Effects of diabetes, vanadium, and insulin on glycogen synthase activation in Wistar rats

Vanadium Compounds with Antidiabetic Potential

Over the last four decades, vanadium compounds have been extensively studied as potential antidiabetic drugs. With the present review, we aim at presenting a general overview of the most promising compounds and the main results obtained with in vivo studies, reported from 1899-2023. The chemistry of vanadium is explored, discussing the importance of the structure and biochemistry of vanadate and the impact of its similarity with phosphate on the antidiabetic effect. The spectroscopic characterization of vanadium compounds is discussed, particularly magnetic resonance methodologies, emphasizing its relevance for understanding species activity, speciation, and interaction with biological membranes. Finally, the most relevant studies regarding the use of vanadium compounds to treat diabetes are summarized, considering both animal models and human clinical trials. An overview of the main hypotheses explaining the biological activity of these compounds is presented, particularly the most accepted pathway involving vanadium interaction with phosphatase and kinase enzymes involved in the insulin signaling cascade. From our point of view, the major discoveries regarding the pharmacological action of this family of compounds are not yet fully understood. Thus, we still believe that vanadium presents the potential to help in metabolic control and the clinical management of diabetes, either as an insulin-like drug or as an insulin adjuvant. We look forward to the next forty years of research in this field, aiming to discover a vanadium compound with the desired therapeutic properties.

A Dioxidovanadium Complex cis-[VO2 (obz) py] Attenuates Hyperglycemia in Streptozotocin (STZ)-Induced Diabetic Male Sprague-Dawley Rats via Increased GLUT4 and Glycogen Synthase Expression in the Skeletal Muscle

Vanadium has demonstrated antihyperglycemic effects in diabetes mellitus (DM) but is, however, associated with toxicity. Therefore, new vanadium complexes envisaged to possess heightened therapeutic potency while rendering less toxicity are being explored. Accordingly, the aim of the study was to investigate the effects of a dioxidovanadium (V) complex, cis-[VO2 (obz) py], on selected glucose metabolism markers in streptozotocin (STZ)-induced diabetic rats. STZ-induced diabetic rats were treated orally with cis-[VO2 (obz) py] (10, 20, and 40 mg/kg) twice every 3rd day for 5 weeks. Blood glucose concentrations, body weight, and food and water intake were monitored weekly, for 5 weeks. Rats were then euthanized after which blood, liver, and muscle tissues were collected for biochemical analysis. The administration of dioxidovanadium complex significantly decreased blood glucose concentrations throughout the 5-week period in comparison with the diabetic control (DC). The attenuation of hyperglycemia was accompanied by an increased glycogen concentration in both liver and muscle tissues in the treated groups. Furthermore, a significant increase was observed in the expression of glucose transporter type 4 (GLUT4) in the skeletal muscle tissues and glycogen synthase in the liver tissues. These findings indicate that our vanadium complex cis-[VO2 (obz) py] may exert antihyperglycemic effects through increased glucose uptake, glycogen synthesis, and increased GLUT4 and glycogen synthase expression.

Vanadium as potential therapeutic agent for COVID-19: A focus on its antiviral, antiinflamatory, and antihyperglycemic effects

An increasing evidence suggests that vanadium compounds are novel potential drugs in the treatment of diabetes, atherosclerosis, and cancer. Vanadium has also demonstrated activities against RNA viruses and is a promising candidate for treating acute respiratory diseases. The antidiabetic, antihypertensive, lipid-lowering, cardioprotective, antineoplastic, antiviral, and other potential effects of vanadium are summarized here. Given the beneficial antihyperglycemic and antiinflammatory effects as well as the potential mechanistic link between the COVID-19 and diabetes, vanadium compounds could be considered as a complement to the prescribed treatment of COVID-19. Thus, further clinical trials are warranted to confirm these favorable effects of vanadium treatment in COVID-19 patients, which appear not to be studied yet.

