Tikkanen M J, Wähälä K, Ojala S, Vihma V, Adlercreutz H
Department of Medicine, University of Helsinki, 00290 Helsinki, Finland.
Proc Natl Acad Sci U S A. 1998 Mar 17;95(6):3106-10. doi: 10.1073/pnas.95.6.3106.
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 isoflavonoid 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 isoflavonoid 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 isoflavonoid levels occurred during soy feeding, but only minute amounts were stably associated with lipoproteins (less than 1% of plasma isoflavonoids 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 soy-derived 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 isoflavonoids promoting resistance to oxidation ex vivo.
当低密度脂蛋白（LDL）颗粒与循环中的水溶性抗氧化剂分离后，其氧化过程被认为发生在动脉内膜。我们推测，源自大豆的异黄酮抗氧化剂可能会掺入脂蛋白中，并有可能保护它们免受氧化，而氧化被认为具有致动脉粥样硬化作用。六名健康志愿者连续两周每天食用3块大豆棒（含有异黄酮抗氧化剂染料木黄酮12毫克和大豆苷元7毫克）。在为期两周的饮食基线期结束时、食用大豆两周后以及停止食用大豆后，分别从采集的血液中分离LDL。食用大豆期间，血浆异黄酮水平大幅升高，但只有极少量与脂蛋白稳定结合（LDL部分中血浆异黄酮的比例不到1%）。对LDL进行体外铜介导的氧化。与未食用大豆时的值相比，食用大豆期间LDL氧化曲线的延迟期平均延长了20分钟（P<0.02），表明氧化敏感性降低。结果表明，摄入源自大豆的抗氧化剂，如染料木黄酮和大豆苷元，可能会为LDL的氧化修饰提供保护。由于在纯化的LDL中仅检测到极少量的这些物质，循环中的异黄酮可能在体内产生了修饰的LDL颗粒，从而促进了体外抗氧化能力。
