Phytoestrogen alpha-zearalanol antagonizes homocysteine-induced imbalance of nitric oxide/endothelin-1 and apoptosis in human umbilical vein endothelial cells.

Although the issue of estrogen replacement therapy on cardiovascular health is debatable, it has presumable benefits for endothelial function in postmenopausal women. However, the fear of breast cancer has intimidated women contemplating estrogen treatment and limited its long-term application. An effective alternative remedy not associated with breast carcinoma is in serious demand. This study was designed to examine the effect of phytoestrogen alpha-zearalanol (alpha-ZAL) and 17beta-estradiol (E2) on nitric oxide (NO) and endothelin (ET)-1 levels, apoptosis, and apoptotic enzymes in human umbilical vein endothelial cells (HUVEC). HUVEC cells were challenged for 24 h with homocysteine (10-3 M), an independent risk factor for a variety of vascular diseases, in the presence of alpha-ZAL or E2 (10-9 to 10-6 M). Release of NO and ET-1 were measured with enzyme immunoassay. Apoptosis was evaluated by fluorescence-activated cell sorter analysis. Expression of endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), Bax, and Bcl-2 were determined using Western blot. NOS activity was evaluated with 3H-arginine to 3H-citrulline conversion. Our results indicated that Hcy significantly reduced NO production, NOS activity, enhanced ET-1/NO ratio and apoptosis, upregulated iNOS, Bax, and downregulated eNOS, Bcl-2 expression. These effects were significantly attenuated by alpha-ZAL and E2. ZAL displayed a similar potency compared with E2 in antagonizing Hcy-induced effects. In summary, these results suggested that alpha-ZAL may effectively preserve Hcy-induced decrease in NO, increase in ET-1/NO ratio and apoptosis, which contributes to protective effects of phytoestrogens on endothelial function.