Human islet amyloid polypeptide (hIAPP) aggregation in type 2 diabetes: Correlation between intrinsic physicochemical properties of hIAPP aggregates and their cytotoxicity

Experimental and computational investigation of the effect of Hsc70 structural variants on inhibiting amylin aggregation

The misfolding and aggregation of human islet amyloid polypeptide (hIAPP), also known as amylin, have been implicated in the pathogenesis of type 2 diabetes (T2D). Heat shock proteins, specifically, heat shock cognate 70 (Hsc70), are molecular chaperones that protect against hIAPP misfolding and inhibits its aggregation. Nevertheless, there is an incomplete understanding of the mechanistic interactions between Hsc70 domains and hIAPP, thus limiting their potential therapeutic role in diabetes. This study investigates the inhibitory capacities of different Hsc70 variants, aiming to identify the structural determinants that strike a balance between efficacy and cytotoxicity. Our experimental findings demonstrate that the ATPase activity of Hsc70 is not a pivotal factor for inhibiting hIAPP misfolding. We underscore the significance of the C-terminal substrate-binding domain of Hsc70 in inhibiting hIAPP aggregation, emphasizing that the removal of the lid subdomain diminishes the inhibitory effect of Hsc70. Additionally, we employed atomistic discrete molecular dynamics simulations to gain deeper insights into the interaction between Hsc70 variants and hIAPP. Integrating both experimental and computational findings, we propose a mechanism by which Hsc70's interaction with hIAPP monomers disrupts protein-protein connections, primarily by shielding the β-sheet edges of the Hsc70-β-sandwich. The distinctive conformational dynamics of the alpha helices of Hsc70 potentially enhance hIAPP binding by obstructing the exposed edges of the β-sandwich, particularly at the β5-β8 region along the alpha helix interface. This, in turn, inhibits fibril growth, and similar results were observed following hIAPP dimerization. Overall, this study elucidates the structural intricacies of Hsc70 crucial for impeding hIAPP aggregation, improving our understanding of the potential anti-aggregative properties of molecular chaperones in diabetes treatment.

β-Carboline Alkaloids Resist the Aggregation and Cytotoxicity of Human Islet Amyloid Polypeptide

β-Carboline alkaloids have a variety of pharmacological activities, such as antitumor, antibiosis and antidiabetes. Harmine and harmol are two structurally similar β-carbolines that occur in many medicinal plants. In this work, we chose harmine and harmol to impede the amyloid fibril formation of human islet amyloid polypeptide (hIAPP) associated with type 2 diabetes mellitus (T2DM), by a series of physicochemical and biochemical methods. The results indicate that harmine and harmol effectively prevent peptide fibril formation and alleviate toxic oligomer species. In addition, both small molecules exhibit strong binding affinities with hIAPP mainly through hydrophobic and hydrogen bonding interactions, thus reducing the cytotoxicity induced by hIAPP. Their distinct binding pattern with hIAPP is closely linked to the molecular configuration of the two small molecules, affecting their ability to impede peptide aggregation. The study is of great significance for the application and development of β-carboline alkaloids against T2DM.

Modulatory role of copper on hIAPP aggregation and toxicity in presence of insulin

Aggregation of the human islets amyloid polypeptide, or hIAPP, is linked to β-cell death in type II diabetes mellitus (T2DM). Different pancreatic β-cell environmental variables such as pH, insulin and metal ions play a key role in controlling the hIAPP aggregation. Since insulin and hIAPP are co-secreted, it is known from numerous studies that insulin suppresses hIAPP fibrillation by preventing the initial dimerization process. On the other hand, zinc and copper each have an inhibitory impact on hIAPP fibrillation, but copper promotes the production of toxic oligomers. Interestingly, the insulin oligomeric equilibrium is controlled by the concentration of zinc ions when the effect of insulin and zinc has been tested together. Lower zinc concentrations cause the equilibrium to shift towards the monomer and dimer states of insulin, which bind to monomeric hIAPP and stop it from developing into a fibril. On the other hand, the combined effects of copper and insulin have not yet been done. In this study, we have demonstrated how the presence of copper affects hIAPP aggregation and the toxicity of the resultant conformers with or without insulin. For this purpose, we have used a set of biophysical techniques, including NMR, fluorescence, CD etc., in combination with AFM and cell cytotoxicity assay. In the presence and/or absence of insulin, copper induces hIAPP to form structurally distinct stable toxic oligomers, deterring the fibrillation process. More specifically, the oligomers generated in the presence of insulin have slightly higher toxicity than those formed in the absence of insulin. This research will increase our understanding of the combined modulatory effect of two β-cell environmental factors on hIAPP aggregation.

