The gut-brain axis: Identifying new therapeutic approaches for type 2 diabetes, obesity, and related disorders.

Background: The gut-brain axis, which mediates bidirectional communication between the gastrointestinal system and central nervous system (CNS), plays a fundamental role in multiple areas of physiology including regulating appetite, metabolism, and gastrointestinal function. The biology of the gut-brain axis is central to the efficacy of glucagon-like peptide-1 (GLP-1)-based therapies, which are now leading treatments for type 2 diabetes (T2DM) and obesity. This success and research to suggest a much broader role of gut-brain circuits in physiology and disease has led to increasing interest in targeting such circuits to discover new therapeutics.

A comparative study of the binding properties, dipeptidyl peptidase-4 (DPP-4) inhibitory activity and glucose-lowering efficacy of the DPP-4 inhibitors alogliptin, linagliptin, saxagliptin, sitagliptin and vildagliptin in mice.

Aims: Since 2006, DPP-4 inhibitors have become established therapy for the treatment of type 2 diabetes. Despite sharing a common mechanism of action, considerable chemical diversity exists amongst members of the DPP-4 inhibitor class, raising the question as to whether structural differences may result in differentiated enzyme inhibition and antihyperglycaemic activity.

Methods: We have compared the binding properties of the most commonly used inhibitors and have investigated the relationship between their inhibitory potency at the level of the enzyme and their acute glucose-lowering efficacy.

Induction of miR-132 and miR-212 Expression by Glucagon-Like Peptide 1 (GLP-1) in Rodent and Human Pancreatic β-Cells.

Better understanding how glucagon-like peptide 1 (GLP-1) promotes pancreatic β-cell function and/or mass may uncover new treatment for type 2 diabetes. In this study, we investigated the potential involvement of microRNAs (miRNAs) in the effect of GLP-1 on glucose-stimulated insulin secretion. miRNA levels in INS-1 cells and isolated rodent and human islets treated with GLP-1 in vitro and in vivo (with osmotic pumps) were measured by real-time quantitative PCR.

Downregulation of carnitine acyl-carnitine translocase by miRNAs 132 and 212 amplifies glucose-stimulated insulin secretion.

We previously demonstrated that micro-RNAs (miRNAs) 132 and 212 are differentially upregulated in response to obesity in two mouse strains that differ in their susceptibility to obesity-induced diabetes. Here we show the overexpression of miRNAs 132 and 212 enhances insulin secretion (IS) in response to glucose and other secretagogues including nonfuel stimuli. We determined that carnitine acyl-carnitine translocase (CACT; Slc25a20) is a direct target of these miRNAs.

Omarigliptin (MK-3102): a novel long-acting DPP-4 inhibitor for once-weekly treatment of type 2 diabetes.

In our effort to discover DPP-4 inhibitors with added benefits over currently commercially available DPP-4 inhibitors, MK-3102 (omarigliptin), was identified as a potent and selective dipeptidyl peptidase 4 (DPP-4) inhibitor with an excellent pharmacokinetic profile amenable for once-weekly human dosing and selected as a clinical development candidate. This manuscript summarizes the mechanism of action, scientific rationale, medicinal chemistry, pharmacokinetic properties, and human efficacy data for omarigliptin, which is currently in phase 3 clinical development.

Optimization of co-agonism at GLP-1 and glucagon receptors to safely maximize weight reduction in DIO-rodents.

The ratio of GLP-1/glucagon receptor (GLP1R/GCGR) co-agonism that achieves maximal weight loss without evidence of hyperglycemia was determined in diet-induced obese (DIO) mice chronically treated with GLP1R/GCGR co-agonist peptides differing in their relative receptor agonism. Using glucagon-based peptides, a spectrum of receptor selectivity was achieved by a combination of selective incorporation of GLP-1 sequences, C-terminal modification, backbone lactam stapling to stabilize helical structure, and unnatural amino acid substitutions at the N-terminal dipeptide. In addition to α-amino-isobutyric acid (Aib) substitution at position two, we show that α,α'-dimethyl imidazole acetic acid (Dmia) can serve as a potent replacement for the highly conserved histidine at position one.

The role of voltage-gated potassium channels Kv2.1 and Kv2.2 in the regulation of insulin and somatostatin release from pancreatic islets.

The voltage-gated potassium channels Kv2.1 and Kv2.2 are highly expressed in pancreatic islets, yet their contribution to islet hormone secretion is not fully understood.

Bombesin receptor subtype-3 (BRS-3) regulates glucose-stimulated insulin secretion in pancreatic islets across multiple species.

Bombesin receptor subtype-3 (BRS-3) regulates energy homeostasis, and BRS-3 agonism is being explored as a possible therapy for obesity. Here we study the role of BRS-3 in the regulation of glucose-stimulated insulin secretion (GSIS) and glucose homeostasis. We quantified BRS-3 mRNA in pancreatic islets from multiple species and examined the acute effects of Bag-1, a selective BRS-3 agonist, on GSIS in mouse, rat, and human islets, and on oral glucose tolerance in mice.

Synthesis and evaluation of [(1R)-1-amino-2-(2,5-difluorophenyl)ethyl]cyclohexanes and 4-[(1R)-1-amino-2-(2,5-difluorophenyl)ethyl]piperidines as DPP-4 inhibitors.

A series of 4-amino cyclohexanes and 4-substituted piperidines were prepared and evaluated for inhibition of DPP-4. Analog 20q displayed both good DPP-4 potency and selectivity against other proteases, while derivative 20k displayed long half life and modest oral bioavailability in rat. The most potent analog, 3-(5-aminocarbonylpyridyl piperidine 53j, displayed excellent DPP-4 activity with good selectivity versus other proline enzymes.

A model selection approach for expression quantitative trait loci (eQTL) mapping.

