Role of Melanocortin Receptors in the Regulation of Gouty Inflammation

Melanocortin therapies to resolve fibroblast-mediated diseases

Stromal cells have emerged as central drivers in multiple and diverse diseases, and consequently, as potential new cellular targets for the development of novel therapeutic strategies. In this review we revise the main roles of fibroblasts, not only as structural cells but also as players and regulators of immune responses. Important aspects like fibroblast heterogeneity, functional specialization and cellular plasticity are also discussed as well as the implications that these aspects may have in disease and in the design of novel therapeutics. An extensive revision of the actions of fibroblasts on different conditions uncovers the existence of numerous diseases in which this cell type plays a pathogenic role, either due to an exacerbation of their 'structural' side, or a dysregulation of their 'immune side'. In both cases, opportunities for the development of innovative therapeutic approaches exist. In this regard, here we revise the existing evidence pointing at the melanocortin pathway as a potential new strategy for the treatment and management of diseases mediated by aberrantly activated fibroblasts, including scleroderma or rheumatoid arthritis. This evidence derives from studies involving models of in vitro primary fibroblasts, in vivo models of disease as well as ongoing human clinical trials. Melanocortin drugs, which are pro-resolving mediators, have shown ability to reduce collagen deposition, activation of myofibroblasts, reduction of pro-inflammatory mediators and reduced scar formation. Here we also discuss existing challenges, both in approaching fibroblasts as therapeutic targets, and in the development of novel melanocortin drug candidates, that may help advance the field and deliver new medicines for the management of diseases with high medical needs.

ACTH vs steroids for the treatment of acute gout in hospitalized patients: a randomized, open label, comparative study

The management of acute gout in the hospital setting may be challenging since most patients are elderly with multiple unstable comorbidities. However, there are no prospective clinical trials for hospitalized patients with gout to guide optimal management. Evidence indicates that steroids or adrenocorticotropic hormone (ACTH) may be effective and safe therapeutic options for these patients. This study aimed at directly comparing the efficacy and safety of ACTH vs betamethasone for the treatment of gout in hospitalized patients. This is the first prospective clinical trial for hospitalized patients with gout. We designed a randomized, open label study to assess the efficacy and safety of a single intramuscular injection of either ACTH or betamethasone in hospitalized patients with acute gout. Primary efficacy endpoints were the change in intensity of pain as recorded using a Visual Analogue Scale (VAS) at baseline compared to 24 h (ΔVAS24h), and 48 h. Moreover, we assessed safety and effects on the hypothalamic-pituitary-adrenal (HPA) axis, glucose and lipid homeostasis, bone metabolism, electrolytes and renal function. 38 patients were recruited. Both treatments were highly effective. The mean ± SE ΔVAS24h and ΔVAS48h for ACTH was 4.48 ± 0.29 and 5.58 ± 0.26, respectively. The mean ± SE ΔVAS24h and ΔVAS48h for betamethasone was 4.67 ± 0.32 and 5.67 ± 0.28, respectively. Direct comparison between the two groups at 24 h and 48 h did not show statistically significant differences. Both treatments were well tolerated and safe. The effects on all metabolic parameters were mostly minimal and transient for both treatments. However, ACTH may affect less the HPA axis and bone metabolism compared to betamethasone, thus leading to the conclusion that. ACTH and betamethasone are effective and safe for the management of acute gout in hospitalized patients but that ACTH may associate with less disturbance of the HPA axis and bone metabolism. Our data support the use of both drugs as first line treatments for hospitalized patients with gout.Clinical trial registration: ClinicalTrials.gov NCT04306653.

