Melanocortin Receptor Agonist Research Articles

Effect of Bremelanotide on Ambulatory Blood Pressure When Administered for Up to 16 Consecutive Days [14B

INTRODUCTION: Bremelanotide is a melanocortin receptor agonist approved for the treatment of hypoactive sexual desire disorder. Bremelanotide 1.75 mg administered subcutaneously on-demand should not be administered more than once per 24 hours (maximum of 8 doses/month). We evaluated the impact of bremelanotide administered once-daily up to 16 consecutive days to determine if there was a cumulative effect on ambulatory blood pressure (ABP) and heart rate (HR) in premenopausal women. METHODS: In this IRB-approved study, 24-hour ABP and HR were assessed at baseline following a single-blind placebo injection, followed by an 8-day treatment period with 1.75 mg bremelanotide daily, and a subsequent 8-day double-blind, parallel-group, randomized (1:1 bremelanotide or placebo) withdrawal period. RESULTS: At baseline (n=142), mean age was 36 years, patients were 61% white, 34% black, and 24-hour mean BP was 109/70±8/6 mmHg. Demographics were balanced in the 127 women randomized at day 8. Maximal change from baseline in BP at 8 or 16 days was 3–4 mmHg 3 to 5 hours post-dose, decreasing to 1–2 mmHg by 12 hours post-dose with no cumulative effect. HR decreased by ≤1 beat/minute. The most common treatment-emergent adverse events were focal hyperpigmentation (38% of women during the first 8 days, with an additional 14% of women randomized to bremelanotide for days 9–16) and nausea (30%). CONCLUSION: No cumulative effects were observed on ABP or HR following daily dosing of bremelanotide for 8 or 16 days. BP returned to baseline after drug cessation. Data from the present study further support the safety of the recommended dosing.

Drug Therapy in Obesity: A Review of Current and Emerging Treatments.

Whilst the prevalence of obesity continues to increase at an alarming rate worldwide, the personal and economic burden of obesity-related complications becomes ever more important. Whilst dietary and lifestyle measures remain the fundamental focus of the patient to counter obesity, more frequently pharmacological and/or surgical interventions are required. Nevertheless, these therapies are often limited by weight loss efficacy, side effects, surgical risks and frequently obesity relapse. Currently, only five drug therapies are approved for the specific treatment of obesity. However, our understanding of the pathophysiology of obesity and of gut hormones has developed precipitously over the last 20–30 years. As a result, there has been a recent movement to create and use analogues that manipulate these gut hormones to support weight loss. In this article we review the efficacy of the currently approved drug therapies and discuss future potential drug mechanisms and early clinical trial results exploring these budding avenues. We discuss the use of glucagon-like peptide-1 (GLP-1) analogues as monotherapy and unimolecular dual or triple agonists that exploit the GLP-1 receptor and/or the gastric inhibitory peptide (GIP) receptor and/or the glucagon receptor. We also explore the use of sodium-glucose co-transporter-2 (SGLT-2) inhibitors, amylin mimetics, leptin analogues, ghrelin antagonists and centrally acting agents to suppress appetite [neuropeptide Y (NPY) antagonists, melanocortin-4 receptor (MC4R) agonists and cannabinoid-1 receptor antagonists]. Whilst further evidence is required to support their clinical use, preclinical and early clinical trial results are encouraging.

Intestine-selective reduction of Gcg expression reveals the importance of the distal gut for GLP-1 secretion

