Coordinate inhibition of alkaline phosphatase and type X collagen syntheses by 1,25-dihydroxyvitamin D3 in primary cultured hypertrophic chondrocytes

Summary The effects of 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) (2.3×10^-12-1.4×10^-6 M]) on alkaline phosphatase, collagen, and cell proliferation were examined in primary cultured hypertrophic chondrocytes prepared from the distal epiphyseal growth plate of the tibias of 12-day chick embryos. 1,25(OH)₂D₃ showed time- and dose-dependent inhibitory effects on the alkaline phosphatase and collagen levels. The inhibition of alkaline phosphatase activity became detectable at 2×10^-11 M] and reached 10% of control at 10^-7 M]. The concentration of 1,25(OH)₂D₃ giving a 50% inhibition of the enzyme level was approximately 3×10^-10 M]. Of the two extracellular collagen pools, a cell-associated matrix pool showed a more dramatic decrease (to 10% of control) than a culture medium pool (to 50% of control) at increased 1,25(OH)₂D₃ concentrations. The degree of inhibition was different for each type of chondrocyte-specific collagen (types II, IX, X, and XI). Types II and IX were inhibited in a parallel manner to only 60–80% of control. On the other hand, types X and XI were more greatly reduced up to 10% of control, and their dose-dependent inhibitory curves were similar to that of alkaline phosphatase. On cell proliferation, 1,25(OH)₂D₃ had a biphasic effect: stimulation at 10^-10–10^-8 M] and inhibition at higher levels. The results revealed the significant involvement of 1,25(OH)₂D₃ in the metabolism of two probable calcification-related products, alkaline phosphatase and type X collagen.