Exendin-4 potently decreases ghrelin levels in fasting rats

Glucagon-like peptide 1 receptor agonist, exendin-4, reduces alcohol-associated fatty liver disease

Fatty liver is the earliest response to excessive ethanol consumption, which increases the susceptibility of the liver to develop advanced stage of liver disease. Our previous studies have revealed that chronic alcohol administration alters metabolic hormone levels and their functions. Of current interest to our laboratory is glucagon-like peptide 1 (GLP-1), a widely studied hormone known to reduce insulin resistance and hepatic fat accumulation in patients with metabolic-associated fatty liver disease. In this study, we examined the beneficial effects of exendin-4 (a GLP-1 receptor agonist) in an experimental rat model of ALD. Male Wistar rats were pair-fed the Lieber-DeCarli control or ethanol diet. After 4 weeks of this feeding regimen, a subset of rats in each group were intraperitoneally injected every other day with either saline or exendin-4 at a dose of 3 nmol/kg/day (total 13 doses) while still being fed their respective diet. At the end of the treatment, rats were fasted for 6 h and glucose tolerance test was conducted. The following day, the rats were euthanized, and the blood and tissue samples collected for subsequent analysis. We found that exendin-4 treatment had no significant effect on body weight gain among the experimental groups. Exendin-4-treated ethanol rats exhibited improved alcohol-induced alterations in liver/body weight and adipose/body weight ratio, serum ALT, NEFA, insulin, adiponectin and hepatic triglyceride levels. Reduction in indices of hepatic steatosis in exendin-4 treated ethanol-fed rats was attributed to improved insulin signaling and fat metabolism. These results strongly suggest that exendin-4 mitigates alcohol-associated hepatic steatosis by regulating fat metabolism.

The Molecular Determinants of Glucagon-like Peptide Secretion by the Intestinal L cell

The intestinal L cell secretes a diversity of biologically active hormones, most notably the glucagon-like peptides, GLP-1 and GLP-2. The highly successful introduction of GLP-1-based drugs into the clinic for the treatment of patients with type 2 diabetes and obesity, and of a GLP-2 analog for patients with short bowel syndrome, has led to the suggestion that stimulation of the endogenous secretion of these peptides may serve as a novel therapeutic approach in these conditions. Situated in the intestinal epithelium, the L cell demonstrates complex relationships with not only circulating, paracrine, and neural regulators, but also ingested nutrients and other factors in the lumen, most notably the microbiota. The integrated input from these numerous secretagogues results in a variety of temporal patterns in L cell secretion, ranging from minutes to 24 hours. This review combines the findings of traditional, physiological studies with those using newer molecular approaches to describe what is known and what remains to be elucidated after 5 decades of research on the intestinal L cell and its secreted peptides, GLP-1 and GLP-2.

The effects of glucagon-like peptide (GLP)-1 receptor agonists on weight and glycaemic control in Prader-Willi syndrome: A systematic review

OBJECTIVE

The mainstay management of hyperphagia and obesity in Prader-Willi syndrome (PWS) relies on dietary restrictions, strict supervision and behavioural modifications, which can be stressful for the patient and caregiver. There is no established pharmacological strategy to manage this aspect of PWS. Theoretically, glucagon-like peptide-1 (GLP-1) receptor agonists (GLP1-RA) used in patients with obesity and type 2 diabetes mellitus (T2DM) may be efficacious in weight and glycaemic control of PWS patients. We conducted a systematic review of the literature to summarize the evidence on the use of GLP1-RA in PWS patients.

DESIGN

Primary studies were searched in major databases using key concepts 'Prader-Willi syndrome' and 'GLP1 receptor agonist' and outcomes, 'weight control OR glycaemic control OR appetite regulation'.

RESULTS

Ten studies included, summarizing GLP1-RA use in 23 PWS patients (age, 13-37 years), who had used either exenatide (n = 14) or liraglutide (n = 9) over a duration of 14 weeks to 4 years. Sixteen (70%) of these patients had T2DM. Ten patients experienced improvement in body mass index, ranging from 1.5 to 16.0 kg/m² , while improvement in HbA1c was seen in 19 of 23 cases, ranging between 0.3% and 7.5%. All five studies reporting appetite or satiety showed improvement in satiety levels. There were no reported serious side effects.

CONCLUSIONS

GLP1-RA appears safe in PWS patients and may have potential benefits for weight, glycaemic and appetite control. Nonetheless, we also highlight a significant gap in the literature on the lack of well-designed studies in this area, which limits the recommendation of GLP1-RA use in PWS patients at present.

Differential effects of intra-ventral tegmental area ghrelin and glucagon-like peptide-1 on the stimulatory action of D-amphetamine and cocaine-induced ethanol intake in male Sprague Dawley rats

In order to further elucidate the role of mesolimbic peptides in the expression of ethanol reward, the present study investigated the effects of ghrelin and glucagon-like peptide-1 (GLP-1) on ethanol intake, in addition to ethanol intake stimulated by systemic d-amphetamine or cocaine treatment. While a number of studies suggest that ghrelin plays an important role in mesolimbic reward, emerging data now indicate that GLP-1 receptor mechanisms inhibit reward signaling, possibly by directly or indirectly inhibiting ghrelinergic activity within the mesolimbic system. In the present study all rats were initially habituated to a 6% ethanol solution. We then demonstrated that intraperitoneal injections of d-amphetamine and cocaine increased ethanol intake compared to the vehicle condition. In subsequent testing we examined the effects of ventral tegmental area (VTA) ghrelin or vehicle paired with a fixed dose of d-amphetamine or vehicle. In separate rats we then investigated the impact of the GLP-1 agonist exendin-4 (Ex-4), injected into the VTA, on ethanol intake alone, or when Ex-4 was co-administered with d-amphetamine or cocaine. Our results indicated that VTA ghrelin significantly increased ethanol intake, and most importantly, potentiated the effect of d-amphetamine and cocaine on ethanol consumption. Conversely, VTA Ex-4 inhibited ethanol intake and antagonized the stimulatory effect of d-amphetamine and cocaine on ethanol consumption. In a final study we further demonstrated that VTA Ex-4 treatment significantly inhibited the combined stimulatory effects of ghrelin paired with d-amphetamine or ghrelin paired with cocaine. Overall our findings are consistent with a critical role for both ghrelin and GLP-1 receptor mechanisms in mesolimbic ethanol reward circuitry. Moreover, our results further suggest that ghrelin and GLP-1 modulate the stimulatory effect of psychostimulants on ethanol intake.

Hunger and Satiety Peptides: Is There a Pattern to Classify Patients with Prader-Willi Syndrome?

Hyperphagia is one of the main problems of patients with Prader-Willi syndrome (PWS) to cope with everyday life. The underlying mechanisms are not yet well understood. Gut-brain hormones are an interrelated network that may be at least partially involved. We aimed to study the hormonal profile of PWS patients in comparison with obese and healthy controls. Thirty adult PWS patients (15 men; age 27.5 ± 8.02 years; BMI 32.4 ± 8.14 kg/m²), 30 obese and 30 healthy controls were studied before and after eating a hypercaloric liquid diet. Plasma brain-derived neurotrophic factor (BDNF), leptin, total and active ghrelin, peptide YY (PYY), pancreatic polypeptide (PP), Glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP) and amylin were determined at times 0′, 30′, 60′ and 120′. Cluster analysis was used. When considering all peptides together, two clusters were established according to fasting hormonal standardized concentrations. Cluster 1 encompassed most of obese (25/30) and healthy controls (28/30). By contrast, the majority of patients with PWS were located in Cluster 2 (23/27) and presented a similar fasting profile with hyperghrelinemia, high levels of leptin, PYY, GIP and GLP-1, compared to Cluster 1; that may reflect a dysfunction of these hunger/satiety hormones. When peptide behavior over the time was considered, PP concentrations were not sustained postprandially from 60 min onwards in Cluster 2. BDNF and amylin did not help to differentiate the two clusters. Thus, cluster analysis could be a good tool to distinguish and characterize the differences in hormone responses between PWS and obese or healthy controls.

Potential Role of Hypothalamic and Plasma Ghrelin in the Feeding Behavior of Obese Type 2 Diabetic Rats with Intraventricular Glucagon-Like Peptide-1 Receptor Agonist Intervention

OBJECTIVE

To investigate the relationship of central and peripheral ghrelin during an exendin-4 (Ex-4) intervention to feeding in obese type 2 diabetic rodents.

METHODS

Animal models of diet-induced obesity (DIO) and type 2 diabetes were developed using male Sprague-Dawley rats fed with a high-fat diet and induced into DIO-streptozotocin diabetic rats. Ex-4 or the glucagon-like peptide-1 (GLP-1) receptor agonist exendin fragment-[9-39] (Ex-9) was intracerebroventricularly (ICV) administered. Multivariate linear regression analysis was performed to investigate potential predictors of food intake after Ex-4 administration.

