Neuroinflammation, cortical activity, and fatiguing behaviour during self-paced exercise

Acute ingestion of Ibuprofen does not influence the release of IL-6 or improve self-paced exercise in the heat despite altering cortical activity

The present study tested the hypothesis that ingesting 800 mg Ibuprofen prior to self-paced cycling at a fixed rating of perceived exertion (RPE) improves performance by attenuating the release of Interleukin (IL)-6 and its signalling molecules, whilst simultaneously modulating cortical activity and cerebral oxygenation to the brain. Eight healthy, recreationally active males ingested 800 mg Ibuprofen or a placebo ~ 1 h prior to performing fixed RPE cycling for 60 min in 35 °C and 60% relative humidity at an intensity of hard to very hard (RPE = 16) with intermittent maximal (RPE = 20) sprints every 10 min. Power output (PO), core and mean skin temperatures (Tc, Tsk), respectively, and heart rate (HR) were measured continuously. Electroencephalography (EEG) recordings at the frontal (Fz), motor (Cz) and Parietal (Pz) areas (90 s) were collected every 5 min. IL-6, soluble glycoprotein receptor (sgp130) and IL-6 receptor (R) were collected at pre-, 30 min and immediately post-exercise. Mean PO, HR, Tc and Tsk, and RPE were not different between trials (P ≥ 0.33). At end-exercise, the change in IL-6, sgp130 and sIL-6R was not different between trials (P ≥ 0.12). The increase in α and β activity did not differ in any cortices between trials (P ≥ 0.07); however, there was a significant reduction in α/β activity in the Ibuprofen compared to placebo trials at all sites (P ≤ 0.05). Ingesting a maximal, over-the-counter dose of Ibuprofen prior to exercise in the heat does not attenuate the release of IL-6, nor improve performance, but may influence cortical activity evidenced by a greater reduction in α/β activity.

Longitudinal Profiling of Plasma Cytokines and Its Association With Postoperative Delirium in Elderly Patients Undergoing Major Lower Limb Surgery: A Prospective Observational Study

BACKGROUND

Surgery is accompanied by a systemic inflammatory response that may presage delirium in susceptible individuals. Little is known about the trajectory of plasma proinflammatory cytokines and their potential associations with postoperative delirium (POD). The current study longitudinally assessed both pro and anti-inflammatory plasma cytokine response and development of POD in older surgical patients to investigate associations with individual and/or clusters of cytokines that may indicate pathogenic mechanisms.

METHODS

A prospective longitudinal study sought to enroll patients >60 years old who were scheduled for major lower limb surgery under general anesthesia. Blood was obtained preoperatively and postoperatively from day 1 through postoperative day 4 for measurement of plasma interleukin-1β (IL-1β), IL-2, IL-4, IL-6, soluble IL-6 receptor (sIL-6R), IL-10, and tumor necrosis factor-α (TNF-α). Participants were assessed for POD twice daily for 4 days using the confusion assessment method. Trajectory of postoperative changes in plasma cytokines was determined by a group-based trajectory modeling analysis that was informed by distinct cytokines identified by time-dependent Cox regression model.

RESULTS

One hundred eighty-eight patients were assessed for eligibility of whom 129 underwent major surgery and 126 had complete datasets for final analysis. POD was diagnosed in 31 of 126 patients (24.6%). Time-dependent Cox regression model identified that higher IL-6 and sIL-6R levels were associated with higher risk of developing POD. A two-cluster model (stable lower and fluctuating higher levels) was considered to be the most statistically appropriate model for IL-6 and sIL-6R trajectory. More participants with fluctuating higher IL-6 were delirious (73.3% vs 18.0%, P = .001) as were those with fluctuating higher sIL-6R (81.3% vs 16.4%, P = .001).

CONCLUSIONS

As higher IL-6 and sIL-6R levels were significantly associated with higher risk of POD and the combination is required for IL-6 trans-signaling, it is possible that activation of this pathway may be associated with POD. Furthermore, it will be important to determine whether high levels of the combination of IL-6 and sIL-6R can be an early biomarker for the subsequent development of POD.

IL-6 signaling in acute exercise and chronic training: Potential consequences for health and athletic performance

The cytokine interleukin-6 (IL-6) is involved in a diverse set of physiological processes. Traditionally, IL-6 has been thought of in terms of its inflammatory actions during the acute phase response and in chronic conditions such as rheumatoid arthritis and obesity. However, IL-6 is also an important signaling molecule during exercise, being acutely released from working muscle fibers with increased exercise duration, intensity, and muscle glycogen depletion. In this context, IL-6 enables muscle-organ crosstalk, facilitating a coordinated response to help maintain muscle energy homeostasis, while also having anti-inflammatory actions. The range of actions of IL-6 can be explained by its dichotomous signaling pathways. Classical signaling involves IL-6 binding to a cell-surface receptor (mbIL-6R; present on only a small number of cell types) and is the predominant signaling mechanism during exercise. Trans-signaling involves IL-6 binding to a soluble version of its receptor (sIL-6R), with the resulting complex having a much greater half-life and the ability to signal in all cell types. Trans-signaling drives the inflammatory actions of IL-6 and is the predominant pathway in disease. A single nucleotide polymorphism (rs2228145) on the IL-6R gene can modify the classical/trans-signaling balance through increasing the levels of sIL-6R. This SNP has clinical significance, having been linked to inflammatory conditions such as rheumatoid arthritis and type 1 diabetes, as well as to the severity of symptoms experienced with COVID-19. This review will describe how acute exercise, chronic training and the rs2228145 SNP can modify the IL-6 signaling pathway and the consequent implications for health and athletic performance.

