Toxicity studies on one-year treatment of non-diabetic and streptozotocin-diabetic rats with vanadyl sulphate

Metabolomics of Type 2 Diabetes Mellitus in Sprague Dawley Rats-In Search of Potential Metabolic Biomarkers

Type 2 diabetes mellitus (T2DM) is an expanding global health concern, closely associated with the epidemic of obesity. Individuals with diabetes are at high risk for microvascular and macrovascular complications, which include retinopathy, neuropathy, and cardiovascular comorbidities. Despite the availability of diagnostic tools for T2DM, approximately 30-60% of people with T2DM in developed countries are never diagnosed or detected. Therefore, there is a strong need for a simpler and more reliable technique for the early detection of T2DM. This study aimed to use a non-targeted metabolomic approach to systematically identify novel biomarkers from the serum samples of T2DM-induced Sprague Dawley (SD) rats using a comprehensive two-dimensional gas chromatography coupled with a time-of-flight mass spectrometry (GCxGC-TOF/MS). Fifty-four male Sprague Dawley rats weighing between 160-180 g were randomly assigned into two experimental groups, namely the type 2 diabetes mellitus group (T2DM) (n = 36) and the non-diabetic control group (n = 18). Results from this study showed that the metabolite signature of the diabetic rats was different from that of the non-diabetic control group. The most significantly upregulated metabolic pathway was aminoacyl-t-RNA biosynthesis. Metabolite changes observed between the diabetic and non-diabetic control group was attributed to the increase in amino acids, such as glycine, L-asparagine, and L-serine. Aromatic amino acids, including L-tyrosine, were associated with the risk of future hyperglycemia and overt diabetes. The identified potential biomarkers depicted a good predictive value of more than 0.8. It was concluded from the results that amino acids that were associated with impaired insulin secretion were prospectively related to an increase in glucose levels. Moreover, amino acids that were associated with impaired insulin secretion were prospectively related to an increase in glucose levels.

Biodistribution of Vanadium Dioxide Particles in Mice by Consecutive Gavage Administration: Effects of Particle Size, Dosage, and Health Condition of Mice

The newly developed vanadium dioxide (VO₂), a material with excellent reversible and multi-stimuli responsible phase transition property, has been widely used in high-performance and energy-saving smart devices. The rapid growth of the VO₂-based emerging technologies and the complex biological effect of vanadium to organisms urge a better understanding of the behavior of VO₂ in vivo for safety purpose. Herein, we study the absorption, distribution, and excretion of two commercial VO₂ (nanoscale SVO₂ and bulk MVO₂) in mice after consecutive gavage administration for up to 28 days. The absorption of both types of VO₂ is as low as less than 1.5% of the injected dose within 28 days, while MVO₂ is several times more difficult to be absorbed than SVO₂. Almost all unabsorbed VO₂ is excreted through feces. For the absorbed vanadium, bone is the organ with the largest accumulation, followed by liver, kidney, and spleen. The vanadium content in organs shows a size-, dosage-, and animal health condition-dependent manner, and increases gradually to a saturation value along with the consecutive administration. Generally, smaller particle size and higher dosage lead to higher vanadium contents in organs, and more vanadium accumulates in bone and liver in diabetic mice than in normal mice. After the treatment is stopped, the accumulated vanadium in organs decreases a lot within 14 days, even reaches to the background level in some organs, but the content of vanadium in the bone remains high after 14 days post-exposure. These findings provide basic information for the safety assessment and safe applications of VO₂-based materials.

Investigations on Modulating Effect of Vanadium Supplementation on Growth and Metabolism Through Improved Immune Response, Antioxidative Profile and Endocrine Variables in Hariana heifers

This study was conducted to investigate the effect of vanadium (V) supplementation on growth, metabolism, antioxidant, and immunological and endocrine variables in Hariana heifers. Eighteen indigenous Hariana heifers (body weight 130.0 ± 3.0 kg; age 10.0 ± 2.0 months) were randomly blocked into three groups, each comprising of six animals. All the animals were on same dietary plan except that the respective groups were additionally supplemented with 0.0, 2.5, and 5.0 mg of V/kg dry matter (DM), during the experimental period of 90 days. There was a linear increase (p < 0.05) in mean DMI and ADG in 5.0 mg of V/kg DM-supplemented group. However, the feed efficiency remained unaffected. Although no effects (p > 0.05) of V supplementation were observed on hemato-biochemical attributes, the mean plasma V concentration showed dose-dependent increase (p < 0.001) on V supplementation. The activity of SOD was significantly higher (p < 0.001), whereas mean values of LPO decreased linearly (p < 0.05) in V-supplemented groups. Plasma total antioxidant status (TAS) also increased linearly (p < 0.05) in V-supplemented groups. Plasma IgG levels increased linearly (p < 0.05). Plasma IGF-1 concentrations showed significant effect (p < 0.05) of V supplementation. Plasma T4 concentration increased linearly (p < 0.05). The results suggest that V supplementation may play a role in modulating the immunity and antioxidant status of growing Hariana heifers. Graphical Abstract.

