Histamine H(1)- and H(4)-receptor signaling cooperatively regulate MAPK activation

Histamine H1 Receptor-Mediated JNK Phosphorylation Is Regulated by Gq Protein-Dependent but Arrestin-Independent Pathways

Arrestins are known to be involved not only in the desensitization and internalization of G protein-coupled receptors but also in the G protein-independent activation of mitogen-activated protein (MAP) kinases, such as extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK), to regulate cell proliferation and inflammation. Our previous study revealed that the histamine H1 receptor-mediated activation of ERK is dually regulated by Gq proteins and arrestins. In this study, we investigated the roles of Gq proteins and arrestins in the H1 receptor-mediated activation of JNK in Chinese hamster ovary (CHO) cells expressing wild-type (WT) human H1 receptors, the Gq protein-biased mutant S487TR, and the arrestin-biased mutant S487A. In these mutants, the Ser487 residue in the C-terminus region of the WT was truncated (S487TR) or mutated to alanine (S487A). Histamine significantly stimulated JNK phosphorylation in CHO cells expressing WT and S487TR but not S487A. Histamine-induced JNK phosphorylation in CHO cells expressing WT and S487TR was suppressed by inhibitors against H1 receptors (ketotifen and diphenhydramine), Gq proteins (YM-254890), and protein kinase C (PKC) (GF109203X) as well as an intracellular Ca2+ chelator (BAPTA-AM) but not by inhibitors against G protein-coupled receptor kinases (GRK2/3) (cmpd101), β-arrestin2 (β-arrestin2 siRNA), and clathrin (hypertonic sucrose). These results suggest that the H1 receptor-mediated phosphorylation of JNK is regulated by Gq-protein/Ca2+/PKC-dependent but GRK/arrestin/clathrin-independent pathways.

Adverse Food Reactions in Inflammatory Bowel Disease: State of the Art and Future Perspectives

Limited knowledge is available about the relationship between food allergies or intolerances and inflammatory bowel disease (IBD). Clinicians frequently encounter patients who report food allergies or intolerances, and gastroenterologists struggle distinguishing between patients with organic disorders and those with functional disorders, which the patients themselves may associate with specific dietary components. This task becomes even more arduous when managing patients with significant underlying organic conditions, like IBD. The aim of this review is to summarize and emphasize any actual associations between food allergies and intolerances and inflammatory diseases, such as ulcerative colitis and Crohn's disease. Through a narrative disceptation of the current literature, we highlight the increased prevalence of various food intolerances, including lactose, fructose, histamine, nickel, and non-celiac gluten sensitivity, in individuals with IBD. Additionally, we explore the association between increased epithelial barrier permeability in IBD and the development of food sensitization. By doing so, we aim to enhance clinicians' awareness of the nutritional management of patients with IBD when facing complaints or evidence of food allergies or intolerances.

Histamine H1- and H4-receptor expression in human colon-derived cell lines

In previous studies, we demonstrated the involvement of H4R in inflammatory bowel disease (IBD) and IBD-associated colon cancer in mice and could ascribe H4R-mediated histamine function to colon epithelial cells. The transferability of obtained data to humans is however lacking. Functional expression of H4R on colon epithelial cells is a prerequisite to pursue the hypothesis of involvement of H4R in carcinogenesis. Thus, we here compared the expression of histamine receptor subtypes in a series of cell lines. Out of these, three colon-derived cell lines displaying different combinations of H1R and H4R expression were submitted to functional analyses. Human hematopoietic HMC-1, HL-60, and U937, lung-derived A549 and Calu-3, and colorectal LoVo, SW 480, Caco-2, HT-29, and HCT116 cells were included in the study. mRNA expression was quantified by RT-qPCR. For functional analyses, Caco-2, HT-29, and HCT116 cells were treated by incubation with 1 - 10 µM histamine in the presence or absence of selective histamine receptor antagonists. Calcium mobilization, cAMP accumulation, and cell proliferation were measured by fluorimetry, mass spectrometry, and real-time bioimpedance measurements, respectively. Histamine receptor expression was heterogeneous in the cell lines tested. In most cell lines, we detected H1R mRNA while H4R mRNAs were found only occasionally. The colon-derived epithelial cell lines LoVo, SW480, and HT-29 expressed H1R mRNA exclusively, while in HCT116 cells H1R and H4R mRNAs and in CaCo-2 H2R mRNA were detectable. Subsequent functional analyses in HT29, Caco-2, and HCT116 cells, however, indicated that only HT-29 responded to histamine stimulation, by means of H1R. For a detailed analysis of histamine receptor function, esp. that of H1R and H4R, in human colon-derived cell lines, the cell lines tested here are not fully convenient unless genetically modified.

