[Antiradical activity of 3-substituted coumarins and their effect on iron-dependent chemiluminescence]

The antioxidant capacity of 3-aminocoumarin, 3-oxycoumarin, 3-acetylaminocoumarin, and 3-coumarin carbonic acid has been investigated with chemiluminescence measurement and by the accumulation of TBA-active products. All coumarins were found to be antioxidants, with 3-oxy-, 3-amino- and 3-acetylamino coumarins being capable of amplifying chemiluminescence at early stages of the process.

Release of 2-thiobarbituric acid reactive products from glutamate, deoxyuridine or DNA during autoxidation of dopamine in the presence of copper ions

Cytotoxic effects of catecholamine are thought to be caused by the formation of 0-semiquinone and superoxide radicals. Dopamine in the presence of copper ions releases aldehydic products from glutamate, deoxyuridine or DNA capable of reacting with 2-thiobarbituric acid (TBA). The formation of TBA reactive products (TBAR) was concentration dependent of both dopamine and copper ion. Complete inhibition of formation of TBAR from glutamate, deoxyuridine or DNA was observed in the presence of thiourea and catalase. Mannitol, albumin and superoxide dismutase offered substantial protection. The present data indicate that dopamine in the presence of copper ions can lead to the formation of reactive hydroxyl radicals which can release aldehydic products from glutamate, deoxyuridine or DNA capable of reacting with TBA.

Effect of radical treatment on erythrocyte lipid peroxidation in Plasmodium vivax-infected malaria patients

Elevated levels of thiobarbituric acid reactive substances and increased in vitro Heinz body formation in erythrocytes of Plasmodium vivax-infected malarial patients were observed. Radical treatment with chloroquine and primaquine increased the per cent maximal release of thiobarbituric acid reactive substances. Antioxidant enzymes, superoxide dismutase and catalase were decreased significantly in vivax malaria. Superoxide dismutase showed restoration of enzyme activity while catalase activity was increased significantly following therapy, suggesting an active involvement of free radical mechanism.

[Intensification of lipid peroxidation upon damage to cell membranes]

It is shown that during sensitized by haematoporphyrin photooxidation accumulation of TBA-active products in destroyed cells (human erythrocytes, rat thymocytes, pig leucocytes) occurs considerably faster than in the intact ones. Similar acceleration is observed in intact erythrocytes after the amount of reduced glutathione in it was decreased. It is supposed that the cause of intensification processes of lipid peroxidation consists in separation of the antioxidant system from the plasma membrane.

Inhibition of microsomal lipid peroxidation by alpha-tocopherol and alpha-tocopherol acetate

1. The antioxidant effects of alpha-tocopherol and alpha-tocopherol acetate were assayed for the (a) oxygen uptake, (b) chemiluminescence and (c) malondialdehyde formation, of tert-butyl hydroperoxide-supplemented rat liver microsomes. 2. Oxygen uptake was inhibited 60% by both alpha-tocopherol and alpha-tocopherol acetate with the half-maximal effect at 5 nmol tocopherol/mg protein. Chemiluminescence and malondialdehyde formation were equally inhibited 35% by both tocopherols with half-maximal effects at 2 nmol tocopherol/mg protein. 3. The rate of O2 uptake by tocopherol-supplemented microsomes was dependent on O2 concentration. A 60% inhibition by 5 nmol tocopherol/mg protein at 0.2 mM O2 is decreased to 5% inhibition at 0.6 mM O2. 4. The inhibition of O2 uptake, chemiluminescence and malondialdehyde formation indicate that both alpha-tocopherol and alpha-tocopherol acetate have similar effects as free radical traps in the hydrophobic domain of biomembranes. The different inhibition observed at different O2 concentrations indicate competition between vitamin E and O2 by unoxygenated lipid radicals.

UVA-induced lipid peroxidation in cultured human fibroblasts

The UVA irradiation of cultured human fibroblasts leads to the formation and to the release of thiobarbituric acid-reactive substances in the supernatant. The major thiobarbituric acid-reactive substance is identified by fluorescence spectroscopy and HPLC, as malondialdehyde or malondialdehyde-forming substances under the thiobarbituric acid assay conditions. Malondialdehyde formation strongly suggests a UVA-induced lipid peroxidation. Lipid peroxidation is also supported by the inhibitory effect of D,L-alpha-tocopherol, the well-known chain breaking antioxidant, by the additional malondialdehyde formation in the dark after the photooxidative stress and by membrane damage revealed by lactate dehydrogenase leakage.

Oxygen-radical-mediated lipid peroxidation and inhibition of ADP-induced platelet aggregation

The effects of lipid peroxidation on ADP-induced aggregation of washed rat platelets were examined using a oxygen-radical-generating system consisting of H2O2 and ferrous ion. Lipid peroxidation was assessed by measurement of thiobarbituric acid-reactive substances (TBARS). Incubation of the platelets with various concentrations of H2O2 (2-10 mM) in the presence of 10 microM Fe2+ resulted in a decrease of the aggregating capacity and an increase of TBARS value, depending on the concentrations of H2O2. Addition of catalase (0.1 mg/ml) to the incubation medium containing 10 microM Fe2+ and 10 mM H2O2 effectively protected the aggregating capacity, but superoxide dismutase (0.1 mg/ml) did not protect H2O2/Fe(2+)-induced inhibition of the platelet aggregation. The results of kinetic studies on the platelet aggregation with varying ADP and Ca2+ concentrations suggested that treatment of the platelets with H2O2/Fe2+ causes decreases in the binding affinities of ADP and Ca2+ for the platelets. On the basis of these results, change in the aggregating capacity of the platelets by treatment with H2O2/Fe2+ is discussed in relation to lipid peroxidation.

The role of xanthine oxidase in paraquat intoxication

The role of xanthine oxidase in the mechanism of paraquat toxicity was assessed by in vitro and in vivo experiments. Paraquat stimulated the reduction of cytochrome c by xanthine-xanthine oxidase system in vitro. Paraquat, when added in vitro, stimulated hypoxanthine-dependent superoxide production in the cytosol of rat lung. Tungsten-feeding inhibits xanthine oxidase activity in a variety of tissues in experimental animals. Its therapeutic effect on paraquat intoxication was studied in this paper. In rats fed a tungsten-enriched diet for 5 weeks prior to intraperitoneal injection of 50 mg/kg paraquat dichloride, the mortality decreased significantly compared with rats fed a standard diet. Pretreatment with oxypurinol (1000 mg/kg, s.c.) also ameliorated the paraquat toxicity in rats. We conclude that xanthine oxidase plays an important role in paraquat toxicity and that xanthine oxidase inhibitors may become antidotes for paraquat intoxication.

Hemoglobin potentiates oxidant injury in isolated rat lungs

Isolated perfused rat lungs were subjected to oxidant injury induced by tert-butyl hydroperoxide (t-buOOH), which caused a significant increase in capillary permeability as assessed by the change in the capillary filtration coefficient. t-buOOH caused an increase in the change in the capillary filtration coefficient (delta Kfc) of 0.27 +/- 0.05 ml.min.cmH2O-1.100 g lung tissue-1 (mean +/- SE) that was accompanied by an increase in thiobarbituric acid reactive products of lipid peroxidation in the lung perfusate. The addition of hemoglobin to the perfusate potentiated t-buOOH-induced lung injury as evidenced by a significantly greater (P = 0.007) delta Kfc of 0.43 +/- 0.05. t-buOOH also caused hemoglobin to release large quantities of free iron in vitro. The potentiation of t-buOOH-induced lung injury by hemoglobin was prevented by apotransferrin as evidenced by a significant reduction (P = 0.001) in delta Kfc to 0.13 +/- 0.02. No statistically significant (P greater than 0.05) changes in segmental resistances or pulmonary vascular pressures occurred in any of the lungs injured with t-buOOH when compared with time controls. These results demonstrate that t-buOOH causes an oxidant injury in isolated rat lungs that can be potentiated by free iron released from hemoglobin.

