Validation and Applications of Protein-Ligand Docking Approaches Improved for Metalloligands with Multiple Vacant Sites

Decoding the interaction between coordination compounds and proteins is of fundamental importance in biology, pharmacy, and medicine. In this context, protein- ligand docking represents a particularly interesting asset to predict how small compounds could interact with biomolecules, but to date, very little information is available to adapt these methodologies to metal-containing ligands. Here, we assessed the predictive capability of a metal-compatible parameter set for the docking program GOLD for metallo ligands with multiple vacant sites and different geometries. The study first presents a benchmark of 25 well-characterized X-ray metallo ligand-protein adducts. In 100% of the cases, the docking solutions are superimposable to the X-ray determination, and in 92% the value of the root-mean-square deviation between the experimental and calculated structures is lower than 1.5 Å. After the validation step, we applied these methods to five case studies for the prediction of the binding of pharmacological active metal species to proteins: (i) the anticancer copper(II) complex [Cu^II(Br)(2-hydroxy-1-naphthaldehyde benzoyl hydrazine)(indazole)] to human serum albumin (HSA); (ii) one of the active species of antidiabetic and antitumor vanadium compounds, V^IVO²⁺ ion, to carboxypeptidase; (iii) the antiarthritic species [Au^I(PEt₃)]⁺ to HSA; (iv) the antitumor oxaliplatin to ubiquitin; (v) the antitumor ruthenium(II) compound RAPTA-PentaOH to cathepsin B. The calculations suggested that the binding modes are in good agreement with the partial information retrieved from spectroscopic and spectrometric analysis and allowed us, in certain cases, to propose additional hypotheses. This method is an important update in protein-metallo ligand docking, which could have a wide field of application, from biology and inorganic biochemistry to medicinal chemistry and pharmacology.

A Versatile Polyoxovanadate in Diverse Cation Matrices: A Supramolecular Perspective

A series of decavanadate based compounds, formulated as [Co(H₂O)₆][{Na₄(H₂O)₁₄}{V₁₀O₂₈}]·4H₂O (1), [Zn(H₂O)₆][Na₃(H₂O)₁₄] [HV₁₀O₂₈]·4H₂O (2), [HMTAH]₂ [{Zn(H₂O)₄}₂{V₁₀O₂₈}]·2H₂O (3), [{Co(3-amp)(H₂O)₅}]₂ [3-ampH]₂ [V₁₀O₂₈] · 6H₂O (4), [4-ampH]₁₀[{Na(H₂O)₆}{HV₁₀O₂₈}][V₁₀O₂₈]·15H₂O (5), [{4-ampH}₆ {Co(H₂O)₆}₃][V₁₀O₂₈]₂·14H₂O (6), and [{4-ampH}₁₀{Zn(H₂O)₆}][V₁₀O₂₈]₂·10H₂O (7), have been synthesized (where HMTAH = mono-protonated hexamethylenetetramine, 3-ampH = protonated 3-amino pyridine and 4-ampH= protonated 4-aminopyridine) from the relevant aqueous sodium-vanadate solution, by varying the pH of the solution and amino pyridine/hexamine derivatives as well as transition metal salts (Co(II)- and Zn(II)-salts). In this series of compounds 1-7, the polyoxovanadate (POV) cluster [V₁₀O₂₈]^6- is the common cluster anion, stabilized by diverse cations. The diverse supramolecular patterns around the decavanadate cluster anion in different cationic matrices have been described to understand the microenvironment in the decavanadate-based minerals. All of these compounds have solvent water molecules in their respective crystal lattices. Since water can interact directly with cations and anions, providing an additional stability and structural diversity, we have analyzed supramolecular water structures in all these compounds to comprehend the role of the lattice water in the formation of natural decavanadate containing minerals. Compounds 1-7, that are isolated at an ambient condition from aqueous solution, are characterized by routine spectral analysis, elemental analyses and finally unambiguously by single crystal X-ray crystallography.

Catalytic Applications of Vanadium: A Mechanistic Perspective

The chemistry of vanadium has seen remarkable activity in the past 50 years. In the present review, reactions catalyzed by homogeneous and supported vanadium complexes from 2008 to 2018 are summarized and discussed. Particular attention is given to mechanistic and kinetics studies of vanadium-catalyzed reactions including oxidations of alkanes, alkenes, arenes, alcohols, aldehydes, ketones, and sulfur species, as well as oxidative C-C and C-O bond cleavage, carbon-carbon bond formation, deoxydehydration, haloperoxidase, cyanation, hydrogenation, dehydrogenation, ring-opening metathesis polymerization, and oxo/imido heterometathesis. Additionally, insights into heterogeneous vanadium catalysis are provided when parallels can be drawn from the homogeneous literature.

Vanadium: History, chemistry, interactions with α-amino acids and potential therapeutic applications

In the last 30 years, since the discovery that vanadium is a cofactor found in certain enzymes of tunicates and possibly in mammals, different vanadium-based drugs have been developed targeting to treat different pathologies. So far, the in vitro studies of the insulin mimetic, antitumor and antiparasitic activity of certain compounds of vanadium have resulted in a great boom of its inorganic and bioinorganic chemistry. Chemical speciation studies of vanadium with amino acids under controlled conditions or, even in blood plasma, are essential for the understanding of the biotransformation of e.g. vanadium antidiabetic complexes at the physiological level, providing clues of their mechanism of action. The present article carries out a bibliographical research emphaticizing the chemical speciation of the vanadium with different amino acids and reviewing also some other important aspects such as its chemistry and therapeutical applications of several vanadium complexes.

