Levels Of Islet Amyloid Polypeptide Research Articles

Okinawa-Based Nordic Diet Decreases Plasma Levels of IAPP and IgA against IAPP Oligomers in Type 2 Diabetes Patients.

Pancreas-derived islet amyloid polypeptide (IAPP) aggregates and deposits in the pancreas and periphery of Type 2 Diabetes (T2D) patients, contributing to diabetic complications. The excess IAPP can be removed by autoantibodies, and increased levels of immunoglobulin (Ig) G against IAPP have been reported in T2D patients. However, whether other Ig classes are also affected and if the levels can be managed is less known. This pre-post study examines IgA levels against IAPP oligomers (IAPPO-IgA) in T2D patients and assesses the impact of the Okinawa-based Nordic (O-BN) diet-a low-carbohydrate, high-fiber diet-on these levels after following the diet for 3 months. IAPP, IAPPO-IgA, and total IgA levels were measured in plasma and fecal samples from n = 30 T2D patients collected at baseline, after 3 months of diet, and after additional 4 months of unrestricted diets (a clinical follow-up). The IAPP and IAPPO-IgA levels were significantly lower after 3 months, with the latter also being significantly reduced at the clinical follow-up. The reduction in plasma IAPP and IAPPO-IgA levels correlated with reductions in plasma levels of metabolic and inflammatory markers. Hence, following the O-BN diet for at least 3 months is sufficient to reduce circulating IAPP and IAPPO-IgA levels, which may be principal in managing T2D.

Association of Islet Amyloid Polypeptide and Inflammatory Markers in Type 2 Diabetes Mellitus

Introduction: Islet Amyloid Polypeptide (IAPP) is co-synthesised and co-secreted with insulin by islets of pancreatic β-cells, its increased concentration in individuals with type 2 diabetes mellitus, may involve in inflammatory processes. Aim: To study and find the association of IAPP with inflammatory markers including high-sensitivity C-reactive protein (hsCRP), Tumor Necrosis Factor (TNF)-a and Interleukin(IL)-6 in patients with type 2 diabetes mellitus. Materials and Methods: This was a cross-sectional study, conducted from, December 2015 to December 2019, on 262 subjects (30-60 years, 147 males and 115 females), including 131 healthy controls and 131 known cases of type 2 diabetes mellitus, Fasting blood glucose and glycated haemoglobin(HbA1c) was estimated by commercially available kit, and serum fasting insulin, IAPP, hsCRP, TNF-α, and IL-6 were analysed by ELISA. Insulin Resistance (IR) and insulin sensitivity were calculated. Statistical analysis was done with Statistical Package Social Sciences (SPSS) version 24 the descriptive statistics were expressed as Mean±SD, Student t-test was applied, and p≤0.05 was considered as statistically significant and highly significant at ≤0.01 at 95% CI. The relationship between IAPP and other variables were done by using Spearman Rank correlation (r). Results: Circulatory level of IAPP was positively associated with serum hsCRP (r=0.312, p≤0.05) in type 2 diabetes mellitus. The elevated levels of IAPP (21.3±10.54pmol/l), insulin (11.74±3.91μU/ml), Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) (5.11±2.01) and inflammatory markers including hsCRP (3.44±1.77mg/l), TNF-α (29.5±4.7pg/ml) and IL-6 (20.2±5.2pg/ml) p≤0.05 with poor glycaemic control (HbA1c 8.78±2.30%, p<0.001), and reduced insulin sensitivity {Quantitative Insulin Sensitivity Check Index (QUICKI) 0.31±0.02, p≤0.05} were compared with healthy control; indicates that hyperamylinemia may induce inflammation in individuals with T2DM. Conclusion: Elevated degree of IAPP can be an important predictor and indicator of inflammatory processes and IR in uncontrolled diabetes.

