# Circulating Antimicrobial Peptides as Biomarkers of Inflammation and Airway Dysfunction After Marathon Running

## TL;DR

Marathon running can temporarily increase immune peptides in blood, which may be linked to breathing issues and could help identify at-risk athletes.

## Contribution

The study identifies specific antimicrobial peptides as potential biomarkers for airway dysfunction after endurance exercise.

## Key findings

- Levels of hBD-2 and S100A8/A9 increased after marathon running and returned to baseline during recovery.
- S100A8 levels remained elevated in runners with exercise-induced bronchoconstriction.
- S100A8 levels correlated negatively with lung function parameters like forced expiratory volume.

## Abstract

Endurance sports such as marathon running are becoming increasingly popular, but they exert intense strain on the body. This physical stress can temporarily weaken the immune system and affect the lungs, occasionally causing breathing problems after exercise. Our study investigated whether specific substances circulating in the blood—antimicrobial peptides, which help the body fight off infections—change after endurance exercise and if they are linked to breathing issues occurring thereafter. We measured these markers in long-distance runners before, immediately after, and several days after a race. We also compared these levels with those of people who do not regularly perform endurance exercise. We found that several of these markers increased after running, particularly in runners who showed signs of airway narrowing, which can make breathing harder. These changes mostly returned to normal after a few days. This suggests a heightened immune activation during and immediately after prolonged running that may play a role in temporary breathing difficulties. Understanding these changes could help identify athletes at risk and improve how we support respiratory health during intense physical activity. Our findings could lead to better training plans and recovery strategies for runners and other endurance athletes.

Marathon running exerts physical stress and may lead to transient immune dysregulation, increasing susceptibility to airway inflammation and exercise-induced bronchoconstriction (EIB). This study investigated systemic levels of antimicrobial peptides in athletes and their association with EIB. Serum concentrations of angiogenin, human beta-defensin 2 (hBD-2), major basic protein (MBP), S100A8, and S100A8/A9 were measured in 34 marathoners and 36 half-marathoners at baseline, immediately after a race, and seven days postrace using enzyme-linked immunosorbent assays and compared with 30 sedentary controls. Lung function was assessed by spirometry to identify bronchoconstriction. Levels of hBD-2 and S100A8/A9 were significantly elevated postrace in runners compared to baseline and controls, returning to baseline during recovery. During recovery, S100A8 levels remained slightly elevated in marathoners with EIB. Similarly, human beta-defensin 2 was modestly increased in runners who developed bronchoconstriction. Notably, S100A8 levels correlated negatively with lung function parameters, including forced expiratory volume and mid-expiratory flows. These findings suggest that endurance running induces systemic inflammatory responses and modulates innate immune peptides, particularly in individuals prone to bronchoconstriction. These peptides may serve as biomarkers of respiratory stress and help guide personalized strategies in endurance sports.