Mitochondria changes in human muscle after prolonged exercise, endurance training and selenium supplementation

Beyond antioxidants: Selenium and skeletal muscle mitochondria

The element, Selenium (Se), has an essential nutritive and biological role as a trace mineral known primarily for its vital antioxidant functions as a constituent of the selenoenzyme, glutathione peroxidase. However, Se also has a much more global biological impact beyond antioxidant function. The objective of this review is to present an overview of prior research on the extra-antioxidant effects of Se with a key focus on skeletal muscle mitochondrial energetics. Cognizance of these additional functions of Se is requisite when formulating and recommending dietary supplementation of Se in humans or animals. Chief amongst its myriad of biological contributions, Se influences mitochondrial capacity and function and, subsequently, muscular health. Dietary Se supplementation has been shown to increase skeletal muscle mitochondrial volume density and within some cell lines, Se treatment increases mitochondrial biogenesis and respiratory capacity. In addition, the selenoproteins H, N, W, and O and deiodinases exhibit varying effects on mitochondrial and/or skeletal muscle function. Selenoprotein H enhances mitochondrial biogenesis whereas selenoproteins N and W appear to influence muscle calcium homeostasis which impacts mitochondrial function. Moreover, selenoprotein O's intramitochondrial residence facilitates Se's redox function. Deiodinases regulate thyroid hormone activation which impacts muscle cell regeneration, metabolism, and reactive oxygen species production. Although the precise relationships between dietary Se and skeletal muscle mitochondria remain unclear, previous research constitutes a firm foundation that portends promising new discoveries by future investigations.

Elevated dietary selenium rescues mitochondrial capacity impairment induced by decreased vitamin E intake in young exercising horses

Maintenance of mitochondrial health, which is supported in part by dietary antioxidants such as selenium (Se) and vitamin E (vitE), is pertinent to optimizing athletic performance. Deficiencies in Se and vitE negatively impact muscle health but mitochondrial adaptations to various levels of dietary Se and vitE are poorly understood. Young Quarter Horses (mean ± SD: 17.6 ± 0.9 mo) undergoing submaximal exercise training were used to test the hypothesis that a proprietary antioxidant blend containing elevated Se yeast (EconomasE, Alltech, Inc., Nicholasville, KY) would improve mitochondrial characteristics compared to Se at current requirements, even with reduced vitE intake. Horses were balanced by age, sex, body weight (BW), and farm of origin and randomly assigned to one of three custom-formulated concentrates fed at 1% BW (dry matter, DM basis) for 12 wk: 1) 100 IU vitE/kg DM and 0.1 mg Se/kg DM (CON, n = 6); 2) no added vitE plus EconomasE to provide 0.1 mg Se/kg DM (ESe1, n = 6); or 3) no added vitE plus EconomasE to provide 0.3 mg Se/kg DM (ESe3, n = 6). Samples collected at week 0 and 12 were analyzed for serum Se and middle gluteal glutathione peroxidase (GPx) and mitochondrial enzyme activities by kinetic colorimetry and mitochondrial capacities by high-resolution respirometry. Data were analyzed using mixed linear models in SAS v9.4 with repeated measures (time) and fixed effects of time, diet, and time × diet; horse(diet) served as a random effect. Serum Se tended to increase in all horses by week 12 (P = 0.08) but was unaffected by diet. Muscle GPx activity remained similar among all horses throughout the duration of the study. Mitochondrial volume density (citrate synthase [CS] activity), integrative function (cytochrome c oxidase [CCO] activity per mg protein), and integrative (per mg tissue) oxidative (P) and electron transfer (E) capacities increased from week 0 to 12 in all horses (P ≤ 0.01). Intrinsic (relative to CS) CCO activity decreased in all horses (P = 0.001), while intrinsic P and E capacities decreased only in ESe1 horses from week 0 to 12 (P ≤ 0.002). These results suggest that feeding EconomasE to provide 0.3 mg Se/kg DM may prevent adverse effects of removing 100 IU dietary vitE/kg DM on mitochondria in young horses. More research is needed to determine optimal dietary Se and vitE levels in performance horses to maximize mitochondrial energy production.

