Leukotriene B4 Mediates Neutrophil Migration Induced by Heme

Abstract

High concentrations of free heme found during hemolytic events or cell damage leads to inflammation, characterized by neutrophil recruitment and production of reactive oxygen species, through mechanisms not yet elucidated. In this study, we provide evidence that heme-induced neutrophilic inflammation depends on endogenous activity of the macrophage-derived lipid mediator leukotriene B4 (LTB4). In vivo, heme-induced neutrophil recruitment into the peritoneal cavity of mice was attenuated by pretreatment with 5-lipoxygenase (5-LO) inhibitors and leukotriene B4 receptor 1 (BLT1) receptor antagonists as well as in 5-LO knockout (5-LO−/−) mice. Heme administration in vivo increased peritoneal levels of LTB4 prior to and during neutrophil recruitment. Evidence that LTB4 was synthesized by resident macrophages, but not mast cells, included the following: 1) immuno-localization of heme-induced LTB4 was compartmentalized exclusively within lipid bodies of resident macrophages; 2) an increase in the macrophage population enhanced heme-induced neutrophil migration; 3) depletion of resident mast cells did not affect heme-induced LTB4 production or neutrophil influx; 4) increased levels of LTB4 were found in heme-stimulated peritoneal cavities displaying increased macrophage numbers; and 5) in vitro, heme was able to activate directly macrophages to synthesize LTB4. Our findings uncover a crucial role of LTB4 in neutrophil migration induced by heme and suggest that beneficial therapeutic outcomes could be achieved by targeting the 5-LO pathway in the treatment of inflammation associated with hemolytic processes.

Purified and Recombinant Hemopexin: Protease Activity and Effect on Neutrophil Chemotaxis

“…LTB4 levels in supernatants of monocytes stimulated with LPS increased with time and peaked at 3 h, similar to prior studies with human alveolar macrophages (33). Heme alone induced a slight increase in LTB4 (34). However, the combination of LPS and heme (1 μmol/L) led to significantly higher concentrations of LTB4 in the culture medium ( Figure 7A).…”

“…An alternative possibility would be that hemopexin bound cell-free heme that induced or primed macrophages to produce chemotaxins such as leukotriene B4 (LTB4). LTB4 has been described as the major chemotaxin induced by heme (34). In our studies, none of the Hx preparations, regardless of protease activity, directly suppressed neutrophil migration.…”

Red alert: labile heme is an alarmin

“…The authors thank Luis Ferreira Moita (Instituto Gulbenkian de Ciência) for critical review of the manuscript and Zélia Gouveia for producing the heme structures in Figure 1 Mø [59,61,62,[67][68][69] and endothelial cells [20]. In some cases this is mediated via a mechanism involving heme sensing by PRR [20,27,28] as well as G coupled proteins…”

Cannabinoid Receptor 2 Suppresses Leukocyte Inflammatory Migration by Modulating the JNK/c-Jun/Alox5 Pathway

“…LTB 4 , which is known as a potent chemoattractant, has been shown to induce activation and migration of leukocytes (32,33). It has been shown that both alox5 knock-out and Alox5 inhibitor treatment lead to a decrease of in vivo leukocyte inflammatory migration of mice (34).…”