Oral vanadium administration to streptozotocin-diabetic rats has marked negative side-effects which are independent of the form of vanadium used

Evaluation of immunotoxicity of sodium metavanadate following drinking water exposure in female B6C3F1/N mice in a 28-day study

Sodium metavanadate (NaVO3 ) is a pentavalent vanadium compound used in the metal industry and dietary supplements; human exposure occurs through inhalation of fumes and dust and ingestion of NaVO3 -containing products. The objective of this study was to assess the potential immunotoxicity of NaVO3 . Female B6C3F1/N mice were exposed to 0-500 ppm NaVO3 in drinking water for 28 days and evaluated for effects on immune cell populations and innate, cellular-mediated, and humoral-mediated immunity. There was a decreasing trend in body weight (BW) and BW gain in NaVO3 exposed mice, with a decrease (p ≤ 0.05) in BW gain at ≥250 ppm, relative to control. Conversely, increasing trends in spleen weights and an increase (p ≤ 0.05) in the spleen:BW ratio at ≥250 ppm NaVO3 were observed. NaVO3 exposure altered antibody production against sheep red blood cells (SRBC). Antibody forming cells (AFC)/106 spleen cells exhibited a decreasing trend, with a decrease (p ≤ 0.05) at 500 ppm NaVO3 , concurrent with an increase in percent B cells. NaVO3 had no effect on the serum anti-SRBC IgM antibody titers or anti-keyhole limpet hemocyanin antibody production. Exposure to NaVO3 decreased the percentage of natural killer cells at all dose levels (p ≤ 0.05), with no effect on the lytic activity. NaVO3 altered T-cell populations at 500 ppm but had no effect on T-cell proliferative responses or the lytic activity of cytotoxic T cells. Collectively, these data indicate that NaVO3 exposure can adversely affect the immune system by inducing alterations in humoral-mediated immunity, specifically the AFC response, with no effect on cell-mediated or innate immunity.

Epigallocatechin-3-gallate Alleviates Vanadium-Induced Reduction of Antioxidant Capacity via Keap1-Nrf2-sMaf Pathway in the Liver, Kidney, and Ovary of Laying Hens

This study evaluated the effect of epigallocatechin-3-gallate (EGCG) alleviating the reduction of antioxidant capacity induced by dietary vanadium (V) in the liver, kidney, and ovary of laying hens. Furthermore, Kelch-like ECH-associated protein 1(Keap1)-nuclear factor erythroid 2-related factor 2 (Nrf2)-small Maf proteins (sMaf) pathway was explored to reveal the molecular mechanism. A total of 768 40-week-old Hyline-Brown laying hens were randomly allocated to 4 groups with 8 pens per group and 24 hens per pen. The experimental groups were as follows: control (basal diet); V15, control + 15 mg/kg V; EGCG150, control + 150 mg/kg EGCG; V15 + EGCG150, V15 + 150 mg/kg EGCG. Our results revealed that dietary EGCG supplementation completely alleviated the V-induced reductions of hen-day egg production, average egg weight, Haugh unit, albumen height, eggshell strength, and eggshell thickness. Dietary EGCG supplementation completely prevented the V-induced reductions of serum follicle-stimulating hormone and luteinizing hormone levels. Besides, dietary EGCG supplementation reversed the V-induced increments of alanine aminotransferase (ALT), aspartate aminotransferase (AST), blood urea nitrogen (BUN), creatinine (Cr), and uric acid (UA). In addition, dietary EGCG supplementation partially alleviated the V-induced reductions of the enzyme activities and gene expressions of superoxidative dismutase (SOD), catalase (CAT), glutathione reductase (GR), and glutathione peroxidase (GSH-Px). Furthermore, dietary EGCG supplementation partially alleviated the V-induced reductions of Nrf2 and sMaf gene expressions, and the increments of Keap1 gene expression. In summary, EGCG partially alleviated V-induced reduction of antioxidant capacity through Keap1-Nrf2-sMaf pathway in the liver, kidney, and ovary of laying hens.

Evaluation of the level of selected iron-related proteins/receptors in the liver of rats during separate/combined vanadium and magnesium administration

BACKGROUND

The current knowledge about the effects of vanadium (V) on iron (Fe)-related proteins and Fe homeostasis (which is regulated at the systemic, organelle, and cellular levels) is still insufficient.

OBJECTIVE

This fact and our earlier results prompted us to conduct studies with the aim to explain the mechanism of anemia accompanied by a rise in hepatic and splenic Fe deposition in rats receiving sodium metavanadate (SMV) separately and in combination with magnesium sulfate (MS).

RESULTS

We demonstrated for the first time that SMV (0.125 mg V/mL) administered to rats individually and in conjunction with MS (0.06 mg Mg/mL) for 12 weeks did not cause significant differences in the hepatic hepcidin (Hepc) and hemojuvelin (HJV) concentrations, compared to the control. In comparison with the control, there were no significant changes in the concentration of transferrin receptor 1 (TfR1) in the liver of rats treated with SMV and MS alone (in both cases only a downward trend of 14% and 15% was observed). However, a significant reduction in the hepatic TfR1 level was found in rats receiving SMV and MS simultaneously. In turn, the concentration of transferrin receptor 2 (TfR2) showed an increasing trend in the liver of rats treated with SMV and/or MS.

CONCLUSIONS

The experimental data suggest that the pathomechanism of the SMV-induced anemia is not associated with the effect of V on the concentration of Hepc in the liver, as confirmed by the unaltered hepatic HJV and TfR1 levels. Therefore, further studies are needed in order to check whether anemia that developed in the rats at the SMV administration (a) results from the inhibitory effect of V on erythropoietin (EPO) production, (b) is related to the effect of V on the induction of matriptase-2 (TMPRSS6) expression, or (c) is associated with the influence of this metal on haem synthesis.

In vitro study of the protective effect of manganese against vanadium-mediated nuclear and mitochondrial DNA damage

We aimed to study the effect of vanadium(V) exposure on cell viability, nuclear DNA (nDNA) and mitochondrial DNA (mtDNA) and to elucidate if these effects can be reverted by co-exposure to V and manganese (Mn). HepG2 cells were incubated with various concentrations of bis(maltolato)oxovanadium(IV) or MnCl2 for 32 h for viability study. The higher concentrations (59   μM V, 54 nM Mn and 59   μM V+54 nM Mn) were used to study DNA damage and uptake of V and Mn. Comet assay was used for the study of nDNA damage; mtDNA damage was studied by determining deletions and number of copies of the ND1/ND4 mtDNA region. Cellular content of V and Mn was determined using ICPMS. Cellular exposure to 59   μM V decreased viability (14%) and damaged nDNA and mtDNA. This effect was partially prevented by the co-exposure to V + Mn. Exposure to V increased the cellular content of V and Mn (812.3% and 153.5%, respectively). Exposure to Mn decreased the content of V and Mn (62% and 56%, respectively). Exposure to V + Mn increased V (261%) and decreased Mn (56%) content. The positive effects on cell viability and DNA damage when incubated with V + Mn could be due to the Mn-mediated inhibition of V uptake.

