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

Genetic and epigenetic modulations in toxicity: The two-sided roles of heavy metals and polycyclic aromatic hydrocarbons from the environment

This study emphasizes the importance of considering the metabolic and toxicity mechanisms of environmental concern chemicals in real-life exposure scenarios. Furthermore, environmental chemicals may require metabolic activation to become toxic, and competition for binding sites on receptors can affect the severity of toxicity. The multicomplex process of chemical toxicity is reflected in the activation of multiple pathways during toxicity of which AhR activation is major. Real-life exposure to a mixture of concern chemicals is common, and the composition of these chemicals determines the severity of toxicity. Nutritional essential elements can mitigate the toxicity of toxic heavy metals, while the types and ratio of composition of PAH can either increase or decrease toxicity. The epigenetic mechanisms of heavy metals and PAH toxicity involves either down-regulation or up-regulation of some non-coding RNAs (ncRNAs) whereas specific small RNAs (sRNAs) may have dual role depending on the tissue and circumstance of expression. Similarly, decrease DNA methylation and histone modification are major players in heavy metals and PAH mediated toxicity and FLT1 hypermethylation is a major process in PAH induced carcinogenesis. Overall, this review provides the understanding of the metabolism of environmental concern chemicals, emphasizing the importance of considering mixed compositions and real-life exposure scenarios in assessing their potential effects on human health and diseases development as well as the dual mechanism of toxicity via genetic or epigenetic axis.

In Vitro Genotoxicity Evaluation of PAHs in Mixtures Using Experimental Design

Settled dusts are sinks for environmental pollutants, including Polycyclic Aromatic Hydrocarbons (PAHs) that are ubiquitous, persistent, and carcinogenic. To assess their toxicity in mixtures, Toxic Equivalent Factors (TEFs) are routinely used and based on the hypothesis of additive effects, although PAH interactions may occur and remain an open issue. This study investigated genotoxic binary interaction effects for six PAHs in mixtures using two in vitro assays and estimated Genotoxic Equivalent Factors (GEFs) to roughly predict the genotoxicity of PAH in mixtures. The Design of the Experiment approach was used with the micronucleus assay for cytostasis and micronuclei frequency and the alkaline comet assay for DNA damage. GEFs were determined for each PAH independently and in a mixture. For the cytostasis endpoint, no PAHs interaction was noted. BbF and BaP had a synergistic effect on DNA damage. All the PAH interacted between them regarding chromosomal damage. Although the calculated GEFs were similar to the TEFs, the latter may underestimate the genotoxic potential of a PAH mixture. GEFs calculated for PAH alone were lower than GEFs for PAHs in mixtures; thus, mixtures induce greater DNA/chromosomal damage than expected. This research helps to advance the challenging issue of contaminant mixtures' effects on human health.

Human primary endothelial cells are impaired in nucleotide excision repair and sensitive to benzo[a]pyrene compared with smooth muscle cells and pericytes

The endothelium represents the inner cell layer of blood vessels and is supported by smooth muscle cells and pericytes, which form the vessel structure. The endothelium is involved in the pathogenesis of many diseases, including the development of atherosclerosis. Due to direct blood contact, the blood vessel endothelium is inevitably exposed to genotoxic substances that are systemically taken up by the body, including benzo[a]pyrene, which is a major genotoxic component in cigarette smoke and a common environmental mutagen and human carcinogen. Here, we evaluated the impact of benzo[a]pyrene diol epoxide (BPDE), which is the reactive metabolite of benzo[a]pyrene, on the three innermost vessel cell types. Primary human endothelial cells (HUVEC), primary human smooth muscle cells (HUASMC) and primary human pericytes (HPC) were treated with BPDE, and analyses of cytotoxicity, cellular senescence and genotoxic effects were then performed. The results showed that HUVEC were more sensitive to the cytotoxic activity of BPDE than HUASMC and HPC. We further show that HUVEC display a detraction in the repair of BPDE-induced adducts, as determined through the comet assay and the quantification of BPDE adducts in post-labelling experiments. A screening for DNA repair factors revealed that the nucleotide excision repair (NER) proteins ERCC1, XPF and ligase I were expressed at lower levels in HUVEC compared with HUASMC and HPC, which corresponds with the impaired NER-mediated removal of BPDE adducts from DNA. Taken together, the data revealed that HUVEC exhibit an unexpected DNA repair-impaired phenotype, which has implications on the response of the endothelium to genotoxicants that induce bulky DNA lesions, including the development of vascular diseases resulting from smoking and environmental pollution.

