Role of free radicals in the mechanisms of hemolysis and lipid peroxidation by silica: comparative ESR and cytotoxicity studies.

Electron spin resonance (ESR) and cytotoxicity measurements were made on newly fractured silica to examine specifically the role of the fracture-induced, silicon-based radicals (Si. and SiO.) and silica-generated hydroxyl (.OH) radicals in the mechanism of the cell membrane damage by silica. The concentration of the Si. and SiO. radicals was controlled through decay processes, thermal annealing, and boiling, while that of the .OH radicals was varied by using catalase, superoxide dismutase, KMnO4, Na2SeO3, ascorbic acid, and metal ions, and monitored via ESR spectroscopy. The dust's cytotoxicity potential was evaluated by measuring the silica-induced hemolysis and also by determining lipid peroxidation (using linoleic acid). From the comparison of hemolysis and ESR results it is deduced that the radicals play little or no role in the silica-induced hemolysis. However, the lipid peroxidation data indicate that the radicals might be involved in the initiation of an oxidative chain reaction leading to the macrophage membrane damage through lipid peroxidation.