Biochemical and biomechanical alterations in equine articular cartilage following an experimentally-induced synovitis.

This research experimented on equine articular cartilage to understand the biochemical and biomechanical changes that occur due to synovitis, an inflammation condition. The inflammation, induced by injecting Escherichia coli lipopolysaccharide (LPS), resulted in an increase in newly synthesized proteoglycan, as well as changes in the cartilage’s biochemical and biomechanical properties over time.

Objectives and Methodology

The research’s main aim was to study the impact of synovitis – an inflammation of the joint’s synovium, on the biochemical and biomechanical properties of the articular cartilage. For their study, the team induced synovitis in the radial facet of the equine third carpal bone using an injection of Escherichia coli’s lipopolysaccharide (LPS).

• Four groups were formed for the experiment: 2 control (or sham-treated) and 2 experimental (synovitis-induced). Group 1 and 3 had synovitis induced at the very start, but group 1 was evaluated at week 6, whereas group 3, at week 2. Group 2 and 4 were the control for group 1 and 3 respectively.

Findings and Results

• The results showed a significant increase in the newly synthesized proteoglycan (PG) in group 3 when compared with the sham-treated groups and group 1. This suggests that chondrocyte PG synthesis increased in the early stages following synovitis, potentially as a reparative response to the inflammation.
• There was no significant difference in the concentration of endogenous or “existing” PG among the groups. This means that no new PG was produced naturally and the increase seen was because of the inflammation.
• Cartilage thickness increased, and the Poisson’s ratio decreased in the synovitis-treated groups. The increase in the cartilage’s thickness was influenced by the site of treatment; the dorsal part registered a greater increase than the palmar part.
• The electrophoresis and Western blot analysis of the late PG peak fractions showed an additional faster-moving component on composite gels, which didn’t react with the antibody in the group 3 palmar site, signifying a qualitative change in the PG composition on the palmar site.
• However, there were no significant changes or differences in the aggregate modulus or permeability constant among the groups. This could indicate that the biomechanical properties of the cartilage, such as its compressive and tensile strength, remained unaltered with the inflammation.

Implications and Conclusion

The study concluded that inflammation caused by LPS did indeed bring about biochemical and biomechanical alterations in the articular cartilage, these alterations differed over time and also varied with the site of inflammation. These changes, chiefly the increased synthesis of PG in the early phase post-synovitis, might serve as a repair process in response to the inflammation. Continued changes in the PG composition in the later stages could indicate a shift in chondrocyte metabolism to replenish the existing cartilage matrix.