Disorders in glutathione metabolism

Sleep deprivation alters gene expression and antioxidant enzyme activity in mice splenocytes

Cellular defence against the formation of reactive oxygen species (ROS) involves a number of mechanisms in which antioxidant enzymes such as catalase (CAT) and superoxide dismutase (SOD) play an important role. The relation between sleep deprivation and oxidative stress has not yet been completely elucidated. Although some authors did not find evidence of this relationship, others found alterations in some oxidative stress markers in response to sleep deprivation. Thus, the objective of this study was to identify changes induced by sleep deprivation in the activity and gene expression of antioxidant enzymes in mice splenocytes, ideally corroborating a better understanding of the observed effects related to sleep deprivation, which could be triggered by oxidative imbalance. Splenocytes from mice sleep deprived for 72 h showed no significant difference in CAT and CuZnSOD gene expression compared with normal sleep mice. However, sleep-deprived mice did show higher MnSOD gene expression than the control group. Concerning enzymatic activity, CuZnSOD and MnSOD significantly increased after sleep deprivation, despite the expression in CuZnSOD remained unchanged. Moreover, CAT activity was significantly lower after sleep deprivation. The data suggest that the antioxidant system is triggered by sleep deprivation, which in turn could influence the splenocytes homoeostasis, thus interfering in physiological responses.

Effect of magnesium on reactive oxygen species production in the thigh muscles of broiler chickens

1. The objective of the present study was to investigate the effect of magnesium (Mg) on reactive oxygen species (ROS) production in the thigh muscles of broiler chickens. A total of 96 1-d-old male Arbor Acre broiler chickens were randomly allocated into two groups, fed either on low-Mg or control diets containing about 1.2 g/kg or 2.4 g Mg/kg dry matter. 2. The low-Mg diet significantly increased malondialdehyde (MDA) concentration and decreased glutathione (GSH) in the thigh muscles of broiler chickens. ROS production in the thigh muscle homogenate was significantly higher in the low-Mg group than in the control group. Compared with the control, muscle Mg concentration of broiler chickens from the low-Mg group decreased by 9.5%. 3. Complex II and III activities of the mitochondrial electron transport chain in broilers on low-Mg diet increased by 23 and 35%, respectively. Significant negative correlations between ROS production and the activities of mitochondrial electron transport chain (ETC) complexes were observed. 4. The low-Mg diet did not influence contents of iron (Fe) or calcium (Ca) in the thigh muscles of broiler chickens and did not influence unsaturated fatty acid composition (except C18:2) in the thigh muscles. 5. A low-Mg diet decreased Mg concentration in the thigh muscles of broiler chickens and then induced higher activities of mitochondrial ETC, consequently increasing ROS production. These results suggest that Mg modulates the oxidation-anti-oxidation system of the thigh muscles at least partly through affecting ROS production.

Cerebral antioxidant status and free radical generation following glutathione depletion and subsequent recovery

This study was aimed to evaluate the oxidative damage, production of reactive oxygen species and the status of antioxidative defenses following cerebral GSH depletion induced by two classical depletors, diethylmaleate (DEM, 3 mmol/kg, i.p.) and phorone (PHO, 4 mmol/kg, i.p.). The treatment decreased (40-43%) brain glutathione levels at 2 h, followed by a partial recovery at 24 h. Cerebral glutathione depletion by these agents increased the levels of superoxide anion and hydroxyl radical at both the time intervals; however, hydrogen peroxide was high at 24 h only. It also produced a dramatic increase in the protein carbonyls at 2 h but not at 24h, without any significant effect on lipid peroxidation and conjugated diene levels. These rats showed a significantly lowered superoxide dismutase activity both at 2 h and 24 h of exposure, as compared to controls. Glutathione depletion enhanced catalase activity markedly at 2 h, followed by some recovery at 24 h. While Se-independent glutathione peroxidase (GPx) and glutathione S-transferase activities were increased at both 2 and 24 h time intervals, Se-dependent GPx and glucose-6-phosphate dehydrogenase were induced at 2 h only. Glutathione depletion decreased ceruloplasmin and vitamin E levels significantly at 2 h. However, ascorbic acid remained unaffected. It may be concluded that an acute cerebral glutathione depletion generates higher levels of reactive oxygen species, which may be responsible for oxidative modification of proteins. Some of these changes appear to recover soon after an activation of a variety of cellular antioxidant defense mechanisms and glutathione restoration. It appears that central nervous system is highly vulnerable to oxidative damage following a moderate glutathione depletion that may result from certain diseases or xenobiotic exposures.

