Antidiabetic activity of Terminalia sericea Burch. Ex DC constituents

Abstract

Diabetes mellitus is an endocrine disorder that affects more than 100 million people worldwide. South African plants namely Terminalia sericea, Euclea natalensis, Warbugia salutaris, Aloe ferox Artemisia afra, Sclerocarya birrea, Spirostachys africana and Psidium guajava were investigated for their in vitro antidiabetic and antioxidant activities. Terminalia sericea stem bark extract showed the best results against α-glucosidase and α-amylase enzymes. Bioassay-guided fractionation of an acetone extract of T. sericea stem bark led to the isolation of four known compounds namely β-sitosterol (1), β-sitosterol-3-acetate (2), lupeol (3), and stigma-4-ene-3-one (4), in addition to two inseparable sets of mixtures of isomers [epicatechin-catechin; (M1) and gallocatechin-epigallocatechin; (M2). 1 and 3 showed best inhibitory activity on α-glucosidase (IC50:54.5 μM and 66.48). The bio-evaluation of purified compound’s inhibitory activity on α-amylase, showed that lupeol and β-sitosterol exhibited IC50 values of 140.72 and 216.02 μM respectively against α-amylase. 2, M1, 3 and M2 were found to be non-toxic to Vero cells. This study is the first to report a-glucosidase, a-amylase of M1, M2, 2 and 4 isolated from T. sericea which validated the traditional use of the bark of T. sericea for diabetes in South Africa.