A Small Insulinomimetic Molecule Also Improves Insulin Sensitivity in Diabetic Mice

Dramatic increase of diabetes over the globe is in tandem with the increase in insulin requirement. This is because destruction and dysfunction of pancreatic β-cells are of common occurrence in both Type1 diabetes and Type2 diabetes, and insulin injection becomes a compulsion. Because of several problems associated with insulin injection, orally active insulin mimetic compounds would be ideal substitute. Here we report a small molecule, a peroxyvanadate compound i.e. DmpzH[VO(O2)2(dmpz)], henceforth referred as dmp, which specifically binds to insulin receptor with considerable affinity (KD-1.17μM) thus activating insulin receptor tyrosine kinase and its downstream signaling molecules resulting increased uptake of [14C] 2 Deoxy-glucose. Oral administration of dmp to streptozotocin treated BALB/c mice lowers blood glucose level and markedly stimulates glucose and fatty acid uptake by skeletal muscle and adipose tissue respectively. In db/db mice, it greatly improves insulin sensitivity through excess expression of PPARγ and its target genes i.e. adiponectin, CD36 and aP2. Study on the underlying mechanism demonstrated that excess expression of Wnt3a decreased PPARγ whereas dmp suppression of Wnt3a gene increased PPARγ expression which subsequently augmented adiponectin. Increased production of adiponectin in db/db mice due to dmp effected lowering of circulatory TG and FFA levels, activates AMPK in skeletal muscle and this stimulates mitochondrial biogenesis and bioenergetics. Decrease of lipid load along with increased mitochondrial activity greatly improves energy homeostasis which has been found to be correlated with the increased insulin sensitivity. The results obtained with dmp, therefore, strongly indicate that dmp could be a potential candidate for insulin replacement therapy.

Effect of Vanadium and Tea Polyphenols on Intestinal Morphology, Microflora and Short-Chain Fatty Acid Profile of Laying Hens

Vanadium (V) is a trace element which can induce dysfunction of gastro-intestine and egg quality deterioration of laying hens. This study was conducted to determine the effect of tea polyphenols (TP) on intestinal morphology, microflora, and short-chain fatty acid (SCFA) profile of laying hens fed vanadium containing diets. A total of 120 Lohman laying hens (67-week-old) were randomly divided into 4 groups with 6 replicates and 5 birds each for a 35-day feeding trial. The dietary treatments were as follows: (1) control (CON), fed a basal diet; (2) vanadium treatment (V10), CON +10 mg V/kg; (3) TP treatment 1 (TP1): V10 + 600 mg TP/kg; (4) TP treatment 2 (TP2): V10 + 1000 mg TP/kg. Fed 10 mg V/kg diets to laying hens did not affect the cecum flora diversity index (H), degree of homogeneity (EH), and richness (S), but hens fed TP2 diet decreased the H, EH, and S (P < 0.05). The cecum butyrate acid concentration was lower in V10 treatment and higher in TP2 treatment (P < 0.05). Addition of 10 mg/kg V resulted in an increased (P < 0.01) duodenal cell apoptosis rate, and 1000 mg/kg TP supplementation overcame (P < 0.01) this reduction effect induced by vanadium. The results indicated that supplementation of 10 mg/kg vanadium increased duodenal cell apoptosis and reduced cecum butyrate acid content. Addition of 1000 mg/kg TP increased the SCFA production to affect cecum flora ecology and protected the duodenal cell from excess apoptosis caused by vanadium.

Comparison of distribution and toxicity following repeated oral dosing of different vanadium oxide nanoparticles in mice

Vanadium is an important ultra-trace element derived from fuel product combustion. With the development of nanotechnology, vanadium oxide nanoparticles (VO NPs) have been considered for application in various fields, thus the possibility of release into the environment and human exposure is also increasing. Considering that verification of bioaccumulation and relevant biological responses are essential for safe application of products, in this study, we aimed to identify the physicochemical properties that determine their health effects by comparing the biological effects and tissue distribution of different types of VO NPs in mice. For this, we prepared five types of VO NPs, commercial (C)-VO2 and -V2O5 NPs and synthetic (S)-VO2, -V2O3, and -V2O5 NPs. While the hydrodynamic diameter of the two types of C-VO NPs was irregular and impossible to measure, those of the three types of S-VO NPs was in the range of 125-170nm. The S- and C-V2O5 NPs showed higher dissolution rates compared to other VO NPs. We orally dosed the five types of VO NPs (70 and 210μg/mouse, approximately 2 and 6mg/kg) to mice for 28 days and compared their biodistribution and toxic effects. We found that S-V2O5 and S-V2O3 NPs more accumulated in tissues compared to other three types of VO NPs, and the accumulated level was in order of heart>liver>kidney>spleen. Additionally, tissue levels of redox reaction-related elements and electrolytes (Na(+), K(+), and Ca(2+)) were most clearly altered in the heart of treated mice. Notably, all S- and C-VO NPs decreased the number of WBCs at the higher dose, while total protein and albumin levels were reduced at the higher dose of S-V2O5 and S-V2O3 NPs. Taken together, we conclude that the biodistribution and toxic effects of VO NPs depend on their dissolution rates and size (surface area). Additionally, we suggest that further studies are needed to clarify effects of VO NPs on functions of the heart and the immune system.

Vanadium compounds for the treatment of human diabetes mellitus: A scientific curiosity? A review of thirty years of research

In the second part of the 1980s, and in the 1990s, a number of investigators demonstrated -mainly in streptozotocin-induced (STZ) diabetic rats-that the vanadate and vanadyl forms of vanadium possessed a number of insulin-like effects in various cells. It was hypothesized that oral vanadium could be an alternative treatment to parenteral insulin in the therapy of diabetes mellitus. However, the long-term and/or chronic administration of vanadium compounds should also mean tissue vanadium accumulation and risks of toxicity. The purpose of this review was to revise the current-state-of-the-art on the use of vanadium in the treatment of human diabetes. It has been conducted more than three decades after the first report on the beneficial insulin-mimetic effects of oral vanadium administration in STZ-diabetic rats. Although the antidiabetic effects of vanadium in STZ-diabetic rodents are well supported, in the few studies on human patients with positive results, that are available in the literature, vanadium compounds were administered during very short periods. We conclude that vanadium administration for the treatment of human diabetes is misplaced.

