Internal dose of vanadium in rats following repeated exposure to vanadyl sulfate and sodium orthovanadate via drinking water.

Vanadium is a ubiquitous environmental contaminant that exists in multiple oxidation states. Humans are exposed to vanadyl (V4+) and vanadate (V5+) from dietary supplements, food, and drinking water and hence there is a concern for adverse human health. The current investigation is aimed at identifying vanadium oxidation states in vitro and in vivo and internal concentrations following exposure of rats to vanadyl sulfate (V4+) or sodium metavanadate (V5+) via drinking water for 14 d. Investigations in simulated gastric and intestinal fluids showed that V4+ was stable in gastric fluid while V5+ was stable in intestinal fluid. Analysis of rodent plasma showed that the only vanadium present was V4+, regardless of the exposed compound suggesting conversion of V5+ to V4+ in vivo and/or instability of V5+ species in biological matrices. Plasma, blood, and liver concentrations of total vanadium, after normalizing for vanadium dose consumed, were higher in male and female rats following exposure to V5+ than to V4+. Following exposure to either V4+ or V5+, the total vanadium concentration in plasma was 2- to 3-fold higher than in blood suggesting plasma as a better matrix than blood for measuring vanadium in future work. Liver to blood ratios were 4-7 demonstrating significant tissue retention following exposure to both compounds. In conclusion, these data point to potential differences in absorption and disposition properties of V4+ and V5+ salts and may explain the higher sensitivity in rats following drinking water exposure to V5+ than V4+ and highlights the importance of internal dose determination in toxicology studies.

Vanadium release in whole blood, serum and urine of patients implanted with a titanium alloy hip prosthesis.

INTRODUCTION: Vanadium (V) is a minor constituent of the Titanium-Aluminum-Vanadium (TiAlV) alloy currently used in cementless hip prostheses. Present study aimed at verifying the correlation of vanadium levels among different matrices and assessing reference levels of the ion in a population of patients wearing a well-functioning hip prosthesis. METHODS: Vanadium was measured using Inductive Coupled Plasma Mass Spectrometry (ICP-MS) in whole blood, serum and urine of 129 patients implanted with a TiAlV-alloy hip prosthesis. RESULTS: The values in the serum were above the upper limit of the reference values in 42% of patients (29% in urine and 13% in whole blood). A good correlation among matrices was observed (p < 0.001). The cohort of patients (N = 32) complaining of pain or in which a loosening or damage to the prosthesis was assessed showed a significantly higher excretion of vanadium in urine as compared with the remaining asymptomatic patients (p = 0.001). The 95th percentile distribution of vanadium in the cohort of patients with a well-functioning prosthesis was 0.3 µg/L in whole blood, 0.5 µg/L in serum and 2.8 µg/L in urine, higher that in the unexposed population, especially for urine. CONCLUSIONS: The presence of a prosthesis, even though well-functioning, may cause a possible release of vanadium into the blood and a significant urinary excretion. The reference values of vanadium of the asymptomatic patients with titanium alloy hip prostheses supplied information regarding the background exposure level of the ions and their lower and upper limits.

Anti-diabetic effects of vanadium(III, IV, V)-chlorodipicolinate complexes in streptozotocin-induced diabetic rats.

