Oxidative stress–induced apoptosis of endothelial cells

Endothelial cells (ECs) are subjected to oxidative stress during many pathological processes, including ischemia/reperfusion and general inflammation. In the present study, we examined the effects of oxidative stress on rates of apoptosis in EC cultures. We treated large and microvessel ECs with menadione for 1 h in vitro to simulate the most common physiological form of oxidative stress, exposure to O2•−. Capillary ECs were resistant to menadione-induced apoptosis when compared with large-vessel ECs. Treatment with 35 μM menadione resulted in an apoptotic rate of not, vert, similar5% in capillary EC cultures compared with not, vert, similar45% in large-vessel EC cultures. At higher concentrations of menadione (35–75 μM), both types of ECs exhibited a concentration-related increase in apoptosis. Necrotic cell death only became evident at menadione concentrations ranging from 75–100 μM for both cell types. The timing of the apoptotic response to a 1 h menadione exposure was very specific. For both EC types, peaks of apoptosis occurred in two distinct waves, at 6–8 and 18–22 h after treatment. Analysis of the events leading up to the first peak of apoptosis indicated that specific matrix metalloproteinases (MMPs) were activated, suggesting that MMPs may be involved in initiating the apoptotic process.