ObjectiveGlucagon-like peptide-1 is a nutrient-sensitive hormone secreted from enteroendocrine L cells within the small and large bowel. Although GLP-1 levels rise rapidly in response to food ingestion, the greatest density of L cells is localized to the distal small bowel and colon. Here, we assessed the importance of the distal gut in the acute L cell response to diverse secretagogues. MethodsCirculating levels of glucose and plasma GLP-1 were measured in response to the administration of L cell secretagogues in wild-type mice and in mice with (1) genetic reduction of Gcg expression throughout the small bowel and large bowel (GcgGut−/-) and (2) selective reduction of Gcg expression in the distal gut (GcgDistalGut−/-). ResultsThe acute GLP-1 response to olive oil or arginine administration was markedly diminished in GcgGut−/- but preserved in GcgDistalGut−/- mice. In contrast, the increase in plasma GLP-1 levels following the administration of the GPR119 agonist AR231453, or the melanocortin-4 receptor (MC4R) agonist LY2112688, was markedly diminished in the GcgDistalGut−/- mice. The GLP-1 response to LPS was also markedly attenuated in the GcgGut−/- mice and remained submaximal in the GcgDistalGut−/- mice. Doses of metformin sufficient to lower glucose and increase GLP-1 levels in the GcgGut+/+ mice retained their glucoregulatory activity, yet they failed to increase GLP-1 levels in the GcgGut−/- mice. Surprisingly, the actions of metformin to increase plasma GLP-1 levels were substantially attenuated in the GcgDistalGut−/- mice. ConclusionThese findings further establish the importance of the proximal gut for the acute response to nutrient-related GLP-1 secretagogues. In contrast, we identify essential contributions of the distal gut to (i) the rapid induction of circulating GLP-1 levels in response to pharmacological selective agonism of G-protein-coupled receptors, (ii) the increased GLP-1 levels following the activation of Toll-Like Receptors with LPS, and iii) the acute GLP-1 response to metformin. Collectively, these results reveal that distal gut Gcg + endocrine cells are rapid responders to structurally and functionally diverse GLP-1 secretagogues.

The Role of PVN MC4R Neural Pathway in Autonomic Control of Metabolic Homeostasis and Cardiovascular Function

Central melanocortin pathways, mainly via acting on melanocortin‐4 receptor (MC4R), play an important role in both energy balance and sympathetic traffics affecting cardiovascular function. MC4R deficiency in both humans and rodents causes obesity, insulin resistance and diabetes while maintaining low to normal sympathetic tone and blood pressure, suggesting a critical role of MC4R signaling in metabolic homeostasis and obesity‐associated sympathetic overdrive and hypertension. MC4R is widely expressed in the brain including hypothalamic paraventricular nucleus (PVN) which functions as an integrative center for energy metabolism and autonomic regulation. However, whether and how PVNMC4R pathways contribute to the sympathetic control of cardiovascular function and metabolic homeostasis remain incompletely understood. In present study, we first comprehensively mapped afferent projections of PVNMC4R neurons by stereotaxically delivering Cre‐dependent AAV driving expression of eYFP into the PVN of MC4R‐Cre knock‐in mice, which allow targeted anterograde tract‐tracing of PVNMC4R neurons throughout the brain. In addition to known brain region for feeding behavior (i.e. parabrachial nucleus), we found broad innervations of PVNMC4R neurons to various brain regions important for autonomic‐cardiovascular control and energy metabolism, including but not limited to nucleus of solitary tractus , dorsal motor nucleus of vagus, rostral ventrolateral medulla (RVLM) and spinal cord. Using a combination of sophisticated viral tools, we further reveal that thoracic spinal cord‐projecting PVNMC4R neurons are exclusively located in the posterolateral PVN and send collateral projections to RVLM. Functionally, microinjection of synthetic MC4R agonist (MTII) into the PVN evokes renal sympathetic nerve activity in anesthetized mice and chemogenetic activation of PVNMC4R neurons elevates blood pressure and decreases food intake in freely moving animals. Additionally, genetic ablation of PVNMC4R neurons in adult mice using Cre‐dependent AAV expressing Casp3 causes hyperphagia and massive weight gain (over 80% increase within 6 weeks). These results provide an important insight into the role of PVNMCR neural circuits in regulating metabolic homeostasis and cardiovascular function. Optogenetic and chemogenetic studies are ongoing to functionally dissect the neural circuits downstream of PVNMC4R neurons.Support or Funding InformationNational Institute of Health (R01), AHA Postdoctoral Grant Award (19POST34450083)

The complicated clinical course in a case of atypical lipodystrophy after development of neutralizing antibody to metreleptin: treatment with setmelanotide.

