Antioxidant activity of lazaroid (U-75412E) and its protective effects against crystalline silica-induced cytotoxicity

Lazaroids (21-amino steroids) are believed to be powerful scavengers of reactive oxygen species (ROS) and inhibitors of lipid peroxidation. Crystalline silica, a potent cytotoxic agent, causes pulmonary fibrosis in experimental animals and humans. ROS have been previously shown to be involved in crystalline silica-induced pulmonary injury and inflammation. In the present study, the reaction rate of lazaroid (U-75412E) with hydroxyl radical ('OH) generated by Fenton reaction (Fe(II) + H₂O₂ Fe(III) + OH- + 'OH) was investigated using ESR spin-trapping competition reactions. The reaction rate constant was found to be 1.0 X 10(10) M(-1)s(-1), which was comparable with those of other efficient 'OH radical scavengers. As indicators of crystalline silica-induced cytotoxicity and its protection by this antioxidant lazaroid (U-75412E) we measured lactate dehydrogenase, N- acetyl-β-D-glucosaminidase, superoxide dis mutase, glutathione peroxidase, and hydrogen peroxide released from rat alveolar macrophages. Lipid peroxidation, a prominent manifestation of 'OH radical-induced cell injury, was also measured to evaluate the protective value of lazaroid. Alveolar macrophages treated with lazaroid (U-75412E) before crystalline silica exposure were protected against cell injury and lipid peroxidation as demonstrated by those indicators. Lazaroid (U-75412E) scavenges 'OH radicals generated by crystalline silica-mediated reaction from H₂O₂ and inhibits lipid peroxidation in macrophages induced by these particles.