Intrathecal Administration of Nanoclusters for Protecting Neurons against Oxidative Stress in Cerebral Ischemia/Reperfusion Injury

Oxidative stress is one of the important mechanisms in cerebral ischemia/reperfusion (I/R) injury. Antioxidants with high brain accumulation are highly desired to help prevent cerebral I/R injury. Herein, intrathecal injection of polyoxometalate (POM) nanoclusters as nano-antioxidants with preferential brain uptake were applied for neuronal protection in cerebral I/R injury. Using powerful positron emission tomography imaging, the uptake of nano-antioxidants in the brain was non-invasively and real-timely monitored. Our results demonstrated that POM nanoclusters rapidly reached the ischemic penumbra after intrathecal injection and effectively scavenged reactive oxygen species (ROS) for inhibiting oxidative stress. The infarct size was reduced, and neurological function was restored in cerebral I/R injury rat models. As a proof-of-concept, the intrathecal injection of nano-antioxidants is an excellent therapeutic strategy to ameliorate cerebral I/R injury.

Stimuli-Responsive "Cluster Bomb" for Programmed Tumor Therapy

In this paper, mesoporous silica nanoparticle (MSN) loaded with doxorubicin (DOX) and capped with tumor-homing/-penetrating peptide tLyP-1-modified tungsten disulfide quantum dots (WS₂-HP) was designed and applied as a stimuli-responsive "Cluster Bomb" for high-performance tumor suppression. The peptide tLyP-1 on the surface can both facilitate the homing of DOX@MSN-WS₂-HP to 4T1 tumor and greatly enhance the penetration of WS₂-HP in tumor. The benzoic-imine bonds as the linkers between "bomblets" and "dispenser" are stable under normal physical conditions and quite labile at pH 6.8. After arriving at the mild acidic tumor microenvironment, the nanoplatform can rapidly break into two parts: (1) electropositive DOX@MSN-NH₂ for efficient chemotherapy on surface tumor cells and (2) small-sized WS₂-HP with improved tumor penetrating ability for near-infrared (NIR)-light-triggered photothermal therapy (PTT) among deep-seated tumor cells. Having killed the tumor cells in different depths, DOX@MSN-WS₂-HP exhibited significant antitumor effect, which will find great potential in clinical trials.

Ultrastructural Analysis of In Vivo Hypoglycemiant Effect of Two Polyoxometalates in Rats with Streptozotocin-Induced Diabetes

Two polyoxometalates (POMs), synthesized through a self-assembling method, were used in the treatment of streptozotocin (STZ)-induced diabetic rats. One of these nanocompounds [tris(vanadyl)-substituted tungsto-antimonate(III)-anions—POM1] was previously described in the literature, whereas the second [tris-butyltin-21-tungsto-9-antimonate(III)-anions—POM2], was prepared by us based on our original formula. In rats with STZ-induced diabetes treated with POMs (up to a cumulative dose of 4 mg/kg bodyweight at the end of the treatments), statistically significant reduced levels of blood glucose were measured after 3 weeks, as compared with the diabetic control groups (DCGs). Ultrastructural analysis of pancreatic β-cells (including the mean diameter of secretory vesicles and of their insulin granules) in the treated diabetic rats proved the POMs contribute to limitation of cellular degeneration triggered by STZ, as well as to the presence of increased amounts of insulin-containing vesicles as compared with the DCG. The two POMs also showed hepatoprotective properties when ultrastructural aspects of hepatocytes in the experimental groups of rats were studied. Based on our in vivo studies, we concluded that the two POMs tested achieved hypoglycemiant effects by preventing STZ-triggered apoptosis of pancreatic β-cells and stimulation of insulin synthesis.

Tungstate promotes β-cell survival in Irs2-/- mice

Pancreatic β-cells play a central role in type 2 diabetes (T2D) development, which is characterized by the progressive decline of the functional β-cell mass that is associated mainly with increased β-cell apoptosis. Thus, understanding how to enhance survival of β-cells is key for the management of T2D. The insulin receptor substrate-2 (IRS-2) protein is pivotal in mediating the insulin/IGF signaling pathway in β-cells. In fact, IRS-2 is critically required for β-cell compensation in conditions of increased insulin demand and for β-cell survival. Tungstate is a powerful antidiabetic agent that has been shown to promote β-cell recovery in toxin-induced diabetic rodent models. In this study, we investigated whether tungstate could prevent the onset of diabetes in a scenario of dysregulated insulin/IGF signaling and massive β-cell death. To this end, we treated mice deficient in IRS2 (Irs2(-/-)), which exhibit severe β-cell loss, with tungstate for 3 wk. Tungstate normalized glucose tolerance in Irs2(-/-) mice in correlation with increased β-cell mass, increased β-cell replication, and a striking threefold reduction in β-cell apoptosis. Islets from treated Irs2(-/-) exhibited increased phosphorylated Erk1/2. Interestingly, tungstate repressed apoptosis-related genes in Irs2(-/-) islets in vitro, and ERK1/2 blockade abolished some of these effects. Gene expression profiling showed evidence of a broad impact of tungstate on cell death pathways in islets from Irs2(-/-) mice, consistent with reduced apoptotic rates. Our results support the finding that β-cell death can be arrested in the absence of IRS2 and that therapies aimed at reversing β-cell mass decline are potential strategies to prevent the progression to T2D.

