Antagonism of the histamine H4 receptor reduces LPS-induced TNF production in vivo

Genetic determinants of ammonia-induced acute lung injury in mice

In this study, a genetically diverse panel of 43 mouse strains was exposed to ammonia, and genome-wide association mapping was performed employing a single-nucleotide polymorphism (SNP) assembly. Transcriptomic analysis was used to help resolve the genetic determinants of ammonia-induced acute lung injury. The encoded proteins were prioritized based on molecular function, nonsynonymous SNP within a functional domain or SNP within the promoter region that altered expression. This integrative functional approach revealed 14 candidate genes that included Aatf, Avil, Cep162, Hrh4, Lama3, Plcb4, and Ube2cbp, which had significant SNP associations, and Aff1, Bcar3, Cntn4, Kcnq5, Prdm10, Ptcd3, and Snx19, which had suggestive SNP associations. Of these genes, Bcar3, Cep162, Hrh4, Kcnq5, and Lama3 are particularly noteworthy and had pathophysiological roles that could be associated with acute lung injury in several ways.

Effects of a histamine H4 receptor antagonist on cisplatin-induced anorexia in mice

Cancer chemotherapy often induces gastrointestinal symptoms such as anorexia, nausea, and vomiting. Antiemetic agents are effective in inhibiting nausea and vomiting, but patients still experience anorexia. We previously reported that chemotherapeutic agent-induced anorexia is associated with an increase of inflammatory cytokines. Other studies also reported that antagonism of the histamine H₄ receptor is anti-inflammatory. In this study, we investigated the involvement of the H₄ receptor in the development of chemotherapy-induced anorexia in mice. Cisplatin-induced anorexia occurred within 24 h of its administration and continued for 3 days. The early phase (day 1), but not the delayed phase (days 2 and 3), of anorexia was inhibited by the daily injection of a 5-HT₃ receptor antagonist (granisetron). However, a corticosteroid (dexamethasone) or selective H₄ receptor antagonist (JNJ7777120) abolished the delayed phases of anorexia. Cisplatin significantly increased TNF-α mRNA expression in the hypothalamus and spleen, and the period of expression increase paralleled the onset period of anorexia. In addition, pretreatment with JNJ7777120 completely inhibited the increased expression. These results suggest that TNF-α mRNA expression via H₄ receptors may contribute to the development of cisplatin-induced anorexia, and that H₄ receptor antagonists are potentially useful treatments.

Clinical Development of Histamine H4 Receptor Antagonists

The discovery of the histamine H₄ receptor (H₄R) provided a new avenue for the exploration of the physiological role of histamine, as well as providing a new drug target for the development of novel antihistamines. The first step in this process was the identification of selective antagonists to help unravel the pharmacology of the H₄R relative to other histamine receptors. The discovery of the selective H₄R antagonist JNJ 7777120 was vital for showing a role for the H₄R in inflammation and pruritus. While this compound has been very successful as a tool for understanding the function of the receptor, it has drawbacks, including a short in vivo half-life and hypoadrenocorticism toxicity in rats and dogs, that prevented advancing it into clinical studies. Further research let to the discovery of JNJ 39758979, which, similar to JNJ 7777120, was a potent and selective H₄R antagonist and showed anti-inflammatory and anti-pruritic activity preclinically. JNJ 39758979 advanced into human clinical studies and showed efficacy in reducing experimental pruritus and in patients with atopic dermatitis. However, development of this compound was terminated due to the occurrence of drug-induced agranulocytosis. This was overcome by developing another H₄R antagonist with a different chemical structure, toreforant, that does not appear to have this side effect. Toreforant has been tested in clinical studies in patients with rheumatoid arthritis, asthma, or psoriasis. In conclusions there have been many H₄R antagonists reported in the literature, but only a few have been studied in humans underscoring the difficulty in finding ligands with all of the properties necessary for testing in the clinic. Nevertheless, the clinical data to date suggests that H₄R antagonists can be beneficial in treating atopic dermatitis and pruritus.

