Oral chymase inhibitor SUN13834 ameliorates skin inflammation as well as pruritus in mouse model for atopic dermatitis

Deciphering epigenetic regulations in the inflammatory pathways of atopic dermatitis

Atopic dermatitis, commonly referred to as atopic eczema, is a persistent inflammatory skin disorder that predominantly manifests in children but may endure into adulthood. Its clinical management poses challenges due to the absence of a definitive cure, and its prevalence varies across ethnicities, genders, and geographic locations. The epigenetic landscape of AD includes changes in DNA methylation, changes in histone acetylation and methylation, and regulation by non-coding RNAs. These changes affect inflammatory and immune mechanisms, and research has identified AD-specific variations in DNA methylation, particularly in the affected epidermis. Histone modifications, including acetylation, have been associated with the disruption of skin barrier function in AD, suggesting the potential therapeutic benefit of histone deacetylase inhibitors such as belinostat. Furthermore, non-coding RNAs, particularly microRNAs and long non-coding RNAs (lncRNAs), have been implicated in modulating various cellular processes central to AD pathogenesis. Therapeutic implications in AD include the potential use of DNA methylation inhibitors and histone deacetylase inhibitors to correct aberrant methylation patterns and modulate gene expression related to immune responses and skin barrier functions. Additionally, the emerging role of lncRNAs suggests the possibility of using small interfering RNAs or antisense oligonucleotides to inhibit lncRNAs and adjust their regulatory impact on gene expression. In conclusion, the importance of epigenetic elements in AD is becoming increasingly clear as studies highlight the contribution of DNA methylation, histone modifications and, control by non-coding RNAs to the onset and progression of the disease. Understanding these epigenetic changes provides valuable insights for developing targeted therapeutic strategies.

Pathophysiological Role of Chymase-Activated Matrix Metalloproteinase-9

Chymase present in mast cells can directly form matrix metalloproteinase (MMP)-9 from proMMP-9. Chymase-activated MMP-9 has been reportedly closely related to the pathogenesis of various diseases, and inflammation-related diseases in particular. Upregulated chymase and MMP-9 have been observed in tissues from patients and animal models of aortic aneurysm, inflammatory gastrointestinal and hepatic diseases, acute pancreatic failure, atopic dermatitis and rheumatoid arthritis. Chymase at these regions is only derived from mast cells, while MMP-9 is derived from macrophages and neutrophils in addition to mast cells. Chymase inhibitors attenuate MMP-9 formation from pro-MMP-9, and ameliorate the development and progression of these disorders, along with reduction in inflammatory cell numbers. MMP-9 activated by chymase might also be involved in angiogenesis in the tumor environment. Development of angiogenesis around several cancers is closely related to the expression of chymase and MMP-9, and postoperative survival curves have revealed that patients with a higher number of chymase positive cells have lower survival rates. In this review, we wanted to clarify the role of chymase-activated MMP-9, which might become an important therapeutic target for various inflammatory disorders.

Novel Insight into the in vivo Function of Mast Cell Chymase: Lessons from Knockouts and Inhibitors

Mast cells are now recognized as key players in diverse pathologies, but the mechanisms by which they contribute in such settings are only partially understood. Mast cells are packed with secretory granules, and when they undergo degranulation in response to activation the contents of the granules are expelled to the extracellular milieu. Chymases, neutral serine proteases, are the major constituents of the mast cell granules and are hence released in large amounts upon mast cell activation. Following their release, chymases can cleave one or several of a myriad of potential substrates, and the cleavage of many of these could potentially have a profound impact on the respective pathology. Indeed, chymases have recently been implicated in several pathological contexts, in particular through studies using chymase inhibitors and by the use of chymase-deficient animals. In many cases, chymase has been shown to account for mast cell-dependent detrimental effects in the respective conditions and is therefore emerging as a promising drug target. On the other hand, chymase has been shown to have protective roles in other pathological settings. More unexpectedly, chymase has also been shown to control certain homeostatic processes. Here, these findings are reviewed.

