Fourteen-Membered Ring Macrolides Inhibit Vascular Cell Adhesion Molecule 1 Messenger RNA Induction and Leukocyte Migration: Role in Preventing Lung Injury and Fibrosis in Bleomycin-Challenged Mice*

Abstract

Although the pathogenesis of interstitial pneumonia and pulmonary fibrosis are not well understood, it has been reported that inflammatory cells, especially neutrophils, and the injurious substances produced by them play important roles in the progression of interstitial pneumonia and subsequent fibrosis. Erythromycin and other 14-membered ring macrolides (14-MRMLs) have been reported to improve the survival of patients with diffuse panbronchiolitis by antineutrophil and several other anti-inflammatory mechanisms. The present study was undertaken to investigate the effects of 14-MRMLs on an experimental model of bleomycin-induced acute lung injury and subsequent fibrosis in mice. Bleomycin was administered IV to ICR mice. At 28 days after bleomycin injection, fibrotic foci were histologically observed in left lung tissues, and hydroxyproline content in right lung tissues was chemically analyzed. The inhibitory effects of 14-MRMLs were assessed by overall comparison between control (normal saline solution [NS] alone), untreated (bleomycin alone), and treated (bleomycin plus 14-MRMLs) groups. For evaluation of early-phase inflammation, cell populations in BAL fluid and induction of messenger RNA (mRNA) of adhesion molecules (E-selectin, P-selectin, intercellular adhesion molecule 1 [ICAM-1], and vascular cell adhesion molecule 1 [VCAM-1]) in lung tissues were examined at 0 to 13 days after bleomycin treatment. These parameters were also compared with those for the control (NS alone), 14-MRML untreated (bleomycin alone), and 14-MRML pretreated (bleomycin plus 14-MRML pretreated) groups. Bleomycin-induced pulmonary fibrosis was inhibited by erythromycin and other 14-MRMLs on day 28 after bleomycin injection in ICR mice, especially those pretreated with 14-MRMLs. Hydroxyproline content in lung tissues was also decreased in the 14-MRML-pretreated groups. The number of neutrophils in BAL fluid significantly increased, with two peaks at 1 day and 9 days (from 6 to 11 days) after bleomycin administration. 14-MRMLs significantly inhibited both peaks of neutrophil infiltration into the airspace. Changes in mRNA expression of adhesion molecules (E-selectin, P-selectin, ICAM-1, VCAM-1) were associated with leukocyte migration into the airspace. 14-MRMLs clearly inhibited the induction of VCAM-1 mRNA, and tended to attenuate that of ICAM-1 mRNA, but inhibited the induction of neither E-selectin mRNA nor P-selectin mRNA. These findings indicate that attenuation of inflammatory cell migration into the airspace by 14-MRMLs, especially of neutrophils and macrophages, resulted in inhibition of lung injury and subsequent fibrosis. 14-MRMLs clearly attenuated the expression of VCAM-1 mRNA during the early phase of bleomycin-induced lung injury, and this might be one mechanism of inhibition of neutrophil and macrophage migration into the airspace by 14-MRMLs. This may be one mechanism of the anti-inflammatory and antifibrotic effects of 14-MRMLs. These findings suggest that prophylactic administration of 14-MRMLs may be clinically efficacious in preventing acute exacerbation of interstitial pneumonia and acute lung injury.