Genotoxicity and induction of DNA damage responsive genes by food-borne heterocyclic aromatic amines in human hepatoma HepG2 cells

Comparing application methods of reishi mushroom (Ganoderma lucidum) extract in deep-fried meatballs: impact on heterocyclic aromatic amine formation

BACKGROUND

The present research was conducted to investigate the impact of reishi mushroom extract (RME) on the formation of heterocyclic aromatic amines (HAAs) in meatballs. Sample preparations involved applying RME using either the spreading or addition method, with varying concentrations (0%, 0.25%, 0.5%, and 1% of RME), followed by deep-frying at temperatures of 150 and 190 °C for 3 min.

RESULTS

The types and levels of HAAs varied based on the frying temperature, method of extract application, and the extract concentration. Notably, total HAA contents increased with rising the frying temperature (P < 0.01) and varied from undetectable levels to 4.91 ng g-1 across all analyzed meatballs. The addition method was more effective than the spreading method (P < 0.01), and among the concentrations tested 0.25% RME exhibited the highest efficacy in reducing total HAAs (P < 0.05). Furthermore, the addition method inhibited lipid oxidation more efficiently compared to the surface spreading method (P < 0.05).

CONCLUSION

This study demonstrated that RME had mitigating effects on HAAs depending on the concentration and frying conditions in deep-fried meatball samples. © 2024 The Author(s). Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Polymorphisms of DNA Repair Genes in Thyroid Cancer

The incidence of thyroid cancer, one of the most common forms of endocrine cancer, is increasing rapidly worldwide in developed and developing countries. Various risk factors can increase susceptibility to thyroid cancer, but particular emphasis is put on the role of DNA repair genes, which have a significant impact on genome stability. Polymorphisms of these genes can increase the risk of developing thyroid cancer by affecting their function. In this article, we present a concise review on the most common polymorphisms of selected DNA repair genes that may influence the risk of thyroid cancer. We point out significant differences in the frequency of these polymorphisms between various populations and their potential relationship with susceptibility to the disease. A more complete understanding of these differences may lead to the development of effective prevention strategies and targeted therapies for thyroid cancer. Simultaneously, there is a need for further research on the role of polymorphisms of previously uninvestigated DNA repair genes in the context of thyroid cancer, which may contribute to filling the knowledge gaps on this subject.

John N, Zaidi F, Doyle F, Fasullo M. High-throughput screening of the Saccharomyces cerevisiae genome for 2-amino-3-methylimidazo [4,5-f] quinoline resistance identifies colon cancer-associated genes

Heterocyclic aromatic amines (HAAs) are potent carcinogenic agents found in charred meats and cigarette smoke. However, few eukaryotic resistance genes have been identified. We used Saccharomyces cerevisiae (budding yeast) to identify genes that confer resistance to 2-amino-3-methylimidazo[4,5-f] quinoline (IQ). CYP1A2 and NAT2 activate IQ to become a mutagenic nitrenium compound. Deletion libraries expressing human CYP1A2 and NAT2 or no human genes were exposed to either 400 or 800 µM IQ for 5 or 10 generations. DNA barcodes were sequenced using the Illumina HiSeq 2500 platform and statistical significance was determined for exactly matched barcodes. We identified 424 ORFs, including 337 genes of known function, in duplicate screens of the "humanized" collection for IQ resistance; resistance was further validated for a select group of 51 genes by growth curves, competitive growth, or trypan blue assays. Screens of the library not expressing human genes identified 143 ORFs conferring resistance to IQ per se. Ribosomal protein and protein modification genes were identified as IQ resistance genes in both the original and "humanized" libraries, while nitrogen metabolism, DNA repair, and growth control genes were also prominent in the "humanized" library. Protein complexes identified included the casein kinase 2 (CK2) and histone chaperone (HIR) complex. Among DNA Repair and checkpoint genes, we identified those that function in postreplication repair (RAD18, UBC13, REV7), base excision repair (NTG1), and checkpoint signaling (CHK1, PSY2). These studies underscore the role of ribosomal protein genes in conferring IQ resistance, and illuminate DNA repair pathways for conferring resistance to activated IQ.

Effect of lipid oxidation on quality attributes and control technologies in dried aquatic animal products: a critical review

Aquatic animals are viewed as a good source of healthy lipids. Although drying is an effective method for the preservation of aquatic animal products (AAPs), the whole process is accompanied by lipid oxidation. This article reviews the main mechanism of lipid oxidation in the drying process. It also summarizes the effects of lipid oxidation on the quality of dried aquatic animal products (DAAPs), including nutrients, color, flavor, and hazard components, especially for those harmful aldehydes and heterocyclic amines. In addition, it concluded that moderate lipid oxidation contributes to improving the quality of products. Still, excessive lipid oxidation produces hazardous substances and induces health risks. Hence, to obtain high-quality DAAPs, some effective control technologies to promote/prevent lipid oxidation are introduced and deeply discussed, including salting, high-pressure processing, irradiation, non-thermal plasma technology, defatting treatments, antioxidants, and edible coating. A systematic review of the effect of lipid oxidation on quality attributes and control technologies in DAAPs is presented, and some perspectives are made for future research.

