Role of amylin in insulin secretion and action in humans: antagonist studies across the spectrum of insulin sensitivity

Amylin receptor agonism enhances the effects of liraglutide in protecting against the acute metabolic side effects of olanzapine

Olanzapine is a second-generation antipsychotic (AP) used in the management of schizophrenia. Although effective at reducing psychoses, APs cause rapid hyperglycemia, insulin resistance, and dyslipidemia, an effect mediated in part by glucagon. We tested if amylin, a hormone that reduces glucagon, or the amylin receptor agonist pramlintide would protect against acute olanzapine-induced impairments in glucose and lipid homeostasis alone or in combination with other glucose-lowering agents such as liraglutide. We demonstrated that pramlintide lowered olanzapine-induced increases in glucagon:insulin ratio with a trend to protect against excursions in blood glucose. There was an additive effect of pramlintide and liraglutide in protecting against olanzapine-induced hyperglycemia, which was mirrored by reductions in glucagon and attenuated markers of dyslipidemia. Our findings provide evidence that pramlintide, although moderately protective against some aspects of olanzapine-induced metabolic dysfunction, can be used to enhance the protective effects of other interventions against acute olanzapine-induced metabolic dysfunction.

Beta Cell Dysfunction in Youth- and Adult-Onset Type 2 Diabetes: An Extensive Narrative Review with a Special Focus on the Role of Nutrients

Traditionally a disease of adults, type 2 diabetes (T2D) has been increasingly diagnosed in youth, particularly among adolescents and young adults of minority ethnic groups. Especially, during the recent COVID-19 pandemic, obesity and prediabetes have surged not only in minority ethnic groups but also in the general population, further raising T2D risk. Regarding its pathogenesis, a gradually increasing insulin resistance due to central adiposity combined with a progressively defective β-cell function are the main culprits. Especially in youth-onset T2D, a rapid β-cell activity decline has been observed, leading to higher treatment failure rates, and early complications. In addition, it is well established that both the quantity and quality of food ingested by individuals play a key role in T2D pathogenesis. A chronic imbalance between caloric intake and expenditure together with impaired micronutrient intake can lead to obesity and insulin resistance on one hand, and β-cell failure and defective insulin production on the other. This review summarizes our evolving understanding of the pathophysiological mechanisms involved in defective insulin secretion by the pancreatic islets in youth- and adult-onset T2D and, further, of the role various micronutrients play in these pathomechanisms. This knowledge is essential if we are to curtail the serious long-term complications of T2D both in pediatric and adult populations.

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.

Classical and non-classical islet peptides in the control of β-cell function

The dual role of the pancreas as both an endocrine and exocrine gland is vital for food digestion and control of nutrient metabolism. The exocrine pancreas secretes enzymes into the small intestine aiding digestion of sugars and fats, whereas the endocrine pancreas secretes a cocktail of hormones into the blood, which is responsible for blood glucose control and regulation of carbohydrate, protein and fat metabolism. Classical islet hormones, insulin, glucagon, pancreatic polypeptide and somatostatin, interact in an autocrine and paracrine manner, to fine-tube the islet function and insulin secretion to the needs of the body. Recently pancreatic islets have been reported to express a number of non-classical peptide hormones involved in metabolic signalling, whose major production site was believed to reside outside pancreas, e.g. in the small intestine. We highlight the key non-classical islet peptides, and consider their involvement, together with established islet hormones, in regulation of stimulus-secretion coupling as well as proliferation, survival and transdifferentiation of β-cells. We furthermore focus on the paracrine interaction between classical and non-classical islet hormones in the maintenance of β-cell function. Understanding the functional relationships between these islet peptides might help to develop novel, more efficient treatments for diabetes and related metabolic disorders.

