Development of novel cellular model for affinity studies of histamine H(4) receptor ligands

The G protein-coupled histamine H4 receptor (H4R) is the last member of histamine receptors family discovered so far. Its expression pattern, together with postulated involvement in a wide variety of immunological and inflammatory processes make histamine H4 receptor an interesting target for drug development. Potential H4R ligands may provide an innovative therapies for different immuno-based diseases, including allergy, asthma, pruritus associated with allergy or autoimmune skin conditions, rheumatoid arthritis and pain. However, none of successfully developed selective and potent histamine H4 receptor ligands have been introduced to the market up to date. For that reason there is still a strong demand for pharmacological models to be used in studies on potent H4R ligands. In current work we present the development of novel mammalian cell line, stably expressing human histamine H4 receptor, with use of retroviral transduction approach. Obtained cell line was pharmacologically characterized in radioligand binding studies and its utility for affinity testing of potent receptor ligands was confirmed in comparative studies with the use of relevant insect cells expression model. Obtained results allow for statement that developed cellular model may be successfully employed in search for new compounds active at histamine H4 receptor.

Identification of histamine receptors and effects of histamine on murine and simian colonic excitability

BACKGROUND

Inflammatory responses can include recruitment of cells of hematopoietic origin to the tunica muscularis. These cells can secrete a variety of factors which can reset the gain of smooth muscle cells (SMC) and influence motor patterns. Histamine (H), a major mediator in inflammation, is released by mast cells and exerts diverse effects in SMC by binding to H receptors. The profiles of H receptor expression in animal models used to study inflammatory diseases are unknown.

METHODS

Histamine receptor expression and electro-mechanical responses to H were tested in simian and murine colonic smooth muscle using qualitative and quantitative PCR, isometric force measurements, microelectrode recordings and patch clamp techniques.

KEY RESULTS

H1, H2, and H4 receptor transcripts were expressed at similar levels in simian colonic tissue whereas only the H2 receptor transcript was detected in murine colonic tissue. Stimulation of simian colonic muscles with H caused depolarization and contraction in the presence of tetrodotoxin. Histamine activated non-selective cation channels in simian SMC. In contrast, H caused hyperpolarization and inhibited contractions of murine colon. The hyperpolarization was inhibited by the K(ATP) channel blocker, glibenclamide. Histamine-activated K(+) currents were inhibited by glibenclamide in murine colonic SMC.

CONCLUSIONS & INFERENCES

Histamine receptor expression in simian SMC was similar to that reported in humans. However, H receptor profile and responses to H were considerably different in mice. Thus, monkey colon may be a more suitable model to study how inflammatory mediators affect the gain of smooth muscle excitability.

Expression and functional properties of canine, rat, and murine histamine H₄ receptors in Sf9 insect cells

The histamine H₄ receptor (H₄R) is expressed on cells of the immune system including eosinophils, dendritic cells, and T cells and plays an important role in the pathogenesis of bronchial asthma, atopic dermatitis, and pruritus. Analysis of the H₄R in these diseases depends on the use of animal models. However, there are substantial pharmacological differences between various H₄R species orthologs. The purpose of this study was to analyze the pharmacological properties of canine, rat, and murine H₄R in comparison to human H₄R expressed in Sf9 insect cells. Only hH₄R and cH₄R exhibited a sufficiently high [³H]histamine affinity for radioligand binding studies. Generally, cH₄R exhibited lower ligand-affinities than hH₄R. Similarly, in high-affinity GTPase studies, ligands were more potent at hH₄R than at other H₄R species orthologs. Unlike the other H₄R species orthologs, hH₄R exhibited high agonist-independent (constitutive) activity. Most strikingly, the prototypical H₄R antagonist (1-[(5-chloro-1H-indol-2-yl)carbonyl]-4-methylpiperazine) (JNJ7777120) exhibited partial agonistic activity at cH₄R, rH₄R, and mH₄R, whereas at hH₄R, JNJ7777120 was a partial inverse agonist. H₄R agonists from the class of N ( G )-acylated imidazolylpropylguanidines and cyanoguanidines exhibited substantial differences in terms of affinity, potency, and efficacy among H₄R species orthologs, too. The species-dependent pharmacological profiles are not due to the highly variable amino acid sequence position 341. Finally, H₄R species orthologs differ from each other in terms of regulation by NaCl. Collectively, there are profound pharmacological differences between H₄R species orthologs. Most importantly, caution must be exerted when interpreting pharmacological effects of "the prototypical H₄R antagonist" JNJ7777120 as H₄R antagonism.