Effects of Curcumin and Fenugreek Soluble Fiber on the Physical Working Capacity at the Fatigue Threshold, Peak Oxygen Consumption, and Time to Exhaustion

Herrick, LP, Goh, J, Menke, W, Campbell, MS, Fleenor, BS, Abel, MG, and Bergstrom, HC. Effects of curcumin and fenugreek soluble fiber on the physical working capacity at the fatigue threshold, peak oxygen consumption, and time to exhaustion. J Strength Cond Res 34(12): 3346-3355, 2020-The purpose of this study was to examine the effects of curcumin in combination with fenugreek soluble fiber (CUR + FEN) or fenugreek soluble fiber alone (FEN) on the neuromuscular fatigue threshold (PWCFT), peak oxygen consumption (V˙o2peak), and time to exhaustion (Tlim) on a graded exercise test (GXT), in untrained subjects. The PWCFT estimates the highest power output that can be maintained without evidence of neuromuscular fatigue. Forty-seven untrained, college-aged subjects were randomly assigned to one of 3 supplementation groups; placebo (PLA, n = 15), CUR + FEN (500 mg·d, n = 18), or FEN (300 mg·d, n = 14). The subjects completed a maximal GXT on a cycle ergometer to determine the PWCFT, V˙o2peak, and Tlim before (PRE) and after (POST) 28 days of daily supplementation. Surface electromyographic signals were recorded from a bipolar electrode arrangement on the vastus lateralis of the right leg during each test. Separate one-way analysis of covariances were used to determine if there were between-group differences for adjusted POST-PWCFT, POST-V˙o2peak, and POST-Tlim values, covaried for the respective PRE-test scores. The adjusted POST-PWCFT for the CUR + FEN group (mean ± SD: 196 ± 58 W) was greater (p = 0.016) than the PLA group (168 ± 49 W) but the FEN group (185 ± 32 W) was not different from the CUR + FEN or PLA groups (p > 0.05). There were no differences for adjusted POST-V˙o2peak (p = 0.612) or POST-Tlim (p = 0.508) among the groups. These findings suggested curcumin combined with fenugreek soluble fiber might delay neuromuscular fatigue.

Antioxidant supplements and endurance exercise: Current evidence and mechanistic insights

Antioxidant supplements are commonly consumed by endurance athletes to minimize exercise-induced oxidative stress, with the intention of enhancing recovery and improving performance. There are numerous commercially available nutritional supplements that are targeted to athletes and health enthusiasts that allegedly possess antioxidant properties. However, most of these compounds are poorly investigated with respect to their in vivo redox activity and efficacy in humans. Therefore, this review will firstly provide a background to endurance exercise-related redox signalling and the subsequent adaptations in skeletal muscle and vascular function. The review will then discuss commonly available compounds with purported antioxidant effects for use by athletes. N-acetyl cysteine may be of benefit over the days prior to an endurance event; while chronic intake of combined 1000 mg vitamin C + vitamin E is not recommended during periods of heavy training associated with adaptations in skeletal muscle. Melatonin, vitamin E and α-lipoic acid appear effective at decreasing markers of exercise-induced oxidative stress. However, evidence on their effects on endurance performance are either lacking or not supportive. Catechins, anthocyanins, coenzyme Q10 and vitamin C may improve vascular function, however, evidence is either limited to specific sub-populations and/or does not translate to improved performance. Finally, additional research should clarify the potential benefits of curcumin in improving muscle recovery post intensive exercise; and the potential hampering effects of astaxanthin, selenium and vitamin A on skeletal muscle adaptations to endurance training. Overall, we highlight the lack of supportive evidence for most antioxidant compounds to recommend to athletes.

