Effect of glutathione peroxidase activity on lipid peroxidation in biological membranes

Urinary malondialdehyde as an indicator of lipid peroxidation in the diet and in the tissues

Although malondialdehyde (MDA) is extensively metabolized to CO2, small amounts are nevertheless excreted in an acid-hydrolyzable form in rat urine. In this study, urinary MDA was evaluated as an indicator of lipid peroxidation in the diet and in the tissues. MDA was released from its bound form(s) in urine by acid treatment and determined as the TBA-MA derivative by HPLC. MDA excretion by the rat was found to be responsive to oral administration of the Na enol salt and to peroxidation of dietary lipids. Urinary MDA also increased in response to the increased lipid peroxidation in vivo produced by vitamin E deficiency and by administration of iron nitrilotriacetate. Chronic feeding of a diet containing cod liver oil led to increases in MDA excretion which were not completely eliminated by fasting or feeding a peroxide-free diet, indicating that there was increased lipid peroxidation in vivo. MDA excretion was not responsive to Se deficiency or CCl4 administration. DPPD, a biologically active antioxidant, but not BHA, a non-biologically active antioxidant, prevented the increase in MDA excretion in vitamin E deficient animals. The results indicate that MDA excretion can serve as an indicator of the extent of lipid peroxidation in the diet and, under conditions which preclude a dietary effect, as an index of lipid peroxidation in vivo.

Skin-tumour promoting activity of methyl ethyl ketone peroxide—a potent lipid-peroxidizing agent

The tumour-promoting activity of methyl ethyl ketone peroxide (MEKP) was tested on the skin of hairless mice using a two-stage initiation-promotion protocol. When ultraviolet radiation in the UVB region (280-320 nm) was used as tumour initiator, MEKP showed weak promoting activity. The promotional activity of MEKP was potentiated by diethyl maleate, which is known to deplete intracellular glutathione, suggesting that lipid peroxidation may be important in the tumour promotion.

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.

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

A GSH-dependent microsomal protein which inhibits lipid peroxidation has been described [R. F. Burk, Biochim. biophys. Acta 757, 21 (1983)]. Studies of its mechanism indicate that it scavenges free radicals. Vitamin E (alpha-tocopherol) and selenium are micronutrients which protect against lipid peroxidation. The effect of nutritional deficiencies of these substances on the GSH-dependent protection against rat liver microsomal lipid peroxidation was studied to determine whether GSH, selenium and alpha-tocopherol function through separate or shared mechanisms. In the ascorbate-iron microsomal lipid peroxidation system, there is a 1-3 min lag phase before lipid peroxidation begins. The length of the lag correlated well (r = 0.87) with the microsomal alpha-tocopherol content as measured by high pressure liquid chromatography. Thus, the selenium-deficient microsomes, which had a shorter lag than controls, had a somewhat lower alpha-tocopherol content. The vitamin E-deficient microsomes, which had no detectable alpha-tocopherol, had the shortest lag, but a distinct lag was present. Addition of 0.1 mM GSH to control microsomes prolonged the lag by 270%. In selenium-deficient and vitamin E-deficient microsomes, which had shorter initial lags, GSH addition caused 345 and 280% increases respectively. This suggests that the function of the GSH-dependent protective mechanism is unimpaired in these deficiencies. Trypsin digestion of microsomes, which abolished the lag completely and destroyed the GSH-dependent protection, had no effect on microsomal alpha-tocopherol content, however. These experiments illustrate the importance of two defenses against microsomal lipid peroxidation: the GSH-dependent protein which is responsible for the existence of the lag, and alpha-tocopherol which affects the length of the lag. They suggest that these defenses function separately to prevent peroxidation of membrane polyunsaturated fatty acids. Selenium appears to affect microsomal alpha-tocopherol content but to have no other effect on the microsomal lipid peroxidation system.

Effects of chlorpromazine on the activities of antioxidant enzymes and lipid peroxidation in the various regions of aging rat brain

In this work, the effect of chronic intraperitoneal administration of chlorpromazine (5 and 10 mg/kg) on the antioxidant enzymes superoxide dismutase (SOD), catalase (CA), glutathione reductase (GR), and glutathione peroxidase (GP); lipid peroxidation; and lipofuscin accumulation in the brains of rats ages 6, 9, and 12 months was studied. Chlorpromazine increased the activities of SOD, GR, and GP in particulate fraction from cerebrum, cerebellum, and brain stem in a dose-dependent manner. While GR and SOD associated with soluble fraction increased, GP associated with soluble fraction was not affected. CA did not change after chlorpromazine administration in any regions of the brain of rats from all age groups. Chlorpromazine, thus, had a somewhat different action on antioxidant enzymes in different subcellular fractions. Chlorpromazine inhibited lipid peroxidation, both in vivo and in vitro, and it also inhibited accumulation of lipid peroxidation fluorescent products (lipofuscin), which was studied histochemically and biochemically as well. The data indicate that chlorpromazine inhibition of lipid peroxidation and of accumulation of lipofuscin can result from elevation of the activity of brain antioxidant enzymes.

