Significance of alterations in hepatic antioxidant enzymes. Primacy of glutathione peroxidase

Modulation of antioxidant gene expressions by Roundup® exposure in the decapod Macrobrachium potiuna

Glyphosate-based herbicides (GBH), including Roundup®, are the most used herbicides in agricultural and non-agricultural areas, which can reach aquatic environments through drift during application or surface runoff. Some studies, mostly in fish, demonstrated that GBH caused oxidative stress in non-target animals. However, only few information is available on the GBH effects in the antioxidant and stress proteins of many other organisms, such as freshwater crustaceans. Thus, we aimed to investigate the effects of environmentally relevant GBH concentrations on the relative transcript expression (RTE) of the superoxide dismutase (sod1), catalase (cat), selenium-dependent glutathione peroxidase (gpx), glutathione-S-transferase (gst), thioredoxin (txn), heat shock protein (hsp70 and hsp90) in the hepatopancreas of the ecologically important freshwater prawn Macrobrachium potiuna. Moreover, this study aimed to assess the gender-differences responses to GBH exposure. Male and female prawns were exposed to three Roundup WG® concentrations (0.0065, 0.065 and 0.28 mg of glyphosate/L) and a control group (0.0 mg/L) for 7 and 14 days. In general, males had an under-expression of the studied genes, indicating an oxidative stress and possible accumulation of ROS in the hepatopancreas. In the opposite, females had an overexpression of the same genes, indicating a more robust antioxidant system, in order to cope with the possible ROS increase after Roundup WG® exposure. Therefore, results confirmed that gender could be a confounding factor in ecotoxicological assessment of GBH effects. Additionally, this work highlights that sod1, cat, gpx, gst, txn, hsp70 and hsp90 gene expressions seem to be useful biomarkers to investigate the oxidative stress caused by Roundup WG® in Macrobrachium sp.

Life history and physiological responses of native and invasive brine shrimps exposed to zinc

Although a substantial amount of research exists on pollution and biological invasions, there is a paucity of understanding of how both factors interact. Most studies show that pollution favours the establishment of invasive species, but pollution may also promote local adaptation of native species and prevent the establishment of new incomers. However, evidence for this is extremely limited because most studies focus on successful invasions and very few on cases where an invasion has been resisted. Here we provide evidence of local adaptation of native species to pollution combining life history and physiological data. We focused on the invasion of the North American brine shrimp Artemia franciscana, which is causing a dramatic biodiversity loss in hypersaline ecosystems worldwide, and one of the last native Artemia populations in SW Europe (A. parthenogenetica from the historically polluted Odiel estuary, SW Spain). Life table response experiments were carried out in the laboratory to compare the demographic responses of A. parthenogenetica and a nearby A. franciscana population to long-term Zn exposure (0.2 mg L^-1). We also evaluated oxidative stress by measuring antioxidant defences (catalase, glutathione reductase and superoxide dismutase) and lipid peroxidation (thiobarbituric acid reactive substances). A high concentration of Zn induced strong mortality in A. franciscana, which also showed high levels of lipid peroxidation, suggesting relatively poor physiological resistance to pollution compared with A. parthenogenetica. The age at maturity was shorter in A. parthenogenetica, which may be an adaptation to the naturally high mortality rate observed in the Odiel population. Exposure to Zn accelerated age at first reproduction in A. franciscana but not in A. parthenogenetica. In contrast, Zn had a stimulatory effect on offspring production in A. parthenogenetica,which also showed higher reproductive parameters (number of broods, total offspring and offspring per brood) than A. franciscana. Overall, the results of this study strongly suggest that native Artemia from Odiel estuary is locally adapted (at both, reproductive and physiological levels) to Zn contamination and that A. franciscana is highly sensitive. This is a good example of how pollution may play a role in the persistence of the last native Artemia populations in the Mediterranean.

Ventilation causes pulmonary vascular dilation and modulates the NOS and VEGF pathway on newborn rats with CDH

BACKGROUND/PURPOSE

Congenital diaphragmatic hernia (CDH) is a defect that presents high mortality because of pulmonary hypoplasia and hypertension. Mechanical ventilation changes signaling pathways, such as nitric oxide and VEGF in the pulmonary arterioles. We investigated the production of NOS2 and NOS3 and expression of VEGF and its receptors after ventilation in rat fetuses with CDH.

METHODS

CDH was induced by Nitrofen. The fetuses were divided into 6 groups: 1) control (C); 2) control ventilated (CV); 3) exposed to nitrofen (N-); 4) exposed to nitrofen ventilated (N-V), 5) CDH and 6) CDH ventilated (CDHV). Fetuses were harvested and ventilated. We assessed body weight (BW), total lung weight (TLW), TLW/BW ratio, the median pulmonary arteriolar wall thickness (MWT). We analyzed the expression of NOS2, NOS3, VEGF and its receptors by immunohistochemistry and Western blotting.

RESULTS

BW, TLW, and TLW/BW ratio were greater on C than on N- and CDH (p<0.05). The MWT was higher in CDH than in CDHV (p<0.001). CDHV showed increased expression of NOS3 (p<0.05) and VEGFR1 (p<0.05), but decreased expression of NOS2 (p<0.05) and VEGFR2 (p<0.001) compared to CDH.

CONCLUSION

Ventilation caused pulmonary vasodilation and changed the expression of NOS and VEGF receptors.

Antioxidant activity of Terminalia arjuna bark extract on N-nitrosodiethylamine induced hepatocellular carcinoma in rats

The present investigation was carried out to evaluate the antioxidant nature of ethanolic extract of Terminalia arjuna bark (EETA) on N-nitrosodiethylamine (DEN) induced liver cancer in male Wistar albino rats. Liver cancer was induced by single intraperitonial injection of DEN (200 mg/kg). After 2 weeks of DEN administration, Phenobarbital (PB) was given to promote the cancer for up to 14 successive weeks. EETA extract (400 mg/kg) was given post-orally for 28 days to hepatocellular carcinoma-bearing rats. After the experimental period, all the animals were sacrificed and serum, liver and kidney samples were collected for further biochemical analysis. The levels of lipid peroxides (LPO) under basal and also in the presence of inducers (H(2)O(2), ascorbate and FeSO(4)) were estimated in serum, liver and kidney of control and experimental animals. Enzymic antioxidants, such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and non-enzymic antioxidants like Vitamin C (Vit-C) and Vitamin E (Vit-E) levels were determined in all the groups of animals. A significant increase in LPO levels were observed while the levels of enzymic and non-enzymic antioxidants were decreased, when subjected to DEN induction. These altered enzyme levels were ameliorated significantly by administration of EETA at the concentration of 400 mg/kg in drug-treated animals. This protective effect of EETA was associated with inhibition of LPO induced by DEN and to maintain the antioxidant enzyme levels. Our results show an antioxidant activity of T. arjuna bark against DEN-induced liver cancer.

