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PubMed2003

Formation, preservation, and cleavage of the disulfide bond by vanadium.

Reaction of the disulfide [HpicanS](2) (HpicanS is the carboxamide based on picolinate (pic) and o-mercaptoaniline (anS); the [] brackets are used to denote disulfides) with [VOCl(2)(thf)(2)] leads to reductive scission of the disulfide bond and formation of the mixed-valence (V(IV)/V(V)) complex anion [(OVpicanS)(2)mu-O](-) (1), with the dianionic ligand coordinating through the pyridine-N atom, the deprotonated amide-N atom, and thiophenolate-S atom. Reductive cleavage of the SbondS bond is also observed as [VCl(2)(tmeda)(2)] (tmeda=tetramethylethylenediamine) is treated with the disulfides [HsalanS](2) or [HvananS](2) (HsalanS and HvananS are the Schiff bases formed between o-mercaptoaniline and salicylaldehyde (Hsal) or vanillin (Hvan), respectively), yielding the V(III) complexes [VCl(tmeda)(salanS)] (2 a), or [VCl(tmeda)(vananS)] (2 b). The disulfide bond remains intact in the aerial reaction between [HsalanS](2) and [VCl(3)(thf)(3)] to yield the V(V) complex [VOCl[salanS](2)] (3), where (salanS)(2-) coordinates through the two phenolate and one of the imine functions. The S-S bond is also preserved as [VO(van)(2)] or [VO(nap)(2)] (Hnap=2-hydroxynaphthalene-1-carbaldehyde) is treated with bis(2-aminophenyl)disulfide, [anS](2), a reaction which is accompanied by condensation of the aldehyde and the diamine, and complexation of the resulting bis(Schiff bases) [HvananS](2) or [HnapanS](2) to form the complexes [VO[vananS](2)] (4 a) or [VO[napanS](2)] (4 b). In 4 a and 4 b, the phenolate and imine functions, and presumably also one of the disulfide-S atoms, coordinate to V(IV). 2-Mercaptophenyl-2'-pyridinecarboxamide (H(2)picanS) retains its identity in the presence of V(III); reaction between [VCl(3)(thf)(3)] and H(2)picanS yields [V[picanS](2)](-) (5). The dithiophenolate 2,6-bis(mercaptophenylthio)dimethylpyridine (6 a) is oxidized, mediated by VO(2+), to the bis(disulfide) octathiadiaza-cyclo-hexaeicosane 6 b. The relevance of these reactions for the speciation of vanadium under physiological conditions is addressed. [HNEt(3)]-1.0.5 NEt(3,) 3.3 CH(2)Cl(2), [HsalanS](2), [HNEt(3)]-5, and 6 b.4 THF have been characterized by X-ray diffraction analysis.

Crystallography, X-Ray↗
PubMedDate not supplied

Chemically and photochemically initiated DNA cleavage by an insulin-mimetic bisperoxovanadium complex.

Chemically and photochemically induced cleavage of DNA by the insulin-mimetic compound NH4[VO(O2)2-(1,10-phenanthroline)], bpV(phen), have been studied. 51V NMR and absorption indicate that photoirradiation with low energy UV light of aqueous solutions containing bpV(phen) leads to the conversion of the compound to simple vanadates. Photoillumination of the compound in the presence of supercoiled pBR322 DNA results in cutting of the plasmid to produce nicked circular and linear DNA. Quantitative analysis of agarose gel data shows that bpV(phen) is a single strand nicking agent exhibiting sequence and/or base specificity.

DNA, Circular↗
PubMed2003

Phosphatidylcholine-specific phospholipase C activity is necessary for the activation of STAT6.

