Wogonin`s structure activity relationship study on antidiabetic activity

Abstract

Wogonin has been reported to exert antihyperglycemic effect and has potential to enhance the current therapy options against type 2 diabetes mellitus. However, the structure-activity relationships (SAR) studies of wogonin against this disease have not been carried out. In this study, thirteen structurally similar compounds to wogonin were taken into account to understand wogonin’s SAR on antidiabetic activity. Initially, powdered leaves of Tetracera indica Merr. (T. indica) was macerated with methanol for 72 h to obtain methanol extract which was subjected to column chromatography (silica gel and sephadex LH 20) to isolate wogonin (MN1). Along with the isolation of wogonin, techtochrysin (MN4), and norwogonin (MN7) were also isolated. Isoscutellarein (MN9), hypolaetin (MN10), kaempferol (MN11) and quercetin (MN12) were also isolated from the Tetracera scandens (T. scandens) leaves methanol extract via similar procedure. To understand the SAR of wogonin, methyl ether of wogonin (MN2), acetate of wogonin (MN3) and acetate of norwogonin (MN8) were also synthesized. Their structures were elucidated through the interpretation of spectroscopic data. Some commercial compounds which have related chemical structures were also bought and compared for their biological activities viz., 8-hydroxy-7-methoxy flavone (MN5), chrysin (MN6), (+) catechin (MN13) and (-) epicatechin (MN14). Wogonin (MN1) obtained as the major flavone from T. indica was administered through intraperitoneal to STZ-NA induced diabetic rats (25, 40, 80 mg/b.w) to examine its antidiabetic potential. The biochemical assays, insulin release and histological alteration were evaluated and compared to standard hypoglycemic drug, metformin (0.5 mg/kg b.w). Then, all compounds were evaluated for their in vitro antioxidant activities using rapid test by dot blot, DPPH, ABTS+, xanthine oxidase inhibitory and FRAP assays. Subsequently, in-vitro antidiabetic activities through DPP-IV and α-glucosidase inhibitory assays were assessed. Subsequently, cell viability of RIN-5F pancreatic cell and pre-adipocyte were initially tested then insulin secretion of RIN-5F as well as adipogenesis, and glucose uptake measurement of adipocyte were investigated. Next, protein expression studies through adipokines (leptin, adiponectin, TNF-α, RBP-4) as well as western blotting against GLUT4 and C/EBP-α were analyzed. The results showed that wogonin at 40 mg/b.w and 80 mg/b.w exhibited significant antihyperglycemic activity without showing any toxicity effect of the liver (p<0.05). In vitro antioxidant and antidiabetic activities (DPP-IV, α-glucosidase) clearly highlighted the importance of the total number and configuration of hydroxyl group, as well as disadvantage of the absence of ketonic group at C-4 and C-2-C-3 double bond. Nevertheless, the results of animal study, cell culture (insulin secretion, adipogenesis, glucose uptake), and protein expression showed that the methyl ether group at position C-8 might be responsible for wogonin’s antidiabetic capacity via β-cells of islets of Langerhans’ recovery as well as through glucose uptake mechanism which was indicated by up regulation of GLUT4 and C/EBP-α. The mechanism could be enhanced by the addition of acetate group at C-5 and C-7 positions. These finding have facilitated us to understand the key pharmacophore of wogonin via SAR and should be encouraged for further future studies, which could lead to the development of nutritional product and semi synthetic analogs that retain substantial antidiabetic capacity with minimal adverse effects.