Provisional Designation of the Interleukin-6 Receptor (IL-6R) as a Novel Marker Gene for Exercise Tolerance

Objectives: Genomic markers linked to exercise-associated health benefits and/or sporting performance are increasingly used to guide decision-making in healthcare and sport/exercise science. This project investigated whether the IL-6R SNP “rs2228145” might be provisionally designated a novel physical activity/exercise marker. rs2228145 results in an Aspartate358/Alanine358 change adjacent to the site where the IL-6R protein is cleaved into two fragments, resulting in ~two-fold increases in blood-borne levels of soluble IL-6R [‘sIL-6R’].Methods: Cohorts of staff/students at Cardiff Metropolitan University donated/completed: [i] finger-prick capillary blood samples (subjected to ELISAs for sIL-6R, the associated signalling protein sgp130, and the IL-6/sIL-6R complex); [ii] cheek-swab samples containing buccal epithelial cell DNA (subjected to PCR-based IL-6R/rs2228145 genotyping assays); [iii] International Physical Activity Questionnaires (to estimate physical activity levels in the week preceding sample donation).Results: As expected, we observed significant genotype-dependent differences in blood-borne sIL-6R levels (CC (44.1±21.7ng/mL) vs. AC (28.6±7.3ng/mL) vs. AA (19.9±6.5ng/mL; P<0.05)); Importantly, AA homozygotes undertook significantly more physical activity than AC heterozygotes (6318±899 v. 3904±2280 MET-mins/week; P<0.01). Genotype was significantly associated with physical activity levels (P<0.05), and sIL-6R (P=0.197) and sgp130 (P=0.160) showed non-significant correlations with physical activity levels.Conclusions: These data suggest that IL-6R/rs2228145 genotype may influence participation in physical activity/exercise, perhaps by impacting on abilities to tolerate activity without experiencing adverse-effects. Although more research is required to confirm these preliminary findings, designation of IL-6R/rs2228145 as a novel marker, and determination of participants’ IL-6R/rs2228145 genotypes, may in future be useful tools to aid exercise-providers in designing personalised exercise programmes matched to clients/patients.

Acute glutamine supplementation does not improve 20-km self-paced cycling performance in the heat

INTRODUCTION

The premise of this study was to investigate the effect of acute glutamine supplementation on 20 km time trial cycling performance in the heat, neuromuscular function, inflammation and endotoxemia.

METHODS

Twelve cyclists completed two, 20-km time trials (20TT) in 35 °C (50% relative humidity). Participants ingested either glutamine (GLUT; 0.9 g kg^-1 fat-free mass) or a placebo (CON) 60 min before each 20TT. Physiological and perceptual measures were recorded during each 20TT, and neuromuscular function assessed pre- and post-exercise. Venous blood was analysed for endotoxins, markers of gut damage (inflammatory fatty acid binding protein; I-FABP) and inflammatory cytokines (interleukin-6, IL-6; tumour necrosis factor-alpha, TNF-α). Data were analysed using linear mixed models in a Bayesian framework.

RESULTS

20TT in the heat increased I-FABP and elevated inflammatory cytokines (IL-6 and TNF-α) compared to pre-exercise values but did not result in endotoxemia. Completion time was not statistically different between conditions (mean difference [95% credible interval] = 11 s [- 23, 44]). Relative to CON, GLUT did not alter any physiological or perceptual measures during the 20TT.

CONCLUSION

Glutamine supplementation does not improve 20TT performance in the heat or preserve neuromuscular function when compared to a placebo. These findings suggest that glutamine is not an ergogenic aid or prophylactic intervention for heat-induced gut damage during short-duration self-paced exercise in hot environments.

The effect of cycling in the heat on gastrointestinal-induced damage and neuromuscular fatigue

PURPOSE

This study investigated the effect of exercise in the heat on neuromuscular function, gastrointestinal damage, endotoxemia and inflammatory cytokines.

METHODS

Eight male cyclists completed two 60 min cycling trials in both hot (HOT 34.5 ± 0.1 °C and 53 ± 1% relative humidity) and temperate environments (CON 20.2 ± 0.3 °C and 55 ± 3% relative humidity). The cycling task comprised of alternating 3 min intervals at a moderate-vigorous intensity (50% and 70% of maximum power output; P_max) for 30 min, followed by 30 min at moderate intensity (40-50% P_max). Neuromuscular function was assessed at pre-, post-exercise and 60 min post-exercise. Circulating levels of endotoxins, inflammatory cytokines and markers of gut permeability and damage were also collected at these time points. Heart rate, core temperature, skin temperature, perceived exertion, thermal sensation and comfort were also measured.

RESULTS

Post-exercise voluntary activation of HOT (87.9% [85.2, 90.8]) was statistically lower (mean difference - 2.5% [- 4.5, - 0.5], d = 2.50) than that of CON (90.5% [87.8, 93.2]). The HOT trial resulted in statistically elevated (+ 69%) markers of gastrointestinal damage compared to CON (mean difference 0.424 ng mL^-1 [0.163, 0.684, d = - 3.26]), although this was not observed for endotoxin, other inflammatory markers, or gastrointestinal permeability.

CONCLUSIONS

This research provides evidence that short-duration cycling in the heat results in sub-optimal neuromuscular activation and increased expression of gastrointestinal damage markers, without a simultaneous elevation in circulating endotoxins or pro-inflammatory cytokines.