Antimicrobial properties of melanocortins: comment to the manuscript "Anti-Candida activity of α-melanocyte-stimulating hormone (α-MSH) peptides" by Isabella Rauch et al.

In their report, Rauch et al. did not find candidacidal activity of α-melanocyte-stimulating hormone (α-MSH) in Sabouraud dextrose broth. The lack of killing activity by the natural α-MSH in broth medium may occur because of accelerated Candida replication or peptide degradation by fungal enzymes. It should be considered that in physiological conditions, there is sustained peptide release by host cells in an autocrine/paracrine manner. However, when the procedure described in the paper published in the Journal Leukocyte Biology was used, the investigation by Rauch et al. found that concentrations of α-MSH in the high micromolar range have candidacidal activity.

Reduced expression of the melanocortin-1 receptor in human liver during brain death.

OBJECTIVE: There is evidence that brain death has detrimental effects on peripheral organs. Clinical and experimental studies on organ donors showed marked inflammation in tissue samples of livers and kidneys collected during brain death. The inflammatory reaction is characterized by release of cytokines and inflammatory cell infiltration. Because melanocortins and their receptors are significant modulators of inflammation, we hypothesized that downregulation of melanocortin receptors during brain death could contribute to enhance inflammation. METHODS: Using real-time polymerase chain reaction (PCR) analysis, we determined expression of melanocortin receptors in liver biopsies obtained from brain-dead organ donors before cold ischemia and in normal liver tissue during resection of benign focal lesions of the liver. Tissue biopsies were also analyzed for expression of intercellular adhesion molecule-1 (ICAM-1), which has a central function in inflammatory cell migration. RESULTS: Expression of melanocortin-1 receptor (MC1R) mRNA was markedly reduced in liver samples obtained from brain-dead organ donors compared to hepatic tissue collected during resection of benign focal lesions of the liver. Conversely, expression of the adhesion molecule ICAM-1 was significantly increased in livers of brain-dead organ donors. CONCLUSIONS: Disruption of the endogenous anti-inflammatory circuit based on MC1R could contribute to tissue damage during brain death.

Inhibitory effects of the peptide (CKPV)2 on endotoxin-induced host reactions.

BACKGROUND: alpha-Melanocyte stimulating hormone (alpha-MSH) is an endogenous peptide that has remarkable anti-inflammatory and antimicrobial effects. These activities have been traced to the C-terminal tripeptide Lys-Pro-Val (KPV). A dimer composed of two KPV sequences connected with a Cys-Cys linker, (CKPV)2, is currently under clinical investigation for antimicrobial use. The present research was designed to evaluate effects of (CKPV)(2) on endotoxin-induced host reactions in vitro and in vivo. MATERIALS AND METHODS: Effects of (CKPV)2, KPV, and [Nle4-dPhe7]-alpha-MSH (NDP-alpha-MSH) on tumor necrosis factor alpha (TNF-alpha) production were determined: 1) in human peripheral blood mononuclear cells (PBMC) stimulated with lipopolysaccharide (LPS) in vitro, and 2) in rats injected with LPS i.v. and sacrificed at 1 h. In additional experiments, dialysis peritonitis was induced in rats by adding LPS to dialysis fluid. Net ultrafiltrate was calculated and concentrations of nitrite (NO2-) and TNF-alpha were measured in blood and peritoneal fluid at 7 h. RESULTS: (CKPV)2 inhibited TNF-alpha production by LPS-stimulated human PBMC. This small peptide was as effective as NDP-alpha-MSH and more potent than KPV. Similar effectiveness was observed in vivo: 1 h after LPS injection, the large increase in circulating TNF-alpha was markedly reduced by (CKPV)2 treatment. In LPS-induced peritonitis, (CKPV)2 restored net ultrafiltrate to control values and significantly inhibited concentrations of TNF-alpha and NO2- both in plasma and in dialysate. CONCLUSIONS: The remarkable capacity of (CKPV)2 to inhibit endotoxin-induced host reactions suggests that it may be useful in treatment of inflammatory disorders.

Gene expression profiling reveals multiple protective influences of the peptide alpha-melanocyte-stimulating hormone in experimental heart transplantation.

