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

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

Vitamin E and glutathione are required for preservation of microsomal glutathione S-transferase from oxidative stress in microsomes

Glutathione (GSH) inhibited lipid peroxidation induced by NADPH-BrCCl3 in vitamin E sufficient microsomes, but did not in phenobarbital (PB)-treated microsomes (containing about 60% of normal vitamin E) or in vitamin E-deficient microsomes (containing about 30% of normal vitamin E). There was a good correlation between the increased formation of CHCl3 from BrCCl3 in the presence of GSH under anaerobic conditions and the vitamin E level in the microsomes. A normal level of vitamin E in microsomes was thus very important for GSH-dependent inhibition of lipid peroxidation and for the efficient formation of CHCl3 from BrCCl3. Bromosulfophthalein (BSP) eliminated the effects of GSH on lipid peroxidation and CHCl3 formation. The apparent Km and Vmax of substrates for GSH S-transferase were changed by in vivo depletion of vitamin E in microsomes, and the Vmax/Km values were significantly reduced. The enzyme activity in microsomes was inactivated following the loss of vitamin E during in vitro lipid peroxidation, and GSH prevented the loss of vitamin E and protected the enzyme from attack by free radicals. GSH inhibited lipid peroxidation induced by NADPH-Fe2+ and the loss of GSH S-transferase activity during the peroxidation in PB-treated microsomes, but did not in the case of induction by NADPH-BrCCl3. A possible relation between the microsomal GSH S-transferase activity and defense by GSH against lipid peroxidation in microsomes is discussed.     

Dietary selenium, glutathione peroxidase activity, and toxicity of 2,3,7,8-tetrachloro-dibenzo-p-dioxin

TCDD has been shown to inhibit selenium-dependent glutathione peroxidase activity. The role of selenium in TCDD toxicity is not known. We have therefore examined the effect of TCDD administration on hepatic glutathione peroxidase, aryl hydrocarbon hydroxylase, glutathione reductase, and glutathione S-transferase activities, glutathione content, and lipid peroxidation in rats fed 0, 0.10, and 2.0 ppm dietary selenium. TCDD treatment significantly inhibited selenium-dependent glutathione peroxidase in animals on diets containing 0.10 and 2.0 ppm selenium. The selenium-dependent glutathione peroxidase activities in rats on 0.10 and 2.0 ppm dietary selenium were 8.3-and 4.7-fold greater than in animals fed a diet containing 0 ppm selenium. TCDD administration enhanced hepatic microsomal lipid peroxidation by factors of 4.0, 4.9, and 9.8 in animals fed diets containing 0, 0.10, and 2.0 ppm selenium, respectively. The administration of a lethal dose of TCDD to rats fed diets containing 0, 0.10, and 2.0 ppm selenium resulted in 0, 46, and 7% survival, respectively, after 66 d. Aryl hydrocarbon hydroxylase, glutathione S-transferase, and glutathione reductase activities were induced by TCDD. The results indicate that optimum dietary selenium provides partial protection from the toxic effects of TCDD.     

硒多糖、亚砷酸钠对大鼠肝微粒体酶和GSH-Px等的影响

研究了硒多糖、亚砷酸钠在体内、外对大鼠肝微粒体酶细胞色素Ｐ－４５０、ｂ５、ＮＡＤ（Ｐ）Ｈ－细胞色素Ｃ还原酶、谷胱甘肽硫转移酶（ＧＳＴ）的影响;并通过测定硒多糖、亚砷酸钠对肝谷胱甘肽过氧化物酶（ＧＳＨ－Ｐｘ）和脂质过氧化（ＬＰＯ）的影响,探讨了硒、砷相互作用的机理。结果表明：连续７天腹腔注射０．２ｍｇ／ｋｇ硒多糖,细胞色素Ｐ－４５０、ｂ５的含量、ＧＳＴ的活性降低（Ｐ＜０．０５）;硒多糖明显诱导ＧＳＨ－Ｐｘ的活性,降低脂质过氧化,拮抗亚砷酸钠对ＬＰＯ的作用。亚砷酸钠显著增强肝细胞脂质过氧化（Ｐ＜０．０５）,对ＧＳＨ－Ｐｘ和肝微粒体酶无明显影响     

Alterations in ATP-dependent calcium uptake by rat renal cortex microsomes following ochratoxin A administration in vivo or addition in vitro.

