Vanadium salts stimulate mitogen-activated protein (MAP) kinases and ribosomal S6 kinases

Vanadium Complexes with Thioanilide Derivatives of Amino Acids: Inhibition of Human Phosphatases and Specificity in Various Cell Models of Metabolic Disturbances

In the text, the synthesis and characteristics of the novel ONS-type vanadium (V) complexes with thioanilide derivatives of amino acids are described. They showed the inhibition of human protein tyrosine phosphatases (PTP1B, LAR, SHP1, and SHP2) in the submicromolar range, as well as the inhibition of non-tyrosine phosphatases (CDC25A and PPA2) similar to bis(maltolato)oxidovanadium(IV) (BMOV). The ONS complexes increased [14C]-deoxy-D-glucose transport into C2C12 myocytes, and one of them, VC070, also enhanced this transport in 3T3-L1 adipocytes. These complexes inhibited gluconeogenesis in hepatocytes HepG2, but none of them decreased lipid accumulation in the non-alcoholic fatty liver disease model using the same cells. Compared to the tested ONO-type vanadium complexes with 5-bromosalicylaldehyde and substituted benzhydrazides as Schiff base ligand components, the ONS complexes revealed stronger inhibition of protein tyrosine phosphatases, but the ONO complexes showed greater activity in the cell models in general. Moreover, the majority of the active complexes from both groups showed better effects than VOSO4 and BMOV. Complexes from both groups activated AKT and ERK signaling pathways in hepatocytes to a comparable extent. One of the ONO complexes, VC068, showed activity in all of the above models, including also glucose utilizatiand ONO Complexes are Inhibitors ofon in the myocytes and glucose transport in insulin-resistant hepatocytes. The discussion section explicates the results within the wider scope of the knowledge about vanadium complexes.

Effects of Vanadyl Complexes with Acetylacetonate Derivatives on Non-Tumor and Tumor Cell Lines

Vanadium has a good therapeutic potential, as several biological effects, but few side effects, have been demonstrated. Evidence suggests that vanadium compounds could represent a new class of non-platinum, metal antitumor agents. In the present study, we aimed to characterize the antiproliferative activities of fluorescent vanadyl complexes with acetylacetonate derivates bearing asymmetric substitutions on the β-dicarbonyl moiety on different cell lines. The effects of fluorescent vanadyl complexes on proliferation and cell cycle modulation in different cell lines were detected by ATP content using the CellTiter-Glo Luminescent Assay and flow cytometry, respectively. Western blotting was performed to assess the modulation of mitogen-activated protein kinases (MAPKs) and relevant proteins. Confocal microscopy revealed that complexes were mainly localized in the cytoplasm, with a diffuse distribution, as in podocyte or a more aggregate conformation, as in the other cell lines. The effects of complexes on cell cycle were studied by cytofluorimetry and Western blot analysis, suggesting that the inhibition of proliferation could be correlated with a block in the G2/M phase of cell cycle and an increase in cdc2 phosphorylation. Complexes modulated mitogen-activated protein kinases (MAPKs) activation in a cell-dependent manner, but MAPK modulation can only partly explain the antiproliferative activity of these complexes. All together our results demonstrate that antiproliferative effects mediated by these compounds are cell type-dependent and involve the cdc2 and MAPKs pathway.

Vanadium in Biological Action: Chemical, Pharmacological Aspects, and Metabolic Implications in Diabetes Mellitus

Vanadium compounds have been primarily investigated as potential therapeutic agents for the treatment of various major health issues, including cancer, atherosclerosis, and diabetes. The translation of vanadium-based compounds into clinical trials and ultimately into disease treatments remains hampered by the absence of a basic pharmacological and metabolic comprehension of such compounds. In this review, we examine the development of vanadium-containing compounds in biological systems regarding the role of the physiological environment, dosage, intracellular interactions, metabolic transformations, modulation of signaling pathways, toxicology, and transport and tissue distribution as well as therapeutic implications. From our point of view, the toxicological and pharmacological aspects in animal models and humans are not understood completely, and thus, we introduced them in a physiological environment and dosage context. Different transport proteins in blood plasma and mechanistic transport determinants are discussed. Furthermore, an overview of different vanadium species and the role of physiological factors (i.e., pH, redox conditions, concentration, and so on) are considered. Mechanistic specifications about different signaling pathways are discussed, particularly the phosphatases and kinases that are modulated dynamically by vanadium compounds because until now, the focus only has been on protein tyrosine phosphatase 1B as a vanadium target. Particular emphasis is laid on the therapeutic ability of vanadium-based compounds and their role for the treatment of diabetes mellitus, specifically on that of vanadate- and polioxovanadate-containing compounds. We aim at shedding light on the prevailing gaps between primary scientific data and information from animal models and human studies.

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.