Murine and human Langerhans cells express a functional histamine H4 receptor: modulation of cell migration and function

BACKGROUND

Histamine is an important mediator of allergic reactions, and recent studies indicated that the function of different types of antigen presenting cells (APC) can be modulated by histamine, in particular via the newly described histamine H(4) receptor (H(4)R). Therefore, we investigated possible interactions of histamine via the H(4)R on Langerhans cells (LC), which represent the professional APC in the skin and therefore have an important role in the initiation and maintenance of allergic skin diseases.

METHODS

The expression of the H(4)R was evaluated by real-time PCR, flow cytometry and immunofluorescence staining. The function of the H(4)R was determined by intracellular flow cytometric measurement of chemokine production and LC migration assays.

RESULTS

Here, we show H(4)R expression on in vitro generated monocyte-derived LC (mRNA and protein) and on primary LC from murine and human skin samples (protein). The immunofluorescence staining in murine and human skin samples clearly proved that LC express the H(4)R in situ. Stimulation with histamine or a H(4)R agonist downregulated the chemokine (C-C motif) ligand 2 (CCL2) in human monocyte-derived LC and primary LC. Prestimulation with a selective H(4)R antagonist abolished this effect. Moreover, migration of LC from the epidermis was increased after H(4)R agonist stimulation in ex vivo migration assays using human epidermis and murine in vivo assays.

CONCLUSION

Our findings show that LC express a functional H(4)R and point towards a possible pathogenic relevance of the H(4)R in inflammatory and allergic diseases.

Potentiation of NF-kappaB-dependent transcription and inflammatory mediator release by histamine in human airway epithelial cells

BACKGROUND AND PURPOSE

In asthma, histamine contributes to bronchoconstriction, vasodilatation and oedema, and is associated with the late phase response. The current study investigates possible inflammatory effects of histamine acting on nuclear factor kappaB (NF-kappaB)-dependent transcription and cytokine release.

EXPERIMENTAL APPROACH

Using BEAS-2B bronchial epithelial cells, NF-kappaB-dependent transcription and both release and mRNA expression of IL-6 and IL-8 were examined by reporter assay, ELISA and quantitative RT-PCR. Histamine receptors were detected using qualitative RT-PCR and function examined using selective agonists and antagonists.

KEY RESULTS

Addition of histamine to TNFalpha-stimulated BEAS-2B cells maximally potentiated NF-kappaB-dependent transcription 1.8 fold, whereas IL-6 and IL-8 protein release were enhanced 7.3- and 2.7-fold respectively. These responses were, in part, NF-kappaB-dependent and were associated with 2.6- and 1.7-fold enhancements of IL-6 and IL-8 mRNA expression. The H(1) receptor antagonist, mepyramine, caused a rightward shift in the concentration-response curves of TNFalpha-induced NF-kappaB-dependent transcription (pA(2)=9.91) and release of IL-6 (pA(2)=8.78) and IL-8 (pA(2)=8.99). Antagonists of histamine H(2), H(3) and H(4) receptors were without effect. Similarly, H(3) and H(4) receptor agonists did not affect TNFalpha-induced NF-kappaB-dependent transcription, or IL-6 and IL-8 release at concentrations below 10 microM. The anti-inflammatory glucocorticoid, dexamethasone, inhibited the histamine enhanced NF-kappaB-dependent transcription and IL-6 and IL-8 release.

CONCLUSIONS AND IMPLICATIONS

Potentiation of NF-kappaB-dependent transcription and inflammatory cytokine release by histamine predominantly involves receptors of the H(1) receptor subtype. These data support an anti-inflammatory role for H(1) receptor antagonists by preventing the transcription and release of pro-inflammatory cytokines.

