Yavelow J, Finlay T H, Kennedy A R, Troll W
Cancer Res. 1983 May;43(5 Suppl):2454s-2459s.
Vegetarian populations show a decreased occurrence of breast, colon, and prostatic cancers. Epidemiological studies have identified seeds (maize, corn, and beans) as protective agents in these cancers. We have selected to study one abundant component of all seeds, protease inhibitors. Synthetic and natural protease inhibitors have been shown to inhibit tumor promotion in vivo and in vitro. In the present study, we report that a typical, natural protease inhibitor, the Bowman-Birk inhibitor isolated from soybeans, survives inactivation by stomach digestion in rodents and appears to be fully active as a protease inhibitor in the small intestine, where it complexes with the proteases occurring there, i.e., trypsin and chymotrypsin. A large part of the inhibitor is excreted as protease:protease inhibitor complexed in the feces. We also report the specific inhibition of transformation caused by ionizing radiation by this protease inhibitor. The mechanism of anticarcinogenesis of ingested protease inhibitors may involve the indirect effect of partially blocking protein absorption. High-protein and high-fat diets are known to increase cancer occurrence. Protease inhibitors reaching specific sites also have anticarcinogenic activities, as demonstrated by the radioprotective effect of a protease inhibitor in vitro. The relative importance of the indirect and direct action of protease inhibitors remains to be established.
素食人群中乳腺癌、结肠癌和前列腺癌的发病率较低。流行病学研究已确定种子（玉米、谷物和豆类）是这些癌症的预防因子。我们选择研究所有种子中的一种丰富成分——蛋白酶抑制剂。合成和天然蛋白酶抑制剂已被证明在体内和体外均能抑制肿瘤的生长。在本研究中，我们报告了一种典型的天然蛋白酶抑制剂——从大豆中分离出的鲍曼-伯克抑制剂，在啮齿动物体内经胃消化后仍能保持活性，并且在小肠中作为蛋白酶抑制剂似乎仍具有完全活性，它在小肠中与那里存在的蛋白酶（即胰蛋白酶和胰凝乳蛋白酶）结合。大部分抑制剂以蛋白酶-蛋白酶抑制剂复合物的形式随粪便排出。我们还报告了这种蛋白酶抑制剂对电离辐射引起的细胞转化具有特异性抑制作用。摄入的蛋白酶抑制剂的抗癌机制可能涉及部分阻断蛋白质吸收的间接作用。已知高蛋白和高脂肪饮食会增加癌症的发病率。到达特定部位的蛋白酶抑制剂也具有抗癌活性，体外实验中一种蛋白酶抑制剂的辐射防护作用就证明了这一点。蛋白酶抑制剂间接和直接作用的相对重要性仍有待确定。
