Melanocortin-4 Receptors Research Articles

Abstract 53: Chronic Angiotensin-(1-7) Treatment May Enhance GABAergic Neurotransmission onto Melanocortin-4 Receptor Neurons in The Hypothalamic Paraventricular Nucleus in a Sex-Specific Manner

Angiotensin (Ang)-(1-7) is a protective hormone of the renin-angiotensin system that lowers blood pressure in animal models of cardiovascular disease; however, the precise mechanisms remain incompletely understood. Recent data from our laboratory suggests that blood pressure lowering effects of Ang-(1-7) may involve the arcuate nucleus of the hypothalamus (ARC). We have shown that Ang-(1-7) activates proopiomelanocortin (POMC)-containing neurons in the ARC. While ARC POMC neuron activation canonically increases blood pressure by stimulating melanocortin-4 receptors (MC4R) in the hypothalamic paraventricular nucleus (PVN), these neurons also release the inhibitory neurotransmitter GABA. Selective activation of these GABAergic POMC neurons could serve as a novel mechanism to lower blood pressure. In this study, we hypothesized that Ang-(1-7) treatment inhibits PVN MC4R neuron activity via enhanced GABAergic function. To test this, male and female MC4R-GFP mice were implanted with osmotic mini pumps at 14 weeks of age and treated chronically with either Ang-(1-7) (400 ng/kg/min) or saline. After six weeks of drug administration, action potential firing of PVN MC4R-expressing neurons was examined using cell attached electrophysiology. To assess GABAergic function, changes in action potential firing frequency following bath application of the GABA A receptor antagonist bicuculline (10 μm) were compared between Ang-(1-7) and saline treated animals (n=4-6 mice/group). While Ang-(1-7) did not alter baseline firing frequency of MC4R PVN neurons in male mice (1.5±0.6 vs. 1.1±0.3 Hz saline; p=0.630, unpaired t-test), it enhanced bicuculline responsiveness as indicated by a greater peak increase in action potential firing frequency (156.9±18.0 vs. 106.2±6.8 % saline; p=0.013). In female mice, Ang-(1-7) increased baseline action potential firing frequency of PVN MC4R neurons (1.5±0.4 vs. 0.3±0.1 Hz saline; p=0.026) but did not alter bicuculline responsiveness (111.0±5.3 vs. 143.2±25.3 % saline; p=0.241). Overall, our data suggest that Ang-(1-7) enhances GABAergic neurotransmission onto PVN MC4R neurons in a sex-specific manner. These data provide new insight into the neural mechanisms of Ang-(1-7), which could have implications for understanding the beneficial cardiovascular effects of this hormone. Additional studies are needed to examine this inhibitory neurocircuit in the context of hypertension as well as precise mechanisms underlying the observed sex differences.

Setmelanotide Administration Improves Cardiac Systolic Function in Sirtuin-3 Deficient Mice

We previously showed that activation of the brain leptin-melanocortin system, particularly melanocortin-4 receptors (MC4R), markedly improves cardiac function in experimental models of heart failure (HF) via mechanisms that are still poorly understood. Sirtuin 3 (Sirt3) is an important regulator of mitochondrial oxidative phosphorylation and deficiency of Sirt3 has been implicated in cardiovascular diseases. We recently found increased Sirt3 expression as well as increased levels of NAD+, the main Sirt3 activator, in cardiomyocytes of rats treated with chronic intracerebroventricular infusion of leptin at a dose that does not spill over into the systemic circulation. Therefore, we hypothesized that stimulation of Sirt3 activity is required for the improvement of cardiac function during activation of the brain leptin-MC4R axis. To test this hypothesis, we first examined if chronic MC4R activation, using an MC4R agonist, setmelanotide, improves cardiac function in naïve Sirt3-deficient (Sirt3-KO) mice. Baseline cardiac function was assessed by echocardiography (VisualSonics-VEVO3100®) in male and female Sirt3-KO and wild-type (WT) control mice (n=5/group) at 20 weeks of age, and then weekly during setmelanotide treatment (2 mg/kg/day — i.p. via osmotic minipump model 1002) for 3 weeks. Chronic MC4R activation with setmelanotide transiently reduced food intake in both groups and promoted weight loss in Sirt3-KO mice. Setmelanotide treatment improved systolic function in WT mice as evidenced by increases in ejection fraction and fractional shortening (EF: 52.8±4.4 vs. 72.4±4.4%; FS: 26.9±2.7 vs. 42.8±6.4%, for baseline vs. week 3, respectively) and other measures of systolic function including circumferential and longitudinal strains. Despite showing a tendency for reduced systolic function compared to WT controls at baseline, Sirt3-KO mice also exhibited improvement in systolic function with setmelanotide administration (EF: 44.1±1.8 vs. 65.3±2.9% and FS: 21.4±1.0 vs. 35.1±2.1%). No major changes were observed in measures of diastolic function. These results suggest that in a non-HF model, MC4R activation does not require stimulation of Sirt3 to improve indices of systolic function. (1R01HL163076, 1R01DK121411, P20GM104357, P30GM149404, U54GM115428, and AHA-835218). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Evolutionary Identification of the Requirement of the Second Intracellular Loop for the Constitutive Activity of Melanocortin-4 Receptors.

