Acute exercise-induced release of innate immune proteins via small extracellular vesicles changes with aerobic fitness and age

AIM

Physical exercise triggers the secretion of small extracellular vesicles (sEVs) into the circulation in humans, enabling signalling crosstalk between tissues. Exercise-derived EVs and their cargo have been proposed to mediate adaptations to exercise; however, our understanding of how exercise-derived EV protein cargo is modulated by factors such as aerobic fitness and age of an individual is currently unknown. Here, we examined the circulating sEV proteome following aerobic exercise in healthy males of different ages and aerobic fitness to understand exercise-induced EV response during the aging process.

METHODS

Twenty-eight healthy men completed a bout of 20-min cycling exercise at 70% estimated VO2peak . Small EVs were isolated from blood samples collected before and immediately after exercise, and then quantified using particle analysis and Western blotting. Small EV proteome was examined using quantitative proteomic analysis.

RESULTS

We identified a significant increase in 13 proteins in small plasma EVs following moderate-to-vigorous intensity exercise. We observed distinct changes in sEV proteome after exercise in young, mature, unfit, and fit individuals, highlighting the impact of aerobic fitness and age on sEV protein secretion. Functional enrichment and pathway analysis identified that the majority of the significantly altered sEV proteins are associated with the innate immune system, including proteins known to be damage-associated molecular patterns (DAMPs).

CONCLUSION

Together, our findings suggest that exercise-evoked acute stress can positively challenge the innate immune system through the release of signalling molecules such as DAMPs in sEVs, proposing a novel EV-based mechanism for moderate-to-vigorous intensity exercise in immune surveillance pathways.

A preliminary systematic review and meta-analysis on the effects of heart rate variability biofeedback on heart rate variability and respiration of athletes

To date, there is no quantitative review examining the influence of heart rate variability biofeedback (HRV BFB) on the athlete population. Such an undertaking may provide valuable information on the autonomic and respiration responses of athletes when performing HRV BFB. Thus, purpose of this preliminary systematic review and meta-analysis on the effects of HRV BFB on HRV and respiration of athletes. Searches of Springerlink, SportDiscus, Web of Science, PROQUEST Academic Research Library, Google Scholar, and ScienceDirect were conducted for studies that met the following criteria: (1) experimental studies involving athletes that underwent randomized control trial; (2) availability of HRV BFB as a treatment compared with a control (CON)/placebo (PLA); (3) any pre and post HRV variable and/or breathing frequency as dependent variable/s; and, (4) peer-reviewed articles written in English. Four out of 660 studies involving 115 athletes (25 females and 90 males) ages 16-30 years old were assessed in this review. Preliminary findings suggest the promising ability of HRV BFB to improve respiratory mechanics in athlete population. More work is needed to determine the autonomic modulatory effect of HRV BFB in athletes.

Exercise increases the release of NAMPT in extracellular vesicles and alters NAD+ activity in recipient cells

Aging is associated with a loss of metabolic homeostasis, with cofactors such as nicotinamide adenine dinucleotide (NAD⁺) declining over time. The decrease in NAD⁺ production has been linked to the age‐related loss of circulating extracellular nicotinamide phosphoribosyltransferase (eNAMPT), the rate‐limiting enzyme in the NAD⁺ biosynthetic pathway. eNAMPT is found almost exclusively in extracellular vesicles (EVs), providing a mechanism for the distribution of the enzyme in different tissues. Currently, the physiological cause for the release of eNAMPT is unknown, and how it may be affected by age and physical exercise. Here, we show that release of small EVs into the bloodstream is stimulated following moderate intensity exercise in humans. Exercise also increased the eNAMPT content in EVs, most prominently in young individuals with higher aerobic fitness. Both mature fit and young unfit individuals exhibited a limited increase in EV‐eNAMPT release following exercise, indicating that this mechanism is related to both the age and physical fitness of a person. Notably, unfit mature individuals were unable to increase the release of eNAMPT in EVs after exercise, suggesting that lower fitness levels and aging attenuate this important signalling mechanism in the body. EVs isolated from exercising humans containing eNAMPT were able to alter the abundance of NAD⁺ and SIRT1 activity in recipient cells compared to pre‐exercise EVs, indicating a pathway for inter‐tissue signalling promoted through exercise. Our results suggest a mechanism to limit age‐related NAD⁺ decline, through the systemic delivery of eNAMPT via EVs released during exercise.

