Electron spin resonance spectroscopy, exercise, and oxidative stress: an ascorbic acid intervention study

Acute exercise and oxidative stress: a 30 year history

The topic of exercise-induced oxidative stress has received considerable attention in recent years, with close to 300 original investigations published since the early work of Dillard and colleagues in 1978. Single bouts of aerobic and anaerobic exercise can induce an acute state of oxidative stress. This is indicated by an increased presence of oxidized molecules in a variety of tissues. Exercise mode, intensity, and duration, as well as the subject population tested, all can impact the extent of oxidation. Moreover, the use of antioxidant supplements can impact the findings. Although a single bout of exercise often leads to an acute oxidative stress, in accordance with the principle of hormesis, such an increase appears necessary to allow for an up-regulation in endogenous antioxidant defenses. This review presents a comprehensive summary of original investigations focused on exercise-induced oxidative stress. This should provide the reader with a well-documented account of the research done within this area of science over the past 30 years.

Effect of exercise on oxidative stress biomarkers

Acute bouts of aerobic and anaerobic exercise can induce a state of oxidative stress, as indicated by an increase in oxidized molecules in a variety of tissues and body fluids. The extent of oxidation is dependent on the exercise mode, intensity, and duration, and is specifically related to the degree of oxidant production. Findings of increased oxidative stress have been reported for both healthy and diseased subjects following single bouts of exercise. While acute exercise has the ability to induce an oxidative stress, this same exercise stimulus appears necessary to allow for an upregulation in endogenous antioxidant defenses. This chapter presents a summary of exercise-induced oxidative stress.

Molecular detection of exercise-induced free radicals following ascorbate prophylaxis in type 1 diabetes mellitus: a randomised controlled trial

AIMS/HYPOTHESIS

Patients with type 1 diabetes mellitus are more susceptible than healthy individuals to exercise-induced oxidative stress and vascular endothelial dysfunction, which has important implications for the progression of disease. Thus, in the present study, we designed a randomised double-blind, placebo-controlled trial to test the original hypothesis that oral prophylaxis with vitamin C attenuates rest and exercise-induced free radical-mediated lipid peroxidation in type 1 diabetes mellitus.

METHODS

All data were collected from hospitalised diabetic patients. The electron paramagnetic resonance spectroscopic detection of spin-trapped alpha-phenyl-tert-butylnitrone (PBN) adducts was combined with the use of supporting markers of lipid peroxidation and non-enzymatic antioxidants to assess exercise-induced oxidative stress in male patients with type 1 diabetes (HbA(1c) 7.9 +/- 1%, n = 12) and healthy controls (HbA(1c) 4.6 +/- 0.5%, n = 14). Following participant randomisation using numbers in a sealed envelope, venous blood samples were obtained at rest, after a maximal exercise challenge and before and 2 h after oral ingestion of 1 g ascorbate or placebo. Participants and lead investigators were blinded to the administration of either placebo or ascorbate treatments. Primary outcome was the difference in changes in free radicals following ascorbate ingestion.

RESULTS

Six diabetic patients and seven healthy control participants were randomised to each of the placebo and ascorbate groups. Diabetic patients (n = 12) exhibited an elevated concentration of PBN adducts (p < 0.05 vs healthy, n = 14), which were confirmed as secondary, lipid-derived oxygen-centred alkoxyl (RO.) radicals (a(nitrogen) = 1.37 mT and abeta(hydrogen) = 0.18 mT). Lipid hydroperoxides were also selectively elevated and associated with a depression of retinol and lycopene (p < 0.05 vs healthy). Vitamin C supplementation increased plasma vitamin C concentration to a similar degree in both groups (p < 0.05 vs pre-supplementation) and attenuated the exercise-induced oxidative stress response (p < 0.05 vs healthy). There were no selective treatment differences between groups in the primary outcome variable.

CONCLUSIONS/INTERPRETATION

These findings are the first to suggest that oral vitamin C supplementation provides an effective prophylaxis against exercise-induced free radical-mediated lipid peroxidation in human diabetic blood.

CLINICAL TRIALS REGISTRATION NUMBER

ISRCTN96164937.

The effect of muscle-damaging exercise on blood and skeletal muscle oxidative stress: magnitude and time-course considerations

The aim of this article is to present the effects of acute muscle-damaging exercise on oxidative stress/damage of animal and human tissues using a quantitative approach and focusing on the time-course of exercise effects. The reviewed studies employed eccentric contractions on a dynamometer or downhill running. The statistical power of each study to detect a 20% or 40% post-exercise change compared with pre-exercise value in each oxidative stress/damage biomarker was calculated. Muscle-damaging exercise can increase free radical levels and augment oxidation of lipids, proteins, glutathione and possibly DNA in the blood. In contrast, the effect of muscle-damaging exercise on concentration of antioxidants in the blood, except for glutathione, was little. Muscle-damaging exercise induces oxidative stress/damage in skeletal muscle, even though this is not fully supported by the original statistical analysis of some studies. In contrast, muscle-damaging exercise does not appear to affect--at least to similar extent as the oxidative stress/damage markers--the levels of antioxidants in skeletal muscle. Based on the rather limited data available, the oxidative stress response of skeletal muscle to exercise was generally independent of muscle fibre type. Most of the changes in oxidative stress/damage appeared and were sustained for days after muscle-damaging exercise. The major part of the delayed oxidative stress/damage production that follows muscle-damaging exercise probably comes from phagocytic cells that are activated and recruited to the site of the initial damage. A point that emerged and potentially explains much of the lack of consensus among studies is the low statistical power of many of them. In summary, muscle-damaging exercise can increase oxidative stress/damage in blood and skeletal muscle of rats and humans that may persist for and/or appear several days after exercise.

Multivitamin-mineral supplementation prevents lipid peroxidation during "the Marathon des Sables"

OBJECTIVE

We investigated the effect of a moderate mutivitamin and mineral supplementation containing mainly vitamin C (150.0 mg.day(-1)), vitamin E (24.0 mg.day(-1)) and beta-carotene (4.8 mg.day(-1)) prior to and during an extreme running competition -the Marathon des Sables (MDS)- that consisted of six long races in the desert.

