Dipeptidyl peptidase IV inhibitors in diabetes: more than inhibition of glucagon-like peptide-1 metabolism?

Neuropeptide Y Peptide Family and Cancer: Antitumor Therapeutic Strategies

Currently available data on the involvement of neuropeptide Y (NPY), peptide YY (PYY), and pancreatic polypeptide (PP) and their receptors (YRs) in cancer are updated. The structure and dynamics of YRs and their intracellular signaling pathways are also studied. The roles played by these peptides in 22 different cancer types are reviewed (e.g., breast cancer, colorectal cancer, Ewing sarcoma, liver cancer, melanoma, neuroblastoma, pancreatic cancer, pheochromocytoma, and prostate cancer). YRs could be used as cancer diagnostic markers and therapeutic targets. A high Y1R expression has been correlated with lymph node metastasis, advanced stages, and perineural invasion; an increased Y5R expression with survival and tumor growth; and a high serum NPY level with relapse, metastasis, and poor survival. YRs mediate tumor cell proliferation, migration, invasion, metastasis, and angiogenesis; YR antagonists block the previous actions and promote the death of cancer cells. NPY favors tumor cell growth, migration, and metastasis and promotes angiogenesis in some tumors (e.g., breast cancer, colorectal cancer, neuroblastoma, pancreatic cancer), whereas in others it exerts an antitumor effect (e.g., cholangiocarcinoma, Ewing sarcoma, liver cancer). PYY or its fragments block tumor cell growth, migration, and invasion in breast, colorectal, esophageal, liver, pancreatic, and prostate cancer. Current data show the peptidergic system's high potential for cancer diagnosis, treatment, and support using Y2R/Y5R antagonists and NPY or PYY agonists as promising antitumor therapeutic strategies. Some important research lines to be developed in the future will also be suggested.

Gut Molecules in Cardiometabolic Diseases: The Mechanisms behind the Story

Atherosclerotic cardiovascular disease is the most common cause of morbidity and mortality worldwide. Diabetes mellitus increases cardiovascular risk. Heart failure and atrial fibrillation are associated comorbidities that share the main cardiovascular risk factors. The use of incretin-based therapies promoted the idea that activation of alternative signaling pathways is effective in reducing the risk of atherosclerosis and heart failure. Gut-derived molecules, gut hormones, and gut microbiota metabolites showed both positive and detrimental effects in cardiometabolic disorders. Although inflammation plays a key role in cardiometabolic disorders, additional intracellular signaling pathways are involved and could explain the observed effects. Revealing the involved molecular mechanisms could provide novel therapeutic strategies and a better understanding of the relationship between the gut, metabolic syndrome, and cardiovascular diseases.

Established and emerging roles peptide YY (PYY) and exploitation in obesity-diabetes

PURPOSE OF REVIEW

The antiobesity effects of activation of hypothalamic neuropeptide Y2 receptors (NPYR2) by the gut-derived hormone, peptide YY (PYY), are established. However, more recent insight into the biology of PYY has demonstrated remarkable benefits of sustained activation of pancreatic beta-cell NPYR1, that promises to open a new therapeutic avenue in diabetes.

RECENT FINDINGS

The therapeutic applicability of NPYR2 agonists for obesity has been considered for many years. An alternative pathway for the clinical realisation of PYY-based drugs could be related to the development of NPYR1 agonists for treatment of diabetes. Thus, although stimulation of NPYR1 on pancreatic beta-cells has immediate insulinostatic effects, prolonged activation of these receptors leads to well defined beta-cell protective effects, with obvious positive implications for the treatment of diabetes. In this regard, NPYR1-specific, long-acting enzyme resistant PYY analogues, have been recently developed with encouraging preclinical effects observed on pancreatic islet architecture in diabetes. In agreement, the benefits of certain types of bariatric surgeries on beta-cell function and responsiveness have also been linked to elevated PYY secretion and NPY1 receptor activation.

SUMMARY

Enzymatically stable forms of PYY, that selectively activate NPYR1, may have significant potential for preservation of beta-cell mass and the treatment of diabetes.

