Effects of aging and/or training on antioxidant enzyme system in diaphragm of mice

Associations Among Physical Activity Level and Skeletal Muscle Antioxidants in Older Adults

BACKGROUND

Endogenous antioxidants are critical to limiting cellular oxidative damage.

METHODS

The authors determined if habitual physical activity (PA) and cardiorespiratory fitness were associated with skeletal muscle expression of endogenous antioxidants (superoxide dismutase, catalase, and glutathione peroxidase) and circulating oxidative stress markers (serum 8-hydroxy-2'-deoxyguanosine [8-OHdG]; oxidized low-density lipoprotein [LDL]) in older adults. Moderate to vigorous PA (MVPA) was estimated using a validated PA questionnaire in 26 older adults (mean [SD]; M/F = 9/17, age = 68 [4] y, body mass index = 26 [3] kg·m-2). Maximal oxygen consumption was estimated using the YMCA submaximal cycle test. Skeletal muscle endogenous antioxidants and serum 8-OHdG and oxidized LDL were measured. Bivariate and partial correlations (controlling for body mass index) were utilized to determine associations among variables.

RESULTS

MVPA (1640 [1176] kcal·wk-1) was correlated with superoxide dismutase 2 (r = .55), catalase (r = .55), glutathione peroxidase 1 (r = .48), and 8-OHdG (r = -.41) (all Ps < .05), but not oxidized LDL. MVPA and 8-OHdG were not significantly correlated when controlling for body mass index (r = -.29). Estimated maximal oxygen consumption was correlated with glutathione peroxidase 1 (r = .48; P < .05).

CONCLUSIONS

These data show that skeletal muscle endogenous antioxidant expression and circulating oxidative damage are associated with habitual MVPA in older adults. Thus, MVPA in older adults may be protective against reactive oxygen species damage due to higher expression of endogenous antioxidants.

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.

Proteomic profiling of mitochondria: what does it tell us about the ageing brain?

Mitochondrial dysfunction is evident in numerous neurodegenerative and age-related disorders. It has also been linked to cellular ageing, however our current understanding of the mitochondrial changes that occur are unclear. Functional studies have made some progress reporting reduced respiration, dynamic structural modifications and loss of membrane potential, though there are conflicts within these findings. Proteomic analyses, together with functional studies, are required in order to profile the mitochondrial changes that occur with age and can contribute to unravelling the complexity of the ageing phenotype. The emergence of improved protein separation techniques, combined with mass spectrometry analyses has allowed the identification of age and cell-type specific mitochondrial changes in energy metabolism, antioxidants, fusion and fission machinery, chaperones, membrane proteins and biosynthesis pathways. Here, we identify and review recent data from the analyses of mitochondria from rodent brains. It is expected that knowledge gained from understanding age-related mitochondrial changes of the brain should lead to improved biomarkers of normal ageing and also age-related disease progression.

Role of Protein Carbonylation in Skeletal Muscle Mass Loss Associated with Chronic Conditions

Muscle dysfunction, characterized by a reductive remodeling of muscle fibers, is a common systemic manifestation in highly prevalent conditions such as chronic heart failure (CHF), chronic obstructive pulmonary disease (COPD), cancer cachexia, and critically ill patients. Skeletal muscle dysfunction and impaired muscle mass may predict morbidity and mortality in patients with chronic diseases, regardless of the underlying condition. High levels of oxidants may alter function and structure of key cellular molecules such as proteins, DNA, and lipids, leading to cellular injury and death. Protein oxidation including protein carbonylation was demonstrated to modify enzyme activity and DNA binding of transcription factors, while also rendering proteins more prone to proteolytic degradation. Given the relevance of protein oxidation in the pathophysiology of many chronic conditions and their comorbidities, the current review focuses on the analysis of different studies in which the biological and clinical significance of the modifications induced by reactive carbonyls on proteins have been explored so far in skeletal muscles of patients and animal models of chronic conditions such as COPD, disuse muscle atrophy, cancer cachexia, sepsis, and physiological aging. Future research will elucidate the specific impact and sites of reactive carbonyls on muscle protein content and function in human conditions.

Can endurance exercise preconditioning prevention disuse muscle atrophy?

