Internal dose of vanadium in rats following repeated exposure to vanadyl sulfate and sodium orthovanadate via drinking water

Vanadium is a ubiquitous environmental contaminant that exists in multiple oxidation states. Humans are exposed to vanadyl (V4+) and vanadate (V5+) from dietary supplements, food, and drinking water and hence there is a concern for adverse human health. The current investigation is aimed at identifying vanadium oxidation states in vitro and in vivo and internal concentrations following exposure of rats to vanadyl sulfate (V4+) or sodium metavanadate (V5+) via drinking water for 14 d. Investigations in simulated gastric and intestinal fluids showed that V4+ was stable in gastric fluid while V5+ was stable in intestinal fluid. Analysis of rodent plasma showed that the only vanadium present was V4+, regardless of the exposed compound suggesting conversion of V5+ to V4+ in vivo and/or instability of V5+ species in biological matrices. Plasma, blood, and liver concentrations of total vanadium, after normalizing for vanadium dose consumed, were higher in male and female rats following exposure to V5+ than to V4+. Following exposure to either V4+ or V5+, the total vanadium concentration in plasma was 2- to 3-fold higher than in blood suggesting plasma as a better matrix than blood for measuring vanadium in future work. Liver to blood ratios were 4-7 demonstrating significant tissue retention following exposure to both compounds. In conclusion, these data point to potential differences in absorption and disposition properties of V4+ and V5+ salts and may explain the higher sensitivity in rats following drinking water exposure to V5+ than V4+ and highlights the importance of internal dose determination in toxicology studies.

Vanadium coordination compounds loaded on graphene quantum dots (GQDs) exhibit improved pharmaceutical properties and enhanced anti-diabetic effects

Vanadium compounds are promising anti-diabetic agents, and graphene quantum dots (GQDs) are emerging as potential drug delivery systems to improve drug solubility in water and membrane transport. Using highly dispersible and water-soluble GQDs, we herein prepared a novel GQD-VO (p-dmada) complex, in which vanadium coordination compounds [VO(p-dmada)] were packed closely on one side of the GQD sheets possibly via the π-π stacking mechanism. The in vitro tests showed that GQD-VO(p-dmada) exhibited membrane permeability (Papp) as good as that of GQDs with reduced cytotoxicity. In vivo tests on type 2 diabetic mice demonstrated that GQD-VO(p-dmada) exhibited a delayed glucose lowering profile but more profound effects on insulin enhancement and β-cell protection after three-week treatment compared to VO(p-dmada) alone. In addition, GQD alone was observed for the first time to effectively lower the blood lipid levels of the db/db mice. Overall, GQD-VO(p-dmada) showed improved pharmacokinetic performance and hypoglycemic effects, and using GQD as a nanoplatform for drug delivery may provide vast opportunities for the further design of metal-based pharmaceutical agents.

Vanadium and cadmium in vivo effects in teleost cardiac muscle: metal accumulation and oxidative stress markers

Several biological studies associate vanadium and cadmium with the production of reactive oxygen species (ROS), leading to lipid peroxidation and antioxidant enzymes alterations. The present study aims to analyse and compare the oxidative stress responses induced by an acute intravenous exposure (1 and 7 days) to a sub-lethal concentration (5 mM) of two vanadium solutions, containing different vanadate n-oligomers (n=1-5 or n=10), and a cadmium solution on the cardiac muscle of the marine teleost Halobatrachus didactylus (Lusitanian toadfish). It was observed that vanadium is mainly accumulated in mitochondria (1.33+/-0.26 microM), primarily when this element was administrated as decameric vanadate, than when administrated as metavanadate (432+/-294 nM), while the highest content of cadmium was found in cytosol (365+/-231 nM). Indeed, decavanadate solution promotes stronger increases in mitochondrial antioxidant enzymes activities (catalase: +120%; superoxide dismutase: +140%) than metavanadate solution. On contrary, cadmium increases cytosolic catalase (+111%) and glutathione peroxidases (+50%) activities. It is also observed that vanadate oligomers induce in vitro prooxidant effects in toadfish heart, with stronger effects induced by metavanadate solution. In summary, vanadate and cadmium are differently accumulated in blood and cardiac subcellular fractions and induced different responses in enzymatic antioxidant defence mechanisms. In the present study, it is described for the first time the effects of equal doses of two different metals intravenously injected in the same fish species and upon the same exposure period allowing to understand the mechanisms of vanadate and cadmium toxicity in fish cardiac muscle.