Differential regulation of histamine H1 receptor-mediated ERK phosphorylation by Gq proteins and arrestins

Gq protein-coupled histamine H1 receptors play crucial roles in allergic and inflammatory reactions, in which the phosphorylation of extracellular signal-regulated kinase (ERK) appears to mediate the production of inflammatory cytokines. ERK phosphorylation is regulated by G protein- and arrestin-mediated signal transduction pathways. Here, we aimed to explore how H1 receptor-mediated processes of ERK phosphorylation might be differentially regulated by Gq proteins and arrestins. For this purpose, we evaluated the regulatory mechanism(s) of H1 receptor-mediated ERK phosphorylation in Chinese hamster ovary cells expressing Gq protein- and arrestin-biased mutants of human H1 receptors, S487TR and S487A, in which the Ser487 residue in the C-terminal was truncated and mutated to alanine, respectively. Immunoblotting analysis indicated that histamine-induced ERK phosphorylation was prompt and transient in cells expressing Gq protein-biased S487TR, whereas it was slow and sustained in cells expressing arrestin-biased S487A. Inhibitors of Gq proteins (YM-254890) and protein kinase C (PKC) (GF109203X), and an intracellular Ca2+ chelator (BAPTA-AM) suppressed histamine-induced ERK phosphorylation in cells expressing S487TR, but not those expressing S487A. Conversely, inhibitors of G protein-coupled receptor kinases (GRK2/3) (cmpd101), β-arrestin2 (β-arrestin2 siRNA), clathrin (hypertonic sucrose), Raf (LY3009120), and MEK (U0126) suppressed histamine-induced ERK phosphorylation in cells expressing S487A, but not those expressing S487TR. These results suggest that H1 receptor-mediated ERK phosphorylation might be differentially regulated by the Gq protein/Ca2+/PKC and GRK/arrestin/clathrin/Raf/MEK pathways to potentially determine the early and late phases of histamine-induced allergic and inflammatory responses, respectively.

Inflammatory Bowel Disease: Crosstalk between Histamine, Immunity, and Disease

Inflammatory bowel disease (IBD) is increasingly recognized as a serious, worldwide public health concern. It is generally acknowledged that a variety of factors play a role in the pathogenesis of this group of chronic inflammatory diseases. The diversity of molecular actors involved in IBD does not allow us to fully assess the causal relationships existing in such interactions. Given the high immunomodulatory activity of histamine and the complex immune-mediated nature of inflammatory bowel disease, the role of histamine and its receptors in the gut may be significant. This paper has been prepared to provide a schematic of the most important and possible molecular signaling pathways related to histamine and its receptors and to assess their relevance for the development of therapeutic approaches.

Nanodelivery of Histamine H3/H4 Receptor Modulators BF-2649 and Clobenpropit with Antibodies to Amyloid Beta Peptide in Combination with Alpha Synuclein Reduces Brain Pathology in Parkinson's Disease

