Antioxidant depletion in aortic crossclamping ischemia: increase of the plasma alpha-tocopheryl quinone/alpha-tocopherol ratio

Antioxidant action of vitamin E in vivo as assessed from its reaction products with multiple biological oxidants

Vitamin E acts as essential antioxidant against detrimental oxidation of biological molecules induced by multiple reactive species. To gain more insight into the physiological role of vitamin E, the levels of its oxidation products in humans under normal and pathological conditions were compared. α-Tocopherol quinone (α-TQ) and 5-nitro-γ-tocopherol (5-NgT) were focused. α-TQ is produced by multiple oxidants including oxygen radicals, peroxynitrite, hypochlorite, singlet oxygen, and ozone, while 5-NgT is produced by nitrogen dioxide radical derived from peroxynitrite and the reaction of nitrite and hypochlorite. The reported concentrations of α-TQ and 5-NgT in healthy human plasma are highly variable ranging from 15 to 360 and 4 to 170 nM, respectively. In general, the molar ratio 5-NgT/γ-tocopherol was higher than the ratio α-TQ/α-tocopherol. Both absolute concentrations of α-TQ and 5-NgT and the molar ratios to the parent tocopherols were elevated significantly in the plasma of patients with various diseases compared with healthy subjects except neurological diseases. The molar ratios of the products to the respective parent compounds decreased in the order of 5-NgT/γ-tocopherol > α-TQ/α-tocopherol > hydroxyoctadecadienoate/linoleate > 3-nitrotyrosine/tyrosine > isoprostane/arachidonate. The molar ratios of nitrated products to the respective parent compounds in human plasma are approximately 10^-2 for 5-NgT and 10^-5 for 3-nitrotyrosine, nitro-oleic acid, and 8-nitroguaine. These data indicate that vitamin E acts as an important physiological antioxidant and that α-TQ and 5-NgT represent biomarker for oxidative stress and nitrative stress respectively.

The Effects of Surgery on Plasma/Serum Vitamin C Concentrations: A Systematic Review and Meta-Analysis

Vitamin C (ascorbic acid) is a water soluble vitamin with an array of biological functions. A number of proposed factors contribute to the vitamin’s plasma bioavailability and ability to exert optimal functionality. The aim of this review was to systematically assess plasma vitamin C levels post-surgery compared with pre-surgery/ the magnitude and timeframe of potential changes in concentration. We searched the PUBMED, SCOPUS, SciSearch and the Cochrane Library databases between 1970 to April 2020 for relevant research papers. Prospective studies, control groups and true placebo groups derived from controlled trials that reported means and standard deviations of plasma vitamin C concentrations pre and post operatively were included into the meta-analysis. Data were grouped into short-term (≤7 days) and long term (> 7 days) post-operative follow-up. 23 of 31 studies involving 642 patients included in the systematic review were suitable for meta-analysis. Pooled data from the meta-analysis revealed a mean depletion of plasma vitamin C concentration of -17.99 µmol/L (39% depletion) (CI = -22.81, -13.17) (trial arms = 25, n = 565, p < 0.001) during the first post-operative week and -18.80 µmol/L (21% depletion) (-25.04, -12.56) (trial arms = 6, n = 166, p < 0.001) 2-3 months post-operatively. Subgroup analyses revealed that these depletions occurred following different types of surgery, however, high heterogeneity was observed amongst trials assessing concentration change during the first post-operative week. Overall, our results warrant larger, long term investigations of changes in post-operative plasma vitamin C concentrations and their potential effects on clinical symptomology.

Advanced Oxidation Protein Products and Carbonylated Proteins Levels in Endovascular and Open Repair of an Abdominal Aortic Aneurysm: The Effect of Pre-, Intra-, and Postoperative Treatment

Background

In recent years, a rapid increase in studies focusing on the role of oxidative stress in the pathogenesis of an abdominal aortic aneurysm (AAA) has been observed. Oxidative modifications of proteins are infrequently evaluated in reference to AAA.

Objectives

The intensity of oxidative protein modifications, presented as advanced oxidation protein products (AOPP) and carbonylated proteins (C=O), in AAA patients qualified for surgery was estimated. The effect of surgical techniques and intraoperative and postoperative treatment on AOPP and C=O levels was evaluated.

Patients

The EVAR group, consisting of 30 patients, was classified for endovascular aneurysm repair, whereas 28 patients were classified for conventional open repair (OR).

Methods

AOPP and C=O were measured using a colorimetric assay kit.

Results

A significantly lower AOPP level obtained 2-4 days after EVAR surgery in comparison with the value found before surgery was noted. In the case of OR postoperative treatment, a tendency of AOPP level to increase was observed. The tendency of C=O to decrease after surgery in the EVAR group was indicated. However, the C=O level tended to increase after OR surgery and reached a significantly higher value 5-7 days after surgery compared with the value obtained before surgery.

Conclusions

Based on our results, it may be concluded that AAA as well as surgical technique contribute to the formation of AOPP and C=O. The analysis of changes in AOPP and C=O values obtained after surgery revealed a significant effect of a patient's condition before surgery as well as the choice of surgery technique on the values of the studied parameters revealed during postoperative treatment.

Oxidant-specific biomarkers of oxidative stress. Association with atherosclerosis and implication for antioxidant effects

The unregulated oxidative modification of lipids, proteins, and nucleic acids induced by multiple oxidants has been implicated in the pathogenesis of many diseases. Antioxidants with diverse functions exert their roles either directly or indirectly in the physiological defense network to inhibit such deleterious oxidative modification of biological molecules and resulting damage. The efficacy of antioxidants depends on the nature of oxidants. Therefore, it is important to identify the oxidants which are responsible for modification of biological molecules. Some oxidation products produced selectively by specific oxidant enable to identify the responsible oxidants, while other products are produced by several oxidants similarly. In this review article, several oxidant-specific products produced selectively by peroxyl radicals, peroxynitrite, hypochlorous acid, lipoxygenase, and singlet oxygen were summarized and their potential role as biomarker is discussed. It is shown that the levels of specific oxidation products including hydroxylinoleate isomers, nitrated and chlorinated products, and oxysterols produced by the above-mentioned oxidants are elevated in the human atherosclerotic lesions, suggesting that all these oxidants may contribute to the development of atherosclerosis. Further, it was shown that the reactivities of physiological antioxidants toward the above-mentioned oxidants vary extensively, suggesting that multiple antioxidants effective against these different oxidants are required, since no single antioxidant alone can cope with these multiple oxidants.

