Metabolic Activation of Pyrrolizidine Alkaloids – Generation of Multiple Reactive Metabolites Leading to DNA Adduct Formation and Potentially Liver Tumor Initiation

Abstract The environmental carcinogen benzo[a]pyrene (BaP) is presumed to exert its genotoxic effects after metabolic activation by cytochrome P450 (CYP) enzymes. However, studies using the Hepatic Reductase Null (HRN) mouse model, in which cytochrome P450 oxidoreductase (POR), the electron donor to CYP enzymes, is deleted specifically in hepatocytes, have shown that loss of hepatic POR-mediated CYP function leads to greater BaP-DNA adduct formation in livers of these mice than in wild-type (WT) mice. Here, we used CRISPR/Cas9 technology to knockout (KO) POR expression in mouse hepatoma Hepa1c1c7 cells to create an in vitro model that can mimic the HRN mouse model. Western blotting confirmed the deletion of POR in POR KO Hepa1c1c7 cells whereas expression of other components of the mixed-function oxidase system including cytochrome b5 (Cyb5) and NADH:cytochrome b5 reductase (which can also serve as electron donors to CYP enzymes), and CYP1A1 was similar in BaP-exposed WT and POR KO Hepa1c1c7 cells. BaP exposure caused cytotoxicity in WT Hepa1c1c7 cells but not in POR KO Hepa1c1c7 cells. In contrast, CYP-catalysed BaP-DNA adduct levels were ~10-fold higher in POR KO Hepa1c1c7 cells than in WT Hepa1c1c7 cells, in concordance with the presence of higher levels of BaP metabolite (e.g. BaP-7,8-dihydrodiol) in the medium of cultured BaP-exposed POR KO Hepa1c1c7 cells. As was seen in the HRN mouse model, these results suggest that Cyb5 contributes to the bioactivation of BaP in POR KO Hepa1c1c7 cells. These results indicate that CYP enzymes may play a more important role in the detoxication of BaP, as opposed to its bioactivation.

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Metabolic activation of 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine and DNA adduct formation depends on p53: Studies inTrp53(+/+),Trp53(+/−) andTrp53(−/−) mice

International Journal of Cancer ◽

10.1002/ijc.29836 ◽

2015 ◽

Vol 138 (4) ◽

pp. 976-982 ◽

Cited By ~ 11

Author(s):

Annette M. Krais ◽

Ewoud N. Speksnijder ◽

Joost P.M. Melis ◽

Rajinder Singh ◽

Anna Caldwell ◽

...

Keyword(s):

Metabolic Activation ◽

Adduct Formation ◽

Dna Adduct

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Constructing Xenobiotic Maps of Metabolism to Predict the Role of Enzymes in DNA Adduct Formation

10.21203/rs.3.rs-157802/v1 ◽

2021 ◽

Author(s):

Maël Conan ◽

Nathalie Théret ◽

Sophie Langouet ◽

Anne Siegel

Keyword(s):

