Amylin secretion from the rat pancreas and its selective loss after streptozotocin treatment

Amylin Modulates a Ventral Tegmental Area-to-Medial Prefrontal Cortex Circuit to Suppress Food Intake and Impulsive Food-Directed Behavior

BACKGROUND

A better understanding of the neural mechanisms regulating impaired satiety to palatable foods is essential to treat hyperphagia linked with obesity. The satiation hormone amylin signals centrally at multiple nuclei including the ventral tegmental area (VTA). VTA-to-medial prefrontal cortex (mPFC) projections encode food reward information to influence behaviors including impulsivity. We hypothesized that modulation of VTA-to-mPFC neurons underlies amylin-mediated decreases in palatable food-motivated behaviors.

METHODS

We used a variety of pharmacological, behavioral, genetic, and viral approaches (n = 4-16/experiment) to investigate the anatomical and functional circuitry of amylin-controlled VTA-to-mPFC signaling in rats.

RESULTS

To first establish that VTA amylin receptor (calcitonin receptor) activation can modulate mPFC activity, we showed that intra-VTA amylin decreased food-evoked mPFC cFos. VTA amylin delivery also attenuated food-directed impulsive behavior, implicating VTA amylin signaling as a regulator of mPFC functions. Palatable food activates VTA dopamine and mPFC neurons. Accordingly, dopamine receptor agonism in the mPFC blocked the hypophagic effect of intra-VTA amylin, and VTA amylin injection reduced food-evoked phasic dopamine levels in the mPFC, supporting the idea that VTA calcitonin receptor activation decreases dopamine release in the mPFC. Surprisingly, calcitonin receptor expression was not found on VTA-to-mPFC projecting neurons but was instead found on GABAergic (gamma-aminobutyric acidergic) interneurons in the VTA that provide monosynaptic inputs to this pathway. Blocking intra-VTA GABA signaling, through GABA receptor antagonists and DREADD (designer receptor exclusively activated by designer drugs)-mediated GABAergic neuronal silencing, attenuated intra-VTA amylin-induced hypophagia.

CONCLUSIONS

These results indicate that VTA amylin signaling stimulates GABA-mediated inhibition of dopaminergic projections to the mPFC to mitigate impulsive consumption of palatable foods.

The processing intermediate of human amylin, pro-amylin(1-48), has in vivo and in vitro bioactivity

Amylin is released by pancreatic beta-cells in response to a meal and its major soluble mature form (37 amino acid-peptide) produces its biological effects by activating amylin receptors. Amylin is derived from larger propeptides that are processed within the synthesizing beta-cell. There are suggestions that a partially processed form, pro-amylin(1-48) is also secreted. We tested the hypothesis that pro-amylin(1-48) has biological activity and that human pro-amylin(1-48) may also form toxic pre-amyloid species. Amyloid formation, the ability to cross-seed and in vitro toxicity were similar between human pro-amylin(1-48) and amylin. Human pro-amylin(1-48) was active at amylin-responsive receptors, though its potency was reduced at rat, but not human amylin receptors. Pro-amylin(1-48) was able to promote anorexia by activating neurons of the area postrema, amylin's primary site of action, indicating that amylin can tolerate significant additions at the N-terminus without losing bioactivity. Our studies help to shed light on the possible roles of pro-amylin(1-48) which may be relevant for the development of future amylin-based drugs.

Novel mechanisms involved in leptin sensitization in obesity

Leptin is a hormone that is secreted by adipocytes in proportion to adipose tissue size, and that informs the brain about the energy status of the body. Leptin acts through its receptor LepRb, expressed mainly in the hypothalamus, and induces a negative energy balance by potent inhibition of feeding and activation of energy expenditure. These actions have led to huge expectations for the development of therapeutic targets for metabolic complications based on leptin-derived compounds. However, the majority of patients with obesity presents elevated leptin production, suggesting that in this setting leptin is ineffective in the regulation of energy balance. This resistance to the action of leptin in obesity has led to the development of "leptin sensitizers," which have been tested in preclinical studies. Much research has focused on generating combined treatments that act on multiple levels of the gastrointestinal-brain axis. The gastrointestinal-brain axis secretes a variety of different anorexigenic signals, such as uroguanylin, glucagon-like peptide-1, amylin, or cholecystokinin, which can alleviate the resistance to leptin action. Moreover, alternative mechanism such as pharmacokinetics, proteostasis, the role of specific kinases, chaperones, ER stress and neonatal feeding modifications are also implicated in leptin resistance. This review will cover the current knowledge regarding the interaction of leptin with different endocrine factors from the gastrointestinal-brain axis and other novel mechanisms that improve leptin sensitivity in obesity.

Neurodevelopmental Programming of Adiposity: Contributions to Obesity Risk

This review analyzes the published evidence regarding maternal factors that influence the developmental programming of long-term adiposity in humans and animals via the central nervous system (CNS). We describe the physiological outcomes of perinatal underfeeding and overfeeding and explore potential mechanisms that may mediate the impact of such exposures on the development of feeding circuits within the CNS-including the influences of metabolic hormones and epigenetic changes. The perinatal environment, reflective of maternal nutritional status, contributes to the programming of offspring adiposity. The in utero and early postnatal periods represent critically sensitive developmental windows during which the hormonal and metabolic milieu affects the maturation of the hypothalamus. Maternal hyperglycemia is associated with increased transfer of glucose to the fetus driving fetal hyperinsulinemia. Elevated fetal insulin causes increased adiposity and consequently higher fetal circulating leptin concentration. Mechanistic studies in animal models indicate important roles of leptin and insulin in central and peripheral programming of adiposity, and suggest that optimal concentrations of these hormones are critical during early life. Additionally, the environmental milieu during development may be conveyed to progeny through epigenetic marks and these can potentially be vertically transmitted to subsequent generations. Thus, nutritional and metabolic/endocrine signals during perinatal development can have lifelong (and possibly multigenerational) impacts on offspring body weight regulation.

Slc12a2 loss in insulin-secreting β-cells links development of overweight and metabolic dysregulation to impaired satiation control of feeding

Male mice lacking the Na+-K+-2Cl- cotransporter Slc12a2 (Nkcc1) specifically in insulin-secreting β-cells (Slc12a2βKO) have reduced β-cell mass and mild β-cell secretory dysfunction associated with overweight, glucose intolerance, insulin resistance, and metabolic abnormalities. Here, we confirmed and extended previous results to female Slc12a2βKO mice, which developed a similar metabolic syndrome-like phenotype as males, albeit milder. Notably, male and female Slc12a2βKO mice developed overweight without consuming excess calories. Analysis of the feeding microstructure revealed that young lean Slc12a2βKO male mice ate meals of higher caloric content and at a relatively lower frequency than normal mice, particularly during the night. In addition, overweight Slc12a2βKO mice consumed significantly larger meals than lean mice. Therefore, the reduced satiation control of feeding precedes the onset of overweight and is worsened in older Slc12a2βKO mice. However, the time spent between meals remained intact in lean and overweight Slc12a2βKO mice, indicating conserved satiety responses to ad libitum feeding. Nevertheless, satiety was intensified during and after refeeding only in overweight males. In lean females, satiety responses to refeeding were delayed relative to age- and body weight-matched control mice but normalized in overweight mice. Since meal size did not change during refeeding, these data suggested that the satiety control of eating after fasting is impaired in lean Slc12a2βKO mice before the onset of overweight and independently of their reduced satiation responses. Therefore, our results support the novel hypothesis that reduced satiation precedes the onset of overweight and the development of metabolic dysregulation.NEW & NOTEWORTHY Obesity, defined as excess fat accumulation, increases the absolute risk for metabolic diseases. Although obesity is usually attributed to increased food intake, we demonstrate that body weight gain can be hastened without consuming excess calories. In fact, impaired meal termination control, i.e., satiation, is detectable before the development of overweight in an animal model that develops a metabolic syndrome-like phenotype.

