Inhibition of <i>Pseudomonas aeruginosa</i> secreted virulence factors reduces lung inflammation in CF mice

<p><b>Background</b>: Cystic fibrosis (CF) lung infection is a complex condition where opportunistic pathogens and defective immune system cooperate in developing a constant cycle of infection and inflammation. The major pathogen, <i>Pseudomonas aeruginosa</i>, secretes a multitude of virulence factors involved in host immune response and lung tissue damage. In this study, we examined the possible anti-inflammatory effects of molecules inhibiting <i>P. aeruginosa</i> virulence factors.</p> <p><b>Methods</b>: Pyocyanin, pyoverdine and proteases were measured in bacterial culture supernatant from different <i>P. aeruginosa</i> strains. Inhibition of virulence factors by sub-inhibitory concentrations of clarithromycin and by protease inhibitors was evaluated. Lung inflammatory response was monitored by in vivo bioluminescence imaging in wild-type and CFTR-knockout mice expressing a luciferase gene under the control of a bovine IL-8 promoter.</p> <p><b>Results</b>: The amount of proteases, pyocyanin and pyoverdine secreted by P. aeruginosa strains was reduced after growth in the presence of a sub-inhibitory dose of clarithromycin. Intratracheal challenge with culture supernatant containing bacteria-released products induced a strong IL-8-mediated response in mouse lungs while lack of virulence factors corresponded to a reduction in bioluminescence emission. Particularly, sole inactivation of proteases by inhibitors Ilomastat and Marimastat also resulted in decreased lung inflammation.</p> <p><b>Conclusions</b>: Our data support the assumption that virulence factors are involved in <i>P. aeruginosa</i> pro-inflammatory action in CF lungs; particularly, proteases seem to play an important role. Inhibition of virulence factors production and activity resulted in decreased lung inflammation; thus, clarithromycin and protease inhibitors potentially represent additional therapeutic therapies for <i>P. aeruginosa</i>-infected patients.