Novel therapies are sought to increase efficiency and survival of transplanted organs. Previous research on experimental heart transplantation showed that treatment with the anti-inflammatory peptide alpha-melanocyte-stimulating hormone (alpha-MSH) prolongs allograft survival. The aim of the present research was to determine the molecular mechanism of this protective activity. Gene expression profile was examined in heart grafts removed on postoperative days 1 and 4 from rats treated with saline or the synthetic alpha-MSH analog Nle4DPhe7 (NDP)-alpha-MSH. On postoperative day 1, the peptide induced expression of cytoskeleton proteins, intracellular kinases, transcription regulators, metallopeptidases, and protease inhibitors. Conversely, NDP-alpha-MSH repressed immune, inflammatory, cell cycle, and protein turnover mediators. Later effects of alpha-MSH treatment included down-regulation of oxidative stress response and up-regulation of ion channels, calcium regulation proteins, phosphatidylinositol signaling system, and glycolipidic metabolism. NDP-alpha-MSH exerted its effects on both Ag-dependent and -independent injury. The results indicate that NDP-alpha-MSH preserves heart function through a broad effect on multiple pathways and suggest that the peptide could improve the outcome of organ transplantation in combination with immunosuppressive treatments.

Design and synthesis of melanocortin peptides with candidacidal and anti-TNF-alpha properties.

Alpha-melanocyte stimulating hormone (alpha-MSH) is an endogenous antiinflammatory peptide with antimicrobial properties. We recently found that a synthetic analogue, [dNal(2')-7, Phe-12]-alpha-MSH (6-13), was considerably more potent in killing Candida albicans, but the anti-cytokine potential of the molecule was not investigated. Because molecules that combine candidacidal and antiinflammatory properties could be very useful in clinical practice, we measured the anti-TNF-alpha potential of [dNal(2')-7, Phe-12]-alpha-MSH (6-13) and explored effects of amino acid deletions and substitutions on both anti-Candida and anti-TNF-alpha activities. The results show that anti-TNF-alpha properties of this candidacidal peptide are only marginally increased relative to the native sequence. Conversely, we found that a closely related candidacidal analogue, [dNal(2')-7, Pro-12]-alpha-MSH (6-13), had enhanced anti-TNF-alpha effects in vitro and in vivo. This peptide, and other melanocortins with a similar dual effect, could be very useful to eradicate infections and, concurrently, reduce inflammatory reactions.

Targeting melanocortin receptors as a novel strategy to control inflammation.

Adrenocorticotropic hormone and alpha-, beta-, and gamma-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 kappaB 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.

Autocrine inhibitory influences of alpha-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 alpha-melanocyte-stimulating hormone (alpha-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 alpha-MSH peptide into supernatants; and express melanocortin 1 receptor (MC1R), the high-affinity receptor for alpha-MSH. Immunoneutralization of MC1R in the cell lines enhanced expression of interleukin-8 (IL-8), IL-6, and transforming growth factor-beta. These molecules promote mesothelioma proliferation and are considered therapeutic targets in this tumor. Coincubation of mesothelioma cells with synthetic alpha-MSH significantly reduced cell proliferation. The present research shows an autocrine-inhibitory circuit based on alpha-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.

Alpha-melanocyte-stimulating hormone is decreased in plasma of patients with acute brain injury.

The neuropeptide alpha-melanocyte-stimulating hormone (alpha-MSH) is a proopiomelanocortin derivative that has potent anti-inflammatory influences within the brain. The aim of the present research was to determine if there are changes in blood concentrations of this peptide in patients with acute traumatic brain injury (TBI) or subarachnoid hemorrhage (SAH). Concomitantly, we recorded clinical parameters and measured blood concentrations of the proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha). Twenty-three patients were enrolled in this study--18 had TBI and five SAH. Blood samples for determination of alpha-MSH and TNF-alpha were collected daily from day 1 to day 4 after injury. Baseline concentration of plasma alpha-MSH in patients with acute brain injury of either traumatic or vascular origin was significantly lower than in controls. Patients with TBI or SAH had similar alpha-MSH concentrations and the peptide remained consistently low over four post-injury days. Circulating TNF-alpha on day one was measurable in all patients and there was a negative correlation between plasma TNF-alpha and alpha-MSH. Alpha-MSH was measured again after the acute phase in eight patients. The peptide was substantially increased in all subjects except for two who had an unfavorable outcome. From the well-known protective anti-inflammatory influences of alpha-MSH in the host, reduction in this circulating peptide may have detrimental consequences in brain injury. The data raise the possibility that restoration of normal circulating alpha-MSH through administration of the peptide could be beneficial in patients with brain injury.

Novel alpha-melanocyte stimulating hormone peptide analogues with high candidacidal activity.

alpha-Melanocyte stimulating hormone (alpha-MSH) is an endogenous linear tridecapeptide with potent antiinflammatory effects. We recently demonstrated that alpha-MSH and its C-terminal sequence Lys-Pro-Val (alpha-MSH (11-13)) have antimicrobial effects against two major and representative pathogens: Staphylococcus aureus and Candida albicans. In an attempt to improve the candidacidal activity of alpha-MSH and to better understand the peptide structure-antifungal activity relations, we designed and synthesized novel peptide analogues. Because previous data suggested that antimicrobial effects of alpha-MSH were receptor-mediated, we chose to focus on the sequence alpha-MSH (6-13), which contains the invariant core sequence His-Phe-Arg-Trp (6-9) that is important for binding to the known melanocortin receptors and also contains the sequence Lys-Pro-Val (11-13) that is known to be important for antimicrobial activity. In this structure-activity study, we discovered several compounds that have greater candidacidal activity than alpha-MSH. The peptide [d-Nal-7,Phe-12]-alpha-MSH (6-13) was the most potent of the analogues tested. The present results are very encouraging because they show the great potential of these peptides as a truly novel class of candidacidal compounds.