Effects of sodium tungstate and vanadyl sulphate on the liberation of prostanoids of the mesenteric vascular bed in diabetic rats

The loss of the modulator role of the endothelium could be involved in the pathogenesis of diabetic vascular complications. Transition metal compounds, such as tungsten and vanadium, have been proposed as possible agents in the treatment of diabetes by simulating the effects of insulin. The mesenteric vascular bed intervenes in vascular resistance and is a source of vasoactive compounds, such as prostanoids. The aim of this work was to study the effects of sodium tungstate and vanadyl sulphate treatments on the metabolic parameters and the release of prostanoids of the mesenteric vascular bed in an experimental model of Streptozotocin-induced diabetes. In diabetic rats, a significant increase was observed in plasma levels of glucose, triglycerides and total cholesterol. On the other hand, there was a significant reduction in the release of vasodilator prostanoids, such as prostacyclin and prostaglandin E₂ and vasoconstrictor thromboxane A₂ through the mesenteric vascular bed. Both sodium tungstate and vanadyl sulphate normalised glycaemia, triglyceridaemia and cholesterolaemia in rats diabetics. On the other hand, only treatment with sodium tungstate reversed the reduction in the release of vasodilator prostanoids, improving in diabetic animals the prostacyclin/thromboxane ratio, an indicator of vascular dysfunction. In conclusion, unlike vanadyl sulphate, sodium tungstate is shown to be more effective in controlling metabolic changes and the production of vasodilator prostanoids observed in experimental diabetes induced by streptozotocin.

Study of the Hypoglycemic Activity of Derivatives of Isoflavones from Cicer arietinum L

The chickpea, a food and medicine used by the people of Xinjiang, has a beneficial hypoglycemic effect. To better utilize this national resource and develop hypoglycemic agents from components of the chickpea, a series of new derivatives of isoflavone compounds from the chickpea were synthesized. An insulin-resistant (IR) HepG2 cell model was used to screen the hypoglycemic activities of these compounds. And the structure-activity relationships of these compounds were explored. Additionally, several combinations of these compound displayed higher hypoglycemic activity than any single compound, and they had similar hypoglycemic activity to that of the positive control group (p > 0.05). In addition, combination 3 and combination 6 exerted different effects on the insulin sensitivity of H4IIE cells stimulated with resistin. And the results indicated that combination 3 would have higher hypoglycemic activity. These findings demonstrate the characteristics of multiple components and targets of Chinese herbal medicine. This evidence may provide new ideas for the development of hypoglycemic drugs.

Effect of aerobic exercise against vanadyl sulphate-induced nephrotoxicity and hepatotoxicity in rats

Introduction: Vanadium compounds are insulin like drugs which are accompanied with nephrotoxicity and hepatotoxicity as their major side effects. Aerobic exercise is well known as an approach to reduce the side effects of many drugs.

Objectives: This study was designed to determine the role of aerobic exercise against vanadyl sulphate induced nephrotoxicity and hepatotoxicity in male rats.

Materials and Methods: Twenty-four male Wistar rats were randomly divided into three groups. Group I had aerobic exercise on a treadmill 5 days/week for 6 weeks. Group II received vanadyl sulphate (50 mg/kg/week; i.p.) for 6 weeks. Group III had combination of exercise and vanadyl sulphate therapy as groups 1 and 2. At the end of study, blood samples were obtained, and the animals were sacrificed for the tissues injury determination.

Results: Vanadyl sulphate alone increased serum levels of blood urea nitrogen (BUN), creatinine (Cr), and kidney weight (KW) and kidney tissue damage score (KTDS) (P<0.05). These observations revealed nephrotoxicity induced by vanadyl sulphate, although exercise training did not attenuate these results. In addition, vanadyl sulphate alone induced liver tissue damage score and exercise training intensified it insignificantly, while the serum levels of aspartate amino transferase and alanine amino transferase were greater in exercise alone group than others groups.

Conclusion: Aerobic exercise could not attenuate vanadyl sulphate induced nephrotoxicity and hepatotoxicity. These findings must be considered when vanadyl sulphate is suggested as insulin like drug.

