Effect of endurance exercise on the tissue 8-hydroxy-deoxyguanosine content in dogs

Mediators of Physical Activity Protection against ROS-Linked Skeletal Muscle Damage

Unaccustomed and/or exhaustive exercise generates excessive free radicals and reactive oxygen and nitrogen species leading to muscle oxidative stress-related damage and impaired contractility. Conversely, a moderate level of free radicals induces the body’s adaptive responses. Thus, a low oxidant level in resting muscle is essential for normal force production, and the production of oxidants during each session of physical training increases the body’s antioxidant defenses. Mitochondria, NADPH oxidases and xanthine oxidases have been identified as sources of free radicals during muscle contraction, but the exact mechanisms underlying exercise-induced harmful or beneficial effects yet remain elusive. However, it is clear that redox signaling influences numerous transcriptional activators, which regulate the expression of genes involved in changes in muscle phenotype. The mitogen-activated protein kinase family is one of the main links between cellular oxidant levels and skeletal muscle adaptation. The family components phosphorylate and modulate the activities of hundreds of substrates, including transcription factors involved in cell response to oxidative stress elicited by exercise in skeletal muscle. To elucidate the complex role of ROS in exercise, here we reviewed the literature dealing on sources of ROS production and concerning the most important redox signaling pathways, including MAPKs that are involved in the responses to acute and chronic exercise in the muscle, particularly those involved in the induction of antioxidant enzymes.

Effects of repeated bouts of long-duration endurance exercise on muscle and urinary levels of 8-hydroxy-2'-deoxyguanosine in moderately trained cyclists

The purpose of this study was to determine the effects of repeated bouts of long-duration endurance exercise on both muscle and urinary levels of oxidative DNA damage in moderately trained individuals. Seven moderately trained male cyclists participated in this study. All participants repeated two sessions consisting of a 5-h cycling period (equivalent to approximately 52%[Formula: see text]O2peak) followed by a 15-h rest, then a 40-km time trial. During the sessions, participants were instructed to take water ad libitum and to consume a standard sports drink consisting of 0.12 g·kg(-1) body weight·hr(-1) of carbohydrates. For each session, 24 h urine output was collected on the day before the 5-h exercise, and also between the 5-h exercise and 40-km time trial, in addition to between days 1-5 post-exercise. Subsequently, muscle and urinary levels of 8-hydroxy-2'- deoxyguanosine (8-OHdG) were determined using high performance liquid chromatography with electrochemical detection. No significant alterations were observed between two sessions at the muscle or urinary levels of 8-OHdG. These results suggest that repeated bouts of exercise with a 7-day washout period may not lead to an accumulation of DNA damage products after a second 5-h stationary cycling bout.

Antioxidant supplementation during exercise training: beneficial or detrimental?

High levels of reactive oxygen species (ROS) produced in skeletal muscle during exercise have been associated with muscle damage and impaired muscle function. Supporting endogenous defence systems with additional oral doses of antioxidants has received much attention as a noninvasive strategy to prevent or reduce oxidative stress, decrease muscle damage and improve exercise performance. Over 150 articles have been published on this topic, with almost all of these being small-scale, low-quality studies. The consistent finding is that antioxidant supplementation attenuates exercise-induced oxidative stress. However, any physiological implications of this have yet to be consistently demonstrated, with most studies reporting no effects on exercise-induced muscle damage and performance. Moreover, a growing body of evidence indicates detrimental effects of antioxidant supplementation on the health and performance benefits of exercise training. Indeed, although ROS are associated with harmful biological events, they are also essential to the development and optimal function of every cell. The aim of this review is to present and discuss 23 studies that have shown that antioxidant supplementation interferes with exercise training-induced adaptations. The main findings of these studies are that, in certain situations, loading the cell with high doses of antioxidants leads to a blunting of the positive effects of exercise training and interferes with important ROS-mediated physiological processes, such as vasodilation and insulin signalling. More research is needed to produce evidence-based guidelines regarding the use of antioxidant supplementation during exercise training. We recommend that an adequate intake of vitamins and minerals through a varied and balanced diet remains the best approach to maintain the optimal antioxidant status in exercising individuals.

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.

