ABSTRACT
In tumor microenvironments, the macrophage population is heterogeneous, but some macrophages can acquire tumor-promoting characteristics. These tumor-associated macrophages (TAM) exhibit an M2-like profile, with deficient production of NO and ROS, characteristics of pro-inflammatory M1 cytotoxic macrophages. Lipoxins (LX) and 15-epi-lipoxins are lipid mediators which can induce certain features of M2 macrophages in mononuclear cells, but their effects on TAM remain to be elucidated. This study tested the hypothesis that ATL-1, a synthetic analogue of 15-epi-lipoxin A4 , could modulate TAM activity profile. We show that human macrophages (MΦ) differentiated into TAM-like cells after incubation with conditioned medium from MV3, a human melanoma lineage cell. Contrasting with the effects observed in other M2 subsets and M1 profile macrophages, ATL-1 selectively decreased M2 surface markers in TAM, suggesting unique behavior of this particular M2 subset. Importantly, these results were replicated by the natural lipoxins LXA4 and the aspirin induced 15-epi-LXA4 (ATL). In parallel, ATL-1 stimulated TAM to produce NO by increasing the iNOS/arginase ratio and activated NADPH oxidase, triggering ROS production. These alterations in TAM profile induced by ATL-1 led to loss of the anti-apoptotic effects of TAM on melanoma cells and increased their cytotoxic properties. Finally, ATL-1 was found to inhibit tumor progression in a murine model in vivo, which was accompanied by alterations in TAM profile and diminished angiogenesis. Together, the results show an unexpected effect of lipoxin, which induces in TAM a change from an M2- to an M1-like profile, thereby triggering tumor cell apoptosis and down-modulating the tumor progression.
Subject(s)
Lipoxins/pharmacology , Macrophages/drug effects , Macrophages/pathology , Melanoma/pathology , Animals , Apoptosis/drug effects , Arginase/metabolism , Biomarkers/metabolism , Disease Progression , Down-Regulation/drug effects , Humans , Mice , Mice, Inbred C57BL , NADPH Oxidases/metabolism , Nitric Oxide Synthase Type II/metabolism , Nitrogen Oxides/metabolism , Reactive Oxygen Species/metabolismABSTRACT
Human monocytes play a central function in several steps of the immune response and the process involved in regulating their survival are critical to population control. Lipoxins are lipid mediators and members of the eicosanoid family that exhibit selective stimulatory but nonphlogistic activities in mononuclear cells. In this study, we investigated the effects of 15-epi-16-(para-fluoro)phenoxy-LXA(4) (ATL-1), a synthetic analog of 15-epi-lipoxin A(4), in human monocytes survival and apoptosis. ATL-1 concentration-dependently increased monocyte survival, as a consequence of cell apoptosis reduction by the analog. Treatment of these cells with PD98059 or LY294002 blocked ATL-1 effects, indicating the involvement of ERK-2 and PI3-K, both pathways associated with cell survival. Confirming the activation of these pathways, we demonstrated an increase in ERK-2 nuclear translocation and Akt phosphorylation. Furthermore, we showed that ATL-1 inhibits Bax translocation to the mitochondria. These results confirm a cytoprotective effect of lipoxins in monocytes and might contribute to the elucidation of the mechanisms associated with the resolution phase of the inflammatory process in different pathophysiological events.