The Structural Basis of Action of Vanadyl (VO2+) Chelates in Cells

Much emphasis has been given to vanadium compounds as potential therapeutic reagents for the treatment of diabetes mellitus. Thus far, no vanadium compound has proven efficacious for long-term treatment of this disease in humans. Therefore, in review of the research literature, our goal has been to identify properties of vanadium compounds that are likely to favor physiological and biochemical compatibility for further development as therapeutic reagents. We have, therefore, limited our review to those vanadium compounds that have been used in both in vivo experiments with small, laboratory animals and in in vitro studies with primary or cultured cell systems and for which pharmacokinetic and pharmacodynamics results have been reported, including vanadium tissue content, vanadium and ligand lifetime in the bloodstream, structure in solution, and interaction with serum transport proteins. Only vanadyl (VO²⁺) chelates fulfill these requirements despite the large variety of vanadium compounds of different oxidation states, ligand structure, and coordination geometry synthesized as potential therapeutic agents. Extensive review of research results obtained with use of organic VO²⁺-chelates shows that the vanadyl chelate bis(acetylacetonato)oxidovanadium(IV) [hereafter abbreviated as VO(acac)₂], exhibits the greatest capacity to enhance insulin receptor kinase activity in cells compared to other organic VO²⁺-chelates, is associated with a dose-dependent capacity to lower plasma glucose in diabetic laboratory animals, and exhibits a sufficiently long lifetime in the blood stream to allow correlation of its dose-dependent action with blood vanadium content. The properties underlying this behavior appear to be its high stability and capacity to remain intact upon binding to serum albumin. We relate the capacity to remain intact upon binding to serum albumin to the requirement to undergo transcytosis through the vascular endothelium to gain access to target tissues in the extravascular space. Serum albumin, as the most abundant transport protein in the blood stream, serves commonly as the carrier protein for small molecules, and transcytosis of albumin through capillary endothelium is regulated by a Src protein tyrosine kinase system. In this respect it is of interest to note that inorganic VO²⁺ has the capacity to enhance insulin receptor kinase activity of intact 3T3-L1 adipocytes in the presence of albumin, albeit weak; however, in the presence of transferrin no activation is observed. In addition to facilitating glucose uptake, the capacity of VO²⁺- chelates for insulin-like, antilipolytic action in primary adipocytes has also been reviewed. We conclude that measurement of inhibition of release of only free fatty acids from adipocytes stimulated by epinephrine is not a sufficient basis to ascribe the observations to purely insulin-mimetic, antilipolytic action. Adipocytes are known to contain both phosphodiesterase-3 and phosphodiesterase-4 (PDE3 and PDE4) isozymes, of which insulin antagonizes lipolysis only through PDE3B. It is not known whether the other isozyme in adipocytes is influenced directly by VO²⁺- chelates. In efforts to promote improved development of VO²⁺- chelates for therapeutic purposes, we propose synergism of a reagent with insulin as a criterion for evaluating physiological and biochemical specificity of action. We highlight two organic compounds that exhibit synergism with insulin in cellular assays. Interestingly, the only VO²⁺- chelate for which this property has been demonstrated, thus far, is VO(acac)₂.

Arylalkylamine vanadium salts as new anti-diabetic compounds

Vanadium compounds show insulin-like effects in vivo and in vitro. Several clinical studies have shown the efficacy of vanadium compounds in type 2 diabetic subjects. However, a major concern is safety, which calls for the development of more potent vanadium compounds. For that reason different laboratories develop strategies to decrease the therapeutic dose of vanadate. One of these strategies use substrates of semicarbazide-sensitive amine oxidase (SSAO)/vascular adhesion protein-1 (VAP-1), a bifunctional protein with amine oxidase activity and adhesive properties implicated in lymphocyte homing at inflammation sites. Substrates of SSAO combined with low concentrations of vanadate strongly stimulate glucose transport and GLUT4 glucose transporter recruitment to the plasma membrane in 3T3-L1 adipocytes and in rat adipocytes. This combination also shows anti-diabetic effects in various animal models of type 1 and type 2 diabetes. Benzylamine/vanadate administration generates peroxovanadium locally in pancreatic islets, which stimulates insulin secretion, and also produces peroxovanadium in adipose tissue, thereby activating glucose metabolism in adipocytes and in neighboring muscle. This opens up the possibility of using the SSAO/VAP-1 activity as a local generator of protein tyrosine phosphatase inhibitors in anti-diabetic therapy. More recently a novel class of arylalkylaminevanadium salts have shown potent insulin-mimetic effects downstream of the insulin receptor. Administration of these compounds lowers glycemia and normalizes the plasma lipid profile in type 1 and type 2 models of diabetes. The combination of different approaches to decrease vanadium doses, among them chelating agents and SSAO substrates, should permit to develop safe and efficient vanadium based agents safe for diabetes treatment.

Vanadium and bone development: putative signaling pathwaysThis paper is one of a selection of papers published in this Special issue, entitled Second Messengers and Phosphoproteins—12th International Conference

Vanadium is a trace element present in practically all cells in plants and animals. It exerts interesting actions in living systems. At pharmacological doses, vanadium compounds display relevant biological actions such as mimicking insulin and growth factors as well as having osteogenic activity. Some vanadium compounds also show antitumoral properties. The importance of vanadium in bone arises from the studies developed to establish the essentiality of this element in animals and humans. Bone tissue, where the element seems to play an important role, accumulates great amounts of vanadium. This paper reviews the physiology of osteoblasts, the involvement of different growth factors on bone development, and the effects of vanadium derivatives on the skeletal system of animal models and bone-related cells. Two cellular lines are discussed in particular; one derived from a rat osteosarcoma (UMR106) and the other is a nontransformed osteoblast cell line (MC3T3-E1). The effects of different growth factors and their mechanisms of action in these cellular lines are reviewed. These models of osteoblasts are especially useful in understanding the intracellular signaling pathways of vanadium derivatives in hard tissues. Vanadium uses an intricate interplay of intracellular mechanisms to exert different biochemical and pharmacological actions. The effects of vanadium derivatives on some cellular signaling pathways related to insulin are compiled in this review. The comprehension of these intracellular signaling pathways may facilitate the design of vanadium compounds with promising therapeutic applications as well as the understanding of secondary side effects derived from the use of vanadium as a therapeutic agent.

