Peptide Conjugates of Benzene Carboxylic Acids as Agonists and Antagonists of Amylin Aggregation

Computational analysis of the alpha-2 domain of apolipoprotein B - 100, a potential triggering factor in LDL aggregation

Atherosclerosis, the major underlying cause of cardiovascular disease, is believed to arise from the accumulation of low-density lipoprotein (LDL) in the arterial subendothelial space, ultimately leading to plaque formation. It is proposed that the accumulation of LDL is linked to its intrinsic aggregation propensity. Although the native LDL is not prone to aggregation, LDL(-), an electronegative LDL characterized in the plasma, has been shown to prime LDL aggregation in a domino-like behavior similar to amyloidogenic proteins. LDL(-) has also been observed to have a misfolded apolipoprotein B-100 (apo B-100), a huge protein consisting of 4563 amino acid residues. As misfolding of proteins is commonly associated with amyloid formation, apo B-100 is therefore being considered as the possible triggering factor in LDL aggregation. Previous computational studies have implicated the α2 domain to be the aggregation-prone region of apo B-100. In this study, the amyloidogenic properties of the α2 domain of apo B-100 were interrogated using both in silico and in vitro techniques. Since the crystal structure of the 570-amino acid α2 domain of apo B-100 is yet to be solved, we used several secondary structure prediction tools to model putative helical regions that make up the α2 domain. The stability of each of the 17 helices thus identified was further probed using molecular dynamics (MD), with the least stable of the helices considered as potentially amyloidogenic. In a 100 ns simulation window, helices k (YFEKLVGFIDDAVK), m (YHQFVDETNDKIREVTQRLNGEIQA), and p (QQELQRYLSLVGQVYS) were the least stable and appeared to transition to β-structures, the hallmark of amyloidogenesis. When the simulation was extended to longer times, only helices k and p formed stable β-sheets that persisted. Analysis of the data indicates that the final β-sheet conformation was stabilized by the π-π stacking interactions between the aromatic rings of Tyr-1 and Phe-8 for helix k and likely π-π stacking contacts between Arg-6 guanidino group and Tyr-15 ring for helix p. Based on the in silico work, we proceeded to synthesize and spectroscopically characterize helices k, m17-25 (QRLNGEIQA), and p. As expected, k and p formed detectable amyloids, with the latter appearing to be substantially more amyloidogenic based on kinetic aggregation assays. Amyloid fibrils formed by p were confirmed using circular dichroism spectroscopy and transmission electron microscopy. Data obtained could be exploited to further investigate the roles of peptides derived from the α2 domain helices of apo B-100 in triggering LDL aggregation. Based on preliminary data, one of the peptides designed based on this work reduced the aggregation of LDL.

Self-Assembly and Gelation Study of Dipeptide Isomers with Norvaline and Phenylalanine

Dipeptides have emerged as attractive building blocks for supramolecular materials thanks to their low-cost, inherent biocompatibility, ease of preparation, and environmental friendliness as they do not persist in the environment. In particular, hydrophobic amino acids are ideal candidates for self-assembly in polar and green solvents, as a certain level of hydrophobicity is required to favor their aggregation and reduce the peptide solubility. In this work, we analyzed the ability to self-assemble and the gel of dipeptides based on the amino acids norvaline (Nva) and phenylalanine (Phe), studying all their combinations and not yielding to enantiomers, which display the same physicochemical properties, and hence the same self-assembly behavior in achiral environments as those studied herein. A single-crystal X-ray diffraction of all the compounds revealed fine details over their molecular packing and non-covalent interactions.

Human islet amyloid polypeptide: A therapeutic target for the management of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) and other metabolic disorders are often silent and go unnoticed in patients because of the lack of suitable prognostic and diagnostic markers. The current therapeutic regimens available for managing T2DM do not reverse diabetes; instead, they delay the progression of diabetes. Their efficacy (in principle) may be significantly improved if implemented at earlier stages. The misfolding and aggregation of human islet amyloid polypeptide (hIAPP) or amylin has been associated with a gradual decrease in pancreatic β-cell function and mass in patients with T2DM. Hence, hIAPP has been recognized as a therapeutic target for managing T2DM. This review summarizes hIAPP's role in mediating dysfunction and apoptosis in pancreatic β-cells via induction of endoplasmic reticulum stress, oxidative stress, mitochondrial dysfunction, inflammatory cytokine secretion, autophagy blockade, etc. Furthermore, it explores the possibility of using intermediates of the hIAPP aggregation pathway as potential drug targets for T2DM management. Finally, the effects of common antidiabetic molecules and repurposed drugs; other hIAPP mimetics and peptides; small organic molecules and natural compounds; nanoparticles, nanobodies, and quantum dots; metals and metal complexes; and chaperones that have demonstrated potential to inhibit and/or reverse hIAPP aggregation and can, therefore, be further developed for managing T2DM have been discussed.

