Glutathione-dependent inhibition of lipid peroxidation by a soluble, heat-labile factor in animal tissues

Lipid peroxidation and ferroptosis: The role of GSH and GPx4

Ferroptosis (FPT) is a form of cell death due to missed control of membrane lipid peroxidation (LPO). According to the axiomatic definition of non-accidental cell death, LPO takes place in a scenario of altered homeostasis. FPT, differently from apoptosis, occurs in the absence of any known specific genetically encoded death pathway or specific agonist, and thus must be rated as a regulated, although not "programmed", death pathway. It follows that LPO is under a homeostatic metabolic control and is only permitted when indispensable constraints are satisfied and the antiperoxidant machinery collapses. The activity of the selenoperoxidase Glutathione Peroxidase 4 (GPx4) is the cornerstone of the antiperoxidant defence. Converging evidence on both mechanism of LPO and GPx4 enzymology indicates that LPO is initiated by alkoxyl radicals produced by ferrous iron from the hydroperoxide derivatives of lipids (LOOH), traces of which are the unavoidable drawback of aerobic metabolism. FPT takes place when a threshold has been exceeded. This occurs when the major conditions are satisfied: i) oxygen metabolism leading to the continuous formation of traces of LOOH from phospholipid-containing polyunsaturated fatty acids; ii) missed enzymatic reduction of LOOH; iii) availability of ferrous iron from the labile iron pool. Although the effectors impacting on homeostasis and leading to FPT in physiological conditions are not known, from the available knowledge on LPO and GPx4 enzymology we propose that it is aerobic life itself that, while supporting bioenergetics, is also a critical requisite of FPT. Yet, when the homeostatic control of the steady state between LOOH formation and reduction is lost, LPO is activated and FPT is executed.

GPx4, Lipid Peroxidation, and Cell Death: Discoveries, Rediscoveries, and Open Issues

SIGNIFICANCE

Iron-dependent lipid peroxidation is a complex oxidative process where phospholipid hydroperoxides (PLOOH) are produced in membranes and finally transformed into a series of decomposition products, some of which are endowed with biological activity. It is specifically prevented by glutathione peroxidase 4 (GPx4), the selenoenzyme that reduces PLOOH by glutathione (GSH). PLOOH is both a product and the major initiator of peroxidative chain reactions, as well as an activator of lipoxygenases. α-Tocopherol both specifically breaks peroxidative chain propagation and inhibits lipoxygenases. Thus, GPx4, GSH, and α-tocopherol are integrated in a concerted anti-peroxidant mechanism. Recent Advances: Ferroptosis has been recently identified as a cell death subroutine that is specifically activated by missing GPx4 activity and inhibited by iron chelation or α-tocopherol supplementation. Ferroptosis induction may underlie spontaneous human diseases, such as major neurodegeneration and neuroinflammation, causing an excessive cell death. The basic mechanism of ferroptosis, therefore, fits the features of activation of lipid peroxidation.

CRITICAL ISSUES

Still lacking are convincing proofs that lipoxygenases are involved in ferroptosis. Also, unknown are the molecules eventually killing cells and the mechanisms underlying the drop of the cellular anti-peroxidant capacity.

FUTURE DIRECTIONS

Molecular events and mechanisms of ferroptosis to be unraveled and validated on animal models are GPx4 inactivation, role of GSH concentration, increased iron availability, and membrane structure and composition. This is expected to drive drug discovery that is aimed at halting cell death in degenerative diseases or boosting it in cancer cells. Antioxid. Redox Signal. 29, 61-74.

Isobaric labeling and tandem mass spectrometry: a novel approach for profiling and quantifying proteins differentially expressed in amniotic fluid in preterm labor with and without intra-amniotic infection/inflammation

OBJECTIVE

Examination of the amniotic fluid (AF) proteome has been previously attempted to identify useful biomarkers in predicting the outcome of preterm labor (PTL). Isobaric Tag for Relative and Absolute Quantitation (iTRAQ) labeling allows direct ratiometric comparison of relative abundance of identified protein species among multiplexed samples. The purpose of this study was to apply, for the first time, the combination of iTRAQ and tandem mass spectrometry to identify proteins differentially regulated in AF samples of women with spontaneous PTL and intact membranes with and without intra-amniotic infection/inflammation (IAI).

METHODS

A cross-sectional study was designed and included AF samples from patients with spontaneous PTL and intact membranes in the following groups: (1) patients without IAI who delivered at term (n = 26); (2) patients who delivered preterm without IAI (n = 25); and (3) patients with IAI (n = 24). Proteomic profiling of AF samples was performed using a workflow involving tryptic digestion, iTRAQ labeling and multiplexing, strong cation exchange fractionation, and liquid chromatography tandem mass spectrometry. Twenty-five separate 4-plex samples were prepared and analyzed.

RESULTS

Collectively, 123,011 MS(2) spectra were analyzed, and over 25,000 peptides were analyzed by database search (X!Tandem and Mascot), resulting in the identification of 309 unique high-confidence proteins. Analysis of differentially present iTRAQ reporter peaks revealed many proteins that have been previously reported to be associated with preterm delivery with IAI. Importantly, many novel proteins were found to be up-regulated in the AF of patients with PTL and IAI including leukocyte elastase precursor, Thymosin-like 3, and 14-3-3 protein isoforms. Moreover, we observed differential expression of proteins in AF of patients who delivered preterm in the absence of IAI in comparison with those with PTL who delivered at term including Mimecan precursor, latent-transforming growth factor beta-binding protein isoform 1L precursor, and Resistin. These findings have been confirmed for Resistin in an independent cohort of samples using ELISA. Gene ontology enrichment analysis was employed to reveal families of proteins participating in distinct biological processes. We identified enrichment for host defense, anti-apoptosis, metabolism/catabolism and cell and protein mobility, localization and targeting.