Melanocortin-4 receptor (MC4R) functions as a crucial neuroendocrine G protein-coupled receptor (GPCR) in the central nervous system of mammals, displaying agonist-independent constitutive activity that is mainly determined by its N-terminal domain. We previously reported that zebrafish MC4R exhibited a much higher basal cAMP level in comparison to mammalian MC4Rs. However, the functional evolution of constitutive activities in chordate MC4Rs remains to be elucidated. Here we cloned and compared the constitutive activities of MC4Rs from nine vertebrate species and showed that the additive action of the N-terminus with the extracellular region or transmembrane domain exhibited a combined pharmacological effect on the MC4R constitutive activity. In addition, we demonstrated that four residues of F149, Q156, V163, and K164 of the second intracellular loop played a vital role in determining MC4R constitutive activity. This study provided novel insights into functional evolution and identified a key motif essential for constitutive modulation of MC4R signaling.

Advances in Anti-obesity Pharmacotherapy: Current Treatments, Emerging Therapies, and Challenges.

Obesity is a major public health concern linked to health risks such as hypertension, hyperlipidemia, type 2 diabetes mellitus (T2DM), stroke, metabolic syndrome, asthma, and cancer. It is among the leading causes of morbidity and mortality worldwide caused by an unhealthy diet and lack of physical activity, but genetic or hormonal factors may also contribute. Over a third of adults in the United States are obese. Pharmacological agents have been designed to reduce weight gain caused by excessive calorie intake and low physical activity. They work by inhibiting the absorption of dietary fat or stimulating the secretion of satiety hormones. These drugs include lipase inhibitors and glucagon-like peptide1 (GLP-1) receptor agonists. However, the current weight-loss strategies do not effectively treat genetic-related diseases, such as generalized lipodystrophy, Bardet-Biedl syndrome, and proopiomelanocortin (POMC) deficiency. Emerging therapies for these gene mutations have been developed targeting leptin and melanocortin-4 receptors (MC4Rs), restoring the normal function of leptin or melanocortin-4 receptors regulating energy balance and appetite. Leptin analogs and MC4R agonists are novel therapies that target genetic or hormonal causes of obesity. This article provides a comprehensive review of anti-obesity medications (AOMs). In this review, we discuss the clinical trials, efficacy, United States FDA-approved indication, contraindications, and serious side effects of different classes of drugs, including lipase inhibitors, GLP-1 agonists, leptin analogs, and MC4R agonists.

