Receptor identification and physiological characterisation of glucagon-like peptide-2 in the rat heart

Gut Hormones in Heart Failure

Heart failure (HF) is a syndrome affecting all organ systems. While some organ interactions have been studied intensively in HF (such as the cardiorenal interaction), the endocrine gut has to some degree been overlooked. However, there is growing evidence of direct cardiac effects of several hormones secreted from the gastrointestinal tract. For instance, GLP-1 (glucagon-like peptide-1), an incretin hormone secreted from the distal intestine following food intake, has notable effects on the heart, impacting heart rate and contractility. GLP-1 may even possess cardioprotective abilities, such as inhibition of myocardial ischemia and cardiac remodeling. While other gut hormones have been less studied, there is evidence suggesting cardiostimulatory properties of several hormones. Moreover, it has been reported that patients with HF have altered bioavailability of numerous gastrointestinal hormones, which may have prognostic implications. This might indicate an important role of gut hormones in cardiac physiology and pathology, which may be of particular importance in the failing heart. We present an overview of the current knowledge on gut hormones in HF, focusing on HF with reduced ejection fraction, and discuss how these hormones may be regulators of cardiac function and central hemodynamics. Potential therapeutic perspectives are discussed, and knowledge gaps are highlighted herein.

Targeting the GLP-2 receptor in the management of obesity

Recent advancements in understanding glucagon-like peptide 2 (GLP-2) biology and pharmacology have sparked interest in targeting the GLP-2 receptor (GLP-2R) in the treatment of obesity. GLP-2 is a proglucagon-derived 33-amino acid peptide co-secreted from enteroendocrine L cells along with glucagon-like peptide 1 (GLP-1) and has a range of actions via the GLP-2R, which is particularly expressed in the gastrointestinal tract, the liver, adipose tissue, and the central nervous system (CNS). In humans, GLP-2 evidently induces intestinotrophic effects (i.e., induction of intestinal mucosal proliferation and improved gut barrier function) and promotes mesenteric blood flow. However, GLP-2 does not seem to have appetite or food intake-reducing effects in humans, but its gut barrier-promoting effect may be of interest in the context of obesity. Obesity is associated with reduced gut barrier function, increasing the translocation of proinflammatory gut content to the circulation. This phenomenon constitutes a strong driver of obesity-associated systemic low-grade inflammation, which in turn plays a major role in the development of most obesity-associated complications. Thus, the intestinotrophic and gut barrier-improving effect of GLP-2, which in obese rodent models shows strong anti-inflammatory potential, may, in combination with food intake-reducing strategies, e.g., GLP-1 receptor (GLP-1) agonism, be able to rectify core pathophysiological mechanism of obesity. Here, we provide an overview of GLP-2 physiology in the context of obesity pathophysiology and review the pharmacological potential of GLP-2R activation in the management of obesity and related comorbidities.

Glucagon-like Peptide-2 Depresses Ileal Contractility in Preparations from Mice through Opposite Modulatory Effects on Nitrergic and Cholinergic Neurotransmission

Glucagon-like peptide-2 (GLP-2) has been reported to influence gastrointestinal motor responses, exerting a modulatory role on enteric neurotransmission. To our knowledge, no data on GLP-2 effects on the motility of the isolated ileum are available; therefore, we investigated whether GLP-2 affects the contractile activity of mouse ileal preparations and the neurotransmitters engaged. Ileal preparations showed tetrodotoxin (TTX)- and atropine-insensitive spontaneous contractile activity, which was unaffected by the nitric oxide synthesis inhibitor, L-NNA. GLP-2 depressed the spontaneous contractility, an effect that was abolished by TTX or L-NNA and not influenced by atropine. Electrical field stimulation induced TTX- and atropine-sensitive contractile responses, which were reduced in amplitude by GLP-2 even in the presence of L-NNA. Immunohistochemical results showed a significant increase in nNOS-positive fibers in the ileal muscle wall and a significant decrease in ChAT-positive myenteric neurons in GLP-2-exposed preparations. The present results offer the first evidence that GLP-2 acts on ileal preparations. The hormone appears to depress ileal contractility through a dual opposite modulatory effect on inhibitory nitrergic and excitatory cholinergic neurotransmission. From a physiological point of view, it could be hypothesized that GLP-2 inhibitory actions on ileal contractility can increase transit time, facilitating nutrient absorption.

