Variation of an epitope of keratan sulphate and total glycosaminoglycans in normal equine joints

An epitope of keratan sulphate (KS) and total glycosaminoglycans (GAG) were measured in synovial fluid samples from joints of 53 horses immediately following humane destruction. Internal examination of the joints post mortem ensured that there was no gross evidence of osteoarthritis or other joint disease. Joints sampled were distal interphalangeal (DIP), proximal interphalangeal (PIP), metacarpophalangeal (MCP), metatarsophalangeal (MTP), tarsometatarsal (TMT), tarsocrural (TC), femoropatellar (FP) and antebrachiocarpal (ABC) Joints. The age of each horse was assessed by examination of the teeth. Samples were analysed for the KS epitope using a monoclonal antibody 5D4 and an inhibition ELISA and for total GAG level by a direct dye binding technique. There was no significant correlation between KS or GAG concentration and age. However, there were significant differences in the concentrations of KS and GAG in different joints. The median level (+ semi interquartile range) of KS:GAG ratio in the MCP was significantly lower than the PIP (0.25 [0.05] vs. 0.35 [0.08]; P<0.007) and also the DIP joints (0.25 [0.05] vs. 0.47 [0.09] P<0.001). This study provides information which is both valuable in the investigation of normal joint metabolism and essential in the interpretation of synovial fluid KS and GAG values in their potential role as aids in the evaluation of joint disease.