Recent advances into vanadyl, vanadate and decavanadate interactions with actin

Non-Covalent and Covalent Binding of New Mixed-Valence Cage-like Polyoxidovanadate Clusters to Lysozyme

The high-resolution X-ray structures of the model protein lysozyme in the presence of the potential drug [VIVO(acetylacetonato)2] from crystals grown in 1.1 M NaCl, 0.1 M sodium acetate at pH 4.0 reveal the binding to the protein of different and unexpected mixed-valence cage-like polyoxidovanadates (POVs): [V15O36(OH2)]5-, which non-covalently interacts with the lysozyme surface, [V15O33(OH2)]+ and [V20O51(OH2)]n- (this latter based on an unusual {V18O43} cage) which covalently bind the protein. EPR spectroscopy confirms the partial oxidation of VIV to VV and the formation of mixed-valence species. The results indicate that the interaction with proteins can stabilize the structure of unexpected - both for dimension and architecture - POVs, not observed in aqueous solution.

Histological and Memory Alterations in an Innovative Alzheimer's Disease Animal Model by Vanadium Pentoxide Inhalation

Background

Previous work from our group has shown that chronic exposure to Vanadium pentoxide (V2O5) causes cytoskeletal alterations suggesting that V2O5 can interact with cytoskeletal proteins through polymerization and tyrosine phosphatases inhibition, causing Alzheimer's disease (AD)-like hippocampal cell death.

Objective

This work aims to characterize an innovative AD experimental model through chronic V2O5 inhalation, analyzing the spatial memory alterations and the presence of neurofibrillary tangles (NFTs), amyloid-β (Aβ) senile plaques, cerebral amyloid angiopathy, and dendritic spine loss in AD-related brain structures.

Methods

20 male Wistar rats were divided into control (deionized water) and experimental (0.02 M V2O5 1 h, 3/week for 6 months) groups (n = 10). The T-maze test was used to assess spatial memory once a month. After 6 months, histological alterations of the frontal and entorhinal cortices, CA1, subiculum, and amygdala were analyzed by performing Congo red, Bielschowsky, and Golgi impregnation.

Results

Cognitive results in the T-maze showed memory impairment from the third month of V2O5 inhalation. We also noted NFTs, Aβ plaque accumulation in the vascular endothelium and pyramidal neurons, dendritic spine, and neuronal loss in all the analyzed structures, CA1 being the most affected.

Conclusions

This model characterizes neurodegenerative changes specific to AD. Our model is compatible with Braak AD stage IV, which represents a moment where it is feasible to propose therapies that have a positive impact on stopping neuronal damage.

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) (V10O286-; 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) (Nb10O286-; 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, VIVO2+, 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 VIVO2+ 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.

Magneto-structural correlations of cyclo-tetravanadates functionalized with mixed-ligand copper(ii) complexes

Bimetallic materials based on tetravanadate anions and mixed ligand copper(ii) complexes were readily synthesized under non-hydrothermal conditions. The compounds show interesting structural and magnetic diversity mediated by copper symmetry.

Covalent and non-covalent binding in vanadium–protein adducts

An integrated method, generalizable to any metals and proteins, based on ESI-MS, EPR and molecular modelling was applied to study the covalent and non-covalent binding of the potential drug [V^IVO(nalidixato)₂(H₂O)] to lysozyme and cytochrome c.

Simultaneous formation of non-oxidovanadium(iv) and oxidovanadium(v) complexes incorporating phenol-based hydrazone ligands in aerobic conditions

A family of non-oxidovanadium(iv) complexes incorporating multidentate hydrazone ligands were synthesized through a thermodynamically unfavourable process along with oxidovanadium(v) species.

