Soy and alfalfa phytoestrogen extracts become potent low-density lipoprotein antioxidants in the presence of acerola cherry extract

Postmenopausal women have an increased risk of coronary heart disease. Oxid ation of low-density lipoprotein (LDL) has been implicated in atherogenesis , and the presence of modified LDL (LDL-) in plasma appears to represent LD L oxidation in vivo. Because previous studies have demonstrated a strong an tiatherogenic effect of estrogen due to its antioxidant activity and simila r antioxidant activity was found for specific isoflavones derived from soy extract, the antioxidant activity of a phytoestrogen extract derived from s oy and alfalfa was studied. Copper-mediated LDL oxidation was inhibited in the presence of soy and alfalfa extracts, and this effect was further enhan ced in the presence of acerola cherry extract, which is rich in ascorbic ac id. Male rabbit aortic endothelial cells pretreated with soy extract were r esistant to the toxic effects of high levels of LDL and LDL-, and a lesser, but significant protection, was also afforded by alfalfa extract. Cell-med iated oxidation of LDL, measured by LDL- formation, was inhibited in the pr esence of soy extract but not alfalfa extract. However, in the presence of acerola cherry extract, both soy and alfalfa extracts potently inhibited th e formation of LDL-. These findings show that acerola cherry extract can en hance the antioxidant activity of soy and alfalfa extracts in a variety of LDL oxidation systems. The protective effect of these extracts is attribute d to the presence of flavonoids in soy and alfalfa extracts and ascorbic ac id in acerola cherry extract, which may act synergistically as antioxidants . It is postulated that this synergistic interaction among phytoestrogens, flavonoids, and ascorbic acid is due to the "peroxidolitic" action of ascor bic acid, which facilitates the copper-dependent decomposition of LDL perox ides to nonradical products; this synergy is complemented by a mechanism in which phytoestrogens stabilize the LDL structure and suppress the propagat ion of radical chain reactions. The combination of these extracts markedly lowers the concentrations of phytoestrogens required to achieve significant antioxidant activity toward LDL.