Amylin uncovered: a review on the polypeptide responsible for type II diabetes

Effect of a SARS-CoV-2 Protein Fragment on the Amyloidogenic Propensity of Human Islet Amyloid Polypeptide

Infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the onset of COVID-19 have been linked to an increased risk of developing type 2 diabetes. While a variety of mechanisms may ultimately be responsible for the onset of type 2 diabetes under these circumstances, one mechanism that has been postulated involves the increased aggregation of human islet amyloid polypeptide (hIAPP) through direct interaction with SARS-CoV-2 viral proteins. Previous computational studies investigating this possibility revealed that a nine-residue peptide fragment known as SK9 (SFYVYSRVK) from the SARS-CoV-2 envelope protein can stabilize the native conformation of hIAPP1-37 by interacting with the N-terminal region of amylin. One of the areas particularly stabilized through this interaction encompasses residues 15-28 of amylin. Given these findings, we investigated whether SK9 could interact with short amyloidogenic sequences derived from this region of amylin. Here, we employ docking studies, molecular dynamics simulations, and biophysical techniques to provide theoretical as well as direct experimental evidence that SK9 can interact with hIAPP12-18 and hIAPP20-29 peptides. Furthermore, we demonstrate that SK9 not only can interact with these sequences but also serves to prevent the self-assembly of these amyloidogenic peptides. In striking contrast, we also show that SK9 has little effect on the amyloidogenic propensity of full-length amylin. These findings are contrary to previous published simulations involving SK9 and hIAPP1-37. Such observations may assist in clarifying potential mechanisms of the SARS-CoV-2 interaction with hIAPP and its relevance to the onset of type 2 diabetes in the setting of COVID-19.

Heterotypic Interactions of Amyloid β and the Islet Amyloid Polypeptide Produce Mixed Aggregates with Non-Native Fibril Structure

Amyloid aggregates are hallmarks of the pathology of a wide range of diseases, including type 2 diabetes (T2D) and Alzheimer's disease (AD). Much epidemiological and pathological evidence points to significant overlap between AD and T2D. Individuals with T2D have a higher likelihood of developing AD; moreover, colocalized aggregates of amyloid β (Aβ) and the islet amyloid polypeptide (IAPP), the two main peptides implicated in the formation of toxic amyloid aggregates in AD and T2D, have also been identified in the brain. However, how these peptides interact with each other is not well understood, and the structural facets of heterotypic mixed fibrils formed via such interactions remain elusive. Here we use atomic force microscopy augmented with infrared spectroscopy to probe the secondary structure of individual aggregates formed via heterotypic interactions of Aβ and IAPP and provide unequivocal direct evidence of mixed aggregates. Furthermore, we show that co-aggregation of the peptides from the monomeric stage leads to the formation of unique polymorphs, in which both peptides undergo structural deviation from their native states, whereas seeding with preformed IAPP fibrils leads to aggregates similar to native Aβ. These findings highlight how heterotypic interactions between amyloidogenic peptides can lead to polymorphic diversity proteinopathies.

Natural compound plumbagin based inhibition of hIAPP revealed by Markov state models based on MD data along with experimental validations

Human islet amyloid polypeptide (amylin or hIAPP) is a 37 residue hormone co-secreted with insulin from β cells of the pancreas. In patients suffering from type-2 diabetes, amylin self-assembles into amyloid fibrils, ultimately leading to the death of the pancreatic cells. However, a research gap exists in preventing and treating such amyloidosis. Plumbagin, a natural compound, has previously been demonstrated to have inhibitory potential against insulin amyloidosis. Our investigation unveils collapsible regions within hIAPP that, upon collapse, facilitates hydrophobic and pi-pi interactions, ultimately leading to aggregation. Intriguingly plumbagin exhibits the ability to bind these specific collapsible regions, thereby impeding the aforementioned interactions that would otherwise drive hIAPP aggregation. We have used atomistic molecular dynamics approach to determine secondary structural changes. MSM shows metastable states forming native like hIAPP structure in presence of PGN. Our in silico results concur with in vitro results. The ThT assay revealed a striking 50% decrease in fluorescence intensity at a 1:1 ratio of hIAPP to Plumbagin. This finding suggests a significant inhibition of amyloid fibril formation by plumbagin, as ThT fluorescence directly correlates with the presence of these fibrils. Further TEM images revealed disappearance of hIAPP fibrils in plumbagin pre-treated hIAPP samples. Also, we have shown that plumbagin disrupts the intermolecular hydrogen bonding in hIAPP fibrils leading to an increase in the average beta strand spacing, thereby causing disaggregation of pre-formed fibrils demonstrating overall disruption of the aggregation machinery of hIAPP. Our work is the first to report a detailed atomistic simulation of 22 μs for hIAPP. Overall, our studies put plumbagin as a potential candidate for both preventive and therapeutic candidate for hIAPP amyloidosis.

Pramlintide an Adjunct to Insulin Therapy: Challenges and Recent Progress in Delivery

Dysregulation of various glucoregulatory hormones lead to failure of insulin monotherapy in patients with diabetes mellitus due to various reasons, including severe hypoglycemia, glycemic hypervariability, and an increased risk of microvascular complications. However, pramlintide as an adjunct to insulin therapy enhances glucagon suppression and thereby offers improved glycemic control. Clinical studies have shown that pramlintide improves glycemic control, reduces postprandial glucose excursions, and promotes weight loss in patients with type 1 and type 2 diabetes. Although clinical benefits of pramlintide are well reported, there still exists a high patient resistance for the therapy, as separate injections for pramlintide and insulin must be administered. Although marketed insulin formulations generally demonstrate a peak action in 60-90 minutes, pramlintide elicits its peak concentration at around 20-30 minutes after administration. Thus, owing to the significant differences in pharmacokinetics of exogenously administered pramlintide and insulin, the therapy fails to elicit its action otherwise produced by the endogenous hormones. Hence, strategies such as delaying the release of pramlintide by using inorganic polymers like silica, synthetic polymers like polycaprolactone, and lipids have been employed. Also, approaches like noncovalent conjugation, polyelectrolyte complexation, and use of amphiphilic excipients for codelivery of insulin and pramlintide have been explored to address the issues with pramlintide delivery and improve patient adherence to the therapy. This approach may usher in a new era of diabetes management, offering patients multiple options to tailor their treatment and improve their quality of life. SIGNIFICANCE STATEMENT: To our knowledge, this is the first report that summarizes various challenges in insulin and pramlintide codelivery and strategies to overcome them. The paper also provides deeper insights into various novel formulation strategies for pramlintide that could further broaden the reader's understanding of peptide codelivery.