Vanadium and the cardiovascular functions

Inorganic and organic compounds of vanadium have been shown to exhibit a large range of insulinomimetic effects in the cardiovascular system, including stimulation of glucose transporter 4 (GLUT-4) translocation and glucose transport in adult cardiomyocytes. Furthermore, administration of vanadium compounds improves cardiac performance and smooth muscle contractility, and modulates blood pressure in various models of hypertension and insulin resistance. Vanadium compounds are potent inhibitors of protein tyrosine phosphatases. As a result, they promote an increase in protein tyrosine phosphorylation of several key components of the insulin signaling pathway, leading to the upregulation of phosphatidylinositol 3-kinase and protein kinase B, two enzymes involved in mediating GLUT-4 trans location and glucose transport. In addition, vanadium has also been shown to activate p38 mitogen-activated protein kinase and increase Ca2+levels in several cell types. The ability of vanadium compounds to activate these signaling events may be responsible for their ability to modulate cardiovascular functions.Key words: vanadium compounds, glucose transport, smooth muscle contractility, insulin signaling pathway.

Prolongation of insulin-induced activation of mitogen-activated protein kinases ERK 1/2 and phosphatidylinositol 3-kinase by vanadyl sulfate, a protein tyrosine phosphatase inhibitor

Vanadium salts such as vanadyl sulfate (VS), potent inhibitors of protein tyrosine phosphatases, have been shown to mimic, augment, and prolong insulin's action. However, the molecular mechanism of responses to these salts is not clear. In the present studies, we examined if VS-induced effects on insulin action are associated with enhancement or augmentation in the activation state of key components of the insulin signaling pathway. Treatment of insulin receptor-overexpressing cells with insulin or VS resulted in a time-dependent transient increase in phosphorylation and activation of extracellular signal-regulated kinases 1 and 2 (ERK 1/2) that peaked at about 5 min, then declined rapidly to about baseline within 30 min. However, when the cells were treated with VS before stimulation with insulin, sustained ERK 1/2 phosphorylation and activation were observed well beyond 60 min. VS treatment also prolonged the insulin-stimulated activation of phosphatidylinositol 3-kinase (PI3-K), which was associated with sustained interaction between insulin receptor substrate-1 (IRS-1) and the p(85 alpha) subunit of phosphatidylinositol 3-kinase (PI3-K) in response to insulin. These data indicate that prolongation of insulin-stimulated ERK 1/2 and PI3-K activation by VS is due to a more stable complex formation of IRS-1 with the p(85 alpha) subunit which may, in turn, be responsible for its ability to enhance and extend the biological effects of insulin.

Neuroprotective effect of postischemic administration of sodium orthovanadate in rats with transient middle cerebral artery occlusion

Orthovanadate is a competitive inhibitor of protein tyrosine phosphatases. Some of its reported biologic effects are its insulin mimetic property and its activation of phosphoinositide 3-kinase and extracellular-signal regulated kinase (ERK). The authors previously reported its neuroprotective effect on delayed neuronal death of gerbil hippocampal CA1 neurons via Akt and ERK activation after transient forebrain ischemia. In the present study, the neuroprotective effect of postischemic intraperitoneal administration of sodium orthovanadate (2 l/kg of 50-mmol/l sodium orthovanadate in saline) was investigated in rats with transient middle cerebral artery occlusion. Ischemic neuronal injury was evaluated 1 day and 28 days after ischemia. The neuroprotective effect of orthovanadate was significant in the cortex but not the caudate putamen (ischemic core) at both 1 and 28 days after ischemia. In orthovanadate group, the activities of Akt and ERK were maintained after reperfusion; they were decreased in saline group. Blood glucose level decreased but within normal range. Regional cerebral blood flow was lower than that of saline group only at 0 hours after reperfusion. These data suggest that orthovanadate has neuroprotective effects in rats with transient middle cerebral artery occlusion and that these effects are mediated by Akt and ERK activation. Furthermore, low blood glucose levels and gradual recovery of regional cerebral blood flow may contribute to neuroprotection.

