The induction of heme oxygenase-1 (HO-1) is widely recognized as an effective cellular strategy to counteract a variety of stressful events. We have shown that curcumin and caffeic acid phenethyl ester, two naturally occurring phytochemicals that possess antioxidant, anti-inflammatory, and anticarcinogenic activities, induce HO-1 in many cell types. This suggests that stimulation of HO-1 could partly underlie the beneficial effects exerted by these plant-derived constituents. Here we examined the ability of additional plant constituents to up-regulate heme oxygenase activity and HO-1 in aortic endothelial cells. Incubation of endothelial cells with a series of polyphenolic chalcones (5-50 microM) resulted in increased heme oxygenase activity; interestingly, the chemical structure dictated the pattern of heme oxygenase induction, which was unique to each particular compound employed. We also found that rosolic acid, a constituent isolated from the rhizome of Plantago asiatica L. dramatically increased HO-1 in a concentration- and time-dependent manner. Severe cytotoxicity was observed after prolonged exposure (24 or 48 h) of cells to curcumin and caffeic acid phenethyl ester, whereas 2'-hydroxychalcone and rosolic acid did not affect cell viability. By using different mitogen-activated protein kinase inhibitors, we determined that the extracellular signal-regulated kinase, p38, and c-Jun NH(2)-terminal protein kinase pathways play only a minor role in the induction of HO-1 by rosolic acid and 2'-hydroxychalcone. On the other hand, increased intra- and extracellular thiols markedly reduced the rise in heme oxygenase activity elicited by rosolic acid. Thus, this study identified novel plant constituents that highly induce HO-1 in endothelial cells and investigated some of the mechanisms involved in this effect.