Evaluation of genotoxicity of oral exposure to tetravalent vanadium in vivo

The trace element vanadium interacts with living cells, in which it exerts a variety of biological effects depending on its chemical form and oxidation state. Tetravalent vanadium was shown to affect several genotoxicity end-points in vitro, but its genotoxic potential in vivo is not elucidated. In this study, the genotoxic effects induced in vivo by subacute oral exposure to vanadyl sulphate (VOSO4), a tetravalent vanadium salt, were investigated. To this aim male CD1 mice were administered with VOSO4 in drinking water over the dose range 2-1000 mg/l for 5 weeks. The incidence of micronucleated blood reticulocytes was measured along treatment period. At the end of treatment, micronuclei in both blood reticulocytes and bone marrow polychromatic erythrocytes were determined; in addition, DNA lesions detectable by comet assay were assessed in marrow and testicular cells. Tissue distribution of vanadium at sacrifice was determined by atomic absorption spectrometry. Comet assays and the analysis of micronuclei in polychromatic erythrocytes did not reveal treatment related effects. A slight increase in micronucleated reticulocytes, with no relationship with the administered dose, was observed in some treated groups. The determination of vanadium content in kidney, liver, spleen, bone, stomach, small intestine and testis highlighted low internal exposure, especially in soft tissues. Overall, data indicate scarce bioavailability for orally administered tetravalent vanadium, and lack of significant genotoxic potential in vivo.

2-Acetyl-1,3-cyclopentanedione–oxovanadium(IV) complexes. Acidity and implications for gastrointestinal absorption

Since vanadyl sulphate has demonstrated insulin-like effects on glucose metabolism in animal and human trials, and organic vanadium complexes are better absorbed by the intestinal tract than vanadyl species, in this work the complexation of oxovanadium(IV) with 2-acetyl-1,3-cyclopentanedione is studied. Kinetic and equilibria in aqueous 1:1 chelation are investigated spectrophotometrically in aqueous solution at 25 degrees C. The mechanism proposed to account for the kinetic data involves a reversible pathway where VO(+2) reacts with the enolate ion of the ligand. From calculated kinetic and thermodynamic parameters, it can be expected that the rates between final and initial monocharged complex concentration could help a better control of the absorption through the lipophilic membranes in the intestinal tract.

Vanadium in diabetes: 100 years from Phase 0 to Phase I

A little over one hundred years ago, a vanadium-containing compound was assessed clinically for use in treatment of human diabetic patients. The results were somewhat ambiguous, but nonetheless, intriguing. In 2000, the first Phase I clinical trial of a designed vanadium-based pharmaceutical agent (bis(ethylmaltolato)oxovanadium(IV), BEOV), was completed by Medeval Ltd., Manchester, UK. Results here, too, were promising, but not without some difficult remaining questions. In this review, we look back at the many questions asked and answered regarding vanadium's glucose-enhancing potential, its biodistribution and biomolecular transformation, and its mechanism(s) of action, and consider some of the newest developments in the field, including novel delivery methods for vanadium in diabetes treatment.

Are vanadium compounds drugable? Structures and effects of antidiabetic vanadium compounds: a critical review

Vanadate can be bioequivalent to phosphate and replace it in cellular metabolism. The detection of insulin-like activity has spurred interest in the development of oral anti-diabetic drugs containing vanadium. We collected and evaluated a vast toxicity data set and discussed molecular aspects related to insulin-mimetic effects of vanadium complexes.

New insights into the interactions of serum proteins with bis(maltolato)oxovanadium(IV): transport and biotransformation of insulin-enhancing vanadium pharmaceuticals

