BACKGROUNDOsteoarthritis (OA) is a chronic and incurable disease, lacking effective treatment. Gene therapy offers a radical different approach to the treatment of arthritis. Even though the etiology of OA remains unclear, there is now considerable evidence to suggest that interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha) are the main mediators in the pathogenesis of OA. The goal of this study was to determine the efficacy of local expression of interleukin-1 receptor antagonist (IL-1Ra) and soluble tumor necrosis factor-alpha receptor type I (sTNF-RI) by direct adenoviral-mediated intra-articular gene delivery in the rabbit model of osteoarthritis.

METHODSAdenoviral vectors containing IL-1Ra or sTNF-RI genes were constructed. OA was induced in both hind knees of 12 New Zealand white rabbits by the excision of the medial collateral ligament plus medial meniscectomy. Five days after surgery, approximately 1 x 10(8) plaque-forming units (pfu) of adenovirus were injected into the joint space of the knee through the patellar tendon. A total of 12 operated rabbits were divided into four groups. Three experimental rabbit groups received 1 x 10(8) pfu of adenovirus encoding either IL-1Ra (3 rabbits), sTNF-RI (3 rabbits) or IL-1Ra and sTNF-RI in combination (3 rabbits), into both knee joints respectively. An inflamed control group of 3 rabbits received approximately 1 x 10(8) pfu of Ad-GFP into both joints. Three days after injection of the adenovirus, both knees of each rabbit were lavaged with 1 ml of saline solution through the patellar tendon. At day 7, the rabbits were sacrificed, and the knees were lavaged, dissected and analyzed for effects of transgene expression. Levels of IL-1Ra and sTNF-RI expression in recovered lavage fluids were measured using a cytokine ELISA kit. Cartilage from the lesion areas of medial femoral condyle and synovium were fixed, embedded, sectioned and stained with hematoxylin and eosin (cartilage and synovium) and toluidine blue (cartilage). The samples were examined by light microscopy and quantitatively evaluated.

RESULTSIntra-articular delivery of IL-1Ra resulted in a significant inhibition of cartilage degradation, but did not affect synovial changes. In contrast, rabbit knee joints receiving sTNF-RI alone showed no detectable reduction in cartilage degradation. However, double gene transfer of IL-1Ra and sTNF-RI resulted in a higher suppression of the cartilage degradation and an observable reduction in synovitis. These data add to and confirm that IL-1Ra has good chondroprotective properties, but TNF-alpha blockade has little effect on joint destruction.

CONCLUSIONThe enhanced therapeutic effects of both antagonists in combination suggest inhibition of multiple inflammatory cytokines may be more efficacious than blockade of either cytokine alone in treating OA.