Evaluating the inhibitory potential of natural compound luteolin on human lysozyme fibrillation

Numerous pathophysiological conditions known as amyloidosis, have been connected to protein misfolding leading to aggregation of proteins. Inhibition of cytotoxic aggregates or disaggregation of the preformed fibrils is thus one of the important strategies in the prevention of such diseases. Growing interest and exploration of identification of small molecules mainly natural compounds can prevent or delay amyloid fibril formation. We examined the mechanism of interaction and inhibition of human lysozyme (HL) aggregates with luteolin (LT). Biophysical and computational approaches have been employed to study the effect of LT on HL amyloid aggregation. Transmission Electronic Microscopy, Thioflavin T fluorescence, UV-vis spectroscopy, and RLS demonstrates that LT inhibit HL fibril formation. ANS fluorescence and hemolytic assay was also employed to examine the effect of the LT on toxicity of HL aggregation. Docking and molecular dynamics results showed that LT interacted with HL via hydrophobic and hydrogen interactions, thus reducing fibrillation levels. These findings highlight the benefit of polyphenols as safe therapy for preventing amyloid related diseases.

Human Islet Amyloid Polypeptide (hIAPP) Protofibril-Specific Antibodies for Detection and Treatment of Type 2 Diabetes

Type 2 diabetes mellitus (T2D) is a major public health concern and is characterized by sustained hyperglycemia due to insulin resistance and destruction of insulin-producing β cells. One pathological hallmark of T2D is the toxic accumulation of human islet amyloid polypeptide (hIAPP) aggregates. Monomeric hIAPP is a hormone normally co-secreted with insulin. However, increased levels of hIAPP in prediabetic and diabetic patients can lead to the formation of hIAPP protofibrils, which are toxic to β cells. Current therapies fail to address hIAPP aggregation and current screening modalities do not detect it. Using a stabilizing capping protein, monoclonal antibodies (mAbs) can be developed against a previously nonisolatable form of hIAPP protofibrils, which are protofibril specific and do not engage monomeric hIAPP. Shown here are two candidate mAbs that can detect hIAPP protofibrils in serum and hIAPP deposits in pancreatic islets in a mouse model of rapidly progressing T2D. Treatment of diabetic mice with the mAbs delays disease progression and dramatically increases overall survival. These results demonstrate the potential for using novel hIAPP protofibril-specific mAbs as a diagnostic screening tool for early detection of T2D, as well as therapeutically to preserve β cell function and target one of the underlying pathological mechanisms of T2D.

Regulation of oxaliplatin and carboplatin on the assembly behavior and cytotoxicity of human islet amyloid polypeptide

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.

Simulations of Cross-Amyloid Aggregation of Amyloid-β and Islet Amyloid Polypeptide Fragments