Plasmodium falciparum uses vitamin E to avoid oxidative stress

BACKGROUND

Plasmodium falciparum is sensitive to oxidative stress in vitro and in vivo, and many drugs such as artemisinin, chloroquine and cercosporin interfere in the parasite's redox system. To minimize the damage caused by reactive radicals, antioxidant enzymes and their substrates found in parasites and in erythrocytes must be functionally active. It was shown that P. falciparum synthesizes vitamin E and that usnic acid acts as an inhibitor of its biosynthesis. Vitamin E is a potent antioxidant that protects polyunsaturated fatty acids from lipid peroxidation, and this activity can be measured by detecting its oxidized product and by evaluating reactive oxygen species (ROS) levels.

RESULTS

Here, we demonstrated that ROS levels increased in P. falciparum when vitamin E biosynthesis was inhibited by usnic acid treatment and decreased to basal levels if exogenous vitamin E was added. Furthermore, we used metabolic labelling to demonstrate that vitamin E biosynthesized by the parasite acts as an antioxidant since we could detect its radiolabeled oxidized product. The treatment with chloroquine or cercosporin of the parasites increased the ratio between α-tocopherolquinone and α-tocopherol.

CONCLUSIONS

Our findings demonstrate that vitamin E produced endogenously by P. falciparum is active as an antioxidant, probably protecting the parasite from the radicals generated by drugs.

The role of lipid peroxidation in neurological disorders

There has been much evidence demonstrating the involvement of oxidative stress in the pathology of neurological disorders. Moreover, the vulnerability of the central nervous system to reactive oxygen species mediated injury is well established since neurons consume large amounts of oxygen, the brain has many areas containing high iron content, and neuronal mitochondria generate large amounts of hydrogen peroxide. Furthermore, neuronal membranes are rich in polyunsaturated fatty acids, which are particularly susceptible to oxidative stress. Recently, the biological roles of products produced by lipid peroxidation have received much attention, not only for their pathological mechanisms associated with neurological disorders, but also for their practical clinical applications as biomarkers. Here, we discuss the production mechanisms of reactive oxygen species in some neurological disorders, including Alzheimer's disease, Down syndrome, Parkinson's disease, and stroke. We also describe lipid peroxidation biomarkers for evaluating oxidative stress.

A history of vitamin E

Vitamin E (α-tocopherol) was discovered nearly 100 years ago because it was required to prevent fetal resorption in pregnant, vitamin E-deficient rats fed lard-containing diets that were easily oxidizable. The human diet contains eight different vitamin E-related molecules synthesized by plants; despite the fact that all of these molecules are peroxyl radical scavengers, the human body prefers α-tocopherol. The biological activity of vitamin E is highly dependent upon regulatory mechanisms that serve to retain α-tocopherol and excrete the non-α-tocopherol forms. This preference is dependent upon the combination of the function of α-tocopherol transfer protein (α-TTP) to enrich the plasma with α-tocopherol and the metabolism of non-α-tocopherols. α-TTP is critical for human health because mutations in this protein lead to severe vitamin E deficiency characterized by neurologic abnormalities, especially ataxia and eventually death if vitamin E is not provided in large quantities to overcome the lack of α-TTP. α-Tocopherol serves as a peroxyl radical scavenger that protects polyunsaturated fatty acids in membranes and lipoproteins. Although specific pathways and specific molecular targets have been sought in a variety of studies, the most likely explanation as to why humans require vitamin E is that it is a fat-soluble antioxidant.

α-Tocopherol suppresses lipid peroxidation and behavioral and cognitive impairments in the Ts65Dn mouse model of Down syndrome

It is widely accepted that oxidative stress is involved in the pathogenesis of Down syndrome, but the effectiveness of antioxidant treatment remains inconclusive. We tested whether chronic administration of α-tocopherol ameliorates the cognitive deficits exhibited by Ts65Dn mice, a mouse model of Down syndrome. α-Tocopherol was administered to pregnant Ts65Dn females, from the day of conception throughout the pregnancy, and to pups over their entire lifetime, from birth to the end of the behavioral testing period. Cognitive deficits were confirmed for Ts65Dn mice fed a control diet, revealing reduced anxiety or regardlessness in the elevated-plus maze task test and spatial learning deficits in the Morris water maze test. However, supplementation with α-tocopherol attenuated both cognitive impairments. In addition, we found that levels of 8-iso-prostaglandin F(2α) in brain tissue and hydroxyoctadecadienoic acid and 7-hydroxycholesterol in the plasma of Ts65Dn mice were higher than those of control mice. Supplementation with α-tocopherol decreased levels of lipid peroxidation products in Ts65Dn mice. Furthermore, we found out that α-tocopherol improved hypocellularity in the hippocampal dentate gyrus of Ts65Dn mice. These results imply that α-tocopherol supplementation from an early stage may be an effective treatment for the cognitive deficits associated with Down syndrome.

Seasonal mercury exposure and oxidant-antioxidant status of James Bay sport fishermen

The effects of a moderate seasonal exposure to methylmercury on plasma low-density lipoprotein (LDL) oxidation and cardiovascular risk indices are not known. The objective of the study was to assess the effects of a seasonal exposure to mercury at similar dose reported to increase cardiovascular risk through fish consumption. Effects on lipoprotein cholesterol and fatty acid profiles, LDL oxidation, and blood oxidant-antioxidant balance were to be assessed in sport fishermen presenting normal blood selenium and omega-3 fatty acid contents. Thirty-one healthy James Bay sport fishermen were assessed for within-subject longitudinal seasonal variations in hair and blood mercury, plasma oxidized LDL, lipophilic antioxidants, homocysteine, blood selenium, and glutathione peroxidase and reductase activities determined before and after the fishing season and compared by matched-pair tests. Hair mercury doubled during the fishing season (2.8+/-0.4 microg/g, P<.0001). Baseline blood selenium, homocysteine, and erythrocyte fatty acid profiles did not change. Plasma high-density lipoprotein cholesterol increased (+5%, P=.05), whereas very low-density lipoprotein cholesterol and oxidized LDL decreased (-8%, P=.05; -18%, P=.008). Blood glutathione peroxidase (+9.7%, P=.001), glutathione reductase (+7.2%, P<.0001), and total glutathione (+45% P<.0001) increased during the fishing season. Plasma total coenzyme Q10 (+13%, P=.02), ubiquinone-10 (+67%, P=.03), and beta-carotene (+46%, P=.01) also increased, whereas vitamin E status was unaffected. Pairwise correlations revealed no association between mercury exposure and any of the biomarkers investigated. In contrast, strong predictors of cardiovascular risk such as high-density lipoprotein cholesterol, oxidized LDL, and glutathione peroxidase improved during the fishing season despite elevated methylmercury exposure. The beneficial effects of seasonal fishing activity and fish consumption on cardiovascular health may suppress detrimental effects of concomitant moderate methylmercury exposure.