Histamine H1 and H2 receptors but not H4 receptors are upregulated during bone marrow regeneration

The role of histamine receptors in radiation-induced bone marrow (BM) regeneration was investigated with aspects of functional genomics. H1R and H2R mRNA expression increased during regeneration in both histidine decarboxylase knockout (HDC-/-) and wild type (HDC+/+) mice, though to a lesser extent in HDC-/- mice. H4R mRNA expression was downregulated in both groups. Mainly CD34+ cells were responsible for the elevation of intracellular histamine and HDC content in HDC+/+ BM cell populations. The differential changes in the expression of its receptors, and also its elevated levels in hematopoietic progenitors support the regulatory role of histamine in BM regeneration, that could be further explored by future gene expression studies.

Histamine H4 receptor agonists have more activities than H4 agonism in antigen-specific human T-cell responses

Histamine not only mediates immediate allergic reactions, it also regulates cellular immune responses. H4R is the most recently identified histamine receptor (HR). In the present study, we examined the in vitro effect of histamine and H4R agonists on the responses of human T cells to purified protein derivative from Mycobacterium tuberculosis (PPD) and to Cry j1, the major allergen of Cryptomeria japonica pollen. Dimaprit, clobenpropit and clozapine, which are H4R agonists, dose-dependently blocked both PPD-induced interferon-gamma and Cry j1-induced interleukin-5 production by both peripheral blood mononuclear cells (PBMCs) and antigen-specific T-cell lines. However, the addition of thioperamide, an H3R/H4R antagonist, as well as a mixture of d-chlropheniramine, famotidine and thioperamide, did not reverse the inhibition. Pretreatment of PBMCs with SQ22536 and 8-bromoadenosine-3',5'-cyclic monophosphorothioate, Rp-isomer, had varying abilities to reverse the inhibitory effects of H4R agonists, except for clobenpropit. Moreover, the addition of H4R agonists induced annexin-V expression on PBMCs, especially in CD19(+) and CD4(+) cells. cDNA microarray analysis revealed that, among 16,600 genes tested, increased expression following treatment with clozapine was seen in 0 x 8% of the genes, whereas decreased expression was seen in 3 x 0% of the genes. These results suggest that H4R agonists inhibit antigen-specific human T-cell responses, although H4R does not appear to be important for this effect. In addition, the present study indicated that there may be orphan receptors or HR subtypes which can bind dimaprit, clobenpropit and clozapine, and that can exert an inhibitory effect on antigen-specific cellular responses via a cAMP/cAMP-dependent protein kinase-dependent, apoptotic pathway.

The use of IRES-based bicistronic vectors allows the stable expression of recombinant G-protein coupled receptors such as NPY5 and histamine 4

Stable expression of G protein coupled receptors in cell lines is a crucial tool for the characterization of the molecular pharmacology of receptors and the screening for new antagonists. However, in some instances, many difficulties have been encountered to obtain stable cell lines expressing functional receptors. Here, we addressed the question of vector optimization to establish cell lines expressing the human neuropeptide Y receptor 5 (NPY5-R) or histamine receptor 4 (HH4R). We have compared bicistronic vectors containing viral or cellular internal ribosome entry sites (IRES), co-expressing the receptor and the neomycine resistance gene from a single mRNA, to a bigenic vector containing two distinct promoters upstream each different genes. This study is the first one to validate the use of three cellular IRESs for long-term transgene expression. Our results demonstrate for both NPY5-R and HH4R that the bicistronic vectors with EMCV, VEGF, FGF1A or FGF2 IRES provide clones expressing functional receptors with yields between 25% and 100%. In contrast, the bigenic vector provided no functional clones, related to a low expression of NPY5R mRNA. The cell lines expressing active receptor were stable after more than 50 passages. These data indicate that IRES-based bicistronic vectors are particularly appropriate to establish cell clones expressing active G-coupled protein receptors with a high yield. In the case of NPY5, it was a new way to produce such a stable cell line. Furthermore, the characteristics-presented herein-of this receptor pharmacological property are perfectly in line with those reported in the literature.

