口服难吸收药物-小檗碱降胆固醇药效的肠道作用新机制

Berberine is characterized by its poorly gastrointestinal absorption and rather low bioavailability. Despite of the definite hypolipidemic effect following oral administration, the proposed mechanism can not well interpret the apparent contradiction between PK and PD. Our primary study and a previous NSFC project suggested that (1) in vivo berberine was fairly low, and berberine was trapped in gut content after the model hamsters were orally given with berberine; (2) Although the exposure level of intragastric-administered berberine was much lower than that of intraperitoneal-administered berberine, it had stronger lipid-lowing effect; (3) Oral administration of berberine elevated the generation of bile acids, which failed to depress CYP7A1 by activating FXR signal pathway(s). These data suggested that the hypolipidemic efficacy of berberine is deeply involved in its potential action on gut, and is closely associated with intestinal FXR/FGF, hepatic FXR/SHP, and enterohepatic circulation and transporting of bile acids. Hence, this project plans to employ both hyperlipidemic model animals and in vitro cell lines to evaluate the effect of berberine on the above mechanism and metabolic enzymes of cholesterol, e.g., CYP7A1和CYP27A1. In summary, the underlying mechanism will be assessed with the emphasis on the regulation of intestinal and hepatic FXR pathways and enterohepatic circulation of bile acids, aiming at approaching to the underlying mechanism, which will be verified using FXR, SHP, FGF knockout mice. Hopefully, this study will provide a solid support for the research and development of new dosage forms and analogous hypolipidemic agents of berberine.

口服难吸收药物小檗碱的降脂作用明确，但目前提出的作用机理无法解释其体内暴露水平低与药效确切之间矛盾。前期NSFC资助与近期研究发现小檗碱在①模型动物灌胃给药后，肠道中蓄积，血液和肝脏中药物及代谢物浓度很低，远达不到相关机理研究的有效浓度；②灌胃后体内暴露水平远低于腹腔注射情况下，降胆固醇作用甚至更强；③ 灌胃后胆汁酸生成增加，胆固醇代谢酶CYP7A1等并未受增多的胆汁酸激活肝肠FXR信号通路而产生的负反馈抑制。提示小檗碱药效与肠道作用密切相关，并与①胆汁酸肠肝循环/转运②肠道FXR/FGF通路③肝脏FXR/SHP通路调控有关。项目计划综合采用模型动物、体外培养细胞，系统研究小檗碱对上述通路及胆固醇代谢酶的影响，以肠道作用为核心、以胆汁酸转运和FXR调控为主线，通过比较灌胃和腹腔注射给药的差异，最终以基因敲除小鼠进行验证，阐明小檗碱药效作用关键靶点、信号通路和作用新机理，为新药研发提供依据。

很多中药药效明确，但其药物成分往往吸收较差、生物利用度低、作用机理不明，是困扰中药创新药物研发的主要难题。小檗碱来源于中药黄连，动物和临床试验均证明其具有良好降脂作用，但该药口服吸收差、体内暴露和生物利用度极低，存在明显的PK-PD不相关问题。前期研究发现小檗碱在肠道中暴露水平很高，可增加体内胆汁酸生成，但体内高水平胆汁酸并未通过常规方式经肝脏FXR信号通路反馈性抑制胆固醇代谢和胆汁酸生成，提示小檗碱降脂药效与肠道FXR信号通路有关。为研究该作用机理，与美国罗格斯大学合作，我方派遣博士生赴美进行为期一年研究，采用肝脏FXR基因敲除、肠道FXR基因敲除和全身FXR基因敲除小鼠进行验证，首次发现小檗碱通过肠道FXR信号通路调控脂质代谢和肝脏胆汁酸代谢机理。.进一步研究了小檗碱对肠道菌群和肠道胆汁酸的影响，发现小檗碱显著改变肠道菌群组成，抑制胆盐水解酶，显著增加肠道中牛磺胆酸（TCA）及牛磺β鼠胆酸的含量，其中TCA与小檗碱具有相似降脂作用和肠道FXR信号通路调控作用。提出小檗碱影响肠道菌群、抑制胆盐水解酶、增加肠道中牛磺胆酸可能是其发挥降脂作用的关键机制。.因发现小檗碱在体内可以代谢生成较多量小檗红碱，小檗红碱也具有小檗碱类似的降脂作用，但具有一定肾脏毒性。课题增加小檗红碱药代动力学性质、体内代谢和成药性初步研究。发现小檗红碱肾脏毒性与其在体内不能正常生成葡萄糖醛酸苷有关，小檗红碱葡萄糖醛酸苷不仅没有明显毒性，还具有良好药效，具有潜在成药性价值。肾脏毒性机理研究发现，小檗红碱影响肾脏UGT酶活性，抑制自身葡萄糖醛酸代谢。其主要原因是小檗红碱干扰体内代谢，导致亚油酸和戊二酸为主的内源性小分子水平显著上升，从而抑制UGT酶活性。该首次发现人体内源性分子显著影响UGT代谢酶，突破了传统上只研究药物/外源性物质对药物代谢酶影响的惯性思维模式。