Induction of neoplastic progression in Syrian hamster embryo cells treated with protein phosphatase inhibitors

In these studies, Syrian hamster embryo cells (SHE), which were isolated at different stages of neoplastic progression, were used to test the ability of the protein phosphatase inhibitors, okadaic acid and sodium orthovanadate (Na3VO4) to induce neoplastic progression. We observed that these chemicals can induce transition of the cells from one stage to the other at different points in the multistep process of neoplastic transformation. Three steps in this multistep process were studied: escape from cellular senescence, loss of a tumor suppressor gene function in immortal cells, and aquisition of anchorage-independent growth. Treatment of normal, primary SHE cells with okadaic acid or Na3VO4 allowed the cells to escape senescence and become immortal at a low frequency. The induction of immortality was associated with nonrandom chromosome changes, including trisomy 8 and 11 and monosomy 13 and Xq. The transition of preneoplastic cells to more advanced stages was also studied in immortal, nontumorigenic cells that either have retained (supB+) or have lost (supB-) the ability to suppress tumorigenicity of a transformed cell line in cell hybrids. SupB+ and supB- cells do not normally grow in agar, but supB- cells will grow in agar if additional growth factors are added. However, upon addition of protein phosphatase inhibitors, supB+ cells exhibited the supB- phenotype; for example, colony formation of supB+ cells was observed in agar supplemented with growth factors and protein phosphatase inhibitors. Following treatment, selection of these colonies showed that 89% of these cells heritably acquired the phenotype of cells that have lost the suppressor gene function (supB-). SupB- cells were also treated with protein phosphatase inhibitors in soft agar in the presence of additional growth factors. While the frequency of colonies in agar supplemented with growth factors in agar was not greatly enhanced, approximately 50% of the colonies acquired the ability to grow in agar autonomously without the supplemented growth factors, similar to tumorigenic cells. These studies suggest that Na3VO4 and okadaic acid induce progression of cells through various stages in this multistep system.

Inhibition of yeast cytochrome P-450 by ammonium metavanadate

Incubation of diploid D7 strain cells of Saccharomyces cerevisiae (grown in 20% glucose) in the presence of ammonium metavanadate (AMV) led to a decrease in the cytochrome P-450-dependent monooxygenase system (cytochrome P-450 level and 7-ethoxycoumarin O-deethylase). The electrophoretic analysis of microsomal fractions of yeast cells treated with metavanadate revealed a decrease in the intensity of the bands corresponding to a M(r) in the range of 51,000-58,000 Da compared with those observed in controls, i.e., cells grown in 20% glucose. Analysis of the cytochrome P-450 transcript showed that AMV treatment reduced the mRNA level. Our results suggest that AMV inhibits the yeast cytochrome P-450 system by acting at both the pre- and post-transcriptional levels.

Improvement in cardiac dysfunction in streptozotocin-induced diabetic rats following chronic oral administration of bis(maltolato)oxovanadium(IV)

Decreased cardiac function in streptozotocin-diabetic rats has been used as a model of diabetes-induced cardiomyopathy, which is a secondary complication in diabetic patients. The present study was designed to evaluate the therapeutic effect of a new organic vanadium complex, bis(maltolato)oxovanadium(IV), (BMOV), in improving heart function in streptozotocin-diabetic rats. There were four groups of male, Wistar rats: control (C), control treated (CT), diabetic (D), and diabetic treated (DT). Treatment consisted of BMOV, 0.5 mg/mL (1.8 mM) for the first 3 weeks and 0.75 mg/mL (2.4 mM) for the next 22 weeks, in the drinking water of rats allowed ad libitum access to food and water. BMOV lowered blood glucose to < 9 mM in 70% of DT animals without any increase in plasma insulin levels, and mean blood glucose and plasma lipid levels were significantly lower in DT vs. D rats. Tissue vanadium levels were measured in plasma, bone, kidney, liver, muscle, and fat of BMOV-treated rats. Plasma vanadium levels averaged 0.84 +/- 0.07 microgram/mL (16.8 microM) in CT rats and 0.76 +/- 0.05 microgram/mL (15.2 microM) in DT animals. The highest vanadium levels at termination of this chronic feeding study were in bone, 18.3 +/- 3.0 micrograms/g (0.37 mumol/g) in CT and 26.4 +/- 2.6 micrograms/g (0.53 mumol/g) in DT rats, with intermediate levels in kidney and liver, and low, but detectable levels in muscle and fat. There were no deaths in either the CT or DT group, and no overt signs of vanadium toxicity were present. Tissue vanadium levels were not correlated with the glucose-lowering effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of chronic vanadium administration in drinking water to rats

