Genotoxic effects of 2-trans-hexenal in human buccal mucosa cells in vivo

Food-Borne Chemical Carcinogens and the Evidence for Human Cancer Risk

Commonly consumed foods and beverages can contain chemicals with reported carcinogenic activity in rodent models. Moreover, exposures to some of these substances have been associated with increased cancer risks in humans. Food-borne carcinogens span a range of chemical classes and can arise from natural or anthropogenic sources, as well as form endogenously. Important considerations include the mechanism(s) of action (MoA), their relevance to human biology, and the level of exposure in diet. The MoAs of carcinogens have been classified as either DNA-reactive (genotoxic), involving covalent reaction with nuclear DNA, or epigenetic, involving molecular and cellular effects other than DNA reactivity. Carcinogens are generally present in food at low levels, resulting in low daily intakes, although there are some exceptions. Carcinogens of the DNA-reactive type produce effects at lower dosages than epigenetic carcinogens. Several food-related DNA-reactive carcinogens, including aflatoxins, aristolochic acid, benzene, benzo[a]pyrene and ethylene oxide, are recognized by the International Agency for Research on Cancer (IARC) as causes of human cancer. Of the epigenetic type, the only carcinogen considered to be associated with increased cancer in humans, although not from low-level food exposure, is dioxin (TCDD). Thus, DNA-reactive carcinogens in food represent a much greater risk than epigenetic carcinogens.

Scientific Opinion on Flavouring Group Evaluation 200, Revision 1 (FGE.200 Rev.1): 74 α,β-unsaturated aliphatic aldehydes and precursors from chemical subgroup 1.1.1 of FGE.19

The Panel on Food Additives and Flavourings of the European Food Safety Authority was requested to evaluate the genotoxic potential of 74 flavouring substances from subgroup 1.1.1 of FGE.19 in the Flavouring Group Evaluation 200 Revision 1 (FGE.200 Rev1). In FGE.200, genotoxicity studies were provided for one representative substance, namely hex-2(trans)-enal [FL-no: 05.073], and for other two substances in the same subgroup, namely 2-dodecenal [FL-no: 05.037] and 2-nonenal [FL-no: 05.171]. The Panel concluded that the concern still remains with respect to genotoxicity for the substances of this subgroup and requested an in vivo Comet assay performed in duodenum and liver for hex-2(trans)-enal [FL-no: 05.073]. For the two other representative substances of subgroup 1.1.1 (nona-2(trans),6(cis)-dienal [FL-no: 05.058] and oct-2-enal [FL-no: 05.060]), the Panel requested a combined in vivo Comet assay and micronucleus assay. These data have been provided and are evaluated in the present opinion FGE.200 Rev1. Industry submitted genotoxicity studies on trans-2-octenal [FL-no: 05.190], instead of oct-2-enal [FL-no: 05.060]. Based on the available data, the Panel concluded that the concern for genotoxicity can be ruled out for hex-2(trans)-enal [FL-no: 05.073], trans-2-octenal [FL-no: 05.190] and nona-2(trans),6(cis)-dienal [FL-no: 05.058], therefore all the 74 substances [FL-no: 02.020, 02.049, 02.050, 02.090, 02.112, 02.137, 02.156, 02.192, 02.210, 02.231, 05.037, 05.058, 05.060, 05.070, 05.072, 05.073, 05.076, 05.078, 05.102, 05.109, 05.111, 05.114, 05.120, 05.144, 05.150, 05.171, 05.172, 05.179, 05.184, 05.189, 05.190, 05.191, 05.195, 06.025, 06.031, 06.072, 09.054, 09.097, 09.109, 09.119, 09.146, 09.233, 09.244, 09.247, 09.276, 09.277, 09.303, 09.312, 09.385, 09.394, 09.395, 09.396, 09.397, 09.398, 09.399, 09.400, 09.410, 09.411, 09.469, 09.482, 09.489, 09.492, 09.493, 09.498, 09.678, 09.701, 09.719, 09.741, 09.790, 09.841, 09.866, 09.947, 09.948, 13.004] can be evaluated through the Procedure for flavouring substances.