Vanadium(III, IV, V)-chlorodipicolinate (dipic-Cl) complexes, including H[VIII(dipic-Cl)2] · 5H2O (V3dipic-Cl), VIVO(dipic-Cl)(H2O)2 (V4dipic-Cl) and K[VVO2(dipic-Cl)] (V5dipic-Cl), were prepared with the indicated oxidation states. Our aim was to evaluate the anti-diabetic effects of V3dipic-Cl, V4dipic-Cl and V5dipic-Cl in streptozotocin-induced diabetic rats. Vanadium complexes were orally administered to diabetic rats at concentrations of 0.1-0.3 mg/ml in the drinking water. We found that vanadium-chlorodipicolinate (V-dipic-Cl) complexes at the concentration of 0.1 mg/ml did not exhibit blood glucose-lowering effects when administered to diabetic rats for 20 days. However, the levels of fasting blood glucose in diabetic rats were decreased after treatment with 0.3 mg/ml of V4dipic-Cl and V5dipic-Cl complexes for the following 20 days. Although administration of both V4dipic-Cl and V5dipic-Cl significantly lowered diabetic hyperglycemia, the vanadium intake from administration of V4dipic-Cl is nearly 1.5-fold greater compared to that of V5dipic-Cl. Treatment with the H2dipic-Cl ligand and all three V-dipic-Cl complexes significantly lowered serum cholesterol, while administration of the V5dipic-Cl complex lowered serum cholesterol significantly more than administration of the ligand alone. Treatment with ligand alone did not have an effect on serum triglyceride, while administration of the V4dipic-Cl and V5dipic-Cl significantly lowered the elevated serum triglyceride associated with diabetes. Oral administration of the ligand and all V-dipic-Cl complexes did significantly lower diabetes elevated serum alkaline phosphatase. Treatment with H2dipic-Cl ligand and V4dipic-Cl and V5dipicCl significantly lowered diabetes elevated aspartate amino transferase. These results indicate that the health of the treated animals did not seem to be further compromised compared to that of diabetic animals. In addition, oral administration of H2dipic-Cl, V3dipic-Cl, V4dipic-Cl and V5dipic-Cl did not alter diabetic serum creatinine and blood urea nitrogen levels, suggesting no significant side effects of vanadium treatment on renal functions at the dose of 0.3 mg/ml in diabetic rats. The results presented here suggest that the anti-diabetic effects of treatment with V-dipic-Cl complexes were likely associated in part with the oxidation state of vanadium.

The uptake and fate of vanadyl ion in ascidian blood cells and a detailed hypothesis for the mechanism and location of biological vanadium reduction. A visible and X-ray absorption spectroscopic study.

Vanadium K-edge X-ray absorption spectroscopy (XAS) has been used to track the uptake and fate of VO(2+) ion in blood cells from Ascidia ceratodes, following exposure to dithiothreitol (DTT) or to DTT plus VO(2+). The full range of endogenous vanadium was queried by fitting the XAS of blood cells with the XAS spectra of model vanadium complexes. In cells exposed only to DTT, approximately 0.4% of a new V(III) species was found in a site similar to Na[V(edta)(H(2)O)]. With exposure to DTT and VO(2+), average intracellular [VO(aq)](2+) increased from 3% to 5%, and 6% of a new complexed form of vanadyl ion appeared evidencing a ligand array similar to [VO(edta)](2-). At the same time, the relative ratio of blood cell [V(H(2)O)(6)](3+) increased at the expense of [V(H(2)O)(5)(SO(4))](+) in a manner consistent with a significant increase in endogenous acidity. In new UV/Visible experiments, VO(2+) could be reduced to 7-coordinate [V(nta)(H(2)O)(3)] or [V(nta)(ida)](2-) with cysteine methyl ester in pH 6.5 solution. Ascorbate reduced [VO(edta)](2-) to 7-coordinate [V(edta)(H(2)O)](-), while [VO(trdta)](2-) was unreactive. These results corroborate the finding that the reductive EMF of VO(2+) is increased by the availability of a 7-coordinate V(III) product. Finally, a new and complete hypothesis is proposed for an ascidian vanadate reductase. The structure of the enzyme active site, the vanadate-vanadyl-vanadic reduction mechanism, the cellular locale, and elements of the regulatory machinery governing the biological reduction of vanadate and vanadyl ion by ascidians are all predicted. Together these constitute the new field of vanadium redox enzymology.

Metallokinetic characteristics of antidiabetic bis(allixinato)oxovanadium(IV)-related complexes in the blood of rat.

