Vanadyl- and vanadate-induced lipid peroxidation in mitochondria and in phosphatidylcholine suspensions

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

Spontaneous and stimulated lipid peroxidation (LPO) after vanadate and magnesium treatment was studied in kidney supernatants obtained from outbred 5-month-old, albino male Wistar rats. The 2-month-old animals daily received: group I (control), deionized water to drink; group II, water solution of sodium metavanadate, NaVO(3) (SMV, 0.125 mg V ml(-1)); group III, water solution of magnesium sulfate, MgSO(4) (MS, 0.06 mg Mg ml(-1)); and 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. FeSO(4), NaVO(3) and MgSO(4) were selected as agents that may modify LPO process in in vitro conditions. Spontaneous malondialdehyde (MDA) levels in kidney supernatants increased significantly in the rats in groups II and IV, compared with groups I and III; and they were also significantly higher in all the groups of rats compared with the liver supernatants. The total antioxidant status (TAS) in groups II and IV tended to be higher too. Vanadium concentration in the kidney of the rats in groups II and IV increased, whereas the kidney Mg content in groups II, III and IV decreased, compared with levels in the liver. As the two-way ANOVA indicated, the changes in the basal MDA level, TAS and Mg concentration in the liver of rats at combined V and Mg application only resulted from independent action of V. As far as the in vitro results are concerned, in the supernatants obtained from the rats in groups II and IV, a significant increase in MDA level was demonstrated in the presence of 30 microm of exogenous FeSO(4) as well as 30, 100, 200 and 400 microm NaVO(3) and 100, 200, 400, 600, 800 and 1000 microm MgSO(4), compared with groups I and III. The 600, 800 and 1000 microm of exogenous MgSO(4) also significantly elevated MDA production in the supernatants obtained from the rats in group III, compared with spontaneously formed MDA in the same supernatants. The three-way ANOVA showed that the changes in LPO induced by in vitro treatment of kidney 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 exogenous Fe (Fe(exog)) and endogenous V (V(end)) and between V(end) and exogenous V (V(exog)). In conclusion, V (as NaVO(3)) consumed by the rats with drinking water at a dose of 12.9 mg V kg(-1) b.w. per 24 h for 12 weeks increased the basal LPO and markedly enhanced TAS in the renal tissue. Its pro-oxidant potential was also found in in vitro conditions. The Mg dose (6 mg Mg kg(-1) b.w. per 24 h) ingested by the rats together with V (12.7 mg V kg(-1) b.w. per 24 h) neither reduced nor intensified the spontaneous LPO, compared with V-only intoxicated animals; however, the stimulating effect of Mg on LPO was revealed in in vitro conditions.

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.

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.

Mitochondrial oxidant production by a pollutant dust and NO-mediated apoptosis in human alveolar macrophage

Residual oil fly ash (ROFA) is a pollutant dust that stimulates production of reactive oxygen species (ROS) from mitochondria and apoptosis in alveolar macrophages (AM), but the relationship between these two processes is unclear. In this study, human AM were incubated with ROFA or vanadyl sulfate (VOSO(4)), the major metal constituent in ROFA, with or without nitro-L-arginine methyl ester (L-NAME), diphenyleneiodonium (DPI), and mitochondrial electron transport inhibitors. Interactions among production of ROS, nitric oxide (NO), and apoptosis of AM were determined. ROFA-stimulated ROS production was attenuated by DPI, rotenone, antimycin, and NaN(3), but not by L-NAME, a pattern mimicked by VOSO(4). ROFA-induced apoptosis was inhibited by L-NAME and a caspase-3-like protease inhibitor, but not by mitochondrial inhibitors. ROFA enhanced NO-mediated increase in caspase-3-like activity. VOSO(4) had minor effects on apoptosis. Thus ROFA-stimulated production of ROS from mitochondria was independent of apoptosis of AM, which was mediated by activation of caspase-3-like proteases and NO. The pro-oxidant effect but not the proapoptotic effect of ROFA was mediated by vanadium.

Effect of pirfenidone against vanadate-induced kidney fibrosis in rats

Renal fibrosis is a complication of kidney injury and can contribute to organ failure. Currently, there are no drugs for the treatment of renal fibrosis. Pirfenidone (PD) has been proven to have antifibrotic effects in animal models of fibrosis. We tested the ability of PD against vanadate-induced kidney fibrosis in rats. The rats were injected subcutaneously with vehicle or vanadate solution (1mg vanadate/kg/day) for 12 or 16 days to produce varying degrees of kidney fibrosis. The vanadate- and vehicle-treated rats were fed a laboratory diet or the same diet mixed with 0.6% PD ad lib. One vanadate-injected group was initially fed the same diet without PD and later switched to the diet containing PD 2 days after the last injection. The rats were killed at 12 and 25 days following the last dose. The changes found in the kidney of vanadate-treated rats included increases in RNA and DNA content and increases in kidney weight. Treatment with PD diminished the vanadate-induced increases in kidney weight and RNA content. The hydroxyproline content of the kidney in vanadate-treated animals was increased significantly (P< or =0.05) from the control level of 1452 microg/kidney to 1765 microg/kidney. Treatment with PD for 37 days caused significant reductions in the vanadate-induced increases in the hydroxyproline level. Similarly, treatment for 41 days also caused significant reductions (1744 microg/kidney) in vanadate-induced increases in the hydroxyproline level (1996 microg/kidney). The histological evaluation revealed that the severity of the lesions in the vanadate-treated group was moderate to severe, and treatment with PD for 41 days decreased the severity to a mild level. In addition, the delayed treatment with PD also minimized the vanadate-induced increases in the collagen content of the kidney. Although it is speculative, PD may potentially be therapeutic in the management of renal fibrosis.