CONCLUSIONS

(1) Proteomics with iTRAQ labeling is a profiling tool capable of revealing differential expression of proteins in AF; (2) We discovered 82 proteins differentially expressed in three clinical subgroups of premature labor, 67 which were heretofore unknown. Of particular importance is the identification of proteins differentially expressed in AF from women who delivered preterm in the absence of IAI. This is the first report of the positive identification of biomarkers in this subgroup of patients.

Characterization and purification of a lipoxygenase inhibitor in human epidermoid carcinoma A431 cells

A lipoxygenase inhibitor in the cytosolic fraction of human epidermoid carcinoma A431 cells was characterized and purified. The cytosolic inhibitor lost the inhibitory activity upon heating at 75 degrees C for 15 min or pretreating with 1 mg/ml trypsin at 37 degrees C for 60 min. Cytosol, after dialysis, lost the inhibitory activity but its inhibitory activity recovered when 1 mM GSH was added to the dialysate. The inhibitory activity of cytosol was also abolished by treatment either with 1 mM iodoacetate at 4 degrees C for 1 h or with 0.5 mM H2O2. The pI of the inhibitor was approx. 7.0. In addition to 12-lipoxygenase, the inhibitor inhibited the activities of 5-lipoxygenase and fatty acid cyclo-oxygenase in a cell-free system. The inhibitor was purified by a series of column chromatographies using CM Sephadex C-50, Sephadex G-100 SF and Mono P columns. A major 22 kDa protein was obtained that was distinct from selenium-dependent glutathione peroxidase.

Fluctuation of trace elements during methylmercury toxication and chelation therapy

The aim of the present investigation was to check the fluctuation in essential elements, such as Na, K, Mg, Mn, Cu, Zn, Cr and Ni in the brain, spinal cord, liver and kidney of mice during methylmercury chloride (MMC) toxication and therapy with monothiols (N-acetyl-DL-homocysteine thiolactone and glutathione) and vitamins (vitamin B complex and E). Mercury deposition and its elimination during chelation therapy were also screened for comparative purposes. The animals were dosed for 7 days with MMC 1 mg/kg/d and some were then kept without treatment for a further. 7 days. Other MMC-treated animals were immediately given one of the above antidotes for 7 days. All the animals were sacrificed on the 15th day. There was a decrease in all elements during MMC toxication with few exceptions, for example, copper was increased in the liver as was sodium in the kidney. Treatment with the thiols and vitamins restored the levels of these elements in certain tissues towards normal, but their concentrations remained abnormal in most instances. The fluctuations in the concentration of these elements were attributed to their association with various macromolecules.

Oxidative stress response in yeast: purification and some properties of a membrane-bound glutathione peroxidase from Hansenula mrakii

Glutathione peroxidase was purified from the total membrane fractions of a yeast, Hansenula mrakii IFO 0895. The purified enzyme gave a single protein band with a molecular mass of 28 kDa on SDS-PAGE. The enzyme showed activity to various lipid hydroperoxides and their methyl esters. The enzyme was also active toward phosphatidylcholine hydroperoxide and cholesterol hydroperoxide. Since the enzyme was not active on hydrogen peroxide, the enzyme was thought to be a kind of glutathione S-transferase, although the purified enzyme did not show the glutathione-conjugating activity with electrophilic compounds such as 1-chloro-2,4-dinitrobenzene and o-dinitrobenzene, which are used as the substrate of glutathione S-transferase in yeast. The glutathione peroxidase in H. mrakii was then suggested to be a novel type of glutathione peroxidase in substrate specificity and intracellular localization, being different from those of other sources purified so far.

Endogenous peroxidatic activity in astrocytes after spinal cord injury

After spinal cord injury, endogenous peroxidatic-like activity develops along the axis of the cord. At 2 weeks postinjury, this activity appears in cells whose processes are intimately associated with microvessels. The objectives of this study were to further characterize this response and to identify the cellular localization of endogenous peroxidatic-like activity. After traumatic injury to the rat spinal cord, adjacent sections of spinal cord were processed in medium to visualize antiglial fibrillary acidic protein, endogenous peroxidatic activity, or cytochrome oxidase activity. In addition, certain sections, stained for endogenous peroxidatic-like activity, were prepared for electron microscopy. To identify the nature of the activity, some sections were exposed to an incubation medium that included inhibitors of either catalase or heme protein activity. The distribution of prominent glial fibrillary acidic protein immunoreactivity in the dorsal columns corresponded to that of marked staining for endogenous peroxidatic-like activity and cytochrome oxidase. At the ultrastructural level, endogenous peroxidatic-like activity was identified in the cytoplasmic compartment of the astrocyte. This activity was abolished when potassium cyanide (an inhibitor of heme protein) was added to the incubation medium. Spinal cord injury elicited a pronounced cellular response along the axis of the cord that was characterized by enhanced staining for antiglial fibrillary acidic protein, cytochrome oxidase activity, and endogenous peroxidatic-like activity. It is not clear whether pronounced cytochrome oxidase activity corresponded to astrocytes that also expressed prominent endogenous peroxidatic-like activity. However, according to both light and ultrastructural findings, endogenous peroxidatic-like activity was prominently associated with the astrocytic cytoplasm. The biochemical nature of the peroxidatic activity is unknown, but these results suggest that it is related to a heme-containing protein.

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.

