Quantitative Determination of Apoptosis of Pancreatic β-Cells in a Murine Model of Type 1 Diabetes Mellitus

Type 1 diabetes mellitus is characterized by a significant deficit in pancreatic b-cell mass, presumably caused by b-cell apoptosis. We investigated the incidence of b-cell apoptosis in streptozotocin-treated mice and nonobese diabetic (NOD) mice with 99m Tc-annexin A5. Methods: Vehicle-treated mice, streptozotocin-treated mice, and NOD mice at the ages of 5, 9, 16, and 20 wk (5–8 mice per group) were injected with 99m Tcannexin A5 and sacrificed 6 h later for autoradiography, and the regional 99m Tc-annexin A5 level in the pancreas was evaluated. Pancreatic islets were identified by insulin immunohistochemical staining, and apoptotic cells were determined by terminal deoxynucleotidyl transferase–mediated dUTP nickend labeling (TUNEL) staining. The 99mTc-annexin A5 level in pancreatic islets was expressed as the percentage injected dose per area of pancreatic islets and normalized by animal body weight (%ID · 10 6 /mm 2 /kg). The level of apoptotic cells in pancreatic islets was expressed as the number of TUNELpositive cells per area of pancreatic islets (cells/mm 2 ). Results: The 99m Tc-annexin A5 accumulation level was significantly higher (2.5 6 0.7 vs. 0.7 6 0.1 %ID · 10 6 /mm 2 /kg, P , 0.05) and the number of TUNEL-positive cells was significantly higher (1,170 6 535 vs. 5 6 6 cells/mm2, P , 0.05) in the pancreatic islets of the streptozotocin-treated mice than in those of the vehicle-treated mice. The 99mTc-annexin A5 accumulation level was significantly higher (1.1 6 0.4 vs. 0.5 6 0.1 %ID · 10 6 /mm 2 / kg, P , 0.05) and the number of TUNEL-positive cells was significantly higher (152 6 82 vs. 4 6 9 cells/mm 2 , P , 0.05) in the pancreatic islets of 16-wk-old NOD mice than in those of 5-wk-old NOD mice. In addition, the level of 99m Tc-annexin A5 correlated with the number of TUNEL-positive cells in the pancreatic islets of the streptozotocin-treated mice (r 5 0.821, P , 0.001) and NOD mice (r 5 0.721, P , 0.001). Conclusion: There is significant islet cell apoptosis with 99m Tc-annexin A5 accumulation in the pancreas of both streptozotocin and NOD mice.