Effect of tea polyphenols on production performance, egg quality, and hepatic antioxidant status of laying hens in vanadium-containing diets

This study was conducted to determine the effect of tea polyphenols (TP) on production performance, egg quality, and hepatic-antioxidant status of laying hens in vanadium-containing diets. A total of 300 Lohman laying hens (67 wk old) were used in a 1 plus 3 × 3 experiment design in which hens were given either a diet without vanadium and TP supplementation (control) or diets supplemented with 5, 10, or 15 mg V/kg and TP (0, 600, 1,000 mg/kg) diets for 8 wk, which included 2 phases: a 5-wk accumulation phase and a 3-wk depletion phase. During the accumulation phase, dietary vanadium addition decreased (linear, P < 0.01) albumen height and Haugh unit (HU), and TP supplementation mitigated (linear effect, P < 0.01) this reduction effect induced by vanadium. Eggshell thickness (linear, P < 0.01), redness (linear and quadratic, P < 0.05), and yellowness (linear and quadratic, P < 0.05) were decreased by vanadium and increased by the effect of TP when a vanadium-containing diet was fed. In the depletion phase, the bleaching effect on eggshells induced by vanadium disappeared one wk after vanadium withdrawal. Eggshell thickness, eggshell strength, albumen height, and HU were lower (P < 0.05) in the 15 mg/kg vanadium group compared with the control diet until 2 wk post vanadium challenge, but hens fed 15 mg/kg vanadium and 600 mg/kg TP showed no difference from the control diet only after 1 wk withdrawal. In the liver, the activity of glutathione S-transferases and glutathione peroxidase was increased (linear, P < 0.01) with the TP addition at 5 wk in the accumulation phase in the vanadium-containing diet; the malondialdehyde content increased (linear effect, P = 0.02) with the addition of vanadium. The results indicate that supplementation of 10 and 15 mg/kg vanadium resulted in reduced albumen quality, bleaching effect on eggshell color, and antioxidant stress in the liver. The effect of TP addition can prevent laying hens from the adverse effect of vanadium on egg quality, liver antioxidant stress and shorten the recovery time.

Structure, physicochemical and biological properties of new complex salt of aqua-(nitrilotriacetato-N,O,O',O")-oxidovanadium(IV) anion with 1,10-phenanthrolinium cation

The crystal structure of new 1,10-phenathrolin-1-ium aqua-(nitrilotriacetato-N,O,O',O")-oxidovanadium(IV) semihydrate of molecular formula (phenH)[VO(NTA)(H2O)]∙1/2H2O was determined. This is the first example of structurally characterized compound that comprises a distinctly separated, monomeric [VO(NTA)(H2O)](-) coordination entity. The crystallographic measurements have subsequently been complemented by the IR spectroscopic characterization and thermal analysis. Furthermore, the electrochemical (cyclic voltammetry) as well as spectrophotometric (UV-vis) studies revealed that the compound is capable of scavenging the superoxide free radicals (O2(-)) as well as stable organic radicals i.e. 2,2'-azinobis(3-ethylbenzothiazoline-6 sulfonic acid) cation radical (ABTS(+)) and 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), but its reactivity towards radicals is lower than that of VOSO4. Finally, biological properties of the complex in the range of 1-100 μM were investigated in relation to its cytoprotective activity against the oxidative damage generated exogenously by using hydrogen peroxide in the hippocampal neuronal HT22 cell line (the MTT and LDH tests). It has been established that in contrast to VOSO4 the title compound protects the HT22 from the oxidative damage. The paper presents a new perspective for oxidovanadium(IV) complexes as candidates for novel, low-molecular mass cytoprotective agents.

Ameliorative effect of vanadium on oxidative stress in stomach tissue of diabetic rats

Between their broad spectrum of action, vanadium compounds are shown to have insulin mimetic/enhancing effects. Increasing evidence in experimental and clinical studies suggests that oxidative stress plays a major role in the pathogenesis of diabetes and on the onset of diabetic complications. Thus, preventive therapy can alleviate the possible side effects of the disease. The aim of the present study was to investigate the effect of vanadyl sulfate supplementation on the antioxidant system in the stomach tissue of diabetic rats. Male Swiss albino rats were randomly divided into 4 groups: control; control+vanadyl sulfate; diabetic; diabetic+vanadyl sulfate. Diabetes was induced by intraperitoneal injection of streptozotocin (STZ; 65 mg/kg body weight). Vanadyl sulfate (100 mg/kg body weight) was given daily by gavage for 60 days. At the last day of the experiment, stomach tissues were taken and homogenized to make a 10% (w/v) homogenate. Catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR), glutathione peroxidase (GPx), glutathione-S-transferase (GST), myeloperoxidase (MPO), carbonic anhydrase (CA), glucose-6-phosphate dehydrogenase (G6PD) and lactate dehydrogenase (LDH) activities were determined in the stomach tissue. CAT, SOD, GR, GPx, GST, CA, G6PD and LDH activities were increased in diabetic rats when compared to normal rats. Vanadium treatment significantly reduced the elevated activities of GR, GPx, GST compared with the diabetic group whereas the decreases in CAT, SOD, CA, G6PD and LDH activities were insignificant. No significant change was seen for MPO activity between the groups. It was concluded that vanadium could be used for its ameliorative effect against oxidative stress in diabetes.

Preclinical and Clinical Studies for Sodium Tungstate: Application in Humans

Diabetes is a complex metabolic disorder triggered by the deficient secretion of insulin by the pancreatic β-cell or the resistance of peripheral tissues to the action of the hormone. Chronic hyperglycemia is the major consequence of this failure, and also the main cause of diabetic problems. Indeed, several clinical trials have agreed in that tight glycemic control is the best way to stop progression of the disease. Many anti-diabetic drugs for treatment of type 2 diabetes are commercially available, but no ideal normoglycemic agent has been developed yet. Moreover, weight gain is the most common side effect of many oral anti-diabetic agents and insulin, and increased weight has been shown to worsen glycemic control and increase the risk of diabetes progression. In this sense, the inorganic salt sodium tungstate (NaW) has been studied in different animal models of metabolic syndrome and diabetes, proving to have a potent effect on normalizing blood glucose levels and reducing body weight, without any hypoglycemic action. Although the liver has been studied as the main site of NaW action, positive effects have been also addressed in muscle, pancreas, brain, adipose tissue and intestine, explaining the effective anti-diabetic action of this salt. Here, we review NaW research to date in these different target organs. We believe that NaW deserves more attention, since all available anti-diabetic treatments remain suboptimal and new therapeutics are urgently needed.

Exposure to bis(maltolato)oxovanadium(IV) increases levels of hepcidin mRNA and impairs the homeostasis of iron but not that of manganese

The aim of this study was to examine whether alterations in iron homeostasis, caused by exposure to vanadium, are related to changes in the gene expression of hepatic hepcidin. Two groups of rats were examined: control and vanadium-exposed. Vanadium, as bis(maltolato)oxovanadium(IV) was supplied in the drinking water. The experiment had a duration of five weeks. Iron and manganese were measured in excreta, serum and tissues. Leptin, ferritin, IL-1β, IL-6, TNF-α, red blood cells, haemoglobin and haematocrit were determined. Protein carbonyl group levels and hepcidin gene expression were determined in the liver. In the vanadium-exposed rats, iron absorption, serum iron and leptin and all haematological parameters decreased. Levels of IL-6, TNF-α and ferritin in serum and of iron in the liver, spleen and heart increased. In the liver, levels of protein carbonyl groups and hepcidin mRNA were also higher in the vanadium-exposed group. Exposure to vanadium did not modify manganese homeostasis. The results obtained from this study provide the first evidence that bis(maltolato)oxovanadium(IV) produces an increase in the gene expression of the hepcidin, possibly caused by an inflammatory process. Both factors could be the cause of alterations in Fe homeostasis and the appearance of anaemia. However, Mn homeostasis was not affected.