Dna Adducts ◽

Environmental Contaminants ◽

Food Additives ◽

Metabolic Activation ◽

Adduct Formation ◽

Dna Adduct ◽

Heterocyclic Aromatic Amines ◽

Reaction Prediction ◽

Prediction Tools

Abstract Background : The liver plays a major role in the metabolic activation of xenobiotics (drugs, chemicals such as pollutants, pesticides, food additives...). Among environmental contaminants of concern, heterocyclic aromatic amines (HAA) are xenobiotics classified as possible or probable carcinogens (2A or 2B) by IARC for which low information exist in humans. While HAA is a family of more than thirty identified chemicals, the metabolism activation and DNA adduct formation have been fully characterized in human liver for few of them (MeIQx, PhIP, AalphaC). Results: We developed a modeling approach in order to predict all the possible metabolite derivatives of a xenobiotic. Our approach relies on the construction of an enriched and annotated map of derivative metabolites from an input metabolite. The pipeline assembles reaction prediction tools (SyGMa), sites of metabolism prediction tools (Way2Drug, SOMP and Fame 3), a tool to estimate the ability of a xenobotics to form DNA adducts (XenoSite Reactivity V1), and a filtering procedure based on Bayesian framework. This prediction pipeline was evaluated using caffeine and then applied to HAAs. The method was applied to determine enzyme profiles associated with the maximization of DNA adducts formation derived from each HAA. These profiles could be very different depending on the chemicals allowing to classify HAAs which have been grouped by their associated profiles. Conclusions: Overall, such a predictive toxicological model based on a in silico systems biology approach open perspectives to estimate genotoxicity of various chemical classes of environmental contaminants. Moreover, our approach based on enzymes profile determination open the perspective to predict various xenobiotics derived metabolites susceptible to bind DNA adducts in both normal and physiopathological situations.

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The impact of p53 function on the metabolic activation of the carcinogenic air pollutant 3-nitrobenzanthrone and its metabolites 3-aminobenzanthrone and N-hydroxy-3-aminobenzanthrone in human cells

Mutagenesis ◽

10.1093/mutage/gey025 ◽

2018 ◽

Vol 33 (4) ◽

pp. 311-321 ◽

Cited By ~ 4

Author(s):

Laura E Wohak ◽

Ann-Christin Baranski ◽

Annette M Krais ◽

Heinz H Schmeiser ◽

David H Phillips ◽

...

Keyword(s):

P53 Protein ◽

Mutant Cell ◽

Metabolic Activation ◽

Adduct Formation ◽

Human Cells ◽

Air Pollutant ◽

Dna Adduct ◽

Tumour Suppressor ◽

Environmental Carcinogen ◽

The Impact

Abstract The tumour suppressor p53, encoded by TP53, is a key player in a wide network of signalling pathways. We investigated its role in the bioactivation of the environmental carcinogen 3-nitrobenzanthrone (3-NBA)found in diesel exhaust and its metabolites 3-aminobenzanthrone (3-ABA) and N-hydroxy-3-aminobenzanthrone (N-OH-3-ABA) in a panel of isogenic human colorectal HCT116 cells differing only with respect to their TP53 status [i.e. TP53(+/+), TP53(+/−), TP53(−/−), TP53(R248W/+) or TP53(R248W/−)]. As a measure of metabolic competence, DNA adduct formation was determined using 32P-postlabelling. Wild-type (WT) p53 did not affect the bioactivation of 3-NBA; no difference in DNA adduct formation was observed in TP53(+/+), TP53(+/−) and TP53(−/−) cells. Bioactivation of both metabolites 3-ABA and N-OH-3-ABA on the other hand was WT-TP53 dependent. Lower 3-ABA- and N-OH-3-ABA-DNA adduct levels were found in TP53(+/−) and TP53(−/−) cells compared to TP53(+/+) cells, and p53’s impact was attributed to differences in cytochrome P450 (CYP) 1A1 expression for 3-ABA whereas for N-OH-3-ABA, an impact of this tumour suppressor on sulphotransferase (SULT) 1A1/3 expression was detected. Mutant R248W-p53 protein function was similar to or exceeded the ability of WT-p53 in activating 3-NBA and its metabolites, measured as DNA adducts. However, identification of the xenobiotic-metabolising enzyme(s) (XMEs), through which mutant-p53 regulates these responses, proved difficult to decipher. For example, although both mutant cell lines exhibited higher CYP1A1 induction after 3-NBA treatment compared to TP53(+/+) cells, 3-NBA-derived DNA adduct levels were only higher in TP53(R248W/−) cells but not in TP53(R248W/+) cells. Our results show that p53’s influence on carcinogen activation depends on the agent studied and thereby on the XMEs that mediate the bioactivation of that particular compound. The phenomenon of p53 regulating CYP1A1 expression in human cells is consistent with other recent findings; however, this is the first study highlighting the impact of p53 on sulphotransferase-mediated (i.e. SULT1A1) carcinogen metabolism in human cells.

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