Reduction of linolenic acid hydroperoxide by a glutathione peroxidase

The glutathione peroxidase family: Discoveries and mechanism

The discoveries leading to our present understanding of the glutathione peroxidases (GPxs) are recalled. The cytosolic GPx, now GPx1, was first described by Mills in 1957 and claimed to depend on selenium by Rotruck et al., in 1972. With the determination of a stoichiometry of one selenium per subunit, GPx1 was established as the first selenoenzyme of vertebrates. In the meantime, the GPxs have grown up to a huge family of enzymes that prevent free radical formation from hydroperoxides and, thus, are antioxidant enzymes, but they are also involved in regulatory processes or synthetic functions. The kinetic mechanism of the selenium-containing GPxs is unusual in neither showing a defined K_M nor any substrate saturation. More recently, the reaction mechanism has been investigated by the density functional theory and nuclear magnetic resonance of model compounds mimicking the reaction cycle. The resulting concept sees a selenolate oxidized to a selenenic acid. This very fast reaction results from a concerted dual attack on the hydroperoxide bond, a nucleophilic one by the selenolate and an electrophilic one by a proton that is unstably bound in the reaction center. Postulated intermediates have been identified either in the native enzymes or in model compounds.

The Selenoprotein Glutathione Peroxidase 4: From Molecular Mechanisms to Novel Therapeutic Opportunities

The selenoprotein glutathione peroxidase 4 (GPX4) is one of the main antioxidant mediators in the human body. Its central function involves the reduction of complex hydroperoxides into their respective alcohols often using reduced Glutathione (GSH) as a reducing agent. GPX4 has become a hotspot therapeutic target in biomedical research following its characterization as a chief regulator of ferroptosis, and its subsequent recognition as a specific pharmacological target for the treatment of an extensive variety of human diseases including cancers and neurodegenerative disorders. Several recent studies have provided insights into how GPX4 is distinguished from the rest of the glutathione peroxidase family, the unique biochemical properties of GPX4, how GPX4 is related to lipid peroxidation and ferroptosis, and how the enzyme may be modulated as a potential therapeutic target. This current report aims to review the literature underlying all these insights and present an up-to-date perspective on the current understanding of GPX4 as a potential therapeutic target.

Influence of chromium citrate on oxidative stress in the tissues of muscle and kidney of rats with experimentally induced diabetes

Chromium is one of the important trace elements that is essential for carbohydrate, protein and lipid metabolism. Chromium improves glucose metabolism and reduces insulin resistance due to increased insulin sensitivity. Therefore, it is important to consider the use of chromium citrate as a nutritional supplement with potential hypoglycemic and hypolipidemic effects. In this research work, we investigated the activity of the antioxidant system and the level of lipid hydroperoxides in the tissues of skeletal muscles and kidneys of experimental diabetic rats and for rats which received in their daily diet chromium citrate in the amounts 0.1 and 0.2 μg/mL of water. We induced the experimental model of diabetes by intraperitoneal injection of alloxan in the amount 150 mg/kg of body weight of the animals. We monitored glucose levels by measuring daily glucose levels with a portable glucose meter. For research, we selected animals with a glucose level > 11.1 mmol/L. We monitored the body weight of rats. On the 40th day of the study, we withdrew the animals from the experiment by decapitation. We selected the tissue for research, namely skeletal muscles and kidneys. In samples of the tissue homogenates, we measured the activity of antioxidant enzymes and the content of lipid peroxide oxidation products. As a result of our research, we found that the products of lipid peroxide oxidation and glutathione peroxidase activity increased in skeletal muscle of animals with diabetes mellitus. The activity of glutathione reductase, catalase, superoxide dismutase, and the content of reduced glutathione decreased at the same time. In the kidneys of diabetic rats, the activity of glutathione peroxidase, glutathione reductase, catalase and content of lipid hydroperoxides increased but the activity of superoxide dismutase and the content of reduced glutathione decreased. The addition of chromium citrate to the diet of animals in amounts 0.1 and 0.2 μg/mL led to the suppression of oxidative stress. The activity of catalase, glutathione peroxidase and the content of lipid hydroperoxides, TBA-positive substances decreased. Also, the activity of superoxide dismutase increased with the addition of chromium citrate. These results indicate normalization of antioxidant defense in the skeletal muscle and kidneys of experimental rats with experimental diabetes given chromium citrate in the amount 0.1 mg/mL of water.

Phytochemical characterization of the Vochysia rufa (Vochysiaceae) extract and its effects on oxidative stress in the pancreata of streptozotocin-induced diabetic rats

Aqueous extract of macerated Vochysia rufa stem bark has been commonly used in the treatment of diabetes. Therefore, we evaluated the antihyperglycemic and antioxidant effects of an extract of V. rufa on the pancreata of streptozotocin (STZ)-induced diabetic rats. Animals received one of the following treatments daily by oral gavage: water (diabetic-control), V. rufa extract (diabetic-V. rufa), or glibenclamide (diabetic-GBD). Total antioxidant capacity; levels of thiobarbituric acid reactive substances, reduced glutathione, and sulfhydryls; and superoxide dismutase, catalase, and glutathione peroxidase (GPx) activities were measured in the pancreas. Biochemical analysis of serum total cholesterol and fractions, triglycerides, creatinine, urea, acid uric, ALP, γ-GT, AST, and ALT was performed, and pancreatic β-cells positive for insulin were evaluated by immunohistochemistry. Rats treated with extract exhibited a decrease in fasting blood glucose compared with levels in diabetic control rats. GPx activity and sulfhydryl levels were significantly lower in diabetic-V. rufa rats compared with those of diabetic-control rats. V. rufa extract acted to normalize the biochemical alterations found in diabetic rats (diabetic-controls), as demonstrated by increases in urea, HDL, ALP, AST, and ALT. Reduction in blood glucose was independent of an increase in insulin. The V. rufa extract was found to be composed of free sugars (inositol, galactose, glucose, mannose, sucrose, arabinose, and ribose) as the main metabolites. Thus, aqueous extract of the stem bark of V. rufa is capable of reducing blood glucose, resulting in an antioxidant effect on the pancreatic tissue of STZ-diabetic rats.

