Glucagon-like peptide 1 as a regulator of food intake and body weight: therapeutic perspectives

[New concepts in the treatment of type 2 diabetes]

The development of a variety of new substances will considerably expand the therapeutic choices in the treatment of type 2 diabetes. In 2006, the endocannabinoid receptor blocker Rimonabant has been approved for the treatment of type 2 diabetes in Germany. This compound has led to significant reductions of body weight along with improvements of HbA1c levels and lipid profiles, but the lack of health insurance coverage limits its large scale use in germany. In April 2007, the first members of the GLP 1 analogues/incretin mimetics (exenatide, Byetta) and DPP 4 inhbitors (sitagliptin, Januvia) have become available for the treatment of type 2 diabetes in Germany. Both drugs have significantly lowered HbA1c levels in clinical studies. In addition, the incretin mimetics have caused a progressive reduction of body weight, while the DPP 4 inhibitors have been rather weight neutral. Sitagliptin can be administered orally, whereas exenatide has to be injected subcutaneously. Neither the DPP 4 inhibitors, nor the incretin mimetics have led to the development of hypoglycaemia, unless combined with sulfonylureas. Overall, the introduction of these new drug classes will certainly broaden our therapeutic choices in the management of type 2 diabetes. The long-term effects of these drugs on the development of diabetic complications in long-term trials remains to be awaited.

GPR119, a novel G protein-coupled receptor target for the treatment of type 2 diabetes and obesity

GPR119 is a G protein-coupled receptor expressed predominantly in the pancreas (beta-cells) and gastrointestinal tract (enteroendocrine cells) in humans. De-orphanization of GPR119 has revealed two classes of possible endogenous ligands, viz., phospholipids and fatty acid amides. Of these, oleoylethanolamide (OEA) is one of the most active ligands tested so far. This fatty acid ethanolamide is of particular interest because of its known effects of reducing food intake and body weight gain when administered to rodents. Agonists at the GPR119 receptor cause an increase in intracellular cAMP levels via G(alphas) coupling to adenylate cyclase. In vitro studies have indicated a role for GPR119 in the modulation of insulin release by pancreatic beta-cells and of GLP-1 secretion by gut enteroendocrine cells. The effects of GPR119 agonists in animal models of diabetes and obesity are reviewed, and the potential value of such compounds in future therapies for these conditions is discussed.

Physiological effects of dietary fructans extracted from Agave tequilana Gto. and Dasylirion spp

Recent data reported that inulin-type fructans extracted from chicory roots regulate appetite and lipid/glucose metabolism, namely, by promoting glucagon-like peptide-1 (GLP-1) production in the colon. The Agave genus growing in different regions of Mexico also contains important amounts of original fructans, with interesting nutritional and technological properties, but only few data report their physiological effect when added in the diet. Therefore, we decided to evaluate in parallel the effect of supplementation with 10 % agave or chicory fructans on glucose and lipid metabolism in mice. Male C57Bl/6J mice were fed a standard (STD) diet or diet supplemented with Raftilose P95 (RAF), fructans from Agave tequilana Gto. (TEQ) or fructans from Dasylirion spp. (DAS) for 5 weeks. The body weight gain and food intake in mice fed fructans-containing diets were significantly lower than the ones of mice fed the STD diet, TEQ leading to the lowest value. Serum glucose and cholesterol were similarly lower in all fructans-fed groups than in the STD group and correlated to body weight gain. Only RAF led to a significant decrease in serum TAG. As previously shown for RAF, the supplementation with agave fructans (TEQ and DAS) induced a higher concentration of GLP-1 and its precursor, proglucagon mRNA, in the different colonic segments, thus suggesting that fermentable fructans from different botanical origin and chemical structure are able to promote the production of satietogenic/incretin peptides in the lower part of the gut, with promising effects on glucose metabolism, body weight and fat mass development.

Design, synthesis and crystallization of a novel glucagon analog as a therapeutic agent

Glucagon and glucagon-like peptide 1 (GLP-1) are drugs or drug candidates for the treatment of metabolic diseases such as diabetes and obesity. The native hormones have pharmacological deficiencies such as short half-life and poor solubility. A novel glucagon receptor agonist named glucagon-Cex has been designed, synthesized and crystallized. This peptide was highly soluble under physiological conditions and crystallized readily. The crystal diffracted X-rays to 2.2 A resolution and the diffraction was consistent with space group P23, with unit-cell parameters a = b = c = 48.20 A, alpha = beta = gamma = 90.0 degrees. The crystals were suitable for a full structural determination to reveal the conformational differences between glucagon-Cex and the native hormone.

Decreased basal levels of glucagon-like peptide-1 after weight loss in obese subjects

OBJECTIVE

Basal glucagon-like peptide-1 (GLP-1) concentrations seem to be attenuated in obese subjects, although statistical significance is unclear. Only a few studies have investigated the effect of weight reduction on GLP-1 concentrations and have found unclear results. The aim of the present study was to determine whether subjects who lose weight on a hypocaloric diet experience the same change in circulating GLP-1 levels as subjects who do not lose weight.

MATERIAL AND METHODS

A population of 99 obese nondiabetic outpatients was analyzed in a prospective way. Weight and blood pressure were determined. Basal glucose, C-reactive protein, insulin, total cholesterol, LDL cholesterol, HDL cholesterol, triglycerides, and basal GLP-1 blood levels were measured before and after 3 months of hypocaloric diet. Bipolar impedance examination was performed in all patients to assess body composition. The lifestyle modification program consisted of a hypocaloric diet (1,520 kcal, 52% carbohydrates, 25% lipids and 23% proteins). The exercise program consisted of aerobic exercise for at least 3 times per week (60 min each).

RESULTS

Ninety-nine patients (20 male/79 female) gave informed consent and were enrolled in the study. Fourteen patients (2 male/12 female) did not lose weight (group I: weight increase of 2 +/- 1.1 kg, NS) and 75 patients (18 male/67 female) lost weight (group II, weight loss of 4 +/- 1.6 kg, p < 0.05). Weight, body mass index, fat mass, waist circumference, insulin, HOMA, LDL cholesterol, triglycerides and systolic blood pressure improved in group II, without significant statistical changes in group I. In group I, basal GLP-1 levels remained unchanged (7.4 +/- 3.1 vs. 7.15 +/- 3.6 ng/ml, NS). In group II, GLP-1 levels decreased significantly (8.4%, 6.88 +/- 2.5 vs. 6.3 +/- 2.4 ng/ml, p < 0.05). In the multivariate analysis with a dependent variable (levels of GLP-1 after hypocaloric diet adjusted by age and sex), only insulin levels remained as an independent predictor in the model (F = 5.9; p < 0.05), with an increase of 0.6 ng/ml (CI 95%: 0.1-1.1) in GLP-1 concentrations with each 1-mIU/ml increase of insulin.

