Comparative toxicity of alloxan, N-alkylalloxans and ninhydrin to isolated pancreatic islets in vitro

The in vitro toxicity of the diabetogenic agent alloxan as documented by the induction of beta cell necrosis was studied in isolated ob/ob mouse pancreatic islets. The effect of alloxan has been compared with that of a number of N-alkyl alloxan derivatives and with that of the structurally related compound, ninhydrin. Alloxan and its derivatives were selectively toxic to pancreatic beta cells, with other endocrine cells and exocrine parenchymal cells being well preserved, even at high concentration. In contrast, ninhydrin was selectively toxic to pancreatic beta cells only at comparatively low concentration, destroying all islet cell types at high concentrations. The ultrastructural changes induced by all the test compounds in pancreatic beta cells in vitro were very similar to those observed during the development of alloxan diabetes in vivo. The relative toxicity of the various compounds to pancreatic beta cells in vitro was not, however, related to their ability to cause diabetes in vivo. Indeed, the non-diabetogenic substances ninhydrin, N-butylalloxan and N-isobutylalloxan were very much more toxic to isolated islets than the diabetogenic compounds alloxan and N-methylalloxan. These results suggest that the differences in diabetogenicity among alloxan derivatives are not due to intrinsic differences in the susceptibility of the pancreatic beta cells to their toxicity, but may reflect differences in distribution or metabolism. High concentrations of glucose protected islets against the harmful effects of alloxan and its derivatives, but not those of ninhydrin. Low levels of glucose, and non-carbohydrate nutrients, afforded little protection, indicating that the effect of glucose is not due to the production of reducing equivalents within the cell, 3-O-Methylglucose, which protects against alloan diabetes in vivo, did not protect against alloxan toxicity in vitro. Since 3-O-methylglucose is known to prevent uptake of alloxan by pancreatic beta cells, it appears that uptake of alloxan by the cell is not a prerequisite for the induction of beta cell necrosis.

Transgenic mice expressing IFN-gamma in pancreatic beta-cells are resistant to streptozotocin-induced diabetes

In 28 adult Ins-IFN-gamma transgenic mice, injection of high doses of streptozotocin (STZ; first injection, 300 microgram/g body weight; second injection, 200 microgram/g body weight 4 h later) failed to induce severe hyperglycemia. To the contrary, 28 BALB/c mice developed diabetes mellitus after identical injections of STZ. Because the STZ-induced islet damage was partially inhibited in Ins-IFN-gamma transgenic mice, their glycemia levels became normal 4 days after STZ administration. Both transgenic and BALB/c mice lost weight after receiving STZ, but the body weights of transgenic mice then returned to pretreatment levels in a nearly parallel manner with the glycemia. Immunolabeling with insulin identified an unusual spreading pattern of insulin immunoreactivity. Ultrastructural observations confirmed that beta-cell necrosis and degranulation were more severe in STZ-treated BALB/c than in Ins-IFN-gamma transgenic mice. Moreover, regeneration of pancreatic duct cells and islet neogenesis were observed in the transgenic mice. Therefore, after STZ treatment, the Ins-IFN-gamma transgenic mice apparently were resistant to the induction of severe diabetes, whereas their BALB/c age-matched counterparts succumbed to the disease.