Effect of inhibition of nitric oxide synthase on Pseudomonas aeruginosa infection of respiratory mucosa in vitro

We studied the effect of the nitric oxide synthase (NOS) inhibitor asymmetric dimethyl arginine (ADMA) and the inactive enantiomer N-G-methyl-D-arginine (D-NMMA) on Pseudomonas aeruginosa infection of the respiratory mucosa in nasal turbinate organ cultures. We also investigated the effect of P. aeruginosa culture filtrate on the expression of inducible NOS (iNOS) messenger RNA (mRNA) by an epithelial cell line (A549). Organ cultures were preincubated with ADMA (0.1 to 4 x 10(-4) M) or D-NMMA (2 x 10(-4) M) for 30 min prior to bacterial infection. Infected organ cultures (8 h) had significantly (P less than or equal to 0.05) greater epithelial damage and fewer ciliated and unciliated cells than did control cultures. There was an increased level of nitrite in the medium feeding infected organ cultures as compared with control cultures. ADMA significantly (P less than or equal to 0.05) reduced both bacterially induced epithelial damage and loss of ciliated cells in a concentration-dependent manner. D-NMMA did not influence the effect of P. aeruginosa infection of the mucosa. ADMA, but not D-NMMA, significantly (P less than or equal to 0.04) reduced total bacterial numbers adherent to the respiratory mucosa. P. aeruginosa culture filtrates (24 h and 36 h) significantly (P = 0.02) increased iNOS with respect to glyceraldehyde-3-phosphate dehydrogenase mRNA expression. These results show that P. aeruginosa stimulates iNOS expression by a cell Line and NO production by an organ culture. ADMA. reduces mucosal damage and loss of ciliated cells, which suggests that NO may be a mediator of epithelial damage caused by P. aeruginosa.