Effects of exogenous factors on the cerebral glutathione in rodents

Since glutathione is thought to be involved in cerebral functions, changes in the glutathione level imply modulations of the neurotransmission in addition to all the known effects of GSH. It was investigated whether alterations of the cerebral glutathione can be induced by consumption of GSH, by inhibition or stimulation of the synthesis of GSH, or by an inhibition of the re-reduction of the oxidized glutathione. Aminophenazone, propyphenazone, acetaminophen, phenytoin, morphine and nitrofurantoin, known to deplete hepatic GSH, had no effects on cerebral GSH. Diethyl maleate (0.6 ml/kg) decreased the cerebral content of GSH and GSSG in adult rats as well as in fetuses. The depletion of the cerebral GSH caused by diethyl maleate treatment for 4 days was followed by an increase up to 125% and a subsequent return to the normal level after 1 week. In rats starved up to 71 h deficiency of exogenous amino acids caused only a minimal or no decrease in cerebral GSH. The specific inhibitor of the gamma-glutamylcysteine synthetase BSO only depleted GSH in the brain of young mice following the repeated s.c. administration of a high dose (890 mg/kg). After cobaltous chloride (20 mg/kg; twice a day for 2 or 4 days) the GSH level in the brain was unchanged. In vivo inhibition of the cerebral glutathione reductase was caused by ammonium metavanadate (12.5 mg/kg; three times a week for 6 weeks). Nitrofurantoin (150 mg/kg) had no effect. After lomustine (10 mg/kg) a minimal increase in glutathione reductase was found, but simultaneously also an increase in GSSG and of the ratio GSSG/total glutathione.

Oxidative damage and changes in the glutathione redox system in erythrocytes from rats treated with hexachlorocyclohexane

The concentration of reduced glutathione in the erythrocytes of rats was significantly decreased 24-72 hr after the rats were treated with 300 mg commercial hexachlorocyclohexane/kg body weight (one-third of the LD50), given ip. The activities of glutathione reductase, glutathione-S-transferase and glucose-6-phosphate dehydrogenase were also significantly decreased 24 hr after treatment but there was no change in glutathione peroxidase activity. The results suggest that hexachlorocyclohexane produces significant changes in the glutathione redox system of rat erythrocytes leading to oxidative membrane damage.

Cytochrome P-450-dependent covalent binding of carbon disulfide to rat liver microsomal protein in vitro and its prevention by reduced glutathione

Carbon disulfide, a hepatotoxic solvent, is metabolized by liver microsomal enzymes to reactive sulfur atoms which get bound to the microsomal enzymes, causing inhibition of the enzyme system. These studies were carried out to examine whether glutathione can protect the liver enzymes from the sulfur binding and against carbon disulfide toxicity. When liver microsomes isolated from phenobarbital-pretreated rats were incubated with 35S-CS2, NADPH and glutathione, almost 60% decrease in sulfur binding to microsomal protein was observed under the experimental conditions. It was further observed that the addition of glutathione to microsomal incubations resulted in almost complete recovery of the activity of the enzyme system as measured by cytochrome P-450 concentration and benzphetamine metabolism. The data suggest that the presence of glutathione in sufficient amount in the liver of subject exposed to CS2 may significantly decrease the liver toxicity of this highly toxic compound.

