Increased vitamin E content in the lung after ozone exposure: a possible mobilization in response to oxidative stress

Modulation of ozone-sensitive genes in alpha-tocopherol transfer protein null mice

Alpha-tocopherol transfer protein (ATTP) null mice (ATTP-/-) have a systemic alpha-tocopherol (AT) deficiency, with their lung AT levels being < 10% of those in AT-replete ATTP(+/+) mice when fed a standard rodent chow diet. ATTP(+/+) and ATTP(-/-) mice (4 wk old male mice, n = 16 per group) were fed a standard diet (35 IU AT/kg diet) for 8-12 wk, exposed 6 h/day for 3 days to either to O(3) (0.5 ppm) or filtered air, then sacrificed. No significant differences in plasma or lung AT concentrations were observed in response to this level of O(3) exposure. Lung genomic responses of the lungs to O(3) were determined using Affymetrix 430A 2.0 arrays containing over 22,600 probe sets representing 14,000 well-characterized mouse genes. As compared with filtered air exposure, O(3) exposure resulted in 99 genes being differentially expressed in ATTP(-/-) mice, as compared to 52 differentially expressed genes in ATTP(+/+) mice. The data revealed an O(3)-induced upregulation of genes related to cell proliferation/DNA repair and inflammatory-immune responses in both ATTP(+/+) and ATTP(-/-) mice, with the expression of 22 genes being common to both, whereas 30 and 77 genes were unique to ATTP(+/+) and ATTP(-/-) mice, respectively. The expressions of O(3) sensitive genes-Timp1, Areg, Birc5 and Tnc-were seen to be further modulated by AT status. The present study reveals AT modulation of adaptive response of lung genome to O(3) exposure.

Vitamin supplementation does not protect against symptoms in ozone-responsive subjects

Vitamin supplements have been reported to reduce the magnitude of symptoms in subjects exposed to oxidant air pollution. To confirm whether supplementation with vitamins C and E could reduce lung function decrements, airway inflammation, and epithelial injury in subjects sensitive to ozone, a double-blinded, crossover control study was performed. Fourteen ozone-responsive subjects were randomly exposed to both air and ozone (0.2 ppm for 2 h) after 7 days of either placebo treatment or supplementation with vitamin C (500 mg/day) and E (100 mg/day). Lung function was assessed pre- and immediately postexposure and blood samples were taken at set intervals. Inflammatory, tissue injury, and antioxidant responses were examined in lavage fluid obtained by bronchoscopy 6 h postexposure. Exposure to ozone resulted in significant (P < 0.01) decrements in FEV1 with no protection observed following vitamin supplementation (-8.5%) versus placebo (-7.3%) treatment. Similarly, ozone-induced neutrophilia were of a similar magnitude after both treatments (P < 0.05). This lack of protection was observed despite elevated plasma vitamin C (+60.1%) and vitamin E (+51.4%) concentrations following supplementation, and increased vitamin C concentrations in the airways after supplementation following ozone exposure. These data do not therefore support the contention that acute ozone-induced symptoms can be attenuated through the use of dietary antioxidants in well-nourished individuals.

Beneficial effects of MnTBAP, a broad-spectrum reactive species scavenger, in rat renal ischemia/reperfusion injury

BACKGROUND

In recent years, several lines of evidence have implicated reactive species as contributors to renal ischemia/reperfusion injury (I/R). This study was designed to investigate the effect of Mn (III) tetrakis (4-benzoic acid) porphyrin (MnTBAP), a broad-spectrum reactive species scavenger, in the prevention of renal I/R injury.

