Expression and function of histamine and its receptors in atopic dermatitis

Emerging trends and hotspots of the itch research: A bibliometric and visualized analysis

AIMS

Itch, a common uncomfortable sensory experience, occurs frequently in inflammatory or allergic disorders. In recent years, with the discovery of itch-specific pathways in the peripheral and central nervous system, the association between immunology and neural pathways has gradually emerged as the main mechanism of itch. Although many studies have been conducted on itch, no bibliometric analysis study focusing on this topic has been conducted. This study aimed to explore the research hotspots and trends in the itch field from a bibliometric perspective.

METHODS

Publications relevant to itch, published from 2003 to 2022, were retrieved from the Science Citation Index-Expanded of Web of Science Core Collection. Publications were critically reviewed and analyzed with CiteSpace software, Vosviewer, and the bibliometric online analysis platform. Visual maps were conducted in terms of annual production, collaborating countries or institutions, productive authors, core journals, co-cited references, and keyword bursts.

RESULTS

2395 articles on itch that met our criteria were identified and the quantity of publications has been increasing rapidly since 2012. The USA was the most influential country. University Hospital Münster was the institution with the most publications. Gil Yosipovitch was the most prolific author. Atopic dermatitis (AD), intradermal serotonin, chronic pruritus, mechanical itch, gastrin-releasing peptide, substance p, interleukin-31 receptor, histamine-induced itch, bile acid, scratching behavior, and h-4 receptor were the top 11 clusters in co-citation cluster analysis. Keyword burst analysis suggested that treatment, inflammation, and AD are current research hotspots.

CONCLUSION

Global publications on itch research have increased steadily and rapidly over the past 20 years. Inflammation and AD are current research hotspots. The neuroimmunological and neuroinflammatory mechanisms of itch, as well as clinical assessment methods and therapeutic targets, will be novel research directions in the future. This study provides guidance for further itch research.

Histamine Receptors: Ex Vivo Functional Studies Enabling the Discovery of Hits and Pathways

Histamine receptors (HRs) are G-protein-coupled receptors involved in diverse responses triggered by histamine release during inflammation or by encounters with venomous creatures. Four histamine receptors (H1R-H4R) have been cloned and extensively characterized. These receptors are distributed throughout the body and their activation is associated with clinical manifestations such as urticaria (H1R), gastric acid stimulation (H2R), regulation of neurotransmitters in neuronal diseases (H3R), and immune responses (H4R). Despite significant homologous overlap between H3R and H4R, much remains unknown about their precise roles. Even though some drugs have been developed for H1R, H2R, and H3R, not a single H4R antagonist has been approved for clinical use. To enhance our understanding and advance innovative therapeutic targeting of H1R, H2R, H3R, and H4R, we established a robust ex vivo functional platform. This platform features the successful heterologous expression of H1R-H4R in Xenopus laevis oocytes, utilizing an electrophysiological readout. Our findings contribute to a deeper understanding of the function and pharmacological properties of the histamine receptors. Researchers can benefit from the utility of this platform when investigating the effects of histamine receptors and exploring potential therapeutic targets. In doing so, it broadens the horizon of drug discovery, offering new perspectives for therapeutic interventions.

In vitro models for investigating itch

Itch (pruritus) is a sensation that drives a desire to scratch, a behavior observed in many animals. Although generally short-lasting and not causing harm, there are several pathological conditions where chronic itch is a hallmark symptom and in which prolonged scratching can induce damage. Finding medications to counteract the sensation of chronic itch has proven difficult due to the molecular complexity that involves a multitude of triggers, receptors and signaling pathways between skin, immune and nerve cells. While much has been learned about pruritus from in vivo animal models, they have limitations that corroborate the necessity for a transition to more human disease-like models. Also, reducing animal use should be encouraged in research. However, conducting human in vivo experiments can also be ethically challenging. Thus, there is a clear need for surrogate models to be used in pre-clinical investigation of the mechanisms of itch. Most in vitro models used for itch research focus on the use of known pruritogens. For this, sensory neurons and different types of skin and/or immune cells are stimulated in 2D or 3D co-culture, and factors such as neurotransmitter or cytokine release can be measured. There are however limitations of such simplistic in vitro models. For example, not all naturally occurring cell types are present and there is also no connection to the itch-sensing organ, the central nervous system (CNS). Nevertheless, in vitro models offer a chance to investigate otherwise inaccessible specific cell–cell interactions and molecular pathways. In recent years, stem cell-based approaches and human primary cells have emerged as viable alternatives to standard cell lines or animal tissue. As in vitro models have increased in their complexity, further opportunities for more elaborated means of investigating itch have been developed. In this review, we introduce the latest concepts of itch and discuss the advantages and limitations of current in vitro models, which provide valuable contributions to pruritus research and might help to meet the unmet clinical need for more refined anti-pruritic substances.

