α-MSH

Functional characterisation of obesity-associated MRAP2 variants on MC4R and GHSR signalling.

Alejandra V Rodríguez Rondón, Karina Prins, Femke Volker +7 more

Melanocortin-2 receptor accessory protein-2 (MRAP2) modulates the activity of hypothalamic melanocortin-4 (MC4R) and growth hormone-secretagogue (GHSR) receptors, which suppress and promote appetite, respectively. We investigate whether obesity-associated variants of MRAP2 alter their ability to modulate MC4R and GHSR signalling as a possible mechanistic link to the development of obesity. Functional effects of five obesity-associated MRAP2 variants were analysed in HEK293 cells by co-expressing wild-type or variant MRAP2 with MC4R or GHSR. Endpoints included cell-surface and total expression, and ligand-induced second-messenger responses, β-arrestin-2 recruitment, and alternative G-protein activation. MRAP2 decreased basal MC4R cell-surface expression while GHSR cell-surface expression was not affected. In MC4R/MRAP2 expressing cells, maximal α-MSH-induced cAMP and β-arrestin-2 recruitment responses were increased. Similarly, ghrelin-induced Ca2+-mobilization in GHSR/MRAP2 expressing cells was increased, but β-arrestin-2 recruitment was suppressed. MRAP2 did not bias G-protein activation by either receptor, although previous reports show MRAP2 biases MC4R signalling towards Gαq/11. The variants did not significantly affect the ability of MRAP2 to modulate MC4R and GHSR signalling. Our results indicate that MRAP2 potentiates the ligand responsiveness of MC4R and GHSR, but has differential effects on β-arrestin-2 recruitment. The MRAP2 variants had no significant effects on the signalling endpoints tested. This suggests that, despite their association with obesity, the variants may be functionally benign, or that the absence of effects reflects limitations inherent to our cellular model. In addition, since MRAP2 can modulate multiple receptors and differentially modulate their signalling, we cannot rule out their influence on body weight regulation via other mechanisms.

[Hormones and skin pigmentation: fundamentals and clinical relevance].

Markus Böhm

Skin pigmentation by the endogenous pigment melanin is a highly coordinated process in which hormones play a crucial role. They are synthesized not only in classical endocrine organs but also in the skin itself, which acts as an independent endocrine organ. Among the endocrine target structures of the skin, the melanocortin 1 receptor (MC1R) is of particular importance. Via its high expression and tonic activity in melanocytes, as well as by binding to natural melanocortins such as α‑melanocyte-stimulating hormone (α-MSH), being generated in the skin following ultraviolet (UV) light irradiation, MC1R crucially contributes to the different skin phototypes. Gene mutations of MC1R resulting in defective cyclic adenosine monophosphate (cAMP)-mediated signalling can lead to a shift of the eumelanin/pheomelanin ratio towards the pro-oxidant, yellowish-orange pheomelanin. In patients with Addison's disease and associated syndromes, ectopic proopiomelanocortin syndrome and primary adrenal cortex insufficiency elevated melanocortin levels result in increased melanin content of the skin. Two synthetic melanocortins, afamelanotide (NDP-α-MSH) and setmelanotide, are currently approved in Germany. By targeting MC1R directly (afamelanotide) or as a bystander effect (setmelanotide), both agents increase the skin melanin content. Non-licenced synthetic melanocortins, on the other hand, are used as lifestyle products in an unregulated manner. Additional hormones regulating melanogenesis and skin pigmentation include estrogens, thyroid hormones, insulin, insulin-like growth-factor‑1 and melatonin. They are of physiological and clinical relevance during pregnancy and in patients with melasma and vitiligo. Autoimmune thyroid disorders and diabetes are associated with non-segmental vitiligo. Melatonin appears to have a lightening effect on skin pigmentation by melanin.

Disrupting the MC1R/α-MSH-pCREB-MITF Axis: Rhein-based PROTAC D16 as a Potent Melanogenesis Inhibitor.

Meng Xu, Ziqing Zhang, Peixi Zhang +12 more

Melanin protects skin from ultraviolet rays, but excessive or misdistributed synthesis can cause issues like melasma, freckles, or melanoma. Rhein from traditional Chinese herbs shows various bioactivities, with recent structural modifications enhancing its derivatives, but its effect on melanogenesis is unreported. The study reports synthesizing and evaluating D16, Rhein-based proteolysis targeting chimera (PROTACs) utilizing pomalidomide as an E3 ligand. D16 exhibited significantly reduced cytotoxicity, with half-maximal inhibitory concentration values exceeding 100 µM in both B16-F10 melanoma and human immortalized keratinocyte cells, indicating a low level of toxicity. In addition, mechanistic studies revealed that D16 suppresses melanin production primarily through the melanocortin 1 receptor/α-melanocyte-stimulating hormone signaling pathway, with further analysis suggesting phosphorylated cyclic adenosine monophosphate-response element binding protein (pCREB) as a key target. Through pCREB degradation, D16 disrupts microphthalmia-associated transcription factor transcription, leading to reduced levels of tyrosine. Molecular docking studies further confirmed strong binding between D16 and pCREB. Animal experiment results indicated that D16 effectively suppressed melanogenesis in mice. These findings underscore the potential of D16 to treat melanin-related disorders by targeting pCREB, advancing both the therapeutic utility of PROTACs and the application of pCREB modulation in pigmentation treatments.

3, 7-dihydroxy-2, 4-dimethoxyphenanthrene protects against UVB-induced skin hyperpigmentation via antioxidant and anti-melanogenic mechanisms.

