Protection by estrogens of biological damage by 2,2'-azobis(2-amidinopropane) dihydrochloride

We examined by using 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) as a radical generator the ability of estrogens to scavenge carbon-centered and peroxyl radicals. Electron spin resonance signals of carbon-centered radicals from AAPH were diminished by catecholestrogens but not by phenolic estrogens, showing that catecholestrogens efficiently scavenged carbon-centered radicals. However, fluorescent decomposition of R-phycoerythrin by AAPH-derived peroxyl radicals was inhibited by catecholestrogens and phenolic estrogens. Evidently, peroxyl radicals were scavenged by catecholestrogens and by phenolic estrogens. However, the scavenging ability of 4-hydroxyestradiol was less than 2-hydroxyestradiol. Strand break of DNA induced by AAPH was inhibited by catecholestrogens, but not by phenolic estrogens under aerobic and anaerobic conditions. Inactivation of lysozyme induced by AAPH was completely blocked by 2-hydroxyestradiol under aerobic and anaerobic conditions, and by 4-hyroxyestradiol only under anaerobic conditions. Peroxidation of arachidonic acid by AAPH was strongly inhibited by catecholestrogens at low concentrations. Only large amounts of phenolic estrogens markedly inhibited lipid peroxidation. These results show that catecholestrogens were antioxidant against AAPH-induced damage to biological molecules through scavenging both carbon-centered and peroxyl radicals, but phenolic estrogens partially inhibited AAPH-induced damage because they scavenged only peroxyl radicals.     

Antioxidant activities of estrogens against aqueous and lipophilic radicals; differences between phenol and catechol estrogens

Natural estrogens have much greater radical-scavenging antioxidant activity than has previously been demonstrated, with activities up to 2.5 times those of vitamin C and vitamin E. The biological significance of this finding remains to be elucidated. In this work the antioxidant activity of a range of estrogens (phenolic, catecholic and stilbene-derived) has been studied. The activity of these substances as hydrogen-donating scavengers of free radicals in an aqueous solution has been determined by monitoring their relative abilities to quench the chromogenic radical cation 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS*+). The results show that the order of reactivity in scavenging this radical in the aqueous phase is dependent on the precise estrogenic structure, with phenolic estrogens being more potent antioxidants than catecholestrogens or diethylstilbestrol. The ability of the same estrogens to scavenge lipid phase radicals has also been assessed, determined by the ex vivo enhancement of the resistance of low-density lipoprotein (LDL) to oxidation; the order of efficacy is different from that in the aqueous phase, with the phenolic estrogens estriol, estrone and 17beta-estradiol being less potent than 2-hydroxyestradiol, 4-hydroxyestradiol, or diethylstilbestrol. In this lipid-based system, phenolic estrogens were found to be unable to regenerate alpha-tocopherol from LDL subjected to oxidative stress, while at the same time 2- and 4-hydroxyestradiol significantly delayed alpha-tocopherol loss. These results indicate that the various estrogens are good scavengers of free radicals generated in both the aqueous and the lipophilic phases. The antioxidant activity of an estrogen depends not only on the hydrophilic or lipophilic nature of the scavenged radical, but also on the phenol and catechol structures of the estrogen compound.     

Inhibition of the metmyoglobin-induced peroxidation of linoleic acid by dietary antioxidants: Action in the aqueous vs. lipid phase