CONCLUSION

Hypocaloric diet decreased GLP-1 levels in patients with weight loss with a significant improvement in anthropometric parameters and cardiovascular risk factors. Nevertheless, patients without weight loss after dietary treatment exhibited unchanged GLP-1 levels. Basal insulin correlates with basal GLP-1.

Peripheral tissue-brain interactions in the regulation of food intake

More than 70 years ago the glucostatic, lipostatic and aminostatic hypotheses proposed that the central nervous system sensed circulating levels of different metabolites, changing feeding behaviour in response to the levels of those molecules. In the last 20 years the rapid increase in obesity and associated pathologies in developed countries has involved a substantial increase in the knowledge of the physiological and molecular mechanism regulating body mass. This effort has resulted in the recent discovery of new peripheral signals, such as leptin and ghrelin, as well as new neuropeptides, such as orexins, involved in body-weight homeostasis. The present review summarises research into energy balance, starting from the original classical hypotheses proposing metabolite sensing, through peripheral tissue-brain interactions and coming full circle to the recently-discovered role of hypothalamic fatty acid synthase in feeding regulation. Understanding these molecular mechanisms will provide new pharmacological targets for the treatment of obesity and appetite disorders.

Fasting glucagon-like peptide-1 and its relation to insulin in obese children before and after weight loss

OBJECTIVE

To study the relationships between glucagon-like peptide-1 (GLP-1), weight status, insulin, and insulin resistance in the fasting state.

PATIENTS AND METHODS

Fasting GLP-1, glucose and insulin concentrations, insulin resistance index as homeostasis model assessment (HOMA), body mass index (BMI), and percentage body fat based on skinfold thickness measurements were determined in 42 obese (median age 11 years) and in 16 lean children of the same age. The HOMA model was used to calculate degree of insulin resistance. Furthermore, the changes in GLP-1, glucose, insulin, and HOMA in the course of 1 year were analyzed in the 42 obese children participating in an obesity intervention.

RESULTS

GLP-1 concentrations did not differ significantly between obese and lean children. In multiple linear regression analyses, GLP-1 was significantly related to insulin (P = 0.028) and HOMA (P = 0.019) but not to glucose, age, sex, pubertal stage, BMI, or percentage body fat. The 15 obese children with substantial weight reduction demonstrated significantly (P < 0.05) decreased GLP-1, insulin, and HOMA levels, whereas these parameters did not change in 27 obese children without substantial weight loss. Changes in GLP-1 correlated significantly with changes in insulin (r = 0.46, P = 0.001) and HOMA (r = 0.28, P = 0.036) but not with changes in glucose, BMI, or percentage of body fat.

CONCLUSIONS

In children, fasting GLP-1 concentrations are independent of age, sex, and pubertal stage. Although GLP-1 did not differ between lean and obese children, weight loss was associated with decreasing GLP-1. Inasmuch as GLP-1 levels were related to insulin concentrations in both cross-sectional and longitudinal analyses, we hypothesize a relationship between GLP-1 and insulin in the fasting state.

Laparoscopic Vertical Sleeve Gastrectomy for Morbid Obesity. The Future Procedure of Choice?

I report the general experience of performing sleeve gastrectomy defined as "a partial gastrectomy that results in removal of most of the stomach," as a first-stage procedure for morbidly and super-obese people. I also explore its potential as a single procedure evaluating its advantages and disadvantages. This procedure is designed to reduce the size of the stomach and its distention, whereby the patient feels full sooner and their appetite is decreased. Some posit-increased satiety results from the decreased ghrelin, secreted by the fundus, which is resected during this procedure. The advantages of sleeve gastrectomy are as follows: the stomach is reduced without loss of function, pyloric preservation prevents dumping, it requires only 1 day in the hospital, it provides an effective first-stage procedure for super-obese patients, it is useful in patients with disorders such as anemia or Crohn's disease, which preclude intestinal bypass, it can be performed laparoscopically, even in patients who weigh over 500 lbs, no band adjustment is required, it does not result in malabsorption, and it provides a good educational teaching base for doctors lacking experience in the treatment of gastric ulcers. The disadvantages include the risk of stapling complications and its irreversibility.

Glucagon-like peptide 1 (GLP-1) suppresses ghrelin levels in humans via increased insulin secretion

INTRODUCTION

Ghrelin is an orexigenic peptide predominantly secreted by the stomach. Ghrelin plasma levels rise before meal ingestion and sharply decline afterwards, but the mechanisms controlling ghrelin secretion are largely unknown. Since meal ingestion also elicits the secretion of the incretin hormone glucagon-like peptide 1 (GLP-1), we examined whether exogenous GLP-1 administration reduces ghrelin secretion in humans.

PATIENTS AND METHODS

14 healthy male volunteers were given intravenous infusions of GLP-1(1.2 pmol x kg(-1) min(-1)) or placebo over 390 min. After 30 min, a solid test meal was served. Venous blood was drawn frequently for the determination of glucose, insulin, C-peptide, GLP-1 and ghrelin.

RESULTS

During the infusion of exogenous GLP-1 and placebo, GLP-1 plasma concentrations reached steady-state levels of 139+/-15 pmol/l and 12+/-2 pmol/l, respectively (p<0.0001). During placebo infusion, ghrelin levels were significantly reduced in the immediate postprandial period (p<0.001), and rose again afterwards. GLP-1 administration prevented the initial postprandial decline in ghrelin levels, possibly as a result of delayed gastric emptying, and significantly reduced ghrelin levels 150 and 360 min after meal ingestion (p<0.05). The patterns of ghrelin concentrations in the experiments with GLP-1 and placebo administration were inversely related to the respective plasma levels of insulin and C-peptide.

CONCLUSIONS

GLP-1 reduces the rise in ghrelin levels in the late postprandial period at supraphysiological plasma levels. Most likely, these effects are indirectly mediated through its insulinotropic action. The GLP-1-induced suppression of ghrelin secretion might be involved in its anorexic effects.

The multiple faces of glucagon-like peptide-1--obesity, appetite, and stress: what is next? A review

By itself, glucagon-like peptide-1(GLP-1) appears to be an excellent drug for appetite control and the treatment of obesity. Unfortunately, few enzymes, such as IV dipeptidyl peptidase and renal excretin, degrade and render GLP-1 inactive within minutes. A receptor agonist, exendin-4, with a longer biological half-life than GLP-1, has been tried. Subcutaneous injection of exendin-4 or continuous IV injection of GLP-1 warrants further research and investigation.

Gut-brain neuropeptides in the regulation of ingestive behaviors and obesity

The prevalence of obesity has increased to epidemic proportions and has become an urgent public health problem. Obesity causes significant morbidity and mortality and its impact on health-care costs in the United States is growing dramatically. Apart from bariatric surgery treatment, options are limited. Future advances in treatment will rely on a better understanding of the pathogenesis and physiology of obesity. Alterations in gastrointestinal (GI) sensory-motor function and symptoms have been associated with obesity. GI neuroendocrine communications between the periphery and the brain regulate energy balance and ingestive behaviors. These interactions are largely mediated by the gut-brain peptides through negative and positive feedback loops that maintain energy homeostasis. Bariatric surgery has been shown effective, but the mechanisms of weight loss following these procedures clearly require further studies and a better understanding of the affects of bariatric surgery on the gut-brain neuropeptide homeostasis. Gut-brain peptides may provide attractive therapeutic targets in the fight against this very morbid disease. We review alterations in GI function and some of the more important gut-brain neuropeptides that occur in obesity.

