Anti-inflammatory effects of alpha-melanocyte-stimulating hormone against rat endotoxin-induced uveitis and the time course of inflammatory agents in aqueous humor

Alpha-Melanocyte-Stimulating Hormone Maintains Retinal Homeostasis after Ischemia/Reperfusion

Augmenting the natural melanocortin pathway in mouse eyes with uveitis or diabetes protects the retinas from degeneration. The retinal cells are protected from oxidative and apoptotic signals of death. Therefore, we investigated the effects of a therapeutic application of the melanocortin alpha-melanocyte-stimulating hormone (α-MSH) on an ischemia and reperfusion (I/R) model of retinal degenerative disease. Eyes were subjected to an I/R procedure and were treated with α-MSH. Retinal sections were histopathologically scored. Also, the retinal sections were immunostained for viable ganglion cells, activated Muller cells, microglial cells, and apoptosis. The I/R caused retinal deformation and ganglion cell loss that was significantly reduced in I/R eyes treated with α-MSH. While α-MSH treatment marginally reduced the number of GFAP-positive Muller cells, it significantly suppressed the density of Iba1-positive microglial cells in the I/R retinas. Within one hour after I/R, there was apoptosis in the ganglion cell layer, and by 48 h, there was apoptosis in all layers of the neuroretina. The α-MSH treatment significantly reduced and delayed the onset of apoptosis in the retinas of I/R eyes. The results demonstrate that therapeutically augmenting the melanocortin pathways preserves retinal structure and cell survival in eyes with progressive neuroretinal degenerative disease.

Therapeutic Effects of Stimulating the Melanocortin Pathway in Regulating Ocular Inflammation and Cell Death

Alpha-melanocyte-stimulating hormone (α-MSH) and its binding receptors (the melanocortin receptors) play important roles in maintaining ocular tissue integrity and immune homeostasis. Particularly extensive studies have demonstrated the biological functions of α-MSH in both immunoregulation and cyto-protection. This review summarizes the current knowledge of both the physiological and pathological roles of α-MSH and its receptors in the eye. We focus on recent developments in the biology of α-MSH and the relevant clinical implications in treating ocular diseases.

Stimulating the Melanocortin System in Uveitis and Diabetes Preserves the Structure and Anti-Inflammatory Activity of the Retina

The endogenous neuropeptide α-Melanocyte Stimulating Hormone (α-MSH) is a potent suppressor of inflammation and has an essential role in maintaining the normal anti-inflammatory microenvironment of the retina. While the therapeutic use of α-MSH peptide in uveitis and diabetic retinopathy models has been demonstrated, its short half-life and instability limit its use as a therapeutic drug. A comparable analog, PL-8331, which has a stronger affinity to melanocortin receptors, longer half-life, and, so far, is functionally identical to α-MSH, has the potential to deliver melanocortin-based therapy. We examined the effects of PL-8331 on two mouse models of retinal disease, Experimental Autoimmune Uveoretinitis (EAU) and Diabetic Retinopathy (DR). PL-8331 therapy applied to mice with EAU suppressed EAU and preserved retinal structures. In diabetic mice, PL-8331 enhanced the survival of retinal cells and suppressed VEGF production in the retina. In addition, retinal pigment epithelial cells (RPE) from PL-8331-treated diabetic mice retained normal anti-inflammatory activity. The results demonstrated that the pan-melanocortin receptor agonist PL-8331 is a potent therapeutic drug to suppress inflammation, prevent retinal degeneration, and preserve the normal anti-inflammatory activity of RPE.

α- MSH plays anti-inflammatory and anti-fungal role in Aspergillus Fumigatus keratitis

PURPOSE

To investigate the anti-inflammatory and anti-fungal role of α-melanocyte stimulating hormone (α-MSH) in Aspergillus Fumigatus (A. fumigatus) keratitis.

METHOD

Corneas of C57BL/6 mice were infected with A. Fumigatus. α-MSH (5 ul, 1x10^-4mmol/ml) was given by subconjunctival injection from day 1 to day 3 post infection (p.i.). After 3 days p.i., clinical score was recored and HE staining was tested. Fungal load in mice corneas was observed by plate counting. Pro-inflammatory mediators and pattern recognition receptors (PRRs) were detected. The numbers of neutrophils and macrophages were tested by immunofluorescence staining. The role of α-MSH in RAW264.7 cells after A. fumigatus stimulation were evaluated by PCR and Western blot, and MPKA protein levels including total-JNK (T-JNK), phosphorylated-JNK (P-JNK), total-ERK (T-ERK) and phosphorylated-ERK (P-ERK) were tested via Western blot with or without α-MSH treatment.

RESULTS

Compared with PBS control group, α-MSH treatment alleviated disease response and decreased clinical score at 3 days p.i. HE staining showed less infiltration in corneal tissue after α-MSH treatment. Plate counting experiment showed that number of viable fungus in corneas of α-MSH treated group was less than control group. mRNA levels of IL-1β, TNF-α, IL-6, MIP-2, LOX-1, Dectin-1 and iNOS were decreased. Protein levels of IL-1β, TNF-α, IL-6 and Dectin-1 were decreased. α-MSH treatment also decreased the infiltrating neutrophils and macrophages. The levels of pro-inflammatory cytokines, Dectin-1 and LOX-1 stimulated by A. fumigatus, were also suppressed by pretreatment of α-MSH in RAW264.7 cells. The ratio of P-JNK/T-JNK and P-ERK/T-ERK were down regulated in α-MSH group compared with PBS control group.

CONCLUSION

α-MSH alleviates the severity and decreases fungal load of A. fumigatus keratitis in mice. Migration of neutrophils and macrophages are restrained. α-MSH downregulates the expression of dectin-1 and the ratio of P-JNK/T-JNK and P-ERK/T-ERK in A. fumigatus infection.