Distribution of tocopheryl quinone in mitochondrial membranes and interference with ubiquinone-mediated electron transfer

Alpha-tocopherol (Toc) is an efficient lipophilic antioxidant present in all mammalian lipid membranes. This chromanol is metabolized by two different pathways: excessive dietary Toc is degraded in the liver by side chain oxidation, and Toc acting as antioxidant is partially degraded to alpha-tocopheryl quinone (TQ). The latter process and the similarity between TQ and ubiquinone (UQ) prompted us to study the distribution of TQ in rat liver mitochondrial membranes and the interference of TQ with the activity of mitochondrial and microsomal redox enzymes interacting with UQ. In view of the contradictory literature results regarding Toc, we determined the distribution of Toc, TQ, and UQ over inner and outer membranes of rat liver mitochondria. Irrespective of the preparation method, the TQ/Toc ratio tends to be higher in mitochondrial inner membranes than in outer membranes suggesting TQ formation by respiratory oxidative stress in vivo. The comparison of the catalytic activities using short-chain homologues of TQ and UQ showed decreasing selectivity in the order complex II (TQ activity not detected)>Q(o) site of complex III>Q(i) site of complex III>complex I approximately cytochrome b(5) reductase>cytochrome P-450 reductase (comparable reactivity of UQ and TQ). TQ binding to some enzymes is comparable to UQ despite low activities. These data show that TQ arising from excessive oxidative degradation of Toc can potentially interfere with mitochondrial electron transfer. On the other hand, both microsomal and mitochondrial enzymes contribute to the reduction of TQ to tocopheryl hydroquinone, which has been suggested to play an antioxidative role itself.

Peroxynitrite Decreases Hemostasis in Human Plasma In Vitro

Coagulopathy has been associated with clinical scenarios that involve reactive nitrogen species such as peroxynitrite (OONO-). Further, OONO- decreases tissue factor and fibrinogen function in vitro. Thus, we hypothesized that exposure of plasma to the OONO- generated with 3-morpholinosydnonimine (SIN-1), a molecule that produces both nitric oxide and superoxide, would result in a decrease in hemostatic function via diminished coagulation protein activity. Hemostatic function of plasma exposed to SIN-1 (0, 1, 5, and 10 mM for 60 min at 37 degrees C) was assessed with thrombelastography, activated partial thromboplastin time, and prothrombin time in the presence or absence of superoxide dismutase (SOD) or an OONO- scavenger. SIN-1 exposure resulted in a significant (P < 0.05), dose-dependent decrease in plasma hemostatic function and concurrent significant (P < 0.05) decreases in activities of factor VII, factor VIII complex, and factor X. Fibrinogen concentration was not affected by SIN-1. Antithrombin and protein C activity also decreased significantly (P < 0.05). Coincubation with SOD or an OONO- scavenger significantly (P < 0.05) attenuated SIN-1 mediated changes in hemostasis and procoagulant/ anticoagulant activity. We conclude that OONO- may decrease hemostatic function in human plasma by nitration of key procoagulants and that OONO- may play a significant role in hemorrhagic states.

Redox-interaction of α-tocopheryl quinone with isolated mitochondrial cytochrome bc1 complex

The homogenous distribution of vitamin E in lipid membranes is a prerequisite for its universal function as lipophilic antioxidant. Its antioxidant activity leads to the irreversible formation of alpha-tocopheryl quinone (TQ) in those membranes. Very little is known about the interference of TQ with redox-cycling enzymes normally interacting with ubiquinone (UQ), which exerts important bioenergetic functions in the mitochondrial respiratory chain. One of the most complex redox reactions of the respiratory chain is the interaction of reduced UQ (UQH(2)) with the cytochrome bc(1) complex (ubiquinol:cytochrome c reductase, EC 1.10.2.2). The aim of this study was to elucidate the influence of TQ on the electron transfer from UQH(2) to cytochrome c via the isolated mitochondrial cytochrome bc(1) complex. Although TQ is present in substoichiometric amounts with respect to UQ in mitochondria and in our experiments with isolated bc(1) complex, we observed a decrease of the total electron transfer rate via the bc(1) complex with increasing amounts of TQ. Both reduced TQ (TQH(2)) and UQH(2) are able to reduce b-cytochromes in the bc(1) complex, however, they act in a completely different way. While reduction of b-cytochromes by UQH(2) can occur both via the Q(o) and the Q(i) pocket of the cytochrome bc(1) complex, TQH(2) can preferably reduce b-cytochromes via the Q(i) pocket. These differences are also reflected by the extremely low turnover numbers of the bc(1) activity for TQ/TQH(2) compared to UQ/UQH(2) suggesting that TQ/TQH(2) acts as a weak competitive inhibitor for binding sites of UQ/UQH(2). In contrast, the oxidation properties of TQ and UQ are similar. Furthermore, oxidized TQ was observed to decrease the O(2)(*)(-) release rate of UQH(2)-consuming cytochrome bc(1) complex. These findings suggest that the irreversible oxidation of vitamin E to TQ in mitochondrial membranes causes a downregulation of respiratory activities as well as a lower O(2)(*)(-) formation rate by the cytochrome bc(1) complex.

Alpha-tocopherol and alpha-tocopheryl quinone levels in cervical intraepithelial neoplasia and cervical cancer

OBJECTIVE

alpha-Tocopherol is a potent antioxidant that protects cell membranes against oxidative damage. Red blood cell alpha-tocopherol levels reflect membrane alpha-tocopherol concentrations, and altered levels may suggest membrane damage. The objective of this study was to determine the levels of alpha-tocopherol and alpha-tocopheryl quinone, the oxidized product of alpha-tocopherol, in plasma and red blood cells that were obtained from control subjects and patients with cervical intraepithelial neoplasia and cervical cancer.

STUDY DESIGN

In this cross-sectional study, 72 women, (32 African American and 40 Hispanic) were recruited. Among these subjects, 37 women had cervical intraepithelial neoplasia; 14 women had cervical cancer, and 21 women were considered control subjects, who had normal Papanicolaou test results. alpha-Tocopherol and alpha-tocopheryl quinone levels were determined in red blood cell and plasma by high-pressure liquid chromatography.

RESULTS

Plasma levels of alpha-tocopherol and alpha-tocopheryl quinone were decreased significantly (P=.012 and=.005, respectively, by Kruskal-Wallis test) in study groups compared with the control group; red blood cell levels of alpha-tocopherol and alpha-tocopheryl quinone were not altered significantly.

