Quantitative Redox Biology of Exercise

Erythrocyte metabolism

Our aim is to present an updated overview of the erythrocyte metabolism highlighting its richness and complexity. We have manually collected and connected the available biochemical pathways and integrated them into a functional metabolic map. The focus of this map is on the main biochemical pathways consisting of glycolysis, the pentose phosphate pathway, redox metabolism, oxygen metabolism, purine/nucleoside metabolism, and membrane transport. Other recently emerging pathways are also curated, like the methionine salvage pathway, the glyoxalase system, carnitine metabolism, and the lands cycle, as well as remnants of the carboxylic acid metabolism. An additional goal of this review is to present the dynamics of erythrocyte metabolism, providing key numbers used to perform basic quantitative analyses. By synthesizing experimental and computational data, we conclude that glycolysis, pentose phosphate pathway, and redox metabolism are the foundations of erythrocyte metabolism. Additionally, the erythrocyte can sense oxygen levels and oxidative stress adjusting its mechanics, metabolism, and function. In conclusion, fine-tuning of erythrocyte metabolism controls one of the most important biological processes, that is, oxygen loading, transport, and delivery.

Redox Profile of Skeletal Muscles: Implications for Research Design and Interpretation

Mammalian skeletal muscles contain varying proportions of Type I and II fibers, which feature different structural, metabolic and functional properties. According to these properties, skeletal muscles are labeled as 'red' or 'white', 'oxidative' or 'glycolytic', 'slow-twitch' or 'fast-twitch', respectively. Redox processes (i.e., redox signaling and oxidative stress) are increasingly recognized as a fundamental part of skeletal muscle metabolism at rest, during and after exercise. The aim of the present review was to investigate the potential redox differences between slow- (composed mainly of Type I fibers) and fast-twitch (composed mainly of Type IIa and IIb fibers) muscles at rest and after a training protocol. Slow-twitch muscles were almost exclusively represented in the literature by the soleus muscle, whereas a wide variety of fast-twitch muscles were used. Based on our analysis, we argue that slow-twitch muscles exhibit higher antioxidant enzyme activity compared to fast-twitch muscles in both pre- and post-exercise training. This is also the case between heads or regions of fast-twitch muscles that belong to different subcategories, namely Type IIa (oxidative) versus Type IIb (glycolytic), in favor of the former. No safe conclusion could be drawn regarding the mRNA levels of antioxidant enzymes either pre- or post-training. Moreover, slow-twitch skeletal muscles presented higher glutathione and thiol content as well as higher lipid peroxidation levels compared to fast-twitch. Finally, mitochondrial hydrogen peroxide production was higher in fast-twitch muscles compared to slow-twitch muscles at rest. This redox heterogeneity between different muscle types may have ramifications in the analysis of muscle function and health and should be taken into account when designing exercise studies using specific muscle groups (e.g., on an isokinetic dynamometer) or isolated muscle fibers (e.g., electrical stimulation) and may deliver a plausible explanation for the conflicting results about the ergogenic potential of antioxidant supplements.

Regular Sport Activity Is Able to Reduce the Level of Genomic Damage

Regular physical activity is considered one of the most valid tools capable of reducing the risk of onset of many diseases in humans. However, it is known that intense physical activity can induce high levels of genomic damage, while moderate exercise can elicit a favorable adaptive response by the organism. We evaluated, by the buccal micronuclei assay, the frequencies of micronuclei, nuclear buds and binucleated cells in a sample of amateur athletes practicing different disciplines, comparing the obtained data with those of subjects who practiced sports just occasionally and subjects that did not practice sport at all. The aim was to evaluate whether physical activity affects background levels of genomic damage and whether the different sports disciplines, as well as some gene polymorphisms, differentially affect these levels. A total of 206 subjects, 125 athletes and 81 controls, were recruited. Athletes showed significantly lower values of micronuclei, nuclear buds and binucleated cells with respect to controls. Sprinters and Martial Artists displayed significantly higher frequencies of micronuclei than other categories of athletes. Finally, neither sex nor gene polymorphisms seemed to influence the levels of genomic damage, confirming that the observed genomic damage is probably due to the nature of the sport activity.

Inter-individual variability in redox and performance responses after antioxidant supplementation: A randomized double blind crossover study

AIM

We aimed to investigate the inter-individual variability in redox and physiological responses of antioxidant-deficient subjects after antioxidant supplementation.

METHODS

Two hundred individuals were sorted by plasma vitamin C levels. A low vitamin C group (n = 22) and a control group (n = 22) were compared in terms of oxidative stress and performance. Subsequently, the low vitamin C group received for 30 days vitamin C (1 g) or placebo, in randomized, double-blind, crossover fashion, and the effects were examined through a mixed-effects model, while individual responses were calculated.