Effect of Dietary Selenite on Hepatic Organic Solvent-Soluble Lipofuscin Pigments

Supplementation of selenium as sodium selenite results in an increase in hepatic organic solvent-soluble lipofuscin pigments, the metabolic end products of lipid peroxidation. Weanling mice fed a basal diet containing 0.05 ppm selenium had a significant increase in hepatic organic solvent-soluble lipofuscin pigments and glutathione peroxidase activity following supplementation of an additional 0.1 ppm selenium as sodium selenite from 5 to 9 months of age. Normal levels of vitamin E (30 mg/kg) were insufficient to protect against the oxidative effect of this increased dose of selenite. However, 10 times the normal level of vitamin E markedly suppressed this oxidative effect.

Biological and physiological role of reactive oxygen species--the good, the bad and the ugly

Reactive oxygen species (ROS) are chemically reactive molecules that are naturally produced within biological systems. Research has focused extensively on revealing the multi-faceted and complex roles that ROS play in living tissues. In regard to the good side of ROS, this article explores the effects of ROS on signalling, immune response and other physiological responses. To review the potentially bad side of ROS, we explain the consequences of high concentrations of molecules that lead to the disruption of redox homeostasis, which induces oxidative stress damaging intracellular components. The ugly effects of ROS can be observed in devastating cardiac, pulmonary, neurodegenerative and other disorders. Furthermore, this article covers the regulatory enzymes that mitigate the effects of ROS. Glutathione peroxidase, superoxide dismutase and catalase are discussed in particular detail. The current understanding of ROS is incomplete, and it is imperative that future research be performed to understand the implications of ROS in various therapeutic interventions.

Selective induction of IL-6 by aluminum-induced oxidative stress can be prevented by selenium

In this study the acute toxic effects of aluminum (Al) on mice have been investigated, including the interactions of Al and selenium (Se). Focus was put on the systemic effects of (co)exposure to Al and Se as a reflection of the redox status in the liver, kidney and brain. Short-term exposure (16 h) to Al resulted in an increase in the systemic inflammation parameters IL-6 and PAI-1, whereas serum levels of TNF-α remained unaffected. The different response pattern of IL-6 and TNF-α probably indicates an increased intracellular oxidative stress and altered redox status in the liver, because the selective increase in IL-6 serves as a protective intrahepatocellular process driven by oxidative stress. The intracellular glutathione concentration GSHtot decreased significantly upon Al exposure. Both the increase in IL-6 and decrease in glutathione status could be prevented by co-exposure to Se, but not the increase in PAI-1. The redox status of the kidney and brain was not markedly affected. Therefore it was concluded that short-term exposure to Al causes adverse effects on the intracellular oxidative stress processes in the liver, as reflected by the selective increase in the IL-6 concentration. This process can be restored by co-administration of the trace element Se as a part of the glutathione redox system.

Glycation of human erythrocyte glutathione peroxidase: effect on the physical and kinetic properties

BACKGROUND

Glutathione peroxidase (GPx) is a significant antioxidant enzyme that plays a key role in protecting the body from reactive oxygen species (ROS) and their toxicity. As a biocatalyst, the enzyme has been shown to reduce hydrogen peroxide to water and lipid hydroperoxides to their respective alcohols. The increased levels of ROS in patients with diabetes have been speculated to arise, in part, from alterations in the activity of glutathione antioxidant enzymes, perhaps, by mechanisms such as the glycation of the protein, in vivo.

METHODS

Under physiological conditions of temperature and pH, we investigated the susceptibility of human glutathione peroxidase to glycation, determined the effects of glycation on the physical and kinetic properties of the enzyme, and identified the protein's vulnerable amino acid sites of glycation.

RESULTS

Circular dichroism, UV and mass spectrometry studies revealed that methylglyoxal and DL-glyceraldehyde are potent glycators of glutathione peroxidase; destabilizing its structure, altering its pH activity and stability profiles and increasing its Km value.

CONCLUSIONS

In comparison to DL-glyceraldehyde, methylglyxol was a more potent glycator of the enzyme and was found to nonenzymatically condense with Arg-177, located near the glutathione binding site of GPx.

Effect of N-acetylcysteine supplementation on intracellular glutathione, urine isoprostanes, clinical score, and survival in hospitalized ill dogs

BACKGROUND

Antioxidant depletion and lipid peroxidation have been correlated with disease severity and associated with poor outcomes.

HYPOTHESIS/OBJECTIVES

Supplementing dogs with N-acetylcysteine (NAC) during the first 48 hours of hospitalization will increase cysteine, normalize glutathione concentrations, and decrease the degree of lipid peroxidation associated with illness.

