The insulin-mimetic effects of vanadate in isolated rat adipocytes. Dissociation from effects of vanadate as a (Na+-K+)ATPase inhibitor

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.

Heteroleptic oxidovanadium(IV)-malate complex improves glucose uptake in HepG2 and enhances insulin action in streptozotocin-induced diabetic rats

Diabetes mellitus, a complex and heterogeneous disease associated with hyperglycemia, is a leading cause of mortality and reduces life expectancy. Vanadium complexes have been studied for the treatment of diabetes. The effect of complex [VO(bpy)(mal)]·H₂O (complex A) was evaluated in a human hepatocarcinoma (HepG2) cell line and in streptozotocin (STZ)-induced diabetic male Wistar rats conditioned in seven groups with different treatments (n = 10 animals per group). Electron paramagnetic resonance and ⁵¹V NMR analyses of complex A in high-glucose Dulbecco's Modified Eagle Medium (DMEM) revealed the oxidation and hydrolysis of the oxidovanadium(IV) complex over a period of 24 h at 37 °C to give low-nuclearity vanadates "V1" (H₂VO₄^-), "V2" (H₂V₂O₇^2-), and "V4" (V₄O₁₂^4-). In HepG2 cells, complex A exhibited low cytotoxic effects at concentrations 2.5 to 7.5 μmol L^-1 (IC₅₀ 10.53 μmol L^-1) and increased glucose uptake (2-NBDG) up to 93%, an effect similar to insulin. In STZ-induced diabetic rats, complex A at 10 and 30 mg kg^-1 administered by oral gavage for 12 days did not affect the animals, suggesting low toxicity or metabolic impairment during the experimental period. Compared to insulin treatment alone, complex A (30 mg kg^-1) in association with insulin was found to improve glycemia (30.6 ± 6.3 mmol L^-1 vs. 21.1 ± 8.6 mmol L^-1, respectively; p = 0.002), resulting in approximately 30% additional reduction in glycemia. The insulin-enhancing effect of complex A was associated with low toxicity and was achieved via oral administration, suggesting the potential of complex A as a promising candidate for the adjuvant treatment of diabetes.

Biomimetic activity of soluble, well-defined, aqueous Ti(IV)-citrate species toward adipogenesis. An in vitro study

Metal-organic complexes bearing physiological substrates have been the target of several investigations, probing into the potential of well-defined atoxic metalloforms to influence fundamental cellular processes overcoming insulin resistance in Diabetes mellitus 2. Outstanding cases of such metals include zinc and vanadium, both being the target of intense synthetic and biological studies toward insulin mimesis. Owing to the close proximity in the periodic table, an early transition metal, titanium, emerges as another potential candidate of biologically relevant complexation, reflecting species capable of promoting insulin mimetic activity. Driven by the so far explored aqueous synthetic chemistry of Ti(IV)-hydroxycaboxylato systems, a well-defined Ti(IV)-citrate compound was synthesized under physiological conditions, isolated, and characterized, followed by its introduction in biological assays, targeting adipogenic events linked to glucose uptake and catabolism. The mononuclear Ti(IV)-citrate complex was introduced to 3T3-L1 cells, thereby probing into its biological activity (toxicity, morphology, migration, and adipogenic capacity). The results project an atoxic profile for the Ti(IV)-citrate species, thus justifying further incorporation in cellular differentiation processes, leading to mature adipocytes in a time- and concentration-dependent fashion. The experiments suggest that Ti(IV)-citrate is a competent agent promoting fibroblast differentiation, as evidenced by key adipogenic biomarkers, while concurrently exhibiting synergistic/enhancing action with insulin. The collective results show, for the first time, that an appropriately configured soluble-bioavailable complex Ti(IV) form exhibits a distinctly unique bioprofile, thereby lending credence to the notion that titanium metallopharmaceuticals hold merit as competent agents in adipogenesis and insulin mimesis in Diabetes mellitus.

Vanadium: Risks and possible benefits in the light of a comprehensive overview of its pharmacotoxicological mechanisms and multi-applications with a summary of further research trends

BACKGROUND

Vanadium (V) is an element with a wide range of effects on the mammalian organism. The ability of this metal to form organometallic compounds has contributed to the increase in the number of studies on the multidirectional biological activity of its various organic complexes in view of their application in medicine.

OBJECTIVE

This review aims at summarizing the current state of knowledge of the pharmacological potential of V and the mechanisms underlying its anti-viral, anti-bacterial, anti-parasitic, anti-fungal, anti-cancer, anti-diabetic, anti-hypercholesterolemic, cardioprotective, and neuroprotective activity as well as the mechanisms of appetite regulation related to the possibility of using this element in the treatment of obesity. The toxicological potential of V and the mechanisms of its toxic action, which have not been sufficiently recognized yet, as well as key information about the essentiality of this metal, its physiological role, and metabolism with certain aspects on the timeline is collected as well. The report also aims to review the use of V in the implantology and industrial sectors emphasizing the human health hazard as well as collect data on the directions of further research on V and its interactions with Mg along with their character.

