Evaluation of a melanocortin-4 receptor (MC4R) agonist (Setmelanotide) in MC4R deficiency

Antiobesity Pharmacotherapy for Patients With Genetic Obesity Due to Defects in the Leptin-Melanocortin Pathway

Lifestyle interventions are the cornerstone of obesity treatment. However, insufficient long-term effects are observed in patients with genetic obesity disorders, as their hyperphagia remains untreated. Hence, patients with genetic obesity often require additional pharmacotherapy to effectively manage and treat their hyperphagia and obesity. Recent advancements in antiobesity pharmacotherapy have expanded the range of available antiobesity medications (AOM). This includes the targeted AOM setmelanotide, approved for specific genetic obesity disorders, as well as nontargeted AOMs such as naltrexone-bupropion and glucagon-like peptide-1 analogues. Targeted AOMs have demonstrated significant weight loss, reduced obesity-related comorbidities, and improved hyperphagia and quality of life in patients with specific genetic obesity disorders. Small observational studies have shown that similar benefits from nontargeted AOMs or off-label pharmacotherapies can be achieved in patients with specific genetic obesity disorders, compared to common multifactorial obesity. In the future, novel and innovative pharmacotherapeutical options, including combination therapies and possibly gene therapy, will emerge, offering promising effects on body weight, hyperphagia, and, most importantly, quality of life for patients with a variety of genetic obesity disorders.

High-resolution deep mutational scanning of the melanocortin-4 receptor enables target characterization for drug discovery

Deep Mutational Scanning (DMS) is an emerging method to systematically test the functional consequences of thousands of sequence changes to a protein target in a single experiment. Because of its utility in interpreting both human variant effects and protein structure-function relationships, it holds substantial promise to improve drug discovery and clinical development. However, applications in this domain require improved experimental and analytical methods. To address this need, we report novel DMS methods to precisely and quantitatively interrogate disease-relevant mechanisms, protein-ligand interactions, and assess predicted response to drug treatment. Using these methods, we performed a DMS of the melanocortin-4 receptor (MC4R), a G-protein-coupled receptor (GPCR) implicated in obesity and an active target of drug development efforts. We assessed the effects of >6600 single amino acid substitutions on MC4R's function across 18 distinct experimental conditions, resulting in >20 million unique measurements. From this, we identified variants that have unique effects on MC4R-mediated Gαs- and Gαq-signaling pathways, which could be used to design drugs that selectively bias MC4R's activity. We also identified pathogenic variants that are likely amenable to a corrector therapy. Finally, we functionally characterized structural relationships that distinguish the binding of peptide versus small molecule ligands, which could guide compound optimization. Collectively, these results demonstrate that DMS is a powerful method to empower drug discovery and development.

Biased signaling in drug discovery and precision medicine

Receptors are crucial for converting chemical and environmental signals into cellular responses, making them prime targets in drug discovery, with about 70% of drugs targeting these receptors. Biased signaling, or functional selectivity, has revolutionized drug development by enabling precise modulation of receptor signaling pathways. This concept is more firmly established in G protein-coupled receptor and has now been applied to other receptor types, including ion channels, receptor tyrosine kinases, and nuclear receptors. Advances in structural biology have further refined our understanding of biased signaling. This targeted approach enhances therapeutic efficacy and potentially reduces side effects. Numerous biased drugs have been developed and approved as therapeutics to treat various diseases, demonstrating their significant therapeutic potential. This review provides a comprehensive overview of biased signaling in drug discovery and disease treatment, highlighting recent advancements and exploring the therapeutic potential of these innovative modulators across various diseases.

The expanding landscape of genetic causes of obesity

Obesity and weight regulation disorders are determined by the combined effects of genetics and environment. Polygenic obesity results from the combination of common variants in several genes which predisposes the individual to obesity and its related complications. In contrast, monogenic obesity results from changes in single genes, especially those in leptin-melanocortin pathway, and presents with early onset severe obesity, with or without other syndromic features. Rare variants in melanocortin 4 receptor are the commonest form of monogenic obesity. In addition, structural variation in small or large segments of chromosomes may also present with syndromic forms of obesity. Prader-Willi Syndrome, caused by imprinting errors in chromosome 15q11-13, is the most prevalent genetic cause of severe hyperphagia and obesity. With the advances in technologies, the past decade has witnessed a revolution in the identification of novel genetic causes of obesity, primarily in genes related to the leptin melanocortin pathway. The availability of safe melanocortin analogs holds the potential for targeted therapies for some of these disorders. This review summarizes known and novel rare genetic forms of obesity, along with approaches for the clinical investigation of copy number and sequence variants. The goal is to provide a reference for practicing clinicians to encourage genetic testing in obesity. IMPACT: What does this article add to the existing literature? Genetic obesity is an expanding frontier with potential to change management. Here, we summarize current information on the genetic causes of obesity and provide guidance for genetic testing. Emerging treatments may provide targeted precise treatment and change management practices.

Management of Obesity-Related Genetic Disorders

Obesity-related genetic disorders are marked by severe, early-onset obesity caused by mutations that disrupt key biological mechanisms regulating hunger, energy balance, and fat storage. These disorders commonly impact systems such as the hypothalamic leptin-melanocortin signaling network, which plays a crucial role in controlling appetite and body weight, mainly through the melanocortin-4 receptor (MC4R) pathway. This review explores current management strategies and emerging therapies for genetic obesity disorders, highlighting the importance of treatment approaches and expanded genetic diagnostics to improve outcomes for affected individuals.

Adverse event profile of setmelanotide in obesity: an integrated assessment and systematic review using disproportionality analysis, case reports and meta-analysis

BACKGROUND

Setmelanotide is approved for genetically determined obesity. While clinical trials and clinical evidence and practice provide some insights, a comprehensive assessment of its adverse event profile is needed that led to carrying out an assessment of reported adverse events in the USFDA Adverse Event Reporting System database, case reports and clinical trials.

RESEARCH DESIGN AND METHODS

Multi-faceted analyses were carried out as follows: disproportionality measures employing frequentist and Bayesian methods; systematic review and meta-analysis (Medline, Cochrane CENTRAL and Google Scholar) generated-pooled estimates [proportion with 95% confidence intervals (CI)]; and published reports with adverse events to setmelanotide.

RESULTS

The disproportionality analysis (n = 228) identified skin hyperpigmentation, injection-site reactions, nausea, melanocytic nevus and ephelides as key safety signals. Meta-analysis (seven trials; n = 185) confirmed high rates of injection-site reactions (96%; 95% CI: 89, 100), skin hyperpigmentation (62%; 95% CI: 43, 78), nausea (36%; 95% CI: 24, 49), vomiting (26%; 95% CI: 18, 34), and diarrhea (21%; 95% CI: 14, 29). Individual case reports corroborated these findings.

CONCLUSION

This study provides a detailed overview of setmelanotide's adverse event profile, highlighting the need for careful patient monitoring, emphasizing the importance of ongoing safety surveillance for at least 1.5 years, and further research to refine patient management strategies.

The MC4R agonist, setmelanotide, is associated with an improvement in hypercapnic chemosensitivity and weight loss in male mice

Obesity increases the risk of respiratory diseases that reduce respiratory chemosensitivity, such as Obesity Hypoventilation Syndrome and sleep apnea. Recent evidence suggests that obesity-related changes in the brain, including alterations in melanocortin signaling via the melanocortin-4 receptor (MC4R), may underly altered chemosensitivity. Setmelanotide, an MC4R agonist, causes weight loss in both humans and animal models. However, it is unknown the extent to which setmelanotide affects respiratory chemosensitivity independent of body weight loss. The present study uses diet-induced obese, male C57bl/6 J mice to determine the extent to which acute setmelanotide treatment affects the hypercapnic ventilatory response (HCVR). We find that ten days of daily setmelanotide treatment at 1 mg/kg, but not 0.2 mg/kg, is sufficient to cause weight loss and increase HCVR. In a separate group of animals, we find that we can emulate setmelanotide's effect on weight loss by restricting daily calories to match the hypophagia triggered by setmelanotide. These pair-fed animals exhibit improvements in HCVR similar to those who receive setmelanotide. We conclude that acute treatment with setmelanotide is as effective as weight loss at improving respiratory hypercapnic chemosensitivity.

