Defective angiogenesis in the inflammatory granulation tissue in histidine decarboxylase-deficient mice but not in mast cell-deficient mice

A negative regulator of delayed prostaglandin D2 production in mouse mast cells

We have previously shown that maturation of mouse bone marrow-derived mast cells (BMMCs) into connective tissue mast cells (CTMCs) upon coculture with fibroblasts in the presence of stem cell factor (kit ligand) is accompanied by marked induction of a panel of genes, one of which was identified as NLRP3. Here we report that NLRP3 acts as a novel negative regulator of delayed prostaglandin (PG) D(2) production in BMMCs. We found that, apart from its cell maturation-associated induction, NLRP3 expression was markedly induced in BMMCs several hours after FcepsilonRI crosslinking or cytokine stimulation. Ectopic expression of NLRP3 in BMMCs resulted in marked attenuation of cyclooxygenase (COX)-2-dependent delayed PGD(2) generation, whereas it had no effects on other effector functions, including degranulation, COX-1-dependent immediate PGD(2) generation and cytokine/chemokine expression. The suppression of delayed PGD(2) generation by NLRP3 was preceded by a transient decrease of NF-kappaB activation and a marked reduction in the expression of COX-2, but not that of cytosolic phospholipase A(2) alpha (cPLA(2)alpha), COX-1 and hematopoietic PGD(2) synthase. Moreover, in CTMC-like differentiated cells in which endogenous NLRP3 expression was induced, cytokine-stimulated induction of COX-2 and attendant delayed PGD(2) generation were markedly reduced. Our results suggest that, in mouse mast cells, NLRP3 counter-regulates COX-2-dependent sustained production of PGD(2), a prostanoid that exhibits both pro- and anti-allergic effects, thereby potentially influencing the duration of allergic and other mast cell-associated inflammatory diseases.

[Inducible histamine protects mice from hepatitis through H2-receptor stimulation]

Histamine is well known for its roles in allergic diseases and anaphylaxis through H(1)-receptor stimulation. The H(1)-receptor stimulation by histamine results in an increase in vascular permeability, vasodilatation, and stimulation of nerve terminals in primary sensory neurons, thereby accelerating the inflammatory responses. On the other hand, histamine has been demonstrated to be involved in the regulation of innate and acquired immune responses through H(2)-receptors. In a previous study with human peripheral blood mononuclear cells, we observed that histamine exerts various regulatory effects on monocyte/macrophage function. In this review, we discuss how inducible histamine protects mice from lethal hepatitis, induced by heat-killed P.acnes (1 mg, i.v.) followed by challenge with a low dose of lipopolysaccharide (1 microg), by reducing the excessive cytokine response in the liver. In addition, from in vivo studies with histidine decarboxylase knockout and H(1)-, H(2)-receptor knockout mice, the protective effect of histamine against fulminant hepatitis is shown to be elicited through H(2)-receptor stimulation.

The usefulness of post-genomics tools for characterization of the amine cross-talk in mammalian cells

Evidence is growing in favour of a relationship between cancer and chronic inflammation, and particularly of the role of a polyamine and histamine metabolic interplay involved in these physiopathological problems, which are indeed highly complex biological systems. Decodification of the complex inter- and intra-cellular signalling mechanisms that control these effects is not an easy task, which must be helped by systems biology technologies, including new tools for location and integration of database-stored information and predictive mathematical models, as well as functional genomics and other experimental molecular approaches necessary for hypothesis validation. We review the state of the art and present our latest efforts in this area, focused on the amine metabolism field.

Involvement of MAP kinases in lipopolysaccharide-induced histamine production in RAW 264 cells

Roles of mitogen-activated protein (MAP) kinases in lipopolysaccharide (LPS)-induced production of histamine in the mouse macrophage-like cell line RAW 264 were analyzed. Incubation of RAW 264 cells in the presence of LPS increased histamine levels in the conditioned medium in a concentration- and time-dependent manner. The levels of histidine decarboxylase (HDC) mRNA and the 74-kDa HDC protein were also increased at 4 to 8 h and 8 to 12 h, respectively. LPS elicited the phosphorylation of p44/42 MAP kinase, p38 MAP kinase, and c-Jun N-terminal kinase (JNK). The MAP kinase-Erk kinase 1 inhibitor U0126 (0.1-10 microM) suppressed the LPS-induced phosphorylation of p44/42 MAP kinase, and inhibited the LPS-induced production of histamine and expression of the HDC mRNA and 74-kDa HDC protein in a concentration-dependent manner. The JNK inhibitor SP600125 (3-30 microM) suppressed the LPS-induced phosphorylation of c-Jun, and inhibited the LPS-induced production of histamine and expression of the HDC mRNA and 74-kDa protein in a concentration-dependent manner. Combined treatment with U0126 (0.3 microM) and SP600125 (10 microM) inhibited the LPS-induced production of histamine additively. The p38 MAP kinase inhibitor SB203580 (0.1-10 microM) partially inhibited the LPS-induced production of histamine. These findings suggest that LPS increases histamine production in RAW 264 cells by inducing the expression of the 74-kDa HDC protein, and that the LPS-induced expression of HDC is up-regulated at the transcriptional level by MAP kinases, especially p44 MAP kinase and JNK.

