Vanadium Compounds with Antidiabetic Potential

Over the last four decades, vanadium compounds have been extensively studied as potential antidiabetic drugs. With the present review, we aim at presenting a general overview of the most promising compounds and the main results obtained with in vivo studies, reported from 1899-2023. The chemistry of vanadium is explored, discussing the importance of the structure and biochemistry of vanadate and the impact of its similarity with phosphate on the antidiabetic effect. The spectroscopic characterization of vanadium compounds is discussed, particularly magnetic resonance methodologies, emphasizing its relevance for understanding species activity, speciation, and interaction with biological membranes. Finally, the most relevant studies regarding the use of vanadium compounds to treat diabetes are summarized, considering both animal models and human clinical trials. An overview of the main hypotheses explaining the biological activity of these compounds is presented, particularly the most accepted pathway involving vanadium interaction with phosphatase and kinase enzymes involved in the insulin signaling cascade. From our point of view, the major discoveries regarding the pharmacological action of this family of compounds are not yet fully understood. Thus, we still believe that vanadium presents the potential to help in metabolic control and the clinical management of diabetes, either as an insulin-like drug or as an insulin adjuvant. We look forward to the next forty years of research in this field, aiming to discover a vanadium compound with the desired therapeutic properties.

Rafting on the Evidence for Lipid Raft-like Domains as Hubs Triggering Environmental Toxicants' Cellular Effects

The plasma membrane lipid rafts are cholesterol- and sphingolipid-enriched domains that allow regularly distributed, sub-micro-sized structures englobing proteins to compartmentalize cellular processes. These membrane domains can be highly heterogeneous and dynamic, functioning as signal transduction platforms that amplify the local concentrations and signaling of individual components. Moreover, they participate in cell signaling routes that are known to be important targets of environmental toxicants affecting cell redox status and calcium homeostasis, immune regulation, and hormonal functions. In this work, the evidence that plasma membrane raft-like domains operate as hubs for toxicants' cellular actions is discussed, and suggestions for future research are provided. Several studies address the insertion of pesticides and other organic pollutants into membranes, their accumulation in lipid rafts, or lipid rafts' disruption by polychlorinated biphenyls (PCBs), benzo[a]pyrene (B[a]P), and even metals/metalloids. In hepatocytes, macrophages, or neurons, B[a]P, airborne particulate matter, and other toxicants caused rafts' protein and lipid remodeling, oxidative changes, or amyloidogenesis. Different studies investigated the role of the invaginated lipid rafts present in endothelial cells in mediating the vascular inflammatory effects of PCBs. Furthermore, in vitro and in vivo data strongly implicate raft-localized NADPH oxidases, the aryl hydrocarbon receptor, caveolin-1, and protein kinases in the toxic mechanisms of occupational and environmental chemicals.

The antihyperglycemic and hypolipidemic activities of a sulfur-oxidovanadium(IV) complex

This study describes the synthesis, characterization, and biological activity of a new class of antidiabetic oxidovanadium(IV)-complexes with S₂O₂ coordination mode. The target complex 3,6-dithio-1,8-octanediolatooxidovanadium(IV), abbreviated as ([V^IVO(octd)]), where octd = 3,6-dithio-1,8-octanediol, is formed from the reaction between the 3,6-dithio-1,8-octanediol and vanadyl sulfate (V^IVOSO₄). The effects of treatment with ([V^IVO(octd)] on blood glucose, lipidic profile, body weight, food intake, water intake, urinary volume, glycogen levels, and biomarkers for liver toxicity were investigated using a streptozotocin (STZ)-induced diabetic Wistar rats model. The results have shown that the [V^IVO(octd)] complex caused a significant decrease in blood glucose (247.6 ± 19.3 mg/dL vs 430.1 ± 37.6 mg/dL diabetic group, p < 0.05), triglycerides (TG, 50%) and very low-density cholesterol (VLDL-C, 50%) levels in STZ-diabetic rats after 3 weeks of treatment. The [V^IVO(octd)] has shown antihyperglycemic activity in diabetic rats as well as a reduction in elevated lipid levels. Time-dependent studies using EPR and ⁵¹V NMR spectroscopy of [V^IVO(octd)] were done in aqueous solutions to determine the complex stability and species present in the oral gavage solution used for complex administration. The spectroscopic studies have shown that the antidiabetic/hypolipidemic activity could be attributed to [V^IVO(octd)], vanadium species resulting from redox processes, the hydrolysis of [V^IVO(octd)] and its decomposition products, or some combination of these factors. In summary, the oxidovanadium(IV) complex containing the S₂O₂ donor ligand has desirable antidiabetic properties eliminating the symptoms of Diabetes mellitus and its comorbidities.