Synthesis, structure, solution behavior, reactivity and biological evaluation of oxidovanadium(iv/v) thiosemicarbazone complexes

The synthesis and characterization of an oxidovanadium(iv) [VIVO(L)(acac)] (1) and of two dioxidovanadium(v) [VVO2(L')] (2) and [VVO2(L)] (2a) complexes of the Schiff base formed from the reaction of 4-(p-fluorophenyl) thiosemicarbazone with pyridine-2-aldehyde (HL) are described. The oxidovanadium(iv) species [VIVO(L)(acac)] (1) was synthesized by the reaction of VIVO(acac)2 with the thiosemicarbazone HL in refluxing ethanol. The recrystallization of [VIVO(L)(acac)] (1) in DMF, CH3CN or EtOH gave the same product i.e. the dioxidovanadium(v) complex [VVO2(L)] (2a); however, upon recrystallization of 1 in DMSO a distinct compound [VVO2(L')] (2) was formed, wherein the original ligand L- is transformed to a rearranged one, L'-. In the presence of DMSO the ligand in complex 1 is found to undergo methylation at the carbon centre attached to imine nitrogen (aldimine) and transformed to the corresponding VVO2-species through in situ reaction. The synthesized HL and the metal complexes were characterized by elemental analysis, IR, UV-Vis, NMR and EPR spectroscopy. The molecular structure of [VVO2(L')] (2) was determined by single crystal X-ray crystallography. The methylation of various other ligands and complexes prepared from different vanadium precursors under similar reaction conditions was also attempted and it was confirmed that the imine methylation observed is both ligand and metal precursor specific. Complexes 1 and 2 show in vitro insulin-like activity against insulin responsive L6 myoblast cells, higher than VIVO(acac)2, with complex 1 being more potent. In addition, the in vitro cytotoxicity studies of HL, and of complexes 1 and 2 against the MCF-7 and Vero cell lines were also done. The ligand is not cytotoxic and complex 2 is significantly more cytotoxic than 1. DAPI staining experiments indicate that an increase in the time of incubation and an increase of concentration of the complexes lead to the increase in cell death.

Speciation in human blood of Metvan, a vanadium based potential anti-tumor drug

The first report on the anti-cancer activity of the compound Metvan, [V^IVO(Me₂phen)₂(SO₄)], where Me₂phen is 4,7-dimethyl-1,10-phenanthroline, dates back to 2001. Although it was immediately identified as one of the most promising multitargeted anti-cancer V compounds, no development on the medical experimentation was carried out. One of the possible reasons is the lack of information on its speciation in aqueous solution and its thermodynamic stability, factors which influence the transport in the blood and the final form which reaches the target organs. To fill this gap, in this work the speciation of Metvan in aqueous solution and human blood was studied by instrumental (EPR, electronic absorption spectroscopy, ESI-MS and ESI-MS/MS), analytical (pH-potentiometry) and computational (DFT) methods. The results suggested that Metvan transforms at physiological pH into the hydrolytic species cis-[VO(Me₂phen)₂(OH)]⁺ and that both citrate and proteins (transferrin and albumin in the blood serum, and hemoglobin in the erythrocytes) form mixed complexes, denoted [VO(Me₂phen)(citrH_-1)]^2- and VO-Me₂phen-Protein with the probable binding of His-N donors. The measurements with erythrocytes suggest that Metvan is able to cross their membrane forming mixed species VO-Me₂phen-Hb. The redox stability in cell culture medium was also examined, showing that ca. 60% is oxidized to V^V after 5 h. Overall, the speciation of Metvan in the blood mainly depends on the V concentration: when it is larger than 50 μM, [VO(Me₂phen)(citrH_-1)]^2- and VO-Me₂phen-Protein are the major species, while for concentrations lower than 10 μM, (VO)(hTf) is formed and Me₂phen is lost. Therefore, it is plausible that the pharmacological activity of Metvan could be due to the synergic action of free Me₂phen, and V^IVO and V^VO/V^VO₂ species.

Coordination environment changes of the vanadium in vanadium-dependent haloperoxidase enzymes

Vanadium-dependent haloperoxidases are a class of enzymes that catalyze oxidation reactions with halides to form halogenated organic products and water. These enzymes include chloroperoxidase and bromoperoxidase, which have very different protein sequences and sizes, but regardless the coordination environment of the active sites is surprisingly constant. In this manuscript, the comparison of the coordination chemistry of V-containing-haloperoxidases of the trigonal bipyramidal geometry was done by data mining. The catalytic cycle imposes changes in the coordination geometry of the vanadium to accommodate the peroxidovanadium(V) intermediate in an environment we describe as a distorted square pyramidal geometry. During the catalytic cycle, this intermediate converts to a trigonal bipyramidal intermediate before losing the halogen and forming a tetrahedral vanadium-protein intermediate. Importantly, the catalysis is facilitated by a proton-relay system supplied by the second sphere coordination environment and the changes in the coordination environment of the vanadium(V) making this process unique among protein catalyzed processes. The analysis of the coordination chemistry shows that the active site is very tightly regulated with only minor changes in the coordination geometry. The coordination geometry in the protein structures deviates from that found for both small molecules crystalized in the absence of protein and the reported functional small molecule model compounds. At this time there are no examples reported of a structurally similar small molecule with the geometry observed for the peroxidovanadium(V) in the active site of the vanadium-containing haloperoxidases.

The chemical biology and coordination chemistry of putrebactin, avaroferrin, bisucaberin, and alcaligin

