Lipid Peroxidation In Rat Liver Research Articles

Effect of acute and chronic administration of sodium valproate on lipid peroxidation and antioxidant system in rat liver.

Changes in glutathione and lipid peroxide levels as well as in the activities of superoxide dismutase, glutathione peroxidase, catalase and glutathione-S-transferase have been studied in rats after acute and chronic sodium valproate treatments. Glutathione levels were decreased only after acute sodium valproate treatment. Neither acute nor chronic treatment influenced lipid peroxidation but induced glutathione-S-transferase activity significantly. On the other hand, no alterations in glutathione peroxidase and superoxide dismutase activities were found, except slight induction of catalase activity after acute administration of sodium valproate. These results indicate that sodium valproate treatment did not induce oxidative stress in the liver.

Role of xanthine oxidase in delayed lipid peroxidation in rat liver induced by acute exhausting exercise.

The aim of this study was to examine whether xanthine oxidase (XOD)-derived hepatic oxidative damage occurs in the main not during but following strenuous exercise. The degree of damage to hepatic tissue catalyzed by XOD was investigated immediately and 3 h after a single bout of exhausting exercise, in allopurinol and saline injected female Wistar rats. Allopurinol treatment resulted in increased hypoxanthine and decreased uric acid contents in the liver compared with the saline treated group, immediately and 3 h after the exercise. Analysis immediately after the exercise showed no changes in hepatic hypoxanthine, uric acid, and thiobarbituric acid-reactive substance (TBARS) contents in the saline treated group, when compared with the resting controls. However, significant increases in uric acid contents in the saline treated livers were observed 3 h after the exercise, relative to the controls. Hepatic TBARS content in the saline treated group were markedly greater than those in both the control and allopurinol treated groups after 3 h of recovery following the exercise. It was concluded that a single bout of exhausting exercise may impose XOD-derived hepatic oxidative damage, primarily during the recovery phase after acute severe exercise.

Inhibition by the bioflavonoid ternatin of aflatoxin B1-induced lipid peroxidation in rat liver.

Aflatoxin B1, a metabolite of Aspergillus flavus is a potent hepatotoxic and hepatocarcinogenic mycotoxin. Lipid peroxidation and oxidative DNA damage are the principal manifestations of aflatoxin B1-induced toxicity which could be mitigated by antioxidants. Many plant constituents, e.g. flavonoids, lignans and spice principles (capsaicin, curcumin, eugenol, etc.) have been reported to prevent liver damage associated with lipid peroxidation. In this study we investigated ternatin, a tetramethoxyflavone isolated from Egletes viscosa, for possible protection against liver injury induced by aflatoxin B1 in rats. Seventy two hours after a single intraperitoneal dose of aflatoxin B1 (1 mg kg(-1)), the concentration of malondialdehyde, the product of lipid peroxidation in liver homogenates, and serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were significantly elevated (P<0.001). Subcutaneous ternatin (25 mg kg(-1)) pretreatment greatly reduced aflatoxin B1-induced increases in the levels of serum enzymes (ALT from 5071+/-763 to 293+/-66 international units L(-1) and AST from 4241+/-471 to 449+/-108 international units L(-1)) and elevated malondialdehyde levels (from 11.37+/-1.27 to 0.79+/-0.22 nmol (mg wet tissue)(-1)) in a manner similar to oral vitamin E (300 mg kg(-1)), a standard antioxidant. Further, histological changes induced by aflatoxin B1 such as hepatocellular necrosis and bile-duct proliferation were markedly inhibited in animals pretreated with ternatin or vitamin E. These data provide evidence that ternatin inhibits lipid peroxidation and affords protection against liver damage induced by aflatoxin B1. Ternatin might, therefore, be a suitable candidate for the chemoprevention of aflatoxicosis associated liver cancer.

Metallothionein induction in rat liver by dietary restriction or exercise and reduction of exercise-induced hepatic lipid peroxidation.