RESULTS AND CONCLUSIONS

Multidirectional studies on V have shown that further analyses are still required for this element to be used as a metallodrug in the fight against certain life-threatening diseases. Studies on interactions of V with Mg, which showed that both elements are able to modulate the response in an interactive manner are needed as well, as the results of such investigations may help not only in recognizing new markers of V toxicity and clarify the underlying interactive mechanism between them, thus improving the medical application of the metals against modern-age diseases, but also they may help in development of principles of effective protection of humans against environmental/occupational V exposure.

Vanadium toxicity in the thymic development

The purpose of this study was to define the toxic effects of vanadium on thymic development in broilers fed on diets supplemented with 0, 5, 15, 30, 45 and 60 mg/kg of vanadium for 42 days. We examined the changes of relative weigh, cell cycle phase, apoptotic cells, and protein expression of Bcl-2, Bax, and caspase-3 in the thymus by the methods of flow cytometry, TUNEL (terminal-deoxynucleotidyl transferase mediated nick end labeling) and immunohistochemistry. The results showed that dietary high vanadium (30 mg/kg, 45 mg/kg and 60 mg/kg) caused the toxic effects on thymic development, which was characterized by decreasing relative weigh, increasing G0/G1 phase (a prolonged nondividing state), reducing S phase (DNA replication) and proliferating index (PI), and increasing percentages of apoptotic thymocytes. Concurrently, the protein expression levels of Bax and caspase-3 were increased, and protein expression levels of Bcl-2 were decreased. The thymic development suppression caused by dietary high vanadium further leads to inhibitive effects on T lymphocyte maturity and activity, and cellular immune function. The above-mentioned results provide new evidences for further understanding the vanadium immunotoxicity. In contrast, dietary 5 mg/kg vanadium promoted the thymic development by increasing relative weigh, decreasing G0/G1 phase, increasing S phase and PI, and reducing percentages of apoptotic thymocytes when compared to the control group and high vanadium groups.

Physiological roles of peroxido-vanadium complexes: Leitmotif as their signal transduction pathway

Evidence exists that supports the various physiological roles of vanadium compounds, although the amount of vanadium in our body is limited. This limited concentration in our body does not attract much attention of the biological chemists, although the fact is present; even in the 19th century, vanadium derivatives were used for the therapeutic reagents. In the middle of the 20th century, the main focus of vanadium chemistry is mainly on the chemical and material fields. After the first discovery of vanadium compounds expressing ATPase activity, oxidovanadium(IV) sulfate was reported to have insulin mimic activity. Additionally, because some vanadium compounds possess cellular toxicity, trials were also carried out to examine the possible use of vanadium compounds as cancer therapeutics. The application of vanadium complexes was extended in recent years especially in the 21st century. In this review, we briefly explain the historical background of vanadium chemistry and also summarize the physiological role of vanadium complexes mainly focusing on the synthesis and physiological role of peroxidovanadium compounds and their interactions with insulin signal transduction pathways.

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.

Protective effect of vanadyl sulfate on skin injury in streptozotocin-induced diabetic rats

The aim of the present study was to investigate the effect of vanadyl sulfate supplementation on the skin tissues of diabetic and control rats. In this study, 6-6.5 months old male Swiss albino rats were used. The animals were randomly divided into the following four groups: group I, control (nondiabetic intact animals); group II, vanadyl sulfate control; group III, streptozotocin (STZ)-diabetic animals and group IV, STZ-diabetic animals given vanadyl sulfate. The animals were made diabetic by intraperitoneal injection of a single dose of 65 mg/kg STZ in 0.01 M citrate buffer (pH = 4.5). From day 1 to day 60, 100 mg/kg vanadyl sulfate was given daily by gavage technique to one of the control and diabetic groups. Body weights and blood glucose levels were estimated on experimental days 0, 1 and 60. On the 60th day, skin tissue samples were taken, glutathione (GSH), lipid peroxidation (LPO), nonenzymatic glycosylation (NEG) and protein levels, catalase (CAT), superoxide dismutase (SOD) and glutathione-S-transferase (GST) activities were determined. Blood glucose, skin LPO and NEG levels increased, but skin GSH levels and CAT, SOD and GST activities decreased in the STZ group. Treatment with vanadyl sulfate reversed these effects. The present study showed that vanadyl sulfate exerted antioxidant properties and may prevent skin damage caused by diabetes.

