Amyloidogenesis Abolished by Proline Substitutions but Enhanced by Lipid Binding

The influence of lipid molecules on the aggregation of a highly amyloidogenic segment of human islet amyloid polypeptide, hIAPP20–29, and the corresponding sequence from rat has been studied by all-atom replica exchange molecular dynamics (REMD) simulations with explicit solvent model. hIAPP20–29 fragments aggregate into partially ordered β-sheet oligomers and then undergo large conformational reorganization and convert into parallel/antiparallel β-sheet oligomers in mixed in-register and out-of-register patterns. The hydrophobic interaction between lipid tails and residues at positions 23–25 is found to stabilize the ordered β-sheet structure, indicating a catalysis role of lipid molecules in hIAPP20–29 self-assembly. The rat IAPP variants with three proline residues maintain unstructured micelle-like oligomers, which is consistent with non-amyloidogenic behavior observed in experimental studies. Our study provides the atomic resolution descriptions of the catalytic function of lipid molecules on the aggregation of IAPP peptides

Small molecule inhibitors of Aβ-aggregation and neurotoxicity

Alzheimer disease (AD) is characterized pathologically by extracellular amyloid deposits composed of Aβ peptide, neurofibrillary tangles (NFTs) made up of hyperphosphorylated tau, and a deficit of cholinergic neurons in the basal forebrain. Presently, only symptomatic therapies are available for the treatment of AD and these therapies have a limited time frame of utility. Amyloid disorders represent the effects of chronic Aβ production and are not a secondary pathological effect caused by a distant trigger; therefore targeting Aβ is a viable pursuit. In this review, we will discuss the various small molecule anti-aggregation inhibitors that have been reported in the literature, with emphasis on compounds that are presently being investigated in clinical trials

Intrinsic Determinants of Aβ12–24 pH-Dependent Self-Assembly Revealed by Combined Computational and Experimental Studies

The propensity of amyloid- (A) peptide to self-assemble into highly ordered amyloid structures lies at the core of their accumulation in the brain during Alzheimer's disease. By using all-atom explicit solvent replica exchange molecular dynamics simulations, we elucidated at the atomic level the intrinsic determinants of the pH-dependent dimerization of the central hydrophobic segment A and related these with the propensity to form amyloid fibrils measured by experimental tools such as atomic force microscopy and fluorescence. The process of A dimerization was evaluated in terms of free energy landscape, side-chain two-dimensional contact probability maps, -sheet registries, potential mean force as a function of inter-chain distances, secondary structure development and radial solvation distributions. We showed that dimerization is a key event in A amyloid formation; it is highly prompted in the order of pH 5.02.98.4 and determines further amyloid growth. The dimerization is governed by a dynamic interplay of hydrophobic, electrostatic and solvation interactions permitting some variability of -sheets at each pH. These results provide atomistic insight into the complex process of molecular recognition detrimental for amyloid growth and pave the way for better understanding of the molecular basis of amyloid diseases

Development of proteolytically stable N-methylated peptide inhibitors of aggregation of the amylin peptide implicated in type 2 diabetes

Islet amyloid polypeptide, also known as amylin, is the main component of the amyloid deposits present in approximately 90% of people with type 2 diabetes mellitus (T2DM). In this disease, amylin aggregates into multimeric β-pleated sheet structures which cause damage to pancreatic islet β-cells. Inhibitors of early-stage amylin aggregation could therefore provide a disease-modifying treatment for T2DM. In this study, overlapping peptides were designed to target the ‘binding’ region (RLANFLVHSS, residues 11-20) of human amylin, and their effects on amyloid fibril formation were determined by Thioflavin-T assay. The first generation peptides showed less than 50% inhibition of aggregation, but a second generation peptide (H2N-RGANFLVHGR-CONH2) showed strong inhibitory effects on amylin aggregation, and this was confirmed by negative stain electron microscopy. Cytotoxicity studies revealed that this peptide protected human pancreatic 1.4E7 (ECACC 10070102) insulin-secreting cells from the toxic effects of human amylin. Unlike the retro-inverso version of this peptide, which stimulated aggregation, two N-methylated peptides (H2N-RGAmNFmLVmHGR-CONH2 and H2N-RGANmFLmVHmR-CONH2) gave very clear dose-dependent inhibition of fibril formation. These two peptides were also stable against a range of different proteolytic enzymes, and in human plasma. These N-methylated peptides could provide a novel treatment for slowing progression of T2DM

Amyloidosis

Amyloidoses are a heterogeneous group of diverse etiology diseases. They are characterized by an endogenous production of abnormal proteins called amyloid proteins, which are not hydrosoluble, form depots in various organs and tissue of animals and humans and cause dysfunctions. Despite many decades of research, the origin of the pathogenesis and the molecular determinants involved in amyloid diseases has remained elusive. At present, there is not an effective treatment to prevent protein misfolding in these amyloid diseases. The aim of this book is to present an overview of different aspects of amyloidoses from basic mechanisms and diagnosis to latest advancements in treatment

Mechanism and Development of Peptide-Based Inhibitors to Human Islet Amyloid Polypeptide (hIAPP) Self-Assembly

Amyloid fibrils formed by of hIAPP1-37 (also known as amylin) has been linked to type-II diabetes mortalities and its formation was found to be related to the three aromatic residues in hIAPP1-37. In this dissertation, the role of aromatic amino acids, particularly that of Phe-23, and its various interactions to the self-assembly of human islet amyloid polypeptide (hIAPP)22-29 were investigated. Using a variety of spectroscopic techniques with emphasis to vibrational spectroscopy (FT-IR and Raman spectroscopies) in conjunction with computational methods, different factors leading to aggregation as well as its inhibition were identified. Among the driving forces identified are aromatic-π stacking between Phe residues which upon disruption by utilizing specially designed peptide-based inhibitors can lead to the abolition of aggregation propensity of hIAPP. In this work, three classes of peptide-based inhibitors were developed. The first group of inhibitors take advantage of the aromaticity of the Phe-23 residue of the hIAPP­22-29 fragment that undergoes π-stacking upon aggregation. These peptides disrupt the aromaticity by introducing electron donating group (EDG) on Phe-23. Although these peptides showed no inherent amyloidogenic properties, their effectivity towards inhibition of full-length hIAPP aggregation was weak. The second batch of inhibitors, also based on hIAPP22-29 where benzenecarboxylic acid groups were conjugated to the N-terminus of the peptide fragment, showed a more promising inhibitory property towards full-length hIAPP aggregation. These peptides were designed to inhibit aggregation by interfering with the formation of the β-turn intermediate during the amyloid formation and at the same time providing electrostatic repulsion between amylin monomers. Although some of the conjugates showed inhibition, others showed promotion of amyloid formation. The third batch of peptide-based inhibitors were designed to exploit cationic-π interactions, a common interaction between aromatic and charged amino acid residues in polypeptides and proteins. In this batch of peptides, some inhibition was achieved primarily on the basis of increased solubility brought about by the peptide inhibitors binding to hIAPP via hydrophobic interactions

Interaction studies between biocompatible polymers and amyloid-B peptides

A informação relativa aos orientadores da tese foi retirada da página do SIFEUPTese de doutoramento. Engenharia Química e Biológica. Faculdade de Engenharia. Universidade do Porto. 200