Effect of hydrostatic pressure of various magnitudes on osteoarthritic chondrocytes exposed to IL-1β

Background & objectives: Several in vitro studies have shown the importance of mechanical compression or hydrostatic pressure (HP) as a modulator of cartilage metabolism. The present study was undertaken to evaluate the in vitro effects of cyclical low HP (1-5 MPa) and continuous high HP (24 MPa) applied in the presence or absence of interleukin (IL)-1β on humanosteoarthritis (OA) chondrocytes. Methods: Chondrocytes obtained from OA cartilage were cultivated for 48 h and then exposed to pressurization in the presence or absence of IL-1β. After pressurization, the culture medium was collected to detect the amount of proteoglycans (PG) and nitric oxide (NO) and the chondrocytes were immediately fxed for transmission electron microscopy (TEM) and processed for immunocytochemistry to localize the inducible nitric oxide synthase (iNOS). Results: A signifcant increase in the level of PG and a small, non-signifcant, decrease in NO production were observed upon exposure to cyclical low HP. On the other hand, exposure to continuous high HP resulted in a signifcant decrease in the PG levels and a signifcant increase in NO production. The presence of IL-1β led to a signifcant decrease in PG levels as well as a signifcant increase in NO production. The cyclical low HP did not increase the PG levels signifcantly but caused a statistically signifcant decrease in NO production in cultures damaged with IL-1β. The continuous high HP in chondrocyte cultures stimulated with IL-1β did not signifcantly decrease PG production, but signifcantly increased NO production. The results concerning metabolic production were further confrmed by morphological fndings obtained by TEM and immunocytochemical studies. Interpretation & conclusion: The fndings of this study confrmed that the response of chondrocytes varies with magnitude and frequency of HP. These fndings are important to understand aetiopathogenetic mechanisms of OA and to fnd out which type of physical activity may be best suited for the prevention and therapy of OA.