Sodium tungstate administration ameliorated diabetes-induced electrical and contractile remodeling of rat heart without normalization of hyperglycemia

Recently, sodium tungstate was suggested to improve cardiac performance of diabetic rats in perfused hearts based on its insulinomimetic activity. In this study, we aimed to investigate the cellular and molecular mechanisms underlying this beneficial effect of sodium tungstate. Tungstate was administered (100 mg/kg/day) to diabetic and control rats intragastrically for 6 weeks. Blood glucose levels increased, whereas body weight, heart weight and plasma insulin levels decreased significantly in diabetic animals. Interestingly, none of these parameters was changed by tungstate treatment. On the other hand, fractional shortening and accompanying intracellular Ca(2+) [Ca(2+)](i) transients of isolated ventricular myocytes were measured, and sodium tungstate was found to improve the peak shortening and the amplitude of [Ca(2+)](i) transients in diabetic cardiomyocytes. Potassium and L-type Ca(2+) currents were also recorded in isolated ventricular cells. Significant restoration of suppressed I (to) and I (ss) was achieved by tungstate administration. Nevertheless, L-type calcium currents did not change either in untreated or treated diabetic rats. Tissue biochemical parameters including TBARS, protein carbonyl content, xanthine oxidase (XO) and xanthine dehydogenase (XDH) were also determined, and diabetes revealed a marked increase in TBARS and carbonyl content which were decreased significantly by tungstate treatment. Conversely, although XO and XDH activities didn't change in untreated diabetic rats, a remarkable but insignificant decrease was detected in treated animals. In conclusion, tungstate treatment improved diabetes-induced contractile abnormalities via restoration of dysregulated [Ca(2+)](i) and altered ionic currents. This beneficial effect is due to antioxidant property of sodium tungstate rather than normalization of hyperglycemia.

Sodium tungstate regulates food intake and body weight through activation of the hypothalamic leptin pathway

AIMS

Sodium tungstate is an anti-obesity drug targeting peripheral tissues. In vivo, sodium tungstate reduces body weight gain and food intake through increasing energy expenditure and lipid oxidation, but it also modulates hypothalamic gene expression when orally administered, raising the possibility of a direct effect of sodium tungstate on the central nervous system.

METHODS

Sodium tungstate was administered intraperitoneally (ip) to Wistar rats, and its levels were measured in cerebrospinal fluid through mass spectrometry. Body weight gain and food intake were monitored for 24 h after its administration in the third ventricle. Hypothalamic protein was obtained and subjected to western blot. In vitro, hypothalamic N29/4 cells were treated with 100 µM sodium tungstate or 1 nM leptin, and protein and neural gene expression were analysed.

RESULTS

Sodium tungstate crossed the blood-brain barrier, reaching a concentration of 1.31 ± 0.07 mg/l in cerebrospinal fluid 30 min after ip injection. When centrally administered, sodium tungstate decreased body weight gain and food intake and increased the phosphorylation state of the main kinases and proteins involved in leptin signalling. In vitro, sodium tungstate increased the phosphorylation of janus kinase-2 (JAK2) and extracellular signal-regulated kinase-1/2 (ERK1/2), but the activation of each kinase did not depend on each other. It regulated c-myc gene expression through the JAK2/STAT system and c-fos and AgRP (agouti-related peptide) gene expression through the ERK1/2 pathway simultaneously and independently.

CONCLUSIONS

Sodium tungstate increased the activity of several kinases involved in the leptin signalling system in an independent way, making it a suitable and promising candidate as a leptin-mimetic compound in order to manage obesity.

Antitumor and antiinflammatory effects of tetrathiotungstate in comparison with tetrathiomolybdate

Tetrathiomolybdate (TM) is an anticopper drug under development for treating Wilson's disease. Its mechanism of action involves forming a tight tripartite complex in the blood with serum albumin and available copper. When available copper levels are lowered in animals with TM, strong antiangiogenic and antitumor effects are observed. Similarly, TM has excellent efficacy in animal models of fibrotic, inflammatory, and autoimmune diseases, and it protects against heart damage from doxorubicin (DXR) and liver damage from acetaminophen, carbon tetrachloride, and concanavalin A. Tetrathiotungstate (TT) also forms a similar tripartite complex in the blood and has similar effects to TM on copper. In this article, whether TT had similar antitumor effects, and similar effects in protecting the heart against DXR toxicity, as TM was evaluated. It was found that the 2 drugs were comparable in their effects when doses were used that lowered copper availability to the same extent.

Phosphorylation events implicating p38 and PI3K mediate tungstate-effects in MIN6 beta cells

Oral administration of sodium tungstate is an effective treatment for diabetes in animal models. Several lines of evidence indicate the pancreatic beta cell as one of the targets of tungstate action. Here, we examined the molecular mechanism by which this compound exerts its effects on the beta cell line MIN6. Tungstate treatment induced phosphorylation and subsequent activation of p38 and PI3K which in turn are implicated in tungstate PDX-1 nuclear localization and activation. Although no effect was observed in glucose-induced insulin secretion we found that tungstate activates basal insulin release, a process driven, at least in part, by activation of p38. These results show a direct involvement of p38 and PI3K phosphorylation in the mechanism of action of tungstate in the beta cell.

