Antagonistic effects of estrogen on iron-induced bone resorption and its mechanism

Abstract

To explore the antagonistic effect of estrogen on iron-induced bone resorption and the role of oxidative stress. In vivo, 8-week-old female imprinting control region mice were randomly divided into 3 groups of ferritin (F), ovariectomy (OVX) and F+OVX. Intervention was made by ferric ammonium citrate (FAC) and OVX. Serum levels of ferritin, malondialdehyde (MDA) and superoxide dismutase (SOD) were measured. The expression changes of TRAP, CTR, matrix metallopeptidase 9 (MMP9) and CTK derived from murine bilateral tibia were detected by reverse transcription-polymerase chain reaction (RT-PCR). A high-resolution micro-computed tomography was utilized for scanning distal femur. In vitro, RAW264.7 cells were used and intervened by FAC and estradiol. Tartrate resistant acid phosphatase (TRAP) staining was performed and wine-red TRAP positive cells were counted. ROS level was detected by 2', 7'-dichloro-dihydrofluorescein diacetate (DCFH-DA) with a multi-detection reader. The serum ferritin were heightened in F and F+OVX groups [(335.30 ± 44.10) vs (41.38 ± 5.56) µg/L, (324.80 ± 38.60) vs (41.38 ± 5.56) µg/L respectively, P < 0.01]. The trend of MDA level was F+OVX>OVX>F while SOD level was quite opposite. Body mass density of F+OVX group was lower than that of OVX group (0.114 ± 0.013 vs 0.187 ± 0.029 mg/mm³, P < 0.05) or F group (0.114 ± 0.013 vs 0.902 ± 0.064 mg/mm³, P < 0.05). TRAP and CTK gene expression of OVX group was lower than that of F+OVX group. However, TRAP, CTR and CTK gene expression of F+OVX group was higher than that of F group. TRAP staining: FAC increased the number of TRAP positive cells (41.7 ± 5.5 vs 20.0 ± 4.0, P < 0.05) while estradiol decreased it (14.8 ± 5.1 vs 41.7 ± 5.5, P < 0.05). DCFH-DA test show that reactive oxygen species was elevated by FAC (160% ± 8% vs 100% ± 9%, P < 0.05) and reduced by estradiol (53% ± 13% vs 160% ± 8%, P < 0.05). The antagonistic effect of estrogen on iron-induced bone resorption is probably regulated by oxidative stress.