A comparison of chondrocyte proteoglycan metabolism in monolayer and agarose cultures.

Bovine chondrocyte cultures were established in agarose and in monolayers to compare the effects of cytokines and drugs on matrix metabolism. The production of sulfated glycosaminoglycans (S-GAG) from the medium and cell surface compartments were measured by a dimethylmethylene blue assay. In the agarose cultures most of the proteoglycan remained in the agar, but was continuously released into the medium for more than 50 days. In the monolayers, the cell surface compartment became saturated with S-GAG in 5-6 days. Then a time-dependent decrease of accumulation occurred in the medium after 8-10 days. The anabolic effects of insulin-like growth factor (IGF) and a protein kinase C activator (PMA) were measured in these cultures. IGF and PMA increased S-GAG accumulation in the medium from monolayers but not from agarose cultures. In the agarose cultures, S-GAG was released into the medium after these cultures were changed to serum-free test conditions. This release overshadowed any increase in S-GAG synthesis. The catabolic effect of IL-1 was more evident in the monolayers than in the agarose cultures. Agarose cultures maintain the chondrocyte phenotype longer than monolayers but for initial drug studies monolayer cultures appear to be more appropriate.