Decreased Glutathione Reductase Activity Research Articles

Glutathione Cycle Impairment Mediates Aβ-induced Cell Toxicity

Alzheimer's disease is widely held to be associated with oxidative stress due, in part, to the action of amyloid beta-peptide (A beta). We observed that A beta 25-35 induced an increase in reactive oxygen species (ROS) in NT2 rho+ cells, leading to protein and lipid oxidation. This oxidative status was partially prevented by the antioxidants, vitamin E, reduced glutathione, and by melatonin. However, NT2 rho0 cells (that lack mitochondrial DNA) in the absence of A beta showed an increase in ROS production, lipid and protein oxidation, as compared with parental rho+ cells. Upon A beta 25-35 treatment, in rho+ cells, a decrease in glutathione reductase activity and in GSH levels was observed, whereas glutathione peroxidase activity was shown to be increased. In NT2 rho0 cells, in the absence of A beta, GSH levels were maintained, whereas glutathione reductase and peroxidase activities were increased. The exposure of A beta to rho0 cells did not induce any change in these parameters. We observed that melatonin prevented caspase activation and DNA fragmentation in rho+ cells treated with A beta. Considering the evidence presented, we argue that the glutathione cycle impairment is a key event in A beta-induced cell toxicity.

Differential effect of sorbitol and polyethylene glycol on antioxidant enzymes in rice leaves

Polyethylene glycol (PEG) and sorbitol (ST) have each been used inosmotically induced water stress studies in plants, however, these osmotica maynot have equivalent effects in plants. The present study was designed to examinewhether antioxidant enzyme responses in rice leaves are different for PEG and STof osmotic potential −1.5 MPa. As judged by relative watercontent, PEG treatment resulted in a higher degree of water stress in riceleaves than ST treatment. PEG treatment markedly increased lipid peroxidation,judged by malondialdehyde content, in rice leaves. However, ST treatment had noeffect on lipid peroxidation. An increase in peroxidase (POX), ascorbateperoxidase (APX) and glutathione reductase (GR) activities was observed in riceleaves treated with ST. PEG treatment had no effect on POX and APX activitiesand decreased GR activity in rice leaves. The decrease in superoxide dismutaseactivity induced by PEG was more pronounced than by ST. Cycloheximide blockedthe enhanced activities of POX, APX and GR by ST, indicating de novo synthesisof the enzymes. Results suggest that ST but not PEG treatment can up-regulateantioxidant system in rice leaves.

Imbalance in the enzymatic system of production and consumption of active oxygen species in liver of AKR mice with spontaneous leucosis.

Activities of protective antioxidant enzymes, the rate of superoxide formation (v) in microsomal membranes and submitochondrial particles (SMP), and the concentrations of reduced and oxidized glutathione in cytosol were studied in the liver of AKR mice during the development of spontaneous leucosis. It was found that in the latent period of leucosis (mice of 3-6 months of age) the glutathione reductase (GR) activity in cytosol and mitochondria decreased and v in SMP increased. The increase in v in SMP did not result in the induction of Mn-SOD. In this stage of leucosis, the activities of Cu,Zn-SOD, GSH-Px, and G-6-PDH in cytosol were unchanged; at the same time, the GR activity and the concentration of reduced glutathione smoothly decreased. In the stage of developed leucosis (mice of 7-9 months of age), non-synchronous changes in the antioxidant system resulting in the shift of metabolism towards the prooxidant state were found. Comparison of our findings and the literature data demonstrates that the observed decrease in the SOD/GSH-Px ratio, the decrease in GR activity, and the increase in the v/Mn-SOD activity ratio are typical for pre-neoplastic changes in cell metabolism.

