Peroxidation of lipids in tissue homogenates as related to vitamin E

Model systems for studying lipid oxidation associated with muscle foods: Methods, challenges, and prospects

Lipid oxidation is a complex process in muscle-based foods (red meat, poultry and fish) causing severe quality deterioration, e.g., off-odors, discoloration, texture defects and nutritional loss. The complexity of muscle tissue -both composition and structure- poses as a formidable challenge in directly clarifying the mechanisms of lipid oxidation in muscle-based foods. Therefore, different in vitro model systems simulating different aspects of muscle have been used to study the pathways of lipid oxidation. In this review, we discuss the principle, preparation, implementation as well as advantages and disadvantages of seven commonly-studied model systems that mimic either compositional or structural aspects of actual meat: emulsions, fatty acid micelles, liposomes, microsomes, erythrocytes, washed muscle mince, and muscle homogenates. Furthermore, we evaluate the prospects of stem cells, tissue cultures and three-dimensional printing for future model system development. Based on this reviewing of oxidation models, tailoring correct model to different study aims could be facilitated, and readers are becoming acquainted with advantages and shortcomings. In addition, insight into recent technology developments, e.g., stem cell- and tissue-cultures as well as three-dimensional printing could provide new opportunities to overcome the current bottlenecks of lipid oxidation studies in muscle.

Analysis of Glutathione-Dependent Enzyme Activities in two Different Rat Hepatomas and in Normal Liver in Relation to their Role in Resistance to Oxidative Stress

The importance of some glutathione metabolic pathways was examined in two highly dedifferentiated hepatomas, Yoshida AH-130 and Morris 3924 A hepatomas, and in normal liver in relation to their role against oxidative stress. The cytosol prepared from Yoshida hepatoma cells decreased the peroxidation rate in normal liver microsomes and mitochondria, but this antioxidant property was not displayed by Morris hepatoma. Glutathione peroxidase and glutathione-S-transferases activities were extremely low in both hepatomas; glutathione reductase activity values were about half the normal liver values. The large decrease in glutathione peroxidase and glutathione-S-transferases suggests that in these two tumors only small amounts of GSH can be used in reduction or conjugation reactions, such as the reduction of hydrogen peroxide and lipid hydroperoxides or the conjugation of GSH with the end products of lipoperoxidation, aldehydes or ketones. The hypothesis of a more efficient GSSG reduction in hepatomas, due to the low glutathione peroxidase/glutathione reductase activity ratio, is also discussed. The described changes in glutathione related enzymes do not seem to have any correlation with the protective effect against the lipoperoxidative processes displayed by some tumors since these enzymatic activities were similar in both hepatomas whereas only Yoshida hepatoma showed antioxidant properties.

Analytic Reviews : Oxygen Toxicity

Oxygen therapy is administered to patients to decrease tissue hypoxia and to relieve arterial hypoxemia. High concentrations of oxygen often are used for short pe riods of time in patients with acute respiratory illnesses, and concentrations only slightly higher than ambient levels are administered for much longer time periods to patients with chronic respiratory diseases. Supplying oxygen to plants, animals, or bacteria has long been known to produce varying amounts of tissue damage; toxicity increases as concentrations of oxygen or the pressure used during exposure increases. End-organ damage from hyperoxia depends on both the concentra tion of oxygen administered and the pressure during the exposure. Prolonged exposure to hyperbaric oxygen (> 2.5 atmosphere of pressure) causes both central nervous system and pulmonary toxicity that results in atelectasis, pulmonary edema, and seizures. Lung dam age as a result of normobaric hyperoxia is the predomi nant manifestation of toxicity. A severe retinopathy (re trolental fibroplasia) also can occur in neonates during oxygen exposures at ambient pressure, and cases have been reported to occur with only modest increases in inspired oxygen concentrations. For these reasons, the lowest possible concentration of oxygen that relieves tissue hypoxia is administered to patients, and the oxy gen concentration is stabilized when the desired thera peutic goals are accomplished.

Lipid peroxidation in rat tissue homogenates: Interaction of iron and ascorbic acid as the normal catalytic mechanism

Iron and ascorbic acid appear to be the normal catalytic components responsible for the lipid peroxidation reaction in aerobically incubated rat tissue homogenates. The amounts of each present in the catalytically-active fractions of rat liver, brain, testis, and kidney are appropriate to explain the lipid peroxidation reaction measured. Utilization of ascorbic acid as part of the normal catalytic mechanism is indicated by the following: The catalytic activity of the tissue soluble phase occurs only in the small molecule fraction eluted from Sephadex, and ascorbic acid occurs only in this fraction; the extent of catalysis by the small molecule fractions of the soluble phases from several tissues is proportional to their ascorbic acid content; and pH effect on lipid peroxidation is the same for both soluble-phase and ascorbic acid catalysis. Utilization of iron as part of the normal catalytic mechanism is indicated by EDTA inhibition studies and by measurements of pH effects. Previous studies have demonstrated the lack of catalytic activity by cations other than iron for the lipid peroxidation reaction in homogenates. Lipid peroxidation is inhibited at high tissue concentration and the inhibition is due to components occurring in the large molecule fraction of the soluble phase.

