Beneficial effects of intermittent fluid pressure of low physiological magnitude on cartilage and inflammation in osteoarthritis. An in vitro study

Objective. To investigate the in vitro effects of low physiological levels of intermittent fluid pressure (0-13 kPa; 0.33 Hz), in the absence of mechanical stress, on articular cartilage, inflammatory cells, and on the combination of these components, present in the osteoarthritic (OA) joint. Methods. Normal and OA cartilage was obtained at autopsy. Mononuclear cells (MNC) were isolated from synovial fluid of patients with osteoarthritis (OA- SF) or peripheral blood from healthy donors (PB). Cartilage and MNC were cultured alone and in co-culture; cultures were carried out with and without exposure to intermittent fluid pressure. Levels of intermittent fluid pressure varied from 0 to 13 kPa (0.33 Hz), comparable with levels present during joint distraction in treatment of OA. Changes in cartilage proteoglycan metabolism and MNC cytokine production were analyzed. Results. Cartilage matrix synthesis was stimulated by intermittent fluid pressure in OA cartilage, while normal cartilage was not affected. No effects on proteoglycan release were detected. Inhibition of cartilage proteoglycan synthesis, induced by OA synovial fluid MNC (OA-SF-MNC) in coculture, was reduced when cultures had been exposed to intermittent fluid pressure. Analysis of conditioned media of OA-SF-MNC revealed that the beneficial effect of intermittent fluid pressure was accompanied by a decrease in production of the catabolic cytokines interleukin 1 and tumor necrosis factor-α. Similar effects were observed for MNC isolated from PB. Conclusion. Low levels of intermittent fluid pressure, as occur in vivo during joint distraction, have beneficial effects on joint tissue in OA, indicating that this factor could be useful in treatment of OA.