Effect of methylprednisolone acetate on proteoglycan and collagen metabolism of articular cartilage explants.

Abstract: The effect of different doses of methylprednisolone acetate (MPA) on proteoglycan and collagen metabolism of articular cartilage from normal equine joints was tested in vitro. Methods: Cultured explants were treated with 0, 0.0004, 0.004, 0.04, 0.4 and 4.0 mg/ml (approximately 10(-6)-10(-2) M) MPA for 72 h. Proteoglycan synthesis was measured by incorporation of sodium [35S]sulfate into proteoglycans and proteoglycan degradation was measured by release of total and radiolabeled proteoglycan into the culture media. The size of the proteoglycans was assessed with size exclusion chromatography under both associative and dissociative conditions. Total protein synthesis was measured by incorporation of [3H]proline and collagen synthesis by formation of [3H]hydroxyproline. Results: Treatments of 0.0004, 0.004, and 0.04 mg/ml MPA caused a significant (p < 0.05) increase in total protein synthesis compared to the control, and doses of 0.0004 and 0.004 mg/ml MPA tended to increase (p < 0.1) collagen synthesis. In contrast, MPA doses of 0.04 mg/ml or less had no effect on proteoglycan synthesis compared to control. Proteoglycan, total protein, and collagen synthesis were severely depressed with the 0.4 and 4.0 mg/ml MPA treatments. The lowest doses of MPA had minimal effect on proteoglycan degradation, while 0.4 and 4.0 mg/ml MPA decreased degradation of total proteoglycan in a dose dependent fashion. Degradation of newly synthesized proteoglycan in the explants was significantly decreased (p < 0.05) by 4.0 mg/ml MPA. There was positive correlation (r = 0.83, p < 0.05) between the effect of MPA on proteoglycan synthesis and the release of total proteoglycan into the culture media. Chromatography under associative conditions showed that treatment with MPA (0.4 and 0.004 mg/ml) decreased the size and increased the polydispersity of aggrecan and induced synthesis of the small nonaggregating proteoglycans. Aggrecan monomers from cartilage treated with MPA included a population of smaller monomers, which resulted in greater polydispersity than those from control cartilage. Conclusions: As well as decreasing synthesis, loss of proteoglycan from MPA treated cartilage in vivo may be partly due to the synthesis of a population of smaller proteoglycans than those extracted from untreated cartilage, and these may not interact with hyaluronan and may not be retained permanently in the matrix. Methylprednisolone acetate may affect posttranslational modification of the core protein with the addition of smaller and possibly fewer glycosaminoglycan chains.