Enhancement of lipid peroxidation in rat liver on acute exposure to styrene and acrylamide a consequence of glutathione depletion

Lipid peroxidation, glutathione level and activity of glutathione-S-transferase were studied in liver and brain of rats 4 and 3 h after a single i.p. administration of 0, 25, 75, 100 mg/kg acrylamide or 0, 50, 100, 200, 600 mg/kg styrene, respectively. In liver both acrylamide and styrene caused an increase in lipid peroxidation and decrease in glutathione contents and activity of glutathione-S-transferase in a dose dependent manner, while in brain only acrylamide produced a decrease in glutathione content. The decrease in glutathione content was not always associated with increase of lipid peroxidation. The enhancement of lipid peroxidation occurred only when glutathione contents were depleted to certain critical levels. No effect of acrylamide or styrene was seen on lipid peroxidation under in vitro conditions. The addition of glutathione in the incubation mixture significantly inhibited the rate of lipid peroxidation of liver homogenates of acrylamide and styrene treated animals.The results suggest that enhancement of lipid peroxidation in liver on exposure to acrylamide or styrene is a consequence of depletion of glutathione to certain critical levels. The inhibition of glutathione-S-transferase activity by acrylamide and styrene suggests that detoxication of these neurotoxic compounds could be suppressed following acute exposure.     

Are the increases in local tumour necrosis factor and lipid peroxidation observed in pre-starved mice infected with Salmonella typhimurium markers of increased liver damage?

Pathogenic microorganisms are known to sense and process signals within their hosts, including those resulting from starvation. Therefore, an attempt was made to evaluate the extent and the possible underlying mechanism of Salmonella typhimurium-induced hepatic damage using pre-starved laboratory mice. The following parameters were analysed, comparing control, fed infected, starved, and starved infected mice: the bacterial load in the liver, fluctuations in liver-derived enzymes alanine-aminotransferase and aspartate-aminotransferase, histopathological changes, lipid peroxidation as well as estimation of reduced glutathione, superoxide dismutase and catalase, along with the TNF content in livers. The number of bacterial cells recovered from starved infected livers at 3 days post-S. typhimurium inoculation was comparable to the number recovered from fed infected livers at 5 days post-Salmonella inoculation, indicating an early increase in the development of the bacteria in starved mice. A marked elevation in liver-derived enzymes in mouse serum and significant histopathological changes are markers of liver damage of higher amplitude in starved infected mice. Analysis of the liver indicated a significant increase in lipid peroxidation in starved infected mice compared to their control counterparts, a process coupled with increased TNF level. Although the reduced glutathione levels showed a marked increase in the starved infected mice, there was a significant decrease in superoxide dismutase and catalase activities in this group.     

Adaptational increase of liver glutathione content during long-term application of cyclosporine A may attenuate toxic side effects.

The concentrations of reduced and oxidized glutathione and of adenine nucleotides were determined in liver, kidney and heart of rats during long-term (four weeks), high-dose therapy with cyclosporine A. In liver and kidney the concentration of oxidized glutathione increased following 4 weeks-therapy suggesting increased formation of free radicals and accelerated lipid peroxidation processes. These processes may be due to an increased activity of the cytochrome P-450 system. Compensatory levels of reduced glutathione were also increased. The adaptational increase of the tissue level of reduced glutathione, presumably the response to a chronic oxidative stress, was more distinct in the liver. The liver did not lose adenine nucleotides. In contrast the kidney, after 4 weeks of cyclosporine A therapy, lost 25% of the adenine nucleotides. These findings suggest that the liver is characterized by a greater potential for effective adaptation to oxidative stress conditions compared to the kidney. These adaptations may prevent distortions of energy and nucleotide metabolism in the liver which is in agreement with the minor ultrastructural changes we have observed.     