In vivo hemoglobin dosimetry of malonaldehyde and ethene in mice after induction of lipid peroxidation. Effects of membrane lipid fatty acid composition

Hemoglobin (Hb) adduct determination by the N-alkyl Edman method was used for in vivo dosimetry of endogenously formed malonaldehyde (MA) and ethene in mice fed diets with different fatty acid composition and induced for lipid peroxidation with carbon tetrachloride (CCl4). In order to amplify lipid peroxidation animals were pretreated with phenobarbital (PB) and the glutathione-depleting agent DL-buthionine-(S,R)-sulfoximine (BSO). Non-treated animals raised on different diets were used as controls. Lipid peroxidation products in liver were measured as 2-thiobarbituric acid reactive compounds (TBA-C). Livers from control mice fed a soya oil based diet (rich in polyunsaturated fatty acids, diet S) showed approximately 6.5-fold higher levels of TBA-C than those from animals raised on a coconut oil based diet (mostly saturated fatty acids, diet C). The level of adducts of MA to Hb, determined as N-(3-hydroxypropyl)valine, was approximately 1.5-fold higher in animals from diet S than in animals raised on diet C. The highest increases in the levels of TBA-C and MA adducts were obtained after a simultaneous treatment of the animals with PB, BSO and CCl4. The increases of TBA-C were 1.3-fold (diet C) and 1.7-fold (diet S). The corresponding increases of MA-Hb adduct levels were 1.3- and 1.6-fold respectively, indicating an increased susceptibility of mice fed diet S to lipid peroxidation. The level of adducts from ethene, determined as N-(2-hydroxyethyl)valine, was also higher in mice from diet S than in animals fed diet C, when all treatment groups were considered. The difference was, however, only slightly significant (P less than 0.02). No difference between control and CCl4-treated animals, with regard to the ethene-Hb adduct, was found. Our results validate the use of Hb dosimetry for monitoring the effects of factors known to influence lipid peroxidation induced in vivo.

Lipid peroxidation, protein thiol oxidation and DNA damage in hydrogen peroxide-induced injury to endothelial cells: role of activation of poly(ADP-ribose)polymerase

These experiments are a continuation of work investigating the mechanism of oxidant-induced damage to cultured bovine pulmonary artery endothelial cells (BPEC). Earlier experiments implicated DNA strand breakage and activation of poly(ADP-ribose)polymerase as critical steps in cell injury. In the current report, a better defined model of oxidant stress was used to investigate DNA damage, lipid peroxidation and protein thiol oxidation in BPEC following oxidant stress. The dose and time response of LDH release following exposure to H2O2 were established. H2O2 was metabolized rapidly by BPEC (t1/2 = 20 min). Hydrogen peroxide-induced increases in thiobarbituric acid (TBA) reactive material were prevented by pretreatment with the lipophilic antioxidant diphenylphenylinediamine (DPPD). However, DPPD did not decrease LDH release. Conversely, pretreatment with 5 mM 3-aminobenzamide (3AB), a competitive inhibitor of poly(ADP-ribose)polymerase, prevented LDH release from BPEC following H2O2 treatment. Dithiothreitol (DTT), a sulfhydryl reducing agent, also prevented LDH release. The effects of 3AB and DTT on H2O2-induced changes in DNA strand breaks and NAD+ and ATP levels were investigated as well as the effect of H2O2 on soluble and protein-bound thiols. As DPPD inhibited peroxidation without preventing LDH release, lipid peroxidation does not appear to play a role in the loss of BPEC viability in response to oxidant stress. As protein thiol oxidation was not caused by H2O2, it does not appear to play a causative role in cytotoxicity, although DTT may protect via maintenance of soluble thiols. H2O2 induces DNA strand breaks, which activate poly(ADP-ribose)polymerase, leading to depletion of cellular NAD+ and ATP and loss in cell viability. This supports earlier studies implicating the activation of poly(ADP-ribose)polymerase in oxidant injury to cultured endothelial cells.

Effect of metal ion catalyzed oxidation of rifamycin SV on cell viability and metabolic performance of isolated rat hepatocytes

The effect of rifamycin SV on metabolic performance and cell viability was studied using isolated hepatocytes from fed, starved and glutathione (GSH) depleted rats. The relationships between GSH depletion, nutritional status of the cells, glucose metabolism, lactate dehydrogenase (LDH) leakage and malondialdehyde (MDA) production in the presence of rifamycin SV and transition metal ions was investigated. Glucose metabolism was impaired in isolated hepatocytes from both fed and starved animals, the effect is dependent on the rifamycin SV concentration and is enhanced by copper (II). Oxygen consumption by isolated hepatocytes from starved rats was also increased by copper (II) and a partial inhibition due to catalase was observed. Cellular GSH levels which decrease with increasing the rifamycin SV concentration were almost depleted in the presence of copper (II). A correlation between GSH depletion and LDH leakage was observed in fed and starved cells. Catalase induced a slight inhibition of the impairment of gluconeogenesis, GSH depletion and LDH leakage in starved hepatocytes incubated with rifamycin SV, iron (II) and copper (II) salts. Lipid peroxidation measured as MDA production by isolated hepatocytes was also augmented by rifamycin SV and copper (II), especially in hepatic cells isolated from starved and GSH depleted rats. Higher cytotoxicity was observed in isolated hepatocytes from fasted animals when compared with fed or GSH depleted animals. It seems likely that in addition to GSH level, there are other factors which may have an influence on the susceptibility of hepatic cells towards xenobiotic induced cytotoxicity.

Different effects of carbon tetrachloride on carcinogen-induced hepatocellular carcinoma and normal liver of the rat: lowered lipid peroxidation and accelerated necrosis in cancer

To investigate molecular responses to lipid peroxidative stimuli in neoplastic cells, lipid peroxidation was induced in liver of rats bearing 3'-methyl-4-dimethylaminoazobenzene-induced hepatocellular carcinoma by injecting a high dose of carbon tetrachloride (CCl4), a strong lipoperoxidative reagent. Normal rat livers with or without CCl4 treatment served as controls. CCl4 administration markedly provoked fatty metamorphosis, visualized by oil red O staining, in normal livers while minimal fatty changes were seen in hepatocellular carcinomas, where necrosis was often observed instead. After CCl4 treatment, the thiobarbituric acid values (representing levels of lipid peroxides in the tissue) were increased two-fold in the untreated normal liver, but were unchanged in the cancer tissue. Levels of vitamin C, an acutely reactive antioxidant, measured by high-performance liquid chromatography were not influenced by the CCl4 injection in the cancer tissue whereas a significant decrease was evident in normal livers. The total fatty acid content, measured by gas chromatography, was significantly lower in the cancer tissue than in the normal liver while the ratio of polyunsaturated fatty acids (PUFAs) in total fatty acids was little changed. Resistance of hepatocellular cancer cells to fatty metamorphosis and their susceptibility to necrosis induced by free radicals may be due to the paucity of the target PUFAs in their cell membrane fraction, resulting in low levels of lipid peroxides. Peroxidation of PUFAs might act as a "shock absorber" against free radical-induced toxic cell death in normal cells.

