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Evidence of Cosecretion of Islet Amyloid Polypeptide and Insulin by -Cells
Abstract
Islet amyloid polypeptide (IAPP) has been identified as the major constituent of the pancreatic amyloid of non-insulin-dependent diabetes mellitus (NIDDM) and is also present in normal beta-cell secretory granules. To determine whether IAPP is a pancreatic secretory product, we measured the quantity of IAPP-like immunoreactivity (IAPP-LI), insulin, and glucagon released into 5 ml of incubation medium during a 2-h incubation of monolayer cultures (n = 5) of neonatal (3- to 5-day-old) Sprague-Dawley rat pancreases under three conditions: 1.67 mM glucose, 16.7 mM glucose, and 16.7 mM glucose plus 10 mM arginine and 0.1 mM isobutylmethylxanthine (IBMX). The quantity of IAPP-LI, insulin, and glucagon in the cell extract was also determined. Mean +/- SE IAPP-LI in the incubation medium increased from 0.041 +/- 0.003 pmol in 1.67 mM glucose to 0.168 +/- 0.029 pmol in 16.7 mM glucose (P less than 0.05) and 1.02 +/- 0.06 pmol in 16.7 mM glucose plus arginine and IBMX (P less than 0.05 vs. 1.67 or 16.7 mM glucose). Insulin secretion increased similarly from 4.34 +/- 0.27 to 20.2 +/- 0.6 pmol (P less than 0.05) and then to 135 +/- 5 pmol (P less than 0.05 vs. 1.67 or 16.7 mM glucose). Glucagon release tended to decrease with the increase in glucose concentration (0.39 +/- 0.01 vs. 0.33 +/- 0.02 pmol, P less than 0.1), whereas with the addition of arginine and IBMX to high glucose, glucagon release increased to 1.32 +/- 0.03 pmol (P less than 0.05 vs. 1.67 or 16.7 mM glucose).(ABSTRACT TRUNCATED AT 250 WORDS)
... Type 2 diabetes in humans is characterized by islet β-cell secretory dysfunction and deposition of islet amyloid (Hull et al., 2004;Kahn et al., 2006). These islet amyloid deposits contain as their unique peptide component islet amyloid polypeptide (IAPP), which is normally co-secreted with insulin and is capable of forming fibrils that are cytotoxic to β-cells (Cooper et al., 1988;Kahn et al., 1990;Westermark et al., 1987). In animal models frequently used to study diabetes (e.g. ...
... Given that we included mIAPP islets with no potential to form amyloid, we were able to assess the independent role of glucose to alter gene expression and thus delineate genes that would appear to be amyloid specific. This approach using mouse islets is important since human islets normally produce amyloidogenic hIAPP, which is co-secreted with insulin, and have the propensity to form amyloid (Kahn et al., 1990;Westermark et al., 1990). Thus, using only human islets would not allow for the discernment of the effect of amyloid from that of increased glucose per se. ...
Aggregation of islet amyloid polypeptide (IAPP) into islet amyloid results in β-cell toxicity in human type 2 diabetes. To determine the effect of islet amyloid formation on gene expression, we performed ribonucleic acid (RNA) sequencing (RNA-seq) analysis using cultured islets from either wild-type mice (mIAPP), which are not amyloid prone, or mice that express human IAPP (hIAPP), which develop amyloid. Comparing mIAPP and hIAPP islets, 5025 genes were differentially regulated (2439 upregulated and 2586 downregulated). When considering gene sets (reactomes), 248 and 52 pathways were up- and downregulated, respectively. Of the top 100 genes upregulated under two conditions of amyloid formation, seven were common. Of these seven genes, only steroidogenic acute regulatory protein (Star) demonstrated no effect of glucose per se to modify its expression. We confirmed this differential gene expression using quantitative reverse transcription polymerase chain reaction (qRT-PCR) and also demonstrated the presence of STAR protein in islets containing amyloid. Furthermore, Star is a part of reactomes representing metabolism, metabolism of lipids, metabolism of steroid hormones, metabolism of steroids and pregnenolone biosynthesis. Thus, examining gene expression that is differentially regulated by islet amyloid has the ability to identify new molecules involved in islet physiology and pathology applicable to type 2 diabetes.
... Islet amyloid polypeptide (IAPP, amylin), a polypeptide hormone of [49] amino acid residues that is released by islet beta cells [50], was identified, isolated, and given the name from islet tumor cells. Under the influence of glucose and other secretagogues, it is mostly deposited in the halo of the secretory granule and secreted in pulses [51]. ...
This literature presents a comprehensive overview of the application of CRISPR-based gene editing technology in the treatment of diabetes mellitus (DM). The introduction highlights the significance of DM as one of the oldest human diseases and the need for effective control to prevent potential consequences. It emphasizes the limitations of conventional medications for hyperglycemia and the challenges in achieving optimal glucose concentrations and minimizing long-term consequences. The abstract then delves into the advancements in CRISPR technology, discussing various delivery methods for the CRISPR-Cas complex, including non-viral vectors, viral vectors, and nanocarriers. The use of CRISPR-Cpf1 as an alternative to Cas9 is explored, highlighting its advantages and functionality. The abstract further explores the potential of CRISPR gene therapy and nanocarriers in treating DM, particularly targeting the NLRP3 inflammasome and downregulating the DPP-4 enzyme. Liposomal particles and lecithin nano-liposomal particles are discussed as efficient delivery systems for CRISPR/Cas9, with potential applications in T2DM treatment. The role of islet amyloid polypeptide (IAPP) in T2DM and its study using CRISPR Cas9-based gene editing technology is also presented. Overall, this abstract provides a comprehensive overview of the current advancements and potential applications of CRISPR technology in the treatment of DM.
... Islet amyloid deposits are present in the majority of individuals with T2D, where they are associated with islet inflammation, decreased bcell mass and increased b-cell death [3e6]. Islet amyloidosis occurs via aggregation of human islet amyloid polypeptide (hIAPP), a b-cell secretory product that is co-secreted with insulin [7,8]. In contrast to hIAPP, rodent IAPP (rIAPP) does not aggregate to form amyloid [8,9], so mouse models with b-cell expression of hIAPP have been developed to model islet amyloidosis in T2D [10,11]. ...
Objective
Aggregation of human islet amyloid polypeptide (hIAPP), a β-cell secretory product, leads to islet amyloid deposition, islet inflammation and β-cell loss in type 2 diabetes (T2D), but the mechanisms that underlie this process are incompletely understood. Receptor interacting protein kinase 3 (RIPK3) is a pro-death signaling molecule that has recently been implicated in amyloid-associated brain pathology and β-cell cytotoxicity. Here, we evaluated the role of RIPK3 in amyloid-induced β-cell loss using a humanized mouse model of T2D that expresses hIAPP and is prone to islet amyloid formation.
Methods
We quantified amyloid deposition, cell death and caspase 3/7 activity in islets isolated from WT, Ripk3−/−, hIAPP and hIAPP; Ripk3−/− mice in real time, and evaluated hIAPP-stimulated inflammation in WT and Ripk3−/− bone marrow derived macrophages (BMDMs) in vitro. We also characterized the role of RIPK3 in glucose stimulated insulin secretion (GSIS) in vitro and in vivo. Finally, we examined the role of RIPK3 in high fat diet (HFD)-induced islet amyloid deposition, β-cell loss and glucose homeostasis in vivo.
Results
We found that amyloid-prone hIAPP mouse islets exhibited increased cell death and caspase 3/7 activity compared to amyloid-free WT islets in vitro, and this was associated with increased RIPK3 expression. hIAPP; Ripk3−/− islets were protected from amyloid-induced cell death compared to hIAPP islets in vitro, although amyloid deposition and caspase 3/7 activity were not different between genotypes. We observed that macrophages are a source of Ripk3 expression in isolated islets, and that Ripk3−/− BMDMs were protected from hIAPP-stimulated inflammatory gene expression (Tnf, Il1b, Nos2). Following 52 weeks of HFD feeding, islet amyloid-prone hIAPP mice exhibited impaired glucose tolerance and decreased β-cell area compared to WT mice in vivo, whereas hIAPP; Ripk3−/− mice were protected from these impairments.
Conclusions
In conclusion, loss of RIPK3 protects from amyloid-induced inflammation and islet cell death in vitro and amyloid-induced β-cell loss and glucose intolerance in vivo. We propose that therapies targeting RIPK3 may reduce islet inflammation and β-cell loss and improve glucose homeostasis in the pathogenesis of T2D.
... Islet amyloid deposits, comprised of aggregated islet amyloid polypeptide (IAPP), are observed in over 90% of individuals with T2D (Cooper et al., 1987;Hull et al., 2004;Westermark et al., 1987). IAPP is a 37-residue peptide hormone that is synthesized in β-cells and is cosecreted with insulin (Kahn et al., 1990). Unlike IAPP in species such as mice and rats, human IAPP is amyloidogenic and forms fibrillar amyloid deposits (Betsholtz et al., 1989;Cao et al., 2010). ...
Type 2 diabetes (T2D) results from insulin secretory dysfunction arising in part from the loss of pancreatic islet β‐cells. Several factors contribute to β‐cell loss, including islet amyloid formation, which is observed in over 90% of individuals with T2D. The amyloid is comprised of human islet amyloid polypeptide (hIAPP). Here we provide evidence that early in aggregation, hIAPP forms toxic oligomers prior to formation of amyloid fibrils. The toxic oligomers contain α‐sheet secondary structure, a nonstandard secondary structure associated with toxic oligomers in other amyloid diseases. De novo, synthetic α‐sheet compounds designed to be nontoxic and complementary to the α‐sheet structure in the toxic oligomers inhibit hIAPP aggregation and neutralize oligomer‐mediated cytotoxicity in cell‐based assays. In vivo administration of an α‐sheet design to mice for 4 weeks revealed no evidence of toxicity nor did it elicit an immune response. Furthermore, the α‐sheet designs reduced endogenous islet amyloid formation and mitigation of amyloid‐associated β‐cell loss in cultured islets isolated from an hIAPP transgenic mouse model of islet amyloidosis. Characterization of the involvement of α‐sheet in early aggregation of hIAPP and oligomer toxicity contributes to elucidation of the molecular mechanisms underlying amyloid‐associated β‐cell loss.
... 4 But not all proteinopathies concern the brain; diabetes type 2 is associated with accumulation in pancreas of amyloid aggregates formed by amylin or human amyloid polypeptide (IAPP), 5 a peptide hormone that is normally co-released with insulin. [6][7][8] Table 1 lists the most common proteinopathies that are associated with degenerative disorders. While most of them involve formation of amyloid aggregates, some others do not: cataract disease is thought to involve non-amyloid aggregation of human lens crystallins, which figure among the most stable proteins in the human body. ...
Metal ions have been implicated in several proteinopathies associated to degenerative and neurodegenerative diseases. While the molecular mechanisms for protein aggregation are still under investigation, recent findings from CryoEM point...
... We have also reported that calcitonin receptor (Calcr) in the medial preoptic area (MPOA) regulate both contact-seeking under social isolation and affiliative contacts under regrouping, while amylin-a Calcr ligand-specifically regulates contact-seeking behaviors (Fukumitsu et al., 2022). Amylin was originally identified as a peptide present in pancreatic B cells consecrated with insulin after food intake (Kahn et al., 1990), that induces a sensation of satiation via binding to amylin receptor complexes consisting of Calcr and RAMP1-3 (Hay et al., 2015). Previously, we used adult female mice as they are more sensitive to social isolation (Martin and Brown, 2010;Matsuda et al., 2018;Palanza, 2001). ...
In many mammalian species, females exhibit higher sociability and gregariousness than males, presumably due to the benefit of group living for maternal care. We have previously reported that adult female mice exhibit contact-seeking behaviors upon acute social isolation via amylin-calcitonin receptor (Calcr) signaling in the medial preoptic area (MPOA). In this study, we examined the sex differences in the behavioral responses to acute social isolation and reunion, and the levels of amylin and Calcr expression in the MPOA. We found that male mice exhibited significantly less contact-seeking upon social isolation. Upon reunion, male mice contacted each other to a similar extent as females, but their interactions were more aggressive and less affiliative compared with females. While Calcr-expressing neurons were activated during social contacts in males as in females, the amylin and Calcr expression were significantly lower in males than in females. Together with our previous findings, these findings suggested that the lower expression of both amylin and Calcr may explain the lower contact-seeking and social affiliation of male mice.
... Human islet amyloid polypeptide (hIAPP, amylin) is co-secreted with insulin in the secretory granule of the pancreatic β-cells in response to blood glucose levels [1][2][3]. Under pathological conditions, the peptide is disturbed to rapidly form amyloid with rich β-sheet structures, causing the death of pancreatic β-cells [4,5]. ...
