Comparative DNA adduct formation and induction of colonic aberrant crypt foci in mice exposed to 2-amino-9H-pyrido[2,3-b]indole, 2-amino-3,4-dimethylimidazo[4,5-f]quinoline, and azoxymethane

The Role of Xenobiotics and Anelloviruses in Colorectal Cancer: Mechanisms and Perspectives

Xenobiotics are non-natural chemical compounds to which the human population is exposed. Chronic exposure to certain xenobiotics is associated with various diseases, including cancer development. Anelloviruses (AVs), including Torque Teno Virus (TTV), Torque Teno Mini Virus (TTMV), and Torque Teno Midi Virus (TTMDV), are ubiquitous viruses found in the general population. As no disease has been definitively associated with AVs, they are sometimes referred to as "viruses awaiting a disease". This review explores the potential roles of xenobiotics and AVs in colorectal cancer (CRC) development and suggests a potential interplay between them. Evidence suggests an association between certain xenobiotics (like pesticides, cigarette smoke components, and dietary factors) and CRC, while such an association is less clear for AVs. The high prevalence of AVs suggests these infections alone may be insufficient to disrupt homeostasis; thus, additional factors might be required to promote disease, potentially including cancer.

DNA modifications: Biomarkers for the exposome?

The concept of the exposome is the encompassing of all the environmental exposures, both exogenous and endogenous, across the life course. Many, if not all, of these exposures can result in the generation of reactive species, and/or the modulation of cellular processes, that can lead to a breadth of modifications of DNA, the nature of which may be used to infer their origin. Because of their role in cell function, such modifications have been associated with various major human diseases, including cancer, and so their assessment is crucial. Historically, most methods have been able to only measure one or a few DNA modifications at a time, limiting the information available. With the development of DNA adductomics, which aims to determine the totality of DNA modifications, a far more comprehensive picture of the DNA adduct burden can be gained. Importantly, DNA adductomics can facilitate a "top-down" investigative approach whereby patterns of adducts may be used to trace and identify the originating exposure source. This, together with other 'omic approaches, represents a major tool for unraveling the complexities of the exposome and hence allow a better a understanding of the environmental origins of disease.

Colon Cancer Risk of a Westernized Diet Is Reduced in Mice by Feeding Cruciferous or Apiaceous Vegetables at a Lower Dose of Carcinogen but Not a Higher Dose

Western-style diets (WD) are associated with greater risk of colon cancer. Exposure to 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP), a food-borne carcinogen, is linked to increased colon cancer risk. In contrast, intake of apiaceous and cruciferous vegetables (APIs and CRUs) is associated with reduced risk. Here we evaluated effects of a WD alone or a WD containing API or CRU, relative to a purified diet (basal), on colon cancer risk in mice. All diets were fed at one of two concentrations of PhIP (100 or 400 ppm). The activity of the hepatic PhIP-activating enzyme, cytochrome P450 (CYP) 1A2, was examined at week 4 and colonic precancerous lesions (aberrant crypt foci, ACF) were enumerated at week 12. In low PhIP-fed groups, CYP1A2 activity was greater for CRU than all other groups, which did not differ from one another. WD had a significantly greater effect on the formation of ACF than the basal diet. In groups fed API or CRU, the ACF number was reduced to the level observed in the basal diet-fed group. In high PhIP-fed groups, all WD-based diets had greater CYP1A2 activity than the basal diet-fed group. Surprisingly, the basal diet group had more ACF than the WD group, and API and CRU groups did not differ from the WD alone group. Thus, at the lower dose of PhIP, the WD increased colon cancer risk in mice, compared to a purified diet, and APIs and CRUs reduced the risk of the WD. However, at the higher dose of PhIP, the enhancement of colon cancer risk by the WD was not evident, nor was the chemopreventive effect of these vegetables.

