Long-term effects of vanadate treatment on glycogen metabolizing and lipogenic enzymes of liver in genetically diabetic (db/db) mice

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.

In Vivo Treatment Efficacy of Essential Oil Isolated from Seeds of Momordica charantia in Streptozotocin-Induced Diabetes Mellitus

BACKGROUND

All parts of Momordica charantia L. have potential hypoglycemic properties in reversing the metabolic disorder of diabetes mellitus. However, there exists a need for preparing an effective and safer formulation of active phytochemicals. We have also reviewed and analyzed certain patents on such preparatory methods for Momordica charantia L. formulations.

OBJECTIVE

This study aimed to isolate essential oil from the seeds of Momordica charantia L., analyze its phytochemicals, and study their anti-diabetic effects.

METHODS

The essential oil was isolated by the hydrodistillation method and analyzed for phytochemicals by GC-MS. Furthermore, its acute toxicity was tested in rats. Anti-diabetic effects were evaluated in Streptozotocin-induced diabetic rats with 17.5 and 55 mg/kg b.wt of essential oil by evaluating blood glucose, serum lipid profile, liver glycogen, protein, and other serum markers such as ALT, AST, ALP, urea, and creatinine. The histologic changes in the liver, pancreas, and kidney were evaluated using Haematoxylin and Eosin staining.

RESULTS

The phytochemicals having hypoglycaemic and insulin induction potency were identified in the GC-MS analysis. A highly significant (p≤0.01; p≤0.001) reduction in blood glucose was observed from 17.5 mg/kg and 55 mg/kg essential oil treatments, respectively. Diabetes-associated metabolic alterations (p≤0.001) observed in diabetic control rats such as lipid profile, enzymes, glycogen, protein, urea, and creatinine were normalized upon treatment with essential oil. Moreover, the histologic changes in vital organs reversed in treated rats.

CONCLUSION

The essential oil of Momordica charantia L. seed has promising potency to normalize the metabolic changes of type II diabetes mellitus.

Vanadium Compounds as Enzyme Inhibitors with a Focus on Anticancer Effects

Vanadium salts and coordination compounds have desirable cellular anticancer effects, and although they have been investigated in detail as a potential treatment for diabetes, less attention has been given to the anticancer effects. The inhibition of some signal transduction enzymes is known, and studies of the metabolism and activation pathways both in vitro and in vivo are important for future investigations and development of vanadium's role as a new potential drug. In addition, a new approach has demonstrated that the enhancement of oncolytic viruses using vanadium salts and coordination complexes for immunotherapy is very promising. Some differences exist between this approach and current antidiabetic and anticancer studies because vanadium(iv) complexes have been found to be most potent in the latter approach, but the few compounds investigated with oncolytic viruses show that vanadium(v) systems are more effective. We conclude that recent studies demonstrate effects on signal transduction enzymes and anticancer pathways, thus suggesting potential applications of vanadium as anticancer agents in the future both as standalone treatments as well as combination therapies.

Metformin-decavanadate treatment ameliorates hyperglycemia and redox balance of the liver and muscle in a rat model of alloxan-induced diabetes

MetfDeca treatment ameliorate glucose and insulin levels, and reduce the levels of oxidized glutathione, reactive oxygen species, malondialdehyde, and 4-hydroxyalkenal; the superoxide and catalase activities, and glutathione levels were regulated.

Antidiabetic effect of an extract of nutricultured Brassica napus containing vanadium from a Jeju water concentrate

The purpose of this study was to determine the antidiabetic effect of an extract of nutricultured Brassica napus containing vanadium (BECV). The BECV was prepared following nutriculture of B. napus with a Jeju water vanadium concentrate for 7 day. The BECV was administered to db/db mice for 8 weeks at different dosages (0.028, 0.14, and 0.7 μg/kg; as vanadium concentration in BECV). After 8 weeks, the BECV results showed mouse blood glucose concentrations to significantly decrease, in a dose-dependent manner, compared with the results for control mice. In addition, the concentrations of triglyceride, total cholesterol, and glycated hemoglobin were significantly lower after 8 weeks of administration of 0.7 μg/kg BECV. Therefore, the BECV may have protective effects against type 2 diabetes.

Toxicological Evaluation of Brassica napus Extract Containing Vanadium, Nutricultured in Jeju Water

This study evaluated the mutagenicity and acute toxicity of the juice extract of nutricultured Brassica napus containing vanadium (BECV). The BECV was prepared by nutriculture for 7 days in Jeju water containing vanadium. The mutagenic effects of BECV were investigated using the bacterial reverse mutation test, chromosome aberration test, and micronucleus test. Based on the results of the mutagenicity test, we propose that BECV is not a mutagenicity-inducing agent. In the acute oral toxicity study, male and female Sprague-Dawley rats were administered a single limiting dose of 0.014, 0.14, or 1.4 μg BECV/kg body weight; the rats were then observed for 7 days. No acute lethal effect was observed at the maximal dose of 1.4 μg BECV/kg body weight. In the subacute study, male and female rats were administered once daily, by oral gavage, a dose of 0.028, 0.14, and 0.7 μg/kg body weight of BECV for 28 days. No significant toxicity was observed not only hematological, biochemical, and pathological parameters but also the body and organ weights when compared to controls. The level of BECV with no observed adverse effects in male and female rats was 0.7 μg/kg body weight (concentration of vanadium in BECV) in the subacute toxicity study.

