The role of melanocortins and their receptors in inflammatory processes, nerve regeneration and nociception

Synthetic Adrenocorticotropic Peptides Modulate the Expression Pattern of Immune Genes in Rat Brain following the Early Post-Stroke Period

Ischemic stroke is an acute local decrease in cerebral blood flow due to a thrombus or embolus. Of particular importance is the study of the genetic systems that determine the mechanisms underlying the formation and maintenance of a therapeutic window (a time interval of up to 6 h after a stroke) when effective treatment can be provided. Here, we used a transient middle cerebral artery occlusion (tMCAO) model in rats to study two synthetic derivatives of adrenocorticotropic hormone (ACTH). The first was ACTH(4-7)PGP, which is known as Semax. It is actively used as a neuroprotective drug. The second was the ACTH(6-9)PGP peptide, which is elucidated as a prospective agent only. Using RNA-Seq analysis, we revealed hundreds of ischemia-related differentially expressed genes (DEGs), as well as 131 and 322 DEGs related to the first and second peptide at 4.5 h after tMCAO, respectively, in dorsolateral areas of the frontal cortex of rats. Furthermore, we showed that both Semax and ACTH(6-9)PGP can partially prevent changes in the immune- and neurosignaling-related gene expression profiles disturbed by the action of ischemia at 4.5 h after tMCAO. However, their different actions with regard to predominantly immune-related genes were also revealed. This study gives insight into how the transcriptome depends on the variation in the structure of the related peptides, and it is valuable from the standpoint of the development of measures for early post-stroke therapy.

Elevated Neuropeptides in Dry Eye Disease and Their Clinical Correlations

PURPOSE

The goal of this study was to assess neuropeptide levels in patients with dry eye disease (DED) and investigate their correlations with clinical characteristics.

METHODS

This study included 38 eyes of 38 patients diagnosed with DED (DED group) and 38 eyes of 38 healthy volunteers without DED (control group). Ocular surface evaluation was performed. The severity of dry eye symptoms and signs in the DED group was graded. Neuropeptides [substance P (SP), alpha-melanocyte-stimulating hormone (α-MSH), β-endorphin, neurotensin, and oxytocin] and inflammatory cytokines levels were measured in basal tears. The link between neuropeptides and clinical parameters was investigated using Spearman rank correlation.

RESULTS

Overall, 76.3% of patients in the DED group showed dry eye symptoms and signs that were inconsistent in severity. Compared with the control group, the DED group showed higher levels of SP, α-MSH, and oxytocin in tears (P = 0.012, P = 0.030, and P = 0.006, respectively), but similar levels of β-endorphin and neurotensin (P = 0.269 and P = 0.052). The levels of SP, α-MSH, and oxytocin were elevated in DED patients with higher grading of symptoms than clinical signs (all P < 0.05). SP, α-MSH, and oxytocin levels in tears were positively correlated with Ocular Surface Disease Index scores, frequency of sensitivity to light, and frequency of blurred vision (all P < 0.05).

CONCLUSIONS

The increased tear levels of SP, α-MSH, and oxytocin may be linked to ocular discomfort in DED. Neuropeptides may play a key role in the development of DED, especially in DED patients with more severe symptoms than clinical signs.

Real-world treatment patterns for repository corticotropin injection in patients with rheumatoid arthritis

Introduction

Repository corticotropin injection (RCI, Acthar^® Gel) is a naturally sourced mixture of adrenocorticotropic hormone analogues and other pituitary peptides with anti-inflammatory and immunomodulatory effects. In a recent clinical trial, RCI was safe and effective for the treatment of refractory rheumatoid arthritis (RA). This study aims to describe real-world use and outcomes of patients with RA who were prescribed RCI in clinical practice through retrospective analysis of an electronic medical record database.

Methods

Patients with RA who were prescribed RCI were identified through the Columbus^TM electronic medical record repository, representing approximately 100 rheumatology practices. Demographics, medications, comorbidities, disease histories, laboratory evaluations, clinical outcomes and patient-reported outcomes were evaluated from 12 months pre-RCI to 12 months post-RCI initiation.

Results

The RCI cohort (n=63) comprised predominantly white women, aged 54 years on average, at 6 years from RA diagnosis, with high disease activity at baseline according to Clinical Disease Activity Index (CDAI) and Routine Assessment of Patient Index Data 3 (RAPID3) scores. Within the 12 months pre-RCI initiation, 87% of patients were prescribed disease-modifying antirheumatic drugs and 67% were prescribed glucocorticoids. Twelve months post-RCI initiation, glucocorticoid, opioid and non-steroidal anti-inflammatory drug prescriptions decreased; disease-modifying antirheumatic drug prescriptions remained stable. Reductions in CDAI, RAPID3, physician global assessment, tender joint count, swollen joint count, and pain visual analogue scale scores were observed 12 months post-RCI initiation. Few discontinuations were due to side effects. Study limitations included small sample size and incomplete electronic medical record data.

Conclusion

These findings support the safety and effectiveness of RCI for short-term adjunctive treatment of refractory RA and provide patient-management insights from routine clinical practice.

Bifunctional Opioid/Melanocortin Peptidomimetics for Use in Neuropathic Pain: Variation in the Type and Length of the Linker Connecting the Two Pharmacophores

Based on the mechanism of neuropathic pain induction, a new type of bifunctional hybrid peptidomimetics was obtained for potential use in this type of pain. Hybrids consist of two types of pharmacophores that are connected by different types of linkers. The first pharmacophore is an opioid agonist, and the second pharmacophore is an antagonist of the pronociceptive system, i.e., an antagonist of the melanocortin-4 receptor. The results of tests in acute and neuropathic pain models of the obtained compounds have shown that the type of linker used to connect pharmacophores had an effect on antinociceptive activity. Peptidomimetics containing longer flexible linkers were very effective at low doses in the neuropathic pain model. To elucidate the effect of linker lengths, two hybrids showing very high activity and two hybrids with lower activity were further tested for affinity for opioid (mu, delta) and melanocortin-4 receptors. Their complexes with the target receptors were also studied by molecular modelling. Our results do not show a simple relationship between linker length and affinity for particular receptor types but suggest that activity in neuropathic pain is related to a proper balance of receptor affinity rather than maximum binding to any or all of the target receptors.