RESULTS

ICV administration of Ex-4 significantly inhibited feeding and decreased weight, plasma active ghrelin, hypothalamic ghrelin, and gastric ghrelin levels. The changes in hypothalamic ghrelin and plasma ghrelin could predict the amount of 8-h average food intake. Central preadministration of Ex-9 followed by treatment with Ex-4 could inhibit the decrease in feeding at 0.5, 2, and 8 h. It could also inhibit the decrease in hypothalamic ghrelin at 0.5, 2, and 8 h, as well as in plasma and gastric ghrelin at 2 and 8 h.

CONCLUSIONS

In a GLP-1 receptor-dependent manner, central and peripheral ghrelin play a vital role in the inhibition of feeding by Ex-4 administration. Hypothalamic ghrelin, but not plasma ghrelin, may be involved in central Ex-4 inhibition of feeding in the very early feeding period.

GLP-1 receptors are involved in the GLP-1 (7-36) amide-induced modulation of glucose homoeostasis, emesis and feeding in Suncus murinus (house musk shrew)

GLP-1 receptor agonists are used for the treatment of type 2 diabetes but they may reduce appetite and cause nausea and emesis. We investigated if GLP-1 (7-36) amide can modulate glucose homoeostasis, emesis and feeding via an exendin (9-39)-sensitive mechanism in Suncus murinus. The effect of GLP-1 (7-36) amide on glucose homeostasis was examined using an intraperitoneal glucose tolerance test. In conscious fasted animals, food and water consumption and behavior were measured for 1 h following drug administration. c-Fos expression in the brain was measured using immunohistochemistry. GLP-1 (7-36) amide reduced blood glucose levels dose-dependently. Exendin (9-39) did not modify blood glucose levels but suppressed the glucose-lowering effect of GLP-1 (7-36) amide. GLP-1 (7-36) amide inhibited food and water intake, induced emesis and elevated c-Fos expression in the brainstem and hypothalamic nuclei in the brain. Exendin (9-39) antagonised the inhibition of food and water intake and emesis induced by GLP-1 (7-36) amide and the effects on c-Fos expression in the hypothalamus and brainstem, excepting for the bed nucleus of the stria terminalis. These data suggest that the action of GLP-1 (7-36) amide to modulate blood glucose, suppress food and water intake and induce emesis involve GLP-1 receptors in the hypothalamus and brainstem.

Glucagon-like peptide-1 receptors and sexual behaviors in male mice

The gut-brain peptide glucagon-like peptide-1 (GLP-1) reduces reward from palatable food and drugs of abuse. Recent rodent studies show that activation of GLP-1 receptors (GLP-1R) within the nucleus of the solitary tract (NTS) not only suppresses the motivation and intake of palatable food, but also reduces alcohol-related behaviors. As reward induced by addictive drugs and sexual behaviors involve similar neurocircuits, we hypothesized that activation of GLP-1R suppresses sexual behavior in sexually naïve male mice. We initially identified that systemic administration of the GLP-1R agonist, exendin-4 (Ex4), decreased the frequency and duration of mounting behaviors, but did not alter the preference for females or female bedding. Thereafter infusion of Ex4 into the NTS decreased various behaviors of the sexual interaction chain, namely social, mounting and self-grooming behaviors. In male mice tested in the sexual interaction test, NTS-Ex4 increased dopamine turnover and enhanced serotonin levels in the nucleus accumbens (NAc). In addition, these mice displayed higher corticosterone, but not testosterone, levels in plasma. Finally, GLP-1R antagonist, exendin-3 (9-39) amide (Ex9), infused into the NTS differentially altered the ability of systemic-Ex4 to suppress the various behaviors of the sexual interaction chain, indicating that GLP-1R within the NTS is one of many sub-regions contributing to the GLP-1 dependent sexual behavior link. In these mice NTS-Ex9 partly blocked the systemic-Ex4 enhancement of corticosterone levels. Collectively, these data highlight that activation of GLP-1R, specifically those in the NTS, reduces sexual interaction behaviors in sexually naïve male mice and further provide a link between NTS-GLP-1R activation and reward-related behaviors.

The role of glucagon-like peptide-1 in reproduction: from physiology to therapeutic perspective

BACKGROUND

Glucagon-like peptide-1 (GLP-1) receptor agonists (GLP-1 RAs) have become firmly established in the treatment of type 2 diabetes and obesity, disorders frequently associated with diminished reproductive health. Understanding of the role of GLP-1 and GLP-1 RAs in reproduction is currently limited and largely unaddressed in clinical studies.

OBJECTIVE AND RATIONALE

The purpose of this narrative review is to provide a comprehensive overview of the role of GLP-1 in reproduction and to address a therapeutic perspective that can be derived from these findings.

SEARCH METHODS

We performed a series of PubMed database systemic searches, last updated on 1 February 2019, supplemented by the authors' knowledge and research experience in the field. A search algorithm was developed incorporating the terms glucagon-like peptide-1, GLP-1, glucagon-like peptide-1 receptor, GLP-1R, or incretins, and this was combined with terms related to reproductive health. The PICO (Population, Intervention, Comparison, Outcome) framework was used to identify interventional studies including GLP-1 RAs and dipeptidyl peptidase-4 (DPP-4) inhibitors, which prevent the degradation of endogenously released GLP-1. We identified 983 potentially relevant references. At the end of the screening process, we included 6 observational (3 preclinical and 3 human) studies, 24 interventional (9 preclinical and 15 human) studies, 4 case reports, and 1 systematic and 2 narrative reviews.

OUTCOMES

The anatomical distribution of GLP-1 receptor throughout the reproductive system and observed effects of GLP-1 in preclinical models and in a few clinical studies indicate that GLP-1 might be one of the important modulating signals connecting the reproductive and metabolic system. The outcomes show that there is mostly stimulating role of GLP-1 and its mimetics in mammalian reproduction that goes beyond mere weight reduction. In addition, GLP-1 seems to have anti-inflammatory and anti-fibrotic effects in the gonads and the endometrium affected by obesity, diabetes, and polycystic ovary syndrome (PCOS). It also seems that GLP-1 RAs and DPP-4 inhibitors can reverse polycystic ovary morphology in preclinical models and decrease serum concentrations of androgens and their bioavailability in women with PCOS. Preliminary data from interventional clinical studies suggest improved menstrual regularity as well as increased fertility rates in overweight and/or obese women with PCOS treated with GLP-1 RAs in the preconception period.

WIDER IMPLICATIONS

GLP-1 RAs and DPP-4 inhibitors show promise in the treatment of diabetes and obesity-related subfertility. Larger interventional studies are needed to establish the role of preconception intervention with GLP-1 based therapies, assessing fertility outcomes in obesity, PCOS, and diabetes-related fertility problems. The potential impact of the dose- and exposure time-response of different GLP-1 RAs need further exploration. Future research should also investigate sex-specific variability of GLP-1 on reproductive outcomes, in particular on the gonads where the observations in males are most conflicting.

Ghrelin and liver disease

Non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) are two of the most common liver diseases associated with obesity, type 2 diabetes and metabolic syndrome. The prevalence of these conditions are increasingly rising and presently there is not a pharmacological option available in the market. Elucidation of the mechanism of action and the molecular underpinnings behind liver disease could help to better understand the pathophysiology of these illnesses. In this sense, in the last years modulation of the ghrelin system in preclinical animal models emerge as a promising therapeutic tool. In this review, we compile the latest knowledge of the modulation of ghrelin system and its intracellular pathways that regulates lipid metabolism, hepatic inflammation and liver fibrosis. We also describe novel processes implicated in the regulation of liver disease by ghrelin, such as autophagy or dysregulated circadian rhythms. In conclusion, the information displayed in this review support that the ghrelin system could be an appealing strategy for the treatment of liver disease.

Exendin-4 antagonizes the metabolic action of acylated ghrelinergic signaling in the hypothalamic paraventricular nucleus

In the current study we investigated the interaction of hypothalamic paraventricular nucleus (PVN) glucagon-like peptide-1 (GLP-1) and ghrelin signaling in the control of metabolic function. We first demonstrated that acylated ghrelin injected directly into the PVN reliably altered the respiratory exchange ratio (RER) of adult male Sprague Dawley rats. All testing was carried out during the initial 2 h of the nocturnal cycle using an indirect open circuit calorimeter. Results indicated that acylated ghrelin induced a robust increase in RER representing a shift toward enhanced carbohydrate oxidation and reduced lipid utilization. In contrast, treatment with comparable dosing of des-acyl ghrelin failed to significantly impact metabolic activity. In separate groups of rats we subsequently investigated the ability of exendin-4 (Ex-4), a GLP-1 analogue, to alter acylated ghrelin's metabolic effects. Rodents were treated with either systemic or direct PVN Ex-4 followed by acyl ghrelin microinjection. While our results showed that both systemic and PVN administration of Ex-4 significantly reduced RER, importantly, Ex-4 pretreatment itself reliably inhibited the impact of ghrelin on RER. Overall, these findings provide increasingly compelling evidence that GLP-1 and ghrelin signaling interact in the neural control of metabolic function within the PVN.