Mengyan Li, Die Li, Yu Zhang +6 more

Excessive reactive oxygen species (ROS) produced by UVB radiation can disrupt the normal redox balance, leading to oxidative cellular damage as well as triggering melanin synthesis by melanocytes. Currently, natural active substances are emphasized in UV protection research. This study explored the protective effect of 3, 7-dihydroxy-2, 4-dimethoxyphenanthrene (DDP), a bioactive compound from Dendrobium lindleyi Stendel, against UVB-induced skin hyperpigmentation and examined its specific mechanism.

Regulation of Melanogenesis in Skin Epidermal Keratinocytes via Activation of α7 Nicotinic Acetylcholine Receptor on the Expression of α-Melanocyte-Stimulating Hormone.

Maggie Suisui Guo, Xiaoyang Wang, Yingjie Xia +5 more

UV irradiation stimulates the production of pro-opiomelanocortin (POMC) and its derived peptides, for example, α-melanocyte stimulating hormone (α-MSH), from keratinocytes that subsequently stimulate melanin production in melanocytes. The idea of "skin synapse" describes the interplay between keratinocytes and melanocytes being modulated by cholinergic signaling, in which acetylcholine (ACh) release is induced by UV irradiation, regulating the process of pigmentation. ObjectiveHere, the role of the cholinergic system in regulating α-MSH production in keratinocytes during UV-induced skin pigmentation was identified. α7 Nicotinic acetylcholine receptor (nAChR) agonists and antagonists, Ca2+ chelator BAPTA-AM, and α7 nAChR shRNA were applied onto HaCaT keratinocytes to evaluate the expression of POMC and production of α-MSH following UVB induction. Moreover, the conditioned medium collected from the treated HaCaT keratinocytes was added to cultured B16F10 melanoma cells to assess melanogenesis. Inhibiting α7 nAChR by its antagonist, or Ca2+ influx by Ca2+ chelator, suppressed the UVB-induced POMC expression and α-MSH production in cultured keratinocytes. Genetic silencing α7 nAChR expression hindered the UVB-induced POMC expression. Besides, the conditioned medium collected from keratinocytes being treated with α7 nAChR antagonist and UVB downregulated melanogenesis, as implied by the reduced expression of melanogenic enzymes, indicating the suppressing effect of α7 nAChR antagonist on the production of α-MSH in keratinocytes. The result suggests that α7 nAChR mediates the regulation of melanogenesis through the modulation of UVB-induced POMC transcription and α-MSH production in keratinocytes.

Development of a genetically encoded melanocortin sensor for high sensitivity in vivo imaging.

Yoon Namkung, Tal Slutzki, Joao Pedroso +4 more

The central melanocortin system, composed of peptides derived from pro-opiomelanocortin (POMC) such as the melanocyte-stimulating hormones (α-, β-, γ-MSH) and melanocortin 4 receptors (MC4R), along with the agouti-related protein (AgRP), plays a pivotal role in controlling energy balance. To elucidate the dynamic role of α-MSH release in regulating appetite, specific, sensitive, and spatiotemporally resolved genetic sensors are required.

Case Report: Improvement in cognitive functioning following setmelanotide initiation in a patient with Bardet-Biedl syndrome.

Menjin Kuk, Jesse Richards, Rachel A Ross

Bardet-Biedl syndrome (BBS) is a rare genetic condition that results from mutations in a variety of genes crucial for ciliary transport. Consequently, patients with BBS present with a wide array of clinical signs and symptoms that include multiple organ systems. In particular there is a high burden of metabolic disturbances, such as obesity, hyperphagia, and type 2 diabetes, due to the impaired leptin-melanocortin-4 receptor (MC4R) pathway that prevents appropriate activation of MC4R that is normally responsible for signaling hunger and satiety. As such, setmelanotide, an MC4R agonist, has been approved for use to target the obesity and hyperphagia experienced by patients with BBS. Here we report a case of a patient with BBS who was started on setmelanotide for weight management following her BBS diagnosis. One month following treatment initiation, the patient not only endorsed reduced appetite, but also demonstrated a significant improvement in cognitive and affective functioning, as noted in her mental status exam and her performance on the Wechsler Adult Intelligence Scale Fourth Edition (WAIS-IV) tests, when compared to results prior to starting setmelanotide. Although previous studies have reported improved quality of life measures in patients with BBS following setmelanotide initiation, this is the first report of improved cognitive and affective functioning following initiation of the medication, highlighting the need to assess the effects of setmelanotide beyond the metabolic domain in patients with BBS.

Polymorphism of Melanocortin Receptor Genes-Association with Inflammatory Traits and Diseases.

Mainak Bardhan, Ayush Anand, Amaan Javed +10 more

Melanocortin receptors (MCRs) are responsible for various functions ranging from skin pigmentation, regulation of appetite, stress response and cognition, steroid synthesis, and energy balance to cellular regeneration and immunomodulation. The genetic polymorphism with tissue distribution ranging from the brain, limbic system, and adrenal cortex to neutrophils, monocytes, and macrophages is evident in MCRs. The mutations in MC1R, MC2R, MC3R, and MC4R genes are associated with risk of melanoma, familial glucocorticoid deficiency, obesity, and type 2 diabetes mellitus, respectively. Meanwhile, MC1R, MC2R, and MC5R genes are involved in the risk of major depressive disorder. Melanocortin receptors are involved in different inflammatory disorders, i.e., atopic dermatitis, autoimmune uveitis, sarcoidosis, respiratory diseases, multiple sclerosis, scleroderma, inflammatory bowel disease, amyotrophic lateral sclerosis, Alzheimer's disease, arthritis, and reperfusion injury. Several newer therapeutic agents related to MCRs have numerous advantages over the current anti-inflammatory drugs, demonstrating therapeutic relevance. Among them, α-MSH analogs play a role in atopic dermatitis and scleroderma, and MC1R agonist Dersimelagon has shown effectiveness in systemic sclerosis. The FDA has recently approved the repository corticotropin injection (RCI) to treat sarcoidosis. The FDA has also approved various melanocortin agonists, i.e., Bremelanotide, Afamelanotide, and Setmelanotide, for the treatment of hypoactive sexual desire disorder, Erythropoietic protoporphyria, and obesity, due to pro-opiomelanocortin and leptin receptor deficiency, respectively. Therefore, this review aims to summarize the function and genetic polymorphism of melanocortin receptors, regulatory pathways involving MCRs, and the existing evidence of the prime effect of MCRs on inflammatory responses via different mechanisms and their potential therapeutic use in inflammatory diseases.