Cateslytin abrogates lipopolysaccharide-induced cardiomyocyte injury by reducing inflammation and oxidative stress through toll like receptor 4 interaction

Global public health is threatened by new pathogens, antimicrobial resistant microorganisms and a rapid decline of conventional antimicrobials efficacy. Thus, numerous medical procedures become life-threating. Sepsis can lead to tissue damage such as myocardium inflammation, associated with reduction of contractility and diastolic dysfunction, which may cause death. In this perspective, growing interest and attention are paid on host defence peptides considered as new potential antimicrobials. In the present study, we investigated the physiological and biochemical properties of Cateslytin (Ctl), an endogenous antimicrobial chromogranin A-derived peptide, in H9c2 cardiomyocytes exposed to lipopolysaccharide (LPS) infection. We showed that both Ctl (L and D) enantiomers, but not their scrambled counterparts, significantly increased cardiomyocytes viability following LPS, even if L-Ctl was effective at lower concentration (1 nM) compared to D-Ctl (10 nM). L-Ctl mitigated LPS-induced LDH release and oxidative stress, as visible by a reduction of MDA and protein carbonyl groups content, and by an increase of SOD activity. Molecular docking simulations strongly suggested that L-Ctl modulates TLR4 through a direct binding to the partner protein MD-2. Molecular analyses indicated that the protection mediated by L-Ctl against LPS-evoked sepsis targeted the TLR4/ERK/JNK/p38-MAPK pathway, regulating NFkB p65, NFkB p52 and COX2 expression and repressing the mRNA expression levels of the LPS-induced proinflammatory factors IL-1β, IL-6, TNF-α and NOS2. These findings indicate that Ctl could be considered as a possible candidate for the development of new antimicrobials strategies in the treatment of myocarditis. Interestingly, L-enantiomeric Ctl showed remarkable properties in strengthening the anti-inflammatory and anti-oxidant effects on cardiomyocytes.

Cardiac and Metabolic Impact of Functional Foods with Antioxidant Properties Based on Whey Derived Proteins Enriched with Hemp Seed Oil

The impaired ability to feed properly, evident in oncologic, elderly, and dysphagic patients, may result in malnutrition and sarcopenia. Increasing the consumption of dietary proteins by functional foods and enriching their composition by adding beneficial nutrients may represent an adjuvant therapy. We aimed to evaluate the safety and the positive effects of a standard diet (SD) supplemented with whey-derived protein puddings (WDPP), with appropriate rheological properties, and hemp seed oil (HSO), rich in polyphenols. Rats were assigned to SD, WDPP, WDPP plus hemp seed oil (HSOP), and HSO supplemented diets for eight weeks. “Anthropometric”, metabolic, and biochemical variables, oxidative stress, tissue injury, liver histology, and cardiac susceptibility to ischemia/reperfusion were analyzed. All the supplementations did not induce significant changes in biochemical and metabolic variables, also in relation to glucose tolerance, and livers did not undergo morphological alteration and injury. An improvement of cardiac post-ischemic function in the Langendorff perfused heart model and a reduction of infarct size were observed in WDPP and HSOP groups, thanks to their antioxidant effects and the activation of Akt- and AMPK-dependent protective pathways. Data suggest that (i) functional foods enriched with WDPP and HSOP may be used to approach malnutrition and sarcopenia successfully under disabling conditions, also conferring cardioprotection, and that (ii) adequate rheological properties could positively impact dysphagia-related problems.

Localization of Glucagon-Like Peptide-2 Receptor Expression in the Mouse

Glucagon-like peptide-2 (GLP-2), secreted from enteroendocrine cells, attenuates gut motility, enhances barrier function, and augments nutrient absorption, actions mediated by a single GLP-2 receptor (GLP-2R). Despite extensive analyses, the precise distribution and cellular localization of GLP-2R expression remains controversial, confounded by the lack of suitable GLP-2R antisera. Here, we reassessed murine Glp2r expression using regular and real-time quantitative PCR (qPCR), in situ hybridization (ISH), and a Glp2rLacZ reporter mouse. Glp2r mRNA expression was detected from the stomach to the rectum and most abundant in the jejunum. Glp2r transcripts were also detected in cerebral cortex, mesenteric lymph nodes, gallbladder, urinary bladder, and mesenteric fat. Surprisingly, Glp2r mRNA was found in testis by qPCR at levels similar to jejunum. However, the testis Glp2r transcripts, detected by different primer pairs and qPCR, lacked 5' mRNA coding sequences, and only a minute proportion of them corresponded to full-length Glp2r mRNA. Within the gut, Glp2r-driven LacZ expression was localized to enteric neurons and lamina propria stromal cells, findings confirmed by ISH analysis of the endogenous Glp2r mRNA. Unexpectedly, vascular Glp2rLacZ expression was localized to mesenteric veins and not arteries. Moreover, mesenteric fat Glp2rLacZ expression was detected within blood vessels and not adipocytes. Reporter LacZ expression was not detected in all tissues expressing an endogenous Glp2r transcript, such as gallbladder, urinary bladder, and mesenteric lymph nodes. Collectively, these findings extend our understanding of the cellular domains of Glp2r expression and highlight limitations inherent in application of commonly used technologies to infer analysis of gene expression.

