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A modeling approach to evaluate the balance between bioactivation and detoxification of MeIQx in human
hepatocytes
Victorien Delannée, Sophie Langouët, Nathalie Théret, Anne Siegel
To cite this version:
Victorien Delannée, Sophie Langouët, Nathalie Théret, Anne Siegel. A modeling approach to evaluate
the balance between bioactivation and detoxification of MeIQx in human hepatocytes. PeerJ, PeerJ,
2017, 5, pp.e3703. �10.7717/peerj.3703�. �hal-01575579�
Submitted 8 February 2017 Accepted 27 July 2017 Published 1 September 2017 Corresponding author Sophie Langouët,
sophie.langouet@inserm.fr Academic editor J. Thomas Sanderson Additional Information and Declarations can be found on page 21
DOI 10.7717/peerj.3703 Copyright
2017 Delannée et al.
Distributed under
Creative Commons CC-BY 4.0
OPEN ACCESS
A modeling approach to evaluate the balance between bioactivation and detoxification of MeIQx in human hepatocytes
Victorien Delannée 1 , 2 , Sophie Langouët 2 , Nathalie Théret 1 , 2 and Anne Siegel 1
1 UMR 6074 IRISA, CNRS, INRIA, University of Rennes 1, Rennes, France
2 UMR Inserm U1085 IRSET, University of Rennes 1, Rennes, France
ABSTRACT
Background. Heterocyclic aromatic amines (HAA) are environmental and food contaminants that are potentially carcinogenic for humans. 2-Amino-3,8- dimethylimidazo[4,5-f ]quinoxaline (MeIQx) is one of the most abundant HAA formed in cooked meat. MeIQx is metabolized by cytochrome P450 1A2 in the human liver into detoxificated and bioactivated products. Once bioactivated, MeIQx metabolites can lead to DNA adduct formation responsible for further genome instability.
Methods. Using a computational approach, we developed a numerical model for MeIQx metabolism in the liver that predicts the MeIQx biotransformation into detoxification or bioactivation pathways according to the concentration of MeIQx.
Results. Our results demonstrate that (1) the detoxification pathway predominates, (2) the ratio between detoxification and bioactivation pathways is not linear and shows a maximum at 10 µ M of MeIQx in hepatocyte cell models, and (3) CYP1A2 is a key enzyme in the system that regulates the balance between bioactivation and detoxification. Our analysis suggests that such a ratio could be considered as an indicator of MeIQx genotoxicity at a low concentration of MeIQx.
Conclusions. Our model permits the investigation of the balance between bioactivation (i.e., DNA adduct formation pathway through the prediction of potential genotoxic compounds) and detoxification of MeIQx in order to predict the behaviour of this environmental contaminant in the human liver. It highlights the importance of complex regulations of enzyme competitions that should be taken into account in any further multi-organ models.
Subjects Computational Biology, Toxicology
Keywords Mathematical modeling, MeIQx bioactivation, Xenobiotic metabolism, Systems Toxicology
INTRODUCTION
Heterocyclic aromatic amines (HAA) are environmental and food contaminants that are formed during cooking of meat and fish, burning of tobacco and diesel exhaust (International Agency for Research on Cancer, 1987). Based on toxicology studies, they have been classified as probable or possible human carcinogens (Group 2A and 2B)
How to cite this article Delannée et al. (2017), A modeling approach to evaluate the balance between bioactivation and detoxification of
MeIQx in human hepatocytes. PeerJ 5:e3703; DOI 10.7717/peerj.3703
N
N N
N NH 2
H 3 C
CH 3
H2O
H2O
N
N N
N NHSO 3
H 3 C
CH 3
H2O
N
N N
N N
H 3 C
H 2 O CH 3
OH H
N
N N
N N
H 3 C
H 2 O CH 3
O
H R
N
N N
N N
H 3 C
H 2 O CH 3
OH
O OH
OH OH
COOH
N
N N
N N H 3 C
H 2 O H 2 O
CH 3 H
O OH
OH OH
COOH
MeIQX
C-‐Hydroxy-‐MeIQx
MeIQx-‐N 2 -‐SO 3 H
