Higher DNA Adduct Levels Research Articles

Investigating the discriminatory potential of urinary DNA adductomics in smokeless tobacco-treated rats and head-neck cancer patients

The genotoxicity of smokeless tobacco (ST) remains an essential public health issue. We conducted a comprehensive study of rats exposed to ST and head and neck cancer patients to elucidate the DNA adduct profiles. ST exposure assessment used alkaloids and tobacco-specific nitrosamines in rat urine. High ST doses led to significantly elevated nicotine, cotinine, N-nitrosonornicotine (NNN), and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) levels, indicating substantial exposure. DNA adductomics identified 17 significant DNA adducts using a neutral loss scan in liquid chromatography-mass spectrometry in rat urine samples upon ST exposure, highlighting the intricate landscape of DNA modifications associated with ST using univariate and multivariate statistical analyses. LC-ESI-QTOF-MS/MS analysis and accurate mass measurements of DNA adducts unveiled specific adducts upregulated in response to ST exposure, particularly those associated with methylation and NNK release. Intriguing correlations emerged between DNA adducts and alkaloids-TSNA in ST-exposed rat urine. Nicotine correlated positively with N2-paraldol-dG and O2/O4-[4-(3-Pyridyl)-4-oxobut-1-yl] thymidine in high-dose rats. NNK correlated with 6O-methylgaunine, while NNN correlated with 6-hydroxy-1-N2-propanodeoxyguanosine and 7-methylguanine. With this aim, we also applied analysis to human samples, where we observed specific DNA adducts for ST users, controls, and subjects with HNC. Two-way ANOVA showed that ST users and cancer patients had higher DNA adduct levels in human urine, which aids cancer risk assessment, early detection, and environmental exposure evaluation. This comprehensive study explores DNA adducts caused by ST exposure across rats and head and neck cancer patients, illuminating genotoxic mechanisms and health risks and providing valuable insights for future preventive and therapeutic strategies.

Abstract C030: Relationship between the oral microbiome and tobacco-induced DNA damage in African American and White persons who smoke

Abstract Exposure to tobacco smoke chemicals and toxicants may cause unique changes to an individual’s oral microbiome, impacting immuno-inflammatory responses, the metabolism of tobacco smoke carcinogens, and overall health status. In our previous study, HPB-releasing DNA adducts (DNA damage derived from tobacco-specific nitrosamines) were higher in oral cells of African American (AA, n=75) when compared to White (WH, n=71) persons who smoke, even after adjusting for key confounders such as smoking dose. In this study, we examined the relationship between the levels of HPB-releasing DNA adducts and microbiome composition in these individuals. 16S rRNA gene sequencing, targeting the V4 hypervariable region, was performed on DNA isolated from mouthwash samples. Sequences were clustered into Amplicon Sequence Variants (ASV) using QIIME, and metagenomic content was inferred using PICRUSt. Our results showed a significant difference in alpha-diversity metrics: observed richness and Shannon indexes (Kruskal-Wallis test, H = 8.42, p <0.01 and H = 6.85, p <0.03, respectively) across levels of DNA damage (low, intermediate, and high). Post hoc tests with pairwise comparisons showed that, for both indexes, individuals with high levels of HPB-releasing DNA adducts had significantly lower alpha diversity than those with intermediate levels (p <0.05). However, there were no differences in beta diversity as measured by Bray-Curtis (R2 = 1.15, p = 0.2) and Jaccard (R2 = 1.1, p = 0.1) indices across individuals with different levels of HPB-releasing DNA adducts. Multivariable association tests revealed that high levels of the DNA adducts were positively associated with Enterobacteriaceae, while intermediate levels were associated with Porphyromonas endodontalis, Prevotella spp, Neisseria spp, Actinomyces spp, and Fusobacterium. In addition, predicted functional profiling showed that intermediate levels of HPB-releasing DNA adducts were positively associated with amino acid, carbohydrate, and hem biosynthesis, along with reductive tricarboxylic acid cycle and formaldehyde degradation pathways. Comparisons between AA and WH persons who smoke showed that AA had significantly higher alpha diversity as assessed by observed bacterial richness and The Shannon index (Wilcoxon rank-sum tests, q-value=0.03 and 0.004, respectively). Differences between AA and WH were also found for beta diversity (Bray-Curtis: R2=2.4, p=0.01, Jaccard: R2=1.9, p=0.01, weighted Unifrac R2=0.02 p=0.007). The abundance of taxa associated with intermediate levels of DNA damage (Prevotella spp, Neisseria spp, Actinomyces spp, Fusobacterium) was also higher in AA persons who smoke. Together, our findings suggest that certain compositional and functional characteristics of the oral microbiome may serve as indicators of macromolecular responses to harmful chemical exposures from tobacco. The potential mechanistic contribution of the oral microbiome to such responses and its potential role in the observed racial/ethnic differences in cancer risk due to smoking should be further investigated. Citation Format: Aleksandra Alcheva. Relationship between the oral microbiome and tobacco-induced DNA damage in African American and White persons who smoke [abstract]. In: Proceedings of the 15th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2022 Sep 16-19; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2022;31(1 Suppl):Abstract nr C030.

