MC-3 receptor and the inflammatory mechanisms activated in acute myocardial infarct

Recent advances in potential targets for myocardial ischemia reperfusion injury: Role of macrophages

Myocardial ischemia-reperfusion injury (MIRI) is a complex process that occurs when blood flow is restored after myocardium infarction (MI) with exacerbated tissue damage. Macrophages, essential cell type of the immune response, play an important role in MIRI. Macrophage subpopulations, namely M1 and M2, are distinguished by distinct phenotypes and functions. In MIRI, macrophages infiltrate in infarcted area, shaping the inflammatory response and influencing tissue healing. Resident cardiac macrophages interact with monocyte-derived macrophages in MIRI, and influence injury progression. Key factors including chemokines, cytokines, and toll-like receptors modulate macrophage behavior in MIRI. This review aims to address recent findings on the classification and the roles of macrophages in the myocardium, spanning from MI to subsequent MIRI, and highlights various signaling pathways implicated in macrophage polarization underlining the complexity of MIRI. This article will shed light on developing advanced therapeutic strategies for MIRI management.

Melanocortin 3,5 receptors immunohistochemical expression in colonic mucosa of inflammatory bowel disease patients: A matter of disease activity?

BACKGROUND

Melanocortin 3 and 5 receptors (i.e., MC3R and MC5R) belong to the melanocortin family. However, data regarding their role in inflammatory bowel diseases (IBD) are currently unavailable.

AIM

This study aims to ascertain their expression profiles in the colonic mucosa of Crohn's disease (CD) and ulcerative colitis (UC), aligning them with IBD disease endoscopic and histologic activity.

METHODS

Colonic mucosal biopsies from CD/UC patients were sampled, and immunohistochemical analyses were conducted to evaluate the expression of MC3R and MC5R. Colonic sampling was performed on both traits with endoscopic scores (Mayo endoscopic score and CD endoscopic index of severity) consistent with inflamed mucosa and not consistent with disease activity (i.e., normal appearing mucosa).

RESULTS

In both CD and UC inflamed mucosa, MC3R (CD: + 7.7 fold vs normal mucosa, P < 0.01; UC: + 12 fold vs normal mucosa, P < 0.01) and MC5R (CD: + 5.5 fold vs normal mucosa, P < 0.01; UC: + 8.1 fold vs normal mucosa, P < 0.01) were significantly more expressed compared to normal mucosa.

CONCLUSION

MC3R and MC5R are expressed in the colon of IBD patients. Furthermore, expression may differ according to disease endoscopic activity, with a higher degree of expression in the traits affected by disease activity in both CD and UC, suggesting a potential use of these receptors in IBD pharmacology.

The Melanocortin System in Inflammatory Bowel Diseases: Insights into Its Mechanisms and Therapeutic Potentials

The melanocortin system is a complex set of molecular mediators and receptors involved in many physiological and homeostatic processes. These include the regulation of melanogenesis, steroidogenesis, neuromodulation and the modulation of inflammatory processes. In the latter context, the system has assumed importance in conditions of chronic digestive inflammation, such as inflammatory bowel diseases (IBD), in which numerous experiences have been accumulated in mouse models of colitis. Indeed, information on how such a system can counteract colitis inflammation and intervene in the complex cytokine imbalance in the intestinal microenvironment affected by chronic inflammatory damage has emerged. This review summarises the evidence acquired so far and highlights that molecules interfering with the melanocortin system could represent new drugs for treating IBD.

Translational advances of melanocortin drugs: Integrating biology, chemistry and genetics

Melanocortin receptors have emerged as important targets with a very unusual versatility, as their widespread distribution on multiple tissues (e.g. skin, adrenal glands, brain, immune cells, exocrine glands) together with the variety of physiological processes they control (pigmentation, cortisol release, satiety mechanism, inflammation, secretions), place this family of receptors as genuine therapeutic targets for many disorders. This review focuses in the journey of the development of melanocortin receptors as therapeutic targets from the discovery of their existence in the early 1990 s to the approval of the first few drugs of this class. Two major areas of development characterise the current state of melanocortin drug development: their role in obesity, recently culminated with the approval of setmelanotide, and their potential for the treatment of chronic inflammatory and autoimmune diseases like rheumatoid arthritis, multiple sclerosis or fibrosis. The pro-resolving nature of these drugs offers the advantage of acting by mimicking the way our body naturally resolves inflammation, expecting fewer side effects and a more balanced (i.e. non-immunosuppressive) response from them. Here we also review the approaches followed for the design and development of novel compounds, the importance of the GPCR nature of these receptors in the process of drug development, therapeutic value, current challenges and successes, and the potential for the implementation of precision medicine approaches through the incorporation of genetics advances.

Non-Canonical Effects of ACTH: Insights Into Adrenal Insufficiency

Introduction

Adrenocorticotropic hormone (ACTH) is produced from proopiomelanocortin, which is predominantly synthetized in the corticotroph and melanotroph cells of the anterior and intermediate lobes of the pituitary gland and the arcuate nucleus of the hypothalamus. Although ACTH clearly has an effect on adrenal homeostasis and maintenance of steroid hormone production, it also has extra-adrenal effects that require further elucidation.