METHODS

Seventeen athletes participated in our double blind, placebo-controlled study. Blood samples were collected prior to the supplementation i.e. three weeks before the competition (D-21), two days prior to the MDS (D-2), after the third race (D3) and at the end of the competition (D7). Erythrocyte antioxidant enzyme activity (glutathione peroxidase (GPx), superoxide dismutase (SOD)), erythrocyte glutathione level (GSH), plasma non-enzymatic antioxidant status (uric acid, vitamin C, alpha-tocopherol, retinol, beta-carotene), markers of plasma lipid peroxidation (thiobarbituric reactive substances (TBARS)), reactive carbonyl derivatives (RCD) and membrane damage (creatine kinase and lactate dehydrogenase activities) were measured.

RESULTS

In both groups, GSH levels, uric acid levels and membrane damage significantly increased during the competition while SOD activity significantly decreased. In Supplemented group, plasma alpha-tocopherol, beta-carotene and retinol levels significantly increased after three weeks of supplementing. In contrast to Placebo group, alpha-tocopherol, vitamin C and retinol levels were significantly affected by the competition in Supplemented group. Moreover, no increase in TBARS was observed in Supplemented group during the competition, whereas TBARS significantly increased at D3 in the placebo group.

CONCLUSION

The moderate multivitamin-mineral supplementation prevented the transient increase in TBARS levels during this extreme competition.

Update: effects of antioxidant and non-antioxidant vitamin supplementation on immune function

The purpose of this manuscript is to review the impact of supplementation with vitamins E and C, carotenoids, and the B vitamins on parameters of innate and adaptive immune function as reported from clinical trials in humans. There is evidence to support causal effects of supplementation with vitamins E and C and the carotenoids singly and in combination on selected aspects of immunity, including the functional capacity of innate immune cells, lymphocyte proliferation, and the delayed-type hypersensitivity (DTH) response. Controlled intervention trials of B vitamin-containing multivitamin supplements suggest beneficial effects on immune parameters and clinical outcomes in HIV-positive individuals.

The influence of antioxidant supplementation on markers of inflammation and the relationship to oxidative stress after exercise

Interest in the relationship between inflammation and oxidative stress has increased dramatically in recent years, not only within the clinical setting but also in the fields of exercise biochemistry and immunology. Inflammation and oxidative stress share a common role in the etiology of a variety of chronic diseases. During exercise, inflammation and oxidative stress are linked via muscle metabolism and muscle damage. Because oxidative stress and inflammation have traditionally been associated with fatigue and impaired recovery from exercise, research has focused on nutritional strategies aimed at reducing these effects. In this review, we have evaluated the findings of studies involving antioxidant supplementation on alterations in markers of inflammation (e.g., cytokines, C-reactive protein and cortisol). This review focuses predominantly on the role of reactive oxygen and nitrogen species generated from muscle metabolism and muscle damage during exercise and on the modulatory effects of antioxidant supplements. Furthermore, we have analyzed the influence of factors such as the dose, timing, supplementation period and bioavailability of antioxidant nutrients.

Oxidative stress : relationship with exercise and training

Free radicals are reactive compounds that are naturally produced in the human body. They can exert positive effects (e.g. on the immune system) or negative effects (e.g. lipids, proteins or DNA oxidation). To limit these harmful effects, an organism requires complex protection - the antioxidant system. This system consists of antioxidant enzymes (catalase, glutathione peroxidase, superoxide dismutase) and non-enzymatic antioxidants (e.g. vitamin E [tocopherol], vitamin A [retinol], vitamin C [ascorbic acid], glutathione and uric acid). An imbalance between free radical production and antioxidant defence leads to an oxidative stress state, which may be involved in aging processes and even in some pathology (e.g. cancer and Parkinson's disease). Physical exercise also increases oxidative stress and causes disruptions of the homeostasis. Training can have positive or negative effects on oxidative stress depending on training load, training specificity and the basal level of training. Moreover, oxidative stress seems to be involved in muscular fatigue and may lead to overtraining.

Dietary antioxidants for the athlete

Physical exercise induces oxidative stress and tissue damage. Although a basal level of reactive oxygen species (ROS) is required to drive redox signaling and numerous physiologic processes, excess ROS during exercise may have adverse implications on health and performance. Antioxidant nutrients may be helpful in that regard. Caution should be exercised against excess antioxidant supplements, however. This article presents a digest for sports practitioners. The following three recommendations are made: 1) it is important to determine the individual antioxidant need of each athlete performing a specific sport; 2) multinutrient preparations, as opposed to megadoses of any single form of nutrient, seem to be a more prudent path to choose; and 3) for outcomes of antioxidant supplementation, performance should not be the only criteria. Overall well being of the athlete, faster recovery, and minimization of injury time could all be affected by antioxidant therapy.

L-cysteine supplementation protects the erythrocyte glucose-6-phosphate dehydrogenase activity from reduction induced by forced training

BACKGROUND

L-cysteine (L-cys) is implicated in the reduction of free radical production.

AIM

To investigate the effect of training and L-cys supplementation on the erythrocyte glucose-6-phosphate dehydrogenase (G6PD) activity.

METHODS

Blood was obtained from 10 basketball players pre-game (group A), post-game (group B) and after 1 week on L-cys (0.5 g/24 h orally) supplementation pre- (group C) and post-training (group D). Total antioxidant status (TAS) and G6PD activity were evaluated with commercial kits.

RESULTS

TAS increased in the groups with l-cys addition (group C and group D). Post-exercise, TAS and G6PD activity were remarkably higher (1.48+/-0.12 mmol/L, 8.9+/-1.7 U/g Hb, respectively) in group D than those in group B (0.92+/-0.10 mmol/L, 4.8+/-1.6 U/g Hb, p<0.01). G6PD activity positively correlated with TAS (r=0.70, p<0.001 pre- and r=0.61, p<0.001 post-training) in all the studied groups.

CONCLUSIONS

G6PD activity is lowered by training probably due to free radical action. L-cys supplementation may protect G6PD activity from reduction by increasing total antioxidant capacity and glutathione production. G6PD activity should be evaluated in the blood of athletes of Mediterranean origin and female G6PD-deficient heterozygotes.