The gastric digestion of food containing oxidizable lipids and iron catalysts for peroxide decomposition such as (met)myoglobin from muscle meat can be accompanied by an extensive formation of potentially toxic lipid hydroperoxides. An early protective action by dietary antioxidants in the gastro-intestinal tract is plausible, especially for poorly bioavailable antioxidants such as polyphenols. Hence, the ability of antioxidants to inhibit lipid peroxidation initiated by dietary iron in mildly acidic emulsions is a valuable and general model. In this work, the ability of some ubiquitous dietary antioxidants representative of the main antioxidant classes (alpha-tocopherol, the flavonol quercetin, beta-carotene) to inhibit the metmyoglobin-induced peroxidation of linoleic acid is investigated by UV-visible spectroscopy and HPLC in mildly acidic emulsions. The phenolic antioxidants quercetin and alpha-tocopherol come up as the most efficient peroxidation inhibitors. Inhibition by quercetin essentially proceeds in the aqueous phase via a fast reduction of an unidentified activated iron species (with a partially degraded heme) produced by reaction of metmyoglobin with the lipid hydroperoxides. This reaction is faster by, at least, a factor 40 than the reduction of ferrylmyoglobin (independently prepared by reacting metmyoglobin with hydrogen peroxide) by quercetin. By contrast, alpha-tocopherol mainly acts in the lipid phase by reducing the propagating lipid peroxyl radicals. The poorer inhibition afforded by beta-carotene may be related to both its slower reaction with the lipid peroxyl radicals and its competitive degradation by autoxidation and/or photo-oxidation.     

Thiols can either enhance or suppress DNA damage induction by catecholestrogens

The estrogen metabolites catecholestrogens (or hydroxyestrogens) are involved in carcinogenesis and the development of resistance to methotrexate. This induction of drug resistance correlates with the relative efficiency of catecholestrogens in the generation of reactive oxygen species (ROS) and the induction of DNA strand breaks. Although antioxidants can neutralize ROS, the generation of these reactive species by catecholestrogens can be enhanced by electron donors like NADH. Therefore, this study was undertaken to determine the ability of different thiol agents (GSH, NAC, DTT, DHLA) to either inhibit or enhance the level of DNA damage induced by the H(2)O(2) generating system 4-hydroxyestradiol/Cu(II). Our results show that GSH, DTT, and DHLA inhibited the induction of the 4-hydroxyestradiol/Cu(II)-mediated DNA damage, with GSH showing the best potential. In contrast, the GSH precursor NAC at low concentrations was able to enhance the level of oxidative damage, as observed with NADH. NAC can reduce Cu(II) to Cu(I) producing the radical NAC&z.rad;, which can generate the superoxide anion. However, the importance of this pathway appears to be relatively minor since the addition of NAC to the 4-hydroxyestradiol/Cu(II) system generates about 15 times more DNA strand breaks than NAC and Cu(II) alone. We suggest that NAC can perpetuate the redox cycle between the quinone and the semiquinone forms of the catecholestrogens, thereby enhancing the production of ROS. In conclusion, this study demonstrates the crucial importance of the choice of antioxidant as potential therapy against the negative biological effects of estrogens.     

Identification of protein kinase C inhibitory activity associated with a polypeptide isolated from a phage display system with homology to PCM-1, the pericentriolar material-1 protein

L-arginine may aid in the liver detoxification and may benefit in the treatment of liver disorders such as liver injury. The present study was to investigate the possible protective and curative effects of L-arginine on carbon tetrachloride (CCl(4)) induced hepatotoxicity. Mice received a single dose of CCl(4). L-arginine treatment was given for 6 days prior or post to CCl(4) injection. CCl(4)-intoxication caused marked liver cell necrosis with inflammatory and apoptotic lesions. L-arginine treatment reduced hepatic necrosis and inflammation. CCl(4)-intoxication also enhanced hepatic lipid peroxidation, decreased hepatic GSH level and inhibited the activities of antioxidant enzymes. Pre-treatment and post-treatment with L-arginine decreased lipid peroxidation and restored the antioxidant status to near normal levels. These results suggest that L-arginine administration has hepatoprotective and hepatocurative effects against CCl(4) induced hepatotoxicity in mice.     

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.     