Lactobacillus acidophilus-Fermented Germinated Brown Rice Suppresses Preneoplastic Lesions of the Colon in Rats

Colorectal cancer (CRC) is a cancer associated with chronic inflammation. Whole grains and probiotics play a protective role against CRC. Fermented grains are receiving increased attention due to their anti-inflammatory and anti-cancer activities. Our previous study found that a combination of germinated brown rice (GBR) with probiotics suppressed colorectal carcinogenesis in rats. However, the cancer-preventive effect of probiotic-fermented GBR has not been reported. This study investigated the preventive effect and possible mechanism of GBR fermented by Lactobacillus acidophilus (FGBR) on colorectal carcinogenesis in rats induced by 1,2-dimethylhydrazine (DMH) and dextran sulfate sodium (DSS). DMH/DSS treatment induced preneoplastic aberrant crypt foci (ACF), elevated serum levels of tumor necrosis factor (TNF)-α, interleukin (IL)-6 and IL-1β, as well as decreased pro-apoptotic Bax expression. GBR and FGBR reduced the primary ACF number and decreased TNF-α, IL-6 and IL-1β levels. GBR and FGBR at the 2.5% level increased pro-apoptotic cleaved caspase-3 and decreased anti-apoptotic B-cell lymphoma 2 (Bcl-2) expressions. FGBR at the 2.5% level further reduced the number of sialomucin-producing ACF (SIM-ACF) and increased Bax expression. These results suggest that FGBR may inhibit preneoplastic lesions of the colon via activating the apoptotic pathway. This fermented rice product may have the potential to be developed as a novel dietary supplement for CRC chemoprevention.

Djulis (Chenopodium Formosanum) Prevents Colon Carcinogenesis via Regulating Antioxidative and Apoptotic Pathways in Rats

Djulis is a cereal crop rich in polyphenols and dietary fiber that may have nutraceutical activity to prevent colon cancer. This study was designed to examine the preventive effect of djulis on colon carcinogenesis in rats treated with 1,2-dimethylhydrazine (DMH). Rats were fed different AIN-93G-based diets: groups N and DMH were fed AIN-93G diet and groups LD, MD, and HD were fed AIN-93G diet containing 5, 10, and 20% djulis, respectively. All rats except for group N were injected with DMH to induce colon carcinogenesis. After 10 weeks, rats were sacrificed and colon and liver tissues were collected for analysis. The results showed that djulis-treated rats had significantly lower numbers of colonic preneoplastic lesions, aberrant crypt foci (ACF), sialomucin-producing (SIM)-ACF, and mucin-depleted foci. Djulis treatment increased superoxide dismutase and catalase activities in colon and liver. Djulis also reduced p53, Bcl-2, and proliferating cell nuclear antigen expressions and increased Bax and caspase-9 expressions. Besides, phenolic compounds and flavonoids were found rich in djulis. These results demonstrate the chemopreventive effect of djulis on carcinogen-induced colon carcinogenesis via regulating antioxidative and apoptotic pathways in rats. Djulis may have the potential to be developed as a valuable cereal product for chemoprevention of colon cancer.

Apiaceous and Cruciferous Vegetables Fed During the Post-Initiation Stage Reduce Colon Cancer Risk Markers in Rats

BACKGROUND

Vegetable consumption reduces colon cancer risk when fed in the initiation stage of carcinogenesis; however, the effect of vegetable consumption during the post-initiation stage has rarely been examined.

OBJECTIVE

We investigated the chemopreventive effects of feeding apiaceous and cruciferous vegetables on colon cancer risk in the post-initiation stage.

METHODS

Thirty male Wistar rats (∼5 wk, 92 g) were subcutaneously injected with 1,2-dimethylhydrazine 1 time/wk for 2 wk. One week after the last dose, rats were randomly assigned to 3 groups: the basal diet, an apiaceous vegetable-containing diet (API; 21% fresh wt/wt), or a cruciferous vegetable-containing diet (CRU; 21% fresh wt/wt). All diets contained ∼20% protein, 7% fat, and 63% digestible carbohydrate. Experimental diets were fed for 10 wk, after which colons were harvested.

