Prevention by sodium 4,5-dihydroxybenzene-1,3-disulfonate (Tiron) of vanadium-induced behavioral toxicity in rats.

Recent studies have shown that oral vanadate (V5+) administration results in behavioral toxicity in rats. The chelating agent Tiron (sodium 4,5-dihydroxybenzene-1,3-disulfonate) is an effective antidote in the removal of vanadium from vanadium-loaded rats. In this study, the protective activity of Tiron on vanadate-induced behavioral toxicity was evaluated in adult rats. Intraperitoneal treatment with Tiron at 235 or 470 mg/kg was initiated after 6 wk of oral sodium metavanadate administration (16 mg/kg/d) and continued for 2 wk. Although vanadate exposure did not result in a significant reduction in the general activity of the animals in an open field, a lower active avoidance acquisition could be observed. However, the vanadate-induced behavioral deficit was reverted by Tiron administration at 470 mg/kg. The present results suggest that Tiron may protect, at least in part, against metavanadate-induced behavioral toxicity.

Influence of chelating agents on the toxicity, distribution and excretion of vanadium in mice.

The effects of the chelating agents Na2Ca-ethylendiaminetetraacetate (EDTA), Na3Ca-diethylentriaminepentaacetate (DTPA), L-cysteine, 4,5-dihydroxy-1,3-benzene-disulfonic acid (Tiron) and deferoxamine mesylate and the reducing agent ascorbic acid on the toxicity, excretion and distribution of i.p. injected vanadium were studied in male Swiss mice. Chelating and reducing agents were administered intraperitoneally at doses equal to one-fourth of their respective LD50. To determine the effects of the various chelators on the mortality of vanadium, various doses of NaVO3 (0.30-1.20 mmol kg-1 i.p.) were given, followed immediately by one of the chelating or reducing agents. Survival was recorded at the end of 14 days. Significant increases in survival were noted with ascorbic acid, Tiron and deferoxamine, with ascorbic acid being the most effective. Deferoxamine and Tiron were the most effective in increasing the excretion of vanadium and reducing the concentration of vanadium found in various tissues. However, ascorbic acid appears to be the most effective agent in the prevention of vanadium intoxication.

Centrally mediated effect of vanadate on diuresis and natriuresis in normal rats. Interaction with ouabain.

Prolonged infusion of vanadate (VO-3) (51 ng/microliter/hr during 15 hr), an in vitro inhibitor of Na,K-ATPase activity, into the 3rd brain ventricle (3BV) increased diuresis, sodium and potassium excretion in normal rats (p less than 0.001). Since the animals did not receive food or water during the infusion period, the effect of VO-3 was not related to hydration or volume expansion. A single injection of ouabain (a specific inhibitor of the sodium pump) 1 microliter, 50 pg/microliter, followed by a single injection of vanadate (1 microliter/51 ng/microliter) 1, 5 or 10 minutes after ouabain, prevented the diuretic and natriuretic effect of VO-3. When vanadate injections were delayed 20 or 30 minutes, diuresis reappeared. Ouabain (50 pg) decreased sodium intake induced by sodium depletion, an effect that lasted for 10 to 15 minutes after injection, a time coincident with the inhibition of the natriuretic effect of VO-3 by OUA. Then the life-span of ouabain effect on prevention of VO-3-induced diuresis as well as on inhibition of sodium intake, lasted between 10 to 15 minutes. These results provide further evidence for the powerful diuretic, natriuretic and kaliuretic effect of centrally injected vanadate. However, the finding that ouabain suppresses this effect, does not support the suggestion that the active transport system might be involved.

Effects of sodium vanadate on various types of vascular smooth muscles.

Effects of sodium vanadate on various vascular smooth muscles of guinea pigs, rabbits, and Wistar Kyoto rats (WKY) were studied. Sodium vanadate of concentrations higher than 10(-5) M induced contractions in the aortae of all animals. The contractile effects varied among vascular smooth muscles, and mesenteric arteries showed no or only weak contractile response to the drug, while aortae showed higher contractile responses. In the portal veins, potentiation of spontaneous contractions was observed by the application of sodium vanadate. These responses were not blocked by treatments with adrenergic blocking agents or indomethacin, indicating the direct action of the drug on vascular smooth muscles. Treatment with 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) blocked completely the contractile effects of sodium vanadate, whereas it showed no effect on K-contractures. Partial depolarization of the membrane by elevations of K concentration potentiated sodium vanadate-induced contractions and minimized the variations of responses among preparations. In K-depolarized preparations, sodium vanadate often induced relaxation of preparations. The contractile effects of sodium vanadate were not blocked by treatment with ouabain, though ouabain also showed contractile actions in a number of preparations. It was suggested that vanadate acts directly on vascular smooth muscles and causes contractions without relation to the inhibition of Na,K-ATPase. It may cause contractions inhibiting Ca-ATPase of sarcoplasmic reticulum and/or of cell membrane, and cause relaxation by inhibiting ATPase of contractile proteins. The variations of the responses may be explained by differences of membrane permeability to vanadate.

