Melatonin delays cell proliferation by inducing G₁ and G ₂/M phase arrest in a human osteoblastic cell line hFOB 1.19

Abstract: A recent prospective study indicated that melatonin supplements may reduce the progression of idiopathic scoliosis, the most common deformity of the spine. This form of scoliosis occurs during rapid skeletal growth. To date, however, there is no direct evidence regarding an antiproliferative effect of melatonin at the level of osteoblasts. Herein, we investigated whether melatonin inhibits cell proliferation in a normal human fetal osteoblastic cell line hFOB 1.19. MTT staining showed that at 1 mm concentrations, melatonin significantly inhibited osteoblast proliferation in time-dependent manner. Flow cytometry demonstrated that melatonin significantly increased the fraction of cells in G₀/G₁ phase of the cell cycle, while simultaneously reducing the proportion in the G₂/M phase rather than the S phase. Western blot and real-time PCR analyses further confirmed that melatonins inhibitory effect was possibly because of downregulation of cyclin D1 and CDK4, related to the G₁ phase, and of cyclin B1 and CDK1, related to the G₂/M phase. There was no downregulation of cyclin E, CDK2, and cyclin A, which are related to G₁/S transition and S phase. In addition, the trypan blue dye exclusion assay showed that cell viability was not changed by melatonin relative to control cells. These findings provide evidence that melatonin may significantly delay osteoblast proliferation in a time-dependent manner and this inhibition involves the downregulation of cyclin D1 and CDK4, related to the G₁ phase, and of cyclin B1 and CDK1, related to the G₂/M phase.