Amyloid-beta (Aβ) and islet amyloid polypeptide (IAPP) are small peptides, classified as amyloids, that have the potential to self-assemble and form cytotoxic species, such as small soluble oligomers and large insoluble fibrils. The formation of Aβ aggregates facilitates the progression of Alzheimer's disease (AD), while IAPP aggregates induce pancreatic β-cell apoptosis, leading to exacerbation of Type 2 diabetes (T2D). Cross-amyloid interactions between Aβ and IAPP have been described both in vivo and in vitro, implying the role of Aβ or IAPP as modulators of cytotoxic self-aggregation of each species, and suggesting that Aβ-IAPP interactions are a potential molecular link between AD and T2D. Using molecular dynamics simulations, "hot spot" regions of the two peptides were studied to understand the formation of hexamers in a heterogenous and homogenous peptide-containing environment. Systems of only Aβ_(16-22) peptides formed antiparallel, β-barrel-like structures, while systems of only IAPP_(20-29) peptides formed stacked, parallel beta sheets and had relatively unstable aggregation structures after 2 μs of simulation time. Systems containing both Aβ and IAPP (1:1 ratio) hexamers showed antiparallel, β-barrel-like structures, with an interdigitated arrangement of Aβ_(16-22) and IAPP_(20-29). These β-barrel structures have features of cytotoxic amyloid species identified in previous literature. Ultimately, this work seeks to provide atomistic insight into both the mechanism behind cross-amyloid interactions and structural morphologies of these toxic amyloid species.

Triterpenoids impede the fibrillation and cytotoxicity of human islet amyloid polypeptide

The inhibition of human islet amyloid polypeptide (hIAPP) deposition to block its toxicity is an important strategy for the prevention and treatment of type II diabetes mellitus (T2DM).Natural compounds with pharmacological properties and low toxicity can serve as a good point to discover potential inhibitors of protein misfolding, which may be useful for the treatment of various amyloidosis-related diseases. Previous studies have reported that triterpenoids, such as maslinic acid (MA) and momordicin I (MI), can modulate glucose metabolism partially by reducing insulin resistance. However, the internal antidiabetic mechanism of these triterpenoids remains unclear. In this study, we examined the inhibition and disaggregation of MAandits isomer MI on the fibrillation of hIAPP using various experimental and computational approaches. The assembly behaviors and peptide-induced cytotoxicity of hIAPP could be effectively resisted by MA and MI. Moreover, the interaction of the two triterpenoids with hIAPP displayed a spontaneous and exothermic process. Moreover, molecular dynamics simulation results of different peptides revealed that MA and MI could bind to Asn and other non-polar residues near the core C-terminal region and reduce the oligomerization of hIAPP. The binding affinity was predominantly contributed by hydrophobic, electrostatic and hydrogen bonding interactions. The present work provides valuable data for MA and MI to treat T2DM and amyloidosis-related diseases.

Disaggregation of Islet Amyloid Polypeptide Fibrils as a Potential Anti-Fibrillation Mechanism of Tetrapeptide TNGQ

Islet amyloid polypeptide (IAPP) fibrillation has been commonly associated with the exacerbation of type 2 diabetes prognosis. Consequently, inhibition of IAPP fibrillation to minimize β-cell cytotoxicity is an important approach towards β-cell preservation and type 2 diabetes management. In this study, we identified three tetrapeptides, TNGQ, MANT, and YMSV, that inhibited IAPP fibrillation. Using thioflavin T (ThT) fluorescence assay, circular dichroism (CD) spectroscopy, dynamic light scattering (DLS), and molecular docking, we evaluated the potential anti-fibrillation mechanism of the tetrapeptides. ThT fluorescence kinetics and microscopy as well as transmission electron microscopy showed that TNGQ was the most effective inhibitor based on the absence of normal IAPP fibrillar morphology. CD spectroscopy showed that TNGQ maintained the α-helical conformation of monomeric IAPP, while DLS confirmed the presence of varying fibrillation species. Molecular docking showed that TNGQ and MANT interact with monomeric IAPP mainly by hydrogen bonding and electrostatic interaction, with TNGQ binding at IAPP surface compared to YMSV, which had the highest docking score, but interact mainly through hydrophobic interaction in IAPP core. The highly polar TNGQ was the most active and appeared to inhibit IAPP fibrillation by disaggregation of preformed IAPP fibrils. These findings indicate the potential of TNGQ in the development of peptide-based anti-fibrillation and antidiabetic nutraceuticals.

