Mineral Fibre-Related Bronchial Lesions

Abstract

The bronchopathogenic potential of crocidolite asbestos and four man-made mineral fibres have been compared. Groups of rats received, respectively, a single intratracheal instillation of UICC crocidolite asbestos, Rockwool 115-4, Carborundum CEF 100, Basaltwool-Isolyth, or Mineralwool-Isolyth dusts into the right lower lobe. At intervals, from 2 days up to 6 months after the treatment, lung histology was performed on animals from each group. Bron chial effects of crocidolite asbestos and the different man-made mineral fibres revealed more quantitative than qualitative differences. In accordance with the literature, inflammatory and regressive lesions were found to dominate the early phase of reaction. Later, adenoma-like structures developed as a result of two different pathomechanisms: (1) Bifurcational, central interception of long fibres and consecutive scarring granulomas induced polypous-papillomatous mucosal proliferations and partition of the bronchus into small, ciliary epithe lial lined lumina. (2) In the chronic phase of reaction, budding and prolifera tion of the mucosal cells resulted in many small lumina in the wall and round the bronchi, without any scar formation. The increased dividing activity in the mucosa, the abnormalities of the secretion, the metaplasia and local prolifera tion of the epithelium, basement membrane disintegration, and changes of the extracellular matrix are typical of mucosal preneoplasias. As a result of the different lesions, first of all the adenomatoid proliferations, and then focal and irreversible remodelling of the bronchial tree had occurred by the end of the experiments.