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Human exposure to mixtures of chemicals is ubiquitous, but regulation has long focused on single compounds. (1) Today investigators are interested in predicting the effects of chemical mixtures based on [...]

Shiga toxins (Stx) are potent AB5 cytotoxins that inhibit eukaryotic protein synthesis, eventually leading to host cell death (1). Infections with bacteria that produce Stx result in hemorrhagic colitis and [...]

BACKGROUND: Exposure to disinfection by-products (DBPs) in drinking water has been associated with cancer risk. A recent study (Villanueva et al. 2007; Am J Epidemiol 165:148-156) found an increased bladder [...]

OBJECTIVES: According to the 2007 National Research Council report Toxicology for the Twenty-First Century, modern methods (e.g., 'omics,' in vitro assays, high-throughput testing, computational methods) will lead to the emergence [...]

Over the past decade, issues of animal use and care in toxicology research and testing have become one of the fundamental concerns for both science and ethics. Emphasis has been given to the use of alternatives to mammals in testing, research and education. Because plants are direct recipients of agrotoxics and therefore important material for genetic tests and for environmental monitoring of places affected by such pollutants, three doses each of the pesticides, dithane (0.196, 0.391, 0.782 % solution), malathion (0.034, 0.069, 0.137 % solution) and garden ripcord (1.015, 2.030, 4.060 % solution) were assessed for cytotoxicity and genotoxicity to onion root tip cells. The doses represented the LC50 (dose that inhibited 50 % of seeds from germinating), 1/2 LC50 and 1/4 LC50 for each pesticide that were determined in a preliminary dose selection experiment. Onion seeds were germinated on moistened filter paper in a petri dish at room temperature until radicles appeared. Germinated seeds were exposed to three concentrations of each pesticide for 20 hours. About 12mm length of root tip was cut, fixed in acetic alcohol, washed in ice cold water, hydrolyzed in warm 1N hydrochloric acid, stained with aceto-carmine and squashed on glass microscope slide. About 3000 cells were scored for each treatment and classified into interphase and normal or aberrant division stage. Cytotoxicity was determined by calculating the mitotic indices and comparing the mitotic indices of treated cells at each dose of each pesticide with that of the negative control group. The mitotic index of the negative control group was reduced to half or less, at the two highest doses of all three pesticides. All three pesticides were therefore cytotoxic to the onion root tip cells. Genotoxicity was measured by comparing the number of cells/1000 in the aberrant division stages at each dose of each pesticide with the number of such cells in the negative control group using the Mann-Whitney statistical test. Dithane was genotoxic (P< 0.05), inducing multipolar anaphases and telophases and lagging chromosomes. Malathion was genotoxic (P< 0.05), inducing lagging chromosomes. Garden ripcord was not genotoxic. Key words: Allium cepa, cytotoxicity, genotoxicity, pesticides, INTRODUCTION Pesticides are used all over the world and, in recent years, their use has increased spectacularly because it has greatly improved agricultural yield through inhibition of disease causing organisms [...]

Genotoxicity screening sensors that measure DNA damage from metabolism of arylamines were developed and evaluated. The sensors feature ultrathin films containing DNA and N-acetyltransferase (NAT) on pyrolytic graphite (PG) electrodes. NAT in the film catalyzed the conversion of the arylamine 2-aminofluorene (2-AF) to 2-acetylaminofluorene (2-AAF) by acetyl coenzyme A (AcCoA) dependent N-acetylation, as verified by liquid chromatography. DNA damage in the films from exposure to reactive 2-AF metabolites was measured subsequent to the enzyme reaction using catalytic voltammetric oxidation with Ru[(bpy).sub.3.sup.2+]. Square wave voltammetric (SWV) peaks increased with enzyme reaction time, and relative DNA damage rates at pH 5.8 were measured within 2 min. Control incubations of DNA/NAT films without AcCoA gave no significant sensor response. CapLC-MS/MS analysis of 2-AAF/DNA reaction products was consistent with 2-AF-guanine adducts formed in the films. DNA damage occurred more rapidly under weakly acidic conditions (pH 5.5-5.8) than at neutral pH, suggesting that genotoxicity from arylamine metabolism by NAT could be more significant in slightly acidic environments.

