Contents lists available at ScienceDirect Mutat Res Gen Tox En journal homepage: www.elsevier.com/locate/gentox Bacterial mutagenicity of selected procarcinogens in the presence of recombinant human or rat cytochrome P4501A1 Rebeca Santes-Palacios 1 , Rafael Camacho-Carranza, Jesús Javier Espinosa-Aguirre ⁎ Departamento de Medicina Genómica y Toxicología Ambiental, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Ciudad Universitaria, Coyoacán, Ciudad de México, C. P. 04510, Mexico ARTICLE INFO Keywords: Polycyclic aromatic hydrocarbons Aromatic amines Heterocyclic amines Molecular docking ABSTRACT Cytochrome P4501A1 (CYP1A1) is an important enzyme of procarcinogen activation. We have studied bacterial (Ames test) mutagenicity resulting from mutagen activation by recombinant human or rat CYP1A1. Mutagenicity depends on both the chemical group and species-specific activation: polycyclic aromatic hydro- carbons showed higher (5-7-fold) mutagenic activity when activated by the human enzyme, whereas hetero- cyclic amines were more mutagenic (5-75-fold) in the presence of the rat enzyme. With regard to the two aromatic amines tested, only 2-aminoanthracene showed a clear species preference, activated 3-fold more ef- fectively by human than by rat CYP1A1. We also analyzed in silico the binding of these compounds to the human and rat enzyme catalytic sites, identifying residues expected to participate in ligand recognition. A phenylalanine residue was involved in CYP-mutagen stabilization through π-π stacking. Variations in the three-dimensional conformations and distances to the heme groups may contribute to differences between human and rat CYP- substrate interactions. In conclusion, CYP1A1 shows significant differences between species, in terms of mutagen activation, which should be considered in the context of human risk assessment. 1. Introduction Cytochrome P4501A1 (CYP1A1) is expressed in extrahepatic tissues and is one of the most important enzymes involved in procarcinogen activation [1]. In this process, substrates - mainly planar and hydro- phobic, such as polycyclic aromatic hydrocarbons (PAH), aromatic amines (AA), and heterocyclic amines (HA) - are converted into highly reactive metabolites [2] which can react with DNA, lipids, or proteins, resulting in carcinogenesis initiation [3]. The identification and development of CYP1A1 modulating sub- stances is relevant to the study of carcinogenesis [4–6]. Because of limitations on the use of human materials, several alternative experi- mental models, such as liver S9 fraction or microsomes, recombinant enzymes, and cell lines, are used as in vitro systems for metabolism studies. In vivo models of tumorigenesis and knockout models (fish, rats, mice) have been developed [7–9]. Recently, new strategies have been proposed for toxicological assessment, including the establishment of dual human-rodent activation models, “humanized” animals for the prediction of pharmacokinetic profiles, mathematical models of tox- icokinetics, molecular dynamic assays, and other computational methods [10–15]. However, it is often difficult to extrapolate data from animal models to human metabolism and health. For example, CYP inducers are typically used to study xenobiotic activation in animal models, resulting in enzyme activity levels higher than those in most human samples. Humans are exposed to multiple lifestyle-related in- ducers, which are difficult to monitor [16]. Gene regulation also differs among species. The promoter of the CYP1A1 gene is well-conserved in mammals, but differs in fish and amphibians [17]. When cultures of human, rat, and quail cells were treated with the widely used P450 inducer aroclor 1524, enzymatic activity of rat CYP1A1 was induced 55-fold, whereas only 3-fold induction was observed with the human and quail cells [18]. Human liver microsomes showed the lowest https://doi.org/10.1016/j.mrgentox.2018.09.001 Received 3 June 2018; Received in revised form 5 September 2018; Accepted 6 September 2018 Abbreviations: CYP1A1, cytochrome P4501A1; BaP, benzo[a]pyrene; DMBA, 7,12-dimethylbenz[a]anthracene; 2AA, 2-aminoanthracene; 2AF, 2-aminofluorene; DiMeIQx, 2-amino-3,4,8-dimethylimidazo[4,5-f]quinoxaline; MeIQx, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline; PAH, polycyclic aromatic hydrocarbon; AA, aromatic amine; HA, heterocyclic amine ⁎ Corresponding author at: Departamento de Medicina Genómica y Toxicología Ambiental, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Ap. Postal 70-228, Ciudad de México, 04510, Mexico. 1 Present address: Laboratorio de Toxicología Genética, Instituto Nacional de Pediatría, Insurgentes Sur 3700-C, Insurgentes Cuicuilco, Coyoacán, Ciudad de México, 04530, México. E-mail addresses: jjea99@gmail.com, jjea@biomedicas.unam.mx (J.J. Espinosa-Aguirre). Mutat Res Gen Tox En 835 (2018) 25–31 Available online 07 September 2018 1383-5718/ © 2018 Elsevier B.V. All rights reserved. T