Andrea Carlin

Melanocortin peptides inhibit production of proinflammatory cytokines and nitric oxide by activated microglia

Inflammatory processes contribute to neurodegenerative disease, stroke, encephalitis, and other central nervous system (CNS) disorders. Activated microglia are a source of cytokines and other inflammatory agents within the CNS and it is therefore important to control glial function in order to preserve neural cells. Melanocortin peptides are pro‐opiomelanocortin‐derived amino acid sequences that include α‐melanocyte‐stimulating hormone (α‐MSH) and adrenocorticotropic hormone (ACTH). These peptides have potent and broad anti‐inflammatory effects. We tested effects of α‐MSH (1‐13), α‐MSH (11‐13), and ACTH (1‐24) on production of tumor necrosis factor α (TNF‐α), interleukin‐6 (IL‐6), and nitric oxide (NO) in a cultured murine microglial cell line (N9) stimulated with lipopolysaccharide (LPS) plus interferon γ (IFN‐γ). Melanocortin peptides inhibited production of these cytokines and NO in a concentration‐related fashion, probably by increasing intracellular cAMP. When stimulated with LPS + IFN‐γ, microglia increased release of α‐MSH. Production of TNF‐α, IL‐6, and NO was greater in activated microglia after immunoneutralization of endogenous α‐MSH. The results suggest that α‐MSH is an autocrine factor in microglia. Because melanocortin peptides inhibit production of proinflammatory mediators by activated microglia they might be useful in treatment of inflammatory/degenerative brain disorders. J. Leukoc. Biol. 63: 740–745; 1998.

The Melanocortin System in Control of Inflammation

Melanocortin peptides, the collective term for α-, β-, and γ-melanocyte-stimulating hormone (α-, β-, γ-MSH) and adrenocorticotropic hormone (ACTH), are elements of an ancient modulatory system. Natural melanocortins derive from the common precursor pro-opiomelanocortin (POMC). Five receptor subtypes for melanocortins (MC1-MC5) are widely distributed in brain regions and in peripheral cells. Melanocortin receptor activation by natural or synthetic ligands exerts marked anti-inflammatory and immunomodulatory effects. The anticytokine action and the inhibitory influences on inflammatory cell migration make melanocortins potential new drugs for treatment of inflammatory disorders. Effectiveness in treatment of acute, chronic, and systemic inflammatory disorders is well documented in preclinical studies. Further, melanocortins are promising compounds in neuroprotection. This review examines the main signaling circuits in anti-inflammatory and immunomodulatory actions of melanocortins, and the potential therapeutic use of these molecules.

α‐MSH in Systemic Inflammation: Central and Peripheral Actions

ABSTRACT: Until recently, inflammation was believed to arise from events taking place exclusively in the periphery. However, it is now clear that central neurogenic influences can either enhance or modulate peripheral inflammation. Therefore, it should be possible to improve treatment of inflammation by use of antiinflammatory agents that reduce peripheral host responses and inhibit proinflammatory signals in the central nervous system (CNS). One such strategy could be based on α‐melanocyte stimulating hormone (α‐MSH). Increases in circulating TNF‐α and nitric oxide (NO), induced by intraperitoneal administration of endotoxin in mice, were modulated by central injection of a small concentration of α‐MSH. Inducible nitric oxide synthase (iNOS) activity and iNOS mRNA in lungs and liver were likewise modulated by central α‐MSH. Increase in lung myeloperoxidase (MPO) activity was significantly less in lungs of mice treated with central α‐MSH. Proinflammatory agents induced by endotoxin were significantly greater after blockade of central α‐MSH. The results suggest that antiinflammatory influences of neural origin that are triggered by α‐MSH could be used to treat systemic inflammation. In addition to its central influences, α‐MSH has inhibitory effects on peripheral host cells, in which it reduces release of proinflammatory mediators. α‐MSH reduces chemotaxis of human neutrophils and production of TNF‐α, neopterin, and NO by monocytes. In research on septic patients, α‐MSH inhibited release of TNF‐α, interleukin‐1β (IL‐1β), and interleukin‐8 (IL‐8) in whole blood samples in vitro. Combined central and peripheral influences can be beneficial in treatment of sepsis.

Inhibition of systemic inflammation by central action of the neuropeptide alpha-melanocyte- stimulating hormone.

