Exogenous ghrelin modulates release of pro-inflammatory and anti-inflammatory cytokines in LPS-stimulated macrophages through distinct signaling pathways.
BACKGROUND
Ghrelin, an orexigenic 28-amino-acid peptide, has been studied primarily in relation to the control of appetite and fat metabolism. In addition to these well-known functions, ghrelin, and its target receptors, growth hormone secretagogue receptors (GHS-Rs), have been localized to neutrophils, lymphocytes, and macrophages, which suggests that ghrelin may be involved in immune modulation.


METHODS
To assess the therapeutic role of ghrelin in production of pro-inflammatory and anti-inflammatory cytokines, the effects of exogenous ghrelin administration on the regulation of cytokine release in lipopolysaccharide (LPS)-activated murine RAW 264.7 macrophages were analyzed.


RESULTS
Ghrelin and GHS-Rs are expressed in murine macrophages. In addition, exogenous ghrelin inhibited the production of pro-inflammatory cytokines IL-1beta and TNF-alpha in LPS-stimulated murine macrophages in a dose dependent and time-dependent fashion. Exogenous ghrelin pretreatment resulted in a decrease in LPS-induced NFkappaB activation and was presumably the reason for this ghrelin-mediated effect. In contrast to these findings, exogenous ghrelin significantly augmented the release of the anti-inflammatory cytokine IL-10 in a dose-dependent and time-dependent fashion from LPS-stimulated murine macrophages. Ghrelin administration enhanced activation of p38 MAPK, which is known to control the release of IL-10 in macrophages independent of the NFkappaB pathway. These effects of ghrelin on both pro-inflammatory and anti-inflammatory cytokines were offset when a specific GHS-R receptor antagonist was added to the culture media.


CONCLUSIONS
These data suggest that ghrelin has potent anti-inflammatory properties through modulation of secretion of both pro-inflammatory and anti-inflammatory cytokines from LPS-stimulated macrophages through distinct signaling cascades. Therapeutic utility of ghrelin to control, modulate, or treat pathologic inflammatory conditions like endotoxemic shock and ulcerative colitis requires additional investigation.
Waseem
Talat
T
Department of Surgery, Brigham and Women's Hospital, Harvard Medical School, Boston, Mass 02115, USA.
Duxbury
Mark
M
Ito
Hiromichi
H
Ashley
Stanley W
SW
Robinson
Malcolm K
MK
D000818:Animals; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism*; D054439:Ghrelin / Q000378:metabolism* / Q000494:pharmacology; D016753:Interleukin-10 / Q000378:metabolism; D053583:Interleukin-1beta / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism*; D051379:Mice; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology*; D051996:Transcription Factor RelA / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D016207:Cytokines; D054439:Ghrelin; D053583:Interleukin-1beta; D008070:Lipopolysaccharides; D051996:Transcription Factor RelA; D014409:Tumor Necrosis Factor-alpha; D016753:Interleukin-10; D048051:p38 Mitogen-Activated Protein Kinases