Gut microbiota and inflammation in chronic kidney disease and their roles in the development of cardiovascular disease

The health and proper functioning of the cardiovascular and renal systems largely depend on crosstalk in the gut-kidney-heart/vessel triangle. Recent evidence suggests that the gut microbiota has an integral function in this crosstalk. Mounting evidence indicates that the development of chronic kidney and cardiovascular diseases follows chronic inflammatory processes that are affected by the gut microbiota via various immune, metabolic, endocrine, and neurologic pathways. Additionally, deterioration of the function of the cardiovascular and renal systems has been reported to disrupt the original gut microbiota composition, further contributing to the advancement of chronic cardiovascular and renal diseases. Considering the interaction between the gut microbiota and the renal and cardiovascular systems, we can infer that interventions for the gut microbiota through diet and possibly some medications can prevent/stop the vicious cycle between the gut microbiota and the cardiovascular/renal systems, leading to a decrease in chronic cardiovascular and renal diseases.

Roles of Gut-Derived Secretory Factors in the Pathogenesis of Non-Alcoholic Fatty Liver Disease and Their Possible Clinical Applications

The rising prevalence of non-alcoholic fatty liver disease (NAFLD) parallels the global increase in the number of people diagnosed with obesity and metabolic syndrome. The gut-liver axis (GLA) plays an important role in the pathogenesis of NAFLD/non-alcoholic steatohepatitis (NASH). In this review, we discuss the clinical significance and underlying mechanisms of action of gut-derived secretory factors in NAFLD/NASH, focusing on recent human studies. Several studies have identified potential causal associations between gut-derived secretory factors and NAFLD/NASH, as well as the underlying mechanisms. The effects of gut-derived hormone-associated drugs, such as glucagon-like peptide-1 analog and recombinant variant of fibroblast growth factor 19, and other new treatment strategies for NAFLD/NASH have also been reported. A growing body of evidence highlights the role of GLA in the pathogenesis of NAFLD/NASH. Larger and longitudinal studies as well as translational research are expected to provide additional insights into the role of gut-derived secretory factors in the pathogenesis of NAFLD/NASH, possibly providing novel markers and therapeutic targets in patients with NAFLD/NASH.

Phoenixin-14: detection and novel physiological implications in cardiac modulation and cardioprotection

Phoenixin-14 (PNX) is a newly identified peptide co-expressed in the hypothalamus with the anorexic and cardioactive Nesfatin-1. Like Nesfatin-1, PNX is able to cross the blood-brain barrier and this suggests a role in peripheral modulation. Preliminary mass spectrography data indicate that, in addition to the hypothalamus, PNX is present in the mammalian heart. This study aimed to quantify PNX expression in the rat heart, and to evaluate whether the peptide influences the myocardial function under basal condition and in the presence of ischemia/reperfusion (I/R). By ELISA the presence of PNX was detected in both hypothalamus and heart. In plasma of normal, but not of obese rats, the peptide concentrations increased after meal. Exposure of the isolated and Langendorff perfused rat heart to exogenous PNX induces a reduction of contractility and relaxation, without effects on coronary pressure and heart rate. As revealed by immunoblotting, these effects were accompanied by an increase of Erk1/2, Akt and eNOS phosphorylation. PNX (EC50 dose), administered after ischemia, induced post-conditioning-like cardioprotection. This was revealed by a smaller infarct size and a better systolic recovery with respect to those detected on hearts exposed to I/R alone. The peptide also activates the cardioprotective RISK and SAFE cascades and inhibits apoptosis. These effects were also observed in the heart of obese rats. Our data provide a first evidence on the peripheral activity of PNX and on its direct cardiomodulatory and cardioprotective role under both normal conditions and in the presence of metabolic disorders.

