Valéria László

Discovery of novel human histamine H4 receptor ligands by large-scale structure-based virtual screening

A structure-based virtual screening (SBVS) was conducted on a ligand-supported homology model of the human histamine H4 receptor (hH4R). More than 8.7 million 3D structures derived from different vendor databases were investigated by docking to the hH4R binding site using FlexX. A total of 255 selected compounds were tested by radioligand binding assay and 16 of them possessed significant [(3)H]histamine displacement. Several novel scaffolds were identified that can be used to develop selective H4 ligands in the future. As far as we know, this is the first SBVS reported on H4R, representing one of the largest virtual screens validated by the biological evaluation of the virtual hits.

Paracrine and autocrine interactions in melanoma: histamine is a relevant player in local regulation

Abstract Malignant melanoma is a life-threatening tumor, with a high rate of metastasis and strong malignant potential. The local immune response against melanoma is compromised by multiple escape mechanisms of the tumor, which have been uncovered partially by thorough molecular and immunological analyses. These analyses were completed recently by gene-expression profiling. In this article, we summarize data suggesting that melanoma-derived histamine should be included as an important factor involved in bi-directional interactions between the tumor tissue and infiltrating immune cells. The presence and activity of histamine seems to be relevant by both directly stimulating or suppressing growth of the melanoma (depending on the local histamine-receptor balance) and indirectly shifting the local T-cell polarization towards a predominance of T helper 2 cells.

Histamine and histamine-receptor antagonists modify gene expression and biosynthesis of interferon gamma in peripheral human blood mononuclear cells and in CD19-depleted cell subsets

The effect of histamine and histamine antagonists was examined on gene expression and biosynthesis of bacterial endotoxin (LPS) induced interferon gamma (IFNgamma) both in human peripheral mononuclear cells (PMBC) and in T-cell enriched fractions. We found, that histamine inhibited the LPS induced transcription of IFNgamma gene and biosynthesis of IFNgamma protein in PMBC and also in CD19-depleted cell populations. The inhibitory effect of histamine could be reversed by the H2 histamine receptor (HR2) antagonists cimetidine and ranitidine both in PMBC and in CD19-depleted cells, but not with triprolidine, an H1 receptor antagonist, suggesting that the inhibition of IFNgamma production is mediated through H2 receptors in these cell populations. In contrast to the inhibitory effect of histamine, cimetidine alone (in the absence of exogenous histamine) strongly stimulated both the IFNgamma mRNA and protein production, whereas this effect was hardly seen by and other H2 receptor blocker, ranitidine. This superinduction of IFNgamma gene by cimetidine disappeared if the CD19+ cells are removed from PMBC. These results suggest, that inhibition of IFNgamma gene expression by histamine is a direct effect of histamine on H2 receptor of T lymphocytes; however, the superinduction of IFNgamma by cimetidine requires the presence of other (probably primarily B) cell subsets.

Secondary cutaneous infiltration in B cell chronic lymphocytic leukemia.

We describe a patient presenting with B cell chronic lymphocytic leukemia (B-CLL) who subsequently developed cutaneous infiltrates. Specimens of the blood, bone marrow and cutaneous infiltrations all showed the same heavy-chain gene rearrangement. Following failure of conventional chemotherapy, and in view of the similarity of the disease to cutaneous T cell lymphoma, interferon-α therapy was employed with satisfactory results. Introduction of this cytokine to the therapeutic modalities for secondary cutaneous B-CLL would hopefully change the poor outcome of this entity, or at least could produce a better quality of life. Loss of histidine decarboxylase activity in the infiltrating cells – in contrast to circulating lymphocytes – may be associated with the transformation of B-CLL to a more aggressive infiltrative form, offering a possible explanation for tissue invasiveness. The changing character of the disease raises the possibility of a second mutational event in the course of B-CLL.

Asthma endophenotypes and polymorphisms in the histamine receptor HRH4 gene

Background: Histamine as an inflammatory mediator plays an important role in chronic allergic and asthmatic conditions. However, the role of genetic polymorphisms of the histamine receptor HRH4 (histamine receptor H4) gene in asthma susceptibility and endophenotypes has not been studied yet. Our aim was to investigate the possible association between single nucleotide polymorphisms (SNPs) in the HRH4 gene and asthma or some endophenotypes of asthma. Methods: Twenty-one SNPs of the HRH4 gene were genotyped in 313 asthmatic patients and 360 controls using Sequenom® iPLEX® Gold Genotyping Technology. Results: Genotype distribution of three HRH4 SNPs, namely rs17187619 [p = 0.002; odds ratio, OR (95% confidence interval, CI) = 2.4 (4.1–1.4)], rs527790 [p = 0.0002; OR (95% CI) = 3.3 (6.1–1.8)] and rs487202 [p = 0.00007; OR (95% CI) = 3.5 (6.6–1.9)] differed significantly between patients with or without infection-induced asthma. Haplotypes, which included the rs4800573–rs527790 CC allele combination, were found to be associated with infection-induced asthma [p = 0.0009, OR (95% CI) = 0.5 (0.4–0.8)]. The rs487202–rs574913 CA haplotype was more frequent among patients with infection-induced asthma [p = 0.0006, OR (95% CI) = 1.9 (1.3–2.6)]. None of the SNPs contributed directly to the risk of asthma. Conclusions: Our results suggest that genetic variation in the HRH4 gene might influence the pathogenesis of infection-induced asthma.

