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Glucokinase (GK) plays a key role in maintaining glucose homeostasis by stimulating insulin secretion from pancreatic β-cells and increasing hepatic glucose uptake. In this study we have investigated the effects of a novel, orally active glucokinase activator (GKA71) on insulin secretion and glucose tolerance in mice with high-fat diet (HFD) induced glucose intolerance. Mice were fed the HFD (58% fat by energy) for 8 weeks prior to administration of GKA71, which was provided in the diet (150 mg GKA71/kg food) giving a daily dose of ∼300 µg GKA71/mouse. Control mice were fed HFD or a normal diet (ND, 11% fat by energy). After 1 and 4 weeks with GKA71, glucose tolerance was studied in intravenous glucose tolerance test (IVGTT). Blood samples were taken just before and 1, 5, 10, 20, 50 and 75 min after the glucose injection (0.75g/kg). After 4-weeks treatment islets and liver were isolated. The GKA treatment significantly reduced basal plasma glucose level (5.3±0.3 vs. 8.3±0.3 mM in HFD, P<0.001, and 7.4±0.3 mM in ND, P<0.001). Basal insulin levels were also reduced by GKA71 (210±20 vs. 520±100 pM in HFD, P<0.01). The IVGTTs showed that GKA71 significantly improved glucose tolerance compared to HFD control mice (K[sub G] 4.0±0.5 vs. 2.5±0.2 %/min in HFD, P<0.01) being similar to ND fed mice (K[sub G] 3.8±0.2 %/min), although without increasing insulin secretion (AIR 485±120 vs. 670±85 pM in HFD, P>0.05). The AIR was 890±74 pM in the ND fed mice. There was no difference between the IVGTT results after 1 or 4 weeks with GKA71, suggesting full effect already after l-weeks treatment. Isolated islets from GKA treated mice demonstrated augmented glucose stimulated insulin secretion. Liver glycogen and triglyceride levels were similar in HFD control and HFD-GKA mice. In conclusion, activation of GK in HFD-fed mice potently reduces glycemia and normalizes glucose tolerance, demonstrating GKA as a potential therapeutic agent for treatment of type 2 diabetes. [ABSTRACT FROM AUTHOR]

Glucokinase (GK) is a metabolic sensor involved in the regulated release of insulin from pancreatic β-cells. Activators of GK may therefore have a possible role in the therapeutic management of type 2 diabetes. Here, we have examined the actions of the GK activator GKA50 on insulin secretion and intracellular Ca[sup 2+] homeostasis ([Ca[sup 2+]][sub i]) in isolated mouse, rat and human islets of Langerhans, and in the MIN6 insulin-secreting cell line. In rodent islets and MIN6 cells, 1µM GKA50 was found to stimulate insulin secretion and raise [Ca[sup 2+]][sub i] in the presence of glucose (2-10mM). Similar effects on insulin release were also seen in isolated human islets. GKA50 (1µM) caused a leftwards shift in the glucose-concentration response profiles and the EC[sub 50] values for glucose were shifted by 3mM in rat islets and approximately 10mM in MIN6 cells. There was no significant effect of GKA50 on the maximal rates of GSIS. In the absence of glucose GKA50 failed to elevate [Ca[sup 2+]][sub i] (1µM GKA50) or stimulate insulin release (30nM-10µM GKA50). At 5mM glucose the EC[sub 50] for GKA50 in MIN6 cells was approximately 0.3µM. Inhibition of GK with mannoheptulose or 5-thioglucose selectively inhibited the action of GKA50 on insulin release but not the effects of tolbutamide. Similarly, compromising glucose metabolism by 3-methoxyglucose prevented GKA50-induced rises in [Ca[sup 2+]][sub i] but not the actions of tolbutamide. Finally, we also show that the K[sub ATP] channel agonist diazoxide (200µM) inhibited GKA50-induced insulin release and its elevation of [Ca[sup 2+]][sub i]. This study illustrates that GKA50 is a glucose-like activator of βcell metabolism and a Ca[sup 2+]-dependent modulator of insulin secretion. [ABSTRACT FROM AUTHOR]