Dihydroxamic acid macrocyclic siderophores comprise four members: putrebactin (putH₂), avaroferrin (avaH₂), bisucaberin (bisH₂), and alcaligin (alcH₂). This mini-review collates studies of the chemical biology and coordination chemistry of these macrocycles, with an emphasis on putH₂. These Fe(III)-binding macrocycles are produced by selected bacteria to acquire insoluble Fe(III) from the local environment. The macrocycles are optimally pre-configured for Fe(III) binding, as established from the X-ray crystal structure of dinuclear [Fe₂(alc)₃] at neutral pH. The dimeric macrocycles are biosynthetic products of two endo-hydroxamic acid ligands flanked by one amine group and one carboxylic acid group, which are assembled from 1,4-diaminobutane and/or 1,5-diaminopentane as initial substrates. The biosynthesis of alcH₂ includes an additional diamine C-hydroxylation step. Knowledge of putH₂ biosynthesis supported the use of precursor-directed biosynthesis to generate unsaturated putH₂ analogues by culturing Shewanella putrefaciens in medium supplemented with unsaturated diamine substrates. The X-ray crystal structures of putH₂, avaH₂ and alcH₂ show differences in the relative orientations of the amide and hydroxamic acid functional groups that could prescribe differences in solvation and other biological properties. Functional differences have been borne out in biological studies. Although evolved for Fe(III) acquisition, solution coordination complexes have been characterised between putH₂ and oxido-V(IV/V), Mo(VI), or Cr(V). Retrosynthetic analysis of 1:1 complexes of [Fe(put)]⁺, [Fe(ava)]⁺, and [Fe(bis)]⁺ that dominate at pH < 5 led to a forward metal-templated synthesis approach to generate the Fe(III)-loaded macrocycles, with apo-macrocycles furnished upon incubation with EDTA. This mini-review aims to capture the rich chemistry and chemical biology of these seemingly simple compounds.

Pharmacological and Toxicological Threshold of Bisammonium Tetrakis 4-(N,N-Dimethylamino)pyridinium Decavanadate in a Rat Model of Metabolic Syndrome and Insulin Resistance

Vanadium(IV/V) compounds have been studied as possible metallopharmaceutical drugs against diabetes mellitus. However, mechanisms of action and toxicological threshold have been tackled poorly so far. In this paper, our purposes were to evaluate the metabolic activity on dyslipidemia and dysglycemia, insulin signaling in liver and adipose tissue, and toxicology of the title compound. To do so, the previously reported bisammonium tetrakis 4-(N,N-dimethylamino)pyridinium decavanadate, the formula of which is [DMAPH]4(NH4)2[V10O28]·8H2O (where DMAPH is 4-dimethylaminopyridinium ion), was synthesized, and its dose-response curve on hyperglycemic rats was evaluated. A Long-Evans rat model showing dyslipidemia and dysglycemia with parameters that reproduce metabolic syndrome and severe insulin resistance was generated. Two different dosages, 5 µmol and 10 µmol twice a week of the title compound (equivalent to 2.43 mg·V/kg/day and 4.86 mg·V/kg/day, resp.), were administered intraperitoneal (i.p.) for two months. Then, an improvement on each of the following parameters was observed at a 5 µmol dose: weight reduction, abdominal perimeter, fatty index, body mass index, oral glucose tolerance test, lipid profile, and adipokine and insulin resistance indexes. Nevertheless, when the toxicological profile was evaluated at a 10 µmol dose, it did not show complete improvement, tested by the liver and adipose histology, as well as by insulin receptor phosphorylation and GLUT-4 expression. In conclusion, the title compound administration produces regulation on lipids and carbohydrates, regardless of dose, but the pharmacological and toxicological threshold for cell regulation are suggested to be up to 5 µmol (2.43 mg·V/kg/day) dose twice per week.

Altered homeostasis of trace elements in the blood of SCA2 patients

Spinocerebellar ataxia type 2 (SCA2) is a neurological disorder characterized by cerebellar dysfunction. The possible association between metals and neurodegenerative diseases is under constant investigation, with particular focus on their involvement in oxidative stress and their potential role as biomarkers of these pathologies. Whole blood samples of SCA2 patients and of healthy individuals were subjected to multi-elemental analysis by inductively coupled plasma-mass spectrometry (ICP-MS). Reduced levels of manganese and copper were found in SCA2 patients, while zinc and vanadium concentrations were significantly higher in patients compared to controls. Copper, manganese and zinc are cofactors of many enzymes (such as superoxide dismutase, SOD) involved in the cellular antioxidant response, whereas vanadium is a transition metal able to produce reactive radicals. A marked decrease of the antioxidant response has been previously reported in SCA2 patients. We suggest that an unbalance of transitional elements in the blood may reflect altered antioxidant homeostasis in SCA2 patients and could constitute a future peripheral biomarker for this disease. In addition, we suggest a possible role of vanadium in the altered lipid metabolism of SCA2 patients.

Nano vanadium dioxide films deposited on biomedical titanium: a novel approach for simultaneously enhanced osteogenic and antibacterial effects

Vanadium is a trace element in the human body, and vanadium compounds have a promising future in biological and medical applications due to their various biological activities and low toxicity. Herein, a novel pure vanadium dioxide (VO₂) nanofilm was deposited on a substrate of biomedical titanium by magnetron sputtering. The antibacterial effect of VO₂ against the methicillin-resistant Staphylococcus aureus (MRSA) was validated in vitro and in vivo. Moreover, the biocompatibility of VO₂ and its osteogenic effects were systematically illustrated. A possible osteogenic mechanism involving the amelioration of highly reactive oxygen species (ROS) levels were investigated. According to the results of our present and previous studies, the simultaneous antibacterial and osteogenic effects of VO₂ are attributed to its differential regulation of ROS levels in rat bone marrow mesenchymal stem cells (rBMSCs) and bacteria. This study is the first to report the simultaneous effects of VO₂ on bactericidal and osteogenic activities through its differential modification of ROS activity in eukaryotic (rBMSCs) and prokaryotic (MRSA) cells. The findings in this work may yield a deeper understanding of the biological activities of vanadium compounds while also paving the way for the further investigation and application of VO₂ in biological and medical materials.

