Coffey M J, Phare S M, Peters-Golden M
Division of Pulmonary and Critical Care Medicine, University of Michigan Medical Center, Ann Arbor 48109, USA.
J Immunol. 2000 Oct 1;165(7):3592-8. doi: 10.4049/jimmunol.165.7.3592.
LPS from bacteria can result in the development of sepsis syndrome and acute lung injury. Although acute exposure to endotoxin primes leukocytes for enhanced synthesis of leukotrienes (LT), little is known about the effect of chronic exposure. Therefore, we determined the effect of prolonged LPS treatment on 5-lipoxygenase (5-LO) metabolism of arachidonic acid in alveolar macrophages (AM) and in peripheral blood monocytes. Pretreatment of AM with LPS caused time- and dose-dependent suppression of LT synthetic capacity. LPS pretreatment failed to inhibit arachidonic acid (AA) release. The fact that LPS inhibited LT synthesis from endogenous AA more than from exogenous AA suggested an effect on 5-LO-activating protein (FLAP). In addition, an inhibitory effect of LPS treatment on AM 5-LO activity was suggested by cell-free 5-LO enzyme assay. No effect on the expression of either 5-LO or FLAP proteins was observed. New protein synthesis was necessary for LPS-induced reduction of 5-LO metabolism in AM, and immunoblotting demonstrated marked induction of NO synthase (NOS). Inhibition by LPS was reproduced by an NO donor and was abrogated by inhibitors of constitutive and inducible NOS. Compared with AM, peripheral blood monocytes exhibited no suppression by LPS of 5-LO metabolism and no induction of inducible NOS. We conclude that prolonged exposure to LPS impairs AM 5-LO metabolism by NO-mediated suppression of both 5-LO and FLAP function. Because LT contribute to antimicrobial defense, this down-regulation of 5-LO metabolism may contribute to the increased susceptibility to pneumonia in patients following sepsis.
细菌来源的脂多糖（LPS）可导致脓毒症综合征和急性肺损伤。尽管急性暴露于内毒素会使白细胞对白三烯（LT）的合成增强，但关于慢性暴露的影响却知之甚少。因此，我们确定了长期LPS处理对肺泡巨噬细胞（AM）和外周血单核细胞中花生四烯酸5-脂氧合酶（5-LO）代谢的影响。用LPS预处理AM会导致LT合成能力出现时间和剂量依赖性抑制。LPS预处理未能抑制花生四烯酸（AA）的释放。LPS对内源性AA的LT合成抑制作用强于外源性AA，这表明其对5-脂氧合酶激活蛋白（FLAP）有影响。此外，无细胞5-LO酶分析表明LPS处理对AM的5-LO活性有抑制作用。未观察到对5-LO或FLAP蛋白表达的影响。LPS诱导的AM中5-LO代谢减少需要新的蛋白质合成，免疫印迹显示一氧化氮合酶（NOS）有明显诱导。LPS的抑制作用可被一氧化氮供体重现，并被组成型和诱导型NOS抑制剂消除。与AM相比，外周血单核细胞未表现出LPS对5-LO代谢的抑制作用，也未诱导出诱导型NOS。我们得出结论，长期暴露于LPS会通过一氧化氮介导的对5-LO和FLAP功能的抑制来损害AM的5-LO代谢。由于LT有助于抗菌防御，5-LO代谢的这种下调可能导致脓毒症患者对肺炎的易感性增加。