A new technique for in vivo imaging of specific GLP-1 binding sites: first results in small rodents

EXPERIMENTAL OBJECTIVES

In vivo imaging of GLP-1 receptor-positive tissues may allow examination of physiologic and pathophysiologic processes. Based on the GLP-1 analog Exendin 4, we have developed a radiolabeled compound specifically targeting the GLP-1 receptor (DTPA-Lys40-Exendin 4). This work aims to detect GLP-1 receptor-positive tissues by biodistribution studies and in vivo small animal imaging studies. For in vivo imaging, a high-resolution multi-pinhole SPECT (single photon emission computed tomography) system was used in conjunction with an MRI (magnetic resonance imaging) system for image fusion.

RESULTS

DTPA-Lys40-Exendin 4 can be labeled with 111In to high specific activity (40 GBq/micromol). The radiochemical purity reliably exceeded 95%. Using this compound for in vivo small animal imaging of rats and mice as well as for biodistribution studies, specific GLP-1 binding sites could be detected in stomach, pancreas, lung, adrenals, and pituitary. Receptor-positive tissues were visualized with a high-resolution SPECT system with a resolution of less than 1 mm.

CONCLUSIONS

The new technique using DTPA-Lys40-Exendin 4 allows highly sensitive imaging of GLP-1 receptor-positive tissues in vivo. Therefore, intra-individual follow-up studies of GLP-1 receptor-positive tissue could be conducted in vivo.

Appetite regulatory hormone responses to various dietary proteins differ by body mass index status despite similar reductions in ad libitum energy intake

CONTEXT

Although dietary protein produces higher acute satiety relative to carbohydrate, the influence of protein source and body mass index (BMI) has not been clearly described.

OBJECTIVE

The objective of the study was to assess postprandial responses to different protein sources, compared with glucose, in males with normal and high BMI.

DESIGN

This was a randomized, crossover study of four preloads followed by blood sampling (+15, 30, 45, 60, 90, 120, 180 min) and buffet meal.

SETTING

The study was conducted at an outpatient clinic.

PARTICIPANTS

The study population included 72 men, with a BMI range 20.6-39.9 kg/m(2).

INTERVENTIONS

Interventions consisted of liquid preloads (1.1 MJ, 450 ml) containing 50 g whey, soy, gluten, or glucose.

MAIN OUTCOME MEASURES

Fasting and postprandial plasma glucose, insulin, ghrelin, glucagon-like peptide-1 (GLP-1) and cholecystokinin (n = 38), ad libitum energy intake, and appetite ratings were measured.

RESULTS

Energy intake was 10% lower after all protein preloads, compared with the glucose treatment (P < 0.05), independent of BMI status and protein type. All protein loads prolonged the postprandial suppression of ghrelin (P < 0.01) and elevation of GLP-1 (P < 0.01) and cholecystokinin (P < 0.05). Fasting GLP-1 concentrations [overweight, 17.5 +/- 1.3; lean, 14.7 +/- 0.1 pg/ml (5.2 +/- 0.4 and 4.4 +/- 0.1 pmol/liter, respectively); P < 0.001] and postprandial responses (P = 0.038) were higher in overweight subjects.

CONCLUSIONS

Whey, soy, and gluten similarly tend to reduce ad libitum food intake 3 h later in lean and overweight males relative to glucose. Postprandial ghrelin, GLP-1, insulin, and cholecystokinin may contribute to this higher satiety after protein consumption. GLP-1 concentrations are increased in overweight subjects, which may affect satiety responses in this group.

Lymphocytic infiltration and immune activation in metallothionein promoter-exendin-4 (MT-Exendin) transgenic mice

Glucagon-like peptide 1 (GLP-1) exhibits considerable potential for the treatment of type 2 diabetes because of its effects on stimulation of insulin secretion and the inhibition of gastric emptying, appetite, and glucagon secretion. However, native GLP-1 undergoes rapid enzymatic inactivation, prompting development of long-acting degradation-resistant GLP-1 receptor agonists such as exendin-4 (Ex-4). To study the consequences of sustained exposure to Ex-4, we generated metallothionein promoter-exendin-4 (MT-Exendin) mice that continuously express a proexendin-4 transgene in multiple murine tissues. We now report that MT-Exendin mice develop extensive tissue lymphocytic infiltration with increased numbers of CD4(+) and CD8a(+) cells in the liver and/or kidney and increased numbers of B220(+) cells present in the pancreas and liver. MT-Exendin mice generate antibodies directed against Ex-4, exendin NH(2)-terminal peptide (ENTP), and proexendin-4 as well as antibodies that cross-react with native GLP-1. Furthermore, lymphocytes isolated from MT-Exendin mice proliferate in response to proexendin-4 but not after exposure to Ex-4 or ENTP. These findings demonstrate that expression of a proexendin-4 transgene may be associated with activation of humoral and cellular immune responses in mice.

Glucagon-like peptide-1-based therapies for the treatment of type 2 diabetes mellitus

The 'incretin effect' describes the phenomenon of an enhanced insulin response following oral ingestion of glucose compared with that after intravenous administration of glucose, leading to identical postprandial plasma glucose excursions. It accounts for up to 60% of the postprandial insulin secretion, but is diminished in patients with type 2 diabetes mellitus. Gastrointestinal hormones that promote the incretin effect are called incretins. Glucagon-like peptide-1 (GLP-1) is an important incretin. Under hyperglycemic conditions in humans, it stimulates insulin secretion and normalizes blood glucose levels. GLP-1 does not stimulate insulin secretion at normal glucose levels; therefore, it does not cause hypoglycemia. Furthermore, it inhibits glucagon secretion and delays gastric emptying. In vitro and animal data have demonstrated that GLP-1 increases beta-cell mass by stimulating islet cell neogenesis and by inhibiting the apoptosis of islet cells. The improvement of beta-cell function due to GLP-1 can be indirectly observed from the increased insulin secretory capacity of humans receiving such treatment. GLP-1 may represent an attractive therapeutic method for patients with type 2 diabetes because of its multiple effects, including the simulation of satiety in the CNS by acting as a transmitter or by crossing the blood brain barrier. Native GLP-1 is degraded rapidly upon intravenous or subcutaneous administration and is therefore not feasible for routine therapy. Long-acting GLP-1 analogs (e.g. liraglutide) and exendin-4 (exenatide) that are resistant to degradation, called 'incretin mimetics', are being investigated in clinical trials. Dipeptidyl peptidase-IV inhibitors (e.g. vildagliptin, sitagliptin, and saxagliptin) that inhibit the enzyme responsible for incretin degradation are also being studied.

