Evaluation of antidiabetic potential of methanolic extract of myrmecodia platytyrea tuber, in vivo and in vitro / Hasbullani Zakaria

Tubers of Myrmecodia platytytrea (Rubiaceae) has been used traditionally as an alternative therapy for the management of cancer and other inflammatory-related disorders. This plant is also believed to have the ability to lower blood glucose level. Nevertheless, no scientific proof is available on its anti-diabetic effect. Type 2 diabetes mellitus (T2DM) is one of the main non-communicable chronic diseases. Individuals present with T2DM have insulin resistance and usually develop insulin deficiency. The aim of this study was to investigate the potency of Myrmecodia platytytrea methanolic tuber extract (MPMTE) as an antihyperglycemic agent, in vitro and in vivo. Firstly, a simple and rapid high performance thin layer chromatography (HPTLC) technique was developed to measure the antioxidant (a direct HPTLCDPPH• assay) and hypoglycemic effects (HPTLC with α-amylase) of Myrmecodia platytyrea tuber extracts (methanol, ethanol, dichloromethane and ethyl acetate extracts). Then, in vitro hypoglycemic effects via α-amylase and α-glucosidase inhibitory assays were conducted on the MPMTE. Cytotoxicity study of MPMTE was done against BRIN-BD11, 3T3-L1 and L6 using MTT assay before glucose uptake of MPMTE in these cell lines was measured by using Glucose Uptake Assay Kit while expression of glucose metabolism-related genes of cells were determined by quantitative RT-PCR. Finally, in vivo antihyperglycaemic effect of MPMTE was investigated for therapeutic and prophylactic treatments. Hyperglycaemia was induced in fasted SD rats with STZ (45 mg/kg; i.p.). In the therapeutic study, rats were treated orally with MPMTE (100, 200 and 400 mg/kg) and metformin (positive control, 100 mg/kg) daily for 14 days while in the prophylactic study rats were given MPMTE (100, 200 and 400 mg/kg) for 28 days before STZ induction. Blood was taken each week to measure fasting blood glucose level and at the end of experiment, for other biochemistry analysis. Our results showed that stigmasterol was detected in all extracts using HPLTC. The highest free radical scavenging activity was observed in the ethanol extract, which is rich in polyphenols and flavonoids. Additionally, MPMTE had both α-amylase and α-glucosidase inhibitory activities. MPMTE showed no cytotoxicity against BRIN-BD11, 3T3-L1 and L6 cells with IC50 values of > 500 μg/mL following 48 h incubation. Furthermore, MPMTE (125, 250 and 500 μg/mL) were able to downregulate expression of G6Pase gene and upregulate GCK, SREBP- 1C, GLUT2 and GLUT4 genes against BRIN-BD11, 3T3-L1 and L6 cells, suggesting MPMTE regulated glucose metabolism. In the therapeutic study, STZ-induced diabetic rats treated with MPMTE (200 and 400 mg/kg) had significant decreased (p < 0.05) in fasting blood glucose, total cholesterol, triglycerides and low-density lipoprotein (LDL) with no significant changes in high-density lipoprotein (HDL) compared to STZ-induced untreated diabetic rats. Administration of MPMTE for 28 days prior to injection of STZ did not prevent the development of diabetes.In conclusion, MPMTE had strong antihyperglycaemic activity that inhibits glucose absorption in the intestine, modulate glucose metabolism, improving β-cell function, initiating insulin release and antioxidant, as well as anti-inflammatory effects due to the presence of high antioxidant compounds in MPMTE including polyphenolic acids, flavonoids and stigmasterol. Hence, MPMTE can be further developed into an adjuvant therapy for diabetic patients.