Predictors of Effectiveness of Glucagon-Like Peptide-1 Receptor Agonist Therapy in Patients with Type 2 Diabetes and Obesity

RATIONALE

It is well known that diabetes mellitus (DM) exacerbates the mechanisms underlying atherosclerosis. Currently, glucagon-like peptide-1 receptor agonists (aGLP-1) have one of the most prominent cardioprotective effects among the antidiabetic agents. However, the treatment with aGLP-1 is effective only in 50-70% of the cases. Taking into account the high cost of these medications, discovery of the predictors of optimal response to treatment is required.

PURPOSE

To identify the predictors of the greater impact of aGLP-1 on HbA1c levels, weight reduction, and improvement in lipid profile.

METHODS

The study group consisted of 40 patients with type 2 DM (T2DM) and obesity who were treated with aGLP-1. The follow-up period was 24 weeks. Patients' evaluation was conducted at baseline and after 24 weeks. In addition, it included the assessment of the hormones involved in glucose and lipid metabolism and appetite regulation.

RESULTS

Patients who have initially higher BMI (body mass index), glycemia, and triglycerides (TG) had better improvement in these parameters undergoing aGLP-1 treatment. In patients with a BMI loss ≥ 5%, GLP-1 and fasting ghrelin levels were higher and ghrelin level in postnutritional status was lower. The HbA1c levels decreased more intensively in participants with higher GLP-1 levels. TG responders had lower baseline fasting glucose-dependent insulinotropic peptide (GIP) and postprandial ghrelin levels.

CONCLUSION

The evaluation of the glycemic control, lipid profile, and GLP-1, GIP, and ghrelin levels are useable for estimating the expected efficacy of aGLP-1.

Exenatide treatment causes suppression of serum fasting ghrelin levels in patients with type 2 diabetes mellitus

AIM

In the present study, we investigated the long-term effects of exenatide treatment on serum fasting ghrelin levels in patients with type 2 diabetes mellitus.

METHODS

Type 2 diabetic patients, who were using metformin with and without the other antihyperglycemic drugs on a stable dose for at least 3 months, were enrolled in the study. BMI>35 kg/m² and HbA1c>7.0% were the additional inclusion criteria. Oral antihyperglycemic drugs, other than metformin, were stopped, and metformin treatment was continued at 2000 mg per day. Exenatide treatment was initiated at 5 µg per dose subcutaneously (sc) twice daily, and after one month, the dose of exenatide was increased to 10 µg twice daily. Changes in anthropometric variables, glycemic control, lipid parameters and total ghrelin levels were evaluated at baseline and following 12 weeks of treatment.

RESULTS

Thirty-eight patients (male/female = 7/31) entered the study. The mean age of patients was 50.5 ± 8.8 years with a mean diabetes duration of 8.5 ± 4.9 years. The mean BMI was 41.6 ± 6.3 kg/m² and the mean HbA1c of patients was 8.9 ± 1.4%. The mean change in the weight of patients was -5.6 kg and the percentage change in weight was -5.2 ± 3.7% following 12 weeks of treatment. BMI, fasting plasma glucose and HbA1c levels of patients were decreased significantly (P < 0.001 and P < 0.001; respectively), while there was no change in lipid parameters. Serum fasting ghrelin levels were significantly suppressed following 12 weeks of exenatide treatment compared with baseline values (328.4 ± 166.8 vs 245.3 ± 164.8 pg/mL) (P = 0.024).

CONCLUSION

These results suggest that the effects of exenatide on weight loss may be related with the suppression of serum fasting ghrelin levels, which is an orexigenic peptide.

The Effect of Feeding Behavior on Hypothalamus in Obese Type 2 Diabetic Rats with Glucagon-like Peptide-1 Receptor Agonist Intervention

OBJECTIVE

To investigate the utility of intravoxel incoherent motion-diffusion weighted imaging (IVIM-DWI) derived parameters in hypothalamus for monitoring the effect of Exendin-4 (Ex-4) intervention on the feeding behavior in obese diabetic rats within early feeding.

METHODS

21 obese and 19 non-obese rats which were treated with streptozotocin injections were initially divided into an obese diabetes group (OD, n = 10), a non-obese diabetes group (D, n = 8), an obese group (O, n = 9) and a non-obese group (N, n = 9). Then, the rats in the 4 groups received subcutaneous injections of Ex-4, and feeding behavior was examined at 5, 35, 65, 95, and 125 min. The hypothalamic function was evaluated by IVIM-DWI. Finally, the relationship between the hypothalamic function and the amount of food intake was analyzed.

RESULTS

In comparison with the N group, the food intake significantly decreased in the O , OD, and D groups in response to Ex-4. Furthermore, a significant positive correlation was found between food intake and D values at different times from 5 to 125 min after Ex-4 intervention in all 4 groups.

CONCLUSION

A direct correlation between the change of hypothalamic function and feeding behavior was detected in OD rats with Ex-4 intervention in the early feeding period. The hypothalamic D value derived from IVIM-DWI is promising to reflect the dynamic change of hypothalamic function due to intervention.

Effects of exenatide on weight and appetite in overweight adolescents and young adults with Prader-Willi syndrome

BACKGROUND

Prader-Willi syndrome (PWS) is associated with hyperphagia and hyperghrelinemia with major morbidity because of obesity without effective medical treatment targeting hyperphagia. Exenatide (Byetta [synthetic Exendin-4]; AstraZeneca, Wilmington DE) is a GLP-1 receptor agonist which reduces appetite and weight and may be an effective treatment in PWS.

OBJECTIVE

The objective of this study is to determine the effect of a 6-month trial of exenatide on appetite, weight and gut hormones in youth with PWS.

METHODS

Ten overweight and obese subjects with PWS (13-25 years) were recruited for a 6-month open-label, non-randomized, longitudinal study conducted at Children's Hospital Los Angeles. Exenatide was given using standard diabetes dosing without dietary modifications. Weight, body mass index (BMI), truncal fat, appetite and plasma acylated ghrelin were measured over 6 months. Mixed meal tolerance tests were performed at 0 and 6 months.

RESULTS

Appetite scores significantly decreased from baseline (32.2 ± 8.7) after 1, 3 and 6 moths of treatment (27.5 ± 8.8, 25.4 ± 9.3, and 25.4 ± 7.2 respectively; p = 0.004). Hemoglobin A1c decreased significantly after treatment, but weight, BMI z-score and adiposity did not. There was no significant change in ghrelin.

CONCLUSIONS

This is the first longitudinal investigation of the effects of exenatide in subjects with PWS. It was effective in decreasing appetite, without change in weight or BMI in the short term. Larger, controlled, longer-term trials in patients with PWS are needed to confirm the efficacy and safety of exenatide and to evaluate whether its use might induce weight loss when given in conjunction with behavioural modification.

Effect of exenatide on postprandial glucose fluxes, lipolysis, and ß-cell function in non-diabetic, morbidly obese patients

AIMS

To investigate the effect of exenatide on glucose disposal, insulin secretion, ß-cell function, lipolysis and hormone concentrations in non-diabetic, morbidly obese subjects under physiological conditions.

MATERIALS AND METHODS

Patients were assigned to exenatide 10 µg twice daily (EXE, n = 15) or control (CT, n = 15) for 3 months. Patients received a meal test/tracer study (MTT) to measure endogenous glucose production (EGP), rate of oral glucose appearance (RaO), insulin secretion rate (ISR), ß-cell function, hepatic insulin resistance (HIR) and adipose tissue insulin resistance (AT-IR) and insulin sensitivity (IS).

RESULTS

Post treatment, the EXE group showed a significant reduction in body weight ( P < .001). The postmeal time-course of glucose, insulin and ISR showed a lower peak between 60 and 180 minutes in phase with a reduction in RaO ( P < .01). After an initial similar suppression, EGP resumed at higher rates between 60 and 180 minutes ( P = .02) in EXE vs CT, while total RaO and EGP were similar throughout the MTT. In EXE, the postmeal glucagon, GLP1 and GIP responses were reduced ( P < .05). Fasting and postprandial lipolysis and ß-cell function were unaltered by active treatment. HIR, AT-IR and IS were all improved after exenatide treatment ( P < .05).

CONCLUSIONS

In morbidly obese non-diabetic subjects, exenatide causes weight loss, decreased postprandial glycaemia and glucagon response without changes in ß-cell function. These effects are consequent upon delayed oral glucose appearance in the circulation. Exenatide treatment is also associated with an improvement in hepatic, adipose tissue and whole-body IS with no influence on postprandial lipolysis.

