Blockade of the apoptotic machinery by cyclosporin A redirects cell death toward necrosis in arterial endothelial cells: regulation by reactive oxygen species and cathepsin D.

Blockade of the mitochondrial permeability transition pore (mPTP) by cyclosporin A (CsA) inhibits apoptosis in various cell types. However, use of CsA in humans is associated with damage to the arterial endothelium. We evaluated whether inhibition of the apoptotic machinery by CsA promotes other forms of cell death in arterial endothelial cells (EC). Exposure of human umbilical artery EC (HUAEC) to clinically relevant concentrations of CsA for up to 24 h was associated with a significant increase in necrotic features. We detected inhibition of apoptosis and a significant increase in necrosis in HUAEC exposed concomitantly to CsA and mitomycin C, a proapoptotic DNA damaging agent. We found that CsA-induced cell death is independent of caspase activation, p53 induction, and calcineurin inhibition. However, bongkrekic acid, another mPTP blocker, also increased necrosis in HUAEC. Dihydroethidium and acridine orange staining revealed increased intracellular production of reactive oxygen species (ROS) followed by lysosomal damage in HUAEC exposed to CsA. Hydroxyl radical and superoxide scavengers and inhibition of cathepsin D activity significantly attenuated CsA-induced EC death. These results suggest that inhibition of the apoptotic machinery by CsA in arterial EC favors development of a necrotic form of cell death regulated by ROS and secondary lysosomal damage.