The impact of thyroid activity variations on some oxidizing-stress parameters in rats

The effect of the thyroid activity on the formation of lipid peroxidation and on liver and heart antioxidant enzyme activities was investigated in Wistar rats. Hypothyroidism and hyperthyroidism conditions were induced for five weeks by the administration of 0.05% benzythiouracile (BTU) and L-thyroxine sodium salt (0.0012%), in drinking water, respectively. No significant effect was observed on the rates of both lipid peroxidation and the vitamin E in hepatic and cardiac tissues of hypothyroidism rats compared to the controls, contrary to the hyperthyroidism rats, which expressed a pronounced increase. The increased glutathione peroxidase activity in rats suffering from hyperthyroidism was associated with a fall of the reduced glutathione in the homogenate and a marked increase in the glutathione reductase activity. An increase in superoxide dismutase and catalase activities was also recorded in hyperthyroidism. Our results explain the thyroid activity variation in relation to the lipid peroxidation and the tissular contents of the enzymatic and the non-enzymatic antioxidants. To conclude, our results show the occurrence of a state of oxidizing stress in relation to hyperthyroidism.     

Protective effect of green tea against lipid peroxidation in the rat liver, blood serum and the brain

This paper reports data on the effect of green tea on the lipid peroxidation products formation and parameters of antioxidative system of the liver, blood serum and central nervous tissue of healthy young rats drinking green tea for five weeks. The rats were permitted free access to solubilized extract of green tea. Bioactive ingredients of green tea extract caused in the liver an increase in the activity of glutathione peroxidase and glutathione reductase and in the content of reduced glutathione as well as marked decrease in lipid hydroperoxides (LOOH), 4-hydroksynonenal (4-HNE) and malondialdehyde (MDA). The concentration of vitamin A increased by about 40%. Minor changes in the measured parameters were observed in the blood serum. GSH content increased slightly, whereas the index of the total antioxidant status increased significantly. In contrast, the lipid peroxidation products, particularly MDA was significantly diminished. In the central nervous tissue the activity of superoxide dismutase and glutathione peroxidase decreased while the activity od glutathione reductase and catalase increased after drinking green tea. Moreover the level of LOOH, 4-HNE and MDA significantly decreased. The use of green tea extract appeared to be beneficial to rats in reducing lipid peroxidation products. These results support and substantiate traditional consumption of green tea as protection against lipid peroxidation in the liver, blood serum, and central nervous tissue.     

Antioxidative status changes in golden syrian hamsters with experimental metabolic syndrome

Some indices of the antioxidant status (content of the alpha-tocopherol, reduced glutathione and ascorbic acid, activity of the glutathione reductase and aryl-esterase) and lipid peroxidation processes in the liver, blood serum, and some blood serum lipoprotein fractions of the Golden Syrian hamsters of different sex and age status under high-caloric diet were investigated. It has been shown that the hypercaloric diet leads to a decreaseng of reduced glutathione content and increase of the level of lipid peroxidation products in the liver of experimental animals. The ascorbic acids content in male liver is decreased and in female liver is increased. In the blood serum under hypercaloric nutrition the accumulation of lipid peroxidation products and alpha-tocopherol content a decrease in ApoB-lipoproteins and HDL is observed. Simultaneously the ascorbic acid content is increased in the blood serum of all experimental animals. Activation of free-radical oxidation both in the liver, and blood serum is more significant in males compared with females. The data obtained allow to suppose that atherosclerotic complications of metabolic syndrome development may be connected to the lipoprotein oxidant status infringement.     

The role of selenium in the regulation of lipid peroxidation in biological membranes and glutathione peroxidase activity

The antioxidative effect of selenium cannot be exclusively due to the functioning of the selenium-dependent glutathione peroxidase mechanism of utilization of various hydroperoxides. This hypothesis is based on the following experimental evidence. Selenium ions are readily incorporated into animal organs and tissues immediately after injection (2 hours) as well as into cell organelles and cytosol where they inhibit lipid peroxidation. The activity of glutathione peroxidase (EC 1.1.1.19) in rat liver and guinea pig cytosol is thereby unchanged but increases drastically after 12 hours reaching a maximum an the 3rd-4th day. The effectiveness of lipid peroxidation inhibition does not increase under these conditions. Although the glutathione peroxidase activity is absent in the nuclei and microsomes, exogenous selenium inhibits lipid peroxidation in these organelles. The activity of the rat liver cytosolic enzyme markedly exceeds that of its guinea pig counterpart. However, lipid peroxidation in guinea pig liver occurs less intensively than that in rat liver cytosol.     