Lack of Histamine H4-Receptor Expression Aggravates TNBS-Induced Acute Colitis Symptoms in Mice

Inflammatory bowel diseases (IBD) are a growing health problem worldwide, severely affecting patients’ life qualities and life expectancies. Therapeutic options, which are rare and focus on symptoms associated with the disease, suffer from increasing numbers of patients refractory to the established strategies. Thus, in order to generate new therapeutic regimens, the detailed understanding of the pathogenic mechanisms causing IBD is necessary. Histamine is an inflammatory mediator associated with IBD. Four histamine receptors are currently known of which the histamine H₄-receptor (H₄R) has been shown to possess a pro-inflammatory function in several experimental models of inflammatory diseases, including dextran sodium sulfate (DSS)-induced colitis in mice. No single model reflects the complexity of human IBD, but each model provides valuable information on specific aspects of IBD pathogenesis. While DSS-induced colitis mostly relies on innate immune mechanisms, trinitrobenzene sulfonic acid (TNBS)-induced colitis rather reflects T-cell mechanisms. Consequently, an observation made in a single model has to be verified in at least one other model. Therefore, in the present study we investigated the effect of genetic blockade of H₄R-signaling in mice subjected to the model of TNBS-induced acute colitis. We analyzed severity and progression of clinical signs of colitis, as well as histopathologic alterations in the colon and local cytokine production. Genetic ablation of H₄R expression worsened clinical signs of acute colitis and histological appearance of colon inflammation after TNBS application. Moreover, TNBS instillation enhanced local synthesis of inflammatory mediators associated with a neutrophilic response, i.e., CXCL1, CXCL2, and interleukin-6. Lastly, also myeloperoxidase concentration, indicative for the presence of neutrophils, was elevated in cola of TNBS-treated mice due to the absence of H₄R expression. Our results indicate an anti-inflammatory role of histamine via H₄R in TNBS-induced acute neutrophilic colitis in mice, thus questioning the strategy of pharmacological H₄R blocked as new therapeutic option for patients suffering from IBD.

Aryl-1,3,5-triazine ligands of histamine H4 receptor attenuate inflammatory and nociceptive response to carrageen, zymosan and lipopolysaccharide

Objective and design

Histamine H₄ receptor (H₄R) offers a great potential for new therapeutic strategies for the treatment of inflammation-based diseases. The aim of this study is to present the pharmacological profile of two recently synthesized ligands of H₄R with particular reference to their anti-inflammatory and analgesic activity.

Materials and subjects

We used mice and rats in the in vivo tests. We also used murine RAW 264.7 cells and isolated guinea-pig ileum in in vitro test.

Treatments

In the in vivo tests, animals were pre-treated with the increasing doses of investigated compounds (12.5, 25 and 50 mg/kg) and reference compounds: JNJ7777120 (25 mg/kg), indomethacin (10 mg/kg). Macrophages were pre-treated with two concentrations of tested compounds 100 and 10 µM.

Methods

We examined anti-inflammatory and analgesic effects of the new H₄R antagonists in the in vivo models of inflammation induced by carrageenan or zymosan. We assessed the level of cAMP and release of cytokines, ROS and NO in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages. Moreover, we assessed the affinity of the investigated compounds for histamine H₁ receptor in functional studies.

Results

Both investigated compounds reduced paw edema, mechanical and thermal hyperalgesia in the carrageenan-induced acute inflammation. Moreover, administration of the investigated compounds resulted in decreased granulocyte influx and attenuated nociceptive reaction in the zymosan-induced peritonitis model. In the same model of inflammation, the investigated compounds reduced vascular permeability; however, this effect was observed only after the highest applied dose. Furthermore, the test compounds had no impact on cell viability in the experiments on RAW 264.7 macrophages. In these cells, stimulated with LPS, the test compounds decreased reactive oxygen species (ROS) production. They increased the cellular concentration of cAMP and attenuated the production of inflammatory cytokines such as TNFα and IL-1β. All results were comparable to those obtained for the reference compound JNJ7777120 with the exception of the impact on NO production. Nevertheless, this effect was similar to that obtained for the other reference compound rolipram, which is a phosphodiesterase 4 (PDE 4) inhibitor. Further experiments revealed that both of the investigated compounds possessed relatively low affinity for histamine H₁ receptor and do not inhibit the activity of the PDE 4B1 enzyme. In addition, all the effects of the investigated compounds in in vivo experiments were observed at doses that did not cause neurologic deficits in rotarod test and did not reduce spontaneous locomotor activity.