Neuronal conditions of spinal cord in dermatitis are improved by olopatadine

Intense pruritus and cutaneous reactivity represent cardinal features of eczema. The resulting scratching behaviors alter neuronal conditions of the spinal dorsal horn where the primary sensory afferent fibers transmit cutaneous stimulation and deteriorate eczematous skin lesions. We investigated the effects of olopatadine hydrochloride (olopatadine) on alteration of neuronal conditions of the spinal dorsal horn and eczematous skin lesions induced by contact dermatitis. Eczematous lesions were induced by repeated application of diphenylcyclopropenone (DCP) in BALB/c mice. Olopatadine suppressed scratching behavior caused by repeated application of DCP in mice. Increased expressions of c-Fos and substance P in the spinal dorsal horn following DCP application were improved by olopatadine. Furthermore, olopatadine diminished the number of infiltrating cells and levels of cytokines in eczematous skin lesions resulting from DCP application. Olopatadine improves neurological conditions in the spinal cord and eczematous skin lesions in a murine contact dermatitis model.

Development of a High-Throughput Assay to Measure Histidine Decarboxylase Activity

Histamine is a well-known mediator of allergic, inflammatory, and neurological responses. More recent studies suggest a role for histamine and its receptors in a wide range of biological processes, including T-cell maturation and bone remodeling. Histamine serum levels are regulated mainly by the activity of the histamine-synthesizing enzyme histidine decarboxylase (HDC). Despite the importance of this enzyme in many physiological processes, very few potent HDC inhibitors have been identified. HDC assays suitable for high-throughput screening have not been reported. The authors describe the development of a fluorescence polarization assay to measure HDC enzymatic activity. They used a fluorescein-histamine probe that binds with high affinity to an antihistamine antibody for detection. Importantly, they show that probe binding is fully competed by histamine, but no competition by the HDC substrate histidine was observed. The automated assay was performed in a total volume of 60 μL, had an assay window of 80 to 100 mP, and had a Z′ factor of 0.6 to 0.7. This assay provides new tools to study HDC activity and pharmacological modulation of histamine levels.

Mast cell quantification in normal peritoneum and during peritoneal dialysis treatment

CONTEXT

Mast cells (MCs) have been implicated in fibrogenesis, angiogenesis, and immunity against bacteria. These 3 mechanisms participate in the peritoneal pathology secondary to peritoneal dialysis (PD) treatment. Despite their potential relevance to PD-related pathology, few studies have focused on MCs.

OBJECTIVE

To evaluate possible variations in the number of MCs during PD treatment.

DESIGN

A quantitative study of tissue MCs in normal and pathologic peritoneum. Parietal peritoneal biopsies were collected from 4 groups: (1) normal controls (n = 9), (2) uremic non-PD patients (n = 16), (3) uremic patients on PD (n = 26), and (4) non-renal patients with inguinal hernia (n = 20). MCs were evaluated using immunohistochemistry for the detection of tryptase. The total number of cross sections of vessels per peritoneal field was examined in 22 of the 26 peritoneal biopsies of PD patients.

RESULTS

PD tissue samples showed fibrosis, mesothelial cell loss, and variable hyalinizing vasculopathy. The number of MCs was similar in normal controls and non-PD uremic patients (mean +/- SE: 7.13 +/- 0.67 and 7.74 +/- 0.74 MCs/mm2, respectively). Peritoneal dialysis patients showed a reduction (4 +/- 0.38 MCs/mm2, P < .001), whereas hernia sac samples showed an increase (10.59 +/- 3.48 MCs/mm2). MC reduction showed no correlation with time on dialysis, fibrosis, number of vessels, or previous episodes of peritonitis.

CONCLUSIONS

The peritoneum of patients receiving PD treatment shows a reduction of MCs. Despite such a reduction, fibrosis takes place, suggesting that MCs do not play a critical role in fibrosis genesis. Mast cell loss may be a contributory factor to peritonitis episodes in PD patients.

Involvement of Sp1 in lipopolysaccharide-induced expression of HDC mRNA in RAW 264 cells

The involvement of Sp1 in the lipopolysaccharide (LPS)-induced transcription of HDC mRNA in the mouse macrophage-like cell line RAW 264 was analyzed. LPS increased the levels of HDC mRNA 4 h after the stimulation in a concentration-dependent manner. Mithramycin A, an inhibitor of the binding of the Sp family to the GC box, reduced the LPS-induced increase in the levels of HDC mRNA at 4 h and HDC protein at 8 h in a concentration-dependent manner. By conducting electrophoretic mobility shift assays, we found that one of the transcription factors binding to the DNA probe containing the GC box sequence of the mouse HDC gene promoter region was Sp1, and that levels of Sp1-DNA probe complexes were increased by stimulation with LPS although the protein levels of Sp1 were not changed. These results suggested that Sp1 is one of the transcription factors that regulate the LPS-induced expression of HDC in RAW 264 cells.