Generation and characterisation of C-terminally stabilised PYY molecules with potential in vivo NPYR2 activity

BACKGROUND

Activation of neuropeptide Y2 receptors (NPYR2) by the N-terminally truncated, dipeptidyl peptidase-4 (DPP-4) generated, Peptide YY (PYY) metabolite, namely PYY(3-36), results in satiating actions. However, PYY(3-36) is also subject to C-terminal enzymatic cleavage, which annuls anorectic effects.

METHODS

Substitution of l-Arg³⁵ with d-Arg³⁵ in the DPP-4 stable sea lamprey PYY(1-36) peptide imparts full C-terminal stability. In the current study, we have taken this molecule and introduced DPP-4 susceptibility by Iso³ substitution.

RESULTS

As expected, [Iso³]sea lamprey PYY(1-36) and [Iso³](d-Arg³⁵)sea lamprey PYY(1-36) were N-terminally degraded to respective PYY(3-36) metabolites in plasma. Only [Iso³](d-Arg³⁵)sea lamprey PYY(1-36) was C-terminally stable. Both peptides possessed similar insulinostatic and anti-apoptotic biological actions to native PYY(1-36) in beta-cells. Unlike native PYY(1-36) and [Iso³](d-Arg³⁵)sea lamprey PYY(1-36), [Iso³]sea lamprey PYY(1-36) displayed some proliferative actions in Npyr1 knockout beta-cells. In addition, [Iso³]sea lamprey PYY(1-36) induced more rapid NPYR2-dependent appetite suppressive effects in mice than its C-terminally stable counterpart. Twice daily administration of either peptide to high fat fed (HFF) mice resulted in significant body weight reduction and improvements in circulating triglyceride levels. [Iso³]sea lamprey PYY(1-36) treatment also prevented elevations in glucagon. Both peptides, and especially [Iso³]sea lamprey PYY(1-36), improved glucose tolerance. The treatment interventions also partially reversed the deleterious effects of sustained high fat feeding on pancreatic islet morphology.

CONCLUSION

The present study confirms that sustained NPYR2 receptor activation by [Iso³](d-Arg³⁵)sea lamprey induced significant weight lowering actions. However, identifiable benefits of this peptide over [Iso³]sea lamprey PYY(1-36), which was not protected against C-terminal degradation, were not pronounced.

Peptide YY (1-36) peptides from phylogenetically ancient fish targeting mammalian neuropeptide Y1 receptors demonstrate potent effects on pancreatic β-cell function, growth and survival

AIM

To investigate the antidiabetic efficacy of enzymatically stable Peptide YY (PYY) peptides from phylogenetically ancient fish.

MATERIALS AND METHODS

N-terminally stabilized, PYY (1-36) sequences from Amia calva (bowfin), Oncorhynchus mykiss (trout), Petromyzon marinus (sea lamprey) and Scaphirhynchus albus (sturgeon), were synthesized, and both biological actions and antidiabetic therapeutic efficacy were assessed.

RESULTS

All fish PYY (1-36) peptides were resistant to dipeptidyl peptidase-4 (DPP-4) degradation and inhibited glucose- and alanine-induced (P < 0.05 to P < 0.001) insulin secretion. In addition, PYY (1-36) peptides imparted significant (P < 0.05 to P < 0.001) β-cell proliferative and anti-apoptotic benefits. Proliferative effects were almost entirely absent in β cells with CRISPR-Cas9-induced knockout of Npyr1. In contrast to human PYY (1-36), the piscine-derived peptides lacked appetite-suppressive actions. Twice-daily administration of sea lamprey PYY (1-36), the superior bioactive peptide, for 21 days significantly (P < 0.05 to P < 0.001) decreased fluid intake, non-fasting glucose and glucagon in streptozotocin (STZ)-induced diabetic mice. In addition, glucose tolerance, insulin sensitivity, pancreatic insulin and glucagon content were significantly improved. Metabolic benefits were linked to positive changes in pancreatic islet morphology as a result of augmented (P < 0.001) proliferation and decreased apoptosis of β cells. Sturgeon PYY (1-36) exerted similar but less impressive effects in STZ mice.

