Vanadium--an element of atypical biological significance

Bioavailability of vanadium extracted by EDTA, HCl, HOAC, and NaNO3 in topsoil in the Panzhihua urban park, located in southwest China

Bioavailable vanadium was evaluated on the basis of soil vanadium single-extraction with ethylenediaminetetraacetic acid (EDTA), hydrochloric acid (HCl), acetic acid (HOAc), and sodium nitrate (NaNO(3)) in Panzhihua urban park. The soil vanadium concentration extracted by HOAc was 0.01-2.07 mg kg(-1), by EDTA 0.28-7.03 mg kg(-1), by NaNO(3) 0.07-0.53 mg kg(-1), and by HCl 0.19-1.36 mg kg(-1). The bioavailable vanadium (bioavailable fraction) obtained with HOAc was 0.01-1.33%, with EDTA 0.27-4.09%, with NaNO(3) 0.13-0.72%, and with HCl 0.06-0.28%. In addition, the impact of soil properties, soil nutrients, and soil enzyme activities on bioavailability of vanadium is discussed in this study. Based on the characteristics of bioavailable vanadium in the soil, ecological and health risks should have been given more attention in the studied area.

The effect of vanadium on platelet function

Vanadium pentoxide (V(2)O(5)) inhalation effect on platelet function in mice was explored, as well as the in vitro effect on human platelets. Mouse blood samples were collected and processed for aggregometry and flow cytometry to assess the presence of P-selectin and monocyte-platelet conjugates. Simultaneously, human platelets were processed for aggregometry(.) The mouse results showed platelet aggregation inhibition in platelet-rich-plasma (PRP) at four-week exposure time, and normality returned at eight weeks of exposure, remaining unchanged after the exposure was discontinued after four weeks. This platelet aggregation inhibition effect was reinforced with the in vitro assay. In addition, P-selectin preserved their values during the exposure, until the exposure was discontinued during four weeks, when this activation marker increased. We conclude that vanadium affects platelet function, but further studies are required to evaluate its effect on other components of the hemostatic system.

Hepatic megalocytosis due to vanadium inhalation: participation of oxidative stress

The aim of this study was to evaluate the morphological changes, liver function test (LFT), and oxidative stress damage caused by thiobarbituric acid reactive substances (TBARS), in mice exposed to vanadium via inhalation. Male CD-1 mice were exposed to vanadium pentoxide (V2O5) via inhalation (0.02 M), 1 hour twice a week for 6 weeks. At the end of the protocol, controls and exposed mice were killed to evaluate the changes. Histological analysis and LFT were performed to detect the damage. TBARS detection was assessed for oxidative stress. Inflammatory infiltration, binucleation, and meganucleus were detected in the liver of V2O5-exposed mice ( p < 0.05). Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels were also significantly increased ( p < 0.05). Lipid peroxidation was significantly higher in V2O5-exposed animals compared to controls ( p < 0.05). V2O5 exposure induced inflammation and cell damage detected by the increase in ALT and AST levels, as well as histological changes that suggest regenerative changes, such as binucleation and meganucleus.

Impact of vanadium complexes treatment on the oxidative stress factors in wistar rats plasma

The aim of this study was to investigate the clinical efficacy of vanadium complexes on triglycerides (TG), total cholesterol (Chol), uric acid (UA), urea (U), and antioxidant parameters: nonenzymatic (FRAP—ferric reducing ability of plasma, and reduced glutathione—GSH) and enzymatic (glutathione peroxidase—GPx, catalase—CAT, and GPx/CAT ratio) activity in the plasma of healthy male Wistar rats. Three vanadium complexes: [VO(bpy)₂]SO₄·2H₂O, [VO(4,4′Me₂bpy)₂]SO₄·2H₂O, and Na[VO(O₂)₂(bpy)]·8H₂O are administered by gavage during 5 weeks in two different diets such as control (C) and high fatty (F) diets. Changes of biochemical and antioxidants parameters are measured in plasma. All three vanadium complexes statistically decrease the body mass growth in comparison to the control and fatty diet. In plasma GSH was statistically increased in all vanadium complexes-treated rats from control and fatty group in comparison to only control group. Calculated GPX/CAT ratio was the highest in the control group in comparison to others.

Anticancer activity of metal complexes: involvement of redox processes

Cells require tight regulation of the intracellular redox balance and consequently of reactive oxygen species for proper redox signaling and maintenance of metal (e.g., of iron and copper) homeostasis. In several diseases, including cancer, this balance is disturbed. Therefore, anticancer drugs targeting the redox systems, for example, glutathione and thioredoxin, have entered focus of interest. Anticancer metal complexes (platinum, gold, arsenic, ruthenium, rhodium, copper, vanadium, cobalt, manganese, gadolinium, and molybdenum) have been shown to strongly interact with or even disturb cellular redox homeostasis. In this context, especially the hypothesis of "activation by reduction" as well as the "hard and soft acids and bases" theory with respect to coordination of metal ions to cellular ligands represent important concepts to understand the molecular modes of action of anticancer metal drugs. The aim of this review is to highlight specific interactions of metal-based anticancer drugs with the cellular redox homeostasis and to explain this behavior by considering chemical properties of the respective anticancer metal complexes currently either in (pre)clinical development or in daily clinical routine in oncology.