FRI381 Melanocortin 4 Receptor Signaling In Sim-1 Neurons Permits Sexual Receptivity In Female Mice

Abstract Disclosure: M.T. Harberson: None. E. Semple: None. J.W. Hill: None. Female sexual dysfunction affects approximately 40% of women in the United States, yet few therapeutic options exist for these patients. The melanocortin system is a new treatment target for hypoactive sexual desire disorder (HSDD), but the neuronal pathways involved are unclear. In this study, female MC4R knockout mice lacking melanocortin 4 receptors (MC4Rs) paired with males were found to approach males less and have reduced receptivity to copulation, as indicated by a low lordosis quotient. The mice were then bred to express MC4Rs exclusively on Sim1 neurons (tbMC4RSim1 mice) or on oxytocin neurons (tbMC4ROxt mice). Lordosis behavior was normalized in tbMC4RSim1 mice and improved in tbMC4ROxt mice. In contrast, approach behavior was unchanged in tbMC4RSim1 mice but greatly increased in tbMC4ROxt animals. The changes were independent of melanocortin-driven metabolic effects. These results implicate MC4R signaling in Oxt neurons in appetitive behaviors and MC4R signaling in Sim1 neurons in female sexual receptivity, while suggesting melanocortin-driven sexual function does not rely on metabolic neural circuits. Presentation: Friday, June 16, 2023

Prefrontal cortex melanocortin 4 receptors (MC4R) mediate food intake behavior in male mice

BackgroundMelanocortin 4 receptor (MC4R) activity in the hypothalamus is crucial for regulation of metabolism and food intake. The peptide ligands for the MC4R are associated with feeding, energy expenditure, and also with complex behaviors that orchestrate energy intake and expenditure, but the downstream neuroanatomical and neurochemical targets associated with these behaviors are elusive. In addition to strong expression in the hypothalamus, the MC4R is highly expressed in the medial prefrontal cortex, a region involved in executive function and decision-making. MethodsUsing viral techniques in genetically modified male mice combined with molecular techniques, we identify and define the effects on feeding behavior of a novel population of MC4R expressing neurons in the infralimbic (IL) region of the cortex. ResultsHere, we describe a novel population of MC4R-expressing neurons in the IL of the mouse prefrontal cortex that are glutamatergic, receive input from melanocortinergic neurons, and project to multiple regions that coordinate appetitive responses to food-related stimuli. The neurons are stimulated by application of MC4R-specific peptidergic agonist, THIQ. Deletion of MC4R from the IL neurons causes increased food intake and body weight gain and impaired executive function in simple food-related behavior tasks. ConclusionTogether, these data suggest that MC4R neurons of the IL play a critical role in the regulation of food intake in male mice.

Melanocortin 4 receptor signaling in Sim-1 neurons permits sexual receptivity in female mice

Female sexual dysfunction affects approximately 40% of women in the United States, yet few therapeutic options exist for these patients. The melanocortin system is a new treatment target for Hypoactive Sexual Desire Disorder (HSDD), but the neuronal pathways involved are unclear. In this study, female MC4R knockout mice lacking melanocortin 4 receptors (MC4Rs) paired with males were found to approach males less and have reduced receptivity to copulation, as indicated by a low lordosis quotient. The mice were then bred to express MC4Rs exclusively on Sim1 neurons (tbMC4RSim1 mice) or on oxytocin neurons (tbMC4ROxt mice). Lordosis behavior was normalized in tbMC4RSim1 mice and improved in tbMC4ROxt mice. In contrast, approach behavior was unchanged in tbMC4RSim1 mice but greatly increased in tbMC4ROxt animals. The changes were independent of melanocortin-driven metabolic effects. These results implicate MC4R signaling in Oxt neurons in appetitive behaviors and MC4R signaling in Sim1 neurons in female sexual receptivity, while suggesting melanocortin-driven sexual function does not rely on metabolic neural circuits. R01HD081792 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Melanocortin 4 receptor signaling in Sim1 neurons permits sexual receptivity in female mice.

Female sexual dysfunction affects approximately 40% of women in the United States, yet few therapeutic options exist for these patients. The melanocortin system is a new treatment target for hypoactive sexual desire disorder (HSDD), but the neuronal pathways involved are unclear. In this study, the sexual behavior of female MC4R knockout mice lacking melanocortin 4 receptors (MC4Rs) was examined. The mice were then bred to express MC4Rs exclusively on Sim1 neurons (tbMC4RSim1 mice) or on oxytocin neurons (tbMC4ROxt mice) to examine the effect on sexual responsiveness. MC4R knockout mice were found to approach males less and have reduced receptivity to copulation, as indicated by a low lordosis quotient. These changes were independent of body weight. Lordosis behavior was normalized in tbMC4RSim1 mice and improved in tbMC4ROxt mice. In contrast, approach behavior was unchanged in tbMC4RSim1 mice but greatly increased in tbMC4ROxt animals. The changes were independent of melanocortin-driven metabolic effects. These results implicate MC4R signaling in Oxt neurons in appetitive behaviors and MC4R signaling in Sim1 neurons in female sexual receptivity, while suggesting melanocortin-driven sexual function does not rely on metabolic neural circuits.