Human islet amyloid polypeptide (hIAPP) is associated with the pathology of Type II diabetes (T2DM) due to its misfolding and amyloid deposition. The peptide is widely concerned as a potential drug target, and the prevention of hIAPP fibrillation is a rational therapeutic strategy for T2DM. Platinum complexes are promising anticancer agents with good biocompatibility, they can resist the aggregation of amyloid peptides, while the effects of oxaliplatin and carboplatin on hIAPP fibrillation are unknown. In the present work, we selected the two platinum drugs to reveal their inhibition and disaggregation against hIAPP fibrillation by various biophysical methods. The two complexes impeded hIAPP fibril formation and dispersed the aggregates into small oligomers and most monomers. They also reduced peptides oligomerization and promoted rat insulinoma β-cells viability. They bound to hIAPP mainly through metal coordination and hydrophobic interactions. Moreover, oxaliplatin showed better inhibition and regulation on peptides aggregation and cytotoxicity than carboplatin. This work is of important biomedical values for clinical platinum drugs against T2DM and other amyloidosis related diseases.
... How Iron leaves the β cells remains in controversy; ferroportin/Ireg 1(FPN1, SLC40A1) thus far remains the only exporter for iron believed to exist in our knowledge [47], as well as islets demonstrate markedly low immunoreactivity with regards to this transporter [48] despite expression of hephaestin by them. This specific protein is implicated for the stabilization of the ferroportin, besides induction of its internalization [49], hence pointed to a positive feedback mode for Iron control at the time of glucose stimulated insulin secretion (GSIS) that gets modulated by ferroportin regulation [50]. ...
Iron constitutes an essential element that is implicated innumerous physiological functions. In the context of the pancreatic β cells, they act as components of the Fe-S cluster proteins, which are a must for the appropriate insulin generation and processing. As far as mitochondria are concerned , in the form of a constituent of the respiratory chain it aids in the generation of ATP along with Reactive oxygen species(ROS),that result in induction of β cells depolarization that causes potentiation of insulin liberation that is calcium based .It is of great importance that a marked fiinetuning gets established with regards to the iron cellular amounts to guarantee normal provision of Iron along with avoidance of iron overload. Actually, in view of the great reaction with oxygen in addition to the generation of free radicals , iron overload might result in Oxidative injury of cells that possess susceptibility to this situations in view of the normal escalation of ROS development besides lesser availability of antioxidant enzymes action .Thus here we conducted a systematic review utilizing usual search engine utilizing the MeSH; iron metabolism; DM; haemochromatosis; thallasemia; Alzheimer's ;Parkinson's disease ; Friedrich's ataxia; Iron homeostasis; Iron binding protein; transferrin bound iron(TBI); non TBINTBI); Divalentmetal transporter I(DMT1); ferroportin; islet amyloid polypeptide; zinc transporter ZIP 14; Chaperone proteins-poly CR binding proteins(PCBPs); mitoferrin(Mfrn); Fe-S clusters-enzyme CDKAL1; hepcidin; hephaestin; frataxin ; labile iron pool (LIP); ABCT7; PDX1;MafA; PHD; MAMs; Miner 1;gestational DM; ferroptosis; ferroportin; iron overload &treatment ;toxicity in brain, GIT; from 1980 till 2022 till date.We found a total of 4500 articles out of which we selected 135 articles for this review. No meta-analysis was done. Main aim of this review was to get a better insight in mode of iron homeostasis in β cells, with mode of changed in this event in their damage. How abnormal iron storage/chaperon proteins might cause diabetes.
... How Iron leaves the β cells remains in controversy; ferroportin/Ireg 1(FPN1, SLC40A1) thus far remains the only exporter for iron believed to exist in our knowledge [47], as well as islets demonstrate markedly low immunoreactivity with regards to this transporter [48] despite expression of hephaestin by them. This specific protein is implicated for the stabilization of the ferroportin, besides induction of its internalization [49], hence pointed to a positive feedback mode for Iron control at the time of glucose stimulated insulin secretion (GSIS) that gets modulated by ferroportin regulation [50]. ...
Iron constitutes an essential element that is implicated innumerous physiological functions. In the context of the pancreatic β cells, they act as components of the Fe –S cluster proteins, which are a must for the appropriate insulin generation and processing. As far as mitochondria are concerned , in the form of a constituent of the respiratory chain it aids in the generation of ATP along with Reactive oxygen species(ROS),that result in induction of β cells depolarization that causes potentiation of insulin liberation that is calcium based .It is of great importance that a marked fiine tuning gets established with regards to the iron cellular amounts to guarantee normal provision of Iron along with avoidance of iron overload. Actually, in view of the great reaction with oxygen in addition to the generation of free radicals , iron overload might result in Oxidative injury of cells that possess susceptibility to this situations in view of the normal escalation of ROS development besides lesser availability of antioxidant enzymes action .Thus here we conducted a systematic review utilizing usual search engine utilizing the MeSH; iron metabolism; DM; haemochromatosis; thallasemia; Alzheimer’s ;Parkinson’s disease ; Friedrich’s ataxia; Iron homeostasis; Iron binding protein; transferrin bound iron(TBI); non TBINTBI); Divalentmetal transporter I(DMT1); ferroportin; islet amyloid polypeptide; zinc transporter ZIP 14; Chaperone proteins- poly CR binding proteins(PCBPs); mitoferrin(Mfrn); Fe-S clusters - enzyme CDKAL1; hepcidin; hephaestin; frataxin ; labile iron pool (LIP); ABCT7; PDX1;MafA; PHD; MAMs; Miner 1;gestational DM; ferroptosis; ferroportin; iron overload &treatment ;toxicity in brain, GIT; from 1980 till 2022 till date. We found a total of 4500 articles out of which we selected 135 articles for this review. No meta-analysis was done. Main aim of this review was to get a better insight in mode of iron homeostasis in β cells, with mode of changed in this event in their damage. How abnormal iron storage/chaperon proteins might cause diabetes.
... In mammals, the genes for IAPP and CGRP are located on chromosomes 12 and 11, respectively, but they probably are the result of a duplication of an ancestral gene. Amylin is mainly produced by pancreatic B cells [14,24,33] where it is co-stored in the same secretory vesicles as insulin [11,15,16,19,29]. It is also produced by various endocrine/paracrine cells of gastrointestinal mucosa [9,21,23,26,30,31]. ...
Immunohistochemical studies were conducted on rat brainstem using a specific polyclonal antiserum against the COOH-terminal (25-37) of human amylin. Amylin-immunoreactive cell bodies were observed in the vestibular, cochlear, trapezoid, and inner cerebellar nuclei and in the mesencephalic nucleus of trigeminal nerve. Positive cell bodies were also found in lateral, gigantocellular and magnocellular reticular nuclei. Numerous amylin-immunoreactive nerve fibers were shown in the trigeminal spinal tract, in the solitary area and in the area postrema. Amylin-immunoreactive cell bodies were often surrounded by a network of tyrosine hydroxylase-immunoreactive nerve fibers. These results provide morphologic evidence that amylin may play a role in some discrete sensory functions.
... glucose metabolism involving intracellular calcium signals has been reported to stimulate amylin expression and release in b-cells. amylin and insulin genes were not co-regulated in cultured human pancreatic islets (13,35,36,48,49). The third hypothesis is that amylin and insulin were potentiated by camP in pancreatic beta-cells. ...
Amylin or islet amyloid polypeptide (IAPP) is a peptide synthesized and secreted with insulin by the pancreatic β-cells. A role for amylin in the pathogenesis of type 2 diabetes (T2D) by causing insulin resistance or inhibiting insulin synthesis and secretion has been suggested by in vitro and in vivo studies. These studies are consistent with the effect of endogenous amylin on pancreatic βcells to modulate and/or restrain insulin secretion. Here, we reported the correlation between amylin and insulin in rat insulinoma INS-1E cells by treating 2-deoxy-D-glucose (2-DG) and/or mannose. Cell viability was not affected by 24 h treatment with 2-DG and/or mannose, but it was significantly decreased by 48 h treatment with 5 and 10 mM 2-DG. in the 24 h treatment, the synthesis of insulin in the cells and the secretion of insulin into the media showed a significant inverse association. in the 48-h treatment, amylin synthesis vs. the secretion and insulin synthesis vs. the secretion showed a significant inverse relation. The synthesis of amylin vs. insulin and the secretion of amylin vs. insulin showed a significant inverse relationship. The p-ERK, antioxidant enzymes (Cu/Zn-superoxide dismutase (SOD), Mn-SOD, and catalase), and endoplasmic reticulum (ER) stress markers (cleaved caspase-12, CHOP, p-SAPK/JNK, and BiP/GRP78) were significantly increased or decreased by the 24 h and 48 h treatments. These data suggest the relative correlation to the synthesis of amylin by cells vs. the secretion into the media, the synthesis of amylin vs. insulin, and the secretion of amylin vs. insulin under 2-DG and/or mannose in rat insulinoma INS-1E cells. Therefore, these results can provide primary data for the hypothesis that the amylin-insulin relationships may be involved with the human amylin toxicity in pancreatic beta cells.
... Of note, IAPP is a hormone co-secreted by β-cells along with insulin in response to nutrient stimuli [59], and both hormones regulate glucose metabolism in a tightly coordinated manner [60]. Lomasney et al. [58] presented a microfluidic device provided with a two-color detection scheme for on-line measurement of rapid changes in insulin and IAPP in response to glucose through a continuous mixing of fluorescent-labeled antibodies with both peptides secreted by the islet pool and allowing their detection with an inverted fluorescent microscope. ...
Diabetes mellitus is a significant public health problem worldwide. It encompasses a group of chronic disorders characterized by hyperglycemia, resulting from pancreatic islet dysfunction or as a consequence of insulin-producing β-cell death. Organ-on-a-chip platforms have emerged as technological systems combining cell biology, engineering, and biomaterial technological advances with microfluidics to recapitulate a specific organ’s physiological or pathophysiological environment. These devices offer a novel model for the screening of pharmaceutical agents and to study a particular disease. In the field of diabetes, a variety of microfluidic devices have been introduced to recreate native islet microenvironments and to understand pancreatic β-cell kinetics in vitro. This kind of platforms has been shown fundamental for the study of the islet function and to assess the quality of these islets for subsequent in vivo transplantation. However, islet physiological systems are still limited compared to other organs and tissues, evidencing the difficulty to study this “organ” and the need for further technological advances. In this review, we summarize the current state of islet-on-a-chip platforms that have been developed so far. We recapitulate the most relevant studies involving pancreatic islets and microfluidics, focusing on the molecular and cellular-scale activities that underlie pancreatic β-cell function.
... Pro-amylin is processed by cleavage at basic residue pairs at both its amino and carboxyl termini with prohormone convertase 1/3 and prohormone convertase 2, and its C-terminus is amidated by carboxypeptidase E and peptidylglycine alpha-amidating monooxygenase 35 . Mature amylin is secreted along with insulin, which is stored in the same granules 36 . The molecular mechanisms that result in refolding of the peptide to convert it from a normally soluble monomer into insoluble fibrils have not been identified. ...
The etiology of type 2 diabetes is multifactorial, in which environmental and genetic factors are involved to varying degrees. This suggests that its pathophysiology may vary depending on the subjects. 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 conduct 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 mechanism 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 may change dynamically depending on the glucose metabolic state. However, it is possible that the numbers of islet cell itself 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 indicate that pathological changes of the islets can be different in each subject with type 2 diabetes and reflect each pathophysiology, which is useful in establishing further subclassifications and developing tailor‐made therapies for type 2 diabetes.
... Amylin is another feeding-related peptide that may serve as a link between fluid intake and motivated behavior. Amylin is produced both in the pancreas [122], where it is co-secreted with insulin from beta cells [123,124], and in the brain [125][126][127]. A robust body of literature shows that central or peripheral administration of amylin or amylin agonists reduces food intake by enhancing satiation, and in turn reduces body weight [128][129][130][131][132][133]. ...
Maintaining fluid balance is critical for life. The central components that control fluid intake are only partly understood. This contribution to the collection of papers highlighting work by members of the Society for the Study of Ingestive Behavior focuses on the role that dopamine has on fluid intake and describes the roles that various bioregulators can have on thirst and sodium appetite by influencing dopamine systems in the brain. The goal of the review is to highlight areas in need of more research and to propose a framework to guide that research. We hope that this framework will inspire researchers in the field to investigate these interesting questions in order to form a more complete understanding of how fluid intake is controlled.
... Because amylin is co-secreted with insulin, 11 conditions with insulin dysregulation, such as insulin resistance and type 2 diabetes, may increase the amount of amylin crossing from blood to the central nervous system. High circulating amylin levels in plasma and cerebrospinal fluid (CSF) 12 could increase the risk for AD. ...
Introduction:
This study assessed the hypothesis that circulating human amylin (amyloid-forming) cross-seeds with amyloid beta (Aβ) in early Alzheimer's disease (AD).
Methods:
Evidence of amylin-AD pathology interaction was tested in brains of 31 familial AD mutation carriers and 20 cognitively unaffected individuals, in cerebrospinal fluid (CSF) (98 diseased and 117 control samples) and in genetic databases. For functional testing, we genetically manipulated amylin secretion in APP/PS1 and non-APP/PS1 rats.