Role of mass spectrometry in the study of interactions between amylin and metal ions

Amylin (islet amyloid polypeptide [IAPP]) is a neuroendocrine hormone synthesized with insulin in the beta cells of pancreatic islets. The two hormones act in different ways: in fact insulin triggers glucose uptake in muscle and liver cells, removing glucose from the bloodstream and making it available for energy use and storage, while amylin regulates glucose homeostasis. Aside these positive physiological aspects, human amyloid polypeptide (hIAPP) readily forms amyloid in vitro. Amyloids are aggregates of proteins and in the human body amyloids are considered responsible of the development of various diseases. These aspects have been widely described and discussed in literature and to give a view of the highly complexity of this biochemical behavior the different physical, chemical, biological and medical aspects are shortly described in this review. It is strongly affected by the presence on metal ions, responsible for or inhibiting the formation of fibrils. Mass spectrometry resulted (and still results) to be a particularly powerful tool to obtain valid and effective experimental data to describe the hIAPP behavior. Aside classical approaches devoted to investigation on metal ion-hIAPP structures, which reflects on the identification of metal-protein interaction site(s) and of possible metal-induced conformational changes of the protein, interesting results have been obtained by ion mobility mass spectrometry, giving, on the basis of collisional cross-section data, information on both the oligomerization processes and the conformation changes. Laser ablation electrospray ionization-ion mobility spectrometry-mass spectrometry (LAESI-IMS-MS), allowed to obtain information on the binding stoichiometry, complex dissociation constant, and the oxidation state of the copper for the amylin-copper interaction. Alternatively to inorganic ions, small organic molecules have been tested by ESI-IMS-MS as inhibitor of amyloid assembly. Also in this case the obtained data demonstrate the validity of the ESI-IMS-MS approach as a high-throughput screen for inhibitors of amyloid assembly, providing valid information concerning the identity of the interacting species, the nature of binding and the effect of the ligand on protein aggregation. Effects of Cu²⁺ and Zn²⁺ ions in the degradation of human and murine IAPP by insulin-degrading enzyme were studied by liquid chromatography/mass spectrometry (LC/MS). The literature data show that mass spectrometry is a highly valid and effective tool in the study of the amylin behavior, so to individuate medical strategies to avoid the undesired formation of amyloids in in vivo conditions.

Expression of the Calcitonin Receptor-like Receptor (CALCRL) in Normal and Neoplastic Tissues

Little information is available concerning protein expression of the calcitonin receptor-like receptor (CALCRL) at the protein level. Here, we developed a rabbit monoclonal antibody, 8H9L8, which is directed against human CALCRL but cross-reacts with the rat and mouse forms of the receptor. We confirmed antibody specificity via Western blot analyses and immunocytochemistry using the CALCRL-expressing neuroendocrine tumour cell line BON-1 and a CALCRL-specific small interfering RNA (siRNA). We then used the antibody for immunohistochemical analyses of various formalin-fixed, paraffin-embedded specimens of normal and neoplastic tissues. In nearly all tissue specimens examined, CALCRL expression was detected in the capillary endothelium, smooth muscles of the arterioles and arteries, and immune cells. Analyses of normal human, rat, and mouse tissues revealed that CALCRL was primarily present in distinct cell populations in the cerebral cortex; pituitary; dorsal root ganglia; epithelia, muscles, and glands of the larger bronchi; intestinal mucosa (particularly in enteroendocrine cells); intestinal ganglia; exocrine and endocrine pancreas; arteries, capillaries, and glomerular capillary loops in the kidneys; the adrenals; Leydig cells in the testicles; and syncytiotrophoblasts in the placenta. In the neoplastic tissues, CALCRL was predominantly expressed in thyroid carcinomas, parathyroid adenomas, small-cell lung cancers, large-cell neuroendocrine carcinomas of the lung, pancreatic neuroendocrine neoplasms, renal clear-cell carcinomas, pheochromocytomas, lymphomas, and melanomas. In these tumours with strong expression of CALCRL, the receptor may represent a useful target structure for future therapies.

Interaction of Human Resistin with Human Islet Amyloid Polypeptide at Charged Phospholipid Membranes

An X-ray reflectivity study on the interaction of recombinant human resistin (hRes) with fibrillation-prone human islet amyloid polypeptide (hIAPP) at anionic phospholipid Langmuir films as model membranes is presented. Aggregation and amyloid formation of hIAPP is considered the main mechanism of pancreatic β-cell loss in patients with type 2 diabetes mellitus. Resistin shows a chaperone-like ability, but also tends to form aggregates by itself. Resistin and hIAPP cross multiply metabolism pathways. In this study, we researched the potential protective effects of resistin against hIAPP-induced lipid membrane rupture. The results demonstrate that resistin can inhibit or prevent hIAPP adsorption even in the presence of aggregation-promoting negatively charged lipid interfaces. Moreover, we found strong hydrophobic interactions of resistin at the bare buffer-air interface.

Easy Production of "Difficult Peptides" Using Cell-Free Protein Synthesis and a New Methionine Analogue as a Latent Peptide Cleavage Site

Aliphatic γ-chloro-α-amino acids incorporated in place of their canonical analogues through cell-free protein synthesis act as heat-labile linkers, offering a useful strategy for the straightforward production of target peptides as fusion proteins, from which the targets are readily released. Until now, the natural abundance of aliphatic amino acids in peptides has limited the scope of the method, as it leads to undesired cleavage sites in synthesized products, but here the authors report the development of a new cleavable chloro amino acid that incorporates in place of the relatively rare amino acid methionine, thus greatly expanding the scope of producible targets. This new strategy is employed for simplified peptide synthesis with a methionine-free fusion partner, allowing single-site incorporation of the cleavable linker for clean release and easy purification of the target peptide. Its utility is demonstrated through the straightforward preparation of two peptides reported to be challenging targets and not accessible through standard solid-phase chemical methodologies, as well as analogues.

Curcumin: A small molecule with big functionality against amyloid aggregation in neurodegenerative diseases and type 2 diabetes

Amyloidosis is a concept that implicates disorders and complications that are due to abnormal protein accumulation in different cells and tissues. Protein aggregation-associated diseases are classified according to the type of aggregates and deposition sites, such as neurodegenerative disorders and type 2 diabetes mellitus. Polyphenolic phytochemicals such as curcumin and its derivatives have anti-amyloid effects both in vitro and in animal models; however, the underlying mechanisms are not understood. In this review, we summarized possible mechanisms by which curcumin could interfere with self-assembly processes and reduce amyloid aggregation in amyloidosis. Furthermore, we discuss clinical trials in which curcumin is used as a therapeutic agent for the treatment of diseases linking to protein aggregates.

Undercover Toxic Ménage à Trois of Amylin, Copper (II) and Metformin in Human Embryonic Kidney Cells

In recent decades, type 2 diabetes complications have been correlated with amylin aggregation, copper homeostasis and metformin side effects. However, each factor was analyzed separately, and only in some rare cases copper/amylin or copper/metformin complexes were considered. We demonstrate for the first time that binary metformin/amylin and tertiary copper (II)/amylin/metformin complexes of high cellular toxicity are formed and lead to the formation of aggregated multi-level lamellar structures on the cell membrane. Considering the increased concentration of amylin, copper (II) and metformin in kidneys of T2DM patients, our findings on the toxicity of amylin and its adducts may be correlated with diabetic nephropathy development.