ACTH(6-9)PGP Peptide Protects SH-SY5Y Cells from H2O2, tert-Butyl Hydroperoxide, and Cyanide Cytotoxicity via Stimulation of Proliferation and Induction of Prosurvival-Related Genes

Stabilized melanocortin analog peptide ACTH(6-9)PGP (HFRWPGP) possesses a wide range of neuroprotective activities. However, its mechanism of action remains poorly understood. In this paper, we present a study of the proproliferative and cytoprotective activity of the adrenocorticotropic hormone fragment 6-9 (HFRW) linked with the peptide prolyine-glycyl-proline on the SH-SY5Y cells in the model of oxidative stress-related toxicity. The peptide dose-dependently protected cells from H2O2, tert-butyl hydroperoxide, and KCN and demonstrated proproliferative activity. The mechanism of its action was the modulation of proliferation-related NF-κB genes and stimulation of prosurvival NRF2-gene-related pathway, as well as a decrease in apoptosis.

Novel bifunctional hybrid compounds designed to enhance the effects of opioids and antagonize the pronociceptive effects of nonopioid peptides as potent analgesics in a rat model of neuropathic pain

ABSTRACT

The purpose of our work was to determine the role of nonopioid peptides derived from opioid prohormones in sensory hypersensitivity characteristics of neuropathic pain and to propose a pharmacological approach to restore the balance of these endogenous opioid systems. Nonopioid peptides may have a pronociceptive effect and therefore contribute to less effective opioid analgesia in neuropathic pain. In our study, we used unilateral chronic constriction injury (CCI) of the sciatic nerve as a neuropathic pain model in rats. We demonstrated the pronociceptive effects of proopiomelanocortin- and proenkephalin-derived nonopioid peptides assessed by von Frey and cold plate tests, 7 to 14 days after injury. The concentration of proenkephalin-derived pronociceptive peptides was increased more robustly than that of Met-enkephalin in the ipsilateral lumbar spinal cord of CCI-exposed rats, as shown by mass spectrometry, and the pronociceptive effect of one of these peptides was blocked by an antagonist of the melanocortin 4 (MC4) receptor. The above results confirm our hypothesis regarding the possibility of creating an analgesic drug for neuropathic pain based on enhancing opioid activity and blocking the pronociceptive effect of nonopioid peptides. We designed and synthesized bifunctional hybrids composed of opioid (OP) receptor agonist and MC4 receptor antagonist (OP-linker-MC4). Moreover, we demonstrated that they have potent and long-lasting antinociceptive effects after a single administration and a delayed development of tolerance compared with morphine after repeated intrathecal administration to rats subjected to CCI. We conclude that the bifunctional hybrids OP-linker-MC4 we propose are important prototypes of drugs for use in neuropathic pain.

Repository Corticotropin Injection for Active Rheumatoid Arthritis Despite Aggressive Treatment: A Randomized Controlled Withdrawal Trial

INTRODUCTION

The objective of this study was to assess efficacy and safety of repository corticotropin injection (RCI) in subjects with active rheumatoid arthritis (RA) despite treatment with a corticosteroid and one or two disease-modifying antirheumatic drugs (DMARDs).

METHODS

All subjects received open-label RCI (80 U) twice weekly for 12 weeks (part 1); only those with low disease activity [LDA; i.e., Disease Activity Score 28 joint count and erythrocyte sedimentation rate (DAS28-ESR) < 3.2] were randomly assigned to receive either RCI (80 U) or placebo twice weekly during the 12-week double-blind period (part 2). The primary efficacy endpoint was the proportion of subjects who achieved LDA at week 12. Secondary efficacy endpoints included proportions of subjects who maintained LDA during weeks 12 through 24 and achieved Clinical Disease Activity Index (CDAI) ≤ 10 at weeks 12 and 24. Safety was assessed via adverse event reports.

RESULTS

Of the 259 enrolled subjects, 235 completed part 1; 154 subjects (n = 77 each for RCI and placebo) entered part 2, and 127 (RCI, n = 71; placebo, n = 56) completed. At week 12, 163 subjects (62.9%) achieved LDA and 169 (65.3%) achieved CDAI ≤ 10 (both p < 0.0001). At week 24, 47 (61.0%) RCI-treated and 32 (42.1%) placebo-treated subjects maintained LDA (p = 0.019); 66 (85.7%) RCI-treated and 50 (65.8%) placebo-treated subjects maintained CDAI ≤ 10 (p = 0.004). No unexpected safety signals were observed.

CONCLUSIONS

RCI was effective and generally safe in patients with active RA despite corticosteroid/DMARD therapy. By week 12, > 60% of patients achieved LDA, which was maintained with 12 additional weeks of treatment. Most patients who achieved LDA maintained it for 3 months after RCI discontinuation.

TRIAL REGISTRATION

Clinicaltrials.gov identifier NCT02919761.

Neuropeptides and Microglial Activation in Inflammation, Pain, and Neurodegenerative Diseases

Microglial cells are responsible for immune surveillance within the CNS. They respond to noxious stimuli by releasing inflammatory mediators and mounting an effective inflammatory response. This is followed by release of anti-inflammatory mediators and resolution of the inflammatory response. Alterations to this delicate process may lead to tissue damage, neuroinflammation, and neurodegeneration. Chronic pain, such as inflammatory or neuropathic pain, is accompanied by neuroimmune activation, and the role of glial cells in the initiation and maintenance of chronic pain has been the subject of increasing research over the last two decades. Neuropeptides are small amino acidic molecules with the ability to regulate neuronal activity and thereby affect various functions such as thermoregulation, reproductive behavior, food and water intake, and circadian rhythms. Neuropeptides can also affect inflammatory responses and pain sensitivity by modulating the activity of glial cells. The last decade has witnessed growing interest in the study of microglial activation and its modulation by neuropeptides in the hope of developing new therapeutics for treating neurodegenerative diseases and chronic pain. This review summarizes the current literature on the way in which several neuropeptides modulate microglial activity and response to tissue damage and how this modulation may affect pain sensitivity.

