A novel long acting DPP-IV inhibitor PKF-275-055 stimulates β-cell proliferation resulting in improved glucose homeostasis in diabetic rats

Integrated serum pharmacochemistry and network pharmacology analyses reveal the bioactive metabolites and potential functional mechanism of ground cherry (Physalis pruinosa L.) in treatment of type 2 diabetes mellitus in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Different Physalis plants have been widely employed in traditional medicine for management of diabetes mellitus. Previous studies with respect to the in vivo antidiabetic activity of Physalis plants illustrated that they improved glucose and lipid metabolism in streptozotocin (STZ) -induced diabetic rats yet the mechanism of action of bioactive constituents of the different organs of Physalis plants on diabetes remains obscure.

AIM OF STUDY

Our objective is to study the effects of the different organs of ground cherry (P. pruinosa) on diabetes in rat models and elucidate their mechanism of actions through serum pharmacochemistry combined to network pharmacology analyses and in-vivo testing.

MATERIALS AND METHODS

Characterization of the constituents in the drug-dosed serum samples relative to the blank serum after treatment with different extracts was performed by UPLC -MS/MS technique. The absorbed metabolites where then subjected to network pharmacology analysis to construct an interaction network linking "compound-target-pathway". In vivo verification was implemented to determine a hypothesized mechanism of action on a STZ and high fat diet induced type II diabetes mellitus (T2DM) model based on functional and enrichment analyses of the Kyoto Encyclopedia of Genes and Genome and Gene Ontology.

RESULTS

Identification of a total of 73 compounds (22 prototypes and 51 metabolites) derived from P. pruinosa extracts was achieved through comparison of the serum samples collected from diabetic control group and extracts treated groups. The identified compounds were found to belong to different classes according to their structural type including withanolides, physalins and flavonoids. The absorbed compounds in the analyzed serum samples were considered as the potential bioactive components. The component-target network was found to have 23 nodes with 17 target genes including MAPK8, CYP1A1 and CYP1B1. Quercetin and withaferin A were found to possess the highest combined score in the C-T network. Integrated serum pharmacochemistry and network pharmacology analyses revealed the enrichment of leaves extract with the active constituents, which can be utilized in T2DM treatment. In the top KEGG pathways, lipid and atherosclerosis metabolic pathways in addition to T2DM pathways were found to be highly prioritized. The diabetic rats, which received leaves extract exhibited a substantial increment in GLUT2, INSR, IRS-1, PI₃K-p85 and AKT-ser473 proteins by 105%, 142%, 109%, 81% and 73%, respectively relative to the untreated diabetic group. The immunoblotting performed for MAPK and ERK1/2 part of the inflammatory pathway studied in STZ induced diabetic rats revealed that leaves, calyces and stems extracts resulted in a substantial diminish in p38-MAPK, ERK 1/2, NF-κB, and TNF-α. Histopathological examination revealed that the hepatic histoarchitecture was substantially improved in the leaves, stems, and clayces-treated rats in comparison with untreated diabetic rats. Further, pancreatic injuries, which induced by STZ were dramatically altered by the treatment with P. pruinosa leaves, calyces and stems extracts. β-cells in diabetic rats received leaves extract disclosed moderate insulin immunostaining with a notable increase in the mean insulin area%.

CONCLUSIONS

The study in hand offers a comprehensive study to clarify the bioactive metabolites of the different organs of P. pruinosa. The basic pharmacological effects and underlying mechanism of actions in the management of STZ and high fat diet induced T2DM were specifically covered in this paper.

Implanted islet mass influences the effects of dipeptidyl peptidase-IV inhibitor LAF237 on transplantation outcomes in diabetic mice

Background

Previous studies showed inconsistent Results of the effects of dipeptidyl peptidase (DPP)-IV inhibitors on syngeneic mouse islet transplantation. We hypothesized that the implanted islet numbers are critical for the effects of DPP-IV inhibitors on the outcomes of transplantation.

Methods

One hundred and fifty or three hundred islets were syngeneically transplanted under the renal capsule of each streptozocin-diabetic C57BL/6 mouse and recipients were then treated without or with LAF237 (10 mg/kg/day, po) for 6 weeks. After transplantation, recipients’ blood glucose, body weight and intraperitoneal glucose tolerance test (IPGTT) were followed-up periodically. The graft was removed for the measurement of β-cell mass at 6 weeks.

