GKAs for diabetes therapy: why no clinically useful drug after two decades of trying?

Compromised chronic efficacy of a glucokinase activator AZD1656 in mouse models for common human GCKR variants

Glucokinase activators (GKAs) have been developed as blood glucose lowering drugs for type 2 diabetes. Despite good short-term efficacy, several GKAs showed a decline in efficacy chronically during clinical trials. The underlying mechanisms remain incompletely understood. We tested the hypothesis that deficiency in the liver glucokinase regulatory protein (GKRP) as occurs with common human GCKR variants affects chronic GKA efficacy. We used a Gckr-P446L mouse model for the GCKR exonic rs1260326 (P446L) variant and the Gckr-del/wt mouse to model transcriptional deficiency to test for chronic efficacy of the GKA, AZD1656 in GKRP-deficient states. In the Gckr-P446L mouse, the blood glucose lowering efficacy of AZD1656 (3 mg/kg body wt) after 2 weeks was independent of genotype. However after 19 weeks, efficacy was maintained in wild-type but declined in the LL genotype, in conjunction with raised hepatic glucokinase activity and without raised liver lipids. Sustained blood glucose lowering efficacy in wild-type mice was associated with qualitatively similar but more modest changes in the liver transcriptome compared with the P446L genotype, consistent with GKA therapy representing a more modest glucokinase excess than the P446L genotype. Chronic treatment with AZD1656 in the Gckr-del/wt mouse was associated with raised liver triglyceride and hepatocyte microvesicular steatosis. The results show that in mouse models of liver GKRP deficiency in conjunction with functional liver glucokinase excess as occurs in association with common human GCKR variants, GKRP-deficiency predisposes to declining efficacy of the GKA in lowering blood glucose and to GKA induced elevation in liver lipids.

Glucokinase activators and imeglimin: new weaponry in the armamentarium against type 2 diabetes

The prevalence of type 2 diabetes (T2D) is increasing relentlessly all over the world, in parallel with a similar increase in obesity, and is striking ever younger patients. Only a minority of patients with T2D attain glycemic targets, indicating a clear need for novel antidiabetic drugs that not only control glycemia but also halt or slow the progressive loss of β-cells. Two entirely novel classes of antidiabetic agents-glucokinase activators and imeglimin-have recently been approved and will be the subject of this review.Allosteric activators of glucokinase, an enzyme stimulating insulin secretion in β-cells and suppressing hepatic glucose production, are oral low-molecular-weight drugs. One of these, dorzagliatin, is approved in China for use in adult patients with T2D, either as monotherapy or as an add-on to metformin. It remains to be seen whether the drug will produce sustained antidiabetic effects over many years and whether the side effects that led to the discontinuation of early drug candidates will limit the usefulness of dorzagliatin.Imeglimin-which shares structural similarities with metformin-targets mitochondrial dysfunction and was approved in Japan against T2D. In preclinical studies, the drug has also shown promising β-cell protective and preservative effects that may translate into disease-modifying effects.Hopefully, these two newcomers will contribute to filling the great medical need for new treatment modalities, preferably with disease-modifying potential. It remains to be seen where they will fit in contemporary treatment algorithms, which combinations of drugs are effective and which should be avoided. Time will tell to what extent these new antidiabetic agents will add value to the current treatment options against T2D in terms of sustained antidiabetic effect, acceptable safety, utility in combination therapy, and impact on hard end-points such as cardiovascular disease.

Targeting Protein Kinases to Protect Beta-Cell Function and Survival in Diabetes

The prevalence of diabetes is increasing worldwide. Massive death of pancreatic beta-cells causes type 1 diabetes. Progressive loss of beta-cell function and mass characterizes type 2 diabetes. To date, none of the available antidiabetic drugs promotes the maintenance of a functional mass of endogenous beta-cells, revealing an unmet medical need. Dysfunction and apoptotic death of beta-cells occur, in particular, through the activation of intracellular protein kinases. In recent years, protein kinases have become highly studied targets of the pharmaceutical industry for drug development. A number of drugs that inhibit protein kinases have been approved for the treatment of cancers. The question of whether safe drugs that inhibit protein kinase activity can be developed and used to protect the function and survival of beta-cells in diabetes is still unresolved. This review presents arguments suggesting that several protein kinases in beta-cells may represent targets of interest for the development of drugs to treat diabetes.

New-Generation Glucokinase Activators: Potential Game-Changers in Type 2 Diabetes Treatment

Achieving glycemic control and sustaining functional pancreatic β-cell activity remains an unmet medical need in the treatment of type 2 diabetes mellitus (T2DM). Glucokinase activators (GKAs) constitute a class of anti-diabetic drugs designed to regulate blood sugar levels and enhance β-cell function in patients with diabetes. A significant progression in GKA development is underway to address the limitations of earlier generations. Dorzagliatin, a dual-acting GKA, targets both the liver and pancreas and has successfully completed two phase III trials, demonstrating favorable results in diabetes treatment. The hepato-selective GKA, TTP399, emerges as a strong contender, displaying clinically noteworthy outcomes with minimal adverse effects. This paper seeks to review the current literature, delve into the mechanisms of action of these new-generation GKAs, and assess their efficacy and safety in treating T2DM based on published preclinical studies and recent clinical trials.

Dorzagliatin for Type 2 Diabetes Mellitus: A Systematic Review and Meta-analysis of Randomized Phase II/III Trials

PURPOSE

Dorzagliatin is a glucokinase agonist with effects on type 2 diabetes mellitus (T2DM). This study included a meta-analysis on the efficacy and safety of dorzagliatin in the treatment of T2DM.

METHODS

The Cochrane Central Registry of Controlled Trials, PubMed, and Embase were searched from inception to July 25, 2022. A total of 3 studies including 1333 patients were identified in this meta-analysis.

FINDINGS

Overall, the meta-analysis showed that dorzagliatin remarkably reduced glycated hemoglobin levels versus placebo by 0.66%. The results of the meta-analysis showed a significant reduction in fasting plasma glucose of 6.77 mg/dL between dorzagliatin and placebo. In addition, dorzagliatin reduced 2-hour postprandial glucose (2h-PPG) by 43.87 mg/dL compared with placebo. Furthermore, the meta-analysis of available data revealed a significant reduction in the Homeostasis Model Assessment of Insulin Resistance of 0.07 between dorzagliatin and placebo. The risk of adverse events was slightly higher with dorzagliatin than with placebo.

IMPLICATIONS

Dorzagliatin significantly reduced glycated hemoglobin levels, fasting plasma glucose levels, 2h-PPG, and homeostasis model assessment 2 of insulin resistance in patients with T2DM. It was well tolerated and had good liver and kidney safety profiles.