Liver lipid peroxidation-related parameters after short-term administration of hexachlorocyclohexane isomers to rats

Rats treated with diets containing 20 ppm of alpha- or gamma-hexachlorocyclohexane (HCH) for 15 or 30 days showed increased levels of liver cytochrome P-450 followed by increased production of both thiobarbituric acid reactants by liver homogenates and microsomes and superoxide anion production by liver microsomes. In these animals superoxide dismutase (SOD) activity was also increased. In consequence, the ratio between SOD activity and microsomal superoxide radical (O2-.) production showed a slight increase after 15 days of treatment. However, after 30 days, there was a tendency for this ratio to decrease. Other parameters studied were liver glucose-6-phosphate dehydrogenase, glutathione peroxidase, glutathione reductase and catalase (CAT) activities. Among them, only CAT activity showed a 26% and 38% increase after 15 or 30 days of treatment with the alpha-isomer. It is suggested that when lipid peroxidation is involved in the mechanism of toxicity of a xenobiotic, this parameter can be used to determine the no-observed-effect level.

Inhibition of diquat-induced lipid peroxidation and toxicity in precision-cut rat liver slices by novel antioxidants

The ability of the novel antioxidants U-74,006F and U-78,517G and a known antioxidant (N,N'-diphenyl-p-phenylenediamine, (DPPD)) to inhibit chemically induced (diquat dibromide) oxidative stress was examined in precision-cut liver slices. Previous studies in rat liver microsomes demonstrated the ability of these antioxidants to inhibit lipid peroxidation without preventing redox cycling of diquat. Diquat (1 mM) initiated lipid peroxidation in liver slices prepared from F344 rats. A 30-min preincubation with antioxidants inhibited formation of thiobarbituric acid reactive substances to control levels; ethane evolution, when elevated, was also inhibited by antioxidants. The toxicity of diquat (100 microM-3 mM) was evaluated in liver slices; 1 and 3 mM diquat caused decreases in intracellular K+ and intracellular LDH. Preincubation with antioxidants substantially decreased the toxicity of diquat as indicated by K+ and LDH. Diquat significantly decreased total glutathione levels in the slices; the antioxidants did not significantly inhibit this diquat-dependent effect. In summary, diquat, a compound which undergoes redox cycling and produces oxidative stress, was shown to produce lipid peroxidation, glutathione depletion, and toxicity in liver slices. Two experimental antioxidants, a 21-aminosteroid (U-74,006F) and a trolox-amine (U-78,517G) as well as a known antioxidant (DPPD) were shown to be effective in preventing lipid peroxidation and reducing the subsequent toxicity.

Effect of oral methionine and vitamin E on blood lipid peroxidation in vitamin B6 deficient rats

Lipid peroxidation in blood of vitamin B6 deficient rats was significantly increased when compared to pair-fed controls. The observed increased lipid peroxidation in vitamin B6 deficiency was correlated with high levels of lipids, metal ions and low levels of antioxidants, alpha-tocopherol, ascorbic acid and reduced GSH. Supplementation of methionine or vitamin E along with the vitamin B6 deficient diet restored the levels of antioxidants to near normal and also protected against oxidative stress. However plasma TBARS level as well as total lipids were still elevated in M-B6 diet fed rats and normalized in E-B6-d rats.

Role of oxidative stress in age dependent hepatocarcinogenesis by the peroxisome proliferator nafenopin in the rat

Recently old rats were found to be much more susceptible than young rats to the hepatocarcinogenic effect of a 55-59-week treatment with the peroxisome proliferator nafenopin (NAF) (B. Kraupp-Grasl, W. Huber, H. Taper, and R. Schulte-Hermann, Cancer Res., 51: 666-671, 1991). In the present study indicators of oxidative stress were measured in the livers of the same animals (male Wistar). NAF enhanced peroxisomal beta-oxidation 10-12-fold and reduced glutathione peroxidase activity by 40-50%. Indicators of lipid peroxidation like thiobarbituric acid reactive substances and malondialdehyde were both decreased by one-third and two-thirds, respectively. Of the oxidation-sensitive polyunsaturated fatty acids linoleic acid and docosahexaenoic acid were decreased by 40% and two-thirds, respectively, but the particularly sensitive arachidonic acid remained unchanged. Taken together these data suggest that NAF did not significantly enhance lipid peroxidation in the present experiment. All NAF effects were of the same magnitude in the old and young animals. Therefore, the considerably stronger induction of hepatocarcinoma by NAF in the old animals was not associated with evidence of enhanced oxidative stress. These findings are consistent with the hypothesis that NAF acts hepatocarcinogenically by promotion of tumor development from preneoplastic lesions occurring spontaneously with age.

Correlation between oxidation of low density lipoproteins and prostacyclin synthesis in cultured smooth muscle cells

The effect of antioxidants on the oxidation of low density lipoproteins in relation to prostacyclin synthesis was investigated in the prescence of rabbit smooth muscle cells (SMC) and Fe-containing culture medium. The lipid peroxidation of low density lipoproteins (LDL) assayed as thiobarbituric acid reactive substances was increased from 0.5 to 1.4 nmol malondialdehyde/mL by the presence of smooth muscle cells. Two potent antioxidants, nordihydroguairetic acid (NDGA) and butylated hydroxytoluene (BHT), inhibited lipoprotein oxidation by IC50 values of 0.2 and 0.8 microM, respectively. Inhibition of lipoprotein oxidation was associated with an increased prostacyclin synthesis by the SMC, the effect being more pronounced with nordihydroguairetic acid than with butylated hydroxytoluene. The stable metabolite of the lipid hydroperoxide, 15-hydroxyeicosatetraenoic acid (15-HETE), formed in the 15-lipoxygenase pathway was measured following antioxidant treatment and found to be eliminated or greatly reduced by both antioxidants. The results presented show that lipid hydroperoxides, formed as a consequence of lipoprotein oxidation and promoted by the smooth muscle cells through a lipoxygenase reaction, may regulate prostacyclin synthase, a process which may be influenced by the addition of antioxidants.

Sex differences in the localization and severity of ferric nitrilotriacetate-induced lipid peroxidation in the mouse kidney

Male mice are much more susceptible than female mice to acute renal proximal tubular necrosis as well as the carcinogenic effect induced by an iron-chelate, ferric nitrilotriacetate (Fe-NTA). In the present study, iron-promoted lipid peroxidation was analyzed histochemically in frozen kidney sections using cold Schiff's reagent and biochemically by measuring thiobarbituric acid-reactive substance in the kidney. When untreated mouse frozen kidney sections were exposed to ascorbic acid-Fe-NTA (0.8 mM, 0.2 mM and 0.4 mM) in vitro for 40 min and washed, diffuse Schiff positivity was obtained along the proximal tubules, and no sex differences were evident. When non-reduced Fe-NTA (0.2 mM and 0.4 mM) was layered on untreated kidney sections from males, about half of the cortical proximal tubules showed a positive reaction with Schiff's reagent, whereas in females the proximal tubules of the outer stripe of the outer medulla were positive. In an ex vivo study, 30 to 40 min after i.p. injection of Fe-NTA (5 mg Fe/kg), Schiff-positive areas corresponded to those observed in the in vitro non-reduced Fe-NTA study in each sex. However, in males, the positive tubular cells gradually became necrotic, whereas in females the positivity disappeared with time and there was no tubular necrosis. Results of the thiobarbituric acid test were correlated with the above findings. In conclusion, the localization and severity of Fe-NTA-induced lipid peroxidation in the tubules differed between the sexes. We suspect that these results reflect functional heterogeneity in the ability of the tubules to reduce iron.