Exercise-induced oxidative stress:myths, realities and physiological relevance

Although assays for the most popular markers of exercise-induced oxidative stress may experience methodological flaws, there is sufficient credible evidence to suggest that exercise is accompanied by an increased generation of free radicals, resulting in a measurable degree of oxidative modifications to various molecules. However, the mechanisms responsible are unclear. A common assumption that increased mitochondrial oxygen consumption leads per se to increased reactive oxygen species (ROS) production is not supported by in vitro and in vivo data. The specific contributions of other systems (xanthine oxidase, inflammation, haem protein auto-oxidation) are poorly characterised. It has been demonstrated that ROS have the capacity to contribute to the development of muscle fatigue in situ, but there is still a lack of convincing direct evidence that ROS impair exercise performance in vivo in humans. It remains unclear whether exercise-induced oxidative modifications have little significance, induce harmful oxidative damage, or are an integral part of redox regulation. It is clear that ROS play important roles in numerous physiological processes at rest; however, the detailed physiological functions of ROS in exercise remain to be elucidated.

Antioxidant requirements of endurance athletes: implications for health

This review discusses studies investigating the effects of antioxidant supplementation on exercise-induced oxidative stress with a focus on the health implications. The aim is to determine antioxidant requirements for endurance athletes. Overall, differences in methodology make it difficult to compare the relatively small number of published studies on this topic. The types of studies needed to more adequately assess the health effects of antioxidant supplements in athletes (long-term interventions with hard end points) have not been done. Therefore, there is currently insufficient evidence to recommend antioxidant supplements for endurance athletes.

The effects of vitamin C supplementation on oxidative stress and antioxidant content in the brains of chronically exercised rats

The purpose of this study was to ascertain whether vitamin C supplementation during chronic exercise training alters rat brain antioxidant content. Female Wistar albino rats were exercised on a treadmill for 30 min/day for 6.5 weeks and were administered daily intraperitoneal injections of vitamin C (20 mg/kg). After the training period, chronically exercised rats showed no significant changes in total brain thiobarbituric acid reactive substances (TBARS) levels. In contrast, rats supplemented with vitamin C during the training period showed significantly elevated brain TBARS levels. If such results were extrapolated to man, where vitamin supplementation is a common practice, this would indicate that vitamin C supplementation may not protect brain tissue against exercise-induced oxidative damage, in such circumstances, this water-soluble antioxidant behaves as a pro-oxidant.

The emerging role of free radicals in delayed onset muscle soreness and contraction-induced muscle injury

The first reported reference to delayed onset muscle soreness (DOMS) was that by Theodore Hough in 1902. Hough stated that when an untrained skeletal muscle performed exercise, it often resulted in discomfort that did not manifest until 8-10 h post-exercise, and concluded that this could not be solely attributed to fatigue. Since Hough's initial observation there has been a proliferation in research into DOMS, and despite this, the exact aetiology remains unclear. This review explores the concept of DOMS in relation to the likely causative factors and also discusses possible reasons for the equivocal findings in the literature. Free radicals are unquestionably produced during and following various forms of contractile activity and are known to result in skeletal muscle damage. Given the link between DOMS and contraction-induced muscle damage, post-exercise free radical production has been associated with DOMS; however, the precise nature of this relationship remains unsubstantiated. This review will address free radical production during and following exercise, discuss methods of assessing their generation, and critically evaluate their relationship with DOMS. There is increasing literature to suggest that free radicals act as signalling molecules, specifically activating redox sensitive transcription factors, which are necessary for muscle regeneration and adaptation following damage. Consequently free radicals may play a key physiological role in the aetiology of DOMS as opposed to a pathological role. Evidence for and against free radicals causing DOMS will be presented, and finally a suggested role of free radicals in DOMS will be proposed.

Dietary antioxidants and exercise

Muscular exercise promotes the production of radicals and other reactive oxygen species in the working muscle. Growing evidence indicates that reactive oxygen species are responsible for exercise-induced protein oxidation and contribute to muscle fatigue. To protect against exercise-induced oxidative injury, muscle cells contain complex endogenous cellular defence mechanisms (enzymatic and non-enzymatic antioxidants) to eliminate reactive oxygen species. Furthermore, exogenous dietary antioxidants interact with endogenous antioxidants to form a cooperative network of cellular antioxidants. Knowledge that exercise-induced oxidant formation can contribute to muscle fatigue has resulted in numerous investigations examining the effects of antioxidant supplementation on human exercise performance. To date, there is limited evidence that dietary supplementation with antioxidants will improve human performance. Furthermore, it is currently unclear whether regular vigorous exercise increases the need for dietary intake of antioxidants. Clearly, additional research that analyses the antioxidant requirements of individual athletes is needed.

Antioxidant supplementation prevents exercise-induced lipid peroxidation, but not inflammation, in ultramarathon runners

To determine if 6 weeks of supplementation with vitamins E and C could alleviate exercise-induced lipid peroxidation and inflammation, we studied 22 runners during a 50 km ultramarathon. Subjects were randomly assigned to one of two groups: (1) placebos (PL) or (2) antioxidants (AO: 1000 mg vitamin C and 300 mg RRR-alpha-tocopheryl acetate). Blood samples were obtained prior to supplementation (baseline), after 3 weeks of supplementation, 1 h pre-, mid-, and postrace, 2 h postrace and for 6 days postrace. Plasma levels of alpha-tocopherol (alpha-TOH), ascorbic acid (AA), uric acid (UA), F2-isoprostanes (F2-IsoPs), tumor necrosis factor alpha (TNF-alpha), interleukin-6 (IL-6), and C-reactive protein (CRP) were measured. With supplementation, plasma alpha-TOH and AA increased in the AO but not the PL group. Although F2-IsoP levels were similar between groups at baseline, 28 +/- 2 (PL) and 27 +/- 3 pg/ml (AO), F2-IsoPs increased during the run only in the PL group (41 +/- 3 pg/ml). In PL women, F2-IsoPs were elevated postrace (p <.01), but returned to prerace concentrations by 2 h postrace. In PL men, F2-IsoP concentrations were higher postrace, 2 h postrace, and 1, 2, 3, 4, and 6 days postrace (PL vs. AO group, each p <.03). Markers of inflammation were increased dramatically in response to the run regardless of treatment group. Thus, AO supplementation prevented endurance exercise-induced lipid peroxidation but had no effect on inflammatory markers.

