Repurposing Therapeutic Drugs Complexed to Vanadium in Cancer

Repurposing drugs by uncovering new indications for approved drugs accelerates the process of establishing new treatments and reduces the high costs of drug discovery and development. Metal complexes with clinically approved drugs allow further opportunities in cancer therapy-many vanadium compounds have previously shown antitumor effects, which makes vanadium a suitable metal to complex with therapeutic drugs, potentially improving their efficacy in cancer treatment. In this review, covering the last 25 years of research in the field, we identified non-oncology-approved drugs suitable as ligands to obtain different vanadium complexes. Metformin-decavanadate, vanadium-bisphosphonates, vanadyl(IV) complexes with non-steroidal anti-inflammatory drugs, and cetirizine and imidazole-based oxidovanadium(IV) complexes, each has a parent drug known to have different medicinal properties and therapeutic indications, and all showed potential as novel anticancer treatments. Nevertheless, the precise mechanisms of action for these vanadium compounds against cancer are still not fully understood.

Evaluation of Gold Complexes to Address Bacterial Resistance, Quorum Sensing, Biofilm Formation, and Their Antiviral Properties against Bacteriophages

The worldwide increase in antibiotic resistance poses a significant challenge, and researchers are diligently seeking new drugs to combat infections and prevent bacterial pathogens from developing resistance. Gold (I and III) complexes are suitable for this purpose. In this study, we tested four gold (I and III) complexes, (1) chlorotrimethylphosphine gold(I); (2) chlorotriphenylphosphine gold(I); (3) dichloro(2-pyridinecarboxylate) gold (III); and (4) 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene gold(I) chloride, for their antibacterial, antibiofilm, antiviral, and anti-quorum sensing activities. Results reveal that 1 significantly inhibits Escherichia coli DSM 1077 and Staphylococcus aureus ATCC 6538, while 2, 3, and 4 only inhibit S. aureus ATCC 6538. The minimum inhibitory concentration (MIC) of 1 for S. aureus ATCC 6538 is 0.59 μg/mL (1.91 μM), and for methicillin-resistant S. aureus strains MRSA 12 and MRSA 15, it is 1.16 μg/mL (3.75 μM). For E. coli DSM 1077 (Gram-negative), the MIC is 4.63 μg/mL (15 μM), and for multi-resistant E. coli I731940778-1, it is 9.25 μg/mL (30 μM). Complex 1 also disrupts biofilm formation in E. coli and S. aureus after 6 h or 24 h exposure. Moreover, 1 and 2 inhibit the replication of two enterobacteria phages. Anti-quorum sensing potential still requires further clarification. These findings highlight the potential of gold complexes as effective agents to combat bacterial and viral infections.

Metals and Metal Complexes in Diseases with a Focus on COVID-19: Facts and Opinions

In the present Special Issue on "Metals and Metal Complexes in Diseases with a Focus on COVID-19: Facts and Opinions", an attempt has been made to include reports updating our knowledge of elements considered to be potential candidates for therapeutic applications and certain metal-containing species, which are extensively being examined towards their potential biomedical use due to their specific physicochemical properties [...].

Biological Consequences of Vanadium Effects on Formation of Reactive Oxygen Species and Lipid Peroxidation

Lipid peroxidation (LPO), a process that affects human health, can be induced by exposure to vanadium salts and compounds. LPO is often exacerbated by oxidation stress, with some forms of vanadium providing protective effects. The LPO reaction involves the oxidation of the alkene bonds, primarily in polyunsaturated fatty acids, in a chain reaction to form radical and reactive oxygen species (ROS). LPO reactions typically affect cellular membranes through direct effects on membrane structure and function as well as impacting other cellular functions due to increases in ROS. Although LPO effects on mitochondrial function have been studied in detail, other cellular components and organelles are affected. Because vanadium salts and complexes can induce ROS formation both directly and indirectly, the study of LPO arising from increased ROS should include investigations of both processes. This is made more challenging by the range of vanadium species that exist under physiological conditions and the diverse effects of these species. Thus, complex vanadium chemistry requires speciation studies of vanadium to evaluate the direct and indirect effects of the various species that are present during vanadium exposure. Undoubtedly, speciation is important in assessing how vanadium exerts effects in biological systems and is likely the underlying cause for some of the beneficial effects reported in cancerous, diabetic, neurodegenerative conditions and other diseased tissues impacted by LPO processes. Speciation of vanadium, together with investigations of ROS and LPO, should be considered in future biological studies evaluating vanadium effects on the formation of ROS and on LPO in cells, tissues, and organisms as discussed in this review.

Polyoxometalates Impact as Anticancer Agents

Polyoxometalates (POMs) are oxoanions of transition metal ions, such as V, Mo, W, Nb, and Pd, forming a variety of structures with a wide range of applications. Herein, we analyzed recent studies on the effects of polyoxometalates as anticancer agents, particularly their effects on the cell cycle. To this end, a literature search was carried out between March and June 2022, using the keywords "polyoxometalates" and "cell cycle". The effects of POMs on selected cell lines can be diverse, such as their effects in the cell cycle, protein expression, mitochondrial effects, reactive oxygen species (ROS) production, cell death and cell viability. The present study focused on cell viability and cell cycle arrest. Cell viability was analyzed by dividing the POMs into sections according to the constituent compound, namely polyoxovanadates (POVs), polyoxomolybdates (POMos), polyoxopaladates (POPds) and polyoxotungstates (POTs). When comparing and sorting the IC₅₀ values in ascending order, we obtained first POVs, then POTs, POPds and, finally, POMos. When comparing clinically approved drugs and POMs, better results of POMs in relation to drugs were observed in many cases, since the dose required to have an inhibitory concentration of 50% is 2 to 200 times less, depending on the POMs, highlighting that these compounds could become in the future an alternative to existing drugs in cancer therapy.

Decavanadate and metformin-decavanadate effects in human melanoma cells

Decavanadate is a polyoxometalate (POMs) that has shown extensive biological activities, including antidiabetic and anticancer activity. Importantly, vanadium-based compounds as well as antidiabetic biguanide drugs, such as metformin, have shown to exert therapeutic effects in melanoma. A combination of these agents, the metformin-decavanadate complex, was also recognized for its antidiabetic effects and recently described as a better treatment than the monotherapy with metformin enabling lower dosage in rodent models of diabetes. Herein, we compare the effects of decavanadate and metformin-decavanadate on Ca²⁺-ATPase activity in sarcoplasmic reticulum vesicles from rabbit skeletal muscles and on cell signaling events and viability in human melanoma cells. We show that unlike the decavanadate-mediated non-competitive mechanism, metformin-decavanadate inhibits Ca²⁺-ATPase by a mixed-type competitive-non-competitive inhibition with an IC₅₀ value about 6 times higher (87 μM) than the previously described for decavanadate (15 μM). We also found that both decavanadate and metformin-decavanadate exert antiproliferative effects on melanoma cells at 10 times lower concentrations than monomeric vanadate. Western blot analysis revealed that both, decavanadate and metformin-decavanadate increased phosphorylation of extracellular signal-regulated kinase (ERK) and serine/threonine protein kinase AKT signaling proteins upon 24 h drug exposure, suggesting that the anti-proliferative activities of these compounds act independent of growth-factor signaling pathways.

