Oral vanadate and Tiron in treatment of diabetes mellitus in rats: improvement of glucose homeostasis and negative side-effects.

It has been shown that improvement of glucose homeostasis by oral vanadate or vanadyl treatment in streptozotocin-induced diabetic rats is accompanied by severe negative side effects (some deaths, decreased weight gain, alteration in renal function as well as tissue vanadium accumulation) which argue against the use of vanadium compounds in diabetes treatment. The present study was undertaken to assess the effectiveness in alleviating some signs of diabetes in streptozotocin-treated rats with oral therapy with sodium metavanadate (NaVO3) and sodium 4,5 dihydroxybenzene-1,3-disulfonate (Tiron), a chelating agent effective in mobilizing vanadium. In a preliminary experiment, diabetic rats were given aqueous solutions of 0.20 mg NaVO3/ml for 4 days. Vanadium-treated rats which showed blood glucose levels significantly lower (p < 0.001) than vanadate-untreated diabetic rats were selected for subsequent experiments. These animals were given 0.20 mg NaVO3/ml in drinking water and 0, 125.6, 314 or 628 mg Tiron/kg/d by gavage for 2 w. Although most of the animals did not become normoglycemic, several characteristic signs of diabetes (hyperglycemia, hyperphagia and polydipsia) were alleviated by the NaVO3 treatment. The administration of 314 mg Tiron/kg/d (approximately 1 NaVO3: 5 Tiron, mole ratio) did not diminish the ameliorative effects of NaVO3 with respect to diabetes, but significantly decreased the level of vanadium accumulation in target organs. These results show that some of the beneficial effects of NaVO3 are maintained in diabetic animals given Tiron, while the administration of the chelator results in a significant decrease in tissue vanadium accumulation. Accordingly, this would diminish the possibility of toxic side effects derived from prolonged oral vanadium administration.