Concerted Action Of Reduced Glutathione And Superoxide Dismutase In Preventing Redox Cycling Of Dihydroxypyrimidines, And Their Role In Antioxidant Defence

Dialuric Acid, the reduced form of the β-cell toxin alloxan, and the related fava bean derivatives divicine and isouramil, autoxidize rapidly in neutral solution by a radical mechanism. GSH promotes redox cycling of each compound, with concomitant GSH oxidation and H₂O₂ production. With superoxide dismutase present, there is a lag period in which little oxidation occurs, followed by rapid oxidation. GSH extends this lag and decreases the subsequent rate of oxidation, so that with superoxide dismutase and a sufficient excess of GSH. coupled oxidation of GSH and each pyrimidine is almost completely suppressed. This mechanism may be a means whereby GSH in combination with superoxide dismutase protects against the cytotoxic effects of these reactive pyrimidines. Superoxide dismutase may also protect cells against oxida-tive stress in other situations where GSH acts as a radical scavenger. and we propose that the concerted action of GSH and superoxide dismutase constitutes an important antioxidant defence     

Glutathione-dependent protection by rat liver microsomal protein against lipid peroxidation

GSH is an important cellular defense against oxidant injury. Its effect in the rat liver microsomal lipid peroxidation system has been examined. Incubation of fresh rat liver microsomes with ascorbic acid and ADP-chelated iron leads to the peroxidation of microsomal lipids (production of thiobarbituric acid-reactive substances and destruction of polyunsaturated fatty acids) following a 2 to 5 min lag. Addition of 0.1 mM GSH to the system lengthened the lag period by 5 to 15 min without affecting the rate or the extent of lipid peroxidation. GSH could not be replaced in prolonging the lag by cysteine, mercaptoethanol, dithiothreitol, propylthiouracil, or GSSG. The GSH effect on the lag was abolished by heating or trypsin digestion of the microsomes, indicating that microsomal protein is required for its expression. Progressively longer lags were observed as the GSH concentration was increased from 0.1 to 5 mM, but there was no evidence of GSH oxidation as a consequence of the protection against lipid peroxidation. GSH protected against heat inactivation of the microsomal protein responsible for the GSH effect. Experiments with an oxygen electrode revealed that the GSH protection did not alter the ratio of O₂ consumed to thiobarbituric acid-reactive substances produced. This implicated free radical scavenging as the mechanism of protection. These results indicate the existence of a GSH-dependent rat liver microsomal protein which scavenges free radical. This protein may be an important defense against free radical injury to the microsomal membrane.     

Evidence against superoxide involvement in tyrosine hydroxylation by mushroom tyrosinase

The possible involvement of superoxide anions in the hydroxylation of tyrosine by mushroom tyrosinase was studied. Superoxide dismutase and scavengers of superoxide ions of smaller MW than superoxide dismutase, such as nitroblue tetrazolium and copper salicylate, had no direct effect on the monohydroxyphenolase activity of mushroom tyrosinase. The kinetics of tyrosine hydroxylation, but not of DOPA oxidation, by mushroom tyrosinase was atrected by the addition of a xanthine-xanthine oxidase system. In the presence of the xanthine-xanthine oxidase system, the lag period of tyrosine hydroxylation was shortened compared to the lag period in the absence of the xanthine-xanthine oxidase system. The xanthine- xanthine oxidase system alone (without mushroom tyrosinase) had no effect on tyrosine conversion to dopachrome. Superoxide dismutase, catalase and hydroxyl radical scavengers counteracted to some extent the shortening of the lag period of tyrosine hydroxylation by mushroom tyrosinase caused by the xanthin e-xanthine oxidase system. It is suggested that the shortening of the lag period is due mainly to hydroxyl radicals generated by the xanthine-xanthine oxidase system via interaction of O₂^?. and hydrogen paroxide (a Haber-Weiss type reaction). The data do not support the direct participation of superoxide anions in tyrosine hydroxylation by mushroom tyrosinase.     

