Chemoprevention of hepatocellular carcinoma by dehydroepiandrosterone and its derivatives

脱氢表雄酮（DHEA）是年轻人体内最丰富的肾上腺雄激素类固醇。DHEA在预防人类癌变中的生理功能仍有争议，但大量报道表明，DHEA药理学剂量对啮齿动物肿瘤具有化学预防和抗增殖作用。本研究旨在为今后临床应用脱氢表雄酮提供基础资料和方法。得到了以下结果：建立了高分辨率气相色谱-质谱联用稳定同位素稀释技术定量测定脱氢表雄酮相关类固醇的灵敏可靠方法。该方法可以同时测定人血清中脱氢表雄酮和脱氢表雄酮衍生物的水平。此外，为了评估脱氢表雄酮对胆固醇代谢的影响，开发了高灵敏度的LC-MS/MS方法，用于定量胆固醇和胆汁酸生物合成途径中的几个关键中间体。研究了脱氢表雄酮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)通过抑制葡萄糖-6-磷酸脱氢酶活性导致NADPH和核糖-5-磷酸的消耗，2)通过抑制HMG-CoA还原酶活性抑制胆固醇生物合成途径，3)干扰细胞增殖信号通路（MAPK级联），4)通过抑制PI3K/Akt信号通路诱导细胞凋亡。高胆固醇血症是肝癌患者重要的副肿瘤综合征之一，DHEA通过抑制胆固醇生物合成途径抑制肝癌的增殖。因此，我们利用肝癌大鼠模型研究高胆固醇血症与肝癌相关的分子机制。结果，肝癌大鼠的高胆固醇血症是由于核受体lxrα的激活导致肿瘤中胆固醇外排增加引起的。固醇调控元件结合蛋白（SREBP）加工系统的过度表达通过维持高水平的组织内作为lxrα核受体配体的氧甾醇，有助于lxrα的激活。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