Histological Analysis of Microbial Colonization and Osteoclastic Activity in Bisphosphonate-Treated Rats

Abstract

Bisphosphonate-Related Osteonecrosis of the Jaw (BRONJ) is an untreatable disease characterized by the presence of exposed, non-vital bone in the oral cavity, following dental procedures with a history of bisphosphonate (BP) therapy. This study compared two regimens of zoledronic acid (ZA) regimens with respect to the induction of clinical features of BRONJ. We hypothesized that, in the treated animals in both models, 1) alveolar bone would show impaired osteoclast (bone-removing cell) activity, 2) this impairment would be more profound at higher doses of BPs, and 3) there would be an increase in microbial colonization at the extraction site. The study involved 100 female Sprague-Dawley rats: 30 were treated with 80μg/kg of intravenous ZA weekly for 13 weeks, 20 with 150μg/kg ZA daily for 16 consecutive days, and 50 with corresponding saline injections. The injections were followed by extraction of the first and second molar teeth (extraction has been known to trigger bone necrosis in bisphosphonatetreated patients). We examined osteoclast and bacterial distribution at one and eight weeks post extraction, using Tartrate-Resistant Acid Phosphatase (TRAP) and Brown and Brenn staining, respectively. The TRAP results indicated a significant decline in osteoclast activity in the treatment groups at 1 week post-extraction compared to the controls. When compared to the clinical dose, the higher dose had more pronounced a decline in the osteoclast recruitment in the treated animals at 8 weeks post-extractions. There was no significant difference in bacterial\ colonization between groups; however, we detected an increase in fungal colonization in the treated animals compared to the controls. The results of this study suggest the legitimacy of considering both animal models for further investigation of BRONJ mechanisms.