Cytolethal distending toxins (CDTs) are inhibitory cyciomodulins, which block eukaryotic cell proliferation and are produced by a diverse group of Gram-negative bacteria, including Escherichia coil strains associated with intestinal and extraintestinal infections. However, the mode of transmission of the toxin gene clusters among diverse bacterial pathogens is unclear. We found that Cdt-I produced by enteropathogenic E. coli strains associated with diarrhea is encoded by a lambdoid prophage, which is inducible and infectious. The genome of Cdt-l converting phage (CDT-1[PHI]) comprises 47,021. nucleotides with 60 predicted ORFs organized into six genomic regions encoding the head and tail, virulence, integrase, unknown functions, regulation, and lysis. The genomic organization of CDT-1[PHI] is similar to those of SfV, a serotype-converting phage of Shigella flexneri, and UTI89, a prophage identified in uropathogenic E. coli. Besides the cdtl gene cluster, the virulence region of CDT-1[PHI] genome contains sequences homologous to a truncated cycle inhibiting factor and a type 3 effector protein. Mutation analysis of susceptible E. coil strain C600 suggested that the outer membrane protein OmpC is a putative receptor for CDT-1[PHI]. CDT-1[PHI] genome was also found to integrate into the host bacterial chromosome forming lysogens, which produced biologically active Cdt-I. Furthermore, phage induction appeared to cause enhanced toxigenicity of the E. coli strains carrying lysogenic CDT-1[PHI]. Our results suggest that CDT-1[PHI] is the latest member of a growing family of lambdoid phages encoding bacterial cyclomodulins and that the phage may have a role in horizontal transfer of these virulence genes. bacterial genotoxin | converting phage | cyclornodulins

The goal of this study was to create an in vitro cell culture system that captures essential features of the in vivo erythroid micronucleus (MN) genotoxicity assay, thus enabling increased throughput and controlled studies of the hematopoietic DNA damage response. We show that adult bone marrow (BM) cultures respond to erythropoietin, the principal hormone that stimulates erythropoiesis, with physiological erythropoietic proliferation, differentiation, and enucleation. We then show that this in vitro erythropoietic system clearly signals exposure to genotoxicants through erythroid MN formation. Furthermore, we determined that DNA repair-deficient ([MGMT.sup.-l-]) BM displayed sensitivity to genotoxic exposure in vivo compared with WT BM and that this phenotypic response was reflected in erythropoietic cultures. These findings suggest that this in vitro erythroid MN assay is capable of screening for genotoxicity on BM in a physiologically reflective manner. Finally, responses to genotoxicants during erythroid differentiation varied with exposure time, demonstrating that this system can be used to study the effect of DNA damage at specific developmental stages. in vitro toxicity screens | genotoxicity | hematopoiesis | DNA damage and repair

A new quantitative method is reported for the detection of prophage induction which directly measures the excision of the prophage from the host chromosome. This new method is based on the use of two converging oligonucleotides, corresponding to each side of the a11P sequence of a temperature phage to amplify the intervening DNA segment by real time PCR.

1,[N.sup.6]-ethanoadenine (EA) forms through the reaction of adenine in DNA with the antitumor agent 1,3-bis(2-chloroethyl)-1-nitrosourea, a chemotherapeutic used to combat various brain, head, and neck tumors. Previous studies of the toxic and mutagenic properties of the DNA adduct EA have been limited to in vitro experiments using mammalian polymerases and have revealed the lesion to be both miscoding and genotoxic. This work explores lesion bypass and mutagenicity of EA replicated in vivo and demonstrates that EA is neither toxic nor mutagenic in wild-type Escherichia coli. Although the base excision repair glycosylase enzymes of both humans and E. coli possess a weak ability to act on the lesion in vitro, an in vivo repair pathway has not yet been demonstrated. Here we show that an enzyme mechanistically unrelated to DNA glycosylases, the adaptive response protein AIkB, is capable of acting on EA via its canonical mechanism of oxidative dealkylation. The reaction alleviates the unrepaired adduct's potent toxicity through metabolism at the C8 position (attached to N1 of adenine), producing a nontoxic and weakly mutagenic [N.sup.6] adduct. AIkB is shown here to be a geno-protective agent that reduces the toxicity of DNA damage by converting the primary adduct to a less toxic secondary product. 1,3-bis(2-chloroethyl)-1-nitrosourea | DNA repair

