In vivo effects of vanadium on GLUT4 translocation in cardiac tissue of STZ-diabetic rats

Elucidating the Therapeutic Potential of Bis(Maltolato)OxoVanadium(IV): The Protective Role of Copper in Cellular Metabolism

Vanadium (V) is a trace mineral whose biological activity, role as a micronutrient, and pharmacotherapeutic applications remain unknown. Over the last years, interest in V has increased due to its potential use as an antidiabetic agent mediated by its ability to improve glycemic metabolism. However, some toxicological aspects limit its potential therapeutic application. The present study aims to evaluate the effect of the co-treatment with copper (Cu) and bis(maltolato)oxovanadium(IV) (BMOV) as a possible strategy to reduce the toxicity of BMOV. Treating hepatic cells with BMOV reduced cell viability under the present conditions, but cell viability was corrected when cells were co-incubated with BMOV and Cu. Additionally, the effect of these two minerals on nuclear and mitochondrial DNA was evaluated. Co-treatment with both metals reduced the nuclear damage caused by BMOV. Moreover, treatment with these two metals simultaneously tended to reduce the ND1/ND4 deletion of the mitochondrial DNA produced with the treatment using BMOV alone. In conclusion, these results showed that combining Cu and V could effectively reduce the toxicity associated with V and enhance its potential therapeutic applications.

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.

Anti-hyperglycaemic effects of dioxidovanadium complex cis-[VO2(obz)py] avert kidney dysfunction in streptozotocin-induced diabetic male Sprague-Dawley rats

Despite the success of antidiabetic drugs in alleviation of hyperglycaemia, diabetic complications, including renal dysfunction, continue to be a burden. This raises the need to seek alternative therapies that will alleviate these complications. Accordingly, the aim of this study was to investigate the effects of dioxidovanadium(V) complex cis-[VO2(obz)py] on renal function in diabetic rats. Streptozotocin-induced diabetic rats were treated with cis-[VO2(obz)py] (40 mg·kg-1) twice every third day for five weeks. Diabetic untreated and insulin-treated rats served as the diabetic control and positive control, respectively. Blood glucose concentrations, water intake, urinary output, and mean arterial pressure (MAP) were monitored weekly for five weeks. Rats were then euthanized, and blood and kidney tissues were collected for biochemical analysis. Significant decreases in blood glucose concentrations, MAP, glomerular filtration rate (GFR), and SGLT2 expression, as well as plasma angiotensin and aldosterone concentrations, were observed in the treated groups compared with the diabetic control. The complex also increased urinary glucose concentrations, antioxidant enzymes GPx and SOD concentrations, and decreased MDA concentrations and kidney injury molecule (KIM-1) concentrations. These findings suggest that the anti-hyperglycaemic effects of this vanadium complex may ameliorate kidney dysfunction in diabetes.

Vanadium in Biosphere and Its Role in Biological Processes

Ultra-trace elements or occasionally beneficial elements (OBE) are the new categories of minerals including vanadium (V). The importance of V is attributed due to its multifaceted biological roles, i.e., glucose and lipid metabolism as an insulin-mimetic, antilipemic and a potent stress alleviating agent in diabetes when vanadium is administered at lower doses. It competes with iron for transferrin (binding site for transportation) and with lactoferrin as it is secreted in milk also. The intracellular enzyme protein tyrosine phosphatase, causing the dephosphorylation at beta subunit of the insulin receptor, is inhibited by vanadium, thus facilitating the uptake of glucose inside the cell but only in the presence of insulin. Vanadium could be useful as a potential immune-stimulating agent and also as an antiinflammatory therapeutic metallodrug targeting various diseases. Physiological state and dose of vanadium compounds hold importance in causing toxicity also. Research has been carried out mostly on laboratory animals but evidence for vanadium importance as a therapeutic agent are available in humans and large animals also. This review examines the potential biochemical and molecular role, possible kinetics and distribution, essentiality, immunity, and toxicity-related study of vanadium in a biological system.

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.

