This study was carried out to investigate the protective effect of prednisolone in rabbit primary cultured articular chondrocytes treated with sodium nitroprusside (SNP), a nitric oxide donor. After a cell phenotype was determined, the MTT assay and Western blot analysis of type II collagen, cylooxygenase-2 (COX-2) and phosphorylated extracellular regulated kinase (pERK) were performed in the control, SNP (298 μg/ml) alone or SNP plus prednisolone (0.05-50 μg/ml)-treated rabbit articular chondrocytes. Immunofluorescence staining of type II collagen was also performed. Cell morphology indicated that SNP treatment induced cytotoxicity, and that the SNP-induced cytotoxicity was inhibited by prednisolone treatment. MTT assay showed that the SNP treatment resulted in a significant decrease in the level of cell viability compared with that of control (p<0.01), and that the prednisolone treatment resulted in a decrease in the SNP-induced cytotoxicity. SNP treatment resulted in a decrease in the level of type II collagen, compared with the control chondrocytes. The prednisolone treatment recovered the down-regulated expression of type II collagen induced by SNP, showing a significant level in 5 μg/ml of the prednisolone treatment group compared to the SNP treatment group (p<0.05). A significant increase in COX-2 was significantly induced by the SNP treatment compared to control chondrocytes (p<0.01). The COX-2 expression was decreased by the prednisolone treatment, showing a significant level in 50 μg/ml of the prednisolone treatment group compared to the SNP treatment group (p<0.05). These phenomena was confirmed by immunofluorescence staining. Furthermore, the SNP treatment significantly induced a decrease of pERK expression compared to the control chondrocytes (p<0.01). The prednisolone treatment recovered its expression, showing a significant level in 0.5 μg/ml of the prednisolone treatment group compared to the SNP treatment group (p<0.05). Taken the above results together, prednisolone is considered to inhibit SNP-induced cell death and dedifferentiation, and modulated expression of COX-2 and pERK in rabbit articular chondrocytes.

Introduction
 Materials and Methods
  Primary chondrocyte culture
  Cell viability
  Western blot analysis
  Immunofluorescence staining of type II collagen
  Statistical analysis
 Results
  Cell viability
  Western blot analysis of type II collagen and COX-2 expression
  Immunofluorescence staining of type II collagen
  Expression of pERK in rabbit articular chondrocytes
 Discussion
 Reference

• Jin Seok Kang(Department of Biomedical Laboratory Science, Namseoul University, Molecular Diagnostics Research Institute, Namseoul University) Corresponding author