Metmyoglobin promotes arachidonic acid peroxidation at acid pH

The ability of metmyoglobin and other heme proteins to promote peroxidation of arachidonic acid under acidic conditions was investigated. Incubation of metmyoglobin with arachidonic acid resulted in a pH-dependent increase in lipid peroxidation as measured by the formation of thiobarbituric acid reactive products and oxygen consumption. Increased peroxidation was observed at pH levels below 6.0, reaching a plateau between pH 5.5 and 5.0. At comparable heme concentrations, metmyoglobin was more efficient than oxymyoglobin, methemoglobin, or ferricytochrome c in promoting arachidonic acid peroxidation. Metmyoglobin also promoted peroxidation of 1-palmityl-2-arachidonyl phosphatidylcholine and methylarachidonate but at significantly lower rates than arachidonic acid. Addition of fatty acid-free albumin inhibited arachidonic acid peroxidation in a molar ratio of 6 to 1 (arachidonic acid:albumin). Both ionic and non-ionic detergents inhibited metmyoglobin-dependent arachidonic acid peroxidation under acidic conditions. The anti-oxidants butylated hydroxytoluene and nordihydroguaiaretic acid and low molecular weight compounds with reduced sulfhydryl groups inhibited the reaction. However, mannitol, benzoic acid, and deferoxamine were without significant effect. Visible absorption spectra of metmyoglobin following reaction with arachidonic acid showed minimal changes consistent with a low level of degradation of the heme protein during the reaction. These observations support the hypothesis that metmyoglobin and other heme proteins can promote significant peroxidation of unsaturated fatty acids under conditions of mildly acidic pH such as may occur at sites of inflammation and during myocardial ischemia and reperfusion. This may be the result of enhanced aggregation of the fatty acid and/or interaction of the fatty acid with heme under acidic conditions.     

Thiol depletion induces lethal cell injury in cultured cardiomyocytes.

Treatment of cultured neonatal cardiomyocytes with ethacrynic acid (EA) induced a rapid depletion of glutathione (GSH) that preceded a gradual elevation of cytosolic Ca2+ (monitored by phosphorylase a activation), a loss of protein thiols, and a marked inactivation of the thiol-dependent enzyme glyceraldehyde-3-phosphate dehydrogenase (G3PD). A subsequent decline of mitochondrial transmembrane potential (delta psi) and ATP occurred prior to the onset of lipid peroxidation which closely paralleled a loss of cardiomyocyte viability. The antioxidant N,N'-diphenyl-p-phenylenediamine prevented lipid peroxidation and cell death but had no effect on elevated cytosolic Ca2+, delta psi loss, GSH depletion, or G3PD inactivation. Pretreatment with the iron chelator, deferoxamine, decreased both lipid peroxidation and cell death. EA-induced lipid peroxidation and cell damage were also diminished by preincubation with acetoxymethyl esters of the Ca2+ chelators Quin-2 and ethylene glycol bis(beta-aminoethyl ether) N,N'-tetraacetic acid, even though cytosolic Ca2+ remained elevated. The extent of GSH depletion was unaltered by either chelator; however, Quin-2 did protect G3PD from inactivation by EA. An inhibitor of the mitochondrial respiratory chain, antimycin A, decreased EA-induced lipid peroxidation and cell death but had no effect on thiol depletion or elevated cytosolic Ca2+. These data suggest that cardiomyocyte thiol status may be linked to intracellular Ca2+ homeostasis and that peroxidative damage originating in the mitochondria is a major event in the onset of cell death in this cardiomyocyte model of thiol depletion.     

Arachidonic acid converts the glutathione depletion-induced apoptosis to necrosis by promoting lipid peroxidation and reducing caspase-3 activity in rat glioma cells

Intracellular glutathione (GSH) depletion induced by buthionine sulfoximine (BSO) caused cell death that seemed to be apoptosis in C6 rat glioma cells. Arachidonic acid (AA) promoted BSO-induced cell death by accumulating reactive oxygen species (ROS) or hydroperoxides. AA inhibited caspase-3 activation and internucleosomal DNA fragmentation during the BSO-induced GSH depletion. Furthermore, AA reduced intracellular ATP content, induced dysfunction of mitochondrial membrane and enhanced 8-hydroxy-2'-deoxyguanosine (8-OH-dG) production. There was significant increase of 12-lipoxygenase activity in the presence of AA under the BSO-induced GSH depletion in C6 cells. These results suggest that AA promotes cell death by changing to necrosis from apoptosis through lipid peroxidation initiated by lipid hydroperoxides produced by 12-lipoxygenase under the GSH depletion in C6 cells. Some ROS such as hydroperoxide produced by unknown pathway make hydroxy radicals and induce 8-OH-dG formation in the cells. The conversion of apoptosis to necrosis may be a possible event under GSH depleted conditions.     