Multiple beneficial effects of melanocortin MC4 receptor agonists in experimental neurodegenerative disorders: Therapeutic perspectives

Melanocortin peptides induce neuroprotection in acute and chronic experimental neurodegenerative conditions. Melanocortins likewise counteract systemic responses to brain injuries. Furthermore, they promote neurogenesis by activating critical signaling pathways. Melanocortin-induced long-lasting improvement in synaptic activity and neurological performance, including learning and memory, sensory-motor orientation and coordinated limb use, has been consistently observed in experimental models of acute and chronic neurodegeneration. Evidence indicates that the neuroprotective and neurogenic effects of melanocortins, as well as the protection against systemic responses to a brain injury, are mediated by brain melanocortin 4 (MC₄) receptors, through an involvement of the vagus nerve. Here we discuss the targets and mechanisms underlying the multiple beneficial effects recently observed in animal models of neurodegeneration. We comment on the potential clinical usefulness of melanocortin MC₄ receptor agonists as neuroprotective and neuroregenerative agents in ischemic stroke, subarachnoid hemorrhage, traumatic brain injury, spinal cord injury, and Alzheimer's disease.

Beneficial Effect of Covalently Grafted α-MSH on Endothelial Release of Inflammatory Mediators for Applications in Implantable Devices

Intravascular devices for continuous glucose monitoring are promising tools for the follow up and treatment of diabetic patients. Limiting the inflammatory response to the implanted devices in order to achieve better biocompatibility is a critical challenge. Herein we report on the production and the characterization of gold surfaces covalently derivatized with the peptide α-alpha-melanocyte stimulating hormone (α-MSH), with a quantifiable surface density. In vitro study demonstrated that the tethered α-MSH is able to decrease the expression of an inflammatory cytokine produced by endothelial cells.

Hsa-miR-34a mediated repression of corticotrophin releasing hormone receptor 1 regulates pro-opiomelanocortin expression in patients with complex regional pain syndrome

Background

Ketamine provides relief for a subset of patients with complex regional pain syndrome (CRPS). The poor responders had a lower body mass index (BMI) relative to responders. Regulation of proopiomelanocortin (POMC) expression is crucial in normal body weight homeostasis. The main objectives of this study were to investigate the mechanisms underlying lower BMI characterizing CRPS patients responding poorly to intravenous ketamine therapy and identify potential biomarkers for predicting response.

Methods

We investigated POMC transcript levels in blood from CRPS patients grouped as responders and poor responders to ketamine therapy. Plasma levels of β-endorphin, ACTH and α-MSH were measured by ELISA. We previously identified differential expression of small noncoding microRNA hsa-miR-34a in blood between responders and poor responders. We investigated whether a 11-fold downregulation of hsa-miR-34a in poor responders relative to responders is contributing to the differences in POMC levels by targeting POMC regulator CRHR1. Binding of miR-34a to CRHR1 was assessed using reporter assay; changes in mRNA and protein levels of CRHR1 were used to determine the regulation of CRHR1 by miR-34a. RNA from blood of CRPS and control subjects were used for quantitative PCR for CRHR1.

Results

Though ketamine treatment did not alter POMC expression, poor responders had higher levels of POMC mRNA than responders, both before and after treatment. Corticotropin-releasing hormone (CRH) is a key regulator of POMC expression and the biological effects are mediated through its receptor corticotrophin releasing hormone receptor 1 (CRHR1). We show that hsa-miR-34a is a negative regulator of CRHR1; overexpression of hsa-miR-34a in Jurkat cells resulted in reduction of CRH-mediated POMC expression. Poor responders had higher expression of CRHR1 transcripts than responders, indicating a regulatory role for miR-34a. In addition, we found positive correlations between the pretreatment levels of miR-34a to BMI and response to ketamine therapy.

Conclusions

Our findings indicate a mechanism by which hsa-miR-34a can regulate the CRH/CRHR1/POMC axis and may influence BMI. Studies in larger patient cohorts are required to confirm the biomarker utility of circulating hsa-miR-34a levels in predicting treatment response to ketamine therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0820-1) contains supplementary material, which is available to authorized users.

Sex, social status and physiological stress in primates: the importance of social and glucocorticoid dynamics

Social status has been associated with health consequences, although the mechanisms by which status affects health are relatively unknown. At the physiological level, many studies have investigated the potential relationship between social behaviour/rank and physiological stress, with a particular focus on glucocorticoid (GC) production. GCs are of interest because of their experimentally established influence on health-related processes such as metabolism and immune function. Studies in a variety of species, in both naturalistic and laboratory settings, have led to complex outcomes. This paper reviews findings from primates and rodents and proposes a psychologically and physiologically relevant framework in which to study the relationship between social status and GC function. We (i) compare status-specific GC production between male and female primates, (ii) review the functional significance of different temporal patterns of GC production, (iii) propose ways to assess these temporal dynamics, and (iv) present novel hypotheses about the relationship between social status and GC temporal dynamics, and potential fitness and health implications. To understand whether GC production mediates social status-related fitness disparities, we must consider social contest conditions and the temporal dynamics of GC production. This framework will provide greater insights into the relationship between social status, physiological stress and health.

Sex, social status and physiological stress in primates: the importance of social and glucocorticoid dynamics

Social status has been associated with health consequences, although the mechanisms by which status affects health are relatively unknown. At the physiological level, many studies have investigated the potential relationship between social behaviour/rank and physiological stress, with a particular focus on glucocorticoid (GC) production. GCs are of interest because of their experimentally established influence on health-related processes such as metabolism and immune function. Studies in a variety of species, in both naturalistic and laboratory settings, have led to complex outcomes. This paper reviews findings from primates and rodents and proposes a psychologically and physiologically relevant framework in which to study the relationship between social status and GC function. We (i) compare status-specific GC production between male and female primates, (ii) review the functional significance of different temporal patterns of GC production, (iii) propose ways to assess these temporal dynamics, and (iv) present novel hypotheses about the relationship between social status and GC temporal dynamics, and potential fitness and health implications. To understand whether GC production mediates social status-related fitness disparities, we must consider social contest conditions and the temporal dynamics of GC production. This framework will provide greater insights into the relationship between social status, physiological stress and health.