Mouse connective tissue mast cell proteases tryptase and carboxypeptidase A3 play protective roles in itch induced by endothelin-1

Background

Itch is an unpleasant sensation that can be debilitating, especially if it is chronic and of non-histaminergic origin, as treatment options are limited. Endothelin-1 (ET-1) is a potent endogenous vasoconstrictor that also has the ability to induce a burning, non-histaminergic pruritus when exogenously administered, by activating the endothelin A receptor (ET_AR) on primary afferents. ET-1 is released endogenously by several cell-types found in the skin, including macrophages and keratinocytes. Mast cells express ET_ARs and can thereby be degranulated by ET-1, and mast cell proteases chymase and carboxypeptidase A3 (CPA3) are known to either generate or degrade ET-1, respectively, suggesting a role for mast cell proteases in the regulation of ET-1-induced itch. The mouse mast cell proteases (mMCPs) mMCP4 (chymase), mMCP6 (tryptase), and CPA3 are found in connective tissue type mast cells and are the closest functional homologs to human mast cell proteases, but little is known about their role in endothelin-induced itch.

Methods

In this study, we evaluated the effects of mast cell protease deficiency on scratching behavior induced by ET-1. To investigate this, mMCP knock-out and transgenic mice were injected intradermally with ET-1 and their scratching behavior was recorded and analyzed.

Results

CPA3-deficient mice and mice lacking all three proteases demonstrated highly elevated levels of scratching behavior compared with wild-type controls. A modest increase in the number of scratching bouts was also seen in mMCP6-deficient mice, while mMCP4-deficiency did not have any effect.

Conclusion

Altogether, these findings identify a prominent role for the mast cell proteases, in particular CPA3, in the protection against itch induced by ET-1.

Small-molecule-based immunotherapy for immunologically mediated skin conditions

A better understanding of the molecular pathogenesis of cutaneous immune disorders, together with advances in pharmaceutical drug development, led to the introduction of small-molecule inhibitors in the therapeutic management of a large spectrum of skin immune conditions. Small molecules are agents with a low molecular weight that are capable of affecting proinflammatory pathways through modulation of intracellular targets. These agents promise to improve the therapeutic management of many skin immune disorders due to their easy administration, high bioavailability and favorable safety profile. Here, we review the major small-molecule inhibitors targeting receptor-associated kinases, second messengers and transcription factors in development for the treatment of cutaneous immune conditions.

Antipruritic Effects of Kappa Opioid Receptor Agonists: Evidence from Rodents to Humans

Centrally administered bombesin induces scratching and grooming in rats. These behaviors were blocked by early benzomorphan kappa opioid receptor (KOR) agonists as reported by Gmerek and Cowan in 1984. This was the first evidence that KORs may be involved in the sensation of itch-like behaviors. Subsequent development of additional animal models for acute and chronic itch has led to important discoveries since then. For example, it was found that (a) gastrin-releasing peptide (GRP), natriuretic polypeptide b and their cognate receptors are keys for the transmission of itch sensation at the spinal cord level, (b) dynorphins (Dyns), the endogenous KOR agonists, work as inhibitory neuromodulators of itch at the spinal cord level, (c) in a mouse model for acute itch, certain KOR antagonists elicit scratching, (d) in mouse models of acute or chronic itch, KOR agonists (e.g., U50,488, nalfurafine, CR 845, nalbuphine) suppress scratching induced by different pruritogens, and (e) nalfurafine, CR 845, and nalbuphine are in the clinic or in clinical trials for pruritus associated with chronic kidney disease and chronic liver disease, as well as pruritus in chronic skin diseases.