Melanocortin receptor 3 and 4 mRNA expression in the adult female Syrian hamster brain.

Melanocortin 3 receptors (MC3R) and melanocortin 4 receptors (MC4R) are vital in regulating a variety of functions across many species. For example, the dysregulation of these receptors results in obesity and dysfunction in sexual behaviors. Only a handful of studies have mapped the expression of MC3R and MC4R mRNA across the central nervous system, with the primary focus on mice and rats. Because Syrian hamsters are valuable models for functions regulated by melanocortin receptors, our current study maps the distribution of MC3R and MC4R mRNA in the Syrian hamster telencephalon, diencephalon, and midbrain using RNAscope. We found that the expression of MC3R mRNA was lowest in the telencephalon and greatest in the diencephalon, whereas the expression of MC4R mRNA was greatest in the midbrain. A comparison of these findings to previous studies found that MC3R and MC4R expression is similar in some brain regions across species and divergent in others. In addition, our study identifies novel brain regions for the expression of MC3Rs and MC4Rs, and identifies cells that co-express bothMC3 and MC4 receptors within certain brain regions.

Melanocortin-4 receptors on neurons in the parabrachial nucleus mediate inflammation-induced suppression of food-seeking behavior

Anorexia is a common symptom during infectious and inflammatory disease. Here we examined the role of melanocortin-4 receptors (MC4Rs) in inflammation-induced anorexia. Mice with transcriptional blockage of the MC4Rs displayed the same reduction of food intake following peripheral injection of lipopolysaccharide as wild type mice but were protected against the anorexic effect of the immune challenge in a test in which fasted animals were to use olfactory cues to find a hidden cookie. By using selective virus-mediated receptor re-expression we demonstrate that the suppression of the food-seeking behavior is subserved by MC4Rs in the brain stem parabrachial nucleus, a central hub for interoceptive information involved in the regulation of food intake. Furthermore, the selective expression of MC4R in the parabrachial nucleus also attenuated the body weight increase that characterizes MC4R KO mice. These data extend on the functions of the MC4Rs and show that MC4Rs in the parabrachial nucleus are critically involved in the anorexic response to peripheral inflammation but also contribute to body weight homeostasis during normal conditions.

Melanocortin-4 receptors activate sympathetic preganglionic neurons and elevate blood pressure via TRPV1.

Melanocortin-4 receptors (MC4Rs) expressed by the central nervous system are essential regulators of energy homeostasis, and Mc4r mutation is the most common cause of human monogenic obesity. Notably, patients with obesity carrying Mc4r mutations are protected against obesity-induced hypertension, and MC4R agonists elevate blood pressure (BP). Although increased sympathetic tone by MC4Rs is suggested to underlie this phenotype, the detailed mechanisms remain unclear. Here, we investigate how MC4Rs regulate the sympathetic preganglionic neurons and find that MC4Rs activate these neurons via the protein kinase A-dependent activation of the transient receptor potential vanilloid 1 (TRPV1) channel. Importantly, we demonstrate that the inhibition of TRPV1 prevents MC4R-induced elevation of BP but does not affect MC4R-induced anorexia. We further show that TRPV1 is responsible for MC4R-dependent activation of the sympathetic preganglionic neurons by high-fat diet. Together, our results provide insight into how MC4Rs regulate sympathetic function.