Intracellular signaling mechanisms of the melanocortin receptors: current state of the art

The melanocortin system is composed by the agonists adrenocorticotropic hormone and α, β and γ-melanocyte-stimulating hormone, and two naturally occurring antagonists, agouti and agouti-related protein. These ligands act by interaction with a family of five melanocortin receptors (MCRs), assisted by MCRs accessory proteins (MRAPs). MCRs stimulation activates different signaling pathways that mediate a diverse array of physiological processes, including pigmentation, energy metabolism, inflammation and exocrine secretion. This review focuses on the regulatory mechanisms of MCRs signaling, highlighting the differences among the five receptors. MCRs signal through G-dependent and independent mechanisms and their functional coupling to agonists at the cell surface is regulated by interacting proteins, namely MRAPs and β-arrestins. The knowledge of the distinct modulation pattern of MCRs signaling and function may be helpful for the future design of novel drugs able to combine specificity, safety and effectiveness in the course of their therapeutic use.

Blockage of melanocortin-4 receptors by intranasal HS014 attenuates single prolonged stress-triggered changes in several brain regions

Melanocortin receptor four (MC4R) is implicated in regulation of stress-related functions. We previously demonstrated that intranasal infusion of MC4R antagonist HS014, shortly before single prolonged stress (SPS) animal model of post-traumatic stress disorder, lessened the development of anxiety- and depression-like behavior depending on the dose. Here, we evaluated effects of HS014 on SPS-elicited changes in hypothalamic-pituitary-adrenal axis and expression of several genes of interest in mediobasal hypothalamus, hippocampus, and locus coeruleus. Rats were given intranasal infusion of HS014 (3.5 ng or 100 μg) and 30 min later subjected to SPS stressors. Short-term responses of HS014 rats in comparison with vehicle-treated, evident 30 min following SPS stressors, included smaller rise in plasma corticosterone (100 μg HS014), absence of induction of corticotrophin-releasing hormone mRNA in mediobasal hypothalamus and of mRNA for tyrosine hydroxylase and dopamine-β hydroxylase in locus coeruleus. Long-term responses found 7 days after SPS stressors, included lower induction corticotrophin-releasing hormone mRNA levels in the mediobasal hypothalamus without effect on mRNAs for the glucocorticoid receptor (GR) and FK506-binding protein 51 (FKBP5), a component of GR co-chaperone complex; and no induction of GR protein in ventral hippocampus. Thus, antagonism of MC4R prior to SPS attenuates development of several abnormalities in gene expression in regions implicated in post-traumatic stress disorder. Blockade of brain melanocortine receptor 4 (MC4R) with intranasal infusion of the MC4R antagonist HS014 to rats prior to single prolonged stress (SPS) leads to faster termination of stress responses (30 min later) and prevents or attenuates SPS-triggered abnormal gene expression related to post-traumatic stress disorder (7 days later). Targeting of brain MC4R is a promising strategy to protect HPA axis, LC-NE (locus coeruleus-norepinephrine) systems and hippocampus from overstimulation.

Resolution of inflammation: examples of peptidergic players and pathways

Appreciation for the resolution of inflammation has increased in recent years, with the detailing of specific mediators and pathways and the identification of (receptor) targets that could be exploited for innovative anti-inflammatory drug discovery programmes. Thus, acute inflammation resolves by the intervention of endogenous anti-inflammatory mediators that reduce white blood cell recruitment and promote removal of migrated leukocytes by apoptosis and phagocytosis by resident 'cleaners', such as the macrophages, resulting ultimately in the repair of the inflamed or injured tissue. Here, we explore a selection of pro-resolving proteinaceous mediators and targets, such as melanocortins and galectins.

Intranasal infusion of melanocortin receptor four (MC4R) antagonist to rats ameliorates development of depression and anxiety related symptoms induced by single prolonged stress

Brain melanocortinergic systems and specifically melanocortin receptor four (MC4R) are implicated in modulation of anxiety- and depressive-like behavior induced by mild or moderate stress. Here we examine whether blockage of central MC4Rs with HS014 before severe traumatic stress may protect against development of anxiety and depression co-morbid with post-traumatic stress disorder (PTSD). Male rats were treated intranasally (IN) with vehicle or varied doses of HS014, 30min prior to single prolonged stress (SPS) animal model of PTSD. IN administration of 100μg HS014 pre-SPS improved despair behavior in forced swim (FS) immediately after immobilization stress part of SPS protocol. During all 4 intervals of 20min FS these rats spent less time immobile than rats given vehicle or 3.5ng HS014. This dose of HS014 also had a long-term beneficial effect manifested as reduction of immobility time in forced swim test performed after SPS. However, both HS014 doses were effective in ameliorating development of anxiety-like behavior after traumatic stress. Thus, rats given IN HS014 prior to SPS exhibited less open arms (OA) visits in elevated plus maze (EPM), spent longer time in OA and less in closed arms, had lower anxiety index, higher risk assessment and more head dips over borders in OA. They also spent longer time in the center of the open field and defecated less. Reduced grooming behavior in EPM was observed with 100μg HS014. This is the first study revealing pronounced resilience effects of HS014 on development of behavioral symptoms co-morbid with PTSD.

Melanocortins in brain inflammation: the role of melanocortin receptor subtypes

The melanocortins (MC) are released from neurons and paracrine cells in the CNS where they are involved in important physiological functions, including regulation of body temperature and immune responses. MC bind to melanocortin receptors, a class of cell surface G-protein-coupled receptors. Of the five subtypes of MC receptors that have been cloned in mammals, the MC1, MC3, MC4 and MC5 receptors are expressed in brain tissues. Expression of MC receptors in both brain cells and cells of the immune system suggests direct involvement of MC in regulation of inflammatory processes in the brain. The binding of MC to MC receptors induces activation of adenylate cyclase, increase in intracellular cAMP level and, consequently, inhibition of the nuclear transcription factor kappaB (NF-κB) signalling. Inflammatory processes contribute to development of severe CNS diseases, both in acute and chronic conditions. Thus far, the anti-inflammatory effects of MC in the CNS have been mainly studied using peptides that are relatively unselective for individual MC receptor subtypes. Consequently, these studies do not allow identification of specific MC receptor(s) involved in the regulation of inflammatory processes. However, recently synthesized ligands selective for individual MC receptors indicated that both MC4 and MC3 agonists are promising anti-inflammatory agents in treatment of brain inflammation.

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.