Translational advances of melanocortin drugs: Integrating biology, chemistry and genetics

Melanocortin receptors have emerged as important targets with a very unusual versatility, as their widespread distribution on multiple tissues (e.g. skin, adrenal glands, brain, immune cells, exocrine glands) together with the variety of physiological processes they control (pigmentation, cortisol release, satiety mechanism, inflammation, secretions), place this family of receptors as genuine therapeutic targets for many disorders. This review focuses in the journey of the development of melanocortin receptors as therapeutic targets from the discovery of their existence in the early 1990 s to the approval of the first few drugs of this class. Two major areas of development characterise the current state of melanocortin drug development: their role in obesity, recently culminated with the approval of setmelanotide, and their potential for the treatment of chronic inflammatory and autoimmune diseases like rheumatoid arthritis, multiple sclerosis or fibrosis. The pro-resolving nature of these drugs offers the advantage of acting by mimicking the way our body naturally resolves inflammation, expecting fewer side effects and a more balanced (i.e. non-immunosuppressive) response from them. Here we also review the approaches followed for the design and development of novel compounds, the importance of the GPCR nature of these receptors in the process of drug development, therapeutic value, current challenges and successes, and the potential for the implementation of precision medicine approaches through the incorporation of genetics advances.

Clinical and immunologic differences in cellulitis vs. pseudocellulitis

Introduction: The immunologic mechanisms between cellulitis and pseudocellulitis differ greatly, even though their clinical presentations may overlap.Areas covered: This article discusses cellulitis and common entities within the pseudocellulitis spectrum including acute lymphedema, superficial venous thrombosis, allergic contact dermatitis, lipodermatosclerosis, stasis dermatitis, erythema nodosum, cutaneous gout, and bursitis. The literature search was conducted from PubMed search engine between March and May 2021.Expert commentary: While immunologic differences in cellulitis and the various entities of pseudocellulitis are clear, there is a practice gap in applying these differences to the clinic and hospital setting. Further, existing studies are weakened by the lack of a gold-standard diagnosis in this disease category. Additional work is necessary in developing a gold-standard for the diagnosis and secondly, to project these immunologic differences as biomarkers to differentiate sterile inflammation from a potential life threatening bacterial or fungal infection.

Adrenocorticotropic hormone: an effective "natural" biologic therapy for acute gout?

Treatment of acute gout consists of non-steroidal anti-inflammatory drugs (NSAIDs), colchicine and steroids. However, the typical patient with gout has multiple comorbidities such as cardiovascular disease, hypertension, renal dysfunction or diabetes/metabolic syndrome that represent contraindications to these therapeutic options. The aim of this study is to review the available evidence regarding the use of ACTH as an alternative therapeutic option for acute gout and explore potential mechanisms of action. We performed an electronic search (MEDLINE, Scopus and Web of Science) using the keywords ACTH or adrenocorticotropic hormone combined with gout or crystal-induced arthritis. ACTH appears suitable for patients with many comorbidities due to its good safety profile. Clinical evidence shows that ACTH is at least as effective as classic agents. The mechanism of action of ACTH in gout is not entirely known. Robust experimental evidence points to the direction that ACTH does not act solely by triggering the release of endogenous steroids but also appears to downregulate inflammatory responses by activating melanocortin receptors on innate immune cells, such as macrophages. Moreover, indirect evidence indicates that ACTH may have an IL-1 antagonistic effect. We propose that ACTH may be an alternative therapeutic option for gout in patients with multiple comorbidities. Large-scale studies assessing the efficacy and safety of ACTH compared to classic therapeutic options are needed.

Melanocortin agonism as a viable strategy to control alveolar bone loss induced by oral infection

Alveolar bone loss is a result of an aggressive form of periodontal disease (PD) associated with Aggregatibacter actinomycetemcomitans (Aa) infection. PD is often observed with other systemic inflammatory conditions, including arthritis. Melanocortin peptides activate specific receptors to exert antiarthritic properties, avoiding excessing inflammation and modulating macrophage function. Recent work has indicated that melanocortin can control osteoclast development and function, but whether such protection takes place in infection-induced alveolar bone loss has not been investigated. The purpose of this study was to evaluate the role of melanocortin in Aa-induced PD. Mice were orally infected with Aa and treated with the melanocortin analog DTrp⁸-γMSH or vehicle daily for 30 d. Then, periodontal tissue was collected and analyzed. Aa-infected mice treated with DTrp⁸-γMSH presented decreased alveolar bone loss and a lower degree of neutrophil infiltration in the periodontium than vehicle-treated animals; these actions were associated with reduced periodontal levels of TNF-α, IFN-γ, and IL-17A. In vitro experiments with cells differentiated into osteoclasts showed that osteoclast formation and resorptive activity were attenuated after treatment with DTrp⁸-γMSH. Thus, melanocortin agonism could represent an innovative way to tame overexuberant inflammation and, at the same time, preserve bone physiology, as seen after Aa infection.-Madeira, M. F. M., Queiroz-Junior, C. M., Montero-Melendez, T., Werneck, S. M. C., Corrêa, J. D., Soriani, F. M., Garlet, G. P., Souza, D. G., Teixeira, M. M., Silva, T. A., Perretti, M. Melanocortin agonism as a viable strategy to control alveolar bone loss induced by oral infection.