Pharmacologic modifications of hormones to improve their therapeutic potential for diabetes management

Rapid-acting genetically engineered insulin analogues emerging in the last 10 years are now established as more effective prandial insulins than traditional short-acting human insulin. The development of analogues for use as basal insulin, however, has been much slower. Methods of pro-tracting the time-action curve of injected insulin include complexing with proteins, insulin crystal formation, shifting the iso-electric point of the amino acid sequence or attaching a fatty-acid side chain to the molecule. The latter two methods have been more successful in producing physiologic insulin profiles when compared with the former methods. The principle of acylation has also been applied to prolong the action of other hormones, such as glucagon-like peptide 1 (GLP-1), as the native peptide has a very short half-life. Preliminary results with this compound and other GLP-1 analogues show promise in treating patients with type 2 diabetes. In summary, the development of new insulin and other hormone preparations by the manipulation of native peptide structure has recently improved our antidiabetic armamentarium, and further research will continue this fruitful approach.

Lifestyle, social class, and obesity-the Copenhagen Male Study

OBJECTIVE

With the implicit purpose of identifying relevant intervention targets, the aim of the study was to test if lifestyle factors associated with obesity are unevenly distributed across social groups, and whether an uneven distribution of such factors may contribute to the explanation of social differences in obesity.

DESIGN

Cross-sectional study of 3290 men aged 53-75 years (mean=63) carried out in 1985-1986 using in addition, data from a previous baseline established in 1970-1971. Information about lifestyle factors was obtained from a questionnaire validated during an interview. Potential risk factors were smoking history, alcohol consumption, leisure time physical activity (LTPA), and from the 1985-1986 study only: consumption of tea and coffee, use of sugar in tea or coffee, and avoidance of fat in foods. The clinical examination included measurements of height and weight. Obesity was defined as a body mass index > or =30 (BMI=kg/m2). Based on information about education and job profile the men were subdivided into five social classes.

RESULTS

Overall, 291 men (8.8%) were obese. The lower the social class the higher the proportion of obese men: in social classes I and II, 4.5% (of 953), social class III, 9.1% (of 636), social class IV, 11.1% (of 1353), and social class V, 11.6% (of 346), P<0.001 (trend test). Leisure time physical activity, alcohol consumption, smoking habits, use of sugar in hot beverages, and consumption of coffee and tea, were all significantly associated with obesity, either positively or negatively, and even significantly associated with social class. Based on these lifestyle factors it was possible to discriminate subgroups with highly different prevalences of obesity. Despite this, adjustment for identified obesity covariates in a multiple logistic regression analysis did in no way explain the association of social class with obesity.

CONCLUSION

Lifestyle factors in concert strongly associated with obesity are unevenly distributed across social classes, yet incapable of explaining the higher prevalence of obesity in lower social classes.

Oligofructose promotes satiety in rats fed a high-fat diet: involvement of glucagon-like Peptide-1

OBJECTIVE

To analyze the putative interest of oligofructose (OFS) in the modulation of food intake after high-fat diet in rats and to question the relevance of the expression and secretion of intestinal peptides in that context.

RESEARCH METHODS AND PROCEDURES

Male Wistar rats were pretreated with standard diet or OFS-enriched (10%) standard diet for 35 days followed by 15 days of high-fat diet enriched or not with OFS (10%) treatment. Body weight, food intake, triglycerides, and plasma ghrelin levels were monitored during the treatment. On day 50, rats were food-deprived 8 hours and anesthetized for blood and intestinal tissue sampling for further proglucagon mRNA, glucagon-like peptide (GLP)-1, and GLP-2 quantification.

RESULTS

The addition of OFS in the diet protects against the promotion of energy intake, body weight gain, fat mass development, and serum triglyceride accumulation induced by a high-fat diet. OFS fermentation leads to an increase in proglucagon mRNA in the cecum and the colon and in GLP-1 and GLP-2 contents in the proximal colon, with consequences on the portal concentration of GLP-1 (increase). A lower ghrelin level is observed only when OFS is added to the standard diet of rats.

DISCUSSION

In rats exposed to high-fat diet, OFS is, thus, able to modulate endogenous production of gut peptides involved in appetite and body weight regulation. Because several approaches are currently used to treat type 2 diabetes and obesity with limited effectiveness, dietary fibers such as OFS, which promote the endogenous production of gut peptides like GLP-1, could be proposed as interesting nutrients to consider in the management of fat intake and associated metabolic disorders.

Peripheral exendin-4 and peptide YY(3-36) synergistically reduce food intake through different mechanisms in mice

Glucagon-like peptide-1(7-36NH2) (GLP-1) and peptide YY(3-36NH2) (PYY(3-36NH2)) are cosecreted from the intestine in response to nutrient ingestion. Peripheral administration of GLP-1 or PYY(3-36NH2) decreases food intake (FI) in rodents and humans; however, the exact mechanisms by which these peptides regulate FI remain unclear. Male C57BL/6 mice were injected (ip) with exendin-4(1-39) (Ex4, a GLP-1 receptor agonist) and/or PYY(3-36NH2) (0.03-3 microg), and FI was determined for up to 24 h. Ex4 and PYY(3-36NH2) alone decreased FI by up to 83 and 26%, respectively (P < 0.05-0.001), whereas a combination of the two peptides (0.06 microg Ex4 plus 3 microg PYY(3-36NH2)) further reduced FI for up to 8 h in a synergistic manner (P < 0.05-0.001). Ex4 and/or PYY(3-36NH2) delayed gastric emptying by a maximum of 19% (P < 0.01-0.001); however, there was no significant effect on locomotor activity nor was there induction of taste aversion. Capsaicin pretreatment prevented the inhibitory effect of Ex4 on FI (P < 0.05), but had no effect on the anorexigenic actions of PYY(3-36NH2). Similarly, exendin-4(9-39) (a GLP-1 receptor antagonist) partially abolished Ex4-induced anorexia (P < 0.05), but did not affect the satiation produced by PYY(3-36NH2). Conversely, BIIE0246 (a Y2 receptor antagonist) completely blocked the anorexigenic effects of PYY(3-36NH2) (P < 0.001), but had no effect on Ex4-induced satiety. Thus, Ex4 and PYY(3-36NH2) suppress FI via independent mechanisms involving a GLP-1 receptor-dependent, sensory afferent pathway (Ex4) and a Y2-receptor mediated pathway (PYY(3-36NH2)). These findings suggest that administration of low doses of Ex4 together with PYY(3-36NH2) may increase the suppression of FI without inducing significant side effects.

