Inhaled glucocorticoids for asthma

Clinical management of asthma in the 1990s. Current therapy and new directions

Asthma is a serious global health problem affecting nearly 100 million people worldwide. Its rising prevalence and associated morbidity and mortality are of increasing concern. Traditionally, symptomatic control of bronchoconstriction with beta 2 agonists and theophylline has been the mainstay of therapy. However, during recent years, inflammation has been recognised as the predominant cause of reversible airway obstruction and airway hyperreactivity. As a result, the emphasis in treatment has shifted to the early use of inhaled corticosteroids to control airway inflammation. beta 2 agonists are best used on an as-needed basis for the relief of acute bronchoconstriction and for the prevention of exercise-induced asthma. Sustained release theophylline or an inhaled long-acting beta 2 agonist may effectively control nocturnal symptoms. Preliminary studies involving agents active in the 5-lipoxygenase pathway as preventive therapy are encouraging. Further studies are needed to define their role in the management of asthma.

Abnormal glucocorticoid receptor-activator protein 1 interaction in steroid-resistant asthma

Glucocorticosteroids are a very effective treatment for asthma and other chronic inflammatory diseases. However, a small proportion of patients is resistant to the therapeutic effects of glucocorticoids. Pharmacokinetic and ligand binding studies suggest that the molecular abnormality in steroid resistance lies distal to nuclear translocation. We have previously reported that there is a decreased ability of glucocorticoid receptors (GR) to bind to the DNA-binding site in peripheral blood mononuclear cells (PBMC) after dexamethasone treatment. This reduced DNA binding was due to a decrease in the number of receptors available rather than an alteration in affinity for DNA. To study this reduced DNA binding, we examined the ability of the nuclear translocated transcription factors activator protein 1 (AP-1), nuclear factor kappa B (NF-kappa B) and cyclic AMP response element-binding protein (CREB) to bind to their DNA-binding sites and to interact with GR in PBMC from patients with steroid-sensitive and steroid-resistant asthma. There was a significant reduction in the interaction between GR and AP-1 in these steroid-resistant patients, although interaction with other transcription factors activated in inflammation (NF-kappa B and CREB) was unaffected. An increase in the basal levels of AP-1 DNA binding was also detected in the nuclei from steroid-resistant asthmatic patients. There were no differences in the amount of messenger RNA detected for the components of AP-1, c-Fos and c-Jun, nor in the sequences of these messenger RNAs. These results suggest either that the ability of the GR to bind to glucocorticoid response elements and AP-1 is altered in steroid-resistant patients or that increased levels of AP-1 prevent GR DNA binding, and that this may be the molecular basis of resistance to the antiinflammatory effect of steroids in these cells.

Molecular mechanisms of antiasthma therapy

Recently there has been a much greater understanding of the molecular mechanisms involved in the actions of antiasthma therapy. beta 2-agonists are the most effective bronchodilators and act predominantly on airway smooth muscle. Recent evidence suggests that beta 2-receptors in airway smooth muscle are coupled directly to maxi-K channels and may thereby bronchodilate without an increase in cyclic AMP. The issue of beta-receptor tolerance has been reawakened by the recognition that the protective effects of beta 2-agonists against bronchoconstrictor stimuli may become tolerant. Inhaled glucocorticoids are the mainstay of treatment in patients with chronic asthma. They suppress asthmatic inflammation predominantly by reducing transcription of genes coding for inflammatory mediators (particularly cytokines) and enzymes (inducible NO synthase, inducible cyclo-oxygenase). The inhibition of gene transcription is mediated predominantly by inhibition of transcription factors, such as activator protein-1 (AP-1) and nuclear factor-kappa B (NF-kappa B). There may be an abnormal activation of AP-1 in steroid-resistant asthma, and high concentrations of beta 2-agonists may induce a secondary resistance by an interaction between the transcription factor CREB and the glucocorticoid receptor. Theophylline may have immunomodulatory effects that are more important than its bronchodilator action. Some effects of theophylline are mediated via inhibition of phosphodiesterases and several PDE IV inhibitors are currently undergoing evaluation in asthma.