The role of different hyaluronic acids in the articular cartilage of rabbit.

Purpose: To elucidate if the differences found in the physico-chemical and rheological behaviour of Hyaluronic Acids result in different in vivo activity. For this purpose two Hyaluronic Acids (HA), HA-1 and HA-2, with similar molecular weight but different percentage of concentration variation, were compared through an osteoarthritis model.

Methods And Materials: Osteoarthritis was induced in white New Zealand rabbits by anterior cruciate ligament section. After the induction period, the animals were allocated to receive HA-1 or HA-2 intra-articularly in one knee whereas the contralateral knee was used as Operated Control. An additional group of non-operated animals was used as Healthy Controls. Samples of cartilage were taken for different measures: apoptosis, nitric oxide (nitrites) and hyaluronic acid in synovial fluid.

Results: The administration of HA-1 had a significant inhibitor effect on apoptosis of the chondrocytes compared to operated untreated animals (p = 0.0089), whereas this difference was not observed in the HA-2 knees. Levels of nitrites determined by HPLC in the HA-1 knees were similar to those in the Healthy group (p = 0.6551) whereas they were significantly higher in Operated Control and HA-2 groups (p = 0.0001). The comparison between HA-1 and HA-2 also revealed significantly lower levels of nitrites in the HA-1 knees (p = 0.0001). Values of hyaluronic acid in synovial fluid did not show statistical differences between the different study groups.

Conclusions: HA-1 and HA-2 showed different physico-chemical characteristics and these differences have resulted in different in vivo behaviour. As a consequence, not all the HA with similar molecular weight can be considered as equivalent.