Emerging evidence suggests that exercise training can provide a level of protection against disuse muscle atrophy. Endurance exercise training imposes oxidative, metabolic, and heat stress on skeletal muscle which activates a variety of cellular signaling pathways that ultimately leads to the increased expression of proteins that have been demonstrated to protect muscle from inactivity -induced atrophy. This review will highlight the effect of exercise-induced oxidative stress on endogenous enzymatic antioxidant capacity (i.e., superoxide dismutase, glutathione peroxidase, and catalase), the role of oxidative and metabolic stress on PGC1-α, and finally highlight the effect heat stress and HSP70 induction. Finally, this review will discuss the supporting scientific evidence that these proteins can attenuate muscle atrophy through exercise preconditioning.

Protein carbonylation and muscle function in COPD and other conditions

Skeletal muscle, the most abundant tissue in mammals, is essential for any activity in life. Muscle dysfunction is a common systemic manifestation in highly prevalent conditions such as chronic obstructive pulmonary disease (COPD), cancer cachexia, and sepsis. It has a significant impact on exercise tolerance, thus worsening the patients' quality of life and survival. Among several factors, oxidative stress is a major player in the etiology of skeletal muscle dysfunction associated with those conditions. Whereas low levels of oxidants are absolutely required for normal cell adaptation, high levels of reactive oxygen species (ROS) alter the function and structure of molecules such as proteins, DNA, and lipids. Specifically, protein carbonylation, a common variety of protein oxidation, was shown to alter the function of key enzymes and structural proteins involved in muscle contractile performance. Moreover, increased levels of ROS may also activate proteolytic systems, thus leading to enhanced protein breakdown in several models. In the current review, the specific modifications induced by carbonylation in protein structure and function in muscles have been described. Furthermore, the potential role of ROS in the activation of proteolytic systems in skeletal muscles is also discussed. The review summarizes the effects of protein carbonylation on muscles in several models and conditions such as COPD, disuse muscle atrophy, cancer cachexia, sepsis, and aging. Future research should focus on the elucidation of the specific protein sites modified by ROS in these muscles using redox proteomics analyses and on the assessment of the consequent alterations in protein function and stability.

Reactive oxygen species in skeletal muscle signaling

Generation of reactive oxygen species (ROS) is a ubiquitous phenomenon in eukaryotic cells' life. Up to the 1990s of the past century, ROS have been solely considered as toxic species resulting in oxidative stress, pathogenesis and aging. However, there is now clear evidence that ROS are not merely toxic species but also-within certain concentrations-useful signaling molecules regulating physiological processes. During intense skeletal muscle contractile activity myotubes' mitochondria generate high ROS flows: this renders skeletal muscle a tissue where ROS hold a particular relevance. According to their hormetic nature, in muscles ROS may trigger different signaling pathways leading to diverging responses, from adaptation to cell death. Whether a "positive" or "negative" response will prevail depends on many variables such as, among others, the site of ROS production, the persistence of ROS flow or target cells' antioxidant status. In this light, a specific threshold of physiological ROS concentrations above which ROS exert negative, toxic effects is hard to determine, and the concept of "physiologically compatible" levels of ROS would better fit with such a dynamic scenario. In this review these concepts will be discussed along with the most relevant signaling pathways triggered and/or affected by ROS in skeletal muscle.

Treadmill but not wheel running improves fatigue resistance of isolated extensor digitorum longus muscle in mice

AIM

The present study is the first to compare the physiological impact of either forced treadmill or voluntary wheel running exercise on hindlimb muscle in mice.

METHODS

Male C57BL/6 mice were subjected to either 6 weeks of forced treadmill or voluntary wheel running exercise. Mice in the treadmill running exercise group (TRE; n = 8) ran 1.9 km day(-1) at a speed of 16 m min(-1) against an uphill incline of 11 degrees. In the running wheel exercise group (RWE; n = 8) animals ran 8.8 +/- 0.2 km per day (average speed 42 +/- 2 m min(-1)). After the experimental period, animals were killed and mechanical performance and oxygen consumption of isolated extensor digitorum longus (EDL) muscle were determined during serial electrical stimulation at 0.5, 1 and 2 Hz.