Catalase-dependent measurement of H2O2 in intact mitochondria

Mitochondria generate potentially damaging amounts of superoxide and H2O2 during oxidative metabolism. Although many assays are available to measure mitochondrial H2O2 generation, most detect H2O2 that has escaped the organelle. To measure H2O2 within mitochondria that contain catalase, we have developed an assay based on the ability of H2O2 to inhibit catalase in the presence of 3-amino-1,2,4-triazole. The assay is simple to perform, does not require expensive instrumentation, and is specific for H2O2. Results from this assay show that H2O2 generation in rat heart mitochondria reflects the activity of the electron transport chain. Further, liver mitochondria prepared from selenium-deficient rats have increased succinate-stimulated rates of H2O2 generation. This indicates that mitochondrial selenoenzymes are important for H2O2 removal. It also demonstrates the utility of this assay in measuring H2O2 release from mitochondria that do not contain catalase. The assay should be useful for study of both superoxide-dependent H2O2 generation in situ, and the role of endogenous mitochondrial catalase in H2O2 removal.

Antioxidant enzyme activities and lipid peroxidation in the freshwater cladoceran Daphnia magna exposed to redox cycling compounds

Contaminant-related changes in antioxidative processes in the freshwater crustacea Daphnia magna exposed to model redox cycling contaminant were assessed. Activities of key antioxidant enzymes including catalase, superoxide dismutase, glutathione peroxidase and glutathione S-transferases and levels of lipid peroxidation measured as thiobarbituric acid-reactive substances (TBARS) and lipofucsin pigment content were determined in D. magna juveniles after being exposed to sublethal levels of menadione, paraquat, endosulfan, cadmium and copper for 48 h. Results denoted different patterns of antioxidant enzyme responses, suggesting that different toxicants may induce different antioxidant/prooxidant responses depending on their ability to produce reactive oxygen species and antioxidant enzymes to detoxify them. Low responses of antioxidant enzyme activities for menadione and endosulfan, associated with increasing levels of lipid peroxidation and enhanced levels of antioxidant enzyme activities for paraquat, seemed to prevent lipid peroxidation, whereas high levels of both antioxidant enzyme activities and lipid peroxidation were found for copper. For cadmium, low antioxidant enzyme responses coupled with negligible increases in lipid peroxidation indicated low potential for cadmium to alter the antioxidant/prooxidant status in Daphnia. Among the studied enzymes, total glutathione peroxidase, catalase and glutathione S-transferase appeared to be the most responsive biomarkers of oxidative stress.

Action of E. coli endotoxin, IL-1beta and TNF-alpha on antioxidant status of cultured hepatocytes

We have previously reported that endotoxin induces in vivo oxidative stress in liver and a significant increase in hepatic and plasma glutathione concentrations during the acute phase of reversible endotoxic shock in rats. In the present study we examined the in vitro effects of E. coli 0111:B4 endotoxin (lipopolysaccharide, LPS), IL-1beta and TNF-alpha on antioxidant status of cultured hepatocytes in order to differentiate between the direct and mediated endotoxin action. LPS increased total glutathione (tGSH) levels after 2 h treatment but decreased oxidized glutathione (GSSG) content which lead to a marked decrease in GSSG/tGSH index. At shorter treatment times a biphasic and dose-dependent behaviour was observed. Cytokines (IL-1beta and TNF-alpha) produced significant decreases in tGSH and GSSG after 30 min treatment. Despite its prooxidant effect, TNF-alpha significantly reduced GSSG/tGSH index. Although no significant effects were observed on glutathione reductase activity, both LPS and cytokines induced an important inhibition of glutathione peroxidase which can justify the lipid peroxidation previously observed both in liver during reversible endotoxic shock and in cultured hepatocytes after treatment with endotoxin. The inhibition of hepatic glutathione peroxidase, besides the stimulation of GSH synthesis by LPS and GSH efflux by cytokines, guarantees the export of hepatic glutathione in its reduced form for other organs, contributing to the interorgan homeostasis. On the other hand, the results presented here support a new role for GSSG/tGSH index different from a mere indicator of oxidative stress.

Therapeutic potential of dietary phase 2 enzyme inducers in ameliorating diseases that have an underlying inflammatory component

Many diseases associated with ageing have an underlying oxidative stress and accompanying inflammatory component, for example, Alzheimer's disease or atherosclerosis. Reviewed in this manuscript are: the role of oxidative stress in activating the transcription factor nuclear factor kappa B (NFκB), the role of NFκB in activating pro-inflammatory gene transcription, strong oxidants produced by cells, anti-oxidant defense systems, the central role of phase 2 enzymes in the anti-oxidant defense, dietary phase 2 enzyme inducers and evidence that dietary phase 2 enzymes decrease oxidative stress. It is likely that a diet containing phase 2 enzyme inducers may ameliorate or even prevent diseases that have a prominent inflammatory component to them. Research should be directed into the potential therapeutic effects of dietary phase 2 enzyme inducers in ameliorating diseases with an underlying oxidative stress and inflammatory component to them.Key words: Alzheimer's disease, atherosclerosis, diet, glutathione, inflammation, stroke.

Management of oxidative stress in the CNS: the many roles of glutathione

An outline is given of mechanisms that generate oxidative stress and inflammation. Considered are the metabolic mechanisms that give rise to peroxides, the source of strong oxidants; the production of dicarbonyls that interact with macromolecules to form advanced glycation endproducts; and the role that activation of the transcription factor NF(Kappa)B has in the expression of pro-inflammatory genes. Management of oxidative stress is considered by outlining the central role of reduced glutathione (GSH) in peroxide scavenging, dicarbonyl scavenging and activation of NF(Kappa)B. Cellular GSH levels are dictated by the balance between consumption, oxidation of GSH, reduction of oxidized-glutathione, and synthesis. The rate-limiting enzyme in GSH synthesis is L-gamma-glutamyl-L-cysteine synthase, a phase II enzyme. Phase II enzyme inducers are found in many fruits and vegetables. It is suggested that dietary phase II enzyme inducers be investigated for their potential for preventing or retarding the development of degenerative diseases that have an underlying oxidative stress and inflammatory component.

