Modulation of hIAPP Fibrillation by Rationally Designed Hexapeptides Revealed by Molecular Dynamics and Experimental Investigations

The misfolding and aggregation of 37-residue neuropancreatic hormone hIAPP (human islet amyloid polypeptide) to cytotoxic aggregates comprising oligomers, protofibrils, and mature fibrils have been linked to the pathogenesis of T2D (type 2 diabetes). Scrocchi et al. (J. Mol. Biol. 2002, 318, 697-706) identified a fragment peptide, SNNFGA (residues 20-25) from the amyloidogenic core region (Ser20-Ser29) of hIAPP as a potential inhibitor of hIAPP fibrillation. In this work, a library of 863 hexapeptides based on SNNFGA has been computationally designed and evaluated for antiaggregation activity against hIAPP fibrillation. The MM-PBSA analysis depicted that peptides TNNWPL (-42.69 ± 1.88 kcal/mol), TQNWAP (-41.82 ± 2.28 kcal/mol), and TQNWVP (-39.38 ± 1.63 kcal/mol) bind to hIAPP with higher affinity than SNNFGA (-27.15 ± 1.83 kcal/mol). Notably, TQNWVP displays a more pronounced inhibition effect than other peptides due to its ability to block the conformational transformation of hIAPP from a random coil to an aggregation-competent β-sheet conformation. The <i>in silico</i> assessment of ADMET values for the designed peptides lies within the range for therapeutic candidates, and the peptides display higher half-life than SNNFGA. To corroborate the computational findings, the peptides were evaluated for their potential to block hIAPP fibrillation using ThT fluorescence assay, DLS, and TEM. Among the synthesized peptides, TQNWVP exhibited the highest inhibitory activity (Inhibition = 75%, IC₅₀ = 6.19 ± 0.31 μM) against hIAPP fibrillation consistent with the computational results. Importantly, DLS analysis confirmed that TQNWVP reduced the size of hIAPP aggregates. Peptides exhibited a satisfactory safety-efficacy profile and efficiently alleviated hIAPP aggregate-induced cytotoxicity in rat insulinoma (INS-1) and human embryonic kidney (HEK293) cells. The combined <i>in silico</i> and <i>in vitro</i> studies in this work identified a new peptide, TQNWVP, as an efficient inhibitor of hIAPP aggregation. Furthermore, illumination of the inhibitory mechanism of SNNFGA and top hit peptides (TNNWPL, TQNWAP, and TQNWVP) against hIAPP aggregation holds significant promise for future therapeutic interventions against hIAPP fibrillation in T2D.