Dipeptidyl-peptidase IV from bench to bedside: an update on structural properties, functions, and clinical aspects of the enzyme DPP IV

A de novo 2.3 Mb deletion in 2q24.2q24.3 in a 20-month-old developmentally delayed girl

We report a 20-month-old girl ascertained at the age of 11 months for developmental delay. She presented with hypotonia and delayed motor development. The patient had severe language impairment and showed behaviour consistent with autism spectrum disorder. She was microcephalic with mild dysmorphic features and had joint hyperlaxity. We detected a 2.3 Mb de novo deletion in 2q24.2q24.3 on her paternal chromosome. We compare the clinical features of our patient to six previously published patients with a deletion in 2q24.2q24.3, and one patient reported in the ECARUCA database. Although the clinical presentation of these patients is not highly consistent, likely due to the different deletion size and gene content, the following features seem to be recurrent: disturbance in the central nervous system, poor growth, hypotonia, and joint hyperlaxity. The region deleted in our patient contains 13 genes including PSMD14, TBR1, SLC4A10, DPP4, KCNH7, and FIGN. We briefly review the knowledge of these genes and their possible involvement in the aetiology of this developmental delay syndrome.

Design, synthesis and biological evaluation of hetero-aromatic moieties substituted pyrrole-2-carbonitrile derivatives as dipeptidyl peptidase IV inhibitors

A series of novel hetero-aromatic moieties substituted α-amino pyrrole-2-carbonitrile derivatives was designed and synthesized based on structure-activity relationships (SARs) of pyrrole-2-carbonitrile inhibitors. All compounds demonstrated good dipeptidyl peptidase IV (DPP4) inhibitory activities (IC50 = 0.004-113.6 μM). Moreover, compounds 6h (IC50 = 0.004 μM) and 6n (IC50 = 0.01 μM) showed excellent inhibitory activities against DPP4, good selectivity (compound 6h, selective ratio: DPP8/DPP4 = 450.0; DPP9/DPP4 = 375.0; compound 6n, selective ratio: DPP8/DPP4 = 470.0; DPP9/DPP4 = 750.0) and good efficacy in an oral glucose tolerance test in ICR mice. Furthermore, compounds 6h and 6n demonstrated moderate PK properties (compound 6h, F% = 37.8%, t1/2 = 1.45 h; compound 6n, F% = 16.8%, t1/2 = 3.64 h).

Novel N-substituted aminobenzamide scaffold derivatives targeting the dipeptidyl peptidase-IV enzyme

Background

The dipeptidyl peptidase-IV (DPP-IV) enzyme is considered a pivotal target for controlling normal blood sugar levels in the body. Incretins secreted in response to ingestion of meals enhance insulin release to the blood, and DPP-IV inactivates these incretins within a short period and stops their action. Inhibition of this enzyme escalates the action of incretins and induces more insulin to achieve better glucose control in diabetic patients. Thus, inhibition of this enzyme will lead to better control of blood sugar levels.

Methods

In this study, computer-aided drug design was used to help establish a novel N-substituted aminobenzamide scaffold as a potential inhibitor of DPP-IV. CDOCKER software available from Discovery Studio 3.5 was used to evaluate a series of designed compounds and assess their mode of binding to the active site of the DPP-IV enzyme. The designed compounds were synthesized and tested against a DPP-IV enzyme kit provided by Enzo Life Sciences. The synthesized compounds were characterized using proton and carbon nuclear magnetic resonance, mass spectrometry, infrared spectroscopy, and determination of melting point.

Results

Sixty-nine novel compounds having an N-aminobenzamide scaffold were prepared, with full characterization. Ten of these compounds showed more in vitro activity against DPP-IV than the reference compounds, with the most active compounds scoring 38% activity at 100 μM concentration.

Conclusion

The N-aminobenzamide scaffold was shown in this study to be a valid scaffold for inhibiting the DPP-IV enzyme. Continuing work could unravel more active compounds possessing the same scaffold.

Recent approaches to medicinal chemistry and therapeutic potential of dipeptidyl peptidase-4 (DPP-4) inhibitors

Dipeptidyl peptidase-4 (DPP-4) is one of the widely explored novel targets for Type 2 diabetes mellitus (T2DM) currently. Research has been focused on the strategy to preserve the endogenous glucagon like peptide (GLP)-1 activity by inhibiting the DPP-4 action. The DPP-4 inhibitors are weight neutral, well tolerated and give better glycaemic control over a longer duration of time compared to existing conventional therapies. The journey of DPP-4 inhibitors in the market started from the launch of sitagliptin in 2006 to latest drug teneligliptin in 2012. This review is mainly focusing on the recent medicinal aspects and advancements in the designing of DPP-4 inhibitors with the therapeutic potential of DPP-4 as a target to convey more clarity in the diffused data.

Peptidomics analysis of human blood specimens for biomarker discovery

This review addresses the concepts, limitations and perspectives for the application of peptidomics science and technologies to discover putative biomarkers in blood specimens. Peptidomics can be defined as the comprehensive multiplex analysis of endogenous peptides contained within a biological sample under defined conditions to describe the multitude of native peptides in a biological compartment. In addition to the discovery of disease associated biomarkers, an emerging field in peptidomics is the analysis of peptides to describe in vivo effects of protease inhibitors. The development and application of peptidomics technologies represent an arena of biomarker research that has the potential for adding significant clinical value.

Peptides in body fluids and tissues as markers of disease

The general awareness of the importance of peptides in physiology and pathophysiology has increased strongly over the last few years. With worldwide progress in the analysis of whole genomes, the knowledge base in gene sequence and expression data useful for protein and peptide analysis has drastically increased. The medical need for relevant biomarkers is enormous. This is particularly true for the many types of cancer, but other diseases such as Type 2 diabetes also lack useful and adequate diagnostic markers with high specificity and sensitivity. Despite advances in imaging technologies for early detection of diseases, proteomic and peptidomic multiplex techniques have evolved in recent years. This review focuses on the application of peptidomics technologies to peptides in health and disease. Peptidomics technologies provide new opportunities for the detection of low-molecular-weight proteome biomarkers (peptides) by mass spectrometry. Improvements in peptidomics research are based on separation of peptides and/or proteins by their physicochemical properties in combination with mass spectrometric detection, identification and sophisticated bioinformatics tools for data analysis. Therefore, peptidomics technologies offer an opportunity to discover novel biomarkers for diagnosis and management of disease (e.g., prognosis, treatment decision and monitoring response to therapy).