Histamine receptors in immune regulation and allergen-specific immunotherapy

The cells involved in the regulation of immune responses and hematopoiesis express histamine receptors and secrete histamine. Histamine acting through four types of its receptors has been shown not only to affect chronic inflammatory responses but also to regulate several essential events in the immune response. Histamine signals have a role in the mechanisms of tolerance induced during allergen-specific immunotherapy (SIT), acting mainly through its receptor (HR) type 2. It positively interferes with the peripheral antigen tolerance induced by T regulatory cells in several pathways. The rationale for the concomitant use of H1 antihistamines during SIT is diverse and includes reduction of its immediate side effects as well as enhancement of mechanisms of specific tolerance and anti-inflammatory effects of vaccination.

The accelerating effect of histamine on the cutaneous wound-healing process through the action of basic fibroblast growth factor

This study revealed that the absence of histamine in histidine decarboxylase gene-knockout (HDC(-/-)) mice resulted in delayed cutaneous wound healing and that exogenously administered histamine compensated this process. With the overproduction of histamine in HDC gene-transgenic mice, the healing was accelerated compared to the HDC(+/+) mice. These results indicate that histamine positively accelerated the cutaneous wound healing. Macrophage recruitment and angiogenesis at the wound edge were specifically impaired in HDC(-/-) mice, and histamine-treated wounds in HDC(-/-) mice demonstrated increased macrophage recruitment and angiogenesis. The amount of basic fibroblast growth factor (bFGF) in protein level at the wound edge was higher in HDC(+/+) mice, especially on the 3rd and 5th day of wound healing compared to those in HDC(-/-) mice. Topically administered SU5402, a specific antagonist to fibroblast growth factor receptor-1 tyrosine kinase, to the wound surface suppressed the wound healing in HDC(+/+) mice but not in HDC(-/-) mice. Moreover, SU5402 reduced macrophage recruitment and angiogenesis in HDC(+/+) mice. From these observations, it was concluded that the accelerated wound-healing activity of histamine was mediated by the activity of bFGF, which leads to angiogenesis, and macrophage recruitment in the wound-healing process.

Cellular and Molecular Dynamics in the Foreign Body Reaction

Intracorporally implanted materials, such as medical devices, will provoke the body to initiate an inflammatory reaction. This inflammatory reaction to implanted materials is known as the foreign body reaction (FBR) and is characterized by 3 distinct phases: onset, progression, and resolution. The FBR proceeds in the creation of a dynamic microenvironment that is spatially well organized. The progression of the FBR is regulated by soluble mediators, such as cytokines, chemokines, and matrix metalloproteinases (MMPs), which are produced locally by tissue cells and infiltrated inflammatory cells. These soluble mediators orchestrate the cascade of cellular processes in the microenvironment that accompanies the FBR, consisting of cellular activation, angiogenesis, extravasation, migration, phagocytosis, and, finally, fibrosis. The nature of the FBR requires that the soluble mediators act in a spatial and temporally regulated manner as well. This regulation is well known for several inflammatory processes, but scarce knowledge exists about the intricate relationship between the FBR and the expression of soluble mediators. This review discusses the key processes during the initiation, progression, and resolution phase, with emphasis on the role of soluble mediators. Besides other sites of implantation, we focus on the subcutaneous implantation model.

A comprehensive view of polyamine and histamine metabolism to the light of new technologies

Polyamines and histamine are biogenic amines with multiple biological roles. In spite of the evidence for the involvement of both polyamines and histamine metabolism impairment in several highly prevalent pathological conditions, multiple questions concerning the molecular processes behind these effects remain to be elucidated. More comprehensive and systemic studies integrating molecular biology, biophysical and bioinformatics tools could contribute to accelerate the advances in this research area. This review is designed to underscore the main questions to be answered in polyamine and histamine research and how these new systemic approaches could help to find these answers.

Histamine receptors are hot in immunopharmacology

In addition to its well-characterized effects in the acute allergic inflammatory responses, histamine has been demonstrated to affect chronic inflammation and regulate several essential events in the immune response. Histamine can selectively recruit the major effector cells into tissue sites and affect their maturation, activation, polarization, and other functions leading to chronic inflammation. Histamine also regulates dendritic cells, T cells and B cells, as well as related antibody isotype responses. In addition, acting through its receptor 2, histamine positively interferes with the peripheral antigen tolerance induced by T regulatory cells in several pathways. The diverse effects of histamine on immune regulation appear to be due to differential expression and regulation of 4 types of histamine receptors and their distinct intracellular signals. In addition, differences in affinities of these receptors for histamine is highly decisive for the biological effects of histamine and drugs that target histamine receptors. This article highlights recent discoveries in histamine immunobiology and discusses their relevance in allergic inflammation.

