Scientific Program (Oral Abstracts) | Poster Abstracts | Speaker List
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 : Effects Independent of Cholesterol Reduction
Effects of Isoflavones On LDL-Cholesterol In Vitro but not In Vivo
Alan Chait.
Clinical Nutrition Research Unit, University of Washington, Seatle, WA.
Soy products contain several isoflavones, the most abundant of which is genistein. Genistein is a tyrosine kinase inhibitor, inhibits angiogenesis and has a chemical structure that suggests that it might have antioxidant properties. Both the oxidation of low density lipoprotein (LDL) and cell proliferation are believed to play important roles in the pathogenesis of atherosclerosis. Therefore, the effect of genistein, and another soy isoflavone, daidzein, which also has antioxidant potential, were tested for their ability to inhibit LDL oxidation in vitro and in vivo. Both genistein and daidzein inhibited LDL oxidation in a time and concentration dependent manner in vitro. Genistein was a more effective antioxidant than daidzein. LDL that was subjected to oxidant stress in the presence of these isoflavones was taken up and degraded by macrophages to a lesser extent than was LDL oxidized in their absence. LDL that was reisolated after incubation with either genistein or daidzein was no longer resistant to oxidation, in contrast to LDL that had been preincubated with probucol, a powerful lipophyllic antioxidant. Thus, genistein and daidzein protect LDL from oxidative modification even though they do not appear to become tightly incorporated into the LDL particle. Therefore, they may exert their antioxidant effect in the aqueous milieu of the lipoprotein in a manner similar to vitamin C.
To test whether a similar antioxidant effect was observed in humans fed diets enriched in soy isoflavones, LDL was isolated from 3 groups of postmenopausal females who consumed diets in which 40 g protein was either from casein (no isoflavones) or from soy protein isolates that contained either 1.8 or 2.3 mg. total isoflavones/g protein. No differences in the lag phase of conjugated diene formation, an index of the susceptibility of LDL to oxidative modification, was observed between the 3 groups after 12 weeks consumption of the diet. Since LDL is removed from its aqueous milieu for these oxidation experiments, these findings are consistent with the in vitro observations.In summary, the antioxidant properties of genistein and daidzein may be of value in the prevention of atherosclerosis, in addition to their potential antiproliferative effects.
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