Heart-protective effect of n-3 PUFA demonstrated in a rat model of diabetic cardiomyopathy

This study was designed to examine in vivo functional changes of the heart in the early stages of streptozotocin (STZ)-induced diabetic cardiomyopathy and to evaluate the effects of n-3 PUFA intake. Moreover, we investigated whether modulation of diabetes-related abnormalities of myocardial connexin-43 (Cx43), β-myosin heavy chain (β-MHC), and β1-adrenergic receptors (β1-AR) might be implicated in the cardioprotective mechanism of n-3 PUFA. Our results showed significantly reduced cardiac output and ejection fraction (using the microtip pressure-volume catheter technique) as well as stroke volume and stroke work, 4 weeks after STZ-induced diabetes, with improvement of these parameters due to n-3 PUFA consumption. Myocardial expression of Cx43 mRNA estimated by real-time polymerase chain reaction did not change in diabetic rats regardless of n-3 PUFA consumption (100 mg/100 g b.w./day). In contrast, the total and functional phosphorylated form of Cx43 protein increased significantly, and its cardiomyocyte-related distribution was disordered in the diabetic heart, but these changes normalized because of n-3 PUFA intake. Furthermore, acute diabetes was accompanied by decrease of myocardial β1-AR mRNA expression and mild yet nonsignificant increase of β-MHC mRNA. These alterations were not significantly affected by n-3 PUFA. In conclusion, the results point out that STZ-diabetic rats benefit from n-3 PUFA consumption particularly because of the attenuation of myocardial Cx43 abnormalities that most likely contributes to improvement of cardiac function.

In-vitro renal epithelial cell infection reveals a viral kidney tropism as a potential mechanism for acute renal failure during Middle East Respiratory Syndrome (MERS) Coronavirus infection

BACKGROUND

The Middle East Respiratory Syndrome Coronavirus (MERS-CoV) causes symptoms similar to Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV), yet involving an additional component of acute renal failure (ARF) according to several published case reports. Impairment of the kidney is not typically seen in Coronavirus infections. The role of kidney infection in MERS is not understood.

FINDINGS

A systematic review of communicated and peer-reviewed case reports revealed differences in descriptions of kidney involvement in MERS versus SARS patients. In particular, ARF in MERS patients occurred considerably earlier after a median time to onset of 11 days (SD ±2,0 days) as opposed to 20 days for SARS, according to the literature. In-situ histological staining of the respective cellular receptors for MERS- and SARS-Coronavirus showed highly similar staining patterns with a focus of a receptor-specific signal in kidney epithelial cells. Comparative infection experiments with SARS- and MERS-CoV in primary human kidney cells versus primary human bronchial epithelial cells showed cytopathogenic infection only in kidney cells, and only if infected with MERS-CoV. Kidney epithelial cells produced almost 1000-fold more infectious MERS-CoV progeny than bronchial epithelial cells, while only a small difference was seen between cell types when infected with SARS-CoV.

CONCLUSION

Epidemiological studies should analyze kidney impairment and its characteristics in MERS-CoV. Virus replication in the kidney with potential shedding in urine might constitute a way of transmission, and could explain untraceable transmission chains leading to new cases. Individual patients might benefit from early induction of renoprotective treatment.

The receptor binding domain of MERS-CoV: the dawn of vaccine and treatment development

The newly emerged Middle East respiratory syndrome coronavirus (MERS-CoV) is becoming another “SARS-like” threat to the world. It has an extremely high death rate (∼50%) as there is no vaccine or efficient therapeutics. The identification of the structures of both the MERS-CoV receptor binding domain (RBD) and its complex with dipeptidyl peptidase 4 (DPP4), raises the hope of alleviating this currently severe situation. In this review, we examined the molecular basis of the RBD-receptor interaction to outline why/how could we use MERS-CoV RBD to develop vaccines and antiviral drugs.

The novel dipeptidyl peptidase-4 inhibitor teneligliptin prevents high-fat diet-induced obesity accompanied with increased energy expenditure in mice

Dipeptidyl peptidase-4 (DPP-4)-deficient mice exhibit prevention of obesity with increased energy expenditure, whereas currently available DPP-4 inhibitors do not induce similar changes. We investigated the impact of the novel DPP-4 inhibitor teneligliptin on body weight, energy expenditure, and obesity-related manifestations in diet-induced obese mice. Six-weeks-old C57BL/6N mice were fed a high-fat diet (60%kcal fat) ad libitum and administered teneligliptin (30 or 60mg/kg) via drinking water for 10 weeks. Mice fed a high-fat diet showed accelerated body weight gain. In contrast, compared with the vehicle group, the administration of teneligliptin reduced body weight to 88% and 71% at dose of 30mg/kg/day and 60mg/kg/day, respectively. Although there was no change in locomotor activity, indirect calorimetry studies showed that teneligliptin (60mg/kg) increased oxygen consumption by 22%. Adipocyte hypertrophy and hepatic steatosis induced by a high-fat diet were suppressed by teneligliptin. The mean adipocyte size in the 60-mg/kg treatment group was 44% and hepatic triglyceride levels were 34% of the levels in the vehicle group. Furthermore, treatment with teneligliptin (60mg/kg) reduced plasma levels of insulin to 40% and increased the glucose infusion rate to 39%, as measured in the euglycemic clamp study, indicating its beneficial effect on insulin resistance. We showed for the first time that the DPP-4 inhibitor prevents obesity and obesity-related manifestations with increased energy expenditure. Our findings suggest the potential utility of teneligliptin for the treatment of a broad spectrum of metabolic disorders related to obesity beyond glycemic control.

Effects of short-term sitagliptin treatment on immune parameters in healthy individuals, a randomized placebo-controlled study

Sitagliptin, a dipeptidyl-peptidase 4 (DPP-4) inhibitor, improves blood glucose control in patients with type 2 diabetes by blocking cleavage of glucagon-like peptide 1 (GLP-1). In type 2 diabetes patients sitagliptin use is associated with an increase in minor infections, and in new-onset type 1 diabetes patients the ability of sitagliptin to dampen autoimmunity is currently being tested. DPP-4, also known as CD26, is expressed on leucocytes and can inactivate many chemokines important for leucocyte migration, as well as act as a co-stimulatory molecule on T cells. Therefore, this study was conducted to test whether sitagliptin is immunomodulatory. In this randomized, placebo-controlled trial, healthy volunteers were given sitagliptin or placebo daily for 28 days, and blood was drawn for immune assays. No significant differences were observed in the percentage of leucocyte subsets within peripheral blood mononuclear cells (PBMCs), plasma chemokine/cytokine levels or cytokines released by stimulation of PBMCs with either lipopolysaccharide (LPS) or anti-CD3. Individuals taking sitagliptin displayed increases in the percentage of cells expressing higher levels of CD26 at early time-points compared to placebo controls, but these differences resolved by day 28 of treatment. Therefore, in healthy volunteers, treatment with sitagliptin daily for 28 days does not overtly alter systemic immune function.

