Efficacy of a selective histamine H2 receptor agonist, dimaprit, in experimental models of endotoxin shock and hepatitis in mice

Drug delivery targets and strategies to address mast cell diseases

INTRODUCTION

Current and developing mast cell therapeutics are reliant on small molecule drugs and biologics, but few are truly selective for mast cells. Most have cellular and disease-specific limitations that require innovation to overcome longstanding challenges to selectively targeting and modulating mast cell behavior. This review is designed to serve as a frame of reference for new approaches that utilize nanotechnology or combine different drugs to increase mast cell selectivity and therapeutic efficacy.

AREAS COVERED

Mast cell diseases include allergy and related conditions as well as malignancies. Here, we discuss the targets of existing and developing therapies used to treat these disease pathologies, classifying them into cell surface, intracellular, and extracellular categories. For each target discussed, we discuss drugs that are either the current standard of care, under development, or have indications for potential use. Finally, we discuss how novel technologies and tools can be used to take existing therapeutics to a new level of selectivity and potency against mast cells.

EXPERT OPINION

There are many broadly and very few selectively targeted therapeutics for mast cells in allergy and malignant disease. Combining existing targeting strategies with technology like nanoparticles will provide novel platforms to treat mast cell disease more selectively.

Acute Intestinal Inflammation Depletes/Recruits Histamine-Expressing Myeloid Cells From the Bone Marrow Leading to Exhaustion of MB-HSCs

BACKGROUND & AIMS

Histidine decarboxylase (HDC), the histamine-synthesizing enzyme, is expressed in a subset of myeloid cells but also marks quiescent myeloid-biased hematopoietic stem cells (MB-HSCs) that are activated upon myeloid demand injury. However, the role of MB-HSCs in dextran sulfate sodium (DSS)-induced acute colitis has not been addressed.

METHODS

We investigated HDC+ MB-HSCs and myeloid cells by flow cytometry in acute intestinal inflammation by treating HDC-green fluorescent protein (GFP) male mice with 5% DSS at various time points. HDC+ myeloid cells in the colon also were analyzed by flow cytometry and immunofluorescence staining. Knockout of the HDC gene by using HDC-/-; HDC-GFP and ablation of HDC+ myeloid cells by using HDC-GFP; HDC-tamoxifen-inducible recombinase Cre system; diphtheria toxin receptor (DTR) mice was performed. The role of H2-receptor signaling in acute colitis was addressed by treatment of DSS-treated mice with the H2 agonist dimaprit dihydrochloride. Kaplan-Meier survival analysis was performed to assess the effect on survival.

RESULTS

In acute colitis, rapid activation and expansion of MB-HSC from bone marrow was evident early on, followed by a gradual depletion, resulting in profound HSC exhaustion, accompanied by infiltration of the colon by increased HDC+ myeloid cells. Knockout of the HDC gene and ablation of HDC+ myeloid cells enhance the early depletion of HDC+ MB-HSC, and treatment with H2-receptor agonist ameliorates the depletion of MB-HSCs and resulted in significantly increased survival of HDC-GFP mice with acute colitis.

CONCLUSIONS

Exhaustion of bone marrow MB-HSCs contributes to the progression of DSS-induced acute colitis, and preservation of quiescence of MB-HSCs by the H2-receptor agonist significantly enhances survival, suggesting the potential for therapeutic utility.

[Analyses of Foxp3+ Treg cells and Tr1 cells in subcutaneous immunotherapy-treated allergic individuals in humans and mice]

Subcutaneous immunotherapy (SCIT) is a causative treatment for allergic diseases. More recently, it has become clear that regulatory T (Treg) cells are increased by SCIT. Treg cells are generally divided into two main groups: 1) CD25⁺ Foxp3⁺ CD4⁺ T cells (Foxp3⁺ Treg cells) and 2) IL-10-producing Foxp3^- CD4⁺ T cells (Tr1 cells). We demonstrated that the number of Tr1 cells in peripheral blood mononuclear cells in SCIT-treated pollinosis patients were significantly higher than that in non-SCIT-treated patients, but Foxp3⁺ Treg cells were not. Consistent with the results of human peripheral blood, Tr1 cells were increased in the lungs of asthmatic mice by SCIT, but Foxp3⁺ Treg cells were not. Moreover, in vitro-induced Tr1 cells were responded to the antigen to produce a large amount of IL-10 in in vitro and in vivo. Adoptive transfer of the induced Tr1 cells significantly suppressed the development of asthma. In any species of human and mouse, the increase in Tr1 cells rather than Foxp3⁺ Treg cells could be important for the effects of SCIT. The increased Tr1 cells by SCIT functionally suppressed allergic asthma probably via production of IL-10 in response to the specific antigen. Therefore, analyses of the induction mechanisms of Tr1 cells and search for compounds which induce Tr1 cells are thought to lead to development of more efficient SCIT.

