Effects of 24-week prebiotic intervention on self-reported upper respiratory symptoms, gastrointestinal symptoms, and markers of immunity in elite rugby union players

OBJECTIVES

Elite rugby union players face numerous physiological and psychological stressors which can increase upper respiratory and gastrointestinal illness risk, and in turn can compromise training and competitive performance. This study aimed to investigate the effect of daily prebiotic supplementation on upper respiratory symptoms, gastrointestinal symptoms, and markers of immune function in elite rugby union players.

METHODS

Thirty-three elite rugby union players were randomly assigned to consume a prebiotic (2.8 g/day galactooligosaccharide) or placebo (2.8 g/day maltodextrin), daily for 168 days under double-blind conditions. Participants completed daily and weekly questionnaires for self-reported upper respiratory and gastrointestinal symptoms respectively. Blood and saliva samples were collected at 0, 84, and 168 days for assessment of plasma TNF-α and CRP, and saliva IgA respectively.

RESULTS

The prebiotic group experienced a 2-day reduction in upper respiratory symptom duration (P = 0.045). Gastrointestinal symptom severity and incidence were lower in the prebiotic group compared to the placebo group (P < 0.001, P = 0.041) respectively. Salivary immunoglobulin A secretion rate was 42% greater in the prebiotic group compared to the placebo group at day 168 (P = 0.004), no differences in CRP and TNF-α were found (P > 0.05).

CONCLUSION

A 168-day dietary prebiotic intervention reduced the duration of upper respiratory symptoms and reduced the incidence and severity of gastrointestinal symptoms in elite rugby union players. These findings suggest that seasonal prebiotic interventions may be beneficial for reducing illness in elite rugby union players, improving their availability to train and compete.Key pointsElite athletes are susceptible to upper respiratory symptoms and gastrointestinal symptoms which may impact upon training availability and competition performance.For the first time, this study shows that a dietary prebiotic intervention can reduce the duration of upper respiratory symptoms by 2 days in elite rugby union players.Dietary prebiotic supplementation can improve the incidence and severity of gastrointestinal symptoms experienced by elite rugby union players.Prebiotic supplementation was able to increase salivary IgA secretion after 168 days.These findings can inform practice suggesting that seasonal prebiotic use has the potential to modulate immune function and reduce illness in elite rugby union, which may improve a player's availability to train and compete.The mechanisms by which prebiotics reduce URS and GIS require further research exploration.

Alveolar type II epithelial cell FASN maintains lipid homeostasis in experimental COPD

Alveolar epithelial type II (AEC2) cells strictly regulate lipid metabolism to maintain surfactant synthesis. Loss of AEC2 cell function and surfactant production are implicated in the pathogenesis of the smoking-related lung disease chronic obstructive pulmonary disease (COPD). Whether smoking alters lipid synthesis in AEC2 cells and whether altering lipid metabolism in AEC2 cells contributes to COPD development are unclear. In this study, high-throughput lipidomic analysis revealed increased lipid biosynthesis in AEC2 cells isolated from mice chronically exposed to cigarette smoke (CS). Mice with a targeted deletion of the de novo lipogenesis enzyme, fatty acid synthase (FASN), in AEC2 cells (FasniΔAEC2) exposed to CS exhibited higher bronchoalveolar lavage fluid (BALF) neutrophils, higher BALF protein, and more severe airspace enlargement. FasniΔAEC2 mice exposed to CS had lower levels of key surfactant phospholipids but higher levels of BALF ether phospholipids, sphingomyelins, and polyunsaturated fatty acid-containing phospholipids, as well as increased BALF surface tension. FasniΔAEC2 mice exposed to CS also had higher levels of protective ferroptosis markers in the lung. These data suggest that AEC2 cell FASN modulates the response of the lung to smoke by regulating the composition of the surfactant phospholipidome.

