Anti-hyperglycaemic globulins from selected Cucurbitaceae seeds used as antidiabetic medicinal plants in Africa.

BACKGROUND: The recent epidemic of diabetes mellitus (DM) in Africa, coupled with rampant poverty, is an indication of the urgent need to develop new efficacious, cheaper and more available drugs to face this growing public health challenge. A number of plants products among which the protein-rich Cucurbitaceae seeds are commonly used in traditional medicine with increasing acclaimed efficacy against DM. The aim of this study was to analyse and evaluate the hypoglycaemic activity of storage proteins of five species of Cucurbitaceae, which include Telfairia occidentalis, Citrullus lanatus, Lagenaria siceraria, Cucumeropsis mannii and Cucurbita moschata. METHODS: The different families of storage proteins were extracted following differential solubility, and their contents were estimated using the Bradford method. The analysis of these proteins was done by electrophoresis in non-denaturing and denaturing conditions. The evaluation of hypoglycaemic properties of various globulins extracted was performed on male Wistar rats by the oral glucose tolerance test. RESULTS: The results showed that among the proteins extracted, globulins constitute the most abundant class of storage proteins in all five species selected. Citrullus lanatus and Cucurbita moschata presented the highest levels of globulin (275.34 and 295.11 mg/g dry matter, respectively). The results of electrophoresis showed that all species possess acidic and neutrals albumins and globulins, with molecular weight of protein subunits ranging from 6.36-44.11 kDa for albumins, 6.5-173.86 kDa for globulins and 6.5-49.66 kDa for glutelins. The 6.36 kDa of albumin subunit protein and the 6.5 kDa of globulin subunit protein were present in all the species. The oral glucose tolerance test showed that the globulins of the seeds of all species except Cucumeropsis mannii caused significant drop in blood sugar (88 - 137.80%, compared to the controls, p<0.05). CONCLUSIONS: These findings showed that the selected Cucurbitaceae seeds contained globulins with significant anti-hyperglycaemic activity. It is therefore highly encouraged to pursue investigations towards development of peptide-drugs and/or phytomedicines from these bioactive proteins which could be used as affordable alternative therapy against DM.

Antioxidant and antidiabetic profiles of two African medicinal plants: Picralima nitida (Apocynaceae) and Sonchus oleraceus (Asteraceae).

BACKGROUND: Diabetes mellitus (DM) is a metabolic disease characterized by chronic hyperglycaemia generally associated with oxidative stress. The present study aims at evaluating the antioxidant and antidiabetic potential of methanol and hydroethanol extracts of the stem bark and leaves of Pricralima nitida and the Sonchus oleraceus whole plant respectively. METHODS: The in vitro antioxidant activity was assessed using 1,1-Diphenyl-2-picrilhydrazyl (DPPH) for free radical-scavenging properties of the extracts, and the Folin-Ciocalteu method in determining their phenol contents. The antidiabetic activity was tested in mice following streptozotocin diabetes induction, and selected oxidative stress markers (Malondialdehyde, Hydrogen peroxides and Catalase) were measured in order to evaluate the level of oxidative stress in treated animals. RESULTS: The in vitro antioxidant activity using DPPH showed IC50 ranging from 0.19 ± 0.08 to 1.00 ± 0.06 mg/mL. The highest activity was obtained with the hydroethanol extracts of S. oleraceus (0.19 mg/mL and P. nitida (0.24 mg/mL). Polyphenol contents ranged from 182.25 ± 16.76 to 684.62 ± 46.66 µg Eq Cat/g. The methanol extract of P. nitida showed the highest activity, followed by the hydroethanol extract of S. oleraceus (616.89 ± 19.20 µEq Cat/g). The hydroethanol extract of whole plants (150 mg/Kg) and methanol leave extract of P. nitida (300 mg/Kg) exhibited significant antidiabetic activities with 39.40% and 38.48% glycaemia reduction, respectively. The measurement of stress markers in plasma, liver and kidney after administration of both extracts showed significant reduction in MDA and hydrogen peroxide levels, coupled with a substantial increase in catalase activity. CONCLUSIONS: These findings suggest that S. oleraceus whole plant and P. nitida leaves possess both antidiabetic and antioxidant properties, and therefore could be used as starting point for the development of herbal medicines and/or source of new drug molecules against diabetes.