Pharmacokinetics of the Melanocortin Type 1 Receptor Agonist PL8177 After Subcutaneous Administration

Background and Objective

PL8177 is a selective melanocortin 1 receptor agonist in development for the treatment of various immunologic and inflammatory conditions. Here we describe the pharmacokinetics of PL8177 after subcutaneous (sc) delivery in animals and humans.

Methods

Mice, rats, and dogs were administered sc PL8177 at single doses of 1.0 and 3.0 mg/kg (mice); 1.0, 5.0, and 25.0 mg/kg/day (rats); or 1.5, 8.0, and 40.0 mg/day (dogs). Blood was collected over 24 h (mice) or 28 days (rats and dogs). Safety and pharmacokinetics of single and multiple sc doses were also examined in human volunteers. Two dose levels were tested in two dosing cohorts of 1.0 and 3.0 mg/day for 7 days. Blood samples were collected through Day 1 and on Days 2 to 6 at peak and trough times based on analysis of the first two single-dose cohorts.

Results

In mice, 3 mg/kg PL8177 resulted in an area under the plasma concentration–time curve from 0 to infinity (AUC_∞) of 1727 ng·h/mL, a maximum plasma concentration (C_max) of 2440 ng/mL, an elimination half-life (t_½) of 0.5 h, and a time to maximum concentration (t_max) of 0.25 h. Results for the 1-mg/kg dose were generally proportional. In rats, mean t_max values were independent of dose and ranged from 0.25 to 1.0 h for single and multiple dosing. C_max values ranged from 516 to 695 ng/mL (1-mg/kg dose) and from 666 to 1180 ng/mL (25-mg/kg dose). In dogs, mean t_max values ranged from 0.4 to 1.3 h for single and multiple dosing. Values for t_max decreased with increasing dose and mean plasma C_max increased less than dose proportionally (96–129 ng·h/mL [1.5 mg], 275–615 ng·h/mL [8.0 mg], and 633–1280 ng·h/mL [40.0 mg]). In humans, PL8177 was observed in the plasma within 15 min after a single dose and persisted for up to 48 h at higher doses. The t_max was 30–45 min (single dose) and 15–45 min (multiple doses). In multiple-dose studies, maximum steady-state plasma concentration (C_max,ss) and AUC_∞ increased with dose. Geometric mean C_max,ss values were 20.1 ng/mL (1.0 mg) and 57.2 ng/mL (3.0 mg). AUC_∞ values were 54.3 ng·h/mL (1.0 mg) and 199 ng·h/mL (3.0 mg). Unchanged PL8177 excreted in the urine was ≤ 1%, and accumulation was minimal.

Conclusion

PL8177 administration resulted in a consistent pharmacokinetic profile. The measured exposure levels resulted in pharmacologically active PL8177 concentrations at the targeted MC1R. Rapid absorption was seen in healthy volunteers, and multiple-dose administration over 7 days resulted in pharmacokinetic characteristics similar to those observed after single-dose administration. Results support the continued development of PL8177 to treat immunologic and inflammatory conditions.

Antifibrotic and Anti-Inflammatory Actions of α-Melanocytic Hormone: New Roles for an Old Player

The melanocortin system encompasses melanocortin peptides, five receptors, and two endogenous antagonists. Besides pigmentary effects generated by α-Melanocytic Hormone (α-MSH), new physiologic roles in sexual activity, exocrine secretion, energy homeostasis, as well as immunomodulatory actions, exerted by melanocortins, have been described recently. Among the most common and burdensome consequences of chronic inflammation is the development of fibrosis. Depending on the regenerative capacity of the affected tissue and the quality of the inflammatory response, the outcome is not always perfect, with the development of some fibrosis. Despite the heterogeneous etiology and clinical presentations, fibrosis in many pathological states follows the same path of activation or migration of fibroblasts, and the differentiation of fibroblasts to myofibroblasts, which produce collagen and α-SMA in fibrosing tissue. The melanocortin agonists might have favorable effects on the trajectories leading from tissue injury to inflammation, from inflammation to fibrosis, and from fibrosis to organ dysfunction. In this review we briefly summarized the data on structure, receptor signaling, and anti-inflammatory and anti-fibrotic properties of α-MSH and proposed that α-MSH analogues might be promising future therapeutic candidates for inflammatory and fibrotic diseases, regarding their favorable safety profile.

Increased Expression of TLR4 in Circulating CD4+T Cells in Patients with Allergic Conjunctivitis and In Vitro Attenuation of Th2 Inflammatory Response by Alpha-MSH

Ocular allergic diseases are frequently seen in ophthalmological clinical practice. Immunological damage is mediated by a local Th2 inflammatory microenvironment, accompanied by changes in circulating cell subsets, with more effector cells and fewer T regulatory cells (Tregs). This study aimed to evaluate the involvement of toll-like receptor 4 (TLR4) and α-melanocyte stimulating hormone (α-MSH) in the immune regulation associated with perennial allergic conjunctivitis (PAC). We performed an Ag-specific stimulation during 72 h of culturing with or without lipopolysaccharide (LPS) or α-MSH in peripheral blood mononuclear cells (PBMC), analyzing the cell subsets and cytokines induced by the stimuli. We also determined α-MSH in tear samples from healthy donors (HD) or PAC patients. Our findings demonstrate an immunological dysregulation characterized by an increased frequency of CD4+TLR4+ in the PBMC of patients with PAC, compared to HD. Most of these CD4+TLR4+ cells were also CD25+, and when α-MSH was added to the culture, the percentage of CD4+CD25+FoxP3+ increased significantly, while the percentage of CD69+ cells and cytokines IL-4 and IL-6 were significantly decreased. In tears, we found an increased concentration of α-MSH in PAC patients, compared with HD. These findings indicate a novel mechanism involved in controlling ocular allergic diseases, in which α-MSH diminishes the concentration of IL-6 and IL-4, restoring the frequency of Tregs and down-regulating CD4 activation. Moreover, we demonstrated the involvement of CD4+TLR4+ cells as an effector cell subset in ocular allergy.

