The effects of low and high concentrations of luteolin on cultured human endothelial cells under normal and glucotoxic conditions: involvement of integrin-linked kinase and cyclooxygenase-2.

Luteolin protects against high glucose (HG)-induced endothelial dysfunction whereas its cytotoxicity has been reported against normal endothelial cells. This study was undertaken to determine luteolin cytoprotective and cytotoxic dose ranges and to elucidate their respective mechanisms. Luteolin prevented HG-induced human umbilical vein endothelial cell (HUVEC) death with an EC50 value of 2.0 ± 0.07 μM. The protective effect of luteolin was associated with decreased intracellular reactive oxygen species (ROS) and Ca(2+) (Cai(2+)) levels and enhanced nitric oxide (NO) production. At high concentrations, luteolin caused HUVEC death in normal glucose (NG) and HG states (LC50 40 ± 2.23 and 38 ± 1.12 μM, respectively), as represented by increased ROS and Cai(2+) and decreased NO. Western blots illustrated that exposure to HG increased cyclooxygenase-2 (COX-2) and integrin-linked kinase (ILK) expression. Luteolin at low concentrations suppressed HG-mediated up-regulation of COX-2 but maintained HG-induced over-expression of ILK while at high concentrations significantly increased COX-2 and decreased ILK expression in both HG and NG states. Our data indicated that cytoprotective action of luteolin was manifested with much lower concentrations, by a factor of approximately 20, compared with cytotoxic activity under both normal or glucotoxic conditions. It appears that luteolin exerts its action, in part, by modulating ILK expression which is associated with regulation of COX-2 expression and NO production in endothelial cells.