The Preyssler-Type Polyoxotungstate Exhibits Anti-Quorum Sensing, Antibiofilm, and Antiviral Activities

The increase in bacterial resistance to antibiotics has led researchers to find new compounds or find combinations between different compounds with potential antibacterial action and with the ability to prevent the development of antibiotic resistance. Polyoxotungstates (POTs) are inorganic clusters that may fulfill that need, either individually or in combination with antibiotics. Herein, we report the ability of the polyoxotungstates (POTs) with Wells-Dawson P2W18, P2W17, P2W15, and Preyssler P5W30 type structures to differently affect Gram-negative and Gram-positive microorganisms, either susceptible or resistant to antibiotics. The compound P5W30 showed the highest activity against the majority of the tested bacterial strains in comparison with the other tested POTs (P2W15, P2W17 and P2W18) that did not show inhibition zones for the Gram-negative bacteria, A. baumanii I73775, E. coli DSM 1077, E. coli I73194, K. pneumoniae I7092374, and P. aeruginosa C46281). Generally, the results evidenced that Gram-positive bacteria are more susceptible to the POTs tested. The compound P5W30 was the one most active against S. aureus ATCC 6538 and MRSA16, reaching <0.83 mg·mL−1 (100 μM) and 4.96 mg·mL−1 (600 μM), respectively. Moreover, it was verified by NMR spectroscopy that the most promising POT, P5W30, remains intact under all the experimental conditions, after 24 h at 37 °C. This prompted us to further evaluate the anti-quorum sensing activity of P5W30 using the biosensor Chromobacterium violaceum CV026, as well as its antibiofilm activity both individually and in combination with the antibiotic cefoxitin against the methicillin-resistant Staphylococcus aureus 16 (MRSA16). P5W30 showed a synergistic antibacterial effect with the antibiotic cefoxitin and chloramphenicol against MRSA16. Moreover, the antibiofilm activity of P5W30 was more pronounced when used individually, in comparison with the combination with the antibiotic cefoxitin. Finally, the antiviral activity of P5W30 was tested using the coliphage Qβ, showing a dose-dependent response. The maximum inactivation was observed at 750 μM (6.23 mg·mL−1). In sum, P5W30 shows anti-quorum sensing and antibiofilm activities besides being a potent antibacterial agent against S. aureus and to exhibit antiviral activities against enteric viruses.

Vanadium compounds therapeutic effects in melanoma

Background

Polyoxometalates are a diverse family of metal-oxo anions of early transitional metal ions in high oxidation states, including vanadium. Such compounds are gaining increasing interest in biomedicine due to their anti-cancer activity. Regarding melanoma, available therapies’ effectiveness is still currently limited, commonly leading to relapse. For this reason, it is vital to identify novel anti-cancer agents.

Methods

To better understand the mechanism of action involved in the anti-cancer vanadium-based compounds in melanoma, we conducted a systematic review. Search was performed in Clinical Trials, Cochrane Library, Pubmed, Scielo, and Web of Science (20/4-8/5/2020). Review articles were excluded. Inclusion criteria considered articles between 2000 and 2020, written in English, in which vanadium compounds were evaluated alone (not combined with other drugs), allowing to recognise the effects exclusively derived from vanadium.

Results

Based on the inclusion/exclusion criteria, a total of 5 articles, published between 2013 and 2020, were analyzed. All tested compounds, including Oxidovanadium(IV) complexes [VIVO(mpp)2] and [VIVO(ppp)2] (VS3, VS4), reduced cellular viability. Moreover, Vanadium pentoxide (V2O5) and Xyloglucan from Copaifera Langsdorffii complexed with Oxovanadium(IV/V) (XGC:VO), in murine B16F10 cells, and Inorganic anion vanadate (VN), [VIVO (dhp)2] (VS2), and N,N’-ethylenebis (pyridoxylideneiminato) vanadium(IV) complex [Pyr2enV(IV)], in A375 cells, induced apoptosis. VN, VS2 and Pyr2enV(IV) increased reactive oxygen species (ROS) levels in A375 cells. In vivo experiments demonstrated that V2O5 prolonged the life of mice implanted with B16F10 cells, with no systemic toxicity.

Conclusions

Several different vanadium-based compounds have anti-cancer potential in melanoma, mainly increasing apoptosis and ROS production. Specific metal-based complexes are potential melanoma treatments, which might have been previously neglected.

Rationalizing the Decavanadate(V) and Oxidovanadium(IV) Binding to G-Actin and the Competition with Decaniobate(V) and ATP

The experimental data collected over the past 15 years on the interaction of decavanadate(V) (V₁₀O₂₈^6-; V₁₀), a polyoxometalate (POM) with promising anticancer and antibacterial action, with G-actin, were rationalized by using several computational approaches (docking, density functional theory (DFT), and molecular dynamics (MD)). Moreover, a comparison with the isostructural and more stable decaniobate(V) (Nb₁₀O₂₈^6-; Nb₁₀) was carried out. Four binding sites were identified, named α, β, γ, and δ, the site α being the catalytic nucleotide site located in the cleft of the enzyme at the interface of the subdomains II and IV. It was observed that the site α is preferred by V₁₀, whereas Nb₁₀ is more stable at the site β; this indicates that, differently from other proteins, G-actin could contemporaneously bind the two POMs, whose action would be synergistic. Both decavanadate and decaniobate induce conformational rearrangements in G-actin, larger for V₁₀ than Nb₁₀. Moreover, the binding mode of oxidovanadium(IV) ion, V^IVO²⁺, formed upon the reduction of decavanadate(V) by the -SH groups of accessible cysteine residues, is also found in the catalytic site α with (His161, Asp154) coordination; this adduct overlaps significantly with the region where ATP is bound, accounting for the competition between V₁₀ and its reduction product V^IVO²⁺ with ATP, as previously observed by EPR spectroscopy. Finally, the competition with ATP was rationalized: since decavanadate prefers the nucleotide site α, Ca²⁺-ATP displaces V₁₀ from this site, while the competition is less important for Nb₁₀ because this POM shows a higher affinity for β than for site α. A relevant consequence of this paper is that other metallodrug-protein systems, in the absence or presence of eventual inhibitors and/or competition with molecules of the organism, could be studied with the same approach, suggesting important elements for an explanation of the biological data and a rational drug design.

The Aquaporin-3-Inhibiting Potential of Polyoxotungstates

Polyoxometalates (POMs) are of increasing interest due to their proven anticancer activities. Aquaporins (AQPs) were found to be overexpressed in tumors bringing particular attention to their inhibitors as anticancer drugs. Herein, we report for the first time the ability of polyoxotungstates (POTs), such as of Wells-Dawson P2W18, P2W12, and P2W15, and Preyssler P5W30 structures, to affect aquaporin-3 (AQP3) activity and impair melanoma cell migration. The tested POTs were revealed to inhibit AQP3 function with different effects, with P2W18, P2W12, and P5W30 being the most potent (50% inhibitory concentration (IC50) = 0.8, 2.8, and 3.2 µM), and P2W15 being the weakest (IC50 > 100 µM). The selectivity of P2W18 toward AQP3 was confirmed in yeast cells transformed with human aquaglyceroporins. The effect of P2W12 and P2W18 on melanoma cells that highly express AQP3 revealed an impairment of cell migration between 55% and 65% after 24 h, indicating that the anticancer properties of these compounds may in part be due to the blockage of AQP3-mediated permeability. Altogether, our data revealed that P2W18 strongly affects AQP3 activity and cancer cell growth, unveiling its potential as an anticancer drug against tumors where AQP3 is highly expressed.

