Geranylgeraniol Application in Human Osteoblasts and Osteoclasts for Reversal of the Effect of Bisphosphonates

Nitrogen-containing bisphosphonates lead to the depletion of geranylgeranyl pyrophosphate involved in the mevalonate pathway. The effect of geranylgeraniol (GGOH) on human osteoblast and osteoclast activities suppressed by zoledronate was investigated in this study. The effect of GGOH on human osteoblasts and osteoclasts subjected to treatment with zoledronate was analyzed by assessing cell viability, osteoclast differentiation, resorption ability, gene expression, and protein synthesis. Cell viability suppressed by bisphosphonates in osteoblasts and osteoprogenitor cells was restored with GGOH. Osteoclast differentiation was analyzed by vitronectin receptor immunofluorescence staining, and the addition of GGOH to zoledronate significantly increased osteoclast differentiation compared with zoledronate alone. A trend of reversal of osteoclast resorption by GGOH was observed; however, it was not significant in all groups. The expression of ALP, type 1 collagen, and RUNX2 in osteoblasts was recovered by the addition of GGOH. Only CALCR expression in osteoclasts was significantly recovered by GGOH addition in the zoledronate group. Although the activities of osteoblasts and osteoclasts were not entirely restored, the possibility that the topical application of GGOH in MRONJ patients or patients with dental problems and bisphosphonates might lessen the risk of development and recurrence of MRONJ is shown.