Ethanol-induced oxidative stress: basic knowledge

After a general introduction, the main pathways of ethanol metabolism (alcohol dehydrogenase, catalase, coupling of catalase with NADPH oxidase and microsomal ethanol-oxidizing system) are shortly reviewed. The cytochrome P(450) isoform (CYP2E1) specifically involved in ethanol oxidation is discussed. The acetaldehyde metabolism and the shift of the NAD/NADH ratio in the cellular environment (reductive stress) are stressed. The toxic effects of acetaldehyde are mentioned. The ethanol-induced oxidative stress: the increased MDA formation by incubated liver preparations, the absorption of conjugated dienes in mitochondrial and microsomal lipids and the decrease in the most unsaturated fatty acids in liver cell membranes are discussed. The formation of carbon-centered (1-hydroxyethyl) and oxygen-centered (hydroxyl) radicals during the metabolism of ethanol is considered: the generation of hydroxyethyl radicals, which occurs likely during the process of univalent reduction of dioxygen, is highlighted and is carried out by ferric cytochrome P(450) oxy-complex (P(450)-Fe(3+)O(2) (.-)) formed during the reduction of heme-oxygen. The ethanol-induced lipid peroxidation has been evaluated, and it has been shown that plasma F(2)-isoprostanes are increased in ethanol toxicity.

Effects of tocotrienol-rich fraction on exercise endurance capacity and oxidative stress in forced swimming rats

The present study aimed to examine the effects of tocotrienol-rich fraction (TRF) on exercise endurance and oxidative stress in forced swimming rats. Rats fed on isocaloric diet were orally given 25 (TRF-25) and 50 (TRF-50) mg/kg of TRF, or 25 mg/kg D-alpha-tocopherol (T-25) whilst the control group received only the vehicle for 28 days, followed by being forced to undergo swimming endurance tests, with measurements taken of various biochemical parameters, including blood glucose, lactate and urea nitrogen, glycogen, total antioxidant capacity, antioxidant enzymes, thiobarbituric acid-reactive substances (TBARS), and protein carbonyl. Results showed that the TRF-treated animals (268.0 +/- 24.1 min for TRF-25 and 332.5 +/- 24.3 min for TRF-50) swam significantly longer than the control (135.5 +/- 32.9 min) and T-25-treated (154.1 +/- 36.4 min) animals, whereas there was no difference in the performance between the T-25 and control groups. The TRF-treated rats also showed significantly higher concentrations of liver glycogen, superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx), as well as of muscle glycogen and SOD than the control and the T-25-treated animals, but lower levels in blood lactate, plasma and liver TBARS, and liver and muscle protein carbonyl. Taken together, these results suggest that TRF is able to improve the physiological condition and reduce the exercise-induced oxidative stress in forced swimming rats.

Cadmium-induced enteropathy in domestic cocks: a biochemical and histological study after subchronic exposure

The biochemical and histological sequelae resulting from a diet containing 50.20 mg cadmium/kg were studied in Lohmann brown cockerels from hatching until 30 days of age. The additional cadmium chloride (CdCl(2)) to the diet induced the formation of lipid peroxides, which via a chain reaction led to accumulation of malondialdehyde in intestinal mucosa. At the end of the study (after 30 days of cadmium exposure) total protein and metallothionein levels in the intestinal mucosa and the relative ileal and duodenal weight increased. Histological data show that CdCl(2) causes an increase in number of goblet cells and granular lymphocytes in the intestinal mucosa. Down-regulation of the serotonin-positive cells in the cadmium-treated animals was observed. Growth retardation (by 27%) occurred in chicken fed the cadmium-enriched diet for 30 days. Cadmium accumulation in the intestine was markedly higher (154 times) in the cadmium-treated animals compared to the control group. Cadmium induced a decrease in zinc (but not copper) content in intestinal mucosa. We suggest that cadmium uptake triggers an inflammatory and secretory response in chicken small intestine.

Roxithromycin inhibits constitutive activation of nuclear factor {kappa}B by diminishing oxidative stress in a rat model of hepatocellular carcinoma

PURPOSE

Recently, 14-member macrolide antibiotics such as clarithromycin and roxithromycin have been shown to have anticancer and antiangiogenic effects. We investigated the suppressive effect of roxithromycin on accelerated hepatocellular carcinoma growth in a rat hepatocarcinogenetic model and compared results with effects from TNP-470.

EXPERIMENTAL DESIGN

Tumor was induced by oral diethylnitrosamine administration for 17 weeks. Normal saline, TNP-470 (50 mg/kg), or roxithromycin (40 or 100 mg/kg) was administered i.p. thrice per week from week 10 to 17.

RESULTS

Carcinomatous tissue growing outside dysplastic nodules and a marked expression of placental glutathione S-transferase were detected in rats with induced carcinogenesis. Tumor growth was accompanied by augmented expression of inducible nitric oxide synthase, activation of nuclear factor kappaB, and increased lipid peroxidation level. All these effects were absent in animals that received roxithromycin or TNP-470. The inhibitory effect of roxithromycin was dose dependent and no clear differences were noted between groups given roxithromycin 100 mg/kg and TNP-470 50 mg/kg.

CONCLUSIONS

Our results indicate that roxithromycin inhibits oxidative stress, nitric oxide production, and nuclear factor kappaB activation induced by experimental hepatocarcinogenesis. The data provide additional evidence for the potential use of roxithromycin in treatment of hepatocellular carcinoma prevention.