Insulin-mimetic and anti-inflammatory potential of a vanadyl-Schiff base complex for its application against diabetes

Insulin-mimetic and anti-inflammatory potential of vanadium oxo complex (VOTP) enhances the GLUT4 translocation by inducing the phosphorylation of tyrosine moiety in insulin receptor substrate (IRS1).

Alteration of local adipose tissue trace element homeostasis as a possible mechanism of obesity-related insulin resistance

The mechanisms of association between obesity and the related metabolic disturbances in general and insulin resistance in particular are extensively studied. Taking into account a key role of adipose tissue insulin resistance in the development of systemic obesity-related insulin resistance, the estimation of mechanisms linking increased adiposity and impaired insulin signaling in adipocytes will allow to develop novel prophylactic and therapeutic approaches to treatment of these states. A number of trace elements like chromium, zinc, and vanadium have been shown to take part in insulin signaling via various mechanisms. Taking into account a key role of adipocyte in systemic carbohydrate homeostasis it can be asked if trace element homeostasis in adipose tissue may influence regulatory mechanisms of glucose metabolism. We hypothesize that caloric excess through currently unknown mechanisms results in decreased chromium, vanadium, and zinc content in adipocytes. Decreased content of trace elements in the adipose tissue causes impairment of intra-adipocyte insulin signaling subsequently leading to adipose tissue insulin resistance. The latter significantly contributes to systemic insulin resistance and further metabolic disruption in obesity. It is also possible that decreased adipose tissue trace element content is associated with dysregulation of insulin-sensitizing and proinflammatory adipokines also leading to insulin resistance. We hypothesize that insulin resistance and adipokine dysbalance increase the severity of obesity subsequently aggravating alteration of adipose tissue trace element balance. Single indications of high relative adipose tissue trace element content, decreased Cr, V, and Zn content in obese adipose tissue, and tight association between fat tissue chromium, vanadium, and zinc levels and metabolic parameters in obesity may be useful for hypothesis validation. If our hypothesis will be confirmed by later studies, adipose tissue chromium, vanadium, and zinc content may be used as a prognostic biomarker of metabolic disturbances in obesity. Hypothetically, development and approbation of drugs increasing adipose tissue chromium, vanadium, and zinc content may help to achieve better metabolic control in obesity and obesity-related insulin resistance. However, stronger basis is required to prove our hypothesis. In particular, future studies should investigate the influence of obesity severity of adipose tissue trace element content, estimate the association between adipose tissue metals and metabolic parameters, and highlight the mechanisms involved in these changes. Both in vivo and in vitro studies are required to support the hypothesis.

Adipose tissue chromium and vanadium disbalance in high-fat fed Wistar rats

The primary objective of the current study is to investigate the relationship between adipose tissue chromium and vanadium content and adipose tissue dysfunction in a model of diet-induced obesity. A total of 26 female Wistar rats were fed either standard or high-fat diet (31.6% of fat from total caloric content) for 3 months. High-fat-feeding resulted in 21 and 33% decrease in adipose tissue chromium and vanadium content, respectively. No change was seen in hair chromium or vanadium levels. Statistical analysis revealed a significant inverse correlation of adipose tissue Cr and V with animal morphometric parameters and adipocyte size. Significant inverse dependence was observed between adipose tissue Cr and V and serum leptin and proinflammatory cytokines' levels. At the same time, adipose tissue Cr and V levels were characterized by positive correlation between serum adiponectin and adiponectin/leptin ratio. Adipose tissue Cr and V were inversely correlated (p<0.05) with insulin and homeostatic model assessment insulin resistance index (HOMA-IR) levels. Cr and V concentrations were not correlated with serum glucose in either high-fat fed or control rats; however, both serum glucose and HOMA-IR levels were significantly higher in high-fat fed, compared to control, rats. The results allow to hypothesize that impairment of adipose tissue Cr and V content plays a certain role in the development of adipose tissue endocrine dysfunction in obesity.

