Geranylgeraniol as a Modulator of Mevalonate Pathway Disruption: A Scoping Review of Cellular Mechanisms and Skeletal...

Background/Objectives: Geranylgeraniol (GGOH), an isoprenoid intermediate of the mevalonate pathway, regulates bone cell viability and function, particularly by mitigating cellular toxicity induced by nitrogen-containing bisphosphonates (N-BPs). Despite this, its role in osteoporosis remains underexplored. This scoping review synthesises evidence on the effects of GGOH in in vitro and in vivo models of osteoporosis. Methods: PubMed, Scopus, and Ovid were searched using GGOH- and osteoporosis-related terms. Primary studies evaluating GGOH exposure in cellular or animal osteoporosis models were eligible. Twenty-nine studies met the inclusion criteria. Results: In vitro findings demonstrate that GGOH reverses N-BP-induced depletion of geranylgeranyl pyrophosphate, restoring protein prenylation which is essential for osteoclast and osteoblast survival, cytoskeletal organisation, and differentiation. GGOH reduced osteoclast apoptosis, restored nuclear factor of activated T-cells 1 and carbonic anhydrase II expression, and prevented N-BP-associated suppression of bone resorption. In osteoblasts and mesenchymal stem cells, GGOH improved viability, upregulated osteogenic markers including runt-related transcription factor 2, alkaline phosphatase, collagen type I, and bone morphogenetic proteins, and rescued mineralisation impaired by alendronate or zoledronate. Independent of N-BPs, GGOH exerted divergent effects on osteoclasts, by inhibiting osteoclastogenesis or promoting retinoic acid receptor-mediated bone resorption and attenuating zoledronate protection in vascular calcification settings in a model-specific manner. In vivo, dietary GGOH supplementation improved trabecular and cortical bone parameters and reduced serum C-terminal telopeptide of type I collagen in obese mice, indicating suppression of bone resorption. Conclusions: Overall, although GGOH shows osteoprotective potential, its capacity to antagonise N-BP efficacy limits systemic co-administration. Current evidence suggests that local delivery may warrant future investigation as a strategy to mitigate N-BP-induced skeletal toxicity. However, studies evaluating bone tissue exposure, pharmacokinetics, and clinically achievable concentrations are required before this approach can be translated.