Background Glucocorticoids (GC) are used for the treatment of many chronic inflammatory diseases. We have previously shown that GC treatment does not simply suppress monocyte functions but rather induces a distinct anti-inflammatory phenotype1. Treatment of inflammatory monocytes with GC leads to re-programming of these cells towards a specific population involved in resolution of inflammation. Gene expression analysis has shown that 12/15-lipoxygenase (12/15-LOX) is one of the most up-regulated genes in GC- and LPS/GC-treated monocytes. Lipoxygenases are known to generate lipid mediators that contribute to the resolution of inflammation2.
Objectives The aim of our studies was to determine lipoxygenase-dependent and independent effects in GC-treated monocytes. Identification of specific GC-induced signaling pathways may elicit molecular targets for novel therapeutic strategies.
Methods Bone marrow–derived monocytes were isolated from wild type (wt) and 12/15-LOX knock-out mice and stimulated with GC and LPS. Gene and protein expression was analyzed using quantitative RT-PCR, Western Blot, Flow Cytometry, ELISA and CBA technology. Functional assays were performed to analyze monocyte migration and oxidative burst.
Results No significant differences in production of pro-inflammatory cytokines were observed between monocytes isolated from wt and 12/15-LOX knock-out mice. Although GC treatment reduced adhesion in monocytes of both mice strains, decrease in adhesion was much more pronounced in cells lacking 12/15-LOX. Migration was enhanced in GC- and LPS/GC-treated monocytes isolated either from wt or 12/15-LOX knock-out mice. Analysis of cell survival revealed that the rate of apoptotic cells was reduced in monocytes treated with GC but also LPS/GC with no significant variations between the two mouse strains. Treatment of resting monocytes with GC reduced the production of ROS only in monocytes from wild type but not from 12/15-LOX knock-out mice whereas GC treatment of pro-inflammatory (LPS-stimulated) monocytes reduced production of ROS in wt as well as 12/15-LOX knock-out mice. GC treatment led to increased phagocytosis of carboxylate-modified latex beads (used as model for phagocytosis of apoptotic cells). However, this effect was much weaker in GC-treated monocytes isolated from 12/15-LOX knock-out mice. In contrast, phagocytosis of latex beads mimicking foreign particles was not significantly altered in monocytes isolated from wild type and 12/15-LOX knock-out mice.
Conclusions GC-treatment induced anti-inflammatory and pro-resolving properties in resting and activated monocytes. Many of GC-induced mechanisms like decreased adhesion, enhanced migration or phagocytosis are 12/15-LOX independent. However, inhibitions of ROS production as well as enhancement of anti-inflammatory phagocytosis of apoptotic cells by GC-treatment are at least partially mediated by 12/15-LOX. Specific targeting of these mechanisms may be a promising strategy to block undesirable inflammation with fewer side effects.
 Barczyk, K. et al. Blood 116, 446-455 (2010).
 Conrad, D.J. Clinical Reviews in Allergy & Immunology 17, 71-89 (1999).
Disclosure of Interest None Declared