Hypoglycemic Properties of Oxovanadium (IV) Coordination Compounds with Carboxymethyl-Carrageenan and Carboxymethyl-Chitosan in Alloxan-Induced Diabetic Mice

In order to avoid low absorption, incorporation, and undesirable side effects of inorganic oxovanadium compounds, the antidiabetic activities of organic oxovanadium (IV) compounds in alloxan-induced diabetic mice were investigated. Vanadyl carboxymethyl carrageenan (VOCCA) and vanadyl carboxymethyl chitosan (VOCCH) were synthesized and administrated through intragastric administration in different doses for 20 days in alloxan-induced diabetic mice. Glibenclamide was administrated as the positive control. Our results showed that low-dose group, middle-dose group, and high-dose group of VOCCA and VOCCH could significantly reduce the levels of blood glucose (P < 0.05) compared with untreated group, but not in normal mice. Besides, high-dose groups of VOCCA and VOCCH exhibited more significant hypoglycemic activities (P < 0.01). After treated with VOCCH, the oral glucose tolerance of high-dose group of VOCCH was improved compared with model control group (P < 0.05).

Hazardous impact and translocation of vanadium (V) species from soil to different vegetables and grasses grown in the vicinity of thermal power plant

The distribution of vanadium (V) species in soil (test soil), vegetables and grasses, collected from the vicinity of a thermal power plant has been studied. For comparison purpose soil (control soil), same vegetable and grass samples were collected from agricultural land devoid of any industrial area. A simple and efficient ultrasonic assisted extraction method has been developed for the extraction of V(5+) species from soil, vegetable and grass samples using Na(2)CO(3) in the range of 0.1-0.5 mol/L. For comparison purpose same sub samples were also extracted by conventional heating method. The total and V species were determined by electrothermal atomic absorption spectrometry using different modifiers. The validity of V(5+) and V(4+) determination had been confirmed by the spike recovery and total amount of V by the analysis of CRM 1570 (spinach leave) and sub samples of agricultural soil. The concentration of total V was found in the range of 90-215 and 11.4-42.3 μg/g in test and control soil samples, respectively. The contents of V(5+) and total V in vegetables and grasses grown around the thermal power plant were found in the range of 2.9-5.25 and 8.74-14.9 μg/g, respectively, which were significantly higher than those values obtained from vegetables and fodders grown in non exposed agricultural site (P<0.01). Statistical evaluations indicate that the sum of concentrations of V(5+) and V(4+) species was not significantly different from total concentration of V in same sub samples of vegetable, grass and soil of both origins, at 95% level of confidence.

PpGalNacT2 participating in vanadium-induced HL-60 cell differentiation

The current study demonstrates vanadium plays the role of antitumor, and its antitumor effect is dosage-dependent. N-acetyl-galactosamine-transferase 2 (polypeptide: N-acetyl-α-galactosaminyl-transferases 2, ppGalNAc-T2) is a member of ppGalNAcTs (polypeptide: N-acetyl-α-galactosaminyl-transferases) family, which proves to play a vital role in the tumor emergence and development process. In this study, we focused on ppGalNAc-T2 and vanadium and aimed to determine whether ppGalNAc-T2 is correlated with vanadium's antitumor effect. We discovered that ppGalNAc-T2 changed with the variation of HL-60 cell growth induced by vanadium at mRNA level. Peanut agglutinin (PNA) is an exogenous lectin. PpGalNacT2 can be indirectly recognized by PNA. By means of flow cytometry and immunofluorescent staining, we found the deviation of PNA binding increased significantly at high concentration vanadium. Then we docked one of the possible compound substances of vanadium onto the body, VO(3) (molecular formula O(13)V(4), partial vanadate tetramer) and ppGalNAcT2, and simulated them via molecular dynamics, which showed that VO(3) may inhibit the activity of the enzyme by stemming conformational changes of a key loop of ppGalNAcT2. To sum up, our results suggested that ppGalNacT2 participated in vanadium induced HL-60 cell differentiation, which might be able to provide a new mechanism of vanadium's antitumor effect.

Cloud point extraction of vanadium in pharmaceutical formulations, dialysate and parenteral solutions using 8-hydroxyquinoline and nonionic surfactant

A cloud point extraction (CPE) method has been developed for the determination of trace quantity of vanadium ions in pharmaceutical formulations (PF), dialysate (DS) and parenteral solutions (PS). The CPE of vanadium (V) using 8-hydroxyquinoline (oxine) as complexing reagent and mediated by nonionic surfactant (Triton X-114) was investigated. The parameters that affect the extraction efficiency of CPE, such as pH of sample solution, concentration of oxine and Triton X-114, equilibration temperature and time period for shaking were investigated in detail. The validity of CPE of V was checked by standard addition method in real samples. The extracted surfactant-rich phase was diluted with nitric acid in ethanol, prior to subjecting electrothermal atomic absorption spectrometry. Under these conditions, the preconcentration of 50 mL sample solutions, allowed raising an enrichment factor of 125-fold. The lower limit of detection obtained under the optimal conditions was 42 ng/L. The proposed method has been successfully applied to the determination of trace quantity of V in various pharmaceutical preparations with satisfactory results. The concentration ranges of V in PF, DS and PS samples were found in the range of 10.5-15.2, 0.65-1.32 and 1.76-6.93 microg/L, respectively.