Methods

We comprehensively reviewed English language articles, regardless of whether they reported the presence or absence of adrenal and extra-adrenal ACTH effects.

Results

In the present review, we provide an overview on the current knowledge on adrenal and extra-adrenal effects of ACTH. In the section on adrenal ACTH effects, we focused on corticosteroid rhythmicity and effects on steroidogenesis, mineralocorticoids and adrenal growth. In the section on extra-adrenal effects, we have analyzed the effects of ACTH on the osteoarticular and reproductive systems, adipocytes, immune system, brain and skin. Finally, we focused on adrenal insufficiency.

Conclusions

The role of ACTH in maintaining the function of the hypothalamic-pituitary-adrenal axis is well known. Conversely, if we broaden our vision and analyze its role as a potential treatment strategy in other conditions, it will be evident in the literature that researchers seem to have abandoned this aspect in studies conducted several years ago. We believe it is worth re-evaluating the role of ACTH considering its noncanonical effects on the adrenal gland itself and on extra-adrenal organs and tissues; however, this would not have been possible without the recent advances in the pertinent technologies.

Alpha-melanocyte-stimulating hormone during exercise recovery has prognostic value for coronary artery disease

PURPOSE

Alpha-melanocyte-stimulating hormone (alpha-MSH) has proven cardiovascular effects and plays a significant role as an endogenous countermeasure to ischemia-reperfusion injury. The aim of the current study was to examine the response of alpha-MSH during exercise in patients diagnosed with coronary artery disease (CAD) and evaluate its value in the assessment of severity and prognosis.

METHODS

Forty subjects with documented CAD (i.e., lesions on coronary angiography ≥ 50%) were included. Cardiopulmonary exercise testing (CPET) on a treadmill (TM) and recumbent ergometer (RE) were performed on two visits, 2-4 days apart, during 2 months of coronary angiography; subsequently, the subjects were followed up for 32 ± 10 months. At rest, at peak CPET, and after 3 min of recovery, plasma levels of alpha-MSH were measured by enzyme-linked immunosorbent assay technique.

RESULTS

Mean ejection fraction was 56.7 ± 9.6%. Alpha-MSH similarly increased from rest to peak CPET on both modalities. There were no significant differences in alpha-MSH values during testing in patients with 1,2- and 3-vesel CAD, nor in patients with a SYNTAX score </≥ 23 (p > 0.05). Among CPET and hormonal parameters, ∆alpha-MSH recovery/peak during RE CPET was the best predictor of cardiac event occurrence (chi-square 6.67, HR = 0.51, CI = 0.25-1.02, p = 0.010).

CONCLUSION

∆alpha-MSH recovery/peak during RE CPET has predictive value for CAD prognosis, demonstrating involvement of alpha-MSH in CAD and a link between stress hormones and cardiac events.

Long Term Osmotic Mini Pump Treatment with Alpha-MSH Improves Myocardial Function in Zucker Diabetic Fatty Rats

The present investigation evaluates the cardiovascular effects of the anorexigenic mediator alpha-melanocyte stimulating hormone (MSH), in a rat model of type 2 diabetes. Osmotic mini pumps delivering MSH or vehicle, for 6 weeks, were surgically implanted in Zucker Diabetic Fatty (ZDF) rats. Serum parameters, blood pressure, and weight gain were monitored along with oral glucose tolerance (OGTT). Echocardiography was conducted and, following sacrifice, the effects of treatment on ischemia/reperfusion cardiac injury were assessed using the isolated working heart method. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity was measured to evaluate levels of oxidative stress, and force measurements were performed on isolated cardiomyocytes to determine calcium sensitivity, active tension and myofilament co-operation. Vascular status was also evaluated on isolated arterioles using a contractile force measurement setup. The echocardiographic parameters ejection fraction (EF), fractional shortening (FS), isovolumetric relaxation time (IVRT), mitral annular plane systolic excursion (MAPSE), and Tei-index were significantly better in the MSH-treated group compared to ZDF controls. Isolated working heart aortic and coronary flow was increased in treated rats, and higher Hill coefficient indicated better myofilament co-operation in the MSH-treated group. We conclude that MSH improves global heart functions in ZDF rats, but these effects are not related to the vascular status.