RESULTS

CRU reduced aberrant crypt foci (ACF) number compared to the basal group (P = 0.014) and API (P = 0.013), whereas API decreased the proportion of dysplastic ACF relative to the basal group (P < 0.05). Both CRU and API reduced doublecortin-like kinase 1-positive marker expression relative to basal by 57.9% (P = 0.009) and 51.4% (P < 0.02). The numbers of CD44-positive ACF did not differ between the groups. We identified 14 differentially expressed microRNAs (miRNAs). Of these, expression of 6 miRNAs were greater or tended to be greater (P ≤ 0.10) in one or both vegetable-containing groups compared to the basal group. Bioinformatic analysis of these expression changes in miRNA predicted a change in WNT/β-catenin signaling, indicating downregulation of β-catenin in the vegetable-fed groups. Consistent with this bioinformatics analysis, β-catenin-accumulated ACF were decreased in CRU (93.1%, P = 0.012), but not in API (54.4%, P = 0.125), compared to the basal group.

CONCLUSION

Both apiaceous and cruciferous vegetables, fed post-initiation, reduce colonic preneoplastic lesions as well as cancer stem cell marker expression in rats, possibly by suppressing oncogenic signaling through changes in miRNA expression.

Germinated brown rice combined with Lactobacillus acidophilus and Bifidobacterium animalis subsp. lactis inhibits colorectal carcinogenesis in rats

Colorectal cancer is a common cancer strongly associated with diet. Certain probiotics and prebiotics possess an inhibitory activity against colorectal cancer, while synbiotics may be more effective in preventing this cancer than either prebiotics or probiotics alone. Germinated brown rice (GBR) is considered as a candidate prebiotics with anticancer potential. However, the effect of GBR combined with probiotics on colorectal cancer is not clear. The present study investigated the preventive effect of combination of GBR and Lactobacillus acidophilus, Bifidobacterium animalis subsp. lactis, or both on colorectal carcinogenesis and the possible mechanism in rats treated with 1,2-dimethylhydrazine (DMH) and dextran sulfate sodium (DSS). DMH/DSS treatment induced preneoplastic aberrant crypt foci (ACF) and mucin-depleted foci (MDF), reduced superoxide dismutase (SOD) activity, increased anti-apoptotic Bcl-2 expression, and decreased the expression of pro-apoptotic p53, Bax, and caspase-3 in the colon. Germinated brown rice alone or combined with probiotics inhibited the formation of MDF in the middle colon, enhanced the colonic expression of p53 and Bax, and increased the ratio of Bax/Bcl-2. Combined treatment of GBR and probiotics inhibited the formation of ACF-producing sialomucin (SIM-ACF) and recovered the activity of SOD in the colon. Combination of GBR and L. acidophilus further increased caspase-3 expression and decreased Bcl-2 expression. These findings suggest that GBR combined with L. acidophilus and/or B. animalis subsp. lactis may inhibit colorectal carcinogenesis by enhancing antioxidative capacity and inducing apoptosis. This synbiotics may be a potential functional food or chemopreventive agent for controlling colorectal cancer.

Facile synthesis of fused polycyclic compounds via intramolecular oxidative cyclization/aromatization of β-tetralone or β-tetralone oximes

A mild and efficient NBS promoted intramolecular oxidative cyclization/aromatization of β-tetralone oximes has been explored. Under the optimized conditions, fused α-carbolines containing pentacyclic rings were obtained in moderate to good yields. Furthermore, various benzo[5,6]chromeno[2,3-b]indoles were successfully synthesized in moderate yields from β-tetralones using slightly modified conditions. We proposed a possible reaction pathway based on the experimental results.