SummaryA patient with atypical partial lipodystrophy who had a transient initial response to metreleptin experienced acute worsening of her metabolic state when neutralizing antibodies against metreleptin appeared. Because her metabolic status continued to deteriorate, a therapeutic trial with melanocortin-4 receptor agonist setmelanotide, that is believed to function downstream from leptin receptor in the leptin signaling system, was undertaken in an effort to improve her metabolic status for the first time in a patient with lipodystrophy. To achieve this, a compassionate use (investigational new drug application; IND) was initiated (NCT03262610). Glucose control, body fat by dual-energy X-ray absorptiometry and MRI, and liver fat by proton density fat fraction were monitored. Daily hunger scores were assessed by patient filled questionnaires. Although there was a slight decrease in hunger scales and visceral fat, stimulating melanocortin-4 receptor by setmelanotide did not result in any other metabolic benefit such as improvement of hypertriglyceridemia or diabetes control as desired. Targeting melanocortin-4 receptor to regulate energy metabolism in this setting was not sufficient to obtain a significant metabolic benefit. However, complex features of our case make it difficult to generalize these observations to all cases of lipodystrophy. It is still possible that melanocortin-4 receptor agonistic action may offer some therapeutic benefits in leptin-deficient patients.Learning points:A patient with atypical lipodystrophy with an initial benefit with metreleptin therapy developed neutralizing antibodies to metreleptin (Nab-leptin), which led to substantial worsening in metabolic control. The neutralizing activity in her serum persisted for longer than 3 years.Whether the worsening in her metabolic state was truly caused by the development of Nab-leptin cannot be fully ascertained, but there was a temporal relationship. The experience noted in our patient at least raises the possibility for concern for substantial metabolic worsening upon emergence and persistence of Nab-leptin. Further studies of cases where Nab-leptin is detected and better assay systems to detect and characterize Nab-leptin are needed.The use of setmelanotide, a selective MC4R agonist targeting specific neurons downstream from the leptin receptor activation, was not effective in restoring metabolic control in this complex patient with presumed diminished leptin action due to Nab-leptin.Although stimulating the MC4R pathway was not sufficient to obtain a significant metabolic benefit in lowering triglycerides and helping with her insulin resistance as was noted with metreleptin earlier, there was a mild reduction in reported food intake and appetite.Complex features of our case make it difficult to generalize our observation to all leptin-deficient patients. It is possible that some leptin-deficient patients (especially those who need primarily control of food intake) may still theoretically benefit from MC4R agonistic action, and further studies in carefully selected patients may help to tease out the differential pathways of metabolic regulation by the complex network of leptin signaling system.

Novel Emerging Therapies for Erectile Dysfunction.

Currently, several treatments exist for the improvement of erectile dysfunction (ED). These include medical therapies such as phosphodiesterase type 5 inhibitors (PDE5-Is), invasive methods such as intracavernosal injection therapy of vaso-active substances, vacuum erection devices, and penile prosthesis implants. However, the percentage of patients that are unresponsive to available treatments and who drop out from treatments remains high. Current evidence reveals that the pathogenesis of ED is related to multiple factors including underlying comorbidities, previous surgery, and psychological factors. Diverse approaches using novel molecular pathways or new technologies have been tested as potential therapeutic options for difficultto-treat ED populations. Melanocortin receptor agonist, a centrally acting agent, showed promising results by initiating erection without sexual stimulation in non-responders to PDE5-Is. Recent clinical and pre-clinical studies using human tissues suggested that new peripherally acting agents including the Max-K channel activator, guanylate cyclase activator, and nitric oxide donor could be potential therapies either as a monotherapy or in combination with PDE5-Is in ED patients. According to several clinical trials, regeneration therapy using stem cells showed favorable data in men with diabetic or post-prostatectomy ED. Low-intensity shock wave therapy also demonstrated promising results in patients with vasculogenic ED. There are growing evidences which suggest the efficacy of these emerging therapies, though most of the therapies still need to be validated by well-designed clinical trials. It is expected that, should their long-term safety and efficacy be proven, the emerging treatments can meet the needs of patients hitherto unresponsive to or unsatisfied by current therapies for ED.