Metabolic Activation of Benzo[a]pyrene by Human Tissue Organoid Cultures.

Organoids are 3D cultures that to some extent reproduce the structure, composition and function of the mammalian tissues from which they derive, thereby creating in vitro systems with more in vivo-like characteristics than 2D monocultures. Here, the ability of human organoids derived from normal gastric, pancreas, liver, colon and kidney tissues to metabolise the environmental carcinogen benzo[a]pyrene (BaP) was investigated. While organoids from the different tissues showed varied cytotoxic responses to BaP, with gastric and colon organoids being the most susceptible, the xenobiotic-metabolising enzyme (XME) genes, CYP1A1 and NQO1, were highly upregulated in all organoid types, with kidney organoids having the highest levels. Furthermore, the presence of two key metabolites, BaP-t-7,8-dihydrodiol and BaP-tetrol-l-1, was detected in all organoid types, confirming their ability to metabolise BaP. BaP bioactivation was confirmed both by the activation of the DNA damage response pathway (induction of p-p53, pCHK2, p21 and γ-H2AX) and by DNA adduct formation. Overall, pancreatic and undifferentiated liver organoids formed the highest levels of DNA adducts. Colon organoids had the lowest responses in DNA adduct and metabolite formation, as well as XME expression. Additionally, high-throughput RT-qPCR explored differences in gene expression between organoid types after BaP treatment. The results demonstrate the potential usefulness of organoids for studying environmental carcinogenesis and genetic toxicology.

DNA damage and health effects in juvenile haddock (Melanogrammus aeglefinus) exposed to PAHs associated with oil-polluted sediment or produced water.

The research objective was to study the presence of DNA damages in haddock exposed to petrogenic or pyrogenic polyaromatic hydrocarbons (PAHs) from different sources: 1) extracts of oil produced water (PW), dominated by 2-ring PAHs; 2) distillation fractions of crude oil (representing oil-based drilling mud), dominated by 3-ring PAHs; 3) heavy pyrogenic PAHs, mixture of 4/5/6-ring PAHs. The biological effect of the different PAH sources was studied by feeding juvenile haddock with low doses of PAHs (0.3–0.7 mg PAH/kg fish/day) for two months, followed by a two-months recovery. In addition to the oral exposure, a group of fish was exposed to 12 single compounds of PAHs (4/5/6-ring) via intraperitoneal injection. The main endpoint was the analysis of hepatic and intestinal DNA adducts. In addition, PAH burden in liver, bile metabolites, gene and protein expression of CYP1A, GST activity, lipid peroxidation, skeletal deformities and histopathology of livers were evaluated. Juvenile haddock responded quickly to both intraperitoneal injection and oral exposure of 4/5/6-ring PAHs. High levels of DNA adducts were detected in livers three days after the dose of the single compound exposure. Fish had also high levels of DNA adducts in liver after being fed with extracts dominated by 2-ring PAHs (a PW exposure scenario) and 3-ring PAHs (simulating an oil exposure scenario). Elevated levels of DNA adducts were observed in the liver of all exposed groups after the 2 months of recovery. High levels of DNA adduct were found also in the intestines of individuals exposed to oil or heavy PAHs, but not in the PW or control groups. This suggests that the intestinal barrier is very important for detoxification of orally exposures of PAHs.