Vanadium and insulin: Partners in metabolic regulation

Since the 1970s, the biological role of vanadium compounds has been discussed as insulin-mimetic or insulin-enhancer agents. The action of vanadium compounds has been investigated to determine how they influence the insulin signaling pathway. Khan and coworkers proposed key proteins for the insulin pathway study, introducing the concept "critical nodes". In this review, we also considered critical kinases and phosphatases that participate in this pathway, which will permit a better comprehension of a critical node, where vanadium can act: a) insulin receptor, insulin receptor substrates, and protein tyrosine phosphatases; b) phosphatidylinositol 3'-kinase, 3-phosphoinositide-dependent protein kinase and mammalian target of rapamycin complex, protein kinase B, and phosphatase and tensin homolog; and c) insulin receptor substrates and mitogen-activated protein kinases, each node having specific negative modulators. Additionally, leptin signaling was considered because together with insulin, it modulates glucose and lipid homeostasis. Even in recent literature, the possibility of vanadium acting against metabolic diseases or cancer is confirmed although the mechanisms of action are not well understood because these critical nodes have not been systematically investigated. Through this review, we establish that vanadium compounds mainly act as phosphatase inhibitors and hypothesize on their capacity to affect kinases, which are critical to other hormones that also act on common parts of the insulin pathway.

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

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

Glutamine supplementation stimulates protein-synthetic and inhibits protein-degradative signaling pathways in skeletal muscle of diabetic rats

In this study, we investigated the effect of glutamine (Gln) supplementation on the signaling pathways regulating protein synthesis and protein degradation in the skeletal muscle of rats with streptozotocin (STZ)-induced diabetes. The expression levels of key regulatory proteins in the synthetic pathways (Akt, mTOR, GSK3 and 4E-BP1) and the degradation pathways (MuRF-1 and MAFbx) were determined using real-time PCR and Western blotting in four groups of male Wistar rats; 1) control, non-supplemented with glutamine; 2) control, supplemented with glutamine; 3) diabetic, non-supplemented with glutamine; and 4) diabetic, supplemented with glutamine. Diabetes was induced by the intravenous injection of 65 mg/kg bw STZ in citrate buffer (pH 4.2); the non-diabetic controls received only citrate buffer. After 48 hours, diabetes was confirmed in the STZ-treated animals by the determination of blood glucose levels above 200 mg/dL. Starting on that day, a solution of 1 g/kg bw Gln in phosphate buffered saline (PBS) was administered daily via gavage for 15 days to groups 2 and 4. Groups 1 and 3 received only PBS for the same duration. The rats were euthanized, and the soleus muscles were removed and homogenized in extraction buffer for the subsequent measurement of protein and mRNA levels. The results demonstrated a significant decrease in the muscle Gln content in the diabetic rats, and this level increased toward the control value in the diabetic rats receiving Gln. In addition, the diabetic rats exhibited a reduced mRNA expression of regulatory proteins in the protein synthesis pathway and increased expression of those associated with protein degradation. A reduction in the skeletal muscle mass in the diabetic rats was observed and was alleviated partially with Gln supplementation. The data suggest that glutamine supplementation is potentially useful for slowing the progression of muscle atrophy in patients with diabetes.

Comparison of hypoglycemic activity of fermented mushroom of Inonotus obliquus rich in vanadium and wild-growing I. obliquus

The effects of vanadium-enriched and wild Inonotus obliquus were tested on hyperglycemic mice. The vanadium content of the culture medium was 0.6%, reaching a concentration of 3.0 mg/g in the cultured mushroom while in the wild variety is 1/100 of that amount. The toxicity of vanadium at the 3.0 mg/g level is negligible, but its anti-diabetic effects are significantly different to those of the wild variety (p < 0.05). Due to its high bioavailability and low toxicity, vanadium-enriched I. obliquus could be used as a means of vanadium supplementation, with expectation of obtaining higher bioavailability and lower toxicity in animals.