Effects of dietary pantethine levels on contents of fatty acids and thiobarbituric acid reactive substances in the liver of rats orally administered varying amounts of autoxidized linoleate

The effects of dietary pantethine levels on the contents and compositions of fatty acids and on the levels of lipid peroxides were investigated with rat liver and its S-9 fraction under administration of 0 (non), 0.2 (low dose), and 0.35 ml (high dose) of autoxidized linoleate (AL) per 100 g body weight of the rats per day for 5 days. AL having 800 meq/kg of peroxide value (PV) and 1,700 meq/kg of carbonyl value (CV) was dosed to the rats of each group given drinking water containing 0 mg% (deficient), 6.25 mg% (adequate), and 125 mg% pantethine (excess). In the pantethine-deficient and -adequate groups, the contents of fatty acids both in the liver homogenate and in the S-9 fraction were correspondingly decreased by increasing dose levels of AL, and the decrease was remarkable especially in the pantethine-deficient group, but was not significant in the pantethine-excess group even by a high dose of AL. Particularly, in the high dose of AL, the notable decreases of oleic acid (C18:1) contents in both the liver and the S-9 fraction were observed in rats of the pantethine-deficient and -adequate groups. The thiobarbituric acid (TBA) values in the liver homogenate and the S-9 fraction were increased correspondingly by increasing dose levels of AL, and the increases were repressed in the pantethine-excess group.

Fluorescence characteristics of peroxidation products in porcine intestinal brush-border membranes

Treatment of the porcine intestinal brush-border membranes with 100 microM ascorbic acid and 10 microM Fe2+ in the presence of various concentrations of tert-butyl hydroperoxide (t-BuOOH) resulted in a marked fluorescence development at 430 nm, depending on the hydroperoxide concentration. This fluorescence formation was closely related to lipid peroxidation of the membranes as assessed by formation of conjugated diene. However there is no linear relation between thiobarbituric acid-reactive substances (TBARS) and fluorescence formation. On the other hand, fluorescence formation in the membranes by treatment with ascorbic acid/Fe2+ or t-BuOOH alone was negligible. The results with antioxidants and radical scavengers suggest that ascorbic acid/Fe2+/t-BuOOH-induced lipid peroxidation of the membranes is mainly due to t-butoxyl and/or t-butyl peroxy radicals. Most TBARS produced during the peroxidation reaction were released from the membranes, but fluorescent products remained in the membrane components. The fluorescence properties of products formed by lipid peroxidation of the membranes were compared with those of products derived from the interaction of malondialdehyde (MDA) or acetaldehyde with the membranes. The fluorescence products in the acetaldehyde-modified membranes also exhibited the emission maximum at 430 nm, while the emission maximum of MDA-modified membranes was 470 nm. The fluorescence intensity of MDA-modified membranes was markedly decreased by treatment with 10 mM NaBH4 but that of the peroxidized or acetaldehyde-modified membranes was enhanced by about two-fold with the treatment. In addition, a pH dependence profile revealed that the fluorescence intensity of the peroxidized or acetaldehyde-modified membranes decreases with increasing pH of the medium, whereas that of MDA-modified ones did not change over the pH range from 5.4 to 8.0. On the basis of these results, the fluorescence properties of products formed in the intestinal brush-border membranes by lipid peroxidation are discussed.

Vitamin E, diethylmaleate and bromotrichloromethane interactions in oxidative damage in vivo

In vivo interactions of vitamin E with diethylmaleate (DEM) and bromotrichloromethane (CBrCl3) were examined in rats fed a diet either without vitamin E or supplemented with 30 IU dl-alpha-tocopheryl acetate/kg. Groups of rats within each dietary group were given two injections 30 min apart. One group received two injections of the mineral oil carrier. The other groups were injected with either DEM and mineral oil, mineral oil and CBrCl3, or DEM and CBrCl3. The rats were killed 10 min after the second injection. Measurements were made of hepatic GSH, thiobarbituric acid-reactive substances (TBARS) as a lipid peroxidation index, and 11 enzymes as potential markers of oxidant damage. Special focus was placed on reactive cysteine-containing aldehyde dehydrogenase (ALDH). Although dietary vitamin E protected ALDH, the enzyme was highly susceptible to oxidant damage. ALDH activity was correlated with GSH (r = 0.83, p less than 0.001) and there was an inverse relationship between the logarithmic values of ALDH activity and TBARS (r = 0.78, p less than 0.001). Similar results were observed for a number of other enzymes when GSH depletion preceded oxidant treatment. Two-way analysis of variance revealed significant effects of vitamin E and of injection treatments on hepatic GSH. There was a significant interaction between vitamin E and the injection treatments on the activities of five enzymes. The results suggested that vitamin E and GSH functioned together to protect sensitive enzymes against oxidant stress. The sensitive enzymes may be useful markers of hepatic damage in vivo.

Intestinal, hepatic and renal production of thiobarbituric acid reactive substances and myeloperoxidase activity after temporary aortic occlusion and reperfusion

Ischemia induced oxygen free radical damage was formerly attributed only to xanthine oxidase in intestine, liver, kidney and heart. A reevaluation indicated neutrophils as one of the major sources of postischemic oxidative tissue damage, chiefly in the intestine. Our data, obtained from the same occlusion time period for intestine, liver and kidney, showed a certain oxidative damage in intestine and kidney already during ischemia, expressed by an increase of thiobarbituric acid reactive substances (TBARS), whereas the liver sustained damage of this kind only during reperfusion. Oxidative stress was expressed by a comparison of the increase of TBARS, though this test is not a measure of a specific product of lipid peroxidation, but rather comprises several breakdown products of free radical damage. Myeloperoxidase as measure of neutrophil stimulation increased in the intestine and liver. The kidney sustained damage without an increase of myeloperoxidase activity, but showed a similar pattern of increase of TBARS as in the intestine. Our data suggest a major role of neutrophils in intestinal ischemia induced damage, where neutrophils can effect initiation and propagation. In the liver neutrophils may play a minor role concerning propagation, but they may act as an important initiating mechanism. Hepatic tissue shows a high ischemic tolerance, which is demonstrated by a missing increase of TBARS in spite of a certain increase of myeloperoxidase activity during ischemia. This can be interpreted by the high capacity of antioxidative mechanisms of liver tissue and the ability of a higher oxygen extraction ratio under nearly ischemic conditions. In the kidney there appears a smaller contribution of neutrophils. The similar pattern of increase of TBARS in kidney and intestine demonstrates a comparable low ischemic tolerance of these two tissues, whereas different initiating and propagating systems may occur.

Linoleic acid-induced endothelial cell injury: role of membrane-bound enzyme activities and lipid oxidation

High plasma levels of linoleic acid (18:2) may injure endothelial cells, resulting in decreased barrier function of the vascular endothelium. The effects of linoleic acid on endothelial barrier function (transendothelial movement of albumin), membrane-bound enzyme activities, and possible autooxidation of linoleic acid under experimental conditions were studied. The exposure of endothelial monolayers to 18:2 for 24 hr at 60, 90, and 120 microM fatty acid concentrations caused a significant increase in transendothelial movement of albumin, with maximum albumin transfer at 90 microM. Fatty acid treatment resulted in the increased appearance of cytosolic lipid droplets. Activities of the membrane-bound enzymes, angiotensin-converting enzyme (ACE), and Ca(2+)-ATPase increased steadily with increasing time of cell exposure to 90 microM 18:2, reaching significance at 24 hr. Treatment of endothelial cultures with up to 120 microM 18:2 did not cause cytotoxicity, as evidenced by a nonsignificant change in cellular release of [3H]-adenine. Incubation of 18:2-supplemented serum-containing culture media with 1000 microM 18:2 at 37 degrees C for up to 48 hr did not result in formation of autooxidation products. These results suggest that 18:2 itself, and not its oxidation products, plays a major role in disrupting endothelial barrier function.

