A Review Into the Effects of Pamidronic Acid and Zoledronic Acid on the Oral Mucosa in Medication-Related Osteonecrosis of the Jaw

Abstract

Medication-related osteonecrosis of the jaw (MRONJ) is a growing problem without an effective treatment, presenting as necrotic bone sections exposed via lesions in the overlying soft tissue. There is currently a lack of clarity on how the factors involved in MRONJ development and progression contribute to disease prognosis and outcomes. Bisphosphonates (BPs), the most common cause of MRONJ, affect bone remodeling, angiogenesis, infection, inflammation and soft tissue toxicity, all of which contribute to MRONJ development. This article reviews the cellular mechanisms through which BPs contribute to MRONJ pathology, with a focus on the effects on cells of the oral mucosa. BPs have been shown to reduce cell viability, reduce proliferation, and increase apoptosis in oral keratinocytes and fibroblasts. BPs have also been demonstrated to reduce epithelial thickness and prevent epithelial formation in three-dimensional tissue engineered models of the oral mucosa. This combination of factors demonstrates how BPs lead to the reduced wound healing seen in MRONJ and begins to uncover the mechanisms through which these effects occur. The evidence presented here supports identification of targets which can be used to develop novel treatment strategies to promote soft tissue wound healing and restore mucosal coverage of exposed bone in MRONJ.

Keywords: bisphosphonate-related osteonecrosis of jaw; oral mucosa; pamidronate; wound healing; zoledronate.

Figure 1

The generic structure of a bisphosphonate. This figure was created by using ChemDraw software.

Figure 2

Apoptosis in oral keratinocytes incubated with pamidronate. TUNEL assay performed on cells incubated with 0.03, 0.1, and 0.3 mM pamidronate did not increase the percentage of TUNEL positive cells when compared to non-treated cells. Staurosporine and cycloheximide treated positive control cells were all apoptotic by 24 h. Reproduced with permission from Landesberg et al. [55].

Figure 3

Effect of zoledronate on integrin-mediated cell-substratum adhesions of oral fibroblasts. Cells were plated on fibronectin-coated coverslips and exposed to 0.03- or 0.06-mmol/L zoledronate with or without the addition of 50-μmol/L GGOH. The cells were fixed after 120 h and then stained with vinculin and phalloidin to visualize the focal adhesions and actin cytoskeleton. (A,B) In cells that were untreated or treated with 50-μmol/L GGOH alone, there was a robust actin cytoskeletal network associated with numerous focal adhesions. (C,E) In cells that were exposed to 0.03- or 0.06-mmol/L zoledronate, there were very few F-actin bundles and a corresponding loss of focal adhesions. (D) The addition of 50-μmol/L GGOH to cells treated with 0.03-mmol/L zoledronate was able to completely rescue both the focal adhesions and the actin stress fibers. In cells treated with 0.06-mmol/L zoledronate and 50-μmol/L GGOH, the focal adhesions and actin cytoskeleton network were also restored (F) but not to the same extent as shown in (D). (Original magnification, ×100). Reprinted with permission from Cozin et al. [56].

Figure 4

The metabolic activity of oral mucosa models when treated with (A) pamidronic acid and (B) zoledronic acid for 7 days after prior culture at air liquid interface (ALI) in control medium for 7 days, measured with a resazurin assay. A blank well reading was subtracted before values were normalized to day 7 value for each model, defining day 7 values as 100% (not shown). N = 3, n = 3. Error bars = SD. Statistical significance against 0 μM at each time point indicated by *p ≤ 0.05. (C–I) H & E-stained sections of oral mucosa models seeded with human oral fibroblasts and immortalized human oral keratinocytes cultured at ALI for 7 days in control medium, then treated with (C) control medium; (D) 50 μM, (E) 75 μM, and (F) 50 μM pamidronic acid; (G) 1 μM, (H) 10 μM, and (I) 30 μM zoledronic acid, respectively, for 7 days. Representative images used. Reproduced from Bullock et al. [61] under a CC BY license.