Immunomodulatory properties of cimetidine: Its therapeutic potentials for treatment of immune-related diseases

Histamine exerts potent modulatory impacts on the cells of innate- [including neutrophils, monocytes, macrophages, dendritic cells (DCs), natural killer (NK) cells and NKT cells] and adaptive immunity (such as Th1-, Th2-, Th17-, regulatory T-, CD8⁺ cytotoxic T cells, and B cells) through binding to histamine receptor 2 (H2R). Cimetidine, as an H2R antagonist, reverses the histamine-mediated immunosuppression, as it has powerful stimulatory effects on the effector functions of neutrophils, monocytes, macrophages, DCs, NK cells, NKT cells, Th1-, Th2-, Th17-, and CD8⁺ cytotoxic T cells. However, cimetidine reduces the regulatory/suppressor T cell-mediated immunosuppression. Experimentally, cimetidine potentiate some immunologic activities in vitro and in vivo. The therapeutic potentials of cimetidine as an immunomodulatory agent were also investigated in a number of human diseases (such as cancers, viral warts, allergic disorders, burn, and bone resorption) and vaccination. This review aimed to provide a concise summary regarding the impacts of cimetidine on the immune system and highlight the cellular mechanisms of action and the immunomodulatory effects of this drug in various diseases to give novel insights regarding the therapeutic potentials of this drug for treatment of immune-related disorders. The review encourages more investigations to consider the immunomodulatory characteristic of cimetidine for managing of immune-related disorders.

Distinct roles of histamine H1- and H2-receptor signaling pathways in inflammation-associated colonic tumorigenesis

Inflammatory bowel disease (IBD) is a well-known risk factor for the development of colorectal cancer. Prior studies have demonstrated that microbial histamine can ameliorate intestinal inflammation in mice. We tested the hypothesis whether microbe-derived luminal histamine suppresses inflammation-associated colon cancer in Apc^min/+ mice. Mice were colonized with the human-derived Lactobacillus reuteri. Chronic inflammation was induced by repeated cycles of low-dose dextran sulfate sodium (DSS). Mice that were given histamine-producing L. reuteri via oral gavage developed fewer colonic tumors, despite the presence of a complex mouse gut microbiome. We further demonstrated that administration of a histamine H1-receptor (H1R) antagonist suppressed tumorigenesis, while administration of histamine H2-receptor (H2R) antagonist significantly increased both tumor number and size. The bimodal functions of histamine include protumorigenic effects through H1R and antitumorigenic effects via H2R, and these results were supported by gene expression profiling studies on tumor specimens of patients with colorectal cancer. Greater ratios of gene expression of H2R ( HRH2) vs. H1R ( HRH1) were correlated with improved overall survival outcomes in patients with colorectal cancer. Additionally, activation of H2R suppressed phosphorylation of mitogen-activated protein kinases (MAPKs) and inhibited chemokine gene expression induced by H1R activation in colorectal cancer cells. Moreover, the combination of a H1R antagonist and a H2R agonist yielded potent suppression of lipopolysaccharide-induced MAPK signaling in macrophages. Given the impact on intestinal epithelial and immune cells, simultaneous modulation of H1R and H2R signaling pathways may be a promising therapeutic target for the prevention and treatment of inflammation-associated colorectal cancer. NEW & NOTEWORTHY Histamine-producing Lactobacillus reuteri can suppress development of inflammation-associated colon cancer in an established mouse model. The net effects of histamine may depend on the relative activity of H1R and H2R signaling pathways in the intestinal mucosa. Our findings suggest that treatment with H1R or H2R antagonists could yield opposite effects. However, by harnessing the ability to block H1R signaling while stimulating H2R signaling, novel strategies for suppression of intestinal inflammation and colorectal neoplasia could be developed.