Ascorbate and glutathione levels in the developing normal and dystrophic rat retina: effect of intense light exposure

Ascorbic acid and glutathione were measured in retinas excised from normal rats reared in a cyclic light or dark environment and in dystrophic rats from the dark environment. Similar measurements were made on retinas from age matched rats exposed to intense visible light for periods of up to 24 hours. In other rats, ascorbic acid was given for various periods before exposure to intense light and the degree of photoreceptor cell death determined subsequently by rhodopsin measurements. In non-intense light treated rats ascorbate and glutathione were 12.1 nmol/retina at 20 days of age and 13.3 - 15.9 nmol/retina in 60 day old animals. In dystrophic rat retinas glutathione was 4-8% higher and ascorbate 10-20% higher than in normal dark reared rats. Although the levels of ascorbate and glutathione per retina increased during development, the molar ratios of the antioxidant materials to rhodopsin decreased by 36% and 60% in normal and dystrophic rats respectively. The levels of glutathione in young cyclic light or dark reared normals were unaffected by intense light exposure of either short (2-4 hrs) or long (24 hrs) duration. However, in both 20 and 40 day old dystrophic rats, intense light exposure resulted in a significant increase in retinal glutathione. In contrast to glutathione, retinal ascorbate decreased in normal rats exposed to intense light for 24 hrs, in an age and prior light environment dependent fashion. At ages greater than 20 days, normal rats exposed to light had significantly lower retinal ascorbate levels than their non-light exposed counterparts. The levels of ascorbate in 21-40 and 41-60 day old dark reared rat retinas were also significantly lower than in comparable intense light treated-cyclic light reared rats. In the youngest dystrophic rats whole eye ascorbate (retina, RPE, choroid and sclera) was 20-30% lower than in non-light treated rats, but in older mutant rats (41-60 day) light had no effect on the level of ascorbate in the retina. As determined by the level of rhodopsin remaining in the eye two weeks after 24 hrs light exposure, cyclic light reared rats lost 50-55% of their visual cells. However, cyclic light rats supplemented with ascorbic acid before intense light exposure lost only 30-35% of their visual cells.

Granulocytic cryopreservation: further studies on the pathogenesis of impaired cellular function

The effects of different methods of purifying peripheral blood granulocytes on their functional capacity after cryopreservation have been studied. The standard method of isolating granulocytes by centrifugation through Lymphoprep sensitizes cells to damage induced by subsequent cryopreservation. Some of this damage occurs during addition of cryoprotectant and we describe how to add and remove dimethyl sulphoxide without impairing cell function. The granulocytic function that suffers most during cryopreservation is granulocyte migration. This impairment may be partially due to uncontrolled entry into the cell of calcium. In contrast the bactericidal capacity in vitro is not so greatly reduced and ability to reduce nitroblue tetrazolium redox dye even less so.

Antioxidant effect of diethyldithiocarbamate on microsomal lipid peroxidation assessed by low-level chemiluminescence and alkane production

Different thiol-containing compounds, such as diethyldithiocarbamate (DDC), glutathione, penicillamine, and dithioerythritol have been chosen to study their effect on ascorbate/Fe-ADP-induced lipid peroxidation, detected by low-level chemiluminescence and alkane production. In the concentration range used, these thiols exerted a temporary protection against lipid peroxidation by lengthening the induction period; after overcoming this induction period, no substantial inhibition of either chemiluminescence or alkane production was observed. DDC was effective in protecting against lipid peroxidation in the nanomolar range, whereas the group of other thiol-containing molecules operated in the millimolar range.

Purification and characterization of selenium-glutathione peroxidase from hamster liver

Hamster liver glutathione peroxidase was purified to homogeneity in three chromatographic steps and with 30% yield. The purified enzyme had a specific activity of approximately 500 mumol cumene hydroperoxide reduced/min/mg of protein at 37 degrees C, pH 7.6, and 0.25 mM GSH. The enzyme was shown to be a tetramer of indistinguishable subunits, the molecular weight of which was approximately 23,000 as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A single isoelectric point of 5.0 was attributed to the active enzyme. Amino acid analysis determined that selenocysteine, identified as its carboxymethyl derivative, was the only form of selenium. One residue of cysteine was found to be present in each glutathione peroxidase subunit. The presence of tryptophan was colorimetrically determined. Pseudo-first-order kinetics of inactivation of the enzyme by iodoacetate was observed at neutral pH with GSH as the only reducing agent. An optimal pH of 8.0 at 37 degrees C and an activation energy of 3 kcal/mol at pH 7.6 were found. A ter-uni-ping-pong mechanism was shown by the use of an integrated-rate equation. At pH 7.6, the apparent second-order rate constants for reaction of glutathione peroxidase with hydroperoxides were as follows: k1 (t-butyl hydroperoxide), 7.06 X 10(5) mM-1 min-1; k1 (cumene hydroperoxide), 1.04 X 10(6) mM-1 min-1; k1 (p-menthane hydroperoxide), 1.2 X 10(6) mM-1 min-1; k1 (diisopropylbenzene hydroperoxide), 1.7 X 10(6) mM-1 min-1; k1 (linoleic acid hydroperoxide), 2.36 X 10(6) mM-1 min-1; k1 (ethyl hydroperoxide), 2.5 X 10(6) mM-1 min-1; and k1 (hydrogen peroxide), 2.98 X 10(6) mM-1 min-1. It is concluded that for bulky hydroperoxides, the more hydrophobic the substrate, the faster its reduction by glutathione peroxidase.