Parkinson's disease (PD) in military personnel engaged in combat operations is likely to develop in their later lives. In order to enhance the quality of lives of PD patients, exploration of novel therapy based on new research strategies is highly warranted. The hallmarks of PD include increased alpha synuclein (ASNC) and phosphorylated tau (p-tau) in the cerebrospinal fluid (CSF) leading to brain pathology. In addition, there are evidences showing increased histaminergic nerve fibers in substantia niagra pars compacta (SNpc), striatum (STr), and caudate putamen (CP) associated with upregulation of histamine H3 receptors and downregulation of H4 receptors in human brain. Previous studies from our group showed that modulation of potent histaminergic H3 receptor inverse agonist BF-2549 or clobenpropit (CLBPT) partial histamine H4 agonist with H3 receptor antagonist induces neuroprotection in PD brain pathology. Recent studies show that PD also enhances amyloid beta peptide (AβP) depositions in brain. Keeping these views in consideration in this review, nanowired delivery of monoclonal antibodies to AβP together with ASNC and H3/H4 modulator drugs on PD brain pathology is discussed based on our own observations. Our investigation shows that TiO₂ nanowired BF-2649 (1 mg/kg, i.p.) or CLBPT (1 mg/kg, i.p.) once daily for 1 week together with nanowired delivery of monoclonal antibodies (mAb) to AβP and ASNC induced superior neuroprotection in PD-induced brain pathology. These observations are the first to show the modulation of histaminergic receptors together with antibodies to AβP and ASNC induces superior neuroprotection in PD. These observations open new avenues for the development of novel drug therapies for clinical strategies in PD.

Cytosolic Phospholipase A2 Is Required for Fexofenadine's Therapeutic Effects against Inflammatory Bowel Disease in Mice

Inflammatory Bowel Disease (IBD) is an autoimmune condition with complicated pathology and diverse clinical signs. TNFα is believed to play a crucial role in the pathogenesis of IBD. We recently identified fexofenadine, a well-known antagonist of histamine H1 receptor, as a novel inhibitor of TNFα signaling. Additionally, cytosolic phospholipase A2 (cPLA2) was isolated as a binding target of fexofenadine, and fexofenadine-mediated anti-TNF activity relied on cPLA2 in vitro. The objective of this study is to determine whether fexofenadine is therapeutic against chemically-induced murine IBD model and whether cPLA2 and/or histamine H1 receptor is important for fexofenadine’s anti-inflammatory activity in vivo by leveraging various genetically modified mice and chemically induced murine IBD models. Both dextran sulfate sodium- and 2, 4, 6-trinitrobenzene sulfonic acid-induced murine IBD models revealed that orally delivered fexofenadine was therapeutic against IBD, evidenced by mitigated clinical symptoms, decreased secretions of the proinflammatory cytokine IL-6 and IL-1β, lowered intestinal inflammation, and reduced p-p65 and p-IĸBα. Intriguingly, Fexofenadine-mediated protective effects against IBD were lost in cPLA2 deficient mice but not in histamine H1 receptor-deficient mice. Collectively, these findings demonstrate the therapeutic effects of over-the-counter drug Fexofenadine in treating DSS-induced IBD murine and provide first in vivo evidence showing that cPLA2 is required for fexofenadine’s therapeutic effects in murine IBD model and probably other inflammatory and autoimmune diseases as well.

The Function of the Histamine H4 Receptor in Inflammatory and Inflammation-Associated Diseases of the Gut

Histamine is a pleiotropic mediator involved in a broad spectrum of (patho)-physiological processes, one of which is the regulation of inflammation. Compounds acting on three out of the four known histamine receptors are approved for clinical use. These approved compounds comprise histamine H1-receptor (H₁R) antagonists, which are used to control allergic inflammation, antagonists at H₂R, which therapeutically decrease gastric acid release, and an antagonist at H₃R, which is indicated to treat narcolepsy. Ligands at H₄R are still being tested pre-clinically and in clinical trials of inflammatory diseases, including rheumatoid arthritis, asthma, dermatitis, and psoriasis. These trials, however, documented only moderate beneficial effects of H₄R ligands so far. Nevertheless, pre-clinically, H₄R still is subject of ongoing research, analyzing various inflammatory, allergic, and autoimmune diseases. During inflammatory reactions in gut tissues, histamine concentrations rise in affected areas, indicating its possible biological effect. Indeed, in histamine-deficient mice experimentally induced inflammation of the gut is reduced in comparison to that in histamine-competent mice. However, antagonists at H₁R, H₂R, and H₃R do not provide an effect on inflammation, supporting the idea that H₄R is responsible for the histamine effects. In the present review, we discuss the involvement of histamine and H₄R in inflammatory and inflammation-associated diseases of the gut.