State of Knowledge and Data Gaps of Middle East Respiratory Syndrome Coronavirus (MERS-CoV) in Humans

BACKGROUND

Between September 2012 and 22 October 2013, 144 laboratory-confirmed and 17 probable MERS-CoV cases from nine countries were notified to WHO.

METHODS

We summarize what is known about the epidemiology, virology, phylogeny and emergence of MERS-CoV to inform public health policies.

RESULTS

The median age of patients (n=161) was 50 years (range 14 months to 94 years), 64.5% were male and 63.4% experienced severe respiratory disease. 76.0% of patients were reported to have ≥1 underlying medical condition and fatal cases, compared to recovered or asymptomatic cases were more likely to have an underlying condition (86.8% vs. 42.4%, p<0.001). Analysis of genetic sequence data suggests multiple independent introductions into human populations and modelled estimates using epidemiologic and genetic data suggest R0 is <1, though the upper range of estimates may exceed 1. Index/sporadic cases (cases with no epidemiologic-link to other cases) were more likely to be older (median 59.0 years vs. 43.0 years, p<0.001) compared to secondary cases, although these proportions have declined over time. 80.9% vs. 67.2% of index/sporadic and secondary cases, respectively, reported ≥1 underlying condition. Clinical presentation ranges from asymptomatic to severe pneumonia with acute respiratory distress syndrome and multi-organ failure. Nearly all symptomatic patients presented with respiratory symptoms and 1/3 of patients also had gastrointestinal symptoms.

CONCLUSIONS

Sustained human-to-human transmission of MERS-CoV has not been observed. Outbreaks have been extinguished without overly aggressive isolation and quarantine suggesting that transmission of virus may be stopped with implementation of appropriate infection control measures.

The serum level of soluble CD26/dipeptidyl peptidase 4 increases in response to acute hyperglycemia after an oral glucose load in healthy subjects: association with high-molecular weight adiponectin and hepatic enzymes

A soluble form of CD26/dipeptidyl peptidase 4 (sCD26/DPP4) is found in serum and it has DPP4 enzymatic activity. We investigated whether the serum level of sCD26/DPP4 was influenced by the oral glucose tolerance test (OGTT) in healthy subjects. The serum sCD26/DPP4 level increased significantly from 824.5 ng/mL (interquartile range, from 699.0 to 1050 ng/mL) at baseline to a peak of 985.0 ng/mL (interquartile range, from 796.5 to 1215 ng/mL) during the OGTT (P < 0.0001). The peak sCD26/DPP4 level correlated positively with the baseline age and body mass index, and fasting plasma glucose (FPG), homeostasis model assessment of insulin resistance (HOMA-IR), triglycerides (TG), alanine aminotransferase, and γ-glutamyl transpeptidase (GGT) levels whereas it correlated negatively with high-density lipoprotein (HDL) cholesterol and the serum levels of total and high-molecular weight (HMW) adiponectin. Stepwise regression analysis was done with forward selection of variables, including age, FPG, HOMA-IR, TG, HDL cholesterol, uric acid, GGT, C-reactive protein, and HMW adiponectin. In a model that explained 57.5% of the variation of the peak sCD26/DPP4 level, GGT (β = 0.382, P = 0.007) and HOMA-IR (β = 0.307, P = 0.034) were independent determinants of the peak serum level of sCD26/DPP4. Serum HMW adiponectin decreased significantly from 4.43 μg/mL (interquartile range, from 2.80 to 6.65 μg/mL) at baseline to 4.17 μg/mL (interquartile range, from 2.48 to 6.96 μg/mL) 120 minutes after the oral glucose load (P < 0.0001). The baseline serum level of sCD26/DPP4 showed a significant negative correlation with the percent change of HMW adiponectin during the OGTT. In conclusion, the serum level of sCD26/DPP4 increased acutely after an oral glucose load in apparently healthy subjects. The abrupt increase of serum sCD26/DPP4 after a glucose load may be a marker of insulin resistance that could come from liver or muscle.

Identification of altered dipeptidyl-peptidase activities as potential biomarkers for unipolar depression

BACKGROUND

Changes in circulatory aminopeptidases [dipeptidyl-peptidase-IV (DPP-IV), Prolyl-oligopeptidase (POP) and Leucine aminopeptidase (LAP)] activities have been found to be associated with psychiatric illnesses and inflammatory diseases.

METHODS

The discriminatory indices of aminopeptidases activities were assessed by enzymatic assays in plasma samples from 240 unipolar depression (UD) patients and 264 matched controls. In addition the relationship between soluble and cellular DPP-IV activity was determined in plasma and blood cells from healthy subjects.

RESULTS

Greater than 95% of the plasma DPP-IV activity could be blocked by inhibitors, demonstrating the specificity of the assay. Also, DPP-IV protein and activity levels were strongly correlated. In contrast, only 50% of the membrane-bound activity in blood cells was inhibited, which suggested that other similar peptidases may be present in these cells. UD patients had decreased plasma levels of DPP-IV and POP activities compared to healthy controls with a concomitant increase in LAP activity. Finally, testing of the LAP/DPP-IV ratio resulted in good discrimination of UD patients from controls with an area under the curve-receiver operating characteristic of 0.70.

LIMITATIONS

Further biological validation studies using different cohorts are warranted.

CONCLUSIONS

The finding that plasma DPP-IV activity was decreased and LAP activity was increased in UD patients suggests the potential value for testing the levels of these enzymes for improved classification of patients. In addition, the changes in these enzymes, suggests that the proteolytic maturation of their proneuropeptide and prohormone subtrates may also be affected in UD, resulting in altered production of the associated bioactive peptides.

The role of dipeptidyl peptidase 4 in hematopoiesis and transplantation

PURPOSE OF REVIEW

Dipeptidyl peptidase 4 (DPP4, CD26) is a protease that cleaves selected amino acids at the N-terminal penultimate position and has the potential to alter the protein function. The regulation and roles of DPP4 activity are not well understood; therefore, the purpose of this review is to discuss the recent literature regarding DPP4 regulation, as well as the variety of molecules it may affect, and their potential clinical applications.