Vanadate but not tungstate prevents the fructose-induced increase in GLUT5 expression and fructose uptake by neonatal rat intestine

Intermediary signals, precociously enhancing GLUT5 transcription in response to perfusion of its substrate, fructose, in the small intestine of neonatal rats, are not known. Because glucose-6-phosphatase (G6Pase), glucose-6-phosphate translocase (G6PT), and fructose-1,6-bisphosphatase (FBPase) expression increases parallel to or precedes that of GLUT5, we investigated the link between these gluconeogenic genes and GLUT5 by using vanadate or tungstate, potent inhibitors of gluconeogenesis. Small intestinal perfusions of 20-d-old rats were performed with fructose alone, fructose + vanadate or tungstate, glucose alone, and glucose + vanadate or tungstate. As expected, fructose, but not glucose nor glucose + inhibitor perfusion, increased GLUT5 mRNA abundance and fructose transport. Fructose perfusion dramatically increased G6Pase mRNA abundance but had no effect on G6Pase activity. In sharp contrast, fructose perfusion did not increase FBPase gene expression but stimulated FBPase activity. Both vanadate and tungstate significantly inhibited G6Pase activity but did not prevent the fructose-induced increases in G6Pase and G6PT gene expression. Perfusion with fructose + vanadate prevented the fructose-induced increases in fructose transport and GLUT5 mRNA abundance, whereas perfusion with fructose + tungstate did not. Interestingly, vanadate, but not tungstate, inhibited the fructose-induced increase in FBPase activity. Thus, vanadate inhibition of fructose-induced increases in FBPase activity paralleled exactly vanadate inhibition of fructose-induced increases in GLUT5 mRNA abundance and activity. Fructose-induced changes in FBPase activity may regulate changes in GLUT5 expression and activity in the small intestine of neonatal rats. The marked increases in intestinal G6Pase and GLUT5 mRNA abundance may be a parallel response to different factors released during fructose perfusion.

Oral administration of sodium tungstate improves cardiac performance in streptozotocin-induced diabetic rats

Normalization of hyperglycemia and hyperlipidemia is an important objective in preventing diabetes-induced cardiac dysfunction. Our study investigated the effects of sodium tungstate on cardiac performance in streptozotocin-induced (STZ) diabetic rats based on its potential antidiabetic and antioxidant activity. Male Wistar rats were made STZ-diabetic and then treated with tungstate in their drinking water for 9 weeks. Body mass, food and fluid intake, plasma glucose, insulin, triglyceride, and free fatty acids levels were measured. At the termination of the study period, an oral glucose tolerance test (OGTT) was performed, and cardiac performance was evaluated using an isolated working heart apparatus. Tungstate-treated STZ-diabetic rats showed a significant reduction in fluid and food intake, plasma glucose, triglycerides, and free fatty acid levels, and improved tolerance to glucose in OGTT, owing to tungstate-mediated enhancement of insulin activity rather than increased insulin levels. Left ventricular pressure development, the rate of contraction (+dP/dT), and the rate of relaxation (-dP/dT) were significantly improved in tungstate-treated diabetic rats. Apart from a decreased rate of body mass gain, no other signs of toxicity or hypoglycemic episodes were observed in tungstate-treated rats. This study extends previous observations on the antidiabetic activities of tungstate, and also reports for the first time the salutary effects in preventing diabetic cardiomyopathy.

Synthesis, characterization, and antitumoral activity of polyoxometalate loaded starch nanocomplexes

Using a reverse-phase microemulsion polymerization method and an encapsulating method, polyoxometalates (POMs) K6SiW11TiO40 incorporating starch microspheres have been prepared and structurally characterized by elemental analyses, IR, UV-vis, and NMR spectroscopy. The size of SiW11TiO40/starch particles is about 40-60 nm. The polyoxometalate encapsulated by a starch microsphere retains the parent structure. The starch microsphere is a good carrier, as it is able to enhance the antitumoral activity of POMs and decrease the toxicity of POMs as well.

Embedded weapons-grade tungsten alloy shrapnel rapidly induces metastatic high-grade rhabdomyosarcomas in F344 rats

Continuing concern regarding the potential health and environmental effects of depleted uranium and lead has resulted in many countries adding tungsten alloy (WA)-based munitions to their battlefield arsenals as replacements for these metals. Because the alloys used in many munitions are relatively recent additions to the list of militarily relevant metals, very little is known about the health effects of these metals after internalization as embedded shrapnel. Previous work in this laboratory developed a rodent model system that mimicked shrapnel loads seen in wounded personnel from the 1991 Persian Gulf War. In the present study, we used that system and male F344 rats, implanted intramuscularly with pellets (1 mm times 2 mm cylinders) of weapons-grade WA, to simulate shrapnel wounds. Rats were implanted with 4 (low dose) or 20 pellets (high dose) of WA. Tantalum (20 pellets) and nickel (20 pellets) served as negative and positive controls, respectively. The high-dose WA-implanted rats (n = 46) developed extremely aggressive tumors surrounding the pellets within 4-5 months after implantation. The low-dose WA-implanted rats (n = 46) and nickel-implanted rats (n = 36) also developed tumors surrounding the pellets but at a slower rate. Rats implanted with tantalum (n = 46), an inert control metal, did not develop tumors. Tumor yield was 100% in both the low- and high-dose WA groups. The tumors, characterized as high-grade pleomorphic rhabdomyosarcomas by histopathology and immunohistochemical examination, rapidly metastasized to the lung and necessitated euthanasia of the animal. Significant hematologic changes, indicative of polycythemia, were also observed in the high-dose WA-implanted rats. These changes were apparent as early as 1 month postimplantation in the high-dose WA rats, well before any overt signs of tumor development. These results point out the need for further studies investigating the health effects of tungsten and tungsten-based alloys.