7-‐ ox o-‐ M eI Qx
MeIQx-‐N 2 -‐Gl HON-‐MeIQx-‐N 2 -‐Gl
Potenal-‐ Genotoxic -‐Compound including Ester-‐O-‐NH-‐MeIQx
N-‐Hydroxy-‐MeIQx
CYP1A2 CYP1A2
UGT
SULT UGT
NAT & SULT
N
N N
N NH 2 COOH
H 2 O
CH 3 N
N N
N NH 2 HOCH 2
H 2 O H 2 O
CH 3
N
N H
N NH
NH 2 H 3 C
H 2 O H 2 O
O
N
N H
N N
NH 2
H 3 C
H 2 O
O
CH 3
N-‐ de sm et hy l-‐
7-‐ ox o-‐ M eI Qx CYP1A2
IQx-‐8-‐COOH 8-‐CH 2 OH-‐IQx
Xa nt hi ne De hy dr og en as e
? HONH-‐MeIQx
ox o-‐ M eI Qx
Figure 1 Global MeIQx Metabolism pathway (Langouët et al., 2001). The metabolism of MeIQx is composed of metabolites involved in the detoxification pathways (printed in green) and components of the bioactivation pathway (printed in orange and red). Full chemical names: MeIQx, 2-amino-3,8- dimethylimidazo[4,5-f ]quinoxaline; HONH-MeIQx, 2-(hydroxyamino)-3,8-dimethylimidazo[4,5- f ]quinoxaline; MeIQx-N 2 -SO3H, N 2 -(3,8-dimethylimidazo[4,5-f ]quinoxalin-2-yl)sulfamic acid;
MeIQx-N 2 -Gl, N 2 - (β-1-glucosiduronyl)-2-amino-3,8-dimethylimidazo- [4,5-f ]quinoxaline; 8-CH2OH- IQx, 2-amino-8-(hydroxymethyl)-3-meth-ylimidazo[4,5-f ]quinoxaline; IQx-8-COOH, 2-amino-3- methyl-imidazo[4,5-f ]quinoxaline-8-carboxylic acid; HON-MeIQx-N 2 -Gl, N 2 -(β-1-glucosiduronyl)- 2-(hydroxyamino)-3,8-dimethylimidazo[4,f -f]quinoxaline; 7-oxo-MeIQx, 2-amino-3,8-dimethyl-6- hydro-7H-imidazo[4,5-f ]quinoxalin-7-one; N-desmethyl-7-oxo-MeIQx, 2-amino-6-hydro-8-methyl-7H- imidazo[4,5-f ]quinoxalin-7-one.
by the International Agency of Research on Cancer. Among the HAA, 2-Amino-3,8- dimethylimidazo[4,5-f ]quinoxaline (MeIQx) is one of the most abundant found in cooked foods, with the level of human exposure estimated to be as high as 2.6 µ g of MeIQx per person per day (Ni et al., 2008).
Metabolism of MeIQx has been investigated in human hepatocytes few years ago and the data clearly demonstrated that MeIQx is actively transformed into a number of metabolites, which are either detoxification products or potentially reactive metabolites (Langouët et al., 2001). Our previous data identified for the first time the formation of 2-Amino-3-methylimidazo[4,5-f ]quinoxaline-8-carboxylic acid (IQx-8-COOH) as a major detoxification pathway catalyzed by two successive CYP1A2 oxidations with 2-amino-8-(hydroxymethyl)-3-methylimidazo[4,5-f ]quinoxaline (8-CH 2 -OH-IQx) as an intermediate (Fig. 1) (Turesky et al., 2002). This new metabolite was predominant at
Delannée et al. (2017), PeerJ , DOI 10.7717/peerj.3703 2/24
levels approaching human exposure while it was minor at higher concentrations. As usual, the mutagenic and carcinogenic metabolites are formed through N-oxidation reactions which are catalyzed by CYP1A2 in the human liver (Gu et al., 2010). Further activation of the N-hydroxylamine metabolites (HONH-MeIQx) occurs by esterifications catalyzed by N-acetyltransferases (NAT) and sulfotranferases (SULT) leading to the formation of several potential conjugates identified as Ester-O-NH-MeIQx in Fig. 1. These conjugates are able to form reactive nitrenium ions able to bind DNA at the N2 and C8 position of guanine (Turesky & Le Marchand, 2011). The reactive HONH-MeIQx metabolites can also be conjugated by UGT forming N2 glucurono-conjugates (HON-MeIQx-N 2 -Gl) able to be eliminated (Fig. 1). Detoxification is also described through MeIQx-N 2 -SO 3 H and MeIQx-N 2 -Gl formation (Fig. 1). N-desmethyl-7-oxo-MeIQx and 7-oxo-MeIQx are probably formed by the reaction catalysed by xanthine dehydrogenase and are less toxic than the parent compound. CYP1A2 catalyzes reactions involved in both the metabolic activation and detoxification pathways of this procarcinogen in humans (Fig. 1). The formation of MeIQx DNA adducts in human hepatocytes are consistent (2 adducts per 10 6 bases) (Nauwelaers et al., 2011).