HepG2 spheroids as a biosensor-like cell-based system for (geno)toxicity assessment

3D spheroids developed from HepG2 cells were used as a biosensor-like system for the detection of (geno)toxic effects induced by chemicals. Benzo(a)pyrene (B(a)P) and amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) with well-known mechanisms of action were used for system validation. HepG2 spheroids grown for 3 days were exposed to BaP and PhIP for 24 and 72 h. The growth and viability of spheroids were monitored by planimetry and Live/Dead staining of cells. Multi-parametric flow cytometric analysis was applied for simultaneous detection of specific end-effects including cell cycle analysis (Hoechst staining), cell proliferation (KI67 marker), and DNA double-strand breaks (ℽH2AX) induced by genotoxic compounds. Depending on the exposure concentration/time, BaP reduced spheroid growth, affected cell proliferation by arresting cells in S and G2 phase and induced DNA double-strand breaks (DSB). Simultaneous staining of ℽH2AX formation and cell cycle analysis revealed that after BaP (10 μM; 24 h) exposure 60% of cells in G0/G1 phase had DNA DSB, while after 72 h only 20% of cells contained DSB indicating efficient repair of DNA lesions. PhIP did not influence the spheroid size whereas accumulation of cells in the G2 phase occurred after both treatment times. The evaluation of DNA damage revealed that at 200 μM PhIP 50% of cells in G0/G1 phase had DNA DSB, which after 72-h exposure dropped to 40%, showing lower repair capacity of PhIP-induced DSB compared to BaP-induced. The developed approach using simultaneous detection of several parameters provides mechanistic data and thus contributes to more reliable genotoxicity assessment of chemicals as a high-content screening tool.

Cyanidin-3-O-glucoside and its metabolite protocatechuic acid ameliorate 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) induced cytotoxicity in HepG2 cells by regulating apoptotic and Nrf2/p62 pathways

The present study investigated the protective effects and mechanism of action of cyanidin-3-O-glucoside (C3G) and its major metabolite protocatechuic acid (PCA) against 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) induced cytotoxicity in HepG2 cells. The results demonstrated that C3G and PCA dose-dependently suppressed PhIP-induced mutation in Salmonella typhimurium TA98, and inhibited PhIP-induced cytotoxicity and apoptosis in HepG2 cells. Western blot analysis indicated that C3G and PCA minimized PhIP-induced cell damage by reversing the abnormal expression of Bax/Bcl-2, Cytochrome c, cleaved Caspase-3, XIAP, Nrf2, HO-1, LC3 and p62 involved in intrinsic apoptotic and Nrf2/p62 pathways. Molecular docking results revealed that C3G and PCA were able to interfere with Nrf2 signaling and apoptotic cascade through binding to Keap1 and Bcl-2. Moreover, the protective effect of C3G was stronger than that of PCA. These findings suggested that dietary consumption of food sources rich in C3G can fight against the health risks of heterocyclic aromatic amines.

Quantitative proteomics and bioinformatics analyses reveal the protective effects of cyanidin-3-O-glucoside and its metabolite protocatechuic acid against 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)-induced cytotoxicity in HepG2 cells via apoptosis-related pathways

The aim of this study was to investigate the mechanism of action of cyanidin-3-O-glucoside (C3G) and its metabolite protocatechuic acid (PCA) mediated protection against 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)-induced cytotoxicity in HepG2 cells. The effects of C3G and PCA on cell viability, LDH release and apoptosis in IQ-induced HepG2 cells were evaluated using CCK-8, LDH release and flow cytometry assays, respectively. TMT-based proteomics was utilized to characterize the proteins and pathways associated with the improvement after C3G and PCA treatment. Results showed that exposure to IQ significantly increased cytotoxicity and apoptosis in HepG2 cells, which were alleviated by C3G and PCA. C3G was more effective than PCA in protecting HepG2 cells against IQ-induced cytotoxicity and regulating the related signaling pathways. Proteomics and bioinformatics analyses and Western blot validation revealed that apoptosis-related signaling pathways played pivotal roles in protecting against the cytotoxicity of IQ by C3G, and XIAP was identified as the target protein. Molecular docking proved that C3G had strong binding affinity to XIAP and hindered the binding of IQ to the BIR3 domain of XIAP, resulting in the inhibition of apoptosis. Our findings suggested that C3G has potential as a preventive food ingredient to prevent carcinogenic risk of heterocyclic aromatic amines.

Hepatocellular carcinoma (HepG2/C3A) cell-based 3D model for genotoxicity testing of chemicals

The major weakness of the current in vitro genotoxicity test systems is the inability of the indicator cells to express metabolic enzymes needed for the activation and detoxification of genotoxic compounds, which consequently can lead to misleading results. Thus, there is a significant emphasis on developing hepatic cell models, including advanced in vitro three-dimensional (3D) cell-based systems, which better imitate in vivo cell behaviour and offer more accurate and predictive data for human exposures. In this study, we developed an approach for genotoxicity testing with 21-day old spheroids formed from human hepatocellular carcinoma cells (HepG2/C3A) using the dynamic clinostat bioreactor system (CelVivo BAM/bioreactor) under controlled conditions. The spheroids were exposed to indirect-acting genotoxic compounds, polycyclic aromatic hydrocarbon [PAH; benzo(a) pyrene B(a)P], and heterocyclic aromatic amine [PhIP]) at non-cytotoxic concentrations for 24 and 96 h. The results showed that both environmental pollutants B(a)P and PhIP significantly increased the level of DNA strand breaks assessed by the comet assay. Further, the mRNA level of selected genes encoding metabolic enzymes from phase I and II, and DNA damage responsive genes was determined (qPCR). The 21-day old spheroids showed higher basal expression of genes encoding metabolic enzymes compared to monolayer culture. In spheroids, B(a)P or PhIP induced compound-specific up-regulation of genes implicated in their metabolism, and deregulation of genes implicated in DNA damage and immediate-early response. The study demonstrated that this model utilizing HepG2/C3A spheroids grown under dynamic clinostat conditions represents a very sensitive and promising in vitro model for genotoxicity and environmental studies and can thus significantly contribute to a more reliable assessment of genotoxic activities of pure chemicals, and complex environmental samples even at very low for environmental exposure relevant concentrations.