Melanocortin regulation of histaminergic neurons via perifornical lateral hypothalamic melanocortin 4 receptors

ObjectiveHistaminergic neurons of the tuberomammillary nucleus (TMN) are wake-promoting and contribute to the regulation of energy homeostasis. Evidence indicates that melanocortin 4 receptors (MC4R) are expressed within the TMN. However, whether the melanocortin system influences the activity and function of TMN neurons expressing histidine decarboxylase (HDC), the enzyme required for histamine synthesis, remains undefined. MethodsWe utilized Hdc-Cre mice in combination with whole-cell patch-clamp electrophysiology and in vivo chemogenetic techniques to determine whether HDC neurons receive metabolically relevant information via the melanocortin system. ResultsWe found that subsets of HDC-expressing neurons were excited by melanotan II (MTII), a non-selective melanocortin receptor agonist. Use of melanocortin receptor selective agonists (THIQ, [D-Trp8]-γ-MSH) and inhibitors of synaptic transmission (TTX, CNQX, AP5) indicated that the effect was mediated specifically by MC4Rs and involved a glutamatergic dependent presynaptic mechanism. MTII enhanced evoked excitatory post-synaptic currents (EPSCs) originating from electrical stimulation of the perifornical lateral hypothalamic area (PeFLH), supportive of melanocortin effects on the glutamatergic PeFLH projection to the TMN. Finally, in vivo chemogenetic inhibition of HDC neurons strikingly enhanced the anorexigenic effects of intracerebroventricular administration of MTII, suggesting that MC4R activation of histaminergic neurons may restrain the anorexigenic effects of melanocortin system activation. ConclusionsThese experiments identify a functional interaction between the melanocortin and histaminergic systems and suggest that HDC neurons act naturally to restrain the anorexigenic effect of melanocortin system activation. These findings may have implications for the control of arousal and metabolic homeostasis, especially in the context of obesity, in which both processes are subjected to alterations.

Activation of Melanocortin-4 Receptor Inhibits Both Neuroinflammation Induced by Early Exposure to Ethanol and Subsequent Voluntary Alcohol Intake in Adulthood in Animal Models: Is BDNF the Key Mediator?

The concept that neuroinflammation induced by excessive alcohol intake in adolescence triggers brain mechanisms that perpetuate consumption has strengthened in recent years. The melanocortin system, composed of the melanocortin 4 receptor (MC4R) and its ligand α-melanocyte-stimulating hormone (α-MSH), has been implicated both in modulation of alcohol consumption and in ethanol-induced neuroinflammation decrease. Chronic alcohol consumption in adolescent rats causes a decrease in an α-MSH release by the hypothalamus, while the administration of synthetic agonists of MC4R causes a decrease in neuroinflammation and a decrease in voluntary alcohol consumption. However, the mechanism that connects the activation of MC4R with the decrease of both neuroinflammation and voluntary alcohol consumption has not been elucidated. Brain-derived neurotrophic factor (BDNF) has been implicated in alcohol drinking motivation, dependence and withdrawal, and its levels are reduced in alcoholics. Deficiencies in BDNF levels increased ethanol self-administration in rats. Further, BDNF triggers important anti-inflammatory effects in the brain, and this could be one of the mechanisms by which BDNF reduces chronic alcohol intake. Interestingly, MC4R signaling induces BDNF expression through the activation of the cAMP-responsive element-binding protein (CREB). We hypothesize that ethanol exposure during adolescence decreases the expression of α-MSH and hence MC4R signaling in the hippocampus, leading to a lower BDNF activity that causes dramatic changes in the brain (e.g., neuroinflammation and decreased neurogenesis) that predispose to maintain alcohol abuse until adulthood. The activation of MC4R either by α-MSH or by synthetic agonist peptides can induce the expression of BDNF, which would trigger several processes that lead to lower alcohol consumption.

Activation of Melanocortin-4 Receptor by a Synthetic Agonist Inhibits Ethanolinduced Neuroinflammation in Rats.