Effects of administration of the standardized Panax ginseng extract G115 on hepatic antioxidant function after exhaustive exercise

The effect of prolonged treatment with the standardized Panax ginseng extract G115 on the antioxidant capacity of the liver was investigated. For this purpose, rats that had received G115 orally at different doses for 3 months and untreated control rats were subjected to exhaustive exercise on a treadmill. A bell-shaped dose response on running time was obtained. The results showed that the administration of G115 significantly increases the hepatic glutathione peroxidase activity (GPX) and the reduced glutathione (GSH) levels in the liver, with a dose-dependent reduction of the thiobarbituric acid reactant substances (TBARS). After the exercise, there is reduced hepatic lipid peroxidation, as evidenced by the TBARS levels in both the controls and the treated animals. The GPX (glutathione peroxidase) and SOD (superoxide dismutase) activity are also significantly increased in the groups receiving G115, compared with the controls. The hepatic transaminase levels, ALT (Alanine-amino-transferase) and AST (Aspartate-amino-transferase), in the recuperation phase 48 h after the exercise, indicate a clear hepatoprotective effect related to the administration of the standardized Panax ginseng extract G115. At hepatic level, G115 increases the antioxidant capacity, with a marked reduction of the effects of the oxidative stress induced by the exhaustive exercise.

Glutathione-linked enzymes in benign and malignant oesophageal tissue

Oxyradicals are involved in multiple mutational events and can contribute to the conversion of healthy cells to cancer cells. Glutathione (GSH) and the GSH-replenishing enzymes keep the antioxidant status of normal cells at a level where they can avert oxyradical derived mutations. The aim of this study was to determine whether in cancer cells the GSH-replenishing, GSH antioxidant and GSH-depleting enzymes were not at appropriate levels and therefore not able to protect cancer cells adequately against oxyradical-induced mutations. Cancer of the oesophagus was chosen since it is the most common gastrointestinal malignancy in South African Blacks. Biopsies and blood from 31 patients with cancer of the oesophagus and 29 non-cancer patients were assessed for these enzymes. The mean activity of the antioxidant and depleting enzyme GSH-peroxidase was elevated significantly by twofold in the cancer tissue compared to normal tissue. However, the activity of the replenishing enzyme GSSG-reductase and the level of the depleting enzyme GSH-s-transferase P1-isoenzyme were significantly reduced by 23% and 33% respectively. As in a previous paper we found that GSH was depleted and gamma-glutamine transpeptidase was diminished in oesophageal cancer. There can be two reasons for GSH depletion. Firstly, elevated GSH-peroxidase will use more GSH in an attempt to cope with the excessive production of oxyradicals as revealed by elevated lipid peroxidation; this was, as shown by us before, elevated sixfold in oesophageal cancer. Secondly, if little replenishment of GSH occurred the level of GSH would become lower. This was confirmed by our findings that the activities of the replenishing enzymes were significantly diminished in oesophageal cancer tissue. Contrary to what was expected, the other depleting enzyme GSH-s-transferase P1 was not elevated in cancer tissue but was significantly lower. However, in the blood of the same patients it was significantly elevated. An explanation for this phenomenon is that, although the production of GST-P1 was enhanced in cancer, it did not show because it was rapidly extruded into the blood by an unknown mechanism operational only in cancer cells.

Selenium deficiency in tissue culture: implications for oxidative metabolism

BACKGROUND

Selenium is located at the catalytic site of the enzyme glutathione peroxidase, and with selenium deficiency the activity of glutathione peroxidase is decreased. Cell culture is an important tool for studying oxidative processes-that is generation and metabolism of oxygen-derived metabolites in the gastrointestinal system. Cell culture is also used to understand the mechanisms of cell injury by oxygen-derived metabolites.

METHODS

To assess the importance of the selenium content of cell culture media, Caco-2 cells and the hepatoma-derived cell lines, Hep3B and HepG2, were grown to confluence and placed in media with various concentrations of selenium. After 7 to 14 days, cells were harvested and assayed for glutathione peroxidase, lactate dehydrogenase, and protein content.

RESULTS

Cells maintained in media unsupplemented with selenium demonstrated a progressive decrease in glutathione peroxidase activity. Cells maintained in media supplemented with various concentrations of selenium demonstrated a dose-dependent increase in glutathione peroxidase until a plateau was reached. The plateau was reached at approximately 400 times the selenium concentration routinely used in cell culture. In the Caco-2 and hepatoma cells, no toxicity was observed at selenium supplementation five times the lowest concentration needed to reach a plateau.

CONCLUSIONS

Cell culture media are routinely deficient in selenium, and cells that are cultured in this medium are deficient in glutathione peroxidase activity. Studies of oxidative metabolism based on cultures deficient in selenium may yield results that could be falsely interpreted. The addition of 1 nM selenium is sufficient for these cell lines to reach a plateau for intracellular glutathione peroxidase activity. These observations may have important ramifications for the study of reactive oxygen metabolite injury in cell culture.

Peroxide-scavenging deficit underlies oligodendrocyte susceptibility to oxidative stress

Previous work showed that the susceptibility of oligodendroglial progenitors to oxidative stress is related to their low reduced-glutathione (GSH) and high iron contents. This suggests that these cells have a poor ability to scavenge peroxides. All peroxides are scavenged by glutathione peroxidase. Glutathione peroxidase activity requires GSH as an electron donor resulting in the formation of oxidized-glutathione. Cellular GSH content is dependent upon synthesis as well as reduction of oxidized-glutathione. The objectives of the present study were to compare several parameters important in the ability to scavenge peroxides between astrocytes and oligodendroglia. Three stages of oligodendroglial differentiation were examined: the proliferative oligodendrocyte progenitor, the proliferative oligodendroblast, and the post-mitotic oligodendrocyte. We demonstrate that oligodendroglia at all stages of differentiation have less than one-half the content of GSH compared to astrocytes. This low level of GSH is due in part to a lower rate of GSH synthesis in oligodendroglia compared to astrocytes and in part to their having only one-half of the glutathione reductase activity of astrocytes. Glutathione peroxidase activity of oligodendroglia is less than 15% of that found in astrocytes. The low GSH and concomitant low glutathione peroxidase activity would tend to maintain peroxides at levels that are dangerously high if iron is released from iron stores. Oligodendroglia have high iron stores, and thus these findings emphasize how vulnerable the oligodendroglial lineage is to perturbations that result in oxidative stress.