2091-P: Effects of Caveolin-1 on the Synthesis and Decomposition of Islet ß-Cell IAPP and Its Mechanism

Objective: Islet amyloid polypeptide(IAPP) is a major component of islet amyloid deposition in type 2 diabetic patients. Our preliminary study showed that membrane protein Caveolin-1 (Cav1) silencing inhibited β-cell apoptosis and promote insulin secretion. The purpose of this study was to investigate the regulation of Cav1 on islet β-cell IAPP and its mechanism. Materials and Methods: Firstly, IAPP secretion of each group of primary islets was detected by ELISA, then Western blot and real-time quantitative PCR (qPCR) were used to detect the expression levels of IAPP, PAM(Peptidyl-glycine alpha-amidating monooxygenase), PC1(Prohormone Convertase-1), BACE2(Beta-secretase 2), IDE(Insulin-Degrading Enzyme), TXNIP(Thioredoxin interacting protein), and finally, it confirmed that Cav1 interacted with the protein of TXNIP by immunofluorescence confocal and co-immunoprecipitation (Co-IP). Results: The secretion of IAPP was decreased in primary pancreatic islets and Cav1 deficiency significantly down-regulated the expression of IAPP in NIT-1 cells, while over-expression of Cav1 in βTC-6 cells significantly up-regulated the expression of IAPP. This effect correlated with Cav1 silencing leading to down-regulation of PAM expression associated with IAPP synthesis and over-expression of Cav1 leading to up-regulation of PC1 associated with IAPP synthesis. On the other hand,Cav1 deficiency resulted in the up-regulation of the expression of BACE2 and IDE, the enzymes associated with IAPP decomposition. While over-expression of Cav1 leaded to down-regulation of BACE2 and IDE. Further studies indicated that Cav1 co-localized with TXNIP, and it interacted with and regulated the expression of TXNIP, which regulates IAPP gene transcription. Conclusion: Cav-1 can regulate the synthesis and decomposition of IAPP in islet β cell by interacting with TXNIP. This study suggests that Cav-1 may protect diabetic islet beta cells by reducing islet amyloid deposition. Disclosure K. Liu: None. W. Zeng: None. S. Lin: None. C. Lin: None. F. Xu: None. N. Cai: None. L. Zeng: None. Funding National Natural Science Funding of China (51873071); Natural Science Foundation of Guangdong Province (2018B030311012)

Dietary Supplementation with Curcumin Reduce Circulating Levels of Glycogen Synthase Kinase-3β and Islet Amyloid Polypeptide in Adults with High Risk of Type 2 Diabetes and Alzheimer's Disease.

Dietary supplementation with curcumin has been previously reported to have beneficial effects in people with insulin resistance, type 2 diabetes (T2D) and Alzheimer’s disease (AD). This study investigated the effects of dietary supplementation with curcumin on key peptides implicated in insulin resistance in individuals with high risk of developing T2D. Plasma samples from participants recruited for a randomised controlled trial with curcumin (180 mg/day) for 12 weeks were analysed for circulating glycogen synthase kinase-3 β (GSK-3β) and islet amyloid polypeptide (IAPP). Outcome measures were determined using ELISA kits. The homeostasis model for assessment of insulin resistance (HOMA-IR) was measured as parameters of glycaemic control. Curcumin supplementation significantly reduced circulating GSK-3β (−2.4 ± 0.4 ng/mL vs. −0.3 ± 0.6, p = 0.0068) and IAPP (−2.0 ± 0.7 ng/mL vs. 0.4 ± 0.6, p = 0.0163) levels compared with the placebo group. Curcumin supplementation significantly reduced insulin resistance (−0.3 ± 0.1 vs. 0.01 ± 0.05, p = 0.0142) compared with placebo group. Dietary supplementation with curcumin reduced circulating levels of IAPP and GSK-3β, thus suggesting a novel mechanism through which curcumin could potentially be used for alleviating insulin resistance related markers for reducing the risk of T2D and AD.

Levels of Retinal Amyloid-β Correlate with Levels of Retinal IAPP and Hippocampal Amyloid-β in Neuropathologically Evaluated Individuals.

