5-Lipoxygenase Activating Protein (FLAP) Dependent Leukotriene Biosynthesis Inhibition (MK591) Attenuates Lipid A Endotoxin-Induced Inflammation

Abstract

The Lipid A moiety of endotoxin potently activates TLR-4 dependent host innate immune responses. We demonstrate that Lipid-A mediated leukotriene biosynthesis regulates pathogen-associated molecular patterns (PAMP)-dependent macrophage activation. Stimulation of murine macrophages (RAW264.7) with E. coli 0111:B4 endotoxin (LPS) or Kdo2-lipid A (Lipid A) induced inflammation and Lipid A was sufficient to induce TLR-4 mediated macrophage inflammation and rapid ERK activation. The contribution of leukotriene biosynthesis was evaluated with a 5-lipoxygenase activating protein (FLAP) inhibitor, MK591. MK591 pre-treatment not only enhanced but also sustained ERK activation for up to 4 hours after LPS and Lipid A stimulation while inhibiting cell proliferation and enhancing cellular apoptosis. Leukotriene biosynthesis inhibition attenuated inflammation induced by either whole LPS or the Lipid A fraction. These responses were regulated by inhibition of the key biosynthesis enzymes for the proinflammatory eicosanoids, 5-lipoxygenase (5-LO), and cyclooxygenase-2 (COX-2) quantified by immunoblotting. Inhibition of leukotriene biosynthesis differentially regulated TLR-2 and TLR-4 cell surface expression assessed by flow cytometry, suggesting a close mechanistic association between TLR expression and 5-LO associated eicosanoid activity in activated macrophages. Furthermore, MK591 pre-treatment enhanced ERK activation and inhibited cell proliferation after LPS or Lipid A stimulation. These effects were regulated in part by increased apoptosis and modulation of cell surface TLR expression. Together, these data clarify the mechanistic association between 5-lipoxygenase activating protein-mediated leukotriene biosynthesis and 5-LO dependent eicosanoid metabolites in mediating the TLR-dependent inflammatory response after endotoxin exposure typical of bacterial sepsis.

Different tissue phagocytes sample apoptotic cells to direct distinct homeostasis programs

“…3f and Extended data Fig. 6d, h) reflecting previous findings that show suppression of 5-lipoxygenase by apoptotic cells 11 . CD103 + dendritic cells also significantly downregulated several innate immune genes including Tlr12 , inflammasome-related Nlrp3 , Casp1 and Il1a 12 (Fig.…”

Histone deacetylase 2 (HDAC2) attenuates lipopolysaccharide (LPS)-induced inflammation by regulating PAI-1 expression

“…Furthermore, sepsis-related mortality is high, but the effectiveness of treatment strategies generally remains poor and requires further research [ 4 ]. In our previous study, we investigated the Toll-like receptor-dependent inflammatory response after endotoxin exposure, which is typical of bacterial sepsis [ 5 ]. Here, we attempted to develop an effective adjunct therapy mediated by a novel mechanism to attenuate overt inflammation.…”

The role of 5-lipoxygenase in the pathophysiology of COVID-19 and its therapeutic implications

“…5-hydroxyeicosatetraenoic acid (5-HETE) , an intermediate in the 5-LOX pathway, is a weak activator of neutrophils and eosinophils . LT receptors are widely distributed on inflammatory cells, smooth muscle cells, platelets, and vascular endothelium [9,[45][46][47][48][49][50][51][52][53][54].…”

“…The expression of some of these enzymes and receptors involved in the synthesis of LT increases during acute inflammation [9,47]. Fang et al, suggested a close association between the expression of toll-like receptors (TLRs) and biosynthesis of LT in activated murine macrophages [46]. TLRs play an essential role in the activation of immune cells in response to an invading pathogen [50].…”