A kinetic assay of mitochondrial ADP-ATP exchange rate in permeabilized cells

We previously described a method to measure ADP-ATP exchange rates in isolated mitochondria by recording the changes in free extramitochondrial [Mg(2+)] reported by an Mg(2+)-sensitive fluorescent indicator, exploiting the differential affinity of ADP and ATP to Mg(2+). In the current article, we describe a modification of this method suited for following ADP-ATP exchange rates in environments with competing reactions that interconvert adenine nucleotides such as in permeabilized cells that harbor phosphorylases and kinases, ion pumps exhibiting substantial ATPase activity, and myosin ATPase activity. Here we report that the addition of BeF(3)(-) and sodium orthovanadate (Na(3)VO(4)) to medium containing digitonin-permeabilized cells inhibits all ADP-ATP-using reactions except the adenine nucleotide translocase (ANT)-mediated mitochondrial ADP-ATP exchange. An advantage of this assay is that mitochondria that may have been also permeabilized by digitonin do not contribute to ATP consumption by the exposed F(1)F(o)-ATPase due to its sensitivity to BeF(3)(-) and Na(3)VO(4). With this assay, ADP-ATP exchange rate mediated by the ANT in permeabilized cells is measured for the entire range of mitochondrial membrane potential titrated by stepwise additions of an uncoupler and expressed as a function of citrate synthase activity per total amount of protein.

Vanadium in the detection, prevention and treatment of cancer: the in vivo evidence

Vanadium, a dietary micronutrient, is yet to be established as an essential part of the human diet. Over the past century, several biological effects of vanadium, such as insulin-mimetic action as well as amelioration of hyperlipidemia and hypertension, have been discovered. This transition element is known to influence a battery of enzymatic systems, namely phosphatases, ATPases, peroxidases, ribonucleases, protein kinases and oxidoreductases. Multiple biochemical and molecular actions of vanadium have been implicated in its inhibitory effects on various tumor cells of human origin. Successful in vitro studies over the past few decades have advanced the anticancer research on vanadium into the preclinical stage. Vanadium in several animal cancer models provides protection against all stages of carcinogenesis--initiation, promotion, and progression. This review focuses on the current advances in cancer prevention and treatment as well as early detection by vanadium compounds in preclinical animal models while pointing to possible mechanisms of such diverse beneficial effects. Clinical pharmacokinetic and potential toxicity studies on vanadium are also highlighted in this review. Supporting and challenging evidence as well as future directions of vanadium research exploring the possibility of using this dietary agent for detection, prevention and treatment of human cancers are critically discussed.

Vanadium compounds induced mitochondria permeability transition pore (PTP) opening related to oxidative stress

Vanadium compounds have been regarded as promising in therapeutic treatment of diabetes and in cancer prevention. In the present work, we studied the effects of vanadium compounds on mitochondria to investigate the mechanisms of toxicity. Mitochondria were isolated from rat liver and incubated with a variety of vanadium compounds, i.e. VOSO(4), NaVO(3), and vanadyl complexes with organic ligands. Our studies indicated that VO(2+), VO(3)(-), VO(acac)(2) and VOcit (1-100microM) could induce mitochondrial swelling in a concentration dependent manner and disrupt mitochondrial membrane potential (Deltapsi(m)) in a time dependent manner, which is quite different from the rapid Deltapsi(m) collapse caused by Ca(2+) or CCCP (carbonyl cyanide m-chlorophenylhydrazone, a mitochondrial uncoupling reagent). Release of cytochrome c (Cyt c) was observed and could be inhibited by cyclosporin A (CsA), an inhibitor of the mitochondrial permeability transition pore (PTP). Interestingly, VOdipic caused release of Cyt c without mitochondrial swelling and Deltapsi(m) disruption, an action previously only observed on the Bax protein, suggesting a potentially role of VOdipic in regulating PTP opening. In addition, all the vanadium compounds tested stimulated mitochondrial production of reactive oxygen species (ROS). Antioxidants, i.e. vitamin C and E, significantly delayed the Deltapsi(m) disruption. Overall, our experimental evidence indicated vanadium compounds exhibited multiple actions on mitochondria. Vanadium compounds did induce oxidative stress on mitochondrial and thus caused PTP opening, which led to collapse of Deltapsi(m) and Cyt c release as the initiation of cell apoptosis.

New vanadium-based magnetic resonance imaging probes: clinical potential for early detection of cancer

We have developed a magnetic resonance imaging (MRI) method for improved detection of cancer with a new class of cancer-specific contrast agents, containing vanadyl (VO(2+))-chelated organic ligands, specifically bis(acetylacetonato)oxovanadium(IV) [VO(acac)(2)]. Vanadyl compounds have been found to accumulate within cells, where they interact with intracellular glycolytic enzymes. Aggressive cancers are metabolically active and highly glycolytic; an MRI contrast agent that enters cells with high glycolytic activity could provide high-resolution functional images of tumor boundaries and internal structure, which cannot be achieved by conventional contrast agents. The present work demonstrates properties of VO(acac)(2) that may give it excellent specificity for cancer detection. A high dose of VO(acac)(2) did not cause any acute or short-term adverse reactions in murine subjects. Calorimetry and spectrofluorometric methods demonstrate that VO(acac)(2) is a blood pool agent that binds to serum albumin with a dissociation constant K (d) ~ 2.5 +/- 0.7 x 10(-7) M and a binding stoichiometry n = 1.03 +/- 0.04. Owing to its prolonged blood half-life and selective leakage from hyperpermeable tumor vasculature, a low dose of VO(acac)(2) (0.15 mmol/kg) selectively enhanced in vivo magnetic resonance images of tumors, providing high-resolution images of their interior structure. The kinetics of uptake and washout are consistent with the hypothesis that VO(acac)(2) preferentially accumulates in cancer cells. Although VO(acac)(2) has a lower relaxivity than gadolinium-based MRI contrast agents, its specificity for highly glycolytic cells may lead to an innovative approach to cancer detection since it has the potential to produce MRI contrast agents that are nontoxic and highly sensitive to cancer metabolism.