Non-reactivity of the selenoenzyme glutathione peroxidase with enzymatically hydroperoxidized phospholipids

Selenium-containing glutathione peroxidase (EC 1.11.1.9) was purified 6000-fold from bovine red blood cells to apparent homogeneity. Lipoxygenase (EC 1.13.11.12) was enriched 20-fold from soybean acetone powder. Linoleic acid was peroxidized with lipoxygenase and then used as a substrate in the glutathione peroxidase reaction. Analogous experiments were conducted with synthetic 1,2-dilinoleoyl-L-alpha-glycerophosphocholine and with natural bovine heart cardiolipin. The peroxidized phospholipids were reactive with glutathione peroxidase only after enzymatic attack by phospholipase A2 (EC 3.1.1.4). This result implies that the membrane-protective function of glutathione peroxidase includes preceeding phospholipase action and excludes a direct interaction of this enzyme with membrane-bound lipid hydroperoxides.

Development of the cytosolic defence system against microsomal lipid peroxidation in rat liver

Ascorbate-induced lipid peroxidation in rat liver microsomes reaches the adult level in 2-3 days. NADPH-induced peroxidation develops more gradually, in parallel with the activity of NADPH-cytochrome P-450 reductase, attaining adult levels by 10-12 days. The glutathione-dependent cytosolic enzyme activity which inhibits peroxidation is inhibited by bromosulphophthalein. The development of this system lags behind the development of microsomal lipid peroxidation between the ages of 2 and 20 days, allowing peroxidation to proceed.

Metabolism of malondialdehyde by rat liver aldehyde dehydrogenase

Mammalian liver contains a group of pyridine nucleotide linked aldehyde dehydrogenases [E.C. 1.2.1.3] which are present in high specific activity and possess wide substrate specificities. Malondialdehyde (MDA), a difunctional three-carbon aldehyde thought to be toxic, is generated during membrane lipid peroxidation in hepatocytes. The role of aldehyde dehydrogenase (ALDH) in the metabolism of MDA was tested in vitro with subcellular fractions and semipurified cytosolic preparations from rat livers. The cytosolic fraction accounted for virtually all of the MDA (50 microM) metabolizing activity observed in the postnuclear supernatant fraction. The rate of MDA disappearance was relatively low in the mitochondrial fraction and was not detectable in reaction mixtures which contained microsomes. Rat liver cytosol contained two ALDHs with MDA metabolizing activity. These enzymes were separated by DEAE-cellulose ion exchange chromatography and had apparent Km values of 16 microM and 128 microM for malondialdehyde. Mitochondria contained an ALDH enzyme with lower affinity (Km of 7.3 mM with NAD+) for malondialdehyde. These data show that rat liver contains at least three ALDH enzymes which oxidize malondialdehyde.

Parallel increase of ascorbic acid and glutathione contents in brown adipose tissue during chronic cold exposure

Spontaneous lipid peroxidation rate was found unchanged in the brown adipose tissue of rats chronically exposed to cold, although oxidative metabolism, ascorbic acid and poly-unsaturated phospholipid amounts increased. It is suggested that the concomitant increase in glutathione concentration may protect the tissue from a possible peroxidative process.