A tea/vanadate decoction delivered orally over 14 months to diabetic rats induces long-term glycemic stability without organ toxicity

Vanadium can induce potent hypoglycemic effects in type 1 and type 2 diabetes mellitus animals, but toxic adverse effects have inhibited the translation of these findings. Administration of vanadate in a black tea decoction has shown impressive hypoglycemic effects without evidence of toxicity in short-term studies. The purpose of this study was to investigate the hypoglycemic action and the toxic adverse effects of a tea/vanadate (T/V) decoction in diabetic rats over a 14-month treatment period. Streptozotocin-induced type 1 diabetes mellitus rats were orally gavaged with 40 mg sodium vanadate in a black tea decoction only when blood glucose levels were greater than 10 mmol/L. Glycemic status and liver and kidney function were monitored over 14 months. All of the diabetic rats in this treatment group (n = 25) required treatment with the T/V decoction at the start of the study to reduce blood glucose levels to less than 10 mmol/L. Diarrhea was uncommon among the T/V-treated animals during the first week of T/V treatment and was absent thereafter. There was no evidence of liver or kidney dysfunction or injury. From 2 to 6 months, fewer animals required the T/V treatment to maintain their blood glucose levels. After 9 months of treatment, none of the diabetic animals required any T/V to maintain their blood glucose levels at less than 10 mmol/L. Oral administration of a T/V decoction provides safe, long-acting hypoglycemic effects in type 1 diabetes mellitus rats. The typical glycemic signs of diabetes were absent for the last 5 months of the study.

Effects of combined vanadate and magnesium treatment on erythrocyte antioxidant defence system in rats

The effect of vanadate and magnesium treatment on erythrocyte defence system was studied in outbred 2-month-old, albino male Wistar rats (14 rats/each group) which daily received: Group I (Control)-deionized water to drink; Group II-water solution of sodium metavanadate (NaVO(3); SMV) at a concentration of 0.125mgV/mL; Group III-water solution of magnesium sulfate (MgSO(4); MS) at a concentration of 0.06mgMg/mL, Group IV-water solution of SMV-MS at the same concentrations over a 12-week time. The fluid intake and the concentration of reduced glutathione (GSH) as well as the activity of Cu, Zn-superoxide dismutase (Cu, Zn-SOD), catalase (CAT) and glutathione reductase (GR) were significantly decreased in the rats receiving SMV alone (Group II) or in combination with MS (Group IV) compared with Groups I and III. The cellular glutathione peroxidase (cGSH-Px) activity was unchanged in all the treated groups. The activity of glutathione S-transferase (GST) fell in the animals in Group II, compared with the rats in Groups I, III and IV; whereas in the rats in Group III its activity was higher than in the control animals. These results showed that V (as SMV) consumed by the rats with drinking water at a dose of 12mgV/kg b.w./24h for 12 weeks may attenuate defence system in rats' erythrocytes (RBCs), which is probably a consequence of vanadium pro-oxidant potential. Therefore, reactive oxygen species (ROS) are suggested to be involved in the alterations in antioxidant defence system in these cells. Mg (as MS) at the dose ingested (6mgMg/kg b.w./24h) at co-exposure to SMV was not able to counteract its deleterious effect. The results also provide evidence that V-Mg interactions may be involved in the decrease of erythrocyte GR activity and Mg concentration in the plasma under concomitant treatment with both metals at the doses of 12.6mgV and 6mgMg/kg b.w./24h.

Lipid peroxidation in the liver of rats treated with V and/or Mg in drinking water

The effect of V(5+) and Mg treatment on spontaneous and stimulated lipid peroxidation (LPO) was studied in liver supernatants obtained from outbred 5-month-old, albino male Wistar rats. The 2-month-old animals daily received deionized water to drink (control, group I); group II - water solution of NaVO(3) (SMV) at a concentration of 0.125 mg V ml(-1); group III - water solution of MgSO(4) (MS) at a concentration of 0.06 mg Mg ml(-1), group IV - water solution of SMV-MS at the same concentrations as in groups II and III for V and Mg, respectively, over a 12-week period. Three metal salts were selected as agents that may modify the LPO process (FeSO(4), NaVO(3) and MgSO(4)). V-intoxicated rats and those treated with V and Mg in combination had higher liver spontaneous malondialdehyde (MDA) formation, compared with the control and Mg-supplemented animals. In the same groups of animals the total antioxidant status (TAS) was also significantly lowered, in comparison with the control. In the supernatants obtained from the above-mentioned groups of rats a significant increase in MDA concentration was found in the presence of exogenous 30 microm FeSO(4) as well as 30, 100, 200 and 400 microm NaVO(3), compared with groups I and III. Significantly elevated MDA production was also observed in the supernatants obtained from the rats exposed to V and Mg in combination in the presence of exogenous 100 and 200 microm MgSO(4) in comparison with the control and group III as well as in the presence of exogenous 400 and 600 microm MgSO(4) compared only with group III. In vitro treatment with 1000 microm MgSO(4 )of control liver supernatants and those obtained from group III significantly enhanced MDA level, compared with spontaneous MDA formation. The two-way ANOVA indicated that the changes in the basal MDA level and in TAS in the rats at combined V and Mg application, were not due to V-Mg interaction, but resulted from independent action of V. In addition, the three-way ANOVA revealed that the changes in LPO induced by in vitro treatment of liver supernatants with exogenous Fe or V or Mg (600, 800 and 1000 microm) were a consequence of independent action of those metals and they also resulted from the interactions between Fe(exog) and V(end) and between V(end) and V(exog). In conclusion, V consumed by the rats with drinking water at a dose of 12 mg V kg(-1) body weight per 24 h for 12 weeks decreased TAS and enhanced spontaneous LPO in the hepatic tissue, which confirms its pro-oxidant potential, was also found in in vitro conditions with regard to LPO. Mg administered to rats in combination with V, at the concentration used, neither reduced nor intensified the basal LPO, compared with V-only treated animals; however, its stimulating effect on LPO was revealed in in vitro conditions, which requires further study.

Selected haematological and biochemical parameters of blood in rats after subchronic administration of vanadium and/or magnesium in drinking water

The purpose of these studies was to evaluate the effect of selected vanadium and magnesium doses on certain haematological and biochemical blood parameters in rats. Outbred 2-month-old, albino male Wistar rats received for a period of 6 weeks, as a sole drinking liquid, the following water solutions: group II, sodium metavanadate (SMV) at a concentration of 0.125 mg V/mL; group III, magnesium sulphate (MS) at a concentration of 0.06 mg Mg/mL; and group IV, SMV-MS solution at the same concentrations. The control group received at this time deionized water to drink. It was calculated that group II ingested with drinking water about 10.7 mg V/kg b. w./24 h, group III 6 mg Mg/kg b. w./24 h, and group IV about 9 mg V and 4.5 mg Mg/kg b. w./24 h. The exposure to vanadium alone (group II) led to a statistically significant decrease in body weight gain, food and fluid intakes. Moreover, in the same group of rats a statistically significant decrease in the RBC count, Hb concentration, MCV, and MCH values was demonstrated. Additionally, a statistically significant decrease in the plasma L-ascorbic acid concentration and a significant increase in MDA concentration in blood in this group were found. Instead, after the administration of magnesium alone (group III), a statistically significant decrease in the fluid intake and in the L-ascorbic acid concentration in plasma was noted. Furthermore, in the same group of rats a statistically significant increase in Hb level and in the plasma magnesium concentration was demonstrated. Two-way analysis of variance (ANOVA) did not reveal the interactions between V and Mg.