Glycoprotein G-protein Coupled Receptors in Disease: Luteinizing Hormone Receptors and Follicle Stimulating Hormone Receptors

Signal transduction by luteinizing hormone receptors (LHRs) and follicle-stimulating hormone receptors (FSHRs) is essential for the successful reproduction of human beings. Both receptors and the thyroid-stimulating hormone receptor are members of a subset of G-protein coupled receptors (GPCRs) described as the glycoprotein hormone receptors. Their ligands, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) and a structurally related hormone produced in pregnancy, human chorionic gonadotropin (hCG), are large protein hormones that are extensively glycosylated. Although the primary physiologic functions of these receptors are in ovarian function and maintenance of pregnancy in human females and spermatogenesis in males, there are reports of LHRs or FSHRs involvement in disease processes both in the reproductive system and elsewhere. In this review, we evaluate the aggregation state of the structure of actively signaling LHRs or FSHRs, their functions in reproduction as well as summarizing disease processes related to receptor mutations affecting receptor function or expression in reproductive and non-reproductive tissues. We will also present novel strategies for either increasing or reducing the activity of LHRs signaling. Such approaches to modify signaling by glycoprotein receptors may prove advantageous in treating diseases relating to LHRs or FSHRs function in addition to furthering the identification of new strategies for modulating GPCR signaling.

Vanadium and insulin: Partners in metabolic regulation

Since the 1970s, the biological role of vanadium compounds has been discussed as insulin-mimetic or insulin-enhancer agents. The action of vanadium compounds has been investigated to determine how they influence the insulin signaling pathway. Khan and coworkers proposed key proteins for the insulin pathway study, introducing the concept "critical nodes". In this review, we also considered critical kinases and phosphatases that participate in this pathway, which will permit a better comprehension of a critical node, where vanadium can act: a) insulin receptor, insulin receptor substrates, and protein tyrosine phosphatases; b) phosphatidylinositol 3'-kinase, 3-phosphoinositide-dependent protein kinase and mammalian target of rapamycin complex, protein kinase B, and phosphatase and tensin homolog; and c) insulin receptor substrates and mitogen-activated protein kinases, each node having specific negative modulators. Additionally, leptin signaling was considered because together with insulin, it modulates glucose and lipid homeostasis. Even in recent literature, the possibility of vanadium acting against metabolic diseases or cancer is confirmed although the mechanisms of action are not well understood because these critical nodes have not been systematically investigated. Through this review, we establish that vanadium compounds mainly act as phosphatase inhibitors and hypothesize on their capacity to affect kinases, which are critical to other hormones that also act on common parts of the insulin pathway.

Synthesis, characterization, and biological properties of oxidovanadium(IV) complexes of acetylsalicylhydroxamic acid (N-acetyloxy-2-hydroxybenzamide) as potential antimicrobials

New oxidovanadium(IV) complexes of composition [VO(AcSHA)2] 1 and [VO(acac)(AcSHA)] 2 are synthesized by reactions of VOSO4.5H2O and [VO(acac)2] with acetylsalicylhydroxamic acid AcSH2A (C6H4(OH)(CONHOCOCH3)) in a 1:2 molar ratio in absolute ethanol. The compounds are characterized by the Fourier-transform infrared spectroscopy, ultraviolet–visible spectroscopy, electron spin resonance, and mass spectrometry along with elemental analyses, molar conductivity, and magnetic moment measurements. The infrared spectra of the complexes suggest bonding through carbonyl and phenolic oxygen atoms (O,O coordination). The magnetic moment, electron spin resonance, and mass spectra of the complexes indicate that both exist as monomers, and a distorted square pyramidal geometry around vanadium is proposed. The thermal behavior of the complexes is studied by thermogravimetry and differential thermal analysis techniques under an N2 atmosphere, yielding VO2 as the decomposition product. The in vitro antimicrobial assays against pathogenic Gram-positive bacteria, Gram-negative bacteria, and fungi (minimum inhibitory concentration method) show the appreciable antimicrobial potential relative to the respective standard drugs, tetracycline hydrochloride, and fluconazole.

Polyoxometalates function as indirect activators of a G protein-coupled receptor

A series of multivalent polyoxovanadates were found to activate signaling of a G protein coupled receptor, the luteinizing hormone receptor.

