Decrease of hypothalamic neuropeptide Y gene expression by vanadyl sulfate in streptozotocin-induced diabetic rats.

In an attempt to elucidate the effect of vanadium compounds on the gene expression of neuropeptide Y (NPY), vanadyl sulfate (VOSO4) was orally administrated at the dose of 1 mg/kg body weight into streptozotocin-induced diabetic rats (STZ-diabetic rats) three times daily for 1 week. We found a marked lowering of plasma glucose with a significant decrease of food and water intake in these STZ-diabetic rats treated with VOSO4, although the weight gain was unaffected. The increase of hypothalamic NPY, both the mRNA level and peptide concentration, in STZ-diabetic rats was also reduced by this oral treatment of VOSO4. However, similar treatment of VOSO4 in normal rats failed to modify the feeding behavior and hypothalamic NPY gene expression. These data suggest that decrease of hypothalamic NPY gene expression by VOSO4 is related to the recovery of hyperphagia in diabetic rats lacking insulin.     

Effects of some vanadyl coordination compounds on the in vitro insulin release from rat pancreatic islets.

Many lines of evidence indicate that vanadium inorganic salts possess insulin-mimetic and insulinotropic properties. However, they are poorly absorbed, so high oral doses are required to achieve effective plasma concentrations with possible undesirable toxic side-effects ensuing. Various organically-chelated vanadium compounds have been synthesized that are more potent than inorganic vanadium salts in their insulin-like effects due to their greater bioavailability. Unfortunately, little is known about the possible insulin secretagogue action of organic vanadyl coordination compounds. Hence, we investigated the effect of [VO(metformin)2]H2O, [VO(salicylidene-ethylenedimmine)2] and [VO(pyrrolidine-N-dithiocarbamate)2](VODTC) on insulin release from isolated rat pancreatic islets, and compared it to that of vanadyl sulfate (VOSO4). Of the three coordination compounds, only VODTC was found to exert insulin secretagogue action. VODTC, within concentrations ranging from 0.1 to 1.0 mM, enhanced both basal and glucose (11 mM)-stimulated insulin release. The effect involves calcium channels, since it was not appreciable in Ca2+-free medium. The stimulating action of VODTC required the presence of the whole metal-chelator complex inasmuch as the chelator DTC alone was ineffective. VOSO4 was unable to bring about any significant rise in insulin release from isolated islets. Taken together, our findings indicate that VODTC may be considered a potential elective pharmaceutical tool in the therapy of diabetes, especially of type 2, through its concomitant stimulatory effect on insulin secretion and insulin-mimetic action.     

Influence of vanadium supplementation on oxidative stress factors in the muscle of STZ-diabetic rats

In recent years, the role of free radical damage consequent to oxidative stress is widely discussed in diabetic complications. In this aspect, the protection of cell integrity by trace elements is a topic to be investigated. Vanadium is a trace element believed to be important for normal cell function and development. The aim of the present study was to investigate the effect of vanadyl sulfate supplementation on the antioxidant system in the muscle tissue of diabetic rats. Diabetes was induced by intraperitoneal injection of streptozotocin (STZ, 65 mg/kg body weight) to male Swiss albino rats. The rats were randomly divided into 4 groups: Group I, control; Group II, vanadyl sulfate control; Group III, STZ-diabetic untreated; Group IV, STZ-diabetic treated with vanadyl sulfate. Vanadyl sulfate (100 mg/kg) was given daily by gavage for 60 days. At the last day of the experiment, rats were killed, muscle tissues were taken, homogenized in cold saline to make a 10% (w/v) homogenate. Body weights and blood glucose levels were estimated at 0, 30 and 60th days. Antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), glutathione peroxidase (GPx), glutathione-S-transferase (GST), as well as carbonic anhydrase (CA), myeloperoxidase (MPO) activities and protein carbonyl content (PCC) were determined in muscle tissue. Vanadyl sulfate administration improved the loss in body weight due to STZ-induced diabetes and decreased the rise in blood glucose levels. It was shown that vanadium supplementation to diabetic rats significantly decrease serum antioxidant enzyme levels, which were significantly raised by diabetes in muscle tissue showing that this trace element could be used as preventive for diabetic complications.     

