Does vanadium play a role in cellular regulation?

The Mechanism of Phillyrin from the Leaves of Forsythia suspensa for Improving Insulin Resistance

Three lignans, phillyrin, forsythia ester A, and rosin-β-D-furan glucose, were isolated from Forsythia suspensa which is a famous Traditional Chinese Medicine used for clearing heat and detoxifying, reducing swelling and dispersing knot, and dispersing wind heat. In this study, the effects of phillyrin, forsythia ester A, and rosin-β-D-furan glucose on insulin resistance of 3T3-L1 adipocytes were investigated by the method of glucose oxidase-peroxidase (GOD-POD) and the mechanism was assayed by the method of western blot. The results indicated that phillyrin, forsythia ester A, and rosin-β-D-furan glucose could improve the glucose uptake in 3T3-L1 adipocytes under insulin resistance (IR). Among them, phillyrin showed significant activity in increasing glucose consumption at the concentrations of 100 μM and 200 μM (P < 0.001). The mechanism of improving insulin resistance may be that phillyrin could raise the protein phosphorylation of IRS-1 and Akt and the expression levels of GLUT4 protein.

Vanadium in Biological Action: Chemical, Pharmacological Aspects, and Metabolic Implications in Diabetes Mellitus

Vanadium compounds have been primarily investigated as potential therapeutic agents for the treatment of various major health issues, including cancer, atherosclerosis, and diabetes. The translation of vanadium-based compounds into clinical trials and ultimately into disease treatments remains hampered by the absence of a basic pharmacological and metabolic comprehension of such compounds. In this review, we examine the development of vanadium-containing compounds in biological systems regarding the role of the physiological environment, dosage, intracellular interactions, metabolic transformations, modulation of signaling pathways, toxicology, and transport and tissue distribution as well as therapeutic implications. From our point of view, the toxicological and pharmacological aspects in animal models and humans are not understood completely, and thus, we introduced them in a physiological environment and dosage context. Different transport proteins in blood plasma and mechanistic transport determinants are discussed. Furthermore, an overview of different vanadium species and the role of physiological factors (i.e., pH, redox conditions, concentration, and so on) are considered. Mechanistic specifications about different signaling pathways are discussed, particularly the phosphatases and kinases that are modulated dynamically by vanadium compounds because until now, the focus only has been on protein tyrosine phosphatase 1B as a vanadium target. Particular emphasis is laid on the therapeutic ability of vanadium-based compounds and their role for the treatment of diabetes mellitus, specifically on that of vanadate- and polioxovanadate-containing compounds. We aim at shedding light on the prevailing gaps between primary scientific data and information from animal models and human studies.

Why Antidiabetic Vanadium Complexes are Not in the Pipeline of "Big Pharma" Drug Research? A Critical Review

Public academic research sites, private institutions as well as small companies have made substantial contributions to the ongoing development of antidiabetic vanadium compounds. But why is this endeavor not echoed by the globally operating pharmaceutical companies, also known as "Big Pharma"? Intriguingly, today's clinical practice is in great need to improve or replace insulin treatment against Diabetes Mellitus (DM). Insulin is the mainstay therapeutically and economically. So, why do those companies develop potential antidiabetic drug candidates without vanadium (vanadium- free)? We gathered information about physicochemical and pharmacological properties of known vanadium-containing antidiabetic compounds from the specialized literature, and converted the data into explanations (arguments, the "pros and cons") about the underpinnings of antidiabetic vanadium. Some discoveries were embedded in chronological order while seminal reviews of the last decade about the Medicinal chemistry of vanadium and its history were also listed for further understanding. In particular, the concepts of so-called "noncomplexed or free" vanadium species (i.e. inorganic oxido-coordinated species) and "biogenic speciation" of antidiabetic vanadium complexes were found critical and subsequently documented in more details to answer the question.

Influence of vanadium on serum lipid and lipoprotein profiles: a population-based study among vanadium exposed workers

BACKGROUND

Some experimental animal studies reported that vanadium had beneficial effects on blood total cholesterol (TC) and triglyceride (TG). However, the relationship between vanadium exposure and lipid, lipoprotein profiles in human subjects remains uncertain. This study aimed to compare the serum lipid and lipoprotein profiles of occupational vanadium exposed and non-exposed workers, and to provide human evidence on serum lipid, lipoprotein profiles and atherogenic indexes changes in relation to vanadium exposure.

METHODS

This cross-sectional study recruited 533 vanadium exposed workers and 241 non-exposed workers from a Steel and Iron Group in Sichuan, China. Demographic characteristics and occupational information were collected through questionnaires. Serum lipid and lipoprotein levels were measured for all participants. The ratios of total cholesterol to high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C) to HDL-C and apoB to apoA-I were used as atherogenic indexes. A general linear model was applied to compare outcomes of the two groups while controlling possible confounders and multivariate logistic regression was performed to evaluate the relationship between low HDL-C level, abnormal atherogenic index and vanadium exposure.

RESULTS

Higher levels of HDL-C and apoA-I could be observed in the vanadium exposed group compared with the control group (P < 0.05). Furthermore, atherogenic indexes (TC/HDL-C, LDL-C/HDL-C, and apoB/apoA-I ratios) were found statistically lower in the vanadium exposed workers (P < 0.05). Changes in HDL-C, TC/HDL-C, and LDL-C/HDL-C were more pronounced in male workers than that in female workers. In male workers, after adjusting for potential confounding variables as age, habits of smoking and drinking, occupational vanadium exposure was still associated with lower HDL-C (OR 0.41; 95% CI, 0.27-0.62) and abnormal atherogenic index (OR 0.38; 95% CI, 0.20-0.70).

CONCLUSION

Occupational vanadium exposure appears to be associated with increased HDL-C and apoA-I levels and decreased atherogenic indexes. Among male workers, a significantly negative association existed between low HDL-C level, abnormal atherogenic index and occupational vanadium exposure. This suggests vanadium has beneficial effects on blood levels of HDL-C and apoA-I.

An evidence-based systematic review of vanadium by the Natural Standard Research Collaboration

An evidence-based systematic review of vanadium by the Natural Standard Research Collaboration consolidates the safety and efficacy data available in the scientific literature using a validated, reproducible grading rationale. This article includes written and statistical analysis of clinical trials, plus a compilation of expert opinion, folkloric precedent, history, pharmacology, kinetics/dynamics, interactions, adverse effects, toxicology, and dosing.

Cardioprotection by vanadium compounds targeting Akt-mediated signaling

Treatment with inorganic and organic compounds of vanadium has been shown to exert a wide range of cardioprotective effects in myocardial ischemia/reperfusion-induced injury, myocardial hypertrophy, hypertension, and vascular diseases. Furthermore, administration of vanadium compounds improves cardiac performance and smooth muscle cell contractility and modulates blood pressure in various models of hypertension. Like other vanadium compounds, we documented bis(1-oxy-2-pyridinethiolato) oxovanadium (IV) [VO(OPT)] as a potent cardioprotective agent to elicit cardiac functional recovery in myocardial infarction and pressure overload-induced hypertrophy. Vanadium compounds activate Akt signaling through inhibition of protein tyrosine phosphatases, thereby eliciting cardioprotection in myocardial ischemia/reperfusion-induced injury and myocardial hypertrophy. Vanadium compounds also promote cardiac functional recovery by stimulation of glucose transport in diabetic heart. We here discuss the current understanding of mechanisms underlying vanadium compound-induced cardioprotection and propose a novel therapeutic strategy targeting for Akt signaling to rescue cardiomyocytes from heart failure.