The enzymatic estimation of organic hydroperoxides in the rat retina

An enzymatic procedure for the estimation of organic hydroperoxides has been adapted to biological tissues and applied to the measurement of hydroperoxides in the rat retina. Hydroperoxides are determined from the coupled activities of glutathione peroxidase and glutathione reductase as measured by the loss of NADPH absorbance. To minimize the effects of tissue catalyzed peroxide degradation, incubations were performed in the presence of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU); which inhibited the activity of retinal tissue glutathione reductase by 85%. For comparisons to the enzymatic technique, retinal tissue hydroperoxides were also estimated by the absorption of tissue extracts at 232 nm. Using the enzymatic procedure the hydroperoxide concentration in whole retina homogenates was significantly higher in 19-day-old rats than in either 35-day or adult animals. Hydroperoxides in the retina of young rats exposed to light for one hour were significantly lower than in non-exposed controls, while in adult rats, following light, hydroperoxides increased 13%. Fractionation of rat retinas into crude ROS and retina minus ROS components revealed that the ROS fractions contain at least twice the hydroperoxide concentration of the remaining retina. The concentration of hydroperoxides in the ROS fractions from dark-reared rats were significantly lower than in cyclic-light-reared animals. In both types of rats, one hour intense light exposure resulted in an increase in ROS hydroperoxides but the increases were not significant. ROS hydroperoxides were also found to be 85-90% water soluble. Estimates of the retinal hydroperoxide content obtained by absorption at 232 nm gave similar results to the enzymatic technique, but the levels were significantly lower. When retinas were maintained in vitro for one hour before analysis, hydroperoxides determined by either technique were significantly higher than in retinas assayed immediately, but A232 hydroperoxides were still significantly lower than hydroperoxides measured by the enzymatic procedure. It is concluded: (1) that the observed retinal hydroperoxide concentration depends upon animal age and the method of measurement; (2) that within the retina the photoreceptor cell contains at least a two-fold higher concentration of hydroperoxides than the remaining retina and that prior light history can affect those hydroperoxide levels (it appears that the photoreceptor cell is also a major site of hydroperoxide formation in the retina); (3) that during intense light exposure of short duration significant levels of hydroperoxides do not accumulate in the retinas of rats.

Pulmonary effects of intermittent subacute exposure to low-level nitrogen dioxide

The pulmonary biochemical and morphological changes resulting from the inhalation of relatively low levels of NO2 for up to 15 wk were investigated. Specific pathogen-free Fischer 344 rats were exposed to 0, 1, or 5 ppm NO2 or 1 ppm with two spikes to 5 ppm NO2 for 7 h/d, 5 d/wk for up to 15 wk. These exposures produced a mild concentration-related pulmonary injury, with the 5-ppm group sustaining the most damage. The other NO2-exposed animals showed similar types of damage, although the extent was less than that observed in the 5-ppm-exposed group. After 15 wk of exposure, histopathological examination revealed focal areas of hyperinflation and alveolar macrophage accumulation in some of the 5-ppm- and 1-5-ppm-exposed-exposed animals. These changes were preceded by a series of biochemical changes in the bronchoalveolar lavage fluid. Cell necrosis was indicated by elevated lavage fluid concentrations of lactate dehydrogenase after 1.7 to 2.7 wk of exposure. Also elevated were alkaline phosphatase and glutathione peroxidase. Lung tissue levels of glutathione reductase and glucose-6-phosphate dehydrogenase were also increased, indicating a possible protective response to the oxidant gas. After 15 wk of exposure, all biochemical indicators of injury has resolved. These data suggest that intermittent exposure to relatively low levels of NO2 with spike concentrations produces biochemical changes that resolve with continued exposure but produce histopathological changes that may persist with continued exposure.

The role of glutathione in detoxication

Glutathione (GSH) is a strong nucleophile which reacts well with soft electrophiles, but poorly with both weak and strong electrophiles. Weak electrophiles have low reactivity with all nucleophiles while strong electrophiles react well with weak nucleophiles including superabundant H(2)O. There are enzymes, the GSH transferases, which catalyze GSH conjugation with all the types of electrophiles described above. In order to deal with the wide variety of potential substrates, a multiplicity of GSH transferases exists-each tissue having its own collection and each enzyme having a different substrate specificity. These enzymes are often very abundant, e.g., in the rat liver cytosol, their concentration is 0.2 mM. THE FOLLOWING SUBSTRATES ARE CONSIDERED IN SOME DETAIL: 1-chloro-2,4-dinitrobenzene, the electrophile derived metabolically from paracetamol N-acetyliminoquinone?), benzo(a)pyrene-4-5-oxide, cholesterol-5alpha,6alpha-oxide, benzo(a)pyrene-7,8-diol-9,10-oxide and the electrophiles derived metabolically from aflatoxin B(1) (the 2,3-oxide?). According to the substrate, optimal enzyme rates vary over seven orders of magnitude from 10(-5) to 10(-12) mole/min/mg. Despite the wide embrace of the GSH transferases, not all metabolically produced electrophiles are substrates. We know of the following examples: N-methylol-4-aminoazobenzene and its 4'-hydroxy derivative (these are soft electrophiles and react well with GSH noncatalytically), N-sulfonyloxy-N-methyl-4-aminoazobenzene, N-sulfonyloxy-N-acetyl-2-aminofluorene (these are strong electrophiles which do not react selectively with GSH) and N-hydroxy-2-aminofluorene which appears to react only slowly with GSH. It is of interest in the present context that all these compounds are derived from either arylamine or arylamide carcinogens. Whether the reaction be enzymic or nonenzymic, conjugation with GSH is a very important means of detoxication accounting in some cases for up to 60% of the biliary metabolites. As seen in the example of aflatoxin B(1), very low enzymic rates observed in vitro are sufficient to account for apparently high rates of biliary excretion of GSH conjugates.GSH transferases have evolved other functions apart from the catalysis of GSH conjugation. GSH transferase B participates in the hepatic uptake of bilirubin and the intracellular distribution of the heme prosthetic group. It also has GSH peroxidase activity which suggests that it might participate in the detoxication of by-products of oxygen utilization including those produced by the action of cytochrome P-450. It is shown that GSH transferase B inhibits lipid peroxidation in vitro.