Immunosuppressive activity of a novel peptide analog of α-melanocyte stimulating hormone (α-MSH) in experimental autoimmune uveitis

Autoimmune uveitis is an inflammatory disorder of the eye that can lead to pain and vision loss. Steroids and immunosuppressive drugs are currently the only therapeutics for uveitis and have serious ocular and systemic toxicities. Therefore, safer alternative therapeutics are desired. Alpha-melanocyte stimulating hormone (α-MSH) is a neuropeptide that suppresses effector T cell functions, induces regulatory T cells and has beneficial effects in certain autoimmune and transplant models. A novel d-amino acid peptide analog of native α-MSH (dRI-α-MSH) was produced that was protected from protease digestion and had increased selectivity for the melanocortin-1 receptor. Systemic delivery of the dRI-α-MSH analog dramatically suppressed disease progression and retained retinal architecture in the experimental autoimmune uveitis (EAU) model. Local delivery by periorbital injection was equally effective. Importantly, treatment with the novel dRI-α-MSH analog suppressed uveitis with a similar magnitude to the corticosteroid, dexamethasone. Data indicate that the novel dRI-α-MSH analogs show anti-inflammatory activities and have potential therapeutic use in uveitis and other autoimmune diseases.

Hypothalamic opioid-melanocortin appetitive balance and addictive craving

Whilst the parallels between drug and food craving are receiving increasing attention, the recently elucidated complex physiology of the hypothalamic appetite regulatory centres has been largely overlooked in the efforts to understand drug craving which is one of the most refractory and problematic aspects of drug and behavioural addictions. Important conceptual gains could be made by researchers from both appetite and addiction neuroscience if they were to have an improved understanding of each others' disciplines. It is well known in addiction medicine that the use of many substances is elevated in opiate dependency. There is voluminous evidence of very high rates of drug use in opiate agonist maintained patients, and the real possibility exists that opiate agonist therapy therefore increases drug craving. Conversely, opiate antagonist therapy with naloxone or naltrexone has been shown to reduce most chemical and behavioural addictions, and naltrexone is now being developed together with bupropion as the anti-obesity drug "Contrave". Hypothalamic melanocortins, particularly α-MSH, are known to constitute the main brake to consumptive behaviour of food. There is a well described antagonism between melanocortins and opioids at many loci including the hypothalamus. Administration of exogenous opiates is known to both suppress α-MSH and to stimulate hedonic food consumption. Opiate maintenance programs are associated with weight gain. As monoamines, opioids and cannabinoids are known to be involved in appetite regulation, and as endorphin opioids are known to be perturbed in other addictions, further exploration of the hypothalamic appetite regulatory centre would appear to be an obvious, albeit presently largely overlooked, locus in which to study drug and other craving mechanisms.

Melanocortin receptors and their accessory proteins

The melanocortin receptor family consists of 5 members which belong to the GPCR superfamily. Their specific ligands, the melanocortins are peptide hormones which are formed by the proteolytic cleavage of the proopiomelanocortin (POMC) protein. It is now recognised that certain GPCRs require accessory proteins for their function. Like these GPCRs the melanocortin receptor family is also known to be associated with accessory proteins that regulate their function. In this review we will summarise the accessory proteins involved in the function of the 5 melanocortin receptors and in particular focus on the melanocortin 2 receptor accessory protein (MRAP) which is crucial for the function of the MC2R.

Identification of domains responsible for specific membrane transport and ligand specificity of the ACTH receptor (MC2R)

The adrenocorticotropic hormone (ACTH) receptor has highly specific membrane expression that is limited to adrenal cells; in other cell types the polypeptide fails to be transported to the cell surface. Unlike other evolutionarily related members of the melanocortin receptor family (MC1R-MC5R) that recognize different melanocortin peptides, ACTHR (MC2R) binds only ACTH. We used a mutagenesis approach involving systematic construction of chimeric ACTHR/MC4R receptors to identify the domains determining the selectivity of ACTHR membrane transport and ACTH binding. In total 15 chimeric receptors were created by replacement of selected domains of human ACTHR with the corresponding regions of human MC4R. We developed an analytical method to accurately quantify cell-membrane localization of recombinant receptors fused with enhanced green fluorescent protein by confocal fluorescence microscopy. The chimeric receptors were also tested for their ability to bind ACTH (1-24) and the melanocyte-stimulating hormone (MSH) analog, Nle4, DPhe7-alpha-MSH, and to induce a cAMP response. Our results indicate that substitution of the MC4R N-terminal segment with the homologous segment of ACTHR significantly decreased membrane transport. We also identified another signal localized in the third and fourth transmembrane regions as the main determinant of ACTHR intracellular retention. In addition, we found that the fourth and fifth transmembrane domains of the ACTHR are involved in ACTH binding selectivity. We discuss the mechanisms involved in bypassing these arrest signals via an interaction with melanocortin 2 receptor accessory protein (MRAP) and the possible mechanisms that determine the high ligand-binding specificity of ACTHR.

In search of analgesia: emerging roles of GPCRs in pain

Of all clinically marketed drugs, greater than thirty percent are modulators of G protein-coupled receptors (GPCRs). Nearly 400 GPCRs (i.e., excluding odorant and light receptors) are encoded within the human genome, but only a small fraction of these seven-transmembrane proteins have been identified as drug targets. Chronic pain affects more than one-third of the population, representing a substantial societal burden in use of health care resources and lost productivity. Furthermore, currently available treatments are often inadequate, underscoring the significant need for better therapeutic strategies. The expansion of the identified human GPCR repertoire, coupled with recent insights into the function and structure of GPCRs, offers new opportunities for the development of novel analgesic therapeutics.

Mahogunin ring finger-1 (MGRN1) E3 ubiquitin ligase inhibits signaling from melanocortin receptor by competition with Galphas