Histamine H3 receptor and cholinesterases as synergistic targets for cognitive decline: Strategies to the rational design of multitarget ligands

The role of histamine and acetylcholine in cognitive functions suggests that compounds able to increase both histaminergic and cholinergic neurotransmissions in the brain should be considered as promising therapeutic options. For this purpose, dual inhibitors of histamine H₃ receptors (H₃ R) and cholinesterases (ChEs) have been designed and assessed. In this context, this paper reviews the strategies used to obtain dual H₃ R/ChEs ligands using multitarget design approaches. Hybrid compounds designed by linking tacrine or flavonoid motifs to H₃ R antagonists were obtained with high affinity for both targets, and compounds designed by merging the H₃ R antagonist pharmacophore with known anticholinesterase molecules were also reported. These reports strongly suggest that key modifications in the lipophilic region (including a second basic group) seem to be a strategy to reach novel compounds, allied with longer linker groups to a basic region. Some compounds have already demonstrated efficacy in memory models, although the pharmacokinetic and toxicity profile should be considered when designing further compounds. In conclusion, the key features to be considered when designing novel H₃ R/ChEs inhibitors with improved pharmacological profile were herein summarized.

Histamine causes an imbalance between pro-angiogenic and anti-angiogenic factors in the retinal pigment epithelium of diabetic retina via H4 receptor/p38 MAPK axis

INTRODUCTION

Systemic histaminergic activity is elevated in patients with diabetes mellitus. There are a few studies suggesting that histamine is implicated in the pathogenesis of diabetes, but the exact role of histamine in the development of diabetic retinopathy is unclear. The aim of this study was to investigate the role of histamine receptor H4 (HRH4) in the regulation of retinal pigment epithelium (RPE)-derived pro-angiogenic and anti-angiogenic factors under diabetic conditions.

RESEARCH DESIGN AND METHODS

The levels of vascular endothelial growth factor (VEGF), interleukin-6 (IL-6), histamine and histidine decarboxylase (HDC) in the serum and vitreous samples of patients with diabetes were compared with those of patients without diabetes. The effect of hyperglycemia on expression levels of HRH4, VEGF, IL-6 and pigment epithelium-derived factor (PEDF) in the RPE was determined. The role of HRH4 in high glucose-induced regulation of VEGF, IL-6 and PEDF in ARPE-19 cells and the underlying regulatory mechanism were verified using an RNA interference-mediated knockdown study.

RESULTS

The serum and vitreous levels of VEGF, IL-6, histamine and HDC were more increased in patients with diabetic retinopathy than in patients without diabetes. HRH4 was overexpressed in RPE both in vitro and in vivo. Histamine treatment upregulated VEGF and IL-6 and downregulated PEDF expression in ARPE-19 cells cultivated under hyperglycemic conditions. Hyperglycemia-induced phosphorylation of p38 and subsequent upregulation of VEGF and IL-6 and downregulation of PEDF were dampened by small interfering RNA-mediated knockdown of HRH4 in ARPE-19 cells.

CONCLUSIONS

Taken together, HRH4 was a critical regulator of VEGF, IL-6 and PEDF in the RPE under hyperglycemic conditions and the p38 mitogen-activated protein kinase pathway mediated this regulatory mechanism.