[The vanadium compounds: chemistry, synthesis, insulinomimetic properties]

The review considers the biological role of vanadium, its participation in various processes in humans and other mammals, and the anti-diabetic effect of its compounds. Vanadium salts have persistent hypoglycemic and antihyperlipidemic effects and reduce the probability of secondary complications in animals with experimental diabetes. The review contains a detailed description of all major synthesized vanadium complexes having antidiabetic activity. Currently, vanadium complexes with organic ligands are more effective and safer than the inorganic salts. Despite the proven efficacy of these compounds as the anti-diabetic agents in animal models, only one organic complex of vanadium is currently under the second phase of clinical trials. All of the considered data suggest that vanadium compound are a new promising class of drugs in modern pharmacotherapy of diabetes.

Improvement of hyperglycaemia and metabolic syndromes in type 2 diabetic KKAy mice by oral treatment with [meso-tetrakis(4-sulfonatophenyl) porphyrinato]oxovanadium(IV)(4-) complex

Recently, we reported that [meso-tetrakis(4-sulfonatophenyl)porphyrinato]oxovanadium(IV)(4-), VO(tpps), shows in-vitro insulin-mimetic and in-vivo anti-diabetic activity in streptozotocin (STZ)-induced type 1 diabetic mice. This result prompted us to examine its ability in type 2 diabetic model KKAy mice with insulin resistance. We studied the in-vivo anti-diabetic activity of VO(tpps), compared with that of vanadium(IV) oxide sulfate, VS, as control. Both compounds were orally administered at doses of 5–10 mg (0.1-0.2 mmol) V/kg body weight to the KKAy mice for 28 days. VO(tpps) normalized the hyperglycaemia within 15 days, while VS lowered the blood glucose concentration only by a small degree. In addition, metabolic syndromes characterized by insulin and leptin resistance were significantly improved in VO(tpps)-treated KKAy mice compared with those treated with VS. The improvement in diabetes was validated by oral glucose tolerance test and decrease in HbA1c concentration. Based on these observations, VO(tpps) is proposed to be an orally active oxovanadium(IV)-porphyrin complex for treating not only type 2 diabetes but also metabolic syndromes in animals.

Potential role of N-myristoyltransferase in pathogenic conditions

N-Myristoyltransferase (NMT) is the enzyme that catalyzes the covalent transfer of myristic acid to the N-terminal glycine residue of a protein substrate. In this review article, I summarize that NMT may have a potential role in cardiac muscle in the experimentally induced ischemia-reperfusion rat model and also in the streptozotoein-induced diabetic rat. Both the expression and activity of NMT were increased by ischemia-reperfusion. Immunohistochemical studies showed cytosolic localization of NMT in normal rat heart and predominant nuclear localization after ischemia followed by reperfusion. However, the localization of NMT is reversed by treatment with a calpain inhibitor (ALLM N-Ac-Leu-Leu-methioninal). During ischemia-reperfusion, the degradation of c-Src, which is a substrate of NMT, was observed. These findings suggested that the Src signaling may be impaired in ischemia-reperfusion owing to the altered localization of NMT from cytoplasm to nucleus. Streptozotocin-induced diabetes (an animal model for insulin-dependent diabetes mellitus) resulted in a 2.0-fold increase in rat liver NMT activity as compared with control animals. In obese (fa/fa) Zucker rats (an animal model for non-insulin-dependent diabetes mellitus), there was an approximately 4.7-fold lower liver particulate NMT activity as compared with control lean rat livers. Administration of sodium orthovanadate to the diabetic rats normalized liver NMT activity. These results would indicate that rat liver particulate NMT activity appears to be inversely proportional to the level of plasma insulin, implicating insulin in the control of N-myristoylation. These are the first studies demonstrating the role of NMT in the pathogenesis of ischemia-reperfusion and diabetes mellitus. These conditions remain an important area of investigation.

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.

