Görg Boris, Qvartskhava Natalia, Keitel Verena, Bidmon Hans J, Selbach Oliver, Schliess Freimut, Häussinger Dieter
Clinic for Gastroenterology, Hepatology and Infectiology, Heinrich-Heine University, Düsseldorf, Germany.
Hepatology. 2008 Aug;48(2):567-79. doi: 10.1002/hep.22345.
Oxidative stress plays a major role in cerebral ammonia toxicity and the pathogenesis of hepatic encephalopathy (HE). As shown in this study, ammonia induces a rapid RNA oxidation in cultured rat astrocytes, vital mouse brain slices, and rat brain in vivo. Ammonia-induced RNA oxidation in cultured astrocytes is reversible and sensitive to MK-801, 1,2-Bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, apocynin, epigallocatechin gallate, and polyphenon 60, suggesting the involvement of N-methyl-D-aspartic acid (NMDA) receptor activation, Ca(2+), nicotinamide adenine dinucleotide phosphate, and reduced form (NADPH) oxidase-dependent oxidative stress. Also, hypo-osmolarity, tumor necrosis factor alpha (TNF-alpha), and diazepam increase RNA oxidation in cultured astrocytes, suggesting that the action of different HE-precipitating factors converges at the level of RNA oxidation. Among the oxidized RNA species, 18S-rRNA and the messenger RNA (mRNA) coding for the glutamate/aspartate transporter (GLAST) were identified. Cerebral RNA oxidation in acutely ammonia-loaded rats in vivo is reversible and predominates in neuronal soma and perivascular astrocyte processes. In neuronal dendrites, oxidized RNA colocalizes with the RNA-binding splicing protein neurooncological ventral antigen (NOVA)-2 within putative RNA transport granules, which are also found in close vicinity to postsynaptic spines. This indicates that oxidized RNA species may participate in postsynaptic protein synthesis, which is a biochemical substrate for learning and memory consolidation. Neuronal and astroglial RNA oxidation increases also in vital mouse brain slices treated with ammonia and TNF-alpha, respectively.
Cerebral RNA oxidation is identified as a not yet recognized consequence of acute ammonia intoxication. RNA oxidation may affect gene expression and local protein synthesis and thereby provide another link between reactive oxygen species (ROS)/reactive nitrogen oxide species (RNOS) production and ammonia toxicity.
氧化应激在脑氨毒性和肝性脑病（HE）的发病机制中起主要作用。如本研究所示，氨在培养的大鼠星形胶质细胞、活的小鼠脑切片和大鼠体内脑组织中诱导快速的RNA氧化。氨诱导的培养星形胶质细胞中的RNA氧化是可逆的，并且对MK-801、1,2-双（邻氨基苯氧基）乙烷-N,N,N',N'-四乙酸、阿朴吗啡、表没食子儿茶素没食子酸酯和多酚60敏感，提示N-甲基-D-天冬氨酸（NMDA）受体激活、Ca(2+)、烟酰胺腺嘌呤二核苷酸磷酸和还原型（NADPH）氧化酶依赖性氧化应激的参与。此外，低渗、肿瘤坏死因子α（TNF-α）和地西泮增加培养星形胶质细胞中的RNA氧化，提示不同的HE诱发因素的作用在RNA氧化水平上汇聚。在氧化的RNA种类中，鉴定出18S-核糖体RNA和编码谷氨酸/天冬氨酸转运体（GLAST）的信使RNA（mRNA）。急性氨负荷大鼠体内脑组织中的RNA氧化是可逆的，并且在神经元胞体和血管周围星形胶质细胞突起中占主导。在神经元树突中，氧化的RNA与RNA结合剪接蛋白神经肿瘤腹侧抗原（NOVA）-2在假定的RNA转运颗粒中共定位，这些颗粒也在突触后棘附近发现。这表明氧化RNA种类可能参与突触后蛋白质合成，这是学习和记忆巩固中的生化底物。在用氨和TNF-α分别处理的活小鼠脑切片中，神经元和星形胶质细胞的RNA氧化也增加。
脑RNA氧化被确定为急性氨中毒尚未被认识的后果。RNA氧化可能影响基因表达和局部蛋白质合成，从而在活性氧（ROS）/活性氮氧化物（RNOS）产生和氨毒性之间提供另一个联系。