Mitochondrial damage by active oxygen species in vitro

Under in vitro conditions involving formation of active oxygen species, rat liver mitochondria were found to undergo swelling, peroxidative decomposition of lipids, and distinct disorganization of ultrastructure. Supplementation with free radical scavengers such as superoxide dismutase (SOD), methionine, histidine, and tryptophan accorded considerable protection to the organelle. A possible correlation between oxygen radicals, membrane integrity, and calcium functions is indicated.

Characterization of the urinary metabolites of merbarone in cancer patients

Phase-I clinical trials in cancer patients of merbarone (MB), a thiobarbituric acid derivative with curative activity against the murine leukemias, were recently completed. Reverse-phase HPLC of urine samples from treated patients showed the presence of two major metabolites, identified as 4'-hydroxymerbarone and 2-oxo-desthiomerbarone, eluting prior to the parent drug. In addition, a third polar metabolite, largely masked in liquid chromatograms by poorly retained endogenous urinary constituents, was detected and characterized as 4'-hydroxy-2-oxo-desthiomerbarone. Several minor metabolites, one of greater polarity and several less polar than MB, remain to be identified. Initial structural elucidations were ascertained from methane chemical ionization mass spectroscopy upon isolating MB and its metabolites from patient urine by solid-phase extraction. Quasi-molecular ion patterns at masses consistent with the drug and three oxidative metabolites were apparent. Molecular ion shifts that occurred after treating the urine isolate with acetic anhydride under Schotten-Baumann conditions indicated that two of the metabolites were phenolic derivatives. A high-resolution 1H-NMR spectrum (500 MHz) of the urine isolate exhibited a well-resolved aromatic region containing peaks consistent with those determined for synthetically prepared reference standards of each metabolite. This evidence was further substantiated by obtaining UV spectra during HPLC with a diode array detector. Chromatographic peak identification was established from the correspondence of retention times and UV spectra with the synthetic compounds. These studies demonstrate that MB is subject to extensive oxidative metabolism in humans. However, metabolite plasma levels are exceedingly low throughout the course of a 5-day continuous infusion, suggesting that metabolite excretion rates may exceed their rates of formation. Furthermore, since the relative concentrations of the major metabolites in urine are appreciably higher than that of MB, metabolite renal clearance is apparently greater than that of the drug.

Studies on lipid peroxidation in pancreatic tissue. In vitro formation of thiobarbituric-acid-reactive substances (TBRS)

In pathogenic studies on acute pancreatitis the importance of a temporary ischemia on induction of autodigestion was demonstrated. Because of the involvement of oxygen-derived free radicals in the ischemia/reperfusion injury of other tissues we have investigated the influence of artificial oxidants, as FeCl3 and H2O2, on pancreatic tissue and isolated pancreatic acinar cells. Lipid peroxidation was determined as thiobarbituric-acid-reactive substances (TBRS). In these experiments the TBRS concentration was elevated within the first min of incubation with FeCl3. The exposure of pancreas homogenates and intact acinar cells to H2O2 had no remarkable effect on formation of TBRS. Under this condition the survival of cells was strongly reduced, while cells exposed to FeCl3 revealed a remarkably slower rate of cytolysis. The missing correlation between cell lysis and elevation of TBRS suggests that lipid peroxidation might not be essential process in pancreatic acinar cell damage.

Relationship among malondialdehyde, TBA-reactive substances, and tocopherols in the oxidation of rapeseed oil

Relationship among malondialdehyde (MDA), 2-thiobarbituric acid (TBA)-reactive substances (TBA-RS), and tocopherols in the oxidation of rapeseed oil was investigated. MDA was determined by a new HPLC method with chemical derivatization. When the oil was heated at 170 degrees C, TBA-RS and MDA increased. The contents of TBA-RS were approximately 1.6 times higher than those of MDA. Correlation between the increase in formed MDA and the decrease in tocopherols was observed. When the oxidation of the oil was initiated using 2,2'-azobis-(2,4-dimethylvaleronitrile) at 40 degrees C, TBA-RS dramatically increased during the initial stage and reached plateau. Thereafter, little increase was observed. The relative ratio of MDA to TBA-RS was much lower in the reaction performed at 40 degrees C than that observed at 170 degrees C. These results indicated that the decrease of tocopherols was accompanied by the increase of MDA but TBA-RS did not correlate with the change of tocopherols.

Malondialdehyde and 4-hydroxynonenal protein adducts in plasma and liver of rats with iron overload

In hepatic iron overload, iron-catalyzed lipid peroxidation has been implicated in the mechanisms of hepatocellular injury. Lipid peroxidation may produce reactive aldehydes such as malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE), which may form aldehyde-protein adducts. We investigated whether lipid peroxidation occurred in rats fed a diet containing 3% carbonyl iron for 5-13 wk, and if this resulted in the formation of MDA- and 4-HNE- protein adducts. Chronic iron feeding resulted in hepatic iron overload (greater than 10-fold) and concomitantly induced a 2-fold increase in hepatic lipid peroxidation. Using an antiserum specific for MDA-lysine protein adducts, we demonstrated by immunohistochemistry the presence of aldehyde-protein adducts in the cytosol of periportal hepatocytes, which co-localized with iron. In addition, MDA- and 4-HNE-lysine adducts were found in plasma proteins of animals with iron overload. Only MDA adducts were detected in albumin, while other plasma proteins including a approximately 120-kD protein had both MDA and 4-HNE adducts. In this animal model of hepatic iron overload, injury occurs primarily in periportal hepatocytes, where MDA-lysine protein adducts and excess iron co-localized.

Hepatotoxicity of diethyldithiocarbamate in rats

Hepatotoxicity of diethyldithiocarbamate (DDC) was investigated in rats. Plasma aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities were markedly elevated 24 hr after subcutaneous administration of DDC and histologically, the liver showed submassive necrosis. A sustained inhibition in the liver of Cu,Zn-superoxide dismutase (Cu-SOD) activity was observed following DDC treatment. DDC produced a significant loss in liver reduced glutathione (GSH) level after 1 hr, but the nadir was observed later than that of Cu-SOD. Catalase activity decreased gradually from 7 hr. Thiobarbituric acid reactive substances (TBARS) in the liver were significantly increased from 15 hr. Hepatic haemodynamics were scarcely changed up to 15 hr. Desferrioxamine (a chelator of iron) and piperonyl butoxide (an inhibitor of cytochrome P-450) prevented DDC-induced increases of both ALT and TBARS, but GSH did not, DDC hepatotoxicity was not changed by phenobarbital induction. Thus, we have shown that subcutaneous dose of DDC caused hepatotoxicity in rats. Although the exact sequence of its hepatotoxic factors is unproven, it seems likely that lipid peroxidation through the dysfunction of antioxidant defence factors and a toxic metabolite contribute to the formation of this liver injury.

Role of cytochrome P-450 in reperfusion injury of the rabbit lung

Reactive oxygen species are a major cause of damage occurring in ischemic tissue after reperfusion. During reperfusion transitional metals such as iron are required for reactive oxygen species to mediate their major toxic effects. Xanthine oxidase is an important source of reactive oxygen species during ischemia-reperfusion injury, but not in all organs or species. Because cytochrome P-450 enzymes are an important pulmonary source of superoxide anion (O2-.) generation under basal conditions and during hyperoxia, and provide iron catalysts necessary for hydroxyl radical (.OH) formation and propagation of lipid peroxidation, we postulated that cytochrome P-450 might have a potential role in mediating ischemia-reperfusion injury. In this report, we explored the role of cytochrome P-450 enzymes in a rabbit model of reperfusion lung injury. The P-450 inhibitors 8-methoxypsoralen, piperonyl butoxide, and cimetidine markedly decreased lung edema from transvascular fluid flux. Cimetidine prevented the reperfusion-related increase in lung microvascular permeability, as measured by movement of 125I-albumin from the vascular space into lung water and alveolar fluid. P-450 inhibitors also prevented the increase in lung tissue levels of thiobarbituric acid reactive products in the model. P-450 inhibitors did not block enhanced O2-. generation by ischemic reperfused lungs, measured by in vivo reduction of succinylated ferricytochrome c in lung perfusate, but did prevent the increase in non-protein-bound low molecular weight chelates of iron after reperfusion. Thus, cytochrome P-450 enzymes are not likely a major source of enhanced O2-. generation, but serve as an important source of iron in mediating oxidant injury to the rabbit lung during reperfusion. These results suggest an important role of cytochrome P-450 in reperfusion injury to the lung and suggest potential new therapies for the disorder.

