An in Silico and in Vitro Study for Investigating Estrogenic Endocrine

environments Article An In Silico and In Vitro Study for Investigating Estrogenic Endocrine Effects of Emerging Persistent Pollutants Using Primary Hepatocytes from Grey Mullet (Mugil cephalus) Paolo Cocci, Gilberto Mosconi and Francesco A. Palermo * School of Biosciences and Veterinary Medicine, University of Camerino, Via Gentile III Da Varano, I-62032 Camerino, MC, Italy; [email protected] (P.C.); [email protected] (G.M.) * Correspondence: [email protected] Abstract: There is growing concern about the environmentally relevant concentrations of new emerging persistent organic pollutants, such as perfluorinated compounds and pharmaceuticals, which are found to bioaccumulate in aquatic organisms at concentrations suspected to cause reproductive toxicity due to the activation of estrogen receptor (ER) α and β subtypes. Here, we use a combined in silico and in vitro approach to evaluate the impact of perfluorononanoic acid (PFNA) and Enalapril (ENA) on grey mullet (Mugil cephalus) hepatic estrogen signaling pathway. ENA had weak agonist activity on ERα while PFNA showed moderate to high agonist binding to both ERs. According to these effects, hepatocytes incubation for 48 h to PFNA resulted in a concentration-dependent upregu- lation of ER and vitellogenin gene expression profiles, whereas only a small increase was observed in ERα mRNA levels for the highest ENA concentration. These data suggest a structure–activity relationship between hepatic ERs and these emerging pollutants. Citation: Cocci, P.; Mosconi, G.; Palermo, F.A. An In Silico and In Keywords: endocrine disruptors; Mugil cephalus; PFNA Vitro Study for Investigating Estrogenic Endocrine Effects of Emerging Persistent Pollutants Using Primary Hepatocytes from Grey Mullet (Mugil cephalus). Environments 1. Introduction 2021, 8, 58. https://doi.org/10.3390/ Chemicals interfering with the endocrine system known as endocrine disrupting environments8060058 chemicals (EDCs) are pollutants that typically occur in aquatic environments as a result of municipal wastewater discharge, landfill leachates, and agricultural and urban runoff [1]. Academic Editor: Sílvia C. Goncalves EDCs are considered a major cause of aquatic wildlife decline and loss of biodiversity [2]. Aquatic organisms such as fish may experience life-long exposures to EDCs and may Received: 14 May 2021 bioaccumulate them developing a wide range of hormonal abnormalities [3]. Today, there Accepted: 16 June 2021 is growing concern about the environmentally relevant concentrations of new emerging Published: 18 June 2021 persistent pollutants, such as perfluorinated compounds (PFCs) and pharmaceuticals (e.g., contraceptives and anti-depressants), which are found to bioaccumulate in aquatic food Publisher’s Note: MDPI stays neutral webs at concentrations suspected to perturb neuro-endocrine processes in living organisms with regard to jurisdictional claims in including humans [4,5]. published maps and institutional affil- PFCs are synthetic chemical compounds that due to high stabilities and low surface iations. tensions are increasingly used in various industrial applications and common consumer products [6]. Among PFCs, the perfluoroalkylated substances (PFAS) have been discovered as global pollutants remaining most persistently in each environmental compartment [7,8]. Although PFAS are considered moderately to highly toxic, some of these (e.g., perfluorooc- Copyright: © 2021 by the authors. tane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA)) are suspected endocrine Licensee MDPI, Basel, Switzerland. disruptors and have been found to cause adverse health effects, especially reproductive This article is an open access article toxicity, in different vertebrate models [9,10]. Similarly, pharmaceuticals that include any distributed under the terms and chemical product used by individuals or agribusiness for promoting personal and livestock conditions of the Creative Commons health, have aroused great interest as environmental pollutants for their ecotoxicological Attribution (CC BY) license (https:// potentials [11,12]. These compounds have been detected, unchanged or as metabolites, in creativecommons.org/licenses/by/ wastewater, surface and drinking waters throughout the world [13–15]. Calamari et al. [16] 4.0/). Environments 2021, 8, 58. https://doi.org/10.3390/environments8060058 https://www.mdpi.com/journal/environments Environments 2021, 8, 58 2 of 13 have defined pharmaceuticals as pseudo-persistent pollutants due to their continuous introduction into the environment, the biotic and/or abiotic transformation and the ability to exert subtle effects in non-target organisms. In this regard, the estrogenic potential of some pharmaceuticals has attracted great concern