Significant new insights into the interactions of the potent insulin-enhancing compound bis(maltolato)oxovanadium(IV) (BMOV) with the serum proteins, apo-transferrin and albumin, are presented. Identical reaction products are observed by electron paramagnetic resonance (EPR) with either BMOV or vanadyl sulfate (VOSO4) in solutions of human serum apo-transferrin. Further detailed study rules out the presence of a ternary ligand-vanadyl-transferrin complex proposed previously. By contrast, differences in reaction products are observed for the interactions of BMOV and VOSO4 with human serum albumin (HSA), wherein adduct formation between albumin and BMOV is detected. In BMOV-albumin solutions, vanadyl ions are bound in a unique manner not observed in comparable solutions of VOSO4 and albumin. Presentation of chelated vanadyl ions precludes binding at the numerous nonspecific sites and produces a unique EPR spectrum which is assigned to a BMOV-HSA adduct. The adduct species cannot be produced, however, from a solution of VOSO4 and HSA titrated with maltol. Addition of maltol to a VOSO4-HSA solution instead results in formation of a different end product which has been assigned as a ternary complex, VO(ma)(HSA). Furthermore, analysis of solution equilibria using a model system of BMOV with 1-methylimidazole (formation constant log K1 = 4.5(1), by difference electronic absorption spectroscopy) lends support to an adduct binding mode (VO(ma)2-HSA) proposed herein for BMOV and HSA. This detailed report of an in vitro reactivity difference between VOSO4 and BMOV may have bearing on the form of active vanadium metabolites delivered to target tissues. Albumin binding of vanadium chelates is seen to have a potentially dramatic effect on pharmacokinetics, transport, and efficacy of these antidiabetic chelates.

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.

Ependymal epithelium disruption after vanadium pentoxide inhalation. A mice experimental model

The blood-brain barrier (BBB) protects the CNS against chemical insults. Regulation of blood-brain tissue exchange is accomplished by ependymal cells, which possess intercellular tight junctions. Loss of BBB function is an etiologic component of many neurological disorders. Vanadium (V) is a metalloid widely distributed in the environment and exerts potent toxic effects on a wide variety of biological systems. The current study examines the effects of Vanadium pentoxide (V2O5) inhalation in mice ependymal epithelium, through the analysis of the brain metal concentrations and the morphological modifications in the ependymal cells identified by scanning and transmission electron microscopy after 8 weeks of inhalation, in order to obtain a possible explanation about the mechanisms that V uses to enter and alter the CNS. Our results showed that V2O5 concentrations increase from the first week of study, stabilizing its values during the rest of the experiment. The morphological effects included cilia loss, cell sloughing and ependymal cell layer detachment. This damage can allow toxicants to modify the permeability of the epithelium and promote access of inflammatory mediators to the underlying neuronal tissue causing injury and neuronal death. Thus, understanding the mechanisms of BBB disruption would allow planning strategies to protect the brain from toxicants such as metals, which have increased in the atmosphere during the last decades and constitute an important health problem.

Pharmacokinetic Study and Trial for Preparation of Enteric-Coated Capsule Containing Insulinomimetic Vanadyl Compounds: Implications for Clinical Use

To treat patients suffering from diabetes mellitus, we developed several types of orally active vanadyl complexes to replace painful insulin injections, and prepared them in the form of enteric-coated capsules containing vanadium compounds. Pharmacokinetic analysis demonstrated that these capsules enhance the bioavailability of pharmacologically active vanadyl species.

Lung deposition and clearance of inhaled vanadium pentoxide in chronically exposed F344 rats and B6C3F1 mice

Female F344 rats and B6C3F1 mice were exposed to vanadium pentoxide (V2O5) at concentrations of 0, 0.5, 1, or 2 mg/m3 (rats) and 0, 1, 2, or 4 mg/m3 (mice) for 6 h/day, 5 days/week (for up to 18 months), by whole-body inhalation. Lung weights and lung burdens of vanadium were determined for exposed animals after 1, 5, and 12 days and after 1, 2, 6, 12, and 18 months of V2O5 exposure. Blood vanadium concentrations were determined at 1, 2, 6, 12, and 18 months for all animals including controls. A model that assumed a first-order deposition rate and a first-order elimination rate for vanadium was employed to fit the lung burden data. Comparisons between exposed groups indicated a progressive increase in lung weight with exposure concentration and time on exposure for both species. The vanadium lung burdens appeared to reach steady state in the lowest exposure groups (0.5 and 1 mg/m3 for rats and mice, respectively) but showed a decline in the higher exposure groups. This deposition pattern was similar between rats and mice but the maximum lung burdens were observed at different times (1 or 2 months in mice vs. 6 months in rats). The vanadium deposition rate decreased faster in mice, while the elimination half-lives of vanadium lung burdens were about six- to nine-fold shorter in mice than in rats at 1 and 2 mg/m3. Thus, the retention of vanadium in the lungs at 18 months was lower in mice (approximately 2% retained) compared with rats (13-15% retained) at the common exposure concentrations of 1 and 2 mg/m3. The lung burden data were approximately proportional to the exposure concentration in both species, likely due to concomitant decreases in deposition and elimination to a similar extent with increasing exposure. The area under the lung burden versus time curves and the area under the blood concentration (control-normalized) versus time curves were also proportional to exposure concentration. The progression of pathological changes in the lung with exposure and time is thought to affect the pattern and/or extent of vanadium deposition in the lungs following repeated exposures to V2O5.