CONCLUSION

The lower alpha-tocopherol level that was observed in this study is consistent with our previous reports of decreased antioxidant concentrations and increased oxidative stress in women with cervical intraepithelial neoplasia. Unaltered red blood cell alpha-tocopherol and alpha-tocopheryl quinone levels suggest undamaged cell membrane. Further studies are needed to investigate the potential role of oxidative stress in cervical intraepithelial neoplasia.

Is elective abdominal aortic aneurysm repair accompanied by high grade oxidative stress?

BACKGROUND AND AIMS

During elective abdominal aortic aneurysm repair (AAAR), lower torso ischaemia-reperfusion event is unavoidable. Previous studies on AAAR have reported the importance of oxidative stress (OS) in ischaemia-reperfusion injury, however, the grade of OS has not been adequately clarified up to now. The aim of this study was to perform a complex investigation of the time-course and grade of systemic and cellular OS in patients undergoing AAAR.

MATERIAL AND METHODS

Arterial blood samples were taken from 18 patients undergoing elective AAAR (at four points in time: before anaesthesia, 5 min after aortic clamping and 5 min and 30 min after clamp removal). Diene conjugates (DC), thiobarbituric acid reactive substances (TBARS), total antioxidative capacity (TAC), glutathione redox ratio (GSSG/GSH), and levels of antioxidative enzymes as superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSHPx) were measured from the radial arterial blood.

RESULTS

30 min after the removal of the aortic cross-clamp, arterial CAT showed significant elevation (96.0 vs 56.9 U/l, p < 0.05); GSHPx was significantly elevated (51.5 vs 39.9 U/g Hgb, p < 0.05) and TAC was decreased (31.4 vs 36.5%, p < 0.05) in comparison with preoperative value.

CONCLUSIONS

We found limited alterations of several OS parameters, which do not characterize either systemic or cellular high-grade OS during elective AAAR.

Infants discriminate between natural and synthetic vitamin E

BACKGROUND

In adults, RRR-alpha-tocopheryl acetate (natural vitamin E) has approximately twice the biological activity of all-rac-alpha-tocopherol (synthetic vitamin E). Similar studies have not been done in term infants.

OBJECTIVE

We evaluated the vitamin E and antioxidant status of term infants fed formulas differing in the amount and form of vitamin E acetate.

DESIGN

A controlled, blinded, multisite study was completed with 77 term infants randomly assigned to 1 of 3 different infant-formula groups. The HIGHNAT-E formula (n = 26) contained 20 IU RRR-alpha-tocopheryl acetate/L (14.5 mg/L), the LOWNAT-E formula (n = 25) contained 10 IU RRR-alpha-tocopheryl acetate/L (7.3 mg/L), and the SYN-E formula (n = 26) contained 13.5 IU synthetic all-rac-alpha-tocopheryl acetate/L (13.5 mg/L). A human milk-fed group (n = 29) served as a reference.

RESULTS

Although the LOWNAT-E formula contained only one-half the concentration of alpha-tocopherol that the SYN-E formula did (7.3 compared with 13.5 mg/L), the infants fed the LOWNAT-E formula had plasma alpha-tocopherol concentrations that were not significantly different from those of the infants fed the SYN-E formula. However, alpha-tocopherol intakes in the study population, when expressed as mg 2R-tocopherol isomers consumed/d, correlated with plasma alpha-tocopherol (r = 0.20, P = 0.02) and the ratio of plasma alpha-tocopherol to lipids (r = 0.19, P = 0.03). There were no significant differences in antioxidant status between the 3 groups, but the LOWNAT-E group showed a trend toward lower plasma isoprostanes.

CONCLUSIONS

This study supports the new definition for vitamin E given in the 2000 Dietary Reference Intakes and suggests that infants discriminate between RRR-alpha-tocopheryl acetate and all-rac-alpha-tocopheryl acetate. All 3 infant formulas supported adequate vitaminE status.

Limited effects of micronutrient supplementation on strength and physical function after abdominal aortic aneurysmectomy

BACKGROUND

Tissue injury following ischemia-reperfusion is mediated in part by free oxygen radicals. We hypothesized that perioperative micronutrient supplementation would augment antioxidant defenses, minimize muscle injury, and minimize postoperative decreases in muscle strength and physical function following abdominal aortic aneurysmectomy.

SETTING

A university-affiliated hospital and regional referral center.

DESIGN

A randomized, double-blind, placebo-controlled trial of supplementation with beta-carotene, vitamins C and E, zinc, and selenium for a period of 2-3 weeks prior to surgery and 1 week thereafter.

STUDY POPULATION

Patients undergoing elective abdominal aortic aneurysmectomy (n=18 per group).

PRINCIPAL MEASUREMENTS

Handgrip and other measures of strength and physical function.

RESULTS

Handgrip and quadriceps strength decreased following surgery, but not to a significantly different extent in the placebo and supplemented groups. Self-rated physical function decreased following surgery in the placebo group and was preserved in the supplemented group.

CONCLUSIONS

Perioperative supplementation with micronutrients with antioxidant properties has limited effects on strength and physical function following major elective surgery.

Multi-antioxidant supplementation does not prevent an increase in gut permeability after lower torso ischemia and reperfusion in humans

BACKGROUND

An increase in gut permeability can have serious consequences leading to sepsis and multiple organ failure. After lower torso ischemia an increase in gut permeability is seen in both animals and humans. There is proof that this can be modified by antioxidant supplementation.

METHODS

In this prospective, randomized study we have looked at the influence of a multiantioxidant supplementation regime, using allopurinol, vitamins E and C, mannitol and N-acetylcysteine, perioperatively. Twenty-two patients received standard treatment and 20 patients received supplementation. Gut permeability was determined using a double sugar test with lactulose and rhamnose.

RESULTS

A significant increase in gut permeability was found neither in the non-treatment group (p = 0.012) nor in the treatment group (p = 0.006) after 6 and 24 h. No difference was found between the group receiving antioxidants and the standard treatment group. p = 0.93 6 h post clamp; p = 0.97 24 h post clamp.

CONCLUSION

In this study we have not found an influence of multiantioxidant supplementation on gut permeability after lower torso ischemia. Possible explanations for this negative result are being discussed.

Extraperitoneal Approach Reduces Neutrophil Activation, Systemic Inflammatory Response and Organ Dysfunctionin Aortic Aneurysm Surgery

OBJECTIVES

to compare the effects of transperitoneal and extraperitoneal approaches on systemic inflammatory response, neutrophil activation and organ dysfunction in elective abdominal aortic aneurysm (AAA) repair.

