，通过血脑屏障的量足以解释 它对氨中毒有什么影响？脑摄取指数(BUI) L-卡尼汀将在大鼠体内测定。然后，BUI将被更改 在药理学上，BUI的变化将与变化相关 氨中毒，如果有的话。研究将表明肉碱是否 影响发生在外周或中枢神经系统内；相关研究将 阐明肉碱在脑中的代谢作用。(2)什么是 肉碱改变氨毒性的机制？肉碱刺激 脂肪酸氧化，从而增加线粒体内Acty-CoA 合成，并最终形成三磷酸腺苷。提高ATP水平可能会保护 中枢神经系统氨中毒直接或可刺激肝尿素 从而降低血氨水平。通过刺激酮 形体肉碱还可以增加中枢神经系统的能量来源，可能 从而节省葡萄糖碳来合成谷氨酰胺。或者，通过 刺激肌肉肉碱中支链氨基酸的使用可能会增加 形成谷氨酰胺，降低血氨水平。这些假设 (可能还有其他的)将在体外和体内使用 假说所需的关键酶的有效和特定的抑制剂 肉碱效应。给药这种抑制剂应该会减少 如果被阻断的通路很重要，肉碱的保护作用。 在之前的研究中已经开发出了几种所需的抑制剂 不相关的研究；在申请中提出了其他研究。

Cirrhosis of the liver is a common disease in which hepatic perfusion is compromised and parenchymal cells are progressively damaged and eventually destroyed. As hepatic function is lost, severe derangements of the central nervous system (CNS) also occur (hepatic encephalopathy). Available therapies are limited, and the long-term prognosis is poor. The CNS effects are believed to represent an intoxication of the brain by compounds normally removed from plasma by the liver. Although many compounds may contribute to the observed encephalopathy, there is abundant evidence that ammonia is a major toxin. S. Grisolia et al. recently reported that ammonia is much less toxic to mice previously given L-carnitine, a mitochondrial transport carrier for long-chain fatty acids. The protective mechanism is unknown. Studies of the biochemical basis for the protective effect of L-carnitine will focus on two questions: (1) Does L-carnitine, given at a protective dose, cross the blood-brain barrier in amounts sufficient to account for its effect on ammonia toxicity? The brain uptake index (BUI) for L-carnitine will be determined in rats. The BUI will then be altered pharmacologically, and the changes in BUI will be correlated with changes in ammonia toxicity, if any. The studies will indicate if the carnitine effect occurs peripherally or within the CNS; related studies will elucidate the metabolic role of carnitine in brain. (2) What is the mechanism by which carnitine alters ammonia toxicity? Carnitine stimulates fatty acid oxidation and thus increases intramitochondrial acety-CoA synthesis and, ultimately, ATP formation. Increased ATP levels may protect the CNS from ammonia toxicity directly or may stimulate hepatic urea formation and thus decrease plasma ammonia levels. By stimulating ketone body formation carnitine could also increase CNS energy sources and may thereby spare glucose carbon for glutamine synthesis. Alternatively, by stimulating branched-chain amino acid use in muscle carnitine may increase glutamine formation and decrease plasma ammonia levels. These hypotheses (and possibly others) will be investigated in vitro and in vivo using potent and specific inhibitors of key enzymes required for the hypothesized carnitine effect. Administration of such inhibitors should diminish the protective effect of carnitine if the blocked pathway is important. Several of the required inhibitors have been developed in previous unrelated studies; others are proposed in the application.