Abstract 112: Role Of Endogenous Brain Melanocortin-4 Receptor Activation In Regulating Blood Pressure And Metabolic Function In Offspring Of Parents With Obesity

We previously demonstrated that activation of the central nervous system (CNS) melanocortin system modulates sympathetic nerve activity (SNA) and blood pressure (BP) in obese Zucker rats and spontaneously hypertensive rats (SHRs). In the present study, we examined whether endogenous activation of the brain melanocortin-4 receptors (MC4R) contributes to the regulation of BP and metabolic function in adult male (24-26 weeks-old) obese and lean offspring from parents fed a normal (N) or high fat diet (H). The rats were implanted with telemetry probes to measure BP and heart rate (HR) 24-hrs/day, and an intracerebroventricular (ICV) cannula was placed into the lateral ventricle. After 1 week to recover from surgery and 2 days of control measurements, the MC4R antagonist (SHU-9119) was infused (1 nmol/h, ICV) for 7 days followed by a 7-day recovery period. MC4R antagonism markedly increased food intake in all groups; however, the increase was more pronounced in obese offspring from obese H-fed parents (HH), especially when analyzing the net cumulative increase in food intake during the 7 days of treatment (191±11 vs. 136±14, 65±18 and 72±12 g) compared with obese offspring from lean N-fed parents (NH), lean offspring from obese H-fed parents (HN) and lean offspring from lean parents (NN), respectively. This increased food intake was associated with more weight gain in HH compared with NH, HN and NN offspring (Δ: 92±12 vs. 81±17, 52±11 and 38±9 g). Plasma leptin and insulin levels were markedly increased in HH offspring compared to NH, HN and NN offspring. Compared to NH and NN offspring from lean parents, HH and HN offspring from obese parents exhibited higher baseline mean arterial pressure (125±2 and 122±3 vs. 118±1 and 113±3 mmHg) and greater reduction in BP during SHU-9119 infusion (average last 3 days of infusion: -14.3±0.1 and -5.6±0.5 vs. -9.8±0.2 and -3.4±0.2 mmHg, respectively). The reduction in HR during SHU-9119 infusion, however, was more pronounced in NH and NN groups compared with HH and HN offspring (average last 3 days of infusion: -55±2 and -43±1 vs. -34±2 and -34±1 bpm). These results suggest that endogenous activation of brain MC4R may contribute to the elevated BP in obese offspring but not lean offspring from obese parents.

Incorporation of Indoylated Phenylalanine Yields a Sub-Micromolar Selective Melanocortin-4 Receptor Antagonist Tetrapeptide.

The melanocortin family is involved in many physiological functions, including pigmentation, steroidogenesis, and appetite. The centrally expressed melanocortin-3 and melanocortin-4 receptors (MC3R and MC4R) possess overlapping but distinct roles in energy homeostasis. Herein, the third and fourth positions of a tetrapeptide lead compound [Ac-Arg-Arg-(pI)DPhe-Tic-NH2], previously reported to possess MC3R agonist and MC4R antagonist activities, were substituted with indoylated phenylalanine (Wsf/Wrf) residues in an attempt to generate receptor subtype selective compounds. At the third position, d-amino acids were required for melanocortin agonist activity, while both l- and d-residues resulted in MC4R antagonist activity. These results indicate that l-indoylated phenylalanine residues at the third position of the scaffold can generate MC4R over MC3R selective antagonist ligands, resulting in a substitution pattern that may be exploited for novel MC4R ligands that can be used to probe the in vivo activity of the MC4R without involvement of the MC3R.

Melanocortin-4 receptor signaling in the central amygdala mediates chronic inflammatory pain effects on nociception

Chronic inflammatory pain represents one of the largest subsets of chronic pain diagnoses, which affect nearly a quarter of individuals in the United States and cost nearly $600 billion dollars annually. Chronic pain leads to persistent sensory hypersensitivities, as well as emotional and cognitive disturbances. Evidence suggests that melanocortin 4 receptors (MC4Rs) mediate pain-signaling and pain-like behaviors via actions at various nodes in the pain-neural axis, but the field lacks a complete understanding of the potential role of MC4Rs in chronic inflammatory pain in males and females. The central amygdala (CeA) expresses high quantities of MC4R and receives pain-related information from the periphery, and in vivo CeA manipulations alter nociceptive behavior in pain-naïve and in animals with chronic pain. Here, we tested the hypothesis that MC4Rs in the CeA modulate thermal nociception and mechanical sensitivity, as well as pain avoidance, in male and female Wistar rats, using a model of chronic inflammatory pain (Complete Freud's Adjuvant; CFA). First, we report that CFA produces long-lasting hyperalgesia in adult male and female Wistar rats, and long-lasting pain avoidance in male Wistar rats. Second, we report that MC4R antagonism in the CeA reduces thermal nociception and mechanical sensitivity in male and female Wistar rats treated with CFA. Finally, we report that MC4R antagonism in the CeA reduces pain avoidance in male, and that this effect is not due to drug effects on locomotor activity. Our results indicate that a model of chronic inflammatory pain produces long-lasting increases in pain-like behaviors in adult male and female Wistar rats, and that antagonism of MC4Rs in the CeA reverses those effects.

