Expression and activity of COX-1 and 2 and 5-LOX in joint tissues from dogs with naturally occurring coxofemoral joint osteoarthritis.

Understanding the neurobiology of pain in naturally occurring models of osteoarthritis (OA) may improve the understanding of human OA pain. Both COX and LOX have been associated with joint pain. This study evaluated COX-1, COX-2, and 5-LOX expression and activity in a naturally occurring canine model of secondary OA. Hip joint capsule with synovial tissue (HJC) and femoral head subchondral bone (FH) was collected from normal dogs and dogs undergoing total hip replacement for coxofemoral joint OA. Tissues were analyzed for COX-1, COX-2, and LOX protein, and PGE(2) and LTB(4). Significantly more COX-2 protein was present in OA HJC than normal joints (p = 0.0009). There was no significant difference in COX-1 or LOX protein, although LOX protein was increased (p = 0.069). PGE(2) concentration in normal and OA HJC was similar (p = 1.0). LTB(4) concentration in OA HJC was significantly greater than normal HJC (p = 0.028). Significantly more COX-1 (p = 0.0098), COX-2 (p = 0.0028), and LOX (p = 0.0095) protein was present in OA FH tissue compared to normal FH tissue. There were no differences in PGE(2) or LTB(4) concentration in normal and OA FH tissue (p = 0.77 and p = 0.11). Together, these data suggest both COX-2 and 5-LOX are appropriate targets for the management of pain associated with naturally occurring OA. (c) 2009 Orthopaedic Research Society.