Anna Catania

Targeting Melanocortin Receptors as a Novel Strategy to Control Inflammation

Adrenocorticotropic hormone and α-, β-, and γ-melanocyte-stimulating hormones, collectively called melanocortin peptides, exert multiple effects upon the host. These effects range from modulation of fever and inflammation to control of food intake, autonomic functions, and exocrine secretions. Recognition and cloning of five melanocortin receptors (MCRs) has greatly improved understanding of peptide-target cell interactions. Preclinical investigations indicate that activation of certain MCR subtypes, primarily MC1R and MC3R, could be a novel strategy to control inflammatory disorders. As a consequence of reduced translocation of the nuclear factor κB to the nucleus, MCR activation causes a collective reduction of the major molecules involved in the inflammatory process. Therefore, anti-inflammatory influences are broad and are not restricted to a specific mediator. Short half-life and lack of selectivity could be an obstacle to the use of the natural melanocortins. However, design and synthesis of new MCR ligands with selective chemical properties are already in progress. This review examines how marshaling MCR could control inflammation.

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.

Changes in viremia and circulating interferon-α during hemodialysis in hepatitis C virus-positive patients: only coincidental phenomena?

BACKGROUND It has been hypothesized that hemodialysis (HD) treatment per se can preserve patients from an aggressive course of hepatitis C virus (HCV) infection by reduction of viral load. The aim of the present study in HCV-positive (HCV+) HD patients is to determine whether HD induces the production of interferon-alpha (IFN-alpha) and if such production can contribute to viremia reduction. METHODS To address this issue, HCV RNA and IFN-alpha levels were determined in 11 HCV+ patients immediately before and at the end of a 4-hour dialysis session using cellulosic membranes and 24 and 48 hours later, ie, immediately before the subsequent dialysis session using the same membrane and at the end of the dialysis session. The same protocol was repeated 1 week later using a high-biocompatibility synthetic membrane. RESULTS HCV titer decreased in all patients after dialysis (range, 3% to 95%; P = 0.001) and thereafter progressively increased and returned to basal levels within 48 hours, with a new reduction during the next dialysis treatment. There was no significant difference in the magnitude of changes in HCV titers in tests performed using cellulosic or synthetic membranes. Plasma IFN-alpha levels increased markedly after dialysis using both cellulosic (in 9 of 11 cases) and synthetic membranes (in 10 of 11 cases; P < 0.01) and returned to basal levels within 48 hours; thereafter, IFN-alpha levels increased again during the next dialysis session. In some patients, plasma IFN-alpha levels after HD were approximately 50% of the level observed after therapeutic administration of 6 million units of IFN-alpha to 4 HD patients with chronic hepatitis. CONCLUSION Although without a proven direct cause-effect relationship between HCV level reduction and induction of IFN-alpha after dialysis, our observation suggests an additional new mechanism for the unusually mild course of HCV infection in HD patients.

Selective melanocortin MC4 receptor agonists reverse haemorrhagic shock and prevent multiple organ damage

In circulatory shock, melanocortins have life‐saving effects likely to be mediated by MC4 receptors. To gain direct insight into the role of melanocortin MC4 receptors in haemorrhagic shock, we investigated the effects of two novel selective MC4 receptor agonists.

Plasma concentrations and anti-L-cytokine effects of alpha-melanocyte stimulating hormone in septic patients