KNDy neurons as the GnRH pulse generator: Recent studies in ruminants

This review considers three aspects of recent work on the role of KNDy neurons in GnRH pulse generation in ruminants. First, work on basic mechanisms of pulse generation includes several tests of this hypothesis, all of which support it, and evidence that Kiss1r-containing neurons form a positive feedback circuit with the KNDy neural network that strengthen the activity of this network. The second section on pathways mediating external inputs focuses on the influence of nutrition and photoperiod, and describes the evidence supporting roles for proopiomelanocortin (POMC) and agouti-related peptide (AgRP) afferents to KNDy cells in each of these. Finally, we review studies exploring the potential applications of manipulating signaling by kisspeptin, and the other KNDy peptides, to control reproductive function in domestic animals and conclude that, although these approaches show some promise, they do not have major advantages over current practices at this time.

Mucosal and hormonal adaptations after Roux-en-Y gastric bypass

The aim of this study was to perform a comprehensive literature review regarding the relevant hormonal and histologic changes observed after Roux-en-Y gastric bypass (RYGB). We aimed to describe the relevant hormonal (glucagon-like peptides 1 and 2 [GLP-1 and GLP-2], peptide YY [PYY], oxyntomodulin [OXM], bile acids [BA], cholecystokinin [CCK], ghrelin, glucagon, gastric inhibitory polypeptide [GIP], and amylin) profiles, as well as the histologic (mucosal cellular) adaptations happening after patients undergo RYGB. Our review compiles the current evidence and furthers the understanding of the rationale behind the food intake regulatory adaptations occurring after RYGB surgery. We identify gaps in the literature where the potential for future investigations and therapeutics may lie. We performed a comprehensive database search without language restrictions looking for RYGB bariatric surgery outcomes in patients with pre- and postoperative blood work hormonal profiling and/or gut mucosal biopsies. We gathered the relevant study results and describe them in this review. Where human findings were lacking, we included animal model studies. The amalgamation of physiologic, metabolic, and cellular adaptations following RYGB is yet to be fully characterized. This constitutes a fundamental aspiration for enhancing and individualizing obesity therapy.

Effects of Drugs and Chemotherapeutic Agents on Dental Implant Osseointegration: Narrative Review

BACKGROUND

Dental implants have been one of the most popular treatments for rehabilitating individuals with single missing teeth or fully edentulous jaws since their introduction. As more implant patients are well-aged and take several medications due to various systemic conditions, clinicians should be mindful of possible drug implications on bone remodeling and osseointegration.

OBJECTIVE

The present study aims to study and review some desirable and some unwelcomed implications of medicine on osseointegration.

METHODS

A broad search for proper relevant studies were conducted in four databases, including Web of Science, Pubmed, Scopus, and Google Scholar.

RESULTS

Some commonly prescribed medicines such as nonsteroidal anti-inflammatory drugs (NSAIDs), glucocorticoids, proton pump inhibitors (PPIs), selective serotonin reuptake inhibitors (SSRIs), anticoagulants, metformin, and chemotherapeutic agents may jeopardize osseointegration. On the contrary, some therapeutic agents such as anabolic, anti-catabolic, or dual anabolic and anti-catabolic agents may enhance osseointegration and increase the treatment's success rate.

CONCLUSION

Systemic medications that enhance osseointegration include mineralization promoters and bone resorption inhibitors. On the other hand, medications often given to the elderly with systemic problems might interfere with osseointegration, leading to implant failure. However, to validate the provided research, more human studies with a higher level of evidence are required.

THERAPY OF ENDOCRINE DISEASE: Amylin and calcitonin - physiology and pharmacology

Type 2 diabetes is a common manifestation of metabolic dysfunction due to obesity and constitutes a major burden for modern health care systems, in concert with the alarming rise in obesity worldwide. In recent years, several successful pharmacotherapies improving glucose metabolism have emerged and some of these also promote weight loss, thus, ameliorating insulin resistance. However, the progressive nature of type 2 diabetes is not halted by these new anti-diabetic pharmacotherapies. Therefore, novel therapies promoting weight loss further and delaying diabetes progression are needed. Amylin, a beta cell hormone, has satiating properties and also delays gastric emptying and inhibits postprandial glucagon secretion with the net result of reducing postprandial glucose excursions. Amylin acts through the six amylin receptors, which share the core component with the calcitonin receptor. Calcitonin, derived from thyroid C cells, is best known for its role in humane calcium metabolism, where it inhibits osteoclasts and reduces circulating calcium. However, calcitonin, particularly of salmon origin, has also been shown to affect insulin sensitivity, reduce the gastric emptying rate and promote satiation. Preclinical trials with agents targeting the calcitonin receptor and the amylin receptors, show improvements in several parameters of glucose metabolism including insulin sensitivity and some of these agents are currently undergoing clinical trials. Here, we review the physiological and pharmacological effects of amylin and calcitonin and discuss the future potential of amylin and calcitonin-based treatments for patients with type 2 diabetes and obesity.

Mediators of Amylin Action in Metabolic Control

Amylin (also called islet amyloid polypeptide (IAPP)) is a pancreatic beta-cell hormone that is co-secreted with insulin in response to nutrient stimuli. The last 35 years of intensive research have shown that amylin exerts important physiological effects on metabolic control. Most importantly, amylin is a physiological control of meal-ending satiation, and it limits the rate of gastric emptying and reduces the secretion of pancreatic glucagon, in particular in postprandial states. The physiological effects of amylin and its analogs are mediated by direct brain activation, with the caudal hindbrain playing the most prominent role. The clarification of the structure of amylin receptors, consisting of the calcitonin core receptor plus receptor-activity modifying proteins, aided in the development of amylin analogs with a broad pharmacological profile. The general interest in amylin physiology and pharmacology was boosted by the finding that amylin is a sensitizer to the catabolic actions of leptin. Today, amylin derived analogs are considered to be among the most promising approaches for the pharmacotherapy against obesity. At least in conjunction with insulin, amylin analogs are also considered important treatment options in diabetic patients, so that new drugs may soon be added to the only currently approved compound pramlintide (Symlin^®). This review provides a brief summary of the physiology of amylin’s mode of actions and its role in the control of the metabolism, in particular energy intake and glucose metabolism.

Upregulation of GLUT4 and PI3K, and downregulation of GSK3 mediate the anti-hyperglycemic effects of proanthocyanidins

Diabetes mellitus is the most common chronic metabolic disorder worldwide. The present study was designed to investigate the potential role of cinnamon bark extract oligomeric proanthocyanidins (OPCs) in controlling streptozotocin (STZ)-induced hyperglycemia and to clarify the underlying molecular mechanisms underlying its effects. For this purpose, 60 male rats were equally divided into six groups as follows: The normal control group; OPC control group (non-diabetic rats treated with OPC at 300 mg/kg orally for 21 days); the untreated diabetic control group; the wortmannin control group [diabetic rats treated with wortmannin at 1 mg/kg, intraperitoneal (i.p.) on the final day of the experiment]; the OPC diabetic group (diabetic rats treated with OPC at 300 mg/kg orally for 21 days); and the OPC diabetic + wortmannin co-treated group (diabetic rats treated with OPC at 300 mg/kg/day for 21 consecutive days and then 24 h after the final OPC dose treated with a single wortmannin injection at 1 mg/kg, i.p.). The results indicated that OPC ameliorated the diabetic state, as evidenced by a significant decrease in serum glucose levels, and a significant increase in the levels of insulin, amylin, insulin receptor phosphorylation, glycogen and glucose transporter-4 translocation; it also improved the lipid profile in STZ-diabetic rats. On the whole, the findings of the present study provide biochemical evidence that OPC treatment is effective as an anti-diabetic and anti-hyperlipidemic agent by enhancing glucose uptake through the activation of insulin receptor kinase activity and the PI3K/Akt pathway.