Evaluation of efficacy and safety of glucokinase activators-a systematic review and meta-analysis

Aims

Glucokinase activators (GKAs) promote the activity of glucokinase (GK) and is under development for the treatment of diabetes. The efficacy and safety of GKAs require evaluation.

Methods

This meta-analysis included randomized controlled trials (RCTs) with a duration of at least 12 weeks conducted in patients with diabetes. The primary objective of this meta-analysis was the difference of hemoglobin A1c (HbA1c) change from baseline to study end between GKA groups and placebo groups. Risk of hypoglycemia and laboratory indicators were also evaluated. Weighted mean differences (WMDs) and 95% confidence intervals (CIs) were calculated for the continuous outcomes, and odds ratios (ORs) and 95% CI were calculated for the risk of hypoglycemia.

Results

Data from 13 RCTs with 2,748 participants treated with GKAs and 2,681 control participants were analyzed. In type 2 diabetes, the level of HbA1c decreased greater in patients with GKA treatment compared with placebo (WMD = -0.339%, 95% CI -0.524 to -0.154%, P < 0.001). The OR comparing GKA versus placebo was 1.448 for risk of hypoglycemia (95% CI 0.808 to 2.596, P = 0.214). The WMD comparing GKA versus placebo was 0.322 mmol/L for triglyceride (TG) levels (95% CI 0.136 to 0.508 mmol/L, P = 0.001). When stratified by drug type, selectivity, and study duration, a significant difference was found between groups. In type 1 diabetes, the result of HbA1c change and lipid indicators showed no significant difference between the TPP399 group and the placebo group.

Conclusions

In patients with type 2 diabetes, GKA treatment was associated with a better glycemic control but a significant elevation in TG concentration in general. The efficacy and safety varied with drug type and selectivity.

Systematic review registration

International Prospective Register of Systematic Reviews, identifier CRD42022378342.

Recent Developments in Islet Biology: A Review With Patient Perspectives

Navigating the coronavirus disease-2019 (COVID-19, now COVID) pandemic has required resilience and creativity worldwide. Despite early challenges to productivity, more than 2,000 peer-reviewed articles on islet biology were published in 2021. Herein, we highlight noteworthy advances in islet research between January 2021 and April 2022, focussing on 5 areas. First, we discuss new insights into the role of glucokinase, mitogen-activated protein kinase-kinase/extracellular signal-regulated kinase and mitochondrial function on insulin secretion from the pancreatic β cell, provided by new genetically modified mouse models and live imaging. We then discuss a new connection between lipid handling and improved insulin secretion in the context of glucotoxicity, focussing on fatty acid-binding protein 4 and fetuin-A. Advances in high-throughput "omic" analysis evolved to where one can generate more finely tuned genetic and molecular profiles within broad classifications of type 1 diabetes and type 2 diabetes. Next, we highlight breakthroughs in diabetes treatment using stem cell-derived β cells and innovative strategies to improve islet survival posttransplantation. Last, we update our understanding of the impact of severe acute respiratory syndrome-coronavirus-2 infection on pancreatic islet function and discuss current evidence regarding proposed links between COVID and new-onset diabetes. We address these breakthroughs in 2 settings: one for a scientific audience and the other for the public, particularly those living with or affected by diabetes. Bridging biomedical research in diabetes to the community living with or affected by diabetes, our partners living with type 1 diabetes or type 2 diabetes also provide their perspectives on these latest advances in islet biology.

Glucokinase Inhibition: A Novel Treatment for Diabetes?

Chronic hyperglycemia increases pancreatic β-cell metabolic activity, contributing to glucotoxicity-induced β-cell failure and loss of functional β-cell mass, potentially in multiple forms of diabetes. In this perspective we discuss the novel paradoxical and counterintuitive concept of inhibiting glycolysis, particularly by targeted inhibition of glucokinase, the first enzyme in glycolysis, as an approach to maintaining glucose sensing and preserving functional β-cell mass, thereby improving insulin secretion, in the treatment of diabetes.

Glucokinase activity in diabetes: too much of a good thing?

Type 2 diabetes (T2D) is a global health problem characterised by chronic hyperglycaemia due to inadequate insulin secretion. Because glucose must be metabolised to stimulate insulin release it was initially argued that drugs that stimulate glucokinase (the first enzyme in glucose metabolism) would enhance insulin secretion in diabetes. However, in the long term, glucokinase activators have been largely disappointing. Recent studies show it is hyperactivation of glucose metabolism, not glucose itself, that underlies the progressive decline in beta-cell function in diabetes. This perspective discusses if glucokinase activators exacerbate this decline (by promoting glucose metabolism) and, counterintuitively, if glucokinase inhibitors might be a better therapeutic strategy for preserving beta-cell function in T2D.

New Horizons: Emerging Antidiabetic Medications

Over the past century, since the discovery of insulin, the therapeutic offer for diabetes has grown exponentially, in particular for type 2 diabetes (T2D). However, the drugs in the diabetes pipeline are even more promising because of their impressive antihyperglycemic effects coupled with remarkable weight loss. An ideal medication for T2D should target not only hyperglycemia but also insulin resistance and obesity. Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) and the new class of GLP1 and gastric inhibitory polypeptide dual RAs counteract 2 of these metabolic defects of T2D, hyperglycemia and obesity, with stunning results that are similar to the effects of metabolic surgery. An important role of antidiabetic medications is to reduce the risk and improve the outcome of cardiovascular diseases, including coronary artery disease and heart failure with reduced or preserved ejection fraction, as well as diabetic nephropathy, as shown by SGLT2 inhibitors. This review summarizes the main drugs currently under development for the treatment of type 1 diabetes and T2D, highlighting their strengths and side effects.

Chronotherapy with a glucokinase activator profoundly improves metabolism in obese Zucker rats

Circadian rhythms play a critical role in regulating metabolism, including daily cycles of feeding/fasting. Glucokinase (GCK) is central for whole-body glucose homeostasis and oscillates according to a circadian clock. GCK activators (GKAs) effectively reduce hyperglycemia, but their use is also associated with hypoglycemia, hyperlipidemia, and hepatic steatosis. Given the circadian rhythmicity and natural postprandial activation of GCK, we hypothesized that GKA treatment would benefit from being timed specifically during feeding periods. Acute treatment of obese Zucker rats with the GKA AZD1656 robustly increased flux into all major metabolic pathways of glucose disposal, enhancing glucose elimination. Four weeks of continuous AZD1656 treatment of obese Zucker rats improved glycemic control; however, hepatic steatosis and inflammation manifested. In contrast, timing AZD1656 to feeding periods robustly reduced hepatic steatosis and inflammation in addition to improving glycemia, whereas treatment timed to fasting periods caused overall detrimental metabolic effects. Mechanistically, timing AZD1656 to feeding periods diverted newly synthesized lipid toward direct VLDL secretion rather than intrahepatic storage. In line with increased hepatic insulin signaling, timing AZD1656 to feeding resulted in robust activation of AKT, mTOR, and SREBP-1C after glucose loading, pathways known to regulate VLDL secretion and hepatic de novo lipogenesis. In conclusion, intermittent AZD1656 treatment timed to feeding periods promotes glucose disposal when needed the most, restores metabolic flexibility and hepatic insulin sensitivity, and thereby avoids hepatic steatosis. Thus, chronotherapeutic approaches may benefit the development of GKAs and other drugs acting on metabolic targets.