Metallothioneins (MTs) occur throughout the animal kingdom and they are induced in vivo by metals, hormones, cytotoxic agents, and some kind of stress. It is well known that various stresses such as starvation and immobilization can induce MT synthesis in animal tissues, but the influence of dietary restriction is unknown. The MT levels in the liver increased by food-deprivation and then decreased by refeeding, and a long period of starvation down-alters hepatic MT levels. When the stress is intensified, the induced quantity of hepatic MT is reduced. It became clear that hepatic MT concentrations are controlled within a two fold limit when stressed by dietary restriction. MT was also induced in rat liver at recovery stage following an exhaustive running exercise, and thionein was synthesized first and then zinc bound to the protein. The half-life of hepatic MT induced by exercise (which is a nonmetallic inducer) was estimated at 5.2 h. Preinduced MT markedly suppressed exercise-induced lipid peroxidation in rat liver.

Relevance of Heat-Shock Protein 70 Expression as Histological Marker of Paraquat-Induced Damage to Rat Liver Cells.

Heat-shock protein 70 (HSP70) is expressed in response to various stressful stimuli, and generally used as a histological marker of cell damage. While paraquat has previously been shown to cause HSP70 expression as a result of the oxidative cell damage, recent study has shown that HSP70 expression induced by paraquat poisoning is no longer observed at 18hr after the drug administration in the senescence-accelerated mouse liver, thereby raising the question whether the cell damage is always accompanied by elevated HSP70 expression. To affirm the relevance of HSP70 expression as a marker of the cell damage, the expression of HSP70 immunoreactivity and lipid peroxidation in paraquatpoisoned rat liver were examined. The immunostaining of HSP70 was still clearly detected at 24hr after the drug administration. Lipid peroxidation, a biochemical maker of the oxidative cell damage, was also elevated by the same treatment, suggesting that the expression of HSP70 immunoreactivity observed here may reflect the oxidative-damage to liver cells. These results seem to provide evidence supporting the relevance of HSP70 expression as a histological marker of paraquat-induceddamage to rat liver cells.

Sesamolin Inhibits Lipid Peroxidation in Rat Liver and Kidney

Although the sesame lignans, sesaminol and sesamolinol, have been shown to possess antioxidative activity, less is known about the metabolism and antioxidative properties of sesamolin, a major constituent of sesame oil. To determine the ability of sesamolin to act as an antioxidant in vivo, we fed rats a diet containing 1% sesamolin for 2 wk and studied its metabolism and its effects on oxidative stress. About 75% of the ingested sesamolin was excreted unmetabolized in feces, but it was not detected in urine. Sesamolin and its metabolites, sesamol and sesamolinol, were excreted primarily as sulfates and glucuronides. The amount of sesamolin and its metabolites was lower in the plasma than in the liver or kidneys. When we compared rats fed a diet containing 1% sesamolin for 14 d with those fed a control diet, we found that liver weight was significantly greater in the former group. Lipid peroxidation activity, measured as 2-thiobarbituric acid reactive substances, was significantly lower in the kidneys and liver of the sesamolin-fed rats than in the controls. In addition, the amount of 8-hydroxy-2′-deoxyguanosine excreted in the urine was significantly lower in the sesamolin-fed rats. These results suggest that sesamolin and its metabolites may contribute to the antioxidative properties of sesame seeds and oil and support our hypothesis that sesame lignans reduce susceptibility to oxidative stress.

Delta-aminolevulinic acid-induced lipid peroxidation in rat kidney and liver is attenuated by melatonin: an in vitro and in vivo study.

Acute intermittent porphyria (AIP) is a genetically inherited disease characterized by a partial block in liver heme biosynthesis and by increased urinary excretion of the delta-aminolevulinic acid (ALA). Recently, it has been proposed that the toxic effects of ALA are related to the generation of free radicals. In the present study the in vitro and in vivo effect of melatonin, a recently described antioxidative agent, on ALA-induced lipid peroxidation in rat liver and kidney was determined. The concentration of malonaldehyde (MDA) and 4-hydroxyalkenals (4-HDA) was assayed as an index of induced membrane oxidative damage. In vitro melatonin protected, in a concentration-dependent manner, against ALA-induced lipid peroxidation in liver and kidney homogenates. In in vivo experiments as well, it was demonstrated that ALA (40 mg/kg)-induced lipid peroxidation in liver and kidney was reduced by acute melatonin (10 mg/kg) treatment. The results support the involvement of free radicals in ALA toxicity and show that in vitro and in vivo melatonin confers protection against this toxicity, likely due to the antioxidative capability of the indole.