Amelioration of insulin resistance in diabetic ob/ob mice by a new type of orally active insulin-mimetic vanadyl complex: bis(1-oxy-2-pyridinethiolato)oxovanadium(IV) with VO(S(2)O(2)) coordination mode

Recently, we have shown that a newly synthesized vanadyl complex, bis(1-oxy-2-pyridinethiolato)oxovanadium(IV), VO(opt)(2), is a potent orally active insulin-mimetic in treating streptozotocin-induced diabetes in rats, with long-term action. In the present study, the anti-diabetic effect of VO(opt)(2) and its mechanism in ob/ob mice, an obese non-insulin-dependent diabetes mellitus (NIDDM) animal model, was investigated. In ob/ob mice, 15-day oral treatment with VO(opt)(2) resulted in a dose-dependent decrease in the levels of glucose, insulin and triglyceride in blood. VO(opt)(2) was also effective in ameliorating impaired glucose tolerance in ob/ob mice, when an oral glucose tolerance test was performed after treatment with VO(opt)(2). Tumor necrosis factor-alpha (TNF-alpha) is a key component of obesity-diabetes link, we therefore examined the attenuating effect of VO(opt)(2) on impaired insulin signal transduction induced by TNF-alpha. Elevated expression of TNF-alpha was observed in the epididymal and subcutaneous fat tissues of ob/ob mice. Incubation of 3T3-L1, mouse adipocytes, with TNF-alpha reduced the phosphorylation of insulin receptor substrate-1 (IRS-1), whereas VO(opt)(2) treatment resulted in an enhancement of IRS-1 phosphorylation, irrespective of the presence or absence of TNF-alpha. Overall, the present study demonstrates that VO(opt)(2) exerts an anti-diabetic effect in ob/ob mice by ameliorating impaired glucose tolerance, and furthermore, attenuates the TNF-alpha-induced decrease in IRS-1 phosphorylation in adipocytes. These results suggest that the anti-diabetic action of VO(opt)(2) is derived from an attenuation of a TNF-alpha induced impaired insulin signal transduction via inhibition of protein tyrosine phosphatase, providing a potential clinical utility for VO(opt)(2) in the treatment of NIDDM.

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.

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.

Treatment of diabetes with vanadium salts: general overview and amelioration of nutritionally induced diabetes in the Psammomys obesus gerbil

BACKGROUND

Numerous investigations have demonstrated the beneficial effect of vanadium salts on diabetes in streptozotocin (STZ)-diabetic rats, in rodents with genetically determined diabetes and in human subjects. The amelioration of diabetes included the abolition of hyperglycemia, preservation of insulin secretion, reduction in hepatic glucose production, enhanced glycolysis and lipogenesis and improved muscle glucose uptake through GLUT4 elevation and translocation. The molecular basis of vanadium salt action is not yet fully elucidated. Although evidence has been provided that the insulin receptor is activated, the possibility exists that cytosolic non-receptor tyrosine kinase, direct phosphorylation of IRS-1 and activation of PI3-K, leading to GLUT4 translocation, are involved. The raised phosphorylation of proteins in the insulin signaling pathway appears to be related to the inhibition of protein tyrosine phosphatase (PTPase) activity by vanadium salts.

NOVEL EXPERIMENTS

The model utilized in our study was Psammomys obesus (sand rat), a desert gerbil which becomes hyperglycemic and hyperinsulinemic on an ad libitum high energy (HE) diet. In contrast to the previously investigated insulin deficient models, vanadyl sulphate was used to correct insulin resistance and hyperinsulinemia, which led to beta-cell loss. Administration of 5 mg/kg vanadyl sulfate for 5 days resulted in prolonged restoration of normoglycemia and normoinsulinemia in most animals, return of glucose tolerance to normal, and a reduction of hepatic phosphoenolpyruvate carboxykinase activity. There was no change in food consumption and in regular growth during or after the vanadyl treatment. Pretreatment with vanadyl sulfate, followed by transfer to a HE diet, significantly delayed the onset of hyperglycemia. Hyperinsulinemic-euglycemic clamp of vanadyl sulfate treated Psammomys demonstrated an improvement in glucose utilization. However, vanadyl sulfate was ineffective when administered to animals which lost their insulin secretion capacity on protracted HE diet, but substantially reduced the hyperglycemia when given together with exogenous insulin. The in vitro insulin activation of liver and muscle insulin receptors isolated from vanadyl treated Psammomys was ineffective. The in vivo vanadyl treatment restored muscle GLUT4 total protein and mRNA contents in addition to membrane GLUT4 protein, in accordance with the increased glucose utilization during the clamp study. These results indicate that short-term vanadyl sulfate treatment corrects the nutritionally induced, insulin resistant diabetes. This action requires the presence of insulin for its beneficial effect. Thus, vanadyl action in P. obesus appears to be the result of insulin potentiation rather than mimicking, with activation of the signaling pathway proteins leading to GLUT4 translocation, probably distal to the insulin receptor.

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.

N-myristoyltransferase

Myristoylation refers to the co-translational addition of a myristoyl group to an amino-terminal glycine residue of a protein by an ubiquitously distributed enzyme myristoyl-CoA:protein N-myristoyltransferase (NMT, EC 2.3.1.97). This review describes the basic enzymology, molecular cloning and regulation of NMT activity in various pathophysiological processes such as colon cancer and diabetes.

