Recent advances in glucokinase activators for the treatment of type 2 diabetes

Clinical investigation of glucokinase activators for the restoration of glucose homeostasis in diabetes

As a sensor, glucokinase (GK) controls glucose homeostasis, which progressively declines in patients with diabetes. GK maintains the equilibrium of glucose levels and regulates the homeostatic system set points. Endocrine and hepatic cells can both respond to glucose cooperatively when GK is activated. GK has been under study as a therapeutic target for decades due to the possibility that cellular GK expression and function can be recovered, hence restoring glucose homeostasis in patients with type 2 diabetes. Five therapeutic compounds targeting GK are being investigated globally at the moment. They all have distinctive molecular structures and have been clinically shown to have strong antihyperglycemia effects. The mechanics, classification, and clinical development of GK activators are illustrated in this review. With the recent approval and marketing of the first GK activator (GKA), dorzagliatin, GKA's critical role in treating glucose homeostasis disorder and its long-term benefits in diabetes will eventually become clear.

In silico docking based screening of constituents from Persian shallot as modulators of human glucokinase

Purpose

Small molecule glucokinase (GK) modulators not only decrease fasting and basal plasma sugar contents but also progress glucose tolerance. The hydro-ethanolic extract of the Persian shallot (Allium hirtifolium Boiss.) decreased blood glucose, improved plasma insulin and amplified GK action. The present study was proposed to screen phytoconstituents from Persian shallot as human GK activators using in silico docking studies.

Methods

A total of 91 phytoconstituents reported in Persian shallot (A. hirtifolium Boiss.) were assessed in silico for the prediction of drug-like properties and molecular docking investigations were carried out with human GK using AutoDock vina with the aim of exploring the binding interactions between the phytoconstituents and GK enzyme followed by in silico prediction of toxicity.

Results

Almost all the phytoconstituents tested showed good pharmacokinetic parameters for oral bioavailability and drug-likeness. In the docking analysis, cinnamic acid, methyl 3,4,5-trimethoxy benzoate, quercetin, kaempferol, kaempferol 3-O-β-D-glucopyranosyl-(1- > 4)-glucopyranoside, 5-hydroxy-methyl furfural, ethyl N-(O-anisyl) formimidate, 2-pyridinethione and ascorbic acid showed appreciable hydrogen bond and hydrophobic type interactions with the allosteric site residues of the GK enzyme.

Conclusion

These screened phytoconstituents may serve as promising hit molecules for further development of clinically beneficial and safe allosteric activators of the human GK enzyme.

Targeting human Glucokinase for the treatment of type 2 diabetes: an overview of allosteric Glucokinase activators

Diabetes mellitus is a worldwide impacting disorder and the ratio through which the number of diabetic patients had increased worldwide, puts medical professionals to serious stress for its effective management. Due to its polygenic origin and involvement of multiple genes to its pathophysiology, leads to understanding of this ailment more complex. It seems that current interventions, such as dietary changes, life style changes and drug therapy such as oral hypoglycaemics and insulin, are unable to halt the trend. There are various novel and emerging targets on which the researchers are paying attention to combat with this ailment successfully. Human glucokinase (GK) enzyme is one of these novel and emerging targets for management of diabetes. Its availability in the pancreas and liver cells makes this target more lucrative. GK's presence in the pancreatic and hepatic cells plays a very important function for the management of glucose homoeostasis. Small molecules that activate GK allosterically provide an alternative strategy for restoring/improving glycaemic regulation, especially in type 2 diabetic patients. Although after enduring many setbacks in the development of the GK activators, interest has been renewed especially due to introduction of novel dual acting GK activator dorzagliatin, and a novel hepato-selective GK activator, TTP399. This review article has been formulated to discuss importance of GK in glucose homeostasis, recent updates on small molecules of GK activators, clinical status of GK activators and challenges in development of GK activators.

Design, Synthesis, Molecular Docking and In vitro Biological Evaluation of Benzamide Derivatives as Novel Glucokinase Activators

Background:

Glucokinase (GK) is a cytoplasmic enzyme that metabolises glucose to glucose-6-phosphate and supports adjusting blood glucose levels within the normal range in humans. In pancreatic β-cells, it plays a leading role in governing the glucose-stimulated secretion of insulin, and in liver hepatocyte cells, it controls the metabolism of carbohydrates. GK acts as a promising drug target for treating patients with type 2 diabetes mellitus (T2DM).

Objectives:

The present work has been designed to discover some novel substituted benzamide derivatives

Method:

This work involved designing novel benzamide derivatives and their screening by docking studies to determine the binding interactions for the best-fit conformations in the binding site of the GK enzyme. Based on the results of docking studies, the selected molecules were synthesized and tested for in vitro GK enzyme assay. The structures of newly synthesized products were confirmed by IR, NMR, and mass spectroscopy.

Results:

Amongst the designed derivatives, compounds 4c, 4d, 4e, 5h, 5j, 5l, 5m, 5n, 5p, and 5r have shown better binding energy than the native ligand present in the enzyme structure. The synthesized compounds were subjected to in vitro GK enzyme assay. Out of all, compounds 4c, 4d, 5h, 5l, and 5n showed more GK activation than control.

Conclusion::

From the present results, we have concluded that the synthesized derivatives can activate the human GK enzyme effectively, which can be helpful in the treatment of T2DM.