How exposure to chronic stress contributes to the development of type 2 diabetes: A complexity science approach

Chronic stress contributes to the onset of type 2 diabetes (T2D), yet the underlying etiological mechanisms are not fully understood. Responses to stress are influenced by earlier experiences, sex, emotions and cognition, and involve a complex network of neurotransmitters and hormones, that affect multiple biological systems. In addition, the systems activated by stress can be altered by behavioral, metabolic and environmental factors. The impact of stress on metabolic health can thus be considered an emergent process, involving different types of interactions between multiple variables, that are driven by non-linear dynamics at different spatiotemporal scales. To obtain a more comprehensive picture of the links between chronic stress and T2D, we followed a complexity science approach to build a causal loop diagram (CLD) connecting the various mediators and processes involved in stress responses relevant for T2D pathogenesis. This CLD could help develop novel computational models and formulate new hypotheses regarding disease etiology.

Involvement of amylin B-H2S-connexin 43 signaling pathway in vascular dysfunction and enhanced ischemia-reperfusion-induced myocardial injury in diabetic rats

The present study was designed to investigate the role of amylin, H₂S, and connexin 43 in vascular dysfunction and enhanced ischemia–reperfusion (I/R)-induced myocardial injury in diabetic rats. A single dose of streptozotocin (65 mg/kg) was employed to induce diabetes mellitus. After 8 weeks, there was a significant decrease in the plasma levels of amylin, an increase in I/R injury to isolated hearts (increase in CK-MB and cardiac troponin release) on the Langendorff apparatus. Moreover, there was a significant impairment in vascular endothelium function as assessed by quantifying acetylcholine-induced relaxation in norepinephrine-precontracted mesenteric arteries. There was also a marked decrease in the expression of H₂S and connexin 43 in the hearts following I/R injury in diabetic rats. Treatment with amylin agonist, pramlintide (100 and 200 µg/kg), and H₂S donor, NaHS (10 and 20 μmol/kg) for 2 weeks improved the vascular endothelium function, abolished enhanced myocardial injury and restored the levels of H₂S along with connexin 43 in diabetic animals. However, pramlintide and NaHS failed to produce these effects the presence of gap junction blocker, carbenoxolone (20 and 40 mg/kg). Carbenoxolone also abolished the myocardial levels of connexin 43 without affecting the plasma levels of amylin and myocardial levels of H₂S. The decrease in the amylin levels with a consequent reduction in H₂S and connexin 43 may contribute to inducing vascular dysfunction and enhancing I/R-induced myocardial injury in diabetic rats.

Salicylate administration suppresses the inflammatory response to nutrients and improves ovarian function in polycystic ovary syndrome

Oxidative stress (OS) and inflammation are often present in polycystic ovary syndrome (PCOS). We examined the effects of salsalate treatment on nutrient-induced OS and inflammation, ovarian androgen secretion, ovulation, and insulin sensitivity in PCOS. Eight lean insulin-sensitive women with PCOS and eight age- and body composition-matched ovulatory controls for baseline comparison participated in the study. The women with PCOS underwent a 12-wk treatment of salsalate, a nonsteroidal anti-inflammatory drug, at a dose of 3 g daily. Markers of OS and inflammation were quantified in mononuclear cells (MNC) and plasma from blood drawn fasting and 2 h after saturated fat ingestion before and after treatment. Ovarian androgen secretion was assessed from blood drawn fasting and 24, 48, and 72 h after human chorionic gonadotropin (HCG) administration before and after treatment. Ovulation was documented based on biphasic basal body temperatures and luteal range progesterone elevations. A two-step pancreatic clamp was performed pre- and posttreatment to measure basal endogenous glucose production (EGP) and the steady-state glucose disposal rate (GDR) during the euglycemic phase and markers of OS and inflammation in MNC and plasma during the hyperglycemic phase. Salsalate administration suppressed lipid- and glucose-stimulated reactive oxygen species generation, activated nuclear factor-κB and circulating tumor necrosis factor-α, normalized basal androgen levels, and lowered HCG-stimulated androgen secretion without altering EGP or GDR. Four salsalate-treated subjects responded with two consecutive ovulations. We conclude that in PCOS, salsalate-induced suppression of OS and inflammation ameliorates ovarian androgen hypersecretion and may induce ovulation while maintaining insulin action.