Vanadium and diabetes

Vanadium is an ultratrace element, widely distributed in nature, yet with no presently known specific physiological function in mammals. The apparent role of vanadium in regulation of intracellular signaling, as a cofactor of enzymes essential in energy metabolism, and as a possible therapeutic agent in diabetes is of increasing interest as more and more research reports present evidence of vanadium's potentially unique biological function. In this mini-review, the author summarizes current knowledge of the bioinorganic chemistry of vanadium, the basic features of diabetes mellitus and its metabolic sequelae, and the in vitro and in vivo effects of both inorganic and organically-chelated vanadium compounds. Results of clinical trials to date, as well as kinetic studies of tissue uptake are covered. Examples of ways to enhance the positive effects of vanadium as an oral therapeutic adjunct in diabetic control, while minimizing potential toxicity, are compared with regard to desirable features and possible drawbacks.

Stimulation of 125I-transferrin binding and 59Fe uptake in rat adipocytes by vanadate: treatment time determines apparent tissue sensitivity

Vanadium compounds have been documented to stimulate a number of insulin biological effects in vitro and in vivo. We previously demonstrated stimulation of glucose transport and insulin-like growth factor-II (IGF-II) binding in rat adipocytes. These actions are associated with translocation of glucose transporters and IGF-II receptors from an intracellular compartment to the plasma membrane. The transferrin receptor is also recruited to the plasma membrane in response to insulin. Freshly isolated rat adipocytes were incubated with vanadate and insulin at 37 degrees C, and after treating the cells with KCN to inhibit further receptor movement, diferric 125I-transferrin binding was assayed. Vanadate stimulated a dose- and time-dependent increase in 125I-transferrin binding, reaching maximum (approximately threefold) stimulation at 1 mmol/L after a 4-hour incubation. This was equivalent to the maximum insulin effect that was obtained with 10(-8) mol/L after 30 minutes. A similar degree of stimulation was achieved with 0.1 mmol/L vanadate after 8 hours of exposure. Dose-response data showed that the apparent sensitivity to vanadate was time-dependent and increased with the duration of exposure (EC50: 30 minutes, 1 mmol/L; 3 hours, 0.35 mmol/L). Scatchard analysis of 125I-transferrin binding showed that both insulin and vanadate increased receptor binding capacity with no effect on receptor affinity. Total cellular transferrin receptor content measured by immunoblotting with monoclonal anti-transferrin receptor antibody (OX-26) was not altered by insulin or vanadate, consistent with receptor translocation. Assessment of 59Fe uptake from 59Fe-labeled diferric transferrin showed that vanadate augmented 59Fe uptake in a dose-dependent manner to an extent similar to insulin, demonstrating the functional activity of the receptors (percent of control: 10(-8) mol/L insulin, 175% +/- 23.8%, P < .02; 0.3 mmol/L vanadate, 188% +/- 17.3%, P < .01). We conclude that vanadate mimics insulin to augment cell surface transferrin receptors and increase Fe uptake in rat adipocytes. The time-dependent apparent increase in sensitivity is consistent with the effectiveness of very low concentrations of vanadate in vivo after several days of administration, and suggests a requirement for vanadate entry into cells to mediate this biological response.

Vanadyl sulphate differently influences insulin response to glucose in isolated pancreas of normal rats after in vivo or in vitro exposure

The effect of the antidiabetic agent vanadyl sulphate (VOSO4) on the endocrine pancreas function of normal rats was studied using the isolated pancreas preparation. A short-term (8 days) i.p. treatment (15 mg/kg per day) resulted in attenuation of high glucose-stimulated insulin release, at day 9 but also at days 19, i.e., after full recovery of appetite and weight, while blood and pancreas vanadium concentrations were still elevated. Six months of oral VOSO4 treatment (0.75 mg/ml in drinking water) resulted in elevated vanadium concentrations while glucose-stimulated insulin release was attenuated as compared to pair-fed animals. Conversely, when directly perfused in pancreas, VOSO4 potentiated glucose-stimulated insulin release. These apparently opposite effects may be related to the ability of VOSO4 to exert both peripheral insulinomimetic effects-leading to chronic reduction in insulin demand-, and a direct pancreatic insulinotropic activity.

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.

Modulation of insulin action by vanadate: evidence of a role for phosphotyrosine phosphatase activity to alter cellular signaling

A number of vanadium compounds (vanadate, vanadyl sulfate, metavanadate) have insulin-mimicking actions both in vitro and in vivo. They have multiple biological effects in cultured cells and interact directly with various enzymes. The inhibitory action on phosphoprotein tyrosine phosphatases (PTPs) and enhancement of cellular tyrosine phosphorylation appear to be the most relevant to explain the ability to mimic insulin. We demonstrated that in rat adipocytes both acute insulin effects, e.g. stimulation of IGF-II and transferrin binding and a chronic effect, insulin receptor downregulation, were stimulated by vanadate. Vanadate also enhanced insulin binding, particularly at very low insulin concentrations, associated with increased receptor affinity. This resulted in increased adipocyte insulin sensitivity. Finally vanadate augmented the extent of activation of the insulin receptor kinase by submaximal insulin concentrations. This was associated with a prolongation of the insulin biological response, lipogenesis, after removal of hormone.