14-Day Toxicity Studies of Tetravalent and Pentavalent Vanadium Compounds in Harlan Sprague Dawley Rats and B6C3F1/N Mice via Drinking Water Exposure

BACKGROUND

The National Toxicology Program (NTP) performed short-term toxicity studies of tetra- and pentavalent vanadium compounds, vanadyl sulfate and sodium metavanadate, respectively. Due to widespread human exposure and a lack of chronic toxicity data, there is concern for human health following oral exposure to soluble vanadium compounds.

OBJECTIVES

To compare the potency and toxicological profile of vanadyl sulfate and sodium metavanadate using a short-term in vivo toxicity assay.

METHODS

Adult male and female Harlan Sprague Dawley (HSD) rats and B6C3F1/N mice, 5 per group, were exposed to vanadyl sulfate or sodium metavanadate, via drinking water, at concentrations of 0, 125, 250, 500, 1000 or 2000 mg/L for 14 days. Water consumption, body weights and clinical observations were recorded throughout the study; organ weights were collected at study termination.

RESULTS

Lower water consumption, up to -80% at 2000 mg/L, was observed at most exposure concentrations for animals exposed to either vanadyl sulfate or sodium metavanadate and was accompanied by decreased body weights at the highest concentrations for both compounds. Animals in the 1000 and 2000 mg/L sodium metavanadate groups were removed early due to overt toxicity. Thinness was observed in high-dose animals exposed to either compound, while lethargy and abnormal gait were only observed in vanadate-exposed animals.

CONCLUSIONS

Based on clinical observations and overt toxicity, sodium metavanadate appears to be more toxic than vanadyl sulfate. Differential toxicity cannot be explained by differences in total vanadium intake, based on water consumption, and may be due to differences in disposition or mechanism of toxicity.

Vanadium compounds in medicine

Vanadium is a transition metal that, being ubiquitously distributed in soil, crude oil, water and air, also found roles in biological systems and is an essential element in most living beings. There are also several groups of organisms which accumulate vanadium, employing it in their biological processes. Vanadium being a biological relevant element, it is not surprising that many vanadium based therapeutic drugs have been proposed for the treatment of several types of diseases. Namely, vanadium compounds, in particular organic derivatives, have been proposed for the treatment of diabetes, of cancer and of diseases caused by parasites. In this work we review the medicinal applications proposed for vanadium compounds with particular emphasis on the more recent publications. In cells, partly due to the similarity of vanadate and phosphate, vanadium compounds activate numerous signaling pathways and transcription factors; this by itself potentiates application of vanadium-based therapeutics. Nevertheless, this non-specific bio-activity may also introduce several deleterious side effects as in addition, due to Fenton's type reactions or of the reaction with atmospheric O2, VCs may also generate reactive oxygen species, thereby introducing oxidative stress with consequences presently not well evaluated, particularly for long-term administration of vanadium to humans. Notwithstanding, the potential of vanadium compounds to treat type 2 diabetes is still an open question and therapies using vanadium compounds for e.g. antitumor and anti-parasitic related diseases remain promising.

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.

Thymine vanadyl(II) compound as a diabetic drug model: chemical spectroscopic and antimicrobial assessments

The aim of this study was to synthesize a novel bifunctionalized thymine vanadyl(II) compound. The solid vanadyl(II) compound has been characterized by elemental analyses (CHN), Raman laser, infrared spectra, molar conductivity, electronic spectra, thermogravimetric analyses (TGA), scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) studies. Electronic and magnetic measurements have confirmed that the speculated geometry of vanadyl(II) compound is square pyramidal geometry. The microbial test was performed for the vanadyl complex against some kinds of bacteria and fungi. The results suggested that [VO(Thy)2] adduct has an anti-diabetic profile.

Alternative therapies for diabetes and its cardiac complications: role of vanadium

It is now well known that a cardiomyopathic state accompanies diabetes mellitus. Although insulin injections and conventional hypoglycemic drug therapy have been of invaluable help in reducing cardiac damage and dysfunction in diabetes, cardiac failure continues to be a common cause of death in the diabetic population. The use of alternative medicine to maintain health and treat a variety of diseases has achieved increasing popularity in recent years. The goal of alternative therapies in diabetic patients has been to lower circulating blood glucose levels and thereby treat diabetic complications. This paper will focus its discussion on the role of vanadium on diabetes and the associated cardiac dysfunction. Careful administration of a variety of forms of vanadium has produced impressive long-lasting control of blood glucose levels in both Type 1 and Type 2 diabetes in animals. This has been accompanied by, in many cases, a complete correction of the diabetic cardiomyopathy. The oral delivery of vanadium as a vanadate salt in the presence of tea has produced particularly impressive hypoglycemic effects and a restoration of cardiac function. This intriguing approach to the treatment of diabetes and its complications, however, deserves further intense investigation prior to its use as a conventional therapy for diabetic complications due to the unknown long-term effects of vanadium accumulation in the heart and other organs of the body.