A disruption of calcium homeostasis, leading to a sustained increase in cytosolic calcium levels, has been associated with cytotoxicity in response to a variety of agents in different cell types. We have observed that administration of a single high dose or multiple lower doses of the carcinogenic nephrotoxin ochratoxin A (OTA) to rats resulted in an increase of the renal cortex endoplasmic reticulum ATP-dependent calcium pump activity. The increase was very rapid, being evident within 10 min of OTA administration and remained elevated for at least 6 hr thereafter. The increase in calcium pump activity was inconsistent with previous observations that OTA enhances lipid peroxidation (ethane exhalation) in vivo, a condition known to inhibit the calcium pump. However, no evidence of enhanced lipid peroxidation was observed in the renal cortex since levels of malondialdehyde and a variety of antioxidant enzymes including catalase, DT-diaphorase, superoxide dismutase, glutathione peroxidase, glutathione reductase and glutathione S-transferase were either unaltered or reduced. In in vitro studies, addition of OTA to cortex microsomes during calcium uptake inhibited the uptake process although the effect was reversible. Preincubation of microsomes with NADPH had a profound inhibitory effect on calcium uptake but inclusion of OTA was able to reverse the inhibition. Changes in the rates of microsomal calcium uptake correlated with changes in the steady-state levels of the phosphorylated Mg2+/Ca(2+)-ATPase intermediate, suggesting that in vivo/in vitro conditions were affecting the rate of enzyme phosphorylation.     

Rat liver microsomal NADPH-supported oxidase activity and lipid peroxidation dependent on ethanol-inducible cytochrome P-450 (P-450IIE1)

The liver microsomal ethanol-inducible cytochrome P-450 (P-450IIE1) form is known to exhibit a high rate of oxidase activity in the absence of substrate and it was therefore of interest to evaluate whether this form of P-450 could contribute to microsomal and liposomal NADPH-dependent oxidase activity and lipid peroxidation. The rate of microsomal NADPH-consumption, O2--formation, H2O2-production and generation of thiobarbituric acid (TBA) reactive substances correlated to the amount of P-450IIE1 in 28 microsomal samples from variously treated rats. Anti-P-450IIE1 IgG inhibited, compared to control IgG, microsomal H2O2-formation by 45% in microsomes from acetone-treated rats and by 22% in control microsomes. NADPH-dependent generation of TBA-reactive products was completely inhibited by these antibodies, whereas preimmune IgG was essentially without effect. Liposomes containing reductase and P-450IIE1 were peroxidized in a superoxide dismutase (SOD) sensitive reaction at a 5-10-fold higher rate than membranes containing 3 other forms of cytochrome P-450. Lipid peroxidation in reconstituted vesicles dependent on the presence of P-450IIB1 was by contrast not inhibited by SOD. Microsomal peroxidase activities, using 15-(S)-hydroperoxy-5-cis-8,11,13-trans-eicosatetraenoic acid as a substrate were high in microsomes from phenobarbital- or ethanol-treated rats but low in membranes from isoniazid-treated rats, having the highest relative level of P-450IIE1. It is suggested that the oxidase activity of P-450IIE1 contributes to microsomal NADPH-dependent lipid peroxidation. The combined action of the oxidase activity by P-450IIE1 and the peroxidase activities by P-450IIB1 and other forms of P-450 may be important for the high rate of lipid peroxidation observed in e.g. microsomes from ethanol- or acetone-treated rats. The possible importance of cytochrome P-450IIE1-dependent lipid peroxidation in vivo after ethanol abuse is discussed.     

Effect of hydrogen peroxide on the initiation of microsomal lipid peroxidation

Hydrogen peroxide reacts with reduced transition metals to generate the highly reactive hydroxyl radical (·OH), most often proposed as the predominant species for initiating microsomal lipid peroxidation. To assess the potential involvement of ·OH, generated from hydrogen peroxide, in microsomal lipid peroxidation, we have altered the concentration of microsomal hydrogen peroxide and measured the resulting rates of malondialdehyde production. Hydrogen peroxide concentration in microsomes was changed by adding exogenous catalase, by washing to reduce both endogenous catalase activity and hydrogen peroxide-dependent glutathione oxidase activity, and by inhibiting endogenous catalase activity with azide in either the presence or absence of exogenous hydrogen peroxide. In only one instance was the rate of lipid peroxidation affected; exogenous hydrogen peroxide added to microsomes, previously incubated with azide, inhibited lipid peroxidation, the opposite effect from that predicted if ·OH, generated from hydrogen peroxide, is actually the major initiating species. Neither these results, nor the inability of known ·OH traps to inhibit microsomal lipid peroxidation, support the role of free hydrogen peroxide in the initiation of microsomal lipid peroxidation.     