A Review on Cellular and Molecular Mechanisms Linked to the Development of Diabetes Complications

Modern lifestyle, changing eating habits and reduced physical work have been known to culminate into making diabetes a global pandemic. Hyperglycemia during the course of diabetes is an important causative factor for the development of both microvascular (retinopathy, nephropathy and neuropathy) and macrovascular (coronary artery disease, stroke and peripheral artery disease) complications. In this article, we summarize several mechanisms accountable for the development of both microvascular and macrovascular complications of diabetes. Several metabolic and cellular events are linked to the augmentation of oxidative stress like the activation of advanced glycation end products (AGE) pathway, polyol pathway, Protein Kinase C (PKC) pathway, Poly-ADP Ribose Polymerase (PARP) and hexosamine pathway. Oxidative stress also leads to the production of reactive oxygen species (ROS) like hydroxyl radical, superoxide anion and peroxides. Enhanced levels of ROS rescind the anti-oxidant defence mechanisms associated with superoxide dismutase, glutathione and ascorbic acid. Moreover, ROS triggers oxidative damages at the level of DNA, protein and lipids, which eventually cause cell necrosis or apoptosis. These physiological insults may be related to the microvascular complications of diabetes by negatively impacting the eyes, kidneys and the brain. While underlying pathomechanism of the macrovascular complications is quite complex, hyperglycemia associated atherosclerotic abnormalities like changes in the coagulation system, thrombin formation, fibrinolysis, platelet and endothelial function and vascular smooth muscle are well proven. Since hyperglycemia also modulates the vascular inflammation, cytokines, macrophage activation and gene expression of growth factors, elevated blood glucose level may play a central role in the development of macrovascular complications of diabetes. Taken collectively, chronic hyperglycemia and increased production of ROS are the miscreants for the development of microvascular and macrovascular complications of diabetes.

Recent Developments in Medicinal Chemistry of Allosteric Activators of Human Glucokinase for Type 2 Diabetes Mellitus Therapeutics

BACKGROUND

Glucokinase (GK), a cytoplasmic enzyme catalyzes the metabolism of glucose to glucose- 6-phosphate with the help of ATP and aids in the controlling of blood glucose levels within the normal range in humans. In pancreatic β-cells, it plays a chief role by controlling the glucose-stimulated secretion of insulin and in liver hepatocyte cells, it controls the metabolism of carbohydrates. GK acts as a promising drug target for the pharmacological treatment of patients with type 2 diabetes mellitus (T2DM) as it plays an important role in the control of carbohydrate metabolism.

METHODS

Data used for this review was based on the search from several science databases as well as various patent databases. The main data search terms used were allosteric GK activators, diabetes mellitus, type 2 diabetes, glucokinase, glucokinase activators and human glucokinase.

RESULTS

This article discusses an overview of T2DM, the biology of GK, the role of GK in T2DM, recent updates in the development of small molecule GK activators reported in recent literature, mechanism of action of GK activators and their clinical status.

CONCLUSION

GK activators are the novel class of pharmacological agents that enhance the catalytic activity of GK enzyme and display their antihyperglycemic effects. Broad diversity of chemical entities including benzamide analogues, carboxamides, acrylamides, benzimidazoles, quinazolines, thiazoles, pyrimidines, pyridines, orotic acid amides, amino acid derivatives, amino phosphates and urea derivatives have been synthesized in past two decades as potent allosteric activators of GK. Presently, the pharmaceutical companies and researchers are focusing on the design and development of liver-selective GK activators for preventing the possible adverse effects associated with GK activators for the long-term treatment of T2DM.

Design, synthesis, and pharmacological evaluation of 2-(4-sulfonylphenyl)-2-[(E)-pyrrolidin-1-ylimino]-N-thiazoleacetamides as glucokinase activators

This paper presents the synthesis and glucokinase activity of novel hydrazone derivatives. The 2-(4-cyclopropylsulfonylphenyl)-2-[(E)-pyrrolidin-1-ylimino]-acetamide derivatives 5a-5h presented the in vitro glucokinase activities and in vivo blood glucose-lowering effects in mice. Particularly, 5h showed an oral hypoglycemic effect in rats at 1 mg/kg. These hydrazone derivatives are a potential new class of glucokinase activators for the treatment of type 2 diabetes.

Prunus amygdalus extract exert antidiabetic effect via inhibition of DPP-IV: in-silico and in-vivo approaches

Prunus amygdalus (PA) is a popular invasive seed utilized in the management of diabetes in Jammu and Kashmir, India. The objective of the current study was to scrutinize the antidiabetic effect of Prunus amygdalus (PA) against Streptozotocin (STZ) induced diabetic rats and explore the possible mechanism of action at cellular and sub-cellular levels. Box Benkan Design (BBD) was performed to determine the effect of PA powder to methanol, extraction time and extraction temperature on DPPH and ABTS free radical scavenging activity of decoction. In-silico study was performed on GLUT1 (5EQG) and dipeptidyl peptidase IV (DPPIV) (2G63) protein. Type II diabetes mellitus was initiated by single intra-peritoneal injection of STZ. The Blood Glucose Level (BGL) and body weight were estimated at regular interval of time. The different biochemical parameters such as hepatic, antioxidant, and lipid parameters were estimated. At end of the study, pancreas was used for histopathological observation. The variation in DPPH antiradical scavenging activity 40.0-90.0% and ABTS antiradical scavenging activity 34-82%, were estimated respectively. STZ induced DM rats showed increased BGL at end of the experimental study. PA treatment significantly (p < 0.001) down-regulated the BGL level. PA significantly (p < 0.001) altered the biochemical, hepatic and antioxidant parameters in a dose-dependent manner. Histopathological examination demonstrated the constructive mass of β-cells in pancreas. Overall, the current study indicates that the PA treatment down-regulated the hyperglycemic, oxidative stress and hyperlipidaemia in diabetic rats, due to inhibition of enzymes or amelioration of oxidative stress. [Formula: see text] Communicated by Ramaswamy H. Sarma.

