Rahim Abu Torab M A, Takahashi Yoko, Yamaki Kohji
National Food Research Institute, National Agricultural and Food Research Organization, 2-1-12 Kannondai, Tsukuba, Ibaraki 305-8642, Japan; Institute of Nutrition and Food Science, University of Dhaka, Dhaka 1000, Bangladesh.
National Food Research Institute, National Agricultural and Food Research Organization, 2-1-12 Kannondai, Tsukuba, Ibaraki 305-8642, Japan.
Food Res Int. 2015 Sep;75:289-294. doi: 10.1016/j.foodres.2015.05.017. Epub 2015 May 12.
Numerous reports have shown plant metabolites as potential inhibitors of pancreatic lipase (PL). The most notable group is plant polyphenols. However, a limited number of reports diagnosed their mode of inhibition delineating conflicting results. To elucidate the kinetic mode of PL inhibition, some selected flavonoid and non-flavonoid polyphenol standards were first screened for their lipase inhibition potency by their half maximal inhibitory concentration (IC) followed by inhibition kinetic analysis. Of the phenolics tested, only gallic acid (GA) and galloyl moiety containing epicatechin, viz., epigallocatechin (EGC) and epigallocatechin gallate (EGCG) showed, comparative to others, higher PL inhibitions (IC, 387.2, 237.3, and 391.2μM respectively). Analysis of enzyme inhibition modalities at various substrate concentrations revealed a dose-dependent inhibition of reaction velocity. Inhibitory rates decreased by the order of EGCG>EGC>GA (Ki, 13.29>35.0>44.61μM respectively). The results, when verified by visual inspection of Lineweaver-Burk as well as Dixon plots, showed inhibitions of PL by GA, EGC, and EGCG that were best fit to competitive inhibitions. A role of the galloyl moiety in enzyme-inhibitor binding has been evident from their structural resemblance. Depicting it further, ethyl gallate (EG), showed a similar competitive inhibition, therefore, indicating a galloyl moiety driven competitive inhibition of PL.
大量报告表明，植物代谢产物可能是胰腺脂肪酶（PL）的抑制剂。最值得注意的一类是植物多酚。然而，仅有少数报告明确了它们的抑制模式，结果相互矛盾。为了阐明PL抑制的动力学模式，首先通过半数最大抑制浓度（IC）筛选了一些选定的黄酮类和非黄酮类多酚标准品的脂肪酶抑制能力，随后进行抑制动力学分析。在所测试的酚类物质中，与其他物质相比，只有没食子酸（GA）以及含有表儿茶素没食子酰基部分的表儿茶素（EGC）和表儿茶素没食子酸酯（EGCG）对PL的抑制作用更强（IC分别为387.2、237.3和391.2μM）。在不同底物浓度下对酶抑制方式的分析表明，反应速度受到剂量依赖性抑制。抑制率按EGCG>EGC>GA的顺序降低（Ki分别为13.29>35.0>44.61μM）。通过Lineweaver-Burk图和Dixon图的直观检查验证结果表明，GA、EGC和EGCG对PL的抑制作用最符合竞争性抑制。没食子酰基部分在酶-抑制剂结合中的作用从它们的结构相似性中已很明显。进一步说明这一点的是，没食子酸乙酯（EG）表现出类似的竞争性抑制，因此表明没食子酰基部分驱动了对PL的竞争性抑制。