Prion Protein-Deficient Neurons Reveal Lower Glutathione Reductase Activity and Increased Susceptibility to Hydrogen Peroxide Toxicity

The prion protein (PrP) has a central role in the pathogenesis of transmissible spongiform encephalopathies (TSE). Accumulating evidence suggests that normal cellular PrP (PrP(c)) may be involved in copper homeostasis and modulation of copper/zinc superoxide dismutase (Cu/ZnSOD) activity in neurons. Hydrogen peroxide (H(2)O(2)) is a toxic reactive oxygen species generated through normal cellular respiration, and neurons contain two important peroxide detoxifying systems (glutathione pathway and catalase). To determine whether PrP expression affects neuronal resistance to H(2)O(2), we exposed primary cerebellar granule neuron cultures derived from PrP knockout (PrP(-/-)) and wild-type (WT) mice to H(2)O(2) for 3, 6, and 24 hours. The PrP(-/-) neurons were significantly more susceptible to H(2)O(2) toxicity than WT neurons after 6 and 24 hours' exposure. The increased H(2)O(2) toxicity may be related to a significant decrease in glutathione reductase activity measured in PrP(-/-) neurons both in vitro and in vivo. This was supported by the finding that inhibition of GR activity with 1,3-bis(2-chloroethyl)-1-nitrosurea (BCNU) increased H(2)O(2) toxicity in WT neurons over the same exposure period. The PrP toxic peptide PrP106-126 significantly reduced neuronal glutathione reductase activity and increased susceptibility to H(2)O(2) toxicity in neuronal cultures suggesting that PrP toxicity in vivo may involve altered glutathione reductase activity. Our results suggest the pathophysiology of prion diseases may involve perturbed PrP(c) function with increased vulnerability to peroxidative stress.

Prokaryotic iron superoxide dismutase replaces cytosolic copper, zinc superoxide dismutase in protecting yeast cells against oxidative stress.

The iron superoxide dismutase (FeSOD) gene of Escherichia coli was cloned in Saccharomyces cerevisiae cells deficient in copper,zinc superoxide dismutase (Cu,ZnSOD). FeSOD replaced Cu,ZnSOD in protecting the yeast cells against oxidative stress. In the recombinant strains the FeSOD gene, which was under the transcriptional control of the yeast phosphoglycerate kinase gene promoter, was functionally expressed at two different levels on episomal and centromeric plasmids. Despite suppression of methionine and lysine auxotrophy, the higher level of FeSOD activity was more beneficial to growth of the mutant yeast cells only when these were exposed to higher levels of oxidative stress induced by paraquat or 100% oxygen. In the presence of paraquat, there was a novel stimulation of FeSOD activity. This was associated with a marked increase in catalase activity, and a decrease in glutathione reductase activity.

A comparison of biochemical responses to oxidative and metal stress in seedlings of barley, Hordeum vulgare L.

Biochemical responses on the bases of activities of antioxidant enzymes; peroxidase, catalase, superoxide dismutase and glutathione reductase as well as estimations of total protein, lipid peroxidation and thiols in the form of protein, non-protein, glutathione and phytochelatin measured in growing seedlings of barley, Hordeum vulgare L., from Day 2 through 8 were compared following treatment of seeds for 2 h with oxidative agents, paraquat 5 × 10 −5, 10 −4, 10 −3 M, H 2O 2 10 −3, 5 × 10 −3, 10 −2 M and a metal salt, CdSO 4 10 −5, 10 −4, 10 −3 M. A significant induction of all antioxidant enzymes along with an increase in the levels of protein, lipid peroxidation and glutathione was noted in response to oxidative stress, CdSO 4 induced significant peroxidase and catalase activities but not superoxide dismutase. In a marked contrast from oxidative stress, CdSO 4 decreased glutathione reductase activity as well as glutathione levels but increased phytochelatin level. The differential biochemical responses thus underlined the crucial involvement of glutathione and phytochelatin in the oxidative and metal-induced adaptive responses, respectively.