Lipid Peroxidation and Antioxidant Systems in Rat Brain: Effect of Chronic Alcohol Consumption

The effect of chronic ethanol exposure, in a liquid diet, on lipid peroxidation and some antioxidant systems of rat brain was investigated. Chronic ethanol administration induced a greater susceptibility to iron/ascorbate-induced lipid peroxidation, estimated as thiobarbituric reactive substances (TBARS) production, in the microsomal fraction, but a lower lipid peroxidation in the total homogenate. Glutathione (GSH) levels as well as GSH peroxidase and GSH reductase were unaffected, while the activity of Cu-Zn superoxide dismutase was decreased and that of catalase increased. Lipid peroxidation experiments performed in the presence of some hydroxyl radical scavengers suggested that a greater OH^· generation may be responsible of the greater TBARS production in the microsomal fraction of ethanol treated rats; differently, in total homogenate of control and ethanol rats a relationship was found between the redox state of iron and TBARS production, suggesting that the lower lipid peroxidation in treated rats may depend on a different modulation of the iron redox state.     

Bilirubin is highly effective in preventing in vivo delta-aminolevulinic acid-induced oxidative cell damage

Delta-aminolevulinic acid (ALA), precursor of heme, accumulates in a number of organs, particularly in liver of patients with acute porphyrias or lead intoxication. This study characterizes the involvement of bilirubin as an antioxidant in a chronic intoxication with ALA. Female Wistar rats were injected intraperitoneally a daily dose of 40 mg ALA/body wt., during 10 days. A marked increase in lipid peroxidation and a decrease in GSH content were observed 24 h after the last injection of ALA. The activities of liver antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase were also diminished. ALA synthase (ALA-S) and heme oxygenase-1 were induced. Both ALA dehydratase (ALA-D) and porphobilinogenase (PBG-ase) activities were inhibited. Administration of bilirubin (5 mmol/kg body wt.) 2 h before ALA treatment entirely prevented the effects of ALA. Co-administration of ALA and Sn-protoporphyrin IX (Sn-PPIX; 100 microg/body wt., i.p.), a potent inhibitor of heme oxygenase, completely abolished its induction and provoked a marked decrease in liver GSH levels as well as an increase in lipid peroxidation. These results add further support to the proposal assigning bilirubin a key protective role against oxidative damage here induced by ALA.     

Mitochondrial electron transport inhibitors cause lipid peroxidation-dependent and -independent cell death: protective role of antioxidants

Mitochondrial electron transport inhibitors induced two distinct pathways for acute cell death: lipid peroxidation-dependent and -independent in isolated rat hepatocytes. The toxic effects of mitochondrial complex I and II inhibitors, rotenone (ROT) and thenoyltrifluoroacetone (TTFA), respectively, were dependent on oxidative stress and lipid peroxidation, while cell death induced by inhibitors of complexes III and IV, antimycin A (AA) and cyanide (CN), respectively, was caused by MMP collapse and loss of cellular ATP. Accordingly, cellular and mitochondrial antioxidant depletion or supplementation, in general, resulted in a dramatic potentiation or prevention, respectively, of toxic injury induced by complex I and II inhibitors, with little or no effect on complex III and IV inhibitor-induced toxicity. ROT-induced oxidative stress was prevented by the addition of d-alpha-tocopheryl succinate (TS) but surprisingly TS did not afford hepatocytes protection against TTFA-induced oxidative damage. TS treatment prevented ROT-induced mitochondrial lipid hydroperoxide formation but had no effect on the loss of mitochondrial GSH or cellular ATP, suggesting a mitochondrial lipid peroxidation-mediated mechanism for ROT-induced acute cell death. In contrast, only fructose treatment provided excellent cytoprotection against AA- and CN-induced toxicity. Our findings indicate that complex III and IV inhibitors cause a rapid and severe depletion of cellular ATP content resulting in acute cell death that is dependent on cellular energy impairment but not lipid peroxidation. In contrast, inhibitors of mitochondrial complex I or II moderately deplete cellular ATP levels and thus cause acute cell death via a lipid peroxidation pathway.     