The Role of Selenium Mineral Trace Element in Exercise: Antioxidant Defense System, Muscle Performance, Hormone Response, and Athletic Performance. A Systematic Review

Exercise overproduces oxygen reactive species (ROS) and eventually exceeds the body’s antioxidant capacity to neutralize them. The ROS produce damaging effects on the cell membrane and contribute to skeletal muscle damage. Selenium (Se), a natural mineral trace element, is an essential component of selenoproteins that plays an important role in antioxidant defense. The activity of the enzyme glutathione peroxidase (GPx), a highly-efficient antioxidant enzyme, is closely dependent on the presence of Se. These properties of Se may be potentially applicable to improve athletic performance and training recovery. We systematically searched for published studies to evaluate the effectiveness of Se supplementation on antioxidant defense system, muscle performance, hormone response, and athletic performance among physically active individuals. We used the Preferred Reporting Elements for Systematic Reviews and Meta-Analysis (PRISMA) guidelines and searched in SCOPUS, Web of Science (WOS), and PubMed databases to identify published studies until March 2020. The systematic review incorporated original studies with randomized controlled crossover or parallel design in which intake of Se administered once a day was compared with the same placebo conditions. No exclusions were applied for the type of physical exercise performed, the sex, nor the age of the participants. Among 150 articles identified in the search, 6 met the criteria and were included in the systematic review. The methodological quality of the studies was evaluated using the McMaster Critical Review Form. Oral Se supplementation with 180 µg/day or 240 µg/day (selenomethionine) and 200 µg/day (Sodium Selenite), significantly decreased lipid hydroperoxide levels and increased GPx in plasma, erythrocyte, and muscle. No significant effects were observed on athletic performance, testosterone hormone levels, creatine kinase activity, and exercise training-induced adaptations on oxidative enzyme activities or on muscle fiber type myosin heavy chain expression. In addition, Se supplementation showed to have a dampening effect on the mitochondria changes in chronic and acute exercise. In summary, the use of Se supplementation has no benefits on aerobic or anaerobic athletic performance but it may prevent Se deficiencies among athletes with high-intensity and high-volume training. Optimal Se plasma levels may be important to minimize chronic exercise-induced oxidative effects and modulate the exercise effect on mitochondrial changes.

Additional Effects of Nutritional Antioxidant Supplementation on Peripheral Muscle during Pulmonary Rehabilitation in COPD Patients: A Randomized Controlled Trial

Background

Skeletal muscle dysfunction in patients with chronic obstructive pulmonary disease (COPD) is not fully reversed by exercise training. Antioxidants are critical for muscle homeostasis and adaptation to training. However, COPD patients experience antioxidant deficits that worsen after training and might impact their muscle response to training. Nutritional antioxidant supplementation in combination with pulmonary rehabilitation (PR) would further improve muscle function, oxidative stress, and PR outcomes in COPD patients.

Methods

Sixty-four COPD patients admitted to inpatient PR were randomized to receive 28 days of oral antioxidant supplementation targeting the previously observed deficits (PR antioxidant group; α-tocopherol: 30 mg/day, ascorbate: 180 mg/day, zinc gluconate: 15 mg/day, selenomethionine: 50 μg/day) or placebo (PR placebo group). PR consisted of 24 sessions of moderate-intensity exercise training. Changes in muscle endurance (primary outcome), oxidative stress, and PR outcomes were assessed.

Results

Eighty-one percent of the patients (FEV₁ = 58.9 ± 20.0%pred) showed at least one nutritional antioxidant deficit. Training improved muscle endurance in the PR placebo group (+37.4 ± 45.1%, p < 0.001), without additional increase in the PR antioxidant group (-6.6 ± 11.3%; p = 0.56). Nevertheless, supplementation increased the α-tocopherol/γ-tocopherol ratio and selenium (+58 ± 20%, p < 0.001, and +16 ± 5%, p < 0.01, respectively), muscle strength (+11 ± 3%, p < 0.001), and serum total proteins (+7 ± 2%, p < 0.001), and it tended to increase the type I fiber proportion (+32 ± 17%, p = 0.07). The prevalence of muscle weakness decreased in the PR antioxidant group only, from 30.0 to 10.7% (p < 0.05).

Conclusions

While the primary outcome was not significantly improved, COPD patients demonstrate significant improvements of secondary outcomes (muscle strength and other training-refractory outcomes), suggesting a potential “add-on” effect of the nutritional antioxidant supplementation (vitamins C and E, zinc, and selenium) during PR. This trial is registered with NCT01942889.

