Radiosensitive antioxidant membrane-bound factors in rat liver microsomes: I. The roles of glutathione and vitamin E

In vitro lipid peroxidation initiated by NADPH/ADP/Fe3+ reveals an alteration of rat liver microsomal antioxidant factors at day D+4 after whole-body gamma irradiation (8Gy). This alteration is partly reversed by GSH, and more efficiently by Trolox C, a water-soluble analog of vitamin E. This reversion by Trolox C, together with the observed 50% decrease in vitamin E content in microsomes of irradiated rats as compared to those of control animals, indicate that Trolox C acts as a free-radical scavenger like and in place of vitamin E. The antioxidant action of Trolox C is not improved in the presence of GSH, which suggests that the former acts earlier than the latter on the autoxidative free-radical chain reactions. Neither GSH, nor Trolox C, nor both antioxidants totally inhibit in vitro lipid peroxidation, which appeals attention on the possible role of extra-microsomal antioxidant factors, especially cytosolic ones.     

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

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

Modulation of glutathione and antioxidant enzymes by Ocimum sanctum and its role in protection against radiation injury

Aqueous extract (OE) of the leaves of Ocimum sanctum, the Indian holy basil, has been found to protect mouse against radiation lethality and chromosome damage and to possess significant antioxidant activity in vitro. Therefore a study was conducted to see if OE protects against radiation induced lipid peroxidation in liver and to determine the role, if any, of the inherent antioxidant system in radioprotection by OE. Adult Swiss mice were injected intraperitoneally (i.p.) with 10 mg/kg of OE for 5 consecutive days and exposed to 4.5 Gy of gamma radiation 30 min after the last injection. Glutathione (GSH) and the antioxidant enzymes glutathione transferase (GST), reductase (GSRx), peroxidase (GSPx) and superoxide dismutase (SOD), as well as lipid peroxide (LPx) activity were estimated in the liver at 15 min, 30 min, 1, 2, 4 and 8 hr post-treatment. LPx was also studied after treatment with a single dose of 50 mg/kg of OE with/without irradiation. OE itself increased the GSH and enzymes significantly above normal levels whereas radiation significantly reduced all the values. The maximum decline was at 30-60 min for GSH and related enzymes and at 2 hr for SOD. Pretreatment with the extract checked the radiation induced depletion of GSH and all the enzymes and maintained their levels within or above the control range. Radiation significantly increased the lipid peroxidation rate, reaching a maximum value at 2 hr after exposure (approximately 3.5 times that of control). OE pretreatment significantly (P < 0.0001) reduced the lipid peroxidation and accelerated recovery to normal levels. The results indicate that Ocimum extract protects against radiation induced lipid peroxidation and that GSH and the antioxidant enzymes appear to have an important role in the protection.     

Lipid Peroxidation in Choline-Methionine Deficiency

A deficiency of choline and methionine is hepatocarcinogenic and is associated with an apparent increase in lipid peroxidation. In this study the susceptibility of microsomes and nuclei to ferritin-dependent lipid peroxidation is examined together with the status of the peroxidation- protective systems. Choline-methionine deficiency caused an increase in Se-independent GSH peroxidases (GSH transferase subunit 2) and membrane vitamin E but a decrease in Se-dependent GSH peroxidase and microsomal GSH peroxidase activity. Choline-methionine deficient microsomes and nuclei were 4-fold more susceptible to lipid peroxidation induced in vitro by physiological concentrations of ferritin/ascorbate/ADP; and the peroxidation was less effectively inhibited by GSH and soluble GSH peroxidases than controls. The results indicate that a decreased level of Se-dependent and membrane GSH peroxidases is involved in the increase in lipid peroxidation observed in choline-methionine deficiency.     

