Bisphosphonate inhibit cell function of HUVECs, fibroblasts and osteoblasts via the inhibition of the geranylgeraniolation of proteins

Introduction: Nitrogen-containig bisphosphonates inhibit the farnesylpyrophosphate, resulting in a decrease in the cellular geranylgeraniol pool. The synthesis of squalenes necessary for cortisone and the prenylation via geranylgeraniol and farnesyl are affected. The aim of this study was to analyze the influence of different isoprenoids on the function of bisphosphonate-treated cells. Materials and Methods: HUVEC, fibroblasts and osteoblasts were incubated with zoledronate. Viability was tested with an MTT test, migration capacity with a scratch wound assay, and the cell morphology was visualized by phallacidin staining. The isoprenoids used were geranylgeraniol, eugenol, farnesol, R-limonene, menthol and squalene. The isoprenoid concentrations for the MTT test were 0, 10, 25, 50 and 100µM. The cells were incubated with 50µM zoledronate for 72h. For the scratch wound assay, the isoprenoid concentrations were 0 and 10µM and 50µM zoledronate. Follow-up or staining occurred after 48h. The tests were performed in triplicate; statistics: ANOVA, post-hoc: Tukey; significance level: p 0.05. Results: Only geranylgeraniol was able to restitute the cell function and morphology of zoledronate-treated cells. Despite the structural similarity of the isoprenoids, the others were not able to do so. Due to the point of interception in the mevalonate pathway of the different isoprenoids, the inhibition of the geranylgeraniolation seems most important since the other isoprenoids were not able to interfere at all. Conclusion: Among the isoprenoids used, only geranylgeraniol is able to minimize the negative effect of bisphosphonates on the viability, migration capacity and morphology of HUVEC, fibroblasts and osteobasts. Therefore only geranylgeraniol could be used as a therapeutic agent. Keywords: Bisphosphonate, bisphosphonate associated osteonecrosis, isoprenoids, geranylgeraniol