Impact of cellular metabolism on the biological effects of benzo[a]pyrene and related hydrocarbons

Comparison of the acute effects of benzo-a-pyrene on adult zebrafish (Danio rerio) cardiorespiratory function following intraperitoneal injection versus aqueous exposure

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants. PAH exposure causes developmental toxicity in multiple fish species, while acute adult fish toxicity is thought to be minimal. The literature increasingly suggests sublethal PAH effects may occur, but differences in exposure route may confound conclusions. We hypothesized that acute PAH exposure in adult fish will cause cardiorespiratory impairment that will not differ with exposure route. In order to investigate this hypothesis, adult zebrafish (Danio rerio) were injected intraperitoneal (i.p.) twice with increasing concentrations of the prototypical PAH, benzo-a-pyrene (BaP; 0.1, 10, and 1000μg/kg) or exposed aqueously (static, renewal at 24h; 16.2 and 162μg/L) for 48h and compared to corresponding dimethylsulfoxide controls. No mortalities or significant effects on weight of the fish were noted at any exposure concentration or route. At 48h, fish were subjected to swimming tests with concurrent oxygen consumption measurement (n=10 fish/treatment) or echocardiography (n=12 fish/treatment). Oxygen consumption (MO2) was increased at three swimming speeds in BaP-injected groups compared to control (p<0.01 in Fisher's LSD tests after two-way ANOVA). In contrast, aqueously BaP-exposed fish showed increased MO2 under only basal conditions. Despite increased oxygen demand, ventricular heart rate was significantly decreased in BaP-exposed fish, both injected and aqueously-exposed. Analysis of BaP body burdens in fish tissue allowed for identification of an overlapping dose group between exposure routes, through which comparisons of cardiorespiratory toxicity were then made. This comparison revealed most effects were similar between the two exposures routes, although minor differences were noted. At similar BaP body burdens, injected fish suffered from more severe bradycardia than aqueously exposed fish and had greater levels of increases in cytochrome P4501A (CYP1A) mRNA levels in liver and heart tissue compared to aqueous exposed fish. In conclusion, acute BaP exposure in adult zebrafish had negative effects on cardiorespiratory function. Differences in effect between exposure routes were attributed primarily to differences in bioavailability, since overall, similar effects were noted between the two exposure routes when similar BaP body burdens were achieved.

Effects of carcinogenic versus non-carcinogenic AHR-active PAHs and their mixtures: lessons from ecological relevance

Polycyclic aromatic hydrocarbons (PAHs) are priority environmental mutagens and carcinogens that occur in the aquatic environment as mixtures rather than the individual compounds for which guidelines are issued. The present work aimed at understanding the interaction effects between carcinogenic and non-carcinogenic PAHs in a model marine fish (Dicentrarchus labrax) in realistic scenarios. Laboratory assays under ecologically-relevant parameters were conducted for 28 days with sediments spiked with low-moderate concentrations (250-800ngg(-1)) of two model PAHs, phenanthrene (non-carcinogenic) and benzo[b]fluoranthene (carcinogenic to experimental animals). Both PAHs induced hepatic histopathological changes that indicate metabolic failure and inflammation, especially in animals exposed to mixtures. Phenanthrene elicited biochemical changes better related to oxidative stress (lipid peroxidation, glutathione and glutathione S-transferase activity) and CYP function, whereas B[b]F disrupted metabolic responses and defences to toxicological challenge. Conversely, mixed PAHs yielded lesions and responses that, altogether, are compatible with the AHR dependent pathway (the basis of PAH mutagenicity), potentially generating supra-additive effects. Nonetheless, the low, ecologically-relevant, concentrations of PAHs diluted dose and time-response relations. Overall, although seemingly predicting the risk of individual PAHs, environmental guidelines may not apply to mixtures by underestimating adverse effects, which calls for a redefinition of standards when determining the true risk of toxicants under realistic circumstances.

