The influence of zoledronic acid and cyclophosphamide on microcirculation regeneration in healing oral mucosal flaps

Abstract

The use of intravenous nitrogenous bisphosphonates and antineoplastic agents as postoperative adjuvant cancer management strategies may influence the course of oral wound healing by altering tissue vascularisation kinetics. The aim of this study was to investigate if single or combined zoledronic acid (ZOL) and cyclophosphamide (CTX) would influence microcirculation regeneration in healing oral mucosal flaps. Twenty female specific-pathogen free New Zealand white rabbits were randomised into four groups. In all animals a mucosal flap was raised; three groups were treated each separately with intravenous infusions of 0.14 mg/kg ZOL, 100 mg/kg CTX, or both, respectively. The fourth group was used as a control. Capillary density measurements, expressed as the mean number of capillaries ± SD per mm² (cpll/mm²), was performed preoperatively using sidestream dark-field (SDF) imaging and repeated immediately postoperatively and on days 2, 4, 7, 9, 11, 14, and 21. Whole blood count and body weight was assessed in each group to monitor pharmacotherapeutic responses. Preoperative mean capillary density was 74 ± 8 cpll/mm² and 40 ± 11 cpll/mm² directly after surgery (P < 0.0001). Post hoc comparisons of follow-up SDF measurements on days 9–21 between control and ZOL vs. CTX and ZOL + CTX were statistically significant (P < 0.05). The present study demonstrates that ZOL did not alter capillary regeneration in healing mucosal flaps. However, although the early healing phase is generally characterised by rapid progression of capillary regeneration, interventions with CTX and ZOL + CTX significantly altered capillary regeneration and persisted beyond the third postoperative week.

Introduction

Bisphosphonates (BPs), inhibitors of osteoclast-mediated bone resorption, are extensively used as concurrent therapeutic agents in cancer treatment to prevent, reduce, and delay cancer-related skeletal complications involving hypercalcemia of malignancy, bone metastasis secondary to soft tissue tumours, and osteolytic lesions of multiple myeloma.1, 2, 3 Numerous reports based on clinical case studies reveal a serious adverse effect associated with systemic infusions of nitrogenous BP which as a consequence result in a painful and debilitating condition known as of osteonecrosis of the jaw.4, 5, 6 BP-related osteonecrosis of the jaw (BRONJ) has an incidence approximating 1–3% in cancer patients receiving intravenous BP therapy.⁷ Growing evidence indicates that third generation nitrogenous BPs such as zoledronic acid (ZOL) and traumatic dentomaxillofacial interventions can significantly elevate the risk of developing osteonecrosis of the jaw.8, 9, 10, 11, 12, 13 Additionally, other pathologic complications reported in literature related to BPs treatment suggest these newer generation BPs to posses an antiangiogenic14, 15, 16 and suppressive effect on endothelial cells.17, 18, 19 A strong association may exist between ZOL use and osteonecrosis of the jaw as post-interventional oral surgical treatments may fail to heal as a result of antiangiogenic properties. However, with limited in vivo studies addressing the effects of antiangiogenesis using ZOL, no information currently exists depicting an association between concomitant postoperative adjuvant intravenous ZOL and chemotherapy (CT) treatment reflecting oral tissue vascularisation kinetics.

Postoperative revascularisation and microcirculatory reperfusion are essential for wound recovery and ensure proper immune support with oxygen and nutrient delivery necessary for repair and regeneration.20, 21, 22 Hence, investigating postoperative wound vascularisation is important in advancing knowledge on the etiopathogenesis of BRONJ in patients indicated for ZOL and CT whom receive surgical interventions to the oral and maxillofacial compartments. Optical spectroscopically based imaging techniques have enabled in vivo observations of tissue microcirculation without the use of invasive preparation procedures and would be advantageous for pharmacological investigations aimed at understanding their influence on the microcirculation during wound healing. Introduced in 2005, sidestream dark-field (SDF) imaging is one such imaging technique able to provide monitoring capabilities of tissue microcirculation in real-time. We hypothesise that systemic administration of ZOL and/or CT as postoperative adjuvant cancer management strategies may influence the course of oral mucosal wound healing by altering tissue neovascularisation kinetics. Therefore, the aim of the present study was to investigate the influence of immediate postoperative systemic infusions with single or combined ZOL and cyclophosphamide (CTX) on wound reperfusion by monitoring and quantifying capillary regeneration in healing oral mucosal flaps using SDF imaging.