Insulino-mimetic and anti-diabetic effects of vanadium compounds

Compounds of the trace element vanadium exert various insulin-like effects in in vitro and in vivo systems. These include their ability to improve glucose homeostasis and insulin resistance in animal models of Type 1 and Type 2 diabetes mellitus. In addition to animal studies, several reports have documented improvements in liver and muscle insulin sensitivity in a limited number of patients with Type 2 diabetes. These effects are, however, not as dramatic as those observed in animal experiments, probably because lower doses of vanadium were used and the duration of therapy was short in human studies as compared with animal work. The ability of these compounds to stimulate glucose uptake, glycogen and lipid synthesis in muscle, adipose and hepatic tissues and to inhibit gluconeogenesis, and the activities of the gluconeogenic enzymes: phosphoenol pyruvate carboxykinase and glucose-6-phosphatase in the liver and kidney as well as lipolysis in fat cells contributes as potential mechanisms to their anti-diabetic insulin-like effects. At the cellular level, vanadium activates several key elements of the insulin signal transduction pathway, such as the tyrosine phosphorylation of insulin receptor substrate-1, and extracellular signal-regulated kinase 1 and 2, phosphatidylinositol 3-kinase and protein kinase B activation. These pathways are believed to mediate the metabolic actions of insulin. Because protein tyrosine phosphatases (PTPases) are considered to be negative regulators of the insulin-signalling pathway, it is suggested that vanadium can enhance insulin signalling and action by virtue of its capacity to inhibit PTPase activity and increase tyrosine phosphorylation of substrate proteins. There are some concerns about the potential toxicity of available inorganic vanadium salts at higher doses and during long-term therapy. Therefore, new organo-vanadium compounds with higher potency and less toxicity need to be evaluated for their efficacy as potential treatment of human diabetes.

Vanadium and the cardiovascular functions

Inorganic and organic compounds of vanadium have been shown to exhibit a large range of insulinomimetic effects in the cardiovascular system, including stimulation of glucose transporter 4 (GLUT-4) translocation and glucose transport in adult cardiomyocytes. Furthermore, administration of vanadium compounds improves cardiac performance and smooth muscle contractility, and modulates blood pressure in various models of hypertension and insulin resistance. Vanadium compounds are potent inhibitors of protein tyrosine phosphatases. As a result, they promote an increase in protein tyrosine phosphorylation of several key components of the insulin signaling pathway, leading to the upregulation of phosphatidylinositol 3-kinase and protein kinase B, two enzymes involved in mediating GLUT-4 trans location and glucose transport. In addition, vanadium has also been shown to activate p38 mitogen-activated protein kinase and increase Ca2+levels in several cell types. The ability of vanadium compounds to activate these signaling events may be responsible for their ability to modulate cardiovascular functions.Key words: vanadium compounds, glucose transport, smooth muscle contractility, insulin signaling pathway.

Role of reactive oxygen species and MAPKs in vanadate-induced G(2)/M phase arrest

Cell growth arrest is an important mechanism in maintaining genomic stability and integrity in response to environmental stress. Using the human lung alveolar epithelial cancer cell line A549, we investigated the role of reactive oxygen species (ROS), extracellular signal-regulated protein kinase (ERK), and p38 protein kinase in vanadate-induced cell growth arrest. Exposure of cells to vanadate led to cell growth arrest at the G(2)/M phase and caused upregulation of p21 and phospho-cdc2 and degradation of cdc25C in a time- and dose-dependent manner. Vanadate stimulated mitogen-activated protein kinases (MAPKs) family members, as determined by the phosphorylation of ERK and p38. PD98059, an inhibitor of ERK, and SB202190, an inhibitor of p38, inhibited vanadate-induced cell growth arrest, upregulation of p21 and cdc2, and degradation of cdc25C. In addition to hydroxyl radical ((*)OH) formation, cellular reduction of vanadate generated superoxide radical (O(2)(*)(-)) and hydrogen peroxide (H(2)O(2)), as determined by confocal microscopy using specific dyes. Generation of O(2)(*)(-) and H(2)O(2) was inhibited by specific antioxidant enzymes, superoxide dismutase (SOD) and catalase, respectively. ROS activate ERK and p38, which in turn upregulate p21 and cdc2 and cause degradation of cdc25C, leading to cell growth arrest at the G(2)/M phase. Specific ROS affect different MAPK family members and cell growth regulatory proteins with different potencies.

Vanadium in cancer treatment

Vanadium compounds exert preventive effects against chemical carcinogenesis on animals, by modifying, mainly, various xenobiotic enzymes, inhibiting, thus, carcinogen-derived active metabolites. Studies on various cell lines reveal that vanadium exerts its antitumor effects through inhibition of cellular tyrosine phosphatases and/or activation of tyrosine phosphorylases. Both effects activate signal transduction pathways leading either to apoptosis and/or to activation of tumor suppressor genes. Furthermore, vanadium compounds may induce cell-cycle arrest and/or cytotoxic effects through DNA cleavage and fragmentation and plasma membrane lipoperoxidation. Reactive oxygen species generated by Fenton-like reactions and/or during the intracellular reduction of V(V) to V(IV) by, mainly, NADPH, participate to the majority of the vanadium-induced intracellular events. Vanadium may also exert inhibitory effects on cancer cell metastatic potential through modulation of cellular adhesive molecules, and reverse antineoplastic drug resistance. It also possesses low toxicity that, in combination with the synthesis of new, more potent and better tolerated complexes, may establish vanadium as an effective non-platinum, metal antitumor agent.

Vanadate stimulates tyrosine phosphorylation of two proteins in Raji human lymphoblastoid cell membranes

A membrane fraction from Raji human lymphoblastoid cells exhibited tyrosine-specific kinase activity. Vanadate increased tyrosine phosphorylation up to 5-fold; serine and threonine phosphorylation were unchanged. The stimulation was detectable within 15 s at 0 degrees C and at concentrations of vanadate (0.3 and 1.0 microM) present in normal tissues and blood. The tyrosine phosphorylation of two substrates, M1 61 000 and 55 000, was dependent upon vanadate and incorporation into these substrates represented the majority of the vanadate-sensitive tyrosine phosphorylation.