Ghrelin Is a Regulator of Glucagon-Like Peptide 1 Secretion and Transcription in Mice

The gut hormones ghrelin, glucagon-like peptide 1 (GLP-1), and glucose-dependent insulinotropic peptide (GIP) have been intensively studied for their role in metabolism. It is, however, not well known whether the hormones interplay and regulate the secretion of each other. In this study, we studied the effect of ghrelin on GLP-1, GIP, and insulin secretion during an oral glucose tolerance test (OGTT) in mice. Intravenous administration of ghrelin caused increased GLP-1 secretion during the OGTT. On the other hand, ghrelin had no effect on circulating levels of glucose, insulin, and GIP. Furthermore, ghrelin treatment reduced proglucagon mRNA expression in GLUTag cells. The effect of ghrelin on GLP-1 secretion and proglucagon transcription was reinforced by the presence of GHS-R1a in human and mouse ileal L-cells, as well as in GLUTag cells. In summary, ghrelin is a regulator of GLP-1 secretion and transcription, and interfering with GHS-R1a signaling may be a way forward to enhance endogenous GLP-1 secretion in subjects with type 2 diabetes.

Exendin-4 decreases ghrelin levels through mTOR signaling

Exendin-4 (EX-4), a long-acting glucagon-like peptide-1 receptor (GLP-1R) agonist, regulates feeding behavior through its ability to inhibit gastric emptying. Ghrelin, a gastric hormone, provides a hunger signal to the central nervous system to stimulate appetite. Here, we report that EX-4 suppresses ghrelin production through the mTORC1-dependent mechanism. Central administration of EX-4 reduces gastric, hypothalamic and plasma ghrelin in both C57BL/6J mice and diet induced obese mice. These changes were associated with a significant increase in mTORC1 activity. Both GLP-1 and EX-4 suppressed the expression and secretion of ghrelin in cultured mHypoE-42 cells, a hypothalamic cell line. These effects were associated with significant changes in mTOR signaling. Inhibition of mTORC1 activity by mTOR siRNA or rapamycin abolished the suppression of ghrelin production induced by GLP-1 and EX-4 in mHypoE-42 cells. Our results identify mTORC1 as a critical signaling pathway for the downregulation of ghrelin induced by activation of GLP-1R.

Short-term administration of the GLP-1 analog liraglutide decreases circulating leptin and increases GIP levels and these changes are associated with alterations in CNS responses to food cues: A randomized, placebo-controlled, crossover study

BACKGROUND

GLP-1 agonists, including liraglutide, have emerged as effective therapies for type 2 diabetes (DM) and obesity. Here, we attempted to delineate how liraglutide, at doses approved for DM, may impact circulating hormones influencing energy homeostasis in diabetics.

BASIC PROCEDURES

Using a randomized, placebo-controlled, double-blind, cross-over trial of 20 patients with type 2 diabetes, we examined the effects of liraglutide as compared to placebo on fasting levels of circulating hormones important to energy homeostasis, including leptin, ghrelin, PYY, and GIP. After 17days (0.6mg for 7days, 1.2mg for 7days and 1.8mg for 3days) of treatment, we also studied changes in fMRI responses to food cues.

MAIN FINDINGS

By design, to avoid any confounding by weight changes, subjects were studied for 17days, i.e. before body weight changed. Participants on liraglutide had significantly increased GLP-1 levels (p<0.001), decreased percent change in leptin levels (p<0.01) and increased GIP levels (p<0.03) in comparison to placebo treated subjects. Whole brain regressions of functional activity in response to food cues reveal that increased GIP levels were associated with deactivation of the attention- and reward-related insula. Decreases in leptin levels were associated with activations in the reward-related midbrain, precuneus, and dorsolateral prefrontal cortex (DLPFC), and sensorimotor-related motor cortex and with deactivations in the attention-related parietal cortex and the cognitive control-related thalamus and pre-SMA.

PRINCIPAL CONCLUSIONS

We demonstrate herein short-term changes to circulating levels of GIP and leptin in response to GLP-1 agonist liraglutide therapy. These findings suggest that liraglutide may alter the circulating levels of hormones important in energy homeostasis that, in turn, influence CNS perception of food cues. This could possibly lead to compensatory changes in energy homeostasis that could over time limit the efficacy of liraglutide to decrease body weight. These novel findings, which, pointing to the potential advantages of combination therapies, may have therapeutic implications, will need to be confirmed by larger and longer-term trials.

Ghrelin Impairs Prandial Glucose Tolerance and Insulin Secretion in Healthy Humans Despite Increasing GLP-1

OBJECTIVES

Administration of ghrelin inhibits the acute insulin response to glucose and worsens IV glucose tolerance in healthy subjects. Evidence from preclinical studies suggests that ghrelin may have differential effects on glucose metabolism during fasting and feeding. Our objective was to test the effects of ghrelin on glucose and insulin responses during a meal tolerance test.

DESIGN

Acyl ghrelin (0.26 and 2.0 μg/kg/h) or saline was infused in 13 healthy subjects on three separate occasions in randomized order. Ghrelin was infused for 45 minutes to achieve steady-state levels and continued for 240 minutes after ingestion of a liquid test meal. Primary outcomes were area under the curve for glucose and insulin secretion.

RESULTS

We found that ghrelin infusions of 0.26 and 2.0 μg/kg/h raised steady-state plasma total ghrelin levels to 1.7- and 4.8-fold above fasting concentrations, but did not alter fasting plasma glucose or insulin levels. During the meal tolerance test, ghrelin decreased insulin sensitivity, impaired β-cell function, and induced glucose intolerance. The high-dose ghrelin infusion also raised postprandial glucagon like peptide 1 secretion without affecting glucose dependent insulinotropic polypeptide, glucagon, or peptide YY concentrations.

CONCLUSIONS

We conclude that both physiologic and pharmacologic doses of ghrelin worsen the glucose and β-cell responses to meal ingestion in healthy humans. The increase in postprandial glucagon like peptide 1 secretion by ghrelin suggests a novel enteroendocrine connection, but does not mitigate the glucose intolerance.

Exenatide Treatment Causes Suppression of Serum Ghrelin Levels following Mixed Meal Test in Obese Diabetic Women

AIM

To investigate the effect of exenatide treatment on serum ghrelin levels in obese female patients with type 2 diabetes mellitus.

METHODS

Fourteen female patients with type 2 diabetes mellitus being treated with metformin and exenatide were enrolled. A mixed meal test was applied to the patients while continuing with their daily medications. Blood samples were taken before and at 60, 120, and 180 minutes following mixed meal test to measure serum total ghrelin, glucose, and insulin levels. The following week, exenatide treatment of the patients was paused for 24 hours and the same experimental procedures were repeated.

RESULTS

Serum ghrelin levels were suppressed significantly at 180 minutes with exenatide treatment compared with baseline (294.4 ± 57.5 versus 234.5 ± 59.4 pg/mL) (p < 0.001). Serum ghrelin levels at 180 minutes were statistically different when percentage change in serum ghrelin levels after mixed meal tests with and without exenatide usage were compared (p = 0.001). Estimated total area under the curve values for serum ghrelin concentrations was also significantly lower with exenatide compared with omitted treatment (p = 0.035).

CONCLUSION

These results suggest that the effect of exenatide on weight loss may be related with the suppression of serum ghrelin levels, which is an orexigenic peptide.

GLP-1 Increases Preovulatory LH Source and the Number of Mature Follicles, As Well As Synchronizing the Onset of Puberty in Female Rats

Control of estrous cycle and reproductive capacity involves a large number of central and peripheral factors, integrating numerous nutritional and metabolic signals. Here we show that glucagon-like peptide-1 (GLP-1), a peptide with anorexigenic and insulinotropic actions, and the GLP-1 receptor agonist Exendin-4 (Ex4) exert a regulatory influence on the gonadal axis, in both adult and prepubertal female rats. In adult rats, Glp-1 receptor expression varies during the estrous cycle at the hypothalamus, pituitary, and ovary. Furthermore, acute treatment with GLP-1 in the morning proestrus doubled the amplitude of the preovulatory LH surge, as well as influencing estradiol and progesterone levels along the estrous cycle. These changes provoked an important increase in the number of Graafian follicles and corpora lutea, as well as in the litter size. Conversely, Ex4 diminished the levels of LH, later producing a partial blockade at the preovulatory surge, yet not affecting either the number of mature follicles or corpora lutea. Chronic administration of low doses of GLP-1 to prepubertal rats synchronized vaginal opening and increased LH levels on the 35th day of life, yet at these doses it did not modify their body weight, food intake, or ovarian and uterine weight. By contrast, chronic exposure to Ex4 produced a significant reduction in ovarian and uterine weight, and serum LH, and the animals treated chronically with Ex4 showed no vaginal opening in the period studied. Overall, our results demonstrate that GLP-1 and Ex4 act on the gonadal axis, involving the hypothalamic kisspeptin system, to influence reproductive efficiency in female rats.