Induced histamine regulates Ni elution from an implanted Ni wire in mice by downregulating neutrophil migration

Histamine regulates various inflammatory reactions. We have reported that the expression of histidine decarboxylase (HDC) was induced by subcutaneous implantation of nickel (Ni) wire. However, the source and functions of histamine in Ni elution and Ni wire-induced inflammation have not been completely studied. We aimed to elucidate the effects of de novo synthesized histamine on leucocyte infiltration and Ni elution. Implantation of Ni wire induced an increase in the Ni ion content of the surrounding tissues and serum and in the mRNA levels of HDC, a histamine-producing enzyme, macrophage inflammatory protein-2 (MIP-2), a chemoattractant for neutrophils, and monocyte chemoattractant protein-1 (MCP-1), a chemoattractant for monocytes. The Ni wire induced HDC expression even in mast cell-deficient WBB6F1-W/W^V mice. In HDC knockout (HDC KO) mice, the Ni wire-induced increase in MIP-2 mRNA expression was significantly higher than that in wild-type mice but not MCP-1. MIP-2 expression was enhanced in histamine H2 receptor knockout (H2R KO) mice but not in WBB6F1-W/W^V mice. Histamine inhibited NiCl₂ -induced MIP-2 mRNA expression in mouse bone marrow-derived macrophages (BMDMs) obtained from wild-type mice; this inhibition was not observed in BMDMs from H2R KO mice. Ni elution increased in HDC KO mice, in which leucocyte infiltration also increased, and was suppressed in mice treated with neutrophil-specific antibody. These results suggest that the Ni wire induced HDC expression in non-mast cells and that, in the chronic phase of inflammation, endogenous histamine reduced Ni elution, probably through regulation of MIP-2 expression and neutrophil migration.

Histamine derived from probiotic Lactobacillus reuteri suppresses TNF via modulation of PKA and ERK signaling

Beneficial microbes and probiotic species, such as Lactobacillus reuteri, produce biologically active compounds that can modulate host mucosal immunity. Previously, immunomodulatory factors secreted by L. reuteri ATCC PTA 6475 were unknown. A combined metabolomics and bacterial genetics strategy was utilized to identify small compound(s) produced by L. reuteri that were TNF-inhibitory. Hydrophilic interaction liquid chromatography-high performance liquid chromatography (HILIC-HPLC) separation isolated TNF-inhibitory compounds, and HILIC-HPLC fraction composition was determined by NMR and mass spectrometry analyses. Histamine was identified and quantified in TNF-inhibitory HILIC-HPLC fractions. Histamine is produced from L-histidine via histidine decarboxylase by some fermentative bacteria including lactobacilli. Targeted mutagenesis of each gene present in the histidine decarboxylase gene cluster in L. reuteri 6475 demonstrated the involvement of histidine decarboxylase pyruvoyl type A (hdcA), histidine/histamine antiporter (hdcP), and hdcB in production of the TNF-inhibitory factor. The mechanism of TNF inhibition by L. reuteri-derived histamine was investigated using Toll-like receptor 2 (TLR2)-activated human monocytoid cells. Bacterial histamine suppressed TNF production via activation of the H₂ receptor. Histamine from L. reuteri 6475 stimulated increased levels of cAMP, which inhibited downstream MEK/ERK MAPK signaling via protein kinase A (PKA) and resulted in suppression of TNF production by transcriptional regulation. In summary, a component of the gut microbiome, L. reuteri, is able to convert a dietary component, L-histidine, into an immunoregulatory signal, histamine, which suppresses pro-inflammatory TNF production. The identification of bacterial bioactive metabolites and their corresponding mechanisms of action with respect to immunomodulation may lead to improved anti-inflammatory strategies for chronic immune-mediated diseases.

The role of histamine H1 receptor and H2 receptor in LPS-induced liver injury

To examine the role of histamine H1 and H2 receptors in the regulation of lipopolysaccharide (LPS)-induced liver injury, a combination of D-galactosamine and LPS (GalN/LPS) was administered to histamine H1 receptor knockout (H1-R KO) and H2 receptor knockout (H2-R KO) mice. The numbers of necrotic and apoptotic hepatocytes in the liver, as well as the levels of serum aspartate transaminase (AST) and alanine transaminase (ALT), were increased significantly by GalN/LPS treatment compared to the appropriate controls. Pretreatment with histamine ameliorated the GalN/LPS-induced necrotic and apoptotic changes in the hepatocytes and inhibited the elevation of serum AST and ALT levels. Histamine attenuated the GalN/LPS-induced increases in the levels of TNF-alpha, but augmented those of IL-10 both in the liver and serum. Histamine inhibited the GalN/LPS-induced caspase-3 activity in the liver. Furthermore, these effects of histamine were completely or partially attenuated in H2-R KO mice, but not in H1-R KO mice. Peritoneal macrophages from H2-R KO mice exhibited blunted changes in the effects of histamine on LPS-induced TNF-alpha and IL-10 production in vitro compared to the wild-type (WT) controls. In summary, the present findings suggest that the histamine H2-R-TNF-alpha and -IL-10 pathways play protective roles in endotoxin-induced hepatic injury.