Interplay of Obesity, Ethanol, and Contaminant Mixture on Clinical Profiles of Cardiovascular and Metabolic Diseases: Evidence from an Animal Study

Obesity, ethanol, and contaminants are known risk factors of cardiovascular and metabolic diseases (CMD). However, their interplay on clinical profiles of these diseases remains unclear, and thus were investigated in this study. Male lean or obese JCR rats were given water or 10% ethanol and orally treated with or without a contaminant mixture (CM) dissolved in corn oil and loaded on two cookies at 0, 1.6, or 16 mg/kg BW/day dose levels for 4 weeks. The CM consisted 22 environmental contaminants found in human blood or serum of Northern populations. Over 60 parameters related to CMD were examined. The results revealed that obesity in JCR rats resembles the clinical profiles of non-alcoholic fatty liver disease in humans. Obesity was also associated with increased serum and organ retention of mercury, one of the chemical components of CM. Exposure to ethanol lightened hyperlipidemia, increased liver retention of mercury, and increased risk for hypertension in the obese rats. CM lessened hyperlipidemia and hyperenzymemia, worsened systemic inflammation and increased the risk for hypertension in the obese rats. CM markedly increased serum ethanol levels with or without ethanol exposure. Tissue total mercury contents significantly correlated with clinical parameters with altered profiles by both ethanol and obesity. These results suggest that obese individuals may be more prone to contaminant accumulation. Ethanol and CM exposure can alter clinical profiles associated with obesity, which may lead to misdiagnosis of CMD associated with obesity. CM can alter endogenous production and/or metabolism of ethanol, further complicating disease progression, diagnosis, and treatment.

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.

Trends in Antidiabetic Drug Discovery: FDA Approved Drugs, New Drugs in Clinical Trials and Global Sales

Type 2 diabetes mellitus (T2DM) continues to be a substantial medical problem due to its increasing global prevalence and because chronic hyperglycemic states are closely linked with obesity, liver disease and several cardiovascular diseases. Since the early discovery of insulin, numerous antihyperglycemic drug therapies to treat diabetes have been approved, and also discontinued, by the United States Food and Drug Administration (FDA). To provide an up-to-date account of the current trends of antidiabetic pharmaceuticals, this review offers a comprehensive analysis of the main classes of antihyperglycemic compounds and their mechanisms: insulin types, biguanides, sulfonylureas, meglitinides (glinides), alpha-glucosidase inhibitors (AGIs), thiazolidinediones (TZD), incretin-dependent therapies, sodium-glucose cotransporter type 2 (SGLT2) inhibitors and combinations thereof. The number of therapeutic alternatives to treat T2DM are increasing and now there are nearly 60 drugs approved by the FDA. Beyond this there are nearly 100 additional antidiabetic agents being evaluated in clinical trials. In addition to the standard treatments of insulin therapy and metformin, there are new drug combinations, e.g., containing metformin, SGLT2 inhibitors and dipeptidyl peptidase-4 (DPP4) inhibitors, that have gained substantial use during the last decade. Furthermore, there are several interesting alternatives, such as lobeglitazone, efpeglenatide and tirzepatide, in ongoing clinical trials. Modern drugs, such as glucagon-like peptide-1 (GLP-1) receptor agonists, DPP4 inhibitors and SGLT2 inhibitors have gained popularity on the pharmaceutical market, while less expensive over the counter alternatives are increasing in developing economies. The large heterogeneity of T2DM is also creating a push towards more personalized and accessible treatments. We describe several interesting alternatives in ongoing clinical trials, which may help to achieve this in the near future.

The role of pregnane X receptor (PXR) in substance metabolism

As a member of the nuclear receptor (NR) superfamily, pregnane X receptor (PXR; NR1I2) is a ligand-activated transcription factor that plays a crucial role in the metabolism of xenobiotics and endobiotics in mammals. The tissue distribution of PXR is parallel to its function with high expression in the liver and small intestine and moderate expression in the kidney, stomach, skin, and blood-brain barrier, which are organs and tissues in frequent contact with xenobiotics. PXR was first recognized as an exogenous substance receptor regulating metabolizing enzymes and transporters and functioning in detoxification and drug metabolism in the liver. However, further research revealed that PXR acts as an equally important endogenous substance receptor in the metabolism and homeostasis of endogenous substances. In this review, we summarized the functions of PXR in metabolism of different substances such as glucose, lipid, bile acid, vitamin, minerals, and endocrines, and also included insights of the application of PXR ligands (drugs) in specific diseases.

The efficacy and safety of glucokinase activators for the treatment of type-2 diabetes mellitus: A meta-analysis

BACKGROUND

Glucokinase activators (GKAs) are a novel family of glucose-lowering agents used for the treatment of type-2 diabetes mellitus. Treatment with different GKAs has been shown to reduce blood glucose levels in these patients. We compared the efficacy/safety of GKAs in patients with type-2 diabetes mellitus through a meta-analysis.

METHODS

We searched the PubMed, Excerpt Medica Database, and Cochrane Central Register of Controlled Trials databases for articles published before December 30, 2020. We computed the weighted mean difference (WMD) and 95% confidence interval (CI) for the change from baseline to the study endpoint for GKA versus placebo treatments.

RESULTS

A total of 4 articles (5 studies) were included in the meta-analysis. GKAs were associated with reductions in glycated hemoglobin levels from baseline (WMD, -0.3%; 95% CI, -0.466% to -0.134%). No significant difference between GKA and placebo treatment was observed in the results of fasting plasma glucose levels from baseline (WMD 0.013 mmol/L; 95% CI, -0.304-0.33 mmol/L). A significantly higher change in 2-hour postprandial plasma glucose (2-h PPG) levels (WMD -2.434 mmol/L; 95% CI, -3.304 to -1.564 mmol/L) was observed following GKA than placebo treatment. GKAs were associated with a higher prevalence of causing hypoglycemic events than placebo treatment (risk difference [RD], 0.06; 95% CI 0.013-0.106). GKAs had no association with the risk of developing adverse effects (RD, 0.038; 95% CI, -0.03-0.106) and serious adverse events (RD, 0.01; 95% CI, -0.004-0.023).

