Prolonged exposure to lipopolysaccharide inhibits macrophage 5-lipoxygenase metabolism via induction of nitric oxide synthesis.
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.
Coffey
M J
MJ
Division of Pulmonary and Critical Care Medicine, University of Michigan Medical Center, Ann Arbor 48109, USA. coffeym@umich.edu
Phare
S M
SM
Peters-Golden
M
M
D058927:5-Lipoxygenase-Activating Proteins; D000818:Animals; D001094:Arachidonate 5-Lipoxygenase / Q000096:biosynthesis / Q000378:metabolism*; D016718:Arachidonic Acid / Q000378:metabolism; D002352:Carrier Proteins / Q000096:biosynthesis; D002474:Cell-Free System / Q000201:enzymology / Q000276:immunology; D002478:Cells, Cultured; D051546:Cyclooxygenase 2; D004306:Dose-Response Relationship, Immunologic; D004789:Enzyme Activation / Q000276:immunology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004794:Enzyme Repression / Q000276:immunology; D005260:Female; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism / Q000502:physiology; D008070:Lipopolysaccharides / Q000494:pharmacology*; D016859:Lipoxygenase Inhibitors; D016676:Macrophages, Alveolar / Q000201:enzymology* / Q000276:immunology* / Q000378:metabolism; D008565:Membrane Proteins / Q000096:biosynthesis; D009000:Monocytes / Q000201:enzymology / Q000276:immunology / Q000378:metabolism; D009569:Nitric Oxide / Q000096:biosynthesis* / Q000502:physiology; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism / Q000502:physiology; D014176:Protein Biosynthesis; D011506:Proteins / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D058927:5-Lipoxygenase-Activating Proteins; C548592:ALOX5AP protein, human; D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D008070:Lipopolysaccharides; D016859:Lipoxygenase Inhibitors; D008565:Membrane Proteins; D011506:Proteins; D016718:Arachidonic Acid; D009569:Nitric Oxide; D001094:Arachidonate 5-Lipoxygenase; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D011451:Prostaglandin-Endoperoxide Synthases