Effects of hyperbaric oxygen exposure on experimental hepatic ischemia reperfusion injury: relationship between its timing and neutrophil sequestration

Recent studies have shown that hyperbaric oxygen therapy (HBOT) reduces neutrophil endothelial adherence in venules and also blocks the progressive arteriolar vasoconstriction associated with ischemia-reperfusion (I-R) injury in the extremities and the brain. In order to elucidate the effects of HBOT after I-R in digestive organs, particularly in the liver, we evaluated the following: 1) the relationship between timing of HBOT and tissue damage; and 2) HBOT's effects on neutrophil sequestration. Using a hepatic I-R (45 minute) model in male rats, survival rate, liver tissue damage, and neutrophil accumulation within the sinusoids in the HBOT-treated group (Group H) were compared to those in the nontreated group (Group C). For the HBOT-treated group, HBOT was administered as 100% oxygen, at 2.5 atm absolute, for 60 minutes. When HBOT was given 30 minute after I-R, the survival rate was much better in Group H than in Group C. HBOT performed within 3 hours of I-R markedly suppressed increases in the malondialdehyde level in tissues of the liver and lessened the congestion in the sinusoids. In addition, HBOT just after I-R caused decreased number of cells stained by the naphthol AS-D chloroacetate esterase infiltrating into the sinusoids. HBOT 3 hours after reperfusion, however, showed no clear effects upon neutrophil sequestration compared to Group C. These results indicate that HBOT performed within 3 hours of I-R alleviates hepatic dysfunction and improves the survival rate after I-R. Herein, we propose 1 possible mechanism for these beneficial effects: early HBOT given before neutrophil-mediated injury phase may suppress the accumulation of neutrophils after I-R. In conclusion, we believe that the present study should lead to an improved understanding of HBOT's potential role in hepatic surgery.

Influence of dietary vitamin E and C supplementation on vitamin E and C content and thiobarbituric acid reactive substances (TBARS) in different tissues of growing pigs

To investigate the influence and possible interactions of dietary vitamin E and C supplementation on vitamin content of both vitamins and oxidative stability of different pork tissues 40 Large White barrows from 25 kg to 106 kg were allocated to four different cereal based diets: Basal diet (B), dl-alpha-tocopherylacetate + 200 mg/kg (E), crystalline ascorbic acid + 300 mg/kg (C) or both vitamins (EC). At slaughtering samples of liver, spleen, heart, kidney, backfat outer layer, ham and M. tongissimus dorsi were obtained. Growth performance of the pigs and carcass characteristics were not influenced by feeding treatments. Dietary vitamin E supplementation had a significant effect on the vitamin E and alpha-tocopherol concentration in all investigated tissues. Backfat outer layer, liver, spleen, kidney and heart had higher vitamin E concentrations than ham and M. longissimus dorsi. Dietary vitamin C supplementation tended towards enhanced vitamin E levels except for ham samples. Therefore, some synergistic actions without dietary vitamin E supplementation between the two vitamins could be shown. The vitamin C concentration and TBARS were increased or at least equal in all tissues due to vitamin C supplementation. Dietary alpha-tocopherol supplementation resulted in lower TBARS in backfat outer layer (malondialdehyde 0.35 mg/kg in B vs. 0.28 mg/kg in E), but increased in heart and ham. When both vitamins were supplemented (EC) TBARS were lower in M. longissimus dorsi and backfat outer layer, equal in heart and higher in liver and ham compared to a single vitamin C supplementation. Rancimat induction time of backfat outer layer was 0.3 h higher in C compared to B and 0.17 h higher in EC than in E. Correlations between levels of both vitamins were positive for kidney (r = 0.169), M. longissimus dorsi (r = 0.499) and ham (r = 0.361) and negative for heart (r = -0.350). In liver and spleen no interaction could be found. In backfat outer layer vitamin E was positively correlated with rancimat induction time (r = 0.550) and negatively with TBARS (r = -0.202), but provided no evidence that dietary vitamin E supply led to better oxidative stability.

The effect of vitamin E treatment on oxidative stress generated in trained rats

The aim of this study was to investigate the effect of vitamin E treatment on increased oxidative stress in rats exposed to a swimming exercise protocol. In order to examine the effects of physical swimming training on the antioxidant defences of tissues and on their susceptibility to damage induced by exercise, the levels of glutathione (GSH) and thiobarbituric acid reacting substances (TBARS) levels, on indicator of lipid peroxidation in various tissues, have been determined. In this study, four groups of female rats were used while the rats were trained to swim for 30 minutes a day and five days a week which lasted eight weeks and vitamin E (vit. E) supplementation (30 mg/kg/day) has been carried out for five days a week. TBARS levels are significantly found lower in both trained and sedentary vit. E supplemented groups, since vit. E is the most important antioxidant in an earlier line of defence in lipid peroxidation. Also, in vit. E supplemented trained rats, the glutathione response is observed to be significantly higher, supporting with the TBARS levels and in accordance with the literature. But in the sedentary group without vit. E supplementation, the GSH levels of the liver and the heart tissues were significantly lower than both vit. E supplemented sedentary and trained groups. These results evaluate that vit. E confers protection to GSH levels in these tissues where the GSH levels were found significantly lower in the groups not supplemented with vit. E.

