微囊藻毒素与黄曲霉毒素低水平联合暴露诱导原发性肝癌发生的人群与机制研究

Primary hepatocellular carcinoma （PHCC）is a serious threat to human, especially in rural China. Virus infection (including HBV and HCV) alone is insufficient to explain all of its etiology. Now in China, due to the special ecological characteristics of the environment and the growing water eutrophication trend, people are exposed to aflatoxins and microcystins，both being hepatotropic toxins, frequently, and animal experiments have showed liver tumor increased obviously when animals were co-exposure to the two toxins. However, up to now, there has neither epidemiology research to verify, nor no study on molecular mechanism to interpret. In our previous studies, we found, YIHE, one town located in Three Gorges Reservoir, which water and food were contaminated by microcystin and aflatoxin, had 1.83 times in percent of hepatic injure children and 4.08-4.74 times of crude liver cancer death rate than the adjacent LIDU, that water was not contaminated town, we hypothesized long-term co-exposure to these two toxins might be the reason. Therefore, in this program, we plan to, firstly, carry out one cross sectional study on the rural towns to analyze the correlation between two toxins co-exposure and PHCC or hepatic injury; and secondly, carry out one case control study on clinic PHCC patients to further confirm the association and the associated degree between coexposure and PHCC, and thirdly, by in vivo animal study and in vitro cell experiment, investigate the molecular mechanism focused on DNA damage and repair in malignant transformation induced by two toxins co-exposure, and finally, based on epidemiological and experimental data, assess the risk of the PHCC or hepatic injury when human expose to this co-exposure. The results will be helpful to ascertain the environmental etiology risk of PHCC, and lay the foundation for the further study.

肝癌严重威胁人类健康，尤其在我国农村。目前病毒感染不足以解释其全部病因。黄曲霉毒素和微囊藻毒素是中国人较常暴露的嗜肝性毒物，动物实验显示两者联合致肝癌效应明显增强，但迄今未见人群水平验证及分子机制研究。我们前期发现，水源和食物同时受到两种毒物污染的三峡库区义和镇，与邻近水源未受污染的李渡镇相比，儿童肝损伤百分比是其1.83倍，肝癌粗死亡率是其4.08～4.74倍，推测长期低水平两种毒物联合暴露是其中重要原因。本项目拟①在上述两镇开展现况研究以确认联合暴露与肝损伤或肝癌的关联；②募集现场及临床肝癌患者开展病例对照研究，进一步确认联合暴露与肝癌的关联及关联程度；③建立联合染毒动物癌变及细胞恶性转化模型，聚焦DNA损伤及修复这一癌变核心环节，观察其中关键基因或蛋白改变；最后④基于人群和实验研究，对联合暴露肝损伤及肝癌发生危险度进行预评估。结果将为认识肝癌环境病因提供新的证据，为后续工作打下基础。

肝癌严重威胁人类健康，尤其在我国农村。目前病毒感染不足以解释其全部病因。黄曲霉毒素（AFs）和微囊藻毒素（MCs）是中国人较常暴露的嗜肝性毒物，动物实验显示两者联合致肝癌效应明显增强，但迄今未见人群水平验证及分子机制研究。我们前期发现，水源和食物同时受到两种毒物污染的三峡库区义和镇，与邻近水源未受污染的李渡镇相比，儿童肝损伤百分比是其 1.83 倍，肝癌粗死亡率是其 4.08~ 4.74 倍，推测长期低水平两种毒物联合暴露是其中重要原因。本项目在上述两镇开展现况研究发现两个镇人群均有不同程度的MCs和AFs污染；乙肝病毒（HBV）、MCs和AFs单独都能升高肝功酶AST和ALT均值水平，MCs对肝损伤的强度不及HBV；当HBV阴性时，两种生物毒素暴露造成的肝损伤风险增加不明显；HBV阳性时，两种生物毒素的肝损伤风险大幅度增加（高HBV+高AFs暴露人群的肝功能异常率OR值5.12~5.48，高HBV+高MCs时OR值7.90~8.01，高HBV+高AFs+高MCs时OR值可达16.40~18.05）；随着HBV、AFB1和MC-LR暴露强度的增加，异常AST和ALT的危险度逐渐升高（P-trend＜0.05); 两种毒素对人群的肝功能损伤与某些基因(OATP1B1、CYP3A4、GSTA1及GSTP1)具有交互作用; MCs也是两镇人群肾功能损伤的最主要因素。原发性肝癌（HCC）病例对照研究发现AFs暴露是该地区原发性肝癌发病的独立危险因素，并与 HBV、饮酒、糖尿病联合暴露在HCC致病过程中具有显著的正交互效应；血清MCs暴露可以显著增加HCC发生风险，这将为MCs的致癌性分级提供新的依据；MCs分别与HBV、饮酒联合暴露时，人群HCC发生风险显著增加；但血清MCs与AFs联合暴露在HCC发生过程中呈负交互作用。实验室机制研究显示两种毒素都可在大鼠诱癌模型及正常肝细胞恶性转化模型中诱导肿瘤发生，MCs本身也具有肿瘤启动效应，虽然相对AFs来说较弱；原癌基因gankyrin、甲基化调节基因、CYP1A1基因等参与两种毒素的单独和联合诱癌过程；氧化应激参与两种毒素对肝细胞的损伤；DNA损伤及修复基因参与两种毒素对肝细胞的损伤。本研究结果为认识为MCs的致癌性提供了新的依据，也为肝癌环境病因提供了新的证据。