Inhibition of β-catenin signalling promotes DNA damage elicited by benzo[a]pyrene in a model of human colon cancer cells via CYP1 deregulation

Deregulation of Wnt/β-catenin signalling plays an important role in the pathogenesis of colorectal cancer. Interestingly, this pathway has been recently implicated in transcriptional control of cytochrome P450 (CYP) family 1 enzymes, which are responsible for bioactivation of a number of dietary carcinogens. In the present study, we investigated the impact of inhibition of Wnt/β-catenin pathway on metabolism and genotoxicity of benzo[a]pyrene (BaP), a highly mutagenic polycyclic aromatic hydrocarbon and an efficient ligand of the aryl hydrocarbon receptor, which is known as a primary regulator of CYP1 expression, in cellular models derived from colorectal tumours. We observed that a synthetic inhibitor of β-catenin, JW74, significantly increased formation of BaP-induced DNA adducts in both colorectal adenoma and carcinoma-derived cell lines. Using the short interfering RNA (siRNA) targeting β-catenin, we then found that β-catenin knockdown in HCT116 colon carcinoma cells significantly enhanced formation of covalent DNA adducts by BaP and histone H2AX phosphorylation, as detected by (32)P-postlabelling technique and immunocytochemistry, respectively, and it also induced expression of DNA damage response genes, such as CDKN1A or DDB2. The increased formation of DNA adducts formed by BaP upon β-catenin knockdown corresponded with enhanced production of major BaP metabolites, as well as with an increased expression/activity of CYP1 enzymes. Finally, using siRNA-mediated knockdown of CYP1A1, we confirmed that this enzyme plays a major role in formation of BaP-induced DNA adducts in HCT116 cells. Taken together, the present results indicated that the siRNA-mediated inhibition of β-catenin signalling, which is aberrantly activated in a majority of colorectal cancers, modulated genotoxicity of dietary carcinogen BaP in colon cell model in vitro, via a mechanism involving up-regulation of CYP1 expression and activity.

Benzo(a)pyrene induced lung cancer: Role of dietary phytochemicals in chemoprevention

Lung cancer is the major cause of overall cancer deaths, and chemoprevention is a promising strategy to control this disease. Benzo(a)pyrene [B(a)P], a polycyclic aromatic hydrocarbon, is one among the principal constituents of tobacco smoke that plays a key role in lung carcinogenesis. The B(a)P induced lung cancer in mice offers a relevant model to study the effect of natural products and has been widely used by many researchers and found considerable success in ameliorating the pathophysiological changes of lung cancer. Currently available synthetic drugs that constitute the pharmacological armamentarium are themselves effective in managing the condition but not without setbacks. These hunches have accelerated the requisite for natural products, which may be used as dietary supplement to prevent the progress of lung cancer. Besides, these agents also supplement the conventional treatment and offer better management of the condition with less side effects. In the context of soaring interest toward dietary phytochemicals as newer pharmacological interventions for lung cancer, in the present review, we are attempting to give a silhouette of mechanisms of B(a)P induced lung carcinogenesis and the role of dietary phytochemicals in chemoprevention.

Specific histone modifications regulate the expression of AhR in 16HBE cells exposed to benzo(a)pyrene

Our study identified specific histone modifications that were involved in down regulation of the transcription of AhR, conferring cells resistance to cellular damage.

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.

The teleostean liver as an immunological organ: Intrahepatic immune cells (IHICs) in healthy and benzo[a]pyrene challenged rainbow trout (Oncorhynchus mykiss)

The existence of a resident population of intrahepatic immune cells (IHICs) is well documented for mammalian vertebrates, however, it is uncertain whether IHICs are present in the liver of teleostean fish. In the present study we investigated whether trout liver contains an IHIC population, and if so, what the relative cellular composition of this population is. The results provide clear evidence for the existence of an IHIC population in trout liver, which constitutes 15-29% of the non-hepatocytes in the liver, and with a cellular composition different to that of the blood leukocyte population. We also analyzed the response of IHICs to a non-infectious liver challenge with the hepatotoxic and immunotoxic chemical, benzo[a]pyrene (BaP). Juvenile trout were treated with BaP (25 or 100mg/kgbw) at levels sufficient to induce the molecular pathway of BaP metabolism while not causing pathological and inflammatory liver changes. The IHIC population responded to the BaP treatments in a way that differed from the responses of the leukocyte populations in trout blood and spleen, suggesting that IHICs are an independently regulated immune cell population.