Alteration of gene expression in rat colon mucosa after exercise

The development of colon cancer is highly influenced by lifestyle factors such as nutrition and physical inactivity. Detailed biological mechanisms are thus far unclear. The purpose of this study was to investigate the effects of regular treadmill exercise on gene expression in rat colon mucosa. For this purpose, 6-week-old male Wistar rats completed a stress-free voluntary treadmill exercise period of 12 weeks. Sedentary rats served as a control group. In the colon mucosa, steady-state mRNA expression levels of approximately 10,000 genes were compared between both groups by micro-array analysis (MWG rat 10K array). A total of 8846 mRNAs were detected above background level. Regular exercise led to a decreased expression of 47 genes at a threshold-factor of 2.0. Three genes were found to be up-regulated in the exercise group. The identified genes encode proteins involved in signal transduction (n=11), transport (n=8), immune system (n=7), cytoskeleton (n=6), protein targeting (n=6), metabolism (n=5), transcription (n=3) and vascularization (n=2). Among the genes regulated by regular exercise, the betaine-homocysteine methyltransferase 2 (BHMT2) seems to be of particular interest. Physical activity may protect against aberrant methylation by repressing the BHMT2 gene and thus contribute to a decreased risk of developing colon cancer. We have also identified vascular endothelial growth factor (VEGF), angiopoietin-2 (ANG-2) and calcium-independent phospholipase a2 (iPL-A2), all of them with markedly reduced transcript levels in the mucosa of active rats. In summary, our experiment presents the first gene expression pattern in rat colon mucosa following regular treadmill activity and represents an important step in understanding the molecular mechanisms responsible for the preventive effect of physical activity on the development of colon cancer.

Progress in the analysis of urinary oxidative DNA damage

Oxidative DNA damage has been implicated to be important in the pathogenesis of many diseases, including cancer and heart disease. The assessment of damage in various biological matrices, such as DNA, serum, and urine, is vital to understanding this role and subsequently devising intervention strategies. Despite the numerous techniques to measure oxidative DNA damage products in urine, it remains unclear what these measurements truly represent. Sources of urinary lesions may include the diet, cell death, and, of most interest, DNA repair. Were it possible to exclude the two former contributions, a noninvasive assay for DNA repair would be invaluable in the study of DNA damage and disease. This review highlights that, although progress has been made, significant work remains. Diet, cell death, and repair need continued examination to further elucidate the kinetics of lesion formation and clearance in vivo. Studies from our laboratory and others are making appreciable progress towards the interpretation of urinary lesion measurements along with the development of urinary assays to evaluate DNA repair. Upon establishment of these details, urinary oxidative DNA damage measurements may become more than a reflection of generalized oxidative stress.

Effect of diet on cancer development: is oxidative DNA damage a biomarker?

Free radicals and other reactive species are generated in vivo and many of them can cause oxidative damage to DNA. Although there are methodological uncertainties about accurate quantitation of oxidative DNA damage, the levels of such damage that escape immediate repair and persist in DNA appear to be in the range that could contribute significantly to mutation rates in vivo. The observation that diets rich in fruits and vegetables can decrease both oxidative DNA damage and cancer incidence is consistent with this. By contrast, agents increasing oxidative DNA damage usually increase risk of cancer development. Such agents include cigarette smoke, several other carcinogens, and chronic inflammation. Rheumatoid arthritis and diabetes are accompanied by increased oxidative DNA damage but the pattern of increased cancer risk seems unusual. Other uncertainties are the location of oxidative DNA damage within the genome and the variation in rate and level of oxidative damage between different body tissues. In well-nourished human volunteers, fruits and vegetables have been shown to decrease oxidative DNA damage in several studies, but data from short-term human intervention studies suggest that the protective agents are not vitamin C, vitamin E, beta-carotene, or flavonoids.

Antioxidant enzyme activities, lipid peroxidation, and DNA oxidative damage: the effects of short-term voluntary wheel running

We examined the effect of voluntary exercise on antioxidant enzyme activities (catalase, glutathione peroxidase, superoxide dismutase) in skeletal muscle (hind- and forelimb) and heart of a model small mammal species: short-tailed field vole Microtus agrestis. In addition, DNA oxidation was determined in lymphocytes and hepatocytes using the comet assay and lipid peroxidation estimated in hindlimb muscle by measurement of thiobarbituric-acid-reactive substances. Voles (approximately 6 weeks old), exposed to a 16L:8D photoperiod (lights on 0500 h), ran almost continuously during darkness. We studied the effects of voluntary running over 1 or 7 days duration, with or without an 8-h rest period, on various biomarkers of oxidative stress compared to nonrunning controls. No differences were observed in antioxidant enzyme activities, except in heart total superoxide dismutase activity (P=0.037), with the lowest levels in 1- and 7-day runners at 0500 h. DNA oxidative damage, in lymphocytes or hepatocytes, and lipid peroxidation did not differ between groups. There was no evidence of any significant increase in any oxidative stress parameter in running individuals, despite having significantly elevated energy expenditures compared to sedentary controls.

Why and how should we measure oxidative DNA damage in nutritional studies? How far have we come?