Protective activity of pyruvate against vanadium-dependent cytotoxicity in Chinese hamster ovary (CHO-K1) cells

With increasing human exposure to vanadium-containing compounds and growing concern over their impact on human health, identification of safe methods for efficient treatment of vanadium poisoning may be of value. In this study, using Chinese hamster ovary (CHO-K1) cells, we show that the toxicity of vanadyl sulphate (VOSO₄) is mitigated in the presence of sodium pyruvate. The exposure of CHO-K1 cells to 100 μM VOSO₄ for 48 h induced significant cytotoxicity (measured with a resazurin assay) and elevation of the contents of malondialdehyde (MDA), a lipid peroxidation product, in the examined cells. When added simultaneously with VOSO₄ to the culture medium, pyruvate (4.5 mM) reduced VOSO₄-mediated cytotoxicity by twofold and inhibited MDA formation. Phase-contrast microscopy confirmed that the general morphology of cell cultures treated with 100 μM VOSO₄ and 4.5 mM pyruvate was improved compared to VOSO₄-only treated cells. The two-way analysis of variance revealed that the reduction of the adverse effects of VOSO₄ in the presence of pyruvate was due to the independent action of pyruvate as well as antagonistic interaction between VOSO₄ and pyruvate. From these data, it can be concluded that the pyruvate treatment may play a beneficial role in reducing vanadium-triggered health hazards.

Bis(picolinato) complexes of vanadium and zinc as potential antidiabetic agents: synthesis, structural elucidation and in vitro insulin-mimetic activity study

The studied vanadium(iv), vanadium(v) and zinc(ii) complexes show inhibition of the free fatty acid release from rat adipocytes.

Spectroscopic, electrochemical, docking and molecular dynamics studies on the interaction of three oxovanadium (IV) Schiff base complexes with bovine serum albumin and their cytotoxicity against cancer

This study was designed to investigate the interaction of three oxovanadium (IV) Schiff base complexes with bovine serum albumin (BSA) by means of various spectroscopic and electrochemical methods along with molecular docking study and molecular dynamics simulations. Binding constants were estimated by fluorescence and UV-Vis spectroscopy. The results indicated a good affinity of the complexes for BSA in which furyl derivative had more activity. Molecular docking study showed that these complexes have the similar binding modes and located within subdomain IB in site III of BSA. The supporting of molecular docking and molecular dynamics results by experimental data, confirms the validity of the interactions data obtained by these methods. Biological activity against cancer cell showed that furyl derivative has higher activity than other complexes. Pharmaceutical analysis also showed that, these complexes potentially can be used as anticancer agents.

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.

Effects of citric acid and the siderophore desferrioxamine B (DFO-B) on the mobility of germanium and rare earth elements in soil and uptake in Phalaris arundinacea

Effects of citric acid and desferrioxamine B (DFO-B) on the availability of Ge and selected rare earth elements (REEs) (La, Nd, Gd, Er) to Phalaris arundinacea were investigated. A soil dissolution experiment was conducted to elucidate the effect of citric acid and DFO-B at different concentrations (1 and 10 mmol L^-1 citric acid) on the release of Ge and REEs from soil. In a greenhouse, plants of P. arundinacea were cultivated on soil and on sand cultures to investigate the effects of citric acid and DFO-B on the uptake of Ge and REEs by the plants. Addition of 10 mmol L^-1 citric acid significantly enhanced desorption of Ge and REEs from soil and uptake into soil-grown plants. Applying DFO-B enhanced the dissolution and the uptake of REEs, while no effect on Ge was observed. In sand cultures, the presence of citric acid and DFO-B significantly decreased the uptake of Ge and REEs, indicating a discrimination of the formed complexes during uptake. This study clearly indicates that citric acid and the microbial siderophore DFO-B may enhance phytoextraction of Ge and REEs due to the formation of soluble complexes that increase the migration of elements in the rhizosphere.

Heteroleptic oxidovanadium(IV) complexes of 2-hydroxynaphtylaldimine and polypyridyl ligands against Trypanosoma cruzi and prostate cancer cells

In Latin America Chagas disease is an endemic illness caused by the parasite Trypanosoma cruzi (T. cruzi), killing more people than any other parasitic disease. Current chemotherapies are old and inadequate, thus the development of efficient ones is urgently needed. Vanadium-based complexes have been shown to be a promising approach both against parasitic diseases and cancer and this study aims to achieve significant advances in the pursue of effective compounds. Heteroleptic vanadium complexes of Schiff bases and polypyridine compounds were prepared and their stability in solution evaluated by EPR (Electronic Paramagnetic Resonance) and NMR spectroscopy. Their in vitro activities were evaluated against T. cruzi and a set of cells lines representative of human cancer conditions, namely ovarian, breast and prostate cancer. In T. cruzi, most of the complexes depicted IC₅₀ values in the low μM range, induced changes of mitochondrial membrane potential and apoptosis. In cancer cells, complexes showed good to moderate activity and in metastatic cells (prostate PC3), some complexes inhibited the migratory ability, this suggesting that they display antimetastatic potential. Interestingly, complex 5 seemed to have a dual effect being the most cytotoxic complex on all cancer cells and also the most active anti-T-cruzi compound of the series. Globally the complexes showed promising anticancer and anti T. cruzi activities and also displayed some characteristics indicating they are worth to be further explored as antimetastatic drugs.

A cross-sectional study measuring vanadium and chromium levels in paediatric patients with CKD

OBJECTIVES

Although many secondary effects of high levels of vanadium (V) and chromium (Cr) overlap with symptoms seen in paediatric patients with chronic kidney disease (CKD), their plasma V and Cr levels are understudied.

DESIGN

Ancillary cross-sectional study to a prospective, longitudinal, randomised controlled trial.

SETTING

Children's Hospital of Western Ontario, London Health Sciences Centre, London, Ontario, Canada.

PARTICIPANTS

36 children and adolescents 4-18 years of age with CKD.

INTERVENTIONS

1-6 trace element measurements per patient. Cystatin C (CysC) estimated glomerular filtration rate (eGFR) was calculated using the Filler formula. Plasma V and Cr levels were measured using high-resolution sector field inductively coupled mass spectrometry. Anthropomorphic data and blood parameters were collected from our electronic chart programme. Water Cr and V data were obtained from the Ontario Water (Stream) Quality Monitoring Network.

PRIMARY AND SECONDARY OUTCOME MEASURES

Primary outcomes: plasma Cr and V.