Results:
Amylin-Aβ cross-seeding was identified in AD brains. High CSF amylin levels were associated with decreased CSF Aβ42 concentrations. AD risk and amylin gene are not correlated. Suppressed amylin secretion protected APP/PS1 rats against AD-associated effects. In contrast, hypersecretion or intravenous injection of human amylin in APP/PS1 rats exacerbated AD-like pathology through disruption of CSF-brain Aβ exchange and amylin-Aβ cross-seeding.
Discussion:
These findings strengthened the hypothesis of circulating amylin-AD interaction and suggest that modulation of blood amylin levels may alter Aβ-related pathology/symptoms.
... Amylin (also known as islet amyloid polypeptide -IAPP) is a peptide hormone co-secreted with insulin by the pancreatic β-cell (1,2). Amylin display several physiologic and pharmacologic roles such as control of appetite, gastric emptying, restoring leptin sensitivity, regulation of glucagon secretion, among others (3)(4)(5)(6). ...
Since the discovery of amylin its use has been discouraged by the inadequacy of the protocol involving multiple injections in addition to insulin. While a combined fixed-dose formulation is thus highly desirable, it has long been limited due to incompatibility as historically documented. We have investigated the compatibility of regular and fast-acting insulin analogues (Aspart, Asp B28 , and LisPro, Lys B28 Pro B29 ) with the amylin analogue pramlintide. Insulin interacts with pramlintide, forming heterodimers as probed by electrospray ionization - ion mobility spectrometry-mass spectrometry. While their interaction is likely to delay the amyloid aggregation of pramlintide in phosphate-buffered solution pH 7.0, they do not prevent aggregation at this condition. At acidic sodium acetate solution pH 5.0, combination of pramlintide and the fast-acting insulin analogues become stable against amyloid aggregation. The co-formulated product at high concentration of both pramlintide (600 μg/mL,150 μM) and LisPro insulin (50 IU/mL, 300 μM) showed also stability against amyloid aggregation. These data indicate a potential for the development of a co-formulation of fast-acting LisPro insulin with pramlintide, which could bring benefits for the combined therapy.
Abbreviations
IAPP, islet amyloid polypeptide;
ESI-IMS-MS, Electrospray Ionization–Ion Mobility Spectrometry–Mass Spectrometry.
... This study shows that quercetin is one of the major active compounds of the ethanolic extract that increases amylin and insulin levels in the brain tissue and improves spatial learning and memory in MWM test compared with diabetic groups. The synthesis and secretion of amylin and insulin is together from the pancreatic β-cells, which are defective in diabetic patients (Kahn et al., 1990). According to these findings, ...
Diabetes mellitus is a metabolic defect with many complications for the patients. Deaths due to diabetes and its complications are increasing, and one of the most serious consequences are the neurological disorders. Chemical treatments have irreversible side effect and therefore the aim of this study is to evaluate the medicinal plants used for treatment of cognitive impairments and neurodegenerative diseases associated with diabetes in 2004-2020 period. Electronic databases used were PubMed, Scopus and Cochrane library. The keywords used were "diabetes," "plant," "herb," "neurodegenerative," "neurodegeneration," "cognitive," "cognition," "Alzheimer," "dementia." The non-English articles, repetitive articles and review studies were excluded. From total of 3,590 results, 58 articles are included in the study. The results show that many chemical treatments considered for this disease simply control hyperglycemia, but cannot improve the complications of diabetes. Herbal medicine could be more effective due to the high antioxidant activity of some medicinal plants. Biologically active substances of medicinal plants can improve the neurologi-cal disorders caused by diabetes via several pathways. The most important pathway is related to antioxidant properties. Other pathways include antiinflammatory, anti-apoptotic, neurotoxicity inhibition, neuronal death, increasing the uptake of glucose by cells and improve neurotransmitters levels involved in learning and memory. K E Y W O R D S cognition, diabetes, herbal medicine, medicinal plants, neurodegeneration, systematic review
... Pancreatic islets, if showing elevated β-cell apoptosis encouraging for amylin amyloid and decreased β-cell region, suggest a role of amylin amyloid in the formation of T2D (Jurgens et al. 2011). Amylin is synthesized and cosecreted along with insulin by pancreatic β-cells (Kahn et al. 1990) and plays a composite role in regulating the peripheral energy balance. However, some of the metabolic effects of insulin are opposite to those of amylin (Leighton and Cooper 1988;Molina et al. 1990;Zierath et al. 1992;Westermark et al. 2011). ...
Alzheimer’s disease (AD) is an irretrievable, mysterious, and devastating neurodegenerative disorder that leads to memory loss and impaired cognitive function. Specifically, AD patients suffer from poor thinking skills and lack potential to perform simple activities. Dementia is multifactorial disorder and considered as the main cause of AD. Alzheimer’s disease is characterized by the presence of large quantities of two remarkable structures, i.e., amyloid plaques and neurofibrillary tangles which are the hallmarks of AD. Both of these structures are misfolded proteins and thought to play an important role in the degeneracy of neurons, ultimately leading to most of AD symptoms. Another common feature of AD is the wrecking of intracellular connections which results in reduced cell function and cell death. Neurofibrillary tangles are twisted fibers which are found inside the neurons and are produced by hyperphosphorylation of a microtubule-associated protein, i.e., tau. Smoking and obesity are the putative risk factors for dementia and cardiovascular disease. Deficiency of vitamins, especially thiamine (B1), riboflavin (B2), niacin (B3), pyridoxine (B6), folate (B9), and cobalamin (B12), is associated with cognitive dysfunction and AD. Type-2 diabetes (T2D) and prediabetic insulin resistance have also been suggested as the risk factors for cerebrovascular injury and cognitive decline, eventually leading to dementia. Cognitive impairment in T2D is caused by deposits of amylin, an amyloidogenic hormone synthesized and cosecreted with insulin by pancreatic β-cells. The menace of AD can be lowered down by certain anti-inflammatory drugs, proper intake of vitamin B, nurturing physical and leisure activities. In addition, AD can also be controlled by decreasing the candidate risk factors for cardiovascular disease. Anti-amyloid approaches such as vaccination may provide a promising tool to establish safer therapeutic approaches.
... Pancreatic islets in T2D are characterized by a deficit in b-cell mass, impaired b-cell function, and the presence of extracellulr amyloid deposits [1e3]. These amyloid deposits are mainly composed of islet amyloid polypeptide (IAPP), a hormone that is produced and secreted as a monomeric form with insulin by b-cells [4]. ...
Objective
Pancreatic β-cell failure is central to the development and progression of type 2 diabetes (T2D). The aggregation of human islet amyloid polypeptide (hIAPP) has been associated with pancreatic islet inflammation and dysfunction in T2D. Alpha1-antitrypsin (AAT) is a circulating protease inhibitor with anti-inflammatory properties. Here we sought to investigate the potential therapeutic effect of AAT treatment in a mouse model characterized by hIAPP overexpression in pancreatic β-cells.
Methods
Mice overexpressing hIAPP (hIAPP-Tg) in pancreatic β-cells were used as a model of amyloid-induced β-cell dysfunction. Glucose homeostasis was evaluated by glucose tolerance tests and insulin secretion assays. Apoptosis and amyloid formation was assessed in hIAPP-Tg mouse islets cultured at high glucose levels. Dissociated islet cells were co-cultured with macrophages obtained from the peritoneal cavity.
Results
Non-treated hIAPP-Tg mice were glucose intolerant and exhibited impaired insulin secretion. Interestingly, AAT treatment improved glucose tolerance and restored the insulin secretory response to glucose in hIAPP-Tg mice. Moreover, AAT administration normalized the expression of the essential β-cell genes MafA and Pdx1, which were downregulated in pancreatic islets from hIAPP-Tg mice. AAT prevented the formation of amyloid deposits and apoptosis in hIAPP-Tg islets cultured at high glucose concentrations. Since islet macrophages mediate hIAPP-induced β-cell dysfunction, we investigated the effect of AAT in co-cultures of macrophages and islet cells. AAT prevented hIAPP-induced β-cell apoptosis in these co-cultures without reducing hIAPP-induced secretion of IL-1β by macrophages. Remarkably, AAT protected β-cells against the cytotoxic effects of conditioned medium from hIAPP-treated macrophages. Similarly, AAT also abrogated the cytotoxic effects of exogenous pro-inflammatory cytokines on pancreatic β-cells.
Conclusions
These results demonstrate that treatment with AAT improves glucose homeostasis in mice overexpressing hIAPP and protects pancreatic β-cells from the cytotoxic actions of hIAPP mediated by macrophages. These results support the use of AAT-based therapies to recover pancreatic β-cell function for the treatment of T2D.
... Pancreatic islets, if showing elevated β-cell apoptosis encouraging for amylin amyloid and decreased β-cell region, suggest a role of amylin amyloid in the formation of T2D (Jurgens et al. 2011). Amylin is synthesized and cosecreted along with insulin by pancreatic β-cells (Kahn et al. 1990) and plays a composite role in regulating the peripheral energy balance. However, some of the metabolic effects of insulin are opposite to those of amylin (Leighton and Cooper 1988;Molina et al. 1990;Zierath et al. 1992;Westermark et al. 2011). ...
Alzheimer’s disease (AD) is an irretrievable, mysterious, and devastating neurodegenerative disorder that leads to memory loss and impaired cognitive function. Specifically, AD patients suffer from poor thinking skills and lack potential to perform simple activities. Dementia is multifactorial disorder and considered as the main cause of AD. Alzheimer’s disease is characterized by the presence of large quantities of two remarkable structures, i.e., amyloid plaques and neurofibrillary tangles which are the hallmarks of AD. Both of these structures are misfolded proteins and thought to play an important role in the degeneracy of neurons, ultimately leading to most of AD symptoms. Another common feature of AD is the wrecking of intracellular connections which results in reduced cell function and cell death. Neurofibrillary tangles are twisted fibers which are found inside the neurons and are produced by hyperphosphorylation of a microtubule-associated protein, i.e., tau. Smoking and obesity are the putative risk factors for dementia and cardiovascular disease. Deficiency of vitamins, especially thiamine (B1), riboflavin (B2), niacin (B3), pyridoxine (B6), folate (B9), and cobalamin (B12), is associated with cognitive dysfunction and AD. Type-2 diabetes (T2D) and prediabetic insulin resistance have also been suggested as the risk factors for cerebrovascular injury and cognitive decline, eventually leading to dementia. Cognitive impairment in T2D is caused by deposits of amylin, an amyloidogenic hormone synthesized and cosecreted with insulin by pancreatic β-cells. The menace of AD can be lowered down by certain anti-inflammatory drugs, proper intake of vitamin B, nurturing physical and leisure activities. In addition, AD can also be controlled by decreasing the candidate risk factors for cardiovascular disease. Anti-amyloid approaches such as vaccination may provide a promising tool to establish safer therapeutic approaches.
... Amylin (also known as islet amyloid polypeptide (IAPP) plays a role in metabolism and glucose homeostasis [22,23]. In addition, amylin and insulin are cosecreted by β-cells [24]. ...
Zinc is a key component of several proteins, interacting with the pancreatic hormones insulin and amylin. The role of zinc in insulin oligomerization and crystallinity is well established, although the effects of dietary zinc restriction on both energetic metabolism and β-pancreatic hormonemia and morphology remain unexplored. Here we report the effects of dietary zinc restriction on the endocrine pancreas and metabolic phenotype of mice. Nontransgenic male Swiss mice were fed a low-zinc or control diet for 4 weeks after weanling. Growth, glycemia, insulinemia and amylinemia were lower and pancreatic islets were smaller in the intervention group despite the preserved insulin crystallinity in secretory granules. We found strong immunostaining for insulin, amylin and oligomers in apoptotic pancreatic islet. High production of β-pancreatic hormones in zinc-restricted animals counteracted the reduced islet size caused by apoptosis. These data suggest that zinc deficiency is sufficient to promote islet β-cell hormonal disruption and degeneration.
... Inspired by the findings on molecules that show cross-inhibition toward multiple amyloidosis [32][33][34][35] , and based on the fact that HW-155 was identified from an OBOC library, we hypothesized that HW-155 could be a non-specific amyloid inhibitor, and as such it may exhibit inhibitory activity toward the aggregation of hIAPP. To test our hypothesis, we synthesized HW-155 and eight (8) analogues (1)(2)(3)(4)(5)(6)(7)(8) with methyl group substitution on each position (similar to an alanine scan), and investigated their ability to prevent the fibrillization of amylin (hIAPP), as well as to disrupt preformed hIAPP aggregates. Furthermore, we studied the aggregation behaviour and morphological characteristics of hIAPP in the presence and absence of various concentrations of HW-155 and its eight (8) analogues using transmission electron microscopy (TEM), time-dependent Thioflavin T (ThT) fluorescence assay, and atomic force microscopy (AFM). ...