Cancer chemopreventive and therapeutic activities of red ginseng

Red ginseng extract A and B are the active components of Panax ginseng. Red ginseng is a classical traditional Chinese medicine. Among Chinese herbs, red ginseng has been considered as one of the tonics. Many studies indicated that red ginseng could enhance immune function of the human body. The effects of red ginseng extracts on transplantable tumors, proliferation of lymphocyte, two-stage model and rat liver lipid peroxidation were studied. In a two-stage model, red ginseng extracts had a significant cancer chemoprevention. At 50–400 mg/kg, they could inhibit DMBA/Croton oil-induced skin papilloma in mice, decrease the incidence of papilloma, prolong the latent period of tumor occurrence and reduce tumor number per mouse in a dose-dependent manner. Red ginseng extract B could effectively inhibit the Fe 2+/cysteine-induced lipid peroxidation of rat liver microsome, suggesting that red ginseng extract B has a stronger antioxidative effect than that of extract A. The results indicated that red ginseng extracts (50≈400 mg/kg) could significantly inhibit the growth of transplantable mouse sarcoma S180 and melanoma B16. Red ginseng extracts A (0.5 mg/ml) and B (0.1 and 0.25 mg/ml) might effectively promote the transformation of T lymphocyte, but there was no influence on lymphocyte proliferation stimulated by concanavalin A. This suggests that red ginseng extracts have potent tumor therapeutic activity and improve the cell immune system.

The Effect of High Dietary Iron and Low Vitamin E on Lipid Peroxidation and Prostaglandin E 2 in a Model of Colon Cancer

LEARNING OUTCOME: To assess the effects of high iron and low vitamin E status on lipid peroxidation and prostaglandin E 2 synthesis in a model of colon cancer In recent years there has been heightened concern that high iron (Fe) status may increase risk of cancer at several sites, including liver and colon. It has been theorized that Fe enhances carcinogenesis by catalyzing free radical production and lipid peroxidation (LPX). Animals with low vitamin E (VE) status may be more susceptible to Fe-enhanced LPX. Also, studies suggest that prostaglandins, which may be altered by Fe and VE status, play a role in colon cancer. The present study examined the effect of Fe and VE status on LPX and prostaglandin E 2 (PGE 2) synthesis in an animal model of colon cancer. In a 2×2×2 factorial design, male Sprague Dawley rats were fed 2 levels of Fe (adequate- 45 mg/kg; high- 450 mg/kg diet), and 2 levels of VE (low- 15 IU/kg; adequate- 100 IU/kg diet) for 3 weeks, and then were treated with saline or the carcinogen azoxymethane (AOM; 30 mg/kg; 2 week protocol). The study continued for an additional 6 weeks. Liver and colonic mucosa were collected for analysis at 3 and 10 weeks. Liver Fe, a key indicator of Fe status, was increased 162% and 71% at 3 and 10 weeks, respectively, in rats fed high Fe diets (p=0.0001). LPX of liver was significantly enhanced by high Fe diets after 3 (p<0.02) and 10 (p<0.03) weeks of treatment. Further, there was a trend toward higher liver LPX in rats fed high Fe, low VE diets (p<0.15) compared to other groups. In colonic mucosa, while lipid peroxidation was increased by AOM (p<0.03), and PGE 2 synthesis was decreased by AOM (p<0.02), neither Fe nor VE status had any effect on these indices. Thus our study suggests that dietary Fe levels 10 times higher than recommended do not alter colon LPX or PGE 2 synthesis in a model of colon carcinogenesis even when VE intake is low. Supported by GA AES #H-757.

