Protective Effects of Glucocorticoids on Nitric Oxide-induced Apoptosis in Leukaemia HL-60 Cells in Man

Inappropriate release of nitric oxide (NO) has been linked to the pathogenesis of several disease states. Glucocorticoids inhibit the synthesis of NO and could be effective in the treatment of NO-mediated diseases. We show the protective effect of dexamethasone on NO-induced apoptosis in leukaemia HL-60 cells in man. Agarose electrophoresis of the DNA extracted from HL-60 cells resulted in a ladder-like pattern of fragmentation after 6-and 9-h exposure of the cells to 1 mM S-nitrosoglutathione, a physiologically relevant NO donor. Pre-incubation of the cells with 1 μM dexamethasone for 6 h blocked NO-induced DNA fragmentation. This effect was abolished by RU-486, a steroid receptor antagonist, and cycloheximide, a protein synthesis inhibitor, suggesting that the protective effect of dexamethasone might require glucocorticoid receptor binding and protein synthesis. Concerning NO signal transduction, we found that dexamethasone efficiently prevented NO-induced activation of caspase-3 proteases, suggesting an inhibitory mechanism upstream of the terminal death pathway. Collectively, these findings highlight a novel protective effect of dexamethasone on NO-mediated cellular injury.