Cartilage-derived retinoic acid-sensitive protein in equine synovial fluid from healthy and diseased joints.
Authors: Berg L C, Lenz J, Kjelgaard-Hansen M, Thomsen P D, Jacobsen S
Journal: Equine veterinary journal
Summary
# Editorial Summary: CD-RAP as a Cartilage Marker in Equine Joints Early detection of cartilage degradation remains a significant diagnostic challenge in equine practice, yet identifying reliable biomarkers could enable earlier intervention in joint disease. Berg and colleagues investigated whether cartilage-derived retinoic acid-sensitive protein (CD-RAP)—a marker of cartilage synthesis and regeneration already validated in humans—could be reliably measured in equine synovial fluid using a commercially available ELISA assay. Synovial fluid samples from 28 healthy horses and 5 horses with experimentally induced inflammatory arthritis (via lipopolysaccharide injection) were analysed, with healthy joints yielding CD-RAP concentrations of 8.2–52 ng/ml; notably, artificially induced joint inflammation produced significantly depressed CD-RAP levels within 12 hours that persisted for 144 hours. Although the assay demonstrated moderate-to-large intra- and interassay variation when applied to equine samples, it proved suitable for longitudinal monitoring within individual horses, and disease state significantly altered CD-RAP concentrations independent of age, sex or joint type. For equine practitioners, these findings suggest CD-RAP warrants further investigation as a potential synovial biomarker for detecting early cartilage involvement in joint disease; however, the assay's current performance characteristics mean it is best used for tracking changes within individual patients over time rather than for absolute diagnostic thresholds between health and disease.
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Practical Takeaways
- •CD-RAP measurement in synovial fluid shows promise as a biomarker for detecting early cartilage changes and joint disease progression in individual horses when monitored longitudinally
- •Since disease significantly alters CD-RAP levels, this test could potentially help differentiate between healthy and diseased joints earlier than traditional clinical or imaging methods
- •The assay's moderate to large variation means results are most reliable for tracking changes within the same horse over time rather than for absolute comparisons between horses
Key Findings
- •CD-RAP was detected in healthy equine synovial fluid at concentrations of 8.2-52 ng/ml with moderate to large assay variation
- •CD-RAP concentrations were significantly lower 12 hours after lipopolysaccharide injection compared to saline and remained suppressed through 144 hours
- •The human CD-RAP ELISA assay is suitable for longitudinal monitoring in individual horses despite cross-species application
- •CD-RAP appears to be a marker of cartilage synthesis and regeneration in horses, similar to findings in humans