Inhibition of Na+/K+- and Ca2+-ATPase activities by phosphotetradecavanadate

Polyoxometalates (POMs) are promising inorganic inhibitors for P-type ATPases. The experimental models used to study the effects of POMs on these ATPases are usually in vitro models using vesicles from several membrane sources. Very recently, some polyoxotungstates, such as the Dawson anion [P₂W₁₈O₆₂]^6-, were shown to be potent P-type ATPase inhibitors; being active in vitro as well as in ex-vivo. In the present study we broaden the spectrum of highly active inhibitors of Na⁺/K⁺-ATPase from basal membrane of epithelial skin to the bi-capped Keggin-type anion phosphotetradecavanadate Cs_5.6H_3.4PV₁₄O₄₂ (PV₁₄) and we confront the data with activity of other commonly encountered polyoxovanadates, decavanadate (V₁₀) and monovanadate (V₁). The X-ray crystal structure of PV₁₄ was solved and contains two trans-bicapped α-Keggin anions H_xPV₁₄O₄₂^(9-x)-. The anion is built up from the classical Keggin structure [(PO₄)@(V₁₂O₃₆)] capped by two [VO] units. PV₁₄ (10 μM) exhibited higher ex-vivo inhibitory effect on Na⁺/K⁺-ATPase (78%) than was observed at the same concentrations of V₁₀ (66%) or V₁ (33%). Moreover, PV₁₄ is also a potent in vitro inhibitor of the Ca²⁺-ATPase activity (IC₅₀ 5 μM) exhibiting stronger inhibition than the previously reported activities for V₁₀ (15 μM) and V₁ (80 μM). Putting it all together, when compared both P-typye ATPases it is suggested that PV₁₄ exibited a high potential to act as an in vivo inhibitor of the Na⁺/K⁺-ATPase associated with chloride secretion.

Polyoxometalates as Potential Next-Generation Metallodrugs in the Combat Against Cancer

Polyoxometalates (POMs) are an emerging class of inorganic metal oxides, which over the last decades demonstrated promising biological activities by the virtue of their great diversity in structures and properties. They possess high potential for the inhibition of various tumor types; however, their unspecific interactions with biomolecules and toxicity impede their clinical usage. The current focus of the field of biologically active POMs lies on organically functionalized and POM-based nanocomposite structures as these hybrids show enhanced anticancer activity and significantly reduced toxicity towards normal cells in comparison to unmodified POMs. Although the antitumor activity of POMs is well documented, their mechanisms of action are still not well understood. In this Review, an overview is given of the cytotoxic effects of POMs with a special focus on POM-based hybrid and nanocomposite structures. Furthermore, we aim to provide proposed mode of actions and to identify molecular targets. POMs are expected to develop into the next generation of anticancer drugs that selectively target cancer cells while sparing healthy cells.

Polyoxovanadate inhibition of Escherichia coli growth shows a reverse correlation with Ca2+-ATPase inhibition

Polyoxovanadates were recently found to be the most active among a series of polyoxometalates against bacteria. In this study, a reverse correlation was found between the Ca²⁺-ATPase IC₅₀ and the E. Coli GI₅₀ values.

The P-type ATPase inhibiting potential of polyoxotungstates

Polyoxometalates (POMs) are transition metal complexes that exhibit a broad diversity of structures and properties rendering them promising for biological purposes. POMs are able to inhibit a series of biologically important enzymes, including phosphatases, and thus are able to affect many biochemical processes. In the present study, we analyzed and compared the inhibitory effects of nine different polyoxotungstates (POTs) on two P-type ATPases, Ca2+-ATPase from skeletal muscle and Na+/K+-ATPase from basal membrane of skin epithelia. For Ca2+-ATPase inhibition, an in vitro study was performed and the strongest inhibitors were determined to be the large heteropolytungstate K9(C2H8N)5[H10Se2W29O103] (Se2W29) and the Dawson-type POT K6[α-P2W18O62] (P2W18) exhibiting IC50 values of 0.3 and 0.6 μM, respectively. Promising results were also shown for the Keggin-based POTs K6H2[CoW11TiO40] (CoW11Ti, IC50 = 4 μM) and Na10[α-SiW9O34] (SiW9, IC50 = 16 μM), K14[As2W19O67(H2O)] (As2W19, IC50 = 28 μM) and the lacunary Dawson K12[α-H2P2W12O48] (P2W12, IC50 = 11 μM), whereas low inhibitory potencies were observed for the isopolytungstate Na12[H4W22O74] (W22, IC50 = 68 μM) and the Anderson-type Na6[TeW6O24] (TeW6, IC50 = 200 μM). Regarding the inhibition of Na+/K+-ATPase activity, for the first time an ex vivo study was conducted using the opercular epithelium of killifish in order to investigate the effects of POTs on the epithelial chloride secretion. Interestingly, 1 μM of the most potent Ca2+-ATPase inhibitor, Se2W29, showed only a minor inhibitory effect (14% inhibition) on Na+/K+-ATPase activity, whereas almost total inhibition (99% inhibition) was achieved using P2W18. The remaining POTs exhibited similar inhibition rates on both ATPases. These results reveal the high potential of some POTs to act as P-type ATPase inhibitors, with Se2W29 showing high selectivity towards Ca2+-ATPase.

The antibacterial activity of polyoxometalates: structures, antibiotic effects and future perspectives

Polyoxometalates (POMs) are, mostly anionic, metal oxide compounds that span a wide range of tunable physical and chemical features rendering them very interesting for biological purposes, an continuously emerging but little explored field. Due to their biological and biochemical effects, including antitumor, -viral and -bacterial properties, POMs and POM-based systems are considered as promising future metallodrugs. In this article, we focus on the antibacterial activity of POMs and their therapeutic potential in the battle against bacteria and their increasing resistance against pharmaceuticals. Recent advances in the synthesis of POMs are highlighted, with emphasis on the development and properties of biologically active POM-based hybrid and nanocomposite structures. By analysing the antibacterial activity and structure of POMs, putative mode of actions are provided, including potential targets for POM-protein interactions, and a structure-activity-relationship was established for a series of POMs against two bacteria, namely Helicobacter pylori and Streptococcus pneumoniae.

An EXAFS Approach to the Study of Polyoxometalate-Protein Interactions: The Case of Decavanadate-Actin

EXAFS and XANES experiments were used to assess decavanadate interplay with actin, in both the globular and polymerized forms, under different conditions of pH, temperature, ionic strength, and presence of ATP. This approach allowed us to simultaneously probe, for the first time, all vanadium species present in the system. It was established that decavanadate interacts with G-actin, triggering a protein conformational reorientation that induces oxidation of the cysteine core residues and oxidovanadium (V^IV) formation. The local environment of vanadium's absorbing center in the [decavanadate-protein] adducts was determined, a V-S_Cys coordination having been verified experimentally. The variations induced in decavanadate's EXAFS profile by the presence of actin were found to be almost totally reversed by the addition of ATP, which constitutes a solid proof of decavanadate interaction with the protein at its ATP binding site. Additionally, a weak decavanadate interplay with F-actin was suggested to take place, through a mechanism different from that inferred for globular actin. These findings have important consequences for the understanding, at a molecular level, of the significant biological activities of decavanadate and similar polyoxometalates, aiming at potential pharmacological applications.