Long-acting amylin analogues for the management of obesity

PURPOSE OF REVIEW

To summarize recent developments of long-acting amylin analogues for the treatment of obesity and to outline their mode of action.

RECENT FINDINGS

Amylin is a pancreatic hormone acting to control energy homeostasis and body weight. Activity at the calcitonin and amylin receptors in the area postrema seems to - at least partly - be responsible for these effects of amylin. Both preclinical and early-stage clinical studies investigating long-acting amylin receptor analogues demonstrate beneficial effects on body weight in obesity. Cagrilintide, a novel amylin analogue suitable for once-weekly administration, is in phase II clinical development and has shown promising body weight reducing effects alone and in combination with the glucagon-like peptide 1 receptor agonist semaglutide.

SUMMARY

Long-acting amylin analogues have emerged as a possible pharmacotherapy against obesity, but more studies are needed to support the utility and long-term effects of this strategy in relevant populations.

Mouse Microglial Calcitonin Receptor Knockout Impairs Hypothalamic Amylin Neuronal pSTAT3 Signaling but Lacks Major Metabolic Consequences

Amylin and leptin synergistically interact in the arcuate nucleus of the hypothalamus (ARC) to control energy homeostasis. Our previous rodent studies suggested that amylin-induced interleukin-6 release from hypothalamic microglia may modulate leptin signaling in agouti-related peptide expressing neurons. To confirm the physiological relevance of this finding, the calcitonin receptor (CTR) subunit of the amylin receptor was selectively depleted in microglia by crossing tamoxifen (Tx) inducible Cx3cr1-Cre^ERT2 mice with CTR-floxed mice. Unexpectedly, male mice with CTR-depleted microglia (KO) gained the least amount of weight of all groups regardless of diet. However, after correcting for the tamoxifen effect, there was no significant difference for body weight, fat mass or lean mass between genotypes. No alteration in glucose tolerance or insulin release was detected. However, male KO mice had a reduced respiratory quotient suggesting a preference for fat as a fuel when fed a high fat diet. Importantly, amylin-induced pSTAT3 was decreased in the ARC of KO mice but this was not reflected in a reduced anorectic response. On the other hand, KO mice seemed to be less responsive to leptin’s anorectic effect while displaying similar ARC pSTAT3 as Tx-control mice. Together, these data suggest that microglial amylin signaling is not a major player in the control of energy homeostasis in mice.

Amylin as a Future Obesity Treatment

Obesity is defined as abnormal or excessive fat accumulation that contributes to detrimental health impacts. One-third of the population suffers from obesity, and it is important to consider obesity as a chronic disease requiring chronic treatment. Amylin is co-secreted with insulin from β pancreatic cells upon nutrient delivery to the small intestine as a satiety signal, acts upon sub-cortical homeostatic and hedonic brain regions, slows gastric emptying, and suppresses post-prandial glucagon responses to meals. Therefore, new pharmacological amylin analogues can be used as potential anti-obesity medications in individuals who are overweight or obese. In this narrative review, we analyse the efficacy, potency, and safety of amylin analogues. The synthetic amylin analogue pramlintide is an approved treatment for diabetes mellitus which promotes better glycaemic control and small but significant weight loss. AM833 (cagrilintide), an investigational novel long-acting acylated amylin analogue, acts as a non-selective amylin receptor. This calcitonin G protein-coupled receptor agonist can serve as an attractive novel treatment for obesity, resulting in reduction of food intake and significant weight loss in a dose-dependent manner.

Diversity of pathophysiology in type 2 diabetes shown by islet pathology

The etiology of type 2 diabetes is multifactorial, in which environmental and genetic factors are involved to varying degrees. This suggests that its pathophysiology might vary depending on the individuals. Knowledge of the differences is critical, because these differences are directly linked to the care and treatment of the patients. Recent studies have attempted to carry out subclassifications of type 2 diabetes based on clinical and genetic differences. However, there is no pathological evidence to support these subclassifications. The pathophysiology of type 2 diabetes is generally divided into insulin resistance in peripheral tissues and pancreatic islet dysfunction. Among them, islet dysfunction causes a deficit in insulin secretion from β-cells. In particular, a deficit in insulin secretion is ascribed to a combination of disruption of the insulin secretory machinery and a decrease in β-cell volume in type 2 diabetes. Recent research has suggested that transdifferentiation and dedifferentiation are involved in the decrease in β-cell volume, and that it might change dynamically depending on the glucose metabolic state. However, it is possible that the numbers of islet cells are decreased in type 2 diabetes. In particular, the loss of endocrine cells due to islet amyloid deposits is an important pathological change in type 2 diabetes in humans. These results show that pathological changes of the islets can be different in each individuals with type 2 diabetes and reflect each pathophysiology, which is useful in establishing further subclassifications and developing tailor-made therapies for type 2 diabetes.

Systemic and Central Amylin, Amylin Receptor Signaling, and Their Physiological and Pathophysiological Roles in Metabolism

This article in the Neural and Endocrine Section of Comprehensive Physiology discusses the physiology and pathophysiology of the pancreatic hormone amylin. Shortly after its discovery in 1986, amylin has been shown to reduce food intake as a satiation signal to limit meal size. Amylin also affects food reward, sensitizes the brain to the catabolic actions of leptin, and may also play a prominent role in the development of certain brain areas that are involved in metabolic control. Amylin may act at different sites in the brain in addition to the area postrema (AP) in the caudal hindbrain. In particular, the sensitizing effect of amylin on leptin action may depend on a direct interaction in the hypothalamus. The concept of central pathways mediating amylin action became more complex after the discovery that amylin is also synthesized in certain hypothalamic areas but the interaction between central and peripheral amylin signaling remains currently unexplored. Amylin may also play a dominant pathophysiological role that is associated with the aggregation of monomeric amylin into larger, cytotoxic molecular entities. This aggregation in certain species may contribute to the development of type 2 diabetes mellitus but also cardiovascular disease. Amylin receptor pharmacology is complex because several distinct amylin receptor subtypes have been described, because other neuropeptides [e.g., calcitonin gene-related peptide (CGRP)] can also bind to amylin receptors, and because some components of the functional amylin receptor are also used for other G-protein coupled receptor (GPCR) systems. © 2020 American Physiological Society. Compr Physiol 10:811-837, 2020.

Amylin/Calcitonin Receptor-Mediated Signaling in POMC Neurons Influences Energy Balance and Locomotor Activity in Chow-Fed Male Mice

Amylin, a pancreatic hormone and neuropeptide, acts principally in the hindbrain to decrease food intake and has recently been shown to act as a neurotrophic factor to control the development of area postrema → nucleus of the solitary tract and arcuate hypothalamic nucleus → paraventricular nucleus axonal fiber outgrowth. Amylin is also able to activate ERK signaling specifically in POMC neurons independently of leptin. For investigation of the physiological role of amylin signaling in POMC neurons, the core component of the amylin receptor, calcitonin receptor (CTR), was depleted from POMC neurons using an inducible mouse model. The loss of CTR in POMC neurons leads to increased body weight gain, increased adiposity, and glucose intolerance in male knockout mice, characterized by decreased energy expenditure (EE) and decreased expression of uncoupling protein 1 (UCP1) in brown adipose tissue. Furthermore, a decreased spontaneous locomotor activity and absent thermogenic reaction to the application of the amylin receptor agonist were observed in male and female mice. Together, these results show a significant physiological impact of amylin/calcitonin signaling in CTR-POMC neurons on energy metabolism and demonstrate the need for sex-specific approaches in obesity research and potentially treatment.