Two-month old Wistar rats of both sexes received, as sole drinking liquid, an aqueous solution of ammonium metavanadate (AMV) at a concentration of 0.01 or 0.05 mg V cm-3 (0.2 or 1.0 mM) for a period of 4 weeks. It was calculated that the animals took up doses of 1.5 and 5-6 mg V kg body weight-1 24 h-1, respectively. Food and AMV solution consumption in the experimental group was similar to food and water consumption in the control group. A statistically significant decrease of consumption of AMV solution at a concentration of 0.05 mg V cm-3 was noted only in males. Hematological examination demonstrated a decrease in the erythrocyte count, hemoglobin level and hematocrit index. This decrease in the erythrocyte count was associated with an increased percentage of reticulocytes in the peripheral blood of the animals drinking the solution with a higher vanadium content. Biochemical analyses demonstrated a decrease of L-ascorbic acid levels in the plasma and erythrocytes of animals drinking the AMV solutions. A distinct tendency for the malonyldialdehyde level to increase in the blood was also observed. Among the enzymes examined in the erythrocytes (catalase, glucose-6-phosphate dehydrogenase, lactate dehydrogenase and delta-aminolevulinic acid dehydratase [ALA-D]) only ALA-D activity was depressed.

Impaired antioxidant status in diabetic rat liver. Effect of vanadate

In vivo effects of vanadate on the antioxidant status of control and alloxan diabetic rats liver were examined. The increased oxidative stress during diabetes caused a decline in the activities of glutathione peroxidase (GPx), catalase (CAT), CuZn superoxide dismutase (CuZn-SOD) and Mn-superoxide dismutase (Mn-SOD) in the liver. Reduced glutathione (GSH) was also depleted, but the level of oxidized glutathione and glutathione reductase activity remained unchanged in the livers of diabetic rats. Vanadate treatment of diabetic rats (0.6 mg/mL in drinking water) resulted in almost complete restoration of GPx and Mn-SOD but caused only a partial restoration of CuZn-SOD. However, CAT and GSH were found to be lowered further in vanadate-treated diabetic rats as compared to untreated diabetic rat. Similar decreases in CAT and GSH levels were also observed in the vanadate-treated controls. These results suggest that vanadate, an insulin-mimetic agent, effectively normalized hyperglycemia, but unlike insulin, could not completely restore the altered endogenous defence mechanisms in diabetic liver.

Variability in the embryotoxicity and fetotoxicity of vanadate with the day of exposure

The aim of this study was to assess the variability in the developmental toxicity of vanadate with the day of administration during gestation. Single ip injections of 25 mg sodium metavanadata/kg were given to albino Swiss mice on one of the days 9-12 of gestation. Dams were killed on day 18 of pregnancy, and fetuses were examined for external, internal and skeletal malformations and variations. The number of dead or resorbed fetuses/litter, as well as the percentage of postimplantation loss, were significantly increased with injections on days 9-12 of gestation. However, the most sensitive time for the induction of metavanadate embryotoxicity was gestational day 12. Metavanadate treatment on day 12, but not days 9-11, resulted in a significant decrease in the fetal body weight/litter. There were no external, internal or skeletal malformations, whereas the most common skeletal variations were a reduced ossification in the parietal bone, metatarsals and metacarpals, bipartite sternebrae and fused ribs. The highest percentage of total skeletal defects was found on day 12 (82.3%). Gestational day 12 is the most sensitive time for metavanadate-induced developmental toxicity in mice.