A rapid, multiplexed kinase activity assay using 8-plex iTRAQ labeling, SPE, and MALDI-TOF/TOF MS

Synthesized peptide substrates have been used for in vitro phosphorylation using purified kinases or cell lysates. For screening assays, a direct readout and comparison among different experimental conditions without using an internal standard would be preferred. In this study, we developed a rapid, quantitative measurement method of multikinase activity based on MALDI-TOF/TOF MS. We combined 8-plex iTRAQ-labeled peptide substrates, solid phase extraction (SPE), and a phosphorylated peptide purification plate to rapidly determine multikinase activity in cell lysates. To enable our platform to be applicable in insulin stimulation and cancer drug inhibition, a list of peptide substrates was designed. By labeling peptide substrates with 8-plex iTRAQ reagents, protein kinase activity in 8 samples could be directly compared using the mass tags on their fragmented ion spectra. The protein amount and incubation time for multikinase activity assays were optimized, and the effect of insulin stimulation and an inhibitory drug on the cellular protein kinase activity was evaluated.

A Recent Achievement In the Discovery and Development of Novel Targets for the Treatment of Type-2 Diabetes Mellitus

Type 2 diabetes (T2DM) is a chronic metabolic disorder. Impaired insulin secretion, enhanced hepatic glucose production, and suppressed peripheral glucose use are the main defects responsible for developing the disease. Besides, the pathophysiology of T2DM also includes enhanced glucagon secretion, decreased incretin secretion, increased renal glucose reabsorption, and adipocyte, and brain insulin resistance. The increasing prevalence of T2DM in the world beseeches an urgent need for better treatment options. The antidiabetic drugs focus on control of blood glucose concentration, but the future treatment goal is to delay disease progression and treatment failure, which causes poorer glycemic regulation. Recent treatment approaches target on several novel pathophysiological defects present in T2DM. Some of the promising novel targets being under clinical development include those that increase insulin sensitization (antagonists of glucocorticoids receptor), decreasing hepatic glucose production (glucagon receptor antagonist, inhibitors of glycogen phosphorylase and fructose-1,6-biphosphatase). This review summarizes studies that are available on novel targets being studied to treat T2DM with an emphasis on the small molecule drug design. The experience gathered from earlier studies and knowledge of T2DM pathways can guide the anti-diabetic drug development toward the discovery of drugs essential to treat T2DM.

Design, synthesis and evaluation of novel 3,5-disubstituted benzamide derivatives as allosteric glucokinase activators

Glucokinase (GK) is the key enzyme expressed in β-cells of pancreas and liver hepatocytes and helps in the maintenance of blood glucose levels in normal range. Activators of GK are the novel category of drug candidates which activate GK enzyme allosterically and show their antidiabetic activity. A new series of 3,5-disubstituted benzamide analogues was designed, synthesized and evaluated as GK activators by in vitro assay as well as in silico docking studies followed by evaluation of antihyperglycemic activity in animal model. Amongst the synthesized derivatives, compounds 5c, 5f, 5i, 6c, 6e and 6h displayed excellent in vitro GK activation. Compounds 6c and 6e exhibited highest antihyperglycemic activity in oral glucose tolerance test in animal model. Compound 6e displayed most significant antihyperglycemic activity and comparable to that of standard drug in animal studies. In addition, antihyperglycemic activity of the synthesized molecules was further supported by the in silico docking studies of the synthesized derivatives in the allosteric site of GK protein.

Recent Updates on Glucokinase Activators and Glucokinase Regulatory Protein Disrupters for the Treatment of Type 2 Diabetes Mellitus

INTRODUCTION

The impairment of glucose metabolism leads to hyperglycemia and type-2 diabetes mellitus. Glucokinase enzyme is the key regulator of glucose homeostasis that catalyzes the conversion of glucose to glucose-6-phosphate in liver and pancreatic cells. In hepatocytes, GK controls the glucose uptake and glycogen synthesis. The action of liver GK is controlled by Glucokinase Regulatory Protein (GKRP) partially. In fasting conditions the GKRP binds with GK and inactivate it from carbohydrate metabolism and serve as new target for treatment of diabetes mellitus. However, the GK activators as potential antidiabetic agents but results in increased risks of hypoglycemia.

CONCLUSION

The allosteric inhibitors of the GK-GKRP interaction are coming as alternative agents that can mitigate the risk associated with GK activators. This review discusses the recent advances and current status of potential molecules targeted to GK activators and GK-GKRP disrupters.