Detection of DNA adducts can serve as a basis for genotoxicty screening of new chemicals and drugs. We report here a simple, sensitive procedure for this purpose using films containing DNA and a biocatalyst to mimic the metabolic action of human liver cytochrome P450s. DNA adducts formed from an in-situ-generated toxic metabolite (styrene oxide) were detected at subpicomole levels after neutral thermal hydrolysis of the DNA films and analysis with capillary liquid chromatography with online column preconcentration and MS/MS detection. An on-line column switching system allowed for increased sample loading volume and analyte preconcentration. This approach provides an estimate of the relative rate of DNA damage.

Byline: M. V. Sukhanova (1), O. I. Lavrik (1), S. N. Khodyreva (1) Keywords: Poly(ADP-ribose) polymerase-1 (PARP-1); poly(ADP-ribosyl)ation; base excision repair; protein--nucleic acid interactions Abstract: Poly(ADP-ribose) polymerase-1 (PARP-1), a nuclear protein of higher eukaryotes, specifically detects strand breaks in DNA. The enzyme is activated in the presence of such breaks and synthesizes poly(ADP-ribose) covalently bound to certain proteins, with PARP-1 itself being the main acceptor. This protein is involved in the majority of DNA-dependent processes, including replication, recombination, repair, and cell death (apoptosis and necrosis). Poly(ADP-ribosyl)ation of proteins is regarded as a mechanism which induces a signal of DNA damage and modulates the function of proteins in response to genotoxic actions. Attention in this review is focused on the role of PARP-1 and poly(ADP-ribosyl)ation in base excision repair (BER), the main process of DNA break repair. The main putative functions of PARP-1 in this process are also considered, namely, its functions as a factor initiating the BER protein complex, a temporary protector of DNA ends, a factor modulating chromatin structure through poly(ADP-ribosyl)ation of histones, and a signal in the mechanism recognizing the degree of DNA damage in the cell. Author Affiliation: (1) Institute of Chemical Biology and Fundamental Medicine, Siberian Division, Russian Academy of Sciences, Novosibirsk, 630090, Russia Article History: Registration Date: 11/12/2004

Interdisciplines are hybridized knowledge fields that are constituted by intentionally porous organizational, epistemological, and political boundaries. To date, these processes are not well understood. This article uses the case of genetic toxicology and draws on framing theory to examine how interdisciplines are made. I argue that the concept of 'collective action frames' and attention to framing processes (Snow et al. 1986) and frame resonance (Snow and Benford 1988) adds much needed refinement to sociologists' understanding of the permeable boundaries that accompany the development of interdisciplines. I develop this argument through an analysis of public lectures, expert testimony, articles, and editorials produced by scientists promoting genetic toxicology during the period 1968-1973. I show how these researchers made the rhetorical case for genetic toxicology by amplifying, extending, and translating a set of interrelated collective action frames and why, in the context of shifting institutional opportunities, framing processes were integral to the rapid consolidation of a new and intensely interdisciplinary environmental health science. The article concludes by noting the study's implications for integrative research on science and social movements.

Research has been conducted on chromiumchromium(VI) mutagenicity. The study of mutational spectrum and the role of oxidative damage and chromium-DNA adducts in chromium(VI) mutagenicity activated by biologically relevant concentrations of ascorbate has been carried out, and the differences in genotoxic and mutagenic responses to chromium-DNA adducts between bacterial and human cells have been investigated and discussed.