The effects of acrylonitrile on hemoglobin and red cell metabolism

The effects of acrylonitrile (VCN) on hemoglobin and red cell metabolism were studied in vitro and in vivo using male Sprague-Dawley rats. Reduced glutathione (GSH) was rapidly depleted by VCN. The reaction between VCN and GSH to form S-cyanoethyl glutathione is both enzymic and nonenzymic. GSH depletion induced oxidation of considerable amount of hemoglobin to methemoglobin. Incubation of nitrite-treated erythrocytes with VCN (2-10 mM) resulted in a significant decrease in methemoglobin reduction. VCN initiated hemolysis in vitro at a concentration of 0.05 M, and at concentrations lower than 0.05 M rendered erythrocytes susceptible to osmotic fragility even at higher concentration of NaCl. Following oral administration of VCN (80 mg/kg), significant perturbations of levels of red-cell GSH, 2,3-diphosphoglycerate, adenosine triphosphate, pyruvate, lactate, and oxidized glutathione occurred within 1 h. These changes returned to normal levels between 6 and 24 h. A strong correlation between the depletion of GSH in vivo and covalent binding [2,3-14C]VCN to hemoglobin was observed. These in vivo and in vitro results suggest that chronic exposure to VCN may lead to methemoglobinemia and consequently may cause impaired delivery of oxygen to various tissues.

The influence of cold restraint stress on some components of the antioxidant defence system in the tissues of rats of various ages

Rats of various ages were subjected to stress by confinement in restraining cages at 2-4 degrees C. Analysis of the plasma of these animals revealed an elevation in corticosteroids of approximately 50% above the control level. The livers of all the groups of cold-restrained animals contained significantly more lipoperoxide (estimated as thiobarbituric-acid-reactive material) than did control hepatic tissue. The plasma of the 12-, 24-, and 32-wk-old groups of rats subjected to stressful treatment also contained significantly higher lipoperoxide levels. There was no significant difference between the lipoperoxide levels of the brain tissue of control or stress-treated rats. The activities of both glutathione peroxidase and glutathione reductase were increased in hepatic, but not brain, tissue of the stressed animals. The perturbation of the activities of these enzymes did not produce any significant change in the ratio of reduced, oxidized glutathione. The livers of the stressed animals had significantly less total glutathione than those of the controls.

Clinical significance of the glutathione-conjugating system

Glutathione displays important functions in living cells of many species, human included. Apart from its direct antioxidative activity, which supports the maintenance of the reduced state of proteinthiols, and its possible role in amino acid transport across membranes, it appears to exert several detoxification functions. These include the conjugation of electrophilic compounds and the reduction of H2O2 and lipid hydroperoxides. Disorders in GSH synthesis and metabolism are known and produce hemolysis in the first place. Little data exist concerning GSH and the GSH-dependent enzymes involved in its various functions in normal and diseased human tissues. The aim of this review is to stimulate research in this area.

Effect of halothane and enflurane anaesthesia on the level of reduced glutathione in human red blood cells

No significant changes were found in packed cell volume, haemoglobin concentration and red cell glutathione levels in patients before and after anaesthesia with halothane or enflurane. These results, though unable to explain the mechanism, support the earlier suggestion that glutathione plays little, if any, role in protecting liver against toxic effects of these anaesthetic agents or their metabolites.

Human renal gamma-glutamyltransferase hydrolysis and transfer reactions with glutathione as substrate

The hydrolysis and transfer reactions of purified human renal gamma-glutamyltransferase were studied in vitro with glutathione as substrate at pH and substrate concentration reflecting the physiological conditions. The pH optimum ranged from 7.48 to 8.44 for hydrolysis and 7.90 to 8.92 for transfer with glutamine as acceptor. The Michaelis constants for glutathione were 13 microM in hydrolysis and 58 microM in transfer reactions respectively. Inhibition of transfer occurred for glutathione concentrations above 0.4 mM. Various ions, urea, creatinine, uric acid and L-amino acids were shown to have no appreciable effect on both reactions except L-glutamine which acts as an activator on the hydrolysis activity. Taken together, our results, if they are transposable in vivo would be relevant of an enzyme acting like an hydrolase rather than like a transferase.