Genotoxic Effects of Cylindrospermopsin, Microcystin-LR and Their Binary Mixture in Human Hepatocellular Carcinoma (HepG2) Cell Line

Simultaneous occurrence of cylindrospermopsin (CYN) and microcystin-LR (MCLR) has been reported in the aquatic environment and thus human exposure to such mixtures is possible. As data on the combined effects of CYN/MCLR are scarce, we aimed to investigate the adverse effects related to genotoxic activities induced by CYN (0.125, 0.25 and 0.5 µg/mL) and MCLR (1 µg/mL) as single compounds and their combinations in HepG2 cells after 24 and 72 h exposure. CYN and CYN/MCLR induced DNA double-strand breaks after 72 h exposure, while cell cycle analysis revealed that CYN and CYN/MCLR arrested HepG2 cells in G0/G1 phase. Moreover, CYN and the combination with MCLR upregulated CYP1A1 and target genes involved in DNA-damage response (CDKN1A, GADD45A). Altogether, the results showed that after 72 h exposure genotoxic activity of CYN/MCLR mixture was comparable to the one of pure CYN. On the contrary, MCLR (1 µg/mL) had no effect on the viability of cells and had no influence on cell division. It did not induce DNA damage and did not deregulate studied genes after prolonged exposure. The outcomes of the study confirm the importance of investigating the combined effects of several toxins as the effects can differ from those induced by single compounds.

Genotoxic activities of wastewater after ozonation and activated carbon filtration: Different effects in liver-derived cells and bacterial indicators

Aim of this study was to investigate the impact of advanced wastewater treatment techniques (combining ozonation with activated carbon filtration) on acute and genotoxic activities of tertiary treated wastewater. Concentrated samples were tested in Salmonella/microsome assays. Furthermore, induction of DNA damage was measured in liver-derived cells (human hepatoma and primary rat hepatocytes) in single cell gel electrophoresis experiments, which are based on the measurement of DNA migration in an electric field. These cell types possess phase I and phase II enzymes, which catalyze the activation/detoxification of mutagens. Acute toxicity was determined with the trypan blue exclusion technique. We found no evidence for mutagenic effects of non-ozonated samples in several bacterial tester strains (TA98, TA100, YG7108, YG7104, YG7112 and YG7113) but clear induction of His⁺ mutants after O₃ treatment in two strains with defective genes encoding for DNA repair, which are highly sensitive towards alkylating agents (YG7108 and YG7104). These effects were reduced after activated carbon filtration. Furthermore, we detected a slight increase of mutagenic activity in strain YG1024 with increased acetyltransferase activity, which is sensitive towards aromatic amines and nitro compounds in untreated water, which was not reduced by O₃ treatment. A completely different pattern of mutagenic activity was seen in liver-derived cells; non ozonated samples caused in both cell types pronounced DNA damage, which was reduced (by ca. 25%) after ozonation. Activated carbon treatment did not cause a substantial further reduction of DNA damage. Additional experiments with liver homogenate indicate that the compounds which cause the effects in the human cells are promutagens which require enzymatic activation. None of the waters caused acute toxicity in the liver-derived cells and in the bacterial indicators. Assuming that hepatic mammalian cells reflect the genotoxic properties of the waters in vertebrates (including humans) more adequately as genetically modified bacterial indicators, we conclude that ozonation has beneficial effects in regard to the reduction of genotoxic properties of treated wastewaters.

Plastics in Cyanobacterial Blooms-Genotoxic Effects of Binary Mixtures of Cylindrospermopsin and Bisphenols in HepG2 Cells

Ever-expanding environmental pollution is causing a rise in cyanobacterial blooms and the accumulation of plastics in water bodies. Consequently, exposure to mixtures of cyanotoxins and plastic-related contaminants such as bisphenols (BPs) is of increasing concern. The present study describes genotoxic effects induced by co-exposure to one of the emerging cyanotoxins-cylindrospermopsin (CYN)-(0.5 µg/mL) and BPs (bisphenol A (BPA), S (BPS), and F (BPF); (10 µg/mL)) in HepG2 cells after 24 and 72 h of exposure. The cytotoxicity was evaluated with an MTS assay and genotoxicity was assessed through the measurement of the induction of DNA double strand breaks (DSB) with the γH2AX assay. The deregulation of selected genes (xenobiotic metabolic enzyme genes, DNA damage, and oxidative response genes) was assessed using qPCR. The results showed a moderate reduction of cell viability and induction of DSBs after 72 h of exposure to the CYN/BPs mixtures and CYN alone. None of the BPs alone reduced cell viability or induced DSBs. No significant difference was observed between CYN and CYN/BPs exposed cells, except with CYN/BPA, where the antagonistic activity of BPA against CYN was indicated. The deregulation of some of the tested genes (CYP1A1, CDKN1A, GADD45A, and GCLC) was more pronounced after exposure to the CYN/BPs mixtures compared to single compounds, suggesting additive or synergistic action. The present study confirms the importance of co-exposure studies, as our results show pollutant mixtures to induce effects different from those confirmed for single compounds.

Heterocyclic amines in braised chicken may mainly infiltrate from reused marinade during braising, instead of thermic generation

BACKGROUND

Sauce braised meat products are popular in Asia, although their complicated processing may lead to potential safety risks. Especially, how hazardous compounds are formed during their preparation is still unclear. In the present study, braised chicken breasts, which are a typical Chinese sauce braised meat product, were used to investigate the formation of heterocyclic amines (HCAs) during heat treatment.

RESULTS

Precursor content (creatine and reducing sugar), HCA level and temperature were measured in different parts of the chicken breast at each processing stage. The results obtained showed that the increasing trends of total HCA content in different parts of chicken breast were not the same. Only total HCA content in the skin (4.93 ± 0.80 ng g^-1 ) increased significantly after deep-frying. During braising, total HCA level in the skin was high (12.1-14.3 ng g^-1 ) and relatively stable. However, total HCA content in pectoralis major muscle (3.90-7.40 ng g^-1 ) and pectoralis minor muscle (1.44-5.31 ng g^-1 ) was much lower than in the skin, and increased steadily with braising time.