Effects of low-dose VOSO(4) on age-related changes in glucose homeostasis in rats

The effects of low doses of vanadyl sulfate (0.2 mg/ml in the drinking water) on the age-related impairment of glucose homeostasis in Sprague-Dawley rats were investigated. VOSO(4) administration was initiated in 5-month-old animals and lasted 3 months. Thus, in 8-month-old rats, we investigated glucose metabolism in vivo and insulin secretory function in vitro. Results showed that VOSO(4) allowed the disposal of an oral glucose load at lower insulin levels than in age-matched controls. No significant changes were found in muscle glucose transporter (GLUT-4) levels or in glycogen content upon VOSO(4) treatment. Islets isolated from VOSO(4)-treated rats released less insulin than control islets, but showed a better preserved sensitivity to secretagogues, in terms of incremental release over basal release, secretory efficiency, and maintenance of the priming effect of glucose. In conclusion, chronic low-dose VOSO(4) treatment facilitates insulin action by a mechanism independent of muscle GLUT-4 levels and helps preserve the appropriate sensitivity of beta cells to stimuli, thereby preventing age-dependent functional alterations.

NADH-dependent decavanadate reductase, an alternative activity of NADP-specific isocitrate dehydrogenase protein

The well known NADP-specific isocitrate dehydrogenase (IDH) obtained from pig heart was found to oxidize NADH with accompanying consumption of oxygen (NADH:O(2)=1:1) in presence of polyvanadate. This activity of the soluble IDH-protein has the following features common with the previously described membrane-enzymes: heat-sensitive, active only with NADH but not NADPH, increased rates in acidic pH, dependence on concentrations of the enzyme, NADH, decavanadate and metavanadate (the two constituents of polyvanadate), and sensitivity to SOD and EDTA. Utilizing NADH as the electron source the IDH protein was able to reduce decavanadate but not metavanadate. This reduced form of vanadyl (V(IV)) was similar in its eight-band electron spin resonance spectrum to vanadyl sulfate but had a 20-fold higher absorbance at its 700 nm peak. This decavanadate reductase activity of the protein was sensitive to heat and was not inhibited by SOD and EDTA. The IDH protein has the additional enzymic activity of NADH-dependent decavanadate reductase and is an example of "one protein--many functions".

Vanadate induces apoptosis in epidermal JB6 P+ cells via hydrogen peroxide-mediated reactions

Apoptosis is a physiological mechanism for the control of DNA integrity in mammalian cells. Vanadium induces both DNA damage and apoptosis. It is suggested that vanadium-induced apoptosis serves to eliminate DNA-damaged cells. This study is designed to clarify a role of reactive oxygen species in the mechanism of apoptosis induced by vanadium. We established apoptosis model with murine epidermal JB6 P+ cells in the response to vanadium stimulation. Apoptosis was detected by a cell death ELISA assay and morphological analysis. The result shows that apoptosis induced by vanadate is dose-dependent, reaching its saturation level at a concentration of 100 microM vanadate. Vanadyl (IV) can also induce apoptosis albeit with lesser potency. A role of reactive oxygen species was analyzed by multiple reagents including specific scavengers of different reactive oxygen species. The result shows that vanadate-induced apoptosis is enhanced by NADPH, superoxide dismutase and sodium formate, but was inhibited by catalase and deferoxamine. Cells exposed to vanadium consume more molecular oxygen and at the same time, produce more H2O2 as measured by the change in fluorescence of scopoletin in the presence of horseradish peroxidase. This change in oxygen consumption and H2O2 production is enhanced by NADPH. Taken together, these results show that vanadate induces apoptosis in epidermal cells and H2O2 induced by vanadate plays a major role in this process.

Effect of oral vanadyl sulfate treatment on serum enzymes and lipids of streptozotocin-diabetic young rats

In this work we investigate the possible toxicity of vanadyl sulfate (VOSO4), a compound capable of reducing hyperglycemia, on the following serum enzymes of diabetic young rats: alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LD) and creatine kinase (CK), as well as its effects on serum lipids. We find that at a concentration of 1 mg/mL VOSO4 has no toxic effect on the liver and muscles of diabetics young rats. These findings suggest that VOSO4 may be an alternative to insulin in the near future, due to its low cost, low toxicity and ready availability.

Vanadium: a review of its potential role in the fight against diabetes

The potential role of vanadium in human health is described as a building material of bones and teeth. However, another very interesting and promising application for vanadium in human health emerges from recent studies that evaluated the role of vanadium in the management of diabetes. Vanadium is present in a variety of foods that we commonly eat. Skim milk, lobster, vegetable oils, many vegetables, grains and cereals are rich source of vanadium (>1 ppm). Fruits, meats, fish, butter, cheese, and beverages are relatively poor sources of vanadium. The daily dietary intake in humans has been estimated to vary from 10 microg to 2 mg of elemental vanadium, depending on the environmental sources of this mineral in the air, water, and food of the particular region tested. In animals, vanadium has been shown essential (1-10 microg vanadium per gram of diet). There is only circumstantial evidence that vanadium is essential for humans. However, in doses ranging from 0.083 mmol/d to 0.42 mmol/d, vanadium has shown therapeutic potential in clinical studies with patients of both insulin-dependent diabetes mellitus (IDDM) and noninsulin-dependent diabetes mellitus (NIDDM) type. Although vanadium has a significant biological potential, it has a poor therapeutic index, and attempts have been made to reduce the dose of vanadium required for therapeutic effectiveness. Organic forms of vanadium, as opposed to the inorganic sulfate salt of vanadium, are recognized as safer, more absorbable, and able to deliver a therapeutic effect up to 50% greater than the inorganic forms. The goal is to provide vanadium with better gastrointestinal absorption, and in a form that is best able to produce the desired biological effects. As a result, numerous organic complexes of vanadium have been developed including bis(maltolato)oxovanadium (BMOV), bis(cysteinamide N-octyl)oxovanadium known as Naglivan, bis(pyrrolidine-N-carbodithioato)oxovanadium, vanadyl-cysteine methyl ester, and bis-glycinato oxovanadium (BGOV). The health benefits of vanadium and the safety and efficacy of the available vanadium supplements are discussed in this review.

Vanadate-induced activation of activator protein-1: role of reactive oxygen species

The present study was undertaken to test the hypothesis that the toxicity and carcinogenicity of vanadium might arise from elevation of reactive oxygen species leading to activation of the transcription factor activator protein-1 (AP-1). The AP-1 transactivation response has been implicated as causal in transformation responses to phorbol esters and growth factors. To investigate the possible activity of vanadium in the activation of AP-1, we treated mouse epidermal JB6 P+ cells stably transfected with an AP-1 luciferase reporter plasmid with various concentrations of vanadate. This resulted in concentration-dependent transactivation of AP-1. Superoxide dismutase (SOD) and catalase inhibited AP-1 activation induced by vanadate, indicating the involvement of superoxide anion radical (O2-*), hydroxyl radical (*OH) and/or H2O2 in the mechanism of vanadate-induced AP-1 activation. However, sodium formate, a specific *OH scavenger, did not alter vanadate-induced AP-1 activation, suggesting a minimal role for the *OH radical. NADPH enhanced AP-1 activation by increasing vanadate-mediated generation of O2-*. N-acetylcysteine, a thiol-containing antioxidant, decreased activation, further showing that vanadate-induced AP-1 activation involved redox reactions. Calphostin C, a specific inhibitor of protein kinase C (PKC), inhibited activation of AP-1, demonstrating that PKC is involved in the cell signal cascades leading to vanadate-induced AP-1 activation. Electron spin resonance (ESR) measurements show that JB6 P+ cells are able to reduce vanadate to generate vanadium(IV) in the presence of NADPH. Molecular oxygen was consumed during the vanadate reduction process to generate O2-* as measured by ESR spin trapping using 5,5-dimethyl-L-pyrroline N-oxide as the spin trapping agent. SOD inhibited the ESR spin adduct signal, further demonstrating the generation of O2-* in the cellular reduction of vanadate. These results provide support for a model in which vanadium, like other classes of tumor promoters, transactivates AP-1-dependent gene expression. In the case of vanadium, AP-1 transactivation is dependent on the generation of O2-* and H2O2, but not *OH.