Septic shock

Septic shock, the most severe complication of sepsis, is a deadly disease. In recent years, exciting advances have been made in the understanding of its pathophysiology and treatment. Pathogens, via their microbial-associated molecular patterns, trigger sequential intracellular events in immune cells, epithelium, endothelium, and the neuroendocrine system. Proinflammatory mediators that contribute to eradication of invading microorganisms are produced, and anti-inflammatory mediators control this response. The inflammatory response leads to damage to host tissue, and the anti-inflammatory response causes leucocyte reprogramming and changes in immune status. The time-window for interventions is short, and treatment must promptly control the source of infection and restore haemodynamic homoeostasis. Further research is needed to establish which fluids and vasopressors are best. Some patients with septic shock might benefit from drugs such as corticosteroids or activated protein C. Other therapeutic strategies are under investigation, including those that target late proinflammatory mediators, endothelium, or the neuroendocrine system.

Blockade of histamine H2 receptors of the periaqueductal gray and inferior colliculus induces fear-like behaviors

Electrical and chemical stimulation of the dorsal periaqueductal gray matter (dPAG) and the inferior colliculus (IC) induces escape behavior, usually accompanied by autonomic responses and antinociception. Recently, we presented evidence for a tonic inhibitory control exerted by H(2) histamine receptors on defensive behaviors generated in these midbrain tectum sites. Since treatments of these areas that elicit the defensive behavior repertoire frequently also have anxiogenic effects, we here used the elevated plus-maze (EPM) test for assessing the effects of microinjections of histamine (5-40 nmol), dimaprit (5-10 nmol) and ranitidine (10-30 nmol) into either dPAG or IC, which have a relative abundance of histamine-containing cells and histaminergic receptors. Dimaprit is an agonist and ranitidine is an antagonist of H(2) histamine receptors. Immediately after the injections, the animals were submitted to the EPM test. Whereas dPAG injections of dimaprit had no behavioral effects, histamine (40 nmol) caused a significant reduction in exploratory activity. On the other hand, ranitidine alone or following saline had aversive-like effects in both structures, i.e. reduced open arm, but not closed arm, entries. This pattern is usually interpreted as representing an anxiogenic effect. These effects were more pronounced after injection into dPAG than into IC. Freezing, the most prominent effect produced by ranitidine, was significantly inhibited by histamine as well as dimaprit. Thus, H(2) receptor blockade has fear-like action in the midbrain tectum with predominance in the dPAG. Such an action can be understood as a concomitant of defensive behavior, which has been shown to be a consequence of H(2) receptor antagonism in both dPAG and IC. The functional significance of the different effects of H(2) receptor blockade in dPAG and IC is discussed in the light of the probable distinct roles of these structures in the organization of defensive behavior.

Influence of Histamine in a Liver Injury Model Induced by Propionibacterium acnes and Lipopolysaccharide

In normal mice, plasma histamine levels were 29.4+/-10.1 pmol/ml. When 0.1 microg of lipopolysaccharide (LPS) was intravenously injected into Propionibacterium acnes (P. acnes)-primed ICR mice, histamine levels increased remarkably to 61.2+/-15.9 pmol/ml (p<0.001). An increase was also observed in liver tissues. Oral administration of histidine at 200 mg/kg once daily for 5 d before intravenous LPS injection increased the plasma alanine aminotransferase (ALT) activity to 2936.5+/-356.3 IU/l, a significant change compared with the controls (2244.8+/-425.5 IU/l, p<0.05). The 24 h survival rate after LPS injection was 72.7% in the mice treated with 50 mg/kg of ranitidine, in contrast with 50% in the control group although the treatment did not significantly decrease the plasma ALT activity. On the other hand, 50 mg/kg of pyrilamine significantly reduced plasma ALT activity (p<0.001). The results suggested that histamine levels are related to hepatic damage in the P. acnes plus LPS induction of liver injury.

