Peroxidase-dependent bioactivation and oxidation of DNA and protein in benzo[a]pyrene-initiated micronucleus formation

Bioaccessible PAH influence on distribution of antibiotic resistance genes and soil toxicity of different types of land use

For a better understanding of the dissemination of antibiotic resistance genes (ARGs) in natural microbial communities, it is necessary to study the factors influencing it. There are not enough studies showing the connection of some pollutants with the dissemination of ARGs and especially few works on the effect of polycyclic aromatic compounds (PAHs) on the spread of resistance in microbiocenosis. In this respect, the aim of the study was to determine the effect of bioaccessible PAHs on soil resistome. The toxicity and the content of bioaccessible PAHs and ARGs were studied in 64 samples of soils of different types of land use in the Rostov Region of Russia. In most soils, a close positive correlation was demonstrated between different ARGs and bioaccessible PAHs with different content of rings in the structure. Six of the seven studied ARGs correlated with the content of 2-, 3-, 4-, 5- or 6-ring PAHs. The greatest number of close correlations was found between the content of PAHs and ARGs in the soils of protected areas, for agricultural purposes, and in soils of hospitals. The diverse composition of microbial communities in these soils might greatly facilitate this process. A close correlation between various toxic effects identified with a battery of whole-cell bacterial biosensors and bioaccessible PAHs of various compositions was established. This correlation showed possible mechanisms of PAHs' influence on microorganisms (DNA damage, oxidative stress, etc.), which led to a significant increase in horizontal gene transfer and spread of some ARGs in soil microbial communities. All this information, taken together, suggests that bioaccessible PAHs can enhance the spread of antibiotic resistance genes.

Metabolomics study of fibroblasts damaged by UVB and BaP

We have recently shown that both UVB and BaP can induce the production of ROS, apoptosis and even cancer. However, the differences in the metabolic profiles of skin damaged by UVB, BaP or UVB combined with BaP have not been studied. Therefore, we examined the metabolic changes in the human foreskin fibroblast injured by UVB or BaP or the combination of the two, using ultra performance liquid chromatography (UPLC) coupled with quadrupole time-of-flight mass spectrometry (qTOF-MS). 24 metabolites were altered in the UVB damage group, 25 in the BaP damage group, and 33 in the UVB combined with BaP group. These alterations indicated that the metabolic mechanisms of HFF-1 cells treated with UVB or BaP are related to multiple main metabolites including glycerophosphocholine (PC), lactosylceramide (LacCer), guanidinosuccinic acid (GSA), glutathione(GSH), and lysophosphatidylcholine (LysoPC) and the main mechanisms involved glycerophospholipid and glutathione metabolism. Thus, our report provided useful insight into the underlying mechanisms of UVB and BaP damage to skin cells.

π-Self-Assembly of a Coronene on Carbon Nanomaterial-Modified Electrode and Its Symmetrical Redox and H2O2 Electrocatalytic Reduction Functionalities

The structure-electroactivity relationship of graphene has been studied using coronene (Cor), polyaromatic hydrocarbon (PAH), and a subunit of graphene as a model system by chemically modified electrode approach. In general, graphene and PAH do not show any redox activity in their native form. Herein, we report a simple electrochemical approach for the conversion of electro-inactive coronene to a highly redox-active molecule (Cor-Redox; E°' = 0.235 ± 0.005 V vs Ag/AgCl) after being adsorbed on graphitic carbon nanomaterial and preconditioned at an applied potential, 1.2 V vs Ag/AgCl, wherein, the water molecule oxidizes to dioxygen via hydroxyl radical (^•OH) intermediate, in acidic solution (pH 2 KCl-HCl). When the same coronene electrochemical experiment was carried out on an unmodified glassy carbon electrode, there was no sign of faradic signal, revealing the unique electrochemical behavior of the coronene molecule on graphitic nanomaterial. The Cor-Redox peak is found to be highly symmetrical (peak-to-peak potential separation of ∼0 V tested by cyclic voltammetry (CV)) and surface-confined (Γ_Cor-Redox = 10.1 × 10^-9 mol cm^-2) and has proton-coupled electron-transfer (∂E°'/∂pH = -56 mV pH^-1) character. Initially, it was speculated that Cor is converted to a hydroxy group-functionalized Cor molecule (dihydroxy benzene derivative) on the graphitic surface and showed the electrochemical redox activity. However, physicochemical characterization studies including Raman, IR, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), redox-site selective oxidation probe, cysteine (for dihydroxy benzene), radical scavenger ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl, TEMPO), and scanning electrochemical microscopy (SECM) using ferricyanide redox couple have revealed that coronene cationic radical species like electroactive molecule is formed on graphitic material upon the electrochemical oxidation reaction at a high anodic potential. It has been proposed that ^•OH generated as an intermediate species from the water oxidation reaction is involved in the coronene cationic radical species. Studies on coronene electrochemical reaction at various carbon nanomaterials like multiwalled carbon, single-walled carbon, graphite, graphene oxide, and carbon nanofiber revealed that graphitic structure (without any oxygen functional groups) and its π-π bonding are key factors for the success of the electrochemical reaction. The coronene molecular redox peak showed an unusual electrocatalytic reduction of hydrogen peroxide similar to the peroxidase enzyme-biocatalyzed reduction reaction in physiological solution.