Vanadate affects nuclear division and induces aberrantly-shaped cells during subsequent cytokinesis in Tetrahymena

Sodium orthovanadate at 0.1-5.0 mM affected cell proliferation of Tetrahymena in a dose-dependent manner. At 1 h the cell increment was 76-12% of the control (100%), but after lag periods in 1-5 mM the growth rate remained at 76% of control in 0.1 mM vanadate and at 64-61% of control in 0.2-5.0 mM vanadate. Endocytosis was affected in both a time- and dose-dependent manner; an increasing number of cells did not form vacuoles. Cell motility increased initially in 0.1 mM vanadate but decreased later as it did in 0.5-2.0 mM vanadate where the proportion of immobile cells increased with time. Cell divisions occurred at all concentrations but macronuclear elongation was disturbed and subsequent cytokinesis resulted in daughter cells containing the entire G2 macronucleus, a large or small portion of it, or no nucleus at all. Moreover, odd cell shapes appeared with time. The size of the cell and nucleus increased but there was great variation with disturbed cytoplasm/nucleus ratios. Treated cells had dilated rough endoplasmic reticulum that included dense material, presumed to be vanadate, which was not seen in control cells. Scant amounts of dense material were found in dense granules, small vacuoles, and abundantly in contractile vacuoles. It is argued that interference with proper microtubular function is the main effect of vanadate.

Diperoxovanadate participates in peroxidation reactions of H2O2 in presence of abundant catalase

Vanadate forms a stable complex with H2O2 at pH 7.0 in competition with catalase and the product, diperoxovanadate, resists scavenger action of catalase. Diperoxovanadate can act as a substrate in a H2O2-user reaction, horseradish peroxidase and can take the place of H2O2 far more effectively in oxidatively inactivating glyceraldehyde-3-phosphate dehydrogenase. By forming peroxo-complexes vanadate can provide a way of preserving cellular H2O2 in presence of abundant catalase and make it available for its functions.

Stimulatory effects of vanadate on amylase release from isolated rat pancreatic acini

The effects of vanadate on exocrine pancreatic function were examined in isolated rat pancreatic acini. Vanadate caused a concentration-dependent stimulation of amylase release above a concentration of 1 mM. Co-incubation of vanadate with vasoactive intestinal polypeptide, 8-bromoadenosine 3':5'-cyclic monophosphate, and the Ca2+ ionophore A23187 produced a synergistic pattern of amylase release, whereas co-incubation with cholecystokinin octapeptide (CCK-8), carbamylcholine, and 12-O-tetradecanoylphorbol 13-acetate produced an additive effect. Vanadate alone had no influence on acinar cyclic AMP content, Ca2+ efflux, or intracellular Ca2+ concentration. However, preincubation with vanadate prevented the plateau phase of CCK-8-induced Ca2+ transient increase from returning to baseline. Moreover, depletion of the intracellular Ca2+ pool by pretreatment of acini with CCK-8 in Ca2+-free medium (plus ethyleneglycol bis[beta-aminoethylether]-N,N'-tetraacetic acid) had no effect on subsequent stimulation by vanadate, although it abolished the response to both CCK-8 and carbamylcholine stimulation. The protein kinase C (PKC) inhibitors staurosporine and calphostin C significantly inhibited vanadate-stimulated amylase release, whereas the protein tyrosine kinase inhibitor genistein had no inhibitory effect. Moreover, vanadate caused a significant translocation of PKC from cytosol to membrane fraction in pancreatic acinar cells. This translocation was inhibited significantly by staurosporine and calphostin C but not by genistein. These results suggest that vanadate acts directly on pancreatic acini and stimulates amylase release by activating PKC without an effect on Ca2+ mobilization, cyclic AMP, or protein tyrosine kinase.

Kinetic analysis and comparison of uptake, distribution, and excretion of 48V-labeled compounds in rats

Vanadium has been found to be orally active in lowering plasma glucose levels; thus it provides a potential treatment for diabetes mellitus. Bis(maltolato)oxovanadium(IV) (BMOV) is a well-characterized organovanadium compound that has been shown in preliminary studies to have a potentially useful absorption profile. Tissue distributions of BMOV compared with those of vanadyl sulfate (VS) were studied in Wistar rats by using 48V as a tracer. In this study, the compounds were administered in carrier-added forms by either oral gavage or intraperitoneal injection. Data analyzed by a compartmental model, by using simulation, analysis, and modeling (i.e., SAAM II) software, showed a pattern of increased tissue uptake with use of 48V-BMOV compared with 48VS. The highest 48V concentrations at 24 h after gavage were in bone, followed by kidney and liver. Most ingested 48V was eliminated unabsorbed by fecal excretion. On average, 48V concentrations in bone, kidney, and liver 24 h after oral administration of 48V-BMOV were two to three times higher than those of 48VS, which is consistent with the increased glucose-lowering potency of BMOV in acute glucose lowering compared with VS.

Reducing agents mitigate protein synthesis inhibition mediated by vanadate and vanadyl compounds in reticulocyte lysates

Recently, we synthesized and characterized vanadyl saccharides to evaluate the effects of various vanadate and vanadyl complexes, which differ in their oxidation states on various biomacromolecules and cellular activities (1, 2). Here, we report that both vanadate (+V oxidation state) and different vanadyl species (+IV oxidation state) such as vanadyl D-glucose, vanadyl diascorbate, and vanadyl sulfate, impair the formation of polysomes and inhibit the initiation of protein synthesis in hemin-supplemented rabbit reticulocyte lysates. Vanadate inhibits protein synthesis more severely than vanadyl species and is consistent with the idea that vanadate is reduced to vanadyl state intracellularly. The inhibition of protein synthesis caused by low concentrations (10-20 microM) of vanadate and vanadyl species is effectively mitigated by reducing agents such as dithiothreitol, reduced glutathione (GSH), or reduced pyridine dinucleotide. A significant decrease in the protein synthesis inhibition in vanadate-treated lysates by GSH suggests that the mechanism of protein synthesis inhibition by vanadate is different than the action of other oxidants such as heavy metal ions and oxidized glutathione. This suggestion is also consistent with the findings that vanadium compounds do not stimulate phosphorylation of the alpha (alpha) subunit of initiation factor 2 (eIF2) or decrease the guanine nucleotide exchange activity of eIF2B, which is required to exchange GDP for GTP in eIF2.GDP binary complex. The reduction of vanadate to vanadyl state and the subsequent complex formation of vanadyl species with the endogenous reducing compounds or with the -SH groups of certain proteins may be the cause for protein synthesis inhibition in lysates.