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.

Microsomal glutathione-dependent protection against lipid peroxidation acts through a factor other than glutathione peroxidase and glutathione S-transferase in rat liver

Ascorbate-Fe3+-induced and NADPH-induced lipid peroxidation of rat liver microsomes were inhibited by glutathione (GSH). This inhibition was due to microsomal GSH-dependent factor. This factor was heat labile, and storage of microsomes at 4 degrees C for 1 week diminished the activity. GSH could not be substituted by other sulfhydryl compounds tested. Deoxycholate (1 mM) and bromosulfophthalein (0.1 mM) inhibited GSH-dependent protection but did not inhibit microsomal GSH peroxidase activity. Iodoacetate (10 mM) inhibited GSH-dependent protection but did not inhibit microsomal GSH S-transferase. N-Ethylmaleimide (0.1 mM) and oxidized glutathione (10 mM) inhibited GSH-dependent protection but activated microsomal GSH S-transferase activity. These results indicate the existence of a heat-labile, microsomal GSH-dependent protective factor against lipid peroxidation that acts through a factor other than GSH-peroxidase and GSH S-transferase.

Role of a partially purified glutathione S-transferase from rat liver nuclei in the inhibition of nuclear lipid peroxidation

Glutathione protects isolated rat liver nuclei against lipid peroxidation by inducing a lag period prior to the onset of peroxidation. This GSH-dependent protection was abolished by exposing isolated nuclei to the glutathione S-transferase inhibitor S-octylglutathione. In incubations containing 0.2 mM S-octylglutathione, the GSH-induced lag period was reduced from 30 to 5 min. S-Octylglutathione (0.2 mM) also completely inhibited nuclear glutathione S-transferase activity and reduced glutathione peroxidase activity by 85%. About 70% of the glutathione S-transferase activity associated with isolated nuclei was solubilized with 0.3% Triton X-100. This solubilized glutathione S-transferase activity was partially purified by utilizing a S-hexylglutathione affinity column. The partially purified nuclear glutathione S-transferase exhibited glutathione peroxidase activity towards lipid hydroperoxides in solution. The data from the present study indicate that a glutathione S-transferase associated with the nucleus may contribute to glutathione-dependent protection of isolated nuclei against lipid peroxidation. Evidence was obtained which indicates that this enzyme is distinct from the microsomal glutathione S-transferase.

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.

Membrane antioxidants

In this chapter, I have discussed both lipid-soluble and water-soluble antioxidants that exert protective action with respect to inhibiting lipid, and in some cases, protein oxidation in both natural and artificial membranes. In addition, recent work has begun to clarify exactly how antioxidant enzymes can protect membranes against peroxidative damage. Although we have some understanding of the mechanisms of several of these antioxidants, much work remains to be done before we can begin making dietary recommendations that may have profound implications with respect to aging, cancer, and the many other human diseases that have been associated with radical-induced damage.

Inhibition of doxorubicin-initiated membrane damage by N-acetylcysteine: possible mediation by a thiol-dependent, cytosolic inhibitor of lipid peroxidation

Peroxidative damages are thought to be a component of doxorubicin-induced cardiac toxicity. Administration of certain thiols, such as N-acetylcysteine, are reported to be protective against the cardiac toxicity and mortality associated with chronic doxorubicin administration. We have investigated the possibility that N-acetylcysteine exerts its protective effect by inhibiting doxorubicin-induced lipid peroxidation in a process mediated by a heat-labile cytosolic factor. Dialyzed rat liver cytosol plus N-acetylcysteine significantly inhibited doxorubicin-induced lipid peroxidation in a microsomal system whereas neither cytosol nor N-acetylcysteine alone does so. Concomitantly, it was observed that N-acetylcysteine is rapidly consumed in a system containing cytosol, microsomes, and doxorubicin. The inhibition of lipid peroxidation by the cytosol and accompanying N-acetylcysteine oxidation is heat labile. Rat heart cytosol showed a similar N-acetylcysteine-dependent inhibition of doxorubicin-induced lipid peroxidation, but heart cytosol was less potent than hepatic cytosol on the basis of protein content. The antioxidant property of heart cytosol as well as its capacity to oxidize N-acetylcysteine was inhibited by prior treatment of the cytosol with iodoacetic acid. This suggested that the factor possessed essential sulfhydryl groups. These results suggest that hepatic and cardiac cytosols contain heat-labile components capable of utilizing N-acetylcysteine as a substrate to suppress the doxorubicin-induced peroxidative damage to microsomes induced by doxorubicin. These components may play a role in the protective effects of N-acetylcysteine against doxorubicin-induced cardiac toxicity and mortality.

An unidentified inhibitor of lipid peroxidation in intestinal mucosa

Lipid peroxidation in vitro was tested by malonaldehyde production in gastrointestinal mucosa and compared with other tissues. It was observed that gastrointestinal mucosa was resistant to both non-enzymatic and enzymatic lipid peroxidation. This was due to the presence of an inhibitor of lipid peroxidation in the membranous fractions of intestinal mucosa. This inhibitor was capable of inhibiting other recognised peroxidation systems, such as liver mitochondria. This effect was confirmed by measurement of diene conjugation and utilisation of arachidonic acid as other markers of peroxidation, in addition to malonaldehyde production. Preliminary characterisation of this inhibitor revealed that it is resistant to proteolysis, non-diffusable and extractable from membranes by organic solvents. It was partially purified by methanol extraction of the mucosa and by three successive preparative thin-layer chromatography steps. The purified material gave a single spot on thin-layer chromatography, using a number of different solvent systems. Mobility of the inhibitor on thin-layer chromatography was different from that of authentic tocopherol, and it was present in the intestine of vitamin-E-deficient animals. These results suggest that the resistance of intestinal mucosa to lipid peroxidation is due to the presence of a novel inhibitor which is lipidic in nature.