Effect of endogenous galanin on glucose transporter 4 expression in cardiac muscle of type 2 diabetic rats

Although galanin has been shown to increase glucose transporter 4 (GLUT4) expression in skeletal muscle and adipocytes of rats, there is no literature available about the effect of galanin on GLUT4 expression in cardiac muscle of type 2 diabetic rats. In this study, we investigated the relationship between intracerebroventricular administration of M35, a galanin receptor antagonist, and GLUT4 expression in cardiac muscle of type 2 diabetic rats. The rats tested were divided into four groups: rats from healthy and type 2 diabetic drug groups were injected with 2 μM M35 for three weeks, while both control groups with 2 μl vehicle control. The euglycemic-hyperinsulinemic clamp test was conducted for an index of glucose infusion rates. The cardiac muscle was processed for determination of GLUT4 expression levels. The present study showed that the plasma insulin and retinol binding protein 4 (RBP4) levels were higher in both drug groups than controls respectively. Moreover, the results showed the inhibitive effect of central M35 treatment on glucose infusion rates in the euglycemic-hyperinsulinemic clamp test and GLUT4 expression levels in the cardiac muscle. These results demonstrate that endogenous galanin, acting through its central receptor, has an important attribute to increase GLUT4 expression, leading to enhance insulin sensitivity and glucose uptake in cardiac muscle of type 2 diabetic rats. Galanin and its fragment can play a significant role in regulation of glucose metabolic homeostasis in cardiac muscle and galanin is an important hormone relative to diabetic heart.

[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.

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.

Trace elements in diabetic cardiomyopathy: An electrophysiological overview

There is a growing body of evidence that Diabetes Mellitus leads to a specific cardiomyopathy apart from vascular disease and bring about high morbidity and mortality throughout the world. Recent clinical and experimental studies have extensively demonstrated that this cardiomyopathy causes impaired cardiac performance manifested by early diastolic and late systolic dysfunction. This impaired cardiac performance most probably have emerged upon the expression and activity of regulatory proteins such as Na⁺/Ca²⁺ exchanger, sarcoplasmic reticulum Ca²⁺-ATPase, ryanodine receptor and phospholamban. Over years many therapeutic strategies have been recommended for treatment of diabetic cardiomyopathy. Lately, inorganic elements have been suggested to have anti-diabetic effects due to their suggested ability to regulate glucose homeostasis, reduce oxidative stress or suppress phosphatases. Recent findings have shown that trace elements exert many biological effects including insulin-mimetic or antioxidant activity and in this manner they have been recommended as potential candidates for treatment of diabetes-induced cardiac complications, an effect based on their modes of action. Some of these trace elements are known to play an essential role as component of enzymes and thus modulate the organ function in physiological and pathological conditions. Besides, they can also manipulate redox state of the channels via antioxidant properties and thus contribute to the regulation of [Ca²⁺]_i homeostasis and cardiac ion channels. On account of little information about some trace elements, we discussed the effect of vanadium, selenium, zinc and tungstate on diabetic heart complications.

Cardioprotection by vanadium compounds targeting Akt-mediated signaling

Treatment with inorganic and organic compounds of vanadium has been shown to exert a wide range of cardioprotective effects in myocardial ischemia/reperfusion-induced injury, myocardial hypertrophy, hypertension, and vascular diseases. Furthermore, administration of vanadium compounds improves cardiac performance and smooth muscle cell contractility and modulates blood pressure in various models of hypertension. Like other vanadium compounds, we documented bis(1-oxy-2-pyridinethiolato) oxovanadium (IV) [VO(OPT)] as a potent cardioprotective agent to elicit cardiac functional recovery in myocardial infarction and pressure overload-induced hypertrophy. Vanadium compounds activate Akt signaling through inhibition of protein tyrosine phosphatases, thereby eliciting cardioprotection in myocardial ischemia/reperfusion-induced injury and myocardial hypertrophy. Vanadium compounds also promote cardiac functional recovery by stimulation of glucose transport in diabetic heart. We here discuss the current understanding of mechanisms underlying vanadium compound-induced cardioprotection and propose a novel therapeutic strategy targeting for Akt signaling to rescue cardiomyocytes from heart failure.

