Hypoglycemic and hypolipidemic effect of Vaccinium myrtillus L. leaf and Phaseolus vulgaris L. seed coat extracts in diabetic rats

The aim of this study was to examine the hypoglycemic and hypolipidemic effects of Vaccinium myrtillus L. leaf (VLE) and Phaseolus vulgaris L. seed coat (PCE) plant extracts, containing polyphenolic compounds, on carbohydrate and lipid metabolism in Wistar rats with streptozotocin (STZ) and high-fructose diet (HFD)-induced diabetes.Male Wistar rats with STZ and HFD-induced diabetes were fed with or without VLE or PCE for 50 d. At different intervals, blood glucose and body weight were recorded. Blood samples were used to determine glycated hemoglobin (HbA) and parameters of lipid profile in serum. Additionally, the levels of serum diene conjugates and malondialdehyde were assessed.Results of HbA and blood glucose level analysis showed the ameliorative effect of VLE on carbohydrate metabolism in diabetic rats. Of the eight diabetic animals treated with bilberry leaf extract, four had normal HbA levels. A significant reduction was observed in VLE group in blood glucose level compared with control diabetic rats (level of hyperglycemia decreased to normal values in 50% of animals versus 0% in the control diabetic group). VLE treatment normalized parameters of lipid metabolism. There was no significant difference from the same parameters in the intact control group. Administration of PCE significantly (P < 0.05) decreased the levels of plasma triacylglycerol (0.81 ± 0.06 mmol/L) and low-density lipoprotein (0.74 ± 0.10 mmol/L) in blood serum compared with the diabetic control group (1.36 ± 0.13 and 1.85 ± 0.30, respectively). Moreover, VLE and PLE showed an antioxidant effect on diene compounds in the blood serum of rats. A significant decrease was found in the plasma diene conjugate levels in PLE group (1.16 ± 0.11 nmol/mL) compared with control diabetic rats (2.09 ± 0.21 nmol/mL; P < 0.05). There was no significant difference from the same parameter in the VLE and intact control groups.The set of results that was obtained in the present study reveals lipid-lowering and antioxidant action related to the administration of VLE and PCE in Wistar rats with diabetes, induced by STZ, in combination with a high-carbohydrate diet. VLE to a certain extent also reduced hyperglycemia in diabetic animals.