Urinary 1-hydroxypyrene is associated with oxidative stress and inflammatory biomarkers in acute Myocardial Infarction

Several studies have associated exposure to environmental pollutants, especially polycyclic aromatic hydrocarbons (PAHs), with the development of cardiovascular diseases. Considering that 1-hydroxypyrene (1-OHP) is the major biomarker of exposure to pyrenes, the purpose of this study was to evaluate the potential association between 1-OHP and oxidative stress/inflammatory biomarkers in patients who had suffered an acute myocardial infarction (AMI). After adopting the exclusion criteria, 58 post-infarction patients and 41 controls were sub-divided into smokers and non-smokers. Urinary 1-OHP, hematological and biochemical parameters, oxidative stress biomarkers (MDA, SOD, CAT, GPx and exogenous antioxidants) and the inflammatory biomarker (hs-CRP) were analyzed. 1-OHP levels were increased in post-infarct patients compared to controls (p < 0.05) and were correlated to MDA (r = 0.426, p < 0.01), CAT (r = 0.474, p < 0.001) and β-carotene (r = -0.309; p < 0.05) in non-smokers. Furthermore, post-infarction patients had elevated hs-CRP, MDA, CAT and GPx levels compared to controls for both smokers and non-smokers. Besides, β-carotene levels and SOD activity were decreased in post-infarction patients. In summary, our findings indicate that the exposure to pyrenes was associated to lipid damage and alterations of endogenous and exogenous antioxidants, demonstrating that PAHs contribute to oxidative stress and are associated to acute myocardial infarction.

Single cell gel electrophoresis (SCGE) and Pig-a mutation assay in vivo-tools for genotoxicity testing from a regulatory perspective: a study of benzo[a]pyrene in Ogg1(-/-) mice

The OECD has developed test guidelines (TG) to identify agents with genotoxic effects. The in vivo alkaline single cell gel electrophoresis (SCGE) assay is currently being prepared to become such a TG. The performance of a combined SCGE/Pig-a gene mutation study was evaluated with the prototypical genotoxicant benzo[a]pyrene (BaP) at an exposure level known to induce germ cell mutation. We aimed to better understand (i) the strengths and weaknesses of the two methods applied in blood and their potential to predict germ cell mutagenicity, and (ii) the involvement of reactive oxygen species (ROS) following in vivo BaP-exposure. To explore the involvement of ROS on BaP genotoxicity, we utilised a mouse model deficient in a DNA glycosylase. Specifically, C57BL/6 mice (Ogg1(+/+) and Ogg1(-/-)) were treated for three consecutive days with 50 mg BaP/kg/day. DNA damage in nucleated blood cells was measured four hours after the last treatment with the SCGE assay, with and without formamidopyrimidine DNA glycosylase (Fpg). Pig-a mutant phenotype blood erythrocytes were analysed two and four weeks after treatment. BaP-induced DNA lesions were not significantly increased in either version of the SCGE assay. The phenotypic mutation frequencies for immature and mature erythrocytes were significantly increased after two weeks. These effects were not affected by genotype, suggesting oxidative damage may have a minor role in BaP genotoxicity, at least in the acute exposure situation studied here. While both assays are promising tools for risk assessment, these results highlight the necessity of understanding the limitations regarding each assay's ability to detect chemicals' genotoxic potential.