Influence of glucagon-like peptide 2 on energy homeostasis

Glucagon like peptide-2 (GLP-2) is a gastrointestinal hormone released from enteroendocrine L-type cells together with glucagon like peptide-1 in response to dietary nutrients. GLP-2 acts through a specific receptor, the GLP-2 receptor, mainly located in the gut and in the brain. Classically, GLP-2 is considered a trophic hormone involved in the maintenance of intestinal epithelial morphology and function. This role has been targeted for therapies promoting repair and adaptive growth of the intestinal mucosa. Recently, GLP-2 has been shown to exert beneficial effects on glucose metabolism specially in conditions related to increased uptake of energy, such as obesity. Several actions of GLP-2 are related to a positive energy balance: GLP-2 increases not only the absorptive surface, but also expression and activity of epithelial brush-border nutrient transporters and digestive enzymes, intestinal blood flow, postprandial chylomicron secretion and it inhibits gastrointestinal motility, providing the opportunity to increase absorption of nutrients. Other actions, including anorexigenic effects, appear in opposition to the energy intake. In this review, we discuss the GLP-2 functions related to energy homeostasis. GLP-2 could be considered an hormone causing positive energy balance, which, however has the role to mitigate the metabolic dysfunctions associated with hyper-adiposity.

Vascular Biology of Glucagon Receptor Superfamily Peptides: Mechanistic and Clinical Relevance

Regulatory peptides produced in islet and gut endocrine cells, including glucagon, glucagon-like peptide-1 (GLP-1), GLP-2, and glucose-dependent insulinotropic polypeptide, exert actions with considerable metabolic importance and translational relevance. Although the clinical development of GLP-1 receptor agonists and dipeptidyl peptidase-4 inhibitors has fostered research into how these hormones act on the normal and diseased heart, less is known about the actions of these peptides on blood vessels. Here we review the effects of these peptide hormones on normal blood vessels and highlight their vascular actions in the setting of experimental and clinical vascular injury. The cellular localization and signal transduction properties of the receptors for glucagon, GLP-1, GLP-2, and glucose-dependent insulinotropic polypeptide are discussed, with emphasis on endothelial cells and vascular smooth muscle cells. The actions of these peptides on the control of blood flow, blood pressure, angiogenesis, atherosclerosis, and vascular inflammation are reviewed with a focus on elucidating direct and indirect mechanisms of action. How these peptides traverse the blood-brain barrier is highlighted, with relevance to the use of GLP-1 receptor agonists to treat obesity and neurodegenerative disorders. Wherever possible, we compare actions identified in cell lines and primary cell culture with data from preclinical studies and, when available, results of human investigation, including studies in subjects with diabetes, obesity, and cardiovascular disease. Throughout the review, we discuss pitfalls, limitations, and challenges of the existing literature and highlight areas of controversy and uncertainty. The increasing use of peptide-based therapies for the treatment of diabetes and obesity underscores the importance of understanding the vascular biology of peptide hormone action.

Influence of endogenous glucagon-like peptide-2 on lipid disorders in mice fed a high-fat diet

AIM

The purpose of the present study was to investigate the influence of endogenous glucagon-like peptide-2 (GLP-2) on lipid profile in mice fed a standard diet (STD) or a high-fat diet (HFD).

MATERIALS AND METHODS

HFD- and age-matched STD mice were injected once a day with GLP-2 (3-33), a GLP-2 receptor (GLP-2R) antagonist, or vehicle for 4 weeks.

RESULTS

HFD mice displayed increased intrahepatic lipid concentration and hepatic steatosis and higher plasma concentrations of cholesterol, LDL, AST, and ALT than STD mice. No difference was observed in lipid fecal elimination. In STD mice, the chronic treatment with GLP-2 (3-33) did not affect any parameter, while in HFD mice, it enhanced plasma triglycerides, cholesterol, ALT, and AST and reduced HDL, it increased intrahepatic lipid concentration, and it worsened the hepatic steatosis degree, without affecting lipid fecal elimination.

CONCLUSIONS

The present results suggest that GLP-2R antagonism worsens lipid disorders in HFD mice, and endogenous GLP-2 might even exert a defensive role against lipid imbalance.