Synthesis of a new vanadyl(IV) complex with trehalose (TreVO): insulin-mimetic activities in osteoblast-like cells in culture

Vanadium compounds show interesting biological and pharmacological properties. Some of them display insulin-mimetic effects and others produce anti-tumor actions. The bioactivity of vanadium is present in inorganic species like the vanadyl(IV) cation or vanadate(V) anion. Nevertheless, the development of new vanadium derivatives with organic ligands which improve the beneficial actions and decrease the toxic effects is of great interest. On the other hand, the mechanisms involved in vanadium bioactivity are still poorly understood. A new vanadium complex of the vanadyl(IV) cation with the disaccharide trehalose (TreVO), Na(6)[VO(Tre)(2)].4H(2)O, here reported, shows interesting insulin-mimetic properties in two osteoblast cell lines, a normal one (MC3T3E1) and a tumoral one (UMR106). The complex affected the proliferation of both cell lines in a different manner. On tumoral cells, TreVO caused a weak stimulation of growth at 5 microM but it inhibited cell proliferation in a dose-response manner between 50 and 100 microM. TreVO significantly inhibited UMR106 differentiation (15-25% of basal) in the range 5-100 microM. On normal osteoblasts, TreVO behaved as a mitogen at 5-25 microM. Different inhibitors of the MAPK pathway blocked this effect. At higher concentrations (75-100 microM), the complex was a weak inhibitor of the MC3T3E1 proliferation. Besides, TreVO enhanced glucose consumption by a mechanism independent of the PI3-kinase activation. In both cell lines, TreVO stimulated the ERK phosphorylation in a dose- and time-dependent manner. Different inhibitors (PD98059, wortmannin, vitamins C and E) partially decreased this effect, which was totally inhibited by their combination. These results suggest that TreVO could be a potential candidate for therapeutic treatments.

Vanadium in cancer treatment

Vanadium compounds exert preventive effects against chemical carcinogenesis on animals, by modifying, mainly, various xenobiotic enzymes, inhibiting, thus, carcinogen-derived active metabolites. Studies on various cell lines reveal that vanadium exerts its antitumor effects through inhibition of cellular tyrosine phosphatases and/or activation of tyrosine phosphorylases. Both effects activate signal transduction pathways leading either to apoptosis and/or to activation of tumor suppressor genes. Furthermore, vanadium compounds may induce cell-cycle arrest and/or cytotoxic effects through DNA cleavage and fragmentation and plasma membrane lipoperoxidation. Reactive oxygen species generated by Fenton-like reactions and/or during the intracellular reduction of V(V) to V(IV) by, mainly, NADPH, participate to the majority of the vanadium-induced intracellular events. Vanadium may also exert inhibitory effects on cancer cell metastatic potential through modulation of cellular adhesive molecules, and reverse antineoplastic drug resistance. It also possesses low toxicity that, in combination with the synthesis of new, more potent and better tolerated complexes, may establish vanadium as an effective non-platinum, metal antitumor agent.

Activation of MAP kinase by insulin and vanadate in adipocytes from young and old rats

Vanadate has insulin-like effects in adipocytes without stimulating insulin receptor kinase activity. However, it activates IRS-1 associated PI 3-kinase, suggesting that it mimics insulin effects by stimulating signaling elements downstream of PI 3-kinase. Here we analysed the stimulation of MAPK by insulin and vanadate and observed that both elicit a rapid 3.5-4 fold activation which is abolished by wortmannin and PD98059. Simultaneous addition of insulin and vanadate does not result in an additive effect neither on MAPK nor in MEK. Whereas insulin action is transient, vanadate stimulation lasts up to 20 min. In insulin-resistant adipocytes from old rats, insulin stimulates poorly MAPK, whereas a normal activation is achieved with vanadate. We conclude that: (a) insulin and vanadate use a common signaling pathway from PI 3-kinase to MEK and MAPK; (b) vanadate but not insulin, elicits a sustained activation of both enzymes; (c) this pathway is functional in old rat adipocytes.

Effect of oxovanadium(IV) complexes on nondiabetic and streptozotocin-diabetic rats

The effects of vanadium complexes with organic ligands, [VO(phen)2]SO4.3H2O, [VO(bpy)2]SO4.2H2O, and [VOCl2(Hmcp)2H2O], on blood glucose and plasma lipid levels were studied in nondiabetic and streptozotocin-diabetic rats and compared to that of [VO(mal)2] (the reference compound). The present results provide evidence that the compounds examined possess lower toxicity than [VO(mal)2]. One of the compounds examined, viz. [VO(bpy)2]SO4.2H2O, decreases, statistically significantly, the glucose level and a second one, viz. [VOCl2(Hmcp)2H2O], decreases, also significantly, the total cholesterol level.

Treatment of mice with EGF and orthovanadate activates cytoplasmic and nuclear MAPK, p70S6k, and p90rsk in the liver

BACKGROUND/AIMS

Although signal transduction pathways activated by EGF have been extensively studied in cultured cells, few such studies have been done in whole animals. In this study, activation of hepatic kinases, phosphatases, and DNA-binding activity of AP-1 was examined after intraperitoneal injections of either EGF or sodium orthovanadate into mice.

METHODS

Cytoplasmic and nuclear proteins, extracted from isolated hepatocytes or whole liver tissue, were immunoprecipitated with either anti-ERK1/2, anti-70S6k, or anti-p90rsk antibodies and kinase activities were measured using specific substrates. Kinase protein levels was evaluated by Western blot analysis. AP-1 DNA binding activity was measured by electrophoretic mobility shift assay.

RESULTS

Systemic administration of EGF induced simultaneous increase in the activities of cytoplasmic and nuclear MAPK, p70S6k, and p90rsk. MAPK and p70S6k were more potently activated in the cytosol while p90rsk activation was more pronounced in the nucleus. Orthovanadate also activated these kinases but to a much lesser degree than EGF. In vitro phosphatase assays showed that neither EGF nor orthovanadate induced measurable changes in phosphatase activities. EGF, but not orthovanadate, activated nuclear AP-1 DNA-binding activity in intact liver, indicating that activation of MAPK, p70S6k, and p90rsk by orthovanadate is not sufficient to activate this transcription factor.