HDAC5-mTORC1 Interaction in Differential Regulation of Ghrelin and Nucleobindin 2 (NUCB2)/Nesfatin-1

Sodium valporate (VPA), a broad-spectrum inhibitor of histone deacetylases (HDACs), increased ghrelin whereas decreased nesfatin-1 in mice fed normal chow diet or high-fat diet. Alterations in ghrelin and nucleobindin 2/nesfatin-1 were mediated by HDAC5 but not HDAC4. Activation of mTORC1 significantly attenuated the effect of VPA on ghrelin and nesfatin-1 levels. HDAC5 coimmunoprecipitated with raptor. Inhibition of HDAC5 by VPA, trichostatin A, or siHDAC5 markedly increased acetylation of raptor Lys840 and subsequent phosphorylation of raptor Ser792, resulting in suppression of mTORC1 signaling. A raptor mutant lacking the Lys840 acetylation site showed a decrement in phosphorylation of raptor Ser792 and subsequent increase in mTORC1 signaling. These alterations were associated with reciprocal changes in ghrelin and nucleobindin 2/nesfatin-1 expression. These findings reveal HDAC5-mTORC1 signaling as a novel mechanism in the differential regulation of gastric ghrelin and nesfatin-1.

Glucagon-like peptide 1 interacts with ghrelin and leptin to regulate glucose metabolism and food intake through vagal afferent neuron signaling

Emerging evidence has suggested a possible physiologic role for peripheral glucagon-like peptide 1 (GLP-1) in regulating glucose metabolism and food intake. The likely site of action of GLP-1 is on vagal afferent neurons (VANs). The vagal afferent pathway is the major neural pathway by which information about ingested nutrients reaches the central nervous system and influences feeding behavior. Peripheral GLP-1 acts on VANs to inhibit food intake. The mechanism of the GLP-1 receptor (GLP-1R) is unlike other gut-derived receptors; GLP-1Rs change their cellular localization according to feeding status rather than their protein concentrations. It is possible that several gut peptides are involved in mediating GLP-1R translocation. The mechanism of peripheral GLP-1R translocation still needs to be elucidated. We review data supporting the role of peripheral GLP-1 acting on VANs in influencing glucose homeostasis and feeding behavior. We highlight evidence demonstrating that GLP-1 interacts with ghrelin and leptin to induce satiation. Our aim was to understand the mechanism of peripheral GLP-1 in the development of noninvasive antiobesity treatments.

Ghrelin-ghrelin O-acyltransferase system in the pathogenesis of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is currently considered as the most common liver disease in Western countries, and is rapidly becoming a serious threat to public health worldwide. However, the underlying mechanisms leading to the development of NAFLD are still not fully understood. The ghrelin-ghrelin O-acyltransferase (GOAT) system has recently been found to play a crucial role in both the development of steatosis and its progression to nonalcoholic steatohepatitis. Ghrelin, the natural ligand of the growth hormone secretagogue receptor, is a 28-amino acid peptide possessing a unique acylation on the serine in position 3 catalyzed by GOAT. The ghrelin-GOAT system is involved in insulin resistance, lipid metabolism dysfunction, and inflammation, all of which play important roles in the pathogenesis of NAFLD. A better understanding of ghrelin-GOAT system biology led to the identification of its potential roles in NAFLD. Molecular targets modulating ghrelin-GOAT levels and the biologic effects are being studied, which provide a new insight into the pathogenesis of NAFLD. This review probes into the possible relationship between the ghrelin-GOAT system and NAFLD, and considers the potential mechanisms by which the ghrelin-GOAT system brings about insulin resistance and other aspects concerning NAFLD.

Novel Regulator of Acylated Ghrelin, CF801, Reduces Weight Gain, Rebound Feeding after a Fast, and Adiposity in Mice

Ghrelin is a 28 amino acid hormonal peptide that is intimately related to the regulation of food intake and body weight. Once secreted, ghrelin binds to the growth hormone secretagogue receptor-1a, the only known receptor for ghrelin and is capable of activating a number of signaling cascades, ultimately resulting in an increase in food intake and adiposity. Because ghrelin has been linked to overeating and the development of obesity, a number of pharmacological interventions have been generated in order to interfere with either the activation of ghrelin or interrupting ghrelin signaling as a means to reducing appetite and decrease weight gain. Here, we present a novel peptide, CF801, capable of reducing circulating acylated ghrelin levels and subsequent body weight gain and adiposity. To this end, we show that IP administration of CF801 is sufficient to reduce circulating plasma acylated ghrelin levels. Acutely, intraperitoneal injections of CF801 resulted in decreased rebound feeding after an overnight fast. When delivered chronically, they decreased weight gain and adiposity without affecting caloric intake. CF801, however, did cause a change in diet preference, decreasing preference for a high-fat diet and increasing preference for regular chow diet. Given the complexity of ghrelin receptor function, we propose that CF801, along with other compounds that regulate ghrelin secretion, may prove to be a beneficial tool in the study of the ghrelin system, and potential targets for ghrelin-based obesity treatments without altering the function of ghrelin receptors.

The regulation of circulating ghrelin - with recent updates from cell-based assays

Ghrelin is a stomach-derived orexigenic hormone with a wide range of physiological functions. Elucidation of the regulation of the circulating ghrelin level would lead to a better understanding of appetite control in body energy homeostasis. Earlier studies revealed that circulating ghrelin levels are under the control of both acute and chronic energy status: at the acute scale, ghrelin levels are increased by fasting and decreased by feeding, whereas at the chronic scale, they are high in obese subjects and low in lean subjects. Subsequent studies revealed that nutrients, hormones, or neural activities can influence circulating ghrelin levels in vivo. Recently developed in vitro assay systems for ghrelin secretion can assess whether and how individual factors affect ghrelin secretion from cells. In this review, on the basis of numerous human, animal, and cell-based studies, we summarize current knowledge on the regulation of circulating ghrelin levels and enumerate the factors that influence ghrelin levels.

Behavioural profile of exendin-4/naltrexone dose combinations in male rats during tests of palatable food consumption

RATIONALE

The glucagon-like peptide 1 receptor (GLP-1R) agonist exendin-4 potently suppresses food intake in animals and humans. However, little is known about the behavioural specificity of this effect either when administered alone or when co-administered with another anorectic agent.

OBJECTIVES

The present study characterises the effects of exendin-4, both alone and in combination with naltrexone, on behaviours displayed by male rats during tests with palatable mash.

METHODS

Experiment 1 examined the dose-response effects of exendin-4 (0.025-2.5 μg/kg, IP), while experiment 2 profiled the effects of low-dose combinations of the peptide (0.025 and 0.25 μg/kg) and naltrexone (0.1 mg/kg).

RESULTS

In experiment 1, exendin-4 dose dependently suppressed food intake as well as the frequency and rate of eating. However, these effects were accompanied by dose-dependent reductions in all active behaviours and, at 2.5 μg/kg, a large increase in resting and disruption of the behavioural satiety sequence (BSS). In experiment 2, while exendin-4 (0.25 μg/kg) and naltrexone each produced a significant reduction in intake and feeding behaviour (plus an acceleration in the BSS), co-treatment failed to produce stronger effects than those seen in response to either compound alone.

CONCLUSION

Similarities between the behavioural signature of exendin-4 and that previously reported for the emetic agent lithium chloride would suggest that exendin-4 anorexia is related to the aversive effects of the peptide. Furthermore, as low-dose combinations of the peptide with naltrexone failed to produce an additive/synergistic anorectic effect, this particular co-treatment strategy would not appear to have therapeutic significance.

Insulin as a Bridge between Type 2 Diabetes and Alzheimer Disease - How Anti-Diabetics Could be a Solution for Dementia

Type 2 diabetes (T2D) and Alzheimer disease (AD) are two major health issues nowadays. T2D is an ever increasing epidemic, affecting millions of elderly people worldwide, with major repercussions in the patients' daily life. This is mostly due to its chronic complications that may affect brain and constitutes a risk factor for AD. T2D principal hallmark is insulin resistance which also occurs in AD, rendering both pathologies more than mere unrelated diseases. This hypothesis has been reinforced in the recent years, with a high number of studies highlighting the existence of several common molecular links. As such, it is not surprising that AD has been considered as the "type 3 diabetes" or a "brain-specific T2D," supporting the idea that a beneficial therapeutic strategy against T2D might be also beneficial against AD. Herewith, we aim to review some of the recent developments on the common features between T2D and AD, namely on insulin signaling and its participation in the regulation of amyloid β (Aβ) plaque and neurofibrillary tangle formation (the two major neuropathological hallmarks of AD). We also critically analyze the promising field that some anti-T2D drugs may protect against dementia and AD, with a special emphasis on the novel incretin/glucagon-like peptide-1 receptor agonists.