Activation of Melanocortin Receptors MC 1 and MC 5 Attenuates Retinal Damage in Experimental Diabetic Retinopathy

We hypothesize that melanocortin receptors (MC) could activate tissue protective circuit in a model of streptozotocin- (STZ-) induced diabetic retinopathy (DR) in mice. At 12–16 weeks after diabetes induction, fluorescein angiography (FAG) revealed an approximate incidence of 80% microvascular changes, typical of DR, in the animals, without signs of vascular leakage. Occludin progressively decreased in the retina of mice developing retinopathy. qPCR of murine retina revealed expression of two MC receptors, Mc1r and Mc5r. The intravitreal injection (5 μL) of the selective MC₁ small molecule agonist BMS-470539 (33 μmol) and the MC₅ peptidomimetic agonist PG-901 (7.32 nM) elicited significant protection with regular course and caliber of retinal vessels, as quantified at weeks 12 and 16 after diabetes induction. Mouse retina homogenate settings indicated an augmented release of IL-1α, IL-1β, IL-6, MIP-1α, MIP-2α, MIP-3α, and VEGF from diabetic compared to nondiabetic mice. Application of PG20N or AGRP and MC₅ and MC₁ antagonist, respectively, augmented the release of cytokines, while the agonists BMS-470539 and PG-901 almost restored normal pattern of these mediators back to nondiabetic values. Similar changes were quantified with respect to Ki-67 staining. Finally, application of MC₃-MC₄ agonist/antagonists resulted to be inactive with respect to all parameters under assessment.

NDP-α-MSH attenuates heart and liver responses to myocardial reperfusion via the vagus nerve and JAK/ERK/STAT signaling

Melanocortin peptides afford cardioprotection during myocardial ischemia/reperfusion via janus kinases (JAK), extracellular signal-regulated kinases (ERK) and signal transducers/activators of transcription (STAT) pathways. Here we investigated whether melanocortin-induced modulation of the JAK/ERK/STAT signaling occurs via the cholinergic anti-inflammatory pathway, focusing our study on cardiac and hepatic responses to prolonged myocardial ischemia/reperfusion. Ischemia was produced in rats by ligature of the left anterior descending coronary artery for 30min; effects of ischemia/reperfusion were evaluated using Western blot of heart and liver proteins. Intravenous treatment, during coronary artery occlusion, with the melanocortin analog (Nle(4), D-Phe(7))α-melanocyte-stimulating hormone (NDP-α-MSH) induced a left ventricle up-regulation of the cardioprotective transcription factors pJAK2, pERK1/2 and pTyr-STAT3 (JAK-dependent), and a reduction in the levels of the inflammatory mediators tumor necrosis factor-α (TNF-α) and pJNK (a transcription factor also involved in apoptosis), as assessed at the end of the 2-h reperfusion period. Further, these beneficial effects of NDP-α-MSH were associated with heart over-expression of the pro-survival proteins heme oxygenase-1 (HO-1) and Bcl-XL, and decrease of ventricular arrhythmias and infarct size. In the liver NDP-α-MSH induced a decrease in the pJAK2 and pTyr-STAT3 levels, and strongly reduced pERK1/2 expression. In the liver of ischemic rats NDP-α-MSH also blunted pJNK activity and TNF-α expression, and up-regulated Bcl-XL. Bilateral cervical vagotomy prevented all effects of NDP-α-MSH, both in the heart and liver. These results indicate that melanocortins inhibit heart and liver damage triggered by prolonged myocardial ischemia/reperfusion likely, as main mechanism, via the vagus nerve-mediated modulation of the JAK/STAT/ERK signaling pathways.

Association analysis of melanocortin 3 receptor polymorphisms with the risk of pulmonary tuberculosis

PURPOSE

Melanocortin 3 Receptor (MC3R) is one of the families of seven-transmembrane G-protein-coupled receptors, and a recent study showed that MCR3 promoter polymorphism was significantly associated with the susceptibility of tuberculosis (TB) in South African population.

METHODS

We analyzed six MC3R polymorphisms to examine the genetic effects on the risk of pulmonary TB in Korean subjects by using TaqMan assays and case-control analyses.

RESULTS

Using statistical analyses, one common promoter polymorphism (MC3R rs11575886 T > C) was found to be associated with an increased risk of pulmonary TB. The frequency of the C-bearing genotype of rs11575886 was higher in pulmonary TB patients than in normal controls (p = 0.03, OR = 1.46) although the significance was not retained after correction. In silico analysis for the difference of transcription binding factor (TF), motif between C and T allele demonstrated that the TF motif and its threshold scores of C allele were lower than those of T allele.

CONCLUSIONS

The C allele of rs11575886 could be a risk allele for the pulmonary TB by affecting the binding of TF. Our findings suggest that polymorphisms in MC3R might be one of genetic factors for the risk of pulmonary TB development in Korean subjects.