Attenuation of free radical production and paracrystalline inclusions by creatine supplementation in a patient with a novel cytochrome b mutation

Mitochondrial cytopathies are associated with increased free radical generation and paracrystalline inclusions. Paracrystalline inclusions were serendipitously found in a young male athlete with a very high respiratory exchange ratio during steady-state exercise; he also had an unusually low aerobic capacity. Direct sequencing of the mitochondrial DNA (mtDNA) coding regions revealed a novel missense mutation (G15497A) resulting in a glycine-->serine conversion at a highly conserved site in the cytochrome b gene in the subject, his mother, and sister. Cybrids, prepared by fusion of the subject's platelets with either U87MG rho degrees or SH-SY5Y rho degrees cells, generated higher basal levels of reactive oxygen species (ROS), had a lower adenosine triphosphate (ATP) content, and were more sensitive to oxygen and glucose deprivation and peroxynitrite generation compared to control cybrids with wild-type mtDNA. Cell survival was significantly enhanced with 50 mmol/L creatine monohydrate (CM) administration. The subject was also treated with CM (10 g/d) for a period of 5 weeks and a repeat muscle biopsy showed no paracrystalline inclusions. The results suggest that the development of exercise-induced paracrystalline inclusions may be influenced by the G15497A mtDNA mutation, and that CM mitigates against the pathological consequences of this mutation.

Physical activity and the common cold in men administered vitamin E and beta-carotene

BACKGROUND AND PURPOSE

It has been proposed that moderate regular aerobic training may enhance immunocompetence, whereas excessive training may cause immunosuppression. We evaluated whether physical activity at work, or at leisure, is associated with the risk of the common cold, and whether the antioxidants vitamin E and beta-carotene affect common cold risk in physically active people.

METHODS

A cohort of 14,401 men aged 50-69 yr and working at study entry was drawn from the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) Study, which examined the effect of vitamin E, 50 mg.d(-1), and beta-carotene, 20 mg.d(-1), on lung cancer in smokers using a 2 x 2 factorial design. The trial was conducted in southwestern Finland in 1985-1993; the intervention lasted for 6.1 yr (median). Physical activity at work, and the type and frequency of leisure-time exercise were recorded at study entry. The subjects were questioned about common cold episodes 3x yr-1. We modeled the cumulative incidence of colds during a 2-yr follow-up period with Poisson regression, adjusting for potential confounders.

RESULTS

Physical activity at work and at leisure had no association with common cold risk. In subjects with physically load-bearing jobs, neither vitamin E nor beta-carotene affected significantly the risk of common cold. In subjects carrying out heavy exercise at leisure, vitamin E and beta-carotene increased the risk of colds when compared with placebo.

CONCLUSIONS

Contrary to previous suggestions, moderate physical activity is not associated with lower risk of common cold in middle-aged male smokers. It has been previously proposed that antioxidant supplementation might be beneficial for subjects carrying out heavy exercise, but in our study vitamin E and beta-carotene increased the risk of colds in subjects carrying out heavy exercise at leisure.

Detection of p53 mutations in precancerous gastric tissue

Intestinal-type gastric cancer is preceded by gastritis and intestinal metaplasia. There is uncertainty regarding the stage at which genetic alterations in the p53 gene occur. Reactive oxygen species (ROS) may participate in the production of mutations and the inactivation of p53 is due to infection by the bacterium Helicobacter pylori. We have investigated whether alterations of the p53 gene can be detected in gastritis and intestinal metaplasia using the restriction site mutation assay. We also assessed the potential contribution of ROS to p53 inactivation using electron spin resonance spectroscopy (ESR) and correlated with the presence of H. pylori. In all, 35% of the gastritis samples and 45% of the intestinal metaplasia samples were found to contain mutations in exons 5–8 of the p53 gene. Electron spin resonance spectroscopy analysis showed a significant increase in free radical levels in gastritis samples compared with normal, intestinal metaplasia and cancer samples, suggesting that free radicals present in gastritis may contribute to p53 mutations. There was no significant difference in free radical levels between the H. pylori-positive and -negative groups. However, a small subpopulation of the H. pylori-negative patients had much higher levels of free radicals. This suggests a more prominent role for other factors in ROS production.

Exercise-induced endotoxemia: the effect of ascorbic acid supplementation

Strenuous, long-duration aerobic exercise results in endotoxemia due to increased plasma levels of lipopolysaccharide (LPS) leading to cytokine release, oxidative stress, and altered gastrointestinal function. However, the effect of short-term strenuous aerobic exercise either with or without antioxidant supplementation on exercise-induced endotoxemia is unknown. A significant increase in the concentration of bacterial LPS (endotoxin) was noted in the venous circulation of healthy volunteers following maximal acute aerobic exercise (0.14(-1) pre-exercise vs. 0.24(-1) postexercise, p <0.01). Plasma nitrite concentration also increased with exercise (0.09 +/- 0.05 nM x ml(-1) vs. 0.14 +/- 0.01 nM x ml(-1), p <0.05) as did ascorbate free radical levels (0.02 +/- 0.001 vs. 0.03 +/- 0.002 arbitrary units, p <0.05). Oral ascorbic acid supplementation (1000 mg) significantly increased plasma ascorbic acid concentration (29.45 mM x l(-1) to 121.22 mM x l(-1), p <0.05), and was associated with a decrease in plasma LPS and nitrite concentration before and after exercise (LPS: 0.01(-1); nitrite: 0.02 +/- 0.02 nM x ml(-1) vs. 0.02 +/- 0.03 nM x ml(-1)). Ascorbic acid supplementation led to a significant increase in ascorbate free radical levels both before (0.04 +/- 0.01 arbitrary units) and after exercise (0.06 +/- 0.02 arbitrary units, p <0.05). In conclusion, strenuous short-term aerobic exercise results in significant increases in plasma LPS levels (endotoxemia) together with increases in markers of oxidative stress. Supplementation with ascorbic acid, however, abolished the increase in LPS and nitrite but led to a significant increase in the ascorbate radical in plasma. The amelioration of exercise-induced endotoxemia by antioxidant pretreatment implies that it is a free radical-mediated process while the use of the ascorbate radical as a marker of oxidative stress in supplemented systems is limited.