Results

In recipients with 150 islets, it was not significantly different between the LAF237- treated group (n = 14) and control group (n = 14) in terms of the blood glucose, body weight, glucose tolerance at 2, 4 and 6 weeks or the graft β-cell mass at 6 weeks. In contrast, in recipients with 300 islets, the LAF237-treated group (n = 24) did have a lower area under the curve of the IPGTT at 4 weeks (p = 0.0237) and 6 weeks (p = 0.0113) as well as more graft β-cell mass at 6 weeks (0.655 ± 0.008 mg vs. 0.435 ± 0.006 mg, p = 0.0463) than controls (n = 24).

Conclusions

Our findings revealed 6-week treatment of LAF237 improves glucose tolerance and increases graft β-cell mass in diabetic mice transplanted with a sufficient number but not a marginal number of islets. These indicate that the effects of DPP-IV inhibitors are influenced by the implanted islet mass.

Metformin and Dipeptidyl Peptidase-4 Inhibitor Differentially Modulate the Intestinal Microbiota and Plasma Metabolome of Metabolically Dysfunctional Mice

OBJECTIVES

Recent evidence indicates that gut microbiota is altered considerably by a variety of commonly prescribed medications. This study assessed the impact of 2 antidiabetic therapeutics on gut microbiota and markers of cardiometabolic disease in metabolically dysfunctional mice.

METHODS

C57BL/6 mice were fed a high-fat diet for 24 weeks while receiving 1 of 2 antidiabetic therapeutics-metformin or dipeptidyl peptidase-4 (DPP-4) inhibitor, PKF-275-055-for the final 12 weeks. Mice were assessed for weight gain, glucose and cholesterol metabolism, and adiposity. In addition, cecal microbiota was analyzed by 16S compositional sequencing, and plasma metabolome was analyzed by liquid chromatography with tandem mass spectrometry.

RESULTS

Both therapeutics had similar metabolic effects, attenuating mesenteric adiposity and improving cholesterol metabolism and insulin sensitivity. However, multivariate analyses of microbiota and metabolomics data revealed clear divergence of the therapeutic groups. Although both metformin and PKF-275-055 mice displayed significantly decreased Firmicutes/Bacteroidetes ratios, only metformin harboured metabolic health-associated Akkermansia, Parabacteroides and Christensenella. Paradoxically, metformin also reduced α diversity, a metric frequently associated with host metabolic fitness. PKF-275-055 mice displayed elevated levels of butyrate-producing Ruminococcus and acetogen Dorea, with reduced levels of certain plasma sphingomyelin, phosphatidylcholine and lysophosphatidylcholine entities. In turn, metformin reduced levels of acylcarnitines, a functional group associated with systemic metabolic dysfunction. Finally, several associations were identified between metabolites and altered taxa.

CONCLUSIONS

This study represents the first direct comparison of the microbiota-modifying effects of metformin and a DPP-4 inhibitor, and proposes several putative microbial targets both in terms of novel therapeutic development and adverse effect prevention.

Modulatory effect of empagliflozin on cellular parameters of endocrine pancreas in experimental pre-diabetes

The effect of empagliflozin (EMPA), a sodium-glucose cotransporter 2 inhibitor (SGLT2i), on the structure of endocrine pancreas in pre-diabetes (Pre-DM) is not yet elucidated. In the current study the relatively enlarged islets of Langerhans seen in the Pre-DM group was restored to control size by administration of EMPA. In addition the disbalance in the percentage of β-cells and α-cells in islets of the Pre-DM was corrected in the Pre-DM + EMPA group with reversal of the significantly increased islet mass, β-cell mass and neogenesis. Administrating EMPA in Pre-DM decreased level of caspase-3, increased that of Bcl-2 to control level and reduced the significantly increased inflammatory cytokines to levels approximated to those of the control group. In Pre-DM + EMPA group, EMPA had efficiently restored the significantly impaired glucose hemostasis to levels nearly similar to those of the control animals. This may indicate that the modulatory effect of EMPA on cells of the islets in Pre-DM is associated with a local pleotropic effect on inflammatory cytokines.