The effect of trait self-control on dyspnoea and tolerance to a CO2 rebreathing challenge in healthy males and females

BACKGROUND

High trait self-control is associated with greater tolerance of unpleasant sensations including effort and pain. Dyspnoea and pain have several commonalities and this study aimed to investigate for the first time whether trait self-control influences responses to a hypercapnic rebreathing challenge designed to induce dyspnoea. As sex also influences tolerance to dyspnoea, we also sought to investigate whether this moderated the role of trait self-control.

METHODS

Participants (n = 65, 32 females) scoring high or low for trait self-control, performed a standardised rebreathing challenge, in which inspired carbon dioxide (CO₂) gradually increased over a period of 6 min or until an intolerable level of dyspnoea. Air hunger (AH) intensity - a distinctive quality of dyspnoea, was measured every 30 s. The multidimensional dyspnoea profile (MDP) was completed after the rebreathing challenge for a more complete overview of breathing discomfort.

RESULTS

Males high in trait self-control (SCHIGH) (302 ± 42 s), tolerated the rebreathing challenge for longer than males low in self-control (SCLOW) (252 ± 66 s, P = 0.021), experienced slower increases in AH intensity during the rebreathing challenge (0.03 ± 0.01 cm^.s ^- 1 vs. 0.04 ± 0.01 cm^.s ^- 1,P = 0.045) and reported lower perceived mental effort on the MDP (4.94 ± 2.46 vs. 7.06 ± 1.60, P = 0.007). There was no difference between SCHIGH and SCLOW females for challenge duration. However, SCHIGH females (9.29 ± 0.66 cm) reported greater air hunger at the end of the challenge than SCLOW females (7.75 ± 1.75 cm, P = 0.003). It is possible that SCLOW females were unwilling to tolerate the same perceptual intensity of AH as the SCHIGH females.

CONCLUSIONS

These results indicate that individuals high in trait self-control are more tolerant of dyspnoea during a CO₂ rebreathing challenge than low self-control individuals. Tolerance of the stimulus was moderated by the sex of the participant, presenting an interesting opportunity for future research.

Macrophage innate training induced by IL-4 and IL-13 activation enhances OXPHOS driven anti-mycobacterial responses

Macrophages are a highly adaptive population of innate immune cells. Polarization with IFNγ and LPS into the 'classically activated' M1 macrophage enhances pro-inflammatory and microbicidal responses, important for eradicating bacteria such as Mycobacterium tuberculosis. By contrast, 'alternatively activated' M2 macrophages, polarized with IL-4, oppose bactericidal mechanisms and allow mycobacterial growth. These activation states are accompanied by distinct metabolic profiles, where M1 macrophages favor near exclusive use of glycolysis, whereas M2 macrophages up-regulate oxidative phosphorylation (OXPHOS). Here, we demonstrate that activation with IL-4 and IL-13 counterintuitively induces protective innate memory against mycobacterial challenge. In human and murine models, prior activation with IL-4/13 enhances pro-inflammatory cytokine secretion in response to a secondary stimulation with mycobacterial ligands. In our murine model, enhanced killing capacity is also demonstrated. Despite this switch in phenotype, IL-4/13 trained murine macrophages do not demonstrate M1-typical metabolism, instead retaining heightened use of OXPHOS. Moreover, inhibition of OXPHOS with oligomycin, 2-deoxy glucose or BPTES all impeded heightened pro-inflammatory cytokine responses from IL-4/13 trained macrophages. Lastly, this work identifies that IL-10 attenuates protective IL-4/13 training, impeding pro-inflammatory and bactericidal mechanisms. In summary, this work provides new and unexpected insight into alternative macrophage activation states in the context of mycobacterial infection.