Serum Preptin and Amylin Levels with Respect to Body Mass Index in Polycystic Ovary Syndrome Patients

Background

Preptin and amylin are pancreatic hormones which participate in glucose homeostasis. This study aimed to evaluate how serum preptin and amylin levels are altered in polycystic ovary syndrome (PCOS) patients and healthy women based on BMI groups (<25 kg/m² and ≥25 kg/m²).

Material/Methods

This was a prospective randomized control study of 40 PCOS patients and 40 healthy women who were matched with respect to BMI (<25 kg/m² and ≥25 kg/m²).

Results

When compared to the healthy women, PCOS patients had significantly higher ovarian volumes, Ferriman-Gallwey scores, and free and total testosterone levels, but significantly lower amylin concentrations (p=0.001, p=0.001, p=0.049, p=0.021, and p<0.001, respectively). Both the normal-weight and overweight PCOS patients had significantly lower amylin levels than the normal-weight and overweight controls (p<0.001, p=0.009, p=0.001, and p=0.001, respectively). Amylin levels were negatively and significantly correlated with the Ferriman-Gallwey scores (r=−0.272, p=0.001) and ovarian volume (r=−0.206, p=0.007). Serum preptin levels were not elevated in either group.

Conclusions

Serum preptin levels are statistically similar in PCOS patients and BMI-matched healthy controls. Serum amylin levels are significantly higher in healthy controls than PCOS patients whether they are slim or overweight. These findings suggest the presence of mechanisms that can prevent the elevation in serum amylin concentrations that can occur in response to the impaired glucose metabolism in PCOS patients.

Functional proteasome complex is required for turnover of islet amyloid polypeptide in pancreatic β-cells

Human islet amyloid polypeptide (hIAPP) is the principal constituent of amyloid deposits and toxic oligomers in the pancreatic islets. Together with hyperglycemia, hIAPP-derived oligomers and aggregates are important culprits in type 2 diabetes mellitus (T2DM). Here, we explored the role of the cell's main proteolytic complex, the proteasome, in hIAPP turnover in normal and stressed β-cells evoked by chronic hyperglycemia. Moderate inhibition (10-35%) of proteasome activity/function in cultured human islets by the proteasome inhibitor lactacystin enhanced intracellular accumulation of hIAPP. Unexpectedly, prolonged (>1 h) and marked (>50%) impairment of proteasome activity/function had a strong inhibitory effect on hIAPP transcription and secretion from normal and stressed β-cells. This negative compensatory feedback mechanism for controlling IAPP turnover was also observed in the lactacystin-treated rat insulinoma β-cell line (INS 832/13), demonstrating the presence of an evolutionarily conserved mechanism for IAPP production. In line with these in situ studies, our current ex vivo data showed that proteasome activity and hIAPP expression are also down-regulated in islets isolated from T2DM subjects. Gene expression and promoter activity studies demonstrated that the functional proteasome complex is required for efficient activation of the hIAPP promoter and for full expression of IAPP's essential transcription factor, FOXA2. ChIP studies revealed that promoter occupancy of FoxA2 at the rat IAPP promoter region is an important and limiting factor for amylin expression in proteasome-impaired murine cells. This study suggests a novel regulatory pathway in β-cells involving proteasome, FOXA2, and IAPP, which can be possibly targeted to regulate hIAPP levels and islet amyloidosis in T2DM.