Mast Cells and Sensory Nerves Contribute to Neurogenic Inflammation and Pruritus in Chronic Skin Inflammation

The intimate interaction between mast cells and sensory nerves can be illustrated by the wheal and surrounding flare in an urticarial reaction in human skin. This reaction is typically associated with an intense itch at the reaction site. Upon activation, cutaneous mast cells release powerful mediators, such as histamine, tryptase, cytokines, and growth factors that can directly stimulate corresponding receptors on itch-mediating sensory nerves. These include, e.g., H1- and H4-receptors, protease-activated receptor-2, IL-31 receptor, and the high-affinity receptor of nerve growth factor (TrkA). On the other hand, sensory nerves can release neuropeptides, including substance P and vasoactive intestinal peptide, that are able to stimulate mast cells to release mediators leading to potentiation of the reciprocal interaction, inflammation, and itch. Even though mast cells are well recognized for their role in allergic skin whealing and urticaria, increasing evidence supports the reciprocal function between mast cells and sensory nerves in neurogenic inflammation in chronic skin diseases, such as psoriasis and atopic dermatitis, which are often characterized by distressing itch, and exacerbated by psychological stress. Increased morphological contacts between mast cells and sensory nerves in the lesional skin in psoriasis and atopic dermatitis as well as experimental models in mice and rats support the essential role for mast cell-sensory nerve communication in consequent pruritus. Therefore, we summarize here the present literature pointing to a close association between mast cells and sensory nerves in pruritic skin diseases as well as review the essential supporting findings on pruritic models in mice and rats.

Chymase inhibitors for the treatment of cardiac diseases: a patent review (2010-2018)

INTRODUCTION

Chymase is primarily found in mast cells (MCs), fibroblasts, and vascular endothelial cells. MC chymase is released into the extracellular interstitium in response to inflammatory signals, tissue injury, and cellular stress. Among many functions, chymase is a major extravascular source for angiotensin II (Ang II) generation. Several recent pre-clinical and a few clinical studies point to the relatively unrecognized fact that chymase inhibition may have significant therapeutic advantages over other treatments in halting progression of cardiac and vascular disease.

AREAS COVERED

The present review covers patent literature on chymase inhibitors for the treatment of cardiac diseases registered between 2010 and 2018.

EXPERT OPINION

Increase in cardiac MC number in various cardiac diseases has been found in pathological tissues of human and experimental animals. Meta-analysis data from large clinical trials employing angiotensin-converting enzyme (ACE) inhibitors show a relatively small risk reduction of clinical cardiovascular endpoints. The disconnect between the expected benefit associated with Ang II blockade of synthesis or activity underscores a greater participation of chymase compared to ACE in forming Ang II in humans. Emerging literature and a reconsideration of previous studies provide lucid arguments to reconsider chymase as a primary Ang II forming enzyme in human heart and vasculature.

The behavioral study on the interactive aggravation between pruritus and depression

BACKGROUND

The interactive aggravation of pruritus and depression is well-known, but an appropriate experimental model that could mimic this behavioral phenomenon is still lacking. Thus, a systematic animal behavioral investigation was carried out in this study. This will promote the research and treatment of pruritus and depression.

METHODS

The 2,4-dinitrofluorobenzene (DNFB)-induced chronic itch model was established to measure the depression index by forced swimming test (FST), tail suspension test (TST), and splash test (ST). The chronic unpredicted mild stress (CUMS)-induced depression model was established to measure spontaneous itch and acute histamine or chloroquine-induced itch behaviors. A depression and itch combining model was also established to measure the scratching and depression behaviors. The motor function of DNFB mice was analyzed by the rotarod test.

RESULTS

The scratching number, the immobility time in the FST and TST, and the grooming number in the ST test were all significantly increased in the chronic itch model. Mice receiving CUMS treatment showed significantly increased spontaneous scratching number, immobility time in the FST and TST tests, and grooming number in the ST. The combined model showed increased immobility time in FST and TST tests and increased grooming number in ST comparing to the depression model, and showed increased scratching number comparing to the chronic itch model. After histamine (His) or chloroquine (CQ) injection, the scratching numbers of CUMS mice were all significantly increased compared to those of His- and CQ-control, respectively. Anti-depression drug ketamine could significantly inhibit the depression-like behaviors of CUMS mice, and simultaneously stopped the promoting effect on His-induced acute itch.

CONCLUSIONS

This study established an appropriate cross aggravation experimental mode and demonstrated that there is cross aggravation between pruritus and depression. The illumination of related mechanisms underlying this cross aggravation effect will provide theoretical basis for the prevention and treatment of depression and pruritus.

