Mechanism of Action of Corticosteroids in Asthma Treatment Quiz

Corticosteroids in Asthma Treatment: Mechanism of Action

Corticosteroids are widely used in the treatment of asthma due to their potent anti-inflammatory properties. They work by suppressing inflammation and reducing airway hyperresponsiveness, which helps control asthma symptoms and prevent exacerbations. The mechanism of action of corticosteroids in asthma treatment can be broadly classified into genomic and nongenomic actions.

Genomic Mechanisms

Restoring Histone Acetylation

One of the primary mechanisms of ICS (inhaled corticosteroids) is the reversal of histone acetylation, which is a critical step in gene transcription. By recruiting histone deacetylase 2 (HDAC2), ICS suppress inflammation by switching off multiple activated inflammatory genes, thereby reducing airway hyperresponsiveness and controlling asthma symptoms. This genomic mechanism acts with a delay of hours or days, making it particularly effective in long-term asthma management.

Inhibiting Vasoactive Inflammatory Mediators

ICS also act indirectly by inhibiting the release of vasoactive inflammatory mediators, which helps counteract the vascular manifestations of airway inflammation in asthma. This genomic effect is crucial in maintaining and, in excess, enhancing vascular tone, which can be beneficial in managing the complex vascular changes associated with asthma.

Suppression of Inflammation

ICS are primarily used to suppress inflammation in asthma, which is characterized by activated mast cells, eosinophils, and T-helper 2 lymphocytes. Corticosteroids reverse histone acetylation of the activated inflammatory genes, which helps to regulate the expression of cytokines, chemokines, adhesion molecules, and inflammatory enzymes and receptors. This is the primary mechanism by which corticosteroids achieve their therapeutic effects in asthma.

Nongenomic Mechanisms

While the major anti-inflammatory effects of corticosteroids are due to transcriptional mechanisms, evidence is growing for actions that are manifested within seconds or minutes. These rapid, nongenomic effects are mediated by cellular mechanisms that do not involve gene expression and have been termed 'nongenomic actions'. Although the exact mechanisms of these nongenomic actions are not well understood, they are believed to play a role in quickly modulating inflammation and cellular responses in asthma.

Implications for Corticosteroid Resistance and COPD

While corticosteroids are highly effective in asthma, they have limited success in suppressing pulmonary inflammation in COPD. This resistance to corticosteroid action in COPD may be due to reduced HDAC2 activity and expression, which is a result of oxidative stress. In severe COPD, high doses of ICS have been shown to reduce exacerbations, but they are not as effective in preventing the progression of the disease.

Understanding the molecular mechanisms of corticosteroid action in asthma is crucial for developing novel corticosteroids with less systemic effects and for exploring new anti-inflammatory approaches. This knowledge may also help elucidate the molecular basis of chronic inflammation and steroid resistance in asthma and COPD.