Alternative therapies for diabetes and its cardiac complications: role of vanadium

It is now well known that a cardiomyopathic state accompanies diabetes mellitus. Although insulin injections and conventional hypoglycemic drug therapy have been of invaluable help in reducing cardiac damage and dysfunction in diabetes, cardiac failure continues to be a common cause of death in the diabetic population. The use of alternative medicine to maintain health and treat a variety of diseases has achieved increasing popularity in recent years. The goal of alternative therapies in diabetic patients has been to lower circulating blood glucose levels and thereby treat diabetic complications. This paper will focus its discussion on the role of vanadium on diabetes and the associated cardiac dysfunction. Careful administration of a variety of forms of vanadium has produced impressive long-lasting control of blood glucose levels in both Type 1 and Type 2 diabetes in animals. This has been accompanied by, in many cases, a complete correction of the diabetic cardiomyopathy. The oral delivery of vanadium as a vanadate salt in the presence of tea has produced particularly impressive hypoglycemic effects and a restoration of cardiac function. This intriguing approach to the treatment of diabetes and its complications, however, deserves further intense investigation prior to its use as a conventional therapy for diabetic complications due to the unknown long-term effects of vanadium accumulation in the heart and other organs of the body.

Anti-diabetic effects of a series of vanadium dipicolinate complexes in rats with streptozotocin-induced diabetes

The effects of oral treatment of rats with streptozotocin-induced diabetes with a range of vanadium dipicolinate complexes (Vdipic) and derivatives are reviewed. Structure-reactivity relationships are explored aiming to correlate properties such as stability, to their insulin-enhancing effects. Three types of modifications are investigated; first, substitutions on the aromatic ring, second, coordination of a hydroxylamido group to the vanadium, and third, changes in the oxidation state of the vanadium ion. These studies allowed us to address the importance of coordination chemistry, and redox chemistry, as modes of action. Dipicolinate was originally chosen as a ligand because the dipicolinatooxovanadium(V) complex (V5dipic), is a potent inhibitor of phosphatases. The effect of vanadium oxidation state (3, 4 or 5), on the insulin-enhancing properties was studied in both the Vdipic and VdipicCl series. Effects on blood glucose, body weight, serum lipids, alkaline phosphatase and aspartate transaminase were selectively monitored. Statistically distinct differences in activity were found, however, the trends observed were not the same in the Vdipic and VdipicCl series. Interperitoneal administration of the Vdipic series was used to compare the effect of administration mode. Correlations were observed for blood vanadium and plasma glucose levels after V5dipic treatment, but not after treatment with corresponding V4dipic and V3dipic complexes. Modifications of the aromatic ring structure with chloride, amine or hydroxyl groups had limited effects. Global gene expression was measured using Affymetrix oligonucleotide chips. All diabetic animals treated with hydroxyl substituted V5dipic (V5dipicOH) and some diabetic rats treated with vanadyl sulfate had normalized hyperlipidemia yet uncontrolled hyperglycemia and showed abnormal gene expression patterns. In contrast to the normal gene expression profiles previously reported for some diabetic rats treated with vanadyl sulfate, where both hyperlipidemia and hyperglycemia were normalized. Modification of the metal, changing the coordination chemistry to form a hydroxylamine ternary complex, had the most influence on the anti-diabetic action. Vanadium absorption into serum was determined by atomic absorption spectroscopy for selected vanadium complexes. Only diabetic rats treated with the ternary V5dipicOH hydroxylamine complex showed statistically significant increases in accumulation of vanadium into serum compared to diabetic rats treated with vanadyl sulfate. The chemistry and physical properties of the Vdipic complexes correlated with their anti-diabetic properties. Here, we propose that compound stability and ability to interact with cellular redox reactions are key components for the insulin-enhancing activity of vanadium compounds. Specifically, we found that the most overall effective anti-diabetic Vdipic compounds were obtained when the compound administered had an increased coordination number in the vanadium complex.

