Soy isoflavones: database development, estrogenic activity of glycitein and hypocholesterolemic effect of daidzein
Soy isoflavones are proposed to have certain health protective activities, including prevention of cancer, lowering blood cholesterol levels and reducing postmenopausal bone loss. To evaluate the health-enhancing properties of isoflavones, a stable and inexpensive source of these compounds is necessary. Chemical synthesis is a practical way to obtain pure isoflavones. The synthesis of daidzein was modified to a simple, fast and high yield method by cyclizing 2,4,4'-trihydroxydeoxybenzoin (THB) with boron trifluoride etherate and methanesulphonyl chloride. The yield was >86%, and the purity of synthesized daidzein was >98%. The intermediate of daidzein synthesis, THB, with a similar structure to the isoflavones, proved to be an excellent internal-standard in soy isoflavone analysis;The estrogenic activity of glycitein was investigated by using in vivo mice uterine enlargement assay and in vitro estrogen receptor (ER) binding assay. Glycitein demonstrated an estrogenic response in mice uterine enlargement assay 3 times greater than genistein, but 30,000 times less than diethlstillbestrol (DES). Glycitein bound to mice uterine cytosol estrogen receptor proteins with an affinity similar to daidzein, but 20 times lower than genistein. This is the first report demonstrates that glycitein has estrogenic activity comparable to daidzein and genistein. Glycitein, although only accounts for 5 to 10% of the total isoflavones in soybeans, can not be neglected in evaluating isoflavones' health enhancing properties and in development of isoflavone database in foods;The dietary effects of soy protein, with or without isoflavones, daidzein and soygerm on plasma cholesterol levels were investigated in Golden Syrian hamsters. Daidzein, soygerm or soygerm extract, when added to casein diet, lowered plasma total cholesterol by 15% to 28% (P < 0.01) and LDL cholesterol by 15 to 50% (P < 0.01) in both male and female hamsters compared with the casein control group. Soy protein and isoflavone-depleted soy protein, when compared with the casein control, significantly lowered total cholesterol (P < 0.01) and LDL cholesterol (P < 0.01) levels for both genders. These data suggest that the isoflavone daidzein, soygerm and soy protein with or without isoflavones, have the ability to lower plasma cholesterol levels in hamsters.