Increased ornithine decarboxylase activity and DNA synthesis in a cartilage damage model of rat knee joint

The inductions of ornithine decarboxylase (ODC) activity and DNA synthesis are important events in cartilage healing after damage. ODC catalyzes the rate-limiting step in the biosynthesis of polyamines that are necessary for cell growth. The purpose of this study was to examine the roles of ODC activity and polyamines in the adaptive response of cartilage by using a cartilage damage model of rat knee joint. We measured ODC activity, polyamine levels and DNA synthesis at 0, 1, 2, 4, 5, 6, 7 days, and 2, 3 and 4 weeks post-injury in the cartilage. Cartilage damage resulted in significant increases in ODC activity,polyamine levels and DNA synthesis in the tissue. Maximal levels of ODC activity, polyamine contents and DNA synthesis in the cartilage were at day 3, day 4 and day 5, respectively, after the damage. These data suggest that the early increases of cartilage ODC activity and polyamine levels after the damage are crucial cellular events for the healing of the cartilage.