Vanadium treatment of type 2 diabetes: a view to the future

3-Hydroxy-2-methyl-4-pyrone and 2-ethyl-3-hydroxy-4-pyrone (maltol and ethyl maltol, respectively) have proven especially suitable as ligands for vanadyl ions, in potential insulin enhancing agents for diabetes mellitus. Both bis(maltolato)oxovanadium(IV) (BMOV), and the ethylmaltol analog, bis(ethylmaltolato)oxovanadium(IV) (BEOV), have the desired intermediate stability for pro-drug use, and have undergone extensive pre-clinical testing for safety and efficacy. Pharmacokinetic evaluation indicates a pattern of biodistribution consistent with fairly rapid dissociation and uptake, binding to serum transferrin for systemic circulation and transport to tissues, with preferential uptake in bone. These bis-ligand oxovanadium(IV) (VOL(2)) compounds have a clear advantage over inorganic vanadyl sulfate in terms of bioavailability and pharmaceutical efficacy. BEOV has now completed Phase I and has advanced to Phase II clinical trials. In the Phase I trial, a range of doses from 10 mg to 90 mg BEOV, given orally to non-diabetic volunteers, resulted in no adverse effects; all biochemical parameters remained within normal limits. In the Phase IIa trial, BEOV (AKP-020), 20 mg, daily for 28 days, per os, in seven type 2 diabetic subjects, was associated with reductions in fasting blood glucose and %HbA1c; improved responses to oral glucose tolerance testing, versus the observed worsening of diabetic symptoms in the two placebo controls.

Metabolic imaging using PET

INTRODUCTION

There is growing evidence that myocardial metabolism plays a key role not only in ischaemic heart disease but also in a variety of diseases which involve myocardium globally, such as heart failure and diabetes mellitus. Understanding myocardial metabolism in such diseases helps to elucidate the pathophysiology and assists in making therapeutic decisions.

MEASUREMENT

As well as providing information on regional changes, PET can deliver quantitative information about both regional and global changes in metabolism. This capability of quantitative measurement is one of the major advantages of PET along with physiological positron tracers, especially relevant in evaluating diseases which involve the whole myocardium.

DISCUSSION

This review discusses major PET tracers for metabolic imaging and their clinical applications and contributions to research regarding ischaemic heart disease and other diseases such as heart failure and diabetic heart disease. Future applications of positron metabolic tracers for the detection of vulnerable plaque are also highlighted briefly.

Increased myocardial fatty acid metabolism in patients with type 1 diabetes mellitus

OBJECTIVES

The purpose of this study was to determine if myocardial fatty acid utilization (MFAU) and myocardial fatty acid oxidation (MFAO) are increased in diabetic patients.

BACKGROUND

Experimental models of diabetes mellitus demonstrate that MFAU and MFAO are increased, and that this dependence on myocardial fatty acid metabolism may be detrimental to cardiac function. Whether similar metabolic changes occur in humans with diabetes mellitus is unclear.

METHODS

Eleven healthy non-diabetic control patients (5 women, ages 25 +/- 5 years) and 11 otherwise healthy patients with type 1 diabetes mellitus (T1DM) (8 women, ages 36 +/- 10 years, HbA1c 8.4 +/- 1.9%) underwent positron emission tomography for the determination of myocardial blood flow (MBF); myocardial oxygen consumption (MVO2); myocardial glucose utilization (MGU); and MFAU, MFAO, and %MFAO.

RESULTS

Plasma lactate, insulin, and MBF levels were similar between the two groups. However, plasma glucose (5.71 +/- 0.98 mumol/ml vs. 5.28 +/- 0.65 mumol/ml, p = 0.04), free fatty acid levels (0.60 +/- 0.24 mumol/ml vs. 0.19 +/- 0.07 mumol/ml, p < 0.0001), and MVO2 (6.64 +/- 2.21 vs. 4.51 +/- 1.39 mumol/g/min, p = 0.007) levels were higher in the T1DM subjects. Furthermore, compared with control patients, T1DM subjects exhibited higher MFAU (213 +/- 135 nmol/g/min vs. 57 +/- 28 nmol/g/min, p = 0.0004), MFAO (206 +/- 131 nmol/g/min s. 50 +/- 26 nmol/g/min, p = 0.0002), and %MFAO (94 +/- 6% vs. 81 +/- 19%, respectively, p = 0.04). In contrast, MGU was lower in T1DM subjects than in controls (207 +/- 108 nmol/g/min vs. 403 +/- 191 nmol/g/min, p = 0.0008).