The discovery of vanadyl and zinc complexes for treating diabetes and metabolic syndromes

The incidence of diabetes mellitus has increased over the decades because of lifestyle changes. The number of people with diabetes mellitus worldwide is expected to increase from 150 million to 220 million by 2010 and to 300 million by 2025. There are two main types of diabetes mellitus. Type 1 diabetes mellitus is due to the autoimmune-mediated destruction of pancreatic β cells, resulting in absolute insulin deficiency; the patients require exogenous insulin injections. Type 2 is characterized by insulin resistance and abnormal insulin secretion and the patients require exercise, diet control and/or oral hypoglycemics. However, each treatment has some adverse effects, including physical burden, formation of self-antibodies for insulin injections, the severe side effects of hypoglycemics and the discontinuation of insulin synthesis in the pancreas. To overcome these adverse effects and replace the use of these agents, the author attempted to develop new antidiabetic agents with novel structures and mechanisms. This review focuses on the authors' recent development of vanadium and zinc complexes for antidiabetic and antimetabolic syndromes.

Systemic treatment with vanadium absorbed by Coprinus comatus promotes femoral fracture healing in streptozotocin-diabetic rats

The purpose of this study was to analyze the impact of vanadium absorbed by Coprinus comatus (VACC) on fracture healing in streptozotocin-diabetic rats. Forty-five male Wistar rats used were divided into three groups: normal rats (control), diabetic rats, and diabetic rats treated with VACC. A standardized fracture-healing model with a stable plate fixation was established for the rat femoral fracture. After a 4-week stable fixation, callus quality was assessed by microcomputerized tomography and histological and biomechanical examinations. In addition, bone samples were obtained to evaluate the content of mineral substances in bones. Compared with the diabetic group, vanadium treatment significantly increased bone mineral content and biomechanical strength and improved microstructural properties of the callus. The ultimate load was increased by 29.1 % (P<0.05), and the total bone volume of callus enhanced by 11.2 % (P<0.05) at 4 weeks post fracture. Vanadium also promoted callus bone formation, which caused a 35.5 % increase in the total area of callus. However, VACC did not accelerate the fracture repair process in histological analysis. In conclusion, the current study suggests that systemic treatment with vanadium could promote fracture healing in streptozotocin-diabetic rats.

Vanadium toxicity in mice: possible impairment of lipid metabolism and mucosal epithelial cell necrosis in the small intestine

Because precise information as to the toxicity of vanadium is required for practical use of vanadium compounds as antidiabetic drugs, we examined vanadium toxicity in mice fed normal diet or high-fat diet (C57BL/6N, male, 7 weeks) by oral administration of ammonium metavanadate (AMV) with a maximum dose of 20 mgV/kg/day. Marked lipid accumulation in hepatocytes, renal epithelial cells, and mucosal epithelial cells of the small and large intestines and severe degeneration, necrosis, and loss of mucosal epithelial cells in the small intestine were observed. These pathological changes were more severe in mice fed high-fat diet than mice fed normal diet, and the intensity of the changes increased with increase in the administered dose of AMV. By electron microscopy, the number and size of lipid droplets in hepatocytes were increased. In the small intestine, a TUNEL assay showed a decreased number of positive cells, and positive cells for acrolein immunohistochemistry were observed specifically in the mucosal epithelial cells indicating degeneration and necrosis in the AMV-treated group, suggesting that a possible factor responsible for cell necrosis in the small intestine could be oxidative stress. In conclusion, AMV may impair cellular lipid metabolism, resulting in lipid accumulation, and induce mucosal epithelial cell necrosis in the small intestine.

Identification of a new anti-diabetic agent by combining VOSO4 and vitamin E in a single molecule: studies on its spectral, thermal and pharmacological properties

Vanadium(IV) complex of vitamin E (Vit E) ligand was reported. In this complex, binuclear ligand acts as a monodentate via oxygen of phenolic group. The vanadyl(II) ion is surrounded by two molecules of Vit E and two water molecules. The [VO(Vit E)(2)(H(2)O)(2)]2H(2)O complex was isolated by the reaction between VOSO(4) and vitamin E in ethanol/water solvent (50/50 w/w) at pH=8. The solid vanadyl(II) complex has been characterized by elemental analyses (CHN), photometric titrations, infrared spectra, molar conductivity, electronic spectra, TGA/DSC, SEM and XRD studies. Electronic and magnetic measurements are confirmed that the speculated geometry of vanadyl(II) complex is square pyramidal geometry. The microbial test was performed for the vanadyl complex against some kinds of bacteria and fungi. The [VO(Vit E)(2)(H(2)O)(2)]2H(2)O complex was proved effective in addressing diabetic of type I in case of experimental animal than other compounds were prepared in the literature.