ANIMALS

Sixty systemically ill hospitalized client-owned dogs and 14 healthy control dogs.

METHODS

Randomized investigator-blinded, placebo-controlled prospective study. Dogs were randomized to treatment with NAC (n = 30) versus placebo (n = 30). Antioxidants, urine 8-isoprostane/creatinine (IP/Cr), and clinical score were determined before and after treatment with NAC. Glutathione, cysteine, and vitamin E concentrations were quantified using high-performance liquid chromatography. Atomic absorption spectroscopy and enzyme-linked immunosorbent assays were used to quantify selenium and isoprostane concentrations, respectively.

RESULTS

Ill dogs had significantly lower vitamin E concentrations (27 versus 55 μg/mL; P = .0005) as well as elevated IP/Cr ratios (872 versus 399 pg/mg; P = .0007) versus healthy dogs. NAC supplementation significantly increased plasma cysteine (8.67 versus 15.1 μM; P < .0001) while maintaining glutathione concentrations. Dogs in the placebo group experienced a statistically significant decrease in glutathione concentrations (1.49 versus 1.44 mM; P = .0463). Illness severity and survival were unchanged after short duration NAC supplementation.

CONCLUSIONS

Ill dogs experience systemic oxidative stress. Supplementation with NAC during the first 48 hours of hospitalization stabilized erythrocyte glutathione concentrations. The clinical impact of this supplementation and glutathione concentration stabilization was undetermined.

Comparison of antioxidant effects of honey, glibenclamide, metformin, and their combinations in the kidneys of streptozotocin-induced diabetic rats

Hyperglycemia-induced increase in oxidative stress is implicated in diabetic complications. This study investigated the effect of metformin and/or glibenclamide in combination with honey on antioxidant enzymes and oxidative stress markers in the kidneys of streptozotocin (60 mg/kg; intraperitoneal)-induced diabetic rats. Diabetic rats were randomized into eight groups of five to seven rats and received distilled water (0.5 mL); honey (1.0 g/kg); metformin (100 mg/kg); metformin (100 mg/kg) and honey (1.0 g/kg); glibenclamide (0.6 mg/kg); glibenclamide (0.6 mg/kg) and honey (1.0 g/kg); metformin (100 mg/kg) and glibenclamide (0.6 mg/kg); or metformin (100 mg/kg), glibenclamide (0.6 mg/kg) and honey (1.0 g/kg) orally once daily for four weeks. Malondialdehyde (MDA) levels, glutathione peroxidase (GPx) and superoxide dismutase (SOD) activities were significantly elevated while catalase (CAT) activity, total antioxidant status (TAS), reduced glutathione (GSH), and GSH:oxidized glutathione (GSSG) ratio was significantly reduced in the diabetic kidneys. CAT, glutathione reductase (GR), TAS, and GSH remained significantly reduced in the diabetic rats treated with metformin and/or glibenclamide. In contrast, metformin or glibenclamide combined with honey significantly increased CAT, GR, TAS, and GSH. These results suggest that combination of honey with metformin or glibenclamide might offer additional antioxidant effect to these drugs. This might reduce oxidative stress-mediated damage in diabetic kidneys.

Antioxidant protection of Malaysian tualang honey in pancreas of normal and streptozotocin-induced diabetic rats

Glucotoxicity contributes to beta-cell dysfunction through oxidative stress. Our previous study demonstrated that tualang honey ameliorated renal oxidative stress and produced hypoglycemic effect in streptozotocin (STZ)-induced diabetic rats. This present study investigated the hypothesis that hypoglycemic effect of tualang honey might partly be due to protection of pancreas against oxidative stress. Diabetes was induced by a single dose of STZ (60 mg/kg; ip). Diabetic rats were randomly divided into two groups and administered distilled water (0.5 ml/d) and tualang honey (1.0 g/kg/d). Similarly, two groups of non-diabetic rats received distilled water (0.5 ml/d) and tualang honey (1.0 g/kg/d). The animals were treated orally for 28 days. At the end of the treatment period, the honey-treated diabetic rats had significantly (p<0.05) reduced blood glucose levels [8.8 (5.8)mmol/L; median (interquartile range)] compared with the diabetic control rats [17.9 (2.6)mmol/L]. The pancreas of diabetic control rats showed significantly increased levels of malondialdehyde (MDA) and up-regulation of superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities. Catalase (CAT) activity was significantly reduced while glutathione-S-transferase (GST) and glutathione reductase (GR) activities remained unchanged in the pancreas of diabetic rats. Tualang honey significantly (p<0.05) reduced elevated MDA levels. Honey treatment also restored SOD and CAT activities. These results suggest that hypoglycemic effect of tualang honey might be attributed to its antioxidative effect on the pancreas.

Oxidative risk for atherothrombotic cardiovascular disease

In the vasculature, reactive oxidant species, including reactive oxygen, nitrogen, or halogenating species, and thiyl, tyrosyl, or protein radicals may oxidatively modify lipids and proteins with deleterious consequences for vascular function. These biologically active free radical and nonradical species may be produced by increased activation of oxidant-generating sources and/or decreased cellular antioxidant capacity. Once formed, these species may engage in reactions to yield more potent oxidants that promote transition of the homeostatic vascular phenotype to a pathobiological state that is permissive for atherothrombogenesis. This dysfunctional vasculature is characterized by lipid peroxidation and aberrant lipid deposition, inflammation, immune cell activation, platelet activation, thrombus formation, and disturbed hemodynamic flow. Each of these pathobiological states is associated with an increase in the vascular burden of free radical species-derived oxidation products and, thereby, implicates increased oxidant stress in the pathogenesis of atherothrombotic vascular disease.