Mechanistic Evidence for Red Meat and Processed Meat Intake and Cancer Risk: A Follow-up on the International Agency for Research on Cancer Evaluation of 2015

The Working Group of the International Agency for Research on Cancer classified the consumption of processed meat as carcinogenic to humans (Group 1), and classified red meat as probably carcinogenic to humans (Group 2A); consumption of both meat types is associated with an increased risk of colorectal cancer. These classifications are based on a compilation of epidemiology data and mechanistic evidence from animal and human studies. The curing of meats with nitrite can produce carcinogenic N-nitroso compounds (NOCs), and the smoking of meat produces polycyclic aromatic hydrocarbons (PAHs). The high-temperature cooking of meat also produces carcinogenic heterocyclic aromatic amines (HAAs). The ingestion of heme from meat can catalyze the formation of NOCs and lipid peroxidation products (LPOs) in the digestive tract. Many of these chemicals form DNA adducts, some of which can induce mutations and initiate carcinogenesis. Another recent hypothesis is that N-glycolylneuraminic acid, a non-human sialic acid sugar present in red meat, becomes incorporated in the cell membrane, triggering the immune response with associated inflammation and reactive oxygen species, which can contribute to DNA damage, tumor promotion, and cancer. The mechanisms by which these chemicals in meat induce DNA damage, and the impact of dietary and host factors that influence the biological potency of these chemicals are highlighted in this updated report.

Thermal processing food-related toxicants: a review

Heterocyclic aromatic amines, acrylamide, 5-hydroxymethylfurfural, furan, polycyclic aromatic hydrocarbons, nitrosamines, acrolein, chloropropanols and chloroesters are generated toxicants formed in some foodstuffs, mainly starchy and protein-rich food during thermal treatment such as frying, roasting and baking. The formation of these chemical compounds is associated with development of aromas, colors and flavors. One of the challenges facing the food industry today is to minimize these toxicants without adversely affecting the positive attributes of thermal processing. To achieve this objective, it is essential to have a detailed understanding of the mechanism of formation of these toxicants in processed foods. All reviewed toxicants in that paper are classified as probable, possible or potential human carcinogens and have been proven to be carcinogenic in animal studies. The purpose of that review is to summarize some of the most frequent occurring heat-generated food toxicants during conventional heating, their metabolism and carcinogenicity. Moreover, conventional and microwave heating were also compared as two different heat treatment methods, especially how they change food chemical composition and which thermal food toxicants are formed during specific method.

Colonic aberrant crypt formation accompanies an increase of opportunistic pathogenic bacteria in C57BL/6 mice fed a high-fat diet

The increasing worldwide incidence of colon cancer has been linked to obesity and consumption of a high-fat Western diet. To test the hypothesis that a high-fat diet (HFD) promotes colonic aberrant crypt (AC) formation in a manner associated with gut bacterial dysbiosis, we examined the susceptibility to azoxymethane (AOM)-induced colonic AC and microbiome composition in C57/BL6 mice fed a modified AIN93G diet (AIN, 16% fat, energy) or an HFD (45% fat, energy) for 14 weeks. Mice receiving the HFD exhibited increased plasma leptin, body weight, body fat composition and inflammatory cell infiltration in the ileum compared with those in the AIN group. Consistent with the gut inflammatory phenotype, we observed an increase in colonic AC, plasma interleukin-6, tumor necrosis factor-α, monocyte chemoattractant protein-1 and inducible nitric oxide synthase in the ileum of the HFD-AOM group compared with the AIN-AOM group. Although the HFD and AIN groups did not differ in bacterial species number, the HFD and AIN diets resulted in different bacterial community structures in the colon. The abundance of certain short-chain fatty acid (SCFA) producing bacteria (e.g., Barnesiella) and fecal SCFA (e.g., acetic acid) content were lower in the HFD-AOM group compared with the AIN and AIN-AOM groups. Furthermore, we identified a high abundance of Anaeroplasma bacteria, an opportunistic pathogen in the HFD-AOM group. Collectively, we demonstrate that an HFD promotes AC formation concurrent with an increase of opportunistic pathogenic bacteria in the colon of C57BL/6 mice.