Further experiments on lipid peroxidation in transplanted and experimental hepatomas

The results of experiments on the subject of lipid peroxidation in hepatomas are described. It is now clear that lipid peroxidation is strongly decreased in most highly dedifferentiated hepatomas. It seems evident that the extent of the decline is strictly related to the degree of dedifferentiation. The model of diethylnitrosamine carcinogenesis, according to the method by Solt, Medline and Farber, has been now adopted to study the stages of carcinogenesis. It was shown that a net decline in lipid peroxidation occurs as early as at the stage of reversible nodules and progresses until the development of clear hepatomas. This change is practically simultaneous with a decline in the efficiency of the enzymes of the drug metabolizing system and in the content of cytochrome P450-Glutathione content and metabolism show also important changes. In fact, a dramatic increase in gamma-glutamyl-transpeptidase takes place very early during carcinogenesis, and is responsible for large decline in total glutathione during incubation of the homogenates. Glutathione peroxidase activity, on the contrary, is decreased, whereas glutathione reductase does not show significant changes. The supernatant of highly anaplastic tumors inhibits lipid peroxidation in normal liver homogenates, suggesting the presence of substances provided with antioxidant properties. These cannot be, however, related to a higher glutathione content. Supernatants from early nodules seem to be unable to block lipid peroxidation in normal liver homogenates. Preliminary experiments done to study the aldehyde pattern produced during lipid peroxidation, both in hepatomas and in nodules, confirm the presence of very poor lipid peroxidation and possibly of different peroxidation kinetics.

Rapid determination of alpha-tocopherol in muscle and adipose tissues of pork

A fast, sensitive and reproducible method for the analysis of alpha-tocopherol in pork tissues is presented. It combines saponification of the tissue and alpha-tocopherol extraction in a single vessel, followed by HPLC separation and fluorescence detection. Added alpha-tocopherol was recovered quantitatively. The reduction of lipid peroxides with potassium iodide before the saponification step did not alter the amounts of alpha-tocopherol detected. Membrane-bound alpha-tocopherol was not oxidized by lipid peroxides during the procedure. The coefficient of variation of alpha-tocopherol analysed using this method was +/- 4.2% for muscle and +/- 2.5% for adipose tissues.

Inhibition of microsomal lipid peroxidation by alpha-tocopherol and alpha-tocopherol acetate

1. The antioxidant effects of alpha-tocopherol and alpha-tocopherol acetate were assayed for the (a) oxygen uptake, (b) chemiluminescence and (c) malondialdehyde formation, of tert-butyl hydroperoxide-supplemented rat liver microsomes. 2. Oxygen uptake was inhibited 60% by both alpha-tocopherol and alpha-tocopherol acetate with the half-maximal effect at 5 nmol tocopherol/mg protein. Chemiluminescence and malondialdehyde formation were equally inhibited 35% by both tocopherols with half-maximal effects at 2 nmol tocopherol/mg protein. 3. The rate of O2 uptake by tocopherol-supplemented microsomes was dependent on O2 concentration. A 60% inhibition by 5 nmol tocopherol/mg protein at 0.2 mM O2 is decreased to 5% inhibition at 0.6 mM O2. 4. The inhibition of O2 uptake, chemiluminescence and malondialdehyde formation indicate that both alpha-tocopherol and alpha-tocopherol acetate have similar effects as free radical traps in the hydrophobic domain of biomembranes. The different inhibition observed at different O2 concentrations indicate competition between vitamin E and O2 by unoxygenated lipid radicals.

Influence of dietary alpha-tocopherol on tocopherol concentrations in chick tissues

1. The effect of feeding alpha-tocopherol (5 to 180 micrograms/g diet) for 24 days on the concentrations of alpha-tocopherol in various chicken tissues was investigated. 2. Tissue alpha-tocopherol concentrations responded to dietary intake in the order: heart congruent to lung greater than liver greater than thigh muscle greater than brain, and in all cases the relationship between the concentrations of dietary and tissue alpha-tocopherol was highly significant (0.997 less than or equal to r less than or equal to 1). 3. Plasma alpha-tocopherol concentration appears to be a good index (r greater than or equal to 0.910, P less than 0.001) of alpha-tocopherol status of lung, liver and heart.

The effects of postharvest treatment and chemical interactions on the bioavailability of ascorbic acid, thiamin, vitamin A, carotenoids, and minerals

All recent health recommendations include admonitions to reduce calories, maintain desirable weight, reduce fat, increase complex carbohydrates, and ensure an adequate intake of nutrients. Such recommendations require that we know not only nutrient composition of foods, but also potential losses and decreased bioavailability due to postharvest treatment and chemical interactions. This article discusses in some detail the reactions of concern that cause such changes and their potential alleviation with several key nutrients. The nutrients discussed were chosen as a result of the conclusions of the Joint Nutrition Monitoring Report of the Department of Health and Human Services and the U.S. Department of Agriculture. Obviously other choices could have been made, but the authors felt that the nutrients chosen--ascorbic acid, thiamin, vitamin A, carotenoids, calcium, and iron--were representative of a key profile of nutrients whose reactivity makes them vulnerable to losses in bioavailability, as well as being noted in the Joint Nutrition Monitoring Report.