A review of current toxicological concerns on vanadium pentoxide and other vanadium compounds: gaps in knowledge and directions for future research

Vanadium pentoxide (V(2)O(5)) and other inorganic vanadium compounds have recently been evaluated by several occupational exposure limit (OEL) setting (occupational exposure limit, OEL) committees and expert groups in response to the publication of several new studies, including the U.S. National Toxicology Program (NTP, 2002) carcinogenicity study of inhaled V(2)O(5) in rats and mice, which concluded that clear evidence of lung tumors was seen in mice of both genders and that there was some evidence of carcinogenicity in male rats. This study reviews the expert evaluations of several OEL committees and expert groups and attempts to understand the strengths and weaknesses in their scientific arguments. This study also evaluates some key studies relating to potential genotoxicity, carcinogenicity, and respiratory effects of vanadium compounds and discusses how they might elucidate the mechanism(s) by which V(2)O(5) induces lung cancer in mice. All expert groups appear to agree that the lung tumors induced in mice in the NTP (2002) study are a site-specific response and, in general, verify that existing in vitro and in vivo studies suggest that tumors were induced by a secondary mechanism (presumably non-genotoxic), which is supported, though not conclusively, by a mechanistic data set. As some vanadium compounds produce a range of DNA and chromosome damage, there is no consensus on which of these changes is critical for the carcinogenic process for V(2)O(5) or whether the findings for the lung tumors seen in mice exposed to V(2)O(5) can be extrapolated to other inorganic vanadium compounds. As such, the various expert committees used the evidence differently, some to read across, i.e., to predict an endpoint for a substance based on the endpoint information of another with similar characteristics (e.g., physicochemical properties [solubility, bioaccessibility, bioavailability], structure, fate [toxicokinetics], and toxicology) for carcinogenicity from V(2)O(5) to other inorganic vanadium compounds. It is noteworthy that the toxicity of metals does not necessarily relate to carcinogenicity in a direct manner; thus, no assumptions should be made a priori when trying to extrapolate from V(2)O(5) to other inorganic vanadium compounds. Recent studies evaluated in this review provided some further insights into possible mechanisms but do not cover all relevant endpoints, address only a limited number of vanadium compounds, and have not established no-effect thresholds for carcinogenicity or respiratory tract irritation. Thresholds need to be established in order for arguments to be made for setting a health-based OEL for non-genotoxic or secondary genotoxic carcinogens. In conclusion, important knowledge gaps preclude confident classification and risk assessment for all vanadium compounds. Evidence suggests that further research that may address some of these critical gaps is needed.

Preliminary studies on the effect of zinc and selenium on vanadium-induced cytotoxicity in vitro

In the present work, we investigated the cytotoxicity of vanadium and the influence of zinc and selenium on vanadium-dependent cell damage in the BALB/c 3T3 cell culture. Treatment of cells for 24 hours with medium containing 50, 100 and 200 microM NaVO3 caused a significant decrease in the cell viability as measured by MTT test. Furthermore, the assays for reactive oxygen species (NBT reduction and phenol red oxidation) demonstrated the increase in superoxide and hydrogen peroxide production. In the cotreatment studies, the cells were exposed to NaVO3 (50, 100 and 200 microM) in the presence of nontoxic concentrations of ZnCl2 (5 microM) or Na2SeO3 (0.5 microM). Following 24 h incubation, the cell viability (assessed in MTT assay) and reactive oxygen species generation were evaluated. Our data suggest that zinc and selenium, in the concentrations mentioned above, provide no protection against adverse actions induced by sodium metavanadate at concentration levels of 50, 100 and 200 microM. To our knowledge, this is the first report from in vitro studies on interaction between pentavalent vanadium and trace elements that function as antioxidants: zinc and selenium.

Effects of dietary vanadium on growth and lipid storage in a larval anuran: results from studies employing ad libitum and rationed feeding

Vanadium (V) exerts a variety of effects related to metabolic function in vertebrates, including modifying glycolytic pathways and lipid metabolism. However, little is known about toxicity of V to wildlife in natural systems. We conducted parallel, independent studies to evaluate the effect of dietary exposure to vanadium on survival, metabolism, growth, and lipid storage of larval leopard frogs (Rana sphenocephala). In one study ("Ad lib") larvae were fed unlimited food and in the other ("Ration") larvae were fed a restricted diet. Experimental diets contained 10 ppm dw V(total) (Control, "C"), 109 ppm (Low, "L"), and 363 ppm (High, "H"). In neither study did V affect metabolic rate or survival to forelimb emergence. However, in the Ration study, 31% of individuals in H that had initiated metamorphosis died prior to completion of metamorphosis, compared with 22% in M and 9% in C, however the difference was not significant at alpha=0.05. Mortality during metamorphosis in the Ad lib study was more variable, yet followed a similar trend (26, 14, and 12% mortality in H, L, and C). In both studies, individuals that died during the metamorphic period were smaller at the time of forelimb emergence than those that survived. In the Ration study, individuals in H also had significantly lower growth rates, delayed metamorphosis, and reduced lipid content at metamorphosis compared to C and L. Growth was not affected by V in the Ad lib study. Our results suggest that habitat contamination by V may present risks to amphibians during the metamorphic period attributable to energetic responses influencing size at the initiation of metamorphosis and body lipid stores. Furthermore, while we cannot make formal comparisons between the studies, our results imply that protocols that employ ad libitum feeding regimes could fail to capture the effects of contaminants as they may be expressed in natural situations in which resources are typically more limited.

