In vitro stimulation of articular chondrocyte differentiated function by 1,25‐dihydroxycholecalciferol or 24R,25‐dihydroxycholecalciferol

The effects of 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) (10−13M-10−8 M) and 24R,25-dihydroxycholecalciferol (24R,25-(OH)2D3) (10−12M-10−7M) on cell proliferation and proteoglycan deposition were examined in our newly developed multilayer culture system for rabbit and human articular chondrocytes. The cells are embedded in an extracellular matrix similar to that seen in vivo and maintain their in vivo phenotype. We extracted and purified native proteoglycans and degraded material from three culture compartments: the medium, intercellular matrix, and cells. Proteoglycan synthesis and deposition were analyzed by measuring 35SO4 incorporation, hexuronic acid, and galactose contents. In both rabbit and human chondrocyte cultures, chronic 1,25-(OH)2D3 treatment inhibited chondrocyte proliferation and stimulated proteoglycan synthesis and accumulation in the three compartments at 10−12-10−8M. maximal effect was at 10−10M. Cell proliferation was reduced by 55% and the content of hexuronic acid (or galactose) was increased to about three times that of controls in all compartments. 1,25-(OH)2D3 did not alter the proteoglycan composition. Chronic 24R,25-(OH)2D3 treatment induced comparable effects with a maximum at 10−8M. When human dermal fibroblasts were treated as above both vitamin D metabolites increase mitosis. 1,25-(OH)2D3 mainly reduced the pericellular deposition of proteoglycans, while 24R,25-(OH)2D3 appeared to reduce their synthesis and deposition in both medium and pericellular compartments. These results suggest that both 1,25-(OH)2D3 and 24R,25-(OH)2D3 act specifically on articular chondrocytes to promote phenotype expression.