METHODS

Experiments were performed on rats anesthetized with pentobarbital. After tracheotomy, the right femoral artery was cannulated and the mean arterial pressure and heart rate were recorded. A midline laparatomy was performed, and the renal arteries were carefully separated from surrounding tissues. After surgery and a stabilization period (60 min), the animals were randomly assigned to four groups: sham-operated; sham+MnTBAP; I/R; I/R+MnTBAP. In I/R groups, the rats were subjected to bilateral renal artery occlusion for 40 min followed by 6 h reperfusion. Other groups underwent the surgery protocol but did not undergo renal artery occlusion, and were maintained under anesthesia for the duration of the experiment. Rats were administered either MnTBAP (10 mg kg(-1), i.v. bolus, 15 min prior to I/R) or saline. Renal function was assessed by plasma creatinine (Cr), blood urea nitrogen (BUN), and aspartate aminotransferase (AST) measurements. The fractional excretion of Na(+) (FE(Na+)) and urinary N-acetyl-beta-D-glucosaminidase (NAG) activities were also measured. Renal section damage was evaluated by light microscopy, and oxidative stress status was evaluated by measurements of plasma and renal vitamin E levels.

RESULTS

We found that MnTBAP significantly reduced the I/R-mediated increases in plasma Cr, BUN, AST, FE(Na+), and NAG and improved the renal tissue histology.

CONCLUSION

Our results showed that MnTBAP was effective in preventing the development of I/R-induced renal injury.

Plasma and lung macrophage responsiveness to carotenoid supplementation and ozone exposure in humans

OBJECTIVE

To examine the effect of ozone exposure and vegetable juice supplementation on plasma and lung macrophage concentrations of carotenoids.

DESIGN

A randomized trial.

SETTING

Subjects were exposed to ambient air prior to antioxidant supplementation and to ozone after antioxidant supplementation or placebo. Exposures occurred while exercising intermittently in a controlled metabolic chamber at the Human Studies Division, US EPA.

SUBJECTS

In all, 23 healthy subjects between ages of 18 and 35 y.

INTERVENTIONS

Subjects consumed a low fruit and vegetable diet for 3 weeks. After the first week, subjects underwent a sham exposure to filtered air with exercise, followed by bronchoalveolar lavage (BAL). Subjects were randomly assigned into supplement (one can vegetable juice, vitamins C and E daily) or placebo (orange soda, placebo pill daily) groups for 2 weeks. After the 2-week intervention, subjects were exposed to 0.4 ppm (784 microg/m(3)) ozone for 2 h with exercise followed by BAL. Blood samples were drawn before, immediately after and 3 h postexposure on each exposure day. The concentrations of nine carotenoids were determined by HPLC in BAL macrophages and plasma samples.

RESULTS

Plasma concentrations of all the carotenoids that were present in the vegetable juice (except cis-beta-carotene) increased significantly in the supplemented group. Lung macrophage alpha-carotene concentrations increased significantly, lycopene isomers increased slightly, and all other carotenoids decreased (nonsignificantly) in the supplementation group following the intervention. Ozone exposure resulted in decreases in several carotenoids in plasma of the placebo group, but not in the supplemented group.

CONCLUSIONS

Lung macrophage concentrations of carotenoids can be manipulated by diet. Ozone is a potent environmental oxidant that appears to reduce plasma carotenoids in nonsupplemented individuals.

In vivo ozone exposure induces antioxidant/stress-related responses in murine lung and skin

Lung and skin are the organs directly exposed to environmental pollution. Ozone (O(3)) is a toxic, oxidant air pollutant, and exposure has been shown to induce antioxidant depletion as well as oxidation of lipids and proteins within the outermost skin layer (stratum corneum) and the lung respiratory tract lining fluids (RTLFs). To further define skin and lung responses to O(3) exposure, SKH-1 hairless mice were exposed to either 0.8 ppm of O(3) (a level occasionally reached in very polluted areas) or ambient air 6 h/day for 6 consecutive days. O(3) exposure resulted in the depletion of alpha-tocopherol in lung and plasma and induction in both skin and lung of heme oxygenase 1, cyclooxygenase 2, and proliferating cell nuclear antigen. O(3)-exposed animals showed a similar extent of upregulation of COX-2 and PCNA in lung and skin, whereas HO-1 was more responsive in skin than in lung (7-fold induction vs. 2-fold induction). In addition to these measures of response to oxidative stress, O(3) exposure led to the activation of nuclear factor kappaB measured as IkappaBalpha phosphorylation in both tissues. We conclude that in this model, O(3) at high pollutant levels is able to affect both lung and skin biology, inducing depletion of alpha-tocopherol and inducing stress-related responses in both skin epidermis and respiratory tract epithelium.