CONCLUSIONS

GKAs were more effective for postprandial blood glucose control. However, these agents showed a significantly high risk of causing hypoglycemia.

PROSPERO REGISTRATION NUMBER

CRD42021220364.

Glucokinase activation or inactivation: Which will lead to the treatment of type 2 diabetes?

Glucokinase, which phosphorylates glucose to form glucose-6-phosphate, plays a critical role in regulating blood glucose levels. On the basis of data of glucokinase-knockout and transgenic mice and humans with glucokinase mutations, glucokinase was targeted for drug development aiming to augment its activity, and thereby reduce hyperglycaemia in patients with diabetes. In fact, various small molecule compounds have been developed and clinically tested as glucokinase activators. However, some have been discontinued because of efficacy and safety issues. One of these issues is loss of the drug's efficacy over time. This unsustained glycaemic efficacy may be associated with the excess glycolysis by glucokinase activation in pancreatic beta cells, resulting in beta-cell failure. Recently, we have shown that glucokinase haploinsufficiency ameliorated glucose intolerance by increasing beta-cell function and mass in a mouse model of diabetes. Given that a similar phenotype has been observed in glucokinase-activated beta cells and diabetic beta cells, glucokinase inactivation may be a new therapeutic target for type 2 diabetes.

Current and emerging gluconeogenesis inhibitors for the treatment of Type 2 diabetes

INTRODUCTION

In the last several decades, fueled by gene knockout and knockdown techniques, there has been substantial progress in detailing the pathways of gluconeogenesis. A host of molecules have been identified as potential targets for therapeutic intervention. A number of hormones, enzymes and transcription factors participate in gluconeogenesis. Many new agents have come into use to treat diabetes and several of these are in development to suppress gluconeogenesis.

AREAS COVERED

Herein, the author reviews agents that have been discovered and/or are in development, which control excess gluconeogenesis. The author has used multiple sources including PubMed, the preprint servers MedRxIv, BioRxIv, Research Gate, as well as Google Search and the database of the U.S. Patent and Trademarks Office to find appropriate literature.

EXPERT OPINION

It is now clear that lipid metabolism and hepatic lipogenesis play a major role in gluconeogenesis and resistance to insulin. Future efforts will focus on the duality of gluconeogenesis and adipose tissue metabolism. The exploration of therapeutic RNA agents will accelerate. The balance of clinical benefit and adverse effects will determine the future of new gluconeogenesis inhibitors.

Ethnopharmacological perspectives of glucokinase activators in the treatment of diabetes mellitus

Traditional medicinal plants have wide-reaching utilisation in the treatment of diabetes especially in developing countries where medical resources are meagre. Traditionally used anti-diabetic plants act by numerous mechanisms, however, only a few of them act through activation of the glucokinase enzyme. Glucokinase is a key regulatory enzyme in glucose metabolism thereby controls glucose homeostasis and insulin secretion. The present review significantly analyses the knowledge about various plant-based glucokinase activators including numerous phytochemicals which modulate the activity and gene expression of glucokinase and would provide data support and perspective regarding future research in the discovery and development of different plant-derived glucokinase activators.

Glucokinase activation as antidiabetic therapy: effect of nutraceuticals and phytochemicals on glucokinase gene expression and enzymatic activity

Diabetes represents an important public health problem. Recently, new molecular targets have been identified and exploited to treat this disease. Due to its pivotal role in glucose homeostasis, glucokinase (GCK) is a promising target for the development of novel antidiabetic drugs; however, pharmacological agents that modulate GCK activity have been linked to undesirable side-effects, limiting its use. Interestingly, plants might be a valuable source of new therapeutic compounds with GCK-activating properties and presumably no adverse effects. In this review, we describe biochemical characteristics related to the physiological and pathological importance of GCK, as well as the mechanisms involved in its regulation at different molecular levels. Posteriorly, we present a compendium of findings supporting the potential use of nutraceuticals and phytochemicals in the management of diabetes through modulation of GCK expression and activity. Finally, we propose critical aspects to keep in mind when designing experiments to evaluate GCK modulation properly.

Glucokinase Inactivation Paradoxically Ameliorates Glucose Intolerance by Increasing β-Cell Mass in db/db Mice

Efficacy of glucokinase activation on glycemic control is limited to a short-term period. One reason might be related to excess glucose signaling by glucokinase activation toward β-cells. In this study, we investigated the effect of glucokinase haploinsufficiency on glucose tolerance as well as β-cell function and mass using a mouse model of type 2 diabetes. Our results showed that in db/db mice with glucokinase haploinsufficiency, glucose tolerance was ameliorated by augmented insulin secretion associated with the increase in β-cell mass when compared with db/db mice. Gene expression profiling and immunohistochemical and metabolomic analyses revealed that glucokinase haploinsufficiency in the islets of db/db mice was associated with lower expression of stress-related genes, greater expression of transcription factors involved in the maintenance and maturation of β-cell function, less mitochondrial damage, and a superior metabolic pattern. These effects of glucokinase haploinsufficiency could preserve β-cell mass under diabetic conditions. These findings verified our hypothesis that optimizing excess glucose signaling in β-cells by inhibiting glucokinase could prevent β-cell insufficiency, leading to improving glucose tolerance in diabetes status by preserving β-cell mass. Therefore, glucokinase inactivation in β-cells, paradoxically, could be a potential strategy for the treatment of type 2 diabetes.

The effects and safety of activators of glucokinase versus placebo in patients with type 2 diabetes mellitus: a systematic review and meta-analysis

We undertook a systematic review and meta-analysis to assess the effects and safety of activators of glucokinase (GKAs) in patients with type 2 diabetes mellitus (T2DM). 11 RCTs, including 2,429 participants, are enrolled in our study. According to different doses, we divided the studies into 3 groups: low-dose group, medium-dose group and high-dose group for subgroup analysis. There were decreases of HbA1c in all dose group (WMD = -0.27, 95%CI (-0.51~ -0.03), Z = 2.17, p = 0.03; WMD = -0.37, 95%CI (-0.58~ -0.16), Z = 3.41, p = 0.0006; WMD = -0.60, 95%CI (-0.86~ -0.33), Z = 4.43, p < 0.00001). Though the total risk of hypoglycemia is absolutely low, in the high-dose group higher hypoglycemia than the placebo can be observed (RR = 0.03, 95%CI (0.00~0.06), Z = 2.27, p = 0.02). In addition, the study found that the drug was less likely to have adverse reactions such as diarrhea, headache and dizziness, nasopharyngitis and upper respiratory tract infection (RR = 0.76, 95%CI (0.36~1.60), Z = 0.73, p = 0.47; RR = 1.26, 95%CI (0.73~2.17), Z = 0.83, p = 0.41; RR = 0.71, 95%CI (0.41~1.22), Z = 1.25, p = 0.21; RR = 1.61, 95%CI (0.77~3.36), Z = 1.26, p = 0.21). It concludes that GKAs are relatively effective and safe in the treatment of patients with T2DM, but in consideration of the potential risk of hypoglycemia in the high-dose group, the low-dose and medium-dose group, in the clinical practice, can be an excellent choice.

