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

Vanadium: Risks and possible benefits in the light of a comprehensive overview of its pharmacotoxicological mechanisms and multi-applications with a summary of further research trends

BACKGROUND

Vanadium (V) is an element with a wide range of effects on the mammalian organism. The ability of this metal to form organometallic compounds has contributed to the increase in the number of studies on the multidirectional biological activity of its various organic complexes in view of their application in medicine.

OBJECTIVE

This review aims at summarizing the current state of knowledge of the pharmacological potential of V and the mechanisms underlying its anti-viral, anti-bacterial, anti-parasitic, anti-fungal, anti-cancer, anti-diabetic, anti-hypercholesterolemic, cardioprotective, and neuroprotective activity as well as the mechanisms of appetite regulation related to the possibility of using this element in the treatment of obesity. The toxicological potential of V and the mechanisms of its toxic action, which have not been sufficiently recognized yet, as well as key information about the essentiality of this metal, its physiological role, and metabolism with certain aspects on the timeline is collected as well. The report also aims to review the use of V in the implantology and industrial sectors emphasizing the human health hazard as well as collect data on the directions of further research on V and its interactions with Mg along with their character.

RESULTS AND CONCLUSIONS

Multidirectional studies on V have shown that further analyses are still required for this element to be used as a metallodrug in the fight against certain life-threatening diseases. Studies on interactions of V with Mg, which showed that both elements are able to modulate the response in an interactive manner are needed as well, as the results of such investigations may help not only in recognizing new markers of V toxicity and clarify the underlying interactive mechanism between them, thus improving the medical application of the metals against modern-age diseases, but also they may help in development of principles of effective protection of humans against environmental/occupational V exposure.

Hepatotoxicity of vanadyl sulfate in nondiabetic and streptozotocin-induced diabetic rats

This study examined the effects of vanadyl sulfate (VOSO₄) on the livers of nondiabetic and streptozotocin-induced diabetic rats. Rats were divided into 6 groups. Groups 1, 2, and 3 consisted of nondiabetic rats that were, respectively, control animals or those receiving an intraperitoneal (i.p.) injection of either 5 or 10 mg·kg^-1 (i.p.) VOSO₄ for 30 days. Groups 4, 5, and 6 consisted of diabetic animals that were, respectively, control animals or those treated with 5 or 10 mg·kg^-1 (i.p.) VOSO₄ for 30 days. Results showed that VOSO₄ reduced body mass in nondiabetic rats, whereas it increased body mass in diabetic groups. Plasma transaminases (aspartate aminotransferase, alanine aminotransferase), lactate dehydrogenase, and alkaline phosphatase activities and malondialdehyde levels were increased, while liver catalase and superoxide dismutase activities were profoundly decreased in diabetic animals in comparison with enzyme activities in the nondiabetic group. Rats in the diabetic group also showed notable oxidative damage to the liver. Treatment of diabetic rats with VOSO₄ decreased the hepatotoxic markers, significantly restored the activities of antioxidant enzymes, and attenuated histopathological changes in liver tissue. In nondiabetic rats, VOSO₄ treatment increased most of the hepatotoxic markers, reduced antioxidant enzyme activities, and induced pronounced oxidative damage in liver tissue. These data suggest that treatment with VOSO₄ exerts toxic effects in healthy animals and significantly prevents liver oxidative damage in streptozotocin-induced diabetic rats, but without total safety. Further studies are needed to clarify its mechanism of action.

Oxidative stress changes observed in selected organs of African giant rats (Cricetomys gambianus) exposed to sodium metavanadate

Vanadium is a contaminant of crude oil that released into the atmosphere through burning of fossil fuels. The mechanism by which it exerts toxic influences had not been fully elucidated in African giant rat (AGR). This study investigates the mechanisms of sodium metavanadate (SMV) induced oxidative stress in AGR. A total of 24 adult male AGR weighing 600-850 g were used. Animals were randomly divided into six groups. Groups 1, 3 and 5 served as control while groups 2, 4 and 6 were treated with intraperitoneal 3 mg/kg body weight of SMV for 3, 7 and 14 days, respectively. Serum, brain, liver, testes, kidneys, spleen and lungs were harvested for biochemical assays. SMV induced significant increase in malondialdehyde, hydrogen peroxide, sulfhydryl (total thiol) and protein carbonyl levels but decreased non-protein thiol levels in tissues accessed. A significant decrease was observed in glutathione-S-transferase (GST), superoxide dismutase (SOD), reduced glutathione (GSH) and glutathione peroxidase (GPx) levels in SMV treated rats compared to controls. Serum myeloperoxidase, xanthine oxidase and Advanced Oxidative Protein Products (AOPP) were markedly increased while nitrous oxide levels were significantly decreased in all treated groups. SMV exposure to AGR induced oxidative stress through generation of reactive oxygen species (ROS) and depletion of the antioxidant defence system. These conditions could become severe with prolonged exposure.