Octanoic acid potentiates glucose-stimulated insulin secretion and expression of glucokinase through the olfactory receptor in pancreatic β-cells

Olfactory receptors (ORs) are G protein-coupled receptors that mediate olfactory chemosensation, leading to the perception of smell. ORs are expressed in many tissues, but their functions are largely unknown. Here, we show that the olfactory receptor Olfr15 is highly and selectively expressed in both mouse pancreatic β-cells and MIN6 cells. In addition, octanoic acid (OA), a medium-chain fatty acid, potentiates glucose-stimulated insulin secretion (GSIS). The OA-induced enhancement of GSIS was inhibited by Olfr15 knockdown. Treatment with a PLC inhibitor or an Ins(1,4,5)P₃ receptor (IP₃R) antagonist also blocked the OA-induced enhancement of GSIS. These results suggest that OA potentiates GSIS via Olfr15 though the PLC-IP₃ pathway. Furthermore, long-term treatment with OA increased cellular glucose uptake in MIN6 cells by up-regulating the expression of glucokinase (GK). Moreover, this process was blocked by an IP₃R antagonist and a Ca²⁺/calmodulin-dependent protein kinase kinase (CaMKK) inhibitor. Similarly, OA stimulated GK promoter activity, while either Olfr15 or CaMKIV knockdown blocked the stimulatory effect of OA on GK promoter activity. These results suggest that long-term treatment of OA induces GK promoter activity via Olfr15 through the IP₃-CaMKK/CaMKIV pathway. In islets from type 2 diabetic mice, the expression level of Olfr15 and the OA-induced enhancement of GSIS were strongly reduced. Collectively, our results highlight the crucial role of the olfactory receptor Olfr15 in potentiating GSIS in pancreatic β-cells, suggesting that Olfr15 may be an important therapeutic target in type 2 diabetes.

Saponin from sea cucumber exhibited more significant effects than ginsenoside on ameliorating high fat diet-induced obesity in C57BL/6 mice

Obesity and its comorbidities are considered to be a severe public health problem. Many natural compounds found in food have been proved to ameliorate the metabolic abnormalities induced by obesity. The purpose of this study was to compare the effects of saponin from sea cucumber (SSC) and ginsenoside (SG) on improving the lipid metabolism in C57BL/6 mice fed with a high fat diet. The mice were randomly divided into six groups including a low fat diet group (LF), a high fat diet group (HF), and four dietary intervention groups. The administration of SSC for 8 weeks exhibited a more significant reduction in HF induced fat mass, weight gain, lipid levels in the liver and serum, and serum glucose and insulin levels than SG. Further research indicated that SSC ameliorated high fat diet-induced obesity in C57BL/6 mice mainly through inhibiting lipid synthesis and accelerating lipid β-oxidation and glycolysis in the liver. These results suggested that saponin from sea cucumber might be applied as a food supplement and/or functional ingredient to relieve metabolic disorders induced by obesity.

Dairy Product Consumption Interacts with Glucokinase (GCK) Gene Polymorphisms Associated with Insulin Resistance

Dairy product intake and a person's genetic background have been reported to be associated with the risk of type 2 diabetes (T2D). The objective of this study was to examine the interaction between dairy products and genes related to T2D on glucose-insulin homeostasis parameters. A validated food frequency questionnaire, fasting blood samples, and glucokinase (GCK) genotypes were analyzed in 210 healthy participants. An interaction between rs1799884 in GCK and dairy intake on the homeostasis model assessment of insulin resistance was identified. Secondly, human hepatocellular carcinoma cells (HepG2) were grown in a high-glucose medium and incubated with either 1-dairy proteins: whey, caseins, and a mixture of whey and casein; and 2-four amino acids (AA) or mixtures of AA. The expression of GCK-related genes insulin receptor substrate-1 (IRS-1) and fatty acid synthase (FASN) was increased with whey protein isolate or hydrolysate. Individually, leucine increased IRS-1 expression, whereas isoleucine and valine decreased FASN expression. A branched-chain AA mixture decreased IRS-1 and FASN expression. In conclusion, carriers of the A allele for rs1799884 in the GCK gene may benefit from a higher intake of dairy products to maintain optimal insulin sensitivity. Moreover, the results show that whey proteins affect the expression of genes related to glucose metabolism.

Discovery of cycloalkyl-fused N-thiazol-2-yl-benzamides as tissue non-specific glucokinase activators: Design, synthesis, and biological evaluation

Glucokinase (GK) activators are being developed for the treatment of type 2 diabetes mellitus (T2DM). However, existing GK activators have risks of hypoglycemia caused by over-activation of GK in islet cells and dyslipidemia caused by over-activation of intrahepatic GK. In the effort to mitigate risks of hypoglycemia and dyslipidemia while maintaining the promising efficacy of GK activator, we investigated a series of cycloalkyl-fused N-thiazol-2-yl-benzamides as tissue non-specific partial GK activators, which led to the identification of compound 72 that showed a good balance between in vitro potency and enzyme kinetic parameters, and protected β-cells from streptozotocin-induced apoptosis. Chronic treatment of compound 72 demonstrated its potent activity in regulation of glucose homeostasis and low risk of dyslipidemia with diabetic db/db mice in oral glucose tolerance test (OGTT). Moreover, acute treatment of compound 72 did not induce hypoglycemia in C57BL/6J mice even at 200 mg/kg via oral administration.