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)

Glutathione redox pathway and reperfusion injury. Effect of N-acetylcysteine on infarct size and ventricular function

Glutathione peroxidase is an important enzyme in the degradative cascade of reactive oxygen free radicals. N-Acetylcysteine (NAC) is a low molecular weight compound that has been used clinically to replenish glutathione. To assess the role of the glutathione redox pathway on reperfusion injury, 23 animals underwent 90 minutes of proximal left anterior descending coronary artery occlusion followed by 24 hours of reperfusion with the administration of NAC (n = 11) or saline (n = 12) beginning 30 minutes into occlusion and continuing for 3 hours after reperfusion. Regional ventricular function was measured with contrast ventriculography, and regional myocardial blood flow was determined with microspheres. At 24 hours, the area at risk was defined in vivo with Monastral Blue, and the area of necrosis was defined by incubation in triphenyltetrazolium. Biopsies were taken from the ischemic and nonischemic zones to determine levels of total glutathione, superoxide dismutase and glutathione peroxidase activity, and reactivity to thiobarbituric acid, an index of lipid peroxidation. The rate-pressure product and myocardial blood flow were similar in the two groups throughout the study. No significant differences were noted in infarct size expressed as a percentage of the area at risk (28.6 +/- 5.3% vs. 36.6 +/- 6.0%) and of the total left ventricle (14.4 +/- 3.2% vs. 16.5 +/- 3.1%), and no differences were noted between the two groups on examination of the ischemic subendocardium by light and electron microscopy. Both groups exhibited similar degrees of dyskinesis during occlusion; however, treated animals showed significant improvement in regional radial shortening at 3 hours (3.4 +/- 2.4% vs. -2.4 +/- 2.1%, p less than 0.02) and 24 hours (9.2 +/- 2.2% vs. -2.5 +/- 6.3%, p less than 0.001) after reperfusion. No differences were present in total glutathione, thiobarbituric acid reactivity, or superoxide dismutase and glutathione peroxidase activity in the ischemic zones of the two groups. This study suggests that N-acetylcysteine treatment before reperfusion may reduce myocardial stunning but does not limit myocyte death after reperfusion.

Promotion of iron-induced rat liver microsomal lipid peroxidation by copper

Although copper has been demonstrated to promote lipid peroxidation in a number of systems, the mechanisms involved have not been fully defined. In this study, the role of copper in modifying lipid peroxidation has been explored in rat hepatic microsomes. In an in vitro system containing reduced glutathione (GSH, 200 microM) and Tris buffer, pH 7.4, cupric sulfate (1-50 microM) potentiated lipid peroxidation induced by ferrous sulfate (10 microM) but was unable to elicit peroxidation in the absence of iron. Higher levels of cupric sulfate (100 microM or greater) were inhibitory. The nature as well as the extent of the peroxidative response of microsomes to cupric sulfate were dependent on glutathione levels in addition to those of iron. Cupric sulfate (100 microM) strongly potentiated ferrous ion-induced lipid peroxidation in the presence of 400-800 microM GSH, while it inhibited peroxidation at lower levels of GSH (0-200 microM) and did not affect ferrous ion-induced peroxidation with glutathione levels of 3-10 mM. The potentiating effect of copper on ferrous ion-induced lipid peroxidation was further explored by investigating: (1) potential GSH-mediated reduction of cupric ions; (2) potential copper/GSH-mediated reduction of ferric ions (formed by oxidation during incubation); and (3) possible promotion of propagation reactions by copper/GSH. Our results indicate that cupric ions are reduced by GSH and thus are converted from an inhibitor to an enhancer of iron-induced lipid peroxidation. Cuprous ions appear to potentiate lipid peroxidation by reduction of ferric ions, rather than by promoting propagation reactions. Iron (in a specific Fe+2/Fe+3 ratio) is then an effective promoter of initiation reactions.

Characterization of glutathione-dependent inhibition of lipid peroxidation of isolated rat liver nuclei

Glutathione (GSH) is known to play an important role in protecting cells against oxidative stress. The present study was undertaken to assess the ability of GSH to protect isolated rat liver nuclei against NADPH-induced peroxidation. Nuclei were isolated from rat liver homogenates by discontinuous sucrose gradient centrifugation, and lipid peroxidation was induced by 1.7 mM ADP, 0.11 mM EDTA, 0.1 mM FeCl3, and either 1 mM NADPH or 0.5 mM ascorbate. The amount of lipid peroxidation was determined by measuring the formation of thiobarbituric acid-reactive products and the disappearance of lipid unsaturated fatty acid moieties. The addition of GSH (0.1 to 1.0 mM) produced a concentration-dependent lag period prior to the onset of lipid peroxidation. This GSH-induced lag period was abolished by pretreatment of nuclei with trypsin, thiol modifying reagents, disulfides, or heating nuclei at 60 degrees C for 15 min. Nuclei which were incubated with GSH also catalyzed the conversion of cumene hydroperoxide to cumyl alcohol. Similarly, this activity was also inhibited by thiol modifying reagents, disulfides, and heating nuclei at 60 degrees C for 15 min. The data suggest that a GSH-dependent peroxidase activity is associated with rat liver nuclear membranes which are capable of inhibiting lipid peroxidation.