Genotoxicity of lipid oxidation compounds

Lipid peroxidation, the oxidative degradation of membrane lipids by reactive oxygen species generates a large variety of breakdown products such as alkanes, aldehydes, ketones, alcohols, furans and others. Due to their reactivity aldehydes (alkanals, 2-alkenals, 2,4-alkadienals, 4-hydroxyalkenals) received a lot of attention, in particular because they can diffuse from the site of formation and interact with proteins and nucleic acids thus acting as second toxic messengers. The major aldehydic peroxidation product of membrane lipids is 4-hydroxynonenal (HNE). Since HNE and other 4-hydroxyalkenals are strong alkylating agents they have therefore been considered to be the biologically most important peroxidation products. Although initially research focused on the toxicological potential of these compounds it is now well known that they play also a crucial role in cell signaling under physiological and pathophysiological conditions. Thus, it is obvious that the biological effects will be determined by the intracellular concentrations which can trigger adaptation, DNA damage and cell death. This review will not cover all these aspects but will concentrate on the genotoxic properties of selected lipid oxidation products important in the context of pathophysiological developments together with a chapter on epigenetic modifications.

Phenotypic and genotypic characterization of antioxidant enzyme system in human population exposed to radiation from mobile towers

In the present era, cellular phones have changed the life style of human beings completely and have become an essential part of their lives. The number of cell phones and cell towers are increasing in spite of their disadvantages. These cell towers transmit radiation continuously without any interruption, so people living within 100s of meters from the tower receive 10,000 to 10,000,000 times stronger signal than required for mobile communication. In the present study, we have examined superoxide dismutase (SOD) enzyme activity, catalase (CAT) enzyme activity, lipid peroxidation assay, and effect of functional polymorphism of SOD and CAT antioxidant genes against mobile tower-induced oxidative stress in human population. From our results, we have found a significantly lower mean value of manganese superoxide dismutase (MnSOD) enzyme activity, catalase (CAT) enzyme activity, and a high value of lipid peroxidation assay in exposed as compared to control subjects. Polymorphisms in antioxidant MnSOD and CAT genes significantly contributed to its phenotype. In the current study, a significant association of genetic polymorphism of antioxidant genes with genetic damage has been observed in human population exposed to radiations emitted from mobile towers.

Assessment of DNA damage as an index of genetic toxicity in welding microenvironments among iron-based industries

Welding is used extensively in different industries. Welders are always at a risk of exposure to a number of gases and metal-containing fumes in their respective microenvironments in which they work. Welding fumes consist of a wide range of complex metal oxide particles which can deposit in different parts of their bodies causing serious health problems. In the present study, 35 welders (age: 33.80 ± 1.04 years) from two iron-based industries have been assessed for DNA damage in peripheral blood lymphocytes using single-cell gel electrophoresis. An equal number of subjects (N = 35; age: 30.40 ± 1.51 years) matched to exposed subjects with respect to sex, age, socioeconomic status, smoking, and alcoholic habits were taken as controls. The results revealed that the damaged cell frequency (DCF) and mean comet tail length (CTL) in welders were significantly higher as compared to the controls (DCF: 69.74 ± 1.68 vs. 31.14 ± 1.67 and CTL: 29.21 ± 1.48 vs. 1.47 ± 0.08; p < 0.05). The effect of confounding factors such as age, duration of exposure, smoking, and drinking habits was also studied. Blood lead levels also showed a positive correlation with duration of exposure and CTL, and the overall results indicated an increased genetic damage as an index of genotoxicity in workers occupationally engaged in welding microenvironments.

QSAR models to predict mutagenicity of acrylates, methacrylates and alpha,beta-unsaturated carbonyl compounds

OBJECTIVE

The purpose of this study is to develop a quantitative structure-activity relationship (QSAR) model that can distinguish mutagenic from non-mutagenic species with alpha,beta-unsaturated carbonyl moiety using two endpoints for this activity - Ames test and mammalian cell gene mutation test - and also to gather information about the molecular features that most contribute to eliminate the mutagenic effects of these chemicals.

METHODS

Two data sets were used for modeling the two mutagenicity endpoints: (1) Ames test and (2) mammalian cells mutagenesis. The first one comprised 220 molecules, while the second one 48 substances, ranging from acrylates, methacrylates to alpha,beta-unsaturated carbonyl compounds. The QSAR models were developed by applying linear discriminant analysis (LDA) along with different sets of descriptors computed using the DRAGON software.

RESULTS

For both endpoints, there was a concordance of 89% in the prediction and 97% confidentiality by combining the three models for the Ames test mutagenicity. We have also identified several structural alerts to assist the design of new monomers.