The antidiabetic effect of vanadium is a widely accepted phenomenon; some oxovanadium(IV) complexes have been found to normalize high blood glucose levels in both type 1 and type 2 diabetic animals. In light of the future clinical use of these complexes, the relationship among their chemical structures, physicochemical properties, metallokinetics, and antidiabetic activities must be closely investigated. Recently, we found that among bis(3-hydroxypyronato)oxovanadium(IV) [VO(3hp)(2)] related complexes, bis(allixinato)oxovanadium(IV) [VO(alx)(2)] exhibits a relatively strong hypoglycemic effect in diabetic animals. Next, we examined its metallokinetics in the blood of rats that received five VO(3hp)(2)-related complexes by the blood circulation monitoring-electron paramagnetic resonance method. The metallokinetic parameters were obtained from the blood clearance curves based on a two-compartment model; most parameters, such as area under the concentration curve and mean residence time, correlated significantly with the in vitro insulinomimetic activity in terms of 1/IC(50) (IC(50) is the 50% inhibitory concentration of the complex required for the release of free fatty acids in adipocytes) and the lipophilicity of the complex (log P (com)). The oxovanadium(IV) concentration was significantly higher and the species resided longer in the blood of rats that received VO(alx)(2) than in the blood of rats that received VO(3hp)(2) or bis(kojato)oxovanadium(IV); VO(alx)(2) also exhibited higher log P (com) and 1/IC(50) values. On the basis of these results, we propose that the introduction of lipophilic groups at the C2 and C6 positions of the 3hp ligand is an effective method to enhance the hypoglycemic effect of the complexes, as supported by the observed in vivo exposure and residence in the blood.

Short-term bioaccumulation of vanadium when ingested with a tea decoction in streptozotocin-induced diabetic rats.

Sodium orthovanadate suspended in a lichee black tea decoction effectively regulates blood glucose levels in rats with insulin-dependent, streptozotocin (STZ)-induced diabetes. The primary advantage of vanadate delivery with the tea decoction over conventional systems that use water suspensions of vanadate is a significant reduction in the toxic side effects of vanadate. It is unknown if the tea alters the bioavailability of vanadate. Male Sprague-Dawley rats were administered an intravenous injection of STZ to induce diabetes. Four days later, the diabetic rats were treated by oral gavage with 40 mg of Na-orthovanadate suspended in double-distilled, deionized water (V/H2O), tea/vanadate (TV) decoction, or were treated with the tea decoction alone. Vanadium concentrations were measured in blood and various tissues at 1 to 24 hours posttreatment using graphite furnace atomic absorption spectrophotometry. With the exception of bone, maximal vanadium concentration in plasma and tissue samples were observed 2 hours after ingestion, but steadily decreased after that. Plasma vanadium levels continued to decrease until 16 hours. In contrast, vanadium steadily accumulated in bone over the 24-hour period. Overall, rats treated with V/H2O contained similar or significantly higher concentrations of vanadium in all tissues compared with TV treatment. The pattern of vanadium accumulation was also similar over time in both treatment groups. Vanadium levels were highest in bone > kidney > liver > pancreas > lung > heart > muscle > brain in both TV- and V/H2O-treated animals. This study demonstrates that the accumulation of vanadium in diabetic rats is reduced when coadministered with a black tea decoction in comparison to administration of vanadium in water. However, this effect is unlikely to be of a magnitude to explain the full capacity of TV to reduce the toxic side effects of vanadate.

Speciation in the aqueous H+/H2VO4-/H2O2/citrate system of biomedical interest.

The speciation in the quaternary aqueous H+/H2VO4-/H2O2/citrate (Cit3-) and H+/H2VO4-/Cit3-/L-(+)-lactate (Lac-) systems has been determined at 25 degrees C in the physiological medium of 0.150 M Na(Cl). A combination of 51V NMR integral intensities and chemical shift (Bruker AMX500) as well as potentiometric data (glass electrode) have been collected and evaluated with the computer program LAKE, which is able to treat multimethod data simultaneously. The pKa-values for citric acid have been determined as 2.94, 4.34 and 5.61. Altogether six vanadate-citrate species have been found in the ternary H+/H2VO4-/Cit3- system in the pH region 2-10, only two of which are mononuclear. Reduction of vanadium(V) becomes more pronounced at pH < 2. Solutions, in which reduction occurred to any extent, were excluded from all calculations. In the quaternary H+/H2VO4-/H2O2/Cit3- system, eight complexes have been found in addition to all binary and ternary complexes over the pH region 2-10, including three mononuclear species. Equilibria in general are fast, but the significant and rapid decomposition of peroxide in acidic solutions limited the final model to pH > 4. In the quaternary H+/H2VO4-/Cit3-/Lac- system, two mixed-ligand species have been determined, with the compositions V2CitLac2- and V2CitLac3- (pKa = 5.0). To our knowledge, this is the first time such complexes have been reported for vanadium(V). 51V NMR chemical shifts, compositions and formation constants are given, and equilibrium conditions are illustrated in distribution diagrams as well as the fit of the model to the experimental data. When suitable, structural proposals are given, based on 13C NMR measurements and available literature data of related compounds.