Vanadium and diabetes

We demonstrated in 1985 that vanadium administered in the drinking water to streptozotocin (STZ) diabetic rats restored elevated blood glucose to normal. Subsequent studies have shown that vanadyl sulfate can lower elevated blood glucose, cholesterol and triglycerides in a variety of diabetic models including the STZ diabetic rat, the Zucker fatty rat and the Zucker diabetic fatty rat. Long-term studies of up to one year did not show toxicity in control or STZ rats administered vanadyl sulfate in doses that lowered elevated blood glucose. In the BB diabetic rat, a model of insulin-dependent diabetes, vanadyl sulfate lowered the insulin requirement by up to 75%. Vanadyl sulfate is effective orally when administered by either single dose or chronic doses. It is also effective by the intraperitoneal route. We have also been able to demonstrate marked long-terrn effects of vanadyl sulfate in diabetic animals following treatment and withdrawal of vanadyl sulfate. Because vanadyl sulfate is not well absorbed we have synthesized and tested a number of organic vanaditun compounds. One of these, bismaltolato-oxovanadiurn IV (BMOV), has shown promise as a therapeutic agent. BMOV is 2-3x more potent than vanadyl sulfate and has shown less toxicity. Recent studies from our laboratory have shown that the effects of vanadium are not due to a decrease in food intake and that while vanadium is deposited in bone it does not appear to affect bone strength or architecture. The mechanism of action of vanadium is currently under investigation. Several studies indicate that vanadiun is a phosphatase inhibitor and that vanadium can activate serine/threonine kineses distal to tbe insulin receptor presumably by preventing dephosphorylation due to inhibition of phosphatases Short-term clinical trials using inorganic vanadium compounds in diabetic patients have been promising.     

Possible mode of action for insulinomimetic activity of vanadyl(IV) compounds in adipocytes

Vanadyl(IV) ions (+4 oxidation state of vanadium) and their complexes have been shown to have in vitro insulinomimetic activity and to be effective in treating animals with diabetes mellitus. Although, researchers have proposed many vanadyl compounds for the treatment of diabetes patients, the mode of action of vanadyl compounds remains controversial. In order to evaluate the mode of action of these compounds, we examined the insulinomimetic activity of VOSO4, bis(picolinato)oxovanadyl(IV), and bis(maltolato)oxovanadyl(IV) in the presence of several inhibitors relevant to the glucose metabolism. After confirming that these vanadyl compounds were incorporated in the adipocytes as estimated by ESR method, we evaluated the mode of action by examining free fatty acids (FFA) release in the adipocytes. Inhibition of FFA release by these vanadyl compounds was found to be reversed by the addition of inhibitors, typically by cytochalasin B (glucose transporter 4 (GLUT4) inhibitor), cilostamide (phosphodiesterase inhibitor), HNMPA-(AM)3 (tyrosine kinase inhibitor), and wortmannin (PI3-k inhibitor), indicating that these compounds affect primarily GLUT4 and phosphodiesterase, as named "ensemble mechanism". Based on these results, we suggest that vanadyl compounds act on at least four sites relevant to the glucose metabolism, and on GLUT4 and phosphodiesterase in particular in rat adipocytes, which in turn normalizes the blood glucose levels of diabetic animals. The obtained results provide evidence for the role of vanadyl ion and its complexes in stimulation of the uptake and degeneration of glucose.     

Guanine versus deoxyribose damage in DNA oxidation mediated by vanadium(IV) and vanadium(V) complexes

Vanadyl sulfate reacts with the peroxy acid oxidant KHSO5 to produce guanine-selective oxidation of a 167-bp restriction fragment of DNA. The oxidized lesions result in strand scission after hot piperidine treatment. Although several reactive intermediates are possible, quenching studies with ethanol and tert-butyl alcohol suggest that a monoperoxysulfate radical or a caged sulfate radical are the likely species responsible for oxidation of guanine. Several oxidants and various vanadium complexes (including insulin mimetic compounds) were studied with DNA for comparison. None of the other vanadium complexes showed modification of the double-stranded 167-bp fragment of DNA in the presence of KHSO5. The reactivity of VOSO4 may be due to its irreversible oxidation potential of 0.77 V (vs. Ag+/AgCl, pH 7.0, 10 mM phosphate), making it an appropriate catalyst for decomposition of monoperoxysulfate.     