Effects of hyperoxia and vitamin E on the fatty acid composition of rat lung microsomes and mitochondria

Peroxidation of lung membrane lipids in vitro produces very specific changes in lung membrane fatty acid content with some fatty acids being affected more than others. We performed a series of experiments to determine the changes occurring in fatty acid composition in lung microsomes and mitochondria during an in vivo hyperoxic exposure. Hyperoxia did produce specific changes in the relative content of fatty acids present in lung microsomes and mitochondria of both vitamin E-supplemented and vitamin E-deficient rats. Changes were noted to occur in saturated and polyunsaturated fatty acids. The total amount of lung lipids extractable in the microsomal fractions decreased after hyperoxia in both the vitamin E-supplemented and the vitamin E-deficient animals with no changes occurring in extraction of lung mitochondrial total lipids. Decreases in lung mitochondrial fatty acids caused by hyperoxia occurred in the same fatty acids in both the vitamin E-supplemented and the vitamin E-deficient animals with few polyunsaturated fatty acids (PUFA) being affected. Decreases in lung microsomal fatty acids occurring during hyperoxia were different in the vitamin E-supplemented animals from those in the vitamin E-deficient animals with many more PUFA decreasing in the vitamin E-deficient group. The greatest number of PUFA found to decrease after hyperoxia when comparing all the different groups occurred in the microsomal fraction of the vitamin E-deficient rats. These data suggest that vitamin E-deficient animals have increased peroxidation of lung microsomal PUFA or a decrease in production of lung microsomal PUFA in vivo during a hyperoxic exposure.

Decrease of the inhibition of lipid peroxidation by glutathione-dependent system in erythrocytes of non-insulin dependent diabetics

The inhibition of lipid peroxidation of erythrocyte membranes by glutathione-dependent protection was studied in patients with non-insulin dependent diabetes mellitus. Incubation of red cells from diabetics with 1.5 mM t-butyl hydroperoxide resulted in a lipid peroxidation increase greater than that of normal controls. Glutathione-dependent and glutathione-independent protection against oxidative damage was examined using an artificial system, in which erythrocyte ghosts were incubated with t-butyl peroxide and dialysed hemolysate in the presence or the absence of 2 mM glutathione. The glutathione-dependent protection of hemolysate from diabetics was approximately 70% of that from normal controls. The results suggest that decrease in glutathione-dependent protection against lipid peroxidation, along with decrease in glutathione levels, increases oxidative damage in erythrocyte membranes taken from diabetic patients.

Physiological antioxidants and antioxidative enzymes in vitamin E-deficient rats

The effects of feeding vitamin E-deficient diets to rats for one year were investigated to analyse the relationship of the vitamin with other antioxidants and some antioxidative enzymes. Long-term vitamin E deficiency lowered the levels of antioxidants like vitamin E, ascorbic acid and glutathione (GSH) in all tissues analysed and thus increasing the extent of tissue peroxidisability. Vitamin E deficiency had also influenced the activities of superoxide dismutase (SOD), catalase and glutathione peroxidase, the enzymes that are involved in detoxification mechanisms of products arising from free radical metabolism.

Effect of dietary vitamin E and selenium on susceptibility of brain regions to lipid peroxidation

The effect of dietary vitamin E and/or selenium (Se) supplementation (200 IU and/or 0.2 ppm, respectively) or deficiency for two months on lipid peroxidation in cerebrum, cerebellum, mid-brain, and brain stem of one-month-old male F344 rats was investigated. Dietary treatment had a minimal effect on weight gain of rats for the period tested. Plasma alpha-tocopherol (alpha-T) concentration and glutathione peroxidase (GSH-Px) activity were reflective of dietary treatments. Supplementation of diets with vitamin E and/or Se increased plasma alpha-T and/or GSH-Px activity, while diets devoid of these nutrients reduced them significantly. Increased GSH-Px activity in Se-supplemented rats was further enhanced by vitamin E supplementation. Differential concentrations of alpha-T among brain regions were affected by dietary vitamin E but not by Se. In vitro lipid peroxidation of brain homogenates was inhibited by dietary vitamin E supplementation and increased by deficiency. Addition of 0.25 mM ascorbic acid or 0.1 mM of Fe2+ to brain homogenates markedly increased in vitro lipid peroxidation. Ascorbic acid-induced lipid peroxidation was inversely correlated with dietary vitamin E and Se in cerebrum. In vitro Fe2+-addition induced the greatest stimulation of lipid peroxidation, with cerebellum and brain stem of vitamin E-deficient rats showing the highest response to Fe2+ challenge. These findings indicate that concentrations of alpha-T among the brain regions are different and can be altered by dietary vitamin E treatments, cerebellum and brain stem are more susceptible to in vitro challenge by peroxidative agents than other regions, and the degree of lipid peroxidation of brain regions is partially affected by dietary vitamin E but not by Se in the levels tested.