Experimental and theoretical insights of functionalized hexavanadates on Na+/K+-ATPase activity; molecular interaction field, ab initio calculations and in vitro assays

The influence of three functionalized hexavanadates (V₆): Na₂ [V₆O₁₃{(OCH₂)₃CCH₃}₂], [H₂]₂ [V₆O₁₃{(OCH₂)₃CCH₂OCOCH₂CH₃}₂] and [(C₄H₉)₄N]₂ [V₆O₁₃{(OCH₂)₃CCH₂OOC(CH₃)₂-COOH}₂ on Na⁺/K⁺-ATPase activity, was investigated in vitro. Including compounds already tested by Xu et al. (Journal of Inorganic Biochemistry 161 (2016) 27-36), all functionalized hexavanadates inhibit the activity of Na⁺/K⁺-ATPase in a dose-dependent manner but with different inhibitory potencies. Na₂ [V₆O₁₃{(OCH₂)₃CCH₃}₂] was found to have the best inhibition properties - showing 50% inhibition IC₅₀ = 5.50 × 10^-5 M, while [(C₄H₉)₄N]₂ [V₆O₁₃{(OCH₂)₃CCH₂OOC(CH₃)₂-COOH}₂] showed the lowest inhibitory power, IC₅₀ = 1.31 × 10^-4 M. In order to understand the bioactivity of functionalized hexavanadates series, we have also used a combined theoretical approach: determination of electrostatic potential from ab initio theoretical calculations and computation of the molecular interaction field (MIF) surface.

Interaction of Vanadium(IV) Species with Ubiquitin: A Combined Instrumental and Computational Approach

The interaction of V^IVO²⁺ ion and five V^IVOL₂ compounds with potential pharmacological application, where L indicates maltolate (ma), kojate (koj), acetylacetonate (acac), 1,2-dimethyl-3-hydroxy-4(1 H)-pyridinonate (dhp), and l-mimosinate (mim), with ubiquitin (Ub) was studied by EPR, ESI-MS, and computational (docking and DFT) methods. The free metal ion V^IVO²⁺ interacts with Glu, Asp, His, Thr, and Leu residues, but the most stable sites (named 1 and 2) involve the coordination of (Glu16, Glu18) and (Glu24, Asp52). In the system with V^IVOL₂ compounds, the type of binding depends on the vanadium concentration. When the concentration is in the mM range, the binding occurs with cis-VOL₂(H₂O), L = ma, koj, dhp, and mim, or with VO(acac)₂: in the first case, the equatorial coordination of His68, Glu16, Glu18, or Asp21 residues yields species with formula n[VOL₂]-Ub where n = 2-3, while with VO(acac)₂ only noncovalent surface interactions are revealed. When the concentration of V is on the order of micromolar, the mono-chelated species VOL(H₂O)₂⁺ with L = ma, koj, acac, dhp, and mim, favored by the hydrolysis, interact with Ub, and adducts with composition n[VOL]-Ub ( n = 1-2) are observed with the contemporaneous coordination of (Glu18, Asp21) or (Glu16, Glu18), and (Glu24, Asp52) or (Glu51, Asp52) donors. The results of this work suggest that the combined application of spectroscopic, spectrometric, and computational techniques allow the complete characterization of the ternary systems formed by a V compound and a model protein such as ubiquitin. The same approach can be applied, eventually changing the spectroscopic/spectrometric techniques, to study the interaction of other metal species with other proteins.

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.

Synthesis, characterization, and cytotoxic and antimicrobial activities of mixed-ligand hydrazone complexes of variable valence VOz+ (z = 2, 3)

Mixed-ligand complexes of VO²⁺ and VO³⁺ motifs incorporating a family of hydrazone ligands were reported, which exhibited promising cytotoxic activity against lung cancer cell line and antimicrobial activity against four pathogenic bacterial stains.

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.

Exploring the effect of substituent in the hydrazone ligand of a family of μ-oxidodivanadium(v) hydrazone complexes on structure, DNA binding and anticancer activity