The Role of Mineral and Trace Element Supplementation in Exercise and Athletic Performance: A Systematic Review

Minerals and trace elements (MTEs) are micronutrients involved in hundreds of biological processes. Deficiency in MTEs can negatively affect athletic performance. Approximately 50% of athletes have reported consuming some form of micronutrient supplement; however, there is limited data confirming their efficacy for improving performance. The aim of this study was to systematically review the role of MTEs in exercise and athletic performance. Six electronic databases and grey literature sources (MEDLINE; EMBASE; CINAHL and SportDISCUS; Web of Science and clinicaltrials.gov) were searched, in accordance with PRISMA guidelines. Results: 17,433 articles were identified and 130 experiments from 128 studies were included. Retrieved articles included Iron (n = 29), Calcium (n = 11), Magnesium, (n = 22), Phosphate (n = 17), Zinc (n = 9), Sodium (n = 15), Boron (n = 4), Selenium (n = 5), Chromium (n = 12) and multi-mineral articles (n = 5). No relevant articles were identified for Copper, Manganese, Iodine, Nickel, Fluoride or Cobalt. Only Iron and Magnesium included articles of sufficient quality to be assigned as 'strong'. Currently, there is little evidence to support the use of MTE supplementation to improve physiological markers of athletic performance, with the possible exception of Iron (in particular, biological situations) and Magnesium as these currently have the strongest quality evidence. Regardless, some MTEs may possess the potential to improve athletic performance, but more high quality research is required before support for these MTEs can be given. PROSPERO preregistered (CRD42018090502).

Cap-Independent Translational Control of Carcinogenesis

Translational regulation has been shown to play an important role in cancer and tumor progression. Despite this fact, the role of translational control in cancer is an understudied and under appreciated field, most likely due to the technological hurdles and paucity of methods available to establish that changes in protein levels are due to translational regulation. Tumors are subjected to many adverse stress conditions such as hypoxia or starvation. Under stress conditions, translation is globally downregulated through several different pathways in order to conserve energy and nutrients. Many of the proteins that are synthesized during stress in order to cope with the stress use a non-canonical or cap-independent mechanism of initiation. Tumor cells have utilized these alternative mechanisms of translation initiation to promote survival during tumor progression. This review will specifically discuss the role of cap-independent translation initiation, which relies on an internal ribosome entry site (IRES) to recruit the ribosomal subunits internally to the messenger RNA. We will provide an overview of the role of IRES-mediated translation in cancer by discussing the types of genes that use IRESs and the conditions under which these mechanisms of initiation are used. We will specifically focus on three well-studied examples: Apaf-1, p53, and c-Jun, where IRES-mediated translation has been demonstrated to play an important role in tumorigenesis or tumor progression.

Effect of selenium supplementation on lipid peroxidation, antioxidant enzymes, and lactate levels in rats immediately after acute swimming exercise

The present study aims to evaluate the effect of selenium supplementation on lipid peroxidation and lactate levels in rats subjected to acute swimming exercise. Thirty-two adult male rats of Sprague-Dawley type were divided into four groups. Group 1, control; group 2, selenium-supplemented; group 3, swimming control; group 4, selenium-supplemented swimming group. The animals in groups 2 and 4 were supplemented with (i.p.) 6 mg/kg/day sodium selenite for 4 weeks. The blood samples taken from the animals by decapitation method were analyzed in terms of erythrocyte-reduced glutathione (GSH), serum glutathione peroxidase (GPx) and superoxide dismutase (SOD), and plasma malondialdehyde (MDA) and lactate using the colorimetric method, and serum selenium values using an atomic emission device. In the study, the highest MDA and lactate values were found in group 3, while the highest GSH, GPx and SOD values were obtained in group 4 (p < 0,001). Group 2 had the highest and group 3 had the lowest selenium levels (p < 0,001). Results of the study indicate that the increase in free radical production and lactate levels due to acute swimming exercise in rats might be offset by selenium supplementation. Selenium supplementation may be important in that it supports the antioxidant system in physical activity.

