We studied the impact of the reactive oxygen species hydrogen peroxide (H₂O₂) and antioxidative enzymes on the pathogenesis of diabetes induced by multiple low doses of streptozotocin (MLD-STZ).

We isolated the islets of C57BL/6 mice. For ex vivo analyses, mice had been injected with MLD-STZ. For in vitro analyses, islets were incubated with different concentrations of STZ, with either of the two moieties of STZ, methylnitrosourea and d-glucose, with H₂O₂ or with alloxan. Levels of H₂O₂ generation were measured by the scopoletin method. We assessed mRNA expression of Cu/Zn and Mn superoxide dismutase, catalase, and glutathione peroxidase (GPX) by semiquantitative polymerase chain reaction. GPX activity was measured spectrophotometrically. In vitro, beta cell function was assayed by measuring basal and d-glucose-stimulated release of immunoreactive insulin using an ELISA kit.

Ex vivo, MLD-STZ significantly increased H₂O₂ generation in male but not in female mice. It also increased GPX activity and mRNA expression of catalase, Cu/Zn and Mn superoxide dismutase, and GPX in female but not in male mice. In vitro, STZ significantly stimulated H₂O₂ generation in islets of male mice only. In male islets, alloxan increased H₂O₂ generation at a highly toxic concentration, but d-glucose and methylnitrosourea did not. Both STZ and H₂O₂ dose-dependently inhibited the release of immunoreactive insulin after a d-glucose challenge.

The results indicate that H₂O₂ participates in the pathogenesis of MLD-STZ diabetes in male C57BL/6 mice, which do not up-regulate antioxidative enzymes in islets. Conversely, female mice are protected, probably due to an increment of several enzymes with the potential to detoxify H₂O₂.