Altered macrophagic THP-1 cell phagocytosis and migration in bisphosphonate-related osteonecrosis of the jaw (BRONJ).

OBJECTIVES: Local immune dysfunction via macrophages is a proposed aetiology of bisphosphonate-related osteonecrosis of the jaw (BRONJ). This study aimed to clarify the effects of various bisphosphonates on macrophage function using a THP-1 monocytic model to examine migration, phagocytosis, and fibrin structure. MATERIALS AND METHODS: THP-1 cell migration was measured in the presence and absence of zoledronate, ibandronate, risedronate, alendronate, pamidronate (0.5, 5 and 50 muM) and clodronate (125, 250 and 500 muM) using the real-time xCELLigence system. Phagocytosis and actin fibre assays were performed after 72 h with zoledronate, ibandronate, alendronate and clodronate. RESULTS: Time to maximum migration for THP-1 cells was significantly reduced (p < 0.05) for high dosages of zoledronate, ibandronate and alendronate compared to controls. All dosages of clodronate and a low dose of zoledronate exhibited prolonged migrations. Phagocytic capacity was significantly reduced in high dosages of all bisphosphonates and for 5 muM zoledronate and ibandronate (p < 0.05). Low bisphosphonate exposure was accompanied by overcharged phagosoms. Altered appearance in F-actin fibrin structure was observed in bisphosphonate-exposed cells. CONCLUSIONS: All bisphosphonates altered the migration of THP-1 cells dose-dependently. Low doses also prolonged migration and altered cell morphology. These findings support the idea of a disturbed local immune function of macrophages even in jaw bone exposed to low concentrations of bisphosphonate. CLINICAL RELEVANCE: These are the first real-time results for disrupted migration and function of macrophagic THP-1 cells in high doses. Low dosages also demonstrated altered macrophage phagocytosis and cell morphology, suggesting a disturbed local immune function in BRONJ pathogenesis.