Oxidative stress, exercise, and antioxidant supplementation

Cells continuously produce free radicals and reactive oxygen species (ROS) as part of metabolic processes. These free radicals are neutralized by an elaborate antioxidant defense system consisting of enzymes such as catalase, superoxide dismutase, glutathione peroxidase, and numerous non-enzymatic antioxidants, including vitamins A, E and C, glutathione, ubiquinone, and flavonoids. Exercise can produce an imbalance between ROS and antioxidants, which is referred to as oxidative stress. Dietary antioxidant supplements are marketed to and used by athletes as a means to counteract the oxidative stress of exercise. Whether strenuous exercise does, in fact, increase the need for additional antioxidants in the diet is not clear. This review examines the markers used to determine oxidative stress in blood and muscle samples (e.g. lipid peroxidation, expired pentane, malondialdehyde (MDA), F2-isoprostanes, congugated dienes, and 8-hydroxy-2'-deoxyguanosine (8-OhdG)), the changes in oxidative stress markers induced by exercise, and whether athletes require antioxidant supplements.

The effects of acute exercise on neutrophils and plasma oxidative stress

PURPOSE

To investigate the influence of intensity versus total energy expenditure on neutrophilia and blood oxidative stress to acute exercise.

METHODS

Nine males (18-30 yr) completed one maximal (Max) and three submaximal exercise sessions: 1) 45 min at 10% above (LT+) lactate threshold (LT), 2) 45 min at 10% below (LT-) LT, and 3) 10% below LT until caloric expenditure equaled the 10%+ trial (LT-kcal). Blood was sampled before (PRE), immediately (POST), 1 h, and 2 h after exercise to measure neutrophils, myeloperoxidase, superoxide (O(2)-), neutrophil activation (O(2)-/neutrophils), ascorbic acid, uric acid, malondialdehyde, and lipid hydroperoxides.

RESULTS

Intensity-dependent neutrophilia occurred POST exercise with significant increases (P <or= 0.05) after Max and LT+. A second neutrophilia wave occurred 2 h postexercise. Superoxide was elevated POST (Max) and 2 h post (Max and LT+). In contrast, O(2)-/neutrophils was increased at 2 h only (Max and LT+). These data indicate that immediately postexercise, total neutrophil number rather than activation best represents neutrophil-generated reactive species within blood. POST Max, ascorbic acid and uric acid were decreased indicating a blood oxidative stress occurred. Alternately, total energy expenditure was not related to any marker of neutrophilia or oxidative stress.

CONCLUSION

Exercise intensity plays a major role in postexercise blood oxidative stress, whereas total exercise energy expenditure does not. Further, neutrophils recruited into circulation during exercise may impose a threshold dependent oxidative stress in blood plasma after exercise.

Nutritional aspects in ultra-endurance exercise

PURPOSE OF REVIEW

Despite much current debate regarding central and peripheral neural mechanisms which may be responsible for the onset of fatigue during prolonged exercise, maintenance of nutritional and hydration status remains critical for successful participation in ultra-endurance exercise. This review focuses on substrate and fluid homeostasis during ultra-endurance exercise and the use of nutritional supplementation both as ergogenic aid and to attenuate exercise-induced immunosuppression.

RECENT FINDINGS

Current evidence continues to support mandatory high carbohydrate intakes (1). before the event to maximize muscle glycogen stores, (2). during the event to prevent hypoglycaemia and (3). after the event to optimize post-event repletion of endogenous carbohydrate stores. No consistent performance benefit has yet been shown following a high-fat diet. Greater utilization of intrafascicular triglyceride stores appears to account for additional fat utilization in females. Recent trends towards excessive fluid intake have resulted in frequent reports of hyponatraemic hyperhydration in ultra-distance athletes, with greater incidence in women than in men. Carbohydrate supplementation during the event attenuates immunosuppressive hormonal and cytokine responses to ultra-endurance exercise, but may impair vitamin C absorption, while the ergogenic value of caffeine supplementation in ultra-endurance performance is currently being questioned.

SUMMARY

Meeting macronutrient and fluid intake demands remains an important priority for ultra-endurance athletes. Yet these athletes are reported to present with a high incidence of disordered eating patterns during periods of training, and excessive fluid replacement strategies have resulted in an increased incidence of water intoxication with resultant central nervous system dysfunction.

Effect of vitamin E and eccentric exercise on selected biomarkers of oxidative stress in young and elderly men

Muscle damage resulting from eccentric exercise provides a useful model of oxyradical-induced injury and can be used to examine age-related responses to oxidative stress. Sixteen young (26.4 +/- 3.3 years) and 16 older (71.1 +/- 4.0 years) healthy men were randomly assigned to 1000 IU/d vitamin E or placebo for 12 weeks and ran downhill for 45 min at 75% VO(2)max, once before and following supplementation. Blood samples were obtained before (baseline) and immediately postexercise (0 h), and at 6, 24, and 72 h postexercise to determine antioxidant status, muscle damage, lipid peroxidation, and DNA damage. Following exercise, young and older men experienced similar increases in serum creatine kinase (CK), F(2alpha)-isoprostanes (iPF(2alpha); p <.001) and malondialdehyde (MDA; p <.01), although iPF(2alpha) peaked at 72 h postexercise and MDA peaked at 0 h. Oxygen Radical Absorbance Capacity (ORAC) decreased at 72 h (p <.01) and correlated with the rise in iPF(2alpha), MDA, and CK in the young men (p <.05). Leukocyte 8-hydroxy-2'-deoxyguanosine (8-OHdG) was unaffected by exercise. Vitamin E decreased peak CK in young men, while in older men it decreased resting levels of iPF(2alpha) and suppressed the 24 h postexercise increases in iPF(2alpha) (p <.05). Thus, vitamin E supplementation induced modest changes eccentric exercise-induced oxidative stress, although differentially between the young and older subjects, while age had no direct influence on these responses among this group of physically fit subjects.