Regional differences in microsomal lipid peroxidation and antioxidant levels in the guinea pig adrenal cortex

Lipid peroxidation (LP) and antioxidant levels were studied in the chromatically distinct inner (zona reticularis) and outer (zona fasciculata + zona glomerulosa) zones of the guinea pig adrenal cortex. Ferrous ion (Fe2+) produced a concentration-dependent (10(-5) to 10(-3) M) stimulation of microsomal LP in both zones, but LP, as estimated by malonaldehyde production, was far greater in the inner zone. Although cytosolic ascorbic acid content was similar in the two zones, microsomal tocopherol levels were approx 4 times greater in the outer than inner zone. Subphysiological concentrations of ascorbic acid, like Fe2+, initiated LP to a greater extent in inner than outer zone microsomes; optimal stimulation of LP by ascorbic acid occurred at concentrations of 100-200 microM in both zones. Physiological concentrations of ascorbic acid (1-5 mM), by contrast, did not initiate LP and, in fact, markedly inhibited Fe2+-induced LP in both inner and outer zone microsomal preparations. Outer zone microsomes were more sensitive to the antioxidant effects of ascorbic acid than were inner zone preparations. Addition of alpha-tocopherol to inner zone microsomal suspensions inhibited Fe2+-induced LP. The results indicate that there are regional differences in adrenocortical LP which may be caused by differences in tocopherol content. alpha-Tocopherol may serve important antioxidant functions within the adrenal cortex, thereby contributing to the functional zonation of the gland.

Lipid peroxidation and mechanisms of toxicity

Aerobic organisms by definition require oxygen, and the importance of iron in aerobic respiration has long been recognized, but despite their beneficial roles, these elements can pose a real threat to the organism. During oxygen reduction, reactive species such as O2-. and H2O2 are formed readily. Iron can combine with these species, or with molecular oxygen itself, to generate free radicals which will attack the polyunsaturated fatty acids of membrane lipids. This oxidative deterioration of membrane lipids is known as lipid peroxidation. To protect itself against this form of attack, the organism possesses several types of defense mechanisms. Under normal conditions, these defenses appear to offer adequate protection for cell membranes, but the possibility exists that certain foreign compounds may interfere with or even overwhelm these defenses, and herein could lie a general mechanism of toxicity. This possible cause of toxicity is discussed in relation to other suggested causes.

Species differences in lipid peroxide levels in lung tissue and investigation of their determining factors

Marked species differences in thiobarbituric acid reactant value (TBA value) in normal lung tissue of five species of animals were found. The order of the values was mouse greater than hamster greater than rat greater than guinea pig greater than rabbit, and the value for mice was 3.6 times higher than that for rabbit. The vitamin E (VE) and nonprotein sulfhydryls (NPSH) contents in lungs varied widely among the five animal species. Species differences were also observed on polyunsaturated fatty acid composition in lung phospholipids. The peroxidizability index (PI), which shows the relative rate of peroxidation reaction, was calculated from the composition ratio and the reactivity of each polyunsaturated fatty acid, and the PI was found to be significantly correlated to the TBA value in lungs (r = 0.853, p less than 0.001). The PI value was normalized by the contents of VE and/or NPSH. Finally, the log-value of PI, normalized by the log values of the reciprocals of VE and NPSH, log(PI/VE X NPSH), showed the highest correlation coefficient (r = 0.907, p less than 0.001). Normalization by the activities of antioxidative protective enzymes in lungs did not show any significant correlation against TBA value. These results suggest that TBA value as an index of lipid peroxides in the lungs of animals may be regulated mainly by the contents of VE and NPSH, the composition ratio and the reactivity of each polyunsaturated fatty acid in lung phospholipid fraction.

Influence of dietary vitamin E and selenium on the ex-vivo synthesis of prostaglandin E2 in brain regions of young and old rats

The potential for synthesis of prostaglandin E2 (PGE2) in cerebrum (CC), cerebellum (CM), mid-brain (MB) and brain stem (BS) was measured in 1 and 15 month old male F344 rats fed diets containing 0, 30, or 200 IU vitamin E (-E, E, +E, respectively) and 0.0, 0.1, or 0.2 ppm selenium (-Se, Se, +Se, respectively) for 8 or 20 weeks. Regardless of dietary treatments, the rank order of PGE2 synthesis was CC greater than CM greater than BS = MB in the young rats; CC greater than MB greater than BS = CM in the old rats; and CC greater than MB greater than BS greater than CM in the aged rats. PGE2 synthesis in all brain regions were significantly influenced by dietary treatments except CC. -E diets increased and +E diets decreased PGE2 production. Young rats were most susceptible to PGE2 alteration by vitamin E deficiency while old rats responded most markedly to supplementation. All brain regions showed decreases in their capacity to synthesize PGE2 with age, except MB where the opposite effect was seen. Dietary Se treatment had a minimal role in PGE2 synthesis in gross anatomical regions of brain. The degree to which PGE2 synthesis is affected is more dependent on dietary vitamin E level and tissue alpha-tocopherol content than on Se. CM and BS of aged rats appear to require more alpha-tocopherol to maintain steady state levels than other areas, thus the synthesis of PGE2 in these regions could be highly susceptible to alterations in dietary vitamin E.

Effect of vitamin E on the balance between pro- and antioxidant activity of ascorbic acid in microsomes from rat heart, kidney and liver

The effect of the vitamin E status of membranes on the balance between pro- and antioxidant activity of ascorbic acid was studied in microsomes from rat heart, kidney and liver. Lipid peroxidation was initiated by 5 microM ferrous ions, in combination with amounts of ascorbic acid ranging from 0-4 mM. Lipid peroxidation was assessed after 1 h of incubation as production of thiobarbituric acid reactive material. It was found that the vitamin E status of the microsomal membranes had little effect on the balance between pro- and antioxidant activity of vitamin C. The sensitivity of the membranes to ferrous ions/ascorbic acid-induced lipid peroxidation, however, was highly dependent on the vitamin E content of the membranes. Vitamin E depletion, in combination with different ascorbic acid concentrations, showed that vitamin E deficiency is not an incontestable model system for enhanced sensitivity to lipid peroxidation in all organs.

