Antioxidants and Skeletal Muscle Performance: "Common Knowledge" vs. Experimental Evidence

Nitrosative Redox Homeostasis and Antioxidant Response Defense in Disused Vastus lateralis Muscle in Long-Term Bedrest (Toulouse Cocktail Study)

Increased oxidative stress by reactive oxygen species (ROS) and reactive nitrogen species (RNS) is a major determinant of disuse-induced muscle atrophy. Muscle biopsies (thigh vastus lateralis, VL) obtained from healthy male subjects enrolled in the Toulouse Cocktail bedrest (BR) study were used to assess efficacy of an antioxidant cocktail (polyphenols, omega-3, vitamin E, and selenium) to counteract the increased redox homeostasis and enhance the antioxidant defense response by using label-free LC–MS/MS and NITRO-DIGE (nitrosated proteins), qPCR, and laser confocal microscopy. Label-free LC–MS/MS indicated that treatment prevented the redox homeostasis dysregulation and promoted structural remodeling (TPM3, MYH7, MYBPC, MYH1, MYL1, HRC, and LUM), increment of RyR1, myogenesis (CSRP3), and skeletal muscle development (MUSTN1, LMNA, AHNAK). These changes were absent in the Placebo group. Glycolysis, tricarboxylic acid cycle (TCA), oxidative phosphorylation, fatty acid beta-oxidation, and mitochondrial transmembrane transport were normalized in treated subjects. Proteins involved in protein folding were also normalized, whereas protein entailed in ion homeostasis decreased. NITRO-DIGE analysis showed significant protein nitrosylation changes for CAT, CA3, SDHA, and VDAC2 in Treatment vs. Placebo. Similarly, the nuclear factor erythroid 2-related factor 2 (Nrf-2) antioxidant response element (Nrf-2 ARE) signaling pathway showed an enhanced response in the Treatment group. Increased nitrosative redox homeostasis and decreased antioxidant defense response were found in post-BR control (Placebo, n = 10) vs. the antioxidant cocktail treated group (Treatment, n = 10). Taken together, increased nitrosative redox homeostasis and muscle deterioration during BR-driven physical inactivity were prevented, whereas decreased antioxidant nitrosative stress defense response was attenuated by Treatment suggesting positive effects of the nutritional intervention protocol in bedrest.

L-arginine Improves Plasma Lipid Profile and Muscle Inflammatory Response in Trained Rats After High-Intense Exercise

Purpose: This study aimed to evaluate whether supplementation with L-arginine alone or in combination with physical exercise training can modulate rats' lipid and inflammatory profiles after a single intense exercise session. Methods: Male Wistar rats were divided into four different groups: control (C), trained (T), supplemented with L-arginine (C + A) and trained and supplemented (T + A). Animals from supplemented groups (C + A and T + A groups) received 300 mg/kg animal body weight L-arginine diluted in 30 mL of drinking water for 8 weeks. Exercise training protocol (moderate intensity-70% achieved in the maximum effort test) was held 5 days/week for 8 weeks. Results: Exercise training induced a decrease in the amount of plasma, cholesterol and triglyceride totals, and skeletal muscle VEGF and CINC. Supplementation alone showed a benefit by reducing LDL levels. Conclusion: Training combined with supplementation showed a pronounced reduction in skeletal muscle VEGF and CINC amount. L-arginine supplementation, especially when associated with the regular aerobic physical exercise at moderate intensity was able to improve not only plasma lipid profile but also the inflammatory response of skeletal muscle immediately after an exhaustive physical exercise session.

Ionic Silicon Protects Oxidative Damage and Promotes Skeletal Muscle Cell Regeneration

