Dibutyltin (DBT) an endocrine disrupter in zebrafish

Abstract

Dibutyltin (DBT) is a plastic stabilizer and metabolite of tributyltin (TBT), other than its immune and neurological effects, little else is known about DBT. We have examined the actions of DBT as an endocrine disruptor in zebrafish (Danio rerio). In HeLa cells transiently co-transfected with plasmid constructs containing zebrafish estrogen receptors (zfERα, zfERβ1 and zfERβ2) and zebrafish estrogen response element (zfERE-luc), ethinylestradiol (EE2) induced luciferase activity 2 to 6-fold and DBT increased that activity. DBT inhibited testosterone induced luciferase activity, in HeLa cells transiently co-transfected with zebrafish androgen receptor (zfAR) and murine androgen receptor response element (ARE-slp-luc). In HeLa cells co-transfected with zfERβ1 and zfERβ2 and a plasmid containing zebrafish aromatase (zfCyp19a-luc), DBT increased EE2-induced luciferase activity. Real-time PCR analysis of sexual differentiation markers and phase II metabolism markers in fish exposed to 0.1 to 0.5mg/kg DBT in vivo revealed a masculinizing effect. In brain there was decreased production of FST. In the liver there was decreased production of FST, zfCYP19a, and zfERβ1 mRNA and in the gonads there was decreased production of FST, DAX1, and zfCYP19a. DBT also increased UGT expression and decreased GST following exposure. DBT in vivo has an overall masculinizing effect but in vitro has a feminizing effect, indicating that DBT has complex actions within zebrafish, which may be due to the metabolism of DBT to monobutyltin (MBT) and action of other reactive metabolites which promote masculinization and mask the feminizing effect of DBT alone. In vitro results show a clear feminizing effect in a system with fewer complexities. These results are discussed in the context of DBT as an endocrine disruptor in zebrafish.