Combined effect of vanadium and zinc on certain selected haematological indices in rats

1. Two-month-old Wistar rats of both sexes received, as sole drinking liquid, an aqueous solution of ammonium metavanadate (AMV) and zinc chloride (ZC) at concentrations of 0.30 mg V/cm3 and 0.12 mg Zn/cm3 respectively, for a period of 4 weeks. 2. The reference groups received for drinking at this time: water, AMV or ZC solutions at the same concentration. 3. In all groups of animals there was a statistically significant decrease in the uptake of food, AMV or ZC, as well AMV-ZC solutions, as compared with the food and water taken up by the control group. 4. In the group of animals receiving AMV or AMV-ZC solution for drinking the body weight increment diminished significantly. 5. In the animals drinking the AMV-ZC solution a statistically significant decrease in the erythrocyte count and haemoglobin level in the peripheral blood were recorded, similar to the groups drinking AMV or ZC solution. 6. In rats drinking aqueous AMV or ZC solutions and in females receiving AMV-ZC solution the percentage of reticulocytes and polychromatophilic erythrocytes increased, moreover, in the peripheral blood. It was not, however, associated with marked percentage changes in the composition of the bone marrow cells.

Embryotoxic and teratogenic effects of intraperitoneally administered metavanadate in mice

Metavanadate was evaluated for developmental toxicity in pregnant Swiss mice. Sodium metavanadate (NaVO3) was administered intraperitoneally on d 6-15 of gestation at doses of 0, 2, 4, or 8 mg/kg/d. On gestation d 18, all live fetuses were examined for external, visceral, and skeletal malformations and variations. Maternal toxicity was observed at 2, 4, and 8 mg/kg/d as evidenced by decreased weight gain during treatment. Increased resorptions and dead fetuses, increased percentage postimplantation loss, and reduced fetal body weight per litter were observed at 4 and 8 mg/kg/d. There were no significant increases in the type or incidence of external and skeletal anomalies, but a significant increase in the incidence of cleft palate was detected at 8 mg/kg/d. The lowest-observed-adverse-effect level (LOAEL) for maternal toxicity was 2 mg NaVO3/kg/d, while 2 mg/kg/d was also the no-observed-adverse-effect level (NOAEL) for significant developmental toxicity.

Proliferation and morphological transformation of BALB/3T3 cells by a prolonged treatment with sodium orthovanadate

BALB/3T3 mouse embryo cells were used to study the effect of sodium orthovanadate on cell proliferation and morphological transformation. In the presence of the chemical (0.25-1.0 micrograms/ml), the cells continued to proliferate after the cultures were confluent. However, contact-inhibited growth was resumed after removal of the chemical from the culture medium. Continued exposure of the cells to the chemical for 4 wk led to the production of numerous foci consisting of morphologically transformed cells. In contrast, as in vitro transformation assay with a 48-hr treatment protocol followed by 4 wk of incubation without the chemical produced negative results. To test the stability of the transformed foci that were produced on prolonged exposure, we isolated 20 foci with distinctly transformed characteristics from treated cultures and grew them in medium without orthovanadate. 15 isolates gradually reverted to contact-inhibited growth and five maintained the transformed phenotype through ten serial subcultures. The results show that the majority of the transformed foci from the orthovanadate-treated culture failed to maintain transformed characteristics in the absence of the chemical. However, a small fraction of the foci appeared to be altered permanently and exhibited a transformed phenotype in the absence of the chemical.