A key regulatory role for histamine in experimental autoimmune encephalomyelitis: disease exacerbation in histidine decarboxylase-deficient mice

Histamine can modulate the cytokine network and influence Th1 and Th2 balance and Ab-isotype switching. Thus, pharmacological blockade or genetic deletion of specific histamine receptors has been shown to reduce the severity of experimental autoimmune encephalomyelitis (EAE), a prototypic Th1-mediated disease with similarities to human multiple sclerosis. To study the comprehensive contribution of endogenous histamine to the expression of EAE, we attempted to induce EAE in histidine decarboxylase-deficient mice, which are genetically unable to make histamine. In this study, we show that EAE is significantly more severe in HDC-/-, histamine-deficient mice, with diffuse inflammatory infiltrates, including a prevalent granulocytic component, in the brain and cerebellum. Unlike splenocytes from wild-type mice, splenocytes from HDC-/- mice do not produce histamine in response to the myelin Ag, whereas production of IFN-gamma, TNF, and leptin are increased in HDC-/- splenocytes in comparison to those from wild-type mice. Endogenous histamine thus appears to regulate importantly the autoimmune response against myelin and the expression of EAE, in this model, and to limit immune damage to the CNS. Understanding which receptor(s) for histamine is/are involved in regulating autoimmunity against the CNS might help in the development of new strategies of treatment for EAE and multiple sclerosis.

Structural basis for inhibition of histamine N-methyltransferase by diverse drugs

In mammals, histamine action is terminated through metabolic inactivation by histamine N-methyltransferase (HNMT) and diamine oxidase. In addition to three well-studied pharmacological functions, smooth muscle contraction, increased vascular permeability, and stimulation of gastric acid secretion, histamine plays important roles in neurotransmission, immunomodulation, and regulation of cell proliferation. The histamine receptor H1 antagonist diphenhydramine, the antimalarial drug amodiaquine, the antifolate drug metoprine, and the anticholinesterase drug tacrine (an early drug for Alzheimer's disease) are surprisingly all potent HNMT inhibitors, having inhibition constants in the range of 10-100nM. We have determined the structural mode of interaction of these four inhibitors with HNMT. Despite their structural diversity, they all occupy the histamine-binding site, thus blocking access to the enzyme's active site. Near the N terminus of HNMT, several aromatic residues (Phe9, Tyr15, and Phe19) adopt different rotamer conformations or become disordered in the enzyme-inhibitor complexes, accommodating the diverse, rigid hydrophobic groups of the inhibitors. The maximized shape complementarity between the protein aromatic side-chains and aromatic ring(s) of the inhibitors are responsible for the tight binding of these varied inhibitors.

Inhibition of scratching behaviour caused by contact dermatitis in histidine decarboxylase gene knockout mice

A neuronal system dedicated to itch consists of primary afferent and spinothalamic projection neurons. Histamine is thought to be one of the main mediators for the transmission of itch sensation. However, there are little available information on the role of histamine in scratching behaviour and sensory transmission of atopic dermatitis and chronic eczema. In the present study, the role of histamine in scratching behaviour and neural conduction of sensation in the chronic eczema model was investigated by using l-histidine decarboxylase (HDC) gene knockout mice lacking histamine. The chronic contact dermatitis was induced with daily application of diphenylcyclopropenone (DCP) on a hind paw of HDC (+/+) and HDC (-/-) mice for 2 months. The observation of scratching behaviour and the hot-plate test were performed in both mice. Histological studies were performed in the skin and spinal cord tissues. Histological examination revealed that both HDC (+/+) and HDC (-/-) mice displayed the similar extent of inflammatory cell infiltration, hyperplastic epidermis and newly spreading of neuronal processes in the skin tissue. Scratching behaviour was exclusively induced in HDC (+/+) mice, whereas it was barely observed in HDC (-/-) mice. The expression of c-Fos was specifically upregulated in HDC (+/+) mice in lamina I of the spinal dorsal horn following repeated DCP application. Scratching behaviour in chronic contact dermatitis in mice was thought mainly mediated with histamine. The afferent pathway of sensation in chronic contact dermatitis model may connect with the central nervous system through lamina I of the spinal dorsal horn.

Histamine production via mast cell-independent induction of histidine decarboxylase in response to lipopolysaccharide and interleukin-1