Synthesis, Characterisation, and Biological Properties of Oxidovanadium(IV) 3,5-Dinitrosalicylhydroxamate Complexes

The new oxidovanadium(iv) complexes of composition [VO(3,5(NO2)2C6H2(OH)CONHO)2] 1 and [VO(acac)(3,5(NO2)2C6H2(OH)CONHO)] 2 (where acac=(CH3COCHCOCH3)–] have been synthesised by the reactions of VOSO4·5H2O and [VO(acac)2] with potassium 3,5-dinitrosalicylhydroxamate (3,5-(NO2)2SHK) and characterised by elemental analyses, molar conductivity, magnetic moment measurements and FT-IR, UV-vis, and electron spin resonance (ESR) spectroscopies and mass spectrometry. Infrared spectra of complexes have indicated bonding through oxygen atoms of carbonyl and hydroxamic groups (O,O coordination). The magnetic moment, ESR, and mass spectra of the complexes suggested their monomeric nature, and a distorted square-pyramidal geometry around the vanadium has tentatively been proposed. The electrochemical behaviour of 1 and 2 has been studied by cyclic voltammetry. Thermal behaviour of the complexes studied by thermogravimetric and differential thermal analysis techniques has yielded VO2 as the decomposition product. The invitro antimicrobial activity of the ligand and complexes has been assayed against pathogenic bacteria and fungi by the minimum inhibitory concentration (MIC) method. The invitro antioxidant activity of the complexes has been determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging method.

Effects of vanadium(IV) compounds on plasma membrane lipids lead to G protein-coupled receptor signal transduction

Luteinizing hormone receptors (LHR), expressed at physiological numbers <30,000 receptors per cell, translocate to and signal within membrane rafts following binding of human chorionic gonadotropin (hCG). Similarly LHR signal in cells when treated with bis(maltolato)oxovanadium(IV) (BMOV), bis(ethylmaltolato)oxovanadium(IV) (BEOV) or VOSO₄, which decrease membrane lipid packing. Overexpressed LHR (>85,000 receptors per cell) are found in larger clusters in polarized homo-transfer fluorescence resonance energy transfer (homo-FRET) studies that were not affected by either hCG or vanadium compounds. Intracellular cyclic adenylate monophosphate (cAMP) levels indicate that only clustered LHR are active and produce the intracellular second messenger, cAMP. When LHR are over-expressed, cell signaling is unaffected by binding of hCG or vanadium compounds. To confirm the existence of intact complex, the EPR spectra of vanadium compounds in cell media were obtained using 1 mM BMOV, BEOV or VOSO₄. These data were used to determine intact complex in a 10 μM solution and verified by speciation calculations. Effects of BMOV and BEOV samples were about two-fold greater than those of aqueous vanadium(IV) making it likely that intact vanadium complex are responsible for effects of LHR function. This represents a new mechanism for activation of a G protein-coupled receptor; perturbations in the lipid bilayer by vanadium compounds lead to aggregation and accumulation of physiological numbers of LHR in membrane raft domains where they initiate signal transduction and production of cAMP, a second messenger involved in signaling.

Confinement Effects on Chemical Equilibria: Pentacyano(Pyrazine)Ferrate(II) Stability Changes within Nanosized Droplets of Water

Nanoscale confinement is known to impact properties of molecules and we observed changes in the reactivity of an iron coordination complex, pentacyano(pyrazine)ferrate(II). The confinement of two coordination complexes in a sodium AOT/isooctane reverse micellar (RM) water droplet was found to dramatically increase the hydrolysis rate of [Fe(CN)₅pyz]3- and change the monomer-dimer equilibria between [Fe(CN)₅pyz]3- and [Fe₂(CN)10pyz]6-. Combined UV-Vis and ¹H-NMR spectra of these complexes in RMs were analyzed and the position of the monomer-dimer equilibrium and the relative reaction times were determined at three different RM sizes. The data show that the hydrolysis rates (loss of pyrazine) are dramatically enhanced in RMs over bulk water and increase as the size of the RM decreases. Likewise, the monomer-dimer equilibrium changes to favor the formation of dimer as the RM size decreases. We conclude that the effects of the [Fe(CN)₅pyz]3- stability is related to its solvation within the RM.

Analytical Techniques in Lipidomics: State of the Art

Current studies related to lipid identification and determination, or lipidomics in biological samples, are one of the most important issues in modern bioanalytical chemistry. There are many articles dedicated to specific analytical strategies used in lipidomics in various kinds of biological samples. However, in such literature, there is a lack of articles dedicated to a comprehensive review of the actual analytical methodologies used in lipidomics. The aim of this article is to characterize the lipidomics methods used in modern bioanalysis according to the methodological point of view: (1) chromatography/separation methods, (2) spectroscopic methods and (3) mass spectrometry and also hyphenated methods. In the first part, we discussed thin layer chromatography (TLC), high-pressure liquid chromatography (HPLC), gas chromatography (GC) and capillary electrophoresis (CE). The second part includes spectroscopic techniques such as Raman spectroscopy (RS), Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR). The third part is a synthetic review of mass spectrometry, matrix-assisted laser desorption/ionization (MALDI), hyphenated methods, which include liquid chromatography-mass spectrometry (LC-MS), gas chromatography-mass spectrometry (GC-MS) and also multidimensional techniques. Other aspects are the possibilities of the application of the described methods in lipidomics studies. Due to the fact that the exploration of new methods of lipidomics analysis and their applications in clinical and medical studies are still challenging for researchers working in life science, we hope that this review article will be very useful for readers.

