Influence of vitamin E and selenium on glutathione-dependent protection against microsomal lipid peroxidation

Does the Selenium (SE) Level and Se-Dependent Enzyme Activity in Blood Plasma Correlate with Human Lymphocyte Subpopulations and Function?

Recent literature data on the effects of Se on subpopulations of T lymphocytes, on autologous mixed lymphocyte reaction (AMLR) and on natural killer (NK) cell cytotoxicity are limited or poorly defined. In healthy volunteers we have estimated se levels, glutathione peroxidase (GSH-Px) activity and lipid peroxide levels in human plasma and simultaneously, the subpopulations of T lymphocytes, proliferation in AMLR, and activity of NK cells.

We found a significantly positive correlation between the selenium level and GSH-Px activity. The proliferative response in AMLR significantly correlated with plasma selenium levels but not with GSH-Px activity. NK cytotoxicity, subpopulations of T lymphocytes, and lipid peroxide levels did not correlate with both selenium concentration and GSH-Px activity. We suppose that the effect of Se on the proliferation of suppressor T lymphocytes (Ts) in AMLR is not mediated through GSH-Px activity and fluctuations of Se concentration within a physiological range in healthy persons do not affect NK cytotoxicity.

Hydrogen Sulfide and Cellular Redox Homeostasis

Intracellular redox imbalance is mainly caused by overproduction of reactive oxygen species (ROS) or weakness of the natural antioxidant defense system. It is involved in the pathophysiology of a wide array of human diseases. Hydrogen sulfide (H₂S) is now recognized as the third “gasotransmitters” and proved to exert a wide range of physiological and cytoprotective functions in the biological systems. Among these functions, the role of H₂S in oxidative stress has been one of the main focuses over years. However, the underlying mechanisms for the antioxidant effect of H₂S are still poorly comprehended. This review presents an overview of the current understanding of H₂S specially focusing on the new understanding and mechanisms of the antioxidant effects of H₂S based on recent reports. Both inhibition of ROS generation and stimulation of antioxidants are discussed. H₂S-induced S-sulfhydration of key proteins (e.g., p66Shc and Keap1) is also one of the focuses of this review.

Multiple roles of microsomal glutathione transferase 1 in cellular protection: a mechanistic study

The aim of this study was to investigate the involvement of membrane-bound microsomal glutathione transferase 1 (MGST1) in cellular resistance against oxidative stress as well as its mechanism of protection. MGST1 is ubiquitously expressed and predominantly located in the endoplasmic reticulum and outer mitochondrial membrane. Utilizing MCF7 cells overexpressing MGST1 we show significant protection against agents that are known to induce lipid peroxidation (e.g., cumene hydroperoxide and tert-butylhydroperoxide) and an end-product of lipid peroxidation (e.g., 4-hydroxy-2-nonenal). Furthermore, our results demonstrate that MGST1 protection can be enhanced by vitamin E when toxicity depends on oxidative stress, but not when direct alkylation is the dominant mechanism. Mitochondria in MGST1-overexpressing cells were shown to be protected from oxidative insult as measured by calcium loading capacity and respiration. MGST1 induces cellular resistance against cisplatin. Here we used vitamin E to elucidate whether oxidative stress caused by cisplatin is significant for cell toxicity. The results indicate that oxidative stress and induction of lipid peroxidation are not the most prominent toxic mechanism of cisplatin in our cell system. We thus conclude that MGST1 protects cells (and mitochondria) by both conjugation and glutathione peroxidase functions. A new protective mechanism against cisplatin is also indicated.

Dietary docosahexaenoic acid-induced generation of liver lipid peroxides is not suppressed further by elevated levels of glutathione in ODS rats

OBJECTIVES

We examined the effects of ascorbic acid (AsA) and glutathione (GSH; experiment 1) and of GSH in acetaminophen-fed rats (experiment 2) on dietary docosahexaenoic acid (DHA)-induced tissue lipid peroxidation.

METHODS

In experiment 1, AsA-requiring Osteogenic Disorder Shionogi/Shi-od/od (ODS) rats were fed soybean protein diets containing DHA (10.0% total energy) and AsA at 50 (low) or 300 (normal) mg/kg without (low) or with (normal) methionine at 2 g/kg for 32 d. In experiment 2, ODS rats were fed diets containing DHA (7.8% total energy) and acetaminophen (4 g/kg) with different levels of dietary methionine (low, moderate, high, and excessive at 0, 3, 6, and 9 g/kg, respectively) for 30 d. Tissue lipid peroxides and antioxidant levels were determined.

RESULTS

In experiment 1, liver lipid peroxide levels in the low-AsA group were lower than those in the normal-AsA group, but kidney and testis lipid peroxide levels in the low-AsA group were higher than those in the normal-AsA group. Dietary methionine tended to decrease tissue lipid peroxide levels but did not decrease vitamin E (VE) consumption. In experiment 2, a high level of methionine (6 g/kg) decreased liver lipid peroxide levels and VE consumption. However, generation of tissue lipid peroxides and VE consumption were not decreased further by a higher dose of methionine (9 g/kg).

CONCLUSIONS

Higher than normal levels of dietary methionine are not necessarily associated with decreased dietary DHA-induced generation of tissue lipid peroxides and VE consumption except that the GSH requirement is increased in a condition such as acetaminophen feeding.

Di-(2-ethylhexyl) phthalate induces severe aspermatogenesis in mice, however, subsequent antioxidant vitamins supplementation accelerates regeneration of the seminiferous epithelium

Di-(2-ethylhexyl) phthalate (DEHP), now regarded as an endocrine disruptor, can experimentally induce spermatogenic disturbance in laboratory animals. Our previous study demonstrated that antioxidant vitamins (vitamins C and E) supplementation during DEHP-treatment significantly protected the rat seminiferous epithelium from DEHP-gonadotoxicity. In the present study, we gave these antioxidant vitamins to mice already having fully developed aspermatogenesis because of DEHP to determine whether or not the vitamins can cure the injured seminiferous epithelium. CD-1 male mice were fed on a DEHP-containing diet for 15 days and then fed on the DEHP-free normal diet with or without supplementation of vitamins C and E in drinking water for another 50 days. The results showed that severe aspermatogenesis was induced by the DEHP-treatment but that the damaged seminiferous epithelium spontaneously recovered whether the vitamins were provided or not. This indicates that the DEHP-induced aspermatogenesis was reversible. However, the supplementation of antioxidant vitamins significantly accelerated regeneration of the injured seminiferous epithelium, suggesting that the vitamins have a therapeutic effect on DEHP-induced aspermatogenesis.