Tyrosine kinase signaling pathways control the expression of retinoic acid receptor-alpha in SK-BR-3 breast cancer cells

Breast carcinomas are frequently characterized by hyperactivated c-erbB receptor tyrosine kinase signaling. Combination of anti-proliferative retinoids with growth-inhibitory c-erbB-specific agents might induce therapeutic benefit. We demonstrate close interactions between the c-erbB and the retinoic acid receptor system in SK-BR-3 breast cancer cells. Epidermal growth factor and heregulin-beta1 activate c-erbB receptors and dose- and time-dependently up-regulate retinoic acid receptor-alpha (RAR-alpha) mRNA. Similar effects have been found for the growth-inhibitory c-erbB-2 receptor tyrosine kinase-activating antibody 4D5 and the tyrosine phosphatase inhibitor orthovanadate. In contrast, the tyrosine kinase-inhibitor herbimycin A reduces tyrosine-specific protein phosphorylation and down-regulates RAR-alpha. Our data demonstrate that the expression of RAR-alpha, which represents a key mediator of the anti-proliferative effects of retinoids in breast cancer cells, is regulated by modulators of tyrosine kinase signaling. The levels of RAR-beta and -gamma mRNAs, however, are not affected by such agents.

Influence of vanadate on glycolysis, intracellular sodium, and pH in perfused rat hearts

Vanadium compounds have been shown to cause a variety of biological and metabolic effects including inhibition of certain enzymes, alteration of contractile function, and as an insulin like regulator of glucose metabolism. However, the influence of vanadium on metabolic and ionic changes in hearts remains to be understood. In this study we have examined the influence of vanadate on glucose metabolism and sodium transport in isolated perfused rat hearts. Hearts were perfused with 10 mM glucose and varying vanadate concentrations (0.7-100 microM) while changes in high energy phosphates (ATP and phosphocreatine (PCr)), intracellular pH, and intracellular sodium were monitored using 31P and 23Na NMR spectroscopy. Tissue lactate, glycogen, and (Na+, K+)-ATPase activity were also measured using biochemical assays. Under baseline conditions, vanadate increased tissue glycogen levels two fold and reduced (Na+, K+)-ATPase activity. Significant decreases in ATP and PCr were observed in the presence of vanadate, with little change in intracellular pH. These changes under baseline conditions were less severe when the hearts were perfused with glucose, palmitate and beta-hydroxybutyrate. During ischemia vanadate did not limit the rise in intracellular sodium, but slowed sodium recovery on reperfusion. The presence of vanadate during ischemia resulted in attenuation of acidosis, and reduced lactate accumulation. Reperfusion in the presence of vanadate resulted in a slower ATP recovery, while intracellular pH and PCr recovery was not affected. These results indicate that vanadate alters glucose utilization and (Na+, K+)-ATPase activity and thereby influences the response of the myocardium to an ischemic insult.

Decavanadate possesses alpha-adrenergic agonist activity and a structural motif common with trans-beta form of noradrenaline

Decavanadate, an inorganic polymer of vanadate, produced contraction of rat aortic rings at a relatively high concentration compared to phenylephrine, an agonist of alpha-adrenergic receptor. This effect was blocked by two known alpha-adrenergic receptor antagonists, prazosin and phenoxybenzamine. Decavanadate, formed by possible dimerization of V5 under acid conditions, possessed a structural feature of two pairs of unshared oxygen atoms at a distance of 3.12 A, not found in its constituents of V4 or V5. A structural motif of O..O..O using such oxygen atoms is recognized in decavanadate. This matches with a similar motif of N..O..O that uses the essential amino and hydroxyl groups of the side-chain and the m-hydroxyl group in trans-beta form of noradrenaline. The interaction of such a structural motif with the membrane receptor is likely to be the basis of the unusual noradrenaline-mimic action of decavanadate.

Vanadium salts as insulin substitutes: mechanisms of action, a scientific and therapeutic tool in diabetes mellitus research

Vanadium and its compounds exhibit a wide variety of insulin-like effects. In this review, these effects are discussed with respect to the treatment of type I and type II diabetes in animal models, in vitro actions, antineoplastic role, treatment of IDDM and NIDDM patients, toxicity, and the possible mechanism(s) involved. Newly established CytPTK plays a major role in the bioresponses of vanadium. It has a molecular weight of approximately 53 kDa and is active in the presence of Co2+ rather than Mn2+. Among the protein-tyrosine kinase blockers, staurosporine is found to be a potent inhibitor of CytPTK but a poor inhibitor of InsRTK. Vanadium inhibits PTPase activity, and this in turn enhances the activity of protein tyrosine kinases. Our data show that inhibition of PTPase and protein tyrosine kinase activation has a major role in the therapeutic efficacy of vanadium in treating diabetes mellitus.

Vesamicol, an inhibitor of acetylcholine vesicle packaging, increases synaptophysin phosphorylation in rat cortical synaptosomes

Vesamicol (AH5183) is an inhibitor (IC50, 50 nM) of acetylcholine (ACh) vesicle packaging. Vesamicol increases the phosphorylation pattern of synaptophysin (p38), identified as a vesicle-specific phosphoprotein involved in vesicle-mediated neurotransmitter release. Percoll fractionation of the rat cortex yielded a cholinergic-enriched synaptosomal Fraction 4. Fraction 4 contained the highest enrichment of cholineacetyl-transferase activity (86 +/- 4.6 mumole AcCh/g protein/hr.) in the Percoll gradient. Fraction 4 demonstrated oxygen consumption (108 +/- 23.4 nmole/mg protein), levels of adenosine triphosphate, ATP, (10.29 +/- 0.45 nmole/mg protein) and adenosine diphosphate, ADP, (10.54 +/- 2.72 nmole/mg protein), energy potential (ATP/[ADP] [Pi], (0.49) phosphate uptake (65-80 nmoles phosphate/mg tissue), 32Pi labelling (130 +/- 12 x 10(5) DPM/mg tissue; 74 +/- 9.8 x 10(2) nmoles phosphate/mg tissue). Synaptophysin was identified by Western blotting and confirmed by qualitative immunoprecipitation. Synaptophysin phosphorylation was confirmed by autoradiograph. Synaptophysin phosphorylation increased (225%) in the presence of vesamicol (ED50, 1 nM) in Fraction 4. Vesamicol (50 nM) and vanadate (54 microM) were compared for their effects on synaptophysin. This study suggests that during the inhibition of acetylcholine packaging by vesamicol that synaptophysin is phosphorylated. Therefore, the phosphorylation and dephosphorylation of synaptophysin may be involved in the transport of acetylcholine in or out of the synaptic vesicle.

