Yeast alpha glucosidase inhibitory and antioxidant activities of six medicinal plants collected in Phalaborwa, South Africa

Recent decades have experienced a sharp increase in the incidence and prevalence of diabetes mellitus. One antidiabetic therapeutic approach \nis to reduce gastrointestinal glucose production and absorption through the inhibition of carbohydrate-digesting enzymes such as α-amylase and \nα-glucosidase and α-amylase. The aim of the current study was to screen six medicinal plant species,with alleged antidiabetic properties for α-glucosidase \ninhibitory activities. Powdered plant materials were extracted with acetone, and tested for ability to inhibit baker's yeast α-glucosidase and α-amylase \nactivities. The largest mass (440 mg from 10 g) of the extract was obtained from Cassia abbreviata, while both Senna italica and Mormordica balsamina \nyielded the lowest mass of the extracts. Extracts of stembark of C. abbreviata inhibited baker's yeast α-glucosidase activity with an IC50 of 0.6 mg/ml. This \nplant species had activity at low concentrations, with 1.0 mg/ml and above resulting in inhibition of over 70%. The other five plant extracts investigated had \nIC50 values of between 1.8 and 3.0 mg/ml. Senna italica only managed to inhibit the activity of enzyme-glucosidase at high concentrations with an IC50 \nvalue of 1.8 mg/ml, while Tinospora fragosa extracts resulted in about 55% inhibition of the activity of the enzyme at a concentration of 3.5 mg/ml, with an \nestimated IC50 value of 2.8 mg/ml. The bark extract of C. abbreviata was the most active inhibitor of the enzyme, based on the IC50 values (0.6 mg/ml). The \nbark extract of C. abbreviata contains non-competitive inhibitor(s) of α-glucosidase, reducing Vmax value of this enzyme from 5 mM·s–1 to 1.67 mM·s–1, \nwhile Km remained unchanged at 1.43 mM for para-nitrophenyl glucopyranoside. Antioxidant activity of the extracts was also investigated. The \nC. abbreviata extractwasmore active as an antioxidant than the positive control, trolox. The extracts did not inhibit alphaamylase activity more than about \n20% at the highest concentration tested.