Ecotoxicological assessment of the anticancer drug cisplatin in the polychaete Nereis diversicolor

Anticancer drugs are designed to inhibit tumor cell proliferation by interacting with DNA and altering cellular growth factors. When released into the waterbodies of municipal and hospital effluents these pharmaceutical compounds may pose a risk to non-target aquatic organisms, due to their mode of action (cytotoxic, genotoxic, mutagenic and teratogenic). The present study aimed to assess the ecotoxicological potential of the alkylating agent cisplatin (CisPt) to the polychaete Nereis diversicolor, at a range of relevant environmental concentrations (i.e. 0.1, 10 and 100ngPtL^-1). Behavioural impairment (burrowing kinetic impairment), ion pump effects (SR Ca²⁺-ATPase), neurotoxicity (AChE activity), oxidative stress (SOD, CAT and GPXs activities), metal exposure (metallothionein-like proteins - MTLP), biotransformation (GST), oxidative damage (LPO) and genotoxicity (DNA damage), were selected as endpoints to evaluate the sublethal responses of the ragworms after 14-days of exposure in a water-sediment system. Significant burrowing impairment occurred in worms exposed to the highest CisPt concentration (100ngPtL^-1) along with neurotoxic effects. The activity of antioxidant enzymes (SOD, CAT) and second phase biotransformation enzyme (GST) was inhibited but such effects were compensated by MTLP induction. Furthermore, LPO levels also increased. Results showed that the mode of action of cisplatin may pose a risk to this aquatic species even at the range of ngL^-1.

Characterization of decavanadate and decaniobate solutions by Raman spectroscopy

The decaniobate ion, (Nb10 = [Nb10O28](6-)) being isoelectronic and isostructural with the decavanadate ion (V10 = [V10O28](6-)), but chemically and electrochemically more inert, has been useful in advancing the understanding of V10 toxicology and pharmacological activities. In the present study, the solution chemistry of Nb10 and V10 between pH 4 and 12 is studied by Raman spectroscopy. The Raman spectra of V10 show that this vanadate species dominates up to pH 6.45 whereas it remains detectable until pH 8.59, which is an important range for biochemistry. Similarly, Nb10 is present between pH 5.49 and 9.90 and this species remains detectable in solution up to pH 10.80. V10 dissociates at most pH values into smaller tetrahedral vanadate oligomers such as V1 and V2, whereas Nb10 dissociates into Nb6 under mildly (10 > pH > 7.6) or highly alkaline conditions. Solutions of V10 and Nb10 are both kinetically stable under basic pH conditions for at least two weeks and at moderate temperature. The Raman method provides a means of establishing speciation in the difficult niobate system and these findings have important consequences for toxicology activities and pharmacological applications of vanadate and niobate polyoxometalates.

Decavanadate Toxicology and Pharmacological Activities: V10 or V1, Both or None?

This review covers recent advances in the understanding of decavanadate toxicology and pharmacological applications. Toxicological in vivo studies point out that V10 induces several changes in several oxidative stress parameters, different from the ones observed for vanadate (V1). In in vitro studies with mitochondria, a particularly potent V10 effect, in comparison with V1, was observed in the mitochondrial depolarization (IC50 = 40 nM) and oxygen consumption (99 nM). It is suggested that mitochondrial membrane depolarization is a key event in decavanadate induction of necrotic cardiomyocytes death. Furthermore, only decavanadate species and not V1 potently inhibited myosin ATPase activity stimulated by actin (IC50 = 0.75 μM) whereas exhibiting lower inhibition activities for Ca(2+)-ATPase activity (15 μM) and actin polymerization (17 μM). Because both calcium pump and actin decavanadate interactions lead to its stabilization, it is likely that V10 interacts at specific locations with these proteins that protect against hydrolysis but, on the other hand, it may induce V10 reduction to oxidovanadium(IV). Putting it all together, it is suggested that the pharmacological applications of V10 species and compounds whose mechanism of action is still to be clarified might involve besides V10 and V1 also vanadium(IV) species.

Cyclosporine A and tacrolimus reduce the amount of GLUT4 at the cell surface in human adipocytes: increased endocytosis as a potential mechanism for the diabetogenic effects of immunosuppressive agents

CONTEXT

Immunosuppressive agents are associated with profound metabolic side effects including new-onset diabetes and dyslipidemia after organ transplantation.

OBJECTIVE

To investigate the effects of cyclosporine A (CsA) and tacrolimus on glucose uptake and insulin signaling in human adipocytes and their impact on the regulation of cellular trafficking of the glucose transporter 4 (GLUT4).

DESIGN

Isolated human adipocytes were incubated with therapeutic concentrations of either CsA or tacrolimus, and glucose uptake and expression of insulin signaling proteins were assessed. Furthermore, we studied effects of CsA and tacrolimus on the regulation of cellular trafficking of GLUT4 in differentiated human preadipocytes and L6 cells.

RESULTS

CsA and tacrolimus had a concentration-dependent inhibitory effect on basal and insulin-stimulated (14)C-glucose uptake in adipocytes. Although phosphorylation at Tyr1146 of the insulin receptor was inhibited by tacrolimus, the phosphorylation and/or protein levels of the insulin signaling proteins IRS1/2, p85-PI3K, PKB, AS160, and mTORC1, as well as GLUT4 and GLUT1, were unchanged by CsA or tacrolimus. Furthermore, CsA and tacrolimus reduced the GLUT4 amount localized at the cell surface of differentiated human preadipocytes and L6 cells in the presence of insulin. This occurred by an increased rate of GLUT4 endocytosis, with no change in the exocytosis rate.

CONCLUSIONS

These results suggest that therapeutic concentrations of CsA and tacrolimus can inhibit glucose uptake independent of insulin signaling by removing GLUT4 from the cell surface via an increased rate of endocytosis. This mechanism can contribute to the development of insulin resistance and diabetes associated with immunosuppressive therapy. In addition, it may provide novel pharmacological approaches for the treatment of diabetes.

Decavanadate in vitro and in vivo effects: facts and opinions

This review covers recent advances in the understanding of the in vitro and in vivo effects of decavanadate, (V10O28)(6-), particularly in mitochondria. In vivo toxicological studies involving vanadium rarely account for the fact that under physiological conditions some vanadium may be present in the form of the decavanadate ion, which may behave differently from ortho- and metavanadates. It has for example been demonstrated that vanadium levels in heart or liver mitochondria are increased upon decavanadate exposure. Additionally, in vitro studies have shown that mitochondrial depolarization (IC50, 40 nM) and oxygen consumption (IC50, 99 nM) are strongly affected by decavanadate, which causes reduction of cytochrome b (complex III). We review these recent findings which together suggest that the observed cellular targets, metabolic pathway and toxicological effects differ according to the species of vanadium present. Finally, the toxicological effects of decavanadate depend on several factors such as the mode of administration, exposure time and type of tissue.

Ion pumps as biological targets for decavanadate

The putative applications of poly-, oligo- and mono-oxometalates in biochemistry, biology, pharmacology and medicine are rapidly attracting interest. In particular, these compounds may act as potent ion pump inhibitors and have the potential to play a role in the treatment of e.g. ulcers, cancer and ischemic heart disease. However, the mechanism of action is not completely understood in most cases, and even remains largely unknown in other cases. In the present review we discuss the most recent insights into the interaction between mono- and polyoxometalate ions with ion pumps, with particular focus on the interaction of decavanadate with Ca(2+)-ATPase. We also compare the proposed mode of action with those of established ion pump inhibitors which are currently in therapeutic use. Of the 18 classes of compounds which are known to act as ion pump inhibitors, the complete mechanism of inhibition is only known for a handful. It has, however, been established that most ion pump inhibitors bind mainly to the E2 ion pump conformation within the membrane domain from the extracellular side and block the cation release. Polyoxometalates such as decavanadate, in contrast, interact with Ca(2+)-ATPase near the nucleotide binding site domain or at a pocket involving several cytoplasmic domains, and therefore need to cross through the membrane bilayer. In contrast to monomeric vanadate, which only binds to the E2 conformation, decavanadate binds to all protein conformations, i.e. E1, E1P, E2 and E2P. Moreover, the specific interaction of decavanadate with sarcoplasmic reticulum Ca(2+)-ATPase has been shown to be non-competitive with respect to ATP and induces protein cysteine oxidation with concomitant vanadium reduction which might explain the high inhibitory capacity of V10 (IC50 = 15 μM) which is quite similar to the majority of the established therapeutic drugs.