Use of Adrenocorticotropic Hormone in Ophthalmology

The ability of the adrenocorticotropic hormone (ACTH) to induce steroidogenesis and upregulate anti-inflammatory processes has long been known. More recently, however, extrasteroidal mechanisms, through which ACTH exerts anti-inflammatory processes, have been described. This has renewed hope that ACTH can combat inflammatory conditions even when resistant to steroids. This review article summarizes the literature on the use of ACTH in ocular disease. Unfortunately, much of the data regarding the clinical utility of ACTH are outdated, with many studies published in the 1950s and 1960s. Many of these older studies are inconsistent or incomplete with their reporting, making it difficult to ascertain the meaning of the outcomes. Despite the limitations, 2 important trends are evident. First, when used to treat an inflammatory disease, ACTH can be effective at decreasing or eliminating ocular inflammation, even in a refractory disease resistant to multiple treatment modalities. Second, adverse effects of ACTH are rare and are most likely to be reported with relatively high doses of ACTH therapy. Taken as a whole, these studies offer initial promising data that ACTH may be a safe and effective alternative in refractory ocular inflammatory disease. However, they highlight an important lack of prospective data to more rigorously understand the true safety and efficacy of this therapy.

Models Contribution to the Understanding of Sarcoidosis Pathogenesis: "Are There Good Models of Sarcoidosis?"

Sarcoidosis is a systemic, granulomatous, and noninfectious disease of unknown etiology. The clinical heterogeneity of the disease (targeted tissue(s), course of the disease, and therapy response) supports the idea that a multiplicity of trigger antigens may be involved. The pathogenesis of sarcoidosis is not yet completely understood, although in recent years, considerable efforts were put to develop novel experimental research models of sarcoidosis. In particular, sarcoidosis patient cells were used within in vitro 3D models to study their characteristics compared to control patients. Likewise, a series of transgenic mouse models were developed to highlight the role of particular signaling pathways in granuloma formation and persistence. The purpose of this review is to put in perspective the contributions of the most recent models in the understanding of sarcoidosis.

Quantitative Study of Human Scleral Melanocytes and Their Topographical Distribution

PURPOSE

While fibroblasts constitute the main cell component of the sclera, the purpose of the present study was to investigate the cell densities of melanocytes at different regions of the sclera, and to compare them with associated scleral fibroblast densities in human donor eye sections.

METHODS

. Paraffin-embedded sections of sclera from 21 human eyes were stained with hematoxylin-eosin (H&E) and immunohistochemical staining (S-100/AEC). Scleral melanocyte and fibroblast numbers were counted in different regions of the sclera. The relationship between the melanocyte density and iris pigmentation was also analyzed.

RESULTS

. Melanocytes were found in the posterior region of the sclera, especially around the vessels and nerves in emmissarial canals, whereas no or rare melanocytes were found in equatorial and anterior regions. In H&E sections, melanocyte densities in eyes with light-colored irides were significantly less than in eyes with medium or dark-colored irides (P < .05). In S-100-stained sections, more melanocytes could be detected than those in the H&E sections in light-colored eyes (P < .05), but not in medium or dark-colored eyes (P > .05). The numbers of scleral fibroblasts were relatively stable in different regions. In the posterior scleral region, the numbers of fibroblasts were slightly higher than the number of melanocytes, however, this differences were not statistically significant (P > .05).

CONCLUSION

. Notable numbers of melanocytes were present in the posterior sclera suggesting that these cells may play a role in ocular physiology and in the pathogenesis of various disorders of the sclera.

Anti-inflammatory effects of α-MSH through p-CREB expression in sarcoidosis like granuloma model

Lung inflammation due to sarcoidosis is characterized by a complex cascade of immunopathologic events, including leukocyte recruitment and granuloma formation. α-melanocyte stimulating hormone (α-MSH) is a melanocortin signaling peptide with anti-inflammatory properties. We aimed to evaluate the effects of α-MSH in a novel in vitro sarcoidosis model. An in vitro sarcoidosis-like granuloma model was developed by challenging peripheral blood mononuclear cells (PBMCs) derived from patients with confirmed treatment-naïve sarcoidosis with microparticles generated from Mycobacterium abscessus cell walls. Unchallenged PBMCsand developed granulomas were treated daily with 10 μM α-MSH or saline as control. Cytokine concentrations in supernatants of culture and in cell extracts were measured using Illumina multiplex Elisa and western blot, respectively. Gene expression was analyzed using RNA-Seq and RT-PCR. Protein secretion and gene expression of IL-7, IL-7R, IFN-γ, MC1R, NF-κB, phosphorylated NF-κB (p-NF-κB), MARCO, and p-CREB were measured with western blot and RNAseq. A significant increase in IL-7, IL-7R, and IFN-γ protein expression was found in developed granulomas comparing to microparticle unchallenged PBMCs. IL-7, IL-7R, and IFN-γ protein expression was significantly reduced in developed granulomas after exposure to α-MSH compared with saline treated granulomas. Compared with microparticle unchallenged PBMCs, total NF-κB and p-NF-κB were significantly increased in developed granulomas, while expression of p-CREB was not changed. Treatment with α-MSH promoted a significantly higher concentration of p-CREB in granulomas. The anti-inflammatory effects of α-MSH were blocked by specific p-CREB inhibition. α-MSH has anti-inflammatory properties in this in vitro granuloma model, which is an effect mediated by induction of phosphorylation of CREB.