Effect of Ca2+ channel blockers, external Ca2+ and phospholipase A2 inhibitors on t-butylhydroperoxide-induced lipid peroxidation and toxicity in rat liver slices.

ObjectivesThis study was undertaken to examine the effect of oxidant on lipid peroxidation and lethal cell injury in rat liver slices.Methodst-Butylhydroperoxide (t-BHP) was employed as a model of an oxidant. The lipid peroxidation and lethal cell injury were estimated by measuring the formation of malondialdehyde (MDA) and lactate dehydrogenase (LDH) release, respectively.Resultst-BHP increased lipid peroxidation and LDH release in a dose-dependent manner over concentrations of 0.5–10mM. t-BHP-induced lipid peroxidation was completely prevented by an antioxidant, N,N-diphenyl-p-phenylenediamine (DPPD), but LDH release was partially decreased. Both t-BHP-induced lipid peroxidation and LDH release were significantly protected by iron chelator, deferoxamine, sulfhydryl reducing agent, dithiothreitol and glutathione. Ca2+ channel blockers, verapamil, diltiazem and nifedipine exerted a significant protective effect against t-BHP-induced lipid peroxidation and LDH release. By contrast, addition of external Ca2+ chelator, ethylene glycol bis(b-aminoethyl ether)-N,N-tetraacetic acid (EGTA) did not alter t-BHP-induced lipid peroxidation, whereas t-BHP-induced lethal cell injury was significantly prevented. Phospholipase A2 (PLA2) inhibitors, mepacrine and butacaine produced a partial protective effect.ConclusionsThese results suggest that t-BHP induces cell injury by lipid peroxidation-dependent and -independent mechanisms which can be partially prevented by Ca2+ channel blockers and PLA2 inhibitors.

Glutathione-Dependent Factors And Inhibition Of Rat Liver Microsomal Lipid Peroxidation

The effects of reduced glutathione (GSH) and glutathione disulfide (GSSG) on lipid peroxidation were investigated in rat liver microsomes containing deficient or adequate amounts of α-tocopherol ( α-TH). Rates of formation of thiobarbituric acid reactive substances (TBARS) as well as rates of consumption of α-TH and O 2 were decreased by GSH and were more pronounced in the NADPH-dependent assay system than in the ascorbate-dependent system. The GSH-dependent inhibition of lipid peroxidation was potentiated by GSSG in the NADPH-dependent assay system, but it had no effect in the nonenzymatic system. Diphenyliodonium chloride, an inhibitor of NADPH cytochrome P-450 reductase, completely prevented lipid peroxidation in the NADPH-dependent assay system whereas it had no effect on the ascorbate-dependent system. This is further evidenced by the fact that purified rat liver microsomal NADPH cytochrome P-450 reductase (EC 1.6.2.4) was inhibited approximately 24% and 52% by 5 mM GSH and 5 mM GSH + 2.5 mM GSSG, respectively. Glutathione disulfide alone had no effect on reductase activity. Similarly, other disulfides such as cystine, cystamine and lipoic acid were without effect on reductase activity. These results clearly delineate different mechanisms underlying the combined effects of GSH and GSSG on microsomal lipid peroxidation in rat liver. One mechanism involves recycling of microsomal α-TH by GSH during oxidative stress via a labile protein, ostensibly associated with “free radical reductase” activity. A second glutathione-dependent mechanism appears to be mediated through the inhibition of NADPH cytochrome P-450 reductase. The enhanced inhibition by GSH + GSSG of microsomal lipid peroxidation in the NADPH-dependent assay system suggests suppression of the initiation phase at the level of NADPH cytochrome P-450 reductase which is independent of microsomal α-TH.