CONCLUSION

Braising is the main factor which affects HCA level in braised chicken. Combining the results of temperature and precursor content, a possible explanation for the large amount of HCAs in braised chicken is the gradual infiltration from reused marinade, instead of thermic generation. © 2019 Society of Chemical Industry.

Detoxification of Heterocyclic Aromatic Amines by Probiotic to Inhibit Medical Hazards

Cancer is the second leading factor of human death in the world. Long-term consumption of cooked red meat brings about various types of cancers like colorectal cancer due to the formation of Heterocyclic Aromatic Amines (HAAs) during the heating process of meat. There are various solutions for the reduction of these toxicants. The aim of this article is to describe probiotic as one of the possible strategies for bioremoval of these carcinogenic and mutagenic substances and change food to functional one as well. The mechanism of biodetoxification is binding by probiotics, which depends on some variables including the probiotic characteristics, kind and content of the mutagens, as well as some properties of media. In this article, after introducing detoxification ability of probiotics and listing of all reported probiotics in this field, the influencing variables are surveyed and finally, opportunities and problems of HAA bioremoval by probiotics are described.

Genetic toxicity assessment using liver cell models: past, present, and future

Genotoxic compounds may be detoxified to non-genotoxic metabolites while many pro-carcinogens require metabolic activation to exert their genotoxicity in vivo. Standard genotoxicity assays were developed and utilized for risk assessment for over 40 years. Most of these assays are conducted in metabolically incompetent rodent or human cell lines. Deficient in normal metabolism and relying on exogenous metabolic activation systems, the current in vitro genotoxicity assays often have yielded high false positive rates, which trigger unnecessary and costly in vivo studies. Metabolically active cells such as hepatocytes have been recognized as a promising cell model in predicting genotoxicity of carcinogens in vivo. In recent years, significant advances in tissue culture and biological technologies provided new opportunities for using hepatocytes in genetic toxicology. This review encompasses published studies (both in vitro and in vivo) using hepatocytes for genotoxicity assessment. Findings from both standard and newly developed genotoxicity assays are summarized. Various liver cell models used for genotoxicity assessment are described, including the potential application of advanced liver cell models such as 3D spheroids, organoids, and engineered hepatocytes. An integrated strategy, that includes the use of human-based cells with enhanced biological relevance and throughput, and applying the quantitative analysis of data, may provide an approach for future genotoxicity risk assessment.

Genotoxic activity of bisphenol A and its analogues bisphenol S, bisphenol F and bisphenol AF and their mixtures in human hepatocellular carcinoma (HepG2) cells

The use of bisphenol A (BPA) in manufacturing of plastics is being gradually replaced by presumably safer analogues such as bisphenol S (BPS), bisphenol F (BPF) and bisphenol AF (BPAF). Despite their widespread occurrence in the environment, there is a knowledge gap in their toxicological profiles. We investigated cytotoxic/genotoxic effects as well as changes in the expression of selected genes involved in the xenobiotic metabolism, response to oxidative stress and DNA damage upon exposure to BPs and their mixtures in human hepatocellular carcinoma HepG2 cells. BPS and BPF slightly decreased the viability of HepG2 cells, while BPAF was the most cytotoxic compound tested. BPA, BPF and BPAF induced the formation of DNA double strand breaks determined with γH2AX assay, while BPS was inactive (5-20 μg/mL). All four BPs up-regulated the expression of CYP1A1 and UGT1A1, while BPS up-regulated and BPAF down-regulated also the expression of GST1A. Only BPA up-regulated oxidative stress responsive gene GCLC, while BPAF up-regulated the expression of CDKN1A and GADD45a. At concentrations relevant for human exposure (ng/mL range) BPA and its analogues as individual compounds and in mixtures did not exert genotoxic activity, whereas BPA and BPAF as well as the mixtures up-regulated the expressions of CYP1A1 and UGT1A1.

Three-dimensional HepaRG spheroids as a liver model to study human genotoxicity in vitro with the single cell gel electrophoresis assay

Many efforts have been made in the last 30 years to develop more relevant in vitro models to study genotoxic responses of drugs and environmental contaminants. While 2D HepaRG cells are one of the most promising models for liver toxicology, a switch to 3D cultures that integrate both in vivo architecture and cell-cell interactions has occurred to achieve even more predictive models. Preliminary studies have indicated that 3D HepaRG cells are suitable for liver toxicity screening. Our study aimed to evaluate the response of HepaRG spheroids exposed to various genotoxic compounds using the single cell gel electrophoresis assay. HepaRG spheroids were used at 10 days after seeding and exposed for 24 and 48 hours to certain selected chemical compounds (methylmethansulfonate (MMS), etoposide, benzo[a]pyrene (B[a]P), cyclophosphamide (CPA), 7,12-dimethylbenz[a]anthracene (DMBA), 2-acetylaminofluorene (2-AAF), 4-nitroquinoline (4-NQO), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-3-methylimidazo[4,5-f]quinolone (IQ), acrylamide, and 2-4-diaminotoluene (2,4-DAT)). After treatment, the comet assay was performed on single cell suspensions and cytotoxicity was determined by the ATP assay. Comet formation was observed for all compounds except IQ, etoposide and 2,4-DAT. Treatment of spheroids with rifampicin increased CYP3A4 activity, demonstrating the metabolic capacity of HepaRG spheroids. These data on genotoxicity in 3D HepaRG spheroids are promising, but further experiments are required to prove that this model can improve the predictivity of in vitro models to detect human carcinogens.