Inhibition of cyclic AMP dependent protein kinase by vanadyl sulfate

Vanadium salts influence the activities of a number of mammalian enzymes in vitro but the mechanisms by which low concentrations of vanadium ameliorate the effects of diabetes in vivo remain poorly understood. The hypothesis that vanadium compounds act by inhibiting protein tyrosine phosphatases has attracted most support. The studies described here further evaluate the possibility that vanadyl sulfate trihydrate (VS) can also inhibit 3′,5′-cyclic adenosine monophosphate (cAMP) dependent protein kinase (PKA). Using conventional assay conditions, VS inhibited PKA only at high concentrations (IC₅₀>400 μM); however, PKA inhibition was seen at dramatically lower concentrations of VS (IC₅₀<10 μM) when sequestration of vanadyl ions was minimized. Vanadyl appears to be the effective PKA inhibitor because sodium orthovanadate did not inhibit PKA and inhibition by vanadyl was abolished by potential chelators such as ethylenediaminetetraacetic acid or glycyl peptides. PKA inhibition by vanadyl appears to be mixed rather than strictly competitive or uncompetitive and may replicate the inhibitory effects of high concentrations of Mg²⁺. The effect of vanadyl on PKA provides a possible explanation for the effects of vanadium salts on fat tissue lipolysis and perhaps on other aspects of energy metabolism that are controlled by cAMP-dependent mechanisms. Considering the high degree of conservation of the active sites of protein kinases, vanadyl may also influence other members of this large protein family. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Anticancer activity of oxovanadium compounds

Cytotoxic and antitumor activities of the biligand vanadyl derivative of L-malic acid, (bis-(L-malato)oxovanadium(IV) (VO(mal)₂), the inorganic vanadium(IV) compound, vanadyl sulfate (VOSO₄), the oxovanadium monocomplex with L-malic acid (VO(mal)), and the vanadyl biscomplex with acetylacetonate (VO(acac)₂) were investigated using several tumor cell lines: mouse fibrosarcoma (L929), rat pheochromocytoma (PC12), human liver carcinoma (HepG2), mouse embryonic fibroblasts (NIH/3T3), and also normal human skin fibroblasts. The results showed that VO(mal)₂ effectively inhibited growth of cancer cell cultures without any toxic effect on normal human skin fibroblasts. The cytotoxic anticancer effect of vanadium complexes depended on concentration of the compounds studied, incubation time, types of cell cultures, and nature of ligands surrounding the central group of the complex (VO²⁺). These studies provide evidence that VO(mal)₂ may be considered as a potential anticancer agent due to its low toxicity for non-tumor cells and significant anticancer activity.     

The fate of cytoplasmic vanadium. Implications on (NA,K)-ATPase inhibition.

The fate of vanadate (+5 oxidation state of vanadium) taken up by the red cell was studied using EPR spectroscopy. The appearance of an EPR signal indicated that most of the cytoplasmic vanadate is reduced to the +4 oxidation state with axial symmetry characteristic of vanadyl ions. The signal at 23 degrees C was characteristic of an immobilized system indicating that the vanadyl ions in the cytoplasm are associated with a large molecule. [48V]Vanadium eluted with hemoglobin when the lysate from Na3[48V[O4-treated red cells was passed through a Sephadex G-100 column and rabbit anti-human hemoglobin serum caused a hemoglobin-specific precipitation of 48V when added to the red cell lysate. Both results indicate that hemoglobin is the protein which binds cytoplasmic vanadyl ions. However, neither sodium vanadate nor vanadyl sulfate bound to purified hemoglobin in vitro. Finally, transient kinetics of vanadyl sulfate interaction with the sodium-and potassium-stimulated adenosine triphosphatase showed that the +4 oxidation state of vanadium is less effective than the +5 oxidation state in inhibiting this enzyme. These results indicate that oxidation-reduction reactions in the cytoplasm are capable of relieving vanadate inhibition of cation transport.     

Effect of vanadium(IV) compounds in the treatment of diabetes: in vivo and in vitro studies with vanadyl sulfate and bis(maltolato)oxovandium(IV)

Vanadyl sulfate (VOSO(4)) was given orally to 16 subjects with type 2 diabetes mellitus for 6 weeks at a dose of 25, 50, or 100 mg vanadium (V) daily [Goldfine et al., Metabolism 49 (2000) 1-12]. Elemental V was determined by graphite furnace atomic absorption spectrometry (GFAAS). There was no correlation of V in serum with clinical response, determined by reduction of mean fasting blood glucose or increased insulin sensitivity during euglycemic clamp. To investigate the effect of administering a coordinated V, plasma glucose levels were determined in streptozotocin (STZ)-induced diabetic rats treated with the salt (VOSO(4)) or the coordinated V compound bis(maltolato)oxovandium(IV) (abbreviated as VO(malto)(2)) administered by intraperitoneal (i.p.) injection. There was no relationship of blood V concentration with plasma glucose levels in the animals treated with VOSO(4), similar to our human diabetic patients. However, with VO(malto)(2) treatment, animals with low plasma glucose tended to have high blood V. To determine if V binding to serum proteins could diminish biologically active serum V, binding of both VOSO(4) and VO(malto)(2) to human serum albumin (HSA), human apoTransferrin (apoHTf) and pig immunoglobulin (IgG) was studied with EPR spectroscopy. Both VOSO(4) and VO(malto)(2) bound to HSA and apoHTf forming different V-protein complexes, while neither V compound bound to the IgG. VOSO(4) and VO(malto)(2) showed differences when levels of plasma glucose and blood V in diabetic rodents were compared, and in the formation of V-protein complexes with abundant serum proteins. These data suggest that binding of V compounds to ligands in blood, such as proteins, may affect the available pool of V for biological effects.     