Research has been conducted on acrolien, a member of the alpha, beta-unsaturated aldehyde family. The role of alpha-OH-1,N (super)2 ?propanodeoxyguanosine adduct in the genotoxicity of this acrolein has been investigated via comparison of alpha-OH-1,N (super)2 ?propanodeoxyguanosine, gamma-OH-1,N (super)2 ?propanodeoxyguanosine and propanodeoxyguanosine by in vitro primer extension studies and in human cells and the details are reported.

Research has been conducted on the functional Cdc2-cyclin B kinase complex. The evidence that this complex is required for the homologous recombination and is necessary to protect cells from the ionizing radiation genotoxic consequences is presented.

An Arabidopsis mutant (mkp1) hypersensitive to genotoxic stress treatments because of disruption of mitogen-activated protein kinase phosphatase (AtMKP) has been identified. A gene that encodes an Arabidopsis homolog of AtMKP is necessary for Arabidopsis genotoxic stress relief. It appears that the MAP kinase cascade has a vital role in genotoxic stress signaling in plants and that AtMKP1 is a vital regulator of MAP kinase activity in vivo. It probably determines outcome of the cellular reaction and the level of genotoxic resistance.

Results point out that 30% of the urinary metabolites contain derivatives of 7-oxo-benz[d]anthracene-3,4-dicarboxylic acid which, arise from benzo[alpha]pyrene (BP) by ring opening pathway. Data reveal that anhydride of the derivative induces DNA dmages thereby suggesting indirect toxicity effect of BP.

The methods and results of p53 induction assays on various chemicals tested for carcinogenicity on rodents are discussed. Comparisons among the p53 induction assay and other carcinogenicity testing indicate high reliability for p53 induction assay.

Research presented concerns the effects of an environmental disruption of genes in a developmental pathway on the likelihood of deformity or cancer. To understand the networks of genes that are critical in development, the scientists study the impact of exposures to toxins on the Hedgehog-Patched-GLI pathway.

Centrosomes and their associated microtubules direct events during mitosis and control the organization of animal cell structures and movement during interphase. The centrosome replicates during the cell cycle, directs the assembly of bipolar mitotic spindles, and plays an important role in maintaining the fidelity of cell division. Recently, tumor suppressors such as p53 and retinoblastoma protein pRB have been localized to the centrosome in a cell cycle-dependent manner. Immunofluorescence microscopy and analysis of isolated centrosomes now provide evidence that BRCA1 protein, a suppressor of tumorigenesis in breast and ovary, also is associated with centrosomes during mitosis. Our results indicate that BRCA1 localizes with the centrosome during mitosis and coimmunoprecipitates with [Gamma]-tubulin, a centrosomal component essential for nucleation of microtubules. Furthermore, [Gamma]-tubulin associates preferentially with a hypophosphorylated form of BRCA1.

An industrial chemical called 5-ethylidene-2-norbornene (ENB) was found to be incapable of inducing a mutagenic or clastogenic activity. ENB failed to produce mutagenic activity with or without metabolic activation from a Salmonella typhirium reverse assay with TA98, TA100, TA1535, TA1537 and TA1538 strains. Such result also holds for a Chinese hamster ovary (CHO) cell forward gene mutation assay (HGPRT locus), a sister chromatid exchange test and a cytogenic study.