Efficacy of histamine H1 receptor antagonists azelastine and fexofenadine against cutaneous Leishmania major infection

Current drug therapies for cutaneous leishmaniasis are often difficult to administer and treatment failure is an increasingly common occurrence. The efficacy of anti-leishmanial therapy relies on a combination of anti-parasite activity of drugs and the patient’s immune response. Previous studies have reported in vitro antimicrobial activity of histamine 1-receptor antagonists (H1RAs) against different pathogens. We used an ex vivo explant culture of lymph nodes from mice infected with Leishmania major to screen H1RAs compounds. Azelastine (AZ) and Fexofenadine (FX) showed remarkable ex vivo efficacy (EC₅₀ = 0.05 and 1.50 μM respectively) and low in vitro cytotoxicity yielding a high therapeutic index. AZ significantly decreased the expression of H1R and the proinflammatory cytokine IL-1ẞ in the ex vivo system, which were shown to be augmented by histamine addition. The anti-leishmanial efficacy of AZ was enhanced in the presence of T cells from infected mice suggesting an immune-modulatory mechanism of parasite suppression. L. major infected BALB/c mice treated per os with FX or intralesionally with AZ showed a significant reduction of lesion size (FX = 69%; AZ = 52%). Furthermore, there was significant parasite suppression in the lesion (FX = 82%; AZ = 87%) and lymph nodes (FX = 81%; AZ = 36%) with no observable side effects. AZ and FX and potentially other H1RAs are good candidates for assessing efficacy in larger studies as monotherapies or in combination with current anti-leishmanial drugs to treat cutaneous leishmaniasis.

Cutaneous leishmaniasis (CL) is a parasitic disease present in more than 90 countries. Different species of Leishmania produce skin ulcers upon infection through the bite of infected sand fly vectors. There are several drugs used to treat CL but most of them are toxic or difficult to administer and there is increasing drug resistance leading to treatment failure. Therefore, new drugs are needed for treating CL. The objective of this study was to determine the anti-leishmanial efficacy of antihistamine drugs. Using cell cultures of lymph nodes obtained from Leishmania major infected mice, we evaluated the parasiticidal activity of the antihistamine drugs azelastine and fexofenadine. Both drugs showed high efficacy against L. major and low toxicity for a human cell line. Treatment of mice infected in the skin with L. major indicated that both azelastine and fexofenadine significantly reduced the size of the lesions and suppressed parasite multiplication. Consequently, these two drugs are good candidates to further evaluate their efficacy as monotherapies or in combination with other anti-leishmanial drugs.

Disruption of histamine/H1R signaling pathway represses cardiac differentiation and maturation of human induced pluripotent stem cells

Background

The efficiency and quality of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are crucial for regenerative medicine, disease modeling, drug screening, and the study of the development events during cardiac specification. However, their applications have been hampered by the differentiation efficiency, poor maturation, and high interline variability. Recent studies have reported that histamine plays important roles in hematopoietic stem cell proliferation and neutrophil maturation. However, its roles in cardiovascular tissue regeneration have not been thoroughly investigated. In the current study, we identified a novel physiological function of the histamine/histamine 1 receptor (H₁R) signal in regulating the differentiation of hiPSC-CMs and heart development.

Methods

Transgenic zebrafish model (cmlc2: mCherry) was treated with histamine and histamine receptor (HR) antagonists. Histological morphology and ultrastructure of zebrafish heart were measured. Histamine-deficient pregnant mice (HDC^−/−) were treated with H₁R antagonist (pyrilamine) by intragastric administration from E8.5 to E18.5. Cardiac histological morphology and ultrastructure were analyzed in neonatal mice, and cardiac function in adult mice was measured. In vitro, histamine and HR antagonists were administrated in the culture medium during hiPSC-CM differentiation at different stages. The efficiency and maturation of cardiac differentiation were evaluated. Finally, histamine-treated hiPSC-CMs were transplanted into ischemic myocardium to detect the possible therapeutic effect.

Results

Administration of H₁R antagonist during heart development induced cardiac dysplasia in zebrafish. Furthermore, using histidine decarboxylase (HDC) knockout mice, we examined abnormal swelling of myocardial mitochondria and autophagy formation under the condition of endogenous histamine deficiency. Histamine significantly promoted myocardial differentiation from human induced pluripotent stem cells (hiPSCs) with better structure and function via a H₁R-dependent signal. The activation of histamine/H₁R signaling pathway augmented hiPSC-derived cardiomyocyte (hiPSC-CM) differentiation through the ERK1/2-STAT3 signaling pathway. In addition, histamine-pre-treated hiPSC-CMs were transplanted into the ischemic hearts of myocardial injured mice and exhibited better survival and myocardial protection.

