Isolation and Characterization of the Anti-diabetic Principle(s) in the Aqueous Extract of Graptophyllum Pictum (linn.) Griff. (Acanthaceae) Leaf.

This research was embarked upon in order to verify the anti-diabetic property reported on the aqueous extract of Graptophyllum pictum leaf and establish an effective dose for the active extract. It aimed to identify and isolate some chemical constituents in the active extract. It also proposed to start the toxicity study of the active extract by testing for acute toxicity. The anti-diabetic investigation was carried out in 4 groups of alloxan induced diabetic rats that were orally administered 4 different doses (50, 100, 150 and 200 mg/kg) of the aqueous extract. Two other groups of the diabetic rats were administered distilled water (vehicle of administration) and metformin (a well known anti-diabetic drug) at 10 mg/kg to serve as controls. The acute toxicity screening of the active extract was carried out on 4 groups of mice at doses that are much higher (1, 2, 3 and 4 g/kg) than the anti-diabetic doses. The methanolic extract of the leaf was investigated for chemical constituents using simple phytochemical tests. The extract was subjected to column and high performance chromatographic techniques and in tandem with chemical ionization mass spectrometry in order to separate and isolate some of its chemical constituents. The structural elucidation of the isolated compounds were achieved with the aid of proton (1H) and carbon (13C) nuclear magnetic resonance (NMR) spectroscopy using 2-dimensional (2D) techniques such as proton-proton correlation spectroscopy (1H-1H COSY), heteronuclear multiple quantum correlations (HMQC) and heteronuclear multiple-bond correlations (HMBC). The tested aqueous extract was found to possess anti-diabetic action which was comparable to that of metformin. The effective dose was established at 100 mg/kg. The phytochemical investigation of the extract revealed the presence of polyphenolic compounds, saponins, reducing sugars and alkaloids; the absence of anthraquinones, cardiac glycosides and cyanogenetic glycosides. The separation/isolation exercise resulted in the isolation of a yellow crystalline compound which did not yield to acid hydrolysis suggesting the likelihood of a C-glycoside as opposed to an O-glycoside. The melting point was found to be 226.3oC. The high resolution atmospheric pressure in tandem with chemical ionization mass spectrometry of the compound showed three molecular ion peaks at m/z 565 corresponding to the molecular formula C26 H28O14 and the fragmentation pattern together with the fragments produced confirmed the isolated compounds to be C-glycosides of apigenin a poly phenol (flavonoid). The analysis of the 13C NMR spectra of the sugar portions also support the suggestion that the sugar(s) were C-bonded for they were revealed as 1 unit of D glucopyranose and L-arabinopyranoside bonded directly to carbon atoms at positions 6 and 8. A search through spectral library helped to identify the isolated compounds as schaftoside, isoschaftoside and neoschaftoside. They were found to be isomers. The aqueous extract of Graptophyllum pictum exhibited anti-diabetic action at 100 mg/kg which is comparable to metfomin a standard anti-diabetic drug. From this active extract, three isomers of apigenin C-glycosides were detected, characterized and elucidated to be schaftoside, isoschaftoside and neoschaftoside.
A Thesis Submitted to the School of Postgraduate Studies, University of Lagos.
Anti-diabetic property , Acute toxicity , Griff leaf , Research Subject Categories::PHARMACY::Toxicology
Olagbende – Dada, S.O (2011), Isolation and Characterization of the Anti-diabetic Principle(s) in the Aqueous Extract of Graptophyllum Pictum (linn.) Griff. (Acanthaceae) Leaf. A Thesis Submitted to University of Lagos School of Postgraduate Studies Phd Thesis and Dissertation, 115pp.