Abnormal response to the anorexic effect of GHS-R inhibitors and exenatide in male Snord116 deletion mouse model for Prader-Willi syndrome

Prader-Willi syndrome (PWS) is a genetic disease characterized by persistent hunger and hyperphagia. The lack of the Snord116 small nucleolar RNA cluster has been identified as the major contributor to PWS symptoms. The Snord116 deletion (Snord116del) mouse model manifested a subset of PWS symptoms including hyperphagia and hyperghrelinemia. In this study, male Snord116del mice were characterized and tested for their acute and chronic responses to anorexic substances related to the ghrelin pathway. In comparison with their wild-type littermates, the food intake rate of Snord116del mice was 14% higher when fed ad libitum, and 32% to 49% higher within 12 hours after fasting. Fasted Snord116del mice were less sensitive to the acute anorexic effect of competitive antagonist [d-Lys(3)]-GHRP6, YIL-781, and reverse agonist [d-Arg(1),d-Phe(5),d-Trp(7,9),Leu(11)]-substance P (SPA) of ghrelin receptor GHS-R. All 3 GHS-R inhibitors failed to inhibit chronic food intake of either Snord116del or wild-type mice due to rapid adaptation. Although fasted Snord116del mice had normal sensitivity to the acute anorexic effect of glucagon-like peptide 1 receptor agonist exenatide, those fed ad libitum required a higher dose and more frequent delivery to achieve ∼15% suppression of long-term food intake in comparison with wild-type mice. Ghrelin, however, is unlikely to be essential for the anorexic effect of exenatide in fed mice, as shown by the fact that exenatide did not reduce ghrelin levels in fed mice and food intake of ghrelin(-/-) mice fed ad libitum could be suppressed by exenatide. In conclusion, this study suggests that GHS-R may not be an effective therapeutic target, and in contrast, exenatide may produce anorexic effect in PWS individuals.

Long-term metabolic benefits of exenatide in mice are mediated solely via the known glucagon-like peptide 1 receptor

Glucagon-like peptide 1 receptors (GLP-1R) are expressed in multiple tissues and activation results in metabolic benefits including enhanced insulin secretion, slowed gastric emptying, suppressed food intake, and improved hepatic steatosis. Limited and inconclusive knowledge exists regarding whether the effects of chronic exposure to a GLP-1R agonist are solely mediated via this receptor. Therefore, we examined 3-mo dosing of exenatide in mice lacking a functional GLP-1R (Glp1r−/−). Exenatide (30 nmol·kg−1·day−1) was infused subcutaneously for 12 wk in Glp1r−/− and wild-type (Glp1r+/+) control mice fed a high-fat diet. Glycated hemoglobin A1c (HbA1c), plasma glucose, insulin, amylase, lipase, alanine aminotransferase (ALT), aspartate aminotransferase (AST), body weight, food intake, terminal hepatic lipid content (HLC), and plasma exenatide levels were measured. At the end of the study, oral glucose tolerance test (OGTT) and rate of gastric emptying were assessed. Exenatide produced no significant changes in Glp1r−/− mice at study end. In contrast, exenatide decreased body weight, food intake, and glucose in Glp1r+/+ mice. When compared with vehicle, exenatide reduced insulin, OGTT glucose AUC0–2h, ALT, and HLC in Glp1r+/+ mice. Exenatide had no effect on plasma amylase or lipase levels. Exenatide concentrations were approximately eightfold higher in Glp1r−/− versus Glp1r+/+ mice after 12 wk of infusion, whereas renal function was similar. These data support the concept that exenatide requires a functional GLP-1R to exert chronic metabolic effects in mice, and that novel “GLP-1” receptors may not substantially contribute to these changes. Differential exenatide plasma levels in Glp1r+/+ versus Glp1r−/− mice suggest that GLP-1R may play an important role in plasma clearance of exenatide and potentially other GLP-1-related peptides.

Functional activity of murine intestinal mucosal cells is regulated by the glucagon-like peptide-1 receptor

To determine whether the glucagon-like peptide-1 receptor (GLP-1r) plays a role in the regulation of intestinal functional activity, we analyzed the distribution of the GLP-1r in mouse tissues and tested if tissues expressing the receptor respond to exendin-4 and exendin (9-39) amide, a GLP-1r agonist and antagonist respectively. In ileum, Glp1r mRNA level was two fold higher in extracts from epithelial cells than non-epithelial tissues. By immunohistochemistry, the receptor was localized to the mucosal cell layer of villi of ileum and colon, to the myenteric and submucosal plexus and to Paneth cells. Intravenous administration of exendin-4 to CD-1 mice induced expression of the immediate early gene c-fos in mucosal cells but not in cells of the enteric plexuses or in L cells of ileum. The induction of c-fos was inhibited by the voltage-gated sodium channel blocker tetrodotoxin. Exendin-4 also increased c-fos expression in ileal segments in vitro, suggesting that this action of the analog was independent of an extrinsic input. The induction of c-fos expression by exendin-4 was inhibited by exendin (9-39) amide, indicating that the action of exendin-4 was mediated by activation of the receptor. Our findings indicate that the GLP-1r is involved in ileal enterocyte and Paneth cell function, that the GLP-1 analog activates c-fos expression in the absence of an extrinsic input and that some of the actions of the receptor is/are mediated by voltage-gated Na channels.

The glucagon-like peptide 1 analogue Exendin-4 attenuates alcohol mediated behaviors in rodents

Development of alcohol use disorders largely depends on the effects of alcohol on the brain reward systems. Emerging evidence indicate that common mechanisms regulate food and alcohol intake and raise the possibility that endocrine signals from the gut may play an important role for alcohol consumption, alcohol-induced reward and the motivation to consume alcohol. Glucagon-like peptide 1 (GLP-1), a gastrointestinal peptide regulating food intake and glucose homeostasis, has recently been shown to target central brain areas involved in reward and motivation, including the ventral tegmental area and nucleus accumbens. Herein we investigated the effects of the GLP-1 receptor agonist, Exendin-4 (Ex4), on various measures of alcohol-induced reward as well as on alcohol intake and alcohol seeking behavior in rodents. Treatment with Ex4, at a dose with no effect per se, attenuated alcohol-induced locomotor stimulation and accumbal dopamine release in mice. Furthermore, conditioned place preference for alcohol was abolished by both acute and chronic treatment with Ex4 in mice. Finally we found that Ex4 treatment decreased alcohol intake, using the intermittent access 20% alcohol two-bottle-choice model, as well as alcohol seeking behavior, using the progressive ratio test in the operant self-administration model, in rats. These novel findings indicate that GLP-1 signaling attenuates the reinforcing properties of alcohol implying that the physiological role of GLP-1 extends beyond glucose homeostasis and food intake regulation. Collectively these findings implicate that the GLP-1 receptor may be a potential target for the development of novel treatment strategies for alcohol use disorders.

Omeprazole improves the anti-obesity and antidiabetic effects of exendin-4 in db/db mice (-4 db/db)*

BACKGROUND

In addition to its glucoregulatory actions, exendin-4, a stable glucagon-like peptide-1 receptor agonist, exhibits protective effects in the pancreas and anti-obesity effects. Suitable combination treatment with other anti-obesity or pancreas protective agents would be an effective approach to optimize these additional effects. In the present study, we investigated the effects of the addition of omeprazole, a proton pump inhibitor, to exendin-4 in db/db mice, an experimental model of obesity and type 2 diabetes.

METHODS

The effects repeated dose treatment for 14 days with exendin-4 (8 μg/kg, s.c.) and omeprazole (30 mg/kg, s.c.) on glycemic control, food intake, and body weight were determined in obese and hyperglycemic db/db mice. The effects of these treatments on plasma gastrin, ghrelin, and leptin levels were determined, along with effects on nausea-like symptoms. The pancreatic effects of the repeated dose treatment were assessed by measuring %HbA1c in the circulation as well as pancreatic insulin and glucagon content and glucokinase activity.

RESULTS

Combination treatment resulted in significant decreases in plasma leptin and ghrelin levels after repeated dosing. Omeprazole improved the anorectic and body weight-lowering effects and reversed the inhibitory effect of exendin-4 on gastrin levels after repeated dose treatment. The 14-day combination treatment significantly reduced glucose excursion and improved insulin levels, with a concomitant decrease in %HbA1c levels. It also improved glucokinase activity and pancreatic insulin content, with a significant decrease in glucagon content.

CONCLUSIONS

Combined treatment with omeprazole with exendin-4 reduces food intake and body weight gain, most likely through changes in plasma ghrelin and leptin levels, and improves pancreatic insulin and glucagon content by improving glucokinase activity.

Acute peripheral administration of synthetic human GLP-1 (7-36 amide) decreases circulating IL-6 in obese patients with type 2 diabetes mellitus: a potential role for GLP-1 in modulation of the diabetic pro-inflammatory state?

