Effects of intra-articular hyaluronic acid on ex vivo responses by third carpal bone cartilage from horses with experimentally induced synovitis

We studied the extent to which intra-articular hyaluronic acid (HA) administered to horses with experimentally induced synovitis in the third middle carpal joint altered cartilage proteoglycans (PGs) and the biomechanical properties of the third carpal bone. Intra-articular HA (Hylartin-V) was administered to the middle carpal joints of healthy horses before and after the induction of synovitis by Escherichia coli lipopolysaccharide (LPS). Two groups of horses received intra-articular HA only, with evaluation 2 and 6 weeks later (group 2 and group 4). Two other groups (group 1 and group 3) received LPS followed by intra-articular HA and evaluation 2 and 6 weeks later. Ex vivo third carpal bone cartilage PG synthesis was measured by SO4 incorporation and third carpal bone cartilage PG content was determined by an assay for glucuronic acid. Biomechanical properties were measured by indentation testing. At the 2-week evaluation, HA did not ablate the quantitative reduction in PG synthesis and PG content in animals with experimental synovitis. However, by 6 weeks, there was a significant rebound effect in that PG synthesis and PG content were elevated in horses with experimental synovitis that had received intra-articular HA, compared with horses that had received HA only for that period of time. There were also alterations in the gel filtration profiles of newly synthesized PGs on Sepharose CL-2B among the groups. However, there were no de novo PG species associated with any of the treatments. Furthermore, we found that the biomechanical properties of third carpal bone cartilage were not altered in any of the groups. These studies showed that intra-articular HA administered to horses with experimentally induced synovitis did not provide short-term (i.e. 2-week) benefit to third carpal bone cartilage PG synthesis. However, a long-term benefit of intra-articular HA may occur after the acute effects of synovitis on PG synthesis and PG content subside.