Antioxidant supplementation and lung functions among children with asthma exposed to high levels of air pollutants

To evaluate whether acute effects of ozone, nitrogen dioxide, and particulates with mass median diameter less than 10 micro m could be attenuated by antioxidant vitamin supplementation, we conducted a randomized trial using a double-blinded design. Children with asthma (n = 158) who were residents of Mexico City were randomly given a daily supplement of vitamins (50 mg/day of vitamin E and 250 mg/day of vitamin C) or a placebo and were followed from October 1998 to April 2000. Pulmonary function tests were carried out twice a week in the morning. During the follow-up observation period, the mean 1-hour maximum ozone level was 102 ppb (SD = 47), and the mean 24-hour average PM(10) level was 56.7 micro g/m(3) (SD = 27.4). In children with moderate and severe asthma, ozone levels 1 day before spirometry were inversely associated significantly with forced expiratory flow (FEF(25-75)) (-13.32 ml/second/10 ppb; p = 0.000), FEV(1) (-4.59 ml/10 ppb; p = 0.036), and peak expiratory flow (PEF) (-15.01 ml/second/10 ppb; p = 0.04) in the placebo group after adjusting for potential confounding factors. No association between ozone and lung functions was observed in the supplement group. We observed significant differences in lung function decrements between groups for FEF(25-75) and PEF. Our results suggest that supplementation with antioxidants might modulate the impact of ozone exposure on the small airways of children with moderate to severe asthma.

Antioxidant supplementation and respiratory functions among workers exposed to high levels of ozone

Ozone exposure has been related to adverse respiratory effects, in particular to lung function decrements. Antioxidant vitamins are free-radical scavengers and could have a protective effect against photo-oxidant exposure. To evaluate whether acute effects of ozone on lung functions could be attenuated by antioxidant vitamin supplementation, we conducted a randomized trial using a double-blind crossover design. Street workers (n = 47) of Mexico City were randomly assigned to take daily a supplement (75 mg vitamin E, 650 mg vitamin C, 15 mg beta carotene) or a placebo and were followed from March to August 1996. Pulmonary function tests were done twice a week at the end of the workday. During the follow-up, the mean 1-h maximum ozone level was 123 ppb (SD = 40). During the first phase, ozone levels were inversely associated with FVC (beta = -1.60 ml/ppb), FEV1 (beta = -2.11 ml/ppb), and FEF25-75 (beta = -4.92 ml/ppb) (p < 0.05) in the placebo group but not in the supplement group. The difference between the two groups was significant for FVC, FEV1, and FEF25-75 (p < 0.01). During the second phase, similar results were observed, but the lung function decrements in the placebo group were smaller, suggesting that the supplementation may have had a residual protective effect on the lung. These results need to be confirmed in larger supplementation studies.

Pulmonary lipid peroxidation and antioxidant defenses during exhaustive physical exercise: the role of vitamin E and selenium

Physical exercise is known to induce oxidative stress leading to the generation of free radicals. This increased generation of free radicals might lead to lipid peroxidation and tissue damage, more so under deficient/impaired antioxidant states. In the present study, we report the role of vitamin E and selenium (Se) during exercise-induced oxidative stress in the pulmonary tissue. Vitamin E and/or Se deficiency in female albino rats resulted in generation of free radicals as revealed by electron spin resonance (ESR) spectra in the lung tissue, indicating the onset of oxidative stress. When these animals were subjected to a single bout of exhaustive exercise, there was an additional increase in the generation of oxy-free radicals, which might lead to tissue damage. However, no such signals were recorded in the lung tissue of vitamin E- and Se-supplemented animals, when subjected to a similar exercise program, suggesting that protection is offered by vitamin E and Se in combating oxidative stress.