Identification of aldehyde oxidase 1 and aldehyde oxidase homologue 1 as dioxin-inducible genes

Aldehyde oxidases are a family of highly related molybdo-flavoenzymes acting upon a variety of compounds of industrial and medical importance. We have identified aldehyde oxidase 1 (AOX1) as a 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin) inducible gene in the mouse hepatoma cell line Hepa-1. AOX1 mRNA levels were not increased by dioxin in mutant derivatives of the Hepa-1 cell line lacking either functional aryl hydrocarbon receptor (AHR) or aryl hydrocarbon receptor nuclear translocator (ARNT) proteins, thus demonstrating that transcriptional induction of AOX1 in response to dioxin occurs through the AHR pathway. Dioxin induction of AOX1 mRNA was also observed in mouse liver. In addition, levels of AOX1 protein as well as those of aldehyde oxidase homologue 1 (AOH1), a recently identified homolog of AOX1, were elevated in mouse liver in response to dioxin. Employing an aldehyde oxidase specific substrate, AOX1/AOH1 activity was shown to be induced by dioxin in mouse liver. This activity was inhibited by a known inhibitor of aldehyde oxidases, and eliminated by including tungstate in the mouse diet, which is known to lead to inactivation of molybdoflavoenzymes, thus confirming that the enzymatic activity was attributable to AOX1/AOH1. Our observations thus identify two additional xenobiotic metabolizing enzymes induced by dioxin.

Influence of food and diabetes on pharmacokinetics of sodium tungstate in rat

In this paper, the influence of food and diabetes on the pharmacokinetics of sodium tungstate in rat was investigated. The compound was administered intravenously (9 mg/kg) and orally in the form of solution (36 mg/kg). An empirical Bayes methodology was used to compute individual pharmacokinetic parameters. Sodium tungstate followed first-order kinetics, and plasma concentration versus time data were described by a two-compartment model. A significant relationship was found between the bioavailability and the status of the animals. Total plasma clearance and elimination half-life averaged 3.1 ml/min/kg and 1.6 h, respectively. Food had some effects on the extent of sodium tungstate absorption. After oral administration, the bioavailability (0.67 versus 0.85), C(max) (6.10 versus 15.2 microg/ml) and AUC (70.7 versus 105 mgh/l) were 20, 60 and 32% lower in fed than in fasted rats, respectively. The presence of cellulose and sulphate anions in rat chow could partially explain the fed state-associated reduction of tungstate bioavailability. In streptozotocin-induced diabetic fed rats, a 25% decrease occurred in AUC and F, and a 14% increase occurred in the elimination rate constant compared with healthy fed rats. These changes could be explain on the one hand, by the increase of liquid consumption and food intake, and on the other hand, by a gastroparesis in the early diabetic rats.

Oral tungstate treatment improves only transiently alteration of glucose metabolism in a new rat model of type 2 diabetes

It has been shown that tungstate is an effective hypoglycemic agent in several animal models of diabetes. In this study, we examined the effectiveness of oral tungstate treatment in a new experimental diabetic syndrome, induced by streptozotocin (STZ) and nicotinamide in adult rats, that shares several features with human type 2 diabetes. Sodium tungstate was administered in the drinking water (2 mg/mL) of control and diabetic rats for 15, 30, 60, and 90 d. Glucose metabolism was explored in vivo by intravenous glucose tolerance test. Insulin secretion and action were assessed in vitro in the isolated perfused pancreas and isolated adipocytes, respectively. Two weeks of tungstate treatment did not modify the moderate hyperglycemia of diabetic rats but reduced their intolerance to glucose, owing to an enhancement of postloading insulin secretion. However, this effect was transient, since it declined after 30 d and vanished after 60 and 90 d of tungstate administration, whereas a trend toward a reduction in basal hyperglycemia was observed on prolonged treatment. Oral tungstate was unable to modify glucose-stimulated insulin secretion in the isolated perfused pancreas, as well as muscle glycogen levels, hepatic glucose metabolism, and insulin-stimulated lipogenesis in isolated adipocytes. Nevertheless, the decreased insulin content of pancreatic islets of diabetic rats was partially restored on prolonged tungstate treatment. In conclusion, in the STZ-nicotinamide model of diabetes, tungstate was unable to permanently correct the alterations in glucose metabolism, despite some indirect evidence of a trophic effect on beta-cells. The ineffectiveness of tungstate could be related to the absence, in this diabetic syndrome, of relevant metabolic alterations in the liver, which thus appear to constitute the major target of tungstate action.

An application of population kinetics analysis to estimate pharmacokinetic parameters of sodium tungstate after multiple-dose during preclinical studies in rats

The purpose of this study was to use a population approach in the preclinical development program of sodium tungstate in the rat in order i) to compute individual pharmacokinetic parameters of this compound after repeated oral administrations, until the 4-week toxicology study, using an empirical Bayes methodology; and ii) to study the influence of the administered dose, of the gender and of the duration of treatment on the pharmacokinetic parameters. Four studies were used representing a mixture of single intravenous administration and multiple oral administrations. The treatment duration ranged from 7 to 28 days. Intravenous dose was 9 mg/kg; three different oral doses were tested, 50, 100 and 200 mg/kg/day. Plasma concentration profiles versus time were compatible with a two-compartment model. A significant gender effect was found on bioavailability. The duration of treatment and the administered dose did not significantly explain part of the interindividual variability of pharmacokinetic parameters. The absorption of tungsten was rapid (1-3 hr). Total plasma clearance and elimination half-life averaged 2.8 ml/min/kg and 3.04 hr in males, and 3 ml/min/kg and 2.74 hr in females. The bioavailability was on an average 70%; being significantly higher in females than in males (0.78 versus 0.61). This compartmental approach should be considered as complementary to the usual non-compartmental approach used for analysis of preclinical data and should be a valuable tool to characterise the pharacokinetic/pharmacodynamic behaviour of a drug.