Reduction of oxidative stress induced vanadium toxicity by complexing with a flavonoid, quercetin: A pragmatic therapeutic approach for diabetes

Vanadium compounds are known to lower blood glucose level in diabetes but are associated with toxicity. In vitro cytotoxicity of VOSO(4) and bis(quercetinato) oxovanadium(IV) (BQOV) was examined in CHO cells. Both the agents showed time and dose dependent increase in ROS generation however it was relatively less in BQOV. Moreover, VOSO(4) also caused higher necrosis. Hypoglycemic potential of VOSO(4) and BQOV was tested in streptozotocin-induced diabetic Balb/c mice. A marked difference was observed in the hypoglycemic action of VOSO(4) and BQOV treated mice that lasted only for about 6 h in VOSO(4) as against 24 h in BQOV. Comparison of acute toxicity of the compounds in normal Balb/c mice revealed negligible nephrotoxicity of BQOV. Kidney analyses of VOSO(4) treated animals' revealed high ROS generation and tubular necrosis. Similarly serum levels of urea and creatinine were elevated in these animals indicating kidney dysfunction. No such abnormality was observed in BQOV treated animals. Reduced nephrotoxicity of BQOV could be due to increased catalase activity found in the kidney of BQOV treated animals and BQOV's radical scavenging activity. The data clearly demonstrates immense hypoglycemic activity and reduced toxicity of BQOV thus making the conjugate a suitable candidate for therapeutic utility.

Short-term bioaccumulation of vanadium when ingested with a tea decoction in streptozotocin-induced diabetic rats

Sodium orthovanadate suspended in a lichee black tea decoction effectively regulates blood glucose levels in rats with insulin-dependent, streptozotocin (STZ)-induced diabetes. The primary advantage of vanadate delivery with the tea decoction over conventional systems that use water suspensions of vanadate is a significant reduction in the toxic side effects of vanadate. It is unknown if the tea alters the bioavailability of vanadate. Male Sprague-Dawley rats were administered an intravenous injection of STZ to induce diabetes. Four days later, the diabetic rats were treated by oral gavage with 40 mg of Na-orthovanadate suspended in double-distilled, deionized water (V/H2O), tea/vanadate (TV) decoction, or were treated with the tea decoction alone. Vanadium concentrations were measured in blood and various tissues at 1 to 24 hours posttreatment using graphite furnace atomic absorption spectrophotometry. With the exception of bone, maximal vanadium concentration in plasma and tissue samples were observed 2 hours after ingestion, but steadily decreased after that. Plasma vanadium levels continued to decrease until 16 hours. In contrast, vanadium steadily accumulated in bone over the 24-hour period. Overall, rats treated with V/H2O contained similar or significantly higher concentrations of vanadium in all tissues compared with TV treatment. The pattern of vanadium accumulation was also similar over time in both treatment groups. Vanadium levels were highest in bone > kidney > liver > pancreas > lung > heart > muscle > brain in both TV- and V/H2O-treated animals. This study demonstrates that the accumulation of vanadium in diabetic rats is reduced when coadministered with a black tea decoction in comparison to administration of vanadium in water. However, this effect is unlikely to be of a magnitude to explain the full capacity of TV to reduce the toxic side effects of vanadate.

Comparative study on the preventing effects of oral vanadyl sulfate and dietary restriction on the age-related glucose intolerance in rats

BACKGROUND AND AIMS

Aging is associated with a progressive impairment of glucose tolerance. The aim of this study was to explore the protective effects of the chronic oral administration of the insulino-mimetic agent vanadyl sulfate (VOSO4) as compared with those exerted by a long-lasting dietary restriction.

METHODS

Male Sprague-Dawley rats, either fed ad libitum (AL) or subjected to 40% dietary restriction (DR), were used. VOSO4 (0.5 mg/mL drinking water) was administered to a subgroup of AL rats for two months, starting at 16 months of age. Rats were subjected to an intravenous glucose tolerance test (IVGTT) at 16 and 18 months of age. Finally, the beta-cell responsiveness to glucose was evaluated in vitro by the isolated perfused pancreas preparation.

RESULTS

The IVGTT performed in 16-month-old rats showed that DR prevented the development of the moderate glucose intolerance observed in AL rats. The IVGTT performed at 18 months of age confirmed the beneficial effect of DR and showed that VOSO4 was able to prevent the further age-related progression of glucose intolerance observed in AL rats. Pancreas perfusion studies showed that no increase in insulin secretion occurred in both VOSO4-treated and DR rats with respect to the age-matched AL controls, consistently with the in vivo observation of post-loading insulinaemic changes.

CONCLUSIONS

On the basis of these results, we conclude that the beneficial effect of both treatments is mostly related to an improvement of tissue sensitivity to insulin rather than to an insulinotropic effect.

Tungstate stimulates insulin release and inhibits somatostatin output in the perfused rat pancreas

In the rat pancreas, infusion of sodium-tungstate stimulates basal insulin release in a dose-dependent manner. We have studied tungstate's effects on the insulin secretion elicited by various B-cell secretagogues. Somatostatin output was also measured. The study was performed in the perfused pancreas isolated from normal or somatostatin-depleted pancreases as induced by cysteamine pre-treatment. In control rats, tungstate co-infusion (5 mM) potentiated the insulin secretory responses to glucose (2.7-fold; P<0.01), arginine (2-fold; P<0.01), exendin-4 (3-fold; P<0.01), glucagon (4-fold; P<0.05), and tolbutamide (2-fold; P<0.01). It also inhibited the somatostatin secretory responses to glucose (90%; P<0.01), arginine (95%; P<0.01), glucagon (80%; P<0.025), exendin-4 (80%; P<0.05) and tolbutamide (85%; P<0.01). In somatostatin-depleted pancreases, the stimulatory effect of tungstate on basal insulin secretion and its potentiation of arginine-induced insulin output were comparable to those found in control rats. Our observations suggest an amplifying effect of tungstate on a common step in the insulin stimulus/secretion coupling process, and would rule out a paracrine effect mediated by the inhibition of somatostatin secretion induced by this compound.