Volumetric muscle loss injuries overwhelm the endogenous regenerative capacity of skeletal muscle, and the associated oxidative damage can delay regeneration and prolong recovery. This study aimed to investigate the effect of silicon-ions on C2C12 skeletal muscle cells under normal and excessive oxidative stress conditions to gain insights into its role on myogenesis during the early stages of muscle regeneration. In vitro studies indicated that 0.1 mM Si-ions into cell culture media significantly increased cell viability, proliferation, migration, and myotube formation compared to control. Additionally, MyoG, MyoD, Neurturin, and GABA expression were significantly increased with addition of 0.1, 0.5, and 1.0 mM of Si-ion for 1 and 5 days of C2C12 myoblast differentiation. Furthermore, 0.1-2.0 mM Si-ions attenuated the toxic effects of H2O2 within 24 h resulting in increased cell viability and differentiation. Addition of 1.0 mM of Si-ions significantly aid cell recovery and protected from the toxic effect of 0.4 mM H2O2 on cell migration. These results suggest that ionic silicon may have a potential effect in unfavorable situations where reactive oxygen species is predominant affecting cell viability, proliferation, migration, and differentiation. Furthermore, this study provides a guide for designing Si-containing biomaterials with desirable Si-ion release for skeletal muscle regeneration.

The effects of chromium picolinate on glucose and lipid metabolism in running rats

BACKGROUND

Chromium picolinate (CrPic) is commonly used to reduce muscle fatigue after exercise. We aimed to elucidate the effects of CrPic on glucose and lipid metabolism and the expression of glucose transporters in exercised rats.

METHODS

Forty-two male Wistar rats (8-week-old) were distributed into six groups (n = 7) as follows: Control, CrPic, Chronic Exercise (CEx), CEx + CrPic, Acute Exercise (AEx), and AEx + CrPic. CEx consists of 30 m/min, 30 min/day, and 5 days/week for 6 weeks. CrPic was supplemented at 400 μg elemental Cr/kg of diet for 6 weeks. In the AEx groups, animals were run on the treadmill at 30 m/min until exhaustion.

RESULTS

CEx significantly lowered blood glucose (BG), total cholesterol (TC) and triglyceride (TG) levels, but elevated insulin concentration (IC), compared with control (P < 0.05). CEx significantly decreased the level of malondialdehyde (MDA) in the serum, liver, and muscle while AEx elevated it (P < 0.001 for all). CrPic significantly decreased BG, TC, TG levels, and increased IC with a remarkable effect in CEx rats (P < 0.01). CrPic also significantly reduced serum, liver, and muscle MDA levels (P < 0.001). Both AEx and CEx increased the expression of liver glucose transporter 2 (GLUT-2) and muscle GLUT-4 with the highest level in CEx rats (P < 0.05). Moreover, CrPic supplementation significantly elevated GLUT-2 and GLUT-4 expressions in the liver and muscle of sedentary and exercise-treated rats (P < 0.05).

CONCLUSION

CrPic improves various metabolic parameters and reduces oxidative stress in CEx and AEx rats by decreasing BG, TC, TG, MDA levels in serum and elevating GLUT-2 and GLUT-4 expression in the liver and muscle samples. The efficacy of CrPic was more pronounced in CEx rats.

Capsaicinoids improve consequences of physical activity

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Capsaicinoids (CAPs) are active compounds in Capsicum fruits.

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CAPs have anti-inflammatory and antioxidant properties.

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CAPs with regular exercise may enhance lipid metabolism.

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CAPs down-regulate muscle SREBP-1c, LXRs, ACLY, FAS in exercised rats.

The purpose of this study was to investigate the effects of capsaicinoids (CAPs) on lipid metabolism, inflammation, antioxidant status and the changes in gene products involved in these metabolic functions in exercised rats. A total of 28 male Wistar albino rats were randomly divided into four groups (n = 7) (i) No exercise and no CAPs, (ii) No exercise + CAPs (iii) Regular exercise, (iv) Regular exercise + CAPs. Rats were administered as 0.2 mg capsaicinoids from 10 mg/kg BW/day Capsimax^® daily for 8 weeks. A significant decrease in lactate and malondialdehyde (MDA) levels and increase in activities of antioxidant enzymes were observed in the combination of regular exercise and CAPs group (P < 0.0001). Regular exercise + CAPs treated rats had greater nuclear factor-E2-related factor-2 (Nrf2) and heme oxygenase-1 (HO-1) levels in muscle than regular exercise and no exercise rats (P < 0.001). Nevertheless, regular exercise + CAPs treated had lower nuclear factor kappa B (NF-κB) and IL-10 levels in muscle than regular exercise and control rats (P < 0.001). Muscle sterol regulatory element-binding protein 1c (SREBP-1c), liver X receptors (LXR), ATP citrate lyase (ACLY) and fatty acid synthase (FAS) levels in the regular exercise + CAPs group were lower than all groups (P < 0.05). However, muscle PPAR-γ level was higher in the regular exercise and CAPs alone than the no exercise rats. These results suggest CAPs with regular exercise may enhance lipid metabolism by regulation of gene products involved in lipid and antioxidant metabolism including SREBP-1c, PPAR-γ, and Nrf2 pathways in rats.