Effect of vanadate on the activity of rat jejunal 6-phosphofructo-1-kinase

The effect of sodium orthovanadate on the activity of 6-phosphofructo-1-kinase (PFK) in the epithelial cells of rat small intestine was investigated. Injection of vanadate (2.5 mg/rat) into rats at 2-day intervals per week for two consecutive weeks resulted in a significant decrease in the maximal activities and activity ratios (activity at 0.5 mM fructose-6-phosphate at pH 7.0/activity at pH 8.0 [v0.5/V]) of the partially purified PFK in rat jejunum. Also, the sensitivity of jejunal PFK to inhibition by ATP increased in rats treated with vanadate. The addition of 1 microM fructose-2,6-biphosphate and 50 microM AMP in the assays released the enzyme inhibition by ATP, and no significant difference was seen between vanadate-injected and control rats. Moreover, the extent of activation with 1 microM fructose-2,6-bisphosphate was significantly higher (79%) in vanadate-injected rats than in control rats (26%). The present results indicate that rat jejunal PFK is highly inhibited with vanadate in vivo. Therefore, although vanadate has been considered to be an insulin-like agent, because of its insulin-like effects on adipocytes and skeletal muscle, the present results may indicate that this behavior could not be applicable to normal rat tissues, because the effect of vanadate on jejunal PFK is clearly opposite that of insulin.

Effect of vanadate on glucose transporter (GLUT4) intrinsic activity in skeletal muscle plasma membrane giant vesicles

Maximally effective concentrations of vanadate (a phosphotyrosine phosphatase inhibitor) increase glucose transport in muscle less than maximal insulin stimulation. This might be due to vanadate-induced decreased intrinsic activity of GLUT4 accompanying GLUT4 translocation. Thus, the effect of vanadate (NaVO3) on glucose transporter (GLUT4) intrinsic activity (V(max) = intrinsic activity x [GLUT4 protein]) was studied in muscle plasma membrane giant vesicles. Giant vesicles (average diameter 7.6 microns) were produced by collagenase treatment of rat skeletal muscle. The vesicles were incubated for 1.5 h with concentrations of vanadate ranging from 3 to 40 mmol l-1 at 34 degrees C before being used for determination of glucose transport. The dose-response curve showed that vanadate decreased the specific D-glucose uptake by a maximum of 70% compared with a control preparation. The vanadate-induced decrease in glucose uptake was not due to a decrease in number of vesicles. To further verify the apparent vanadate-induced decrease in GLUT4 intrinsic activity, the kinetics of glucose transport were also examined. In the presence of 10 mmol l-1 vanadate the V(max) and K(m) were decreased (P < 0.05, n = 6) 55% and 60%, respectively, compared with control. The plasma membrane GLUT4 protein content was not changed in response to vanadate. It is concluded that vanadate decreased glucose transport per GLUT4 (intrinsic activity). This finding suggests that regulation of glucose transport in skeletal muscle can involve changes in GLUT4 intrinsic activity.

Activation of the HIV long terminal repeat and viral production by H2O2-vanadate

The long terminal repeat (LTR) of human immunodeficiency virus type 1 (HIV-1) contains sequences required for the initiation of gene transcription. Among the substances known to activate the HIV-1 LTR is hydrogen peroxide (H2O2). We report here that H2O2-induced activation of the LTR in the macrophage cell line THP-1 and the lymphocyte cell line, Jurkat, is greatly increased by vanadate. Activation of the LTR by phorbol myristate acetate, tumor necrosis factor alpha, lipopolysaccharide, or Staphylococcus epidermidis extract was not increased by vanadate, indicating some selectivity for H2O2. H2O2 and vanadate also acted synergistically to increase the production of HIV-1 virions by the latently infected macrophage cell line U-1 as determined by p24 antigen release and the detection of intact virions by electron microscopy. Effects were observed at H2O2 and vanadate concentrations down to 3 x 10(-6) M, with high concentrations leading to cell toxicity. Catalase was strongly inhibitory when added prior to the interaction of H2O2 and vanadate, but was considerably less inhibitory when the H2O2 and vanadate were allowed to preincubate prior to the catalase addition. H2O2 reacts with vanadate to form peroxides of vanadate that have potent biological effects. Our findings suggest that among these is the activation of the HIV-1 LTR.

Vanadium salts stimulate mitogen-activated protein (MAP) kinases and ribosomal S6 kinases

Effect of several vanadium salts, sodium orthovanadate, vanadyl sulfate and sodium metavanadate on protein tyrosine phosphorylation and serine/threonine kinases in chinese hamster ovary (CHO) cells overexpressing a normal human insulin receptor was examined. All the compounds stimulated protein tyrosine phosphorylation of two major proteins with molecular masses of 42 kDa (p42) and 44 kDa (p44). The phosphorylation of p42 and p44 was associated with an activation of mitogen activated protein (MAP) kinase as well as increased protein tyrosine phosphorylation of p42mapk and p44mapk. Vanadium salts also activated the 90 kDa ribosomal s6 kinase (p90rsk) and 70 kDa ribosomal s6 kinase (p70s6k). Among the three vanadium salts tested, vanadyl sulfate appeared to be slightly more potent than others in stimulating MAP kinases and p70s6k activity. It is suggested that vanadium-induced activation of MAP kinases and ribosomal s6 kinases may be one of the mechanisms by which insulin like effects of this trace element are mediated.

Mechanisms of inotropic responses of the isolated rat hearts to vanadate

In view of the invariable development of insulin resistance in different types of cardiovascular diseases, considerable attention has been focused on vanadate because of its ability to exert insulin-like effects in the body. Since vanadate, like insulin, has been shown to exert a beneficial effect in diabetic cardiomyopathy, this study was undertaken to examine the mechanisms of its action on the heart. Vanadate, at 5-10 microM concentrations, produced a positive inotropic effect in the isolated perfused rat heart, whereas at higher concentrations (20 microM), it decreased the contractile force development. The positive inotropic effect of 10 microM vanadate was not affected by the pretreatment of animals with reserpine as well as the presence of propranolol or phenoxybenzamine in the perfusion medium. The increase in contractile force development due to vanadate at low (0.3-0.6 mM) concentrations of Ca2+ was markedly augmented, but this agent produced a negative inotropic action at high concentrations of Ca2+ (2.0-3.0 mM). Preperfusion of hearts with verapamil enhanced the positive inotropic effect of vanadate whereas hearts preperfused with ouabain, low sodium or amiloride showed negative inotropic effects of vanadate. Vanadate was found to inhibit sarcoplasmic reticular Ca(2+)-pump and sarcolemmal Ca(2+)-pump as well as Na(+)-K(+)-ATPase activities but the sarcolemmal effects were evident at lower concentrations in comparison to that on the sarcoplasmic reticulum. The actions of vanadate on membrane Ca2+ transport and ATPase systems were specific since this agent exerted no effect on sarcolemmal Na(+)-Ca2+ exchange or myofibrillar ATPase activities. In isolated cardiomyocytes suspended in buffer containing 0.5 or 1.0 mM Ca2+, vanadate increased the intracellular concentration of Ca2+; this increase in intracellular Ca2+ was more pronounced at 0.5 mM Ca2+. These results indicate that increased intracellular concentration of Ca2+ due to inhibition of sarcolemmal Na(+)-K(+)-ATPase and sarcolemmal Ca(2+)-pump may be the primary mechanism of the positive inotropic action of vanadate in the heart. It is suggested that vanadate may serve as an inotropic agent and that this mechanism may contribute towards its beneficial effects on cardiac dysfunction in different cardiovascular diseases.