Effective control of glycemic status and toxicity in Zucker diabetic fatty rats with an orally administered vanadate compound

A novel black tea decoction containing vanadate has successfully replaced insulin in a rat model of insulin-dependent diabetes but is untested in non-insulin-dependent diabetic animals. A tea-vanadate decoction (TV) containing 30 or 40 mg sodium orthovanadate was administered by oral gavage to two groups of Zucker diabetic fatty rats and a conventional water vehicle containing 30 or 40 mg of sodium orthovanadate to two others. In the latter group receiving the 30-mg dose, vanadate induced diarrhea in 50% of the rats and death in 10%. In contrast, TV-treated rats had no incidence of diarrhea and no deaths. Symptoms were more severe in both groups with higher vanadate doses, so these were discontinued. After approximately 16 weeks, the level of vanadium in plasma and tissue extracts was negligible in a further group of untreated rats but highly elevated after vanadate treatment. Vanadium levels were not significantly different between the TV-treated diabetic rats and the diabetic rats given vanadate in a water vehicle. Over the 115 days of the study, blood glucose levels increased from approximately 17 to 25 mmol/L in untreated diabetic rats. This was effectively lowered (to <10 mmol/L) by TV treatment. Fasting blood glucose levels were 5, 7, and 20 mmol/L in control (nondiabetic, untreated), TV-treated and untreated diabetic rats, respectively. Rats required treatment with TV for only approximately 50% of the days in the study. Increase in body mass during the study was significantly lower in untreated diabetic rats (despite higher food intake) than the other groups. Body mass gain and food intake were normal in TV-treated rats. Water intake was 28 mL/rat daily in control rats, 130 mL/rat daily in untreated diabetic rats, and 52 mL/rat daily in TV-treated diabetic rats. Plasma creatinine and aspartate aminotransferase levels were significantly depressed in untreated diabetic rats, and TV treatment normalized this. Our results demonstrate that a novel oral therapy containing black tea and vanadate possesses a striking capacity to regulate glucose and attenuates complications in a rat model of type II diabetes.

The effects of peroxovanadate and peroxovanadyl on glucose metabolism in vivo and identification of signal transduction proteins involved in the mechanism of action in isolated soleus muscle

The insulin-like effects of peroxovanate (POV) and peroxovanadyl (PSV) on rates of lactate formation and glycogen synthesis were measured in isolated incubated soleus muscle preparations. In another experiment rats were made insulin deficient by streptozotocin injection and treated with POV and PSV (0.25 mM) administered in the drinking water and in the course of 7 days glycemia were determined. Also, signal transduction proteins ERK 1 and ERK 2 involved in the insulin signaling were measured in soleus muscle of diabetic rats treated with POV and PSV. Peroxides of vanadate and vanadyl significantly stimulated glucose utilization in soleus muscle preparations in vitro. The stimulation of glycogen synthesis and lactate formation by POV and PSV was similar to insulin stimuli. Rats treated with POV or PSV presented reduction of glycemia, food and fluid intake with amelioration of the diabetic state during the short period of treatment (7 days). POV and PSV modulated ERK1/2 phosphorilation and the insulin administration in these rats caused an addictive effect on phosphorilation state of these proteins.

Codelivery of a tea extract prevents morbidity and mortality associated with oral vanadate therapy in streptozotocin-induced diabetic rats

Oral administration of vanadate has a strong hypoglycemic effect but results in toxic side effects like life-threatening diarrhea. Tea is known to have potent antidiarrhea effects. We investigated the potential of suspending the vanadate in a tea decoction to reduce the diarrheatic action of vanadate. A concentrated extract of Lichee black tea was, therefore, added to sodium orthovanadate. Streptozotocin (STZ)-induced diabetic rats were orally gavaged with vanadate suspended in water or in the tea decoction, or with the tea extract alone. Blood glucose levels were assessed daily over 11 weeks with levels greater than 10 mmol/L warranting therapeutic intervention. Both the vanadate/water and vanadate/tea solutions acutely reduced blood glucose. The tea extract alone had no effect. The majority of vanadate/water-treated rats developed diarrhea and mortality rates approached 40%. Vanadate/tea-treated diabetic rats experienced no diarrhea or mortality and liver and kidney analyses (plasma ALT and creatinine, blood urea nitrogen [BUN], and urine-specific gravity) were normal. Animals treated with vanadate/tea retained blood glucose levels less than 10 mmol/L for an average of 24 consecutive days without subsequent treatments. Cataract formation was completely prevented. The mechanism of action of vanadate may have involved beta-cell stimulation because vanadate/tea-treated diabetic rats exhibited normal plasma insulin levels. In summary, because of its long-lasting effects, oral administration, and lack of side effects, vanadate/tea represents a potentially important alternative therapy for an insulin-deficient diabetic state.

Effect of chromium picolinate on histopathological alterations in STZ and neonatal STZ diabetic rats

Earlier studies from our laboratory have indicated insulin sensitizing action of chromium picolinate as the mechanism of its anti-diabetic activity in experimental models of type I and type II diabetes. In the present investigation, we have evaluated the effects of chronic administration of chromium picolinate on the functional and histological alterations of streptozotocin (STZ)-induced diabetes in rats. Type I diabetes was induced by intravenous injection of STZ (40 mg/kg) in adult rats, whereas, type II diabetes was induced by intraperitoneal injection of STZ (90 mg/kg) in 2-day old rat pups which in adulthood develop abnormalities resembling type II diabetes. Chromium picolinate was administered at 8 microg/ml in drinking water for 6 weeks and was found to improve glucose tolerance and increase insulin sensitivity of STZ-diabetic rats. This treatment decrease elevated serum creatinine and urea levels as well as elevated serum levels of hepatic enzymes of both groups of diabetic rats. Histopathological studies of kidney and liver show decrease in the intensity and incidence of vacuolations, cellular infiltration and hypertrophy of STZ and nSTZ (neonatal STZ) diabetic rats. Chronic treatment with chromium picolinate however, did not alter the normal function or morphology of control rats. Chronic chromium picolinate at the therapeutic doses that improved glucose tolerance, was observed to have no hepatotoxic or nephrotoxic potential. It was rather found to improve renal and hepatic function and to reduce abnormalities associated with STZ-diabetes. Chromium picolinate could play an important role in the long term management of diabetes mellitus.

Behavioral and developmental outcomes of prenatal and postnatal vanadium exposure in the rat

The developmental and behavioral outcomes of uninterrupted exposure to vanadium was studied in the rat. Starting 3 days before birth and up to the 100th day of extrauterine life, rats received as drink either a water solution of vanadyl sulphate (300 mg l(-1)containing 70 mg l(-1)of vanadium element, which is equal to an ingested dose of about 10 mg kg(-1)per day of vanadium element) plus NaCl 5 g l(-1), or a water solution of NaCl 5 g l(-1), or plain water [up to weaning (25th day of extrauterine life) treatment was given to dams and offspring]. At weaning, survivors were fewer and body weight was found to be significantly lower in the offspring of vanadium plus NaCl-treated dams than in the offspring of the other two groups. After weaning, growth retardation continued to be significant in both vanadium plus NaCl- and NaCl-treated rats. Such an effect was more pronounced in males than in females. Locomotor activity--evaluated at 1 month of age--was not significantly different in the three groups of rats. In the open-field, male (but not female) vanadium plus NaCl-treated rats had a reduced outer ambulation, rearing posture and grooming activity, and an increased defecation, in comparison with the males of the NaCl group, and reduced rearing in comparison with control males. As concerns ingestive behaviors, the only significant datum was an increased water intake in NaCl-treated males. Finally, at the 100th day of life, working memory was significantly impaired in both vanadium plus NaCl- and NaCl-treated rats.