Mechanistic Insights into the Polymorphic Associations and Cross-Seeding of Aβ and hIAPP in the Presence of Histidine Tautomerism: An All-Atom Molecular Dynamic Study

Hundreds of millions of people around the world have been affected by Type 2 diabetes (T2D) which is a metabolic disorder. Clinical research has revealed T2D as a possible risk factor for Alzheimer's disease (AD) development (and vice versa). Amyloid-β (Aβ) and human islet amyloid polypeptide are the main pathological species in AD and T2D, respectively. However, the mechanisms by which these two amyloidogenic peptides co-aggregate are largely uninvestigated. Herein, for the first time, we present the cross-seeding between Amylin1-37 and Aβ40 considering the particular effect of the histidine tautomerism at atomic resolution applying the all-atom molecular dynamics (MD) simulations for heterodimeric complexes. The results via random seed MD simulations indicated that the Aβ40(δδδ) isomer in cross-talking with Islet(ε) and Islet(δ) isomers could retain or increase the β-sheet content in its structure that may make it more prone to further aggregation and exhibit higher toxicity. The other tautomeric isomers which initially did not have a β-sheet structure in their monomeric forms did not show any generated β-sheet, except for one seed of the Islet(ε) and Aβ40(εεε) heterodimers complex that displayed a small amount of formed β-sheet. This computational research may provide a different point of view to examine all possible parameters that may contribute to the development of AD and T2D and provide a better understanding of the pathological link between these two severe diseases.

Inhibition of Islet Amyloid Polypeptide Fibrillation by Structurally Diverse Phenolic Compounds and Fibril Disaggregation Potential of Rutin and Quercetin

The influence of 12 food-derived phenolic compounds on islet amyloid polypeptide (IAPP) fibrillation was investigated. Results from thioflavin T assay demonstrated that gallic acid, caffeic acid, and rutin and its aglycone, quercetin, inhibited IAPP fibrillation at 1:0.5, 1:1, and 1:2 IAPP-phenolic molar ratios. Circular dichroism and dynamic light scattering at the 1:1 IAPP-phenolic ratio confirmed the inhibition of fibril formation. Rutin and quercetin increased the lag time by 90 and 6%, and the relative α-helix content by 63 and 48%, respectively. Gallic acid decreased the elongation rate by 30%, whereas caffeic acid decreased the maximum fluorescence intensity by 65%. Furthermore, fluorescence microscopy and transmission electron microscopy (TEM) showed IAPP fibril morphologies indicative of fibrillation reduction by the compounds. Molecular docking and TEM showed that rutin and quercetin disaggregated preformed IAPP fibrils potentially through fibrillar-monomeric equilibrium shifts. These findings demonstrate important structural features of phenolic compounds for disaggregating IAPP fibrils or inhibiting their formation.

Anti-IAPP Monoclonal Antibody Improves Clinical Symptoms in a Mouse Model of Type 2 Diabetes

Type 2 Diabetes Mellitus (T2DM) is a chronic progressive disease, defined by insulin resistance and insufficient insulin secretion to maintain normoglycemia. Amyloidogenic aggregates are a hallmark of T2DM patients; they are cytotoxic for the insulin producing β-cells, and cause inflammasome-dependent secretion of IL-1β. To avoid the associated β-cell loss and inflammation in advanced stage T2DM, we developed a novel monoclonal therapy targeting the major component of aggregates, islet amyloid polypeptide (IAPP). The here described monoclonal antibody (mAb) m81, specific for oligomeric and fibrils, but not for soluble free IAPP, is able to prevent oligomer growth and aggregate formation in vitro, and blocks islet inflammation and disease progression in vivo. Collectively, our data show that blocking fibril formation and prevention of new amyloidogenic aggregates by monoclonal antibody therapy may be a potential therapy for T2DM.