It is well established that Janus kinase (JAK) tyrosine kinases play a key role in the activation of STAT6 by IL-4. In this study, we investigated additional molecules involved in this process. We previously found that IL-4 and TNF-alpha cooperate in the activation of STAT6 and NF-kappaB, suggesting that these transcription factors are regulated by common intracellular signaling pathways. To test this hypothesis, we analyzed the effect of known inhibitors of NF-kappaB on the activation of STAT6. We discovered that inhibitors of phosphatidylcholine-specific phospholipase C (PC-PLC), but not other lipases, blocked the activation of STAT6 by IL-4. The activation of PC-PLC seems to be an early event in IL-4 signaling, because its inhibition abrogated JAK activation and STAT6 tyrosine phosphorylation. Interestingly, we found that the effects of pervanadate and sodium orthovanadate on STAT6 activation correspond to their effect on PC-PLC. Thus, pervanadate by itself activated PC-PLC, JAK, and STAT6, whereas sodium orthovanadate suppressed PC-PLC, JAK, and STAT6 activation by IL-4. We further found that PC-PLC activation is necessary but not sufficient to promote STAT6 activation, and therefore, additional intracellular pathways regulated by IL-4 and pervanadate may collaborate with PC-PLC to signal STAT6 activation. It has been reported that IL-4 signals PC-PLC activation; in this study, we provide evidence that this phospholipase plays a key role in IL-4 signaling.

Animals↗
PubMedDate not supplied

Homonuclear vanadium-51 dipolar couplings in inorganic solids obtained via hahn spin echo decay NMR spectroscopy.

Dipolar dephasing of the magnetization following a Hahn spin echo pulse sequence potentially provides a quantitative means for determining the dipolar second moment in solids. In this work, the possibility of employing Hahn spin echo decay spectroscopy to obtain quantitative 51V-51V dipolar second moments is explored. Theoretical spin echo response curves are compared to experimental ones for a collection of crystalline vanadium-containing compounds. This work suggests that 51V dipolar second moments can be obtained by selectively exciting the central m = 1/2 --> -1/2 by a Hahn echo sequence for vanadate compounds with line broadening no greater than approximately 220 ppm. For vanadates with greater broadening of the central transition due to chemical shift, second-order quadrupolar, and dipolar interactions, off-resonance effects lead to an oscillatory time dependence of the spin echo. Experimentally determined second moments of the normalized echo decay intensities lie within 10-33% of the calculated values if the second moments are extrapolated to zero evolution time due to the time scale dependence of spin exchange among neighboring vanadium nuclei. Alternatively, the second moments can be obtained to within 10-25% of the calculated values if the broadening of the central transition due to chemical shift and second-order quadrupolar effects can be estimated.

Journal Article↗
PubMed2001

The effect of charged axial ligands on the EPR parameters in oxovanadium(IV) compounds: an unusual reduction of the Az (51V) values.

Two series of octahedral oxovanadium(IV) compounds, containing charged or neutral axial ligands, with the tetradentate amidate molecules Hcapca and H2capcah of the general formulae trans-[V(IV)OX(capca)]0/+ (where X = Cl- (1.CH2Cl2), SCN- (2), N3 (3), CH3COO- (4), PhCOO- (5), imidazole (6. CH3NO2), and eta-nBuNH2 (7)) and cis-[V(VI)OX(Hcapcah)]0/+ (where X = Cl- (8.0.5CH2Cl2), SCN (9), N3 (10.2CH3OH), and imidazole (11)), were synthesized and characterized by X-ray crystallography (1.CH3OH,8.CHCl3, 9.2CH3CN, 10.CH3CN and cis-[VO(imidazole)(Hcapcah)+) and continuous-wave electron paramagnetic resonance (cw EPR) spectroscopy. In addition to the synthesis, crystallographic and EPR studies, the optical, infrared and magnetic properties (room temperature) of these compounds are reported. Ab initio calculations were also carried out on compound 8 CHCl3 and revealed that this isomer is more stable than the trans isomer, in good agreement with the experimental data. The cw EPR studies of compounds 1-5, that is, the V(IV)O2+ species containing monoanionic axial ligands, revealed a novel phenomenon of the reduction of their A, components by about 10% relative to the N4 reference compounds ([V(IV)O-(imidazole)4]2+ and [V(IV)O(2,2-bipyridine)2]2+). In marked contrast, such a reduction is not observed in compounds 6. CH3NO2-11, which contain neutral axial ligands. Based on the spin-Hamiltonian formalism a theoretical explanation is put forward according to which the observed reduction of Az is due to a reduction of the electron - nuclear dipolar coupling (P). The present findings bear strong relevance to cw EPR studies of oxovanadium(IV) in vanadoproteins, V(IV)O2+-substituted proteins, and in V(IV)O2+ model compounds, since the hyperfine coupling constant, Az, has been extensively used as a benchmark for identification of equatorial-donor-atom sets in oxovanadium(IV) complexes.