Ischemia and reperfusion of skeletal muscle lead to the appearance of a stable lipid free radical in the circulation

Both ischemia and reperfusion injury and contractile activity are associated with the generation of reactive oxygen species and free radicals by skeletal muscle. In addition, exercise has been reported to lead to the formation of a circulating free radical species that is detectable in the blood by spin trapping before analysis by electron-spin resonance (ESR) techniques. Previous analysis of the ESR signal indicated that the circulating species is either a carbon- or oxygen-centered lipid-derived free radical. The current data indicate that this species is present in the blood of anesthetized rats after 4-h ischemia and 1 h of reperfusion of a single hindlimb. During 4 h of ischemia, the species was also present in microdialysates from the tibialis anterior muscle but was unchanged in magnitude compared with control tissue. During 1 h of reperfusion, the signal intensity increased by a mean of 420% (P < 0.05, n = 4). Hydroxyl radical activity in the interstitial fluid also significantly increased during ischemia and further increased by a mean of 210% (P < 0.05, n = 4) during reperfusion. No changes in interstitial superoxide levels were seen, but interstitial PGE(2) content also increased during reperfusion. A significant positive correlation was found between the magnitude of the ESR signal and both the hydroxyl radical activity and PGE(2) content of microdialysis fluids. These data support the hypothesis that the circulating free radical species is formed in the interstitial fluid by hydroxyl radical interaction with a lipid that may be released from reperfused tissue with a similar pattern to prostanoids.

N-acetylcysteine infusion alters blood redox status but not time to fatigue during intense exercise in humans

Infusion of the antioxidant N-acetylcysteine (NAC) reduces fatigability in electrically evoked human muscle contraction, but due to reported adverse reactions, no studies have investigated NAC infusion effects during voluntary exercise in humans. We investigated whether a modified NAC-infusion protocol (125 mg. kg(-1). h(-1) for 15 min, then 25 mg. kg(-1). h(-1)) altered blood redox status and enhanced performance during intense, intermittent exercise. Eight untrained men participated in a counterbalanced, double-blind, crossover study in which they received NAC or saline (control) before and during cycling exercise, which comprised three 45-s bouts and a fourth bout that continued to fatigue, at 130% peak oxygen consumption. Arterialized venous blood was analyzed for glutathione status, hematology, and plasma electrolytes. NAC infusion induced no severe adverse reactions. Exercise decreased the reduced glutathione (P < 0.005) and increased oxidized glutathione concentrations (P < 0.005); NAC attenuated both effects (P < 0.05). NAC increased the rise in plasma K(+) concentration-to-work ratio (P < 0.05), indicating impaired K(+) regulation, although time to fatigue was unchanged (NAC 102 +/- 45 s; saline 107 +/- 53 s). Thus NAC infusion altered blood redox status during intense, intermittent exercise but did not attenuate fatigue.

Antioxidants attenuate the plasma cytokine response to exercise in humans

Exercise increases plasma TNF-alpha, IL-1beta, and IL-6, yet the stimuli and sources of TNF-alpha and IL-1beta remain largely unknown. We tested the role of oxidative stress and the potential contribution of monocytes in this cytokine (especially IL-1beta) response in previously untrained individuals. Six healthy nonathletes performed two 45-min bicycle exercise sessions at 70% of Vo(2 max) before and after a combination of antioxidants (vitamins E, A, and C for 60 days; allopurinol for 15 days; and N-acetylcysteine for 3 days). Blood was drawn at baseline, end-exercise, and 30 and 120 min postexercise. Plasma cytokines were determined by ELISA and monocyte intracellular cytokine level by flow cytometry. Before antioxidants, TNF-alpha increased by 60%, IL-1beta by threefold, and IL-6 by sixfold secondary to exercise (P < 0.05). After antioxidants, plasma IL-1beta became undetectable, the TNF-alpha response to exercise was abolished, and the IL-6 response was significantly blunted (P < 0.05). Exercise did not increase the percentage of monocytes producing the cytokines or their mean fluorescence intensity. We conclude that in untrained humans oxidative stress is a major stimulus for exercise-induced cytokine production and that monocytes play no role in this process.

Influence of vitamin C supplementation on oxidative and salivary IgA changes following an ultramarathon

This randomized study measured the influence of vitamin C ( N=15) compared to placebo ( N=13) supplementation on oxidative and salivary immunoglobulin A (sIgA) changes in runners competing in an ultramarathon race. Seven days prior to the race, subjects ingested in randomized, double-blind fashion three 500-mg tablets of vitamin C or placebo each day. On race day, blood and saliva samples were collected 1 h pre-race, after 32 km of running, and then again immediately post-race. During the race, runners received 1 l/h carbohydrate beverages (60 g/l) with vitamin C (150 mg/l) or without in a double-blinded fashion. The runners also ingested two to three carbohydrate gel packs per hour (25 g each). Subjects in both groups ran a mean of 69 km (range 48-80 km) in 9.8 h (range 5-12 h) and maintained an intensity of approximately 75% maximal heart rate (HR(max)) throughout the ultramarathon race. Plasma ascorbic acid was higher in the vitamin C compared to placebo group pre-race, and increased significantly in the vitamin C group during the race [post-race, 3.21 (0.29) and 1.28 (0.12) microg/100 microl, respectively, P<0.001]. No significant group or interaction effects were measured for lipid hydroperoxide and F(2)-isoprostane, but both oxidative measures rose significantly during the ultramarathon race. Saliva volume, sIgA concentration, sIgA secretion and sIgA:saliva protein ratio all decreased significantly (P<0.001) during the race, but the pattern of change in all saliva measures did not differ significantly between groups. No significant correlations were found between post-race plasma vitamin C, oxidative, and saliva measures, except for a positive correlation between post-race serum cortisol and serum vitamin C (r=0.50, P=0.006). These data indicate that vitamin C supplementation in carbohydrate-fed runners does not serve as a countermeasure to oxidative and sIgA changes during or following a competitive ultramarathon race.