Retinal arterial occlusive vasculitis following intravitreal brolucizumab administration

Purpose

To describe retinal arterial occlusion and vasculitis following intravitreal brolucizumab administration in a patient with neovascular age-related macular degeneration (nAMD).

Observation

An 88-year-old Caucasian woman with neovascular age-related macular degeneration (nAMD) complained of painless loss of vision with light sensitivity in both eyes (OU) four weeks after bilateral intravitreal brolucizumab. Upon examination, her visual acuity decreased to 20/40 in the right eye (OD) and 20/50 in the left eye (OS). Examination revealed 0.5+ and 1+ anterior chamber cells in OD and OS, respectively. The patient was treated with 1% prednisolone acetate eyedrops in both eyes, and after several weeks, the anterior chamber cells resolved. However, the patient still reported a decline in visual acuity (VA). Fluorescein angiography (FA) revealed retinal arterial occlusion, vasculitis, and optic nerve inflammation in the left eye. Retinal intra-arterial grayish materials were also detected. Laboratory evaluations were performed for common infectious and inflammatory causes and were normal or negative. A delayed inflammatory reaction to brolucizumab was suspected as the cause of the ocular inflammation and retinal vasculitis. An intravitreal dexamethasone implant was inserted into the left eye to treat the inflammation. One week after the dexamethasone implant, VA improved to 20/40 in OU; FA showed improvement, but residual peri-vascular leakage remained.

Conclusion

Medication-associated uveitis is a rare adverse effect that can lead to vision loss. The index report illustrates a case of intraocular inflammation, retinal arterial vaso-occlusion and vasculitis associated with intravitreal brolucizumab. The delay in developing uveitis suggests that the inflammation is due to a delayed hypersensitivity reaction which can occur several days or weeks after administration of the inciting agent. Recently, several cases of uveitis and vasculitis associated with brolucizumab have been presented and those cases have similar features compared to the index case (1). Therapy with steroids (either intraocular or systemic), after infectious etiologies have been excluded, may be beneficial in halting inflammation and preventing further vision loss.

Adrenocorticotropic hormone gel for patients with non-infectious uveitis

Purpose

To describe the potential role of adrenocorticotropic hormone (ACTH) gel treatment in patients with chronic non-infectious uveitis.

Observations

We report the clinical course of three patients with bilateral, non-infectious anterior and intermediate uveitis, treated with ACTH gel for ≥12 months. All three patients had chronic and steroid-dependent ocular inflammation with subsequent development of ocular complications. Twice-weekly treatment with subcutaneous 80 unit/day ACTH gel was administered, and clinical outcome measures were observed. After a mean period of 14 months, all patients demonstrated significant improvement in disease activity, stable visual acuity, and an absence of side effects. Systemic steroids dosage was successfully reduced from a mean dose of 16 mg/day upon the initiation of ACTH gel treatment to 2 mg/day at last follow up.

Conclusions and Importance

Subcutaneous ACTH gel has shown to be a safe and effective therapy in the management of non-infectious uveitis. Specifically, ACTH gel plays a role in refractory and steroid-dependent cases and in those who do not respond to or are unable to tolerate other immunomodulatory therapies.

Immunoregulatory Effects of Neuropeptides on Endothelial Cells: Relevance to Dermatological Disorders

Many skin diseases, including psoriasis and atopic dermatitis, have a neurogenic component. In this regard, bidirectional interactions between components of the nervous system and multiple target cells in the skin and elsewhere have been receiving increasing attention. Neuropeptides released by sensory nerves that innervate the skin can directly modulate functions of keratinocytes, Langerhans cells, dermal dendritic cells, mast cells, dermal microvascular endothelial cells and infiltrating immune cells. As a result, neuropeptides and neuropeptide receptors participate in a complex, interdependent network of mediators that modulate the skin immune system, skin inflammation, and wound healing. In this review, we will focus on recent studies demonstrating the roles of α-melanocyte-stimulating hormone, calcitonin gene-related peptide, substance P, somatostatin, vasoactive intestinal peptide, pituitary adenylate cyclase-activating peptide, and nerve growth factor in modulating inflammation and immunity in the skin through their effects on dermal microvascular endothelial cells.

Negative regulators that mediate ocular immune privilege

The ocular microenvironment has adapted several negative regulators of inflammation to maintain immune privilege and health of the visual axis. Several constitutively produced negative regulators within the eye TGF-β2, α-melanocyte stimulating hormone (α-MSH), Fas ligand (FasL), and PD-L1 standout because of their capacity to influence multiple pathways of inflammation, and that they are part of promoting immune tolerance. These regulators demonstrate the capacity of immune privilege to prevent the activation of inflammation, and to suppress activation of effector immune cells even under conditions of ocular inflammation induced by endotoxin and autoimmune disease. In addition, these negative regulators promote and expand immune cells that mediate regulatory and tolerogenic immunity. This in turn makes the immune cells themselves negative regulators of inflammation. This provides for a greater understanding of immune privilege in that it includes both molecular and cellular negative regulators of inflammation. This would mean that potentially new approaches to the treatment of autoimmune disease can be developed through the use of molecules and cells as negative regulators of inflammation.

