Cartilage-derived retinoic acid-sensitive protein in equine synovial fluid from healthy and diseased joints.

This research examines the potential for a protein called cartilage-derived retinoic acid-sensitive protein (CD-RAP) to serve as an indicator of joint health in horses. The researchers used a human diagnostic test to measure CD-RAP levels in horses and found results consistent with previous human studies, which suggests CD-RAP may be useful in monitoring cartilage health and regeneration in horses.

Objective and Need for the Study

• Joint health is of vital importance to performance and well-being in horses. Traditional diagnostic methods for assessing joint health are, however, not highly sensitive or specific, which makes early detection of cartilage issues harder.
• Cartilage-derived retinoic acid-sensitive protein (CD-RAP) is a protein known to act as a marker of cartilage synthesis and regeneration. This study aims to expand on knowledge of this protein by conducting the first study on its presence in equine synovial fluid.
• The main goal was to examine how well an existing diagnostic test designed for humans could detect this protein in horse joint fluid samples, and thereby determine if CD-RAP could be a useful marker for diagnosing joint health issues in horses.

Methodology

• The researchers collected joint fluid from 28 healthy horses and 5 horses with induced inflammatory arthritis. They measured the concentrations of CD-RAP in these samples using an enzyme-linked immunosorbent assay (ELISA) that is typically used for detecting the protein in humans.
• To test the reliability of the assay measurements, they performed multiple measures on pooled equine synovial fluid and evaluated the variations both within the experiment and between different assays.
• Additionally, the researchers studied how the CD-RAP levels in the fluid varied with factors such as repeated joint fluid collection (arthrocentesis), age, joint location, and gender, and after inducing inflammation.

Results

• While the ELISA showed moderate to large variation in measurements when applied to equine synovial fluid, it was still able to detect CD-RAP in the horses’ joint fluid. The protein concentrations ranged between 8.2 and 52 ng/ml in healthy horses. Factors including gender, age, joint and repeated arthrocentesis didn’t significantly alter these levels.
• The CD-RAP levels significantly dropped 12 hours after inducing inflammation via injection of a toxin into the joint and stayed low for 144 hours, suggesting that joint diseases could influence CD-RAP concentrations.

Conclusions

• The ELISA is suitably sensitive for tracking CD-RAP levels over time in individual horses. Because disease status seems to significantly change the protein’s levels, the researchers conclude that, as in humans, CD-RAP could act as a marker of cartilage health and regeneration in horses, thus providing a novel approach to monitoring and diagnosing joint health problems.