Biased agonism as a novel strategy to harness the proresolving properties of melanocortin receptors without eliciting melanogenic effects

There is a need for novel approaches to control pathologies with overexuberant inflammatory reactions. Targeting melanocortin (MC) receptors represents a promising therapy for obesity and chronic inflammation, but lack of selectivity and safety concerns limit development. A new way to increase selectivity of biological effects entails the identification of biased agonists. In this study, we characterize the small molecule AP1189 as a biased agonist at receptors MC1 and MC3. Although not provoking canonical cAMP generation, AP1189 addition to MC1 or MC3, but not empty vector, transfected HEK293 cells caused ERK1/2 phosphorylation, a signaling responsible for the proefferocytic effect evoked in mouse primary macrophages. Added to macrophage cultures, AP1189 reduced cytokine release, an effect reliant on both MC1 and MC3 as evident from the use of Mc1r(-/-) and Mc3r(-/-) macrophages. No melanogenesis was induced by AP1189 in B16-F10 melanocytes. In vivo, oral AP1189 elicited anti-inflammatory actions in peritonitis and, upon administration at the peak of inflammation, accelerated the resolution phase by ∼3-fold. Finally, given the clinical efficacy of adrenocorticotropin in joint diseases, AP1189 was tested in experimental inflammatory arthritis, where this biased agonist afforded significant reduction of macroscopic and histological parameters of joint disruption. These proof-of-concept analyses with AP1189, an active oral anti-inflammatory and resolution-promoting compound, indicate that biased agonism at MC receptors is an innovative, viable approach to yield novel anti-inflammatory molecules endowed with a more favorable safety profile.

Resolution of inflammation: mechanisms and opportunity for drug development

Inflammation is a beneficial host reaction to tissue damage and has the essential primary purpose of restoring tissue homeostasis. Inflammation plays a major role in containing and resolving infection and may also occur under sterile conditions. The cardinal signs of inflammation dolor, calor, tumor and rubor are intrinsically associated with events including vasodilatation, edema and leukocyte trafficking into the site of inflammation. If uncontrolled or unresolved, inflammation itself can lead to further tissue damage and give rise to chronic inflammatory diseases and autoimmunity with eventual loss of organ function. It is now evident that the resolution of inflammation is an active continuous process that occurs during an acute inflammatory episode. Successful resolution requires activation of endogenous programs with switch from production of pro-inflammatory towards pro-resolving molecules, such as specific lipid mediators and annexin A1, and the non-phlogistic elimination of granulocytes by apoptosis with subsequent removal by surrounding macrophages. These processes ensure rapid restoration of tissue homeostasis. Here, we review recent advances in the understanding of resolution of inflammation, highlighting the pharmacological strategies that may interfere with the molecular pathways which control leukocyte survival and clearance. Such strategies have proved beneficial in several pre-clinical models of inflammatory diseases, suggesting that pharmacological modulation of the resolution process may be useful for the treatment of chronic inflammatory diseases in humans.

Systemic and local ACTH produced during inflammatory states promotes osteochondrogenic mesenchymal cell differentiation contributing to the pathologic progression of calcified atherosclerosis