Synthesis, characterization and antidiabetic properties of N(1)-2,4-dihydroxybenzylidene-N(4)-2-hydroxybenzylidene-S-methyl-thiosemicarbazidato-oxovanadium(IV)

A new oxovanadium(IV) chelate [VOL] (L: N(1)-2,4-dihydroxybenzylidene-N(4)-2-hydroxybenzylidene-S-methyl-thiosemicarbazidato) was synthesized and characterized by elemental analysis, conductivity and magnetic measurements, UV-vis, IR, EPR spectroscopy and mass spectrometry. The biochemical and immunohistochemical effects of the administration of the vanadium complex (VOL) into the pancreas of normal and streptozotocin-induced diabetic rats were profoundly investigated. The animals were randomly divided into four groups. Group I: control (intact) animals. Group II: control animals administered with VOL. Group III: STZ-induced diabetic animals. Group IV: STZ-induced diabetic animals administered with VOL. VOL was given to some of the experimental animals by gavage at a dose of 0.2mM/kg every day for 12 days. Blood samples were collected from animals, on 0 and 1, 6 and 12 days after STZ injection. On day 12, the pancreatic tissues were taken from the animals. The tissue sections were labelled with streptavidin biotin peroxidase technique for insulin. In the diabetic group, the blood glucose levels, aspartate and alanine transaminases, alkaline phosphatase activities were increased. But, in the diabetic+VOL groups, the blood glucose levels, aspartate and alanine transaminases, alkaline phosphatase activities were reduced. In the diabetic group, a decrease in the pancreatic glutathione levels, glutathione peroxidase and superoxide dismutase activities and an increase in the pancreatic lipid peroxidation level and catalase activities were observed. The administration of VOL to the diabetic rats reversed this diabetic effect due to its insulinomimetic effects. According to the immunohistochemical and biochemical results obtained, it was concluded that VOL can regenerate B cells of the pancreas in experimental diabetes and has an antidiabetic and protective effects on the pancreas.

Trends in speciation analysis of vanadium in environmental samples and biological fluids--a review

A comprehensive review is presented addressing recent trends in the speciation and determination of vanadium in environmental and biological sample matrices, including important analytical aspects such as sample clean up, pre-concentration and method development. Methodology based on both separation and spectroscopic techniques for the determination of vanadium speciation is discussed. A brief outline of analytical principles, together with an overview of the recent developments and applications of vanadium speciation determination is included. The newer methods for detecting metal ions including hyphenated spectroscopic techniques and sample preparation schemes are also discussed.

P-glycoprotein in proteoliposomes with low residual detergent: the effects of cholesterol

PURPOSE

There is evidence that cholesterol affects the ATPase and transport functions of P-glycoprotein (P-gp). To study the influence of cholesterol on P-gp in a well defined lipid environment, we reconstituted P-gp in egg phosphatidylcholine (PhC) and PhC/cholesterol proteoliposomes with negligible residual amounts of detergents.

MATERIALS AND METHODS

P-gp proteoliposomes were prepared by continuous dialysis from micelles consisting of P-gp, lipids, sodium dodecyl sulfate and cholate. Basal and modulator-induced ATPase activities were studied in an established enzyme assay. Modulator affinities to P-gp and to the lipid bilayers were determined by equilibrium dialysis.

RESULTS

In the absence of cholesterol the basal ATPase activity was six fold lower than in the presence of 20 or 40% cholesterol, and no P-gp binding and ATPase induction was detected for the tested modulators verapamil and progesterone. In proteoliposomes containing 20 and 40% cholesterol, respectively, the modulators showed significant P-gp binding and ATPase activation. The concentration of the modulators for half maximal activation of the ATPase was higher with 40% than with 20% cholesterol.

CONCLUSIONS

Cholesterol influences P-gp in three ways: (a) it enhances its basal ATPase activity, (b) it renders P-gp sensitive towards the modulators verapamil and progesterone and (c) it affects the modulator concentration at half maximal ATPase activation.