SECONDARY OUTCOMES

age, season, CysC, CysC eGFR, and Cr and V levels in environmental water.

RESULTS

The median (IQR) eGFR was 51 mL/min/1.73 m² (35, 75). The median V level was 0.12 µg/L (0.09, 0.18), which was significantly greater than the 97.5th percentile of the reference interval of 0.088 µg/L; 32 patients had at least one set of V levels above the published reference interval. The median Cr level was 0.43 µg/L (0.36, 0.54), which was also significantly greater than the established reference interval; 34 had at least one set of Cr levels above the published reference interval. V and Cr levels were moderately correlated. Only some patients had high environmental exposure.

CONCLUSIONS

Our study suggests that paediatric patients with CKD have elevated plasma levels of V and Cr. This may be the result of both environmental exposure and a low eGFR. It may be necessary to monitor V and Cr levels in patients with an eGFR <30 mL/min/1.73 m².

TRIAL REGISTRATION NUMBER

NCT02126293; HC#172241.

Characterization and cytotoxic effect of aqua-(2,2',2''-nitrilotriacetato)-oxo-vanadium salts on human osteosarcoma cells

The use of protonated N-heterocyclic compound, i.e. 2,2'-bipyridinium cation, [bpyH+], enabled to obtain the new nitrilotriacetate oxidovanadium(IV) salt of the stoichiometry [bpyH][VO(nta)(H2O)]H2O. The X-ray measurements have revealed that the compound comprises the discrete mononuclear [VO(nta)(H2O)]- coordination ion that can be rarely found among other known compounds containing nitrilotriacetate oxidovanadium(IV) moieties. The antitumor activity of [bpyH][VO(nta)(H2O)]H2O and its phenanthroline analogue, [phenH][VO(nta)(H2O)](H2O)0.5, towards human osteosarcoma cell lines (MG-63 and HOS) has been assessed (the LDH and BrdU tests) and referred to cis-Pt(NH3)2Cl2 (used as a positive control). The compounds exert a stronger cytotoxic effect on MG-63 and HOS cells than in untransformed human osteoblast cell line. Thus, the [VO(nta)(H2O)]- containing coordination compounds can be considered as possible antitumor agents in the osteosarcoma model of bone-related cells in culture.

Vanadium and zinc complexes of 5-cyanopicolinate and pyrazine derivatives: synthesis, structural elucidation and in vitro insulino-mimetic activity study

Inhibition of free fatty acid release from rat adipocytes was observed for vanadium(iv), vanadium(v) and zinc(ii) complexes.

Evaluation of cellular uptake, cytotoxicity and cellular ultrastructural effects of heteroleptic oxidovanadium(IV) complexes of salicylaldimines and polypyridyl ligands

Searching for prospective vanadium-based drugs for cancer treatment, a new series of structurally related [V^IVO(L-2H)(NN)] compounds (1-8) was developed. They include a double deprotonated salicylaldimine Schiff base ligand (L-2H) and different NN-polypyridyl co-ligands having DNA intercalating capacity. Compounds were characterized in solid state and in solution. EPR spectroscopy suggests that the NN ligands act as bidentate and bind through both nitrogen donor atoms in an axial-equatorial mode. The cytotoxicity was evaluated in human tumoral cells (ovarian A2780, breast MCF7, prostate PC3). The cytotoxic activity was dependent on type of cell and incubation time. At 24h PC3 cells presented low sensitivity, but at 72h all complexes showed high cytotoxic activity in all cells. Human kidney HEK293 and ovarian cisplatin resistant A2780cisR cells were also included to evaluate selectivity towards cancer cells and potency to overcome cisplatin resistance, respectively. Most complexes showed no detectable interaction with plasmid DNA, except 2 and 7 which depicted low ability to induce single strand breaks in supercoiled DNA. Based on the overall cytotoxic profile, complexes with 2,2´-bipyridine and 1,10-phenanthroline ligands (1 and 2) were selected for further studies, which consisted on cellular distribution and ultrastructural analyses. In the A2780 cells both depicted different distribution profiles; the former accumulates mostly at the membrane and the latter in the cytoskeleton. Morphology of treated cells showed nuclear atypia and membrane alterations, more severe for 1. Complexes induce different cell death pathways, predominantly necrosis for 1 and apoptosis for 2. Complexes alternative mode of cell death motivates the possibility for further developments.

Influence of Primary Ligands (ODA, TDA) on Physicochemical and Biological Properties of Oxidovanadium (IV) Complexes with Bipy and Phen as Auxiliary Ligands

The influence of the oxydiacetate (ODA) and thiodiacetate (TDA) ligands on the physicochemical and biological properties of the oxidovanadium(IV) ternary complexes of the VO(L)(B) type, where L denotes ODA or TDA and B denotes 2,2'-bipyridine (bipy) or 1,10-phenanthroline (phen), has been investigated. The stability of the complexes in aqueous solutions, assessed based on the potentiometric titration method, increases in the following direction: VO(TDA)(bipy) < VO(ODA)(bipy) < VO(TDA)(phen) < VO(ODA)(phen). Furthermore, the influence of the TDA and ODA ligands on the antioxidant activity of the oxidovanadium(IV) complexes toward superoxide free radical (O₂^•-), 2,2'-azinobis(3-ethylbenzothiazoline-6 sulfonic acid) cation radical (ABTS^+•) and 2,2-diphenyl-1-picrylhydrazyl radical (DPPH^•) has been examined and discussed. The reactivity of the complexes toward O₂^•- increases in the following direction: VO(TDA)(phen) < VO(TDA)(bipy) ≈ VO(ODA)(bipy) < VO(ODA)(phen). The antioxidant activity against ABTS^+• and DPPH^• free radicals is higher for phen complexes, whereas the thiodiacetate complexes are more reactive than are the corresponding oxydiacetate ones. Finally, herein, the cytoprotective activity of the complexes against the oxidative damage generated exogenously by hydrogen peroxide in the hippocampal neuronal HT22 cell line (the MTT and LDH tests) is reported. In a low concentration (1 μM), the cytoprotective action of thiodiacetate complexes is much higher than that of the corresponding oxydiacetate complexes. However, in the higher concentration range (10 and 100 μM), the antioxidant activity of the complexes is overcompensated by their cytotoxic effect.