Central control of energy balance by amylin and calcitonin receptor agonists and their potential for treatment of metabolic diseases

The prevalence of obesity and associated comorbidities such as type 2 diabetes and cardiovascular disease is increasing globally. Body-weight loss reduces the risk of morbidity and mortality in obese individuals, and thus, pharmacotherapies that induce weight loss can be of great value in improving the health and well-being of people living with obesity. Treatment with amylin and calcitonin receptor agonists reduces food intake and induces weight loss in several animal models, and a number of companies have started clinical testing for peptide analogues in the treatment of obesity and/or type 2 diabetes. Studies predominantly performed in rodent models show that amylin and the dual amylin/calcitonin receptor agonist salmon calcitonin achieve their metabolic effects by engaging areas in the brain associated with regulating homeostatic energy balance. In particular, signalling via neuronal circuits in the caudal hindbrain and the hypothalamus is implicated in mediating effects on food intake and energy expenditure. We review the current literature investigating the interaction of amylin/calcitonin receptor agonists with neurocircuits that induce the observed metabolic effects. Moreover, the status of drug development of amylin and calcitonin receptor agonists for the treatment of metabolic diseases is summarized.

Brain Distribution and Sexually Dimorphic Expression of Amylin in Different Reproductive Stages of the Zebra Finch (Taeniopygia guttata) Suggest Roles of the Neuropeptide in Song Learning and Social Behaviour

The expression of the recently identified neuropeptide, amylin, is restricted in rodents to the postpartum preoptic area and may play a role in the control of parental behaviours and food intake. These processes are substantially different between bird and rodent parents as birds do not lactate but often show biparental care of the offspring. To establish the presence and role of amylin in the bird brain, in the present study, we investigated the distribution of amylin in brains of adult male and female zebra finches in three different reproductive stages (i.e. paired without young, incubating eggs or provisioning nestlings) and in unpaired control birds living in same sex flocks. Amylin mRNA was identified in the hypothalamus of zebra finch by RT-PCR, which was also used to produce probes for in situ hybridisation. Subsequently, in situ hybridisation histochemistry was performed in brain sections, and the labelling signal was quantified and compared between the groups. Amylin showed a much wider brain distribution than that of rodents. A strong and, in some regions, sexually dimorphic label was found in the striatum and several brain regions of the social behavioural network in both males and females. Many regions responsible for the learning of birdsong also contained amylin-positive neurons, and some regions showed sex differences reflecting the fact that vocalisation is sexually dimorphic in the zebra finch: only males sing. Area X (Ar.X), a striatal song centre present only in males, was labelled in paired but not unpaired male. Ar.X, another song centre, the lateral part of the magnocellular nucleus of the anterior nidopallium (lMAN) also contained amylin and had higher amylin label in paired, as opposed to unpaired birds. The wider distribution of amylin in birds as compared to rodents suggests a more general role of amylin in social or other behaviours in avian species than in mammals. Alternatively, parental care in birds may be a more complex behavioural trait involving a wider set of brain regions. The sex differences in song centres, and the changes with reproductive status suggest a participation of amylin in social behaviours and related changes in the singing of males.

RAMP1 and RAMP3 Differentially Control Amylin's Effects on Food Intake, Glucose and Energy Balance in Male and Female Mice

Amylin is a pancreatic peptide, which acts as a key controller of food intake and energy balance and predominately binds to three receptors (AMY 1-3). AMY 1-3 are composed of a calcitonin core receptor (CTR) and associated receptor-activity modifying proteins (RAMPs) 1-3. Using RAMP1, RAMP3 and RAMP1/3 global KO mice, this study aimed to determine whether the absence of one or two RAMP subunits affects food intake, glucose homeostasis and metabolism. Of all the RAMP-deficient mice, only high-fat diet fed RAMP1/3 KO mice had increased body weight. Chow-fed RAMP3 KO and high-fat diet fed 1/3 KO male mice were glucose intolerant. Fat depots were increased in RAMP1 KO male mice. No difference in energy expenditure was observed but the respiratory exchange ratio (RER) was elevated in RAMP1/3 KO. RAMP1 and 1/3 KO male mice displayed an increase in intermeal interval (IMI) and meal duration, whereas IMI was decreased in RAMP3 KO male and female mice. WT and RAMP1, RAMP3, and RAMP1/3 KO male and female littermates were then assessed for their food intake response to an acute intraperitoneal injection of amylin or its receptor agonist, salmon calcitonin (sCT). RAMP1/3 KO were insensitive to both, while RAMP3 KO were responsive to sCT only and RAMP1 KO to amylin only. While female mice generally weighed less than male mice, only RAMP1 KO showed a clear sex difference in meal pattern and food intake tests. Lastly, a decrease in CTR fibers did not consistently correlate with a decrease in amylin- induced c-Fos expression in the area postrema (AP). Ultimately, the results from this study provide evidence for a role of RAMP1 in mediation of fat utilization and a role for RAMP3 in glucose homeostasis and amylin's anorectic effect.

Amylin and Leptin interaction: Role During Pregnancy, Lactation and Neonatal Development

Amylin is co-secreted with insulin by pancreatic β-cells in response to a meal and produced by neurons in discrete hypothalamic brain areas. Leptin is proportionally secreted by the adipose tissue. Both hormones control food intake and energy homeostasis post-weaning in rodents. While amylin's main site of action is located in the area postrema (AP) and leptin's is located in the mediobasal hypothalamus, both hormones can also influence the other's signaling pathway; amylin has been shown enhance hypothalamic leptin signaling, and amylin signaling in the AP may rely on functional leptin receptors to modulate its effects. These two hormones also play major roles during other life periods. During pregnancy, leptin levels rise as a result of an increase in fat depot resulting in gestational leptin-resistance to prepare the maternal body for the metabolic needs during fetal development. The role of amylin is far less studied during pregnancy and lactation, though amylin levels seem to be elevated during pregnancy relative to insulin. Whether amylin and leptin interact during pregnancy and lactation remains to be assessed. Lastly, during brain development, amylin and leptin are major regulators of cell birth during embryogenesis and act as neurotrophic factors in the neonatal period. This review will highlight the role of amylin and leptin, and their possible interaction, during these dynamic time periods of pregnancy, lactation, and early development.

From sensory circumventricular organs to cerebral cortex: Neural pathways controlling thirst and hunger

Much progress has been made during the past 30 years with respect to elucidating the neural and endocrine pathways by which bodily needs for water and energy are brought to conscious awareness through the generation of thirst and hunger. One way that circulating hormones influence thirst and hunger is by acting on neurones within sensory circumventricular organs (CVOs). This is possible because the subfornical organ and organum vasculosum of the lamina terminalis (OVLT), the sensory CVOs in the forebrain, and the area postrema in the hindbrain lack a normal blood-brain barrier such that neurones within them are exposed to blood-borne agents. The neural signals generated by hormonal action in these sensory CVOs are relayed to several sites in the cerebral cortex to stimulate or inhibit thirst or hunger. The subfornical organ and OVLT respond to circulating angiotensin II, relaxin and hypertonicity to drive thirst-related neural pathways, whereas circulating amylin, leptin and possibly glucagon-like peptide-1 act at the area postrema to influence neural pathways inhibiting food intake. As a result of investigations using functional brain imaging techniques, the insula and anterior cingulate cortex, as well as several other cortical sites, have been implicated in the conscious perception of thirst and hunger in humans. Viral tracing techniques show that the anterior cingulate cortex and insula receive neural inputs from thirst-related neurones in the subfornical organ and OVLT, with hunger-related neurones in the area postrema having polysynaptic efferent connections to these cortical regions. For thirst, initially, the median preoptic nucleus and, subsequently, the thalamic paraventricular nucleus and lateral hypothalamus have been identified as likely sites of synaptic links in pathways from the subfornical organ and OVLT to the cortex. The challenge remains to identify the links in the neural pathways that relay signals originating in sensory CVOs to cortical sites subserving either thirst or hunger.

