The Effects of Intravenous Bisphosphonates on Saliva

Bisphosphonates appear to reduce wound healing but the mechanism of bisphosphonate osteonecrosis of the jaws (BONJ), is poorly understood. Saliva is composed of a variety of proteins and growth factors, some of which contribute to wound healin and recently, intravenous bisphosphonates have been detected in saliva.. Objectives: The aim of the study was to investigate the effect of bisphosphonates on the composition of saliva. Methods: Informed consent was obtained from all volunteers (approved by London REC, Ref 10/H0718/11). Unstimulated and stimulated whole mouth saliva was collected from 11 patients (suffering from prostate or breast cancer) pre-bisphosphonate therapy, and again at 3 and 6 doses thereafter (zoledronic acid, 4mg/ml infusion). The pH, buffer capacity and flow rate were recorded using a commercial chair-side kit (GC Corp., America). Collected samples were clarified by centrifugation, aliquoted and stored at -20°C. Protein composition was assessed by SDS-PAGE and western blotting. Total protein was quantified by absorbance 280nm and specific proteins, including IgA and b2-Microglobulin, were quantified by ELISA. Results: Preliminary results indicated little change in mean saliva flow rate, pH and buffer capacities between pre- and post-therapy samples. The overall profile of salivary proteins and glycoproteins visualised by SDS-PAGE showed some changes. No difference was observed in the Cystatin S content but b2-microglobulin was reduced in post therapy samples (p<0.05, paired t-test). IgA levels were also reduced compared with baseline readings (p<0.05, paired t-test). Conclusions: Zoledronic acid appears to have an effect on the protein composition of saliva but a minimal effect on salivary flow rate and pH. Altered salivary protein composition may influence the susceptibility of patients on zoledronic acid in developing BONJ. This study provides a basis for further exploratory salivary research in relation to bisphosphonate drugs and BONJ.