A New Family of Insulin-Mimetic Vanadium Complexes Derived from 5-Carboalkoxypicolinates

The reaction of 5-carboalkoxypicolinic acid (5 ROpicH, R=Me, Et, iPr, sBu; 1 a-d) with vanadyl sulfate yielded the complexes [VO(H(2)O)(5 ROpic)(2)], 2 a-d, with H(2)O and one of the picolinato ligands in the equatorial positions, and the second picolinate occupying equatorial (N) and axial (O) positions. Reaction of 1 a with [NH(4)][VO(3)] yielded [NH(4)][VO(2)(5 MeOpic)(2)], [NH(4)]-3, in which the N functions of the picolinates are trans to the doubly bonded, cis-positioned oxo groups. Complexes 1 a.H(2)O, 1 b, 1 c, 2 a.3.5 H(2)O and [NH(4)]-3.4 H(2)O have been structurally characterised. A detailed pH-potentiometric solution speciation analysis of the system VO(2+)-1 a revealed a dominance of VO(5 OMepic)(2) between pH 2 and 6, with the same coordination pattern, evidenced by EPR spectroscopy, as in the crystalline solid state. In ternary systems containing physiological concentrations of the low molecular mass biogenic binders (B) lactate, oxalate, citrate or phosphate, ternary species of general composition VO(5 MeOpic)B dominate at physiological pH, with citrate being the most effective competitor for picolinate. All of the complexes trigger glucose uptake and degradation by simian virus modified mice fibroblasts at non-toxic concentrations (<100 microM), with 2 a, [VO(2)(pic)(2)](-) and [VO(2)(dipic)](-) being at least as effective as insulin. Vanadium uptake by the cells is most effective in the case of 2 a. 2 a also effectively inhibits free fatty acid release by rat adipocytes treated with epinephrine, thus mimicking the inhibition of lipolysis by insulin.

The therapeutic potential of insulin-mimetic vanadium complexes

Throughout the world, the number of patients suffering from diabetes mellitus (DM) is increasing on a daily basis, probably due to change in lifestyle. DM is mainly classified as either insulin-dependent Type 1 or non-insulin-dependent Type 2, according to the definition of WHO. To treat DM, which has many severe complications, several types of insulin preparations and synthetic drugs for Type 1 and Type 2 DM, respectively, have been developed and are in clinical use. However, there are several problems concerning the insulin preparations and synthetic drugs, such as physical and mental pain due to daily insulin injections and defects involving side effects, respectively. Consequently, a new class of therapeutic agents is anticipated. For this purpose, vanadium-containing complexes are expected to treat or improve both types of DM by using unique characteristics of the transition metal. In this article, the current state of research on insulin-mimetic vanadium complexes are reviewed, with special focus on the paramagnetic vanadyl (+4 oxidation state of vanadium) complexes with different coordination modes. To analyse the blood glucose-lowering effects of the vanadyl complexes, new results on the organ distribution and pharmacokinetic analysis of the vanadyl state in the blood of rats are also described.

NTP toxicology and carcinogensis studies of vanadium pentoxide (CAS No. 1314-62-1) in F344/N rats and B6C3F1 mice (inhalation)