A Quantitative Toxicogenomics Assay for High-throughput and Mechanistic Genotoxicity Assessment and Screening of Environmental Pollutants

The ecological and health concern of mutagenicity and carcinogenicity potentially associated with an overwhelmingly large and ever-increasing number of chemicals demands for cost-effective and feasible method for genotoxicity screening and risk assessment. This study proposed a genotoxicity assay using GFP-tagged yeast reporter strains, covering 38 selected protein biomarkers indicative of all the seven known DNA damage repair pathways. The assay was applied to assess four model genotoxic chemicals, eight environmental pollutants and four negative controls across six concentrations. Quantitative molecular genotoxicity end points were derived based on dose response modeling of a newly developed integrated molecular effect quantifier, Protein Effect Level Index (PELI). The molecular genotoxicity end points were consistent with multiple conventional in vitro genotoxicity assays, as well as with in vivo carcinogenicity assay results. Further more, the proposed genotoxicity end point PELI values quantitatively correlated with both comet assay in human cell and carcinogenicity potency assay in mice, providing promising evidence for linking the molecular disturbance measurements to adverse outcomes at a biological relevant level. In addition, the high-resolution DNA damaging repair pathway alternated protein expression profiles allowed for chemical clustering and classification. This toxicogenomics-based assay presents a promising alternative for fast, efficient and mechanistic genotoxicity screening and assessment of drugs, foods, and environmental contaminants.

The protective effect of astragaloside IV against benzo[a]pyrene induced endothelial progenitor cell dysfunction

AIMS

Benzo[a]pyrene (BaP), a prominent component of tobacco, has been revealed to induce damage to endothelial progenitor cells (EPCs). Astragaloside IV (AS-IV) is widely used for the treatment of cardiovascular diseases in China. In this study, we evaluated the effects of AS-IV on the function of human EPCs after BaP exposure and explored the underlying mechanism.

MATERIALS AND METHODS

Human umbilical cord blood mononuclear cells were isolated using density gradient centrifugation. Cells of the 4th passage were randomly divided into 6 groups. EPCs of experimental groups were pre-treated with different concentrations (2, 10 and 50 μg/mL) of AS-IV for 2h before exposure to BaP (20 μM) for 24h. The proliferation, migration, and adhesion of the treated EPCs were evaluated using a cell counting kit-8, Transwell assay and adhesion assay respectively. Interleukin-1β, tumor necrosis factor-α, malondialdehyde and SOD contents in the supernatant were evaluated. The expression of RAGE protein was measured by Western blotting.

KEY FINDINGS

The results demonstrated that AS-IV pre-treatment significantly improved BaP-induced dysfunction of EPCs in terms of proliferation, migration and adhesion. Furthermore, AS-IV reduced the production of reactive oxygen species, malondialdehyde, interleukin-1β and tumor necrosis factor-α of the BaP-treated EPCs. Finally AS-IV pre-treated EPCs showed an increased SOD activity and decreased RAGE protein expression.

SIGNIFICANCE

AS-IV is able to prevent BaP-mediated EPC dysfunction by at least inhibiting oxidative stress through the RAGE pathway.