New vanadium-based magnetic resonance imaging probes: clinical potential for early detection of cancer

We have developed a magnetic resonance imaging (MRI) method for improved detection of cancer with a new class of cancer-specific contrast agents, containing vanadyl (VO(2+))-chelated organic ligands, specifically bis(acetylacetonato)oxovanadium(IV) [VO(acac)(2)]. Vanadyl compounds have been found to accumulate within cells, where they interact with intracellular glycolytic enzymes. Aggressive cancers are metabolically active and highly glycolytic; an MRI contrast agent that enters cells with high glycolytic activity could provide high-resolution functional images of tumor boundaries and internal structure, which cannot be achieved by conventional contrast agents. The present work demonstrates properties of VO(acac)(2) that may give it excellent specificity for cancer detection. A high dose of VO(acac)(2) did not cause any acute or short-term adverse reactions in murine subjects. Calorimetry and spectrofluorometric methods demonstrate that VO(acac)(2) is a blood pool agent that binds to serum albumin with a dissociation constant K (d) ~ 2.5 +/- 0.7 x 10(-7) M and a binding stoichiometry n = 1.03 +/- 0.04. Owing to its prolonged blood half-life and selective leakage from hyperpermeable tumor vasculature, a low dose of VO(acac)(2) (0.15 mmol/kg) selectively enhanced in vivo magnetic resonance images of tumors, providing high-resolution images of their interior structure. The kinetics of uptake and washout are consistent with the hypothesis that VO(acac)(2) preferentially accumulates in cancer cells. Although VO(acac)(2) has a lower relaxivity than gadolinium-based MRI contrast agents, its specificity for highly glycolytic cells may lead to an innovative approach to cancer detection since it has the potential to produce MRI contrast agents that are nontoxic and highly sensitive to cancer metabolism.

Effects on the bones of vanadyl acetylacetonate by oral administration: a comparison study in diabetic rats

Oral delivery, rather than parenteral administration, would be beneficial for treating diabetic mellitus owing to the need for a long-term regimen. The objectives of this study were to evaluate oral delivery tolerance and the effects on the bone of accumulated vanadium following the long-term administration of vanadyl acetylacetonate (VAC). Normal and diabetic rats were intragastrically administered VAC at a dose of 3 mg vanadium/kg body weight once daily for 35 consecutive days. VAC did not cause any obvious signs of diarrhea, any changes in kidney or liver, or deaths in any group. The phosphate levels in the bone were slightly increased, and the calcium levels in the bone were not obviously changed as compared with those of the rat group not receiving VAC. After administration of VAC, the decreased ultimate strength, trabecular thickness, mineral apposition rate, and plasma osteocalcin in diabetic rats were either improved or normalized, but reduced bone mineral density (BMD) in diabetic rats was not improved. None of the parameters evaluated in normal rats were altered. The results indicate that the oral VAC is tolerated and benefits the diabetic osteopathy of rats, but seems not to influence the bone of normal rats. They also suggest that VAC improves diabetes-related bone disorders, primarily by improving the diabetic state.

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

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

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.

Pharmacodynamics and pharmacokinetics of the insulin-mimetic agent vanadyl acetylacetonate in non-diabetic and diabetic rats

The objectives of this study were to evaluate the pharmacodynamics and pharmacokinetics of vanadyl acetylacetonate (VAC) in rats. Pharmacodynamic study was carried out using non-diabetic and diabetic rats by subcutaneous (s.c.) and intragastric (i.g.) administrations at single dose or multiple doses. Pharmacokinetic study was performed using non-diabetic rats. Results showed that VAC resulted in a significant decrease of plasma glucose levels in diabetic rats in all dosing levels, and nearly restored hyperglycemic values to normal values after s.c. injection at a single dose of 2, 4, and 8 mg vanadium (V)/kg, or after i.g. administration at multiple doses of 3 and 6 mg V/kg once daily for seven consecutive days, respectively. The VAC could be rapidly absorbed and T(max) values ranged from 0.9 +/- 0.3 h for s.c. injection to 3.0 +/- 0.9 h for i.g. administration. The average absolute bioavailabilities for i.g. administrations at a single dose of 3, 6, and 10 mg V/kg were 34.7%, 28.1%, and 22.8%, respectively. After i.g. administration at a single dose of 10 mg V/kg, the average elimination half-lives obtained from non-diabetic rats were very long ranging from 144.7 +/- 8.7 h in plasma to 657.3 +/- 34.8 h in femur tissue. In conclusion, VAC widely distributed in various tissues and accumulated more in the femur tissue. The time to reach maximal vanadium level after s.c. injection or i.g. administration was not coincident with the time to reach maximal hypoglycemic effect. The accumulated vanadium in bone, kidney or other tissues may gradually release and exert a longer action. In present dosing levels and administration routes, VAC was effective for lowering plasma glucose levels in diabetic rats and could reverse the higher triglyceride and cholesterol levels to the normal ranges. VAC did not influence the insulin levels in plasma and not cause obvious toxic signs like diarrhea.

