Enhancement of inflammatory mediator release by beta(2)-adrenoceptor agonists in airway epithelial cells is reversed by glucocorticoid action.

BACKGROUND AND PURPOSE: Due to their potent bronchodilator properties, beta(2)-adrenoceptor agonists are a mainstay of therapy in asthma. However, the effects of beta(2)-adrenoceptor agonists on inflammation are less clear. Accordingly, we have investigated the effects of beta(2)-adrenoceptor agonists on inflammatory mediator release. EXPERIMENTAL APPROACH: Transcription factor activation, and both release and mRNA expression of IL-6 and IL-8 were examined by luciferase reporter assay, elisa and real-time RT-PCR in bronchial human epithelial BEAS-2B cells or primary human bronchial epithelial cells grown at an air-liquid interface. KEY RESULTS: Pre-incubation with beta(2)-adrenoceptor agonists (salbutamol, salmeterol, formoterol) augmented the release and mRNA expression of IL-6 and IL-8 induced by IL-1beta and IL-1beta plus histamine, whereas NF-kappaB-dependent transcription was significantly repressed, and AP-1-dependent transcription was unaffected. These effects were mimicked by other cAMP-elevating agents (PGE(2), forskolin). Enhancement of cytokine release by beta(2)-adrenoceptor agonists also occurred in primary bronchial epithelial cells. Addition of dexamethasone with salmeterol repressed IL-6 and IL-8 release to levels that were similar to the repression achieved in the absence of salmeterol. IL-6 release was enhanced when salmeterol was added before, concurrently or after IL-1beta plus histamine stimulation, whereas IL-8 release was only enhanced by salmeterol addition prior to stimulation. CONCLUSIONS AND IMPLICATIONS: Enhancement of IL-6 and IL-8 release may contribute to the deleterious effects of beta(2)-adrenoceptor agonists in asthma. As increased inflammatory mediator expression is prevented by the addition of glucocorticoid to the beta(2)-adrenoceptor, our data provide further mechanistic support for the use of combination therapies in asthma management.

Iron acquisition and virulence in Helicobacter pylori: a major role for FeoB, a high-affinity ferrous iron transporter.

The genome sequence of Helicobacter pylori suggests that this bacterium possesses several Fe acquisition systems, including both Fe2+- and Fe3+-citrate transporters. The role of these transporters was investigated by generating insertion mutants in feoB, tonB, fecA1 and fecDE. Fe transport in the feoB mutant was approximately 10-fold lower than in the wild type (with 0.5 microM Fe), irrespective of whether Fe was supplied in the Fe2+ or Fe3+ form. In contrast, transport rates were unaffected by the other mutations. Complementation of the feoB mutation fully restored both Fe2+ and Fe3+ transport. The growth inhibition exhibited by the feoB mutant in Fe-deficient media was relieved by human holo-transferrin, holo-lactoferrin and Fe3+-dicitrate, but not by FeSO4. The feoB mutant had less cellular Fe and was more sensitive to growth inhibition by transition metals in comparison with the wild type. Biphasic kinetics of Fe2+ transport in the wild type suggested the presence of high- and low-affinity uptake systems. The high-affinity system (apparent Ks = 0.54 microM) is absent in the feoB mutant. Transport via FeoB is highly specific for Fe2+ and was inhibited by FCCP, DCCD and vanadate, indicating an active process energized by ATP. Ferrozine inhibition of Fe2+ and Fe3+ uptake implied the concerted involvement of both an Fe3+ reductase and FeoB in the uptake of Fe supplied as Fe3+. Taken together, the results are consistent with FeoB-mediated Fe2+ uptake being a major pathway for H. pylori Fe acquisition. feoB mutants were unable to colonize the gastric mucosa of mice, indicating that FeoB makes an important contribution to Fe acquisition by H. pylori in the low-pH, low-O2 environment of the stomach.