Soil quality in the Lomellina area using in vitro models and ecotoxicological assays

Soil quality is traditionally evaluated by chemical characterization to determine levels of pollutants. Biological tools are now employed for soil monitoring since they can take account of the global biological effects induced by all xenobiotics. A combined monitoring of soils based on chemical analyses, human-related in vitro models and ecotoxicological assay was applied in the Lomellina, a semirural area of northern Italy. Chemical characterization indicated overall good quality of the soils, with low levels of toxic and carcinogenic pollutants such as heavy metals, PAHs, PCDD/Fs and PCBs. HepG2 cells were used as a model for the human liver and BALB/c 3T3 cells to evaluate carcinogenic potential. Cells were treated with soil extractable organic matter (EOM) and the MTS assay, DNA release and morphological transformation were selected as endpoints for toxicity and carcinogenicity. Soil EOMs induced dose-dependent inhibition of cell growth at low doses and cytotoxicity only at doses of 500 and 1000 mg soil equivalents/ml. Potential issues for human health can be hypothesized after ingestion of soil samples from some sites. No statistically significant inductions of foci were recorded after exposure to EOMs, indicating that the levels of the soil-extracted organic pollutants were too low to induce carcinogenesis in our experimental conditions. An acute phytotoxicity test and studies on Caenorhabditis elegans were used as ecotoxicological assays for plants and small invertebrates. No significant alerts for ecotoxicity were found. In this proposed case study, HepG2 cells detected differences in the toxicity of soil EOMs, indicating that this cell line could be appropriate to assess the potential harm caused by the ingestion of contaminated soil. Additional information on the carcinogenic potential of mixtures was provided by the cell transformation assay, strengthening the combined approach.

Ethynylflavones, highly potent, and selective inhibitors of cytochrome P450 1A1

The flavone backbone is a well-known pharmacophore present in a number of substrates and inhibitors of various P450 enzymes. In order to find highly potent and novel P450 family I enzyme inhibitors, an acetylene group was incorporated into six different positions of flavone. The introduction of an acetylene group at certain locations of the flavone backbone lead to time-dependent inhibitors of P450 1A1. 3′-Ethynylflavone, 4′-ethynylflavone, 6-ethynylflavone, and 7-ethynylflavone (K_I values of 0.035–0.056 μM) show strong time-dependent inhibition of P450 1A1, while 5-ethynylflavone (K_I value of 0.51 μM) is a moderate time-dependent inhibitor of this enzyme. Meanwhile, 4′-ethynylflavone and 6-ethynylflavone are highly selective inhibitors toward this enzyme. Especially, 6-ethynylflavone possesses a K_i value of 0.035 μM for P450 1A1 177- and 15-fold lower than those for P450s 1A2 and 1B1, respectively. The docking postures observed in the computational simulations show that the orientation of the acetylene group determines its capability to react with P450s 1A1 and 1A2. Meanwhile, conformational analysis indicates that the shape of an inhibitor determines its inhibitory selectivity toward these enzymes.

Exposure to low dose benzo[a]pyrene during early life stages causes symptoms similar to cardiac hypertrophy in adult zebrafish

Growing evidence indicates that polycyclic aromatic hydrocarbons (PAHs) can lead to cardiac hypertrophy and recent research indicates that exposure to low dose crude oil during early embryonic development may lead to impacts on heart health at later life stages. The aim of this study was to evaluate whether exposure during early life stages to low dose benzo[a]pyrene (BaP), as a high-ring PAH, would lead to cardiac hypertrophy at later life stages. Zebrafish were exposed to low dose BaP until 96 hpf, then transferred to clean water and maintained for a year before histological and molecular biological analysis. Our results showed that exposure to low level BaP during early life stages increased heart weight to body weight ratios and deposited collagen in the heart of adult zebrafish. ANP, BNP and c-Myc were also induced in the heart of adult zebrafish by BaP. These results proved that low level BaP exposure during early life stages caused symptoms similar to cardiac hypertrophy in adult zebrafish. Our results displayed an elevated expression of CdC42, RhoA, p-ERK1, 2 and Rac1. Therefore, the mechanism of the cardiac hypertrophy caused by BaP exposure during early life stages may be through inducing the expression of CdC42, RhoA and Rac1, together with activating ERK1, 2.