Signalling metabolite L-2-hydroxyglutarate activates the transcription factor HIF-1α in lipopolysaccharide-activated macrophages

Activated macrophages undergo metabolic reprogramming, which not only supports their energetic demands but also allows for the production of specific metabolites that function as signaling molecules. Several Krebs cycles, or Krebs-cycle-derived metabolites, including succinate, α-ketoglutarate, and itaconate, have recently been shown to modulate macrophage function. The accumulation of 2-hydroxyglutarate (2HG) has also been well documented in transformed cells and more recently shown to play a role in T cell and dendritic cell function. Here we have found that the abundance of both enantiomers of 2HG is increased in LPS-activated macrophages. We show that L-2HG, but not D-2HG, can promote the expression of the proinflammatory cytokine IL-1β and the adoption of an inflammatory, highly glycolytic metabolic state. These changes are likely mediated through activation of the transcription factor hypoxia-inducible factor-1α (HIF-1α) by L-2HG, a known inhibitor of the HIF prolyl hydroxylases. Expression of the enzyme responsible for L-2HG degradation, L-2HG dehydrogenase (L-2HGDH), was also found to be decreased in LPS-stimulated macrophages and may therefore also contribute to L-2HG accumulation. Finally, overexpression of L-2HGDH in HEK293 TLR4/MD2/CD14 cells inhibited HIF-1α activation by LPS, while knockdown of L-2HGDH in macrophages boosted the induction of HIF-1α-dependent genes, as well as increasing LPS-induced HIF-1α activity. Taken together, this study therefore identifies L-2HG as a metabolite that can regulate HIF-1α in macrophages.

ACLY-matizing Macrophages to Histone Modification during Immunometabolic Reprogramming

Metabolic reprogramming in macrophages supports effector functions and differs depending on the activating stimulus. Lauterbach et al. now show that early metabolic alterations in macrophages driven by LPS signaling serve to increase the acetyl-CoA pool via citrate metabolism by the ATP-citrate lyase (ACLY), leading to histone acetylation and regulation of TLR-driven gene expression.

A Role for the Krebs Cycle Intermediate Citrate in Metabolic Reprogramming in Innate Immunity and Inflammation

Metabolism in immune cells is no longer thought of as merely a process for adenosine triphosphate (ATP) production, biosynthesis, and catabolism. The reprogramming of metabolic pathways upon activation is also for the production of metabolites that can act as immune signaling molecules. Activated dendritic cells (DCs) and macrophages have an altered Krebs cycle, one consequence of which is the accumulation of both citrate and succinate. Citrate is exported from the mitochondria via the mitochondrial citrate- carrier. Cytosolic metabolism of citrate to acetyl-coenzyme A (acetyl-CoA) is important for both fatty-acid synthesis and protein acetylation, both of which have been linked to macrophage and DC activation. Citrate-derived itaconate has a direct antibacterial effect and also has been shown to act as an anti-inflammatory agent, inhibiting succinate dehydrogenase. These findings identify citrate as an important metabolite for macrophage and DC effector function.

Mitochondrial iron chelation ameliorates cigarette smoke-induced bronchitis and emphysema in mice

Chronic obstructive pulmonary disease (COPD) is linked to both cigarette smoking and genetic determinants. We have previously identified iron-responsive element-binding protein 2 (IRP2) as an important COPD susceptibility gene and have shown that IRP2 protein is increased in the lungs of individuals with COPD. Here we demonstrate that mice deficient in Irp2 were protected from cigarette smoke (CS)-induced experimental COPD. By integrating RNA immunoprecipitation followed by sequencing (RIP-seq), RNA sequencing (RNA-seq), and gene expression and functional enrichment clustering analysis, we identified Irp2 as a regulator of mitochondrial function in the lungs of mice. Irp2 increased mitochondrial iron loading and levels of cytochrome c oxidase (COX), which led to mitochondrial dysfunction and subsequent experimental COPD. Frataxin-deficient mice, which had higher mitochondrial iron loading, showed impaired airway mucociliary clearance (MCC) and higher pulmonary inflammation at baseline, whereas mice deficient in the synthesis of cytochrome c oxidase, which have reduced COX, were protected from CS-induced pulmonary inflammation and impairment of MCC. Mice treated with a mitochondrial iron chelator or mice fed a low-iron diet were protected from CS-induced COPD. Mitochondrial iron chelation also alleviated CS-induced impairment of MCC, CS-induced pulmonary inflammation and CS-associated lung injury in mice with established COPD, suggesting a critical functional role and potential therapeutic intervention for the mitochondrial-iron axis in COPD.