Understanding the Role of Protein Glycation in the Amyloid Aggregation Process

Protein function and flexibility is directly related to the native distribution of its structural elements and any alteration in protein architecture leads to several abnormalities and accumulation of misfolded proteins. This phenomenon is associated with a range of increasingly common human disorders, including Alzheimer and Parkinson diseases, type II diabetes, and a number of systemic amyloidosis characterized by the accumulation of amyloid aggregates both in the extracellular space of tissues and as intracellular deposits. Post-translational modifications are known to have an active role in the in vivo amyloid aggregation as able to affect protein structure and dynamics. Among them, a key role seems to be played by non-enzymatic glycation, the most unwanted irreversible modification of the protein structure, which strongly affects long-living proteins throughout the body. This study provided an overview of the molecular effects induced by glycation on the amyloid aggregation process of several protein models associated with misfolding diseases. In particular, we analyzed the role of glycation on protein folding, kinetics of amyloid formation, and amyloid cytotoxicity in order to shed light on the role of this post-translational modification in the in vivo amyloid aggregation process.

Self-Assembled Nanochaperones Inhibit the Aggregation of Human Islet Amyloid Polypeptide Associated with Type 2 Diabetes

Human islet amyloid polypeptide (hIAPP) aggregation is closely associated with dysfunction and apoptosis of pancreatic β-cells in type 2 diabetes (T2D). Accordingly, hIAPP amyloid inhibitors have shown promise against T2D. Here, by mimicking the function of natural molecular chaperones, nanochaperones (nChaps) based on self-assembled polymeric micelles with tunable surface microdomains for T2D treatment are reported. By capturing the aggregation-prone species of hIAPP onto the hydrophobic microdomains and segregating them by hydrophilic PEG chains, this kind of nChaps could effectively prevent hIAPP aggregation, block cell adhesion of hIAPP, facilitate hIAPP aggregates degradation and reduce hIAPP-related cytotoxicity. Therefore, our work will provide useful insights to develop a biomimetic strategy for the treatment of T2D.

A review on recent advances in amino acid and peptide-based fluorescence and its potential applications

Fluorescence is widely used to detect functional groups and ions, and peptides are used in various fields due to their excellent biological activity.

Proteostasis unbalance of nucleophosmin 1 in Acute Myeloid Leukemia: An aggregomic perspective

The role exerted by the nucleus in the regulation of proteostasis in both health and disease is recognized of outmost importance, even though not fully understood. Many recent investigations are focused on its ability to modulate and coordinate protein quality control machineries in mammalian cells. Nucleophosmin 1 (NPM1) is one of the most abundant nucleolar proteins and its gene is mutated in ~30% of Acute Myeloid Leukemia (AML) patients. Mutations are localized in the C-terminal domain of the protein and cause cytoplasmatically delocalized and possibly aggregated forms of NPM1 (NPM1c+). Therapeutic interventions targeted on NPM1c+ are in demand and, to this end, deeper knowledge of NPM1c+ behavior in the blasts' cytosol is required. Here by means of complementary biophysical techniques we compared the conformational and aggregative behavior of the entire C-terminal domains of NPM1wt and type A NPM1c+ (bearing the most common mutation). Overall data show that only Cterm_mutA is able to form amyloid-like assemblies with fibrillar morphology and that the oligomers are toxic in human neuroblastoma SHSY cells. This study adds a novel piece of knowledge to the comprehension of the molecular roles exerted by cytoplasmatic NPM1c+ and suggests the exploitation of the amyloidogenic propensity of NPM1c+ as a new strategy for targeting AML with NPM1 mutations.

Protein-conformational diseases in childhood: Naturally-occurring hIAPP amyloid-oligomers and early β-cell damage in obesity and diabetes

BACKGROUND AND AIMS

This is the first time that obesity and diabetes mellitus (DM) as protein conformational diseases (PCD) are reported in children and they are typically diagnosed too late, when β-cell damage is evident. Here we wanted to investigate the level of naturally-ocurring or real (not synthetic) oligomeric aggregates of the human islet amyloid polypeptide (hIAPP) that we called RIAO in sera of pediatric patients with obesity and diabetes. We aimed to reduce the gap between basic biomedical research, clinical practice-health decision making and to explore whether RIAO work as a potential biomarker of early β-cell damage.

MATERIALS AND METHODS

We performed a multicentric collaborative, cross-sectional, analytical, ambispective and blinded study; the RIAO from pretreated samples (PTS) of sera of 146 pediatric patients with obesity or DM and 16 healthy children, were isolated, measured by sound indirect ELISA with novel anti-hIAPP cytotoxic oligomers polyclonal antibody (MEX1). We carried out morphological and functional studied and cluster-clinical data driven analysis.