Background:Previous studies have used immunohistology to demonstrate Alzheimer’s disease (AD) characteristic accumulation of amyloid-β (Aβ) in the retina of AD patients, a finding indicating retina examination as a potential diagnostic tool for AD pathology.Objective:To further explore this idea by investigating whether levels of Aβ42 and Aβ40 in retina are associated with corresponding levels in hippocampus, neuropathological assessments, apolipoprotein E (APOE) genotype, and levels of islet amyloid polypeptide (IAPP).Methods:Levels of high molecular weight (HMW) Aβ42, Aβ40, and IAPP in ultra-centrifuged homogenates of retina and hippocampus from patients with AD, multiple sclerosis, AD with Lewy bodies, and non-demented controls were analyzed using Mesoscale Discovery electrochemiluminescence technology employing immunoassay and enzyme-linked immunosorbent assay.Results:Higher levels of retinal and hippocampal Aβ42-HMW, Aβ40-HMW, and IAPP-HMW were found in individuals with high neuropathological scores of Aβ plaques and in individuals carrying the APOE ɛ4 allele. The retinal levels of Aβ42-HMW and Aβ40-HMW correlated with corresponding levels in hippocampus as well as with neurofibrillary tangles (NFT) and Aβ scores. Retinal IAPP-HMW correlated with retinal levels of Aβ42-HMW and with NFT and Aβ scores.Conclusion:These results show that different isoforms of Aβ can be detected in the human retina and moreover support the growing number of studies indicating that AD-related pathological changes occurring in the brain could be reflected in the retina.

Levels of islet amyloid polypeptide in cerebrospinal fluid and plasma from patients with Alzheimer's disease.

The biologically active pancreatic hormone peptide islet amyloid polypeptide (IAPP) regulates brain functions such as appetite and cognition. It also plays a role in clearance of amyloid beta (Aβ), a peptide implicated in the dementia disorder Alzheimer’s disease (AD). If IAPP becomes modified, it loses its biological activity and starts to aggregate. Such aggregations have been found in the AD brain and decreased plasma levels of the unmodified IAPP (uIAPP) have been shown in the same patients. In the current study, we analyze levels of uIAPP and total IAPP (unmodified and modified) in cerebrospinal fluid (CSF) to investigate its potential as a biomarker for AD. We found no differences in neither CSF nor plasma levels of uIAPP or total IAPP in AD patients compared to cognitive healthy individuals (NC). The levels of uIAPP in CSF of NC were positively correlated with uIAPP in plasma, Q-albumin and albumin levels in CSF, but negatively correlated with CSF levels of t-tau and p-tau. These findings were not seen in AD patients. Levels of total CSF IAPP correlated positively with total Q-albumin and albumin levels in CSF in both AD and NC. In addition, total plasma IAPP correlated positively with CSF t-tau and p-tau in NC and negatively with CSF Aβ42 in AD patients. To conclude, our studies did not find evidence supporting the use of CSF IAPP as an AD biomarker. However, our findings, indicating a compromised translocation of uIAPP in and out of the brain in AD patients as well as the correlations between total plasma IAPP and AD biomarkers, encourage further research on the role for IAPP in AD.

Levels of retinal IAPP are altered in Alzheimer's disease patients and correlate with vascular changes and hippocampal IAPP levels.

Islet amyloid polypeptide (IAPP) forms toxic aggregates in the brain of patients with Alzheimer's disease (AD). Whether IAPP also affects the retina in these patients is still unknown. Levels of IAPP in soluble and insoluble homogenate fractions of retina and hippocampus from AD patients and nondemented controls were analyzed using ELISA. Number of pericytes and vessel length were determined by analysis of immunostained retina and hippocampus. Insoluble retinal fractions of AD patients contained lower levels of unmodified IAPP, whereas soluble retinal fractions contained increased levels of the same. Total IAPP levels and pericyte numbers in retina mirrored corresponding variables in the hippocampus. Moreover, levels of total unmodified IAPP correlated negatively with the vessel length both in retina and hippocampus across the group and positively with pericyte numbers in retina in AD patients. Our studies indicate that changes in brain IAPP are reflected by corresponding levels in the retina. Our results also suggest modification of IAPP as an important event implicated in vascular changes associated with AD.