In vitro metabolism of benzo[a]pyrene and dibenzo[def,p]chrysene in rodent and human hepatic microsomes

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous and often carcinogenic contaminants released into the environment during natural and anthropogenic combustion processes. Benzo[a]pyrene (B[a]P) is the prototypical carcinogenic PAH, and dibenzo[def,p]chrysene (DBC) is a less prevalent, but highly potent transplacental carcinogenic PAH. Both are metabolically activated by isoforms of the cytochrome P450 enzyme superfamily to form reactive carcinogenic and cytotoxic metabolites. Metabolism of B[a]P and DBC was studied in hepatic microsomes of male Sprague-Dawley rats, naïve and pregnant female B6129SF1/J mice, and female humans, corresponding to available pharmacokinetic data. Michaelis-Menten saturation kinetic parameters including maximum rates of metabolism (VMAX, nmol/min/mg microsomal protein), affinity constants (KM, μM), and rates of intrinsic clearance (CLINT, ml/min/kg body weight) were calculated from substrate depletion data. CLINT was also estimated from substrate depletion data using the alternative in vitro half-life method. VMAX and CLINT were higher for B[a]P than DBC, regardless of species. Clearance for both B[a]P and DBC was highest in naïve female mice and lowest in female humans. Clearance rates of B[a]P and DBC in male rat were more similar to female human than to female mice. Clearance of DBC in liver microsomes from pregnant mice was reduced compared to naïve mice, consistent with reduced active P450 protein levels and elevated tissue concentrations and residence times for DBC observed in previous in vivo pharmacokinetic studies. These findings suggest that rats are a more appropriate model organism for human PAH metabolism, and that pregnancy's effects on metabolism should be further explored.

Cooperative interaction of benzo[a]pyrene and ethanol on plasma membrane remodeling is responsible for enhanced oxidative stress and cell death in primary rat hepatocytes

Several epidemiologic studies have shown an interactive effect of heavy smoking and heavy alcohol drinking on the development of hepatocellular carcinoma. It has also been recently described that chronic hepatocyte death can trigger excessive compensatory proliferation resulting later in the formation of tumors in mouse liver. As we previously demonstrated that both benzo[a]pyrene (B[a]P), an environmental agent found in cigarette smoke, and ethanol possess similar targets, especially oxidative stress, to trigger death of liver cells, we decided to study here the cellular and molecular mechanisms of the effects of B[a]P/ethanol coexposure on cell death. After an 18-h incubation with 100nM B[a]P, primary rat hepatocytes were supplemented with 50mM ethanol for 5 or 8h. B[a]P/ethanol coexposure led to a greater apoptotic cell death that could be linked to an increase in lipid peroxidation. Plasma membrane remodeling, as depicted by membrane fluidity elevation and physicochemical alterations in lipid rafts, appeared to play a key role, because both toxicants acted with specific complementary effects. Membrane remodeling was shown to induce an accumulation of lysosomes leading to an important increase in low-molecular-weight iron cellular content. Finally, ethanol metabolism, but not that of B[a]P, by providing reactive oxygen species, induced the ultimate toxic process. Indeed, in lysosomes, ethanol promoted the Fenton reaction, lipid peroxidation, and membrane permeabilization, thereby triggering cell death. To conclude, B[a]P exposure, by depleting hepatocyte membrane cholesterol content, would constitute a favorable ground for a later toxic insult such as ethanol intoxication. Membrane stabilization of both plasma membrane and lysosomes might be a potential target for further investigation considering cytoprotective strategies.

p53 modulates Hsp90 ATPase activity and regulates aryl hydrocarbon receptor signaling