Protease-activated receptors and itch

Protease-activated receptors (PARs) have been implicated in a variety of physiological functions, as well as somatosensation and particularly itch and pain. Considerable attention has focused on PARs following the finding they are upregulated in the skin of atopic dermatitis patients. The present review focuses on recent studies showing that PARs are critically involved in itch and sensitization of itch. PARs are expressed by diverse cell types including primary sensory neurons, keratinocytes, and immune cells and are activated by proteases that expose a tethered ligand. Endogenous proteases are also released from diverse cell types including keratinocytes and immune cells. Exogenous proteases released from certain plants and insects contacting the skin can also induce itch. Increased levels of proteases in the skin contribute to inflammation that is often accompanied by chronic itch which is not predominantly mediated by histamine. The neural pathway signaling itch induced by activation of PARs is distinct from that mediating histamine-induced itch. In addition, there is evidence that PARs play an important role in sensitization of itch signaling under conditions of chronic itch. These recent findings suggest that PARs and other molecules involved in the itch-signaling pathway are good targets to develop novel treatments for most types of chronic itch that are poorly treated with antihistamines.

Novel investigational therapies for atopic dermatitis

Introduction: Atopic dermatitis (AD) is a common skin disease. Although most patients are well served by existing therapies, a subset of patients with severe AD are still not adequately treated. An improved understanding of the pathogenic mechanisms behind the disease has led to the development of a range of potential new drugs for this indication. Areas covered: The authors provide a narrative review of the drugs in Phase II trials listed on Clinicaltrials.gov. The authors supplement this information with recently published literature located through PubMed. The main target of new treatments appears to be the inflammation process, whereas drugs aimed at reducing itching or increasing the barrier function are fewer to nonexistent. A wide range of drugs, including small molecules and antibodies, are being tested. Expert opinion: The focus on inflammation is not only driven by the limitations posed by our current understanding of biology, but also by the broader scope of these drugs, which may be used in other diseases. In alignment with the recent drug development of other dermatological diseases, antibodies directed at key molecules in the pathogenesis of AD appear to be the most promising.

Involvement of chymase in allergic conjunctivitis of guinea pigs

It has been reported that chymase activity was increased in allergic conjunctivitis patients and this activity was correlated with the severity of the disease. However, the precise roles of chymase in allergic conjunctivitis are unclear, and whether chymase inhibitors are effective for allergic conjunctivitis has not been reported even in experimental animal models. In this study, the roles of chymase in the pathogenesis were evaluated using a selective chymase inhibitor, ONO-WH-236, in a guinea pig model of allergic conjunctivitis induced by cedar pollen. Sensitized guinea pigs were challenged by the pollen, followed by assessing redness and edema in the conjuntiva, and counting the frequency of eye scratching as an itch-associated response. Treatment with the ONO-WH-236 (40 and 80 mg/kg, p.o.) dose-dependently inhibited the induction of redness, edema and scratching behavior. An anti-histaminic drug, ketotifen (3 mg/kg, p.o.), also significantly inhibited conjunctivitis symptoms. Chymase activity was increased in ophthalmic lavage fluid immediately after the pollen challenge. The increase in chymase activity was inhibited by in vivo treatment with ONO-WH-236. Interestingly, increased histamine in the ophthalmic lavage fluid immediately after the challenge was also inhibited by the chymase inhibitor. Administration of human recombinant chymase by eye dropping (0.09 and 0.9 μg/eye) dose-dependently induced scratching behavior, which was inhibited by not only ONO-WH-236 but also ketotifen; however, chymase administration induced only weak redness in the conjunctiva, which was resistant to treatment with anti-histaminic drugs. In conclusion, it was suggested that chymase was released from mast cells after antigen challenge, followed by the induction of conjunctivitis symptoms through histamine release from mast cells. Thus, chymase could be a potential target for pharmacotherapy for allergic conjunctivitis.