The anti-diabetic effects and pharmacokinetic profiles of bis(maltolato)oxovanadium in non-diabetic and diabetic rats

The purpose of this study was to evaluate the anti-diabetic effects and pharmacokinetics of bis(maltolato)oxovanadium (BMOV) in rats. The anti-diabetic study was carried out in non-diabetic and diabetic rats by single-dose subcutaneous and intragastric administration. Pharmacokinetic investigation was performed using non-diabetic rats. Results showed that BMOV significantly decreased plasma glucose levels in diabetic rats at all given doses, and restored hyperglycaemic values to normal values after subcutaneous injections at doses of 4 and 8 mg vanadium (V)/kg or after intragastric administration at doses of 14 and 28 mgV/kg, respectively, but did not affect the plasma glucose level in non-diabetic rats. BMOV could be rapidly absorbed, slowly eliminated from plasma, widely distributed in various tissues and accumulated to a greater extent in the femur tissue. The average absolute bioavailability for intragastric administration at a single dose of 3, 6 and 12 mgV/kg was 28.1%, 33.7% and 21.4%, respectively. The presence of the peak vanadium level in the plasma was not coincident with that of the maximum effect of lowering plasma glucose levels. In conclusion, at the present dosing levels and administration routes, BMOV was effective in lowering plasma glucose levels in diabetic rats. BMOV has a promising outlook as an oral glucose-lowering drug.

Kinetics of inhibition of rabbit intestine alkaline phosphatase by heteroligand peroxo complexes of vanadium(V) and tungsten(VI)

The present work was undertaken to examine and compare some biologically important properties of peroxo compounds of V(V) and W(VI) containing biogenic species as ancillary ligand. New anionic peroxovanadate(V) complex of the type Na[VO(O(2))(2)(triglycine)].3H(2)O (pV1) and a molecular peroxotungstate(VI) [WO(O(2))(2)(triglycine)].3H(2)O (pW1) were synthesized and characterized for the purpose and their stability in solution was ascertained. Studies on kinetics of inhibition of alkaline phosphatase activity by the newly synthesized compounds and series of dipeptide and amino acid containing peroxo complexes of vanadium and tungsten synthesized previously by us viz., Na[VO(O(2))(2)(gly-gly)(H(2)O)].H(2)O (gly-gly = glycyl-glycine), Na[VO(O(2))(2)(asn)].H(2)O (asn = asparagine), Na[VO(O(2))(2)(gln)].H(2)O (gln = glutamine), and [WO(O(2))(2)(gly-gly)(H(2)O)].3H(2)O, revealed that each of these species is a potent mixed-type inhibitor of the enzyme. Significant difference was noted between the peroxovanadium (pV) and peroxotungsten (pW) compounds in terms of their oxidant activity with reduced glutathione.

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.

The mixed-lineage kinase DLK undergoes Src-dependent tyrosine phosphorylation and activation in cells exposed to vanadate or platelet-derived growth factor (PDGF)

Some data in the literature suggest that serine/threonine phosphorylation is required for activation of the mixed-lineage kinases (MLKs), a subgroup of mitogen-activated protein kinase kinase kinases (MAPKKKs). In this report, we demonstrate that the MLK family member DLK is activated and concurrently tyrosine-phosphorylated in cells exposed to the protein tyrosine phosphatase inhibitor vanadate. Tyrosine phosphorylation appears crucial for activation as incubation of vanadate-activated DLK molecules with a tyrosine phosphatase substantially reduced DLK enzymatic activity. Interestingly, the effects of vanadate on DLK are completely blocked by treatment with a Src family kinase inhibitor, PP2, or the expression of short hairpin RNA (shRNA) directed against Src. DLK also fails to undergo vanadate-stimulated tyrosine phosphorylation and activation in fibroblasts which lack expression of Src, Yes and Fyn, but reintroduction of wild-type Src or Fyn followed by vanadate treatment restores this response. In addition to vanadate, stimulation of cells with platelet-derived growth factor (PDGF) also induces tyrosine phosphorylation and activation of DLK by a Src-dependent mechanism. DLK seems important for PDGF signaling because its depletion by RNA interference substantially reduces PDGF-stimulated ERK and Akt kinase activation. Thus, our findings suggest that Src-dependent tyrosine phosphorylation of DLK may be important for regulation of its activity, and they support a role for DLK in PDGF signaling.

Impairment of mineralization by metavanadate and decavanadate solutions in a fish bone-derived cell line

Vanadium, a trace metal known to accumulate in bone and to mimic insulin, has been shown to regulate mammalian bone formation using in vitro and in vivo systems. In the present work, short- and long-term effects of metavanadate (containing monomeric, dimeric, tetrameric and pentameric vanadate species) and decavanadate (containing decameric vanadate species) solutions on the mineralization of a fish bone-derived cell line (VSa13) were studied and compared to that of insulin. After 2 h of incubation with vanadate (10 microM in monomeric vanadate), metavanadate exhibited higher accumulation rates than decavanadate (6.85 +/- 0.40 versus 3.95 +/- 0.10 microg V/g of protein, respectively) in fish VSa13 cells and was also shown to be less toxic when applied for short periods. In longer treatments with both metavanadate and decavanadate solutions, similar effects were promoted: stimulation of cell proliferation and strong impairment (75%) of extracellular matrix (ECM) mineralization. The effect of both vanadate solutions (5 microM in monomeric vanadate), on ECM mineralization was increased in the presence of insulin (10 nM). It is concluded that chronic treatment with both vanadate solutions stimulated fish VSa13 cells proliferation and prevented ECM mineralization. Newly developed VSa13 fish cells appeared to be appropriate in the characterization of vanadate effects on vertebrate bone formation, representing a good alternative to mammalian systems.