Regulation of skeletal muscle mitochondrial function: genes to proteins

The impact of ageing on mitochondrial function and the deterministic role of mitochondria on senescence continue to be topics of vigorous debate. Many studies report that skeletal muscle mitochondrial content and function are reduced with ageing and metabolic diseases associated with insulin resistance. However, an accumulating body of literature suggests that physical inactivity typical of ageing may be a more important determinant of mitochondrial function than chronological age, per se. Reports of age-related declines in mitochondrial function have spawned a vast body of literature devoted to understanding the underlying mechanisms. These mechanisms include decreased abundance of mtDNA, reduced mRNA levels, as well as decreased synthesis and expression of mitochondrial proteins, ultimately resulting in decreased function of the whole organelle. Effective therapies to prevent, reverse or delay the onset of the aforementioned mitochondrial changes, regardless of their inevitability or precise underlying causes, require an intimate understanding of the processes that regulate mitochondrial biogenesis, which necessitates the coordinated regulation of nuclear and mitochondrial genomes. Herein we review the current thinking on regulation of mitochondrial biogenesis by transcription factors and transcriptional co-activators and the role of hormones and exercise in initiating this process. We review how exercise may help preserve mitochondrial content and functionality across the lifespan, and how physical inactivity is emerging as a major determinant of many age-associated changes at the level of the mitochondrion. We also review evidence that some mitochondrial changes with ageing are independent of exercise or physical activity and appear to be inevitable consequences of old age.

Mitochondrial function as a determinant of life span

Average human life expectancy has progressively increased over many decades largely due to improvements in nutrition, vaccination, antimicrobial agents, and effective treatment/prevention of cardiovascular disease, cancer, etc. Maximal life span, in contrast, has changed very little. Caloric restriction (CR) increases maximal life span in many species, in concert with improvements in mitochondrial function. These effects have yet to be demonstrated in humans, and the duration and level of CR required to extend life span in animals is not realistic in humans. Physical activity (voluntary exercise) continues to hold much promise for increasing healthy life expectancy in humans, but remains to show any impact to increase maximal life span. However, longevity in Caenorhabditis elegans is related to activity levels, possibly through maintenance of mitochondrial function throughout the life span. In humans, we reported a progressive decline in muscle mitochondrial DNA abundance and protein synthesis with age. Other investigators also noted age-related declines in muscle mitochondrial function, which are related to peak oxygen uptake. Long-term aerobic exercise largely prevented age-related declines in mitochondrial DNA abundance and function in humans and may increase spontaneous activity levels in mice. Notwithstanding, the impact of aerobic exercise and activity levels on maximal life span is uncertain. It is proposed that age-related declines in mitochondrial content and function not only affect physical function, but also play a major role in regulation of life span. Regular aerobic exercise and prevention of adiposity by healthy diet may increase healthy life expectancy and prolong life span through beneficial effects at the level of the mitochondrion.

Impact of endurance training on murine spontaneous activity, muscle mitochondrial DNA abundance, gene transcripts, and function

We hypothesized that enhanced skeletal muscle mitochondrial function following aerobic exercise training is related to an increase in mitochondrial transcription factors, DNA abundance [mitochondrial DNA (mtDNA)], and mitochondria-related gene transcript levels, as well as spontaneous physical activity (SPA) levels. We report the effects of daily treadmill training on 12-wk-old FVB mice for 5 days/wk over 8 wk at 80% peak O(2) consumption and studied the training effect on changes in body composition, glucose tolerance, muscle mtDNA muscle, mitochondria-related gene transcripts, in vitro muscle mitochondrial ATP production capacity (MATPC), and SPA levels. Compared with the untrained mice, the trained mice had higher peak O(2) consumption (+18%; P < 0.001), lower percentage of abdominal (-25.4%; P < 0.02) and body fat (-19.5%; P < 0.01), improved glucose tolerance (P < 0.04), and higher muscle mitochondrial enzyme activity (+19.5-43.8%; P < 0.04) and MATPC (+28.9 to +32.4%; P < 0.01). Gene array analysis showed significant differences in mRNAs of mitochondria-related ontology groups between the trained and untrained mice. Training also increased muscle mtDNA (+88.4 to +110%; P < 0.05), peroxisome proliferative-activated receptor-gamma coactivator-1alpha protein (+99.5%; P < 0.04), and mitochondrial transcription factor A mRNA levels (+21.7%; P < 0.004) levels. SPA levels were higher in trained mice (P = 0.056, two-sided t-test) and significantly correlated with two separate substrate-based measurements of MATPC (P < 0.02). In conclusion, aerobic exercise training enhances muscle mitochondrial transcription factors, mtDNA abundance, mitochondria-related gene transcript levels, and mitochondrial function, and this enhancement in mitochondrial function occurs in association with increased SPA.