Ameliorated Effects of (-)-Epigallocatechin Gallate Against Toxicity Induced by Vanadium in the Kidneys of Wistar Rats

The aim of the study was to assess the protective effect of (-)-epigallocatechin gallate (EGCG), a flavonoid abundant in green tea, against ammonium metavanadate (AMV)-induced oxidative stress in male Wistar rats. Four groups of animals have been used, a control group and three test groups. In the first test group, AMV was intra-peritoneally (i.p) injected daily (5 mg/kg body weight for five consecutive days). The second test group of animals was also injected daily with EGCG (5 mg/kg body weight) during the same period. However, the third test group was i.p. injected with both AMV and EGCG (5 mg/kg body weight for five consecutive days). When given alone, AMV induced an oxidative stress evidenced by an increase of lipid peroxidation levels (expressed as TBARS concentration) in kidney. In these animals, activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX) were significantly decreased, suggesting significant reduction of the antioxidant defense system at the cell level. Kidney histological sections, showed glomerular hypertrophy and tubular dilatation. In AMV-treated animals receiving EGCG, the oxidative stress was much less pronounced and activities of antioxidant enzymes were kept close to control values. Histopathological changes were less prominent. Our results confirm that green tea and other sources of flavonoids might confer a strong protection against ammonium metavanadate-induced oxidative stress.

Efflux of glutathione and glutathione complexes from human erythrocytes in response to vanadate

The main objective of the present study was to investigate if vanadate is extruded from the cells in a glutathione dependent manner resulting in the appearance of extracellular glutathione and complexes of glutathione with vanadium. Vanadate significantly depleted intracellular non-protein sulfhydryl (NPSH) levels in a time- and concentration-dependent manner. The intracellular NPSH level was decreased to 0.0 ± 0.0 μmol/ml erythrocyte when exposed to 10 mM of vanadate for 4h. Extracellular NPSH level was increased concomitantly with the intracellular decrease and reached to 0.1410 ± 0.005 μmol/ml erythrocyte in 4h. Intracellular decrease and extracellular increase in NPSH levels were significantly inhibited in the presence of DIDS, a chloride-bicarbonate exchanger which also mediates phosphate and arsenate transport in erythrocytes. In parallel with the increase in extracellular NPSH levels, significant increases in extracellular glutathione levels were detected following exposure to vanadate. Extracellular glutathione levels reached to 0.0150 ± 0.0.001, 0.0330 ± 0.001, and 0.0576 ± 0.002 μmol/ml erythrocyte with 1, 5, and 10 mM of vanadate respectively. Dimercaptosuccinic acid treatment of supernatants significantly increased the glutathione levels measured in the extracellular media. Utilization of MK571 an MRP inhibitor decreased the rate of glutathione efflux from erythrocytes suggesting a role for this membrane transporter in the process. A known methylation inhibitor periodate oxidized adenosine decreased the rate of glutathione efflux from erythrocytes. This observed decrease in extracellular GSH levels suggests that GSH release partly requires a proper cellular methylation process and that part of GSH detected in the extracellular media may arise from GSH-vandium complexes. The results of the present study indicate that human erythrocyte efflux glutathione in reduced free form and in conjugated form/s that can be recovered with dimercaptosuccinic acid when exposed to vanadate.

The effect of vanadium on platelet function

Vanadium pentoxide (V(2)O(5)) inhalation effect on platelet function in mice was explored, as well as the in vitro effect on human platelets. Mouse blood samples were collected and processed for aggregometry and flow cytometry to assess the presence of P-selectin and monocyte-platelet conjugates. Simultaneously, human platelets were processed for aggregometry(.) The mouse results showed platelet aggregation inhibition in platelet-rich-plasma (PRP) at four-week exposure time, and normality returned at eight weeks of exposure, remaining unchanged after the exposure was discontinued after four weeks. This platelet aggregation inhibition effect was reinforced with the in vitro assay. In addition, P-selectin preserved their values during the exposure, until the exposure was discontinued during four weeks, when this activation marker increased. We conclude that vanadium affects platelet function, but further studies are required to evaluate its effect on other components of the hemostatic system.