PATIENTS AND METHODS

twenty patients admitted for elective infrarenal AAA repair were prospectively randomised into transperitoneal (n =10) or extraperitoneal ( n =10) groups. Neutrophil activation was assessed by measuring the plasma levels of neutrophil elastase/alpha(1)-anti-trypsin complexes before surgery, intraoperatively and at 6 h, 12 h, 24 h and then daily after surgery. Venous blood samples for estimation of liver function tests, full blood counts, urea and electrolytes and arterial samples for blood gas analysis were taken daily from preoperatively to day 5 after surgery. Multiple organ dysfunction (MOD) and systemic inflammatory response (SIR) scores were calculated daily.

RESULTS

the concentrations of neutrophil elastase/alpha(1)-anti-trypsin complexes were significantly higher in the transperitoneal group at 6 h after surgery compared to the extraperitoneal group (799(455-921) ng/ml (median(i.q.r.)) vs 307(171-395) ng/ml, p<0.005), and at 12 h (397(364-936) ng/ml vs 319(134-352) ng/ml, p <0.05). The MOD scores were significantly higher in the transperitoneal group in comparison to the extraperitoneal group at day 1 (2.5(2-3.3) vs 1(0-1), p<0.001) and day 2 (2.5(2-3.3) vs 1(0-1), p <0.001). The SIR scores were also significantly higher at day 1 (1(0-2) vs 0, p <0.01), day 2 (1.5(0-2.3) vs 0, p <0.01), and day 3 (1(0-1) vs 0, p <0.05).

CONCLUSIONS

neutrophil activation, systemic inflammatory response and organ dysfunction are increased in elective AAA repair when a transperitoneal approach is used. This may be related to intestinal manipulation and mesenteric traction which are reduced in the extraperitoneal approach.

Profiles of antioxidants in human plasma

The profile of antioxidants in biological fluids and tissues may be helpful in assessing oxidative stress in humans. Plasma antioxidants can be decreased as compared to established normal values, in abnormal or subnormal conditions, for instance as a consequence of disease-related free radical production. Alternatively, plasma antioxidants may be below the normal range due to insufficient dietary supply. Therefore, the profile of antioxidants can be of use only in conjunction with other parameters of the oxidative stress status. This article examines the profiles of plasma antioxidants in oxidative stress-related conditions, e.g., diabetes and some other diseases, as well as smoking and smoking cessation.

Systemic consequences of oxidative stress following aortic surgery correlate with the degree of antioxidant defenses

The purpose of this study was to correlate the preoperative level of antioxidant defenses, measured by the plasma total antioxidant capacity (TAC), to the degree of postoperative systemic inflammatory response, measured by the severity of pulmonary injury following elective aortic surgery. Twenty-four patients had TAC measured preoperatively and 24 hr postoperatively. Chest radiography and arterial blood gases were obtained preoperatively and serially during the first 24 hr after surgery. Using objective radiologic criteria and blood gas analysis, the degree of pulmonary edema and pulmonary dysfunction were quantified. All patients showed evidence of pulmonary dysfunction in the first 24 hr following surgery. Fifteen of the 24 patients showed radiographic evidence of noncardiogenic pulmonary edema in the immediate postoperative period. In this group, the TAC was lower than in those without pulmonary edema immediately following surgery (p = 0.03). Preoperative TAC was associated with the degree of pulmonary edema in the postoperative period (r = -0.372, p = 0.067). These results suggest that preoperative antioxidant supplementation may favorably impact the severity of systemic inflammatory response following ischemia and reperfusion injury.

Quantification of the alpha- and gamma-tocopherol metabolites 2,5,7, 8-tetramethyl-2-(2'-carboxyethyl)-6-hydroxychroman and 2,7, 8-trimethyl-2-(2'-carboxyethyl)-6-hydroxychroman in human serum

alpha- and gamma-tocopherol are the major vitamin E compounds found in human blood and tissues. The metabolites are 2,5,7, 8-tetramethyl-2-(2'-carboxyethyl)-6-hydroxychroman (alpha-CEHC) and 2,7,8-trimethyl-2-(2'-carboxyethyl)-6-hydroxychroman (gamma-CEHC, LLU-alpha), respectively. alpha-CEHC is excreted mainly as glucuronide or sulfate conjugates in the urine. Here we describe a sensitive and reliable method to analyze alpha- and gamma-CEHC in human serum. The concentration of alpha-CEHC in human serum is in the range of 5-10 pmol/ml but increases significantly up to 200 pmol/ml upon supplementation with RRR-alpha-tocopherol. About one-third of the alpha-CEHC circulating in the blood is present as a glucuronide conjugate. Baseline levels of gamma-CEHC are about 50 to 85 pmol/ml.

Comparative study on dynamics of antioxidative action of alpha-tocopheryl hydroquinone, ubiquinol, and alpha-tocopherol against lipid peroxidation

Alpha-tocopheryl quinone is a metabolite of alpha-tocopherol (TOH) in vivo. The antioxidant action of its reduced form, alpha-tocopheryl hydroquinone (TQH2), has received much attention recently. In the present study, the antioxidative activity of TQH2 was studied in various systems in vitro and compared with that of ubiquinol-10 (UQH2) or TOH to obtain the basic information on the dynamics of the antioxidant action of TQH2. First, their hydrogen-donating abilities were investigated in the reaction with galvinoxyl, a stable phenoxyl radical, and TQH2 was found to possess greater second-order rate constant (1.0 x 10(4) M(-1) s(-1)) than UQH2 (6.0 x 10(3) M(-1) s(-1)) and TOH (2.4 x 10(3) M(-1) s(-1)) at 25 degrees C in ethanol. The stoichiometric numbers were obtained as 1.9, 2.0, and 1.0 for TQH2, UQH2, and TOH, respectively, in reducing galvinoxyl. Second, their relative reactivities toward peroxyl radicals were assessed in competition with N,N'-diphenyl-p-phenylenediamine (DPPD) and found to be 6.0 (TQH2), 1.9 (UQH2), and 1.0 (TOH). Third, their antioxidant efficacies were evaluated in the oxidation of methyl linoleate in organic solvents and in aqueous dispersions. The antioxidant potency decreased in the order TOH > UQH2 > TQH2, as assessed by either the extent of the reduction in the rate of oxidation or the duration of inhibition period. The reverse order of their reactivities toward radicals and their antioxidant efficacies was interpreted by the rapid autoxidation of TQH2 and UQH2, carried out by hydroperoxyl radicals. Although neither TQH2 nor UQH2 acted as a potent antioxidant by itself, they acted as potent antioxidants in combination with TOH. TQH2 and UQH2 reduced alpha-tocopheroxyl radical to spare TOH, whereas TOH suppressed the autoxidation of TQH2 and UQH2. In the micelle oxidation, the antioxidant activities of TQH2, UQH2, and TOH were similar, whereas 2,2,5,7,8-pentamethyl-6-chromanol exerted much more potent efficacy than TQH2, UQH2, or TOH. These results clearly show that the antioxidant potencies against lipid peroxidation are determined not only by their chemical reactivities toward radicals, but also by the fate of an antioxidant-derived radical and the mobility of the antioxidant at the microenvironment.

