Phytochemical Analysis, in vitro Antioxidant Activity and Inhibition of Key Diabetic Enzymes by Selected Nigerian Medicinal Plants with Antidiabetic Potential

Background: Diabetes is one of the most common metabolic disorders worldwide and the disease is generally believed to be incurable. However, the historical success of natural products as therapeutic agents has led to the search for more herbs with antidiabetic potential. Aim: To investigate the antioxidative and antidiabetic activities of some common medicinal plants traditionally used to treat diabetes in Nigeria. Materials and Methods: Twenty one plant samples comprising leaves, seeds and stem bark were separately extracted using three solvents of increasing polarity namely ethanol, methanol and distilled water. The extracts were subsequently screened for their phenolic profile, ferric reducing power as well as inhibition of alpha-amylase and haemoglobin glycosylation activities as markers of in vitro antidiabetic activity. Results: Solvents extracts of 7 out of the 21 plants examined namely Anacardium occidentate (leaf), Carica papaya (leaf), Ficus asperifolia (leaf), Hibiscus sabdariffa (stem bark), Khaya senega/ensis (stem bark), Ocimum gratissimum (leaf) and Parkia biglobosa (stem bark) had significant concentrations of total polyphenol and flavonoid compared to the other plants. Similarly, for all the in vitro models used in this study, the same set of plants demonstrated significantly (p < 0.05) higher effects which were comparable to ascorbic acid, acarbose and gallic acid. Conclusion: Findings from this study indicate strong correlation between polyphenolic concentration and antidiabetic activity. The study also confirmed the potential of some Nigerian herbs in antidiabetic drug discovery; and identified a number of promising plants for further in vivo investigation as plant-based antidiabetic agents.