Lipoxygenase-mediated glutathione oxidation and superoxide generation

Soybean lipoxygenase-mediated cooxidation of reduced glutathione (GSH) and concomitant superoxide generation was examined. The oxidation of GSH was dependent on the concentration of linoleic acid (LA), GSH, and the enzyme. The optimal conditions to observe maximal enzyme velocity included the presence of 0.42 mM LA, 2 mM GSH, and 50 pmole of enzyme/mL. The GSH oxidation was linear up to 10 minutes and exhibited a pH optimum of 9.0. The reaction displayed a K_m of 1.49 mM for GSH and V_max of 1.35 ± 0.02 μmoles/min/nmole of enzyme. Besides LA, arachidonic and γ-linolenic acids also supported the lipoxygenase-mediated GSH oxidation. Hydrogen peroxide and 13-hydroperoxylinoleic acid supported GSH cooxidation, but to a very limited extent. Oxidized glutathione (GSSG) was identified as the major product of the reaction based on the depletion of nicotinamide-adenine dinucleotide 3′-phosphate (NADPH) in the presence of glutathione reductase. The GSH oxidation was accompanied by the reduction of ferricytochrome c, which can be completely abolished by superoxide dismutase (SOD), suggesting the generation of superoxide anion radicals. Under optimal conditions, the rate of superoxide generation (measured as the SOD-inhibitable reduction of ferricytochrome c) was 10 ± 1.0 nmole/min/nmole of enzyme. These results clearly suggest that lipoxygenase is capable of oxidizing GSH to GSSG and simultaneously generating superoxide anion radicals, which may contribute to oxidative stress in cells under certain conditions.     

Oxidative stress response in eukaryotes: effect of glutathione,superoxide dismutase and catalase on adaptation to peroxide and menadione stresses in Saccharomyces cerevisiae

Abstract

Aiming to clarify the mechanisms by which eukaryotes acquire tolerance to oxidative stress, adaptive and cross-protection responses to oxidants were investigated in Saccharomyces cerevisiae. Cells treated with sub-lethal concentrations of menadione (a source of superoxide anions) exhibited cross-protection against lethal doses of peroxide; however, cells treated with H₂O₂ did not acquire tolerance to a menadione stress, indicating that menadione response encompasses H₂O₂ adaptation. Although, deficiency in cytoplasmic superoxide dismutase (Sod1) had not interfered with response to superoxide, cells deficient in glutathione (GSH) synthesis were not able to acquire tolerance to H₂O₂ when pretreated with menadione. These results suggest that GSH is an inducible part of the superoxide adaptive stress response, which correlates with a decrease in the levels of intracellular oxidation. On the other hand, neither the deficiency of Sod1 nor in GSH impaired the process of acquisition of tolerance to H₂O₂ achieved by a mild pretreatment with peroxide. Using a strain deficient in the cytosolic catalase, we were able to conclude that the reduction in lipid peroxidation levels produced by the adaptive treatment with H₂O₂ was dependent on this enzyme. Corroborating these results, the pretreatment with low concentrations of H₂O₂ promoted an increase in catalase activity.     

Inhibitors of superoxide dismutases: A cautionary tale

An extensive search resulted in the identification of pamoic acid as an inhibitor of superoxide dismutases. Pamoic acid appeared to rapidly and reversibly inhibit all types of superoxide dismutases and did so in both the cytochrome c reduction and in the dianisidine photooxidation assays, used to measure this activity. It could nevertheless be shown that pamoic acid did not at all inhibit superoxide dismutase but rather diminished the sensitivity of the assays. The mechanism proposed to account for this effect involved oxidation of pamoate, by O₂^?, to yield a pamoate radical which can then reduce cytochrome c or oxidize pyrogallol. Pamoate thus competes with superoxide dismutase for the available O₂^?, without affecting the observable effects of that O₂^? upon cytochrome c or upon pyrogallol. It consequently makes these assays less responsive to superoxide dismutase, while appearing to be without effect in the absence of superoxide dismutase. Several of the predicted consequences of this proposal were affirmed. Other workers, interested in finding inhibitors for superoxide dismutases, are hereby forwarned of this subtle snare.     

Roles of superoxide and myeloperoxidase in ascorbate oxidation in stimulated neutrophils and H2O2-treated HL60 cells