New therapeutic strategies for the treatment of type 2 diabetes mellitus based on incretins

Orally ingested glucose leads to a greater insulin response compared to intravenously administered glucose leading to identical postprandial plasma glucose excursions, a phenomenon referred to as the "incretin effect". The incretin effect comprises up to 60% of the postprandial insulin secretion and is diminished in type 2 diabetes. One of the very important gastrointestinal hormones promoting this effect is glucagon-like peptide 1 (GLP-1). It only stimulates insulin secretion and normalizes blood glucose in humans under hyperglycemic conditions, therefore it does not cause hypoglycemia. Other important physiological actions of GLP-1 are the inhibition of glucagon secretion and gastric emptying. It further acts as a neurotransmitter in the hypothalamus stimulating satiety. In vitro and animal data demonstrated that GLP-1 increases beta-cell mass by stimulating islet cell neogenesis and by inhibiting apoptosis of islets. In humans, the improvement of beta-cell function can be indirectly observed from the increased insulin secretory capacity after GLP-1 infusions. GLP-1 represents an attractive therapeutic principle for type 2 diabetes. However, native GLP-1 is degraded rapidly upon exogenous administration and is therefore not feasible for routine therapy. The first long-acting GLP-1 analog ("incretin mimetic") Exenatide (Byetta) has just been approved for type 2 diabetes therapy. Other compounds are being investigated in clinical trials (e.g. liraglutide, CJC1131). Dipeptidyl-peptidase IV inhibitors (DPP-IV inhibitors; e.g. Vildagliptin, Sitagliptin) that inhibit the enzyme responsible for incretin degradation are also under study.

Effects of liraglutide (NN2211), a long-acting GLP-1 analogue, on glycaemic control and bodyweight in subjects with Type 2 diabetes

AIMS

Liraglutide (NN2211) is a long-acting GLP-1 analogue, with a pharmacokinetic profile suitable for once-daily administration. This multicentre, double-blind, parallel-group, double-dummy study explored the dose-response relationship of liraglutide effects on bodyweight and glycaemic control in subjects with Type 2 diabetes.

METHODS

Subjects (BMI 27-42 kg/m(2)) with Type 2 diabetes who were previously treated with an OAD (oral anti-diabetic drug) monotherapy (69% with metformin), and had HbA(1c) < or = 10% were enrolled. After a 4-week metformin run-in period, 210 subjects (27-73 years, 60% female) were randomised to receive liraglutide (0.045-0.75 mg) once daily or continued on metformin 1000 mg b.d. for 12 weeks.

RESULTS

Mean baseline values for the six treatment groups ranged from 6.8 to 7.5% for HbA(1c), and 8.06-9.44 mmol/l (145-170 mg/dl) for fasting plasma glucose. After 12-week treatment, a weight change of -0.05 to -1.9% was observed for the six treatment groups. Mean HbA(1c) changes from baseline for 0.045, 0.225, 0.45, 0.6, 0.75 mg liraglutide and metformin were +1.28%, +0.86%, +0.22%, +0.16%, +0.30% and +0.09%, respectively. No significant differences in HbA(1c) were observed between liraglutide and metformin groups at the three highest liraglutide dose levels (0.45, 0.6 and 0.75 mg). The lowest two liraglutide doses (0.045 mg and 0.225 mg) were not sufficient to maintain the fasting plasma glucose values achieved by metformin. No major hypoglycaemic episodes were reported. Episodes of nausea and/or vomiting were reported by 11 patients (6.3%) receiving liraglutide and three (8.8%) receiving metformin.

CONCLUSIONS

Once-daily liraglutide improved glycaemic control and weight, in a comparable degree to metformin. Liraglutide appeared to be safe and generally well tolerated. Higher doses of liraglutide merit study in future clinical trials.

Biological actions of the incretins GIP and GLP-1 and therapeutic perspectives in patients with type 2 diabetes

Incretin hormones are defined as intestinal hormones released in response to nutrient ingestion, which potentiate the glucose-induced insulin response. In humans, the incretin effect is mainly caused by two peptide hormones, glucose-dependent insulin releasing polypeptide GIP, and glucagon-like peptide-1 GLP-1. GIP is secreted by K cells from the upper small intestine while GLP-1 is mainly produced in the enteroendocrine L cells located in the distal intestine. Their effect is mediated through their binding with specific receptors, though part of their biological action may also involve neural modulation. GIP and GLP-1 are both rapidly degraded into inactive metabolites by the enzyme dipeptidyl-peptidase-IV (DPP-IV). In addition to its effects on insulin secretion, GLP-1 exerts other significant actions, including stimulation of insulin biosynthesis, inhibition of glucagon secretion, inhibition of gastric emptying and acid secretion, reduction of food intake, and trophic effects on the pancreas. As the insulinotropic action of GLP-1 is preserved in type 2 diabetic patients, this peptide was a candidate as a therapeutic agent for this disease. A number of pharmacological strategies have been developed to provide continuous delivery of GLP-1 and to prevent degradation of GLP-1, including continuous administration of GLP-1, DPP-IV inhibitors and DPP-IV resistant GLP-1 analogues. Recent results of the most clinically advanced incretin mimetics confirmed their efficacy to improve glycemic control in type 2 diabetic patients. Further results are expected to confirm the efficacy/safety profile of these compounds, and to find their place in the therapeutic strategy of type 2 diabetes.

S 23521 decreases food intake and body weight gain in diet-induced obese rats

OBJECTIVE

To investigate the effect of S 23521, a new glucagon-like peptide-1-(7-36) amide analogue, on food intake and body weight gain in obese rats, as well as on gene expression of several proteins involved in energy homeostasis.

RESEARCH METHODS AND PROCEDURES

Lean and diet-induced obese rats were treated with either S 23521 or vehicle. S 23521 was given either intraperitoneally (10 or 100 microg/kg) or subcutaneously (100 microg/kg) for 14 and 20 days, respectively. Because the low-dose treatment did not affect food intake and body weight, the subcutaneous treatment at high dose was selected to test the effect on selected end-points.

RESULTS

Treated obese rats significantly decreased their cumulative energy intake in relation to vehicle-treated counterparts (3401 +/- 65 vs. 3898 +/- 72 kcal/kg per 20 days; p < 0.05). Moreover, their body weight gain was reduced by 110%, adiposity was reduced by 20%, and plasma triglyceride levels were reduced by 38%. The treatment also improved glucose tolerance and insulin sensitivity of obese rats. Regarding gene expression, no changes in uncoupling protein-1, uncoupling protein-3, leptin, resistin, and peroxisome proliferator-activated receptor (PPAR)-gamma were observed.

DISCUSSION

S 23521 is an effective glucagon-like peptide-1-(7-36) amide analogue, which induced a decrease in energy intake, body weight, and adiposity in a rat model of diet-induced obesity. In addition, the treatment also improved glucose tolerance and insulin sensitivity of obese rats. These results strongly support S 23521 as a putative molecule for the treatment of obesity.