Conclusions

Our results demonstrate the anti-inflammatory and analgesic activity of the new aryl-1,3,5-triazine derivatives, which are primarily H₄R–dependent.

In vitro study of histamine and histamine receptor ligands influence on the adhesion of purified human eosinophils to endothelium

It is a well-known fact that histamine is involved in eosinophil-dependent inflammatory responses including cellular chemotaxis and migration. Nevertheless, the relative role of histamine receptors in the mechanisms of eosinophils adhesion to endothelial cells is not known. Therefore the aim of presented study was to examine the effect of selective histamine receptors ligands on eosinophils adhesion to endothelium. For that purpose the highly purified human eosinophils have been isolated from the peripheral blood. The viability and functional integrity of isolated eosinophils have been validated in several tests. Histamine as well as 4-methylhistamine (selective H4 agonist) in concentration-dependent manner significantly increased number of eosinophils that adhere to endothelium. Among the selective histamine receptors antagonist or H1 inverse agonist only JNJ7777120 (histamine H4 antagonist) and thioperamide (dual histamine H3/H4 antagonist) had direct effect on eosinophils adhesion to endothelial cells. Antagonists of H1 (diphenhydramine, mepyramine) H2 (ranitidine and famotidine) and H3 (pitolisant) histamine receptors were ineffective. To the best of our knowledge, this is the first study to demonstrate that histamine receptor H4 plays a dominant role in histamine-induced eosinophils adhesion to endothelium.

International Union of Basic and Clinical Pharmacology. XCVIII. Histamine Receptors

Histamine is a developmentally highly conserved autacoid found in most vertebrate tissues. Its physiological functions are mediated by four 7-transmembrane G protein-coupled receptors (H1R, H2R, H3R, H4R) that are all targets of pharmacological intervention. The receptors display molecular heterogeneity and constitutive activity. H1R antagonists are long known antiallergic and sedating drugs, whereas the H2R was identified in the 1970s and led to the development of H2R-antagonists that revolutionized stomach ulcer treatment. The crystal structure of ligand-bound H1R has rendered it possible to design new ligands with novel properties. The H3R is an autoreceptor and heteroreceptor providing negative feedback on histaminergic and inhibition on other neurons. A block of these actions promotes waking. The H4R occurs on immuncompetent cells and the development of anti-inflammatory drugs is anticipated.

Peripheral Adenosine A3 Receptor Activation Causes Regulated Hypothermia in Mice That Is Dependent on Central Histamine H1 Receptors

Adenosine can induce hypothermia, as previously demonstrated for adenosine A1 receptor (A1AR) agonists. Here we use the potent, specific A3AR agonists MRS5698, MRS5841, and MRS5980 to show that adenosine also induces hypothermia via the A3AR. The hypothermic effect of A3AR agonists is independent of A1AR activation, as the effect was fully intact in mice lacking A1AR but abolished in mice lacking A3AR. A3AR agonist-induced hypothermia was attenuated by mast cell granule depletion, demonstrating that the A3AR hypothermia is mediated, at least in part, via mast cells. Central agonist dosing had no clear hypothermic effect, whereas peripheral dosing of a non-brain-penetrant agonist caused hypothermia, suggesting that peripheral A3AR-expressing cells drive the hypothermia. Mast cells release histamine, and blocking central histamine H1 (but not H2 or H4) receptors prevented the hypothermia. The hypothermia was preceded by hypometabolism and mice with hypothermia preferred a cooler environmental temperature, demonstrating that the hypothermic state is a coordinated physiologic response with a reduced body temperature set point. Importantly, hypothermia is not required for the analgesic effects of A3AR agonists, which occur with lower agonist doses. These results support a mechanistic model for hypothermia in which A3AR agonists act on peripheral mast cells, causing histamine release, which stimulates central histamine H1 receptors to induce hypothermia. This mechanism suggests that A3AR agonists will probably not be useful for clinical induction of hypothermia.