Vanadium--an element of atypical biological significance

The biological image of the transition element vanadium ferments a great deal of contradiction-from toxicity to essentiality. Importance of this element as micro-nutrient is yet to be unequivocally accepted by biologists and biomedical scientists. In spite of toxicity, it seems interesting to analyze the different biological roles of the element. Vanadium compounds have been proven to be associated with various implications in the pathogenesis of some human diseases and also in maintaining normal body functions. Salts of vanadium interfere with an essential array of enzymatic systems such as different ATPases, protein kinases, ribonucleases and phosphatases. While vanadium deficiency accounts for several physiological malfunctionings including thyroid, glucose and lipid metabolism, etc., several genes are regulated by this element or by its compounds, which include genes for tumor necrosis factor-alpha (TNF-alpha), Interleukin-8 (IL-8), activator protein-1 (AP-1), ras, c-raf-1, mitogen activated protein kinase (MAPK), p53, nuclear factors-kappaB, etc. All these seem to be not far from its recognition as an element of pharmacological and nutritional significance, which is revealed through its increasing therapeutic uses in diabetes. Vanadium is also emerging as a potent anti-carcinogenic agent. This review summarizes the developments related to vanadium biology as a whole by analyzing the general biochemical functions of vanadium.

The influence of sodium metavanadate on the process of diabetogenesis in BB rats

Vanadium has been shown to be beneficial in the oral treatment of animal models of type 1 and type 2 diabetes. The aim of the study was to evaluate the short-term effects of sodium metavanadate in prediabetic BB-DP rats. To do this, 96 rats were divided into 4 equal groups. Groups V1, V2, V3 were treated with sodium metavanadate (0.1, 0.2 and 0.3 mg/ml respectively) and sodium chloride (0.5 mg/ml) in drinking water for 7 days. Group C received only sodium chloride (0.5 mg/ml). Blood glucose (BG), glycosuria, ketonuria, body weight and insulinemia were determined. The age of onset of diabetes was significantly higher for groups V2, V3 compared to group C, (p<0.05) and depends on the metavanadate concentration (V3 vs. V1, p=0.006). The incidence of diabetes was lower in the rats treated with metavanadate than in the control group, but this difference was not statistically significant. In diabetic rats, the BG at the onset was higher in group C than in groups V, p<0.05. Insulinemia, at the onset of the treatment as well as immediately after its cessation showed a drop in the treatment groups, proportionally to the dosage of vanadium, but later increased slowly and continuously until the end of the experiment. In conclusion, metavanadate delays the development of diabetes in BB-DP rats, but does not prevent its onset. A milder form of diabetes occurs in diabetic rats treated with metavanadate. The effects depend on the metavanadate concentration and 0.2 mg/ml is preferable.

Inhibition of gluconeogenesis by vanadium and metformin in kidney-cortex tubules isolated from control and diabetic rabbits

Effect of vanadyl acetylacetonate (VAc) and metformin on gluconeogenesis has been studied in isolated hepatocytes and kidney-cortex tubules of rabbit. Glucose formation from alanine+glycerol+octanoate, pyruvate or dihydroxyacetone was inhibited by 50-80% by 100 microM VAc or 500 microM metformin in renal tubules of control and alloxan-diabetic animals, while the inhibitory action of these compounds in hepatocytes was less pronounced (by about 20-30%). In contrast to VAc, metformin increased the rate of lactate formation by about 2-fold in renal tubules incubated with alanine+glycerol+octanoate. In view of VAc-induced changes in intracellular gluconeogenic intermediates and gluconeogenic enzyme activities, it is likely that this compound may decrease fluxes through pyruvate carboxylase, phosphoenolpyruvate carboxykinase, fructose-1,6-bisphosphatase and glucose-6-phosphatase. In contrast to VAc, metformin-induced decrease in renal gluconeogenesis may result from a decline of cytosolic oxaloacetate level and consequently PEPCK activity. Following 6 days of VAc administration (1.275 mg Vkg(-1) body weight daily) the blood glucose level in alloxan-diabetic rabbits was normalised while blood glucose changes in control animals were not observed. On the contrary, in diabetic animals treated for 6 days with metformin (200 mg kg(-1) body weight day(-1)) a high blood glucose level was maintained. Unfortunately, VAc-treated control and diabetic rabbits exhibited elevated serum urea and creatinine levels. In VAc-treated animals vanadium was accumulated in kidney-cortex up to 7.6+/-0.6 microg Vg(-1) dry weight. In view of a potential vanadium nephrotoxicity a therapeutic application of vanadium compounds needs a critical re-evaluation.