Correlation between pancreatic mast cells and the low grade inflammation in adipose tissue of experimental prediabetes

The role of mast cells (MCs) in prediabetes (Pre-DM) is not clearly elucidated. In the current study rats (n = 22 each) were divided equally into; control and Pre-DM (received high fat diet, HFD) groups. Samples from pancreas as well as from visceral adipose tissue (VAT) were studied for the consequent changes. We detected a significantly increased mast cell count (MCC) in the pancreas of Pre-DM compared to that of control. Frequent degranulation of MC granules was observed in Pre-DM. VAT of the Pre-DM had significantly increased (p < 0.05) macrophages (CD68⁺) and mast cells (tryptase⁺) compared to that of the control. A significant increase (p < 0.05) in CD68 mRNA expression as well as in the level of IL-1 β, IL-6, TNF-α and TGF- β1 was detected in VAT of Pre-DM with a significant positive correlation (p < 0.05) with the MCC. All these findings may indicate a potential role of MC in the low grade inflammation of VAT in Pre-DM.

The Effects of Sinapic Acid on the Development of Metabolic Disorders Induced by Estrogen Deficiency in Rats

Sinapic acid is a natural phenolic acid found in fruits, vegetables, and cereals, exerting numerous pharmacological effects. The aim of the study was to investigate the influence of sinapic acid on biochemical parameters related to glucose and lipid metabolism, as well as markers of antioxidant abilities and parameters of oxidative damage in the blood serum in estrogen-deficient rats. The study was performed on 3-month-old female Wistar rats, divided into 5 groups, including sham-operated control rats, ovariectomized control rats, and ovariectomized rats administered orally with estradiol (0.2 mg/kg) or sinapic acid (5 and 25 mg/kg) for 28 days. The levels of estradiol, progesterone, interleukin 18, insulin, glucose, fructosamine, lipids, and enzymatic and nonenzymatic antioxidants (superoxide dismutase, catalase, and glutathione); total antioxidant capacity; and oxidative damage parameters (thiobarbituric acid-reactive substances, protein carbonyl groups, and advanced oxidation protein products) were determined in the serum. Estradiol counteracted the carbohydrate and cholesterol metabolism disorders induced by estrogen deficiency. Sinapic acid increased the serum estradiol concentration; decreased insulin resistance and the triglyceride and total cholesterol concentrations; and favorably affected the parameters of antioxidant abilities (reduced glutathione, superoxide dismutase) and oxidative damage (advanced oxidation protein products).

SVMDLF: A novel R-based Web application for prediction of dipeptidyl peptidase 4 inhibitors

Dipeptidyl peptidase 4 (DPP4) is a well-known target for the antidiabetic drugs. However, currently available DPP4 inhibitor screening assays are costly and labor-intensive. It is important to create a robust in silico method to predict the activity of DPP4 inhibitor for the new lead finding. Here, we introduce an R-based Web application SVMDLF (SVM-based DPP4 Lead Finder) to predict the inhibitor of DPP4, based on support vector machine (SVM) model, predictions of which are confirmed by in vitro biological evaluation. The best model generated by MACCS structure fingerprint gave the Matthews correlation coefficient of 0.87 for the test set and 0.883 for the external test set. We screened Maybridge database consisting approximately 53,000 compounds. For further bioactivity assay, six compounds were shortlisted, and of six hits, three compounds showed significant DPP4 inhibitory activities with IC₅₀ values ranging from 8.01 to 10.73 μm. This application is an OpenCPU server app which is a novel single-page R-based Web application for the DPP4 inhibitor prediction. The SVMDLF is freely available and open to all users at http://svmdlf.net/ocpu/library/dlfsvm/www/ and http://www.cdri.res.in/svmdlf/.

DPP-4 inhibitors in diabetic complications: role of DPP-4 beyond glucose control

Dipeptidyl peptidase-4 (DPP-4) inhibitors (gliptins) are an emerging class of antidiabetic drugs that constitutes approximately fifty percent of the market share of the oral hypoglycemic drugs. Its mechanism of action for lowering blood glucose is essentially via inhibition of the rapid degradation of incretin hormones, such as glucagon-like peptide (GLP)-1 and gastric inhibitory polypeptide (GIP), thus the plasma concentration of GLP-1 increases, which promotes insulin secretion from the pancreatic β cells and suppresses glucagon secretion from the α cells. In addition to the direct actions on the pancreas, GLP-1 exhibits diverse actions on different tissues through its action on GLP-1 receptor, which is expressed ubiquitously. Moreover, DPP-4 has multiple substrates besides GLP-1 and GIP, including cytokines, chemokines, neuropeptides, and growth factors, which are involved in many pathophysiological conditions. Recently, it was suggested that DPP-4 is a new adipokine secreted from the adipose tissue, which plays an important role in the regulation of the endocrine function in obesity-associated type 2 diabetes. Consequently, DPP-4 inhibitors have been reported to exhibit cytoprotective functions against various diabetic complications affecting the liver, heart, kidneys, retina, and neurons. This review outlines the current understanding of the effect of DPP-4 inhibitors on the complications associated with type 2 diabetes, such as liver steatosis and inflammation, dysfunction of the adipose tissue and pancreas, cardiovascular diseases, nephropathy, and neuropathy in preclinical and clinical studies.