Beyond satiety: unraveling the complex roles of POMC neurons in behavior and metabolism.

Victor Jouque, Cristina Miralpeix, Antonio J López-Gambero +3 more

Hypothalamic pro-opiomelanocortin (POMC) neurons are classically viewed as mediators of satiety, acting in response to metabolic and hormonal cues and in opposition to Agouti-related protein (AgRP) neurons to maintain energy balance. This model, centered on the appetite-suppressant effects of the POMC-derived neuropeptide α-melanocyte-stimulating hormone (α-MSH) through its activation of melanocortin-4 receptors (MC4R), has shaped our understanding of feeding and body weight regulation for decades. However, recent discoveries have challenged and expanded this traditional view, revealing that POMC neurons are not a uniform population dedicated solely to satiety control. Single-cell transcriptomic analyses have revealed striking molecular heterogeneity, reflected in distinct anatomical distributions, receptor expression profiles, electrophysiological properties, and projection patterns - all supporting the idea of functional specialization within this neuronal population. In this review, we propose a conceptual framework that integrates POMC neuronal heterogeneity with the regulation of appetite, metabolic physiology, and behavior beyond feeding. We highlight emerging evidence showing that discrete POMC neuronal subpopulations respond to specific combinations of interoceptive and environmental cues to orchestrate diverse adaptive responses. This perspective underscores the developmental plasticity and functional versatility of POMC neurons, offering new insights into the mechanisms of obesity and potentially paving the way for novel targeted therapeutic strategies.

Repurposing the Antibiotic D-Cycloserine for the Treatment of Hyperpigmentation: Therapeutic Potential and Mechanistic Insights.

Ye-Jin Lee, Chang-Gu Hyun

Melanin overproduction contributes to hyperpigmentation disorders such as melasma and solar lentigines, leading to increasing demand for safe and effective skin-lightening agents. D-cycloserine (DCS), a known antimicrobial agent, has not been previously evaluated for dermatological applications. This study aimed to explore the potential of DCS as a novel anti-melanogenic compound and to elucidate its underlying molecular mechanisms in melanogenesis inhibition. The cytotoxicity and anti-melanogenic effects of DCS were assessed in B16F10 melanoma cells stimulated with α-MSH. Cell viability was determined via MTT assays, while melanin content, tyrosinase activity, and the expression levels of MITF, TYR, TRP-1, TRP-2, and major signaling proteins (e.g., CREB, MAPKs, GSK-3β/β-catenin) were evaluated using colorimetric assays and Western blotting. A 3D human skin model was also used to confirm in vitro findings, and a primary skin irritation test was conducted to assess dermal safety. DCS significantly reduced α-MSH-induced melanin content and tyrosinase activity without cytotoxicity at concentrations ≤100 µM. It downregulated MITF and melanogenic enzyme expression and modulated signaling pathways by enhancing ERK activation while inhibiting CREB, JNK, and p38 phosphorylation. Additionally, DCS suppressed β-catenin stabilization via GSK-3β activation. These effects were confirmed in a 3D human skin model, and a clinical skin irritation study revealed no adverse reactions in human volunteers. DCS exerts its anti-melanogenic effect by targeting multiple pathways, including CREB/MITF, MAPK, and GSK-3β/β-catenin signaling. Its efficacy and safety profiles support its potential as a novel cosmeceutical agent for the treatment of hyperpigmentation. Further clinical studies are warranted to confirm its therapeutic utility in human skin pigmentation disorders.

Post-stress modulation of the HPA and melanocortin systems alleviates migraine-like behaviors in mice.