Histamine H4 receptor knockout mice display reduced inflammation in a chronic model of atopic dermatitis

BACKGROUND

The histamine H4 receptor (H4R) was brought into focus as a new therapeutic target for the treatment of allergic disorders such as atopic dermatitis (AD). H4R antagonists have already been tested in several animal models of AD, but these studies have yielded conflicting results.

MATERIAL AND METHODS

The development of ovalbumin-induced AD-like skin lesions was analysed in H4R(-/-) mice and in H4R antagonist (JNJ28307474)-treated mice.

RESULTS

H4R(-/-) mice showed a clear amelioration of the skin lesions, with a diminished influx of inflammatory cells and a reduced epidermal hyperproliferation at lesional skin sites. H4R(-/-) mice had a reduced amount of ovalbumin-specific IgE, a reduced number of splenocytes and lymph node cells with a decreased number of CD4+ T cells. The H4R modulated the cytokine secretion of CD4+ T cells and splenocytes and altered the cellular profile in the lymph nodes. The anti-inflammatory effect could only partially be mimicked by JNJ28307474 and only when the H4R antagonist was given during sensitization and challenge and not when JNJ28307474 was only given during the provocation phase of the allergic reaction.

CONCLUSION

The H4R modulates inflammation in a chronic allergic dermatitis setting. However, results of this study indicate that it is necessary to block the H4R during ontogeny and development of the allergic inflammation.

The histamine H4 receptor: from orphan to the clinic

The histamine H4 receptor (H4R) was first noted as a sequence in genomic databases that had features of a class A G-protein coupled receptor. This putative receptor was found to bind histamine consistent with its homology to other histamine receptors and thus became the fourth member of the histamine receptor family. Due to the previous success of drugs that target the H1 and H2 receptors, an effort was made to understand the function of this new receptor and determine if it represented a viable drug target. Taking advantage of the vast literature on the function of histamine, a search for histamine activity that did not appear to be mediated by the other three histamine receptors was undertaken. From this asthma and pruritus emerged as areas of particular interest. Histamine has long been suspected to play a role in the pathogenesis of asthma, but antihistamines that target the H1 and H2 receptors have not been shown to be effective for this condition. The use of selective ligands in animal models of asthma has now potentially filled this gap by showing a role for the H4R in mediating lung function and inflammation. A similar story exists for chronic pruritus associated with conditions such as atopic dermatitis. Antihistamines that target the H1 receptor are effective in reducing acute pruritus, but are ineffective in pruritus experienced by patients with atopic dermatitis. As for asthma, animal models have now suggested a role for the H4R in mediating pruritic responses, with antagonists of the H4R reducing pruritus in a number of different conditions. The anti-pruritic effect of H4R antagonists has recently been shown in human clinical studies, validating the preclinical findings in the animal models. A selective H4R antagonist inhibited histamine-induced pruritus in health volunteers and reduced pruritus in patients with atopic dermatitis. The history to date of the H4R provides an excellent example of the deorphanization of a novel receptor and the translation of this into clinical efficacy in humans.

Suppression of Laser-Induced Choroidal Neovascularization by the Oral Medicine Targeting Histamine Receptor H4 in Mice

PURPOSE

This study aimed to examine relationship of histamine receptor H4 (HRH4) and the pathogenesis of laser-induced choroidal neovascularization (laser-CNV) and to determine whether oral administration of HRH4 antagonists suppressed laser-CNV in mice.

METHODS

Laser photocoagulation was performed in mice to induce the laser-CNV. Histamine was administered intravitreously, and CNV volume was measured. Laser photocoagulation and intravitreous injection of HRH4 antagonist JNJ7777120 were performed after intraperitoneal injection of clodronate liposome, which depletes circulating monocyte-derived macrophages; CNV volume was compared with that in mice injected with control (dimethyl sulfoxide [DMSO]/PBS). Three days after laser-CNV, the F4/80⁺CD11b⁺ macrophage population in retinal pigment epithelium (RPE)/choroid complex was quantified with flow cytometry in wild-type and Hrh4^-/- mice. The long-acting HRH4 antagonist JNJ28307474 was then administrated periorally, and the laser-CNV volume was compared with controls.

