The amylin peptide implicated in type 2 diabetes stimulates copper-mediated carbonyl group and ascorbate radical formation

Abstract

Human amylin (hA), which is toxic to islet β-cells, can self-generate H2O2, and this process is greatly enhanced in the presence of Cu(II) ions. Here we show that carbonyl groups, a marker of oxidative modification, were formed in hA incubated in the presence of Cu(II) ions or Cu(II) ions plus H2O2, but not in the presence of H2O2 alone. Furthermore, under similar conditions (i.e., in the presence of both Cu(II) ions and H2O2), hA also stimulated ascorbate radical formation. The same observations concerning carbonyl group formation were made when the histidine residue (at position 18) in hA was replaced by alanine, indicating that this residue does not play a key role. In complete contrast to hA, rodent amylin, which is nontoxic, does not generate H2O2, and binds Cu(II) ions only weakly, showed none of these properties. We conclude that the hA–Cu(II)/Cu(I) complex is redox active, with electron donation from the peptide reducing the oxidation state of the copper ions. The complex is capable of forming H2O2 from O2 and can also generate •OH via Fenton chemistry. These redox properties of hA can explain its ability to stimulate copper-mediated carbonyl group and ascorbate radical formation. The formation of reactive oxygen species from hA in this way could hold the key to a better understanding of the damaging consequences of amyloid formation within the pancreatic islets of patients with type 2 diabetes mellitus.