Unraveling the venom chemistry with evidence for histamine as key regulator in the envenomation by caterpillar Automeris zaruma

Over the past decades, envenomation by caterpillars of Automeris spp. became an increasing health problem in Latin America. Accidental contact with the stinging spines of these caterpillars cause acute local pain, itching, inflammation and skin rashes that persists for days. Even when the cause is obvious, the exact molecular mechanisms responsible for the observed symptoms are yet to be elucidated. Here, we describe for the first time, an active compound in the venom and the study of the bioactivity of the venom extracted from the spines of the caterpillar Automeris zaruma. Electrophysiological screening of a library of membrane proteins important for pain and itch enabled us to investigate and reveal the mode of action of the venom of A. zaruma. Further mass spectrometric analysis (Q-TOF-MS) made it possible to establish a link between the bioactivity and the components found in the venom. We show that the spine extract of A. zaruma contains histamine that potently activates the four types of the human histamine receptors (H1R, H2R, H3R and H4R) with a selectivity preference towards H3R and H4R. Furthermore, a modulation of the target MRGPRX2 was found. Together, these findings are the first to explain the symptomology of A. zaruma envenomation, enabling us a better understanding of caterpillar envenomation and predict that the hurdle of the scarce efficacy of the currently used antihistaminic drugs can be overcome by including H3R and H4R blockers in the clinical used medication. Such an approach might be used for other caterpillar envenomation in the world and represent a significant improvement for the well-being of the patient.

From Emollients to Biologicals: Targeting Atopic Dermatitis

Atopic dermatitis (AD) is the most common chronic inflammatory skin disease and significantly impacts patients' lives, particularly in its severe forms. AD clinical presentation varies over the course of the disease, throughout different age groups, and across ethnicities. AD is characterized by a spectrum of clinical phenotypes as well as endotypes. Starting from the current description of AD pathogenesis, this review explores the rationale of approved AD therapies from emollients to biologicals and introduces novel promising drugs.

Role of Amine Neurotransmitters and Their Receptors in Skin Pigmentation: Therapeutic Implication

Skin pigmentation can occur due to increased melanin, including melanocyte proliferation, melanin biosynthesis, or melanocyte migration. There are many factors that influence the melanin production process, but the role of neurotransmitters in this process is still unclear. We found that histamine and serotonin influence the different stages of melanogenesis and melanogenesis, which increase melanogenesis. Since then, several related papers have been published, and from these papers, it has been recognised that the role of neurotransmitters in skin-pigment-related diseases needs to be summarised. By introducing the role of neurotransmitters in the regulation of various pigment disorders, including vitiligo and melasma, through this review, many researchers can be expected to try to apply neurotransmitter-related agonists and antagonists as treatments for skin pigment disorders.

