[Insulin-like effect of vanadium compounds].
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In this study oral treatment with bis(kojato)oxovanadium(IV) solution was administered twice. The first, short vanadium treatment (so called pretreatment) was used to accustom animals to the flavour of this liquid. After 2-2.5 weeks the second treatment, in high concentration and for a longer time served as a "drug". The physiological parameters such as weights of animals and their livers, reduction of liquid and food intake were lower than in control. Activity of Golgi marker enzyme GalT was significantly lower in both vanadium treated groups (p < 0.01), but in diabetic vanadium treated group it was higher, albeit not significantly, than in control vanadium treated rats. The morphology of Golgi complexes in diabetic rats on prolonged vanadium treatment was similar to that in the one week treated rats (see Part I). Rounded stacks of cisternae characteristic of untreated streptozotocin (STZ)-diabetes were also seen in vanadium treated diabetic rats, but in comparison with untreated diabetic livers, the secretory activities of Golgi complexes were preserved or even stimulated.
The present study was performed to determine the phosphotyrosine-protein levels induced by insulin and by four vanadium derivatives in MC3T3E1 osteoblast-like cells. We have also attempted to associate these patterns with the vanadium-induced growth and morphological changes of such cells. Vanadate (Vi), vanadyl (VO), bis(maltolato)oxovanadium (IV) (BMOV) and bis(maltolato)dioxovanadium (V) (BMV) stimulate cell growth in a narrow range of concentration, but are also inhibitors for the cells at high concentrations. Vanadium-treated cells displayed clear changes in their morphology after overnight incubation. However, BMV was the least cytotoxic and the weakest inducer of morphological changes. All the compounds promote the phosphorylation of tyrosine residues in several proteins. This effect was more pronounced at low than at high doses. At low doses (10 microM), BMV showed a phosphorylation pattern similar to that of insulin, while Vi, VO and BMOV induced strong phosphorylation of cell proteins. The present findings suggest that the vanadium-induced growth regulation and morphological changes in MC3T3E1 osteoblast-like cells are associated with the ability of these agents to increase the phosphotyrosine protein levels and to inhibit phosphotyrosine phosphatases. These properties are dependent on the oxidation state as well as on the organic ligand which coordinates the vanadium atom.
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Vanadate and vanadyl have been reported to have insulin-like properties and have recently been demonstrated to be beneficial in the treatment of diabetic animals. In this study, we determined whether vanadium ions mimic the effect of insulin on calmodulin activity of liver and adipose tissues in streptozotocin-induced diabetic rats and examined their effect with respect to concentration and time. Calmodulin activities in the hormone-sensitive tissues decreased in diabetes and returned to normal after sodium metavanadate or vanadyl sulfate treatment for 3 weeks (0.2, 0.4, and 0.8 mg/mL in drinking water). These results demonstrate that V5+ and V4+ forms of vanadium can restore the activity of calmodulin in experimental diabetes induced by streptozotocin.
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In comparison with untreated control, reduced body and liver weights were found in two groups of rats (such as control and STZ-diabetic) treated orally with bis(kojato)oxovanadium(IV) solution. Free blood sugar in STZ-diabetic rats was lower by about 38%, but did not achieve euglycemic values. Yields of Golgi-rich fraction were lower than those in untreated controls, similar to the activity of galactosyl transferase (GalT) in both vanadium treated groups (control and diabetic). Under electron microscope in the control kojate-treated group, subcellular changes were observed. The morphology of Golgi apparatus was typical, resembled that in untreated animals. In diabetic animals treated with kojate subcellular changes were less severe. Golgi apparatus was usually semicircular or arched in shape similar to that observed previously in diabetic untreated rats.
Bis(kojato)oxovanadium(IV) [abbreviated VO(ka)2], a close chemical analog of the insulin-mimetic lead compound bis(maltolato)oxovanadium(IV)--abbreviated BMOV or VO(ma)2--is reported and its reaction chemistry and insulin-mimetic properties are presented. VO(ka)2 [log K1 = 7.61(10), log K2 = 6.89(6), log beta 2 = 14.50(16)] has a reaction chemistry which directly parallels that of VO(ma)2. In aqueous solution it is more slowly oxidized by molecular oxygen to [VO2(ka)2]- than is VO(ma)2 to [VO2(ma)2]-. Variable pH electrochemistry and variable pH 51V NMR of solutions of VO(ka)2 are presented and contrasted with the corresponding results for VO(ma)2. Time course studies (24 hr) in STZ-diabetic rats following the oral or i.p. administration of VO(ka)2, VO(ma)2, VO2+ (vanadyl) as vanadyl sulfate (VOSO4), and [VO2(ma)2]- as its [NH4]+ salt have been performed, as have chronic oral studies comparing VO(ka)2 and VO(ma)2 over a six week period. In all studies, the most potent form of vanadium was the neutrally charged, water soluble, complex VO(ma)2.
Intratracheally instilled 48V2O5 was rapidly cleared from the lung into blood, liver and bone. Approx. 40% of the recovered 48V was excreted, primarily in urine by day 3, while the skeleton accounted for 30% by day 7. The behavior of instilled 48VO2Cl was similar to that of 48V2O5. Uptake of gavaged 48V2O5 was 2.6% of administered dose. Skeleton, lung, kidney and liver are primary targets for intratracheally instilled 48V with uptake being much greater via the intratracheal route than by the oral route.
Sodium metavanadate (10(-4)-10(-6) M) stimulates the activity of adenylate cyclase and decreases the activity of Na+, K+-ATRase and 5'-nucleotidase in the sarcolemma fraction of chicken skeletal muscles at the embryonal and postembryonal developmental stages. Under conditions of a combined action of vanadate and guanylic nucleotides on the adenylate cyclase activity their effects are found to be potentiated. Epinephrine in vitro removes an inhibitory influence of vanadate on Na+, K+-ATPase from the third week of twe embryonal period. The restoring effect of epinephrine is blocked by propranol--a beta-adrenoblocker.
In rat adrenal membrane, vanadyl sulfate, but not vanadate, inhibits the nonhydrolyzable GTP analogs-, forskolin- and NaF-stimulated activation process of adenylate cyclase. In these reactions, the half-maximum concentration of vanadyl for inhibition was approx. 0.3 mM. The binding of [3H]guanyl-5'-yl imidodiphosphate to the membrane (Kd = 2 microM) was not affected by vanadyl sulfate under the conditions in which the vanadyl sulfate inhibits the activation process. Also, the binding of ACTH to its receptor was inhibited by neither vanadyl sulfate nor vanadate, and the catalytic unit of adenylate cyclase appears to be unaffected by vanadyl sulfate. When the activation by nonhydrolyzable GTP analog was enhanced by Ca2+, vanadyl sulfate strongly inhibited the activation of adenylate cyclase.