Metabolism of vitamin A in the heart increases after a myocardial infarction

The supply of vitamin A to the myocardium by storage organs during increased oxidative stress subsequent to myocardial infarction (MI) was examined in hemodynamically assessed rats using compartment analysis of a radio-labeled vitamin A. 3H-Vitamin A was injected into two groups of rats: an MI group and a control group. There were no differences in the plasma or myocardial content of total vitamin A (unlabeled + labeled) between the two groups. However, the proportion of 3H-vitamin A was greater in the myocardium as well as plasma of MI rats. Rats with MI also had significantly lower 3H-vitamin A levels in liver and kidney than sham controls. The greatest difference in vitamin A content was in the concentrations of 3H-labeled storage forms of vitamin A in the liver of MI animals. Activity of bile salt-dependent retinyl ester hydrolase, an enzyme responsible for hydrolyzing vitamin A storage forms, was significantly increased in the liver of MI animals. These data indicate that analysis of plasma concentrations of vitamin A to ascertain links to cardiac conditions may be inappropriate. Specifically, during MI, increased amounts of vitamin A are mobilized from the liver to the heart without changing plasma concentrations. This is facilitated by an increase in the activity of an enzyme that hydrolyzes vitamin A storage forms.

Mobilization of antioxidant vitamin pools and hemodynamic function after myocardial infarction

BACKGROUND

Although most previous studies have attempted to correlate plasma concentrations of vitamins with specific cardiovascular end points, metabolic considerations suggest that changes in myocardial tissue and storage organs may be better indicators of myocardial oxidative stress.

METHODS AND RESULTS

Rats fed commercial chow or a diet enriched with vitamin E for 2 weeks were subjected to either a surgical myocardial infarction (MI) or a sham procedure. Rats were hemodynamically assessed 16 weeks after surgery, and their heart, liver, kidney, and plasma were analyzed for antioxidant vitamins E (tocopherol) and A (retinol and total retinyl esters). At 16 weeks, MI rats on a control diet showed depressed peak systolic and elevated diastolic pressures in both right and left ventricles compared with their sham controls. Plasma concentrations of vitamins E and A in MI rats were not different from sham controls fed the same diet. However, concentrations of vitamin E in left ventricle and liver and of vitamin A in liver (retinol) and kidney (retinyl esters) were decreased in rats with MI compared with the sham controls. Vitamin E supplementation improved hemodynamic function in rats with MI and increased plasma, myocardial, liver, and kidney concentrations of vitamin E. The vitamin E diet also prevented the loss of total retinyl esters from the kidney but not of retinol from the liver in MI rats.

CONCLUSIONS

Dietary supplements of vitamin E can sustain better cardiac function subsequent to MI. Antioxidant vitamin levels in the myocardium or in storage organs and not in plasma may be better indicators of myocardial oxidative stress.

The effects of chronic alpha-tocopherol administration on lipid peroxidation in an experimental model of acute spinal cord injury

Most of the numerous experimental studies to research pathophysiological changes following acute spinal cord injury suggest a two-step mechanism of damage to the spinal cord in which the primary (direct) or mechanical injury caused by the trauma initiates secondary (indirect) or progressive autodestructive injury of the cord. During recent years, free oxygen radical generation and lipid peroxidation have been considered to be responsible for secondary autodestructive injury. Alpha tocopherol occupies an important and unique position in the overall antioxidant defense. Alpha tocopherol-depleted animals are generally more susceptible to the adverse effects of environmental agents than are supplemented animals. This study was planned to study the effectiveness in counteracting this autodestructive process by supplementing alpha-tocopherol in rats maintained on a nutritionally adequate diet, and also to evaluate whether it will provide additional protection or not. Eighty healthy Wistar rats (treatment and controls) were included. The treatment group received 100 mg/kg alpha tocopherol each day, intraperitoneally for seven days. Using a standard acute spinal cord trauma model in Wistar rats trauma was applied, an malondialdehyde (MDA) which is a lipid peroxidation product was measured in the traumatized spinal cord at various times following the trauma in order to indirectly evaluate the lipid peroxidation and generation of free oxygen radicals in a time sequence. Statistical analysis of the values demonstrated that malondialdehyde formation in the alpha-tocopherol administered group was significantly lower than in the control group. These findings indicate that longterm administration of alpha-tocopherol may be useful to decrease lipid peroxidation following acute spinal cord trauma.

Effect of alpha-tocopherol pretreatment on high energy metabolites in rabbit skeletal muscle after ischemia-reperfusion

The ability of skeletal muscle to recover high energy phosphate compounds in response to pretreatment with vitamin E was investigated in a rabbit hindlimb ischemia/reperfusion model (2. 5 h/2 h). High energy metabolites were measured in the adductor magnus muscle of untreated animals and compared to the treatment group (all rac-alpha-tocopheryl acetate, 3 mg/kg body weight, supplemented i.v. before the onset of ischemia). Phosphocreatine (PCr) levels decreased after ischemia more than 65% in untreated and treatment groups, but tended to recover in treatment group after reperfusion. Adenosine triphosphate (ATP) values decreased by 50% of basal level after reperfusion in the untreated group, whereas alpha-tocopherol pretreatment prevented ATP depletion.

Plasma vitamins E and C concentrations of adult patients during cardiopulmonary bypass

OBJECTIVE

This study was designed with two aims: 1) to determine if the coronary artery bypass graft (CABG) procedure alters plasma vitamin E and C concentrations of adult patients through repeated determinations of vitamin levels at time points before, during and following CABG, and 2) to assess whether plasma vitamin E concentrations reflect myocardial tissue content.

METHODS

A consecutive sample of 38 patients undergoing CABG surgery at a Midwest tertiary care hospital was enrolled. Patients receiving blood transfusions before or during surgery were excluded.