Markers of oxidative stress and antioxidant activity in plasma and erythrocytes in neonatal respiratory distress syndrome

Markers of oxidative stress and antioxidant activity in plasma and erythrocytes were studied for 14 d after birth in infants with neonatal respiratory distress syndrome (n = 9) and controls (n = 36). In plasma, the total radical trapping antioxidant capacity and the chain-breaking antioxidants vitamin C, sulfhydryl groups and bilirubin were similar. The differences in uric acid levels were not consistent, but vitamin E levels and vitamin E/total-lipid ratio were lower in the neonatal respiratory distress group (p < 0.01). In erythrocytes, the antioxidant enzymes glutathione peroxidase, glutathione reductase and superoxide dismutase did not differ postnatally. Indicators of oxidative damage in plasma (sulfhydryl/protein ratio and thiobarbituric acid reactive substances) showed the same postnatal course in both groups and were not influenced by oxygen therapy. In erythrocytes the reduced/oxidized glutathione ratio showed no consistent differences. In conclusion, this study, using erythrocytes and plasma, does not provide convincing evidence of oxidative damage and diminished antioxidant defenses in preterm infants with neonatal respiratory distress syndrome.

Dietary restriction mitigates ozone-induced lung inflammation in rats: a role for endogenous antioxidants

Studies were undertaken to determine whether dietary restriction protects against acute pulmonary oxidant challenge. Male F344 rats were fed NIH-31 diet either ad libitum or at restricted levels equal to 75% that of ad libitum intake. After 3 wk of dietary adaptation, animals were exposed by inhalation to 2.0 ppm ozone (O3) for 2 h or chamber air and evaluated for cellular and biochemical indices of pulmonary toxicity. Compared to air controls, bronchoalveolar lavage fluid (BALF) from O3 exposed ad libitum fed rats contained increased protein (145 versus 380 microg/ml), PMN infiltration (0 versus 11%) and fibronectin (45 versus 607 U/ml). Diet restriction abrogated these indicators of pulmonary inflammation induced by ozone. Binding of 18O3 to BALF protein and cells was significantly decreased in diet restricted rats while BALF ascorbate and glutathione levels, but not alpha-tocopherol or urate, were elevated compared to ad libitum fed rats. Taken together, these results indicate that dietary restriction affords protection against O3-induced oxidant toxicity. Protection is mediated partially by increases in ascorbate in the fluid bathing the lung surface, thereby providing an antioxidant sink which minimizes the ability of O3 to reach biological targets.

The effects of gentamicin and vitamin E on enzymatic antioxidant defence in guinea-pig lung

OBJECTIVE

To study the possible effects of gentamicin on the enzymic free-radical defence system in the lung.

METHOD

Activities of cytoplasmic superoxide dismutase (CuZn-SOD), mitochondrial superoxide dismutase (Mn-SOD), glutathione peroxidase (GSH-Px) and catalase (CAT) enzymes were studied in lung tissues from gentamicin-treated guinea-pigs compared to controls.

RESULTS

Levels of those enzymes were higher in the gentamicin group except for xanthine oxidase (XO) activity. Vitamin E given concomitantly with gentamicin caused significant decreases in CuZn-SOD, Mn-SOD and GSH-Px activities but an increase in CAT activity in the lung tissue. Only vitamin treatment caused significant decreases in the activities of CuZn-SOD, Mn-SOD and GSH-Px enzymes and an increase in CAT activity.

CONCLUSION

The results suggest that lung tissue is able to respond quickly and effectively against the adverse effects of some oxidant substances by inducing and/or activating the enzymatic free-radical defence system.