Histamine modulates immune responses. There are at least two ways histamine might be supplied: one is its release from cells that pool pre-formed histamine and the other is its de novo formation via induction of histidine decarboxylase (HDC). Lipopolysaccharide (LPS) and the proinflammatory cytokine interleukin (IL)-1 induce a marked elevation of HDC activity in various tissues or organs. To examine the contribution of mast cells to HDC induction in mice given LPS or IL-1, we examined the effects of LPS and IL-1 on HDC activity and/or histamine content in various organs (liver, lung, spleen or bone marrow) in mast cell-deficient mice (W/Wv), their normal littermates (+/+) and BALB/c mice deficient in IL-1alpha, IL-1beta and tumor necrosis factor (TNF)-alpha (IL-1alpha beta/TNFalphaKO mice). In non-stimulated mice, the histamine in the lung and spleen was contained largely within mast cells. The LPS-stimulated increase in HDC activity in a given organ was similar between +/+ and W/W(v) mice, and between IL-1alpha beta/TNFalphaKO BALB/c and control BALB/c mice, and led to increases in histamine. In W/Wv and +/+ mice, IL-1alpha also elevated HDC activity. These results suggest that (i) in liver, lung and spleen, either the major cells supplying histamine via HDC induction in response to LPS and IL-1 are not mast cells, or mast cells are not a prerequisite for the induction of HDC; (ii) the cells in which HDC is induced by LPS and IL-1 are similar or identical in a given organ; and (iii) neither IL-1 nor TNF-alpha is a prerequisite for the induction of HDC by LPS.

Role of histamine produced by bone marrow-derived vascular cells in pathogenesis of atherosclerosis

To clarify the role of histamine-producing cells and its origin in atherosclerosis, we investigated histidine decarboxylase (HDC; histamine-producing enzyme) expression in murine arteries with vascular injuries after the animal had received transplanted bone marrow (BM) from green fluorescent protein (GFP)-transgenic mice. The neointima in the ligated carotid arteries contained BM-derived HDC+ cells that expressed macrophage (Mac-3) or smooth muscle cell antigen (alpha-SMA). In contrast, the HDC+ BM-derived cells, which were positive for Mac-3, were mainly located in the adventitia in the cuff replacement model. In apolipoprotein E-knockout mice on a high cholesterol diet, BM-derived cells expressing Mac-3 in the atheromatous plaques were also positive for HDC. In comparison with wild-type mice, HDC-/- mice showed reduced neointimal thickening and a decreased intima-to-media ratio after ligation and cuff replacement. These results indicate that histamine produced from BM-derived progenitor cells, which could transdifferentiate into SMC- or macrophage-like cells, are important for the formation of neointima and atheromatous plaques.

Histamine in allergic inflammation and immune modulation

Histamine, originally considered as a mediator of acute inflammatory and immediate hypersensitivity responses has also been demonstrated to affect chronic inflammation and regulate several essential events in the immune response. On the other hand, various cytokines control histamine synthesis, release and expression of histamine receptors (HRs). The cells involved in the regulation of immune response and hematopoiesis express HRs and also secrete histamine, which can selectively recruit the major effector cells into tissue sites and affect their maturation, activation, polarization and effector functions leading to chronic inflammation. Histamine, acting through its receptor type 2, positively interferes with the peripheral antigen tolerance induced by T regulatory cells in several pathways. Histamine also regulates antigen-specific Th1 and Th2 cells, as well as related antibody isotype responses. The diverse effects of histamine on immune regulation are due to differential expression and regulation of four HRs and their distinct intracellular signals. In addition, differences in affinities of these receptors are highly decisive on the biological effects of histamine and agents that target HRs. This article highlights the findings leading to a change of perspective in histamine immunobiology.

Histamine elevates the expression of Ets-1, a protooncogen in human melanoma cell lines through H2 receptor

Histamine is known to act, at least in part, as a growth factor for several cell types, and as production of this biogen amine has been found to accelerate the rate of tissue proliferation in wound repair, embryogenesis and malignant growth. Abundant experimental and clinical data suggest that histamine augments in vivo tumour cell proliferation via histamine H2 receptors (H2R). Here, we report that exogenously added histamine stimulates Ets-1 (v-ets erythroblastosis virus E26 oncogene homolog 1) synthesis in human melanoma cells. Involvement of histamine receptors in the histamine induced ets-1 expression has been also studied. Our data show that these newly recognized actions of histamine are mediated by the H2R. Modification of local protooncogen Ets-1 level is likely being involved in the regulation of melanoma growth.

Histamine-cytokine connection in immunity and hematopoiesis

A number of recent studies have led to a reappraisal of the functional capacities of histamine in immunity and hematopoiesis. This change of perspective was provided by the following findings: (1) the evidence for multiple cellular sources of histamine, differing from mature basophils and mast cells by their ability to newly synthesize and liberate the mediator without prior storage, (2) the discovery of a novel histamine receptor (H4R), preferentially expressed on hematopoietic and immunocompetent cells, (3) the potential intracellular activity of histamine through cytochrome P450 and (4) the demonstration of a histamine-cytokine cross-talk. Indeed, cytokines not only modulate the degranulation process of histamine but also control its neosynthesis by the histamine-forming enzyme, histidine decarboxylase (HDC), at transcriptional and post-transcriptional levels. In turn, histamine intervenes in the intricate cytokine network, regulating cytokine production by immune cells through distinct receptors signaling distinct biological effects. This type of regulation is particularly relevant in the context of TH1/TH2 differentiation, autoimmunity and tumor immunotherapy.