Adipogenic action of vanadium: a new dimension in treating diabetes

Vanadium is a well known anti-diabetic agent which mimics most of the actions of insulin on mature adipocytes. We report here the effect of vanadium on proliferation and differentiation of 3T3-L1 preadipocytes. Like insulin, vanadium treatment leads to increased proliferation as evidenced by H(3)thymidine uptake studies and differentiation of 3T3-L1 cells into adipocytes as evidenced by oil-red-O staining. Adipogenic potential of vanadium can be attributed to CREB activation, as documented by phospho-CREB antibody staining. This adipogenic potential is of significance in an in vivo scenario as the new adipocytes are likely to be insulin sensitive as against resistant existing mature adipocytes and thus indirectly may help in reduction of insulin resistance. Till today decrease in insulin resistance by vanadium treatment has been mainly attributed to its potential to inhibit PTP-1B, however the present study opens a new dimension in vanadium treatment for diabetes due to its novel role in adipogenesis.

Hypoglycemic effects of vanadium on alloxan monohydrate induced diabetic dogs

The hypoglycemic effects after oral administration of vanadium have been studied previously in many species such as rats, mice and even humans. However, there has been no prior report on the glucose lowering effect of vanadium on diabetic dogs. Therefore, the purpose of this study was to evaluate the hypoglycemic effects of oral vanadium on diabetic dogs. Diabetes mellitus in the dogs studied was induced by alloxan monohydrate intravenous injection. The dogs were divided into two groups, one was the diabetic control (DC) group (n = 4) and the other was the vanadium treated (DV) group (n = 6). Fresh water was supplied to the dogs in the DC group, but sodium metavanadate solution (0.1~0.2 mg/ml) was given to the dogs in DV group from one week after the alloxan injection. The fasting glucose levels, fructosamine and serum chemistry profiles were compared between the two groups weekly for three weeks. The fasting blood glucose levels in DV group were significantly lower than those in the DC group (p < 0.01). Fructosamine levels in the DV group were also lower than those in the DC group (p < 0.05). The serum chemistry profiles were not significantly different in comparisons between the two groups. However, the cholesterol levels were significantly lower in the DV group compared to the DC group (p < 0.05). Our findings showed that oral vanadium administration had a hypoglycemic effect on chemically induced diabetic dogs.

The Effect of Cinnamtannin B1 on Cell Proliferation and Glucose Uptake of 3T3-L1 Cells

The effects of cinnamtannin B1 on cell proliferation and glucose uptake of 3T3-L1 cells were examined. Cinnamtannin B1 promoted cell proliferation of 3T3-L1 adipocytes at a concentration range between 0.11-0.17 mM. The effect of cinnamtannin B1 on cellular 2-deoxy-D-[1-3H] glucose uptake in differentiated 3T3-L1 adipocytes, following treatment with a 0.11 mM concentration of cinnamtannin B1 for 15, 30 and 60 minutes, was an increase in the glucose uptake from a basal value to 702.0, 1111.0 and 2226.0 cpm, respectively (p<0.005). The comparable glucose uptakes with insulin treatment were 660.0, 1039.0 and 2135.0 cpm, respectively. Wortmannin and cytochalasin B were found to inhibit cinnamtannin B1-stimulated glucose uptake, but sodium orthovanadate increased the glucose uptake.

Follow-up studies on glycosylated flavonoids and their complexes with vanadium: Their anti-hyperglycemic potential role in diabetes