BACKGROUND

To explore the effects of acute administration of GLP-1 and GIP on circulating levels of key adipocyte-derived hormones and gut-brain peptides with established roles in energy and appetite regulation, modulation of insulin sensitivity and inflammation.

METHODS

Six obese male patients with diet-treated type 2 diabetes (T2DM) and 6 healthy lean subjects were studied. The protocol included 4 experiments for each participant that were carried out in randomised order and comprised: GLP-1 infusion at a rate of 1 pmol/kg/min for 4h, GIP at a rate of 2 pmol/kg/min, GLP-1+GIP and placebo infusion. Plasma leptin, adiponectin, IL-6, insulin, ghrelin and obestatin were measured at baseline, 15, 60, 120, 180 and 240 min following the start of infusion.

RESULTS

Patients with T2DM had higher baseline IL-6 compared with healthy [day of placebo infusion: T2DM IL-6 mean (SEM) 1.3 (0.3) pg/ml vs 0.3 (0.1)pg/ml, p=0.003]. GLP-1 infusion in T2DM was associated with a significant reduction in circulating IL-6 [baseline IL-6 1.2 pg/ml vs IL-6=0.7 at 120 min, p=0.0001; vs IL-6=0.8 at 180 min, p=0.001]. There was no significant change in leptin, adiponectin, ghrelin or obestatin compared to baseline on all 4 experimental days in both groups.

CONCLUSION

Short-term infusion of supraphysiological concentrations of GLP-1 in T2DM results in suppression of IL-6, a key inflammatory mediator strongly linked to development of obesity and T2DM-related insulin resistance. It remains to be confirmed whether GLP-1-based diabetes therapies can impact favourably on cardiovascular outcomes.

Pulmonary GLP-1 receptor increases at birth and exogenous GLP-1 receptor agonists augmented surfactant-protein levels in litters from normal and nitrofen-treated pregnant rats

The glucagon-like peptide-1 receptor (GLP-1R) is found in a variety of tissues outside of the pancreas. For example, GLP-1R is expressed in the lung, where it has been implicated in the regulation of the lipid fraction of surfactants, suggesting it fulfills an important role in lung function. Here, we show that GLP-1R expression is strongly up-regulated immediately after birth in neonatal rats, particular in male offspring. Moreover, administering long half-life GLP-1R agonists to the mother from gestational day 14 to birth (exendin-4 or liraglutide) increased surfactant protein (SP)-A and SP-B mRNA expression and the amount of SPs in the amniotic fluid at the end of pregnancy. These effects were similar or more potent to those induced by the glucocorticoid dexamethasone, which also increased GLP-1R expression in fetuses just before delivery. Lir increased fetal SP-A and GLP-1R expression in control rats and in a nitrofen-induced model of lung hypoplasia. Moreover, lung size increased in controls after Lir administration, which also prevented the decrease in lung weight and the poor neonatal survival of the offspring from nitrofen-treated dams, effects that were not produced by dexamethasone. Taken together, our results demonstrate the importance of the GLP-1 system in regulating SP production and lung development.

Separation of emetic and anorexic responses of exendin-4, a GLP-1 receptor agonist in Suncus murinus (house musk shrew)

The use of glucagon-like peptide-1 (7-36) amide (GLP-1) receptor agonists for the treatment of type 2 diabetes mellitus is commonly associated with nausea and vomiting. Therefore, the present studies investigated the potential of GLP-1 receptor ligands to modulate emesis and feeding in Suncus murinus. Exendin-4, a selective GLP-1 receptor agonist, was administered subcutaneously (1-30 nmol/kg) or intracerebroventricularly (0.03-3 nmol) after 12-h of fasting. In other studies, animals were pretreated with the GLP-1 receptor antagonist, exendin (9-39), or saline (5 μl) 15 min prior to exendin-4 (3 nmol, i.c.v.). Behaviour of animals and food and water intake were then recorded for 1-2 h; c-Fos expression was also assessed in the brains of animals in the i.c.v. studies. The subcutaneous administration of exendin-4 reduced food and water intake (p < 0.001) and induced emesis in 40% of animals (p > 0.05). The intracerebroventricular administration of exendin-4 also prevented feeding, and induced emesis (p < 0.01). In these studies, exendin (9-39) (30 nmol, i.c.v.) antagonised emesis induced by exendin-4 and the increased c-Fos expressions in the brainstem and hypothalamus (p < 0.05), but it was ineffective in reversing the exendin-4-induced inhibition of food and water intake (p > 0.05). These data suggest that exendin-4 exerts its emetic effects in the brainstem and/or hypothalamus via GLP-1 receptors. The action of exendin-4 to suppress feeding may involve non-classical GLP-1 receptors or other mechanisms.

Crosstalk between diabetes and brain: glucagon-like peptide-1 mimetics as a promising therapy against neurodegeneration

According to World Health Organization estimates, type 2 diabetes (T2D) is an epidemic (particularly in under development countries) and a socio-economic challenge. This is even more relevant since increasing evidence points T2D as a risk factor for Alzheimer's disease (AD), supporting the hypothesis that AD is a "type 3 diabetes" or "brain insulin resistant state". Despite the limited knowledge on the molecular mechanisms and the etiological complexity of both pathologies, evidence suggests that neurodegeneration/death underlying cognitive dysfunction (and ultimately dementia) upon long-term T2D may arise from a complex interplay between T2D and brain aging. Additionally, decreased brain insulin levels/signaling and glucose metabolism in both pathologies further suggests that an effective treatment strategy for one disorder may be also beneficial in the other. In this regard, one such promising strategy is a novel successful anti-T2D class of drugs, the glucagon-like peptide-1 (GLP-1) mimetics (e.g. exendin-4 or liraglutide), whose potential neuroprotective effects have been increasingly shown in the last years. In fact, several studies showed that, besides improving peripheral (and probably brain) insulin signaling, GLP-1 analogs minimize cell loss and possibly rescue cognitive decline in models of AD, Parkinson's (PD) or Huntington's disease. Interestingly, exendin-4 is undergoing clinical trials to test its potential as an anti-PD therapy. Herewith, we aim to integrate the available data on the metabolic and neuroprotective effects of GLP-1 mimetics in the central nervous system (CNS) with the complex crosstalk between T2D-AD, as well as their potential therapeutic value against T2D-associated cognitive dysfunction.

Euglycemic agent-mediated hypothalamic transcriptomic manipulation in the N171-82Q model of Huntington disease is related to their physiological efficacy

Our aim was to employ novel analytical methods to investigate the therapeutic treatment of the energy regulation dysfunction occurring in a Huntington disease (HD) mouse model. HD is a neurodegenerative disorder that is characterized by progressive motor impairment and cognitive alterations. Changes in neuroendocrine function, body weight, energy metabolism, euglycemia, appetite function, and gut function can also occur. It is likely that the locus of these alterations is the hypothalamus. We determined the effects of three different euglycemic agents on HD progression using standard physiological and transcriptomic signature analyses. N171-82Q HD mice were treated with insulin, Exendin-4, and the newly developed GLP-1-Tf to determine whether these agents could improve energy regulation and delay disease progression. Blood glucose, insulin, metabolic hormone levels, and pancreatic morphology were assessed. Hypothalamic gene transcription, motor coordination, and life span were also determined. The N171-82Q mice exhibited significant alterations in hypothalamic gene transcription signatures and energy metabolism that were ameliorated, to varying degrees, by the different euglycemic agents. Exendin-4 or GLP-1-Tf (but not insulin) treatment also improved pancreatic morphology, motor coordination, and increased life span. Using hypothalamic transcription signature analyses, we found that the physiological efficacy variation of the drugs was evident in the degree of reversal of the hypothalamic HD pathological signature. Euglycemic agents targeting hypothalamic and energy regulation dysfunction in HD could potentially alter disease progression and improve quality of life in HD.

Glucagon-like peptide-1 receptor agonist, exendin-4, regulates feeding-associated neuropeptides in hypothalamic neurons in vivo and in vitro

Exendin-4, a long-acting glucagon-like peptide-1 receptor (GLP-1R) agonist, is a potential regulator of feeding behavior through its ability to inhibit gastric emptying, reduce food intake, and induce satiety. GLP-1R activation by exendin-4 induces anorexia; however, the specific populations of neuropeptidergic neurons activated by exendin-4 within the hypothalamus, the central regulator of energy homeostasis, remain unclear. This study determines whether exendin-4 regulates hypothalamic neuropeptide expression and explores the signaling mechanisms involved. The distribution and quantity of exendin-4-induced c-Fos immunoreactivity were evaluated to determine activation of α-melanocyte-stimulating hormone/proopiomelanocortin, neuropeptide Y, neurotensin (NT), and ghrelin neurons in hypothalamic nuclei during exendin-4-induced anorexia in mice. Additionally, exendin-4 action on NT and ghrelin transcript regulation was examined in immortalized hypothalamic neurons. With anorexia induced by intracerebroventricular exendin-4, α-melanocyte-stimulating hormone/proopiomelanocortin and neuropeptide Y neurons were activated in the arcuate nucleus, with simultaneous activation of NT-expressing neurons in the paraventricular nucleus, and ghrelin-expressing neurons in the arcuate nucleus, paraventricular nucleus, and periventricular hypothalamus, suggesting that neurons in one or more of these areas mediate the anorexic action of exendin-4. In the hypothalamic neuronal cell models, exendin-4 increased cAMP, cAMP response element-binding protein/activating transcription factor-1 and c-Fos activation, and via a protein kinase A-dependent mechanism regulated NT and ghrelin mRNA expression, indicating that these neuropeptides may serve as downstream mediators of exendin-4 action. These findings provide a previously unrecognized link between central GLP-1R activation by exendin-4 and the regulation of hypothalamic NT and ghrelin. Further understanding of this central GLP-1R activation may lead to safe and effective therapeutics for the treatment of metabolic disorders.