Impact of histamine on dendritic cell functions

A rapidly growing body of evidence highlighted that histamine, a small biogenic amine, is implicated in the regulation of DC (dendritic cell) functions. It is well established that DCs represent the most potent antigen‐presenting cells of the body, linking innate and acquired immunity and regulating the outcome of immune responses. Signals, associated with ongoing inflammation and uptake of foreign antigens, promote maturation of DCs and activation of T‐cell responses in secondary lymphatic organs. These bone marrow‐derived cells patrol continuously all over the body. During their persistent migration, several mediators may influence the behaviour and functions of DCs. Histamine, produced by mast cells, basophils or DCs themselves, may have an important role in the life cycle of DCs. From the differentiation, through their never‐ending circulation, until the induction of T‐cell response, histamine is present and influences the life cycle of DCs. Here, we summarize recent progress in histamine research with respect to DC functions. We also point out some controversial aspects of histamine action on DCs.

Histamine modulates multiple functional activities of monocyte-derived dendritic cell subsets via histamine receptor 2

Expression of CD1a proteins in human monocyte-derived dendritic cells (DCs) specifies functionally distinct subsets with different inflammatory properties. Histamine is recognized as an inflammatory mediator released by various cell types including DCs. The diverse biological effects of histamine are mediated by G-protein-coupled histamine receptors (HRs), which are able to modulate the functional activities of DC subsets. The goal of the present study was to compare the expression and activity of HRs in the CD1a(-) and CD1a(+) monocyte-derived DC subsets and to test the effects of histamine on the differentiation, activation and functional activities of these subsets. We show that H2R is present at high levels in both DC subsets, whereas H1R and H4R are expressed in a subset-specific manner. Histamine shifts DC differentiation to the development of CD1a(-) DCs and modulates DC activation through its inhibitory effect on CD1a(+) DC differentiation. Histamine-induced reduction of CD1a(+) DCs is associated with increased secretion of IL-6 and IL-10, up-regulation of a typical combination of chemokines, expression C5aR1 by the CD1a(-) DC subset and enhanced migration of both activated DC subsets supported by the production of MMP-9 and MMP-12 enzymes. All these effects were shown to be mediated in a H2R-specific manner as revealed by the specific antagonist of the receptor. As H2R is expressed at high levels in both DC subsets, we propose that it may dominate the regulation of multiple DC functions. In contrast, H1R and H4R with opposing subset-related expression may have a regulatory or fine-tuning role in histamine-induced functional activities.

Histidine decarboxylase and intracellular histamine in melanoma cells and in a T cell line

Action of exogeneous histamine is mediated by binding to its specific cell-surface receptor(s) resulting in converting the extracellular signal to intracellular events. Recently numerous studies suggest basic role for histamine as one of the intracellular messenger moieties [1, 2]. Both the cellular expression of histidine decarboxylase [3] (HDC) in proliferating cells and a putative receptor activity for intracellular histamine (HRIC), confirm general effectiveness of histamine in embryonic development, hematopoiesis and wound healing [4, 5]. In our studies the expression of HDC has been studied in human melanoma tissue, cell lines and in a human T lymphocyte cell line, Jurkat.

Intracellular histamine content increases during in vitro dendritic cell differentiation

Dendritic cells are potent antigen-presenting cells, which can stimulate T-cell responses. Dendritic cells can be differentiated in vitro from peripheral blood monocytes with the use of GM-CSF and IL-4 [1, 2]. Acting as an autocrine mediator, histamine may have a possible role in cell proliferation, differentiation, hematopoiesis, embryonal development and regeneration. Histamine is formed by the histidine-decarboxylase (HDC) enzyme, which is expressed in every proliferating cell. We found previously that human monocytes contain histidine decarboxylase, and that HDC is upregulated during M-CSF-induced in vitro differentiation of monocytes to macrophages [3]. Here, we investigated the changes in intracellular histamineand HDC-content during in vitro dendritic cell differentiation accelerated by GM-CSF and IL-4.

Characterization by flow cytometry of hemopoietic progenitors in bone marrow of histidine decarboxylase knock out and wild type mice.

Histamine has a definite, but still partly unclear role in hematopoiesis since during cell differentiation the level of intracellular histamine increases due to the elevated amount and activity of histidine decarboxylase (HDC). In vitro investigations have verified that histamine synthesis increases in hematopoietic cells after treatment with IL-3 [1]. Earlier, we observed that treatment with histamine antagonists or HDC enzyme-blockers modulated in vitro hemopoietic stem cell differentiation [2]. The aim of this study was to use a four colour flow cytometric method to characterize the subsets of bone marrow progenitors during hemopoiesis in mice with a disrupted HDC gene (HDC ko) compared to those of wild type (HDCwt).