Airway epithelial changes evident in asthmatic smokers
MedWire News: Asthma patients who smoke show evidence of abnormal epithelial changes, researchers have found.
However, Martine Broekema (University Medical Center Groningen, The Netherlands) and team also say that epithelial characteristics are similar in asthmatic ex-smokers and never smokers, suggesting that the abnormal epithelial changes associated with smoking are reversible.
The researchers studied bronchial inflammation and remodeling in 147 patients with asthma, of whom 66 were never-smokers, 46 were ex-smokers, and 35 were current smokers.
The participants, who were aged between 19 and 71 years, underwent lung function tests, exhaled nitric oxide (NO) assessments, and completed a questionnaire on respiratory symptoms. They also supplied sputum samples and bronchial biopsies were taken.
The researchers found that smokers had significantly lower mean bronchial NO levels than ex-smokers and never-smokers, at 0.38 nl/s compared with 0.93 and 1.02 nl/s, respectively.
Smokers had higher numbers of goblet cells (65 per mm of basement membrane), and a higher percentage of mucus-positive epithelium (16.9%) than never-smokers (31 per mm and 6.2%, respectively). They also had a thicker epithelial layer and more proliferation of intact epithelium than never-smokers.
Furthermore, smokers had higher numbers of mast cells (12 per 0.1 mm2 ) than never-smokers (6 per 0.1 mm2).
Ex-smokers had similar numbers of goblet cells and mast cells, percentage of mucus-positive epithelium, epithelial thickness, and epithelial proliferation rate as never-smokers.
The team also found that the severity of self-reported phlegm production correlated significantly with the number of goblet cells, presence of mucus-positive epithelium, and epithelial thickness, while the severity of self-reported shortness of breath correlated significantly with epithelial thickness.
Broekema and team conclude in the American Journal of Respiratory and Critical Care Medicine: “We show in a large population of patients with asthma that cigarette smoking induces epithelial changes in association with increases in asthma symptoms, such as shortness of breath and phlegm production. Cigarette smoking in asthma was associated with lower bronchial eosinophil and higher mast cell numbers.”
They add: “The fact that epithelial changes and higher mast cell numbers were not observed in ex-smokers with asthma suggests that these smoke-induced changes can be reversed by smoking cessation.”
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By Mark Cowen