Modulation of antioxidant defence system by dietary fat in rats intoxicated with o-toluidine

o-Toluidine was administered to rats in the diet for four weeks at levels approximately 40, 80 and 160 mg/kg b.w. per day. Two types of diet have been used, standard (4% fat) and high fat (14% fat). Activity of antioxidant enzymes, level of glutathione and thiobarbituric acid reactive substances were measured in liver. Glutathione peroxidase was significantly increased in all treated groups while glutathione S-transferase and glutathione reductase were elevated in rats fed high-fat diet. o-Toluidine slightly enhanced catalase activity regardless of the kind of diet. Superoxide dismutase was the only enzyme whose activity was lowered in almost all treated groups. Enzymatic and nonenzymatic microsomal lipid peroxidation was enhanced 2- to 3-fold in both diet groups. Reduced glutathione level in liver was 2.3- to 4.0-fold increased in all treated groups. Our findings indicate that free radical processes can be involved in the toxic effects of o-toluidine and dietary fat can modify the response of some antioxidant enzymes to this compound.     

Attenuation of benzoyl peroxide-mediated cutaneous oxidative stress and hyperproliferative response by the prophylactic treatment of mice with spearmint (Mentha spicata).

The modulating effect of spearmint (Mentha spicata) on benzoyl peroxide-induced responses of tumor promotion in murine skin was investigated. Benzoyl peroxide (BPO) is an effective cutaneous tumor promoter acting through the generation of oxidative stress, induction of ornithine decarboxylase activity and by enhancing DNA synthesis. BPO treatment (20 mg/animal) increased cutaneous microsomal lipid peroxidation and hydrogen peroxide generation. The activity of cutaneous antioxidant enzymes, namely catalase, glutathione peroxidase, glutathione reductase and glutathione S-transferase, was decreased and the level of cutaneous glutathione was depleted. BPO treatment also induced the ornithine decarboxylase activity and enhanced the [3H]thymidine uptake in DNA synthesis in murine skin. Prophylactic treatment of mice with spearmint extract (10, 15 and 20 mg/kg) 1 hr before BPO treatment resulted in the diminution of BPO-mediated damage. The susceptibility of cutaneous microsomal membrane to lipid peroxidation and hydrogen peroxide generation was significantly reduced (P < 0.05 ). In addition, depleted levels of glutathione, inhibited activity of glutathione dependent and antioxidant enzymes were recovered to a significant level (P < 0.01, P < 0.05 and P < 0.01, respectively). Similarly, the elevated ornithine decarboxylase activity and enhanced thymidine uptake in DNA synthesis was inhibited significantly (P < 0.05 ) in a dose-dependent manner. The protective effect of spearmint was dose dependent in all parameters. The result suggests that spearmint is an effective chemopreventive agent that may suppress BPO-induced cutaneous oxidative stress, toxicity and hyperproliferative effects in the skin of mice.     

Lupeol, a triterpene, inhibits early responses of tumor promotion induced by benzoyl peroxide in murine skin.