Destabilisation and subsequent lysis of human erythrocytes induced by Plasmodium falciparum haem products

In falciparum malaria, both infected and uninfected red cells have structural and functional alterations. To investigate the mechanisms of these modifications, we studied the effects of two Plasmodium falciparum haem products (haematin and malaria pigment in the synthetic form beta-haematin) on isolated human red blood cells (RBCs) and purified RBC ghosts. A dose- and time-dependent incorporation of haematin into RBC ghosts and intact cells was observed, which was in proportion to the extent of haematin- induced haemolysis. RBCs pre-incubated with haematin were more sensitive to haemolysis induced by hypotonic shock, low pH, H2O2 or haematin itself. Haemolysis was not related to membrane lipid peroxidation and only partially to oxidation of protein sulphydryl groups and it could not be prevented by scavengers of lipid peroxidation or hydroperoxide groups. N-acetylcysteine partly protected the oxidation of SH groups and significantly reduced haemolysis. In contrast, beta-haematin was neither haemolytic nor oxidative towards protein sulphydryl groups. Beta-haematin did destabilise the RBC membrane, but to a lesser extent than haematin, inducing increased susceptibility to lysis caused by hypotonic medium, H2O2 or haematin. This study suggests that the destabilising effect of haematin and, to a much less extent, beta-haematin on the RBC membrane does not result from oxidative damage of membrane lipids but from direct binding or incorporation which may affect the reciprocal interactions between the membrane and cytoskeleton proteins. These changes could contribute to the reduced red cell deformability associated with severe malaria.

Protective effect of macrocyclic binuclear oxovanadium complex on oxidative stress in pancreas of streptozotocin induced diabetic rats

Chronic hyperglycemia in diabetes is a major causative factor of free radical generation which further leads to many secondary diabetic complications via the damage to cellular proteins, membrane lipids, nucleic acids and eventually to cell death. Recently we have reported on the hypoglycemic efficacy of a new macrocyclic binuclear oxovanadium complex and its non-toxic nature. This study focuses on the effect of the above complex in ameliorating oxidative stress in the pancreas of diabetic rats. Streptozotocin induced diabetic rats were treated orally with the vanadium complex (5 mg/kg/body weight) for 30 days and the level of pancreatic antioxidants and lipid peroxides were determined. Treatment with the macrocyclic binuclear oxovanadium complex decreased the lipid peroxides and the antioxidant enzymes such as superoxide dismutase, catalase and glutathione peroxidase to near control levels. Histological examinations also revealed the protective effect of the complex on pancreatic beta cells. The results demonstrate the protective effect of the macrocyclic binuclear oxovanadium complex on the pancreatic antioxidant status.

Antioxidant associated chemoprevention by selenomethionine in murine tumor model

Effectiveness of selenium in different forms like sodium selenite, selenocysteine and selenomethionine has been compared in four different doses, namely 4, 6, 8 and 10 ppm of each, in terms of their bioavailability and prolongation of survival of Dalton's lymphoma (DL) bearing mice. Selenomethionine, at a dose of 8 ppm, was found to be the most bioavailable and least-cytotoxic form that was capable of increasing the life span of the tumour bearing hosts maximally (almost two-fold). Beneficiality of selenomethionine has also been studied by observing continuous changes brought about by this compound on the glutathione (GSH) level, glutathione peroxidase (GPx) activity and extent of lipid peroxidation in the hepatic tissue of the tumour bearing hosts, which are indispensable for a cell to function normally and are found to exhibit significantly altered behaviour in neoplastic cells. Selenomethionine caused the maintenance of high steady state GSH level and a normal GPx activity during the fist phase of tumour growth. It also controlled lipid peroxidation during the first 15-20 days following tumour transplantation. These conditions helped in the maintenance of intracellular redox balance, cellular integrity and metabolic rhythms of cells in DL bearing mice receiving selenomethionine.

Biochemical studies on the toxicity of 1, 1'-dimethyl-4, 4'-bipyridylium dichloride in the rat

The effect of intraperitoneal administration of lethal dose (50 mg/kg) of paraquat on the microsomal cysteine levels in the plasma, liver and lung of adult male Wistar rats has been investigated using Rank Chromaspek amino acid analyzer. The microsomal alanine levels were also determined to help in assessing the extent of paraquat interference with cellular protein. DL-Buthionine-[S,R]-Sulfoximine (BSO) and Diethyl maleate (DEM) were used to potentiate the toxic effect of the bipyridyl. The microsomal cysteine levels were significantly (P < or = 0.05) depressed in the plasma, liver and lung of the paraquat-treated rats compared with the saline-injected group but the alanine levels were not similarly affected. Probably, paraquat poisoning interferes specifically with the cellular cysteine content in the rat. These findings could provide a valuable information on the biochemical mechanism of paraquat intoxication.