Genetic activation of α-cell glucokinase in mice causes enhanced glucose-suppression of glucagon secretion during normal and diabetic states

Objective

While the molecular events controlling insulin secretion from β-cells have been documented in detail, the exact mechanisms governing glucagon release by α-cells are understood only partially. This is a critical knowledge gap, as the normal suppression of glucagon secretion by elevated glucose levels fails in type 2 diabetes (T2D) patients, contributing to hyperglycemia through stimulation of hepatic glucose production. A critical role of glycolytic flux in regulating glucagon secretion was supported by recent studies in which manipulation of the activity and expression of the glycolytic enzyme glucokinase altered the setpoint for glucose-suppression of glucagon secretion (GSGS). Given this precedent, we hypothesized that genetic activation of glucokinase specifically in α-cells would enhance GSGS and mitigate T2D hyperglucagonemia.

Methods

We derived an inducible, α-cell-specific glucokinase activating mutant mouse model (Gck^{LoxPGck∗/LoxPGck∗}; Gcg-CreER^T2; henceforth referred to as “α-mutGCK”) in which the wild-type glucokinase gene (GCK) is conditionally replaced with a glucokinase mutant allele containing the ins454A activating mutation (Gck∗), a mutation that increases the affinity of glucokinase for glucose by almost 7-fold. The effects of α-cell GCK activation on glucose homeostasis, hormone secretion, islet morphology, and islet numbers were assessed using both in vivo and ex vivo assays. Additionally, the effect of α-cell GCK activation on GSGS was investigated under diabetogenic conditions of high-fat diet (HFD) feeding that dysregulate glucagon secretion.

Results

Our study shows that α-mutGCK mice have enhanced GSGS in vivo and ex vivo, independent of alterations in insulin levels and secretion, islet hormone content, islet morphology, or islet number. α-mutGCK mice maintained on HFD displayed improvements in glucagonemia compared to controls, which developed the expected obesity, glucose intolerance, elevated fasting blood glucose, hyperinsulinemia, and hyperglucagonemia.

Conclusions

Using our novel α-cell specific activation of GCK mouse model, we have provided additional support to demonstrate that the glycolytic enzyme glucokinase is a key determinant in glucose sensing within α-cells to regulate glucagon secretion. Our results contribute to our fundamental understanding of α-cell biology by providing greater insight into the regulation of glucagon secretion through α-cell intrinsic mechanisms via glucokinase. Furthermore, our HFD results underscore the potential of glucokinase as a druggable target which, given the ongoing development of allosteric glucokinase activators (GKAs) for T2D treatment, could help mitigate hyperglucagonemia and potentially improve blood glucose homeostasis.

•

Inducible and cell type-specific point mutation in glucokinase enables analysis of glucose suppression of glucagon secretion.

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Glycolytic flux through glucokinase determines the set-point for glucagon secretion in pancreatic α-cells.

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Pancreatic α-cells are a physiologically relevant target of glucokinase activator drugs.

Chronic glucokinase activator treatment activates liver Carbohydrate response element binding protein and improves hepatocyte ATP homeostasis during substrate challenge

AIM

To test the hypothesis that glucokinase activators (GKAs) induce hepatic adaptations that alter intra-hepatocyte metabolite homeostasis.

METHODS

C57BL/6 mice on a standard rodent diet were treated with a GKA (AZD1656) acutely or chronically. Hepatocytes were isolated from the mice after 4 or 8 weeks of treatment for analysis of cellular metabolites and gene expression in response to substrate challenge.

RESULTS

Acute exposure of mice to AZD1656 or a liver-selective GKA (PF-04991532), before a glucose tolerance test, or challenge of mouse hepatocytes with GKAs ex vivo induced various Carbohydrate response element binding protein (ChREBP) target genes, including Carbohydrate response element binding protein beta isoform (ChREBP-β), Gckr and G6pc. Both glucokinase activation and ChREBP target gene induction by PF-04991532 were dependent on the chirality of the molecule, confirming a mechanism linked to glucokinase activation. Hepatocytes from mice treated with AZD1656 for 4 or 8 weeks had lower basal glucose 6-phosphate levels and improved ATP homeostasis during high substrate challenge. They also had raised basal ChREBP-β mRNA and AMPK-α mRNA (Prkaa1, Prkaa2) and progressively attenuated substrate induction of some ChREBP target genes and Prkaa1 and Prkaa2.

CONCLUSIONS

Chronic GKA treatment of C57BL/6 mice for 8 weeks activates liver ChREBP and improves the resilience of hepatocytes to compromised ATP homeostasis during high-substrate challenge. These changes are associated with raised mRNA levels of ChREBP-β and both catalytic subunits of AMP-activated protein kinase.

Insights into the binding of dorzagliatin with glucokinase: A molecular dynamics simulation

Human glucokinase (GK) is a potentially attractive target for diabetes, playing a prominent role in the control of glucose homeostasis. Dorzagliatin is the first GK activator (GKA) to enter phase III clinical trial. In this study, the possible binding mode of dorzagliatin with GK was investigated via the molecular simulation method. Two other systems in the absence of dorzagliatin and glucose were also studied to disclose the roles of dorzagliatin and glucose. The outcomes revealed that dorzagliatin can create the characteristic hydrogen bonds of GKA with Arg63, and Arg63 can form hydrogen bonds with nearby residues, making a tight binding hydrogen bond network around dorzagliatin. The presence of dorzagliatin can stabilize glucokinase for a period of time, and the binding of glucose may prevent the GK conformational change to a certain extent. Our results may be beneficial to mechanism understanding of GKA, and will be useful in design of novel GKAs for treating metabolic diseases.

Metabolic control analysis of hepatic glycogen synthesis in vivo

Hepatic glycogen synthesis plays a critical role in maintaining normal glucose homeostasis; however, the rate-controlling step regulating this process is unknown. Applying metabolic control analysis in vivo, we show that the regulation of insulin-stimulated hepatic glycogen synthesis under both normal and pathophysiological conditions of fatty liver-associated hepatic insulin resistance is controlled at the glucokinase (GCK) step through GCK translocation.