Tick-human interactions: from allergic klendusity to the α-Gal syndrome

Ticks and the pathogens they transmit, including bacteria, viruses, protozoa, and helminths, constitute a growing burden for human and animal health worldwide. The ability of some animal species to acquire resistance to blood-feeding by ticks after a single or repeated infestation is known as acquired tick resistance (ATR). This resistance has been associated to tick-specific IgE response, the generation of skin-resident memory CD4+ T cells, basophil recruitment, histamine release, and epidermal hyperplasia. ATR has also been associated with protection to tick-borne tularemia through allergic klendusity, a disease-escaping ability produced by the development of hypersensitivity to an allergen. In addition to pathogen transmission, tick infestation in humans is associated with the α-Gal syndrome (AGS), a type of allergy characterized by an IgE response against the carbohydrate Galα1-3Gal (α-Gal). This glycan is present in tick salivary proteins and on the surface of tick-borne pathogens such as Borrelia burgdorferi and Anaplasma phagocytophilum, the causative agents of Lyme disease and granulocytic anaplasmosis. Most α-Gal-sensitized individuals develop IgE specific against this glycan, but only a small fraction develop the AGS. This review summarizes our current understanding of ATR and its impact on the continuum α-Gal sensitization, allergy, and the AGS. We propose that the α-Gal-specific IgE response in humans is an evolutionary adaptation associated with ATR and allergic klendusity with the trade-off of developing AGS.

The role of basophils in acquired protective immunity to tick infestation

Ticks are blood-feeding ectoparasites that transmit a variety of pathogens to host animals and humans, causing severe infectious diseases such as Lyme disease. In a certain combination of animal and tick species, tick infestation elicits acquired immunity against ticks in the host, which can reduce the ability of ticks to feed on blood and to transmit pathogens in the following tick infestations. Therefore, our understanding of the cellular and molecular mechanisms of acquired tick resistance (ATR) can advance the development of anti-tick vaccines to prevent tick infestation and tick-borne diseases. Basophils are a minor population of white blood cells circulating in the bloodstream and are rarely observed in peripheral tissues under steady-state conditions. Basophils have been reported to accumulate at tick-feeding sites during re-infestation in cattle, rabbits, guinea pigs and mice. Selective ablation of basophils resulted in a loss of ATR in guinea pigs and mice, illuminating the essential role of basophils in the manifestation of ATR. In this review, we discuss the recent advance in the elucidation of the cellular and molecular mechanisms underlying basophil recruitment to the tick-feeding site and basophil-mediated ATR.

Use of H-1 Antihistamine in Dermatology: More than Itch and Urticaria Control: A Systematic Review

H-1 antihistamines are commonly used in dermatological practice for itch and urticaria control. The widespread expression of H-1 receptor on different cells in the skin and various biologic functions of H-1 antihistamines indicate the possible treatment potentials of H-1 antihistamines in dermatology. A literature search was performed on PubMed and Embase, targeting articles reporting use of antihistamine for purposes other than itch and urticaria control in dermatological practice. Several off-label usages of antihistamines were identified, including alopecia, acne, Darier disease, eosinophilic dermatoses, paraneoplastic dermatoses, psoriasis, lichen nitidus, radiation dermatitis, skin dysesthesia, and cutaneous malignancies. Additional benefits were observed when H-1 antihistamines were used either alone or in combination with other therapeutic modalities. Although various novel uses of H-1 antihistamines have been uncovered, the evidence level of most included studies is weak. Further randomized control trials are warranted to better evaluate the efficacy and dosage of H-1 antihistamine for dermatological disorders.

Histamine Induced Production of Chemokine CXCL8 Through H1R/PLC and NF-κB Signaling Pathways in Nasal Fibroblasts

Background and Objectives: Histamine has been suggested to play an important role during allergic and inflammatory reactions, affecting allergic rhinitis and chronic rhinosinusitis. CXCL8 is a pro-inflammatory chemokine and a critical factor that causes many airway inflammatory diseases including allergic rhinitis and chronic rhinosinusitis.Materials and Method: Histamine cytotoxicity was measured by MTT assay. Real-time polymerase chain reaction was used to identify histamine type 1 receptor in nasal fibroblasts. The fibroblasts were then treated with histamine with or without a histamine type 1 receptor antagonist and the CXCL8 protein was assessed using an enzyme-linked immunosorbent assay (ELISA). The downstream signaling molecules, including phospholipase C and phospho-p50, were evaluated by western blot and immunofluorescent staining.Results: Histamine had no significant cytotoxic effect until the concentration reached 1,000 μM. Histamine type 1 receptor mRNA was expressed in nasal fibroblasts. CXCL8 protein expression level was significantly increased following histamine stimulation. However, the expression level of CXCL8 decreased when phospholipase C was inhibited by U73122. Histamine increased phospho-p50 expression as seen in western blot results. The BAY11-7082, NF-κB inhibitor significantly reduced CXCL8 production in histamine-stimulated nasal fibroblasts.Conclusion: Histamine can induce the production of NF-κB controlled-chemokine CXCL8 by nasal fibroblasts, which supports a role for histamine in upper airway inflammatory diseases.

