Bone-resorbing activity and prostaglandin E produced by human periodontal ligament cells in vitro

Human periodontal ligament (PDL) cells were derived from healthy premolars extracted for orthodontic treatment and were utilized for in vitro experiments in passages 4-6. Human PDL cells were seeded in tissue culture tubes and incubated with interleukin-1 alpha (IL-1 alpha), IL-1 beta, tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), indomethacin, parathyroid hormone (PTH), or their combinations, for 1 h. The medium was then replaced with serum-free BGJb medium and incubated for 24 h without further additions. Prostaglandin E (PGE) concentrations in the conditioned media (CM) were measured by radioimmunoassay, and bone-resorbing activity was measured using 45Ca-labeled neonatal mouse calvariae. The results of this study indicated that (1) unstimulated cultured PDL cells produced PGE, and PDL CM stimulated bone resorption; (2) cytokine-treated (IL-1 alpha, IL-1 beta, and TNF-alpha) PDL cells had increased production of PGE and bone-resorbing activity compared to unstimulated PDL cells; (3) indomethacin completely inhibited PGE production from unstimulated PDL cells but only partially inhibited bone-resorbing activity, indicating that PDL cells produced nonprostaglandin bone-resorbing factor(s); (4) IFN-gamma did not change PGE or bone-resorbing activity production by cytokine-stimulated PDL cells; and (5) PTH treatment of PDL cells in addition to cytokines (IL-1 alpha, IL-1 beta, and TNF-alpha) had additive effects on the production of bone-resorbing activity and synergistic effects on PGE production compared to cytokine treatment alone.