Erythropoiesis: Comparison of Cytotoxic Aldehyde Generation in Beta-Thalassemia Patients Chelated with Deferoxamine or Deferiprone (L1) Versus NO Chelation

The mechanism of iron-induced organ failure in iron overload disorders is not known, but it is conjectured that excess iron-catalyzed free radical generation contributes to organ damage. We hypothesized that free radical generation, quantified by the presence of 20 separate cytotoxic aldehydes in plasma, would be significantly increased in non-chelated beta-thalassemia major patients, in comparison to those chelated with either deferiprone (L1) or deferoxamine (desferal). We also report on red cell glutathione peroxidase activity in these patient groups, an enzyme involved in averting the damaging effects of free radicals. Ten patients were chelated with nightly subcutaneous infusions of desferal and 10 received the experimental oral chelator L1. Body iron burden was assessed by serum ferritin and hepatic iron concentrations. In comparison to non-chelated controls, significant decreases of 62% and 64% in total cytotoxic aldehyde concentrations were observed in patients chelated with desferal and L1, respectively (p < 0.001). Significantly lower red cell glutathione peroxidase activity was also observed in non-chelated controls, in comparison to those chelated with either desferal or L1 (p < 0.001). This is the first report on the concentrations of cytotoxic aldehydes in non-chelated beta-thalassemia major patients, and the first to report on the effects of L1 against cytotoxic aldehyde formation in plasma of patients with iron-overload.

Spermatogenic disturbance induced by di-(2-ethylhexyl) phthalate is significantly prevented by treatment with antioxidant vitamins in the rat

Phthalate esters, now regarded as endocrine disruptors, are widely used in the plastics industry. In particular, di-(2-ethylhexyl) phthalate (DEHP) is produced in large quantities, and is used in blood storage bags, catheters and haemodialysis instruments. Previous studies have demonstrated that treatment of rats with DEHP induces testicular atrophy with liver enlargement, although the precise nature and mechanism of the action of DEHP on these organs remains unclear. In the present study, we produced an experimental model of DEHP-induced spermatogenic disturbance in rats by feeding them a DEHP-containing diet. Liver enlargement occurred in rats fed either a 1 or 2% DEHP-containing diet. However, testicular atrophy accompanied by aspermatogenesis was induced by feeding with the 2% but not with the 1% DEHP-containing diet. This suggests that the critical DEHP dose for gonadotoxicity is higher than that for hepatotoxicity. Using the 2% DEHP-dose, the effect of simultaneous administration of antioxidant vitamins (= vitamins C and E) was next examined. It was found that the vitamin supplementation significantly prevented the testicular injury. The results suggest that antioxidant vitamins can protect the testes from DEHP-toxicity.

Effect of dietary vitamin E on antioxidant status and antioxidant enzyme activities in Sprague-Dawley rats

The effect of dietary vitamin E on plasma, red blood cells (RBC), hepatic antioxidant status, and antioxidant enzyme activities was investigated. Three groups of six Sprague-Dawley rats were fed 0, 100, or 1,500 ppm vitamin E for eight weeks. Plasma alpha-tocopherol level was increased significantly by increasing dietary vitamin E (p < 0.05). Plasma lipid peroxidation (thiobarbituric acid-reactive substances) stimulation by 1 mM t-butyl hydroperoxide was correlated with dietary vitamin E level and was significantly greater in rats fed no vitamin E than in rats fed 100 or 1,500 ppm vitamin E (p < 0.05). RBC reduced glutathione (GSH) level was positively correlated with dietary vitamin E and was significantly greater in rats fed 1,500 ppm vitamin E than in rats fed 0 or 100 ppm vitamin E (p < 0.05). RBC oxidized glutathione was negatively correlated with dietary vitamin E. GSH redox status was expressed as the GSH-to-total GSH ratio; the ratio was also positively correlated with dietary vitamin E and was significantly greater in rats fed 1,500 ppm vitamin E than in rats fed no vitamin E (p < 0.05). For antioxidant enzymes, superoxide dismutase activity in hepatic cytosolic fraction was significantly greater in rats fed 1,500 ppm vitamin E than in rats fed 100 ppm vitamin E. Hepatic GSH reductase activity was significantly greater in rats fed 100 ppm vitamin E than in rats fed no vitamin E (p < 0.05). Dietary vitamin E had no effect on plasma vitamin C and protein thiol levels. In the systems studied, results indicated that dietary vitamin E selectively influences plasma vitamin E level, RBC GSH status, and hepatic cytosolic superoxide dismutase and GSH reductase activities.

Glutathione-dependent factors and inhibition of rat liver microsomal lipid peroxidation

The effects of reduced glutathione (GSH) and glutathione disulfide (GSSG) on lipid peroxidation were investigated in rat liver microsomes containing deficient or adequate amounts of alpha-tocopherol (alpha-TH). Rates of formation of thiobarbituric acid reactive substances (TBARS) as well as rates of consumption of alpha-TH and O2 were decreased by GSH and were more pronounced in the NADPH-dependent assay system than in the ascorbate-dependent system. The GSH-dependent inhibition of lipid peroxidation was potentiated by GSSG in the NADPH-dependent assay system, but it had no effect in the nonenzymatic system. Diphenyliodonium chloride, an inhibitor of NADPH cytochrome P-450 reductase, completely prevented lipid peroxidation in the NADPH-dependent assay system whereas it had no effect on the ascorbate-dependent system. This is further evidenced by the fact that purified rat liver microsomal NADPH cytochrome P-450 reductase (EC 1.6.2.4) was inhibited approximately 24% and 52% by 5 mM GSH and 5 mM GSH + 2.5 mM GSSG, respectively. Glutathione disulfide alone had no effect on reductase activity. Similarly, other disulfides such as cystine, cystamine and lipoic acid were without effect on reductase activity. These results clearly delineate different mechanisms underlying the combined effects of GSH and GSSG on microsomal lipid peroxidation in rat liver. One mechanism involves recycling of microsomal alpha-TH by GSH during oxidative stress via a labile protein, ostensibly associated with "free radical reductase" activity. A second glutathione-dependent mechanism appears to be mediated through the inhibition of NADPH cytochrome P-450 reductase. The enhanced inhibition by GSH + GSSG of microsomal lipid peroxidation in the NADPH-dependent assay system suggests suppression of the initiation phase at the level of NADPH cytochrome P-450 reductase which is independent of microsomal alpha-TH.

Simultaneous determination of alpha-tocopherol and alpha-tocopherolquinone by high-performance liquid chromatography and coulometric detection in the redox mode

A simple, selective and highly sensitive assay method for the simultaneous determination of alpha-tocopherol and alpha-tocopherolquinone in plasma or erythrocyte membrane by high-performance liquid chromatography (HPLC) with a series of multiple coulometric working electrodes (CWE) was investigated. For good separation of alpha-tocopherol and alpha-tocopherolquinone, an MC MEDICAL C18 reversed-phase column and a mobile phase consisting of 96% methanol [methanol-HPLC-grade distilled water (96:4, v/v)] with 40 mM sodium perchlorate were used. Also, selective, highly sensitive and simultaneous detection of these substances was performed in redox mode using a series of four CWE. In this detection mode, the first, second and third CWE were set at -0.45 V for pre-reaction and to prevent interference, the fourth CWE was used as an electrode for actual measurement with its potential set at +0.40 V against a palladium reference electrode. The detection limits were 50-100 pg. Excellent chromatograms of alpha-tocopherol and alpha-tocopherolquinone were obtained within 8 min. The usefulness of reversed-phase HPLC with the redox detection mode was confirmed by application to the determination of the concentrations of alpha-tocopherol and alpha-tocopherolquinone in a crude ethanol-hexane extract of rat plasma or erythrocyte membrane. These findings suggest that reversed-phase HPLC with the redox detection mode using a series of four CWE is applicable to study the preventive effect of alpha-tocopherol on lipid peroxidation.