Generation of glucagon-like peptide-2-expressing Saccharomyces cerevisiae and its improvement of the intestinal health of weaned rats

We aimed to assess the feasibility of enhancing the intestinal development of weaned rats using glucagon-like peptide-2 (GLP-2)-expressing Saccharomyces cerevisiae (S. cerevisiae). GLP-2-expressing S. cerevisiae (GLP2-SC) was generated using a recombinant approach. The diet of weaned rats was supplemented with the GLP2-SC strain. The average daily gain (ADG), the intestinal morphology and the activities of the digestive enzymes in the jejunum were tested to assess the influence of the GLP2-SC strain on intestinal development. The proliferation of rat enterocytes was also assessed in vitro. The study revealed that the ADG of the weaned rats that received GLP2-SC was significantly greater than that of the controls fed a basal diet (Control) and S. cerevisiae harbouring an empty vector (EV-SC) (P < 0.05) but was equivalent to that of positive control rats fed recombinant human GLP-2 (rh-GLP2) (P > 0.05). Furthermore, GLP2-SC significantly increased villous height (P < 0.01) and digestive enzyme activity (P < 0.05) in the jejunum. Immunohistochemistry analysis further affirmed that enterocyte proliferation was stimulated in rats fed the GLP2-SC strain, as indicated by the greater number of enterocytes stained with proliferative cell nuclear antigen (P < 0.05). In vitro, the proliferation of rat enterocytes was also stimulated by GLP-2 expressed by the GLP2-SC strain (P < 0.01). Herein, the combination of the GLP-2 approach and probiotic delivery constitute a possible dietary supplement for animals after weaning.

The innovative "Bio-Oil Spread" prevents metabolic disorders and mediates preconditioning-like cardioprotection in rats

BACKGROUND AND AIMS

Obesity is often associated with an increased cardiovascular risk. The food industry and the associated research activities focus on formulating products that are a perfect mix between an adequate fat content and health. We evaluated whether a diet enriched with Bio-Oil Spread (SD), an olive oil-based innovative food, is cardioprotective in the presence of high-fat diet (HFD)-dependent obesity.

METHODS AND RESULTS

Rats were fed for 16 weeks with normolipidic diet (ND; fat: 6.2%), HFD (fat: 42%), and ND enriched with SD (6.2% of fat + 35.8% of SD). Metabolic and anthropometric parameters were measured. Heart and liver structures were analyzed by histochemical examination. Ischemic susceptibility was evaluated on isolated and Langendorff-perfused cardiac preparations. Signaling was assessed by Western blotting. Compared to ND rats, HFD rats showed increased body weight and abdominal obesity, dyslipidemia, and impaired glucose tolerance. Morphological analyses showed that HFD is associated with heart and liver modifications (hypertrophy and steatosis, respectively), lesser evident in the SD group, together with metabolic and anthropometric alterations. In particular, IGF-1R immunodetection revealed a reduction of hypertrophy in SD heart sections. Notably, SD diet significantly reduced myocardial susceptibility against ischemia/reperfusion (I/R) with respect to HFD through the activation of survival signals (Akt, ERK1/2, and Bcl2). Systolic and diastolic performance was preserved in the SD group.

CONCLUSIONS

We suggest that SD may contribute to the prevention of metabolic disorders and cardiovascular alterations typical of severe obesity induced by an HFD, including the increased ischemic susceptibility of the myocardium. Our results pave the way to evaluate the introduction of SD in human alimentary guidelines as a strategy to reduce saturated fat intake.

GLP2: an underestimated signal for improving glycaemic control and insulin sensitivity

Glucagon-like peptide 2 (GLP2) is a proglucagon-derived peptide produced by intestinal enteroendocrine L-cells and by a discrete population of neurons in the brainstem, which projects mainly to the hypothalamus. The main biological actions of GLP2 are related to the regulation of energy absorption and maintenance of mucosal morphology, function and integrity of the intestine; however, recent experimental data suggest that GLP2 exerts beneficial effects on glucose metabolism, especially in conditions related to increased uptake of energy, such as obesity, at least in the animal model. Indeed, mice lacking GLP2 receptor selectively in hypothalamic neurons that express proopiomelanocortin show impaired postprandial glucose tolerance and hepatic insulin resistance (by increased gluconeogenesis). Moreover, GLP2 acts as a beneficial factor for glucose metabolism in mice with high-fat diet-induced obesity. Thus, the aim of this review is to update and summarize current knowledge about the role of GLP2 in the control of glucose homeostasis and to discuss how this molecule could exert protective effects against the onset of related obesity type 2 diabetes.

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.

