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SECOND INTERNATIONAL SYMPOSIUM
ON THE ROLE OF SOY
IN PREVENTING AND TREATING CHRONIC DISEASESeptember 15-18, 1996
Brussells, Belgium
SCIENTIFIC PROGRAM
(Oral Abstracts)Soy and Heart Disease : Hypercholesterolemic Effects of Soy :
Potential MechanismsThe Lack of Effect of Isoflavones on Plasma Lipid Concentrations in Ovariectomized Cynomolgus Monkeys and LDL Susceptibility to Oxidation
Sulistiyani, L. Tumbelaka, J. Sutanto, D. Sajuthi
Primate Research Center, Bogor Agricultural University, Bogor, Indonesia.The beneficial effect of estrogen replacement therapy in reducing the risk of coronary heart disease (CHD) in postmenopausal women is only partly explained by its effect on plasma lipid profile. It is thought that estrogen exert this beneficial effect through other mechanisms, one of which is attributed to its potency as an antioxidant. The use of estrogens, however, has been shown to increase the risk for breast and uterine cancer. One alternative is to use the plant estrogen isoflavone that have been reported to reduce the risk of CHD also. In the present study, we tested the effect of isoflavone genistein on plasma lipid concentrations of ovariectomized cholesterol-fed cynomolgus monkeys. Its in vivo effect as antioxidant on LDL susceptibility to in vitro oxidation was also determined at the end of the study. Forty-five ovariectomized animals were divided into three groups of 15: the first group was receiving atherogenic diet (0.23% cholesterol), the two other groups were receiving atherogenic diet plus genistein (30 mg/day) or genistein and vitamin E (179 IU/day). All groups received their diet for 24 months. The mean total plasma cholesterol concentrations (TPC) was increased to about 400 mg/dL for all groups upon consumption of cholesterol diet. Neither genistein nor its combination with vitamin E affected total plasma cholesterol, triglyceride, and HDL-cholesterol concentrations. Since the severe hypercholesterolemia might overwhelm the effect of isoflavone/or its combination with vitamin E, the plasma cholesterol concentration was reduced by decreasing the amount of the cholesterol in the diet to 0.11% for the last 6 months of the experimental period. As a result, TPC for all groups was decreased to about 200 mg/dL. Nevertheless, no effect on plasma lipid concentrations was observed. Isoflavone alone did not reduce the amount of thiobarbituric acid-reactive substances (TBARS) when LDL from each individual was subjected to copper-medicated oxidative modification. However, its combination with vitamin E significantly reduce the susceptibility of LDL to oxidation (40% reduction).
Although effect of isoflavone in vivo was not observed, isoflavone in vitro (10-5M) inhibit LDL oxidation by 48%, compared to 17-estradiol (10-5M) which reduced LDL oxidation down to 72%. These observations are consistent with others on the antioxidant potency of estrogens and isoflavonoid compounds. This study demonstrates that isoflavone beneficial effect in vivo is not mediated through alteration on plasma lipid profiles or prevention of LDL oxidation.
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