Plasma and Pancreatic Tissue Levels of Islet Amyloid Polypeptide in Type 1 and Type 2Diabetes: A Review

Plasma and Pancreatic Tissue Levels of Islet Amyloid Polypeptide in Type 1 and Type 2Diabetes: A Review

Autophagy defends pancreatic β cells from human islet amyloid polypeptide-induced toxicity.

Type 2 diabetes (T2D) is characterized by a deficiency in β cell mass, increased β cell apoptosis, and extracellular accumulation of islet amyloid derived from islet amyloid polypeptide (IAPP), which β cells coexpress with insulin. IAPP expression is increased in the context of insulin resistance, the major risk factor for developing T2D. Human IAPP is potentially toxic, especially as membrane-permeant oligomers, which have been observed to accumulate within β cells of patients with T2D and rodents expressing human IAPP. Here, we determined that β cell IAPP content is regulated by autophagy through p62-dependent lysosomal degradation. Induction of high levels of human IAPP in mouse β cells resulted in accumulation of this amyloidogenic protein as relatively inert fibrils within cytosolic p62-positive inclusions, which temporarily averts formation of toxic oligomers. Mice hemizygous for transgenic expression of human IAPP did not develop diabetes; however, loss of β cell-specific autophagy in these animals induced diabetes, which was attributable to accumulation of toxic human IAPP oligomers and loss of β cell mass. In human IAPP-expressing mice that lack β cell autophagy, increased oxidative damage and loss of an antioxidant-protective pathway appeared to contribute to increased β cell apoptosis. These findings indicate that autophagy/lysosomal degradation defends β cells against proteotoxicity induced by oligomerization-prone human IAPP.

High Plasma Levels of Islet Amyloid Polypeptide in Young with New-Onset of Type 1 Diabetes Mellitus

Aims/HypothesisIslet 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.ResultsPlasma 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/InterpretationPlasma 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.

インスリン非依存型糖尿病患者および境界型耐糖能異常者における膵ラ島アミロイド蛋白(IAPP/Amylin)の血中動態(第2報)

インスリン非依存型糖尿病患者および境界型耐糖能異常者における膵ラ島アミロイド蛋白(IAPP/Amylin)の血中動態(第2報)

Glucose Regulates Islet Amyloid Polypeptide Gene Transcription in a PDX1- and Calcium-dependent Manner

Islet amyloid polypeptide (IAPP) and insulin are expressed in the beta-cells of the islets of Langerhans. They are co-secreted in response to changes in glucose concentration, and their mRNA levels are also regulated by glucose. The promoters of both genes share similar cis-acting sequence elements, and both bind the homeodomain transcription factor PDX1, which plays an important role in the regulation of the insulin promoter and insulin mRNA levels by glucose. Here we examine the role of PDX1 in the regulation of the human IAPP promoter by glucose. The experiments were facilitated by the availability of a human beta-cell line (NES2Y) that lacks PDX1. NES2Y cells also lack operational K(ATP) channels, resulting in a loss of control of calcium signaling. We have previously used these cells to show that glucose regulation of the insulin gene is dependent on PDX1, but not calcium. In the mouse beta-cell line Min6, glucose (16 mm) stimulated a 3.5-4-fold increase in the activity of a -222 to +450 IAPP promoter construct compared with values observed in 0.5 mm glucose. In NES2Y cells, glucose failed to stimulate transcriptional activation of the IAPP promoter. Overexpression of PDX1 in NES2Y cells failed to reinstate glucose-responsive control of the IAPP promoter. Glucose effects on the IAPP promoter were observed only in the presence of PDX1 when normal calcium signaling was restored by overexpression of the two K(ATP) channel subunits SUR1 and Kir6.2. The importance of calcium was further emphasized by an experiment in which glucose-stimulated IAPP promoter activity was inhibited by the calcium channel blocker verapamil (50 microm). Verapamil was further shown to inhibit the stimulatory effect of glucose on IAPP mRNA levels. These results demonstrate that like the insulin promoter, glucose regulation of the IAPP promoter is dependent on the activity of PDX1, but unlike the insulin promoter, it additionally requires the activity of another, as yet uncharacterized factor(s), the activity of which is calcium-dependent.