Estimation of pharmacokinetic parameters of sodium tungstate after multiple-dose during preclinical studies in beagle dogs

In this paper, an empirical Bayes methodology was used to determine the pharmacokinetic profile of sodium tungstate in beagle dogs after multiple oral dosing using the P-PHARM computer program. The population estimation algorithm used in P-PHARM is an EM-type procedure. Sodium tungstate was administered orally, three times a day, (i) for 11 days (21 and 42 mg/kg per day) to 18 dogs (nine males and nine females) and (ii) for 13 weeks (15, 30 and 60 mg/kg per day) to 28 dogs (14 males, 14 females). Six other dogs received the compound intravenously (25 and 50 mg/kg). Plasma concentration profiles versus time were compatible with a two-compartment model and first-order kinetics. After oral administration, F (0.61+/-0.086 vs. 0.48+/-0.093), and normalized (to a 7-mg/kg dose of sodium tungstate) AUC (54+/-8.4 vs. 41.2+/-8.5 mg/l x h), C(max) (10.6+/-0.49 vs. 8.5+/-0.57 microg/ml) and C(min) (3.04+/-0.23 vs. 2.04+/-0.22 microg/ml), were higher in male than in female dogs. However, the introduction of the gender in the final model did not contribute statistically to an improvement of the fit of the population pharmacokinetic model. In males, t(1/2) elimination averaged 3.1+/-0.56 vs. 2.6+/-0.18 h in females. The duration of treatment did not modify statistically the pharmacokinetic parameters. After repeated multiple oral administration of 15-60 mg/kg per day of sodium tungstate, tungsten plasma concentrations increased in proportion to dose. No dose-dependent changes in pharmacokinetic parameters occurred.

Insulin mimetic effect of a tungstate cluster. Effect of oral administration of homo-polyoxotungstates and vanadium-substituted polyoxotungstates on blood glucose level of STZ mice

Aqueous vanadate and aqueous tungstate have been known to mimic all or most of the actions of insulin in intact cell systems with respect to normalization of the blood glucose level. By carrying out oral administration in vivo experiments on the blood glucose level of streptozotocin (STZ)-induced diabetes (STZ mice), the insulin-mimetic (IM) effects of metal-oxide clusters of all-inorganic composition were examined using many types of polyoxometalates (POM) with and without vanadium substitution. Several homo-POM and vanadium-substituted POM showed hypoglycemic effects. The observed hypoglycemic effects indicated that POM with the Dawson structure [[alpha-P(2)W(18)O(62)](6-) (W-2), [alpha-P(2)W(17)V(V)O(62)](7-) (V-19) and [alpha-1,2,3-P(2)W(15)V(V)(3)O(62)](9-) (V-04)] are more effective than those with the Keggin structure [[alpha-PW(12)O(40)](3-) (W-1), [alpha-PW(11)V(V)O(40)](4-) (V-01), [alpha-1,2-PW(10)V(V)(2)O(40)](5-) (V-02), [alpha-1,2,3-PW(9)V(V)(3)O(40)](6-) (V-03) and [alpha-1,4,9-PW(9)V(V)(3)O(40)](6-) (V-13)]. The vanadate cluster [V(10)O(28)](6-) (V-15) also showed a hypoglycemic effect. (31)P and (51)V NMR measurements showed that the Dawson POM (W-2, V-04 and V-19) are stable in aqueous solution under the conditions used. The effect of all POM on the body weight of STZ mice was also examined. The decrease in body weight after administration of W-2 was much less than for V-19, V-04 and V-15. This suggests that not only monomeric tungstate and vanadate, but also the structure factors of tungstate and vanadate clusters, can play a significant role in their biological action.

[Activity of digestive enzymes during intraperitoneal intake of metal compounds]

Digestive function was studied when three compounds from Group VIB of the Mendeleev periodic system of elements were intraperitoneally administered during 100 days. Potassium bichromate, ammonium molybdate in a dose of 0.2 mg/kg and sodium tungstate in a dose of 5.0 mg/kg (in terms of metal) were found to have a resorptive effect on pancreatic function and a local effect on the small intestinal mucosa.

Tungstate is an effective antidiabetic agent in streptozotocin-induced diabetic rats: a long-term study

AIMS/HYPOTHESIS

Recent studies have shown the anti diabetic effects of oral sodium tungstate treatment in several animal models of diabetes based on short-term experiments. In this study, we examined the effectiveness of long-term tungstate treatment of streptozotocin-induced-diabetic rats.

METHODS

Tungstate was administered to the drinking water of rats for eight months.