Free radicals and other reactive species are constantly generated in vivo and cause oxidative damage to DNA at a rate that is probably a significant contributor to the age-related development of cancer. Agents that decrease oxidative DNA damage should thus decrease the risk of cancer development. That is, oxidative DNA damage is a "biomarker" for identifying persons at risk (for dietary or genetic reasons, or both) of developing cancer and for suggesting how the diets of these persons could be modified to decrease that risk. This biomarker concept presupposes that we can measure oxidative damage accurately in DNA from relevant tissues. Little information is available on whether oxidative DNA damage in blood cells mirrors such damage in tissues at risk of cancer development. Measurement of 8-hydroxylated guanine (eg, as 8-hydroxy-2'-deoxyguanosine; 8OHdG) is the commonest method of assessing DNA damage, but there is no consensus on what the true levels are in human DNA. If the lowest levels reported are correct, 8OHdG may be only a minor product of oxidative DNA damage. Indeed, 8OHdG may be difficult to measure because of the ease with which it is formed artifactually during isolation, hydrolysis, and analysis of DNA. Mass spectrometry can accurately measure a wide spectrum of DNA base damage products, but the development of liquid chromatography-mass spectrometry techniques and improved DNA hydrolysis procedures is urgently required. The available evidence suggests that in Western populations, intake of certain fruit and vegetables can decrease oxidative DNA damage, whereas ascorbate, vitamin E, and beta-carotene cannot.

Urinary 8-oxo-2'-deoxyguanosine--source, significance and supplements

Oxidative damage to cellular biomolecules, in particular DNA, has been proposed to play an important role in a number of pathological conditions, including carcinogenesis. A much studied consequence of oxygen-centred radical damage to DNA is 8-oxo-2'-deoxyguanosine (8-oxodG). Using numerous techniques, this lesion has been quantified in various biological matrices, most notably DNA and urine. Until recently, it was understood that urinary 8-oxodG derives solely from DNA repair, although the processes which may yield the modified deoxynucleoside have never been thoroughly discussed. This review suggests that nucleotide excision repair and the action of a specific endonuclease may, in addition to the nucleotide pool, contribute significantly to levels of 8-oxodG in the urine. On this basis, urinary 8-oxodG represents an important biomarker of generalised, cellular oxidative stress. Current data from antioxidant supplementation trials are examined and the potential for such compounds to modulate DNA repair is considered. It is stressed that further work is required to link DNA, serum and urinary levels of 8-oxodG such that the kinetics of formation and clearance may be elucidated, facilitating greater understanding of the role played by oxidative stress in disease.

Muscle soreness-induced reduction in force generation is accompanied by increased nitric oxide content and DNA damage in human skeletal muscle

We examined the effect of exercise-induced muscle soreness on maximal force generation, tissue nitric oxide (NO) and 8-hydroxydeoxyguanosine (8-OHdG) content in human skeletal muscle. Female volunteers were assigned to control (C) and muscle soreness (MS) groups (n = 6 in each). MS group performed 200 eccentric muscle actions of the rectus femoris to induce muscle soreness. Maximal force generation was measured 24 h before and after exercise in both groups. Needle biopsy samples were assayed for NO content with electron spin resonance spectroscopy after ex vivo spin trapping, and 8-OHdG content were measured with an enzyme-linked immuno assay. Maximal force decreased by 11+/-5.4% (p < .05) 24 h after exercise in MS group. Muscle soreness increased NO and 8-OHdG contents from their control values of 0.39+/-0.08 arbitrary units and 0.035+/-0.004 pmol/micromol DNA to 0.96+/-0.05 (p < .05) arbitrary units and 0.044+/-0.005 (p < .05) pmol/micromol DNA, respectively. This is the first demonstration that muscle soreness-induced decrease in maximal force generation is a result of an increase in muscular NO content and associated with enhanced formation of 8-OHdG in human skeletal muscle.

Can oxidative DNA damage be used as a biomarker of cancer risk in humans? Problems, resolutions and preliminary results from nutritional supplementation studies

Damage to DNA by oxygen radicals and other reactive oxygen/nitrogen/chlorine species occurs in vivo despite the presence of multiple antioxidant defence and repair systems. Such damage is thought to make a significant contribution to the age-related development of cancer. Modulation of oxidative DNA damage by diet thus constitutes a "biomarker" putatively predictive of the effect of diet on cancer incidence, provided that DNA damage can be accurately quantitated by validated methods. Current issues addressed in this article include the problems of artifactual DNA oxidation during isolation and analysis, the relative merits of different analytical methods, the advantages and disadvantages of relying on measurement of 8-hydroxydeoxyguanosine (8OHdG, 8-oxodG) as an index of oxidative DNA damage, and the limited data that are so far available on how diet can affect "steady-state" levels of oxidative DNA damage in humans. It appears that such damage can be modulated by vegetable intake, although the effects of vegetables may be mediated by components different from the "classical" antioxidants vitamin C, alpha-tocopherol and beta-carotene.