Yin and Yang - the Gastric X/A-like Cell as Possible Dual Regulator of Food Intake

Ingestion of food affects secretion of hormones from enteroendocrine cells located in the gastrointestinal mucosa. These hormones are involved in the regulation of various gastrointestinal functions including the control of food intake. One cell in the stomach, the X/A-like has received much attention over the past years due to the production of ghrelin. Until now, ghrelin is the only known orexigenic hormone that is peripherally produced and centrally acting to stimulate food intake. Subsequently, additional peptide products of this cell have been described including desacyl ghrelin, obestatin and nesfatin-1. Desacyl ghrelin seems to be involved in the regulation of food intake as well and could play a counter-balancing role of ghrelin's orexigenic effect. In contrast, the initially proposed anorexigenic action of obestatin did not hold true and therefore the involvement of this peptide in the regulation of feeding is questionable. Lastly, the identification of nesfatin-1 in the same cell in different vesicles than ghrelin extended the function of this cell type to the inhibition of feeding. Therefore, this X/A-like cell could play a unique role by encompassing yin and yang properties to mediate not only hunger but also satiety.

Role of ghrelin in the pathophysiology of eating disorders: implications for pharmacotherapy

Ghrelin is the only known circulating orexigenic hormone. It increases food intake by interacting with hypothalamic and brainstem circuits involved in energy balance, as well as reward-related brain areas. A heightened gut-brain ghrelin axis is an emerging feature of certain eating disorders such as anorexia nervosa and Prader-Willi syndrome. In common obesity, ghrelin levels are lowered, whereas post-meal ghrelin levels remain higher than in lean individuals. Agents that interfere with ghrelin signalling have therapeutic potential for eating disorders, including obesity. However, most of these drugs are only in the preclinical phase of development. Data obtained so far suggest that ghrelin agonists may have potential in the treatment of anorexia nervosa, while ghrelin antagonists seem promising for other eating disorders such as obesity and Prader-Willi syndrome. However, large clinical trials are needed to evaluate the efficacy and safety of these drugs.

Ghrelin - a pleiotropic hormone secreted from endocrine x/a-like cells of the stomach

The gastric X/A-like endocrine cell receives growing attention due to its peptide products with ghrelin being the best characterized. This peptide hormone was identified a decade ago as a stimulator of food intake and to date remains the only known peripherally produced and centrally acting orexigenic hormone. In addition, subsequent studies identified numerous other functions of this peptide including the stimulation of gastrointestinal motility, the maintenance of energy homeostasis and an impact on reproduction. Moreover, ghrelin is also involved in the response to stress and assumed to play a role in coping functions and exert a modulatory action on immune pathways. Our knowledge on the regulation of ghrelin has markedly advanced during the past years by the identification of the ghrelin acylating enzyme, ghrelin-O-acyltransferase, and by the description of changes in expression, activation, and release under different metabolic as well as physically and psychically challenging conditions. However, our insight on regulatory processes of ghrelin at the cellular and subcellular levels is still very limited and warrants further investigation.

The ghrelin/GOAT/GHS-R system and energy metabolism

Ghrelin is a brain-gut peptide that was discovered through reverse pharmacology and was first isolated from extracts of porcine stomach. Ghrelin binds to growth hormone secretagogue receptor (GHS-R) and is acylated on its serine 3 residue by ghrelin O-acyltransferase (GOAT). Several important biological functions of ghrelin have been identified, which include its growth hormone-releasing and appetite-inducing effects. Ghrelin exerts its central orexigenic effect mainly by acting on the hypothalamic arcuate nucleus via the activation of the GHS-R. Peripherally ghrelin has multiple metabolic effects which include promoting gluconeogenesis and fat deposition. These effects together with the increased food intake lead to an overall body weight gain. AMP-activated protein kinase, which is a key enzyme in energy homeostasis, has been shown to mediate the central and peripheral metabolic effects of ghrelin. The hypothalamic fatty acid pathway, hypothalamic mitochondrial respiration and uncoupling protein 2 have all been shown to act as the downstream targets of AMPK in mediating the orexigenic effects of ghrelin. Abnormal levels of ghrelin are associated with several metabolic conditions such as obesity, type 2 diabetes, Prader-Willi syndrome and anorexia nervosa. The ghrelin/GOAT/GHS-R system is now recognised as a potential target for the development of anti-obesity treatment.

Advances in the treatment of type 2 diabetes mellitus

There is a rising worldwide prevalence of diabetes, especially type 2 diabetes mellitus (T2DM), which is one of the most challenging health problems in the 21st century. The associated complications of diabetes, such as cardiovascular disease, peripheral vascular disease, stroke, diabetic neuropathy, amputations, renal failure, and blindness result in increasing disability, reduced life expectancy, and enormous health costs. T2DM is a polygenic disease characterized by multiple defects in insulin action in tissues and defects in pancreatic insulin secretion, which eventually leads to loss of pancreatic insulin-secreting cells. The treatment goals for T2DM patients are effective control of blood glucose, blood pressure, and lipids (if elevated) and, ultimately, to avert the serious complications associated with sustained tissue exposure to excessively high glucose concentrations. Prevention and control of diabetes with diet, weight control, and physical activity has been difficult. Treatment of T2DM has centered on increasing insulin levels, either by direct insulin administration or oral agents that promote insulin secretion, improving sensitivity to insulin in tissues, or reducing the rate of carbohydrate absorption from the gastrointestinal tract. This review presents comprehensive and up-to-date information on the mechanism(s) of action, efficacy, pharmacokinetics, pleiotropic effects, drug interactions, and adverse effects of the newer antidiabetic drugs, including (1) peroxisome proliferator-activated-receptor-γ agonists (thiazolidinediones, pioglitazone, and rosiglitazone); (2) the incretin, glucagon-like peptide-) receptor agonists (incretin-mimetics, exenatide. and liraglutide), (3) inhibitors of dipeptidyl-peptidase-4 (incretin enhancers, sitagliptin, and vildagliptin), (4) short-acting, nonsulfonylurea secretagogue, meglitinides (repaglinide and nateglinide), (5) amylin anlog-pramlintide, (6) α-glucosidase inhibitors (miglitol and voglibose), and (7) colesevelam (a bile acid sequestrant). In addition, information is presented on drug candidates in clinical trials, experimental compounds, and some plants used in the traditional treatment of diabetes based on experimental evidence. In the opinion of this reviewer, therapy based on orally active incretins and incretin mimetics with long duration of action that will be efficacious, preserve the β-cell number/function, and block the progression of diabetes will be highly desirable. However, major changes in lifestyle factors such as diet and, especially, exercise will also be needed if the growing burden of diabetes is to be contained.

Interaction between gastric and upper small intestinal hormones in the regulation of hunger and satiety: ghrelin and cholecystokinin take the central stage

Several peptides are produced and released from endocrine cells scattered within the gastric oxyntic and the small intestinal mucosa. These peptide hormones are crucially involved in the regulation of gastrointestinal functions and food intake by conveying their information to central regulatory sites located in the brainstem as well as in the forebrain, such as hypothalamic nuclei. So far, ghrelin is the only known hormone that is peripherally produced in gastric X/A-like cells and centrally acting to stimulate food intake, whereas the suppression of feeding seems to be much more redundantly controlled by a number of gut peptides. Cholecystokinin produced in the duodenum is a well established anorexigenic hormone that interacts with ghrelin to modulate food intake indicating a regulatory network located at the first site of contact with nutrients in the stomach and upper small intestine. In addition, a number of peptides including leptin, urocortin 2, amylin and glucagon-like peptide 1 interact synergistically with CCK to potentiate its satiety signaling effect. New developments have led to the identification of additional peptides in X/A-like cells either derived from the pro-ghrelin gene by alternative splicing and posttranslational processing (obestatin) or a distinct gene (nucleobindin2/nesfatin-1) which have been investigated for their influence on food intake.