Vanadium(IV)-chlorodipicolinate inhibits 3T3-L1 preadipocyte adipogenesis by activating LKB1/AMPK signaling pathway

Our previous studies demonstrated that vanadium(IV) complex with 4-chlorodipicolinic acid (VOdipic-Cl) alleviates lipid abnormalities in streptozotocin (STZ)-induced diabetic rats. However, the molecular mechanisms are not fully understood. In the present study, the effect of VOdipic-Cl on adipogenesis and mechanisms of action in 3T3-L1 preadipocytes were investigated. The 3T3-L1 preadipocytes were induced to differentiate in the presence or absence of VOdipic-Cl for 8days. The cells were determined for proliferation, differentiation, lipid accumulation as well as the protein expressions of molecular targets that are involved in fatty acid synthesis. The results demonstrated that VOdipic-Cl at concentrations ranging from 2.5μM to 10μM reduced the intracellular lipid content by 10%, 22% and 30% compared to control. VOdipic-Cl down-regulated the expression of peroxisome proliferator-activated receptor (PPARγ), CCAAT element binding protein a (C/EBPα), sterol regulatory element binding protein 1c (SREBP-1c), fatty acid synthase (FAS) and fatty acid-binding protein 4 (FABP4) and activated the phosphorylation of acetyl coenzyme A carboxylase (ACC), adenosine monophosphate-activated protein kinase (AMPK) and liver kinase B1 (LKB1) in a dose-dependent manner. Further studies showed that AMPK small interfering RNA (siRNA) markedly up-regulated PPARγ, C/EBPα, FAS and FABP4 expression in the presence of VOdipic-Cl, respectively. When LKB1 was silenced with siRNA, the effect of VOdipic-Cl on AMPK phosphorylation was diminished. Taken together, these results suggested that VOdipic-Cl can inhibit 3T3-L1 preadipocyte differentiation and adipogenesis through activating the LKB1/AMPK-dependent signaling pathway. These findings raise the possibility that VOdipic-Cl may be a promising therapy in treatment of obesity.

Antidiabetic, Chemical, and Physical Properties of Organic Vanadates as Presumed Transition-State Inhibitors for Phosphatases

Studies of antidiabetic vanadium compounds, specifically the organic vanadate esters, are reviewed with regard to their chemistry and biological properties. The compounds are described from the perspective of how the fundamental chemistry and properties of organic vanadate esters impact their effects as inhibitors for phosphatases based on the structural information obtained from vanadium-phosphatase complexes. Vanadium compounds have been reported to have antidiabetic properties for more than a century. The structures and properties of organic vanadate complexes are reviewed, and the potency of such vanadium coordination complexes as antidiabetic agents is described. Because such compounds form spontaneously in aqueous environments, the reactions with most components in any assay or cellular environment has potential to be important and should be considered. Generally, the active form of vanadium remains elusive, although studies have been reported of a number of promising vanadium compounds. The description of the antidiabetic properties of vanadium compounds is described here in the context of recent characterization of vanadate-phosphatase protein structures by data mining. Organic vanadate ester compounds are generally four coordinate or five coordinate with the former being substrate analogues and the latter being transition-state analogue inhibitors. These studies demonstrated a framework for characterization of five-coordinate trigonal bipyramidal vanadium inhibitors by comparison with the reported vanadium-protein phosphatase complexes. The binding of the vanadium to the phosphatases is either as a five-coordinate exploded transition-state analogue or as a high energy intermediate, respectively. Even if potency as an inhibitor requires trigonal bipyramidal geometry of the vanadium when bound to the protein, such geometry can be achieved upon binding from compounds with other geometries. Desirable properties of ligands are identified and analyzed. Ligand interactions, as reported in one peptidic substrate, are favorable so that complementarity between phosphatase and coordinating ligand to the vanadium can be established resulting in a dramatic enhancement of the inhibitory potency. These considerations point to a frameshift in ligand design for vanadium complexes as phosphatase inhibitors and are consistent with other small molecule having much lower affinities. Combined, these studies do suggest that if effective delivery of potentially active antidiabetic compound such a the organic vanadate peptidic substrate was possible the toxicity problems currently reported for the salts and some of the complexes may be alleviated and dramatic enhancement of antidiabetic vanadium compounds may result.