The present study sought to evaluate the hypoglycemic activities of free glycosylated flavonoids and flavonoid complexes with vanadium(IV), (VO(IV)), on glycemia in experimental diabetic rats. Besides free kaempferol-3,7-O-(alpha)-dirhamnoside and kaempferol-3-neohesperidoside, complexes of these flavonoids with VO(IV) were administered by different routes in order to compare the potency of the compounds as well as the efficacy of insulin or VO(IV) in lowering serum glucose. Wistar rats were made diabetic by alloxan. The glycemia was assessed at different times after the administering of compounds. The equilibrium constants were determined by potentiometric study and two species with VO(IV) are proposed at physiological pH, VOH(2)L(2) for kaempferitrin and VOHL for kaempferol-3-neohesperidoside. The latter exhibited hypoglycemic activity at all times examined with 50 and 100 mg/kg and the former reduced the glycemia from 0 to 6h by i.p. route. The administering of the complexes or 0.0146 mmol/kg VO(IV) resulted in a serum glucose-lowering effect over time in the case of i.p. treatment. A marked hypoglycemic effect was observed for 0.5IU of insulin (67.5%); 0.0146 mmol VO(IV) (16.8%); 0.0294 mmol kaempferitrin-VO(IV) (17.8%) and 0.0286 mmol kaempferol-3-neohesperidoside-VO(IV) (56.0%) at 3h after i.p. treatment when compared with respective zero time in diabetic groups. Kaempferol-3-neohesperidoside-VO(IV) was 2.5 times more effective than VO(IV), twice as effective as the free compound and three times more effective than kaempferitrin-VO(IV). This is of particular interest since kaempferol-3-neohesperidoside appears to represent a suitable ligand for VO(IV) to mimic the efficacy of insulin in lowering serum glucose levels.

Binding of oxovanadium ions to the major and minor grooves of DNA duplex: stability and structural models

Vanadate induces DNA strand breaks in cultured human fibroblasts at doses that are relative to the occupational exposure. Oxovanadium compounds also exert preventive effects against chemical carcinogenesis in animals and form complexes with DNA in vivo. This study was designed to examine the interaction of calf-thymus DNA with VO2+and VO3¯ions in aqueous solution at physiological pH, with a constant DNA concentration of 12.5 mmol/L and vanadium–DNA (phosphate) molar ratios (r) of 1:160 to 1:2. Capillary electrophoresis and Fourier transform infrared difference spectroscopy were used to determine the cation binding site, the binding constant, the helix stability, and DNA conformation in the oxovanadium–DNA complexes. Structural analysis showed that VO2+binds DNA through guanine and adenine N-7 atoms and the backbone PO2group with apparent binding constants of KG= 8.8 × 105(mol/L)–1and KA= 3.4 × 105(mol/L)–1. The VO3¯shows weaker binding through thymine, adenine, and guanine bases, with K = 1.9 × 104(mol/L)–1and no interaction with the backbone phosphate group. A partial B-to-A DNA transition occurred upon VO–DNA complexation, while DNA remains in the B-family structure in the VO3¯complexes.

Solution equilibrium characterization of insulin-mimetic Zn(II) complexes

Solution speciation (stoichiometry and stability constants) of the insulin mimetic Zn(II) complexes of several bidentate ligands with (O,O), (N,O) or (S,O) coordination modes have been determined by pH-metry at 25 degrees Celsius and I=0.2M (KCl). All ligands were found to coordinate in a bidentate way forming mono, bis and tris complexes, besides a mixed hydroxo bis complex ZnL(2)(OH) detected in the slightly basic pH range together with the tris complex. Relationships between the stability data, lipophilicity of the complexes and earlier biological data are evaluated. The validity of the linear free energy relationships (LFER) between the proton and Zn(II) complexes and also between the VO(IV) and Zn(II) complexes is tested.

Effect of insulin-mimetic vanadyl sulfate on cytochrome P450 2E1-dependent p-nitrophenol hydroxylation in the liver microsomes of streptozotocin-induced type 1 diabetic rats

CYP2E1 is known to be induced in streptozotocin (STZ)-treated diabetic rats (STZ rats), and its induction is improved by insulin. We have examined the age-dependent changes of CYP2E1 in the liver microsomes of type 1 diabetic STZ rats, the effects of VOSO4 on the contents of total P450 and CYP2E1, and the activities of CYP2E1 in terms of p-nitrophenol hydroxylation. The contents of P450 and CYP2E1 and CYP2E1 activity were enhanced with the development of diabetes. When the hyperglycemia of STZ rats was improved by daily intraperitoneal injections of VOSO4 for 10 days at the doses of 7 mg/kg body weight for 5 days, 5 mg/kg for the following 3 days, and then 2.5 mg/kg for 2 days, the P450 and CYP2E1 levels and CYP2E1 activity were lowered than those in the untreated STZ rats. To understand the mechanism underlying CYP2E1-dependent hydroxylation activity, the production of reactive oxygen species was examined in the NADPH-liver microsomal systems by ESR spin-trapping. Singlet oxygen (1O2) was detected in all microsomal systems, while superoxide anion radical(*O2-) and hydroxyl radical (*OH) were not. On the basis of these results, we conclude that (1) CYP2E1 level and activity are enhanced in the diabetic state, however, they are improved by VOSO4 treatment, and (2) 1O2 is generated during CYP2E1-dependent substrate oxygenation.