Epicatechin ameliorates ionising radiation-induced oxidative stress in mouse [corrected] liver

The current study was intended to evaluate the hepatoprotective effect of Epicatechin (EC) against radiation-induced oxidative stress, in terms of inflammation and lipid peroxidation. Swiss albino mice were administered with EC (15 mg/kg body weight) for three consecutive days before exposing them to a single dose of 5-Gy (60)Co gamma (γ) irradiation. Mice were necropsied and livers were taken for immunohistochemistry, western blot analysis and biochemical tests for the detection of markers of hepatic oxidative stress. Nuclear translocation of nuclear factor kappa B (NF-κB) and lipid peroxidation were increased whereas the activities of superoxide dismutase (SOD) and catalase (CAT), reduced glutathione (GSH) content and ferric reducing antioxidant power (FRAP) were diminished upon radiation exposure compared to control. Translocation of NF-κB from cytoplasm to nucleus and lipid peroxidation were found to be inhibited whereas an increase in SOD, CAT, GSH and FRAP was observed in the mice treated with EC prior to irradiation. Thus, pre-treatment with EC offers protection against γ-radiation induced hepatic alterations.     

Epicatechin ameliorates ionising radiation-induced oxidative stress in mouse liver

Abstract

The current study was intended to evaluate the hepatoprotective effect of Epicatechin (EC) against radiation-induced oxidative stress, in terms of inflammation and lipid peroxidation. Swiss albino mice were administered with EC (15 mg/kg body weight) for three consecutive days before exposing them to a single dose of 5-Gy ⁶⁰Co gamma (γ) irradiation. Mice were necropsied and livers were taken for immunohistochemistry, western blot analysis and biochemical tests for the detection of markers of hepatic oxidative stress. Nuclear translocation of nuclear factor kappa B (NF-κB) and lipid peroxidation were increased whereas the activities of superoxide dismutase (SOD) and catalase (CAT), reduced glutathione (GSH) content and ferric reducing antioxidant power (FRAP) were diminished upon radiation exposure compared to control. Translocation of NF-κB from cytoplasm to nucleus and lipid peroxidation were found to be inhibited whereas an increase in SOD, CAT, GSH and FRAP was observed in the mice treated with EC prior to irradiation. Thus, pre-treatment with EC offers protection against γ-radiation induced hepatic alterations.     

Inhibition of protein carbonyl formation and lipid peroxidation by glutathione in rat liver microsomes.

The peroxidation of rat liver microsomal lipids is stimulated in the presence of iron by the addition of NADPH or ascorbate and is inhibited by the addition of glutathione (GSH). The fate of GSH and the oxidative modification of proteins under these conditions have not been well studied. Rat liver microsomes were incubated at 37 degrees C under 95% O2:5% CO2 in the presence of 10 microM ferric chloride, 400 microM ADP, and either 450 microM ascorbic acid or 400 microM NADPH. Lipid peroxidation was assessed in the presence 0, 0.2, 0.5, 1, or 5 mM GSH by measuring thiobarbituric acid reactive substance (TBARS) and oxidative modification of proteins by measuring protein thiol and carbonyl groups. GSH inhibited TBARS and protein carbonyl group formation in both ascorbate and NADPH systems in a dose-dependent manner. Heat denaturing of microsomes or treatment with trypsin resulted in the loss of this protection. The formation of protein carbonyl groups could be duplicated by incubating microsomes with 4-hydroxynonenal. Ascorbate-dependent peroxidation caused a loss of protein thiol groups which was diminished by GSH only in fresh microsomes. Both boiling and trypsin treatment significantly decreased the basal protein thiol content of microsomes and enhanced ascorbate-stimulated lipid peroxidation. Protection against protein carbonyl group formation by GSH correlated with the inhibition of lipid peroxidation and appeared not to be due to the formation of the GSH conjugate of 4-hydroxynonenal as only trace amounts of this conjugate were detected. Ninety percent of the GSH lost after 60 min of peroxidation was recoverable as borohydride reducible material in the supernatant fraction. The remaining 10% could be accounted for as GSH-bound protein mixed disulfides. However, only 75% of the GSH lost during peroxidation appeared as glutathione disulfide, suggesting that some was converted to other soluble borohydride reducible forms. These data support a role for protein thiol groups in the GSH-mediated protection of microsomes against lipid peroxidation.     