Conclusions

Thus, these findings indicated that histamine/H₁R and its downstream signals were not only involved in cardiac differentiation but also provided a better survival environment for stem cell transplanted into ischemic myocardium.

Upregulation of histamine receptor H1 promotes tumor progression and contributes to poor prognosis in hepatocellular carcinoma

H1 histamine receptor (H1HR) belongs to the family of rhodopsin-like G-protein-coupled receptors. Recent studies have shown that H1HR expression is increased in several types of cancer. However, its functional roles in tumor progression remain largely unknown, especially in hepatocellular carcinoma (HCC). We found that H1HR is frequently unregulated in HCC, which is significantly associated with both recurrence-free survival and overall survival in HCC patients. Functional experiments revealed that H1HR promoted both the growth and metastasis of HCC cells by inducing cell cycle progression, formation of lamellipodia, production of matrix metalloproteinase 2, and suppression of cell apoptosis. Activation of cyclic adenosine monophosphate-dependent protein kinase A was found to be involved in H1HR-mediated HCC cell growth and metastasis. In addition, we found that overexpression of H1HR was mainly due to the downregulation of miR-940 in HCC cells. Moreover, the H1HR inhibitor terfenadine significantly suppressed tumor growth and metastasis in an HCC xenograft nude mice model. Our findings demonstrate that H1HR plays a critical role in the growth and metastasis of HCC cells, which provides experimental evidence supporting H1HR as a potential drug target for the treatment of HCC.

Systemic injection of an H4 receptor agonist induces a decrease in CREB and pCREB levels in the cerebellar vermis and prefrontal cortex in mice

Studies have shown that an injection with the histamine H4 receptor agonist VUF-8430 modulates emotional memory processes. In the present study, the aim was to verify if intraperitoneal (ip) injection of VUF-8430 (500 ng/kg) in mice affects the synthesis of proteins required for memory consolidation processes by activating the phosphorylation of CREB (pCREB) in classical structures linked to emotional memory (prefrontal cortex, amygdala, and hippocampus) and the cerebellar vermis, a structure that has also been recently implicated in emotional memory. The results obtained using western blot analysis demonstrated that VUF-8430 induced a decrease in CREB and pCREB levels in the cerebellar vermis and prefrontal cortex, suggesting that this dose impaired the activation of cell signaling pathways in these structures. There was no change in protein expression in the amygdala and hippocampus. Our results are preliminary, and further investigations are needed to investigate the role of the H4 receptors in the central nervous system.

H4 Receptor Inhibits Lipopolysaccharide-induced NF-κB Activation by Interacting with Tumor Necrosis Factor Receptor-Associated Factor 6

Microglia, the resident immune cells of the central nervous system (CNS), are activated at the beginning of the inflammatory response and induce detrimental neuroinflammation by producing excessive pro-inflammatory cytokines. Nuclear factor kappa B (NF-κB) signaling facilitates the onset of microglia activation. However, the molecular mechanisms underlying the negative regulation of NF-κB remain to be fully elucidated. In the present study, our results indicated that H4R expression increased in a rat model of lipopolysaccharide (LPS)-induced CNS inflammation. Knockdown of H4R in microglia HAPI cells enhanced the production of cytokines following LPS stimulation. Co-immunoprecipitation experiments further revealed an interaction between H4R and tumor necrosis factor receptor-associated factor 6 (TRAF6) in microglia, which was verified both in vivo and in vitro. Our experimental results support our hypothesis that H4R interacts with TRAF6 to inhibit the release of inflammatory cytokines in LPS-induced microglia cells by decreasing TRAF6-mediated ubiquitination of K63. These findings provide theoretical and experimental evidence regarding the role of H4R in the microglia inflammatory response, which may aid in the development of novel treatments for inflammation.

