A caspase inhibitor decreases oxidized low-density lipoprotein-induced apoptosis in bovine endothelial cells

Background. Apoptosis is a pathway of cell death orchestrated by a family o f proteases called caspases. Oxidized low density lipoprotein (oxLDL) is a putative cause of atherogenesis. We examined the effect of oxLDL on endothe lial cell (EC) apoptosis and the ability of a caspase antagonist to inhibit oxLDL-induced EC injury. Methods. Bovine ECs were plated at a concentration of 5.0 x 10(5) cells/ml and exposed to LDL oxidized by ultraviolet radiation at a concentration of 100 mu g oxLDL/ml for 20 h. Some ECs were pretreated with an irreversible c aspase inhibitor (ZVAD). Samples were analyzed histologically. Apoptosis wa s measured using the Annexin V assay (flow cytometry) which detects phospha tidylserine on plasma membranes and confirmed by TUNEL assay (flow cytometr y). Statistical assessments were performed using ANOVA. Results. ECs treated with LDL were morphologically similar to untreated cel ls. Cells treated with oxLDL demonstrated cytoplasmic shrinkage, plasma mem brane blebbing, chromatin condensation, and loss of adhesion. These effects were diminished after pretreatment with the caspase inhibitor ZVAD. The An nexin V assay showed: (a) cells exposed to LDL had a 12 +/- 1% apoptosis ra te, (b) exposure to oxLDL induced apoptosis in 30 +/- 0.3% of the cells, an d (c) pretreatment with the caspase inhibitor ZVAD decreased the oxLDL-indu ced apoptosis to 16 +/- 1% (P < 0.05). This decrease in apoptosis was also reflected by an increase in the percentage of alive cells from 34 +/- 7% af ter oxLDL exposure to 55 +/- 6% after apoptosis inhibition with ZVAD. TUNEL assay demonstrated a 2.5-fold reduction in mean fluorescence intensity bet ween cells treated with oxLDL alone and those treated with ZVAD, suggesting a significant decrease in apoptosis in the latter group. Conclusions. We conclude that treatment of bovine ECs with oxLDL induces ap optosis which can be significantly reduced by a specific caspase inhibitor. (C) 1999 Academic Press.