High molecular weight hyaluronan promotes repair of IL-1 beta-damaged cartilage explants from both young and old bovines.

Objective: The addition of exogenous high molecular weight hyaluronic acid (HA) reverses cartilage damage caused by fibronectin fragments (Fn-fs) added to explant cultures of bovine and human cartilage and by Fn-fs in an experimental in vivo model of rabbit knee joint damage. Our objective was to test whether HA was also effective in an IL-1 damage model and whether this repair was stable and occurred in older bovine cartilage.

Design: Bovine cartilage explants from 18-month-old or 6-year-old bovines in 10% serum/Dulbecco's modified Eagle's medium were exposed to Fn-f or to IL-1 and the ability of 1mg/ml HA of 800 kDa to block damage or promote restoration of proteoglycan (PG) after the damage was measured. The damage phase as well as the exposure to HA were varied.

Results: Exposure of exogenous HA decreased Fn-f-mediated damage, but did not decrease IL-1 beta-induced cartilage damage. If explants from 18-month-old bovines were damaged by a 7-day exposure to Fn-f or IL-1 beta and then exposed for 7 days to HA, PG was restored. This reparative activity persisted up to 4 weeks after the removal of HA from the culture medium. The restoration of PG did not occur in 0.1% serum-free cultures, was less when the exposure to the Fn-f was doubled and failed when exposure to IL-1 beta was doubled. In explants from 6-year-old bovines damaged with IL-1 beta for 7 days, HA fully restored PG content to normal levels.

Conclusions: The reparative activities of HA occur not only in a Fn-f damage model, but also in an IL-1 damage model and occur with older bovine cartilage.