Activation of NF-kappa B in human skin fibroblasts by the oxidative stress generated by UVA radiation

We have examined the role of the nucleus and the membrane in the activation of nuclear factor (NF)-kappa B by oxidant stress generated via the UVA (320-380 nm) component of solar radiation. Nuclear extracts from human skin fibroblasts that had been irradiated with UVA at doses that caused little DNA damage contained activated NF-kappa B that bound to its recognition sequence in DNA. The UVA radiation-dependent activation of NF-kappa B in enucleated cells confirmed that the nucleus was not involved. On the other hand, UVA radiation-dependent activation of NF-kappa B appeared to be correlated with membrane damage, and activation could be prevented by alpha-tocopherol and butylated hydroxytoluene, agents that inhibited UVA radiation-dependent peroxidation of cell membrane lipids. The activation of NF-kappa B by the DNA damaging agents UVC (200-290 nm) and UVB (290-320 nm) radiation also only occurred at doses where significant membrane damage was induced, and, overall, activation was not correlated with the relative levels of DNA damage induced by UVC/UVB and UVA radiations. We conclude that the oxidative modification of membrane components may be an important factor to consider in the UV radiation-dependent activation of NF-kappa B over all wavelength ranges examined.

Some basic properties of ascorbate-dependent antioxidative-defence factors from rat liver cytosol

Properties of the ascorbate-dependent antioxidative-defence factors from rat liver cytosol (Antonenkov and Sies, 1992, Biol. Chem. Hoppe-Seyler 373, 1111-1116) were investigated. The factors are assayed by their capacity to inhibit Fe/ADP-ascorbate (nonenzymatic) lipid peroxidation. Ammonium sulfate fractionation and gel-filtration of the dialysed cytosol on Sephadex G-200 or Sephacryl S-400 led to the separation of factors A and B, with approximate molecular masses of > 400 kDa and 60 kDa, respectively. After fractionation of cytosol, factors A and B required the presence of the thiol- reducing agent, dithioerythritol, for their activity; factor B more so than factor A. Inhibiting activity of factor B is displayed at higher ascorbate concentrations than that of factor A. Increasing the ionic strength strongly stimulated the inhibitory capacity of factor A, but only slightly that of factor B. Differences were observed in pH-dependence, though both factors were more active in neutral media (pH 6.2-6.8). Factors A and B had different time-courses of inhibition of TBARS formation and suppression of chemiluminescence intensity. Factor B was more stable in the course of thermal treatment. Repeated freezing and thawing did not affect the activity of both factors. However, factor A could be inactivated by ultrasonic treatment, whereas factor B was unaffected. A function of these factors could be to create more favourable conditions for the interaction of ascorbate as a very hydrophilic molecule with membrane-bound hydrophobic radicals.

The widely used anesthetic agent propofol can replace alpha-tocopherol as an antioxidant

The cell membrane is protected against lipid peroxidation through endogenous antioxidants such as the lipid soluble alpha-tocopherol. The anesthetic agent propofol (2,6-diisopropylphenol) has a chemical structure which is similar to alpha-tocopherol, since it also contains a phenolic OH-group. The transient protection of GSH against lipid peroxidation in control liver microsomes is not observed in microsomes deficient in alpha-tocopherol. Introducing propofol (2 and 5 microM) restored the protective effect of GSH. Similar to the control microsomes the GSH-protective effect did not occur in previously heated microsomes. These results suggest that propofol acts similarly to alpha-tocopherol as a chain breaking antioxidant in liver microsomal membranes.

Involvement of vitamin E and protein thiols in the inhibition of microsomal lipid peroxidation by glutathione

Iron-ascorbate stimulated lipid peroxidation in rat liver microsomes can be inhibited by glutathione (GSH). The role of protein thiols and vitamin E in this process was studied in liver microsomes isolated from rats fed diets either sufficient or deficient in vitamin E and incubated at 37 degrees C under 100% O2. Lipid peroxidation was induced by adding 400 microM adenosine 5'-triphosphate, 2.5 to 20 microM FeCl3, and 450 microM ascorbic acid. One mL of the incubation mixture was removed at defined intervals for the measurement of thiobarbituric acid reactive substances (TBARS), protein thiols and vitamin E. In vitamin E sufficient microsomes, the addition of GSH enhanced the lag time prior to the onset of maximal TBARS accumulation and inhibited the loss of vitamin E. Treatment of these microsomes with the protein thiol oxidant diamide resulted in a 56% loss of protein thiols, but did not significantly change vitamin E levels. However, diamide treatment abolished the GSH-mediated protection against TBARS formation and loss of vitamin E during ascorbate-induced peroxidation. Liver microsomes isolated from rats fed a vitamin E deficient diet contained 40-fold less vitamin E and generated levels of TBARS similar to vitamin E sufficient microsomes at a 4-fold lower concentration of iron. GSH did not affect the lag time prior to the onset of maximal TBARS formation in vitamin E deficient microsomes although total TBARS accumulation was inhibited. Similar to what was previously found in vitamin E sufficient microsomes [Palamanda and Kehrer, (1992) Arch. Biochem. Biophys. 293, 103-109], GSH prevented the loss of protein thiols in vitamin E deficient microsomes.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence that rat liver microsomal glutathione transferase is responsible for glutathione-dependent protection against lipid peroxidation

Evidence that rat liver microsomal glutathione transferase is responsible for the glutathione-dependent inhibition of lipid peroxidation in liver microsomes has been obtained. Activation of the microsomal glutathione transferase in microsomes by cystamine renders this organelle even more resistant to lipid peroxidation in the presence of glutathione compared with untreated microsomes. Upon examining the effect of seven glutathione analogues on lipid peroxidation, it was found that only those that serve as good substrates for the microsomal glutathione transferase (Glutaryl-L-Cys-Gly and alpha-L-Glu-L-Cys-Gly) can inhibit lipid peroxidation. The lack of inhibition by the other five analogues (alpha-D-Glu-L-Cys-Gly, gamma-D-Glu-L-Cys-Gly, beta-L-Asp-L-Cys-Gly, alpha-L-Asp-L-Cys-Gly and alpha-D-Asp-L-Cys-Gly) shows the specificity of the protection and rules out any non-enzymic component. Inhibitors of selenium-dependent glutathione peroxidase (mercaptosuccinate at 50 microM) and phospholipid hydroperoxide glutathione peroxidase (iodoacetate, 1 mM + glutathione, 0.5 mM) do not inhibit the glutathione-dependent protection of rat liver microsomes against lipid peroxidation. Purified microsomal glutathione transferase, NADPH-cytochrome P450 reductase and cytochrome P450 were reconstituted in microsomal phospholipid vesicles by cholate dialysis. The resulting membranes contained functional enzymes and did display enzymic lipid peroxidation induced by 75 microM NADPH and 10 microM Fe-EDTA (2:1). This model system was used to investigate whether microsomal glutathione transferase could inhibit lipid peroxidation in a glutathione-dependent manner. The results show that 5 mM glutathione did inhibit lipid peroxidation when functional microsomal glutathione transferase was included. This was not the case when the enzyme had been pre-inactivated with diethylpyrocarbonate. Furthermore, the protective effect of glutathione could be partly reversed by an inhibitor (100 microM bromosulphophtalein) of the enzyme. Apparently, rat liver microsomal glutathione transferase has the capacity to inhibit lipid peroxidation in a reconstituted system.