Crystallography, X-Ray↗
PubMed1994

One-year treatment of streptozotocin-induced diabetic rats with vanadyl sulphate.

Streptozotocin-diabetic and non-diabetic rats were given various concentrations of vanadyl sulphate in drinking water for one year. It was found that vanadyl sulphate caused significant decreases in body weight gain and plasma insulin level in non-diabetic rats, but did not significantly alter fluid and food intakes or plasma levels of glucose, triglycerides, or cholesterol. In diabetic animals, vanadyl treatment significantly alleviated or prevented the occurrence of hyperglycaemia, hypoinsulinaemia, hyperphagia, polydipsia, hyperlipidaemia, or cataract formation, but the slower body weight gain was not improved. There were gradual decreases in the intake of the compound required to correct hyperglycaemia in the values of ED50 with age of the rats. The beneficial effects of vanadyl treatment persisted 16 weeks following the withdrawal of the compound. It is concluded that vanadyl sulphate is an effective agent for chronic therapy of streptozotocin-induced diabetes in rats, and its prolonged use does not lead to the development of tolerance.

Administration, Oral↗
PubMedDate not supplied

The chemistry of peroxovanadium compounds relevant to insulin mimesis.

The inorganic coordination chemistry of peroxovanadium compounds relevant to insulin mimesis is reviewed. The structure and kinetic reactivity of solutions of vanadate anion, vanadyl complexes and peroxovanadate complexes are briefly compared. Peroxovanadium compounds contain an oxo group, one or two peroxo ligands (O2(2-)) and an ancillary ligand which is usually bidentate. These compounds approximate a trigonal bipyramidal structure which can be divided conceptually into a polar 'oxo' half and a relatively non-polar organic half. This presents a number of interesting design variations which are discussed with respect to the development of a rudimentary structure-activity correlation of insulin mimetic ability.

Insulin↗
PubMed2003

Crystal structure and spectroscopic characterization of K8(VO)2O(SO4)6.

Red and yellow dichroistic crystals of a vanadium(V) compound, potassium (mu-oxo, di-mu-sulfato)bis(oxodisulfatovanadate), K(8)(VO)(2)O(SO(4))(6), have been obtained from the ternary catalytic model melt system K(2)S(2)O(7)[bond]K(2)SO(4)[bond]V(2)O(5). By slow cooling of the melt from 420 to 355 degrees C, crystal growth occurred, using solid V(2)O(5) crystals present in the melt as nucleation promoter. The compound crystallizes in the monoclinic space group P2(l) with a = 13.60(9) A, b = 13.93(9) A, c = 14.05(9) A, beta = 90.286(10) degrees, and Z = 2. It contains two VO(6) octahedra linked together by a mu-oxo and two mu-sulfato bridges. Furthermore, each octahedron has two monodentate sulfate ligands, making the dimeric entity coordinatively saturated. IR spectroscopy shows bands arising from V[bond]O[bond]V and V[double bond]O stretches as well as splitting of sulfate bands due to the different degrees of freedom present for different conformations of sulfate ligands. The coordination of vanadium in K(8)(VO)(2)O(SO(4))(6) is discussed in relation to the reaction mechanism of SO(2) oxidation catalysis.

Journal Article↗
PubMed2000

Insulin resistance and the modulation of rat cardiac K(+) currents.