The aryl hydrocarbon receptor (AhR), a client protein of heat shock protein 90 (Hsp90), is a ligand-activated transcription factor that plays a role in polycyclic aromatic hydrocarbon (PAH)-induced carcinogenesis. Tobacco smoke activates AhR signaling leading to increased transcription of CYP1A1 and CYP1B1, which encode proteins that convert PAHs to mutagens. Recently, p53 was found to regulate Hsp90 ATPase activity via effects on activator of Hsp90 ATPase (Aha1). It is possible, therefore, that AhR-dependent expression of CYP1A1 and CYP1B1 might be affected by p53 status. The main objective of this study was to determine whether p53 modulated AhR-dependent gene expression and PAH metabolism. Here, we show that silencing p53 led to elevated Aha1 levels, increased Hsp90 ATPase activity, and enhanced CYP1A1 and CYP1B1 expression. Overexpression of wild-type p53 suppressed levels of CYP1A1 and CYP1B1. The significance of Aha1 in mediating these p53-dependent effects was determined. Silencing of Aha1 led to reduced Hsp90 ATPase activity and downregulation of CYP1A1 and CYP1B1. In contrast, overexpressing Aha1 was associated with increased Hsp90 ATPase activity and elevated levels of CYP1A1 and CYP1B1. Using p53 heterozygous mutant epithelial cells from patients with Li-Fraumeni syndrome, we show that monoallelic mutation of p53 was associated with elevated levels of CYP1A1 and CYP1B1 under both basal conditions and following treatment with benzo[a]pyrene. Treatment with CP-31398, a p53 rescue compound, suppressed benzo[a]pyrene-mediated induction of CYP1A1 and CYP1B1 and the formation of DNA adducts. Collectively, our results suggest that p53 affects AhR-dependent gene expression, PAH metabolism, and possibly carcinogenesis.

Regulation of p53-targeting microRNAs by polycyclic aromatic hydrocarbons: Implications in the etiology of multiple myeloma

Multiple myeloma (MM) is a common and deadly cancer of blood plasma cells. A unique feature of MM is the extremely low somatic mutation rate of the p53 tumor suppressor gene, in sharp contrast with about half of all human cancers where this gene is frequently mutated. Eleven miRNAs have been reported to repress p53 through direct interaction with the 3' untranslated region. The expression of nine of them is higher in MM plasma cells than in healthy donor counterparts, suggesting that miRNA overexpression is responsible for p53 inactivation in MM. Here, we report that the environmental carcinogen benzo[a]pyrene (BaP) upregulated the expression of seven p53-targeting miRNAs (miR-25, miR-15a, miR-16, miR-92, miR-125b, miR-141, and miR-200a), while 2,3,7,8-tetrachlorodibenzo-ρ-dioxin (TCDD) upregulated two of them (miR-25 and miR-92) in MM cells. The miR-25 promoter was activated by both BaP and TCDD, and this response was mediated by the aryl hydrocarbon receptor (AhR). We screened 727 compounds that inhibit MM cell survival and down-regulate the expression of p53-targeting miRNAs. We found that (-)-epigallocatechin-3-gallate (EGCG), a constituent of green tea and a major component of the botanical drug Polyphenon® E, reduced the expression of four p53-targeting miRNAs, including miR-25, miR-92, miR-141, and miR-200a. Collectively, these data implicate polycyclic aromatic hydrocarbons and AhR in the regulation of p53-targeting miRNAs in MM and identify a potential therapeutic and preventive agent to combat this deadly disease.

The protective effect of dietary Arthrospira (Spirulina) maxima against mutagenicity induced by benzo[alpha]pyrene in mice

Benzo[alpha]pyrene (B[α]P) was used to test the possible antimutagenic effects of Arthrospira (Spirulina) maxima (SP) on male and female mice. SP was orally administered at 0, 200, 400, or 800 mg/kg of body weight to animals of both sexes for 2 weeks before starting the B[α]P (intraperitoneal injection) at 125 mg/kg of body weight for 5 consecutive days. For the male dominant lethal test, each male was caged with two untreated females per week for 3 weeks. For the female dominant lethal test, each female was caged for 1 week with one untreated male. All the females were evaluated 13-15 days after mating for incidence of pregnancy, total corpora lutea, total implants and pre- and postimplant losses. SP protected from B[α]P-induced pre- and postimplant losses in the male dominant lethal test, and from B[α]P-induced postimplantation losses in treated females. Moreover, SP treatment significantly reduced the detrimental effect of B[α]P on the quality of mouse semen. Our results illustrate the protective effects of SP in relation to B[α]P-induced genetic damage to germ cells. We conclude that SP, owing mainly to the presence of phycocyanin, could be of potential clinical interest in cancer treatment or prevention of relapse.