Anti-diabetic and toxic effects of vanadium compounds

Compounds of the trace element vanadium have been shown to mimic insulin in in vitro and in vivo systems. These compounds have been found to exert anti-diabetic effects in rodent models of type 1 and type 2 diabetes mellitus as well as in a limited number of studies in human diabetic subjects. Thus, vanadium compounds have emerged as agents for potential use in diabetes therapy. However, treatment of diabetic animals with inorganic vanadium salts has also been associated with some toxic side-effects such as gastrointestinal discomfort and decreased body weight gain. In addition, vanadium salts have been reported to exert toxic effects on the liver and kidney. More recently, it was shown that organic vanadium compounds were much safer than inorganic vanadium salts and did not cause any gastrointestinal discomfort, hepatic or renal toxicity. This review briefly summarizes the anti-diabetic and toxic effects of vanadium compounds.

Normalization of hyperglycaemia by oral vanadyl sulfate does not reverse diabetes-induced protection against cisplatin nephrotoxicity in streptozotocin-diabetic rats

Streptozotocin- and galactose-induced diabetic rats are protected against nephrotoxic effects of cisplatin. While the mechanism remains to be defined, protection is associated with a decrease in the accumulation of platinum in renal cortical tissues of streptozotocin-diabetic versus non-diabetic rats. A physiological abnormality common to streptozotocin and galactosemic models of diabetes is hyperglycaemia, suggesting that elevated sugars are involved in mediating protection of diabetic kidney against cisplatin nephrotoxicity. The current study focused on the effect of normalization of hyperglycaemia by vanadyl sulfate trihydrate on the initiation of protection and accumulation of platinum in kidneys of streptozotocin-diabetic rats. Streptozotocin-diabetic rats were treated with 0.75 mg/ml of vanadyl sulfate trihydrate in drinking water to normalize streptozotocin-induced hyperglycaemia. Vanadyl sulfate treatment normalized plasma glucose and glycosylated haemoglobin levels in streptozotocin-diabetic rats to values observed for non-diabetic rats. Intraperitoneal administration of cisplatin (5 mg/kg body weight) increased blood urea nitrogen by a factor >2.5 over baseline in both untreated and vanadyl-treated non-diabetic groups. Cisplatin-induced increases in blood urea nitrogen were 1.6 times baseline in both untreated and vanadyl-treated streptozotocin-diabetic rats. Renal platinum accumulation was significantly lower in streptozotocin-diabetic versus non-diabetic rats regardless of vanadyl sulfate treatment. Renal vanadium levels in all groups of diabetic rats were not significantly different from each other. These results indicate that normalization of plasma glucose levels with vanadyl sulfate in streptozotocin-diabetic rats did not reverse protection of streptozotocin-diabetic kidney against cisplatin nephrotoxicity.

Prevention by sodium 4,5-dihydroxybenzene-1,3-disulfonate (Tiron) of vanadium-induced behavioral toxicity in rats

Recent studies have shown that oral vanadate (V5+) administration results in behavioral toxicity in rats. The chelating agent Tiron (sodium 4,5-dihydroxybenzene-1,3-disulfonate) is an effective antidote in the removal of vanadium from vanadium-loaded rats. In this study, the protective activity of Tiron on vanadate-induced behavioral toxicity was evaluated in adult rats. Intraperitoneal treatment with Tiron at 235 or 470 mg/kg was initiated after 6 wk of oral sodium metavanadate administration (16 mg/kg/d) and continued for 2 wk. Although vanadate exposure did not result in a significant reduction in the general activity of the animals in an open field, a lower active avoidance acquisition could be observed. However, the vanadate-induced behavioral deficit was reverted by Tiron administration at 470 mg/kg. The present results suggest that Tiron may protect, at least in part, against metavanadate-induced behavioral toxicity.

Vanadium

Vanadium is a steel-grey, corrosion-resistant metal, which exists in oxidation states ranging from -1 to +5. Metallic vanadium does not occur in nature, and the most common valence states are +3, +4, and +5. The pentavalent form (VO3-) predominates in extracellular body fluids whereas the quadrivalent form (VO+2) is the most common intracellular form. Because of its hardness and its ability to form alloys, vanadium (i.e., ferrovanadium) is a common component of hard steel alloys used in machines and tools. Although most foods contain low concentrations of vanadium (< 1 ng/g), food is the major source of exposure to vanadium for the general population. High air concentrations of vanadium occur in the occupation setting during boiler-cleaning operations as a result of the presence of vanadium oxides in the dust. The lungs absorb soluble vanadium compounds (V2O5) well, but the absorption of vanadium salts from the gastrointestinal tract is poor. The excretion of vanadium by the kidneys is rapid with a biological half-life of 20-40 hours in the urine. Vanadium is probably an essential trace element, but a vanadium-deficiency disease has not been identified in humans. The estimated daily intake of the US population ranges from 10-60 micrograms V. Vanadyl sulfate is a common supplement used to enhance weight training in athletes at doses up to 60 mg/d. In vitro and animal studies indicate that vanadate and other vanadium compounds increase glucose transport activity and improve glucose metabolism. In general, the toxicity of vanadium compounds is low. Pentavalent compounds are the most toxic and the toxicity of vanadium compounds usually increases as the valence increases. Most of the toxic effects of vanadium compounds result from local irritation of the eyes and upper respiratory tract rather than systemic toxicity. The only clearly documented effect of exposure to vanadium dust is upper respiratory tract irritation characterized by rhinitis, wheezing, nasal hemorrhage, conjunctivitis, cough, sore throat, and chest pain. Case studies have described the onset of asthma after heavy exposure to vanadium compounds, but clinical studies to date have not detected an increased prevalence of asthma in workers exposed to vanadium.

Vanadium: a review of its potential role in the fight against diabetes

The potential role of vanadium in human health is described as a building material of bones and teeth. However, another very interesting and promising application for vanadium in human health emerges from recent studies that evaluated the role of vanadium in the management of diabetes. Vanadium is present in a variety of foods that we commonly eat. Skim milk, lobster, vegetable oils, many vegetables, grains and cereals are rich source of vanadium (>1 ppm). Fruits, meats, fish, butter, cheese, and beverages are relatively poor sources of vanadium. The daily dietary intake in humans has been estimated to vary from 10 microg to 2 mg of elemental vanadium, depending on the environmental sources of this mineral in the air, water, and food of the particular region tested. In animals, vanadium has been shown essential (1-10 microg vanadium per gram of diet). There is only circumstantial evidence that vanadium is essential for humans. However, in doses ranging from 0.083 mmol/d to 0.42 mmol/d, vanadium has shown therapeutic potential in clinical studies with patients of both insulin-dependent diabetes mellitus (IDDM) and noninsulin-dependent diabetes mellitus (NIDDM) type. Although vanadium has a significant biological potential, it has a poor therapeutic index, and attempts have been made to reduce the dose of vanadium required for therapeutic effectiveness. Organic forms of vanadium, as opposed to the inorganic sulfate salt of vanadium, are recognized as safer, more absorbable, and able to deliver a therapeutic effect up to 50% greater than the inorganic forms. The goal is to provide vanadium with better gastrointestinal absorption, and in a form that is best able to produce the desired biological effects. As a result, numerous organic complexes of vanadium have been developed including bis(maltolato)oxovanadium (BMOV), bis(cysteinamide N-octyl)oxovanadium known as Naglivan, bis(pyrrolidine-N-carbodithioato)oxovanadium, vanadyl-cysteine methyl ester, and bis-glycinato oxovanadium (BGOV). The health benefits of vanadium and the safety and efficacy of the available vanadium supplements are discussed in this review.