Mahogunin ring finger-1 (MGRN1) is a RING domain-containing ubiquitin ligase mutated in mahoganoid, a mouse mutation causing coat color darkening, congenital heart defects, high embryonic lethality, and spongiform neurodegeneration. The melanocortin hormones regulate pigmentation, cortisol production, food intake, and body weight by signaling through five G protein-coupled receptors positively coupled to the cAMP pathway (MC1R-MC5R). Genetic analysis has shown that mouse Mgrn1 is an accessory protein for melanocortin signaling that may inhibit MC1R and MC4R by unknown mechanisms. These melanocortin receptors (MCRs) regulate pigmentation and body weight, respectively. We show that human melanoma cells express 4 MGRN1 isoforms differing in the C-terminal exon 17 and in usage of exon 12. This exon contains nuclear localization signals. MGRN1 isoforms decreased MC1R and MC4R signaling to cAMP, without effect on beta(2)-adrenergic receptor. Inhibition was independent on receptor plasma membrane expression, ubiquitylation, internalization, or stability and occurred upstream of Galpha(s) binding to/activation of adenylyl cyclase. MGRN1 co-immunoprecipitated with MCRs, suggesting a physical interaction of the proteins. Significantly, overexpression of Galpha(s) abolished the inhibitory effect of MGRN1 and decreased co-immunoprecipitation with MCRs, suggesting competition between MGRN1 and Galpha(s) for binding to MCRs. Although all MGRN1s were located in the cytosol in the absence of MCRs, exon 12-containing isoforms accumulated in the nuclei upon co-expression with the receptors. Therefore, MGRN1 inhibits MCR signaling by a new mechanism involving displacement of Galpha(s), thus accounting for key features of the mahoganoid phenotype. Moreover, MGRN1 might provide a novel pathway for melanocortin signaling from the cell surface to the nucleus.

Functional recovery after delayed treatment of ischemic stroke with melanocortins is associated with overexpression of the activity-dependent gene Zif268

Melanocortin peptides afford strong neuroprotection and improve functional recovery in experimental ischemic stroke; they also have established neurotrophic actions. The expression of the immediate early gene Zif268 is dependent on synaptic activity and is involved in injury repair and memory formation. Here, we investigated the role of Zif268 in learning and memory recovery after delayed treatment of ischemic stroke with the melanocortin analog [Nle(4), D-Phe(7)]alpha-MSH (NDP-alpha-MSH). A 10-min period of global cerebral ischemia was induced by occluding both common carotid arteries in gerbils. Treatment with a nanomolar dose of NDP-alpha-MSH (every 12h for 11 days) was performed starting 3h or 9h after stroke induction; where indicated, gerbils were pretreated with the melanocortin MC(4) receptor antagonist HS024. Animals were subjected to the Morris water-maze test (four sessions from 4 to 50 days after the ischemic episode). Fifty days after stroke, histological damage and Zif268 expression were investigated in the hippocampus. Treatment with NDP-alpha-MSH significantly reduced hippocampal damage, including neuronal death, and improved learning and memory recovery. This protective effect was long-lasting (50 days, at least) and associated with Zif268 overexpression, with both schedules of NDP-alpha-MSH treatment. Pharmacological blockade of MC(4) receptors prevented these effects. Our data indicate that MC(4) receptor-mediated actions of melanocortins could trigger repair mechanisms able to improve neuronal functionality and synaptic plasticity, and to promote long-lasting functional recovery from ischemic stroke with Zif268 gene involvement.

Alpha-melanocyte stimulating hormone and adrenocorticotropic hormone: an alternative approach when thinking about restless legs syndrome?

Alpha-melanocyte stimulating hormone (alpha-MSH) and adrenocorticotropic hormone (ACTH) possess properties suggesting that they may be involved in the pathogenesis of restless legs syndrome (RLS). We sought to determine if alpha-MSH and ACTH when administered centrally in rat recapitulate features reminiscent of RLS: increased activity, sleep fragmentation, and periodic movements during sleep. Rats were instrumented with electroencephalography, electromyography, and intracerebral cannulae and recorded for the measurement of sleep, periodic movements, and behavior following intracerebroventricular administration of alpha-MSH, ACTH, or saline. Studied behavior included grooming, locomotion, and rearing during wake and limb movements during sleep. Vigilance states included active wake (AW), quiet wake (QW), slow wave sleep I (SWSI), slow wave sleep II (SWSII), and paradoxical sleep (PS). All rats received normal saline acting as their own controls. Different rats received alpha-MSH in doses of 0.05, 0.5, 1.0, 2.0, and 6.0 microg or ACTH in doses of 0.5, 1.0, and 2.0 microg. Administered alpha-MSH caused an increase in waking behavior and prolongation of sleep latency, while ACTH stimulated waking behavior and fragmented sleep, yielding more AW and less SWSII and PS. Both hormones increased periodic movements during sleep. When administered centrally in rat, alpha-MSH and ACTH stimulate motor activity in wake, cause changes in sleep architecture, and increase periodic movements in sleep. These melanocortin hormones may play a role in the pathogenesis of RLS.

Opioid and melanocortin receptors: do they have overlapping pharmacophores?

We have identified compound 1 as a novel ligand for opioid and melanocortin (MC) receptors, which is derived from the overlapping of a well known structure for the delta opioid receptor, 2,6-dimethyltyrosine (Dmt)-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic), and a small molecule for the MC receptor, Tic-DPhe(p-Cl)-piperidin-4-yl-N-phenyl-propionamide. Ligand 1 showed that there is an overlapping pharmacophore between opioid and MC receptors through the Tic residue. The ligand displayed high biological activities at the delta opioid receptor (Ki = 0.38 nM in binding assay, EC(50) = 0.48 nM in GTP-gamma-S binding assay, IC(50) = 74 nM in MVD) as an agonist instead of an antagonist and showed selective binding affinity (IC(50) = 2.3 muM) at the MC-3 receptor rather than at the MC-5 receptor. A study of the structure-activity relationships demonstrated that the residues in positions 2, 3, and the C-terminus act as a pharmacophore for the MC receptors, and the residues in positions 1 and 2 act as a pharmacophore for the opioid receptors. Thus, this structural construct can be used to prepare chimeric structures with adjacent or overlapping pharmacophores for opioid and MC receptors.

Beta-melanocyte-stimulating hormone potently reduces appetite via the hypothalamus in chicks

The melanocortin system together with other appetite-related systems plays a significant role in appetite regulation. The appetite-related effects of one such melanocortin, beta-melanocyte-stimulating hormone (MSH), are well documented in rodents; however, its effects in the avian class are not thoroughly understood. Thus, we designed a study to determine the effects of i.c.v. beta-MSH injection on food and water intake, plasma corticosterone concentration, ingestive and non-ingestive behaviours, and hypothalamic neuronal activation using Cobb-500 chicks. Chicks responded to beta-MSH-treatment with a reduction in food and water intake; however when water intake was measured independently of food intake, it was not affected. beta-MSH-treated chicks also had increased plasma corticosterone concentrations and increased c-Fos reactivity in the periventricular, paraventricular and infundibular nuclei, and the ventromedial hypothalamus; however, the lateral hypothalamus was not affected. The effect on food intake is primary because behaviours that may be competitive with food intake were not increased in beta-MSH-treated chicks. Based on these results, we conclude that beta-MSH causes anorexigenic effects that are likely primarily mediated via stimulation of satiety-related hypothalamic nuclei in broiler-type chicks.