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.     

Evaluation of the antioxidant properties of thyroid hormones and propylthiouracil in the brain-homogenate autoxidation system and in the free radical-mediated oxidation of erythrocyte membranes

The antioxidant capacity of thyroid hormones and the antithyroid drug propylthiouracil was studied in three model systems, namely, autoxidation of rat brain homogenates and oxidation of rat erythrocyte plasma membranes (EPM) induced by either 2,2'-azobis-(2-amidinopropane) (AAP) thermolysis or by gamma irradiation. Thyroid hormones significantly inhibited the development of lipid peroxidation in these systems at micromolar concentrations, as assessed either by visible light emission, thiobarbituric acid reactive substances accumulation or oxygen uptake. This behaviour was not observed when L-3,3',5-triiodothyronine (T3) and L-thyroxine (T4) were assayed at nanomolar concentrations. In EPM exposed to AAP or gamma irradiation, propylthiouracil inhibited the induced lipid peroxidation, with Q1/2 values of 112-150 microM. It is concluded that the antioxidant capacity of thyroid hormones found in vitro may not be of relevance in physiological conditions, which exhibit variations of T3 and T4 levels in the nanomolar range. On the other hand, the behaviour of propylthiouracil as an inhibitor of EPM lipid peroxidation is observed at concentrations close to the therapeutic levels, thus representing a possible complementary action to its antithyroid activity.     

Concentration dependent antioxidant/pro-oxidant activity of curcumin studies from AAPH induced hemolysis of RBCs

The antioxidant properties of curcumin have been studied by evaluating its ability to protect RBCs from AAPH (2,2'-azobis (2-amidinopropane) hydrochloride) induced oxidative damage. RBCs are susceptible to oxidative damage, resulting in peroxidation of the membrane lipids, release of hemoglobin (hemolysis), release of intracellular K(+) ions and depletion of glutathione (GSH). In this paper, lipid peroxidation, hemolysis and K(+) ion loss in RBCs were assessed respectively by formation of thiobarbituric acid reactive substances (TBARS), absorbance of hemoglobin at 532nm and flame photometry. The treatment of RBCs with curcumin showed concentration dependant decrease in level of TBARS and hemolysis. The IC(50) values for inhibition of lipid peroxidation and hemolysis were estimated to be 23.2+/-2.5 and 43+/-5microM respectively. However in contrast to the above mentioned effects, curcumin in similar concentration range, did not prevent release of intracellular K(+) ions during the process of hemolysis, rather curcumin induced its release even in the absence of hemolysis. The ability of curcumin to prevent oxidation of intracellular GSH due to hemolysis showed mixed results. At low concentrations of curcumin (<10microM) it prevented GSH depletion and at higher concentrations, the GSH levels decreased gradually. Curcumin scavenges the peroxyl radical generated from AAPH. Based on these results, it is concluded that curcumin exhibits both antioxidant/pro-oxidant activity, in a concentration dependent manner.     

Estrogen prevents oxidative damage to the mitochondria in Friedreich's ataxia skin fibroblasts

Estrogen and estrogen-related compounds have been shown to have very potent cytoprotective properties in a wide range of disease models, including an in vitro model of Friedreich's ataxia (FRDA). This study describes a potential estrogen receptor (ER)-independent mechanism by which estrogens act to protect human FRDA skin fibroblasts from a BSO-induced oxidative insult resulting from inhibition of de novo glutathione (GSH) synthesis. We demonstrate that phenolic estrogens, independent of any known ER, are able to prevent lipid peroxidation and mitochondrial membrane potential (ΔΨm) collapse, maintain ATP at near control levels, increase oxidative phosphorylation and maintain activity of aconitase. Estrogens did not, however, prevent BSO from depleting GSH or induce an increased expression level of GSH. The cytoprotective effects of estrogen appear to be due to a direct overall reduction in oxidative damage to the mitochondria, enabling the FRDA fibroblast mitochondria to generate sufficient ATP for energy requirements and better survive oxidative stress. These data support the hypothesis that phenol ring containing estrogens are possible candidate drugs for the delay and/or prevention of FRDA symptoms.     