K(+) currents were measured using a whole cell voltage-clamp method in enzymatically isolated rat ventricular myocytes obtained from two hyperinsulinemic, insulin-resistant models. Fructose-fed rats as well as genetically obese rats, both of which are resistant to the metabolic effects of insulin, were used. The normal augmentation of a calcium-independent sustained K(+) current was reduced or abolished in insulin-resistant states. This resistance can be reversed by the insulin-sensitizing drug metformin. Vanadyl sulfate (3-4 wk treatment or after 5-6 h in vitro) enhanced the sustained K(+) current. The in vitro effect of vanadyl was blocked by cycloheximide. Insulin resistance of the K(+) current was not reversed by vanadyl sulfate. The results show that insulin resistance is expressed in terms of insulin actions on ion channels, in addition to its actions on metabolism. This resistance can be reversed by the insulin-sensitizing drug metformin. Vanadate compounds, which mimic the effects of insulin on metabolism, also mimic the augmenting effects of insulin on a cardiac K(+) current in a manner suggesting synthesis of new channels.

Animals↗
PubMed2003

AVNb3Cl11 (A = K, Rb, Cs, Tl): a series of layered vanadium niobium halides based on triangular Nb3 clusters.

The first quaternary vanadium niobium compounds containing triangular Nb(3) clusters corresponding to the general formula, AVNb(3)Cl(11) (A = K, Rb, Cs, Tl), have been prepared in sealed quartz tubes from stoichiometric amounts of ACl (A = K, Rb, Cs), or Tl metal, VCl(3), Nb powder, and NbCl(5) heated at 740 degrees C. The compounds crystallize in the orthorhombic space group Pnma (No. 62). The crystal structures of the Rb and Tl members were determined by single-crystal X-ray diffraction techniques. Crystal data: a = 12.771(3) A, b = 6.811(2) A, c = 17.183(3) A, V = 1494.6(1) A(3), and Z = 4 for A = Rb; and a = 12.698(5) A, b = 6.798(3) A, c = 17.145(10) A, V = 1480.0(13) A(3), and Z = 4 for A = Tl. The crystal structure of AVNb(3)Cl(11) consists of triangular Nb(3)Cl(13) clusters (Nb-Nb = 2.826 A) connected to each other via four outer ligands to form infinite chains along the b-axis. The chains are connected by vanadium atoms located in an octahedral environment to form puckered sheets. The A(+) counterions are located between adjacent sheets and coordinate to twelve chlorine ligands in anticubeoctahedral geometry. Electronic structure calculations show bonding orbitals similar to those in Nb(3)Cl(8). Magnetic susceptibility measurements show paramagnetic Curie Weiss behavior.

Journal Article↗
PubMed1975

Effect of vanadium on growth, chlorophyll formation and iron metabolism in unicellular green algae.

In the presence of vanadium, growth of Scenedesmus obliquus and Chlorella pyrenoidosa was increased five to sixfold as determined by dry weight, when cultured under autotrophic conditions for 7 days. The stimulation by vanadium decreased with increasing stability towards hydrolysis of the iron(III)-compounds added. Pentavalent vanadium (20 mug V/1 as NH4VO3) was able to overcome completely a limited iron-deficiency in the algae following growth in presence of 1.8 - 10(-5) m ferric chloride. Vanadium did not alter the iron uptake into the algal cells. 90% of offered 48V was taken up by Scenedesmus obliquus during 5 days of growth, and 21% thereof were found in the chloroplast fraction. In presence of vanadium, the chlorophyll formation was stimulated in Scenedesmus obliquus. This stimulation by vanadium was found to be light-dependent but occurred to a certain extent in the dark also. The main porphyrin of the yellow mutant 211-11h/20 of Chlorella vulgaris was identified as protoporphyrin-IX. The formation of this compound was stimulated by vanadium within 10 days up to 83%. The role of vanadium in the biosynthesis of chlorophylls is discussed.

Chlorella↗
PubMed1996

A characterization of pervanadate, an inducer of cellular tyrosine phosphorylation and inhibitor of gap junctional intercellular communication.

