S 50131 and S 51434, two novel small molecule glucokinase activators, lack chronic efficacy despite potent acute antihyperglycaemic activity in diabetic mice.

BACKGROUND AND PURPOSE: Small molecule glucokinase activators (GKAs) have been associated with potent antidiabetic efficacy and hepatic steatosis in rodents. This study reports the discovery of S 50131 and S 51434, two novel GKAs with an original scaffold and an atypical pharmacological profile. EXPERIMENTAL APPROACH: Activity of the compounds was assessed in vitro by measuring activation of recombinant glucokinase, stimulation of glycogen synthesis in rat hepatocytes and increased insulin secretion from rat pancreatic islets of Langerhans. Efficacy and safety in vivo were evaluated after oral administration in db/db mice by measuring glycaemia, HbA1c and dyslipidaemia-associated events. KEY RESULTS: S 50131 and S 51434 activated GK and stimulated glycogen synthesis in hepatocytes and insulin secretion from pancreatic islets. Unexpectedly, while both compounds effectively lowered glycaemia after acute oral administration, they did not decrease HbA1c after a 4-week treatment in db/db mice. This lack of antidiabetic efficacy was associated with increased plasma free fatty acids (FFAs), contrasting with the effect of GKA50 and N00236460, two GKAs with sustained HbA1c lowering activity but neutral regarding plasma FFAs. S 50131, but not S 51434, also induced hepatic steatosis, as did GKA50 and N00236460. However, a shorter, 4-day treatment resulted in increased hepatic triglycerides without changing the plasma FFA levels, demonstrating dynamic alterations in the lipid profile over time. CONCLUSIONS AND IMPLICATIONS: In addition to confirming the occurrence of dyslipidaemia with GKAs, these findings provide new insights into understanding how such compounds may sustain or lose efficacy over time.

Small molecule glucokinase activators disturb lipid homeostasis and induce fatty liver in rodents: a warning for therapeutic applications in humans.

BACKGROUND AND PURPOSE: Small-molecule glucokinase activators (GKAs) are currently being investigated as therapeutic options for the treatment of type 2 diabetes (T2D). Because liver overexpression of glucokinase is thought to be associated with altered lipid profiles, this study aimed at assessing the potential lipogenic risks linked to oral GKA administration. EXPERIMENTAL APPROACH: Nine GKA candidates were qualified for their ability to activate recombinant glucokinase and to stimulate glycogen synthesis in rat hepatocytes and insulin secretion in rat INS-1E cells. In vivo activity was monitored by plasma glucose and HbA1c measurements after oral administration in rodents. Risk-associated effects were assessed by measuring hepatic and plasma triglycerides and free fatty acids, as well as plasma aminotransferases, and alkaline phosphatase. KEY RESULTS: GKAs, while efficiently decreasing glycaemia in acute conditions and HbA1c levels after chronic administration in hyperglycemic db/db mice, were potent inducers of hepatic steatosis. This adverse outcome appeared as soon as 4 days after daily oral administration at pharmacological doses and was not transient. GKA treatment similarly increased hepatic triglycerides in diabetic and normoglycaemic rats, together with a pattern of metabolic phenotypes including different combinations of increased plasma triglycerides, free fatty acids, alanine and aspartyl aminotransferases, and alkaline phosphatase. GKAs belonging to three distinct structural families induced hepatic steatosis in db/db mice, arguing in favour of a target-mediated, rather than a chemical class-mediated, effect. CONCLUSION AND IMPLICATIONS: Given the risks associated with fatty liver disease in the general population and furthermore in patients with T2D, these findings represent a serious warning for the use of GKAs in humans. LINKED ARTICLE: This article is commented on by Rees and Gloyn, pp. 335-338 of this issue. To view this commentary visit http://dx.doi.org/10.1111/j.1476-5381.2012.02201.x.

Exploring functional beta-cell heterogeneity in vivo using PSA-NCAM as a specific marker.