FDA-approved drugs featuring macrocycles or medium-sized rings

Macrocycles or medium-sized rings offer diverse functionality and stereochemical complexity in a well-organized ring structure, allowing them to fulfill various biochemical functions, resulting in high affinity and selectivity for protein targets, while preserving sufficient bioavailability to reach intracellular compartments. These features have made macrocycles attractive candidates in organic synthesis and drug discovery. Since the 20th century, more than three-score macrocyclic drugs, including radiopharmaceuticals, have been approved by the US Food and Drug Administration (FDA) for treating bacterial and viral infections, cancer, obesity, immunosuppression, inflammatory, and neurological disorders, managing cardiovascular diseases, diabetes, and more. This review presents 17 FDA-approved macrocyclic drugs during the past 5 years, highlighting their importance and critical role in modern therapeutics, and the innovative synthetic approaches for the construction of these macrocycles.

An overview of benefits and risks of chronic melanocortin-1 receptor activation

The melanocortin-1 receptor (MC1R) is a G protein-coupled receptor that plays a pivotal role in human skin pigmentation, melanin synthesis, redox homeostasis and inflammation. Loss-of-function MC1R variants suppress G protein-coupled receptor coupling or cell surface expression leading to a decrease in adenyl cyclase activation and intracellular levels of cyclic adenosine monophosphate. Chronic activation of MC1R can occur in certain medical conditions such as Addison's disease and physiologic states such as pregnancy melasma. MC1R activation is more commonly caused by environmental exposure to ultraviolet (UV) radiation. Approved pharmacologic melanocortin agonists that activate MC1R signalling in a targeted manner or as a bystander effect have recently become available for erythropoietic protoporphyria, sexual desire disorders, monogenic obesity and syndromic obesity. Further, small peptide analogues of α-melanocortin-stimulating hormone, human MC1R selective agonists, are photoprotective, decreasing the adverse impact of UV radiation (a primary risk factor for skin cancer) and are being investigated as potential chemoprevention strategies. MC1R activation through induction of UV-protective skin pigmentation increased DNA repair, and control of aberrant cell growth may reduce the risk of melanoma but importantly does not prevent melanoma particularly in individuals with risk factors and regular skin examination remains critical in high-risk individuals.

Stochastic neuropeptide signals compete to calibrate the rate of satiation

Neuropeptides have important roles in neural plasticity, spiking and behaviour1. Yet, many fundamental questions remain regarding their spatiotemporal transmission, integration and functions in the awake brain. Here we examined how MC4R-expressing neurons in the paraventricular nucleus of the hypothalamus (PVHMC4R) integrate neuropeptide signals to modulate feeding-related fast synaptic transmission and titrate the transition to satiety2-6. We show that hunger-promoting AgRP axons release the neuropeptide NPY to decrease the second messenger cAMP in PVHMC4R neurons, while satiety-promoting POMC axons release the neuropeptide αMSH to increase cAMP. Each release event is all-or-none, stochastic and can impact multiple neurons within an approximately 100-µm-diameter region. After release, NPY and αMSH peptides compete to control cAMP-the amplitude and persistence of NPY signalling is blunted by high αMSH in the fed state, while αMSH signalling is blunted by high NPY in the fasted state. Feeding resolves this competition by simultaneously elevating αMSH release and suppressing NPY release7,8, thereby sustaining elevated cAMP in PVHMC4R neurons throughout a meal. In turn, elevated cAMP facilitates potentiation of feeding-related excitatory inputs with each bite to gradually promote satiation across many minutes. Our findings highlight biochemical modes of peptide signal integration and information accumulation to guide behavioural state transitions.

Charting New Territories in Obesity Management- Traditional Techniques to Tirzepatide

BACKGROUND

Obesity, a pervasive global health challenge affecting more than 2 billion people, requires comprehensive interventions. Traditional approaches, including lifestyle modification, and diverse drugs targeting a gastrointestinal hormone, including glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 (Liraglutide, Semaglutide, Exenatide, Albiglutide, Dulaglutide, Lixisenatide, Orlistat, Phentermine/Topiramate, Lorcaserin, Sibutramine, and Rimonabant) offer tailored strategies; yet their effectiveness is limited and some drugs were taken off the market. Moreover, various surgical modalities, such as Roux-en-Y Bypass surgery, sleeve gastrectomy, intragastric balloons, biliopancreatic diversion with duodenal switch, laparoscopic adjustable gastric band, and vagal nerve blockade can be considered but are associated with numerous side effects and require careful monitoring. Consequently, there is a pressing need for novel anti-obesity treatments.

METHODS

This comprehensive review was based on the available data to discuss the traditional pharmaceutical and surgical therapeutical strategies for obesity, going further to discuss tirzepatide's mode of action, its outcomes for obesity, and the associated side effects.

RESULTS

In this landscape, tirzepatide, initially designed for type 2 diabetes management, emerges as a potential game-changer. Functioning as a dual glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 receptor agonist, it not only addresses control but also introduces a fresh perspective on weight reduction. This review intricately explores tirzepatide's mechanism, dissecting insights from clinical studies and positioning it as a major force in obesity treatment.

CONCLUSIONS

In the middle of significant shifts in obesity management, tirzepatide presents itself as a promising and cost-effective intervention. Its Food and Drug Administration approval marks a milestone in the realm of obesity therapeutics. Going beyond a recapitulation of findings, the conclusion emphasizes the imperative for ongoing exploration and vigilant safety monitoring in tirzepatide's application.

Exploring the therapeutic potential of precision medicine in rare genetic obesity disorders: a scientific perspective

The prevalence of obesity is increasing worldwide, affecting both children and adults. This obesity epidemic is mostly driven by an increase in energy intake (abundance of highly palatable energy-dense food and drinks) and to a lesser degree a decrease in energy expenditure (sedentary lifestyle). A small proportion of individuals with obesity are affected by genetic forms of obesity, which often relate to mutations in the leptin-melanocortin pathway or are part of syndromes such as the Bardet-Biedl syndrome. These rare forms of obesity have provided valuable insights into the genetic architecture of obesity. Recent advances in understanding the molecular mechanisms that control appetite, hunger, and satiety have led to the development of drugs that can override genetic defects, enabling precision treatment. Leptin deficiency is uniquely treated with recombinant human metreleptin, while those with LEPR, PCSK1, or POMC deficiency can now be treated with the MC4R agonist setmelanotide. This review highlights the most frequent monogenic and syndromic forms of obesity, and the future outlook of precision treatment for these conditions.

Epigenetic regulation is involved in reversal of obesity

Epigenetic processes play a crucial role in mediating the impact of environmental energetic challenges, from overconsumption to starvation. Over-nutrition of energy-dense foods and sedentary lifestyles contribute to the development of obesity, characterized by excessive fat storage and impaired metabolic signaling, stemming from disrupted brain signaling. Conversely, dieting and physical activity facilitate body weight rebalancing and trigger adaptive neural responses. These adaptations involve the upregulation of neurogenesis, synaptic plasticity and optimized brain function and energy homeostasis, balanced hormone signaling, normal metabolism, and reduced inflammation. The transition of the brain from a maladaptive to an adaptive state is partially guided by epigenetic mechanisms. While epigenetic mechanisms underlying obesity-related brain changes have been described, their role in mediating the reversal of maladaptation/obesity through lifestyle interventions remains less explored. This review focuses on elucidating epigenetic mechanisms involved in hypothalamic adaptations induced by lifestyle interventions. Given that lifestyle interventions are widely prescribed and accessible approaches for weight loss and maintenance, it is our challenge to uncover epigenetic mechanisms moderating these hypothalamic-functional beneficial changes.

