Figure 1.

Levels of alkaline phosphatase and osteocalcin in human osteoarthritis subchondral bone osteoblasts. Alkaline phosphatase activity (a) and osteocalcin level (b) were determined after treatment with chondroitin sulfate (CS) (200 μg/mL), glucosamine sulfate (GS) (50 or 200 μg/mL), or both (200 μg/mL each) in the absence or presence of vitamin D₃ at 50 nM. Alkaline phosphatase activity (a) was determined in the cell lysate by substrate hydrolysis using p-nitrophenylphosphate, whereas osteocalcin level (b) was determined in the culture media by using a specific enzyme immunoassay. Data are from eight independent experiments. Statistical significance was assessed by paired Student t test. P value indicates the statistical difference between control (C, basal conditions) and vitamin D₃-treated specimens.