In vitro effects of bis(1,2-dimethyl-3-hydroxy-4-pyridinonato)oxidovanadium(IV), or VO(dmpp)2, on insulin secretion in pancreatic islets of type 2 diabetic Goto-Kakizaki rats

Vanadium compounds have been explored as therapy of diabetes, and most studies have focussed on insulin mimetic effects, i.e. reducing hyperglycemia by improving glucose sensitivity and thus glucose uptake in sensitive tissues. We have recently shown that bis(1,2-dimethyl-3-hydroxy-4-pyridinonato)oxidovanadium(IV), VO(dmpp)2, has promising effects when compared to another vanadium compound, bis(maltolato)oxidovanadium(IV), BMOV, and insulin itself, in isolated adipocytes and in vivo in Goto-Kakizaki (GK) rats, an animal model of hereditary type 2 diabetes (T2D).We now have investigated in GK rats whether VO(dmpp)2 also modulates another important defect in T2D, impaired insulin secretion. VO(dmpp)2, but not BMOV, stimulated insulin secretion from isolated GK rat pancreatic islets at high, 16.7mM, but not at low–normal, 3.3 mM, glucose concentration. Mechanistic studies demonstrate that the insulin releasing effect of VO(dmpp)2 is due to its interaction with several steps in the stimulus-secretion coupling for glucose, including islet glucose metabolism and K-ATP channels, L-type Ca2+ channels, modulation by protein kinases A and C, as well as the exocytotic machinery. In conclusion, VO(dmpp)2 exhibits properties of interest for treatment of the insulin secretory defect in T2D, in addition to its well-described insulin mimetic activity.

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.

Evaluating transition state structures of vanadium-phosphatase protein complexes using shape analysis

Shape analysis of coordination complexes is well-suited to evaluate the subtle distortions in the trigonal bipyramidal (TBPY-5) geometry of vanadium coordinated in the active site of phosphatases and characterized by X-ray crystallography. Recent studies using the tau (τ) analysis support the assertion that vanadium is best described as a trigonal bipyramid, because this geometry is the ideal transition state geometry of the phosphate ester substrate hydrolysis (C.C. McLauchlan, B.J. Peters, G.R. Willsky, D.C. Crans, Coord. Chem. Rev. http://dx.doi.org/10.1016/j.ccr.2014.12.012 ; D.C. Crans, M.L. Tarlton, C.C. McLauchlan, Eur. J. Inorg. Chem. 2014, 4450-4468). Here we use continuous shape measures (CShM) analysis to investigate the structural space of the five-coordinate vanadium-phosphatase complexes associated with mechanistic transformations between the tetrahedral geometry and the five-coordinate high energy TBPY-5 geometry was discussed focusing on the protein tyrosine phosphatase 1B (PTP1B) enzyme. No evidence for square pyramidal geometries was observed in any vanadium-protein complexes. The shape analysis positioned the metal ion and the ligands in the active site reflecting the mechanism of the cleavage of the organic phosphate in a phosphatase. We identified the umbrella distortions to be directly on the reaction path between tetrahedral phosphate and the TBPY-5-types of high-energy species. The umbrella distortions of the trigonal bipyramid are therefore identified as being the most relevant types of transition state structures for the phosphoryl group transfer reactions for phosphatases and this may be related to the possibility that vanadium is an inhibitor for enzymes that support both exploded and five-coordinate transition states.

Oxidovanadium(IV/V) complexes as new redox mediators in dye-sensitized solar cells: a combined experimental and theoretical study

Corrosiveness is one of the main drawbacks of using the iodide/triiodide redox couple in dye-sensitized solar cells (DSSCs). Alternative redox couples including transition metal complexes have been investigated where surprisingly high efficiencies for the conversion of solar to electrical energy have been achieved. In this paper, we examined the development of a DSSC using an electrolyte based on square pyramidal oxidovanadium(IV/V) complexes. The oxidovanadium(IV) complex (Ph4P)2[V(IV)O(hybeb)] was combined with its oxidized analogue (Ph4P)[V(V)O(hybeb)] {where hybeb(4-) is the tetradentate diamidodiphenolate ligand [1-(2-hydroxybenzamido)-2-(2-pyridinecarboxamido)benzenato}and applied as a redox couple in the electrolyte of DSSCs. The complexes exhibit large electron exchange and transfer rates, which are evident from electron paramagnetic resonance spectroscopy and electrochemistry, rendering the oxidovanadium(IV/V) compounds suitable for redox mediators in DSSCs. The very large self-exchange rate constant offered an insight into the mechanism of the exchange reaction most likely mediated through an outer-sphere exchange mechanism. The [V(IV)O(hybeb)](2-)/[V(V)O(hybeb)](-) redox potential and the energy of highest occupied molecular orbital (HOMO) of the sensitizing dye N719 and the HOMO of [V(IV)O(hybeb)](2-) were calculated by means of density functional theory electronic structure calculation methods. The complexes were applied as a new redox mediator in DSSCs, while the cell performance was studied in terms of the concentration of the reduced and oxidized form of the complexes. These studies were performed with the commercial Ru-based sensitizer N719 absorbed on a TiO2 semiconducting film in the DSSC. Maximum energy conversion efficiencies of 2% at simulated solar light (AM 1.5; 1000 W m(-2)) with an open circuit voltage of 660 mV, a short-circuit current of 5.2 mA cm(-2), and a fill factor of 0.58 were recorded without the presence of any additives in the electrolyte.

