Endothelial cell (EC) death may play an important role in the development of increased vascular permeability and capillary leak syndrome during systemic inflammatory response syndrome. However, the mode of EC death and the mechanisms involved remain unclear. In this study we employed the proinflammatory mediators lipopolysaccharide (LPS) and tumor necrosis factor-alpha (TNF-alpha), the chemical reagent sodium arsenite, and heat shock to trigger the stress gene responses. Human ECs were used as surrogates of the microvasculature to test the hypothesis that the induction of the heat shock response and the oxidative stress response might combine to induce apoptosis rather than necrosis in human ECs. Sodium arsenite at 80-320 microM, which induced heat shock protein 72 (HSP72) expression and reactive oxygen intermediate (ROI) generation in ECs, resulted in EC apoptosis. TNF-alpha alone (5-75 ng/ml) increased EC ROI generation but did not induce EC apoptosis. Heat shock alone (42 degrees C, 45 min) or sodium arsenite (40 microM) alone, each of which induced HSP72 expression, did not result in EC apoptosis. However, the combination of TNF-alpha with heat shock or 40 microM sodium arsenite led to EC apoptosis as HSP72 expression and ROI were induced. Furthermore, sodium arsenite (80 microM) in the presence of antioxidants failed to induce EC apoptosis. Apoptotic ECs also exhibited functional disturbances as represented by the depression of intercellular adhesion molecule-1 expression as well as the disruption of EC monolayer integrity. These results indicate that the simultaneous induction of a heat shock response and an oxidative stress response is responsible for human EC apoptosis.