RESULTS

The treatment resulted in a reduction in serum glucose concentrations in diabetic rats, but no change in glycaemia was detected in healthy rats. Alterations in the hepatic glucose metabolism due to diabetes were almost completely counteracted by tungstate treatment. The partial recovery of glucokinase activity, not found in diabetic animals, normalised glycogen and glucose 6-phosphate concentrations. Tungstate treatment also restored pyruvate kinase activity and fructose 2,6-bisphosphate concentrations. In healthy rats, tungstate treatment did not modify the majority of the hepatic parameters studied. Moreover, tungstate treatment prevented diabetes-induced morphological changes in the kidney and ocular lens and also reduced mortality. Furthermore, no hypoglycaemic episodes or undesirable side effects were observed in treated diabetic or healthy rats. In addition, there is no evidence of intolerance developing after prolonged use.

CONCLUSION/INTERPRETATION

Tungstate could play a helpful part in the long-term treatment of diabetes.

Antiviral activity of mixed-valence rare earth borotungstate heteropoly blues against influenza virus in mice

The acute and accumulated toxicity of the rare earth borotungstate heteropoly blues, HPB-2, Ce2H3[BW9(VI)W2(V)Mn(H2O)O39].12H2O, which is active against influenza virus in Kunming mice, were investigated in Kunming mice following oral and intraperitoneal administration. The activity of HPB-2 against influenza virus (FM1) in the mice was then investigated. HPB-2, given either orally (p.o.) or intraperitoneally (i.p.), was shown to have activity. HPB-2 was shown to be more effective than the positive control, ribavirin, and it was also found that i.p. administration was more effective than p.o. administration.

Changes in F-actin organization induced by hard metal particle exposure in rat pulmonary epithelial cells using laser scanning confocal microscopy

Chronic inhalation of hard metal (WC-Co) particles causes alveolitis and the eventual development of pulmonary fibrosis. The initial inflammatory response includes a change in the alveolar epithelial cell-capillary barrier, which has been shown to be regulated by the state of assembly and organization of the actin cytoskeletal network. The objective of this study was to evaluate the effect WC-Co particles have on F-actin organization of lung epithelial cells in an in vitro culture system. Rat lung epithelial (L2) cells were exposed to 5, 25, and 100 microg/mL of WC-Co particles, as well as the individual components (Co and WC) of the hard metal mixture particles for 24 h. The effect on F-actin organization was visualized by laser scanning confocal microscopy (LSCM) following Bodipy-Phallacidin staining. Minimal changes in the F-actin microfilaments of L2 cells were observed by LSCM after exposure to WC and WC-Co at 5 and 25 microg/mL, while at 100 microg/mL, there was a noticeable disruption in the uniform distribution of L2 cell F-actin microfilaments. After exposure to Co, a dose-dependent change in the F-actin organization of the L2 cells was observed. Little change in F-actin assembly was observed after treatment with 5 microg/mL of Co (the concentration equivalent to the 5% amount of Co commonly present in 100 microg/mL of the WC-Co sample mixture). However, at 100 microg/mL of Co, the microfilaments aggregated into homogeneous masses within the cells, and a significant loss in the organization of L2 F-actin was observed. These dramatic alterations in F-actin organization seen after exposure to the higher doses of Co were attributed to an increase in L2 cell injury as measured by lactate dehydrogenase and trypan blue exclusion. We conclude the pulmonary response evoked in the lung by inhalation of high levels of WC-Co particles is unlikely due to alterations in the F-actin microfilaments of lung-epithelial cells.

Effects of tungstate in neonatally streptozotocin-induced diabetic rats: mechanism leading to normalization of glycaemia

The effects of oral administration of tungstate to an animal model of non-insulin-dependent diabetes mellitus (NIDDM), the neonatally streptozotocin-induced diabetic rat was studied. Islet insulin content and beta-cell mass were lowered in these animals. Furthermore, the islets lost their ability to release insulin in response to an increase in glucose concentration. However, the hepatic glucose metabolism in these diabetic animals before the treatment was not significantly altered with regard to glycogen content, or glucokinase or glycogen phosphorylase activities compared with healthy animals. On the other hand, the activation state of glycogen synthase was higher although the total activity was unchanged. Moreover, a 20% increase in the concentrations of liver glucose 6-phosphate compared to their healthy siblings was observed. Oral administration of tungstate for 15 days normalized glycaemia in these diabetic animals (4.6 vs 7.8 mmol/l). Tungstate administration was also able to normalize beta-cell insulin secretion in response to 16.7 mmol/l glucose stimulus, reaching values similar to those observed in healthy animals. Concomitantly, a partial recovery in the insulin content and in preproinsulin mRNA levels was found in the islets of treated animals, which was associated with an increase in the number of beta-cells in the pancreas (1.73 vs 0.86%). The treatment did not change the liver parameters studied, except that it restored glucose 6-phosphate concentrations to healthy values. These data suggest that tungstate administration causes a normalization of glycaemia through the restoration of islet function.

Tungstic acid reduction of cold-resistant stress-induced ulceration in rats

Sprague-Dawley rats were restrained at 4 degrees C for 2 h (stress). Tungstic acid in a single dose of 0.01, 0.1, 1, 10, 100 or 300 mg/kg (dissolved in distilled water) was administered intragastrically to animals 30 min prior to stress. Stress induced significant gastric mucosal damage, whereas tungstic acid pretreatment dose-dependently reduced lesion formation. Doses of tungstic acid of 1 mg/kg and higher significantly (P < 0.05-0.001) decreased ulcers. The mucosal mast cell counts in rats pretreated with tungstic acid were significantly higher than those of control rats. In motility experiments using oral administration of amberlite pellets, pretreatment with tungstic acid dose-dependently reduced the gastric emptying rate during a 1 h period of stress. Gastric mucosal xanthine oxidase and superoxide dismutase (SOD) activities, after pretreatment with a single dose of tungstic acid, were not altered in stressed animals. It is suggested that tungstic acid effectively antagonizes stress-induced gastric ulcers, possibly by decreasing motility and mass cell degranulation. Xanthine oxidase and SOD activities and mucous content were not changed in the gastric mucosa by the present method of tungstic acid administration.

