Attenuation of apoptosis and enhancement of proteoglycan synthesis in rabbit cartilage defects by hyperbaric oxygen treatment are related to the suppression of nitric oxide production

Proinflammatory cytokine, nitric oxide (NO) and localized hypoxia-induced apoptosis and proteoglycan (PG) degradation are thought to be correlated to the degree of cartilage injury. This study evaluated hyperbaric oxygen (HBO)-induced changes in joint cavity oxygen tension, antigenickeratan sulfate (KS) content, inducible nitric oxide synthase (iNOS) expression, PG synthesis, and cell apoptosis in full-thickness defects of rabbit cartilage. The HBO group was exposed to 100% oxygen at 2.5 atm for 2 h daily, 5 days per week. Meanwhile, the control group was kept in housing cages with normal air. The joint cavity oxygen tension was determined with an oxygen sensor. Blood serum KS was quantified by competitive indirect enzyme-linked immunosorbent assay (ELISA). After sacrifice, specimen sections were sent for histological and histochemical examination with a standardized scoring system. In situ analysis of iNOs expression and apoptosis detection were performed using immunostaining and TUNEL staining, respectively and quantified by a computerized imagine analysis system. This study demonstrated that HBO treatment increased joint cavity oxygen tension but decreased blood KS content. Histological and histochemical score results showed that HBO treatment significantly increased the cartilage repair. Moreover, immunostaining and TUNEL staining showed that HBO treatment suppressed the iNOs expression and apoptosis of chondrocytes, respectively. Accordingly, HBO offers a potential treatment method for cartilage injury.