Acute inflammatory reactions caused by histamine via monocytes/macrophages chronically participate in the initiation and progression of atherosclerosis

Previously we demonstrated that histidine decarboxylase (HDC), which produces histamine from l-histidine, was detected in monocytes/macrophages located in human atherosclerotic lesions. As monocytic migration is a key event of atherogenesis, we investigated whether histamine induces monocytic expression of monocyte chemoattractant protein (MCP)-1 and its receptors CCR2-A and -B, and also endothelial expression of ICAM-1 and VCAM-1. Furthermore, we studied the effect of interleukin (IL)-4, which inhibits the HDC expression, on the expression of MCP-1 and CCR2. Histamine stimulated monocytes, but not macrophages, to express MCP-1 and CCR2-A and -B. The expression of MCP-1 was inhibited by histamine H2 blocker. In contrast, IL-4 enhanced CCR2 expression but not MCP-1. Histamine stimulated endothelial cells to express ICAM-1 and VCAM-1. These results indicate that histamine and IL-4, which are both synthesized in the arterial intima, chronically participates in the pathogenesis of atherosclerosis via the enhanced expression of monocytic MCP-1, CCR2 and endothelial adhesion molecules.

The C-terminus of rat L-histidine decarboxylase specifically inhibits enzymic activity and disrupts pyridoxal phosphate-dependent interactions with L-histidine substrate analogues

Full-length rat HDC (L-histidine decarboxylase) translated in reticulocyte cell lysate reactions is inactive, whereas C-terminally truncated isoforms are capable of histamine biosynthesis. C-terminal processing of the approximately 74 kDa full-length protein occurs naturally in vivo, with the production of multiple truncated isoforms. The minimal C-terminal truncation required for the acquisition of catalytic competence has yet to be defined, however, and it remains unclear as to why truncation is needed. Here we show that approximately 74 kDa HDC monomers can form dimers, which is the conformation in which the enzyme is thought to be catalytically active. Nevertheless, the resulting dimer is unable to establish pyridoxal phosphate-dependent interactions with an L-histidine substrate analogue. Protein sequences localized to between amino acids 617 and 633 specifically mediate this inhibition. Removing this region or replacing the entire C-terminus with non-HDC protein sequences permitted interactions with the substrate analogue to be re-established. This corresponded exactly with the acquisition of catalytic competence, and the ability to decarboxylate natural L-histidine substrate. These studies suggested that the approximately 74 kDa full-length isoform is deficient in substrate binding, and demonstrated that C-terminally truncated isoforms with molecular masses between approximately 70 kDa and approximately 58 kDa have gradually increasing specific activities. The physiological relevance of our results is discussed in the context of differential expression of HDC isoforms in vivo.

Role of macrophage-derived histamine in atherosclerosis-- chronic participation in the inflammatory response --

The atherosclerotic intimal lesion contains endothelial cells, smooth muscle cells, monocytes/macrophages and T lymphocytes, which constitute a histamine-cytokine network that participates in chronic inflammatory responses. Monocytes/macrophages and T lymphocytes express the histamine-producing enzyme histidine decarboxylase (HDC), and specific histamine receptors (HHR), which are switched from HH2R to HHR1 during macrophage differentiation. Endothelial and smooth muscle cells also express HHR in response to histamine. The effects of histamine on these cells include a regulation of atherosclerosis-related events such as cell proliferation, expression of matrix metalloproteinase, adhesion molecules and cytokines. Furthermore, recent studies have indicated that histamine and the activation of its specific receptors modulate the Th1/Th2 balance in inflammatory lesions through the regulation of cytokine production from inflammatory cells. The histamine-cytokine network in the atherosclerotic intima could regulate inflammatory and immune responses, including Th1/Th2 balance, and contribute to atherogenesis.

Inducible histamine protects mice from P. acnes-primed and LPS-induced hepatitis through H2-receptor stimulation

BACKGROUND & AIMS

Inducible histamine and histamine H2-receptors have been suggested to be involved in innate immune response.

METHODS

We examined a functional role of inducible histamine in the protection against hepatic injury and lethality in Propionibacterium acnes -primed and lipopolysaccharide-induced hepatitis, using histidine decarboxylase knockout and H2-receptor knockout mice.

RESULTS

Lipopolysaccharide challenge after Propionibacterium acnes priming increased histidine decarboxylase activity in the liver of wild-type mice, associated with a marked elevation of histamine turnover. Histidine decarboxylase-like immunoreactivity was observed in CD68-positive Kupffer cells/macrophages. Treatment of wild-type mice with famotidine or ranitidine but not d -chlorpheniramine augmented hepatic injury and inhibited the survival rate significantly. The same dose of Propionibacterium acnes and lipopolysaccharide induced severe hepatitis and high lethality in histidine decarboxylase knockout and H2-receptor knockout mice; the former were rescued by the subcutaneous injection of histamine. Immunohistochemical study supported the protective role of histamine against the apoptosis of hepatocytes. Histamine suppressed the expression of IL-18 and tumor necrosis factor alpha in the liver, leading to the reduced plasma levels of cytokines including IL-18, TNF-alpha, IL-12, IFN-gamma, and IL-6.