Small molecules as activators in medicinal chemistry (2000-2016)

INTRODUCTION

From therapeutic point of view, it is often beneficial to enhance the expression of certain enzymes whose low expression is responsible for the observed ailment. Small molecules as activators of several enzymes have great biological potential as anti-microbial and anti-cancer agents, for the treatment of diabetes, obesity, metabolic disorders, and for the treatment of neurological disorders including Alzheimer's disease. This review covers patents describing small molecules as activators, and provides structural leads for the design of even more potent activators. Area covered: This review is focused on small molecules that have been explored as activators of enzymes in the last and current decade (2000-2016). Expert opinion: The ability to modulate activity of enzymes has long been a quest of medicinal chemistry. This has been the impetus behind the development of a plethora of drugs as enzyme inhibitors. However only a few enzyme activators as drugs have made it to the market. Disorders characterized by supressed enzyme activity can be treated by enhancing the activity of a specific enzyme.

Therapeutic molecules against type 2 diabetes: What we have and what are we expecting?

World Health Organization (WHO) has identified diabetes as one of the fastest growing non-communicable diseases with 422 million patients around the world in 2014. Diabetes, a metabolic disease, is characterized primarily by hyperglycemia which results in various macrovascular and microvascular complications like cardiovascular disease and neuropathies which can significantly deteriorate the quality of life. The body either does not manufactures enough insulin (type 1 diabetes or T1DM) or becomes insensitive to physiologically secreted insulin or both (type 2 diabetes or T2DM). The majority of the diabetic population is affected by type 2 diabetes. Currently, hyperglycemia is treated by a broad range of molecules such as biguanides, sulfonylurea, insulin, thiazolidinediones, incretin mimetics, and DPP-4 inhibitors exerting different mechanisms. However, new drug classes have indeed come in the market such as SGLT-2 inhibitors and other are in the experimental stages such as GPR 40 agonists, GSK-3 inhibitors, GK activators and GPR21 inhibitors which definitely could be anticipated as safe and effective for diabetes therapy. This article reviews the general approach to currently approved therapies for type 2 diabetes and focusing on novel approaches that could be a panacea and might be useful in the future for diabetes patients.

Effects of a Novel Glucokinase Activator, HMS5552, on Glucose Metabolism in a Rat Model of Type 2 Diabetes Mellitus

Glucokinase (GK) plays a critical role in the control of whole-body glucose homeostasis. We investigated the possible effects of a novel glucokinase activator (GKA), HMS5552, to the GK in rats with type 2 diabetes mellitus (T2DM). Male Sprague-Dawley (SD) rats were divided into four groups: control group, diabetic group, low-dose (10 mg/kg) HMS5552-treated diabetic group (HMS-L), and high-dose (30 mg/kg) HMS5552-treated diabetic group (HMS-H). HMS5552 was administered intragastrically to the T2DM rats for one month. The levels of total cholesterol, triglyceride, fasting plasma insulin (FINS), and glucagon (FG) were determined, and an oral glucose tolerance test was performed. The expression patterns of proteins and genes associated with insulin resistance and GK activity were assayed. Compared with diabetic rats, the FINS level was significantly decreased in the HMS5552-treated diabetic rats. HMS5552 treatment significantly lowered the blood glucose levels and improved GK activity and insulin resistance. The immunohistochemistry, western blot, and semiquantitative RT-PCR results further demonstrated the effects of HMS5552 on the liver and pancreas. Our data suggest that the novel GKA, HMS5552, exerts antidiabetic effects on the liver and pancreas by improving GK activity and insulin resistance, which holds promise as a novel drug for the treatment of T2DM patients.

Antidiabetic effect of total saponins from Polygonatum kingianum in streptozotocin-induced daibetic rats

BACKGROUND

Polygonatum kingianum has been used in the prevention and treatment of diabetes, hyperlipidemia and related metabolic syndrome in Asian counties for centuries. In this study, the blood glucose regulation activity and mechanism of total saponins from P. kingianum (TSPK) were investigated in streptozotocin (STZ)-induced diabetic rats in this research.

METHODS

TSPK (0.025g/kg and 0.1mg/kg) was administrated by gavage to STZ-induced diabetic rats for 8 weeks. Changes of body weight, food intakes, blood glucose, serum insulin and lipid indexes were observed. Genome-wide expression profiling was applied to explore the gene expression alternation after treated with TSPK. Expressions of adenosine monophosphate activated protein kinase (AMPK), phosphoenolpyruvate carboxykinase (PEPCK), the relative transcript level of glucose kinase and glucose-6-phosphatase (GK/G6P) in the liver were investigated. Meanwhile, contents of AMPK, and glucose transporter subtype-4 (GLUT4) in skeletal muscle, and peroxysome proliferator-activated receptor (PPAR-γ) in adipose tissue were investigated.

RESULTS

TSPK could effectively alleviate hyperglycemia and hyperlipidemia in diabetic rats. Genome-wide expression profiling showed that TSPK up-regulated the expression of GLUT4 while down-regulated the expression of G6P in insulin signal pathway. In the liver, the expression of AMPK and GK are increased. Further more, TSPK promoted the expressions of GLUT4 in skeletal muscle, and PPAR-γ in adipose tissue, respectively.

CONCLUSION

These results provide possible mechanisms for the antidiabetic effects of TSPK. TSPK could promote not only glycogenesis but also glucose utilization in peripheral tissue. Our results suggested that TSPK may be used as adjuvant therapy to control blood glucose and insulin resistance in type 2 diabetic individuals.