Vanadium (V) and magnesium (Mg) - In vivo interactions: A review

Vanadium (V) and magnesium (Mg) arouse interest of many research centres worldwide. Many aspects of their action have already been recognized but some of them have not been fully elucidated yet. Relatively little is known about the mechanisms of absorption, transport, and excretion of V. There is also a lack of sufficient data about the most sensitive biomarkers of V toxicity and the mechanisms of its toxic action, which have not been fully explained yet. There is also a lack of comprehensive research on the consequences, character, and mechanisms of mutual interactions of V (which has strong pro-oxidant properties) with elements with an antioxidant potential such as Mg, the recognition of which, besides the cognitive value, may have great practical importance. It should be highlighted that the question of interactions between elements is always up to date and it is still an important issue in toxicology. A comprehensive research on interactions of V with Mg can be particularly important in the studies of the usage of V (which has a narrow margin of safety) in the treatment of certain diseases in humans, especially diabetes, which is accompanied by changes in the level of Mg in the tissues and weakening of the antioxidant barrier and oxidative stress. Therefore, the aspect concerning the possible interaction of V (as a potent pro-oxidant) with Mg (as an antioxidant) was the subject of our special interest. In addition, the examination of the effects of the interactions between V and Mg is very important especially for extending the knowledge of the mechanism of the influence of V on the organism and a potential role of Mg (which is characterized by a wide therapeutic window) in prevention of V toxicity. This review summarizes the most important results obtained from our experiments in a rodent model referring to the interactions of V with Mg on the background of the in vivo experimental data published by other researchers of this issue. Our studies have shown that V and Mg supplied in combination are able to modulate the response in an interactive manner to produce a specific effect that is distinct from that observed during separate administration thereof. The present report also provides the most important information about the effects of the action of V and Mg with other metals.

Behavior of the potential antitumor V(IV)O complexes formed by flavonoid ligands. 3. Antioxidant properties and radical production capability

The radical production capability and the antioxidant properties of some V(IV)O complexes formed by flavonoid ligands were examined. In particular, the bis-chelated species of quercetin (que), [VO(que)2](2-), and morin (mor), [VO(mor)2], were evaluated for their capability to reduce the stable radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) and produce the hydroxyl radical (•)OH by Fenton-like reactions, where the reducing agent is V(IV)O(2+). The results were compared with those displayed by other V(IV)O complexes, such as [VO(H2O)5](2+), [VO(acac)2] (acac=acetylacetonate) and [VO(cat)2](2-) (cat=catecholate). The capability of the V(IV)O flavonoids complexes to reduce DPPH is much larger than that of the V(IV)O species formed by non-antioxidant ligands and it is due mainly to the flavonoid molecule. Through the 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin trapping assay of the hydroxyl radical it was possible to demonstrate that in acidic solution V(IV)O(2+) has an effectiveness in producing (•)OH radicals comparable to that of Fe(2+). When V(IV)O complexes of flavonoids were taken into account, the amount of hydroxyl radicals produced in Fenton-like reactions depends on the specific structure of the ligand and on their capability to reduce H2O2 to give (•)OH. Both the formation of reactive oxygen species (ROS) under physiological conditions by V(IV)O complexes of flavonoid ligands and their radical scavenging capability can be put in relationship with their antitumor effectiveness and it could be possible to modulate these actions by changing the features of the flavonoid coordinated to the V(IV)O(2+) ion, such as the entity, nature and position of the substituents and the number of phenolic groups.

Metforminium Decavanadate as a Potential Metallopharmaceutical Drug for the Treatment of Diabetes Mellitus

New potential drugs based on vanadium are being developed as possible treatments for diabetes mellitus (DM) and its complications. In this regard, our working group developed metforminium decavanadate (MetfDeca), a compound with hypoglycemic and hypolipidemic properties. MetfDeca was evaluated in models of type 1 and type 2 diabetes mellitus, on male Wistar rats. Alloxan-induction was employed to produce DM1 model, while a hypercaloric-diet was employed to generate DM2 model. Two-month treatments with 3.7 μg (2.5 μM)/300 g/twice a week for DM2 and 7.18 μg (4.8 μM)/300 g/twice a week for DM1 of MetfDeca, respectively, were administered. The resulting pharmacological data showed nontoxicological effects on liver and kidney. At the same time, MetfDeca showed an improvement of carbohydrates and lipids in tissues and serum. MetfDeca treatment was better than the monotherapies with metformin for DM2 and insulin for DM1. Additionally, MetfDeca showed a protective effect on pancreatic beta cells of DM1 rats, suggesting a possible regeneration of these cells, since they recovered their insulin levels. Therefore, MetfDeca could be considered not only as an insulin-mimetic agent, but also as an insulin-enhancing agent. Efforts to elucidate the mechanism of action of this compound are now in progress.

