The glycosaminoglycan metabolism of chondrocyte monolayer cultures under normal and pathological conditions. A...

Chondrocyte cultures may serve as a model in investigating changes of the cartilage metabolism. Adherent chondrocytes in vitro maintain polygonal morphology at high cell density in the primary and secondary culture. Collagen type II is only clearly detected in multilayered or nodular areas. The differentiation of the chondrocytes is also indicated by a low HA concentration of the cultural medium. It depends on high cell density, a low number of subcultures and their duration. However, the medium GAG of chondrocyte cultures does not exactly mirror the state of cell differentiation but can partly be used to check it. Subcultures of chondrocytes on small cover slides (minicultures) are used to determine proteoglycan synthesis and degradation for 48 h each. Both synthesis and degradation of cell-associated GAG or proteoglycans, resp., follow similar complex kinetics. The half lives of sulfated GAG or proteoglycans are initially 10 h (T-1 for O-6 h of chase), later 39 h or 95 h (T-2 for 6-48 h of chase). Conditioned medium of casein-elicited rat peritoneal macrophages reduce the sulfate incorporation into chondrocyte proteoglycans and their degradation rates increase. In the additional presence of E. coli endotoxin (0.5 microgram/ml) the synthesis of proteoglycans is only little affected; the degradation rate is stronger increased. To peritoneal macrophages of rats manifold pretreated with BCG and perhaps desensitized, LPS is added in vitro. Conditioned medium of these MP does not affect the chondrocyte proteoglycan synthesis but enhances the degradation rates in a concentration-dependent manner. Thus it can be demonstrated that chondrocyte monolayer miniscale cultures may serve to elucidate changes in the proteoglycan synthesis and different degradative steps.