Luteinizing hormone receptors are confined in mesoscale plasma membrane microdomains throughout recovery from receptor desensitization

We examined the involvement of membrane microdomains during human luteinizing hormone (LH) receptor recovery from receptor desensitization after removal of bound hormone. Lateral motions of individual desensitized LH receptors expressed on the surface of Chinese hamster ovary cells and transient association of these receptors with detergent-resistant membrane (DRM) microdomains isolated using isopycnic sucrose gradient ultracentrifugation were assessed. Single particle tracking experiments showed untreated individual LH receptors to be confined within cell-surface membrane compartments with an average diameter of 199 ± 17 nm and associated with membrane fractions characteristic of bulk plasma membrane. After brief exposure to human chorionic gonadotropin (hCG), LH receptors remained for several hours desensitized to hCG challenge. Throughout this period, significantly increased numbers of LH receptors were confined within smaller diameter (<120 nm) membrane compartments and associated with DRM fragments of characteristically low density. By 5 h, when cells again produced cAMP in response to hCG, unoccupied LH receptors were found in larger 169 ± 22 nm diameter cell-surface membrane compartments and >90 % of LH receptors were again found in high-density membrane fragments characteristic of bulk plasma membrane. Taken together, these results suggest that, during recovery from LH receptor desensitization, LH receptors are both located with DRM lipid environments and confined within small, mesoscale (80-160 nm) cell-surface compartments. This may reflect hormone-driven translocation of receptors into DRM and formation there of protein aggregates too large or too rigid to permit effective signaling. Once bound hormone is removed, receptor structures would have to dissociate before receptors can again signal effectively in response to hormone challenge. Moreover, such larger protein complexes would be more easily constrained laterally by membrane structural elements and so appear resident in smaller cell-surface compartments.

Vanadium methyl-bipyridine organoligand and its influence on energy balance and organs mass

In the treatment of lifestyle diseases, including metabolic syndrome and type 2 diabetes, it is important to lower body mass and fat tissue, and consequently, to increase insulin-sensitivity. Unfortunately, it often happens that low-energy diet which would lower overweight is not observed and, thus, it does not bring the expected effects. This paper discusses the influence of three diets-control, high-fructose, and high-fatty diet-on absorption of energy from food in order to transform it into body mass. The kJ/g ratio which describes this process has been calculated. In the tested diets, the addition of fructose (79.13 ± 2.47 kJ/g) or fat (82.48 ± 2.28 kJ/g) results in higher transformation of energy into body mass than in the case of control diet (89.60 ± 1.86 kJ/g). The addition of Na[VO(O2)2(4,4′-Me2-2,2′-bpy)]•8H2O (where 4,4′-Me2-2,2′-bpy = 4,4′-dimethyl-2,2′-bipyridine) results in statistical increase of that ratio: fructose diet (86.88 ± 0.44 kJ/g), fat diet (104.68 ± 3.01 kJ/g), and control diet (115.98 ± 0.56 kJ/g), respectively. Fat diet statistically influences the decrease of kidney mass in comparison to the other diets. The application of the tested vanadium compound results also in the statistical decrease of the fatty liver caused by fructose and fat diet.

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.

Coordination chemistry may explain pharmacokinetics and clinical response of vanadyl sulfate in type 2 diabetic patients

Vanadium, abbreviated V, is an early transition metal that readily forms coordination complexes with a variety of biological products such as proteins, metabolites, membranes and other structures. The formation of coordination complexes stabilizes metal ions, which in turn impacts the biodistribution of the metal. To understand the biodistribution of V, V in oxidation state iv in the form of vanadyl sulfate (25, 50, 100 mg V daily) was given orally for 6 weeks to 16 persons with type 2 diabetes. Elemental V was determined using Graphite Furnas Atomic Absorption Spectrometry against known concentrations of V in serum, blood or urine. Peak serum V levels were 15.4 ± 6.5, 81.7 ± 40 and 319 ± 268 ng ml(-1) respectively, and mean peak serum V was positively correlated with dose administered (r = 0.992, p = 0.079), although large inter-individual variability was found. Total serum V concentration distribution fit a one compartment open model with a first order rate constant for excretion with mean half times of 4.7 ± 1.6 days and 4.6 ± 2.5 days for the 50 and 100 mg V dose groups respectively. At steady state, 24 hour urinary V output was 0.18 ± 0.24 and 0.97 ± 0.84 mg in the 50 and 100 mg V groups respectively, consistent with absorption of 1 percent or less of the administered dose. Peak V in blood and serum were positively correlated (r = 0.971, p < 0.0005). The serum to blood V ratio for the patients receiving 100 mg V was 1.7 ± 0.45. Regression analysis showed that glycohemoglobin was a negative predictor of the natural log(ln) peak serum V (R(2) = 0.40, p = 0.009) and a positive predictor of the euglycemic-hyperinsulinemic clamp results at high insulin values (R(2) = 0.39, p = 0.010). Insulin sensitivity measured by euglycemic-hyperinsulinemic clamp was not significantly correlated with ln peak serum V. Globulin and glycohemoglobin levels taken together were negative predictors of fasting blood glucose (R(2) = 0.49, p = 0.013). Although V accumulation in serum was dose-dependent, no correlation between total serum V concentration and the insulin-like response was found in this first attempt to correlate anti-diabetic activity with total serum V. This study suggests that V pools other than total serum V are likely related to the insulin-like effect of this metal. These results, obtained in diabetic patients, document the need for consideration of the coordination chemistry of metabolites and proteins with vanadium in anti-diabetic vanadium complexes.