Polycyclic aromatic hydrocarbons in consumer goods made from recycled rubber material: A review

Vast amounts of rubber waste are produced every year, where end-of-life tires (ELT) mount up the largest share with several million tonnes in the EU each year. This points up the necessity for reusing end-of-life rubber material. The recycled material shows nearly the same advantages like the origin materials. In consequence, the recycled material is predestined for the use in sport facilities, which explains that around half of the recycled ELTs are used to produce artificial turf, sports flooring and injury-prevention pavements on playgrounds. Since tires contain potentially toxic components, there is worry concerning the release of such chemical substances stemming from these products. As tires contain highly aromatic oils and carbon black, the presence of polycyclic aromatic hydrocarbons (PAH) and their carcinogenic properties are discussed controversially. This review issues a comprehensive overview of PAH release and a conclusive assessment on human health risk. Analytical studies dealing with the PAH content of consumer goods made from recycled rubber material and associated risk assessments are reviewed. In conclusion PAHs can be detected in consumer goods made from recycled rubber and are released into the environment. They reach humans via leaching (soil, ground water, rivers), oral intake, dermal exposure and inhalation. Thereby, dermal contact or inhalation is the primary route of exposure, whereas oral intake and environmental pollution are regarded as secondary risks. The amount of PAHs that could potentially harm humans is in the magnitude of urban pollution. Risk assessment studies reviewed in this article show no serious risk potential.

1-Aminobenzotriazole: A Mechanism-Based Cytochrome P450 Inhibitor and Probe of Cytochrome P450 Biology

1-Aminobenzotriazole (1-ABT) is a pan-specific, mechanism-based inactivator of the xenobiotic metabolizing forms of cytochrome P450 in animals, plants, insects, and microorganisms. It has been widely used to investigate the biological roles of cytochrome P450 enzymes, their participation in the metabolism of both endobiotics and xenobiotics, and their contributions to the metabolism-dependent toxicity of drugs and chemicals. This review is a comprehensive evaluation of the chemistry, discovery, and use of 1-aminobenzotriazole in these contexts from its introduction in 1981 to the present.

Establishment, characterization, and toxicological application of loggerhead sea turtle (Caretta caretta) primary skin fibroblast cell cultures

Pollution is a well-known threat to sea turtles but its impact is poorly understood. In vitro toxicity testing presents a promising avenue to assess and monitor the effects of environmental pollutants in these animals within the legal constraints of their endangered status. Reptilian cell cultures are rare and, in sea turtles, largely derived from animals affected by tumors. Here we describe the full characterization of primary skin fibroblast cell cultures derived from biopsies of multiple healthy loggerhead sea turtles (Caretta caretta), and the subsequent optimization of traditional in vitro toxicity assays to reptilian cells. Characterization included validating fibroblast cells by morphology and immunocytochemistry, and optimizing culture conditions by use of growth curve assays with a fractional factorial experimental design. Two cell viability assays, MTT and lactate dehydrogenase (LDH), and an assay measuring cytochrome P4501A (CYP1A) expression by quantitative PCR were optimized in the characterized cells. MTT and LDH assays confirmed cytotoxicity of perfluorooctanoic acid at 500 μM following 72 and 96 h exposures while CYP1A5 induction was detected after 72 h exposure to 0.1-10 μM benzo[a]pyrene. This research demonstrates the validity of in vitro toxicity testing in sea turtles and highlights the need to optimize mammalian assays to reptilian cells.