Chemical speciation of insulinomimetic VO(IV) complexes of pyridine-N-oxide derivatives: binary and ternary systems.

In order to estimate the impact of the low-molecular-mass (l.m.m.) VO(IV) binders of blood serum on the potentially insulin-enhancing compound VO(HPO)(2) (HPO, 2-hydroxypyridine-N-oxide): and VO(MPO)(2) (MPO, 2-mercaptopyridine-N-oxide), the speciation in the binary system VO(IV)-HPO and VO(IV)-MPO and in the ternary systems VO(IV)-HPO(MPO)-ligand B (B=oxalate, lactate, citrate or phosphate) was studied by pH-potentiometry. The stability constants of the complexes formed were determined in aqueous solution at I=0.2 M (KCl) and T=25 degrees C. The most probable binding modes of the complexes were determined by EPR method. The pyridine-N-oxides were found to form very stable bis complexes, which are predominant in the pH range 2-7. The results in the ternary systems demonstrate that only the citrate is a strong enough VO(IV) binder to compete with the carrier ligands. The binding ability of the high-molecular-mass (h.m.m.) serum proteins albumin and transferrin were also assessed and transferrin was found to be an efficient binder molecule. The actual solution state of these compounds in blood serum is compared with that of other insulin-mimic VO(IV) complexes.

Speciation of insulin-mimetic VO(IV)-containing drugs in blood serum.

The biospeciations of three potential insulin-mimetic VO(IV) compounds, VO(maltolate)2, VO(picolinate)2 and VO(6-Me-picolinate)2, in blood serum were assessed via modelling calculations, using the stability constants reported in the literature for the binary insulin-mimetic complexes and their ternary complexes formed with the most important low molecular mass binders in the serum: oxalic acid, lactic acid, citric acid and phosphate. The binding capabilities of two high molecular mass serum proteins, albumin and transferrin, were also taken into account.

Metallokinetic analysis of disposition of vanadyl complexes as insulin-mimetics in rats using BCM-ESR method.

Among vanadium's wide variety of biological functions, its insulin-mimetic effect is the most interesting and important. Recently, the vanadyl ion (+4 oxidation state of vanadium) and its complexes have been shown to normalize the blood glucose levels of streptozotocin-induced diabetic rats (STZ-rats). During our investigations to find more effective and less toxic vanadyl complexes, the vanadyl-methylpicolinate complex (VO-MPA) was found to exhibit higher insulin-mimetic activity and less toxicity than other complexes, as evaluated by both in vitro and in vivo experiments. Electron spin resonance (ESR) is capable of measuring the paramagnetic species in biological samples. We have developed the in vivo blood circulation monitoring-electron spin resonance (BCM-ESR) method to analyze the ESR signals due to stable organic radicals in real time. In the present investigation, we have applied this method to elucidate the relationship between the blood glucose normalizing effect of VO-MPA and the global disposition of paramagnetic vanadyl species. This paper describes the results of vanadyl species in the circulating blood of rats following intravenous administration of vanadyl compounds. ESR spectra due to the presence of vanadyl species were obtained in the circulating blood, and their pharmacokinetic parameters were estimated using compartment models. The results indicate that vanadyl species are distributed considerably to the peripheral tissues, as estimated by BCM-ESR, and eliminated from the body through the urine, as estimated by ESR at 77 K. The exposure of vanadyl species in the blood was found to be enhanced by VO-MPA treatment. Given these results, we concluded that the pharmacokinetic character of vanadyl species is closely related with the structure and antidiabetic activity of the vanadyl compounds.

Ternary complex formation between VO(IV)-picolinic acid or VO(IV)-6-methylpicolinic acid and small blood serum bioligands.

