Histamine reverses IL-5-afforded human eosinophil survival by inducing apoptosis: pharmacological evidence for a novel mechanism of action of histamine

IL-33 induces histidine decarboxylase, especially in c-kit+ cells and mast cells, and roles of histamine include negative regulation of IL-33-induced eosinophilia

OBJECTIVE AND METHODS

IL-33 is present in endothelial, epithelial, and fibroblast-like cells and released upon cell injury. IL-33 reportedly induces mast-cell degranulation and is involved in various diseases, including allergic diseases. So, IL-33-related diseases seem to overlap with histamine-related diseases. In addition to the release from mast cells, histamine is newly formed by the induction of histidine decarboxylase (HDC). Some inflammatory and/or hematopoietic cytokines (IL-1, IL-3, etc.) are known to induce HDC, and the histamine produced by HDC induction is released without storage. We examined the involvement of HDC and histamine in the effects of IL-33.

RESULTS

A single intraperitoneal injection of IL-33 into mice induced HDC directly and/or via other cytokines (including IL-5) within a few hours in various tissues, particularly strongly in hematopoietic organs. The major cells exhibiting HDC-induction were mast cells and c-kit⁺ cells in the bone marrow. HDC was also induced in non-mast cells in non-hematopoietic organs. HDC, histamine, and histamine H4 receptors (H4Rs) contributed to the suppression of IL-33-induced eosinophilia.

CONCLUSION

IL-33 directly and indirectly (via IL-5) induces HDC in various cells, particularly potently in c-kit⁺ cells and mature mast cells, and the newly formed histamine contributes to the negative regulation of IL-33-induced eosinophilia via H4Rs.

Comparative analysis of the in vitro cytotoxicity of the dietary biogenic amines tyramine and histamine

Tyramine and histamine, the most toxic biogenic amines (BA), are often found in high concentrations in certain foods. Prompted by the limited knowledge of BA toxicity, and increasing awareness of the risks associated with high intakes of dietary BA, the in vitro cytotoxicity of tyramine and histamine was investigated. Tyramine and histamine were toxic for HT29 intestinal cell cultures at concentrations commonly found in BA-rich food, as determined by real-time cell analysis. Surprisingly, tyramine had a stronger and more rapid cytotoxic effect than histamine. Their mode of action was also different, while tyramine caused cell necrosis, histamine induced apoptosis. To avoid health risks, the BA content of foods should be reduced and legal limits established for tyramine.

Histamine 1 Receptor Blockade Enhances Eosinophil-Mediated Clearance of Adult Filarial Worms

Filariae are tissue-invasive nematodes that cause diseases such as elephantiasis and river blindness. The goal of this study was to characterize the role of histamine during Litomosoides sigmodontis infection of BALB/c mice, a murine model of filariasis. Time course studies demonstrated that while expression of histidine decarboxylase mRNA increases throughout 12 weeks of infection, serum levels of histamine exhibit two peaks—one 30 minutes after primary infection and one 8 weeks later. Interestingly, mice treated with fexofenadine, a histamine receptor 1 inhibitor, demonstrated significantly reduced worm burden in infected mice compared to untreated infected controls. Although fexofenadine-treated mice had decreased antigen-specific IgE levels as well as lower splenocyte IL-5 and IFNγ production, they exhibited a greater than fourfold rise in eosinophil numbers at the tissue site where adult L. sigmodontis worms reside. Fexofenadine-mediated clearance of L. sigmodontis worms was dependent on host eosinophils, as fexofenadine did not decrease worm burdens in eosinophil-deficient dblGATA mice. These findings suggest that histamine release induced by tissue invasive helminths may aid parasite survival by diminishing eosinophilic responses. Further, these results raise the possibility that combining H1 receptor inhibitors with current anthelmintics may improve treatment efficacy for filariae and other tissue-invasive helminths.

Filariae are tissue-invasive parasitic roundworms that infect over 100 million people worldwide and cause debilitating conditions such as river blindness and elephantiasis. One of the major factors limiting our ability to eliminate these infections is the lack of drugs that kill adult worms when given as a short course therapy. Additionally, the mechanisms by which adult worms are cleared from infected individuals remains poorly understood. In this study, we demonstrate that treatment of infected mice with fexofenadine, an inhibitor of histamine receptor 1, significantly reduces adult worm numbers through a mechanism dependent on host eosinophils. These findings suggest that histamine release induced by parasitic worms may aid parasite survival by decreasing eosinophilic responses. Further, as antihistamines are generally safe medications, these results raise the possibility that antihistamine therapy may be useful either alone, or potentially in combination with other antifilarial medications such as diethylcarbamazine (DEC), to eliminate adult filarial worms from infected individuals.

Regulation of spontaneous eosinophil apoptosis-a neglected area of importance

Asthma is characterized by the accumulation of eosinophils in the airways in most phenotypes. Eosinophils are inflammatory cells that require an external survival-prolonging stimulus such as granulocyte macrophage-colony-stimulating factor (GM-CSF), interleukin (IL)-5, or IL-3 for survival. In their absence, eosinophils are programmed to die by spontaneous apoptosis in a few days. Eosinophil apoptosis can be accelerated by Fas ligation or by pharmacological agents such as glucocorticoids. Evidence exists for the relevance of these survival-prolonging and pro-apoptotic agents in the regulation of eosinophilic inflammation in inflamed airways. Much less is known about the physiological significance and mechanisms of spontaneous eosinophil apoptosis even though it forms the basis of regulation of eosinophil longevity by pathophysiological factors and pharmacological agents. This review concentrates on discussing the mechanisms of spontaneous eosinophil apoptosis compared to those of glucocorticoid- and Fas-induced apoptosis. We aim to answer the question whether the external apoptotic stimuli only augment the ongoing pathway of spontaneous apoptosis or truly activate a specific pathway.