The reaction of 2-hydroxybenzoylhydrazine (H₂bh) separately with equimolar amounts of [V^IVO(aa)₂] and [V^IVO(ba)₂] in CHCl₃ afforded the complexes [VO₃(HL¹)₂] (1) and [VO₃(HL²)₂] (2) respectively in good to excellent yield ((HL¹)^2- and (HL²)^2- represent respectively the dianionic form of 2-hydroxybenzoylhydrazones of acetylacetone (H₃L¹) and benzoylacetone (H₃L²) (general abbreviation H₃L)). From X-ray structure analysis, the V^V-O-V^V angle was found to be ∼115° and 180° in 1 and 2 respectively. Upon one-electron reduction selectively at one V centre at an appropriate potential, each of 1 and 2 generated mixed-valence [(HL)V^VO-(μ-O)-OV^IV(HL)]^- species 1A and 2A respectively, which showed valence delocalization at room temperature and localization at 77 K, and the V^IV-O-V^V bond angles were calculated to be 177.5° and 180° respectively. The intercalative mode of binding of the two complexes 1 and 2 with CT DNA has been suggested by UV-visible spectroscopy (K_b = 7.31 × 10⁵ M^-1 and 8.71 × 10⁵ M^-1 respectively for 1 and 2), fluorescence spectroscopy (K_sv = 6.85 × 10⁵ M^-1 and 8.53 × 10⁵ M^-1 respectively for 1 and 2) and circular dichroism spectroscopy. Such intercalative mode of binding of these two complexes with CT DNA and HPV DNA has also been confirmed by molecular docking study. Both complexes 1 and 2 exhibited promising anti-cancer activity against SiHa cervical cancer cells with IC₅₀ values of 28 ± 0.5 μM and 25 ± 0.5 μM respectively for 24 h which is significantly better than that of widely used cisplatin (with IC₅₀ value of 63.5 μM). Nuclear staining experiments reveal that these complexes kill the SiHa cells through apoptotic mode. It is interesting to note that these two complexes are non-toxic to normal T293 cell line. Complex 2 showed higher DNA binding ability with CT DNA and HPV DNA as well as better anti-cancer properties towards SiHa cervical cancer cells in comparison to complex 1, a fact which can be explained by considering the lower energy of LUMO (which favours electron transition from DNA to the metal complex) and also the higher surface area of complex 2 in comparison to complex 1 due to the presence of one extra electron-withdrawing phenyl group in the former.

Selective Isolation of Myosin Subfragment-1 with a DNA-Polyoxovanadate Bioconjugate

The bioconjugation of a polyoxometalate (POMs), i.e., dodecavanadate (V₁₂O₃₂), to DNA strands produces a functional labeled DNA primer, V₁₂O₃₂-DNA. The grafting of DNA primer onto streptavidin-coated magnetic nanoparticles (SVM) produces a novel composite, V₁₂O₃₂-DNA@SVM. The high binding-affinity of V₁₂O₃₂ with the ATP binding site in myosin subfragment-1 (S1) facilitates favorable adsorption of myosin, with an efficiency of 99.4% when processing 0.1 mL myosin solution (100 μg mL^-1) using 0.1 mg composite. Myosin adsorption fits the Langmuir model, corresponding to a theoretical adsorption capacity of 613.5 mg g^-1. The retained myosin is readily recovered by 1% SDS (m/m), giving rise to a recovery of 58.7%. No conformational change is observed for myosin after eliminating SDS by ultrafiltration. For practical use, high-purity myosin S1 is obtained by separation of myosin from the rough protein extract from porcine left ventricle, followed by digestion with α-chymotryptic and further isolation of S1 subfragment. The purified myosin S1 is identified with matrix-assisted laser desorption/ionization time-of-flight/mass spectrometry, giving rise to a sequence coverage of 38%.

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.

Exploring the effect of hydroxylic and non-hydroxylic solvents on the reaction of [VIVO(β-diketonate)2] with 2-aminobenzoylhydrazide in aerobic and anaerobic conditions