Inhibition of lipid peroxidation by selenium in chick embryos

Toxic doses of Selenium (Se) (12.5 and 37.5 micro moles/Kg egg wt.) administered to 14 day old chick embryos reduced the level of lipid peroxides (LPO) significantly both in hepatic and brain tissues. However, the LPO formation was inhibited maximally at early hours after exposure (3 h and 6 h) and it was gradually increased thereafter to normal levels by 48 h. Further, the effect of Se on some of the antioxidant enzymes like glutathione peroxidase (GPx), glutathione transferase (GST), glutathione reductase (GR), superoxide dismutase (SOD) and catalase were studied. In hepatic tissues GPx, GST and SOD activities were increased at 6 h post treatment with no change in the activities of GR and catalase. However, at 48 h GST and catalase activities were found to be increased, while GPx, GR and SOD activities were not affected. In brain at 6 h increase in the activities of GPx, GST, GR and SOD and no change of catalase were observed. At 6 h glutathione (GSH) levels were reduced in both hepatic and brain tissues. Our results suggest that the elevated levels of antioxidant enzymes at early hours were successful in bringing LPO levels back to normal.

Selenium status is decreased in patients with intrinsic asthma

Lowered selenium (Se) status has been observed in asthma patients. An increased production of reactive oxygen species (ROS) owing to inflammatory condition has also been found in these patients and thus antioxidant properties of Se via glutathione peroxidase (GPx) activity are of great importance. Concentrations of Se in plasma and erythrocytes as well as erythrocyte GPx activity in 22 intrinsic asthma patients (five patients; all women were aspirin-sensitive) were compared with those of 33 control subjects. Se concentrations in both plasma and erythrocytes and GPx activity were decreased in intrinsic asthma patients. There were no significant differences in investigated parameters of Se status between aspirin-tolerant and aspirin-intolerant patients within intrinsic asthma group. Significantly high positive correlation between plasma and erythrocyte Se concentrations was found when regarding all subjects as a whole. Se supplementation might be beneficial to patients with intrinsic asthma, which may be at risk of Se deficiency.

Decreased glutathione peroxidase activity in mice in response to nafenopin is caused by changes in selenium metabolism

The activity of selenium-dependent glutathione peroxidase is known to be reduced in the liver of both rats and mice after exposure to nafenopin, as well as other peroxisome proliferators. The mechanism for this down-regulation is not known, but might involve changes in incorporation of selenium into selenoproteins. In this paper we show that both incorporation of selenium into selenoproteins and the level of selenium in liver is reduced in mice treated with nafenopin. The activity of selenium dependent glutathione peroxidase (GPx), as well as incorporation of selenium into its 23 kD subunit were found to be decreased. Contrary to what might have been expected, the decreased GPx activity was detected concomitantly with a slight increase in mRNA levels after 10 days of treatment, while a small decrease in mRNA levels was detected in treated animals after 26 weeks, together with the decrease in GPx-activity. Incorporation of selenium into liver fatty acid binding protein (L-FABP) was also decreased, even though large increases in protein and mRNA levels were detected. Taken together these data suggest that the decrease in GPx-activity in response to nafenopin is due to post-transcriptional mechanisms, involving changes in selenium metabolism.

Cadmium-induced lipid peroxidation and the status of the antioxidant system in rat tissues

Cadmium may induce oxidative damage in different tissues by enhancing peroxidation of membrane lipids and altering the antioxidant system of the cells. The peroxidative damage to the cell membrane may cause injury to cellular components due to the interaction of metal ions with the cell organelles. The treatment with Cd (0.4 mg/kg body wt, ip) significantly increased lipid peroxidation (LPO) in heart within 3 h of the Cd injection, while the increase in kidney and liver followed 6 to 12 h after Cd intoxication. The antioxidant enzymes and other antioxidants provide protection to the cells against oxidative damage. The superoxide dismutase (SOD) activity increased in heart, kidney and liver within 24 h of Cd intoxication. The CAT activity increased significantly in heart 9 h after Cd injection; however, no significant change in CAT activity was observed in kidney and liver tissues. The GSH content and the activity of GR decreased in heart, kidney and liver 72 h after Cd administration, which has been suggested to be the cause for increased LPO in the tissues. The hexose monophosphate (HMP) shunt enzymes generate NADPH required for the activity of GR which may affect the GSH content in the tissues. The generalised decrease in glucose 6-phosphate dehydrogenase (G6PDH) and 6 phospho gluconate dehydrogenase (6PGDH) at 9 h followed by an increase in these enzymes in tissues 72 h after Cd intoxication suggest that the production of NADPH by the HMP shunt is required to reduce the oxidative damage. The results show that Cd induced LPO in the tissues and the condition was partially counteracted by the antioxidant system.

The effect of age and selenium on some biochemical parameters in rat liver

Two age groups, 3 and 15 mo, were used to investigate whether age-associated changes in some parameters related to lipid peroxidation occur in the liver of male Wistar rats and to observe possible effects of dietary selenium supplementation (0.25 and 0.50 ppm) for 12 mo on the same parameters. At these experimental conditions, the most important observation was that peroxidation did not change by aging, at least until 15 mo of age. In addition, the activity of Se-dependent glutathione peroxidase (GSH-Px, EC 1.11.1.9) was higher in the liver of the older animals. It is suggested that the enzyme could have a role in the unchanged hepatic peroxidation observed in aged male rats. On the other hand, an effect of dietary selenium supplementation on those parameters was not observed, probably because the selenium levels were still at an adequate plateau.

