Activation of nitric oxide synthesis in human endothelial cells by red clover extracts.
OBJECTIVE
The unexpected findings of the Women's Health Initiative trial, where surrogate cardiovascular risk markers have failed to predict the cardiovascular performance of hormone therapy, showing no reduction of cardiovascular disease in postmenopausal women receiving hormonal preparations inducing a favorable lipid profile, raise the interest on how molecules with hormone-like activity used for the treatment of menopausal symptoms act on vascular cells. This is particularly important for estrogen-like compounds such as phytoestrogens, whose mechanisms of action may significantly differ from those of other estrogenic compounds.


METHODS
Because endothelial-derived nitric oxide (NO) is a key regulator of vascular tone and atherogenesis as well as a well-characterized estrogen-regulated molecule, we studied the regulation of NO synthesis in cultured human endothelial cells by phytoestrogens contained in red clover extracts.


RESULTS
We show that red clover extracts activate NO synthesis in endothelial cells by recruiting transcriptional pathways but are not capable of inducing rapid NO synthesis through nongenomic mechanisms. During prolonged exposures, red clover extracts enhance the expression as well as the activity of endothelial nitric oxide synthase. These effects are mediated by a recruitment of estrogen receptor-beta. Moreover, we show that red clover-derived isoflavones synergize with 17beta-estradiol in increasing endothelial nitric oxide synthase activity and expression, therefore being devoid of antiestrogenic effects in human endothelial cells.


CONCLUSIONS
These results help to understand the mechanisms of action of phytoestrogens on the cardiovascular system and have relevant clinical implications.
Simoncini
Tommaso
T
Molecular and Cellular Gynecological Endocrinology Laboratory (MCGEL), Department of Reproductive Medicine and Child Development, Division of Obstetrics and Gynecology, University of Pisa, Via Roma, 57, 56100, Pisa, Italy. t.simoncini@obgyn.med.unipi.it
Fornari
Letizia
L
Mannella
Paolo
P
Caruso
Antonella
A
Garibaldi
Silvia
S
Baldacci
Chiara
C
Genazzani
Andrea R
AR
D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D042783:Endothelial Cells / Q000187:drug effects*; D004730:Endothelium, Vascular / Q000378:metabolism; D047628:Estrogen Receptor alpha / Q000378:metabolism; D047629:Estrogen Receptor beta / Q000378:metabolism; D006801:Humans; D009569:Nitric Oxide / Q000096:biosynthesis*; D019001:Nitric Oxide Synthase / Q000378:metabolism; D048789:Phytoestrogens / Q000494:pharmacology*; D010936:Plant Extracts / Q000494:pharmacology*; D015398:Signal Transduction; D029921:Trifolium
D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D048789:Phytoestrogens; D010936:Plant Extracts; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase