Beyond the histamine receptor: effect of antihistamines on mast cells

The Effect of Levagen+ (Palmitoylethanolamide) Supplementation on Symptoms of Allergic Rhinitis-A Double-Blind Placebo-Controlled Trial

BACKGROUND

Allergic rhinitis (AR) is an inflammatory, symptomatic disorder stimulated by antigen-specific immunoglobulin E inflammation in response to allergens. Current treatments include the use of corticosteroids and antihistamines to reduce inflammation by preventing histamine release. Palmitoylethanolamide (PEA) is reported to be an alternative treatment, shown to downregulate mast cell activation and increase the synthesis of endocannabinoid 2-Arachidonoylglycerol to reduce histamine and the symptoms of AR.

METHOD

A double-blind, randomised, placebo-controlled clinical trial in which 108 participants presenting with seasonal AR were supplemented with either 350 mg of PEA (Levagen+) or a placebo daily for two weeks. Symptom scores were recorded using the reflective total nasal symptom score (rTNSS) twice a day (morning and evening) for the two weeks, and blood was taken at baseline and week 2.

RESULTS

101 participants completed the study with no baseline group differences. No significant difference was seen between groups for allergy symptoms scores (rTNSS) throughout the 14 days of treatment. A sub-group analysis of participants scoring over four (mild-to-moderate) on the total rTNSS at baseline showed that Levagen+ significantly reduced scores compared to the placebo group. Only 36 participants had full sets of blood taken due to COVID-19. The pathology results showed a significant difference in change from baseline between groups. The Levagen+ group had a significant decrease from baseline in histamine, IL-4, IL-8, IL-10, and TNF-α. The placebo group only had a reduction in IL-4.

CONCLUSION

The results of this study show that Levagen+ can alleviate AR symptoms, resulting in a reduction in histamine and inflammatory markers.

T helper 2 and regulatory T-cell cytokine production by mast cells: a key factor in the pathogenesis of IgG4-related disease

IgG4-related disease is a systemic disorder with unique clinicopathological features and uncertain etiological features and is frequently related to allergic disease. T helper 2 and regulatory T-cell cytokines have been reported to be upregulated in the affected tissues; thus, the production of these cytokines by T helper 2 and regulatory T cells has been suggested as an important factor in the pathogenesis of IgG4-related disease. However, it is not yet clear which cells produce these cytokines in IgG4-related disease, and some aspects of the disorder cannot be completely explained by T-cell-related processes. To address this, we analyzed paraffin-embedded sections of tissues from nine cases of IgG4-related submandibular gland disease, five cases of submandibular sialolithiasis, and six cases of normal submandibular gland in order to identify potential key players in the pathogenesis of IgG4-related disease. Real-time polymerase chain reaction analysis confirmed the significant upregulation of interleukin (IL)4, IL10, and transforming growth factor beta 1 (TGFβ1) in IgG4-related disease. Interestingly, immunohistochemical studies indicated the presence of mast cells expressing these cytokines in diseased tissues. In addition, dual immunofluorescence assays identified cells that were double-positive for each cytokine and for KIT, which is expressed by mast cells. In contrast, the distribution of T cells did not correlate with cytokine distribution in affected tissues. We also found that the mast cells were strongly positive for IgE. This observation supports the hypothesis that mast cells are involved in IgG4-related disease, as mast cells are known to be closely related to allergic reactions and are activated in the presence of elevated non-specific IgE levels. In conclusion, our results indicate that mast cells produce T helper 2 and regulatory T-cell cytokines in tissues affected by IgG4-related disease and possibly have an important role in disease pathogenesis.

Mast cell dependent vascular changes associated with an acute response to cold immersion in primary contact urticaria

BACKGROUND

While a number of the consequences of mast cell degranulation within tissues have been documented including tissue-specific changes such as bronchospasm and the subsequent cellular infiltrate, there is little known about the immediate effects of mast cell degranulation on the associated vasculature, critical to understanding the evolution of mast cell dependent inflammation.

OBJECTIVE

To characterize the microcirculatory events that follow mast cell degranulation.