Discovery of a Chiral DNA‐Targeted Platinum–Acridine Agent with Potent Enantioselective Anticancer Activity

AbstractA structure–activity relationship study was performed for a set of rigidified platinum–acridine anticancer agents containing linkers derived from chiral pyrrolidine and piperidine scaffolds. Screening a library of microscale reactions and selected resynthesized compounds in non‐small‐cell lung cancer (NSCLC) cells showed that cytotoxicities varied by more than three orders of magnitude. A potent hit compound was discovered containing a (R)‐N‐(piperidin‐3‐yl) linker (P2‐6R), which killed NCI‐H460 and A549 lung cancer cells 100 times more effectively than the S enantiomer (P2‐6S). P2‐6R accumulated in A549 cells significantly faster and produced 50‐fold higher DNA adduct levels than P2‐6S. Ligand similarity analysis suggests that only module 6R may be compatible with strainless monofunctional intercalative binding. NCI‐60 screening and COMPARE analysis highlights the spectrum of activity and potential utility of P2‐6R for treating NSCLC and other solid tumors.

Formaldehyde-activated WEHI-150 induces DNA interstrand crosslinks with unique structural features

Mitoxantrone is an anticancer anthracenedione that can be activated by formaldehyde to generate covalent drug-DNA adducts. Despite their covalent nature, these DNA lesions are relatively labile. It was recently established that analogues of mitoxantrone featuring extended side-chains terminating in primary amino groups typically yielded high levels of stable DNA adducts following their activation by formaldehyde. In this study we describe the DNA sequence-specific binding properties of the mitoxantrone analogue WEHI-150 which is the first anthracenedione to form apparent DNA crosslinks mediated by formaldehyde. The utility of this compound lies in the versatility of the covalent binding modes displayed. Unlike other anthracenediones described to date, WEHI-150 can mediate covalent adducts that are independent of interactions with the N-2 of guanine and is capable of adduct formation at novel DNA sequences. Moreover, these covalent adducts incorporate more than one formaldehyde-mediated bond with DNA, thus facilitating the formation of highly lethal DNA crosslinks. The versatility of binding observed is anticipated to allow the next generation of anthracenediones to interact with a broader spectrum of nucleic acid species than previously demonstrated by the parent compounds, thus allowing for more diverse biological activities.

Impact of p53 function on the sulfotransferase-mediated bioactivation of the alkylated polycyclic aromatic hydrocarbon 1-hydroxymethylpyrene in vitro.

The tumor suppressor p53, encoded by TP53, is known as the "guardian of the genome." Sulfotransferases (SULTs) are involved in the metabolism of alkylated polycyclic aromatic hydrocarbons such as 1-hydroxymethylpyrene (1-HMP), which is a known substrate for SULT1A1. To investigate the impact of TP53 on the metabolic activation of 1-HMP, a panel of isogenic human colorectal HCT116 cells having TP53(+/+), TP53(+/-), or TP53(-/-) were treated with 10 μM 1-HMP for 24 hr. 1-HMP-DNA adduct formation was determined by ultraperformance liquid chromatography-tandem mass spectrometry analysis, which quantified two nucleoside adducts N2 -(1-methylpyrenyl)-2'-deoxyguanosine and N6 -(1-methylpyrenyl)-2'-deoxyadenosine. 1-HMP treatment resulted in significantly (~40-fold) higher DNA adduct levels in TP53(+/+) cells than in the other cell lines. Higher levels of 1-HMP-induced DNA adducts in TP53(+/+) cells correlated with higher basal expression of SULT1A1/3 in this cell line, but 1-HMP treatment showed no effect on the expression of this protein. These results indicate that the cellular TP53 status is linked to the SULT1A1/3-mediated bioactivation of 1-HMP, thereby broadening the spectrum of p53's targets. Environ. Mol. Mutagen., 60:752-758, 2019. © 2019 Wiley Periodicals, Inc.

