Role of microvascular permeability on physiologic differences in asthma and eosinophilic bronchitis

Asthma and eosinophilic bronchitis are characterized by a similar type of eosinophilic inflammation. However, eosinophilic bronchitis differs from asthma in that there is no variable airflow obstruction or airway hyperresponsiveness. We evaluated the roles of vascular endothelial growth factor (VEGF) and microvascular permeability in causing these differences between the two diseases. Inflammatory indexes in induced sputum, exhaled nitric oxide levels, and vascular permeability index were examined in 11 normal control subjects, 19 beclomethasone dipropionate (BDP)-treated subjects with asthma, 20 non-BDP-treated subjects with asthma, and 17 patients with eosinophilic bronchitis. The percentage of eosinophils in sputum and exhaled nitric oxide levels were significantly higher in non-BDP-treated subjects with asthma and patients with eosinophilic bronchitis than in other two groups; however, VEGF levels and vascular permeability index were significantly higher in non-BDP-treated (VEGF: mean; 4,710 [SD; 1,150] pg/ml, p < 0.0001; vascular permeability index: 0.028 [0.009], p < 0.0001) and BDP-treated (2,560 [1,070] pg/ml, p = 0.0002; 0.016 [0.006], p = 0.004) subjects with asthma than in patients with eosinophilic bronchitis (1,120 [800] pg/ml; 0.01 [0.005]) and normal control subjects (1,390 [1,280] pg/ml; 0.008 [0.003]). We found significant correlations between the VEGF level and the airway vascular permeability index in all patient groups. Thus, interaction between airway microcirculation and VEGF may be a key element in differences in airway function between asthma and eosinophilic bronchitis.