l-Arginine supplementation improves rats' antioxidant system and exercise performance

Reactive species have great importance in sports performance, once they can directly regulate energy production, muscular contraction, inflammation, and fatigue. Therefore, the redox control is essential for athletes' performance. Studies demonstrated that l-arginine has an important role in the synthesis of urea, cell growth and production of nitric oxide, moreover, there are indications that it is also able to induce benefits to muscle antioxidant system through the upregulation of some antioxidant enzymes, and by inhibiting some pathways of reactive species production. Therefore, the aim of this study was to evaluate the effects of l-arginine supplementation on performance and oxidative stress of male rats (trained or not), submitted to a single session of high intensity exercise. Forty male Wistar rats were divided into four groups, control (C), control+l-arginine (C + A), trained (T), and trained+l-arginine (T + A). The aerobic training was conducted for 8 weeks. Data of maximum speed and time from tests were used as indicators of performance. Variables related to oxidative stress and antioxidant system were also evaluated. Aerobic training was capable to induce enhancements on animals' exercise performance and on their redox state. Additionally, supplementation improved rats' physical performance on both groups, control and trained. Different improvements between groups on the antioxidant capacity were observed. Nevertheless, considering the ergogenic effect of l-arginine and the lack of all positive adaptations promoted by the exercise training, untrained animals may be more exposed to oxidative damages after the practice of intense exercises.

Effects of Exercise Training under Hyperbaric Oxygen on Oxidative Stress Markers and Endurance Performance in Young Soccer Players: A Pilot Study

The aim of the present study was to determine the effects of three weeks of hyperbaric oxygen (HBO₂) training on oxidative stress markers and endurance performance in young soccer players. Participants (18.6 ± 1.6 years) were randomized into hyperbaric-hyperoxic (HH) training (n = 6) and normobaric normoxic (NN) training (n = 6) groups. Immediately before and after the 5th, 10th, and 15th training sessions, plasma oxidative stress markers (lipid hydroperoxides and uric acid), plasma antioxidant capacity (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid [TROLOX]), arterial blood gases, acid-base balance, bases excess (BE), and blood lactate analyses were performed. Before and after intervention, maximal oxygen uptake (VO₂max) and peak power output (PPO) were determined. Neither HH nor NN experienced significant changes on oxidative stress markers or antioxidant capacity during intervention. VO₂max and PPO were improved (moderate effect size) after HH training. The results suggest that HBO₂ endurance training does not increase oxidative stress markers and improves endurance performance in young soccer players. Our findings warrant future investigation to corroborate that HBO₂ endurance training could be a potential training approach for highly competitive young soccer players.

Omega-3 fatty acids differentially modulate enzymatic anti-oxidant systems in skeletal muscle cells

During physical activity, increased reactive oxygen species production occurs, which can lead to cell damage and in a decline of individual's performance and health. The use of omega-3 polyunsaturated fatty acids as a supplement to protect the immune system has been increasing; however, their possible benefit to the anti-oxidant system is not well described. Thus, the aim of this study was to evaluate whether the omega-3 fatty acids (docosahexaenoic acid and eicosapentaenoic acid) can be beneficial to the anti-oxidant system in cultured skeletal muscle cells. C2C12 myocytes were differentiated and treated with either eicosapentaenoic acid or docosahexaenoic acid for 24 h. Superoxide content was quantified using the dihydroethidine oxidation method and superoxide dismutase, catalase, and glutathione peroxidase activity, and expression was quantified. We observed that the docosahexaenoic fatty acids caused an increase in superoxide production. Eicosapentaenoic acid induced catalase activity, while docosahexaenoic acid suppressed superoxide dismutase activity. In addition, we found an increased protein expression of the total manganese superoxide dismutase and catalase enzymes when cells were treated with eicosapentaenoic acid. Taken together, these data indicate that the use of eicosapentaenoic acid may present both acute and chronic benefits; however, the treatment with DHA may not be beneficial to muscle cells.

