[Inhibition effect of soybean isoflavones on the oxidative modification of low-density lipoprotein]

In order to investigate the effect of soybean isoflavones(SI) on the oxidative modification to low-density lipoprotein(LDL) and to differentiate the effect of SI and alpha-tocopherol, in vitro and in vivo test were conducted. An in vitro model of LDL oxidative modification induced by copper-ion was established by monitoring the production of thiobarbituric acid-reactive substances (TBARS) and conjugated dienes after SI or alpha-tocopherol was added. The in vivo test was conducted by feeding rats with a high fat diet supplemented with SI and measured the sensitivity of LDL oxidative modification mediated by Cu2+ in vitro. The results revealed that when SI was added into the in vitro LDL oxidation system, the content of TBARS or conjugated dienes in the system was much reduced with a dose-effect relationship, whether lipid oxidation being initiated or not by copper-ion at 37 degrees C. In comparison with SI, only a significant inhibiting effect on lipid oxidation while alpha-tocopherol was added before the initiation of oxidation. High fat diet induced a rising of LDL sensitivity of oxidative stress, and adding SI to the high fat diet could counteract the sensitivity of LDL oxidative modification significantly. It is concluded that SI is a valuable natural antioxidant different from alpha-tocopherol in inhibiting LDL oxidative modification both in vitro and inv vivo.