The lymphotoxic action of vanadate

The acute toxicity of ammonium metavanadate (15.5 mg/kg) in mice was investigated to examine the induction of lymphoid necrosis to (1) verify the reproducibility of the lesions in the thymus, lymph nodes, and spleen; (2) determine whether the necrosis of lymphoid tissue previously observed during the first 3 days post-treatment but absent at 14 days was the result of differences in sensitivity of the mice or the result of recovery from the effects of vanadium; and (3) determine whether differences in the presence and the degree of necrosis between thymus and spleen were correlated with differences in the uptake of vanadium in these tissues. A timed sacrificed study was conducted in conjunction with a 48V tracer. In this study, BALB/C mice were injected subcutaneously (s.c.) with ammonium metavanadate solution (15.5 mg/kg). Groups of mice were sacrificed at 0.5, 1, 2, 3, 4, 6, 8, 10, 12, 14, 21, and 28 days postexposure. Lymphoid necrosis was found in the thymus, spleen, lymph nodes, and bone marrow, with the necrosis being most severe in the thymus. The necrosis was moderate at 0.5 days, most severe at 2 to 3 days, with recovery beginning at 4 days, and proceeding to full recovery at 14 to 28 days. At 0.5 days post-treatment, the concentration of vanadium in thymus and spleen was 4.4 and 8.3 micrograms/g, respectively. At all post-treatment periods, with the exception of the 1- and the 4-day periods, the concentration of vanadium in spleen was significantly higher than in the thymus, p less than 0.05. The treated animals showed neurological signs (ataxia, convulsion, dyspnea, and paralysis of hind legs) between 5 min and 54 hr post-treatment, but the concentration of vanadium in the brain was very low during this period (less than 5.2% of blood concentration).

Tiron administration minimizes the toxicity of vanadate but not its insulin mimetic properties in diabetic rats

Although it has been reported that vanadate is effective in diminishing the expression of diabetes in the rat, the severe toxic side effects noted in the vanadate-treated animals suggest that chronic oral administration of vanadate argues against its use in human diabetes. The present study was conducted to evaluate the effects of the chelator Tiron on the mobilization of vanadium after administration of sodium metavanadate in the drinking water (0.20 mg/ml) of streptozotocin-induced diabetic rats for 35 days. Intraperitoneal treatment with Tiron (300 or 600 mg/kg) was initiated after three weeks of vanadate administration and continued for two weeks. The ameliorative effects of vanadium with respect to diabetes were not diminished by the administration of Tiron, but the accumulation of vanadium in kidney and bone was significantly decreased in the Tiron-treated groups and diabetes associated increases in serum GOT, GPT and cholesterol were diminished with Tiron treatment. It is concluded that the coadministration of metavanadate and Tiron may be of potential value for treatment of diabetes mellitus.

Developmental toxicity evaluation of orthovanadate in the mouse

Sodium orthovanadate in deionized water was administered once daily by gavage on gestational days 6-15 to mice at doses of 0, 7.5, 15, 30, and 60 mg/kg. Dams were killed on day 18 of pregnancy, and fetuses were examined for external, visceral, and skeletal defects. Maternal toxicity was observed at the highest doses of sodium orthovanadate, as evidenced by a significant number of deaths (60 and 30 mg/kg/d) and reduced weight gain and food consumption (30 and 15 mg/kg/d). Embryolethality and teratogenicity were not observed at maternally toxic doses and below, but fetal toxicity was evidenced by a significant delay in the ossification process of some skeletal districts at 30 mg/kg/d. The no-observed-adverse-effect level (NOAEL) for maternal toxicity was 7.5 mg/kg/d, and 15 mg/kg/d represented a NOAEL for developmental toxicity in mice under the conditions of this study.

Effect of ammonium metavanadate on the mouse peritoneal macrophage lysosomal enzymes

Female B6C3F1 mice were injected intraperitoneally with ammonium metavanadate (2.5 or 10 mg V/kg), ammonium chloride, or sodium phosphate buffer (0.1 M, pH 7.2) every 3 d for 6 wk. Resident peritoneal macrophage (PEM) cytolysates were prepared and assayed for intracellular enzyme activities of beta-glucuronidase, N-acetyl-beta-D-glucosaminidase, acid phosphatase, and lysozyme, to investigate possible reasons for the depressive effect of ammonium metavanadate on the intracellular killing of Listeria monocytogenes by murine PEM. Acid phosphatase activity per 10(6) cells for the 2.5 and 10 mg V/kg groups was depressed by 22.8 and 44.7%, respectively, when compared to phosphate buffer controls. No significant effect by vanadium treatment was observed with regard to the other three enzymes. Kinetic studies (in vitro) on the effect of ammonium metavanadate (5, 10, 15, and 20 mM) on the above enzymes showed similar patterns of effect by vanadium. Lineweaver-Burk analysis of acid phosphatase indicated linear noncompetitive inhibition by vanadium with a Kj of 14.8 mM. NH4Cl and 10 mg V/kg treatments also enhanced extracellular secretion of beta-glucuronidase and lysozyme from PEM, which could be attributed to the presence of ammonium ion. The decrease in acid phosphatase activity might contribute, in part through its interference in the phosphorylation/dephosphorylation, to the diminished intracellular killing ability of PEM.