High ethanol intake induces a neuroinflammatory response resulting in the subsequent maintenance of chronic alcohol consumption. The melanocortin system plays a pivotal role in the modulation of alcohol consumption. Interestingly, it has been shown that the activation of melanocortin-4 receptor (MC4R) in the brain decreases the neuroinflammatory response in models of brain damage other than alcohol consumption, such as LPS-induced neuroinflammation, cerebral ischemia, glutamate excitotoxicity, and spinal cord injury. In this work, we aimed to study whether MC4R activation by a synthetic MC4R-agonist peptide prevents ethanol-induced neuroinflammation, and if alcohol consumption produces changes in MC4R expression in the hippocampus and hypothalamus. Ethanol-preferring Sprague Dawley rats were selected offering access to 20% ethanol on alternate days for 4 weeks (intermittent access protocol). After this time, animals were i.p. administered an MC4R agonist peptide in the last 2 days of the protocol. Then, the expression of the proinflammatory cytokines interleukin 6 (IL-6), interleukin 1-beta (IL-1β), and tumor necrosis factor-alpha (TNF-α) were measured in the hippocampus, hypothalamus and prefrontal cortex. It was also evaluated if ethanol intake produces alterations in the expression of MC4R in the hippocampus and the hypothalamus. Alcohol consumption increased the expression of MC4R in the hippocampus and the hypothalamus. The administration of the MC4R agonist reduced IL-6, IL-1β and TNF-α levels in hippocampus, hypothalamus and prefrontal cortex, to those observed in control rats that did not drink alcohol. High ethanol consumption produces an increase in the expression of MC4R in the hippocampus and hypothalamus. The administration of a synthetic MC4R-agonist peptide prevents neuroinflammation induced by alcohol consumption in the hippocampus, hypothalamus, and prefrontal cortex. These results could explain the effect of α-MSH and other synthetic MC4R agonists in decreasing alcohol intake through the reduction of the ethanol-induced inflammatory response in the brain.

193 Bremelanotide for Hypoactive Sexual Desire Disorder: Contraceptive Subgroups Efficacy Analysis

Hypoactive sexual desire disorder (HSDD) is the most common sexual dysfunction associated with personal distress in women, and is characterized by an absence or deficiency of sexual desire accompanied by distress. HSDD affects approximately 10% of women, with a similar prevalence regardless of age. Bremelanotide, a melanocortin receptor agonist and an analog of the endogenous neuropeptide α-melanocortin stimulating hormone, has been approved for the treatment of acquired, generalized HSDD in premenopausal women. The RECONNECT studies, which comprised two double-blind, randomized, placebo-controlled studies, demonstrated that subcutaneous self-administration of bremelanotide significantly improved sexual desire and decreased personal distress in premenopausal women with HSDD. To investigate the efficacy of bremelanotide across hormonal contraceptive subgroups in the RECONNECT studies. Patients self-administered bremelanotide 1.75 mg or placebo subcutaneously for 24 weeks, using an autoinjector pen as needed prior to sexual activity. Patients were evaluated (“yes” and “no” subgroups) based on concurrent use of hormonal contraceptives (including oral contraceptives and other estrogen-containing products). Efficacy was assessed using RECONNECT co-primary endpoints: change from baseline to end-of-study (EOS) for Female Sexual Function Index–desire domain (FSFI-D) and Female Sexual Distress Scale–Desire/Arousal/Orgasm (FSDS-DAO) Item 13 scores.

Discovery of a Highly Selective MC1R Agonists Pentapeptide to Be Used as a Skin Pigmentation Enhancer and with Potential Anti-Aging Properties.

One of the first lines of cutaneous defense against photoaging is (a) the synthesis of melanin and (b) the initiation of an oxidative stress response to protect skin against the harmful effects of solar radiation. Safe and selective means to stimulate epidermal pigmentation associated with oxidative stress defense are; however, scarce. Activation of the melanocortin-1 receptor (MC1R) on epidermal melanocytes represents a key step in cutaneous pigmentation initiation and, additionally, it regulates cellular defense mechanisms like oxidative stress and DNA-repair. Thus, making the activation of MC1R an attractive strategy for modulating skin pigmentation and oxidative stress. In this context, we designed and synthesized pentapeptides that act as MC1R agonists. These peptides bound, with high potency, to MC1R and activated cAMP synthesis in CHO cells expressing human MC1R. Using one lead pentapeptide, we could show that this activation of MC1R was specific as testing the activation of other G-protein coupled receptors, including the MC-receptor family, was negative. In vitro efficacy on mouse melanoma cells showed similar potency as for the synthetic MC1R agonist alpha-melanocyte stimulating hormone (NDP-alpha-MSH). Moreover, we could reproduce this activity in human skin tissue culture. The lead pentapeptide was able to induce ex-vivo protein expression of key melanogenesis markers melanocyte inducing transcription factor (MITF), tyrosinase (TYR), and tyrosinase-related protein 1 (TYRP-1). Concerning oxidative stress response, we found that the pentapeptide enhanced the activation of Nrf2 after UVA-irradiation. Our results make this pentapeptide an ideal candidate as a skin pigmentation enhancer that mimics alpha-MSH and may also have anti-photoaging effects on the skin.