Vanadium pentoxide, commercially the most important compound of vanadium, presents a potential occupational hazard during the cleaning of oil-fired boilers and furnaces, the handling of catalysts, and during the refining, processing, or burning of vanadium-rich mineral ores or fossil fuels. Vanadium pentoxide was nominated for study by the National Cancer Institute as a representative of the metals class study. Male and female F344/N rats and B6C3F1 mice were exposed to vanadium pentoxide (99% pure) by inhalation for 16 days, 14 weeks, or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium and mouse peripheral blood. 16-DAY STUDY IN RATS: Groups of five male and five female rats were exposed to particulate aerosols of vanadium pentoxide at concentrations of 0, 2, 4, 8, 16, or 32 mg/m(3) by inhalation, 6 hours per day, 5 days per week for 16 days. Three males in the 32 mg/m(3) group died before the end of the study. Mean body weights of males and females exposed to 8 mg/m(3) or greater were less than those of the chamber controls. Clinical findings included rapid respiration and hypoactivity in rats exposed to 16 or 32 mg/m(3). Relative lung weights of 4 mg/m(3) or greater males and 2 mg/m(3) or greater females were significantly greater than those of the chamber controls. Lavage fluid analysis indicated an inflammatory response in the lung that was either directly mediated by vanadium pentoxide or was secondary to lung damage induced by vanadium pentoxide exposure. 16-DAY STUDY IN MICE: Groups of five male and five female mice were exposed to particulate aerosols of vanadium pentoxide at concentrations of 0, 2, 4, 8, 16, or 32 mg/m(3) by inhalation, 6 hours per day, 5 days per week for 16 days. All males exposed to 32 mg/m(3) and one 8 mg/m(3) male died or were killed moribund before the end of the study. Mean body weights of 16 mg/m(3) males and 8 mg/m(3) or greater females were significantly less than those of the chamber controls, and the 32 mg/m(3) females lost weight during the study. Absolute and relative lung weights of 4 mg/m(3) or greater males and all exposed groups of females and liver weights of 16 mg/m(3) males were significantly greater than those of the chamber controls. The mediastinal lymph nodes were enlarged in 4, 8, and 16 mg/m(3) males and females, and lymphoid hyperplasia was confirmed histologically. Lavage fluid analysis indicated an inflammatory response in the lung that was either directly mediated by vanadium pentoxide or was secondary to lung damage induced by vanadium pentoxide exposure. 3-MONTH STUDY IN RATS: Groups of 10 male and 10 female rats were exposed to particulate aerosols of vanadium pentoxide at concentrations of 0, 1, 2, 4, 8, or 16 mg/m(3) by inhalation, 6 hours per day, 5 days per week for 3 months. Seven males and three females exposed to 16 mg/m(3) died during the study. Mean body weights were significantly less in males exposed to 4 mg/m(3) or greater and in females exposed to 16 mg/m(3). Abnormal breathing, thinness, lethargy, abnormal posture, and ruffled fur were observed in rats exposed to 16 mg/m(3). Hematology results indicated that exposure of rats to vanadium pentoxide induced a microcytic erythrocytosis in males and females. Absolute and relative lung weights were significantly greater for 4 mg/m(3) or greater males and females than for the chamber controls as were the relative lung weights of 2 mg/m(3) males. The estrous cycle of females exposed to 8 mg/m(3) was significantly longer than that of the chamber control group, and the number of cycling females in the 16 mg/m(3) group was reduced. The incidences of several nonneoplastic lesions of the lung and nose were significantly increased in males and females exposed to 2 mg/m(3) or greater. Data from pulmonary function analyses indicated that a restrictive lung disease was present in male and female rats exposed to 4 mg/m(3) or greater, while an obstructive lung disease was present only in the 16 mg/m(3) groups. 