Determining oxidative and non-oxidative genotoxic effects driven by estuarine sediment contaminants on a human hepatoma cell line

Estuarine sediments may be reservoirs of hydrophilic and hydrophobic pollutants, many of which are acknowledged genotoxicants, pro-mutagens and even potential carcinogens for humans. Still, studies aiming at narrowing the gap between ecological and human health risk of sediment-bound contaminant mixtures are scarce. Taking an impacted estuary as a case study (the Sado, SW Portugal), HepG2 (human hepatoma) cells were exposed in vitro for 48 h to extracts of sediments collected from two areas (urban/industrial and Triverine/agricultural), both contaminated by distinct mixtures of organic and inorganic toxicants, among which are found priority mutagens such as benzo[a]pyrene. Comparatively to a control test, extracts of sediments from both impacted areas produced deleterious effects in a dose-response manner. However, sediment extracts from the industrial area caused lower replication index plus higher cytotoxicity and genotoxicity (concerning total DNA strand breakage and clastogenesis), with emphasis on micronucleus induction. On the other hand, extracts from the rural area induced the highest oxidative damage to DNA, as revealed by the FPG (formamidopyrimidine-DNA glycosylase) enzyme in the Comet assay. Although the estuary, on its whole, has been classified as moderately contaminated, the results suggest that the sediments from the industrial area are significantly genotoxic and, furthermore, elicit permanent chromosome damage, thus potentially being more mutagenic than those from the rural area. The results are consistent with contamination by pro-mutagens like polycyclic aromatic hydrocarbons (PAHs), potentiated by metals. The sediments from the agriculture-influenced area likely owe their genotoxic effects to metals and other toxicants, probably pesticides and fertilizers, and able to induce reactive oxygen species without the formation of DNA strand breakage. The findings suggest that the mixtures of contaminants present in the assayed sediments are genotoxic to HepG2 cells, ultimately providing a useful approach to hazard identification and an effective line-of-evidence in the environmental monitoring of anthropogenically-impacted coastal ecosystems.

Using a multibiomarker approach and behavioural responses to assess the effects of anthracene in Palaemon serratus

Polycyclic aromatic hydrocarbons (PAHs) are recognised as one of the main groups of contaminants that assume more importance in the marine environment, enhancing the need of studies concerning their adverse effects and more efficient and ecologically relevant tools for environmental monitoring purposes. This study aims to apply an integrated approach including several multi-level biological responses (accumulation levels, biochemical responses important for different physiological functions and behavioural alterations) to assess the ecological relevance of the effects induced by sub-lethal concentrations of anthracene (ANT) in Palaemon serratus (common prawn). ANT accumulation was assessed by measuring the levels of ANT-type compounds in prawn digestive gland, muscle and eye; biochemical responses were determined using biomarkers involved in biotransformation, oxidative damage, energy production and neurotransmission processes; and behavioural alterations through swimming performance after 96 h exposure bioassay (ANT:16-1,024 μg/L). The rationale behind this approach is to assess the ecologically relevant effects induced by ANT in prawn, given by the association between behavioural alterations with biochemical responses, in search for more efficient tools for environmental risk assessment. Results show a significant decrease of swimming velocity (LOEC=128 μg/L) along with increased levels of ANT-type compounds in digestive gland (LOEC=128 μg/L), muscle (LOEC=256 μg/L) and eye (LOEC=32 μg/L) in prawn exposed to ANT. Increased activities of glutathione peroxidase (GPx) and catalase (CAT), involved in anti-oxidant defence system, were also observed (LOEC=256 μg/L; 1024μg/L, respectively) in the digestive gland of prawn, induction of oxidative damage in lipids (LPO) also occurred (LOEC=32 μg/L). The inhibition of swimming velocity showed a correlation with some biochemical parameters measured, including the levels of ANT-type compounds in tissues and LPO, and thus these may be considered sensitive and ecologically relevant criteria as well as early warning endpoints for assessing polycyclic aromatic compounds exposure effects on marine organisms.