Skin reactivity to histamine and expression of histamine receptors mRNA in lymphocytes of healthy subjects and non-small-cell lung cancer patients before and after surgery

Histamine modulates an immunological response through stimulation of appropriate receptor--H1R proinflammatory or H2R suppressive. The participation of histamine in regulation of an immunological response in the course of neoplastic disease is determined by the expression of particular receptor. The aim of our work was the investigation of the expression of mRNA of two types of histamine receptors in peripheral blood lymphocytes and the evaluation of skin-prick test with histamine in lung cancer patients before and after surgery. The investigation was performed on 15 patients qualified to surgery before and 7-10 days after treatment and on 12 healthy subjects. Reverse transcriptase polymerase chain reaction (RT-PCR) with primers labeled with fluorescent dyes was performed. Intensity of fluorescence was expressed as relative fluorescence units (RFU). The data were analysed using ABI Prism 310 GeneScan collection software Version 3.1. Skin-prick test with histamine was evaluated after 10 min by measuring the diameter of the weal. The expression of H1R and H2R mRNA in healthy subjects was not significantly different in contrast to the lung cancer patients in which a significant prevalence of H2R mRNA expression was observed before surgery and only slightly decreased after (P < 0.001). Skin-prick test--negative in one patient before surgery, after treatment was positive in all patients and the diameter of histamine weal was significantly increased (P < 0.001). One may assume that the prevalence of the expression of H2R mRNA in patients reflects the status of immunosuppression caused by cancer. Since histamine exerts its suppressive activity trough H2R it seems reasonably to include the antagonists of this receptor to the cancer therapy which may restore a relative balance between accessibility of both types of histamine receptors.

Putative histamine-gated chloride channel subunits of the insect visual system and thoracic ganglion

Histamine-gated chloride channels, members of the ligand-gated ion channel superfamily, are thought to be peculiar for arthropods. Their cognate ligand, histamine, is the transmitter of all arthropod photoreceptors and of thoracic mechanoreceptors. To identify putative histamine-gated chloride channel subunits we scanned the Drosophila genome for putative ligand-gated chloride channel subunits and found 12 candidate genes. We found four groups of transcripts based on their expression pattern. Only members of the last group show an expression pattern that is consistent with our knowledge about histamine-gated chloride channels in insects. In the brain these transcripts (Dm HA-Cl I and II) are exclusively present in interneurones postsynaptic to photoreceptors. Within the lamina (the first visual ganglion) only the L1-L3 neurones are labelled. The lack of non-photoreceptor dependent staining in the brain indicates that mechanosensory transmission differs between the head and the thorax/abdomen, and that the receptors responding to brain-intrinsic histaminergic cells use different signalling pathways. The putative histamine-gated chloride channels show the greatest homology mammalian glycine receptors. These ion-channels are the first specific molecular markers for postsynaptic cells in the insect visual system, thus representing ideal tools to study its physiology and development.

Histamine stimulates production of osteoclast differentiation factor/receptor activator of nuclear factor-kappaB ligand by osteoblasts

Histamine H(1),H(2), and H(3) receptors are expressed by osteoblastic MC3T3-E1 (E1) cells derived from mouse calvaria. Expression of the osteoclast differentiation factor (ODF)/receptor activator of nuclear factor-kappaB ligand (RANKL) transcript was induced in E1 cells and bone marrow stromal cells (ST2). Histamine markedly increased the steady-state level of ODF/RANKL mRNA in a dose-dependent manner. The effect of histamine on expression of ODF/RANKL mRNA by E1 cells was transient, with a peak at 6h. Western blot analysis revealed that histamine increased production of ODF/RANKL protein by E1 cells at 12h. In cocultures of E1 cells and mouse bone marrow cells, histamine stimulated osteoclastogenesis in the presence of 1,25-dihydroxyvitamin D(3) and this effect was blocked by preincubation with neutralizing antibody against ODF/RANKL. These results suggest that histamine regulates osteoclastogenesis, at least in part, through induction of ODF/RANKL expression by osteoblasts and bone marrow stromal cells.

Gastric carcinoid with histamine production, histamine transporter and expression of somatostatin receptors