Vanadate enhances insulin-receptor binding in gestational diabetic human placenta

Although vanadium is found abundantly in animal and plant kingdoms its biological effects are not clear. Vanadate compounds have been shown to normalize blood glucose levels in streptozotocin treated rats, enhance glucose oxidation and improve the sensitivity to insulin by enhanced receptor binding in rat adipocytes. The aim of the present study was to investigate the effect of vanadate, at high (0-8 mmol l-1) and low (0-1.0 mmol l-1) physiological concentrations, on [125I]-insulin binding in the placenta of three groups of patients, namely from normal (N) controls, gestational diabetics (GDM) and women with risk factors in their medical history for developing diabetes mellitus (RF). Vanadate at low concentrations (0.2-0.6 mmol l-1) enhanced the maximal binding 2-fold in GDM placenta but only increased (up to 1.2-fold) the binding slightly at high concentrations (5 mmol l-1). However with placenta from normal or women at risk, vanadate increased the [125I]-insulin binding up to 1.2-fold both at low and high concentrations. Thus it appears that vanadate augments insulin binding in the placenta from women with gestational diabetes mellitus.

Vanadate, molybdate and tungstate for orthomolecular medicine

Recent studies indicate that oxyanions, such as vanadate (V) or vanadyl (IV), cause insulin-like effects on rats by stimulating the insulin receptor tyrosine kinase. Tungstate (VI) and molybdate (VI) show the same effects on rat adipocytes and hepatocytes. Results of uncontrolled trials on volunteers accumulated in Japan also suggest that tungstate effectively regulates diabetes mellitus without detectable side effects. Since these oxyanions naturally exist in organisms, oxyanion therapy, the oral administration of vanadate, vanadyl, molybdate, or tungstate, can be considered to be orthomolecular medicine. Therefore, these oxyanions may provide a viable alternative to chemotherapy. Many diseases in addition to diabetes mellitus might also be treated since the implication of these results is that tyrosine kinases are involved in a variety of diseases.

Acute systemic vanadate poisoning presenting as cerebrovascular ischemia with prolonged reversible neurological deficits (PRIND)

A 22-year-old woman is reported who attempted suicide by oral ingestion of approximately 10-15 g ammonium metavanadate (NH4VO3). A few hours later she developed gastrointestinal symptoms followed by a transient right sensomotor hemiparesis and aphasic disturbances. Brain MRI and SPECT with 99mTc-HMPAO revealed a lesion in the left parietal cortex. Plasmapheresis, ascorbic acid and desferoxamine led to a complete clinical recovery within a few days.

Multiple reactions in vanadyl-V(IV) oxidation by H2O2

Oxidation of vanadyl sulfate by H2O2 involves multiple reactions at neutral pH conditions. The primary reaction was found to be oxidation of V(IV) to V(V) using 0.5 equivalent of H2O2, based on the loss of blue color and the visible spectrum. The loss of V(IV) and formation V(V) compounds were confirmed by ESR and 51V-NMR spectra, respectively. In the presence of excess H2O2 (more than two equivalents), the V(V) was converted into diperoxovanadate, the major end-product of these reactions, identified by changes in absorbance in ultraviolet region and by the specific chemical shift in NMR spectrum. The stoichiometric studies on the H2O2 consumed in this reaction support the occurrence of reactions of two-electron oxidation followed by complexing two molecules of H2O2. Addition of a variety of compounds--Tris, ethanol, mannitol, benzoate, formate (hydroxyl radical quenching), histidine, imidazole (singlet oxygen-consumption that also used V(IV) as the reducing source. This reaction requires concomitant oxidation of vanadyl by H2O2, favoured at low H2O2:V(IV) ratio. Another secondary reaction of oxygen release was found to occur during vanadyl oxidation by H2O2 in acidic medium in which the end-product was not diperoxovanadate but appears to be a mixture of VO3+ (-546 ppm), VO3+ (-531 ppm) and VO2+ (-512 ppm), as shown by the 51V-NMR spectrum. This reaction also occurred in phosphate-buffered medium but only on second addition of vanadyl. The compounds that stimulated the oxygen-consumption reaction were found to inhibit the oxygen-release reaction. A combination of these reactions occur depending on the proportion of the reactants (vanadyl and H2O2), the pH of the medium and the presence of some compounds that affect the secondary reactions.

Interaction of vanadate and iodate oxyanions with adenylyl cyclase of ciliary processes

Vanadate (VO3-) was found to activate adenylyl cyclase (AC) in ocular ciliary process membrane. This response was additive to that of isoproterenol (ISO) and vasoactive intestinal peptide (VIP), but it was potentiative with forskolin (FSK) and also with Ca2+/calmodulin activation of AC activity. The potentiated response of FSK in the presence of VO3- was due to an increase in Vmax without a change in the apparent affinity of FSK or VO3-, and therefore differs from the potentiated response of activated G-protein (Gs) and FSK, where the affinity of FSK was increased by 1-2 orders of magnitude. Potentiation occurred at low Mg2+ and was not observed at free [Mg2+] > 3 mM. Iodate (IO3-) inhibited the FSK, ISO, and VO3- activations of AC in ciliary process membranes (IC50, 0.3 mM). In vivo topical treatment of the rabbit eye with 50 microL of 5% NaIO3 had no effect alone but completely blocked the intraocular pressure response to a 50-microL topical dose of 1% FSK and partially blocked the response to a 50-microL dose of 0.001% ISO. These findings indicate that some AC enzymes may have a binding site for oxyanions which can directly regulate enzyme activity.

Impaired antioxidant status in diabetic rat liver. Effect of vanadate

In vivo effects of vanadate on the antioxidant status of control and alloxan diabetic rats liver were examined. The increased oxidative stress during diabetes caused a decline in the activities of glutathione peroxidase (GPx), catalase (CAT), CuZn superoxide dismutase (CuZn-SOD) and Mn-superoxide dismutase (Mn-SOD) in the liver. Reduced glutathione (GSH) was also depleted, but the level of oxidized glutathione and glutathione reductase activity remained unchanged in the livers of diabetic rats. Vanadate treatment of diabetic rats (0.6 mg/mL in drinking water) resulted in almost complete restoration of GPx and Mn-SOD but caused only a partial restoration of CuZn-SOD. However, CAT and GSH were found to be lowered further in vanadate-treated diabetic rats as compared to untreated diabetic rat. Similar decreases in CAT and GSH levels were also observed in the vanadate-treated controls. These results suggest that vanadate, an insulin-mimetic agent, effectively normalized hyperglycemia, but unlike insulin, could not completely restore the altered endogenous defence mechanisms in diabetic liver.