METHODOLOGY/PRINCIPAL FINDINGS

Perturbations in dermal blood flow, temperature and skin color were analyzed using laser-speckle contrast imaging, infrared and polarized-light colorimetry following cold-hand immersion (CHI) challenge in patients with cold-induced urticaria compared to the response in healthy controls. Evidence for mast cell degranulation was established by documentation of serum histamine levels and the localized release of tryptase in post-challenge urticarial biopsies. Laser-speckle contrast imaging quantified the attenuated response to cold challenge in patients on cetirizine. We found that the histamine-associated vascular response accompanying mast cell degranulation is rapid and extensive. At the tissue level, it is characterized by a uniform pattern of increased blood flow, thermal warming, vasodilation, and recruitment of collateral circulation. These vascular responses are modified by the administration of an antihistamine.

CONCLUSIONS/SIGNIFICANCE

Monitoring the hemodynamic responses within tissues that are associated with mast cell degranulation provides additional insight into the evolution of the acute inflammatory response and offers a unique approach to assess the effectiveness of treatment intervention.

The role of histamine H1 and H4 receptors in allergic inflammation: the search for new antihistamines

Histamine has a key role in allergic inflammatory conditions. The inflammatory responses resulting from the liberation of histamine have long been thought to be mediated by the histamine H1 receptor, and H1-receptor antagonists--commonly known as antihistamines--have been used to treat allergies for many years. However, the importance of histamine in the pathology of conditions such as asthma and chronic pruritus may have been underestimated. Here, we review accumulating evidence suggesting that histamine indeed has roles in inflammation and immune function modulation in such diseases. In particular, the discovery of a fourth histamine receptor (H4) and its expression on numerous immune and inflammatory cells has prompted a re-evaluation of the actions of histamine, suggesting a new potential for H4-receptor antagonists and a possible synergy between H1 and H4-receptor antagonists in targeting various inflammatory conditions.

Treatment of eosinophilic esophagitis: drugs, diet, or dilation?

A number of recent studies have demonstrated that a variety of treatments effectively improve symptoms and histology in the majority of patients with eosinophilic esophagitis. Therapeutic options include pharmacologic treatments, such as oral and topical corticosteroids and leukotriene-receptor antagonists. In children, the high response rates to dietary modification and elimination suggest that certain foods may serve as environmental triggers for the eosinophilic infiltration. Because many adults present with strictures, endoscopic esophageal dilation is another management modality. Despite these treatment options, several controversies exist in the recommended treatment strategy. Whether the goal of therapy is resolution of symptoms, tissue eosinophilia, or both remains uncertain owing to the paucity of data on the natural history of the condition. Furthermore, important differences in the clinical presentations of eosinophilic esophagitis in children and adults point toward the possible need for different treatment approaches in the two patient populations.

Inflammatory basis of exercise-induced bronchoconstriction

RATIONALE

Exercise-induced bronchoconstriction (EIB) is a highly prevalent condition with unclear pathogenesis. Two competing theories of the pathogenesis of EIB differ regarding the inflammatory basis of this condition.

OBJECTIVES

Our goals were to establish whether epithelial cell and mast cell activation with release of inflammatory mediators occurs during EIB and how histamine and cysteinyl leukotriene antagonists alter the airway events occurring during EIB.

METHODS

Induced sputum was used to measure mast cell mediators and eicosanoids at baseline and 30 minutes after exercise challenge in 25 individuals with asthma with EIB. In a randomized, double-blind crossover study, the cysteinyl leukotriene antagonist montelukast and antihistamine loratadine or two matched placebos were administered for two doses before exercise challenge.

MAIN RESULTS

The percentage of columnar epithelial cells in induced sputum at baseline was associated with the severity of EIB. After exercise challenge, histamine, tryptase, and cysteinyl leukotrienes significantly increased and prostaglandin E(2) and thromboxane B(2) significantly decreased in the airways, and there was an increase in columnar epithelial cells in the airways. The concentration of columnar epithelial cells was associated with the levels of histamine and cysteinyl leukotrienes in the airways. Treatment with montelukast and loratadine inhibited the release of cysteinyl leukotrienes and histamine into the airways, but did not inhibit the release of columnar epithelial cells into the airways.

CONCLUSIONS

These data indicate that epithelial cells, mast cell mediators, and eicosanoids are released into the airways during EIB, supporting an inflammatory basis for EIB.

