In vitro α-Glucosidase and α-Amylase Activities of Wild and Cultivated Amaranthus spp. and Isolated Compounds

Introduction: Diabetes mellitus is a serious metabolic disorder that affects many South Africans. There is urgent need for alternative and affordable diabetic therapy from edible wild plants which have been used by the indigenous people for many years. This study presents in vitro antidiabetic effects of methanol leaf extracts of wild and cultivated Amaranthus spp. and isolated compounds. Methods: The inhibitory effects against yeast α-glucosidase and porcine α-amylase were determined using a dilution series of ethanolic extracts of wild and cultivated leaf extracts and isolated compounds of Amaranthus spp. The aerial parts of the plant material were subjected to silica gel chromatography to yield three compounds. Results: Wild A. hybridus showed potent α-glucosidase enzyme activity (89.92±0.04%) at the lowest concentration tested (0.125 mg/mL) in comparison to acarbose which exhibited 80.20±0.13% inhibition at the same concentration. Cultivated A. cruentus extracts inhibited α-glucosidase enzyme activity (84.95 ± 0.04%) at the lowest concentration compared to cultivated A. hybridus which exhibited inhibitory activities of 72.28 ± 0.06%. In addition, three compounds namely, α-spinasterol, palmitic acid and pheophorbide A-methyl ester isolated from wild A.cruentus were tested for in vitro antidiabetic activity. Palmitic acid demonstrated the highest inhibition against α-glucosidase for all the concentrations tested. Tested separately, the isolated compounds were weaker α-amylase enzyme inhibitors however, when the compounds were combined, inhibition of α-amylase increased to 58.49± 002% at 0.5 mg/mL. Conclusions: Extracts and compounds of Amaranthus showed strong α-glucosidase activity inhibition and mild α-amylase activity inhibition suggesting that the extracts and compounds slow glucose absorption.