Potential of ATP toward Prevention of hIAPP Oligomerization and Destabilization of hIAPP Protofibrils: An In Silico Perspective

The aggregation of an intrinsically disordered protein, human islet amyloid polypeptide (hIAPP), leads to one of the most prevalent endocrine disorders, type II diabetes mellitus (T2DM). Hence inhibition of hIAPP aggregation provides a possible therapeutic approach for the treatment of T2DM. In this regard, a new aspect of adenosine triphosphate (ATP), which is widely known as the energy source for biological reactions, has recently been discovered, where it can inhibit the formation of protein aggregates and simultaneously dissolve preformed aggregates at a millimolar concentration scale. In this work, we investigate the effect of ATP on the aggregation of an amyloidogenic segment of hIAPP, hIAPP_22-28, and also of the full length sequence. Using all-atom classical molecular dynamics simulations, we observe that the tendency of hIAPP to oligomerize into β-sheet conformers is inhibited by ATP, due to which the peptides remain distant, loosely packed random monomers. Moreover, it can also disassemble preformed hIAPP protofibrils. ATP preferentially interacts with the hydrophobic residues of hIAPP_22-28 fragment and the terminal and turn residues of the full length peptide. The hydrogen bonding, hydrophobic, π-π, and N-H-π stacking interactions are the driving forces for the ATP induced inhibition of hIAPP aggregation. Interestingly, the hydrophobic adenosine of ATP is found to be more in contact with the peptide residues than the hydrophilic triphosphate moiety. The insight into the inhibitory mechanism of ATP on hIAPP aggregation can prove to be beneficial for the design of novel amyloid inhibitors in the future.

The pro-apoptotic domain of BIM protein forms toxic amyloid fibrils

BIM is a key apoptotic protein, participating in diverse cellular processes. Interestingly, recent studies have hypothesized that BIM is associated with the extensive neuronal cell death encountered in protein misfolding diseases, such as Alzheimer's disease. Here, we report that the core pro-apoptotic domain of BIM, the BIM-BH3 motif, forms ubiquitous amyloid fibrils. The BIM-BH3 fibrils exhibit cytotoxicity, disrupt mitochondrial functions, and modulate the structures and dynamics of mitochondrial membrane mimics. Interestingly, a slightly longer peptide in which BIM-BH3 was flanked by four additional residues, widely employed as a model of the pro-apoptotic core domain of BIM, did not form fibrils, nor exhibited cell disruptive properties. The experimental data suggest a new mechanistic role for the BIM-BH3 domain, and demonstrate, for the first time, that an apoptotic peptide forms toxic amyloid fibrils.

Metabolic Regulator IAPP (Amylin) Is Required for BRAF and RAS Oncogene-Induced Senescence

Cellular senescence is characterized by a prolonged and predominantly irreversible cell-cycle arrest state, which is linked to loss of tissue function and aging in mammals. Moreover, in response to aberrant oncogenic signals such as those from oncogenic RAS or BRAF, senescence functions as an intrinsic tumor suppressor mechanism restraining tumor progression. In addition to this durable proliferative block, senescent cells adopt altered morphologies, transcriptional profiles, and metabolism, while often possessing unusual heterochromatin formation termed senescence-associated heterochromatic foci. To uncover genes that are required to permit proliferation in the face of sustained oncogene signaling, we conducted an shRNA-based genetic screen in primary cells expressing inducible BRAF. Here we show that depletion of a known glycolysis regulator, islet amylin polypeptide (IAPP also known as amylin), prevents RAS and BRAF oncogene-induced senescence (OIS) in human cells. Importantly, depletion of IAPP resulted in changes of the cells' metabolome and this metabolic reprogramming was associated with widespread alterations in chromatin modifications compared with senescent cells. Conversely, exogenous treatment of IAPP-depleted cells with amylin restored OIS. Together, our results demonstrate that the metabolic regulator IAPP is important regulator of OIS. Moreover, they suggest that IAPP analog treatment or activation of IAPP signaling in RAS/BRAF mutant tumors may have therapeutic potential through senescence induction. IMPLICATIONS: These findings demonstrate that IAPP is a novel metabolic regulator of oncogene-induced senescence and use of IAPP analogs may be therapeutically effective to restore growth arrest to BRAF and/or RAS mutant cancers.

Interaction of ApoMyoglobin with Heme-hIAPP complex

Human Islet Amyloid Polypeptide (hIAPP) or amylin, can bind heme and the resultant complexes are prone to generate partially reduced oxygen species (PROS). The formation of PROS and the related oxidative stress highlight the importance of Heme-hIAPP in the onset and development of Type 2 Diabetes mellitus (T2Dm) in humans. In this study, the interaction of Heme-hIAPP with apomyoglobin (ApoMb) has been investigated using a combination of spectroscopic and electrophoresis techniques. Absorption, resonance Raman data and gel electrophoresis results confirm that ApoMb can uptake heme from Heme-hIAPP and constitute a six-coordinate high-spin ferric heme active site identical to that of myoglobin (Mb). The heme transfer reaction has two distinct kinetic steps. A possible mechanism of this reaction involves heme transfer to the apoprotein in the first step followed by a reorganisation of the protein chain to form the active site of native Mb. Increase in the pH of the reaction medium enhances the rate of the second step of heme transfer. This possibly corresponds to the deprotonation of a propionate side chain of the heme moiety at high pH which facilitates secondary interactions with the conserved distal Lys45 residue of horse heart Mb. Additionally, ApoMb sequesters ligand bound heme from Heme-hIAPP. After the heme transfer reaction, the amount of PROS formed by Heme-hIAPP complex diminishes significantly. This not only potentially diminishes heme-induced toxicity in the pancreatic β-cells but also produces Mb which has well-documented functions throughout the respiratory system and can thereby likely reduce the risks associated with T2Dm.

Neuroprotective Effects of the Amylin Analog, Pramlintide, on Alzheimer's Disease Are Associated with Oxidative Stress Regulation Mechanisms

Administration of the recombinant analog of the pancreatic amyloid amylin, Pramlintide, has shown therapeutic benefits in aging and Alzheimer's disease (AD) models, both on cognition and amyloid-β (Aβ) pathology. However, the neuroprotective mechanisms underlying the benefits of Pramlintide remain unclear. Given the early and critical role of oxidative stress in AD pathogenesis and the known reactive oxygen species (ROS) modulating function of amyloids, we sought to determine whether Pramlintide's neuroprotective effects involve regulation of oxidative stress mechanisms. To address this, we treated APP/PS1 transgenic mice with Pramlintide for 3 months, starting at 5.5 months prior to widespread AD pathology onset, and measured cognition (Morris Water Maze), AD pathology, and oxidative stress-related markers and enzymes in vivo. In vitro, we determined the ability of Pramlintide to modulate H2O2-induced oxidative stress levels. Our data show that Pramlintide improved cognitive function, altered amyloid-processing enzymes, reduced plaque burden in the hippocampus, and regulated endogenous antioxidant enzymes (MnSOD and GPx1) and the stress marker HO-1 in a location specific manner. In vitro, Pramlintide treatment in neuronal models reduced H2O2-induced endogenous ROS production and lipid peroxidation in a dose-dependent manner. Together, these results indicate that Pramlintide's benefits on cognitive function and pathology may involve antioxidant-like properties of this compound.