Setmelanotide, a Novel, Selective Melanocortin Receptor-4 Agonist Exerts Anti-inflammatory Actions in Astrocytes and Promotes an Anti-inflammatory Macrophage Phenotype.

To date, available treatment strategies for multiple sclerosis (MS) are ineffective in preventing or reversing progressive neurologic deterioration, creating a high, and unmet medical need. One potential way to fight MS may be by limiting the detrimental effects of reactive astrocytes, a key pathological hallmark for disease progression. One class of compounds that may exert beneficial effects via astrocytes are melanocortin receptor (MCR) agonists. Among the MCR, MC4R is most abundantly expressed in the CNS and several rodent studies have described that MC4R is—besides neurons—expressed by astrocytes. Activation of MC4R in astrocytes has shown to have potent anti-inflammatory as well as neuroprotective effects in vitro, suggesting that this could be a potential target to ameliorate ongoing inflammation, and neurodegeneration in MS. In this study, we set out to investigate human MC4R expression and analyze its downstream effects. We identified MC4R mRNA and protein to be expressed on astrocytes and observed increased astrocytic MC4R expression in active MS lesions. Furthermore, we show that the novel, highly selective MC4R agonist setmelanotide ameliorates the reactive phenotype in astrocytes in vitro and markedly induced interleukin−6 and −11 production, possibly through enhanced cAMP response element-binding protein (CREB) phosphorylation. Notably, stimulation of human macrophages with medium from astrocytes that were exposed to setmelanotide, skewed macrophages toward an anti-inflammatory phenotype. Taken together, these findings suggest that targeting MC4R on astrocytes might be a novel therapeutic strategy to halt inflammation-associated neurodegeneration in MS.

Melanocortin receptors (version 2019.4) in the IUPHAR/BPS Guide to Pharmacology Database

Melanocortin receptors (provisional nomenclature as recommended by NC-IUPHAR [36]) are activated by members of the melanocortin family (α-MSH, β-MSH and γ-MSH forms; δ form is not found in mammals) and adrenocorticotrophin (ACTH). Endogenous antagonists include agouti and agouti-related protein. ACTH(1-24) was approved by the US FDA as a diagnostic agent for adrenal function test, whilst NDP-MSH was approved by EMA for the treatment of erythropoietic protoporphyria. Several synthetic melanocortin receptor agonists are under clinical development.

Bremelanotide: First Approval.

Bremelanotide (Vyleesi™) is a melanocortin receptor agonist recently approved in the USA for the treatment of premenopausal women with acquired, generalized hypoactive sexual desire disorder (HSDD), as characterized by low sexual desire that causes marked distress or interpersonal difficulty. It is a self-administered, on-demand subcutaneous therapy. Initially developed by Palatin Technologies who sponsored the Phase 3 clinical trials, bremelanotide was subsequently out-licensed to AMAG Pharmaceuticals Inc. for exclusive North American rights to develop and commercialize the drug, including submitting the New Drug Application to the US FDA. Bremelanotide is a synthetic peptide analogue of the neuropeptide hormone alpha melanocyte-stimulating hormone (α-MSH) with high affinity for the melanocortin type 4 receptor (thought to be important for sexual function), giving it the potential to modulate brain pathways involved in sexual response. This article summarizes the milestones in the development of bremelanotide leading to this first regulatory approval.

Current Mechanistic and Pharmacodynamic Understanding of Melanocortin-4 Receptor Activation.

In this work we summarize our understanding of melanocortin 4 receptor (MC4R) pathway activation, aiming to define a safe and effective therapeutic targeting strategy for the MC4R. Delineation of cellular MC4R pathways has provided evidence for distinct MC4R signaling events characterized by unique receptor activation kinetics. While these studies remain narrow in scope, and have largely been explored with peptidic agonists, the results provide a possible correlation between distinct ligand groups and differential MC4R activation kinetics. In addition, when a set of small-molecule and peptide MC4R agonists are compared, evidence of biased signaling has been reported. The results of such mechanistic studies are discussed.