Antioxidant defense system in diabetic kidney: a time course study

Oxygen free radicals (OFRs) have been suggested to be a contributory factor in complications of diabetes mellitus. In the present study, we investigated the lipid peroxide level measured as thiobarbituric acid reactive substances (TBARS) and activities of antioxidant enzymes viz., [superoxide dismutase (SOD), catalase (CAT) and glutathione-peroxidase (GSH-Px)] in the kidney of streptozotocin induced diabetic rats at various stages of development of diabetes. Sprague Dawley rats were divided into two groups: group I, control (n = 42) and group II, diabetic (n = 42). Each group was further subdivided into seven groups each consisting of six rats. Rats in subgroups were studied at weekly intervals (0 to 6 weeks). Blood glucose levels were estimated at the time of sacrifice. TBARS levels and activity of antioxidant enzymes were measured in kidney. The levels of TBARS in the diabetic group increased initially, dropped to baseline level after 2 weeks and then progressively increased at 5th and 6th week (p < 0.05). There was an increase in catalase activity at first week after that it decreased as compared to control group. However, GSH-Px activity in the diabetic group increased after 1 week and then remained at the same level except a small drop in the 2nd week. Total SOD and CuZn-SOD activity increased significantly in diabetic kidney as compared to controls at all time intervals, while Mn-SOD activity showed no change. The present findings suggest that oxidative stress accompanies at early onset of diabetes mellitus and the susceptibility of the kidney to oxidative stress during the early stages may be an important factor in the development of diabetic nephropathy.

Lipid peroxidation of erythrocytes during anemia of the hamsters infected with Leishmania donovani

Visceral leishmaniasis has been found to be associated with severe anemia and premature lysis of erythrocytes. Peroxidative damage of red cells has been noted in several hemolytic anemias. Present study shows enhanced formation of methemoglobin in hamsters infected with Leishmania donovani. Increased formation of malonyldialdehyde and diene conjugate has been noted in the erythrocytes of the infected animals with the progress of anemia. Results showed decreased activities of protective enzymes like superoxide dismutase, catalase and glutathione reductase against peroxidative attack. An increase in the membrane cholesterol/phospholipid ratio and a decrease in membrane fluidity of erythrocytes were observed under the diseased condition. Densitometric scan after SDS-PAGE of red cell membrane of the infected animals revealed significant degradation of band 3 and band 4.1 proteins. The results suggest that alteration in the membrane may lead to reduced life span of the red cells in experimental visceral leishmaniasis.

Endogenous skeletal muscle antioxidants

Skeletal muscle is susceptible to oxidative deterioration due to a combination of lipid oxidation catalysts and membrane lipid systems that are high in unsaturated fatty acids. To prevent or delay oxidation reactions, several endogenous antioxidant systems are found in muscle tissue. These include alpha-tocopherol, histidine-containing dipeptides, and antioxidant enzymes such as glutathione peroxidase, superoxide dismutase, and catalase. The contribution of alpha-tocopherol to the oxidative stability of skeletal muscle is largely influenced by diet. Dietary supplementation of tocopherol has been shown to increase muscle alpha-tocopherol concentrations and inhibit both lipid oxidation and color deterioration. Dietary selenium supplementation has also been shown to increase the oxidative stability of muscle presumably by increasing the activity of glutathione peroxidase. The oxidative stability of skeletal muscle is also influenced by the histidine-containing dipeptides, carnosine and anserine. Whereas carnosine and anserine are affected by diet less than alpha-tocopherol and glutathione peroxidase, their concentrations vary widely with species and muscle type. In pigs, beef, and turkey muscle, carnosine concentrations are greater than anserine, while the opposite is true in rabbit, salmon, and chicken muscle. Anserine and carnosine are found in greater concentrations in muscle high in white fibers, with chicken white muscle containing over fivefold more anserine and carnosine than red muscle. Anserine and carnosine are thought to inhibit lipid oxidation by a combination of free radical scavenging and metal chelation.

Effects of diethyl maleate (DEM), a glutathione depletor, on prostaglandin synthesis in the isolated perfused spleen of rabbits

To investigate the role of glutathione (GSH) on prostaglandin (PG) synthesis, isolated rabbit spleens were perfused with Tyrode's solution with or without the addition of diethyl maleate (DEM) in concentrations up to 1 mM. In the absence of DEM, PG synthesis was stimulated by the Ca2+ ionophore A23187 (20 nmole) or arachidonate (0.4 mumole). Prostaglandin (PG) E2 was a major product, accounting for 60-70% of the total cyclooxygenase products. Small amounts of PGF2 alpha, 6-keto-PGF1 alpha, PGD2 and thromboxane (Tx) B2 were also produced. When DEM was added to the perfusion medium, GSH content decreased dose-dependently with increasing DEM concentration. Lactate dehydrogenase activity was not detected in the venous effluent, indicating that DEM depleted intrasplenic GSH without causing any lysis of cellular membranes. A23187-induced production of PGs and of Tx was decreased with increasing concentrations of DEM up to 0.5 mM, whereas at 1.0 mM DEM, these products showed a tendency to increase as compared with levels at 0.5 mM DEM. However, this increase was only significant for TxB2, which returned to levels obtained in the absence of DEM. DEM 1 mM did not cause cell lysis, but it appears to perturb the cell membrane to a degree similar to that which occurs with stimulation of phospholipase A2. The small but significant increase of TxB2 with 1.0 mM DEM could be a result of decreased PGE2 isomerase activity. Perfusion with arachidonate gave virtually identical results: 1.0 mM DEM attenuated the production of all prostanoids except for TxB2 as compared with untreated controls. These results suggest that GSH contributes to the regulation and/or maintenance of PGs synthesis.