RESULTS

Steady-state half-width time (HWT) of twitch contraction at 0.5 Hz was significantly shorter in TRE and RWE than controls (CON) (41.3 +/- 0.2, 41.3 +/- 0.1 and 44.3 +/- 0.1 s respectively; P < 0.05). The rate of fatigue development and HWT lengthening at 2 Hz was the same in RWE and CON but lower in TRE (1.2-fold and twofold respectively; P < 0.05). EDL oxygen consumption, mitochondrial content and myosin heavy chain (MyHC) composition were not different between the groups.

CONCLUSION

These results indicate that both exercise modalities have an effect on a hindlimb fast-twitch muscle in mice, with the greatest impact seen with forced treadmill running.

Myocardial antioxidant status and oxidative stress after combined action of exercise training and ethanol in two different age groups of male albino rats

The interaction of exercise training and ethanol on the myocardial antioxidant enzymes and the oxidative stress markers was investigated in the Wistar strain male albino rats. We also tested the interactive effects of exercise training and ethanol on the age-associated free radical production and antioxidant defense system. We found a significant decrease (p<0.05) in the activity levels of superoxide dismutase (SOD) and catalase (CAT) in the myocardium of old rats when compared to young rats by 26% and 58%, respectively, suggesting the onset of age-dependent decrease in the myocardial antioxidant enzyme system. In contrast to the decreased antioxidant enzyme activity, xanthine oxidase (XOD) and lipid peroxidation (LPO) levels were elevated, suggesting the age-induced oxidative stress. Exercise training significantly (p < 0.05) elevated the activities of SOD, CAT, XOD and LPO levels in both the age groups of animals. Ethanol consumption significantly lowered the SOD and CAT activities in both the age groups, whereas a significant increase was observed in the XOD and LPO levels. In contrast, the combination of exercise training plus ethanol lowered XOD and LPO levels in both the age groups of rats compared to ethanol treated rats. A significant (p < 0.05) increase in the activities of SOD and CAT was reported in the rats treated with the combination of exercise training plus ethanol. This increase was more pronounced in the younger rats than the older rats. The findings of the present investigation on the potential role of antioxidant enzymes to counter the ethanol-induced pro-oxidants showed an increase with the interaction of exercise training. With age, a decrease in the antioxidant enzyme capacity was observed. This reveals that the old age rats were more affected to the pro-oxidants when compared to the young age rats. In conclusion it is demonstrated that two months treadmill endurance exercise training is beneficial to both young and old rats in improving antioxidant defense to challenge the oxidative stress in the myocardial tissue and thereby successfully countering the free radical production due to ethanol intoxication.

Aging, sex differences, and oxidative stress in human respiratory and limb muscles

Oxidative stress is involved in the sarcopenia of aging muscles. On the grounds that ventilatory muscles are permanently active, and their activity may even increase with aging, we hypothesized that the levels of oxidative stress would probably be increased in the external intercostals of elderly healthy individuals. We conducted a case-control study in which reactive carbonyl groups, malondialdehyde-protein adducts, 3-nitrotyrosine immunoreactivity, Mn-superoxide dismutase (Mn-SOD), and catalase were detected using immunoblotting in external intercostals and quadriceps (open muscle biopsies) obtained from 12 healthy elderly and 12 young individuals of both sexes. In elderly subjects, reactive carbonyls, malondialdehyde-protein adducts, 3-nitrotyrosine, Mn-SOD, and catalase were significantly greater in the external intercostals than in the young controls. A post hoc analysis, in which men and women from both groups were analyzed separately, revealed that the external intercostals of elderly women, but not those of elderly men, showed significantly increased levels of reactive carbonyls, malondialdehyde-protein adducts, 3-nitrotyrosine, and Mn-SOD compared to those of control females. This study suggests that differences in muscle activity might explain the differential pattern of oxidative stress observed in human respiratory and limb muscles with aging as well as the likely existence of a sex-related regulation of this phenomenon in these muscles.