Glucagon-like peptide 1(GLP-1) in biology and pathology

Post-translational proteolytic processing of the preproglucagon gene in the gut results in the formation of glucagon-like peptide 1 (GLP-1). Owing to its glucose-dependent insulinotropic effect, this hormone was postulated to primarily act as an incretin, i.e. to augment insulin secretion after oral glucose or meal ingestion. In addition, GLP-1 decelerates gastric emptying and suppresses glucagon secretion. Under physiological conditions, GLP-1 acts as a part of the 'ileal brake', meaning that is slows the transition of nutrients into the distal gut. Animal studies suggest a role for GLP-1 in the development and growth of the endocrine pancreas. In light of its multiple actions throughout the body, different therapeutic applications of GLP-1 are possible. Promising results have been obtained with GLP-1 in the treatment of type 2 diabetes, but its potential to reduce appetite and food intake may also allow its use for the treatment of obesity. While rapid in vivo degradation of GLP-1 has yet prevented its broad clinical use, different pharmacological approaches aiming to extend the in vivo half-life of GLP-1 or to inhibit its inactivation are currently being evaluated. Therefore, antidiabetic treatment based on GLP-1 may become available within the next years. This review will summarize the biological effects of GLP-1, characterize its role in human biology and pathology, and discuss potential clinical applications as well as current clinical studies.

Intravenous infusion of glucagon-like peptide-1 potently inhibits food intake, sham feeding, and gastric emptying in rats

Glucagon-like peptide-1(7-36)-amide (GLP-1) is postulated to act as a hormonal signal from gut to brain to inhibit food intake and gastric emptying. A mixed-nutrient meal produces a 2 to 3-h increase in plasma GLP-1. We determined the effects of intravenous infusions of GLP-1 on food intake, sham feeding, and gastric emptying in rats to assess whether GLP-1 inhibits food intake, in part, by slowing gastric emptying. A 3-h intravenous infusion of GLP-1 (0.5-170 pmol.kg(-1).min(-1)) at dark onset dose-dependently inhibited food intake in rats that were normally fed with a potency (mean effective dose) and efficacy (maximal % inhibition) of 23 pmol.kg(-1).min(-1) and 82%, respectively. Similar total doses of GLP-1 administered over a 15-min period were less potent and effective. In gastric emptying experiments, GLP-1 (1.7-50 pmol.kg(-1).min(-1)) dose-dependently inhibited gastric emptying of saline and ingested chow with potencies of 18 and 6 pmol.kg(-1).min(-1) and maximal inhibitions of 74 and 83%, respectively. In sham-feeding experiments, GLP-1 (5-50 pmol.kg(-1).min(-1)) dose-dependently reduced 15% aqueous sucrose intake in a similar manner when gastric cannulas were closed (real feeding) and open (sham feeding). These results demonstrate that intravenous infusions of GLP-1 dose-dependently inhibit food intake, sham feeding, and gastric emptying with a similar potency and efficacy. Thus GLP-1 may inhibit food intake in part by reducing gastric emptying, yet can also inhibit food intake independently of its action to reduce gastric emptying. It remains to be determined whether intravenous doses of GLP-1 that reproduce postprandial increases in plasma GLP-1 are sufficient to inhibit food intake and gastric emptying.

Structural requirements of the N-terminal region of GLP-1-[7-37]-NH2 for receptor interaction and cAMP production

A series of GLP-1-[7-36]-NH(2) (tGLP-1) and GLP-1-[7-37] analogs modified in position 7, 8, 9 and 36, have been designed and evaluated on murine GLP-1 receptors expressed in RIN T3 cells for both their affinity and activity. Ten of the synthesized peptides were found full agonists with activities superior or at least equal to that of the native hormone. Five of them were investigated for their plasmatic stability and the most stable, [a(8)-desR(36)]GLP-1-[7-37]- NH(2) (Compound 8), evaluated in vivo in a glucose tolerance test which confirmed a clearly longer activity than that of the native hormone. We also performed circular dichroism study and propose a hypothetical structural model explaining the most part of observed activities of GLP-1 analogs on RIN T3 cells.

Potential modulation of plasma ghrelin and glucagon-like peptide-1 by anorexigenic cannabinoid compounds, SR141716A (rimonabant) and oleoylethanolamide

The CB1 cannabinoid receptor antagonist, N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methylpyrazole-3-carboxamide (rimonabant; SR141716A), and oleoylethanolamide (OEA) are known to reduce food consumption, by, at least partially, a peripheral regulation of feeding. The effects of systemic SR141716A or OEA (5 mg/kg) administrations on food consumption in 24 h food-deprived and fed rats were investigated. In fasted rats, SR141716A and OEA produced an inhibition in food intake measurable the first 20 min following injection. The increase in ghrelin levels observed in the vehicle-injected rats was abolished in animals receiving OEA and significantly reduced with SR141716A. Neither OEA nor SR141716A modified glucagon-like peptide-1 (7-36) amide portal levels 20 min after the administration. In fed rats, plasma ghrelin levels of SR141716A- and OEA-treated rats were 35% lower as compared with those of the vehicle-injected rats. These results show an influence of cannabinoid agents on circulating ghrelin levels and suggest that their short-term action on appetite seems to be in accordance with the control of secretion of gastrointestinal orexigenic peptides, mainly expressed in the upper part of the gastrointestinal tract.

Clinical endocrinology and metabolism. Glucagon-like peptide-1 and glucagon-like peptide-2

The glucagon-like peptides (glucagon-like peptide-1 (GLP-1) and glucagon-like peptide-2 (GLP-2)) are released from enteroendocrine cells in response to nutrient ingestion. GLP-1 enhances glucose-stimulated insulin secretion and inhibits glucagon secretion, gastric emptying and feeding. GLP-1 also has proliferative, neogenic and antiapoptotic effects on pancreatic beta-cells. More recent studies illustrate a potential protective role for GLP-1 in the cardiovascular and central nervous systems. GLP-2 is an intestinal trophic peptide that stimulates cell proliferation and inhibits apoptosis in the intestinal crypt compartment. GLP-2 also regulates intestinal glucose transport, food intake and gastric acid secretion and emptying, and improves intestinal barrier function. Thus, GLP-1 and GLP-2 exhibit a diverse array of metabolic, proliferative and cytoprotective actions with important clinical implications for the treatment of diabetes and gastrointestinal disease, respectively. This review will highlight our current understanding of the biology of GLP-1 and GLP-2, with an emphasis on both well-characterized and more novel therapeutic applications of these peptides.