Treatment of Hypothalamic Obesity With GLP-1 Analogs

Introduction

Congenital and acquired damage to hypothalamic nuclei or neuronal circuits controlling satiety and energy expenditure results in hypothalamic obesity (HO). To date, successful weight loss and satiety has only been achieved in a limited number of affected patients across multiple drug trials. Glucagon-like peptide-1 (GLP-1) acts via central pathways that are independent from the hypothalamus to induce satiety. GLP-1 receptor agonists (GLP-1RAs) may provide an alternative approach to treating HO.

Methods

We performed a comprehensive search in Medline, Google Scholar, and clinical trials registries (ClinicalTrials.gov; clinicaltrialsregister.eur). This nonsystematic literature review was conducted to identify scientific papers published from January 2005 to February 2024 using the Pubmed and Embase databases. Key words used were GLP-1, GLP-1RA, hypothalamic obesity, suprasellar tumor, and craniopharyngioma.

Results

Our search identified 7 case studies, 5 case series, and 2 published clinical trials relating to the use of GLP-1RAs in HO. All case studies demonstrated weight loss and improved metabolic function. In contrast, results from case series were variable, with some showing no weight loss and others demonstrating moderate to significant weight loss and improved metabolic parameters. In the ECHO clinical trial, nearly half the subjects randomized to weekly exenatide showed reduced body mass index (BMI). Paradoxically, BMI reduction was greater in patients with more extensive hypothalamic injuries.

Conclusion

GLP-1RAs potentially offer a new approach to treating HO. There is a need to stratify patients who are more likely to respond. Further randomized controlled trials are required to determine their efficacy either in isolation or combined with other therapies.

Investigating genetic variants in early-onset obesity through exome sequencing: A retrospective cohort study

OBJECTIVE

This study aimed to examine clinical data and analyze exome sequencing (ES) findings in children diagnosed with early-onset obesity.

METHODS

We screened children presenting with severe (body mass index-standard deviation score >3) and early-onset (<7 years) obesity using ES. Participants were categorized into either the "no variant identified" group or the "variant identified" group, facilitating the exploration of correlations between clinical-demographic characteristics and genetic mutations linked to early-onset obesity. The functional implications of identified variants were assessed through in silico analyses.

RESULTS

Of the patients, 32 (35.5 %) possessed one or more mutations in pathways associated with obesity, all of which were heterozygous and patients with more than two obesity-associated variants were more obese. This cohort included 29 novel mutations distinct to our study population, 7 previously reported pathogenic variants, two instances of uniparental disomy, and one mitochondrial hotspot mutation. Variants in the SH2B1 gene emerged as a prevalent genetic determinant of obesity within our group, accounting for 16.6 % of cases. Statistical evaluations showed no significant differences in demographic attributes between the two groups.

CONCLUSION

Exome sequencing proves to be an instrumental approach for uncovering new variants and broadening the spectrum of mutations in early-onset obesity among children. Concurrently, further functional studies, both in vitro and in vivo, are crucial to elucidate the contributions of these variants to obesity's pathogenesis.

Obesity Medications and Their Impact on Cardiovascular Health: A Narrative Review

Obesity is a major global issue linked to cardiovascular diseases (CVDs). While lifestyle changes are the primary treatment, medications are often required for long-term weight management and reducing risk in patients with obesity. The cardiovascular effects of many obesity medications are still being studied. This review examines the cardiovascular impact of commonly prescribed obesity medications, focusing on their mechanisms, effectiveness, and safety. A review of the literature was conducted to evaluate the cardiovascular effects of these drugs, including their impact on major cardiovascular outcomes, cholesterol, blood pressure, and other heart-related factors. Some medications, like glucagon-like peptide-1 receptor agonists (GLP-1 RAs), show cardiovascular benefits, while others like orlistat have a lesser effect. Medications such as naltrexone-bupropion and phentermine-topiramate offer weight loss but still require further review for their cardiovascular safety. Data on setmelanotide's long-term effects are limited. Obesity medications differ in their effects on cardiovascular health, with some offering more consistent benefits. More studies are needed to fully understand their long-term risks and benefits, but combining medication with lifestyle changes remains key to improving both weight and heart health.

Updates in pharmacotherapy of obesity

Obesity is now recognized as a chronic, progressive condition requiring early intervention and long-term management to achieve health benefits and improve metabolic risk factors. The main objective of obesity pharmacotherapy is weight loss and weight loss maintenance. There is increasing acceptance of anti-obesity medications as an adjunct to lifestyle modifications and/or surgery. In recent years there has been an evolution in management approach and pharmacologic options for treatment. As a result, there is increased focus on the efficacy and safety of these agents. We provide a historical perspective, review of recent studies on anti-obesity medication outcomes showing efficacy, potential side effects and promising therapies in development.

Setmelanotide: A Melanocortin-4 Receptor Agonist for the Treatment of Severe Obesity Due to Hypothalamic Dysfunction

Obesity is a silent global pandemic. It is a condition associated with multiple risk factors and adverse outcomes that arise from the intertwined relationship between environmental factors and genetics. The genetic factors that cause phenotypic expression are variable. Monogenic obesity is a severe early-onset and rarer form of obesity, which presents with co-morbidities such as abnormal feeding behaviour. Monogenic obesity causes impaired weight regulation in the hypothalamus due to defects in the leptin-melanocortin signalling pathway. The emergence of a new therapeutic treatment, the melanocortin-4 receptor agonist setmelanotide (originally RM-493), has represented a breakthrough in the management of monogenic obesity and has raised hope in managing complex obesity. This review provides an overview of the setmelanotide trials that have taken place, as well as its mechanism of action, side effects and weight loss outcomes that led to its approval in the treatment of pro-opiomelanocortin (POMC) deficiency and proprotein convertase subtilisin/kexin type 1 (PCSK1) deficiency. It also explores setmelanotide's role in other genetic forms of obesity, such as hypothalamic obesity, Prader-Willi syndrome, Alström syndrome and other rare genetic conditions that are being investigated. This review aims to help to understand the pathophysiology of genetic obesity and aid in future treatment options for people with severe, complex genetic obesity.

Medical semiology of patients with monogenic obesity: A systematic review

Patients with monogenic obesity display numerous medical features on top of hyperphagic obesity, but no study to date has provided an exhaustive description of their semiology. Two reviewers independently conducted a systematic review of MEDLINE, Embase, and Web of Science Core Collection databases from inception to January 2022 to identify studies that described symptoms of patients carrying pathogenic mutations in at least one of eight monogenic obesity genes (ADCY3, LEP, LEPR, MC3R, MC4R, MRAP2, PCSK1, and POMC). Of 5207 identified references, 269 were deemed eligible after title and abstract screening, full-text reading, and risk of bias and quality assessment. Data extraction included mutation spectrum and mode of inheritance, clinical presentation (e.g., anthropometry, energy intake and eating behaviors, digestive function, puberty and fertility, cognitive features, infectious diseases, morphological characteristics, chronic respiratory disease, and cardiovascular disease), biological characteristics (metabolic profile, endocrinology, hematology), radiological features, and treatments. The review provides an exhaustive description of mandatory, non-mandatory, and unique symptoms in heterozygous and homozygous carriers of mutation in eight monogenic obesity genes. This information is critical to help clinicians to orient genetic testing in subsets of patients with suspected monogenic obesity and provide actionable treatments (e.g., recombinant leptin and MC4R agonist).

Structure elucidation of a human melanocortin-4 receptor specific orthosteric nanobody agonist

The melanocortin receptor 4 (MC4R) belongs to the melanocortin receptor family of G-protein coupled receptors and is a key switch in the leptin-melanocortin molecular axis that controls hunger and satiety. Brain-produced hormones such as α-melanocyte-stimulating hormone (agonist) and agouti-related peptide (inverse agonist) regulate the molecular communication of the MC4R axis but are promiscuous for melanocortin receptor subtypes and induce a wide array of biological effects. Here, we use a chimeric construct of conformation-selective, nanobody-based binding domain (a ConfoBody Cb80) and active state-stabilized MC4R-β2AR hybrid for efficient de novo discovery of a sequence diverse panel of MC4R-specific, potent and full agonistic nanobodies. We solve the active state MC4R structure in complex with the full agonistic nanobody pN162 at 3.4 Å resolution. The structure shows a distinct interaction with pN162 binding deeply in the orthosteric pocket. MC4R peptide agonists, such as the marketed setmelanotide, lack receptor selectivity and show off-target effects. In contrast, the agonistic nanobody is highly specific and hence can be a more suitable agent for anti-obesity therapeutic intervention via MC4R.