In vitro effects of alloxan-vanadium combination on lipid peroxidation and on antioxidant enzyme activity

1. The in vitro effects of alloxan, dialuric acid and vanadium ions, alone or in combination, on lipid peroxidation and on antioxidant enzyme activity in rat liver and kidney were studied. 2. Unlike alloxan, alloxan-glutathione (GSH) and dialuric acid increased lipid peroxidation, which could be explained by the decreased activity of catalase and GSH peroxidase during incubation. 3. Vanadium(IV) ions increased the amount of thiobarbituric acid-reacting substances, but neither vanadium(IV) nor vanadium(V) changed the enzyme activity. 4. The combination of vanadium ions and alloxan-GSH or dialuric acid had no additive effect on lipid peroxidation. Vanadium ions decreased the dialuric acid-induced inhibition of catalase activity. 5. The present results suggest the therapeutic value of vanadium as an antidiabetic agent.

Hydroxyl radicals production in the vanadium ions/dialuric acid systems

1. The effects of vanadium ions on the .OH radical production in the presence of and in the absence of dialuric acid were studied. 2. Dialuric acid enhanced deoxyribose degradation. 3. Vanadium ions and vanadium/EDTA complexes decreased the degradation of deoxyribose in the presence and in the absence of dialuric acid. 4. The question as to whether or not free .OH radicals are formed via reaction of vanadium ions with H2O2 in the presence of dialuric acid is discussed. 5. The results are interpreted with a view to the vanadium ability to decrease the toxic effects of dialuric acid.

Lipid peroxidation and antioxidant enzymes in vanadate-treated rats

Male Wistar rats received an aqueous solution of ammonium metavanadate (AMV) of 0.15 mg/V/ml concentration instead of water for 14 days. The erythrocyte count and haemoglobin level in blood were not changed; the haematocrit index was slightly increased. The spontaneous lipid peroxidation in kidney and liver homogenates was increased. The Fe(II)- or ascorbate-induced lipid peroxidation was more pronounced in the kidney than in the liver. No changes in lipid peroxidation were observed in erythrocytes after AMV treatment. The AMV treatment resulted in a decrease in the activity of the antioxidant enzymes, catalase and glutathione peroxidase in the kidney and liver; the cytosolic Cu,Zn-SOD and mitochondrial Mn-SOD were unchanged. The activity of the enzymes in blood was not changed. The results are discussed with a view to the participation of lipid peroxidation in vanadium toxicity.

Vanadium redox cycling, lipid peroxidation and co-oxygenation of benzo(a)pyrene-7,8-dihydrodiol

Mechanism of lipid peroxidation triggered by vanadium in human term placental microsomes was reinvestigated in vitro. Production of lipid peroxyl radicals was estimated from co-oxygenation of benzo(a)pyrene and benzo(a)pyrene-7,8-dihydrodiol. Vanadyl(IV), but not vanadate(V) caused a dose-dependent co-oxygenation. Vanadate(V) required the presence of reduced nicotinamide adenine dinucleotide phosphate to trigger co-oxygenation of benzo(a)pyrene-7,8-dihydrodiol. To determine the role of pre-formed lipid hydroperoxides, the results obtained with partially peroxidized linoleic acid were compared with those of fresh linoleate. Superoxide dismutase inhibited the co-oxygenation of reaction when fresh linoleic acid was used. To further characterize the role of superoxide anion-radical in the vanadium redox cycling, the increase of optical density of vanadate(V) dissolved in Tris buffer was measured at 328 nm during the addition of KO2. The rate of this reaction producing peroxy-vanadyl complex was decreased by superoxide dismutase, especially, in the presence of catalase. It is suggested that vanadium catalyzes two separate processes, both leading to enhanced lipid peroxidation: (i) initiation, dependent on superoxide and triggered by peroxy-vanadyl; (ii) propagation, dependent on pre-formed lipid hydroperoxide not sensitive to superoxide dismutase. It is postulated that the vanadium-triggered initiation of lipid peroxidation may be crucial for toxicity in organs with limited endogenous lipid peroxidation.