Vanadate-induced cell death is dissociated from H2O2 generation

Vanadium is an environmentally toxic metal with peculiar and sometimes contradictory cellular effects. It is insulin-mimetic, it can either stimulate cell growth or induce cell death, and it has both mutagenic and antineoplastic properties. However, the mechanisms involved in those effects are poorly understood. Several studies suggest that H(2)O(2) is involved in vanadate-induced cell death, but it is not known whether cellular sensitivity to vanadate is indeed related to H(2)O(2) generation. In the present study, the sensitivity of four cell lines from different origins (K562, K562-Lucena 1, MDCK, and Ma104) to vanadate and H(2)O(2) was evaluated and the production of H(2)O(2) by vanadate was analyzed by flow cytometry. We show that cell lines very resistant to H(2)O(2) (K562, K562-Lucena 1, and Ma104 cells) are much more sensitive to vanadate than MDCK, a cell line relatively susceptible to H(2)O(2), suggesting that vanadate-induced cytotoxicity is not directly related to H(2)O(2) responsiveness. In accordance, vanadate concentrations that reduced cellular viability to approximately 60-70% of the control (10 mumol/L) did not induce H(2)O(2) formation. A second hypothesis, that peroxovanadium (PV) compounds, produced once vanadate enters into the cells, are responsible for the cytotoxicity, was only partially confirmed because MDCK cells were resistant to both vanadate and PV compounds (10 micromol/L each). Therefore, our results suggest that vanadate toxicity occurs by two distinct pathways, one dependent on and one independent of H(2)O(2) production.

New Methodological Approach for the Vanadium K-Edge X-ray Absorption Near-Edge Structure Interpretation: Application to the Speciation of Vanadium in Oxide Phases from Steel Slag

This paper presents a comparison between several methods dedicated to the interpretation of V K-edge X-ray absorption near-edge structure (XANES) features. V K-edge XANES spectra of several V-bearing standard compounds were measured in an effort to evaluate advantages and limits of each method. The standard compounds include natural minerals and synthetic compounds containing vanadium at various oxidation state (from +3 to +5) and in different symmetry (octahedral, tetrahedral, and square pyramidal). Correlations between normalized pre-edge peak area and its centroid position have been identified as the most reliable method for determining quantitative and accurate redox and symmetry information for vanadium. This methodology has been previously developed for the Fe K edge. It is also well adapted for the V K edge and is less influenced by the standard choice than other methods. This methodology was applied on an "environmental sample," i.e., a well-crystallized leached steel slag containing vanadium as traces. Micro-XANES measurements allowed elucidating the microdistribution of vanadium speciation in leached steel slag. The vanadium exhibits an important evolution from the unaltered to the altered phases. Its oxidation state increases from +3 to +5 together with the decrease of its symmetry (from octahedral to tetrahedral).

Evaluation of genotoxicity of oral exposure to tetravalent vanadium in vivo

The trace element vanadium interacts with living cells, in which it exerts a variety of biological effects depending on its chemical form and oxidation state. Tetravalent vanadium was shown to affect several genotoxicity end-points in vitro, but its genotoxic potential in vivo is not elucidated. In this study, the genotoxic effects induced in vivo by subacute oral exposure to vanadyl sulphate (VOSO4), a tetravalent vanadium salt, were investigated. To this aim male CD1 mice were administered with VOSO4 in drinking water over the dose range 2-1000 mg/l for 5 weeks. The incidence of micronucleated blood reticulocytes was measured along treatment period. At the end of treatment, micronuclei in both blood reticulocytes and bone marrow polychromatic erythrocytes were determined; in addition, DNA lesions detectable by comet assay were assessed in marrow and testicular cells. Tissue distribution of vanadium at sacrifice was determined by atomic absorption spectrometry. Comet assays and the analysis of micronuclei in polychromatic erythrocytes did not reveal treatment related effects. A slight increase in micronucleated reticulocytes, with no relationship with the administered dose, was observed in some treated groups. The determination of vanadium content in kidney, liver, spleen, bone, stomach, small intestine and testis highlighted low internal exposure, especially in soft tissues. Overall, data indicate scarce bioavailability for orally administered tetravalent vanadium, and lack of significant genotoxic potential in vivo.

Vanadyl Sulfate, Taurine, and Combined Vanadyl Sulfate and Taurine Treatments in Diabetic Rats: Effects on the Oxidative and Antioxidative Systems

BACKGROUND

Vanadyl sulfate (VS) and taurine are two promising agents in the treatment of diabetes related to their antihyperglycemic, antihyperlipidemic, and hyperinsulinemic effects. Data about the effects of VS on the oxidant-antioxidant system is limited and controversial. However, taurine is a well-documented antioxidant agent and our aim was to investigate the effects of VS, taurine and VS and taurine combination on the oxidative-antioxidative systems in streptozotocin-nicotinamide (STZ-NA) diabetic rats.

METHODS

Nicotinamide (230 mg/kg, i.p.) and streptozotocin (65 mg/kg, i.p.) were administered. VS (0.75 mg/mL) and taurine (1%) were added to drinking water for 5 weeks. Rats were divided as control (C), diabetes (D), diabetes+VS (D+VS), diabetes+taurine (D+T), diabetes+VS and taurine (D+VST). Plasma and tissue malondialdehyde (MDA) levels were measured by high-performance liquid chromatography and spectrophotometry, respectively. Paraoxonase and arylesterase activities were measured by spectrophotometric methods and superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities were determined using commercial kits.

RESULTS

VS, taurine and VS and taurine combination treatments reduced the enhanced blood glucose, serum total cholesterol and triglyceride, tissue MDA and plasma MDA (except in the D+VS group) levels and increased the reduced serum insulin level, serum paraoxonase and arylesterase activities, GSH-Px activity and SOD activity (except in the D+VS group).

CONCLUSIONS

The findings of the present study suggest that VS and taurine exert beneficial effects on the blood glucose and lipid levels in STZ-NA diabetic rats. However, VS might exert prooxidative or antioxidative effects in various components of the body and taurine and VS combination might be an alternative for sole VS administration.

