Principles for integrating reactive species into in vivo biological processes:examples from exercise physiology

The equivocal role of reactive species and redox signaling in exercise responses and adaptations is an example clearly showing the inadequacy of current redox biology research to shed light on fundamental biological processes in vivo. Part of the answer probably relies on the extreme complexity of the in vivo redox biology and the limitations of the currently applied methodological and experimental tools. We propose six fundamental principles that should be considered in future studies to mechanistically link reactive species production to exercise responses or adaptations: 1) identify and quantify the reactive species, 2) determine the potential signaling properties of the reactive species, 3) detect the sources of reactive species, 4) locate the domain modified and verify the (ir)reversibility of post-translational modifications, 5) establish causality between redox and physiological measurements, 6) use selective and targeted antioxidants. Fulfilling these principles requires an idealized human experimental setting, which is certainly a utopia. Thus, researchers should choose to satisfy those principles, which, based on scientific evidence, are most critical for their specific research question

Short-Term L-Citrulline Supplementation Does Not Affect Inspiratory Muscle Oxygenation and Respiratory Performance in Older Adults

In sports nutrition, nitric oxide (NO•) precursors such as L-citrulline are widely used to enhance NO• bioavailability, which is considered an ergogenic aid. Our study aimed to examine the effect of short-term L-citrulline supplementation on respiratory muscles’ performance, fatigue, and oxygenation in older adults. Fourteen healthy older males took 6 g of L-citrulline or a placebo for seven days in a double-blind crossover design. Pulmonary function via spirometry (i.e., forced expired volume in 1 s (FEV1), forced vital capacity (FVC), and their ratio)), fractional exhaled nitric oxide (NO•), maximal inspiratory pressure (MIP), rate of perceived exertion, and sternocleidomastoid muscle oxygenation (i.e., oxyhemoglobin (Δ[O2Hb]) and de-oxyhemoglobin (Δ[HHb]), total hemoglobin concentration (Δ[tHb]), and tissue saturation index (TSI%)) were evaluated at baseline, after seven days of L-citrulline supplementation, and after incremental resistive breathing to task failure of the respiratory muscles. The exhaled NO• value was only significantly increased after the supplementation (26% p •, no ergogenic aids were found on the examined parameters at rest and after resistive breathing to task failure in older adults

Chronic Eccentric Exercise and Antioxidant Supplementation: Effects on Lipid Profile and Insulin Sensitivity

Eccentric exercise has been shown to exert beneficial effects in both lipid profile and insulin sensitivity. Antioxidant supplementation during chronic exercise is controversial as it may prevent the physiological training-induced adaptations. The aim of this study was to investigate: 1) the minimum duration of the eccentric exercise training required before changes on metabolic parameters are observed and 2) whether antioxidant supplementation during training would interfere with these adaptations. Sixteen young healthy men were randomized into the Vit group (1 g of vitamin C and 400 IU vitamin E daily) and the placebo (PL) group. Subjects received the supplementation for 9 weeks. During weeks 5-9 all participants went through an eccentric exercise training protocol consisting of two exercise sessions (5 sets of 15 eccentric maximal voluntary contractions) per week. Plasma triglycerides (TG), total cholesterol (TC), high density lipoprotein (HDL), low density lipoprotein (LDL), apolipoproteins (Apo A1, Apo B and Lpa) and insulin sensitivity (HOMA) were assessed before the supplementation (week 0), at weeks 5, 6, 7, 8 and 9. TG, TC and LDL were significantly lower compared to pre supplementation at both weeks 8 and 9 (P<0.05) in both groups. HDL was significantly elevated after 4 weeks of training (p < 0.005) in both groups. There was no effect of the antioxidant supplementation in any of the variables. There was no effect of either the training or the supplementation protocol in apolipoproteins levels and insulin sensitivity. A minimum duration of 3 weeks of eccentric exercise training is required before beneficial effects in lipid profile can be observed in healthy young men. Concomitant antioxidant supplementation does not interfere with the training-induced adaptations

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

The automatic escalator device was invented, designed and constructed by our group and it is the first of its kind offering both stair descending (eccentric-biased) and stair ascending (concentric-biased) exercise.

<p>The automatic escalator device was invented, designed and constructed by our group and it is the first of its kind offering both stair descending (eccentric-biased) and stair ascending (concentric-biased) exercise.</p

The effect of the two bouts of descending (filled circles, solid line) and ascending (open circles, dash line) exercise on torque (A), ROM (B) DOMS (C) and CK (D) (mean ± SEM).

<p>*Significantly different from the pre-exercise value in the same session (<i>P</i><0.05). ^#Significant difference between session 1 and session 2 at the same time-point (<i>P</i><0.05). ^¶Significant difference between ascending and descending group in the same session at the same time point (<i>P</i><0.05).</p

The effect of the two bouts of descending (filled circles, solid line) and ascending (open circles, dash line) exercise on TG (A), TC (B) HDL (C) and LDL (D) concentration as well as TC/HDL (E) ratio (mean ± SEM).

<p>*Significantly different from the pre-exercise value in the same session (<i>P</i><0.05). ^#Significant difference between session 1 and session 2 at the same time-point (<i>P</i><0.05).</p

Redox status indices at pre exercise, immediately post exercise and at day 2 and day 4 post exercise after the stair descending and stair ascending exercise (mean ± SEM).

<p>GSH, reduced glutathione; GSSG, oxidized glutathione; TAC, total antioxidant capacity; TBARS, thiobarbituric acid–reactive substances. G×B×T: 3-way interaction for group, bout and time; G×B: 2-way interaction for group and bout; G×T: 2-way interaction for group and time; B×T: 2-way interaction for bout and time; G: Main effect of training group; B: Main effect of bout; T: Main effect of time.</p>*<p>Significantly different from the pre-exercise value in the same bout (P<0.05).</p>#<p>Significant difference between bout 1 and bout 2 at the same time-point (P<0.05).</p>¶<p>Significant difference between ascending and descending group in the same bout at the same time point (P<0.05).</p