Recombinant Passenger Proteins Can Be Conveniently Purified by One-Step Affinity Chromatography

Fusion tag is one of the best available tools to date for enhancement of the solubility or improvement of the expression level of recombinant proteins in Escherichia coli. Typically, two consecutive affinity purification steps are often necessitated for the purification of passenger proteins. As a fusion tag, acyl carrier protein (ACP) could greatly increase the soluble expression level of Glucokinase (GlcK), α-Amylase (Amy) and GFP. When fusion protein ACP-G2-GlcK-Histag and ACP-G2-Amy-Histag, in which a protease TEV recognition site was inserted between the fusion tag and passenger protein, were coexpressed with protease TEV respectively in E. coli, the efficient intracellular processing of fusion proteins was achieved. The resulting passenger protein GlcK-Histag and Amy-Histag accumulated predominantly in a soluble form, and could be conveniently purified by one-step Ni-chelating chromatography. However, the fusion protein ACP-GFP-Histag was processed incompletely by the protease TEV coexpressed in vivo, and a large portion of the resulting target protein GFP-Histag aggregated in insoluble form, indicating that the intracellular processing may affect the solubility of cleaved passenger protein. In this context, the soluble fusion protein ACP-GFP-Histag, contained in the supernatant of E. coli cell lysate, was directly subjected to cleavage in vitro by mixing it with the clarified cell lysate of E. coli overexpressing protease TEV. Consequently, the resulting target protein GFP-Histag could accumulate predominantly in a soluble form, and be purified conveniently by one-step Ni-chelating chromatography. The approaches presented here greatly simplify the purification process of passenger proteins, and eliminate the use of large amounts of pure site-specific proteases.

The effect of unhealthy β-cells on insulin secretion in pancreatic islets

Background

Insulin secreted by pancreatic islet β-cells is the principal regulating hormone of glucose metabolism and plays a key role in controlling glucose level in blood. Impairment of the pancreatic islet function may cause glucose to accumulate in blood, and result in diabetes mellitus. Recent studies have shown that mitochondrial dysfunction has a strong negative effect on insulin secretion.

Methods

In order to study the cause of dysfunction of pancreatic islets, a multiple cell model containing healthy and unhealthy cells is proposed based on an existing single cell model. A parameter that represents the function of mitochondria is modified for unhealthy cells. A 3-D hexagonal lattice structure is used to model the spatial differences among β-cells in a pancreatic islet. The β-cells in the model are connected through direct electrical connections between neighboring β-cells.

Results

The simulation results show that the low ratio of total mitochondrial volume over cytoplasm volume per β-cell is a main reason that causes some mitochondria to lose their function. The results also show that the overall insulin secretion will be seriously disrupted when more than 15% of the β-cells in pancreatic islets become unhealthy.

Conclusion

Analysis of the model shows that the insulin secretion can be reinstated by increasing the glucokinase level. This new discovery sheds light on antidiabetic medication.

Discovery of novel urea derivatives as dual-target hypoglycemic agents that activate glucokinase and PPARγ

Motivated by the discovery of a potential ligand that activates both glucokinase (GK) and perioxisome proliferator-activated receptor-γ (PPARγ), this work presents the rational design and synthesis of a series of novel urea derivatives as potent dual-target ligands of GK and PPARγ. The derivatives obtained, particularly compounds 14j, 14m, 15g, 15j, and 15s, showed relatively high enzyme activity and moderate blood glucose-lowering efficacy in normal ICR mice (GK activation fold >1.7, PPARγ activation percentage >38.8%, relative to rosiglitazone). The discovery of a dual-acting agent may provide an effective approach for treating type 2 diabetes mellitus.

Pathogenesis of chronic hyperglycemia: from reductive stress to oxidative stress

Chronic overnutrition creates chronic hyperglycemia that can gradually induce insulin resistance and insulin secretion impairment. These disorders, if not intervened, will eventually be followed by appearance of frank diabetes. The mechanisms of this chronic pathogenic process are complex but have been suggested to involve production of reactive oxygen species (ROS) and oxidative stress. In this review, I highlight evidence that reductive stress imposed by overflux of NADH through the mitochondrial electron transport chain is the source of oxidative stress, which is based on establishments that more NADH recycling by mitochondrial complex I leads to more electron leakage and thus more ROS production. The elevated levels of both NADH and ROS can inhibit and inactivate glyceraldehyde 3-phosphate dehydrogenase (GAPDH), respectively, resulting in blockage of the glycolytic pathway and accumulation of glycerol 3-phospate and its prior metabolites along the pathway. This accumulation then initiates all those alternative glucose metabolic pathways such as the polyol pathway and the advanced glycation pathways that otherwise are minor and insignificant under euglycemic conditions. Importantly, all these alternative pathways lead to ROS production, thus aggravating cellular oxidative stress. Therefore, reductive stress followed by oxidative stress comprises a major mechanism of hyperglycemia-induced metabolic syndrome.

Glucose homeostasis and the enteroinsular axis in the horse: a possible role in equine metabolic syndrome

One of the principal components of equine metabolic syndrome (EMS) is hyperinsulinaemia combined with insulin resistance. It has long been known that hyperinsulinaemia occurs after the development of insulin resistance. But it is also known that hyperinsulinaemia itself can induce insulin resistance and obesity and might play a key role in the development of metabolic syndrome. This review focuses on the physiology of glucose and insulin metabolism and the pathophysiological mechanisms in glucose homeostasis in the horse (compared with what is already known in humans) in order to gain insight into the pathophysiological principles underlying EMS. The review summarizes new insights on the oral uptake of glucose by the gut and the enteroinsular axis, the role of diet in incretin hormone and postprandial insulin responses, the handling of glucose by the liver, muscle and fat tissue, and the production and secretion of insulin by the pancreas under healthy and disrupted glucose homeostatic conditions in horses.