Bromosulfophthalein abolishes glutathione-dependent protection against lipid peroxidation in rat liver mitochondria

The effect of bromosulfophthalein (BSP) on GSH-dependent protection against lipid peroxidation in rat liver mitochondria was examined. Mitochondrial lipid peroxidation induced by ascorbate-Fe2+ was prevented by GSH, and addition of BSP abolished the protective effect of GSH. The effect of BSP was apparently not due to causing disappearance of GSH from the reaction mixture by interacting directly with GSH. BSP strongly inhibited the mitochondrial GSH S-transferase activity rather than the GSH peroxidase activity. Ascorbate-Fe2+-induced lipid peroxidation in mitochondria without addition of GSH was also stimulated to some extent by BSP, and the stimulation seems likely to be due to abolition of the inhibitory effect of endogenous GSH. GSH could not be replaced as an inhibitor of lipid peroxidation by cysteine, beta-mercaptoethanol, or dithiothreitol. The inhibitory effect of GSH on lipid peroxidation was not observed in vitamin E-deficient mitochondria. No inhibitory effect of exogenous vitamin E was demonstrated either in vitamin E-deficient mitochondria or in vitamin E-sufficient mitochondria in the presence of BSP, whether GSH was added or not. These results indicate that a mitochondrial GSH-dependent factor which inhibits lipid peroxidation requires vitamin E to exert its function. It is suggested that mitochondrial GSH S-transferase(s) may be responsible for GSH-dependent inhibition of lipid peroxidation in mitochondria, probably by scavenging lipid radicals.

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

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

Lipid peroxidation and mechanisms of toxicity

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

Mechanistic aspects on chemical induction of spindle disturbances and abnormal chromosome numbers

Work on the chemical induction of spindle disturbances and abnormal chromosome numbers, and work on the composition and biochemistry of the spindle are reviewed. Some early investigations have shown that there is an unspecific mechanism for chemical induction of spindle disturbances. This mechanism is based on the interaction of compounds with cellular hydrophobic compartments. Some compounds act differently and are more active than predicted from their lipophilic character. Selected compounds of that kind and their possible mechanisms of action are discussed. Changes in sulfhydryl and ATP levels, oxidative damage of membranes and impaired control of cytoplasmic Ca2+ levels are discussed in this context.

Prevention of microsomal production of hydroxyl radicals, but not lipid peroxidation, by the glutathione-glutathione peroxidase system

The glutathione-glutathione peroxidase system is an important defense against oxidative stress. The ability of this system to protect against iron-catalyzed microsomal production of hydroxyl radicals [oxidation of 4-methylmercapto-2-oxo-butyrate (KMBA)] and lipid peroxidation was evaluated. When rat liver cytosol was added to microsomes, strong inhibition against KMBA oxidation was observed. No protection was found when the cytosol was boiled or dialyzed. In the latter case, the addition of 0.5 mM glutathione restored almost complete protection, whereas in the former case protection could be restored by the addition of both glutathione and glutathione peroxidase. Cysteine could not replace glutathione, nor could glutathione S-transferase replace glutathione peroxidase. The glutathione-glutathione peroxidase system was also very effective in decreasing production of hydroxyl radicals stimulated by the addition of menadione or paraquat to microsomes. In the absence of cytosol, the addition of glutathione plus glutathione peroxidase was also effective; however, 5 mM glutathione was necessary to protect against KMBA oxidation. The effective concentration of glutathione required for protection was lowered when glutathione reductase was added to the system, to regenerate reduced glutathione. These results indicate that low concentrations of glutathione in conjunction with glutathione peroxidase plus reductase can be very effective in preventing microsomal formation of hydroxyl radicals catalyzed by iron and other toxic compounds. Microsomal lipid peroxidation was decreased 40% by glutathione alone, and this decrease was potentiated in the presence of glutathione reductase. In contrast to KMBA oxidation, the combination of glutathione plus glutathione peroxidase was not any more effective than glutathione alone in preventing lipid peroxidation. The differences in sensitivities of microsomal lipid peroxidation and KMBA oxidation to glutathione peroxidase suggest that these two processes can be distinguished from each other, and that free H2O2 and hydroxyl radicals are involved in KMBA oxidation, but not lipid peroxidation.

Effects of 2-mercaptopropionyl glycine on radiation-induced lipid peroxidation in liposomes and in rat liver microsomal suspensions

gamma-Irradiation of rat liver microsomal suspensions resulted in the accumulation of both malondialdehyde (MDA) and lipid hydroperoxides. The presence of 2-mercaptopropionylglycine (MPG) during the irradiation period decreased the formation of MDA and lipid hydroperoxides in a dose (MPG)-dependent manner. This may be attributed to the ability of MPG to scavenge the free radicals produced by irradiation. Post-irradiation incubation of microsomes further enhanced the production of both MDA and lipid hydroperoxides; when high concentrations of MPG were present during the incubations the production of MDA and lipid hydroperoxides was substantially decreased. This antioxidant role of MPG was demonstrated for both pre-irradiated microsomes and liposomes and is thought to be due to the conversion of the hydroperoxy to hydroxy fatty acids within the lipid bilayer, as well as the scavenging action on initiating free radicals.

