Inhibition of insulin secretion, but normal peripheral insulin sensitivity, in a patient with a malignant endocrine pancreatic tumour producing high amounts of an islet amyloid polypeptide-like molecule

RAGE binds preamyloid IAPP intermediates and mediates pancreatic β cell proteotoxicity

Islet amyloidosis is characterized by the aberrant accumulation of islet amyloid polypeptide (IAPP) in pancreatic islets, resulting in β cell toxicity, which exacerbates type 2 diabetes and islet transplant failure. It is not fully clear how IAPP induces cellular stress or how IAPP-induced toxicity can be prevented or treated. We recently defined the properties of toxic IAPP species. Here, we have identified a receptor-mediated mechanism of islet amyloidosis-induced proteotoxicity. In human diabetic pancreas and in cellular and mouse models of islet amyloidosis, increased expression of the receptor for advanced glycation endproducts (RAGE) correlated with human IAPP-induced (h-IAPP-induced) β cell and islet inflammation, toxicity, and apoptosis. RAGE selectively bound toxic intermediates, but not nontoxic forms of h-IAPP, including amyloid fibrils. The isolated extracellular ligand-binding domains of soluble RAGE (sRAGE) blocked both h-IAPP toxicity and amyloid formation. Inhibition of the interaction between h-IAPP and RAGE by sRAGE, RAGE-blocking antibodies, or genetic RAGE deletion protected pancreatic islets, β cells, and smooth muscle cells from h-IAPP-induced inflammation and metabolic dysfunction. sRAGE-treated h-IAPP Tg mice were protected from amyloid deposition, loss of β cell area, β cell inflammation, stress, apoptosis, and glucose intolerance. These findings establish RAGE as a mediator of IAPP-induced toxicity and suggest that targeting the IAPP/RAGE axis is a potential strategy to mitigate this source of β cell dysfunction in metabolic disease.

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.

Renal Effects

Amylin bound to kidney cortex in a distinctive pattern. Binding appeared specific in that it was displaceable with amylin antagonists. It was associated with activation of cyclic AMP (cAMP), and was thereby likely to represent receptor binding and activation. Amylin's principal effects at the kidney included a stimulation of plasma renin activity, reflected in aldosterone increases at quasi-physiological amylin concentrations. It was unclear whether this was a local or a systemic effect. Other renal effects in rats included a diuretic effect and a natriuretic effect. The latter was mainly driven by the diuresis, since urinary sodium concentration did not change. Amylin had a transient effect to lower plasma potassium concentration. This effect was likely to be a consequence of activation of Na+/K+-ATPase, an action shared with insulin and catecholamines. Amylin lowered plasma calcium, particularly ionized calcium, likely due to an antiresorptive effect at osteoclasts. Immunoreactive amylin was detected in the developing kidney. It appeared to have a trophic effect in kidney, and its absence resulted in renal dysgenesis. Neurons in the subfornical organ (SFO), which has a role in fluid/electrolyte homeostasis, were potently activated by amylin. The dipsogenic and renal effects of amylin may be related to effects at the SFO.

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).

Diabetes mellitus: a risk factor for pancreatic cancer?

The relationship between pancreatic cancer (PC) and diabetes is controversial. While some investigators assume that type II diabetes is a predisposition to PC, recent data argue that diabetes and altered glucose metabolism are a consequence of PC, and yet, the clinical presentation of the altered glucose metabolism in these patients varies considerably. Around 70% of patients with PC have impaired glucose tolerance (IGT) or frank diabetes. Of these, nearly 60% show an improvement of IGT or diabetes after surgery, whereas the rest show only mild or no improvement. It appears that biologically there are three types of PC: (1) PC not associated with IGT or diabetes; (2) PC associated with IGT or diabetes in which the abnormality improves postoperatively; (3) PC associated with IGT or diabetes in which the abnormality does not improve postoperatively. Based on our own studies, we suggest that the reason for impaired glucose metabolism in most patients is the alteration of islet cells either by the carcinogen directly, or by diabetogenic substances released by cancer cells. The extent of the islet alteration (i.e. focal or diffuse) may determine whether the removal of tumor alone can improve the metabolic alteration. The elucidation of the mechanism is of immense importance for providing an early tumor marker and for developing preventative or therapeutic modalities.

Islet cell tumor arising from a heterotopic pancreas in the duodenal wall with ulceration

A rare case of symptomatic islet cell tumor arising from heterotopic pancreas in the duodenum with ulceration is described. Gastrointestinal bleeding was the only sign observed in this patient. Tagged red blood cell scan, upper endoscopy, and computed tomography scan showed active bleeding ulcer from a periampullary mass. Removal of the submucosal tumor was done to prevent future re-bleeding. Histologic and immunohistochemical characterization of the tumor showed an endocrine tumor that expressed a variety of endocrine peptides.