Chemistry of Monomeric and Dinuclear Non-Oxido Vanadium(IV) and Oxidovanadium(V) Aroylazine Complexes: Exploring Solution Behavior

A series of mononuclear non-oxido vanadium(IV) [V(IV)(L(1-4))2] (1-4), oxidoethoxido vanadium(V) [V(V)O(L(1-4))(OEt)] (5-8), and dinuclear μ-oxidodioxidodivanadium(V) [V(V)2O3(L(1))2] (9) complexes with tridentate aroylazine ligands are reported [H2L(1) = 2-furoylazine of 2-hydroxy-1-acetonaphthone, H2L(2) = 2-thiophenoylazine of 2-hydroxy-1-acetonaphthone, H2L(3) = 1-naphthoylazine of 2-hydroxy-1-acetonaphthone, H2L(4) = 3-hydroxy-2-naphthoylazine of 2-hydroxy-1-acetonaphthone]. The complexes are characterized by elemental analysis, by various spectroscopic techniques, and by single-crystal X-ray diffraction (for 2, 3, 5, 6, 8, and 9). The non-oxido V(IV) complexes (1-4) are quite stable in open air as well as in solution, and DFT calculations allow predicting EPR and UV-vis spectra and the electronic structure. The solution behavior of the [V(V)O(L(1-4))(OEt)] compounds (5-8) is studied confirming the formation of at least two different types of V(V) species in solution, monomeric corresponding to 5-8, and μ-oxidodioxidodivanadium [V(V)2O3(L(1-4))2] compounds. The μ-oxidodioxidodivanadium compound [V(V)2O3(L(1))2] (9), generated from the corresponding mononuclear complex [V(V)O(L(1))(OEt)] (5), is characterized in solution and in the solid state. The single-crystal X-ray diffraction analyses of the non-oxido vanadium(IV) compounds (2 and 3) show a N2O4 binding set and a trigonal prismatic geometry, and those of the V(V)O complexes 5, 6, and 8 and the μ-oxidodioxidodivanadium(V) (9) reveal that the metal center is in a distorted square pyramidal geometry with O4N binding sets. For the μ-oxidodioxidodivanadium species in equilibrium with 5-8 in CH2Cl2, no mixed-valence complexes are detected by chronocoulometric and EPR studies. However, upon progressive transfer of two electrons, two distinct monomeric V(IV)O species are detected and characterized by EPR spectroscopy and DFT calculations.

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

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

Water soluble heterometallic potassium-dioxidovanadium(V) complexes as potential antiproliferative agents

Two water soluble heterometallic potassium–dioxidovanadium polymers, [KVO2(L1)]n (1) and [KVO2(L2)(H2O)]n (2) [H2L1= (2,3-dihydroxybenzylidene)-2-hydroxybenzohydrazide and H2L2=(2,3-dihydroxybenzylidene)benzohydrazide], have been synthesized and characterized by IR, NMR, elemental analysis and single crystal X-ray diffraction. The antiproliferative potentials of 1 and 2 were examined towards human colorectal carcinoma (HCT116), and lung (A549) and breast (MCF7) adenocarcinoma cell lines. 1 exhibits a high cytotoxic activity against colorectal carcinoma cells (HCT116), with IC50 lower than those for cisplatin.

Vanadium compounds in medicine

Vanadium is a transition metal that, being ubiquitously distributed in soil, crude oil, water and air, also found roles in biological systems and is an essential element in most living beings. There are also several groups of organisms which accumulate vanadium, employing it in their biological processes. Vanadium being a biological relevant element, it is not surprising that many vanadium based therapeutic drugs have been proposed for the treatment of several types of diseases. Namely, vanadium compounds, in particular organic derivatives, have been proposed for the treatment of diabetes, of cancer and of diseases caused by parasites. In this work we review the medicinal applications proposed for vanadium compounds with particular emphasis on the more recent publications. In cells, partly due to the similarity of vanadate and phosphate, vanadium compounds activate numerous signaling pathways and transcription factors; this by itself potentiates application of vanadium-based therapeutics. Nevertheless, this non-specific bio-activity may also introduce several deleterious side effects as in addition, due to Fenton's type reactions or of the reaction with atmospheric O2, VCs may also generate reactive oxygen species, thereby introducing oxidative stress with consequences presently not well evaluated, particularly for long-term administration of vanadium to humans. Notwithstanding, the potential of vanadium compounds to treat type 2 diabetes is still an open question and therapies using vanadium compounds for e.g. antitumor and anti-parasitic related diseases remain promising.

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.

51V magic angle spinning NMR spectroscopy and quantum chemical calculations in vanadium bio-inorganic systems: current perspective

In recent years, 51V magic angle spinning (MAS) NMR spectroscopy has been widely used to characterize vanadium centers in biology, biomimetic complexes, and inorganic compounds of medicinal and industrial relevance. It has been demonstrated that 51V NMR parameters are sensitive probes of the coordination geometry and chemical environment of the metal center, beyond the first coordination sphere. To establish the relationships between NMR parameters and structure of the vanadium centers, over the past decade a large series of coordination complexes have been analyzed by MAS NMR spectroscopy. It has been demonstrated that the interpretation of the NMR parameters requires the use of theoretical methods, such as density functional (DFT) theory, whereby the experimental NMR observables are linked to the electronic and structural properties of a molecule. DFT calculations have been successfully employed to not only predict NMR parameters but to also yield valuable information regarding the structure and function of various vanadium compounds. In this report, we review the current state of the field, and present a survey of bioinorganic vanadium complexes as well as vanadium-dependent haloperoxidases analyzed using 51V MAS NMR spectroscopy and DFT calculations, to illustrate the rich information content available from such a combined approach.

Reactivity and Speciation of Anti-Diabetic Vanadium Complexes in Whole Blood and Its Components: The Important Role of Red Blood Cells