Moderate caloric restriction increases diaphragmatic antioxidant enzyme mRNA, but not when combined with lifelong exercise

Diaphragmatic antioxidant enzymes are upregulated following acute and long-term treadmill exercise, but the effect of lifelong voluntary exercise (E) on diaphragmatic antioxidants is unknown. Therefore, 10-week old Fisher 344 rats were assigned to either: (a) sedentary ad libitum (AL) fed (24AL; n = 6); (b) E + 8% caloric restriction (24ECR; n = 9); or (c) sedentary + 8% caloric restriction (24CR; n = 9) groups. Diaphragms were harvested from animals at 24 months of age. Heme oxygenase-1 (HO-1) mRNA in addition to catalase (CAT), glutathione peroxidase (GPX), copper-zinc superoxide dismutase (Cu-ZnSOD) and manganese superoxide dismutase (MnSOD) mRNA and protein levels were measured. Reduced glutathione (GSH) and citrate synthase (CS) activity were measured to assess antioxidant status and oxidative capacity, respectively. The 24CR group demonstrated increased GPX, HO-1, MnSOD, and CAT mRNA compared to 24AL and 24ECR. Interestingly, the increased mRNA in 24CR animals did not result in elevated protein levels. No group differences in Cu-ZnSOD mRNA, CS activity, or GSH were observed, although GSH was 30% greater in 24CR animals (p = 0.085). In summary, although CR elevated the mRNA of key antioxidant enzymes in the diaphragm, lifelong CR alone or in combination with voluntary exercise did not alter diaphragm CS activity, antioxidant protein quantity, or GSH levels.

ROS in the local and systemic pathogenesis of COPD

An imbalance between oxidants and antioxidants is proposed in the pathogenesis of COPD. Potential alterations responsible for an imbalance in oxidant production and intra- and extracellular antioxidant defense systems are discussed with respect to COPD-related changes in the pulmonary compartment. In line with the current view of COPD as a disease with multiple systemic consequences, there is increasing evidence that imbalances in the redox milieu extend beyond the diseased lung in COPD patients. Skeletal muscle dysfunction is often observed in COPD and may result from imbalances in the redox environment of skeletal muscle. Potential triggers of oxidative stress in the muscle compartment include inflammation and hypoxia, and local sources of reactive oxygen and nitrogen species are discussed, as well the mechanisms by which skeletal muscle trophical state, contractility and fatigability may be affected by oxidative stress, resulting in skeletal muscle dysfunction.

Lipid peroxidation and antioxidant status in professional American football players during competition

BACKGROUND

Oxidative stress occurs during strenuous physical exercise, perhaps as a result of increased consumption of oxygen.

MATERIALS AND METHODS

In this study, different markers of oxidative stress were determined in eight national league American football players. Before (March) and at three time-points during the competition season (May, June, July) serum total peroxide concentrations, auto-antibody titres against oxidized low-density lipoprotein (oLab), and lag time of reactive oxygen species-induced degradation of the fluorophore 1-palmitoyl-2-((2-(4-(6-phenyl-trans-1,3,5-hexatrienyl)phenyl)ethyl)- carbonyl)-sn-glycero-3-phosphocholine (DPHPC) were measured along with serum ascorbate, alpha- and gamma-tocopherol, and beta-carotene concentrations.

RESULTS

Before the competition season, serum antioxidant concentrations were within the lower normal range; ascorbate concentrations increased significantly during the competition period (P < 0.05). Serum peroxide concentrations were within the normal range and increased significantly during the competition period (P < 0.05); in four of the eight subjects the increase was several times the baseline values, while four athletes did not show any increase. The oLab titres increased significantly at the mid-competition period time-point (P < 0.01), but levelled off thereafter.

DISCUSSION

Given that it could not be predicted from the baseline oxidative stress and antioxidant status which subject would respond to strenuous exercise with an increase in oxidative stress status, it is concluded that oxidative stress should be monitored in all athletes.

Exercise-induced oxidative stress in older adults as a function of habitual activity level

OBJECTIVES

It has been suggested that regular physical activity might maintain and promote the antioxidant defense capacity against oxidative stress. Therefore, we assessed exercise-induced oxidative stress in relation to habitual physical activity level (PAL) in older adults.

DESIGN

The study included a 2-week observation period for the measurement of average daily metabolic rate (ADMR) and PAL. Exercise-induced oxidative stress was measured during a 45-minute cycling test at submaximal intensity.

SETTING

A university medical research center.

PARTICIPANTS

Twenty-six subjects volunteered for the study (n = 26; mean age +/- standard deviation 60 +/- 1; body mass index 27 +/- 1 kg/m2).