Development and validation of a rapid liquid chromatographic method for the determination of oxatomide and its related impurities

A rapid liquid chromatographic method was developed for the determination of oxatomide in its finished active pharmaceutical ingredient form and in the presence of its process impurities. The method was developed on a sub 2 µm Hypersil Zorbax XDB C18 column (30 × 4.6 mm, i.d., 1.8 µm). The rapid method employed a gradient mobile phase consisting of solvent A: 0.01 M tetrabutylammonium hydrogen sulfate and 0.5% (w/v) ammonium acetate in water and solvent B: acetonitrile. A flow rate of 2 mL/min was employed with the diode-array detector set at 230 nm. The original method supplied by Janssen Pharmaceuticals Ltd was run on a Thermo Scientific octadecylsilyl silica gel C18 column (100 × 4.6 mm, i.d., 5 µm) with an analysis time of 20 min. The main aim was to substantially reduce the analysis time while maintaining good efficiency. Run-time was reduced to 6.5 min with a total loss in analysis time of 68%. Solvent consumption was also reduced by 68%. Validation according to the International Conference of Harmonization guidelines was undertaken. The parameters examined were accuracy, precision, linearity, selectivity, robustness, limit of detection and limit of quantification; all criteria were met. Sample stability testing was also carried out. Oxatomide proved stable under ambient and 4°C temperatures and in the presence of light for up to 24 h.

Eosinophil intracellular signalling: apoptosis

Eosinophil apoptosis is considered critical for the resolution of eosinophilic inflammation in the airways of asthmatics. Apoptosis can be mediated by an extrinsic receptor-activated pathway or alternatively by an intrinsic pathway via distortion of mitochondrial function. Both of these pathways lead to activation of the caspase cascade resulting in degradation of cellular components. We describe here two methods to explore intracellular mechanisms mediating eosinophil apoptosis. Eosinophil staining by fluorescent probe JC-1 followed by flow cytometric analysis is a reliable method for determination of the state of mitochondrial membrane potential (∆Ψm). Lost ∆Ψm indicates distorted mitochondrial function and apoptosis. We also describe a method to explore the activation of effector caspase-6 by assessing degradation of its substrate lamin A/C by immunoblotting.

Physical interactions between mast cells and eosinophils: a novel mechanism enhancing eosinophil survival in vitro

BACKGROUND

Mast cells (MCs) and eosinophils (Eos) are the key effector cells of the allergic reaction. Although classically associated with different stages of the response, the cells co-exist in the inflamed tissue in the late and chronic phases in high numbers and are likely to cross-talk. While some mediators of MCs are known to affect Eos biology and vice versa, paracrine and physical interplay between the two cells has not been described yet. We aimed to investigate whether intercellular MC-Eos communication could take place in the allergic response and exert functional bidirectional changes on the cells.

METHODS

Tissue sections from various allergic disorders were specifically stained for both cells. Human cord blood-derived MCs and peripheral blood Eos, co-cultured under different conditions, were studied by advanced microscopy and flow cytometry.

RESULTS

Several co-localized MC-Eos pairs were detected in human nasal polyps and asthmatic bronchi, as well in mouse atopic dermatitis. In vitro, MCs and Eos formed stable conjugates at high rates, with clear membrane contact. In the presence of MCs, Eos were significantly more viable under several co-culture conditions and at both IgE-activated and steroid-inhibited settings. MC regulation of Eos survival required communication through soluble mediators but was even more dependent on physical cell-cell contact.

CONCLUSIONS

Our findings provide the first evidence for a complex network of paracrine and membrane interactions between MCs and Eos. The prosurvival phenotype induced by this MC-Eos interplay may be critical for sustaining chronic allergic inflammation.

Nitric oxide induces apoptosis in GM-CSF-treated eosinophils via caspase-6-dependent lamin and DNA fragmentation

Asthma is characterized by accumulation of eosinophils in the lungs and delayed apoptosis may be one mechanism leading to eosinophilia. Nitric oxide (NO), present in inflamed lungs, has been shown to possess both anti- and proeosinophilic properties. We previously showed that NO induces apoptosis in the presence of survival prolonging cytokine IL-5 in human eosinophils. In the present study, we examined the intracellular mechanisms of NO-induced apoptosis in granulocyte macrophage-colony stimulating factor (GM-CSF)-treated eosinophils concentrating on the role of caspases and calpains. Eosinophils were isolated from human blood and apoptosis was determined by relative DNA fragmentation assay, morphological analysis and/or Annexin-V FITC assay. We showed that NO-donor S-nitroso-N-acetyl-d,l-penicillamine (SNAP) induced apoptosis in GM-CSF-treated eosinophils. SNAP-induced DNA fragmentation was totally prevented by an inhibitor of caspase-6 (Z-VEID-FMK). Decreased levels of caspase-6 proenzyme and increased amounts of cleaved lamin A/C in SNAP-treated cells indicated activation of caspase-6. Furthermore, SNAP-induced lamin A/C and B fragmentation was totally abolished by an inhibitor of caspase-6. According to our results, caspase-6 mediates lamin and DNA fragmentation also in spontaneously dying eosinophils. Inhibitor of calpains prevented most of DNA fragmentation related to spontaneous apoptosis but had no effect in eosinophils undergoing NO-induced apoptosis. In the present study we showed that caspase-6 is essential for the executive phase involving lamin and DNA fragmentation in both NO-induced and spontaneous eosinophil apoptosis. However, differences in the involvement of calpains suggest that the intracellular signalling in NO-induced apoptosis has specific features at the level of proteases. This study demonstrates new mechanisms for NO-induced and spontaneous apoptosis in human eosinophils.