The Genetics of Obesity

Understanding the genetic causes of obesity permits anticipatory guidance and targeted treatments. Children with hyperphagia and severe early-onset obesity should receive genetic testing for rare monogenic and syndromic disorders caused by pathogenic variants involving a single gene or single chromosomal region. Gene panels covering the leptin pathway, the key regulator of energy balance, are becoming more widely available and at lower cost. Polygenic obesity is much more common and involves multiple genes throughout the genome, although the overlap in genes for rare and common disorders suggests a spectrum of severity and the potential of shared precision medicine approaches for treatment.

MC4R Variants Modulate α-MSH and Setmelanotide Induced Cellular Signaling at Multiple Levels

CONTEXT

The melanocortin-4 receptor (MC4R) plays an important role in body weight regulation. Pathogenic MC4R variants are the most common cause of monogenic obesity.

OBJECTIVE

We have identified 17 MC4R variants in adult and pediatric patients with obesity. Here we aimed to functionally characterize these variants by analyzing 4 different aspects of MC4R signaling. In addition, we aimed to analyze the effect of setmelanotide, a potent MC4R agonist, on these MC4R variants.

MATERIALS AND METHODS

Cell surface expression and α-melanocyte stimulating hormone (α-MSH)- or setmelanotide-induced cAMP response, β-arrestin-2 recruitment, and ERK activation were measured in cells expressing either wild type or variant MC4R.

RESULTS

We found a large heterogeneity in the function of these variants. We identified variants with a loss of response for all studied MC4R signaling, variants with no cAMP accumulation or ERK activation but normal β-arrestin-2 recruitment, and variants with normal cAMP accumulation and ERK activation but decreased β-arrestin-2 recruitment, indicating disrupted desensitization and signaling mechanisms. Setmelanotide displayed a greater potency and similar efficacy as α-MSH and induced significantly increased maximal cAMP responses of several variants compared to α-MSH. Despite the heterogeneity in functional response, there was no apparent difference in the obesity phenotype in our patients.

CONCLUSION

We show that these obesity-associated MC4R variants affect MC4R signaling differently yet lead to a comparable clinical phenotype. Our results demonstrate the clinical importance of assessing the effect of MC4R variants on a range of molecular signaling mechanisms to determine their association with obesity, which may aid in improving personalized treatment.

Harnessing the melanocortin system in the control of food intake and glucose homeostasis

The central and peripheral melanocortin system, comprising of five receptors and their endogenous ligands, is responsible for a wide array of physiological functions such as skin pigmentation, sexual function and development, and inflammation. A growing body of both clinical and pre-clinical research is demonstrating the relevance of this system in metabolic health. Disruption of hypothalamic melanocortin signalling is the most common cause of monogenic obesity in humans. Setmelanotide, an FDA-approved analogue of alpha-melanocyte stimulating hormone (α-MSH) that functions by restoring central melanocortin signalling, has proven to be a potent pharmacological tool in the treatment of syndromic obesity. As the first effective therapy targeting the melanocortin system to treat metabolic disorders, its approval has sparked research to further harness the links between these melanocortin receptors and metabolic processes. Here, we outline the structure of the central and peripheral melanocortin system, discuss its critical role in the regulation of food intake, and review promising targets that may hold potential to treat metabolic disorders in humans.

The complex web of obesity: from genetics to precision medicine

INTRODUCTION

Obesity is a growing public health concern affecting both children and adults. Since it involves both genetic and environmental components, the management of obesity requires both, an understanding of the underlying genetics and changes in lifestyle. The knowledge of obesity genetics will enable the possibility of precision medicine in anti-obesity medications.

AREAS COVERED

Here, we explore health complications and the prevalence of obesity. We discuss disruptions in energy balance as a symptom of obesity, examining evolutionary theories, its multi-factorial origins, and heritability. Additionally, we discuss monogenic and polygenic obesity, the converging biological pathways, potential pharmacogenomics applications, and existing anti-obesity medications - specifically focussing on the leptin-melanocortin and incretin pathways. Comparisons between childhood and adult obesity genetics are made, along with insights into structural variants, epigenetic changes, and environmental influences on epigenetic signatures.

EXPERT OPINION

With recent advancements in anti-obesity drugs, genetic studies pinpoint new targets and allow for repurposing existing drugs. This creates opportunities for genotype-informed treatment options. Also, lifestyle interventions can help in the prevention and treatment of obesity by altering the epigenetic signatures. The comparison of genetic architecture in adults and children revealed a significant overlap. However, more robust studies with diverse ethnic representation is required in childhood obesity.

Housing mice near vs. below thermoneutrality affects drug-induced weight loss but does not improve prediction of efficacy in humans

Evaluation of weight loss drugs is usually performed in diet-induced obese mice housed at ∼22°C. This is a cold stress that increases energy expenditure by ∼35% compared to thermoneutrality (∼30°C), which may overestimate drug-induced weight loss. We investigated five anti-obesity mechanisms that have been in clinical development, comparing weight loss in mice housed at 22°C vs. 30°C. Glucagon-like peptide-1 (GLP-1), human fibroblast growth factor 21 (hFGF21), and melanocortin-4 receptor (MC4R) agonist induced similar weight losses. Peptide YY elicited greater vehicle-subtracted weight loss at 30°C (7.2% vs. 1.4%), whereas growth differentiation factor 15 (GDF15) was more effective at 22°C (13% vs. 6%). Independent of ambient temperature, GLP-1 and hFGF21 prevented the reduction in metabolic rate caused by weight loss. There was no simple rule for a better prediction of human drug efficacy based on ambient temperature, but since humans live at thermoneutrality, drug testing using mice should include experiments near thermoneutrality.

Sequencing methods, functional characterization, prevalence, and penetrance of rare coding mutations in panels of monogenic obesity genes from the leptin-melanocortin pathway: A systematic review

The recent development of next-generation sequencing (NGS) technologies has led to an increase of mutation screening reports of monogenic obesity genes in diverse experimental designs. However, no study to date has summarized their findings. Two reviewers independently conducted a systematic review of MEDLINE, Embase, and Web of Science Core Collection databases from inception to September 2022 to identify monogenic non-syndromic obesity gene screening studies. Of 1051 identified references, 31 were eligible after title and abstract screening and 28 after full-text reading and risk of bias and quality assessment. Most studies (82%) used NGS methods. The number of genes screened varied from 2 to 12 genes from the leptin-melanocortin pathway. While all the included studies used in silico tools to assess the functional status of mutations, only 2 performed in vitro tests. The prevalence of carriers of pathogenic/likely pathogenic monogenic mutations is 13.24% on average (heterozygous: 12.31%; homozygous/heterozygous composite: 0.93%). As no study reported the penetrance of pathogenic mutations on obesity, we estimated that homozygous carriers exhibited a complete penetrance (100%) and heterozygous carriers a variable penetrance (3-100%). The review provides an exhaustive description of sequencing methods, functional characterization, prevalence, and penetrance of rare coding mutations in monogenic non-syndromic obesity genes.