Vanadyl as a catalyst of human lipoprotein oxidation

Lipoprotein oxidation, which is relevant to atherogenesis, can be induced by redox-active transition metals, such as copper. Vanadium is a metal usually used as vanadyl to improve metabolic control in diabetic patients; given its redox-active properties, we have investigated possible oxidative effects of the metal on lipoproteins from healthy and diabetic subjects. Beginning from 10 microM, vanadyl, but not vanadate, induced oxidation of the non-HDL fraction, which was inhibited by EDTA, butylated hydroxytoluene and Vitamins E and C, but not by mannitol, SOD and catalase. Differently from copper, vanadyl could oxidize directly lipoprotein lipids, although it showed a lower oxidant activity against critical tryptophan residues of the lipoprotein protein moiety. Moreover, the non-HDL fraction of diabetic patients was more susceptible to vanadyl-dependent oxidation than that of controls. Thus, vanadium, in its reduced form which may be used in humans, can oxidize the non-HDL fraction through oxidative effects exerted especially on lipoprotein lipids; the specific pro-oxidant activity of vanadyl is more evident with lipoproteins of diabetic patients. Given also the tissue accumulating capacity of vanadium conceivably in a reduced form, its prolonged administration to humans, especially to diabetic patients without adequate antioxidant supplementation, needs caution.

Neuroprotective effect of sodium orthovanadate on delayed neuronal death after transient forebrain ischemia in gerbil hippocampus

In transient forebrain ischemia, sodium orthovanadate as well as insulinlike growth factor-1 (IGF-1) rescued cells from delayed neuronal death in the hippocampal CA1 region. Adult Mongolian gerbils were subjected to 5-minute forebrain ischemia. Immunoblotting analysis with anti-phospho-Akt/PKB (Akt) antibody showed that phosphorylation of Akt at serine-473 (Akt-Ser-473) in the CA1 region decreased immediately after reperfusion, and in turn transiently increased 6 hours after reperfusion. The decreased phosphorylation of Akt-Ser-473 was not observed in the CA3 region. The authors then tested effects of intraventricular injection of orthovanadate and IGF-1, which are known to activate Akt. Treatment with orthovanadate or IGF-1 30 minutes before ischemia blocked delayed neuronal death in the CA1 region. The neuroprotective effects of orthovanadate and IGF-1 were associated with preventing decreased Akt-Ser-473 phosphorylation in the CA1 region observed immediately after reperfusion. Immunohistochemical studies with the anti-phospho-Akt-Ser-473 antibody also demonstrated that Akt was predominantly in the nucleus and was moderately activated in the cell bodies and dendrites of pyramidal neurons after orthovanadate treatment. The orthovanadate treatment also prevented the decrease in phosphorylation of mitogen-activated protein kinase (MAPK). Pretreatment with combined blockade of phosphatidylinositol 3-kinase and MAPK pathways totally abolished the orthovanadate-induced neuroprotective effect. These results suggest that the activation of both Akt and MAPK activities underlie the neuroprotective effects of orthovanadate on the delayed neuronal death in the CA1 region after transient forebrain ischemia.

Vanadium pharmacokinetics and oral bioavailability upon single-dose administration of vanadyl sulfate to rats

Vanadium pharmacokinetic parameters and oral bioavailability were determined after administration of vanadyl sulfate, an antidiabetic agent, to male Wistar rats. An optimal sampling design was used over a 21-day period; vanadium was measured in blood by atomic absorption spectrophotometry (AAS). After i.v. bolus injection (3.025 mg V/kg body weight), a three-compartment model was fitted to the data. Mean (+/- SD) half-lives were 0.90 +/- 0.56 hours, 24.8 +/- 14.5 h and 201 +/- 74 h, respectively, for the three phases observed. Vanadium clearance averaged 37.6 +/- 15.8 mL/h. Initial volume of distribution was 2.43 +/- 1.22 L/kg whereas total volume of distribution was 25.4 +/- 3.9 L/kg; these values largely exceeded body weight (i.e. 300 g), in agreement with a great uptake and retention of vanadium in tissues. After oral gavage administration (15.12 and 7.56 mg V/kg body weight), vanadium disposition was best described by a three-compartment model, with absorption appearing to occur by a zero-order rate. This process lasted 10.3 +/- 1.3 h and 10.9 +/- 1.1 h for the two dosage levels, respectively. Half-lives corresponding to the terminal log-linear part of the curve were 173.5 +/- 1.6 h and 172 +/- 6 h (Bayesian estimates). No dose-dependency was observed for any of the parameters determined. Absolute bioavailabilities, with reference to the i.v. administration, were 12.5% and 16.8% when determined from AUCmod. Bioavailability appeared to be higher than generally stated in the literature.

Mechanisms of vanadium action: insulin-mimetic or insulin-enhancing agent?

