Patients with asthma-COPD overlap (ACO) show distinct airway changes compared to people with asthma or COPD alone, raising hopes for more targeted therapy for the under-recognised condition, Australian researcher say.
Their study compared remodelling changes in 90 large airway endobronchial biopsies obtained from the Tasmanian Respiratory and Newcastle biobanks. Donors were adults with confirmed ACO, asthma only, COPD only, healthy volunteers, and smokers with normal lung function.
The study found a significantly thicker epithelium (p=0.0263) and higher epithelial cell numbers in ACO samples compared to healthy controls.
Goblet cell numbers in ACO were also significantly higher than in healthy controls (p=0.0028) and COPD patients who were ex-smokers (COPD-ES).
“Furthermore, we demonstrate an increase in percent goblet cells in ACO, which constituted 3.5% of their total epithelial cell population compared to 2.4%, 1.2%, and 0.4% in asthma, COPD-current smokers and COPD-ES, respectively.”
The study, published in Lung Cellular and Molecular Physiology, also found changes in the reticular basement membrane (RBM), and the lamina propria (LP) and smooth muscle area.
In patients with ACO, RBM (11.95 [8.5-16.95] μm) was significantly thicker than healthy controls (6.74 [2.81-14.37] μm, p=0.0002), tended to be thicker than in asthma patients, COPD-ES and smokers with normal lung function, and was thinner than in COPD-current smokers.
There were also more RBM cells in the ACO RBM compared to other groups, except for people with asthma who had higher cellularity.
LP cells per mm2 were highest in asthma patients and other pathological groups, while cellularity in COPD-current smokers and smokers with normal lung function was the lowest.
“The present finding of a high number of total LP cells in asthma could reflect the disease pathology, and to date, studies have shown the increased cellularity and abundance of inflammatory cells such as eosinophils and mast cells in the asthmatic airway,” the researchers said.
They noted a significantly reduced smooth muscle area in ACO (0.061 [0.035-0.116]) as compared to asthma (0.133 [0.086-0.322], p=0.001) and COPD-current smokers (0.131 [0.079-0.191], p=0.0290).
These findings were consistent with other evidence that increased smooth muscle thickness is one of the characteristic features of airway remodelling in both asthma and COPD.