The abnormal folding and aggregation of functional proteins into amyloid is a typical feature of many age-related diseases, including Type II diabetes. Growing evidence has revealed that the prevention of aggregate formation in culprit proteins could retard the progression of amyloid diseases. Human Amylin, also known as human islet amyloid polypeptide (hIAPP), is the major factor for categorizing Type II diabetes as an amyloid disease. Specifically, hIAPP has a great aggregation potential, which always results in a lethal situation for the pancreas. Many peptide inhibitors have been constructed from the various segments of the full-length hIAPP peptide; however, only a few have their origin from the screening of combinatorial peptidomimetic library. In this study, based on HW-155, which was previously discovered from a one–bead–one compound (OBOC) library to inhibit Aβ40 aggregation, we investigated eight (8) analogues and evaluated their amyloid-prevention capabilities for inhibiting fibrillization of hIAPP. Characterization studies revealed that all analogues of HW-155, as well as HW-155, were effective inhibitors of the fibril formation by hIAPP.
... In humans, the degree of islet amyloid deposition is directly correlated with the rate of β-cell apoptosis and inversely correlated with β-cell mass (Jurgens et al., 2011). Islet amyloid polypeptide (IAPP, also known as amylin), a normal β-cell secretory product (Kahn et al., 1990), is a unique protein constituent of islet amyloid deposits (Westermark et al., 1987;Cooper et al., 1987). Human IAPP (hIAPP) and rodent IAPP (rIAPP) differ in a few critical amino acid residues, which results in hIAPP being amyloidogenic and cytotoxic, while rIAPP is not (Westermark et al., 1990;Lorenzo et al., 1994). ...
Islet amyloid is a pathologic feature of type 2 diabetes (T2D) that is associated with β-cell loss and dysfunction. These amyloid deposits form via aggregation of the β-cell secretory product islet amyloid polypeptide (IAPP) and contain other molecules including the heparan sulfate proteoglycan perlecan. Perlecan has been shown to bind amyloidogenic human IAPP (hIAPP) via its heparan sulfate glycosaminoglycan (HS GAG) chains and to enhance hIAPP aggregation in vitro. We postulated that reducing the HS GAG content of perlecan would also decrease islet amyloid deposition in vivo. hIAPP transgenic mice were crossed with Hspg2Δ3/Δ3 mice harboring a perlecan mutation that prevents HS GAG attachment (hIAPP;Hspg2Δ3/Δ3), and male offspring from this cross were fed a high fat diet for 12 months to induce islet amyloid deposition. At the end of the study body weight, islet amyloid area, β-cell area, glucose tolerance and insulin secretion were analyzed. hIAPP;Hspg2Δ3/Δ3 mice exhibited significantly less islet amyloid deposition and greater β-cell area compared to hIAPP mice expressing wild type perlecan. hIAPP;Hspg2Δ3/Δ3 mice also gained significantly less weight than other genotypes. When adjusted for differences in body weight using multiple linear regression modeling, we found no differences in islet amyloid deposition or β-cell area between hIAPP transgenic and hIAPP;Hspg2Δ3/Δ3 mice. We conclude that loss of perlecan exon 3 reduces islet amyloid deposition in vivo through indirect effects on body weight and possibly also through direct effects on hIAPP aggregation. Both of these mechanisms may promote maintenance of glucose homeostasis in the setting of T2D.
... Human islet amyloid polypeptide (hIAPP) is a 37-residue polypeptide hormone which is secreted by pancreatic b-cells [1,2]. The misfolding, aggregation and fibrillation of hIAPP aggregates are correlated with type-II diabetes mellitus because of their cytotoxicity to islet beta cells [3][4][5][6]. ...
The misfolding, aggregation and fibrillation of human islet amyloid polypeptide (hIAPP) has been acknowledged as a hallmark event in type-II diabetes. Hence, inhibiting the misfolding, aggregation and fibrillation of hIAPP have been accepted as a vital factor to treat the disease. Here cichoric acid was extracted from witloof to explore its inhibition effects on misfolding, aggregation and fibrillation of hIAPP. Thioflavin-T (ThT) fluorescence assay, dynamic light scattering (DLS) and atomic force microscopy (AFM) images showed that cichoric acid inhibited the aggregation and fibrillation of hIAPP in a dosage-dependent manner. Circular dichroism (CD) spectra showed that cichoric acid inhibited the misfolding of hIAPP from unfolded to β-sheet. Molecular docking and further experiments revealed interactions between hIAPP and cichoric acid. Cichoric acid could bind to K1 and R11 of hIAPP via electrostatic interaction. In addition, cichoric acid could form π-π stacking with hIAPP residues F15 and F23. These interactions inhibited the misfolding, aggregation and fibrillation of hIAPP. These results, together with cichoric acid's good cytocompatibility and significant protective effects in hIAPP lesioned cell models, not only showed that cichoric acid could be used to fight against amyloidosis, but also brought a new perspective for Chinese herbal medicine as natural compound's medical potential.
... Islet amyloid polypeptide (IAPP, amylin) was discovered, extracted and named from islet tumor cells and is a polypeptide hormone containing 37 amino acid residues; IAPP is secreted by islet beta cells 12 . It is mainly stored in the halo of the secretory granule, secreted in a pulsed manner under the action of glucose and other secretagogues 13 . ...
Diabetes has become one of the major noninfectious diseases that seriously endanger public health. The formation of islet amyloid polypeptide (IAPP) affects the normal physiological functions of the body, such as glucose metabolism and lipid metabolism. The mature human IAPP protein (hIAPP) has a strong tendency to misfold and is considered to be one of the major causes of amyloid changes in islets. Deposition of hIAPP is considered to be one of the leading causes of type 2 diabetes mellitus (T2DM). Miniature pigs are experimental animal models that are well suited for research on gene function and human diabetes. In our study, we obtained IAPP gene-humanized miniature pigs via the CRISPR/Cas9 system and somatic cell nuclear transfer (SCNT) technology. The hIAPP pigs can be used to further study the pathogenesis and related complications of T2DM and to lay a solid foundation for the prevention and treatment of T2DM.
... This is likely due to the concurrent increase in insulin secretion at this stage. Amylin and insulin are co-secreted from β-cells and the tripro-hA transgene is expressed under the rat insulin 2 promotor, thus driving further overexpression when insulin expression is increased 3,24 . Amylin and insulin levels are also mirrored in transgenic mice at T3. ...
Type 2 diabetes mellitus is a major health concern worldwide; however, the molecular mechanism underlying its development is poorly understood. The hormone amylin is postulated to be involved, as human amylin forms amyloid in the pancreases of diabetic patients, and oligomers have been shown to be cytotoxic to β-cells. As rodent amylin is non-amyloidogenic, mice expressing human amylin have been developed to investigate this hypothesis. However, it is not possible to differentiate the effects of amylin overexpression from β-cell loss in these models. We have developed transgenic mice that overexpress [25, 28, 29 triprolyl]human amylin, a non-amyloidogenic variant of amylin, designated the Line 44 model. This model allows us to investigate the effects of chronic overexpression of non-cytotoxic amylin. We characterised this model and found it developed obesity, hyperglycaemia and hyperinsulinaemia. This phenotype was associated with alterations in the expression of genes involved in the amylin, insulin and leptin signalling pathways within the brain. This included genes such as c-Fos (a marker of amylin activation); Socs3 (a leptin inhibitor); and Cart, Pomc and Npy (neuropeptides that control appetite). We also examined Socs3 protein expression and phosphorylated Stat3 to determine if changes at the mRNA level would be reflected at the protein level.
... 12 Amylin (also known as islet amyloid polypeptide), is a 37-amino acid peptide synthesized and cosecreted with insulin in response to physiological stimuli. [13][14][15] It is normally soluble, crosses the blood brain barrier, and binds to neurons in the feeding centers participating in the regulation of gastric fluxes. 16 Amylin from humans and a few other species, including cats, dogs, and monkeys, but not rodents, has an increased propensity to aggregate, forming amyloid 17 (i.e., amylin dyshomeostasis). ...
In the setting of type-2 diabetes, there are declines of structural stability and functionality of blood capillaries and red blood cells (RBCs), increasing the risk for microcirculatory disturbances. Correcting hyperglycemia is not entirely effective at reestablishing normal cellular metabolism and function. Therefore, identification of pathological changes occurring before the development of overt hyperglycemia may lead to novel therapeutic targets for reducing the risk of microvascular dysfunction. Here we determine whether RBC-capillary interactions are altered by prediabetic hypersecretion of amylin, an amyloid forming hormone co-synthesized with insulin, and is reversed by endothelial cell-secreted epoxyeicosatrienoic acids. In patients, we found amylin deposition in RBCs in association with type-2 diabetes, heart failure, cancer and stroke. Amylin-coated RBCs have altered shape and reduced functional (non-glycated) hemoglobin. Amylin-coated RBCs administered intravenously in control rats upregulated erythropoietin and renal arginase expression and activity. We also found that diabetic rats expressing amyloid-forming human amylin in the pancreas (the HIP rat model) have increased tissue levels of hypoxia-inducible transcription factors, compared to diabetic rats that express non-amyloid forming rat amylin (the UCD rat model). Upregulation of erythropoietin correlated with lower hematocrit in the HIP model indicating pathologic erythropoiesis. In the HIP model, pharmacological upregulation of endogenous epoxyeicosatrienoic acids protected the renal microvasculature against amylin deposition and also reduced renal accumulation of HIFs. Thus, prediabetes induces dysregulation of amylin homeostasis and promotes amylin deposition in RBCs and the microvasculature altering RBC-capillary interaction leading to activation of hypoxia signaling pathways and pathologic erythropoiesis. Hence, dysregulation of amylin homeostasis could be a therapeutic target for ameliorating diabetic vascular complications.
... GLP-1 incorporation within the basal layer of a PEG-based LBL islet coating scheme increased insulin secretion in comparison to naked islets [406]. Similar results were obtained for insulin-secreting cells encapsulated in a GLP-1-mimetic peptide amphiphile nanogel [407]. Localized presentation at the islet surface, which can be accomplished by nano-thin coatings, may improve its efficacy as GLP-1 interacts with the GLP-1 receptor on the islet cell surface to impart function [191]. ...
Islet encapsulation and transplantation promises to improve upon current treatments for type 1 diabetes mellitus, though several limitations remain. Macroscale devices have been designed for in vivo transplantation and retrieval, but traditional geometries do not support clinically adequate mass transfer of nutrients to and insulin from the encapsulated tissue. Microcapsule technologies have improved mass transfer properties, but their clinical translation remains challenging as their complete retrieval is difficult, should the graft become a safety concern. Here, the design, characterization and testing of a novel encapsulation structure, comprised of elastomer‐reinforced interconnected toroidal hydrogels is reported. These donut‐shaped hydrogels feature a high surface area, higher than conventional spherical capsules of the same volume, bestowing suitable mass transport conditions, while allowing interconnection and reversible deformation for intraperitoneal implantation and retrieval. Diabetes correction up to 12 weeks and complete retrieval is achieved in a diabetic mouse model, providing a proof‐of‐concept for the potential application as a type 1 diabetes cell replacement therapy.
... Interestingly, both glucose [64] and free fatty acids [23] promote islet amyloidosis in human islets via upregulation of IAPP expression. IAPP and insulin are cosecreted from β-cells [65,66] and since insulin secretion is increased in prediabetes to compensate for increased insulin demand [67], IAPP secretion is increased as well. Among other mechanisms, such as insufficiently processed IAPP that is found in failing human islet grafts [68], the increased concentration of IAPP might be a trigger for amyloid deposition. ...
Metabolic diseases including type 2 diabetes are associated with meta-inflammation. β-Cell failure is a major component of the pathogenesis of type 2 diabetes. It is now well established that increased numbers of innate immune cells, cytokines, and chemokines have detrimental effects on islets in these chronic conditions. Recently, evidence emerged which points to initially adaptive and restorative functions of inflammatory factors and immune cells in metabolism. In the following review, we provide an overview on the features of islet inflammation in diabetes and models of prediabetes. We separately emphasize what is known on islet inflammation in humans and focus on in vivo animal models and how they are used to elucidate mechanistic aspects of islet inflammation. Further, we discuss the recently emerging physiologic signaling role of cytokines during adaptation and normal function of islet cells.
... GLP-1 incorporation within the basal layer of a PEG-based LBL islet coating scheme increased insulin secretion in comparison to naked islets [406]. Similar results were obtained for insulin-secreting cells encapsulated in a GLP-1mimetic peptide amphiphile nanogel [407]. Localized presentation at the islet surface, which can be accomplished by nano-thin coatings, may improve its efficacy as GLP-1 interacts with the GLP-1 receptor on the islet cell surface to impart function [191]. ...
... Figure 1 illustrates that the conformation of islet amyloid in type 1 diabetes is indistinguishable from that observed in type 2 diabetes, and the deposits are located in proximity to residual b-cells (S.E.K., A.T.T., and R.L.H., unpublished observation). This location of the amyloid deposits is in keeping with IAPP, their unique peptide component, being a secretory product of the b-cell that typically has to be exocytosed for amyloid to form (22,23). We have proposed that b-cell dysfunction and impaired processing of proIAPP are linked to its aggregation and amyloid formation (24,25), raising the possibility that a common pathway leads to amyloid formation in both type 2 diabetes and in some cases of type 1 diabetes in which residual b-cells remain. ...
... The islet amyloid polypeptide (IAPP) is a protein component of fibrils that are forming the amyloid deposits (Westermark et al. 1987;Cooper et al. 1987). IAPP is getting produced in the islet cells and released together with insulin (Kahn et al. 1990). When islet amyloid increases in the monkey, the glucose tolerance gets worse (Howard 1986). ...