The effects of vanadium (V) absorbed by Coprinus comatus on bone in streptozotocin-induced diabetic rats

The purpose of this study was to evaluate the effects of vanadium absorbed by Coprinus comatus (VACC) treatment on bone in streptozotocin (STZ)-induced diabetic rats. Forty-five Wistar female rats used were divided into three groups: (1) normal rats (control), (2) diabetic rats, and (3) diabetic rats treated with VACC. Normal and diabetic rats were given physiological saline, and VACC-treated rats were administered VACC intragastrically at doses of 0.18 mg vanadium/kg body weight once daily. Treatments were performed over a 12-week period. At sacrifice, one tibia and one femur were removed, subjected to micro computed tomography (micro-CT) for determination of trabecular bone structure, and then processed for histomorphometry to assess bone turnover. Another femoral was used for mechanical testing. In addition, bone samples were collected to evaluate the content of mineral substances in bones. Treatment with VACC increased trabecular bone volume fraction in diabetic rats. Vanadium-treated animals had significant increases in ultimate load, trabecular thickness, and osteoblast surface. However, vanadium treatment did not seem to affect bone stiffness, bone energy absorption, trabecular separation, and osteoclast number. P levels in the femurs of diabetic rats treated with VACC were significantly higher than those of diabetic animals. Ca levels in diabetic and diabetic rats treated with vanadium showed no obvious changes. In conclusion, our results provide an important proof of concept that VACC may represent a powerful approach to treating or reversing diabetic osteopathy in humans.

Vanadium-Enriched Cordyceps sinensis, a Contemporary Treatment Approach to Both Diabetes and Depression in Rats

This article studies a contemporary treatment approach toward both diabetes and depression management by vanadium-enriched Cordyceps sinensis (VECS). Streptozotocin-induced hyperglycemic rats were used in the study. After the rats were administered with VECS, a significant reduction in blood glucose levels was seen (P < .05) and the levels of serum insulin increased significantly (P < .05). At the same time, the study revealed a significant decrease in immobility with a corresponding increase in the swimming and climbing behavior in hyperglycemic rats following VECS treatment. The results described herein demonstrate that VECS is a contemporary treatment approach that advocates an aggressive stance toward both diabetes and depression management.

Comparison of hypoglycemic activity and toxicity of vanadium (IV) and vanadium (V) absorbed in fermented mushroom of Coprinus comatus

This study was designed to evaluate the effect and toxicity of administration of vanadium (IV, V) absorbed by Coprinus comatus (VACC) on alloxan-induced and sucrosefed hyperglycemic mice, respectively. The blood glucose, lipid profile, and the organ masses of the mice were analyzed. After the mice were administered with VACC, the blood glucose and the lipid profile of hyperglycemic mice decreased, irrespective of the VACC produced by vanadium (IV) or vanadium (V). However, the organ masses of the mice were significantly different after the mice were treated with vanadium (IV) and vanadium (V) 9 weeks later. The results indicate both vanadium (IV) and vanadium (V) absorbed in C. comatus have hypoglycemic activity on hyperglycemic mice. However, vanadium (IV) absorbed in C. comatus is less toxic to mice than vanadium (V).

Hypoglycemic activity of Grifola frondosa rich in vanadium

The hypoglycemic activity of fermented mushroom of Grifola frondosa rich in vanadium (GFRV) was studied in this paper. Alloxan- and adrenalin-induced hyperglycemic mice were used in the study. The blood glucose and the HbA1c of the mice were analyzed respectively. After the mice were administered (ig) with GFRV, the blood glucose and the HbA1c of alloxan-induced hyperglycemic mice decreased (p < 0.05, p < 0.01) and ascension of blood glucose induced by adrenalin was inhibited (p < 0.01). Also, the bodyweight of the alloxan-induced hyperglycemic mice was increased gradually. In the fermented mushroom of G. frondosa, vanadium at lower doses in combination with G. frondosa induced significant decreases of the blood glucose and HbA1c levels in hyperglycemic mice.