RESULTS

Plasma vitamin E/total lipid ratios rose with reperfusion, remained elevated immediately following bypass, and fell to preoperative concentrations by 24 hours. Plasma vitamin E/total cholesterol levels varied little throughout this time course. Both plasma uric acid and ascorbate concentrations (corrected for hemodilution) also rose by the preischemic interval, and remained elevated until a return to preoperative levels by 24 hours. Corrected malondialdehyde (MDA) concentrations rose by pre-ischemia but returned more quickly to preoperative levels. Atrial appendage tissue vitamin E concentrations bore a significant relationship to those of plasma prior to surgery (r=+0.49, p=0.004). Reported supplement use, plasma concentrations and body mass index contributed to the variability in atrial tissue concentrations of vitamin E.

CONCLUSIONS

In short, when not confounded by transfusions or hemodilution, several peripheral indices of antioxidants increase with the reperfusion segment of CABG procedure and return to baseline levels within 24 hours of surgery. Parallel changes in MDA were observed. The observed changes are consistent with the hypothesis that oxidative stress accompanies the ischemia-reperfusion components of the CABG procedure.

Alpha-tocopheryl hydroquinone is an efficient multifunctional inhibitor of radical-initiated oxidation of low density lipoprotein lipids

As the oxidation of low density lipoprotein (LDL) lipids may be a key event in atherogenesis, there is interest in antioxidants as potential anti-atherogenic compounds. Here we report that alpha-tocopheryl hydroquinone (alpha-TQH2) strongly inhibited or completely prevented the (per)oxidation of ubiquinol-10 (CoQ10H2), alpha-tocopherol (alpha-TOH), and both surface and core lipids in LDL exposed to either aqueous or lipophilic peroxyl radicals, Cu2+, soybean lipoxygenase, or the transition metal-containing Ham's F-10 medium in the absence or presence of human monocyte-derived macrophages. The antioxidant activity of alpha-TQH2 was superior to that of several other lipophilic hydroquinones, including endogenous CoQ10H2, which is regarded as LDL's first line of antioxidant defence. At least three independent activities contributed to the antioxidant action of alpha-TQH2. First, alpha-TQH2 readily associated with LDL and instantaneously reduced the lipoprotein's ubiquinone-10 to CoQ10H2, thereby maintaining this antioxidant in its active form. Second, alpha-TQH2 directly intercepted aqueous peroxyl radicals, as indicated by the increased rate of its consumption with increasing rates of radical production, independent of LDL's content of CoQ10H2 and alpha-TOH. Third, alpha-TQH2 rapidly quenched alpha-tocopheroxyl radical in oxidizing LDL, as demonstrated directly by electron paramagnetic resonance spectroscopy. Similar antioxidant activities were also seen when alpha-TQH2 was added to high-density lipoprotein or the protein-free Intralipid, indicating that the potent antioxidant activity of alpha-TQH2 was neither lipoprotein specific nor dependent on proteins. These results suggest that alpha-TQH2 is a candidate for a therapeutic lipid-soluble antioxidant. As alpha-tocopherylquinone is formed in vivo at sites of oxidative stress, including human atherosclerotic plaque, and biological systems exist that reduce the quinone to the hydroquinone, our results also suggest that alpha-TQH2 could be a previously unrecognized natural antioxidant.

Vitamin E protects human skeletal muscle from damage during surgical ischemia-reperfusion

PURPOSE

The biochemical and morphological alterations induced in lower limb skeletal muscle by ischemia-reperfusion (I-R) during aortic surgery and the effect of vitamin E pretreatment were investigated.

METHODS

Two groups of patients undergoing aortic aneurysm resection, one untreated and one treated with vitamin E, were examined. Quadricep muscle biopsies were taken after induction of anesthesia, at the end of ischemia, and after reperfusion. The malondialdehyde (MDA) content and morphology of biopsies were examined to assess peroxidative processes.

RESULTS

Ischemia did not induce an increase in MDA content but did increase neutrophil infiltration in muscle fibers of untreated patients. Reperfusion led to a significant increase in MDA content and to intermyofibrillar edema and mitochondrial swelling. The MDA content was not increased during ischemia and neutrophil infiltration was minimal in vitamin E treated patients. At reperfusion, the MDA content, the ultrastructural injuries and neutrophil infiltration were significantly reduced by the treatment.

CONCLUSIONS

Vitamin E is effective in reducing the oxidative muscle damage occurring after a period of I-R.

Lipid peroxidation-associated oxidative stress during percutaneous transluminal coronary angioplasty in humans

Animal studies suggest that myocardial ischemia/reperfusion causes oxidative stress. We, therefore, examined whether routinely performed percutaneous transluminal coronary angioplasty (PTCA) might be a human ischemia/reperfusion model for oxidative stress-induced lipid peroxidation. Fasting antecubital venous blood was sampled from 13 patients on the morning of PTCA, and 2 d after PTCA. Venous and coronary arterial blood were sampled just before and 10 min after the first balloon inflation. Samples were analyzed for plasma and LDL lipid hydroperoxide levels, in vitro oxidation of LDL, and LDL antioxidant levels. Lipid hydroperoxide levels in plasma and LDL remained unchanged throughout the study. During the first 10 min of PTCA, the lag time during oxidation of LDL in vitro did not change, but the maximum rate of oxidation decreased in venous and arterial samples (Wilcoxon signed rank test: p < .002). At the same time, total tocopherol levels in LDL significantly increased by 6.3% (p = .048) in arterial, but not in venous samples. Total carotenoid levels increased by 3.8% (p = .127) in arterial samples and decreased by 2.9% (p = .040) in venous samples. Forty hours after PTCA, LDL oxidation parameters and LDL antioxidant levels were similar to baseline, except for about 17% lower levels of delta-tocopherol (p = .037) and gamma-tocopherol (p = .014). Our results, therefore, do not support that PTCA in humans is associated with oxidative stress-induced lipid peroxidation.

Antioxidant depletion during aortic aneurysm repair

Ischaemia-reperfusion injury generates oxygen-derived free radicals leading to local and distant damage. A simple method of following oxidative activity is to measure the consumption of endogenous scavenging antioxidants; an enhanced chemiluminescent assay was used to study this phenomenon in 21 patients undergoing surgery for abdominal aortic aneurysm (AAA). Samples of peripheral venous blood were taken before induction of anaesthesia and then from a central venous line and the inferior mesenteric vein before, during, and after clamping of the aorta. Further specimens were taken from the central line at 2, 6 and 24 h after operation. Antioxidant concentration in the peripheral, central and inferior mesenteric blood were similar, indicating that anaesthesia and surgical dissection had no effect. Levels decreased significantly in central and inferior mesenteric blood during and after clamping, but returned to normal by 24 h. These results confirm ischaemia-reperfusion phenomena in AAA repair.

