Chemoprevention of hepatocellular carcinoma by dehydroepiandrosterone and its derivatives

脱氢表雄酮（DHEA）是年轻成人中含量最丰富的肾上腺雄激素类固醇。脱氢表雄酮在预防人类肿瘤发生中的生理功能仍有争议，但大量研究表明，药理剂量的脱氢表雄酮对啮齿类动物肿瘤具有化学预防和抗增殖作用。本研究旨在为DHEA的临床应用提供基础数据和方法。主要研究结果如下：1.建立了一种灵敏、可靠的高分辨GC-MS同位素稀释技术定量分析DHEA相关甾体化合物的方法。该方法使得同时测定人血清中DHEA和DHEA衍生物水平成为可能。此外，为了评价DHEA对胆固醇代谢的影响，开发了用于定量胆固醇和胆汁酸生物合成途径中几个关键中间体的高灵敏度LC-MS/MS方法。 关于我们 对肝癌细胞株增殖的影响。我们证明了DHEA抗增殖的以下四种机制：1）由于葡萄糖-6-磷酸脱氢酶活性的抑制而导致NADPH和核糖-5-磷酸的消耗，2）通过抑制HMG-CoA还原酶活性而抑制胆固醇生物合成途径，3）干扰细胞增殖信号传导途径（MAPK级联反应）;和4）通过抑制PI 3 K/Akt信号通路诱导细胞凋亡。高胆固醇血症是肝癌患者的重要副肿瘤综合征之一，DHEA通过抑制胆固醇生物合成途径抑制肝癌细胞增殖。因此，我们通过肝癌大鼠模型研究了肝癌相关的高胆固醇血症的分子机制。因此，肝癌大鼠的高胆固醇血症是由于核受体LXR α激活导致的肿瘤胆固醇流出增加所致。固醇调节元件结合蛋白（SREBP）加工系统的过表达通过维持作为该核受体配体的氧化固醇的高组织水平而有助于LXR α的活化。少

Dehydroepiandrosterone (DHEA) is the most abundant adrenal androgenic steroid in young adult humans. The physiological functions of DHEA in preventing human carcinogenesis are still controversial, but a lot of reports have shown that pharmacological doses of DHEA show chemopreventive and anti-proliferative effects on tumors in rodents. The present study was undertaken to obtain basic data and methods for the clinical use of DHEA in the future. The following results were obtained.1.Sensitive and reliable method for the quantification of DHEA-related steroids by a stable isotope-dilution technique using high-resolution GC-MS was developed. The method made it possible to determine simultaneously DHEA and DHEA derivative levels in human serum. In addition, to evaluate the effects of DHEA on cholesterol metabolism, highly sensitive LC-MS/MS methods for the quantification of several key intermediates in the cholesterol and bile acid biosynthetic pathways were developed.2.The effects of DHEA … More on the proliferation of hepatic cancer cell lines were studied. We demonstrated the following four mechanisms of the anti-proliferation by DHEA : 1) depletion of NADPH and ribose-5-phosphate due to the inhibition of glucose-6-phosphate dehydrogenase activity, 2) suppression of cholesterol biosynthetic pathway by inhibition of HMG-CoA reductase activity, 3) interference with a cell proliferation signaling pathway (MAPK cascade), and 4)induction of apoptosis through the inhibition of the PI3K/Akt signaling pathway.3. Hypercholesterolemia is one of the important paraneoplastic syndromes in patients with hepatocellular carcinoma and DHEA inhibits the proliferation of hepatocellular carcinoma by inhibiting cholesterol biosynthetic pathway. Therefore, we investigated the molecular mechanisms of hypercholesterolemia associated with hepatoma by using a hepatoma-bearing rat model. As a result, hypercholesterolemia in the hepatoma-bearing rats was caused by the increased cholesterol efflux from tumors due to the activation of a nuclear receptor, LXRalpha. Over-expression of the sterol regulatory element-binding protein (SREBP) processing system contributes to the activation of LXRalpha by maintaining high tissue levels of oxysterols that are ligands for this nuclear receptor. Less