Estrogen Increases Nitric-Oxide Production in Human Bronchial Epithelium

Although sex differences in asthma severity are recognized, the mechanisms by which sex steroids such as estrogen influence the airway are still under investigation. Airway tone, a key aspect of asthma, represents a balance between bronchoconstriction and dilation. Nitric oxide (NO) from the bronchial epithelium is an endogenous bronchodilator. We hypothesized that estrogens facilitate bronchodilation by generating NO in bronchial epithelium. In acutely dissociated human bronchial epithelial cells from female patients exposure to 17 beta-estradiol (E-2; 10 pM-100 nM) resulted in rapid increase of diaminofluorescein fluorescence (NO indicator) within minutes, comparable with that induced by ATP (20 mu M). Estrogen receptor (ER) isoform-specific agonists (R,R)-5,11-diethyl-5,6,11,12-tetrahydro-2,8-chrysenediol (THC) (ER alpha) and diaryl-propionitrile (DPN) (ER beta) stimulated NO production to comparable levels and at comparable rates, whereas the ER antagonist 7 alpha, 17 beta-[9-[(4,4,5,5,5-pentafluoropentyl)sulfinyl]nonyl]estra-1,3,5(10)-triene-3,17-diol (ICI 182,780) (1 mu M) was inhibitory. Estrogen effects on NO were mediated via caveolin-1 (blocked using the caveolin-1 scaffolding domain peptide) and by increased intracellular calcium concentration [prevented by 20 mu M 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl) ester but not by blocking Ca2+ influx using LaCl3]. Estrogen increased endothelial NO synthase activation (inhibited by 100 mu M N-G-nitro-L-arginine methyl ester) and phosphorylated Akt. In epithelium-intact human bronchial rings contracted with acetylcholine (1 mu M), E-2, THC, and DPN all produced acute bronchodilation in a dose-dependent fashion. Such bronchodilatory effects were substantially reduced by epithelial denudation. Overall, these data indicate that estrogens, acting via ER alpha or ER beta, can acutely produce NO in airway epithelium (akin to vascular endothelium). Estrogen-induced NO and its impairment may contribute to altered bronchodilation in women with asthma.