Aspirin aggravates the degeneration of canine joint cartilage caused by immobilization.

The effect of aspirin on the degeneration of knee cartilage caused by immobilization was examined. If dogs were fed aspirin daily (serum salicylate = 20-25 mg/dl) for 6 weeks while one hind limb was immobilized in a cast, the decreases in uronic acid content and net proteoglycan synthesis in cartilage from the immobilized knee were significantly greater than the decreases in cartilage from immobilized knees of dogs that had not received aspirin (P less than 0.01). Furthermore, neither aspirin administration nor immobilization alone affected the extractability of proteoglycans from the cartilage. However, in organ cultures of cartilage from the immobilized knee of dogs fed aspirin, the proportion of the total 35S-proteoglycans present in the culture medium was nearly twice that from cultures of cartilage of the contralateral knee. Also, more than twice as many of the total tissue proteoglycans (uronic acid) were extractable with 0.4 M guanidinium chloride, a nondissociating solvent (P less than 0.01). Regardless of whether the dogs received aspirin, the in vitro interaction of proteoglycans with hyaluronic acid from cartilage of the immobilized knee was diminished, apparently due to an abnormality in the hyaluronate-binding region of the core protein. Although these results indicate that aspirin had an adverse effect in vivo on articular cartilage of immobilized joint, aspirin administration did not preclude reversal of all of the above changes if the dog was allowed to walk about in a pen for 3 weeks after cast removal. If, however, the dog was run daily on a treadmill for 3 weeks after cast removal, the decrease in uronic acid content in cartilage from the immobilized knee persisted and was more profound if the animal had received aspirin than if it had not (P less than 0.01).