A relay model of lipid peroxidation in biological membranes

It is believed that in lipid peroxidation in membranes an important role is played by unoxygenated hydrocarbon radicals whose movement within the hydrocarbon moiety of the membrane is through intra-and intermolecular relay rearrangements (H-shift). in membranes containing a high concentration of polyunsaturated lipids, mobility may be higher than the lateral diffusion of the lipids allowed by the microviscosity of the membrane. The action mechanism of antioxidants having a side hydrocarbon tail (e.g., tocopherols) rests upon the relay radical reaction, as a multistep process. The initial step is the relay transfer of unoxygenated free radical to the side hydrocarbon chain of antioxidant. In subsequent steps the aroxyl radical is formed by the intramolecular rearrangement of radical in an antioxidant molecule. Hence, the inhibitor interrupts the propagation chain in the membrane by the scavenge of unoxygenated hydrocarbon radical.

Cigarette smoke exposure alters [14C]arachidonic acid metabolism in aortas and platelets of rats fed various levels of selenium and vitamin E

Rats were placed on a basal diet supplemented with 0, 0.03, or 3 ppm selenium and 0 or 20 ppm vitamin E for 41-43 wk. Selenium deficiency decreased hepatic glutathione peroxidase activity and lowered both aortic prostacyclin (PGI2) and platelet thromboxane (TXA2) production compared to selenium- and vitamin E-supplemented animals. Vitamin E deficiency increased hepatic lipid peroxidation and decreased aortic PGI2 synthesis. Rats exposed daily for 31-32 wk to fresh smoke from a UK 2R1 reference cigarette had carboxyhemoglobin levels of 0.75 +/- 0.12 and 4.73 +/- 0.12% in sham- and smoke-exposed groups, respectively. Animals chronically exposed to cigarette smoke displayed a nearly twofold increase in pulmonary arylhydrocarbon hydroxylase activity. Smoke exposure produced a 26-33% decrease in aortic PGI2 synthesis compared to shams in the Se3E20, Se0.03E20, and Se3E0 groups. Smoking also increased platelet thromboxane 91% and 98% in the Se3E20 and Se3E0 groups compared to shams. It is concluded that cigarette-smoke exposure and selenium or vitamin E deficiency alter aortic PGI2 and platelet TXA2 production.

Release of ethane and pentane from rat tissue slices: effect of vitamin E, halogenated hydrocarbons, and iron overload

The effects of in vitro addition of halogenated hydrocarbons on the susceptibility of various rat tissues to lipid peroxidation, and of iron overload and dietary vitamin E in the intact rat on subsequent lipid peroxidation in rat tissue slices were examined. The ease and speed of tissue slice preparation allowed testing of multiple tissues from the same animals. Total ethane and pentane (TEP) released from the slices was as reliable as and more sensitive than thiobarbituric acid-reactive substances as an index of lipid peroxidation. TEP was released by tissues from vitamin E-deficient rats in the following order of magnitude:intestine = brain = kidney greater than liver = lung greater than heart greater than testes = diaphragm greater than skeletal muscle. The potency of halogenated hydrocarbons for causing increased TEP release from vitamin E-deficient rat liver slices was CBrCl3 greater than CCl4 = 1,1,2,2-tetrabromoethane = 1,1,2,2-tetrachloroethane greater than perchloroethylene. CBrCl3 also stimulated TEP release from kidney, intestine, and heart slices, thus identifying these as potential target organs for CBrCl3 toxicity. Dietary vitamin E decreased TEP release from liver and, to a lesser extent, from kidney. Iron overload in the rat increased TEP release by slices from all tissues tested except the brain.

New developments in the regulation of heme metabolism and their implications

Various endogenous and exogenous chemicals, such as hormones, drugs, and carcinogens and other environmental pollutants are enzymatically converted to polar metabolites as a result of their oxidative metabolism by the mixed-function oxidase system. This enzyme complex constitutes the major detoxifying system of man and utilizes the hemoprotein--cytochrome P-450--as the terminal oxidase. Recent studies with trace metals have revealed the potent ability of these elements to alter the synthesis and to enhance the degradation of heme moiety of cytochrome P-450. An important consequence of these metal actions is to greatly impair the ability of cells to oxidatively metabolize chemicals because of the heme dependence of this metabolic process. In this report the effects of exposure to trace metals on drug oxidations is reviewed within the framework of metal alterations of heme metabolism, including both its synthesis and degradation, since these newly discovered properties of metals have made it possible to define a major dimension of metal toxicity in terms of a unified cellular mechanism of action.