... As already mentioned, neuroinflammation is strongly associated with DM and other metabolic disorders, whereas diabetic patients are at higher risk for cerebrovascular injury (Luchsinger, 2012;Nelson et al., 2009;Ott et al., 1999aOtt et al., , 1999b that, in turn, further promotes neuroinflammation. Patients with DM and dementia or AD accumulate the pancreatic hormone amylin, an islet amyloid polypeptide (Jackson et al., 2013) synthesized and co-secreted with insulin by pancreatic β-cells (Kahn et al., 1990) to modulate metabolism. In mammals, amylin reduces glycogen synthesis and glucose uptake in isolated muscle strips (Leighton and Cooper, 1988), as well as causes oxidative stress (Zraika et al., 2009) and inflammation (Westwell-Roper et al., 2011). ...
Diabetes mellitus (DM) is a common metabolic disorder that affects multiple organ systems. DM also affects brain processes, contributing to various CNS disorders, including depression and Alzheimer’s disease. Despite active research in humans, rodent models and in-vitro systems, the pathogenetic link between DM and brain disorders remains poorly understood. Novel translational models and new model organisms are therefore essential to more fully study the impact of DM on CNS. The zebrafish (Danio rerio) is a powerful novel model species to study metabolic and CNS disorders. Here, we discuss how DM alters brain functions and behavior in zebrafish, and summarize their translational relevance to studying DM-related CNS pathogenesis in humans. We recognize the growing utility of zebrafish models in translational DM research, as they continue to improve our understanding of different brain pathologies associated with DM, and may foster the discovery of drugs that prevent or treat these diseases.
... Human-IAPP (hIAPP: human islet amyloid polypeptide, also known as amylin) is a 37 residue peptide hormone (Fig. S1A) that is co-secreted at a 1:100 M ratio with insulin in response to blood glucose levels that normally contributes to satiety and the slowing of gastric emptying [1]. In type II diabetes, the increase in insulin production causes a simultaneous increase in the generation of hIAPP, which increases hIAPP amyloid formation resulting in β cell death [2,3]. Biophysical studies have reported that hIAPP aggregation results in the disruption of lipid membranes via a two-step mechanism: fibril-independent pore formation and a fibril-dependent fragmentation of the lipid bilayer [4]. ...
Amyloid aggregation of human islet amyloid polypeptide (hIAPP) is linked to insulin-producing islet cell death in type II diabetes. Previous studies have shown that zinc (Zn(II)) and insulin, co-secreted with hIAPP, have an inhibition effect on hIAPP aggregation. Lipid membranes have also been shown to significantly influence the aggregation kinetics of hIAPP. An increasing number of studies report the importance of developing small molecule inhibitors to suppress the hIAPP's aggregation and subsequent toxicity. The ability of epigallocatechin-gallate (EGCG) to inhibit aggregation of a variety of amyloid peptide/proteins initiated numerous studies as well as the development of derivative compounds to potentially treat amyloid diseases. In this study, a combination of Thioflavin-T fluorescence kinetics, transmission electron microscopy, isothermal titration calorimetery, circular dicrosim and nucelar magnetic resonance experiments were used to demonstrate a significant enhancement in EGCG's efficiency when complexed with Zn(II). We demonstrate that the Zn-EGCG complex is able to significantly suppress hIAPP's amyloid aggregation both in presence and absence of lipid membrane. Circular dichroism experiments indicate the formation and stabilization of a helical structure of hIAPP in presence of the EGCG:Zn(II) complex. Our results also reveal the ability of EGCG or EGCG:Zn(II) to efficiently suppress hIAPP's cellular toxicity. We believe that the reported results could be useful to develop strategies to trap hIAPP intermediates for further biophysical and structural studies, and also to devise approaches to abolish amyloid aggregation and cellular toxicity.
... Amyloid has also been linked to beta cell failure in transplanted human islets [5,6]. Human islet amyloid polypeptide (hIAPP), the unique peptide component of islet amyloid [7,8], is a peptide hormone synthesised by the beta cell and is co-secreted with insulin [9]. In vitro and in vivo models of islet amyloidosis have demonstrated that hIAPP aggregation results in oxidative and inflammatory stress leading to beta cell death [10][11][12] and various lines of research are now aimed at preventing islet amyloid formation and the resulting cytotoxicity [13][14][15][16]. ...
Aims/hypothesis:
Islet amyloid deposits contribute to beta cell dysfunction and death in most individuals with type 2 diabetes but non-invasive methods to determine the presence of these pathological protein aggregates are currently not available. Therefore, we examined whether florbetapir, a radiopharmaceutical agent used for detection of amyloid-β deposits in the brain, also allows identification of islet amyloid in the pancreas.
Methods:
Saturation binding assays were used to determine the affinity of florbetapir for human islet amyloid polypeptide (hIAPP) aggregates in vitro. Islet amyloid-prone transgenic mice that express hIAPP in their beta cells and amyloid-free non-transgenic control mice were used to examine the ability of florbetapir to detect islet amyloid deposits in vitro, in vivo and ex vivo. Mice or mouse pancreases were subjected to autoradiographic, histochemical and/or positron emission tomography (PET) analyses to assess the utility of florbetapir in identifying islet amyloid.
Results:
In vitro, florbetapir bound synthetic hIAPP fibrils with a dissociation constant of 7.9 nmol/l. Additionally, florbetapir bound preferentially to amyloid-containing hIAPP transgenic vs amyloid-free non-transgenic mouse pancreas sections in vitro, as determined by autoradiography (16,475 ± 5581 vs 5762 ± 575 density/unit area, p < 0.05). In hIAPP transgenic and non-transgenic mice fed a high-fat diet for 1 year, intravenous administration of florbetapir followed by PET scanning showed that the florbetapir signal was significantly higher in amyloid-laden hIAPP transgenic vs amyloid-free non-transgenic pancreases in vivo during the first 5 min of the scan (36.83 ± 2.22 vs 29.34 ± 2.03 standardised uptake value × min, p < 0.05). Following PET, pancreases were excised and florbetapir uptake was determined ex vivo by γ counting. Pancreatic uptake of florbetapir was significantly correlated with the degree of islet amyloid deposition, the latter assessed by histochemistry (r = 0.74, p < 0.001).
Conclusions/interpretation:
Florbetapir binds to islet amyloid deposits in a specific and quantitative manner. In the future, florbetapir may be useful as a non-invasive tool to identify islet amyloid deposits in humans.
... Islet amyloid polypeptide (IAPP), also known as amylin, is a 37-amino-acid residue polypeptide (1), which is co-synthetized and secreted with insulin by β cells (2,3). Islet amyloid deposit, primarily derived from IAPP, is a pathological feature of 90% of patients with type 2 diabetes mellitus (T2DM) (4-7). ...
Oligomerization of human islet amyloid polypeptide (hIAPP) is toxic and contributes to progressive reduction of β cell mass in patients with type 2 diabetes mellitus. Autophagy is a highly conserved homeostatic mechanism in eukaryotes. Previous studies have confirmed that hIAPP can promote autophagy in β cells, but the underlying molecular mechanism and cellular regulatory pathway of hIAPP‑induced autophagy remains not fully elucidated. Accumulation of reactive oxygen species (ROS) causes hIAPP induced‑β cell death. At present, little is known about the association between hIAPP‑induced oxidative stress and autophagy in β cells. Therefore, the present study investigated the underlying molecular mechanism and regulatory pathway of hIAPP‑induced autophagy. Transmission electron microscopy was used to observe the number of autophagosome in cells. Cell viability was determined by an MTT test. A 2',7'‑dichlorofluorescin diacetate assay was used to measure the relative levels of reactive ROS. Western blotting was used to detect expression of adenosine monophosphate‑activated protein kinase (AMPK) and autophagic markers p62 and microtubule associated protein 1 light chain 3. The results demonstrated that hIAPP induces autophagy through ROS‑mediated AMPK signaling pathway in INS‑1 cells. Upregulation of autophagy by AMPK activator 5‑aminoimidazole‑4‑carboxamide1‑β‑D‑ribofuranoside decreased ROS and malondialdehyde generation, whereas inhibition of autophagy by 3‑methyladenine and AMPK inhibitor compound C aggravated hIAPP‑induced oxidative stress and toxicity in INS‑1 cells. Taken together, the present study suggested that hIAPP induces autophagy via a ROS‑mediated AMPK signaling pathway. Furthermore, autophagy serves as a cell‑protective mechanism against hIAPP‑induced toxicity and chemical promotion of autophagy through AMPK signaling pathway attenuates hIAPP induced cytotoxicity and oxidative stress in INS‑1 cells.
... STZ-induced diabetic rats had significantly reduced both amylin and insulin concentrations in the brain as compared to the normal control rats. Amylin is a 37 amino acid peptide that is synthesized and co-secreted with insulin by the pancreatic b-cells (Kahn et al., 1990). The presence of insulin in the brain remains controversial either it is synthesized in the brain or fully transported from the pancreas. ...
Azadirachta excelsa increases the secretion of plasma insulin with subsequent reduction of fasting blood glucose. However, its protective effect towards brain amylin and insulin levels as well as the memory and learning functions remain elusive. Thus, this study aimed to ascertain the effect of A. excelsa and quercetin consumptions on the brain amylin and insulin concentrations as well as memory and learning abilities of the streptozotocin (STZ)-induced diabetic rats. Diabetic condition was induced in the male Sprague Dawley rats by the intraperitoneal injection of 60 mg/kg body weight (bwt) STZ. The experimental animals were divided into normal control (saline), diabetic control (saline), Metformin-treated diabetic (1000 mg/kg bwt) (positive control), A. excelsa-treated diabetic (250 mg/kg bwt) and Quercetin-treated diabetic (40 mg/kg bwt) rats. All treatments were administered orally by oral gavage once daily throughout the 8 weeks of the treatment period. Amylin and insulin concentrations were determined by using the commercial rat amylin and insulin immunoassay kits, while learning and memory consolidation parameters were conducted using Morris Water Maze (MWM) paradigm. Treatment with A. excelsa had significantly (p < 0.05) improved the concentration of both brain amylin and insulin. In MWM test, the administration of A. excelsa and quercetin significantly (p < 0.05) attenuated the learning and memory impairments in STZ-induced diabetic rats. These analytical results provide evidence that A. excelsa can improve learning and memory impairments due to diabetes by increasing the amylin and insulin levels. These also suggest that, quercetin might only improve the learning and memory impairment, but not be the one that contributed to the improvement in the brain amylin and insulin concentrations.
... IAPP, also called amylin, is a peptide hormone consisting of 37 amino acid residues. Initially produced as an 89-residue preproprotein in β-cells of the pancreas, it undergoes a series of proteolytic and posttranslational modifications leading to its final mature form [26,27]. Mainly produced by β-cells of the islets of Langerhans, IAPP is copackaged and co-secreted with insulin in the secretory granules of the β-cells [28,29]. Although not all tissue targets and physiological functions of IAPP are completely known, it is thought to mainly affect the liver, gut, and brain, where it might play a role in the control of glucose homeostasis and satiety [30,31]. ...
Abnormal protein aggregation is a hallmark of various human diseases. α-Synuclein, a protein implicated in Parkinson's disease, is found in aggregated form within Lewy bodies that are characteristically observed in the brains of PD patients. Similarly, deposits of aggregated human islet amyloid polypeptide (IAPP) are found in the pancreatic islets in individuals with type 2 diabetes mellitus. Significant number of studies have focused on how monomeric, disaggregated proteins transition into various amyloid structures leading to identification of a vast number of aggregation promoting molecules and processes over the years. Inasmuch as these factors likely enhance the formation of toxic, misfolded species, they might act as risk factors in disease. Cellular membranes, and particularly certain lipids, are considered to be among the major players for aggregation of α-synuclein and IAPP, and membranes might also be the target of toxicity. Past studies have utilized an array of biophysical tools, both in vitro and in vivo, to expound the membrane-mediated aggregation. Here, we focus on membrane interaction of α-synuclein and IAPP, and how various kinds of membranes catalyze or modulate the aggregation of these proteins and how, in turn, these proteins disrupt membrane integrity, both in vitro and in vivo. The membrane interaction and subsequent aggregation has been briefly contrasted to aggregation of α-synuclein and IAPP in solution. This article is part of a Special Issue entitled: Protein Aggregation and Misfolding at the Cell Membrane Interface edited by Ayyalusamy Ramamoorthy.
... Amylin, also called islet amyloid polypeptide (IAPP), is a 37-amino acid residue peptide, which is mainly co-expressed and co-secreted with insulin in a ratio between 1:10 and 1:100 (IAPP:insulin) in β-cells, but also in some other cell types (Betsholtz et al., 1989;Kahn et al., 1990;Mulder et al., 1995Mulder et al., , 1994Toshimori et al., 1990;Westermark et al., 1987;German et al., 1992;Kahn et al., 1991;Mulder et al., 1996). Initially, IAPP is expressed as 89-amino acid PrePro-peptide, which is subsequently cleaved to the Pro-peptide by peptidases in the endoplasmic reticulum (ER) and finally to the mature IAPP by prohormone convertase 2, prohormone convertase 1/3 and carboxypeptidase E in the Golgi apparatus. ...