A case of sporadic, histamine-producing gastric carcinoid with liver metastases is reported. The patient was treated with somatostatin analogue (octreotide) combined with cortisone and blockade of histamine receptors prior to surgery, which included subtotal gastrectomy, excision of lymph node metastases and superficial liver metastases. Residual liver metastases were injected with ethanol. These interventions markedly reduced the urinary excretion of the main histamine metabolite (MelmAA). Eighteen months later combined immuno- and chemotherapy was initiated due to tumour progression and recurrent hormonal symptoms with good clinical results over 12 months. Scintigraphy, using 111In-DTPA-D-Phe1-octreotide, visualized somatostatin receptors (sstr) in primary tumour, lymph node metastases and liver metastases. The tissue/blood 111In concentration ratios of tumour biopsies were very high. Northern analyses confirmed expression of all subtypes of sstr1-5. Immunocytochemically, tumour cells were strongly positive for chromogranin A, histamine and vesicular monoamine transporter (VMAT) 2 (histamine transporter), but negative for VMAT 1, suggesting an origin from gastric enterochromaffin-like cells. In primary tumour cell cultures, histamine, 5-HTP and 5-HIAA, but not 5-HT, could be detected in conditioned culture medium, indicating a defective decarboxylation of the tryptamine precursor. This rare case of histamine-producing gastric carcinoid demonstrates that excellent symptom relief can be achieved despite disseminated disease, if active, multimodal treatment strategy is instituted. The presence of high numbers of sstr in tumour tissue also raises the possibility of receptor-guided radiotherapy.

G proteins endogenously expressed in Sf 9 cells: interactions with mammalian histamine receptors

Expression of functionally active mammalian histamine H1- and H2-receptors was recently demonstrated in Sf 9 cells. Either receptor elicited phosphoinositide degradation leading to an increased cytoplasmic calcium concentration. In the present study we focussed on identifying the Sf 9 guanine nucleotide-binding proteins (G proteins) involved. Immunodetection of Sf 9 membranes showed expression of G alpha isoforms belonging to all four G protein subfamilies. During prolonged baculovirus infection of Sf 9 cells, binding of guanosine 5'-o-(3-thiotriphosphate) as well as the intensities of G protein immunoreactivity, pertussis toxin-mediated ADP-ribosylation, GTP azidoanilide labelling of G alpha, and phosphate-labelling of G beta declined in cell membranes. Some 48 h after infection with mammalian histamine receptor-encoding viruses virtually no functional coupling of ligand-activated receptors to insect G proteins was observed despite a high level of expressed receptors. In contrast, Sf 9 cells infected only for 28 h allowed studies on histamine-induced G protein coupling. In membranes obtained from H1-receptor-expressing cells, histamine increased incorporation of GTP azidoanilide into Gq/11-like proteins whereas in membranes containing H2-receptors histamine enhanced GTP azidoanilide-labelling of Gq/11-like and G(S)-like proteins. In fura-loaded H1- and H2-receptor-expressing cells histamine induced the release of calcium from intracellular stores. This study shows firstly that Sf 9 G proteins couple to mammalian histamine receptors and secondly that H1-receptors activate only Gq/11, whereas H2-receptors activate Gq/11 and G(S), but neither receptor couples to Gi/o or G12. Finally, the time following baculovirus infection is critical for studying the functional coupling between recombinantly expressed and endogenous signal transduction components.

Pharmacologic effects of autacoids on subsets of T cells. Regulation of expression/function of histamine-2 receptors by a subset of suppressor cells

Autacoids (principally histamine, beta adrenergic catecholamines, and prostaglandins E and A) have only recently been recognized as substantive moderators of a number of immune functions. If autacoids are to be considered as potential therapeutic immunomodulators, it is necessary to understand their effects on subsets of T cells while they are and are not in contact with each other. This report demonstrates that autacoid receptors are nonrandomly distributed on phenotypically and functionally distinct subsets of human T cells. Each human T cell subset responded to both histamine and isoproterenol, but the dose response curve and maximal efficacy varied widely between the subsets. The suppressor T cells were more responsive to both histamine and isoproterenol than helper/inducer T cells (TH) or cytotoxic T cells (Tc). We found that after mitogenic stimulation the response to histamine, but not isoproterenol, was greatly increased only in TH (Leu 3+) and Tc (Leu 2+, 9.3+) subsets, and that this effect may be regulated by suppressor T cells (Leu 2+, 9.3-). The dramatic rise in cAMP accumulation in response to histamine in mitogen-treated TH and Tc was totally blocked by an H2 antagonist (cimetidine), but not by an H1 antagonist (mepyramine). These findings indicate interdependence of (a) immunologically uncommitted subsets in their response to selected drugs, and (b) control of basal- and autacoid-induced cAMP production, as well as (c) increased qualitative and quantitative selectivity, which is caused by mitogen. If we had performed these experiments only on unseparated cells we would not have observed the remarkable selectivity of autacoid effects on subsets of T cells.