Responses to histamine and selective H2-receptor agonists in lung parenchymal strips from normal and sensitized guinea-pigs

Models to understand contractile function in the airways

Although the role of contractile function in the airways is controversial, there is general consensus on the importance of airway smooth muscle (ASM) as a therapeutic target for diseases characterized by airway obstruction, such as asthma or chronic obstructive pulmonary disease. Indeed, the use of bronchodilators to relax ASM is the most common and effective practice to treat airflow obstruction. Excessive pathologic bronchoconstriction may originate from primary alterations of ASM mechanical function and/or from the effects exerted on ASM function by disease processes, such as inflammation and remodeling. An in depth knowledge of the potentially multiple mechanisms that distinctively regulate primary and secondary alterations in ASM contractile function would be essential for the development of new therapeutic approaches aimed at preventing the occurrence or reducing the severity of bronchoconstriction. The present review discusses studies that have addressed the mechanisms of altered ASM contractile function in models of airway hyperresponsiveness. Although not comprehensively, in the present review, animal models of intrinsic airway hyperresponsiveness, normal ontogenesis, and allergic sensitization are analyzed in the attempt to summarize the current knowledge on regulatory mechanisms of ASM contractile function in health and disease. Studies in human ASM and the need for additional models to understand contractile function in the airways are also discussed.

Constitutive expression of endothelin in bronchial epithelial cells of patients with symptomatic and asymptomatic asthma and modulation by histamine and interleukin-1

BACKGROUND

An upregulation of endothelin-1 expression occurs in bronchial epithelial cells of asthmatic patients. This peptide may mediate bronchoconstriction in asthma, but the mechanisms that modulate endothelin-I synthesis and release are unknown.

OBJECTIVE

This study was done to compare the pattern of endothelin-1 expression in patients with symptomatic and asymptomatic asthma and evaluate the ability of inflammatory factors to upregulate endothelin-1 synthesis and release in the epithelial cells of subjects who are free of symptoms.

METHODS

Two groups of 10 asthmatic patients were selected. One group had symptomatic asthma with airflow obstruction and moderately to severely increased airway responsiveness. The second group was free of symptoms: they did not show airflow obstruction, and airway responsiveness was borderline or slightly increased. Bronchial biopsy specimens were obtained by means of bronchoscopy and used for immunohistochemical evaluation, epithelial cell isolation, and stimulation experiments with interleukin-1 and histamine.

RESULTS

Endothelin-1 immunoreactivity was detected in vivo in the bronchial epithelial cells of all the patients with symptoms and in only two subjects without current symptoms. Incubation of bronchial epithelial cells from patients with asymptomatic asthma with interleukin-1 or histamine, for 8 to 24 hours, resulted in increased expression of endothelin-1 messenger RNA and release of appreciable amounts of the peptide to the culture medium. Those effects were dose- and time-dependent. Histamine and interleukin-1 were effective at concentrations similar to those detected in the bronchoalveolar lavage of patients with symptomatic asthma.

CONCLUSION

Endothelin-expression is upregulated in bronchial epithelial cells of asthmatic patients with symptoms and evidence of functional derangement as compared with patients without symptoms and airflow obstruction. Exposure of cells from patients with asymptomatic asthma to factors that are released during acute exacerbation of the disease induces endothelin synthesis and release.

Activation by histamine of bronchial epithelial cells from nonasthmatic subjects

Histamine is a major mediator of the mast cells that are present between epithelial cells in asthma. In asthma, there is an increased expression of ICAM-1 and HLA-DR and an increased spontaneous release of fibronectin. The effect of histamine was tested on bronchial epithelial cells obtained by bronchial brushing from 22 nonasthmatic subjects. The activation of epithelial cells was assessed by immunocytochemical analysis of the expression of membrane markers (ICAM-1 and HLA-DR) using the alkaline phosphatase-anti-alkaline phosphatase method and the release of fibronectin (enzyme immunoassay). Time-response (three experiments) and dose-response (six experiments) curves showed that the maximal effect was obtained after an incubation time of 24 h and a dose of 1 microM of histamine. For this time course and concentration, there was a highly significant increase in the number of cells expressing ICAM-1 (before histamine: 10 +/- 11%; after histamine: 32 +/- 20%; P < 0.001) and HLA-DR (before histamine: 8 +/- 7%; after histamine: 23 +/- 20%; P < 0.001) and in the release of fibronectin (before histamine: 30 +/- 20 ng/10(5) viable cells; after histamine: 61 +/- 35 ng/10(5) viable cells; P < 0.003). Cycloheximide blocked these effects, suggesting that histamine requires protein synthesis for its action. Pyrilamine (H1-blocker) and ranitidine (H2-blocker) at a concentration of 10 microM decreased the effect of histamine. However, there was no additive effect when both antagonists were added. This study suggests that mast cells present in the airways have a role in the activation of epithelial cells.

The response of a human bronchial epithelial cell line to histamine: intracellular calcium changes and extracellular release of inflammatory mediators

Epithelial cells are likely to modulate inflammation and tissue repair in the airways, but the factors responsible for these processes remain unclear. Because human airway epithelia are infrequently available for in vitro studies, transformed epithelial cell lines are of interest as models. We therefore investigated the response of an SV-40/adenovirus-transformed human bronchial epithelial cell line (BEAS-2B) to histamine, a mediator with relevance for airway diseases. The intracellular calcium response to histamine (10(-4) M) was measured, using Fura-2 and microspectrofluorimetry. Histamine induced a transient increase in intracellular calcium that originated from intracellular sources; this effect was inhibited by the H1 receptor antagonist diphenhydramine, suggesting that BEAS cells retain functioning histamine receptors. BEAS cells were grown to confluence on microporous, collagen-coated filters, allowing measurement of vectorial release of soluble mediators. Monolayers exposed to histamine for 30 min released interleukin-6 and fibronectin in the apical direction, in a dose-dependent manner. Little eicosanoid production was induced by histamine, either in the apical or the basolateral direction, although BEAS cells constitutively produced small amounts of prostaglandin E2 and 15-HETE. However, these cells formed large amounts of eicosanoids in response to ozone exposure as a positive control. Comparison of our data with published reports for human airway epithelia in primary culture suggests that the BEAS cell line is, in a number of respects, a relevant model for the study of airway epithelial responses to a variety of stimuli.