Protection of mice against the lethal effects of sodium metavanadate: a quantitative comparison of a number of chelating agents.

10 Chelating agents were administered to mice by intraperitoneal (i.p.) injection in order to compare their relative effectiveness in preventing death after a single i.p. injection of NaVO3. Ascorbic acid, Tiron (4,5-dihydroxy-1,3-benzene-disulfonic acid) and deferoxamine were the most effective antidotes for acute NaVO3-toxicity. The therapeutic index of ascorbic acid against 0.61 mmol/kg NaVO3 was found to be 95.2. This was 4.6 and 12.2 times greater than those of Tiron and Deferoxamine respectively. L-Cysteine greater than Na2CaEDTA greater than Na3CaDTPA reduced the acute mortality of mice following i.p. injection of NaVO3. Sodium salicylate, D,L-penicillamine, DMSA and DDC were not effective as antidotes for acute NaVO3-toxicity.

Quinacrine antagonizes the effects of Na,K-ATPase inhibitors on renal prostaglandin E2 release but not their effects on renin secretion.

Previous results have demonstrated that two inhibitors of Na-and-K-activated adenosine triphosphatase (ouabain, vanadate) lead to stimulated prostaglandin E2 release and to inhibited renin secretion in the rat renal cortical slice preparation. It was speculated that stimulation of phospholipase A2 activity accounted for the effect on prostaglandin E2 release. We used the same preparation in the present experiments, and showed that another inhibitor of Na-and-K-activated adenosine triphosphatase (K-free incubation medium) stimulates prostaglandin E2 release and inhibits renin secretion. Quinacrine antagonized the stimulatory effects of ouabain, vanadate, and K-free medium on prostaglandin E2 release (consistent with phospholipase A2 involvement), but did not antagonize their inhibitory effects on renin secretion. Collectively, these observations lend further weight to the argument against a mediatory role of prostaglandin synthesis in the renin secretory process.

Vanadyl (VO2+) and vanadate (VO-3) ions inhibit the brain microsomal Na,K-ATPase with similar affinities. Protection by transferrin and noradrenaline.

The activity of Na,K-ATPase was measured in brain microsomes as the function of increasing concentrations of vanadyl (VOSO4, V4+) and the vanadate (NaVO3, V5+) ions. Both forms of vanadium inhibited the Na,K-ATPase activity with high affinity -Ki (vanadate) = 3 X 10(-7)M and Ki (vanadyl = 1 X 10(-6)M. The stability of V4+ in ATPase reaction media (Tris buffers) was measured by electron spin resonance spectroscopy. Without any reducing agent, V4+ was quickly oxidised by atmospheric oxygen. When a reducing agent such as dithiothreitol was added, the V4+ was stable for at least 30 min and the inhibition pattern of Na,K-ATPase by V4+ was not changed. The blocking effect of V4+ in the presence of dithiothreitol was counteracted by pre-incubation with equimolar concentrations of transferrin or 100 times excess of noradrenaline. The regulation of brain Na,K-ATPase by vanadate may be represented by competition between low-capacity inhibitory binding sites localized on the enzyme molecule and high-capacity sites of intracellular proteins. Preferential binding of vanadyl to the latter type of sites will decrease the intracellular concentration of the free metal and thus eliminate the enzyme inhibition.

The therapeutic effect of ascorbic acid and EDTA in manic-depressive psychosis: double-blind comparisons with standard treatments.

The effect of ascorbic acid and ethylene diamine tetra acetic acid (EDTA) in the treatment of manic-depressive psychosis was compared, using double-blind procedures, with recognized treatment regimes. There was no significant difference between the response of depressed patients to amitriptyline or ascorbic acid and EDTA. Manic patients responded significantly better to lithium than to ascorbic acid and EDTA. These results are in keeping with the suggestion that vanadium may be of aetiological importance in depressive psychosis, but do not support such a suggestion for mania.

Inhibition of active transport of chloride and sodium by vanadate in the cornea.

Vanadate, an inhibitor of (Na+ + K+)ATPase, also inhibits active transepithelial Na+ and Cl- transport (measured as short-circuit current) in the isolated cornea in concentrations of 10(-4)M to 10(-3)M. The disulfonic stilbene, DIDS, does not affect the short-circuit current per se, but it prevents the inhibitory effect of vanadate on Na+ and Cl- transport. Since vanadate acts in other systems from the cytoplasmic side, it is postulated that DIDS interferes with vanadate penetration into the epithelial cells. These results also strengthen the notion of a Na-Cl co-transport system in the corneal epithelium.