Modulation of radiation-induced alteration in the antioxidant status of mice by naringin

The alteration in the antioxidant status and lipid peroxidation was investigated in Swiss albino mice treated with 2 mg/kg b.wt. naringin, a citrus flavoglycoside, before exposure to 0.5, 1, 2, 3, and 4 Gy gamma radiation. Lipid peroxidation, glutathione, glutathione peroxidase, catalase and superoxide dismutase were determined in the liver and small intestine of mice treated or not with naringin at 0.5, 1, 2, 4 and 8 h post-irradiation. Whole-body irradiation of mice caused a dose-dependent elevation in the lipid peroxidation while a dose-dependent depletion was observed for glutathione, glutathione peroxidase, superoxide dismutase and catalase in both liver as well as small intestine. Treatment of mice with 2 mg/kg b. wt. naringin inhibited the radiation-induced elevation in the lipid peroxidation as well as depletion of glutathione, glutathione peroxidase, superoxide dismutase and catalase in liver and small intestine. Radiation-induced lipid peroxidation increased with time, which was greatest at 2 h post-irradiation and declined thereafter in the liver and small intestine. Similarly, a maximum decline in the glutathione glutathione peroxidase, and superoxide dismutase was observed at 1 h, while catalase showed a maximum decline at 2 h post-irradiation. Our study demonstrates that naringin protects mouse liver and intestine against the radiation-induced damage by elevating the antioxidant status and reducing the lipid peroxidation.     

Effect of dietary fish on antioxidant parameters of normal and cholesterol stressed rats

Feeding fish (Sardinella longiceps) to normal rats increased lipid peroxidation and total and Se-dependent glutathione peroxidase (GSH-px) activity in erythrocytes and manganese dependent superoxide dismutase (Mn-SOD) activity in liver. Feeding fish to cholesterol stressed rats showed a significant increase in the activity of GSH-px and cholesterol feeding alone, resulted in a significant increase in the lipid peroxidation and liver Mn-SOD activity. The results suggest that the high polyunsaturated fatty acid content of S. longiceps, the fish abundantly available in the west coast of India, does not have any deleterious effect by way of free radical generation. The observed lipid peroxidation is not critical as is evident from the results of glutathione level and other scavenging enzymes.     

Hepatoprotective effects of Liv-52 on ethanol induced liver damage in rats

The mechanism of protective effects of Liv-52, a multiherbal hepatoprotective drug, on ethanol induced hepatic damage has been investigated. The results indicate that Liv-52 treatment prevents ethanol induced increase in the activity of the enzyme gamma-glutamyl transpeptidase. Concomitantly there was also a decrease in ethanol accentuated lipid peroxidation in liver following Liv-52 treatment. The activity of antioxidant enzymes; superoxide dismutase, glutathione peroxidase and the levels of glutathione were decreased following ethanol ingestion. Liv-52 treatment was found to have protective effects on the activity of superoxide dismutase and the levels of glutathione. The results obtained from the study indicate hepatoprotective nature of Liv-52 which might be attributed to its ability to inhibit lipid peroxidation.     

Effect of thiols on lipid peroxidation in rat liver microsomes

The stimulatory or inhibitory effects of various thiol compounds on in vitro lipid peroxidation by iron-ascorbate in rat liver microsomes were determined. Glutathione had no measurable pro-oxidant capacity, in contrast, it protected against lipid peroxidation. N-Acetyl l-cysteine and S-methyl-glutathione had no effect on in vitro lipid peroxidation. l-Cysteine stimulated lipid peroxidation and also of d-penicillamine and dl-dithiothreitol the pre-oxidant capacity predominated the anti-oxidant capacity. Cysteamine afforded a pronounced protection against in vitro lipid peroxidation. In contrast to the labile character of the glutathione dependent protection, the protection by cysteamine was not affected by heat-pretreatment of the liver microsomes or alkylating protein sulfhydryl groups by N-ethyl maleimide. Again in contrast to glutathione, the protection against in vitro microsomal lipid peroxidation by cysteamine was not reduced after in vivo lipid peroxidation induced by CC14. This suggests that even after the process of lipid peroxidation has been started, administration of cysteamine might still be beneficial.     