Ozone-induced DNA strand breaks In guinea pig tracheobronchial epithelial cells

Ozone (O3), the major oxidant of photochemical smog, is thought to be genotoxic and a potential respiratory carcinogen or promoter of carcinogenic processes. Because of oxidative reactions with the mucus in the upper airway, O3 reaction products are able to penetrate into the tracheobronchial epithelial (TE) cells. The carcinogenic effects of O3 on the TE cells are especially of interest since most previous studies have focused on the morphology or permeability changes of tracheas only. Therefore, the objective of this study was to examine the potential O3 genotoxicity in TE cells after an in vivo exposure, using DNA strand breaks as an index. Two-month-old male Dunkin-Hartley guinea pigs, specific pathogen free, 4 in each group, were exposed to 1.0 ppm O3 for 0, 12, 24, 48, 72, or 96 h. Animals exposed to filtered air without O3 exposure were used as controls. After O3 exposure, the trachea with two main bronchi was removed from each animal, and TE cells were isolated and employed for determination of DNA strand breaks by fluorometric analysis of DNA unwinding (FADU). The statistical significance level was set at alpha = .05. Compared with controls, ozone exposure did not alter the TE cell yield or viability, but caused an increase in protein content in tracheal lavage and an increase in DNA strand breaks. The amount of DNA left in the alkali lysate of TE cells found at 72 h exposure was significantly decreased from controls for 3 different alkali incubation times. An increase of the double-stranded DNA left in the alkali lysate of TE cells was observed at 96 h of exposure and approached the value of 24 h of exposure. The same pattern was seen with all 3 different alkali incubation times at 15 degrees C. One Qd unit was estimated to correspond to 100 strand breaks per cell. The Qd was also used as an indicator for O3 damage. Compared to controls, the Qd increases significantly after 1 ppm O3 exposure for 72 h, regardless of the alkali incubation time at 15 degrees C.

Determinants of antioxidant status in humans

Antioxidant status in humans reflects the dynamic balance between the antioxidant system and prooxidants and has been suggested as a useful tool in estimating the risk of oxidative damage. This paper reviews determinants of antioxidant status such as diet including antioxidant nutrient and nonnutrient intake, absorption and bioavailability, dietary components such as polyunsaturated fatty acids and transition metals, food storage and processing, chemical form, chirality and formulation of supplemental compounds and alcohol intake; environmental factors such as pollutants, ultraviolet radiation and smoking; injury and disease, medications and other medical treatments such as radiation; strenuous exercise; and physiological stage or conditions such as those in premature babies and the elderly. It is proposed that, in addition to current focus on tissues, the antioxidant status of digesta should be considered because of its effect on specific tissues and potential health implications.

Effect of vitamin E deficiency and supercritical fluid aerosolized vitamin E supplementation on interleukin-1-induced oxidative lung injury in rats

We hypothesized that alterations in lung vitamin E levels would impact the development of acute oxidative lung injury. We found that dietary induced deficiency of vitamin E diminished lung tissue levels of vitamin E and increased lung leak following intratracheal administration of interleukin-1 (IL-1) to rats. Conversely, rats administered vitamin E directly to the lungs as an inhaled aerosol (0.3-3 microns particles) formed by supercritical fluid aerosolization (SFA) had increased lung tissue vitamin E levels and decreased IL-1 induced lung leak compared to control rats. Lung myeloperoxidase (MPO) activities, reflecting neutrophil concentrations, were increased in rats given IL-1 intratracheally compared to rats given saline intratracheally but were not different for control or vitamin E depleted rats. Lung MPO activities in rats given IL-1 intratracheally were slightly higher in SFA vitamin E treated rats than in control rats. Our results suggest that vitamin E levels affect susceptibility to IL-1 induced, neutrophil-dependent lung injury. We speculate that supercritical fluid aerosol (SFA) delivery of vitamin E can rapidly increase lung vitamin E levels and decrease acute oxidative lung injury.