Role of histamine and platelet-activating factor in allergic rhinitis

This review is focused on the effects of histamine and platelet-activating factor (PAF) in allergic rhinitis and the plausible implications for therapy. Rhinitis is defined as a heterogeneous disorder resulting from an IgE-mediated reaction associated with nasal inflammation of variable intensity. Two phases of response are triggered by an IgE/allergen cross-linking event: the first is the release of preformed mediators such as histamine or interleukins from mast cells and basophils; the second begins when cells start producing lipid-derived mediators. One of these mediators is PAF. Apart from leukotrienes, PAF is perhaps the most potent inflammatory mediator in allergic rhinitis for inducing vascular leakage, a response that may contribute to the appearance of rhinorrhea and nasal congestion.

Human skin mast cells express H2 and H4, but not H3 receptors

Mast cells generate and release histamine during anaphylactic reactions, and there is pharmacological evidence that histamine regulates this process via specific receptors. Therefore, we examined human leukemic (HMC-1) and normal skin mast cells for the expression of all four currently known histamine receptors. Both cell types expressed H2 and H4 receptors at mRNA and protein levels, whereas H3 receptor specific mRNA and receptor protein was undetectable. Similarly, immunohistochemistry of cutaneous tissue showed an absence of H3 receptor in these cells. Despite transcription of mRNA, H1 receptor protein was only moderately expressed in HMC-1 cells and was virtually absent in skin mast cells. Furthermore, only H1, H2, and H4 receptors were detectable by Western blot analysis of HMC-1 cells. Radiolabeled histamine binding was strongly inhibited only by H2 (ranitidine)- and H3/H4 (FUB 108)-specific antagonists. Histamine-induced increase of cAMP was inhibited by the H2 receptor antagonist famotidine, whereas induction of IP3 was not observed, making signaling via the H1 receptor unlikely. These data show that human mast cells constitutively express primarily H2 and H4 receptors and that H2 receptors are functionally linked to cellular processes. They provide new insights into the mechanisms that govern auto- and paracrine histamine-induced mast cell functions.

Endoscopy in eosinophilic esophagitis: "feline" esophagus and perforation risk

BACKGROUND & AIMS

Idiopathic eosinophilic esophagitis is an underdiagnosed disease with typical endoscopic findings, which have not been well described.

METHODS

Charts and pathology reports at two tertiary care centers from June 1993 to April 2002 were reviewed to describe the endoscopic findings of this disease and to correlate them with clinical characteristics. Eight patients were identified as having eosinophilic esophagitis based on clinical symptoms and pathology reports.

RESULTS

Soft and subtle ring(s) in the esophagus were found in 7 of 8 patients. In 3 of 8 patients, the esophagus appeared rigid. Mucosal rents occurred with simple passage of the endoscope in 5 of 8 patients. One patient developed a perforation after simple passage of the endoscope. Endoscopic findings can be normal or very subtle in these patients, and the findings can easily be missed during endoscopy. Tearing of the esophagus can occur with simple passage of the endoscope or biopsy even in the absence of overt rings. A minimum of 8 weeks of medical therapy (proton pump inhibitor, histamine antagonists, immunosuppressants) should be undertaken before considering dilation because of the high risk involved with the procedure and the good response to medical therapy.

CONCLUSIONS

We recommend considering dilation only in patients with eosinophilic esophagitis who do not respond to medical therapy and have rings that appear to be obstructing the lumen.

A role for histamine in cytokine modulation by the adenosine A(3) receptor agonist, 2-Cl-IB-MECA