In order to assess the role of the low molecular mass bioligands of blood serum in vanadium binding, a study was made of the interactions of the complexes formed in the VO(IV)-picolinic acid and VO(IV)-6-methylpicolinic acid systems with various low molecular mass constituents of blood serum, such as oxalate, lactate, citrate and phosphate. The speciation of VO(IV) in these ternary systems and also in the binary VO(IV)-picolinic acid and VO(IV)-6-methylpicolinic acid systems was studied by pH-potentiometry at 25 degrees C and at an ionic strength I = 0.2 M (KCl). The binding modes of the complexes formed were determined by spectral (electronic absorption and EPR) methods. Picolinic acid and 6-methylpicolinic acid were found to form mono and bis complexes through the pyridine nitrogen and carboxylate oxygen, but the presence of the methyl group in 6-methylpicolinic acid surprisingly decreases the stability of its complexes significantly. The results obtained on the ternary systems reveal that mixed ligand complex formation is favoured in these systems, especially with citrate, and must therefore be taken into account in the speciation description of VO(IV) in blood serum.

Gluconeogenesis in non-obese diabetic (NOD) mice: in vivo effects of vandadate treatment on hepatic glucose-6-phoshatase and phosphoenolpyruvate carboxykinase.

The contribution of gluconeogenesis to hyperglycemia in non-obese diabetic (NOD) mice has been investigated using oral vanadate administration. Vanadate compounds have been shown to mimic many actions of insulin; however, the exact mechanism is poorly understood. The aims of the present study were (1) to elucidate vanadate's action in vivo, and to assess the possibility that its glucose-reducing effect is dependent on the presence of a minimal concentration of insulin; and (2) to evaluate the effects of vanadate administration on the key hepatic gluconeogenesis enzymes, glucose-6-phosphatase (G-6-Pase) and phosphoenolpyruvate carboxykinase (PEPCK), as well as glucose-6-phosphate dehydrogenase (G-6-PDH). Vanadate caused a significant reduction in blood glucose but failed to normalize it, despite effective serum vanadate concentrations (26.2 +/- 1.6 micromol/L). Two weeks after initiation of treatment, blood glucose levels were 26.0 +/- 1.8, 21.7 +/- 3.0, 16.0 +/- 1.6, and 14.3 +/- 2.3 mmol/L in the control (C), insulin (I), vanadate (V), and combined vanadate and insulin (V + I) groups, respectively (P < .001). G-6-Pase activity was significantly reduced by vanadate (622 +/- 134 v365 +/- 83 nmol/min/mg protein in C vV, P < .05). PEPCK activity was also significantly reduced (844 +/- 370, 623 +/- 36, 337 +/- 43, and 317 +/- 75 nmol/min/mg in the C, I, V, and V + I groups, respectively, P < .001). No significant differences in the hepatic glycogen stores and G-6-PDH activity were noted between treatment groups. Our study suggests that the inhibition of hepatic G-6-Pase and PEPCK activity by vanadate plays an important role in reducing blood glucose levels in NOD mice.

Acute and chronic response to vanadium following two methods of streptozotocin-diabetes induction.

Controversial reports on the efficacy and possible toxicity of vanadium obtained from various studies may be attributed to differences in the method of diabetes induction and (or) to differences in animal strains. The objective of this study was to evaluate the contribution of these two factors to the effects of vanadium in the treatment of experimental diabetes. Two methods of streptozotocin induction of diabetes in rats have been used for studying the antidiabetic effects of vanadium. One involves a single intravenous injection of 60 mg/kg streptozotocin, and the other uses two subcutaneous injections of 40 mg/kg streptozotocin, to either Wistar or Sprague-Dawley rats. In a 7-week chronic study, Sprague-Dawley rats appeared to develop a more severe diabetes (indicated by higher plasma cholesterol and higher fasting plasma glucose levels) following the single intravenous injection of streptozotocin than rats made diabetic by two subcutaneous injections of streptozotocin. Irrespective of the method of diabetes induction, the responses of all the diabetic animals to chronic vanadyl sulphate treatment were similar. In an acute study, Wistar diabetic rats were more responsive than Sprague-Dawley diabetic rats to vanadyl sulphate and to lower doses (0.6 and 0.8 mmol/kg) of a new organic vanadium compound, bis(maltolato)oxovanadium(i.v.).

Stimulation of human erythrocyte 2,3-bisphosphoglycerate phosphatase by vanadate.

