Inhibition of chemiluminescence in granulocytes and alveolar macrophages by azelastine

Interleukin-1beta attenuates endothelin B receptor-mediated airway contractions in a murine in vitro model of asthma: roles of endothelin converting enzyme and mitogen-activated protein kinase pathways

BACKGROUND

Asthma is a chronic airway disease, known to involve several inflammatory mediators. Little is known about how these mediators interact in order to produce or attenuate even basic features of the disease, like airway hyper-reactivity and remodelling. Endothelin-1 (ET-1) and IL-1beta are two mediators suggested to play important roles in the induction of airway inflammation.

OBJECTIVE

To investigate the interactions between ET-1 and IL-1beta, using a novel in vitro model of asthma, focusing on airway smooth muscle contractility.

METHODS

Isolated murine tracheal segments were cultured from 1 to 8 days in the absence and presence of IL-1beta. The subsequent contractile responses to sarafotoxin 6c (S6c) (selective agonist for ETB receptor) and sarafotoxin 6b (S6b) (ETA and ETB receptor agonist) were recorded by a myographs system. In all experiments, ETB receptors were desensitized before the contractile response to S6b was recorded. Thus, the response to S6b is only mediated by ETA receptors in the present study. The mRNA expressions for ET-1 and endothelin (ET) receptors were quantified by real-time PCR.

RESULTS

Organ culture in the presence of IL-1beta attenuated the maximal contraction induced by S6c, but not S6b. This reduction was concentration-dependent and was significant after 2, 4 and 8 days of culture. To investigate the mechanisms behind this, inhibitors for endothelin converting enzyme (ECE) phosphoramidon, c-JUN N-terminal kinase (JNK) SP600125, extracellular-signal-regulated kinase 1/2(ERK 1/2) PD98059 and p38 pathway SB203580 were used. Individually, SP600125 and PD98059, but not SB203580, could partly reverse the reduction induced by IL-1beta. An additional effect was obtained when SP600125 and PD98059 were combined. The mRNA expressions for ET-1 and ETB receptor were up- and down-regulated, respectively, by IL-1beta.

CONCLUSION

Presence of IL-1beta in the airways attenuate the contractile response mediated via ETB receptors, an effect dependent on ECE, JNK and ERK 1/2 pathways.

H1-antihistamines: inverse agonism, anti-inflammatory actions and cardiac effects

This review addresses novel concepts of histamine H1-receptor function and attempts to relate them to the anti-inflammatory effects of H1-antihistamines. Furthermore, the molecular mechanisms underlying the cardiotoxic effects of H1-antihistamines are discussed. H1-receptors are G-protein-coupled-receptors (GPCRs), the inactive and active conformations of which coexist in equilibrium. The degree receptor activation in the absence of histamine is its 'constitutive activity'. In this two-state model, histamine acts as an agonist by combining with and stabilizing the activated conformation of the H1-receptor to shift the equilibrium towards the activated state. Drugs classified previously as antagonists act as either inverse agonists or neutral antagonists. Inverse agonists combine with and stabilize the inactive conformation of the receptor to shift the equilibrium towards the inactive state. Thus, they may down-regulate constitutive receptor activity, even in the absence of histamine. Neutral antagonists combine equally with both conformations of the receptor, do not affect basal receptor activity but do interfere with agonist binding. All H1-antihistamines examined to date are inverse agonists. As the term 'H1-receptor antagonists' is obviously erroneous, we suggest that it be replaced by 'H1-antihistamines'. The observations that H1-receptors modulate NF-kappaB activation and that there are complex interactions between GPCRs, has allowed us to postulate receptor dependent-mechanisms for some anti-inflammatory effects of H1-antihistamines, e.g. inhibition of ICAM-1 expression and the effects of bradykinin. Finally, the finding that blockade of HERG1 K+ channels is the mechanism by which some H1-antihistamines may cause cardiac arrhythmias has allowed the development of preclinical tests to predict such activity.

Differential adrenomedullin release and endothelin receptor expression in distinct subpopulations of human airway smooth-muscle cells