Alpha-tocopherol attenuates lung edema and lipid peroxidation caused by acute zymosan-induced peritonitis

BACKGROUND

Inflammation-induced disease as seen with trauma and infection can lead to increased lung oxidant activity resulting in cell membrane lipid peroxidation. Acute zymosan-induced peritonitis in rats produces lung inflammation, edema, and lipid peroxidation. We determined whether administered alpha-tocopherol (vitamin E), the key antioxidant protection against cell membrane lipid peroxidation, would improve this process.

METHODS

Male Wistar rats were given 0.75 mg/kg of intraperitoneal zymosan, volume resuscitated, monitored, and killed at 4 or 24 hours. Lung histologic changes and levels of conjugated dienes, a marker of lipid peroxidation, were used to monitor injury. The levels of vitamin E, vitamin C, and catalase were used to monitor antioxidant defenses. The effect of administering alpha-tocopherol (50 mg/kg) by gavage immediately after zymosan on the degree of the lung injury was then determined.

RESULTS

Twenty-four hours after zymosan was administered, the vitamin E levels in plasma were significantly decreased, but lung tissue vitamin E levels were maintained, whereas tissue catalase and vitamin E levels decreased. Lung tissue-conjugated diene levels, alveolar edema, and neutrophil count were significantly increased. alpha-Tocopherol treatment increased the postzymosan plasma vitamin E levels by 50%. Lung tissue vitamin E levels did not increase; however, the degree of lung injury and lipid peroxidation was significantly attenuated. Tissue catalase levels were also maintained.

CONCLUSIONS

We conclude that alpha-tocopherol given at the onset of a progressing inflammatory injury can protect the lung from oxidant damage and attenuate the degree of lung injury.

Ozonation of DNA forms adducts: a 32P-DNA labeling and thin-layer chromatography technique to measure DNA environmental biomarkers

Little direct documented evidence of ozone's genotoxicity exists. Deoxyribonucleic acid (DNA) adducts are produced by environmental toxic agents, including ozone. We have described a modified thin-layer chromatography (TLC) technique that can assess adduct formation as a biomarker of ozone injury. This requires 32P-labeling DNA, digestion of deoxynucleotides (dNMPs), and separation in two-dimensional PEI-cellulose TLC. We have applied this technique to control DNAs, to control DNA in solution exposed to acute ambient ozone, and to control DNA exposed to acute bubbled-through ozone (2 ppm for 24 h). We detected stable DNA adducts, including hydroxymethyluracil (HMU), thymine glycol (TG), 8-hydroxyguanine (8-OHG), and demonstrated, as yet, unidentified adducts that may serve as a "fingerprint" pattern of DNA adduction. This technique quantifies low-molecular-mass DNA adducts, both in vivo and in vitro, with potential applications to environmental toxicology.

New aspects of brain oxidative stress induced by tert-butylhydroperoxide

Many diseases and aging may be associated with oxidative stress in the brain. However, the effects of oxidative stress in the brain should be more clearly described, especially in terms of effects on brain reduced glutathione (GSH). This issue was addressed by intracerebroventricular injection of a direct-acting oxidative stress inducing agent, tert-butylhydroperoxide. Oxidized glutathione (GSSG) levels in the brain increased by as much as 90-fold during tert-butylhydroperoxide-induced oxidative stress. At the same time, brain GSH levels decreased. The brain appears to retain GSSG and not reduce it or export it efficiently. Vitamin E levels in the striatum increased during tert-butylhydroperoxide-induced oxidative stress. Aging alters the ability of the brain to detoxify an oxidative stress, in that 8-month-old mice retain GSSG in their brains much more than 2-month-old mice. Eight-month-old mice were much more susceptible to tert-butylhydroperoxide-induced toxicity than 2-month-old mice. This may indicate that aging makes the brain more susceptible to oxidative damage.