Cyto- and genotoxicity of a vanadyl(IV) complex with oxodiacetate in human colon adenocarcinoma (Caco-2) cells: potential use in cancer therapy

The complex of vanadyl(IV) cation with oxodiacetate, VO(oda) caused an inhibitory effect on the proliferation of the human colon adenocarcinoma cell line Caco-2 in the range of 25-100 μM (P < 0.001). This inhibition was partially reversed by scavengers of free radicals. The difference in cell proliferation in the presence and the absence of scavengers was statistically significant in the range of 50-100 μM (P < 0.05). VO(oda) altered lysosomal and mitochondria metabolisms (neutral red and MTT bioassays) in a dose-response manner from 10 μM (P < 0.001). Morphological studies showed important transformations that correlated with the disassembly of actin filaments and a decrease in the number of cells in a dose response manner. Moreover, VO(oda) caused statistically significant genotoxic effects on Caco-2 cells in the low range of concentration (5-25 μM) (Comet assay). Increment in the oxidative stress and a decrease in the GSH level are the main cytotoxic mechanisms of VO(oda). These effects were partially reversed by scavengers of free radicals in the range of 50-100 μM (P < 0.05). Besides, VO(oda) interacted with plasmidic DNA causing single and double strand cleavage, probably through the action of free radical species. Altogether, these results suggest that VO(oda) is a good candidate to be evaluated for alternative therapeutics in cancer treatment.

Effects of combined vanadate and magnesium treatment on erythrocyte antioxidant defence system in rats

The effect of vanadate and magnesium treatment on erythrocyte defence system was studied in outbred 2-month-old, albino male Wistar rats (14 rats/each group) which daily received: Group I (Control)-deionized water to drink; Group II-water solution of sodium metavanadate (NaVO(3); SMV) at a concentration of 0.125mgV/mL; Group III-water solution of magnesium sulfate (MgSO(4); MS) at a concentration of 0.06mgMg/mL, Group IV-water solution of SMV-MS at the same concentrations over a 12-week time. The fluid intake and the concentration of reduced glutathione (GSH) as well as the activity of Cu, Zn-superoxide dismutase (Cu, Zn-SOD), catalase (CAT) and glutathione reductase (GR) were significantly decreased in the rats receiving SMV alone (Group II) or in combination with MS (Group IV) compared with Groups I and III. The cellular glutathione peroxidase (cGSH-Px) activity was unchanged in all the treated groups. The activity of glutathione S-transferase (GST) fell in the animals in Group II, compared with the rats in Groups I, III and IV; whereas in the rats in Group III its activity was higher than in the control animals. These results showed that V (as SMV) consumed by the rats with drinking water at a dose of 12mgV/kg b.w./24h for 12 weeks may attenuate defence system in rats' erythrocytes (RBCs), which is probably a consequence of vanadium pro-oxidant potential. Therefore, reactive oxygen species (ROS) are suggested to be involved in the alterations in antioxidant defence system in these cells. Mg (as MS) at the dose ingested (6mgMg/kg b.w./24h) at co-exposure to SMV was not able to counteract its deleterious effect. The results also provide evidence that V-Mg interactions may be involved in the decrease of erythrocyte GR activity and Mg concentration in the plasma under concomitant treatment with both metals at the doses of 12.6mgV and 6mgMg/kg b.w./24h.

Antioxidant enzyme activity and lipid peroxidation in the blood of rats co-treated with vanadium (V(+5)) and chromium (Cr (+3))

Selected biochemical parameters were studied in the blood of outbred, male Wistar rats which daily received to drink deionized water (Group I, control) or solutions of: sodium metavanadate (SMV; 0.100 mg V/mL)-Group II; chromium chloride (CC; 0.004 mg Cr/mL)-Group III; and SMV-CC (0.100 mg V and 0.004 mg Cr/mL)-Group IV for a 12-week period. The diet and fluid intake, body weight gain, and food efficiency ratio (FER) diminished significantly in the rats of Groups II and IV, compared with Groups I and III. The plasma total antioxidant status (TAS) as well as the MDA and the L: -ascorbic acid level in the erythrocytes (RBCs) remained unchanged in all the groups, whereas the plasma L: -ascorbic acid concentration decreased markedly in Group II, compared with Group III. The activities of Cu,Zn-superoxide dismutase (Cu,Zn-SOD), catalase (CAT), cellular glutathione peroxidase (cGSH-Px), and glutathione reductase (GR) in RBCs remained unaltered in all the treated rats. However, the activity of glutathione S-transferase (GST) and the content of reduced glutathione (GSH) in RBCs decreased and increased, respectively, in Groups II, III, and IV, compared with Group I. A vanadium-chromium interaction which affected the GST activity was also found. To summarize, SMV and CC administered separately or in combination in drinking water for 12 weeks did not alter either lipid peroxidation (LPO) or the activities of Cu,Zn-SOD, CAT, cGSH-Px, and GR, which allows a conclusion that both metals in the doses ingested did not reveal their pro-oxidant potential on RBCs.