Ascorbate is present at high concentrations in neutrophils and becomes oxidized when the cells are stimulated. We have investigated the mechanism of oxidation by studying cultured HL60 cells and isolated neutrophils. Addition of H₂O₂ to ascorbate-loaded HL60 cells resulted in substantial oxidation of intracellular ascorbate. Oxidation was myeloperoxidase-dependent, but not attributable to hypochlorous acid, and can be explained by myeloperoxidase (MPO) exhibiting direct ascorbate peroxidase activity. When neutrophils were stimulated with phorbol myristate acetate, about 40% of their intracellular ascorbate was oxidized over 20 min. Ascorbate loss required NADPH oxidase activity but in contrast to the HL60 cells did not involve myeloperoxidase. It did not occur when exogenous H₂O₂ was added, was not inhibited by myeloperoxidase inhibitors, and was the same for normal and myeloperoxidase-deficient cells. Neutrophil ascorbate loss was enhanced when endogenous superoxide dismutase was inhibited by cyanide or diethyldithiocarbamate and appears to be due to oxidation by superoxide. We propose that in HL60 cells, MPO-dependent ascorbate oxidation occurs because cellular ascorbate can access newly synthesized MPO before it becomes packaged in granules: a mechanism not possible in neutrophils. In neutrophils, we estimate that ascorbate is capable of competing with superoxide dismutase for a small fraction of the superoxide they generate and propose that the superoxide responsible is likely to come from previously identified sites of intracellular NADPH oxidase activity. We speculate that ascorbate might protect the neutrophil against intracellular effects of superoxide generated at these sites.     

Mechanism of the peroxidase activity of Cu,Zn superoxide dismutase

In addition to its very efficient catalysis of the dismutation of superoxide ( O₂^- ) into O₂ plus H₂O₂, Cu, Zn SOD acts less efficiently as a non-specific peroxidase. This peroxidase activity is CO₂ dependent although very slow peroxidation of some substrates occurs in the absence of CO2. The mechanism of that CO₂ dependence is explained by the generation of a strong oxidant at the copper site by two sequential reactions with H₂O₂, followed by the oxidation of CO₂ to the carbonate radical that then diffuses into the bulk solution. This diffusible carbonate radical is then responsible for the diverse oxidations that have been reported. A different mechanism that involves the reduction of peroxymonocarbonate by the reduced superoxide dismutase to yield carbonate radical has been proposed. We will demonstrate that this mechanism is not supported by the available data. It seems likely that generation of the carbonate radical has relevance to the oxidative stress faced by aerobic organisms.     

Inactivation of the human CuZn superoxide dismutase during exposure to O-2 and H2O2

Human copper-zinc superoxide dismutase undergoes inactivation when exposed to O₂^? and H₂O₂ generated during the oxidation of acetaldehyde by xanthine oxidase at pH 7.4 and 37° C. In contrast, human manganese superoxide dismutase is not inactivated under the same conditions. Catalase and Mn-superoxide dismutase protect CuZn superoxide dismutase from inactivation. Similar protection is observed with hydroxyl radical (OH.) scavengers, such as formate and mannitol. In contrast, other OH. scavengers such as ethanol and tert-butyl alcohol, have no protective action. The latter results indicate that “free OH.” is not responsible for the inactivation. Furthermore, H₂O₂ generated during the oxidation of glucose by glucose oxidase, i.e., without production of O₂^?, does not induce CuZn superoxide dismutase inactivation. A mechanism accounting for this $\text{O}{}_2{}^{\mathrm{?}}\text{H}{}_2\text{O}{}_2$-dependent inactivation of CuZn superoxide dismutase is proposed.     

Pycnogenol enhances endothelial cell antioxidant defenses

Summary

Reactive oxygen species (ROS) such as hydrogen peroxide (H₂O₂), superoxide anion (O₂^?), and hydroxyl radical (OH^?) have been implicated in mediating various pathological events such as cancer, atherosclerosis, diabetes, ischemia, inflammatory diseases, and the aging process. The glutathione (GSH) redox cycle and antioxidant enzymes—superoxide dismutase (SOD) and catalase (CAT)—play an important role in scavenging ROS and preventing cell injury. Pycnogenol has been shown to protect endothelial cells against oxidant-induced injury. The present study determined the effects of pycnogenol on cellular metabolism of H₂O₂ and O₂^? and on glutathione-dependent and -independent antioxidant enzymes in bovine pulmonary artery endothelial cells (PAEC). Confluent monolayers of PAEC were incubated with pycnogenol, and oxidative stress was triggered by hypoxanthine and xanthine oxidase or H₂O₂. Pycnogenol caused a concentration-dependent enhancement of H₂O₂ and O₂^? clearance. It increased the intracellular GSH content and the activities of GSH peroxidase and GSH disulfide reductase. It also increased the activities of SOD and CAT. The results suggest that pycnogenol promotes a protective antioxidant state by upregulating important enzymatic and nonenzymatic oxidant scavenging systems.     