Inulin-type fructans modulate gastrointestinal peptides involved in appetite regulation (glucagon-like peptide-1 and ghrelin) in rats

The hypothesis tested in the present study is that dietary fructans are able to modulate gastrointestinal peptides involved in the control of food intake, namely glucagon-like peptide (GLP)-1 (7-36) amide and ghrelin. After 3 weeks of treatment with a standard diet (control) or the same diet enriched with 100 g fructans varying in their degrees of polymerization (oligofructose (OFS), Synergy 1 (Syn) or long chain inulin)/kg, male Wistar rats were deprived of food for 8 h before sample collection. Dietary energy intake throughout the experiment was significantly lower (P<0.05) in fructans-fed rats than in control rats, leading to a significant decrease (P<0.01) in epidydimal fat mass at the end of the treatment in OFS- and Syn-treated rats. GLP-1 (7-36) amide concentration in portal vein serum was higher in OFS- and Syn-fed than in control rats. Both GLP-1 (7-36) amide concentration and proglucagon mRNA concentrations were significantly greater (P<0.05) in the proximal colonic mucosa of fructans-fed rats v. controls. Normally active ghrelin concentration in plasma increases during food deprivation and rapidly falls during a meal. In the present study, after 8 h of food deprivation, active ghrelin in the plasma remained significantly lower (P<0.05) in OFS and Syn-fed than in control rats. These results are in accordance with the modifications of dietary intake and fat-mass development in short-chain fructans-treated rats and demonstrate the potential modulation of GLP-1 (7-36) amide and ghrelin by fermentable fibres such as fructans, which are rapidly and extensively fermented in the proximal part of the colon.

Glucagon-like peptide 2 improves intestinal wound healing through induction of epithelial cell migration in vitro—evidence for a TGF-β-mediated effect

BACKGROUND/AIMS

In vitro studies suggest that glucagon-like peptide 2 (GLP-2), secreted from enteroendocrine cells in the gastrointestinal tract after food intake, is able to ameliorate mucosal injury in settings of human disease characterized by injury and dysfunction of the intestinal mucosal epithelium. We evaluated this potential of GLP-2 after epithelial trauma by using two in vitro models measuring intestinal epithelial cell proliferation and cell migration.

MATERIALS AND METHODS

Injuries were induced in confluent monolayers of the small intestinal cells lines IEC-6 and IEC-18, as well as in the colonic cell lines Caco-2 and Colo 320. GLP-2 (50-500 nM) or other peptides were added to the media. Wound healing was investigated after 24 h by quantification of the number of cells migrating across the wound edge. Proliferation of cells was assessed by using photometric mitochondrial incorporation measurement of MTT (3-[4,5-Dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide). Monoclonal TGF-beta antibodies were added to wounded monolayers to examine whether the GLP-2-induced wound healing was TGF-beta-mediated.

RESULTS

Migration assessments revealed a significant stimulation of GLP-2-induced migration in IEC-6 and IEC-18 monolayers compared to the placebo group. No effect was observed in the colon cancer cell lines Caco-2 and Colo 320. Results of the proliferation assays show a significant inhibition of proliferation by GLP-2 in small intestinal cell lines whereas a dose-dependent stimulation of proliferation in colonic epithelial cells was observed. Addition of neutralizing TGF-beta1 antibodies to wounded IEC-6 and IEC-18 monolayers incubated with GLP-2 significantly reduced the number of migrating cells to the level of the placebo group.

CONCLUSIONS

In our in vitro model, it was shown that the GLP-2-induced improvement of intestinal wound healing is TGF-beta-mediated. These effects were predominant in the epithelium of the small intestine compared to colonic epithelium. Our findings provide further insight into mechanisms leading to GLP-2-induced mucosal wound healing. These results suggest that GLP-2 or analogues of this peptide may potentially be useful for the treatment of intestinal disorders characterized by injury and ineffective repair of the intestinal mucosa.

A recombinant human glucagon-like peptide (GLP)-1-albumin protein (albugon) mimics peptidergic activation of GLP-1 receptor-dependent pathways coupled with satiety, gastrointestinal motility, and glucose homeostasis

Peptide hormones exert unique actions via specific G protein-coupled receptors; however, the therapeutic potential of regulatory peptides is frequently compromised by rapid enzymatic inactivation and clearance from the circulation. In contrast, recombinant or covalent coupling of smaller peptides to serum albumin represents an emerging strategy for extending the circulating t(1/2) of the target peptide. However, whether larger peptide-albumin derivatives will exhibit the full spectrum of biological activities encompassed by the native peptide remains to be demonstrated. We report that Albugon, a human glucagon-like peptide (GLP)-1-albumin recombinant protein, activates GLP-1 receptor (GLP-1R)-dependent cAMP formation in BHK-GLP-1R cells, albeit with a reduced half-maximal concentration (EC(50)) (0.2 vs. 20 nmol/l) relative to the GLP-1R agonist exendin-4. Albugon decreased glycemic excursion and stimulated insulin secretion in wild-type but not GLP-1R(-/-) mice and reduced food intake after both intracerebroventricular and intraperitoneal administration. Moreover, intraperitoneal injection of Albugon inhibited gastric emptying and activated c-FOS expression in the area postrema, the nucleus of the solitary tract, the central nucleus of the amygdala, the parabrachial, and the paraventricular nuclei. These findings illustrate that peripheral administration of a larger peptide-albumin recombinant protein mimics GLP-1R-dependent activation of central and peripheral pathways regulating energy intake and glucose homeostasis in vivo.

Oxyntomodulin and glucagon-like peptide-1 differentially regulate murine food intake and energy expenditure

BACKGROUND & AIMS

Gut-derived peptides including ghrelin, cholecystokinin (CCK), peptide YY (PYY), glucagon-like peptide (GLP-1), and GLP-2 exert overlapping actions on energy homeostasis through defined G-protein-coupled receptors (GPCRs). The proglucagon-derived peptide (PGDP) oxyntomodulin (OXM) is cosecreted with GLP-1 and inhibits feeding in rodents and humans; however, a distinct receptor for OXM has not been identified.

METHODS

We examined the mechanisms mediating oxyntomodulin action using stable cell lines expressing specific PGDP receptors in vitro and both wild-type and knockout mice in vivo.

RESULTS

OXM activates signaling pathways in cells through glucagon or GLP-1 receptors (GLP-1R) but transiently inhibits food intake in vivo exclusively through the GLP-1R. Both OXM and the GLP-1R agonist exendin-4 (Ex-4) activated neuronal c-fos expression in the paraventricular nucleus of the hypothalamus, the area postrema, and the nucleus of the solitary tract following intraperitoneal (i.p.) injection. However, OXM transiently inhibited food intake in wild-type mice following intracerebroventricular (i.c.v.) but not i.p. administration, whereas Ex-4 produced a more potent and sustained inhibition of food intake following both i.c.v. and i.p. administration. The anorectic effects of OXM were preserved in Gcgr(-/-) mice but abolished in GLP-1R(-/-) mice. Although central Ex-4 and OXM inhibited feeding via a GLP-1R-dependent mechanism, Ex-4 but not OXM reduced VO2 and respiratory quotient in wild-type mice.

CONCLUSIONS

These findings demonstrate that structurally distinct PGDPs differentially regulate food intake and energy expenditure by interacting with a GLP-1R-dependent pathway. Hence ligand-specific activation of a common GLP-1R increases the complexity of gut-central nervous system pathways regulating energy homeostasis and metabolic expenditure.

