Coffee Components Inhibit Amyloid Formation of Human Islet Amyloid Polypeptide in Vitro: Possible Link between Coffee Consumption and Diabetes Mellitus

Abstract

Global epidemic studies have suggested that coffee consumption is reversely correlated with the incidence of type 2 diabetes mellitus (T2DM), a metabolic disease. The misfolding of human islet amyloid polypeptide (hIAPP) is regarded as one of the causative factors of T2DM. Coffee extracts have three major active components: caffeine, caffeic acid (CA), and chlorogenic acid (CGA). In this study, the effects of these major coffee components, as well as dihydrocaffeic acid (DHCA) (a major metabolite of CGA and CA), on the amyloidogenicity of hIAPP were investigated by thioflavin-T based fluorescence emission, transmission electronic microscopy, circular dichroism, light-induced cross-linking, dynamic light scattering, and MTT-based cell viability assays. The results suggest that all components show varied inhibitory effects on the formation of toxic hIAPP amyloids, in which CA shows the highest potency in delaying the conformational transition of the hIAPP molecule with the most prolonged lag time, whereas caffeine shows the lowest potency. At a 5-fold excess molar ratio of compound to hIAPP, all coffee-derived compounds affect the secondary structures of incubated hIAPP as suggested by the circular dichroism spectra and CDPro deconvolution analysis. Further photoinduced cross-linking based oligomerization and dynamic light scattering studies suggested CA and CGA significantly suppressed the formation of hIAPP oligomers, whereas caffeine showed no significant effect on oligomerization. Cell protection effects were also observed for all three compounds, with the protection efficiency being greatest for CA and least for CGA. These findings suggest that the beneficial effects of coffee consumption on T2DM may be partly due to the ability of the major coffee components and metabolites to inhibit the toxic aggregation of hIAPP.

Design and study of lipopeptide inhibitors on preventing aggregation of human islet amyloid polypeptide residues 11‐20

“…Fluorescence measurement was conducted to monitor the extent of fibril formation of hIAPP [11][12][13][14][15][16][17][18][19][20] by LS55 Fluorescence Spectrofluorometer system (PerkinElmer Inc, UK). Time curves of thermophoresis for binding affinity were obtained on the microscale thermophoresis (MST) setup (Monolith NT.115 system, NanoTemper Technologies GmbH, Germany).…”

“…As lipopeptides have some hydrophobic groups, which are similar to the reported aggregation inhibitors, and some lipopeptides could prevent cells from depositing of amyloid fibrils, several potential lipopeptide inhibitors have been engineered and synthesized, which have been assessed for their inhibitory effect in preventing amyloid fibrils formation of hIAPP [11][12][13][14][15][16][17][18][19][20] by using the conventional thioflavin-T fluorescence assay and new technique microscale thermophoresis (MST). The final amyloid fibrils of hIAPP [11][12][13][14][15][16][17][18][19][20] were characterized by transmission electron microscopy. Results suggested that with the increasing length of alkyl chain, the antiaggregation efficiency of lipopeptide inhibitors towards hIAPP 11-20 increased gradually.…”

“…The most common small molecular inhibitors are polyphenol compounds [20][21][22][23][24] designed by modifying the scaffold obtained from these polyphenols. [25,26] Most peptide inhibitors come from the fragment regions of the full-length hIAPP [7,27] or slight modification of these fragments.…”

“…On the basis of our previous study about different synthesized peptides modulating the self-assembly [30] of hIAPP [11][12][13][14][15][16][17][18][19][20] , most of the inhibitors that could effectively inhibit amyloid formation possess hydrophobic amino acids. Hence, in this study, several potential lipopeptide inhibitors containing hydrophobic alkyl chains and hydrophilic amino acids as head group have been engineered and synthesized, Cx-RRRR-NH 2 (x = 4, 6, 8, 10, 12, and 14; lipopeptides with x carbon atoms) and C14-Rn-NH 2 (n = 2, 3, 4, and 5; lipopeptides with n arginines) ( Figure 1).…”

“…Hence, in this study, several potential lipopeptide inhibitors containing hydrophobic alkyl chains and hydrophilic amino acids as head group have been engineered and synthesized, Cx-RRRR-NH 2 (x = 4, 6, 8, 10, 12, and 14; lipopeptides with x carbon atoms) and C14-Rn-NH 2 (n = 2, 3, 4, and 5; lipopeptides with n arginines) ( Figure 1). The extent of hIAPP [11][12][13][14][15][16][17][18][19][20] fibrilization under the influence of these inhibitors was assessed, and the binding events between amyloidogenic peptides and inhibitors were investigated. This study will help to deduce a rational template of lipopeptide inhibitor design for hIAPP.…”