Estradiol metabolites inhibit endothelin synthesis by an estrogen receptor-independent mechanism

Estradiol inhibits endothelin-1 synthesis, an effect that may contribute to the cardiovascular protective effects of estradiol. Recent findings that estradiol inhibits neointima formation in mice lacking estrogen receptors suggests that the cardiovascular protective effects of estradiol may be mediated by means of an estrogen receptor-independent mechanism. Because 2-hydroxyestradiol and 2-methoxyestradiol, metabolites of estradiol with little/no affinity for estrogen receptors, are more potent than estradiol in inhibiting vascular smooth muscle cell growth, we investigated whether these metabolites also inhibit endothelin-1 synthesis by means of an receptor-independent mechanism. Treatment of porcine coronary artery endothelial cells for 4 to 24 hours with 0.001 to 1 micromol/L of estradiol, 2-hydroxyestradiol, or 2-methoxyestradiol concentration-dependently inhibited basal as well as serum-induced (2.5%), TNFalpha-induced (10 ng/mL), angiotensin II-induced (100 nmol/L), and thrombin-induced (4 U/mL) endothelin-1 synthesis. Estradiol, 2-hydroxyestradiol, and 2-methoxyestradiol also inhibited serum-induced mitogen-activated protein kinase activity. As compared with estradiol, its metabolites were more potent in inhibiting endothelin-1 secretion and mitogen activated protein kinase activity. The inhibitory effects of 2-hydroxyestradiol and 2-methoxyestradiol on endothelin-1 release and mitogen-activated protein kinase activity were not blocked by ICI182780 (50 micromol/L), an estrogen receptor antagonist. Our findings indicate that the estradiol metabolites 2-hydroxyestradiol and 2-methoxyestradiol potently inhibit endothelin-1 synthesis by means of an estrogen receptor-independent mechanism. This effect of estradiol metabolites may be mediated by inhibition of mitogen activated protein kinase activity and may contribute to the cardioprotective effects of estradiol.