Structural and redox requirements for the action of anti-diabetic vanadium compounds

This study presents the first systematic investigation of the anti-diabetic properties of non-oxido V(IV) complexes. In particular, the insulin-mimetic activity of [V(IV)(taci)2](4+), [V(IV)(inoH-3)2](2-), [V(IV)(dhab)2], [V(IV)(hyph(Ph))2], [V(IV)(cat)3](2-) and [V(IV)(pdbh)2]--where taci is 1,3,5-triamino-1,3,5-trideoxy-cis-inositol, ino is cis-inositol, H2dhab is 2,2'-dihydroxyazobenzene, H2hyph(Ph) is 3,5-bis(2-hydroxyphenyl)-1H-1,2,4-triazole, H2cat is catechol and H2pdbh is pentan-2,4-dione benzoylhydrazone--was evaluated in terms of free fatty acid (FFA) release. Among the six compounds examined, only [V(IV)(pdbh)2], [V(IV)(cat)3](2-) and [V(IV)(hyph(Ph))2], which at the physiological pH convert to the corresponding V(IV)O complexes, were found to exhibit a significant insulin-mimetic activity compared to VOSO4. In contrast, [V(taci)2](4+), [V(inoH-3)2](2-) and [V(dhab)2], which at pH 7.4 keep their 'bare' non-oxido structure, did not cause any inhibition of FFA. The results, therefore, suggest that a V(IV)O functionality is necessary for vanadium complexes to exhibit anti-diabetic effects. This agrees with the notion that the biotransformations of V compounds in the organism are more important than the nature of the species.

Correlation of insulin-enhancing properties of vanadium-dipicolinate complexes in model membrane systems: phospholipid langmuir monolayers and AOT reverse micelles

We explore the interactions of V(III) -, V(IV) -, and V(V) -2,6-pyridinedicarboxylic acid (dipic) complexes with model membrane systems and whether these interactions correlate with the blood-glucose-lowering effects of these compounds on STZ-induced diabetic rats. Two model systems, dipalmitoylphosphatidylcholine (DPPC) Langmuir monolayers and AOT (sodium bis(2-ethylhexyl)sulfosuccinate) reverse micelles present controlled environments for the systematic study of these vanadium complexes interacting with self-assembled lipids. Results from the Langmuir monolayer studies show that vanadium complexes in all three oxidation states interact with the DPPC monolayer; the V(III) -phospholipid interactions result in a slight decrease in DPPC molecular area, whereas V(IV) and V(V) -phospholipid interactions appear to increase the DPPC molecular area, an observation consistent with penetration into the interface of this complex. Investigations also examined the interactions of V(III) - and V(IV) -dipic complexes with polar interfaces in AOT reverse micelles. Electron paramagnetic resonance spectroscopic studies of V(IV) complexes in reverse micelles indicate that the neutral and smaller 1:1 V(IV) -dipic complex penetrates the interface, whereas the larger 1:2 V(IV) complex does not. UV/Vis spectroscopy studies of the anionic V(III) -dipic complex show only minor interactions. These results are in contrast to behavior of the V(V) -dipic complex, [VO2 (dipic)](-) , which penetrates the AOT/isooctane reverse micellar interface. These model membrane studies indicate that V(III) -, V(IV) -, and V(V) -dipic complexes interact with and penetrate the lipid interfaces differently, an effect that agrees with the compounds' efficacy at lowering elevated blood glucose levels in diabetic rats.