The immunosuppressive agents rapamycin, cyclosporin A and tacrolimus increase lipolysis, inhibit lipid storage and alter expression of genes involved in lipid metabolism in human adipose tissue

Cyclosporin A (CsA), tacrolimus and rapamycin are immunosuppressive agents (IAs) associated with insulin resistance and dyslipidemia, although their molecular effects on lipid metabolism in adipose tissue are unknown. We explored IAs effects on lipolysis, lipid storage and expression of genes involved on lipid metabolism in isolated human adipocytes and/or adipose tissue obtained via subcutaneous and omental fat biopsies. CsA, tacrolimus and rapamycin increased isoproterenol-stimulated lipolysis and inhibited lipid storage by 20-35% and enhanced isoproterenol-stimulated hormone-sensitive lipase Ser552 phosphorylation. Rapamycin also increased basal lipolysis (~20%) and impaired insulin's antilipolytic effect. Rapamycin, down-regulated the gene expression of perilipin, sterol regulatory element-binding protein 1 (SREBP1) and lipin 1, while tacrolimus down-regulated CD36 and aP2 gene expression. All three IAs increased IL-6 gene expression and secretion, but not expression and secretion of TNF-α or adiponectin. These findings suggest that CsA, tacrolimus and rapamycin enhance lipolysis, inhibit lipid storage and expression of lipogenic genes in adipose tissue, which may contribute to the development of dyslipidemia and insulin resistance associated with immunosuppressive therapy.

Decavanadate, decaniobate, tungstate and molybdate interactions with sarcoplasmic reticulum Ca(2+)-ATPase: quercetin prevents cysteine oxidation by vanadate but does not reverse ATPase inhibition

Recently we demonstrated that the decavanadate (V(10)) ion is a stronger Ca(2+)-ATPase inhibitor than other oxometalates, such as the isoelectronic and isostructural decaniobate ion, and the tungstate and molybdate monomer ions, and that it binds to this protein with a 1 : 1 stoichiometry. The V(10) interaction is not affected by any of the protein conformations that occur during the process of calcium translocation (i.e. E1, E1P, E2 and E2P) (Fraqueza et al., J. Inorg. Biochem., 2012). In the present study, we further explore this subject, and we can now show that the decaniobate ion, [Nb(10) = Nb(10)O(28)](6-), is a useful tool in deducing the interaction and the non-competitive Ca(2+)-ATPase inhibition by the decavanadate ion [V(10) = V(10)O(28)](6-). Moreover, decavanadate and vanadate induce protein cysteine oxidation whereas no effects were detected for the decaniobate, tungstate or molybdate ions. The presence of the antioxidant quercetin prevents cysteine oxidation, but not ATPase inhibition, by vanadate or decavanadate. Definitive V(IV) EPR spectra were observed for decavanadate in the presence of sarcoplasmic reticulum Ca(2+)-ATPase, indicating a vanadate reduction at some stage of the protein interaction. Raman spectroscopy clearly shows that the protein conformation changes that are induced by V(10), Nb(10) and vanadate are different from the ones induced by molybdate and tungstate monomer ions. Here, Mo and W cause changes similar to those by phosphate, yielding changes similar to the E1P protein conformation. The putative reduction of vanadium(V) to vanadium(IV) and the non-competitive binding of the V(10) and Nb(10) decametalates may explain the differences in the Raman spectra compared to those seen in the presence of molybdate or tungstate. Putting it all together, we suggest that the ability of V(10) to inhibit the Ca(2+)-ATPase may be at least in part due to the process of vanadate reduction and associated protein cysteine oxidation. These results contribute to the understanding and application of these families of mono- and polyoxometalates as effective modulators of many biological processes, particularly those associated with calcium homeostasis.

mTOR inhibition with rapamycin causes impaired insulin signalling and glucose uptake in human subcutaneous and omental adipocytes

Rapamycin is an immunosuppressive agent used after organ transplantation, but its molecular effects on glucose metabolism needs further evaluation. We explored rapamycin effects on glucose uptake and insulin signalling proteins in adipocytes obtained via subcutaneous (n=62) and omental (n=10) fat biopsies in human donors. At therapeutic concentration (0.01 μM) rapamycin reduced basal and insulin-stimulated glucose uptake by 20-30%, after short-term (15 min) or long-term (20 h) culture of subcutaneous (n=23 and n=10) and omental adipocytes (n=6 and n=7). Rapamycin reduced PKB Ser473 and AS160 Thr642 phosphorylation, and IRS2 protein levels in subcutaneous adipocytes. Additionally, it reduced mTOR-raptor, mTOR-rictor and mTOR-Sin1 interactions, suggesting decreased mTORC1 and mTORC2 formation. Rapamycin also reduced IR Tyr1146 and IRS1 Ser307/Ser616/Ser636 phosphorylation, whereas no effects were observed on the insulin stimulated IRS1-Tyr and TSC2 Thr1462 phosphorylation. This is the first study to show that rapamycin reduces glucose uptake in human adipocytes through impaired insulin signalling and this may contribute to the development of insulin resistance associated with rapamycin therapy.

Sarcoplasmic reticulum calcium ATPase interactions with decaniobate, decavanadate, vanadate, tungstate and molybdate

Over the last few decades there has been increasing interest in oxometalate and polyoxometalate applications to medicine and pharmacology. This interest arose, at least in part, due to the properties of these classes of compounds as anti-cancer, anti-diabetic agents, and also for treatment of neurodegenerative diseases, among others. However, our understanding of the mechanism of action would be improved if biological models could be used to clarify potential toxicological effects in main cellular processes. Sarcoplasmic reticulum (SR) vesicles, containing a large amount of Ca(2+)-ATPase, an enzyme that accumulates calcium by active transport using ATP, have been suggested as a useful model to study the effects of oxometalates on calcium homeostasis. In the present article, it is shown that decavanadate, decaniobate, vanadate, tungstate and molybdate, all inhibited SR Ca(2+)-ATPase, with the following IC(50) values: 15, 35, 50, 400 μM and 45 mM, respectively. Decaniobate (Nb(10)), is the strongest P-type enzyme inhibitor, after decavanadate (V(10)). Atomic-absorption spectroscopy (AAS) analysis, indicates that decavanadate binds to the protein with a 1:1 decavanadate:Ca(2+)-ATPase stoichiometry. Furthermore, V(10) binds with similar extension to all the protein conformations, which occur during calcium translocation by active transport, namely E1, E1P, E2 and E2P, as analysed by AAS. In contrast, it was confirmed that the binding of monomeric vanadate (H(2)VO(4)(2-); V(1)) to the calcium pump is favoured only for the E2 and E2P conformations of the ATPase, whereas no significant amount of vanadate is bound to the E1 and E1P conformations. Scatchard plot analysis, confirmed a 1:1 ratio for decavanadate-Ca(2+)-ATPase, with a dissociation constant, k(d) of 1 μM(-1). The interaction of decavanadate V(10)O(28)(6-) (V(10)) with Ca(2+)-ATPase is prevented by the isostructural and isoelectronic decaniobate Nb(10)O(28)(6-) (Nb(10)), whereas no significant effects were detected with ATP or with heparin, a known competitive ATP binding molecule, suggesting that V(10) binds non-competitively, with respect to ATP, to the protein. Finally, it was shown that decaniobate inhibits SR Ca(2+)-ATPase activity in a non competitive type of inhibition, with respect to ATP. Taken together, these data demonstrate that decameric niobate and vanadate species are stronger inhibitors of the SR calcium ATPase than simple monomeric vanadate, tungstate and molybdate oxometalates, thus affecting calcium homeostasis, cell signalling and cell bioenergetics, as well many other cellular processes. The ability of these oxometalates to act either as phosphate analogues, as a transition-state analogue in enzyme-catalysed phosphoryl group transfer processes and as potentially nucleotide-dependent enzymes modulators or inhibitors, suggests that different oxometalates may reveal different mechanistic preferences in these classes of enzymes.