CONCLUSION

These observations reveal, for the first time, that PYY (1-36) peptide sequences from phylogenetically ancient fish replicate the pancreatic β-cell benefits of human PYY (1-36) and have clear potential for the treatment of type 2 diabetes.

Development and characterisation of a peptidergic N-and C-terminally stabilised mammalian NPY1R agonist which protects against diabetes induction

BACKGROUND

PYY (1-36) peptides from phylogenetically ancient fish, such as sea lamprey, have previously been shown to function as specific neuropeptide Y1 receptor (NPYR1) agonists. Although, sea lamprey PYY (1-36) is N-terminally stable, we reveal in this study that the peptide is subject to endopeptidase mediated C-terminal dipeptide degradation. In an attempt to prevent this, (d-Arg³⁵)-sea lamprey PYY (1-36) was developed.

METHODS

In vitro bioassays assessed enzymatic stability, insulinostatic activity as well as beta-cell anti-apoptotic actions of (d-Arg³⁵)-sea lamprey PYY (1-36). Follow-up studies examined the impact of twice daily administration of sea lamprey PYY (1-36) or (d-Arg³⁵)-sea lamprey PYY (1-36) in multiple low dose STZ-induced diabetic mice.

RESULTS

(d-Arg³⁵)-sea lamprey PYY (1-36) was fully resistant to plasma enzymatic degradation. The peptide possessed similar significant insulinostatic, as well as positive anti-apoptotic biological actions, as the parent peptide. Sea lamprey PYY (1-36) and (d-Arg³⁵)-sea lamprey PYY (1-36) delayed diabetes progression in STZ mice. Both treatment interventions induced a significant decrease in body weight, food and fluid intake as well as glucose and glucagon concentrations. In addition, glucose tolerance, plasma and pancreatic insulin were partially normalised. (d-Arg³⁵)-sea lamprey PYY (1-36) was significantly more effective than sea lamprey PYY (1-36) in terms of enhancing glucose-stimulate insulin release. Both treatments improved pancreatic islet morphology, linked to decreased apoptosis of beta-cells.

CONCLUSION

We present (d-Arg³⁵)-sea lamprey PYY (1-36) as the first-in-class N- and C-terminally stable PYY (1-36) peptide analogue.

GENERAL SIGNIFICANCE

Enzymatically stable, long-acting PYY (1-36) peptides highlight the therapeutic benefits of sustained activation of NPYR1's in diabetes.

Incretin-based therapy for diabetic ulcers: from bench to bedside

INTRODUCTION

Diabetic foot ulcers are a serious complication of diabetes and are associated with pain, disability, and poor quality of life. Incretin-based therapy is available for type-2 diabetes. Aside from glucose control, such treatment can impart numerous beneficial effects.

AREAS COVERED

This review summarizes the preclinical and clinical evidence supporting incretin-based treatment approaches for diabetic ulcers.

EXPERT OPINION

Incretin-based therapy may have a role in the treatment of diabetic foot ulcers; the benefits of such treatment arise from attenuation of inflammatory response, improvement of keratinocyte migration, induction of angiogenesis, and the enhancement of tissue remodeling. Large-scale clinical trials are required to determine the advantages of GLP-1 receptor agonists and DPP4 inhibitors. Future research on the topical application of incretin-based therapy is necessary. Such therapeutic approaches may provide new hope in improving the treatment of impaired diabetic foot ulcers.

Emerging therapeutic potential for peptide YY for obesity-diabetes

The vast majority of research to date on the gut hormone Peptide YY (PYY) has focused on appetite suppression and body weight regulation effects. These biological actions are believed to occur through interaction of PYY with hypothalamic Y₂ receptors. However, more recent studies have added additional knowledge to understanding of the physiological, and potential therapeutic, roles of PYY beyond obesity alone. Thus, PYY has now been shown to impart improvements in pancreatic beta-cell survival and function, with obvious benefits for diabetes. This effect has been linked mainly to binding and activation of Y₁ receptors by PYY, but more evidence is still required in this regard. Given the potential therapeutic promise of PYY-derived compounds, and complexity of receptor interactions, it is important to fully understand the complete biological action profile of PYY. Therefore, the current review aims to compile, evaluate and summarise current knowledge on PYY, with particular emphasis on obesity and diabetes treatment, and the importance of specific Y receptor interactions for this.