Antioxidants and resistance against oxidation of porcine LDL subfractions

The objective of this study was to determine the level of antioxidants, the content of fatty acids and peroxidation products, and the resistance against oxidation of native porcine LDL1 and LDL2. There were no significant differences in the fatty acid distribution of both native low density lipoprotein (LDL) subfractions, which was similar to that of human LDL. The total amount of alpha- and gamma-tocopherol of pig LDL was significantly lower than in human LDL, and beta-carotene, lycopene, and retinyl esters were totally absent. Levels of thiobarbituric acid-reacting substances (TBARS) and lipid peroxides in freshly isolated pig LDL subfractions were below or only slightly above the detection limit. The susceptibility to oxidation of both LDL subfractions was investigated by addition of Cu2+ as prooxidant. The results show that pig LDL subfractions are much more susceptible to oxidation as measured by the duration of the lag phase preceding the onset of rapid lipid peroxidation. From the low content of vitamin E one would expect even much shorter lag phases. The possibility therefore exists that pig LDL contains additional, and as yet unidentified, antioxidants.

Polychlorinated biphenyls-induced lipid peroxidation as measured by thiobarbituric acid-reactive substances in liver subcellular fractions of rats

Rats were given a 0.05% polychlorinated biphenyls (PCB) diet supplemented with adequate nutrients for 10 days and not only PCB-induced lipid peroxidation as measured by thiobarbituric acid (TBA)-reactive substances but also variations of lipid peroxides scavengers in liver and its subcellular fractions (nuclei and cell debris, mitochondrial, microsomal and cytosolic fractions) were investigated. The lipid peroxidation in liver and subcellular fractions in the PCB-treated group increased significantly except in the nuclei and cell debris fraction. The increase in lipid peroxidation in the microsomal fraction appeared to be associated in part with the decrease in vitamin E (alpha-tocopherol) content and induction of drug-metabolizing enzymes. In the cytosolic fraction, the total lipid content increased, glutathione peroxidase (GSHPx) activity decreased and the quantity of free radical-reactive substances suppressing lipid peroxidation was low as measured by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) value. From these results, the increase in lipid peroxidation in the cytosolic fraction in the PCB-treated group was ascribed to the abundance and availability of oxidizable substrate attended with fatty liver, to the decline in GSHPx activity, and to the insufficiency in antioxygenic activity as observed by the decrease in the DPPH value.

[Study of acute gastric mucosal lesion induced by endotoxemia]

Acute gastric mucosal lesion (AGML) was induced six hours after the administration of endotoxin. The decrease of gastric mucosal blood flow, used to be supposed as an important factor of the formation of AGML, was not found, but thiobarbituric acid (TBA) reactants in the gastric mucosa were increased three hours after endotoxin injection, 198 +/- 18.2 (vs control 130 +/- 18.2). The administration of platelet activating factor (PAF) inhibitor, CV3988, reduced the formation of AGML and increase of the TBA reactants. These results suggested that the chemical mediator like PAF and free radicals may play an important role in the pathogenesis of gastric mucosal injury induced by endotoxemia, without the decrease of mucosal blood flow.

Influence of dietary vitamin E deficiency on compression injury of rat spinal cord

The influences of vitamin E deficiency on compression injury of the rat spinal cord associated with ischemia were investigated. Growing rats were divided into two groups and given a diet containing either 2 IU/100 g or less than 0.1 IU/100 g of alpha-tocopherol acetate, respectively, for 6-8 weeks before experiments. Motor disturbances induced by spinal cord injury were found to be enhanced by vitamin E deficiency. The spinal cord blood flow (SCBF) was reduced by compression and subsequently increased transiently and then decreased gradually in both groups, but the level was lower in the vitamin E-deficient group than in the control group. After injury, the vitamin E-deficient group showed lower recoveries than the control group in the amplitude and latency of spinal cord evoked potentials and greater pathological changes of the spinal cord, such as bleeding and edema. The increase in the level of TBA-reactive substances in the spinal cord after injury increased with decrease in the dietary level of vitamin E. These results suggest that vitamin E may have a protective effects against ischemic spinal cord injury by its antioxidant effect.

Vitamin E content and low density lipoprotein oxidizability induced by free radicals

Human LDL, HDL and lipoprotein deficient plasma isolated from 15 normal subjects was exposed to oxygen free radicals generated by gamma rays and the formation of peroxides and changes in levels of LDL alpha-tocopherol were measured. LDL exhibited an initial resistance against oxidation stress when compared to HDL. The results obtained for different individuals showed that there was no correlation between the initial levels of vitamin E in LDL or plasma and the amount of peroxide formed after exposure of the LDL to a standard quantity of oxygen radicals. Kinetic experiments with original LDL and LDL containing incorporated alpha-tocopherol demonstrated that the vitamin performed its antioxidant role by conferring some early protection to the lipids, being consumed in the process, but it was clear that additional factors are also instrumental in determining the total antioxidant potential of the human LDL.

Comparative drug exsorption in the perfused rat intestine

The factors affecting drug exsorption into the gastrointestinal tract are uncertain. In this study, the intestinal clearance (CLi) of compounds which vary in their lipophilicity, serum protein binding, molecular weight and ionic charge at physiological pH, has been measured. Male Sprague-Dawley rats with ligated bile ducts were infused with the test compounds through the jugular vein. The small intestine was intubated and perfused with Tyrode solution at 20 mL h-1. The CLi of the compounds investigated (urea, polyethylene glycol, inulin, albumin, dextran, barbituric acid, salicylic acid, thiobarbital, thiopental, thioseconal, theophylline, S-disopyramide and quinidine) was determined under anaesthesia by dividing the rate of a component's appearance rate in the perfusate by its carotid arterial concentration. Serum protein binding of the compounds was determined by equilibrium dialysis. The n-octanol-water partition coefficients of the compounds were measured as indices of lipophilicity. The CLi values of dextran, albumin, inulin, polyethylene glycol and urea were 0.56, 1.03, 4.5, 4.8 and 12.0 mL h-1, respectively. The larger the molecular weight of a compound, the smaller its CLi. The molecular weight is apparently one of the major determinants of CLi. Thiobarbital, thiopental and thioseconal are compounds of similar structure with increasing lipophilicity and serum protein binding. The CLi of thiobarbital, thiopental and thioseconal was proportional to the unbound fraction in serum. The unbound clearance (CLui) of three thiobarbiturates were similar (approximately 11 mL h-1). The unbound fraction of drug in serum appears to be a factor determining their CLi. Barbituric acid and salicylic acid, two acidic compounds, showed a low CLi (less than 1 mL h-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary supplements of vitamin E, beta-carotene, coenzyme Q10 and selenium protect tissues against lipid peroxidation in rat tissue slices

A tissue slice model was employed to assess the effects of dietary antioxidant supplements on lipid peroxidation. In one experiment, rats were fed diets containing, either alone or in combination, vitamin E, selenium, beta-carotene or coenzyme Q10 for 42 d, and the extent of spontaneous and induced lipid peroxidation was determined by release of thiobarbituric acid-reactive substances (TBARS) into the medium. Vitamin E exhibited the greatest protection against lipid peroxidation in liver, heart and spleen; in kidney, selenium was most protective. Coenzyme Q10 was active against lipid peroxidation induced by tertbutyl hydroperoxide (t-BHP). In a second experiment, rats were fed diets containing varying amounts of vitamin E, selenium, beta-carotene and coenzyme Q10 for 30 d. Spontaneous lipid peroxidation in liver, kidney and heart decreased with increasing levels of dietary antioxidants. With increasing amounts of antioxidants, there was a diminution in TBARS released by liver and kidney slices incubated with t-BHP; in heart, only the highest levels of antioxidants significantly decreased production of TBARS. Inverse correlations between dietary vitamin E and TBARS, tissue vitamin E and TBARS, and tissue selenium-glutathione peroxidase and TBARS were highly significant. The procedure used here can evaluate dietary supplements that may find practical applications in decreasing the oxidant radical portion of disease processes.