especially in the aquatic environment [17,18]. Estrogen-like EDCs (xenoestrogens) have the capability to bind to the estrogen receptors (ERs), mimicking the female steroid hormone, 17β-estradiol (E2), and thus activating intracellular signaling pathways. Activation of the ER-mediated signaling pathway has been extensively studied in several models, particularly fish in which feminization has been considered a direct result of xenoestrogen contamination [19–23]. In this regard, the ER-induced hepatic vitellogenin (Vtg) production is typically used to confirm exposure to estrogenic compounds in male fish [24,25]. Of the different fish organ cells, liver cells are widely used in in vitro primary culture models due to their ability to retain na- tive liver properties including estrogen responsiveness [26–28]. For that reason, in vitro methods using primary cultures of fish hepatocytes represent a fundamental and recom- mendable alternative to in vivo studies for investigating several toxicologically relevant mechanisms [29,30]. In the present work, we focused our attention on the ability of perfluorononanoic acid (PFNA) and enalapril (ENA) to interfere with estrogen receptor signaling using a combined in silico/in vitro approach. The selected compounds belong to the most frequently detected classes of emerging EDCs in the aquatic environment such as PFAS and pharmaceuticals [31–35]. The Endocrine Disruptome program package was used to predict their potential interference with nuclear ERs in silico. A bioassay that uses primary hepatocytes from the grey mullet (Mugil cephalus) was then employed for screening estrogenic potential by assessing classical biomarker responses such as VTG protein and ER isoform mRNA expression. In addition, cytotoxicity using Alamar Blue and 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays was evaluated after 24 and 48 h exposure. 2. Materials and Methods 2.1. Endocrine Disruptome Screening Tool A molecular docking approach for predicting interactions between PFNA/ENA and estrogen receptor α (ERα) and β (ERβ) ligand binding domains has been performed with Endocrine Disruptome Simulation (EDS) Tool. This web service has already been successfully adopted as a software tool for predicting the endocrine disruption potential of compounds, using well-validated crystal structures of 14 different human nuclear receptors including ER subtypes [36]. The crystal structures of 1A52, 3OLS, 1SJ0, and 1QKN have been chosen as templates on the basis of their sequence identity with fish receptors (higher than 60%). The docking scores reported are a measure of how the contaminants fit within the receptor-binding pocket, taking into account continuum and discreet parameters. According to the threshold calculations sensitivity (SE), it is possible to obtain four broad groups indicating predicted affinity for ER isoforms as follows: “red” (SE < 0.25), high probability; “orange” (0.25 < SE < 0.50) and “yellow” (0.50 < SE < 0.75), medium probability; and “green” (SE > 0.75), low probability of binding [36]. 2.2. Hepatocyte Isolation and Primary Cell Culture Flathead grey mullet (Mugil cephalus) males (95.5 ± 10.9 g initial weight) were pro- vided by professional fishermen during fishing activities. Fish were acclimated for 2 weeks in 2.00 m × 2.00 m × 0.60 m tanks with constant aeration and natural photoperiod at Unità di Ricerca e Didattica of San Benedetto del Tronto (URDIS), University of Camerino in San Benedetto del Tronto (AP, Italy). Water quality parameters were monitored daily showing −1 ◦ the following values: pH 8.4 ± 0.2, O2 = 10.3 ± 0.5 mg L , and temperature = 20–22 C, salinity 36 ± 2 psu; undetectable level of nitrites and ammonia. Following the acclima- tion, fish were randomly euthanized using MS-222 within 5 min after capture. Animal manipulation was executed following the procedures established by the Italian law (Leg- Environments 2021, 8, 58 3 of 13 islative Decree 116/1992), the European Communities Council Directive (86/609/EEC and 2010/63/EU) for animal welfare and under the supervision of the authorized inves- tigators. The liver tissue was collected to obtain hepatocytes under a laminar flow hood, according to Cocci et al. [37] and Palermo et al. [38]. Purified hepatocytes were suspended in Leibovitz (L-15) phenol red-free medium, antibiotic-antimycotic solution (100 U/mL) and 10 mM HEPES. The cell density was measured in a Burker Chamber and the viability of hepatocytes was over 90%, as assessed with the Trypan blue exclusion assay. Cells were seeded on 24-well Falcon Primaria culture plates (1 × 106 cells per well) in L-15 phenol red-free medium, antibiotic-antimycotic solution (100 U/mL) and 10 mM HEPES. Cells were cultured for 24 h in an incubator at 23 ◦C before chemical

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