Accelerated clearance of Escherichia coli in experimental peritonitis of histamine-deficient mice

We prepared a model of experimental peritonitis by introducing Escherichia coli into the peritoneal cavity of the histamine-deficient mice generated by a disruption of the gene for histidine decarboxylase (HDC), the unique histamine-synthesizing enzyme. When we inoculated E. coli into the peritoneal cavities of the HDC(-/-) (histamine-deficient) mice, they eliminated E. coli more efficiently than did the wild-type mice. Histamine was released efficiently from the peritoneal cells after E. coli inoculation in HDC(+/+) mice, although only trace amounts were detected in the peritoneal cells of HDC(-/-) mice. Two histamine agonists (6-[2-(4-imidazolyl)ethylamino]-N-(4-trifluoromethylphenyl)hepatanecarboxamide (H(1)) and dimaprit (H(2))) impaired the clearance of E. coli from the peritoneal cavity in HDC(-/-) mice, suggesting that the activation of both H(1) and H(2) receptors suppresses the clearance. In contrast, two kinds of H(1) and H(2) receptor antagonists, cimetidine and pyrilamine, promoted the clearance of E. coli in HDC(+/+) mice. Phagocytosis appeared to be enhanced in HDC(-/-) mice, since the number of neutrophils in the peritoneal cavity of HDC(-/-) mice was markedly increased. This enhanced recruitment of neutrophils was suppressed in the presence of the histamine agonists, 6-[2-(4-imidazolyl)ethylamino]-N-(4-trifluoromethylphenyl)hepatanecarboxamide and dimaprit. In this report histamine was first shown to be an important mediator in an E. coli infectious peritonitis model, causing a delay in the elimination of bacteria. This also raised the possibility of the use of antihistamine drugs for bacterial infection.

Identification of a nitric oxide-regulated zinc finger containing transcription factor using motif-directed differential display

We report here the isolation of human zinc finger 2 (HZF2), a putative zinc-finger transcription factor, by motif-directed differential display of mRNA extracted from histamine-stimulated human vein endothelial cells. The expression of HZF2 mRNA in venous endothelial cells was verified by Northern blot analysis, which also revealed an enrichment of HZF2 mRNA in lymphocytes and monocytes. Histamine induced a time- and concentration-dependent upregulation of HZF2 level with a 6-fold peak increase of mRNA at 30 min. HZF2 upregulation was abolished by different NOS isozyme inhibitors. Guanylate cyclase inhibition resulted in a significant decrease of HZF2 expression. These observations indicate HZF2 as a potentially interesting new target for studies concerning rapid NO-mediated gene regulation.

Isolation and characterisation of the human rab18 gene after stimulation of endothelial cells with histamine

Here we report the isolation of a cDNA encoding the complete human rab18 protein from histamine-stimulated endothelial cells using differential display. The amino acid sequence showed 98% homology with the previously isolated mouse rab18 protein, which is implicated in apical/basolateral endocytosis. Northern blot analysis revealed two transcripts (2.5 kb and 1 kb) ubiquitously expressed in all examined organs, as well as in human umbilical vein endothelial and aortic cells. In blood cells rab18 transcripts were hardly detectable. The histamine-induced time-dependent increase of rab18 mRNA expression in human umbilical vein endothelial cells and peripheral blood mononuclear cells indicates for the first time a link between receptor-mediated signal transduction and the regulation of rab gene expression. This finding might also imply a role for rab proteins in inflammation.

Modulation by cytokines of induction of oral tolerance to type II collagen

OBJECTIVE

To determine whether the simultaneous administration of drugs and/or cytokines such as transforming growth factor beta (TGFbeta) can render oral tolerance to type II collagen (CII) more effective in causing resistance to collagen-induced arthritis (CIA) in mice, and to investigate whether oral tolerance can still be induced when high levels of anti-CII are present.

METHODS

Tolerance was induced by intragastric feeding of low-dose CII to DBA/1 mice during a 2-week period, either before immunization with CII in Freund's complete adjuvant or after initiation of arthritis. Some mice were simultaneously injected with TGFbeta1 or with the H2 receptor agonist dimaprit.

RESULTS

Both TGFbeta1 and dimaprit increased the degree of oral tolerance obtained. TGFbeta1 augmented the induction of immunoregulatory CD8 T cells, which transferred the resistance to CIA induction to normal recipients. Feeding of CII for 2 weeks, starting after the onset of arthritis, still significantly ameliorated the course of CIA.

CONCLUSION

Administration of TGFbeta1 or dimaprit, both of which are believed to promote the development of immunoregulatory T cells, may reinforce induction of oral tolerance, even after the onset of arthritis.