Bis(acetylacetonato)-oxovanadium(iv), bis(maltolato)-oxovanadium(iv) and sodium metavanadate induce antilipolytic effects by regulating hormone-sensitive lipase and perilipin via activation of Akt

The increased plasma free fatty acid levels due to the deregulated lipolysis in adipocytes are considered as one of the major risk factors for developing type II diabetes. Vanadium compounds are well-known for their antidiabetic effects both on glucose and lipid metabolism, but the mechanisms are still not completely understood. The present study suggests a mechanism for how vanadium compounds exert antilipolytic effects. It demonstrates that all the three vanadium compounds, bis(acetylacetonato)-oxovanadium(iv) (VO(acac)2), bis(maltolato)-oxovanadium(iv) (VO(ma)2) and sodium metavanadate (NaVO3), attenuated basal lipolysis in 3T3L1 adipocytes in a dose- (from 100 to 400 μM for VO(acac)2 and VO(ma)2, 1.0 to 4.0 mM for vanadate) and time-dependent (from 0.5 to 4 h) manner using the glycerol release as a marker of lipolysis. In addition, the three compounds inhibited lipolysis to a different extent. Among them, VO(acac)2 (from 100 to 400 μM) exerted the most potent effect and reduced the lipolysis to ∼60-20% of control after 4 h treatment. The antilipolytic effects of vanadium compounds were further evidenced by a decrease of the levels of phosphorylated HSL at Ser660 and phosphorylated perilipin, which were counteracted by inhibitors of PI3K or Akt but not by an MEK inhibitor. This indicates that though both Akt and ERK pathways are activated by the vanadium compounds, only Akt activation contributes to the antilipolytic effect of the vanadium compounds, without the involvement of ERK activation. We previously demonstrated that VO(acac)2 can block cell cycle progression at the G1/S phase via a highly activated ERK signal in human hepatoma HepG2 cells. Together with this study, we show that similar activated pathways may lead to differential biological consequences for cancer cells and adipocytes, indicating that vanadium compounds may be used in the prevention and treatment of both diabetes and cancer.

Raft localization of type I Fcε receptor and degranulation of RBL-2H3 cells exposed to decavanadate, a structural model for V2O5

Vanadium oxides (VOs) have been identified as low molecular weight sensitizing agents associated with occupational asthma and compromised pulmonary immunocompetence. Symptoms of adult onset asthma result, in part, from increased signal transduction by Type I Fcε receptors (FcεRI) leading to release of vasoactive compounds including histamine from mast cells. Exposure to (VOs) typically occurs in the form of particles which are insoluble. Upon contact with water or biological fluids, (VOs) form a series of soluble oxoanions, one of which is decavanadate, V10O28(6-) abbreviated V10, which is structurally related to a common vanadium oxide, that is vanadium pentoxide, V2O5. Here we investigate whether V10 may be initiating plasma membrane events associated with activation of FcεRI signal transduction. We show that exposure of RBL-2H3 cells to V10 causes a concentration-dependent increase in degranulation of RBL-2H3 and, in addition, an increase in plasma membrane lipid packing as measured by the fluorescent probe, di-4-ANEPPDHQ. V10 also increases FcεRI accumulation in low-density membrane fragments, i.e., lipid rafts, which may facilitate FcεRI signaling. To determine whether V10 effects on plasma membrane lipid packing were similarly observed in Langmuir monolayers formed from dipalmitoylphosphatidylcholine (DPPC), the extent of lipid packing in the presence and absence of V10 and vanadate was compared. V10 increased the surface area of DPPC Langmuir monolayers by 6% and vanadate decreased the surface area by 4%. These results are consistent with V10 interacting with this class of membrane lipids and altering DPPC packing.

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.

Interaction of vanadium(IV) with human serum apo-transferrin

The interaction of V(IV)O-salts as well as of a few V(IV)O(carrier)n complexes with human serum transferrin (hTF) is studied focusing on the determination of the nature and stoichiometry of the binding of V(IV)O(2+) to hTF, as well as whether the conformation of hTF upon binding to V(IV)O(2+) or to its complexes is changed. Circular dichroism (CD) spectra measured for solutions containing V(IV)O(2+) and apo-hTF, and V(IV)O-maltol and apo-hTF, clearly indicate that hTF-V(IV)O-maltol ternary species form with a V(IV)O:maltol stoichiometry of 1:1. For V(IV)O salts and several V(IV)O(carrier)n complexes (carrier ligand=maltolato, dhp, picolinato and dipicolinato) (Hdhp=1,2-dimethyl-3-hydroxy-4-pyridinone) the maximum number of V(IV)O(2+) bound per mole of hTF is determined to be ~2 or lower in all cases. The binding of V(IV)O to apo-hTF most certainly involves several amino acid residues of the Fe-binding site, and as concluded by urea gel electrophoresis experiments, the formation of (V(IV)O)2hTF species may occur with the closing of the hTF conformation as is the case in (Fe(III))2hTF, which is an essential feature for the transferrin receptor recognition.