Insulin sensitizing actions of fenugreek seed polyphenols, quercetin & metformin in a rat model.

Background & objectives: Plant polyphenols have been known to exert anti-diabetic action and promote insulin action. The present study was carried out to compare the effects of administration of fenugreek seed polyphenolic extract (FPEt), quercetin and metformin (a positive control) in an acquired model of insulin resistance (IR). Methods: Adult male Wistar rats divided into seven groups (n=12). IR was induced in groups (groups 2, 3, 4 and 5) by feeding a high fructose diet (FRU) (60 g/100 g diet) for 60 days. From day 16, FRU rats were administered either FPEt (200 mg/kg bw) (group 3), quercetin (50mg/kg bw) (group 4) or metformin (50 mg/kg bw) (group 5) for the next 45 days. Group 1 served as normal control while groups 6 and 7 served as FPEt and quercetin controls respectively. Oral glucose tolerance test (OGTT) was done on day 59 to assess glucose tolerance. At the end of 60 days, the levels of glucose, insulin, triglycerides (TG) and free fatty acids (FFA) were measured in the blood and the activities of insulin-inducible and suppressible enzymes in cytosolic and mitochondrial fractions of liver and skeletal muscle. The extent of tyrosine phosphorylation of proteins in response to insulin was determined by assaying protein tyrosine kinase (PTK) and protein tyrosine phosphatase (PTP) in liver. Results: Fructose caused increased levels of glucose, insulin, TG and FFA, alterations in insulin sensitivity indices, enzyme activities and reduced glycogen content. Higher PTP activity and lower PTK activity suggest reduced tyrosine phosphorylation status. Administration of FPEt or quercetin improved insulin sensitivity and tyrosine phosphorylation in fructose-fed animals and the effect was comparable with that of metformin. Interpretation & conclusions: Our findings indicated that FPEt and quercetin improved insulin signaling and sensitivity and thereby promoted the cellular actions of insulin in this model.

Evaluation of in vitro antioxidant activity of Indian bay leaf, Cinnamomum tamala (Buch. -Ham.) T. Nees & Eberm using rat brain synaptosomes as model system.

The study investigated the perturbation of oxidant-antioxidant balance in brain synaptosomes of diabetic rats and determined the antioxidant and free radical-scavenging property of the Indian bay leaf. Brain synaptosomes were isolated from control and streptozotocin-induced diabetic animals and oxidative stress parameters were assayed. A methanolic extract of bay leaf (BLE) was tested for the polyphenolic content and antioxidant activity by in vitro assays. A significant increase in the levels of lipids and lipid peroxidation products and a decline in antioxidant potential were observed in diabetic rat brain synaptosomes. The total polyphenolic content of BLE was found to be 6.7 mg gallic acid equivalents (GAE)/100g. BLE displayed scavenging activity against superoxide and hydroxyl radicals in a concentration-dependent manner. Further, BLE showed inhibition of Fe(2+)-ascorbate induced lipid peroxidation in both control and diabetic rat brain synaptosomes. Maximum inhibition of lipid peroxidation, radical scavenging action and reducing power of BLE were observed at a concentration of 220 microg GAE. These effects of BLE in vitro were comparable with that of butylated hydroxyl toluene (BHT), a synthetic antioxidant. It can be concluded that synaptosomes from diabetic rats are susceptible to oxidative damage and the positive effects of bay leaf in vitro, could be attributed to the presence of antioxidant phytochemicals.