Osteoblast or bone marrow stromal cell-derived RANKL is the major effector molecule essential for osteoclastogenesis. Previous studies have shown that tetracyclines have beneficial therapeutic effects in the prevention and treatment of inflammatory bone disease including periodontal disease. Periodontal ligament cells are thought not only to play an important role in the progression of periodontal disease, but to play an important role in alveolar bone remodeling. Previous studies indicated that receptor activation of nuclear factor κB ligand (RANKL) and osteoprotegerin (OPG) are expressed in periodontal ligament cells by pro-inflammatory cytokine, such as IL-1β and TNF-α.

This study was designed to investigate the inhibitory effect of doxycycline on RANKL and OPG mRNA in rat periodontal ligament cells induced by IL-1β(1 ng/ml).

The results are as follows;

1. MTT assay showed that doxycycline at the concentration of 1-50 µg/ml didn't result in statistically significant cell death at day 1 and 3.

2. RANKL mRNA expression was increased to 2.6 folds by IL-1β. When cells were treated with doxycycline (50 µg/ml), IL-1β-induced mRANKL expression was reduced by 33%. In contrast to RANKL, OPG mRNA expression was not inhibited by pre-treatment with doxycycline.

These results suggest that doxycycline decrease the expression of mRANKL resulting in regulation of osteoclastogenesis in rat periodontal ligament cells.