Anti-Obesity Therapy: from Rainbow Pills to Polyagonists

With their ever-growing prevalence, obesity and diabetes represent major health threats of our society. Based on estimations by the World Health Organization, approximately 300 million people will be obese in 2035. In 2015 alone there were more than 1.6 million fatalities attributable to hyperglycemia and diabetes. In addition, treatment of these diseases places an enormous burden on our health care system. As a result, the development of pharmacotherapies to tackle this life-threatening pandemic is of utmost importance. Since the beginning of the 19th century, a variety of drugs have been evaluated for their ability to decrease body weight and/or to improve deranged glycemic control. The list of evaluated drugs includes, among many others, sheep-derived thyroid extracts, mitochondrial uncouplers, amphetamines, serotonergics, lipase inhibitors, and a variety of hormones produced and secreted by the gastrointestinal tract or adipose tissue. Unfortunately, when used as a single hormone therapy, most of these drugs are underwhelming in their efficacy or safety, and placebo-subtracted weight loss attributed to such therapy is typically not more than 10%. In 2009, the generation of a single molecule with agonism at the receptors for glucagon and the glucagon-like peptide 1 broke new ground in obesity pharmacology. This molecule combined the beneficial anorectic and glycemic effects of glucagon-like peptide 1 with the thermogenic effect of glucagon into a single molecule with enhanced potency and sustained action. Several other unimolecular dual agonists have subsequently been developed, and, based on their preclinical success, these molecules illuminate the path to a new and more fruitful era in obesity pharmacology. In this review, we focus on the historical pharmacological approaches to treat obesity and glucose intolerance and describe how the knowledge obtained by these studies led to the discovery of unimolecular polypharmacology.

Role and Cytotoxicity of Amylin and Protection of Pancreatic Islet β-Cells from Amylin Cytotoxicity

Amylin, (or islet amyloid polypeptide; IAPP), a 37-amino acid peptide hormone, is released in response to nutrients, including glucose, lipids or amino acids. Amylin is co-stored and co-secreted with insulin by pancreatic islet β-cells. Amylin inhibits food intake, delays gastric emptying, and decreases blood glucose levels, leading to the reduction of body weight. Therefore, amylin as well as insulin play important roles in controlling the level of blood glucose. However, human amylin aggregates and human amylin oligomers cause membrane disruption, endoplasmic reticulum (ER) stress and mitochondrial damage. Since cytotoxicity of human amylin oligomers to pancreatic islet β-cells can lead to diabetes, the protection of pancreatic islet β cells from cytotoxic amylin is crucial. Human amylin oligomers also inhibit autophagy, although autophagy can function to remove amylin aggregates and damaged organelles. Small molecules, including β-sheet breaker peptides, chemical chaperones, and foldamers, inhibit and disaggregate amyloid formed by human amylin, suggesting the possible use of these small molecules in the treatment of diabetes. In this review, we summarize recent findings regarding the role and cytotoxicity of amylin and the protection of pancreatic islet β-cells from cytotoxicity of amylin.

Amylin in Alzheimer's disease: Pathological peptide or potential treatment?

Alzheimer's disease (AD) is a neurodegenerative disease for which we currently lack effective treatments or a cure. The pancreatic peptide hormone amylin has recently garnered interest as a potential pharmacological target for the treatment of AD. A number of studies have demonstrated that amylin and amylin analogs like the FDA-approved diabetes drug pramlintide can reduce amyloid burden in the brain and improve cognitive symptoms of AD. However, other data suggest that amylin may have pathological effects in AD due to its propensity to misfold and aggregate under certain conditions. Here, the literature supporting a beneficial versus harmful role of amylin in AD is reviewed. Additionally, several critical gaps in the literature are discussed, such as our limited understanding of the amylin system during aging and in disease states, as well as complexities of amylin receptor signaling and of changing pathophysiology during AD progression that might underlie the seemingly conflicting or contradictory results in the amylin/AD literature. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

Amylin Selectively Signals Onto POMC Neurons in the Arcuate Nucleus of the Hypothalamus

Amylin phosphorylates ERK (p-ERK) in the area postrema to reduce eating and synergizes with leptin to phosphorylate STAT3 in the arcuate (ARC) and ventromedial (VMN) hypothalamic nuclei to reduce food intake and body weight. The current studies assessed potential amylin and amylin-leptin ARC/VMN interactions on ERK signaling and their roles in postnatal hypothalamic pathway development. In amylin knockout mice, the density of agouti-related protein (AgRP)-immunoreactive (IR) fibers in the hypothalamic paraventricular nucleus (PVN) was increased, while the density of α-melanocyte-stimulating hormone (αMSH) fibers was decreased. In mice deficient of the amylin receptor components RAMP1/3, both AgRP and αMSH-IR fiber densities were decreased, while only αMSH-IR fiber density was decreased in rats injected neonatally in the ARC/VMN with an adeno-associated virus short hairpin RNA against the amylin core receptor. Amylin induced p-ERK in ARC neurons, 60% of which was present in POMC-expressing neurons, with none in NPY neurons. An amylin-leptin interaction was shown by an additive effect on ARC ERK signaling in neonatal rats and a 44% decrease in amylin-induced p-ERK in the ARC of leptin receptor-deficient and of ob/ob mice. Together, these results suggest that amylin directly acts, through a p-ERK-mediated process, on POMC neurons to enhance ARC-PVN αMSH pathway development.

IAPP/amylin and β-cell failure: implication of the risk factors of type 2 diabetes

In type 2 diabetes (T2D), the most significant pathological change in pancreatic islets is amyloid deposits, of which a major component is islet amyloid polypeptide (IAPP), also called amylin. IAPP is expressed in β-cells and co-secreted with insulin. Together with the inhibitory effects of synthetic human IAPP (hIAPP) on insulin secretion, our studies, using hIAPP transgenic mice, in which glucose-stimulated insulin secretion was moderately reduced without amyloid deposit, and hIAPP gene-transfected β-cell lines, in which insulin secretion was markedly impaired without amyloid, predicted that soluble hIAPP-related molecules would exert cytotoxicity on β-cells. Human IAPP is one of the most aggregation-prone peptides that interact with cell membranes. While it is widely reported that soluble hIAPP oligomers promote cytotoxicity, this is still a hypothesis since the mechanisms are not yet fully defined. Several hIAPP transgenic mouse models did not develop diabetes; however, in models with backgrounds characterized for diabetic phenotypes, β-cell function and glucose tolerance did worsen, compared to those in non-transgenic models with similar backgrounds. Together with these findings, many studies on metabolic and molecular disorders induced by risk factors of T2D suggest that in T2D subjects, toxic IAPP oligomers accumulate in β-cells, impair their function, and reduce mass through disruption of cell membranes, resulting in β-cell failure. IAPP might be central to β-cell failure in T2D. Anti-amyloid aggregation therapeutics will be developed to create treatments with more durable and beneficial effects on β-cell function.

The New Biology and Pharmacology of Glucagon

In the last two decades we have witnessed sizable progress in defining the role of gastrointestinal signals in the control of glucose and energy homeostasis. Specifically, the molecular basis of the huge metabolic benefits in bariatric surgery is emerging while novel incretin-based medicines based on endogenous hormones such as glucagon-like peptide 1 and pancreas-derived amylin are improving diabetes management. These and related developments have fostered the discovery of novel insights into endocrine control of systemic metabolism, and in particular a deeper understanding of the importance of communication across vital organs, and specifically the gut-brain-pancreas-liver network. Paradoxically, the pancreatic peptide glucagon has reemerged in this period among a plethora of newly identified metabolic macromolecules, and new data complement and challenge its historical position as a gut hormone involved in metabolic control. The synthesis of glucagon analogs that are biophysically stable and soluble in aqueous solutions has promoted biological study that has enriched our understanding of glucagon biology and ironically recruited glucagon agonism as a central element to lower body weight in the treatment of metabolic disease. This review summarizes the extensive historical record and the more recent provocative direction that integrates the prominent role of glucagon in glucose elevation with its under-acknowledged effects on lipids, body weight, and vascular health that have implications for the pathophysiology of metabolic diseases, and the emergence of precision medicines to treat metabolic diseases.