Ameliorative effects of docosahexaenoic acid on the toxicity induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin in cultured rat hepatocytes

The 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is an environmental contaminant toxicant that mediates carcinogenic effects associated with oxidative DNA damage. Docosahexaenoic acid (DHA) with antioxidant functions has many biochemical, cellular, and physiological functions for cells. The present study assessed, for the first time, the ameliorative effect of DHA in alleviating the toxicity of TCDD on primary cultured rat hepatocytes (HEPs). In vitro, isolated HEPs were incubated with TCDD (5 and 10 μM) in the presence and absence of DHA (5, 10, and 20 μM) for 48 h. The cell viability was detected by 3-(4,5-dimethylthiazol-2-yl) 2,5-diphenyltetrazolium bromide (MTT) assay and lactate dehydrogenase (LDH) release. DNA damage was analyzed by liver micronucleus assay and 8-oxo-2-deoxyguanosine (8-OH-dG) level. In addition, total antioxidant capacity (TAC) and total oxidative stress (TOS) were assessed to determine the oxidative injury in HEPs. The results of MTT and LDH assays showed that TCDD decreased cell viability but not DHA. On the basis of increasing treatment concentrations, the dioxin caused significant increases of micronucleated HEPs and 8-OH-dG as compared to control culture. TCDD also led to significant increases in TOS content. On the contrary, in cultures treated with DHA, the level of TAC was significantly increased during treatment in a concentration-dependent fashion. DHA showed therapeutic potential against TCDD-mediated cell viability and DNA damages. As conclusion, this study provides the first evidence that DHA has protective effects against TCDD toxicity on primary cultured rat hepatocytes.

meta-Tyrosine in Festuca rubra ssp. commutata (Chewings fescue) is synthesized by hydroxylation of phenylalanine

m-Tyrosine is a non-protein amino acid that is structurally similar to the common protein amino acids p-tyrosine and phenylalanine. Copious amounts of m-tyrosine can be found in root exudates of the fine fescue cultivar, Festuca rubra L. ssp. commutata (Chewings fescue). The phytotoxicity of m-tyrosine may contribute to the allelopathic potential of F. rubra. m-Tyrosine in Euphorbia myrsinites (donkey-tail spurge), was previously shown to be synthesized via transamination of m-hydroxyphenylpyruvate. Here we show that m-tyrosine biosynthesis in F. rubra occurs through direct hydroxylation of phenylalanine in the root tips, perhaps through the activity of a cytochrome P450 enzyme. Hence, E. myrsinites and F. rubra, the only two plant species known to produce m-tyrosine, use distinct biosynthetic pathways that likely arose independently in evolutionary history.

HPLC/APCI-FTICR-MS as a tool for identification of partial polar mutagenic compounds in effect-directed analysis

Identification of unknown compounds remains one of the biggest challenges for the assignment of adverse effects of sediment contamination and other complex environmental mixtures to responsible toxicants by effect-directed analysis (EDA). The identification depends on information gained from biotesting, chromatographic separation, and mass spectrometric detection. Thus, a methodology is provided for non-target identification of partial polar mutagenic polyaromatic compounds in sediment extracts by using polymeric reversed-phase HPLC column, high-resolution mass spectrometry and PubChem database. After visualization and processing the chromatogram constituents by using deconvolution software, the unambiguous elemental compositions generated were used as input in PubChem database to find a possible identity for the suspected species. The retrieved structures from the database search were refined by characterized chromatographic and mass spectrometric classifiers based on 55 model compounds comprising eight different classes representing mutagenic substructures. The applicability of the method was demonstrated by positive and tentative identification of constituents of mutagenic sediment fractions similar to selected model compounds.

Embryonic oxidative stress as a mechanism of teratogenesis with special emphasis on diabetic embryopathy

Reactive oxygen species (ROS) are involved in the etiology of numerous diseases including cardio-vascular diseases and diabetes mellitus. There is evidence that several teratogens affect the developing embryo by increasing its oxidative stress and, because of its relatively weak antioxidant defense, especially at the early stages of organogenesis, result in severe embryonic damage. This mechanism seems to operate in diabetes-induced embryonic damage as well as in the mechanism of teratogenicity caused by ionizing radiation, hypoxia, alcohol and cocaine use and cigarette smoking. We studied the role of oxidative stress in diabetic induced embryopathy, both in vivo and in vitro. Under diabetic condition there was a significant decrease in the activity of endogenous antioxidant enzymes and of vitamins C and E in the embryos and their yolk sacs. The lowest activity was observed in the malformed experimental embryos when compared to experimental embryos without anomalies. Similar results were obtained in the Cohen diabetic rats, where the diabetic prone (CDs) rats were unable to increase their antioxidant enzyme activity in spite of the diabetes. Studies performed by other investigators show similar results. Human and animal studies show that the main mechanism of fetal damage induced by high levels of ionizing irradiation, cocaine and alcohol abuse, hypoxia and cigarette smoking is also by increased embryonic oxidative stress. Similarly, several drugs exert their teratogenic activity via embryonic oxidative stress. Abnormal placentation may also cause enhanced placental oxidative stress, resulting in embryonic death, preeclampsia or congenital anomalies. Inability of the developing embryo to cope with that stress may result in embryonic death and/or congenital anomalies. Animal studies also show that a variety of antioxidants are effective in decreasing the damaging effects of heightened oxidative stress induced by teratogens. Effective antioxidants, which might also be of clinical use, include vitamins C and E, carotenoids, folic acid, as well as synthetic products. Appropriate clinical studies with antioxidants in pregnancies of high risk to develop oxidative stress are needed, since non-toxic antioxidants might prove an efficient and inexpensive way to reduce the rate of some serious and sometimes fatal congenital anomalies.

