IAPP - oligomerisation levels in plasma of people with type 2 diabetes

Abstract

Islet amyloid polypeptide (IAPP) is co-secreted with insulin from pancreatic ß-cells. Its oligomerisation is regarded as disease driving force in type 2 diabetes (T2D) pathology. Up to now, IAPP oligomers have been detected in affected tissues. IAPP oligomer concentrations in blood have not been analysed so far. Using the IAPP single-oligomer-sensitive and monomer-insensitive surface-based fluorescence intensity distribution analysis (sFIDA) technology, levels of IAPP oligomers in blood plasma from healthy controls and people with T2D in different disease stages where determined. Subsequently, the level of IAPP oligomerisation was introduced as the ratio between the IAPP oligomers determined with sFIDA and the total IAPP concentration determined with ELISA. Highest oligomerisation levels were detected in plasma of people with T2D without late complication and without insulin therapy. Their levels stand out significantly from the control group. Healthy controls presented with the lowest oligomerisation levels in plasma. In people with T2D without complications, IAPP oligomerisation levels correlated with disease duration. The results clearly demonstrate that IAPP oligomerisation in insulin-naïve patients correlates with duration of T2D. Although a correlation per se does not identify, which is cause and what is consequence, this result supports the hypothesis that IAPP aggregation is the driving factor of T2D development and progression. The alternative and conventional hypothesis explains development of T2D with increasing insulin resistance causing exhaustion of pancreatic ß-cells due to over-secretion of insulin, and thus IAPP, too, resulting in subsequent IAPP aggregation and fibril deposition in the pancreas. Further experiments and comparative analyses with primary tissues are warranted.

Keywords: Diabetes; Disease driven protein expression; IAPP; Oligomers; sFIDA.

Figure 1

Scheme of surface-based fluorescence intensity distribution analysis. The capture antibody against IAPP (EPR-22556-138) is immobilised on the glass surface of a 384-well plate. IAPP oligomers and monomers can bind the capture antibodies, but only IAPP oligomers can be detected by the fluorescence labelled detection antibody EPR-22556-138 CF633, as the epitope of the monomers is already masked by the capture antibody. Created with BioRender.com.

Figure 2

Oligomerisation levels based on diabetes subgroups. Oligomerisation levels of T2D group without complications are significantly elevated compared to the controls (P value: 0.037). ● indicates single individuals. – indicates the median. A two-sided Mann–Whitney U Test (confidence interval: 0.05) was carried out to investigate differences between the groups. Significant differences were labelled with *. Please, note the two-part y-axis, which removes free space.

Figure 3

Relationship between oligomerisation level and disease duration in people with T2D without complications. In the first 10 years the oligomerisation level of T2D group without complications correlates strongly positive with the duration of the disease (Spearman r value: 0.617, P value: 0.033). The line represents a fitted Huber regression. The surrounding marked area represents the confidence interval. Data for the entirety of the T2D subgroups are shown in Supplementary Fig. 4.