Neuronal death and sphingolipid following occlusion of the middle cerebral artery

在麻醉大鼠中，通过阻塞大脑中动脉近端的主干来诱导局灶性脑缺血。为了更好地定义局灶性脑缺血期间的鞘脂代谢，在大脑中动脉闭塞产生的局灶性缺血期间，测定了大鼠大脑皮层中神经酰胺、鞘磷脂、神经节苷脂和神经节苷脂的水平。鞘磷脂在缺血2小时开始减少，并持续减少96小时。相反，神经酰胺在缺血后6小时增加并在96小时增加至4.2倍，并且神经酰胺的脂肪酸组成仅为类似于鞘磷脂的非羟基化脂肪酸。羟基化脂肪酸连接的腺苷在缺血6小时减少，而非羟基化脂肪酸连接的腺苷在缺血96小时没有发生任何显著减少。神经节苷脂水平无可测量的变化。这些结果表明，脑缺血早期，脑皮层鞘磷脂降解产生神经酰胺，近年来发现鞘磷脂降解产生的神经酰胺作为第二信使参与HL-60白血病细胞的程序性死亡、生长和分化。采用沙土鼠短暂性前脑缺血再灌注模型，研究了致死性和亚致死性脑缺血后海马鞘氨醇含量的变化。用薄层色谱法（TLC）从海马总脂中分离鞘磷脂，并用气液色谱法（GLC）进行分析。致死性缺血（5分钟缺血）后再循环过程中的鞘磷脂水平在30分钟时显著降低，然后在60分钟时恢复到对照水平。亚致死性缺血（2分钟缺血和5分钟缺血后获得缺血耐受）后的再循环未引起鞘磷脂水平的任何变化。

Focal cerebral ischemia was induced in anesthetized rats by occluding the stem of the proximal middle cerebral artery. To better define the sphingolipid metabolism during focal brain ischemia, levels of ceramide, sphingomyelin, cerebroside and gangliosides were determined in rat cerebral cortex during focal ischemia produced by occlusion of the middle cerebral artery. Sphingomyelin began to decrease at 2 hours of ischemia and continued to decrease for 96 hours. In contrast, ceramide increased at 6 hours and increased to 4.2-fold at 96 hours after ischemia, and the fatty acid composition of ceramide was solely nonhydroxylated fatty acid similar to sphingomyelin. Hydroxylated fatty acid-linked cerebroside decreased at 6 hours of ischemia, whereas any significant decrease of non-hydroxylated fatty acid-linked cerebroside didn't occur for 96 hours of ischemia. There were no measurable changes in the levels of gangliosides. These results suggested that ceramide was produced in the cerebral cortex by the breakdown of sphingomyelin during early ischemia.Recently ceramide generated by sphingomyelin degradation has been described as a second messenger involved in programd cell death, cell growth and differentiation in HL-60 leukemic cells. We studied on the differences in sphingomylin levels in gerbil hippocampus induced by lethal or sublethal ischemia using the transient forebrain ischemia-reperfusion gerbil model. Sphingomyelin was separated by thin layr chromatography (TLC) from hippocampal total lipids and analyzed by gas liquid chromatography (GLC). The sphingomyelin levels during recirculation after lethal ischemia (a 5-min.of ischemia) were significantly decreased at 30 min.and then returned to the control level at 60 min. The recirculation after a sublethal ischemia (2 min ischemia and 5 min.ischemia after acquired ischemic tolerance) did not induce any changes in sphingomyelin levels.