Increase of lipid peroxidation in rat liver microsomes by dehydroepiandrosterone feeding

Oral administration of the adrenal steroid dehydroepiandrosterone (DHEA), a peroxisome proliferator and hepatocarcinogen in the rat, caused an increase in NADPH-dependent lipid peroxidation in microsomes isolated from rat liver and kidney cortex, but not from brain. The increase of liver microsomal lipid peroxidation was greater in male than in female rats. The effect of DHEA on lipid peroxidation became discernible after feeding steroid-containing diet (0.6%) to male and female rats for 2 and 3 days and reached maximal levels at 1 and 2 weeks, respectively. The increase of microsomal lipid peroxidation reached a plateau stimulation at 0.05% in the diet. The addition of DHEA in the concentration range 0.1–100 μM to microsomes isolated from control rats had no effect on lipid peroxidation. Furthermore, a significant increase of the endogenous concentration of thiobarbituric acid reactive substances was found in microsomes after DHEA-administration at 0.05% in the diet. These results provide in vivo evidence that DHEA can cause lipid peroxidation in rat liver. Administration of DHEA at 0.6% in the diet for 7 consecutive days also significantly enhanced NADH- and ascorbate-dependent lipid peroxidation in liver microsomes. The DHEA-stimulated rat liver microsomal lipid peroxidation was completely inhibited by EDTA but not by superoxide dismutase, catalase or mannitol applied as OH-radical scavenger. The findings indicate that membrane lipid peroxidation is an early effect of DHEA, and that this process may be involved in the steroid-induced carcinogenesis in rats.

Effect of Strychnos nux vomica alcohol extract on lipid peroxidation in rat liver

This report investigates the antioxidant properties of the purified Strychnos nux vomica L. seed extract for protection against non-enzymatic formation of lipid peroxides and on reduced glutathione (GSH) levels in rat liver homogenate. Results were compared with the natural antioxidant vitamin E. For the first time it could be reported that this drug protects against cumene hydroperoxide (CHP) induced lipid peroxidation in a dose dependent manner. It also inhibits the process of the lipid peroxidation, once induced. The drug significantly maintains the hepatic content of glutathione in a dose and time dependent manner, even in the presence of the above toxin (CHP). Thus it appears that S. nux vomica is a potent antioxidant and the mechanism of action could be through the scavenging of free radicals.

Effects of ethanol administration on cerebral non-protein sulfhydryl content in rats exposed to styrene vapour

Glutathione (GSH) and other non-protein sulfhydryls (NPS) are known to protect cells from oxidative stress and from potentially toxic electrophiles formed by biotransformation of xenobiotics. This study examined the effect of a simultaneous administration of styrene and ethanol on NPS content and lipid peroxidation in rat liver and brain. Hepatic cytochrome P450 and cytochrome b 5 content, aniline hydroxylase and aminopyrine N-demethylase activities as well as the two major urinary metabolites of styrene, mandelic and phenylglyoxylic acids were also measured. Groups of rats given ethanol for 3 weeks in a liquid diet were exposed, starting from the second week, to 326 ppm of styrene (6 h daily, 5 days a week, for 2 weeks). In control pair-fed animals, styrene produced about 30% depletion of brain NPS and 50% depletion of hepatic NPS. Subchronic ethanol treatment did not affect hepatic NPS levels, but caused 23% depletion of brain NPS. Concomitant administration of ethanol and styrene caused a NPS depletion in brain tissue in the order of 60%. These results suggest that in the rat, simultaneous exposure to ethanol and styrene may lead to considerable depletion of brain NPS. This effect is seen when both compounds are given on a subchronic basis, a situation which better resembles possible human exposure.

PHGPx and phospholipase A 2/GPx: Comparative importance on the reduction of hydroperoxides in rat liver mitochondria

The comparative importance of phospholipid hydroperoxide glutathione peroxidase (PHGPx) and of “classic” glutathione peroxidase (GPx) in the reduction of phospholipid hydroperoxides is unclear. Although GPx activity is 500-fold higher than that of PHGPx in rat liver 1, the reduction of phospholipid hydroperoxides by glutathione (GSH) through GPx may be strongly limited by a low PLA2 activity. We address this issue using a moderately detailed kinetic model of mitochondrial lipid peroxidation in rat liver. The model was based on published data and was subjected to validation as reported in the references. 2 It is analysed by computer simulation and sensitivity analysis. Results suggest that in rat liver mitochondria PHGPx is responsible for almost all phospholipid hydroperoxide reduction. Under physiological conditions, the estimated flux of phospholipid hydroperoxides reduction through PHGPx is about four orders of magnitude higher than the estimated hydrolysis flux through PLA2. On the other hand, virtually all hydrogen peroxide is reduced through GPx. Therefore, a functional complementarity between PHGPx and GPx is suggested. Because the results are qualitatively robust to changes of several orders of magnitude in PLA2 and PHGPx levels, the conclusions may not be limited to mitochondria.