Modulation of rat erythrocyte antioxidant defense system by buthionine sulfoximine and its reversal by glutathione monoester therapy

The protective effects of glutathione monoester (GME) on buthionine sulfoximine (BSO)-induced glutathione (GSH) depletion and its sequel were evaluated in rat erythrocyte/erythrocyte membrane. Animals were divided into three groups (n=6 in each): control, BSO and BSO+GME group. Administration of BSO, at a concentration of 4 mmol/kg bw, to the albino rats resulted in depletion of blood GSH level to about 59%. GSH was elevated several folds in the GME group as compared to the control (P<0.05) and BSO (P<0.001) groups. Decreased concentration of vitamin E was found in the erythrocyte membrane isolated from BSO-administered animals. Antioxidant enzymes, catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPX) were also found to be altered due to BSO-induced GSH depletion in blood erythrocytes. The SOD and CAT activities in BSO group were significantly lower (P<0.001) than the other groups. Lipid peroxidation index and malondialdehyde (MDA) levels in erythrocytes and their membranes were increased to about 45% and 40%, respectively. The activities of Ca2+ ATPase, Mg2+ ATPase and Na+K+ ATPase were lower than those of control group (P<0.05), whereas the activities of these enzymes were found to be restored to normal followed by GME therapy (P<0.05). Cholesterol, phospholipid and C/P ratio and some of the phospholipid classes like phosphatidylcholine (PC), lysophosphatidylcholine (LPC) and sphingomyelin were significantly (P<0.05) altered in the erythrocyte membranes of BSO-administered rats compared with those of control group. These parameters were restored to control group levels in GME-treated group. Oxidative stress may play a major role in the BSO-mediated gamma glutamyl cysteine synthetase (gamma-GCS) inhibition and hence the depletion of GSH. In conclusion, our findings have shown that antioxidant status decreased and lipid peroxidation increased in BSO-treated rats. GME potentiates the RBC and blood antioxidant defense mechanisms and decreases lipid peroxidation.     

Amelioration of ionizing radiation induced lipid peroxidation in mouse liver by Moringa oleifera Lam. leaf extract

Protective effect of Moringa oleifera leaf extract (MoLE) against radiation-induced lipid peroxidation has been investigated. Swiss albino mice, selected from an inbred colony, were administered with MoLE (300 mg/kg body wt) for 15 days before exposing to a single dose of 5 Gy 60Co-gamma radiation. After treatments, animals were necropsied at different post irradiation intervals (days 1, 7 and 15) and hepatic lipid peroxidation and reduced glutathione (GSH) contents were estimated to observe the relative changes due to irradiation and its possible amelioration by MoLE. It was observed that, MoLE treatment restored GSH in liver and prevented radiation induced augmentation in hepatic lipid peroxidation. Phytochemical analysis showed that MoLE possess various phytochemicals such as ascorbic acid, phenolics (catechin, epicatechin, ferulic acid, ellagic acid, myricetin) etc., which may play the key role in prevention of hepatic lipid peroxidation by scavenging radiation induced free radicals.     

Tryptophan fluorescence of erythrocyte ghosts following irradiation and Fe2+ initiation of lipid peroxidation

It was shown that under the effect of Fe2+-initiated lipid peroxidation and ionizing radiation tryptophan fluorescence parameters (i.e. intensity and polarization) were subjected to similar changes. Shortly (15 min) after irradiation no changes were observed in the level of products reacting with thiobarbituric acid. It is concluded that the process and products of lipid peroxidation do not markedly contribute to the postirradiation alteration of tryptophan fluorescence. At the same time additional postirradiation damages to proteins can be attributed to activation of lipid peroxidation.     