There are many well-known roles for the proopiomelanocortin (POMC) derived peptides and their receptors, the melanocortin receptors (MC-R). The focus here is on the evolving role of the melanocortin system in inflammation. Chronic inflammatory states such as those occurring in diabetes and obesity are associated with both a hyperactive hypothalamic-pituitary-adrenal (HPA) axis as well as increased incidence of atherosclerosis. An inflammation-induced hyperactive HPA axis along with increased leukocyte infiltration can lead to significant exposure to melanocortin peptides, particularly ACTH, in an inflamed vasculature. Mesenchymal progenitor cells are present throughout the vasculature, express receptors for the melanocortin peptides, and respond to ACTH with increased osteochondrogenic differentiation. Coupled to the increased exposure to ACTH during HPA hyperactivity is increased glucocorticoid (GC) exposure. GCs also promote chondrogenic differentiation of mesenchymal progenitors and increase their expression of MC-R as well as their expression of POMC and its cleavage products. It is hypothesized that during inflammatory states systemically produced ACTH and glucocorticoid as well as ACTH produced locally by macrophage and other immune cells, can influence and potentiate mesenchymal progenitor cell differentiation along the osteochondrogenic lineages. In turn the increase in osteochondrogenic matrix contributes to the pathophysiological progression of the calcified atherosclerotic plaque. The roles of the melanocortin system in inflammation and its resolution have just begun to be explored. Investigations into the ACTH-induced matrix changes among mesenchymal cell populations are warranted. ACTH signaling through the MC-R represents a new therapeutic target for the prevention and treatment of calcified atherosclerosis.

The vasopressin-deficient Brattleboro rat: lessons for the hypothalamo-pituitary-adrenal axis regulation

Adaptation to stress is indispensable to life and the hypothalamo-pituitary-adrenocortical axis is one of the major components of the adaptation. The hypothalamic component consists of corticotropin-releasing hormone and arginine vasopressin, with a questionable contribution of the latter. Vasopressin was more important in the regulation of the adrenocorticotropin secretion in the perinatal vasopressin-deficient Brattleboro rats than in adulthood, where its role depended on the nature of the stressor encountered. In adults, the vasopressin deficiency did not influence the development of chronic stress response. In the neonatal rats, the role of vasopressin was supported by the inhibitory action of a V1b antagonist and vasopressin antiserum. As the corticosterone response to stress did not follow the adrenocorticotropin levels, we assume the presence of an adrenocorticotropin independent adrenal gland regulation in the neonates. We have shown that the apparent dissociation of the corticosterone and adrenocorticotropin responses is not due to the different time course of the two hormone responses, to different level of the corticosterone binding globulin or to changes in the adrenal gland sensitivity. In vitro experiments point to the contribution of beta-adrenoceptors in the process. It was also confirmed by in vivo tests using the vasopressin-deficient Brattleboro pup as a model organism, where corticosterone levels may rise without adrenocorticotropin level changes. Another important question is the role of adrenocorticotropin beyond the corticosterone secretion regulation, which could be supposed, e.g., in cardiovascular events, immunological processes, and metabolism. We can conclude that Brattleboro rats gave us much information about the stress-axis regulation far beyond the role of vasopressin itself.

Functional melanocortin-2 receptors are expressed by mouse aorta-derived mesenchymal progenitor cells

A local melanocortin system is active during tissue injury and inflammation. Thus far this system has been described as autocrine in nature where local production of pro-opiomelanocortin (POMC) peptides by leukocytes feeds back on melanocortin receptor (MC-R) expressing immune cells to quell inflammatory cytokine production. Here we present evidence that POMC peptides may generate extracellular matrix (ECM) changes by inducing matrix production by cells of the mesenchymal lineage through activation of the MC2-R. Using immunoblot, we determined that mouse aorta-derived mesenchymal progenitor cells express both MC2-R and MC3-R. These progenitors respond to treatment with ACTH by increasing collagen matrix synthesis as assessed by picrosirius red stain and (3)H-proline incorporation. ACTH also induces transient increases in intracellular calcium ([Ca(2+)](i)) as assessed using the fluorescent Ca(2+) indicator, fura-2. The ACTH-induced changes in [Ca(2+)](i) are consistent with MC2-R signaling and consist of both an intracellular release and an extracellular influx of Ca(2+). Both mouse aortic mesenchymal progenitors and mouse macrophage cells express POMC and the prohormone convertase 1/3 (PC1/3) indicating they have the potential to contribute to the local production of POMC peptides. These data demonstrate functional MC2-R expression in mouse aorta-derived mesenchymal progenitors and implicate both macrophage and mesenchymal cells as relevant sources of local POMC peptides.