RESULTS

We demonstrated by western blot, Transmission Electron Microscopy and cell viability experiments that RIAO circulate in the blood and can be measured by ELISA; are elevated in serum of childhood obesity and diabetes; are neurotoxics and works as biomarkers of early β-cell failure. We explored the range of evidence-based medicine clusters that included the RIAO level, which allowed us to classify and stratify the obesity patients with high cardiometabolic risk.

CONCLUSIONS

RIAO level increases as the number of complications rises; RIAOs > 3.35 μg/ml is a predictor of changes in the current indicators of β-cell damage. We proposed a novel physio-pathological pathway and shows that PCD affect not only elderly patients but also children. Here we reduced the gap between basic biomedical research, clinical practice and health decision making.

Date palm (Phoenix dactylifera L.) fruit's polyphenols as potential inhibitors for human amylin fibril formation and toxicity in type 2 diabetes

BACKGROUND

β-Cell death is the key feature of type 2 diabetes mellitus (T2DM). The misfolding of human Islet Amyloid Polypeptide (hIAPP) is regarded as one of the causative factors of T2DM. Recent studies suggested that a diet based on date fruits presents various health benefits, as these fruits are naturally enriched in plant polyphenols.

METHOD

In this study, we used a broad biophysical approach, using cell biology techniques and bioinformatic tools, to demonstrate that various polyphenols from date palm (Phoenix dactylifera L.) fruit significantly inhibited hIAPP aggregation and cytotoxicity.

RESULT

Our results suggest that all of the polyphenols showed inhibitory effects, albeit varied, on the formation of toxic hIAPP amyloids. Correlation between cell viability assay, permeabilization of synthetic phospholipid vesicles tests, and ANS florescence measurements, revealed that both classes of polyphenols protected INS-1E cells from the toxicity of amylin aggregates. Docking results showed that the used polyphenols physically interacted with both hIAPP amyloidogenic region (residues Ser20-Ser29) and the non-amyloidogenic regions via hydrophobic and hydrogen interactions, thus reducing aggregation levels.

CONCLUSION

These findings highlight the benefits of consuming dates and the great potential of its polyphenols as a potential therapy for the prevention and treatment of T2DM as well as for many other amyloid-related diseases.

Inhibition of human islet amyloid polypeptide aggregation and cellular toxicity by oleuropein and derivatives from olive oil

Loss of β-cell function and β-cell death is the key feature of type 2 diabetes mellitus (T2DM). One hypothesis for the mechanism of this feature is amyloid formation by the human islet amyloid polypeptide (hIAPP). Despite the global prevalence of T2DM, there are no therapeutic strategies for the treatment of or prevention of amylin amyloidosis. Clinical trials and population studies indicate the healthy virtues of the Mediterranean diet, especially the extra virgin olive oil (EVOO) found in this diet. This oil is enriched in phenolic compounds shown to be effective against several aging and lifestyle diseases. Oleuropein (Ole), one of the most abundant polyphenols in EVOO, has been reported to be anti-diabetic. Some of Ole's main derivative have attracted our interest due to their multi-targetted effects, including interference with amyloid aggregation path. However, the structure-function relationship of Ole and its metabolites in T2DM are not yet clear. We report here a broad biophysical approach and cell biology techniques that enabled us to characterize the different molecular mechanisms by which tyrosol (TYR), hydroxytyrosol (HT), oleuropein (Ole) and oleuropein aglycone (OleA) modulate the hIAPP fibrillation in vitro and their effects on cell cytotoxicity. The OleA formed by enolic acid and hydroxytyrosol moiety was found to be more active than the Ole and HT at low micromolar concentrations. We further demonstrated that OleA inhibit the cytotoxicity induced by hIAPP aggregates by protecting more the cell membrane from permeabilization and then from death. These findings highlight the benefits of consuming EVOO and the great potential of its polyphenols, mainly OleA. Moreover, they support the possibility to validate and optimize the possible pharmacological use of EVOO polyphenols for T2DM prevention and therapy and also for many other amyloid related diseases.