Gap junctional intercellular communication (GJIC), phosphorylation status of the gap junction protein, connexin43 (Cx43), and cellular tyrosine phosphorylation in Syrian hamster embryo cells have been employed for a biological characterization of pervanadate (a mixture of H2O2 and vanadate). In addition, electron paramagnetic resonance (EPR) spectroscopy was used to follow the appearance and disappearance of vanadyl (V(IV)). It has previously been suggested that pervanadate is vanadyl hydroperoxide (V(4+)OOH). This assumption was tested by using mixtures with different molar ratios of H2O2 and orthovanadate, metavanadate or vanadyl sulfate. The maximal biological activity of the mixtures were found at a molar ratio of 2:1 (H2O2:orthovanadate or metavanadate) or 2.5:1 (H2O2:alkaline vanadyl sulfate). No V(IV) EPR spectrum appeared upon mixing orthovanadate or metavanadate and H2O2. The V(IV) EPR spectrum disappeared when vanadyl sulfate was incubated with H2O2 in a 0.5:1 molar ratio (H2O2:alkaline vanadyl sulfate). Spectrophotometrically, a V(V)-like peak at 265 nm had its optimum at this ratio. These results are consistent with pervanadate being diperoxovanadate. The individual compounds were prominently less active than the per-compound mixtures in affecting the biological parameters. The decreases in GJIC showed a concentration-dependent correlation with the onset of the alterations of the Cx43 band pattern and the amount of phosphotyrosine in cellular proteins, but the correlation was not absolute. All the studied biological parameters were reversible, also under continuous exposure to pervanadate.

Animals↗
PubMed2002

[The synthesis and spectral study of multicomponent heteropoly compounds with Keggin structure. II].

The multicomponent heteropoly compounds [Me4N]4 + x[SiVxMoyW12 - x - yO40].n H2O with Keggin structure have been synthesized and characterized by FTIR. The vibrational frequencies of containing-oxygen bonds (Si-Oa,M=Od, M-Ob-M and M-Oc-M) in these heteropoly compounds have been studied. The vibrational frequencies nu as(M=Od) and nu as(M-Ob-M) are demonstrated to explain why the acidity of the heteropoly compounds becomes weaker and the oxidative ability becomes stronger when W atoms are substituted by V atoms. The rule of the change is similar with [PVxMoyW12 - x - yO40](3 + x)-. In addition, the acidity of P series is stronger than the acidity of the corresponding Si series.

Hydrogen-Ion Concentration↗
PubMed1997

Cytokine production by human airway epithelial cells after exposure to an air pollution particle is metal-dependent.

Despite the many epidemiological studies supporting the contention that ambient air pollution particles can adversely affect human health, there is no clear agreement as to a biologically plausible mechanism which can explain the acute mortality and morbidity associated with exposure to particles less than 10 microm in size. We tested the hypothesis that metals present in an air pollution particle can induce the synthesis and expression of the inflammatory cytokines IL-8, IL-6, and TNFalpha. A residual oil fly ash (ROFA) containing the transition metals vanadium, nickel, and iron was used as a model emission source air pollution particle. Normal human bronchial epithelial (NHBE) cells were exposed for either 2 or 24 hr to 0, 5, 50, or 200 microg/ml ROFA. Concentrations of IL-8, IL-6, and TNF-alpha proteins were measured with commercially available ELISA kits. mRNA for these same cytokines was quantified by RT-PCR. NHBE cells exposed to ROFA produced significant amounts of IL-8, IL-6, and TNF, as well as mRNAs coding for these cytokines. Cytokine production was inhibited by the inclusion of either the metal chelator deferoxamine (1.0 mM) or the free radical scavenger dimethylthiourea (1.0 mM). In addition, vanadium containing compounds, but not iron or nickel sulfates, mimicked the effects of intact ROFA. These results demonstrate that metals present in ROFA may be responsible for production and release of inflammatory mediators by the respiratory tract epithelium and suggest that these mediators may contribute to the toxic effects of particulate air pollutants reported in epidemiology studies.