The neuropeptide α-melanocyte stimulating hormone (α-MSH) reduces fever and acute inflammation in the skin when administered centrally. The aim of the present research was to determine whether central α-MSH can also reduce signs of systemic inflammation in mice with endotoxemia. Increases in serum tumor necrosis factor-α and nitric oxide, induced by intraperitoneal administration of endotoxin, were modulated by central injection of a small concentration of α-MSH. Inducible nitric oxide synthase (iNOS) activity and iNOS mRNA in lungs and liver were likewise modulated by central α-MSH. Lung myeloperoxidase activity, a marker of neutrophil infiltration, was increased in endotoxemic mice; the increase was significantly less in lungs of mice treated with central α-MSH. Intraperitoneal administration of the small dose of α-MSH that was effective centrally did not alter any of the markers of inflammation. In experiments using immunoneutralization of central α-MSH, we tested the idea that endogenous peptide induced within the brain during systemic inflammation modulates host responses to endotoxic challenge in peripheral tissues. The data showed that proinflammatory agents induced by endotoxin in the circulation, lungs, and liver were significantly greater after blockade of central α-MSH. The results suggest that anti-inflammatory influences of neural origin that are triggered by α-MSH could be used to treat systemic inflammation.

The Neuropeptide α-MSH in Host Defense

Abstract: The presence of the ancient peptide a‐melanocyte‐stimulating hormone (α‐MSH) in barrier organs such as gut and skin suggests that this potent anti‐inflammatory molecule may be a component of the innate host defense. In tests of antimicrobial activities, α‐MSH and its fragment KPV showed inhibitory influences against the gram‐positive bacterium Staphylococcus aureus and the yeast Candida albicans. Anti‐tumor necrosis factor and antimicrobial effects of a‐MSH suggest that the peptide might likewise reduce replication of human immunodeficiency virus (HIV). Treatment with α‐MSH reduced HIV replication in chronically and acutely infected human monocytes. At the molecular level, α‐MSH inhibited activation of the transcription factor NF‐κB known to enhance HIV expression. α‐MSH that combines antipyretic, anti‐inflammatory, and antimicrobial effects could be useful in the treatment of disorders in which infection and inflammation coexist.

Antimicrobial Properties of α-MSH and Related Synthetic Melanocortins

The natural antimicrobial peptides are ancient host defense effector molecules, present in organisms across the evolutionary spectrum. Several properties of α-melanocyte stimulating hormone (α-MSH) suggested that it could be a natural antimicrobial peptide. α-MSH is a primordial peptide that appeared during the Paleozoic era, long before adaptive immunity developed and, like natural antimicrobial molecules, is produced by barrier epithelia, immunocytes, and within the central nervous system. α-MSH was discovered to have antimicrobial activity against two representative pathogens, Staphylococcus aureus and Candida albicans. The candidacidal influences of α-MSH appeared to be mediated by increases in cell cyclic adenosine monophosphate (cAMP). The cAMP-inducing capacity of α-MSH likely interferes with the yeasts own regulatory mechanisms of this essential signaling pathway. It is remarkable that this mechanism of action in yeast mimics the influences of α-MSH in mammalian cells in which the peptide binds to G-protein-linked melanocortin receptors, activates adenylyl cyclase, and increases cAMP. When considering that most of the natural antimicrobial peptides enhance the local inflammatory reaction, the anti-inflammatory and antipyretic effects of α-MSH confer unique properties to this molecule relative to other natural antimicrobial molecules. Synthetic derivatives, chemically stable and resistant to enzymatic degradation, could form the basis for novel therapies that combine anti-inflammatory and antimicrobial properties.

Anti-inflammatory effects of α-melanocyte-stimulating hormone in celiac intestinal mucosa