Favorable outcomes of hydroxychloroquine in insulin resistance may be accomplished by adjustment of the endothelial dysfunction as well as the skewed balance of adipokines

Hydroxychloroquine (HCQ) has been demonstrated to reduce the risk to develop diabetes mellitus (DM). However no previous experimental study had investigated its effect on the structure of the endocrine pancreas, islets of Langerhans (IOL), in insulin resistance (IR). In addition, the mechanism by which HCQ can prevent DM is not well understood. In this study, we hypothesized that the possible favorable outcome of HCQ may be partly achieved by its molecular effect on the endothelial stress markers as well as on the imparied balance of the adipokines that usually accompanies IR. A total of 54 rats were divided equally into; control, high fat diet (HFD) and HFD+HCQ groups (received standard chow, HFD and HFD+HCQ respectively). After 12 weeks, samples from pancreas as well as visceral adipose tissue (VAT) were histologically studied for the consequent changes. In the HFD group, there were mild degenerative changes and expansion of the IOL accompanied with a significantly increased (p<0.05) β-cell area%, mass, proliferation and neogenesis as well as a significantly decreased (p<0.05) α-cell area% compared with the other groups. On combining HCQ with HFD, reversal of these changes along with correction of the impaired adipokines levels (leptin, adiponectin, resistin, visfatin and lipocalin-2) and significant decrease (p<0.05) of the vascular endothelial stress markers (sE-selectin, sICAM and sVICAM) were manifested compared with the HFD group. Therefore, HCQ favorable effects in IR may be attributed to relieving of the endothelial stress as well as normalization of the skewed balance of adipokines.

Hydroxychloroquine hindering of diabetic isletopathy carries its signature on the inflammatory cytokines

Hydroxychloroquine (HCQ) is supposed to have favorable effects in diabetes mellitus (DM). However no previous experimental studies had investigated its effect on the structure of the endocrine pancreas, islets of Langerhans (IOL), in DM. In addition, the mechanism by which HCQ acts in DM is not well understood. In this study, we hypothesized that the possible favorable effects of HCQ in DM at the structural as well as at metabolic levels could be accomplished, in part, by its anti-inflammatory action. A total of 45 rats were divided equally into; control, DM and HCQ + DM groups (received citrate buffer, 27.5 mg/kg single ip STZ and STZ + HCQ 200 mg/kg/w respectively). After 4 weeks, samples from pancreas were histologically studied for the resulting changes. The HCQ + DM group showed preservation of IOL structure, a significant increase (p < 0.05) in the β-cell area, %, mass, IOL proliferation and neogenesis as well as correction of the significantly increased (p < 0.05) α-cell area, %, disturbed glucose homeostasis and lipid profile compared with the DM group. The significantly elevated inflammatory cytokines in the latter were lowered in the HCQ + DM group. Therefore, HCQ showed definite favorable effects on the histological as well as the metabolic profiles in DM which may be partly attributed to its anti-inflammatory action. This notable improvement of DM by HCQ deserves further studies to distinctly approve HCQ as a promising oral hypoglycemic agent.

Antidiabetic Effect of Galantamine: Novel Effect for a Known Centrally Acting Drug