Removal of H₂O₂ and generation of superoxide radical: role of cytochrome c and NADH

In cells, mitochondria, endoplasmic reticulum, and peroxisomes are the major sources of reactive oxygen species (ROS) under physiological and pathophysiological conditions. Cytochrome c (cyt c) is known to participate in mitochondrial electron transport and has antioxidant and peroxidase activities. Under oxidative or nitrative stress, the peroxidase activity of Fe³⁺cyt c is increased. The level of NADH is also increased under pathophysiological conditions such as ischemia and diabetes and a concurrent increase in hydrogen peroxide (H₂O₂) production occurs. Studies were performed to understand the related mechanisms of radical generation and NADH oxidation by Fe³⁺cyt c in the presence of H₂O₂. Electron paramagnetic resonance (EPR) spin trapping studies using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) were performed with NADH, Fe³⁺cyt c, and H₂O₂ in the presence of methyl-β-cyclodextrin. An EPR spectrum corresponding to the superoxide radical adduct of DMPO encapsulated in methyl-β-cyclodextrin was obtained. This EPR signal was quenched by the addition of the superoxide scavenging enzyme Cu,Zn-superoxide dismutase (SOD1). The amount of superoxide radical adduct formed from the oxidation of NADH by the peroxidase activity of Fe³⁺cyt c increased with NADH and H₂O₂ concentration. From these results, we propose a mechanism in which the peroxidase activity of Fe³⁺cyt c oxidizes NADH to NAD^•, which in turn donates an electron to O₂, resulting in superoxide radical formation. A UV-visible spectroscopic study shows that Fe³⁺cyt c is reduced in the presence of both NADH and H₂O₂. Our results suggest that Fe³⁺cyt c could have a novel role in the deleterious effects of ischemia/reperfusion and diabetes due to increased production of superoxide radical. In addition, Fe³⁺cyt c may play a key role in the mitochondrial “ROS-induced ROS-release” signaling and in mitochondrial and cellular injury/death. The increased oxidation of NADH and generation of superoxide radical by this mechanism may have implications for the regulation of apoptotic cell death, endothelial dysfunction, and neurological diseases. We also propose an alternative electron transfer pathway, which may protect mitochondria and mitochondrial proteins from oxidative damage.     

The oxidatin of NADH by vanadate plus sugars

Sugars and sugar phosphates enable vanadate to catalyze the oxidation of NADH. Superoxide dismutase inhibits this oxidation. Incubation of sugars with vanadate, prior to addition of NADH, accelerates this oxidation of subsequently added NADH and eliminates the lag phase otherwise noted. Incubation of sugars with vanadate also results in the reduction of vanadate to vanadyl, with appearance of a blue-green color probably associated with a vanadyl-vanadate complex. It appears that sugars reduce vanadate to vanadyl which, in turn, reduces O₂ to O₂⁻ and that vanadate plus O₂⁻ then catalyzes the oxidation of NAD(P)H by a free radical chain reaction. Such oxidation of NAD(P)H may account for several of the biological effects of vanadate.     

Nitrofuran enhancement of microsomal electron transport, superoxide anion production and lipid peroxidation

Addition of nifurtimox (a nitrofuran derivative used for the treatment of Chagas' disease) to rat liver microsomes produced an increase of (a) electron flow from NADPH to molecular oxygen, (b) generation of both superoxide anion radical (O₂^?) and hydrogen peroxide, and (c) lipid peroxidation. The nifurtimox-stimulated NADPH oxidation was greatly inhibited by NADP⁺ and p-chloromercuribenzoate, and to a lesser extent by SKF-525-A and metyrapone. These inhibitions reveal the function of both the NADPH-cytochrome P-450 (c) reductase and cytochrome P-450 in nifurtimox reduction. Superoxide dismutase, catalase (in the presence of superoxide dismutase), and hydroxyl radical scavengers (mannitol, 5,5-dimethyl-1-pyrroline-1-oxide) inhibited the nifurtimox-stimulated NADPH oxidation, in accordance with the additional operation of a reaction chain including the hydroxyl radical. Further evidence supporting the role of superoxide anion and hydroxyl radicals in the nifurtimox-induced NADPH oxidation resulted from the effect of specific inhibitors on NADPH oxidation by O₂^? (generated by the xanthine oxidase reaction) and by OH. (generated by an iron chelate or the Fenton reaction). Production of O₂^? by rat kidney, testes and brain microsomes was significantly stimulated by nifurtimox in the presence of NADPH. It is postulated that enhanced formation of free radicals is the basis for nifurtimox toxicity in mammals, in good agreement with the postulated mechanism of the trypanocide effect of nifurtimox on Trypanosoma cruzi.     