Reactions with blood components are crucial for controlling the antidiabetic, anticancer, and other biological activities of V(V) and V(IV) complexes. Despite extensive studies of V(V) and V(IV) reactions with the major blood proteins (albumin and transferrin), reactions with whole blood and red blood cells (RBC) have been studied rarely. A detailed speciation study of Na3[V(V)O4] (A), K4[V(IV)2O2(citr)2]·6H2O (B; citr = citrato(4-)); [V(IV)O(ma)2] (C; ma = maltolato(-)), and (NH4)[V(V)(O)2(dipic)] (D; dipic = pyridine-2,6-dicarboxylato(2-)) in whole rat blood, freshly isolated rat plasma, and commercial bovine serum using X-ray absorption near-edge structure (XANES) spectroscopy is reported. The latter two compounds are potential oral antidiabetic drugs, and the former two are likely to represent their typical decomposition products in gastrointestinal media. XANES spectral speciation was performed by principal component analysis and multiple linear regression techniques, and the distribution of V between RBC and plasma fractions was measured by electrothermal atomic absorption spectroscopy. Reactions of A, C, or D with whole blood (1.0 mM V, 1-6 h at 310 K) led to accumulation of ∼50% of total V in the RBC fraction (∼10% in the case of B), which indicated that RBC act as V carriers to peripheral organs. The spectra of V products in RBC were independent of the initial V complex, and were best fitted by a combination of V(IV)-carbohydrate (2-hydroxyacid moieties) and/or citrate (65-85%) and V(V)-protein (15-35%) models. The presence of RBC created a more reducing environment in the plasma fraction of whole blood compared with those in isolated plasma or serum, as shown by the differences in distribution of V(IV) and V(V) species in the reaction products of A-D in these media. At physiologically relevant V concentrations (<50 μM), this role of RBC may promote the formation of V(III)-transferrin as a major V carrier in the blood plasma. The results reported herein have broad implications for the roles of RBC in the transport and speciation of metal pro-drugs that have broad applications across medicine.

Oxidovanadium(IV) sulfate-induced glucose uptake in HepG2 cells through IR/Akt pathway and hydroxyl radicals

The insulin-mimetic and anti-diabetic properties of vanadium and related compounds have been well documented both in vitro and in vivo. However, the molecular basis of the link between vanadium and the insulin signaling pathway in diabetes mellitus is not fully described. We investigated the effects of reactive oxygen species (ROS) induced by oxidovanadium(IV) sulfate (VOSO4) on glucose uptake and the insulin signaling pathway in human hepatoma cell line HepG2. Exposure of cells to VOSO4 (5-50 μM) resulted in an increase in glucose uptake, insulin receptor (IR) and protein kinase B (Akt) phosphorylation and intracellular ROS generation. Using Western blot, we found that catalase and sodium formate, but not superoxide dismutase, prevented the increase of hydroxyl radical (·OH) generation and significantly decreased VOSO4-induced IR and Akt phosphorylation. These results suggest that VOSO4-induced ·OH radical, which is a signaling species, promotes glucose uptake via the IR/Akt signaling pathway.

Aqueous citrato-oxovanadate(IV) precursor solutions for VO2: synthesis, spectroscopic investigation and thermal analysis

An aqueous precursor solution, containing citrato-VO(2+) complexes, is synthesized for the formation of monoclinic VO2. With regard to the decomposition of the VO(2+) complexes towards vanadium oxide formation, it is important to gain insights into the chemical structure and transformations of the precursor during synthesis and thermal treatment. Hence, the conversion of the cyclic [V4O12](4-) ion to the VO(2+) ion in aqueous solution, using oxalic acid as an acidifier and a reducing agent, is studied by (51)Vanadium nuclear magnetic resonance spectroscopy. The citrate complexation of this VO(2+) ion and the differentiation between a solution containing citrato-oxalato-VO(2+) and citrato-VO(2+) complexes are studied by electron paramagnetic resonance and Fourier transform infra-red spectroscopy. In both solutions, the VO(2+) containing complex is mononuclear and has a distorted octahedral geometry with a fourfold R-CO2(-) ligation at the equatorial positions and likely a fifth R-CO2(-) ligation at the axial position. Small differences in the thermal decomposition pathway between the gel containing citrato-oxalato-VO(2+) complexes and the oxalate-free gel containing citrato-VO(2+) complexes are observed between 150 and 200 °C in air and are assigned to the presence of (NH4)2C2O4 in the citrato-oxalato-VO(2+) solution. Both precursor solutions are successfully used for the formation of crystalline vanadium oxide nanostructures on SiO2, after thermal annealing at 500 °C in a 0.1% O2 atmosphere. However, the citrato-oxalato-VO(2+) and the oxalate-free citrato-VO(2+) solution result in the formation of monoclinic V6O13 and monoclinic VO2, respectively.

Biotransformations of Antidiabetic Vanadium Prodrugs in Mammalian Cells and Cell Culture Media: A XANES Spectroscopic Study

The antidiabetic activities of vanadium(V) and -(IV) prodrugs are determined by their ability to release active species upon interactions with components of biological media. The first X-ray absorption spectroscopic study of the reactivity of typical vanadium (V) antidiabetics, vanadate ([V^VO₄]^3–, A) and a vanadium(IV) bis(maltolato) complex (B), with mammalian cell cultures has been performed using HepG2 (human hepatoma), A549 (human lung carcinoma), and 3T3-L1 (mouse adipocytes and preadipocytes) cell lines, as well as the corresponding cell culture media. X-ray absorption near-edge structure data were analyzed using empirical correlations with a library of model vanadium(V), -(IV), and -(III) complexes. Both A and B ([V] = 1.0 mM) gradually converged into similar mixtures of predominantly five- and six-coordinate V^V species (∼75% total V) in a cell culture medium within 24 h at 310 K. Speciation of V in intact HepG2 cells also changed with the incubation time (from ∼20% to ∼70% V^IV of total V), but it was largely independent of the prodrug used (A or B) or of the predominant V oxidation state in the medium. Subcellular fractionation of A549 cells suggested that V^V reduction to V^IV occurred predominantly in the cytoplasm, while accumulation of V^V in the nucleus was likely to have been facilitated by noncovalent bonding to histone proteins. The nuclear V^V is likely to modulate the transcription process and to be ultimately related to cell death at high concentrations of V, which may be important in anticancer activities. Mature 3T3-L1 adipocytes (unlike for preadipocytes) showed a higher propensity to form V^IV species, despite the prevalence of V^V in the medium. The distinct V biochemistry in these cells is consistent with their crucial role in insulin-dependent glucose and fat metabolism and may also point to an endogenous role of V in adipocytes.

The first detailed speciation study of typical antidiabetic vanadium(V/IV) complexes in mammalian cell culture systems showed that the complexes decomposed rapidly in cell culture media and were further metabolized by the cells, which included interconversions of V^V and V^IV species.