Age-dependent sensitivity to streptozotocin of pancreatic islets isolated from female NOD mice

Newly weaned nonobese diabetic mice show heightened early diabetes sensitivity to multiple low doses of streptozotocin than nondiabetes-prone CD-1 mice: initial beta-cell damage a key trigger for type 1 diabetes?

OBJECTIVES

We determined if newly weaned female nonobese diabetic (NOD) mice show greater diabetes sensitivity to dose-adjusted regimens of multiple low doses of streptozotocin (Stz) than nondiabetes-prone CD-1 mice.

METHODS

Female NOD mice received 5 daily doses of Stz from day 21 (0, 5, 10, 15, 20, 30, and 40 mg/kg body weight) and CD-1 mice 20, 30, and 40 mg.

RESULTS

: Streptozotocin, at the 15-, 20-, 30-, and 40-mg dose, induced rapid diabetes in NOD mice. By day 100, 90% to 95% of NOD mice became diabetic after the 40- and 30-mg dose and 33% to 40% with the 15- and 20-mg dose. In comparison, only about 50% and 33% of CD-1 mice developed diabetes with the 40- and 30-mg dose, respectively, and 5.5% with the 20-mg dose. In NOD mice, the 20-mg dose also partially suppressed spontaneous diabetes. All diabetic mice displayed insulitis, variable immunostaining for insulin, and redistribution of glucagon and somatostatin cells. Glucose transporter-2 was markedly attenuated in selective beta cells.

CONCLUSIONS

Newly weaned female NOD mice show heightened early sensitivity to low doses of Stz than CD-1 mice. At diabetes, several beta cells remain and show variable immunostaining for insulin and an attenuated expression for glucose transporter-2. Specific low doses of Stz may also suppress spontaneous diabetes.

Young NOD mice show increased diabetes sensitivity to low doses of streptozotocin

In type 1 diabetes, environmentally induced early-limited beta cell damage may pre-empt the subsequent immune-mediated beta cell destruction. Low doses of streptozotocin (Stz), given early to diabetes-prone mice, may cause limited beta cell destruction during the early phase and precipitate diabetes. Here, we aimed to see if young NOD mice are more diabetes-sensitive to various multiple low doses of Stz than non-diabetes-prone mice. We also determined the molecular pathology of islets following administration of the diabetogen. Female NOD and CD-1 mice received 5 daily doses of Stz at day 21 (20, 30, and 40 mg/kg body weight; 18 mice per group) or diluent, and diabetes was monitored. Pancreas were studied histochemically and immunohistochemically at various time points after Stz administration. Following administration of Stz, NOD mice showed a much earlier onset and increased diabetes rate, at all three doses, than CD-1 mice. By day 80, the final diabetes rates following the 40, 30, and 20 mg dose in NOD mice were 95%, 85%, and 33%, respectively, compared with 33%, 28%, and 5.5%, respectively, in CD-1 mice. However, following the 20 mg dose, only 2 of the 12 remaining NOD mice developed the disease between 90 and 250 days compared with 19 of 24 NOD mice that did not receive Stz at day 21. Stz-administered NOD and CD-1 mice showed an initial loss of beta cells, with redistribution of islet endocrine cells, early macrophage infiltration, and increasing insulitis.

Immunohistochemical Demonstration of Nitrotyrosine, a Biomarker of Oxidative Stress, in Islet Cells of the NOD Mouse

Reactive oxygen species and nitric oxide generated within the beta cell or by intraislet immune cells may be major mediators of beta cell death during insulin-dependent diabetes mellitus. Here, the intraislet expression of nitrotyrosine, a biomarker of oxidative damage, and its cellular sources were examined in the islets of NOD mice at various stages of spontaneous and cyclophosphamide-accelerated diabetes. At day 30, nitrotyrosine-positive cells were undetectable; they were rare at day 40, being expressed in only a few beta cells and in macrophages located in the periphery of some islets. At day 90 and at onset of diabetes, an increasing number of macrophages and beta cells were nitrotyrosine positive. In the cyclophosphamide group at day 4, the number of beta cells and macrophages with positive immunolabeling declined slightly from day 0 (day of cyclophosphamide injection = day 90). This pattern of immunolabeling increased gradually by day 7 but increased markedly by days 11 and 14 after cyclophosphamide administration. In the spontaneous and cyclophosphamide groups, macrophages were the predominant source of nitrotyrosine and were present within the intraislet and periislet regions. Nitrotyrosine labeling was observed in a significant number of beta cells but less than in immunolabeled macrophages. We conclude that protein nitration in beta cells and macrophages is an important feature of the diabetogenic process in the NOD mouse. Whether this deleterious process also occurs during the very early stages of the disease and preceding insulitis is unclear.

Expression of Activated Notch3 in Transgenic Mice Enhances Generation of T Regulatory Cells and Protects against Experimental Autoimmune Diabetes

Thymic-derived dysregulated tolerance has been suggested to occur in type 1 diabetes via impaired generation of CD4(+)CD25(+) T regulatory cells, leading to autoimmune beta cell destruction. In this study, we demonstrate that Notch3 expression is a characteristic feature of CD4(+)CD25(+) cells. Furthermore, streptozotocin-induced autoimmune diabetes fails to develop in transgenic mice carrying the constitutively active intracellular domain of Notch3 in thymocytes and T cells. The failure to develop the disease is associated with an increase of CD4(+)CD25(+) T regulatory cells, accumulating in lymphoid organs, in pancreas infiltrates and paralleled by increased expression of IL-4 and IL-10. Accordingly, CD4(+) T cells from Notch3-transgenic mice inhibit the development of hyperglycemia and insulitis when injected into streptozotocin-treated wild-type mice and display in vitro suppressive activity. These observations, therefore, suggest that Notch3-mediated events regulate the expansion and function of T regulatory cells, leading to protection from experimental autoimmune diabetes and identify the Notch pathway as a potential target for therapeutic intervention in type 1 diabetes.