COMPARATIVE GUT PHYSIOLOGY SYMPOSIUM: Comparative physiology of glucagon-like peptide-2: Implications and applications for production and health of ruminants

Glucagon-like peptide-2 (GLP-2) is a 33-amino acid peptide derived from proteolytic cleavage of proglucagon by prohormone convertase 1/3 in enteroendocrine L cells. Studies conducted in humans, in rodent models, and in vitro indicate that GLP-2 is secreted in response to the presence of molecules in the intestinal lumen, including fatty acids, carbohydrates, amino acids, and bile acids, which are detected by luminal chemosensors. The physiological actions of GLP-2 are mediated by its G protein-coupled receptor expressed primarily in the intestinal tract on enteric neurons, enteroendocrine cells, and myofibroblasts. The biological activity of GLP-2 is further regulated by dipeptidyl peptidase IV, which rapidly cleaves the N-terminus of GLP-2 that is responsible for GLP-2 receptor activation. Within the gut, GLP-2 increases nutrient absorption, crypt cell proliferation, and mesenteric blood flow and decreases gut permeability and motility, epithelial cell apoptosis, and inflammation. Outside the gut, GLP-2 reduces bone resorption, can suppress appetite, and is cytoprotective in the lung. Thus, GLP-2 has been studied intensively as a therapeutic to improve intestinal function of humans during parenteral nutrition and following small bowel resection and, more recently, as a treatment for osteoporosis and obesity-related disorders and to reduce cellular damage associated with inflammation of the gut and lungs. Recent studies demonstrate that many biological actions and properties of GLP-2 in ruminants are similar to those in nonruminants, including the potential to reduce intestinal nitro-oxidative stress in calves caused by parasitic diseases such as coccidiosis. Because of its beneficial impacts on nutrient absorption, gut healing, and normal gut development, GLP-2 therapy offers significant opportunities to improve calf health and production efficiency. However, GLP-2 therapies require an extended time course to achieve desired physiological responses, as well as daily administration because of the hormone's short half-life. Thus, practical means of administration and alternative strategies to enhance basal GLP-2 secretion (e.g., through specific feed additives), which are more likely to achieve consumer acceptance, are needed. Opportunities to address these challenges are discussed.

GPER mediates cardiotropic effects in spontaneously hypertensive rat hearts

Estrogens promote beneficial effects in the cardiovascular system mainly through the estrogen receptor (ER)α and ERβ, which act as ligand-gated transcription factors. Recently, the G protein-coupled estrogen receptor (GPER) has been implicated in the estrogenic signaling in diverse tissues, including the cardiovascular system. In this study, we demonstrate that left ventricles of male Spontaneously Hypertensive Rats (SHR) express higher levels of GPER compared to normotensive Wistar Kyoto (WKY) rats. In addition, we show that the selective GPER agonist G-1 induces negative inotropic and lusitropic effects to a higher extent in isolated and Langendorff perfused hearts of male SHR compared to WKY rats. These cardiotropic effects elicited by G-1 involved the GPER/eNOS transduction signaling, as determined by using the GPER antagonist G15 and the eNOS inhibitor L-NIO. Similarly, the G-1 induced activation of ERK1/2, AKT, GSK3β, c-Jun and eNOS was abrogated by G15, while L-NIO prevented only the eNOS phosphorylation. In hypoxic Langendorff perfused WKY rat heart preparations, we also found an increased expression of GPER along with that of the hypoxic mediator HIF-1α and the fibrotic marker CTGF. Interestingly, G15 and L-NIO prevented the ability of G-1 to down-regulate the expression of both HIF-1α and CTGF, which were found expressed to a higher extent in SHR compared to WKY rat hearts. Collectively, the present study provides novel data into the potential role played by GPER in hypertensive disease on the basis of its involvement in myocardial inotropism and lusitropism as well as the expression of the apoptotic HIF-1α and fibrotic CTGF factors. Hence, GPER may be considered as a useful target in the treatment of some cardiac dysfunctions associated with stressful conditions like the essential hypertension.