Comparison of vanadium-rich activity of three species fungi of basidiomycetes

A comparison of vanadium-rich activity of three species fungi of Basidiomycetes, Ganoderma lucidum, Coprinus comatus, and Grifola frondosa, was studied. By fermentation and atomic absorption spectroscopy analysis, the biomass of G. lucidum and G. frondosa declined rapidly when the concentration of vanadium exceeded 0.3% but the biomass of C. comatus did not decline rapidly until the concentration of vanadium exceeded 0.4% and the content of vanadium accumulated in the mycelia was 3529.3 microg/g. After the mice were administered (intragastrically) with vanadium-rich C. comatus, the blood glucose of alloxan-induced hyperglycemic mice was decreased (p < 0.05) and the body weight of the alloxan-induced hyperglycemic mice was increased gradually. Thus, we selected C. comatus to absorb vanadium and chose 0.4% as the optimal concentration of vanadium for the pharmacological works.

A comparison of hypoglycemic activity of three species of basidiomycetes rich in vanadium

The hypoglycemic activity of fermented mushroom of three fungi of basidiomycetes rich in vanadium was studied in this paper. Alloxan- and adrenalin-induced hyperglycemic mice were used in the study. The blood glucose and the sugar tolerance were determined. After the mice were administered (ig) with Coprinus comatus rich in vanadium, the blood glucose of alloxan-induced hyperglycemic mice decreased (p < 0.05), ascension of blood glucose induced by adrenalin was inhibited (p < 0.01) and the sugar tolerance of the normal mice was improved. However, the same result did not occur in Ganoderma lucidum and Grifola frondosa group. Compared with Ganoderma rich in vanadium and Grifola frondosa rich in vanadium, the hypoglycemic effects of Coprinus comatus rich in vanadium on hyperglycemic animals are significant; it may be used as a hypoglycemic food or medicine for hyperglycemic people.

Insulin reduces cerebral ischemia/reperfusion injury in the hippocampus of diabetic rats: a role for glycogen synthase kinase-3beta

OBJECTIVE

There is evidence that insulin reduces brain injury evoked by ischemia/reperfusion (I/R). However, the molecular mechanisms underlying the protective effects of insulin remain unknown. Insulin is a well-known inhibitor of glycogen synthase kinase-3beta (GSK-3beta). Here, we investigate the role of GSK-3beta inhibition on I/R-induced cerebral injury in a rat model of insulinopenic diabetes.

RESEARCH DESIGN AND METHODS

Rats with streptozotocin-induced diabetes were subjected to 30-min occlusion of common carotid arteries followed by 1 or 24 h of reperfusion. Insulin (2-12 IU/kg i.v.) or the selective GSK-3beta inhibitor TDZD-8 (0.2-3 mg/kg i.v.) was administered during reperfusion.

RESULTS

Insulin or TDZD-8 dramatically reduced infarct volume and levels of S100B protein, a marker of cerebral injury. Both drugs induced phosphorylation of the Ser9 residue, thereby inactivating GSK-3beta in the rat hippocampus. Insulin, but not TDZD-8, lowered blood glucose. The hippocampi of the drug-treated animals displayed reduced oxidative stress at 1 h of reperfusion as shown by the decreased generation of reactive oxygen species and lipid peroxidation. I/R-induced activation of nuclear factor-kappaB was attenuated by both drug treatments. At 24 h of reperfusion, TDZD-8 and insulin significantly reduced plasma levels of tumor necrosis factor-alpha; neutrophil infiltration, measured as myeloperoxidase activity and intercellular-adhesion-molecule-1 expression; and cyclooxygenase-2 and inducible-NO-synthase expression.

CONCLUSIONS

Acute administration of insulin or TDZD-8 reduced cerebral I/R injury in diabetic rats. We propose that the inhibitory effect on the activity of GSK-3beta contributes to the protective effect of insulin independently of any effects on blood glucose.