Gene expression analysis and classification of mode of toxicity of polycyclic aromatic hydrocarbons (PAHs) in Escherichia coli

Escherichia coli is known to respond to certain toxic chemicals through an increased expression of various stress genes. In this study, therefore, the expression of recA, katG, fabA and grpE genes was used as a representative for DNA, oxidative, membrane and protein damage, respectively, after E. coli was exposed to different polycyclic aromatic hydrocarbons (PAHs), i.e., phenanthrene, naphthalene and benzo[a]pyrene. To accomplish this, the expression levels of these four genes were quantified using a real-time RT-PCR analysis when E. coli cultures were under stressful conditions, such as those caused by an exposure to mitomycin C, hydrogen peroxide and phenol. It was found that the primary toxic effect of each chemical is clearly seen when the expression levels of the different genes are compared. Tests with the PAHs showed naphthalene and benzo[a]pyrene to be genotoxic, while phenanthrene had no clear effect on the expression of any of these genes. Based on these results, the effects due to these toxic chemicals and the extent of each stress can be evaluated with ease using the expression levels of different stress responsive genes.

Propolis protects human spermatozoa from DNA damage caused by benzo[a]pyrene and exogenous reactive oxygen species

Many environmental, physiological and genetic factors have been implicated in defective sperm function, the most common cause of infertility. In addition, sperm preparation techniques such as centrifugation, used prior to in vitro fertilization, are associated with the generation of reactive oxygen species (ROS) and an increase in the level of DNA damage. Factors that can offer spermatozoa protection are, therefore, of great importance. This study was designed to examine in vitro the effect of a Chilean propolis ethanolic extract on human spermatozoa treated with benzo[a]pyrene and exogenous reactive oxygen species. Our experimental evidence demonstrated that the natural drug under investigation is able to protect genomic DNA by damage induced by benzo[a]pyrene, hydrogen peroxide (H2O2) and hydrogen peroxide in combination with adenosine 5'-diphosphate (ADP) and ferrous sulfate (FeSO4), determining a significant reduction of the intracellular oxidants. An increase in membrane damage, measured by monitoring the formation of thiobarbituric acid-reactive substances (TBARS) and lactic dehydrogenase (LDH) release, was observed only in sperm treated with H2O2, ADP and FeSO4. The propolis extract was shown to possess the capacity to protect sperm membrane from the deleterious action of oxidative attack, reducing TBARS formation and LDH release. In summary, our results evidence that the protective effect exhibited by this natural compound in human spermatozoa is correlated, at least in part, to the antioxidant capacity of its active components, and suggest that propolis may have a role in protection against male infertility.

Glucuronidation and the UDP-glucuronosyltransferases in health and disease

This article is an updated report of a symposium held at the June 2000 annual meeting of the American Society for Pharmacology and Experimental Therapeutics in Boston. The symposium was sponsored by the ASPET Divisions for Drug Metabolism and Molecular Pharmacology. The report covers research from the authors' laboratories on the structure and regulation of UDP-glucuronosyltransferase (UGT) genes, glucuronidation of xenobiotics and endobiotics, the toxicological relevance of UGTs, the role of UGT polymorphisms in cancer susceptibility, and gene therapy for UGT deficiencies.

Extended-term cultures of human T-lymphocytes and the comet assay: a useful combination when testing for genotoxicity in vitro?