Multiple insulin-regulated enzymes participate in hepatic glycogen synthesis, and the rate-controlling step responsible for insulin stimulation of glycogen synthesis is unknown. We demonstrate that glucokinase (GCK)-mediated glucose phosphorylation is the rate-controlling step in insulin-stimulated hepatic glycogen synthesis in vivo, by use of the somatostatin pancreatic clamp technique using [¹³C₆]glucose with metabolic control analysis (MCA) in three rat models: 1) regular chow (RC)-fed male rats (control), 2) high fat diet (HFD)-fed rats, and 3) RC-fed rats with portal vein glucose delivery at a glucose infusion rate matched to the control. During hyperinsulinemia, hyperglycemia dose-dependently increased hepatic glycogen synthesis. At similar levels of hyperinsulinemia and hyperglycemia, HFD-fed rats exhibited a decrease and portal delivery rats exhibited an increase in hepatic glycogen synthesis via the direct pathway compared with controls. However, the strong correlation between liver glucose-6-phosphate concentration and net hepatic glycogen synthetic rate was nearly identical in these three groups, suggesting that the main difference between models is the activation of GCK. MCA yielded a high control coefficient for GCK in all three groups. We confirmed these findings in studies of hepatic GCK knockdown using an antisense oligonucleotide. Reduced liver glycogen synthesis in lipid-induced hepatic insulin resistance and increased glycogen synthesis during portal glucose infusion were explained by concordant changes in translocation of GCK. Taken together, these data indicate that the rate of insulin-stimulated hepatic glycogen synthesis is controlled chiefly through GCK translocation.

Acetylene Group, Friend or Foe in Medicinal Chemistry

The use of an acetylene (ethynyl) group in medicinal chemistry coincides with the launch of the Journal of Medicinal Chemistry in 1959. Since then, the acetylene group has been broadly exploited in drug discovery and development. As a result, it has become recognized as a privileged structural feature for targeting a wide range of therapeutic target proteins, including MAO, tyrosine kinases, BACE1, steroid receptors, mGlu5 receptors, FFA1/GPR40, and HIV-1 RT. Furthermore, a terminal alkyne functionality is frequently introduced in chemical biology probes as a click handle to identify molecular targets and to assess target engagement. This Perspective is divided into three parts encompassing: (1) the physicochemical properties of the ethynyl group, (2) the advantages and disadvantages of the ethynyl group in medicinal chemistry, and (3) the impact of the ethynyl group on chemical biology approaches.

Reducing Glucokinase Activity to Enhance Insulin Secretion: A Counterintuitive Theory to Preserve Cellular Function and Glucose Homeostasis

Pancreatic beta-cells are the only cells in the body that can synthesize and secrete insulin. Through the process of glucose-stimulated insulin secretion, beta-cells release insulin into circulation, stimulating GLUT4-dependent glucose uptake into peripheral tissue. Insulin is normally secreted in pulses that promote signaling at the liver. Long before type 2 diabetes is diagnosed, beta-cells become oversensitive to glucose, causing impaired pulsatility and overstimulation in fasting levels of glucose. The resulting hypersecretion of insulin can cause poor insulin signaling and clearance at the liver, leading to hyperinsulinemia and insulin resistance. Continued overactivity can eventually lead to beta-cell exhaustion and failure at which point type 2 diabetes begins. To prevent or reverse the negative effects of overstimulation, beta-cell activity can be reduced. Clinical studies have revealed the potential of beta-cell rest to reverse new cases of diabetes, but treatments lack durable benefits. In this perspective, we propose an intervention that reduces overactive glucokinase activity in the beta-cell. Glucokinase is known as the glucose sensor of the beta-cell due to its high control over insulin secretion. Therefore, glycolytic overactivity may be responsible for hyperinsulinemia early in the disease and can be reduced to restore normal stimulus-secretion coupling. We have previously reported that reducing glucokinase activity in prediabetic mouse islets can restore pulsatility and enhance insulin secretion. Building on this counterintuitive finding, we review the importance of pulsatile insulin secretion and highlight how normalizing glucose sensing in the beta cell during prediabetic hyperinsulinemia may restore pulsatility and improve glucose homeostasis.

Discovery and preclinical development of AR453588 as an anti-diabetic glucokinase activator

Glucose flux through glucokinase (GK) controls insulin release from the pancreas in response to high levels of glucose. Flux through GK is also responsible for reducing hepatic glucose output. Since many individuals with type 2 diabetes appear to have an inadequacy or defect in one or both of these processes, identifying compounds that can activate GK could provide a therapeutic benefit. Herein we report the further structure activity studies of a novel series of glucokinase activators (GKA). These studies led to the identification of pyridine 72 as a potent GKA that lowered post-prandial glucose in normal C57BL/6J mice, and after 14d dosing in ob/ob mice.

The Central Role of Glucokinase in Glucose Homeostasis: A Perspective 50 Years After Demonstrating the Presence of the Enzyme in Islets of Langerhans

It is hypothesized that glucokinase (GCK) is the glucose sensor not only for regulation of insulin release by pancreatic β-cells, but also for the rest of the cells that contribute to glucose homeostasis in mammals. This includes other cells in endocrine pancreas (α- and δ-cells), adrenal gland, glucose sensitive neurons, entero-endocrine cells, and cells in the anterior pituitary. Glucose transport is by facilitated diffusion and is not rate limiting. Once inside, glucose is phosphorylated to glucose-6-phosphate by GCK in a reaction that is dependent on glucose throughout the physiological range of concentrations, is irreversible, and not product inhibited. High glycerol phosphate shuttle, pyruvate dehydrogenase, and pyruvate carboxylase activities, combined with low pentose-P shunt, lactate dehydrogenase, plasma membrane monocarboxylate transport, and glycogen synthase activities constrain glucose-6-phosphate to being metabolized through glycolysis. Under these conditions, glycolysis produces mostly pyruvate and little lactate. Pyruvate either enters the citric acid cycle through pyruvate dehydrogenase or is carboxylated by pyruvate carboxylase. Reducing equivalents from glycolysis enter oxidative phosphorylation through both the glycerol phosphate shuttle and citric acid cycle. Raising glucose concentration increases intramitochondrial [NADH]/[NAD⁺] and thereby the energy state ([ATP]/[ADP][Pi]), decreasing [Mg²⁺ADP] and [AMP]. [Mg²⁺ADP] acts through control of K_ATP channel conductance, whereas [AMP] acts through regulation of AMP-dependent protein kinase. Specific roles of different cell types are determined by the diverse molecular mechanisms used to couple energy state to cell specific responses. Having a common glucose sensor couples complementary regulatory mechanisms into a tightly regulated and stable glucose homeostatic network.

