International journal of experimental pathology
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Comparative Study
Effects of cigarette smoke on the clearance of short asbestos fibres from the lung and a comparison with the clearance of long asbestos fibres.
Long asbestos fibres are generally considered to have greater disease-producing potential than short asbestos fibres. However, recent reports have suggested that short fibre asbestos appears to be as effective an inducer of macrophage growth factors and toxic oxygen species as long fibre asbestos, but that short fibres are readily removed from lung and do not gain access to tissues. Because smoke is believed to impair the clearance of asbestos fibres from lung, we examined the clearance of a short (geometric mean length 1.3 microns) amosite preparation administered by intratracheal instillation to guinea-pigs. ⋯ By contrast, a long fibre amosite preparation (geometric mean length 8.9 microns) showed approximately the same increase in fibre retention in macrophages, but only a twofold increase in tissue retention. We conclude that (1) cigarette smoke markedly impairs the clearance of short amosite fibres from the lung with enhanced retention of fibres in both macrophages and tissue; (2) the effects of smoke on short fibre tissue retention appear to be greater than those on long fibre retention; (3) with the long fibre preparation, smoke causes increased tissue retention of relatively shorter fibres; (4) for both fibre size experiments, the increase in total fibres in macrophages in smoke-exposed animals reflects an increase in the total number of fibre-containing macrophages, rather than an increase in the number of fibres phagocytized per macrophage; (5) enhanced short fibre retention markedly increases total fibre surface area, a parameter which has been suggested as a measure of fibre toxicity, to the point where short fibres might under some circumstances have roughly the same potential toxicity as long fibres. These observations suggest that short asbestos fibres could play an important role in the pathogenesis of some types of asbestos-related disease in cigarette smokers.