Initiation of Apaf-1 translation by internal ribosome entry

The apoptotic protease activating factor (Apaf-1) plays a central role in apoptosis: interaction of this protein with procaspase-9 leads to cleavage and activation of this initiator caspase. In common with other mRNAs whose protein products have a major regulatory function, the 5' untranslated region (UTR) of Apaf-1 is long, G-C rich and has the potential to form secondary structure. We have shown that the 5' UTR of Apaf-1 contains an internal ribosome entry segment, located in a 233 nucleotide region towards the 3' end of the leader, and that the translation initiation of this mRNA occurs only by internal ribosome entry. The Apaf-1 IRES is active in almost all human cell types tested, including Human cervical carcinoma (HeLa), Human liver carcinoma (HepG2), Human breast carcinoma (MCF7), Human embryonic kidney (HK293), African Green Monkey kidney (COS7) and Human lung (MRC5). The Apaf-1 IRES initiates translation as efficiently as the HRV IRES, but is less active than the c-myc IRES. We propose that the Apaf-1 IRES ensures that a constant cellular level of Apaf-1 protein is maintained even under conditions where cap-dependent translation is compromised. Oncogene (2000) 19, 899 - 905.

Biochemical parameters for the diagnosis of mitochondrial respiratory chain deficiency in humans, and their lack of age-related changes

It is now widely acknowledged that a large number of human diseases originate from respiratory-chain dysfunctions. Because the molecular bases of these diseases are still poorly known, a biochemical approach has to be used in the screening procedures for the diagnoses of these conditions. Assessment of respiratory-chain function in human samples faces several problems: (i) the small size of available samples, (ii) the determination of discriminating parameters, and (iii) the interfering factors, such as age and physical activity. The present study focuses on isolated mitochondria prepared from a minute amount (100-200 mg) of skeletal-muscle biopsies from 201 patients between 0 and 65 years. Whereas 42 patients presented an isolated complex (C)I, CII, CIII or CIV deficiency, no respiratory-chain dysfunction or indirect evidence for a mitochondrial disorder could be attested in 159 of these patients. In this reference group, there was little correlation between enzyme activities and age, whatever the age class considered, 0-3 or 0-65 years of age. However, a confident handling of data points was largely hampered by the marked scattering of enzyme activities measured in the reference population. Activity ratios between the various respiratory-chain complexes presenting a much reduced scattering may be considered as diagnostic tools. As to the effect of age, no correlation with any of the enzyme-activity ratios could be shown. Use of age-matched controls for the diagnosis of respiratory-chain disorders may therefore be avoided, enzyme-activity ratios being highly discriminating and age-independent parameters.

The consequences of a mild respiratory chain deficiency on substrate competitive oxidation in human mitochondria

The competition between the respiratory substrates to gain access simultaneously to the respiratory chain depends on the dehydrogenase activity, the mitochondrial ubiquinone pool, and the oxidizing activity of the cytochrome segment. By studying the co-oxidation of NADH and succinate by control human liver homogenates, we found that a change in the balance between respiratory chain complex activities may affect significantly the ability of the mitochondria to oxidize one or the other substrate. Accordingly, in the particular case of a patient presenting with a partial complex I and IV deficiency, we observed a strongly reduced ability to oxidize NADH in the presence of succinate. It therefore appeared that even a slight imbalance between respiratory chain enzyme activities may result in a full blockade of a given substrate oxidation.