[关键词]
[摘要]
目的 应用体外实验方法筛选淫羊藿次苷Ⅱ在肝微粒体中的尿苷二磷酸葡萄糖醛酸转移酶(UGT)抑制剂,为改善淫羊藿次苷Ⅱ生物利用度提供新思路。方法 首先选择槲皮素、山柰酚、桔皮素、柚皮素、水飞蓟素、草质素、胡椒碱、甘草查尔酮A以及异银杏双黄酮作为抑制剂筛选对象,对以上9种化合物在人肝微粒体、人肠微粒体、大鼠肝微粒体、猴肝微粒体及小型猪肝微粒体中对淫羊藿次苷Ⅱ葡萄糖醛酸化反应的抑制作用进行初步研究。抑制剂分别选择低、中、高3个浓度(1、10、100 μmol/L),采用超快速高效液相色谱(UFLC)法测定代谢产物生成速率,以UGT代谢酶残余活性评价抑制能力。从中筛选出抑制能力较强的化合物(半数抑制浓度IC50≤10 μmol/L),对其在人肝微粒体中的抑制机制进行系统研究并计算IC50及抑制常数(Ki)值。IC50值的测定采用单一底物浓度法,在不同浓度代谢酶抑制剂的孵育体系中,代谢产物的生成速率不同,应用非线性回归分析计算而得。Ki的测定需在孵育体系中设计3~4个底物浓度以及4~5个包括0点在内的抑制剂浓度,抑制动力学类型通过Dixon作图法和Lineweaver-Burk作图法确定,采用二次作图法计算Ki。结果 山柰酚、槲皮素及甘草查尔酮A对淫羊藿次苷Ⅱ在不同种属肝微粒体及人肠微粒体中的葡萄糖醛酸化反应均具有较强的抑制作用;对在人肝微粒体中的葡萄糖醛酸化反应抑制作用的IC50值分别为(1.01±0.26)、(4.65±0.51)、(5.34±1.00) μmol/L;Dixon作图法及Lineweaver-Burk作图法表明,甘草查尔酮A能够竞争性抑制淫羊藿次苷Ⅱ在人肝微粒体中的葡萄糖醛酸化反应,Ki值为0.18 μmol/L;槲皮素遵循混合型抑制动力学模型,Ki值为0.23 μmol/L;山柰酚符合非竞争型抑制动力学模型,Ki值为0.36 μmol/L。结论 山柰酚、槲皮素及甘草查尔酮A能够降低淫羊藿次苷Ⅱ在不同种属肝微粒体中的葡萄糖醛酸化反应速率,使代谢产物生成减少,清除减慢。
[Key word]
[Abstract]
Objective To screen the UDP-glucuronosyltransferase (UGT) inhibitors of icariside Ⅱ in liver microsomes in vitro and provide a new idea to improve the bioavailability of icariside Ⅱ. Methods In this study, the inhibitory effects of quercetin, kaempferol, hesperetin, naringenin, silymarin, piperine, herbacetin, licochalcone A, and isoginkgetin against icariside Ⅱ glucuronidation were assessed firstly. Icariside Ⅱ was incubated in human, rat, monkey, minipig liver microsomes and human intestinal microsomes with varying inhibitors concentration (1, 10, and 100 μmol/L). An UFLC based method was used to quantify the glucuronide of icariside Ⅱ. The residual activity of UGT enzymes was used to evaluate the inhibitory capacity. The inhibitory mechanism and kinetic parameters of inhibitors with the IC50 values less than or equal to 10 μmol/L were investigated in human liver microsomes. IC50 values were determined by using a single substrate concentration with various concentration of inhibitors and were calculated by non-linear regression analysis. Inhibition kinetic parameters (Ki) were determined by using various concentration of icariside Ⅱ in the presence or absence of various concentration of inhibitors. The inhibition kinetic type was evaluated by determining the intersection point in Dixon and Lineweaver-Burk plots. The second plot of slopes from Lineweaver-Burk plot vs inhibitors concentration was utilized to calculate the corresponding inhibition parameter values. Results The catalytic activities of human, rat, and monkey minipig liver microsomes and human intestinal microsomes were strongly inhibited by quercetin, kaempferol, and licochalcone A in icariside Ⅱ glucuronidation. The calculated IC50 values of quercetin, kaempferol, and licochalcone A in human liver microsomes were (1.01±0.26), (4.65±0.51), and (5.34±1.00) μmol/L, respectively. Both Lineweaver-Burk and Dixon plots demonstrated that licochalcone A was a competitive inhibitor for icariside Ⅱ glucuronidation in human liver microsoms with the Ki value of 0.18 μmol/L. Quercetin was a mixed inhibitor for human liver microsomes mediated icariside Ⅱ glucuronidation with the Ki value of 0.23 μmol/L. Kaempferol is a noncompetitive inhibitor for icariside Ⅱ glucuronidation in human liver microsomes with the Ki value of 0.36 μmol/L. Conclusion The glucuronidation of icariside Ⅱ in different species liver microsomes can be strongly inhibited by quercetin, kaempferol, and licochalcone A.
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[基金项目]
国家重点基础研究发展计划(973计划)项目(2013CB531800)