The role of metabolism in the antioxidant function of vitamin E

Vitamin E (alpha-tocopherol), the principal chain-breaking antioxidant in biological membranes, prevents toxicant- and carcinogen-induced oxidative damage by trapping reactive oxyradicals. Although alpha-tocopherol antioxidant reactions appear to be not under direct metabolic control, alpha-tocopherol may function through redox cycles, which deliver reducing equivalents for antioxidant reactions and link antioxidant function to cellular metabolism. This review describes the antioxidant chemistry of alpha-tocopherol and evaluates the experimental evidence for the linkage of alpha-tocopherol turnover to cellular metabolism through redox cycles. Numerous in vitro experiments demonstrate antioxidant synergism between alpha-tocopherol and ascorbate, reduced glutathione, NADPH, and cellular electron transport proteins. Nevertheless, evidence that a one-electron redox cycle regenerates alpha-tocopherol from the tocopheroxyl radical is inconclusive. The difficulty of separating tocopheroxyl recycling from direct antioxidant actions of other antioxidants has complicated interpretation of the available data. A two-electron redox cycle involving alpha-tocopherol oxidation to 8a-substituted tocopherones followed by tocopherone reduction to alpha-tocopherol may occur, but would require enzymatic catalysis in vivo. Metabolism of antioxidant-inactive alpha-tocopheryl esters releases alpha-tocopherol, whereas reductive metabolism of alpha-tocopherylquinone, an alpha-tocopherol oxidation product, yields alpha-tocopherylhydroquinone, which also may provide antioxidant protection.

Influence of bile acids on stimulated lipid peroxidation and hydrogen peroxide production in rat liver microsomes

Bile acids were found to be effective antioxidants in bile and intestine. The influence of different bile acids on the NADPH-Fe(++)-stimulated lipid peroxidation (LPO) and cytochrome P-450 dependent hydrogen peroxide production (H2O2) in rat liver microsomes was investigated in vitro. LPO was determined as production of thiobarbituric acid reactants (TBAR). Different tri-, di- and monohydroxylated bile acids and cholesterol were given to the incubation mixture in concentrations ranging from 10(-5) to 10(-3) M. Sodium salts of cholic, tauroglycocholic and deoxycholic acids as well as cheno-deoxycholic, ursodeoxycholic, lithocholic acids and cholesterol did not alter the microsomal production of TBAR. H2O2 formation was significantly decreased by sodium deoxycholate whereas cholesterol increased H2O2 production up to 4 times. These results show that bile acids were not able to protect microsomal membrane lipids against peroxidative damage. Cholesterol mediated H2O2 formation as a source of hydroxyl radicals had no toxic effect concerning LPO, TBAR were not enhanced significantly.

Protection by glutathione and other thiol compounds against the loss of protein thiols and tocopherol homologs during microsomal lipid peroxidation

Microsomes from rat liver were used to investigate the mechanisms by which thiol compounds protect cellular membranes against damage from oxidants. Glutathione (GSH), dihydrolipoate and dithioerythritol, but not cysteine, ameliorated the loss of thiol groups of microsomal proteins attacked by Fe/ADP/NADPH or Fe/ADP/ascorbate prooxidant systems. The protection by GSH, but not dihydrolipoate or dithioerythritol, appeared to be enzymic since it was lost after microsomes were heated or treated with trypsin. The blocking of microsomal protein thiols with N-ethylmaleimide also diminished the protective effect of GSH. Lipid peroxidation, as assessed by chemiluminescence and vitamin-E loss, was inhibited in parallel with the protection of protein thiols. In microsomes lacking vitamin E, the protection of protein thiols by exogenous thiols was diminished. However, the GSH-dependent protection of vitamin E showed no preference for alpha-tocopherol over other tocopherol homologs. It is suggested that a GSH-dependent enzyme maintains protein thiols in the face of oxidative damage during microsomal peroxidation. A maintenance of protein thiols might not only protect important metabolic functions, but may also afford an antioxidant capacity to membranes, and account for one facet of the GSH-dependent inhibition of lipid peroxidation.

Dihydrolipoic acid--a universal antioxidant both in the membrane and in the aqueous phase. Reduction of peroxyl, ascorbyl and chromanoxyl radicals

Thioctic (lipoic) acid is used as a therapeutic agent in a variety of diseases in which enhanced free radical peroxidation of membrane phospholipids has been shown to be a characteristic feature. It was suggested that the antioxidant properties of thioctic acid and its reduced form, dihydrolipoic acid, are at least in part responsible for the therapeutic potential. The reported results on the antioxidant efficiency of thioctic and dihydrolipoic acids obtained in oxidation models with complex multicomponent initiation systems are controversial. In the present work we used relatively simple oxidation systems to study the antioxidant effects of dihydrolipoic and thioctic acids based on their interactions with: (1) peroxyl radicals which are essential for the initiation of lipid peroxidation, (2) chromanoxyl radicals of vitamin E, and (3) ascorbyl radicals of vitamin C, the two major lipid- and water-soluble antioxidants, respectively. We demonstrated that: (1) dihydrolipoic acid (but not thioctic acid) was an efficient direct scavenger of peroxyl radicals generated in the aqueous phase by the water-soluble azoinitiator 2,2'-azobis(2-amidinopropane)-dihydrochloride, and in liposomes or in microsomal membranes by the lipid-soluble azoinitiator 2,2'-azobis(2,4-dimethylvaleronitrile); (2) both dihydrolipoic acid and thioctic acid did not interact directly with chromanoxyl radicals of vitamin E (or its synthetic homologues) generated in liposomes or in the membranes by three different ways: UV-irradiation, peroxyl radicals of 2,2'-azobis(2,4-dimethylvaleronitrile), or peroxyl radicals of linolenic acid formed by the lipoxygenase-catalyzed oxidation; and (3) dihydrolipoic acid (but not thioctic acid) reduced ascorbyl radicals (and dehydroascorbate) generated in the course of ascorbate oxidation by chromanoxyl radicals. This interaction resulted in ascorbate-mediated dihydrolipoic acid-dependent reduction of the vitamin E chromanoxyl radicals, i.e. vitamin E recycling. We conclude that dihydrolipoic acid may act as a strong direct chain-breaking antioxidant and may enhance the antioxidant potency of other antioxidants (ascorbate and vitamin E) in both the aqueous and the hydrophobic membraneous phases.