Islet amyloid polypeptide and insulin relationship in a longitudinal study of the genetically obese (ob/ob) mouse.

Obese mice (Umeå ob/ob) and their lean litter-mates were investigated from 7 to 52 weeks of age with respect to the plasma concentration of islet amyloid polypeptide (IAPP) and insulin. Plasma levels of IAPP were highly elevated in the ob/ob mice and remained unchanged until age 33 weeks, after which a sudden significant increase occurred at age 40 weeks. The plasma concentration of insulin gradually increased from start to end and reached extremely high levels. In the lean mice, there were no age-related differences in plasma levels of IAPP and insulin, being of the same magnitude as in normal NMRI mice. The plasma IAPP/insulin molar ratio was similar in lean and obese mice until age 14 weeks. At 21 weeks, the ratio in the ob/ob mice had decreased dramatically and remained markedly (sixfold) lower than in the lean mice until the end of the study. The IAPP concentration in the pancreata of 21-week-old ob/ob mice was 25-fold higher than that in the lean mice. Immunohistochemically, a majority of the ob/ob mice displayed enlarged and more numerous pancreatic islets, compared with the lean mice, and the IAPP- and insulin-labeling intensity was equal for all animals. At the electron-microscopic level, there was an increase in the number of IAPP- and insulin-immunoreactive gold particles per whole granule area as well as per core granule area. We conclude that the dramatically increased IAPP levels in severely hyperinsulinemic ob/ob mice may be of importance for the development of insulin resistance. Further, the disproportionate secretion of IAPP and insulin in the adult obese mouse might indicate a disturbed negative feedback effect of IAPP on insulin secretory mechanisms, resulting in very high plasma insulin levels.

Islet amyloid polypeptide/amylin messenger RNA and protein expression in human insulinomas in relation to amyloid formation.

Islet amyloid polypeptide (IAPP), also named amylin, is the predominant protein component of amyloid deposits in human islet beta cell tumours of the pancreas (insulinomas). IAPP is co-produced with insulin by islet beta cells. We investigated IAPP expression in relation to insulin expression and to amyloid formation in eleven insulinomas. RNA and protein extracts were prepared from the same pieces of tumour tissue, and from specimens of two normal human pancreata. IAPP and insulin mRNA and peptide content were quantified using Northern blot analysis and radioimmunoassay (RIA) respectively. Molecular forms of IAPP immunoreactivity were analysed by reversed-phase high-performance liquid chromatography (HPLC). The presence of islet hormones and of amyloid was assessed by (immuno)histochemical staining of paraffin sections. Plasma levels of IAPP and insulin prior to tumour resection were determined by RIA. IAPP and insulin mRNA and peptide content varied widely between the tumour specimens, and there was considerable intratumour heterogeneity of peptide content. HPLC analysis indicated correct proteolytic processing of the IAPP precursor protein. Amyloid deposits were detected only in the three tumours with the highest IAPP content. In contrast to insulin, plasma levels of IAPP were not elevated in the insulinoma patients. The spectrum of hormone production by insulinomas cannot be inferred from only a few tissue sections due to intratumour heterogeneity. Expression of the IAPP and insulin genes is not coupled in insulinomas, which produce properly processed mature IAPP. In addition to IAPP overproduction, additional factors such as intracellular accumulation of IAPP are involved in amyloidogenesis in insulinomas.

Sufficiency of postprandial plasma levels of islet amyloid polypeptide for suppression of feeding in rats.

Our objective was to study whether islet amyloid polypeptide (IAPP) produces satiety by an endocrine mechanism. We used a rat model to determine whether postprandial plasma levels of IAPP are comparable to those required to inhibit feeding when IAPP is administered by continuous intravenous infusion. Food intake in rats with aortic catheters increased plasma IAPP levels from a fasting level of 10.8 +/- 0.5 pM to a peak level of 19.0 +/- 1.0 pM at 2.2 +/- 0.5 h. In rats with jugular vein and aortic catheters, the threshold intravenous dose for IAPP suppression of feeding was between 1 and 3 pmol . kg-1 . min-1. The 3 pmol . kg-1 . min-1 dose decreased 4-h intake by approximately 25% by decreasing meal frequency rather than meal size. This dose increased plasma IAPP by approximately 24 pM. These results suggest that postprandial plasma levels of IAPP are not quite sufficient to independently produce satiety.