3-MONTH STUDY IN MICE: Groups of 10 male and 10 female mice were exposed to particulate aerosols of vanadium pentoxide at concentrations of 0, 1, 2, 4, 8, or 16 mg/m(3) by inhalation, 6 hours per day, 5 days per week for 3 months. One male exposed to 16 mg/m(3) died before the end of the study. Mean body weights of 8 and 16 mg/m(3) males and 4 mg/m(3) or greater females were significantly less than those of the chamber controls. Absolute and relative lung weights of males and females exposed to 4 mg/m(3) or greater were significantly greater than those of the chamber controls. The epididymal spermatozoal motility of males exposed to 8 or 16 mg/m(3) was significantly decreased. Some mice exposed to 2 or 4 mg/m(3) had inflammation of the lung, and all mice exposed to 8 or 16 mg/m(3) had inflammation and epithelial hyperplasia of the lung. 16-DAY SPECIAL STUDY IN RATS: Groups of 60 female rats were exposed to particulate aerosols of vanadium pentoxide at concentrations of 0, 1, or 2 mg/m(3) and groups of 40 female rats were exposed to 4 mg/m(3) by inhalation, 6 hours per day, 5 days per week for 16 days. Alveolar and bronchiolar epithelial hyperplasia was observed in most rats exposed to 2 or 4 mg/m(3) on days 6 and 13. Histiocytic infiltration and inflammation occurred in a time- and concentration-related manner. Cell turnover rates were increased in the terminal bronchioles on days 6 and 13 and in the alveoli in the 4 mg/m(3) group on day 6 and in all exposed groups on day 13. Assessment of lung vanadium concentrations suggested deposition and clearance exhibited linear kinetics over the exposure range studied. Lung clearance half-times ranged from 4.42 to 4.96 days. 16-DAY SPECIAL STUDY IN MICE: Groups of 60 female mice were exposed to particulate aerosols of vanadium pentoxide at concentrations of 0, 2, or 4 mg/m(3) and groups of 40 female mice were exposed to 8 mg/m(3) by inhalation, 6 hours per day, 5 days per week for 16 days. Alveolar and bronchiolar epithelial hyperplasia occurred with similar incidences and severities among the exposed groups on days 6 and 13, and time- and concentration-related increases in the incidences of interstitial inflammation and histiocytic infiltration also occurred in these groups. Cell turnover rates were increased in the terminal bronchioles on day 6 and remained greater than those of the chamber controls on day 13. In the alveoli, cell turnover rates were increased in an exposure concentration-related manner on day 13; cell turnover rates were increased only in the 8 mg/m(3) group on day 6. Assessment of lung vanadium concentrations suggested deposition and clearance exhibited linear kinetics over the exposure range studied. Lung clearance half-times ranged from 2.40 to 2.55 days. 2-YEAR STUDY IN RATS: Groups of 50 male and 50 female rats were exposed to particulate aerosols of vanadium pentoxide at concentrations of 0, 0.5, 1, or 2 mg/m(3) by inhalation, 6 hours per day, 5 days per week for 104 weeks. Survival and body weights of males and females were generally similar to those of the chamber controls. Mean body weights of females exposed to 2 mg/m(3) were less than those of the chamber controls throughout the study. Alveolar/bronchiolar neoplasms were present in exposed groups of male rats, and the incidences often exceeded the historical control ranges. Alveolar/bronchiolar adenomas were present in 0.5 and 1 mg/m(3) females; one 2 mg/m(3) female also had an alveolar/bronchiolar carcinoma. The incidence of alveolar/bronchiolar adenoma in the 0.5 mg/m(3) group was at the upper end of the historical control ranges. Nonneoplastic lesions related to vanadium pentoxide exposure occurred in the respiratory system (lung, larynx, and nose) of male and female rats, and the severities of these lesions generally increased with increasing exposure concentration. 2-YEAR STUDY IN MICE: Groups of 50 male and 50 female mice were exposed to particulate aerosols of vanadium pentoxide at concentrations of 0, 1, 2, or 4 mg/m(3) by inhalation, 6 hours per day, 5 days per week for 104 weeks. Survival of 4 mg/m(3) males was significantly less than that of the chamber controls. Mean body weights of 4 mg/m(3) males and all exposed groups of females were generally less than those of the chamber controls throughout the study, and those of males exposed to 2 mg/m(3) were less from week 85 to the end of the study. Many mice exposed to vanadium pentoxide were thin, and abnormal breathing was observed in some mice, particularly those exposed to 2 or 4 mg/m(3). The incidences of alveolar/bronchiolar neoplasms were significantly increased in all groups of exposed males and females. Nonneoplastic lesions related to vanadium pentoxide exposure occurred in the respiratory system (lung, larynx, and nose) of male and female mice, and the severities of these lesions generally increased with increasing exposure concentration. Bronchial lymph node hyperplasia was present in many exposed females.