Refluxing [V^IVO(β-diketonate)₂], namely [V^IVO(acetylacetonate)₂] and [V^IVO(benzoylacetonate)₂], separately with an equivalent or excess amount of 2-aminobenzoylhydrazide (ah) in laboratory grade (LG) CH₃OH in aerobic conditions afforded non-oxidovanadium(iv) and oxidovanadium(v) complexes of the type [V^IV(L¹)₂] (1), [V^VO(L¹)(OCH₃)]₂ (3) and [V^IV(L²)₂] (2), and [V^VO(L²)(OCH₃)] (4), respectively. (L¹)^2- and (L²)^2- represent the dianionic forms of 2-aminobenzoylhydrazone of acetylacetone (H₂L¹) and benzoylacetone (H₂L²), respectively, (general abbreviation, H₂L), which was formed by the in situ condensation of ah with the respective coordinated [β-diketonate] in medium-to-good yield. The yield of different resulting products was dependent upon the ratio of ah to [V^IVO(β-diketonate)₂]. For example, the yield of 1 and 2 complexes increased significantly associated with a decrease in the amount of 3 and 4 with an increase in the molar ratio of ah. Upon replacing CH₃OH by a non-hydroxylic solvent, LG CHCl₃, the above reaction yielded only oxidovanadium(v) complexes of the type [V^VO(L¹)(OH)]₂ (5), [V^VO(L²)(OH)] (6) and [VO₃(L)₂] (7, 8) whereas, upon replacing CHCl₃ by another non-hydroxylic solvent, namely LG CH₃CN, only the respective [VO₃(L)₂] (7, 8) complex was isolated in 72-78% yield. However, upon performing the above reactions in the absence of air using dry CH₃OH or dry CHCl₃, only the respective [V^IV(L)₂] complex was obtained, suggesting that aerial oxygen was the oxidising agent and the type of pentavalent product formed was dependent upon the nature of solvent used. Complexes 3 and 4 were converted, respectively, to 7 and 8 on refluxing in LG CHCl₃via the respective unstable complex 5 and 6. The DFT calculated change in internal energy (ΔE) for the reactions 2[V^VO(L²)(OCH₃)] + 2H₂O → 2[V^VO(L²)(OH)] + 2CH₃OH and 2[V^VO(L²)(OH)] → [VO₃(L²)₂] + H₂O was, respectively, +3.61 and -7.42 kcal mol^-1, suggesting that the [V^VO(L²)(OH)] species was unstable and readily transformed to the stable [VO₃(L²)₂] complex. Upon one-electron reduction at an appropriate potential, each of 7 and 8 generated mixed-valence [(L)V^VO-(μ-O)-OV^IV(L)]^- species, which showed valence-delocalisation at room temperature and localisation at 77 K. Some of the complexes showed a wide range of toxicity in a dose-dependent manner against lung cancer cells comparable with that observed with cis-platin.

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.

Semimetal-functionalised polyoxovanadates

Polyoxovanadates (POVs), known for their wide applicability and relevance in chemical, physical and biological sciences, are a subclass of polyoxometalates and usually self-assemble in aqueous-phase, pH-controlled condensation reactions. Archetypical POVs such as the robust [VO42](12-) polyoxoanion can be structurally, electronically and magnetically altered by heavier group 14 and 15 elements to afford Si-, Ge-, As- or Sb-decorated POV structures (heteroPOVs). These main-group semimetals introduce specific chemically engineered functionalities which cause the generally hydrophilic heteroPOV compounds to exhibit interesting reactivity towards organic molecules, late transition metal and lanthanoid ions. The fully-oxidised (V(V)), mixed-valent (V(V)/V(IV) and V(IV)/V(III)), "fully-reduced" (V(IV)) and "highly-reduced" (V(III)) heteroPOVs possess a number of intriguing properties, ranging from catalytic to molecular magnet characteristics. Herein, we review key developments in the synthetic and structural chemistry as well as the reactivity of POVs functionalised with Si-, Ge-, As- or Sb-based heterogroups.

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.

Chemical, biochemical, and biological behaviors of vanadate and its oligomers

Vanadate is widely used as an inhibitor of protein tyrosine phosphatases (PTPase) and is routinely applied in cell lysis buffers or immunoprecipitations of phosphotyrosyl proteins. Additionally, vanadate has been extensively studied for its antidiabetic and anticancer effects. In most studies, orthovanadate or metavanadate was used as the starting compound, whereas these "vanadate" solutions may contain more or less oligomerized species. Whether and how different species of vanadium compounds formed in the biological media exert specific biological effect is still a mystery. In the present commentary, we focus on the chemical, biochemical, and biological behaviors of vanadate. On the basis of species formation of vanadate in chemical and biological systems, we compared the biological effects and working mechanism of monovanadate with that of its oligomers, especially the decamer. We propose that different oligomers may exert a specific biological effect, which depends on their structures and the context of the cell types, by different modes of action.

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.