Development of resistance to antimicrobial therapy by bacteria is one of the most serious and challenging health problems worldwide. N-acyl-homoserine lactones (AHLs) are signal molecules used by many Gram-negative bacteria, including Pseudomonas aeruginosa. These signals coordinate both bacterial biofilm formation, which increases intrinsic resistance to antibiotics and immune cells, and the expression of virulence factors, which leads to host cell damage. Targeting bacterial AHL molecules is therefore an attractive therapeutic strategy to control these infections. In people with cystic fibrosis (CF) P. aeruginosa is associated with chronic lung infections that result in severe inflammation, increased rate of lung function decline, and increased mortality.
The intracellular human paraoxonase enzyme, PON2, is expressed by a wide range of cells including respiratory epithelium, and possesses both lactonase, that specifically hydrolyses and inactivates AHL molecules, and antioxidant activity. We hypothesise that a therapy consisting of inhaled recombinant human PON2 (rhPON2) will protect the lungs of people with CF P. aeruginosa infection by attenuating biofilm formation and virulence, and thereby enhance the efficacy of co-administered antibiotics, and preventing AHL-mediated host cell damage.
rhPON2 treatment of P. aeruginosa prevents accumulation of bacterial AHL, decreases expression of QS-regulatory genes, decreases biofilm formation and increases sensitivity of P. aeruginosa to conventional antibiotics.
The P. aeruginosa produced AHL can readily diffuse across the mammalian cell membrane and has been demonstrated to affect mammalian cell behaviour. Addition of rhPON2 to cultured human respiratory epithelial cells treated with AHL or live bacteria prevents severe upregulation of inflammation pathways and inhibits AHL-induced apoptosis and intracellular stress.
Treatment of mice with aerosolized rhPON2 at the time of P. aeruginosa lung infection, prevents upregulation of inflammatory pathways in the lungs.
A therapy consisting of rhPON2 could attenuate P. aeruginosa virulence, increase antibiotic sensitivity and protect lungs from AHL-mediated effects associated with P. aeruginosa infection.