Proteasome regulates turnover of toxic human amylin in pancreatic cells

Toxic human amylin (hA) oligomers and aggregates are implicated in the pathogenesis of type 2 diabetes mellitus (T2DM). Although recent studies demonstrated a causal connection between hA uptake and toxicity in pancreatic cells, the mechanism of amylin's clearance following its internalization and its relationship to toxicity is yet to be determined, and hence was investigated here. Using pancreatic rat insulinoma β-cells and human islets as model systems, we show that hA, following its internalization, first accumulates in the cytosol followed by its translocation into nucleus, and to a lesser extent lysosomes, keeping the net cytosolic amylin content low. An increase in hA accumulation in the nucleus of pancreatic cells correlated with its cytotoxicity, suggesting that its excessive accumulation in the nucleus is detrimental. hA interacted with 20S core and 19S lid subunits of the β-cell proteasomal complex, as suggested by immunoprecipitation and confocal microscopy studies, which subsequently resulted in a decrease in the proteasome's proteolytic activity in these cells. In vitro binding and activity assays confirmed an intrinsic and potent ability of amylin to interact with the 20S core complex thereby modulating its proteolytic activity. Interestingly, less toxic and aggregation incapable rat amylin (rA) showed a comparable inhibitory effect on proteasome activity and protein ubiquitination, decoupling amylin aggregation/ toxicity and amylin-induced protein stress. In agreement with these studies, inhibition of proteasomal proteolytic activity significantly increased intracellular amylin content and toxicity. Taken together, our results suggest a pivotal role of proteasomes in amylin's turnover and detoxification in pancreatic cells.

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.

Effect of a test meal on meal responses of satiation hormones and their association to insulin resistance in obese adolescents

OBJECTIVE

The role of gastrointestinal (GI) hormones in the pathophysiology of obesity is unclear, although they are involved in the regulation of satiation and glucose metabolism. To (i) examine glucagon-like peptide 1 (GLP-1), amylin, ghrelin, and glucagon responses to a meal in obese adolescents and to (ii) test which GI peptides are associated with insulin resistance are presented.

METHODS

A total of 16 obese (body mass index (BMI) ≥ 97th percentile for age and gender) and 14 control (BMI between 25th and 75th percentiles) adolescents were included. Subjects were instructed to eat a test meal (490 kcal). Plasma samples were collected for hormone and glucose analysis.

RESULTS

Obese adolescents were insulin resistant as expressed by the Homeostasis Model Assessment (HOMA) index and had significantly increased fasting glucagon and amylin levels compared to the control group (P = 0.003 and 0.044, respectively). In response to the meal, the increase in GLP-1 levels was reduced in obese adolescents (P < 0.001). In contrast, amylin secretion was significantly increased in the obese population compared to the control group (P < 0.005).

CONCLUSIONS

Obese adolescents have increased fasting glucagon and amylin levels and attenuated post-prandial GLP-1 concentrations compared with the control group. These factors could contribute to the metabolic syndrome.

Human IAPP amyloidogenic properties and pancreatic β-cell death

A hallmark of type 2 diabetes mellitus (T2DM) is the presence of extracellular amyloid deposits in the islets of Langerhans. These deposits are formed by the human islet amyloid polypeptide, hIAPP (or amylin), which is a hormone costored and cosecreted with insulin. Under normal conditions, the hormone remains in solution but, in the pancreas of T2DM individuals, it undergoes misfolding giving rise to oligomers and cross-β amyloid fibrils. Accumulating evidence suggests that the amyloid deposits that accompany type 2 diabetes mellitus are not just a trivial epiphenomenon derived from the disease progression. Rather, hIAPP aggregation induces processes that impair the functionality and viability of β-cells and may lead to apoptosis. The present review article aims to summarize a few aspects of the current knowledge of this amyloidogenic polypeptide. In the first place, the physicochemical properties which condition its propensity to misfold and form aggregates. Secondly, how these properties confer hIAPP the capacity to interfere with some signaling of the pancreatic β-cell, interact with membranes, form channels or affect natural ion channels, including calcium channels. Finally, how misfolded hIAPP cytotoxicity results in apoptosis. A number of pathophysiological changes of the T2DM islet can be related to the amyloidogenic properties of hIAPP. However, in a certain way, the in vivo aggregation of the polypeptide also reflects a failure of chaperones and, in general, of cellular proteostasis, supporting the view that T2DM may also be considered as a conformational disorder.