The modulating effect of Lupeol [lup-20(29)-en-3 beta -ol], a triterpene found in many fruits and medicinal plants, on benzoyl peroxide-induced tumor promotion responses or tumor promotion in murine skin is described. Benzoyl peroxide is an effective cutaneous tumor promoter acting through the generation of oxidative stress, the induction of ornithine decarboxylase activity and the enhancement of DNA synthesis. Benzoyl peroxide treatment increases cutaneous microsomal lipid peroxidation and hydrogen peroxide generation. The activity of the cutaneous antioxidant enzymes, namely catalase, glutathione peroxidase, glutathione reductase and glutathione S-transferase, is decreased and levels of cutaneous glutathione are depleted. Benzoyl peroxide treatment also induces ornithine decarboxylase activity and enhances [3H]thymidine uptake in DNA synthesis. Prophylactic treatment of mice with lupeol (0.75 and 1.5 mg per animal) 1 hour before benzoyl peroxide treatment resulted in a diminution of benzoyl peroxide-mediated damage. The susceptibility of cutaneous microsomal membrane to lipid peroxidation and hydrogen peroxide generation was significantly reduced (P< 0.01 and P< 0.01, respectively). In addition, depleted levels of glutathione and inhibited activity of antioxidant enzymes were recovered to a significant level (P< 0.01, P< 0.05 and P< 0.01, respectively). Similarly, the elevated ornithine decarboxylase activity and enhanced thymidine uptake in DNA synthesis were inhibited significantly (P< 0.05) in a dose-dependent manner. The protective effect of lupeol was dose dependent in all parameters. The results suggest that lupeol is an effective skin chemopreventive agent that may suppress benzoyl peroxide-induced cutaneous toxicity.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-induced alterations in lipid peroxidation, enzymes, and divalent cations in rat testis

1. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) produces atrophy, morphological changes, impaired spermatogenesis, and epididymal lesions in testis of experimental animals. The effects of TCDD administration to male rats on various parameters in the testes were examined. 2. Nine days after TCDD administration, significant decreases in body and testes weights occurred. However, the testes weight as a percent of body weight was higher in treated than control animals. 3. An increase in lipid peroxidation (content of thiobarbituric acid reactive substances) occurred in conjunction with the decrease in testicular weights. 4. TCDD administration produced a 3-fold increase in protein kinase C activity, small but significant decrease is superoxide dismutase and glutathione peroxidase activities, and no effect on catalase, glutathione reductase or glutathione S-transferase activities in the testes. 5. Nine days after treatment with TCDD, in the testes the iron content of whole tissue and cytosol increased while a decrease in microsomal iron was observed. The copper content of mitochondria and microsomes decreased with a corresponding increase in cytosol copper content. A small increase in the zinc content of whole testes occurred. 6. The data indicate that testicular atrophy due to TCDD may be associated with lipid mobilization and peroxidation.     

Effects of BHA, d-alpha-tocopherol and retinol acetate on TCDD-mediated changes in lipid peroxidation, glutathione peroxidase activity and survival

Daily treatment of female rats with butylated hydroxyanisole (BHA) protected against 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxicity. This protective effect was associated with reduced microsomal lipid peroxidation, increased glutathione peroxidase (GSH-PX) activity and decreased aryl hydrocarbon hydroxylase (AHH) activity. Retinol acetate (vitamin A) inhibited lipid peroxidation, elevated GSH-PX activity, and enhanced AHH activity. Thirty per cent of vitamin A-treated animals were alive 25 d after a lethal dose of TCDD. d-alpha-Tocopherol (vitamin E) inhibited markedly microsomal lipid peroxidation, enhanced AHH activity, and had no effect on GSH-PX activity. Only 10% of the vitamin E-treated animals were alive 25 d after a lethal dose of TCDD. The mechanism of TCDD toxicity may involve in part inhibition of GSH-PX activity with resultant lipid peroxidation by hydrogen peroxide.     

The role of lipid peroxidation in the nephrotoxicity of cisplatin.

The possible role of lipid peroxidation in the nephrotoxicity of the antitumour drug cisplatin was studied in vitro. In contrast to Adriamycin, cisplatin did not induce lipid peroxidation in rat kidney microsomes containing a NADPH-generating system. Pretreatment of rat kidney microsomes with cisplatin did not reduce the activity of a microsomal glutathione (GSH)-dependent protective factor against lipid peroxidation induced by Fe(2+)-ascorbate. However, pretreatment of rat kidney microsomes with 0.1 mM N-ethyl maleimide (NEM) did reduce this GSH-dependent protection. Cisplatin also did not reduce the activity of a cytosolic GSH-dependent protective factor against Fe(2+)-ascorbate-induced lipid peroxidation. The results of our experiments indicate that, in contrast to Adriamycin, cisplatin does not induce lipid peroxidation in vitro in various test systems. It also does not destroy microsomal and cytosolic GSH-dependent protective factors against lipid peroxidation.     