CONCLUSION

These observations provide groundwork for future studies to examine the role of EGF-induced kinase cascades and transcription factors in liver regeneration and other growth factor-mediated hepatic processes.

Effects of bis(maltolato) oxovanadium (IV) on protein serine kinases in skeletal muscle of streptozotocin-diabetic rats

The in vivo effects of bis(maltolato)oxovanadium (IV) (BMOV) on the activity of protein serine kinases in skeletal muscle of STZ-diabetic Wistar rats were studied. BMOV was administered to STZ-diabetic rats at a concentration of 0.75 mg/ml for 8 weeks. Chronic BMOV treatment completely normalized plasma glucose levels in the diabetic animals after 8 weeks of treatment. Insulin-stimulated ERK-1 and ERK-2 activity was markedly increased in STZ-diabetic rats. Chronic BMOV treatment normalized the activity of ERK-2 in the diabetic treated animals, whereas the activity of ERK-1 was unaffected. In contrast to ERK-1 and ERK-2, the activity of the ribosomal S6 kinase p90rsk was decreased in STZ-diabetic rats. BMOV treatment restored the activity to normal levels. Basal p70 S6K activity was increased about 2.5-fold in the untreated diabetic group and no further increase in activity was observed after insulin stimulation. BMOV treatment did not correct the changes in p70 S6K activity in either the basal or insulin-stimulated states. In conclusion (i) the activity of ERK-1, ERK-2 and p90rsk were altered in skeletal muscle of STZ-diabetic rats; (ii) the glucoregulatory effects of BMOV were accompanied by concurrent improvement in the activities of ERK-2 and p90rsk; and (iii) there appears to be a dissociation between the activation of ERK-2 and p90rsk, suggesting that the regulation of p90rsk may be much more complex in vivo.

Phosphatidylinositol 3-kinase requirement in activation of the ras/C-raf-1/MEK/ERK and p70(s6k) signaling cascade by the insulinomimetic agent vanadyl sulfate

The mechanisms by which inorganic salts of the trace element vanadium mediate their insulinomimetic effects are not clearly understood and were investigated. We have shown previously that vanadium salts activate mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase activities (PI3-K) via a pathway that does not involve the insulin receptor (IR) tyrosine kinase function [Pandey, S. K., Anand-Srivastava, M. B., and Srivastava, A. K. (1998) Biochemistry 37, 7006-7014]. Herein, we have examined a possible role of PI3-K in the vanadyl sulfate (VS)-mediated increase in the level of ras-MAPK activation as well as the contribution of signaling components upstream to MAPK in this VS response. Treatment of IR-overexpressing cells with VS resulted in an increased level of tyrosine phosphorylation of p44(mapk) (ERK-1) and p42(mapk) (ERK-2) along with stimulation of MAPK, MAPK kinase (MEK), and C-raf-1 activities, and ras activation. Preincubation with wortmannin and LY294002, two structurally and mechanistically different inhibitors of PI3-K, blocked the VS-mediated increase in MAPK activity and phosphorylation of ERK-1 and ERK-2. Furthermore, wortmannin inhibited activation of ras, C-raf-1, and MEK in response to VS. The addition of a farnesyltransferase inhibitor, B581, to cells reduced the level of MAPK activation as well as ERK-1 and ERK-2 phosphorylation stimulated by VS. Finally, VS increased PI3-K activity in ras immunoprecipitates. A VS-mediated increase in p70(s6k) activity was also found to be inhibited by wortmannin. Taken together, these results demonstrate that the insulinomimetic effects of VS may be mediated, in part, by PI3-K-dependent stimulation of the ras-MAPK and p70(s6k) pathways.

Activation of the EGF receptor signaling pathway in human airway epithelial cells exposed to metals

We have previously shown that exposure to combustion-derived metals rapidly (within 20 min) activated mitogen-activated protein kinases (MAPK), including extracellular signal-regulated kinase (ERK), in the human bronchial epithelial cell line BEAS. To study the mechanisms responsible for metal-induced activation of ERK, we examined the effect of noncytotoxic exposures to As, Cu, V, or Zn on the kinases upstream of ERK in the epidermal growth factor (EGF) receptor signaling pathway. Western blotting using phospho-specific ERK1/2 antibody demonstrated the selective MEK1/2 inhibitor PD-98059 blocked metal-induced phosphorylation of ERK1/2. Meanwhile, Western blotting using a phospho-specific MEK1/2 antibody showed that these metals induce a rapid phosphorylation of MEK1/2. Kinase activity assays confirmed the activation of MEK1/2 by metal treatment. Immunoprecipitation studies demonstrated that As, Cu, V, or Zn induces EGF receptor phosphorylation. Furthermore, the EGF receptor-specific tyrosine kinase inhibitor (PD-153035) significantly blocked the phosphorylation of MEK1/2 initiated by metals. Interestingly, we observed low levels of Raf-1 activity that were not increased by metal exposure in these cells through kinase activity assay. Finally, transfection assays showed that MEK1/2 inhibition could inhibit trans-activation of Elk1, a transcription factor in the ERK pathway, in BEAS cells exposed to metals. Together, these data demonstrate that As, Cu, V, and Zn can activate the EGF receptor signaling pathway in BEAS cells and suggest that this mechanism may be involved in pulmonary responses to metal inhalation.