RECENT FINDINGS

Recent insight into the number of proteins that have DPP4 sites, and how DPP4 truncation may alter hematopoiesis based on the protein full length vs. truncated state, has shown that DPP4 truncation of colony-stimulating factors (CSFs) alters their function and that the activity of these CSFs can be enhanced when DPP4 activity is inhibited. DPP4 inhibition has recently been used in a clinical trial to attempt to enhance the engraftment of cord blood cells, and an endogenous DPP4 inhibitor tissue factor pathway inhibitor has been discovered, increasing our understanding of the potential importance of DPP4.

SUMMARY

DPP4 plays a role in regulating the activity of CSFs and other cytokines involved in hematopoiesis. This information may be useful for enhancing hematopoietic cell transplantation, blood cell recovery after stress, and for understanding the physiology and pathophysiology of blood and other cell systems.

Food protein hydrolysates as a source of dipeptidyl peptidase IV inhibitory peptides for the management of type 2 diabetes

The prevalence of type 2 diabetes mellitus (T2DM) is increasing and it is estimated that by 2030 approximately 366 million people will be diagnosed with this condition. The use of dipeptidyl peptidase IV (DPP-IV) inhibitors is an emerging strategy for the treatment of T2DM. DPP-IV is a ubiquitous aminodipeptidase that cleaves incretins such as glucagon like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), resulting in a loss in their insulinotropic activity. Synthetic DPP-IV drug inhibitors are being used to increase the half-life of the active GLP-1 and GIP. Dietary intervention is accepted as a key component in the prevention and management of T2DM. Therefore, identification of natural food protein-derived DPP-IV inhibitors is desirable. Peptides with DPP-IV inhibitory activity have been identified in a variety of food proteins. This review aims to provide an overview of food protein hydrolysates as a source of the DPP-IV inhibitory peptides with particular focus on milk proteins. In addition, the proposed modes of inhibition and structure-activity relationship of peptide inhibitors are discussed. Milk proteins and associated peptides also display insulinotropic activity and help regulate blood glucose in healthy and diabetic subjects. Therefore, milk protein derived peptide inhibitors may be a unique multifunctional peptide approach for the management of T2DM.

Novel water-soluble prodrugs of acyclovir cleavable by the dipeptidyl-peptidase IV (DPP IV/CD26) enzyme

We herein report for the first time the successful use of the dipeptidyl peptidase IV (DPPIV/CD26) prodrug approach to guanine derivatives such as the antiviral acyclovir (ACV). The solution- and solid-phase synthesis of the tetrapeptide amide prodrug 3 and the tripeptide ester conjugate 4 of acyclovir are reported. The synthesis of the demanding tetrapeptide amide prodrug of ACV 3 was first established in solution and successfully transferred onto solid support by using Ellman's dihydropyran (DHP) resin. In contrast with the valyl ester prodrug (valacyclovir, VACV), the tetrapeptide amide prodrug 3 and the tripeptide ester conjugate 4 of ACV proved fully stable in PBS. Both prodrugs converted to VACV (for 4) or ACV (for 3) upon exposure to purified DPPIV/CD26 or human or bovine serum. Vildagliptin, a potent inhibitor of DPPIV/CD26 efficiently inhibited the DPPIV/CD26-catalysed hydrolysis reaction. Both amide and ester prodrugs of ACV showed pronounced anti-herpetic activity in cell culture and significantly improved the water solubility in comparison with the parent drug.

The activity of circulating dipeptidyl peptidase-4 is associated with subclinical left ventricular dysfunction in patients with type 2 diabetes mellitus

Background

Patients with type 2 diabetes mellitus (T2DM) present subclinical left ventricular systolic and/or diastolic dysfunction (LVD). Dipeptidyl peptidase-4 (DPP4) inactivates peptides that possess cardioprotective actions. Our aim was to analyze whether the activity of circulating DPP4 is associated with echocardiographically defined LVD in asymptomatic patients with T2DM.

Methods

In this cross-sectional study, we examined 83 T2DM patients with no coronary or valve heart disease and 59 age and gender-matched non-diabetic subjects. Plasma DPP4 activity (DPP4a) was measured by enzymatic assay and serum amino-terminal pro-brain natriuretic peptide (NT-proBNP) was measured by enzyme-linked immunosorbent assay. LV function was assessed by two-dimensional echocardiographic imaging, targeted M-mode recordings and Doppler ultrasound measurements. Differences in means were assessed by t-tests and one-way ANOVA. Associations were assessed by adjusted multiple linear regression and logistic regression analyses.

Results

DPP4a was increased in T2DM patients as compared with non-diabetic subjects (5855 ± 1632 vs 5208 ± 957 pmol/min/mL, p < 0.05). Clinical characteristics and echocardiographic parameters assessing LV morphology were similar across DPP4a tertiles in T2DM patients. However, prevalence of LVD progressively increased across incremental DPP4a tertiles (13%, 39% and 71%, all p < 0.001). Multivariate regression analysis confirmed the independent associations of DPP4a with LVD in T2DM patients (p < 0.05). Similarly, multiple logistic regression analysis showed that an increase of 100 pmol/min/min plasma DPP4a was independently associated with an increased frequency of LVD with an adjusted odds ratio of 1.10 (95% CI, 1.04 to 1.15, p = 0.001).

Conclusions

An excessive activity of circulating DPP4 is independently associated with subclinical LVD in T2DM patients. Albeit descriptive, these findings suggest that DPP4 may be involved in the mechanisms of LVD in T2DM.

Incretin hormones and beta-cell mass expansion: what we know and what is missing?

Pancreatic beta-cell mass expands through beta-cell proliferation and neogenesis while it decreases mainly via apoptosis. The loss of balance between beta-cell death and regeneration leads to a reduction of beta-cell functional mass, thus contributing to the pathogenesis of type 2 diabetes mellitus (T2DM). The pathogenetic mechanisms causing T2DM are complex, and also include a significant reduction of the incretin effect. A better understanding of the role of incretin hormones in glucose homeostasis has led to the development of incretin-based therapies. Recently, incretin hormones have been shown to stimulate the beta-cell growth and differentiation from pancreas-derived stem/progenitor cells, as well as to exert cytoprotective, antiapoptotic effects on beta-cells. However, the role and the molecular mechanisms by which GLP-1 and its agonists regulate beta-cell mass have not been fully investigated. This review focuses the current findings and the missing understanding of the effects of incretin hormones on beta-cell mass expansion.