Temporal expression of genes encoding free radical-metabolizing enzymes is associated with higher mRNA levels during in utero development in mice

The interaction of reactive oxygen metabolites with DNA is well characterized and may result in mutagenesis, chromosome aberrations, and modulation of gene expression. Superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) catalyze enzymatic reactions to remove oxidant stresses, particularly O2- and H2O2. The role of these enzymes during in utero development of the embryo and the developmental pattern of expression of the embryonic genes encoding them is not known. We examined the in utero developmental expression and activity of the three free-radical-metabolizing enzymes in mice. We collected mouse fetuses at different stages of development and examined total RNA populations by Northern and slot blots using gene-specific cDNA probes. In addition to quantifying the probe-specific RNAs, activities of the three enzymes were also evaluated on the same tissue samples. The gene-specific RNAs and the associated enzyme activities are detectable with somite formation (day 8 postcoitus [p.c.]) in mice. The relative RNA values for each of the genes studied are higher in in utero stages as compared with the adult. The specific activities of these enzymes, on the other hand, follow a characteristic increase with development and growth. The relative RNA levels for each of the genes studied are higher during in utero growth and development than the relative enzyme activity values (between day 8 and day 18, third trimester) in the liver and carcass. This may suggest that the mRNA specific to these genes may accumulate in utero and are not translated immediately. Such accumulating transcripts are translated efficiently after birth, when these enzymes are particularly needed with the advent of aerobic respiration.

Glutathione-dependent enzymes in intact rod outer segments

We have compared the specific activities of glutathione-dependent enzymes in rod outer segments (ROS) and in whole retina of rabbits and rats, using three different assays. In the first, glutathione peroxidase (GSH-Px) activity was measured as the combined activities of the Se-dependent and Se-independent forms using cumene hydroxide as a substrate. In the second, Se-dependent GSH-Px alone was measured using hydrogen peroxide (H2O2) as a substrate. In the third, the combined activities of several enzymes, collectively known as GSH-S-transferase, were measured. The latter includes the activity of the Se-independent GSH-Px. GSH-Px activity (Se-dependent and Se-independent combined) in ROS of rat and rabbit were found to be 47.7 +/- 8.2 and 72.9 +/- 11.9 nmol of GSH oxidized min-1 mg-1 soluble protein, respectively. From whole retina, values were 67.3 +/- 6.0 and 128.8 +/- 12.3, respectively. Se-dependent GSH-Px specific activities from the above tissues were 43.5 +/- 2.9 (rat ROS). 70.6 +/- 11.3 (rabbit ROS), 30.6 +/- 9.6 (rat whole retina), and 113.2 +/- 12.2 (rabbit whole retina). GSH-S-transferase activity was negligible in rabbit ROS, whereas, in rat ROS, it was 40.4 +/- 8.0, expressed as nmol of S-2,4-dinitrophenylglutathione produced min-1 mg-1 soluble protein. In contrast, the GSH-S-transferase specific activity in whole rabbit retinas was about eight times that found in the rat retina (101.5 +/- 12.3 for rat retina and 885.3 +/- 60.0 for rabbit retina). These results demonstrate that ROS contain glutathione enzymes which are important in protecting membranes from oxidative stresses by reducing hydrogen peroxide and lipid hydroperoxides at the site of their formation.

Irreversible erythrocyte volume expansion induced by tellurite

Tellurite (K2TeO3) has been suggested as a potential anti-sickling compound because it causes a selective increase in the water content of RBC. To investigate the conditions underlying the increase in RBC volume due to tellurite, normal RBCs were incubated with the compound in a physiological medium and the cells washed with a 10-fold volume of the medium. The washed cells were then incubated at 24 degrees C for periods up to 4 h and the following parameters were determined: MCV, MCH, MCHC and supernatant haemoglobin concentration by standard methods, the density distribution profile by phthalate esters and cell morphology by scanning electron microscopy (SEM). The effect of hypertonic PBS on the tellurite-treated cells was also tested. K2TeO3 induced concentration and time dependent increases in MCV and decreases in MCHC without any apparent change in MCH. The median density and the transitional 60% density range of the cell distribution profile respectively decreased and increased in proportion to [K2TeO3] and time. Hypertonic PBS did not inhibit or reverse the tellurite-induced changes in MCV and MCHC. SEM and photovolumetric measurements demonstrated tellurite-induced large vesicles ranging in size from 24 to 32 micron 3. The proportion of these vesicles increased with time and K2TeO3 concentration. Since tellurite is an oxidant, these findings suggest that its influx into the red cell results in irreversible reactions that disrupt the ion and water regulatory properties of the membrane.

Biochemical and functional effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the heart of female rats

Biochemical, functional and morphologic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the hearts of female rats were examined. Six days after the treatment of rats with TCDD, the blood pressures and resting heart rates were significantly less than in control animals. Treated animals were also less responsive to the effects of the beta-1 agonist, (-)isoproterenol. No histopathologic changes were observed in the heart although extensive centrilobular necrosis occurred in the liver after TCDD administration. Serum levels of thyroxine were 66% less than in control animals. Marked lipid peroxidation was produced in the liver with small but significant increases occurring in the heart. TCDD administration had no effect on catalase activity in the heart, but produced a 20% decrease in superoxide dismutase activity relative to control animals. The effects of TCDD on cardiac function do not appear to be due to a direct action of the xenobiotic on the heart but possibly to a down-regulation of beta-receptors in the heart as a result of the hypothyroid state.