Extended-term cultures of human lymphocytes provide a source of uniform human cells that can be used for several experiments performed over a long time, avoiding the variability arising from taking blood samples for individual experiments. The use of extended-term cultures of human T-lymphocytes in the alkaline single-cell gel electrophoresis assay (comet assay) was evaluated as a test for the potential genotoxicity of chemicals. The DNA-damaging effects of five DNA-reactive mutagens and clastogens (benzo[a]pyrene, cyclophosphamide, formaldehyde, 4-nitroquinoline-N-oxide (4NQO) and N-nitrosopiperidine) was determined and compared with the effects of one non-DNA-reactive mutagen (5-hydroxyurea), and one non-mutagenic agent (ethanol). The alkylating and/or DNA-adduct forming agents N-nitrosopiperidine, cyclophosphamide, 4-nitroquinoline-N-oxide and benzo[a]pyrene increased the DNA migration in a dose-dependent manner. In contrast, the DNA/protein-crosslinking agent formaldehyde decreased the migration of DNA during the electrophoresis. The lowest observed effect levels (LOELs) under the experimental conditions used in the present study, were: 0.0001 mM (4-nitroquinoline-N-oxide without S9), 0.05 mM (benzo[a]pyrene with S9), 0.1mM (formaldehyde without S9), 0.25 mM (cyclophosphamide with S9), and 0.5mM (N-nitrosopiperidine with S9), respectively. The antimetabolite 5-hydroxyurea was also found to increase the tail moment, but only in cells that had been exposed to rather high concentrations (> or =10mM) of the compound. Ethanol did not affect the tail moment, not even in cells that had been exposed to an apparently cytotoxic concentration (500 mM). The results of the present study are in qualitative agreement with those obtained using other cells in the alkaline comet assay and it is therefore concluded that extended-term cultures of human T-lymphocytes and the alkaline version of the single-cell gel electrophoresis assay is a useful combination when testing for the potential genotoxicity of chemicals.

Biotransformation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in peripheral human lung microsomes

The contributions of different enzymes to 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) biotransformation were assessed in human lung microsomes prepared from peripheral lung specimens obtained from seven subjects. Metabolite formation was expressed as a percentage of total recovered radioactivity from [5-3H]NNK and its metabolites per milligram of protein per minute. 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol was the major metabolite formed in the presence of an NADPH-generating system, with production ranging from 0.5186 to 1.268%/mg of protein/min, and total NNK bioactivation (represented by the sum of the four alpha-carbon hydroxylation endpoint metabolites) ranged from 0.002100 to 0.005685% alpha-hydroxylation/mg of protein/min. Overall, production of bioactivation metabolites was greater than that of detoxication (i.e., N-oxidation) products. Based on total bioactivation, subjects could be classified as high or low NNK bioactivators. In the presence of an NADPH-generating system, microsomal formation of the endpoint metabolite 1-(3-pyridyl)-1-butanone-4-carboxylic acid (keto acid) was consistently higher than that of all other alpha-carbon hydroxylation endpoint metabolites. Contributions of cytochrome p450 (p450) enzymes to NNK oxidation were demonstrated by NADPH dependence, inhibition by carbon monoxide, and inhibition by the nonselective p450 inhibitors proadifen hydrochloride (SKF-525A) and 1-aminobenzotriazole (ABT), particularly in lung microsomes from high bioactivators. At 5.0 mM, ABT inhibited total NNK bioactivation by 54 to 100%, demonstrating the importance of ABT-sensitive enzyme(s) in human pulmonary NNK bioactivation. Contributions of CYP2A6 and/or CYP2A13, as well as CYP2B6, to NNK bioactivation were also suggested by selective chemical and antibody inhibition in lung microsomes from some subjects. It is likely that multiple p450 enzymes contribute to human pulmonary microsomal NNK bioactivation, and that these contributions vary between individuals.

Detailed low-dose study of 1,1-bis(p-chlorophenyl)-2,2,2- trichloroethane carcinogenesis suggests the possibility of a hormetic effect

