Phytoestrogen α-Zearalanol attenuates homocysteine-induced apoptosis in human umbilical vein endothelial cells.

Hyperhomocysteinemia is an independent risk factor for cardiovascular diseases. The enhanced nitrative stress plays an important role in homocysteine-induced endothelial dysfunction. Previous studies have showed that phytoestrogen α -zearalanol alleviated endothelial injury in ovariectomized hyperhomocysteinemic rats; however, the underlying mechanism remains to be clarified. This study was to investigate the effects of α -zearalanol on homocysteine-induced endothelial apoptosis in vitro and explore the possible role of nitrative stress in these effects. Results showed that homocysteine (500 µ mol/L, 24 h) induced the apoptosis of human umbilical vein endothelial cells (HUVECs) obviously, and this effect was significantly attenuated by pretreatment with α -zearalanol (10(-8)~10(-6) mol/L). Moreover, α -zearalanol downregulated proapoptotic protein Bax, upregulated antiapoptotic proteins Bcl-2 and Bcl-XL, and decreased the expression and activity of caspase-9. These findings demonstrated that α -zearalanol could effectively alleviate homocysteine-induced endothelial apoptosis, and this antiapoptosis effect might be related to the inhibition of the intrinsic pathway. Western blot indicated an enhanced 3-nitrotyrosine expression in HUVECs when challenged with homocysteine, which was attenuated by pretreatment with α -zearalanol. This result implied that inhibition of nitrative stress might play a role in the protective effect of α -zearalanol on endothelial cells. Such discovery may shed a novel light on the antiatherogenic activities of α -zearalanol in hyperhomocysteinemia.

Phytoestrogen α-zearalanol improves vascular function in ovariectomized hyperhomocysteinemic rats.

Previous studies have showed that phytoestrogen α-zearalanol (α-ZAL) could antagonize homocysteine (Hcy) induced endothelin-1 (ET-1) expression, oxidative stress and apoptosis in human umbilical vein endothelial cells in vitro, however, its effect on vascular function in vivo remains to be determined. This study was designed to investigate the effects of α-ZAL on vascular function in ovariectomized (OVX) hyperhomocysteinemia (HHcy) rats and explore the mechanisms involved primarily. HHcy rat model was induced by diets containing 2.5% methionine (Met) for 12 weeks. Forty adult female Wistar rats were assigned randomly into five groups: (1) Con; (2) Met; (3) OVX+Met; (4) OVX+Met+α-ZAL; (5) OVX+Met+17ß-E(2) (17ß-estradiol). Blood was collected to analyze plasma estradiol, Hcy and ET-1. Thoracic aortas were isolated to detect its response to phenylephrine (PE) and acetylcholine (ACh) or sodium nitroprusside (SNP). Aortas eNOS expression was determined by Western blot. Thoracic aortas histological characterization was analyzed by optical microscope and scanning electron microscope (SEM). Rat plasma Hcy was significantly elevated after fed with 2.5% methionine diets, and ovariectomy aggravated this elevation. Phytoestrogen α-ZAL or 17ß-E(2) could attenuate this elevation. Plasma ET-1 levels increased significantly in ovariectomized HHcy rats, and supplement with α-ZAL or 17ß-E(2) could reverse these changes. In rats of OVX+Met group, PE elicited significantly greater contraction in a dose-dependent manner in endothelium-intact thoracic aortas rings; ACh elicited significantly less percentage relaxation. These effects were significantly attenuated by supplement with α-ZAL or 17ß-E(2). There was no significant difference between groups in relaxation induced by SNP whether endothelium intact or not. Thoracic aortas morphology study also showed severe endothelium injury in ovariectomized HHcy rats, both α-ZAL and 17ß-E(2) could attenuate this change. Aortas eNOS expression was decreased in ovariectomized HHcy rats, and supplement with α-ZAL or 17ß-E(2) could reverse these changes. These findings demonstrated that α-ZAL could effectively alleviate the impairment of endothelial cells and improve vascular function in ovariectomized HHcy rats by decreasing plasma Hcy and antagonizing decreasing of aortas eNOS expression. This protective effect is somewhat similar with 17ß-E(2).