基于苦杏仁苷立体选择性吸收和脱氨代谢途径的麻黄-杏仁药对配伍减毒的机制研究

Herba Ephedrae (Mahuang in Chinese) and Semen Armeniacae Amarum (Xingren in Chinese) constitute a classical herb pair known as Mahuang-Xingren. Mahuang combined with Xingren to maintain the balance of the nature of the herbs indicated that not only improve herbal efficacy but also reduce the toxicity. Xingren has “slight toxicity”, detoxification study underlying Mahuang-Xingren is still unclear and merits investigation. D-Amygdalin is reported as the toxicity source of Xingren. Our previous study had shown that stereoselective pharmacokinetics of amygdalin facilitated by Mahuang occurred in vivo, which led to reduced its peak concentration and bioavailability. Furthermore, conversion of nitrile to amide in amygdalin molecule may occur in context of Mahuang-Xingren. Therefore, disposition of amygdalin in vivo may be the mechanism that Mahuang antagonize the toxicity of Xingren. Based on these observations, we hypothesis the change of transportation of amygdalin in vivo is the premise and then the block of metabolism pathway of cyanide generation may be the core mechanism in detoxification of Xingren by Mahuang. In this proposal, permeability and transport of amygdalin using Caco-2 cell monolayer and vascularly perfused rat intestine-liver model will be performed to investigate its absorption characteristics. Expression of SGLT transporter is used to explore the possible mechanism of stereoselective pharmacokinetics. Moreover, effect on deamination pathway of amygdalin induced by Mahuang will be evaluated by quantitative analysis of absorbed chemical profiles and activity & expression of relevant drug metabolism enzyme such as CYP2E2 and CYP3A4. This study would provide a scientific basis for Mahuang-Xingren combination and promote understanding of its safe application.

麻黄和杏仁是经方药对，两药一宣一降且互制其偏，增效之中亦有减毒之意。杏仁有“小毒”，目前两药配伍减毒研究却较为薄弱。D-苦杏仁苷是杏仁中毒性成分，生氰过程是毒性发生的关键。前期研究发现：配伍麻黄可促进苦杏仁苷药动学的立体选择性，降低D-苦杏仁苷的达峰浓度及生物利用度；苦杏仁苷可能存在氰基酰胺化进而脱氨的代谢途径。我们由此提出研究假说：立体选择性吸收和脱氨代谢途径是麻黄-杏仁配伍减毒的重要环节。D-苦杏仁苷体内吸收减少是配伍减毒的基本前提；生氰通路阻断是减毒机制的核心体现。本课题拟采用Caco-2/HT29细胞转运、大鼠在体肝肠灌流实验，明确配伍前后D-苦杏仁苷的吸收特征；分析转运体SGLT表达，阐述苦杏仁苷立体选择性的吸收机制；通过移行成分定量、生氰代谢酶CYP2E1和氰基氧化酶CYP3A4活性与表达分析，探讨配伍麻黄对脱氨代谢途径的影响。本研究可为麻杏药对临床遣方用药安全性提供科学依据。

麻黄-杏仁是经方药对，两药一宣一降且互制其偏，增效之中亦有减毒之意。杏仁有“小毒”， D-苦杏仁苷是杏仁中毒性成分，生氰过程是毒性发生的关键。前期研究发现：配伍麻黄可促进苦杏仁苷药动学的立体选择性，降低D-苦杏仁苷的达峰浓度及生物利用度；苦杏仁苷可能存在氰基酰胺化进而脱氨的代谢途径。由此提出研究假说：立体选择性吸收和脱氨代谢途径是麻黄-杏仁配伍减毒的重要环节。在国家自然科学基金青年基金项目资助下，本课题通过Caco-2、MDCK细胞转运模型、大鼠在体肠灌流模型，确认苦杏仁苷立体选择性吸收与汤剂化学环境有关：苦杏仁苷立体选择性主要由汤剂介导发生，配伍麻黄则进一步促进D-苦杏仁苷吸收。因此，苦杏仁苷立体选择性吸收是汤剂化学环境和配伍作用的共同体现。配伍显著提升苦杏仁苷及野樱苷生物利用度的同时，降低D-苦杏仁苷并提升D-野樱苷相对体内暴露水平（降低D-野樱苷代谢速率），呈现“促进吸收，体内缓释”配伍效应。该机制可能与配伍麻黄促进SGLT1表达有关。上述结果证实苦杏仁苷体内过程的立体选择性是麻杏配伍减毒增效的关键因素；苦杏仁苷存在糖苷水解、氰基酰胺化、羧酸化和甲基化等16种代谢产物，其中酰胺化、羧酸化等“脱氨代谢”是其非生氰途径的主要特征。“苦杏仁苷“脱氨代谢”是麻杏配伍体内外共同的解毒代谢途径，其中肠道及其肠道菌酶可能是其代谢主要场所；麻杏共煎也可以促进汤剂中苦杏仁苷“脱氨代谢”进程。本研究阐释了麻杏配伍增效之中亦有减毒之意的科学内涵，进一步拓展对苦杏仁苷毒性的体内处置规律的系统认识。