Natural Polyphenols as Modulators of the Fibrillization of Islet Amyloid Polypeptide

Diabetes mellitus type 2 (type-2 diabetes) is a metabolic disorder characterized by the increased blood glucose concentration and insulin resistance in peripheral tissues (e.g., muscles and adipose tissue). The initiation of the pathological cascade of events that lead to type-2 diabetes has been subject of debate; however, it has been commonly accepted that the oversecretion of human islet amyloid polypeptide (hIAPP, a hormone co-secreted with insulin) by the pancreatic 𝛽-cells is the main trigger of type-2 diabetes. In fact, 90% of the type-2 diabetes patients present hIAPP deposits in the extracellular space of the 𝛽-cells. These hIAPP supramolecular arrangements (both fibrillar and oligomeric) have been reported to be the origin of cytotoxicity, which leads to 𝛽-cell dysfunction through a series of different mechanisms, including the interaction of hIAPP oligomers with the cell membrane that leads to the influx of Ca²⁺ and increase in the cellular oxidative stress, among others. This overview shows the importance of developing type-2 diabetes treatment strategies able to (1) remodel of the secondary structure of cytotoxic hIAPP oligomers entrapping them into off-pathway nontoxic species and (2) reestablish physiological levels of oxidative stress. Natural polyphenols are a class of antioxidant compounds that are able to perform both functions. Herein we review the published literature of the most studied polyphenols, in particular for their ability to remodel the hIAPP aggregation pathway, to rescue the in vitro pancreatic 𝛽-cell viability and function, as well as to perform under a complex biological environment, i.e., in vivo animal models and clinical trials. Overall, natural polyphenols are able to control the cytotoxic hIAPP aggregation and minimize hIAPP-mediated cellular dysfunction and can be considered as important lead compounds for the treatment of type-2 diabetes.

Early Biomarkers of Neurodegenerative and Neurovascular Disorders in Diabetes

Diabetes mellitus (DM) is a common disease worldwide. There is a strong association between DM and neurovascular and neurodegenerative disorders. The first group mainly consists of diabetic retinopathy, diabetic neuropathy and stroke, whereas, the second group includes Alzheimer's disease, Parkinson's disease, mild cognitive impairment and dementia. The aforementioned diseases have a common pathophysiological background including insulin resistance, oxidative stress, atherosclerosis and vascular injury. The increasing prevalence of neurovascular and neurodegenerative disorders among diabetic patients has resulted in an urgent need to develop biomarkers for their prediction and/or early detection. The aim of this review is to present the potential application of the most promising biomarkers of diabetes-related neurodegenerative and neurovascular disorders, including amylin, β-amyloid, C-reactive protein (CRP), dopamine, gamma-glutamyl transferase (GGT), glycogen synthase kinase 3β, homocysteine, microRNAs (mi-RNAs), paraoxonase 1, phosphoinositide 3-kinases, tau protein and various growth factors. The most clinically promising biomarkers of neurovascular and neurodegenerative complications in DM are hsCRP, GGT, homocysteine and miRNAs. However, all biomarkers discussed in this review could become a part of the potential multi-biomarker screening panel for diabetic patients at risk of neurovascular and neurodegenerative complications.

d-Retro Inverso Amylin and the Stability of Amylin Fibrils

Motivated by the role that amylin aggregates play in type-II diabetes, we compare the stability of regular amylin fibrils with the stability of fibrils where l-amino acid chains are replaced by d-retro inverso (DRI) amylin, that is, peptides where the sequence of amino acids is reversed, and at the same time, the l-amino acids are replaced by their mirror images. Our molecular dynamics simulations show that despite leading to only a marginal difference in the fibril structure and stability, aggregating DRI-amylin peptides have different patterns of contacts and hydrogen bonding. Because of these differences, DRI-amylin, when interacting with regular (l) amylin, alters the elongation process and lowers the stability of hybrid amylin fibrils. Our results not only suggest the potential use of DRI-amylin as an inhibitor of amylin fibril formation but also point to the possibility of using the insertion of DRI proteins in l-assemblies as a way to probe the role of certain kinds of hydrogen bonds in supramolecular assemblies or aggregates.

Cationic Carbosilane Dendritic Systems as Promising Anti-Amyloid Agents in Type 2 Diabetes

The most common denominator of many of the neurodegenerative diseases is badly folded protein accumulation, which results in the formation of insoluble protein deposits located in different parts of the organism, causing cell death and tissue degeneration. Dendritic systems have turned out to be a promising new therapeutic approach for the treatment of these diseases due to their ability to modulate the folding of these proteins. With this perspective, and focused on type 2 diabetes (T2D), characterized by the presence of deposits containing the amyloidogenic islet amyloid polypeptide (IAPP), we demonstrate how different topologies of cationic carbosilane dendrimers inhibit the formation of insoluble protein deposits in pancreatic islets isolated from transgenic Tg-hIAPP mice. Also, the results obtained by the modification of dendritic carbosilane wedges with the chemical chaperone 4-phenylbutyric acid (4-PBA) at the focal point confirmed their potential as anti-amyloid agents with a concentration efficiency in their therapeutic action five orders of magnitude lower than that observed for free 4-PBA. Computational studies, which determined the main interaction between IAPP and dendrimers at the atomic level, support the experimental work.

Evidence for different in vitro oligomerization behaviors of synthetic hIAPP obtained from different sources

Type 2 diabetes is characterized by the aggregation of human islet amyloid polypeptide (hIAPP), from monomer to amyloid deposits that are made of insoluble fibrils. Discrepancies concerning the nature of formed species or oligomerization kinetics among reported in vitro studies on hIAPP aggregation process have been highlighted. In this work, we investigated if the sample itself could be at the origin of those observed differences. To this aim, four hIAPP samples obtained from three different sources or suppliers have been analyzed and compared by ThT fluorescence spectroscopy and by two recently developed techniques, capillary electrophoresis (CE), and ESI-IMS-QToF-MS. Lots provided by the same supplier were shown to be very similar whatever the analytical technique used to characterize them. In contrast, several critical differences could be pointed out for hIAPP provided by different suppliers. We demonstrated that in several samples, some oligomerized peptides (e.g., dimer) were already present upon reception. Purity was also different, and the proneness of the peptide solution to form fibrils in vitro within 24 h could vary considerably from one sample source to another but not from lot to lot of the same source. All those results demonstrate that the initial state of conformation, oligomerization, and quality of the hIAPP can greatly impact the aggregation kinetics, and thus the information provided by these in vitro tests. Finally, a careful selection of the peptide batch and source is mandatory to perform relevant in vitro studies on hIAPP oligomerization and to screen new molecules modulating this pathological process. Graphical abstract.

Peptides from Natural or Rationally Designed Sources Can Be Used in Overweight, Obesity, and Type 2 Diabetes Therapies

Overweight and obesity are among the most prominent health problems in the modern world, mostly because they are either associated with or increase the risk of other diseases such as type 2 diabetes, hypertension, and/or cancer. Most professional organizations define overweight and obesity according to individual body-mass index (BMI, weight in kilograms divided by height squared in meters). Overweight is defined as individuals with BMI from 25 to 29, and obesity as individuals with BMI ≥30. Obesity is the result of genetic, behavioral, environmental, physiological, social, and cultural factors that result in energy imbalance and promote excessive fat deposition. Despite all the knowledge concerning the pathophysiology of obesity, which is considered a disease, none of the existing treatments alone or in combination can normalize blood glucose concentration and prevent debilitating complications from obesity. This review discusses some new perspectives for overweight and obesity treatments, including the use of the new orally active cannabinoid peptide Pep19, the advantage of which is the absence of undesired central nervous system effects usually experienced with other cannabinoids.