MEASUREMENTS

PAL was determined as ADMR combined with a measurement of basal metabolic rate (BMR): PAL = ADMR/BMR. ADMR was measured over 2 weeks with the doubly labeled water method, preceded by a BMR measurement with a ventilated hood. Antipyrine oxidation was used as marker for oxidative stress in vivo. Reaction of antipyrine with hydroxyl radicals results in the formation of para-hydroxyantipyrine (p-APOH) and ortho-hydroxyantipyrine (o-APOH), where o-APOH is not formed through alternative oxygenetic pathways.

RESULTS

PAL was inversely related to the exercise-induced increase in the ratio of o-APOH to native antipyrine (r = 0.49, P = .010). The relationship between PAL and exercise-induced increase in the ratio of p-APOH (r = 0.30, P = .140) or thiobarbituric acid reactive species (r = 0.31, P = .130) did not reach the level of significance.

CONCLUSION

Physically active older adults have a reduced exercise-induced oxidative stress than older adults with a lower level of physical activity. It seems that regular physical activity improves the antioxidant defense capacity.

Exercise training and oxidative stress in the elderly as measured by antipyrine hydroxylation products

Effects of 12 wk exercise training on oxidative stress were examined in elderly humans. We measured oxidative stress during a 45 min cycling test by using antipyrine hydroxylation products. Antipyrine breakdown is independent of blood flow to the liver, which is important during exercise. Furthermore, antipyrine reacts quickly with hydroxyl radicals to form para- and ortho-hydroxyantipyrine. Ortho-hydroxyantipyrine is not formed in man through the mono-oxygenase pathway of cytochrome P450. Twenty subjects (9 women; 60 +/- 3 y) participated in the training program. Thirteen subjects (5 women; 64 +/- 7 y) served as inactive controls. Subjects trained, twice a week for 1 h, at a fitness center. After 12 wk, maximal oxygen uptake (p < .005) and workload capacity (p < .001) were only significantly elevated in the training group. After 12 wk, both groups observed no change in the ratios of antipyrine hydroxylates, para- and ortho-hydroxyantipyrine, to native antipyrine. Furthermore, no differences were observed within or between groups in the exercise-induced increase in the plasma level of thiobarbituric acid reactive species. In conclusion, 12-wk training had no effect on exercise-induced oxidative stress in elderly humans as measured by free radical reaction products of antipyrine. Despite the fact that training in elderly humans improves functional capacity, it appears not to compromise antioxidant defense mechanisms.

Effect of almitrine on upper airway muscle contraction in young and old rats

The effects of almitrine on the contractile properties of isolated geniohyoid and sternohyoid muscles were determined in physiological salt solution at 30 degrees C in young and old rats. In young rats, almitrine had no effect on twitch or tetanic tension, twitch:tetanic tension ratio, contractile kinetics, active or passive tension-length relationships or frequency-tension relationship in both muscles. Almitrine significantly increased resistance to fatigue in both muscles. In old rats, almitrine had no effect on twitch or tetanic tension, twitch:tetanic tension ratio, contractile kinetics, active or passive tension-length relationships, frequency-tension relationship or fatigue in both muscles. These results show that almitrine, in both young and old rats, has no effect on most of the contractile properties of isolated geniohyoid and sternohyoid muscles. However, almitrine increases resistance to fatigue in both muscles in young but not in old rats.

Hydroxyl radical generation during exercise increases mitochondrial protein oxidation and levels of urinary dityrosine

Isolated mitochondria are well-established sources of oxidants in vitro. There is little direct evidence that mitochondria promote oxidative stress in vivo, however. Model system studies demonstrate that ortho-tyrosine, meta-tyrosine, and o,o'-dityrosine increase in proteins oxidized by hydroxyl radical. To determine whether mitochondria generate oxidants in vivo, we used isotope dilution gas chromatography mass spectrometry to quantify levels of these markers in the heart muscle of control and exercised rats. Exercise led to a 50% increase in ortho-tyrosine, metatyrosine, and o,o'-dityrosine in the mitochondrial proteins but not cytosolic proteins of heart muscle. This increase was transient, and levels returned to normal when exercised animals were allowed to rest. There also was a transient increase in the level of o,o'-dityrosine in the urine of exercised rats. This relationship between mitochondrial and urine levels of o,o'-dityrosine suggests that urine assays of this oxidized amino acid may serve as noninvasive measures of oxidative stress. These observations also provide direct evidence that heart muscle mitochondria produce an intermediate resembling the hydroxyl radical that promotes protein oxidation in vivo.