Positive regulation of ERK activation and MKP-1 expression by peroxovanadium complex bpV (phen)

Lower micromolar concentrations of peroxovanadium compound potassium bisperoxo(1,10-phenanthroline)oxovanadate (V) [bpV (phen)] stimulate RINm5F cell metabolic activity. 1 and 3 micromol/L bpV (phen) induces strong and sustained activation of extracellular signal-regulated kinase (ERK). However, it seems that bpV (phen) does not effect c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) phosphorylation. In addition, bpV (phen) induces mitogen-activated protein kinase phosphatase-1 (MKP-1) expression. We found that ERK activation could be completely abolished if RINm5F cells were incubated with both bpV (phen) and PD 98059, a specific inhibitor of upstream ERK kinase MEK1. On the other hand, this combined treatment up-regulated activation of stress kinases, JNK and p38 MAPK, significantly suppressed MKP-1 expression and induced cell death. Thus, our results suggest that the mechanism underlying bpV (phen) survival-enhancing effect could be associated with induced ERK activation and MKP-1 expression.

Shp2 is required for protein kinase C-dependent phosphorylation of serine 307 in insulin receptor substrate-1

The function of insulin receptor substrate-1 (IRS-1), a key molecule of insulin signaling, is modulated by phosphorylation at multiple serine/threonine residues. Phorbol ester stimulation of cells induces phosphorylation of two inhibitory serine residues in IRS-1, i.e. Ser-307 and Ser-318, suggesting that both sites may be targets of protein kinase C (PKC) isoforms. However, in an in vitro system using a broad spectrum of PKC isoforms (alpha, beta1, beta2, delta, epsilon, eta, mu), we detected only Ser-318, but not Ser-307 phosphorylation, suggesting that phorbol ester-induced phosphorylation of this site in intact cells requires additional signaling elements and serine kinases that link PKC activation to Ser-307 phosphorylation. As we have observed recently that the tyrosine phosphatase Shp2, a negative regulator of insulin signaling, is a substrate of PKC, we studied the role of Shp2 in this context. We found that phorbol ester-induced Ser-307 phosphorylation is reduced markedly in Shp2-deficient mouse embryonic fibroblasts (Shp2-/-) whereas Ser-318 phosphorylation is unaltered. The Ser-307 phosphorylation was rescued by transfection of mouse embryonic fibroblasts with wild-type Shp2 or with a phosphatase-inactive Shp2 mutant, respectively. In this cell model, tumor necrosis factor-alpha-induced Ser-307 phosphorylation as well depended on the presence of Shp2. Furthermore, Shp2-dependent phorbol ester effects on Ser-307 were blocked by wortmannin, rapamycin, and the c-Jun NH2-terminal kinase (JNK) inhibitor SP600125. This suggests an involvement of the phosphatidylinositol 3-kinase/mammalian target of rapamycin cascade and of JNK in this signaling pathway resulting in IRS-1 Ser-307 phosphorylation. Because the activation of these kinases does not depend on Shp2, it is concluded that the function of Shp2 is to direct these activated kinases to IRS-1.

Insulino-mimetic and anti-diabetic effects of vanadium compounds

Compounds of the trace element vanadium exert various insulin-like effects in in vitro and in vivo systems. These include their ability to improve glucose homeostasis and insulin resistance in animal models of Type 1 and Type 2 diabetes mellitus. In addition to animal studies, several reports have documented improvements in liver and muscle insulin sensitivity in a limited number of patients with Type 2 diabetes. These effects are, however, not as dramatic as those observed in animal experiments, probably because lower doses of vanadium were used and the duration of therapy was short in human studies as compared with animal work. The ability of these compounds to stimulate glucose uptake, glycogen and lipid synthesis in muscle, adipose and hepatic tissues and to inhibit gluconeogenesis, and the activities of the gluconeogenic enzymes: phosphoenol pyruvate carboxykinase and glucose-6-phosphatase in the liver and kidney as well as lipolysis in fat cells contributes as potential mechanisms to their anti-diabetic insulin-like effects. At the cellular level, vanadium activates several key elements of the insulin signal transduction pathway, such as the tyrosine phosphorylation of insulin receptor substrate-1, and extracellular signal-regulated kinase 1 and 2, phosphatidylinositol 3-kinase and protein kinase B activation. These pathways are believed to mediate the metabolic actions of insulin. Because protein tyrosine phosphatases (PTPases) are considered to be negative regulators of the insulin-signalling pathway, it is suggested that vanadium can enhance insulin signalling and action by virtue of its capacity to inhibit PTPase activity and increase tyrosine phosphorylation of substrate proteins. There are some concerns about the potential toxicity of available inorganic vanadium salts at higher doses and during long-term therapy. Therefore, new organo-vanadium compounds with higher potency and less toxicity need to be evaluated for their efficacy as potential treatment of human diabetes.