Reducing Glucokinase Activity Restores Endogenous Pulsatility and Enhances Insulin Secretion in Islets From db/db Mice

An early sign of islet failure in type 2 diabetes (T2D) is the loss of normal patterns of pulsatile insulin release. Disruptions in pulsatility are associated with a left shift in glucose sensing that can cause excessive insulin release in low glucose (relative hyperinsulinemia, a hallmark of early T2D) and β-cell exhaustion, leading to inadequate insulin release during hyperglycemia. Our hypothesis was that reducing excessive glucokinase activity in diabetic islets would improve their function. Isolated mouse islets were exposed to glucose and varying concentrations of the glucokinase inhibitor d-mannoheptulose (MH) to examine changes in intracellular calcium ([Ca2+]i) and insulin secretion. Acutely exposing islets from control CD-1 mice to MH in high glucose (20 mM) dose dependently reduced the size of [Ca2+]i oscillations detected by fura-2 acetoxymethyl. Glucokinase activation in low glucose (3 mM) had the opposite effect. We then treated islets from male and female db/db mice (age, 4 to 8 weeks) and heterozygous controls overnight with 0 to 10 mM MH to determine that 1 mM MH produced optimal oscillations. We then used 1 mM MH overnight to measure [Ca2+]i and insulin simultaneously in db/db islets. MH restored oscillations and increased insulin secretion. Insulin secretion rates correlated with MH-induced increases in amplitude of [Ca2+]i oscillations (R2 = 0.57, P < 0.01, n = 10) but not with mean [Ca2+]i levels in islets (R2 = 0.05, not significant). Our findings show that correcting glucose sensing can restore proper pulsatility to diabetic islets and improved pulsatility correlates with enhanced insulin secretion.

Dorzagliatin (HMS5552), a novel dual-acting glucokinase activator, improves glycaemic control and pancreatic β-cell function in patients with type 2 diabetes: A 28-day treatment study using biomarker-guided patient selection

AIMS

To investigate the pharmacokinetics and pharmacodynamics of a dual-acting glucokinase activator, dorzagliatin, and its safety, tolerability and effect on pancreatic β-cell function in Chinese patients with type 2 diabetes (T2D).

MATERIALS AND METHODS

A total of 24 T2D patients were selected, utilizing a set of predefined clinical biomarkers, and were randomized to receive dorzagliatin 75 mg twice or once daily (BID, QD respectively) for 28 days. Changes in HbA1c and glycaemic parameters from baseline to Day 28 were assessed. In addition, changes in β-cell function from baseline to Day 32 were evaluated.

RESULTS

Significant reductions in HbA1c were observed in both regimens on Day 28 (-0.79%, 75 mg BID; -1.22%, 75 mg QD). Similar trends were found in the following parameters, including reductions from baseline in fasting plasma glucose by 1.20 mmol/L and 1.51 mmol/L, in 2-hour postprandial glucose by 2.48 mmol/L and 5.03 mmol/L, and in glucose AUC_0-24 by 18.59% and 20.98%, for the BID and QD groups, respectively. Both regimens resulted in improvement in β-cell function as measured by steady state HOMA 2 parameter, %B, which increased by 36.31% and 40.59%, and by dynamic state parameter, ΔC₃₀ /ΔG₃₀ , which increased by 24.66% and 167.67%, for the BID and QD groups, respectively. Dorzagliatin was well tolerated in both regimens, with good pharmacokinetic profiles.

CONCLUSIONS

Dorzagliatin treatment for 28 days in Chinese T2D patients, selected according to predefined biomarkers, resulted in significant improvement in β-cell function and glycaemic control. The safety and pharmacokinetic profile of dorzagliatin supports a subsequent Phase II trial design and continued clinical development.

Functional characterization of MODY2 mutations in the nuclear export signal of glucokinase

Glucokinase (GCK) plays a key role in glucose homeostasis. Heterozygous inactivating mutations in the GCK gene cause the familial, mild fasting hyperglycaemia named MODY2. Besides its particular kinetic characteristics, glucokinase is regulated by subcellular compartmentation in hepatocytes. Glucokinase regulatory protein (GKRP) binds to GCK, leading to enzyme inhibition and import into the nucleus at fasting. When glucose concentration increases, GCK-GKRP dissociates and GCK is exported to the cytosol due to a nuclear export signal (NES). With the aim to characterize the GCK-NES, we have functionally analysed nine MODY2 mutations located within the NES sequence. Recombinant GCK mutants showed reduced catalytic activity and, in most cases, protein instability. Most of the mutants interact normally with GKRP, although mutations L306R and L309P impair GCK nuclear import in cotransfected cells. We demonstrated that GCK-NES function depends on exportin 1. We further showed that none of the mutations fully inactivate the NES, with the exception of mutation L304P, which likely destabilizes its α-helicoidal structure. Finally, we found that residue Glu300 negatively modulates the NES activity, whereas other residues have the opposite effect, thus suggesting that some of the NES spacer residues contribute to the low affinity of the NES for exportin 1, which is required for its proper functioning. In conclusion, our results have provided functional and structural insights regarding the GCK-NES and contributed to a better knowledge of the molecular mechanisms involved in the nucleo-cytoplasmic shuttling of glucokinase. Impairment of this regulatory mechanism by some MODY2 mutations might contribute to the hyperglycaemia in the patients.

Tryptophan Fluorescence Yields and Lifetimes as a Probe of Conformational Changes in Human Glucokinase

Five variants of glucokinase (ATP-D-hexose-6-phosphotransferase, EC 2.7.1.1) including wild type and single Trp mutants with the Trp residue at positions 65, 99, 167 and 257 were prepared. The fluorescence of Trp in all locations studied showed intensity changes when glucose bound, indicating that conformational change occurs globally over the entire protein. While the fluorescence quantum yield changes upon glucose binding, the enzyme's absorption spectra, emission spectra and fluorescence lifetimes change very little. These results are consistent with the existence of a dark complex for excited state Trp. Addition of glycerol, L-glucose, sucrose, or trehalose increases the binding affinity of glucose to the enzyme and increases fluorescence intensity. The effect of these osmolytes is thought to shift the protein conformation to a condensed, high affinity form. Based upon these results, we consider the nature of quenching of the Trp excited state. Amide groups are known to quench indole fluorescence and amides of the polypeptide chain make interact with excited state Trp in the relatively unstructured, glucose-free enzyme. Also, removal of water around the aromatic ring by addition of glucose substrate or osmolyte may reduce the quenching.

Opposite effects of a glucokinase activator and metformin on glucose-regulated gene expression in hepatocytes

AIM

Small molecule activators of glucokinase (GKAs) have been explored extensively as potential anti-hyperglycaemic drugs for type 2 diabetes (T2D). Several GKAs were remarkably effective in lowering blood glucose during early therapy but then lost their glycaemic efficacy chronically during clinical trials.

