The smaller heparin fragments bind non-specifically through the IAPP sequence: An in silico study

Inhibitory mechanism of lithospermic acid on the fibrillation of type 2 diabetes associated islet amyloid polypeptide

The abnormal fibrillation of a 37-residue peptide hormone human islet amyloid polypeptide (hIAPP) is linked with type 2 diabetes (T2D). Pang et al. depicted a prominent role of lithospermic acid (LA) in blocking hIAPP fibrillation and alleviating the hIAPP aggregates-induced cytotoxicity. LA is a polyphenolic compound present in extra virgin olive oil with therapeutic properties. Despite its notable inhibitory effect on hIAPP fibrillation, the inhibition mechanism remains unclear. Here, molecular dynamics (MD) simulations have been utilized to shed light on the putative binding mechanism and inhibitory mechanism of LA against hIAPP fibrillation. The molecular docking predicted favourable binding (-7.1 kcal/mol) of LA with hIAPP. Interestingly, LA increases the helix content in hIAPP and blocks the conformational transition to the aggregation-competent conformations. The conformational clustering and hydrogen bond analyses depicted that LA formed hydrogen bonds with Asn21 of hIAPP, which play an important role in hIAPP aggregation. LA binds favourably to hIAPP (ΔGbinding = -49.62 ± 3.34 kcal/mol) with a major contribution from the van der Waals interactions. The MD simulations highlighted that LA dramatically interfered with the intrapeptide interactions and inhibited sampling of aggregation-competent β-sheet conformations in hIAPP via hydrogen bonds through its hydroxyl groups, van der Waals interactions with hIAPP residues, thus blocking hIAPP aggregation to β-sheet rich cytotoxic fibrillar aggregates. The MD simulations illuminated specific interactions between hIAPP and LA, which will benefit in developing new chemical entities against hIAPP fibrillation.

Pharmacology of Heparin and Related Drugs: An Update

Heparin has been used extensively as an antithrombotic and anticoagulant for close to 100 years. This anticoagulant activity is attributed mainly to the pentasaccharide sequence, which potentiates the inhibitory action of antithrombin, a major inhibitor of the coagulation cascade. More recently it has been elucidated that heparin exhibits anti-inflammatory effect via interference of the formation of neutrophil extracellular traps and this may also contribute to heparin's antithrombotic activity. This illustrates that heparin interacts with a broad range of biomolecules, exerting both anticoagulant and nonanticoagulant actions. Since our previous review, there has been an increased interest in these nonanticoagulant effects of heparin, with the beneficial role in patients infected with SARS2-coronavirus a highly topical example. This article provides an update on our previous review with more recent developments and observations made for these novel uses of heparin and an overview of the development status of heparin-based drugs. SIGNIFICANCE STATEMENT: This state-of-the-art review covers recent developments in the use of heparin and heparin-like materials as anticoagulant, now including immunothrombosis observations, and as nonanticoagulant including a role in the treatment of SARS-coronavirus and inflammatory conditions.

Silybins inhibit human IAPP amyloid growth and toxicity through stereospecific interactions

Type 2 Diabetes is a major public health threat, and its prevalence is increasing worldwide. The abnormal accumulation of islet amyloid polypeptide (IAPP) in pancreatic β-cells is associated with the onset of the disease. Therefore, the design of small molecules able to inhibit IAPP aggregation represents a promising strategy in the development of new therapies. Here we employ in vitro, biophysical, and computational methods to inspect the ability of Silybin A and Silybin B, two natural diastereoisomers extracted from milk thistle, to interfere with the toxic self-assembly of human IAPP (hIAPP). We show that Silybin B inhibits amyloid aggregation and protects INS-1 cells from hIAPP toxicity more than Silybin A. Molecular dynamics simulations revealed that the higher efficiency of Silybin B is ascribable to its interactions with precise hIAPP regions that are notoriously involved in hIAPP self-assembly i.e., the S20-S29 amyloidogenic core, H18, the N-terminal domain, and N35. These results highlight the importance of stereospecific ligand-peptide interactions in regulating amyloid aggregation and provide a blueprint for future studies aimed at designing Silybin derivatives with enhanced drug-like properties.

Proteostasis of Islet Amyloid Polypeptide: A Molecular Perspective of Risk Factors and Protective Strategies for Type II Diabetes

The possible link between hIAPP accumulation and β-cell death in diabetic patients has inspired numerous studies focusing on amyloid structures and aggregation pathways of this hormone. Recent studies have reported on the importance of early oligomeric intermediates, the many roles of their interactions with lipid membrane, pH, insulin, and zinc on the mechanism of aggregation of hIAPP. The challenges posed by the transient nature of amyloid oligomers, their structural heterogeneity, and the complex nature of their interaction with lipid membranes have resulted in the development of a wide range of biophysical and chemical approaches to characterize the aggregation process. While the cellular processes and factors activating hIAPP-mediated cytotoxicity are still not clear, it has recently been suggested that its impaired turnover and cellular processing by proteasome and autophagy may contribute significantly toward toxic hIAPP accumulation and, eventually, β-cell death. Therefore, studies focusing on the restoration of hIAPP proteostasis may represent a promising arena for the design of effective therapies. In this review we discuss the current knowledge of the structures and pathology associated with hIAPP self-assembly and point out the opportunities for therapy that a detailed biochemical, biophysical, and cellular understanding of its aggregation may unveil.