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  Objective:We investigated the effects of DBP and MBP on thyroid system at environmentally relevant concentrations in vivo,and explored the molecular mechanisms. Methods and Results:Stage 51 Xenopus laevis were exposed to DBP and MBP(2,10 or 15 mg/L) for 21 days.The test chemicals decelerated spontaneous metamorphosis in X.laevis at concentrations of 10 and 15mg/L.Moreover,MBP seemed to possess stronger activity.The effects of DBP and MBP on inducing changes of expression of selected thyroid hormone response genes:thyroid hormone receptor-beta,retinoid X receptor gamma,α-andβ-subunits of thyroid-stimulating hormone were detected by quantitative real-time polymerase chain reaction at all concentrations of the compounds.Using mammalian two-hybrid assay in vitro,we further demonstrated that DBP and MBP enhanced the interactions between co-repressor(Silence Mediator of Retinoic acid and Thyroid hormone) and thyroid hormone receptor in a dose-dependent manner,and MBP displayed more markedly. Additionally,the methylation status of TRβgene promoter region was altered in head tissue of X.laevis exposed to MBP. Conclusions:These findings highlighted the danger of DBP and MBP as environmental thyroid disruptors,and provided the information in vivo for the risk assessments of the two compounds for human health.……