A structural basis for lithium and substrate binding of an inositide phosphatase.

Inositol polyphosphate 1-phosphatase (INPP1) is a prototype member of metal-dependent/lithium-inhibited phosphomonoesterase protein family defined by a conserved three-dimensional core structure. Enzymes within this family function in distinct pathways including inositide signaling, gluconeogenesis, and sulfur assimilation. Using structural and biochemical studies, we report the effect of substrate and lithium on a network of metal binding sites within the catalytic center of INPP1. We find that lithium preferentially occupies a key site involved in metal-activation only when substrate or product is added. Mutation of a conserved residue that selectively coordinates the putative lithium-binding site results in a dramatic 100-fold reduction in the inhibitory constant as compared with wild-type. Furthermore, we report the INPP1/inositol 1,4-bisphosphate complex which illuminates key features of the enzyme active site. Our results provide insights into a structural basis for uncompetitive lithium inhibition and substrate recognition and define a sequence motif for metal binding within this family of regulatory phosphatases.

Approaches towards the development of chimeric DPP4/ACE inhibitors for treating metabolic syndrome.

Designing drug candidates exhibiting polypharmacology is one of the strategies adopted by medicinal chemists to address multifactorial diseases. Metabolic disease is one such multifactorial disorder characterized by hyperglycaemia, hypertension and dyslipidaemia among others. In this paper we report a new class of molecular framework combining the pharmacophoric features of DPP4 inhibitors with those of ACE inhibitors to afford potent dual inhibitors of DPP4 and ACE.

Genes involved in pancreatic islet cell rejuvenation.

Pancreas plays an important role in maintaining the glucose homeostasis. The deterioration of ß-cells in the pancreas is a crucial factor in the progression of diabetes mellitus; therefore, the restoration of ß-cell mass and its function is of vital importance for effective therapeutic strategies. The precise mechanism for increase in functional ß-cell mass is still unknown. This review focuses on the importance of certain genes which are involved in the rejuvenation of pancreas. These genes are divided according to their functions into three categories: participate either in proliferation (mitotic division of differentiated ß-cells), neogenesis/transdifferentiation (development from precursor cells) or inhibition of ß-cell apoptosis (programmed cell death). The rate of ß-cell rejuvenation is the balance among the rates of ß-cell proliferation, neogenesis and apoptosis. Understanding these genes and their pathways may lead to the discovery of new drugs, target based gene delivery and development of safer antidiabetic drugs.

Biological evaluation of RBx-0128, a potent and selective dipeptidyl peptidase-IV inhibitor in type 2 diabetes genetic model.

AIM: Dipeptidyl peptidase IV (DPP-IV) inhibition to modulate the incretin effect is a proven strategy to treat type 2 diabetes mellitus. The present study describes the pharmacological profile of a novel DPP-IV inhibitor RBx-0128, as an antidiabetic agent. MATERIAL AND METHODS: DPP-IV assay was carried out to evaluate in vitro potency of RBx-0128 using human, mouse, and rat plasma as an enzyme source. Selectivity was assessed with various serine proteases. In vivo efficacy was assessed in ob/ob mice. The pharmacokinetic (PK) profile was performed in Wistar rats. RESULTS: RBx-0128 inhibited human, mouse, and rat plasma DPP-IV activity with IC50 values of 10.6, 18.1, and 56.0 nM respectively, selective over various serine proteases (900-9000-fold). The inhibition was reversible and competitive in nature. In ob/ob mice, RBx-0128 significantly (P<0.05) inhibited plasma DPP-IV and stimulated GLP-1 and insulin at 10 mg/kg. In the oral glucose tolerance test (OGTT), glucose lowering effect was better than sitagliptin (23 vs. 17%) at 10 mg/kg. The effect was sustained till 8 hours (30-35%) at 10 mg/kg with favorable PK profile (plasma clearance: 39.3 ml/min/kg; Cmax 790 ng/ml; t1/2 1.6 hours; tmax 4.8 hours, Vss 3.24 l/kg and Foral 55%) in Wistar rats. CONCLUSIONS: The present study showed that RBx-0128 is a novel, DPP-IV inhibitor with an antihyperglycemic effect. It can be a promising candidate for the treatment of type 2 diabetes mellitus.

RBx-0597, a potent, selective and slow-binding inhibitor of dipeptidyl peptidase-IV for the treatment of type 2 diabetes.