Bulky DNA adducts, microRNA profiles, and lipid biomarkers in Norwegian tunnel finishing workers occupationally exposed to diesel exhaust

ObjectivesThis study aimed to assess the biological impact of occupational exposure to diesel exhaust (DE) including DE particles (DEP) from heavy-duty diesel-powered equipment in Norwegian tunnel finishing workers (TFW).MethodsTFW (n=69)...

Unravelling essential key events in mitochondrial adverse outcome pathways

3-Nitrobenzanthrone (3-NBA), a potential human carcinogen, is present in diesel exhaust. The main metabolite of 3-NBA, 3-aminobenzanthrone, was detected in urine of miners occupationally exposed to diesel emissions. Environmental and occupational factors play an important role in development of bladder cancer (BC), one of the most frequent malignancies. It is expected that exposure of urothelium to 3-NBA and its metabolites may induce BC initiation and/or progression. To test this hypothesis, we studied geno- and cytotoxicity of 3-NBA using an in vitro BC model. 3-NBA induced higher levels of DNA adducts, reactive oxygen species and DNA breaks in aggressive T24 cells than in more differentiated RT4 cells. To understand the nature of this difference we examined the role of several enzymes that were identified as 3-NBA bio activators. However, the difference in DNA adduct formation cannot be directly linked to the different activity of any of the examined enzymes. Conversely, the difference of tested cell lines in p53 status can partly explain the distinct levels of 3-NBA-DNA adducts and DNA damage induced by 3-NBA. Therefore, we assume that more aggressive T24 cells are more predisposed for DNA adduct formation, DNA damage and, possibly, mutations and as a result further tumorigenesis.

Chronic Ethanol Consumption and Generation of Etheno-DNA Adducts in Cancer-Prone Tissues.

Chronic ethanol consumption is a risk factor for several human cancers. A variety of mechanisms may contribute to this carcinogenic effect of alcohol including oxidative stress with the generation of reactive oxygen species (ROS), formed via inflammatory pathways or as byproducts of ethanol oxidation through cytochrome P4502E1 (CYP2E1). ROS may lead to lipidperoxidation (LPO) resulting in LPO-products such as 4-hydoxynonenal (4-HNE) or malondialdehyde. These compounds can react with DNA bases forming mutagenic and carcinogenic etheno-DNA adducts. Etheno-DNA adducts are generated in the liver (HepG2) cells over-expressing CYP2E1 when incubated with ethanol;and are inhibited by chlormethiazole. In liver biopsies etheno-DNA adducts correlated significantly with CYP2E1. Such a correlation was also found in the esophageal- and colorectal mucosa of alcoholics. Etheno-DNA adducts also increased in liver biopsies from patients with non alcoholic steatohepatitis (NASH). In various animal models with fatty liver either induced by high fat diets or genetically modified such as in the obese Zucker rat, CYP2E1 is induced and paralleled by high levels of etheno DNA-adducts which may be modified by additional alcohol administration. As elevation of adduct levels in NASH children were already detected at a young age, these lesions may contribute to hepatocellular cancer development later in life. Together these data strongly implicate CYP2E1 as an important mediator for etheno-DNA adduct formation, and this detrimental DNA damage may act as a driving force for malignant disease progression.

Effect of Benzo[a]Pyrene on Spindle Misorientation and Fidelity of Chromosome Segregation in Lung Epithelial BEAS-2B Cells.