2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline Alters Autophagosome Maturation, Cellular Lipidomic Profiles, and Expression of Core Pluripotent Factors

2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), one of the most abundant heterocyclic aromatic amines (HAAs) found in the human diet, is primarily produced during high-temperature meat or fish cooking. While MeIQx has been investigated as a potential carcinogen, the cytotoxicity and related molecular mechanisms remain unclear. Here, we demonstrate that autophagosome maturation is blocked by MeIQx. Mechanistically, MeIQx inhibits acidification of lysosomes rather than prevents autophagosome-lysosome fusion. Moreover, cellular lipid profiles are altered by MeIQx treatment. Notably, many phospholipids and sphingolipids are significantly upregulated after exposure to MeIQx. Furthermore, MeIQx decreases expression of pluripotency-associated proteins in mouse embryonic stem cells (ESCs). Together, MeIQx blocks autophagosome maturation through inhibiting acidification of lysosomes, alters lipid metabolism, and decreases expression of pluripotent factors. Our studies provide more cytotoxic evidence and elucidate related mechanisms on the risk of HAA exposure and are expected to promote supervision of food safety and human health.

Gut microbial transformation of the dietary mutagen MeIQx may reduce exposure levels without altering intestinal transport

The mutagen and probable human carcinogen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) is metabolized in the colon to 9-hydroxyl-2,7-dimethyl-7,9,10,11-tetrahydropyrimido[2',1':2,3]imidazo[4,5-f]quinoxaline (MeIQx-M1) by conjugation with microbially generated acrolein. However, whether this microbiota-controlled process alters systemic exposure and hepatotoxicity of MeIQx remains unclear. The physiological relevance of this microbial transformation on the systemic exposure of MeIQx was investigated using an in vitro-in vivo extrapolation approach. To address whether microbial transformation influences intestinal transport of MeIQx, the intestinal uptake of MeIQx and its metabolite MeIQx-M1 was quantified using Ussing chambers mounted with different intestinal segments from male Fischer 344 rats. Up to 0.4% of both MeIQx and MeIQx-M1 were transported from the mucosal side to the serosal side of intestinal tissue within 90 min, suggesting that the intestinal uptake of both compounds is similar. With the uptake rates of both compounds, physiologically based pharmacokinetic (PBPK) modeling of the fate of MeIQx in the human body including microbial transformation of MeIQx was performed. Results indicate for the first time that high levels of microbe-derived acrolein would be required to significantly reduce systemic exposure of MeIQx in humans. Finally, neither MeIQx nor MeIQx-M1 were cytotoxic towards human liver HepaRG cells at dietary or higher concentrations of MeIQx. In summary, these findings suggest that gut microbial transformation of heterocyclic amines has the potential to influence systemic human exposure to some extent, but may require significant gut microbial production of acrolein and that further investigations are needed to understand physiological levels of acrolein and competing biotransformation pathways.

Cytome micronucleus assays with a metabolically competent human derived liver cell line (Huh6): A promising approach for routine testing of chemicals?

One of the main problems of in vitro genotoxicity tests is the inadequate representation of drug metabolizing enzymes in most indicator cell lines which are currently used. We identified recently a human derived liver cell line (Huh6) which detected induction of DNA damage by representatives of different groups of promutagens without enzyme mix and showed that these cells are more suitable in terms of reproducibility and sensitivity as other currently used liver derived lines. We developed a protocol for micronucleus (MN) cytome assays with these cells and validated the procedure in experiments with representatives of different groups of directly and indirectly acting genotoxic carcinogens (MMS, cisplatin, PhIP, IQ, NDMA, B(a)P, AFB1, etoposide, and H₂ O₂ ). The optimal cytochalasin B concentration in combination with 48 hr treatment was found to be 1.5 μg/mL and leads to a cytokinesis block proliferation index in the range between 1.7 and 2.0. The morphological characteristics of different nuclear anomalies which reflect DNA damage (MN, nuclear bridges, and buds) and their baseline frequencies in untreated cells were characterized, and the rates which are required to cause significant effects were calculated. All compounds caused dose dependent induction of MN when the cells were treated for 24 hr, longer and shorter exposure times were less effective. Experiments with different serum levels (fetal bovine serum [FBS]) showed that 10% FBS in the medium (instead of 4%) causes a substantial increase of the sensitivity of the cells. Our results indicate that the new protocol is a promising approach for routine testing of chemicals. Environ. Mol. Mutagen. 60: 134-144, 2019. © 2018 The Authors. Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.

Genotoxicity of heterocyclic amines (HCAs) on freshly isolated human peripheral blood mononuclear cells (PBMC) and prevention by phenolic extracts derived from olive, olive oil and olive leaves

In this study we investigated the genotoxic potential of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, (PhIP); 2-amino-3-methyl-3H-imidazo[4,5-f]quinoline, (IQ); 2-amino-3,8-dimethyl-imidazo[4,5-f]quinoxaline, (MeIQx) and 2-amino-3,4,8-trimethyl-3H-imidazo[4,5-f]quinoxaline (DiMeIQx) on human freshly isolated peripheral blood mononuclear cells (PBMC) by the comet assay. The preventive ability of three different phenolic extracts derived from olive (O-PE), virgin olive oil (OO-PE) and olive leaf (OL-PE) on PhIP induced DNA damage was also investigated. PhIP and IQ induced a significant DNA damage at the lowest concentration tested (100 μM), while the genotoxic effect of MeIQx and DiMeIQx become apparent only in the presence of DNA repair inhibitors Cytosine b-D-arabinofuranoside and Hydroxyurea (AraC/HU). The inclusion of metabolic activation (S9-mix) in the culture medium increased the genotoxicity of all HCAs tested. All three phenolic extracts showed an evident DNA damage preventive activity in a very low concentration range (0.1-1.0 μM of phenols) which could be easily reached in human tissues "in vivo" under a regular intake of virgin olive oil. These data further support the observation that consumption of olive and virgin olive oil may prevent the initiation step of carcinogenesis. The leaf waste could be an economic and simple source of phenolic compounds to be used as food additives or supplements.