MOLECULAR ONCOLOGY STUDIES

K-ras codon 12 mutation and loss of heterozygosity on chromosome 6 were detected in vanadium pentoxide-induced alveolar/bronchiolar carcinomas from mice.

GENETIC TOXICOLOGY

Vanadium pentoxide was not mutagenic in Salmonella typhimurium strain TA97, TA98, TA100, TA102, or TA1535, with or without induced rat or hamster liver S9 enzymes.

CONCLUSIONS

Under the conditions of this 2-year inhalation study, there was some evidence of carcinogenic activity of vanadium pentoxide in male F344/N rats and equivocal evidence of carcinogenic activity of vanadium pentoxide in female F344/Nrats based on the occurrence of alveolar/bronchiolar neoplasms. There was clear evidence of carcinogenic activity of vanadium pentoxide in male and female B6C3F1 mice based on increased incidences of alveolar/bronchiolar neoplasms. (ABSTRACT TRUNCATED)

Enteric-coating capsulation of insulinomimetic vanadyl sulfate enhances bioavailability of vanadyl species in rats

In recent years, there have been improvements in the treatment of type 2 diabetes by oral administration of vanadyl sulfate (VOSO4, VS). The maintenance of vanadyl levels in the blood of subjects with type 2 diabetes was found to be important for the insulinomimetic activity of VS. However, owing to low bioavailability of VS and the development of mild gastrointestinal symptoms and side-effects in some subjects, it is necessary to design more effective and safer dosages of VS. After discovering that VS is absorbed more thoroughly at the ileum than at other gastrointestinal sites, we investigated the absorption processes following oral administration of VS by preparing enteric-coated capsules (ECC). Although Cmax values were unchanged by the dosage forms, Tmax and MRT values associated with the enteric-coating capsulation were prolonged when compared with those observed with use of gelatin capsules (GC). An important finding was that the bioavailability of VS from ECC (9.8%) was almost double that of VS from either GC (4.0%) or the solution (4.8%). Administration of VS-containing ECC to diabetic patients is proposed to improve vanadyl absorption over that achieved by the administration of either GC or the solution.

Influence of chelation and oxidation state on vanadium bioavailability, and their effects on tissue concentrations of zinc, copper, and iron

Today, vanadium compounds are frequently included in nutritional supplements and are also being developed for therapeutic use in diabetes mellitus. Previously, tissue uptake of vanadium from bis(maltolato)oxovanadium(IV) (BMOV) was shown to be increased compared to its uptake from vanadyl sulfate (VS). Our primary objective was to test the hypothesis that complexation increases vanadium uptake and that this effect is independent of oxidation state. A secondary objective was to compare the effects of vanadium complexation and oxidation state on tissue iron, copper, and zinc. Wistar rats were fed either ammonium metavanadate (AMV), VS, or BMOV (1.2 mM each in the drinking water). Tissue uptake of V following 12 wk of BMOV or AMV was higher than that from VS (p < 0.05). BMOV led to decreased tissue Zn and increased bone Fe content. The same three compounds were compared in a cellular model of absorption (Caco-2 cells). Vanadium uptake from VS was higher than that from BMOV or AMV at 10 min, but from BMOV (250 microM only, 60 min), uptake was far greater than from AMV or VS. These results show that neither complexation nor oxidation state alone are adequate predictors of relative absorption, tissue accumulation, or trace element interactions.

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

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

Metabolic effects of vanadyl sulfate in humans with non-insulin-dependent diabetes mellitus: in vivo and in vitro studies

To investigate the efficacy and mechanism of action of vanadium salts as oral hypoglycemic agents, 16 type 2 diabetic patients were studied before and after 6 weeks of vanadyl sulfate (VOSO4) treatment at three doses. Glucose metabolism during a euglycemic insulin clamp did not increase at 75 mg/d, but improved in 3 of 5 subjects receiving 150 mg VOSO4 and 4 of 8 subjects receiving 300 mg VOSO4. Basal hepatic glucose production (HGP) and suppression of HGP by insulin were unchanged at all doses. Fasting glucose and hemoglobin A1c (HbA1c) decreased significantly in the 150- and 300-mg VOSO4 groups. At the highest dose, total cholesterol decreased, associated with a decrease in high-density lipoprotein (HDL). There was no change in systolic, diastolic, or mean arterial blood pressure on 24-hour ambulatory monitors at any dose. There was no apparent correlation between the clinical response and peak serum level of vanadium. The 150- and 300-mg vanadyl doses caused some gastrointestinal intolerance but did not increase tissue oxidative stress as assessed by thiobarbituric acid-reactive substances (TBARS). In muscle obtained during clamp studies prior to vanadium therapy, insulin stimulated the tyrosine phosphorylation of the insulin receptor, insulin receptor substrate-1 (IRS-1), and Shc proteins by 2- to 3-fold, while phosphatidylinositol 3-kinase (PI 3-kinase) activity associated with IRS-1 increased 4.7-fold during insulin stimulation (P = .02). Following vanadium, there was a consistent trend for increased basal levels of insulin receptor, Shc, and IRS-1 protein tyrosine phosphorylation and IRS-1-associated PI 3-kinase, but no further increase with insulin. There was no discernible correlation between tyrosine phosphorylation patterns and glucose disposal responses to vanadyl. While glycogen synthase fractional activity increased 1.5-fold following insulin infusion, there was no change in basal or insulin-stimulated activity after vanadyl. There was no increase in the protein phosphatase activity of muscle homogenates to exogenous substrate after vanadyl. Vanadyl sulfate appears safe at these doses for 6 weeks, but at the tolerated doses, it does not dramatically improve insulin sensitivity or glycemic control. Vanadyl modifies proteins in human skeletal muscle involved in early insulin signaling, including basal insulin receptor and substrate tyrosine phosphorylation and activation of PI 3-kinase, and is not additive or synergistic with insulin at these steps. Vanadyl sulfate does not modify the action of insulin to stimulate glycogen synthesis. Since glucose utilization is improved in some patients, vanadyl must also act at other steps of insulin action.