BACKGROUND: The mass of pancreatic beta-cells varies according to increases in insulin demand. It is hypothesized that functionally heterogeneous beta-cell subpopulations take part in this process. Here we characterized two functionally distinct groups of beta-cells and investigated their physiological relevance in increased insulin demand conditions in rats. METHODS: Two rat beta-cell populations were sorted by FACS according to their PSA-NCAM surface expression, i.e. beta(high) and beta(low)-cells. Insulin release, Ca(2+) movements, ATP and cAMP contents in response to various secretagogues were analyzed. Gene expression profiles and exocytosis machinery were also investigated. In a second part, beta(high) and beta(low)-cell distribution and functionality were investigated in animal models with decreased or increased beta-cell function: the Zucker Diabetic Fatty rat and the 48 h glucose-infused rat. RESULTS: We show that beta-cells are heterogeneous for PSA-NCAM in rat pancreas. Unlike beta(low)-cells, beta(high)-cells express functional beta-cell markers and are highly responsive to various insulin secretagogues. Whereas beta(low)-cells represent the main population in diabetic pancreas, an increase in beta(high)-cells is associated with gain of function that follows sustained glucose overload. CONCLUSION: Our data show that a functional heterogeneity of beta-cells, assessed by PSA-NCAM surface expression, exists in vivo. These findings pinpoint new target populations involved in endocrine pancreas plasticity and in beta-cell defects in type 2 diabetes.

Newly approved and promising antidiabetic agents.

Type 2 diabetes is an endocrine/metabolic disease characterized by hyperglycemia. It is now well established that insulin resistance and pancreatic beta-cell dysfunction/failure are the two major components of the physiopathology of the disease. Current available therapies do not successfully enable patients with type 2 diabetes to reach glycemic goals. Even with intensive treatment type 2 diabetic patients may face spikes in blood glucose after meals, weight gain, and a loss of effectiveness of their treatments over time. The novel agents recently developed by the Pharmaceutical Industry may either provide an alternative therapeutic strategy or offer useful adjuncts to existing therapies. Glucagon-like peptide 1 (GLP-1), produced in the small intestine and amylin, produced by beta cells in the pancreas, also have glucose lowering effects. Amylin is an hormone secreted after a meal, having a complementary action to insulin. GLP-1, also released in a post-prandial manner, promotes insulin production and secretion, reduces glucagon secretion, delays gastric emptying and induces a feeling of fullness. The most promising effect of GLP-1 is its ability to increase beta-cell mass by stimulating neogenesis and reducing apoptosis in rodents. However the fact that GLP-1 is rapidly degraded by dipeptidylpeptidase IV (DPPIV) in vivo reduces its usefulness. Thus, in order to improve therapeutic efficacy, two approaches have been investigated: the development of GLP-1 analogs resistant to degradation or the development of DPP-IV inhibitors. Synthetic analogs of amylin (pramlintide), GLP-1 (exenatide) and inhibitors of the degradation of GLP-1 (sitagliptin, DPP-IV inhibitor) are now available for clinical use. Promising biological targets being investigated include those leading to insulin sensitization (11beta-HSD-1 inhibitors and antagonists of glucocorticoids receptor), reducing hepatic glucose output (antagonist of glucagon receptor, inhibitors of glycogen phosphorylase and fructose-1,6-biphosphatase) and finally increasing urinary elimination of excess glucose (SGLT inhibitors). A particular role is played by glucokinase activators (GKA) which can both increase insulin secretion and improve hepatic glucose metabolism. In this review, we present a summary of the data available on newly approved treatments (amylin and GLP-1 analogs as well as DPP-IV inhibitors) and give an overview of the targets currently being studied for the treatment of type 2 diabetes with an emphasis on the small molecule drug design.

Dynamic changes in {beta}-cell mass and pancreatic insulin during the evolution of nutrition-dependent diabetes in psammomys obesus: impact of glycemic control.