Effects of wrist position on eccentric exercise-induced muscle damage of the elbow flexors

We tested the hypothesis that the magnitude of changes in indirect muscle damage markers would be greater after maximal elbow flexor eccentric exercise in the supinated (shorter biceps brachii) than neutral wrist (longer) position, and the difference in the magnitude would be associated with greater elongation over contractions for the supinated than neutral position, rather than the initial muscle length. Ten untrained men (21-39 years) performed two bouts of 10 sets of 6 maximal isokinetic eccentric contractions of the elbow flexors in the supinated position for one arm and neutral position for the other arm separated by 2 weeks in a randomized order. Biceps brachii myotendinous junction (MTJ) movements during eccentric contractions were recorded by B-mode ultrasonography, and the displacement from the start to end of each contraction was quantified. Peak torque (supinated: 367.8 ± 112.5 Nm, neutral: 381.5 ± 120.4 Nm) and total work (1816 ± 539 J, 1865 ± 673 J) produced during eccentric contractions were similar between conditions. The average MTJ displacement increased (P < .05) from the 1st set (8.0 ± 2.0 mm) to 10th set (15.8 ± 1.9 mm) for the supinated condition, but no such increase was found in the neutral condition (1st set: 5.1 ± 1.0 mm, 10th set: 5.0 ± 0.8 mm). Changes in indirect muscle damage markers (maximal voluntary isometric contraction torque, range of motion, serum creatine kinase activity, and muscle soreness) after exercise were greater (P < .05) for the supinated than neutral condition. These results suggest that the greater muscle damage marker changes for the supinated than neutral wrist position was associated with the greater muscle lengthening (strain).

Coronavirus (COVID-19), Coagulation, and Exercise: Interactions That May Influence Health Outcomes

The proinflammatory cytokine storm associated with coronavirus disease 2019 (COVID-19) negatively affects the hematological system, leading to coagulation activation and endothelial dysfunction and thereby increasing the risk of venous and arterial thrombosis. Coagulopathy has been reported as associated with mortality in people with COVID-19 and is partially reflected by enhanced D-dimer levels. Poor vascular health, which is associated with the cardiometabolic health conditions frequently reported in people with severer forms of COVID-19, might exacerbate the risk of coagulopathy and mortality. Sedentary lifestyles might also contribute to the development of coagulopathy, and physical activity participation has been inherently lowered due to at-home regulations established to slow the spread of this highly infectious disease. It is possible that COVID-19, coagulation, and reduced physical activity may contribute to generate a “perfect storm,” where each fuels the other and potentially increases mortality risk. Several pharmaceutical agents are being explored to treat COVID-19, but potential negative consequences are associated with their use. Exercise is known to mitigate many of the identified side effects from the pharmaceutical agents being trialled but has not yet been considered as part of management for COVID-19. From the limited available evidence in people with cardiometabolic health conditions, low- to moderate-intensity exercise might have the potential to positively influence biochemical markers of coagulopathy, whereas high-intensity exercise is likely to increase thrombotic risk. Therefore, low- to moderate-intensity exercise could be an adjuvant therapy for people with mild-to-moderate COVID-19 and reduce the risk of developing severe symptoms of illness that are associated with enhanced mortality.

Acquired and Genetic Thrombotic Risk Factors in the Athlete

While athletes are often considered the epitome of health due to their physique and lowered potential for metabolic and cardiovascular diseases, they may also be at risk for the onset and development of venous thromboembolism (VTE). In an attempt to achieve and remain competitive, athletes are frequently exposed to numerous athlete-specific risk factors, which may predispose them to VTE through the disruption of factors associated with Virchow's triad (i.e., hypercoagulability, venous stasis, and vessel wall injury). Indeed, hypercoagulability within an athletic population has been well documented to occur due to a combination of multiple factors including exercise, dehydration, and polycythemia. Furthermore, venous stasis within an athletic population may occur as a direct result of prolonged periods of immobilization experienced when undertaking long-distance travels for training and competition, recovery from injury, and overdevelopment of musculature. While all components of Virchow's triad are disrupted, injury to the vessel wall has emerged as the most important factor contributing to thrombosis formation within an athletic population, due to its ability to influence multiple hemostatic mechanisms. Vessel wall injury within an athletic population is often related to repetitive microtrauma to the venous and arterial walls as a direct result of sport-dependent trauma, in addition to high metabolic rates and repetitive blood monitoring. Although disturbances to Virchow's triad may not be detrimental to most individuals, approximately 1 in 1,000 athletes will experience a potentially fatal post-exercise thrombotic incidence. When acquired factors are considered in conjunction with genetic predispositions to hypercoagulability present in some athletes, an overall increased risk for VTE is present.