Strenuous resistive breathing induces plasma cytokines: role of antioxidants and monocytes

Inspiratory resistive breathing increases plasma cytokines, yet the stimulus (or stimuli) and source(s) remain unknown. We tested the role of reactive oxygen species as stimuli and of monocytes as sources of resistive breathing-induced cytokines. Six healthy subjects performed two resistive breathing sessions at 75% of maximum inspiratory pressure before and after a combination of antioxidants (vitamin E 200 mg, vitamin A 50,000 IU, and vitamin C 1,000 mg per day for 60 days, allopurinol 600 mg/day for 15 days, and N-acetylcysteine 2 g/day for 3 days before the second session). Blood was drawn before, at the end, and at 30 and 120 minutes after resistive breathing. Before antioxidants, plasma cytokine levels (determined by enzyme-linked immunosorbent assay) increased secondary to resistive breathing (tumor necrosis factor-alpha and interleukin [IL]-6 by twofold and IL-1beta by threefold). After antioxidants, plasma IL-1beta became undetectable. The tumor necrosis factor-alpha response to resistive breathing was abolished, and the IL-6 response was significantly blunted. Intracellular cytokine detection (by flow cytometry) showed no change in either the percentage of monocytes producing the cytokines or their mean fluorescence intensity both before and after antioxidants. We conclude that oxidative stress is a major stimulus for the resistive breathing-induced cytokine production and that monocytes play no role in this process.

[Free radicals and oxidative stress: targeted ESR measurement of free radicals]

The detection of free radicals generated within the body may contribute to clarifying the pathophysiological role of free radicals in disease processes. As an appropriate procedure to examine the generation of free radicals in a biological system, electron spin resonance (ESR) has emerged as a powerful tool for detection and identification. A method for determination of oxygen radical scavenging activity using ESR and the spin trapping technique was developed. Oxygen radicals were trapped by 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) or alpha-phenyl-N-t-butylnitrone (PBN), and the DMPO or PBN spin adduct signal was measured quantitatively by an ESR spectrometer. The spin trapping method using ESR has also been reported for not only in vitro and ex vivo measurements but also in vivo measurements. In in vivo ESR, nitroxyl radical is being used as a spin trap well. ESR signal intensities of nitroxyl radical are measured after administration to animals and the signal decay rates of nitroxyl radical have reported to be influenced by various types of oxidative stress. With this method, it is possible to specify the type of radical or the location at which the free radicals are produced. The spin trapping method by in vivo ESR is an effective procedure for giving non-invasive measurements in animals. ESR imaging in the organs of live animals can also be obtained after injection of nitroxyl radicals as an imaging agent using ESR-computed tomography. In vivo ESR imaging has been established as a powerful technique for determining the spatial distribution of free radicals in living organs and tissues.

Influence of vitamin C supplementation on oxidative and immune changes after an ultramarathon

The purpose of this randomized study was to measure the influence of vitamin C (n = 15 runners) compared with placebo (n = 13 runners) supplementation on oxidative and immune changes in runners competing in an ultramarathon race. During the 7-day period before the race and on race day, subjects ingested in randomized, double-blind fashion 1,500 mg/day vitamin C or placebo. On race day, blood samples were collected 1 h before race, after 32 km of running, and then again immediately after race. Subjects in both groups maintained an intensity of approximately 75% maximal heart rate throughout the ultramarathon race and ran a mean of 69 km (range: 48-80 km) in 9.8 h (range: 5-12 h). Plasma ascorbic acid was markedly higher in the vitamin C compared with placebo group prerace and rose more strongly in the vitamin C group during the race (postrace: 3.21 +/- 0.29 and 1.28 +/- 0.12 microg/100 microl, respectively, P < 0.001). No significant group or interaction effects were measured for lipid hydroperoxide, F2-isoprostane, immune cell counts, plasma interleukin (IL)-6, IL-10, IL-1-receptor antagonist, or IL-8 concentrations, or mitogen-stimulated lymphocyte proliferation and IL-2 and IFN-gamma production. These data indicate that vitamin C supplementation in carbohydrate-fed runners does not serve as a countermeasure to oxidative and immune changes during or after a competitive ultramarathon race.

Antioxidants in exercise nutrition

Physical exercise may be associated with a 10- to 20-fold increase in whole body oxygen uptake. Oxygen flux in the active peripheral skeletal muscle fibres may increase by as much as 100- to 200-fold during exercise. Studies during the past 2 decades suggest that during strenuous exercise, generation of reactive oxygen species (ROS) is elevated to a level that overwhelms tissue antioxidant defence systems. The result is oxidative stress. The magnitude of the stress depends on the ability of the tissues to detoxify ROS, that is, antioxidant defences. Antioxidants produced by the body act in concert with their exogenous, mainly dietary, counterparts to provide protection against the ravages of reactive oxygen as well as nitrogen species. Antioxidant supplementation is likely to provide beneficial effects against exercise-induced oxidative tissue damage. While universal recommendations specifying types and dosages of antioxidants are difficult to make, it would be prudent for competitive athletes routinely engaged in strenuous exercise to seek an estimate of individual requirement. A new dimension in oxidant biology has recently unfolded. Although excessive oxidants may cause damage to tissues, lower levels of oxidants in biological cells may act as messenger molecules enabling the function of numerous physiological processes. It is plausible that some exercise-induced beneficial effects are actually oxidant-mediated. Such developments call for an even more careful analysis of the overall significance of types and amounts of antioxidants in diet. While these complexities pose significant challenges, experts agree that if used prudently, oxidants and antioxidants may serve as potent therapeutic tools. Efforts to determine individual needs of athletes and a balanced diet rich in antioxidant supplements are highly recommended.

The oxidative stress hypothesis of congestive heart failure: radical thoughts

There is extensive experimental evidence from in vitro and animal experiments that congestive heart failure (CHF) is a state of oxidative stress. Moreover, in animal models, the development of CHF is accompanied by changes in the antioxidant defense mechanisms of the myocardium as well as evidence of oxidative myocardial injury. This has led to the hypothesis that oxidative stress may be a mechanism of disease progression in CHF. Indeed, many patients consume antioxidant supplements making the assumption that no harm will result and, possibly, that this therapy will yield some clinical benefits. The focus of this review is to examine the oxidative stress hypothesis of CHF as it pertains to humans. To date, human studies that have sought evidence for a role of oxidative stress in patients with CHF have fallen short of providing strong support for this hypothesis. Studies that have demonstrated an association between oxidant stress and CHF are small and are hindered by methodologic limitations that diminish the impact of their conclusions. Randomized trials of antioxidant supplementation for CHF are scarce, and to our knowledge no study yet convincingly demonstrates any benefit from consuming antioxidant supplements. Therefore, the available evidence is insufficient to support or negate the oxidative stress hypothesis of CHF and the use of antioxidants cannot be recommended as a specific therapy for this condition.