Glucagon-like peptide-2 and mouse intestinal adaptation to a high-fat diet

Endogenous glucagon-like peptide-2 (GLP2) is a key mediator of refeeding-induced and resection-induced intestinal adaptive growth. This study investigated the potential role of GLP2 in mediating the mucosal responses to a chronic high-fat diet (HFD). In this view, the murine small intestine adaptive response to a HFD was analyzed and a possible involvement of endogenous GLP2 was verified using GLP2 (3-33) as GLP2 receptor (GLP2R) antagonist. In comparison with animals fed a standard diet, mice fed a HFD for 14 weeks exhibited an increase in crypt-villus mean height (duodenum, 27.5±3.0%; jejunum, 36.5±2.9%; P<0.01), in the cell number per villus (duodenum, 28.4±2.2%; jejunum, 32.0±2.9%; P<0.01), and in Ki67-positive cell number per crypt. No change in the percent of caspase-3-positive cell in the villus-crypt was observed. The chronic exposure to a HFD also caused a significant increase in GLP2 plasma levels and in GLP2R intestinal expression. Daily administration of GLP2 (3-33) (30-60  ng) for 4 weeks did not modify the crypt-villus height in control mice. In HFD-fed mice, chronic treatment with GLP2 (3-33) reduced the increase in crypt-villus height and in the cell number per villus through reduction of cell proliferation and increase in apoptosis. This study provides the first experimental evidence for a role of endogenous GLP2 in the intestinal adaptation to HFD in obese mice and for a dysregulation of the GLP2/GLP2R system after a prolonged HFD.

Nesfatin-1 as a novel cardiac peptide: identification, functional characterization, and protection against ischemia/reperfusion injury

Nesfatin-1 is an anorexic nucleobindin-2 (NUCB2)-derived hypothalamic peptide. It controls feeding behavior, water intake, and glucose homeostasis. If intracerebrally administered, it induces hypertension, thus suggesting a role in central cardiovascular control. However, it is not known whether it is able to directly control heart performance. We aimed to verify the hypothesis that, as in the case of other hypothalamic satiety peptides, Nesfatin-1 acts as a peripheral cardiac modulator. By western blotting and QT-PCR, we identified the presence of both Nesfatin-1 protein and NUCB2 mRNA in rat cardiac extracts. On isolated and Langendorff-perfused rat heart preparations, we found that exogenous Nesfatin-1 depresses contractility and relaxation without affecting coronary motility. These effects did not involve Nitric oxide, but recruited the particulate guanylate cyclase (pGC) known as natriuretic peptide receptor A (NPR-A), protein kinase G (PKG) and extracellular signal-regulated kinases1/2 (ERK1/2). Co-immunoprecipitation and bioinformatic analyses supported an interaction between Nesfatin-1 and NPR-A. Lastly, we preliminarily observed, through post-conditioning experiments, that Nesfatin-1 protects against ischemia/reperfusion (I/R) injury by reducing infarct size, lactate dehydrogenase release, and postischemic contracture. This protection involves multiple prosurvival kinases such as PKCε, ERK1/2, signal transducer and activator of transcription 3, and mitochondrial K(ATP) channels. It also ameliorates contractility recovery. Our data indicate that: (1) the heart expresses Nesfatin-1, (2) Nesfatin-1 directly affects myocardial performance, possibly involving pGC-linked NPR-A, the pGC/PKG pathway, and ERK1/2, (3) the peptide protects the heart against I/R injury. Results pave the way to include Nesfatin-1 in the neuroendocrine modulators of the cardiac function, also encouraging the clarification of its clinical potential in the presence of nutrition-dependent physio-pathologic cardiovascular diseases.

Review article: a comparison of glucagon-like peptides 1 and 2

BACKGROUND

Recent advancements in understanding the roles and functions of glucagon-like peptide 1 (GLP-1) and 2 (GLP-2) have provided a basis for targeting these peptides in therapeutic strategies.

AIM

To summarise the preclinical and clinical research supporting the discovery of new therapeutic molecules targeting GLP-1 and GLP-2.

METHODS

This review is based on a comprehensive PubMed search, representing literature published during the past 30 years related to GLP-1 and GLP-2.

RESULTS

Although produced and secreted together primarily from L cells of the intestine in response to ingestion of nutrients, GLP-1 and GLP-2 exhibit distinctive biological functions that are governed by the expression of their respective receptors, GLP-1R and GLP-2R. Through widespread expression in the pancreas, intestine, nervous tissue, et cetera, GLP-1Rs facilitates an incretin effect along with effects on appetite and satiety. GLP-1 analogues resistant to degradation by dipeptidyl peptidase-IV and inhibitors of dipeptidyl peptidase-IV have been developed to aid treatment of diabetes and obesity. The GLP-2R is expressed almost exclusively in the stomach and bowel. The most apparent role for GLP-2 is its promotion of growth and function of intestinal mucosa, which has been targeted for therapies that promote repair and adaptive growth. These are used as treatments for intestinal failure and related conditions.

CONCLUSIONS

Our growing understanding of the biology and function of GLP-1, GLP-2 and corresponding receptors has fostered further discovery of fundamental biological function as well as new categories of potent therapeutic medicines.