Ya-Yu Hu, Hao-Ruei Mei, Shruti Sankar +4 more

BackgroundStress is a major trigger for migraine attacks. Stress activates the hypothalamic-pituitary-adrenal (HPA) axis, releasing glucocorticoids (GCs) to maintain homeostasis, and migraine attacks may occur as an adverse effect of this response. We previously demonstrated in a mouse model that inhibiting corticosterone (CORT) synthesis by administering metyrapone before stress prevented stress-induced migraine-like behaviors. Given the unpredictable nature of stressors and their onset or termination, it is critical to better understand the adaptive and maladaptive effects of the HPA stress response. Here, we aimed to evaluate the effects of HPA axis modulation following the end of stress exposure.MethodsRepeated stress induces migraine-like behaviors and priming to sodium nitroprusside (SNP) in mice. Metyrapone (to inhibit CORT synthesis), CORT (to evaluate its effects after exogenous administration), and adrenocorticotropic hormone (ACTH) (to test the effects of a hormone upstream to CORT) were administered post-stress. Additionally, α-melanocyte-stimulating hormone (α-MSH, an ACTH cleavage product) and tetrahydroisoquinoline (THIQ), a melanocortin 4 receptor (MC4R) agonist, were administered to examine melanocortin receptor involvement. Facial hypersensitivity was assessed via von Frey testing and grimace scoring was used to evaluate non-evoked pain. Serum CORT levels were measured in both control and stressed mice following ACTH administration.ResultsWe examined post-stress HPA axis modulation on stress-induced facial hypersensitivity. Metyrapone reduced acute-phase hypersensitivity and reduced priming to SNP, suggesting sustained synthesis of CORT after stress plays a role in development of migraine-like behavior. Surprisingly, both CORT and ACTH treatments at 1- and 24-h post-stress alleviated stress-induced behaviors and priming. To determine if ACTH effects were mediated by an elevation in circulating CORT, metyrapone was administered before the ACTH injection. Metyrapone increased the ACTH reversal of stress effects on facial hypersensitivity. Furthermore, post-stress ACTH injections significantly increased serum CORT levels within 30 min. In addition to ACTH effects on CORT levels, ACTH effects could be mediated by the melanocortin system. Post-stress administration of α-MSH or the MC4R agonist THIQ, reduced migraine-like behaviors.ConclusionsThere is a complex relationship between stress, the HPA axis, and melanocortin signaling, in the effects of repeated stress exposure on migraine-like behaviors. In the early post-stress response phase, there are contributions from both CORT and MC4R signaling in the maintenance of behavioral effects. These findings suggest that targeting the HPA axis and MC4R after stress may be a potential therapeutic approach for stress-induced migraine attacks.

SASH1 Mutations and Hereditary Disorders of Pigmentation: Review of Literature.

Anuradha Bishnoi, Aarushi Arunima, Keshavamurthy Vinay +2 more

Dyschromatosis universalis hereditaria (DUH) is a rare genodermatosis characterized by asymptomatic hyper- and hypopigmented macules appearing in infancy and persisting for life. Although mutations in ABCB6 account for many DUH cases, recently, the SAM and SH3 domain-containing 1 (SASH1) gene has emerged as a key player in DUH. Additionally, SASH1 mutations have been associated with the pure-lentiginous phenotype of familial pigmentation. In this review of literature, we found 22 different SASH1 mutations, most inherited in an autosomal dominant manner. These variants cause distinct phenotypes, including DUH, lentiginosis, and rarely, an autosomal recessive syndromic form with alopecia, palmoplantar keratoderma, and increased risk of malignancies. Functional studies have revealed that SASH1 acts as both a tumor suppressor and a pro-melanogenic factor. It modulates key pathways such as p53-POMC-α-MSH-MC1R-MITF and Gαs-SASH1-IQGAP1-E-cadherin pathways, affecting melanosome production, transport, and melanocyte migration. This unique dual role of SASH1 highlights its importance in melanocyte homeostasis and UV-induced pigmentation. Understanding the role of SASH1 in regulating pigmentation can help foster novel therapeutic approaches for these genodermatoses and related pigmentary anomalies, ultimately improving patient care and outcomes.

Multifunctional cosmetic potential of extracellular vesicle‑like nanoparticles derived from the stem of Cannabis sativa in treating pigmentation disorders.

Hyeon Jin Lee, Yun Hye Kim, Seo Jun Lee +5 more

While natural products and synthetic chemicals are used in functional cosmetics, their potential side effects remain a concern. This has driven the need for safer and more effective agents to treat skin disorders. This has driven the need safer and more effective agents to treat skin disorders. Therefore, the present study aimed to explore the functional properties of Cannabis sativa stem‑derived nanoparticles (CSS‑NPs) and evaluate their potential as a cosmetic ingredient. Using nanoparticle analysis, CSS‑NPs, with a mean diameter of ~120 nm exhibited notable resistance to external stress conditions, including pH fluctuation and enzymatic degradation by DNase, RNase and proteinase K. They also contained 48 distinct biochemical components. In vitro assays revealed that CSS‑NPs significantly downregulated the expression of genes and proteins associated with melanin synthesis in mouse B16F10 melanoma cells under α‑melanocyte stimulating hormone (α‑MSH)‑induced hyperpigmentation. These inhibitory effects were mediated by the activation of ERK and Akt signaling pathways. Furthermore, CSS‑NPs improved the viability of α‑MSH‑treated B16F10 cells; this was accompanied by the upregulation of antioxidant‑associated enzymes and a decrease in α‑MSH‑induced reactive oxygen species levels. Collectively, these findings suggested that CSS‑NPs carry out a key role in mitigating skin pigmentation and enhancing antioxidant defenses by modulating the ERK/Akt axis during excessive melanin synthesis. Thus, CSS‑NPs represent a promising multifunctional cosmetic ingredient with potential in treating pigmentation disorders and protecting skin cells.

Anti-inflammatory treatment using alpha melanocyte stimulating hormone (α-MSH) does not alter osteoblasts differentiation and fracture healing.

Johanna Graue, Melanie Timmen, Katharina Schmitz +5 more

Alpha-melanocyte-stimulating-hormone (α-MSH) has been identified as a new anti-inflammatory treatment compound in rheumatoid arthritis (RA) and other inflammatory diseases. However, its direct effect on bone cell differentiation or on bone regeneration, which is an inflammatory process, too, has not been investigated, yet. Bone tissue is significantly affected in inflammatory joint diseases. Additionally, inflammatory signaling is essential -in bone regeneration during fracture healing. Therefore, we evaluated the impact of α-MSH-treatment on bone forming cells in an inflammatory setting in vitro and as a treatment approach in a murine fracture healing model in vivo.

The in vitro and in vivo skin-whitening activity of Ectoine through enhanced autophagy in melanocytes and keratinocytes and zebrafish model.

