Incorporation of esterified soybean isoflavones with antioxidant activity into low density lipoprotein

We have recently reported that dietary intake of soybean isoflavone phytoes trogens resulted in increased oxidation resistance of isolated low density lipoprotein (LDL). In order to explore the underlying mechanisms we designe d two types of in vitro experiments. First, we prepared several different i soflavone fatty acid esters to increase their lipid solubility and studied their incorporation into LDL. Second, the oxidation resistance of the isofl avone-containing LDLs was investigated with Esterbauer's 'conjugated diene' method using Cu2+ as prooxidant. Unesterified daidzein and genistein as we ll as genistein stearic acid esters were incorporated into LDL to a relativ ely small extent (0.33 molecules per LDL particle, or less) and they did no t significantly influence oxidation resistance. The oleic acid esters of is oflavones were incorporated more effectively, reaching a level of 2.19 mole cules per LDL particle or more, and the 4',7-O-dioleates of daidzein and ge nistein exhibited prolongations of lag times by 46% (P < 0.05) and 202% (P < 0.01), respectively. A smaller but significant increase in lag time (20.5 %, P < 0.01) was caused by daidzein 7-mono-oleate. In summary, esterificati on of soybean isoflavones daidzein and genistein with fatty acids at differ ent hydroxyl groups provided lipophilicity needed for incorporation into LD L. Some isoflavone oleic acid esters increased oxidation resistance of LDL following their incorporation. (C) 1999 Elsevier Science B.V. All rights re served.