Preliminary data on hard metal workers exposure to tungsten oxide fibres

The first personal exposure data for tungsten oxide fibres, in two hard metal manufacturing industries is presented. Occupational exposure was studied by static and personal measurements during tungsten metal production. Three different initial materials were used, ammonium-paratungstate (APT), blue oxide and tungsten trioxide. In both factories, airborne tungsten oxide fibres were detected both in static and personal samples. Fibre exposure varies for different activities. Charging of raw material, changing the hammer, cleaning-work on the cyclone and the micro-filter were found to be among the most high dusty operations. However, as workers use respirators during cleaning operations, these filters could not be related to personal exposure. The calcination of APT to the blue oxide generates fibrous dust. The raw material imported as blue oxide is also fibrous material and both charging it into the calcination furnace and re-charging it into the reduction furnace generates unnecessarily additional dusty periods. A single reduction-stage is, therefore, preferable. Furthermore, the tungsten trioxide raw material is non-fibrous, therefore, calcination of APT to tungsten trioxide and its reduction to tungsten metal is preferable with respect to minimising workers exposure to tungsten oxide fibres.

Lung injury after hepatoenteric ischemia-reperfusion: role of xanthine oxidase

Oxidant stress plays a major role in the pathophysiologic processes associated with ischemia-reperfusion injury. Xanthine oxidase (XO) is often implicated as a significant source of oxidants and increases in the circulation after hepatoenteric ischemia-reperfusion. We hypothesized that pulmonary injury is associated with hepatic ischemia-reperfusion resulting from descending thoracic aorta occlusion-reperfusion (AoOR). We also proposed that this remote pulmonary injury is attenuated through inactivation of circulating and tissue XO by tungstate, implicating an XO-dependent mechanism. Aortic occlusion was established in rabbits (standard or tungstate diet) for 40 min by 2 h reperfusion. Sham operated rabbits (standard or tungstate diet) served as controls. Hepatic reperfusion injury, as manifested by release of the hepatocellular enzyme alanine aminotransferase (ALT), was markedly increased after AoOR. Suprarenal-infrahepatic occlusion failed to increase ALT release. Tungstate pretreatment significantly (p < 0.05) reduced XO activity and ameliorated liver and intestinal injury (p < 0.05). Lung injury, manifested by increased bronchoalveolar lavage (BAL) protein concentration, BAL lactate dehydrogenase (LDH) activity and increased lung edema was significantly associated with liver injury (p < 0.05) and circulating XO activity (p < 0.001). XO inactivation significantly decreased BAL protein concentration, BAL LDH activity, and lung edema (p < 0.05). We conclude that remote pulmonary injury is significantly influenced by the extent of liver injury and circulating XO activity.

Alveolar macrophages accumulate iron and ferritin after in vivo exposure to iron or tungsten dusts

Extracellular iron present in alveolar structures may contribute to oxidative lung injury induced by toxic mineral dusts by enhancing dust-induced generation of hydroxyl radicals. Alveolar macrophages (AMs) can sequester iron within ferritin and limit generation of hydroxyl radicals. In the current study we sought to assess whether AMs accumulate iron and ferritin after in vivo exposure to a dust with high iron content, to iron oxide, or to an inflammatory dust, calcium tungstate. We performed lung lavage 1, 7, 14, 28, 42, and 56 days after intratracheal instillation of mineral dust in saline solution or instillation of saline solution alone and quantitated cell recovery and AM content of iron and ferritin. Instillation of iron oxide increased neutrophil recovery only on a day 1 when compared with results in controls, whereas calcium tungstate increased neutrophil recovery through day 14. AMs recovered after instillation of iron oxide contained increased amounts of iron and ferritin, beginning on day 1 and progressing through day 56 after treatment (7.57 +/- 0.38 microgram iron per 10(6) AMs vs 1.54 +/- 0.28 microgram iron per 10(6) AMs for controls, p < 0.001; and 5908 +/- 768 ng ferritin per 10(6) AMs vs 395 +/- 20 ng ferritin per 10(6) AMs, p < 0.001). AMs recovered after calcium tungstate instillation also contained increased amounts of iron and ferritin beginning 14 days after treatment, with greatest content 42 days after treatment (4.85 +/- 0.68 microgram iron per 10(6) AMs, p < 0.001, and 2274 +/- 736 ng ferritin per 10(6) AMs, p < 0.001). Tumor necrosis factor, which can enhance iron accumulation by macrophages, was spontaneously released by AMs recovered from tungsten-treated rats. These studies indicate that AMs accumulate iron and ferritin in response to both iron loading of the lungs with iron oxide exposure and lung inflammation induced by calcium tungstate exposure.