Wei-Chen Jane, Siang-Jyun Chen, Jhih-Hsuan Hseu +6 more

Ectoine, a natural bacterial osmolyte, suppressed UVA irradiated-α-melanocyte stimulating hormone (MSH) stimulated melanogenesis through antioxidant Nrf2 pathways in human keratinocytes; however, the underlying skin whitening mechanisms were not elucidated. The depigmenting efficiency of Ectoine (0-400 μM) through antimelanogenesis and melanin degradation by autophagy promotion was investigated in melanoma (B16F10) and melanin-feeding keratinocyte (HaCaT) cells and in vivo zebrafish model. MTT assay, Western blotting, GFP-LC3 puncta, AVO formation, melanin assay, immunofluorescence staining, TEM techniques, siLC3 transfection, and zebrafish model were utilized. Ectoine-induced autophagy in B16F10 and HaCaT cells was shown by enhanced LC3-II accumulation, autophagosome GFP-LC3 puncta, autolysosome AVOs formation, ATG4B downregulation, and Beclin-1/Bcl-2 dysregulation. The immunoprecipitation data revealed that Ectoine increased the association between LC3-II and p62 proteins in B16F10 and HaCaT cells. Importantly, antioxidant NAC pretreatment antagonized the Ectoine-induced ATG4B diminution in B16F10 and HaCaT cells. Ectoine inhibited melanogenesis by suppressing melanosome gp100, tyrosinase, TRP-1/-2, and/or melanin formation via autophagy in α-MSH-stimulated B16F10 and melanin-feeding HaCaT cells. TEM findings displayed that Ectoine increased melanosome-engulfing autophagosomes and autolysosomes in α-MSH-stimulated B16F10 and melanin-feeding HaCaT cells. Ectoine-inhibited melanogenesis in α-MSH-stimulated B16F10 cells and melanin-feeding HaCaT cells was reversed by pretreatment with the autophagy inhibitor 3-MA or LC3 silencing. In vivo study demonstrated that Ectoine (5 mM) suppressed endogenous body pigmentation by antimelanogenesis and melanin degradation through autophagy induction in a zebrafish model. The in vitro and in vivo study demonstrated that Ectoine inhibits melanogenesis and enhances melanin degradation by triggering autophagy. Ectoine could be utilized as a whitening ingredient in cosmetic formulations.

Discovery of MT-7117 (Dersimelagon Phosphoric Acid): A Novel, Potent, Selective, and Nonpeptidic Orally Available Melanocortin 1 Receptor Agonist.

Atsushi Sato, Kenji Morokuma, Takashi Adachi +8 more

Activation of the melanocortin 1 receptor (MC1R) mediates melanogenesis in melanocytes, anti-inflammatory effects in inflammatory cells, and antifibrotic effects in fibroblasts. Thus, MC1R agonists are expected to be beneficial for treating skin, autoimmune, inflammatory, and fibrotic diseases. Afamelanotide, an α-melanocyte-stimulating hormone (α-MSH) analogue MC1R agonist, is used clinically for treating erythropoietic protoporphyria (EPP) as a subcutaneous implant formulation. We explored nonpeptidic small-molecule MC1R agonists with the aim of identifying more convenient oral drugs. By exploring the structure of previously reported compound 5, we discovered compound 11 (MT-7117: dersimelagon phosphoric acid). This compound exhibited strong MC1R agonistic activity, good pharmacokinetic properties, and excellent safety profiles. Furthermore, compound 11 was effective in animal pigmentation evaluation and skin fibrosis model studies. Compound 11 is currently in clinical trials for the treatment of EPP, X-linked protoporphyria (XLP), and systemic sclerosis (SSc). Proof of concept was obtained in phase 2 clinical studies on EPP and XLP.

Mineralocorticoid receptor activates postnatal adiposity in zebrafish lacking proopiomelanocortin.

Jithine J Rajeswari, Erin Faught, Helio Santos +1 more

The proopiomelanocortin (Pomc)-derived peptides, including adrenocorticotropic hormone and α-melanocyte stimulating hormone (α-Msh), play both a central and a peripheral role in modulating the stress response. The central role is predominantly associated with nutrient homeostasis, while peripherally they play an important role in the synthesis of glucocorticoids (GCs) in response to stress. Pomc mutations are a major risk factor in the development of early-onset childhood obesity in humans. This is attributed primarily to their central effects on melanocortin receptor dysfunction leading to hyperphagia and reduced energy expenditure, while the peripheral mechanism contributing to obesity has largely been unexplored. Here, we tested the hypothesis that Pomc mutation-mediated adrenal insufficiency and the associated changes in GC signaling contribute to postnatal adiposity using zebrafish as a model. We generated a ubiquitous Pomc knockout zebrafish that mimicked the mammalian mutant phenotype of adrenal insufficiency and enhanced adiposity. The loss of Pomc inhibited stress-induced cortisol production and reprogrammed GC signaling by reducing glucocorticoid receptor responsiveness, whereas the mineralocorticoid receptor (Mr) signaling was enhanced. Larval feeding led to enhanced growth and adipogenesis in the Pomc mutants, and this was inhibited by eplerenone, an Mr antagonist. Altogether, our results underscore a key role for Mr signaling in early developmental adipogenesis and a possible target for therapeutic intervention for early-onset childhood obesity due to Pomc dysfunction.

Giant Centella asiatica, a novel cultivar rich in madecassoside and asiaticoside, suppresses α‑melanocyte‑stimulating hormone‑induced melanogenesis through MC1R binding.