The effect of chronic diazepam administration on lipid peroxidation and Ca2+ -ATPase activity in rat liver

Chronic administration of diazepam (DZP) caused an increase in malondialdehyde (MDA) levels and a decrease in glutathione (GSH) content. DZP also markedly lowered Ca2+ATPase activity. Treatment with Se plus vitamin E reduced MDA levels and increased GSH content. Our results suggest that, increased lipid peroxidation together with alteration in Ca2+ -ATPase activity may play a role in DZP induced hepatic injury and Se plus vitamin E treatment may contribute to the attenuation of DZP induced hepatotoxicity.     

Peroxyl Radical-Mediated Hemolysis: Role of Lipid, Protein and Sulfhydryl Oxidation

The objective of this study was to define the relationship between peroxyl radical-mediated cytotoxicity and lipid, protein and sulfhydryl oxidation using human erythrocytes as the target mammalian cell. We found that incubation of human erythrocytes with the peroxyl radical generator 2,2' azobis (2-amidinopropane) hydrochloride (AAPH) resulted in a time and dose-dependent increase in hemolysis such that at 50 mM AAPH maximum hemolysis was achieved at 120min. Hemolysis was inhibited by hypoxia and by the addition of certain water soluble free radical scavengers such as 5-aminosalicylic acid (5-ASA), 4-ASA, N-acetyl-5-ASA and dimethyl thiourea. Peroxyl radical-mediated hemolysis did not appear to involve significant peroxidation of erythrocyte lipids nor did they enhance protein oxidation at times preceding hemolysis. Peroxyl radicals did however, significantly reduce by approximately 80% the intracellular levels of GSH and inhibit by approximately 90% erythrocyte Ca²⁺ -Mg²⁺ ATPase activity at times preceding the hemolytic event. Our data as well as others suggest that extracellular oxidants promote the oxidation of intracellular compounds by interacting with certain redox active membrane components. Depletion of intracellular GSH stores using diamide did not result in hemolysis suggesting that oxidation of GSH alone does not promote hemolysis. Taken together, our data suggest that neither GSH oxidation, lipid peroxidation nor protein oxidation alone can account for peroxyl radical-mediated hemolysis. It remains to be determined whether free radical-mediated inactivation of Ca²⁺-Mg²⁺ ATPase is an important mechanism in this process.     

Relations Between Tocopherol Depletion and Coenzyme Q During Lipid Peroxidation in rat Liver Mitochondria

In order to evaluate different mitochondrial antioxidant systems, the depletion of alpha-tocopherol and the levels of the reduced and oxidized forms of CoQ were measured in rat liver mitochondria during Fe⁺⁺/ascorbate and NADPH/ADP/Fe⁺⁺ induced lipid peroxidation. During the induction phase of malondialdehyde formation, alpha-tocopherol declined moderately to about 80% of initial contents, whereas the total CoQ pool remained nearly unchanged, but reduced CoQ9 continuously declined. At the start of massive malondialdehyde formation, CoQ9 reaches its fully oxidized state. At the same time alpha-tocopherol starts to decline steeply, but never becomes fully exhausted in both experimental systems. Evidently the oxidation of the CoQ9 pool constitutes a prerequisite for the onset of massive lipid peroxidation in mitochondria and for the subsequent depletion of alpha-tocopherol. Trapping of the GSH by addition of dinitrochlorbenzene (a substrate of the GSH transferase), results in a moderate acceleration of lipid peroxidation, but alpha-tocopherol and ubiquinol levels remained unchanged when compared with the controls. Addition of succinate to GSH depleted mitochondria effectively suppressed MDA formation as well as alpha-tocopherol and ubiquinol depletion. The data support the assumption that the protective effect of respiratory substrates against lipid peroxidation in the absence of mitochondrial GSH is mediated by the regeneration of the lipid soluble antioxidants CoQ and alpha-tocopherol.     

