Inhibitory effects of five medicinal plants on ratalpha-glucosidase: Comparison with their effects on yeast alpha-glucosidase

The mammalian and yeast α-glucosidase inhibitory activities of Senna italica, Tinospora fragosa, Manilkara mochisia, Xanthocercis zambesiaca, Ozoroa cf. albicans, Peltophorum africanum, Cassia abbreviata were investigated using p-nitrophenyl glucopyranoside as a substrate. All the plant species tested had low inhibitory activity against rat intestinal α-glucosidase. The highest concentration of C. abbreviata resulted in no observable loss of rat intestinal α-glucosidase activity. At 2.5 mg/ml, X. zambesiaca managed only 25% inhibition of rat intestinal glucosidase activity. M. mochisia led to about 60% loss of activity at 5 mg/ml. On the other hand, all plant species tested had good inhibitory activity against Baker’s yeast α-glucosidase. These findings suggest that a chemical substance that inhibits yeast α-glucosidase activity will not necessarily inhibit mammalian α-glucosidase. The validatation of the antidiabetic activity of medicinal plant extracts, with the focus on the inhibition of carbohydrate-digesting enzymes, will require, in addition, investigation of mammalian enzymes. The antioxidant activity of these plant species was also investigated, with C. abbreviata and ascorbic acid as the positive controls. The IC50 values were estimated. P. africanum had good antioxidant activity with an IC50 value of 0.030 mg/ml, similar to the IC50 value resulting from the positive control, ascorbic acid.   Key words: Diabetes mellitus, α-glucosidase activity, antioxidant activity, plant extracts.