The Role of Glycation on the Aggregation Properties of IAPP

Epidemiological evidence shows an increased risk for developing Alzheimer's disease in people affected by diabetes, a pathology associated with increased hyperglycemia. A potential factor that could explain this link could be the role that sugars may play in both diseases under the form of glycation. Contrary to glycosylation, glycation is an enzyme-free reaction that leads to formation of toxic advanced glycation end-products (AGEs). In diabetes, the islet amyloid polypeptide (IAPP or amylin) is found to be heavily glycated and to form toxic amyloid-like aggregates, similar to those observed for the Aβ peptides, often also heavily glycated, observed in Alzheimer patients. Here, we studied the effects of glycation on the structure and aggregation properties of IAPP with several biophysical techniques ranging from fluorescence to circular dichroism, mass spectrometry and atomic force microscopy. We demonstrate that glycation occurs exclusively on the N-terminal lysine leaving the only arginine (Arg11) unmodified. At variance with recent studies, we show that the dynamical interplay between glycation and aggregation affects the structure of the peptide, slows down the aggregation process and influences the aggregate morphology.

The flanking peptides issue from the maturation of the human islet amyloid polypeptide (hIAPP) slightly modulate hIAPP-fibril formation but not hIAPP-induced cell death

Type 2 diabetes mellitus is a disease characterized by the formation of amyloid fibrillar deposits consisting mainly in human islet amyloid polypeptide (hIAPP), a peptide co-produced and co-secreted with insulin. hIAPP and insulin are synthesized by pancreatic β cells initially as prehormones resulting after sequential cleavages in the mature peptides as well as the two flanking peptides (N- and C-terminal) and the C-peptide, respectively. It has been suggested that in the secretory granules, the kinetics of hIAPP fibril formation could be modulated by some internal factors. Indeed, insulin is known to be a potent inhibitor of hIAPP fibril formation and hIAPP-induced cell toxicity. Here we investigate whether the flanking peptides could regulate hIAPP fibril formation and toxicity by combining biophysical and biological approaches. Our data reveal that both flanking peptides are not amyloidogenic. In solution and in the presence of phospholipid membranes, they are not able to totally inhibit hIAPP-fibril formation neither hIAPP-membrane damage. In the presence of INS-1 cells, a rat pancreatic β-cell line, the flanking peptides do not modulate hIAPP fibrillation neither hIAPP-induced cell death while in the presence of human islets, they have a slightly tendency to reduce hIAPP fibril formation but not its toxicity. These data demonstrate that the flanking peptides do not strongly contribute to reduce mature hIAPP amyloidogenesis in solution and in living cells, suggesting that other biochemical factors present in the cells must act on mature hIAPP fibril formation and hIAPP-induced cell death.

Unpacking the aggregation-oligomerization-fibrillization process of naturally-occurring hIAPP amyloid oligomers isolated directly from sera of children with obesity or diabetes mellitus

The formation of amyloid oligomers and fibrils of the human islet amyloid polypeptide (hIAPP) has been linked with β- cell failure and death which causes the onset, progression, and comorbidities of diabetes. We begin to unpack the aggregation-oligomerization-fibrillization process of these oligomers taken from sera of pediatric patients. The naturally occurring or real hIAPP (not synthetic) amyloid oligomers (RIAO) were successfully isolated, we demonstrated the presence of homo (dodecamers, hexamers, and trimers) and hetero-RIAO, as well as several biophysical characterizations which allow us to learn from the real phenomenon taking place. We found that the aggregation/oligomerization process is active in the sera and showed that it happens very fast. The RIAO can form fibers and react with anti-hIAPP and anti-amyloid oligomers antibodies. Our results opens the epistemic horizon and reveal real differences between the four groups (Controls vs obesity, T1DM or T2DM) accelerating the process of understanding and discovering novel and more efficient prevention, diagnostic, transmission and therapeutic pathways.