IN CONCLUSION

in rat adipocytes vanadate promotes insulin action by three mechanisms, 1) a direct insulin-mimetic action, 2) an enhancement of insulin sensitivity and 3) a prolongation of insulin biological response. These data suggest that PTP inhibitors have potential as useful therapeutic agents in insulin-resistant and relatively insulin-deficient forms of diabetes mellitus.

Vanadate induces normolipidemia and a reduction in the levels of hepatic lipogenic enzymes in obese Zucker rat

The effects of vanadate administration on the plasma lipids and hepatic lipogenic enzymes were investigated in Zucker (fa/fa) rat, a model for obesity and non insulin-dependent diabetes. These animals were administered sodium orthovanadate through drinking water for a period of four months. The plasma levels of insulin, triacylglycerols and total cholesterol were significantly (p < 0.001) elevated in untreated obese control rats as compared to the lean animals. In the livers of obese rats, the number of insulin receptors decreased by 60% and the activities of lipogenic enzymes acetyl-CoA carboxylase and ATP-citrate lyase increased by 4.7- and 5.6-folds, respectively. The messenger RNA for ATP-citrate lyase as measured by Northern blot analysis showed a parallel increase in obese control rats. Treatment of these rats with vanadate caused 56-77% decreases in the plasma levels of insulin, triacylglycerols and total cholesterol. The insulin receptor numbers in vanadate-treated obese rats increased (119%) compared to levels in untreated obese animals. The elevated activities of acetyl-CoA carboxylase and ATP-citrate lyase observed in livers of obese rats were significantly reduced by vanadate. The messenger RNA for ATP-citrate lyase also decreased in vanadate-treated obese rats back to the lean control levels. This study demonstrates that vanadate exerts potent actions on lipid metabolism in diabetic animals in addition to the recognized effects on glucose homeostasis.

In vivo modulation of N-myristoyltransferase activity by orthovanadate

N-Myristoyltransferase (NMT) catalyses the transfer of myristate from myristoyl-CoA to the NH2-terminal glycine residue of several proteins and are important in signal transduction. STZ-induced diabetes (an animal model for insulin-dependent diabetes mellitus, IDDM) resulted in a 2-fold increase in rat liver NMT activity as compared with control animals. In obese Zucker (fa/fa) rats (an animal model for non-insulin dependent diabetes mellitus, NIDDM) there was a approximately 4.7-fold lower liver particulate NMT activity as compared with the control lean rat livers. Administration of sodium orthovanadate to the diabetic rats normalised liver NMT activity. These results would indicate that the rat liver particulate N-myristoyltransferase activity appears to be inversely proportional to the level of plasma insulin, implicating insulin in the control of N-myristoylation.

In vivo effects of vanadate on hepatic glycogen metabolizing and lipogenic enzymes in insulin-dependent and insulin-resistant diabetic animals

The insulin-mimetic action of vanadate is well established but the exact mechanism by which it exerts this effect is still not clearly understood. The role of insulin in the regulation of hepatic glycogen metabolizing and lipogenic enzymes is well known. In our study, we have, therefore, examined the effects of vanadate on these hepatic enzymes using four different models of diabetic and insulin-resistant animals. Vanadate normalized the blood glucose levels in all animal models. In streptozotocin-induced diabetic rats, the amount of liver glycogen and the activities of the active-form of glycogen synthase, both active and inactive-forms of phosphorylase, and lipogenic enzymes like glucose 6-phosphate dehydrogenase and malic enzyme were decreased and vanadate treatment normalized all of these to near normal levels. The other three animal models (db/db mouse, sucrose-fed rats and fa/fa obese Zucker rats) were characterized by hyperinsulinemia, hypertriglyceridemia, increases in activities of lipogenic enzymes, and marginal changes in glycogen metabolizing enzymes. Vanadate treatment brought all of these values towards normal levels. It should be noted that vanadate shows differential effects in the modulation of lipogenic enzymes activities in type I and type II diabetic animals. It increases the activities of lipogenic enzymes in streptozotocin-induced diabetic animals and prevents the evaluation of activities of these enzymes in hyperinsulinemic animals. The insulin-stimulated phosphorylation of insulin receptor beta subunit and its tyrosine kinase activity was increased in streptozotocin-induced diabetic rats after treatment with vanadate. Our results support the view that insulin receptor is one of the sites involved in the insulin-mimetic actions of vanadate.

