Molecular docking of bisphenol A and its nitrated and chlorinated metabolites onto human estrogen-related receptor-gamma Sainath Babu a , Nadeem A. Vellore b , Agasthya V. Kasibotla a , Harlan J. Dwayne c , Michael A. Stubblefield c , Rao M. Uppu a,⇑ a Department of Environmental Toxicology, Southern University and A&M College, Baton Rouge, LA, United States b Department of Medicinal Chemistry, University of Utah, Salt Lake City, UT, United States c Department of Mechanical Engineering, Southern University and A&M College, Baton Rouge, LA, United States article info Article history: Received 14 August 2012 Available online 23 August 2012 Keywords: Bisphenol A Metabolites of bisphenol A Xenoestrogens Estrogen receptors Human estrogen-related receptor AutoDock 4.2 software abstract A xenoestrogen and known endocrine disruptor, bisphenol A (BPA) binds the human estrogen-related receptor-gamma (ERRc) with high affinity (Kd  5.5 nM). It is likely that BPA undergoes oxidative bio- transformation by hypochlorite/hypochlorous acid (  OCl/HOCl) and peroxynitrite (PN) and the products formed in these reactions may serve as secondary estrogens and contribute to the toxicodynamics of BPA. Therefore, in the present study we have examined the formation of chlorinated and nitrated BPA in reactions of BPA with  OCl/HOCl and PN(+CO 2 ) performed around the neutral pH. We have identified four major products in these reactions and they include 3-chloro-BPA (CBPA), 3,3 0 -dichloro-BPA (DCBPA), 3-nitro-BPA (NBPA) and 3,3 0 -dinitro-BPA (DNBPA). Towards understanding the toxicodynamics and estro- genic activity of BPA in biological systems, we have performed molecular docking of BPA, CBPA, DCBPA, DNBPA and NBPA onto the ERRc using AutoDock 4.2 software and compared the binding energies with those of estradiol, the natural ligand. Based on the genetic algorithm, the three best conformations were selected and averaged for each ligand and a detailed analysis of molecular interactions based on free ener- gies of binding (kcal/mol) was computed. The results indicate the following rank order of binding to ERRc: BPA (8.78 ± 0.06) > CBPA (8.53 ± 0.41) > NBPA (7.36 ± 0.74) > DCBPA (5.24 ± 0.17) > DNBPA (4.95 ± 0.78) > estradiol (4.94 ± 1.04). The docking studies revealed that the OH group of one of the phenyl rings forms a hydrogen bond with Glu275/Arg316, while the OH group of other phenyl ring was bound to Asp346. These results suggest that both BPA and its putative chlorinated and nitrated metabo- lites have strong binding affinity compared to estradiol. Ó 2012 Elsevier Inc. All rights reserved. 1. Introduction Bisphenol A (BPA; Fig. 1), a xenoestrogen and semi-persistent organic pollutant in urban environments, adversely affects the endocrine system even at low doses in experimental animals and humans [1–3]. Recent studies show that BPA binds strongly to the human estrogen-related receptor-gamma (ERRc; Kd  5.5 nM) as compared to the estrogen receptor (ER) itself [4,5]. ERRc belongs to the group orphan nuclear receptors, and these are closely related to ER. As on date, three different ERR proteins (a, b, c) have been identified [5]. The function of ERRc is not well known, however, high levels of this receptor are expressed in the fetal brain and in other tissues of adult rodents and humans [6,7]. Approximately 20–25% of BPA is known to undergo metabolic transformation by enzymes of cytochrome P450 system [8,9] and, possibly, neutrophil and macrophage derived oxidants, viz., hypochlorite/hypochlorous acid (  OCl/HOCl) and peroxynitrite (PN). The direct reaction of BPA with  OCl/HOCl has been studied in the context of bioremediation and treatment of waste water and industrial effluents [10,11]. These reactions mainly produce chlorinated BPA. Interestingly, the reaction of BPA with PN has never been studied; however, an analogy of reactions of PN (±CO 2 ) with most phenolic compounds [12–14] suggests nitrated BPA could be the major products. Studies have shown that chlori- nated and nitrated BPA exhibit greater toxicity than native BPA it- self and elaborates mutagenic and/or genotoxic effects [15–17]. Therefore, it is likely that these chlorinated and nitrated BPA if formed in biological systems can serve as secondary estrogens and relay, at least, in part, the toxic effects of BPA. In order to understand the molecular targets for BPA and its putative chlorinated and nitrated products and the likely disrup- tion of endocrine function, in the current study, we carried out the reactions of  OCl/HOCl and PN (+CO 2 ) with BPA around the neutral pH. We identified the major products formed in these 0006-291X/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.bbrc.2012.08.065 ⇑ Corresponding author. Fax: +1 225 771 5350. E-mail address: rao_uppu@subr.edu (R.M. Uppu). Biochemical and Biophysical Research Communications 426 (2012) 215–220 Contents lists available at SciVerse ScienceDirect Biochemical and Biophysical Research Communications journal homepage: www.elsevier.com/locate/ybbrc