Pulmonary responses to silica dust : the influence of crystalline structures and physico-chemical properties

The inhalation of silica crystalline polymorphs leads to the development of pulmonary nodules that vary in extent and in fibrotic content. In this study, a single protocol was used to test different silica samples (i.e., 2 non-crystalline samples: one vitreous silica, one diatomaceous earth , 4 crystalline samples: one pure a-quartz ground in a wet atmosphere, one of the same quartz heated until it becomes oc-cristobalite and 2 cristobalites obtained by heating diatomaceous earth). Wistar rats received a single intra-tracheal injection of alveolar dust and were followed over a period of 3 months. The results were exploited using macroscopic examination (wet lung weight), histological examination and biochemical dosing (hydroxyproline, lipid, and silica content). The results showed that vitreous silica, diatomaceous earth, wet-ground quartz and both types of cristobalites are responsible to a greater or lesser extent for the pulmonary reaction typical of exposure to silica (i.e., nodules ); with different cellular and fibrotic surface areas for each sample. a-cristobalite (obtained from the wet-ground quartz heated to a very high temperature; 1,300 °C) leads to the formation of only small foreign-body granulomas. All crystalline minerals tested caused alveolar lipoproteinosis. It was thus concluded that the crystalline structure plays a less important role than the surface state in the formation of silicotic nodules

Localisation ultra-structurale de l’activité oxydasique chez

Des toxoplasmes de souche RH ont été étudiés au microscope électronique à transmission et les activités suivantes ont été recherchées : peroxydase, cytochrome oxydase, phosphatase acide. Une activité respiratoire cytochrome oxydasique a été observée. Elle est localisée au niveau des crêtes et de la membrane périphérique des mitochondries de Toxoplasma gondii. Dans les conditions expérimentales données, aucune activité comparable n’est apparue au niveau des autres organites du parasite, ni dans les vacuoles des cellules-hôtes contenant des toxoplasmes vivants mais les organites de ces cellules-hôtes présentaient bien une activité oxydasique