Bisphosphonates impair the adhesion of gingival fibroblasts and epithelial cells

Objectives: Nitrogenous bisphosphonates (BPs) are used extensively in the management of patients with skeletal diseases characterized by excessive bone resorption, including multiple myeloma, bone metastases and osteoporosis. Their long-term administration has been associated with osteonecrosis of the jaw (BP associated Osteonecrosis: BON). BPs inhibit osteoclastic activity, mainly via impairment of the podosomes that form the sealing zone where mineralized bone matrix is degraded. The purpose of this study is to examine the effect of BPs on the cytoskeleton organization, focal contacts and cell adhesion of human gingival fibroblasts and epithelial cells.

Methods: Primary human gingival fibroblasts (HGF) and epithelial cells (G-S) were treated with increasing concentrations of Alendronate and Pamidronate. Actin remodeling at the membrane protrusions in fibroblasts and epithelial cells was tested by immunostaining with actin-phalloidin. Focal adhesion abundance and distribution were evaluated by immunostaining for paxillin and FAK. Cell adhesion was evaluated after plating cells for 30 min on fibronectin.

Results: Actin-phalloidin immunostaining revealed abundant stress fibers and actin accumulation at the filopodial extensions of gingival fibroblasts and epithelial cells. Treatment with increasing concentration of BPs showed a marked decrease in the actin staining at the fibroblast and epithelial membrane. This observation was confirmed when we tested for the focal adhesions. Staining for the focal complex proteins paxillin and FAK revealed an inhibition of the focal adhesions. Focal adhesion abundance and distribution were decreased at the higher BP concentrations and BP-treated cells demonstrated impaired adhesion on fibronectin.

Conclusions: BPs impair the actin-rich filopodia and inhibit focal contacts and cell adhesion of oral fibroblasts and epithelial cells. The inhibitory effect of BPs on soft tissue cells may contribute to the characteristic impaired healing of BON as an additional mechanism in the pathogenesis of osteonecrosis.