Changes in pulmonary surfactant function and composition in bleomycin-induced pneumonitis and fibrosis

Abstract

Bleomycin is a widely accepted cancer drug but may induce life-threatening interstitial lung disease in a subset of patients. We evaluated the effect of bleomycin administration on pulmonary surfactant function and composition in rabbit lungs. In order to obtain a uniform response to bleomycin, aerosol technology was employed for bronchoalveolar delivery of 1.8 U/kg b.w. bleomycin. On days 4, 8, 16, 24, 32, and 64 after challenge, bronchoalveolar lavages were performed. Sham-aerosolized rabbits served as controls. In the early acute respiratory distress syndrome (ARDS)-like post-bleomycin period (4–16 days), marked loss of surface activity of the large surfactant aggregate (LA) fraction of surfactant was noted. In parallel, reduced percentages of LA, but only minor changes in surfactant apoproteins (SP)-A, SP-B, and SP-C, were encountered. Analysis of the surfactant lipid profile showed impressively enhanced cholesterol and significantly decreased phosphatidylglycerol (PG) levels. The relative content of dipalmitoyl-PC (DPPC) was slightly increased, and a several-fold increase within the 1- O-alkyl-2-acyl subclass of PC was observed. During the prolonged fibroproliferative period, a highly significant downregulation of SP-B and SP-C levels was observed. This was paralleled by an upregulation of the total extracellular phospholipid pool, with a far-reaching normalization of the (phospho)-lipid profile. The biophysical surfactant function never fully normalized within the 64-day observation period. In conclusion, bleomycin caused marked abnormalities of pulmonary surfactant, with the profile of changes being different between the early ARDS and the late fibrotic phase.