DPP8 and DPP9 expression in cynomolgus monkey and Sprague Dawley rat tissues

Dipeptidyl peptidases (DPPs) are proteolytic enzymes that regulate many physiological systems by degrading signaling peptides. DPP8 and DPP9 are distinct from DPP4 in sequence, cellular localization and expression levels, thus implying distinct functions. However, DPP8 and DPP9 expression needs further delineation. We evaluated DPP4, DPP8 and DPP9 expression using three independent methods at the mRNA, protein, and functional levels to better understand the local physiological contribution of each enzyme. Sprague Dawley rats and cynomolgus monkeys were selected for DPP4, DPP8 and DPP9 expression profiling to represent animal species commonly utilized for drug preclinical safety evaluation. A novel Xhibit assay of DPP protease activity was applied in addition to newly available antibodies for immunohistochemical localization. This combined approach can facilitate a functional evaluation of protease expression, which is important for understanding physiological relevance. Few inter-species differences were observed. Tissue mRNA and protein levels generally correlated to functional DPP4 and DPP8/9 enzymatic activity. All three proteins were seen in epithelial cells, lymphoid cells and some endothelial and vascular smooth muscle cells. Combined DPP8/DPP9 enzymatic activity was uniformly intracellular across tissues at approximately 10-fold lower levels than non-renal DPP4. Consistent levels of each DPP were detected among most non-renal tissues in rats and monkeys. DPP4 was ubiquitous, principally detected on cell membranes of epithelial and endothelial cells and was greatest in the kidney. The expression patterns suggest that DPP8 and DPP9 may act similarly across tissues, and that their actions might in part overlap with DPP4.

Processed B-Type Natriuretic Peptide Is a Biomarker of Postinterventional Restenosis in Ischemic Heart Disease

BACKGROUND

Restenosis, a condition in which the lesion vessel renarrows after a coronary intervention procedure, remains a limitation in management. A surrogate biomarker for risk stratification of restenosis would be welcome. B-type natriuretic peptide (BNP) is secreted in response to pathologic stress from the heart. Its use as a biomarker of heart failure is well known; however, its diagnostic potential in ischemic heart disease is less explored. Recently, it has been reported that processed forms of BNP exist in the circulation. We hypothesized that circulating processed forms of BNP might be a biomarker of ischemic heart disease.

METHODS

We characterized processed forms of BNP by a newly developed mass spectrometry–based detection method combined with immunocapture using commercial anti-BNP antibodies.

RESULTS

Measurements of processed forms of BNP by this assay were found to be strongly associated with presence of restenosis. Reduced concentrations of the amino-terminal processed peptide BNP(5–32) relative to BNP(3–32) [as the index parameter BNP(5–32)/BNP(3–32) ratio] were seen in patients with restenosis [median (interquartile range) 1.19 (1.11–1.34), n = 22] vs without restenosis [1.43 (1.22–1.61), n = 83; P &lt; 0.001] in a cross-sectional study of 105 patients undergoing follow-up coronary angiography. A sensitivity of 100% to rule out the presence of restenosis was attained at a ratio of 1.52.

CONCLUSIONS

Processed forms of BNP may serve as viable potential biomarkers to rule out restenosis.

The Middle East respiratory syndrome--how worried should we be?

Ten years after the severe acute respiratory syndrome epidemic, a second coronavirus, the Middle East respiratory syndrome coronavirus (MERS-CoV), has been identified as the cause of a highly lethal pneumonia in patients in the Middle East and in travelers from this region. Over the past 9 months, since the virus was first isolated, much has been learned about the biology of the virus. It is now clear that MERS-CoV is transmissible from person to person, and its close relationship with several bat coronaviruses suggests that these animals may be the ultimate source of the infection. However, many key issues need to be addressed, including identification of the proximate, presumably zoonotic, source of the infection, the prevalence of the infection in human populations, details regarding clinical and pathological features of the human infection, the establishment of a small rodent model for the infection, and the virological and immune basis for the severe disease observed in most patients. Most importantly, we do not know whether a MERS-CoV epidemic is likely or not. Infection with the virus has so far resulted in only 91 cases and 46 deaths (as of 29 July 2013), but it is nonetheless setting off alarm bells among public health officials, including Margaret Chan, Director-General of the World Health Organization, who called MERS-CoV “a threat to the entire world.” This article reviews some of the progress that has been made and discusses some of the questions that need to be answered.

Overview of food products and dietary constituents with antidiabetic properties and their putative mechanisms of action: a natural approach to complement pharmacotherapy in the management of diabetes

Diabetes is one of the fastest growing chronic, noncommunicable diseases worldwide. Currently, 11 major classes of pharmacotherapy are available for the management of this metabolic disorder. However, the usage of these drugs is often associated with undesirable side effects, including weight gain and hypoglycemia. There is thus a need for new, safe and effective treatment strategies. Diet is known to play a major role in the prevention and management of diabetes. Numerous studies have reported the putative association of the consumption of specific food products, or their constituents, with the incidence of diabetes, and mounting evidence now suggests that some dietary factors can improve glycemic regulation. Foods and dietary constituents, similar to synthetic drugs, have been shown to modulate hormones, enzymes, and organ systems involved in carbohydrate metabolism. The present article reviews the major classes and modes of action of antidiabetic drugs, and examines the evidence on food products and dietary factors with antidiabetic properties as well as their plausible mechanisms of action. The findings suggest potential use of dietary constituents as a complementary approach to pharmacotherapy in the prevention and/or management of diabetes, but further research is necessary to identify the active components and evaluate their efficacy and safety.

Implications of DPP4 modification of proteins that regulate stem/progenitor and more mature cell types

Dipeptidylpeptidase (DPP) 4 has the potential to truncate proteins with a penultimate alanine, proline, or other selective amino acids at the N-terminus. DPP4 truncation of certain chemokines, colony-stimulating factors, and interleukins have recently been linked to regulation of hematopoietic stem/progenitor cells, more mature blood cells, and other cell types. We believe that the potential role of DPP4 in modification of many regulatory proteins, and their subsequent effects on numerous stem/progenitor and other cell-type functions has not been adequately appreciated. This review addresses the potential implications of the modifying effects of DPP4 on a large number of cytokines and other growth-regulating factors with either proven or putative DPP4 truncation sites on hematopoietic cells, and subsequent effects of DPP4-truncated proteins on multiple aspects of steady-state and stressed hematopoiesis, including stem/progenitor cell, and more mature cell, function.