Effects of dietary linseed oil and marine oil on lipid peroxidation in monkey liver in vivo and in vitro

Diets rich in linoleic acid (CO) from corn oil, or in linoleic acid and either alpha-linolenic acid (LO) based on linseed oil or n-3 fatty acids (MO) from menhaden oil were fed to male and female Cynomolgus monkeys for 15 wk. In the liver a 40% reduction of alpha-tocopherol occurred in the MO group relative to the CO and LO groups followed by increased formation of lipofuscin in vivo. A four-fold increase of alpha-tocopherol in the MO diet (MO + E) brought the level in the liver to that found with CO and LO. The increased peroxidation in the MO group in the liver phospholipids was associated with the replacement of 60% of the n-6 fatty acids by n-3 fatty acids from menhaden oil. Similar fatty acid profiles were found in groups fed MO and MO + E, respectively. Compared to the CO fed group, feeding alpha-linolenic acid only resulted in a slight incorporation of n-3 fatty acids in the liver membranes mainly due to a direct incorporation of alpha-linolenic acid. However, in monkeys fed menhaden oil more than 30% of the total fatty acids in the liver phospholipids were n-3 fatty acids. The various diets did not influence the activity of liver catalase (EC 1.11.1.6) nor superoxide dismutase (EC 1.15.1.1), but glutathione-peroxidase activity (EC 1.11.1.9) was higher in monkeys fed the MO diet. The catalase activity in females was 20% higher than in males.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxidative stress: from basic research to clinical application

The occurrence of reactive oxygen species, known as pro-oxidants, is an attribute of normal aerobic life. The steady-state formation of pro-oxidants is balanced by a similar rate of their consumption by antioxidants that are enzymatic and/or nonenzymatic. "Oxidative stress" results from imbalance in this pro-oxidant-antioxidant equilibrium in favor of the pro-oxidants. A number of diseases are associated with oxidative stress, being the basis of antioxidant therapy. Current evidence in clinical research does not show unequivocal distinction between causal or associative relationships of pro-oxidants to the disease process.

Influences of Ginkgo biloba on cyclosporin A induced lipid peroxidation in human liver microsomes in comparison to vitamin E, glutathione and N-acetylcysteine

The in vitro effect of cyclosporin A (CsA) on lipid peroxidation in human liver microsomes was investigated, and efforts were made to prevent the resulting toxic effect of CsA. Microsomes were prepared from human liver resection material and incubated with CsA (0, 10, 30, 100, 300, 1000 micrograms/mL) for one hour (pH 7.4, 37 degrees, 95% O2, 5% CO2). Subsequently the resulting concentrations of malondialdehyde equivalents (MDA) were determined, a breakdown product of lipid peroxidation. Furthermore the duration of incubation was varied (0, 15, 30, 60, 90 min) using a CsA concentration of 300 micrograms/mL. CsA was shown to stimulate MDA-formation to up to 10-fold of the control value in both a time and concentration dependent manner. The dosage dependent experiment stated above was repeated, adding alpha-tocopherol (vitamin E, 1 mM), reduced glutathione (GSH, 1 mM), N-acetylcysteine (0.1, 0.3, 1, 3 mM), and Ginkgo biloba extract (Gbe, 15, 50, 150 micrograms/mL), respectively, to the medium of incubation. Vitamin E, a potent radical scavenger, proved to inhibit lipid peroxidation almost totally. Both GSH and N-acetylcysteine were also able to prevent lipid peroxidation, suggesting that the antioxidant effect of GSH might be caused by its thiol group and does not depend on the integrity of the whole molecule. Gbe inhibited CsA induced lipid peroxidation in a concentration dependent manner. This effect of Gbe was diminished yet not totally abolished when FeCl3 was added to the medium of incubation, whereas N-acetylcysteine even slightly enhanced CsA stimulated lipid peroxidation in the presence of iron. These results suggest that Gbe might be able to prevent radical mediated damage to human membranes caused by CsA.

Effect of chronic ethanol treatment on the t-butyl hydroperoxide-dependent lipid peroxidation in rat liver

1. The effect of chronic ethanol consumption on the level of the t-butyl hydroperoxide (Bu'OOH)-induced lipid peroxidation in rat liver homogenate and subcellular fractions was measured using chemiluminescence technique and malondialdehyde formation. 2. It was shown that under the action of ethanol the rate of lipid peroxidation was decreased in the whole and "postnuclear" liver homogenates. 3. Ethanol significantly decreased the intensity of lipid peroxidation in microsomes, but did not affect the Bu'OOH-dependent process in mitochondria. 4. The level of lipid peroxidation was reduced after incubation of the total particulate fraction (mitochondria plus microsomes) with the undialysed cytosol from ethanol-treated rat liver. Dialysis of the cytosol prevented depressive effect of ethanol treatment on lipid peroxidation. 5. Reduced glutathione (0.1-1.0 mM) was shown to decrease the rate of lipid peroxidation in rat liver microsomes, but did not affect its level in mitochondria. 6. Pyrazole injections to rats reduced and phenobarbital treatment increased the level of the Bu'OOH-dependent lipid peroxidation in liver microsomes. 7. The data obtained indicate that the Bu'OOH-dependent lipid peroxidation is not an appropriate marker of the ethanol-induced oxidative stress in rat liver cells.

Absorption, transport and metabolism of vitamin E

Vitamin E includes eight naturally occurring fat-soluble nutrients called tocopherols and dietary intake of vitamin E activity is essential in many species. alpha-Tocopherol has the highest biological activity and the highest molar concentration of lipid soluble antioxidant in man. Deficiency of vitamin E may cause neurological dysfunction, myopathies and diminished erythrocyte life span. alpha-Tocopherol is absorbed via the lymphatic pathway and transported in association with chylomicrons. In plasma alpha-tocopherol is found in all lipoprotein fractions, but mostly associated with apo B-containing lipoproteins in man. In rats approximately 50% of alpha-tocopherol is bound to high density lipoproteins (HDL). After intestinal absorption and transport with chylomicrons alpha-tocopherol is mostly transferred to parenchymal cells of the liver were most of the fat-soluble vitamin is stored. Little vitamin E is stored in the non-parenchymal cells (endothelial, stellate and Kupffer cells). alpha-Tocopherol is secreted in association with very low density lipoprotein (VLDL) from the liver. In the rat about 90% of total body mass of alpha-tocopherol is recovered in the liver, skeletal muscle and adipose tissue. Most alpha-tocopherol is located in the mitochondrial fractions and in the endoplasmic reticulum, whereas little is found in cytosol and peroxisomes. Clinical evidence from heavy drinkers and from experimental work in rats suggests that alcohol may increase oxidation of alpha-tocopherol, causing reduced tissue concentrations of alpha-tocopherol. Increased demand for vitamin E has also been observed in premature babies and patients with malabsorption, but there is little evidence that the well balanced diet of the healthy population would be improved by supplementation with vitamin E.