Importance of Se-glutathione peroxidase, catalase, and Cu/Zn-SOD for cell survival against oxidative stress

Eukaryotic cells have to constantly cope with highly reactive oxygen-derived free radicals. Their defense against these free radicals is achieved by natural antioxidant molecules but also by antioxidant enzymes. In this paper, we review some of the data comparing the efficiency of three different antioxidant enzymes: Cu/Zn-superoxide dismutase (Cu/Zn-SOD), catalase, and selenium-glutathione peroxidase. We perform our comparison on one experimental model (human fibroblasts) where the activities of these three antioxidant enzymes have been modulated inside the cells, and the repercussion of these changes was investigated in different conditions. We also focus our attention on the protecting role of selenium-glutathione peroxidase, because this enzyme is very rarely studied due to the difficulties linked to its biochemical properties. These studies evidenced that all three antioxidant enzymes give protection for the cells. They show a high efficiency for selenium-glutathione peroxidase and emphasize the fact that each enzyme has a specific as well as an irreplaceable function. They are all necessary for the survival of the cell even in normal conditions. In addition, these three enzymes act in a cooperative or synergistic way to ensure a global cell protection. However, optimal protection is achieved only when an appropriate balance between the activities of these enzymes is maintained. Interpretation of the deleterious effects of free radicals has to be analyzed not only as a function of the amount of free radicals produced but also relative to the efficiency and to the activities of these enzymatic and chemical antioxidant systems. The threshold of protection can indeed vary dramatically as a function of the level of activity of these enzymes.

Antioxidant system in rat testicular cells

The activity of the enzymes involved in the antioxidant defence--superoxide dismutase (SOD), glutathione peroxidase (GPx), reductase (GR), S-transferase (GST)--as well as the glutathione (GSH) levels were measured in different rat testicular cell populations. A differential distribution of these components among testicular cell types was clearly observed. Sertoli and peritubular cells had elevated SOD and GSH-dependent enzyme activities associated with a high GSH content. Compared with the somatic cells, pachytene spermatocytes (PS) and round spermatids (RS) presented a different antioxidant system characterized by higher SOD activity and GSH content associated with very low GSH-dependent enzyme activity. Spermatozoa exhibited the same enzymatic system as PS and RS but were devoid of GSH. Interstitial tissue displayed high GSH content, moderate SOD and GSH-related enzyme activity except for GPx which was very elevated. It is concluded that the different categories of testicular cells probably display a highly variable susceptibility to oxidative stress.

Decreased activity of scavenger enzymes in human hepatocellular carcinoma, but not in liver metastases

To investigate the role of oxygen free radicals in hepatocellular carcinoma we assayed tissue scavenger enzymes (superoxide dismutase and selenium-dependent glutathione peroxidase) in liver homogenate, plasma concentrations of vitamins A and E and the serum selenium level from 19 control patients, 23 cases of hepatocellular carcinoma and 18 cases of metastases to liver from different carcinomas. In hepatocellular carcinoma tissue the enzyme activities were all significantly lower than in control liver and in metastases-bearing liver; the enzyme activities of the latter tissues were not different from control liver. In contrast, normal liver adjacent to the hepatocellular carcinoma had decreased activity of superoxide dismutase. Serum selenium concentrations were significantly decreased in patients with hepatocellular carcinoma and those with liver metastases, while vitamin A was significantly decreased only in the former. These findings suggest that hepatocellular carcinoma develops in liver with severe impairment of cellular antioxidant systems, since, in patients with liver metastases from different cancers, despite low selenium concentrations, cellular scavenger enzymes have normal activities.

Intracellular catalase inhibition does not predispose rat heart to ischemia-reperfusion and hydrogen peroxide-induced injuries

The objective of this study was to determine whether inhibition of intracellular catalase would decrease the tolerance of the heart to ischemia-reperfusion and hydrogen peroxide-induced injuries. Isolated bicarbonate buffer-perfused rat hearts were used in the study. Intracellular catalase was inhibited with 3-amino-1,2,4-triazole (ATZ, 1.5 g/kg body weight, two hours prior to heart perfusion). In the ischemia-reperfusion protocol, hearts were arrested with St. Thomas'II cardioplegic solution, made ischemic for 35 min at 37 degrees C, and reperfused with Krebs-Henseleit buffer for 30 min. The extent of ischemic injury was assessed using postischemic contractile recovery and lactate dehydrogenase (LDH) leakage into reperfusate. In the hydrogen peroxide infusion protocol, hearts were perfused with increasing concentrations of hydrogen peroxide (inflow rates 0.05-1.25 mumol/min). Inhibition of catalase activity (30.4 +/- 1.8 mU/mg protein in control vs 2.4 +/- 0.3 mU/mg in ATZ-treated hearts) affected neither pre-ischemic aerobic cardiac function nor post-ischemic functional recovery and LDH release in hearts subjected to 35 min cardioplegic ischemic arrest. Myocardial contents of lipid hydroperoxides were similar in control and ATZ-treated animals after 20 min aerobic perfusion, ischemia, and ischemia-reperfusion. During hydrogen peroxide perfusion, there was an increase in coronary flow rate followed by an elevation in diastolic pressure and inhibition of contractile function in comparison with control hearts. The functional parameters between control and ATZ-treated groups remained unchanged. The concentrations of myocardial lipid hydroperoxides were the same in both groups. We conclude that inhibition of myocardial catalase activity with ATZ does not predispose the rat heart to ischemia-reperfusion and hydrogen peroxide-induced injury.

Role of selenium-dependent glutathione peroxidase in protecting against t-butyl hydroperoxide-induced damage in hepatocytes

The role of the selenoenzyme glutathione peroxidase (Se-GSHPx) in protecting against oxidative injury was studied in hepatocytes isolated from rats fed either a low-selenium (Se-) or a selenium-adequate (Se+, control) diet. In rats fed Se- diet for eight weeks the selenium content of plasma and liver was lowered to 15 and 8%, respectively. No Se-GSHPx and only 5% of total GSHPx activity was detected in Se- hepatocytes. However, the Se- hepatocytes were as resistant as the Se+ cells to oxidative injury by 0.8 mM tert-butyl hydroperoxide (t-BuOOH), or 0.2 mM t-BuOOH plus 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), an inhibitor of oxidized glutathione (GSSG) reductase. Only at 1.5 mM t-BuOOH or at 0.5 mM t-BuOOH with BCNU were cell damage and lipid peroxidation more evident in Se- cells. At all t-BuOOH concentrations used the depletion of cellular glutathione (GSH) was similar in magnitude in Se- and Se+ cells, but Se+ cells released more glutathione (mainly GSSG), obviously due to their higher Se-GSHPx activity. These results suggest that hepatocytes devoid of Se-GSHPx activity maintain a high capacity to resist peroxidative attack, either via residual (non-Se)GSHPx activity or other compensatory GSH-associated detoxication mechanisms.