Tanshinone IIA and Baicalin inhibiting the formation of benzo[a]pyrene and benzo[a]pyrene induced cytotoxicity: correlation with scavenging free radical

Benzo[a]pyrene (BaP), a ubiquitous environmental pollutant, is formed by incomplete combustion of organic materials, and causes oxidative damage to cells and tissues due to reactive oxygen species (ROS). The purpose of this study is to investigate the inhibition of Tanshinone IIA and Baicalin on the formation of BaP as well as the cytotoxicity in human umbilical vein endothelial cells (HUVECs) induced by BaP. The results showed that BaP formations in mainstream smoke were inhibited by 21μg/cigarette of Tanshinone IIA with a 12.8% decrease, and by 60μg/cigarette of Baicalin with an 11.1% decrease, respectively. Tanshinone IIA could protect HUVECs from the damage caused by BaP in a dose-dependent manner from 7.5 to 30μg/ml. 6μg/ml Baicalin significantly increased the cell survival rate from 47.37% to 84.21% compared with BaP-treated cells. Both Tanshinone IIA and Baicalin markedly attenuated the increase of LDH release, enhanced the activity of SOD and GPx and inhibited the generation of MDA in BaP-damaged HUVECs in vitro. In vivo exploration showed that the two compounds were capable of enhancing the activity of SOD and inhibiting generation of MDA in mainstream smoke-damaged in mice. Superoxide anion radical and hydroxyl radical were obviously inhibited by Tanshinone IIA and Baicalin. These data demonstrate an inhibition of Tanshinone IIA and Baicalin on the formation of BaP and the cytotoxicity on HUVECs related to free Radical induced by BaP.

Mitochondrial decay is involved in BaP-induced cervical damage

Benzo[a]pyrene (BaP) is a polycyclic aromatic hydrocarbon and a potent inducer of carcinogenesis. Many studies have reported that the carcinogenic effects of BaP might be due to its intermediate metabolites and to reactive oxygen species (ROS) that cause oxidative damage to the cells. However, the mechanisms of BaP-induced oxidative damage in cervical tissue are still not clear. We studied these mechanisms in female ICR mice treated with BaP either orally or intraperitoneally by measuring (1) several general biomarkers of oxidative stress in serum, (2) mitochondrial function in the cervix, and (3) the morphology of mitochondria in cervical tissue. BaP treatment (1) significantly lowered levels of vitamins A, C, and E and of glutathione; (2) reduced activities of superoxide dismutase, catalase, glutathione peroxidase, and glutathione S-transferases; and (3) significantly increased lipid peroxidation levels. In addition, significant increases in the levels of superoxide anion, hydrogen peroxide, and hydroxyl radical were observed. These results were confirmed by morphological changes in mitochondria and by decreases in membrane potential levels and in succinate dehydrogenase and malate dehydrogenase activities. The changes in these biomarkers and mitochondrial damage were BaP-dose-dependent and eventually induced both cell apoptosis and necrosis in cervical tissue. As mitochondria are the major sites of ROS generation, these findings show that mitochondrial decay greatly contributes to BaP-induced cervical damage.

Polycyclic aromatic hydrocarbons in binary mixtures modulate the efficiency of benzo[a]pyrene to form DNA adducts in human cells

Exposure to polycyclic aromatic hydrocarbons (PAHs) always involves complex mixtures that may induce synergistic or antagonistic effects on the genotoxic properties and make risk assessment more difficult. In this study, we evaluated how particulate PAHs modulated the formation of DNA damage induced by carcinogenic benzo[a]pyrene (B[a]P). Single strand breaks and alkali labile sites, as well as BPDE-N²-dGuo DNA adducts were measured in the competent HepG2 cells by Comet assay and HPLC-tandem mass spectrometry, respectively. B[a]P, alone or in binary mixture with other PAHs (1 μM each), led to low amounts of strand breaks. In contrast, formation of BPDE-N²-dGuo adducts was significant and found to be enhanced in HepG2 co-treated for 14 h by B[a]P in the presence of either benzo[b]fluoranthene (B[b]F), dibenz[a,h]anthracene (DB[a,h]A) or indeno[1,2,3-cd]pyrene (IP). Opposite results were obtained with benzo[k]fluoranthene (B[k]F). The same observations were made when cells were pre-incubated with PAH before incubation with B[a]P. These results show that the interactions between PAHs are not direct competition reactions. Emphasis was then placed on the modulation of B[a]P-induced DNA damage by B[b]F and B[k]F. No difference in the time-course formation of DNA damage was observed. However, dose-response relationship differed between these two PAHs with a concentration-dependent inhibition of BPDE-N²-dGuo DNA by B[k]F whereas a constant level of potentiation for B[b]F was observed for concentrations higher than 1 μM. Altogether, these results show that the genotoxicity of B[a]P in binary mixtures with other carcinogenic PAH may be modulated. In such cases, a potentiation of BPDE-N²-dGuo adduct formation is most often observed with exception of B[k]F. Several biological mechanisms may account for these observations, including binding of PAHs to the Ah receptor (AhR), their affinity toward CYP450 and competition for metabolism. These different interactions have to be considered when addressing the intricate issue of the toxicity of mixtures.