The cholinergic anti-inflammatory pathway is one of the putative biochemical pathways that link diabetes with Alzheimer disease. Hence, we aimed to verify the potential antidiabetic effect of galantamine, unveil the possible mechanisms and evaluate its interaction with vildagliptin. The n5-STZ rat model was adopted and the diabetic animals were treated with galantamine and/or vildagliptin for 4 weeks. Galantamine lowered the n5-STZ-induced elevation in body weight, food/water intake, serum levels of glucose, fructosamine, and ALT/AST, as well as AChE in the tested organs. Moreover, it modulated successfully the lipid profile assessed in serum, liver, and muscle, and increased serum insulin level, as well as % β-cell function, in a pattern similar to that of vildagliptin. Additionally, galantamine confirmed its antioxidant (Nrf2, TAC, MDA), anti-inflammatory (NF-κB, TNF-α, visfatin, adiponectin) and anti-apoptotic (caspase-3, cytochrome c) capabilities by altering the n5-STZ effect on all the aforementioned parameters. On the molecular level, galantamine/vildagliptin have improved the insulin (p-insulin receptor, p-Akt, GLUT4/GLUT2) and Wnt/β-catenin (p-GSK-3β, β-catenin) signaling pathways. On almost all parameters, the galantamine effects surpassed that of vildagliptin, while the combination regimen showed the best effects. The present results clearly proved that galantamine modulated glucose/lipid profile possibly through its anti-oxidant, -apoptotic, -inflammatory and -cholinesterase properties. These effects could be attributed partly to the enhancement of insulin and Wnt/β-catenin signaling pathways. Galantamine can be strongly considered as a potential antidiabetic agent and as an add-on therapy with other oral antidiabetics.

Sitagliptin alleviated myocardial remodeling of the left ventricle and improved cardiac diastolic dysfunction in diabetic rats

OBJECTIVE

Sitagliptin, a dipeptidyl peptidase IV (DPP-Ⅳ) inhibitor, has a biological role in improving the serum levels of glucagon-like peptide 1 (GLP-1). Hence, we sought to determine the effect of sitagliptin on myocardial inflammation, collagen metabolism, lipid content and myocardial apoptosis in diabetic rats.

MATERIALS AND METHODS

The type 2 diabetic rat model was induced by low-dose streptozotocin and a high-fat diet. Characteristics of diabetic rats were evaluated by electrocardiography, echocardiography and blood analysis. Cardiac inflammation, fibrosis, cardiomyocyte density, lipid accumulation, and receptor-interacting protein kinase 3 (RIP3) level, related to apoptosis, were detected by histopathologic analysis, RT-PCR and western blot analysis to evaluate the effects of sitagliptin on myocardial remodeling of the left ventricle.

RESULTS

Diabetic rats showed myocardial hypertrophy or apoptosis, inflammation, lipid accumulation, myocardial fibrosis, elevated collagen content, RIP3 overexpression, and left-ventricular dysfunction. Sitagliptin could reverse the overexpression of RIP3 and alleviate cellular apoptosis in myocardial tissues. It could significantly improve left-ventricular systolic pressure and +dp/dt max, reduce the E/E' ratio, left ventricular end diastolic pressure, -dp/dt max and Tau in diabetic rats.

CONCLUSIONS

Sitagliptin might have a myocardial protective effect by inhibiting apoptosis, inflammation, lipid accumulation and myocardial fibrosis in diabetic rats, for a potential role in improving left-ventricular function in diabetes.

Crosstalk between advanced glycation end products (AGEs)-receptor RAGE axis and dipeptidyl peptidase-4-incretin system in diabetic vascular complications

Advanced glycation end products (AGEs) consist of heterogenous group of macroprotein derivatives, which are formed by non-enzymatic reaction between reducing sugars and amino groups of proteins, lipids and nucleic acids, and whose process has progressed at an accelerated rate under diabetes. Non-enzymatic glycation and cross-linking of protein alter its structural integrity and function, contributing to the aging of macromolecules. Furthermore, engagement of receptor for AGEs (RAGE) with AGEs elicits oxidative stress generation and subsequently evokes proliferative, inflammatory, and fibrotic reactions in a variety of cells. Indeed, accumulating evidence has suggested the active involvement of accumulation of AGEs in diabetes-associated disorders such as diabetic microangiopathy, atherosclerotic cardiovascular diseases, Alzheimer's disease and osteoporosis. Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are incretins, gut hormones secreted from the intestine in response to food intake, both of which augment glucose-induced insulin release, suppress glucagon secretion, and slow gastric emptying. Since GLP-1 and GIP are rapidly degraded and inactivated by dipeptidyl peptidase-4 (DPP-4), inhibition of DPP-4 and/or DPP-4-resistant GLP-1 analogues have been proposed as a potential target for the treatment of diabetes. Recently, DPP-4 has been shown to cleave multiple peptides, and blockade of DPP-4 could exert diverse biological actions in GLP-1- or GIP-independent manner. This article summarizes the crosstalk between AGEs-RAGE axis and DPP-4-incretin system in the development and progression of diabetes-associated disorders and its therapeutic intervention, especially focusing on diabetic vascular complications.