RESULTS

Intravitreous injection of histamine did not affect laser-CNV volume. The laser-CNV from the eye injected with JNJ7777120 was equivalent to that injected with the DMSO/PBS in mice that had intraperitoneally received clodronate liposome. Flow cytometry after laser-CNV induction revealed a smaller F4/80⁺CD11b⁺ macrophage population in the RPE/choroid complex of Hrh4^-/- mice than in wild-type mice. Oral administration of JNJ28307474 significantly reduced laser-CNV volume in wild-type mice.

CONCLUSIONS

Our results suggested that HRH4-positive macrophages played an important role in the pathogenesis of laser-CNV and that they require a different ligand from that of histamine. The oral administration of an HRH4 antagonist successfully reduced laser-CNV.

TRANSLATIONAL RELEVANCE

Our results indicate that drugs targeting HRH4 are potentially a novel oral treatment for age-related macular degeneration.

Emerging role of Toll-like receptor 4 in hepatocellular carcinoma

Toll-like receptor (TLR) signaling has been implicated in inflammatory-related cancers. The upregulation of TLR signaling in hepatocellular carcinoma (HCC) suggests that it may play an essential role in the prognosis of chronic and inflammatory diseases that ultimately culminate in HCC. Here, we provide evidence about the involvement of the TLR pathway in the initiation, progression, and metastasis of HCC. The differential expression of TLR in epithelial cells has also been discussed. In particular, we emphasize the physiological role of TLR4 in the development and pathogenesis of HCC and propose novel and promising approaches for HCC therapeutics with the aid of TLR ligands.

Trilobatin attenuates the LPS-mediated inflammatory response by suppressing the NF-κB signaling pathway

We investigated the anti-inflammatory effect of trilobatin, the flavonoid isolated from the leaves of Lithocarpus polystachyus Rehd, as well as the underlying molecular mechanisms. Treatment with trilobatin (0.005-5 μM) dose-dependently inhibited the lipopolysaccharide (LPS)-induced mRNA expression and secretion of pro-inflammatory cytokines, including tumor necrosis factor α (TNFα), interleukin-1β (IL-1β) and interleukin-6 (IL-6), in RAW 264.7 macrophages. However, no further inhibition was detected when the concentration of trilobatin was increased to 50 μM. Western blot analysis confirmed that the mechanism of the anti-inflammatory effect was correlated with the inhibition of LPS-induced inhibitor of nuclear factor-kappa B α (IκBα) degradation and nuclear factor-kappa B (NF-κB) p65 phosphorylation. In addition, trilobatin also showed a significant inhibition of LPS-induced TNFα and IL-6 at both the mRNA and protein levels in a mouse model. Our results suggest that trilobatin potentially inhibits the LPS-induced inflammatory response by suppressing the NF-κB signaling pathway.

Discovery and SAR of 6-alkyl-2,4-diaminopyrimidines as histamine H₄ receptor antagonists

This report discloses the discovery and SAR of a series of 6-alkyl-2-aminopyrimidine derived histamine H4 antagonists that led to the development of JNJ 39758979, which has been studied in phase II clinical trials in asthma and atopic dermatitis. Building on our SAR studies of saturated derivatives from the indole carboxamide series, typified by JNJ 7777120, and incorporating knowledge from the tricyclic pyrimidines led us to the 6-alkyl-2,4-diaminopyrimidine series. A focused medicinal chemistry effort delivered several 6-alkyl-2,4-diaminopyrimidines that behaved as antagonists at both the human and rodent H4 receptor. Further optimization led to a panel of antagonists that were profiled in animal models of inflammatory disease. On the basis of the preclinical profile and efficacy in several animal models, JNJ 39758979 was selected as a clinical candidate; however, further development was halted during phase II because of the observation of drug-induced agranulocytosis (DIAG) in two subjects.