Lipid peroxidation in the liver of rats treated with V and/or Mg in drinking water

The effect of V(5+) and Mg treatment on spontaneous and stimulated lipid peroxidation (LPO) was studied in liver supernatants obtained from outbred 5-month-old, albino male Wistar rats. The 2-month-old animals daily received deionized water to drink (control, group I); group II - water solution of NaVO(3) (SMV) at a concentration of 0.125 mg V ml(-1); group III - water solution of MgSO(4) (MS) at a concentration of 0.06 mg Mg ml(-1), group IV - water solution of SMV-MS at the same concentrations as in groups II and III for V and Mg, respectively, over a 12-week period. Three metal salts were selected as agents that may modify the LPO process (FeSO(4), NaVO(3) and MgSO(4)). V-intoxicated rats and those treated with V and Mg in combination had higher liver spontaneous malondialdehyde (MDA) formation, compared with the control and Mg-supplemented animals. In the same groups of animals the total antioxidant status (TAS) was also significantly lowered, in comparison with the control. In the supernatants obtained from the above-mentioned groups of rats a significant increase in MDA concentration was found in the presence of exogenous 30 microm FeSO(4) as well as 30, 100, 200 and 400 microm NaVO(3), compared with groups I and III. Significantly elevated MDA production was also observed in the supernatants obtained from the rats exposed to V and Mg in combination in the presence of exogenous 100 and 200 microm MgSO(4) in comparison with the control and group III as well as in the presence of exogenous 400 and 600 microm MgSO(4) compared only with group III. In vitro treatment with 1000 microm MgSO(4 )of control liver supernatants and those obtained from group III significantly enhanced MDA level, compared with spontaneous MDA formation. The two-way ANOVA indicated that the changes in the basal MDA level and in TAS in the rats at combined V and Mg application, were not due to V-Mg interaction, but resulted from independent action of V. In addition, the three-way ANOVA revealed that the changes in LPO induced by in vitro treatment of liver supernatants with exogenous Fe or V or Mg (600, 800 and 1000 microm) were a consequence of independent action of those metals and they also resulted from the interactions between Fe(exog) and V(end) and between V(end) and V(exog). In conclusion, V consumed by the rats with drinking water at a dose of 12 mg V kg(-1) body weight per 24 h for 12 weeks decreased TAS and enhanced spontaneous LPO in the hepatic tissue, which confirms its pro-oxidant potential, was also found in in vitro conditions with regard to LPO. Mg administered to rats in combination with V, at the concentration used, neither reduced nor intensified the basal LPO, compared with V-only treated animals; however, its stimulating effect on LPO was revealed in in vitro conditions, which requires further study.

Selected haematological and biochemical parameters of blood in rats after subchronic administration of vanadium and/or magnesium in drinking water

The purpose of these studies was to evaluate the effect of selected vanadium and magnesium doses on certain haematological and biochemical blood parameters in rats. Outbred 2-month-old, albino male Wistar rats received for a period of 6 weeks, as a sole drinking liquid, the following water solutions: group II, sodium metavanadate (SMV) at a concentration of 0.125 mg V/mL; group III, magnesium sulphate (MS) at a concentration of 0.06 mg Mg/mL; and group IV, SMV-MS solution at the same concentrations. The control group received at this time deionized water to drink. It was calculated that group II ingested with drinking water about 10.7 mg V/kg b. w./24 h, group III 6 mg Mg/kg b. w./24 h, and group IV about 9 mg V and 4.5 mg Mg/kg b. w./24 h. The exposure to vanadium alone (group II) led to a statistically significant decrease in body weight gain, food and fluid intakes. Moreover, in the same group of rats a statistically significant decrease in the RBC count, Hb concentration, MCV, and MCH values was demonstrated. Additionally, a statistically significant decrease in the plasma L-ascorbic acid concentration and a significant increase in MDA concentration in blood in this group were found. Instead, after the administration of magnesium alone (group III), a statistically significant decrease in the fluid intake and in the L-ascorbic acid concentration in plasma was noted. Furthermore, in the same group of rats a statistically significant increase in Hb level and in the plasma magnesium concentration was demonstrated. Two-way analysis of variance (ANOVA) did not reveal the interactions between V and Mg.