MATERIALS AND METHODS

We used rat hepatocytes to test the hypothesis that GKAs raise hepatocyte glucose 6-phosphate (G6P, the glucokinase product) and down-stream metabolites with consequent repression of the liver glucokinase gene ( Gck). We compared a GKA with metformin, the most widely prescribed drug for T2D.

RESULTS

Treatment of hepatocytes with 25 mM glucose raised cell G6P, concomitantly with Gck repression and induction of G6pc (glucose 6-phosphatase) and Pklr (pyruvate kinase). A GKA mimicked high glucose by raising G6P and fructose-2,6-bisphosphate, a regulatory metabolite, causing a left-shift in glucose responsiveness on gene regulation. Fructose, like the GKA, repressed Gck but modestly induced G6pc. 2-Deoxyglucose, which is phosphorylated by glucokinase but not further metabolized caused Gck repression but not G6pc induction, implicating the glucokinase product in Gck repression. Metformin counteracted the effect of high glucose on the elevated G6P and fructose 2,6-bisphosphate and on Gck repression, recruitment of Mlx-ChREBP to the G6pc and Pklr promoters and induction of these genes.

CONCLUSIONS

Elevation in hepatocyte G6P and downstream metabolites, with consequent liver Gck repression, is a potential contributing mechanism to the loss of GKA efficacy during chronic therapy. Cell metformin loads within the therapeutic range attenuate the effect of high glucose on G6P and on glucose-regulated gene expression.

Identification of mangiferin as a potential Glucokinase activator by structure-based virtual ligand screening

The natural product mangiferin (compound 7) has been identified as a potential glucokinase activator by structure-based virtual ligand screening. It was proved by enzyme activation experiment and cell-based assays in vitro, with potency in micromolar range. Meanwhile, this compound showed good antihyperglycemic activity in db/db mice without obvious side effects such as excessive hypoglycaemia.

In type 1 diabetics, high-dose biotin may compensate for low hepatic insulin exposure, promoting a more normal expression of glycolytic and gluconeogenic enyzymes and thereby aiding glycemic control

In type 1 diabetics, hepatic exposure to insulin is chronically subnormal even in the context of insulin therapy; as a result, expression of glycolytic enzymes is decreased, and that of gluconeogenic enzymes is enhanced, resulting in a physiologically inappropriate elevation of hepatic glucose output. Subnormal expression of glucokinase (GK) is of particular importance in this regard. Possible strategies for correcting this perturbation of hepatic enzyme expression include administration of small molecule allosteric activators of GK, as well as a procedure known as chronic intermittent intravenous insulin therapy (CIIIT); however, side effects accompany the use of GK activators, and CIIIT is time and labor intensive. Alternatively, administration of high-dose biotin has potential for modulating hepatic enzyme expression in a favorable way. Studies in rodents and in cultured hepatocytes demonstrate that, in the context of low insulin exposure, supra-physiological levels of biotin induce increased expression of GK while suppressing that of the key gluconeogenic enzyme phosphoenolpyruvate carboxykinase. These effects may be a downstream consequence of the fact that biotin down-regulates mRNA expression of FOXO1; insulin's antagonism of the activity of this transcription factor is largely responsible for its modulatory impact on hepatic glycolysis and gluconeogenesis. Hence, high-dose biotin may compensate for subnormal insulin exposure by suppressing FOXO1 levels. High-dose biotin also has the potential to oppose hepatic steatosis by down-regulating SREBP-1 expression. Two pilot trials of high-dose biotin (16 or 2mg per day) in type 1 diabetics have yielded promising results. There is also some reason to suspect that high-dose biotin could aid control of diabetic neuropathy and nephropathy via its stimulatory effect on cGMP production. Owing to the safety, good tolerance, moderate expense, and current availability of high-dose biotin, this strategy merits more extensive evaluation in type 1 diabetes.

Safety, tolerability, pharmacokinetics, and pharmacodynamics of novel glucokinase activator HMS5552: results from a first-in-human single ascending dose study

Background

HMS5552, a novel fourth-generation glucokinase (GK) activator, has demonstrated promising effects on glycemic control in preclinical models of type 2 diabetes. This single ascending dose study was conducted to investigate the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of HMS5552 during its first-in-human exposure.

Methods

Sixty healthy subjects were enrolled. In each of six dose-cohorts (5, 10, 15, 25, 35, and 50 mg), ten subjects were randomized with eight subjects receiving the same cohort-dose of HMS5552 and two receiving placebo. Plasma HMS5552 exposure, glucose, and insulin were measured repeatedly during fasting and after a standardized meal. Assessment included safety, PK, and PD endpoints.

Results

HMS5552 showed dose-proportional increases in area under the curve 0 to the last quantifiable concentration (AUC_0–t) and maximum plasma concentration (C_max). Slopes estimated by linear regression for AUC_0–t and C_max were ~1.0 (0.932 and 0.933, respectively). Geometric mean elimination half-life ranged from 4.48 to 7.51 hours and apparent clearance ranged from 11.5 to 13.1 L/h across all doses. No significant sex effect was observed in PK parameters. HMS5552 also demonstrated dose-related PD responses in terms of maximum glucose change from baseline (%) and mean glucose area under effect curve 0–4 hours change from baseline (%) (P<0.001). Fifteen adverse events were reported by nine subjects (ten with HMS5552 and five with the placebo). All adverse events were mild in intensity and resolved without any treatment.

Conclusion

This first-in-human single ascending dose study provided predicted PK of HMS5552 with dose-proportional increases in AUC_0–t and C_max, as well as dose-related glucose-lowering effects over the range of 5–50 mg in healthy subjects. HMS5552 at doses up to 50 mg in healthy subjects was safe and well-tolerated.

Regulation of hepatic energy metabolism by the nuclear receptor PXR

The pregnane X receptor (PXR) is a nuclear receptor that is traditionally thought to be specialized for sensing xenobiotic exposure. In concurrence with this feature PXR was originally identified to regulate drug-metabolizing enzymes and transporters. During the last ten years it has become clear that PXR harbors broader functions. Evidence obtained both in experimental animals and humans indicate that ligand-activated PXR regulates hepatic glucose and lipid metabolism and affects whole body metabolic homeostasis. Currently, the consequences of PXR activation on overall metabolic health are not yet fully understood and varying results on the effect of PXR activation or knockout on metabolic disorders and weight gain have been published in mouse models. Rifampicin and St. John's wort, the prototypical human PXR agonists, impair glucose tolerance in healthy volunteers. Chronic exposure to PXR agonists could potentially represent a risk factor for diabetes and metabolic syndrome. This article is part of a Special Issue entitled: Xenobiotic nuclear receptors: New Tricks for An Old Dog, edited by Dr. Wen Xie.