Leptin/Melanocortin pathway hormones in obese patients after laparoscopic sleeve gastrectomy.

The melanocortin system is an important neural system underlying the control of body weight and food intake. This system has recently received great attention as a potential target for obesity treatment. Therefore, the objective of this study was to find out the leptin-melanocortin pathway before and after Laparoscopic Sleeve Gastrectomy (LSG) in obese patients. The study was carried out with a total of 144 individuals in 3 groups [control, obese group before LSG and obese group after LSG (who underwent LSG one year ago)]. The amount of leptin (LEP), leptin receptor (LEPR), tropomyosin receptor kinase receptor B (TrkB), brain-derived neurotrophic factor (BDNF), pro-opiomelanocortin (POMC) and melanocortin-4 receptors (MC4R) molecules were measured by using Enzyme-Linked Immunosorbent Assays. A statistically significant difference was found between the groups in terms of body mass index (BMI) values (p = 0.001). There was also statistically significant difference present between obese before LSG group and obese after LSG group regarding the levels of LEP, TrkB, BDNF and proteins (p < 0.05). A decline was determined in the LEP and BDNF levels one year follow-up after LSG. The evidence suggests that the leptin melanocortin pathway strictly regulates food intake and BMI before and after LSG surgery. This pathway should be kept under control for effectively reducing food intake and body weight in the treatment of obesity.

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.

Influence of Selective Melanocortin-4 Receptor Antagonist HS014 on Hypersensitivity After Nervous System Injuries in a Model of Rat Neuropathic Pain: A Narrative Review of the Literature.

Background and Objective: The melanocortin-4 (MC4) receptor has been evaluated as a possible new therapeutic for neuropathic pain treatment. The purpose of this review article was to review and evaluate all recent in vivo studies on the effect of the MC4 receptor antagonist HS014 on rat hypersensitivity caused by neuropathic pain.Methods: An electronic search was carried out using Scopus, Web of Science, PubMed, and Google Scholar. The following inclusion criteria were used: rat models of neuropathic pain-induced hypersensitivity, with investigated effects of the selective antagonist HS014. The included duration of the search was within the last ten years. Data regarding HS014, neuropathic pain model, post-treatment administration time and dose (days post-injury), behavior assessment assays, treatment frequency, and route of delivery were collected and subjected descriptively as complementary data in this narrative review.Results: This narrative review included four papers that fulfilled the eligibility criteria. The findings demonstrate that as compared to vehicle-treated rats, administration of the MC4 receptor antagonist HS014 remarkably raised paw withdrawal threshold (PWT) in three studies and heat withdrawal latency in four studies among rat models subjected to neuropathic pain.Conclusions: In rat neuropathic pain models, the MC4 receptor antagonist HS014 is helpful in reducing hypersensitivity. However, further studies are needed to determine the ideal treatment dosage and timing. In addition, further investigations are required for the role of this selective receptor antagonist (HS014) and compared with other types of MC4 receptors in neuropathic pain in humans.

Novel Targets Explored in the Treatment of Alcohol Withdrawal Syndrome.

