Osteoprotegerin (OPG) is a secreted glycoprotein and a member of the tumor necrosis factor (TNF) receptor family that inhibits bone resorption by suppressing osteoclastogenesis. Gingival fibroblasts (GF) play a role in periodontal disease progression, and the purpose of this experiment was to evaluate influence of osteotropic factors on the expression of osteoprotegerin mRNA in these cells.

In this experiment, the influence of osteoclastogenic factors, interleukin-1 beta (IL-1β), TNF-α, prostanglandin E2 (PGE₂). parathyroid hormone (PTH) and 1α, 25-dihydroxyvitamin D₃ on the expression of osteoprotegerin mRNA in GF was studied by Northern blot hybridization.

As expected, PGE₂ tended to inhibit OPG levels and this was most prominent at 24 hours of culture with 10^-7M of PGE₂. TNF-α at 10ng/ml and also at 25ng/ml decreased OPG levels to almost 30% of the control at 24 hours. This contrasts with reports of increased OPG levels from osteoblast/stromal cells and gingival fibroblasts stimulated by TNF-α. Decrease of OPG levels with PGE₂ and TNF-α suggests a pathway whereby these mediators exert their resorptive effects. However, OPG levels were increased almost 3-fold at 24 hours with IL-1β(1 to 15ng/ml) and increased 1.4 fold with 24-hour treatment of 10^-7M PTH.

Increase of OPG levels suggests that these 'osteoclastogenic' factors act in more complex ways and may act to inhibit bone resorption in inflammatory periodontitis. This result supports the role of OPG as a negative feedback mechanism in osteoclastic activity.