Copper(II)-human amylin complex protects pancreatic cells from amylin toxicity

Human amylin-derived oligomers and aggregates are believed to play an important role in the pathogenesis of type II diabetes mellitus (T2DM). In addition to amylin-evoked cell attrition, T2DM is often accompanied by elevated serum copper levels. Although previous studies have shown that human amylin, in the course of its aggregation, produces hydrogen peroxide (H2O2) in solution, and that this process is exacerbated in the presence of copper(II) ions (Cu2+), very little is known about the mechanism of interaction between Cu2+ and amylin in pancreatic beta-cells, including its pathological significance. Hence, in this study we investigated the mechanism by which Cu2+ and human amylin catalyze formation of reactive oxygen species (ROS) in cells and in vitro, and examined the modulatory effect of Cu2+ on amylin aggregation and toxicity in pancreatic rat insulinoma (RIN-m5F) beta-cells. Our results indicate that Cu2+ interacts with human and rat amylin to form metalo-peptide complexes with low aggregative and oxidative properties. Human and non-amyloidogenic rat amylin produced minute (nM) amounts of H2O2, the accumulation of which was slightly enhanced in the presence of Cu2+. In a marked contrast to human and rat amylin, and in the presence of the reducing agents glutathione and ascorbate, Cu2+ produced mu M concentrations of H2O2 surpassing the amylin effect by several fold. The current study shows that human and rat amylin not only produce but also quench H2O2, and that human but not rat amylin significantly decreases the amount of H2O2 in solution produced by Cu2+ and glutathione. Similarly, human amylin was found to also decrease hydroxyl radical formation elicited by Cu2+ and glutathione. Furthermore, Cu2+ mitigated the toxic effect of human amylin by inhibiting activation of pro-apoptotic caspase-3 and stress-kinase signaling pathways in rat pancreatic insulinoma cells in part by stabilizing human amylin in its native conformational state. This sacrificial quenching of metal-catalyzed ROS by human amylin and copper's anti-aggregative and anti-apoptotic properties suggest a novel and protective role for the copper-amylin complex.