Gut Microbial Transformation of the Dietary Imidazoquinoxaline Mutagen MelQx Reduces Its Cytotoxic and Mutagenic Potency

The diverse community of microbes present in the human gut has emerged as an important factor for cancer risk, potentially by altering exposure to chemical carcinogens. In the present study, human gut bacteria were tested for their capacity to transform the carcinogenic heterocyclic amine 2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MelQx). Eubacterium hallii, Lactobacillus reuteri, and Lactobacillus rossiae were able to convert MelQx to a new microbial metabolite characterized on the basis of high-resolution mass spectrometry and NMR as 9-hydroxyl-2,7-dimethyl-7,9,10,11-tetrahydropyrimido[2′,1′:2,3]imidazo[4,5-f]quinoxaline (MelQx-M1), resulting from conjugation with activated glycerol. Acrolein derived from the decomposition of 3-hydroxypropionaldehyde, which is the product of bacterial glycerol/diol dehydratase activity, was identified as the active compound responsible for the formation of MelQx-M1. A complex human gut microbial community obtained from invitro continuous intestinal fermentation was found to also transform MelQx to MelQx-M1. MelQx-M1 had slightly reduced cytotoxic potency toward human colon epithelial cells invitro, and diminished mutagenic potential toward bacteria after metabolic activation. As bacterially derived acrolein also transformed 2 other HCAs, namely 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and 2-amino-3-methylimidazo[4,5-f]quinoline, these results generalize the capacity of gut microbiota to detoxify HCAs in the gut, potentially modulating cancer risk.

Unraveling the inhibitory effect of dihydromyricetin on heterocyclic aromatic amines formation

BACKGROUND

Heterocyclic aromatic amines (HAAs) are mutagens and rodent carcinogens. Flavonoids have attracted considerable attention for development into effective inhibitors against the formation of genotoxic HAAs in thermally processed foods.

RESULTS

The inhibitory effect of dihydromyricetin (DMY) on the formation of key HAAs, including 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-3,8-dimethylimidazo[4,5-f]-quinoxaline (MeIQx), and 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (4,8-DiMeIQx), was significant. In chemical models, DMY (0.05 mmol, 0.1 mmol, and 0.2 mmol) significantly decreased the amount of PhIP formed (43.0%, 54.7%, and 75.7% respectively). A significant inhibitory effect on the formation of MeIQx and 4,8-DiMeIQx was also observed. Moreover, DMY (0.05%, 0.1%, and 0.2%) reduced the generation of PhIP (by 48.0%, 59.0%, and 80.1% respectively) and that of MeIQx (by 45.8%, 62.0%, and 76.7% respectively) in fried beef patties.

CONCLUSION

The results indicate that DMY could be converted into myricetin during thermal processing, and both DMY and myricetin could trap phenylacetaldehyde, a major Strecker aldehyde of phenylalanine, in a similar manner to thus inhibit the generation of PhIP. This study provides valuable information for the development of effective strategies to minimize HAA content in thermally processed foods and also sheds light on the mechanism that accounts for the inhibitory effect. © 2017 Society of Chemical Industry.

Functional role and tobacco smoking effects on methylation of CYP1A1 gene in prostate cancer

Cytochrome P450 (CYP) 1A1 is a phase I enzyme that can activate various compounds into reactive forms and thus, may contribute to carcinogenesis. In this study, we investigated the expression, methylation status, and functional role of CYP1A1 on prostate cancer cells. Increased expression of CYP1A1 was observed in all cancer lines (PC-3, LNCaP, and DU145) compared to BPH-1 (P < 0.05); and was enhanced further by 5-aza-2′-deoxycytidine treatment (P < 0.01). Methylation-specific PCR (MSP) and sequencing of bisulfite-modified DNA of the xenobiotic response element (XRE) enhancer site XRE-1383 indicated promoter methylation as a regulator of CYP1A1 expression. In tissue, microarrays showed higher immunostaining of CYP1A1 in prostate cancer than normal and benign prostatic hyperplasia (BPH; P < 0.001), and methylation analyses in clinical specimens revealed significantly lower methylation levels in cancer compared to BPH at all enhancer sites analyzed (XRE-1383, XRE-983, XRE-895; P < 0.01). Interestingly, smoking affected the XRE-1383 site where the methylation level was much lower in cancer tissues from smokers than non-smokers (P < 0.05). CYP1A1 levels are thus increased in prostate cancer and to determine the functional effect of CYP1A1 on cells, we depleted the gene in LNCaP and DU145 by siRNA. We observe that CYP1A1 knockdown decreased cell proliferation (P < 0.05) and increased apoptosis (P < 0.01) in both cell lines. We analyzed genes affected by CYP1A1 silencing and found that apoptosis-related BCL2 was significantly down-regulated. This study supports an oncogenic role for CYP1A1 in prostate cancer via promoter hypomethylation that is influenced by tobacco smoking, indicating CYP1A1 to be a promising target for prostate cancer treatment.