Recent studies ascribe a major role to pancreatic beta-cell loss in type 2 diabetes. We investigated the dynamics of beta-cell mass during diabetes evolution in Psammomys obesus, a model for nutrition-dependent type 2 diabetes, focusing on the very early and the advanced stages of the disease. P. obesus fed a high-calorie diet for 26 days developed severe hyperglycemia, beta-cell degranulation, and markedly reduced pancreatic insulin content. Reducing calories for 7 days induced normoglycemia in 90% of the animals, restoring beta-cell granulation and insulin content. To dissociate effects of diet from blood glucose reduction, diabetic animals received phlorizin for 2 days, which normalized glycemia and increased the pancreatic insulin reserve to 50% of control, despite a calorie-rich diet. During diabetes progression, beta-cell mass decreased initially but recovered spontaneously to control levels, despite persistent hyperglycemia. Strikingly, however, beta-cell mass did not correlate with degree of hyperglycemia or pancreatic insulin content. We conclude that reduced insulin reserve is the main cause of diabetes progression, whereas irreversible beta-cell mass reduction is a late event in P. obesus. The rapid recovery of the pancreas by phlorizin-induced normoglycemia implies a causal relationship between hyperglycemia and islet dysfunction. Similar mechanisms could be operative during the evolution of type 2 diabetes in humans.

Role of glucose in IRS signaling in rat pancreatic islets: specific effects and interplay with insulin.

We investigated the possible interplay between insulin and glucose signaling pathways in rat pancreatic beta-cell with a special focus on the role of glucose in IRS signaling in vivo. Three groups of rats were constituted by combining simultaneous infusion during 48 h either of glucose and/or insulin, or glucose+diazoxide: Hyperglycemic-Hyperinsulinemic (HGHI), euglycemic-Hyperinsulinemic (eGHI), Hyperglycemic-euinsulinemic (HGeI). Control rats were infused with 0,9%NaCl. In HGHI and HGeI rats plasma glucose levels were maintained at 20-22 mmol/l. In eGHI rats, plasma glucose was not different from that of controls, whereas plasma insulin was much higher than in controls. In HGHI rats, IRS-2 mRNA expression, total protein and phosphorylated protein amounts were increased compared to controls. In HGeI rats, only IRS-2 mRNA expression was increased. No change was observed in eGHI rats whatever the parameter considered. In all groups, mRNA concentration of IRS-1 was similar to that of controls. The quantity of total and phosphorylated IRS-1 protein was dramatically increased in HGHI rats and to a lesser extent in eGHI rats. Neither mRNA nor IRS-1 protein expression were modified in HGeI rats. The data suggest that glucose and insulin play at once a specific and a complementary role in islet IRSs signaling. Especially, glucose stimulates IRS-2 mRNA expression whatever the insulin status and independently of the secretory process. The differential regulation of IRS-1 and IRS-2 expressions is in agreement with their supposed different involvement in the control of beta-cell growth and function.

Specific and combined effects of insulin and glucose on functional pancreatic beta-cell mass in vivo in adult rats.

We investigated the specific and associated effects of insulin and glucose on beta-cell growth and function in adult rats. By combining simultaneous infusion either of glucose and/or insulin or glucose and diazoxide, three groups of rats were constituted: hyperglycemic-hyperinsulinemic rats (high glucose-high insulin), hyperglycemic-euinsulinemic rats (high glucose), and euglycemic-hyperinsulinemic rats (high insulin). All the infusions lasted 48 h. Control rats were infused with 0.9% NaCl (saline controls). In all groups, beta-cell mass was significantly increased, compared with controls (by 70% in high glucose-high insulin rats, 65% in high glucose rats, and 50% in high insulin rats). The stimulation of neogenesis was suggested by the high number of islets budding from pancreatic ducts in high glucose-high insulin and high glucose rats and by the presence of numerous clusters of few beta-cells within the exocrine pancreas in high insulin rats. beta-Cell hypertrophy was observed only in high glucose-high insulin rats. The rate of beta-cell proliferation was similar to that of controls in high glucose-high insulin rats after a 48-h glucose infusion, dropped dramatically in high insulin rats, and dropped to a lesser extent in high glucose rats. In high glucose-high insulin and high glucose rats, beta-cell mass increase was related to a higher beta-cell responsiveness to glucose in vitro as measured by islet perifusion studies, whereas in high insulin rats, no significant enhancement of glucose induced insulin secretion could be noticed. The data show that glucose and insulin may have specific stimulating effects on beta-cell growth and function in vivo in adult rats independently of the influence they exert each other on their respective plasma concentration.