Vanadium exposure through lactation produces behavioral alterations and CNS myelin deficit in neonatal rats

The current study was performed to assess the vanadium(V)-induced developmental toxicity in sucklings of Wistar rats. Dams of treated litters were intraperitoneally injected with 3 mg NaVO(3)/kg body weight/day during 12 days starting on postnatal day (PND) 10. Surface righting reflex, negative geotaxy and hindlimb support tests were performed on pups every 48 h, from 8th to 18th PND. Open field test was performed on the 21st PND. On 22nd PND, some animals were transcardially perfusion-fixed and their brains were removed and cut with a cryostat. Brain sections were processed for myelin histochemistry and for anti-myelin basic protein immunohistochemistry. Delay in eye opening and decreased muscular strength and locomotion were observed in V-exposed pups of both sexes. A decreased myelin staining in corpus callosum and cerebellum in these pups was also observed. Results suggest that vanadium exposure through lactation would induce neurotoxicity in rat developing CNS.

Improvement of peripheral endothelial dysfunction by protein tyrosine phosphatase inhibitors in heart failure

BACKGROUND

Chronic heart failure (CHF) induces endothelial dysfunction characterized by a decrease in nitric oxide (NO) production in response to flow (flow-mediated dilatation [FMD]). Because activation of endothelial NO synthase (eNOS) by flow requires tyrosine phosphorylation, we tested whether endothelial dysfunction could be corrected by increasing phosphotyrosine levels using protein tyrosine phosphatase (PTP) inhibitors and especially inhibitors of PTP1B.

METHODS AND RESULTS

CHF was induced by coronary ligation in mice, and FMD was assessed in isolated and cannulated mesenteric artery segments (2 mm in length and <300 microm in diameter). CHF almost abolished FMD but only moderately affected the response to acetylcholine. In mice with CHF, the PTP1B inhibitors AS279, AS098, and AS713 restored FMD to levels similar to those of normal mice. This restoration was reduced by inhibitors of eNOS and phosphatidylinositol-3 kinase. Polymerase chain reaction and Western blot showed that arteries express PTP1B, and this expression was not affected by CHF. Immunolocalization revealed the presence of PTP1B in the endothelium and the adventitia. Flow induced a transient eNOS phosphorylation that was absent in CHF. PTP1B inhibition stimulated early eNOS phosphorylation and increased phosphorylation of Akt.

CONCLUSIONS

Our results demonstrate for the first time that PTP1B inhibitors may be potent treatments for endothelial dysfunction.

Vanadate but not tungstate prevents the fructose-induced increase in GLUT5 expression and fructose uptake by neonatal rat intestine

Intermediary signals, precociously enhancing GLUT5 transcription in response to perfusion of its substrate, fructose, in the small intestine of neonatal rats, are not known. Because glucose-6-phosphatase (G6Pase), glucose-6-phosphate translocase (G6PT), and fructose-1,6-bisphosphatase (FBPase) expression increases parallel to or precedes that of GLUT5, we investigated the link between these gluconeogenic genes and GLUT5 by using vanadate or tungstate, potent inhibitors of gluconeogenesis. Small intestinal perfusions of 20-d-old rats were performed with fructose alone, fructose + vanadate or tungstate, glucose alone, and glucose + vanadate or tungstate. As expected, fructose, but not glucose nor glucose + inhibitor perfusion, increased GLUT5 mRNA abundance and fructose transport. Fructose perfusion dramatically increased G6Pase mRNA abundance but had no effect on G6Pase activity. In sharp contrast, fructose perfusion did not increase FBPase gene expression but stimulated FBPase activity. Both vanadate and tungstate significantly inhibited G6Pase activity but did not prevent the fructose-induced increases in G6Pase and G6PT gene expression. Perfusion with fructose + vanadate prevented the fructose-induced increases in fructose transport and GLUT5 mRNA abundance, whereas perfusion with fructose + tungstate did not. Interestingly, vanadate, but not tungstate, inhibited the fructose-induced increase in FBPase activity. Thus, vanadate inhibition of fructose-induced increases in FBPase activity paralleled exactly vanadate inhibition of fructose-induced increases in GLUT5 mRNA abundance and activity. Fructose-induced changes in FBPase activity may regulate changes in GLUT5 expression and activity in the small intestine of neonatal rats. The marked increases in intestinal G6Pase and GLUT5 mRNA abundance may be a parallel response to different factors released during fructose perfusion.

Biological activity of vanadium compounds

Vanadium compounds are characterised by a broad spectrum of action in vivo and in vitro. Their insulin-mimetic activity is manifested in their ability to normalize changes observed in both clinical and experimental diabetes (i.e. hyperglycaemia, hyperlipidaemia, lowered cell sensitivity to insulin) through the regulation of carbohydrate and lipid metabolism and the removal of secondary symptoms of this disease (as e.g. retinopathy, cardiomyopathy, nephropathy). Nevertheless, vanadium is considered to be a toxic element in both cationic and anionic form, although the latter type has more serious side effects. This is accounted for by the faster absorption of anionic forms, although the chemical structure, geometry, and the manner of synthesis of its derivatives also contributes to this elevated toxicity. Besides their antidiabetic properties, vanadium derivatives have also been observed to influence processes related to mitogenic cell responses (apoptosis, proliferation, neoplastic transformation). However, both anti-and pro-neoplastic properties of vanadium are reported.