Vitamin E and glutathione are required for preservation of microsomal glutathione S-transferase from oxidative stress in microsomes

Glutathione (GSH) inhibited lipid peroxidation induced by NADPH-BrCCl3 in vitamin E sufficient microsomes, but did not in phenobarbital (PB)-treated microsomes (containing about 60% of normal vitamin E) or in vitamin E-deficient microsomes (containing about 30% of normal vitamin E). There was a good correlation between the increased formation of CHCl3 from BrCCl3 in the presence of GSH under anaerobic conditions and the vitamin E level in the microsomes. A normal level of vitamin E in microsomes was thus very important for GSH-dependent inhibition of lipid peroxidation and for the efficient formation of CHCl3 from BrCCl3. Bromosulfophthalein (BSP) eliminated the effects of GSH on lipid peroxidation and CHCl3 formation. The apparent Km and Vmax of substrates for GSH S-transferase were changed by in vivo depletion of vitamin E in microsomes, and the Vmax/Km values were significantly reduced. The enzyme activity in microsomes was inactivated following the loss of vitamin E during in vitro lipid peroxidation, and GSH prevented the loss of vitamin E and protected the enzyme from attack by free radicals. GSH inhibited lipid peroxidation induced by NADPH-Fe2+ and the loss of GSH S-transferase activity during the peroxidation in PB-treated microsomes, but did not in the case of induction by NADPH-BrCCl3. A possible relation between the microsomal GSH S-transferase activity and defense by GSH against lipid peroxidation in microsomes is discussed.

Biokinetics of dietary RRR-alpha-tocopherol in the male guinea pig at three dietary levels of vitamin C and two levels of vitamin E. Evidence that vitamin C does not "spare" vitamin E in vivo

The net rates of uptake of "new" and loss of "old" 2R,4'R,8'R-alpha-tocopherol (RRR-alpha-TOH, which is natural vitamin E) have been measured in the blood and in nine tissues of male guinea pigs over an eight week period by feeding diets containing deuterium-labelled alpha-tocopheryl acetate (d6-RRR-alpha-TOAc). There was an initial two week "lead-in" period during which 24 animals [the "high" vitamin E (HE) group] received diets containing 36 mg of unlabelled (d0) RRR-alpha-TOAc and 250 mg of ascorbic acid per kg diet, while another 24 animals [the "low" vitamin E (LE) group] received diets containing 5 mg d0-RRR-alpha-TOAc and 250 mg ascorbic acid per kg diet. The HE group was then divided into three equal subgroups, which were fed diets containing 36 mg d6-RRR-alpha-TOAc and 5000 mg [the "high" vitamin C (HEHC) subgroup], 250 mg [the "normal" vitamin C (HENC) subgroup] and 50 mg [the "low" vitamin C (HELC) subgroup] ascorbic acid per kg diet. One animal from each group was sacrificed each week and the blood and tissues were analyzed for d0- and d6-RRR-alpha-TOH by gas chromatography-mass spectrometry. The LE group was similarly divided into three equal subgroups with animals receiving diets containing 5 mg d6-RRR-alpha-TOAc and 5,000 mg (LEHC), 250 mg (LENC) and 50 mg (LELC) ascorbic acid per kg diet with a similar protocol being followed for sacrifice and analyses. In the HE group the total (d0(-) + d6-) RRR-alpha-TOH concentrations in blood and tissues remained essentially constant over the eight week experiment, whereas in the LE group the total RRR-alpha-TOH concentrations declined noticeably (except in the brain, an organ with a particularly slow turnover of vitamin E). There were no significant differences in the concentrations of "old" d0-RRR-alpha-TOH nor in the concentrations of "new" d6-RRR-alpha-TOH found in any tissue at a particular time between the HEHC, HENC and HELC subgroups, nor between the LEHC, LENC and LELC subgroups. We conclude that the long-postulated "sparing" action of vitamin C on vitamin E, which is well documented in vitro, is of negligible importance in vivo in guinea pigs that are not oxidatively stressed in comparison with the normal metabolic processes which consume vitamin E (e.g., by oxidizing it irreversibly) or eliminate it from the body.(ABSTRACT TRUNCATED AT 400 WORDS)

The cooperative action of vitamins E and C in the protection against peroxidation of parinaric acid in human erythrocyte membranes

The influence of vitamins E and C on the initial stages of lipid peroxidation in human erythrocyte membranes was assessed with the fluorescent polyunsaturated fatty acid, parinaric acid, as probe molecule. Cumene hydroperoxide was used as initiator with either haemin-Fe3+ or Cu2+ as metal ion cofactor. The effect of vitamin C (pro- or antioxidant) appeared to be determined by the localisation of the metal ions, either in the water phase or in the membrane. Vitamin C is only able to reduce metal ions in the water phase, which results in acceleration of radical generation and subsequent enhancement of parinaric acid peroxidation. Thus, interaction of vitamin C with Cu2+ in the water phase led to drastically enhanced peroxidation of parinaric acid. In contrast, when only membrane-associated haemin-Fe3+ was present, vitamin C functioned as an antioxidant at all concentrations tested (0-10 microM). In a system with haemin-Fe3+ equilibrated between the water phase and the membranes, less than 5 microM vitamin C produced an overall prooxidant, and greater than 15 microM vitamin C an overall antioxidant effect. At vitamin C concentrations of 5-15 microM, continuous measurement of parinaric acid fluorescence revealed a shift in the vitamin C effect from antioxidant to prooxidant within the time-course of an assay. Vitamin E exhibited a protective effect on peroxidation initiated by cumene (per)oxyl radicals with haemin-Fe3+ as cofactor, by inducing a concentration-dependent extension of the lag-phase in parinaric acid peroxidation. Vitamin E appeared to be much more effective compared with vitamin C in scavenging radicals in this system. This indicates that vitamin C has only a limited ability to react with cumene (per)oxyl radicals in the membrane. The combination of vitamins E and C produced a protective effect on parinaric acid peroxidation exceeding the sum of their individual contributions. Moreover, the rate of vitamin E consumption was drastically lowered in the presence of vitamin C, whereas the rate of vitamin C consumption hardly decreased in the presence of vitamin E. The results are discussed in terms of a reaction scheme where the relative contributions of a number of reactions are considered to determine the total effect of added vitamin C or E. Vitamin E radicals constitute an additional substrate for vitamin C, resulting in a more than additive shift in the overall effect to the antioxidant side.

Glutathione disulfide enhances the reduced glutathione inhibition of lipid peroxidation in rat liver microsomes

Experiments were undertaken to examine the effects of reduced (GSH) and oxidized (GSSG) glutathione on lipid peroxidation of rat liver microsomes. Dependence on microsomal alpha-tocopherol was shown for the GSH inhibition of lipid peroxidation. However, when GSH (5 mM) and GSSG (2.5 mM) were combined in the assay system, inhibition of lipid peroxidation was enhanced markedly over that with GSH alone in microsomes containing alpha-tocopherol. Surprisingly, the synergistic inhibitory effect of GSH and GSSG was also observed for microsomes that were deficient in alpha-tocopherol. These data suggest that there may be more than one factor responsible for the glutathione-dependent inhibition of lipid peroxidation. The first is dependent upon microsomal alpha-tocopherol and likely requires GSH for alpha-tocopherol regeneration from the alpha-tocopheroxyl radical during lipid peroxidation. The second factor appears to be independent of alpha-tocopherol and may involve the reduction of lipid hydroperoxides to their corresponding alcohols. One, or possibly both, of these factors may be activated by GSSG through thiol/disulfide exchange with a protein sulfhydryl moiety.

