ASTHMA-OBESITY NEUTROPHILIC INFLAMMATION AS A DISTINCT PHENOTYPE

Abstract

Background & objectives: Asthma in obese subjects has been suggested to differ from classical phenotypes of asthma. Obesity is associated with activation of innate immune response in which neutrophilic activation is a fundamental process. However, airway inflammation in obese asthmatics is not well characterized, but may involve neutrophils. The present work was designed to study the possible airway and systemic neutrophilic inflammation as a distinct feature of asthma in obese asthma phenotype. Methods: Study included 30 obese asthmatics (BMI ≥ 30 kg/m2), 8 non-obese asthmatics (BMI< 25 kg/m2) and 7 normal non-obese subjects (BMI< 25 kg/m2). Anthropometric measurements and pulmonary flow rates were assessed for all subjects. Methacholine inhalation challenge was performed only in asthmatics. Blood and sputum samples were tested for neutrophilic and eosinophilic counts, as well as levels of interleukin-8 (IL-8)and myeloperoxidase (MPO) enzyme, as markers of neutrophilic activity.Results: There was no significant difference between obese and non-obese asthmatics as regard the mean value of the provocative dose of methacholine (PD20-FEV1). Compared to non-obese asthmatics, obese asthmatics demonstrated significantly higher blood and sputum neutrophilic counts and significantly lower blood and sputum eosinophilic counts. However, on comparing IL-8 and MPO levels between the obese asthmatic group and non-obese asthmatic group, there were insignificant trends toward increased serum and sputum levels of IL-8 and serum level of MPO in the obese asthmatic group. In asthmatic subjects, there was a significant positive correlation between BMI and serum MPO levels. Conversely, BMI showed significant negative correlations with both sputum eosinophilic count and blood absolute eosinophilic count. Conclusions: Findings suggest that neutrophil predominant airway inflammation is more likely to be a distinct inflammatory phenotype of asthma in obese asthmatic subjects, though further studies are needed to detect significant effects of obesity on markers of neutrophil activity in asthmatic subjects to shed more light on the possible role of neutrophilic inflammation in the association between obesity and asthma. Keywords: Obesity, Bronchial asthma, Asthma phenotypes.