Prostaglandin synthesis is increased in selenium supplemented human mesangial cells despite suppression of phospholipase A2-activity

Antioxidants play an important role in the regulation of phospholipid hydrolysis and arachidonate metabolism. Supplementation of cultured human mesangial cells with selenium resulted in suppression of phospholipase A2-activity and significantly increased production of three major prostaglandins. However, prostacyclin synthesis benefits most from selenium supplementation, suggesting that there is a specific action of selenium-dependent glutathione peroxidase on this pathway. Like in endothelial cells, production of platelet activating factor is significantly inhibited by selenium supplementation.

Dehydroepiandrosterone and a beta-agonist, energy transducers, alter antioxidant enzyme systems: influence of chronic training and acute exercise in rats

We examined the influence of dehydroepiandrosterone (DHEA), a beta-agonist, and exercise training on enzymes that detoxify toxic oxygen species. Feeding 0.4% DHEA decreased hepatic cytosolic (c) selenium-dependent glutathione peroxidase (GPX), (-26%, P less than 0.0001) and increased hepatic mitochondrial (m) Mn superoxide dismutase (SOD), (+38%, P less than 0.001). DHEA decreased myocardial c-GPX (-21%, P less than 0.05) when compared to a beta-agonist (beta A; L644969 Merck and Co.) fed at 5 ppm but neither differed from the Control (C). In contrast, the beta A increased hepatic m-GPX (+25%, P less than 0.05). In skeletal muscle, DHEA and beta A decreased muscle c-GPX by 20 and 12%, respectively (P less than 0.0009). DHEA increased both muscle (+20%, P less than 0.01) and myocardial (+20%, P less than 0.05) c-glutathione S-transferase (GST) over beta A (+20%, P less than 0.01) but neither was significantly different from C. Similar to DHEA, chronic training (Tr) (1 h/day, 5 days/week at 27 m/min, 15% grade on treadmill) decreased hepatic c-GPX (-16%, P less than 0.003). Tr elevates muscle c-GPX (+36%, P less than 0.05) in C. Tr increased myocardial c-GPX by 28% in the beta A-treated rats, whereas Tr decreased myocardial c-GPX by 22% in the C (P less than 0.05, interaction). One hour of acute exercise (Ex) (70% VO2 max relative work load) decreased hepatic homogenate catalase (-12%, P less than 0.02) and increased hepatic m-Mn SOD (+28%, P less than 0.03). Ex decreased myocardial c-GST (P less than 0.05) only in the DHEA-treated rats. DHEA and Tr may improve efficiency of oxygen utilization at the tissue level with lower antioxidant enzyme activity in liver and locally protective up-regulation in muscle. beta A stresses oxygen utilization systems and liver responds by up-regulation of antioxidant enzymes. The increase in myocardial c-GPX activity in the beta A-treated group may be a protective effect against indirect catecholamine-induced myocardial necrosis which results from free radical generation.

The relative roles of the glutathione redox cycle and catalase in the detoxification of H2O2 by cultured rabbit lens epithelial cells

The relative roles of the glutathione redox cycle and catalase in the detoxification of H2O2 were investigated in cultured rabbit lens epithelial cells. Exposure of cells to H2O2 was carried out following inhibition of either of the two antioxidant systems. Two different procedures were used to expose the cells to extracellular H2O2, one in which a low, steady state level of 0.025 mM H2O2 was maintained in the culture medium with the use of glucose oxidase and the other in which H2O2 was added to the medium as a single pulse at levels ranging from 0.03 to 0.5 mM. When lens cells were treated with a low, steady state level of H2O2, the glutathione redox cycle was the primary means of defense against oxidative damage. Cells with fully active catalase but with inhibited glutathione reductase were not able to resist the cytotoxic effects of a 0.025 mM level of extracellular H2O2. Under these conditions the cells were nearly completely depleted of reduced glutathione within 15 min. The cellular damage observed after 1.5 hr of culture included loss of cell-to-cell contact, rounding up of the cells and formation of numerous blebs. In contrast, cells with completely inhibited catalase but with an unimpaired glutathione redox cycle suffered few damaging effects from a 3-hr exposure to 0.025 mM H2O2. When lens cells were pulsed with a single challenge of 0.5 mM H2O2, both the glutathione redox cycle and catalase were found to be essential for survival of the cells. While control cells were able to withstand the pulse of H2O2, cells with impaired activities of either the glutathione redox cycle or catalase were killed. Control cells treated with 0.5 mM H2O2 may have been protected from damage by the fact that the cellular level of GSH never dropped below 35% of normal. The cause of cell death following inhibition of catalase appeared to be related to an inability of the cells to remove peroxide from the culture medium, at a rapid rate, following the H2O2-pulse. Although cells with impaired glutathione reductase activity removed H2O2 from the medium at a rate comparable to that of control cells (due to uninhibited catalase activity), they did not survive the challenge.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the role of lipid peroxidation in the acute toxicity of TCDD in rats

Lipid peroxidation has been shown to be enhanced following exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), but its role in TCDD toxicity is unclear. The present study was undertaken to further elucidate the relations between lipid peroxidation and TCDD lethality. A time course and dose-response experiment in Long-Evans (L-E; LD50 ca. 10 micrograms/kg) and Han/Wistar (H/W; LD50 greater than 3000 micrograms/kg) rats showed that hepatic lipid peroxidation, measured as the amount of thiobarbituric acid-reactive substances (TBA-RS), was induced by TCDD dose-dependently in L-E, but not in H/W rats. Hepatic glutathione peroxidase activity was suppressed in much the same manner in both strains. Lipid peroxidation correlated with body weight loss in L-E rats alone. When 500 micrograms/kg of TCDD was given to L-E rats, lipid peroxidation increased about 3-fold on Day 11 in the liver, while no change was seen in cardiac or renal TBA-RS. The pair-fed controls did not survive the 11-day test period and exhibited gastrointestinal hemorrhages. At 6 days, liver atrophy and elevated (over 2-fold) TBA-RS values were recorded in pair-fed controls but not in their TCDD-treated counterparts. TCDD decreased hepatic glutathione peroxidase activity by almost 50% at 6 days, while pair-feeding was without effect. Liver morphology was different between TCDD-treated and pair-fed rats. Moreover, the livers of TCDD-treated L-E rats contained much higher concentrations of probably peripheral fat-derived fatty acids than did the livers of pair-fed or ad libitum control rats. Restricted feeding over 6 days induced hepatic lipid peroxidation more in H/W than in L-E rats. Endotoxin increased liver TBA levels similarly in both strains having an additive effect with high doses of TCDD in H/W rats. Added as a 0.5% concentration in chow, butylated hydroxyanisole (BHA), but not ethoxyquin, tended to increase survival rate and time in L-E rats exposed to 20 micrograms/kg of TCDD; at 50 micrograms/kg the only survivor was again in the BHA group. However, neither antioxidant had any effect on initial body weight loss. It is concluded that lipid peroxidation mainly arises as a secondary phenomenon in TCDD toxicity, is not the cause of the typical histopathological liver lesion, but may contribute to lethality.