Benzo[a]pyrene (B[a]P) is an environmental carcinogen found in tobacco smoke. It leads to high levels of DNA adducts in the lungs of cigarette smokers contributing to genomic instability. Alterations in the mitotic spindle apparatus play a major role in the generation of genomic instability through promoting chromosome mis-segregation and aneuploidy. To date, the effect of B[a]P exposure on altering the mitotic apparatus in normal lung epithelial cells remains unknown. In our study, BEAS-2B human bronchial epithelial cells were exposed to B[a]P and spindle dynamics were evaluated. Confocal imaging showed that B[a]P exposure significantly alters spindles misorientation, leading to chromosome mis-segregations in the form of chromosome lags and bridges. In addition, centrosome duplication and premature centriole disengagement were induced leading to misaligned and multipolar spindle formation. Comparative genomic analysis of mitotic spindle associated genes, revealed downregulation of AurA-Plk1-AurB signaling cascade by B[a]P. In addition, we analyzed the status of p53 and its downstream p21 in B[a]P-treated cells and showed a suppression of p53-p21 axis. When the extent of DNA damage associated with induced mitotic abnormalities was investigated using γ-H2AX, a significant increase and persistence in DNA damage was observed. Overall, our findings show that B[a]P potently induces mitotic abnormalities, DNA damage, and genetic instability.

Exposure to meat-derived carcinogens and bulky DNA adduct levels in normal-appearing colon mucosa

IntroductionMeat consumption is a risk factor for colorectal cancer. This research investigated the relationship between meat-derived carcinogen exposure and bulky DNA adduct levels, a biomarker of DNA damage, in colon mucosa. MethodsLeast squares regression was used to examine the relationship between meat-derived carcinogen exposure (PhIP and meat mutagenicity) and bulky DNA adduct levels in normal-appearing colon tissue measured using 32P-postlabelling among 202 patients undergoing a screening colonoscopy. Gene-diet interactions between carcinogen exposure and genetic factors relevant to biotransformation and DNA repair were also examined. Genotyping was conducting using the MassARRAY® iPLEX® Gold SNP Genotyping assay. ResultsPhIP and higher meat mutagenicity exposures were not associated with levels of bulky DNA adducts in colon mucosa. The XPC polymorphism (rs2228001) was found to associate with bulky DNA adduct levels, whereby genotypes conferring lower DNA repair activity were associated with higher DNA adduct levels than the normal activity genotype. Among individuals with genotypes associated with lower DNA repair (XPD, rs13181 and rs1799179) or detoxification activity (GSTP1, rs1695), higher PhIP or meat mutagenicity exposures were associated with higher DNA adduct levels. Significant interactions between the XPC polymorphism (rs2228000) and both dietary PhIP and meat mutagenicity on DNA adduct levels was observed, but associations were inconsistent with the a priori hypothesized direction of effect. ConclusionExposure to meat-derived carcinogens may be associated with increased DNA damage occurring directly in the colon among genetically susceptible individuals.

Human T lymphocytes bioactivate heterocyclic aromatic amines by forming DNA adducts.

Heterocyclic aromatic amines (HAA) are formed in cooked meat, poultry and fish but also arise in tobacco smoke and exhaust gases. HAA are potential human carcinogens, which require metabolic activation to exert their genotoxicity. Human tissues can bioactivate HAA to produce reactive intermediates that bind to DNA. HAA DNA adduct formation occurs in human hepatocytes; however, the potential of HAA to form DNA adducts has not been investigated in human T lymphocytes. In this study, we investigated the ability of human T lymphocytes activated with PMA/Ionomycin or CD3/CD28 to express functional CYP1 activity and bioactivate three major HAA: 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), and 2-amino-9H-pyrido[2,3-b]indole (AαC) to form DNA adducts. Adducts were measured by ultraperformance liquid chromatography-electrospray ionization/multistage scan mass spectrometry. The highest level of DNA adducts occurred for AαC (16 adducts per 109 nucleotides), followed by PhIP (9 adducts per 109 nucleotides). In contrast, DNA adducts formed from MeIQx and the structurally related aromatic amine 4-aminobiphenyl, a known human carcinogen, were below the limit of detection (< 3 adducts per 109 nucleotides). Moreover, we demonstrate that AαC is a potent inducer of CYP1A1 and CYP1B1 activity through a transcriptional mechanism involving the AhR pathway. Overall, our results highlight the capacity of activated human T lymphocytes to more efficiently bioactivate AαC to form DNA adducts than other prominent HAA or 4-ABP. Environ. Mol. Mutagen. 57:656-667, 2016. © 2016 Wiley Periodicals, Inc.