Objectives: The peptide α-melanocyte-stimulating hormone (α-MSH) possesses potent anti-inflammatory activities and has been previously implicated in the endogenous control of inflammatory reactions. The aim of the present research was to determine whether α-MSH and its receptors participate in a localized anti-inflammatory response in the duodenal mucosa of celiac patients. Methods: Three series of experiments were performed, using duodenal biopsy pairs from 53 adult celiac patients and 14 normal subjects, in order to determine: (1) mucosal immunoreactivity for α-MSH and melanocortin receptors (MCRs), and gene expression of α-MSH precursor pro-opiomelanocortin and MCRs; (2) α-MSH and inflammatory cytokine production by duodenal specimens in vitro, and the influence of synthetic α-MSH on such cytokine production, and (3) the influence of stimulation with gliadin (the subfraction of gluten that is toxic to patients with celiac disease) on α-MSH and cytokine production in vitro and the effect of α-MSH on gliadin-stimulated cytokine production. Results: Elements of a localized anti-inflammatory influence based on α-MSH and its receptors were found: duodenal mucosa showed immunostaining for α-MSH and two of its receptor subtypes, MC1R and MC5R. α-MSH and MC1R immunoreactivity was more intense in specimens from celiac patients. Release of interleukin 6 from gliadin-stimulated duodenal mucosa was inhibited by synthetic α-MSH in vitro. Conclusions: Presence of α-MSH and its receptors in celiac mucosa suggests the presence of a local reaction to control the inflammatory response elicited by gliadin. In selected cases of refractory celiac disease, treatment with exogenous peptides might be considered.

α-Melanocyte-Stimulating Hormone Is Decreased in Plasma of Patients with Acute Brain Injury

The neuropeptide α-melanocyte-stimulating hormone (α-MSH) is a proopiomelanocortin derivative that has potent anti-inflammatory influences within the brain. The aim of the present research was to d...

Protective action of NDP-MSH in experimental subarachnoid hemorrhage.

Subarachnoid hemorrhage (SAH) is still a major cause of morbidity and mortality. α-Melanocyte stimulating hormone (α-MSH) and other melanocortin peptides exert potent neuroprotective action and they might modulate key molecules involved in SAH-induced vasospasm. The aim of this research was to determine whether treatment with the α-MSH analog Nle4,DPhe7-α-MSH (NDP-MSH) exerts protective effects in experimental SAH in the rat. Initial experiments examined effects of NDP-MSH on the basilar artery phenotype in the absence of injury. In these tests intrathecal injection of small concentrations (10ng) of the peptide induced a tolerant phenotype similar to that observed after ischemic preconditioning. Then the effect of systemic treatment with NDP-MSH (100μg i.v.) on experimental SAH was evaluated. SAH was induced by a single-blood injection into the cisterna magna. The basilar artery phenotype was examined at 4h and the artery caliber at 5days following SAH. Expression of 96 genes was analyzed by real-time reverse transcription polymerase chain reaction (RT-PCR) using Custom Taqman Low-Density Arrays. Four hours after SAH, the transcriptional profile of the basilar artery was deeply disrupted. Transcript alteration included genes involved in inflammation, stress response, apoptosis, and vascular remodeling. Treatment with NDP-MSH prevented most of these transcription changes and decreased phosphorylation of extracellular-signal-regulated kinases (ERK1/2) and inhibitor protein IκBα. Vasospasm on day 5 was significantly reduced by NDP-MSH administration. These results combine with others on CNS inflammation to suggest that the melanocortins could be safe and effective therapeutic candidates to treat SAH-related complications.

Autocrine inhibitory influences of α-melanocyte-stimulating hormone in malignant pleural mesothelioma

Malignant pleural mesothelioma is a highly aggressive tumor arising from the mesothelial cells that line the pleural cavities. This tumor is resistant to most conventional anticancer treatments and appears to be very sensitive to growth‐promoting influences of cytokines and growth factors. Identification of natural inhibitory pathways that control growth should aid discovery of novel therapeutic approaches. We hypothesized that α‐melanocyte‐stimulating hormone (α‐MSH), which is produced by many cell types and antagonizes cytokines and growth factors, could be an endogenous inhibitory molecule in mesothelioma. Twelve mesothelioma cell lines were established from pleural effusions of patients with malignant mesothelioma. Mesothelioma cells were found to express mRNA for proopiomelanocortin and its processing enzymes; release α‐MSH peptide into supernatants; and express melanocortin 1 receptor (MC1R), the high‐affinity receptor for α‐MSH. Immunoneutralization of MC1R in the cell lines enhanced expression of interleukin‐8 (IL‐8), IL‐6, and transforming growth factor‐β. These molecules promote mesothelioma proliferation and are considered therapeutic targets in this tumor. Coincubation of mesothelioma cells with synthetic α‐MSH significantly reduced cell proliferation. The present research shows an autocrine‐inhibitory circuit based on α‐MSH and its receptor MC1R. Activation of MC1R by selective peptides or peptidomimetics might provide a novel strategy to reduce mesothelioma cell proliferation by taking advantage of this endogenous inhibitory circuit.