Vanadyl Sulfate Administration Protects the Streptozotocin-Induced Oxidative Damage to Brain Tissue in Rats

Diabetes mellitus manifests itself in a wide variety of complications and the symptoms of the disease are multifactorial. The present study was carried out to investigate the effects of vanadyl sulfate on biochemical parameters, enzyme activities and brain lipid peroxidation, glutathione and nonenzymatic glycosylation of normal- and streptozotocin-diabetic rats. Streptozotocin (STZ) was administered as a single dose (65 mg/kg) to induce diabetes. A dose of 100 mg/kg vanadyl sulfate was orally administered daily to STZ-diabetic and normal rats, separately until the end of the experiment, at day 60. In STZ-diabetic group, blood glucose, serum sialic and uric acid levels, serum catalase (CAT) and lactate dehydrogenase (LDH) activities, brain lipid peroxidation (LPO) and nonenzymatic glycosylation (NEG) increased, while brain glutathione (GSH) level and body weight decreased. In the diabetic group given vanadyl sulfate, blood glucose, serum sialic and uric acid levels, serum CAT and LDH activities and brain LPO and NEG levels decreased, but brain GSH and body weight increased.The present study showed that vanadyl sulfate exerted antioxidant effects and consequently may prevent brain damage caused by streptozotocin-induced diabetes.     

Synthesis of vanadium(IV,V) hydroxamic acid complexes and in vivo assessment of their insulin-like activity

We synthesized vanadyl (oxidation state +IV) and vanadate (oxidation state +V) complexes with the same hydroxamic acid derivative ligand, and assessed their glucose-lowering activities in relation to the vanadium biodistribution behavior in streptozotocin-induced diabetic mice. When the mice received an intraperitoneal injection of the complexes, the vanadate complex more effectively lowered the elevated glucose levels compared with the vanadyl one. The glucose-lowering effect of the vanadate complex was linearly related to its dose within the range from 2.5 to 7.5 mg V/kg. In addition, pretreatment of the vanadate complex induced a larger insulin-enhancing effect than the vanadyl complex. Both complexes were more effective than the corresponding inorganic vanadium compounds. The vanadyl and vanadate complexes, but not the inorganic vanadium compounds, resulted in almost the same organ vanadium distribution. Consequently, the observed differences in the insulin-like activity between the complexes would reflect the potency of the two compounds in the +IV and +V oxidation states in the subcellular region.     

Redox and specific effects of vanadium ions on respiratory enzymes

The effects of vanadium ions on the activities of enzymes of aerobic and anaerobic respiratory chains were investigated in vitro and in situ employing ¹H-, ¹⁴N-, ³¹P- and ⁵¹V- nuclear magnetic resonance spectroscopy, electron paramagnetic resonance spectroscopy and spectrophotometry. Vanadate and vanadyl ions produced either non-specific redox or specific activation or inhibition of respiratory enzymes. The oxidants molybdate and chromate and the reductant dithiothreitol were used to distinguish between non-specific and specific effects of vanadium ions on enzyme activities. The results suggested that components of anaerobic respiratory chains were more susceptible to vanadium ions than those of the aerobic respiratory chain     

白柄肉齿菌Sarcodon leucopus多酚生物碱提取物的体外抗氧化及降血糖活性

为探讨西藏白柄肉齿菌Sarcodon leucopus子实体多酚生物碱提取物(PAE)的抗氧化和降糖活性,本研究考察了PAE对DPPH自由基清除能力、细胞内抗氧化能力(CAA)和糖尿病关键酶(大鼠小肠来源麦芽糖酶、蔗糖酶和α-淀粉酶)活性的抑制能力.结果表明,PAE具有一定的抗氧化活性,对DPPH自由基的半数抑制浓度(...     

