Evaluation of six plant species used traditionally in the treatment and control of diabetes mellitus in South Africa using in vitro methods.

CONTEXT: Numerous plants are used by the local communities of South Africa for the treatment and management of type II diabetes.
OBJECTIVES: For this study, we undertook a survey of the plants sold for the management of diabetes in the town of Newcastle, South Africa. Identified plants were subsequently evaluated for their in vitro antidiabetic activity.
MATERIALS AND METHODS: Plants were identified through an interview with a herbalist at the market. Antidiabetic activity of extracts of purchased plants was evaluated using in vitro α-amylase and α-glucosidase activity, as well as islets of Langerhans excretory activity.
RESULTS: Senna alexandrina Mill. (Fabaceae), Cymbopogon citrates Stapf. (Poaceae), Cucurbita pepo L. (Cucuribitaceae), Nuxia floribunda Benth. (Stilbaceae), Hypoxis hemerocallidea Fisch. and Mey (Hypoxidaceae), and Cinnamomum cassia Blume (Lauraceae) were identified. The hexane extract of S. alexandrina (EC50=0.083 mg/ml), ethyl acetate extract of H. hemerocallidea (EC50=0.29 mg/ml), and methanol extracts of Cymbopogon citratus (EC50=0.31 mg/ml) and Cinnamomum cassia (EC50=0.12 mg/ml) had the highest α-amylase inhibitory activity, albeit lower than acarbose (EC50=0.50 mg/ml). All the plants had good α-glucosidase inhibitory activity (>50%) with the exception of some methanol (Cinnamomum cassia, N. floribunda, and Cymbopogon citratus) and acetone extracts (Cucurbita pepo and N. floribunda). Only the H. hemerocallidea acetone extract had an insulin stimulatory effect (2.5 U/ml at 8 μg/ml).
CONCLUSION: All the evaluated plants demonstrated inhibitory activity against the specific GIT enzyme systems evaluated. Only H. hemerocallidea had insulin secretory activity, adding evidence to the traditional use of these purchased plants in the management of the type II diabetic post-prandial hyperglycemia.