Pro- and anti-inflammatory effects of histamine on tissue factor and TNFα expression in monocytes of human blood

BACKGROUND

Histamine is classified as an inflammatory mediator and has been reported to have anti- as well as pro-inflammatory properties. The aim of this study was to explore the role of histamine on the production of LPS-induced tissue factor (TF) activity and TNFα in monocytes of whole blood in the absence and presence of TNFα or PMA.

METHODS

Human blood anticoagulated with Fragmin was subjected to stimulation by LPS in the presence and absence of TNFα or PMA and various concentrations of histamine. Tissue factor (TF) activity was measured in lyzed cells after isolation of mononuclear cells whereas TNFα was quantified in plasma after centrifugation of cells.

RESULTS

Histamine gave a dose dependent inhibitory effect on LPS-induced TF activity in monocytes of whole blood, with a 50% reduction at 0.033 μM. A similar effect was seen when the blood cells were stimulated with the combination of LPS and TNFα although TNFα enhanced LPS-induced TF activity almost two fold. In contrast, when blood was incubated with LPS and PMA in whole blood, histamine gave a significant rise in TF activity at 0.01 μM and 0.33 μM histamine. The effect of histamine was less at 0.1 μM or higher concentrations giving a biphasic profile. Contrary to the effect of histamine on LPS plus PMA induced TF activity, histamine caused a significant reduction in TNFα albeit less than in the absence of PMA. Intake of aspirin caused a significant rise in LPS-induced TF activity that was almost abolished by histamine at 0.033 μM.

CONCLUSION

Our study shows that histamine has an anti-inflammatory effect on LPS and LPS/TNFα stimulated monocytes of whole blood. In contrast when blood cells are activated by a combination of LPS and PMA whereby PKC is activated, histamine has a procoagulant/pro-inflammatory effect through enhancement of TF activity expression.

Histamine induces chemotaxis and phagocytosis in murine bone marrow-derived macrophages and RAW 264.7 macrophage-like cells via histamine H4-receptor

OBJECTIVE

Expression and function of histamine H4-receptor, an immunomodulatory receptor involved in inflammatory diseases, on murine macrophages, which are vital for immunity, were investigated.

MATERIALS AND METHODS

The expression pattern of histamine receptors on bone marrow-derived macrophages of BALB/c mice and on RAW 264.7 cells was studied at the mRNA level by reverse transcription polymerase chain reaction. The functional relevance of histamine receptors was investigated by analyzing histamine-induced chemotaxis and phagocytosis in the presence of histamine receptor antagonists mepyramine (histamine H1-receptor), famotidine (histamine H2-receptor), thioperamide (histamine H3/4-receptors) and JNJ7777120 (histamine H4-receptor).

RESULTS

Both bone marrow-derived macrophages and RAW 264.7 cells express mRNA for histamine H1-receptor and histamine H4-receptor. Residual amounts of histamine H2-receptor mRNA are found in bone marrow-derived macrophages only. In both cellular models, histamine induced chemotaxis and phagocytic activity, which was reduced by thioperamide as well as by JNJ 7777120, but not by mepyramine or famotidine.

CONCLUSION

In murine bone marrow-derived macrophages and RAW 264.7 macrophage-like cells histamine H4-receptor mediates chemotaxis and phagocytic activity.

Role of innate immunity in the development of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common form of liver cancer worldwide. It is caused by a variety of risk factors, most common ones being infection with hepatitis viruses, alcohol, and obesity. HCC often develops in the background of underlying cirrhosis, and even though a number of interventional treatment methods are currently in use, recurrence is fairly common among patients who have had a resection. Therefore, whole liver transplantation remains the most practical treatment option for HCC. Due to the growing incidence of HCC, intense research efforts are being made to understand cellular and molecular mechanisms of the disease so that novel therapeutic strategies can be developed to combat liver cancer. In recent years, it has become clear that innate immunity plays a critical role in the development of a number of liver diseases, including HCC. In particular, the activation of Toll-like receptor signaling results in the generation of immune responses that often results in the production of pro-inflammatory cytokines and chemokines, and could cause acute inflammation in the liver. In this review, the current knowledge on the role of innate immune responses in the development and progression of HCC is examined, and emerging therapeutic strategies based on molecular mechanisms of HCC are discussed.

