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The role of serine and metalloproteinases in silica and coal dust induced connective tissue breakdown Zay, Katalin


The exposure of the lung to silica and coal dusts causes acute inflammation and the recruitment of neutrophils and macrophages to the site of the injury. Upon activation both cell types are able to release a series of potent substances such as oxygen radicals and proteinases that can damage lung cells and break down the components of the lung's extracellular matrix. The aim of this study was to test the hypothesis that different dusts provoke different inflammatory responses, meaning that macrophages and neutrophils react differently depending on the nature of the dust, therefore the damage causing proteinase profiles of these two cell types are consequently different for each dust. The experimental model in this study consisted of C57B1/6 mice exposed to intratracheal instillation of silica and coal dusts. The mice were examined for recruitment of neutrophils and macrophages into the lung. The bronchoalveolar lavage fluids were tested by HPLC for connective tissue breakdown products originating from collagen and elastin fibers (hydroxyproline and desmosine respectively). The lung tissue was categorized into 'lung tissue',' bronchoalveolar lavage fluid' and 'cells that were washed out with the lavage fluid'. Each fraction was tested for collagenolytic and elastolytic activity of serine and metalloproteinases by gelatin, casein and Kelastin zymographies. The a-l antitrypsin levels and elastase inhibitory capacity were measured in the bronchoalveolar lavage fluids. The results showed that the primary response to silica dust damage to the lung was led by neutrophils, and after fourteen days both neutrophils and macrophages played role in the process of inflammation. In case of coal dust exposure after an initial rapid neutrophil recruitment to the site of injury the inflammatory response seemed to be mediated almost exclusively by macrophages. The levels of hydroxyproline increased after silica and coal induced injury similarly to the number of macrophages. The desmosine levels showed direct relationship with the neutrophil numbers after both silica and coal dust induced injury. In the lung tissue and in the bronchoalveolar lavage fluid after both silica and coal dust exposure the increase in 92 kD gelatinase levels showed direct correlation with the increase of the number of neutrophils present in the lavage fluid. The 72 kD gelatinase levels showed no close relationship with macrophage numbers, suggesting that in addition to macrophages, other cells of the lung tissue, such as fibroblasts, epithelial and endothelial cells may be responsible for the increased levels of this enzyme. The study showed that both neutrophils and macrophages play role in silica and coal dust induced lung injury, but the respective patterns of the mflarnmation and the damage-causing proteinase profile for both dusts is different.

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