Vanadate ingestion enhances the organization and collagen fibril diameters of rat healing medical collateral ligaments

Although an injured medial collateral ligament (MCL) will naturally heal, the quality of healing tissue is inferior to the uninjured MCL tissue. Previous studies have shown promising results of sodium orthovanadate (vanadate) in enhancing the quality of rat skin wounds. This study therefore investigated whether vanadate enhances the quality of the rat healing MCL in terms of the collagen fibril organization and diameter. Six mature male Sprague-Dawley rats, with weight ranges of 475-505 g and ages of 25 weeks, were used in this study. Three rats in the experimental group received vanadate (0.2 mg/ml) in their saline drinking water (150 mM NaCl), whereas three rats in the control group were only given saline water. Three weeks after transection, the rat MCLs were harvested for hematoxylin and eosin (H&E) staining and transmission electron microscopy. It was found that vanadate promoted organization of collagen fibrils and significantly increased the diameters of collagen fibrils by 14% in healing MCL (P<0.001). These results indicate that application of vanadate may be a promising tissue engineering approach to enhance the quality of healing tissues such as injured MCLs.

Stress proteins (Hsp72/73, Grp94) expression pattern in rat organs following metavanadate administration. Effect of green tea drinking

Expression pattern of heat shock proteins (Hsp) 72/73 and glucose regulated protein (Grp) 94 was studied in liver, kidney and testis of rats injected with sublethal doses of ammonium metavanadate (5 mg/kg/day). In addition, some batches of animals were given green tea decoction, known to be rich in anti-oxidative compounds, as sole beverage in order to evaluate its protective properties. In control animals, the stress proteins expression was found to be organ-dependent: anti-Grp94 antibody revealed two bands at 96 and 98 kDa in kidney and liver whereas the 98 kDa band only was found in testis; anti-Hsp72/73 antibody revealed that the constitutive Hsp73 was present in all organs whereas the inducible Hsp72 was only present in kidney and testis. In kidney of vanadium-treated rats, Hsp73 was over-expressed by about 50% whereas Hsp72 was down-regulated by 50-80%. No such effects were observed in liver and testis. In liver and kidney of vanadium-treated rats, Grp94 was over-expressed by 50% and 150% respectively whereas no change was found in testis. In rats given green tea as sole beverage, the 96 kDa protein expression level in liver was reduced both in controls and in vanadium-treated animals. However, green tea drinking failed to prevent the vanadium-induced Hsp72 under-expression in kidney of vanadium-treated rats.

Synthesis, characterization, and biological activity of oxovanadium(IV) complexes with polyalcohols

Oxovanadium(IV) complexes of the polyalcohols sorbitol, galactitol, and mannitol, of stoichiometry Na(2)[VO(L)(2)].H(2)O, were obtained from aqueous alkaline solutions. They were characterized by elemental analysis, infrared and UV-vis spectroscopies, thermoanalytical (thermogravimetric and differential thermal analysis) data, and magnetic susceptibility measurements. The biological activities of the complexes on the proliferation, differentiation, and glucose consumption were tested on osteoblast-like cells (MC3T3E1 osteoblastic mouse calvaria-derived cells and UMR106 rat osteosarcoma-derived cells) in culture. The three complexes exerted a biphasic effect on cell proliferation, being slight stimulating agents at low concentrations and inhibitory in the range of 25-100 microM. All the complexes inhibited cell differentiation in tumor osteoblasts. Their effects on glucose consumption were also discussed. The free ligands did not show any effect on the studied biological parameters.

Combined effect of vanadium(V) and chromium(III) on lipid peroxidation in liver and kidney of rats

Since chromium(III) was demonstrated to have antioxidative action, we have decided to study the effect of this element on V-induced LPO in liver and kidney of rats. Outbred 2-month-old, albino male Wistar rats received daily, for a period of 12 weeks: group I (control), deionized water to drink; group II, sodium metavanadate (SMV) solution at a concentration of 0.100mgV/mL; group III, chromium chloride (CC) solution at a concentration of 0.004mgCr/mL and group IV, SMV-CC solution at a concentration of 0.100mgV and 0.004mgCr/mL. The particular experimental groups took up with drinking water about 8.6mgV/kg b.w./24h (group II), 0.4mgCr/kg b.w./24h (group III), 9mgV and 0.36mgCr/kg b.w./24h (group IV). The V- or Cr-treated groups had higher concentrations of these two elements in liver and kidney compared to the controls. The administration of vanadium alone caused a significant decrease in fluid intake and in body weight gain compared to the controls. In liver supernatants obtained from all tested rats a statistically significant increase in MDA concentration was demonstrated in spontaneous LPO in comparison with the control rats. Moreover, in rats intoxicated with vanadium alone a statistically significant increase in liver MDA level was observed in the presence of 100microM NaVO(3). Instead, in supernatants of liver received from rats treated with chromium alone, a statistically significant increase in MDA concentration in comparison with the controls was found in the presence of 400microM NaVO(3). In kidney supernatants obtained from rats treated with chromium alone, a statistically significant increase in lipid peroxidation was shown in the presence of 30microM FeSO(4) and 400microM NaVO(3). These results show that the tested doses of vanadium(V) and chromium(III) ingested by rats with their drinking water caused significant alterations in internal organs, especially in liver. Under the conditions of our experiment, Cr(III) did not demonstrate antioxidant action, it rather had an oxidant effect.