Stress proteins (Hsp72/73, Grp94) expression pattern in rat organs following metavanadate administration. Effect of green tea drinking

Expression pattern of heat shock proteins (Hsp) 72/73 and glucose regulated protein (Grp) 94 was studied in liver, kidney and testis of rats injected with sublethal doses of ammonium metavanadate (5 mg/kg/day). In addition, some batches of animals were given green tea decoction, known to be rich in anti-oxidative compounds, as sole beverage in order to evaluate its protective properties. In control animals, the stress proteins expression was found to be organ-dependent: anti-Grp94 antibody revealed two bands at 96 and 98 kDa in kidney and liver whereas the 98 kDa band only was found in testis; anti-Hsp72/73 antibody revealed that the constitutive Hsp73 was present in all organs whereas the inducible Hsp72 was only present in kidney and testis. In kidney of vanadium-treated rats, Hsp73 was over-expressed by about 50% whereas Hsp72 was down-regulated by 50-80%. No such effects were observed in liver and testis. In liver and kidney of vanadium-treated rats, Grp94 was over-expressed by 50% and 150% respectively whereas no change was found in testis. In rats given green tea as sole beverage, the 96 kDa protein expression level in liver was reduced both in controls and in vanadium-treated animals. However, green tea drinking failed to prevent the vanadium-induced Hsp72 under-expression in kidney of vanadium-treated rats.

Combined effect of vanadium(V) and chromium(III) on lipid peroxidation in liver and kidney of rats

Since chromium(III) was demonstrated to have antioxidative action, we have decided to study the effect of this element on V-induced LPO in liver and kidney of rats. Outbred 2-month-old, albino male Wistar rats received daily, for a period of 12 weeks: group I (control), deionized water to drink; group II, sodium metavanadate (SMV) solution at a concentration of 0.100mgV/mL; group III, chromium chloride (CC) solution at a concentration of 0.004mgCr/mL and group IV, SMV-CC solution at a concentration of 0.100mgV and 0.004mgCr/mL. The particular experimental groups took up with drinking water about 8.6mgV/kg b.w./24h (group II), 0.4mgCr/kg b.w./24h (group III), 9mgV and 0.36mgCr/kg b.w./24h (group IV). The V- or Cr-treated groups had higher concentrations of these two elements in liver and kidney compared to the controls. The administration of vanadium alone caused a significant decrease in fluid intake and in body weight gain compared to the controls. In liver supernatants obtained from all tested rats a statistically significant increase in MDA concentration was demonstrated in spontaneous LPO in comparison with the control rats. Moreover, in rats intoxicated with vanadium alone a statistically significant increase in liver MDA level was observed in the presence of 100microM NaVO(3). Instead, in supernatants of liver received from rats treated with chromium alone, a statistically significant increase in MDA concentration in comparison with the controls was found in the presence of 400microM NaVO(3). In kidney supernatants obtained from rats treated with chromium alone, a statistically significant increase in lipid peroxidation was shown in the presence of 30microM FeSO(4) and 400microM NaVO(3). These results show that the tested doses of vanadium(V) and chromium(III) ingested by rats with their drinking water caused significant alterations in internal organs, especially in liver. Under the conditions of our experiment, Cr(III) did not demonstrate antioxidant action, it rather had an oxidant effect.

Activation of JNK by vanadate induces a Fas-associated death domain (FADD)-dependent death of cerebellar granule progenitors in vitro

Apoptosis is a highly regulated process that plays a critical role in neuronal development as well as the homeostasis of the adult nervous system. Vanadate, an environmental toxicant, causes developmental defects in the central nervous system. Here, we demonstrated that vanadate induced apoptosis in cultured cerebellar granule progenitors (CGPs). Treatment of cultured CGPs with vanadate activated ERKs and JNKs but not p38 MAPK and also induced c-Jun phosphorylation. In addition, vanadate induced FasL production, Fas (CD95) aggregation, and its association with the Fas-associated death domain (FADD), as well as the activation of caspase-8. Furthermore, vanadate generated reactive oxygen species (ROS) in CGPs; however, ROS was not involved in vanadate-mediated MAPK activation. Vanadate-induced FasL expression was ROS-dependent but JNK-independent. In contrast, vanadate-elicited Fas aggregation and Fas-FADD association, as well as caspase-8 activation, were dependent on JNK activation but were minimally regulated by ROS generation. The hydrogen peroxide scavenger, catalase, blocked vanadate-induced FasL expression and partially mitigated vanadate-induced cell death. On the other hand, dominant negative FADD and caspase-8 inhibitor completely eliminated vanadate-induced apoptosis. Thus, JNK signaling plays a major role in vanadate-mediated activation of the Fas-FADD-caspase-8 pathway that accounts for vanadate-induced apoptosis of CGPs.