Decrease in protein tyrosine phosphatase activities in vanadate-treated obese Zucker (fa/fa) rat liver

The inhibitory action of vanadate towards protein tyrosine phosphatase (PTPase) has been considered as a probable mechanism by which it exerts insulin-like effects. In this study, we have examined the in vivo effects of vanadate on PTPases in the liver of obese Zucker rats, a genetic animal model for obesity and type II diabetes. These animals were characterized by hyperinsulinemia and mild hyperglycemia. The number of insulin receptors were significantly (p < 0.01) decreased in liver. After chronic administration of vanadate in obese rats, 80% decrease in the plasma levels of insulin was observed. The insulin receptor numbers were significantly (p < 0.01) higher in vanadate-treated obese rats as compared to the untreated ones. The hepatic PTPase activities in cytosolic and particulate fractions, with phosphorylated poly glu:tyr (4:1) and the insulin receptor peptide (residues 1142-1153) as substrates, increased in obese rats. In vanadate-treated obese rat livers, the PTPase activities in both subcellular fractions with these substrates decreased significantly (p < 0.001). The decreases in PTPase activities from these groups of rats were further supported by chromatography on a Mono Q column. These data support the view that inhibition of PTPases plays a role in the insulin-mimetic action of vanadate.

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

Effect of several vanadium salts, sodium orthovanadate, vanadyl sulfate and sodium metavanadate on protein tyrosine phosphorylation and serine/threonine kinases in chinese hamster ovary (CHO) cells overexpressing a normal human insulin receptor was examined. All the compounds stimulated protein tyrosine phosphorylation of two major proteins with molecular masses of 42 kDa (p42) and 44 kDa (p44). The phosphorylation of p42 and p44 was associated with an activation of mitogen activated protein (MAP) kinase as well as increased protein tyrosine phosphorylation of p42mapk and p44mapk. Vanadium salts also activated the 90 kDa ribosomal s6 kinase (p90rsk) and 70 kDa ribosomal s6 kinase (p70s6k). Among the three vanadium salts tested, vanadyl sulfate appeared to be slightly more potent than others in stimulating MAP kinases and p70s6k activity. It is suggested that vanadium-induced activation of MAP kinases and ribosomal s6 kinases may be one of the mechanisms by which insulin like effects of this trace element are mediated.

Effects of vanadate on the expression of genes involved in fuel homeostasis in animal models of Type I and Type II diabetes

Vanadium is a trace element that has raised increasing interest in diabetology since the discovery of its insulin-like properties in vitro and in vivo. This brief article reviews the most recent data concerning the beneficial effects of vanadium compounds on fuel homeostasis in animal models of insulinopenic (Type I) or insulin-resistant (Type II) diabetes. These studies open obvious therapeutic possibilities in diabetes, and more particularly, in states of insulin resistance.

Long-term correction of STZ-diabetic rats after short-term i.p. VOSO4 treatment: persistence of insulin secreting capacities assessed by isolated pancreas studies

We have previously shown that 3 week oral VOSO4 treatment of streptozotocin (STZ, 60 mg/kg)-induced diabetic rats was able to correct diabetes for 13 weeks after treatment withdrawal. In the present study, we investigated whether a short-term (8 days) i.p. VOSO4 treatment was similarly able to reverse the diabetic state. Insulin secretory capacities were assessed at distance of treatment using the isolated pancreas preparation. Seven treatment-groups were performed: high dose VOSO4-treated diabetics (HVD, 1.3 mM/kg/8 days), food-restricted diabetics (FRD, food adjusted to HVD levels), low dose VOSO4-treated diabetes (LVD, 0.06 mM/kg/day), insulin-treated diabetics (ID, dose adjusted to normalize glycaemia) and VOSO4 (0.06 mM/kg/day) + insulin (dose adjusted to normalize glycaemia in the presence of vanadium)-treated diabetics (IVD), in addition to the corresponding untreated non-diabetic controls (C) and diabetics (D). Our results indicate that long-term correction of diabetes (a) can be obtained after an 8 day treatment using i.p. VOSO4 in diabetic animals retaining some degree of pancreatic function, (b) is not obtained with insulin treatment or food restriction although the association of VOSO4 and insulin was found beneficial, (c) can be prolonged in some individuals for at least 4 months, i.e. in conditions such that tissue vanadium concentrations had returned to values close to pre-treatment levels, (d) is associated with improved and in some cases normalized insulin secretion from isolated pancreas. The protective or corrective role of VOSO4 on diabetes-related pancreatic alterations, as well as the potential of the VOSO4-insulin association should be further studied in view of the possible use of vanadium derivatives in the treatment of diabetes.