Neurogenic-committed human pre-adipocytes express CYP1A isoforms

Stem cell models offer an opportunity both for therapeutic use and for the assessment of alternative in vitro models. Human lipoaspirate is a source of adult stem cells (pre-adipocytes), which are able to differentiate into various phenotypes, such as neurogenic lineage. Here, we analyse the suitability of these in vitro models in screening exogenous compounds, such as environmental pollutants, that may affect adipose cells and neurogenic development. To evaluate neurogenic differentiation, we analysed expression of cholinergic system and acetylcholinesterase immunoreactivity. Heterocyclic derivatives of polycyclic aromatic hydrocarbons (PAHs) are often significant components of environmental contaminants. As they contain inducers of cytochrome P450 1A1 (CYP1A1), we explored the activity of CYP1A1-related enzymes, i.e. 7-ethoxycoumarin- and 7-ethoxyresorufin-O-deethylase (ECOD and EROD) in both cell systems in basal conditions and after exposure to non-cytotoxic doses of beta-naphthoflavone (BNF), a well-known PAH-type inducer. Both cell models showed basal and inducible levels of ECOD. Analysis of CYP1A1 protein expression and EROD-related enzyme activity confirmed the inducibility of the CYP1A1 isoform by BNF. These results demonstrate that mesenchymal adult stem cells can constitute innovative models. We therefore propose the use of pre-adipocytes and their neurogenic derivates to evaluate the cytotoxic/biological effects of unintended exposure to contaminants.

Genotoxicity studies of a desealant solvent mixture, SR-51

The Royal Australian Air Force (RAAF) has reported that personnel involved in F-111 fuel tank maintenance were concerned that exposure to a range of chemicals during the period 1977 to mid-1990s was the cause of health problems, including cancer. Particular concern was directed at SR-51, a desealant chemical mixture containing the following four solvents: aromatic 150 solvent (Aro150), dimethylacetamide, thiophenol (TP), and triethylphosphate. The present study examined the mutagenic potential of SR-51 using a range of well-known mutagen and genotoxin assays. The tests used were i) a modified version of the Ames test, ii) the mouse lymphoma assay, iii) the comet assay (a single-cell gel electrophoresis assay), and iv) a mouse micronucleus test. The modified Ames test used mixed bacterial strains in liquid suspension media. The Ames test results showed that SR-51 (tested up to the cytotoxic concentration of 36 microg/ml, 30 min incubation) in the presence and absence of S9 metabolic activation was not mutagenic. The mouse lymphoma assay used cultured mouse lymphoma cells in a microwell suspension method. The mouse lymphoma assay was also negative with SR-51 (tested up to the cytotoxic concentration of 22.5 microg/ml, 3 h incubation) in the presence and absence of S9 metabolic activation. The Comet assay, using cultured mouse lymphoma cells, showed no evidence of DNA damage in cells exposed up to the cytotoxic concentration of SR-51 at 11.25 microg/ml. The in-vivo mouse micronucleus test was undertaken in wild-type C57Bl6J male mice dosed orally with SR-51for 14 days with a single daily dose up to 360 mg/kg/day (the maximum-tolerated dose). No increases were observed in micronuclei (MN) frequency in bone marrow collected (24 h after final dose) from SR-51-treated mice compared to the number of MN observed in bone marrow collected from untreated mice. Tissues collected from treated mice at necropsy demonstrated a significant increase in spleen weights in the high dose mice. Gas chromatography analysis of SR-51 identified more than 40 individual components and an oxidation product, diphenyldisulfide derived from TP under conditions of mild heating. In conclusion, there was no evidence that SR-51 is mutagenic.