Jiwon Seo, Chanhyeok Jeong, Seung Man Oh +9 more

The present study investigated the anti‑melanogenesis effects of Giant Centella asiatica (GCA), a new cultivator of Centella asiatica (CA) cataloged by the Korea Forest Service in 2022, and compared its efficacy with that of traditional CA. GCA has a high yield per unit area and enhanced antioxidant properties. The anti‑melanogenic effects of GCA were investigated using B16F10 melanoma cells and a 3D human skin‑equivalent model. Key molecular mechanisms were elucidated through western blotting, cAMP assays and molecular docking studies. Focus was addressed on the effect of GCA on skin whitening by comparing the ability of a GCA extract to inhibit melanin production in B16F10 melanoma cells and a 3D human skin‑equivalent model to that of CA. The results showed that the GCA extracts more effectively reduced melanin production, which was attributed to their higher content of two active components, madecassoside and asiaticoside. Further investigation revealed that GCA primarily inhibited melanogenesis through the PKA‑cAMP response element‑binding (CREB)‑microphthalmia‑associated transcription factor (MITF) axis, a key regulatory pathway in melanin synthesis. Notably, the present study, to the best of our knowledge, is the first to demonstrate that madecassoside and asiaticoside, the two principal compounds in GCA, directly bound to MC1R, which contributed to the significant skin‑whitening effects. Moreover, GCA reduced melanin production in a 3D human skin‑equivalent model, showing efficacy within a complex skin environment. These results demonstrated the superior effectiveness of GCA to that of CA for skin anti‑melanogenesis, indicating its potential as a promising natural material for targeting pigmentation disorders.

Journey through the spectacular landscape of melanocortin 1 receptor.

P R Upadhyay, V B Swope, R J Starner +2 more

The physiological role of α-melanocyte stimulating hormone in regulating integumental pigmentation of many vertebrate species has been recognized since the 1960's. However, its physiological significance for human pigmentation remained enigmatic until the 1990's. α-Melanocyte stimulating hormone and related melanocortins are synthesized locally in the skin, primarily by keratinocytes, in addition to the pituitary gland, and therefore act as paracrine factors for melanocytes. Human melanocytes express the melanocortin 1 receptor, which recognizes α-melanocyte stimulating hormone and the related adrenocorticotropic hormone as agonists. This review summarizes the current knowledge of the pleotropic effects of the activated melanocortin 1 receptor that maintain human melanocyte homeostasis by regulating melanogenesis and the response to environmental stressors, mainly solar radiation. Certain allelic variants of the melanocortin 1 receptor gene are associated with specific pigmentary phenotypes in various human populations. Variants associated with red hair phenotype compromise the function of the encoded receptor. Activation of the human melanocortin 1 receptor regulates eumelanin synthesis and enhances DNA damage response of melanocytes to solar radiation and oxidative stressors. We describe how synthetic selective melanocortin 1 receptor agonists can be efficacious as sunless tanning agents, for treatment of vitiligo and photosensitivity disorders, and for prevention of skin cancer, including melanoma.

Antioxidant and Skin-Whitening Efficacy of a Novel Decapeptide (DP, KGYSSYICDK) Derived from Fish By-Products.

Sung-Gyu Lee, Jin-Woo Hwang, Hyun Kang

The skin is vulnerable to damage from ultraviolet rays and oxidative stress, which can lead to aging and pigmentation issues. This study investigates the antioxidant and whitening efficacy of a decapeptide (DP, KGYSSYICDK) derived from marine fish by-products and evaluates its potential as a new skin-whitening agent. DP demonstrated high antioxidant activity, showing comparable or superior performance to Vitamin C (Vit. C) in ferric reducing antioxidant power (FRAP) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging assays. In hydrogen peroxide (H2O2)-treated HaCaT cells, DP increased cell viability and reduced reactive oxygen species (ROS) generation. Furthermore, DP inhibited tyrosinase activity and decreased melanin production in α-melanocyte stimulating hormone (α-MSH)-induced B16F10 melanoma cells in a dose-dependent manner. Reverse transcription polymerase chain reaction (RT-PCR) analysis revealed that DP reduces the mRNA expression of MITF, tyrosinase, and MC1R, thus suppressing melanin production. DP exhibits strong binding interactions with multiple amino acid residues of tyrosinase, indicating potent inhibitory effects on the enzyme. These results suggest that DP possesses significant antioxidant and whitening properties, highlighting its potential as a skin-whitening agent. Future research should focus on optimizing DP's structure and exploring structure-activity relationships.

MC4R Localizes at Excitatory Postsynaptic and Peri-Postsynaptic Sites of Hypothalamic Neurons in Primary Culture.

Haven Griffin, Jude Hanson, Kevin D Phelan +1 more

The melanocortin-4 receptor (MC4R) is a G protein-coupled receptor (GPCR) that is expressed in several brain locations encompassing the hypothalamus and the brainstem, where the receptor controls several body functions, including metabolism. In a well-defined pathway to decrease appetite, hypothalamic proopiomelanocortin (POMC) neurons localized in the arcuate nucleus (Arc) project to MC4R neurons in the paraventricular nuclei (PVN) to release the natural MC4R agonist α-melanocyte-stimulating hormone (α-MSH). Arc neurons also project excitatory glutamatergic fibers to the MC4R neurons in the PVN for a fast synaptic transmission to regulate a satiety pathway potentiated by α-MSH. By using super-resolution microscopy, we found that in hypothalamic neurons in a primary culture, postsynaptic density protein 95 (PSD95) colocalizes with GluN1, a subunit of the ionotropic N-methyl-D-aspartate receptor (NMDAR). Thus, hypothalamic neurons form excitatory postsynaptic specializations. To study the MC4R distribution at these sites, tagged HA-MC4R under the synapsin promoter was expressed in neurons by adeno-associated virus (AAV) gene transduction. HA-MC4R immunofluorescence peaked at the center and in proximity to the PSD95- and NMDAR-expressing sites. These data provide morphological evidence that MC4R localizes together with glutamate receptors at postsynaptic and peri-postsynaptic sites.