Melanocortin-4 Receptors and Sympathetic Nervous System Activation in Hypertension.

To highlight the role of the brain melanocortin 4 receptor (MC4R) for sympathetic nervous system (SNS) activation in hypertension. Hypertension is the most significant risk factor for developing cardiovascular disease. Although excess weight gain is associated with at least two thirds of primary hypertension cases, the pathophysiological mechanisms involved remain the subject of intense investigation. Multiple studies demonstrate an important role for increased sympathetic nervous system (SNS) activity in development and maintenance of hypertension, and that the brain MC4R modulates SNS activity to thermogenic, cardiovascular, and kidney tissues. These studies also support the concept that MC4R activation is critical for obesity-induced hypertension as well as other forms of hypertension associated with increased SNS activity. MC4R is a potential target for antiobesity therapy, although there are challenges in using MC4R agonists to induce weight loss without evoking increases in SNS activity.

Relationship of α-MSH and AgRP axons to the perikarya of melanocortin-4 receptor neurons

The central melanocortin system is composed of neurons that express either the proopiomelanocortin (POMC) or the agouti-related protein (AgRP). POMC is cleaved in bioactive peptides, including the α-melanocyte-stimulating hormone (α-MSH). α-MSH activates the melanocortin-4 receptor (MC4R) inducing satiety, whereas AgRP acts as an inverse agonist of MC4R. However, only limited information is available regarding possible area-specific differences in the interaction between α-MSH and AgRP terminals on MC4R-expressing cells. Therefore, the objective of the present study was to compare the distribution pattern of α-MSH and AgRP terminals on the perikarya of MC4R-expressing neurons. We performed a triple-label immunofluorescence reaction in brain series of MC4R-reporter mice to visualize MC4R-expressing neurons together with AgRP and α-MSH terminals. POMC and AgRP neurons project to areas that contain MC4R-expressing cells, although several brain nuclei exhibit AgRP and α-MSH terminals, but they do no express MC4R, while other brain areas contain MC4R-expressing cells and receive no apparent innervation of AgRP and POMC neurons. AgRP terminals make more presumptive appositions than α-MSH on the soma of MC4R-expressing neurons of the medial preoptic area and paraventricular nucleus of the hypothalamus (Pa). Additionally, a higher percentage of MC4R cells receive at least one presumptive apposition from AgRP terminals in the median preoptic nucleus and Pa, compared to α-MSH appositions. Thus, our study revealed area-specific differences in the interaction between α-MSH and AgRP terminals and the soma of MC4R-expressing neurons. These findings provide new insights about the relationship between first- and second-order neurons of the central melanocortin system.

Synthetic Corticotropin Therapy Reduces Microglial Activation in a Rodent TBI Model

Traumatic brain injury (TBI) is a leading cause of mortality/morbidity and is associated with chronic neuroinflammation. Melanocortin receptor (MCR) agonists (e.g., ACTH or adrenocorticotropic hormone) that target MC3R/4R ameliorate inflammation and provide a novel therapeutic approach. Following TBI, quiescent microglia become activated resulting in anti and pro‐inflammatory responses and morphological changes. We examined the effect of Cosyntropin (synthetic ACTH) administration on microglial activation through quantification of microglia morphology in a rodent TBI model. We hypothesized that Cosyntropin administration would reduce injury‐induced microglia morphological changes following experimental TBI in rats. We used CCI in adult Sprague‐Dawley rats, randomized to 4 groups: sham‐vehicle (N = 2), sham‐Cosyntropin (N = 2), CCI‐vehicle (N = 4), and CCI‐Cosyntropin (N = 4). Subcutaneous injections of Cosyntropin (120U/kg/day; West Therapeutic Development; Grayslake, IL) were given 30 minutes after CCI and every 12 hours for 7 days thereafter. Microglia activation was quantified based on morphology. Sectioned brains were immunostained (Iba1) and visualized with diaminobenzidine. Image processing and quantification were conducted with FIJI and FracLac for ImageJ resulting in 15 morphological values/cell. Parameters included cell area, fractal dimension, circularity, and cell perimeter and density. CCI animals exhibited increased microglia in the lesion site with no difference in cell count between vehicle and treated. Microglia from CCI animals exhibited no change in cell area, decreased cell perimeter and increased density and circularity compared to sham animals. Cosyntropin treatment altered CCI‐induced microglia changes in cell area, cell perimeter, and cell density. Cosyntropin‐treated CCI animals showed reduced morphological changes in microglia suggesting a reduced activation state. Decreased activation may decrease long‐term deleterious neuroinflammatory effects and may be mediated by Cosyntropin effects on melanocortin receptor signaling.Support or Funding InformationSupported in part by the Pediatric Epilepsy Research Foundation. Cosyntropin was supplied by West Therapeutic Development (Grayslake, IL).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Hypothalamic POMC or MC4R deficiency impairs counterregulatory responses to hypoglycemia in mice

