Glutamine-induced free radical production in cultured astrocytes
Glutamine-induced free radical production in cultured astrocytes
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DOI：
10.1002/glia.20003
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发表时间：
2004-05-01
期刊：
影响因子：
6.2
通讯作者：
Norenberg, MD
中科院分区：
文献类型：
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作者：
Jayakumar, AR;Rao, KVR;Norenberg, MD
氨是一种神经毒素，与肝性脑病、雷氏综合征、先天性尿素循环错误、戊二酸尿症和其他代谢性脑病的发病机制有关。在星形胶质细胞中，脑氨主要通过谷氨酰胺合成酶代谢为谷氨酰胺。虽然合成谷氨酰胺通常被视为氨解毒的主要手段，但这种假定的有益作用受到了质疑，因为越来越多的证据表明，氨的一些有害影响可能是由谷氨酰胺介导的，而不是氨本身。由于已知氨能诱导培养的星形胶质细胞产生自由基，我们调查了这种产生是否可能由谷氨酰胺介导。用谷氨酰胺(4.5 mM)处理星形胶质细胞2-3分钟(95%，P<0.05)，以及1小时和3小时(分别为42%和49%，P<0.05)。同样的处理，培养的神经元不能产生自由基。谷氨酰胺产生的自由基被抗氧化剂去铁胺(40um)和α-苯基-N-叔丁基硝酮(250um)以及一氧化氮合酶抑制剂N-omega-硝基-L-精氨酸甲酯(500um)阻断。谷氨酰胺酶抑制剂6-重氮-5-氧代-L去甲亮氨酸(1 MM)也能抑制自由基的产生，提示谷氨酰胺水解释放的氨气可能与自由基的产生有关。此外，线粒体通透性转换抑制剂环孢菌素A可阻止谷氨酰胺产生自由基。结果表明，谷氨酰胺暴露后，产生自由基的是星形胶质细胞，而不是神经元。谷氨酰胺诱导的氧化和/或亚硝化应激可能是氨神经毒性的关键机制。(C)2004年Wiley-Liss公司
Ammonia is a neurotoxin implicated in the pathogenesis of hepatic encephalopathy, Reye's syndrome, inborn errors of the urea cycle, glutaric aciduria, and other metabolic encephalopathies. Brain ammonia is predominantly metabolized to glutamine in astrocytes by glutamine synthetase. While the synthesis of glutamine has generally been viewed as the principal means of ammonia detoxification, this presumed beneficial effect has been questioned as growing evidence suggest that some of the deleterious effects of ammonia may be mediated by glutamine rather than ammonia per se. Since ammonia is known to induce the production of free radicals in cultured astrocytes, we investigated whether such production might be mediated by glutamine. Treatment of astrocytes with glutamine (4.5 mM) increased free radical production at 2-3 min (95%; P < 0.05), as well as at 1 and 3 h (42% and 49%, respectively; P < 0.05). Similarly treated cultured neurons failed to generate free radicals. Free radical production by glutamine was blocked by the antioxidants deferoxamine (40 muM) and alpha-phenyl-N-tert-butyl-nitrone (250 muM), as well as by the nitric oxide synthase inhibitor N-omega-nitro-L-arginine methyl ester (500 muM). Free radical production was also blocked by 6-diazo-5-oxo-L-norleucine (1 mM), an inhibitor of glutaminase, suggesting that ammonia released by glutamine hydrolysis may be responsible for the generation of free radicals. Additionally, the mitochondrial permeability transition inhibitor, cyclosporin A, blocked free radical production by glutamine. The results indicate that astrocytes, but not neurons, generate free radicals following glutamine exposure. Glutamine-induced oxidative and/or nitrosative stress may represent a key mechanism in ammonia neurotoxicity. (C) 2004 Wiley-Liss, Inc.