Genotoxic and cytotoxic effects of the environmental pollutant 3-nitrobenzanthrone on bladder cancer cells

3-Nitrobenzanthrone (3-NBA), a potential human carcinogen, is present in diesel exhaust. The main metabolite of 3-NBA, 3-aminobenzanthrone, was detected in urine of miners occupationally exposed to diesel emissions. Environmental and occupational factors play an important role in development of bladder cancer (BC), one of the most frequent malignancies. It is expected that exposure of urothelium to 3-NBA and its metabolites may induce BC initiation and/or progression. To test this hypothesis, we studied geno- and cytotoxicity of 3-NBA using an in vitro BC model. 3-NBA induced higher levels of DNA adducts, reactive oxygen species and DNA breaks in aggressive T24 cells than in more differentiated RT4 cells. To understand the nature of this difference we examined the role of several enzymes that were identified as 3-NBA bio activators. However, the difference in DNA adduct formation cannot be directly linked to the different activity of any of the examined enzymes. Conversely, the difference of tested cell lines in p53 status can partly explain the distinct levels of 3-NBA-DNA adducts and DNA damage induced by 3-NBA. Therefore, we assume that more aggressive T24 cells are more predisposed for DNA adduct formation, DNA damage and, possibly, mutations and as a result further tumorigenesis.

Toxic Effects of the Major Components of Diesel Exhaust in Human Alveolar Basal Epithelial Cells (A549).

We investigated the toxicity of benzo[a]pyrene (B[a]P), 1-nitropyrene (1-NP) and 3-nitrobenzanthrone (3-NBA) in A549 cells. Cells were treated for 4 h and 24 h with: B[a]P (0.1 and 1 μM), 1-NP (1 and 10 μM) and 3-NBA (0.5 and 5 μM). Bulky DNA adducts, lipid peroxidation, DNA and protein oxidation and mRNA expression of CYP1A1, CYP1B1, NQO1, POR, AKR1C2 and COX2 were analyzed. Bulky DNA adducts were induced after both treatment periods; the effect of 1-NP was weak. 3-NBA induced high levels of bulky DNA adducts even after 4-h treatment, suggesting rapid metabolic activation. Oxidative DNA damage was not affected. 1-NP caused protein oxidation and weak induction of lipid peroxidation after 4-h incubation. 3-NBA induced lipid peroxidation after 24-h treatment. Unlike B[a]P, induction of the aryl hydrocarbon receptor, measured as mRNA expression levels of CYP1A1 and CYP1B1, was low after treatment with polycyclic aromatic hydrocarbon (PAH) nitro-derivatives. All test compounds induced mRNA expression of NQO1, POR, and AKR1C2 after 24-h treatment. AKR1C2 expression indicates involvement of processes associated with reactive oxygen species generation. This was supported further by COX2 expression induced by 24-h treatment with 1-NP. In summary, 3-NBA was the most potent genotoxicant, whereas 1-NP exhibited the strongest oxidative properties.

Beyond monotherapy: Integrating immunotherapy into current treatment regimens

While we have shown that these urinary metabolites are risk biomarkers for lung cancer in these studies, they are not fully predictive. This is because these biomarkers are mainly measuring exposure but do not take into account the critical metabolic activation step leading to the formation of DNA adducts which cause the multiple mutations observed in lung cancer. Quantitation of DNA adducts is challenging because of their low levels, typically less than 1 adduct per 10 normal bases, and the small amounts of DNA available for studies in living humans. To address this question, we are developing high resolution mass spectrometric methods for quantifying oral cell DNA adducts as a surrogate for DNA adduct formation in the lung. In one recent study, we found remarkably high levels of DNA adducts of tobaccospecific compounds in in the oral mucosa cells of smokers compared to non-smokers. We are also able to quantify formaldehyde-DNA adducts in oral mucosa cells. As mass spectrometric methods for analysis of carcinogen-DNA adducts become increasingly more sensitive and specific, it appears likely that quantitation of a panel of tobacco carcinogen DNA adducts in smokers, leading to identification of susceptible individuals, may be feasible.