Recent advances into vanadyl, vanadate and decavanadate interactions with actin

Although the number of papers about "vanadium" has doubled in the last decade, the studies about "vanadium and actin" are scarce. In the present review, the effects of vanadyl, vanadate and decavanadate on actin structure and function are compared. Decavanadate (51)V NMR signals, at -516 ppm, broadened and decreased in intensity upon actin titration, whereas no effects were observed for vanadate monomers, at -560 ppm. Decavanadate is the only species inducing actin cysteine oxidation and vanadyl formation, both processes being prevented by the natural ligand of the protein, ATP. Vanadyl titration with monomeric actin (G-actin), analysed by EPR spectroscopy, reveals a 1:1 binding stoichiometry and a K(d) of 7.5 μM(-1). Both decavanadate and vanadyl inhibited G-actin polymerization into actin filaments (F-actin), with a IC(50) of 68 and 300 μM, respectively, as analysed by light scattering assays, whereas no effects were detected for vanadate up to 2 mM. However, only vanadyl (up to 200 μM) induces 100% of G-actin intrinsic fluorescence quenching, whereas decavanadate shows an opposite effect, which suggests the presence of vanadyl high affinity actin binding sites. Decavanadate increases (2.6-fold) the actin hydrophobic surface, evaluated using the ANSA probe, whereas vanadyl decreases it (15%). Both vanadium species increased the ε-ATP exchange rate (k = 6.5 × 10(-3) s(-1) and 4.47 × 10(-3) s(-1) for decavanadate and vanadyl, respectively). Finally, (1)H NMR spectra of G-actin treated with 0.1 mM decavanadate clearly indicate that major alterations occur in protein structure, which are much less visible in the presence of ATP, confirming the preventive effect of the nucleotide on the decavanadate interaction with the protein. Putting it all together, it is suggested that actin, which is involved in many cellular processes, might be a potential target not only for decavanadate but above all for vanadyl. By affecting actin structure and function, vanadium can regulate many cellular processes of great physiological significance.

Recent perspectives into biochemistry of decavanadate

The number of papers about decavanadate has doubled in the past decade. In the present review, new insights into decavanadate biochemistry, cell biology, and antidiabetic and antitumor activities are described. Decameric vanadate species (V₁₀) clearly differs from monomeric vanadate (V₁), and affects differently calcium pumps, and structure and function of myosin and actin. Only decavanadate inhibits calcium accumulation by calcium pump ATPase, and strongly inhibits actomyosin ATPase activity (IC₅₀ = 1.4 μmol/L, V₁₀), whereas no such effects are detected with V₁ up to 150 μmol/L; prevents actin polymerization (IC₅₀ of 68 μmol/L, whereas no effects detected with up to 2 mmol/L V₁); and interacts with actin in a way that induces cysteine oxidation and vanadate reduction to vanadyl. Moreover, in vivo decavanadate toxicity studies have revealed that acute exposure to polyoxovanadate induces different changes in antioxidant enzymes and oxidative stress parameters, in comparison with vanadate. In vitro studies have clearly demonstrated that mitochondrial oxygen consumption is strongly affected by decavanadate (IC₅₀, 0.1 μmol/L); perhaps the most relevant biological effect. Finally, decavanadate (100 μmol/L) increases rat adipocyte glucose accumulation more potently than several vanadium complexes. Preliminary studies suggest that decavanadate does not have similar effects in human adipocytes. Although decavanadate can be a useful biochemical tool, further studies must be carried out before it can be confirmed that decavanadate and its complexes can be used as anticancer or antidiabetic agents.

Implications of oxidovanadium(IV) binding to actin

Oxidovanadium(IV), a cationic species (VO(2+)) of vanadium(IV), binds to several proteins, including actin. Upon titration with oxidovanadium(IV), approximately 100% quenching of the intrinsic fluorescence of monomeric actin purified from rabbit skeletal muscle (G-actin) was observed, with a V(50) of 131 μM, whereas for the polymerized form of actin (F-actin) 75% of quenching was obtained and a V(50) value of 320 μM. Stern-Volmer plots were used to estimate an oxidovanadium(IV)-actin dissociation constant, with K(d) of 8.2 μM and 64.1 μM VOSO(4), for G-actin and F-actin, respectively. These studies reveal the presence of a high affinity binding site for oxidovanadium(IV) in actin, producing local conformational changes near the tryptophans most accessible to water in the three-dimensional structure of actin. The actin conformational changes, also confirmed by (1)H NMR, are accompanied by changes in G-actin hydrophobic surface, but not in F-actin. The (1)H NMR spectra of G-actin treated with oxidovanadium(IV) clearly indicates changes in the resonances ascribed to methyl group and aliphatic regions as well as to aromatics and peptide-bond amide region. In parallel, it was verified that oxidovanadium(IV) prevents the G-actin polymerization into F-actin. In the 0-200 μM range, VOSO(4) inhibits 40% of the extent of polymerization with an IC(50) of 15.1 μM, whereas 500 μM VOSO(4) totally suppresses actin polymerization. The data strongly suggest that oxidovanadium(IV) binds to actin at specific binding sites preventing actin polymerization. By affecting actin structure and function, oxidovanadium(IV) might be responsible for many cellular effects described for vanadium.

Early disruption of the actin cytoskeleton in cultured cerebellar granule neurons exposed to 3-morpholinosydnonimine-oxidative stress is linked to alterations of the cytosolic calcium concentration

Cytoskeleton damage is a frequent feature in neuronal cell death and one of the early events in oxidant-induced cell injury. This work addresses whether actin cytoskeleton reorganization is an early event of SIN-1-induced extracellular nitrosative/oxidative stress in cultured cerebellar granule neurons (CGN). The actin polymerization state, i.e. the relative levels of G-/F-actin, was quantitatively assessed by the ratio of the fluorescence intensities of microscopy images obtained from CGN double-labelled with Alexa594-DNase-I (for actin monomers) and Bodipy-FL-phallacidin (for actin filaments). Exposure of CGN to a flux of peroxynitrite as low as 0.5-1μM/min during 30min (achieved with 0.1mM SIN-1) was found to promote alterations of the actin cytoskeleton dynamics as it increases the G-actin/F-actin ratio. Because L-type voltage-operated Ca(2+) channels (L-VOCC) are primary targets in CGN exposed to SIN-1, the possible role of Ca(2+) dynamics on the perturbation of the actin cytoskeleton was also assessed from the cytosolic Ca(2+) concentration response to the L-VOCC's agonist FPL-64176 and to the L-VOCC's blocker nifedipine. The results showed that SIN-1 induced changes in the actin polymerization state correlated with its ability to decrease Ca(2+) influx through L-VOCC. Combined analysis of cytosolic Ca(2+) concentration and G-actin/F-actin ratio alterations by SIN-1, cytochalasin D, latrunculin B and jasplakinolide support that disruption of the actin cytoskeleton is linked to cytosolic calcium concentration changes.