Effect of centrophenoxine on the antioxidative enzymes in various regions of the aging rat brain

This study investigated the effect (in vivo) of centrophenoxine (Helfergin) on the activity of antioxidant enzymes (glutathione peroxidase GSH-PER, glutathione reductase GSSG-RED, superoxide dismutase SOD and catalase) in subcellular fractions from the regions of the brain (cerebrum, cerebellum and brain stem) of rats aged 6, 9 and 12 months. In all age groups, normal (control) activity of GSH-PER, GSSG-RED and SOD in the three brain regions was higher in the soluble fractions than in the particulate fractions. The three regions of the brain showed different levels of the enzyme activities. Enzymes in soluble fractions (except GSSG-RED in cerebrum of rats aged 12 months) did not change with age. In particulate fractions, however, the enzymes showed age-related changes: GSH-PER decreased with age in cerebellum and brain stem, but showed an age-related increase in cerebrum, GSSG-RED and SOD increased with age in all the three brain regions. Catalase activity in all the three brain regions remained unchanged in all age groups. Six week administration of centrophenoxine (once a day in doses of 80 mg/Kg and 120 mg/Kg) to the experimental animals produced increases in the activity of SOD, GSH-PER and GSSG-RED in particulate fractions from all the three brain regions. In the soluble fractions, however, only SOD and GSH-PER activity was increased. In vitro also centrophenoxine stimulated the activity of GSH-PER. A dosage of 80 mg/Kg produced greater changes than a 120 mg/Kg dosage. The drug had no effect on the activity of catalase. Centrophenoxine also reduced lipofuscin deposits (studied both biochemically and histochemically) thus indicating that the drug inhibited lipofuscin accumulation by elevating the activity of the antioxidant enzymes. The data suggest that alleviation of senescence by centrophenoxine may, at least, partly be due to activation by it of antioxidant enzymes.

Lipid peroxidation: a possible mechanism of cephaloridine-induced nephrotoxicity

Cephaloridine produces renal cortical injury, but the precise mechanism responsible for this nephrotoxicity remains unclear. Recently cephaloridine has been shown to deplete reduced glutathione (GSH) concentration selectively in renal cortex. Cephaloridine nephrotoxicity can be potentiated by diethyl maleate (a GSH depletor), but no glutathione conjugate can be detected. Thus, it was of interest to investigate further the mechanism of depletion of renal cortical GSH by cephaloridine. In the present study, cephaloridine markedly decreased GSH in rat and rabbit renal cortex while concomitantly increasing oxidized glutathione (GSSG). Furthermore, cephaloridine increased lipid peroxidation specifically in renal cortical cells. Conjugated diene formation (an index of lipid peroxidation) was increased in renal cortex but not in the liver shortly following administration of cephaloridine. Removal of selenium and/or vitamin E from the diet, which should enhance lipid peroxidation, potentiated cephaloridine nephrotoxicity and enhanced cephaloridine-induced morphological damage in the kidney. These findings are consistent with a major role of lipid peroxidation in the etiology of cephaloridine nephrotoxicity.

Biochemical studies on strain differences of mice in the susceptibility to nitrogen dioxide

Strain differences of mice in their susceptibility to nitrogen dioxide (NO2) were examined by measuring the activities of antioxidative protective enzymes, and the amounts of antioxidants and lipid peroxides in lungs. Four strains of mice: ICR, BALB/c, ddy and C57BL/6 were used in this study and their LC50 values after exposure to NO2 for 16 hr were: 38, 49, 51 and 64 ppm, respectively (1). Genetic strain differences were observed in the enzyme activities, the antioxidant contents and lipid peroxide contents among these four different strains. The activities of glutathione peroxidase (GPX), glutathione S-transferase, and superoxide dismutase (SOD), and the contents of non-protein sulfhydryls (NPSH), alpha-tocopherol (alpha-Toc) and total lipids in lungs of the four strains were related to their LC50, while TBA reactants in lungs of the four strains were inversely related to their LC50. After exposure to 20 ppm NO2 for 16 hr, the activities of the protective enzymes and the contents of NPSH decreased, while the level of alpha-Toc increased markedly. The activities of GPX, 6-phosphogluconate dehydrogenase, SOD and disulfide reductase, and the contents of NPSH, alpha-Toc and total lipids were also related to their LC50. On the other hand, TBA reactants increased higher than those of the control groups and were inversely related to their LC50. These results suggest that the protective enzymes and the antioxidants are important factors at defence mechanism in lungs to NO2 and that the intensity of the protective systems in pigmented strains is generally greater than that in albino strains.