CONCLUSIONS

Humans with diabetes mellitus exhibit increased MFAU and MFAO and reduced MGU consistent with observations obtained in experimental models of diabetes.

Effect of a Novel Molybdenum Ascorbate Complex on Ex Vivo Myocardial Performance in Chemical??Diabetes Mellitus

BACKGROUND

The insulin-like action of metal complexes on target tissues, including the heart, has been reported in experimental diabetes mellitus. Since streptozotocin-induced diabetes is associated with insulin deficiency and left ventricular dysfunction, this study was designed to determine whether the novel metal complex molybdenum ascorbate [MoO(2)(aa)(2)] would improve cardiac function in this model of diabetes.

METHODS

Diabetes was induced in Sprague-Dawley rats (n = 6) following an intravenous injection of streptozotocin (60 mg/kg). After 8 weeks of diabetes, cardiac function was determined in isolated working hearts perfused with 11 mmol/L glucose, 1.2 mmol/L palmitate and 3% albumin. MoO(2)(aa)(2 )was added directly into the perfusate of working hearts at a concentration of 200 micromol/L for a period of 30 minutes. Age-matched control rats served as controls (n = 6).

RESULTS

Cardiac function, expressed as heart rate (HR) and aortic flow, was significantly decreased in diabetic hearts compared with control hearts. The diabetic state was associated with 23% and 60% reductions in HR and aortic flow, respectively. Short-term addition of MoO(2)(aa)(2) was beneficial and partially prevented the attenuation in diabetic rat heart function. MoO(2)(aa)(2 )increased HR by 15%, while aortic flow was increased by 85%. In control hearts, MoO(2)(aa)(2) had no effect on HR and increased aortic flow by 12%.

CONCLUSION

This study extends previous observations on the benefit of metal complexes in experimental diabetes. Our results indicate that short-term treatment with MoO(2)(aa)(2) partially reversed the left ventricular dysfunction associated with the streptozotocin model of diabetes.

Vascular endothelial dysfunction in diabetic cardiomyopathy: pathogenesis and potential treatment targets

Cardiovascular complications account for significant morbidity and mortality in the diabetic population. Diabetic cardiomyopathy, a prominent cardiovascular complication, has been recognized as a microvascular disease that may lead to heart failure. Pathogenesis of diabetic cardiomyopathy involves vascular endothelial cell dysfunction, as well as myocyte necrosis. Clinical trials have identified hyperglycemia as the key determinant in the development of chronic diabetic complications. Sustained hyperglycemia induces several biochemical changes including increased non-enzymatic glycation, sorbitol-myoinositol-mediated changes, redox potential alterations, and protein kinase C (PKC) activation, all of which have been implicated in diabetic cardiomyopathy. Other contributing metabolic abnormalities may include defective glucose transport, increased myocyte fatty acid uptake, and dysmetabolism. These biochemical changes manifest as hemodynamic alterations and structural changes that include capillary basement membrane (BM) thickening, interstitial fibrosis, and myocyte hypertrophy and necrosis. Diabetes-mediated biochemical anomalies show cross-interaction and complex interplay culminating in the activation of several intracellular signaling molecules. Studies in both animal and human diabetes have shown alteration of several factors including vasoactive molecules that may be instrumental in mediating structural and functional deficits at both the early and the late stages of the disease. In this review, we will highlight some of the important vascular changes leading to diabetic cardiomyopathy and discuss the emerging potential therapeutic interventions.