Photooxidation of cell membranes in the presence of hematoporphyrin derivative: reactivity of phospholipid and cholesterol hydroperoxides with glutathione peroxidase

The susceptibility of photodynamically-generated lipid hydroperoxides to reductive inactivation by glutathione peroxidase (GPX) has been investigated, using hematoporphyrin derivative as a photosensitizing agent and the human erythrocyte ghost as a target membrane. Photoperoxidized ghosts were reactive in a glutathione peroxidase/reductase (GPX/GRD)-coupled assay only after phospholipid hydrolysis by phospholipase A2 (PLA2). However, enzymatically determined lipid hydroperoxide values were consistently approx. 40% lower than iodometrically determined values throughout the course of photooxidation. Moreover, when irradiated ghosts were analyzed iodometrically during PLA2/GSH/GPX treatment, a residual 30-40% of non-reactive lipid hydroperoxide was observed. The possibility that cholesterol product(s) account for the non-reactive lipid hydroperoxide was examined by tracking cholesterol hydroperoxides in [14C]cholesterol-labeled ghosts. The sum of cholesterol hydroperoxides and GPX/GRD-detectable lipid hydroperoxides was found to agree closely with iodometrically determined lipid hydroperoxide throughout the course of irradiation. Thin-layer chromatography of total lipid extracts indicated that cholesterol hydroperoxide was unaffected by PLA2/GSH/GPX treatment, whereas most of the phospholipid peroxides were completely hydrolyzed and the released fatty acid peroxides were reduced to alcohols. It appears, therefore, that the GPX-resistant lipid hydroperoxides in photooxidized ghosts were derived primarily from cholesterol. Ascorbate plus Fe3+ produced a burst of free-radical lipid peroxidation in photooxidized, PLA2-treated ghosts. As expected for fatty acid hydroperoxide inactivation, the lipid peroxidation was inhibited by GSH/GPX, but only partially so, suggesting that cholesterol hydroperoxide-derived radicals play a major role in the reaction.     

Inhibition of erythrocyte Ca2+-ATPase by activated oxygen through thiol- and lipid-dependent mechanisms

We have studied erythrocyte Ca2+-ATPase as a model target for elucidating effects of activated oxygen on the erythrocyte membrane. Either intracellular or extracellular generation of activated oxygen causes parallel decrements in Ca2+-ATPase activity and cytoplasmic GSH, oxidation of membrane protein thiols, and lipid peroxidation. Subsequent incubation with either dithiothreitol or glucose allows only partial recovery of Ca2+-ATPase, indicating both reversible and irreversible components which are modeled herein using diamide and t-butyl hydroperoxide. The reversible component reflects thiol oxidation, and its recovery depends upon GSH restoration. The irreversible component is largely due to lipid peroxidation, which appears to act through mechanisms involving neither malondialdehyde nor secondary thiol oxidation. However, some portion of the irreversible component could also reflect oxidation of thiols which are inaccessible for reduction by GSH, since we demonstrate existence of different classes of thiols relevant to Ca2+-ATPase activity. Activated oxygen has an exaggerated effect on Ca2+-ATPase of GSH-depleted cells. Sickle erythrocytes treated with dithiothreitol show a heterogeneous response of Ca2+-ATPase activity. These findings are potentially relevant to oxidant-induced hemolysis. They also may be pertinent to oxidative alteration of functional or structural membrane components in general, since many components share with Ca2+-ATPase both free thiols and close proximity to unsaturated lipid.     

Glutathione correlates with lipid peroxidation in liver mitochondria of triiodothyronine-injected hypophysectomized rats

The temporal relationship of changes in state 3 respiration, lipid peroxidation, and glutathione (GSH) content was investigated in liver mitochondria of hypophysectomized rats after an injection of 3,3',5-triiodo-L-thyronine (T3). Lipid peroxidation induced by ADP/Fe3+/NADPH was determined by the amount of malondialdehyde formed. Hypophysectomy decreased respiration and lipid peroxidation (from 19.88 +/- 3.04 to 14.19 +/- 1.14 nmol malondialdehyde.mg protein-1.10 min-1) but increased GSH content (from 7.06 +/- 2.08 to 12.46 +/- 3.58 nmol/mg protein). Daily injections of a low dose (5 micrograms/100 g) of T3 for 7 days restored the parameters. Time course (up to 96 h) of these changes was followed after one injection of a moderate (100 micrograms/100 g) and high (1000 micrograms/100 g) dose of the hormone. Respiration showed a significant increase at 24 h and declined slightly at 96 h. There was a slow loss of respiratory control ratio after 24 h. Lipid peroxidation remained unchanged at 24 h and showed a gradual increase, becoming significantly higher at 72-96 h depending on the hormone dosage. Changes in GSH content followed a time course similar to that of lipid peroxidation except that it showed a decrease instead of an increase. There was a high degree of inverse linear correlation between lipid peroxidation and GSH (correlation coefficient = 0.95). Because GSH is required for detoxification of hydroperoxides generated by the respiratory chain, it is suggested that lipid peroxidation may play a major role in the modulation of intramitochondrial GSH.     