To obtain information on the effects of nongenotoxic carcinogens at low doses for human cancer risk assessment, the carcinogenic potential of the organochlorine insecticide, 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT), in the liver was assessed in F344 rats. In experiment 1, 240 male animals, 21 days old, were administered 0, 0.5, 1.0, 2.0, 5.0, 20, 100 and 500 ppm DDT in the diet for 16 weeks. Experiment 2 was conducted to elucidate the carcinogenic potential of DDT at lower levels using 180 rats given doses of 0, 0.005, 0.01, 0.1, 0.2 and 0.5 ppm. The livers of all animals were immunohistochemically examined for expression of glutathione S-transferase placental form (GST-P), putative preneoplastic lesions. Quantitative values for GST-P-positive foci in the liver were increased dose-dependently in rats given 20 ppm DDT and above with statistical significance as compared with the concurrent control value. In contrast, doses of 0.005 and 0.01 ppm were associated with a tendency for decrease below the control value, although not significantly. Western blotting analysis show that cytochrome P-450 3A2 (CYP3A2) protein expression tended to decrease at 0.005 and 0.01 ppm, a good correlation being observed with the change in the number of GST-P-positive foci. These findings suggest that a DDT hepatocarcinogenicity may show nonlinear response, that is, hormetic response at low doses. Furthermore, since CYP3A2 protein expression appears to be important for the effects of phenobarbital and the alpha-isomer of benzene hexachloride, mRNAs for IL-1 receptor type 1 (IL-1R1) and TNF-alpha receptor type 1 (TNFR1) whose ligands have roles not only in downregulating CYP3A2 expression but also in inducing antiproliferative effect or apoptosis in hepatocyte were examined. Increase was observed at low doses of DDT. Oxidative stress in liver DNA, assessed in terms of 8-hydroxydeoxyguanosine as a marker, was also decreased. These findings suggest that the possible hormetic effect that was observed in our detailed low-dose study of DDT carcinogenesis, although not statistically significant, may be linked to levels of oxidative stress and proinflammatory cytokines.

Micronucleus induction in Syrian hamster embryo cells following exposure to 50 Hz magnetic fields, benzo(a)pyrene, and TPA in vitro

Electromagnetic fields (EMFs) have been associated with increased incidence of cancer suggested by epidemiological studies. To test the carcinogenic potency of EMF, the in vitro micronucleus assay with SHE cells has been used as a screening method for genotoxicity. A 50Hz magnetic field (MF) of 1mT field strength was applied either alone or with the tumour initiator benzo(a)pyrene (BP) or the tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). All three treatments were applied in single, double or triple treatment regimes. MF or TPA (1nM) alone did not affect the number of micronuclei (MN) in initiated and non-initiated SHE cells. Changing the schedule of the typical initiation protocol, namely applying the initiator (BP) during exposure to MF, results in an 1.8-fold increased MN formation compared to BP treatment alone. Combined experiment with BP, TPA and MF did not cause further MN formation. Since initiation during MF exposure caused a significant increased MN formation, our findings suggest that MFs enhance the initiation process of BP. We think that this MF-enhanced co-carcinogenic effect is caused by an indirect "cell activation" process. The resulting genomic instability is proposed to be due to free radicals and/or to the unscheduled "switching-on" of signal transduction pathways.

Ability of fractionated petroleum refinery effluent to elicit cyto- and photocytotoxic responses and to induce 7-ethoxyresorufin-O-deethylase activity in fish cell lines

The ability of fractionated petroleum refinery effluent to cause cellular responses in fish cell lines was evaluated. The cellular responses, which included direct and indirect cytotoxicity, photocytotoxicity and induction of 7-ethoxyresorufin-O-deethylase (EROD) activity, may potentially be linked to sublethal effects observed in effluent-exposed fish and fish larvae. In order to be able to quantify cellular responses rapidly, microtitre plates were used along with fluorescent probes. For the quantification of cyto- and photocytotoxicity, the fluorescent probes were alamar Blue and carboxyfluorescein diacetate acetoxymethyl ester (CFDA-AM), which monitor metabolic activity and cell membrane integrity, respectively. EROD activity was measured as the rate of conversion by EROD of the substrate 7-ethoxyresorufin to its fluorescent product, resorufin. Effluent from an Ontario refinery was fractionated into aqueous and particulate phase. As well, a solid phase extract (SPE) was used to prepare concentrated effluent for testing in the cell lines. The effluent was able to elicit all of the responses of interest although significant cyto- and photocytotoxicity required effluent equivalent concentrations above 100% effluent and could only be revealed upon exposure of cells to the SPE concentrated effluent. Based on their retention on C18, the cytotoxicants are likely to be non-polar to moderately polar chemicals. The presence of polar compounds affecting cellular metabolism was indicated by the responses of exposed cells to a 90% aqueous phase effluent. In contrast to cyto- and photocytotoxicity, EROD induction occurred at effluent equivalent concentrations well below 100% effluent and was elicited by the SPE and the particulate fraction thereby suggesting that most EROD-inducers were particle-bound. Among other applications, the described techniques could help to determine the source of causative agents of sublethal effects in the refining process.

