Erythromycin increases bactericidal activity of surface liquid in human airway epithelial cells.

Macrolide antibiotics have clinical benefits in patients with diffuse panbronchiolitis and in patients with cystic fibrosis. Although many mechanisms have been proposed, the precise mechanisms are still uncertain. We examined the effects of erythromycin on bactericidal activity of airway surface liquid secreted by cultured human tracheal epithelial cells. Airway surface liquid was collected by washing the surface of human tracheal epithelial cells with a sodium solution (40 meq/l). Methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa were incubated with airway surface liquid, and the number of surviving bacteria was examined. The number of bacteria in airway surface liquid from the cells cultured in medium alone was significantly lower than that in the sodium solution. Furthermore, the number of bacteria in airway surface liquid from the cells treated with erythromycin was significantly lower than that in airway surface liquid from the cells treated with solvent alone. The production of mRNA and protein of human beta-defensin-1 and human beta-defensin-2 was significantly increased by erythromycin. Bactericidal activity of airway surface liquid was observed at low concentrations (40 meq/l) of sodium but not at higher concentrations (> or =80 meq/l). Airway surface liquid did not contain significant amounts of antibiotics supplemented in the culture medium. Erythromycin at the levels in airway surface liquid and in culture medium did not inhibit bacterial growth. These results suggest that erythromycin may increase bactericidal activity of airway surface liquid in human airway epithelial cells through human beta-defensins production and reduce susceptibility of the airway to bacterial infection.

Bilirubin ameliorates bleomycin-induced pulmonary fibrosis in rats.

Many possible treatments for pulmonary fibrosis have been investigated, but except for some current clinical trials, none have succeeded in clinical trials. On the basis of the antioxidant action of bilirubin (BIL), we examined the effects of hyperbilirubinemia on the development of bleomycin (BLM)-induced pulmonary fibrosis in rats. The animals' plasma BIL level was kept within 3 and 10 mg/dl by repeated intravenous infusion of a high dose of BIL. We studied the inhibitory effects of hyperbilirubinemia on BLM-induced pulmonary fibrosis through histopathologic and biochemical analyses. Mortality of rats with BLM-induced pulmonary fibrosis was significantly lower in the three groups with hyperbilirubinemia. The ameliorating effect of hyperbilirubinemia on pulmonary fibrosis was shown by lung histology, as well as by a decreased lung content of hydroxyproline and reduced bronchoalveolar lavage fluid (BALF) concentration of transforming growth factor (TGF)-beta(1). The number of polymorphonuclear leukocytes and lymphocytes in BALF was also decreased in the groups with hyperbilirubinemia. Furthermore, oxidative metabolites of BIL in urine were present at significantly higher levels in BLM-treated rats with hyperbilirubinemia than in those without hyperbilirubinemia. These data suggest that the antioxidative action of BIL can attenuate BLM-induced pulmonary fibrosis, partly by inhibiting lung inflammation and production of TGF-beta1.

Acid stimulation reduces bactericidal activity of surface liquid in cultured human airway epithelial cells.

To examine the effects of acid exposure with moderate acidity (pH 3.0-5.0) on bactericidal activity of airway surface liquid (ASL), ASL was collected by washing the surface of primary cultures of human tracheal epithelial cells 24 h after treatment with phosphate-buffered saline (PBS) adjusted to a pH of 3.0, 4.0, or 5.0. In all ASL, bactericidal activity was sensitive to sodium concentration. Escherichia coli (500 colony forming units [CFU]) was incubated in ASL, and the number of surviving bacteria was examined. The number of surviving bacteria in ASL from cultured cells with acid exposure at pH 3.0-5.0 was significantly higher than that in control ASL. The minimum inhibitory dilution ratio of ASL against 500 CFU of E. coli was also examined by microdilution assays. According to this assay, the bactericidal activity in ASL with acid challenge at a pH of 3.0 was less than half of that in control ASL. Reverse transcription-polymerase chain reaction and Western blot analysis showed that the production of mRNA and protein of human beta-defensin (HBD)-1 were significantly decreased by acid exposure at pH 3.0-5.0. In contrast, acid exposure did not change the production of mRNA and protein of HBD-2 and beta-actin mRNA. These results indicate that acid exposure, even with moderate acidity, may inhibit the production of bactericidal molecules, including HBD-1, in airway epithelial cells. Acid exposure may reduce bactericidal activity of ASL in human airway epithelial cells and may increase susceptibility of the airway to bacterial infection.