ISOLATION AND CHARACTERIZATION OF ACTIVE ANTIHYPERGLYCEMIC COMPONENT OF URTICA DIOICA LEAVES

Abstract

Urtica dioica (U.dioica) commonly known as the stinging nettle is a herbaceous perennial plant belonging to the plant family Urticaceae. The aqueous extract of the plant have been shown to have antihyperglycemic activity though the bioactive compounds of the extract have not been previously isolated. This study isolated and characterized four compounds which include 1’,4’,7-trimethylcyclohex-2ylnaphthalene given the trivial name urticol and three terpenoids from the leaves extract of the plant. It further established the general mechanism of action of the extract in treatment of diabetes. The air dried plant material (1.5 kg) was macerated in DCM/MeOH solvent system (1:1 v/v) for 72h to yield 40 g of the crude extract. The extract was then separated and purified using silica gel column chromatography under n-hexane/DCM/EtOAc/MeOH gradient followed by sephadex LH-20 column chromatography. Structure elucidation of the compounds was done by employing spectroscopic techniques such as IR, mass spectrometry, 1D NMR and 2D NMR experiments. Urticol and the terpenoids were assayed for their potential stimulation of hepatic glucose uptake using freshly isolated primary rat hepatocytes incubated in a humidified 5 % CO2 incubator and the glucose concentrations for 15, 30, 45 and 60 minutes intervals determined spectrophotometrically using 3,5-dinitrosalicyclic acid colorimetric assay method. Urticol like pioglitazone significantly upregulated the uptake of glucose by 28.57 % compared to the untreated control in rat hepatocytes cultured in DMEM supplemented with 100 M of urticol and 100 M of pioglitazone (p<0.05). The other compounds were found to be non-bioactive at both 50 M and 100 M. Although urticol had comparable activity to pioglitazone, it increased the uptake of glucose by 11.45 % relative to pioglitazone. This showed that urticol is better than pioglitazone in stimulation of glucose uptake. Therefore, the findings show urticol as a potent antihyperglycemic agent. This work may provide a scientific proof of the folklore antidiabetic activity of U.dioica. Previous studies found out that the crude extract of U.dioica leaves inhibited glucosidase enzyme and activated PPAR- in the liver. glucosidase is an enzyme which is responsible for endogenous production of glucose in the liver while PPAR- is responsible for improving insulin sensitivity. Increased glucose uptake in the liver enhances hepatic insulin sensitivity which leads to a decrease in endogenous glucose production. Urticol could possibly inhibit glucosidase but activate PPAR- v