Brain alanine formation as an ammonia-scavenging pathway during hyperammonemia: effects of glutamine synthetase inhibition in rats and astrocyte-neuron co-cultures
Brain alanine formation as an ammonia-scavenging pathway during hyperammonemia: effects of glutamine synthetase inhibition in rats and astrocyte-neuron co-cultures
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DOI：
10.1038/jcbfm.2013.73
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发表时间：
2013-08-01
影响因子：
6.3
通讯作者：
Waagepetersen, Helle S.
中科院分区：
文献类型：
--
作者：
Dadsetan, Sherry;Kukolj, Eva;Waagepetersen, Helle S.
高氨血症是肝性脑病发生发展中的一个主要病因性毒性因素。脑内氨的解毒主要在星形胶质细胞中通过谷氨酰胺合成酶（GS）进行，并且有人提出在高氨血症期间升高的谷氨酰胺水平会导致星形胶质细胞肿胀和脑水肿。然而，氨也可能通过谷氨酸脱氢酶（GDH）和丙氨酸氨基转移酶（ALAT）的协同作用进行解毒，从而将氨捕获在丙氨酸中，而丙氨酸在体内可能会离开大脑。我们的目的是研究GS抑制剂甲硫氨酸亚砜亚胺（MSO）在急性高氨血症期间是否会增强（NH₄⁺）-N - 15在丙氨酸中的掺入。我们观察到，用MSO处理的大鼠脑内丙氨酸中（NH₄）-N - 15的掺入量增加了四倍。此外，在有或无MSO存在的情况下，暴露于（NH₄Cl）-N - 15的神经元和星形胶质细胞共培养物显示出（NH₄）-N - 15掺入丙氨酸呈剂量依赖性，同时谷氨酸中N - 15的掺入也增加。这些发现提供了证据，表明氨在体内和体外都通过GDH和ALAT的协同作用解毒，在MSO存在的情况下该机制会加速，从而降低脑内谷氨酰胺水平。因此，GS可能是治疗肝性脑病患者高氨血症的一个潜在药物靶点。
Hyperammonemia is a major etiological toxic factor in the development of hepatic encephalopathy. Brain ammonia detoxification occurs primarily in astrocytes by glutamine synthetase (GS), and it has been proposed that elevated glutamine levels during hyperammonemia lead to astrocyte swelling and cerebral edema. However, ammonia may also be detoxified by the concerted action of glutamate dehydrogenase (GDH) and alanine aminotransferase (ALAT) leading to trapping of ammonia in alanine, which in vivo likely leaves the brain. Our aim was to investigate whether the GS inhibitor methionine sulfoximine (MSO) enhances incorporation of (NH4+)-N-15 in alanine during acute hyperammonemia. We observed a fourfold increased amount of (NH4)-N-15 incorporation in brain alanine in rats treated with MSO. Furthermore, co-cultures of neurons and astrocytes exposed to (NH4Cl)-N-15 in the absence or presence of MSO demonstrated a dose-dependent incorporation of (NH4)-N-15 into alanine together with increased N-15 incorporation in glutamate. These findings provide evidence that ammonia is detoxified by the concerted action of GDH and ALAT both in vivo and in vitro, a mechanism that is accelerated in the presence of MSO thereby reducing the glutamine level in brain. Thus, GS could be a potential drug target in the treatment of hyperammonemia in patients with hepatic encephalopathy.