Vanadate-resistant yeast mutants are defective in protein glycosylation

Spontaneous recessive orthovanadate-resistant mutants of Saccharomyces cerevisiae were obtained in five complementation groups, and all show defects in protein glycosylation that mimic the previously isolated mnn mutants. Three of the groups are allelic to the known mnn8, mnn9, and mnn10 mutants, whereas the other two groups show other glycosylation defects. The vanadate-resistant phenotype was associated with enhanced hygromycin B sensitivity. The glycosylation phenotypes of the mutants are all reflections of defects in glycoprotein trafficking, and the easy isolation of vanadate-resistant or hygromycin B-sensitive mutants should facilitate the study of this process.

Effect of antioxidants on vanadate-induced toxicity towards isolated perfused rat livers

The effect of trolox C, a water soluble vitamin E analogue, propyl gallate and ascorbate on vanadate hepatotoxicity was investigated in vitro. In isolated perfused livers from fasted rats, sodium orthovanadate (2 mmol/l) led to toxic responses including reduction of oxygen consumption, release of cytosolic (glutamate-pyruvate-transaminase (GPT) and lactate dehydrogenase (LDH)) and mitochondrial (glutamate-dehydrogenase (GLDH)) enzymes, intracellular accumulation of calcium, a marked depletion of glutathione (GSH) and an enhanced formation and release of thiobarbituric acid- (TBA) reactive material. Trolox C and propyl gallate inhibited the release of GPT and LDH partially and that of GLDH totally, but had no influence on vanadate-induced calcium accumulation or on the reduction of oxygen consumption. Both agents suppressed vanadate-induced lipid peroxidation (LPO) and partially prevented GSH depletion. Ascorbate failed to provide any protection probably due to the interference of its pro-oxidant potential with its antioxidant activity. The protection, mainly of mitochondria, afforded by those agents which also inhibited LPO substantiates our previous findings that the pro-oxidant activity of vanadate is mainly responsible for its direct hepatotoxic actions [2]. Besides, reduction of organ perfusion rate due to vasoconstriction also contributes to vanadate toxicity, but oxidative stress is not involved in this indirect toxic activity.

Genotoxicity of vanadium compounds in yeast and cultured mammalian cells

The ability of vanadium compounds to induce genetic activity was investigated in D7 and D61M strains of Saccharomyces cerevisiae and in Chinese hamster V79 cell line. In our previous work, ammonium metavanadate (pentavalent form, V5) induced mitotic gene conversion and point reverse mutation in the D7 strain of yeast. The genotoxicity was reduced by the presence of S9 fraction, which probably reduced pentavalent vanadium to the tetravalent form. In the present study, vanadyl sulfate (tetravalent form, V4) induced no convertants and revertants in yeast cells harvested from stationary growth phase. With yeast cells from logarithmic growth phase, which contain high levels of cytochrome P-450, a significant increase in genetic effects was observed. Further experiments, performed by treating cells harvested from logarithmic growth phase in the presence of cytochrome P-450 inhibitors, indicated that the monooxygenase system influenced the genotoxicity of metavanadate while the genetic activity of vanadyl remained unaffected. Aneuploidy effect in the D61M strain of Saccharomyces cerevisiae was induced by either V5 or V4, confirming that vanadium compounds are potentially antitubulin agents in eukaryotic cells. Although these compounds are very toxic in V79 cells, no mutagenic effect was observed in the presence or in the absence of S9 fraction.