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Misfolded species of hIAPP form toxic oligomers in pancreatic β-cells.

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hIAPP amyloids has been detected in the pancreas of about 90% subjects with T2DM.

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Inhibitors of hIAPP aggregation can help manage T2DM.

Targeting Human Islet Amyloid Polypeptide Aggregation and Toxicity in Type 2 Diabetes: An Overview of Peptide-Based Inhibitors

Type 2 diabetes (T2D) is a chronic metabolic disease characterized by insulin resistance and a progressive loss of pancreatic islet β-cell mass, which leads to insufficient secretion of insulin and hyperglycemia. Emerging evidence suggests that toxic oligomers and fibrils of human islet amyloid polypeptide (hIAPP) contribute to the death of β-cells and lead to T2D pathogenesis. These observations have opened new avenues for the development of islet amyloid therapies for the treatment of T2D. The peptide-based inhibitors are of great value as therapeutic agents against hIAPP aggregation in T2D owing to their biocompatibility, feasibility of synthesis and modification, high specificity, low toxicity, proteolytic stability (modified peptides), and weak immunogenicity as well as the large size of involved interfaces during self-aggregation of hIAPP. An understanding of what has been done and achieved will provide key insights into T2D pathology and assist in the discovery of more potent drug candidates for the treatment of T2D. In this article, we review various peptide-based inhibitors of hIAPP aggregation, including those derived from the hIAPP sequence and those not based on the sequence, consisting of both natural as well as unnatural amino acids and their derivatives. The present review will be beneficial in advancing the field of peptide medicine for the treatment of T2D.

γ-AApeptides-based Small Molecule Ligands That Disaggregate Human Islet Amyloid Polypeptide

The abnormal folding and aggregation of functional proteins into amyloid is a typical feature of many age-related diseases, including Type II diabetes. Growing evidence has revealed that the prevention of aggregate formation in culprit proteins could retard the progression of amyloid diseases. Human Amylin, also known as human islet amyloid polypeptide (hIAPP), is the major factor for categorizing Type II diabetes as an amyloid disease. Specifically, hIAPP has a great aggregation potential, which always results in a lethal situation for the pancreas. Many peptide inhibitors have been constructed from the various segments of the full-length hIAPP peptide; however, only a few have their origin from the screening of combinatorial peptidomimetic library. In this study, based on HW-155, which was previously discovered from a one-bead-one compound (OBOC) library to inhibit Aβ40 aggregation, we investigated eight (8) analogues and evaluated their amyloid-prevention capabilities for inhibiting fibrillization of hIAPP. Characterization studies revealed that all analogues of HW-155, as well as HW-155, were effective inhibitors of the fibril formation by hIAPP.

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.

Chiral Effect at Nano-Bio Interface: A Model of Chiral Gold Nanoparticle on Amylin Fibrillation

Protein/Peptide amyloidosis is the main cause of several diseases, such as neurodegenerative diseases. It has been widely acknowledged that the unnatural fibrillation of protein/peptides in vivo is significantly affected by the physical and chemical properties of multiscale biological membranes. For example, previous studies have proved that molecule chirality could greatly influence the misfolding, fibrillation and assembly of β-Amyloid peptides at the flat liquid-solid surface. However, how the nanoscale chirality influences this process remains unclear. Here we used gold nanoparticles (AuNPs, d = 4 ± 1 nm)-modified with N-isobutyl-L(D)-cysteine (L(D)-NIBC) enantiomers-as a model to illustrate the chiral effect on the amylin fibrillation at nano-bio interface. We reported that both two chiral AuNPs could inhibit amylin fibrillation in a dosage-dependent manner but the inhibitory effect of L-NIBC-AuNPs was more effective than that of D-NIBC-AuNPs. In-situ real time circular dichroism (CD) spectra showed that L-NIBC-AuNPs could inhibit the conformation transition process of amylin from random coils to α-helix, while D-NIBC-AuNPs could only delay but not prevent the formation of α-helix; however, they could inhibit the further conformation transition process of amylin from α-helix to β-sheet. These results not only provide interesting insight for reconsidering the mechanism of peptides amyloidosis at the chiral interfaces provided by biological nanostructures in vivo but also would help us design therapeutic inhibitors for anti-amyloidosis targeting diverse neurodegenerative diseases.