Postprandial oxidative stress and gastrointestinal hormones: is there a link?

Background

Abnormal postprandial elevation of plasma glucose and lipids plays an important role in the pathogenesis of diabetes and strongly predicts cardiovascular mortality. In patients suffering from type 2 diabetes (T2D) postprandial state is associated with oxidative stress, cardiovascular risk and, probably, with impairment of both secretion and the effect of gastrointestinal peptides. Evaluating postprandial changes of gastrointestinal hormones together with changes in oxidative stress markers may help to understand the mechanisms behind the postprandial state in diabetes as well as suggest new preventive and therapeutical strategies.

Methods

A standard meal test has been used for monitoring the postprandial concentrations of gastrointestinal hormones and oxidative stress markers in patients with T2D (n = 50) compared to healthy controls (n = 50). Blood samples were drawn 0, 30, 60, 120 and 180 minutes after the standard meal.

Results

Both basal and postprandial plasma concentrations of glucose and insulin proved to be significantly higher in patients with T2D, whereas plasma concentrations of ghrelin showed significantly lower values during the whole meal test. In comparison with healthy controls, both basal and postprandial concentrations of almost all other gastrointestinal hormones and lipoperoxidation were significantly increased while ascorbic acid, reduced glutathione and superoxide dismutase activity were decreased in patients with T2D. A positive relationship was found between changes in GIP and those of glucose and immunoreactive insulin in diabetic patients (p<0.001 and p<0.001, respectively) and between changes in PYY and those of glucose (p<0.01). There was a positive correlation between changes in GIP and PYY and changes in ascorbic acid in patients with T2D (p<0.05 and p<0.001, respectively).

Conclusion/Interpretation

Apart from a positive relationship of postprandial changes in GIP and PYY with changes in ascorbic acid, there was no direct link observed between gastrointestinal hormones and oxidative stress markers in diabetic patients.

Trial Registration

ClinicalTrials.gov NCT01572402

Oral salmon calcitonin enhances insulin action and glucose metabolism in diet-induced obese streptozotocin-diabetic rats

We previously reported that oral delivery of salmon calcitonin (sCT) improved energy and glucose homeostasis and attenuated diabetic progression in animal models of diet-induced obesity (DIO) and type 2 diabetes, although the glucoregulatory mode of action was not fully elucidated. In the present study we hypothesized that oral sCT as pharmacological intervention 1) exerted anti-hyperglycemic efficacy, and 2) enhanced insulin action in DIO-streptozotocin (DIO-STZ) diabetic rats. Diabetic hyperglycemia was induced in male selectively bred DIO rats by a single low dose (30mg/kg) injection of STZ. Oral sCT by gavage was delivered as once-daily administration with lead-in (2mg/kg) and maintenance (0.5mg/kg) dose of oral sCT for a total of 21 days. Food intake, body weight, blood glucose, HbA1c, glucose and insulin tolerance test, and parameters of insulin sensitivity were investigated. Plasma glucoregulatory hormones and pancreatic insulin content were analyzed. Oral sCT treatment induced a pronounced anorectic action during the 7 days lead-in period and markedly reduced food intake and body weight in conjunction with improved glucose homeostasis. During the maintenance period, oral sCT normalized food intake and attenuated weight loss, albeit sustained glycemic control by reducing fasting blood glucose and HbA1c levels compared to those of vehicle-treated rats at the end of study. Notably, plasma levels of insulin, glucagon, leptin and adiponectin were unaltered, albeit insulin action was enhanced in conjunction with protection of pancreatic insulin content. The results of the present study indicate that oral sCT exerts a novel insulin-sensitizing effect to improve glucose metabolism in obesity and type 2 diabetes.

