Circadian variation in biochemical markers of bone cell activity and insulin-like growth factor-I in two-year-old horses.

The research investigates the 24-hour shifts in the levels of specific biochemical markers related to bone cell activity and insulin-like growth factor-I (IGF-I) in two-year-old horses. Despite the lack of a noticeable daytime change in some markers, the study revealed that a consistent sample collection is crucial when measuring bone turnover biomarkers in horses.

Objective of the Study

• The primary goal of the study was to identify any circadian (24-hour cycle) changes in serum concentrations of three biochemical markers of bone cell activity in six 2-year-old female Thoroughbred horses. Additionally, the team sought to establish if there was any daytime variability in insulin-like growth factor-I (IGF-I), a hormone aiding in bone development.

Biochemical Markers in Focus

• The three biochemical markers measured in the serum were osteocalcin (a measure of bone formation), the carboxy-terminal propeptide of type-I collagen (another measure of bone formation), and the carboxy-terminal telopeptide of type-I collagen (a marker of bone resorption).

Analyzing Process

• The method used for analyzing the data was the cosinor technique. This statistical method seeks to fit a 24-hour cycle onto each dataset, enabling the detection of regular rhythmic patterns.

Main Findings

• A noticeable circadian rhythm was discovered for osteocalcin, with 7.6% of the mean (95% confidence interval 1.3% to 16.3%), peaking at 9 am. However, the identified rhythm for the carboxy-terminal telopeptide of type-I collagen was not significant, nor were the changes in concentrations of the carboxy-terminal propeptide of type-I collagen over the 24-hour period.
• The study also found a minor but impactful daytime rhythm for IGF-I, peaking at 5:30 pm.

Implications and Future Research Direction

• The research hints at a possible link between circadian changes in IGF-I and osteocalcin in horses, which necessitates further investigation. Though no significant daily oscillations were discovered in the levels of the carboxy-terminal propeptide of type-I collagen and the carboxy-terminal telopeptide of type-I collagen, the researchers suggest this might be due to the skeletal immaturity of the horses used in the study.
• Therefore, future research should investigate whether circadian rhythms in these markers are present when the growth of the horses is complete.
• Lastly, despite these findings, the study encourages maintaining a specific time of sampling when measuring biochemical markers of bone turnover in horses.