Role of vanadium in nutrition: metabolism, essentiality and dietary considerations

Vanadium is a pervasive element of biological systems, being widely distributed across the food supply. Food refining and processing appear to increase vanadium content. At higher intakes, it accumulates in body tissues such as liver, kidney and bone. Essentiality of the nutrient has been established in lower life forms but the significance and extent of vanadium's role in humans has been overshadowed by the absence of deficiency symptoms in man. While the pharmacological properties of vanadium have stimulated much interest, knowledge of basic metabolic processes regulating vanadium remains incomplete. Ultimate determination of essentiality for humans will depend on greater understanding of the fundamental biochemical roles of vanadium.

Polyvanadate-stimulated NADH oxidation by plasma membranes--the need for a mixture of deca and meta forms of vanadate

Polyvanadate solutions obtained by extracting vanadium pentoxide with dilute alkali over a period of several hours contained increasing amounts of decavanadate as characterized by NMR and ir spectra. Those solutions having a metavanadate:decavanadate ratio in the range of 1-5 showed maximum stimulation of NADH oxidation by rat liver plasma membranes. Reduction of decavanadate, but not metavanadate, was obtained only in the presence of the plasma membrane enzyme system. High simulation of activity of NADH oxidation was obtained with a mixture of the two forms of vanadate and this further increased on lowering the pH. Addition of increasing concentrations of decavanadate to metavanadate and vice versa increased the stimulatory activity, reaching a maximum when the metavanadate:decavanadate ratio was in the range of 1-5. Increased stimulatory activity can also be obtained by reaching these ratios by conversion of decavanadate to metavanadate by alkaline phosphate degradation, and of metavanadate to decavanadate by acidification. These studies show for the first time that both deca and meta forms of vanadate present in polyvanadate solutions are needed for maximum activity of NADH oxidation.

Characterization of oxygen free radicals generated during vanadate-stimulated NADH oxidation

The oxidation of NADH and accompanying reduction of oxygen to H2O2 stimulated by polyvanadate was markedly inhibited by SOD and cytochrome c. The presence of decavanadate, the polymeric form, is necessary for obtaining the microsomal enzyme-catalyzed activity. The accompanying activity of reduction of cytochrome c was found to be SOD-insensitive and therefore does not represent superoxide formation. The reduction of cytochrome c by vanadyl sulfate was also SOD-insensitive. In the presence of H2O2, all the forms of vanadate were able to oxidize reduced cytochrome c, which was sensitive to mannitol, tris and also catalase, indicating H2O2-dependent generation of hydroxyl radicals. Using ESR and spin trapping technique only hydroxyl radicals, but not superoxide anion radicals, were detected during polyvanadate-dependent NADH oxidation.

Desferrioxamine enhances the reactivity of vanadium (IV) and vanadium (V) toward ferri- and ferrocytochrome c

Ligands, especially desferrioxamine, affect the rate at which vanadium reduces or oxidizes cytochrome c. Whether reduction or oxidation occurs, and how fast, depends on the nature of the ligand, the state of reduction of the vanadium, the pH (6.0, 7.0, or 7.4), and the availability of oxygen. In general, oxidation of ferrocytochrome c was favored by (1) low pH, (2) an oxidized state of the vanadium, (3) the presence of oxygen, and (4) more strongly binding ligands (desferrioxamine much greater than histidine = ATP greater than EDTA greater than albumin greater than aquo). Thus, at pH 6.0, desferrioxamine accelerated the V(V)-catalyzed ferrocytochrome c oxidation 160-fold aerobically, and 3500-fold anaerobically. In general, strongly binding ligands slowed oxidations, especially at higher pH. Desferrioxamine was unique among the five ligands in that it not only accelerated oxidation of ferrocytochrome c at pH 6.0, but at pH 7.4 the redox balance shifted to the point where it paradoxically reduced ferricytochrome c. V(V) is an improbable electron donor, but desferrioxamine will reduce cytochrome c, and V(V) accelerates this process. Oxidation of cytochrome c by V(V):desferrioxamine was faster anaerobically, and reduction by V(IV):desferrioxamine was faster aerobically. Although V(V) did not oxidize ferrocytochrome c at pH 7.4, V(IV) did, provided oxygen and desferrioxamine were both present. V(IV):desferrioxamine almost completely reduced ferricytochrome c, and this reduction was followed by a slow, progressive oxidation. This latter oxidation of cytochrome c is mediated by active species generated in the reaction between V(IV):desferrioxamine and oxygen, because none of these reagents alone can induce oxidation at a comparable rate. The mediating species were transient, and generated in reactions with oxygen.(ABSTRACT TRUNCATED AT 250 WORDS)

Sodium-dependent magnesium uptake by ferret red cells

1. Magnesium uptake can be measured in ferret red cells incubated in media containing more than 1 mM-magnesium. Uptake is substantially increased if the sodium concentration in the medium is reduced. 2. Magnesium uptake is half-maximally activated by 0.37 mM-external magnesium when the external sodium concentration is 5 mM. Increasing the external sodium concentration increases the magnesium concentration needed to activate the system. 3. Magnesium uptake is increased by reducing the external sodium concentration. Uptake is half-maximum at sodium concentrations of 17, 22 and 62 nM when the external magnesium concentrations are 2, 5 and 10 mM respectively. 4. Replacement of external sodium with choline does not affect the membrane potential of ferret red cells over a 45 min period. 5. Magnesium uptake from media containing 5 mM-sodium is inhibited by amiloride, quinidine and imipramine. It is not affected by ouabain or bumetanide. Vanadate stimulates magnesium uptake but has no effect on magnesium efflux. 6. When cell ATP content is reduced to 19 mumol (1 cell)-1 by incubating cells for 3 h with 2-deoxyglucose, magnesium uptake falls by 50% in the presence of 5 mM-sodium and is completely abolished in the presence of 145 mM-sodium. Some of the inhibition may be due to the increase in intracellular ionized magnesium concentration ([Mg2+]i) from 0.7 to 1.0 mM which occurs under these conditions. 7. Magnesium uptake can be driven against a substantial electrochemical gradient if the external sodium concentration is reduced sufficiently. 8. These findings are discussed in terms of several possible models for magnesium transport. It is concluded that the majority of magnesium uptake observed in low-sodium media is via sodium-magnesium antiport. A small portion of uptake is through a parallel leak pathway. It is believed that the antiport is responsible for maintaining [Mg2+]i below electrochemical equilibrium in these cells at physiological external sodium concentration. Thus in ferret red cells the direction of magnesium transport can be reversed by reversing the sodium gradient.