SIGNIFICANCE

These individual models and especially their combination are attractive from the point of view of molecular modeling and could be used for the prediction and design of new monomers that do not pose a human health risk.

Assessment of DNA damage and its modulation by dietary and genetic factors in smokers using the Comet assay: a biomarker model

Methods are needed to assess exposure to genotoxins in humans and to improve understanding of dietary cancer prevention. The Comet assay was used to detect smoking-related exposures and dietary modulations in target tissues. Buccal scrapings, blood and faeces were collected from 38 healthy male volunteers (smokers and non-smokers) during a dietary intervention study with bread supplemented with prebiotics+/-antioxidants. GSTM1-genotype was determined with PCR. Buccal and peripheral lymphocytes were analysed for DNA damage using the Comet assay. Genotoxicity of faecal water (FW) was assayed in human colon HT29 clone 19A cells. 'Tail intensity' (TI) was used as a quantitative indicator of DNA damage in the Comet assay. Intervention with bread reduced DNA damage in lymphocytes of smokers (8.3+/-1.7% TI versus 10.2+/-4.1% TI, n=19), but not of non-smokers (8.6+/-2.8% TI versus 8.3+/-2.7% TI, n=15). Faecal water genotoxicity was reduced only in non-smokers (9.4+/-2.9% TI versus 18.9+/-13.1% TI, n=15) but not in smokers (15.5+/-10.7% TI versus 20.4+/-14.1% TI, n=13). The Comet assay was efficient in the detection of both smoking-related exposure (buccal cells) and efficacy of dietary intervention (faecal samples). Smokers and non-smokers profited differently from the intervention with prebiotic bread+/-antioxidants. Stratification of data by genotype enhanced specificity/sensitivity of the intervention effects and contributed important information on the role of susceptibility.

New revival of an old biomarker: characterisation of buccal cells and determination of genetic damage in the isolated fraction of viable leucocytes

Buccal cells serve as targets to assess oral exposures. We have refined isolation methods to characterise yield, viabilities, types of cells and baseline levels of genetic damage. Buccal cells were isolated from mouthwashes of 27 volunteers. They were characterised microscopically and different methods (using antibody-labelled magnetic beads, filtration and gradient centrifugation) were compared to separate epithelial cells from leucocytes. Viability of cells, DNA damage, and activity of glutathione S-transferase (GST) were measured with dye exclusion, microgelelectrophoresis, and biochemically. Mouthwashes contained approximately equal amounts of epithelial cells and leucocytes with detectable GST-activities. Repetitive determinations with mouthwashes from four individuals yielded per sample (3.5+/-1.4)x10(6) epithelial cells and (4.7+/-3.9)x10(6) leucocytes with viabilities of 8 and 94%, respectively. Epithelial cells could not be isolated using antibody-labelled beads, but cell separation with the leukocyte-specific antibody CD45 succeeded, yielding 37% leucocytes with a purity of 95% and viability of 65%. Filtering the mouthwash through a 10 microm filter yielded 57% leucocytes, with 86% purity and 94% viability. When using density gradient centrifugation as the separation method, the recovery of leucocytes was low (22%), but good results were scored for purity (95%) and cell viability (88%). This method was used to isolate leucocytes, which were then subjected to a micro-scale comet assay-modification. It was found that buccal leucocytes obtained from smokers had more DNA damage than cells from non-smokers. In conclusion, suspensions of buccal cells consist in approximately equal parts of epithelial cells and leucocytes. Only leucocytes are sufficiently viable for measuring parameters of cytotoxicity and genotoxicity or for studying modulation of gene expression. The cells are useful targets of non-invasive biomarkers, which could be incorporated as tools in many types of intervention studies.

Internal hazards: baseline DNA damage by endogenous products of normal metabolism

Recent improvements in the ability to detect chemically modified bases in DNA have revealed that not only does the genetic material incur damage by foreign chemicals, but that it also sustains injury by reactive products of normal physiological processes. This review summarises current understanding of the DNA-damaging potential of various substances of endogenous origin, including oxidants, lipid peroxidation products, alkylating agents, estrogens, chlorinating agents, reactive nitrogen species, and certain intermediates of various metabolic pathways. The strengths and weaknesses of the existing database for DNA damage by each class of substance are discussed, as are future strategies for resolving the difficult question of whether endogenous chemicals are significant contributors to spontaneous mutagenesis and cancer development in vivo.