Melanocortins and the cholinergic anti-inflammatory pathway

Experimental evidence indicates that small concentrations of inflammatory molecules produced by damaged tissues activate afferent signals through ascending vagus nerve fibers, that act as the sensory arm of an "inflammatory reflex". The subsequent activation of vagal efferent fibers, which represent the motor arm of the inflammatory reflex, rapidly leads to acetylcholine release in organs of the reticuloendothelial system. Acetylcholine interacts with α7 subunit-containing nicotinic receptors in tissue macrophages and other immune cells and rapidly inhibits the synthesis/release of tumor necrosis factor-α and other inflammatory cytokines. This neural anti-inflammatory response called "cholinergic anti-inflammatory pathway" is fast and integrated through the central nervous system. Preclinical studies are in progress, with the aim to develop therapeutic agents able to activate the cholinergic anti-inflammatory pathway. Melanocortin peptides bearing the adrenocorticotropin/α-melanocyte-stimulating hormone sequences exert a protective and life-saving effect in animals and humans in conditions of circulatory shock. These neuropeptides are likewise protective in other severe hypoxic conditions, such as prolonged respiratory arrest, myocardial ischemia, renal ischemia and ischemic stroke, as well as in experimental heart transplantation. Moreover, experimental evidence indicates that melanocortins reverse circulatory shock, prevent myocardial ischemia/reperfusion damage and exert neuroprotection against ischemic stroke through activation of the cholinergic anti-inflammatory pathway. This action occurs via stimulation of brain melanocortin MC3/MC4 receptors. Investigations that determine the molecular mechanisms of the cholinergic anti-inflammatory pathway activation could help design of superselective activators of this pathway.

Melanocortins as potential therapeutic agents in severe hypoxic conditions

Melanocortin peptides with the adrenocorticotropin/melanocyte-stimulating hormone (ACTH/MSH) sequences and synthetic analogs have protective and life-saving effects in experimental conditions of circulatory shock, myocardial ischemia, ischemic stroke, traumatic brain injury, respiratory arrest, renal ischemia, intestinal ischemia and testicular ischemia, as well as in experimental heart transplantation. Moreover, melanocortins improve functional recovery and stimulate neurogenesis in experimental models of cerebral ischemia. These beneficial effects of ACTH/MSH-like peptides are mostly mediated by brain melanocortin MC(3)/MC(4) receptors, whose activation triggers protective pathways that counteract the main ischemia/reperfusion-related mechanisms of damage. Induction of signaling pathways and other molecular regulators of neural stem/progenitor cell proliferation, differentiation and integration seems to be the key mechanism of neurogenesis stimulation. Synthesis of stable and highly selective agonists at MC(3) and MC(4) receptors could provide the potential for development of a new class of drugs for a novel approach to management of severe ischemic diseases.

Approaches to the rational design of selective melanocortin receptor antagonists

INTRODUCTION

When establishing the physiological roles of specific receptors in normal and disease states, it is critical to have selective antagonist ligands for each receptor in a receptor system with several subtypes. The melanocortin receptors have five subtypes referred to as the melanocortin 1 receptor, melanocortin 2 receptor, melanocortin 3 receptor, melanocortin 4 receptor and melanocortin 5 receptor, and they are of critical importance for many aspects of human health and disease.

AREAS COVERED

This article reviews the current efforts to design selective antagonistic ligands for the five human melanocortin receptors summarizing the currently published orthosteric and allosteric antagonists for each of these receptors.

EXPERT OPINION

Though there has been progress, there are still few drugs available that address the many significant biological activities and diseases that are associated with these receptors, which is possibly due to the lack of receptor selectivity that these designed ligands are currently showing. The authors believe that further studies into the antagonists' 3D conformational and topographical properties in addition to future mutagenesis studies will provide greater insight into these ligands which could play a role in the treatment of various diseases in the future.

Genetic and pharmacologic blockade of central melanocortin signaling attenuates cardiac cachexia in rodent models of heart failure

The central melanocortin system plays a key role in the regulation of food intake and energy homeostasis. We investigated whether genetic or pharmacologic blockade of central melanocortin signaling attenuates cardiac cachexia in mice and rats with heart failure. Permanent ligation of the left coronary artery (myocardial infarction (MI)) or sham operation was performed in wild-type (WT) or melanocortin-4 receptor (MC4R) knockout mice. Eight weeks after surgery, WT-Sham mice had significant increases in lean body mass (LBM; P<0.05) and fat mass (P<0.05), whereas WT-MI did not gain significant amounts of LBM or fat mass. Resting basal metabolic rate (BMR) was significantly lower in WT-Sham mice compared to WT-MI mice (P<0.001). In contrast, both MC4-Sham and MC4-MI mice gained significant amounts of LBM (P<0.05) and fat mass (P<0.05) over the study period. There was no significant difference in the BMR between MC4-Sham and MC4-MI mice. In the second experiment, rats received aortic bands or sham operations, and after recovery received i.c.v. injections of either artificial cerebrospinal fluid (aCSF) or the melanocortin antagonist agouti-related protein (AGRP) for 2 weeks. Banded rats receiving AGRP gained significant amount of LBM (P<0.05) and fat mass (P<0.05) over the treatment period, whereas banded rats receiving aCSF did not gain significant amounts of LBM or fat mass. These results demonstrated that genetic and pharmacologic blockade of melanocortin signaling attenuated the metabolic manifestations of cardiac cachexia in murine and rat models of heart failure.