RESULTS

The low vitamin C group exhibited lower vitamin C (-25 μmol/L; 95%CI[-31.7, -18.3]; p < 0.001), higher F2 -isoprostanes (+17.1 pg/mL; 95%CI[6.5, 27.7]; p = 0.002), impaired VO2max (-8.2 mL/kg/min; 95%CI[-12.8, -3.6]; p < 0.001) and lower isometric peak torque (-41.5 Nm; 95%CI[-61.8, -21.2]; p < 0.001) compared to the control group. Regarding antioxidant supplementation, a significant treatment effect was found in vitamin C (+11.6 μmol/L; 95%CI[6.8, 17.1], p < 0.001), F2 -isoprostanes (-13.7 pg/mL; 95%CI[-18.9, -8.4], p < 0.001), VO2max (+5.4 mL/kg/min; 95%CI[2.7, 8.2], p = 0.001) and isometric peak torque (+18.7; 95%CI[11.8, 25.7 Nm], p < 0.001). The standard deviation for individual responses (SDir) was greater than the smallest worthwhile change (SWC) for all variables indicating meaningful inter-individual variability. When a minimal clinically important difference (MCID) was set, inter-individual variability remained for VO2max , but not for isometric peak torque.

CONCLUSION

The proportion of response was generally high after supplementation (82.9%-95.3%); however, a few participants did not benefit from the treatment. This underlines the potential need for personalized nutritional interventions in an exercise physiology context.

Acute exercise and high-glucose ingestion elicit dynamic and individualized responses in systemic markers of redox homeostasis

Background

Biomarkers of oxidation-reduction (redox) homeostasis are commonly measured in human blood to assess whether certain stimuli (e.g., high-glucose ingestion or acute exercise) lead to a state of oxidative distress (detrimental to health) or oxidative eustress (beneficial to health). Emerging research indicates that redox responses are likely to be highly individualized, yet few studies report individual responses. Furthermore, the effects of complex redox stimuli (e.g., high-glucose-ingestion after exercise) on redox homeostasis remains unclear. We investigated the effect of acute exercise (oxidative eustress), high-glucose ingestion (oxidative distress), and high-glucose ingestion after exercise (both oxidative eu/distress), on commonly measured redox biomarkers in serum/plasma.

Methods

In a randomized crossover fashion, eight healthy men (age: 28 ± 4 years; BMI: 24.5 ± 1.5 kg/m2 [mean ± SD]) completed two separate testing conditions; 1) consumption of a high-glucose mixed-nutrient meal (45% carbohydrate [1.1 g glucose.kg-1], 20% protein, and 35% fat) at rest (control trial), and 2) consumption of the same meal 3 h and 24 h after 1 h of moderate-intensity cycling exercise (exercise trial). Plasma and serum were analyzed for an array of commonly studied redox biomarkers.

Results

Oxidative stress and antioxidant defense markers (hydrogen peroxide, 8-isoprostanes, catalase, superoxide dismutase, and nitrate levels) increased immediately after exercise (p &lt; 0.05), whereas nitric oxide activity and thiobarbituric acid reactive substances (TBARS) remained similar to baseline (p &gt; 0.118). Nitric oxide activity and nitrate levels decreased at 3 h post-exercise compared to pre-exercise baseline levels. Depending on when the high-glucose mixed nutrient meal was ingested and the postprandial timepoint investigated, oxidative stress and antioxidant defense biomarkers either increased (hydrogen peroxide, TBARS, and superoxide dismutase), decreased (hydrogen peroxide, 8-isoprostanes, superoxide dismutase, nitric oxide activity, nitrate, and nitrite), or remained similar to pre-meal baseline levels (hydrogen peroxide, 8-isoprostanes, TBARS, catalase, superoxide dismutase and nitrite). Redox responses exhibited large inter-individual variability in the magnitude and/or direction of responses.

Conclusion

Findings highlight the necessity to interpret redox biomarkers in the context of the individual, biomarker measured, and stimuli observed. Individual redox responsiveness may be of physiological relevance and should be explored as a potential means to inform personalized redox intervention.

Data Processing to Probe the Cellular Hydrogen Peroxide Landscape

Hydrogen peroxide (H₂O₂) regulates signaling pathways by modulating the activity of redox-sensitive proteins denominated redox switches. The magnitude of the transient variations in localized H₂O₂ pools during signaling events and how these variations impact redox switches present in the cell remain elusive. A canonical model with two chemical reactions comprising the oxidation/reduction cycle of a redox switch is described. The model is dimensionless with respect to the redox switch concentration. Thus, the time-series data required to apply the equations deduced is the percentage of oxidation of a redox switch, avoiding the application of absolute concentrations that are often difficult to measure experimentally. Here, we describe detailed protocols for the processing of experimental data with the canonical model to probe the absolute concentrations of H₂O₂ found in the vicinity of redox switches and probes, as well as the kinetic parameters that describe the reduction and oxidation of redox switches. The protocols are an analytical tool that helps to depict the cellular hydrogen peroxide signaling landscape, giving new insights on H₂O₂ signaling mechanisms, and hold the potential to be a framework for a future redox kinetomics analytical platform.