Although adrenomedullin (ADM) is implicated in the control of airway tone, regulation of ADM release from airway smooth-muscle cells (ASMCs) has not been explored. Preliminary experiments have indicated that human ASMC populations were heterogeneous in their rate of ADM release and expression of endothelin (ET)(A) and ET(B) receptors. We isolated these phenotypically distinct ASMCs from explants derived from the same airway segment. ASMCs possessing exclusively ET(A) receptors appeared smaller and proliferated faster than ET(A)/ET(B) isolates. Macroautoradiographic analysis confirmed the presence of both receptors in human bronchi. ADM release and messenger RNA expression was greater in ET(A)/ET(B) isolates compared with ET(A) isolates. No measurable ET release was detected from ASMCs. Exogenous ET-1 (1 to 100 nM) more potently stimulated the release of ADM from ET(A)/ET(B) compared with ET(A) isolates. In addition, ET-3 (1 to 100 nM) stimulated ADM release only from ET(A)/ET(B) isolates, implicating the ET(B) receptor in this response. Exogenous ET-1 potentiated platelet- derived growth factor-stimulated [3H]thymidine uptake in ET(A)/ ET(B) but not ET(A) isolates. ET-3 did not affect [3H]thymidine uptake in either cell type. Possession of ET(A)/ET(B) receptors is associated with higher rates of ADM release and slower proliferation, but a capacity for ET-1 stimulated DNA synthesis via ET(A) receptors. These results support a paracrine role for the regulation of ADM release predominantly via the ET(B) receptor in human ASMCs.

Endothelin-1-induced bronchoconstriction in asthma

Endothelin-1 (ET-1) has been indirectly implicated in the pathophysiology of asthma, and it is a potent bronchoconstrictor both in vitro and by inhalation in animal models in vivo. We examined the effect of inhaled ET-1 on airway tone in comparison with methacholine in eight asthmatics and five healthy volunteers in a double-blind randomized fashion. After a screening methacholine challenge each asthmatic had two ET-1 (doubling dose range, 0.96 to 15.36 nmol) and one methacholine (doubling dose range, 0.33 to 21.0 mumol) challenge, and normal subjects had a single ET-1 challenge. Inhalations were delivered using a dosimeter, and lung function measurements were made using constant-volume body plethysmography, with end points being a 35% fall in specific airway conductance (SGaw) and a 15% fall in FEV1. Samples for plasma ET-1 were taken before and after the inhalations, and pulse, blood pressure and oxygen saturation were monitored throughout the inhalations. All the asthmatic subjects displayed rapid-onset (< 5 min) dose-dependent bronchoconstriction to ET-1 across the dose range used, with mean (range) ET-1 PC35SGaw values of 5.15 (1.4 to 13.9) nmol, and 4.3 (1.2 to 8.3) nmol for the two ET-1 inhalations, and 0.42 (0.2 to 0.7) mumol for methacholine. Albuterol completely and rapidly reversed ET-1-induced bronchoconstriction, and in two patients not given albuterol, bronchoconstriction lasted 60 to 90 min. No significant bronchoconstriction was observed in any of the healthy volunteers across the ET-1 dose range used (mean PC35SGaw > 15.36 nmol). Oxygen saturation did not alter in either group, and plasma ET-1 did not change after ET-1 inhalation. Noninvasive blood pressure measurements revealed a fall in systolic blood pressure in normal subjects, with no change in asthmatics. Endothelin-1 is a potent bronchoconstrictor in asthma, with a bronchoconstrictor potency around 100 times that of methacholine in asthma. Asthmatics exhibit bronchial hyperreactivity to ET-1, and inhaled ET-1 can safely be given to asthmatics and normal subjects in the nebulized dose range 0.96 to 15.36 nmol.

Influence of azelastine and some selected drugs on mucociliary clearance

The effect of azelastine and some selected compounds on ciliary beating frequency (CBF) was investigated in vitro using human mucosal samples and in vivo using anesthetized guinea pigs. Further influence of azelastine on mucus secretion was evaluated in mice and on mucociliary clearance in anesthetized rabbits. Azelastine influenced the ciliary beating frequency neither in vitro nor in vivo. Azelastine, similarly to salbutamol, ambroxol, and bromhexine, increased mucus secretion measured by the tracheal output of phenol red. Azelastine dose-dependently enhanced mucociliary clearance measured by elimination of 99mTc-labeled erythrocytes in rabbits. The activity of azelastine proved to be about 10 times stronger than that of bromhexine. Since the ciliary activity remained unchanged under the influence of azelastine, it is likely that azelastine increases the mucociliary clearance by enhancing bronchial secretion. It is possible that the observed increase in mucociliary clearance may contribute to the beneficial effect of azelastine in the treatment of respiratory diseases.

Influence of azelastine on IL-1 beta generation in vitro and IL-1 beta-induced effect in vivo

The effects of the novel antiasthmatic/antiallergic compound azelastine on IL-1 beta were investigated in vitro and in vivo. In leukocytes both, intra- and extracellular IL-1 generation stimulated by LPS was inhibited dose dependently. In contrast azelastine did not prevent IL-1 beta-induced immigration of PMNs into the mouse ear. These findings suggest that azelastine is not an IL-1 antagonist but inhibits IL-1 synthesis and/or release in leukocytes.