The demonstration that the trace element vanadium has insulin-like properties in isolated cells and tissues and in vivo has generated considerable enthusiasm for its potential therapeutic value in human diabetes. However, the mechanisms by which vanadium induces its metabolic effects in vivo remain poorly understood, and whether vanadium directly mimics or rather enhances insulin effects is considered in this review. It is clear that vanadium treatment results in the correction of several diabetes-related abnormalities in carbohydrate and lipid metabolism, and in gene expression. However, many of these in vivo insulin-like effects can be ascribed to the reversal of defects that are secondary to hyperglycemia. The observations that the glucose-lowering effect of vanadium depends on the presence of endogenous insulin whereas metabolic homeostasis in control animals appears not to be affected, suggest that vanadium does not act completely independently in vivo, but augments tissue sensitivity to low levels of plasma insulin. Another crucial consideration is one of dose-dependency in that insulin-like effects of vanadium in isolated cells are often demonstrated at high concentrations that are not normally achieved by chronic treatment in vivo and may induce toxic side effects. In addition, vanadium appears to be selective for specific actions of insulin in some tissues while failing to influence others. As the intracellular active forms of vanadium are not precisely defined, the site(s) of action of vanadium in metabolic and signal transduction pathways is still unknown. In this review, we therefore examine the evidence for and against the concept that vanadium is truly an insulin-mimetic agent at low concentrations in vivo. In considering the effects of vanadium on carbohydrate and lipid metabolism, we conclude that vanadium acts not globally, but selectively and by enhancing, rather than by mimicking the effects of insulin in vivo.

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.

Partial preservation of pancreatic beta-cells by vanadium: evidence for long-term amelioration of diabetes

Streptozotocin (STZ)-diabetic rats treated with vanadium can remain euglycemic for up to 20 weeks following withdrawal from vanadium treatment. In this study, we examined the effects of short-term vanadium treatment in preventing or reversing the STZ-induced diabetic state. Male Wistar rats were untreated (D) or treated (DT) with vanadyl sulfate for 1 week before administering STZ. Treatment was subsequently maintained for 3 days (DT3) or 14 days (DT14) post-STZ, after which vanadium was withdrawn. At 4 to 5 weeks post-STZ and following long-term withdrawal from vanadium, DT14 rats demonstrated levels of food and fluid intake and glucose tolerance that were not significantly different from those of age-matched untreated nondiabetic rats, and had significantly reduced glycemic levels in the fed state compared with D and DT3 groups. The proportion of animals that were euglycemic (fed plasma glucose < 9.0 mmol/L) was significant in DT14 (five of 10) relative to D (one of 10) and DT3 (one of 10) (P = .01). All euglycemic animals had an improved pancreatic insulin content that, albeit low (12% of control), was strongly linked to euglycemia in the fed state (r = -.91, P < .0001). Moreover, the highly significant correlation persisted with the analysis of untreated STZ-rats alone (r = -.95, P < .0001). Similarly, improvements in glucose tolerance and insulin secretory function in euglycemic rats were strongly correlated with small changes in residual insulin content. Hence, as vanadium pretreatment did not prevent STZ-induced beta-cytotoxicity, the vanadium-induced amelioration of the diabetic state appears to be secondary to the preservation of a functional portion of pancreatic beta cells that initially survived STZ toxicity. The partial preservation of pancreatic beta cells, albeit small in proportion to the total insulin store, was both critical and sufficient for a long-term reversal of the diabetic state. These results suggest that apparently modest effects in preserving residual pancreatic insulin content can have profound consequences on glucose homeostasis and may bear important implications for interventions that have "limited" protective effects on beta cells.

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.

The role of vanadium in the management of diabetes

Diabetes mellitus results from an absolute or relative deficiency in insulin secretion and a resistance of target tissues to the action of insulin, in proportions that vary with the type of the disease. The shortage of insulin can be corrected by administration of exogenous insulin or stimulation of pancreatic beta-cells with sulphonylureas. However, insulin resistance remains a major therapeutic problem. Here, Sonia Brichard and Jean-Claude Henquin review the recent discoveries that indicate a possible role for vanadium in management of the disease. In vitro, vanadium salts mimic most effects of insulin on the main target tissues of the hormone, and in vivo they induce a sustained fall in blood glucose levels in insulin-deficient diabetic rats, and improve glucose homeostasis in obese, insulin-resistant diabetic rodents. Recent short-term clinical trials with vanadium salts also seem promising in type II (non-insulin-dependent) diabetic patients in whom liver and peripheral insulin resistance was attenuated, indicating the therapeutic potential of vanadium salts, pending demonstration of their long-term innocuity.