Islet inflammation in type 2 diabetes and physiology

The finding of islet inflammation in type 2 diabetes (T2D) and its involvement in β cell dysfunction has further highlighted the significance of inflammation in metabolic diseases. The number of intra-islet macrophages is increased in T2D, and these cells are the main source of proinflammatory cytokines within islets. Multiple human studies of T2D have shown that targeting islet inflammation has the potential to be an effective therapeutic strategy. In this Review we provide an overview of the cellular and molecular mechanisms by which islet inflammation develops and causes β cell dysfunction. We also emphasize the regulation and roles of macrophage polarity shift within islets in the context of T2D pathology and β cell health, which may have broad translational implications for therapeutics aimed at improving islet function.

Insulin Prevents Hyperfiltration and Proteinuria but Not Glomerular Hypertrophy and Increases Mesangial Matrix Expansion in Diabetic Rats

OBJECTIVE

The aim of this work was to study the effect of 7 days of strict glycemic control with insulin on glomerular function and structure in streptozotocin (STZ)-diabetic rats.

MATERIALS AND METHODS

Three groups of adult male Fischer rats were studied: controls (n = 15), diabetics (n = 15), and insulin-treated diabetics (n = 15). Diabetes was induced by treating the rats with STZ (55 mg/kg i.p.). One week after the induction of diabetes, blood glucose, protein excretion rate (PER), glomerular filtration rate (GFR), and renal plasma flow (RPF) were estimated in each group. Furthermore, morphometric analysis was performed to estimate the tuft volume and changes in mesangial matrix area. The results are expressed as the mean ± SEM.

RESULTS

STZ diabetes caused significant increases in GFR (0.89 ± 0.1 to 1.21 ± 0.1 mL/min/100 g; p < 0.01) and RPF (1.78 ± 0.37 to 3.32 ± 0.6 mL/min/100 g; p < 0.05). Furthermore, the diabetic rats had higher glomerular volumes but mesangial matrix areas similar to controls. Insulin treatment prevented the increases in blood glucose (4.5 ± 0.2 mM), PER (66.1 ± 7.8 mg/day), GFR (0.6 ± 0.07 mL/min/100 g), and RPF (1.72 ± 0.36 mL/min/100 g), but did not prevent glomerular hypertrophy (21.7% increase), but induced mesangial matrix expansion (25% increase).

CONCLUSIONS

Insulin prevented the diabetes-induced hyperfiltration and proteinuria, but did not prevent glomerular growth, and induced mesangial expansion. Hyperglycemic episodes could be partly responsible for persistent glomerular growth and accelerated mesangial growth.

IL-6 ameliorates defective leptin sensitivity in DIO ventromedial hypothalamic nucleus neurons

Rats selectively bred to develop diet-induced obesity (DIO) have an early onset reduction in the sensitivity of their ventromedial hypothalamic nucleus (VMN) neurons to leptin compared with diet-resistant (DR) rats. This reduced sensitivity includes decreased leptin receptor (Lepr-b) mRNA expression, leptin receptor binding, leptin-induced phosphorylation of STAT3 (pSTAT3), and impaired leptin excitation (LepE) of VMN neurons. When administered exogenously, the pancreatic peptide, amylin, acts synergistically to reduce food intake and body weight in obese, leptin-resistant DIO rats by increasing VMN leptin signaling, likely by stimulation of microglia IL-6, which acts on its receptor to increase leptin-induced pSTAT3. Here, we demonstrate that incubation of cultured VMN neurons of outbred rats with IL-6 increases their leptin sensitivity. Control, dissociated DIO VMN neurons express 66% less Lepr-b and 75% less Bardet Biedl Syndrome-6 (BBS6) mRNA and have reduced leptin-induced activation of LepE neurons compared with DR neurons. Incubation for 4 days with IL-6 increased DIO neuron Lepr-b expression by 77% and BBS6 by 290% and corrected their defective leptin activation of LepE neurons to DR levels. Since BBS6 enhances trafficking of Lepr-b to the cell membrane, the increases in Lepr-b and BBS6 expression appear to account for correction of the reduced leptin excitation of DIO LepE neurons to that of control DR rats. These data support prior findings suggesting that IL-6 mediates the leptin-sensitizing effects of amylin on VMN neurons and that the inherent leptin resistance of DIO rats can be effectively reversed at a cellular level by IL-6.

Targeting adipose tissue in the treatment of obesity-associated diabetes

Adipose tissue regulates numerous physiological processes, and its dysfunction in obese humans is associated with disrupted metabolic homeostasis, insulin resistance and type 2 diabetes mellitus (T2DM). Although several US-approved treatments for obesity and T2DM exist, these are limited by adverse effects and a lack of effective long-term glucose control. In this Review, we provide an overview of the role of adipose tissue in metabolic homeostasis and assess emerging novel therapeutic strategies targeting adipose tissue, including adipokine-based strategies, promotion of white adipose tissue beiging as well as reduction of inflammation and fibrosis.

Amylin-mediated control of glycemia, energy balance, and cognition

Amylin, a peptide hormone produced in the pancreas and in the brain, has well-established physiological roles in glycemic regulation and energy balance control. It improves postprandial blood glucose levels by suppressing gastric emptying and glucagon secretion; these beneficial effects have led to the FDA-approved use of the amylin analog pramlintide in the treatment of diabetes mellitus. Amylin also acts centrally as a satiation signal, reducing food intake and body weight. The ability of amylin to promote negative energy balance, along with its unique capacity to cooperatively facilitate or enhance the intake- and body weight-suppressive effects of other neuroendocrine signals like leptin, have made amylin a leading target for the development of novel pharmacotherapies for the treatment of obesity. In addition to these more widely studied effects, a growing body of literature suggests that amylin may play a role in processes related to cognition, including the neurodegeneration and cognitive deficits associated with Alzheimer's disease (AD). Although the function of amylin in AD is still unclear, intriguing recent reports indicate that amylin may improve cognitive ability and reduce hallmarks of neurodegeneration in the brain. The frequent comorbidity of diabetes mellitus and obesity, as well as the increased risk for and occurrence of AD associated with these metabolic diseases, suggests that amylin-based pharmaceutical strategies may provide multiple therapeutic benefits. This review will discuss the known effects of amylin on glycemic regulation, energy balance control, and cognitive/motivational processes. Particular focus will be devoted to the current and/or potential future clinical use of amylin pharmacotherapies for the treatment of diseases in each of these realms.

Amylin: Pharmacology, Physiology, and Clinical Potential

Amylin is a pancreatic β-cell hormone that produces effects in several different organ systems. Here, we review the literature in rodents and in humans on amylin research since its discovery as a hormone about 25 years ago. Amylin is a 37-amino-acid peptide that activates its specific receptors, which are multisubunit G protein-coupled receptors resulting from the coexpression of a core receptor protein with receptor activity-modifying proteins, resulting in multiple receptor subtypes. Amylin's major role is as a glucoregulatory hormone, and it is an important regulator of energy metabolism in health and disease. Other amylin actions have also been reported, such as on the cardiovascular system or on bone. Amylin acts principally in the circumventricular organs of the central nervous system and functionally interacts with other metabolically active hormones such as cholecystokinin, leptin, and estradiol. The amylin-based peptide, pramlintide, is used clinically to treat type 1 and type 2 diabetes. Clinical studies in obesity have shown that amylin agonists could also be useful for weight loss, especially in combination with other agents.