Effect of Ibuprofen as an Albumin Binder on Melanoma-Targeting Properties of 177Lu-Labeled Ibuprofen-Conjugated Alpha-Melanocyte-Stimulating Hormone Peptides.

Zheng Qiao, Jingli Xu, Fabio Gallazzi +4 more

The purpose of this study was to examine how the introduction of ibuprofen (IBU) affected tumor-targeting and biodistribution properties of 177Lu-labeled IBU-conjugated alpha-melanocyte-stimulating hormone peptides. The IBU was used as an albumin binder and conjugated to the DOTA-Lys moiety without or with a linker to yield DOTA-Lys(IBU)-GG-Nle-CycMSHhex {1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-Lys(IBU)-Gly-Gly-Nle-c[Asp-His-DPhe-Arg-Trp-Lys]-CONH2}, DOTA-Lys(Asp-IBU)-GGNle-CycMSHhex, DOTA-Lys(Asn-IBU)-GGNle-CycMSHhex, and DOTA-Lys(Dab-IBU)-GGNle-CycMSHhex peptides. Their melanocortin-receptor 1 (MC1R) binding affinities were determined on B16/F10 melanoma cells first. Then the biodistribution of 177Lu-labeled peptides was determined on B16/F10 melanoma-bearing C57 mice at 2 h postinjection to choose the lead peptide for further examination. The full biodistribution and melanoma imaging properties of 177Lu-DOTA-Lys(Asp-IBU)-GGNle-CycMSHhex were further evaluated using B16/F10 melanoma-bearing C57 mice. DOTA-Lys(IBU)-GG-Nle-CycMSHhex, DOTA-Lys(Asp-IBU)-GGNle-CycMSHhex, DOTA-Lys(Asn-IBU)-GGNle-CycMSHhex, and DOTA-Lys(Dab-IBU)-GGNle-CycMSHhex displayed the IC50 values of 1.41 ± 0.37, 1.52 ± 0.08, 0.03 ± 0.01, and 0.58 ± 0.06 nM on B16/F10 melanoma cells, respectively. 177Lu-DOTA-Lys(Asp-IBU)-GGNle-CycMSHhex exhibited the lowest liver and kidney uptake among all four designed 177Lu peptides. Therefore, 177Lu-DOTA-Lys(Asp-IBU)-GGNle-CycMSHhex was further evaluated for its full biodistribution and melanoma imaging properties. The B16/F10 melanoma uptake of 177Lu-DOTA-Lys(Asp-IBU)-GGNle-CycMSHhex was 19.5 ± 3.12, 24.12 ± 3.35, 23.85 ± 2.08, and 10.80 ± 2.89% ID/g at 0.5, 2, 4, and 24 h postinjection, respectively. Moreover, 177Lu-DOTA-Lys(Asp-IBU)-GGNle-CycMSHhex could clearly visualize the B16/F10 melanoma lesions at 2 h postinjection. The conjugation of IBU with or without a linker to GGNle-CycMSHhex affected the MC1R binding affinities of the designed peptides. The charge of the linker played a key role in the liver and kidney uptake of 177Lu-Asp-IBU, 177Lu-Asn-IBU, and 177Lu-Dab-IBU. 177Lu-Asp-IBU exhibited higher tumor/liver and tumor/kidney uptake ratios than those of 177Lu-Asn-IBU and 177Lu-Dab-IBU, underscoring its potential evaluation for melanoma therapy in the future.

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

Patrick Swan, Brett Johnson, Carel W le Roux +1 more

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.

A Nude Mouse Model of Xenografted Hypertrophic Scar Cells to Test Therapeutics in the Skin.

Bonnie C Carney, Cynthia M Simbulan-Rosenthal, Dean S Rosenthal +1 more

Existing animal models for testing therapeutics in the skin are limited. Mouse and rat models lack similarity to human skin in structure and wound healing mechanism. Pigs are regarded as the best model with regards to similarity to human skin; however, these studies are expensive, time-consuming, and only small numbers of biologic replicates can be obtained. In addition, local-regional effects of treating wounds that are closely adjacent to one-another with different treatments make assessment of treatment effectiveness difficult in pig models. Therefore, here, a novel nude mouse model of xenografted porcine hypertrophic scar (HTS) cells was developed. This model system was developed to test if supplying hypo-pigmented cells with exogenous alpha melanocyte stimulating hormone (α-MSH) will reverse pigment loss in vivo.

Interruption of p38MAPK-MSK1-CREB-MITF-M pathway to prevent hyperpigmentation in the skin.