Relations Between Tocopherol Depletion and Coenzyme Q During Lipid Peroxidation in rat Liver Mitochondria

In order to evaluate different mitochondrial antioxidant systems, the depletion of alpha-tocopherol and the levels of the reduced and oxidized forms of CoQ were measured in rat liver mitochondria during Fe⁺⁺/ascorbate and NADPH/ADP/Fe⁺⁺ induced lipid peroxidation. During the induction phase of malondialdehyde formation, alpha-tocopherol declined moderately to about 80% of initial contents, whereas the total CoQ pool remained nearly unchanged, but reduced CoQ9 continuously declined. At the start of massive malondialdehyde formation, CoQ9 reaches its fully oxidized state. At the same time alpha-tocopherol starts to decline steeply, but never becomes fully exhausted in both experimental systems. Evidently the oxidation of the CoQ9 pool constitutes a prerequisite for the onset of massive lipid peroxidation in mitochondria and for the subsequent depletion of alpha-tocopherol. Trapping of the GSH by addition of dinitrochlorbenzene (a substrate of the GSH transferase), results in a moderate acceleration of lipid peroxidation, but alpha-tocopherol and ubiquinol levels remained unchanged when compared with the controls. Addition of succinate to GSH depleted mitochondria effectively suppressed MDA formation as well as alpha-tocopherol and ubiquinol depletion. The data support the assumption that the protective effect of respiratory substrates against lipid peroxidation in the absence of mitochondrial GSH is mediated by the regeneration of the lipid soluble antioxidants CoQ and alpha-tocopherol.     

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.     

Lipid peroxidation in hepatomas of different degrees of deviation

Lipid peroxidation rate in four different hepatomas is quite different and seems to be related to their degree of deviation, low deviation tumours displaying higher peroxidative ability. Moreover, the supernatant of the highly anaplastic Yoshida hepatoma is able to decrease the peroxidation rate in normal liver microsomes. This antioxidant ability is not dependent upon an increased level of glutathione. The concentration of reduced glutathione (GSH) declines strongly during incubation in conditions favouring lipid peroxidation. Unlike normal liver homogenates, this decline of GSH in hepatomas is not due to the transformation of GSH into oxidized glutathione (GSSG) but mostly to the increased activity of the γ-glutamyl-transpeptidase pathway.     

Modulatory effects of garlic and neem leaf extracts on N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced oxidative stress in Wistar rats

The effects of garlic and neem leaf extracts on lipid peroxidation and antioxidant status during administration of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), a carcinogenic nitrosamine were evaluated in male Wistar rats. Extracts of garlic and neem leaf were administered orally for five consecutive days before intraperitoneal injection of MNNG. Enhanced lipid peroxidation in the stomach, liver and circulation of MNNG-treated rats was accompanied by a significant decrease in glutathione (GSH) and the activities of glutathione peroxidase (GPx), glutathione-S-transferase (GST) and gamma glutamyl transpeptidase (GGT). Administration of garlic and neem leaf extracts significantly decreased the formation of lipid peroxides and enhanced the levels of antioxidants and detoxifying enzymes in stomach, the primary target organ for MNNG, as well as in the liver and circulation. The results of the present study suggest that garlic and neem may exert their protective effects by modulating lipid peroxidation and enhancing the levels of GSH and GSH-dependent enzymes.