Insulin based analogs HLVEALYLV and LVEALYLV to inhibit the formation of amyloid fibrils in beta cells

Human islet amyloid polypetide (hIAPP) is a 37 amino acid peptide, co-secreted along with insulin in the islets of Langerhans of pancreatic beta cells. Aggregation of hIAPP fibrils is believed to be toxic to beta cells and responsible for beta cell dysfunction and death associated with type 2 diabetes. Insulin has been found to act against the actions of hIAPP. The internal sequence of insulin, HLVEALYLV, recognizes and binds the 10-19 region of hIAPP. Since insulin reportedly blocks the formation of amyloid fibers, insulin analogs may protect cell membranes from damage. In an effort to study this effect, truncated analogs of insulin, namely HLVEALYLV and LVEALYLV, were synthesized and tested in the presence of hIAPP. Carboxyfluorescein-encapsulating vesicles that mimic the $-cell were created using a 7:3 ratio of the lipids 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dioleoyl-sn-glycero-3- (phospho-L-serine) (DOPS), respectively, and the percent leakage of fluorescent dye from the vesicles in the presence of the peptides was calculated as compared to a 100% Triton-X detergent-treated control. The activity of the truncated analogs was compared to that of insulin under the same conditions. Whereas insulin was somewhat protective of the effects of hIAPP, the shorter analogs were found to increase the damage caused by hIAPP rather than reducing it, possibly by co-aggregating with the hIAPP

Modeling the Interface between Islet Amyloid Polypeptide and Insulin-Based Aggregation Inhibitors: Correlation to Aggregation Kinetics and Membrane Damage

Human islet amyloid polypeptide (hIAPP) forms cytotoxic fibrils in type-2 diabetes and insulin is known to inhibit formation of these aggregates. In this study, a series of insulin-based inhibitors were synthesized and assessed for their ability to slow aggregation and impact hIAPP-induced membrane damage. Computational studies were employed to examine the underlying mechanism of inhibition. Overall, all compounds were able to slow aggregation at sufficiently high concentrations (10× molar excess); however, only two peptides showed any inhibitory capability at the 1:1 molar ratio (EALYLV and VEALYLV). The results of density functional calculations suggest this is due to the strength of a salt bridge formed with the Arg11 side chain of hIAPP and the inhibitors’ ability to span from the Arg11 to past the Phe15 residue of hIAPP, blocking one of the principal amyloidogenic regions of the molecule. Unexpectedly, slowing fibrillogenesis actually increased damage to lipid membranes, suggesting that the aggregation process itself, rather than the fibrilized peptide, may be the cause of cytotoxicity in vivo