Activation of melanocortin 4 receptors reduces the inflammatory response and prevents apoptosis induced by lipopolysaccharide and interferon-gamma in astrocytes

Alpha-MSH exerts an immunomodulatory action in the brain and may play a neuroprotective role acting through melanocortin 4 receptors (MC4Rs). In the present study, we show that MC4Rs are constitutively expressed in astrocytes as determined by immunocytochemistry, RT-PCR, and Western blot analysis. alpha-MSH (5 microm) reduced the nitric oxide production and the expression of inducible nitric oxide synthase (iNOS) induced by bacterial lipopolysaccharide (LPS, 1 microg/ml) plus interferon-gamma (IFN-gamma, 50 ng/ml) in cultured astrocytes after 24 h. alpha-MSH also attenuated the stimulatory effect of LPS/IFN-gamma on prostaglandin E(2) release and cyclooxygenase-2 (COX-2) expression. Treatment with HS024, a selective MC4R antagonist, blocked the antiinflammatory effects of alpha-MSH, suggesting a MC4R-mediated mechanism in the action of this melanocortin. In astrocytes, LPS/IFN-gamma treatment reduced cell viability, increased the number of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive cells and activated caspase-3. alpha-MSH prevented these apoptotic events, and this cytoprotective effect was abolished by HS024. LPS/IFN-gamma decreased Bcl-2, whereas it increased Bax protein expression in astrocytes, thus increasing the Bax/Bcl-2 ratio. Alpha-MSH produced a shift in Bax/Bcl-2 ratio toward astrocyte survival because it increased Bcl-2 expression and also prevented the effect of LPS/IFN-gamma on Bax and Bcl-2 expression. In summary, these findings suggest that alpha-MSH, through MC4R activation, attenuates LPS/IFN-gamma-induced inflammation by decreasing iNOS and COX-2 expression and prevents LPS/IFN-gamma-induced apoptosis of astrocytes by modulating the expression of proteins of the Bcl-2 family.

Potent and Selective Peptide Agonists of ?-Melanocyte Stimulating Hormone (?MSH) Action at Human Melanocortin Receptor 5; their Synthesis and Biological Evaluation in vitro

Melanocortin receptors (MC1-5R) and their endogenous ligands (melanocyte-stimulating hormones and adrenocorticotropic hormone) are involved in many physiological processes in humans. Of those receptors, the actions of MC5R are the least understood despite its broad presence in the numerous peripheral tissues and brain. In this study, we describe synthesis and pharmacological properties in vitro (receptor-binding affinity and agonist activity) of several cyclic analogs of alphaMSH which are potent agonists at hMC5R (EC(50) below 1 nM) and of enhanced receptor subtype selectivity (more than 2000-fold versus hMC1b,3R and about 70- to 200-fold versus hMC4R). These compounds are analogs of Ac-Nle(4)-cyclo[Asp(5)-His(6)-D-Nal(2')(7)-Pip(8)-Trp(9)-Lys(10)]-NH(2) (Pip: pipecolic acid) in which His(6) has been replaced with sterically hindered amino acids. They may be useful tools in the elucidation of the MC5R role in skin disorders and in immunomodulatory and in anti-inflammatory actions of alphaMSH.

Potent and selective agonists of human melanocortin receptor 5: cyclic analogues of alpha-melanocyte-stimulating hormone

The physiological role of melanocortin receptor 5 (MC5R) in humans is not clear despite its broad presence in various peripheral sites and in the brain, cortex, and cerebellum. To differentiate between functions of this receptor and those of the other melanocortin receptors (hMC1,3,4R), peptides with improved receptor subtype selectivity are needed. The endogenous ligands, melanocortins, and their various synthetic analogues are not particularly selective for hMC5R. In this study, cyclic peptides derived from MTII, Ac-Nle-cyclo(Asp-His6-D-Phe7-Arg8-Trp-Lys)-NH2 (a pan-agonist at the melanocortin receptors) were prepared and tested in binding and functional assays on CHO cells expressing hMC1b,3-5R. The analogues included in their structures sterically constrained hydrophobic amino acids in positions 6 (His) and 8 (Arg), and the D-4,4'-biphenyl residue in position 7 (D-Phe). Several of the new compounds were selective potent agonists at hMC5R. They are exemplified by peptide 29, Ac-Nle-cyclo(Asp-Oic6-D-4,4'-Bip7-Pip8-Trp-Lys)-NH2 (Oic=octahydroindole-2-COOH; 4,4'-Bip=4,4'-biphenylalanine; Pip=pipecolic acid) of IC50=0.95 nM and EC50=0.99 nM at hMC5R and selectivity for this receptor with respect to the other melanocortin receptors greater than 5000-fold.

Melanocortin receptor 4 is induced in nerve‐injured motor and sensory neurons of mouse

We previously identified melanocortin receptor 4 (MC4R) in a search for genes associated with hypoglossal nerve regeneration. As melanocortins promote nerve regeneration after axonal injury, we investigated whether MC4R functions as a key receptor for peripheral nerve regeneration. In situ hybridization revealed that MC4R mRNA is induced in mouse hypoglossal motor neurons after axonal injury, whereas mRNAs for MC1R, MC2R, MC3R, and MC5R are not expressed either before or after nerve injury. This result was confirmed by RT-PCR. The level of MC4R mRNA expression increased significantly from day 3 after axotomy, reached a peak on day 5, and decreased to the control level on day 14. Similar induction of MC4R was observed in axotomized mouse dorsal root ganglia (DRGs). MC4R mRNA expression was induced exclusively among the MCR family in the L4-6 DRG after sciatic nerve injury. We further examined whether alpha-melanocortin stimulating hormone (alpha-MSH) promotes neurite elongation via MC4R. In mouse DRG neuron culture, alpha-MSH significantly promoted neurite outgrowth at a concentration of 10(-8) mol/L. This neurite-elongation effect was entirely inhibited by the addition of a selective MC4R blocker, JKC-363. Therefore, it is concluded that alpha-MSH could stimulate neurite elongation via MC4R in DRG neurons. The present results suggest that induction of MC4R is crucial for motor and sensory neurons to regenerate after axonal injury.