L-Glutamic acid gamma-monohydroxamate. A potentiator of vanadium-evoked glucose metabolism in vitro and in vivo

We report that the vanadium ligand L-Glu(gamma)HXM potentiates the capacity of free vanadium ions to activate glucose uptake and glucose metabolism in rat adipocytes in vitro (by 4-5-fold) and to lower blood glucose levels in hyperglycemic rats in vivo (by 5-7-fold). A molar ratio of two L-Glu(gamma)HXM molecules to one vanadium ion was most effective. Unlike other vanadium ligands that potentiate the insulinomimetic actions of vanadium, L-Glu(gamma)HXM partially activated lipogenesis in rat adipocytes in the absence of exogenous vanadium. This effect was not manifested by D-Glu(gamma)HXM. At 10-20 microM L-Glu(gamma)HXM, lipogenesis was activated 9-21%. This effect was approximately 9-fold higher (140 +/- 15% of maximal insulin response) in adipocytes derived from rats that had been treated with vanadium for several days. Titration of vanadium(IV) with L-Glu(gamma)HXM led to a rapid decrease in the absorbance of vanadium(IV) at 765 nm, and (51)V NMR spectroscopy revealed that the chemical shift of vanadium(IV) at -490 ppm disappeared with the appearance of a signal characteristic to vanadium(V) (-530 ppm) upon adding one equivalent of L-Glu(gamma)HXM. In summary, L-Glu(gamma)HXM is highly active in potentiating vanadium-activated glucose metabolism in vitro and in vivo and facilitating glucose metabolism in rat adipocytes in the absence of exogenous vanadium probably through conversion of trace intracellular vanadium into an active insulinomimetic compound. We propose that the active species is either a 1:1 or 2:1 L-Glu(gamma)HXM vanadium complex in which the endogenous vanadium(IV) has been altered to vanadium(V). Finally we demonstrate that L-Glu(gamma)HXM- and L-Glu(gamma)HXM.vanadium-evoked lipogenesis is arrested by wortmannin and that activation of glucose uptake in rat adipocytes is because of enhanced translocation of GLUT4 from low density microsomes to the plasma membrane.

Tyrosine phosphatases as targets in metal-induced signaling in human airway epithelial cells

We previously showed that exposure to metal-laden combustion particles disregulates protein tyrosine phosphate homeostasis in human airway epithelial cells (HAEC). More recently, we reported that exposure to certain metal ions activates mitogen-activated protein kinases in HAEC. To study the mechanism responsible, we examined the effects of arsenic (As), vanadium (V), and zinc (Zn) on tyrosine phosphate catabolism in BEAS S6 cells or cultured human bronchial epithelial cells. Western blots and immunocytochemical analyses showed that exposure to noncytotoxic levels of As, V, or Zn resulted in increased levels of protein phosphotyrosines in HAEC. Tyrosine phosphatase activity, measured against [(32)P]-labeled PolyGlu:Tyr, was markedly inhibited in cells treated with V or Zn but was unaffected by exposure to As. Fast performance liquid chromatography fractionation and subsequent in-gel phosphatase activity assay of HAEC protein extracts revealed the presence of numerous tyrosine phosphatases, of varying molecular weights, that were effectively inhibited by exposure to V or Zn ions. As had no discernible effect on these enzymes. The protein tyrosine phosphatase PTP1B, immunoprecipitated from HAEC, was similarly inhibited by V and Zn but not by As ions. These data show that V and Zn may induce tyrosine phosphate accumulation by inhibiting dephosphorylation and implicate kinase activation as the mechanism in HAEC exposed to As. These findings suggest that metal exposure can activate signaling pathways through multiple mechanisms.

Inactivation of glucose oxidase by diperoxovanadate-derived oxidants

Inactivation of glucose oxidase occurred in the presence of bromide, vanadate, H(2)O(2), and phosphate (the bromide system), and this was prevented by NADH or phenol red, a bromine acceptor. Glucose oxidase present during the reaction between diperoxovanadate and a reduced form of vanadate, vanadyl (the vanadyl system), but not added after mixing the reactants, was inactivated, and this was accompanied by a loss of binding of the dye, Coomassie blue, to the protein. The transient intermediate of the type OVOOV(O(2)), known to form in these reactions and used in the oxidation of bromide ion and NADH, appears to be responsible for inactivating glucose oxidase. In both systems, the inactivation of the enzyme was prevented by histidine and DTT, known to quench singlet-oxygen. By direct measurement of 1270-nm emission of singlet-oxygen, its generation was demonstrated in the bromide system, and in the reaction of hypohalous acids with diperoxovanadate, but not in the vanadyl system. By themselves both hypohalous acids, HOCl and HOBr inactivated glucose oxidase, and their prior reaction with H(2)O(2) during which singlet-oxygen was released, protected the enzyme. The results provide support for possible oxidative inactivation of glucose oxidase by diperoxovanadate-derived oxidants.