The ubiquitin-proteasomal-system (UPS) and the autophagy-lysosomal-system (ALS) are both highly susceptible for disturbances leading to the accumulation of cellular damage. A decline of protein degradation during aging results in the formation of oxidatively damaged and aggregated proteins finally, resulting in failure of cellular functionality. Besides protein aggregation in response to oxidative damage, amyloids are a different type of protein aggregates able to distract proteostasis and interfere with cellular functionality. Amyloids are clearly linked to the pathogenesis of age-related degenerative diseases such as Alzheimer's disease. Human amylin is one of the peptides forming fibrils in β-sheet conformation finally leading to amyloid formation. In contrast to rodent amylin, human amylin is prone to form amyloidogenic aggregates, proposed to play a role in the pathogenesis of Type 2 Diabetes by impairing β-cell functionality. Since aggregates such as lipofuscin and β-amyloid are known to impair proteostasis, it is likely to assume similar effects for human amylin. In this review, we focus on the effects of IAPP on UPS and ALS and their role in amylin degradation, since both systems play a crucial role in maintaining proteome balance thereby influencing, at least in part, cellular fate and aging.
... Pathological aggregation of the endocrine hormone human islet amyloid polypeptide (h-IAPP, also known as amylin) is a key feature in islet amyloidosis. h-IAPP is cosecreted with insulin and plays an adaptive role in metabolism (6,(13)(14)(15)(16), but in T2D, it aggregates by an unknown mechanism and is deposited as pancreatic islet amyloid plaques associated with reduced β cell volume (2,4,7,8,17,18). Aggregation of h-IAPP into amyloid fibrils involves 3 observable stages: Preamyloid oligomers (or prefibrillar intermediates) formed in the lag phase (LP) (first phase) assemble into amyloid fibrils in the growth phase (GP) (second phase), leading to an equilibrium between amyloid fibrils and residual soluble peptide in the saturation phase (SP) (third phase) (Supplemental Figure 1, A and B; supplemental material available online with this article; https:// doi.org/10.1172/JCI85210DS1). ...
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.
Background
Islet amyloid polypeptide (amylin) secreted from the pancreas crosses the blood brain barrier into the brain parenchyma and interacts with Alzheimer’s disease (AD) associated cerebral β‐amyloid (Aβ) plaques, which are found in both sporadic and early‐onset familial AD. Immunoprecipitated amylin from human AD brain tissue analyzed by Western blot using an anti‐Aβ antibody detects Aβ immunoreactivity, which indicates that the amylin and Aβ peptides aggregate in the brains of humans with AD, forming amylin‐Aβ hetero‐oligomers that are sodium dodecyl sulfate (SDS)‐soluble. We report the development of an ELISA to detect amylin‐Aβ hetero‐oligomers in brain tissue and blood.
Method
The amylin‐Aβ ELISA relies on a monoclonal anti‐Aβ middomain antibody (detection) and a polyclonal anti‐amylin antibody (capture) designed to recognize an epitope that is distinct from the high affinity amylin‐Aβ binding sites. We screened temporal cortex homogenates obtained from 13 cognitively unaffected (CU) humans and 47 persons with sporadic AD (sAD) for amylin‐Aβ hetero‐oligomers. Individuals were of similar age (sAD, 85.65 ± 7.04 years vs . CU, 87.22 ± 7.30 years; p = 0.482). Brain tissue amylin and Aβ concentrations were measured using conventional ELISAs. Amylin‐Aβ oligomer levels were also measured in whole blood lysates from APP/PS1 rats and APP/PS1 rats expressing amyloid forming amylin in the pancreas (APP/PS1/HIP rats; all rats age‐matched, 16‐months).
Result
The brains of most AD patients had detectable amylin‐Aβ hetero‐oligomer concentrations, whereas about half of those CU had brain tissue amylin‐Aβ hetero‐oligomers below the detection limit (0.02 ng/mg total protein; one‐way ANOVA, P < 0.0001). Amylin‐Aβ hetero‐oligomers were more common in brains with frequent neuritic plaques (CERAD C). Higher brain tissue amylin‐Aβ hetero‐oligomer levels were associated with greater brain tissue amylin concentrations ( r = 0.38 ; P < 0.05 ). There was no correlation between cerebral amylin‐Aβ hetero‐oligomer accumulation and age in the analysis of samples from sAD and CU groups ( r = ‐0.22 ; P > 0.05 ). Levels of amylin‐Aβ hetero‐oligomers in whole blood lysates obtained from APP/PS1/HIP rats were higher than those from APP/PS1 littermates ( P < 0.05 ).
Conclusion
Studies are needed to determine the extent to which amylin‐Aβ hetero‐oligomerization can be detected in human blood.
Islet amyloid polypeptide (amylin) secreted from the pancreas crosses from the blood to the brain parenchyma and forms cerebral mixed amylin-β amyloid (Aβ) plaques in persons with Alzheimer’s disease (AD). Cerebral amylin-Aβ plaques are found in both sporadic and early-onset familial Alzheimer’s disease (AD); however, the role of amylin-Aβ co-aggregation in potential mechanisms underlying this association remains unknown, in part due to lack of assays for detection of these complexes. Here, we report the development of an ELISA to detect amylin-Aβ hetero-oligomers in brain tissue and blood. The amylin-Aβ ELISA relies on a monoclonal anti-Aβ middomain antibody (detection) and a polyclonal anti-amylin antibody (capture) designed to recognize an epitope that is distinct from the high affinity amylin-Aβ binding sites. The utility of this assay is supported by analysis of molecular amylin-Aβ co-deposition in post-mortem brain tissue obtained from persons with and without AD pathology. By using transgenic AD-model rats, we show that this new assay can detect circulating amylin-Aβ hetero-oligomers in the blood and is sensitive to their dissociation to monomers. This is important because therapeutic strategies to block amylin-Aβ co-aggregation could reduce or delay the development and progression of AD.
Objectives:
To investigate the factors associated with the circulating levels of oxyntomodulin in healthy individuals and individuals after an episode of acute pancreatitis (AP).
Methods:
Blood samples were collected from all participants after an overnight fast and analyzed for 28 biomarkers. Participants also underwent comprehensive body composition analysis on a 3-T magnetic resonance imaging scanner. Regression analyses were done to investigate the associations between oxyntomodulin and the studied factors.
Results:
The study included 105 individuals who had a primary diagnosis of AP and 58 healthy individuals. Peptide YY (B coefficient, 0.094; 95% confidence interval [95% CI], 0.164-0.123), pancreatic polypeptide (0.048; 95% CI, 0.030-0.066), and leptin (0.394; 95% CI, 0.128-0.661) had significant associations with oxyntomodulin in healthy individuals. Peptide YY was the most prominent factor associated with oxyntomodulin, explaining 60% of its variance in health. Cholecystokinin (0.014; 95% CI, 0.010-0.018), amylin (-0.107; 95% CI, -0.192 to -0.021), and glycated hemoglobin (-0.761; 95% CI, -1.249 to -0.273) had significant associations with oxyntomodulin in individuals after AP. Cholecystokinin was the most prominent factor associated with oxyntomodulin, explaining 44% of its variance after AP.
Conclusions:
Factors affecting the circulating levels of oxyntomodulin are different in health and after AP. These insights will enable the determination of populations that benefit from oxyntomodulin therapeutics in the future.
The relative contributions of reduced insulin sensitivity and beta-cell dysfunction to the pathogenesis of Type 2 diabetes are unknown. In addition, the influence of islet amyloid polypeptide (IAPP) and proinsulin secretion upon disease expression have not been fully characterised. In 1994 a 10 year-follow-up study of 96 previously non-diabetic, 1st degree relatives of Type 2 diabetic subjects was undertaken, with a physiological test-CIGMA(Continuous infusion of glucose with model assessment). The aims were to determine the conversion rate to diabetes, together with the most sensitive baseline predictors for disease progression. Results showed a cumulative prevalence for diabetes of 29% in the case of the siblings by mean age 60(10)y with an additional 8% having Impaired Fasting Glucose (fasting plasma glucose 6.1mmol/1 (IFG), and in the offspring, 10% by mean age 44(8)y with an additional 5% having IFG. The major predictor for conversion to diabetes was the degree of fasting glycaemia at baseline. Neither beta cell function nor insulin sensitivity were predictive. In a separate study, cross-sectional analyses of plasma IAPP and proinsulin concentrations in 58 non-diabetic relatives, 19 control subjects and 39 Type 2 diabetic patients, showed both peptides increased proportionally to C-peptide from normoglycaemia (FPG<5.5mmol/l) to IFG. Once diabetes was established, disproportionate hyperproinsulinaemia occurred, particularly in relation to the lower C-peptide concentrations in the insulin treated diabetics. IAPP levels were highest in relatives with IFG and in the diet and tablet treated diabetics and, like the C-peptide levels were significantly reduced in the insulin treated group. In summary, this study confirms the high prevalence and incidence of Type 2 diabetes in 1st degree relatives of white Caucasian diabetic patients. Raised fasting plasma glucose was the most sensitive predictor of diabetes. It is unlikely that routine assessment of beta-cell function or insulin sensitivity will give clinically useful information indicating which patients with IFG are at greater risk of developing diabetes. Disproportionate secretion of proinsulin did not occur until diabetes was established and is likely to be a secondary phenomenon.
The role of chronic inflammation in the pathogenesis of type 2 diabetes mellitus and associated complications is now well established. Therapeutic interventions counteracting metabolic inflammation improve insulin secretion and action, glucose control, and may prevent long-term complications. Thus, a number of anti-inflammatory drugs approved for the treatment of other inflammatory conditions are evaluated in patients with metabolic syndrome. Most advanced are clinical studies with interleukin-1 antagonists showing improved β-cell function and glycaemia, prevention of cardiovascular diseases and heart failure. However, alternative anti-inflammatory treatments, alone or in combinations, may turn out to be more effective, depending on genetic predispositions, duration and manifestation of the disease. Thus, there is a great need for comprehensive and well-designed clinical studies to implement anti-inflammatory drugs in the treatment of patients with metabolic syndrome and its associated conditions.
Pancreatic islet transplantation has become an established approach to β-cell replacement therapy for the treatment of insulin deficient diabetes. Recent progress in techniques for islet isolation, islet culture, and peri-transplant management of the islet transplant recipient have resulted in substantial improvements in metabolic and safety outcomes for patients. For patients requiring total or sub-total pancreatectomy for benign disease of the pancreas, isolation of islets from the diseased pancreas with intrahepatic transplantation of autologous islets can prevent or ameliorate post-surgical diabetes, and for patients previously experiencing painful recurrent acute or chronic pancreatitis, quality-of-life is substantially improved. For patients with type 1 diabetes or insulin deficient forms of pancreatogenic (type 3c) diabetes, isolation of islets from a deceased donor pancreas with intrahepatic transplantation of allogeneic islets can ameliorate problematic hypoglycemia, stabilize glycemic lability, and maintain on-target glycemic control, consequently with improved quality-of-life, and often without the requirement for insulin therapy. Because the metabolic benefits are dependent on the numbers of islets transplanted that survive engraftment, recipients of autoislets are limited to receive the number of islets isolated from their own pancreas, while recipients of alloislets may receive islets isolated from more than one donor pancreas. The development of alternative sources of islet cells for transplantation, whether from autologous, allogeneic, or xenogeneic tissues, is an active area of investigation that promises to expand access and indications for islet transplantation in the future treatment of diabetes.
Misfolding and amyloid formation of human islet amyloid polypeptide (IAPP) is believed to be critical in the pathogenesis of type 2 diabetes. Inhibitors that can effectively prevent protein aggregation and fibrillation are considered as potential therapeutics for the prevention and treatment of type 2 diabetes. Here we report that oligotyrosines manipulate IAPP amyloid formation in vitro and modulate IAPP-induced cytotoxicity in a manner that is related to the number of tyrosine units. Tyr2 and Tyr3 can effectively inhibit the aggregation of IAPP, either in bulk solution or in the presence of lipid membranes, and alleviate IAPP-mediated cytotoxicity. On the contrary, Tyr, Tyr4, and Tyr6 do not show significant inhibitory effects on the IAPP aggregation at the same conditions. To the best of our knowledge, this is the first time to report a residue-number dependent inhibition of IAPP aggregation by oligotyrosines, and Tyr2 and Tyr3 are proved to be potent inhibitors of IAPP amyloid formation. The interactions between oligotyrosines and IAPP have been simulated through molecular docking, which provides us an insight about the inhibition mechanism of IAPP amyloid formation that will be helpful for developing anti-diabetic drug candidates.
