Effect of soybean phytoestrogen intake on low density lipoprotein oxidation resistance

Abstract

The oxidation of low density lipoproteins (LDLs) is thought to take place in the arterial intima when the particles have become isolated from circulating water-soluble antioxidants. We hypothesized that isof lavonoid antioxidants derived from soy could be incorporated into lipoproteins and possibly could protect them against oxidation, which is regarded as atherogenic. Six healthy volunteers received 3 soy bars [containing the isof lavonoid antioxidants genistein (12 mg) and daidzein (7 mg)] daily for 2 weeks. LDLs were isolated from blood drawn at the the end of a 2-week dietary baseline period, after 2 weeks on soy, and after discontinuation of soy. Large increases in plasma isof lavonoid levels occurred during soy feeding, but only minute amounts were stably associated with lipoproteins (less than 1% of plasma isof lavonoids in the LDL fraction). The LDLs were subjected to copper-mediated oxidation in vitro. Compared with off soy values, lag phases of LDL oxidation curves were prolonged by a mean of 20 min (P < 0.02) during soy intake, indicating a reduced susceptibility to oxidation. The results suggest that intake of soyderived antioxidants, such as genistein and daidzein, may provide protection against oxidative modification of LDL. As only very small amounts of these substances were detected in purified LDL, modified LDL particles may have been produced in vivo by circulating isof lavonoids promoting resistance to oxidation ex vivo.

Role of plasma lipoproteins in the transport of the soyabean isoflavones daidzein and daidzein-7-O-β-d-glucoside

“…The concentrations of DAI in the different fractions obtained after lipoprotein separation of 2 ml plasma were measured by GC/MS using a stable isotopically labelled internal standard [3,4,[8][9][10][11][12][13] C]DAI. Total DAI was determined after extraction and enzymic hydrolysis with a mix of b-glucuronidase and sulfatase.…”

“…The separated lipoprotein fractions were equilibrated with 100 pmol [3,4,[8][9][10][11][12][13] C]DAI for 30 min at room temperature and diluted with five volumes of 0·5 M-triethylammonium sulfate (pH 5). Further details on sample clean-up, enzymic hydrolysis and derivatisation for GC/MS analysis are described by Rüfer et al (4) .…”

“…GC/MS conditions can be found in Rüfer et al (4) . The selected ion monitoring was applied to monitor two ions for each analyte, where the first was used for quantification and the second was used as confirmation of the presence of the analyte: m/z 398 and 383 for DAI as well as m/z 401 and 386 for [3,4,[8][9][10][11][12][13] C]DAI. DAI was quantified using ten calibration levels between 0 and 10 pmol.…”

“…[3,4,[8][9][10][11][12][13] C]DAI was obtained from Nigel Botting, University of St Andrews (St Andrews, UK). Enzymes and all other chemicals used were obtained from SigmaAldrich (Taufkirchen, Germany).…”

Design and baseline characteristics of a trial on health effects of soy protein with isoflavones in postmenopausal women

“…There is limited evidence in humans that bone metabolism is affected favorably by the isoflavone derivative ipriflavone [21] and by soy isoflavones [22,23]. Studies in humans have shown that phytoestrogens decrease plasma lipids [24,25], LDL oxidation [26,27], arterial compliance [28] and endothelial cell damage [26]. These observations are strengthened by experimental data in atherosclerotic non-human primates, indicating that cardiovascular risk factors [29,30], coronary artery atherosclerosis [31], coronary vascular reactivity [32] and aortic cholesteryl ester content [30] are influenced favorably.…”