High plasma levels of islet amyloid polypeptide in young with new-onset of type 1 diabetes mellitus

Aims/Hypothesis

Islet amyloid polypeptide (IAPP) is a beta cell hormone secreted together with insulin upon glucose stimulation. IAPP participates in normal glucose regulation, but IAPP is also known for its ability to misfold and form islet amyloid. Amyloid fibrils form through smaller cell toxic intermediates and deposited amyloid disrupts normal islet architecture. Even though IAPP and amyloid formation are much discussed in type 2 diabetes, our aim was to study the significance of IAPP in type 1 diabetes.

Results

Plasma IAPP levels in children and adolescents with newly diagnosed type 1 diabetes (n = 224) were analysed and concentrations exceeding 100 pmol/L (127.2 – 888.7 pmol/L) were found in 11% (25/224). The IAPP increase did not correlate with C-peptide levels.

Conclusions/Interpretation

Plasma levels of IAPP and insulin deviate in a subpopulation of young with newly-diagnosed type 1 diabetes. The determined elevated levels of IAPP might increase the risk for IAPP misfolding and formation of cell toxic amyloid in beta cells. This finding add IAPP-aggregation to the list over putative pathological factors causing type 1 diabetes.

Impact of incretin therapy on islet dysfunction: an underlying defect in the pathophysiology of type 2 diabetes

Glucose homeostasis is governed by a complex interplay of hormonal signaling and modulation. Insulin, glucagon, amylin, the incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), and other hormones and enzymes interact to maintain glucose homeostasis and normal cellular metabolism. Derangements in these hormonal interactions, particularly insulin deficits and impaired insulin action, result in the development of type 2 diabetes-but only in individuals who have experienced significant dysfunction or loss of beta-cells, located in the pancreatic islets of Langerhans. Much less is known about the impact of alpha-cell dysregulation on glucose homeostasis, although it has been demonstrated that glucagon-secreting alpha-cells, also located in the pancreatic islets, play an important role in glucose metabolism. Because beta-cell dysfunction occurs early in the course of type 2 diabetes and is progressive, early intervention with therapies that improve beta-cell function is desirable. In addition to reducing HbA1c and fasting plasma glucose, the recently developed diabetes therapies GLP-1 receptor agonists (eg, exenatide, liraglutide) and dipeptidyl peptidase-4 (DPP-4) inhibitors (eg, sitagliptin, vildagliptin) appear to have beneficial effects on beta-cell dysfunction and, possibly, on alpha-cell dysregulation.

Amylin and its relation to insulin and lipids in obese children before and after weight loss

OBJECTIVE

There are limited data concerning the relationships between amylin, weight status, lipids, insulin, and insulin resistance in obese humans. Therefore, the aim was to study these relationships in cross-sectional and longitudinal analyses.

RESEARCH METHODS AND PROCEDURES

Fasting amylin, insulin, glucose, triglycerides, low-density lipoprotein (LDL)- and high-density lipoprotein (HDL)-cholesterol, and percentage body fat based on skinfold measurements were determined in 37 obese children (median age, 11.5 years) and compared with 16 lean children of the same age and gender. Furthermore, we analyzed the changes of these variables in the obese children after participating in a one-year weight loss intervention program.

RESULTS

Obese children had significantly (p < 0.01) higher amylin, triglycerides, LDL-cholesterol, and insulin levels as compared with the lean children. In multiple linear regression analysis, amylin was significantly (p < 0.05) correlated to insulin and triglycerides, but not to age, gender, pubertal stage, or BMI. Changes of amylin correlated significantly (p < 0.001) to changes of insulin (r = 0.54) and triglycerides (r = 0.49), but not to changes of BMI or percentage body fat. Substantial weight loss in 17 children led to a significant (p < 0.05) decrease of amylin, triglycerides, and insulin, in contrast to the 20 children without substantial weight loss.

CONCLUSION

Amylin levels were related to insulin concentrations in both cross-sectional and longitudinal analyses, suggesting a relationship between amylin and insulin secretion. Amylin levels were reversibly increased in obesity and related to triglyceride concentrations.