Cynomolgus Monkeys With Spontaneous Type-2-Diabetes-Mellitus-Like Pathology Develop Alpha-Synuclein Alterations Reminiscent of Prodromal Parkinson's Disease and Related Diseases

Available evidence suggests that diabetes mellitus (DM) is a non-genetic risk factor for Parkinson’s disease (PD). PD and DM have shared similarities in pathogenetic mechanisms, including age, environmental factors, inflammatory reaction, and protein aggregation, etc. α-Synuclein is the primary protein component in the protein inclusions in PD, while islet amyloid polypeptide (IAPP) aggregates to form amyloid structures in β cells in type 2 diabetes mellitus (T2DM). Pancreatic and cerebral functions, pancreas and brain α-synuclein deposition as well as striatal alterations, were assessed in spontaneously developed T2DM monkeys and age-matched normal monkeys. We demonstrated increased accumulation, aggregation, and phosphorylation of α-synuclein, and IAPP in the pancreatic islets of spontaneously developed T2DM monkeys, compared to the age-matched normal subjects. Double immunofluorescence analyses showed complete overlap between α-synuclein and IAPP in the pancreatic islets. In addition, in T2DM monkeys’ brain, we observed concomitantly increased accumulation and phosphorylation of α-synuclein in the cortex, pre-commissural putamen and dopaminergic neurons in the substantia nigra, which interestingly showed high correlation with levels of fasting plasma glucose (FPG), triglyceride (TG), and high density lipoprotein (HDL). Our data indicates the close association between IAPP and α-synuclein and the potential link between T2DM and PD, which implies that T2DM may facilitate PD disease onset and progress by interfering with the pathological protein aggregation both in the pancreatic islets and the brain.

Monomer-targeting affinity peptide inhibitors of amyloid with no self-fibrillation and low cytotoxicity

A monomer-targeting strategy based on solution-phase biopanning to obtain peptide inhibitors increases the suppression efficiency and reduces the cytotoxicity of amylin.

Molecular and clinical insights into protein misfolding and associated amyloidosis

The misfolding of normally soluble proteins causes their aggregation and deposition in the tissues which disrupts the normal structure and function of the corresponding organs. The proteins with high β-sheet contents are more prone to form amyloids as they exhibit high propensity of self-aggregation. The self aggregated misfolded proteins act as template for further aggregation that leads to formation of protofilaments and eventually amyloid fibrils. More than 30 different types of proteins are known to be associated with amyloidosis related diseases. Several aspects of the amyloidogenic behavior of proteins remain elusive. The exact reason that causes misfolding of the protein and its association into amyloid fibrils is not known. These misfolded intermediates surpass the over engaged quality control system of the cell which clears the misfolded intermediates. This promotes the self-aggregation, accumulation and deposition of these misfolded species in the form of amyloids in the different parts of the body. The amyloid deposition can be localized as in Alzheimer disease or systemic as reported in most of the amyloidosis. The amyloidosis can be of acquired type or familial. The current review aims at bringing together recent updates and comprehensive information about protein amyloidosis and associated diseases at one place.

Amyloid Pan-inhibitors: One Family of Compounds To Cope with All Conformational Diseases

Amyloids are ubiquitous protein aggregates sharing common internal structural features; they are present in all organisms, from prokaryotes to eukaryotes, where they play physiological or pathological roles. Importantly, amyloids, which are generated by aggregation of a range of distinct proteins, could be a key factor in a number of major human disorders, the so-called conformational diseases. Because all amyloids exhibit similar cross-β motifs, one may envisage that molecules capable of blocking the formation of β-sheet structures could abolish aggregation of all amyloid proteins, albeit with different efficacies. Herein, two different β-sheet blockers were tested against a selection of amyloidogenic proteins, encompassing all the major types of amyloid-based disorders. Analysis of their blocking efficiency, using a simple but contrasted cell-based screening procedure, unequivocally confirms that they indeed behave as aggregation pan-inhibitors. The significant inhibitory effects observed for these compounds against all tested amyloidogenic proteins could spur a broader biological evaluation of other known and new amyloid aggregation inhibitors to further determine the potential use of this class of compounds for the universal treatment of conformational diseases.

Killing Two Angry Birds with One Stone: Autophagy Activation by Inhibiting Calpains in Neurodegenerative Diseases and Beyond

Proteolytic machineries execute vital cellular functions and their disturbances are implicated in diverse medical conditions, including neurodegenerative diseases. Interestingly, calpains, a class of Ca²⁺-dependent regulatory proteases, can modulate the degradational system of autophagy by cleaving proteins involved in this pathway. Moreover, both machineries are common players in many molecular pathomechanisms and have been targeted individually or together, as a therapeutic strategy in experimental setups. In this review, we briefly introduce calpains and autophagy, with their roles in health and disease, and focus on their direct pathologically relevant interplay in neurodegeneration and beyond. The modulation of calpain activity may comprise a promising treatment approach to attenuate the deregulation of these two essential mechanisms.

A Possible Connection Between Plant Longevity and the Absence of Protein Fibrillation: Basis for Identifying Aggregation Inhibitors in Plants

The ability of proteins to aggregate to form well-organized β-sheet rich amyloid fibrils is increasingly viewed as a general if regrettable property of the polypeptide chain. Aggregation leads to diseases such as amyloidosis and neurodegeneration in humans and various mammalian species but is also found in a functional variety in both animals and microbes. However, there are to our knowledge no reports of amyloid formation in plants. Plants are also the source of a large number of aggregation-inhibiting compounds. We reasoned that the two phenomena could be connected and that one of (many) preconditions for plant longevity is the ability to suppress unwanted protein aggregation. In support of this, we show that while protein extracts from the sugar maple tree Acer saccharum fibrillate readily on their own, this process is efficiently abolished by addition of small molecule extracts from the same plant. Further analysis of 44 plants showed a correlation between plant longevity and ability to inhibit protein aggregation. Extracts from the best performing plant, the sugar maple, were subjected to chromatographic fractionation, leading to the identification of a large number of compounds, many of which were shown to inhibit aggregation in vitro. One cautious interpretation is that it may have been advantageous for plants to maintain an efficient collection of aggregation-inhibiting metabolites as long as they do not impair metabolite function. From a practical perspective, our results indicate that long-lived plants may be particularly appropriate sources of new anti-aggregation compounds with therapeutic potential.

The Early Events That Initiate β-Amyloid Aggregation in Alzheimer's Disease

Alzheimer’s disease (AD) is characterized by the development of amyloid plaques and neurofibrillary tangles (NFTs) consisting of aggregated β-amyloid (Aβ) and tau, respectively. The amyloid hypothesis has been the predominant framework for research in AD for over two decades. According to this hypothesis, the accumulation of Aβ in the brain is the primary factor initiating the pathogenesis of AD. However, it remains elusive what factors initiate Aβ aggregation. Studies demonstrate that AD has multiple causes, including genetic and environmental factors. Furthermore, genetic factors, many age-related events and pathological conditions such as diabetes, traumatic brain injury (TBI) and aberrant microbiota also affect the aggregation of Aβ. Here we provide an overview of the age-related early events and other pathological processes that precede Aβ aggregation.

Effect of IAPP on the proteome of cultured Rin-5F cells

Background

Islet amyloid polypeptide (IAPP) or amylin deposits can be found in the islets of type 2 diabetes patients. The peptide is suggested to be involved in the etiology of the disease through formation of amyloid deposits and destruction of β islet cells, though the underlying molecular events leading from IAPP deposition to β cell death are still largely unknown.

Results

We used OFFGEL™ proteomics to study how IAPP exposure affects the proteome of rat pancreatic insulinoma Rin-5F cells. The OFFGEL™ methodology is highly effective at generating quantitative data on hundreds of proteins affected by IAPP, with its accuracy confirmed by In Cell Western and Quantitative Real Time PCR results. Combining data on individual proteins identifies pathways and protein complexes affected by IAPP. IAPP disrupts protein synthesis and degradation, and induces oxidative stress. It causes decreases in protein transport and localization. IAPP disrupts the regulation of ubiquitin-dependent protein degradation and increases catabolic processes. IAPP causes decreases in protein transport and localization, and affects the cytoskeleton, DNA repair and oxidative stress.