The co-effect of vanadium and fermented mushroom of Coprinus comatus on glycaemic metabolism

The effect of fermented mushroom of Coprinus comatus rich in vanadium (CCRV) on glycaemic metabolism was studied in this paper. Alloxan-induced hyperglycemic mice were used in this study. The insulin secretion and glycogen synthesis of the mice were analyzed. At the same time, the gluconeogenesis of the normal mice was also determined. The alloxan-damaged pancreatic beta-cells of the mice were also studied in this paper. After the mice were administered (i.g.) with CCRV, the level of insulin secretion and glycogen synthesis of alloxan-induced hyperglycemic mice elevated (p<0.05, p<0.01) and the gluconeogenesis of the normal mice was inhibited (p<0.01). Also, the alloxan-damaged pancreatic beta-cells of the mice were partly recovered gradually after the mice were administered (i.g.) with CCRV 15 days later. These may account for the causes of CCRV-induced significant decreases of the blood glucose in hyperglycemic mice.

Effect of vanadate on gene expression of the insulin signaling pathway in skeletal muscle of streptozotocin-induced diabetic rats

An insulin signaling pathway microarray was used to evaluate the gene expression profiling of the insulin signaling pathway in the skeletal muscle of streptozotocin-induced diabetic, NaVO(3)-treated diabetic and insulin-treated diabetic rats for the investigation of the effect of vanadium and insulin on the insulin signaling pathway. Of 96 genes surveyed, transcriptional patterns of 19 genes (20%) showed alterations in diabetic rats compared with controls. Although most of these changed gene expressions were improved after treatment with NaVO(3) (14, 74%) and insulin (16, 84%), NaVO(3) and insulin treatment resulted in the alteration of 20 and 12 additional gene transcripts compared no treatment. We found that both NaVO(3) and insulin treatment achieved a desirable glucose level and most of the alterative gene transcripts in diabetic rats were normalized with NaVO(3) and insulin treatment. Comparison of the gene expression profiling indicates that there is a significant difference between the NaVO(3)-treated group and the insulin-treated group. The present study demonstrated for the first time that several candidate genes of the insulin signaling pathway are involved in the effect of vanadium treatment on hyperglycemia. This study opens the way for more focused investigations that may identify the genes responsible for diabetes and vanadium treatment in the global insulin signaling pathway.

Glycogen synthase kinase-3 (GSK3): inflammation, diseases, and therapeutics

Deciphering what governs inflammation and its effects on tissues is vital for understanding many pathologies. The recent discovery that glycogen synthase kinase-3 (GSK3) promotes inflammation reveals a new component of its well-documented actions in several prevalent diseases which involve inflammation, including mood disorders, Alzheimer's disease, diabetes, and cancer. Involvement in such disparate conditions stems from the widespread influences of GSK3 on many cellular functions, with this review focusing on its regulation of inflammatory processes. GSK3 promotes the production of inflammatory molecules and cell migration, which together make GSK3 a powerful regulator of inflammation, while GSK3 inhibition provides protection from inflammatory conditions in animal models. The involvement of GSK3 and inflammation in these diseases are highlighted. Thus, GSK3 may contribute not only to primary pathologies in these diseases, but also to the associated inflammation, suggesting that GSK3 inhibitors may have multiple effects influencing these conditions.

Hypoglycemic activity of fermented mushroom of Coprinus comatus rich in vanadium

The hypoglycemic activity of fermented mushroom of Coprinus comatus rich in vanadium (CCRV) was studied in this paper. Alloxan and adrenalin induced hyperglycemic mice were used in the study. The blood glucose and the HbA1c of the mice were analyzed, respectively. At the same time, the sugar tolerance of the normal mice was also determined. After the mice were administered (ig) with CCRV, the blood glucose and the HbA1c of alloxan-induced hyperglycemic mice decreased (p < 0.05, p < 0.01), ascension of blood glucose induced by adrenalin was inhibited (p < 0.01) and the sugar tolerance of the normal mice was improved. Also, the body weight of the alloxan-induced hyperglycemic mice was increased gradually. In the fermented mushroom of C. comatus, vanadium at lower doses in combination with C. comatus, induced significant decreases of the blood glucose and HbA1c levels in hyperglycemic mice.