Pro-oxidant and antioxidant processes in gas gland and other tissues of cod (Gadus morhua)

Partial reduction of molecular oxygen produces reactive oxyradicals, including the superoxide anion radical (O _- ² ) and hydroxyl radical (·OH). The gas gland functions under hyperoxic and acidic conditions and therefore is likely to be subjected to enhanced oxidative stress. Aspects of pro- and antioxidant processes in gas gland were compared with other tissues likely to be subject to differing degrees of oxyradical production, viz. liver (site of chemically-mediated oxyradical production), gills and skeletal muscle. Antioxidant enzyme activities (superoxide dismutase, catalase, selenium-dependent and total glutathione peroxidase) per g wet weight were highest in liver and lowest in muscle. Catalase and glutathione peroxidase activies per g wet weight were higher in gills than in gas gland, whereas the reverse was seen for superoxide dismutase. Cytosolic superoxide dismutase activities per mg protein were two- and nine-fold higher in gas gland than in liver and gills. The pH characteristics of the antioxidant enzymes were generally similar in all the tissues. Glutathione, vitamin E and unsaturated (peroxidizable) lipid levels were generally highest in liver followed by gas gland. Lipid peroxidation (malonaldehyde equivalents) was evident in all tissues except gas gland. Hydrogen peroxide and O _- ² were involved in the NAD(P)H-dependent ferric/EDTA-mediated formation of ·OH (as measured by 2-keto-4-methiolbutyrate oxidation) by mitochondrial and postmitochondrial fractions of gas gland. Tissue maximal potentials for ·OH production paralled superoxide dismutase but not catalase or glutathione peroxidase activities. Overall, the results confirm the presence of effective antioxidant defences in gas gland and support previous workers' contentions of a central role for superoxide dismutase in this process.Abbreviations EDTA di-sodium ethylenediaminetetra-acetic acid - G-6-P glucose-6-phosphate - GPX total glutathione peroxidase - GSH reduced glutathione - GSSG oxidised glutathione - GST glutathion-S-transferase - HPLC high performance liquid chromatography - KMBA 2-keto-4-methiolbutyric acid - MOPS 3-[N-morpholino] propane-sulphonic acid - PMS postmitochondrial supernatant - Se-GPX selenium-dependent glutathion peroxidase - SOD superoxide dismutase - TCA trichloroacetic acid     

The oxidation of phenylhydrazine: superoxide and mechanism.

The oxidation of phenylhydrazine in buffered aqueous solutions is a complex process involving several intermediates. It can be initiated by metal cations, such as Cu2+; in which case EDTA acts as an inhibitor. It can also be intiated by oxyhemoglobin; in which case chelating agents do not interfere. Superoxide radical is both a product of this reaction and a chain propagator. The formation of O2- could be demonstrated in terms of a reduction of nitroblue tetrazolium, which was prevented by superoxide dismutase. The importance of O2- in carrying the reaction chains was shown by the inhibition of phenylhydrazine oxidation by superoxide dismutase. Hydrogen peroxide accumulated during the reaction and could be detected with catalase. The progress of this oxidation could be monitored in terms of oxygen consumption and by following increases in absorbance at 280 or 320 nm. The oxidation was markedly autocatalytic and superoxide dismutase had the effect of extending the lag period. The absorbance at 280 nm was due to an intermediate which first accumulated and was then consumed. This intermediate appears to be benzendiazonium ion. The absorbance at 320 nm was due to a stable product, which was not identified. The time course of oxygen consumption paralleled the increase in absorbance at 320 nm and lagged behind the changes at 280 nm. Exogenous benzenediazonium ion accelerated the oxidation of phenylhydrazine and eliminated the lag phase. Benzenediazonium ion must therefore react with phenylhydrazine to produce a very reactive intermediate, possibly phenyldiazene. A mechanism was proposed which is consistent with the data. The intermediates and products of the oxidation of phenylhydrazine include superoxide radical, hydrogen peroxide, phenylhydrazyl radical, phenyldiazene, and benzenediazonium ion. This is a minimal list: others remain to be detected and identified. It appears likely that the diverse biological effects of phenylhydrazine are largely due to the reactivities of these intermediates and products.     