L-arginine and tetrahydrobiopterin, but not sodium nitrite partially restored erectile dysfunction in aged rats

Aging is associated with erectile dysfunction (ED), in which nitric oxide synthase (NOS) activity and NO bioavailability are reduced due to deficiencies of NOS cofactor (tetrahydrobiopterin, BH(4)) and substrate (L-arginine). We determined whether the prolonged treatment with sodium nitrite (NaNO(2)) as a storage form of NO ameliorates ED in aged rats. Male Sprague-Dawley rats were divided: younger, aged and NaNO(2)-treated (20 mg/kg per day) aged groups. The erectile (intracavernosal pressure [ICP]/mean arterial pressure [MAP]) and corpus cavernous (CC) responses were evaluated after 12 weeks. The ICP/MAP in aged rats was lower than in young controls, which was not improved by the NaNO(2) treatment. Immunohistochemical (IHC) staining for endothelial NOS and collagen deposition was performed. We assayed NO indirectly by measuring the level of its stable end products, nitrite/nitrate, using the Griess reagent. The relaxations to ACh and EFS in the aged group were considerably less than in the younger group, which were normalized by acute incubations of l-arginine or BH(4) of aged CC. In conclusion, NaNO(2) treatment did not restore erectile response while nitrate levels were enhanced in aged penis. The cofactor or substrate administrations, but not chronic exogenous modulation of NO system may be beneficial in aged men with ED.

Discovery of 2-Pyridylpyrimidines as the First Orally Bioavailable GPR39 Agonists

The identification of highly potent and orally bioavailable GPR39 agonists is reported. Compound 1, found in a phenotypic screening campaign, was transformed into compound 2 with good activity on both the rat and human GPR39 receptor. This compound was further optimized to improve ligand efficiency and pharmacokinetic properties to yield GPR39 agonists for the potential oral treatment of type 2 diabetes. Thus, compound 3 is the first potent GPR39 agonist (EC50s ≤ 1 nM for human and rat receptor) that is orally bioavailable in mice and robustly induced acute GLP-1 levels.

Effects of Dipeptidyl Peptidase-4 Inhibition with MK-0431 on Syngeneic Mouse Islet Transplantation

Dipeptidyl peptidase (DPP)-4 inhibitors increase circulating levels of glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide which may promote β-cell proliferation and survival. This study tested if DPP-4 inhibition with MK-0431 is beneficial for diabetic mice syngeneically transplanted with a marginal number of islets. We syngeneically transplanted 150 C57BL/6 mouse islets under the kidney capsule of each streptozotocin-diabetic mouse and then treated recipients with (n = 21) or without (n = 17) MK-0431 (30 mg/kg/day, po) for 6 weeks. After islet transplantation, blood glucose levels decreased in both MK-0431-treated and control groups. However, the blood glucose and area under the curve of the intraperitoneal glucose tolerance test at 2, 4, and 6 weeks were not significantly different between MK-0431-treated mice and controls. During 6 weeks, both groups exhibited increased body weights over time. However, the weight between two groups did not differ throughout the study period. At 6 weeks after transplantation, the graft beta-cell mass (0.024 ± 0.005 versus 0.023 ± 0.007 mg, P = 0.8793) and insulin content (140 ± 48 versus 231 ± 63 ng, P = 0.2939) were comparable in the MK-0431-treated group and controls. Our results indicate posttransplant DPP-4 inhibition with MK-0431 in the diabetic recipient with a marginal number of islets is not beneficial to transplantation outcome or islet grafts.

Linagliptin as add-on therapy to insulin for patients with type 2 diabetes

Type 2 diabetes mellitus (T2DM) is a highly prevalent, progressive disease that often is poorly controlled. The combination of an incretin-based therapy and insulin is a promising approach to optimize the management of glycemic control without hypoglycemia and weight gain. Linagliptin, a recently approved oral dipeptidyl peptidase-4 inhibitor, has a unique pharmacological profile. The convenient, once-daily dosing does not need adjustment in patients with hepatic and/or renal impairment. In clinical studies linagliptin shows an important reduction of blood glucose with an overall safety profile similar to that of placebo. So far, the combination of linagliptin and insulin has been tested in three major clinical studies in different populations. It has been shown that linagliptin is an effective and safe add-on therapy to insulin in patients with T2DM. The efficacy and safety of this combination was also shown in vulnerable, elderly T2DM patients and in patients with T2DM and renal impairment. Favorable effects regarding the counteraction of hypoglycemia make linagliptin especially interesting as an add-on therapy to insulin. This review aims to present the existing clinical studies on the efficacy and safety of linagliptin as add-on therapy to insulin in patients with T2DM in the context of current literature. Additionally, the possible advantages of linagliptin as an add-on therapy to insulin in relation to cardiovascular safety, patient-centered therapy and the prevention of hypoglycemia, are discussed.

