Micronuclei in bone marrow and liver in relation to hepatic metabolism and antioxidant response due to coexposure to chloroform, dichloromethane, and toluene in the rat model.

Javier Belmont-Díaz,Ana Paulina López-Gordillo,Eunice Molina Garduño,Regina D Montero-Montoya,Omar Arellano-Aguilar,Noemí Cárdenas-Rodríguez,Luis Serrano-García,Elvia Coballase-Urrutia

doi:10.1155/2014/425070

Abstract

Genotoxicity in cells may occur in different ways, direct interaction, production of electrophilic metabolites, and secondary genotoxicity via oxidative stress. Chloroform, dichloromethane, and toluene are primarily metabolized in liver by CYP2E1, producing reactive electrophilic metabolites, and may also produce oxidative stress via the uncoupled CYP2E1 catalytic cycle. Additionally, GSTT1 also participates in dichloromethane activation. Despite the oxidative metabolism of these compounds and the production of oxidative adducts, their genotoxicity in the bone marrow micronucleus test is unclear. The objective of this work was to analyze whether the oxidative metabolism induced by the coexposure to these compounds would account for increased micronucleus frequency. We used an approach including the analysis of phase I, phase II, and antioxidant enzymes, oxidative stress biomarkers, and micronuclei in bone marrow (MNPCE) and hepatocytes (MNHEP). Rats were administered different doses of an artificial mixture of CLF/DCM/TOL, under two regimes. After one administration MNPCE frequency increased in correlation with induced GSTT1 activity and no oxidative stress occurred. Conversely, after three-day treatments oxidative stress was observed, without genotoxicity. The effects observed indicate that MNPCE by the coexposure to these VOCs could be increased via inducing the activity of metabolism enzymes.

Highlights

Genotoxic compounds are known to exert their effects on DNA either in a direct way or through their metabolites after going through an enzymatic transformation
In order to gain insight into the relationship of metabolism, oxidative stress, and micronucleus production related with the coexposure to CLF, TOL, and DCM, our study considered two different regimes of exposure in a rat model: a single-day treatment and a three-day treatment
CYP2E1 is involved in the biotransformation of the three compounds tested, whereas glutathione-S-transferase T1 (GSTT1) participates in the bioactivation of DCM, producing a metabolite suspected to be the precursor of formaldehyde, a known genotoxic carcinogen [1] (Figure 3)

Summary

Introduction

Genotoxic compounds are known to exert their effects on DNA either in a direct way or through their metabolites after going through an enzymatic transformation. Some compounds have been described as being genotoxic via alternative pathways, like the production of ROS. Under circumstances where CYP2E1 activity is inhibited or saturated it can be metabolized into S-chloromethylglutathione by GSTT1 [2] and form DNA adducts [3]. CLF is another compound of this kind, capable of increasing malondialdehyde deoxyguanosine (M1dG) adducts and lipid peroxidation in HepG2 cells [4] via a CYP2E1 mediated oxidation where phosgene and, under anoxic conditions, dichloromethyl are produced [5], both being highly reactive electrophiles, able to form irreversible covalent bonds with biomolecules like lipids, proteins, and reduced glutathione (GSH) and to induce oxidative stress [6, 7]

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