Age-related increase in erythrocyte oxidant sensitivity

Unlike erythrocytes from elderly humans, red blood cells from old mice are not more sensitive than are cells from young animals to lysis in hypotonic solutions, probably because the mean corpuscular volume decreases rather than increases with age in this species. However, when subjected to an oxidant stress (sodium ascorbate) red blood cells from old animals accumulate more methemoglobin and fewer remain intact than is the case with red blood cells from young mice. The data suggest that this increased vulnerability to oxidative damage is manifest relatively early in the lifespan of red blood cells from old animals and is not solely a property of the older cells. The pathogenesis of the decreased resistance to peroxidation is not known, but it does not appear to be the result of changes in reduced glutathione, NADH: methemoglobin reductase, superoxide dismutase, glutathione reductase, glutamic-oxaloacetic transaminase, or glucose 6-phosphodehydrogenase.

Effect of nitrogen dioxide exposure on cyclic GMP in rat lung

In vivo exposure of rats to 10 ppm nitrogen dioxide (NO2) for 6 h caused approx. 5-fold increase in the content of cyclic GMP in lung tissue. This increased cyclic GMP level lasted up to 24 h but returned to the normal level within 2 days, even when the NO2 exposure continued. This increase in the content of cyclic GMP of lung tissue by NO2 exposure was observed in both young and aged rats. There were no statistically significant changes in the content of cyclic AMP in lung tissue.

On the lipid peroxidation of rat liver hepatocytes, the formation of fluorescent chromolipids and high molecular weight protein

1. The formation of malondialdehyde by intact hepatocytes, induced by ADP/Fe3+ or cumene hydroperoxide, can be inhibited by the addition of thiourea. This may indicate that hydroxyl radicals are involved in this process. 2. Lipid peroxidation of intact hepatocytes leads to the formation of fluorescent chromolipids. When similar amounts of malondialdehyde are formed by either ADP/Fe3+ or cumene hydroperoxide, the lipid peroxidation induced by cumene hydroperoxide generates more fluorescent chromolipids than does the lipid peroxidation induced by ADP/Fe3+. 3. The formation of chromolipids is accompanied by the genesis of high molecular weight protein. With cumene hydroperoxide more high molecular weight protein is formed than with ADP/Fe3+. 4. It can be concluded that the defense system against lipid peroxidation of intact hepatocytes does not prevent the formation of lipofuscin-like chromolipids and high molecular weight protein as found earlier in microsomes. Cumene hydroperoxide, at least in this system, can be considered as an effective inducer of chromolipids.

Purification from pig liver of a protein which protects liposomes and biomembranes from peroxidative degradation and exhibits glutathione peroxidase activity on phosphatidylcholine hydroperoxides

The cell sap from pig liver contains a protein which protects phosphatidylcholine liposomes and biomembranes from peroxidative degradation in the presence of glutathione. The activity of this protein has been assayed by measuring the inhibition of aged phosphatidylcholine liposome peroxidation induced by the Fe3+-triethylenetetramine complex. The peroxidation-inhibiting protein from pig liver has been purified 585-fold to homogeneity with overall recovery of activity of 12%. (NH4)2SO4 precipitation, ion-exchange chromatography on DEAE-Sepharose CL-6B and CM23-cellulose, affinity chromatography on glutathione-bromosulfophthalein-Sepharose and gel filtration on Sephadex G-50 were used. Gel filtration and SDS- polyacrylamide gel electrophoresis indicated a molecular weight of approximately 20 000. The protein inhibited peroxidation by Fe3+-triethylenetetramine following a 15 min preincubation of phosphatidylcholine liposomes in the presence of 5mM glutathione or 2-mercapthoethanol. The pure protein exhibited glutathione peroxidase activity on hydroperoxide groups of phosphatidylcholine and on cumene and t-butyl hydroperoxides, with specific activities of 2.2, 3.8 and 0.9 mumol/min per mg protein, respectively. The protein appears to be distinct from the selenoenzyme glutathione peroxidase and from any known glutathione S-transferase. The peroxidation was studied also with fresh phosphatidylcholine liposomes and was induced in this case by Fe-ascorbate. To obtain protection by the peroxidation-inhibiting protein and glutathione, preincubation was not necessary, but alpha-tocopherol, incorporated in the liposomes in the molar ratio 1:250 to phosphatidylcholine, was required. Lipid peroxidation of rat liver mitoplasts and microsomes was blocked when these preparations were incubated in the peroxidizing mixture in the presence of peroxidation-inhibiting protein and glutathione. The protection from Fe3+-triethylenetetramine-induced peroxidation is related apparently to reduction of hydroperoxide groups in polyunsaturated fatty acid residues of phospholipids and to inhibition of free radicals formation by chain branching. Protection from the Fe-ascorbate-induced peroxidation is apparently attributable to the same mechanism. However, the requirement of alpha-tocopherol for protection in the Fe-ascorbate-induced peroxidation suggests that the cooperation of a free-radical scavenger is necessary. It is probable that the glutathione peroxidase activity is involved also in the glutathione-dependent protection exhibited by the protein on lipid peroxidation of biomembranes.