Cisplatin-induced changes in cytochrome P-450, lipid peroxidation and drug-metabolizing enzyme activities in rat kidney cortex

This study investigates the effects of 3 successive cisplatin administrations on rat kidney cytochrome P-450 and drug-metabolizing enzyme activities. Furthermore, because glutathione (GSH) and its related enzymatic system are involved in cellular detoxification processes, we examined the effects of cisplatin on lipid peroxidation, GSH levels, and GSH reductase and peroxidase activities. Cisplatin induced a decrease in cytochrome P-450, GSH, GSH S-transferase, GSH reductase and GSH peroxidase activities, and an increase in N-glucuronyl transferase, lipid peroxidation and oxidized glutathione (GSSG) in kidney cortical microsomes and cytosolic fractions. It is suggested that cisplatin nephrotoxicity could be explained by its affinity for SH-groups of several enzymes and SH-containing compounds. Among these, GSH and its related enzymatic system play a primary role. Moreover, cisplatin increases lipid peroxidation, which might participate in cisplatin nephrotoxicity.     

Inhibitory effects of Maharishi-4 and Maharishi-5 on microsomal lipid peroxidation.

The effects of Maharishi-4 (M-4) and Maharishi-5 (M-5) on microsomal lipid peroxidation were examined in vitro. Rat liver microsomes were incubated with an NADPH-generating system or with sodium ascorbate and an ADP-iron complex to stimulate enzymatic or nonenzymatic lipid peroxidation respectively. Alcoholic or aqueous extracts of M-4 or M-5, when added to these incubation systems, inhibited hepatic microsomal lipid peroxidation in a concentration-dependent manner. The aqueous extract of M-4 was the most effective antiperoxidant in these systems. A 10% (w/v) aqueous extract of M-4 inhibited ascorbate or NADPH-induced lipid peroxidation by approximately 50% when added at volumes of 8 microliters and 3.5 microliters respectively to the incubation mixtures (total incubation volume, 2 ml). These findings suggest that M-4 and M-5, by virtue of their antiperoxidant properties, may be useful in the treatment of free radical-linked drug toxicities and disease states.     

Myrica nagi attenuates cumene hydroperoxide-induced cutaneous oxidative stress and toxicity in Swiss albino mice

In recent years, considerable efforts have been made to identify new chemopreventive agents which could be useful for man. Myrica nagi, a subtropical shrub, has been shown to possess significant activity against hepatotoxicity and other pharmacological and physiological disorders. We have shown a chemopreventive effect of Myrica nagi on cumene hydroperoxide-induced cutaneous oxidative stress and toxicity in mice. Cumene hydroperoxide treatment at a dose level of 30 mg/animal/0.2 ml acetone enhances susceptibility of cutaneous microsomal membrane for iron-ascorbate-induced lipid peroxidation and induction of xanthine oxidase activity which are accompanied by decrease in the activities of cutaneous antioxidant enzymes such as catalase, glutathione peroxidase, glutathione reductase, glucose-6-phosphate dehydrogenase and depletion in the level of cutaneous glutathione. Parallel to these changes a sharp decrease in the activities of phase II metabolizing enzymes such as glutathione S-transferase and quinone reductase has been observed. Application of Myrica nagi at doses of 2.0 mg and 4.0 mg/kg body weight in acetone prior to that of cumene hydroperoxide (30 mg/animal/0.2 ml acetone) treatment resulted in significant inhibition of cumene hydroperoxide-induced cutaneous oxidative stress and toxicity in a dose-dependent manner. Enhanced susceptibility of cutaneous microsomal membrane for lipid peroxidation induced by iron ascorbate and xanthine oxidase activities were significantly reduced (P<0.05). In addition the depleted level of glutathione, the inhibited activities of antioxidants, and phase II metabolizing enzymes were recovered to a significant level (P<0.05). The protective effect of Myrica nagi was dose-dependent. In summary our data suggest that Myrica nagi is an effective chemopreventive agent in skin and capable of ameliorating cumene hydroperoxide-induced cutaneous oxidative stress and toxicity.     