Time and dose-response study of the effects of vanadate in rats: changes in blood cells, serum enzymes, protein, cholesterol, glucose, calcium, and inorganic phosphate

A daily dosage of vanadate (0.9 mgV/kg) injected subcutaneously for 16 days to adult rats produced significant changes in blood cells and serum elements. The hematological changes included an increase in white blood cell count at two days after the last injection. At five days, red blood cell count (RBC), hemoglobin, and packed cell volume (PCV) were low. At 12 days, there were reductions in RBC, hemoglobin, PCV, and lymphocyte counts and an increase in polymorphonuclear cell (PMN) counts. At 25 days, RBC, hemoglobin, and PCV were still low. At 40 days, the only change was a reduction in RBC. Changes in the serum at two days posttreatment were a reduction in lactic dehydrogenase activity (LDH), alkaline phosphatase activity (AP), calcium, albumin, and total protein and an increase in cholesterol. At five days, glutamic-oxalacetic transaminase (GOT), lactic dehydrogenase (LDH), inorganic phosphate, and total protein were low and calcium was high. At 12 days, GOT, glutamic-pyruvic transaminase (GPT), and LDH were reduced, and the levels of calcium and cholesterol were elevated. At 25 days, there was a reduction in GPT and LDH and an increase in glucose, calcium, and albumin. At 40 days, the levels of GOT, LDH, AP, and inorganic phosphate were still low. Vanadate at lower dosage levels (0.3-0.6 mg V/kg per day for 16 days) also produced significant changes in blood cellular and serum elements but at lesser degrees of severity. These findings show that the exposure of rats repeatedly to low levels of Vanadate caused anemia, elevation in blood cholesterol levels, and a reduction in serum enzymes activities.

Peripheral erythrocyte levels, hemolysis and three vanadium compounds

Three vanadium compounds of different valence states were administered to adult mice. Two, four, and eight days following treatment of vanadium, cardiac blood was collected. The blood sample was used to ascertain the peripheral erythrocyte count (cell/mm3) and to determine the in vitro hemolytic index of erythrocytes obtained from mice treated in vivo with either the tri-, tetra-, or pentavalent vanadium compound. Data indicate that the tetravalent form was the most effective test substance in 1) promoting rupture of isolated erythrocytes compared to red cells retrieved from control mice and 2) depressing the erythrocyte count obtained from heart blood; maximum effects were manifest four days post-treatment. For all treatments there appeared to be a good correlation between the degree of vanadium-induced hemolysis and the peripheral erythrocyte count reduction following exposure to the vanadium.

An assessment of the genotoxicity of vanadium

The activities of vanadium oxide (V2O3), vanadyl sulfate (VOSO4) and ammonium metavanadate (NH4VO3) in inducing sister chromatid exchange (SCE) and chromosomal aberrations (CAb) were assayed in Chinese hamster ovary cells. The toxic concentrations (TC50) for these compounds were found to be 25, 23 and 16 micrograms elemental vanadium/ml, respectively. At does 1/50-1/4 TC50, vanadium compounds were able to induce significant increases (P less than 0.01) in the SCE frequency with or without the addition of rat hepatic S9 mix. These compounds also induced CAb in the cells at doses closely equivalent to the TC50.

Insulin-mimetic effects of vanadate. Possible implications for future treatment of diabetes