Time of day and short-duration high-intensity exercise influences on coagulation and fibrinolysis

Exercise has been demonstrated to have considerable effects upon haemostasis, with activation dependent upon the duration and intensity of the exercise bout. In addition, markers of coagulation and fibrinolysis have been shown to possess circadian rhythms, peaking within the morning (0600-1200 h). Therefore, the time of day in which exercise is performed may influence the activation of the coagulation and fibrinolytic systems. This study aimed to examine coagulation and fibrinolytic responses to short-duration high-intensity exercise when completed at different times of the day. Fifteen male cyclists (VO_2max: 60.3 ± 8.1 ml kg^-1 min^-1) completed a 4-km cycling time trial (TT) on five separate occasions at 0830, 1130, 1430, 1730 and 2030. Venous blood samples were obtained pre- and immediately post-exercise, and analysed for tissue factor (TF), tissue factor pathway inhibitor (TFPI), thrombin-anti-thrombin complexes (TAT) and D-Dimer. Exercise significantly increased plasma concentrations of TF (p < .0005), TFPI (p < .0006), TAT complexes (p < .0012) and D-Dimer (p < .0003). There was a time-of-day effect in pre-exercise TF (p = .004) and TFPI (p = .031), with 0830 greater than 1730 (p  .001), while 1730 was less than 2030 h (p = .008), respectively. There was no significant effect of time of day for TAT (p = .364) and D-Dimer (p = .228). Power output, TT time and heart rate were not significantly different between TTs (p > .05); however, percentage VO_2max was greater at 1730 when compared to 2030 (p = .04). Due to a time-of-day effect present within TF, peaking at 0830, caution should be applied when prescribing short-duration high-intensity exercise bout within the morning in populations predisposed to hypercoagulability.

Assessment of Muscle Pain Induced by Elbow-Flexor Eccentric Exercise

CONTEXT

Delayed-onset muscle soreness (DOMS) is a common muscle pain that many people experience and is often used as a model of acute muscle pain. Researchers have reported the effects of various interventions on DOMS, but different DOMS assessment protocols used in these studies make it difficult to compare the effects.

OBJECTIVE

To investigate DOMS characteristics after elbow-flexor eccentric exercise to establish a standardized DOMS assessment protocol.

DESIGN

Descriptive laboratory study.

SETTING

Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Ten healthy, untrained men (21-39 years).

INTERVENTION(S)

Participants performed 10 sets of 6 maximal isokinetic eccentric contractions of the elbow flexors.

MAIN OUTCOME MEASURE(S)

Indirect muscle-damage markers were maximal voluntary isometric contraction torque, range of motion, and serum creatine kinase activity. Muscle pain was assessed before exercise, immediately postexercise, and 1 to 5 days postexercise using (1) a visual analog scale (VAS), (2) a category ratio-10 scale (CR-10) when applying static pressure and palpation at different sites (3, 9, and 15 cm above the elbow crease), and (3) pressure-pain thresholds (PPTs) at 50 sites (pain mapping).

RESULTS

Maximal voluntary isometric contraction and range of motion decreased and creatine kinase activity increased postexercise, indicating muscle damage. Palpation induced greater pain than static pressure, and longitudinal and transverse palpations induced greater pain than circular palpation (P < .05). The PPT was lower in the medial region before exercise, but the pain-sensitive regions shifted to the central and distal regions of the biceps brachii at 1 to 3 days postexercise (P < .05). The VAS was correlated with the CR-10 scale (r = 0.91, P < .05) but not with the PPT (r = -0.28, P = .45).

CONCLUSIONS

The way in which muscles are assessed affects the pain level score. This finding suggests that pain level and pain threshold cannot be used interchangeably and that the central and distal regions of the biceps brachii should be included in DOMS assessment using the VAS, CR-10 scale, and PPT after elbow-flexor eccentric exercise.

Reduced muscle lengthening during eccentric contractions as a mechanism underpinning the repeated-bout effect

This study investigated biceps brachii distal myotendinous junction (MTJ) displacement during maximal eccentric elbow flexor contractions to test the hypothesis that muscle length change would be smaller (less MTJ displacement) during the second than the first exercise bout. Ten untrained men performed two eccentric exercise bouts (ECC1 and ECC2) with the same arm consisting of 10 sets of six maximal isokinetic (60°/s) eccentric elbow flexor contractions separated by 4 wk. Biceps brachii distal MTJ displacement was assessed using B-mode ultrasonography, and changes in the displacement (muscle length change) from the start to the end of each contraction during each set and over 10 sets were compared between bouts by two-way repeated-measures ANOVA. Several indirect muscle damage markers were also measured and compared between bouts by two-way repeated-measures ANOVA. The magnitude of MTJ displacement (average of six contractions) increased from set 1 (8.2 ± 4.7 mm) to set 10 (16.4 ± 4.7 mm) during ECC1 (P < 0.05), but no significant changes over sets were evident during ECC2 (set 1: 8.5 ± 4.0 mm; set 10: 9.3 ± 3.1 mm). Changes in maximal voluntary isometric contraction strength, range of motion, muscle thickness, ultrasound echo intensity, serum creatine kinase activity, and muscle soreness (visual analog scale) were smaller (P < 0.05) following ECC2 than ECC1, showing less damage in the repeated bout. These results indicate that the magnitude of muscle lengthening was less during the second than the first eccentric exercise bout, which appears to be a mechanism underpinning the repeated-bout effect.