Effect of Cadmium Ions on Antioxidant Defense System in Sunflower Cotyledons

Sunflower (Helianthus annuus L.) seeds were germinated and grown in the presence of 50, 100 and 200 μM CdCl₂. The lower concentration (50 μM) of Cd² ions produced slight decrease in reduced glutathione (GSH) content and overall increase (except superoxide dismutase) in antioxidant enzyme activities, and in H₂O₂ concentration. Chlorophyll content, lipid peroxidation and protein oxidation were not affected under 50 μM CdCl₂. GSH content was diminished under 100 and 200 μM CdCl₂, and except for superoxide dismutase, which activity remained unaltered, overall decreases in the antioxidant enzyme activities (catalase, ascorbate peroxidase, dehydroascorbate peroxidase, glutathione reductase) and in guaiacol peroxidase were observed. These Cd² concentrations caused a decrease in chlorophyll content as well as an increase in lipid peroxidation, protein oxidation and H₂O₂ concentration. All the observed effects were more evident with the highest concentration of cadmium chloride used. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of selenium and grape seed extract on indomethacin-induced gastric ulcers in rats

Indomethacin (IND) is a non-steroid anti-inflammatory agent that is known to induce severe gastric mucosal lesions. In this study, we investigated the protective effect of selenium (SEL), grape seed extract (GSE), and both on IND-induced gastric mucosal ulcers in rats. Sprague–Dawley rats (200–250 g) were given SEL, GSE, and both by oral gavage for 28 days, and then gastric ulcers were induced by oral administration of 25 mg/kg IND. Malondialdehyde (MDA), non-enzymatic (reduced glutathione, GSH) and enzymatic (superoxide dismutase, catalase, and glutathione peroxidase) antioxidants, prostaglandin E₂ (PGE₂) in gastric mucosa, and serum tumor necrosis factor alpha (TNF-α) were measured. Moreover, gastric ulcer index and preventive index were determined. Indomethacin increased the gastric ulcer index, MDA, TNF-α, and decreased PGE₂ and non-enzymatic (GSH) and enzymatic (superoxide dismutase, catalase, and glutathione peroxidase) antioxidants. Pretreatment with SEL, GSE, and both significantly decreased the gastric ulcer index, MDA, and TNF and increased antioxidants and PGE₂. Histopathological observations confirm the gastric ulcer index and biochemical parameters. Selenium and GSE have a protective effect against IND-induced gastric ulcers through prevention of lipid peroxidation, increase of GSH, activation of radical scavenging enzymes, PGE₂ generation, and anti-inflammatory activity. Co-administration of GSE and SEL is more effective than GSE or SEL alone.     

Semiquinone derivative isolated from Bacillus sp. INM-1 protects cellular antioxidant enzymes from γ-radiation-induced renal toxicity

This study was focused to evaluate protection of indigenous antioxidant system of mice against gamma radiation-induced oxidative stress using a semiquinone (SQGD)-rich fraction isolated from Bacillus sp. INM-1. Male C57bl/6 mice were administered SQGD (50 mg/kgb.w.i.p.) 2 h before irradiation (10 Gy) and modulation in antioxidant enzymes activities was estimated at different time intervals and compared with irradiated mice which were not pretreated by SQGD. Compared to untreated controls, SQGD pretreatment significantly (p < 0.05) accelerates superoxide dismutase, catalase, GSH, and glutathione-S-transferase activities. Similarly, significant (p < 0.05) increase in the expression of superoxide dismutase, catalase, GSH, and glutathione-S-transferase was observed in irradiated mice pretreated by SQGD, compared to only irradiated groups. Total antioxidant status equivalent to trolox was estimated in renal tissue of the mice after SQGD administration. Significant ABTS⁺ radical formation was observed in H₂O₂-treated kidney homogenate, due to oxidative stress in the tissue. However, significant decrease in the levels of ABTS⁺ radical was observed in kidney homogenate of the mice pretreated with SQGD. Therefore, it can be concluded that SQGD neutralizes oxidative stress by induction of antioxidant enzymes activities and thus improved total antioxidant status in cellular system and hence contributes to radioprotection.     

The oxidation of NADH by tetravalent vanadium

Vanadyl (V_(IV)) salts autoxidize in neutral aqueous solution yielding O₂⁻ plus vanadate (V_(V)) and these, in turn, cause the oxidation of NADH, by a free radical chain reaction. This oxidation of NADH was inhibited by superoxide dismutase, but not by a scavenger of HO.. When H₂O₂ was present V_(IV)) caused rapid oxidation of NADH by a process which was unaffected by superoxide dismutase but was inhibited by a scavenger of HO.. This appeared to be dependent upon reduction of H₂O₂ to OH⁻ plus HO., by V_(IV)), followed by oxidation of NADH by HO.. Since there are reductants, within cells, capable of reducing V_(V)) to V_(IV), these reactions are likely to contribute to the toxicity of vanadate.