New era of biologic therapeutics in atopic dermatitis

INTRODUCTION

Atopic dermatitis (AD) is a common inflammatory skin disease regulated by genetic and environmental factors. Both skin barrier defects and aberrant immune responses are believed to drive cutaneous inflammation in AD. Existing therapies rely largely on allergen avoidance, emollients and topical and systemic immune-suppressants, some with significant toxicity and transient efficacy; no specific targeted therapies are in clinical use today. As our specific understanding of the immune and molecular pathways that cause different subsets of AD increases, a variety of experimental agents, particularly biologic agents that target pathogenic molecules bring the promise of safe and effective therapeutics for long-term use.

AREAS COVERED

This paper discusses the molecular pathways characterizing AD, the contributions of barrier and immune abnormalities to its pathogenesis, and development of new treatments that target key molecules in these pathways. In this review, we will discuss a variety of biologic therapies that are in development or in clinical trials for AD, perhaps revolutionizing treatment of this disease.

EXPERT OPINION

Biologic agents in moderate to severe AD offer promise for controlling a disease that currently lacks good and safe therapeutics posing a large unmet need. Unfortunately, existing treatments for AD aim to decrease cutaneous inflammation, but are not specific for the pathways driving this disease. An increasing understanding of the immune mechanisms underlying AD brings the promise of narrow targeted therapies as has occurred for psoriasis, another inflammatory skin disease, for which specific biologic agents have been demonstrated to both control the disease and prevent occurrence of new skin lesions. Although no biologic is yet approved for AD, these are exciting times for active therapeutic development in AD that might lead to revolutionary therapeutics for this disease.

Update in clinical allergy and immunology

In the recent years, a tremendous body of studies has addressed a broad variety of distinct topics in clinical allergy and immunology. In this update, we discuss selected recent data that provide clinically and pathogenetically relevant insights or identify potential novel targets and strategies for therapy. The role of the microbiome in shaping allergic immune responses and molecular, as well as cellular mechanisms of disease, is discussed separately and in the context of atopic dermatitis, as an allergic model disease. Besides summarizing novel evidence, this update highlights current areas of uncertainties and debates that, as we hope, shall stimulate scientific discussions and research activities in the field.

IgE, mast cells, and eosinophils in atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease with specific immune and inflammatory mechanisms. Atopy is among the major features of the diagnosis criteria for AD but is not an essential feature. Thus, patients diagnosed with AD can be atopic or non-atopic. This review focuses on the role of IgE, mast cells, and eosinophils in the pathogenesis of AD. The known functions of IgE in allergic inflammation suggest that IgE and IgE-mediated mast cell and eosinophil activation contribute to AD, but direct evidence supporting this is scarce. The level of IgE (thus the degree of allergic sensitization) is associated with severity of AD and contributed by abnormality of skin barrier, a key feature of AD. The function of IgE in development of AD is supported by the beneficial effect of anti-IgE therapy in a number of clinical studies. The role of mast cells in AD is suggested by the increase in the mast cell number and mast cell activation in AD lesions and the association between mast cell activation and AD. It is further suggested by their role in mouse models of AD as well as by the effect of therapeutic agents for AD that can affect mast cells. The role of eosinophils in AD is suggested by the presence of eosinophilia in AD patients and eosinophil infiltrates in AD lesions. It is further supported by information that links AD to cytokines and chemokines associated with production, recruitment, and activation of eosinophils.

Pharmacokinetic/pharmacodynamic analyses of chymase inhibitor SUN13834 in NC/Nga mice and prediction of effective dosage for atopic dermatitis patients

A chymase inhibitor SUN13834 has been shown to improve skin condition in animal models for atopic dermatitis. In the present study, effective dosages of SUN13834 for atopic dermatitis patients were predicted by pharmacokinetic/pharmacodynamic (PK/PD) analyses of SUN13834 in NC/Nga mice, which spontaneously develop atopic dermatitis-like skin lesions. For the PK/PD analyses, we utilized the minimum effective plasma concentration of unbound SUN13834 in late-phase reaction of trinitrochlorobenzene (TNCB)-induced biphasic dermatitis in mice, based on the assumption that the minimum effective plasma concentrations are the same among the two animal models. In late-phase reaction of biphasic dermatitis, SUN13834 was most effective when its plasma concentration was highest at the elicitation, and the minimum effective plasma concentration of unbound SUN13834 at the elicitation was calculated to be 0.13-0.2 ng/mL. Oral administration of SUN13834 improved dermatitis in NC/Nga mice at 15 mg/kg (twice a day; bid) and 30 mg/kg (once a day; qd), but not at 60 mg/kg (every other day; eod). At the three dosages, the duration times over the plasma level of 0.13-0.2 ng/mL were 16.1-20.3, 10.7-12.2 and 7.8-8.8h, respectively, suggesting an importance of maintenance of the minimum effective plasma concentration for at least about 10-12h. The clinical effective dosage predicted in this paper is also discussed in relation to a recently conducted Phase 2a study.

