Downregulation of the Expression of Intercellular Adhesion Molecule (ICAM)-1 on Bronchial Epithelial Cells by Fenoterol, a β₂-Adrenoceptor Agonist

Abstract

Inflammatory airway disorders, such as asthma and chronic bronchitis, are characterized by overexpression of adhesion molecules on airway epithelial and endothelial cells. This phenomenon is associated with increased adherence and activation of polymorphonuclear leukocytes (PMNs). With the knowledge that β₂-adrenoceptor agonists demonstrate some anti-inflammatory activity in vitro, the present study was designed to evaluate whether fenoterol could interfere with adhesion molecule expression on airway epithelium. Human bronchial epithelial cells (HBECs), obtained by protease digestion from surgically resected bronchi, were stimulated with human recombinant interferon-γ(rh IFN-γ) in the presence of (a) fenoterol (10⁻¹²-10-⁻⁵ M); (b) dexamethasone (10-⁻¹²-10-⁻⁵ M); and (c) fenoterol and dexamethasone. Because desensitization after high-dose exposure to agonists has been described for many membrane-associated receptors, in additional sets of experiments HBECs were preexposed to fenoterol and, as control, to dexamethasone for 8 hr, then washed and stimulated with rh IFN-γ in the presence of fresh drugs. The cells were harvested after 24-hr culture and stained by specific monoclonal antibodies. The intensity of intercellular adhesion molecule-1 (ICAM-1) expression was then measured by flow cytometry analysis and expressed as mean fluorescence channel (mfc). The significant increase in ICAM-1 expression on HBECs induced by rh IFN-y was inhibited, in a dose-dependent manner, by the two drugs, but fenoterol was more efficient than dexamethasone at all of the concentrations tested (p < 0.05, all comparisons). In addition, the inhibitory activity of fenoterol was not enhanced by the simultaneous presence of dexamethasone in rh IFN-γ-stimulated HBEC cultures (p > 0.05, all comparisons). Finally, pre-exposure to fenoterol or to dexamethasone did not induce any modification of the inhibitory effect of the two drugs on ICAM-1 expression (p > 0.05, all comparisons). These results suggest that clinical efficacy of fenoterol in patients with obstructive lung disease may include downregulation of adhesion molecule expression on airway epithelial cells.

Key Words:

• Bronchial epithelial cells
• ICAM-1 expression
• Interferon-γ
• β₂-agonists