Tyrosine phosphorylation and morphological transformation induced by four vanadium compounds on MC3T3E1 cells

The present study was performed to determine the phosphotyrosine-protein levels induced by insulin and by four vanadium derivatives in MC3T3E1 osteoblast-like cells. We have also attempted to associate these patterns with the vanadium-induced growth and morphological changes of such cells. Vanadate (Vi), vanadyl (VO), bis(maltolato)oxovanadium (IV) (BMOV) and bis(maltolato)dioxovanadium (V) (BMV) stimulate cell growth in a narrow range of concentration, but are also inhibitors for the cells at high concentrations. Vanadium-treated cells displayed clear changes in their morphology after overnight incubation. However, BMV was the least cytotoxic and the weakest inducer of morphological changes. All the compounds promote the phosphorylation of tyrosine residues in several proteins. This effect was more pronounced at low than at high doses. At low doses (10 microM), BMV showed a phosphorylation pattern similar to that of insulin, while Vi, VO and BMOV induced strong phosphorylation of cell proteins. The present findings suggest that the vanadium-induced growth regulation and morphological changes in MC3T3E1 osteoblast-like cells are associated with the ability of these agents to increase the phosphotyrosine protein levels and to inhibit phosphotyrosine phosphatases. These properties are dependent on the oxidation state as well as on the organic ligand which coordinates the vanadium atom.

From Vanadis to Atropos: vanadium compounds as pharmacological tools in cell death signalling

Vanadium compounds exert a variety of biological responses, the most notable being their effects as insulin mimetics. More recently, they have been used as pharmacological tools to investigate signalling pathways. Some peroxovanadium compounds act as powerful protein tyrosine phosphatase inhibitors, modulating both the extent and duration of phosphotyrosine signals at the level of the transmembrane growth factor receptors and targets in the cytoplasm and nucleus. A brief history of vanadium compounds, selected chemical properties of vanadium compounds and the ability of peroxovanadium complexes to modulate the activities of protein tyrosine phosphatases and tyrosine kinases are presented in this review by Anne Morinville, Dusica Maysinger and Alan Shaver. From the range of biological activities of these compounds, this review focuses on cytotoxic effects and possible roles of mitogen-activated protein kinases in mediating the effects exerted by vanadium compounds.

Activation of MAPKs in human bronchial epithelial cells exposed to metals

We have previously shown that in vitro exposure to metallic compounds enhances expression of interleukin (IL)-6, IL-8, and tumor necrosis factor-alpha in human bronchial epithelial cells. To characterize signaling pathways involved in metal-induced expression of inflammatory mediators and to identify metals that activate them, we studied the effects of As, Cr, Cu, Fe, Ni, V, and Zn on the mitogen-activated protein kinases (MAPK) extracellular receptor kinase (ERK), c-Jun NH2-terminal kinase (JNK), and P38 in BEAS cells. Noncytotoxic concentrations of As, V, and Zn induced a rapid phosphorylation of MAPK in BEAS cells. Activity assays confirmed marked activation of ERK, JNK, and P38 in BEAS cells exposed to As, V, and Zn. Cr and Cu exposure resulted in a relatively small activation of MAPK, whereas Fe and Ni did not activate MAPK under these conditions. Similarly, the transcription factors c-Jun and ATF-2, substrates of JNK and P38, respectively, were markedly phosphorylated in BEAS cells treated with As, Cr, Cu, V, and Zn. The same acute exposure to As, V, or Zn that activated MAPK was sufficient to induce a subsequent increase in IL-8 protein expression in BEAS cells. These data suggest that MAPK may mediate metal-induced expression of inflammatory proteins in human bronchial epithelial cells.

Diperoxovanadate participates in peroxidation reactions of H2O2 in presence of abundant catalase

Vanadate forms a stable complex with H2O2 at pH 7.0 in competition with catalase and the product, diperoxovanadate, resists scavenger action of catalase. Diperoxovanadate can act as a substrate in a H2O2-user reaction, horseradish peroxidase and can take the place of H2O2 far more effectively in oxidatively inactivating glyceraldehyde-3-phosphate dehydrogenase. By forming peroxo-complexes vanadate can provide a way of preserving cellular H2O2 in presence of abundant catalase and make it available for its functions.

Tyrosine kinases and calcium dependent activation of endothelial cell phospholipase D by diperoxovanadate

Reactive oxygen species (ROS) mediated modulation of signal transduction pathways represent an important mechanism of cell injury and barrier dysfunction leading to the development of vascular disorders. Towards understanding the role of ROS in vascular dysfunction, we investigated the effect of diperoxovanadate (DPV), derived from mixing hydrogen peroxide and vanadate, on the activation of phospholipase D (PLD) in bovine pulmonary artery endothelial cells (BPAECs). Addition of DPV to BPAECs in the presence of .05% butanol resulted in an accumulation of [32P] phosphatidylbutanol (PBt) in a dose- and time-dependent manner. DPV also caused an increase in tyrosine phosphorylation of several protein bands (Mr 20-200 kD), as determined by Western blot analysis with antiphosphotyrosine antibodies. The DPV-induced [32P] PBt-accumulation was inhibited by putative tyrosine kinase inhibitors such as genistein, herbimycin, tyrphostin and by chelation of Ca2+ with either EGTA or BAPTA, however, pretreatment of BPAECs with the inhibitor PKC bisindolylmaleimide showed minimal inhibition. Also down-regulation of PKC alpha and epsilon, the major isotypes of PKC in BPAECs, by TPA (100 nM, 18 h) did not attenuate the DPV-induced PLD activation. The effects of putative tyrosine kinase and PKC inhibitors were specific as determined by comparing [32P] PBt formation between DPV and TPA. In addition to tyrosine kinase inhibitors, antioxidants such as N-acetylcysteine and pyrrolidine dithiocarbamate also attenuated DPV-induced protein tyrosine phosphorylation and PLD stimulation. These results suggest that oxidation, prevented by reduction with thiol compounds, is involved in DPV-dependent protein tyrosine phosphorylation and PLD activation.