Comet assay: a reliable tool for the assessment of DNA damage in different models

New chemicals are being added each year to the existing burden of toxic substances in the environment. This has led to increased pollution of ecosystems as well as deterioration of the air, water, and soil quality. Excessive agricultural and industrial activities adversely affect biodiversity, threatening the survival of species in a particular habitat as well as posing disease risks to humans. Some of the chemicals, e.g., pesticides and heavy metals, may be genotoxic to the sentinel species and/or to non-target species, causing deleterious effects in somatic or germ cells. Test systems which help in hazard prediction and risk assessment are important to assess the genotoxic potential of chemicals before their release into the environment or commercial use as well as DNA damage in flora and fauna affected by contaminated/polluted habitats. The Comet assay has been widely accepted as a simple, sensitive, and rapid tool for assessing DNA damage and repair in individual eukaryotic as well as some prokaryotic cells, and has increasingly found application in diverse fields ranging from genetic toxicology to human epidemiology. This review is an attempt to comprehensively encase the use of Comet assay in different models from bacteria to man, employing diverse cell types to assess the DNA-damaging potential of chemicals and/or environmental conditions. Sentinel species are the first to be affected by adverse changes in their environment. Determination of DNA damage using the Comet assay in these indicator organisms would thus provide information about the genotoxic potential of their habitat at an early stage. This would allow for intervention strategies to be implemented for prevention or reduction of deleterious health effects in the sentinel species as well as in humans.

Unexpected DNA damage caused by polycyclic aromatic hydrocarbons under standard laboratory conditions

The genotoxicity of 15 polycyclic aromatic hydrocarbons was determined with the alkaline version of the comet assay employing V79 lung fibroblasts of the Chinese hamster as target cells. These cells lack the enzymes necessary to convert PAHs to DNA-binding metabolites. Surprisingly, 11 PAHs, i.e., benzo[a]pyrene (BaP), benz[a]anthracene, 7,12-dimethylbenz[a]anthracene, 3-methylcholanthrene, fluoranthene, anthanthrene, 11H-benzo[b]fluorene, dibenz[a,h]anthracene, pyrene, benzo[ghi]perylene and benzo[e]pyrene caused DNA strand breaks even without external metabolic activation, while naphthalene, anthracene, phenanthrene and naphthacene were inactive. When the comet assay was performed in the dark or when yellow fluorescent lamps were used for illumination the DNA-damaging effect of the 11 PAHs disappeared. White fluorescent lamps exhibit emission maxima at 334.1, 365.0, 404.7, and 435.8 nm representing spectral lines of mercury. In the case of yellow fluorescent lamps these emissions were absent. Obviously, under standard laboratory illumination many PAHs are photo-activated, resulting in DNA-damaging species. This feature of PAHs should be taken into account when these compounds are employed for the initiation of skin cancer. The genotoxicity of BaP that is metabolically activated in V79 cells stably expressing human cytochrome P450-dependent monooxygenase (CYP1A1) as well as human epoxide hydrolase (V79-hCYP1A1-mEH) could not be detected with the comet assay performed under yellow light. Likewise the DNA-damaging effect of r-7,t-8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BaPDE) observed with the comet assay was only weak. However, upon inhibition of nucleotide excision repair (NER), which is responsible for the removal of stable DNA adducts caused by anti-BaPDE, the tail moment rose 3.4-fold in the case of BaP and 12.9-fold in the case of anti-BaPDE. These results indicate that the genotoxicity of BaP and probably of other compounds producing stable DNA adducts are reliably detected with the comet assay only when NER is inhibited.