BpV (phen) induces apoptosis of RINm5F cells by modulation of MAPKs and MKP-1

We investigated the mechanism of toxicity of peroxovanadium complex bpV (phen) in RINm5F cells. Treatment with bpV (phen) provoked cell death, predominantly by apoptosis. This compound induced strong and sustained JNK and p38 MAPK activation. However, ERK phosphorylation was not affected. The level of expression of MAPK phosphatase MKP-1 was suppressed after bpV (phen) treatment. In addition, this compound did not stimulate proteolytic processing of procaspase-3, suggesting that caspase-3 is not activated during the course of bpV (phen)-induced apoptosis. A correlative inhibition of JNK activation by immunosuppressive drug FK 506 induced ERK activation and MKP-1 expression, and suppressed RINm5F cell death. A specific p38 inhibitor SB 203580 also stimulated ERK activation and cell survival. Furthermore, simultaneous pretreatment with both FK 506 and SB 203580 almost completely abolished cell death. Thus, our results suggest that stress kinases and MKP-1 have a role in bpV (phen)-induced apoptosis of RINm5F cells.

A possible role of oxidative stress in the vanadium-induced cytotoxicity in the MC3T3E1 osteoblast and UMR106 osteosarcoma cell lines

The cytotoxicity and free radical production induced by vanadium compounds were investigated in an osteoblast (MC3T3E1) and an osteosarcoma (UMR106) cell lines in culture. Vanadate induced cell toxicity, reactive oxygen species (ROS) formation and thiobarbituric acid reactive substances (TBARS) increased in a concentration-dependent manner (0.1-10 mM) after 4 h. The concentration-response curve of vanadate-induced cytotoxicity and oxidative stress in MC3T3E1 cells was shifted to the left of the UMR106 curve, suggesting a greater sensitivity of the non-transformed cells in comparison to the osteosarcoma UMR106 cells. Supplementing with vitamin E acetate (80 microM) significantly inhibited ROS and TBARS formation but did not improve the vanadate-dependent decrease in cell number. Other vanadium compounds (vanadyl, pervanadate, and VO/Aspi, a complex of vanadyl(IV) with aspirin) showed different degrees of cell toxicity and induced oxidative stress. Altogether these results suggest that oxidative stress is involved in vanadium induced osteoblastic cytotoxicity, although the mechanism is unknown.

Vanadate induces apoptosis in epidermal JB6 P+ cells via hydrogen peroxide-mediated reactions

Apoptosis is a physiological mechanism for the control of DNA integrity in mammalian cells. Vanadium induces both DNA damage and apoptosis. It is suggested that vanadium-induced apoptosis serves to eliminate DNA-damaged cells. This study is designed to clarify a role of reactive oxygen species in the mechanism of apoptosis induced by vanadium. We established apoptosis model with murine epidermal JB6 P+ cells in the response to vanadium stimulation. Apoptosis was detected by a cell death ELISA assay and morphological analysis. The result shows that apoptosis induced by vanadate is dose-dependent, reaching its saturation level at a concentration of 100 microM vanadate. Vanadyl (IV) can also induce apoptosis albeit with lesser potency. A role of reactive oxygen species was analyzed by multiple reagents including specific scavengers of different reactive oxygen species. The result shows that vanadate-induced apoptosis is enhanced by NADPH, superoxide dismutase and sodium formate, but was inhibited by catalase and deferoxamine. Cells exposed to vanadium consume more molecular oxygen and at the same time, produce more H2O2 as measured by the change in fluorescence of scopoletin in the presence of horseradish peroxidase. This change in oxygen consumption and H2O2 production is enhanced by NADPH. Taken together, these results show that vanadate induces apoptosis in epidermal cells and H2O2 induced by vanadate plays a major role in this process.