Vanadyl sulfate-stimulated glycogen synthesis is associated with activation of phosphatidylinositol 3-kinase and is independent of insulin receptor tyrosine phosphorylation

Salts of the trace element vanadium, such as sodium orthovanadate and vanadyl sulfate (VS), exhibit a myriad of insulin-like effects, including stimulation of glycogen synthesis and improvement of glucose homeostasis in type I and type II animal models of diabetes mellitus. However, the cellular mechanism by which these effects are mediated remains poorly characterized. We have shown earlier that different vanadium salts stimulate the MAP kinase pathway and ribosomal-S-6-kinase (p70s6k) in chinese hamster ovary cells overexpressing human insulin receptor (CHO-HIR cells) [Pandey, S. K., Chiasson, J.-L., and Srivastava, A. K. (1995) Mol. Cell. Biochem. 153, 69-78]. In the present studies, we have investigated if similar to insulin, VS also activates phosphatidylinositol 3-kinase (PI3-k) activity, and whether VS-induced activation of the PI3-k, MAP kinase, and p70s6k pathways contributes to glycogen synthesis. Treatment of CHO-HIR cells with VS resulted in increased glycogen synthesis and PI3-k activity which were blocked by pretreatment of the cells with wortmannin and LY294002, two specific inhibitors of PI3-k. On the other hand, PD98059 and rapamycin, specific inhibitors of the MAP kinase pathway and p70s6k, respectively, were unable to inhibit VS-stimulated glycogen synthesis. Moreover, VS-stimulated glycogen synthesis and PI3-k were observed without any change in the tyrosine phosphorylation of insulin receptor (IR) beta-subunit but were associated with increased tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1). In addition, PI3-k activation was detected in IRS-1 immunoprecipitates from VS-stimulated cells, indicating that tyrosine-phosphorylated IRS-1 was able to interact and thereby activate PI3-k in response to VS. Taken together, these results provide evidence that tyrosine phosphorylation of IRS-1 and activation of PI3-k play a key role in mediating the insulinomimetic effect of VS on glycogen synthesis independent of IR-tyrosine phosphorylation.

Stimulation of MAP kinase and S6 kinase by vanadium and selenium in rat adipocytes

To explore the mechanism underlying the insulin-mimetic actions of vanadium and selenium we examined their effects on the mitogen activated protein/myelin basic protein kinases (MAPK) and ribosomal S6 protein kinases, which are among the best characterized of the kinases that comprise the phosphorylation cascade in insulin signal transduction. We observed a transient activation of MAPK and S6 kinases by insulin in rat adipocytes, while both sodium selenate and vanadyl sulphate produced prolonged activation of the kinases. Vanadyl sulphate stimulated the activity of MAPK and S6 kinase by as much as 6 fold and 15 fold, respectively. Pretreatment of the cells with genistein did not affect the activation of MAPK by insulin, but partially blocked the effects of sodium selenate and vanadyl sulphate. Genistein did not change the activation of S6 kinase by insulin, but blocked the activation in vanadyl sulphate- and sodium selenate-treated-cells, suggesting that a genistein sensitive tyrosine kinase may be involved in the activation by these two compounds. Rapamycin, a specific inhibitor of the p70s6k isoform of S6 kinase, partially reduced the activation of S6 kinase activity by sodium selenate, indicating a role for this kinase in the overall activity of the S6 kinase in sodium selenate-treated cells. A similar trend was noted in vanadyl sulphate-treated cells. Thus, this study supports the involvement of MAPK and S6 kinases in the insulin-mimetic actions of vanadium and selenium.

Vanadium salts as insulin substitutes: mechanisms of action, a scientific and therapeutic tool in diabetes mellitus research

Vanadium and its compounds exhibit a wide variety of insulin-like effects. In this review, these effects are discussed with respect to the treatment of type I and type II diabetes in animal models, in vitro actions, antineoplastic role, treatment of IDDM and NIDDM patients, toxicity, and the possible mechanism(s) involved. Newly established CytPTK plays a major role in the bioresponses of vanadium. It has a molecular weight of approximately 53 kDa and is active in the presence of Co2+ rather than Mn2+. Among the protein-tyrosine kinase blockers, staurosporine is found to be a potent inhibitor of CytPTK but a poor inhibitor of InsRTK. Vanadium inhibits PTPase activity, and this in turn enhances the activity of protein tyrosine kinases. Our data show that inhibition of PTPase and protein tyrosine kinase activation has a major role in the therapeutic efficacy of vanadium in treating diabetes mellitus.