Sulfur mustard induces apoptosis and necrosis in endothelial cells

Sulfur Mustard (SM) is a vesicant or blistering chemical warfare agent, for which there still is no effective therapy. Endothelial cells are one of the major cellular targets for SM. The mechanism of endothelial cell death during SM injury is poorly understood. We studied the effect of exposure of endothelial cells to 0-1000 microM SM over the time course of 2-24 hr to determine the role of apoptotic and necrotic patterns of cell death in endothelial injury induced by SM. SM concentrations < or = 250 microM induced exclusively apoptosis which was observed after 5 hr in 30% of endothelial cells. Exposure to SM concentrations > or = 500 microM caused apoptosis and necrosis to the same extent in 60-85% of all cells after 5 to 6 hr. Necrosis was accompanied by a significant (approximately 50%) depletion of intracellular ATP, while in apoptotic cells ATP remained at the level similar to healthy cells. Interestingly, disruption of the long actin filament stress fibers and rounding of cells preceded other features of apoptosis--DNA fragmentation, membrane budding, and apoptotic body formation. In apoptotic cells, microfilaments formed constricted perinuclear bands, which were not observed in necrotic cells. Pretreatment with 50 mM N-acetyl-L-cysteine (NAC), a sulfhydryl donor and antioxidant, nearly eliminated the apoptotic features of cell death but did not prevent necrosis in response to SM. NAC pretreatment alone induced reorganization of actin filaments into an enhanced network of long stress fibers instead of a dominant cortical band of actin. NAC pretreatment prevented loss of cell adherence and cell rounding following exposure to 250 microM SM. The effect of NAC on cytoskeletal organization and its ability to eliminate SM-induced apoptosis suggests that actin filament organization may be an important element in cellular susceptibility to apoptotic stimuli.