Ma Z, Ramanadham S, Corbett J A, Bohrer A, Gross R W, McDaniel M L, Turk J
Division of Endocrinology, Diabetes and Metabolism, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
J Biol Chem. 1996 Jan 12;271(2):1029-42. doi: 10.1074/jbc.271.2.1029.
Interleukin-1 (IL-1) impairs insulin secretion from pancreatic islets and may contribute to the pathogenesis of insulin-dependent diabetes mellitus. IL-1 increases islet expression of nitric oxide (NO) synthase, and the resultant overproduction of NO participates in inhibition of insulin secretion because NO synthase inhibitors, e.g. NG-monomethyl-arginine (NMMA), prevent this inhibition. While exploring effects of IL-1 on islet arachidonic acid metabolism, we found that IL-1 increases islet production of the 12-lipoxygenase product 12-hydroxyeicosatetraenoic acid 12-(HETE). This effect requires NO production and is prevented by NMMA. Exploration of the mechanism of this effect indicates that it involves increased availability of the substrate arachidonic acid rather than enhanced expression of 12-lipoxygenase. Evidence supporting this conclusion includes the facts that IL-1 does not increase islet 12-lipoxygenase protein or mRNA levels and does not enhance islet conversion of exogenous arachidonate to 12-HETE. Mass spectrometric stereochemical analyses nonetheless indicate that 12-HETE produced by IL-1-treated islets consists only of the S-enantiomer and thus arises from enzyme action. IL-1 does enhance release of nonesterified arachidonate from islets, as measured by isotope dilution mass spectrometry, and this effect is suppressed by NMMA and mimicked by the NO-releasing compound 3-morpholinosydnonimine. Although IL-1 increases neither islet phospholipase A2 (PLA2) activities nor mRNA levels for cytosolic or secretory PLA2, a suicide substrate which inhibits an islet Ca(2+)-independent PLA2 prevents enhancement of islet arachidonate release by IL-1. IL-1 also impairs esterification of [3H8]arachidonate into islet phospholipids, and this effect is prevented by NMMA and mimicked by the mitochondrial ATP-synthase inhibitor oligomycin. Experiments with exogenous substrates indicate that NMMA does not inhibit and that the NO-releasing compound does not activate islet 12-lipoxygenase or PLA2 activities. These results indicate that a novel action of NO is to increase levels of nonesterified arachidonic acid in islets.
白细胞介素-1（IL-1）会损害胰岛的胰岛素分泌，可能参与胰岛素依赖型糖尿病的发病机制。IL-1会增加胰岛中一氧化氮（NO）合酶的表达，由此产生的NO过量生成参与对胰岛素分泌的抑制，因为NO合酶抑制剂，如NG-单甲基精氨酸（NMMA），可阻止这种抑制作用。在探究IL-1对胰岛花生四烯酸代谢的影响时，我们发现IL-1会增加胰岛中12-脂氧合酶产物12-羟基二十碳四烯酸（12-HETE）的生成。这种作用需要NO的生成，并可被NMMA阻止。对这种作用机制的探究表明，它涉及底物花生四烯酸可用性的增加，而非12-脂氧合酶表达的增强。支持这一结论的证据包括：IL-1不会增加胰岛12-脂氧合酶蛋白或mRNA水平，也不会增强胰岛将外源性花生四烯酸转化为12-HETE的能力。然而，质谱立体化学分析表明，经IL-1处理的胰岛产生的12-HETE仅由S-对映体组成，因此是由酶作用产生的。通过同位素稀释质谱法测定，IL-1确实会增强非酯化花生四烯酸从胰岛中的释放，这种作用被NMMA抑制，并被释放NO的化合物3-吗啉代 sydnonimine模拟。虽然IL-1既不会增加胰岛磷脂酶A2（PLA2）的活性，也不会增加胞质或分泌型PLA2的mRNA水平，但一种抑制胰岛非钙依赖性PLA2的自杀底物可阻止IL-1增强胰岛花生四烯酸的释放。IL-1还会损害[3H8]花生四烯酸酯化到胰岛磷脂中，这种作用被NMMA阻止，并被线粒体ATP合酶抑制剂寡霉素模拟。使用外源性底物的实验表明，NMMA不会抑制，释放NO的化合物也不会激活胰岛12-脂氧合酶或PLA2的活性。这些结果表明，NO的一种新作用是增加胰岛中非酯化花生四烯酸的水平。