Protective effect of macrocyclic binuclear oxovanadium complex on oxidative stress in pancreas of streptozotocin induced diabetic rats

Chronic hyperglycemia in diabetes is a major causative factor of free radical generation which further leads to many secondary diabetic complications via the damage to cellular proteins, membrane lipids, nucleic acids and eventually to cell death. Recently we have reported on the hypoglycemic efficacy of a new macrocyclic binuclear oxovanadium complex and its non-toxic nature. This study focuses on the effect of the above complex in ameliorating oxidative stress in the pancreas of diabetic rats. Streptozotocin induced diabetic rats were treated orally with the vanadium complex (5 mg/kg/body weight) for 30 days and the level of pancreatic antioxidants and lipid peroxides were determined. Treatment with the macrocyclic binuclear oxovanadium complex decreased the lipid peroxides and the antioxidant enzymes such as superoxide dismutase, catalase and glutathione peroxidase to near control levels. Histological examinations also revealed the protective effect of the complex on pancreatic beta cells. The results demonstrate the protective effect of the macrocyclic binuclear oxovanadium complex on the pancreatic antioxidant status.

Effect of macrocyclic binuclear oxovanadium complex on tissue defense system in streptozotocin-induced diabetic rats

BACKGROUND

Oxidative stress plays an important role in chronic complications of diabetes mellitus and hence the regulation of free radicals is essential in the treatment of diabetes. The protective effect of a new macrocyclic binuclear oxovanadium complex on antioxidant defense systems of liver and kidney was examined in streptozotocin-induced experimental diabetes in rats.

METHODS

The levels of lipid peroxides, glutathione and the activities of superoxide dismutase, catalase, glutathione peroxidase and glutathione-S-transferase were assayed according to standard procedures in the liver and kidney of control and experimental groups of rats.

RESULTS

A significant decrease (p < 0.05) was observed in both the glutathione content and in the activities of antioxidant enzymes such as superoxide dismutase, catalase, glutathione peroxidase and a concomitant increase in the level of lipid peroxides in diabetic rats. The observed alterations in the antioxidant status of tissues reverted back to near normal levels after the oral administration of macrocyclic vanadium complex at a dose of 5 mg/kg body weight/rat/day for a period of 30 days.

CONCLUSION

The normoglycemic efficacy of the vanadium complex alleviates oxidative stress in streptozotocin-induced diabetes in rats.

A new candidate for insulinomimetic vanadium complex: synergism of oxovanadium(IV)porphyrin and sodium ascorbate

Vanadyl-meso-tetrakis(1-methylpyridinium-4-yl)porphyrin, VOTMpyP with the VO(N(4)) coordination mode, was found to have a potent insulinomimetic activity on the basis of in vitro and in vivo experiments. When the complex was given simultaneously with sodium ascorbate, the high blood glucose levels of type 1 diabetic model STZ-rats were lowered by synergistic effect, probably sustaining the vanadyl state by means of ascorbate distributed in the organs and tissues of animals. This is the first finding on not only the insulinomimetic vanadyl-porphyrin complex but also the occurrence of a synergistic effect of VOTMpyP and sodium ascorbate to lower the high blood glucose levels in diabetic animals.

Synthesis and insulinomimetic activities of novel mono- and tetranuclear oxovanadium(IV) complexes with 3-hydroxypyridine-2-carboxylic acid

Two chargeless VO(IV) complexes with 3-hydroxypyridine-2-carboxylic acid (H2hpic), [VO(Hhpic-O,O)(Hhpic-O,N)(H2O)].3H2O (1) and the cyclic tetramer [(VO)4(mu-(hpic-O,O',N))4(H2O)4].8H3O (2), have been synthesized and characterized by elemental analysis, mass, infrared, electronic absorption, electron spin resonance (ESR) spectroscopies, and X-ray crystallography. Their coordination structures are similar to each other (and 1 is readily transformed into 2), but are quite different from that of bis(pyridine-2-carboxylato)oxovanadium(IV). The magnetic susceptibility of 2 indicates the presence of a weak ferromagnetic intramolecular interaction between the V atoms at low temperature, in addition to a weak antiferromagnetic intermolecular interaction. The ESR signal of 2 was broad, while 1 showed an eight-line hyperfine splitting pattern due to coupling of the unpaired electron with the 51V nucleus (I=7/2). The ESR spectrum and cyclic voltammogram of 2 clearly show that the cyclic tetramer remains intact in solution. The insulinomimetic activity of 1 and 2 was evaluated by means of in vitro measurements of the inhibition of free fatty acid release from epinephrine-treated isolated rat adipocytes. While 1 exerted higher insulinomimetic activity than VOSO4, the activity of 2 was significantly lower than that of VOSO4. Hence 2 appears to retain its cyclic structure during the in vitro test. These results indicate that the rational ligand design for VO complexes might be a promising approach to obtain superior insulinomimetic activity.