Mechanisms for the cardiovascular effects of glucagon-like peptide-1

Over the past three decades, at least 10 hormones secreted by the enteroendocrine cells have been discovered, which directly affect the cardiovascular system through their innate receptors expressed in the heart and blood vessels or through a neural mechanism. Glucagon-like peptide-1 (GLP-1), an important incretin, is perhaps best studied of these gut-derived hormones with important cardiovascular effects. In this review, I have discussed the mechanism of GLP-1 release from the enteroendocrine L-cells and its physiological effects on the cardiovascular system. Current evidence suggests that GLP-1 has positive inotropic and chronotropic effects on the heart and may be important in preserving left ventricular structure and function by direct and indirect mechanisms. The direct effects of GLP-1 in the heart may be mediated through GLP-1R expressed in atria as well as arteries and arterioles in the left ventricle and mainly involve in the activation of multiple pro-survival kinases and enhanced energy utilization. There is also good evidence to support the involvement of a second, yet to be identified, GLP-1 receptor. Further, GLP-1(9-36)amide, which was previously thought to be the inactive metabolite of the active GLP-1(7-36)amide, may also have direct cardioprotective effects. GLP-1's action on GLP-1R expressed in the central nervous system, kidney, vasculature and the pancreas may indirectly contribute to its cardioprotective effects.

A molecular connection of Pterocarpus marsupium, Eugenia jambolana and Gymnema sylvestre with dipeptidyl peptidase-4 in the treatment of diabetes

CONTEXT

Pterocarpus marsupium (PM) (Leguminosae), Eugenia jambolana (EJ) (Myrtaceae) and Gymnema sylvestre (GS) (Asclepiadaceae) are the most important medicinal plants in the Indian system of traditional medicine for the treatment of hyperglycemia.

OBJECTIVES

Dipeptidyl peptidase-4 (DPP-4) inhibitors are the emerging class of anti-diabetic agents. However, only few compounds are commercially available. Therefore, in the present study we tried to explore the naturally occurring PM, EJ and GS semi-standardized extracts for their potential DPP-4 inhibition in vitro and in vivo.

MATERIALS AND METHODS

DPP-4 inhibition was evaluated by in vitro inhibitory assay, and enzyme kinetics were calculated using one-phase exponential decay equation. Glucose load (2 g/kg) was administered to control and diabetic rats 30 min following extract administration (100, 200 and 400 mg/kg) orally once, and blood samples were withdrawn at 0, 0.5, 1, 1.5, 2 and 3 h to measure plasma active glucagon-like peptide-1 (GLP-1) levels.

RESULTS

PM and EJ inhibit DPP-4 potently with IC50 values of 273.73 ± 2.96 and 278.94 ± 6.73 µg/mL, respectively, compared to GS (773.22 ± 9.21 µg/mL). PM, EJ and GS exhibit long duration of action with enzyme inhibitory half-lives of 462.3, 317.2 and 153.8 min, respectively. Extracts significantly increase GLP-1 levels compared to negative control groups and peak GLP-1 level was observed at 2 h for PM and EJ, whereas for GS it was at 1.5 h

DISCUSSION AND CONCLUSION

Taken together, results suggest the extracts may have potent DPP-4 inhibitory action, and their hypoglycemic action attributed through an increase in plasma active GLP-1 levels.