Enzymatic defense against radiation damage in mice. Effect of selenium and vitamin E depletion

Radiation effects are mediated in part by the generation of oxygen-derived free radicals and hydrogen peroxide. Membrane polyunsaturated fatty acids are important biological targets of these toxic molecules which cause lipid peroxidation. Radiation damage to DNA is also known to result in base hydroperoxides, especially thymidine hydroperoxide. Glutathione (GSH) is known to inhibit lipid peroxidation both chemically and through its interaction with the selenium-dependent glutathione peroxidase (GSH-Px). Although cytosolic GSH-Px can metabolize organic lipid peroxides in solution, it cannot metabolize phospholipid peroxides in micelles. This may be due to the interference of phase differences between the aqueous cytosol and the membrane, or the result of steric hindrance. Recent studies have suggested the presence of a membrane-bound GSH-dependent peroxidase system. We examined the cytosolic versus membrane-associated GSH-Px, in various tissues of mice on a selenium and vitamin E deficient diet, and found significant differences among organs in the distribution of enzyme activity in these two subcellular fractions. The effect of single high-dose whole body irradiation did not appear to be related to the activity of these enzymes.

Metabolism of prostaglandin E analogs in guinea pig and rat liver microsomes

Tritium-labelled 16,16-dimethyl-PGE2, 9-methylene-PGE2 (9-deoxo-16,16-dimethyl-9-methylene-prostaglandin E2) and tetranor-9-methylene-PGE2 were incubated with guinea pig liver microsomes. All three compounds were converted to omega-oxidized products in yields of a few per cent. In addition, from incubations with 9-methylene-PGE2 and tetranor-9-methylene-PGE2 were also obtained metabolites with the methylene group transformed into a dihydrodiol. In a comparative study with rat liver microsomes, it was found that these converted tetranor-9-methylene-PGE2 in a 50 per cent yield to omega-oxidized products. Finally, 20.000 X G supernatants from guinea pig and rat liver were compared with respect to omega-oxidation. The rat liver 20.000 X G supernatant was found to convert the substrate to the same extent as washed microsomes. By contrast, the guinea pig liver 20.000 X G supernatant was considerably more efficient than washed microsomes.

Interaction of PGBx and peroxides with cytochrome c and inhibition of lipid peroxidation

PGBx, a derivative of prostaglandin B1, stimulated the oxidation of cytochrome c in the presence of H2O2. Although the reaction was nonenzymatic, the apparent activation energies of 12 and 4.9 kcal above and below the transition at 21.5 degrees C were similar to those for oxidation by cytochrome oxidase. Depletion of H2O2 and oxidation of cytochrome c followed similar time courses, suggesting that H2O2 was consumed in the reaction. PGBx was a specific requirement, but organic hydroperoxides (ethyl and T-butyl) could replace H2O2. Low concentrations of ethyl or t-butyl hydroperoxide initially stimulated the oxidation of cytochrome c; this stimulation disappeared before completion of the oxidation, but was restored when the hydroperoxide concentration was renewed, suggesting that these hydroperoxides were probably also consumed in the reaction. The concentration of PGBx (8.9 microM) required for half-maximum stimulation of the oxidation was similar to the apparent Kd for its dissociation from oxidized cytochrome c (6.8 microM). Binding data and CD spectra suggested that a 1:1 complex between cytochrome c and PGBx was formed, altering the conformation of the heme region. This conformational change caused a shift of the Soret absorption peak from 410 to 406 nm and may be responsible for the enhanced oxidizability of the cytochrome c by H2O2. Cytochrome c inhibited lipid peroxidation in microsomes, an effect enhanced by the addition of PGBx. In the absence of lipid peroxidation, cytochrome c and PGBx stimulated NADPH oxidation via NADPH-cytochrome c reductase. Thus the inhibition of lipid peroxidation by cytochrome c and PGBx may involve either the removal of hydroperoxides or deviation of electron transfer away from the pathway for lipid peroxidation.

GSH-dependent inhibition of lipid peroxidation: properties of a potent cytosolic system which protects cell membranes

Properties of a heat labile, nondialyzable cytosolic factor which prevents lipid peroxidation in membranous organelles are described. The factor is present in liver and other animal tissues, and its capacity to inhibit lipid peroxidation in membranes subjected to oxidative stress is greatly potentiated by glutathione (GSH), although GSH by itself has no inhibitory effect on lipid peroxidation. The data obtained thus far indicate that one or more sulfhydryl groups associated with the factor is required for the inhibition. The mechanism by which lipid peroxidation is inhibited must involve prevention of initiation of peroxidation in the membranes, presumably by a process requiring one or more sulfhydryl groups associated with the heat labile factor. The latter appears to be protected by GSH while the factor is exerting its inhibitory effect on lipid peroxidation. The factor is not one of the known GSH-dependent enzymes, and appears to be a potent and ubiquitous system for stabilizing cell membranes against oxidative damage.

Glutathione peroxidase activity in surgical and autopsied human brains

Glutathione peroxidase (GSHPx) activity was assayed in normal cerebral gray and white matter samples obtained from frontal, temporal, occipital and parietal lobes during surgical approach to an underlying lesion, and also in normal autopsied human frontal gray and white matter. GSHPx was assayed by a 2 step enzyme reaction which was monitored by following the oxidation of NADPH at 340 nm. It was found that all the brain samples studied contained GSHPx activity. Parietal lobe appeared to have the lowest GSHPx activity compared to temporal, occipital or frontal lobes. Mean enzyme activity in autopsied samples was comparable to that in surgical material. However, considerable loss of activity was observed after 10 years of tissue storage at -80 degrees C.