Actin as a potential target for decavanadate

ATP prevents G-actin cysteine oxidation and vanadyl formation specifically induced by decavanadate, suggesting that the oxometalate-protein interaction is affected by the nucleotide. The ATP exchange rate is increased by 2-fold due to the presence of decavanadate when compared with control actin (3.1×10(-3) s(-1)), and an apparent dissociation constant (k(dapp)) of 227.4±25.7 μM and 112.3±8.7 μM was obtained in absence or presence of 20 μM V(10), respectively. Moreover, concentrations as low as 50 μM of decameric vanadate species (V(10)) increases the relative G-actin intrinsic fluorescence intensity by approximately 80% whereas for a 10-fold concentration of monomeric vanadate (V(1)) no effects were observed. Upon decavanadate titration, it was observed a linear increase in G-actin hydrophobic surface (2.6-fold), while no changes were detected for V(1) (0-200 μM). Taken together, three major ideas arise: i) ATP prevents decavanadate-induced G-actin cysteine oxidation and vanadate reduction; ii) decavanadate promotes actin conformational changes resulting on its inactivation, iii) decavanadate has an effect on actin ATP binding site. Once it is demonstrated that actin is a new potential target for decavanadate, being the ATP binding site a suitable site for decavanadate binding, it is proposed that some of the biological effects of vanadate can be, at least in part, explained by decavanadate interactions with actin.

Peroxynitrite-mediated oxidative modifications of myosin and implications on structure and function

Abstract The peroxynitrite-induced functional impairment of myosin was studied in different reaction conditions, known to alter the oxidative chemistry of peroxynitrite, to better understand the molecular mechanisms of this interaction. It is shown that peroxynitrite is able to enhance the basal MgATPase activity up to 2-fold while inhibiting the actin-stimulated ATPase activity of myosin and that the extent of these functional alterations is dependent on the reaction medium. The observed changes in the stimulation of the MgATPase activity correlate with the extent of carbonyl formation in myosin. The enzyme inhibition is more potent in conditions where the efficiency of tyrosine nitration and peroxynitrite reactivity towards sulphydryls are lower. Together with the observation that reversion of sulphydryl oxidation did not lead to the recovery of myosin functional and structural impairments, these results point out to the importance of protein carbonylation as a post-translational modification in the peroxynitrite-induced myosin functional impairment.

Effects of decavanadate and insulin enhancing vanadium compounds on glucose uptake in isolated rat adipocytes

The effects of different vanadium compounds namely pyridine-2,6-dicarboxylatedioxovanadium(V) (V5-dipic), bis(maltolato) oxovanadium(IV) (BMOV) and amavadine, and oligovanadates namely metavanadate and decavanadate were analysed on basal and insulin stimulated glucose uptake in rat adipocytes. Decavanadate (50 microM), manifest a higher increases (6-fold) on glucose uptake compared with basal, followed by BMOV (1 mM) and metavanadate (1 mM) solutions (3-fold) whereas V5 dipic and amavadine had no effect. Decavanadate (100 microM) also shows the highest insulin like activity when compared with the others compounds studied. In the presence of insulin (10 nM), only decavanadate increases (50%) the glucose uptake when compared with insulin stimulated glucose uptake whereas BMOV and metavanadate, had no effect and V5 dipic and amavadine prevent the stimulation to about half of the basal value. Decavanadate is also able to reduce or eradicate the suppressor effect caused by dexamethasone on glucose uptake at the level of the adipocytes. Altogether, vanadium compounds and oligovanadates with several structures and coordination spheres reveal different effects on glucose uptake in rat primary adipocytes.

Decavanadate: a journey in a search of a role

Currently, efforts have been directed towards using decavanadate as a tool for the understanding of several biochemical processes such as muscle contraction, calcium homeostasis, in vivo changes of oxidative stress markers, mitochondrial oxygen consumption, mitochondrial membrane depolarization, actin polymerization and glucose uptake, among others. In addition, studies have been conducted in order to make vanadium available and safe for clinical use, for instance with decavanadate compounds that present interesting pharmacological properties, eventually useful for the treatment of diabetes. Here, recent contributions of decavanadate to the effects of vanadium in biological systems, not only in vitro, but also in vivo, are analysed.

Decavanadate interactions with actin: cysteine oxidation and vanadyl formation

Incubation of actin with decavanadate induces cysteine oxidation and oxidovanadium(IV) formation. The studies were performed combining kinetic with spectroscopic (NMR and EPR) methodologies. Although decavanadate is converted to labile oxovanadates, the rate of deoligomerization can be very slow (half-life time of 5.4 h, at 25 degrees C, with a first order kinetics), which effectively allows decavanadate to exist for some time under experimental conditions. It was observed that decavanadate inhibits F-actin-stimulated myosin ATPase activity with an IC(50) of 0.8 microM V(10) species, whereas 50 microM of vanadate or oxidovanadium(IV) only inhibits enzyme activity up to 25%. Moreover, from these three vanadium forms, only decavanadate induces the oxidation of the so called "fast" cysteines (or exposed cysteine, Cys-374) when the enzyme is in the polymerized and active form, F-actin, with an IC(50) of 1 microM V(10) species. Decavanadate exposition to F- and G-actin (monomeric form) promotes vanadate reduction since a typical EPR oxidovanadium(IV) spectrum was observed. Upon observation that V(10) reduces to oxidovanadium(IV), it is proposed that this cation interacts with G-actin (K(d) of 7.48 +/- 1.11 microM), and with F-actin (K(d) = 43.05 +/- 5.34 microM) with 1:1 and 4:1 stoichiometries, respectively, as observed by EPR upon protein titration with oxidovanadium(IV). The interaction of oxidovanadium(IV) with the protein may occur close to the ATP binding site of actin, eventually with lysine-336 and 3 water molecules.

Decavanadate (V10 O28 6-) and oxovanadates: oxometalates with many biological activities

The decameric vanadate species V(10)O(28)(6-), also referred to as decavanadate, impact proteins, lipid structures and cellular function, and show some effects in vivo on oxidative stress processes and other biological properties. The mode of action of decavanadate in many biochemical systems depends, at least in part, on the charge and size of the species and in some cases competes with the simpler oxovanadate species. The orange decavanadate that contains 10 vanadium atoms is a stable species for several days at neutral pH, but at higher pH immediately converts to the structurally and functionally distinct lower oxovanadates such as the monomer, dimer or tetramer. Although the biological effects of vanadium are generally assumed to derive from monomeric vanadate or the vanadyl cation, we show in this review that not all effects can be attributed to these simple oxovanadate forms. This topic has not previously been reviewed although background information is available [D.C. Crans, Comments Inorg. Chem. 16 (1994) 35-76; M. Aureliano (Ed.), Vanadium Biochemistry, Research Signpost Publs., Kerala, India, 2007]. In addition to pumps, channels and metabotropic receptors, lipid structures represent potential biological targets for decavanadate and some examples have been reported. Decavanadate interact with enzymes, polyphosphate, nucleotide and inositol 3-phosphate binding sites in the substrate domain or in an allosteric site, in a complex manner. In mitochondria, where vanadium was shown to accumulate following decavanadate in vivo administration, nM concentration of decavanadate induces membrane depolarization in addition to inhibiting oxygen consumption, suggesting that mitochondria may be potential targets for decameric toxicity. In vivo effects of decavanadate in piscine models demonstrated that antioxidant stress markers, lipid peroxidation and vanadium subcellular distribution is dependent upon whether or not the solutions administered contain decavanadate. The present review summarizes the reports on biological effects of decavanadate and highlights the importance of considering decavanadate in evaluations of the biological effects of vanadium.