Melanocortins counteract inflammatory and apoptotic responses to prolonged myocardial ischemia/reperfusion through a vagus nerve-mediated mechanism

Recently we reported that an efferent vagal fibre-mediated cholinergic protective pathway, activated by melanocortins acting at brain melanocortin MC(3) receptors, is operative in a condition of short-term myocardial ischemia/reperfusion associated with a high incidence of severe arrhythmias and death. Here we investigated melanocortin effects, and the role of the vagus nerve-mediated cholinergic protective pathway, in a rat model of prolonged myocardial ischemia/reperfusion associated with marked inflammatory and apoptotic reactions, and a large infarct size. Ischemia was produced in rats by ligature of the left anterior descending coronary artery for 30 min. At the end of the 2-h reperfusion, western blot analysis of the inflammatory and apoptotic markers tumor necrosis factor-alpha (TNF-alpha), c-jun N-terminal kinases (JNK) and caspase-3, as well as of the anti-apoptotic extracellular signal-regulated kinases (ERK 1/2), was performed in the left ventricle. In saline-treated ischemic rats there was an increase in TNF-alpha levels and in the activity of JNK and caspase-3 accompanied, despite an appreciable ERK 1/2 activation, by a large infarct size. Intravenous treatment, during coronary artery occlusion, with the melanocortin analog [Nle(4), D-Phe(7)]alpha-melanocyte-stimulating hormone (NDP-alpha-MSH) produced a reduction in TNF-alpha levels and in the activity of JNK and caspase-3, associated with marked activation of the pro-survival kinases ERK 1/2, and consequent attenuation of infarct size. Bilateral cervical vagotomy blunted the protective effects of NDP-alpha-MSH. These results indicate that melanocortins modulate the inflammatory and apoptotic cascades triggered by prolonged myocardial ischemia/reperfusion, and reduce infarct size, seemingly by activation of the vagus nerve-mediated cholinergic protective pathway.

Preconditioning by toll-like receptor 2 agonist Pam3CSK4 reduces CXCL1-dependent leukocyte recruitment in murine myocardial ischemia/reperfusion injury

OBJECTIVE

To test whether preconditioning with a toll-like receptor (TLR) 2 agonist protects against myocardial ischemia and reperfusion by interfering with chemokine CXCL1 release from cardiomyocytes.

DESIGN

C3H mice were challenged with vehicle or synthetic TLR2 agonist Pam3Cys-Ser-Lys4 (Pam3CSK4; 1 mg/kg) 24 hrs before myocardial ischemia (20 mins) and reperfusion (2 hrs or 24 hrs). Infarct size, troponin T release, and leukocyte recruitment were quantified. In murine cardiomyocytes (HL-1), we studied the expression/activation profile of TLR2 in response to stimulation with Pam3CSK4 (0.01-1 mg/mL). Furthermore, we studied the chemokine ligand 1 (CXCL1) response to Pam3CSK4 and ischemia/reperfusion in vivo and in vitro.

SETTING

University hospital research laboratory.

SUBJECTS

Anesthetized male mice and murine cardiomyocytes.

MEASUREMENTS AND MAIN RESULTS

Preconditioning by Pam3CSK4 reduced infarct size and troponin T release. This was accompanied by a decreased recruitment of leukocytes into the ischemic area and an improved cardiac function. In HL-1 cells, TLR2 activation amplified the expression of the receptor in a time-dependent manner and led to CXCL1 release in a concentration-dependent manner. Preconditioning by Pam3CSK4 impaired CXCL1 release in response to a second inflammatory stimulus in vivo and in vitro.

CONCLUSIONS

Preconditioning by TLR2 agonist Pam3CSK4 reduces myocardial infarct size after myocardial ischemia/reperfusion. One of the mechanisms involved is a diminished chemokine release from cardiomyocytes, which subsequently limits leukocyte infiltration.

The peptide NDP-MSH induces phenotype changes in the heart that resemble ischemic preconditioning

alpha-Melanocyte-stimulating hormone (alpha-MSH) is a pro-opiomelanocortin (POMC)-derived peptide that exerts multiple protective effects on host cells. Previous investigations showed that treatment with alpha-MSH or synthetic melanocortin agonists reduces heart damage in reperfusion injury and transplantation. The aim of this preclinical research was to determine whether melanocortin treatment induces preconditioning-like cardioprotection. In particular, the plan was to assess whether melanocortin administration causes phenotype changes similar to those induced by repetitive ischemic events. The idea was conceived because both ischemic preconditioning and melanocortin signaling largely depend on cAMP response element binding protein (CREB) phosphorylation. Rats received single i.v. injections of 750microg/kg of the alpha-MSH analogue Nle(4),DPhe(7)-alpha-MSH (NDP-MSH) or saline and were sacrificed at 0.5, 1, 3, or 5h. Western blot analysis showed that rat hearts expressed melanocortin 1 receptor (MC1R) protein. Treatment with NDP-MSH was associated with early and marked increase in interleukin 6 (IL-6) mRNA. This was followed by signal transducer and activator of transcription 3 (STAT3) phosphorylation and induction of suppressor of cytokine signaling 3 (SOCS3). There were no changes in expression of other cytokines of the IL-6 family. Expression of IL-10, IL-1beta, and TNF-alpha was likewise unaltered. In hearts of rats treated with NDP-MSH there was increased expression of the orphan nuclear receptor Nur77. The data indicate that NDP-MSH induces phenotype changes that closely resemble ischemic preconditioning and likely contribute to its established protection against reperfusion injury. In addition, the increased expression of Nur77 and SOCS3 could be part of a broader anti-inflammatory effect.

