Preliminary insights on the daily rhythm of CRP and IL-6 in athletic horses.

Overview

• This study investigated the daily biological rhythms of two inflammatory biomarkers, C-reactive protein (CRP) and Interleukin-6 (IL-6), in healthy athletic horses over a 48-hour period.
• The research found that both CRP and IL-6 exhibit strong circadian rhythms, with their peak concentrations occurring at specific times during the night and early day, respectively.

Background

• Homeostasis vs. Inflammation: The body balances homeostasis (stable internal conditions) with inflammation (immune response to injury or infection), and these processes are influenced by the circadian clock, which regulates physiological activities in roughly 24-hour cycles.
• CRP and IL-6: Both are key biomarkers related to inflammation. CRP is a protein that increases during systemic inflammation, while IL-6 is a cytokine that plays a role in immune signaling and inflammation regulation.
• Relevance in horses: Understanding the rhythmic pattern of these biomarkers in horses can improve insight into their health and inflammatory status, especially important for athletic horses undergoing training or competition.

Study Design and Methods

• Participants: Eight clinically healthy Italian saddle gelding horses were involved in the study.
• Environment: Horses were housed individually with a natural 12-hour light / 12-hour dark (L/D) cycle to simulate typical daily environmental conditions.
• Sampling: Blood samples were collected every 4 hours over a continuous 48-hour period to capture fluctuations in CRP and IL-6 levels throughout the day and night.
• Data analysis: The researchers examined correlations between CRP and IL-6 and analyzed their rhythmic patterns to identify peak times (acrophases) and the robustness of these rhythms.

Key Findings

• Positive Correlation: A significant positive correlation was found between CRP and IL-6 levels on both days, indicating these markers may be regulated together or interact during circadian cycles.
• Daily Rhythms Detected:
  • CRP: Peaked roughly in the middle of the scotophase (the dark phase, or night).
  • IL-6: Reached its peak at the beginning of the light phase (early morning).
• Robustness: Both CRP and IL-6 rhythms showed high robustness (>75%), implying strong and consistent circadian patterning in these horses.

Conclusions

• The study provides preliminary but valuable insights into how inflammatory biomarkers fluctuate in a daily rhythm in healthy athletic horses.
• The distinct peak times for CRP and IL-6 suggest specific roles or timing in inflammation regulation tied to the circadian clock.
• Understanding these rhythms can help veterinarians and animal scientists better interpret inflammatory biomarker levels depending on the time of day, potentially improving diagnostics and treatment strategies for equine health.
• Further research is needed to explore how external factors such as environment, management practices, and physical exercise may influence these circadian patterns in inflammatory markers.

Implications for Future Research and Practical Applications

• Investigating the impact of varying environmental conditions (e.g., artificial lighting, temperature fluctuations) on CRP and IL-6 rhythmicity.
• Studying whether training or intense physical exercise affects the amplitude or timing of these inflammatory rhythms in horses.
• Evaluating how disruptions in these rhythms might relate to stress, disease, or recovery in equine athletes.
• Potential development of time-optimized diagnostic testing and therapeutic interventions by aligning with the horse’s biological rhythms.