Complementary measures for promoting insulin sensitivity in skeletal muscle

Insulin resistance of skeletal muscle is fundamental to both syndrome X and its frequent sequel, type II diabetes. In these disorders, excessive exposure of muscle to free fatty acids (FFAs) and their metabolic derivatives appears to play a prominent role in the induction of insulin resistance. Recent evidence suggests that activation of novel isoforms of protein kinase C (PKC) by diacylglycerol may mediate at least part of the adverse impact of FFAs on muscle insulin sensitivity. Vitamin E and fish oil omega-3s, by promoting the activity of diacylglycerol kinase and inhibiting that of phosphatidate phosphohydrolase, should reduce diacylglycerol levels, thus accounting for their documented favorable impact on insulin sensitivity. Thiazolidinediones such as troglitazone, on the other hand, appear to intervene in the signaling pathway whereby PKC down-regulates insulin function. The insulin-sensitizing activity of chromium picolinate may be attributable, at least in part, to increased expression of insulin receptors. In combination with lifestyle modifications which reduce FFA exposure--weight loss, very-low-fat eating, excessive training--these measures can be expected to work in a complementary way to promote increased numbers of insulin receptors that are more functionally competent. As these measures appear to be safe and well-tolerated, they may have utility for the prevention of diabetes as well as its therapy. When they do not prove sufficient to achieve optimal glycemic control, excessive hepatic glucose output and impaired cell response to glucose can be addressed with metformin and sulfonylureas, respectively. The prospects for a rational medical management of type II diabetes, obviating the need for injectible insulin, have never been brighter.

Inhibitory effect of vanadium compounds on glutamate dehydrogenase activity in mitochondria and hepatocytes isolated from rabbit liver

The effect of orthovanadate, vanadyl sulphate and vanadyl acetylacetonate on glutamate dehydrogenase activity was studied in liver mitochondria and isolated hepatocytes of rabbit. In permeabilized mitochondria with free access of substrates and drugs to glutamate dehydrogenase, orthovanadate and vanadyl sulphate at 200 microM concentrations decreased both glutamate synthesis and glutamate deamination by 80 and 50%, respectively, while vanadyl acetylacetonate was less potent. In view of kinetic data obtained at various ammonium concentrations, orthovanadate appeared to be a competitive inhibitor (Ki = 40 +/- 3 microM), while vanadyl sulphate was a non-competitive one (Ki = 147 +/- 10 microM). In contrast to orthovanadate, vanadyl sulphate augmented the inhibitory action of increased above 0.5 mM 2-oxoglutarate concentrations. All these effects on the enzyme activity were partially reversed in the presence of L-leucine and ADP, which are allosteric activators of glutamate dehydrogenase. Moreover, all compounds studied suppressed both glutamate formation and glutamate deamination in isolated hepatocytes incubated under various metabolic conditions, as concluded from decreased rates of glutamate and urea synthesis, respectively. In view of these observations it seems likely that vanadium-containing compounds may be potent inhibitors of glutamate metabolism in liver.

Effects of vanadium on activity and learning in rats

The effects of vanadate administration on activity and learning were assessed in rats. Four groups of adult male rats were given by gavage 0, 4.1, 8.2, and 16.4 mg/kg/day of sodium metavanadate for eight consecutive weeks. Three weeks after the cessation of the treatment, general motor activity of all animals was measured in an open-field. Rats were also tested for two-way shock avoidance learning in an automatic reflex conditioner. At the end of the testing period, rats were killed and vanadium concentration was determined in a number of tissues. Vanadium exposure caused an observable but not significant effect on body weight gain, while a persistent presence of vanadium was observed in all tissues measured. The results of the behavioral testing show that oral vanadate administration resulted in significant reductions in both general activity and learning.

Glucose-lowering properties of vanadium compounds: comparison of coordination complexes with maltol or kojic acid as ligands

Bis(kojato)oxovanadium(IV) [abbreviated VO(ka)2], a close chemical analog of the insulin-mimetic lead compound bis(maltolato)oxovanadium(IV)--abbreviated BMOV or VO(ma)2--is reported and its reaction chemistry and insulin-mimetic properties are presented. VO(ka)2 [log K1 = 7.61(10), log K2 = 6.89(6), log beta 2 = 14.50(16)] has a reaction chemistry which directly parallels that of VO(ma)2. In aqueous solution it is more slowly oxidized by molecular oxygen to [VO2(ka)2]- than is VO(ma)2 to [VO2(ma)2]-. Variable pH electrochemistry and variable pH 51V NMR of solutions of VO(ka)2 are presented and contrasted with the corresponding results for VO(ma)2. Time course studies (24 hr) in STZ-diabetic rats following the oral or i.p. administration of VO(ka)2, VO(ma)2, VO2+ (vanadyl) as vanadyl sulfate (VOSO4), and [VO2(ma)2]- as its [NH4]+ salt have been performed, as have chronic oral studies comparing VO(ka)2 and VO(ma)2 over a six week period. In all studies, the most potent form of vanadium was the neutrally charged, water soluble, complex VO(ma)2.

Oral vanadyl sulphate does not affect blood cells, viscosity or biochemistry in humans

Vanadyl sulphate (VOSO4) is used to improve performance in weight training athletes. Concerns about its safety have arisen because vanadium compounds may cause anaemia and changes in the leukocyte system. In this study, the effects of oral VOSO4 (0.5 mg/kg/day) on haematological indices (red and white cell and platelet counts, red cell mean cell volume and haemoglobin level), blood viscosity (haematocrit, plasma viscosity and blood viscosity at 10s-1 and 100s-1 shear rates) and biochemistry (lipids and indices of liver and kidney function) were investigated in a twelve week, double blind, placebo controlled trial in 31 weight training athletes. Blood viscosity was evaluated at 0, 2, 4, 8 and 12 weeks and haematological indices and biochemistry were measured before and at the end of treatment. Both the treatment group and placebo group showed increases in haematocrit (3.3-3.6%) and blood viscosity (9-11% at 100s-1 shear; 35-38% at 10s-1 shear) but there were no significant effects of treatment. Similarly there were no treatment effects on haematological indices and biochemistry. Concerns about the adverse effects of oral vanadyl sulphate on blood are not supported by the results of this trial.

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.