Monocyte Chemoattractant Protein-1 and 5-Lipoxygenase Products Recruit Leukocytes in Response to Platelet-Activating Factor-Like Lipids in Oxidized Low-Density Lipoprotein

Abstract

Oxidized low-density lipoprotein (LDL) contains inflammatory agents, including oxidatively fragmented phospholipids that activate the platelet-activating factor (PAF) receptor, but in vivo events caused by these pathologically generated agents are not well defined. Injection of PAF-like lipids derived from oxidized LDL, or C4-PAF that is a major PAF-like lipid in these particles, into the pleural cavity of mice resulted in rapid monocyte, neutrophil, and eosinophil accumulation. Increased numbers of intracellular lipid bodies in these cells show they were in an inflammatory environment. Leukocyte recruitment was abolished by a PAF receptor antagonist, as expected. PAF-like lipids induced 5-lipoxygenase expression in leukocytes, mRNA expression for monocyte chemoattractant protein-1 (MCP-1) and other chemokines, synthesis of MCP-1, and leukotriene B4. The 5-lipoxygenase inhibitor zileuton impaired neutrophil influx, while MCP-1 had a more global role, as determined with MCP-1−/− mice. The lack of MCP-1 abrogated leukocyte accumulation and lipid body formation both in vivo and in vitro and chemokine transcription in vivo, and reduced in vivo leukotriene B4 production. Thus, PAF-like phospholipids in oxidized LDL induce an inflammatory infiltrate through the PAF receptor, chemokine transcription, lipid body formation, and 5-lipoxygenase expression in leukocytes. MCP-1 has a key role in this inflammatory response, and 5-lipoxygenase products are essential for neutrophil recruitment into the inflamed pleural cavity.

Mechanisms of leukocyte lipid body formation and function in inflammation

“…Indeed, stimuli known to prime leukocytes to induce eicosanoid generation, including PKC activators, arachidonate and PAF, are also active in stimulating lipid body formation. Accordingly, others and we observed a significant correlation between lipid body formation and enhanced generation of both LO-and COX- derived eicosanoids in vitro (Bozza et al 1996a, b, 1997, Bartmenes et al 1999 as well as in vivo , Silva et al 2002, de Assis et al 2003. Analogously, agents that inhibited lipid body formation also resulted in inhibited priming for eicosanoid production.…”

“…Although PAF may act at intracellular binding sites to induce cell activation (Bazan et al 1994), results are suggestive that PAF is acting in a paracrine/autocrine way to induce lipid body formation, since the PAF-receptor antagonist used in those studies would act preferentially at membrane receptors and confirmed by findings that LPS or oxLDL induced lipid body formation were inhibitable by treatment with extracellular PAH-acetylhidrolase (Silva et al 2002).…”

“…Increased lipid body formation in neutrophils and macrophages could also be observed in experimentally induced inflammation triggered either by LPS or OxLDL (oxidized low density lipoprotein) but not by native LDL , Silva et al 2002. LPS administration into mice induced a dose-and time-dependent increase in lipid body numbers.…”

“…PAF and PAF-like lipids are believed to play an important role in lipid body formation induced by LPS or by oxLDL in vivo since the pretreatment with three structurally unrelated PAF receptor antagonists completely inhibited this phenomenon , Silva et al 2002. Although PAF may act at intracellular binding sites to induce cell activation (Bazan et al 1994), results are suggestive that PAF is acting in a paracrine/autocrine way to induce lipid body formation, since the PAF-receptor antagonist used in those studies would act preferentially at membrane receptors and confirmed by findings that LPS or oxLDL induced lipid body formation were inhibitable by treatment with extracellular PAH-acetylhidrolase (Silva et al 2002).…”

ALOX5AP expression, but not gene haplotypes, is associated with obesity and insulin resistance

“…[12][13][14] Both MCP1 and 5LO products recruit leukocytes to sites of inflammation. 15 These data indirectly suggest that ALOX5AP also might play a role in obesity.…”