Preparation of hydroperoxy and hydroxy derivatives of rat liver phosphatidylcholine and phosphatidylethanolamine

A convenient method for the preparation of hydroperoxy and hydroxy derivatives of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) is described. PC and PE obtained from rat liver were oxidized with singlet oxygen by using methylene blue as the photosensitizer, and their hydroperoxides were isolated with the aid of reverse phase liquid chromatography. The hydroxy derivatives were obtained by reducing the hydroperoxides with sodium borohydride. The results of gas chromatography mass spectrometry revealed that hydroxy fatty acid components of the hydroxy derivatives were derived from isomeric hydroperoxides of oleic acid, linoleic acid, arachidonic acid and docosahexanoic acid. Normal phase high performance liquid chromatography did not separate the hydroperoxy and hydroxy derivatives from the respective unoxidized phospholipids, although unoxidized PC and PE were separated from each other. However, the hydroperoxy and hydroxy derivatives could be distinguished from unoxidized phospholipid species on reversed phase thin layer chromatography.

Initial observations on the role of glutathione peroxidases in Euglena

The algae Euglena gracilis possesses two glutathione (GSH) peroxidase: a GSH peroxidase that reduces organic hydroperoxides as well as hydrogen peroxide (GSH peroxidase 1); and a GSH peroxidase associated with GSH transferase that is active only with organic hydroperoxide substrates (GSH peroxidase 2). Preliminary experiments with Euglena were conducted to explore the in vivo role of the GSH peroxidases. The enzymes were not induced in response to the stimulation of cellular processes that generate oxidant species, such as beta-oxidation or photosynthesis. The levels of GSH peroxidase 1 were approximately twofold higher in autotrophic cultures containing the herbicide DCMU. GSH peroxidase 1 was most active in stationary phase cells; while the levels of GSH peroxidase 2 were fairly constant throughout growth. Under conditions where lipid peroxidation was induced in Euglena, the addition of either GSH peroxidase plus GSH reduced the lipid peroxide levels more than tenfold.

Consecutive action of phospholipase A2 and glutathione peroxidase is required for reduction of phospholipid hydroperoxides and provides a convenient method to determine peroxide values in membranes

The purpose of this study was to investigate the ability of selenium-dependent glutathione peroxidase to reduce phospholipid hydroperoxides in membrane bilayers and to develop a method to measure the peroxide content of phospholipids. Phospholipid hydroperoxides were synthesized by photooxidation of 1-palmitoyl 2-linoleoyl phosphatidylcholine and characterized by gas chromatography-mass spectrometry. Phospholipid hydroperoxides in phosphatidylcholine bilayers showed no detectable reactivity with Se-dependent glutathione peroxidase (the reaction is at least 65,000 times slower than with an available hydroperoxide). However, after the phospholipid hydroperoxides were preincubated with phospholipase A2, the free fatty acid hydroperoxides became available as a substrate for Se-dependent glutathione peroxidase. The enzyme assay can be used for convenient determination of peroxide values in phospholipids at the 1 nmole level and free fatty acid hydroperoxides can be distinguished from phospholipid hydroperoxides by omitting phospholipase A2. The accuracy of the enzymatic method was confirmed using an improved colorimetric chemical assay to measure peroxide values of phospholipid hydroperoxides to the same sensitivity. The chemical assay was not linear in the presence of high levels of lipid, but at low levels of lipid the peroxide values of phospholipid hydroperoxides measured by both methods agreed to within 1%. Since high levels of lipid inhibited the chemical assay, the enzyme assay is more accurate for determination of peroxides in membranes and tissues. The possible role of phospholipase deficiencies as a causal factor in degenerative diseases thought to be due to lipid peroxidation, such as Neuronal Ceroid Lipofuscinosis (Battens disease), is discussed.

Inhibition of microsomal lipid peroxidation by cytosolic protein in presence of ADP and high concentration of Fe2+

Microsomal lipid peroxidation induced by NADPH, but not by ascorbate, was found to be inhibited by liver cytosol. This inhibition was not dependent on glutathione and was enhanced by ADP in presence of Fe2+ at a concentration of 50 microM or higher. ATP was also effective, but not AMP or cyclic AMP. The cytosolic factor appeared to be a protein as it was heat-labile (greater than 70 degrees C), was non-dialyzable and was precipitated by ammonium sulfate and acetone. It was stable for several months in frozen state and also when heated at 50 degrees C for 10 min. The inhibition by the cytosolic protein was obtained by producing a lag in the activity of lipid peroxidation and was reversed by ceruloplasmin but not by catalase, cytochrome c, hemoglobin or superoxide dismutase. This inhibitory effect by cytosol was limited to formation of lipid peroxides whereas oxygen uptake and NADPH oxidation remained unaffected. Regulation of lipid peroxidation by nucleotide-Fe complexes and cytosolic proteins is indicated by these studies.

Reduction of polyunsaturated fatty acid hydroperoxides by human brain glutathione peroxidase

Glutathione peroxidase (GSHPx) activity in the normal human brain was investigated using lipid hydroperoxides as substrates. Samples were obtained from autopsied frontal gray matter of 5 normal human males with no known central nervous system (CNS) disease. Aliquots were homogenized in 0.9% NaCl-0.5% Triton X-100, and the supernatant solution, obtained after centrifugation at 105,000 X g, was used for GSHPx assay. Glutathione peroxidase was measured by following the oxidation of NADPH at 340 nm. Hydroperoxides of linoleic, linolenic, gamma linolenic, 11,14 eicosodienoic, homo gamma linolenic, arachidonic, docosotetraenoic and docosohexaenoic acids were prepared and used as substrates. All these hydroperoxides were reduced by the brain GSHPx system, but at different rates. Gamma linolenic and docosotetraenoic hydroperoxides were reduced rapidly, whereas the peroxides of docosohexaenoic and 11,14 eicosodienoic were reduced at the lowest rate. Arachidonic hydroperoxide had the highest affinity for the enzyme and linolenic the lowest. Our results suggest that the brain GSHPx system is capable of reducing hydroperoxides of polyunsaturated fatty acids.

