Cinnamic acid exerts anti-diabetic activity by improving glucose tolerance in vivo and by stimulating insulin secretion in vitro.

Although the anti-diabetic activity of cinnamic acid, a pure compound from cinnamon, has been reported but its mechanism(s) is not yet clear. The present study was designed to explore the possible mechanism(s) of anti-diabetic activity of cinnamic acid in in vitro and in vivo non-obese type 2 diabetic rats. Non-obese type 2 diabetes was developed by injecting 90 mg/kg streptozotocin in 2-day-old Wistar pups. Cinnamic acid and cinnamaldehyde were administered orally to diabetic rats for assessing acute blood glucose lowering effect and improvement of glucose tolerance. Additionally, insulin secretory activity of cinnamic acid and cinnamaldehyde was evaluated in isolated mice islets. Cinnamic acid, but not cinnamaldehyde, decreased blood glucose levels in diabetic rats in a time- and dose-dependent manner. Oral administration of cinnamic acid with 5 and 10 mg/kg doses to diabetic rats improved glucose tolerance in a dose-dependent manner. The improvement by 10 mg/kg cinnamic acid was comparable to that of standard drug glibenclamide (5 mg/kg). Further in vitro studies showed that cinnamaldehyde has little or no effect on glucose-stimulated insulin secretion; however, cinnamic acid significantly enhanced glucose-stimulated insulin secretion in isolated islets. In conclusion, it can be said that cinnamic acid exerts anti-diabetic activity by improving glucose tolerance in vivo and stimulating insulin secretion in vitro.

The antidiabetic effect of Geigeria alata is mediated by enhanced insulin secretion, modulation of ß-cell function, and improvement of antioxidant activity in streptozotocin-induced diabetic rats.

In Sudanese folk medicine, Geigeria alata roots have been used for the management of diabetes for a long time. However, its antidiabetic activity is unreported. In this study, G. alata methanolic extract was tested for its antidiabetic, antioxidant, and ß-cell modulatory effects in a streptozotocin-induced diabetic rat model. In this model of diabetic rats, the oral glucose tolerance test with G. alata extract at 125, 250, and 500  mg/kg doses revealed the efficacy of the 250  mg/kg dose in improving glucose tolerance comparable to the standard drug glibenclamide. Diabetic rats were treated with a 250  mg/kg dose of G. alata extract orally for 2  h (acute) or 14 days (chronic). In the case of acute treatment, the extract lowered blood glucose levels significantly at 120  min both in nondiabetic and diabetic rats. Chronic treatment of diabetic rats with 250  mg/kg of G. alata extract resulted in a significant decrease in blood glucose level closer to that of nondiabetic rats. Interestingly, increased serum insulin, improved ß-cell function, and antioxidant status were observed in G. alata-treated diabetic rats. G. alata also showed strong antioxidant and α-glucosidase inhibitory activities in in vitro assays. These data show direct evidence that G. alata has antidiabetic activity and suggest that the antidiabetic activity is due to enhanced insulin secretion, modulation of ß-cell function, and improvement of antioxidant status.

Asparagus officinalis extract controls blood glucose by improving insulin secretion and ß-cell function in streptozotocin-induced type 2 diabetic rats.

The aim of the present study was to evaluate the anti-diabetic mechanism of Asparagus officinalis, a dietary agent used for the management of diabetes. Streptozotocin (90 mg/kg) was injected in 2-d-old Wistar rat pups to induce non-obese type 2 diabetes. After confirmation of diabetes on the 13th week, diabetic rats were treated with a methanolic extract of A. officinalis seeds (250 and 500 mg/kg per d) or glibenclamide for 28 d. After the treatment, fasting blood glucose, serum insulin and total antioxidant status were measured. The pancreas was examined by haematoxylin-eosin staining and immunostained ß- and α-cells were observed using a fluorescence microscope. Treatment of the diabetic rats with the A. officinalis extract at doses of 250 and 500 mg/kg suppressed the elevated blood glucose in a dose- and time-dependent manner. The 500 mg/kg, but not 250 mg/kg, dose significantly improved serum insulin levels in the diabetic rats. The insulin:glucose ratio was significantly increased at both doses in the A. officinalis-treated rats. Both qualitative and quantitative improvements in ß-cell function were found in the islets of the A. officinalis-treated rats. The extract showed potent antioxidant activity in an in vitro assay and also improved the total antioxidant status in vivo. In most cases, the efficacy of A. officinalis (500 mg/kg) was very similar to a standard anti-diabetic drug, glibenclamide. Thus, the present study suggests that A. officinalis extract exerts anti-diabetic effects by improving insulin secretion and ß-cell function, as well as the antioxidant status.

Modulation of pancreatic ß-cells in neonatally streptozotocin-induced type 2 diabetic rats by the ethanolic extract of Momordica charantia fruit pulp.

Effective doses of the Momordica charantia fruit pulp (MCF) ethanolic extract on pancreatic ß-cells modulation in neonatally streptozotocin-induced type 2 diabetic rats were studied. Diabetic rats (n=8) were treated with MCF extract (400 mg kg(-1) day(-1)) or glibenclamide (5 mg kg(-1)) for 28 days. Control rats (n=11) and untreated diabetic rats (n=8) received only water. Fasting glucose, serum insulin (by ELISA) and ß-cell function (HOMA %B by homeostasis model assessment) were measured. ß- and α-cells were identified by immunostaining, nuclei by DAPI, and ß-cell size and number by morphometry. Significant improvement of fasting blood glucose, serum insulin and ß-cell function was observed with the MCF extract for the diabetic rat model. The islet size, total ß-cell area and number of ß-cells were increased to almost double in the diabetic rats treated with MCF extract as compared to the untreated diabetic rats. The number of α-cells did not change significantly. Insulin granules in ß-cells were notably reduced in diabetic islets as compared to control islets. However, extract-treated diabetic rat ß-cells were abundant with insulin granules, which was comparable to non-diabetic control islets. The modulation of pancreatic ß-cells may be involved in the experimental observation of anti-diabetic effects of M. charantia extract.