Immunobiology of Acquired Resistance to Ticks

Ticks are blood-sucking arthropods of great importance in the medical and veterinary fields worldwide. They are considered second only to mosquitos as vectors of pathogenic microorganisms that can cause serious infectious disorders, such as Lyme borreliosis and tick-borne encephalitis. Hard (Ixodid) ticks feed on host animals for several days and inject saliva together with pathogens to hosts during blood feeding. Some animal species can acquire resistance to blood-feeding by ticks after a single or repeated tick infestation, resulting in decreased weights and numbers of engorged ticks or the death of ticks in subsequent infestations. Importantly, this acquired tick resistance (ATR) can reduce the risk of pathogen transmission from pathogen-infected ticks to hosts. This is the basis for the development of tick antigen-targeted vaccines to forestall tick infestation and tick-borne diseases. Accumulation of basophils is detected in the tick re-infested skin lesion of animals showing ATR, and the ablation of basophils abolishes ATR in mice and guinea pigs, illustrating the critical role for basophils in the expression of ATR. In this review article, we provide a comprehensive overview of recent advances in our understanding of the cellular and molecular mechanisms responsible for the development and manifestation of ATR, with a particular focus on the role of basophils.

Crucial Role for Basophils in Acquired Protective Immunity to Tick Infestation

Ticks are blood-sucking arthropods that can transmit various pathogenic organisms to host animals and humans, causing serious infectious diseases including Lyme disease. Tick feeding induces innate and acquired immune responses in host animals, depending on the combination of different species of animals and ticks. Acquired tick resistance (ATR) can diminish the chance of pathogen transmission from infected ticks to the host. Hence, the elucidation of cellular and molecular mechanism underlying ATR is important for the development of efficient anti-tick vaccines. In this review article, we briefly overview the history of studies on ATR and summarize recent findings, particularly focusing on the role for basophils in the manifestation of ATR. In several animal species, including cattle, guinea pigs, rabbits and mice, basophil accumulation is observed at the tick re-infestation site, even though the frequency of basophils among cellular infiltrates varies in different animal species, ranging from approximately 3% in mice to 70% in guinea pigs. Skin-resident, memory CD4⁺ T cells contribute to the recruitment of basophils to the tick re-infestation site through production of IL-3 in mice. Depletion of basophils before the tick re-infestation abolishes ATR in guinea pigs infested with Amblyomma americanum and mice infested with Haemaphysalis longicornis, demonstrating the crucial role of basophils in the manifestation of ATR. The activation of basophils via IgE and its receptor FcεRI is essential for ATR in mice. Histamine released from activated basophils functions as an important effector molecule in murine ATR, probably through promotion of epidermal hyperplasia which interferes with tick attachment or blood feeding in the skin. Accumulating evidence suggests the following scenario. The 1^st tick infestation triggers the production of IgE against tick saliva antigens in the host, and blood-circulating basophils bind such IgE on the cell surface via FcεRI. In the 2^nd infestation, IgE-armed basophils are recruited to tick-feeding sites and stimulated by tick saliva antigens to release histamine that promotes epidermal hyperplasia, contributing to ATR. Further studies are needed to clarify whether this scenario in mice can be applied to ATR in other animal species and humans.