A review of dolutegravir-associated weight gain and secondary metabolic comorbidities

Dolutegravir is an integrase inhibitor and is recommended by the World Health Organization as the preferred first-line and second-line human immunodeficiency virus treatment in all populations. Excessive weight gain associated with dolutegravir-based regimens is an emerging issue; however, the long-term metabolic consequences of this effect have not been fully understood. Growing evidence shows that this leads to a higher incidence of hyperglycemia, hypertension, and metabolic syndrome, along with elevated cardiovascular risk. Dolutegravir-based regimens, also associated with greater adipocyte differentiation and greater expression of markers associated with lipid storage, continue to be a problem among patients living with human immunodeficiency virus. The mechanisms by which certain antiretroviral therapy agents differentially contribute to weight gain remain unknown. Some clinical investigators speculate that dolutegravir could interfere with central nervous system appetite regulation (melanocortin-4 receptor) and insulin signaling, or may have better penetration of adipose tissue where they could exert a direct impact on adipose tissue adipogenesis, fibrosis, and insulin resistance. This review summarizes our current understanding of weight gain and fat changes associated with dolutegravir and its possible secondary metabolic comorbidities.

Functional coupling between MC4R and Kir7.1 contributes to clozapine-induced hyperphagia

Most antipsychotic drugs (APDs) induce hyperphagia and weight gain. However, the neural mechanisms are poorly understood, partly due to challenges replicating their metabolic effects in rodents. Here, we report a new mouse model that recapitulates overeating induced by clozapine, a widely prescribed APD. Our study shows that clozapine boosts food intake by inhibiting melanocortin 4 receptor (MC4R) expressing neurons in the paraventricular nucleus of the hypothalamus. Interestingly, neither clozapine nor risperidone, another commonly used APD, affects receptor-ligand binding or the canonical Gαs signaling of MC4R. Instead, they inhibit neuronal activity by enhancing the coupling between MC4R and Kir7.1, leading to the open state of the inwardly rectifying potassium channel. Deletion of Kir7.1 in Mc4r-Cre neurons prevents clozapine-induced weight gain, while treatment with a selective Kir7.1 blocker mitigates overeating in clozapine-fed mice. Our findings unveil a molecular pathway underlying the effect of APDs on feeding behavior and suggest its potential as a therapeutic target.

Setmelanotide for the treatment of acquired hypothalamic obesity: a phase 2, open-label, multicentre trial

BACKGROUND

Hypothalamic obesity resulting from hypothalamic damage might affect melanocortin signalling. We investigated the melanocortin-4 receptor agonist setmelanotide for treatment of hypothalamic obesity.

METHODS

This phase 2, open-label, multicentre trial was done in five centres in the USA. Eligible patients were aged between 6 and 40 years with obesity and history of hypothalamic injury or diagnosis of a non-malignant tumour affecting the hypothalamus that was treated with surgery, chemotherapy, or radiation. Setmelanotide was titrated up to a dose of 3·0 mg and administered subcutaneously once a day for a total duration of 16 weeks. The primary endpoint was the proportion of patients with a reduction in BMI of at least 5% from baseline after 16 weeks, compared with a historic control rate of less than 5% in this population. The primary endpoint was analysed using the full analysis set, which includes all patients with baseline data who received at least one dose of setmelanotide. Safety was assessed in all patients who received at least one dose of study drug. This trial is registered with ClinicalTrials.gov (NCT04725240) and is complete.

FINDINGS

Between June 6, 2021, and Jan 13, 2022, 19 patients were screened for inclusion. One patient was excluded, and 18 were enrolled and received at least one dose of setmelanotide. Patients were primarily White (n=14 [78%]) and male (n=11 [61%]). Enrolled patients had a mean age of 15·0 years (SD 5·3) and a mean BMI of 38·0 kg/m2 (SD 6·5). Of 18 patients enrolled, 16 (89%) of 18 patients completed the study and met the primary endpoint of reduction in BMI of at least 5% from baseline after 16 weeks (p<0·0001). The mean reduction in BMI across all patients was 15% (SD 10). A composite proportion of patients had a clinically meaningful change (89%, 90% CI 69-98%; p<0·0001), comprising a reduction in BMI Z score of at least 0·2 points for patients younger than 18 years (92%, 68-100%; p<0·0001) and reduction in bodyweight of at least 5% for patients aged 18 years or older (80%, 34-99%; p<0·0001). Patients aged 12 years or older had a mean reduction in hunger score of 45%. Frequent adverse events included nausea (61%), vomiting (33%), skin hyperpigmentation (33%), and diarrhoea (22%). Of 14 patients who continued treatment in a long-term extension study (NCT03651765), 12 completed at least 12 months of treatment at the time of publication and had a mean change in BMI of -26% (SD 12) from index trial baseline.

INTERPRETATION

These findings support setmelanotide as a novel effective treatment of hypothalamic obesity.

FUNDING

Rhythm Pharmaceuticals.

Obesity medications: A narrative review of current and emerging agents

The aim of this narrative review is to synthesize the available data describing the efficacy and safety of medications approved for obesity management and to provide an overview of upcoming agents in development. A literature search of PubMed, Medline, and Embase databases identified relevant articles describing medications approved in the U.S., Australia, U.K., and/or Europe. Papers were selected based on relevance and originality, with phase 3 clinical trials and meta-analyses preferentially included. Six medications are widely approved for long-term weight management in conjunction with lifestyle interventions in people with body mass index (BMI) ≥30 ​kg/m2 or BMI ≥27 ​kg/m2 and at least one medical condition related to excess weight. Compared with lifestyle interventions alone, all medications approved for obesity management are more effective for long-term weight loss and improvements in cardiometabolic risk factors. Older obesity medications are associated with mean weight losses in the range of 5-10%. The new generation of agents, including the injectable incretin analogues semaglutide and tirzepatide are associated with sustained mean weight reductions of 15-20%, along with substantial benefits on a range of health outcomes. Several novel agents are under development, with multi-hormone receptor agonists and oral formulations likely to become available in the coming years. As effective treatment options expand, cost and availability will need to be addressed to enable equitable access to treatment. Other important challenges for clinical practice and research include the need for long-term strategies to prevent and manage weight regain and loss of lean muscle and bone mineral density.

IMPROVE 2022 International Meeting on Pathway-Related Obesity: Vision of Excellence

Nearly 90 clinicians and researchers from around the world attended the first IMPROVE 2022 International Meeting on Pathway-Related Obesity. Delegates attended in person or online from across Europe, Argentina and Israel to hear the latest scientific and clinical developments in hyperphagia and severe, early-onset obesity, and set out a vision of excellence for the future for improving the diagnosis, treatment, and care of patients with melanocortin-4 receptor (MC4R) pathway-related obesity. The meeting co-chair Peter Kühnen, Charité Universitätsmedizin Berlin, Germany, indicated that change was needed with the rapidly increasing prevalence of obesity and the associated complications to improve the understanding of the underlying mechanisms and acknowledge that monogenic forms of obesity can play an important role, providing insights that can be applied to a wider group of patients with obesity. World-leading experts presented the latest research and led discussions on the underlying science of obesity, diagnosis (including clinical and genetic approaches such as the role of defective MC4R signalling), and emerging clinical data and research with targeted pharmacological approaches. The aim of the meeting was to agree on the questions that needed to be addressed in future research and to ensure that optimised diagnostic work-up was used with new genetic testing tools becoming available. This should aid the planning of new evidence-based treatment strategies for the future, as explained by co-chair Martin Wabitsch, Ulm University Medical Center, Germany.

Appetite- and Weight-Regulating Neuroendocrine Circuitry in Hypothalamic Obesity

Since hypothalamic obesity (HyOb) was first described over 120 years ago by Joseph Babinski and Alfred Fröhlich, advances in molecular genetic laboratory techniques have allowed us to elucidate various components of the intricate neurocircuitry governing appetite and weight regulation connecting the hypothalamus, pituitary gland, brainstem, adipose tissue, pancreas, and gastrointestinal tract. On a background of an increasing prevalence of population-level common obesity, the number of survivors of congenital (eg, septo-optic dysplasia, Prader-Willi syndrome) and acquired (eg, central nervous system tumors) hypothalamic disorders is increasing, thanks to earlier diagnosis and management as well as better oncological therapies. Although to date the discovery of several appetite-regulating peptides has led to the development of a range of targeted molecular therapies for monogenic obesity syndromes, outside of these disorders these discoveries have not translated into the development of efficacious treatments for other forms of HyOb. This review aims to summarize our current understanding of the neuroendocrine physiology of appetite and weight regulation, and explore our current understanding of the pathophysiology of HyOb.