Effects of mansonones on lipid peroxidation, P450 monooxygenase activity, and superoxide anion generation by rat liver microsomes

Several structurally related ortho-naphthoquinones isolated from Mansonia altissima Chev (mansonones C, E and F) (a) inhibited NADPH-dependent, iron-catalyzed microsomal lipid peroxidation; (b) prevented NADPH-dependent cytochrome P450 destruction; (c) inhibited NADPH-supported aniline 4-hydroxylase activity; (d) inhibited Fe(III)ADP reduction by NADPH-supplemented microsomes; (e) stimulated superoxide anion generation by NADPH-supplemented microsomes; and (f) stimulated ascorbate oxidation. ESR investigation of ascorbate-reduced mansonone F demonstrated semiquinone formation. Mansonone C had a greater effect than mansonones E and F on NADPH-dependent lipid peroxidation, O2- production and ascorbate oxidation, whereas mansonone E was more effective than mansonones C and F on aniline 4-hydroxylase activity. Mansonones E and F did not inhibit hydroperoxide-dependent lipid peroxidation, cytochrome P450 destruction or microsomal aniline 4-hydroxylase activity. Mansonone C inhibited to a limited degree tert-butyl hydroperoxide-dependent lipid peroxidation, this inhibition being increased by NADPH. Mansonone A, a tetrahydro orthonapthoquinone derivative, was in all respects relatively less effective than mansonones C, E and F. It is postulated that mansonones C, E and F inhibited microsomal lipid peroxidation and cytochrome P450 catalyzed reactions by diverting reducing equivalents from NADPH to dioxygen, but mansonone C (including its reduced form) may also exert direct antioxidant activity.     

Effects of BHA,d-α-tocopherol and retinol acetate on TCDD-mediated changes in lipid peroxidation,glutathione peroxidase activity and survival

1. Daily treatment of female rats with butylated hydroxyanisole (BHA) protected against 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxicity. This protective effect was associated with reduced microsomal lipid peroxidation, increased glutathione peroxidase (GSH-PX) activity and decreased aryl hydrocarbon hydroxylase (AHH) activity.

2. Retinol acetate (vitamin A) inhibited lipid peroxidation, elevated GSH-PX activity, and enhanced AHH activity. Thirty per cent of vitamin A-treated animals were alive 25 d after a lethal dose of TCDD.

3. d-α-Tocopherol (vitamin E) inhibited markedly microsomal lipid peroxidation, enhanced AHH activity, and had no effect on GSH-PX activity. Only 10% of the vitamin E-treated animals were alive 25 d after a lethal dose of TCDD.

4. The mechanism of TCDD toxicity may involve in part inhibition of GSH-PX activity with resultant lipid peroxidation by hydrogen peroxide.     

Chrysotile Inhibits Glutathione-Dependent Protection against the Onset of Lipid Peroxidation in Rat Lung Microsomes

Abstract: The glutathione and vitamin E-dependent protection of lipid peroxidation in an NADPH (0.4 mM) and chrysotile (500 μg/ml) containing system were investigated in vitro in rat lung microsomes. Addition of 1 mM glutathione to the above reaction system containing microsomes supplemented with vitamin E (1 nmol/mg protein) reduced lipid peroxidation. Similar protection by glutathione could be observed in normal unsupplemented microsomes though the degree of protection was less pronounced. Addition of free radical scavengers such as, superoxide dismutase (100 units/ml), catalase (150 units/ml), mannitol (1 mM) and β-carotene (0.5 mM) to the reaction system showed an insignificant effect on lipid peroxidation. When the reaction was carried out in absence of glutathione, vitamin E content of peroxidizing microsomes decreased rapidly. In this system a concomitant increase in the activity of microsomal glutathione-S-transferase was observed which may serve as an alternative pathway to detoxify lipid peroxides. Addition of glutathione alone to the reaction system prevented both against the loss in vitamin E content and increase in the activity of glutathione-S-transferase. Supplementation of both vitamin E and glutathione was found to be effective in lowering glutathione-S-transferase activity to that of normal basal level. Our results suggest that chrysotile-mediated stimulation of NADPH-dependent lipid peroxidation may be due to hampering of glutathione-dependent protection which may ultimately exhaust membrane bound vitamin E. Our data further suggest that the lung tissue may have an inbuilt mechanism whereby glutathione-S-transferase may be triggered to cope with the excessive production of lipid peroxides.     

Effect of chitosan oligosaccharide on 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced oxidative stress in mice

The abilities of two types of chitosan oligosaccharides, chitosan oligosaccharide I (1-kDa相似文献