Update on the protective molecular pathways improving pancreatic beta-cell dysfunction

The primary function of pancreatic beta-cells is to produce and release insulin in response to increment in extracellular glucose concentrations, thus maintaining glucose homeostasis. Deficient beta-cell function can have profound metabolic consequences, leading to the development of hyperglycemia and, ultimately, diabetes mellitus. Therefore, strategies targeting the maintenance of the normal function and protecting pancreatic beta-cells from injury or death might be crucial in the treatment of diabetes. This narrative review will update evidence from the recently identified molecular regulators preserving beta-cell mass and function recovery in order to suggest potential therapeutic targets against diabetes. This review will also highlight the relevance for novel molecular pathways potentially improving beta-cell dysfunction.

Dipeptidyl peptidase 4 is a functional receptor for the emerging human coronavirus-EMC

Most human coronaviruses cause mild upper respiratory tract disease but may be associated with more severe pulmonary disease in immunocompromised individuals. However, SARS coronavirus caused severe lower respiratory disease with nearly 10% mortality and evidence of systemic spread. Recently, another coronavirus (human coronavirus-Erasmus Medical Center (hCoV-EMC)) was identified in patients with severe and sometimes lethal lower respiratory tract infection. Viral genome analysis revealed close relatedness to coronaviruses found in bats. Here we identify dipeptidyl peptidase 4 (DPP4; also known as CD26) as a functional receptor for hCoV-EMC. DPP4 specifically co-purified with the receptor-binding S1 domain of the hCoV-EMC spike protein from lysates of susceptible Huh-7 cells. Antibodies directed against DPP4 inhibited hCoV-EMC infection of primary human bronchial epithelial cells and Huh-7 cells. Expression of human and bat (Pipistrellus pipistrellus) DPP4 in non-susceptible COS-7 cells enabled infection by hCoV-EMC. The use of the evolutionarily conserved DPP4 protein from different species as a functional receptor provides clues about the host range potential of hCoV-EMC. In addition, it will contribute critically to our understanding of the pathogenesis and epidemiology of this emerging human coronavirus, and may facilitate the development of intervention strategies.

Evolving therapeutic options for type 2 diabetes mellitus: an overview

INTRODUCTION

Many oral antidiabetic drugs (OADs) are available for patients with type 2 diabetes mellitus (T2DM). However, it is recognized that additional therapies are needed and several new compounds are in advanced stages of development.

PURPOSE

This narrative review considers the essential features of a successful OAD, the main classes of OADs that are currently used, and the therapies that may be available in the upcoming years.

RESULTS AND CONCLUSIONS

The first OADs (sulfonylureas and biguanides) were discovered by chance. Although effective in reducing blood glucose levels, early sulfonylureas were associated with significant off-target effects, and the biguanide phenformin was discontinued due to adverse events. Although metformin is in the same drug class, it has a better safety profile and is now recommended as first-line treatment, except when contraindicated. Nonetheless, many patients require additional glucose control (even on metformin) with an agent that has a complementary mechanism of action. Developments in bench science have facilitated the selection of agents for specific therapeutic targets, with the thiazolidinediones providing an interesting example. This OAD class initially appeared encouraging, yet in clinical practice was associated with safety concerns. As a result, newer agents, such as dipeptidyl peptidase-4 inhibitors, are undergoing more rigorous safety evaluations than OADs of previous generations. Promising compounds with novel mechanisms of action include the sodium-glucose co-transporter 2 inhibitors, the G-protein-coupled receptor agonists, and the balanced dual peroxisome proliferator-activated receptor-α/γ agonists. There is optimism that in the next few years, novel classes of OADs that are currently under development will offer additional blood glucose control options via complementary mechanisms of action. However, history has shown that compounds of the same class can have different safety profiles and treatment effects. Therefore, high-quality clinical trial evidence is needed for every compound.

Dipeptidyl peptidase-IV inhibitory peptides generated by tryptic hydrolysis of a whey protein concentrate rich in β-lactoglobulin

Dipeptidyl peptidase-IV (DPP-IV) is a serine protease involved in the degradation and inactivation of incretin hormones that act by stimulating glucose-dependent insulin secretion after meal ingestion. DPP-IV inhibitors have emerged as new and promising oral agents for the treatment of type 2 diabetes. The purpose of this study was to investigate the potential of β-lactoglobulin as natural source of DPP-IV inhibitory peptides. A whey protein concentrate rich in β-lactoglobulin was hydrolysed with trypsin and fractionated using a chromatographic separation at semipreparative scale. Two of the six collected fractions showed notable DPP-IV inhibitory activity. These fractions were analysed by HPLC coupled to tandem mass spectrometry (HPLC-MS/MS) to identify peptides responsible for the observed activity. The most potent fragment (IPAVF) corresponded to β-lactoglobulin f(78-82) which IC50 value was 44.7μM. The results suggest that peptides derived from β-lactoglobulin would be beneficial ingredients of foods against type 2 diabetes.

Anagliptin, a DPP-4 inhibitor, suppresses proliferation of vascular smooth muscles and monocyte inflammatory reaction and attenuates atherosclerosis in male apo E-deficient mice

Dipeptyl peptidase-4 (DPP-4) inhibitors modulate the progression of atherosclerosis. To gain insights into their mechanism of action, 9-wk-old male apolipoprotein E (apoE)-deficient mice were fed a DPP-4 inhibitor, anagliptin-containing diet. The effects of anagliptin were investigated in, a monocyte cell line, human THP-1 cells, and rat smooth muscle cells (SMCs). Treatment with anagliptin for 16 wk significantly reduced accumulation of monocytes and macrophages in the vascular wall, SMC content in plaque areas, and oil red O-stained area around the aortic valve without affecting glucose tolerance or body weight. Serum DPP-4 concentrations were significantly higher in apoE-deficient mice than control mice, and the levels increased with aging, suggesting the involvement of DPP-4 in the progression of atherosclerosis. Indeed, soluble DPP-4 augmented cultured SMC proliferation, and anagliptin suppressed the proliferation by inhibiting ERK phosphorylation. In THP-1 cells, anagliptin reduced lipopolysaccharide-induced TNF-α production with inhibiting ERK phosphorylation and nuclear translocation of nuclear factor-κB. Quantitative analysis also showed that anagliptin reduced the area of atherosclerotic lesion in apoE-deficient mice. These results indicated that the anti-atherosclerotic effect of anagliptin is mediated, at least in part, through its direct inhibition of SMC proliferation and inflammatory reaction of monocytes.