The melanocortin-4 receptor pathway and the emergence of precision medicine in obesity management

Over the past few decades, there has been a global surge in the prevalence of obesity, rendering it a globally recognized epidemic. Contrary to simply being a medical condition, obesity is an intricate disease with a multifactorial aetiology. Understanding the precise cause of obesity remains a challenge; nevertheless, there seems to be a complex interplay among biological, psychosocial and behavioural factors. Studies on the genetic factors of obesity have revealed several pathways in the brain that play a crucial role in food intake regulation. The best characterized pathway, thus far, is the leptin-melanocortin pathway, from which disruptions are responsible for the majority of monogenic obesity disorders. The effectiveness of conservative lifestyle interventions in addressing monogenic obesity has been limited. Therefore, it is crucial to complement the management strategy with pharmacological and surgical options. Emphasis has been placed on developing drugs aimed at replacing the absent signals, with the goal of restoring the pathway. In both monogenic and polygenic forms of obesity, outcomes differ across various interventions, likely due to the multifaceted nature of the disease. This underscores the need to explore alternative therapeutic strategies that can mitigate this heterogeneity. Precision medicine can be regarded as a powerful tool that can address this concern, as it values the understanding of the underlying abnormality triggering the disease and provides a tailored treatment accordingly. This would assist in optimizing outcomes of the current therapeutic approaches and even aid in the development of novel treatments capable of more effectively managing the global obesity epidemic.

Semaglutide, a Long-Acting GLP-1 Analogue, for the Management of Early-Onset Obesity due to MC4R Defect: A Case Report

INTRODUCTION

Childhood obesity is a global concern and has both nutritional and genetic causative factors. One of the most common monogenic causes of obesity is heterozygous mutations in the Melanocortin 4 receptor (MC4R), which are found in 5.7-8.6% of individuals with early-onset obesity. We report, the effect of semaglutide, a long-acting glucagon-like peptide (GLP-1) analogue, in the treatment of severe obesity in an adolescent boy with a heterozygous mutation in MC4R.

CASE PRESENTATION

A 13-year-old boy with a history of excessive weight gain since infancy was referred to the specialised weight management team. He was born at full term with a birth weight of 3.57 kg (50th centile), but his weight consistently exceeded the 99.6th percentile after the age of 1 year. At the age of 5 years, he was diagnosed with autism spectrum disorder (ASD). Diagnostic investigations revealed insulin resistance and dyslipidaemia, while genetic testing confirmed a heterozygous mutation in MC4R (E61K), inherited from his mother. Managing his condition was challenging due to his rapid weight gain, needle phobia, and behavioural difficulties. Despite intense multidisciplinary lifestyle interventions, he continued to gain weight, reaching a peak weight of 187.5 kg (+16.65 standard deviation score [SDS]), body mass index (BMI) of 56.9 kg/m2 (+4.19 SDS), and body fat of 63.9% at the age of 13 years. Due to severe ASD and needle phobia, he was not keen on daily GLP-1 injections. He was commenced on semaglutide subcutaneous injection at a dose of 0.25 mg weekly, gradually increasing to the maximum dose of 1 mg weekly. Over the course of 12 weeks, his BMI decreased to 52.2 kg/m2 (+4.08 SDS) and weight dropped to 176.8 kg (+14.76 SDS, body fat: 52.7%). At the 3-month and 12-month reviews post-treatment, he achieved weight loss of 5.7% and 11%, respectively. The quality of life questionnaire showed improved scores from 35.95 to 60.36 at 12-month review, indicating enhanced well-being. The continuous glucose monitor demonstrated an improvement in time in range.

CONCLUSION

Semaglutide was approved by the US Food and Drug Administration (FDA) for weight management in adolescents aged 12 years and above in December 2022. A recent case series underscored the benefits of therapy with liraglutide, a short-acting GLP-1 analogue, in rare genetic cases of early-onset obesity. To our knowledge, this is the first case report to highlight the efficacy and safety of semaglutide in an adolescent with heterozygous MC4R mutation. Semaglutide could be a potential treatment option for monogenic obesity and will benefit from further research.

Exploring FDA-Approved Frontiers: Insights into Natural and Engineered Peptide Analogues in the GLP-1, GIP, GHRH, CCK, ACTH, and α-MSH Realms

Peptides continue to gain significance in the pharmaceutical arena. Since the unveiling of insulin in 1921, the Food and Drug Administration (FDA) has authorised around 100 peptides for various applications. Peptides, although initially derived from endogenous sources, have evolved beyond their natural origins, exhibiting favourable therapeutic effectiveness. Medicinal chemistry has played a pivotal role in synthesising valuable natural peptide analogues, providing synthetic alternatives with therapeutic potential. Furthermore, key chemical modifications have enhanced the stability of peptides and strengthened their interactions with therapeutic targets. For instance, selective modifications have extended their half-life and lessened the frequency of their administration while maintaining the desired therapeutic action. In this review, I analyse the FDA approval of natural peptides, as well as engineered peptides for diabetes treatment, growth-hormone-releasing hormone (GHRH), cholecystokinin (CCK), adrenocorticotropic hormone (ACTH), and α-melanocyte stimulating hormone (α-MSH) peptide analogues. Attention will be paid to the structure, mode of action, developmental journey, FDA authorisation, and the adverse effects of these peptides.

Novel Cocrystal Structures of Peptide Antagonists Bound to the Human Melanocortin Receptor 4 Unveil Unexplored Grounds for Structure-Based Drug Design

Melanocortin 4 receptor (MC4-R) antagonists are actively sought for treating cancer cachexia. We determined the structures of complexes with PG-934 and SBL-MC-31. These peptides differ from SHU9119 by substituting His6 with Pro6 and inserting Gly10 or Arg10. The structures revealed two subpockets at the TM7-TM1-TM2 domains, separated by N2857.36. Two peptide series based on the complexed peptides led to an antagonist activity and selectivity SAR study. Most ligands retained the SHU9119 potency, but several SBL-MC-31-derived peptides significantly enhanced MC4-R selectivity over MC1-R by 60- to 132-fold. We also investigated MC4-R coupling to the K+ channel, Kir7.1. Some peptides activated the channel, whereas others induced channel closure independently of G protein coupling. In cell culture studies, channel activation correlated with increased feeding, while a peptide with Kir7.1 inhibitory activity reduced eating. These results highlight the potential for targeting the MC4-R:Kir7.1 complex for treating positive and restrictive eating disorders.

Novel Melanocortin-3 and -4 Receptor Functional Variants in Asian Children With Severe Obesity

CONTEXT

Genetic variants in melanocortin 3 receptor (MC3R) and melanocortin 4 receptor (MC4R) genes are strongly associated with childhood obesity.

OBJECTIVE

This study aims to identify and functionally characterize MC3R and MC4R variants in an Asian cohort of children with severe early-onset obesity.

METHODS

Whole-exome sequencing was performed to screen for MC3R and MC4R coding variants in 488 Asian children with severe early-onset obesity (body mass index for age ≥97th percentile). Functionality of the identified variants were determined via measurement of intracellular cyclic adenosine monophosphate (cAMP) concentrations and luciferase activity.

RESULTS

Four MC3R and 2 MC4R heterozygous nonsynonymous rare variants were detected. There were 3 novel variants: MC3R c.151G > C (p.Val51Leu), MC4R c.127C > A (p.Gln43Lys), and MC4R c.272T > G (p.Met91Arg), and 3 previously reported variants: MC3R c.127G > A (p.Glu43Lys), MC3R c.97G > A (p.Ala33Thr), and MC3R c.437T > A (p.Ile146Asn). Both MC3R c.127G > A (p.Glu43Lys) and MC4R c.272T > G (p.Met91Arg) variants demonstrated defective downstream cAMP signaling activity. The MC4R c.127C > A (p.Gln43Lys) variant showed reduced cAMP signaling activity at low substrate concentration but the signaling activity was restored at high substrate concentration. The MC3R c.151G > C (p.Val51Leu) variant did not show a significant reduction in cAMP signaling activity compared to wild-type (WT) MC3R. Coexpression studies of the WT and variant MC3R/MC4R showed that the heterozygous variants did not exhibit dominant negative effect.