The effects of adenosine receptor agonists on cytokine production in vivo were investigated in mouse models of endotoxemia. Selective adenosine A(3) (2-chloro-N(6)-(3-iodobenzyl) adenosine-5'-N-methyluronamide) (2-Cl-IB-MECA) and A(2A) (2-p-(2-carboxyethyl) phenethylamino-5'-N-ethylcarboxamido adenosine hydrochloride) (CGS 21860) receptor agonists were found to modulate endotoxin-induced cytokine responses in mice sensitized to D-galactosamine or primed with Corynebacterium parvum. The adenosine receptor agonists had similar effects in these models of endotoxemia, suppressing the production of tumor necrosis factor alpha (TNF-alpha) and interleukin-12 while enhancing that of interleukin-10. However, 2-Cl-IB-MECA also caused a dramatic increase in circulating histamine levels shortly after its injection into mice. The cytokine modulatory activities of 2-Cl-IB-MECA were mimicked by the mast cell depleting compound 48/80 and both drugs only produced such effects at doses that caused an elevation in circulating histamine levels. Furthermore, the capacity of 2-Cl-IB-MECA to modulate cytokine responses was greatly diminished when the drug was administered to mast cell deficient (WBB6F-W/W(V)) mice. Together, these results strongly suggest a role for histamine in cytokine modulation by 2-Cl-IB-MECA. Cimetidine, a histamine H(2) receptor antagonist, did not reverse cytokine modulation by 2-Cl-IB-MECA and pyrilamine, a histamine H(1) receptor antagonist, prevented the increase in serum histamine that was induced by 2-Cl-IB-MECA. This effect of pyrilamine and other histamine H(1) receptor antagonists confounded attempts to determine a role for the histamine H(1) receptor in cytokine modulation by 2-Cl-IB-MECA. However, under some experimental conditions, pyrilamine appeared to antagonize the modulatory effects of the adenosine A(3) receptor agonist on cytokine responses. The apparent antagonism of pyrilamine was unrelated to its suppressive effects on histamine release and appeared to reflect activity at the level of the histamine H(1) receptor.

Fexofenadine in chronic idiopathic urticaria: a clinical and immunohistochemical evaluation

Fexofenadine is a non-sedating selective third-generation antihistamine, which also exerts an anti-inflammatory action. The aim of this study was to evaluate the influence on the expression of inflammatory skin mediators, together with the efficacy and tolerability, of fexofenadine in chronic idiopathic urticaria (CIU). Fexofenadine 180mg was administered once daily for 4 weeks after a placebo run-in phase of 3 to 7 days. Efficacy paramaters were obtained from patients' assessment of urticaria symptoms. Non-lesional skin of patients with active CIU was studied immunohistochemically before and after treatment. The expression of the following mediators was evaluated: adhesion molecules (ICAM-1, ELAM-1, VCAM-1); mast cell proteases (chymase and tryptase) and proinflammatory cytokines (IL-1beta, IL-3, IL-6 and TNF-alpha). Of the 20 subjects enrolled, 3 dropped out of the study. Treatment proved successful in most cases (88.2%) (p <0.01) and a significant improvement of all symptoms was registered. Treatment was well-tolerated by all patients; adverse events, neither serious nor drug-related, occurred in any case. Immunochemistry revealed at the baseline a significant expression of ELAM-1, VCAM-1, tryptase, chymase, and TNF-alpha (p= 0.05) in non-lesional skin of patients compared to normal controls. After treatment with fexofenadine, there was a significant decrease in the expression of ELAM-1 (p= 0.02), VCAM-1 (p= 0.04) and tryptase (p= 0.04), whereas no relevant change was observed for the other parameters examined. This work confirms the efficacy and tolerability of fexofenadine HCl 180mg in CIU. These preliminary data show a trend towards a decrease in the expression of tryptase and some adhesion molecules after treatment, suggesting an anti-inflammatory activity of fexofenadine.

Therapeutic options in allergic disease: antihistamines as systemic antiallergic agents

As has been reported throughout this supplement, the pathophysiologic factors of allergic diseases involve many elements of systemic disease-effector-cell recruitment from circulation, stimulation of bone marrow progenitors, systemic effector-cell priming, anaphylactic reactions, and others. With this understanding, allergic inflammation can be thought of as a reflection of systemic immunologic responses with compartmentalized manifestations in various organ systems, including the upper respiratory tract, lungs, gastrointestinal tract, and skin. Thus, any therapeutic approach to the treatment of allergic disease should address, in addition to the localized disease manifestations, the systemic immunologic dysregulation. Second-generation antihistamines (cetirizine, fexofenadine, loratadine) have been used since the 1980s to treat localized allergy symptoms in upper airways, skin, and, in some cases, the lungs; however, the efficacy of these agents in controlling systemic immune dysregulation and chronic allergic inflammation (eg, nasal congestion) has not been proved. The potential role of newer antihistamines in the amelioration of both localized and systemic aspects of allergic disease represents an active area of interest. Desloratadine, a new selective histamine H(1)-receptor antagonist with potent antihistaminic and anti-inflammatory activity, is introduced and its potential for treating the systemic aspects of allergic disease is discussed.