Molecular tweezers inhibit islet amyloid polypeptide assembly and toxicity by a new mechanism

In type-2 diabetes (T2D), islet amyloid polypeptide (IAPP) self-associates into toxic assemblies causing islet β-cell death. Therefore, preventing IAPP toxicity is a promising therapeutic strategy for T2D. The molecular tweezer CLR01 is a supramolecular tool for selective complexation of K residues in (poly)peptides. Surprisingly, it inhibits IAPP aggregation at substoichiometric concentrations even though IAPP has only one K residue at position 1, whereas efficient inhibition of IAPP toxicity requires excess CLR01. The basis for this peculiar behavior is not clear. Here, a combination of biochemical, biophysical, spectroscopic, and computational methods reveals a detailed mechanistic picture of the unique dual inhibition mechanism for CLR01. At low concentrations, CLR01 binds to K1, presumably nucleating nonamyloidogenic, yet toxic, structures, whereas excess CLR01 binds also to R11, leading to nontoxic structures. Encouragingly, the CLR01 concentrations needed for inhibition of IAPP toxicity are safe in vivo, supporting its development toward disease-modifying therapy for T2D.

Amylin-induced central IL-6 production enhances ventromedial hypothalamic leptin signaling

Amylin acts acutely via the area postrema to reduce food intake and body weight, but it also interacts with leptin over longer periods of time, possibly via the ventromedial hypothalamus (VMH), to increase leptin signaling and phosphorylation of STAT3. We postulated that amylin enhances VMH leptin signaling by inducing interleukin (IL)-6, which then interacts with its gp130 receptor to activate STAT3 signaling and gene transcription downstream of the leptin receptor. We found that components of the amylin receptor (RAMPs1-3, CTR1a,b) are expressed in cultured VMH astrocytes, neurons, and microglia, as well as in micropunches of arcuate and ventromedial hypothalamic nuclei (VMN). Amylin exposure for 5 days increased IL-6 mRNA expression in VMH explants and microglia by two- to threefold, respectively, as well as protein abundance in culture supernatants by five- and twofold, respectively. Amylin had no similar effects on cultured astrocytes or neurons. In rats, 5 days of amylin treatment decreased body weight gain and/or food intake and increased IL-6 mRNA expression in the VMN. Similar 5-day amylin treatment increased VMN leptin-induced phosphorylation of STAT3 expression in wild-type mice and rats infused with lateral ventricular IgG but not in IL-6 knockout mice or rats infused with ventricular IL-6 antibody. Lateral ventricular infusion of IL-6 antibody also prevented the amylin-induced decrease of body weight gain. These results show that amylin-induced VMH microglial IL-6 production is the likely mechanism by which amylin treatment interacts with VMH leptin signaling to increase its effect on weight loss.

The brain and brown fat

Brown adipose tissue (BAT) is a specialized organ responsible for thermogenesis, a process required for maintaining body temperature. BAT is regulated by the sympathetic nervous system (SNS), which activates lipolysis and mitochondrial uncoupling in brown adipocytes. For many years, BAT was considered to be important only in small mammals and newborn humans, but recent data have shown that BAT is also functional in adult humans. On the basis of this evidence, extensive research has been focused on BAT function, where new molecules, such as irisin and bone morphogenetic proteins, particularly BMP7 and BMP8B, as well as novel central factors and new regulatory mechanisms, such as orexins and the canonical ventomedial nucleus of the hypothalamus (VMH) AMP- activated protein kinase (AMPK)-SNS-BAT axis, have been discovered and emerged as potential drug targets to combat obesity. In this review we provide an overview of the complex central regulation of BAT and how different neuronal cell populations co-ordinately work to maintain energy homeostasis.

Amylin receptor signaling in the nucleus accumbens negatively modulates μ-opioid-driven feeding

Amylin is a peptide co-secreted with insulin that penetrates into the brain, and produces satiation-like effects via actions in the brainstem, hypothalamus, and mesencephalon. Little is known, however, about the effects of amylin in the nucleus accumbens shell (AcbSh), where a circumscribed zone of intense amylin receptor (AMY-R) binding overlaps reported mappings of a 'hotspot' for μ-opioid receptor (μ-OR) amplification of food reward. Here, the ability of intra-AcbSh AMY-R signaling to modulate μ-OR-driven feeding was explored. Amylin (1-30 ng) was administered with the μ-OR agonist, D-Ala2, N-MePhe4, Gly-ol]-enkephalin (DAMGO) (0.25 μg), directly into the AcbSh of ad libitum-maintained rats. Amylin dose-dependently reversed DAMGO-induced hyperphagia; 3 ng of amylin reduced DAMGO-mediated feeding by nearly 50%. This dose was, however, completely ineffective at altering DAMGO-induced feeding in the anterior dorsal striatum. Intra-AcbSh amylin alone (3-30 ng) modestly suppressed 10% sucrose intake in ad libitum-maintained rats, and chow in food-deprived rats, but only at the 30-ng dose. This result indicates that reversal of AcbSh DAMGO-induced feeding at a 10-fold lower dose was neither due to malaise nor motoric impairment. Finally, intra-AcbSh infusion of the AMY-R antagonist, AC187 (20 μg), significantly attenuated the ability of prefeeding to suppress DAMGO-induced food intake, with no effects in non-prefed rats. Hence, AMY-R signaling negatively modulates μ-OR-mediated appetitive responses at the level of the AcbSh. The results with AC187 indicate that endogenous AMY-R transmission in the AcbSh curtails opioid function in the postprandial period, suggesting a novel pathway for peripheral-central integration in the control of appetitive motivation and opioid reward.

Enhanced nicotine self-administration and suppressed dopaminergic systems in a rat model of diabetes

Patients with diabetes display a heightened propensity to use tobacco; however, it is unclear whether they experience enhanced rewarding effects of nicotine. Thus, this study examined the reinforcing effects of nicotine in a rodent model of diabetes involving administration of streptozotocin (STZ), a drug that is toxic to pancreatic insulin-producing cells. The first study compared STZ- and vehicle-treated rats that had 23-hour access to intravenous self-administration (IVSA) of nicotine or saline and concomitant access to food and water. In order to examine the contribution of dopamine to our behavioral effects, dopamine transporter (DAT), D1 and D2 receptor levels were compared in the nucleus accumbens (NAc) following 10 days of nicotine or saline IVSA. Dopamine levels in the NAc were also compared following nicotine administration. Lastly, nicotine metabolism and dose-dependent effects of nicotine IVSA were assessed. The results revealed that STZ-treated rats displayed enhanced nicotine intake and a robust increase in food and water intake relative to controls. Protein analysis revealed an increase in DAT and a decrease in D1 receptor levels in the NAc of STZ- versus vehicle-treated rats regardless of IVSA condition. STZ-treated rats also displayed suppressed NAc dopamine levels during baseline and in response to nicotine. STZ treatment did not alter our assessment of nicotine metabolism. Furthermore, STZ treatment increased nicotine IVSA in a dose-dependent manner. Our findings suggest that STZ-treatment increased the rewarding effects of nicotine. This suggests that strong reinforcing effects of nicotine may contribute to greater tobacco use in patients with diabetes.

