Inhibition of baker’s yeast alpha glucosidase by extract and fractions of stem bark of Terminalia catappa Linn. (Combretaceae)

Background: Paucity of clinically applicable inhibitors has limited alpha glucosidase inhibition therapeutic strategy of type 2 diabetes management. The current investigation was aimed at evaluating the anti-diabetic alpha glucosidase inhibitory potentials of Terminalia catappa stem bark extract and its fractions, modeling the implicated intestinal brush border membrane alpha glucosidases with the baker’s yeast alpha glucosidase maltase.

Methods: A crude stem bark extract of Terminalia catappa and its n-hexane-, dichloromethane- and methanol-soluble fractions were incubated with the baker’s yeast alpha glucosidase at various final assay mixture concentrations, carrying along acarbose as reference standard. IC50 values were calculated from % inhibition vs concentration plots and analyzed using one-way ANOVA with Tukey’s post hoc comparison.

Results: The methanol, n-hexane and dichloromethane fractions inhibited alpha glucosidase with IC50 values 173.85 ± 6.90 ?g/ml, 258.56 ± 12.90 ?g/ml and 329.90 ± 10.67 ?g/ml respectively which are in the same order as that of acarbose (123.26 ± 15.56 ?g/ml) and significantly smaller (p < 0.0001) than that of the crude extract (527.67 ± 16.32 ?g/ml).

Conclusion: The three fractions potently inhibited baker’s yeast alpha glucosidase, indicating presence of alpha glucosidase inhibitory molecules of diverse polarity and, hence, structures in the T. catappa stem bark extract. This investigation has suggested alpha glucosidase inhibition as a possible action mechanism of the anti-diabetic use of T. catappa, unmasking its stem bark extract as a repertoire for the discovery of compounds of diverse molecular structures with possible anti-diabetic alpha glucosidase inhibitory activities.

背景：临床上可用的抑制剂匮乏，限制了α-葡萄糖苷酶（alpha glucosidase）抑制策略在2型糖尿病管理中的治疗应用。本研究旨在评估榄仁树（Terminalia catappa）茎皮提取物及其各组分的抗糖尿病α-葡萄糖苷酶抑制潜力，并利用酿酒酵母α-葡萄糖苷酶（麦芽糖酶）对相关肠道刷状缘膜α-葡萄糖苷酶进行建模。

方法：将榄仁树茎皮粗提物及其正己烷、二氯甲烷和甲醇可溶性组分，在不同的最终测定混合物浓度下与酿酒酵母α-葡萄糖苷酶孵育，并以阿卡波糖（acarbose）作为参考标准。通过抑制率与浓度的关系曲线计算IC50值，并采用单因素方差分析（one-way ANOVA）结合Tukey事后检验（Tukey’s post hoc comparison）进行分析。

结果：甲醇、正己烷和二氯甲烷组分对α-葡萄糖苷酶的抑制IC50值分别为173.85±6.90 μg/ml、258.56±12.90 μg/ml和329.90±10.67 μg/ml，其顺序与阿卡波糖（123.26±15.56 μg/ml）一致，且显著低于粗提物的IC50值（527.67±16.32 μg/ml，p < 0.0001）。

结论：上述三种组分对酿酒酵母α-葡萄糖苷酶具有强效抑制作用，表明榄仁树（T. catappa）茎皮提取物中存在极性多样、结构各异的α-葡萄糖苷酶抑制分子。本研究提示α-葡萄糖苷酶抑制可能是榄仁树抗糖尿病作用的机制之一，其茎皮提取物可作为发现具有潜在抗糖尿病α-葡萄糖苷酶抑制活性、分子结构多样的化合物的资源库。