Evidence of multiple metabolic routes in vanadium's effects on layers. Ascorbic acid differential effects on prepeak egg production parameters following prolonged vanadium feeding

The development of V toxicity was followed over a 28-d period in 25-wk-old Leghorn layers fed 20 mg ammonium metavanadate/kg diet (Days 1 to 14) followed by 30 mg/kg diet (Days 15 to 28). Then, over a second 28-d period, the responses to V and supplemental ascorbic acid (AA) fed at 500 or 1,000 mg/kg diet (Days 29 to 42) followed by 1,500 or 3,000 mg/kg diet (Days 43 to 56) were examined. Feed consumption, egg weight, Haugh units (HU), and BW measurements indicated that the response to V was multifactorial, but of differing intensities and time-frames for the variables. Haugh units were lowered rapidly (3 d, P < .05) in response to V feeding, but HU values decreased only slightly when dietary V was increased to 30 mg/kg. In contrast, egg production was decreased moderately by 20 mg V/kg and a considerable further reduction in egg production resulted from increasing the V to 30 mg/kg. Ascorbic acid supplementation differentially affected these responses: BW, egg production, and egg weight were improved significantly in the V-fed group receiving an AA supplement, as compared with those fed V only. Haugh unit values, however, were not improved by AA supplementation in groups receiving V. Foam functional properties, which also were changed by V feeding, were not corrected by AA feeding. The results suggest that the toxic effects of V are mediated through more than one physiological mechanism. One mechanism, which includes negative effects on BW, egg production, and egg weight, is responsive to the additional reducing equivalents provided by supplemental AA. Another mechanism, which is apparent from the effect of V on egg HU values, is not ameliorated by AA supplementation after toxicity developed.

Activation of mitogen activated protein (MAP) kinases by vanadate is independent of insulin receptor autophosphorylation

Treatment of Chinese hamster ovary (CHO) cells over-expressing the human insulin receptor (CHO-HIRc) with the insulin mimetic agent, vanadate, resulted in a dose- and time-dependent tyrosine phosphorylation of two proteins with apparent molecular sizes of 42 kDa (p42) and 44 kDa (p44). However, vanadate was unable to stimulate the tyrosyl phosphorylation of the beta-subunit of the insulin receptor. By using myelin basic protein (MBP) as the substrate to measure mitogen-activated protein (MAP) kinase activity in whole cell lysates, vanadate-stimulated tyrosyl phosphorylation of p42 and p44 was associated with a dose- and time-dependent activation of MAP kinase activity. Furthermore, affinity purification of cell lysates on anti-phosphotyrosine agarose column followed by immunoblotting with a specific antibody to MAP kinases demonstrated that vanadate treatment increased the tyrosyl phosphorylation of both p44mapk and p42mapk by several folds, as compared to controls, in concert with MAP kinase activation. In addition, retardation in gel mobility further confirmed that vanadate treatment increased the phosphorylation of p44mapk and p42mapk in CHO-HIRc. A similar effect of vanadate on MAP kinase tyrosyl phosphorylation and activation was also observed in CHO cells over-expressing a protein tyrosine kinase-deficient insulin receptor (CHO-1018). These results demonstrate that the protein tyrosine kinase activity of the insulin receptor may not be required in the signaling pathways leading to the vanadate-mediated tyrosyl phosphorylation and activation of MAP kinases.

Diabetes can be prevented by reducing insulin production

Hypersecretion of insulin increases the chance of the incidence of diabetes type I and II, while inhibiting insulin secretion helps prevent diabetes. Trace elements like zinc and vanadium prevent hyperinsulinemia, partly because of their own insulin activity, which is also a property of interleukin-1 (IL-1), particularly during periods of illness and stress. Like vanadium, IL-1 can replace insulin for many hours and regulate glucose metabolism. Vanadium, zinc and IL-1 ensure that insulin-producing beta-cells in the pancreas do not lose too much zinc, which leaves the beta-cells together with insulin. Zinc forms a complex with metallothionein in beta-cells that provides protection against free (oxygen) radicals, which become active during immune responses triggered by bacteria and viruses, for instance. In addition, zinc is the only non-toxic trace element in the body that regulates concentration-dependent immune responses on many levels. Avoiding deficiencies of trace elements will enable the reduction of the incidence of diabetes.

Does the insulin-mimetic action of vanadate involve insulin receptor kinase?

Effects of vanadate administration on the insulin receptor status in liver were examined in streptozotocin-induced diabetic rats. Diabetic rats were characterized by hyperglycemia (4-fold increase), hypoinsulinemia (81% decrease) and a significant (P < 0.01) increase in hepatic insulin receptor numbers. Autophosphorylation of the beta subunit of insulin receptor and its tyrosine kinase activity towards the synthetic peptide (poly glut4tyr1) decreased by approximately 60% as a result of diabetes. After chronic treatment of these rats with sodium orthovanadate, the plasma glucose levels were normalized to near control values with the hypoinsulinemia remaining unaltered. The insulin-stimulated phosphorylation of the beta subunit increased significantly (P < 0.001) in diabetic rats after treatment with vanadate. However, the improvement in the tyrosine kinase activity was marginal. In vitro, vanadate prevented the dephosphorylation of the phosphorylated insulin receptor and increased its tyrosine kinase activity in the absence as well as presence of insulin. The findings of this study further support the view that insulin receptor is one of the sites involved in the insulin-mimetic actions of vanadate.