GPR119 agonists: a promising approach for T2DM treatment? A SWOT analysis of GPR119

Ever since its advent as a promising therapeutic target for type 2 diabetes mellitus (T2DM), G-protein-coupled receptor 119 (GPR119) has received much interest from the pharmaceutical industry. This interest peaked in June 2010, when Sanofi-Aventis agreed to pay Metabolex (Cymabay Therapeutics) US$375 million for MBX-2982, which was a representative orally active GPR119 agonist. However, Sanofi-Aventis opted to terminate the deal in May 2011 and another leading GPR119 agonist, GSK1292263, had a loss of efficacy during its clinical trial. In this review, I discuss the pros and cons of GPR119 through a strengths, weaknesses, opportunities, and threats (SWOT) analysis and propose development strategies for the eventual success of a GPR119 agonist development program.

Treatment with glucokinase activator, YH-GKA, increases cell proliferation and decreases glucotoxic apoptosis in INS-1 cells

Glucokinase (GK), an enzyme that phosphorylates glucose to form glucose-6-phosphate, has a role in regulating insulin secretion and proliferation in beta cells. GK activators (GKAs) have been developed as new therapies for type 2 diabetes. In this study, we evaluated the proliferation and anti-apoptotic actions of YH-GKA, a novel and potent GKA, in INS-1 pancreatic β-cells. YH-GKA treatment increased cell numbers at 3 mM glucose via upregulation of insulin receptor substrate-2 and subsequent activation of AKT/protein kinase B phosphorylation. YH-GKA also increased beta-catenin and cyclin D2 mRNA expression and inactivated GSK3β by increasing phosphorylation. These proliferative effects of YH-GKA were attenuated by IRS-2 downregulation. Moreover, YH-GKA reduced annexin-V-stained cells and expression levels of cleaved poly (ADP-ribose) polymerase and caspase-3 induced by glucotoxicity. YH-GKA inhibited apoptotic signaling via induction of ATP content, mitochondrial membrane potential, and citrate synthase activity and was correlated with changes of the mitochondrial function-related genes. YH-GKA also increased interaction between GK and voltage-dependent anion-selective channel protein. Our results suggest that the novel GKA, YH-GKA, promotes beta cell growth and prevents glucotoxic beta cell apoptosis. Therefore, YH-GKA may provide a therapy that compensates for beta cell loss in patients with type 2 diabetes.

[Type 2 diabetes mellitus: new treatments]

The benefits and problems associated with traditional hypoglycemic drugs, such as failure of beta cells, hypoglycemia and weight gain, that lead to a worsening of diabetes, are reviewed. New hypoglycemic drugs with incretin effect (glucagon-like peptide-1 agonists and dipeptidyl peptidase 4 inhibitors), achieve, in a glucose dependent manner, an glycosylated hemoglobin reduction without hypoglycemia or increase in body weight. Recently, another group of oral hypoglycemic drugs, sodium-glucose cotransporter type 2 inhibitors, have demonstrated efficacy in diabetes control by inhibiting renal glucose reabsorption. However, long-term effects and cardiovascular prevention remain to be demonstrated. We have more and better drugs nowadays. Hypoglycemic treatment should be customized (glycosylated hemoglobin levels, risk-benefit, risk of hypoglycemia, weight changes, cardiovascular risk), with a combination of drugs being necessary in most cases. However, we do not have yet an ideal hypoglycemic drug. Moreover we must remember that an early and intensive treatment of dyslipidemia and hypertension is essential for the prevention of cardiovascular disease in patients with type 2 diabetes.

FM19G11 favors spinal cord injury regeneration and stem cell self-renewal by mitochondrial uncoupling and glucose metabolism induction

Spinal cord injury is a major cause of paralysis with no currently effective therapies. Induction of self-renewal and proliferation of endogenous regenerative machinery with noninvasive and nontoxic therapies could constitute a real hope and an alternative to cell transplantation for spinal cord injury patients. We previously showed that FM19G11 promotes differentiation of adult spinal cord-derived ependymal stem cells under hypoxia. Interestingly, FM19G11 induces self-renewal of these ependymal stem cells grown under normoxia. The analysis of the mechanism of action revealed an early increment of mitochondrial uncoupling protein 1 and 2 with an early drop of ATP, followed by a subsequent compensatory recovery with activated mitochondrial metabolism and the induction of glucose uptake by upregulation of the glucose transporter GLUT-4. Here we show that phosphorylation of AKT and AMP-activated kinase (AMPK) is involved in FM19G11-dependent activation of GLUT-4, glucose influx, and consequently in stem cell self-renewal. Small interfering RNA of uncoupling protein 1/2, GLUT-4 and pharmacological inhibitors of AKT, mTOR and AMPK signaling blocked the FM19G11-dependent induction of the self-renewal-related markers Sox2, Oct4, and Notch1. Importantly, FM19G11-treated animals showed accelerated locomotor recovery. In vivo intrathecal sustained administration of FM19G11 in rats after spinal cord injury showed more neurofilament TUJ1-positive fibers crossing the injured area surrounded by an increase of neural precursor Vimentin-positive cells. Overall, FM19G11 exerts an important influence on the self-renewal of ependymal stem progenitor cells with a plausible neuroprotective role, providing functional benefits for spinal cord injury treatment.

