Geranylgeraniol in Bone Cement Rescues Osteoclasts from the Toxic Effects of Pamidronate and Restores Function

Abstract

BackgroundExposed intraoral bone in medically related osteonecrosis of the jaw (MRONJ) is a devastatingly side effect of treatment with nitrogen containing bisphosphonates(NBPs) The pathogenesis of the condition is thought to be caused by NBP inhibition of farnesyl diphosphate synthase (FDPS), a critical enzyme in the mevalonate pathway. This block suppresses the prenylation of factors necessary for the maintenance and survival of osteoclasts. Geranylgeraniol (GGOH), a metabolite in the mevalonate pathway downstream of FDPS, reverses the block NBPs impose on osteoclasts. However, no effective method currently exists to deliver GGOH locally to NBP-induced lesions in the mouth. The purpose of this study is to develop a biocompatible, resorbable and tunable carrier to deliver GGOH intraorally and thereby reverse the damaging effects of MRONJ.MethodsPrimary human oral fibroblasts and RAW264.7 osteoclasts were exposed to pamidronate in vitro and GGOH contained within a bone cement pellet and survival of the cells was measured. The kinetics of release of 3HGGOH from the bone cement was measured.. The resorptive function of osteoclasts exposed to pamidronate with or without GGOH was quantitated by measuring the release of bound fluorescent dye from a CaPO4 coated plate. Resorption areas on this plate were photographed.ResultsHuman gingival fibroblasts exposed to pamidronate (100uM) alone decreased survival by 49% (p<0.001) over 72 hours, 2mM GGOH incorporated into bone cement rescued these cells from the toxic effect of NBP (p=0.0024).Exposure of osteoclasts to 400 and 800uM pamidronate over 72 hours showed a 49% and 69% loss of viability respectively. (p<0.0001 for each concentration). 2mM GGOH incorporated into bone cement increased survival by 247% (p=0.0001) for the cells treated with 800uM pamidronate and 4mM GGOH by 450% (p<0.0001). Pamidronate at both concentrations reduced osteoclast function and 4mM GGOH completely restored resorbtive function. At a powder to liquid ration of 2.5:1 92% of the loaded metabolite was released into medium after in 96 hours.ConclusionsGGOH contained in a bone cement carrier can rescue osteoclast function from the toxic effects of pamidronate. This carrier may be the first step in local delivery of this metabolite in the oral cavity.

The Role of Geranylgeraniol in Managing Bisphosphonate-Related Osteonecrosis of the Jaw

“…This aspect would require further investigation at the preclinical stage. In a preprint article, GGOH (4 mM) has been incorporated in bone cement and shown the ability to reverse pamidronate-mediated suppression of osteoclast viability and resorption activity in vitro ( Feldman et al, 2020 ).…”