The rates of vanadate-stimulated hydrolysis of 2,3-bisphosphoglycerate in metabolically competent erythrocytes and in hemolysates were determined from data on time courses up to 35 min employing 31P nuclear magnetic resonance spectroscopy. The enhanced rate of hydrolysis of the bisphosphate was attributed principally to the activation of the phosphatase activity of 2,3-bisphosphoglycerate synthase both in cell suspensions and in hemolysates. Information on the concentrations of vanadate and vanadyl present in the preparations was obtained employing 51V nuclear magnetic resonance spectroscopy and electron paramagnetic resonance spectroscopy. Redox reactions involving vanadium ions appeared to be important in establishing the final equilibrium concentrations of the oxy- and oxo-ions (vanadate and vanadyl, respectively), but the data suggested that the activation of the enzyme resulted from direct action of the vanadium ions on the enzyme and not as a consequence of the alteration in the equilibrium of intracellular oxidants and reductants.

[Characteristics of the structural-functional status of erythrocyte membranes in 3 strains of rats with spontaneous genetic hypertension]. / Kharakteristika strukturno-funktsional'nogo sostoianiia membrany éritrotsitov trekh linii krys so spontannoi geneticheskoi gipertenziei.

Erythrocyte membrane 22Na and 45Ca transport, osmotic stability and antigenic composition were investigated in 3 strains of rats with spontaneous hereditary hypertension (SHR, SHR SP, MHS), as well as normotensive controls for SHR and SHR SP (WKY) and for MHS (MHS). All strains of spontaneously hypertensive rats showed increased passive membrane permeability for sodium, that was due to increased operation rate of the Na+, K+-cotransport system. Metabolizing sodium is increased in the erythrocytes of Japanese rats (SHR and SHR SP), and decreased in Milan rats (MHS), as compared to normotensive controls. After four hours of incubation with orthovanadate, erythrocyte 45Ca levels were 2-3 times as high in SHR and SHR SP as they were in WKY. In the presence of valinomycin, erythrocyte resistance to hypoosmotic hemolysis was essentially higher in SHR and SHR SP than it was in WKY. These differences are related to a changed rate of anion transport through the band 3 protein. There were no differences in this respect between MHS and MNS. An antigen with a molecular weight of 37-39 kD was detected in erythrocyte membranes of WKY and could not be detected in erythrocytes of other rat groups, including the MNS. It is suggested that different molecular origins of membrane disorders may be an immediate cause of different mechanisms of arterial hypertension in Japanese and Milan animals.

Effect of sodium-ascorbate and vanadate on the Rb+-uptake of human red blood cells.

To follow the Rb+-uptake of human red blood cells (rbc-s) under different circumstances, a micro-method was developed. According to our experiments the Rb+-uptake of rbc-s in a healthy person was about 3.5-4.0 mumoles Rb/mg Fe at 37 degrees C during 120 minutes. When red cells were incubated with solutions containing different concentrations, between 15 and 120 mmole/l, of Na-ascorbate [Na-ascorbate was applied at the expense of Na-isethionate (sodium salt of 2-hydroxyethan-1-sulfonic acid)] the Rb+-uptake of red cells increased at 37 degrees C with 37 to 70% respectively. In other experiments it was established that the ouabain-sensitive Rb+-uptake of rbc-s decreased with 50% in the presence of 0.1 mmole/l vanadate, while if Na-ascorbate was applied simultaneously with different concentrations of vanadate, or after a preincubation with 1 mmole/l vanadate, the Rb+-uptake of red cells, which had been reduced by vanadate, returned close to that of control. This effect can be explained by the reductive property of Na-ascorbate, i.e. by the transformation of vanadate to vanadil.

EPR characterization of vanadyl (IV) species in blood cells of ascidians.

EPR spectra due to vanadyl species of blood cells of Ascidia ahodori collected from different places in Japan (Ushimado and Asamushi) were measured. The EPR spectral pattern as well as their EPR parameters for these two species were found to be different from each other. EPR analysis correlating g parallel and A parallel indicated that vanadyl ion in the animals from Ushimado was in a much stronger ligand field than those from Asamushi. Vanadyl species in the Ushimado animals was comparable to the stable complexes such as the vanadyl-ATP complex prepared at pH 12.