Supplementation of persimmon leaf ameliorates hyperglycemia, dyslipidemia and hepatic fat accumulation in type 2 diabetic mice

Persimmon Leaf (PL), commonly consumed as herbal tea and traditional medicines, contains a variety of compounds that exert antioxidant, α-amylase and α-glucosidase inhibitory activity. However, little is known about the in vivo effects and underlying mechanisms of PL on hyperglycemia, hyperlipidemia and hepatic steatosis in type 2 diabetes. Powered PL (5%, w/w) was supplemented with a normal diet to C57BL/KsJ-db/db mice for 5 weeks. PL decreased blood glucose, HOMA-IR, plasma triglyceride and total cholesterol levels, as well as liver weight, hepatic lipid droplets, triglycerides and cholesterol contents, while increasing plasma HDL-cholesterol and adiponectin levels. The anti-hyperglycemic effect was linked to decreased activity of gluconeogenic enzymes as well as increased glycogen content, glucokinase activity and its mRNA level in the liver. PL also led to a decrease in lipogenic transcriptional factor PPARγ as well as gene expression and activity of enzymes involved in lipogenesis, with a simultaneous increase in fecal lipids, which are seemingly attributable to the improved hyperlipidemia and hepatic steatosis and decreased hepatic fatty acid oxidation. Furthermore, PL ameliorated plasma and hepatic oxidative stress. Supplementation with PL may be an effective dietary strategy to improve type 2 diabetes accompanied by dyslipidemia and hepatic steatosis by partly modulating the activity or gene expression of enzymes related to antioxidant, glucose and lipid homeostasis.

Novel therapeutics and targets for the treatment of diabetes

The microvascular complications of insufficiently controlled diabetes (neuropathy, retinopathy and nephropathy) and the marked increased risk of macrovascular events (e.g., stroke and myocardial infarction) have a dire impact on society in both human and economic terms. In Type 1 diabetes total β-cell loss occurs. In Type 2 diabetes, partial β-cell loss occurs before diagnosis, and the progressive β-cell loss during the life of the patient increases the severity of the disease. In patients with diabetes, increased insulin resistance in the muscle and liver are key pathophysiologic defects. In addition, defects in metabolic processes in the fat, GI tract, brain, pancreatic α-cells and kidney are detrimental to the overall health of the patient. This review addresses novel therapies for these deficiencies in clinical and preclinical evaluation, emphasizing their potential to address glucose homeostasis, β-cell mass and function, and the comorbidities of cardiovascular disease and obesity.

Effects of a glucokinase activator on hepatic intermediary metabolism: study with 13C-isotopomer-based metabolomics

GKAs (glucokinase activators) are promising agents for the therapy of Type 2 diabetes, but little is known about their effects on hepatic intermediary metabolism. We monitored the fate of (13)C-labelled glucose in both a liver perfusion system and isolated hepatocytes. MS and NMR spectroscopy were deployed to measure isotopic enrichment. The results demonstrate that the stimulation of glycolysis by GKA led to numerous changes in hepatic metabolism: (i) augmented flux through the TCA (tricarboxylic acid) cycle, as evidenced by greater incorporation of (13)C into the cycle (anaplerosis) and increased generation of (13)C isotopomers of citrate, glutamate and aspartate (cataplerosis); (ii) lowering of hepatic [Pi] and elevated [ATP], denoting greater phosphorylation potential and energy state; (iii) stimulation of glycogen synthesis from glucose, but inhibition of glycogen synthesis from 3-carbon precursors; (iv) increased synthesis of N-acetylglutamate and consequently augmented ureagenesis; (v) increased synthesis of glutamine, alanine, serine and glycine; and (vi) increased production and outflow of lactate. The present study provides a deeper insight into the hepatic actions of GKAs and uncovers the potential benefits and risks of GKA for treatment of diabetes. GKA improved hepatic bioenergetics, ureagenesis and glycogenesis, but decreased gluconeogenesis with a potential risk of lactic acidosis and fatty liver.

Development of novel cell lines of diabetic dysfunction model fit for cell-based screening tests of medicinal materials

Pdx-1 and Irs-1, genes highly associated with diabetes onset, were knocked down in mouse embryonic stem (ES) cells in order to develop cell line models for diabetes. ES cells with different gene knockdown levels were induced to differentiate to the stage of insulin production. Among the cell lines that differentiated, we identified two in which the levels of expression of both genes were 20-40 % of that of control cells. These cell lines showed appreciable deficiencies in three characteristic malfunctions associated with diabetes, namely, insulin production, insulin reception signaling, and glucose-stimulated insulin secretion. These dysfunctions were consistent with results reported elsewhere from in vivo and in vitro studies. Both cell lines did not show any abnormal morphology such as size, shape, color, and surface roughness. No abnormal expression profiles for 17 genes relevant to diabetes were observed. Therefore, these cell lines fulfilled the criteria for a validated cell model for diabetes. The model cell lines developed here are promising biomaterials for cell-based screening tests of new medicines that may be effective in treating diabetes.