Human
islet amyloid polypeptide (hIAPP), the major component of the
amyloid deposits found in the pancreatic islets of patients with
type 2 diabetes mellitus (T2DM), plays a central role in the loss of
insulin-secreting pancreatic beta cells. Misfolded hIAPP fibrillating in islet beta cells may be one of the causations for T2DM. Studies have showed that
fibrosis of hIAPP was inhibited by
copper compounds while hIAPP-induced cytotoxicity was greatly stimulated. In this study, the suppression effects of three different forms of
copper compounds
CuCl2, CuSO4 and Cu(Gly)2 on
amyloid fibril formation were examined in vitro. The results demonstrated that Cu(II) could interact with hIAPP to suppress the
fibrosis without involvement of the
anions. The
fibrosis of hIAPP was inhibited by
CuCl2, CuSO4 and Cu(Gly)2 with a similar degree. The particle size of hIAPP aggregates was decreased, which was further confirmed in atomic force microscopy (AFM) and transmission electron microscopy (TEM) images. Moreover, approximative cytotoxicity-enhancing levels between
CuCl2, CuSO4 and Cu(Gly)2 on hIAPP were also observed in INS-1 cells. Studies on the action mechanisms displayed that
copper compounds increased hIAPP-induced cytotoxicity by facilitating apoptosis-promoting effect of hIAPP, which was dominated mainly by
cation. Furthermore, Cu(II)-promoted ROS overproduction and mitochondrial disruption might be the main reason for the enhanced apoptosis. Taken together, our studies demonstrate clear interaction mechanisms of Cu(II) and hIAPP in pancreatic beta cells, and provide useful information for our understanding and treatment of T2DM.