Estrogen Receptor-β Agonist Diarylpropionitrile: Biological Activities of R- and S- Enantiomers on Behavior and Hormonal Response to Stress

Estrogens have been shown to have positive and negative effects on anxiety and depressive-like behaviors, perhaps explained by the existence of two distinct estrogen receptor (ER) systems, ER alpha and ER beta. The ER beta agonist, diarylpropionitrile (DPN) has been shown to have anxiolytic properties in rats. DPN exists as a racemic mixture of two enantiomers, R-DPN and S-DPN. In this study, we compared R-DPN and S-DPN for their in vitro binding affinity, ability to activate transcription in vitro at an estrogen response element, and in vivo endocrine and behavioral responses. In vitro binding studies using recombinant rat ER beta revealed that S-DPN has a several fold greater relative binding affinity for ER beta than does R-DPN. Furthermore, cotransfection of N-38 immortalized hypothalamic cells with an estrogen response element-luc reporter and ER beta revealed that S-DPN is a potent activator of transcription in vitro, whereas R-DPN is not. Subsequently, we examined anxiety-like behaviors using the open-field test and elevated plus maze or depressive-like behaviors, using the forced swim test. Ovariectomized young adult female Sprague Dawley rats treated with racemic DPN, S-DPN, and the ER beta agonist, WAY-200070, showed significantly decreased anxiety-like behaviors in both the open-field and elevated plus maze and significantly less depressive-like behaviors in the forced swim test compared with vehicle-, R-DPN-, or propylpyrazoletriol (ER alpha agonist)-treated animals. In concordance with the relative binding affinity and transcriptional potency, these results demonstrate that the S-enantiomer is the biologically active form of DPN. These studies also indicate that estrogen's positive effects on mood, including its anxiolytic and antidepressive actions, are due to its actions at ER beta. (Endocrinology 150: 1817-1825, 2009)