Syntheses of vanadyl and zinc(II) complexes of 1-hydroxy-4,5,6-substituted 2(1H)-pyrimidinones and their insulin-mimetic activities

Control of the glucose level in the blood plasma has been achieved in vitro and in vivo by administration of vanadium and zinc in form of inorganic salts. It has been shown that elements are poorly absorbed in their inorganic forms and required high doses which have been associated with undesirable side effects. Many researchers, therefore, have focused on metal complexes that were prepared from VOSO(4) or ZnSO(4) and low-molecular-weight bidentate ligands. Seven kinds of 1-hydroxy-4,6-disubstituted and 1-hydroxy-4,5,6-trisubstituted-2(1H)-pyrimidinones were synthesized by reaction of N-benzyloxyurea and beta-diketones and subsequent removal of the protecting group. Six kinds of 1-hydroxy-4-(substituted)amino-2(1H)-pyrimidinones were synthesized by the substitution reaction of 1-benzyloxy-4-(1',2',4'-triazol-1'-yl)-2(1H)-pyrimidinone with various alkyl amines or amino acids. Treatment with VOSO(4) and ZnSO(4) or Zn(OAc)(2) afforded vanadyl(IV) and zinc(II) complexes which were characterized by means of (1)H NMR, IR, EPR, and UV-vis spectroscopies, and combustion analysis. The in vitro insulin-mimetic activity of these complexes was evaluated from 50% inhibitory concentrations (IC(50)) on free fatty acid (FFA) release from isolated rat adipocytes treated with epinephrine. Vanadyl complexes of 4,6-disubstituted-2(1H)-pyrimidinones showed higher insulin-mimetic activities than those of 4,5,6-trisubstituted ones. On the other hand, Zn(II) complexes showed lower insulin-mimetic activities than VOSO(4) and ZnSO(4) as positive controls. It was found that the balance of the hydrophilicity and/or hydrophobicity is important for higher insulin-mimetic activity. The in vivo insulin-mimetic activity was evaluated with streptozotocin (STZ)-induced diabetic rats. Blood glucose levels were lowered from hyperglycemic to normal levels after the treatment with bis(1,2-dihydro-4,6-dimethyl-2-oxo-1-pyrimidinolato)oxovanadium(IV) by daily intraperitoneal injections. The improvement in glucose tolerance was also confirmed by an oral glucose tolerance test.     

Synthesis,structure analysis,solution chemistry,and in vitro insulinomimetic activity of novel oxovanadium(IV) complexes with tripodal ligands containing an imidazole group derived from amino acids

Structures, chemical properties, and in vitro insulinomimetic activities of new vanadyl [oxovanadium(IV), VO(2+)] complexes with five tripodal ligands containing an imidazole functionality were examined. The ligands, N-(carboxymethyl)- N-(4-imidazolylmethyl)amino acids, contain glycine, ( S)- and ( R)-alanine, and ( S)- and ( R)-leucine residues. The molecular structures of the latter four alanine- and leucine-containing complexes were determined by X-ray analysis. The coordination geometry around each vanadium center was octahedral, where an imino nitrogen occupied the apical site and two carboxylate oxygens, an imidazole nitrogen, and a water molecule coordinated in the equatorial plane. The spectroscopic properties of the complexes were characterized by means of IR, electronic absorption, and CD spectra. Acid dissociation constants (p K(a)) and protonation sites of the ligands were determined by a combination of potentiometric titrations and (1)H NMR spectra. The potentiometric study demonstrated that stability constants (log beta) were not so different among the present complexes (14.0-14.9) and a species of molecular complex with a 1:1 metal:ligand ratio existed predominantly at physiological pH 7.4. EPR parameters indicated that the species at pH 7.4 had an octahedral structure similar to the complex in the solid state. On the other hand, an EPR study in phosphate buffer (pH 7.4) suggested that inorganic phosphate coordinated to the vanadium center instead of the imidazole group in the presence of excess phosphate ion. Cyclic voltammograms in the phosphate buffer showed chemically reversible oxidation waves, whereas irreversible oxidation waves were observed in non-coordinating HEPES buffer. Moreover, the oxidation potential of each complex in phosphate buffer was more positive than that in HEPES buffer. Partition coefficients of the present complexes in a n-octanol/saline system were very low, probably due to hydrophilicity of the imidazole group. The in vitro insulinomimetic activities were estimated on the basis of the ability of the complexes to inhibit epinephrine-stimulated free fatty acid release from isolated rat adipocytes. The achiral glycine-derivative complex exhibited the highest insulinomimetic activity, which was higher than that of VOSO(4) as a positive control. Putting our previous observations together, it was found that the vanadyl complexes with tetradentate amino acid derivatives having no alkyl side chain tend to have high in vitro insulinomimetic activity.