Studies on the hyperplasia ('regeneration') of the rat liver following partial hepatectomy. Changes in lipid peroxidation and general biochemical aspects

Using the experimental model of partial hepatectomy in the rat, we have examined the relationship between cell division and lipid peroxidation activity. In rats entrained to a regime of 12 h light/12 h dark and with a fixed 8 h feeding period in the dark phase, partial hepatectomy is followed by a rapid regeneration of liver mass with cycles of synchronized cell division at 24 h intervals. The latter phenomenon is indicated in this study by pulses of thymidine kinase activity having maxima at 24 h, 48 h and 72 h after partial hepatectomy. Microsomes prepared from regenerating livers show changes in lipid peroxidation activity (induced by NADPH/ADP/iron or by ascorbate/iron), which is significantly decreased relative to that in microsomes from sham-operated controls, again at 24 h, 48 h and 72 h after the operation. This phenomenon has been investigated with regard to possible underlying changes in the content of microsomal fatty acids, the microsomal enzymes NADPH:cytochrome c reductase and cytochrome P-450, and the physiological microsomal antioxidant alpha-tocopherol. The cycles of decreased lipid peroxidation activity are apparently due, at least in part, to changes in microsomal alpha-tocopherol content that are closely associated in time with thymidine kinase activity.

Application of deuterated alpha-tocopherols to the biokinetics and bioavailability of vitamin E

alpha-Tocopherol, a superior chain-breaking, peroxyl radical-trapping antioxidant and the most active component of vitamin E, is elevated in liver tumor cells, contributing to their greater resistance towards lipid peroxidation compared to cells from normal tissues. Also, in regenerating rat liver the level of vitamin E has been found to fluctuate in phase with the rate of cell division. In order to study the biokinetics and mechanisms of the distribution of vitamin E in organs and within tissues of animals, deuterated forms of alpha-tocopherol have been synthesized and their uptake into blood and tissues has been measured by gas chromatography-mass spectrometry. Measurement of the competitive uptake from a mixture of the RRR- and SRR-alpha-tocopherol stereoisomers labelled with different amounts of deuterium shows that the liver exerts a strong preference for secretion of the natural (RRR) stereoisomer into the plasma. It is suggested that a tocopherol-binding protein plays a key role in this process.

Activity of rat liver microsomal glutathione transferase toward products of lipid peroxidation and studies of the effect of inhibitors on glutathione-dependent protection against lipid peroxidation

Rat liver microsomal glutathione transferase displays glutathione peroxidase activity with linoleic acid hydroperoxide, linoleic acid ethyl ester hydroperoxide, and dilinoleoyl phosphatidylcholine hydroperoxide, with rates of 0.2, 0.3, and 0.3 mumol/min/mg, respectively. The activities are increased between three- and fourfold when the enzyme is activated with N-ethylmaleimide. Microsomal glutathione transferase can also conjugate 4-hydroxynon-2-enal with a specific activity of 0.5 mumol/min/mg. These findings show that the enzyme can remove harmful products of lipid peroxidation and thereby possibly protect intracellular membranes against oxidative stress. A set of glutathione transferase inhibitors (rose bengal, tributyltin acetate, S-hexylglutathione, indomethacin, cibacron blue, and bromosulfophtalein) which abolish the glutathione-dependent protection against lipid peroxidation in liver microsomes have been characterized. These inhibitors were found to be effective in the micromolar range and could prove valuable in studying the factor responsible for glutathione-dependent protection against lipid peroxidation.

Reduced glutathione effects on alpha-tocopherol concentration of rat liver microsomes undergoing NADPH-dependent lipid peroxidation

Factors involved in reduced glutathione (GSH) and vitamin E-mediated inhibition of NADPH-dependent rat liver microsomal lipid peroxidation were examined. Lipid peroxidation was monitored over a time-course of 180 min by thiobarbituric acid reactive product formation. The addition of 5 mM GSH to the reaction system containing microsomes from rats fed a diet supplemented with 150 IU/kg of alpha-tocopherol acetate for eight weeks produced a lag in peroxidation of greater than 30 min. This effect was not observed for microsomes prepared from rats fed a diet deficient in vitamin E. Indeed, a prooxidant effect of 5 mM GSH was observed in assays containing microsomes from rats fed a diet deficient in vitamin E. The inhibition by GSH of lipid peroxidation in microsomes prepared from livers of vitamin E supplemented rats was not restricted by its availability, for it was found that approximately 92% of the GSH remained in the reduced form after 60 min. Additional experiments revealed that the alpha-tocopherol content of peroxidizing microsomes decreased rapidly in the absence of GSH. The addition of 5 mM GSH to the assay system markedly depressed the loss of microsomal alpha-tocopherol. The results of in vivo labeling of liver microsomes with [14C]alpha-tocopherol demonstrated that i) GSH addition to the in vitro peroxidizing medium reduced the disappearance of alpha-tocopherol, and ii) a compound that interfered with the determination of alpha-tocopherol was separated by HPLC and was not an oxidation product of alpha-tocopherol. A portion of the microsomal 14C-labeled alpha-tocopherol was converted to an unidentified product with HPLC retention characteristics that was similar, but not identical, to alpha-tocopherol quinone.

Class-specific effects of selenium on PWM-driven human antibody synthesis in vitro

The influence of inorganic and organic forms of selenium (Se) on human antibody production was studied in a Pokeweed Mitogen (PWM)-driven in vitro system. Mitogen-stimulated peripheral blood mononuclear cells (PBMC) of eight healthy donors were cultured with different Se compounds at concentrations between 10(-3) and 10(-9) M. At high Se levels (10(-3)-10(-4) M), IgM and IgG production of all donors were strongly inhibited owing to reduced cell viability. However, in five of eight donors, low levels of Se enhanced IgG secretion. This was most effective in the presence of inorganic Se, whereas selenomethionine and selenocystine were less effective. In contrast to IgG, IgM synthesis was significantly reduced by low Se levels in five donors. No significant correlation between donor serum Se levels and antibody production in vitro was found. The addition of low levels of Se to PBMC, stimulated with PHA or PWM, showed no effect on proliferation, whereas a high concentration (5 x 10(-3) M) of sodium selenite and selenocystine suppressed proliferation owing to reduced cell viability. Thus, the present results show that Se supplementation can enhance human antibody production and, moreover, suggest some selectivity of Se action on human immune responses that may result in increased switching from IgM to IgG production.