Aortic antioxidant defence mechanisms: time-related changes in cholesterol-fed rabbits

In 24 rabbits fed a hyperlipidic diet (0.5% cholesterol, 5% lard and 5% peanut oil) for 10 (group A1), 30 group B1) and 60 days, (Group C1), compared to 24 control rabbits fed a standard diet for the same periods, antioxidant defence system (total superoxide dismutase, catalase, total thiol compounds selenium-dependent and selenium-independent glutathione peroxidase, glutathione reductase, glutathione transferase) and lipid peroxidation (thiobarbituric acid-reactive substances) in the aortic wall were tested. The percent of intima with grossly apparent atherosclerosis, is assessed by staining with the lipophilic dye Sudan IV, was negligible in group A1, but increased progressively in groups B1 (22.7-6.7%) and C1 (56.8-8.8%). Compared to the controls, a significant rise in superoxide dismutase activity was observed after 30 days of hyperlipidic diet, with a further marked increase at 60 days. Total thiol compounds and selenium-dependent glutathione peroxidase activity rose progressively from 10 to 30 and 60 days in cholesterol-fed rabbits. On the contrary, catalase, glutathione reductase and glutathione transferase activities significantly decreased in all experimental groups. Selenium-independent glutathione peroxidase activity was not detectable. Thiobarbituric acid-reactive substances increased about 3 times in hyperlipidemic rabbits. In conclusion, the changes in aortic antioxidant defence mechanisms and lipid peroxidation precede the massive vascular lipid infiltration in cholesterol-fed rabbits; some antioxidant mechanisms are stressed (superoxide, dismutase, glutathione peroxidase, total thiol compounds), whereas others are depressed (catalase, glutathione reductase, and glutathione transferase), thus potentially reducing or increasing vascular susceptibility to oxidative injury.

The protective effects of glutathione against methylmercury cytotoxicity

Mouse neuroblastoma cells exposed to 2.5 and 5.0 microM methylmercury for 24 h appeared rounded with the loss of processes. Immunohistochemical staining directed against beta-tubulin revealed severe alterations in microtubular architecture. Non-membrane-bound condensation product was visualized ultrastructurally in the treated cells and appeared similar to what was seen histochemically. Reduced and oxidized glutathione levels suggest that methylmercury may manifest its deleterious effects via oxidation of tubulin sulfhydryls, and by alterations due to peroxidative injury. Cells exposed to methylmercury showed a decrease in glutathione peroxidase activity. Simultaneous administration of 10 mM glutathione with 2.5 and 5.0 microM methylmercury dramatically prevented cell injury.

Coisolation of glutathione peroxidase, catalase and superoxide dismutase from human erythrocytes

Glutathione peroxidase (GSH-Px; glutathione: hydrogen peroxide oxidoreductase; EC 1.11.1.9), catalase (H2O2: H2O2 oxidoreductase; EC 1.11.1.6) and superoxide dismutase (superoxide: superoxide oxidoreductase; EC 1.15.1.1) were coisolated from human erythrocyte lysate by chromatography on DEAE-cellulose. Glutathione peroxidase was separated from superoxide dismutase and catalase by thiol-disulfide exchange chromatography and then purified to approximately 90% homogeneity by gel permeation chromatography and dye-ligand affinity chromatography. Catalase and superoxide dismutase were separated from each other and purified further by gel permeation chromatography. Catalase was then purified to approximately 90% homogeneity by ammonium sulfate precipitation and superoxide dismutase was purified to apparent homogeneity by hydrophobic interaction chromatography. The results for glutathione peroxidase represent an improvement of approximately 10-fold in yield and 3-fold in specific activity compared with the established method for the purification of this enzyme. The yields for superoxide dismutase and catalase were high (45 mg and 232 mg, respectively, from 820 ml of washed packed cells), and the specific activities of both enzymes were comparable to values found in the literature.

Oxidation of glutathione during hydroperoxide metabolism in isolated hepatocytes of rainbow trout (Salmo gairdneri)

Freshly isolated rainbow trout hepatocytes were exposed to tert-butyl hydroperoxide (BuOOH), a substrate for glutathione peroxidase. BuOOH at a concentration approximately equimolar (1 mM) with intracellular reduced glutathione (GSH) caused a reversible increase in intracellular glutathione disulphide (GSSG) but did not compromise cell viability or damage membrane lipids. BuOOH at 10 mM caused a large irreversible increase in intracellular GSSG followed by efflux into the medium. Considerable leakage of lactate dehydrogenase and loss of highly unsaturated fatty acids, particularly docosahexaenoic acid also occurred. Dependence of hydroperoxide removal on flux through the hexose monophosphate pathway was suggested by the increased release of (14)CO2 from [1-(14)C] glucose from hepatocytes incubated with BuOOH.

A comparison of the effects of dietary cadmium on heart and kidney antioxidant enzymes: evidence for the greater vulnerability of the heart to cadmium toxicity

This study demonstrates the greater susceptibility of the heart as compared to the kidney to cadmium in the presence of high dietary selenium. Male weanling rats were fed an adequate-copper low-selenium feed supplemented with 0, 10 or 50 ppm copper with or without 50 ppm dietary cadmium for 7 weeks. All rats received 0.5 ppm selenium in their drinking water. Cadmium treatment resulted in histopathological lesions in the heart, but not in the kidney. Although cadmium treatment resulted in more extensive effects on glutathione peroxidase and superoxide dismutase in the heart as compared to the kidney, no increase in peroxidation was noted in either organ, suggesting that cadmium cardiotoxicity can be dissociated from tissue peroxidation. Mean cadmium concentrations in the heart ranged from 0.55 to 1.22 micrograms cadmium g-1 tissue, wet weight, and in the kidney from 11.53 to 21.04 micrograms cadmium g-1 tissue, wet weight. In both tissues examined, cadmium levels were influenced by dietary copper and heart cadmium concentrations did not correlate with either the biochemical or histological lesions observed. Thus, tissue cadmium levels alone may not be adequate for predicting cadmium toxicity.

