BIOCHEMICAL AND BIOMECHANICAL ALTERATIONS IN EQUINE ARTICULAR-CARTILAGE FOLLOWING AN EXPERIMENTALLY-INDUCED SYNOVITIS

The effects of inflammation on the biochemical and biomechanical prope rties of articular cartilage at two sites (dorsal and palmar) from the radial facet of the equine third carpal bone were examined in respons e to a synovitis induced with Escherichia coli lipopolysaccharide (LPS ). Four groups were studied. In group 1 synovitis was induced at time zero and evaluated at week 6. Group 2 was the sham-treated control for group 1. In group 3 synovitis was induced at time zero and evaluated at week 2. Group 4 was the sham-treated control for group 3. There was a significant increase (P < 0.05) in newly synthesized proteoglycan P G from both sites in group 3 as compared to the sham-treated groups an d group 1. No significant difference in the endogenous PG concentratio n between groups or sites was detected. Sepharose CL-2B revealed two p eaks of newly synthesized PG in all groups; an early peak (K-av 0.11-0 .13) and a late peak (K-av 0.48-0.64). Newly synthesized PG profiles f rom sham-treated groups and group 3 were similar, but the group 3 PG p rofile exhibited a more pronounced early peak. Conversely, the PG prof ile from group 1 demonstrated a more prominent late peak. Electrophore sis and Western blot analysis of the pooled late PG peak fractions fro m the sham-treated and group 1 showed a single toluidine blue stained band from both sites which reacted with monoclonal antibody (MAb) 1C6. By contrast, the late peak from the palmar site in group 3 showed an additional faster moving component on composite gels which did not rea ct with MAb 1C6. There was a significant decrease in Poisson's ratio a nd a significant increase in cartilage thickness in groups 1 and 3 whi ch had received synovitis. The increase in cartilage thickness of grou ps 1 and 3 was also significantly affected by site (dorsal > palmar). There was no significant difference in aggregate modulus or permeabili ty constant among groups. Primary joint inflammation induced by LPS al ters the biochemical and biomechanical properties of the articular car tilage as a function of time and site. An increase in chondrocyte PG s ynthesis in the early period following synovitis may be a reparative r esponse to the inflammatory insult. Continued alterations in the quali tative PG composition in the later period following synovitis may repr esent a shift in chondrocyte metabolism to repopulate the existing car tilage matrix.