Levels of osteoprotegerin (OPG), receptor activator of nuclear factor-kappa B ligand (RANKL), and OPG/RANKL ratio in human osteoarthritis subchondral bone osteoblasts. Expression and production of OPG (a), expression of RANKL (b), and expression ratio of OPG/RANKL (c) of cells incubated in the absence or presence of 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. Total RNA was extracted and processed for quantitative polymerase chain reaction (qPCR), and the data are expressed as the mean ± standard error of the mean of arbitrary unit. The release of OPG was determined in the culture medium by a specific enzyme-linked immunosorbent assay. Data are from eight independent experiments. Statistical significance was assessed by paired Student t test versus autologous control. Underlined p value indicates the statistical difference between control (C, basal conditions) and vitamin D3-treated specimens.