The Role of Alpha-MSH as a Modulator of Ocular Immunobiology Exemplifies Mechanistic Differences between Melanocortins and Steroids

Melanocortins are a highly conserved family of peptides and receptors that includes multiple proopiomelanocortin-derived peptides and five defined melanocortin receptors. The melanocortins have an important role in maintaining immune homeostasis and in suppressing inflammation. Within the healthy eye, the melanocortins have a central role in preventing inflammation and maintaining immune privilege. A central mediator of the anti-inflammatory activity is the non-steroidogenic melanocortin peptide alpha-melanocyte stimulating hormone. In this review we summarize the major findings of melanocortin regulation of ocular immunobiology with particular interest in the ability of melanocortin to induce immune tolerance and cytoprotection. The melanocortins have therapeutic potential because their mechanisms of action in regulating immunity are distinctly different from the actions of steroids.

The alpha-melanocyte stimulating hormone induces conversion of effector T cells into treg cells

The neuropeptide alpha-melanocyte stimulating hormone (α-MSH) has an important role in modulating immunity and homeostasis. The production of IFN-γ by effector T cells is suppressed by α-MSH, while TGF-β production is promoted in the same cells. Such α-MSH-treated T cells have immune regulatory activity and suppress hypersensitivity, autoimmune diseases, and graft rejection. Previous characterizations of the α-MSH-induced Treg cells showed that the cells are CD4(+) T cells expressing the same levels of CD25 as effector T cells. Therefore, we further analyzed the α-MSH-induced Treg cells for expression of effector and regulatory T-cell markers. Also, we examined the potential for α-MSH-induced Treg cells to be from the effector T-cell population. We found that the α-MSH-induced Treg cells are CD25(+)  CD4(+) T cells that share similar surface markers as effector T cells, except that they express on their surface LAP. Also, the α-MSH treatment augments FoxP3 message in the effector T cells, and α-MSH induction of regulatory activity was limited to the effector CD25(+) T-cell population. Therefore, α-MSH converts effector T cells into Treg cells, which suppress immunity targeting specific antigens and tissues.

Immunosuppressive activity of a novel peptide analog of α-melanocyte stimulating hormone (α-MSH) in experimental autoimmune uveitis

Autoimmune uveitis is an inflammatory disorder of the eye that can lead to pain and vision loss. Steroids and immunosuppressive drugs are currently the only therapeutics for uveitis and have serious ocular and systemic toxicities. Therefore, safer alternative therapeutics are desired. Alpha-melanocyte stimulating hormone (α-MSH) is a neuropeptide that suppresses effector T cell functions, induces regulatory T cells and has beneficial effects in certain autoimmune and transplant models. A novel d-amino acid peptide analog of native α-MSH (dRI-α-MSH) was produced that was protected from protease digestion and had increased selectivity for the melanocortin-1 receptor. Systemic delivery of the dRI-α-MSH analog dramatically suppressed disease progression and retained retinal architecture in the experimental autoimmune uveitis (EAU) model. Local delivery by periorbital injection was equally effective. Importantly, treatment with the novel dRI-α-MSH analog suppressed uveitis with a similar magnitude to the corticosteroid, dexamethasone. Data indicate that the novel dRI-α-MSH analogs show anti-inflammatory activities and have potential therapeutic use in uveitis and other autoimmune diseases.

Melanin and melanogenesis in adipose tissue: possible mechanisms for abating oxidative stress and inflammation?

Obesity has become a worldwide epidemic and can lead to multiple chronic diseases. Adipose tissue is increasingly thought to play an active role in obesity-related pathologies such as insulin resistance and non-alcoholic fatty liver disease. Obesity has been strongly associated with systemic inflammation and, to a lesser degree, with oxidative stress, although the causal relationships among these factors are unclear. A recent study demonstrating an expression of the components of the melanogenic pathway and the presence of melanin in visceral adipose has raised questions regarding the possible role of melanogenesis in adipose tissue. As this study also found larger amounts of melanin in the adipose tissue of obese patients relative to lean ones, we hypothesize that melanin, a pigment known for its antioxidant and anti-inflammatory properties, may scavenge reactive oxygen species and abate oxidative stress and inflammation in adipose tissue. This review considers the evidence to support such a hypothesis, and speculates on the role of melanin within adipocytes. Furthermore, we consider whether the α-melanocyte-stimulating hormone or its synthetic analogues could be used to stimulate melanin production in adipocytes, should the hypothesis be supported in future experiments.

The neuropeptide alpha-melanocyte-stimulating hormone is critically involved in the development of cytotoxic CD8+ T cells in mice and humans

BACKGROUND

The neuropeptide alpha-melanocyte-stimulating hormone is well known as a mediator of skin pigmentation. More recently, it has been shown that alpha-melanocyte-stimulating hormone also plays pivotal roles in energy homeostasis, sexual function, and inflammation or immunomodulation. Alpha-melanocyte-stimulating hormone exerts its antiinflammatory and immunomodulatory effects by binding to the melanocortin-1 receptor, and since T cells are important effectors during immune responses, we investigated the effects of alpha-melanocyte-stimulating hormone on T cell function.

METHODOLOGY/PRINCIPAL FINDINGS

T cells were treated with alpha-melanocyte-stimulating hormone, and subsequently, their phenotype and function was analyzed in a contact allergy as well as a melanoma model. Furthermore, the relevance of alpha-melanocyte-stimulating hormone-mediated signaling for the induction of cytotoxicity was assessed in CD8(+) T cells from melanoma patients with functional and nonfunctional melanocortin-1 receptors. Here we demonstrate that the melanocortin-1 receptor is expressed by murine as well as human CD8(+) T cells, and we furthermore show that alpha-melanocyte-stimulating hormone/melanocortin-1 receptor-mediated signaling is critical for the induction of cytotoxicity in human and murine CD8(+) T cells. Upon adoptive transfer, alpha-melanocyte-stimulating hormone-treated murine CD8(+) T cells significantly reduced contact allergy responses in recipient mice. Additionally, the presented data indicate that alpha-melanocyte-stimulating hormone via signaling through a functional melanocortin-1 receptor augmented antitumoral immunity by up-regulating the expression of cytotoxic genes and enhancing the cytolytic activity in tumor-specific CD8(+) T cells.