Anti-oxidant enzymes in fetal guinea pig brain during development and the effect of maternal hypoxia

The development of the anti-oxidant enzymes superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, and glucose-6-phosphate dehydrogenase was studied in the fetal guinea pig brain at 30, 35, 40, 45, 50, 55, and 60 days of gestation. The activities of these enzymes remained constant during 30-45 days of gestation and increased significantly during the 45-60 day period, with the exception of superoxide dismutase, which remained unchanged throughout the gestational period. The enzyme activities in fetal brain tissue at every gestational age were unaffected by maternal hypoxia (inspired oxygen, 7% for 40 min). The concurrent development of glucose-6-phosphate dehydrogenase, glutathione reductase, and glutathione peroxidase during 45-60 days of gestation indicates an increased ability of the fetal brain to detoxify lipid peroxidation products by reinforcing the glutathione system. The results of this study indicate that the anti-oxidant enzymatic defense mechanisms in the guinea pig brain are fairly mature at birth. However, these mechanisms are underdeveloped during the early stages of gestation and, therefore, during this period the brain might be at potential risk for lipid peroxidative damage under conditions leading to increased formation of oxygen free radicals.

The effects of in vitro lipid peroxidation on the activity of rat liver microsomal glutathione S-transferase from rats supplemented or deficient in antioxidants

Glutathione S-transferases are a group of multifunctional isozymes that play a central role in the detoxification of hydrophobic xenobiotics with electrophilic centers (1). In this study we investigated the effects of in vitro lipid peroxidation on the activity of liver microsomal glutathione S-transferases from rats either supplemented or deficient in both vitamin E and selenium. Increased formation of malondialdehyde (MDA), a by-product of lipid peroxidation, was associated with a decreased activity of rat liver microsomal glutathione S-transferase. The inhibition of glutathione S-transferase occurred rapidly in microsomes from rats fed a diet deficient in both vitamin E and selenium (the B diet) but was delayed for 15 minutes in microsomes from rats fed the same diet but supplemented with these micro-nutrients (B+E+Se diet). Lipid peroxidation inhibits microsomal glutathione S-transferase and this inhibition is modulated by dietary antioxidants.

Glutathione depleting agents and lipid peroxidation

The mechanisms by which glutathione (GSH) depleting agents produce cellular injury, particularly liver cell injury have been reviewed. Among the model molecules most thoroughly investigated are bromobenzene and acetaminophen. The metabolism of these compounds leads to the formation of electrophilic reactants that easily conjugate with GSH. After substantial depletion of GSH, covalent binding of reactive metabolites to cellular macromolecules occurs. When the hepatic GSH depletion reaches a threshold level, lipid peroxidation develops and severe cellular damage is produced. According to experimental evidence, the cell death seems to be more strictly related to lipid peroxidation rather than to covalent binding. Loss of protein sulfhydryl groups may be an important factor in the disturbance of calcium homeostasis which, according to several authors, leads to irreversible cell injury. In the bromobenzene-induced liver injury loss of protein thiols as well as impairment of mitochondrial and microsomal Ca2+ sequestration activities are related to lipid peroxidation. However, some redox active compounds such as menadione and t-butylhydroperoxide produce direct oxidation of protein thiols.

Purification and characterization of human plasma glutathione peroxidase: a selenoglycoprotein distinct from the known cellular enzyme

Glutathione peroxidase (GSHPx), (glutathione:H2O2 oxidoreductase, EC 1.11.1.9) was purified to homogeneity from human plasma. This resulted in a 6800-fold purification of the enzyme with a 2.8% yield. The purification process involved ammonium sulfate fractionation, DEAE-cellulose batch and column chromatographies, hydroxyapatite, and Sephadex G-200 and DEAE-Sephadex A-25 chromatographies. The major peak on DEAE-Sephadex A-25 column chromatography was found to be homogeneous on polyacrylamide gel electrophoresis in the presence or absence of sodium dodecyl sulfate (SDS). Relative mobility in nondenaturing polyacrylamide gel electrophoresis at pH 8.2 was 0.5 for the purified enzyme as detected by both protein staining and enzyme activity compared with 0.38 for erythrocyte GSHPx. The molecular weight of the plasma enzyme as determined by gel filtration was found to be approximately 100,000. SDS-gel electrophoresis of the plasma enzyme gave a subunit molecular weight of approximately 23,000. This suggests that the plasma enzyme exists as a tetramer in its native state, similar to that seen for the erythrocyte enzyme, but with slightly different mobility on SDS-gel electrophoresis. Plasma GSHPx, like the erythrocyte enzyme, was found to contain approximately four atoms of selenium per mole of protein. Utilizing iodinated concanavalin A, it was found that plasma GSHPx, but not the erythrocyte GSPx, is a glycoprotein. Purified plasma enzyme catalyzes both the reduction of tertiary butyl hydroperoxide and hydrogen peroxide. The apparent Km of plasma GSHPx for GSH is 5.3 mM and for tertiary butyl hydroperoxide it is 0.57 mM. Copper, mercury, and zinc strongly inhibit the enzyme activity of plasma GSHPx. Rabbit antibodies directed against the human erythrocyte GSHPx do not precipitate the enzyme activity of the purified plasma enzyme. Radioimmunoassay utilizing erythrocyte GSHPx and anti-erythrocyte GSHPx antibodies showed that less than 0.13% of the antigenically detectable protein is found in the purified GSHPx from plasma.