Comparison of the dipeptidyl peptidase-4 gene methylation levels between severely obese subjects with and without the metabolic syndrome

BACKGROUND

The dipeptidyl peptidase-4 (DPP4) enzyme is a novel adipokine potentially involved in the development of the metabolic syndrome (MetS). Previous observations demonstrated higher visceral adipose tissue (VAT) DPP4 gene expression in non-diabetic severely obese men with (MetS+) vs. without (MetS-) MetS. DPP4 mRNA abundance in VAT correlated also with CpG site methylation levels (%Meth) localized within and near its exon 2 (CpG94 to CpG102) in non-diabetic severely obese women, regardless of their MetS status. The actual study tested whether DPP4 %Meth levels in VAT are different between MetS- and MetS+ non-diabetic severely obese subjects, whether variable metabolic and plasma lipid profiles are observed between DPP4 %Meth quartiles, and whether correlation exists in DPP4 %Meth levels between VAT and white blood cells (WBCs).

METHODS

DNA was extracted from the VAT of 26 men (MetS-: n=12, MetS+: n=14) and 79 women (MetS-: n=60; MetS+: n=19), as well as from WBCs in a sub-sample of 17 women (MetS-: n=9; MetS+: n=8). The %Meth levels of CpG94 to CpG102 were assessed by pyrosequencing of sodium bisulfite-treated DNA. ANOVA analyses were used to compare the %Meth of CpGs between MetS- and MetS+ groups, and to compare the metabolic phenotype and plasma lipid levels between methylation quartiles. Pearson correlation coefficient analyses were computed to test the relationship between VAT and WBCs CpG94-102 %Meth levels.

RESULTS

No difference was observed in CpG94-102 %Meth levels between MetS- and MetS+ subjects in VAT (P=0.67), but individuals categorized into CpG94-102 %Meth quartiles had variable plasma total-cholesterol concentrations (P=0.04). The %Meth levels of four CpGs in VAT were significantly correlated with those observed in WBCs (r=0.55-0.59, P≤0.03).

CONCLUSIONS

This study demonstrated that %Meth of CpGs localized within and near the exon 2 of the DPP4 gene in VAT are not associated with MetS status. The actual study also revealed an association between the %Meth of this locus with plasma total-cholesterol in severe obesity, which suggests a link between the DPP4 gene and plasma lipid levels.

Vildagliptin preserves the mass and function of pancreatic β cells via the developmental regulation and suppression of oxidative and endoplasmic reticulum stress in a mouse model of diabetes

AIM

We investigated the molecular mechanisms by which vildagliptin preserved pancreatic β cell mass and function.

METHODS

Morphological, biochemical and gene expression profiles of the pancreatic islets were investigated in male KK-A(y) -TaJcl(KK-A(y) ) and C57BL/6JJcl (B6) mice aged 8 weeks which received either vildagliptin or a vehicle for 4 weeks.

RESULTS

Body weight, food intake, fasting blood glucose, plasma insulin and active glucagon-like peptide-1 were unchanged with vildagliptin treatment in both mice. In KK-A(y) mice treated with vildagliptin, increased plasma triglyceride (TG) level and islet TG content were decreased, insulin sensitivity significantly improved, and the glucose tolerance ameliorated with increases in plasma insulin levels. Furthermore, vildagliptin increased glucose-stimulated insulin secretion, islet insulin content and pancreatic β cell mass in both strains. By vildagliptin, the expression of genes involved in cell differentiation/proliferation was upregulated in both strains, those related to apoptosis, endoplasmic reticulum stress and lipid synthesis was decreased and those related to anti-apoptosis and anti-oxidative stress was upregulated, in KK-A(y) mice. The morphological results were consistent with the gene expression profiles.

CONCLUSION

Vildagliptin increases β cell mass by not only directly affecting cell kinetics but also by indirectly reducing cell apoptosis, oxidative stress and endoplasmic reticulum stress in diabetic mice.

Diabetes Mellitus: New Challenges and Innovative Therapies

Diabetes is a common chronic disease affecting an estimated 285 million adults worldwide. The rising incidence of diabetes, metabolic syndrome, and subsequent vascular diseases is a major public health problem in industrialized countries. This chapter summarizes current pharmacological approaches to treat diabetes mellitus and focuses on novel therapies for diabetes mellitus that are under development.

There is great potential for developing a new generation of therapeutics that offer better control of diabetes, its co-morbidities and its complications. Preclinical results are discussed for new approaches including AMPK activation, the FGF21 target, cell therapy approaches, adiponectin mimetics and novel insulin formulations. Gene-based therapies are among the most promising emerging alternatives to conventional treatments. Therapies based on gene silencing using vector systems to deliver interference RNA to cells (i.e. against VEGF in diabetic retinopathy) are also a promising therapeutic option for the treatment of several diabetic complications.

In conclusion, treatment of diabetes faces now a new era that is characterized by a variety of innovative therapeutic approaches that will improve quality of life in the near future.

Digestive physiology of the pig symposium: involvement of gut chemosensing in the regulation of mucosal barrier function and defense mechanisms

Meal ingestion is followed by release of numerous hormones from enteroendocrine cells interspersed among the epithelial cells lining the intestine. Recently, the de-orphanization of G protein-coupled receptor (GPCR)-type nutrient receptors, expressed on the apical membranes of enteroendocrine cells, has suggested a plausible mechanism whereby luminal nutrients trigger the release of gut hormones. Activation of nutrient receptors triggers intracellular signaling mechanisms that promote exocytosis of hormone-containing granules into the submucosal space. Hormones released by foregut enteroendocrine cells include the glucagon-like peptides (GLP) affecting glycemic control (GLP-1) and releasing pro-proliferative, hypertrophy-inducing growth factors (GLP-2). The foregut mucosa, being exposed to pulses of concentrated HCl, is protected by a system of defense mechanisms, which includes epithelial bicarbonate and mucus secretion and augmentation of mucosal blood flow. We have reported that luminal co-perfusion of AA with nucleotides in anesthetized rats releases GLP-2 into the portal vein, associated with increased bicarbonate and mucus secretion and mucosal blood flow. The GLP-2 increases bicarbonate secretion via release of vasoactive intestinal peptide (VIP) from myenteric nerves. Luminal bile acids also release gut hormones due to activation of the bile-acid receptor known as G Protein-Coupled Receptor (GPR) 131, G Protein Bile Acid Receptor (GPBAR) 1, or Takeda G Protein-Coupled Receptor (TGR) 5, also expressed on enteroendocrine cells. The GLP are metabolized by dipeptidyl peptidase IV (DPPIV), an enzyme of particular interest to pharmaceutical, because its inhibition increases plasma concentrations of GLP-1 to treat diabetes. We have also reported that DPPIV inhibition enhances the secretory effects of nutrient-evoked GLP-2. Understanding the release mechanism and the metabolic pathways of gut hormones is of potential utility to the formulation of feedstuff additives that, by increasing nutrient absorption due to increased mucosal mass, can increase yields.