Conclusions

Results are consistent with a model where IAPP aggregates overwhelm the ability of a cell to degrade proteins via the ubiquitin system. Ultimately this leads to apoptosis. IAPP aggregates may be also toxic to the cell by causing oxidative stress, leading to DNA damage or by decreasing protein transport. The reversal of any of these effects, perhaps by targeting proteins which alter in response to IAPP, may be beneficial for type II diabetes.

Electronic supplementary material

The online version of this article (10.1186/s12858-018-0099-3) contains supplementary material, which is available to authorized users.

Characterisation of the Structure and Oligomerisation of Islet Amyloid Polypeptides (IAPP): A Review of Molecular Dynamics Simulation Studies

Human islet amyloid polypeptide (hIAPP) is a naturally occurring, intrinsically disordered protein whose abnormal aggregation into amyloid fibrils is a pathological feature in type 2 diabetes, and its cross-aggregation with amyloid beta has been linked to an increased risk of Alzheimer's disease. The soluble, oligomeric forms of hIAPP are the most toxic to β-cells in the pancreas. However, the structure of these oligomeric forms is difficult to characterise because of their intrinsic disorder and their tendency to rapidly aggregate into insoluble fibrils. Experimental studies of hIAPP have generally used non-physiological conditions to prevent aggregation, and they have been unable to describe its soluble monomeric and oligomeric structure at physiological conditions. Molecular dynamics (MD) simulations offer an alternative for the detailed characterisation of the monomeric structure of hIAPP and its aggregation in aqueous solution. This paper reviews the knowledge that has been gained by the use of MD simulations, and its relationship to experimental data for both hIAPP and rat IAPP. In particular, the influence of the choice of force field and water models, the choice of initial structure, and the configurational sampling method used, are discussed in detail. Characterisation of the solution structure of hIAPP and its mechanism of oligomerisation is important to understanding its cellular toxicity and its role in disease states, and may ultimately offer new opportunities for therapeutic interventions.

No effects without causes: the Iron Dysregulation and Dormant Microbes hypothesis for chronic, inflammatory diseases

Since the successful conquest of many acute, communicable (infectious) diseases through the use of vaccines and antibiotics, the currently most prevalent diseases are chronic and progressive in nature, and are all accompanied by inflammation. These diseases include neurodegenerative (e.g. Alzheimer's, Parkinson's), vascular (e.g. atherosclerosis, pre-eclampsia, type 2 diabetes) and autoimmune (e.g. rheumatoid arthritis and multiple sclerosis) diseases that may appear to have little in common. In fact they all share significant features, in particular chronic inflammation and its attendant inflammatory cytokines. Such effects do not happen without underlying and initially 'external' causes, and it is of interest to seek these causes. Taking a systems approach, we argue that these causes include (i) stress-induced iron dysregulation, and (ii) its ability to awaken dormant, non-replicating microbes with which the host has become infected. Other external causes may be dietary. Such microbes are capable of shedding small, but functionally significant amounts of highly inflammagenic molecules such as lipopolysaccharide and lipoteichoic acid. Sequelae include significant coagulopathies, not least the recently discovered amyloidogenic clotting of blood, leading to cell death and the release of further inflammagens. The extensive evidence discussed here implies, as was found with ulcers, that almost all chronic, infectious diseases do in fact harbour a microbial component. What differs is simply the microbes and the anatomical location from and at which they exert damage. This analysis offers novel avenues for diagnosis and treatment.

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

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

Amylin in Alzheimer's disease: Pathological peptide or potential treatment?

Alzheimer's disease (AD) is a neurodegenerative disease for which we currently lack effective treatments or a cure. The pancreatic peptide hormone amylin has recently garnered interest as a potential pharmacological target for the treatment of AD. A number of studies have demonstrated that amylin and amylin analogs like the FDA-approved diabetes drug pramlintide can reduce amyloid burden in the brain and improve cognitive symptoms of AD. However, other data suggest that amylin may have pathological effects in AD due to its propensity to misfold and aggregate under certain conditions. Here, the literature supporting a beneficial versus harmful role of amylin in AD is reviewed. Additionally, several critical gaps in the literature are discussed, such as our limited understanding of the amylin system during aging and in disease states, as well as complexities of amylin receptor signaling and of changing pathophysiology during AD progression that might underlie the seemingly conflicting or contradictory results in the amylin/AD literature. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

A Rationally Designed Hsp70 Variant Rescues the Aggregation-Associated Toxicity of Human IAPP in Cultured Pancreatic Islet β-Cells

Molecular chaperones are key components of the protein homeostasis system against protein misfolding and aggregation. It has been recently shown that these molecules can be rationally modified to have an enhanced activity against specific amyloidogenic substrates. The resulting molecular chaperone variants can be effective inhibitors of protein aggregation in vitro, thus suggesting that they may provide novel opportunities in biomedical and biotechnological applications. Before such opportunities can be exploited, however, their effects on cell viability should be better characterised. Here, we employ a rational design method to specifically enhance the activity of the 70-kDa heat shock protein (Hsp70) against the aggregation of the human islet amyloid polypeptide (hIAPP, also known as amylin). We then show that the Hsp70 variant that we designed (grafted heat shock protein 70 kDa-human islet amyloid polypeptide, GHsp70-hIAPP) is significantly more effective than the wild type in recovering the viability of cultured pancreatic islet β-cells RIN-m5F upon hIAPP aggregation. These results indicate that a full recovery of the toxic effects of hIAPP aggregates on cultured pancreatic cells can be achieved by increasing the specificity and activity of Hsp70 towards hIAPP, thus providing evidence that the strategy presented here provides a possible route for rationally tailoring molecular chaperones for enhancing their effects in a target-dependent manner.

Adsorption and Fibrillization of Islet Amyloid Polypeptide at Self-Assembled Monolayers Studied by QCM-D, AFM, and PM-IRRAS

Aggregation and fibrillization of human islet amyloid polypeptide (hIAPP) plays an important role in the development of type 2 diabetes mellitus. Understanding the interaction of hIAPP with interfaces such as cell membranes at a molecular level therefore represents an important step toward new therapies. Here, we investigate the fibrillization of hIAPP at different self-assembled alkanethiol monolayers (SAMs) by quartz crystal microbalance with dissipation monitoring (QCM-D), atomic force microscopy (AFM), and polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). We find that hydrophobic interactions with the CH₃-terminated SAM tend to retard hIAPP fibrillization compared to the carboxylic acid-terminated SAM where attractive electrostatic interactions lead to the formation of a three-dimensional network of interwoven fibrils. At the hydroxyl- and amino-terminated SAMs, fibrillization appears to be governed by hydrogen bonding between the peptide and the terminating groups which may even overcome electrostatic repulsion. These results thus provide fundamental insights into the molecular mechanisms governing amyloid assembly at interfaces.