Increasing lipid peroxidation by vitamin E deficiency does not augment adriamycin-induced inhibition of hepatic drug metabolism

Adriamycin treatment in vivo or addition to incubation mixtures in vitro inhibits hepatic drug metabolism. It has been suggested that adriamycin-induced membrane lipid peroxidation may be a mechanism responsible for this activity in vitro. To determine if similar mechanisms operate in vivo, adriamycin inhibition of drug metabolism was compared in rats whose tissue lipid peroxidizability was altered by manipulating dietary levels of vitamin E. Weanling rats maintained on vitamin E deficient (0 ppm) or supplemented (10 or 100 ppm) diets for 12 weeks were given either adriamycin, 5 mg/kg/week, or equal volumes of the saline vehicle for 3 weeks intraperitoneally. Vitamin E deficiency alone (0 ppm, saline pretreatment) produced a 37% increase in hepatic lipid peroxidation without any appreciable alteration in hepatic aniline hydroxylase, ethylmorphine N-demethylase or aryl hydrocarbon hydroxylase activities. Adriamycin pretreatment altered hepatic lipid peroxidizability over corresponding saline pretreated controls dependent on dietary vitamin E. No increase was seen in the 100 ppm group, while 44% and 500% increases occurred at 10 and 0 ppm vitamin E, respectively. Adriamycin pretreatment decreased drug-metabolizing enzyme activity by an average of 32% for aniline hydroxylase, 26% for ethylmorphine N-demethylase and 63% for aryl hydrocarbon hydroxylase. Statistically, decreases in drug metabolism were independent of dietary vitamin E and did not correlate with lipid peroxidizability. These data would suggest that in vivo adriamycin-induced depression of hepatic drug-metabolizing enzymes is not mediated by elevated lipid peroxidation.

Effects of lipid peroxidation on adrenal microsomal monooxygenases

Incubation of guinea pig adrenal microsomes with 10(-6) M ferrous (Fe2+) ion and adrenal cytosol initiated high levels of lipid peroxidation as measured by the production of malonaldehyde. Cytosol or Fe2+ alone had little effect on microsomal malonaldehyde formation. When microsomes were incubated in the presence of Fe2+ and cytosol, malonaldehyde levels continued to increase for at least 60 min. Accompanying the lipid peroxidation was a decline in adrenal microsomal monooxygenase activities. The rates of metabolism of xenobiotics (benzphetamine demethylase, benzo[a]pyrene hydroxylase) as well as steroids (21-hydroxylation) decreased as malonaldehyde levels increased. In addition, cytochrome P-450 levels, NADPH- and NADH-cytochrome c reductase activities, and substrate interactions with cytochrome(s) P-450 decreased as lipid peroxidation progressed. Inhibition of lipid peroxidation by increasing microsomal protein concentrations during the incubation period prevented the changes in microsomal metabolism. Malonaldehyde had no direct effects on adrenal microsomal enzyme activities. The results indicate that lipid peroxidation may have significant effects on adrenocortical function, diminishing the capacity for both xenobiotic and steroid metabolism.

Chlorphentermine-induced alterations in the lungs of vitamin E-deficient and supplemented rats: 1. Biochemical and morphometric analysis of the pulmonary response

Male Sprague-Dawley rats were maintained on diets containing 0.60, or 300 ppm vitamin E (VE) for 9 weeks with chlorphentermine (CP) or saline vehicle (SV) treatments administered over the last 3 weeks (20 mg CP/kg for one week and 30 mg CP/kg for subsequent 2 weeks or equivalent volume of saline vehicle). Spontaneous erythrocyte hemolysis averaged 68% for VE-deficient (0 ppm) and less than 9% for VE-supplemented (60 and 300 ppm) animals prior to saline and CP treatments. These values were not changed significantly by vehicle or drug administration. The lung-to-body weight ratios nearly doubled and the total lung phospholipid levels increased equivalently (three- to fourfold) in all three CP-treated VE groups as compared to corresponding SV controls. The levels of thiobarbituric acid-reactive material (TBA-RM), an index of lipid peroxidation, was increased in the lung tissue above SV controls in all dietary groups with the deficient group being the highest. There was no difference in the TBA-RM values of 60 and 300 ppm groups within each group. Quantitative morphometric analysis revealed that in the VE-supplemented groups, CP treatment caused a significant increase in the number of alveolar macrophage foam cells (FC) with a slight increase in the volume density of surfactant-like material (SLM). By comparison, there were fewer FCs but a larger quantity of SLM in the VE-deficient group. The results suggest that VE deficiency modifies the pulmonary response to CP resulting in lipid peroxidation-induced FC disintegration and the accumulation of SLM.

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 gamma-glutamyl-transpeptidase pathway.

Effects of vitamin E deficiency and nitrogen dioxide exposure on lung lipid peroxidation: use of lipid epoxides and malonaldehyde as measures of peroxidation

The effect of vitamin E deficiency in male Sprague-Dawley rats upon lipid peroxidation in lung tissue was examined by measuring malonaldehyde and lipid epoxide production. In addition to controls, some animals were also exposed to 3 +/- 0.1 ppm NO2 continuously for 7 d in order to study the effects of oxidant stress on lung lipid peroxidation and vitamin E content. The observed changes in malonaldehyde and epoxide content could serve as good indices of lipid peroxidation, particularly under conditions of vitamin E deprivation. The responses measured indicated an inverse relation in the lung between tissue vitamin E content and quantity of lipid peroxidation products. Measurement of lipid epoxides served as a reliable indicator of lung tissue lipid peroxidation. Finally, NO2 inhalation appeared to elicit a response characterized by increased assimilation of vitamin E into lung tissue.