Islet hormone secretion in pancreatic cancer patients with diabetes.

The diabetes or impaired glucose tolerance that occurs in most patients with pancreatic cancer is characterized by profound insulin resistance. Recent evidence suggests that the diabetes may result from the presence of the tumor rather than being a predisposing factor to development of the malignancy. Some islet hormones have been shown to exhibit diabetogenic effects. To investigate the potential role of these hormones in the diabetic state associated with pancreatic cancer, we measured islet hormones during fasting in pancreatic cancer patients (n = 30), patients with other malignancies (n = 43), and healthy controls (n = 25). Preoperative pancreatic cancer patients were classified as normal glucose tolerance (NGTT), impaired glucose tolerance (IGTT), non-insulin-requiring diabetes (NIRD), and insulin-requiring diabetes (IRD). Nine pancreatic cancer patients were studied after tumor removal by subtotal pancreatectomy. Some preoperative pancreatic cancer patients (n = 19), postoperative patients (n = 9), and controls (n = 8) were also studied during hyperglycemia and following glucagon injection. Fasting plasma C-peptide was elevated in NIRD pancreatic cancer patients compared to controls. Fasting levels of islet amyloid polypeptide (IAPP), glucagon, and somatostatin were elevated in NIRD and IRD patients. IAPP and glucagon, but not somatostatin, normalized following subtotal pancreatectomy. During hyperglycemia, increases in C-peptide and IAPP were seen only in controls and in NGTT and postoperative pancreatic cancer patients. After glucagon infusion, IAPP levels increased in controls and nondiabetic cancer patients; C-peptide levels increased in controls, nondiabetic patients, and NIRD. Responses of C-peptide and IAPP to glucagon normalized after pancreatectomy. During hyperglycemia, glucagon levels fell in all groups except IGTT patients and a decrease in somatostatin concentrations was seen in controls.

Differential effect of insulin treatment on islet amyloid polypeptide (amylin) and insulin gene expression in streptozotocin-induced diabetes in rats.

Islet amyloid polypeptide (IAPP) is a beta cell hormone, which forms islet amyloid in non-insulin-dependent diabetes mellitus and may oppose insulin action and release. Therefore, the previously observed relative overexpression of IAPP compared with insulin in streptozotocin-treated rats could be unfavourable if it occurs in diabetes. Using quantitative in situ hybridization, we examined whether insulin treatment affected IAPP and insulin gene expression and their ratio at day 8 and 20 after induction of streptozotocin diabetes (plasma glucose approximately 30 mM). Total islet IAPP mRNA levels were less reduced than those of insulin at both time points. Differential regulation of the two hormones was further reflected by mean IAPP mRNA levels in the remaining islet cells being unaffected by streptozotocin treatment, whereas those of insulin were reduced. At both time points, insulin treatment decreased total islet levels of IAPP and insulin mRNA even more, IAPP mRNA levels being less reduced. Mean insulin mRNA levels, but not IAPP mRNA levels, in the remaining islet cells were reduced by insulin treatment. Between time points, total islet mRNA levels were higher at day 20, while mean mRNA levels in the remaining islet cells were unchanged, suggesting that regeneration of beta cells had occurred. In contrast, insulin gene expression was the same at both time points in insulin-treated rats, suggesting that insulin impaired insulin expression. To summarize, we found that IAPP and insulin were differentially expressed in experimental diabetes and that insulin treatment inhibited insulin, but not IAPP, gene expression. It is therefore unlikely that insulin will protect against amyloid formation and metabolic perturbations which may arise as a consequence of IAPP overexpression.

The role of Langerhans islets in pancreatic ductal adenocarcinoma.