Influence of glycine on the damage induced in isolated perfused rat liver by five hepatotoxic agents

Livers of fasted rats were perfused over 120 min in a recirculating hemoglobin-free system. Hepatotoxic injury induced by the addition of 1-butanol (130.2 mmol/l), CdCl2 (0.1 mmol/l), CuCl2 (0.03 mmol/l), Na3VO4 (2 mmol/l) or t-butylhydroperoxide (t-BuOOH, 0.5 mmol/l) to the perfusate was shown by strong increases in lactate dehydrogenase (LDH) and glutamate-pyruvate transaminase (GPT) release, decreased oxygen consumption between 50 and 60%, and a nearly complete suppression of bile flow. Hepatic adenosine triphosphate (ATP) and reduced glutathione (GSH) concentrations were reduced by between 30 and 80%, and 20 and 80% respectively. Only Na3VO4 and t-BuOOH evoked increased releases of glutamate dehydrogenase (GLDH) in the perfusate. Malondialdehyde (MDA) concentrations were enhanced by all toxicants in the perfusate and by all except 1-butanol in the liver. The MDA increase, however, was much higher after Na3VO4 and t-BuOOH than after the other toxicants. When glycine (12 mmol/l) was added 30 min before the toxicants to the perfusate it prevented the enzyme releases induced by all hepatotoxic agents by about 80%. Furthermore, glycine prevented the Na3VO4 induced increase of MDA in liver and perfusate, the hepatic ATP and GSH level reductions induced by 1-butanol and attenuated the reduction of oxygen consumption induced by CuCl2 and t-BuOOH. Glycine, however, did not reverse the reductions of oxygen consumption induced by CdCl2 and Na3VO4, the suppressions of bile flow and, with the exception of 1-butanol, the decreases of hepatic ATP levels induced by all agents.

Vanadium salts as insulin substitutes: mechanisms of action, a scientific and therapeutic tool in diabetes mellitus research

Vanadium and its compounds exhibit a wide variety of insulin-like effects. In this review, these effects are discussed with respect to the treatment of type I and type II diabetes in animal models, in vitro actions, antineoplastic role, treatment of IDDM and NIDDM patients, toxicity, and the possible mechanism(s) involved. Newly established CytPTK plays a major role in the bioresponses of vanadium. It has a molecular weight of approximately 53 kDa and is active in the presence of Co2+ rather than Mn2+. Among the protein-tyrosine kinase blockers, staurosporine is found to be a potent inhibitor of CytPTK but a poor inhibitor of InsRTK. Vanadium inhibits PTPase activity, and this in turn enhances the activity of protein tyrosine kinases. Our data show that inhibition of PTPase and protein tyrosine kinase activation has a major role in the therapeutic efficacy of vanadium in treating diabetes mellitus.

Vanadium(IV)-mediated free radical generation and related 2'-deoxyguanosine hydroxylation and DNA damage

Free radical generation, 2'-deoxyguanosine (dG) hydroxylation and DNA damage by vanadium(IV) reactions were investigated. Vanadium(IV) caused molecular oxygen dependent dG hydroxylation to form 8-hydroxyl-2'-deoxyguanosine (8-OHdG). During a 15 min incubation of 1.0 mM dG and 1.0 mM VOSO4 in phosphate buffer solution (pH 7.4) at room temperature under ambient air, dG was converted to 8-OHdG with a yield of about 0.31%. Catalase and formate inhibited the 8-OHdG formation while superoxide dismutase enhanced it. Metal ion chelators, DTPA and deferoxamine, blocked the 8-OHdG formation. Incubation of vanadium(IV) with dG in argon did not generate any significant amount of 8-OHdG, indicating the role of molecular oxygen in the mechanism of vanadium(IV)-induced dG hydroxylation. Vanadium(IV) also caused molecular oxygen-dependent DNA strand breaks in a pattern similar to that observed for dG hydroxylation. ESR spin trapping measurements demonstrated that the reaction of vanadium(IV) with H2O2 generated OH radicals, which were inhibited by DTPA and deferoxamine. Incubation of vanadium(IV) with dG or with DNA in the presence of H2O2 resulted in an enhanced 8-OHdG formation and substantial DNA double strand breaks. Sodium formate inhibited 8-OHdG formation while DTPA had no significant effect. Deferoxamine enhanced the 8-OHdG generation by 2.5-fold. ESR and UV measurements provided evidence for the complex formation between vanadium(IV) and deferoxamine. UV-visible measurements indicate that dG, vanadium(IV) and deferoxamine are able to form a complex, thereby, facilitating site-specific 8-OHdG formation. Reaction of vanadium(IV) with t-butyl hydroperoxide generated hydroperoxide-derived free radicals, which caused 8-OHdG formation from dG and DNA strand breaks. DTPA and deferoxamine attenuated vanadium(IV)/t-butyl-OOH-induced DNA strand breaks.

