Geranylgeraniol reverses alendronate-induced MC3T3 cell cytotoxicity and alteration of osteoblast function via cell cytoskeletal maintenance.

Abstract

Alendronate (ALN) is a bisphosphonate, which is prescribed as an anti-osteoporotic drug. ALN has been shown to increase osteoblast cell death and decrease bone mineralization. ALN inhibits a key regulatory enzyme in the mevalonate pathway, consequently reducing geranylgeranyl pyrophosphate (GGPP). Geranylgeraniol (GGOH) can be converted to GGPP. The aim of this study was to investigate the effects of exogenous GGOH on MC3T3 cell viability, cell cycle, osteoblast function, and cell cytoskeleton under ALN treatment. MC3T3 cells and osteoblast precursors, were incubated with ALN (0-50µmol/L) and GGOH (0-50µmol/L). After treatment, cells were evaluated for cell viability, cell cycle, osteoblast function, and cell cytoskeleton by MTT, flow cytometry, alizarin red S assay, and fluorescent microscopy, respectively. ALN reduced cell viability and bone nodule formation in a dose-dependent manner. GGOH partially inhibited the negative effects of ALN on cell viability and function. ALN increased the percentages of cell apoptosis and necrosis and arrested cells in G2M phase. Co-incubation with GGOH partially reduced late cell apoptosis and rescued cell cycle arrest. Furthermore, ALN altered MC3T3 morphology and decreased cell area, actin stress fiber density as well as nuclear area. GGOH abolished the effect of ALN on cell area, actin stress fiber density, and nuclear area. GGOH partially inhibited negative effects of ALN on cell viability, cell cycle, function, and cell cytoskeleton. It might be an additional option for increasing osteoblast function and reducing apoptosis of osteoblasts in the condition treated with low bisphosphonate concentration.