Transitory metabolic disruption and cytotoxicity elicited by benzo[a]pyrene in two cell lines from rainbow trout liver

Two cell lines, RTL-W1 and R1, from rainbow trout liver were used to investigate the effects of benzo[A]pyrene (BaP). BaP induced a catalytic measure of CYP1A, 7-ethoxyresorufin-O-deethylase (EROD) activity, in the rainbow trout liver cell line RTL-W1 but not in R1. Geldanamycin inhibited EROD induction by BaP. Potential BaP metabolites, BaP-7,8-dihydrodiol (BDP) and 6,12-BaP quinone (BQ) also induced EROD activity in RTL-W1. Very low BaP concentrations slightly stimulated cell proliferation in both cell lines. Higher BaP concentrations caused cytotoxicity in RTL-W1 but not in R1. Cytotoxicity was detected in a cell viability assay with 5-carboxyfluorescein diacetate acetoxymethyl ester, and as a decline in cell number. In both cell lines, BaP exposure impaired the reduction of the redox dye, alamar Blue (AB). After BaP removal, AB reduction recovered. Similar results were observed with BQ. As AB monitors metabolic activity, this novel phenomenon was termed transitory metabolic disruption. This decline in AB readings that was caused by BaP was ameliorated in RTL-W1 by alpha-naphthoflavone and geldanamycin, which suggests a role for CYP1A, and in R1 by indomethacin, which suggests involvement of prostaglandin-H-synthase. The significance of the response to BaP that is detected with AB and whether other PAHs cause it will be interesting future questions.

Evaluation of benzo(a)pyrene-induced DNA damage in human endothelial cells using alkaline single cell gel electrophoresis

The alkaline version of the 'comet assay' was used to evaluate DNA damage in human umbilical vein endothelial cells (HUVEC) exposed to 0.1, 1.0, or 10 microM benzo(a)pyrene for 90min. The genotoxicity was monitored in HUVEC pretreated with the Ah-receptor agonist beta-naphthoflavone (BNF), previously shown to induce cytochrome P4501A1 (CYP1A1) activity in these cells, and in vehicle-treated HUVEC with only constitutive levels of this enzyme. Increased DNA damage was observed only in cells that had been exposed to 10 microM benzo(a)pyrene, cells exposed to BNF being subjected to the most extensive damage. The CYP1A/B-inhibitor alpha-naphthoflavone (ANF) reduced the benzo(a)pyrene-induced DNA-damage in the BNF-treated HUVEC to the same level as in the uninduced cells. The fact that benzo(a)pyrene induced DNA damage in vehicle-treated HUVEC suggests that there may be at least one alternative route of bioactivation for benzo(a)pyrene in these cells. Consequently, judging from the present results it seems as if tobacco-related polycyclic aromatic hydrocarbons (PAHs) may disrupt the function of the endothelial lining in blood vessels with low monooxygenase activity. It is proposed that exposure to Ah receptor agonists via, for example, tobacco smoke, may enhance the DNA-damaging effects of smoke-related genotoxic PAHs in human endothelial cells. The role of PAHs in endothelial dysfunction of tobacco smokers should therefore be further studied.

Xenobiotic-metabolizing cytochromes P450 convert prostaglandin endoperoxide to hydroxyheptadecatrienoic acid and the mutagen, malondialdehyde

Cyclooxygenases catalyze the oxygenation of arachidonic acid to prostaglandin endoperoxides. Cyclooxygenase-2- and the xenobiotic-metabolizing cytochrome P450s 1A and 3A are all aberrantly expressed during colorectal carcinogenesis. To probe for a role of P450s in prostaglandin endoperoxide metabolism, we studied the 12-hydroxyheptadecatrienoate (HHT)/malondialdehyde (MDA) synthase activity of human liver microsomes and purified P450s. We found that human liver microsomes have HHT/MDA synthase activity that is concentration-dependent and inhibited by the P450 inhibitors, ketoconazole and clotrimazole with IC(50) values of 1 and 0.4 microM, respectively. This activity does not require P450 reductase. HHT/MDA synthase activity was present in purified P450s but not in heme alone or other heme proteins. The catalytic activities of various purified P450s were determined by measuring rates of MDA production from prostaglandin endoperoxide. At 50 microM substrate, the catalytic activities of purified human P450s varied from 10 +/- 1 to 0.62 +/- 0.02 min(-1), 3A4 >> 2E1 > 1A2. Oxabicycloheptane analogs of prostaglandin endoperoxide, U-44069 and U-46619, induced spectral changes in human P450 3A4 with K(s) values of 240 +/- 20 and 130 +/- 10 microM, respectively. These results suggest that co-expression of cyclooxygenase-2 and P450s in developing cancers may contribute to genomic instability due to production of the endogenous mutagen, MDA.