Role of endogenous amylin in glucagon secretion and gastric emptying in rats demonstrated with the selective antagonist, AC187

Amylin is a 37-amino acid polypeptide co-secreted with insulin from the pancreatic beta-cells. It complements insulin's stimulation of the rate of glucose disappearance (Rd) by slowing the rate of glucose appearance (Ra) through several mechanisms, including an inhibition of mealtime glucagon secretion and a slowing of gastric emptying. To determine if endogenous amylin tonically inhibits these processes, we studied the effects of the amylin receptor blocker AC187 upon glucagon secretion during euglycemic, hyperinsulinemic clamps in Sprague-Dawley (HSD) rats, upon gastric emptying in HSD rats, and upon gastric emptying and plasma glucose profile in hyperamylinemic, and genetically obese, Lister Albany/NIH rats during a glucose challenge. Amylin blockade increased glucagon concentration, accelerated gastric emptying of liquids, and resulted in an exaggerated post-challenge glycemia. These data collectively indicate a physiologic role for amylin in glucose homeostasis via mechanisms that include regulation of glucagon secretion and gastric emptying.

Newer therapeutic options for children with diabetes mellitus: theoretical and practical considerations

Recent studies in adult patients with type 1 diabetes mellitus (T1DM) and T2DM have examined the potential utility, benefits, and side effects of agents that augment insulin secretion after oral ingestion of nutrients in comparison with intravenous nutrient delivery, the so-called incretins. Two families of incretin-like substances are now approved for use in adults. Glucagon-like peptide-1 (GLP-1) or agents that bind to its receptor (exenatide, Byetta) or agents that inhibit its destruction [dipeptidyl peptidase-IV (DPP-IV) inhibitors, Vildagliptin] improve insulin secretion, delay gastric emptying, and suppress glucagon secretion while decreasing food intake without increasing hypoglycemia. Pramlintide, a synthetic amylin analog, also decreases glucagon secretion and delays gastric emptying, improves hemoglobin A1c (HbA1C), and facilitates weight reduction without causing hypoglycemia. We review the historical discovery of these agents, their physiology [corrected] and their current applications. Remarkably, only one or two studies have been reported in children. Pediatricians caring for children with T1DM and T2DM should become familiar with these agents and investigate their applicability, as they seem likely to enhance our therapeutic armamentarium to treat children with diabetes mellitus.

Chronically administered islet amyloid polypeptide in rats serves as an adiposity inhibitor and regulates energy homeostasis

AIMS/HYPOTHESIS

Islet amyloid polypeptide (IAPP) reduces food intake and body weight in laboratory animals. In addition, IAPP appears to regulate nutrient metabolism. In the present studies, we investigated the effect of chronic IAPP treatment on different aspects of energy homeostasis.

METHODS

IAPP was infused (25 pmol/kg/min) from subcutaneous osmotic pumps for 2-7 days. Rats in 2 saline-infused control groups were fed ad libitum (AF) or pair-fed (PF) against the IAPP-treated rats.

RESULTS

As expected, the IAPP infusion reduced food intake and body weight gain. In addition, the IAPP treatment decreased the epididymal fat pad (vs. PF rats, p < 0.05) and lowered circulating levels of triglycerides (vs. PF rats, p < 0.05), free fatty acids (vs. PF rats, p < 0.05), leptin (vs. both AF and PF rats, p < 0.05) and insulin (vs. AF rats, p < 0.05). In contrast, glucose and protein metabolism in the IAPP-treated rats was largely unchanged, as shown in results regarding serum glucose, glucose transport in skeletal muscle, blood urea nitrogen, and glycogen and protein content in the liver and in skeletal muscle.

CONCLUSION/INTERPRETATION

In summary, chronic IAPP exposure led to a changed lipid metabolism, which was characterized by decreased adiposity, hypolipidemia and hypoleptinemia, and to unchanged glucose and protein homeostasis. These results were similar to those seen in rodents during chronic exposure to another satiety/adiposity regulator, leptin. In conclusion, chronically administered IAPP plays a role as a satiety and adiposity signal in rats, and helps regulate energy homeostasis.