Star Polymers Reduce Islet Amyloid Polypeptide Toxicity via Accelerated Amyloid Aggregation

Protein aggregation into amyloid fibrils is a ubiquitous phenomenon across the spectrum of neurodegenerative disorders and type 2 diabetes. A common strategy against amyloidogenesis is to minimize the populations of toxic oligomers and protofibrils by inhibiting protein aggregation with small molecules or nanoparticles. However, melanin synthesis in nature is realized by accelerated protein fibrillation to circumvent accumulation of toxic intermediates. Accordingly, we designed and demonstrated the use of star-shaped poly(2-hydroxyethyl acrylate) (PHEA) nanostructures for promoting aggregation while ameliorating the toxicity of human islet amyloid polypeptide (IAPP), the peptide involved in glycemic control and the pathology of type 2 diabetes. The binding of PHEA elevated the β-sheet content in IAPP aggregates while rendering a new morphology of "stelliform" amyloids originating from the polymers. Atomistic molecular dynamics simulations revealed that the PHEA arms served as rodlike scaffolds for IAPP binding and subsequently accelerated IAPP aggregation by increased local peptide concentration. The tertiary structure of the star nanoparticles was found to be essential for driving the specific interactions required to impel the accelerated IAPP aggregation. This study sheds new light on the structure-toxicity relationship of IAPP and points to the potential of exploiting star polymers as a new class of therapeutic agents against amyloidogenesis.

Fasting levels of insulin and amylin after acute pancreatitis are associated with pro-inflammatory cytokines

BACKGROUND

The prevalence of metabolic diseases continues to rise worldwide, with a growing recognition of metabolic dysregulation after acute inflammatory diseases such as acute pancreatitis (AP). Adipokines and cytokines play an important role in metabolism and the course of AP, but there is a paucity of research investigating their relationship with pancreatic hormones after AP. This study aimed to explore associations between pancreatic hormones and adipokines as well as cytokines to provide insights into the pathophysiology of altered pancreatic hormone secretion following AP [corrected].

METHODS

A total of 83 patients previously diagnosed with AP and no prior diabetes or pre-diabetes were recruited into this cross-sectional follow up study. Fasting venous blood samples were collected to analyse a panel of pancreatic hormones and derivatives (amylin, C-peptide, glucagon, insulin, pancreatic polypeptide, somatostatin), adipokines (adiponectin, leptin, retinol binding protein-4, and resistin), and cytokines (interleukin-6 (IL-6), monocyte chemoattractant protein-1 (MCP-1), and tumour necrosis factor-α (TNF-α)). Linear regression analyses were used, and potential confounders were adjusted for in multivariate analyses.

RESULTS

Insulin was significantly associated with IL-6 in both unadjusted and adjusted models (p = .029 and p = .040, respectively). Amylin was significantly associated with MCP-1 in the unadjusted model (p = .046), and TNF-α in unadjusted and adjusted models (p = .025 and p = .027, respectively).

CONCLUSIONS

Insulin and amylin have a strong positive association with pro-inflammatory cytokines in patients following an episode of AP. These associations have possible relevance in the development of diabetes associated with diseases of the exocrine pancreas, providing the opportunity to develop novel treatment paradigms.

Lipopolysaccharide-binding protein (LBP) reverses the amyloid state of fibrin seen in plasma of type 2 diabetics with cardiovascular co-morbidities

Type 2 diabetes (T2D) has many cardiovascular complications, including a thrombotic propensity. Many such chronic, inflammatory diseases are accompanied (and may be exacerbated, and possibly even largely caused) by amyloid fibril formation. Recognising that there are few strong genetic associations underpinning T2D, but that amyloidogenesis of amylin is closely involved, we have been seeking to understand what might trigger the disease. Serum levels of bacterial lipopolysaccharide are raised in T2D, and we recently showed that fibrin(ogen) polymerisation during blood clotting can be affected strongly by LPS. The selectivity was indicated by the regularisation of clotting by lipopolysaccharide-binding protein (LBP). Since coagulopathies are a hallmark of T2D, we wondered whether they might too be caused by LPS (and reversed by LBP). We show here, using SEM and confocal microscopy, that platelet-poor-plasma from subjects with T2D had a much greater propensity for hypercoagulability and for amyloidogenesis, and that these could both be reversed by LBP. These data imply that coagulopathies are an important feature of T2D, and may be driven by ‘hidden’ LPS. Given the prevalence of amyloid formation in the sequelae of diabetes, this opens up novel strategies for both the prevention and treatment of T2D.

Identification of Key Interactions in the Initial Self-Assembly of Amylin in a Membrane Environment

Islet amyloid polypeptide, also known as amylin, forms aggregates that reduce the amount of insulin-producing cells in patients with type II diabetes mellitus. Much remains unknown about the process of aggregation and cytotoxicity, but it is known that certain cell membrane components can alter the rate of aggregation. Using atomistic molecular dynamics simulations combined with the highly mobile membrane mimetic model incorporating enhanced sampling of lipid diffusion, we investigate interaction of amylin peptides with the membrane components as well as the self-assembly of amylin. Consistent with experimental evidence, we find that an initial membrane-bound α-helical state folds into stable β-sheet structures upon self-assembly. Our results suggest the following mechanism for the initial phase of amylin self-assembly. The peptides move around on the membrane with the positively charged N-terminus interacting with the negatively charged lipid headgroups. When the peptides start to interact, they partly unfold and break some of the contacts with the membrane. The initial interactions between the peptides are dominated by aromatic and hydrophobic interactions. Oligomers are formed showing both intra- and interpeptide β-sheets, initially with interactions mainly in the C-terminal domain of the peptides. Decreasing the pH to 5.5 is known to inhibit amyloid formation. At low pH, His18 is protonated, adding a fourth positive charge at the peptide. With His18 protonated, no oligomerization is observed in the simulations. The additional charge gives a strong midpoint anchoring of the peptides to negatively charged membrane components, and the peptides experience additional interpeptide repulsion, thereby preventing interactions.

To What Extent Are the Terminal Stages of Sepsis, Septic Shock, Systemic Inflammatory Response Syndrome, and Multiple Organ Dysfunction Syndrome Actually Driven by a Prion/Amyloid Form of Fibrin?

A well-established development of increasing disease severity leads from sepsis through systemic inflammatory response syndrome, septic shock, multiple organ dysfunction syndrome, and cellular and organismal death. Less commonly discussed are the equally well-established coagulopathies that accompany this. We argue that a lipopolysaccharide-initiated (often disseminated intravascular) coagulation is accompanied by a proteolysis of fibrinogen such that formed fibrin is both inflammatory and resistant to fibrinolysis. In particular, we argue that the form of fibrin generated is amyloid in nature because much of its normal α-helical content is transformed to β-sheets, as occurs with other proteins in established amyloidogenic and prion diseases. We hypothesize that these processes of amyloidogenic clotting and the attendant coagulopathies play a role in the passage along the aforementioned pathways to organismal death, and that their inhibition would be of significant therapeutic value, a claim for which there is considerable emerging evidence.