The role of selenium peroxidases in the protection against oxidative damage of membranes

The present review deals with the chemical properties of selenium in relation to its antioxidant properties and its reactivity in biological systems. The interaction of selenite with thiols and glutathione and the reactivity of selenocompounds with hydroperoxides are described. After a short survey on distribution, metabolism and organification of selenium, the role of this element as a component of the two seleno-dependent glutathione peroxidases is described. The main features of glutathione peroxidase and phospholipid hydroperoxide glutathione peroxidase are also reviewed. Both enzymes reduce different hydroperoxides to the corresponding alcohols and the major difference is the reduction of lipid hydroperoxides in membrane matrix catalyzed only by the phospholipid hydroperoxide glutathione peroxidase. However, in spite of the different specificity for the peroxidic substrates, the kinetic mechanism of both glutathione peroxidase and phospholipid hydroperoxide glutathione peroxidase seems identical and proceeds through a tert-uni ping pong mechanism. In the reaction cycle, indeed, as supported by the kinetic data, the oxidation of the ionized selenol by the hydroperoxide yields a selenenic acid that in turn is reduced back by two reactions with reduced glutathione. Special emphasis has been given to the role of selenium-dependent glutathione peroxidases in the prevention of membrane lipid peroxidation. While glutathione peroxidase is able to reduce hydrogen peroxide and other hydroperoxides possibly present in the soluble compartment of the cell, this enzyme fails to inhibit microsomal lipid peroxidation induced by NADPH or ascorbate and iron complexes. On the other hand, phospholipid hydroperoxide glutathione peroxidase, by reducing the phospholipid hydroperoxides in the membranes, actively prevents lipid peroxidation, provided a normal content of vitamin E is present in the membranes. In fact, by preventing the free radical generation from lipid hydroperoxides, phospholipid hydroperoxide glutathione peroxidase decreases the vitamin E requirement necessary to inhibit lipid peroxidation. Finally, the possible regulatory role of the selenoperoxidases on the arachidonic acid cascade enzymes (cyclooxygenase and lipoxygenase) is discussed.

Lipid peroxidation and mechanisms of toxicity

Aerobic organisms by definition require oxygen, and the importance of iron in aerobic respiration has long been recognized, but despite their beneficial roles, these elements can pose a real threat to the organism. During oxygen reduction, reactive species such as O2-. and H2O2 are formed readily. Iron can combine with these species, or with molecular oxygen itself, to generate free radicals which will attack the polyunsaturated fatty acids of membrane lipids. This oxidative deterioration of membrane lipids is known as lipid peroxidation. To protect itself against this form of attack, the organism possesses several types of defense mechanisms. Under normal conditions, these defenses appear to offer adequate protection for cell membranes, but the possibility exists that certain foreign compounds may interfere with or even overwhelm these defenses, and herein could lie a general mechanism of toxicity. This possible cause of toxicity is discussed in relation to other suggested causes.

The effects of reduced glutathione and cysteine on prostaglandin synthesis in rabbit kidney medulla slices

The effects of GSH and cysteine on the generation of medullary prostaglandins E2 and F2 alpha were examined. The formation of prostaglandin E2 was enhanced by GSH, but was reduced by cysteine in a dose-related manner. GSH inhibited prostaglandin F2 alpha production, while cysteine stimulated it. These results suggest that GSH and cysteine have contrary effects on prostaglandins E2 and F2 alpha synthesis by affecting endoperoxide E2 isomerase or endoperoxide reductase.

High-performance liquid chromatography as a tool for identification of linolenic acid hydroperoxide prepared with soybean lipoxygenase

Linolenic acid hydroperoxide, enzymatically produced by soybean lipoxygenase from linolenic acid, was purified by high-performance liquid chromatography (HPLC) using a Supelco LC-8 (5 microns), 22 cm X 4.6 mm I.D. column with a solvent system of acetonitrile-tetrahydrofuran-0.1% phosphoric acid (50.4:21.6:28, v/v/v). The hydroperoxide was converted to several derivatives, the hydroxy, methyl, and stearate which were analyzed by HPLC and identified by gas chromatography-mass spectrometry. The 13-hydroperoxy linolenic acid was the major hydroperoxide produced by soybean lipoxygenase.

Glutathione peroxidase activity and reduced glutathione content in erythrocytes of patients with chronic renal failure

Erythrocytes from 18 patients with chronic renal failure (CRF) and 10 healthy subjects were examined with respect to glutathione peroxidase (GSH-Px) activity and reduced glutathione (GSH) contents. The activity of GSH-Px and GSH content were found to be lower in RBC from CRF patients as compared with normal RBC. These reduced levels of GSH and GSH-Px in the red cells of uraemic patients may predispose the cells to oxidative damage.

Presence of lipid hydroperoxide in human plasma

Using purified prostaglandin (PG) H synthase, which synthesizes PGG2 and PGH2 from arachidonic acid, we were able to assay for the presence of peroxide activators in biological tissues. This assay system, capable of detecting both hydrogen peroxide (H2O2) and lipid hydroperoxides, detected a significant amount of synthase activator in plasma. Treatment of the active preparations with catalase and glutathione peroxidase showed that the principal activator in normal human plasma was a lipid hydroperoxide rather than H2O2.