The anti-estrogenic activity of indole-3-carbinol in neonatal rat osteoblasts is associated with the estrogen receptor antagonist 2-hydroxyestradiol
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To gain new insight into the roles of cruciferous vegetable-derived bioactive phytochemicals in bone cells, we investigated the effects of indole-3-carbinol (I3C) on cell proliferation and differentiation in estradiol (E2)-exposed calvarial osteoblasts that were obtained from neonatal rats.
Osteoblast activity was assessed by analyzing cellular DNA, cell-associated osteocalcin (OC) levels and alkaline phosphatase (AP) activity. We also examined [3H]-estrone (E1) metabolism and estrogen-agonistic and estrogen-antagonistic activities of 2-hydroxy (OH) E1 and 2-OHE2 and their capacity to displace [3H]-E2 at ER binding sites using competition studies.
I3C did not affect on cellular DNA, OC levels or AP activity. However, I3C completely inhibited E2-induced increases in cell proliferation and differentiation in neonatal rat osteoblasts. Metabolic studies demonstrated that I3C promoted the conversion of [3H]-E1 to 2-OHE1 and 2-OHE2 and those higher rates of conversion (twofold–threefold) were archived when a higher dose of I3C was applied. Proliferation and differentiation studies showed that 2-OHE2 but not 2-OHE1 inhibited E2-induced increases in cell proliferation and differentiation via an ER-mediated mechanism. Likewise, Esr1 was expressed at high level than Esr2. 2-OHE1 showed no activity or affinity for ER.
This study is the first to show that a bioactive compound derived from cruciferous vegetables, I3C, abolishes the E2-mediated stimulation of cell activities including, proliferation and differentiation, in rat osteoblasts and increases the 2-hydroxylation of E1, resulting in the formation of inactive and anti-estrogenic metabolites. These results suggest that in neonatal rat osteoblasts, the anti-estrogenic effect of I3C is mediated by 2-OHE2 through ER-α.
KeywordsOsteoblast 2-hydroxylation Estrogen metabolites Indole-3-carbinol Osteoblasts differentiation Osteoblasts proliferation
This study was fully supported by the Department of Reproductive Biology, INCMNSZ. The authors thank Dr. Verónica Navarro for technical assistance.
Compliance with ethical standards
Conflict of interest
All authors declare that there are no actual or potential conflicts of interest, including financial, personal or other relationships, with other people or organizations that could inappropriately influence this work.
All procedures were performed in accordance with the institutional guidelines, and approved by the animal research ethical committee at INCMNSZ.
This article does not contain any studies with human participants performed by any of the authors.
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