Studies on biochemical effects of nitrogen dioxide. II. Changes of the protective systems in rat lungs and of lipid peroxidation by acute exposure

This work was done to clarify the relation between the change of lipid peroxidation and the protective systems in lungs after NO2 exposures. JCL:Wistar 8-wk-old male rats were exposed continuously to 10 ppm NO2 for 2 wk. Lipid peroxidation, measured by ethane exhalation in the breath of the rats and by the reaction of thiobarbituric acid with lung homogenates, increased to a maximum at 3 d after a decline at 1 d, and then returned to the initial level (of d 0). Activities of glutathione peroxidase (GPx), glutathione reductase (GR), glucose-6-phosphate dehydrogenase (G6PD), 6-phosphogluconate dehydrogenase (6PGD), disulfide reductase (DSR), and superoxide dismutase (SOD) in the 105,000 X g supernatant of lung homogenates were depressed slightly at 1 d. Thereafter, they increased significantly to their maximum levels from 5 to 10 d, and these maximum levels were maintained until d 14. The pattern of change of these protective enzymes was symmetric to that of lipid peroxidation after 3 d. The order of the ratio of the increased value to the initial value was G6PD greater than DSR greater than 6PGD greater than GR greater than GPx greater than SOD. The time course of nonprotein sulfhydryls was similar to that of the protective enzymes. In contrast, the amounts of vitamin E increased to a maximum at 2 d and then returned to the initial level. The periodic change of vitamin E was similar to that of lipid peroxidation rather than that of the protective enzymes. These results suggest that the ability of the enzyme systems in lungs to protect against NO2 fluctuated in a complex manner and the activities of the protective enzymes varied inversely with lipid peroxidation.

Studies on paracetamol-induced lipid peroxidation

Post-mitochondrial supernatants isolated from livers of rats given a single large oral dose of paracetamol (800 mg/kg) showed rapid rates of lipid peroxidation when incubated in vitro. As a result of paracetamol administration the level of reduced glutathione (GSH) declined to approx. 20-25% of the peak physiological value. Addition of reduced GSH to the supernatant inhibited the peroxidation. Paracetamol-induced lipid peroxidation was inhibited in vitro by antioxidants (e.g. vitamin E) but was unaffected by superoxide dismutase and mannitol. N-acetyl cysteine and cysteamine inhibited lipid peroxidation in vitro in a cytosol-dependent manner in the absence of glutathione. Lipid peroxidation probably occurs simultaneously with the proposed covalent binding of the active metabolite of paracetamol. Since the former process is known to cause severe and extensive membrane damage, it may be a very important factor in paracetamol-induced liver necrosis.

Glutathione and non-protein sulfhydryl in cerebral cortex and lung in mice exposed to high oxygen pressure

Mice were exposed to 6 atm of 100% O2, and killed at the onset of hyperactivity, convulsions, and 10(s) post convulsions. Examination of brain cortex from mice killed at these stages of O2 toxicity revealed no change in oxidized glutathione (GSSG), non-protein sulfhydryls (NPSH), total glutathione (GSH + GSSG), the GSH/GSSG ratio, glutathione reductase and glutathione peroxidase. Mice exposed to 4 atm for 1 h or 6 atm for 16 min exhibited a 36% and 33% decrease in lung NPSH respectively, but no change in cortical NPSH was observed. Although intraventricular diethylmaleate (DEM) decreased cerebral NPSH 72%, no change in the susceptibility of mice to O2 convulsions was found. Disulfiram, an effective O2 convulsive protectant had no effect on either cortical NPSH or total glutathione.

Metabolism of epoxidized phosphatidylcholine by phospholipase A2 and epoxide hydrolase

The isolation and measurement of phospholipid epoxides as major peroxidation products in biomembrane preparations prompted an investigation of enzymatic mechanisms which may be responsible for their elimination. Analysis of microsomal epoxide hydrolase and phospholipase A2 activity against a phospholipid epoxide commonly encountered in tissues indicated it to be a poor substrate for epoxide hydrolase, but rapidly hydrolyzed by phospholipase A2. Microsomal and purified phospholipase A2 preparations hydrolyzed the phospholipid epoxide at rates 2-fold greater than were observed with a monoenoic phospholipid from which the epoxide would be derived. The product fatty acid epoxide, cis-9,10-epoxystearic acid, was rapidly hydrated by microsomal and cytosolic epoxide hydrolase. On the basis of earlier reports demonstrating increased phospholipase activity against oxidized phospholipids, and on the results of the present study, a model for the metabolism of oxidized membrane phospholipids is proposed.