Dipeptidyl peptidase IV and its inhibitors: therapeutics for type 2 diabetes and what else?

The proline-specific dipeptidyl aminopeptidase IV (DPP IV, DPP-4, CD26), widely expressed in mammalians, releases X-Pro/Ala dipeptides from the N-terminus of peptides. DPP IV is responsible of the degradation of the incretin peptide hormones regulating blood glucose levels. Several families of DPP IV inhibitors have been synthesized and evaluated. Their positive effects on the degradation of the incretins and the control of blood glucose levels have been demonstrated in biological models and in clinical trials. Presently, several DPP IV inhibitors, the "gliptins", are approved for type 2 diabetes or are under clinical evaluation. However, the gliptins may also be of therapeutic interest for other diseases beyond the inhibition of incretin degradation. In this Perspective, the biological functions and potential substrates of DPP IV enzymes are reviewed and the characteristics of the DPP IV inhibitors are discussed in view of type 2 diabetes and further therapeutic interest.

Oral L-glutamine increases active GLP-1 (7-36) amide secretion and improves glycemic control in stretpozotocin-nicotinamide induced diabetic rats

L-glutamine is a non-essential amino acid. It decreased blood sugar, stimulated insulin secretion in type 2 diabetic patients. The objective of the present investigation was to evaluate L-glutamine increases glucagon like peptide-1 (GLP-1) (7-36) amide secretion in streptozotocin-nicotinamide (STZ-NTM) induced diabetic Sprague Dawley rats. Molecular docking study was performed to elucidate the molecular basis for GLP-1 receptor agonistic activity. Type 2 diabetes was induced in overnight fasted Sprague Dawley rats pre-treated with nicotinamide (100 mg/kg, i.p.) followed by 20 min after administration of streptozotocin (55 mg/kg, i.p.). The rats were divided into; I - nondiabetic, II - diabetic control, III - sitagliptin (5 mg/kg, p.o.), IV - L-glutamine (250 mg/kg, p.o.), V - L-glutamine (500 mg/kg, p.o.) and VI - L-glutamine (1000 mg/kg, p.o.). The L-glutamine and sitagliptin treatment was 8 week. Plasma glucose was estimated every week. Body weight, food and water intake were recorded daily. Glycosylated haemoglobin, lipid profile, plasma and colonic active (GLP-1) (7-36) amide, mRNA expression of proglucagon GLP-1, plasma and pancreatic insulin, histology of pancreata and biomarkers of oxidative stress (superoxidase dismutase, reduced glutathione, malondialdehyde, glutathione peroxidase, glutathione S transferase) were measured after 8 week. In acute study, the rats were divided into I - glucose (2.5 g/kg, p.o.), II - sitagliptin (5 mg/kg, p.o.), III - L-glutamine (250 mg/kg, p.o.), IV - L-glutamine (500 mg/kg, p.o.) and V - L-glutamine (1000 mg/kg, p.o.). Plasma glucose, active GLP-1 (7-36) amide concentration and insulin levels were measured after glucose loading. The docking data indicated that l-glutamine bind to the GLP-1 receptor. L-glutamine decreased plasma glucose, increased plasma and pancreatic insulin, increased plasma and colonic active GLP-1 (7-36) amide secretion as well as decreased oxidative stress in streptozotocin-nicotinamide induced diabetic rats.

Acute assessment of an aspalathin-enriched green rooibos (Aspalathus linearis) extract with hypoglycemic potential