The histamine H4 receptor mediates inflammation and Th17 responses in preclinical models of arthritis

Objective

The histamine H₄ receptor (H₄R) has been shown to drive inflammatory responses in models of asthma, colitis and dermatitis, and in these models it appears to affect both innate and adaptive immune responses. In this study, we used both H₄R-deficient mice and a specific H₄R antagonist, JNJ 28307474, to investigate the involvement of the H₄R in mouse arthritis models.

Methods

H₄R-deficient mice and wild-type mice administered the H₄R antagonist were studied in models of collagen antibody-induced arthritis (CAIA) and collagen-induced arthritis (CIA). The impact on Th17 cells was assessed by restimulation of inguinal lymphocytes in the disease or immunisation models and with in vitro stimulation of whole blood.

Results

Both H₄R-deficient mice and mice treated with the H₄R antagonist exhibited reduced arthritis disease severity in both CAIA and CIA models. This was evident from the reduction in disease score and in joint histology. In the CIA model, treatment with the H₄R antagonist reduced the number of interleukin (IL)-17 positive cells in the lymph node and the total production of IL-17. Th17 cell development in vivo was reduced in H₄R-deficient mice or in mice treated with an H₄R antagonist. Finally, treatment of both mouse and human blood with an H₄R antagonist reduced the production of IL-17 when cells were stimulated in vitro.

Conclusions

These results implicate the H₄R in disease progression in arthritis and in the production of IL-17 from Th17 cells. This work supports future clinical exploration of H₄R antagonists for the treatment of rheumatoid arthritis.

An mRNA atlas of G protein-coupled receptor expression during primary human monocyte/macrophage differentiation and lipopolysaccharide-mediated activation identifies targetable candidate regulators of inflammation

G protein-coupled receptors (GPCRs) are among the most important targets in drug discovery. In this study, we used TaqMan Low Density Arrays to profile the full GPCR repertoire of primary human macrophages differentiated from monocytes using either colony stimulating factor-1 (CSF-1/M-CSF) (CSF-1 Mϕ) or granulocyte macrophage colony stimulating factor (GM-CSF) (GM-CSF Mϕ). The overall trend was a downregulation of GPCRs during monocyte to macrophage differentiation, but a core set of 10 genes (e.g. LGR4, MRGPRF and GPR143) encoding seven transmembrane proteins were upregulated, irrespective of the differentiating agent used. Several of these upregulated GPCRs have not previously been studied in the context of macrophage biology and/or inflammation. As expected, CSF-1 Mϕ and GM-CSF Mϕ exhibited differential inflammatory cytokine profiles in response to the Toll-like Receptor (TLR)4 agonist lipopolysaccharide (LPS). Moreover, 15 GPCRs were differentially expressed between these cell populations in the basal state. For example, EDG1 was expressed at elevated levels in CSF-1 Mϕ versus GM-CSF Mϕ, whereas the reverse was true for EDG6. 101 GPCRs showed differential regulation over an LPS time course, with 65 of these profiles being impacted by the basal differentiation state (e.g. GPRC5A, GPRC5B). Only 14 LPS-regulated GPCRs showed asynchronous behavior (divergent LPS regulation) with respect to differentiation status. Thus, the differentiation state primarily affects the magnitude of LPS-regulated expression, rather than causing major reprogramming of GPCR gene expression profiles. Several GPCRs showing differential profiles between CSF-1 Mϕ and GM-CSF Mϕ (e.g. P2RY8, GPR92, EMR3) have not been widely investigated in macrophage biology and inflammation. Strikingly, several closely related GPCRs displayed completely opposing patterns of regulation during differentiation and/or activation (e.g. EDG1 versus EDG6, LGR4 versus LGR7, GPRC5A versus GPRC5B). We propose that selective regulation of GPCR5A and GPCR5B in CSF-1 Mϕ contributes to skewing toward the M2 macrophage phenotype. Our analysis of the GPCR repertoire expressed during primary human monocyte to macrophage differentiation and TLR4-mediated activation provides a valuable new platform for conducting future functional analyses of individual GPCRs in human macrophage inflammatory pathways.