Alpha-amylase Inhibition and Brine Shrimp Lethality Activities of Nine Medicinal Plant Extracts from South-West Nigerian Ethnomedicine

Acanthospermum hispidum, Alchornea laxiflora, Calyptrochilum christyanum, Heliotropicum indicum, Holarrhena floribunda, Ipomoea asarifolia, Nauclea diderrichii, Piper guineense, and Tetracera scandens were extracted into methanol and screened for the availability of alpha-amylase inhibitors. Plant extracts' toxicity was determined by brine shrimp lethality assay (BSLA). The most active plant, Nauclea diderichii, was fractionated into four solvent systems (n-hexane fractions, ethyl acetate, dichloromethane, and n-butanol) and tested. All the extracts showed varying degrees of alpha-amylase inhibitory activity. N. diderrichii with IC50 = 248.30 ± 0.27 µg.mL–1 had the highest inhibitory activity, while its butanol fraction with IC50 = 137.8 µg.mL–1 had activity comparable to the standard α-amylase inhibitor acarbose (IC50 = 177.50 ± 0.42 µg.mL–1). LC50 values for BSLA ranged from 11.35 to 1,127.50 µg.mL–1, with T. scandens being the most toxic with 11.35 µg.mL–1 and N. diderrichii the least toxic with 1,127.50 µg.mL–1.