口服难吸收药物-小檗碱降胆固醇的肠道作用新机理

Berberine is characterized by its poorly gastrointestinal absorption and rather low bioavailability. Despite of the definite hypolipidemic effect, the proposed mechanism can not well interpret the apparent contradiction between PK and PD. Our primary study suggested that serum berberine was fairly low, and berberine was trapped in gut content after the model hamsters were orally given with berberine. Although the bioavailability of intragastric-administered berberine was much lower than that of intraperitoneal-administered berberine, it had stronger lipid-lowing effect, indicating that the gut was the potential therapeutic target. It has been well documented that the elimination of cholesterol is closely associated with intestinal and hepatic FXR signal pathways, enterohepatic circulation and transporting of bile acids, and the alternation of gut flora. Hence, this program plans employ hyperlipidemic model animals, in vitro cell lines and specific gene-knockout mice to evaluate the effect of berberine and its metabolites on (1) intestinal and hepatic FXR signal pathways, and metabolic enzymes of cholesterol, e.g., CYP7A1和CYP27A1； (2) enterohepatic circulation of bile acids and transporters involved; and (3) the production of acetylacetate CoA, short chain fatty acids and the synthesis enzymes of cholesterol and fatty acids involved. In summary, the underlying mechanism will be assessed with the emphasis on the catabolism, synthesis, re-absorption and elimination of cholesterol, which will be a solid support for the research and development of new dosage forms and hypolipidemic agents.

小檗碱口服很难吸收，但降胆固醇药效明确。目前提出的肝靶点作用机理无法解释口服小檗碱药效作用。因为我们发现模型动物灌胃给药后，绝大部分小檗碱滞留于肠道，血液和肝脏中药物浓度极低，远远达不到提出作用机理研究中小檗碱有效浓度。且在小檗碱灌胃生物利用度远低于腹腔注射情况下，降胆固醇作用更强。提示肠道是口服小檗碱药效作用主要靶点。最新研究证实：体内胆固醇水平与其代谢物-胆汁酸影响肠道和肝脏法尼醇受体(FXR)信号通路对胆固醇代谢的负反馈调控、胆汁酸肠肝循环与转运等密切相关。项目首次综合采用模型动物、体外培养细胞和基因敲除小鼠研究小檗碱及代谢物对(1)胆固醇代谢酶的影响；(2)肠道与肝脏FXR负反馈信号通路调控；(3)胆汁酸肠肝循环及相关转运体调控。最终以小檗碱肠道作用为核心、以小檗碱对胆汁酸肠肝循环和FXR调控为主线，从胆固醇代谢消除的上游调控通路阐明小檗碱降胆固醇作用机理，为相关新药研发提供依据。

本课题为国家自然科学基金一年期小额资助项目，重点针对审评专家提出的“小檗碱体内代谢产物是否是其发挥降脂作用的主要物质”问题进行研究。课题预算总经费16万元，目前已经按计划使用完毕。发表SCI论文一篇，影响因子3.35，申请专利2项，参加学术会议两次，作大会报告一次。本课题培养博士研究生2名（1名已毕业）、硕士研究生1名。具体研究结果如下：.采用金黄地鼠和C57BL/6小鼠高脂模型，分别研究了小檗碱及其主要代谢物去甲基小檗碱的降脂作用及其对胆固醇代谢酶、肝脏与肠道FXR信号通路、胆汁酸生成与消除的影响。发现去甲基小檗碱虽然具有良好的降脂效果，但肾脏毒性明显。而去亚甲基小檗碱只有在腹腔注射时才显示良好的降脂效果。体外细胞结果显示小檗碱及其代谢物去甲基小檗碱、去亚甲基小檗碱在正常给药剂量所能达到的浓度范围内对肝细胞中胆固醇代谢酶CYP7A1及CYP27A1的m RNA表达及蛋白表达均无明显作用，提示小檗碱降脂作用靶点不位于肝脏。另外，发现小檗碱灌胃给药可以显著抑制金黄地鼠回肠与空肠中FXR的mRNA表达水平，小檗碱对C57BL/6小鼠回肠FXR表达有显著抑制作用，但其代谢物并无作用。上述研究结果提示：小檗碱主要代谢物去甲基小檗碱与去亚甲基小檗碱不是小檗碱降脂作用的主要贡献者，小檗碱很可能是通过肠道FXR信号通路影响肝脏FXR与胆固醇代谢酶CYP7A1的表达与活性，发挥增强胆固醇的代谢。