Multiple low-dose and single high-dose treatments with streptozotocin do not generate nitric oxide

Streptozotocin (STZ) is a widely used diabetogenic agent that damages pancr eatic islet beta cells by activating immune mechanisms, when given in multi ple low doses, and by alkylating DNA, when given at a single high dose. Act ually, STZ contains a nitroso moiety. incubation of rat islets with this co mpound has been found to generate nitrite; moreover, photoinduced NO produc tion from STZ has been demonstrated. These reports have suggested that dire ct NO generation may be a mechanism for STZ toxicity in diabetogenesis. Sev eral other studies have denied such a mechanism of action. This study has s hown that (1) the multiple low-dose (MLDS) treatment does not stimulate NO production at the islet level; in fact, nitrite + nitrate levels and aconit ase activity (also in the presence of an NO synthase inhibitor, namely NAME ) remain unmodified: RT-PCR analysis demonstrates that this treatment does not stimulate iNOS activity; (2) the high-dose (HDS) treatment does not sti mulate NO production; in fact nitrite + nitrate levels remain unmodified an d iNOS mRNA levels are not altered, although aconitase activity is signific antly decreased. Moreover, we have confirmed that the MLDS treatment is abl e to decrease SOD activity by day 11 and that STZ, given in a single high d ose, transiently increases superoxide dismutase (SOD) values (24 h from the administration), then dramatically lowers SOD levels. On the basis of our results, we conclude that STZ, "in vivo" is unable to generate NO, both as a MLDS or HDS treatment, thus excluding that NO exerts a role in streptozot ocin-dependent diabetes mellitus. J. Cell. Biochem. 77:82-91,2000. (C) 2000 Wiley-Liss. Inc.