Analysis of cartilage and systemic toxicity of recombinant TRAIL (rTRAIL). (a) To assess the toxicity of TRAIL protein on joints, the shaved cartilage under synovial lining was sectioned for evaluation of cartilage structure. Histological examination of hematoxylin and eosin (H&E) and TUNEL stained cartilage sections (100×) made from rTRAIL treated and saline control joints are shown. Examples of apoptotic cells are indicated by the arrows. (b) Analysis of glycosaminoglycan (GAG) synthesis by cartilage following rTRAIL injection. Cartilage shavings were taken from the femoral condyles of rabbits 48 h post-injection and analyzed for GAG synthesis as described in Materials and methods. The results are shown as percentage change (mean ± standard error of the mean) following rTRAIL treatment relative to 100% in the saline control. (c) Analysis of possible systemic adverse effects caused by intra-articular injection of rTRAIL. The effect of rTRAIL injection on hepatic function and injury was examined by measuring serum alanine aminotransferase (ALT) levels in rabbits prior to injection of IL-1β expressing cells (day 0), 3 days post-injection of IL-1β expressing cells (day 3) and 3 days post-injection of either saline or rTRAIL into arthritic rabbit knees (day 6).