UV-B exposure reduces locomotor performance by impairing muscle function but not mitochondrial ATP production

Ultraviolet B radiation (UV-B) can reduce swimming performance by increasing reactive oxygen species (ROS) formation. High concentrations of ROS can damage mitochondria, resulting in reduced ATP production. ROS can also damage muscle proteins, thereby leading to impaired muscle contractile function. We have shown previously that UV-B exposure reduces locomotor performance in mosquitofish (Gambusia holbrooki) without affecting metabolic scope. Our aim was therefore to test whether UV-B influences swimming performance of mosquitofish by ROS-induced damage to muscle proteins without affecting mitochondrial function. In a fully factorial design, we exposed mosquitofish to UV-B and no-UV-B controls in combination with exposure to N-acetylcysteine (NAC) plus no-NAC controls. We used NAC, a precursor of glutathione, as an antioxidant to test whether any effects of UV-B on swimming performance were at least partly due to UV-B-induced ROS. UV-B significantly reduced critical sustained swimming performance and tail beat frequencies, and it increased ROS-induced damage (protein carbonyl concentrations and lipid peroxidation) in muscle. However, UV-B did not affect the activity of sarco-endoplasmic reticulum ATPase (SERCA), an enzyme associated with muscle calcium cycling and muscle relaxation. UV-B did not affect ADP phosphorylation (state 3) rates of mitochondrial respiration, and it did not alter the amount of ATP produced per atom of oxygen consumed (P:O ratio). However, UV-B reduced the mitochondrial respiratory control ratio. Under UV-B exposure, fish treated with NAC showed greater swimming performance and tail beat frequencies, higher glutathione concentrations, and lower protein carbonyl concentrations and lipid peroxidation than untreated fish. Tail beat amplitude was not affected by any treatment. Our results showed, firstly, that the effects of UV-B on locomotor performance were mediated by ROS and, secondly, that reduced swimming performance was not caused by impaired mitochondrial ATP production. Instead, reduced tail beat frequencies indicate that muscle of UV-B exposed fish were slower, which was likely to have been caused by slower contraction rates, because SERCA activities remained unaffected.

Potential molecular mechanisms underlying muscle fatigue mediated by reactive oxygen and nitrogen species

Intense contractile activity causes a dramatic decline in the force and velocity generating capacity of skeletal muscle within a few minutes, a phenomenon that characterizes fatigue. Much of the research effort has focused on how elevated levels of the metabolites of ATP hydrolysis might inhibit the function of the contractile proteins. However, there is now growing evidence that elevated levels of reactive oxygen and nitrogen species (ROS/RNS), which also accumulate in the myoplasm during fatigue, also play a causative role in this type of fatigue. The most compelling evidence comes from observations demonstrating that pre-treatment of intact muscle with a ROS scavenger can significantly attenuate the development of fatigue. A clear advantage of this line of inquiry is that the molecular targets and protein modifications of some of the ROS scavengers are well-characterized enabling researchers to begin to identify potential regions and even specific amino acid residues modified during fatigue. Combining this knowledge with assessments of contractile properties from the whole muscle level down to the dynamic motions within specific contractile proteins enable the linking of the structural modifications to the functional impacts, using advanced chemical and biophysical techniques. Based on this approach at least two areas are beginning emerge as potentially important sites, the regulatory protein troponin and the actin binding region of myosin. This review highlights some of these recent efforts which have the potential to offer uniquely precise information on the underlying molecular basis of fatigue. This work may also have implications beyond muscle fatigue as ROS/RNS mediated protein modifications are also thought to play a role in the loss of muscle function with aging and in some acute pathologies like cardiac arrest and ischemia.

