Vitamin D receptor agonists inhibit pro-inflammatory cytokine production from the respiratory epithelium in cystic fibrosis

Background

1,25-Dihydroxycholecalciferol (1,25(OH)₂D₃) has been shown to mitigate epithelial inflammatory responses after antigen exposure. Patients with cystic fibrosis (CF) are at particular risk for vitamin D deficiency. This may contribute to the exaggerated inflammatory response to pulmonary infection in CF.

Methods

CF respiratory epithelial cell lines were exposed to Pseudomonas aeruginosa lipopolysaccharide (LPS) and Pseudomonas conditioned medium (PCM) in the presence or absence of 1,25(OH)₂D₃ or a range of vitamin D receptor (VDR) agonists. Levels of IL-6 and IL-8 were measured in cell supernatants, and cellular total and phosphorylated IκBα were determined. Levels of human cathelicidin antimicrobial peptide (hCAP18) mRNA and protein were measured in cells after treatment with 1,25(OH)₂D₃.

Results

Pretreatment with 1,25(OH)₂D₃ was associated with significant reductions in IL-6 and IL-8 protein secretion after antigen exposure, a finding reproduced with a range of low calcaemic VDR agonists. 1,25(OH)₂D₃ treatment led to a decrease in IκBα phosphorylation and increased total cellular IκBα. Treatment with 1,25(OH)₂D₃ was associated with an increase in hCAP18/LL-37 mRNA and protein levels.

Conclusions

Both 1,25(OH)₂D₃ and other VDR agonists significantly reduce the pro-inflammatory response to antigen challenge in CF airway epithelial cells. VDR agonists have significant therapeutic potential in CF.