Dose-dependent DNA adduct formation by cinnamaldehyde and other food-borne α,β-unsaturated aldehydes predicted by physiologically based in silico modelling

Genotoxicity of α,β-unsaturated aldehydes shown in vitro raises a concern for the use of the aldehydes as food flavourings, while at low dose exposures the formation of DNA adducts may be prevented by detoxification. Unlike many α,β-unsaturated aldehydes for which in vivo data are absent, cinnamaldehyde was shown to be not genotoxic or carcinogenic in vivo. The present study aimed at comparing dose-dependent DNA adduct formation by cinnamaldehyde and 18 acyclic food-borne α,β-unsaturated aldehydes using physiologically based kinetic/dynamic (PBK/D) modelling. In rats, cinnamaldehyde was predicted to induce higher DNA adducts levels than 6 out of the 18 α,β-unsaturated aldehydes, indicating that these 6 aldehydes may also test negative in vivo. At the highest cinnamaldehyde dose that tested negative in vivo, cinnamaldehyde was predicted to form at least three orders of magnitude higher levels of DNA adducts than the 18 aldehydes at their respective estimated daily intake. These results suggest that for all the 18 α,β-unsaturated aldehydes DNA adduct formation at doses relevant for human dietary exposure may not raise a concern. The present study illustrates a possible use of physiologically based in silico modelling to facilitate a science-based comparison and read-across on the possible risks posed by DNA reactive agents.

Abstract 2721: Induction of aberrant crypt foci in the colon of mice exposed to tobacco carcinogen 2-amino-9H-pyrido[2,3-b]indole

Abstract Epidemiological studies indicate that tobacco smoking is a risk factor for colon cancer. However, the etiological agents in tobacco smoke remain uncertain. Heterocyclic aromatic amines (HAAs) that are produced during high-temperature cooking of the proteinaceous food are associated with the elevated risk of colon cancer. Tobacco smoking also produces HAAs, the most abundant one being 2-amino-9H-pyrido[2,3-b]indole (AαC). The carcinogenic potency of AαC is unknown in humans, but AαC forms DNA adducts in multiple organs, including liver and colon, as well as being carcinogenic in rodents. In this study, AαC-induced colon cancer risk was assessed by determining DNA adducts and putative colonic precancerous lesions, aberrant crypt foci (ACF) and dysplastic ACF. For comparison, the HAA, 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), a liver and colon carcinogen in mice, and azoxymethane (AOM), a potent colon carcinogen in rodents, were also administered. AαC (400 ppm) or MeIQ (300 ppm) were fed in a high-fat diet to A/J mice (n = 12 per group) for 4 weeks. AOM was injected intraperitoneally to another 12 mice at 5 mg/kg body weight weekly for 6 weeks. At the end of carcinogen treatment, liver and colon were harvested from 4 mice from each group for DNA adduct measurement. dG-C8-AαC, dG-C8-MeIQ, and O6-methyl-dG DNA adducts were measured by liquid chromatography/mass spectrometry. The remaining 8 mice from each group were then fed a carcinogen-free diet for additional 8 weeks, and then colons harvested. Colonic total and dysplastic ACF were counted by light microscopy after appropriate staining. AαC feeding induced the greatest number of DNA adducts in liver, followed by AOM and MeIQ. AOM administration and AαC feeding induced similar numbers of DNA adducts in the colon, both of which were significantly greater than MeIQ. However, AOM administration induced a significantly greater number of total and dysplastic ACF in the colons than did feeding either AαC or MeIQ, which had similar numbers of ACF and dysplastic ACF. The high levels of AαC DNA adducts and induced dysplastic ACF in this animal model, provide biological plausibility for a causal role for AαC in tobacco-induced colorectal carcinogenesis. However, DNA adduct numbers induced by these three carcinogens was not proportional to the colonic ACF or dysplastic ACF number, suggesting that different types of DNA adducts differ in their ability to promote colonic precancerous lesions. Citation Format: Sangyub Kim, Jingshu Guo, Sabrina P. Trudo, Daniel D. Gallaher, Robert J. Turesky. Induction of aberrant crypt foci in the colon of mice exposed to tobacco carcinogen 2-amino-9H-pyrido[2,3-b]indole. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2721. doi:10.1158/1538-7445.AM2015-2721