Immunohistochemical techniques were employed to investigate the distribution of amylin-like immunoreactive cells in the pancreas of gecko Homopholis fasciata. Four types of endocrine cells were distinguished: insulin immunoreactive (B cells), pancreatic polypeptide immunoreactive (PP cells), glucagon and pancreatic polypeptide immunoreactive (A/PP cells) and somatostatin immunoreactive cells (D cells). Pancreatic islets contained B, A/PP and D cells, whereas extrainsular regions contained B, D and PP cells. In the pancreatic islets, amylin-like immunoreactive cells corresponded to B cells, but not to A/PP or D cells. In the extrainsular regions, amylin-like immunoreactive cells corresponded to either B or PP cells. Amylin secreted from intrainsular B cells may regulate pancreatic hormone secretion in an autocrine and/or a paracrine fashion. On the other hand, amylin secreted from extrainsular PP and B cells, and/or intrainsular B cells may participate in the modulation of calcium homoeostasis in an endocrine fashion.
(1) Congenital syphilitic pancreatitis retards the development of the glandular acini but does not affect the islands of Langerhans. Embedded in the stroma, but not invaded by it, the latter maintain their continuity with the small ducts and acini with which they have a common origin.
(2) Two types of chronic interstitial inflammation affecting the developed pancreas are distinguishable:
(a) Interlobular Pancreatitis.—In the interlobular variety the inflammatory process is localized chiefly at the periphery of the lobule and implicates the islands of Langerhans only when the sclerotic process has reached a very advanced grade. When pancreatitis has followed obstruction of the ducts, the islands long remain unaltered though embedded in dense scar-like tissue.
(b) Interacinar Pancreatitis.—In the interacinar type the process is diffuse, invading the lobules and separating individual acini. The inflammatory change invades the islands of Langerhans.
(3) A relationship has been observed between lesions of the islands of Langerhans and the occurrence of diabetes mellitus.
(a) In one of eleven cases of interlobular panereatitis diabetes of mild intensity occurred. The sclerosis, which in this case followed obstruction of the ducts by calculi, was far advanced and affected the islands of Langerhans.
(b) In two of three cases of interacinar pancreatitis, diabetes was present. The third case was associated with a condition, hæmochromatosis, which at a later stage is associated with diabetes, the result of pancreatic lesion.
(c) In a fourth case of diabetes, hyaline deposit between the capillaries and the parenchymatous cells had so completely altered the islands of Langerhans that they were no longer recognizable.
Cats and humans, unlike most rodent species, develop amyloid in the islets of Langerhans in conjunction with non-insulin-dependent diabetes mellitus. The amyloid consists of a 37-amino acid polypeptide referred to as islet amyloid polypeptide (IAPP). The primary structures of IAPP from human and three rodent species have previously been determined. Sequence divergence was seen in the region corresponding to amino acid residues 20-29, which in human IAPP has been suggested to confer the amyloidogenic properties to the molecule. Using polymerase chain-reaction methodology, we determined the primary sequence of cat IAPP. Amino acid region 20-29 shows specific similarities and differences compared with human and rodent IAPP, respectively. A synthetic cat IAPP20-29 decapeptide formed amyloid fibrils spontaneously in vitro. Comparison between the structure and amyloid fibril-forming activity of various synthetic peptides suggests that the amino acid residues at positions 25-26 in mature IAPP are important for the amyloidogenic properties of the molecule.
Amyloid deposits occurring in the islets of Langerhans in patients with noninsulin-dependent diabetes mellitus and some insulinomas contain a 37-amino acid peptide that is structurally related to calcitonin gene-related peptide. We have identified three cDNA clones encoding islet amyloid polypeptide (IAPP) or diabetes-associated peptide (DAP) by oligonucleotide screening of a lambda gt10 human insulinoma cDNA library. Two of the three cDNAs contained a domain encoding IAPP/DAP but had an intron-like sequence in their 5' region. The other cDNA contained an open reading frame encoding an 89-amino acid precursor having a typical signal peptide followed by a small prohormone-like sequence containing within it the IAPP/DAP peptide bracketed at its NH2 and COOH termini by Lys-Arg and Gly-Lys-Arg, respectively. These data indicate that this amyloid peptide is generated by proteolytic processing similar to that for proinsulin and other islet prohormones and also that the peptide may be carboxyamidated. The isolation of cDNA clones having 5'-unprocessed intron-like sequences suggests that inefficient or alternative splicing of this mRNA occurred in the insulinoma.
Deposition of amyloid in pancreatic islets is a common feature in human type 2 diabetic subjects but because of its insolubility and low tissue concentrations, the structure of its monomer has not been determined. We describe a peptide, of calculated molecular mass 3905 Da, that was a major protein component of amyloid-rich pancreatic extracts of three type 2 diabetic patients. After collagenase treatment, an extract containing 20-50% amyloid was solubilized by sonication into 70% formic acid and the peptide was purified by gel filtration followed by reverse-phase high-performance liquid chromatography. We term this peptide diabetes-associated peptide, as it was not detected in extracts of pancreas from any of six normal subjects. Diabetes-associated peptide contains 37 amino acids and is 46% identical to the sequences of rat and human calcitonin gene-related peptide, indicating that these peptides are related in evolution. Sequence identities with conserved residues of the insulin A chain were also seen in a 16-residue segment. On extraction, the islet amyloid is particulate and insoluble like the core particles of Alzheimer disease. Their monomers have similar molecular masses, each having a hydropathic region that can probably form beta-pleated sheets. The accumulation of amyloid, including diabetes-associated peptide, in islets may impair islet function in type 2 diabetes mellitus.
We have cloned and sequenced a human islet amyloid polypeptide (IAPP) cDNA. A secretory 89 amino acid IAPP protein precursor is predicted from which the 37 amino acid IAPP molecule is formed by amino- and carboxyterminal proteolytic processing. The IAPP peptide is 43–46% identical in amino acid sequence to the two members of the calcitonin gene-related peptide (CGRP) family. Evolutionary conserved proteolytic processing sites indicate that similar proteases are involved in the maturation of IAPP and CGRP and that the LAPP amyloid polypeptide is identical to the normal proteolytic product of the IAPP precursor. A synthetic peptide corresponding to a carboxyteminal fragment of human IAPP is shown to spontaneously form amyloid-like fibrils in vitro. Antibodies against this peptide cross-react with IAPP from species that develop amyloid in pancreatic islets in conjunction with age-related diabetes mellitus (human, cat, racoon), but do not cross-react with IAPP from other tested species (mouse, rat, guinea pig, dog). Thus, a species-specific structural motif in the putative amyloidogenic region of IAPP is associated with both amyloid formation and the development of age-related diabetes mellitus. This provides a new molecular clue to the pathogenesis of this disease.
Amyloid in the islets of Langerhans increases with increasing severity of diabetes mellitus in Macaca nigra. The amount of insular amyloid was quantified, and diabetic monkeys averaged eight times more islet amyloid than did normal monkeys. The quantity of insular amyloid correlated significantly with glucose clearance in intravenous glucose tolerance tests and with serum glucose, triglycerides, immunoreactive insulin, and prebetallipoprotein measured after an overnight fast. As with human beings, insular amyloid appeared to be more prevalent in aging monkeys. The results support the hypothesis that the interrelated islet pathologic and metabolic events, which result in the appearance of insular amyloid concomitant with islet cell necrosis, may contribute more to maturity-onset diabetes in aging individuals than has been heretofore realized.
The hormone content of 72 endocrine tumors was determined by immunofluorescence and their amyloid content was investigated. Seventeen of the 72 tumors contained amyloid. Amyloid was frequently found in tumors producing calcitonin, insulin, or growth hormone, but was rarely found in other tumors. Thus, there is a relationship between the occurrence of amyloid in an endocrine tumor and the type of hormone it produces. The reason for this is not known, but there is evidence that the amyloid fibrils contain proteins related to the hormone produced by the tumors.
The insulin secretory granule of the pancreatic B cell is a complex intracellular organelle comprised of a many proteins with different catalytic activities and messenger functions. With the advent of tumour models of the B cells and the application of immunological and molecular cloning techniques considerable progress has been made in recent years towards the elucidation of the structure and function of these granule proteins. A number of examples are selected here for review. Particular emphasis given to how the activities of quite different granule proteins are interdependent and how this contributes to the co-ordination and integration of the organelle's biological functions.
Islet amyloid peptide (or diabetes-associated peptide), the major component of pancreatic islet amyloid found in type-2 diabetes, has been identified by electron-microscopic immunocytochemistry in pancreatic B-cells from five non-diabetic human subjects, and in islets from five type-2 diabetic patients. The greatest density of immunoreactivity for islet amyloid peptide was found in electron-dense regions of some lysosomal or lipofuscin bodies. The peptide was also localised by quantification of immunogold in the secretory granules of B-cells, and was present in cytoplasmic lamellar bodies. Acid phosphatase activity was also demonstrated in these organelles. Immunoreactivity for insulin was found in some lysosomes. These results suggest that islet amyloid peptide is a constituent of normal pancreatic B-cells, and accumulates in lipofuscin bodies where it is presumably partially degraded. In islets from type-2 diabetic subjects, amyloid fibrils and lipofuscin bodies in B-cells showed immunoreactivity for the amyloid peptide. Abnormal processing of the peptide within B-cells could lead to the formation of islet amyloid in type-2 diabetes.
Islet amyloid polypeptide (IAPP) is the 37-amino acid peptide subunit of amyloid found in pancreatic islets of type 2 diabetic patients and in insulinomas. Recently, we isolated the human gene encoding IAPP [(1988) FEBS Lett. 239, 227-232]. We now report the nucleotide sequences of a human insulinoma cDNA encoding a complete IAPP precursor, and of the corresponding parts of the IAPP gene. Two exons, which are approx. 5 kb apart in the human genome, encode the 89-amino acid pre-pro-IAPP. At least one additional exon is present further upstream in the IAPP gene. A putative signal sequence at the amino-terminus of the precursor suggests that IAPP is a secreted protein.
Amyloid deposits in the islets of Langerhans of the pancreas are a common finding in non-insulin-dependent diabetes mellitus. The main protein constituent of these deposits is a 37-amino acid peptide known as amylin that resembles calcitonin gene-related peptide, a neuropeptide. We have isolated cDNA clones corresponding to the rat amylin precursor from an islet cDNA library and we show that this peptide is encoded in a 0.9-kilobase mRNA that is translated to yield a 93-amino acid precursor. The amylin peptide is bordered by dibasic residues, suggesting that it is proteolyzed like calcitonin gene-related peptide. The peptide sequences flanking the amylin sequence do not resemble the calcitonin gene-related peptide flanking sequences. RNA hybridization studies show that amylin mRNA is abundant in the islets of Langerhans but is not present in the brain or seven other tissues examined. Dietary changes, such as fasting or fasting and refeeding, have little effect on amylin mRNA expression. This tissue specificity suggests that amylin is involved in specific signaling pathways related to islet function.
Islet amyloid polypeptide has 37 amino acids and is a major component of amyloid deposition in pancreatic islets of patients with type 2 diabetes mellitus. To determine whether the peptide is involved in the impaired insulin secretion in this type of diabetes mellitus, we synthesized islet amyloid polypeptide and its fragments and examined its effect on insulin secretion. Islet amyloid polypeptide inhibited the glucose-stimulated insulin secretion from isolated rat pancreatic islets, as calcitonin gene-related peptide did, but the fragments failed to inhibit the secretion. Thus, we propose that amyloid deposition may be an important factor in the impairment of insulin secretion in type 2 diabetes mellitus.
Islet amyloid polypeptide is a novel 37 amino-acid-residues polypeptide which has been isolated from amyloid deposits in an insulinoma, and in human and cat islets of Langerhans. The molecule has 46% homology with the calcitonin gene-related peptide. Light microscopy examination of the pancreas shows that islet amyloid polypeptide immunoreactivity is restricted to the islet B cells. The present study utilized a rabbit antiserum against a synthetic peptide corresponding to positions 20-29 of islet amyloid polypeptide, a sequence without any amino-acid identity with calcitonin gene-related peptide. By applying the immunogold technique at the ultrastructural level, it was shown that both insulin and islet amyloid polypeptide immunoreactivity occurs in the central granular core of the human B cell secretory granules, while the A cells remain unlabelled. The demonstration that islet amyloid polypeptide is a granular protein of the B cells may indicate that it is released together with insulin. Further studies are necessary to evaluate the functional role of islet amyloid polypeptide.
Adult cats determined by clinical laboratory evaluations to be normal, impaired glucose tolerant, or overtly diabetic were used to explore prospectively the relationships among pancreatic beta cell islet amyloid polypeptide (IAPP) immunoreactivity, islet amyloid (IA) deposition, and diabetogenesis. IAPP-derived IA was found in 11 of 14 (79%) diabetic cats, in four of nine (44%) impaired glucose tolerant cats, and in two of eight (25%) normal adult cats. The presence of IA even in very small amounts, therefore, predicts a very high probability (88%) that an animal has either impaired glucose tolerance or overt DM. Although all overtly diabetic cats had a marked decrease or absence of beta cell IAPP immunoreactivity, six of six cats with impaired glucose tolerance retained IAPP immunoreactivity with 1:15,000 dilutions of antisynthetic IAPP 7-17, whereas only one of seven normal cats had IAPP immunoreactivity beyond 1:10,000 dilutions. These findings suggest that increased IAPP production preceding the development of overt DM is linked to the progressive formation of insoluble IA deposits that are apparent in most overtly diabetic individuals. Of most importance, in that IAPP has been reported to inhibit both basal and insulin-stimulated rates of glycogen synthesis, is the possibility that increased production and release of IAPP by pancreatic beta cells plays a key role in the development of the insulin resistance and impaired glucose tolerance, both of which occur in Type 2 DM.
