Inhibition of islet amyloid polypeptide aggregation in type-II diabetes

Accumulating evidence suggests that the aggregation of islet amyloid polypeptide (IAPP, a.k.a. amylin) is associated with β-cell death in type 2 diabetes (T2D). IAPP is co-secreted with insulin by pancreatic beta-cells, and also works together with insulin to control the serum glucose level. In vitro studies suggest that IAPP is one of the most amyloidogenic peptide, which forms amyloid fibrils within hours at micromolar concentrations. However, no apparent IAPP amyloid aggregates are observed in healthy individuals where IAPP is stored in β-cell granules at milimolar concentrations for hours before being secreted to the blood stream. Therefore, physiological conditions of β-cell granules natively inhibit the amyloid aggregation of IAPP.

The cellular environment of β-cell granules is unique in its high concentrations of Zn2+, insulin and proinsulin c-peptide in addition to IAPP. C-peptide is the co-product of insulin synthesis, which connects insulin A- and B-chains in the precursor proinsulin and is co-secreted with insulin in equal molar. A high concentration of Zn2+, maintained by a β-cell specific zinc transporter – ZnT8, is believed to be important for the efficient storage of insulin: zinc coordinates the formation of insulin hexamers, which form crystals in the dense core of β-cell granules. ). We hypothesize that intermolecular interactions with insulin, zinc and c-peptide are important for the native inhibition of IAPP aggregation inside β-cell granules. Using state-of-the-art discrete molecular dynamics (DMD) simulations, we showed that both insulin monomers and dimers could bind IAPP monomer and inhibit IAPP self-association by competing with same amyloidogenic regions, subsequently preventing aggregation. Therefore, comparing to high zinc concentrations where insulin is insoluble in the crystal form, zinc-deficiency due to loss-of-function mutations of ZnT8 shifts insulin oligomer/crystallization equilibrium toward soluble monomers and dimers, which can efficiently inhibit IAPP aggregation and reduce T2D risk. Currently, we are trying to understand the effects of other granule molecules, including zinc, c-peptide, and their complex, on IAPP aggregation.

We are also actively exploring other approaches to inhibit IAPP aggregation. There are many reports about natural-occurring polyphenols, including resveratrol from grape, curcumin from turmeric, EGCG from green tea, and so on, which have inhibitory effects on IAPP aggregation. The advantage of these natural-occurring polyphenols is their low toxicity and the fact that they can be administrated for a long period of time. Understanding their mechanism is important for designing de novo anti-amyloid drugs to treat T2D. Additionally, nanomedicinal approach is also an attractive approach to serve as not only drug carriers but also as anti-amyloid agents themselves. Therefore, we are also looking for anti-amyloid nanoparticles and trying to identify their physicochemical determinants for optimal drug loading and amyloid inhibiting functions.

8. X. Ge, A. Kakinen, E.N. Gurzov, W. Yang, L. Pang, E.H. Pilkington, P. Govindan-Nedumpully, P. Chen, F. Separovic, T.P. Davis, P. C. Ke, and F. Ding, “Zinc-coordination and C-peptide complexation: a potential mechanism for the endogenous inhibition of IAPP aggregation”, Chem. Comm., in press (2017) [link]

7. P.C. Ke, M. Sani, F. Ding, A. Kakinen, I. Javed, F. Separovic, T. P. Davis, and R. Mezzenga, Implications of Peptide Assemblies in Amyloid Diseases, Chem. Soc. Rev., in press (2017)

6. Pilkington E.H., Xing Y., Wang B., Kakinen A., Wang M., Davis T.P., Ding F., Ke P.C., “Effects of Protein Corona on IAPP Amyloid Aggregation, Fibril Remodelling, and Cytotoxicity”, Scientific Reports, in press (2017)

5. E.N. Gurzov, B. Wang, E.H. Pilkington, P. Chen,A. Kakinen, W.J. Stanley, S.A. Litwak, E.G. Hanssen,T.P. Davis, F. Ding, and P.Chun Ke, “Inhibition of hIAPP Amyloid Aggregation and Pancreatic β-cell Toxicity by OH-terminated PAMAM Dendrimer”, Small, in press (2016)

4. P. Nedumpully-Govindan, E.N. Gurzov, P. Chen, E.H. Pilkington, W.J. Stanley, S.A. Litwak, T.P. Davis, P.C. Ke, and F. Ding, “Graphene Oxide Inhibits hIAPP Amyloid Fibrillation and Toxicity in Insulin-Producing NIT-1 Cells”, PCCP, 18:94-100 (2016) [download]

3. P. Nedumpully-Govindan, A. Kakinen, E.H. Pilkington, T.P. Davis, P.C. Ke and F. Ding, “Stabilizing Off-pathway Oligomers by Polyphenol Nanoassemblies for IAPP Aggregation Inhibition”, Scientific Reports, in press (2015)

2. P. Nedumpully-Govindan, Y. Yang, R. Andorfer, W. Cao, and F. Ding, “Promotion or Inhibition of IAPP Aggregation by Zinc Coordination Depends on Its Relative Concentration”, Biochemistry, in press (2015)

1. Nedumpully-Govindan P. and Ding F., “Inhibition of IAPP aggregation by insulin depends on the insulin oligomeric state regulated by zinc ion concentration”, Scientific Reports 5, (2015)