Stress initiated during isolation of rat renal proximal tubules limits in vitro survival

The effects of oxidative damage were assessed in rat proximal tubule fragments (isolated by collagenase perfusion) by monitoring lactate dehydrogenase release (LDH-R) to measure cell viability and thiobarbituric acid (TBA) reactive material to follow oxidative damage. Increasing the oxygen content in the incubation atmosphere from 10 to 95% significantly increased LDH-R and TBA reactants. Addition of butylated hydroxytoluene or deferoxamine (DF) to the medium prevented these changes, but ascorbic acid or mannitol had no positive effect. Lima bean trypsin inhibitor also reduced LDH leakage significantly when added to the medium, but not when added to the perfusion buffers. In contrast, adding DF to the perfusate during tubule isolation produced the most pronounced benefit; net LDH-R after 4 hr was about 10% in tubules prepared this way compared to 20% when DF was omitted. Basal oxygen consumption declined to approximately the same extent as LDH-R increased. Maintenance of nystatin-stimulated respiration, ATP/ADP, GSH content and total adenine nucleotides indicated good cell function. These results suggest that oxidative damage initiated during the tubule isolation procedure limits cell survival but this effect can be counteracted substantially by the addition of DF to the perfusion buffer.

Prenatal oxidative stress: I. Malondialdehyde in hypoxic and hyperoxic chick embryos

Evidence suggests a positive correlation between metabolic rate (VO2), or ambient oxygen (O2) tension, and the rate of formation of free radicals from O2. We have previously demonstrated that the rates of growth, VO2, protein and DNA accumulation, and the activity of cytochrome oxidase (a key mitochondrial respiratory enzyme), are increased significantly by exposing the chick embryo to 72 h of hyperoxia (60% O2) late in incubation. To test the hypothesis that the chick embryo responds to a prenatal alteration in O2 availability in such a way as to protect its tissues from oxidative damage, we have used the thiobarbituric acid assay to estimate lipid peroxidation (a major form of free radical damage) in selected organs from chick embryos exposed to altered O2 availability. We found significantly higher concentrations of malondialdehyde (MDA, a secondary product of lipid peroxidation) in liver than in chorioallantoic membrane, brain, or heart. However, embryos exposed to brief (72 h) hypoxia (15% O2) or hyperoxia (60% O2) late in incubation, or 48 h of such exposure followed by 24 h of incubation in pure O2, exhibited no significant difference in MDA levels compared to normoxic (21% O2) controls in any of the tissues examined. We conclude that the increase in aerobic metabolism induced in the chick embryo by 3 days of hyperoxia is not accompanied by an increase in lipid peroxidation. We postulate that the chick embryo adapts to hyperoxia in such a way as to escape additional free radical damage, perhaps by increasing the capacity of its antioxidant defenses to compensate for a potential increase in the rate of free radical generation.

Aminotriazole effects on lung and heart H2O2 detoxifying enzymes and TBA-RS at two pO2

In order to clarify the physiological role in vivo of H2O2-detoxifying enzymes at low and high levels of O2 tension we studied catalase (CAT), glutathione peroxidases (GP), and in vivo peroxidation (TBA-RS) in the lung and heart of Rana perezi frogs chronically treated with hyperoxia, aminotriazole (AT) -a CAT inhibitor-, or both. Hyperoxia did not change CAT, GP or TBA-RS. Aminotriazole caused an almost complete depletion of CAT, a 30% decrease of GP and a 132% (lung) to 200% (heart) increase of TBA-RS. Changes similar to these were found in the group treated with AT in hyperoxia. No mortality or changes in total or organ weight occurred in the experimental groups. Main conclusions are: (1) The maximal hyperoxia tolerance showed by frogs among vertebrates does not need antioxidant enzyme induction from lung or heart and is probably related to the presence of high constitutive levels of GP in relation to metabolic rate. (2) Even in normoxia the tissues present significant amounts of H2O2, and CAT is needed to avoid oxidative damage. GP does not compensate its absence. The implications of these results in relation to oxygen toxicity in man is discussed.

Antioxidant action of guilingji in the brain of rats with FeCl3-induced epilepsy

The effects of Guilingji, an antiaging prescription comprised of traditional Chinese medicinal herbs and animal components, on the brain level of thiobarbituric acid reactive substances (TBARS) and superoxide dismutase (SOD) activity in the brain of rats with FeCl3-induced epilepsy were examined with fluorophotometry and electron spin resonance (ESR) spectrometry, respectively. The results showed that pretreatment of rats with Guilingji decreased the levels of TBARS in the left cortex, midbrain, and olfactory lobe, and increased the SOD activity in the midbrain and hypothalamus. These results are the first to demonstrate that Guilingji may possess an antiepileptic effect further to its proposed antiaging action, because decreasing the TBARS elevation and increasing the SOD attenuation in the brain are suggested to be important characteristics of antiepileptic agents. These results suggest that both the proposed antiaging and antiepileptic effects of Guilingji may operate through the mechanism of antioxidation.

Malondialdehyde and thiobarbituric acid-reactivity as diagnostic indices of lipid peroxidation and peroxidative tissue injury

Increasing appreciation of the causative role of oxidative injury in many disease states places great importance on the reliable assessment of lipid peroxidation. Malondialdehyde (MDA) is one of several low-molecular-weight end products formed via the decomposition of certain primary and secondary lipid peroxidation products. At low pH and elevated temperature, MDA readily participates in nucleophilic addition reaction with 2-thiobarbituric acid (TBA), generating a red, fluorescent 1:2 MDA:TBA adduct. These facts, along with the availability of facile and sensitive methods to quantify MDA (as the free aldehyde or its TBA derivative), have led to the routine use of MDA determination and, particularly, the "TBA test" to detect and quantify lipid peroxidation in a wide array of sample types. However, MDA itself participates in reactions with molecules other than TBA and is a catabolic substrate. Only certain lipid peroxidation products generate MDA (invariably with low yields), and MDA is neither the sole end product of fatty peroxide formation and decomposition nor a substance generated exclusively through lipid peroxidation. Many factors (e.g., stimulus for and conditions of peroxidation) modulate MDA formation from lipid. Additional factors (e.g., TBA-test reagents and constituents) have profound effects on test response to fatty peroxide-derived MDA. The TBA test is intrinsically nonspecific for MDA; nonlipid-related materials as well as fatty peroxide-derived decomposition products other than MDA are TBA positive. These and other considerations from the extensive literature on MDA. TBA reactivity, and oxidative lipid degradation support the conclusion that MDA determination and the TBA test can offer, at best, a narrow and somewhat empirical window on the complex process of lipid peroxidation. The MDA content and/or TBA reactivity of a system provides no information on the precise structures of the "MDA precursor(s)," their molecular origins, or the amount of each formed. Consequently, neither MDA determination nor TBA-test response can generally be regarded as a diagnostic index of the occurrence/extent of lipid peroxidation, fatty hydroperoxide formation, or oxidative injury to tissue lipid without independent chemical evidence of the analyte being measured and its source. In some cases, MDA/TBA reactivity is an indicator of lipid peroxidation; in other situations, no qualitative or quantitative relationship exists among sample MDA content, TBA reactivity, and fatty peroxide tone. Utilization of MDA analysis and/or the TBA test and interpretation of sample MDA content and TBA test response in studies of lipid peroxidation require caution, discretion, and (especially in biological systems) correlative data from other indices of fatty peroxide formation and decomposition.