CONCLUSION

Our functional assays demonstrated that MC3R c.127G > A (p.Glu43Lys) and MC4R c.272T > G (p.Met91Arg) variants might predispose individuals to early-onset obesity, and further studies are needed to establish the causative effect of these variants in the pathogenesis of obesity.

Immunogenetic Aspects of Sarcopenic Obesity

Sarcopenic obesity (SO) is a combination of obesity and sarcopenia, with diagnostic criteria defined as impaired skeletal muscle function and altered body composition (e.g., increased fat mass and reduced muscle mass). The mechanism of SO is not yet perfectly understood; however, the pathogenesis includes aging and its complications, chronic inflammation, insulin resistance (IR), and hormonal changes. Genetic background is apparent in the pathogenesis of isolated obesity, which is most often polygenic and is characterized by the additive effect of various genetic factors. The genetic etiology has not been strictly established in SO. Still, many data confirm the existence of pathogenic gene variants, e.g., Fat Mass and Obesity Associated Gene (FTO), beta-2-adrenergic receptor (ADRB2) gene, melanocortin-4 receptor (MC4R) and others with obesity. The literature on the role of these genes is scarce, and their role has not yet been thoroughly established. On the other hand, the involvement of systemic inflammation due to increased adipose tissue in SO plays a significant role in its pathophysiology through the synthesis of various cytokines such as monocyte chemoattractant protein-1 (MCP-1), IL-1Ra, IL-15, adiponectin or CRP. The lack of anti-inflammatory cytokine (e.g., IL-15) can increase SO risk, but further studies are needed to evaluate the exact mechanisms of implications of various cytokines in SO individuals. This manuscript analyses various immunogenetic and non-genetic factors and summarizes the recent findings on immunogenetics potentially impacting SO development.

Syndromic and Monogenic Obesity: New Opportunities Due to Genetic-Based Pharmacological Treatment

Obesity is a significant health problem with a continuously increasing prevalence among children and adolescents that has become a modern pandemic during the last decades. Nowadays, the genetic contribution to obesity is well-established. For this narrative review article, we searched PubMed and Scopus databases for peer-reviewed research, review articles, and meta-analyses regarding the genetics of obesity and current pharmacological treatment, published in the English language with no time restrictions. We also screened the references of the selected articles for possible additional articles in order to include most of the key recent evidence. Our research was conducted between December 2022 and December 2023. We used the terms "obesity", "genetics", "monogenic", "syndromic", "drugs", "autosomal dominant", "autosomal recessive", "leptin-melanocortin pathway", and "children" in different combinations. Recognizing the genetic background in obesity can enhance the effectiveness of treatment. During the last years, intense research in the field of obesity treatment has increased the number of available drugs. This review analyzes the main categories of syndromic and monogenic obesity discussing current data on genetic-based pharmacological treatment of genetic obesity and highlighting the necessity that cases of genetic obesity should follow specific, pharmacological treatment based on their genetic background.

Automated Patch Clamp Recordings of GPCR-Gated Ion Channels: Targeting the MC4-R/Kir7.1 Potassium Channel Complex

Automated patch clamp recording is a valuable technique in drug discovery and the study of ion channels. It allows for the precise measurement and manipulation of channel currents, providing insights into their function and modulation by drugs or other compounds. The melanocortin 4 receptor (MC4-R) is a G protein-coupled receptor (GPCR) crucial to appetite regulation, energy balance, and body weight. MC4-R signaling is complex and involves interactions with other receptors and neuropeptides in the appetite-regulating circuitry. MC4-Rs, like other GPCRs, are known to modulate ion channels such as Kir7.1, an inward rectifier potassium channel, in response to ligand binding. This modulation is critical for controlling ion flow across the cell membrane, which can influence membrane potential, excitability, and neurotransmission. The MC4-R is the target for the anti-obesity drug Imcivree. However, this drug is known to lack optimal potency and also has side effects. Using high-throughput techniques for studying the MC4-R/Kir7.1 complex allows researchers to rapidly screen many compounds or conditions, aiding the development of drugs that target this system. Additionally, automated patch clamp recording of this receptor-channel complex and its ligands can provide valuable functional and pharmacological insights supporting the development of novel therapeutic strategies. This approach can be generalized to other GPCR-gated ion channel functional complexes, potentially accelerating the pace of research in different fields with the promise to uncover previously unknown aspects of receptor-ion channel interactions.

Body Fat Distribution Contributes to Defining the Relationship between Insulin Resistance and Obesity in Human Diseases

The risk for metabolic and cardiovascular complications of obesity is defined by body fat distribution rather than global adiposity. Unlike subcutaneous fat, visceral fat (including hepatic steatosis) reflects insulin resistance and predicts type 2 diabetes and cardiovascular disease. In humans, available evidence indicates that the ability to store triglycerides in the subcutaneous adipose tissue reflects enhanced insulin sensitivity. Prospective studies document an association between larger subcutaneous fat mass at baseline and reduced incidence of impaired glucose tolerance. Case-control studies reveal an association between genetic predisposition to insulin resistance and a lower amount of subcutaneous adipose tissue. Human peroxisome proliferator-activated receptorgamma (PPAR-γ) promotes subcutaneous adipocyte differentiation and subcutaneous fat deposition, improving insulin resistance and reducing visceral fat. Thiazolidinediones reproduce the effects of PPAR-γ activation and therefore increase the amount of subcutaneous fat while enhancing insulin sensitivity and reducing visceral fat. Partial or virtually complete lack of adipose tissue (lipodystrophy) is associated with insulin resistance and its clinical manifestations, including essential hypertension, hypertriglyceridemia, reduced HDL-c, type 2 diabetes, cardiovascular disease, and kidney disease. Patients with Prader Willi syndrome manifest severe subcutaneous obesity without insulin resistance. The impaired ability to accumulate fat in the subcutaneous adipose tissue may be due to deficient triglyceride synthesis, inadequate formation of lipid droplets, or defective adipocyte differentiation. Lean and obese humans develop insulin resistance when the capacity to store fat in the subcutaneous adipose tissue is exhausted and deposition of triglycerides is no longer attainable at that location. Existing adipocytes become large and reflect the presence of insulin resistance.

G protein-coupled receptors and obesity

G protein-coupled receptors (GPCRs) have emerged as important drug targets for various chronic diseases, including obesity and diabetes. Obesity is a complex chronic disease that requires long term management predisposing to type 2 diabetes, heart disease, and some cancers. The therapeutic landscape for GPCR as targets of anti-obesity medications has undergone significant changes with the approval of semaglutide, the first peptide glucagon like peptide 1 receptor agonist (GLP-1RA) achieving double digit weight loss (≥10%) and cardiovascular benefits. The enhanced weight loss, with the expected beneficial effect on obesity-related complications and reduction of major adverse cardiovascular events (MACE), has propelled the commercial opportunity for the obesity market leading to new players entering the space. Significant progress has been made on approaches targeting GPCRs such as single peptides that simultaneously activate GIP and/or GCGR in addition to GLP1, oral tablet formulation of GLP-1, small molecules nonpeptidic oral GLP1R and fixed-dose combination as well as add-on therapy for patients already treated with a GLP-1 agonist.