Lipid peroxidation inhibitory factors in liver and muscle of rat, mouse, and chicken

Glutathione- or sulfhydryl-dependent antioxidant factors that act to prevent lipid peroxidation have been reported in both microsomes and cytoplasm from rat liver. The cytoplasmic factor has been identified in several other tissues and species, but the distribution of the microsomal factor has not been reported. Chicken and mouse livers had much lower activities of the glutathione-dependent membrane-associated and cytoplasmic antioxidant factors than rat liver. Peroxidative damage to membranes has been hypothesized as a mechanism of tissue damage in muscular dystrophy. However, neither the chicken, mouse, nor rat had significant activities of the antioxidant factors in muscle. There was also no significant difference between normal and dystrophic chicken livers in the activity of the antioxidant factors associated with the microsomes or the cytoplasm, nor of the liver microsomal factor in normal and dystrophic mice. The results do not support an important role for the antioxidant factors in the pathogenesis of muscular dystrophy, and raise questions as to whether such factors are physiologically important in species other than rat or in tissues other than liver.

Iron overload and the predisposition of cells to antioxidant consumption and peroxidative damage

We have investigated the effects of iron overload in vivo on the tocopherol levels and the extent of lipid peroxidation in rat liver microsomes and their response to subsequent oxidative stress in vitro. The results demonstrate a direct correlation between consumption of antioxidant defences and the induction and extent of malondialdehyde production in microsomes prepared from iron-loaded rats. The data are consistent with the requirement for iron (II)/iron (III) ratios in lipid peroxidation in control microsomes.

Effect of chronic ethanol treatment on lipid peroxidation in rat liver homogenate and subcellular fractions

1. The effect of chronic ethanol treatment on the level of lipid peroxidation in rat liver homogenate and subcellular fractions was measured using chemiluminescence technique and malondialdehyde formation. 2. It was shown that after chronic ethanol treatment the level of Fe/ADP-ascorbate-induced lipid peroxidation was decreased in the whole and "postnuclear" liver homogenates. Dilution of the homogenates prevented depressive effect of ethanol on lipid peroxidation. 3. Chronic ethanol treatment did not affect the intensity of the Fe/ADP-ascorbate-induced process in rat liver mitochondria and microsomes. 4. Peroxidative alteration of the liver lipids in vivo was evaluated by measurement of conjugated dienes (absorbance at 233 nm). It was shown that ethanol did not increase the level of u.v. absorption of lipids from mitochondria and microsomes. Chronic alcohol treatment did not influence the steady-state concentration of malonic dialdehyde in the whole liver homogenate. 5. The data obtained indicate that cytosol from the ethanol treated rat liver contains a factor(s) which prevents Fe/ADP-ascorbate-dependent lipid peroxidation in biological membranes.

Effect of chronic ethanol, catalase inhibitor 3-amino-1,2,4-triazole and clofibrate treatment on lipid peroxidation in rat myocardium

1. The effect of chronic alcohol consumption, catalase inhibitor 3-amino-1,2,4-triazole (amino-triazole) and peroxisome proliferator clofibrate on the level of Fe/ADP-ascorbate-induced lipid peroxidation has been studied in the rat myocardium. The intensity of lipid peroxidation was measured using chemiluminescence technique and malondialdehyde formation. 2. Combined us well as separate treatment with ethanol (36% of dietary calories) and aminotriazole caused elevation of the rate of lipid peroxidation in the nuclear-free homogenate or total particulate fraction of the rat heart. The most pronounced effect was noted during combined application of ethanol and aminotriazole. 3. Prolonged clofibrate treatment significantly increased the level of nonenzymatic lipid peroxidation in the rat myocardium. 4. Peroxidative alteration of the myocardial lipids in vivo was evaluated by measurement of conjugated dienes (absorbance at 233 nm). Separate ethanol, aminotriazole or clofibrate treatment did not affect the level of u.v. absorption of lipids from the total particulate fraction. However, when ethanol and aminotriazole were administered simultaneously an increase of conjugated diene formation was observed. 5. The data obtained confirm the hypothesis that ethanol or clofibrate-induced activation of the myocardial lipid peroxidation may be due to the increase of hydrogen peroxide-generating capacity of the heart microperoxisomes.

Cell calcium, vitamin E, and the thiol redox system in cytotoxicity

The controversial role of extracellular Ca2+ in toxicity to in vitro hepatocyte systems is reviewed. Recent reports demonstrate that extracellular Ca2+-related cytotoxicity is dependent on Ca2+-influenced vitamin E (alpha-tocopherol) content of isolated hepatocytes. Based on a Ca2+-omission model of in vitro oxidative stress, the role of vitamin E in cytotoxicity is further explored. This model demonstrates the interdependence of the GSH redox system and vitamin E as protective agents during oxidative stress. Following chemical oxidant-induced depletion of intracellular GSH, cell morphology and viability are maintained by the continuous presence of cellular alpha-tocopherol above a threshold level of 0.6-1.0 nmol/10(6) cells. alpha-Tocopherol threshold-dependent cell viability is directly correlated with the prevention of the loss of cellular protein thiols in the absence of intracellular GSH. Potential mechanisms for this phenomenon are explored and include a direct reductive action of alpha-tocopherol on protein thiyl radicals, and the prevention of oxidation of protein thiols by scavenging of lipid peroxyl radicals by alpha-tocopherol. It is suggested that in light of the threshold phenomenon of vitamin E prevention of potentially severe oxidative stress-induced cytotoxicity, its use as a protective agent against an oxidative challenge in vivo should be reassessed.

Effects of aurothioglucose on iron-induced rat liver microsomal lipid peroxidation

Aurothioglucose (ATG), an inhibitor of selenium-dependent glutathione peroxidase activity, at a concentration of 100 microM, strongly increases lipid peroxidation of rat liver microsomes exposed to either ferrous ion (10 microM) or the combination of ferric ion (10 microM) and ascorbic acid (500 microM), in the presence of reduced glutathione (GSH, 800 microM). This effect was not achieved using heat-inactivated microsomes and was dependent on the presence of GSH. ATG did not affect the lag period associated with ascorbic acid/ferric ion-induced microsomal lipid peroxidation (previously attributed to an undefined GSH-dependent microsomal agent), but did increase the rate of peroxidation subsequent to the lag period. The potent GSH-dependent inhibition of microsomal lipid peroxidation by cytosol (10% of total volume) was completely reversed by ATG (100 microM). ATG similarly reversed an inhibition of phosphatidylcholine hydroperoxide-dependent liposomal peroxidation that has been attributed to phospholipid hydroperoxide glutathione peroxidase (PHGPX), an enzyme distinct from the classical glutathione that cannot utilize intact phospholipids. ATG inhibited, in addition to the classical selenium-dependent glutathione peroxidase, both cytosolic and microsomal (basal and N-ethyl maleimide-stimulated) glutathione S-transferase activities with greater than 80% inhibition achieved at 100 microM ATG. ATG, at concentrations up to 250 microM, did not inhibit PHGPX activity measured by the coupled-enzyme method in the presence of Triton X-100 (0.1%).(ABSTRACT TRUNCATED AT 250 WORDS)