Diabetes and its relationship to pancreatic carcinoma

INTRODUCTION

The mechanism of impaired glucose metabolism that develops in most patients with pancreatic cancer (PC) is obscure and the association between PC and diabetes is controversial. According to the published data, about 70% of patients with PC have an impaired glucose tolerance (IGT) or frank diabetes, whereas 30% do not. Up to 60% of the patients with IGT or diabetes show improvement in glucose metabolism after surgery, whereas other patients show only mild or no improvement.

AIM

To investigate our theory that there are three types of PC: 1) PC not associated with IGT or diabetes (IGT- subtype, approximately 20-30%); 2) PC associated with IGT or diabetes (IGT+ subtype, approximately 70-80%), in which the abnormality improves postoperatively (IGT+/- subtype, approximately 40-60%); or 3) PC associated with IGT or diabetes that does not improve after the tumor resection (IGT+/+ subtype, approximately 40-60%).

METHODOLOGY AND RESULTS

The review of the literature and our own experience, which is the subject of this article, suggests that the reason for impaired glucose metabolism in most patients is the alteration of islet cells, from which, in our view, cancer cells develop. There is a good possibility that the altered islet cells, and/or tumors derived from them, produce diabetogenic substances. The extent of the islet alteration (i.e., focal or diffuse) may determine whether the removal of the tumor alone can improve the metabolic alteration.

CONCLUSION

The elucidation of the mechanism is of immense importance for providing an early tumor marker and for developing preventative and therapeutic modalities.

Increased insulin secretion and glucose tolerance in mice lacking islet amyloid polypeptide (amylin)

Islet amyloid polypeptide (IAPP or amylin) is costored and cosecreted with insulin and may regulate insulin secretion and blood glucose handling. However, the role and importance of endogenous IAPP in the regulation of insulin release and glucose homeostasis have been controversial. Here we report on the generation and phenotypic analysis of IAPP-deficient mice. These mice have normal, or near to normal, basal levels of circulating insulin and glucose. However, following glucose administration, IAPP-deficient males presented increased insulin responses paralleled with a more rapid blood glucose elimination compared to wild-type controls. Blood glucose elimination was also found to be enhanced in IAPP-deficient females, but the insulin response in this gender did not differ from controls. In a transgenic rescue experiment, using an insulin-promoter human-IAPP fusion gene, insulin responses and blood glucose elimination were reversed in IAPP-deficient males, whereas the female phenotype appeared unaffected. Our results provide the first firm evidence of a physiological role for endogenous IAPP and indicate that IAPP, apparently in a gender-dependent manner, limits the degree of glucose-induced insulin secretion and the rate of blood glucose elimination.

Expression of human islet amyloid polypeptide/amylin impairs insulin secretion in mouse pancreatic beta cells

Non-insulin-dependent diabetes mellitus (NIDDM) is associated histopathologically with islet amyloid deposits of which a major component is islet amyloid polypeptide (IAPP)/amylin. We examined whether endogenous IAPP controls insulin secretion via a local effect within pancreatic islets and whether overexpression of this peptide contributes to pancreatic beta-cell dysfunction in this disease. Transgenic mice expressing human IAPP in pancreatic beta cell were used in this study. Human IAPP expression did not influence the mouse proinsulin mRNA level and insulin content. Glucose-induced insulin secretion was decreased in the isolated pancreatic islets of transgenic mice. MIN6, a glucose-responsive pancreatic beta-cell line, was transfected with human IAPP cDNA by a lipofectin method. Human IAPP expression was confirmed by RNA blot and immunohistochemical analysis. In two transfectants expressing the largest amount of human IAPP, insulin secretion was increased in response to glucose stimulation; however, the magnitude of the insulin response in cells transfected with human IAPP was smaller than in control clones. Insulin content was not influenced by the expression. We conclude that endogenous IAPP inhibits insulin secretion via an autocrine effect within pancreatic islets, and that the impaired insulin secretion in this disease may be partly caused by overexpression of IAPP.

The pharmacologic approach to the treatment of obesity

Obesity is a major risk factor for morbidity and mortality, and a series of pharmacologic approaches are available for helping to manage the problem. Obesity is caused by an imbalance between caloric intake and energy expenditure, which is influenced by both environmental and genetic factors. Pharmacologic treatments include anorexigenic agents, which fall into two broad categories: those that act via brain catecholamine pathways and those that act via serotonin pathways. The most recent oral agents approved are dexfenfluramine, which is currently being marketed, and sibutramine. Both agents inhibit the control reuptake of serotonin but in addition may have effects on thermogenesis. Under investigation are agents that increase energy expenditure: the beta 3-adrenergic receptor agonists and drugs that prevent the intestinal absorption of free fatty acids and cholesterol. In development are innovative approaches to influence leptin and its receptors, various obesity genes, and biologic substances thought to influence satiety (neuropeptide Y, enterostatin, cholecystokinin, bombesin, and amylin). Obesity has now become a major target for drug development not only for affecting obesity per se but also for managing and preventing comorbid conditions such as diabetes and cardiovascular disease.