Mechanisms of ethylenediurea (EDU) induced ozone protection: Reexamination of free radical scavenger systems in snap bean exposed to O 3

Ethylenediurea (EDU), N- [2-(2-oxo-1-imidazolidinyl) ethyl]-N′-phenylurea is known to prevent ozone (O 3) damage to leaf tissues. However, the mechanisms of protection are unclear. We tested the hypothesis that EDU protects against O 3 damage by scavenging hydroxyl free radicals (OH). An in vitro study involving the use of high-performance liquid chromatography equipped with an electrochemical detector (HPLC-EC) showed that EDU does not serve as an antioxidant to remove OH free radicals. Effects of O 3 and EDU (soil drench) on leaf antioxidant scavenger systems (AOSS) were also studied. The first fully expanded trifoliate leaves of O 3-sensitive snap bean ( Phaseolus vulgaris cv. Bush Blue Lake 290) was examined. Measurements were made before and after a single O 3 exposure (0.30 μl 1 −1 O 3 for 3 h). Pretreatment with EDU 48 h before exposure protected against O 3-induced necrosis and chlorosis. EDU pretreatments did not alter superoxide dismutase (SOD), guaiacol-peroxidase (GPX), ascorbate peroxidase (APX) and glutathione reductase (GR) activities. However, O 3-fumigated plants (no EDU) showed elevated SOD activity with decreased GR activity. EDU-treated plants exposed to O 3 stress showed no measurable loss of GR activity. These tissues maintained high levels of total glutathione [i.e. reduced glutathione (GSH) + oxidized glutathione (GSSG)] contents, and had higher GSH/GSSG ratios than the controls at the end of 3 h exposure to O 3. These data suggest that EDU protection against O 3 damage in plants do not necessarily involve the direct stimulation or induction of antioxidative enzyme defense mechanisms. Instead, protection may result from a more general retention of chlorophyll and maintenance of GR and GSH levels during O 3 exposure.

Carbamoylation of glutathione reductase by n,n-bis(2-chloroethyl)- n-nitrosourea associated with inhibition of multidrug resistance protein (MRP) function

Intracellular glutathione (GSH) concentrations have been implicated recently as a regulatory determinant of multidrug resistance protein (MRP)-mediated drug efflux. Inhibition of glutathione reductase (GR) activity of N,N-bis(2-chloroethyl)- N-nitrosourea (BCNU) has been employed extensively to investigate the role of GSH redox cycle in cellular function. The present study examined the effect of BCNU on the MRP-mediated efflux of doxorubicin in the multidrug-resistant human fibrosarcoma cell line HT1080/DR4 overexpressing MRP. No significant difference in GR activity between HT1080 (parental) and multidrugresistant HT1080/DR4 cells was detected (38.6 ± 2.2 and 37.8 ± 5.28 nmol/min/10 6 cells, respectively). Exposure of HT1080 and HT1080/DR4 cells to 100–500 μM BCNU decreased GR activity concentration dependently with subsequent reduction in cellular GSH pools in both cell lines. Inhibition of GSH biosynthesis by d,l-buthionine-( S,R)-sulfoximine (D,L-BSO), a specific inhibitor of γ-glutamylcysteine synthetase, significantly reduced MRP-mediated drug efflux and potentiated the cytotoxicity of doxorubicin in MRP-expressing HT1080/DR4 cells (dose modifying factor 20.8). While equally effective inhibition of GR activity by BCNU was observed in parental and resistant cells, a significant increase in intracellular retention of doxorubicin was only achieved in MRP-expressing HT1080/DR4 cells. Furthermore, inhibition of MRP function following treatment with BCNU or d,l-BSO was directly related to the degree of GSH depletion in MRP-expressing tumor cells [r = 0.94 (P < 0.001) and 0.99 (P < 0.001), respectively]. Based on northern blot analysis of MRP mRNA levels, exposure of HT1080/DR4 cells to BCNU did not produce down-regulation of MRP gene expression. The results reported herein indicate that derivatives of nitrosourea with carbamoylating properties are potent inhibitors of MRP function. Depletion of intracellular GSH pools by inhibition of the GSH redox cycle or GSH de novo biosynthesis significantly inhibited MRP-mediated doxorubicin transport and restored intracellular drug concentrations in vitro.