Development of Peptide-Based Inhibitors of Amylin Aggregation Employing Aromatic and Electrostatic Repulsion

Human islet amyloid polypeptide (hIAPP) is a 37-residue hormone that is co-stored and co-secreted with insulin. In type 2 diabetes, the polypeptide misfolds to form amyloid plaques in the pancreas. The self-assembly of hIAPP has been linked to the loss of insulin production and β-cell death. Recent investigations have revealed that soluble oligomers of hIAPP are the cytotoxic species responsible for β-cell death and not insoluble amyloid fibrils. Compounds that prevent the self-assembly of hIAPP or drive self-assembly to the state of innocuous insoluble amyloid may be of potential therapeutic value. In this report we summarize key methods employed in our efforts to identify peptide-based modulators of amylin self-assembly that utilize π-electronic effects or electrostatic charge repulsion. These peptide-based modulators may serve as lead compounds for the development of more drug-like molecules and demonstrate that tuning π-electron density and employing charged amyloid disrupting elements are viable approaches toward the design of potential amyloid inhibitors.

Lysine acylation in superoxide dismutase-1 electrostatically inhibits formation of fibrils with prion-like seeding

The acylation of lysine residues in superoxide dismutase-1 (SOD1) has been previously shown to decrease its rate of nucleation and elongation into amyloid-like fibrils linked to amyotrophic lateral sclerosis. The chemical mechanism underlying this effect is unclear, i.e. hydrophobic/steric effects versus electrostatic effects. Moreover, the degree to which the acylation might alter the prion-like seeding of SOD1 in vivo has not been addressed. Here, we acylated a fraction of lysine residues in SOD1 with groups of variable hydrophobicity, charge, and conformational entropy. The effect of each acyl group on the rate of SOD1 fibril nucleation and elongation were quantified in vitro with thioflavin-T (ThT) fluorescence, and we performed 594 iterate aggregation assays to obtain statistically significant rates. The effect of the lysine acylation on the prion-like seeding of SOD1 was assayed in spinal cord extracts of transgenic mice expressing a G85R SOD1-yellow fluorescent protein construct. Acyl groups with >2 carboxylic acids diminished self-assembly into ThT-positive fibrils and instead promoted the self-assembly of ThT-negative fibrils and amorphous complexes. The addition of ThT-negative, acylated SOD1 fibrils to organotypic spinal cord failed to produce the SOD1 inclusion pathology that typically results from the addition of ThT-positive SOD1 fibrils. These results suggest that chemically increasing the net negative surface charge of SOD1 via acylation can block the prion-like propagation of oligomeric SOD1 in spinal cord.

Conformational Differentiation of α-Cyanohydroxycinnamic Acid Isomers: A Raman Spectroscopic Study

Two α-cyanohydroxycinnamic acid positional isomers, α-cyano-4-hydroxycinnamic acid (CHCA4) and α-cyano-3-hydroxycinnamic acid (CHCA3), were characterized using Raman spectroscopy. We analyzed the implications of the collected Raman spectral shifts, and verified them through other spectroscopic techniques, to arrive at plausible three dimensional structures of CHCA3 and CHCA4. The positions of these groups were mapped by systematically analyzing the orientation and type of interactions functional groups make in each CHCA isomer. We determined whether or not the carboxylic moieties are forming dimeric links and ascertained the existence of ring-ring π-stacking interactions. We also assessed the nature of the hydrogen bonding between -CN and -OH groups. The results were then taken together to model plausible three dimensional structures for each compound. The data revealed a structure for CHCA4 that matches the published x-ray crystallographic structure. We then applied the same spectral analysis to CHCA3 to reveal its plausible three dimensional structure. The structural details revealed may account for the functional properties of the two α-cyanohydroxycinnamic acid positional isomers.