CONCLUSIONS

These findings as a whole indicated that endogenously produced histamine in Kupffer cells/macrophages plays a very important role in preventing excessive innate immune response in endotoxin-induced fulminant hepatitis through the stimulation of H2-receptors.

L-histidine decarboxylase as a probe in studies on histamine

Because the Falck-Hillarp formaldehyde fluorescence method, which was superbly applied to identify catecholaminergic and serotonergic neurons, is not applicable to histamine, the first author (T.W.) developed an antibody to L-histidine decarboxylase (HDC) for identification of the histaminergic neuron system in the brain. The anti-HDC antibody was of great use for mapping the location and distribution of this histaminergic neuron system. (S)-alpha-fluoromethylhistidine, a specific and potent irreversible inhibitor of HDC, was also very useful in studies on functions of the neuron system. The activity of HDC is increased by various agents, treatments, and physiological conditions. We found new compounds that increased HDC activity (i.e., tetradecanoylphobol acetate (TPA), other tumor promoters, and staphylococcal enterotoxin A); and using mast cell-deficient mutant (W/W(v)) mice, we obtained evidence that this increase occurred in macrophages. To further characterize the mechanism of increases in HDC activity, the second author (H.O.) cloned human HDC cDNA and a human HDC gene. In studies on the regulation mechanism of the HDC gene, which is expressed only in limited types of cells such as mast cells, enterochromaffin-like cells in the stomach, cells in the tuberomammillary nucleus of the brain, and macrophages, CpG islands in the promoter region of the HDC gene were found to be demethylated in cells expressing the gene, whereas they are methylated in other cells that do not express the HDC gene. In collaboration with many other researchers, we developed HDC knockout mice. The resulting research is producing a lot of interesting findings in our laboratory as well as in others. In summary, HDC has been and will be useful in studies on functions of histamine.

Reduced pain hypersensitivity and inflammation in mice lacking microsomal prostaglandin e synthase-1

We examined the in vivo role of membrane-bound prostaglandin E synthase (mPGES)-1, a terminal enzyme in the PGE2-biosynthetic pathway, using mPGES-1 knockout (KO) mice. Comparison of PGES activity in the membrane fraction of tissues from mPGES-1 KO and wild-type (WT) mice indicated that mPGES-1 accounted for the majority of lipopolysaccharide (LPS)-inducible PGES in WT mice. LPS-stimulated production of PGE2, but not other PGs, was impaired markedly in mPGES-1-null macrophages, although a low level of cyclooxygenase-2-dependent PGE2 production still remained. Pain nociception, as assessed by the acetic acid writhing response, was reduced significantly in KO mice relative to WT mice. This phenotype was particularly evident when these mice were primed with LPS, where the stretching behavior and the peritoneal PGE2 level of KO mice were far less than those of WT mice. Formation of inflammatory granulation tissue and attendant angiogenesis in the dorsum induced by subcutaneous implantation of a cotton thread were reduced significantly in KO mice compared with WT mice. Moreover, collagen antibody-induced arthritis, a model for human rheumatoid arthritis, was milder in KO mice than in WT mice. Collectively, our present results provide unequivocal evidence that mPGES-1 contributes to the formation of PGE2 involved in pain hypersensitivity and inflammation.

Local changes in the catalytic site of mammalian histidine decarboxylase can affect its global conformation and stability

Mature, active mammalian histidine decarboxylase is a dimeric enzyme of carboxy-truncated monomers (approximately 53 kDa). By using a biocomputational approach, we have generated a three-dimensional model of a recombinant 1/512 fragment of the rat enzyme, which shows kinetic constants similar to those of the mature enzyme purified from rodent tissues. This model, together with previous spectroscopic data, allowed us to postulate that the occupation of the catalytic center by the natural substrate, or by substrate-analogs, would induce remarkable changes in the conformation of the intact holoenzyme. To investigate the proposed conformational changes during catalysis, we have carried out electrophoretic, chromatographic and spectroscopic analyses of purified recombinant rat 1/512 histidine decarboxylase in the presence of the natural substrate or substrate-analogs. Our results suggest that local changes in the catalytic site indeed affect the global conformation and stability of the dimeric protein. These results provide insights for new alternatives to inhibit histamine production efficiently in vivo.

Histamine in the immune regulation of allergic inflammation

Histamine was the first mediator implicated in mechanisms of allergy, asthma, and anaphylactic shock because it has been discovered to mimic several features of these diseases. In addition to its well-characterized effects in the acute inflammatory and allergic responses, it was recently demonstrated that histamine regulates several essential events in the immune response. Histamine affects the maturation of immune system cells and alters their activation, polarization, chemotaxis, and effector functions. Histamine also regulates antigen-specific T(H)1 and T(H)2 cells, as well as related antibody isotype responses. Histamine binds to 4 different G protein-coupled receptors that transduce signals to cells through distinct pathways. The expression of these receptors on different cells and cell subsets is regulated, and apparently, the diverse effects of histamine on immune regulation are due to differential expression of 4 histamine receptors and their distinct intracellular signals. This article highlights novel discoveries in histamine immunobiology and discusses clinical findings or disease models that indicate immune regulation by histamine.