ObjectiveLife-threatening hypoglycemia is a major limiting factor in the management of diabetes. While it is known that counterregulatory responses to hypoglycemia are impaired in diabetes, molecular mechanisms underlying the reduced responses remain unclear. Given the established roles of the hypothalamic proopiomelanocortin (POMC)/melanocortin 4 receptor (MC4R) circuit in regulating sympathetic nervous system (SNS) activity and the SNS in stimulating counterregulatory responses to hypoglycemia, we hypothesized that hypothalamic POMC as well as MC4R, a receptor for POMC derived melanocyte stimulating hormones, is required for normal hypoglycemia counterregulation. MethodsTo test the hypothesis, we induced hypoglycemia or glucopenia in separate cohorts of mice deficient in either POMC or MC4R in the arcuate nucleus (ARC) or the paraventricular nucleus of the hypothalamus (PVH), respectively, and measured their circulating counterregulatory hormones. In addition, we performed a hyperinsulinemic-hypoglycemic clamp study to further validate the function of MC4R in hypoglycemia counterregulation. We also measured Pomc and Mc4r mRNA levels in the ARC and PVH, respectively, in the streptozotocin-induced type 1 diabetes mouse model and non-obese diabetic (NOD) mice to delineate molecular mechanisms by which diabetes deteriorates the defense systems against hypoglycemia. Finally, we treated diabetic mice with the MC4R agonist MTII, administered stereotaxically into the PVH, to determine its potential for restoring the counterregulatory response to hypoglycemia in diabetes. ResultsStimulation of epinephrine and glucagon release in response to hypoglycemia or glucopenia was diminished in both POMC- and MC4R-deficient mice, relative to their littermate controls. Similarly, the counterregulatory response was impaired in association with decreased hypothalamic Pomc and Mc4r expression in the diabetic mice, a phenotype that was not reversed by insulin treatment which normalized glycemia. In contrast, infusion of an MC4R agonist in the PVH restored the counterregulatory response in diabetic mice. ConclusionIn conclusion, hypothalamic Pomc as well as Mc4r, both of which are reduced in type 1 diabetic mice, are required for normal counterregulatory responses to hypoglycemia. Therefore, enhancing MC4R function may improve hypoglycemia counterregulation in diabetes.

Amplification of the Melanocortin-1 Receptor in Nephrotic Syndrome Identifies a Target for Podocyte Cytoskeleton Stabilization

The melanocortin-1 receptor (MC1R) in podocytes has been suggested as the mediator of the ACTH renoprotective effect in patients with nephrotic syndrome with the mechanism of action beeing stabilization of the podocyte actin cytoskeleton. To understand how melanocortin receptors are regulated in nephrotic syndrome and how they are involved in restoration of filtration barrier function, melanocortin receptor expression was evaluated in patients and a rat model of nephrotic syndrome in combination with cell culture analysis. Phosphoproteomics was applied and identified MC1R pathways confirmed using biochemical analysis. We found that glomerular MC1R expression was increased in nephrotic syndrome, both in humans and in a rat model. A MC1R agonist protected podocytes from protamine sulfate induced stress fiber loss with the top ranked phoshoproteomic MC1R activated pathway beeing actin cytoskeleton signaling. Actin stabilization through the MC1R consisted of ERK1/2 dependent phosphorylation and inactivation of EGFR signaling with stabilization of synaptopodin and stressfibers in podocytes. These results further explain how patients with nephrotic syndrome show responsiveness to MC1R receptor activation by decreasing EGFR signaling and as a consequence restore filtration barrier function by stabilizing the podocyte actin cytoskeleton.