Reactive oxygen species (ROS) are important mediators for several biologic responses, including apoptosis. The present study evaluated the time course of changes in intracellular ROS production and apoptosis-related proteins, as well as apoptotic changes in human tubular proximal cells (HK-2 cells) exposed to hyperglycemia. Apoptosis (annexin V binding), ROS formation (fluorescence probe dichlorofluorescin diacetate and FACScan flow cytometry), and X chromosome-linked protein (XIAP; Western blot) were studied in HK-2 cells grown in a medium containing normal (NG) or high glucose (HG) concentrations (5.5 or 30 mM, respectively) for 18 to 48 h. HG promoted an increase (65% at 18 h and 73% at 24 h; P < 0.05 versus NG) in intracellular ROS generation. At 18 h, the NF-kB binding activity (evaluated by electrophoretic mobility-shift assay) was suppressed by HG. At the same time, the expression of NF-kB-induced antiapoptotic XIAP was reduced in HG-treated cells. Apoptotic changes were observed at 48 h (34 +/- 7% in HG versus 10 +/- 3% in NG; P < 0.001). Changes in ROS production at 24 h predicted changes in the apoptotic index at 48 h (r = 0.96, P < 0.0001). These results suggest that hyperglycemia induces apoptotic changes in human tubular cells via an increase in oxidative stress and that a downregulation of antiapoptotic protein XIAP is a component of this response.