Lipid peroxidation induced by phenylbutazone radicals

Lipid peroxidation was investigated to evaluate the deleterious effect on tissues by phenylbutazone (PB). PB induced lipid peroxidation of microsomes in the presence of horseradish peroxidase and hydrogen peroxide (HRP-H2O2). The lipid peroxidation was completely inhibited by catalase but not by superoxide dismutase. Mannitol and dimethylsulfoxide had no effect. These results indicated no paticipation of superoxide and hydroxyl radical in the lipid peroxidation. Reduced glutathione (GSH) efficiently inhibited the lipid peroxidation. PB radicals emitted electron spin resonance (ESR) signals during the reaction of PB with HRP-H2O2. Microsomes and arachidonic acid strongly diminished the ESR signals, indicating that PB radicals directly react with unsaturated lipids of microsomes to cause thiobarbituric acid reactive substances. GSH sharply diminished the ESR signals of PB radicals, suggesting that GSH scavenges PB radicals to inhibit lipid peroxidation. Also, 2-methyl-2-nitrosopropan strongly inhibited lipid peroxidation. R-Phycoerythrin, a peroxyl radical detector substance, was decomposed by PB with HRP-H2O2. These results suggest that lipid peroxidation of microsomes is induced by PB radicals or peroxyl radicals, or both.     

Ferrylmyoglobin impairs secretion of VLDL triacylglycerols from stored intracellular pools: involvement of lipid peroxidation

Ferrylmyoglobin (ferrylMb) may play a major role in vivo under certain pathological conditions. Preliminary experiments showed that ferrylmyoglobin induced a mild oxidative stress in rat hepatocytes, mainly reflected by early lipid peroxidation. One of the major functions of hepatocytes is the synthesis, secretion and distribution of lipids to other cells. The aim of this work was to examine whether ferrylMb affected the synthesis and secretion of triacylglycerols (TAG), and the possible involvement of lipid peroxidation on these effects. The heme protein completely impaired VLDL secretion, affecting both the lipid and apoB components of the lipoprotein particle. The incorporation of [(3)H]-oleate into newly synthesized diacylglycerol and TAG was not altered by ferrylMb. The co-treatment of cells with alpha-tocopherol prevented lipid peroxidation and concomitantly reverted VLDL TAG secretion to control values. Importantly, although ferrylMb dramatically blocked prelabeled TAG secretion, newly synthesized TAG secretion was not impaired. These data indicate that lipid peroxidation elicited by ferrylMb modulates the VLDL TAG secretion process, specifically affecting the stored intracellular TAG mobilization, rather than de novo synthesis. Apart from its potential role in vivo, ferrylmyoglobin constitutes a useful model for studying the interactions between lipid peroxidation and the specific TAG pool dependence for VLDL secretion.     

Polyunsaturated fatty acids promote 8-hydroxy-2-deoxyguanosine formation through lipid peroxidation under the glutamate-induced GSH depletion in rat glioma cells

It has been reported that glutamate decreased the intracellular glutathione (GSH) concentration and thereby induced cell death in C6 rat glioma cells. Polyunsaturated fatty acids such as arachidonic acid, gamma-linolenic acid, and linoleic acid enhanced lipid peroxidation promoting 8-hydroxy-2'-deoxyguanosine (8-OH-dG) formation under the glutamate-induced GSH-depletion. The enhancement of lipid peroxidation by polyunsaturated fatty acids was species-dependent. Some antioxidants capable of scavenging oxygen and lipid radicals and some iron or copper scavengers inhibited both the lipid peroxidation and the 8-OH-dG formation, consequently protecting against cell death induced by glutamate-induced GSH depletion. These results suggest that GSH depletion caused by glutamate induces lipid peroxidation and consequently 8-OH-dG formation and that polyunsaturated fatty acids enhance lipid peroxidation associated with mediated 8-OH-dG formation through a chain reaction.     

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.