Toxicology of vanadium compounds in diabetic rats: the action of chelating agents on vanadium accumulation

The possible use of vanadium compounds in the treatment of diabetic patients is now being evaluated. However, previously to establish the optimal maximum dose for diabetes therapy, it should be taken into account that vanadium is a highly toxic element to man and animals. The toxic effects of vanadium are here reviewed. The tissue vanadium accumulation, which would mean an additional risk of toxicity following prolonged vanadium administration is also discussed. Recently, it has been shown that coadministration of vanadate and TIRON, an effective chelator in the treatment of vanadium intoxication, reduced the tissue accumulation of this element, decreasing the possibility of toxic side effects derived from chronic vanadium administration without diminishing the hypoglycemic effect of vanadium. However, previously to assess the effectiveness of this treatment in diabetic patients, a critical reevaluation of the antidiabetic action of vanadium and its potential toxicity is clearly needed.

One-electron reduction of vanadate by ascorbate and related free radical generation at physiological pH

The one-electron reduction of vanadate (vanadium(V)) by ascorbate and related free radical generation at physiological pH was investigated by ESR and ESR spin trapping. The spin trap used was 5,5-dimethyl-1-pyrroline N-oxide (DMPO). Incubation of vanadium(V) with ascorbate generated significant amounts of vanadium(IV) in phosphate buffer (pH 7.4) but not in sodium cacodylate buffer (pH 7.4) nor in water. The vanadium(IV) yield increased with increasing ascorbate concentration, reaching a maximum at a vanadium(V): ascorbate ratio of 2:1. Addition of formate to the incubation mixture containing vanadium(V), ascorbate, and phosphate generated carboxylate radical (.COO-), indicating the formation of reactive species in the vanadium(V) reduction mechanism. In the presence of H2O2 a mixture of vanadium(V), ascorbate, and phosphate buffer generated hydroxyl radical (.OH) via a Fenton-like reaction (vanadium(IV)+H2O2-->vanadium(V)+.OH+OH-). The .OH yield was favored at relatively low ascorbate concentrations. Omission of phosphate sharply reduced the .OH yield. The vanadium(IV) generated by ascorbate reduction of vanadium(V) in the presence of phosphate was also capable of generating lipid hydroperoxide-derived free radicals from cumene hydroperoxide, a model lipid hydroperoxide. Because of the ubiquitous presence of ascorbate in cellular system at relatively high concentrations, one-electron reduction of vanadium(V) by ascorbate together with phosphate may represent an important vanadium(V) reduction pathway in vivo. The resulting reactive species generated by vanadium(IV) from H2O2 and lipid hydroperoxide via a Fenton-like reaction may play a significant role in the mechanism of vanadium(V)-induced cellular injury.

Abnormal hepatic mitochondrial respiration and cytochrome C oxidase activity in rats with long-term copper overload

BACKGROUND

Dietary copper overload in the rat is associated with morphological abnormalities and lipid peroxidation of hepatic mitochondria. This study was designed to determine if copper hepatotoxicity was associated with functional alterations in mitochondrial respiration in conjunction with lipid peroxidation.

METHODS

Weanling male rats were pair-fed for 8 weeks on diets containing normal or high levels of copper in combination with sufficient vitamin E. Serum and liver samples were obtained, and hepatic mitochondria were isolated by differential centrifugation.

RESULTS

Oxidant injury (decreased levels of hepatic glutathione and alpha tocopherol and increased levels of mitochondrial thiobarbituric acid-reacting substances) was present in the copper-overloaded rats. Serum aminotransferase levels correlated with concentrations of mitochondrial copper and thiobarbituric acid-reacting substances. Copper overload caused a decrease in state 3 respiration and the respiratory control ratio in hepatic mitochondria when several electron donors were used. Analysis of the oxidoreductase activities of the four mitochondrial electron transport protein complexes showed that complex IV (cytochrome C oxidase) activity was reduced by 60% in copper overload.

CONCLUSIONS

Functional abnormalities of mitochondria accompany lipid peroxidation and the morphological alterations caused by copper overload, supporting the hypothesis that the mitochondrion is one of the major intracellular targets in copper hepatotoxicity.

Hydroxyl radical generation in the NADH/microsomal reduction of vanadate

ESR spin trapping measurements demonstrate generation of hydroxyl (.OH) radical from reduction of vanadate by rat liver microsomes/NADH without exogenous H2O2. Catalase decreases the .OH signal while increasing a vanadium (4+) signal. Addition of superoxide dismutase (SOD) or measurements under an argon atmosphere show decreased .OH radical production. The results suggest that during the one-electron vanadate reduction process by microsomes/NADH, molecular oxygen is reduced to H2O2, which then reacts with vanadium (4+) to generate .OH radical via a Fenton-like mechanism.