Abstract
BackgroundAzithromycin (Azm) is a macrolide recognized for its disease-modifying effects and reduction in exacerbation of chronic airway diseases. It is not clear whether the beneficial effects of Azm are due to its anti-microbial activity or other pharmacological actions. We have shown that Azm affects the integrity of the bronchial epithelial barrier measured by increased transepithelial electrical resistance. To better understand these effects of Azm on bronchial epithelia we have investigated global changes in gene expression.MethodsVA10 bronchial epithelial cells were treated with Azm and cultivated in air-liquid interface conditions for up to 22 days. RNA was isolated at days 4, 10 and 22 and analyzed using high-throughput RNA sequencing. qPCR and immunostaining were used to confirm key findings from bioinformatic analyses. Detailed assessment of cellular changes was done using microscopy, followed by characterization of the lipidomic profiles of the multivesicular bodies present.ResultsBioinformatic analysis revealed that after 10 days of treatment genes encoding effectors of sterol and cholesterol metabolism were prominent. Interestingly, expression of genes associated with epidermal barrier differentiation, KRT1, CRNN, SPINK5 and DSG1, increased significantly at day 22. Together with immunostaining, these results suggest an epidermal differentiation pattern. We also found that Azm induced the formation of multivesicular and lamellar bodies in two different airway epithelial cell lines. Lipidomic analysis revealed that Azm was entrapped in multivesicular bodies linked to different types of lipids, most notably palmitate and stearate. Furthermore, targeted analysis of lipid species showed accumulation of phosphatidylcholines, as well as ceramide derivatives.ConclusionsTaken together, we demonstrate how Azm might confer its barrier enhancing effects, via activation of epidermal characteristics and changes to intracellular lipid dynamics. These effects of Azm could explain the unexpected clinical benefit observed during Azm-treatment of patients with various lung diseases affecting barrier function.
Highlights
Azithromycin (Azm) is a macrolide recognized for its disease-modifying effects and reduction in exacerbation of chronic airway diseases
We have previously shown that Azm increases transepithelial electrical resistance (TEER) in a bronchial-derived basal epithelial cell line, VA10, when cultured in air-liquid interface (ALI) conditions [21]
Azm induces an increase in TEER that corresponds to a decrease in paracellular flux, in both the VA10 and the bronchial-derived basal cell line BCi-NS1.1 [25].This suggests that Azm treatment of cultured airway epithelial cells results in increased integrity of an epithelial barrier in culture and enhanced barrier functions
Summary
Azithromycin (Azm) is a macrolide recognized for its disease-modifying effects and reduction in exacerbation of chronic airway diseases. Patients with lung diseases including COPD, asthma, diffuse panbronchiolitis and cystic fibrosis (CF) are often admitted to hospitals with acute exacerbations [1] These admissions can be due to underlying bacterial infections for which the first line of treatment includes macrolide antibiotics [2,3,4,5,6,7,8]. Patients that receive macrolide therapy show improved prognosis with fewer and less severe acute exacerbations resulting in fewer hospital admissions [8,9,10,11] These beneficial effects appear to be independent of bactericidal activity [12] and are shown to improve health in patients with COPD regardless of the status of the airway bacterial infections, including that of P. aeruginosa colonization [2, 13, 14]. Sputum samples neither indicated significant anti-microbial activity, nor changes in the number of inflammatory cells [20]
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