Physiological and pathological changes in glucose regulate brain Akt and glycogen synthase kinase-3

Insulin regulates the phosphorylation and activities of Akt and glycogen synthase kinase-3 (GSK3) in peripheral tissues, but in the brain it is less clear how this signaling pathway is regulated in vivo and whether it is affected by diabetes. We found that Akt and GSK3 are sensitive to glucose, because fasting decreased and glucose administration increased by severalfold the phosphorylation of Akt and GSK3 in the cerebral cortex and hippocampus of non-diabetic mice. Brain Akt and GSK3 phosphorylation also increased after streptozotocin administration (3 days), which increased blood glucose and depleted blood insulin, indicating regulation by glucose availability even with deficient insulin. Changes in Akt and GSK3 phosphorylation and activities in epididymal fat were opposite to those of brain after streptozotocin treatment. Streptozotocin-induced hyperglycemia and increased brain Akt and GSK3 phosphorylation were reversed by lowering blood glucose with insulin administration. Long term hyperglycemia also increased brain Akt and GSK3 phosphorylation, both 4 weeks after streptozotocin and in db/db insulin-resistant mice. Thus, the Akt-GSK3 signaling pathway is regulated in mouse brain in vivo in response to physiological and pathological changes in insulin and glucose.

Insulino-mimetic and anti-diabetic effects of vanadium compounds

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

Chronic glucose-lowering effects of rosiglitazone and bis(ethylmaltolato)oxovanadium(IV) in ZDF rats

The aim of this study was to determine if there was a synergistic or additive effect of a thiazolidinedione derivative (rosiglitazone (ROS)) and a vanadium compound (bis(ethylmaltolato)oxovanadium(IV) (BEOV)) on plasma glucose and insulin levels following chronic oral administration to Zucker diabetic fatty (ZDF) rats. Whole-blood vanadium levels were determined at time 0 and at days 1, 6, and 18. The doses of BEOV (0.1 mmol/kg) and ROS (2.8 µmol/kg) were selected to produce a glucose-lowering effect in 30% (ED30) of animals. Both drugs were administered daily by oral gavage as suspensions in 1% carboxymethylcellulose (CMC) in a volume of 2.5 mL/kg. The total volume administered to all rats was 5 mL/(kg·day). The combination of BEOV and ROS was effective in lowering plasma glucose levels to <9 mmol/L in 60% of fatty animals as compared with 30% for BEOV and 10% for ROS alone. The age-dependent decrease in plasma insulin levels associated with β-cell failure in the ZDF rats did not occur in the BEOV-treated fatty groups. There was no effect of any treatment on body weight; however, there was a significant reduction in both food and fluid intake in fatty groups treated with BEOV. There were no overt signs of toxicity and no mortality in this study. Both BEOV and ROS were effective in lowering plasma glucose levels, as stated above, and there was at least an additive effect when BEOV and ROS were used in combination.Key words: rosigitazone, bis(ethylmaltolato)oxovanadium(IV), diabetes, ZDF rats.