Cigarette smoking and oxidative damage in the lung

Cigarette smoke contains a large variety of compounds, including many oxidants and free radicals that are capable of initiating or promotes oxidative damage. Also, oxidative damage may result from reactive oxygen species generated by the increased and activated phagocytes following cigarette smoking. In vitro studies are generally supportive of the hypothesis that cigarette smoke can initiate or promote oxidative damage. However, information obtained from in vivo studies is inconclusive. Contrary to expectations, the levels of lipid peroxidation products were found to be decreased or unchanged in the lungs of chronically smoked rats. Metabolic adaptation, such as accumulation of vitamin E in the lung, and increased activities of superoxide dismutase in alveolar macrophages and pulmonary tissues of chronically smoked animals may enable smoked subjects to counteract oxidative stress and to resist further damage to smoke exposure. However, it is also possible that the metabolic adaptation may be secondary to inflammatory response and injury repair process following smoking exposure. More studies are needed to better understand the role of oxidative damage in the etiology of smoking-related disorders.

Dietary supplementation of vitamin E fails to prevent the development of hyperoxic lung injury in the premature guinea pig

1. The benefit of dietary vitamin E supplementation in preventing oxidative-induced lung injury was investigated. Three day preterm guinea pig pups were exposed to hyperoxic (85% O2) or normoxic (21% O2) conditions. The animals were fed either a standard low birthweight human infant formula milk (6.4 mg/l vitamin E), or a vitamin E supplemented milk (100 mg/l) for up to 7 days. 2. After 3 days vitamin E supplementation, plasma but not erythrocyte vitamin E concentrations were elevated, while following 7 days both plasma and erythrocyte vitamin E concentrations were significantly increased. 3. Lung and liver vitamin E concentrations were elevated at both 3 and 7 days. At 3 days the increase in lung vitamin E was oxygen-dependent, suggesting that the lung increases uptake of vitamin E in response to oxidative stress. 4. Despite an increase in the vitamin E concentration of the lungs of preterm guinea pigs, no amelioration of the lung injury was observed. These results suggest that although vitamin E is a potent antioxidant, it is unable to protect adequately the lungs from reactive oxygen species in the absence of sufficient primary enzymatic antioxidant defences.

The role of metabolism in the antioxidant function of vitamin E

Vitamin E (alpha-tocopherol), the principal chain-breaking antioxidant in biological membranes, prevents toxicant- and carcinogen-induced oxidative damage by trapping reactive oxyradicals. Although alpha-tocopherol antioxidant reactions appear to be not under direct metabolic control, alpha-tocopherol may function through redox cycles, which deliver reducing equivalents for antioxidant reactions and link antioxidant function to cellular metabolism. This review describes the antioxidant chemistry of alpha-tocopherol and evaluates the experimental evidence for the linkage of alpha-tocopherol turnover to cellular metabolism through redox cycles. Numerous in vitro experiments demonstrate antioxidant synergism between alpha-tocopherol and ascorbate, reduced glutathione, NADPH, and cellular electron transport proteins. Nevertheless, evidence that a one-electron redox cycle regenerates alpha-tocopherol from the tocopheroxyl radical is inconclusive. The difficulty of separating tocopheroxyl recycling from direct antioxidant actions of other antioxidants has complicated interpretation of the available data. A two-electron redox cycle involving alpha-tocopherol oxidation to 8a-substituted tocopherones followed by tocopherone reduction to alpha-tocopherol may occur, but would require enzymatic catalysis in vivo. Metabolism of antioxidant-inactive alpha-tocopheryl esters releases alpha-tocopherol, whereas reductive metabolism of alpha-tocopherylquinone, an alpha-tocopherol oxidation product, yields alpha-tocopherylhydroquinone, which also may provide antioxidant protection.