Depletion of brain glutathione results in a decrease of glutathione reductase activity; an enzyme susceptible to oxidative damage

Loss of the intracellular antioxidant glutathione (GSH) from the substantia nigra is considered to be an early event in the pathogenesis of Parkinson's disease (PD). While the cause of the loss is unclear, an imbalance in the enzymes associated with the synthesis, utilisation, degradation and translocation of GSH has been implicated. The enzyme glutathione reductase is also important in GSH homeostasis: it regenerates GSH from the oxidised form (GSSG). However, to date the activity and regulation of glutathione reductase in conditions such as PD have not been explored. In view of this we have measured the effects of GSH depletion on glutathione reductase activity of the rat brain. Other glutathione related enzymes were also measured. Using pre-weanling rats, brain GSH was depleted by up to 60% by subcutaneous administration of l-buthionine sulfoximine. The only enzyme affected by GSH depletion was glutathione reductase; its activity being reduced by approximately 40%. As GSH inactivates a number of oxidising species including peroxynitrite (ONOO −), we additionally investigated the susceptibility of glutathione reductase to ONOO − in vitro, using purified enzyme. ONOO − decreased glutathione reductase activity in a concentration dependent manner with an apparent 50% inhibition occurring at an initial concentration of 0.09 mM. These data suggest that GSH is important in the maintenance glutathione reductase activity. This may arise in part from its ability to inactivate oxidising agents such as ONOO −.

Glutathione reductase activity following re-aeration of hypoxically pretreated wheat roots

SynopsisDuring the first 2 h of oxygen re-exposure, the GSH level was almost constant, while the GSSG increased about 10-fold. This results in a decline of the GSH/GSSG ratio, which reflects oxidative stress induced by re-aeration following hypoxic pretreatment. Further evidence for this is an increase in lipid peroxidation measured as thiobarbituric acid-reactive material (TBA-rm) and the affected content of sulfydryl-groups in the root tissues.In spite of the high level of reduced glutathione in the roots under hypoxia-inducing conditions, they contained a retarded glutathione reductase (GR) activity compared with aerobically grown roots. Re-aeration up to 2 h resulted in a further decrease in GR activity. Only at the end of the 16-h period of re-aeration the enzyme activity was able to recover, by overshooting slightly those values of the continuously aerated controls. This was accompanied by a restoring a high GSH/GSSG ratio and an enhanced level of GSH.

Inhibition of glutathione reductase activity by a carbomoylating nitrosourea: Effect on cellular radiosensitivity

Nitrosoureas inactivate cellular glutathione reductase. N,′N′1,3-bis(trans-4-hydroxycyclohexyl)-N′-nitrosoureas (BCyNU), a nitrosourea reported to selectively inhibit glutathione reductase (GR) activity, was examined to determine if it could be used as a means to inhibit cellular levels of this enzyme in radiobiology studies. Confirmation of drug-induced inhibition of GR activity was demonstrated using a cell-free model system employing purified GR. Cellular studies with Chinese hamster V79A03 showed that BCyNU decreased cellular glutathione content concomitant with an inhibition of specific GR activity. Under relatively nontoxic conditions, cellular exposure to BCyNU (25 μM, 0.25 h) either before or after radiation treatment, increased cellular radiosensitivity with the optimum time for drug addition being immediately following radiation. At a BCyNU dosage which produced ≤5% cell toxicity, a marked decrease in radioresistance was characterized as a reduction in both D q (24 ± 1.5%) and D o (8 ± 0.5%) concomitant with a 25 ± 2% decrease in cellular glutathione reductase (GR) activity. AT cytotoxic drug dosages (25 μM, 1 h; cell survival 79 ± 7%), a marked radiosensitization manifested by a 1.25 ± .07-fold reduction in the D q was observed concomitant with a 49 ± 4% decrease in GR activity. Using cells enriched in different stages of the cell cycle, BCyNU caused cell-age dependent cytotoxicity with preferential killing of cells in the radioresistant late-S-phase, a likely explanation for its radiosensitizing capabilities at high drug dosages. Data obtained at nontoxic drug dosages suggest that GR-inactivation may be an important component of cellular response to free-radical induced damage.