Vanadate-induced toxicity towards isolated perfused rat livers: the role of lipid peroxidation

The toxic potential of sodium orthovanadate towards isolated perfused rat livers was investigated at a dose of 2 mmol/l. In livers from fasted rats, vanadate led to a release of cytosolic (glutamate-pyruvate-transaminase (GPT) and lactate dehydrogenase (LDH] and mitochondrial (glutamate dehydrogenase (GLDH] enzymes, an accumulation of calcium in the liver, a marked depletion of hepatic glutathione and an enhanced release of it into the perfusate, as well as an augmented formation and release of thiobarbituric acid-reactive material by the liver. Furthermore, a marked inhibition of oxygen consumption was observed. Vanadate-induced vasoconstriction resulted in a progressive decrease in perfusate flow rate. Control experiments with similarly reduced flow rates led to a comparable reduction in oxygen consumption. GPT and LDH release and hepatic glutathione depletion were also evident, though to a lesser extent than in the presence of vanadate, but no increase in GLDH release, in tissue calcium content or TBA-reactive material in the liver or the perfusate were observed. Thus, indirect toxic effects due to a reduced flow rate contribute only partly to vanadate hepatotoxicity and do not affect mitochondrial integrity. Omission of calcium from the perfusate did not prevent hepatotoxic responses to vanadate, although less calcium was present in the treated livers than in the control organs, indicating that calcium influx is not involved in vanadate-induced hepatotoxicity in the intact organ, in contrast to isolated hepatocytes. Feeding the animals, resulting in an activation of anaerobic energy conservation reactions, strongly attenuated vanadate hepatotoxicity indicating that the energetic status of the liver is the main target of vanadate. Superoxide dismutase did not affect the hepatotoxic responses of livers from fasted rats towards vanadate, while allopurinol and deferrioxamine inhibited lipid peroxidation and hepatotoxicity due to vanadate. The strong correlation between induction of lipid peroxidation and hepatotoxicity and the inhibition of both processes in parallel by antioxidants are suggestive of a causative role for lipid peroxidation in vanadate-induced hepatotoxicity.

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.

Vanadyl causes hydroxyl radical mediated degradation of deoxyribose

Vanadyl caused a time- and dose-dependent degradation of deoxyribose to carbonyl products detectable with thiobarbituric acid. This process was inhibited by catalase, ethanol or HEPES; whereas superoxide dismutase was without effect. Vanadate did not substitute for vanadyl even in the presence of a source of O2- plus H2O2; but it did so in the presence of reductants such as thiols or NADH. It appears that hydrogen peroxide, generated by the autoxidation of vanadyl, is reduced by vanadyl to the hydroxyl radical; which, in turn, was responsible for the degradation of deoxyribose. A similar process might contribute to the toxic and pharmacological effects of vanadium salts.

Vanadate-catalyzed, conformationally specific photocleavage of the Ca2(+)-ATPase of sarcoplasmic reticulum

Vanadate-sensitized photocleavage of the Ca2(+)-ATPase of rabbit sarcoplasmic reticulum was observed upon illumination of sarcoplasmic reticulum vesicles or the purified Ca2(+)-ATPase by ultraviolet light in the presence of 1 mM monovanadate or decavanadate. The site of the photocleavage is influenced by the Ca2+ concentration of the medium. When the [Ca2+] is maintained below 10 nM by EGTA, the vanadate-catalyzed photocleavage yields fragments of approximately equal to 87 and approximately equal to 22 kDa, while in the presence of 2-20 mM Ca, polypeptides of 71 and 38 kDa are obtained as the principal cleavage products. These observations indicate that the site of the vanadate-catalyzed photocleavage is altered by changes in the conformation of Ca2(+)-ATPase. Selective tryptic proteolysis, at Arg-505-Ala-506, combined with covalent labeling of Lys-515 by fluorescein 5'-isothiocyanate and with the use of anti-ATPase antibodies of defined specificity, permitted the tentative allocation of the sites of photocleavage to the A fragment near the T2 cleavage site in the absence of Ca2+, and to the B fragment between Lys-515 and Asp-659 in the presence of 2-20 mM Ca2+. The loss of ATPase activity during illumination is accelerated by calcium in the presence of vanadate. The vanadate-catalyzed photocleavage in the presence of Ca2+ is consistent with the existence of an ATPase-Ca2(+)-vanadate complex (Markus et al. (1989) Biochemistry 28, 793-799).

Vanadate-stimulated oxidation of NAD(P)H

Vanadate stimulates the oxidation of NAD(P)H by biological membranes because such membranes contain NAD(P)H oxidases which are capable of reducing dioxygen to O2- and because vanadate catalyzes the oxidation of NAD(P)H by O2-, by a free radical chain mechanism. Dihydropyridines, such as reduced nicotinamide mononucleotide (NMNH), which are not substrates for membrane-associated NAD(P)H oxidases, are not oxidized by membranes plus vanadate unless NAD(P)H is present to serve as a source of O2-. When [NMNH] greatly exceeds [NAD(P)H], in such reaction mixtures, one can observe the oxidation of many molecules of NMNH per NAD(P)H consumed. This reflects the chain length of the free radical chain mechanism. We have discussed the mechanism and significance of this process and have tried to clarify the pertinent but confusing literature.