Caryophyllane sesquiterpenes inhibit DNA-damage by tobacco smoke in bacterial and mammalian cells

In the present study, the ability of the natural sesquiterpene β-caryophyllene (CRY) and its metabolite β-caryophyllene oxide (CRYO) to inhibit the genotoxicity of a condensate of cigarette smoke (CSC) was evaluated both in bacterial and mammalian cells. Also, the inhibition of the CSC-mediated STAT3 phosphorylation and intracellular oxidative stress was evaluated as potential chemopreventive mechanism. Under our experimental conditions, both the sesquiterpenes exhibited antimutagenic properties, being CRY the most potent compound. The antimutagenicity was highlighted in all experimental protocols, being particularly strong in the co- and post-treatments. The test substances also reduced the micronuclei frequency induced by CSC, with a major effectiveness of CRY. CRY was also able to reduce the CSC-mediated increase of the Y705- pSTAT3 levels, in spite of a lacking effect of CRYO. Furthermore, the sesquiterpenes CRY and CRYO displayed a moderate antioxidant activity, with a 25 % and 40 % inhibition of the ROS-levels increased by CSC, respectively. On the basis of these results, CRY seems to be a multi-target chemopreventive agent, although the genoprotective and antioxidant effects of CRYO suggest that both compounds deserve to be deeply investigated for a possible application in the prevention and treatment of different smoke-related ailments.

Use of HuH6 and other human-derived hepatoma lines for the detection of genotoxins: a new hope for laboratory animals?

Cell lines which are currently used in genotoxicity tests lack enzymes which activate/detoxify mutagens. Therefore, rodent-derived liver preparations are used which reflect their metabolism in humans only partly; as a consequence misleading results are often obtained. Previous findings suggest that certain liver cell lines express phase I/II enzymes and detect promutagens without activation; however, their use is hampered by different shortcomings. The aim of this study was the identification of a suitable cell line. The sensitivity of twelve hepatic cell lines was investigated in single cell gel electrophoresis assays. Furthermore, characteristics of these lines were studied which are relevant for their use in genotoxicity assays (mitotic activity, p53 status, chromosome number, and stability). Three lines (HuH6, HCC1.2, and HepG2) detected representatives of five classes of promutagens, namely, IQ and PhIP (HAAs), B(a)P (PAH), NDMA (nitrosamine), and AFB₁ (aflatoxin), and were sensitive towards reactive oxygen species (ROS). In contrast, the commercially available line HepaRG, postulated to be a surrogate for hepatocytes and an ideal tool for mutagenicity tests, did not detect IQ and was relatively insensitive towards ROS. All other lines failed to detect two or more compounds. HCC1.2 cells have a high and unstable chromosome number and mutated p53, these features distract from its use in routine screening. HepG2 was frequently employed in earlier studies, but pronounced inter-laboratory variations were observed. HuH6 was never used in genotoxicity experiments and is highly promising, it has a stable karyotype and we demonstrated that the results of genotoxicity experiments are reproducible.

2-amino-1-methyl-6-phenylimidazo(4,5-b) pyridine (PhIP) induces gene expression changes in JAK/STAT and MAPK pathways related to inflammation, diabetes and cancer

Background

2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP), a heterocyclic aromatic amine (HCA) formed in meat that is cooked at high temperatures and then ingested, can potentially be retained in human adipose tissues.

Methods

To determine if PhIP is bioactive in the adipocyte, we exposed a human adipocyte cell line,HepG2 and Caco-2 cells to low dose PhIP. Uptake and retention of PhIP was determined and cytotoxicity was assessed by the TUNEL assay. Relative expression of PhIP-activating genes (CYP1A1, CYP1A2, SULT1A1 and UGT1A1) was determined by RT-PCR and global expression changes were also examined.

Results

The percent retention of 0.1 μCi [¹⁴C]-PhIP over a 24 h period was significantly higher in the adipocyte than the HepG2 (p = 0.0001) and Caco-2 (p = 0.0007) cell lines. Cytotoxicity rates were 14.4 and 2.6 % higher compared to controls in Caco-2 and HepG2 cells (p < 0.001 and 0.054, respectively); no significant differences were detected in adipocyte cells (p = 0.18). Caco-2 and HepG2 cells, respectively, had significantly higher basal expression of CYP1A1 (p = 0.001, p = 0.003), SULT1A1 (p = 0.04, p < 0.001) and UGT1A1 (p < 0.001, p = 0.01) compared to the adipocyte. Exposure to 5nM PhIP did not significantly induce expression of these genes in any of the cell lines. Global gene expression analysis of mature adipocytes exposed to 5nM PhIP for 72 h resulted in statistically significant changes in 8 genes (ANGPTL2, CD14, CIDEA, EGR1, FOS, IGFBP5, PALM and PSAT1). Gene-gene interaction and pathway analysis indicates that PhIP modulates genes controlled by the STAT3 transcriptional factor and initiates leptin signaling via the JAK/STAT and MAPK pathway cascades. Early growth response 1 (EGR1) and prostaglandin synthase 2 (COX-2) were down-regulated via c-Fos, while insulin binding protein 5 (IBP5) was up regulated. Expression of transcription factors (ANGPTL2, HP, LEP, SAA1, SAA2), genes related to inflammation (SAA1, LEP), diabetes (IGFBP5) and cancer risk (SAA2) were also elevated upon exposure to 5 nM PhIP..

Conclusions

PhIP mediates gene expression changes within the adipocyte, and the pathways most affected are related to cancer and other chronic diseases. Further studies are needed on the relationship between dietary carcinogens such as PhIP with cancer, obesity and diabetes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-016-0111-0) contains supplementary material, which is available to authorized users.

