Long-term treatment of macrolide antibiotics is considered an effective treatment for diffuse panbronchiolitis (DPB). Although hypersecretion is a common feature of this disease, and it is known that macrolides inhibit mucin production, the mechanism of the effect on mucin production is unclear. The aim of our study was to determine the production of muc5ac core protein, a major core protein of mucin in airway secretion, and the effect of clarithromycin treatment on such production in a mouse model mimicking DPB. Alcian blue-periodic acid-Schiff-positive cells were detected in the lungs of Pseudomonas aeruginosa-infected mice. Western blots of these mice showed muc5ac glycoprotein at day 1 and increased progressively from day 4 to day 14 after inoculation of bacteria. Clarithromycin (10 mg · kg-1 · day-1 for 7 days) significantly reduced the muc5ac expression at both the mRNA and protein levels. To investigate the role of molecules upstream in muc5ac regulation, we examined the role of mitogen-activated protein kinase. Extracellular signal-regulated kinase 1/2 phosphorylation increased in the infected lung and decreased after treatment. Our results suggest that overproduction of muc5ac plays an important role in the pathogenesis of DPB and that clinical improvement following macrolide therapy seems to involve, at least in part, its inhibition of mucin overproduction, through modulation of intracellular signal transduction.

Idiopathic pulmonary fibrosis is a chronic inflammatory lung disease with interstitial fibrosis. As a potent proinflammatory cytokine, TNF has been suggested to play critical roles in the pathogenesis of the human disease and its animal model, bleomycin-induced pneumopathy. However, studies using TNF-deficient mice have demonstrated that TNF also has an anti-inflammatory function. To determine the role of TNF in pulmonary inflammation induced by bleomycin, we injected bleomycin intratracheally into TNF-deficient mice. In this study, we demonstrated persistent and intense inflammation in TNF-deficient mice due to reduced apoptosis of inflammatory cells. We also showed that in TNF-deficient mice, challenge via airways with murine, but not human rTNF, efficiently eliminated inflammatory cells from the bronchoalveolar space by apoptosis, and thus promoted tissue repair of damaged lungs. Contrary to previous reports that showed that TNF was a central mediator of pulmonary inflammation, we have demonstrated that TNF is essential for repressing pulmonary inflammation in bleomycin-induced pneumopathy.

There had been no reports of investigations into biofilms in chronic respiratory infection in vivo. Recently, we established a new murine model of chronic respiratory infection with Pseudomonas aeruginosa. In the present study, we examined the bacteriological effect of combined clarithromycin and levofloxacin against chronic respiratory infection with P. aeruginosa. Scanning electron micrograph of the surface of the catheter intubated in mouse bronchus for 7 days demonstrated in vivo formation of a biofilm containing blood cells, complex fibrous structures and bacteria. Treatment with either clarithromycin alone or levofloxacin alone had no statistical effect on the number of viable bacteria in lung. The combined use of both drugs resulted in a significant decrease in the number of viable bacteria. The present experiment demonstrates that the newly established murine model was useful to investigate the treatment of biofilm-associated chronic respiratory infection with P. aeruginosa, and combination therapy with clarithromycin and levofloxacin was effective in biofilm-associated chronic respiratory infection.

Fourteen-membered macrolides (e.g. clarithromycin and erythromycin), but not 16-membered macrolides (e.g. josamycin), are effective in diffuse panbronchiolitis. However, there are no studies that have compared the effects of 14- and 16-membered macrolide antibiotics on biofilm formation. Treatment with high-dose clarithromycin (100 mg/kg) resulted in a significant decrease in the number of viable bacteria in an experimental murine model. Josamycin at a dose of up to 100 mg/kg had no effect on the number of viable bacteria in the lung. Our results may explain, at least in part, the clinical efficacy of 14-membered macrolide antibiotics in patients with chronic pneumonia caused by Pseudomonas aeruginosa.

Diffuse panbronchiolitis (DPB) is a chronic lower respiratory tract infection commonly associated with persistent late-stage Pseudomonas aeruginosa infection. However, low-dose long-term therapy with certain macrolides is effective in most patients with DPB. The present study was designed to examine the effects of long-term erythromycin (ERY) therapy by using our established murine model of chronic respiratory P. aeruginosa infection. ERY or saline was administered from day 80 after intubation with a P. aeruginosaprecoated tube for the subsequent 10, 20, 40, and 80 days. Bacteriologic and histologic analyses of the murine lungs and electron microscopy of the intubated tube were performed. In the murine model, treatment with ERY for 80 days significantly reduced the number of viable P. aeruginosa organisms in the lungs (P < 0.05). The biofilm formed in situ by P. aeruginosa on the inner wall of the inoculation tube placed into the murine bronchus became significantly thinner after 80 days of ERY treatment. We conclude that the clinical efficacy of macrolides in DPB may be due at least in part to the reduction in P. aeruginosa biofilm formation.