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 β-cell mass, presumably caused by β-cell apoptosis. We investigated the incidence of β-cell apoptosis in streptozotocin-treated mice and nonobese diabetic (NOD) mice with ^99mTc-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 ^99mTc- annexin A5 and sacrificed 6 h later for autoradiography, and the regional ^99mTc-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/mm²/kg). The level of apoptotic cells in pancreatic islets was expressed as the number of TUNEL-positive cells per area of pancreatic islets (cells/mm²). Results: The ^99mTc-annexin A5 accumulation level was significantly higher (2.5 ± 0.7 vs. 0.7 ± 0.1%ID × 10⁶/mm²/kg, P < 0.05) and the number of TUNEL-positive cells was significantly higher (1,170 ± 535 vs. 5 ± 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 ± 0.4 vs. 0.5 ± 0.1%ID × 10⁶/mm²/kg, P < 0.05) and the number of TUNEL-positive cells was significantly higher (152 ± 82 vs. 4 ± 9 cells/mm², 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 ^99mTc-annexin A5 correlated with the number of TUNEL-positive cells in the pancreatic islets of the streptozotocin-treated mice (r = 0.821, P < 0.001) and NOD mice (r = 0.721, P < 0.001). Conclusion: There is significant islet cell apoptosis with ^99mTc- annexin A5 accumulation in the pancreas of both streptozotocin and NOD mice.