The soy isoflavone genistein induces a late but sustained activation of the endothelial nitric oxide-synthase system in vitro

Cardiovascular diseases are known as the major causes of death or disability in western countries. Decreased bioavailability of endothelial derived nitric oxide (NO) is recognized as an important promoter in cardiovascular disease. In vivo studies suggest that phytoestrogens, especially isoflavones from soy, enhance endothelium-dependent vasoreactivity. We hypothesized that isoflavones may affect the expression of endothelial-type nitric oxide synthase (eNOS) and thereby NO formation in vitro. Human EA.hy926 endothelial cells were treated with the soybean isoflavones biochanin A and formononetin and with their metabolites genistein and daidzein. eNOS promoter activity was examined by a luciferase reporter gene assay (20 h). Active eNOS was detected by quantifying conversion of L-arginine to L-citrulline and by measuring NO released from endothelial cells using the fluorescent probe DAF-2 (20-96 h).eNOS promoter activity increased in response to isoflavone treatment (20 h). NO and L-citrulline production by EA.hy926 cells rose up to 1.7-fold of control levels after stimulation with genistein for 48-96 h. From these results, we conclude that the suggested positive effects of soy isoflavones on vascular reactivity may be indeed mediated via a long-term effect on the eNOS system.