CONCLUSIONS/SIGNIFICANCE

Together, these results point to an important role of alpha-melanocyte-stimulating hormone in MHC class I-restricted cytotoxicity. Therefore, treatment of contact allergies or skin cancer with alpha-melanocyte-stimulating hormone or other more stable agonists of melanocortin-1 receptor might ameliorate disease or improve antitumoral immune responses.

Applications of the role of α-MSH in ocular immune privilege

There is an important role for α-MSH and the melanocortin receptors in ocular immunity, development and health. This chapter will cover what is known about how α-MSH is part of the mechanisms of ocular immune privilege, about the expression of melanocortin receptors and the implications of these findings on the role of α-MSH in ocular physiology and its potential use to treat ocular pathologies.

Local treatment with alpha-melanocyte stimulating hormone reduces corneal allorejection

BACKGROUND

Corneal grafting is by far the most common form of transplantation. Many grafts suffer from immune rejection and current therapies are associated with many side effects, requiring more effective and safe therapies. alpha-Melanocyte stimulating hormone (alpha-MSH) is a neuropeptide that suppresses host inflammatory defense mechanisms. The purpose of this study was to determine the role of local therapy with alpha-MSH on corneal allograft survival, and the mechanisms by which it may influence graft outcome.

METHODS

Orthotopic corneal transplantation was performed, with recipients receiving subconjunctival alpha-MSH or sham injections twice weekly. Grafts were followed up for 70 days, and graft inflammation/opacification was compared between the two groups in a masked fashion. Graft infiltration and ocular gene expression of select inflammatory cytokines was evaluated at different timepoints. Additionally, allospecific delayed-type hypersensitivity was compared among the groups 3 weeks posttransplantation.

RESULTS

Results showed a significant increase in corneal graft survival in alpha-MSH-treated recipients compared with controls. Although 75% of allografts in alpha-MSH-treated hosts survived at 70 days, 43% survived in controls (P=0.04). Graft infiltration studies demonstrated a significant decrease in the number of mononuclear and polymorphonuclear cells in alpha-MSH-treated mice compared with controls at days 7 and 14 after transplantation. Furthermore, allospecific delayed-type hypersensitivity and gene expression of interferon-gamma and interleukin-2 showed a significantly reduced expression in alpha-MSH-treated mice compared with controls.

CONCLUSIONS

This study provides for the first time, in vivo evidence that treatment with local alpha-MSH may significantly reduce allorejection of orthotopic transplants.

Injection of an alpha-melanocyte stimulating hormone expression plasmid is effective in suppressing experimental autoimmune uveitis

PURPOSE

The neuropeptide, alpha-melanocyte stimulating hormone (alpha-MSH), is an endogenous antagonist of inflammation. Injections of alpha-MSH peptide into inflamed tissues have been found to be very effective in suppressing autoimmune and endotoxin mediated diseases. We evaluated the potential to suppress ocular autoimmune disease (uveitis) by augmenting the expression of alpha-MSH through subconjunctival injections of naked adrenocorticotropic hormone amino acids 1-17 (ACTH1-17) plasmid.

METHODS

We clinically scored the uveitis over time in B10.RIII, C57BL/6, and melanocortin 5 receptor knock-out (MC5r((-/-))) mice with experimental autoimmune uveitis (EAU) that were conjunctively injected with a naked DNA plasmid encoding ACTH1-17 at the time of EAU onset and three days later. The post-EAU retina histology of plasmid injected eyes was examined, and post-EAU concentrations of alpha-MSH in aqueous humor was assayed by ELISA.

RESULTS

The subconjunctival injection of ACTH1-17 plasmid augmented the concentration of alpha-MSH in the aqueous humor of all post-EAU mice. The injection of ACTH1-17 suppressed the severity of EAU in the B10.RIII and C57BL/6 mice but the MC5r((-/-)) mice. In all the models of EAU, the ACTH1-17 injection helped to preserve the structural integrity of the retina; however, post-EAU aqueous humor was not immunosuppressive.

CONCLUSIONS

The subconjunctival injection of the alpha-MSH expression vector ACTH1-17 plasmid is effective in suppressing EAU. The suppressive activity is dependent on MC5r expression, and possibly works though alpha-MSH antagonism of inflammation than on alpha-MSH directly modulating immune cells. The results suggest that an effective therapy for uveitis could include a gene therapy approach based on delivering alpha-MSH.

Ocular immune privilege

It has been over 60 years since the phrase immune privilege was used by Sir Peter Medawar to describe the lack of an immune response against allografts placed into the ocular microenvironment. Since then, we have come to understand that the mechanisms of ocular immune privilege include unique anatomical features of a blood barrier and a lack of direct lymphatic drainage. Also, we know that the ocular microenvironment is rich with immunosuppressive molecules that influence the activity of immune cells. Moreover, the placement of foreign antigen into the ocular microenvironment can induce a systemic form of tolerance to the foreign antigen called anterior chamber-associated immune deviation (ACAID). Many soluble immunomodulators are found in aqueous humour, and are a mixture of growth factors, cytokines, neuropeptides, and soluble receptors. This is a continuously growing list. The mechanisms of ocular immune privilege induce apoptosis, promote the production of anti-inflammatory cytokines, and mediate the activation of antigen-specific regulatory immunity. These mechanisms of immune privilege also attempt to impose themselves upon immunity within the uveitic eye. The adaptation of several anatomical and biochemical mechanisms to establish an immune privileged microenvironment within the eye makes the eye immunologically unique. It is a tissue site where we may learn how immunity is regulated in inflammation and at rest. Success in translating the lessons of ocular immune privilege to other tissues has the potential to drastically change the therapy and clinical outcomes of autoimmune diseases and allograft survival.

