Theoretical Investigation of the Inhibitory Mechanism of Norepinephrine on hIAPP Amyloid Aggregation and the Destabilization of Protofibrils.

The search for an appropriate drug to completely eradicate type II diabetes (T2D), a metabolic disorder from which over 40 million people suffer worldwide, has not yet led to any satisfactory result. The misfolding of human islet amyloid polypeptide (hIAPP) into toxic oligomers is a pathogenic feature of this disease, due to which the prevention of hIAPP aggregation is considered the rational approach to combat T2D. Hence, we study the role of a catecholamine, norepinephrine, on the amyloid aggregation of hIAPP, which has previously displayed inhibitory effect on amyloid-β aggregation. Via all-atom molecular dynamics simulations, we observe that norepinephrine can not only inhibit the aggregation of hIAPP but also partially disassemble the preformed fibrils. For comparison, the influence of two other molecules (aspirin and benzimidazole, both of which have previously reported to have no inhibitory impact on hIAPP aggregation) is also analyzed. We observe that the conformational preference of hIAPP changes from a β-sheet conformation to a disordered state when norepinephrine is added to the peptides. However, no such effect is observed in the presence of aspirin or benzimidazole. In-depth investigation reveals that the β-sheets formed between Leu12-His18 and Leu27-Gly33 enhance the peptide-peptide interactions that are broken by norepinephrine, which itself interacts with the peptides via hydrogen bonding, hydrophobic, and aromatic stacking interactions, preferentially with the C-terminal residues of hIAPP. The molecular mechanism action of norepinephrine on hIAPP aggregation can provide useful insight for the drug design against T2D.