Is alpha-tocopherol a reservoir for alpha-tocopheryl hydroquinone?

The products of oxidation of the alpha-tocopherol model compound, 2,2,5,7,8-pentamethyl-6-chromanol (PH) by t-butyl hydroperoxide in chloroform varied with the amount of water present. In the presence of a trace of water, the main products were the spirodimer (PSD) and spirotrimer (PST). As the content of water increased, the main product became 2-(3-hydroxy-3-methylbutyl)-3,5,6-trimethyl-1,4-benzoquinone (PQ). Oxidation of PH in aqueous liposome suspension also produced PQ as the major product. These results suggested that, in aqueous solutions, the major oxidation product of PH would be PQ and of alpha-tocopherol (TH) would be alpha-tocopheryl quinone (TQ). The ease of reduction of PQ and TQ was studied in chemical and biological systems. PQ, TQ, and ubiquinone-10 (UQ) were rapidly reduced to their respective hydroquinones (PQH2, TQH2, and UQH2) at pH 7.3 by NADH plus FAD. Whole blood reduced PQ rapidly at 37 degrees C to PQH2 but did not reduce TQ to TQH2. Human peripheral blood mononuclear cells took up TQ from a bovine serum albumin complex and reduced it to TQH2. Ingestion of TQ (350 mg) by one of us (PSK) resulted in the formation of TQH2 during a 5 h period. These results demonstrate that several biological systems are able to reduce TQ to TQH2 and that it is a reaction that may occur normally in vivo.

Sequential oxidative damage, and changes in iron-binding and iron-oxidising plasma antioxidants during cardiopulmonary bypass surgery

Cardiopulmonary bypass patients undergoing heart valve replacement surgery appear to be under oxidative stress, when compared with normal healthy controls, by showing increased levels of protein and lipid damage. During bypass surgery two further episodes of oxidative stress occur. The first is seen when patients are placed on extracorporeal blood circulation and oxygenation which results in a rise in lipid peroxides and thiobarbituric acid-reactive substances. The second phase of oxidative stress occurs during reperfusion of the myocardium following removal of the aortic cross clamp. Coincident with evidence of increased oxidative damage to lipids during these latter phases of oxidative stress were decreases in plasma iron-binding and iron-oxidising antioxidant activities.

Vitamin, trace element and peroxide status in HIV seropositive patients: asymptomatic patients present a severe beta-carotene deficiency

We have investigated whether nutritional status and peroxidation process are associated with the degree of development of HIV infection. This was done by measuring the status of vitamins (E, A and beta-carotene), of antioxidant trace elements (zinc, selenium) and lipid peroxide levels (lipid hydroperoxides and thiobarbituric acid reactants) in HIV-seropositive patients at CDC II and CDC IV stages and in comparison with normal subjects. There was a decrease in vitamin and trace element levels related to the severity of disease. The most dramatic decrease, however, was seen for carotenoids (0.94 +/- 0.46 mumol/l) and beta-carotene (0.24 +/- 0.14 mumol/l vs. 0.56 +/- 0.29 mumol/l) whose stage II levels were only half the normal value. Paradoxically, lipid peroxidation was higher at stage II than at stage IV. This can be attributed to an overproduction of oxygen radicals by polymorphonuclears in stage II. This deficiency in antioxidant status, often found in patients suffering from peroxidative diseases, may have important consequences on cellular immunity. Furthermore, the concomitant overproduction of free radicals may also affect HIV multiplication.

Ascorbyl free radical: a noninvasive marker of oxidative stress in human open-heart surgery

To assess the development of oxidative stress in cardiac ischemia/reperfusion, the resulting depletion of plasma ascorbate was monitored by electron spin resonance spectroscopic detection of ascorbyl free radical (AFR) in a homogeneous group of 12 patients undergoing aortic valve replacement. Dimethyl sulfoxide (DMSO) was used as an enhancer and stabilizer for AFR in plasma separated from blood samples collected 15 min before incision, 10 min before aortic declamping, and sequentially during the initial 30 min of reperfusion. Plasma DMSO/AFR levels of patients were found to be significantly lower than in healthy subjects (-25%), further decreased upon ischemia (-35%), dropped to their lowest values within the first 10 min of reperfusion (-46%), and did not recover their initial values within 30 min following reflow. Cardiac index measurements revealed a still depressed heart function 4 h postdeclamping and a more delayed tissue injury was evidenced by cardiac myosin and myoglobin release in plasma. DMSO/AFR levels at early reperfusion were slightly (+ 12%) higher in plasma obtained from coronary sinus samples than in plasma from peripheral blood, suggesting an extra ascorbate release from the injured heart tissue. The close analogy between these results and the reported measurements of other plasma markers of oxidative stress, including ascorbate, indicates that the present method could be of great value in clinical practice.

Antioxidant effectiveness in ischemia-reperfusion tissue injury

In summary, much evidence supports the formation of toxic oxygen metabolites in ischemic reperfused tissue. Tissues are equipped with both an intracellular and extracellular antioxidant defense system. The defense system can also be divided into enzymatic and nonenzymatic defenses. Important components of a nonenzymatic antioxidant include alpha-tocopherol, ascorbic acid, and beta-carotene as well as other compounds that can react with radicals to form less reactive products such as sulfur-containing amino acids. Extracellular fluid comprises a second line of defense against oxidant injury. These extracellular antioxidants include ceruloplasmin, albumin, transferrin, haptoglobin, and uric acid. The oxidant injury can potentially occur during ischemia and reperfusion due to (1) an excess production of oxygen free radicals, (2) a decrease in antioxidant defenses, or (3) both. Because antioxidants function by removing the toxic oxygen metabolites, they are generally highly effective in reducing ischemia-reperfusion injury.

Loss of alpha-tocopherol upon exposure to nitric oxide or the sydnonimine SIN-1

SIN-1 which spontaneously decomposes to yield nitric oxide (NO.) and superoxide anion (O2.-) radicals caused a loss of microsomal alpha-tocopherol paralleled by the formation of alpha-tocopheryl quinone. The loss was partially prevented by superoxide dismutase but not by catalase. The SIN-1-induced loss of alpha-tocopherol also occurred when tocopherol was dissolved in ethanol/potassium phosphate buffer (20/80, v/v). Likewise, addition of authentic NO. to alpha-tocopherol dissolved in ethanol resulted in loss of the vitamin and quinone formation. These results suggest that NO. or its products such as peroxynitrite or nitrogen dioxide react with alpha-tocopherol, the quinone derivative being a major oxidation product. Depletion of vitamin E by NO. may contribute to tissue injury, e.g. in neuronal tissues.