Anti-diabetic activity of extracts and a bioactive compound isolated from Hypoxis hemerocallidea (Hypoxidaceae) in a murine model of spontaneous diabetes

Abstract

A previous study investigated and demonstrated that Hypoxis hemerocallidea (Fisch and Mey) (Hypoxidaceae) corm extracts used traditionally, stimulated insulin secretion from pancreatic _ cells maintained under ex vivo conditions. The effect was also related to the antioxidant activity of extracts. In order to find leads with unique chemical structures which may exert a hitherto unexploited mode of action, phytochemical investigation on extracts of the plant was carried out. This involved the following steps: authentication and extraction of the plant material, separation and isolation of the constituents of interest, characterization of the isolated compounds and quantitative evaluation. Furthermore, the following study also followed the normal sequence of principles of replacement, in that all necessary non-animal and ex vivo animal models were first to optimise evaluation of the product, before testing using a mouse model. With H. hemerocallidea being traditionally used as wild bulbs, we firstly ascertained the risk of this tradional use with specific focus on heavy metals. This is important as certain soil minerals are known to increase antioxidant capacity in plants, and associated extracts, as a stress response to soil heavy metal content. However, the use of these wild plants may pose a safety concern to the person consuming the plant as a result of their potential heavy metal content. Corms collected from the wild from five different geographical regions of South Africa, were evaluated for their concentration of metal concentrations and associated antioxidant activity. Among the trace metals investigated, iron was the highest, for the corm collected from Ga-rankuwa. No link was found between the corm’s antioxidant activity and environmental conditions. We further investigated the corm from Ga-rankuwa, since it had the highest antioxidant activity for its anti-diabetic activity. Assays included glucose uptake in C2C12 myocytes, 3T3-L1 preadipocytes and insulin secretion in rat insulinoma RiNm5F cells in total five different fractions and three compounds isolated. Only the methanol crude extract, fraction III & V and isolated _-sitosterol significantly increased insulin release and lowered blood glucose levels both in C2C12 myocytes and 3T3-L1 preadipocytes to a degree. All the crude extracts, fractions and tested compounds had relatively low cytotoxicity against all the diabetic cell lines used. In the final study we determined the effect of H. hemerocallidea and its isolated compound, _-sitosterol in a murine mouse model of spotaneous diabetes. The _-sitosterol induced slight weight loss in the mice and stabilised blood glucose concentration after the 4 weeks treatment course. No changes in the haematology were evident while clinical chemistry evaluations showed slight treatment-related changes in triglycerides and total cholesterol. The study concludes that H. Hemerocallidae was not a suitable as a sole treatment agent in the management of diabetes. However it holds promise as an add-on treatment to lifestyle intervention for the management of type-II diabetes.