Locomotor muscle fatigue is not critically regulated after prior upper body exercise

This study examined the effects of prior upper body exercise on subsequent high-intensity cycling exercise tolerance and associated changes in neuromuscular function and perceptual responses. Eight men performed three fixed work-rate (85% peak power) cycling tests: 1) to the limit of tolerance (CYC); 2) to the limit of tolerance after prior high-intensity arm-cranking exercise (ARM-CYC); and 3) without prior exercise and for an equal duration as ARM-CYC (ISOTIME). Peripheral fatigue was assessed via changes in potentiated quadriceps twitch force during supramaximal electrical femoral nerve stimulation. Voluntary activation was assessed using twitch interpolation during maximal voluntary contractions. Cycling time during ARM-CYC and ISOTIME (4.33 ± 1.10 min) was 38% shorter than during CYC (7.46 ± 2.79 min) (P < 0.001). Twitch force decreased more after CYC (-38 ± 13%) than ARM-CYC (-26 ± 10%) (P = 0.004) and ISOTIME (-24 ± 10%) (P = 0.003). Voluntary activation was 94 ± 5% at rest and decreased after CYC (89 ± 9%, P = 0.012) and ARM-CYC (91 ± 8%, P = 0.047). Rating of perceived exertion for limb discomfort increased more quickly during cycling in ARM-CYC [1.83 ± 0.46 arbitrary units (AU)/min] than CYC (1.10 ± 0.38 AU/min, P = 0.003) and ISOTIME (1.05 ± 0.43 AU/min, P = 0.002), and this was correlated with the reduced cycling time in ARM-CYC (r = -0.72, P = 0.045). In conclusion, cycling exercise tolerance after prior upper body exercise is potentially mediated by central fatigue and intolerable levels of sensory perception rather than a critical peripheral fatigue limit.

Thermotolerance of Escherichia coli O157:H7 ATCC 43,894, Escherichia coli B, and an rpoS-deficient mutant of Escherichia coli O157:H7 ATCC 43,895 following exposure to 1.5% acetic acid

On a beef carcass, Escherichia coli may sequentially encounter acid- and heat-intervention steps. This study tested whether acid stress (1.5% [vol/vol] acetic acid, pH 4.0, 37 degrees C, 15 min) would enhance subsequent heat resistance of E. coli. Initially, cells (E. coli O157:H7 ATCC 43894, nonpathogenic E. coli B [strain FRIK-124], and rpoS-deficient mutant 813-6 [derived from E. coli O157:H7 ATCC 43895]) were acid stressed and transferred to 54 degrees C trypticase soy broth (TSB), and survivors were immediately enumerated after at least three intervals of 12, 2, and 6 min, respectively, by plating. The ATCC 43894 and 813-6 strains survived the acid stress but strain FRIK-124 did not. Acid-stressed ATCC 43894 had significantly lower D values than the non-acid-stressed controls. Strain 813-6 had significantly lower D values than strain ATCC 43894, with no significant difference between acid-stressed and non-acid-stressed cells. In a second experiment, cooling of cells prior to plating resulted in an increased D value for acid-stressed ATCC 43894 cells, such that it was not significantly different from the D value for non-acid-stressed controls. Using this protocol, there was no significant difference in D values between acid-stressed and non-acid-stressed ATCC 43894 cells in prewarmed TSB (54, 58, and 62 degrees C), in prewarmed ground beef slurry (GBS; 58 degrees C), or in TSB and GBS inoculated at 5 degrees C and heated to 58 degrees C. The acid stress tested does not enhance subsequent heat resistance of E. coli.