Distinct transcriptomic profiles of early-onset atopic dermatitis in blood and skin of pediatric patients

BACKGROUND

Atopic dermatitis (AD) predominantly affects young children, but our understanding of AD pathogenesis is based on skin and blood samples from long-standing adult AD. Genomic biopsy profiling from early pediatric AD showed significant Th2 and Th17/Th22-skewing, without the characteristic adult Th1 up-regulation. Because obtaining pediatric biopsies is difficult, blood gene expression profiling may provide a surrogate for the pediatric skin signature.

OBJECTIVE

To define the blood profile and associated biomarkers of early moderate-to-severe pediatric AD.

METHODS

We compared microarrays and reverse transcription polymerase chain reaction (RT-PCR) of blood cells from 28 AD children (<5 years and within 6 months of disease onset) to healthy control blood cells. Differentially expressed genes (DEGs) in blood (fold change [FCH] > 1.2 and false discovery rate [FDR] < 0.05) were then compared with skin DEGs.

RESULTS

Eosinophil and Th2 markers (IL5RA, IL1RL1/ST2, HRH4, CCR3, SIGLEC8, PRSS33, CLC from gene arrays; IL13/IL4/CCL22 from RT-PCR) were up-regulated in early pediatric AD blood, whereas IFNG/Th1 was decreased. Th1 markers were negatively correlated with clinical severity (EASI, pruritus, transepidermal water loss [TEWL]), whereas Th2/Th17-induced interleukin (IL)-19 was positively correlated with SCORAD. Although a few RT-PCR-defined immune markers (IL-13/CCL22) were increased in blood, as previously also reported for skin, minimal overlap based on gene array DEGs was seen.

CONCLUSION

The whole blood signature of early moderate-to-severe pediatric AD blood cells show predominantly a Th2/eosinophil profile; however, markers largely differ from the skin profile. Given their complementarity, pooling of biomarkers from blood and skin may improve profiling and predictions, providing insight regarding disease course, allergic comorbidity development, and response to systemic medications.

Regulatory effects of chrysophanol, a bioactive compound of AST2017-01 in a mouse model of 2,4-dinitrofluorobenzene-induced atopic dermatitis

The aim of this study is to determine whether AST2017-01 which consists of Rumex crispus and Cordyceps militaris would improve atopic dermatitis (AD). We analyzed anti-AD effects of AST2017-01 and chrysophanol, a bioactive compound of AST2017-01, using a 2,4-dinitrofluorobenzene-induced AD murine model. AST2017-01 and chrysophanol relieved clinical severity in AD-like skin lesions and significantly decreased scratching behavior. The thickness of epidermis and infiltration of inflammatory cells in AD-like skin lesions were reduced by AST2017-01 or chrysophanol. AST2017-01 and chrysophanol significantly suppressed the levels of histamine, immunoglobulin E, thymic stromal lymphopoietin (TSLP), interleukin (IL)-4, IL-6, and tumor necrosis factor-α in serum of AD mice. The protein levels of TSLP, intercellular adhesion molecule-1, and macrophage inflammatory protein 2 were significantly inhibited in the skin lesions. The mRNA expressions of TSLP, thymus and activation-regulated chemokine/CCL17, and C-C chemokine receptor 3 were inhibited in the skin lesions by AST2017-01 or chrysophanol. In addition, AST2017-01 and chrysophanol significantly suppressed the expressions and activities of caspase-1 in the skin lesions. Taken together, these results suggest that AST2017-01 has beneficial effects on AD and may be used as a health functional food in AD.

Histamine Released From Skin-Infiltrating Basophils but Not Mast Cells Is Crucial for Acquired Tick Resistance in Mice

