The mechanism of action of ursolic acid as insulin secretagogue and insulinomimetic is mediated by cross-talk between calcium and kinases to regulate glucose balance.

BACKGROUND: The effect of in vivo treatment with ursolic acid (UA) on glycemia in hyperglycemic rats and its mechanism of action on muscle were studied. METHODS: The UA effects on glycemia, glycogen, LDH, calcium and on insulin levels were evaluated after glucose tolerance curve. The ß-cells were evaluated through the transmission electron microscopy. UA mechanism of action was studied on muscles through the glucose uptake with/without specific insulin signaling inhibitors. The nuclear effect of UA and the GLUT4 expression on muscle were studied using thymidine, GLUT4 immunocontent, immunofluorescence and RT-PCR. RESULTS: UA presented a potent antihyperglycemic effect, increased insulin vesicle translocation, insulin secretion and augmented glycogen content. Also, UA stimulates the glucose uptake through the involvement of the classical insulin signaling related to the GLUT4 translocation to the plasma membrane as well as the GLUT4 synthesis. These were characterized by increasing the GLUT4 mRNA expression, the activation of DNA transcription, the expression of GLUT4 and its presence at plasma membrane. Also, the modulation of calcium, phospholipase C, protein kinase C and PKCaM II is mandatory for the full stimulatory effect of UA on glucose uptake. UA did not change the serum LDH and serum calcium balance. CONCLUSIONS: The antihyperglycemic role of UA is mediated through insulin secretion and insulinomimetic effect on glucose uptake, synthesis and translocation of GLUT4 by a mechanism of cross-talk between calcium and protein kinases. GENERAL SIGNIFICANCE: UA is a potential anti-diabetic agent with pharmacological properties for insulin resistance and diabetes therapy.

Incretinomimetic and Insulinomimetic Effect of (2E)-N'-(1'-Naphthyl)-3,4,5-Trimethoxybenzohydrazide for Glycemic Homeostasis.

To characterize the role and the mechanism of action of (2E)-N'-(1'-naphthyl)-3,4,5-trimethoxybenzohydrazide (BZD) on incretin secretion, glucose uptake in skeletal muscle and α-glucosidase activity on intestine, targets for glucose homeostasis. It was assayed on glucose tolerance test (GTT) to analyze GLP-1 secretion and the activity of DPP-4 enzyme in vitro. In skeletal muscle, mechanism of action on glucose uptake was carried out by in vitro experiments. The activity of intestinal disaccharidases was performed after in vivo and in vitro experiments. The compound improved the glucose tolerance around 30%, 25%, and 20% at 15, 30, and 60 min, respectively and potentiated the sitagliptin effect, an inhibitor of the enzyme that removes GLP-1, about 50, 45, and 54% at 15, 30, and 60 min, respectively. Additionally, BZD did not modify the activity of DPP-4 enzyme. The acute effect of BZD on glucose uptake is mediated by increasing GLUT4 expression (around 140%) and its translocation to the plasma membrane in soleus muscle. The genomic effect as well as GLUT4 translocation involve the activation of PI-3K and MAPK pathways and require the microtubules integrity to the complete stimulatory effect of this compound on glucose uptake. Beyond, BZD acts in an alternative target to ameliorate glycaemia, intestinal disaccharidases. In a whole, these data point an incretino- and insulinomimetic effect of the compound for glycemic control.

Mechanism of Action of Novel Glibenclamide Derivatives on Potassium and Calcium Channels for Insulin Secretion.

Glibenclamide is widely used and remains a cornerstone and an effective antihyperglycemic drug. After the casual discovery of its hypoglycemic potential, this compound was introduced for diabetes treatment. However, the long-term side effects reveal that glibenclamide should be replaced by new molecules able to maintain the health of ß-cells, protecting them from hyperstimulation/hyperexcitability, hyperinsulinemia, functional failure and cell death. The aim of this review was to highlight the main mechanism of action of glibenclamide and the influence of its derivatives, such as acylhydrazones, sulfonamides and sulfonylthioureas on ß-cells potassium and calcium channels for insulin secretion as well as the contribution of these new compounds to restore glucose homeostasis. Furthermore, the role of glibenclamide-based novel structures that promise less excitability of ß-cell in a long-term treatment with effectiveness and safety for diabetes therapy was discussed.

Acylhydrazones contribute to serum glucose homeostasis through dual physiological targets.

In this study the in vivo and in vitro antidiabetic effects of four acylhydrazone derivatives were investigated in rats. The secretagogue action, oral glucose tolerance, insulinogenic index and mechanism of action of these acylhydrazones in relation to calcium uptake in pancreatic islets were studied. Also, the insulinomimetic effect on glycemia in diabetic rats was verified. Of the acylhydrazones studied, 1 and 4 were able to increase glucose tolerance in an acute time-course. A powerful secretagogue effect was exhibited by 1 and glibenclamide with an insulinogenic index around 3.9 and 1.3-fold higher than that of the hyperglycemic group, respectively. Moreover, an acute and dose-dependent effect of glibenclamide and 1 on calcium uptake in pancreatic islets was observed. The rapid stimulatory effect of 1 on calcium uptake seems to be mediated, at least in part, by ATP-dependent K+ channels (K+-ATP) since the stimulatory effect of 1 was similar to that observed for glibenclamide but was not potentiated by sulphonylurea. Furthermore, both extracellular and calcium from stocks mediate the signal transduction of stimulatory effect of 1 on calcium uptake which may contribute to insulin secretion. In addition, the insulinomimetic effect of 1 was evidenced through the level of serum glucose lowering in alloxan-induced diabetic rats. Also, 1 induced a significant increase in glycogen content in vivo and glucose uptake in soleus muscle in vitro. The results of this study indicate dual physiological targets for the acylhydrazone 1, i.e., pancreatic islets and skeletal muscle, as a result of insulin secretagogue and insulinomimetic action.