Organo-vanadium compounds are potent activators of the protein kinase B signaling pathway and protein tyrosine phosphorylation: mechanism of insulinomimesis

Organo-vanadium compounds (OVC) have been shown to be more effective than inorganic vanadium compounds in ameliorating glucose homeostasis and insulin resistance in rodent models of diabetes mellitus. However, the precise molecular mechanism of OVC efficiency remains poorly defined. Since inorganic vanadium compounds have been found to activate several key components of the insulin signaling cascade, such as protein kinase B (PKB), the objective of the present study was to investigate if stimulation of PKB and its downstream target glycogen synthase kinase-3 (GSK-3), are responsible for the more potent insulinomimetic effects of OVC. Among several vanadium compounds tested, vanadium (IV) oxo bis (acetylacetonate) and vanadium (IV) oxo bis(maltolato) markedly induced the phosphorylation of PKB as well as GSK-3beta compared to vanadyl sulfate (VS), an inorganic vanadium salts in Chinese hamster ovary cells overexpressing the insulin receptor (IR). Furthermore, the OVC were stronger inhibitors of protein tyrosine phosphatase (PTPase) activity than VS. The higher PTPase inhibitory potential of the OVC was associated with more robust tyrosine phosphorylation of several cellular proteins, including the IRbeta subunit and insulin receptor substrate-1 (IRS-1). In addition, greater IRS-1/p85alpha interaction was elicited by the OVC than by VS. These data indicate that the higher PTPase inhibitory potential of OVC translates into greater phosphorylation of PKB and GSK-3beta, which, in turn, may contribute to a more potent effect of OVC on glucose homeostasis.

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.

Effects of amino acid supplementation on left ventricular remodeling in patients with chronic heart failure with decreased systolic function and diabetes mellitus: rationale and design of a magnetic resonance imaging study

A considerable number of patients with reduced systolic function caused by primary or ischemic cardiomyopathy have viable and noncontractile myocardium. This may be related to numerous and perhaps overlapping factors, such as chronic ischemia (stunning/hibernation), neurohormonal abnormalities, oxidative stress, metabolic imbalances, and/or nutritional depletion. Changes in myocardial substrate utilization have adverse effects on the metabolism of the viable but noncontractile myocardium. Shifting the energy substrate preference away from fatty acids and replenishing the tricarboxylic acid cycle components via amino acids rather than via fatty acids would increase adenosine triphosphate production, with positive effects on cellular metabolism. A proposed study design is described and will be piloted through the Effects of Diatrofen on Myocardial Function in Patients with Chronic Heart Failure trial (D-CHF), an evaluation of an oral amino acid supplementation treatment in outpatients with heart failure.

Diabetic cardiomyopathy: a metabolic perspective

Patients with diabetes mellitus have a >3-fold increased risk of coronary ischemic events and congestive heart failure. Several hypotheses have been provided to explain the increased cardiac vulnerability in individuals with diabetes; among these are the metabolic abnormalities. Diabetes is associated with profound changes in cardiac metabolism, characterized by diminished glucose utilization, diminished rates of lactate oxidation, and increased use of fatty acids. Very few investigations have focused on amino acid disturbances at the level of the heart. This area of research is potentially relevant because cardiac amino acid alterations may not only result in a reduced energy reserve but could also lead to quantitative and qualitative abnormalities of contractile protein present in the diabetic heart.

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.

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.

Modulation of glucose transporters in rat diaphragm by sodium tungstate

Oral administration of sodium tungstate is an effective treatment for diabetes in animal models. We examined the effects of 6 weeks of oral administration of tungstate on glucose transporters (GLUT) in streptozotocin-induced diabetic rat diaphragm. Diabetes decreased GLUT4 expression while tungstate treatment normalized not only GLUT4 protein but also GLUT4 mRNA in the diabetic rats. Furthermore, treatment increased GLUT4 protein in plasma and internal membranes, suggesting a stimulation of its translocation to the plasma membrane. Tungstate had no effect on healthy animals. There were no differences in the total amount of GLUT1 transporter in any group. We conclude that the normoglycemic effect of tungstate may be partly due to a normalization of the levels and subcellular localization of GLUT4, which should result in an increase in muscle glucose uptake.

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.