An emerging role of glucagon-like peptide-1 in preventing advanced-glycation-end-product-mediated damages in diabetes

Glucagon-like peptide-1 (GLP-1) is a gut hormone produced in the intestinal epithelial endocrine L cells by differential processing of the proglucagon gene. Released in response to the nutrient ingestion, GLP-1 plays an important role in maintaining glucose homeostasis. GLP-1 has been shown to regulate blood glucose levels by stimulating glucose-dependent insulin secretion and inhibiting glucagon secretion, gastric emptying, and food intake. These antidiabetic activities highlight GLP-1 as a potential therapeutic molecule in the clinical management of type 2 diabetes, (a disease characterized by progressive decline of beta-cell function and mass, increased insulin resistance, and final hyperglycemia). Since chronic hyperglycemia contributed to the acceleration of the formation of Advanced Glycation End-Products (AGEs, a heterogeneous group of compounds derived from the nonenzymatic reaction of reducing sugars with free amino groups of proteins implicated in vascular diabetic complications), the administration of GLP-1 might directly counteract diabetes pathophysiological processes (such as pancreatic β-cell dysfunction). This paper outlines evidence on the protective role of GLP-1 in preventing the deleterious effects mediated by AGEs in type 2 diabetes.

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.

Antihyperglycemic activity with DPP-IV inhibition of alkaloids from seed extract of Castanospermum australe: Investigation by experimental validation and molecular docking

The antidiabetic actions of Castanospermum australe Cunn., seed (CAS) extract were evaluated in Poloxamer-407 (PX-407) induced T2DM rats. The CAS extract (100 and 150 mg/kg body weight) was administered orally once a day for 5 weeks after the animals were confirmed diabetic. A significant increase in blood glucose, HbA₁c and serum insulin levels were observed in T2DM rats in comparison to citrate control rats. Treatment with CAS extract in T2DM rats reduced the elevated levels of blood glucose, HbA₁c and insulin with significant (p≤0.001) improvement in OGT. The CAS extract treatment also increased (p≤0.001) the K(ITT) and prevented increase in HOMA-R level in T2DM rats. The DPP-IV inhibitory potential of CAS extract showed IC₅₀ value of 13.96 μg/ml whilst the standard Diprotin A displayed the IC₅₀ value of 1.543 μg/ml. Molecular docking of the three reported alkaloids from the seeds of C. australe showed comparable DPP-IV inhibition with berberine. Our data suggest that CAS extract (150 mg/kg body weight) normalizes hyperglycemia in T2DM rats with strong DPP-IV inhibitory potential. The molecular docking showed that among the three alkaloids of seed extract 7-Deoxy-6-epi-castanospermine is a potent DPP-IV inhibitor similar to berberine.

Incretin-based Therapies for Type 2 Diabetes

There is a growing interest in developing therapeutic strategies for type 2 diabetes based on the actions of the hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). These hormones are the major incretins released from the intestine in response to nutrient ingestion, and they stimulate insulin secretion in a glucosedependent manner. Both peptides are degraded by the enzyme dipeptidyl peptidase-4 (DPP-4), thus terminating their actions. Studies in animal models of diabetes have shown that the incretins also exert a number of additional actions that improve glucose disposal. GLP-1 reduces food intake and gastric emptying, as well as inhibiting glucagon secretion. Injectable formulations of DPP-4-resistant GLP-1-related peptides (incretin mimetics) that are now in clinical use (exenatide) or undergoing trials (e.g. liraglutide) have been shown to reduce fasting and postprandial glucose and glycosylated hemoglobin (A1C) levels and induce weight loss. Oral administration of DPP-4 inhibitors potentiates the actions of incretins released during a meal. Clinical trials have demonstrated that DPP-4 inhibitors are weight-neutral drugs that also effectively reduce plasma glucose and A1C levels. One inhibitor, sitagliptin, is now available in Canada and the United States, and another, vildagliptin, has recently been approved by the European Union. Other inhibitors are under development. Preclinical studies indicate that treatment with incretin mimetics or DPP-4 inhibitors also preserves beta cell mass by exerting mitogenetic and prosurvival effects. It is not known whether similar effects occur in humans.

Suppression of food intake by glucagon-like peptide-1 receptor agonists: relative potencies and role of dipeptidyl peptidase-4

Administration of the glucagon-like peptide-1 (GLP-1) receptor agonists GLP-1 and exendin-4 (Ex-4) directly into the central nervous system decreases food intake. But although Ex-4 potently suppresses food intake after peripheral administration, the effects of parenteral GLP-1 are variable and not as strong. A plausible explanation for these effects is the rapid inactivation of circulating GLP-1 by dipeptidyl peptidase-4 (DPP-4), an enzyme that does not alter Ex-4 activity. To test this hypothesis, we assessed the relative potency of Ex-4 and GLP-1 under conditions in which DPP-4 activity was reduced. Outbred rats, wild-type mice, and mice with a targeted deletion of DPP-4 (Dpp4(-/-)) were treated with GLP-1 alone or in combination with the DPP-4 inhibitor vildagliptin, Ex-4, or saline, and food intake was measured. GLP-1 alone, even at high doses, did not affect feeding in wild-type mice or rats but did reduce food intake when combined with vildagliptin or given to Dpp4(-/-) mice. Despite plasma clearance similar to DPP-4-protected GLP-1, equimolar Ex-4 caused greater anorexia than vildagliptin plus GLP-1. To determine whether supraphysiological levels of endogenous GLP-1 would suppress food intake if protected from DPP-4, rats with Roux-en-Y gastric bypass and significantly elevated postprandial plasma GLP-1 received vildagliptin or saline. Despite 5-fold greater postprandial GLP-1 in these animals, vildagliptin did not affect food intake in Roux-en-Y gastric bypass rats. Thus, in both mice and rats, peripheral GLP-1 reduces food intake significantly less than Ex-4, even when protected from DPP-4. These findings suggest distinct potencies of GLP-1 receptor agonists on food intake that cannot be explained by plasma pharmacokinetics.