Dipeptidyl peptidase IV (DPP-IV) inhibiton is a well recognized approach to treat Type 2 diabetes. RBx-0597 is a novel DPP-IV inhibitor discovered in our laboratory. The aim of the present study was to characterize the pharmacological profiles of RBx-0597 in vitro and in vivo as an anti-diabetic agent. RBx-0597 inhibited human, mouse and rat plasma DPP-IV activity with IC(50) values of 32, 31 and 39nM respectively. RBx-0597 exhibited significant selectivity over dipeptidyl peptidase8 (DPP-8), dipeptidyl peptidase9 (DPP-9) (150-300 fold) and other proline-specific proteases (>200-2000 fold). Kinetic analysis revealed that RBx-0597 is a competitive and slow binding DPP-IV inhibitor. In ob/ob mice, RBx-0597 (10mg/kg) inhibited plasma DPP-IV activity upto 50% 8h post-dose and showed a dose-dependent glucose excursion. RBx-0597 (10mg/kg) showed a significant glucose lowering effect (∼25% AUC of △ blood glucose) which was sustained till 12h, significantly increased the active glucagon-like peptide-1(GLP-1) and insulin levels. It showed a favourable pharmacokinetic profile (plasma clearance:174ml/min/kg; C(max) 292ng/ml; T(1/2) 0.28h; T(max) 0.75h and V(ss) 4.13L/kg) in Wistar rats with the oral bioavailability (F(oral)) of 65%. In summary, the present studies indicate that RBx-0597 is a novel DPP-IV inhibitor with anti-hyperglycemic effect and a promising candidate for further development as a drug for the treatment of type 2 diabetes.

Discovery of conformationally rigid 3-azabicyclo[3.1.0]hexane-derived dipeptidyl peptidase-IV inhibitors.

The induction of conformationally restricted N-(aryl or heteroaryl)-3-azabicyclo[3.1.0]hexane derivatives at P(2) region of compounds of 2-cyanopyrrolidine class was explored to develop novel DPP-IV inhibitors. The synthesis, structure-activity relationship, and selectivity against related proteases are delineated.

From a glucocentric to a lipocentric approach towards metabolic syndrome.

Insulin resistance, the essential component of metabolic syndrome, has traditionally been defined from a glucocentric viewpoint, with glucotoxicity playing a lead role. However, as overabundant circulating fatty acids are now known to be overt contributors, there is a paradigm shift in the understanding of metabolic syndrome acknowledging the importance of lipotoxicity as a major perpetuator of insulin resistance. Ectopic accumulation of fat in liver, adipose, muscle and pancreatic islets, provokes insulin resistance through various mechanisms. Chronic inflammation/adipocytokine generation, endoplasmic reticulum stress and mitochondrial dysfunction/oxidative stress also contribute significantly towards insulin resistance. Targets that can act as counter regulators/master switches at the converging point of all these metabolic pathways are currently under intense development.

Topiramate and type 2 diabetes: an old wine in a new bottle.

Topiramate, a marketed antiepileptic drug, has been used to treat seizures and allied neurological problems since 1999. Recently, a series of newer findings for the use of topiramate have cropped up, which include Type 2 diabetes and obesity. In a series of clinical studies, a subset of neurological patients with Type 2 diabetes mellitus (T2DM) serendipitously showed better glycaemic control when treated with topiramate. It has since been demonstrated that topiramate can act both as an insulin secretagogue and sensitiser in T2DM animal models. Pathogenesis of Type 2 diabetes involves both beta-cell dysfunction and insulin resistance. Therefore, an agent that has dual action (insulin secretagougue and sensitisation) is preferred for T2DM. Topiramate seems to act through multiple mechanisms to ameliorate diabetic symptoms, some of them unknown. Hence, it becomes imperative to discuss its probable modes of action. Topiramate raises new hope as an antidiabetic agent or a potential new chemotype with a better safety profile for the treatment of T2DM.

Combination of dipeptidylpeptidase IV inhibitor and low dose thiazolidinedione: preclinical efficacy and safety in db/db mice.