There is evidence that demonstrates the importance of human biological models to study biotransformation of environmental contaminants (Turesky & Le Marchand, 2011).
Most of them are very difficult to handle and limited studies exist on HAA metabolism in humans including MeIQx. Although several tissues might be able to metabolize MeIQX, with for instance possible formation of DNA adducts in colon, rectum and kidney, liver is by far the most metabolically active tissue in the biotransformation of MeIQx experiments were performed in human primary hepatocytes. Moreover, the liver is the primary target organ for MeIQx-induced tumors in the rat (Kato et al., 1988; Kushida et al., 1994; Rich et al., 1992). Therefore, primary human hepatocytes are considered as state of the art cell culture models to study the behaviour of xenobiotic in the human liver, however their availability is very limited (Langouët et al., 2002). This limitation led to the development of predictive approaches in order to reduce experimental studies using human hepatocytes.
System toxicology approach is a novative and promising area and numerous topics have been recently documented in a special issue of Chemical Research in Toxicology (Sturla
& Hollenberg, 2014). Such integrative and modeling approaches allow predictions of xenobiotic metabolism and enlighten complex biological processes. Indeed, some complex biological mechanisms have been experimentally shown this last years (Masubuchi et al., 1993; Pritchett, Kuester & Sipes, 2002), but to our knowledge the bibliography concerning the study of the consequences of such mechanisms on the bioactivation is limited. At this present time, a lot of studies aimed to understand the regioselective change has been carried out. These studies attempt mainly to explain regioselective process by performing amine acid mutations. Indeed, some residues are important to orient the substrate in the catalytic site and mutation of these residues can affect the regioselectivity (Parikh, Josephy
& Guengerich, 1999; Josephy, Bibeau & Evans, 2000). In addition, a study has shown that regioselective change could also provide by a structural change of the substrate affecting the preferred formation of a metabolism product (Upthagrove & Nelson, 2001).
Delannée et al. (2017), PeerJ , DOI 10.7717/peerj.3703 3/24
Figure 2 Distribution of MeIQx Metabolites as a function of MeIQx treatment in human hepatocytes (Langouët et al., 2001). Data illustrated by a histogram (A) completed by a table (B) are expressed as per- centage of the initial dose of MeIQx.
In the present study, we implement a system approach to model and understand the effects of a complex mechanism affecting the balance between bioactivation and detoxification. To deepen this assessment, we focus our study on MeIQx metabolism, which has been demonstrated to modulate its detoxification in function of it concentration by an unknown mechanism and without knowing the effect on bioactivation.
MATERIALS & METHODS
Compound concentrations in human hepatocytes in response to MeIQx initial concentrations
The data set used for this present work has been previously published (Langouët et al., 2001). Briefly, human hepatocytes isolated from human liver biopsies were treated with low concentration of MeIQx (1, 10 and 50 µ M) not to induce cytotoxic effects (Langouët et al., 2001). The culture media were retrieved at 24 h and the metabolites were purified and quantified by mass spectrometry. Figure 2 shows the percentage of total metabolite quantity for the ten following compounds: MeIQx, MeIQx-N 2 -Gl, MeIQx-N 2 -SO 3 H, N-desmethyl-7-oxo-MeIQx, 7-oxo-MeIQx, IQx-8-COOH, 8-CH 2 - OH-IQx, HON-MeIQx-N 2 -Gl, HONH-MeIQx, and Potential-Genotoxic-Compound.
To describe the metabolism of MeIQx with a numerical model based on ordinary
Delannée et al. (2017), PeerJ , DOI 10.7717/peerj.3703 4/24
N
N N
N NH
2H
3C
CH
3H2O
H2O N
N N
N NHSO3
H3C
CH3 H2O
H2O
N
N N
N N
H3C
H2O CH3
OH H
N
N N
N N
H3C
H2O CH3
O
H R
N
N N
N N
H3C
H2O CH3
OH
O OH
OH OH
COOH
N
N N
N N
H3C
H2O H2O
CH3 H
O OH
OH OH
COOH
MeIQx C-‐Hydroxy-‐MeIQx
MeIQx-‐N 2 -‐SO 3 H
oxo-‐MeIQx
MeIQx-‐N 2 -‐Gl HON-‐MeIQx-‐N 2 -‐Gl
Potenal-‐ Genotoxic -‐Compound including Ester-‐O-‐NH-‐MeIQx
N-‐Hydroxy-‐MeIQx
(1-‐α) CYP1A2 α CYP1A2
β UGT
SULT (1-‐β) UGT
NAT & SULT
N
N N
N NH2
COOH
H2O H2O
CH3
N
N H
N N NH2 H3C
H2O H2O
O
CH3 or H