ROLE OF FEMALE HORMONE AND FOOD FACTORS IN PREVENTION OF ATHEROSCLEROSIS -INVESTIGATIONS USING KNOCKOUT MICE

众所周知，绝经后妇女缺血性心脏病和动脉粥样硬化等心血管疾病的发病率高于绝经期妇女。其原因是绝经后妇女血清雌激素水平明显下降，这种下降与动脉粥样硬化的发生有关。雌激素是由睾酮通过存在于卵巢中的芳香化酶细胞色素P-450的酶催化产生的。我们在2000年至2001年的研究中发现，在高胆固醇和高脂肪饮食喂养4个月的芳香化酶敲除小鼠中不能观察到动脉粥样硬化。小鼠是一种大鼠型动物，其主要的血浆脂蛋白是高密度脂蛋白（HDL），这是一种抗动脉粥样硬化的脂蛋白，因此在小鼠中动脉粥样硬化的发生率非常低。提示雌激素缺乏本身可能不是小鼠动脉粥样硬化发病的唯一因素。我们正在尝试建立一种新的模型小鼠，一种载脂蛋白E和芳香化酶基因均被破坏的双基因敲除小鼠。大豆分离蛋白（SPI）含有抗动脉粥样硬化的活性成分。以大豆分离蛋白（SPI）为原料，经水提取后，采用离子交换柱层析法制备了不含胆甾酮的SPI（IF-SPI）。我们让apo E基因敲除小鼠（8个月大）用SPI或IF-SPI饮食喂养3周。与IF-SPI饮食的小鼠相比，饲喂SPI饮食的apo E基因敲除小鼠的血浆总胆固醇降低。相反，HDL-胆固醇增加与SPI饮食。在SPI饮食的情况下，动脉粥样硬化的程度弱于IF-SPI饮食的情况。这些结果表明，大豆蛋白本身而不是大豆蛋白具有动脉粥样硬化保护作用。

It is well known that the incidence of cardiovascular diseases such as ischemic heart disease and atherosclerosis is higher in the post-menopausal women than in the menopausal women. The reason is explained by the fact that the serum level of female hormone, estrogen is decreased very much in the post-menopausal women, and the decrease must be related to the pathogenesis of atherosclerosis. Estrogen is produced from testosterone by the enzymatic catalysis of aromatase cytochrome P-450 which exists in the ovary. We found from our investigation in 2000〜2001 that atherosclerosis cannot be observed in aromatase knockout mice fed on a high cholesterol and high fat diet for 4 months. Mouse is an animal of rat type whose major plasma lipoprotein is HDL, atheroprotective lipoprotein, thereby the incidence of atherosclerosis is very rare in mice. These findings suggest that the deficiency of estrogen itself may not be a sole factor of the pathogenesis of atherosclerosis in mice. We are now trying to make a new model mouse, a double knockout mouse whose genes of both apo E and aromatase are destroyed. It is known that soy protein isolate (SPI) which contains isoflavone is anti-atherogenic. We prepared isoflavone-free SPI (IF-SPI) using ion exchange column chromatography after extraction of SPI with water. We kept apo E-knockout mice (8 months old) fed on a diet with SPI or IF-SPI for 3 weeks. The plasma total cholesterol in apo E-knockout mice fed on an SPI-diet was decreased compared with the mice on an IF-SPI diet. On the contrary, HDL-cholesterol was increased with an SPI-diet. The extent of atherosclerosis in the case of SPI-diet was weaker than in the case of IF-SPI diet. These results suggest that isoflavone itself rather than soy protein has atheroprotective effect.