Ticks are blood-feeding arthropods that can transmit pathogens to humans and animals, leading to serious infectious diseases such as Lyme disease. After single or multiple tick infestation, some animal species develop resistance to tick feeding, leading to reduced risk of pathogen transmission. In mice infested with larval Haemaphysalis longicornis ticks, both mast cells and basophils reportedly play key roles in the manifestation of acquired tick resistance (ATR), but it remains ill-defined how they contribute to it. Here, we investigated their products responsible for ATR. Treatment of mice with antihistamine abolished the ATR while histamine or histamine H1 receptor agonist reduced tick-feeding even in the first infestation. In accordance with these, mice deficient for histamine production showed little or no ATR, indicating the crucial role for histamine in the expression of ATR. Adoptive transfer of mast cells and basophils derived from histamine-sufficient or deficient mice to recipient mice lacking mast cells and basophils, respectively, revealed that histamine produced by basophils but not mast cells is essential for the manifestation of ATR, in contrast to the case of local and systemic anaphylaxis where mast cell-derived histamine is the major player. During the second but not first tick infestation, basophils accumulated and made a cluster, surrounding a tick mouthpart, in the epidermis whereas mast cells were scattered and localized mainly in the dermis, more distantly from a tick mouthpart. This appears to explain why basophil-derived histamine is much more effective than mast cell-derived one. Histamine-sufficient, but not -deficient mice showed the thickened epidermis at the second tick-feeding site. Taken together, histamine released from skin-infiltrating basophils rather than skin-resident mast cells plays a crucial role in the manifestation of ATR, perhaps through promotion of epidermal hyperplasia that may inhibit tick feeding.

Current insights into the role of human β-defensins in atopic dermatitis

Anti-microbial peptides or host defence peptides are small molecules that display both anti-microbial activities and complex immunomodulatory functions to protect against various diseases. Among these peptides, the human β-defensins (hBDs) are localized primarily in epithelial surfaces, including those of the skin, where they contribute to protective barriers. In atopic dermatitis skin lesions, altered skin barrier and immune dysregulation are believed to be responsible for reduced hBD synthesis. Impaired hBD expression in the skin is reportedly the leading cause of increased susceptibility to bacterial and viral infection in patients with atopic dermatitis. Although hBDs have considerable beneficial effects as anti-microbial agents and immunomodulators and may ameliorate atopic dermatitis clinically, recent evidence has also suggested the negative effects of hBDs in atopic dermatitis development. In the current review, we provide an overview of the regulation of hBDs and their role in the pathogenesis of atopic dermatitis. The efforts to utilize these molecules in clinical applications are also described.

Adjunctive Management of Itch in Atopic Dermatitis

Itch, or pruritus, is a hallmark feature of atopic dermatitis (AD). The impact of AD-related pruritus can range from mildly distressing or distracting to completely disabling. Traditionally, management of itch in AD patients has focused on restoring the altered skin barrier with topical emollients and/or reducing inflammation. A growing emphasis has been placed on directly targeting the neural transmission pathways that mediate itch signaling. Off-label use of neuromodulatory agents has helped reduce this aggravating symptom in atopic patients. This article reviews the current literature on the use of neuromodulatory agents and nonpharmacologic alternative therapies used to treat AD-related pruritus.

Glycomacropeptide Attenuates Inflammation, Pruritus, and Th2 Response Associated with Atopic Dermatitis Induced by 2,4-Dinitrochlorobenzene in Rat

Atopic dermatitis (AD) is one of the most common skin diseases, whose incidence is increasing in industrialized countries. The epicutaneous application of a hapten, such as 2,4-dinitrochlorobenzene (DNCB), evokes an experimental murine AD-like reaction. Glycomacropeptide (GMP) is a dairy bioactive peptide derived from hydrolysis of κ-casein by chymosin action. It has anti-inflammatory, prebiotic, and immunomodulatory effects. The present study was aimed to investigate the effect of GMP administration on DNCB-induced AD in rats. The severity of inflammatory process, pruritus, production of cytokines, and total immunoglobulin E (IgE) content were measured, and the histopathological features were analyzed. GMP reduced the intensity of inflammatory process and edema of DNCB-induced dermatitis, with a significant decrease in eosinophils recruitment and mast cells hyperplasia. In addition GMP suppressed the serum levels of total IgE and IL-4, IL-5, and IL-13 expression in AD-lesions. Besides, the levels of IL-10 were significantly increased. Remarkably, GMP administration before AD-induction abolished pruritus in dermatitis-like reactions in the rats. Taken together, these results indicate that GMP has an inhibitory effect on AD by downregulating Th2 dominant immune response, suggesting GMP as a potential effective alternative therapy for the prevention and management of AD.