Inflamed phenotype of the mesenteric microcirculation of melanocortin type 3 receptor-null mice after ischemia-reperfusion

The existence of anti-inflammatory circuits centered on melanocortin receptors (MCRs) has been supported by the inhibitory properties displayed by melanocortin peptides in models of inflammation and tissue injury. Here we addressed the pathophysiological effect that one MCR, MCR type 3 (MC3R), might have on vascular inflammation. After occlusion (35 min) and reopening of the superior mesenteric artery, MC3R-null mice displayed a higher degree of plasma extravasation (45 min postreperfusion) and cell adhesion and emigration (90 min postreperfusion). These cellular alterations were complemented by higher expression of mesenteric tissue CCL2 and CXCL1 (mRNA and protein) and myeloperoxydase, as compared with wild-type animals. MC1R and MC3R mRNA and protein were both expressed in the inflamed mesenteric tissue; however, no changes in vascular responses were observed in a mouse colony bearing an inactive MC1R. Pharmacological treatment of animals with a selective MC3R agonist ([d-Trp⁸]-γ-melanocyte-stimulating hormone; 10 μg i.v.) produced marked attenuation of cell adhesion, emigration, and chemokine generation; such effects were absent in MC3R-null mice. These new data reveal the existence of a tonic inhibitory signal provided by MC3R in the mesenteric microcirculation of the mouse, acting to down-regulate cell trafficking and local mediator generation.—Leoni, G., Patel, H. B., Sampaio, A. L. F., Gavins, F. N. E., Murray, J. F., Grieco, P., Getting, S. J., Perretti, M. Inflamed phenotype of the mesenteric microcirculation of melanocortin type 3 receptor-null mice after ischemia-reperfusion.

Functions of acidic transmembrane residues in human melanocortin-3 receptor binding and activation

The melanocortin-3 receptor (MC3R) is an important regulator of energy homeostasis, inflammation, and cardiovascular function. Inactivating mutations in MC3R gene are associated with childhood obesity. How MC3R binds to its ligands has rarely been studied. In the present study, we systematically mutated all ten acidic residues in transmembrane (TM) domains and measured the cell surface expression levels as well as ligand binding and signaling properties of these mutants. Our results showed that of the 19 mutants stably expressed in HEK293 cells, all were expressed on the cell surface, although some mutants had decreased levels of cell surface expression. We showed that with the superpotent analog [Nle(4), D-Phe(7)]-alpha-melanocyte stimulating hormone (MSH), E92, E131, D154, D158, D178, and D332 are important for ligand binding. D121 and D332 are important for binding and signaling. Further experiments using other ligands such as D-Trp(8)-gamma-MSH, alpha-MSH and gamma-MSH showed that different ligands induce or select different conformations. In summary, we showed that acidic residues in TMs 1 and 3 are important for ligand binding whereas the acidic residues in TMs 2 and 7 are important for both ligand binding and signaling.

Endosomal colocalization of melanocortin-3 receptor and beta-arrestins in CAD cells with altered modification of AKT/PKB

The melanocortin 3-receptor is involved in regulating energy metabolism, body fluid composition and inflammatory responses. Melanocortin receptors function by activating membrane bound adenylate cyclase. However, the literature reports indicate that some G protein coupled receptors (GPCRs) can also activate mitogen activated protein kinase (MAPK) or phosphoinositide 3 kinase (PI3K) signaling pathways consequent to their endocytosis. These studies were undertaken to evaluate the role of these pathways in MC3R signaling in brain-stem neuronal cells. Recruitment of arrestins is implicated in the activation of secondary pathways by GPCRs and our data shows the colocalization of either arrestin B1 or B2 with MC3R in endosomes. An alteration in PKB phosphorylation pattern was observed in MC3R expressing cells independent of agonist stimulation. MC3R transfectants exhibited increased proliferation rates and inhibition of PKB pathway with triciribine abrogated cell proliferation in both vector control and MC3R transfectants. PKB is constitutively active in proliferating CAD cells but could be further activated by culturing the cells in differentiation medium. These studies suggest that the AKT/PKB pathway plays an important role in the proliferation of CAD cells and suggest a link between MC3R and cell growth pathways that may involve the alteration of AKT/PKB signaling pathway.