Biodegradation of benzo[a]pyrene with immobilized laccase: genotoxicity of the products in HaCat and A3 cells

Benzo[a]pyrene (BaP) is listed as a priority pollutant by the U.S. Environmental Protection Agency because it is one of the most potent carcinogens of all known polycyclic aromatic hydrocarbons (PAHs). The biodegradation of BaP is of interest as a means for mitigating its effects in polluted ecosystems. In the present study, BaP was oxidized with laccase from Trametes versicolor, which was immobilized on functionalized kaolinite particles, and the cytotoxicity and genotoxicity of BaP and its degradation intermediates were measured in human HaCaT keratinocytes and A3 T lymphocytes. Cytotoxicity was assessed by fluorescein diacetate (FDA) uptake, while the alkaline Comet assay measured genotoxicity, using tail moment, tail DNA content, and tail length as metrics for DNA damage. On the basis of first-order reaction kinetics, the half life (t(1/) (2)) for the oxidization of BaP by immobilized laccase was 58.5 hr. After 87 hr of oxidation, 20 muM of BaP had decreased to 9.6 muM. HPLC analysis identified 1,6-benzo[a]pyrene quinone (1,6-BaQ), 3,6-benzo[a]pyrene quinone (3,6-BaQ), and 6,12-benzo[a]pyrene quinone (6,12-BaQ) among the oxidation products. Most treatments of HaCaT cells and A3 lymphocytes with BaP or its quinone intermediates resulted in significant decreases in viability (P < 0.05); dose-dependent decreases in cell viability were detected at concentrations of 0.1, 1, and 5 muM, but none of these treatments resulted in decreases of >30%. While treatment of HaCaT cells with as little as 0.1 muM 6,12-BaQ caused significant DNA damage, DNA damage was detected in HaCaT cells only with 1 and 5 muM 1,6-BaQ and 3,6-BaQ, and 5 muM BaP. In Comet assays conducted with A3 lymphocytes, all three quinone intermediates caused significant increase in tail DNA content at 1 and 5 muM. The results indicate that immobilized laccase is capable of degrading BaP, but several of those biodegradation products produce significant levels of DNA damage in human cells.

The effect of smoking on DNA effects in the comet assay: a meta-analysis

The comet assay (alkaline single-cell gel electrophoresis, SCG or SCGE) is frequently used in biomonitoring to detect genotoxic effects in humans exposed at the workplace or in their environment. Because of its ready accessibility, blood is most frequently used in such studies. Many studies investigated cigarette smoking either as a genotoxic exposure itself or as a potential confounding factor in occupational studies. However, although smoking is considered to be a relevant exposure towards various genotoxins, conflicting results have been reported in the comet assay studies. The actual reasons for this discrepancy are not known. To further evaluate evidence for smoking-related DNA effects in the comet assay, we now used a meta-analysis approach based on a literature search. We identified 38 studies from 37 publications which were suited for a formal meta-analysis based on the standardized mean difference (SMD) between the study groups. The evaluation of these 38 studies indicated higher levels of DNA damage in smokers than in non-smokers [under a random effects model, SMD = 0.55, 95% confidence interval = (0.16-0.93)]. Subdividing these studies into studies investigating the effect of smoking as a genotoxic exposure (Type A studies, n = 12) and studies investigating smoking as a potential confounder in occupational studies (Type B, n = 26) indicated a significant difference only in Type A studies but not in Type B studies. Furthermore, studies using image analysis or image length measurements (n = 23) only indicated a tendency for a genotoxic effect of smoking, whereas studies using an arbitrary score (n = 15) found a significantly higher level of DNA damage in smokers.

