Elevation in urinary levels of pyridinium cross-links of collagen following chymopapain-induced degradation of articular cartilage in the rabbit knee provides evidence of metabolic changes in bone.

To measure urinary levels of two pyridinium cross-links of collagens at various times, rabbits were injected in the left knee with 0.2 mg (N = 11) or 2.0 mg chymopapain (N = 11). Urinary levels of the bone-specific deoxy-pyridinoline cross-link and of the hydroxylysyl pyridinoline cross-link, found in large amounts in articular cartilage and bone, were measured by high performance liquid chromatography (HPLC). The urinary levels were correlated with histological evidence of progressive articular cartilage destruction in animals injected with 2.0 mg chymopapain and of successful repair in rabbits injected with the lower dose. Rabbits injected with 2.0 mg chymopapain showed a very large increase in urinary levels of deoxy-pyridinoline during the first 30 days after the injection. This rise was not seen in animals injected with the lower dose. A rise in urinary level of the hydroxylysyl pyridonline cross-link was observed in all rabbits but was more pronounced and lasted longer in animals receiving the higher dose. The failure of rabbits injected with 2.0 mg chymopapain to repair the damaged articular cartilage was strongly associated with a marked increase in the catabolism of the bone-specific deoxy-pyridinoline cross-link and to a lesser extent with the catabolism of the hydroxylysyl pyridinoline found in bone and in articular cartilage.