Alpha-melanocyte stimulating hormone in modulation of inflammatory reactions.

Although adrenal stimulatory effects of ACTH and pigmentary influences of MSH have been known for decades, it has become clear only recently that melanocortin peptides have 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 melanocortin receptors (MCRs) has greatly improved understanding of peptide-target cell interactions. Synthetic melanocortins, with selective affinities for specific MCRs, could be the basis for new classes of therapeutic molecules. This review examines promising targets for a-MSH and closely related peptides in inflammatory disorders.

alpha-Melanocyte-stimulating hormone protects the allograft in experimental heart transplantation.

BACKGROUND: With the increasing need for organ transplantation and the use of "marginal" organs, novel approaches are sought to increase the efficiency and survival of transplanted tissue. We tested the idea that treatment with the anti-inflammatory peptide, alpha-melanocyte-stimulating hormone (alpha-MSH), an endogenous hormone that does not cause marked immunosuppression but does reduce reperfusion injury, may protect allografts and prolong their survival. METHODS: Donor cardiac grafts (Brown Norway) were transplanted heterotopically into the abdomen of recipient (Lewis) rats. Treatments consisted of intraperitoneal injections of Nle DPhe -alpha-MSH (NDP-alpha-MSH) or saline from the time of transplantation until sacrifice or spontaneous rejection. Allografts were removed on day 1, day 4, or at the time of rejection and examined for histopathology and expression of molecules prominent in reperfusion injury, transplant rejection, and apoptosis. RESULTS: NDP-alpha-MSH treatment caused a significant increase in allograft survival and a marked decrease in leukocyte infiltration. Expression of molecules such as endothelin 1, chemokines, and adhesion molecules, which are involved in allograft rejection, was significantly inhibited in NDP-alpha-MSH-treated rats. CONCLUSIONS: The results indicate that protection of the allograft from early injury with alpha-MSH can postpone rejection. Addition of this early protection with the peptide to usual treatment with immunosuppressive agents may, therefore, improve success of organ transplants.

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

OBJECTIVES: The peptide alpha-melanocyte-stimulating hormone (alpha-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 alpha-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 alpha-MSH and melanocortin receptors (MCRs), and gene expression of alpha-MSH precursor pro-opiomelanocortin and MCRs; (2). alpha-MSH and inflammatory cytokine production by duodenal specimens in vitro, and the influence of synthetic alpha-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 alpha-MSH and cytokine production in vitro and the effect of alpha-MSH on gliadin-stimulated cytokine production. RESULTS: Elements of a localized anti-inflammatory influence based on alpha-MSH and its receptors were found: duodenal mucosa showed immunostaining for alpha-MSH and two of its receptor subtypes, MC1R and MC5R. alpha-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 alpha-MSH in vitro. CONCLUSIONS: Presence of alpha-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.

Peptide modulation of fever and inflammation within the brain.

The importance of melanocortin peptides to host responses was recognized with the observation of the antipyretic effect of centrally administered alpha-melanocyte stimulating hormone (alpha-MSH). It is now clear that this neuropeptide also exerts remarkable antiinflammatory activity via direct actions on peripheral host cells, descending neurogenic antiinflammatory pathways stemming from CNS melanocortin receptors, and local actions on receptors that control inflammation within the brain. Recent studies of the latter influence indicate that alpha-MSH inhibits brain tumor necrosis factor-alpha (TNF-alpha), previously linked to human neurodegenerative diseases, induced by local injection of lipopolysaccharide. Ischemia/reperfusion of the brain, a model of stroke, induces inflammation marked by disturbance of CNS function. alpha-MSH given systemically modulates disturbances of auditory evoked potentials induced by ischemia/reperfusion in the posterior circulation. Such influences of the peptide may occur through inhibition of inflammatory agents produced by glia: alpha-MSH 1-13 and 11-13 modulate TNF-alpha and nitric oxide produced by activated murine microglia, and TNF-alpha produced by human astrocytes. Because glia can secrete alpha-MSH and express melanocortin receptors, they may, like peripheral macrophages, contain autocrine regulatory circuits based on the peptide. alpha-MSH thus modulates both fever and inflammation in the brain by acting on local melanocortin receptors.