Temporal kinetics of serum amyloid A (SAA) concentration and identification of SAA isoforms in blood and synovial fluid of horses with experimentally induced septic arthritis, non-septic synovitis, and systemic inflammation.

The research aims to understand the role of a bio-marker, Serum Amyloid A (SAA), in the detection and diagnosis of septic arthritis in horses. This is done by studying how the concentration of SAA changes over time and identifying different versions of SAA present in the blood and joint fluid of horses with septic arthritis, non-septic synovitis, and systemic inflammation.

Objective of the Study

• The study aims to evaluate the variance of SAA levels in the blood and joint fluid of horses with different health conditions, namely septic arthritis, non-septic synovitis, and systemic inflammation. It also sets out to identify different types of SAA that were produced locally in the joint involved.

Temporal Kinetics of Systemic and Synovial Fluid SAA

• The researchers found a profound rise in SAA concentration in joint fluid, not only in affected joints of horses with septic arthritis but also in unaffected joints when systemic inflammation was present. In particular, this rise led to SAA reaching levels up to 1,830 mg/L in contralateral nonaffected joints and 352 mg/L in unaffected joints with systematic inflammation, compared to the baseline at time 0 which was less than 0.2 mg/L.

Identification and Comparison of SAA Isoforms

• On top of the systemic increase, the study also detected a version of SAA that seemed to be produced directly within the joint (termed as a “putative locally produced joint SAA”). This SAA peptide found in the joint fluid differed by one amino acid from the systemic SAA peptides found in both the plasma and joint fluid.
• The study deduced that this particular SAA version was present in joints of horses with both septic arthritis and systemic inflammation.

Implications of Findings

• These findings put forth the possibility that the detected increase in SAA in the joint fluid could be due to both an overflow of SAA from the bloodstream into the joints, as well as the local production of SAA directly in the joints. This supported the researchers’ initial hypothesis.
• This could have significant implications for the diagnosis and treatment of equine septic arthritis. The differential presence of systemic and locally produced SAA could be used to more accurately identify cases of septic arthritis or systemic inflammatory conditions in horses.