Immunotoxicological effects of streptozotocin and alloxan: In vitro and in vivo studies

• Streptozotocin induces higher immunosuppression compared to alloxan in mice.
• Islet xenografts survived longer in mice treated with streptozotocin compared to that seen in mice treated with alloxan.
• Streptozotocin showed higher cytotoxic effect on HL60 cells compared to alloxan.

Streptozotocin (STZ) and alloxan (ALX), widely used to induce diabetes in experimental animals, have different structures and mechanisms of action. We investigated those effects of these drugs on the immune system that might influence engraftment efficiency and graft survival in transplantation models, and their cytotoxicity on hematopoietic cell lines.We used the minimum dose to induce diabetes in a mouse, i.e. 180 mg/kg i.v. STZ and 75 mg/kg i.v. ALX. Both groups exhibited significant decrease in body weight during 4 days post-treatment as compared to controls. We found that blood glucose in ALX-injected mice increased faster than in STZ-injected mice. The total number of recovered splenocytes was lower in STZ-injected animals than in ALX-injected animals. The survival periods of rat islet grafts in recipient mice were longer and more diverse in STZ-injected recipients (7–24 days) compared to ALX-injected recipients (6–7 days). The in vitro study showed that ALX was less cytotoxic in cell lines with IC50 values of 2809, 3679 and >4000 μg/ml for HL60, K562 and C1498 cells respectively. STZ was more toxic, especially in HL60 cells, with IC50 values of 11.7, 904 and 1024 μg/ml for HL60, K562 and C1498 cells respectively. Furthermore, in response to concanavalin A (Con-A), splenocytes from STZ-injected mice produced higher amounts of interferon-gamma (IFN-γ) than those from ALX-injected mice. In conclusion, STZ was more cytotoxic than ALX in vitro and in vivo. STZ caused lymphocytopenia, which may result in longer graft survival in STZ-treated animals than in ALX-treated animals.