Synthetic Hydroxyapatite Inhibits Bisphosphonate Toxicity to the Oral Mucosa In Vitro

Abstract

Medication-related osteonecrosis of the jaw (MRONJ) is a side effect of bisphosphonate therapy, characterised by exposed necrotic bone. The soft tissues of the oral mucosa no longer provide a protective barrier and MRONJ patients experience pain, infections and difficulties eating. We hypothesised that hydroxyapatite (Ca5(PO4)3(OH)) could reduce bisphosphonate concentrations and protect the oral mucosa by exploiting bisphosphonate’s calcium binding affinity. The effect of zoledronic acid (ZA) and pamidronic acid (PA) on the metabolism of oral fibroblasts, oral keratinocytes and three-dimensional oral mucosa models was investigated and then repeated in the presence of hydroxyapatite granules. Without hydroxyapatite, ZA and PA significantly reduced the metabolic activity of oral cells in a dose-dependent manner. Both drugs reduced epithelial thickness and 30 µM ZA resulted in loss of the epithelium. Hydroxyapatite granules had a protective effect on oral cells, with metabolic activity retained. Oral mucosa models retained their multi-layered epithelium when treated with ZA in the presence of hydroxyapatite granules and metabolic activity was comparable to controls. These results demonstrate hydroxyapatite granules protected oral soft tissues from damage caused by bisphosphonate exposure. Porous hydroxyapatite granules are currently used for socket preservation and this data suggests their potential to prevent MRONJ in at-risk patients.

Nutritional, Antioxidant, Antimicrobial, and Toxicological Profile of Two Innovative Types of Vegan, Sugar-Free Chocolate

“…The situation changes when the final products are tested on primary dermal and gingival fibroblasts, respectively, when cytotoxic effects were recorded in a dose-dependent manner, dermal cells being more sensitive compared to gingival ones. Similar results were reported by Bullock et al in 2020 who revealed that oral fibroblasts were more sensitive to external agents than oral keratinocytes [ 89 ]. We may assume that because of stem-like features and higher proliferation rates keratinocytes exhibit superior resistance to external agents compared to fibroblasts.…”

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

“…To examine healthy mucosa, models were cultured in standard media and epithelia allowed to stratify before BP treatment. PA treatment has been demonstrated to reduce epithelial thickness in studies from our group, and Kim et al [ 58 , 61 ]. Kim et al witnessed a thinner basal layer and intact keratinised layers, and suggested that BP treatment may speed up keratinocyte differentiation.…”

“…PA has been demonstrated to be toxic to human oral fibroblasts from 24 h of administration, with lower concentrations causing toxicity after longer the treatment length. For example an IC 50 of 43 μM was generated at 72 h of treatment in work from our group [ 61 ], while at 96 h, Kim et al demonstrated a 10 μM PA treatment significantly reduced viability [ 58 ]. There is some variability within the results, however the toxic effect of PA at physiologically relevant concentrations and over short time scales is clear.…”

“…Toxicity has been seen from concentrations as low as 14.7 μM at 48 h with human gingival fibroblasts (HGFs) [ 62 ]. Work from our group and Jung et al demonstrated toxicity from ≈5 μM ZA after 72 h [ 61 , 71 ]. The toxicity has been studied following 4 weeks of treatment, where concentrations ranging from 0.15625 to 2.5 μM were shown to have a dose dependent, significant effect on viability [ 51 ].…”

“…Our work, shown in Figure 4 , examined the metabolic activity of these models, which interestingly showed no difference between any BP treatment or non-treated controls despite changes in epithelial thickness. ZA was also examined in our study, and a much more pronounced effect was seen, with 10 μM ZA thinning the epithelia and 30 μM treatment almost entirely removing the epithelium [ 61 ]. Metabolic activity was significantly reduced following 30 μM treatment in models using OKF6/TERT-2 cells, and both 10 μM and 30 μM in models with primary keratinocytes [ 70 ].…”