Rooibos, an endemic South African plant, known for its use as herbal tea, has potential as an antidiabetic herbal product, following recent demonstration of the glucose lowering effect of its major flavonoid, the dihydrochalcone C-glucoside aspalathin. The purpose of this study was to confirm antidiabetic activity for rooibos extract high in aspalathin content. An extract (SB1) was selected after screening for high aspalathin content and α-glucosidase inhibition activity. On-line HPLC-biochemical detection confirmed α-glucosidase inhibitory activity for aspalathin. In vitro the extract induced a dose response increase in glucose uptake (5 × 10⁻⁵ to 5 μg/ml) on C2C12 myotubules. Aspalathin was effective at 1, 10 and 100 μM, while rutin was effective at 100 μM. In the Chang cells only the extract was effective. In vivo the extract sustained a glucose lowering effect comparable to metformin over a 6h period after administration (25mg/kg body weight (BW)) to STZ-induced diabetic rats. In an oral glucose tolerance test the extract (30 mg/kg BW) was more effective than vildagliptin (10mg/kg BW), a dipeptidyl peptidase-4 inhibitor. An aspalathin-rutin mixture (1:1; m/m) dosed at 1.4 mg/kg BW, but not the single compounds separately, reduced blood glucose concentrations of STZ-induced diabetic rats over a 6h monitoring period. The improved hypoglycemic activity of the aspalathin-rutin mixture and the extract illustrated synergistic interactions of polyphenols in complex mixtures.

Chronic DPP-IV inhibition with PKF-275-055 attenuates inflammation and improves gene expressions responsible for insulin secretion in streptozotocin induced diabetic rats

Inhibitors of dipeptidyl peptidase-4 (DPP-IV), a key regulator of the actions of incretin hormones, exert antihyperglycemic effects in type 2 diabetic patients. A major question concerns the potential ability of long term DPP-IV inhibition to have beneficial disease-modifying effects, specifically to attenuate loss of pancreatic β-cell mass due to oxidative stress induced inflammation. Here, we investigated the effects of a potent and selective DPP-4 inhibitor, an analog of vildagliptin (PKF-275-055), on glycemic control, pancreatic β-cell mass, genes and proteins expressions, tumor necrosis factor-alpha, and nitric oxide in an n2-STZ diabetic model of rat with defects in insulin sensitivity and secretion. To induce NIDDM, streptozotocin (STZ) 90 mg/kg was administered i.p. to a group of 2 days old pups. Diabetic rats were administered orally with vildagliptin analog PKF-275-055. Saline treated animals served as diabetic control. Significant and dose-dependent correction of postprandial hyperglycemia was observed in diabetic rats following 8 weeks of chronic therapy. Treatment with PKF-275-055 showed increased the number of insulin-positive β-cells in islets and improved the expressions of genes and proteins are responsible for insulin secretions. In addition, treatment of rats with PKF-275-055 significantly increased insulin content, glycogen content and total proteins content; and decreased the inflammatory markers i.e. nitric oxide and TNF-alpha. The present studies indicate that PKF-275-055 is a novel selective DPP-IV inhibitor having potential to reduce inflammation that might be a potential agent for type 2 diabetes.

Vildagliptin selectively ameliorates GLP-1, GLUT4, SREBP-1c mRNA levels and stimulates β-cell proliferation resulting in improved glucose homeostasis in rats with streptozotocin-induced diabetes

OBJECTIVE

Inhibitors of dipeptidyl peptidase-4 (DPP-4), a key regulator of the actions of incretin hormones, exert antihyperglycemic effects in type 2 diabetic patients. A major unanswered question concerns the potential ability of DPP-4 inhibition to have beneficial disease-modifying effects, specifically to attenuate loss of pancreatic β-cell mass and function due to oxidative stress induced inflammation. Here, we investigated the effects of a potent and selective DPP-4 inhibitor vildagliptin on glycemic control, pancreatic β-cell mass and function, genes and proteins expressions, tumor necrosis factor-alpha, and nitric oxide in an n2-STZ diabetic model of rat with defects in insulin sensitivity and secretion.

METHOD

To induce NIDDM, STZ (sigma chemicals, USA) (90 mg/kg) was administered i.p. to a group of 2 days old pups. Another group of pups received only saline. The pups were weaned for 21 days, and 6 weeks after the injection of STZ, the animals were checked for fasting glucose level (FPG) ≥160 mg/dl were considered as diabetic.

RESULTS

Significant and dose-dependent correction of postprandial and fasting hyperglycemia was observed in diabetic rats following 8 weeks of chronic therapy. Treatment with vildagliptin showed increase in the number of insulin-positive β-cells in islets and improved the expressions of genes and proteins are responsible for insulin secretions. In addition, treatment of rats with vildagliptin significantly increased insulin content; and decreased the nitric oxide and TNF-alpha concentration.

CONCLUSION

These findings suggest that DPP-4 inhibitors may offer long-lasting efficacy in the treatment of diabetes mellitus by modifying the courses of the disease.