Inhibition of the melanocortin-3 receptor (MC3R) causes generalized sensitization to anorectic agents

The melanocortin-3 receptor (MC3R) acts presynaptically to regulate GABA release from agouti-related protein (AgRP) nerve terminals and thus may be a negative regulator of multiple circuits involved in feeding behavior and energy homeostasis. Here, we examined the role of MC3R in regulating the response to various anorexigenic agents. Our findings reveal that genetic deletion or pharmacological inhibition of MC3R improves the dose responsiveness to Glucagon-like peptide 1 (GLP1) agonists, as assayed by inhibition of food intake and weight loss. An enhanced anorectic response to other agents, including the acute satiety factors peptide YY (PYY3-36) and cholecystokinin (CCK) and the long-term adipostatic factor, leptin, demonstrated that increased sensitivity to anorectic agents is a generalized result of MC3R antagonism. Enhanced neuronal activation in multiple nuclei, including ARH, VMH, and DMH, was observed using Fos immunohistochemistry following low-dose liraglutide in MC3R knockout mice (Mc3r-/-), supporting the hypothesis that the MC3R is a negative regulator of circuits regulating multiple aspects of feeding behavior. The enhanced anorectic response in Mc3r -/- mice after administration of GLP1 analogs was also independent of the incretin effects and malaise induced by GLP1R analogs, suggesting that MC3R antagonists may have value in enhancing the dose-response range of obesity therapeutics.

Management of Monogenic and Syndromic Obesity

Similar to the general population, lifestyle interventions focused on nutrition and physical activity form the foundation for treating obesity caused by rare genetic disorders. Additional therapies, including metreleptin and setmelanotide, that target defects within the leptin signaling pathway can effectively synergize with lifestyle efforts to treat monogenic disorders of leptin, leptin receptor, proopiomelanocortin (POMC), and proprotein convertase subtilisin/kexin type 1 (PCSK1) and syndromic conditions, such as the ciliopathies Bardet-Biedl and Alström syndromes, whose pathophysiological mechanisms also converge on the leptin pathway. Investigational treatments for Prader-Willi syndrome target specific defects caused by reduced expression of paternally derived genes within the chromosome 15q region.

Obesity: A Review of Pathophysiology and Classification

Obesity is a chronic, multifactorial, and morbid disease. In the United States, 69% of adults are overweight or have obesity, and the global prevalence of obesity is increasing. Obesity is influenced by genetic, neurologic, metabolic, enteric, and behavioral processes. It remains a key modifiable risk factor for many comorbid diseases, including cardiovascular disease, diabetes mellitus, and cancer. Whereas there are recent and significant advances in obesity therapy, including diets, lifestyle modifications, pharmacotherapies, endoscopic procedures, and bariatric surgeries, there is an immense need for a better understanding of the heterogeneity in the pathophysiologic process of obesity and outcomes. Here we review salient pathophysiologic mechanisms underlying the development and morbidity of obesity as well as pathophysiologically based classification systems that inform current obesity management and may inform improved and individualized management in the future.

Aqueous remote loading of setmelanotide in poly(lactic-co-glycolic acid) microspheres for long-term obesity treatment

Setmelanotide (Imcivree™) was developed as a daily injectable therapeutic peptide for the treatment of rare forms of syndromic obesity, such as POMC deficiency and leptin receptor deficiency. The important option of poly(lactic-co-glycolic acid) (PLGA) controlled release microspheres has become more attractive for this class of drugs upon the discovery that net positively charged peptides can be remote-loaded rapidly from aqueous peptide solution into blank microspheres at high loading and encapsulation efficiency. Here we sought to remote-load setmelanotide in PLGA microspheres and examine its potential for long-term controlled release and body weight control. The influence of PLGA microsphere porosity was investigated with respect to morphology, drug loading, and in vitro release profiles. Increased density of the microspheres inhibited the progress of encapsulation of the dicationic peptide. A diet-induced obese murine model was then used to determine the pharmacokinetic profile and to evaluate long-term efficacy of an optimal formulation. Remote loaded PLGA formulations encapsulated setmelanotide as high as ∼63% (∼6.3% w/w loading) and exhibited slow and continuous peptide release over ∼6 weeks in vitro largely independent of microsphere porosity. The obtained in vivo release pattern from deconvolution of the pharmacokinetics after subcutaneous microsphere injection was consistent with the in vitro release profile but with a lower initial burst release and overall slightly faster release rate. After a single injection of remote-loaded setmelanotide, continuous long-term inhibition of food intake and body weight control was observed over 17 and 30 days, respectively. The improvement in body weight control over drug-free microsphere vehicle-treated control groups matched the observed PK profile. This study provides the first report of long-acting release formulation for 1-month controlled release of setmelanotide and body weight control in a diet induced obese murine model, and supports the further development of long-acting treatment options for obese patients.

Functional Characterization of Novel MC4R Variants Identified in Two Unrelated Patients with Morbid Obesity in Qatar

The leptin-melanocortin pathway is pivotal in appetite and energy homeostasis. Pathogenic variants in genes involved in this pathway lead to severe early-onset monogenic obesity (MO). The MC4R gene plays a central role in leptin-melanocortin signaling, and heterozygous variants in this gene are the most common cause of MO. A targeted gene panel consisting of 52 obesity-related genes was used to screen for variants associated with obesity. Variants were analyzed and filtered to identify potential disease-causing activity and validated using Sanger sequencing. We identified two novel heterozygous variants, c.253A>G p.Ser85Gly and c.802T>C p.Tyr268His, in the MC4R gene in two unrelated patients with morbid obesity and evaluated the functional impact of these variants. The impact of the variants on the MC4R gene was assessed using in silico prediction tools and molecular dynamics simulation. To further study the pathogenicity of the identified variants, GT1-7 cells were transfected with plasmid DNA encoding either wild-type or mutant MC4R variants. The effects of allelic variations in the MC4R gene on cAMP synthesis, MC4R protein level, and activation of PKA, ERB, and CREB signaling pathways in both stimulated and unstimulated ɑ-MSH paradigms were determined for their functional implications. In silico analysis suggested that the variants destabilized the MC4R structure and affected the overall dynamics of the MC4R protein, possibly leading to intracellular receptor retention. In vitro analysis of the functional impact of these variants showed a significant reduction in cell surface receptor expression and impaired extracellular ligand binding activity, leading to reduced cAMP production. Our analysis shows that the variants do not affect total protein expression; however, they are predicted to affect the post-translational localization of the MC4R protein to the cell surface and impair downstream signaling cascades such as PKA, ERK, and CREB signaling pathways. This finding might help our patients to benefit from the novel therapeutic advances for monogenic forms of obesity.

Dimerization of melanocortin 4 receptor controls puberty onset and body size polymorphism

Xiphophorus fish exhibit a clear phenotypic polymorphism in puberty onset and reproductive strategies of males. In X. nigrensis and X. multilineatus, puberty onset is genetically determined and linked to a melanocortin 4 receptor (Mc4r) polymorphism of wild-type and mutant alleles on the sex chromosomes. We hypothesized that Mc4r mutant alleles act on wild-type alleles by a dominant negative effect through receptor dimerization, leading to differential intracellular signaling and effector gene activation. Depending on signaling strength, the onset of puberty either occurs early or is delayed. Here, we show by Förster Resonance Energy Transfer (FRET) that wild-type Xiphophorus Mc4r monomers can form homodimers, but also heterodimers with mutant receptors resulting in compromised signaling which explains the reduced Mc4r signaling in large males. Thus, hetero- vs. homo- dimerization seems to be the key molecular mechanism for the polymorphism in puberty onset and body size in male fish.

Obesity and thinness: insights from genetics

Genetic disruption of key molecular components of the hypothalamic leptin-melanocortin pathway causes severe obesity in mice and humans. Physiological studies in people who carry these mutations have shown that the adipose tissue-derived hormone leptin primarily acts to defend against starvation. A lack of leptin causes an intense drive to eat and increases the rewarding properties of food, demonstrating that human appetite has a strong biological basis. Genetic studies in clinical- and population-based cohorts of people with obesity or thinness continue to provide new insights into the physiological mechanisms involved in weight regulation and identify molecular targets for weight loss therapy. This article is part of a discussion meeting issue 'Causes of obesity: theories, conjectures and evidence (Part II)'.