Alcohol Withdrawal Syndrome (AWS) is characterized as the termination of chronic and sustained alcohol use that leads to severe symptoms of distress or loss of daily functions when less or no alcohol is consumed. It is a debilitating manifestation of alcohol dependence and responds poorly to the available clinical therapies. Alcohol drinking is continuously increasing all over the world. It causes 3.3 million deaths every year (5.9% of all deaths) and 5.1% of the global burden of disease. Alcohol Withdrawal syndrome leads to various changes in the brain's neurotransmitters system, such as GABA, glutamate, non-epinephrine, serotonin. These symptoms arose from the imbalance in brain receptors between gamma-aminobutyric acid (GABA) and N methyl aspartate (NMDA) that develop on the discontinuation of alcohol. Studies from various in vivo and in vitro animal models of alcohol withdrawal explored new targets for the treatment of alcohol withdrawal syndrome. Advancements in the elucidation of the AWS mechanism have revealed a number of key targets that hypothesize to modulate clinical status. The present review discusses the pathophysiology, neurobiology, and treatment of alcohol withdrawal syndrome and its novel targets like corticotrophin-releasing factor, sigma, melanocortin-4 receptors, opioid, potassium channels, ghrelin, and endocannabinoid receptors, and gut microbiota. This review discusses the various clinical and pre-clinical aspects related to alcohol dependence. The exploration of novel pharmacological targets may provide effective therapeutic interventions for the management of alcohol withdrawal syndrome.

Discovery of Nanomolar Melanocortin-3 Receptor (MC3R)-Selective Small Molecule Pyrrolidine Bis-Cyclic Guanidine Agonist Compounds Via a High-Throughput "Unbiased" Screening Campaign.

The central melanocortin-3 and melanocortin-4 receptors (MC3R, MC4R) are key regulators of body weight and energy homeostasis. Herein, the discovery and characterization of first-in-class small molecule melanocortin agonists with selectivity for the melanocortin-3 receptor over the melanocortin-4 receptor are reported. Identified via "unbiased" mixture-based high-throughput screening approaches, pharmacological evaluation of these pyrrolidine bis-cyclic guanidines resulted in nanomolar agonist activity at the melanocortin-3 receptor. The pharmacological profiles at the remaining melanocortin receptor subtypes tested indicated similar agonist potencies at both the melanocortin-1 and melanocortin-5 receptors and antagonist or micromolar agonist activities at the melanocortin-4 receptor. This group of small molecules represents a new area of chemical space for the melanocortin receptors with mixed receptor pharmacology profiles that may serve as novel lead compounds to modulate states of dysregulated energy balance.

A Gut-Intrinsic Melanocortin Signaling Complex Augments L-Cell Secretion in Humans

Hypothalamic melanocortin 4 receptors (MC4R) are a key regulator of energy homeostasis. Brain-penetrant MC4R agonists have failed, as concentrations required to suppress food intake also increase blood pressure. However, peripherally located MC4R may also mediate metabolic benefits of MC4R activation. Mc4r transcript is enriched in mouse enteroendocrine L cells and peripheral administration of the endogenous MC4R agonist, α-melanocyte stimulating hormone (α-MSH), triggers the release of the anorectic hormones Glucagon-like peptide-1 (GLP-1) and peptide tyrosine tyrosine (PYY) in mice. This study aimed to determine whether pathways linking MC4R and L-cell secretion exist in humans. GLP-1 and PYY levels were assessed in body mass index-matched individuals with or without loss-of-function MC4R mutations following an oral glucose tolerance test. Immunohistochemistry was performed on human intestinal sections to characterize the mucosal MC4R system. Static incubations with MC4R agonists were carried out on human intestinal epithelia, GLP-1 and PYY contents of secretion supernatants were assayed. Fasting PYY levels and oral glucose-induced GLP-1 secretion were reduced in humans carrying a total loss-of-function MC4R mutation. MC4R was localized to L cells and regulates GLP-1 and PYY secretion from exvivo human intestine. α-MSH immunoreactivity in the human intestinal epithelia was predominantly localized to L cells. Glucose-sensitive mucosal pro-opiomelanocortin cells provide a local source of α-MSH that is essential for glucose-induced GLP-1 secretion in small intestine. Our findings describe a previously unidentified signaling nexus in the human gastrointestinal tract involving α-MSH release and MC4R activation on L cells in an autocrine and paracrine fashion. Outcomes from this study have direct implications for targeting mucosal MC4R to treat human metabolic disorders.