Higher plants used extensively in traditional medicines are increasingly being screened for their role in modulating the activity of environmental genotoxicants. The property of preventing carcinogenesis has been reported in many plant extracts. The observation of a close association between carcinogenesis and mutagenesis has extended the survey to include plant extracts and plant products able to modify the process of mutagenesis, which involves alteration in the genetic material. Natural plant products may, apart from inducing mutations, modify the action of other known mutagens on the living organisms by 1) activating the existing mutagens within the cell, 2) inhibiting the production of mutagens in the cell, 3) synergising the activity of existing mutagens, or 4) activating the promutagens within the cell into mutagens. This review deals with data obtained in the course of research on the modulatory effects of plant extracts on mutagenesis and clastogenesis, two genotoxic phenomena associated with carcinogenesis. In screening for antimutagenic effects, extracts of different plant parts have been used, ranging from leafy vegetables, fruits, and underground storage organs to whole plants. The extracts were prepared mainly in water or organic solvents. Several of these assays have indicated the involvement of certain factors that are intrinsic components of the extracts, ranging from specific compounds like ascorbic acid to vegetable fibres which could act as nonspecific redox agents, free radical scavengers, or ligands for binding metals or toxic principles. The possible ways in which inhibitors of mutagenesis can act include the inhibition of interaction between genes and biochemically reactive mutagens and the inhibition of metabolic activation of indirectly acting mutagens. The effects of toxicants can be observed at the level of chromosomes (clastogenesis) through alterations in chromosome structure (chromosomal aberrations) and number (aneuploidy, polyploidy). A wide range of short-term and long-term screening procedures is available. The most common ones use higher plants or rodents in vivo as test systems for monitoring chromosomal aberrations. Experiments with a number of crude vegetable and fruit extracts have demonstrated their anticlastogenic activities against known cytotoxic agents. The individual components of the extracts - e.g., sulfhydryl and flavonoid compounds, gallic acid, ellagic acid, mucic acid, citric acid, reducing sugars, tannin - are observed to have an additive interaction with the major constituents chlorophyll and ascorbic acid, when modulating the effects of the clastogens. Under certain conditions, plant products may induce mutagenic effects, due to the presence of multiple biological properties. Some inhibitors can stimulate simultaneously both enhancing and detoxifying mechanisms, e.g., inducers of coordinated enzyme activities. Many oxidants can, depending on the redox potential, either accept or donate electrons, rendering them protective or harmful. Plants also play an active role in the accumulation, metabolism, and environmental distribution of xenobiotics. The property of plants to activate promutagens that may enter the food chain is of great significance in view of the large number and types of chemicals to which the plants are exposed. A promutagen is a chemical that is not mutagenic itself but that can be biologically transformed by a plant system into a mutagen. Several methods for studying promutagens from plants were developed both in vivo and in vitro, including plant cell-free systems. Both mutagens and antimutagens can be extracted from the same plant extract depending on the nature of solvents used for extraction. Interaction between inhibitors may lead to synergistic effects. Such combined action may take place through the different inhibitors acting at different levels or being localised at different cellular areas. The greater protection afforded by crude plant extract as compared with an equivalent amount of the purified or synthetic ingredients, as observed with Phyllanthus emblica L. and Beta vulgaris L. var. benghalensis Hort., may be related to this phenomenon. Specific biological action of a drug is due to its specific binding to a functional molecular receptor. In complex plant extracts, the variable observed effects can be attributed to the many chemically reactive species that are formed during the processing and ingestion of the extract, which could act as non-specific redox agents, scavengers of free radicals, and ligands for binding to toxicants. The final effects are obviously the outcome of interactions between the components and their individual and collective interaction with the toxicant. The specificity and efficacy of such responses will be influenced also by the physiological factors influencing the plants and the process of administration of the extract. In utilizing pharmacologically active herbs, both beneficial and potential adverse effects must be taken into account. The actual dose and form of the plant also need to be worked out., II. Introduction Traditional medicines based on plants have been useful in discovering new drugs from natural products, in helping to identify new biochemical loci for drug action, and in developing [...]

A study was conducted on four bacterial genotoxicity assays recommended for screening large sample numbers, namely, Salmonella/microsome assay, SOS Chromotest, Microscreen phage-induction assay and differential DNA repair test. The assays are being eyed for several environmental applications. SOS Chromotest showed to be the most efficient for routine screening of water samples.

Toxicity induction in Escherichia coli in response to chemical toxicants, when regulated by a uspA'::lux fused gene, exhibits clear distinctions among toxicants. This differential response is useful to detect toxicants. Toxicant response of this gene is similar to that of the thermal shock-responsive gene fusion grpE'::lux, except that the grpE'::lux strain exhibits a greater magnitude of induction.