The effects of glutathione on protein thiols and α-tocopherol in rat liver microsomes following storage and during NADPH-dependent lipid peroxidation

Liver microsomes from rats fed a diet supplemented with vitamin E (+E) were stored at 2°C in Tris buffers containing 5.0 mM reduced glutathione (GSH), GSH + 2.5 mM glutathione disulfide (GSSG) or no additions for up to 4 days. Thoroughly washed microsomes were then subjected to NADPH-dependent lipid peroxidation assays containing glutathione in combinations of its reduced and oxidized forms. These experiments demonstrated the presence of at least two glutathione-dependent factors in the inhibition of microsomal lipid peroxidation in rat liver. The first was quite labile and required GSH for its expression. The second factor was comparatively stable and showed a marked potentiation of GSH by GSSG. Changes in membrane protein thiols (PrSH) and α-tocopherol (α-TH) were also determined during storage of the microsomes in the various buffers and during assays of lipid peroxidation. Total membrane PrSH was higher in native (freshly prepared) liver microsomes from +E rats than in microsomes from rats fed a diet deficient in vitamin E (−E). The addition of GSH or GSH + GSSG diminished the extent of PrSH depletion during storage in both +E and −E microsomes, but the protective effect was greater for the +E microsomes. The loss of α-TH was also reduced in microsomes stored in buffers containing either GSH or GSH + GSSG compared to Tris buffer alone. Changes in PrSH during lipid peroxidation were pronounced in the absence of GSH or GSH + GSSG and were independent of the α-TH content of the membranes. Addition of either GSH or GSH + GSSG to the assays markedly reduced the depletion of PrSH during lipid peroxidation. For +E microsomes, the depletion of PrSH and α-TH in the presence or absence of GSH were parallel. The rate and extent of this depletion, however, were much greater in the absence of GSH. These data demonstrated that membrane α-TH was not essential in maintaining PrSH in the absence of GSH once lipid peroxidation was initiated. It also appeared that the potentiating effect of GSH by GSSG on the inhibition of rat liver microsomal lipid peroxidation, which was also resistant to inactivation during storage, was not through selective maintenance of α-TH or general sparing of PrSH.

Effect of tea (Camellia sinensis L.) on lipid peroxidation in rat liver and kidney: a comparison of green and black tea feeding.

The antioxidant effects in the liver and kidney obtained from rat fed diets containing 3% green or black tea leaf powder, which were prepared from the same lot tea leaves, were studied using the tissue slice-antioxidant evaluation method with two lipid peroxidation inducers. After 50 d on the diets, liver slices prepared from green and black tea-supplemented rats showed significant inhibitory effects against tert-butyl hydroperoxide-induced lipid peroxidation. These effects, however, were not proportional to the amounts of (-)-epicatechins and antioxidant vitamins in the tea leaves. In the kidney, the antioxidant effect was observed only in the green tea-fed group. A similar antioxidant effect on the kidney was observed after oral administration of a major tea polyphenol, (-)-epigallocatechin gallate (50 mg/kg body weight for 7 d). Liver slices from black tea-fed rats also inhibited bromotrichloromethane-induced lipid peroxidation. These results demonstrated that dietary green and black tea had antioxidant effects on tissue lipid peroxidation ex vivo.

Inhibition of microsomal chemiluminescence by cytosolic fractions containing fatty acid binding protein.