Increased 4-hydroxynonenal levels in experimental alcoholic liver disease: association of lipid peroxidation with liver fibrogenesis

The precise role of lipid peroxidation in the pathogenesis of alcoholic liver disease is still being debated. To explore the issue, this study was undertaken to investigate the status of lipid peroxidation, antioxidants and prooxidants at two discrete stages of experimental alcoholic liver disease. Male Wistar rats were intragastrically fed a high-fat diet plus ethanol for 5 or 16 wk (the duration that resulted in initiation of centrilobular liver necrosis or liver fibrosis, respectively). Lipid peroxidation was assessed in isolated microsomes and mitochondria with three parameters: malondialdehyde equivalents as determined by thiobarbituric acid assay, conjugated diene formation and 4-hydroxynonenal as a 2,4-dinitrophenylhydrazone derivative. To assess antioxidant systems, hepatic concentrations of glutathione, methionine and alpha-tocopherol were determined. The concentration of nonheme iron, a known prooxidant, was also measured. At wk 5, centrilobular liver necrosis was already evident in the ethanol-fed animals, with two- or threefold increases in plasma AST and ALT levels. At this stage, neither malondialdehyde equivalents nor conjugated diene values were elevated, and the 4-hydroxynonemal level was below 0.2 nmol/mg protein. Hepatic concentrations of methionine and alpha-tocopherol in these animals were increased two- and threefold, respectively, whereas the reduced glutathione level remained unchanged. When alcoholic liver disease had progressed to perivenular or bridging fibrosis at wk 16, all three parameters of lipid peroxidation showed consistent increases that were accompanied by significant reductions in the hepatic glutathione and methionine levels. Interestingly, the control animals pair-fed with the high-fat diet also had significantly elevated 4-hydroxynonenal levels at wk 16 compared to the wk 5 level.(ABSTRACT TRUNCATED AT 250 WORDS)

Exposure of rats to low concentration of cigarette smoke increases myocardial sensitivity to ischaemia/reperfusion

It is suggested that passive smoking or smoke-exposure increase the risk of coronary heart disease. The same mechanisms as active smoking might play a role. The aim of this study was to determine whether exposure to smoke aggravated ischaemia/reperfusion injury. As a parameter of cellular function and integrity mitochondrial oxidative function was measured. Low molecular weight iron (LMWI) and alpha-tocopherol levels were determined to assess the possibility of toxic hydroxyl radical involvement in myocardial ischaemia/reperfusion injury of smoke-exposed rats. Rats were exposed to a small concentration of cigarette smoke for 2 months (the carboxyhemoglobin concentration did not increase), whereafter hearts were isolated and subjected to ischaemia and ischaemia followed by reperfusion. Mitochondrial oxidative function, low molecular weight iron and alpha-tocopherol were determined. The impairment in mitochondrial oxidative function, LMWI content elevation and the decrease in alpha-tocopherol concentration during ischaemia/reperfusion were significantly more severe in hearts of smoke-exposed rats than non-smokers. These results suggest that exposure to smoke increased the sensitivity of hearts to ischaemia/reperfusion injury, and that a free radical mechanism might participate.

Antioxidant vitamin supplementation of smoke-exposed rats partially protects against myocardial ischaemic/reperfusion injury

Our previous studies showed that exposure of rats to limited periods of cigarette smoke resulted in more severe myocardial damage when their hearts were subjected to myocardial ischaemia/reperfusion. The aim of this study was to determine whether supplementation of rats with antioxidant vitamins alpha-tocopherol and beta-carotene was able to protect their hearts against the increase in ischaemia/reperfusion injury caused by smoke-exposure. The parameters measured were mitochondrial oxidative function, cellular levels of alpha-tocopherol and low molecular weight iron (LMWI). Supplementation with antioxidant vitamins resulted in significantly less mitochondrial functional oxidative damage compared to that observed in the controls. Supplementation did not affect the cellular LMWI content, suggesting that the generation rate of hydroxyl radicals was similar in both groups. The protective effect of alpha-tocopherol and beta-carotene supplementation on the mitochondrial function against ischaemia/reperfusion could be due to their free radical scavenging action. Supplementation with antioxidant vitamins, therefore, had a beneficial effect on the excessive myocardial ischaemia/reperfusion injury of smoke exposed rats.