A meta-analysis and review examining a possible role for oxidative stress and singlet oxygen in diverse diseases

From kinetic data (k, T) we calculated the thermodynamic parameters for various processes (nucleation, elongation, fibrillization, etc.) of proteinaceous diseases that are related to the β-amyloid protein (Alzheimer's), to tau protein (Alzheimer's, Pick's), to α-synuclein (Parkinson's), prion, amylin (type II diabetes), and to α-crystallin (cataract). Our calculations led to ΔG^≠ values that vary in the range 92.8-127 kJ mol^-1 at 310 K. A value of ∼10-30 kJ mol^-1 is the activation energy for the diffusion of reactants, depending on the reaction and the medium. The energy needed for the excitation of O₂ from the ground to the first excited state (¹Δ_g, singlet oxygen) is equal to 92 kJ mol^-1 So, the ΔG^≠ is equal to the energy needed for the excitation of ground state oxygen to the singlet oxygen (¹Δ_g first excited) state. The similarity of the ΔG^≠ values is an indication that a common mechanism in the above disorders may be taking place. We attribute this common mechanism to the (same) role of the oxidative stress and specifically of singlet oxygen, (¹Δ_g), to the above-mentioned processes: excitation of ground state oxygen to the singlet oxygen, ¹Δ_g, state (92 kJ mol^-1), and reaction of the empty π* orbital with high electron density regions of biomolecules (∼10-30 kJ mol^-1 for their diffusion). The ΔG^≠ for cases of heat-induced cell killing (cancer) lie also in the above range at 310 K. The present paper is a review and meta-analysis of literature data referring to neurodegenerative and other disorders.

Destabilization of Human Insulin Fibrils by Peptides of Fruit Bromelain Derived From Ananas comosus (Pineapple)

Deposition of insulin aggregates in human body leads to dysfunctioning of several organs. Effectiveness of fruit bromelain from pineapple in prevention of insulin aggregate was investigated. Proteolyses of bromelain was done as par human digestive system and the pool of small peptides was separated from larger peptides and proteins. Under conditions of growth of insulin aggregates from its monomers, this pool of peptides restricted the reaction upto formation of oligomers of limited size. These peptides also destabilized preformed insulin aggregates to oligomers. These processes were followed fluorimetrically using Thioflavin T and 1-ANS, size-exclusion HPLC, dynamic light scattering, atomic force microscopy, and transmission electron microscopy. Sequences of insulin (A and B chains) and bromelain were aligned using Clustal W software to predict most probable sites of interactions. Synthetic tripeptides corresponding to the hydrophobic interactive sites of bromelain showed disaggregation of insulin suggesting specificity of interactions. The peptides GG and AAA serving as negative controls showed no potency in destabilization of aggregates. Disaggregation potency of the peptides was also observed when insulin was deposited on HepG2 liver cells where no formation of toxic oligomers occurred. Amyloidogenic des-octapeptide (B23-B30 of insulin) incapable of cell signaling showed cytotoxicity similar to insulin. This toxicity could be neutralized by bromelain derived peptides. FT-IR and far-UV circular dichroism analysis indicated that disaggregated insulin had structure distinctly different from that of its hexameric (native) or monomeric states. Based on the stoichiometry of interaction and irreversibility of disaggregation, the mechanism/s of the peptides and insulin interactions has been proposed. J. Cell. Biochem. 118: 4881-4896, 2017. © 2017 Wiley Periodicals, Inc.

Novel therapeutic interventions for p53-altered tumors through manipulation of its family members, p63 and p73

TP53 is highly mutated in human cancers, thus targeting this tumor suppressor pathway is highly desirable and will impact many cancer patients. (1,2) Therapeutic strategies to reactivate the p53-pathway have been challenging, (3,4) and no effective treatment exists. (5) We utilized the p53-family members, p63 and p73, which are not frequently mutated in cancer, to treat p53-defective cancers. The N-terminal splice variants of p63 and p73 are denoted as the TA and ΔN isoforms. We recently demonstrated that deletion of either ΔNp63 or ΔNp73 in p53-deficient mouse tumors results in tumor regression mediated by metabolic programming. Using this strategy, we identified pramlintide, a synthetic analog of amylin, as an effective treatment for p53 deficient and mutant tumors. Here, we show the utility of using pramlintide, as a potential cancer preventive option for p53-deficient tumors in mouse models. Additionally, we found that in vivo inhibition of both ΔNp63 and ΔNp73 in combination accelerates tumor regression and increases survival of p53-deficient mice. We report that inhibition of both ΔNp63 and ΔNp73 in combination results in upregulation of 3 key metabolic regulators, IAPP, GLS2, and TIGAR resulting in an increase in apoptosis and tumor regression in ΔNp63/ΔNp73/p53 deficient thymic lymphomas. These data highlight the value of generating inhibitors that will simultaneously target ΔNp63 and ΔNp73 to treat cancer patients with alterations in p53.

Conformational Dynamics of the Human Islet Amyloid Polypeptide in a Membrane Environment: Toward the Aggregation Prone Form

Human islet amyloid polypeptide (hIAPP) is a 37-residue peptide hormone, which upon misfolding changes from the physiologically active monomer into pathological amyloid fibril aggregates in the pancreas of type 2 diabetes mellitus patients. During this process, the insulin-producing pancreatic β-cells are damaged; however, the underlying mechanism of this mode of cytotoxicity remains elusive. It is known that anionic lipids accelerate amyloid fibril formation, implicating the importance of the cellular membrane in the process, and that a pH close to the level in the β-cell secretory granules (pH 5.5) inhibits amyloid fibril formation. Using all-atom molecular dynamics simulations, we have investigated the membrane-associated monomer state of α-helical hIAPP, analyzed specific interactions of hIAPP with a mixed anionic-zwitterionic lipid membrane and examined the influence of pH on the structure and dynamics of hIAPP and its interaction with the membrane. We find that hIAPP primarily interacts with the membrane by forming favorable interactions between anionic lipids and the positively charged residues in the N-terminal part of the peptide. Rationalizing experimental findings, the simulations show that the N-terminal part of the peptide interacts with the membrane in the lipid headgroup region. At neutral pH, the C-terminal part of the peptide, which contains the residues that initiate fibril formation, displays a highly dynamic, unfolded state, which interacts with the membrane significantly less than the N-terminal part. Such an unfolded form can be proposed to contribute to the acceleration of fibril formation. At low pH, protonation of His18 mediates a stronger interaction of the C-terminal part with the membrane, resulting in the immobilization of the C-terminal part on the membrane surface that might constitute a mechanism by which low pH inhibits fibril formation.

Inhibition of hIAPP Amyloid Aggregation and Pancreatic β-Cell Toxicity by OH-Terminated PAMAM Dendrimer

Human islet amyloid polypeptide (hIAPP, or amylin) forms amyloid deposits in the islets of Langerhans, a phenomenon that is associated with type-2 diabetes impacting millions of people worldwide. Accordingly, strategies against hIAPP aggregation are essential for the prevention and eventual treatment of the disease. Here, it is shown that generation-3 OH-terminated poly(amidoamine) dendrimer, a polymeric nanoparticle, can effectively halt the aggregation of hIAPP and shut down hIAPP toxicity in pancreatic MIN6 and NIT-1 cells as well as in mouse islets. This finding is supported by high-throughput dynamic light scattering experiment and thioflavin T assay, where the rapid evolution of hIAPP nucleation and elongation processes is halted by the addition of the dendrimer up to 8 h. Discrete molecular dynamics simulations further reveal that hIAPP residues bound strongly with the dendrimer near the c-terminal portion of the peptide, where the amyloidogenic sequence (residues 22-29) locates. Furthermore, simulations of hIAPP dimerization reveal that binding with the dendrimer significantly reduces formation of interpeptide contacts and hydrogen bonds, thereby prohibiting peptide self-association and amyloidosis. This study points to a promising nanomedicinal strategy for combating type-2 diabetes and may have broader implications for targeting neurological disorders whose distinct hallmark is also amyloid fibrillation.