A novel bioassay model to determine clinically significant bisphosphonate levels

Bisphosphonate-associated osteonecrosis (BON) is a recently recognized oral complication of bisphosphonate (BP) therapy. Currently, research into the pathogenesis of BON has been hampered by being deficient in studies capable of measuring the level of BP in saliva or at the bone-soft tissue interface. The objective of this current study was to develop a novel bioassay model representative of the oral levels of BPs in patients presenting with or at risk for BON.

Zoledronic acid (ZA) injectable was used to develop standardized MTS cell proliferation assay curves at concentrations of 0-10 microM, which were used either in a dilution in normal media, mimicking BP freed from bone or used to "spike" saliva individuals not taking BPs and mimicking BP levels being excreted. This bioassay was then used to estimate BP levels from samples of saliva and bone ex vivo from patients with and without BON.

Saliva and bone from patients with existing BON showed levels of BP ranging from 0.4 to 4.6 microM, while patients receiving IV infusion of BP and naïve to BON showed levels in saliva ranging from 0.4 to 5 microM. All control specimens and patients naïve to BP showed levels at 0 microM.

Given the fact that BPs are poor candidates for detection using standard methods (HPLC), this bioassay provides us with the ability to estimate clinically relevant concentrations of BP capable of producing apoptosis and the inhibition cell proliferation of oral mucosal cells based on previous studies. Subsequently, apoptosis and the inhibition of proliferation could lead to BON, secondary to the exposure of the bone in the unique microenvironment of the oral cavity.