Cadmium-induced alterations in ocular trace elements. Influence of dietary selenium and copper

The present report demonstrates, for the first time, that feeding rats 50 ppm cadmium for just 7 wk results in detectable levels of cadmium in the eye of rats. Furthermore, these ocular cadmium concentrations affect significant alterations in the levels of the essential trace elements selenium, calcium, iron, and copper in the eye. Rats were fed a low-selenium (less than 0.02 ppm selenium), high-copper basal diet (50 ppm copper) supplemented with 0, 0.1, and 0.5 ppm selenium. The animals were either untreated or treated with 50 ppm cadmium admixed with their feed. Cadmium treatment resulted in significant reductions (up to 50%) in ocular selenium. Furthermore, rats fed the basal diet and given 100 ppm cadmium via their feed for 6 wk exhibited a 69% reduction in the activity of the selenoenzyme, glutathione peroxidase, in the eye. Cadmium treatment also resulted in reductions of up to 50% in ocular calcium, irrespective of dietary selenium supplementation. Iron levels were increased by 30% in rats fed the low-selenium diet and decreased by as much as 40% in rats fed the selenium-supplemented diets, compared to animals fed identical levels of selenium without cadmium. Ocular copper levels were significantly increased only in rats fed the low-selenium diet and treated with cadmium. Ocular zinc levels were not significantly affected by dietary cadmium or selenium.

Selenium-independent glutathione peroxidase activity associated with glutathione S-transferase from the housefly, Musca domestica

1. A glutathione S-transferase having Se-independent glutathione peroxidase activity was isolated from 100,000 g supernatant from housefly homogenate. 2. The specific activity of the partially purified Se-independent glutathione peroxidase was 1776 nmol NADPH oxidized/min/mg protein, representing an 87-fold purification. 3. The Mr of this enzyme was estimated to be 37,000 and 26,000 by gel filtration chromatography and gel electrophoresis, respectively. 4. Selenium-dependent glutathione peroxidase activity could not be detected in this same supernatant. 5. Se-independent glutathione peroxidase activity should be considered in future studies of the insect antioxidant defense system.

Catalase is needed to avoid tissue peroxidation in Rana perezi in normoxia

1. In order to clarify the relative role of catalase (CAT) and glutathione peroxidases (GSH-Px) at normal and high O2 tensions, Rana perezi frogs were chronically treated with aminotriazole (AT), hyperoxia, or both. 2. A 100% survival was observed with both treatments. Hyperoxia increased liver catalase and kidney TBA-RS and decreased GSH-Px. 3. AT caused quantitatively higher alterations than hyperoxia in both organs: CAT was depleted, TBA-RS increased (114% in kidney) and GSH-Px decreased. 4. It is concluded that in Rana perezi (a) CAT, in spite of its much higher KM and Vmax in relation to GSH-Px, is needed to avoid oxidative stress even in normoxia; (b) normoxic tissues have significative amounts of H2O2; (c) GSH-Px does not compensate the lack of CAT.

Tyrosyl-tRNA synthetase from baker's yeast. Order of substrate addition, discrimination of 20 amino acids in aminoacylation of tRNATyr-C-C-A and tRNATyr-C-C-A(3'NH2)

The order of substrate addition to tyrosyl-tRNA synthetase from baker's yeast was investigated by bisubstrate kinetics, product inhibition and inhibition by dead-end inhibitors. The kinetic patterns are consistent with a random bi-uni uni-bi ping-pong mechanism. Substrate specificity with regard to ATP analogs shows that the hydroxyl groups of the ribose moiety and the amino group in position 6 of the base are essential for recognition of ATP as substrate. Specificity with regard to amino acids is characterized by discrimination factors D which are calculated from kcat and Km values obtained in aminoacylation of tRNATyr-C-C-A. The lowest values are observed for Cys, Phe, Trp (D = 28,000-40,000), showing that, at the same amino acid concentrations, tyrosine is 28,000-40,000 times more often attached to tRNATyr-C-C-A than the noncognate amino acids. With Gly, Ala and Ser no misacylation could be detected (D greater than 500,000); D values of the other amino acids are in the range of 100,000-500,000. Lower specificity is observed in aminoacylation of the modified substrate tRNATyr-C-C-A(3'NH2) (D1 = 500-55,000). From kinetic constants and AMP-formation stoichiometry observed in aminoacylation of this tRNA species, as well as in acylating tRNATyr-C-C-A hydrolytic proof-reading factors could be calculated for a pretransfer (II 1) and a post-transfer (II 2) proof-reading step. The observed values of II 1 = 12-280 show that pretransfer proof-reading is the main correction step whereas post-transfer proof-reading is marginal for most amino acids (II 2 = 1-2). Initial discrimination factors caused by differences in Gibbs free energies of binding between tyrosine and noncognate amino acids are calculated from discrimination and proof-reading factors. Assuming a two-step binding process, two factors (I1 and I2) are determined which can be related to hydrophobic interaction forces. The tyrosine side chain is bound by hydrophobic forces and hydrogen bonds formed by its hydroxyl group. A hypothetical model of the amino acid binding site is discussed and compared with results of X-ray analysis of the enzyme from Bacillus stearothermophilus.

Antioxidant and free radical-scavenging enzymes in chronically ethanol-consuming rats: controversy over hepatic lipid peroxidation

In rats given ethanol 20% (v/v) in drinking water the hepatic antioxidant enzymes, superoxide dismutase (SOD), catalase and glutathione peroxidase were assayed at the end of 4 and 10 months of ethanol consumption. Simultaneously hepatic lipid peroxidation was monitored. At 4 months SOD and catalase were unaffected, while glutathione peroxidase was decreased by 48%. By the end of 10 months SOD had declined by 16% and glutathione peroxidase activity increased by 49%, while catalase again remained stable. However, hepatic lipid peroxidation was not significantly affected throughout the study. The controversy in the literature over the conflicting results of hepatic lipid peroxidation in chronically ethanol-fed rats is discussed in the light of mode, dose, duration of ethanol consumption, nutritional status of the rat, and primacy of glutathione peroxidase.