Antihyperglycemic activity and antidiabetic effect of methyl caffeate isolated from Solanum torvum Swartz. fruit in streptozotocin induced diabetic rats

Natural remedies from medicinal plants are considered to be effective and safe alternatives to treat diabetes mellitus. Solanum torvum Swartz. fruit is widely used in the traditional system of medicine to treat diabetes. In the present study methyl caffeate, isolated from S. torvum fruit, was screened for its efficacy in controlling diabetes in animal models. Antihyperglycemic effect of methyl caffeate was studied in normal glucose-fed rats. The effects of oral administration of methyl caffeate (10, 20 and 40 mg/kg) for 28 days on body weight, fasting blood glucose, plasma insulin, hemoglobin, glycated hemoglobin, total protein, hepatic glycogen and carbohydrate metabolism enzymes in streptozotocin induced diabetic rats were investigated. Histological observations in the pancreas and GLUT4 expression in skeletal muscles were also studied. Methyl caffeate at 40 mg/kg significantly prevented the increase in blood glucose level after glucose administration at 60 min in comparison to the hyperglycemic control group. In streptozotocin induced diabetic rats, methyl caffeate produced significant reduction in blood glucose and increased body weight. The levels and/or activities of other biochemical parameters were near normal due to treatment with methyl caffeate. Methyl caffeate treated diabetic rats showed upregulation of GLUT4 and regeneration of β-cells in the pancreas. These results substantiated that methyl caffeate possessed hypoglycemic effect, and it could be developed into a potent oral antidiabetic drug.     

Antidiabetic activity of γ-sitosterol isolated from Lippia nodiflora L. in streptozotocin induced diabetic rats

Lippia nodiflora L. (Verbenaceae) is a creeping perennial herb widely used in traditional system of medicine to treat ulcers, bronchitis and heart diseases; it also possesses antidiabetic property. In the present study, γ-sitosterol isolated from Lippia nodiflora was screened for its antidiabetic property in streptozotocin (STZ) induced diabetic rats. Insulin secretion in response to glucose was evaluated in isolated rat islets. Oral administration of γ-sitosterol (20 mg/kg body weight) once daily for 21 days in STZ-induced diabetic rats resulted in a significant decrease in blood glucose and glycosylated hemoglobin with a significant increase in plasma insulin level, body weight and food intake. Furthermore γ-sitosterol showed antihyperlipidemic activity as evidenced by significant decrease in serum total cholesterol, triglycerides and very low density lipoprotein-cholesterol levels coupled with elevation of high density lipoprotein-cholesterol levels in treated rats. A significant decrease in the activities of alanine aminotransaminase, aspartate aminotransaminase, alkaline phosphatase and acid phosphatase in γ-sitosterol treated rats when compared to diabetic control rats indicated its protective role against liver damage. γ-Sitosterol increased insulin secretion in response to glucose. Immunohistochemical study of pancreas also confirmed the biochemical findings. These results indicated that γ-sitosterol, the compound isolated from L. nodiflora, possessed antihyperglycemic activity.     

Antidiabetic effect of plumbagin isolated from Plumbago zeylanica L. root and its effect on GLUT4 translocation in streptozotocin-induced diabetic rats

Plumbago zeylanica L. root is widely used in Indian medicine to treat diabetes mellitus. The aim of the present investigation was to evaluate the antidiabetic effects of plumbagin isolated from P. zeylanica L. root and its effect on GLUT4 translocation in STZ-induced diabetic rats. Plumbagin (15 and 30 mg/kg b wt) was orally administered to STZ-induced diabetic rats for 28 days. An oral glucose tolerance test was performed on 21st day. The effect of plumbagin on body weight, blood glucose, plasma insulin, total protein, urea, creatinine, liver glycogen, plasma enzymes (SGOT, SGPT and ALP) and carbohydrate metabolism enzymes (glucose-6-phosphatase, fructose-1,6-bisphosphatase and hexokinase) were investigated. GLUT4 mRNA and protein expression in skeletal muscles were also studied. Plumbagin significantly reduced the blood glucose and significantly altered all other biochemical parameters to near normal. Further, plumbagin increased the activity of hexokinase and decreased the activities of glucose-6-phosphatase and fructose-1,6-bisphosphatase significantly in treated diabetic rats. Enhanced GLUT4 mRNA and protein expression were observed in diabetic rats after treatment with plumbagin. The results indicated that plumbagin enhanced GLUT4 translocation and contributed to glucose homeostasis. It could be further probed for use as a drug to treat diabetes.