DPP4 deficiency preserved cardiac function in abdominal aortic banding rats

Dipeptidyl peptidase-4 (DPP4) enzyme inhibition has been reported to increase plasma glucagon-like peptide-1 (GLP-1) level for controlling postprandial glucose concentration. A prominent GLP-1 level in DPP4-deficient rats contributed to the resistance of endotoxemia and myocardial infarction. DPP4 deficiency also increased the capability against H₂O₂-induced stress in cardiomyocyte. However, long term effect of loss DPP4 activity on cardiac performance remained unclear. We used abdominal aortic banding (AAB) to induce pressure overload in wild-type and DPP4-deficient rats, and investigated the progression of heart failure. Cardiac histology and function were determined. Blood sample was collected for the plasma biochemical marker measurement. Heart weight to body weight ratio increased 1.2-fold after 6 weeks of AAB surgery. Cardiac function was compensated against pressure overload after 6 weeks of AAB surgery, but progressed to deterioration after 10 weeks of AAB surgery. AAB induced cardiac dysfunction was alleviated in DPP4-deficient rats. DPP4 activity increased significantly in wild-type rats after 10 weeks of AAB surgery, but remained unchanged in DPP4-deficient rats. In contrast, GLP-1 concentration was elevated by AAB after 6 weeks of surgery in DPP4-deficient rats, and remained high after 10 weeks of surgery. Ang II level markedly increased after 6 weeks of AAB surgery, but were less in DPP4-deficient rats. Massive collagen deposits in wild-type rat hearts appeared after 10 weeks of AAB surgery, which were alleviated in DPP4-deficient rats. Long term deficiency of DPP4 activity improved cardiac performance against pressure overload in rat, which may be attributed to a great quantity of GLP-1 accumulation during AAB.

Antiobesity pharmacotherapy: new drugs and emerging targets

Obesity is a growing pandemic, and related health and economic costs are staggering. Pharmacotherapy, partnered with lifestyle modifications, forms the core of current strategies to reduce the burden of this disease and its sequelae. However, therapies targeting weight loss have a significant history of safety risks, including cardiovascular and psychiatric events. Here, evolving strategies for developing antiobesity therapies, including targets, mechanisms, and developmental status, are highlighted. Progress in this field is underscored by Belviq (lorcaserin) and Qsymia (phentermine/topiramate), the first agents in more than 10 years to achieve regulatory approval for chronic weight management in obese patients. On the horizon, novel insights into metabolism and energy homeostasis reveal guanosine 3',5'-cyclic monophosphate (cGMP) signaling circuits as emerging targets for antiobesity pharmacotherapy. These innovations in molecular discovery may elegantly align with practical off-the-shelf approaches, leveraging existing approved drugs that modulate cGMP levels for the management of obesity.

Modulation of taste responsiveness by the satiation hormone peptide YY

It has been hypothesized that the peripheral taste system may be modulated in the context of an animal's metabolic state. One purported mechanism for this phenomenon is that circulating gastrointestinal peptides modulate the functioning of the peripheral gustatory system. Recent evidence suggests endocrine signaling in the oral cavity can influence food intake (FI) and satiety. We hypothesized that these hormones may be affecting FI by influencing taste perception. We used immunohistochemistry along with genetic knockout models and the specific reconstitution of peptide YY (PYY) in saliva using gene therapy protocols to identify a role for PYY signaling in taste. We show that PYY is expressed in subsets of taste cells in murine taste buds. We also show, using brief-access testing with PYY knockouts, that PYY signaling modulates responsiveness to bitter-tasting stimuli, as well as to lipid emulsions. We show that salivary PYY augmentation, via viral vector therapy, rescues behavioral responsiveness to a lipid emulsion but not to bitter stimuli and that this response is likely mediated via activation of Y2 receptors localized apically in taste cells. Our findings suggest distinct functions for PYY produced locally in taste cells vs. that circulating systemically.

New advances in models and strategies for developing anti-obesity drugs

INTRODUCTION

Obesity is a worldwide pandemic. Obesity-related health and economic costs are staggering. Existing strategies to combat obesity through lifestyle improvements and medical intervention have had limited success. Pharmacotherapy, in combination with lifestyle modification, may play a vital role in reversing the disease burden. However, past and current weight-loss medications have had serious safety risks, notably cardiovascular and psychiatric events.

