Low dose of doxycyline promotes early differentiation of preosteoblasts by partially regulating the expression of estrogen receptors

Background: The tetracycline (TC) family, including minocycline and doxycycline (DC), has long been used in the medical field owing to its well-characterized antimicrobial properties. Moreover, TCs have been reported to have effects on bone formation and bone metabolism. Results have shown that more new bone formation is achieved when TCs have been applied in combination with bone graft material. Methods: In the present study, the effects of TCs (TC, minocycline, and DC) on osteoprecursor cells were evaluated. The cell viability was determined using the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay. Differentiation and mineralization were evaluated using an alkaline phosphatase activity test and alizarin red-S staining. In addition, the expression of proteins related to bone formation, such as estrogen receptor (ER)-α, bone morphogenetic protein receptor-IA, bone morphogenetic protein-2, and phospho-Smad1/5, were evaluated by using Western blot analysis. Results: The morphology of the cells seemed normal, and their viability was not affected in the treated groups compared with the control. Alkaline phosphatase activity significantly increased in cultures grown in the presence of 0.1 and 1.0 μM of DC. No statistically significant increase in the mineralization was seen the treated groups. The results of the Western blot analysis revealed that the addition of DC upregulated ER-α, bone morphogenetic protein-2, and phospho-Smad1/5 expression with a statistically significant difference in ER-α expression. Conclusions: From our findings, it was concluded that a low dose of DC could produce positive effects on the differentiation of osteoprecursor cells at an early stage. Our results also suggested that DC has osteoinductive effects that were achieved mainly through the ER pathway by enhancing the expression of ER-α.