The melanocortin system in leukocyte biology

The melanocortin system is composed of the melanocortin peptides, adrenocorticotropic hormone and alpha-, beta-, and gamma-melanocyte-stimulating hormone, the melanocortin receptors (MCRs), and the endogenous antagonists agouti- and agouti-related protein. Melanocortin peptides exert multiple effects upon the host, including anti-inflammatory and immunomodulatory effects. Leukocytes are a source of melanocortins and a major target for these peptides. Because of reduced translocation of the nuclear factor NF-kappaB to the nucleus, MCR activation by their ligands causes a collective reduction of the most important molecules involved in the inflammatory process. This review examines how melanocortin peptides and their receptors participate in leukocyte biology.

Cell signaling and trafficking of human melanocortin receptors in real time using two-photon fluorescence and confocal laser microscopy: differentiation of agonists and antagonists

Melanocortin hormones and neurotransmitters regulate a vast array of physiologic processes by interacting with five G-protein-coupled melanocortin receptor types. In the present study, we have systematically studied the regulation of individual human melanocortin receptor wild subtypes using a synthetic rhodamine-labeled human melanotropin agonist and antagonist, arrestins fused to green fluorescent protein in conjunction with two-photon fluorescence laser scanning microscopy and confocal microscopy. Stimulation of the melanocortin receptors by its cognate agonist triggered rapid arrestin recruitment and receptor internalization for all four human melanocortin receptors examined. Antagonists-bound melanocortin receptors, on the other hand, did not recruit beta-arrestins, and remained in the cell membrane even after long-term (30 min) treatment. Agonist-mediated internalization of all melanocortin receptor subtypes was sensitive to inhibitors of clathrin-dependent endocytosis, but not to caveolae inhibitors. In summary, agonist-mediated internalization of all subtypes of melanocortin receptors are dependent upon beta-arrestin-mediated clathrin-coated pits, whereas, beta-arrestin-2 conjugated green fluorescence protein (beta-arrestin-2-GFP) recruitment is not dependent on protein kinase A activation. Real time two-photon fluorescence laser scanning microscopy is a most powerful tool to study the dynamic processes in living cells and tissues, without inflicting significant and often lethal damage to the specimen.

Design, synthesis, and evaluation of proline and pyrrolidine based melanocortin receptor agonists. A conformationally restricted dipeptide mimic approach

The design, synthesis, and structure-activity relationships (SAR) of a series of novel proline and pyrrolidine based melanocortin receptor (MCR) agonists are described. To validate a conformationally constrained Arg-Nal dipeptide analogue strategy, we first synthesized and evaluated a test set of cis-(2R,4R)-proline analogues (21a-g). All of these compounds showed significant binding and agonist potency at the hMC1R, hMC3R, and hMC4R. Potent cis-(2S,4R)-pyrrolidine based MCR agonists (35a-g) were subsequently developed by means of this design approach. A SAR study directed toward probing the effect of the two chiral centers in the pyrrolidine ring on biological activity revealed the importance of the (S) absolute configuration at the 2-position for binding affinity, agonist potency, and receptor selectivity. Among the four sets of the pyrrolidine diastereomers investigated, analogues with the (2S,4R) configuration were the most potent agonists across the three receptors, followed by those possessing the (2S,4S) configuration.

Privileged structure based ligands for melanocortin-4 receptors—Aliphatic piperazine derivatives

Aliphatic carbocyclic replacement of the benzyl group of compound 1 yielded compounds with high affinity for the melanocortin-4 receptor (MC4R). Compounds with a cyclohexyl group showed a consistent high affinity, while different polar groups with less basicity were good replacements for the original diethyl amines. Substitution of the polar group found in these privileged structures with an aliphatic moiety produced compounds with high affinity for MC4R.

[Kinetics of Semax penetration into the brain and blood of rats after its intranasal administration]

The radioactive peptide analogue Semax corresponding to the ACTH(4-10) sequence (Met-Glu-His-Phe-Pro-Gly-Pro) with a molar radioactivity of 56 Ci/mmol labeled with tritium at the C-terminal Pro was prepared. The labeled peptide was used for studying the kinetics of Semax penetration into rat brain and blood after its intranasal administration (50 microg/kg, 20 microl of solution) to nonbred white rats of body mass 200-250 g. It was demonstrated that 0.093% of the total introduced radioactivity per gram can be found in the rat brain 2 min after the administration, 80% of this radioactivity belonged to Semax, and the rest, to its metabolites. The peptide undergoes rapid enzymatic degradation, with the tripeptide Pro-Gly-Pro prevailing in biological samples relative to the total content of Semax and its metabolites.

Broad therapeutic treatment window of [Nle(4), D-Phe(7)]alpha-melanocyte-stimulating hormone for long-lasting protection against ischemic stroke, in Mongolian gerbils

Melanocortin peptides have been shown to produce neuroprotection in experimental ischemic stroke. The aim of the present investigation was to identify the therapeutic treatment window of melanocortins, and to determine whether these neuropeptides chronically protect against damage consequent to brain ischemia. A 10-min period of global cerebral ischemia in gerbils, induced by occluding both common carotid arteries, caused impairment in spatial learning and memory (Morris test: four sessions from 4 to 67 days after the ischemic episode), associated with neuronal death in the hippocampus. Treatment with a nanomolar dose (340 microg/kg i.p., every 12 h for 11 days) of the melanocortin analog [Nle(4), D-Phe(7)]alpha-melanocyte-stimulating hormone (NDP-alpha-MSH), starting 3-18 h after the ischemic episode, reduced hippocampal damage with improvement in subsequent functional recovery. The protective effect was long-lasting (67 days, at least) with all schedules of NDP-alpha-MSH treatment; however, in the latest treated (18 h) gerbils, some spatial memory deficits were detected. Pharmacological blockade of melanocortin MC(4) receptors prevented the protective effects of NDP-alpha-MSH. Our findings indicate that, in conditions of brain ischemia, melanocortins can provide strong and long-lasting protection with a broad therapeutic treatment window, and with involvement of melanocortin MC(4) receptors, 18 h being the approximately time-limit for stroke late treatment to be effective.

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.