On-line competitive immunoassay for insulin based on capillary electrophoresis with laser-induced fluorescence detection

An on-line competitive immunoassay for insulin has been developed and applied to monitoring insulin concentration in a flowing stream. In the assay, solutions of fluorescein-labeled insulin (FITC-insulin), monoclonal anti-insulin, and sample containing insulin are pumped into a cross where they begin to mix. The mixture flows through a fused silica reactor capillary to a flow-gated interface. During transfer to the interface, insulin and FITC-insulin compete to form a complex with the antibody. At the interface, a plug of the mixture is injected into a separation capillary, where the bound and free FITC-insulin are separated and detected by capillary electrophoresis with laser-induced fluorescence detection. The amount of bound FITC-insulin, amount of free FITC-insulin, or bound/free ratio can be used to quantify insulin concentration. Typical relative standard deviations of bound over free ratio are 5%. The detection limit of the immunoassay in the on-line mode is < 0.3 nM. Each separation requires as little as 3 s, and over 1600 consecutive assays can be acquired with no need to rinse the separation capillary. Thus, the system can be used to monitor insulin in a flowing stream for flow injection analysis or for sensor-like monitoring. Dilution and zone broadening during transfer of sample to the interface limit the response time of the on-line system to about 25 s. As a demonstration of the on-line immunoassay, the insulin content of single islets of Langerhans was determined by flow injection analysis.

Amylin stimulates plasma renin concentration in humans

Although insulin resistance and hypertension are commonly associated, the underlying cause for this association remains unknown. Plasma concentrations of the recently described hormone amylin, which is cosecreted with insulin by the pancreatic beta cell, are reported to be elevated in various states of insulin resistance, including hypertension and obesity. Preliminary studies by our group have suggested that there are amylin binding sites in the kidney. In nine healthy humans an infusion of human amylin that resulted in steady state plasma amylin levels in the subnanomolar range led to significant increases in plasma renin and aldosterone concentrations. These changes occurred in the absence of significant changes in plasma electrolytes, catecholamines, vasopressin, total renin, or osmolality. Diastolic pressure at 30 minutes and plasma glucose at 60 minutes rose modestly. Since amylin has both metabolic and renal actions, this peptide may be an important link between hypertension, insulin resistance, and the renin-angiotensin system.

Pancreatic islet amyloid formation in patients with noninsulin-dependent diabetes mellitus. Implication for therapeutic strategy

Islet amyloid polypeptide (IAPP or amylin) is the main component of pancreatic islet amyloid found in the vast majority of patients with noninsulin-dependent (Type-2) diabetes mellitus (NIDDM). IAPP may also act as a hormone that antagonizes the effects of insulin on peripheral tissues, but the results with IAPP overproducing transgenic mice and other recent findings indicate that IAPP overproduction is unlikely to induce peripheral insulin resistance in NIDDM. However, IAPP may contribute to the progression of NIDDM by impairing beta-cell function via islet amyloid formation. This may be initiated by locally elevated IAPP concentrations, induced by insulin-resistance-associated beta-cell hyperactivity. In order to improve therapeutic results, we propose strategies to inhibit IAPP production and islet amyloid formation during the pathogenesis of NIDDM.

Islet amyloid polypeptide (IAPP) in patients with neuroendocrine tumours

Although IAPP was first discovered and isolated from amyloid deposits in an endocrine pancreatic tumour (EPT), surprisingly few reports have investigated the potential use of IAPP as a marker for neuroendocrine tumour growth. In this study we present results from plasma measurements of IAPP in 102 patients with neuroendocrine tumours. Four of 35 patients (11%) with midgut carcinoid tumours, but none of the patients (4 and 5, respectively) with lung carcinoids or with rectal carcinoids displayed elevated plasma levels of IAPP. Five of 31 patients (16%) with sporadic EPT and 3 of 27 patients (11%) with EPT and multiple endocrine neoplasia type 1 syndrome disclosed elevated IAPP levels. Within the different syndromes, 1/11 individuals with insulinoma, 2/16 with gastrinoma, 0/2 with glucagonoma, 0/3 with VIPoma and 5/26 with non-functioning tumours showed elevated plasma levels of IAPP. In two patients, the plasma IAPP levels were extremely elevated. These patients also exhibited altered glucose homeostasis. In response to a standardised mixed meal test, IAPP increased in parallel to the insulin, pancreatic polypeptide, gastrin and glucose responses. In MEN1 patients with hypercalcaemia due to increased secretion of parathyroid hormone, the plasma levels of IAPP were significantly higher before than after surgical removal of the parathyroid adenomas. However in normocalcaemic patients, no correlation between the blood calcium and plasma IAPP levels was found. Immunocytochemical staining of tumour tissue showed that 9/13 (69%) of insulin producing tumours, 4/14 (29%) of non-functioning tumours and 1/9 (11%) of gastrin producing tumours were IAPP immunoreactive. Amyloid deposits were always IAPP immunoreactive. In conclusion, increased circulating levels of IAPP occurred in 12% of 102 patients with neuroendocrine tumours. In 2 patients with extremely elevated plasma levels of IAPP, effects on glucose homeostasis were recorded. Thus, IAPP may be useful as an additional marker for neuroendocrine tumour growth in selected cases.