A study using NMR was conducted to determine the oncogenetic activity of aflatoxin B1 (AFB1), a common fungal metabolite found contaminating food and cosmetic products. Aflatoxin B1 is metabolized by cytochrome P450 into AFB1 exo-8,9-epoxide, which reacts with the N7 of guanine to form trans-8,9-dihydro-8-(N7-guanyl)-9-hydroxyaflatoxin B1 adduct. The aflatoxin moiety and the extra adenosine nucleotide which it causes to be inserted in the complementary DNA strand form a stable intrahelical structure in DNA which could be a cause of oncogenesis.

A study using NMR examination of oligodeoxynucleotides of the human n-ras protooncogene was conducted to determine the oncogenic properties of styrene oxide, a by-product of plastics and resin manufacturing. The results show that styrene oxide forms adducts at codon 61 of the human n-ras, leading to protooncogene activation, which is an early stage of carcinogenesis.

The use of potassium polyethylene glycol (KPEG) for the dehalogenation of pentachlorophenol-containing wood preserving waste was investigated. The results showed that KPEG was effective in dehalogenating the pentachlorophenol contained in the waste material. In addition, it was found that dehalogenation using KPEG decreases, but does not completely eliminate, waste genotoxicity during treatment.

Until recently, the mechanism of carcinogenesis has been regarded as a two-stage phenomenon involving damage to the genetic material, which initiates the process, followed by a cell-division stimulus, which promotes the development of the tumour. However, exposure to some chemicals has been shown to result in carcinogenesis without involvement of the initiation step. The mechanism of non-genotoxic carcinogenesis is not fully understood, but is believed to involve stimulation of cell division with a consequent increased probability of a mutation occurring spontaneously. In this article, Ian Shaw and Huw Jones review the theories of non-genotoxic carcinogenesis with reference to specific examples of known non-genotoxic carcinogens.

An analysis of three vinyl chloride-induced DNA lesions epsilon-Ade, epsilon-Cyt and the imidazole lesion beta, reveals that beta- and epsilon-Cyt are equally mutagenic, whereas epsilon-Ade is the least mutagenic. All three lesions have different mutagenic specificities. Analysis of phage transferred DNA-containing lesions reveals that beta is the most genotoxic of the three DNA lesions due to the lack of purine and pyrimidine structures in beta. Epsilon-Cyt's toxicity is more than double that of epsilon-Ade's.

Identical classifications of RTX-toxins of Actinobacillus pleuropneumoniae and their genes were proposed after studying three diverse pore-forming RTX-toxins of this organism. The RTX-toxin derived from the reference strains for serotypes 1, 5a, 5b, 9, 10 and 11 were termed Apxl. This protein was found to be highly haemolytic and reveals increased cytotoxic activity toward pig alveolar macrophages and neutrophils, and has a molecular mass between 105 and 110kDa.

The synthesis of the 3-amino-1,4-dimethyl and 3-amino-1-methyl derivatives of 5H-pyrido(4,3-b)indole (Trp-P-1 and Trp-P-2) proceeds through the thermal electrocyclic reaction of the 1-azahexa-1,3,5-triene system involving the indole (b) bond. N-(benzenesulfonyl)indole provides the 2-vinylindole substrates via a four-step sequence. Trp-P-1 and Trp-P-2 are genotoxic heterocyclic amines produced by the overcooking of protein-containing food.

The L-type Ca2+ channels found in smooth and cardiac muscles contain receptor sites susceptible to either dihydropyridine or phenylalkylamine modulation. These binding sites promote high conservation in the Ca2+ channel alpha1 subunits involving Ca2+ channel antagonist reactions resulting in therapeutic effects. Moreover, results indicate that phenylalkylamine hinders Ca2+ ion movement via pore-blocking while dihydropyridine functions via extracellular gating alterations.