Rainbow trout liver microsomal lipid peroxidation. The effect of purified glutathione peroxidase, glutathione S-transferase and other factors

Glutathione peroxidase (glutathione: hydrogen-peroxide oxidoreductase, EC 1.11.1.9) was purified approximately 600-fold from rainbow trout liver soluble fraction and its activity in the NADPH microsomal lipid peroxidation system tested. The enzyme has an approximate molecular weight of 100 000, contains four subunits and four atoms of selenium per mol protein. No selenium-independent glutathione peroxidase activity could be attributed to glutathione S-transferase (EC 2.5.1.18) in trout liver. Glutathione peroxidase together with glutathione (GSH) did not provide any additional protection in the in vitro liver microsomal lipid peroxidation system over and above that provided by GSH alone. Microsomal lipid peroxidation was, however, reduced by a partially purified glutathione S-transferase together with GSH. The protection provided by dialysed liver cytosol in this system was not GSH-dependent, showing that other factors in addition to glutathione S-transferase are involved. Of other possible factors, vitamin E reduced lipid peroxidation in this system. Concentrations of vitamin E in microsomes before and after peroxidation in vitro indicated that protective cytosolic factor(s) act prior to the termination of the free radical chain reactions effected by vitamin E. A GSH-dependent protective factor was present in microsomal protein, malondialdehyde formation in the in vitro microsomal system being markedly reduced in the presence of 5 mM GSH but not significantly lowered by 1 mM GSH.

Inhibition of microsomal lipid peroxidation by glutathione and glutathione transferases B and AA. Role of endogenous phospholipase A2

Lipid peroxidation in vitro in rat liver microsomes (microsomal fractions) initiated by ADP-Fe3+ and NADPH was inhibited by the rat liver soluble supernatant fraction. When this fraction was subjected to frontal-elution chromatography, most, if not all, of its inhibitory activity could be accounted for by the combined effects of two fractions, one containing Se-dependent glutathione (GSH) peroxidase activity and the other the GSH transferases. In the latter fraction, GSH transferases B and AA, but not GSH transferases A and C, possessed inhibitory activity. GSH transferase B replaced the soluble supernatant fraction as an effective inhibitor of lipid peroxidation in vitro. If the microsomes were pretreated with the phospholipase A2 inhibitor p-bromophenacyl bromide, neither the soluble supernatant fraction nor GSH transferase B inhibited lipid peroxidation in vitro. Similarly, if all microsomal enzymes were heat-inactivated and lipid peroxidation was initiated with FeCl3/sodium ascorbate neither the soluble supernatant fraction nor GSH transferase B caused inhibition, but in both cases inhibition could be restored by the addition of porcine pancreatic phospholipase A2 to the incubation. It is concluded that the inhibition of microsomal lipid peroxidation in vitro requires the consecutive action of phospholipase A2, which releases fatty acyl hydroperoxides from peroxidized phospholipids, and GSH peroxidases, which reduce them. The GSH peroxidases involved are the Se-dependent GSH peroxidase and the Se-independent GSH peroxidases GSH transferases B and AA.

Glutathione depletion by methyl chloride and association with lipid peroxidation in mice and rats

Inhalation of methyl chloride (CH3Cl) by male B6C3F1 mice resulted in a concentration-dependent depletion of glutathione (GSH) in liver, kidney, and brain. Exposure for 6 hr to 100 ppm CH3Cl decreased the concentration of GSH in mouse liver by 45%, while exposure to 2500 ppm for 6 hr lowered liver GSH to approximately 2% of control levels. For those exposures which decreased liver GSH to less than 20% of control levels, the extent of liver GSH depletion was closely correlated with the capacity of a 9000g supernatant fraction from the liver to undergo lipid peroxidation in vitro. GSH was depleted to a lesser extent in mouse brain and kidney, compared to liver, and no relationship to peroxidation was observed for single exposures to CH3Cl. A dose-dependent decrease in liver GSH was also produced by diethyl maleate, although a nearly lethal amount (2 ml/kg) was required to lower liver GSH to less than 10% of control levels. Under these conditions the amount of lipid peroxidation was 3.5-fold less than in mice exposed to 2000 ppm CH3Cl. Exposure of rats to 2000 ppm CH3Cl reduced liver GSH to 20% of control levels, compared to 4.5% in mice similarly exposed, and under these exposure conditions the amount of lipid peroxidation measured in vitro was 40-fold greater in mouse liver than in rat liver. During exposure of mice to 2500 ppm CH3Cl, ethane expiration increased to an extent comparable to that produced by administration of 2 ml/kg of CCl4. These findings suggest that GSH depletion in liver may be an important component of CH3Cl-induced hepatotoxicity.

Lipid peroxidation in alcoholic myopathy and cardiomyopathy

The hypothesis is presented that lipid peroxidation is responsible for the damage in skeletal and cardiac muscle of chronic alcoholic subjects. The enhanced lipid peroxidation is caused by the accumulation of oxygen radicals. Both excessive production and decreased disposal of oxygen radicals can arise from the acetaldehyde formed in the oxidation of ethanol. Although acetaldehyde from hepatic sources may contribute, muscle itself can generate significant amounts of acetaldehyde through the action of muscle catalase. The effects of alcohol on other tissues, and its known long-term effects on membranes lend support to this hypothesis. The ultrastructural features of the alcoholic myopathies provide further support. The resemblance between vitamin E-deficiency myopathy and the alcoholic myopathies is strong additional evidence in favor of this hypothesis.