Song-Hee Kim, Jiyeon Lee, Jihye Jung +8 more

Background: Melanocortin 1 receptor (MC1R), a receptor of α-melanocyte-stimulating hormone (α-MSH), is exclusively present in melanocytes where α-MSH/MC1R stimulate melanin pigmentation through microphthalmia-associated transcription factor M (MITF-M). Toll-like receptor 4 (TLR4), a receptor of endotoxin lipopolysaccharide (LPS), is distributed in immune and other cell types including melanocytes where LPS/TLR4 activate transcriptional activity of nuclear factor (NF)-κB to express cytokines in innate immunity. LPS/TLR4 also up-regulate MITF-M-target melanogenic genes in melanocytes. Here, we propose a molecular target of antimelanogenic activity through elucidating inhibitory mechanism on α-MSH-induced melanogenic programs by benzimidazole-2-butanol (BI2B), an inhibitor of LPS/TLR4-activated transcriptional activity of NF-κB. Methods: Ultraviolet B (UV-B)-irradiated skins of HRM-2 hairless mice and α-MSH-activated melanocyte cultures were employed to examine melanogenic programs. Results: Topical treatment with BI2B ameliorated UV-B-irradiated skin hyperpigmentation in mice. BI2B suppressed the protein or mRNA levels of melanogenic markers, such as tyrosinase (TYR), MITF-M and proopiomelanocortin (POMC), in UV-B-exposed and pigmented skin tissues. Moreover, BI2B inhibited melanin pigmentation in UV-B-irradiated co-cultures of keratinocyte and melanocyte cells and that in α-MSH-activated melanocyte cultures. Mechanistically, BI2B inhibited the activation of cAMP response element-binding protein (CREB) in α-MSH-induced melanogenic programs and suppressed the expression of MITF-M at the promoter level. As a molecular target, BI2B primarily inhibited mitogen-activated protein kinase (MAPK) kinase 3 (MKK3)-catalyzed kinase activity on p38MAPK. Subsequently, BI2B interrupted downstream pathway of p38MAPK-mitogen and stress-activated protein kinase-1 (MSK1)-CREB-MITF-M, and suppressed MITF-M-target melanogenic genes, encoding enzymes TYR, TYR-related protein-1 (TRP-1) and dopachrome tautomerase (DCT) in melanin biosynthesis, and encoding proteins PMEL17 and Rab27A in the transfer of pigmented melanosomes to the overlaying keratinocytes in the skin. Conclusion: Targeting the MKK3-p38MAPK-MSK1-CREB-MITF-M pathway was suggested as a rationale to inhibit UV-B- or α-MSH-induced facultative melanogenesis and as a strategy to prevent acquired pigmentary disorders in the skin.

The whitening effect of cuscutin responsible for traditional use of Bergenia purpurascens.

Yang-Yang Liu, Yue Zhang, Ling Jiang +5 more

The roots and rhizomes of Bergenia purpurascens (Hook. f. et Thomson) Engl., was used as a sunscreen to protect against ultraviolet rays in Tibet of China historically, but its skin whitening constituents and pharmacological effects of this plant remained unknown.

Inhibition of α-melanocyte-stimulating hormone-induced melanogenesis and molecular mechanisms by polyphenol-enriched fraction of Tagetes erecta L. flower.

Sobarathne Senel Sanjaya, Mi Hyeon Park, Wisurumuni Arachchilage Hasitha Maduranga Karunarathne +7 more

The pursuit for safe and efficacious skin-whitening agents has prompted a dedicated exploration of plant-derived compounds. Notably, Tagetes erecta L. flowers have been used as a medicinal extract and possessed in vitro mushroom tyrosinase activity. However, whether polyphenol-enriched fraction extracted from T. erecta L. flowers (TE) regulates melanogenesis within cellular and animal models has not yet been investigated.

The in vitro and in vivo depigmentation activity of coenzyme Q0, a major quinone derivative from Antrodia camphorata, through autophagy induction in human melanocytes and keratinocytes.

You-Cheng Hseu, Jou-Tsen Yeh, Chithravel Vadivalagan +8 more

Coenzyme Q0 (CoQ0), a novel quinone derivative of Antrodia camphorata, has been utilized as a therapeutic agent (including antioxidant, anti-inflammatory, antiangiogenic, antiatherosclerotic, and anticancer agents); however, its depigmenting efficiency has yet to be studied.

Targeting phosphorylation circuits on CREB and CRTCs as the strategy to prevent acquired skin hyperpigmentation.

Song-Hee Kim, Changseon Na, Cheng-Yong Yun +9 more

Background: The cAMP response element-binding protein (CREB) and CREB-regulated transcription coactivators (CRTCs) cooperate in the transcriptional activation of microphthalmia-associated transcription factor subtype M (MITF-M) that is a master regulator in the biogenesis, pigmentation and transfer of melanosomes at epidermal melanocytes. Here, we propose the targeting of phosphorylation circuits on CREB and CRTCs in the expression of MITF-M as the rationale to prevent skin hyperpigmentation by elucidating the inhibitory activity and mechanism of yakuchinone A (Yaku A) on facultative melanogenesis. Methods: We employed human epidermal melanocyte cell, mouse skin, and mouse melanoma cell, and applied Western blotting, reverse transcription-polymerase chain reaction, immunoprecipitation and confocal microscopy to conduct this study. Results: This study suggested that α-melanocyte stimulating hormone (α-MSH)-induced melanogenic programs could switch on the axis of protein kinase A-salt inducible kinases (PKA-SIKs) rather than that of PKA-AMP activated protein kinase (PKA-AMPK) during the dephosphorylation of CRTCs in the expression of MITF-M. SIK inhibitors rather than AMPK inhibitors stimulated melanin production in melanocyte cultures in the absence of extracellular melanogenic stimuli, wherein SIK inhibitors increased the dephosphorylation of CRTCs but bypassed the phosphorylation of CREB for the expression of MITF-M. Treatment with Yaku A prevented ultraviolet B (UV-B)-irradiated skin hyperpigmentation in mice and inhibited melanin production in α-MSH- or SIK inhibitor-activated melanocyte cultures. Mechanistically, Yaku A suppressed the expression of MITF-M via dually targeting the i) cAMP-dependent dissociation of PKA holoenzyme at the upstream from PKA-catalyzed phosphorylation of CREB coupled with PKA-SIKs axis-mediated dephosphorylation of CRTCs in α-MSH-induced melanogenic programs, and ii) nuclear import of CRTCs after SIK inhibitor-induced dephosphorylation of CRTCs. Conclusions: Taken together, the targeting phosphorylation circuits on CREB and CRTCs in the expression of MITF-M could be a suitable strategy to prevent pigmentary disorders in the skin.