Thiazolidinediones (TZDs) are currently the most efficacious class of oral antidiabetics. However, they carry the burden of weight gain and haemodilution, which may lead to cardiovascular complications. The present study was designed to ascertain whether a combination of dipeptidyl peptidase IV (DPP IV) inhibitor with low dose of a thiazolidinedione absolves TZD associated weight gain and oedema without compromising its efficacy. In this study, we examined the efficacy and safety of lower dose (1 mg/kg/day) of rosiglitazone, a thiazolidinedione, in combination with 5 mg/kg/day dose of LAF-237 (vildagliptin), a known DPP IV inhibitor, in aged db/db mice after 14 days of treatment and compared the combination with therapeutic dose (10 mg/kg) of rosiglitazone. The combination therapy showed similar efficacy as that of 10 mg/kg/day rosiglitazone in lowering random blood glucose (53.8%, p<0.001 and 54.3%, p<0.001 respectively), AUC ((0-120) min) during oral glucose tolerance test (OGTT) (38.6 %, p<0.01; 38.3%, p<0.01 respectively) and triglyceride levels (63.9% and 61% respectively; p<0.01). Plasma active glucagon like peptide-1 (GLP-1) and insulin levels were found to be elevated significantly (p<0.01 and p<0.05 respectively) in both LAF-237 and combination treated groups following oral glucose load. LAF-237 alone had no effect on random glucose and glucose excursion during OGTT in severely diabetic db/db mice. Interestingly, the combination treatment showed no significant increase in body weight as compared to the robust weight gain by therapeutic dose of rosiglitazone. Rosiglitazone at 10 mg/kg/day showed significant reduction (p<0.05) in haematocrit, RBC count, haemoglobin pointing towards haemodilution associated with increased mRNA expression of Na(+), K(+)-ATPase-alpha and epithelial sodium channel gamma (ENaCgamma) in kidney. The combination therapy escaped these adverse effects. The results suggest that combination of DPP IV inhibitor with low dose of thiazolidinedione can interact synergistically to represent a therapeutic advantage for the clinical treatment of type 2 diabetes without the adverse effects of haemodilution and weight gain associated with thiazolidinediones.

Fatty acid receptors as new therapeutic targets for diabetes.

G-protein-coupled receptors (GPCRs) are key regulators of several physiological functions. Their roles in cellular signal transduction have made them the target for majority of all currently prescribed drugs. Additionally, there are many orphan GPCRs that provide potential novel therapeutic targets. Several GPCRs are involved in metabolic regulation and glucose homeostasis such as GLP-1 receptor, glucagon receptor, adiponectin receptor and so on. Recently, free fatty acids (FFAs) have been demonstrated as ligands for orphan GPCRs and have been proposed to play a critical role in physiological glucose homeostasis. GPR40 and GPR120 are activated by medium and long-chain FFAs, whereas GPR41 and GPR43 can be activated by short-chain FFAs. GPR40, which is preferentially expressed in pancreatic beta-cells, mediates the majority of the effects of FFAs on insulin secretion. In this review, these findings and also critical analysis of these GPCRs as novel targets for diabetes are discussed.

Small molecule antagonists of complement receptor type 3 block adhesion and adhesion-dependent oxidative burst in human polymorphonuclear leukocytes.

The leukocyte integrin complement receptor type 3 (CR3, Mac-1, CD11b/CD18) is the predominant beta(2) integrin receptor of polymorphonuclear leukocytes (PMNs). This cell surface receptor plays a central role in innate immunity against pathogens as well as being a major cellular effector of inflammation and tissue injury. Two small molecules, compounds 1 and 2, have been identified, that interact with CR3 and prevent CR3 from binding to its natural ligand, C3bi. Compounds 1 and 2 have IC(50) values of 0.14 and 0.33 microM, respectively, for the inhibition of binding of monomeric C3bi-alkaline phosphatase to immobilized CR3. Both compounds also inhibit binding of CR3 to biotinylated sheep red blood cells opsonized with C3bi, with IC(50) values in the micromolar range. Inhibition of ligand binding by the compounds is not easily reversed and requires light, suggesting the formation of a covalent adduct through photoactivation. Compounds 1 and 2 also inhibit adhesion of human PMNs to fibrinogen in response to tumor necrosis factor (TNF) or PMA, with IC(50) values of 2.5 to >10 microM. They block the adhesion-dependent production of H(2)O(2) stimulated by TNF or phorbol 12-myristate 13-acetate (PMA) with IC(50) values of 0.2 to 0.8 microM and 1 to 3 microM, respectively. Limited structure-activity relationship studies based on compound 2 indicate the importance of the two benzothiazole rings, an ethyl side chain, and the length of the carbon chain linking the rings. Further modification of these groups may help in making compounds appropriate for in vivo studies.