Use of Small Organic Molecules to Improve Pancreatic Beta Cell Resilience to IAPP-Induced Proteotoxic Stress

The cytotoxic effect of islet amyloid polypeptide (IAPP) misfolding and aggregation has a well-recognized role in the pathogenesis of type 2 diabetes mellitus, mediated by failure of the beta cell's protein quality control system to rescue the cell from overwhelming proteotoxic stress induced by IAPP aggregates, ultimately leading to apoptosis. A small but growing body of research also links IAPP-mediated proteotoxic stress to the pathogenesis of type 1 diabetes and to the functional decline of transplanted islets. Among the most promising therapeutic approaches under investigation are small organic molecules that may act as direct chemical chaperones to prevent IAPP aggregation, promote the activity of endogenous chaperones, or alter gene networks of the unfolded protein response (UPR) to promote pro-survival rather than pro-apoptotic pathways in response to IAPP-mediated proteotoxic stress. Compounds warranting special attention include 4-phenylbutyrate (PBA), tauroursodeoxycholic acid (TUDCA), and epigallocatechin gallate (EGCG), as each has a growing body of evidence supporting their ability to ameliorate this process, and given that each of these are already known to have good safety profiles in humans, potentially accelerating the timeline to interventional studies. This review explores the evidence for IAPP-mediated proteotoxicity in multiple forms of diabetes, the mechanisms of cytotoxicity at different levels of the cell's protein quality control systems, how these small organic compounds may act on these processes including new insights on the role of thioredoxin-interacting protein (TXNIP), and the current evidence supporting each of these compounds in mitigating diabetogenesis.