Studies were carried out to determine the relationship between Fe(++)-ascorbate initiated chemiluminescence and lipid peroxidation in rat liver, lung, kidney and brain microsomes. In order to follow the time course of membrane lipid peroxidation, we measured simultaneously physical and biochemical changes. Thus we determined the fatty acid composition of microsomal membranes from those tissues after peroxidation with and without ascorbic acid. Fractionation of cytosolic proteins with ammonium sulfate 70% saturation yielded a soluble fraction (enriched in fatty acid binding protein) that inhibited ascorbate-Fe++ dependent lipid peroxidation. The inhibitory effect was concentration dependent and was not abolished by heating of the soluble fraction during 5 min at 100 degrees C. Preparations from kidney, lung, heart and brain showed similar effect on lipid peroxidation of liver microsomal membranes. It is especulated that retinyl esters bound to fatty acid binding protein may act as antioxidants against lipid peroxidation.

Molecular analysis of anthracycline toxicity in human heart

In order to elucidate the effect on mammal systems of new derivatives from 2-hydroxy-3-allyl-naphthoquinone, α-iodinated naphthofuranquinone (NPPN-3223), β-iodinated naphthofuranquinone (NPPN-3222) and β-methyl naphthofuranquinone (NPPN-3226) synthesized as possible trypanocidal agents, their effect on rat liver microsomal lipid peroxidation was investigated. They (a) inhibited NADPH-dependent, iron-catalyzed microsomal rat liver lipid peroxidation; (b) did not inhibit the tert-butyl hydroperoxide-dependent lipid peroxidation; (c) did not inhibit ascorbate–lipid peroxidation with the exception of NPPN-3226 which did inhibit it; (d) stimulated NADPH oxidation and microsomal oxygen uptake; (e) increased superoxide anion formation by NADPH-supplemented microsomes and (f) stimulated ascorbate oxidation. The three drugs were reduced to their seminaphthofuranquinone radical by the liver NADPH–P450 reductase system, as detected by ESR measurements. These results support the hypothesis that naphthofuranquinones reduction by microsomal NADPH–P450 reductase and semiquinone oxidation by molecular oxygen diverts electrons, preventing microsomal lipid peroxidation. In addition, hydroquinones and/or semiquinones formed by naphthofuranquinones reduction would be capable of lipid peroxidation inhibition and on interacting with the lipid peroxide radicals can lead to an antioxidant effect as we suggested for NPPN-3226 in close agreement to the inhibition of ascorbate–lipid peroxidation. Due to the properties of these molecules and their incoming structure developments, naphthofuranquinones would be considered as potentially promising therapeutic agents, mainly against Chagas disease.

Influence of the xanthine derivative denbufylline and the anti-inflammatory agent nabumetone on microsomal free radical production and lipid peroxidation in rat liver

The influence of denbufylline, nabumetone and its main metabolite BRL 10,720 on iron stimulated lipid peroxidation (LPO), cytochrome P 450 dependent H2O2 and chemiluminescence (CL) production was investigated in rat liver microsomes in vitro (10(-5)-10(-3) M) and in vivo after treatment of rats (5-300 mg/kg b.m. orally on three consecutive days). In rat liver slices the release of thiobarbituric acid reactants (TBAR) was measured after 1 hour of incubation with the drugs. Denbufylline, nabumetone and BRL 10,720 exerted a significant inhibition of iron stimulated LPO in vitro. Nabumetone showed the strongest antioxidative activity, which was also seen in liver slices. These antioxidative effects were not found after in vivo treatment of rats. Denbufylline (10(-3) M) additionally inhibited H2O2 formation and the luminol and lucigenin amplified CL in vitro. Unexpectedly, nabumetone increased H2O2 formation both in vitro and in vivo, but in vitro only lucigenin amplified CL. BRL 10,720 increased microsomal H2O2 production in vivo. Moreover, BRL 10,720 enhanced CL in vitro and in vivo significantly, which is interpreted as an increase of the production of superoxide anion radicals and other reactive oxygen species such as H2O2, but lipid peroxidation in liver microsomes was not enhanced. These results suggest that denbufylline, nabumetone and BRL 10,720 in contrast to the in vitro effects did not exert antioxidative activities after treatment of rats. On the contrary, BRL 10,720 was found to support the formation of reactive oxygen species in liver microsomes.