CYTOCHROME P4501A INDUCED DIFFERENTIALLY IN ENDOTHELIAL CELLS CULTURED FROM DIFFERENT ORGANS OF ANGUILLA ROSTRATA

Endothelial cells are a structural barrier and an active regulator of many bodily processes. Cytochrome P4501A (CYP1A) activity is induced in the endothelium of teleosts and mammals exposed to lipophilic xenobiotics, such as polycyclic aromatic hydrocarbons, and can have significant consequences for endothelial functions. We exposed cultures of characterized endothelial cells from the heart, kidney, and rete mirabile of the eel, Anguilla rostrata, to aryl hydrocarbon receptor (AhR) agonists. In heart endothelial cells, the maximum response (based on O-deethylation of 7-ethoxyresorufin to resorufin [EROD] activity) to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 113 pmol/mg/min, was at 1 nM TCDD and the peak response to beta-napthoflavone (betaNF), 135 pmol/mg/min, was at 3 microM betaNF. The maximum response to TCDD in the kidney endothelial cells is 12 pmol/mg/min at 0.3 nM TCDD. The rete mirabile capillary endothelial cells responded minimally or not at all to exposure to TCDD and betaNF. Both the heart and kidney endothelial cells (but not the rete mirabile capillary cells) have a low level of EROD activity (12.7 and 5.2 pmol/mg/min, respectively) in untreated or dimethylsulfoxide-treated cells. The robust response of the heart endothelial cells to induction and the lack of response in the rete mirabile capillary endothelial cells indicate that these cells are a good resource to use to investigate the physiological consequences of AhR agonist exposure and CYP1A induction in different areas of the vasculature.

Reoxygenation after hypoxia and glucose depletion causes reactive oxygen species production by mitochondria in HUVEC

In hemorrhagic shock, local hypoxia is present and followed by reoxygenation during the therapeutic process. In endothelium, reactive oxygen species (ROS) have been identified as a cause of inflammatory reactions and tissular lesions in ischemic territory during reoxygenation. This study was designed to identify the enzymatic mechanisms of ROS formation during reoxygenation after hypoxia. Because severe shock, in vivo, can affect both O2and nutriments, we combined hypoxia at a level close to that found in terminal vessels during shock, with glucose depletion, which induces a relevant additional stress. Human umbilical vein endothelial cells (HUVEC) underwent 2 h of hypoxia (Po2∼20 mmHg) without glucose and 1 h of reoxygenation (Po2∼120 mmHg) with glucose. ROS production was measured by the fluorescent marker 2′,7′-dichlorodihydrofluorescein diacetate, and cell death by propidium iodide. After 1 h of reoxygenation, fluorescence had risen by 143 ± 17%. Cell death was equal to 8.6 ± 2.4%. Antimycin A and stigmatellin, which inhibits the type III mitochondrial respiratory chain complex, reduced ROS production to values of 61 ± 10 and 59 ± 7%, respectively, but inhibitors of other chain complexes did not affect it. In addition, the increase in fluorescence was not affected by inhibition of NADPH oxidase, xanthine oxidase, NOS, cyclooxygenase, cytochrome P-450 monooxygenase, or monoamine oxidase. We did not observe any increase in cell death. These results show that, in HUVEC, mitochondria are responsible for ROS production after hypoxia and reoxygenation and suggest that a ROS release site is activated in the cytochrome b of the type III respiratory chain complex.

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.

DNA damage in T- and B-lymphocytes and granulocytes in emission inspection and incineration workers exposed to polycyclic aromatic hydrocarbons

In this study, we investigated by using comet assay the effects of polycyclic aromatic hydrocarbon (PAH) as a major factor on DNA damage of workers exposed to exhaust fumes. Twenty-four workers from three automobile emission inspection companies, 28 workers from a waste incinerating company, and 43 matched, unexposed healthy subjects were enrolled in the study. The mean values of 1-hydroxypyrene (1-OHP) in automobile emission inspection and waste incineration workers were 0.27+/-0.19 and 0.57+/-0.46 micromol/mol creatinine, respectively, and the mean values of 2-naphthol in automobile emission inspectors and waste incineration workers were 4.80+/-4.01 and 8.30+/-4.79 mol/mol creatinine, respectively. Significant difference in urinary metabolites, 1-hydroxypyrene and 2-naphthol was found between smokers and non-smokers in exposed groups and it may be due to the amounts of smoking cigarettes. In T-lymphocytes, DNA damage in control subjects, emission inspection workers and incineration workers were 1.42+/-0.22, 1.41+/-0.22 and 1.76+/-0.27, respectively. DNA damage of B-lymphocytes in the three groups showed the most significant differences of three cell types. The tail moments of the B-lymphocytes of control subjects, emission inspection and incineration workers were 1.40+/-0.27, 2.44+/-0.32 and 2.36+/-0.37, respectively. In granulocytes, DNA damage was also different, the tail moments being 2.72+/-0.59, 3.32+/-0.38 and 2.85+/-0.49, respectively. Although 1-OHP and 2-naphthol levels were statistically increased in smokers in workers exposed to PAHs, exposed smoking and non-smoking workers did not show any significantly difference in terms of Olive tail moments. Our results suggest that PAH causes single strand DNA breakage in human T- and B-lymphocytes, and granulocytes. A comparison of DNA damage in three groups showed that B-lymphocytes are useful target in the biomonitoring of human exposure.