Oral treatment with vanadium of Zucker fatty rats activates muscle glycogen synthesis and insulin-stimulated protein phosphatase-1 activity

Since the glucose-lowering effects of vanadium could be related to increased muscle glycogen synthesis, we examined the in vivo effects of vanadium and insulin treatment on glycogen synthase (GS) activation in Zucker fatty rats. The GS fractional activity (GSFA), protein phosphatase-1 (PP1), and glycogen synthase kinase-3 (GSK-3) activity were determined in fatty and lean rats following treatment with bis(maltolato)oxovanadium(IV) (BMOV) for 3 weeks (0.2 mmol/kg/day) administered in drinking water. Skeletal muscle was freeze-clamped before or following an insulin injection (5 U/kg i.v.). In both lean and fatty rats, muscle GSFA was significantly increased at 15 min following insulin stimulation. Vanadium treatment resulted in decreased insulin levels and improved insulin sensitivity in the fatty rats. Interestingly, this treatment stimulated muscle GSFA by 2-fold (p < 0.05) and increased insulin-stimulated PP1 activity by 77% (p < 0.05) in the fatty rats as compared to untreated rats. Insulin resistance, vanadium and insulin in vivo treatment did not affect muscle GSK-3beta activity in either fatty or lean rats. Therefore, an impaired insulin sensitivity in the Zucker fatty rats was improved following vanadium treatment, resulting in an enhanced muscle glucose metabolism through increased GS and insulin-stimulated PPI activity.

Vanadium increases GLUT4 in diabetic rat skeletal muscle

The effect of vanadium in lowering blood glucose in diabetic animals is well established; however, the exact mechanism of action of vanadium still eludes us. There are several reports from in vitro studies indicating that vanadium increases enzyme activity in insulin signalling pathways; however, these findings have not been duplicated in vivo. Glucose transporters (GLUT) have a major role to play in any glucoregulatory effects. Insulin dependent GLUT4 is a major glucose transporter present in skeletal muscle, adipocytes and heart. In the present study we found that the plasma glucose in streptozotocin (STZ) diabetic animals was restored to normal following treatment with a single dose of BMOV, an organic vanadium compound, given by oral gavage (0.6 mmol/kg), similar to the response with chronic BMOV treatment. The response to BMOV by oral gavage was rapid and the animals were normoglycemic within 24 h of treatment and still demonstrated a significant effect even after 72 h. Using a specific antibody against GLUT4 we found an overall reduction in the GLUT4 in the total membrane fraction in skeletal muscle of diabetic animals. However, with a single dose of BMOV the GLUT4 level was restored to normal. This is the first report that establishes a direct effect of vanadium on the regulation of GLUT4 expression in diabetic animals in vivo, and may at least partially explain the glucoregulatory effects of vanadium.

Bis(maltolato)oxovanadium(IV) inhibits the activity of PTP1B in Zucker rat skeletal muscle in vivo

The insulin signalling pathway consists of a series of phosphorylation and dephosphorylation steps inside the target cell. Phosphotyrosine phosphatase 1B (PTP1B) dephosphorylates phosphotyrosine (pTyr) residues present on the insulin receptor (IR). In this study we examined the effect of bis(maltolato)oxovanadium(IV) (BMOV) on PTP1B and its possible role in the amelioration of insulin resistance. Fourteen to sixteen week old fatty Zucker rats (F), an animal model of insulin resistance, were treated with BMOV in drinking water for 3 weeks (FT) along with age matched lean littermate controls. The fatty rats responded to vanadium with a significant decrease in plasma insulin, (F = 5.1+/-0.8 FT = 3.3+/-0.7 ng/ml). During insulin resistance the activity of PTP1B has been shown to increase, thus diminishing insulin signalling in the target tissues. Hence, PTP1B is an important target for anti-diabetic drug research. In our investigation we found that the PTP1B activity was increased to 200% in the skeletal muscle of untreated Zucker fatty rats compared to lean littermates. Three weeks of BMOV treatment reduced the activity of PTP1B by 25% in fatty treated rats, in vivo, compared to untreated fatty rats. There was no significant change in the activity of PTP1B in the lean treated rats. There was also no difference in the gene expression of PTP1B in the skeletal muscle of different groups of rats. Vanadium compounds also inhibited PTP1B in vitro. These results indicate that PTP1B may be a potential target for the action of BMOV at least in the Zucker fatty rat model.