Separation and identification of polar degradation products of benzo[a]pyrene with ozone by atmospheric pressure chemical ionization-mass spectrometry after optimized column chromatographic clean-up

The environmental relevance of oxidized degradation products of polycyclic aromatic hydrocarbons (PAHs) increases due to enhanced combustion of organic matter and fossil fuels. For PAHs consisting of more than three condensed aromatic rings, soot aerosols are the main carrier, on the surface of which they can react with trace gases like ozone. In this study the clean-up procedure and analysis of ozonized benzo[a]pyrene (B[a]P) was optimized. B[a]P and its degradation products were preseparated into three fractions. Different reversed-phase materials were evaluated for high-performance liquid chromatographic separation. Among these, a phenyl-modified silica material proved best-suited and the chromatographic separation was optimized on this material. For the detection of separated degradation products, liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS) was used. With this method, 29 components could be characterized. Besides the three known main degradation products (B[a]P-1,6-dione, B[a]P-3,6-dione, B[a]P-6,12-dione, B[a]P-4,5-dione and 4-oxa-benzo[d,e,f]chrysene-5-one (B[def]C-lactone), were identified for the first time with the help of reference substances. B[def]C-lactone is known as a substance with a mutagenic potential similar to B[a]P. Several other compounds could be tentatively identified.

Oxidative damage in chemical teratogenesis

The teratogenicity of many xenobiotics is thought to depend at least in part upon their bioactivation by embryonic cytochromes P450, prostaglandin H synthase (PHS) and lipoxygenases (LPOs) to electrophilic and/or free radical reactive intermediates that covalently bind to or oxidize cellular macromolecules such as DNA, protein and lipid, resulting in in utero death or teratogenesis. Using as models the tobacco carcinogens benzo[a]pyrene (B[a]P) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), the anticonvulsant drug phenytoin, structurally related anticonvulsants (e.g. mephenytoin, nirvanol, trimethadione, dimethadione) and the sedative drug thalidomide, we have examined the potential teratologic relevance of free radical-initiated, reactive oxygen species (ROS)-mediated oxidative molecular target damage, genotoxicity (micronucleus formation) and DNA repair in mouse and rabbit models in vivo and in embryo culture, and in vitro using purified enzymes or cultured rat skin fibroblasts. These teratogens were bioactivated by PHS and LPOs to free radical reactive intermediary metabolites, characterized by electron spin resonance spectrometry, that initiated ROS formation, including hydroxyl radicals, which were characterized by salicylate hydroxylation. ROS-initiated oxidation of DNA (8-hydroxy-2'-deoxyguanosine formation), protein (carbonyl formation), glutathione (GSH) and lipid (peroxidation), and embryotoxicity were shown for phenytoin, its major hydroxylated metabolite 5-(p-hydroxyphenyl)-5-phenylhydantoin [HPPH], thalidomide, B[a]P and NNK in vivo and/or in embryo culture, the latter indicating a teratologically critical role for embryonic, as distinct from maternal, processes. DNA oxidation and teratogenicity of phenytoin and thalidomide were reduced by PHS inhibitors. Oxidative macromolecular lesions and teratogenicity also were reduced by the free radical trapping agent phenylbutylnitrone (PBN), and the antioxidants caffeic acid and vitamin E. In embryo culture, addition of superoxide dismutase (SOD) to the medium enhanced embryonic SOD activity, and SOD or catalase blocked the oxidative lesions and embryotoxicity initiated by phenytoin and B[a]P, suggesting a major contribution of ROS, as distinct from covalent binding, to the teratologic mechanism. In in vivo studies, other antioxidative enzymes like GSH peroxidase, GSH reductase and glucose-6-phosphate dehydrogenase (G6PD) were similarly protective. Even untreated G6PD-deficient mice had enhanced embryopathies, indicating a teratological role for endogenous oxidative stress. In cultured fibroblasts, B[a]P, NNK, phenytoin and HPPH initiated DNA oxidation and micronucleus formation, which were inhibited by SOD. Oxidation of DNA may be particularly critical, since transgenic mice with +/- or -/- deficiencies in the p53 tumor suppressor gene, which facilitates DNA repair, are more susceptible to phenytoin and B[a]P teratogenicity. Even p53-deficient mice treated only with normal saline showed enhanced embryopathies, suggesting the teratological importance of endogenous oxidative stress, as observed with G6PD deficiency. These results suggest that oxidative macromolecular damage may play a role in the teratologic mechanism of xenobiotics that are bioactivated to a reactive intermediate, as well in the mechanism of embryopathies occurring in the absence of xenobiotic exposure.