Air Pollutants, Occupational↗
PubMed2003

Protein tyrosyl phosphatases in T cell activation: implication for human immunodeficiency virus transcriptional activity.

The protein tyrosine phosphatases (PTPs) superfamily is a large group of enzymes showing a wide diversity of structure and biological functions. Their implication in the regulation of signal transduction processes is critical for homeostasis and efficient cellular activation. Disturbance of the delicate balance between protein tyrosine kinase and protein tyrosine phosphatase activities is at the heart of a large number of diseases. Control of cellular activation is especially important for human immunodeficiency virus type 1 (HIV-1) since this retrovirus requires activated T cells in order to replicate efficiently. Identification of PTPs implicated in signaling pathways leading to upregulation of HIV-1 gene transcription therefore contributes to the general understanding of cellular factors needed for strong HIV-1 replication and progression to AIDS. The use of bisperoxovanadium compounds as potent, specific, and highly purified PTP inhibitors releases HIV-1 from PTP control and strongly increases HIV-1 gene expression. These inhibitors can thus be used to study signal transduction mechanisms regulated by PTP activity that are important for HIV-1 replication and provide new and interesting therapeutic avenues for the efficient control of this debilitating retroviral infection.

Amino Acid Sequence↗
PubMed1999

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

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

Administration, Oral↗
PubMed2000

Analysis of genes encoding an alternative nitrogenase in the archaeon Methanosarcina barkeri 227.

Methanosarcina barkeri 227 possesses two clusters of genes potentially encoding nitrogenases. We have previously demonstrated that one cluster, called nif2, is expressed under molybdenum (Mo)-sufficient conditions, and the deduced amino acid sequences for nitrogenase structural genes in that cluster most closely resemble those for the Mo nitrogenase of the gram-positive eubacterium Clostridium pasteurianum. The previously cloned nifH1 from M. barkeri shows phylogenetic relationships with genes encoding components of eubacterial Mo-independent eubacterial alternative nitrogenases and other methanogen nitrogenases. In this study, we cloned and sequenced nifD1 and part of nifK1 from M. barkeri 227. The deduced amino acid sequence encoded by nifD1 from M. barkeri showed great similarity with vnfD gene products from vanadium (V) nitrogenases, with an 80% identity at the amino acid level with the vnfD gene product from Anabaena variabilis. Moreover, there was a small open reading frame located between nifD1 and nifK1 with clear homology to vnfG, a hallmark of eubacterial alternative nitrogenases. Stimulation of diazotrophic growth of M. barkeri 227 by V in the absence of Mo was demonstrated. The unusual complement of nif genes in M. barkeri 227, with one cluster resembling that from a gram-positive eubacterium and the other resembling a eubacterial V nitrogenase gene cluster, suggests horizontal genetic transfer of those genes.

Bacterial Proteins↗
PubMed2001

MKP-1 as a target for pharmacological manipulations in PC12 cell survival.

Dual specificity mitogen activated protein kinase phosphatase-1 (MKP-1) inactivates extracellular signal-regulated kinase (ERK), p38 and/or c-jun N-terminal protein kinase (JNK) by dephosphorylation via a negative feed-back loop. The aim of the present study was to assess the role of expression of MKP-1 and phosphorylation status of mitogen-activated protein kinases (MAPKs) in promoting cell survival in PC12 cells. We used FK506 and three different monoperoxovanadium complexes (mpVs) as pharmacological tools for manipulation of MKP-1 expression. Peroxovanadium compounds, known to be insulinomimetic agents and protein tyrosine phosphatase inhibitors, are cytotoxic to the cells, they activate JNK and down-regulate MPK-1. On the other hand, FK 506 has transient effect on ERK activation. However, when the agents are used in combination, ERK phosphorylation is prolonged and intensified, MKP-1 expression is increased, and cell survival is enhanced. The concomitant alterations observed in intensities and duration of phospho-ERKs and phospho-JNKs signals suggest that monoperoxovanadium complexes in combination with FK 506 enhance survival of PC12 cells by an induction of MKP-1 expression.

Animals↗