Adrenocorticotrope hormone fragment (4-10) attenuates the ischemia/reperfusion-induced cardiac injury in isolated rat hearts

The aim of our study was to investigate the contribution of the adrenocorticotropic hormone fragment, ACTH (4-10), on the recovery of postischemic cardiac function. Effects of ACTH (4-10) on caspase-3 activity, cardiomyocyte and endothelial apoptosis, and HO-1 protein expression were studied. Rats were treated with various doses of ACTH (4-10), and then 12 h later, anesthetized, hearts were isolated, perfused, and subjected to 30-min ischemia followed by 120-min reperfusion. Cardiac function including heart rate, coronary flow, aortic flow, and left ventricular developed pressure were recorded. After 120-min reperfusion, 200 mug/kg of ACTH (4-10) significantly improved the recovery of aortic flow, coronary flow, and left ventricular developed pressure from their untreated control values of 15.3 +/- 0.9 ml/min, 6.5 +/- 0.9 ml/min, and 10 +/- 0.6 kPa to 20.7 +/- 1.3 ml/min, 24.8 +/- 1.8 ml/min and 13.7 +/- 0.7 kPa, respectively. Heart rate did not show significant changes during reperfusion. ACTH (4-10) treatment resulted in a reduction in infarct size, caspase 3 activity, apoptosis, and an increase in HO-1 expression. When ACTH (4-10) was given at the moment of reperfusion, the drug failed to improve the postischemic recovery of the myocardium. Thus, ACTH (4-10) can be a useful tool for the prevention of the development of ischemia/reperfusion-induced injury.

Design, synthesis and biological evaluation of ligands selective for the melanocortin-3 receptor

The processed products of the proopiomelanocortin gene (ACTH, alpha-MSH, beta-MSH, gamma-MSH, etc.) interact with five melanocortin receptors, the MC1R, MC2R, MC3R, MC4R, and MC5R to modulate and control many important biological functions crucial for good health both peripherally (as hormones) and centrally (as neurotransmitters). Pivotal biological functions include pigmentation, adrenal function, response to stress, fear/flight, energy homeostasis, feeding behavior, sexual function and motivation, pain, immune response, and many others, and are believed to be involved in many disease states including pigmentary disorders, adrenal disorders, obesity, anorexia, prolonged and neuropathic pain, inflammatory response, etc. The melanocortin-3 receptor (MC3R) is found primarily in the brain and spinal cord and also in the periphery, and its biological functions are still not well understood. Here we review some of the biological functions attributed to the MC3R, and then examine in more detail efforts to design and synthesize ligands that are potent and selective for the MC3R, which might help resolve the many questions still remaining about its function. Though some progress has been made, there is still much to be done in this critical area.

Melanocortin 3 receptors control crystal‐induced inflammation

In this study we have characterized the anti-inflammatory profile of a selective melanocortin type 3 receptor (MC3-R) ligand [D-Trp8]-gamma-MSH, validating in vitro results with analyses in mice deficient for this receptor subtype. In wild-type (WT) macrophages, [D-Trp8]-gamma-MSH activated MC3-R (as tested by accumulation of cyclic AMP) and inhibited (approximately 50%) the release of interleukin (IL)-1 and the chemokine KC (CXCL1), but was ineffective in cells taken from MC3-R null mice. In vivo, administration of 3-30 microg [D-Trp8]-gamma-MSH significantly inhibited leukocyte influx and cytokine production in a model of crystal-induced peritonitis, and these effects were absent in MC3-R null mice or blocked by coadministration of an MC3-R antagonist. Finally, in a model of gouty arthritis, direct injection of urate crystals into the rat joint provoked a marked inflammatory reaction that was significantly inhibited (approximately 70%) by systemic or local administration of [D-Trp8]-gamma-MSH. In conclusion, using an integrated transgenic and pharmacological approach, we provide strong proof of concept for the development of selective MC3-R agonists as novel anti-inflammatory therapeutics.

Targeting melanocortin receptors as potential novel therapeutics

Adrenocorticotrophic hormone (ACTH(1-39)) and the melanocortins (alpha, beta and gamma-melanocyte-stimulating hormone [MSH]) are derived from a larger precursor molecule known as the pro-opiomelanocortin (POMC) protein. They exert their numerous biological effects by activating 7 transmembrane G-protein coupled receptors (GPCR), leading to adenylyl cyclase activation and subsequent cAMP accumulation within the target cell. To date, 5 melanocortin receptors (MCR) have been identified and termed MC1R to MC5R, they have been shown to have a wide and varied distribution throughout the body, being found in the central nervous system (CNS), periphery and immune cells. Melanocortins have a multitude of actions including: (i) modulating disease pathologies including arthritis, asthma, obesity; (ii) affecting functions, for example erectile dysfunction, skin tanning; and (iii) organ systems, for example cardiovascular system. Recently a mechanistic approach has been identified with alpha-MSH preventing NF-kappaB activation via the preservation and expression of IkappaBalphaprotein. This leads to a reduction of pro-inflammatory mediators including cytokines and inhibition of adhesion molecule expression, with subsequent reduction in leukocyte emigration. Development of selective ligands with an appropriate pharmacokinetic profile will enable a pharmacological evaluation of the potential beneficial effects of the melanocortins. In this review I have discussed the potential mechanistic action for the melanocortins and some of the disease pathologies shown to be modulated. This review proposes targeting the MCR with the ultimate aim of controlling many of the diseases that we face today.