A miRNA signature for an environmental heterocyclic amine defined by a multi-organ carcinogenicity bioassay in the rat

Heterocyclic amines (HCAs) produced during high-temperature cooking have been studied extensively in terms of their genotoxic/genetic effects, but recent work has implicated epigenetic mechanisms involving non-coding RNAs. Colon tumors induced in the rat by 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) have altered microRNA (miRNA) signatures linked to dysregulated pluripotency factors, such as c-Myc and Krüppel-like factor 4 (KLF4). We tested the hypothesis that dysregulated miRNAs from PhIP-induced colon tumors would provide a "PhIP signature" for use in other target organs obtained from a 1-year carcinogenicity bioassay in the rat. Downstream targets that were corroborated in the rat were then investigated in human cancer datasets. The results confirmed that multiple let-7 family members were downregulated in PhIP-induced skin, colon, lung, small intestine, and Zymbal's gland tumors, and were associated with c-myc and Hmga2 upregulation. PhIP signature miRNAs with the profile mir-21high/mir-126low/mir-29clow/mir-215low/mir-145low were linked to reduced Klf4 levels in rat tumors, and in human pan-cancer and colorectal cancer. It remains to be determined whether this PhIP signature has predictive value, given that more than 20 different genotoxic HCAs are present in the human diet, plus other agents that likely induce or repress many of the same miRNAs. Future studies should define more precisely the miRNA signatures of other HCAs, and their possible value for human risk assessment.

Quantification of Hemoglobin and White Blood Cell DNA Adducts of the Tobacco Carcinogens 2-Amino-9H-pyrido[2,3-b]indole and 4-Aminobiphenyl Formed in Humans by Nanoflow Liquid Chromatography/Ion Trap Multistage Mass Spectrometry

Aromatic amines covalently bound to hemoglobin (Hb) as sulfinamide adducts at the cysteine 93 residue of the Hb β chain have served as biomarkers to assess exposure to this class of human carcinogens for the past 30 years. In this study, we report that 2-amino-9H-pyrido[2,3-b]indole (AαC), an abundant carcinogenic heterocyclic aromatic amine formed in tobacco smoke and charred cooked meats, also reacts with Hb to form a sulfinamide adduct. A novel nanoflow liquid chromatography/ion trap multistage mass spectrometry (nanoLC-IT/MS3) method was established to assess exposure to AαC and the tobacco-associated bladder carcinogen 4-aminobiphenyl (4-ABP) through their Hb sulfinamide adducts. Following mild acid hydrolysis of Hb in vitro, the liberated AαC and 4-ABP were derivatized with acetic anhydride to form the N-acetylated amines, which were measured by nanoLC-IT/MS3. The limits of quantification (LOQ) for AαC- and 4-ABP-Hb sulfinamide adducts were ≤7.1 pg/g Hb. In a pilot study, the mean level of Hb sulfinamide adducts of AαC and 4-ABP were, respectively, 3.4-fold and 4.8-fold higher in smokers (>20 cigarettes/day) than nonsmokers. In contrast, the major DNA adducts of 4-ABP, N-(2'-deoxyguanosin-8-yl)-4-aminobiphenyl, and AαC, N-(2'-deoxyguanosin-8-yl)-2-amino-9H-pyrido[2,3-b]indole, were below the LOQ (3 adducts per 109 bases) in white blood cell (WBC) DNA of smokers and nonsmokers. These findings reaffirm that tobacco smoke is a major source of exposure to AαC. Hb sulfinamide adducts are suitable biomarkers to biomonitor 4-ABP and AαC; however, neither carcinogen binds to DNA in WBC, even in heavy smokers, at levels sufficient for biomonitoring.

Bioactive phytochemicals in barley

Epidemiological studies have consistently shown that regular consumption of whole grain barley reduces the risk of developing chronic diseases. The presence of barley fiber, especially β-glucan in whole grain barley, has been largely credited for these health benefits. However, it is now widely believed that the actions of the fiber component alone do not explain the observed health benefits associated with the consumption of whole grain barley. Whole grain barley also contains phytochemicals including phenolic acids, flavonoids, lignans, tocols, phytosterols, and folate. These phytochemicals exhibit strong anti-oxidant, antiproliferative, and cholesterol lowering abilities, which are potentially useful in lowering the risk of certain diseases. Therefore, the high concentration of phytochemicals in barley may be largely responsible for its health benefits. This paper reviews available information regarding barley phytochemicals and their potential to combat common nutrition-related diseases including cancer, cardiovascular disease, diabetes, and obesity.

