[32] Elimination of Macrophages with Silica and Asbestos

Abstract

This chapter discusses the practical use of some of these agents as selective toxins for mononuclear phagocytes. It explores that silica and asbestos are naturally occurring, silicon-containing compounds which are widely distributed within geologic deposits in the earth's crust. Asbestos differs from silica in that, unlike silica, asbestos particulates have a fibrous character. The chapter discusses that certain types of asbestos and silica are toxic to macrophages, both in vitro and in vivo. When macrophages are exposed in vitro to these toxic agents, they exhibit extreme cytoplasmic vacuolation, karyopyknosis, disappearance of pseudopodia, and effacement of plasma membranes. Similar morphologic abnormalities have been observed in alveolar macrophages after experimental silica or asbestos inhalation in animals. It reviews that the cytoplasmic enzyme and lactate dehydrogenase have proved to be a useful marker for assessing macrophage cytotoxicity induced by these mineral dusts. Thus, the release of this enzyme into macrophage culture supernatants provides confirmatory evidence of macrophage lysis. The lethal action of silica is believed to result from a hydrogen bonding interaction of silicic acid with membrane protein and phospholipid moieties. Chrysotile asbestos, on the other hand, appears to exert its cytotoxic effect through an electrostatic interaction of its surface magnesium groups with ionized carboxyl groups of membrane glycoprotein sialic acid residues. © 1984, Elsevier Inc. All rights reserved.