Vitamin C and E supplementation blunts increases in total lean body mass in elderly men after strength training

The aim of this study was to investigate the effects of vitamin C and E supplementation on changes in muscle mass (lean mass and muscle thickness) and strength during 12 weeks of strength training in elderly men. Thirty-four elderly males (60-81 years) were randomized to either an antioxidant group (500 mg of vitamin C and 117.5 mg vitamin E before and after training) or a placebo group following the same strength training program (three sessions per week). Body composition was assessed with dual-energy X-ray absorptiometry and muscle thickness by ultrasound imaging. Muscle strength was measured as one-repetition maximum (1RM). Total lean mass increased by 3.9% (95% confidence intervals: 3.0, 5.2) and 1.4% (0, 5.4) in the placebo and antioxidant groups, respectively, revealing larger gains in the placebo group (P = 0.04). Similarly, the thickness of m. rectus femoris increased more in the placebo group [16.2% (12.8, 24.1)] than in the antioxidant group [10.9% (9.8, 13.5); P = 0.01]. Increases of lean mass in trunk and arms, and muscle thickness of elbow flexors, did not differ significantly between groups. With no group differences, 1RM improved in the range of 15-21% (P < 0.001). In conclusion, high-dosage vitamin C and E supplementation blunted certain muscular adaptations to strength training in elderly men.

Antioxidant treatments do not improve force recovery after fatiguing stimulation of mouse skeletal muscle fibres

The contractile performance of skeletal muscle declines during intense activities, i.e. fatigue develops. Fatigued muscle can enter a state of prolonged low-frequency force depression (PLFFD). PLFFD can be due to decreased tetanic free cytosolic [Ca(2+) ] ([Ca(2+) ]i ) and/or decreased myofibrillar Ca(2+) sensitivity. Increases in reactive oxygen and nitrogen species (ROS/RNS) may contribute to fatigue-induced force reductions. We studied whether pharmacological ROS/RNS inhibition delays fatigue and/or counteracts the development of PLFFD. Mechanically isolated mouse fast-twitch fibres were fatigued by sixty 150 ms, 70 Hz tetani given every 1 s. Experiments were performed in standard Tyrode solution (control) or in the presence of: NADPH oxidase (NOX) 2 inhibitor (gp91ds-tat); NOX4 inhibitor (GKT137831); mitochondria-targeted antioxidant (SS-31); nitric oxide synthase (NOS) inhibitor (l-NAME); the general antioxidant N-acetylcysteine (NAC); a cocktail of SS-31, l-NAME and NAC. Spatially and temporally averaged [Ca(2+) ]i and peak force were reduced by ∼20% and ∼70% at the end of fatiguing stimulation, respectively, with no marked differences between groups. PLFFD was similar in all groups, with 30 Hz force being decreased by ∼60% at 30 min of recovery. PLFFD was mostly due to decreased tetanic [Ca(2+) ]i in control fibres and in the presence of NOX2 or NOX4 inhibitors. Conversely, in fibres exposed to SS-31 or the anti ROS/RNS cocktail, tetanic [Ca(2+) ]i was not decreased during recovery so PLFFD was only caused by decreased myofibrillar Ca(2+) sensitivity. The cocktail also increased resting [Ca(2+) ]i and ultimately caused cell death. In conclusion, ROS/RNS-neutralizing compounds did not counteract the force decline during or after induction of fatigue.

Impact of polyphenol antioxidants on cycling performance and cardiovascular function

This investigation sought to determine if supplementation with polyphenol antioxidant (PA) improves exercise performance in the heat (31.5 °C, 55% RH) by altering the cardiovascular and thermoregulatory responses to exercise. Twelve endurance trained athletes ingested PA or placebo (PLAC) for 7 days. Consecutive days of exercise testing were performed at the end of the supplementation periods. Cardiovascular and thermoregulatory measures were made during exercise. Performance, as measured by a 10 min time trial (TT) following 50 min of moderate intensity cycling, was not different between treatments (PLAC: 292 ± 33 W and PA: 279 ± 38 W, p = 0.12). Gross efficiency, blood lactate, maximal neuromuscular power, and ratings of perceived exertion were also not different between treatments. Similarly, performance on the second day of testing, as assessed by time to fatigue at maximal oxygen consumption, was not different between treatments (PLAC; 377 ± 117 s vs. PA; 364 ± 128 s, p = 0.61). Cardiovascular and thermoregulatory responses to exercise were not different between treatments on either day of exercise testing. Polyphenol antioxidant supplementation had no impact on exercise performance and did not alter the cardiovascular or thermoregulatory responses to exercise in the heat.