An intimate relationship between the exocrine and endocrine pancreas has been convincingly demonstrated in recent years. Animal experiments have shed some light into the complex dialog between the two tissues. This interaction is pronounced in diseases of the pancreas, especially in experimentally-induced and human pancreatic cancers. New evidence highlights the importance of intact islets in the development of exocrine pancreatic cancer. Although tumors arise from large and small ducts, invasive and malignant adenocarcinomas of ductal phenotype also derive from stem cells within islets. Development of cancer within islets explains the association between pancreatic cancer and impaired glucose tolerance or diabetes. Hence, the previous epidemiological studies suggesting that diabetes is a predisposing factor for pancreatic cancer are refuted. The available evidence suggests that pancreatic cancer in a large number of pancreatic cancer patients ultimately leads to diabetes, and that removal of the tumors improves or cures the diabetes. Both in the hamster pancreatic cancer model and in patients, the development of cancer is associated with elevated plasma levels of islet amyloid polypeptide, which may be used as a tumor marker.

Chronic infusion of islet amyloid polypeptide causes anorexia in rats.

Islet amyloid polypeptide (IAPP) is a hormonal peptide that at high doses has been shown to reduce food intake. In the present study, the dose-response effects of subcutaneous infusion of IAPP (0, 2, 7, and 25 pmol.kg-1.min-1) for 8 days on food intake and meal patterns in rats were investigated. At the end of the experiment, plasma was obtained and levels of IAPP were measured by radioimmunoassay. IAPP dose-dependently and transiently inhibited food intake. The minimal effective dose (2 pmol.kg-1.min-1) caused a small but significant (up to 14%, P < 0.01) inhibition of food intake that lasted 5 days. The highest dose administered (25 pmol.kg-1.min-1) had the greatest effect (up to 44%, P < 0.001), which lasted throughout the 8-day period. Reductions in feeding during light and dark phases occurred through a decrease in number of meals consumed rather than meal size or meal duration. IAPP also decreased body weight gain and water intake dose dependently. IAPP infusion of 2, 7, and 25 pmol.kg-1.min-1 increased plasma IAPP concentrations from a basal level of 10.3 +/- 0.7 pM to 35.1 +/- 5.4, 78.1 +/- 11.2, and 236.6 +/- 23.6 pM, respectively, values that are likely to be close to physiological and within the pathophysiological ranges. Thus IAPP may play an important physiological or pathophysiological role in control of food intake.

Non-parallelism of islet amyloid polypeptide (amylin) and insulin gene expression in rat islets following dexamethasone treatment

Islet amyloid polypeptide (IAPP), a novel islet hormone candidate, has been reported to be over-expressed relative to insulin in rats following dexamethasone treatment. In order to investigate the expression of IAPP and insulin following dexamethasone treatment of rats for 12 days, we applied in situ hybridization and immunocytochemistry, allowing us to evaluate islet changes in gene expression and morphology. Tissue concentrations of IAPP and insulin were measured by radioimmunoassay. A low dose of dexamethasone (0.2 mg/kg daily) increased the islet levels of IAPP and insulin mRNA to 249 +/- 13% and 150 +/- 24% of controls, respectively (p < 0.001 and p < 0.01). A high dose of dexamethasone (2.0 mg/kg daily) increased the islet levels of IAPP and insulin mRNA to 490 +/- 13% and 203 +/- 9% of controls, respectively (p < 0.001 and p < 0.001). The pancreatic concentration of IAPP increased more than that of insulin (p < 0.05). Morphometric analysis revealed that dexamethasone treatment induced both hyperplasia and hypertrophy of insulin cells. Changes in the cellular localization of IAPP and insulin mRNA were not observed. Thus, we conclude that the increased level of IAPP mRNA is due to both an increase at the cellular level as well as hyperplasia/hypertrophy of insulin cells. In contrast, the increased level of insulin mRNA appears to be due to hyperplasia/hypertrophy of insulin cells, since insulin gene expression decreased at the cellular level (p < 0.001 vs controls). These observations provide further evidence that IAPP and insulin gene expression are regulated in a non-parallel fashion, which may be relevant to the pathogenesis of non-insulin-dependent diabetes mellitus.