CYP1A1 and CYP1B1 in blood-brain interfaces: CYP1A1-dependent bioactivation of 7,12-dimethylbenz(a)anthracene in endothelial cells

Immunohistochemistry and autoradiography were used to identify sites of the cytochrome P450 enzymes (P450) 1A1 and 1B1 expression and activation of 7,12-dimethylbenz(a)anthracene (DMBA), in the brain of rodents pretreated with the aryl hydrocarbon receptor (AhR) agonists beta-naphthoflavone (BNF), 3,3',4,4',5-pentachlorobiphenyl or vehicle. Immunohistochemistry revealed that CYP1A1 was preferentially induced in endothelial cells (EC) in the choroid plexus, in veins in the leptomeninges, and in cerebral veins of AhR agonist-pretreated mice. No induction occurred in cerebral capillary EC. In vehicle-treated mice no localization of CYP1A1 in EC was observed. CYP1B1 was expressed in smooth muscle cells of arteries in the leptomeninges, in cerebral arteries/arterioles and to a low extent in ependymal cells of AhR agonist- and vehicle-treated mice. No CYP1B1 was detected in capillary loops of the choroid plexus or in cerebral capillaries. Following administration of [(3)H]DMBA to BNF-pretreated mice, a marked irreversible binding in EC of the choroid plexus and of veins in the leptomeninges was observed but not in cerebral capillaries. In vehicle-treated mice, there was no [(3)H]DMBA-binding at these sites. Furthermore, a high level of irreversibly bound [(3)H]DMBA occurred in EC at these sites in precision-cut mouse/rat brain slices and in excised blood-brain interfaces incubated with [(3)H]DMBA. Since [(3)H]DMBA binding sites corresponded with the sites of CYP1A1 induction, we conclude that rodents express a constitutively low but highly inducible and functional CYP1A1 in EC of some of the blood-brain interfaces. The role of CYP1A1/1B1 and environmental pollutants in the etiology of cerebrovascular disease needs further consideration.

The comet assay with MCL-5 cells as an indicator of genotoxic treatment with chemicals and cigarette smoke condensates

The metabolically competent human lymphoblastoid cell line MCL-5 was treated with a panel of mutagens to assess the induction of DNA damage. Treatment effects were observed by monitoring cell proliferation and by single-cell gel electrophoresis (SCGE). The direct-acting mutagens benzo[a]pyrene-7,8-diol 9,10-epoxide (BPDE) and 1-methyl-3-nitro-1-nitrosoguanidine (MNNG), as well as pro-mutagens requiring metabolic activation, i.e. benzo[a]pyrene (BaP), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 4-N-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and cigarette-smoke condensate (CSC), were assayed by SCGE. Assay schemes were adapted for the MCL-5 cell line and for low levels of strand break induction, by inclusion of the DNA synthesis inhibitors cytosine arabinoside and hydyroxyurea, and by extending the electrophoresis time. For all mutagens tested, dose-dependent increases of median and average tail moment values among 50 nucleoids per slide were observed. The determining factors for selecting the treatment doses for mutation-induction experiments were the solubility of BaP and PhIP in the exposure medium, and the cytotoxicity exhibited by BPDE, MNNG and CSC. Induction of DNA strand breaks was obtained at mutagen concentrations permitting sufficient cell proliferation, except in the case of MNNG.