Impact of DNA repair on the dose-response of colorectal cancer formation induced by dietary carcinogens

Colorectal cancer (CRC) is one of the most frequently diagnosed cancers, which is causally linked to dietary habits, notably the intake of processed and red meat. Processed and red meat contain dietary carcinogens, including heterocyclic aromatic amines (HCAs) and N-nitroso compounds (NOC). NOC are agents that induce various N-methylated DNA adducts and O⁶-methylguanine (O⁶-MeG), which are removed by base excision repair (BER) and O⁶-methylguanine-DNA methyltransferase (MGMT), respectively. HCAs such as the highly mutagenic 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) cause bulky DNA adducts, which are removed from DNA by nucleotide excision repair (NER). Both O⁶-MeG and HCA-induced DNA adducts are linked to the occurrence of KRAS and APC mutations in colorectal tumors of rodents and humans, thereby driving CRC initiation and progression. In this review, we focus on DNA repair pathways removing DNA lesions induced by NOC and HCA and assess their role in protecting against mutagenicity and carcinogenicity in the large intestine. We further discuss the impact of DNA repair on the dose-response relationship in colorectal carcinogenesis in view of recent studies, demonstrating the existence of 'no effect' point of departures (PoDs), i.e. thresholds for genotoxicity and carcinogenicity. The available data support the threshold concept for NOC with DNA repair being causally involved.

Bioactivation of Heterocyclic Aromatic Amines by UDP Glucuronosyltransferases

2-Amino-9H-pyrido[2,3-b]indole (AαC) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) are carcinogenic heterocyclic aromatic amines (HAA) that arise during the burning of tobacco and cooking of meats. UDP-glucuronosyltransferases (UGT) detoxicate many procarcinogens and their metabolites. The genotoxic N-hydroxylated metabolite of AαC, 2-hydroxyamino-9H-pyrido[2,3-b]indole (HONH-AαC), undergoes glucuronidation to form the isomeric glucuronide (Gluc) conjugates N(2)-(β-d-glucosidurony1)-2-hydroxyamino-9H-pyrido[2,3-b]indole (AαC-HON(2)-Gluc) and O-(β-d-glucosidurony1)-2-hydroxyamino-9H-pyrido[2,3-b]indole (AαC-HN(2)-O-Gluc). AαC-HON(2)-Gluc is a stable metabolite but AαC-HN(2)-O-Gluc is a biologically reactive intermediate, which covalently adducts to DNA at levels that are 20-fold higher than HONH-AαC. We measured the rates of formation of AαC-HON(2)-Gluc and AαC-HN(2)-O-Gluc in human organs: highest activity occurred with liver and kidney microsomes, and lesser activity was found with colon and rectum microsomes. AαC-HN(2)-O-Gluc formation was largely diminished in liver and kidney microsomes, by niflumic acid, a selective inhibitor UGT1A9. In contrast, AαC-HON(2)-Gluc formation was less affected and other UGT contribute to N(2)-glucuronidation of HONH-AαC. UGT were reported to catalyze the formation of isomeric Gluc conjugates at the N(2) and N3 atoms of 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (HONH-PhIP), the genotoxic metabolite of PhIP. However, we found that the N3-Gluc of HONH-PhIP also covalently bound to DNA at higher levels than HONH-PhIP. The product ion spectra of this Gluc conjugate acquired by ion trap mass spectrometry revealed that the Gluc moiety was linked to the oxygen atom of HONH-PhIP and not the N3 imidazole atom of the oxime tautomer of HONH-PhIP as was originally proposed. UGT1A9, an abundant UGT isoform expressed in human liver and kidney, preferentially forms the O-linked Gluc conjugates of HONH-AαC and HONH-PhIP as opposed to their detoxicated N(2)-Gluc isomers. The regioselective O-glucuronidation of HONH-AαC and HONH-PhIP, by UGT1A9, is a mechanism of bioactivation of these ubiquitous HAAs.