We aimed at identifying molecular mechanisms for anti-inflammatory effects of azithromycin (AZM) suggested by clinical evidences. IL-8 expression and DNA binding activity of two key pro-inflammatory transcription factors (TF), NF-kappa B and AP-1, were investigated in cystic fibrosis (CF) and isogenic non-CF airway epithelial cell lines. AZM reduced about 40% of IL-8 mRNA and protein expression (n = 9, p = 0.02, and n = 4, p = 0.00011) in CF cells reaching the levels of non-CF cells. In the presence of AZM we found about 50% and 70% reduction of NF-kappa B and AP-1 DNA binding, respectively (n = 3, p = 0.01, and n = 3, p = 0.0017), leading to levels of non-CF cells. The relevance of NF-kappa B and AP-1 in regulating IL-8 promoter transcriptional activity was demonstrated by gene reporter assays (17 = 4, p = 8.54 x 10(-7), and n = 4,p = 6.45 x 10(-6)). Our data support the anti-inflammatory effects of AZM in CF cells, indicating inhibition of transcription of pro-inflammatory genes as possible mechanism, thus providing a rationale for the possible use of specific TF inhibitors for therapy. (c) 2006 Elsevier Inc. All rights reserved.