The delayed lung responses to single and repeated intratracheal administration of pure cobalt and hard metal powder in the rat

Epidemiological and clinical studies suggest that inhalation of cobalt metal dust (Co) mixed with tungsten carbide particles (WC), but not of cobalt dust alone, may cause interstitial pulmonary lesions (hard metal disease). In previous experimental studies in the rat, we have demonstrated the greater acute pulmonary toxicity of a WC-Co mixture compared to Co or WC alone. The present study was undertaken to compare in the same animal model the delayed lung response after intratracheal administration of Co or WC-Co particles (cobalt particle 6.3 wt%). The responses were also compared with those obtained after treatment with arsenic trioxide and crystalline silica used a reference materials producing an acute toxic insult and a progressive fibrogenic response, respectively. Cellular (total and differential counts) and biochemical parameters (LDH, N-acetyl-beta-D-glucosaminidase, total protein, albumin, fibronectin, and hyaluronic acid) were measured in bronchoalveolar lavage fluid following single and repeated intratracheal instillations. The results indicate that the delayed lung response observed after WC-Co is different from that after cobalt metal alone. A single intratracheal dose of WC-Co (1, 5, or 10 mg/100 g body wt) induced an acute alveolitis which persisted for at least 1 month. Four months after a single instillation of WC-Co, no clear histological lung fibrosis could however be evidenced, indicating a reversibility of the lesions. The effects of cobalt (0.06, 0.3, or 0.6 mg/100 g body wt) or tungsten carbide alone (1, 5, 10 mg/ 100 g body wt) were very modest, if any. Following repeated intratracheal instillations (four administrations at 1-month interval), increased lung hydroxyproline content and histopathological evidence of interstitial fibrosis were observed after WC-Co (4 x 1 mg/100 g body wt), but not after administration of each component separately, i.e., Co (4 x 0.06 mg/100 g body wt) or WC (4 x 1 mg/100 g body wt). The mechanism of the fibrotic reaction induced by WC-Co seems different from the progressive inflammatory reaction induced by crystalline silica. We suggest that it might result from a scarring reaction elicited by repeated acute insults as observed after repeated administration of arsenic trioxide.

Thiotungstate-copper interactions II. The effects of tetrathiotungstate on systemic copper metabolism in normal and copper-treated rats

The intraperitoneal administration of tetrathiotungstate to rats (6-17.4 mg W/Kg BW) caused profound changes in copper metabolism in both normal rats and in rats pretreated with copper. Plasma copper associated with albumin increased, liver copper, particularly cytosol copper, was depleted, and biliary excretion was increased. There was also a movement of copper to higher molecular weight proteins in both liver cytosol and bile. In contrast to penicillamine, tetrathiotungstate did not increase liver cytosolic apometallothionein levels and reduced the rise provoked by copper. Metallothionein-bound copper was removed. Ceruloplasmin oxidase activity was inhibited and there was evidence for increased movement of copper into subcellular organelles, probably lysosomes. It is concluded that tetrathiotungstate has a genuine "decoppering" effect and could be considered as an alternative to thiomolybdates in the treatment of copper storage diseases.

Thiotungstate-copper interactions. I. Studies on the metabolism of [185W] tetrathiotungstate and the systemic interactions of labeled pharmacological doses with copper in rats

[185W] tetrathiotungstate was employed to study the metabolism of thiocompounds in rats after i.v. injection. At tracer levels (12.5 micrograms W) the most important plasma binding protein eluted in the position of ceruloplasmin but the association did not prevent uptake of thiotungstate by the liver. At higher dose levels (1.5 mg W) there was considerable hydrolysis immediately after injection with rapid excretion of label in urine. The [185W] tetrathiotungstate remaining in plasma was associated with albumin and the amount retained was increased by pretreatment of the rats with copper. The increased binding to albumin did not prevent hepatic uptake and over the short-term pretreatment with copper increased the movement of the isotope into subcellular organelles, probably lysosomes. The excretion in bile was increased and the label was associated with high molecular weight proteins. In liver cytosol the 185W was bound by specific, as yet uncharacterized, proteins. At the higher dose levels there was some movement to higher molecular weight proteins and this was greatly increased by the pretreatment with copper. The studies show that the metabolism of 185W tetrathiotungstate is sufficiently similar to 99Mo or 35S tetrathiomolybdate for work on the systemic interactions of thiocompounds and copper in man and animals.

Morphological evidence for migration of particle-laden macrophages through the interalveolar pores of Kohn in the murine lung

We have investigated the topography of particle-laden macrophages in the pulmonary tissue of CD-1 mice after intratracheal instillation of a suspension of 250 micrograms of calcium tungstate. The mice were sacrificed 1, 3, 7 and 14 days after the particle deposition. Lung fragments were studied by scanning electron microscopy (SEM) coupled with X-ray microanalysis that allowed in situ elemental identification of tungsten in the lungs. Tungsten-positive macrophages were distinctly located in the lungs of mice sacrificed at 1-3 days when compared with samples from mice killed 7-14 days after the calcium tungstate instillation. At 1-3 days, the tungsten-carrying macrophages were accumulated near the terminal bronchioles whereas they were seen predominantly in the alveolar ducts and sacs in the 7- to 14-day groups of mice. This suggests that during pulmonary inflammation there is a redistribution of the particle-containing macrophages throughout the deep lung tissue. In high-magnification SEM views, we observed that the tungsten-positive macrophages presented numerous surface microvilli. Tungsten-laden phagocytes were detected in interalveolar fenestrae, at the so-called Kohn pores. This finding documents that the Kohn pores may be used by inflammatory cells as a pathway for the migration of phagocytes in between adjacent alveolar sacs.