A Coaching Perspective on Modern Training Metrics and Return from Injury and Illness

Guiding cyclists in their return from illness and injury can be managed in many ways. Understanding how cyclists use power-derived training metrics can give care providers a common language to aid in this return. A general understanding of these metrics may be used to monitor cyclists for signs of nonfunctional overreaching or overtraining. Understanding aspects of training and detraining, particularly hematological, is helpful in communicating fitness expectations. Three populations of cyclists are discussed in terms of their expected knowledge of these metrics, typical training volume and intensity, and relationship with a coach or coaches.

The redox signal: A physiological perspective

A signal in biology is any kind of coded message sent from one place in an organism to another place. Biology is rich in claims that reactive oxygen and nitrogen species transmit signals. Therefore, we define a "redox signal as an increase/decrease in the level of reactive species". First, as in most biology disciplines, to analyze a redox signal you need first to deconstruct it. The essential components that constitute a redox signal and should be characterized are: (i) the reactivity of the specific reactive species, (ii) the magnitude of change, (iii) the temporal pattern of change, and (iv) the antioxidant condition. Second, to be able to translate the physiological fate of a redox signal you need to apply novel and bioplausible methodological strategies. Important considerations that should be taken into account when designing an experiment is to (i) assure that redox and physiological measurements are at the same or similar level of biological organization and (ii) focus on molecules that are at the highest level of the redox hierarchy. Third, to reconstruct the redox signal and make sense of the chaotic nature of redox processes, it is essential to apply mathematical and computational modeling. The aim of the present study was to collectively present, for the first time, those elements that essentially affect the redox signal as well as to emphasize that the deconstructing, decoding and reconstructing of a redox signal should be acknowledged as central to design better studies and to advance our understanding on its physiological effects.

High intensity muscle stimulation activates a systemic Nrf2-mediated redox stress response

High intensity exercise is a popular mode of exercise to elicit similar or greater adaptive responses compared to traditional moderate intensity continuous exercise. However, the molecular mechanisms underlying these adaptive responses are still unclear. The purpose of this pilot study was to compare high and low intensity contractile stimulus on the Nrf2-mediated redox stress response in mouse skeletal muscle. An intra-animal design was used to control for variations in individual responses to muscle stimulation by comparing a stimulated limb (STIM) to the contralateral unstimulated control limb (CON). High Intensity (HI - 100Hz), Low Intensity (LI - 50Hz), and Naïve Control (NC - Mock stimulation vs CON) groups were used to compare these effects on Nrf2-ARE binding, Keap1 protein, and downstream gene and protein expression of Nrf2 target genes. Muscle stimulation significantly increased Nrf2-ARE binding in LI-STIM compared to LI-CON (p = 0.0098), while Nrf2-ARE binding was elevated in both HI-CON and HI-STIM compared to NC (p = 0.0007). The Nrf2-ARE results were mirrored in the downregulation of Keap1, where Keap1 expression in HI-CON and HI-STIM were both significantly lower than NC (p = 0.008) and decreased in LI-STIM compared to LI-CON (p = 0.015). In addition, stimulation increased NQO1 protein compared to contralateral control regardless of stimulation intensity (p = 0.019), and HO1 protein was significantly higher in high intensity compared to the Naïve control group (p = 0.002). Taken together, these data suggest a systemic redox signaling exerkine is activating Nrf2-ARE binding and is intensity gated, where Nrf2-ARE activation in contralateral control limbs were only seen in the HI group. Other research in exercise induced Nrf2 signaling support the general finding that Nrf2 is activated in peripheral tissues in response to exercise, however the specific exerkine responsible for the systemic signaling effects is not known. Future work should aim to delineate these redox sensitive systemic signaling mechanisms.

Sustaining efficient immune functions with regular physical exercise in the COVID-19 era and beyond

The new coronavirus (SARS-CoV-2) appearance in Wuhan, China, did rise the new virus disease (COVID-19), which spread globally in a short time, leading the World Health Organization to declare a new global pandemic. To contain and mitigate the spread of SARS-CoV-2, specific public health procedures were implemented in virtually all countries, with a significant impact on society, making it difficult to keep the regular practice of physical activity. It is widely accepted that an active lifestyle contributes to the improvement of general health and preservation of cardiovascular, respiratory, osteo-muscular and immune system capacities. The positive effects of regular physical activity on the immune system have emerged as a pivotal trigger of general health, underlying the beneficial effects of physical activity on multiple physiological systems. Accordingly, recent studies have already pointed out the negative impact of physical inactivity caused by the social isolation imposed by the public sanitary authorities due to COVID-19. Nevertheless, there are still no current narrative reviews evaluating the real impact of COVID-19 on active lifestyle or even discussing the possible beneficial effects of exercise-promoted immune upgrade against the severity or progression of COVID-19. Based on the consensus in the scientific literature, in this review, we discuss how an exercise adherence could adequately improve immune responses in times of the 'COVID-19 Era and beyond'.