Differential lipid peroxidative response of rat liver and lung tissues to glutathione depletion induced in vivo by diethyl maleate: effect of the antioxidant flavonoid (+)-cyanidanol-3

The administration of a single dose of diethyl maleate (DEM) to fed rats elicited a drastic decrease in the content of reduced glutathione (GSH) both in liver and lung tissues after 6 h of treatment. Cellular GSH depletion induced by DEM was accompanied by a marked increase in pulmonary lipid peroxidation which was completely abolished by (+)-cyanidanol-3, without changes in the liver. Superoxide dismutase (SOD) activity remained unchanged in both tissues in this situation. Hepatic and pulmonary GSH depletion induced by a second dose of DEM given 24 h later produced a further increase in lung lipid peroxidation and a diminution of pulmonary SOD activity. In this condition, hepatic lipid peroxidation and SOD activity were not altered. These results indicate that lung and liver tissues exhibit a different lipid peroxidative response to chemically-induced GSH depletion.     

Prophylactic effect of melatonin on lead-induced inhibition of heme biosynthesis and deterioration of antioxidant systems in male rats

We studied the protective role of the pineal hormone melatonin on lead-induced suppression of the heme synthesis pathway as a consequence of reduced antioxidant systems in rat. We injected rats intramuscularly with lead acetate (10 mg/kg body weight) daily for 7 days, which significantly abolished heme synthesis as evidenced by decreased blood hemoglobin, liver delta-aminolevulinic acid synthetase, erythrocytic delta-aminolevulinic acid dehydratase, and hepatic iron content. These effects were accompanied with marked elevation of hepatic lipid peroxidation and decreased enzymatic antioxidants such as glutathione reductase, glutathione-S-transferase, superoxide dismutase, and catalase, as well as nonenzymatic antioxidants such as total sulfhydryl groups and glutathione. Furthermore, lead treatment caused hepatic deficiency in copper and zinc accompanied by a significant elevation of lead concentration in both plasma and liver. Daily pretreatment with melatonin (30 mg/kg body weight) intragastrically prevented the suppressive effects of lead on heme-synthesizing enzymes and iron deficiency. In addition, preadministration of melatonin reduced the inhibitory effect of lead on both enzymatic and nonenzymatic antioxidants. This was accompanied by marked normalization of lipid peroxidation and modulation of copper and zinc levels in liver. The action of melatonin on lead-induced changes was attributed to protection of the antioxidant capacity in cells in addition to the ability of melatonin to scavenge free radicals.     

Effect of DL-alpha-lipoic acid on mitochondrial enzymes in aged rats.

Mitochondrial dysfunction appears to contribute to some of the loss of function accompanying ageing. Mitochondria from aged tissue use oxygen inefficiently impairing ATP synthesis and results in increased oxidant production. A high flux of oxidants not only damages mitochondria, but other important cell biomolecules as well. In the present investigation, the levels of lipid peroxidation, oxidized glutathione, non-enzymatic antioxidants and the activities of mitochondrial enzymes were measured in liver and kidney mitochondria of young and aged rats before and after lipoic acid supplementation. In both liver and kidney increase in the levels of mitochondrial lipid peroxidation and oxidized glutathione and decrease in the levels of antioxidants and the activities of mitochondrial enzymes were observed in aged rats. DL-alpha-lipoic acid supplemented aged rats showed a decrease in the levels of lipid peroxidation and oxidized glutathione and increase in the levels of reduced glutathione, vitamins C and E and the activities of mitochondrial enzymes like isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, succinate dehydrogenase, NADH-dehydrogenase and cytochrome-c-oxidase. Thus, lipoic acid reverses the age-associated decline in endogenous low molecular weight antioxidants and mitochondrial enzymes and, therefore, may lower the increased risk of oxidative damage that occurs during ageing. From our results it can be concluded that lipoic acid supplementation enhances the activities of mitochondrial enzymes and antioxidant status and thereby protects mitochondria from ageing.     

Increase in glutathione disulfide level regulates the activity of microsomal glutathione S-transferase in rat liver

Glutathione disulfide stimulates the activity of rat liver microsomal glutathione S-transferase 2-fold after incubation at 25 degrees C for 10 min. When the microsomes were incubated with the disulfide for over 20 min, the transferase activity increased to the same extent as in the case of N-ethylmaleimide (6-fold). Even in the presence of reduced glutathione, some enhancement of the transferase activity was observed. The data presented here are evidence that increase in glutathione disulfide level, e.g. by lipid peroxidation, on endoplasmic reticulum causes the upregulation of microsomal glutathione S-transferase activity.     

