A review of the fate of inhaled a-quartz in the lungs of rats

摘要

The distribution of dust particles within the lungs and their excretion are highly associated with their pulmonary toxicity. Literature was reviewed to discern pulmonary translocation pathways for inhaled a-quartz compared to those for inhaled TiO2. Accordingly, it was hypothesized a-quartz particles in the alveoli were phagocytized by alveolar macrophages but silica-containing macrophages remained in the alveoli for longer time in contrast to the rapid elimination from the alveoli seen for Ti02-con-taining macrophages. In addition, it was presumed that free silica particles are translocated in the interstitium, possibly through the cytoplasm of Type I epithelial cells, as observed with TiO2. Free silica particles are presumed to be phagocytized by interstitial macrophages soon after the particles penetrate the interstitium; these dust cells are then translocated to the ciliated airway regions in the lumen through bronchus-associated lymphoid tissue (BALT). The pulmonary retention half-time of dust particles in rats exposed to a-quartz is several times longer than that of rats exposed to TiO2, as long as the lung dust burden is w 3 mg. The reduced pulmonary particle clearance ability in rats exposed to a-quartz aerosol is presumably attributed to the long-term retention of dust cells both in the alveoli and in the interstitium; this retention may be caused by the reduced chemotactic abilities of a-quartz-containing dust cells. However, the accumulation of a-quartz-containing dust cells in the lungs is not associated with the occurrence of pulmonary inflammation.