Warskulat Ulrich, Görg Boris, Bidmon Hans-J, Müller Hans Werner, Schliess Freimut, Häussinger Dieter
Clinic for Gastroenterology, Hepatology and Infectiology, Heinrich Heine University, Düsseldorf, Germany.
Glia. 2002 Dec;40(3):324-36. doi: 10.1002/glia.10128.
Ammonia is a key factor in the pathogenesis of hepatic encephalopathy (HE), which is a major complication in acute and chronic liver failure and other hyperammonemic states. The molecular mechanisms underlying ammonia neurotoxicity and the functional consequences of ammonia on gene expression in astrocytes are incompletely understood. Using cDNA array hybridization technique we identified ammonia as a trigger of heme oxygenase-1 (HO-1) mRNA levels in cultured rat astrocytes. As shown by Northern and Western blot analysis, HO-1 mRNA levels were upregulated by ammonia (0.1-5 mmol/L) after 24 h and protein expression after 72 h in astrocytes. These ammonia effects on HO-1 are probably triggered to a minor extent by ammonia-induced glutamine synthesis or by astrocyte swelling, because HO-1 expression was not inhibited by the glutamine synthetase inhibitor methionine sulfoximine (which abrogated ammonia-induced cell swelling in cultured astrocytes), and ammonia-induced HO-1 expression could only partly be mimicked by hypoosmotic astrocyte swelling. Hypoosmotic (205 mOsm/L) exposure of astrocytes led even to a decrease in HO-1 mRNA levels within 4 h, whereas hyperosmotic (405 mOsm/L) exposure increased HO-1 mRNA expression. After 24 h, hypoosmolarity slightly raised HO-1 mRNA expression. Taurine and melatonin diminished ammonia-induced HO-1 mRNA or protein expression, whereas other antioxidants (dimethylthiourea, butylated hydroxytoluene, N-acetylcysteine, and reduced glutathione) increased HO-1 mRNA levels under ammonia-free conditions. An in vivo relevance is suggested by the finding that increased HO-1 expression occurs in the brain cortex from acutely ammonia-intoxicated rats. It is concluded that ammonia-induced HO-1 expression may contribute to cerebral hyperemia in hyperammonic states.
氨是肝性脑病（HE）发病机制中的关键因素，肝性脑病是急性和慢性肝衰竭及其他高氨血症状态下的主要并发症。氨神经毒性的分子机制以及氨对星形胶质细胞基因表达的功能影响尚未完全明确。我们利用cDNA阵列杂交技术发现，氨可引发培养的大鼠星形胶质细胞中血红素加氧酶-1（HO-1）mRNA水平的升高。Northern印迹和Western印迹分析表明，在星形胶质细胞中，氨（0.1 - 5 mmol/L）作用24小时后HO-1 mRNA水平上调，72小时后蛋白质表达上调。氨对HO-1的这些影响可能在较小程度上是由氨诱导的谷氨酰胺合成或星形胶质细胞肿胀引发的，因为谷氨酰胺合成酶抑制剂蛋氨酸亚砜胺（它可消除培养的星形胶质细胞中氨诱导的细胞肿胀）并未抑制HO-1的表达，而且氨诱导的HO-1表达只能部分地被低渗性星形胶质细胞肿胀模拟。星形胶质细胞暴露于低渗环境（205 mOsm/L）4小时内甚至会导致HO-1 mRNA水平下降，而高渗环境（405 mOsm/L）暴露则会增加HO-1 mRNA表达。24小时后，低渗状态会轻微提高HO-1 mRNA表达。牛磺酸和褪黑素可减少氨诱导的HO-1 mRNA或蛋白质表达，而其他抗氧化剂（二甲基硫脲、丁基羟基甲苯、N-乙酰半胱氨酸和还原型谷胱甘肽）在无氨条件下会增加HO-1 mRNA水平。急性氨中毒大鼠大脑皮质中HO-1表达增加这一发现提示了其在体内的相关性。研究得出结论，氨诱导的HO-1表达可能在高氨血症状态下导致脑充血。
