Effects of tamoxifen on fetal cartilage development, adult cartilage metabolism and endochondral ossification in mice.

OBJECTIVE: Tamoxifen (TAM) has been used to treat human breast cancer and induce gene knockout in the Cre/loxP system in mice. However, the effects of TAM as a CreER recombinase inducer on bone metabolism, cartilage metabolism, and endochondral ossification have not been thoroughly evaluated.

METHODS: Mice received 5 intraperitoneal TAM injections in the trauma and age-induced osteoarthritis (OA) model and the fracture model. The samples were harvested and underwent micro-computed tomography, histological and immunofluorescence analyses. Pregnant mice at gestation day 15.5 were administered with TAM, and their P0 offspring were used for alcian blue and alizarin red S staining. MLO-Y4 cells and primary chondrocytes were used to determine the effects of TAM on bone and cartilage homeostasis.

RESULTS: TAM caused complete loss of the growth plate and increased the volume of calcified meniscus and synovium (95% confidence interval [95%CI] 0.1789 to 1.31) in aged mice. TAM also decreased the cartilage area in the trauma-induced OA group compared to the control group (95%CI -0.04054 to -0.002148). Besides, TAM significantly increased the expression of Aggrecan (95%CI 1.335 to 10.15) and Col2a1 (95%CI 1.524 to 7.019) in the callus, which indicated that the fracture healing process was impaired. However, the skeletal phenotype of newborn mice did not significantly alter. In vitro, TAM altered the metabolism of extracellular matrix in chondrocytes, while significantly altering gene expression in osteocytes.

CONCLUSIONS: TAM significantly affected bone and cartilage homeostasis. In transgenic mice experiments using the Cre/loxP system, the control should be injected with TAM to avoid off-target effects or the doses should be optimized.