New functions of histamine found in histidine decarboxylase gene knockout mice

Gene targeting techniques have revolutionized the investigation of the effects of bioactive substances in pathological and physiological conditions. Histamine synthesis is uniquely catalyzed by L-histidine decarboxylase. The knockout mice of this gene express no histamine-producing activity and lack histamine. These mice have been used to examine the mechanisms of histamine in several known phenotypes, e.g., gastric acid secretion, contraction of smooth muscles, vascular permeability, and awakening, and have also been used to explore unreported effects of histamine in the whole body. First, we will review the former mechanisms and then move to the latter, new effects. Especially, in the latter mechanisms, we focus on several important roles of histamine in angiogenesis, neutrophil and eosinophil recruitment, bacterial infection, and systemic anaphylaxis in this review. Moreover, to our surprise, the morphology of mast cells in the knockout mice was severely affected by the absence of histamine in terms of their granules.

Regulation by prostaglandin E2 and histamine of angiogenesis in inflammatory granulation tissue

In an air pouch-type carrageenin-induced inflammation model in rats, the selective cyclooxygenase (COX)-2 inhibitor NS-398 dose dependently inhibited the granulation tissue formation, angiogenesis and the level of vascular endothelial growth factor (VEGF) in the granulation tissue. In culture of the minced granulation tissue, PGE2 induced VEGF production in a concentration-dependent manner. Histamine also induced VEGF production in the granulation tissue in vitro. The H2 receptor antagonist cimetidine, the cAMP antagonist Rp-cAMP and the protein kinase A inhibitor H-89 suppressed the histamine-induced VEGF production in the granulation tissue. However, the H1 receptor antagonist pyrilamine maleate, the H3 receptor antagonist thioperamide, the protein kinase C inhibitors Ro 31-8425 and calphostin C or the tyrosine kinase inhibitor genistein showed no effect. Subcutaneous implantation of a cotton thread in the dorsum of histidine decarboxylase-deficient (HDC-/-) mice, but not in mast cell-deficient (WBB6F1-W/Wv) mice, induced less angiogenesis with lower levels of VEGF in the granulation tissue than in their corresponding wild-type (HDC+/+ and WBB6F1(-)+/+) mice. In HDC-/- mice, the topical injection of histamine or the H2 receptor agonist dimaprit rescued the defective angiogenesis and granulation tissue formation. In addition, cimetidine but not pyrilamine maleate and thioperamide inhibited the histamine-induced angiogenesis in the granulation tissue in HDC-/- mice. These findings suggest that PGE2 and histamine augment angiogenesis in the inflammatory granulation tissue by inducing VEGF production, and histamine induces VEGF production possibly through the H2 receptor--cAMP--protein kinase A pathway.

Inhibition by acharan sulphate of angiogenesis in experimental inflammation models

1. The effects of acharan sulphate, a glycosaminoglycan isolated from the giant African snail Achatina fulica, on angiogenesis in the granulation tissue were analysed using an air pouch-type carrageenin-induced inflammation model in rats and a cotton thread-induced inflammation model in mice. 2. In the carrageenin-induced inflammation model in rats, intra-pouch injections of acharan sulphate (5 and 50 micro g) inhibited the pouch fluid accumulation and the granulation tissue formation as well as the angiogenesis in the granulation tissue at day 6 in a dose-dependent manner. 3. The inhibitory effects of acharan sulphate at 50 micro g on the pouch fluid accumulation and the leucocyte infiltration into the pouch fluid was not so effective as that of the cyclo-oxygenase inhibitor indomethacin at 100 micro g, but the inhibitory effects of acharan sulphate at 50 micro g on the granulation tissue formation and angiogenesis in the granulation tissue were almost the same as those of indomethacin at 100 micro g. 4. Acharan sulphate did not affect levels of vascular endothelial growth factor (VEGF) in the granulation tissue and in the pouch fluid at day 6, but indomethacin significantly lowered them. 5. In the cotton thread-induced inflammation model in mice, injections of acharan sulphate (10 micro g) at the site of the cotton thread implantation inhibited the granulation tissue formation and angiogenesis as indomethacin (20 micro g) did. Acharan sulphate (10 micro g) did not affect levels of VEGF in the cotton thread-induced granulation tissue at day 5, but indomethacin (20 micro g) significantly lowered them. 6. In culture of human vascular endothelial cells, acharan sulphate at 10 and 100 micro g ml(-1) inhibited VEGF-induced capillary tube formation. 7. These findings suggest that the inhibitory effect of acharan sulphate on angiogenesis in carrageenin- and cotton thread-induced granulation tissues is not due to the inhibition of VEGF protein induction, but is due to the inhibition of VEGF-induced vascular tube formation.