Sarcoplasmic reticulum calcium ATPase is inhibited by organic vanadium coordination compounds: pyridine-2,6-dicarboxylatodioxovanadium(V), BMOV, and an amavadine analogue

The general affinity of the sarcoplasmic reticulum (SR) Ca (2+)-ATPase was examined for three different classes of vanadium coordination complexes including a vanadium(V) compound, pyridine-2,6-dicarboxylatodioxovanadium(V) (PDC-V(V)), and two vanadium(IV) compounds, bis(maltolato)oxovanadium(IV) (BMOV), and an analogue of amavadine, bis( N-hydroxylamidoiminodiacetato)vanadium(IV) (HAIDA-V(IV)). The ability of vanadate to act either as a phosphate analogue or as a transition-state analogue with enzymes' catalysis phosphoryl group transfer suggests that vanadium coordination compounds may reveal mechanistic preferences in these classes of enzymes. Two of these compounds investigated, PDC-V(V) and BMOV, were hydrolytically and oxidatively reactive at neutral pH, and one, HAIDA-V(IV), does not hydrolyze, oxidize, or otherwise decompose to a measurable extent during the enzyme assay. The SR Ca (2+)-ATPase was inhibited by all three of these complexes. The relative order of inhibition was PDC-V(V) > BMOV > vanadate > HAIDA-V(IV), and the IC 50 values were 25, 40, 80, and 325 microM, respectively. Because the observed inhibition is more potent for PDC-V(V) and BMOV than that of oxovanadates, the inhibition cannot be explained by oxovanadate formation during enzyme assays. Furthermore, the hydrolytically and redox stable amavadine analogue HAIDA-V(IV) inhibited the Ca (2+)-ATPase less than oxovanadates. To gauge the importance of the lipid environment, studies of oxidized BMOV in microemulsions were performed and showed that this system remained in the aqueous pool even though PDC-V(V) is able to penetrate lipid interfaces. These findings suggest that the hydrolytic properties of these complexes may be important in the inhibition of the calcium pump. Our results show that two simple coordination complexes with known insulin enhancing effects can invoke a response in calcium homeostasis and the regulation of muscle contraction through the SR Ca (2+)-ATPase.

Impairment of mineralization by metavanadate and decavanadate solutions in a fish bone-derived cell line

Vanadium, a trace metal known to accumulate in bone and to mimic insulin, has been shown to regulate mammalian bone formation using in vitro and in vivo systems. In the present work, short- and long-term effects of metavanadate (containing monomeric, dimeric, tetrameric and pentameric vanadate species) and decavanadate (containing decameric vanadate species) solutions on the mineralization of a fish bone-derived cell line (VSa13) were studied and compared to that of insulin. After 2 h of incubation with vanadate (10 microM in monomeric vanadate), metavanadate exhibited higher accumulation rates than decavanadate (6.85 +/- 0.40 versus 3.95 +/- 0.10 microg V/g of protein, respectively) in fish VSa13 cells and was also shown to be less toxic when applied for short periods. In longer treatments with both metavanadate and decavanadate solutions, similar effects were promoted: stimulation of cell proliferation and strong impairment (75%) of extracellular matrix (ECM) mineralization. The effect of both vanadate solutions (5 microM in monomeric vanadate), on ECM mineralization was increased in the presence of insulin (10 nM). It is concluded that chronic treatment with both vanadate solutions stimulated fish VSa13 cells proliferation and prevented ECM mineralization. Newly developed VSa13 fish cells appeared to be appropriate in the characterization of vanadate effects on vertebrate bone formation, representing a good alternative to mammalian systems.

Vanadate proliferative and anti-mineralogenic effects are mediated by MAPK and PI-3K/Ras/Erk pathways in a fish chondrocyte cell line

We recently reported proliferative and anti-mineralogenic effects of vanadate on fish chondrocytes and here we investigate the signalling pathways associated with these effects. Our data show that vanadate stimulates chondrocyte proliferation through the MAPK pathway, using signalling mechanisms similar to those used by IGF-1, while it inhibits chondrocyte differentiation/mineralization through a putative PI-3K/Ras/Erk signalling, a pathway shared with insulin. Our data also suggest that vanadate impairs ECM mineralization not only by interfering with regulatory pathways but also by inhibiting enzymatic activity of ALP. Finally, this work provides additional evidence for the conservation, throughout evolution, of mechanisms regulating chondrocyte proliferation and differentiation.

Vanadium and cadmium in vivo effects in teleost cardiac muscle: metal accumulation and oxidative stress markers

Several biological studies associate vanadium and cadmium with the production of reactive oxygen species (ROS), leading to lipid peroxidation and antioxidant enzymes alterations. The present study aims to analyse and compare the oxidative stress responses induced by an acute intravenous exposure (1 and 7 days) to a sub-lethal concentration (5 mM) of two vanadium solutions, containing different vanadate n-oligomers (n=1-5 or n=10), and a cadmium solution on the cardiac muscle of the marine teleost Halobatrachus didactylus (Lusitanian toadfish). It was observed that vanadium is mainly accumulated in mitochondria (1.33+/-0.26 microM), primarily when this element was administrated as decameric vanadate, than when administrated as metavanadate (432+/-294 nM), while the highest content of cadmium was found in cytosol (365+/-231 nM). Indeed, decavanadate solution promotes stronger increases in mitochondrial antioxidant enzymes activities (catalase: +120%; superoxide dismutase: +140%) than metavanadate solution. On contrary, cadmium increases cytosolic catalase (+111%) and glutathione peroxidases (+50%) activities. It is also observed that vanadate oligomers induce in vitro prooxidant effects in toadfish heart, with stronger effects induced by metavanadate solution. In summary, vanadate and cadmium are differently accumulated in blood and cardiac subcellular fractions and induced different responses in enzymatic antioxidant defence mechanisms. In the present study, it is described for the first time the effects of equal doses of two different metals intravenously injected in the same fish species and upon the same exposure period allowing to understand the mechanisms of vanadate and cadmium toxicity in fish cardiac muscle.

Vanadate induces necrotic death in neonatal rat cardiomyocytes through mitochondrial membrane depolarization

Besides the well-known inotropic effects of vanadium in cardiac muscle, previous studies have shown that vanadate can stimulate cell growth or induce cell death. In this work, we studied the toxicity to neonatal rat ventricular myocytes (cardiomyocytes) of two vanadate solutions containing different oligovanadates distribution, decavanadate (containing decameric vanadate, V 10) and metavanadate (containing monomeric vanadate and also di-, tetra-, and pentavanadate). Incubation for 24 h with decavanadate or metavanadate induced necrotic cell death of cardiomyocytes, without significant caspase-3 activation. Only 10 microM total vanadium of either decavanadate (1 microM V 10) or metavanadate (10 microM total vanadium) was needed to produce 50% loss of cell viability after 24 h (assessed with MTT and propidium iodide assays). Atomic absorption spectroscopy showed that vanadium accumulation in cardiomyocytes after 24 h was the same when incubation was done with decavanadate or metavanadate. A decrease of 75% of the rate of mitochondrial superoxide anion generation, monitored with dihydroethidium, and a sustained rise of cytosolic calcium (monitored with Fura-2-loaded cardiomyocytes) was observed after 24 h of incubation of cardiomyocytes with decavanadate or metavanadate concentrations close to those inducing 50% loss of cell viability produced. In addition, mitochondrial membrane depolarization within cardiomyocytes, monitored with tetramethylrhodamine ethyl esther or with 3,3',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolcarbocyanine iodide, were observed after only 6 h of incubation with decavanadate or metavanadate. The concentration needed for 50% mitochondrial depolarization was 6.5 +/- 1 microM total vanadium for both decavanadate (0.65 microM V 10) and metavanadate. In conclusion, mitochondrial membrane depolarization was an early event in decavanadate- and monovanadate-induced necrotic cell death of cardiomyocytes.