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Antidiabetic and toxicological properties of some African medicinal plants used in the treatment of diabetes and its complications.

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This study investigated the antioxidant, antidiabetic and toxicity properties of antidiabetic medicinal plants comprising of Vernonia amygdalina, Cola nitida, Raffia palm (Raphia hookeri) wine, Phaseolus lunatus, Dacryodes edulis, and Clerodendrum volubile using in vitro, ex vivo, in silico and in vivo models. The leaves of V. amygdalina and D. edulis, as well as C. volubile flower were sequentially extracted with solvents of increasing polarity to yield ethyl acetate, ethanol and aqueous extracts. Cola nitida and V. amygdalina were infused in hot water to yield infusion extracts. Phaseolus lunatus was subjected to aqueous extraction to yield aqueous extract, while Raffia palm wine was concentrated to yield the concentrate. The extracts and concentrate were screened for their in vitro and ex vivo antioxidant activities, as well as their inhibitory effect on α-glucosidase, α-amylase and pancreatic lipase activities, and their ability to stimulate muscle glucose uptake and inhibit intestinal glucose absorption in vitro. The ethanol extracts of D. edulis, C. volubile and V. amygdalina were subjected to GC-MS analysis, while the aqueous extract of P. lunatus, palm wine concentrate and the infusions were analyzed with LC-MS to elucidate the active compounds that may be responsible for their bioactivities. The ethanol extracts of C. volubile and D. edulis were further subjected to liquid-liquid fractionation to yield the hexane, dichloromethane, ethyl acetate, butanol and aqueous fractions. These fractions were also assayed for their antioxidant and antidiabetic properties in vitro and ex vivo. The dichloromethane, ethyl acetate and butanol fractions were subjected to GC-MS analysis to elucidate their active compounds. The identified compounds were molecularly docked with the test enzymes in silico to further validate their bioactivities. The antidiabetic properties of palm wine concentrate, C. nitida infusion, and D. edulis butanol fraction were investigated in a type 2 diabetes rat model. The in vivo study revealed a potent hypoglycemic activity, with concomitant amelioration of oxidative stress in the serum, pancreas, testes and brain. This was further substantiated by the downregulation of Nrf2 expressions in the pancreas and brain. These results further validate the use and safety of these plants in diabetes management.


Doctoral Degree. University of KwaZulu-Natal, Durban.