Alpha-melanocyte-stimulating hormone and related tripeptides: biochemistry, antiinflammatory and protective effects in vitro and in vivo, and future perspectives for the treatment of immune-mediated inflammatory diseases

Alpha-MSH is a tridecapeptide derived from proopiomelanocortin. Many studies over the last few years have provided evidence that alpha-MSH has potent protective and antiinflammatory effects. These effects can be elicited via centrally expressed melanocortin receptors that orchestrate descending neurogenic antiinflammatory pathways. alpha-MSH can also exert antiinflammatory and protective effects on cells of the immune system and on peripheral nonimmune cell types expressing melanocortin receptors. At the molecular level, alpha-MSH affects various pathways implicated in regulation of inflammation and protection, i.e., nuclear factor-kappaB activation, expression of adhesion molecules and chemokine receptors, production of proinflammatory cytokines and mediators, IL-10 synthesis, T cell proliferation and activity, inflammatory cell migration, expression of antioxidative enzymes, and apoptosis. The antiinflammatory effects of alpha-MSH have been validated in animal models of experimentally induced fever; irritant and allergic contact dermatitis, vasculitis, and fibrosis; ocular, gastrointestinal, brain, and allergic airway inflammation; and arthritis, but also in models of organ injury. One obstacle limiting the use of alpha-MSH in inflammatory disorders is its pigmentary effect. Due to its preserved antiinflammatory effect but lack of pigmentary action, the C-terminal tripeptide of alpha-MSH, KPV, has been delineated as an alternative for antiinflammatory therapy. KdPT, a derivative of KPV corresponding to amino acids 193-195 of IL-1beta, is also emerging as a tripeptide with antiinflammatory effects. The physiochemical properties and expected low costs of production render both agents suitable for the future treatment of immune-mediated inflammatory skin and bowel disease, fibrosis, allergic and inflammatory lung disease, ocular inflammation, and arthritis.

The diminishment of experimental autoimmune encephalomyelitis (EAE) by neuropeptide alpha-melanocyte stimulating hormone (alpha-MSH) therapy

The neuropeptide alpha-melanocyte stimulating hormone (alpha-MSH) plays an important role in immune privilege by its suppression of inflammation, and its induction of regulatory T cells. This finding led us to test the possibility that we can use alpha-MSH to suppress autoimmune diseases, and promote re-establishment of immune tolerance to autoantigens. To test this possibility, SJL mice with experimental autoimmune encephalomyelitis (EAE) were injected with alpha-MSH at the first signs of paralysis. The alpha-MSH-treated mice in comparison with untreated EAE mice had a profound diminishment in the severity and tempo of EAE. The spleen cells in alpha-MSH-treated EAE produced TGF-beta in response to PLP-antigen stimulation in contrast to untreated mice spleen cells that produced IFN-gamma. When the alpha-MSH-treated EAE mice were reimmunized there was a delay of a week before the second episode of EAE. Although this delay maybe because of the induction of TGF-beta-producing spleen cells by the alpha-MSH-treatment, it was not adequate to suppress IFN-gamma-production by PLP-antigen stimulated spleen cells from untreated mice, nor able to suppress the eventual second episode of EAE. Therefore, the injection of alpha-MSH at the onset of paralysis is extremely effective in diminishing the severity and tempo of EAE, and the subsequent induction of potential PLP-specific Treg cells suggests that an alpha-MSH therapy could be attempted as part of a therapeutic regiment to impose immunoregulation and immunosuppression on an autoimmune disease of the central nervous system.

A role for tumor necrosis factor-alpha in experimental Bacillus cereus endophthalmitis pathogenesis

PURPOSE

To determine the contribution of tumor necrosis factor-alpha (TNFalpha) in the pathogenesis of experimental Bacillus cereus endophthalmitis.

METHODS

Experimental B. cereus endophthalmitis was induced in wild-type control (B6.129F1) and age-matched homozygous TNFalpha knockout mice (TNFalpha(-/-), B6.129S6-Tnf(tm1Gk1)/J). At various times after infection, eyes were analyzed by electroretinography and were harvested for quantitation of bacteria, myeloperoxidase, proinflammatory cytokines and chemokines, and histologic analysis.

RESULTS

B. cereus replicated more rapidly in the eyes of TNFalpha(-/-) mice than in the eyes of B6.129F1 mice. Retinal function decreased more rapidly in TNFalpha(-/-) mice than in B6.129F1 mice. Retinal layers were not as structurally intact at 6 and 12 hours after infection in TNFalpha(-/-) eyes as in B6.129F1 eyes. Histologic analysis suggested less polymorphonuclear leukocyte (PMN) infiltration into the vitreous of TNFalpha(-/-) mice than of B6.129F1 mice. B6.129F1 eyes also had greater myeloperoxidase concentrations than did eyes of TNFalpha(-/-) mice. In general, concentrations of proinflammatory cytokines and chemokines (IL-1beta, KC, IL-6, and MIP-1alpha) were greater in eyes of TNFalpha(-/-) mice than of B6.129F1 mice.