Objectives: The aim of this research was to investigate endogenous concentrations and anti‐cytokine effects of the anti‐inflammatory peptide α‐melanocyte stimulating hormone (α‐MSH) in patients with systemic inflammation. The objectives were to determine the following: changes over time of plasma α‐MSH and relationship with patient outcome, correlation between plasma α‐MSH and tumor necrosis factor (TNF)‐α plasma concentration and production in whole blood samples, and influences of α‐MSH on production of TNF‐α and interleukin (IL)‐1β in whole blood samples stimulated with lipopolysaccharide (LPS). Design: Prospective, nonrandomized, clinical study. Setting: Intensive care unit of a university hospital. Patients: A total of 21 patients with sepsis syndrome/septic shock and an equal number of healthy volunteers. Interventions: Circulating α‐MSH and TNF‐α concentrations and TNF‐α production in supernatants of LPS (1 ng/mL)‐stimulated whole blood were measured repeatedly. To determine whether α‐MSH can modulate production of TNF‐α and IL‐1 β, these cytokines were measured in whole blood samples stimulated with LPS (1 ng/mL) in the presence or absence of concentrations of the peptide. Measurements and Main Results: Plasma α‐MSH was low in early samples and gradually increased in patients who recovered but not in those who died. There was a negative correlation between plasma concentrations of α‐MSH and TNF‐α. In blood samples taken at early phases of sepsis syndrome, production of TNF‐α was reduced relative to control values; such production increased in patients who recovered but not in those who died. Addition of α‐MSH to LPS‐stimulated whole blood samples inhibited production of TNF‐α and IL‐1β in a concentration‐dependent manner. Conclusions: In patients with systemic inflammation, there are substantial changes over time in plasma concentrations of α‐MSH that are reduced in early phases of the disease. Reduction of this endogenous modulator of inflammation could be detrimental to the host. Addition of α‐MSH to LPS‐stimulated blood samples reduces production of cytokines involved in development of septic syndrome. This inhibition by α‐MSH, a peptide that is beneficial in treatment of experimental models of sepsis, might therefore be useful to treat sepsis syndrome in humans.

The Anticytokine Neuropeptide α-Melanocyte-Stimulating Hormone in Synovial Fluid of Patients with Rheumatic Diseases: Comparisons with Other Anticytokine Molecules

The aim of this study was to determine if the anticytokine neuropeptide alpha-melanocyte-stimulating hormone (alpha-MSH) occurs, along with interleukin 1 receptor antagonist (IL-1ra) and soluble tumor necrosis factor receptor (sTNFr), in synovial fluid of patients with rheumatoid arthritis (RA), juvenile chronic arthritis (JCA), or osteoarthritis. The data show that alpha-MSH does occur in the synovial fluid and its concentrations are greater in patients with RA than in those with osteoarthritis. Synovial fluid concentrations of IL-1ra and sTNFr were likewise greater in RA. Further, concentrations of alpha-MSH, IL-1-ra, and sTNFr were greater in patients with polyarticular/systemic-onset JCA than in those with pauciarticular disease, that is in patients with greater joint inflammation. Concentrations of alpha-MSH were greater in synovial fluid than in plasma in a substantial proportion of patients, suggesting local production of the peptide; this is the first indication that the anticytokine molecule alpha-MSH is produced within a site of inflammation. Further, it appears that local production of alpha-MSH is induced particularly in those arthritic joints that have more intense inflammatory reactions. This finding, combined with previous evidence of the marked anti-inflammatory activity of alpha-MSH, suggests that the peptide acts locally to modulate proinflammatory influences in rheumatic diseases.

Plasma Concentration of Cytokine Antagonists in Patients with HIV Infection

There is increasing evidence that cytokines contribute to the immunopathogenesis of human immunodeficiency virus (HIV) infection. It may be, therefore, that compensatory rises in circulating cytokine antagonists also occur in HIV infection and that such changes mark disease progression. To test this idea, plasma concentrations of the cytokine antagonists alpha-melanocyte-stimulating hormone (alpha-MSH), interleukin-1 receptor antagonist (IL-1ra), and soluble tumor necrosis factor receptor (sTNFr) were measured in patients of different Centers for Disease Control (CDC) categories of HIV infection and in seronegative controls. Plasma levels of all these cytokine antagonists were higher in HIV-infected patients. IL-1ra and sTNFr concentrations were correlated with indicators of disease activity: positively with plasma neopterin and negatively with CD4+ T lymphocyte counts. alpha-MSH and sTNF r were greater in CDC groups III and IV, whereas IL-1ra was elevated only in the latter group. Because cytokines activate the hypothalamic-pituitary-adrenal axis and adrenal steroids inhibit cytokine production, we measured circulating adrenocorticotropic hormone (ACTH) and cortisol in HIV-infected patients and investigated relations among these hormones, cytokine antagonists, and markers of disease progression. It appears that these physiological modulators of cytokine activity are not closely linked to sTNFr, IL-1ra and alpha-MSH: there were no significant correlations between plasma concentrations of ACTH or cortisol and those of cytokine antagonists, nor were there correlations between hormones and markers of disease progression such as neopterin or CD4+ T cell counts. It is notable that severe adrenal insufficiency was extremely rare (3%) in HIV-infected patients; it was confined to the AIDS group and was consistently secondary to ACTH deficiency.(ABSTRACT TRUNCATED AT 250 WORDS)

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.