Non-insulin-like action of sodium orthovanadate in the isolated perfused liver of fed, non-diabetic rats

Vanadium compounds exert insulin-like effects on isolated rat adipocytes and skeletal muscle and improve glucose homeostasis in diabetic rats and mice. However, reports on metabolic actions of vanadium in the liver are still contradictory. Thus, the acute effect of sodium orthovanadate infusion on net glucose production was measured in isolated perfused livers of non-fasting, non-diabetic rats. Continuous infusion (0.2 ml/min; 90 min) of vanadate (10-500 mumol/l) rapidly increased hepatic glucose (p < 0.001), but not cyclic AMP output, reaching peak values after 20 min. The cumulative glucose release displayed concentration dependence with a maximal net effect of 394.3 mumol/100 g body weight and an apparent half-maximal effective vanadate concentration of 19.6 mumol/l. The glycogenolytic response to vanadate was almost completely blocked by 100 mU/l insulin (p < 0.005), by 0.1 mmol/l indomethacin (p < 0.05) and in the absence of Ca2+ (p < 0.001). These results indicate that sodium orthovanadate stimulates glycogenolysis in livers of fed, non-diabetic rats by a Ca(2+)-dependent mechanism, which may involve the release of prostaglandins.

Effects of vanadate administration on the high sucrose diet-induced aberrations in normal rats

Effects of feeding sucrose rich diet supplemented with and without the insulinmimetic agent vanadate for a period of six weeks were studied in rats. Sucrose diet caused hypertriglyceridemia (140% increase), hyperinsulinemia (120% increase) and significant elevations in the levels of glucose (p < 0.001) and cholesterol (p < 0.05) in plasma as compared to control starch fed rats. Activities of hepatic lipogenic enzymes, ATP-citrate lyase, glucose 6-phosphate dehydrogenase and malic enzyme increased by 100-150% as a result of sucrose feeding. However, glycogen content and the activities of glycogen synthase and phosphorylase in liver remained unaltered in these animals. The plasma levels of triacylglycerols and insulin in the rats fed on vanadate supplemented sucrose diet were 65% and 85% less, respectively as compared to rats on sucrose diet without vanadate. The concentrations of glucose and cholesterol in plasma and the activities of lipogenic enzymes in liver did not show any elevation in sucrose fed rats when supplemented with vanadate. These data indicate that the sucrose diet-induced metabolic aberrations can be prevented by the insulin-mimetic agent, vanadate.

Effects of high sucrose diet on insulin-like effects of vanadate in diabetic rats

The insulin-like effects of vanadate were compared in streptozotocin-induced diabetic rats fed on high starch control and high sucrose diets for a period of six weeks. Diabetic rats in both diet groups were characterized by hypoinsulinemia, hyperglycemia (6.8-7.0 fold increase) and significant decreases (p < 0.001) in the activities of glycogen synthase, phosphorylase and lipogenic enzymes, ATP-citrate lyase, glucose 6-phosphate dehydrogenase and malic enzyme in liver. There were no diet-dependent differences in these abnormalities. However, the insulin-mimetic agent vanadate was more effective in diabetic rats fed sucrose diet as compared to animals fed control starch diet. Vanadate administration resulted in 30% and 64% decreases in plasma glucose levels in diabetic rats fed control and sucrose diets, respectively. The activities of glycogen synthase (active) and phosphorylase (active and total) were restored significantly by vanadate in control (p < 0.05-0.01) and sucrose (p < 0.001) diets fed diabetic rats. This insulin-mimetic agent increased the activities of hepatic lipogenic enzymes in control diet fed rats to 38-47% of normal levels whereas in sucrose fed group it completely restored the activities. Sucrose diet caused a distinct effect on the plasma levels of triacylglycerol (4-fold increase) and apolipoprotein B (2.8-fold increase) in diabetic rats and vanadate supplementation decreased their levels by 65-75%. These data indicate that vanadate exerts insulin-like effects in diabetic rats more effectively in sucrose fed group than the animals fed control diet. In addition, vanadate also prevents sucrose-induced hypertriglyceridemia.

Vanadate potentiates the glycogenic action of insulin-like growth factors on isolated diaphragm

Na3VO4 (6.5 mumol/100 g rat weight), co-injected with a trace amount of [14C]glucose, increased within 15 min the incorporation of radiolabel in diaphragmal glycogen. After 2 h the vanadate-induced increases were 12-fold in the diaphragm and 7-8-fold in heart and liver. In contrast, when added to isolated diaphragms for up to 1 h, vanadate (0.1-5 mM) had no effect on the synthesis of glycogen from 5 mM glucose. In search of a putative mediator of vanadate's action in vivo, insulin and the insulin-like growth factors (IGFs) were considered. Their plasma concentration was not affected by vanadate treatment. In isolated diaphragms, 1 mM vanadate did not potentiate insulin-induced glycogen synthesis, but it caused a several-fold increase in glycogen synthesis in the presence of concentrations of IGF-I which, alone, had no effect. A similar synergism occurred between vanadate and IGF-II. We propose that the glycogenic action of vanadate in vivo, at least in some tissues, involves a potentiation of the action of IGF-I.