Recovery study from anemia and alterations of glutathione metabolism in erythrocytes induced by chronic inhalation of ethylene oxide

A study was made on the recovery from anemia induced by chronic exposure of ethylene oxide. When rats were exposed to ethylene oxide at a concentration of 500 ppm, 6 h a day, 3 d a week for 13 wk, macrocytic normochromic anemia with a high reticulocyte count was observed. The hematological values were also evaluated 4 and 13 wk after the end of exposure and the values were found to have already recovered at 4 wk. We reported previously that anemia induced by ethylene oxide was accompanied with a decrease in glutathione reductase activity and instability of glutathione. In this study, alterations of glutathione redox cycle after the end of exposure were examined. The recovery in the decrease of glutathione reductase was slow and the speed of recovery seemed to be dependent on the life span of erythrocytes of the rats. The decrease in glutathione content completely recovered at 4 wk after the exposure. It was concluded from these observations that anemia induced by ethylene oxide is reversible.

Effects of vitamins on chromium(VI)-induced damage.

The effects of vitamin E and vitamin B2 on DNA damage and cellular reduction of chromium(VI) were investigated using Chinese hamster V-79 cells. Pretreatment with alpha-tocopherol succinate (vitamin E) resulted in a decrease of DNA single-strand breaks produced by Na2CrO4, while similar treatment with riboflavin (vitamin B2) enhanced levels of DNA breaks. In contrast, levels of DNA-protein crosslinks induced by Na2CrO4 were unaffected by these vitamins. Electron spin resonance (ESR) studies showed that incubation of cells with Na2CrO4 resulted in the formation of both chromium(V) and chromium(III) complexes, and cellular pretreatment with vitamin E reduced the level of the chromium(V) complex, whereas pretreatment with vitamin B2 enhanced the level of this intermediate. However, the levels of chromium(III) were unchanged by these vitamins. The uptake of chromate was not affected by vitamin E or vitamin B2, nor were the levels of glutathione or glutathione reductase activity, which are both capable of reducing chromate. ESR studies demonstrated that a chromium(V) species was formed by the reaction of Na2CrO4 with vitamin B2 and that vitamin B2 enhanced the formation of hydroxyl radicals during the reaction of Na2CrO4 and hydrogen peroxide. Treatment cells with Na2CrO4 resulted in a decrease of glutathione reductase activity, and pretreatment with vitamin E restored the enzyme activity suppressed by this metal. However, pretreatment with vitamin B2 enhanced the inhibition of this enzyme by Na2CrO4. Using a colony-forming assay, pretreatment with vitamin E dramatically decreased the cytotoxicity of Na2CrO4, while pretreatment with vitamin B2 was found to result in only a decrease of cell lethality of this metal.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Vitamins on Chromium(VI)-Induced Damage

