LDL-antioxidant pterocarpans from roots of Glycine max (L.) Merr

The methanolic root extract of Glycine max (L.) Merr. was chromatographed, which yielded 10 flavonoids, including three isoflavones 1-3, five pterocarpans 4-8, one flavonol 9, and one anthocyanidin 10. All isolated compounds were examined for LDL-antioxidant activities using four different assay systems on the basis of Cu2+-mediated oxidation. Among them, seven compounds showed potent LDL-antioxidant activities in the thiobarbituric acid reactive substances (TBARS) assay, the lag time of conjugated diene formation, relative electrophoretic mobility (REM), and fragmentation of apoB-100 on copper-mediated LDL oxidation. Three pterocarpans 4, 6, and 7, never reported as LDL-antioxidant, showed potent activities with IC50 values of 19.8, 0.9, 45.0 microM, respectively, in comparison with probucol (IC50 = 5.6 microM) as positive control. Interestingly, coumestrol 6 (IC50 = 0.9 microM) showed 20 times more activity in the TBARS assay than genistein (IC50 = 30.1 microM) and daidzein (IC50 = 21.6 microM), representative antioxidants in soybean. Moreover, coumestrol 6 had an extended lag time of 190 min at 3.0 microM in measuring conjugated diene formation, while both genistein (120 min) and daidzein (93 min) lag times were extended to less than 120 min at the same concentration.