In vivo Evidence for Partial Activation of Eosinophils via the Histamine H4-Receptor: Adoptive Transfer Experiments Using Eosinophils From H4R-/- and H4R+/+ Mice

Our previous in vitro studies revealed that histamine via histamine the H₄-receptors (H₄R), as compared to other stimuli, such as eotaxin or formylpeptides, rather partially activates eosinophilic granulocytes (eosinophils). In order to evaluate the H₄R-mediated activation of eosinophils in vivo, we employed dextran sodium sulfate (DSS)-induced colitis in mice, closely resembling human ulcerative colitis (UC), which is largely characterized by a local eosinophilic infiltration of the colon. IL-5-deficient BALB/c mice served as a model with reduced endogenous numbers of eosinophils, in which wild-type (H₄R^+/+) or H₄R-deficient (H₄R^−/−) eosinophils were adoptively transferred during the course of DSS-induced colitis. During the 1-week observation period, transfer of eosinophils transiently reversed the acute clinical colitis-like phenotype (body weight loss, perianal bleeding, soft stool consistency) resulting from IL-5-deficiency. This reversion was significantly more pronounced upon transfer of eosinophils from H₄R^+/+ mice as compared to those from H₄R^−/− mice. Already at the end of the observation period, the clinical effects of the transfer of H₄R^+/+ and H₄R^−/− eosinophils became similar, as were the results of the histological examination of the cola and the analyses of cytokine production in cola and in re-stimulated lymph node cells performed at this time. Thus, analyzing clinical and pathological parameters representative of colitis in this model, we demonstrate that as well as in vitro, also in vivo histamine via the H₄R only partially activates eosinophils.

Role of Histamine in Modulating the Immune Response and Inflammation

Inflammatory mediators, including cytokines, histamine, bradykinin, prostaglandins, and leukotrienes, impact the immune system, usually as proinflammatory factors. Other mediators act as regulatory components to establish homeostasis after injury or prevent the inflammatory process. Histamine, a biogenic vasoactive amine, causes symptoms such as allergies and has a pleiotropic effect that is dependent on its interaction with its four histamine receptors. In this review, we discuss the dualistic effects of histamine: how histamine affects inflammation of the immune system through the activation of intracellular pathways that induce the production of inflammatory mediators and cytokines in different immune cells and how histamine exerts regulatory functions in innate and adaptive immune responses. We also evaluate the interactions between these effects.

Combined blockade of the histamine H1 and H4 receptor suppresses peanut-induced intestinal anaphylaxis by regulating dendritic cell function

BACKGROUND

Signaling through histamine receptors on dendritic cells (DCs) may be involved in the effector phase of peanut-induced intestinal anaphylaxis.

OBJECTIVES

The objective of this study was to determine the role of histamine H1 (H1R) and H4 receptors (H4R) in intestinal allergic responses in a model of peanut allergy.

METHODS

Balb/c mice were sensitized and challenged with peanut. During the challenge phase, mice were treated orally with the H1R antagonist, loratadine, and/or the H4R antagonist, JNJ7777120. Bone marrow-derived DCs (BMDCs) were adoptively transferred to nonsensitized WT mice. Symptoms, intestinal inflammation, and mesenteric lymph node and intestine mucosal DCs were assessed. Effects of the drugs on DC chemotaxis, calcium mobilization, and antigen-presenting cell function were measured.

RESULTS

Treatment with loratadine or JNJ7777120 individually partially suppressed the development of diarrhea and intestinal inflammation and decreased the numbers of DCs in the mesenteric lymph nodes and lamina propria. Combined treatment with both drugs prevented the development of diarrhea and intestinal inflammation. In vitro, the combination suppressed DC antigen-presenting cell function to T helper cells and DC calcium mobilization and chemotaxis to histamine.

CONCLUSION

Blockade of both H1R and H4R in the challenge phase had additive effects in preventing the intestinal consequences of peanut sensitization and challenge. These effects were mediated through the limitation of mesenteric lymph node and intestinal DC accumulation and function. Identification of this histamine H1R/H4R-DC-CD4⁺ T-cell axis provides new insights into the development of peanut-induced intestinal allergic responses and for prevention and treatment of peanut allergy.