Mitochondrial pathways in sarcopenia of aging and disuse muscle atrophy

Muscle loss during aging and disuse is a highly prevalent and disabling condition, but knowledge about cellular pathways mediating muscle atrophy is still limited. Given the postmitotic nature of skeletal myocytes, the maintenance of cellular homeostasis relies on the efficiency of cellular quality control mechanisms. In this scenario, alterations in mitochondrial function are considered a major factor underlying sarcopenia and muscle atrophy. Damaged mitochondria are not only less bioenergetically efficient, but also generate increased amounts of reactive oxygen species, interfere with cellular quality control mechanisms, and display a greater propensity to trigger apoptosis. Thus, mitochondria stand at the crossroad of signaling pathways that regulate skeletal myocyte function and viability. Studies on these pathways have sometimes provided unexpected and counterintuitive results, which suggests that they are organized into a complex, heterarchical network that is currently insufficiently understood. Untangling the complexity of such a network will likely provide clinicians with novel and highly effective therapeutics to counter the muscle loss associated with aging and disuse. In this review, we summarize the current knowledge on the mechanisms whereby mitochondrial dysfunction intervenes in the pathogenesis of sarcopenia and disuse atrophy, and highlight the prospect of targeting specific processes to treat these conditions.

Doublet discharge stimulation increases sarcoplasmic reticulum Ca2+ release and improves performance during fatiguing contractions in mouse muscle fibres

Double discharges (doublets) of motor neurones at the onset of contractions increase both force and rate of force development during voluntary submaximal contractions. The purpose of this study was to examine the role of doublet discharges on force and myoplasmic free [Ca(2+)] ([Ca(2+)]i) during repeated fatiguing contractions, using a stimulation protocol mimicking the in vivo activation pattern during running. Individual intact fibres from the flexor digitorum brevis muscle of mice were stimulated at 33°C to undergo 150 constant-frequency (five pulses at 70 Hz) or doublet (an initial, extra pulse at 200 Hz) contractions at 300 ms intervals. In the unfatigued state, doublet stimulation resulted in a transient (∼10 ms) approximate doubling of [Ca(2+)]i, which was accompanied by a greater force-time integral (∼70%) and peak force (∼40%) compared to constant frequency contractions. Moreover, doublets markedly increased force-time integral and peak force during the first 25 contractions of the fatiguing stimulation. In later stages of fatigue, addition of doublets increased force production but the increase in force production corresponded to only a minor portion of the fatigue-induced reduction in force. In conclusion, double discharges at the onset of contractions effectively increase force production, especially in early stages of fatigue. This beneficial effect occurs without additional force loss in later stages of fatigue, indicating that the additional energy cost induced by doublet discharges to skeletal muscle is limited.

Effects of physical activity and inactivity on muscle fatigue

The aim of this review was to examine the mechanisms by which physical activity and inactivity modify muscle fatigue. It is well known that acute or chronic increases in physical activity result in structural, metabolic, hormonal, neural, and molecular adaptations that increase the level of force or power that can be sustained by a muscle. These adaptations depend on the type, intensity, and volume of the exercise stimulus, but recent studies have highlighted the role of high intensity, short-duration exercise as a time-efficient method to achieve both anaerobic and aerobic/endurance type adaptations. The factors that determine the fatigue profile of a muscle during intense exercise include muscle fiber composition, neuromuscular characteristics, high energy metabolite stores, buffering capacity, ionic regulation, capillarization, and mitochondrial density. Muscle fiber-type transformation during exercise training is usually toward the intermediate type IIA at the expense of both type I and IIx myosin heavy-chain isoforms. High-intensity training results in increases of both glycolytic and oxidative enzymes, muscle capillarization, improved phosphocreatine resynthesis and regulation of K⁺, H⁺, and lactate ions. Decreases of the habitual activity level due to injury or sedentary lifestyle result in partial or even compete reversal of the adaptations due to previous training, manifested by reductions in fiber cross-sectional area, decreased oxidative capacity, and capillarization. Complete immobilization due to injury results in markedly decreased force output and fatigue resistance. Muscle unloading reduces electromyographic activity and causes muscle atrophy and significant decreases in capillarization and oxidative enzymes activity. The last part of the review discusses the beneficial effects of intermittent high-intensity exercise training in patients with different health conditions to demonstrate the powerful effect of exercise on health and well being.