Effects of temperature on the nitric oxide-dependent modulation of the Frank-Starling mechanism: the fish heart as a case study

The Frank-Starling law is a fundamental property of the vertebrate myocardium which allows, when the end-diastolic volume increases, that the consequent stretch of the myocardial fibers generates a more forceful contraction. It has been shown that in the eel (Anguilla anguilla) heart, nitric oxide (NO) exerts a direct myocardial relaxant effect, increasing the sensitivity of the Frank-Starling response (Garofalo et al., 2009). With the use of isolated working heart preparations, this study investigated the relationship between NO modulation of Frank-Starling response and temperature challenges in the eel. The results showed that while, in long-term acclimated fish (spring animals perfused at 20 °C and winter animals perfused at 10 °C) the inhibition of NO production by L-N5 (1-iminoethyl)ornithine (L-NIO) significantly reduced the Frank-Starling response, under thermal shock conditions (spring animals perfused at 10 or 15 °C and winter animals perfused at 15 or 20 °C) L-NIO treatment resulted without effect. Western blotting analysis revealed a decrease of peNOS and pAkt expressions in samples subjected to thermal shock. Moreover, an increase in Hsp90 protein levels was observed under heat thermal stress. Together, these data suggest that the NO synthase/NO-dependent modulation of the Frank-Starling mechanism in fish is sensitive to thermal stress.

Glucagon-like peptide-2 (GLP-2) modulates the cGMP signalling pathway by regulating the expression of the soluble guanylyl cyclase receptor subunits in cultured rat astrocytes

The aim of this work was to study the effect of glucagon-like peptide-2 (GLP-2) on the cyclic guanosine monophosphate (cGMP) signalling pathway and whether insulin or epidermal growth factor (EGF) might modulate the effects of GLP-2. GLP-2 produced a dose-dependent decrease in intracellular sodium nitroprusside-induced cGMP production. However, insulin induced an increase in the levels of cGMP that was dose-dependently decreased by the addition of GLP-2. By contrast, EGF induced a decrease in cGMP production, which was further reduced by the addition of GLP-2. To assess whether variations in cGMP production might be related with changes in some component of soluble guanylyl cyclase (sGC), the expression of the α1, α2, and β1 subunits were determined by Western blot analysis. At 1 h, GLP-2 produced a decrease in the expression of both α1 and β1 in the cytosolic fraction, but at 24 h only β1was reduced. As expected, insulin induced an increase in the expression of both subunits after 1 h of incubation; this was decreased by the addition of GLP-2. Likewise, incubation with EGF for 24 h produced a decrease in the expression of both subunits that was maximal when GLP-2 was added. In addition, incubation with insulin for 1 h produced an increase in the expression of the α2 subunit, which was reduced by the addition of GLP-2. These results suggest that GLP-2 inhibits cGMP production by decreasing the cellular content of at least one subunit of the heterodimeric active form of the sGC, independently of the presence of insulin or EFG. This may open new insights into the actions of this neuropeptide.

Cardiovascular biology of the incretin system

Glucagon-like peptide-1 (GLP-1) is an incretin hormone that enhances glucose-stimulated insulin secretion and exerts direct and indirect actions on the cardiovascular system. GLP-1 and its related incretin hormone, glucose-dependent insulinotropic polypeptide, are rapidly inactivated by the enzyme dipeptidyl peptidase 4 (DPP-4), a key determinant of incretin bioactivity. Two classes of medications that enhance incretin action, GLP-1 receptor (GLP-1R) agonists and DPP-4 inhibitors, are used for the treatment of type 2 diabetes mellitus. We review herein the cardiovascular biology of GLP-1R agonists and DPP-4 inhibitors, including direct and indirect effects on cardiomyocytes, blood vessels, adipocytes, the control of blood pressure, and postprandial lipoprotein secretion. Both GLP-1R activation and DPP-4 inhibition exert multiple cardioprotective actions in preclinical models of cardiovascular dysfunction, and short-term studies in human subjects appear to demonstrate modest yet beneficial actions on cardiac function in subjects with ischemic heart disease. Incretin-based agents control body weight, improve glycemic control with a low risk of hypoglycemia, decrease blood pressure, inhibit the secretion of intestinal chylomicrons, and reduce inflammation in preclinical studies. Nevertheless, there is limited information on the cardiovascular actions of these agents in patients with diabetes and established cardiovascular disease. Hence, a more complete understanding of the cardiovascular risk to benefit ratio of incretin-based therapies will require completion of long-term cardiovascular outcome studies currently underway in patients with type 2 diabetes mellitus.