Effect of Montelukast on the Airway Remodeling in Asthma Patients: Physiological-radiological Correlation

Accumulated data have suggested that the distal lung, which includes airways of < 2mm in diameter and lung parenchyma, contribute to asthma pathogenesis and symptoms. In addition to persisting inflammation, distal lung undergoes remodeling, as demonstrated by the reduced elastic fiber content and abnormal alveolar attachments, with the latter thought to result in a loss of elastic recoil and a reduction in FEV1.0. Furthermore, recent studies have shown that airway remodeling is observed from early onset of the disease and may, therefore, be characteristic of asthma. Amounting evidence has revealed that airway remodeling of asthmatic airways accounts for a large component of airway hyperresponsiveness (AHR) and excessive airway narrowing.

Since remodeling processes occur in parallel to, or may even be obligatory for, the establishment of persistent inflammation, the pathogenesis of airway remodeling and the implications of therapeutic interventions that are designed to diminish airway remodeling remain important areas of both research and clinic. Inhale corticosteroid (ICS) is mainstay for the treatment of asthma, however, ICS provides very little benefit for airway remodeling.

Cysteinyl leukotrienes (CysLT) play important role in the pathogenesis of airway remodeling and antileukotrienes work to exert a certain degree of anti-inflammatory effect. The cysteinyl leukotriene antagonist Montelukast, for example, has been in vivo shown to significantly inhibit ovalbumin induced airway smooth muscle hyperplasia and subepithelial fibrosis in sensitized mice. Montelukast, a systemically delivered leukotriene receptor antagonist, has been strongly recommended to treat asthma by several guidelines. Clinically, the systemically acting oral agent montelukast has been shown to improve proximal and distal lung physiology. In particular, improvements in distal lung function correlate with improvements in asthma symptoms. The in vivo experiments performed in rodent animal challenged by OVA have shown that Montelukast can reverse airway remodeling, as well as inhibit inflammation.

To determine the occurrence of airway remodeling in human being, bronchial biopsy samples obtained with a bronchoscope are subjected to histological examination. However, bronchial biopsy is invasive and causes considerable pain, while assessment of the peripheral small airways and of changes in the deep submucosal tissue and airway smooth muscle in large airways is technically difficult. This technique does not allow the longitudinal analysis of airway wall dimensions.

Noninvasive evaluation of airways by means of imaging with high-resolution computed tomography (HRCT) has therefore been tried as an alternative procedure, and was found to have the potential to evaluate airways in patients with obstructive pulmonary disease. The measurement of airway wall thickness by HRCT in patients with asthma has been demonstrated to correlate with the severity of asthma. Computed tomographic imaging of the airways by HRCT has been widely applied to investigate the alterations in the structure of the airways termed airway remodeling in patients with airway obstructive diseases (see references 1-4).