An insulin-degrading enzyme inhibitor decreases amylin degradation, increases amylin-induced cytotoxicity, and increases amyloid formation in insulinoma cell cultures.
Amylin (islet amyloid polypeptide) is the chief component of the islet amyloid found in type 2 diabetes, and amylin fibril precursors may be cytotoxic to pancreatic beta-cells. Little is known about the prevention of amylin aggregation. We investigated the role of insulin-degrading enzyme (IDE) in amylin degradation, amyloid deposition, and cytotoxicity in RIN-m5F insulinoma cells. Human (125)I-labeled amylin degradation was inhibited by 46 and 65% with the addition of 100 nmol/l human amylin or insulin, respectively. (125)I-labeled insulin degradation was inhibited with 100 nmol/l human amylin, rat amylin, and insulin (by 50, 50, and 73%, respectively). The IDE inhibitor bacitracin inhibited amylin degradation by 78% and insulin degradation by 100%. Amyloid staining by Congo red fluorescence was detectable at 100 nmol/l amylin and was pronounced at 1,000 nmol/l amylin treatment for 48 h. Bacitracin treatment markedly increased staining at all amylin concentrations. Bacitracin with amylin caused a dramatic decrease in cell viability compared with amylin alone (68 and 25%, respectively, at 10 nmol/l amylin). In summary, RIN-m5F cells degraded both amylin and insulin through a common proteolytic pathway. IDE inhibition by bacitracin impaired amylin degradation, increased amyloid formation, and increased amylin-induced cytotoxicity, suggesting a role for IDE in amylin clearance and the prevention of amylin aggregation.
Bennett
Robert G
RG
Department of Internal Medicine, University of Nebraska Medical Center, and Veterans Affairs Medical Center, Omaha, Nebraska 68105, USA. rgbennett@unmc.edu
Hamel
Frederick G
FG
Duckworth
William C
WC
D000682:Amyloid / Q000378:metabolism* / Q000493:pharmacokinetics* / Q000633:toxicity; D000818:Animals; D001414:Bacitracin / Q000494:pharmacology; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007004:Hypoglycemic Agents / Q000493:pharmacokinetics; D007328:Insulin / Q000493:pharmacokinetics; D007340:Insulinoma; D007339:Insulysin / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007457:Iodine Radioisotopes; D058228:Islet Amyloid Polypeptide; D010190:Pancreatic Neoplasms; D051381:Rats; D014407:Tumor Cells, Cultured
D000682:Amyloid; D004791:Enzyme Inhibitors; D007004:Hypoglycemic Agents; D007328:Insulin; D007457:Iodine Radioisotopes; D058228:Islet Amyloid Polypeptide; D001414:Bacitracin; D007339:Insulysin