Responses of lung epithelium and connective tissue cells in Syrian hamster to amiodarone

Pulmonary fibrosis is an often fatal disease characterized by hyperplasia of interstitial cells and excessive accumulation of extracellular matrix components ultimately leading to remodeling of the lung architecture. The precise series of events leading to this scarring is yet to be elucidated. Amiodarone is a Class III antiarrhythmic drug that is known to cause pulmonary fibrosis, but its mechanism of action leading to this condition is unknown. Transforming growth factor beta (TGF-beta), a multifunctional cytokine, plays a significant role in this process. The objective of this study was to determine the role of TGF-beta in amiodarone-induced pulmonary fibrosis and the effect of altering its autoregulation on the fibrotic process with particular emphasis on inflammation and elastin production. Morphologic analysis of Syrian hamsters treated intratracheally with amiodarone (1.5 mg/kg) demonstrated an intense inflammatory reaction followed by thickening of interstitial areas and eventual remodeling of the lung architecture. Within twenty-four hours of toxicant exposure inflammatory cells were present in the airspaces and slight thickening of the interstitial cells was observed. Areas of cellular hyperplasia in the interstitium and inflammatory cells were more numerous forty-eight hours after treatment. Destruction of alveolar cell walls was observed within seventy-two hours of amiodarone exposure. By eight weeks, animals exposed to amiodarone exhibited honeycomb lung. Immunohistochemical analysis revealed increases in TGF-beta protein production in hamsters treated with amiodarone. Such increases were observed in the interstitial cells and alveolar macrophages. Peak TGF-beta levels were detected twenty-four hours post treatment followed by a steady decline. Analysis of bronchoalveolar lavage fluid from amiodarone-treated animals by ELISA techniques confirmed such findings. The concentration of TGF-beta in animals euthanized at twenty-four hours was 294 pg/mg of protein, forty-eight hours was 215 pg/mg of protein and seventy-two hours was 190 pg/mg of protein. Sources of TGF-beta in the lungs of amiodarone-treated animals were localized using in situ techniques. A biotin-labeled TGF-beta antisense oligonucleotide probe was hybridized to tissue sections obtained from animals euthanized twenty-four hours post amiodarone treatment. The probe identified parenchymal cells as the origins of TGF-beta production. TGF-beta mRNA translation was inhibited in hamsters treated with antisense oligonucleotides prior to amiodarone treatment. (Abstract shortened by UMI.)...