Intra-articular injection of the cyclooxygenase-2 inhibitor parecoxib attenuates osteoarthritis progression in anterior cruciate ligament-transected knee in rats: role of excitatory amino acids

Objective: Our present study examined the effect of intra-articular cyclooxygenase-2 (COX-2) inhibitor parecoxib on osteoarthritis (OA) progression and the concomitant changes in excitatory amino acids' (EAAs) levels of the anterior cruciate ligament-transected (ACLT) knee joint dialysates. Methods: OA was induced in Wistar rats by anterior cruciate ligament transection of the knee of one hindlimb, the other was left unoperated and untreated. Rats were placed into four groups: Group ACLT/P received intra-articular parecoxib injection (100 mu g) in the ACLT knee once a week for 5 consecutive weeks starting at 8 weeks after surgery. Group ACLT/S received the same procedure as group ACLT/P with saline injection instead. Naive (Naive/P) rats received only intra-articular parecoxib injection in one knee once a week for 5 consecutive weeks without surgery. The sham-operated rats underwent arthrotomy only without treatment. Twenty weeks after surgery, knee joint dialysates were collected and EAAs' concentration was assayed by high-performance liquid chromatography, and gross morphology and histopathology (Mankin and synovitis grading) were examined on the medial femoral condyles and synovia. Results: Parecoxib alone had no effect on cartilage and synovium of normal knees in Naive/P rats. In ACLT/P rats, parecoxib treatment showed a significant inhibition of cartilage degeneration of the medial femoral condyle at both the macroscopic level (1.15 +/- 0.17 vs 2.55 +/- 0.12, P < 0.05) and the Mankin scores (3.03 +/- 0.28 vs 8.82 +/- 0.43, P < 0.05). Intra-articular parecoxib injection also suppressed the synovial inflammation of ACLT joint compared to the ACLT/S group (3.92 +/- 0.41 vs 9.25 +/- 0.32, P < 0.05). Moreover, glutamate and aspartate levels were also significantly reduced in the ACLT/P group compared to the ACLT/S group by parecoxib treatment (91.2 +/- 9.4% vs 189.5 +/- 17.0%, P < 0.05 and 98.2 +/- 11.6% vs 175.3 +/- 12.4%, P < 0.05, respectively). Conclusion: This study shows that intra-articular injection of COX-2 inhibitor parecoxib inhibits the ACLT-induced OA progression; it was accompanied by a reduction of glutamate and aspartate concentration in the ACLT joint dialysates. From our present results, we suggested that intra-articular parecoxib injection, in addition to the anti-inflammatory effect, inhibiting the EAAs' release, may also play a role in inhibiting the traumatic knee injury induced CA progression. (c) 2006 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.