Spin trapping of free radicals and lipid peroxidation in microsomal preparations from malignant hyperthermia susceptible pigs

Microsomes were prepared from livers of malignant hyperthermia susceptible (MHS) or resistant (MHR) pigs. On incubation with the spin trap alpha-(4-pyridyl-l-oxide)-N-tert-butylnitrone (4-POBN), the microsomes from MHS pigs produced a characteristic electron spin resonance (ESR) signal at a greater rate than those from MHR pigs. Increased formation in the incubations of thiobarbituric acid reactive substances (TBARS) by the microsomes of the MHS pigs indicated an enhanced susceptibility to free radical-mediated lipid peroxidation. These results provide further evidence that MHS pigs have an antioxidant abnormality which may contribute to the fatal MH response. However the nature of the abnormality is unclear. The enhanced formation of unstable free radicals and indices of lipid peroxidation was not due to decreased vitamin E concentration or glutathione peroxidase activity in the microsomes. Furthermore, fatty acid profiles were similar in microsomes from MHS and MHR pigs indicating similar amounts of potential substrate for TBARS formation.

Effect of propionyl-L-carnitine on rat spinal cord ischaemia and post-ischaemic reperfusion injury

In this study we have examined the effect of propionyl-L-carnitine (PC) on rat spinal cord ischaemia and post-ischaemic reperfusion injury by evaluating two lipid peroxidation indices, thiobarbituric acid reactive substances (TBARS) and diene conjugation, before and after the addition of an ADP-Fe+2 complex to spinal cord homogenates. Aerobic, ischaemic, and post ischaemic reperfusion rat spinal cord homogenates from PC treated and untreated animals did not show any statistically significant difference in their TBARS and conjugated diene content. The addition of the ADP-Fe+2 complex to these homogenates resulted in an increased production of both the lipid peroxidation indices, though the magnitude of such formation was related to the type of experimental intervention. The post-ischaemic reperfusion samples of untreated rats showed the highest TBARS and conjugated diene content, while ischaemic samples in either treated and untreated rats did not show any statistically significant difference with respect to the aerobic samples. The post-ischaemic reperfusion samples of treated rats showed a statistically significant decrease of TBARS and conjugated diene production in comparison to the untreated samples. In addition, PC was also able to partially inhibit TBARS and conjugated diene formation in linoleic acid micelles exposed to hemoglobin, though it did not protect albumin fragmentation from the irradiation of water with an X-ray source.

Induction of lipid peroxidation in mice by hexavalent chromium and its relation to the toxicity

Comparative effects of hexavalent (K2Cr2O7:Cr(VI)) and trivalent chromium (Cr(NO3)3:Cr(III)) on the development of lipid peroxidation, and the relationship between the lipid peroxidation and damage to tissues were studied using male ddY strain mice. The animals were administered with either of two chemicals at a dose of 20 mg Cr/kg by a single intraperitoneal injection. The results obtained were as follows: (1) Lipid peroxidation in the liver, as measured by the synthesis of thiobarbituric acid reactive substances (TBARS), showed a significant increase at 24 and 48 hr after Cr(VI) injection, while in the kidney it was observed only at 48 hr. In the mice administered with Cr(III), TBARS formation in the liver went down below the control levels, while no change was observed in the kidney. (2) Chromium contents in the liver and kidney showed a maximum level at 6 hr after injection of Cr(VI) and then those declined to the half of the maximum level at 48 hr, respectively. Chromium contents in the liver and kidney of the mice injected with Cr(III) were lower than those injected with Cr(VI) during the experimental period. (3) Increases of TBARS formation in the liver, chromium content in the liver and kidney, and ornithine carbamyl transferase (OCT) activity indicative of the liver cell damage, and urea nitrogen content in the serum, indicative of the kidney damage, observed at 24 hr after injection of Cr(VI) were inhibited by simultaneous injection of 100 mg/kg of L-ascorbic acid, as antichrome agent, respectively. These observations might suggest a possible causative role of lipid peroxidation in Cr(VI) toxicity.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutathione peroxidase and iron-thiol dependent lipid peroxidation

Role of glutathione peroxidase in iron-thiol-mediated lipid peroxidation was examined. The enzyme was unable to prevent peroxidation of extracted rat liver microsomal lipids. In contrast, when arachidonic acid was the substrate, glutathione peroxidase did decrease the formation of thiobarbituric acid-reactive material. Superoxide dismutase produced a consistent but partial inhibition of peroxidation and catalase was without effect. Our results suggest that iron-thiol-dependent lipid peroxidation cannot be completely blocked by protective enzymes that are effective in other systems.

Oxidative stress in trisomy 21. A possible role in cataractogenesis

Previous studies have suggested that free radicals and related species play a role in lens damage. The molecules involved may include proteins, lipids and DNA. Focal cortical changes and cortical liquefaction have been reported in patients with Down's syndrome over the age of 15 years. There is evidence supporting the hypothesis that trisomy 21 patients have an increase in free radical reactions and lipoperoxidation susceptibility. This could be due to an increase in the H2O2 generation catalysed by CuZn SOD although the activity of other gene products coded for on chromosome 21 cannot be excluded. Thiobarbituric acid reactive products were measured in human erythrocytes of nine DS patients and nine age-matched controls. There was a significant increase in the first group (21.0 +/- 2.3 nmol MDA/g Hb vs 16.4 +/- 2.9 nmol MDA/g Hb; p less than or equal to 0.01). In plasma, however, TBA products and antioxidant levels (ascorbic acid, tocopherol and uric acid) were not significantly different. Further studies should be carried out, namely through the use of more specific and sensitive methods, to assess the possible association between oxidative stress and cortical lens damage in DS patients.

Release of 2-thiobarbituric acid reactive products from glutamate or deoxyribonucleic acid by 1,2,4-benzenetriol or hydroquinone in the presence of copper ions

Cytotoxic effects of various quinone compounds are thought to be due to the formation of semiquinone free radicals. Hydroquinone and 1,2,4-benzenetriol in the presence of copper ions release from glutamate or DNA aldehydic products capable of reacting with 2-thiobarbituric acid (TBA). The formation of TBA reactive products (TBAR) was greater in the presence of 1,2,4-benzenetriol in comparison with hydroquinone. Complete inhibition of formation of TBAR from glutamate by 1,2,4-benzenetriol and copper was observed in the presence of catalase, thiourea and mannitol. Albumin and superoxide dismutase offered substantial protection. Complete protection of formation of TBAR from DNA was observed in the presence of catalase and thiourea. Presence of albumin, mannitol and superoxide dismutase caused only partial inhibition. The formation of TBAR from glutamate or DNA is dependent on copper ion concentration. The present data indicate that hydroquinone and 1,2,4-benzenetriol in the presence of copper ions can lead to the formation of reactive hydroxyl radicals which can release TBAR from glutamate or DNA.