Premium
Environmental Phthalate Diesters as hMT 1 and hMT 2 Melatonin Receptor Ligands
Author(s) -
Jones Anthony J,
Dubocovich Margarita L,
Rajnarayanan Rajendram V
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.1061.2
Subject(s) - phthalate , chemistry , receptor , melatonin , docking (animal) , in silico , melatonin receptor , stereochemistry , biochemistry , endocrinology , organic chemistry , biology , medicine , nursing , gene
Phthalates esters are commonly used plasticizers that have been linked to endocrine disruption and developmental alterations. Humans are exposed to these ubiquitous synthetic compounds via inhalation of ambient air, dermal contact with consumer products, and ingestion through food and drinking water. It is estimated from urinary metabolite levels that in the US, median adult daily exposure values for phthalate levels are about 8.5–16.8 μg/kg bw/day (Wittassek et al. , Mol Nutr Food Res . 55:7–31, 2011). Using integrated pharmacoinformatics‐molecular docking approaches we discovered that several phthalate diesters show structural similarities to melatonin receptor ligands and bind with relatively high docking scores to melatonin binding pockets on in silico hMT 1 and hMT 2 melatonin receptor models. An assortment of phthalates including three monoesters and ten diesters with alkyl and/or aromatic substituents were tested for competition with 2‐[ 125 I]‐iodomelatonin (100 nM) binding to hMT 1 and hMT 2 receptors stably expressed in CHO cells to assess binding affinity (K i ) as well as apparent intrinsic efficacy in the presence of GTP (100 μM). In GPCR binding assays, GTP decouples G proteins from receptors causing decreased affinity (rightward shift) for agonists but not for antagonists. Phthalate diesters with aromatic substituents (BBzP: Benzyl Butyl Phthalate; DPP: Diphenyl Phthalate) exhibited the highest affinities toward both hMT 1 (BBzP K i : 2.6 ± 0.3 μM, n=8; DPP K i : 2.9 ± 0.7 μM, n=8) and hMT 2 (BBzP K i : 1.3 ± 0.2 μM, n=9; DPP K i : 0.66 ± 0.10 μM, n=9) receptors. Among phthalates with alkyl substituents , four carbon (C4; DBP: Dibutyl Phthalate) and six carbon (C6; DHP: Dihexyl Phthalate) chain length diesters best competed for binding to hMT 1 receptors with affinities ranging from 5 to 8 μM. hMT 2 receptors did not show any preference to chain lengths of C6 or shorter (DEP: Diethyl Phthalate; DMP: Dimethyl Phthalate; DPrP: Dipropyl Phthalate; DBP; DHP), as all K i values were between 2 and 7 μM. DBP and BBzP bound to melatonin receptors with affinities in the low micromolar range, however their respective monoester metabolites, MBP (Monobutyl Phthalate) and MBzP (Monobenzyl Phthalate), did not compete for binding to either receptor. The presence of GTP caused a leftward shift of the binding competition curves for both BBzP and DPP at hMT 1 melatonin receptors (BBzP K iGTP /K iControl : 3.8; DPP K iGTP /K iControl : 2.6) suggesting inverse agonist efficacy. Little or no shift (BBzP K iGTP /K iControl : 1.3; DPP K iGTP /K iControl : 1.5) on competition curves for hMT 2 melatonin receptors suggests antagonist efficacy. Together these data suggest that phthalate diesters could interact with hMT 1 and hMT 2 receptors to disrupt melatonin receptor‐mediated signaling processes in target tissues. Support or Funding Information Supported by ES 023684 to MLD and RVR.