Identifying the genetic basis of complex traits remains an important and challenging problem with the potential to affect a broad range of biological endeavors. A number of statistical methods are available for mapping quantitative trait loci (QTL), but their application to high-throughput phenotypes has been limited as most require user input and interaction. Recently, methods have been developed specifically for expression QTL (eQTL) mapping, but they too are limited in that they do not allow for interactions and QTL of moderate effect.

Discovery of 5-aryloxy-2,4-thiazolidinediones as potent GPR40 agonists.

Systematic structure-activity relationship (SAR) studies of a screening lead led to the discovery of a series of thiazolidinediones (TZDs) as potent GPR40 agonists. Among them, compound C demonstrated an acute mechanism-based glucose-lowering in an intraperitoneal glucose tolerance test (IPGTT) in lean mice, while no effects were observed in GPR40 knock-out mice.

Inhibition of DPP-4 with sitagliptin improves glycemic control and restores islet cell mass and function in a rodent model of type 2 diabetes.

Inhibition of dipeptidyl peptidase-4 (DPP-4) activity has been shown to improve glycemic control in patients with type 2 diabetes by prolonging and potentiating the actions of incretin hormones. This study is designed to determine the effects of the DPP-4 inhibitor sitagliptin on improving islet function in a mouse model of insulin resistance and insulin secretion defects. ICR mice were pre-treated with high fat diet and a low dose of streptozotocin to induce insulin resistance and impaired insulin secretion, respectively.

Mechanism of action of inhibitors of dipeptidyl-peptidase-4 (DPP-4).

Dipeptidyl-peptidase IV (DPP-4) inhibitors inhibit the degradation of the incretins, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP). The first available DPP-4 inhibitors are sitagliptin and vildagliptin. These compounds are orally active and have been shown to be efficacious and well tolerated.

Obesity and genetics regulate microRNAs in islets, liver, and adipose of diabetic mice.

Type 2 diabetes results from severe insulin resistance coupled with a failure of b cells to compensate by secreting sufficient insulin. Multiple genetic loci are involved in the development of diabetes, although the effect of each gene on diabetes susceptibility is thought to be small. MicroRNAs (miRNAs) are noncoding 19-22-nucleotide RNA molecules that potentially regulate the expression of thousands of genes.

Aminopiperidine-fused imidazoles as dipeptidyl peptidase-IV inhibitors.

A new series of DPP-4 inhibitors derived from piperidine-fused benzimidazoles and imidazopyridines is described. Optimization of this class of DPP-4 inhibitors led to the discovery of imidazopyridine 34. The potency, selectivity, cross-species DMPK profiles, and in vivo efficacy of 34 is reported.

Silencing of cytosolic or mitochondrial isoforms of malic enzyme has no effect on glucose-stimulated insulin secretion from rodent islets.

We have previously demonstrated a role for pyruvate cycling in glucose-stimulated insulin secretion (GSIS). Some of the possible pyruvate cycling pathways are completed by conversion of malate to pyruvate by malic enzyme. Using INS-1-derived 832/13 cells, it has recently been shown by other laboratories that NADP-dependent cytosolic malic enzyme (MEc), but not NAD-dependent mitochondrial malic enzyme (MEm), regulates GSIS.

Phosphodiesterase 3 and 4 comprise the major cAMP metabolizing enzymes responsible for insulin secretion in INS-1 (832/13) cells and rat islets.

cAMP is a key modulator for glucose-dependent insulin secretion (GDIS). Members of the phosphodiesterase (PDEs) gene family regulate intracellular levels of cAMP by hydrolyzing cAMP to the corresponding inactive 5'AMP derivative. These studies examined the expression and function of all 18 cAMP-specific PDEs in the rat insulinoma derived INS-1 (832/13) cell and isolated rat islets using quantitative PCR and siRNA-mediated gene-specific knockdown.

Discovery of new binding elements in DPP-4 inhibition and their applications in novel DPP-4 inhibitor design.

Probing with tool molecules, and by modeling and X-ray crystallography the binding modes of two structurally distinct series of DPP-4 inhibitors led to the discovery of a rare aromatic fluorine H-bond and the spatial requirement for better biaryl binding in the DPP-4 enzyme active site. These newly found binding elements were successfully incorporated into novel DPP-4 inhibitors.

Selective small-molecule agonists of G protein-coupled receptor 40 promote glucose-dependent insulin secretion and reduce blood glucose in mice.

Objective: Acute activation of G protein-coupled receptor 40 (GPR40) by free fatty acids (FFAs) or synthetic GPR40 agonists enhances insulin secretion. However, it is still a matter of debate whether activation of GPR40 would be beneficial for the treatment of type 2 diabetes, since chronic exposure to FFAs impairs islet function. We sought to evaluate the specific role of GPR40 in islets and its potential as a therapeutic target using compounds that specifically activate GPR40.

Enzymatic activity of the Staphylococcus aureus SplB serine protease is induced by substrates containing the sequence Trp-Glu-Leu-Gln.

Proteases are of significant importance for the virulence of Staphylococcus aureus. Nevertheless, their subset, the serine protease-like proteins, remains poorly characterized. Here presented is an investigation of SplB protease catalytic activity revealing that the enzyme possesses exquisite specificity and only cleaves efficiently after the sequence Trp-Glu-Leu-Gln.

Fluoroolefins as amide bond mimics in dipeptidyl peptidase IV inhibitors.

The synthesis, selectivity, rat pharmacokinetic profile, and drug metabolism profiles of a series of potent fluoroolefin-derived DPP-4 inhibitors (4) are reported. A radiolabeled fluoroolefin 33 was shown to possess a high propensity to form reactive metabolites, thus revealing a potential liability for this class of DPP-4 inhibitors.