Role of glutathione, lipid peroxidation and antioxidants on acute bile-duct obstruction in the rat

The aim of this work was to evaluate the role of lipid peroxidation and glutathione on liver damage induced by 7-day biliary obstruction in the rat. Male Wistar rats were bile-duct-ligated and divided in groups of 10 animals. Groups received vitamin E (400 IU/rat, p.o., daily) or trolox (50 mg/kg, p.o., daily) or both. Lipid peroxidation increased significantly in the livers of bile-duct-ligated rats. Vitamin E and trolox prevented lipid peroxidation. GSH was oxidized in the BDL group and the GSH/GSSG ratio decreased as a consequence. However, total glutathione content increased in liver and blood indicating a possible induction in de novo synthesis of GSH. Antioxidants preserved the normal GSH/GSSG ratio. Despite the observation that antioxidants verted lipid peroxidation and oxidation of GSH, liver injury (as assessed by serum enzyme activities, bilirubin concentration, liver glycogen content and histology) was not affected by the treatments. These results suggest that drugs that inhibit lipid peroxidation and oxidation of glutathione have no effect on conventional biochemical markers of liver injury and on liver histology of bile-duct-ligated rats for 7 days. It seems more likely that the detergent action of bile salts is responsible for solubilization of plasma membranes and cell death, which in turn may lead to oxidative stress, GSH oxidation and lipid peroxidation.     

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

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

Mechanistic aspects of enhanced lipid peroxidation following glutathione depletion in vivo

Several agents known to conjugate with glutathione (GSH) were administered to phenobarbital-induced rats resulting in a more or less pronounced depletion of hepatic GSH. In vitro incubations showed that a large enhancement of spontaneous lipid peroxidation was observed when the GSH content was below 1 μmol/g liver. This effect was inhibited by addition of exogenous GSH in a concentration-dependent manner, the GSH-concentration yielding 50% inhibition (I₅₀) being 1 μM. Using phorone (diisopropylidene acetone), which proved to be the most potent GSH-depletor, the time- and dose-dependence of the GSH-depletion and the consequent lipid peroxidation was studied. Again it was assured that the GSH concentration must reach a critical value of about 20% of the initial hepatic GSH content, before an enhanced lipid peroxidation is seen. Employing scavengers of excited oxygen species no evidence was found for the involvement of free oxygen radicals. Hepatoprotective agents and inhibitors of mixed-function oxidases exerted a more or less pronounced inhibitory action. Our findings are further support of our previous postulate that GSH depletion per se might lead to an increased lipid peroxidation, possibly due to its lack as a part of the cellular defence system against endogenous toxic intermediates.     

Modulation of CYP4502E1 and oxidative stress by testosterone in liver and kidney of benzene treated rats

Bilateral castration increased lipid peroxidation and consequently reduced glutathione in both liver and kidney. Testosterone administration reduced lipid peroxidation in the liver of castrated and benzene treated rats, however, reduced glutathione status could not be restored. Benzene depleted CYP4502E1 in castrated rats, however, the enzyme was restored in liver and kidney both after testosterone treatment. The results suggest that testosterone affects the metabolism and disposition of benzene by influencing CYP4502E1. Other hormonal and cellular/molecular factors may also alter the actions of testosterone. Testosterone dependent mechanism of toxicity of benzene in the liver and kidney has been discussed.     

Prevention of N-nitrosodiethylamine-induced hepatocarcinogenesis by S-allylcysteine

Chemopreventive effect of S-allylcysteine (constituent of garlic) on N-nitrosodiethylamine (NDEA)-induced hepatocarcinogenesis was evaluated in Wistar rats. Significantly decreased lipid peroxidation products (thiobarbituric acid reactive substances-TBARS and lipid hydroperoxides) with increased level of reduced glutathione, increased activities of glutathione S-transferase, and glutathione peroxidase were observed in liver of NDEA-treated rats when compared with control rats. The activities of superoxide dismutase and catalase were significantly decreased in tumor tissue when compared with control. Administration of S-allylcysteine (SAC) showed the inhibition of tumor incidence, modulated the lipid peroxidation, and increased the reduced glutathione, glutathione-dependent enzymes, superoxide dismutase, and catalase in NDEA-induced carcinogenesis. From our results, we speculate that S-allylcysteine mediates its chemopreventive effects by modulating lipid peroxidation, GST stimulation, and by increasing the antioxidants. Hence SAC prevents cells from loss of oxidative capacity in NDEA-induced hepatocarcinogenesis.