Influence of selected anti-cancer drugs on the induction of DNA double-strand breaks and changes in gene expression in human hepatoma HepG2 cells

In chemotherapy, various anti-cancer drugs with different mechanisms of action are used and may represent different risk of undesirable delayed side effects in treated patients as well as in occupationally exposed populations. The aim of the present study was to evaluate genotoxic potential of four widely used anti-cancer drugs with different mechanisms of action: 5-fluorouracil (5-FU), cisplatin (CDDP) and etoposide (ET) that cause cell death by targeting DNA function and imatinib mesylate (IM) that inhibits targeted protein kinases in cancer cells in an experimental model with human hepatoma HepG2 cells. After 24 h of exposure all four anti-cancer drugs at non-cytotoxic concentrations induced significant increase in formation of DNA double strand breaks (DSBs), with IM being the least effective. The analysis of the changes in the expression of genes involved in the response to DNA damage (CDKN1A, GADD45A, MDM2), apoptosis (BAX, BCL2) and oncogenesis (MYC, JUN) showed that 5-FU, CDDP and ET upregulated the genes involved in DNA damage response, while the anti-apoptotic gene BCL2 and oncogene MYC were downregulated. On the contrary, IM did not change the mRNA level of the studied genes, showing different mechanism of action that probably does not involve direct interaction with DNA processing. Genotoxic effects of the tested anti-cancer drugs were observed at their therapeutic concentrations that may consequently lead to increased risk for development of delayed adverse effects in patients. In addition, considering the genotoxic mechanism of action of 5-FU, CDDP and ET an increased risk can also not be excluded in occupationally exposed populations. The results also indicate that exposure to 5-FU, CDDP and ET represent a higher risk for delayed effects such as cancer, reproductive effects and heritable disease than exposure to IM.

Protective activity of probiotic bacteria against 2-amino-3-methyl-3H-imidazo[4,5-f]quinoline (IQ) and 2-amino-1-methyl-6-phenyl-1H-imidazo[4,5-b]pyridine (PhIP) - an in vitro study

Heterocyclic aromatic amines (HAAs) are carcinogenic compounds present in a typical Western diet rich in thermally processed meat. These nutritional factors can modulate the cytotoxicity of faecal water (FW) and induce tumours in the human gastrointestinal tract. Supplementation with probiotics is promising in terms of reducing the harmful effects of HAAs in the human body. The aim of the study was in vitro assessment of the protective activity of the probiotic strains Lb. rhamnosus 0900, Lb. rhamnosus 0908, Lb. casei 0919 and Lb. casei DN 114001 against IQ (2-amino-3-methyl-3H-imidazo[4,5-f]quinoline) and PhIP (2-amino-1-methyl-6-phenyl-1H-imidazo[4,5-b]pyridine) after incubation with faeces from 15 persons aged 4 months to 82 years (children, adults and the elderly). The highest mean cytotoxicity of FW was observed for the elderly (63.2% ± 3.7%) and the lowest for children (28.0% ± 9.5%), as estimated by a neutral red uptake assay. The probiotics lowered the average cytotoxicity of FW exposed to IQ or PhIP. The concentration of IQ and PhIP in FW was most effectively reduced by Lb. rhamnosus 0900 (47.5%) and Lb. casei 0919 (45.8%), respectively, as determined by high -performance liquid chromatography. All the tested strains bound PhIP to a higher extent than IQ. In an alkaline comet assay, Lb. casei 0919 and Lb. rhamnosus 0908 displayed the strongest protective effect against IQ and PhIP (up to 80% reduction of DNA damage). Also in a comet assay, Lb. rhamnosus 0908 exhibited antioxidative activity toward H2O2 and PhIP (up to 63% and 69.5% reduction of oxidative DNA damage, respectively). The protective activity of the probiotic strains was specific to a given person's FW, which implies the involvement of intestinal microbiota in the process.

Identification of fipronil metabolites by time-of-flight mass spectrometry for application in a human exposure study

Fipronil is a phenylpyrazole insecticide commonly used in residential and agricultural applications. To understand more about the potential risks for human exposure associated with fipronil, urine and serum from dosed Long Evans adult rats (5 and 10mg/kg bw) were analyzed to identify metabolites as potential biomarkers for use in human biomonitoring studies. Urine from treated rats was found to contain seven unique metabolites, two of which had not been previously reported-M4 and M7 which were putatively identified as a nitroso compound and an imine, respectively. Fipronil sulfone was confirmed to be the primary metabolite in rat serum. The fipronil metabolites identified in the respective matrices were then evaluated in matched human urine (n=84) and serum (n=96) samples from volunteers with no known pesticide exposures. Although no fipronil or metabolites were detected in human urine, fipronil sulfone was present in the serum of approximately 25% of the individuals at concentrations ranging from 0.1 to 4ng/mL. These results indicate that many fipronil metabolites are produced following exposures in rats and that fipronil sulfone is a useful biomarker in human serum. Furthermore, human exposure to fipronil may occur regularly and require more extensive characterization.

Egg consumption is associated with increased risk of ovarian cancer: Evidence from a meta-analysis of observational studies

BACKGROUND

The findings of epidemiologic studies on the association between egg consumption and ovarian cancer risk remain conflicting. The aim of this meta-analysis was to investigate whether an association exists between egg intake and ovarian cancer risk in epidemiologic studies.

METHODS

A literature search was carried out using PUBMED, EMBASE, and Cochrane Library Central database for all medical literature published in English-language journals up to August 2013. Before meta-analysis, between-study heterogeneity and publication bias were assessed using adequate statistical tests. Fixed-effect and random-effect models were used to estimate summary relative risks (RR) and the corresponding 95% confidence intervals (CIs). Subgroup analyses and sensitivity analysis were also performed.

RESULTS

A total of 12 eligible studies (six case-control studies and six cohort studies) were included, involving 629,453 subjects and 3728 ovarian cancer cases. We found that high egg intake (comparing the highest with the lowest category) was associated with a significant increased risk of ovarian cancer (RR = 1.21, 95% CI [1.06, 1.38]). When we examined whether the associations differed by study type, statistically significant effect of egg intake on ovarian cancer was observed among case-control studies (RR = 1.22, 95% CI [1.03, 1.43]), but not among cohort studies (RR = 1.20, 95% CI [0.97, 1.48]).

CONCLUSIONS

Our findings suggest that egg consumption may increase ovarian cancer risk. Additional studies, especially large prospective cohort studies, are warranted to confirm the findings.