The role of the area postrema in the anorectic effects of amylin and salmon calcitonin: behavioral and neuronal phenotyping

Amylin reduces meal size by activating noradrenergic neurons in the area postrema (AP). Neurons in the AP also mediate the eating-inhibitory effects of salmon calcitonin (sCT), a potent amylin agonist, but the phenotypes of the neurons mediating its effect are unknown. Here we investigated whether sCT activates similar neuronal populations to amylin, and if its anorectic properties also depend on AP function. Male rats underwent AP lesion (APX) or sham surgery. Meal patterns were analysed under ad libitum and post-deprivation conditions. The importance of the AP in mediating the anorectic action of sCT was examined in feeding experiments of dose-response effects of sCT in APX vs. sham rats. The effect of sCT to induce Fos expression was compared between surgery groups, and relative to amylin. The phenotype of Fos-expressing neurons in the brainstem was examined by testing for the co-expression of dopamine beta hydroxylase (DBH) or tryptophan hydroxylase (TPH). By measuring the apposition of vesicular glutamate transporter-2 (VGLUT2)-positive boutons, potential glutamatergic input to amylin- and sCT-activated AP neurons was compared. Similar to amylin, an intact AP was necessary for sCT to reduce eating. Further, co-expression between Fos activation and DBH after amylin or sCT did not differ markedly, while co-localization of Fos and TPH was minor. Approximately 95% of neurons expressing Fos and DBH after amylin or sCT treatment were closely apposed to VGLUT2-positive boutons. Our study suggests that the hindbrain pathways engaged by amylin and sCT share many similarities, including the mediation by AP neurons.

Convergent chemoenzymatic synthesis of a library of glycosylated analogues of pramlintide: structure-activity relationships for amylin receptor agonism

Pramlintide (Symlin®), a synthetic analogue of the naturally occurring pancreatic hormone amylin, is currently used with insulin in adjunctive therapy for type 1 and type 2 diabetes mellitus. Herein we report a systematic study into the effect that N-glycosylation of pramlintide has on activation of amylin receptors. A highly efficient convergent synthetic route, involving a combination of solid phase peptide synthesis and enzymatic glycosylation, delivered a library of N-glycosylated variants of pramlintide bearing either GlcNAc, the core N-glycan pentasaccharide [Man3(GlcNAc)2] or a complex biantennary glycan [(NeuAcGalGlcNAcMan)2Man(GlcNAc)2] at each of its six asparagine residues. The majority of glycosylated versions of pramlintide were potent receptor agonists, suggesting that N-glycosylation may be used as a tool to optimise the pharmacokinetic properties of pramlintide and so deliver improved therapeutic agents for the treatment of diabetes and obesity.

The central question of type 2 diabetes

Type 2 diabetes (T2D) represents a significant global epidemic with more than 285 million people affected worldwide. Regulating glycemia in T2D patients can be partially achieved with currently available treatment, but intensive research during the last decades have led to the discovery of modified compounds or new targets that could represent great hope for safe and effective treatment in the future. Among them, targets in the CNS that are known to control feeding and body weight have been also shown to exert glucoregulatory actions, and could be a key in the development of a new generation of drugs in the field of T2D. Such drugs would be of great interest since they can be used both in the treatment of diabetes and obesity. This patent review aims to establish an overview of recent patents disclosing new therapeutic opportunities targeting peripheral, as well as central targets for the treatment of T2D.

Antipsychotic-like actions of the satiety peptide, amylin, in ventral striatal regions marked by overlapping calcitonin receptor and RAMP-1 gene expression

Amylin is a calcitonin-related peptide co-secreted with insulin, which produces satiety through brainstem-localized receptors; however, its effects in forebrain are poorly understood. The nucleus accumbens shell (AcbSh) exhibits among the densest concentrations of high-affinity amylin binding; nevertheless, these receptors have not been explored beyond one study showing dopamine antagonist-like effects of intra-Acb amylin on feeding and associated behavior (Baldo and Kelley, 2001). Here, we investigated whether intra-Acb amylin signaling modulates prepulse inhibition (PPI), a measure of sensorimotor gating deficient in several illnesses including schizophrenia. First, in situ hybridization revealed marked anatomical gradients for both receptor activity-modifying protein-1 (RAMP-1) and calcitonin receptor gene (CT-R) expression in striatum [coexpression of these genes yields a high-affinity amylin-1 receptor (AMY1-R)], with highest overlap in the medial AcbSh. Intra-AcbSh amylin infusions in rats (0, 30, and 100 ng) reversed amphetamine (AMPH)-induced PPI disruption without affecting baseline startle; dorsal striatal amylin infusions had no effect. Coinfusion of AC187 (20 μg), an antagonist for AMY1-R, blocked the ability of amylin to normalize AMPH-induced PPI disruption, showing the specificity of AcbSh amylin effects to the AMY1-R. Intra-AcbSh AC187 on its own disrupted PPI in a haloperidol-reversible manner (0.1 mg/kg). Thus, AMY1-R may be a potential target for the development of putative antipsychotics or adjunct treatments that oppose metabolic side effects of current medications. Moreover, AMY1-Rs may represent a novel way to modulate activity preferentially in ventral versus dorsal striatum.

Incretins and amylin: neuroendocrine communication between the gut, pancreas, and brain in control of food intake and blood glucose

Arguably the most fundamental physiological systems for all eukaryotic life are those governing energy balance. Without sufficient energy, an individual is unable to survive and reproduce. Thus, an ever-growing appreciation is that mammalian physiology developed a redundant set of neuroendocrine signals that regulate energy intake and expenditure, which maintains sufficient circulating energy, predominantly in the form of glucose, to ensure that energy needs are met throughout the body. This orchestrated control requires cross talk between the gastrointestinal tract, which senses the incoming meal; the pancreas, which produces glycemic counterregulatory hormones; and the brain, which controls autonomic and behavioral processes regulating energy balance. Therefore, this review highlights the physiological, pharmacological, and pathophysiological effects of the incretin hormones glucagon-like peptide-1 and gastric inhibitory polypeptide, as well as the pancreatic hormone amylin, on energy balance and glycemic control.

Amylin activates distributed CNS nuclei to control energy balance

Amylin is a pancreas-derived neuropeptide that acts in the central nervous system (CNS) to reduce food intake. Much of the literature describing the anorectic effects of amylin are focused on amylin's actions in the area postrema, a hindbrain circumventricular structure. Although the area postrema is certainly an important site that mediates the intake-suppressive effects of amylin, several pieces of evidence indicate that amylin may also promote negative energy balance through action in additional CNS nuclei, including hypothalamic and mesolimbic structures. Therefore, this review highlights the distributed neural network mediating the feeding effects of amylin signaling with special attention being devoted to the recent discovery that the ventral tegmental area is physiologically relevant for amylin-mediated control of feeding. The production of amylin by alternative, extra-pancreatic sources and its potential relevance to food intake regulation is also considered. Finally, the utility of amylin and amylin-like compounds as a component of combination pharmacotherapies for the treatment of obesity is discussed.

Calcitonin gene related family peptides: importance in normal placental and fetal development

Synchronized molecular and cellular events occur between the uterus and the implanting embryo to facilitate successful pregnancy outcome. Nevertheless, the molecular signaling network that coordinates strategies for successful decidualization, placentation and fetal growth are not well understood. The discovery of calcitonin/calcitonin gene-related peptides (CT/CGRP) highlighted new signaling mediators in various physiological processes, including reproduction. It is known that CGRP family peptides including CGRP, adrenomedulin and intermedin play regulatory functions during implantation, trophoblast proliferation and invasion, and fetal organogenesis. In addition, all the CGRP family peptides and their receptor components are found to be expressed in decidual, placental and fetal tissues. Additionally, plasma levels of peptides of the CGRP family were found to fluctuate during normal gestation and to induce placental cellular differentiation, proliferation, and critical hormone signaling. Moreover, aberrant signaling of these CGRP family peptides during gestation has been associated with pregnancy disorders. It indicates the existence of a possible regulatory role for these molecules during decidualization and placentation processes, which are known to be particularly vulnerable. In this review, the influence of the CGRP family peptides in these critical processes is explored and discussed.