Melanocortin receptor signaling in RAW264.7 macrophage cell line

Melanocortin peptides modulate cytokine release and adhesion molecule expression. Here we have investigated the early cell-signaling pathway responsible for the induction of interleukin-10 (IL-10) in RAW264.7 cells. Cell incubation with ACTH(1-39) or MTII (melanotan II) did not alter ERK1/2 and JNK phosphorylation, while p38 phosphorylation and intracellular cAMP accumulation occurred within minutes. ACTH(1-39) and MTII provoked a time-dependent accumulation of IL-10 that was abrogated by the PKA inhibitor H-89 and only partially blocked by the p38 MAPK inhibitor SB203580. Thus, in RAW264.7 cells, IL-10 induction by the melanocortins is via the PKA pathway, and this mechanism could contribute to their anti-inflammatory profile.

The melanocortin peptide HP228 displays protective effects in acute models of inflammation and organ damage

The clinically efficacious melanocortin peptide HP228 has here been investigated for its anti-inflammatory efficacy. In this study we have investigated the efficacy of HP228 in murine acute models of inflammation and myocardial ischaemia. Systemic treatment of mice with HP228 inhibited neutrophil accumulation in zymosan; urate crystal and carrageenan induced inflammatory models. In the urate model this was due to inhibition of pro-inflammatory chemokines and cytokines, whilst different mechanisms exist for zymosan peritonitis and carrageenan-induced air-pouch inflammation. HP228 was next evaluated in a model of myocardial ischaemia, another condition where cytokines and neutrophils are thought to play a causal role. HP228 caused a 50% reduction in myocardial damage following reperfusion. HP228 therefore inhibits the most important facet of the host inflammatory response namely leukocyte migration. These data show for the first time that the clinically efficacious peptide HP228 displays protective effects in models of inflammation and organ damage.

Activation of an efferent cholinergic pathway produces strong protection against myocardial ischemia/reperfusion injury in rats

OBJECTIVE

A vagus nerve-mediated, brain cholinergic protective mechanism activated by melanocortin peptides is operative in conditions of circulatory shock; moreover, there is anatomical evidence of dual vagal-cardiac efferent pathways in rats, which could play different roles in controlling heart function. Therefore, we investigated the role and functional mechanism of such vagal efferent pathway(s) in an experimental model of ischemic heart disease.

DESIGN

Randomized experimental study.

SETTING

Research laboratory.

SUBJECTS

Adult Wistar rats of either sex.

INTERVENTIONS

After bilateral cervical vagotomy (with or without pretreatment with atropine), efferent vagal fibers were electrically stimulated in rats subjected to coronary artery occlusion (5 mins) followed by reperfusion (5 mins). Other rats (intact, vagotomized, or pretreated with atropine) were treated with nanomolar doses of melanocortin peptides.

MEASUREMENTS AND MAIN RESULTS

Electrical stimulation of efferent vagal fibers (5 V, 2 m secs, 1-9 Hz, for the whole period of ischemia/reperfusion) strongly reduced the high incidence of severe arrhythmias and lethality, reduced the increase in free radical blood levels and left-ventricle histologic alterations, and augmented the extracellular signal-regulated kinase activation. Treatment with the melanocortin peptides adrenocorticotropin and gamma2-melanocyte-stimulating hormone (162 nmol/kg intravenously or 16.2 nmol/kg intracerebroventricularly, during coronary occlusion) produced the same protective effects of electrical stimulation and with the same muscarinic acetylcholine receptor-dependent mechanism, seemingly through brain activation (mediated by melanocortin MC3 receptors, as previously described) of such efferent vagal pathway.

CONCLUSIONS

The present results give evidence for the identification of a protective, melanocortin-activated, efferent vagal cholinergic pathway, operative in conditions of myocardial ischemia/reperfusion. These data suggest that melanocortins and pertinent compounds able to activate such a pathway could provide the potential for development of a new class of drugs for a novel approach to management of ischemic heart disease.

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.

Molecular mechanisms of the neural melanocortin receptor dysfunction in severe early onset obesity

The neural melanocortin receptors, melanocortin-3 and -4 receptors (MC3R and MC4R), have been shown to regulate different aspects of energy homeostasis in rodents. Human genetic studies showed that mutations in the MC4R gene are the most common monogenic form of obesity. Functional analyses of the mutant receptors revealed multiple defects. A classification scheme is presented for cataloguing the ever-increasing array of MC4R mutations. Functional analysis of the only inactivating MC3R mutation is also summarized. Insights from the analyses of the naturally occurring mutations in the MC3R and MC4R on the structure and function of these receptors are highlighted.