(39) Mechanism of Action of Geranylgeraniol in Reversing Nitrogen Containing Bisphosphonate-Induced Osteoclast Toxicity

Abstract: Currently, there is no cause -based treatment for medication-related osteonecrosis of the jaw (MRONJ) This morbid condition is most often characterized by the presence of exposed, infected bone and, in advanced cases, mandibular fractures in osteoporotic individuals and metastatic cancers patients treated with nitrogen containing bisphosphonates (NBP). These drugs inhibit farnesyl diphosphate synthase (FDPS) in the mevalonate pathway, depriving osteoclasts and other bone cells of small GTPases necessary for their function and survival.1 In particular, the NBP, pamidronate, is considered to be responsible for MRONJ by blocking the formation of geranylgeraniol (GGOH) in the mevalonic acid pathway and inhibiting the prenylation of G-proteins necessary for osteoclast survival.2 We have previously shown that adding back GGOH by incorporating it into a bone cement carrier can restore osteoclast function and increase healing of mandibular osteotomies in a proven animal model of MRONJ.[2] The goal of the study is to assess the effect of the NBP, pamidronate, on global gene expression and determine whether GGOH can restore gene expression. RAW osteoclast-like cells were maintained in monolayer culture and treated with RANKL in the presence and absence of NBP. Pamidronate-treated cells were also treated with GGOH to restore normal function. RNA was extracted from pelleted RANKL treated cells, sequenced and pathway analyzed. Pamidronate downregulated genes associated with immune function, oxidative metabolism and osteoclast differentiation and angiogenesis. Surprisingly, Rho j, a small GTPase was down-regulated 238 fold (P < .001) while RGS18 protein, a regulator of G-protein signaling, was repressed 126 fold (p < 0.001). Substantial changes in expression of more than 20 other G-proteins were observed. When cells were treated with GGOH, the effects of the NBP were abrogated and G-protein expression was restored. (see heat map figure). It is concluded that GGOH can be used to maintain normal osteoclastic activity in the presence of NBP by maintaining G-protein expression.References1. Dunford JE et al Structure – Activity Relationships Among the Nitrogen Containing Bisphosphonates in Clinical Use and Other Analogues: Time-Dependent Inhibition of Human Farnesyl Pyrophosphate Synthase Journal of Medicinal Chemistry (2008)51 (7), 2187-2195 DOI: 10.1021/jm70157332. Feldman G et al Geranylgeraniol (GGOH), incorporated into a bone cement pellet promotes osteoclast function and healing in a model of medication-related osteonecrosis of the jaw J Oral Biol and Craniofacial Research (2024)14, 126-132.

Heat map of genes up or down regulated by pamidronate in osteoclasts whose expression is normalized by geranylgeraniol