Isoflavone aglycone-rich extract without soy protein attenuates atherosclerosis development in cholesterol-fed rabbits

The antiatherogenic effect of soy protein with intact isoflavones is well e stablished, but the effects of isoflavones without soy protein have not bee n determined. We investigated the antiatherogenic effect of an isoflavone a glycone-rich extract (containing 429.4 mg/g isoflavone aglycones) without s oy protein from fermented soy in cholesterol-fed rabbits. We fed 12-wk-old New Zealand white male rabbits diets containing 1 g/100 g cholesterol with 0, 0.33 or 1 g/100 g isoflavone aglycones for 8 wk. We also fed the rabbits a diet containing 1 g/100 g cholesterol with 1.09 g/100 g soy saponin-rich extract, a component other than isoflavone aglycones in the isoflavone agl ycone-rich extract. Controls did not consume cholesterol, isoflavone aglyco nes or saponins. The isoflavone aglycone- and saponin-rich extracts did not affect the serum lipid profile of cholesterol-fed rabbits. The serum conce ntration of daidzein in its conjugated form was significantly higher in the high isoflavone group than in the low isoflavone group. The level of chole steryl ester hydroperoxide (ChE-OOH) induced by CuSO4 in plasma in the high isoflavone group was significantly less than that in the cholesterol group , and the ChE-OOH levels of LDL in the low and high isoflavone groups were significantly less than those in the cholesterol group. The ChE-OOH levels in plasma and LDL in the saponin group did not differ from the cholesterol group. In the aortic arch, the cholesterol concentration was significantly lower in the high isoflavone group, and malondialdehyde concentration was s ignificantly lower in the low and high isoflavone groups compared with the cholesterol group; however these concentrations in the saponin group did no t differ from those in the cholesterol group. The atherosclerotic lesion ar ea of the aortic arch was significantly lower in the isoflavone groups (26. 3% lower in the low isoflavone group and 36.9% lower in the high isoflavone group) than in the cholesterol group. The lesion areas were not different in the soy saponin and cholesterol groups. Immunohistochemical analysis rev ealed fewer oxidized LDL-positive macrophage-derived foam cells in atherosc lerotic lesions in the aortic arch of isoflavone groups compared with that of the cholesterol group. These results suggest that the antioxidative acti on of isoflavones and their antioxidative metabolites inhibit the oxidation of LDL, thereby exerting an antiatherosclerotic effect.