Amylin and the integrated control of nutrient influx

The most potent actions of amylin that occur at physiological plasma concentrations include inhibition of food intake, gastric emptying, acid and digestive enzyme secretion, and glucagon secretion. These actions share a common outcome; they each help regulate the rate at which nutrients (including glucose) appear in the blood (Ra). Amylin physiologically orchestrates, via several parallel processes, the rate of entry of nutrient into the circulation, as shown schematically in Fig. 1. In this way, amylin's function may be viewed as complementary to that of insulin (secreted from the same pancreatic beta-cells), which orchestrates the exit of nutrient from blood and its storage in peripheral tissues. The following discussion addresses the emerging picture that, although amylin is co-secreted with an endocrine hormone from endocrine tissue (the pancreatic islets), the target for its most potent and physiologically relevant effects appears to be the central nervous system. Amylin thus may be primarily regarded as a neuroendocrine hormone (Young et al., 2000).

Inhibition of insulin secretion

Reports of the effects of amylin and amylin agonists on insulin secretion have varied widely. Some confusion can be attributed to the use of human amylin, which has been shown to readily fall out of solution resulting in low estimates of bioactivity. Some confusion can be resolved by assessing the probability that this had happened. The view taken here, supported by authors using reliable and well-characterized ligands (representing the preponderance of recent studies), is that exogenously administered amylin agonists inhibit insulin secretion, at least partly via activation of an amylin-like receptor linked to Gi-mediated inhibition of cAMP in islets. There may additionally be autonomic extrapancreatic effects of amylin on insulin secretion that derive from its action at the area postrema. Studies with amylin receptor antagonists, including human studies, indicate that endogenously secreted amylin may physiologically inhibit beta-cell secretion (insulin and amylin) via feedback inhibition that is characteristic of many other hormones. Part of this inhibition may be local (paracrine), as indicated by the amylin sensitivity of isolated preparations and the fact that the concentration of secreted products in the islet interstitium can be over 100-fold higher than in the circulation (Bendayan, 1993).

Amylin agonists: a novel approach in the treatment of diabetes

Amylin is a peptide hormone that is cosecreted with insulin from the pancreatic beta-cell and is thus deficient in diabetic people. It inhibits glucagon secretion, delays gastric emptying, and acts as a satiety agent. Amylin replacement could therefore possibly improve glycemic control in some people with diabetes. However, human amylin exhibits physicochemical properties predisposing the peptide hormone to aggregate and form amyloid fibers, which may play a part in beta-cell destruction in type 2 diabetes. This obviously makes it unsuitable for pharmacological use. A stable analog, pramlintide, which has actions and pharmacokinetic and pharmacodynamic properties similar to the native peptide, has been developed. The efficacy and safety of pramlintide administration has been tested in a vast number of clinical trials. Approximately 5,000 insulin-treated patients have received pramlintide and approximately 250 for > or =2 years. The aims of this review are to 1) briefly describe actions of amylin as demonstrated in animal and human models and 2) primarily review results from clinical trials with the amylin analog pramlintide.

The genetics of adiponectin

Adiponectin encoded by the APMI gene is one of the adipocyte-expressed proteins that function in the homeostatic control of glucose, lipid, and energy metabolism. Its dysregulation has been suggested to be involved in disorders covering the metabolic X syndrome, such as insulin resistance, obesity, type 2 diabetes, and coronary artery disease. Recent data present evidence of a genetic modulation of the adiponectin level, and linkage of the 3q27 locus, where the APMI gene lies, with diabetes and features of the metabolic X syndrome playing a putative role of the APMI gene in this syndrome. In this article, we present an overview of the results available to date and discuss positive evidence for a role of genetic variants of the APMI gene and questions that genetic data raise.