The effects of vitamin E and vitamin B2 on DNA damage and cellular reduction of chromium(VI) were investigated using Chinese hamster V-79 cells. Pretreatment with alpha-tocopherol succinate (vitamin E) resulted in a decrease of DNA single-strand breaks produced by Na2CrO4, while similar treatment with riboflavin (vitamin B2) enhanced levels of DNA breaks. In contrast, levels of DNA-protein crosslinks induced by Na2CrO4 were unaffected by these vitamins. Electron spin resonance (ESR) studies showed that incubation of cells with Na2CrO4 resulted in the formation of both chromium(V) and chromium(III) complexes, and cellular pretreatment with vitamin E reduced the level of the chromium(V) complex, whereas pretreatment with vitamin B2 enhanced the level of this intermediate. However, the levels of chromium(III) were unchanged by these vitamins. The uptake of chromate was not affected by vitamin E or vitamin B2, nor were the levels of glutathione or glutathione reductase activity, which are both capable of reducing chromate. ESR studies demonstrated that a chromium(V) species was formed by the reaction of Na2CrO4 with vitamin B2 and that vitamin B2 enhanced the formation of hydroxyl radicals during the reaction of Na2CrO4 and hydrogen peroxide. Treatment cells with Na2CrO4 resulted in a decrease of glutathione reductase activity, and pretreatment with vitamin E restored the enzyme activity suppressed by this metal. However, pretreatment with vitamin B2 enhanced the inhibition of this enzyme by Na2CrO4. Using a colony-forming assay, pretreatment with vitamin E dramatically decreased the cytotoxicity of Na2CrO4, while pretreatment with vitamin B2 was found to result in only a decrease of cell lethality of this metal.(ABSTRACT TRUNCATED AT 250 WORDS)

Riboflavin Deficiency and the Function and Fluidity of Rat Erythrocyte Membranes

The effect of riboflavin deficiency on the fluidity and function of the red blood cell (RBC) membrane and on the activity of some enzymes involved in antioxidant defense mechanisms was studied. Growing male rats were fed an experimental (riboflavin-deficient) or a control (riboflavin-supplemented) diet. Following 7 wk of feeding, RBC from riboflavin-deficient rats contained higher levels of peroxidation products, most likely due to decreased glutathione reductase activity. An elevation in glutathione peroxidase activity was also observed whereas the activity of catalase and superoxide dismutase was not affected. Membrane fluidity was studied by fluorescence polarization, using 1,6-diphenyl-1,3,5 hexatriene (DPH) as a probe. The fluidity of RBC membranes isolated from riboflavin-deficient rats was significantly lower than that of the controls. This decreased fluidity was accompanied by an increase in the activity of the membrane-bound enzyme acetylcholinesterase. This study demonstrated that a decrease in cells' ability to cope with peroxidative damage as a result of riboflavin deficiency may lead to changes in the fluidity and function of membranes.

Effect of vitamin E on survival, glutathione reductase and formation of chromium (V) in Chinese hamster V-79 cells treated with sodium chromate (VI).

The effect of vitamin E on cytotoxicity induced by Na2CrO4 was evaluated by colony-forming assay using Chinese hamster V-79 cells. Pre-treatment with alpha-tocopherol succinate (vitamin E) for 24 h prior to exposure to Na2CrO4 resulted in a marked decrease in the cytotoxicity caused by this compound. The reduction of chromate-induced cytotoxicity was observed at all concentrations of Na2CrO4 (5-15 microM), and the protective effect increased with higher concentrations of vitamin E (5-25 microM). The level of glutathione reductase activity, which is capable of reducing chromate, was not affected by cellular pre-treatment with vitamin E. However, Na2CrO4 decreased glutathione reductase activity in a concentration-dependent fashion (5-15 microM) and pretreatment with vitamin E resulted in a significant recovery of enzyme activity suppressed by Na2CrO4, suggesting that this enzyme inhibition is linked to the cytotoxicity of this metal. Electron spin resonance studies showed that a paramagnetic chromium (V) complex was formed in cells treated with Na2CrO4, and that cellular pre-treatment with vitamin E reduced the formation of this chromium (V) intermediate. These results indicate that vitamin E protects cells from chromate-induced cytotoxicity as well as from enzyme inhibition, and also suggest that Na2CrO4-induced cytotoxicity is mediated by the generation of a reactive intermediate.

Glutathione reductase during and after brain ischemia in gerbils.