Vanadate ions, low-molecular-weight phosphate analogues, mimic most of the rapid actions of insulin in various cell types. When administered orally to diabetic hyperglycemic rats, vanadate reaches the circulation, mimics insulin stimulation of glucose uptake and metabolism, and leads to normoglycemic and partial anabolic states. In addition, vanadate restores tissue responsiveness to insulin and hepatic glycogen levels and activates new synthesis of key enzymes for carbohydrate metabolism. This suggests that correcting hyperglycemia is sufficient to correct the typical metabolic alterations found in streptozocin-induced diabetic rats. Several weeks of oral administration of vanadate to diabetic rats has not produced detectable liver or kidney toxicity. The mechanism by which vanadate mimics the actions of insulin is still obscure. Unlike insulin, vanadate does not seem to stimulate the autophosphorylation and endogenous tyrosine phosphorylation of insulin-receptor kinase or other intracellular proteins either directly or by virtue of its known inhibitory effect on protein phosphotyrosine phosphatase. Results from many studies support a model in which vanadate activates glucose metabolism by either utilizing an alternative (insulin-independent) cascade or bypassing the early events of the insulin-dependent cascade. Either of these possibilities is of clinical importance, because early insulin events may become defective, as a result of severe hyperinsulinemia, and may contribute to insulin resistance. Alternative pathways by which vanadate may stimulate glucose metabolism, e.g., by increasing intracellular Ca2+ levels and/or regulating intracellular and intravesicular pH, are discussed. From a clinical perspective, studies should be continued in evaluating the level of vanadate toxicity after prolonged treatment and searching for agents that potentiate its insulin mimetic actions in vitro and in vivo.

Time and dose-response study of the effects of vanadate on rats: morphological and biochemical changes in organs

Vanadate at a dosage level of 0.9 mg V/kg per day produced acute toxic signs in rats when injected subcutaneously for 16 days. These signs were weakness, loss of appetite, dehydration, significant reduction in body weight, nose bleeding, and death. The pathological and biochemical changes were most severe in kidney tissue. The kidney lesions were bilateral and multifocal. At two days, degenerative and necrotic changes of the tubular and glomerular epithelium, thickening of glomerular membrane, vascular congestion, and edema were observed. At five days, proliferation of tubular epithelial and interstitial cells was observed. At 12 days, the cellular proliferation in both cortex and medulla was significantly greater. Fibrosis was observed at glomerular tuft, preglomeruli, pretubules, and interstitium (cortex and medulla). At 25 days, the collagen deposition reached the highest level in all regions, cellular proliferation decreased, and thickening of the arteriolar wall became prominent. The renal lesions were coupled with changes in the levels of protein, RNA, DNA, and hydroxyproline. At 40 days, the kidney showed signs of recovery. Blood urea nitrogen levels were significantly elevated at 2-25 days post-treatment. Stained tissue sections from liver, lung, heart, spleen, thymus, lymph nodes, testes, and adrenal glands of the treated rats were examined microscopically and appeared normal. Biochemically, significant changes (p less than .05) in protein, RNA, DNA, and hydroxyproline were also observed in these organs. At lower dosage (0.6 mg V/kg per day for 16 days), similar but less severe pathological and biochemical changes in kidneys and other organs were observed. At 0.3 mg V/kg per day for 16 days, the changes in the tissues were detected only at the biochemical level. These results indicate that the toxic effects of vanadium are cumulative and that vanadium-produced fibrosis in tissues is dose-dependent.

On the role of mitochondria in cell injury caused by vanadate-induced Ca2+ overload

Incubation of isolated rat hepatocytes with vanadate (0.25, 0.5 and 1 mM) resulted in progressive accumulation of Ca2+ in the intracellular compartments. Vanadate- induced Ca2+ accumulation was related to inhibition of the plasma membrane Ca2+-extruding system, but did not involve either enhanced plasma membrane permeability to Ca2+ or the enhanced operation of a putative Na+/Ca2+ exchanger. After an initial rise in the cytosolic free Ca2+ concentration, as revealed by phosphorylase activation, Ca2+ was sequestered predominantly by the mitochondria with little contribution from the endoplasmic reticulum. As the amount of Ca2+ in the mitochondria increased, a progressive decrease in mitochondrial membrane potential occurred, together with an impairment of the ability of these organelles to further sequester Ca2+. Associated with this, there was a decrease in intracellular ATP level, formation of surface blebs and cytotoxicity. Addition of an uncoupler to vanadate-treated hepatocytes dramatically accelerated the appearance of plasma membrane blebs and toxicity. Our results demonstrate that under conditions in which the plasma membrane Ca2+ pump is inhibited, mitochondria play an important role in protecting hepatocytes against damage induced by Ca2+ overload.