Kinetic analysis and comparison of uptake, distribution, and excretion of 48V-labeled compounds in rats

Vanadium has been found to be orally active in lowering plasma glucose levels; thus it provides a potential treatment for diabetes mellitus. Bis(maltolato)oxovanadium(IV) (BMOV) is a well-characterized organovanadium compound that has been shown in preliminary studies to have a potentially useful absorption profile. Tissue distributions of BMOV compared with those of vanadyl sulfate (VS) were studied in Wistar rats by using 48V as a tracer. In this study, the compounds were administered in carrier-added forms by either oral gavage or intraperitoneal injection. Data analyzed by a compartmental model, by using simulation, analysis, and modeling (i.e., SAAM II) software, showed a pattern of increased tissue uptake with use of 48V-BMOV compared with 48VS. The highest 48V concentrations at 24 h after gavage were in bone, followed by kidney and liver. Most ingested 48V was eliminated unabsorbed by fecal excretion. On average, 48V concentrations in bone, kidney, and liver 24 h after oral administration of 48V-BMOV were two to three times higher than those of 48VS, which is consistent with the increased glucose-lowering potency of BMOV in acute glucose lowering compared with VS.

Mechanism on insulin-like action of vanadyl sulfate: studies on interaction between rat adipocytes and vanadium compounds

When rats with streptozotocin (STZ)-induced diabetes were given a daily intraperitoneal (i.p.) injection of VOSO4 (+4 oxidation state of vanadium), their serum glucose dropped from hyperglycemic level to normal level within 2d and serum free fatty acid (FFA) level also dropped to normal level. Vanadium was incorporated in most organs as well as in the adipose tissues, as detected by neutron activation analysis (NAA). The mechanism for the insulin-like action vanadium in terms of FFA release from isolated rat adipocytes was investigated: (1) Vanadyl (IV) and vanadic (III) ions normalize the FFA release in the adipocytes treated with epinephrine; (2) vanadate (V) ion treated with ascorbic acid, cysteine or glucose is effective in normalizing the FFA release but vanadate ion alone has no effect on FFA release; (3) vanadyl ion is incorporated into the adipocytes, while vanadate ion is not, as indicated by ESR spectroscopy; and (4) vanadyl ion can act on the glucose transporter, as indicated by experiments using cytochalasin B which is an inhibitor of this transporter. From these results, the normalization of both serum glucose and FFA levels by vanadyl ion was concluded to be due to the incorporation of vanadyl ion into the adipocytes, in which the metal ion acts on the glucose transporter and induces both the promotion of glucose uptake and the decrease of FFA release form peripheral adipocytes. The vanadyl state was suggested to be a possible pharmacologically active form of vanadium allowing the insulin-like action.(ABSTRACT TRUNCATED AT 250 WORDS)

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

Streptozotocin-diabetic and non-diabetic rats were given vanadyl sulphate in drinking water at concentrations of 0.5-1.5 mg/ml for one year. It was found that vanadyl treatment did not produce persistent changes in plasma aspartate aminotransferase, alanine aminotransferase, and urea, specific morphological abnormalities in the brain, thymus, heart, lung, liver, spleen, pancreas, kidney, adrenal, or testis, or abnormal organ weight/body weight ratio for these organs in either non-diabetic or diabetic animals. Treatment significantly reduced the incidence of the occurrence of urinary stones in non-diabetic rats. In diabetic animals vanadyl treatment significantly reduced the mortality rate and prevented the elevation of plasma levels of alanine aminotransferase and urea, the increases in organ size, and the occurrence of megacolon but did not affect the development of renal and testicular tumours. Plasma and tissue concentrations of vanadium were determined and found to have the following order of distribution: bone > kidney > testis > liver > pancreas > plasma > brain. Vanadium was retained in these organs at 16 weeks following vanadyl withdrawal while the plasma levels were beneath detection limits. It is concluded that vanadyl sulphate at antidiabetic doses is not significantly toxic to rats following a one-year administration in drinking water, but vanadium may be retained in various organs for months after cessation of treatment.