EFFECT OF METHYLPREDNISOLONE ACETATE ON PROTEOGLYCAN AND COLLAGEN-METABOLISM OF ARTICULAR-CARTILAGE EXPLANTS

Objective. 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 expla nts were treated with 0, 0.0004, 0.004, 0.04, 0.4 and 4.0 mg/ml (simil ar to 10(-6)-10(-2) M) MPA for 72 h. Proteoglycan synthesis was measur ed by incorporation of sodium [S-35]sulfate into proteoglycans and pro teoglycan degradation was measured by release of total and radiolabele d proteoglycan into the culture media. The size of the proteoglycans w as assessed with size exclusion chromatography under both associative and dissociative conditions. Total protein synthesis was measured by i ncorporation of [H-3]proline and collagen synthesis by formation of [H -3]hydroxyproline. Results. Treatments of 0.0004, 0.004, and 0.04 mg/m l MPA caused a significant (p < 0.05) increase in total protein synthe sis compared to the control, and doses of 0.0004 and 0.004 mg/ml MPA t ended to increase (p < 0.1) collagen synthesis. In contrast, MPA doses of 0.04 mg/ml or less had no effect on proteoglycan synthesis compare d to control. Proteoglycan, total protein, and collagen synthesis were severely depressed with the 0.4 and 4.0 mg/ml MPA treatments. The low est 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 proteoglyca n 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 e ffect of MPA on proteoglycan synthesis and the release of total proteo glycan into the culture media. Chromatography under associative condit ions showed that treatment with MPA (0.4 and 0.004 mg/ml) decreased th e size and increased the polydispersity of aggrecan and induced synthe sis 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 carti lage. Conclusion. As well as decreasing synthesis, loss of proteoglyca n from MPA treated cartilage in vivo may be partly due to the synthesi s of a population of smaller proteoglycans than those extracted from u ntreated 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 th e addition of smaller and possibly fewer glycosaminoglycan chains.