Brain circuits regulating energy homeostasis

For decades, increasingly sophisticated methods have been designed to address the problem of the involvement of the brain in the physiology of energy homeostasis and the pathogenesis of obesity. A vast number of experimental observations have been made from novel genetic and physiologic approaches that allowed the identification of metabolic hormones and their relationship to key peptidergic systems in the brain. Although the central integration of afferent signals reflecting acute and chronic energy requirements is becoming clearer, the blueprint of the central regulation of energy expenditure is not known. This review offers a look at central neuronal circuitries that are implicated in metabolism regulation and strongly suggests that without a blueprint, attempts to intervene and control energy balance will remain futile.

Minireview: Gut peptides regulating satiety

The gastrointestinal tract and the pancreas release hormones regulating satiety and body weight. Ghrelin stimulates appetite, and glucagon-like peptide-1, oxyntomodulin, peptide YY, cholecystokinin, and pancreatic polypeptide inhibit appetite. These gut hormones act to markedly alter food intake in humans and rodents. Obesity is the current major cause of premature death in the United Kingdom, killing almost 1000 people per week. Worldwide, its prevalence is accelerating. There is currently no effective answer to the pandemic of obesity, but replacement of the low levels of peptide YY observed in the obese may represent an effective antiobesity therapy.

Glucagon-like peptide 1 agonists and the development and growth of pancreatic beta-cells

Glucagon-like peptide 1 (GLP-1) is an intestine-derived insulinotropic hormone that stimulates glucose-dependent insulin production and secretion from pancreatic beta-cells. Other recognized actions of GLP-1 are to suppress glucagon secretion and hepatic glucose output, delay gastric emptying, reduce food intake, and promote glucose disposal in peripheral tissues. All of these actions are potentially beneficial for the treatment of type 2 diabetes mellitus. Several GLP-1 agonists are in clinical trials for the treatment of diabetes. More recently, GLP-1 agonists have been shown to stimulate the growth and differentiation of pancreatic beta-cells, as well as to exert cytoprotective, antiapoptotic effects on beta-cells. Recent evidence indicates that GLP-1 agonists act on receptors on pancreas-derived stem/progenitor cells to prompt their differentiation into beta-cells. These new findings suggest an approach to create beta-cells in vitro by expanding stem/progenitor cells and then to convert them into beta-cells by treatment with GLP-1. Thus GLP-1 may be a means by which to create beta-cells ex vivo for transplantation into patients with insulinopenic type 1 diabetes and severe forms of type 2 diabetes.

Glucagon-like peptide 1 and gastric inhibitory polypeptide: potential applications in type 2 diabetes mellitus

Although the insulinotropic actions of gastric inhibitory polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) have been known for almost 2 decades, the incretin hormones have not yet become available for clinical application. This can be explained by their unfavourable pharmacological properties. Both hormones are rapidly inactivated by the enzyme dipeptidyl peptidase IV (DPP IV), yielding biologically inactive fragments. There have been several attempts to make use of the antidiabetogenic potential of the incretin hormones. Various analogues of GLP-1 and GIP have been generated in order to achieve resistance to DPP IV degradation. The natural GLP-1 receptor agonist exendin-4, found in the saliva of the Gila monster, has a longer biological half-life after subcutaneous injection than GLP-1, and inhibition of DPP IV using, for example, pyrrolidine derivatives provides elevated concentrations of intact, biologically active GIP and GLP-1 endogenously released from the gut. A continuous intravenous infusion of native GLP-1 for a limited time may be suitable in certain clinical situations. Numerous clinical studies are currently underway to evaluate these approaches. Therefore, an antidiabetic treatment based on incretin hormones may become available within the next 5 years.

Peripheral regulation of food intake: new insights

Appetite is controlled by a complicated system with hunger and satiety signals interacting in complex pathways both peripherally and centrally. Insulin, leptin and ghrelin are key hormonal regulators of food intake. Ghrelin enhances appetite while leptin is a satiety signal. A novel peripheral regulator of food intake, peptide YY(3-36), is released from the gastrointestinal tract postprandially. In this review old and new peripheral signals and their interaction in the control of food intake are briefly discussed.

Neural systems controlling food intake and energy balance in the modern world

PURPOSE OF REVIEW

Obesity continues to increase around the globe, and creates a major health problem because of its comorbidities such as diabetes and cardiovascular disease. Considering that the major cause of most human obesities is the modern lifestyle in a rapidly changing environment, this suggests that the battle is between brain areas controlling internal metabolic homeostasis and those dealing with cognitive and emotional processing of external information. Thus, this review is intended to bridge this apparent neural dichotomy and highlight possible ways of interactions between these homeostatic and nonhomeostatic systems.

RECENT FINDINGS

Rapid progress has been made in identifying the molecular mechanisms underlying the neural circuits regulating food intake and energy balance. Specific populations of peptidergic neurons in the medial hypothalamus can be considered metabolic integrators sensing both short and long-term availability of fuels. These cell groups in turn connect with various other brain regions to orchestrate adaptive responses through changes in food intake, as well as endocrine and autonomic responses. Alternatively, the impact of the environmental changes on ingestive behavior have been documented, and many of the underlying cortico-limbic pathways are starting to be identified. It has been proposed that a switch from instinctual control of energy balance to a more cognitive control will be necessary to stop the obesity epidemic.

SUMMARY

The realization that there is nothing wrong with the homeostatic regulatory system in common obesity suggests that a systematic investigation of pathways that link the 'cognitive' with the 'metabolic' brain might be a more promising area of research. Such an investigation would reveal new molecular and cellular mechanisms providing new drug targets, leading to behavioral therapies that are directed more towards the causes of common obesity.

Effect of leptin on the acute feeding-induced hypothalamic serotonergic stimulation in normal rats

Both hypothalamic serotonin and leptin reduce energy intake and stimulate expenditure. There are evidence that increased serotonin metabolism may be involved in leptin actions. Using microdialysis, we directly assessed the effect of an intracerebroventricular leptin injection on 5-HT release in the lateral hypothalamus of normal rats. When LH microdialysates were collected in the absence of food intake, neither artificial cerebrospinal fluid (CSF) nor 10 microg leptin i.c.v. caused significant variations in 5-HT release, measured for 2 h post-injection, at 20-min periods. When food was ingested after CSF, 5-HT release increased significantly, with a maximal elevation of 51+/-16% above baseline occurring at the 100-120 min post-injection interval. Leptin inhibited food intake (-75% at 0-20 min and -73% at 20-40 min) while it accentuated the food-induced serotonergic activation. At the 0-20 min interval, serotonin release was significantly higher after leptin (42+/-12% above baseline) than after CSF (6+/-5%) and the maximal increase after leptin was of 126+/-53% above baseline (100-120 min, p>0.05 vs. CSF). These observations indicate that leptin probably interacts with the serotonergic-stimulating mechanisms elicited by food intake, intensifying them. The additional serotonergic activation induced by leptin may be significant for the hormone effects on energy balance.