AREAS COVERED

The authors review the strategies for designing new anti-obesity drugs by describing those currently in development. They describe their target, mechanism of action and developmental or regulatory status. Furthermore, they discuss the problem of weight regain following weight loss, and its relevance to the long-term success of anti-obesity pharmacotherapy.

EXPERT OPINION

For weight management drugs to achieve the safety and efficacy required to be impactful, current studies are uncovering and characterizing new targets, including new signaling circuits and hormones regulating appetite and metabolism, and re-evaluating the role of pharmacotherapy in weight management. To avoid the safety failures of many past weight-loss drugs, the models and strategies covered in this article incorporate recent advances in knowledge and technology. We discuss the emergence of cGMP signaling as a potentially transformative target in weight management. Modulating cGMP signaling may represent an ideal goal for an anti-obesity pharmacotherapy, reflecting some of the major themes described in the present review: targeting pathways that are newly realized as relevant for weight management; promoting safety by re-purposing drugs that are safe, proven, and approved for clinical use; and having a synergistic effect on multiple, reinforcing pathways.

DPP4 deficiency exerts protective effect against H2O2 induced oxidative stress in isolated cardiomyocytes

Apart from the antihyperglycemic effects, DPP4 inhibitors and GLP-1 molecules are involved in the preservation of cardiac functions. We have demonstrated that DPP4-deficient rats possess resistance to endotoxemia and ischemia/reperfusion stress. However, whether the decrease of DPP4 activity simply augmented the GLP-1 signaling or that such decrease resulted in a change of cellular function remain unclear. Accordingly, we investigated the responses of H₂O₂-induced oxidative stress in adult wild-type and DPP4-deficient rats isolated cardiomyocytes. The coadministration of GLP-1 or DPP4 inhibitor was also performed to define the mechanisms. Cell viability, ROS concentration, catalase activity, glucose uptake, prosurvival, proapoptotic signaling, and contractile function were examined after cells exposed to H₂O₂. DPP4-deficient cardiomyocytes were found to be resistant to H₂O₂-induced cell death via activating AKT signaling, enhancing glucose uptake, preserving catalase activity, diminishing ROS level and proapoptotic signaling. GLP-1 concentration-dependently improved cell viability in wild-type cardiomyocyte against ROS stress, and the ceiling response concentration (200 nM) was chosen for studies. GLP-1 was shown to decrease H₂O₂-induced cell death by its receptor-dependent AKT pathway in wild-type cardiomyocytes, but failed to cause further activation of AKT in DPP4-deficient cardiomyocytes. Acute treatment of DPP4 inhibitor only augmented the protective effect of low dose GLP-1, but failed to alter fuel utilization or ameliorate cell viability in wild-type cardiomyocytes after H₂O₂ exposure. The improvement of cell viability after H₂O₂ exposure was correlated with the alleviation of cellular contractile dysfunction in both DPP4-deficient and GLP-1 treated wild-type cardiomyocytes. These findings demonstrated that GLP-1 receptor-dependent pathway is important and exert protective effect in wild-type cardiomyocyte. Long term loss of DPP4 activity increased the capability against ROS stress, which was more than GLP-1 dependent pathway.

Peptide regulators of peripheral taste function

The peripheral sensory organ of the gustatory system, the taste bud, contains a heterogeneous collection of sensory cells. These taste cells can differ in the stimuli to which they respond and the receptors and other signaling molecules they employ to transduce and encode those stimuli. This molecular diversity extends to the expression of a varied repertoire of bioactive peptides that appear to play important functional roles in signaling taste information between the taste cells and afferent sensory nerves and/or in processing sensory signals within the taste bud itself. Here, we review studies that examine the expression of bioactive peptides in the taste bud and the impact of those peptides on taste functions. Many of these peptides produced in taste buds are known to affect appetite, satiety or metabolism through their actions in the brain, pancreas and other organs, suggesting a functional link between the gustatory system and the neural and endocrine systems that regulate feeding and nutrient utilization.