Inhibitory effects of decavanadate on several enzymes and Leishmania tarentolae in vitro.

Multiple studies report apparent effects of vanadium on various systems in vivo and in vitro. Vanadium species may be possible deterrents for the growth of the Leishmania parasite, which causes the sometimes deadly diseases known as leishmaniasis. The current studies focus specifically on decavanadate V(10)O(28)(6-) (V10), which has a potential to be a potent effector for disease treatment. The X-ray structure of a new solvate salt of V10, namely (NH(4))(6)V(10)O(28)·5H(2)O, is also reported. Other vanadium complexes with imidazole carboxylate, anthranilate, or picolinate were also evaluated. The yellow-orange oxoanion, used as the (NH(4))(6)V(10)O(28)·6H(2)O salt, was tested (at 1-100 μM) directly with two strains of Leishmania tarentolae promastigotes in culture to evaluate the effect on cell viability. Vanadium coordination complexes are known effective inhibitors of phosphatases. Using the artificial phosphatase substrate para-nitrophenylphosphate in the presence of a bovine calf intestine alkaline phosphatase enzyme, V10 (from 5 to 100 μM) was shown to be a mixed inhibitor for this enzyme and decreased the activity of the other two phosphatases tested. The effect of V10 and the other vanadium complexes on the activity of phosphoglycerate mutase B (PGAM), an important enzyme in glycolysis and gluconeogenesis, was also evaluated. At 10 μM, V10 was the most potent inhibitor of PGAM, with an apparent reduction of about 50%. Taken together, we speculate that V10 could have a role in treating Leishmania diseases.