The content of islet amyloid polypeptide (IAPP) in isolated rat pancreatic islets was determined by a radioimmunoassay. Reverse-phase high-performance liquid chromatography analysis revealed that a main peak of IAPP immunoreactivity in the extracts from the islets corresponded to a synthetic rat IAPP. Secretion of IAPP from the cells is regulated by the extracellular glucose concentration. Thus, IAPP may be a novel regulator for glucose homeostasis and changes in the secretion perhaps relate to insular amyloid deposits and impaired glucose tolerance in type 2 diabetes mellitus.
Islet amyloid polypeptide (IAPP) is a 37-amino-acid putative hormone which is expressed by islet B-cells and most probably is co-released with insulin. IAPP is synthesized as an 89-amino-acid prepropeptide in which IAPP is flanked by two short peptides. The two short peptides are ultimately cleaved off at basic residues. In the present study, we used antisera to three different synthetic peptides corresponding to positions 18-30, 40-50 and 53-62 of prepro-IAPP. The two latter peptides fall within the mature IAPP molecule while the first peptide corresponds to the N-terminal flanking peptide. We demonstrate that normal B-cells and islet amyloid both react immunohistochemically with all of these antisera. Using the immunogold labelling technique, we also demonstrate electron microscopically that both the IAPP immunoreactivity and the pro1-IAPP immunoreactivity in amyloid deposits are confined to the amyloid fibrils per se. These data indicate that not only mature IAPP but also the N-terminal flanking peptide is present in islet amyloid deposits. It remains to be shown if the propeptide segments are involved in the pathogenesis of these amyloid depositions.
Impaired islet function is a feature of non-insulin-dependent diabetes mellitus (NIDDM), which is manifested in part by disproportionate proinsulin release. A disproportionate increase in proinsulin also occurs in insulinomas, suggesting that enhanced proinsulin release results from an increase in synthesis and premature release of proinsulin-rich immature granules in both conditions. However, recent human and animal studies suggest that normal beta-cells respond to an increase in synthetic demand by enhancing their ability to process proinsulin. Thus, impaired processing of proinsulin is likely in NIDDM. A new point of similarity with insulinoma has been the demonstration of a novel pancreatic peptide isolated from insulinomas and the pancreas of patients with NIDDM. This peptide, named islet amyloid polypeptide or amylin, is also present in normal islets. Because of its association with two apparently dissimilar disease states, we propose a hypothesis that encompasses the observations related to proinsulin and islet amyloid polypeptide and suggest they are manifestations of the same abnormality. In this hypothesis, we suggest that this new pancreatic peptide is a normal participant in the process of proinsulin processing and storage. We also suggest that in the presence of defective proinsulin processing and insulin release, as occurs in NIDDM, hyperglycemia stimulates amylin biosynthesis so that this peptide is deposited in increased quantities in the islet as amyloid. This then further exacerbates the diabetic process, resulting in progressive hyperglycemia and deterioration in islet function.
Amyloid deposits localized to the islets of Langerhans are typical of non-insulin-dependent human diabetes mellitus and of diabetes mellitus in adult cats. Amyloid deposits also commonly occur in insulin-producing pancreatic tumors. We have purified a major protein--insulinoma or islet amyloid polypeptide (IAPP)--from human and cat islet amyloid and from amyloid of a human insulinoma. IAPP from human insulinoma contained 37 amino acid residues and had a theoretical molecular mass of 3850 Da. The amino acid sequence is unique but has greater than 40% identity with the human calcitonin gene-related peptide. A partial amino acid sequence of cat islet IAPP corresponding to positions 1-27 of human insulinoma IAPP was identical to the human IAPP except for substitutions in three positions. An antiserum raised to a synthetic human insulinoma IAPP-(7-17) undecapeptide showed specific immunohistochemical reactivity with human and cat islet amyloid and with islet B cells. The significance of this pancreatic neuropeptide-like protein is unknown, but it is suggested that it may exert an important endocrine regulatory effect.
Insulin resistance occurs in a variety of conditions, including diabetes, obesity and essential hypertension, but its underlying molecular mechanisms are unclear. In type 2 (non-insulin-dependent) diabetes mellitus, it is insulin-resistance in skeletal muscle, the chief site of insulin-mediated glucose disposal in humans, that predominantly accounts for the low rates of glucose clearance from the blood, and hence for impaired glucose tolerance. Human type 2 diabetes is characterized by a decrease in non-oxidative glucose storage (muscle glycogen synthesis), and by the deposition of amyloid in the islets of Langerhans. Amylin is a 37-amino-acid peptide which is a major component of islet amyloid and has structural similarity to human calcitonin gene-related peptide-2 (CGRP-2; ref. 8). CGRP is a neuropeptide which may be involved in motor activity in skeletal muscle. We now report that human pancreatic amylin and rat CGRP-1 are potent inhibitors of both basal and insulin-stimulated rates of glycogen synthesis in stripped rat soleus muscle in vitro. These results may provide a basis for a new understanding of the molecular mechanisms that cause insulin resistance in skeletal muscle.
A novel putative polypeptide hormone identified as islet amyloid polypeptide (IAPP) was recently purified from islet amyloid (IA) of diabetic humans and cats, and also from amyloid of a human insulinoma. Although the function of IAPP is yet unknown, its occurrence in pancreatic endocrine tissue and its partial amino acid sequence identity with calcitonin gene-related peptide (CGRP) suggests an endocrine regulatory effect. In the present investigation, the authors utilized antisera to insulin, glucagon, somatostatin, pancreatic polypeptide, synthetic human CGRP, and a synthetic human IAPP (7-17) undecapeptide to immunohistochemically (PAP technique) document the presence of IAPP immunoreactive cells in the islets of the cat, dog, mouse, and rat, but not in the islets of the horse or calf. In serial sections of islets from these species it was shown that IAPP immunoreactivity occurred in insulin-reactive beta cells. This observation was confirmed immunocytochemically in cat islets by means of protein A-gold probes. With protein A-gold labeling techniques, IAPP immunoreactivity was localized to the outer lucent compartment of the beta cell secretory granule, whereas insulin immunoreactivity was associated with the electron-dense core. These findings provide strong evidence that IAPP or an IAPP precursor is synthesized by beta cells and is stored in beta cell granules for subsequent co-secretion with insulin. The conservation of IAPP in humans and multiple animal species and the localization of IAPP to pancreatic beta cells provide further evidence that IAPP has an important endocrine regulatory function. The propensity of IAPP to polymerize and form IA fibrils in diabetes associated with aging may indicate that IAPP is in some way also linked to the development of Type 2 diabetes.
Amyloid deposition is a very typical alteration in the islets of Langerhans in human Type 2 (non-insulin-dependent) diabetes mellitus and in feline diabetes mellitus. Amyloid infiltration is also commonly found in insulin-producing pancreatic tumors. It was shown recently that amyloid purified from an insulinoma was composed mainly of a novel polypeptide (insulinoma amyloid polypeptide, IAPP), which had partial identity with the neuropeptide calcitonin gene-related peptide (CGRP). Cat islet amyloid contained a similar polypeptide. This finding is verified in the present study, and it is shown that the cat IAPP differs from the human peptide only in two of the 16 elucidated amino acid residues. The authors now also show by N-terminal amino acid sequence analysis that human islet amyloid is of IAPP origin. Although the significance of IAPP is unknown, its occurrence in pancreatic endocrine tissue and partial identity with a known neuropeptide suggests an endocrine regulatory function.
The relationship between the degree of amyloidosis in pancreatic islet tissue and the frequency of islets containing amyloid was studied in an autopsy material. A very strong positive correlation was found between these two variables in both the head and the tail of the pancreas. There was also a positive correlation between the degree of amyloidosis in islets containing amyloid and their frequency. This may indicate that the deposition of amyloid in the islets of Langerhans is a continuous process affecting progressively increasing numbers of islets. It is probable that the amyloid formation in the islets is influenced by some factor or factors that affect the different islets to different degrees. It is conceivable that one such factor may be vascular changes. The strong correlation between the frequency of islets containing amyloid and the degree of amyloidosis can be utilized as a simple and rapid method of determining the latter.
Benzamidine, an inhibitor of plasmin, was compared with aprotinin (Trasylol) to determine whether it would protect against the degradation of glucagon in human plasma. At concentrations of benzamidine exceeding .05m, insignificant degradation of [125I] glucagon occurred in undiluted plasma up to 72 hr at 4 C. In plasma diluted 1:5 with buffer, glucagon destruction was inhibited by 0.01m benzamidine, which also did not interfere with antigen-antibody affinity using a rabbit antiserum with a high specificity for pancreatic glucagon (Unger antiserum 30K). When added to undiluted plasma in 0.05m benzamidine, recovery of glucagon exceeded 85% as measured by radioimmunoassay in 0.01m benzamidine. Values for immunoreactive glucagon in plasma of subjects after an overnight fast and following arginine stimulation were similar in the presence of benzamidine or Trasylol. At 1% of the cost of Trasylol, benzamidine was found to be as effective as Trasylol in the prevention of glucagon degradation in human plasma.
Dihydrosomatostatin (0.001–1.0 ug/ml) inhibited both insulin and glucagon secretion by monolayer cell cultures of newborn rat pancreas. When cultures were incubated with somatostatin and then rinsed, the effect of somatostatin appeared to last longer on the pancreatic alpha cell than on the beta cell as indicated by a more prolonged inhibition of glucagon secretion than of insulin release. Submaximal inhibition of glucose-stimulated insulin release by somatostatin was partially reversed by increasing the concentration of glucose. We conclude that the effect of somatostatin appears to be mediated directly on the pancreatic endocrine cells.
A modified plasma radioimmunoassay has been developed that uses a cellulose slurry to separate bound from free insulin. This material, which is commercially available, shelf stable, and simple to prepare, makes it possible to run the entire method in test tubes and to use a low specific activity insulin. Details concerning conditions and materials that determined sensitivity, accuracy, and precision are reported. The method is sensitive to about 10 μU/ml. of plasma and has a reproducibility of approximately ± 15 per cent. This method is proposed for use by those who desire to measure rises in plasma insulin by a simple, rapid and reasonably accurate technic.
Unlabelled:
Monolayer cultures of neonatal rat pancreatic islets were superfused to examine phasic insulin secretion. When stimulated with a constant glucose concentration of 300 mg/dl, insulin secretion promptly rose to a peak more than eightfold higher than the basal levels observed with glucose 30 mg/dl. This first-phase peak was followed by a quick decline in insulin to a level about four- to fivefold higher than basal, representing second-phase insulin secretion. Addition of sodium salicylate 20 mg/dl enhanced glucose-stimulated insulin secretion. Addition of salicylate concurrently with glucose greatly enhanced second-phase insulin secretion, but did not affect the first-phase peak, thereby converting the biphasic pattern to one that appeared to be monophasic. However, when cultures were superfused with salicylate both before and concurrent with stimulation by glucose, both the first-phase peak and the second phase of insulin secretion were increased, resulting in not only preservation but enhancement of the biphasic pattern. Salicylate had no effect on basal insulin secretion at glucose 30 mg/dl. During the transition from glucose 300 mg/dl to 30 mg/dl, immediately as glucose concentration began to fall in the superfusate, insulin secretion showed a transient increase ("off response").
Conclusions:
(1) Cultures of neonatal rat pancreatic islet cells respond with a biphasic pattern of insulin secretion when exposed to a continuous and constant glucose stimulus. (2) When endogenous prostaglandin synthesis is inhibited by sodium salicylate, the biphasic pattern not only remains but is enhanced, indicating that endogenous prostaglandin synthesis exerts a tonic restraint throughout the entire period of glucose-stimulated phasic insulin release.(ABSTRACT TRUNCATED AT 250 WORDS)
Inhibitory action of diabetes-associated peptide and calcitonin gene-related peptide on insulin release (Abstract)
- M Kogire
- J-K Chang
- J C Thompson
- G H Greeley
Kogire M, Chang J-K, Thompson JC, Greeley GH Jr: Inhibitory action of
diabetes-associated peptide and calcitonin gene-related peptide on insulin release (Abstract). In Proc Annu Meet Endocr Soc, 70th, Seattle,
WA, 1989, p. 55
Phasic glucose-stimulated insulin secretion by DIABETES
- Wy Fujimoto
- Sa Metz
Fujimoto WY, Metz SA: Phasic glucose-stimulated insulin secretion by
DIABETES, VOL. 39, MAY 1990
AND 8-CELLS neonatal rat pancreatic islet cells: enhancement by sodium salicylate
IAPP, INSULIN, AND 8-CELLS
neonatal rat pancreatic islet cells: enhancement by sodium salicylate.
Diabetes 33:872-78, 1984