Overexpression of Metallothionein in Pancreatic β-Cells Reduces Streptozotocin-Induced DNA Damage and Diabetes

Overexpression of Metallothionein in Pancreatic β-Cells Reduces Streptozotocin-Induced DNA Damage and Diabetes Hainan Chen 1 , Edward C. Carlson 2 , Lori Pellet 3 , Jon T. Moritz 3 and Paul N. Epstein 1 1 Department of Pediatrics, University of Louisville, Louisville, Kentucky 2 Department of Anatomy and Cell Biology, University of North Dakota, Grand Forks, North Dakota 3 Department of Pharmacology, Physiology and Therapeutics, University of North Dakota, Grand Forks, North Dakota Abstract The release of reactive oxygen species (ROS) has been proposed as a cause of streptozotocin (STZ)-induced β-cell damage. This initiates a destructive cascade, consisting of DNA damage, excess activation of the DNA repair enzyme poly(ADP-ribose) polymerase, and depletion of cellular NAD + . Metallothionein (MT) is an inducible antioxidant protein that has been shown to protect DNA from chemical damage in several cell types. Therefore, we examined whether overexpression of MT could protect β-cell DNA and thereby prevent STZ-induced diabetes. Two lines of transgenic mice were produced with up to a 30-fold elevation in β-cell MT. Cultured islets from control mice and MT transgenic mice were exposed to STZ. MT was found to decrease STZ-induced islet disruption, DNA breakage, and depletion of NAD + . To assess in vivo protection, transgenic and control mice were injected with STZ. Transgenic mice had significantly reduced hyperglycemia. Ultrastructural examination of islets from STZ-treated mice showed that MT prevented degranulation and cell death. These results demonstrate that MT can reduce diabetes and confirm the DNA damage mechanism of STZ-induced β-cell death. Footnotes Address correspondence and reprint requests to Paul N. Epstein, Department of Pediatrics, University of Louisville, Louisville, KY 40202. E-mail: paul.epstein{at}louisville.edu . Received for publication 26 September 2000 and accepted in revised form 15 June 2001. BSA, bovine serum albumin; FBS, fetal bovine serum; HBSS, Hanks’ balanced salt solution; KRBB, Krebs-Ringer bicarbonate buffer; MT, metallothionein; ROS, reactive oxygen species; STZ, streptozotocin.