Osmolarity influences chondrocyte repair after injury in human articular cartilage

BACKGROUND: The purpose was to determine the influence of irrigation solution osmolarity on articular chondrocytes survival and metabolic state following mechanical injury. METHODS: Osteochondral explants were harvested from patients undergoing total knee arthroplasty for osteoarthritis and then cut through their full thickness to establish mechanical injury models. Cartilage explants were incubated in irrigation solutions (saline and balanced salt) with different osmolarities (180, 280, 380, 580 mOsm/L) for 2 h. The percentage of cell death (100 × number of dead cells/number of dead and live cells) was quantified with the laser confocal microscopy. The terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay was performed to detect apoptosis index of injured cartilage. The contents of proteoglycan elution were determined by spectrophotometer at 530 nm, and HIF-1α and type II collagen mRNA yields were quantified with real-time PCR. RESULTS: In situ dead chondrocytes were mainly localized to the superficial tangential region of injured cartilage edge after mechanical injury. The percentage of cell death was decreased, and proteoglycan elution was gradually reduced with the increasing of osmolarity. The apoptosis indices of TUNEL assay in different osmolarities had no significant difference (P = 0.158). HIF-1α and type II collagen mRNA yields were the least for chondrocytes exposed to 180 mOsm/L medium and were the greatest for chondrocytes exposed to 380 mOsm/L medium. Compared with the saline group, the cell death of superficial zone was significantly decreased (P = 0.001) and contents of proteoglycan elution were also significantly decreased (P = 0.045) in the balanced salt. HIF-1α (P = 0.017) and type II collagen (P = 0.034) mRNA yields in the chondrocytes exposed to the balanced salt were significantly more than the saline group. CONCLUSION: The osmolarity of irrigation solutions plays an important role in the survival and metabolic state of chondrocytes following mechanical injury, and the chondrocyte death is not caused by apoptosis. Increasing osmolarity of irrigation solutions may be chondroprotective with decreasing the chondrocyte death, reducing inhibition of metabolism and proteoglycan elution, ultimately preventing cartilage degeneration and promoting integrative repair.