Potency variation of small-molecule chymase inhibitors across species

Chymases (EC 3.4.21.39) are mast cell serine proteinases that are variably expressed in different species and, in most cases, display either chymotryptic or elastolytic substrate specificity. Given that chymase inhibitors have emerged as potential therapeutic agents for treating various inflammatory, allergic, and cardiovascular disorders, it is important to understand interspecies differences of the enzymes as well as the behavior of inhibitors with them. We have expressed chymases from humans, macaques, dogs, sheep (MCP2 and MCP3), guinea pigs, and hamsters (HAM1 and HAM2) in baculovirus-infected insect cells. The enzymes were purified and characterized with kinetic constants by using chromogenic substrates. We evaluated in vitro the potency of five nonpeptide inhibitors, originally targeted against human chymase. The inhibitors exhibited remarkable cross-species variation of sensitivity, with the greatest potency observed against human and macaque chymases, with K(i) values ranging from approximately 0.4 to 72nM. Compounds were 10-300-fold less potent, and in some instances ineffective, against chymases from the other species. The X-ray structure of one of the potent phosphinate inhibitors, JNJ-18054478, complexed with human chymase was solved at 1.8A resolution to further understand the binding mode. Subtle variations in the residues in the active site that are already known to influence chymase substrate specificity can also strongly affect the compound potency. The results are discussed in the context of selecting a suitable animal model to study compounds ultimately targeted for human chymase.

Mast cells in atopic dermatitis

Mast cells play as the major effector cells in immediate hypersensitivity through activation via the high-affinity IgE receptor, Fc epsilon RI, although many other functions have recently been discovered for this cell type. Given the broad array of proinflammatory mediators secreted from Fc epsilon RI-activated mast cells, as well as sensitization to allergens, IgE elevation, and increased mast cells in a majority of atopic dermatitis patients, mast cells are believed to be involved in the pathogenesis of atopic dermatitis. Numerous animal models have been used to study this epidemic disease. Here we review the recent progress to synthesize our current understanding of this disease and potential mechanisms for a mast cell's role in the disease.

Cellular and molecular mechanisms in atopic dermatitis

Atopic dermatitis (AD) is a pruritic inflammatory skin disease associated with a personal or family history of allergy. The prevalence of AD is on the rise and estimated at approximately 17% in the USA. The fundamental lesion in AD is a defective skin barrier that results in dry itchy skin, and is aggravated by mechanical injury inflicted by scratching. This allows entry of antigens via the skin and creates a milieu that shapes the immune response to these antigens. This review discusses recent advances in our understanding of the abnormal skin barrier in AD, namely abnormalities in epidermal structural proteins, such as filaggrin, mutated in approximately 15% of patients with AD, epidermal lipids, and epidermal proteases and protease inhibitors. The review also dissects, based on information from mouse models of AD, the contributions of the innate and adaptive immune system to the pathogenesis of AD, including the effect of mechanical skin injury on the polarization of skin dendritic cells, mediated by keratinocyte-derived cytokines such as thymic stromal lymphopoietin (TSLP), IL-6, and IL-1, that results in a Th2-dominated immune response with a Th17 component in acute AD skin lesions and the progressive conversion to a Th1-dominated response in chronic AD skin lesions. Finally, we discuss the mechanisms of susceptibility of AD skin lesions to microbial infections and the role of microbial products in exacerbating skin inflammation in AD. Based on this information, we discuss current and future therapy of this common disease.