Potential Application of Benzo(a)Pyrene-Associated Adducts (Globin or Lipid) as Blood Biomarkers for Target Organ Exposure and Human Risk Assessment

In order to investigate the potential application of blood biomarkers as surrogate indicators of carcinogen–adduct formation in target-specific tissues, temporal formation of benzo[a]pyrene (BaP)-associated DNA adducts, protein adducts, or lipid damage in target tissues such as lung, liver, and kidney was compared with globin adduct formation or plasma lipid damage in blood after continuous intraperitoneal (ip) injection of [3H]BaP into female ICR mice for 7 d. Following treatment with [3H]BaP, formation of [3H]BaP–DNA or –protein adducts in lung, liver, and kidney increased linearly, and persisted thereafter. This finding was similar to the observed effects on globin adduct formation and plasma lipid damage in blood. The lungs contained a higher level of DNA adducts than liver or kidneys during the treatment period. Further, the rate of cumulative adduct formation in lung was markedly greater than that in liver. Treatment with a single dose of [3H]BaP indicated that BaP–globin adduct formation and BaP–lipid damage in blood reached a peak 48 h after treatment. Overall, globin adduct formation and lipid damage in blood were significantly correlated with DNA adduct formation in the target tissues. These data suggest that peripheral blood biomarkers, such as BaP–globin adduct formation or BaP–lipid damage, may be useful for prediction of target tissue-specific DNA adduct formation, and for risk assessment after exposure.

Influence of genetic polymorphisms on biomarkers of exposure and effects in children living in Upper Silesia

This article is a follow-up to our previous molecular epidemiology studies on the DNA damage in children from the Upper Silesia region of Poland. It is expected that metabolic and DNA repair gene polymorphisms may modulate individual susceptibility to environmental exposure. In this study, we investigate the association between polymorphisms of metabolising (CYP2D, EPHX1, GSTM1, GSTP1, GSTT1, NAT2) and DNA repair (XPD, XRCC1, XRCC3) genes and selected biomarkers of exposure and effect such as levels of 1-hydroxypyrene (1-OHP) and urinary mutagenicity, aromatic DNA adducts, sister chromatid exchange (SCE) and micronuclei (MN) in 74 children. Both 1-OHP concentration and urinary mutagenicity tested by TA98+S9 were significantly higher in individuals with EPHX1 (exon 4) Arg/Arg genotype than in individuals with other genotype. The EPHX1 (exon 3) significantly affected urinary mutagenicity tested with strain YG1024+S9. The urinary mutagenicity in individuals with Tyr/Tyr homozygotes was lower than in individuals with Tyr/His and His/His (1057±685 vs. 1432±1003 revertants/mol creatinine). XRCC3 Met/Met genotype was associated with significantly higher levels of 1-OHP in urine compared with only The/Met genotype. The PAH-DNA adduct levels in the subgroup with GSTM1 null genotype was 2-fold higher than in individuals with GSTM1 active (7.06±5.12 vs. 13.14±9.81 adduct/10(8) nucleotides). The mean level of aromatic DNA adducts in children with deletion of the GSTT1 gene was significantly higher compared with individuals with that gene present (8.03±6.23 vs. 14.66±10.70 adduct/10(8) nucleotides). Also the carriers of the XPD Lys/Lys genotype showed higher levels of DNA adducts than heterozygotes (13.16±9.70 vs. 6.81±5.86 adducts/10(8) nucleotides). Children carrying the XRCC3-241 Met/Met genotype exhibited a higher number of SCE in peripheral blood lymphocytes than carriers of Thr/Met allele (8.15±0.86 vs. 7.62±0.79 SCE/cell). It was also observed that children with the GSTP1 slow conjugator had significantly elevated MN in peripheral blood lymphocytes compared with fast conjugator (4.23±3.49 vs. 6.56±5.00 MN/1000 cells).