IDENTIFICATION OF A BROMINATED FLAME RETARDANT AS A POTENT ACTIVATOR OF THE HUMAN ANDROGEN RECEPTOR

Abstract

There is increasing awareness over the adverse effects of environmental contaminants on the health and well-being of both humans and wildlife. Many compounds have been shown to interact with steroid receptors and thereby cause a variety of developmental and reproductive disorders. Substances that result in reproductive disorders and interfere with the endocrine system are commonly referred to as endocrine disrupting substances (EDS). While numerous estrogen agonists have been identified, and shown to interfere with reproduction, the presence of androgenic compounds has so far been inferred from studies of masculinization of animals. However, several compounds have been shown to possess low androgen receptor (AR) binding affinity and to act as AR antagonists and other studies have also shown that estrogenic compounds can act as anti-androgens. In order to investigate AR activation by exogenous compounds, a combination of experimental analysis and theoretical modeling was used to compare a set of brominated flame retardants (BFR) to dihydrotestosterone (DHT) with regard to ligand docking, AR binding and AR activation in human hepatocellular liver carcinoma cells (HepG2), as well as analysis of the interacting energy between receptor and ligand. Modeling of receptor docking was found to be a useful first step in predicting the potential to translocate to the ligand-pocket of the receptor, and the computed interaction energy was found to correlate with the observed binding affinity. Flexible alignment studies of the BFR compounds demonstrated that 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (BCH) closely overlap DHT. Combining the theoretical modeling with in vitro ligand-binding and receptor-activation assays we show that BCH binds to and activates the human AR. The remaining BFRs did not successfully interact with the ligand pocket in the modeling, were not able to replace a synthetic androgen from the receptor in the binding study, and failed to activate the receptor in vitro. Further research is now underway to determine if BCH interacts with AR from non-mammalian species. (platform)