Lipid peroxide formation and membrane damage in endotoxin-poisoned mice

Lipid peroxide formation and plasma membrane damage in mouse liver following the administration of Salmonella endotoxin were examined. The liver lipoperoxide level was markedly elevated in animals given endotoxin compared with that in the controls, and returned to its normal range after 2 days. On the other hand, superoxide dismutase activity was decreased by 18--48 hr after endotoxin injection, thereafter tending to increase. Glutathione reductase and glutathione peroxidase activities declined in the liver 18 hr after the injection. The endotoxin resulted in much lower lipoperoxide formation in the livers of tolerant mice than in those of the poisoned mice. The lipoperoxide level in endotoxin-poisoned mice after the administration of alpha-tocopherol was lower than that in the controls, and alpha-tocopherol administration prevented completely the membrane protein damage that arose from endotoxin challenge. After glutathione administration the membranes of the poisoned mice also returned to almost the normal disk electrophoretic profile. These results suggest that lipid peroxide formation in the liver plasma membrane caused by free radicals might occur in a tissue ischemic state in endotoxicosis.

Studies on biochemical effects of nitrogen dioxide: I. Lipid peroxidation as measured by ethane exhalation of rats exposed to nitrogen dioxide

This research was in order to follow the periodic fluctuation of lipid peroxidation by a new method in rats exposed to nitrogen dioxide. Wistar male rats were examined for lipid peroxidation as demonstrated by ethane exhalation. In rats continuously exposed to 10 ppm nitrogen dioxide for 2 weeks, the amount of ethane exhaled fluctuated in a complex manner during the exposure. Ethane exhalation decreased slightly after the first day of exposure and then increased rapidly. The maximal values were observed after the fourth day of exposure and then decreased gradually to the initial level. Furthermore, the activity of glutathione peroxidase in lungs of rats exposed to 10 ppm nitrogen dioxide varied symmetrically against the change of ethane formation. Similar changes in ethane exhalation were observed in rats exposed to the lowest levels of nitrogen dioxide (0.4, 1.2 and 4.0 ppm) for 4 months. Compared to 10 ppm nitrogen dioxide exposure for 14 days, the characteristics in rats exposed to the low levels (0.4-4.0 ppm) of nitrogen dioxide were: the decline of ethane formation, the delay in alterations, and the tendency toward gradual increase during the longer period exposure.

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

A glutathione-dependent, cytosolic factor (previously thought to be glutathione peroxidase), inhibits lipid peroxidation in both microsomal and mitochondrial membranes. Studies in this laboratory had shown that the inhibition was due to prevention of peroxidative attack on the polyunsaturated fatty acids in the membrane lipids even under conditions that would otherwise promote rapid lipid peroxidation. A glutathione-dependent factor is also present in rat liver cytosol which can utilize peroxides of both free fatty acid salts in solution and free fatty acids in micellar suspension as substrates. It does not, however, utilize peroxidized lipids of microsomal and mitochondrial membranes as substrates. Whether or not this is the same factor which inhibits lipid peroxidation is not known with certainty, but current information indicates that they are not the same. Data presented in this report support the conclusion that neither glutathione peroxidase nor glutathione S-transferase activities appear to be responsible for the inhibition of lipid peroxidation in biological membranes. After partial purification of active preparations of both of these peroxidases, it was observed that neither preparation inhibited lipid peroxidation. The results of this study further support the conclusion that the glutathione-dependent cytosolic factor which inhibits lipid peroxidation in biological membranes does so by preventing the peroxidation rather than by reducing lipid peroxides.

Free radical initiation in proteins and amino acids by ionizing and ultraviolet radiations and lipid oxidation--part III: free radical transfer from oxidizing lipids

Parallels and similarities in chemical and functional damage to proteins by ionizing and uv radiations and oxidizing lipids have been recognized for some time. However, only recently have oxidizing lipids been shown directly by electron spin resonance to be radiomimetic also in their capacity for protein free radical production. Free radicals play a key role in the transformation of energy to molecular and cellular damage. It is thus of critical importance to elucidate the general mechanisms of free radical formation and reactions in proteins in order to understand protein involvement in various pathological conditions and in food deterioration. Accordingly, this review is a detailed comparison of gamma-radiation, UV radiation, and lipid oxidation for what is presently known concerning (1) the specific modes of energy deposition and free radical formation, (2) the free radicals formed in proteins and amino acids, and (3) the typical damage correlating with these radicals.

Effect of oxidized oil on lipogenic enzymes

Male Wistar rats were fed for 4 wk on diets containing 2% oxidized corn oil. Liver tissue was then studied to determine the effect of feeding peroxidized oil on lipogenic enzymes. Although substances which reacted with thiobarbituric acid increased in liver microsomes and mitochondria with increasing peroxide values of the dietary corn oil fed, the activities of glucose-6-phosphate dehydrogenase, malic enzyme and acetyl-CoA carboxylase in liver were unchanged. However, when rats were fed for 2 wk on diets containing 10% fat, of which 0.5, 5 or 10% was unoxidized corn oil and the remainder was hydrogenated beef tallow filler, the lipogenic enzyme activities and also the liver triglyceride levels were observed to decrease with increasing amounts of dietary corn oil. Therefore, although a synthetic diet containing corn oil was easy to oxidize spontaneously, the reductions of lipogenic enzymes in rats fed the diet would not have been caused by lipid peroxides but by unsaturated fatty acids themselves.