CONCLUSIONS

TNFalpha is important to intraocular pathogen containment by PMNs during experimental B. cereus endophthalmitis. In the absence of TNFalpha, fewer PMNs migrated into the eye, facilitating faster bacterial replication and retinal function loss. Although greater concentrations of proinflammatory cytokines were synthesized in the absence of TNFalpha, the resultant inflammation was diminished, and an equally devastating course of infection occurred.

alpha-MSH related peptides: a new class of anti-inflammatory and immunomodulating drugs

alpha-Melanocyte-stimulating hormone (alpha-MSH) is a tridecapeptide derived from the proopiomelanocortin by post-translational processing. In addition to its effects on melanocytes, alpha-MSH has potent anti-inflammatory effects when administered systemically or locally. The anti-inflammatory effects of alpha-MSH are mediated by direct effects on cells of the immune system as well as indirectly by affecting the function of resident non-immune cells. alpha-MSH affects several pathways implicated in regulation of inflammatory responses such as NF-kappaB activation, expression of adhesion molecules and chemokine receptors, production of pro-inflammatory cytokines and other mediators. Thus alpha-MSH may modulate inflammatory cell proliferation, activity and migration. The anti-inflammatory effects of alpha-MSH have been confirmed by means of animal models of inflammation such as irritant and allergic contact dermatitis, cutaneous vasculitis, asthma, inflammatory bowel disease, rheumatoid arthritis, ocular and brain inflammation. Most of the anti-inflammatory activities of alpha-MSH can be attributed to its C-terminal tripeptide KPV. K(D)PT, a derivative of KPV corresponding to the amino acid 193-195 of IL-1beta, is currently emerging as another tripeptide with potent anti-inflammatory effects. The anti-inflammatory potential together with the favourable physiochemical properties most likely will allow these agents to be developed for the treatment of inflammatory skin, eye and bowel diseases, allergic asthma and arthritis.

Effect of Berberine on Monocyte Chemotactic Protein-1 and Cytokine-Induced Neutrophil Chemoattractant-1 Expression in Rat Lipopolysaccharide-Induced Uveitis

PURPOSE

The aims of this study were to examine the in vivo effects of berberine, an alkaloid isolated from some medicinal herbs, on monocyte chemotactic protein-1 (MCP-1) and cytokine-induced neutrophil chemoattractant-1 (CINC-1) expression in rat lipopolysaccharide (LPS)-induced uveitis.

METHODS

LPS was injected intraperitoneally. Berberine was orally administered. MCP-1 mRNA and CINC-1 mRNA were measured by semiquantitative reverse-transcription polymerase chain reaction and real-time polymerase chain reaction. MCP-1 and CINC-1 protein concentration in the aqueous humor were measured by enzyme-linked immunosorbent assay. Histopathologic study was performed in the anterior ocular segments.

RESULTS

Berberine dose-dependently inhibited LPS-induced MCP-1 mRNA and CINC-1 mRNA expression of the iris-ciliary body. The alkaloid inhibited chemokines, protein and cell levels in the aqueous humor in rats stimulated with LPS. On histopathologic study, the inflammatory cell infiltration was diminished by the berberine treatment.

CONCLUSIONS

These findings indicate that berberine dose-dependently inhibited the expression of MCP-1 and CINC-1 induced by LPS and diminished the anterior uveitis.

The melanocortin system in leukocyte biology

The melanocortin system is composed of the melanocortin peptides, adrenocorticotropic hormone and alpha-, beta-, and gamma-melanocyte-stimulating hormone, the melanocortin receptors (MCRs), and the endogenous antagonists agouti- and agouti-related protein. Melanocortin peptides exert multiple effects upon the host, including anti-inflammatory and immunomodulatory effects. Leukocytes are a source of melanocortins and a major target for these peptides. Because of reduced translocation of the nuclear factor NF-kappaB to the nucleus, MCR activation by their ligands causes a collective reduction of the most important molecules involved in the inflammatory process. This review examines how melanocortin peptides and their receptors participate in leukocyte biology.

Peptidergic nerves in the eye, their source and potential pathophysiological relevance

Over the last five decades, several neuropeptides have been discovered which subsequently have been found to be highly conserved during evolution, to be widely distributed both in the central and peripheral nervous system and which act as neurotransmitters and/or neuromodulators. In the eye, the first peptide to be explored was substance P which was reported to be present in the retina but also in peripherally innervated tissues of the eye. Substance P is certainly the best characterized peptide which has been found in sensory neurons innervating the eye. Functionally, it has been shown to act trophically on corneal wound healing and to participate in the irritative response in lower mammals, a model for neurogenic inflammation, where it mediates the noncholinergic nonadrenergic contraction of the sphincter muscle. Over the last three decades, the interest has extended to investigate the presence and distribution of other neuropeptides including calcitonin gene-related peptide, vasoactive intestinal polypeptide, neuropeptide Y, pituitary adenylate cyclase-activating polypeptides, cholecystokinin, somatostatin, neuronal nitric oxide, galanin, neurokinin A or secretoneurin and important functional results have been obtained for these peptides. This review focuses on summarizing the current knowledge about neuropeptides in the eye excluding the retina and retinal pigment epithelium and to elucidate their potential functional significance.

The immunomodulating neuropeptide alpha-melanocyte-stimulating hormone (alpha-MSH) suppresses LPS-stimulated TLR4 with IRAK-M in macrophages

Since alpha-MSH suppresses endotoxin-induced inflammation by innate immunity, it is possible that alpha-MSH can suppress the interface between innate and adaptive immunity mediated by TLR4-stimulated macrophages. Endotoxin-stimulated macrophages treated with alpha-MSH are suppressed in nitric oxide and IL-12p70 production, and cannot enhance antigen-stimulated IFN-gamma production by Th1 cells. In macrophages treated with alpha-MSH, the inhibitory molecule IRAK-M is bound to IRAK-1, the proximal intracellular signal molecule of endotoxin-bound TLR4. These results further demonstrate the dynamic contribution of the nervous system, and the role of alpha-MSH in modulating the innate and adaptive immune interface in an inflammatory response.