Carrageenan-induced transient inflammation in a rabbit knee model: molecular changes consistent with an early osteoarthritis phenotype

Inflammation following a knee injury is one of the factors associated with initiation of cartilage degeneration leading to osteoarthritis (OA). The hypothesis tested was that inflammation results in elevated expression of proteinases implicated in OA. Mature female rabbits received a single carrageenan injection to the right hind knee and the left knee served as the control. Five animals were killed at time points of 1, 2 and 4 weeks. The synovium and cartilage from both knees were collected and analysed for specific mRNA levels. Interleukin (IL)-1 beta and IL-6 mRNA levels peaked at 2 weeks and returned to normal levels in tissues by 4 weeks post-carrageenan treatment. Matrix metalloproteinase (MMP)-13, MMP-1, MMP-3 and cathepsin K followed the trend set by the inflammatory cytokines. Both synovium and cartilage tissues exhibited similar patterns of molecular expression, with cartilage from the tibial plateau responding more strongly than the femoral condyles. The acute inflammatory milieu controls the transient expression of many degradative proteinases in the knee. However, a single acute exposure to inflammation in the rabbit knee is insufficient to create a chronic inflammatory environment and other complementary factors, such as persistent mechanical instability and/or injury, may contribute to the establishment of OA.