The activity of glutathione reductase (GR) was measured in crude mitochondrial fraction isolated from cerebral cortex and basal ganglia of Mongolian gerbils subjected to bilateral carotid occlusion of various duration (1, 2, 3, 5, 10, and 15 min), or reflow (1, 24, and 96 hr) following ischemia (5 or 15 min). Ischemia up to 5 min does not induce changes in GR activity in either structure. Basal ganglia activity is halved at 10 min and cortical at 15 min of ischemia. In reflow, basal ganglia GR activity is diminished, while cortical GR is transiently reduced at day 1 of reflow. The persistent and profound decrease in GR activity in basal ganglia following ischemia is indicative of the lowered antioxidative capacity of these cells, being possibly related to their greater vulnerability toward ischemia.

Impaired pentose phosphate shunt function in sickle cell disease: a potential mechanism for increased Heinz body formation and membrane lipid peroxidation.

The red cells' antioxidant defense mechanisms were compared between individuals with sickle cell disease and those with hemolytic anemia and reticulocytosis. In sickle cell disease, there was a significant increase in incubated Heinz body formation (p less than .001), a decrease in reduced glutathione concentration (p less than .01), an increase in glucose-6-phosphate dehydrogenase activity (p less than .01), and a decrease in glutathione reductase activity (p less than .005). The patients with sickle cell disease hd an absolute increase in the activity of the pentose shunt in the intact red cell after methylene blue stimulation (p less than .05) and in red cell hemolysates (p less than .0250. Heinz body formation (r = .75) and pentose shunt activity in red cell hemolysates (r = .83) were strongly related to the degree of reticulocytosis. Although there was a correlation between the pentose shunt activity in the stimulated red cell and in red cell hemolysates for the patients with hemolytic anemia (r = .58), stimulated shunt activity did not increase as the hemolysate shunt activity increased for the patients with sickle cell disease. There were very strong relationships between the ATP concentration and the reticulocyte count (r = .80) and the hemolysate pentose shunt activity (r = .77) in sickle cel disease. These data suggest that in spite of an absolute increase in stimulated pentose shunt activity, there Is a relative suppression of stimulated shunt activity in the youngest sickle erythrocytes. This may be related, in part, to the inhibitory effects of high concentrations of ATP on the activity of glucose-6-phosphate dehydrogenase.

The effect of bcnu (carmustine) on tissue glutathione reductase activity

A single, 50 mg/kg i.p. dose of 1,3-bis-(2-chloroethyl)-1-nitrosourea (BCNU) to mice significantly inhibited glutathione reductase activity in liver within 10 min, and in lung and heart within 30 min. Maximal inhibition was reached at 4 h in all tissues and glutathione reductase activity remained significantly depressed for 48 h in liver and for 96 h in lung and heart. BCNU doses of less than 25 mg/kg had no effect on glutathione reductase activity. Increasing the BCNU dose to 100 mg/kg caused greater inhibition of glutathione reductase activity in all tissues. In spite of significantly decreased glutathione reductase activity, reduced glutathione (GSH) levels were unaffected in all tissues both 1 and 24 h after 50 mg/kg BNCU. These results suggest that lower than normal glutathione reductase activity is sufficient to maintain GSH levels. These results also demonstrate that BCNU inhibits tissue glutathione reductase activity for several days, but only at doses significantly greater than previously reported.

Studies of lens enzyme activities in relation to cataract type and plasma constituents.

The specific activities of glutathione reductase (GR), EC 1.6.4.2, and aldolase, (ALD) EC 4.1.2.13, were determined in the homogenates of 60 cataractous lenses. Concentrations of certain plasma constituents and the morphological types of cataract of the patients were known. Investigations were aimed at establishing a possible correlation between enzyme activities and plasma constituents as well as between the specific activities of GR and ALD and type of cataract. A correlation between the specific activity of GR and the urea content of the blood could be identified. Results also indicated a relationship between the decrease in GR activity and the formation of cortical cataracts.