Antioxidant supplementation and exercise-induced oxidative stress in the 60-year-old as measured by antipyrine hydroxylates

The effects of 12 weeks of antioxidant supplementation on exercise-induced oxidative stress were investigated in older adults (60 (SE 1) years; BMI 26 (SE 1) kg/m(2)). Subjects were randomly divided in two groups: supplementation (n 11) with 100 mg dl-alpha-tocopheryl acetate, 200 mg ascorbic acid, and 2 mg beta-carotene, and placebo (n 9). Before and after the 12 week supplementation period, subjects cycled for 45 min at submaximal intensity (50 % maximal workload capacity). Antipyrine was used as marker for oxidative stress. Antipyrine reacts quickly with hydroxyl radicals to form para- and ortho-hydroxyantipyrine. The latter metabolite is not formed in man through the mono-oxygenase pathway of cytochrome P450. Daily supplementation significantly increased plasma concentrations of alpha-tocopherol and beta-carotene in the supplemented group (Delta 14.4 (SE 3.2) and 0.4 (se 0.1) micromol/l; P<0.001 and P<0.01). No significant differences, within and between groups, were observed in the exercise-induced increase in the ratios para- and ortho-hydroxyantipyrine to antipyrine. In addition, supplementation did not affect the exercise-induced increase in thiobarbituric acid reactive substances in plasma. In conclusion, in 60-year-old subjects antioxidant supplementation had no effect on the exercise-induced increase in oxidative stress as measured by free radical products of antipyrine.

Acute mountain sickness; prophylactic benefits of antioxidant vitamin supplementation at high altitude

Acute mountain sickness; prophylactic benefits of Free-radical-mediated damage to the blood-brain barrier may be implicated in the pathophysiology of acute mountain sickness (AMS). To indirectly examine this, we conducted a randomized double-blind placebo-controlled trial to assess the potentially prophylactic benefits of enteral antioxidant vitamin supplementation during ascent to high altitude. Eighteen subjects aged 35 +/- 10 years old were randomly assigned double-blind to either an antioxidant (n = 9) or placebo group (n = 9). The antioxidant group ingested 4 capsules/day(-1) (2 after breakfast/2 after evening meal) that each contained 250 mg of L-ascorbic acid, 100 IU of dl-a-tocopherol acetate and 150 mg of alpha-lipoic acid. The placebo group ingested 4 capsules of identical external appearance, taste, and smell. Supplementation was enforced for 3 weeks at sea level and during a 10-day ascent to Mt. Everest base camp (approximately 5,180 m). Antioxidant supplementation resulted in a comparatively lower Lake Louise AMS score at high altitude relative to the placebo group (2.8 +/- 0.8 points versus 4.0 +/- 0.4 points, P = 0.036), higher resting arterial oxygen saturation (89 +/- 5% versus 85 +/- 5%, P = 0.042), and total caloric intake (13.2 +/- 0.6 MJ/day(-1) versus 10.1 +/- 0.7 MJ/day(-1), P = 0.001); the latter is attributable to a lower satiety rating following a standardized meal. These findings indicate that the exogenous provision of water and lipid-soluble antioxidant vitamins at the prescribed doses is an apparently safe and potentially effective intervention that can attenuate AMS and improve the physiological profile of mountaineers at high altitude.

Evidence against oxidative stress as mechanism of endothelial dysfunction in methionine loading model

Endothelial dysfunction reflects reduced nitric oxide (NO) bioavailability due to either reduced production, inactivation of NO, or reduced smooth muscle responsiveness. Oral methionine loading causes acute endothelial dysfunction in healthy subjects and provides a model in which to study mechanisms. Endothelial function was assessed using flow-mediated dilatation (FMD) of the brachial artery in humans. Three markers of oxidative stress were measured ex vivo in venous blood. NO responsiveness was assessed in vascular smooth muscle and platelets. Oral methionine loading induced endothelial dysfunction (FMD decreased from 2.8 +/- 0.8 to 0.3 +/- 0.3% with methionine and from 2.8 +/- 0.8 to 1.3 +/- 0.3% with placebo; P < 0.05). No significant changes in measures of plasma oxidative stress or in vascular or platelet sensitivity to submaximal doses of NO donors were detected. These data suggest that oxidative stress is not the mechanism of endothelial dysfunction after oral methionine loading. Furthermore, the preservation of vascular and platelet NO sensitivity makes a signal transduction abnormality unlikely.

Influence of vitamin C supplementation on cytokine changes following an ultramarathon

The influence of vitamin C supplementation on the pattern of change in plasma cytokine concentrations was measured in 29 runners following a 90-km ultramarathon. The study was based on a 3 (groups) by 4 (blood samples at 16 prerace, postrace, and 24 h and 48 h postrace) repeated measures design. Groups included placebo control (n = 7) and two groups supplementing vitamin C at 500 mg/day (vit C-500, n = 10) or 1500 mg/day (vit C-1500, n = 12) for 7 days before the race, on race day, and for 2 days after the race. All measured plasma cytokine concentrations were significantly elevated immediately postrace, with the magnitude of increase for tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) much smaller than for IL-6, IL-10, IL-8, and IL-1 receptor antagonist (IL-1RA). Cortisol increased in all groups immediately after the race but significantly less in the vit C-1500 group. Group x time interaction statistics were not significant for any of the plasma cytokines. However, when the placebo and vit C-500 groups were combined (n = 17) and compared with the vit C-1500 group (n = 12), immediate postrace plasma concentrations were significantly lower in the vit C-1500 group for IL-1RA (-57%) and IL-10 (-57%), with a trend measured for IL-6 (-27%, p = 0.11) and IL-8 (-26%, p = 0.14). In summary, runners completing the 90-km Comrades Ultramarathon experienced strong increases in concentrations of plasma IL-6, IL-10, IL-1RA, and IL-8. These increases were attenuated in runners ingesting 1500 mg but not 500 mg vitamin C supplements for 1 week prior to the race and on race day.