Detection of key enzymes, free radical reaction products and activated signaling molecules as biomarkers of cell damage induced by benzo[a]pyrene in human keratinocytes

Benzo[a]pyrene (BaP) is a known carcinogenic and cell damaging agent. The underlying cell damaging pathomechanisms have not been totally revealed. Especially BaP-related induction of oxidative and nitrosative stress has not been previously investigated in detail. The presented study investigated these effects in order to elucidate the pathomechanism and as well to identify potential biological markers that may indicate a BaP exposure. Human immortalized keratinocytes (HaCaT cells) were exposed to BaP (1 μM) for either 5 min or 6 h, respectively. BaP-induced cellular damage was evaluated by immunocytochemistry analysis of multiple signaling cascades (e.g. apoptosis, Akt, MAPK, NOS, nitrotyrosine and 8-isoprostane formation), detection of nitrosative stress using diaminofluorescein (DAF-FM) and oxidative stress using 3' -(p-aminophenyl)fluorescein (APF). Our results show that BaP exposure significantly enhanced NO and ROS productions in HaCaT cells. BaP led to eNOS-phosphorylation at Ser(1177), Thr(495) and Ser(116) residues. Using specific inhibitors, we found that the Erk1/2 pathways seemed to have strong impact on eNOS phosphorylation. In addition, BaP-induced apoptosis was observed by caspase-3 activation and PARP cleavage. Our results suggest that BaP mediates its toxic effect in keratinocytes through oxidative and nitrosative stress which is accompanied by complex changes of eNOS phosphorylation and changes of Akt and MAPK pathways.

Mitochondrial targeting of cytochrome P450 (CYP) 1B1 and its role in polycyclic aromatic hydrocarbon-induced mitochondrial dysfunction

We report that polycyclic aromatic hydrocarbon (PAH)-inducible CYP1B1 is targeted to mitochondria by sequence-specific cleavage at the N terminus by a cytosolic Ser protease (polyserase 1) to activate the cryptic internal signal. Site-directed mutagenesis, COS-7 cell transfection, and in vitro import studies in isolated mitochondria showed that a positively charged domain at residues 41-48 of human CYP1B1 is part of the mitochondrial (mt) import signal. Ala scanning mutations showed that the Ser protease cleavage site resides between residues 37 and 41 of human CYP1B1. Benzo[a]pyrene (BaP) treatment induced oxidative stress, mitochondrial respiratory defects, and mtDNA damage that was attenuated by a CYP1B1-specific inhibitor, 2,3,4,5-tetramethoxystilbene. In support, the mitochondrial CYP1B1 supported by mitochondrial ferredoxin (adrenodoxin) and ferredoxin reductase showed high aryl hydrocarbon hydroxylase activity. Administration of benzo[a]pyrene or 2,3,7,8-tetrachlorodibenzodioxin induced similar mitochondrial functional abnormalities and oxidative stress in the lungs of wild-type mice and Cyp1a1/1a2-null mice, but the effects were markedly blunted in Cyp1b1-null mice. These results confirm a role for CYP1B1 in inducing PAH-mediated mitochondrial dysfunction. The role of mitochondrial CYP1B1 was assessed using A549 lung epithelial cells stably expressing shRNA against NADPH-cytochrome P450 oxidoreductase or mitochondrial adrenodoxin. Our results not only show conservation of the endoprotease cleavage mechanism for mitochondrial import of family 1 CYPs but also reveal a direct role for mitochondrial CYP1B1 in PAH-mediated oxidative and chemical damage to mitochondria.

Human hepatoma cells exposed to estuarine sediment contaminant extracts permitted the differentiation between cytotoxic and pro-mutagenic fractions

Complex toxicant mixtures present in estuarine sediments often render contaminant screening unfeasible and compromise determining causation. HepG2 cells were subjected to bioassays with sediment extracts obtained with a series of progressively polar solvents plus a crude extract. The sediments were collected from an impacted area of an estuary otherwise regarded as pristine, whose stressors result mostly from aquaculture effluents and hydrodynamic shifts that enhance particle deposition. Compared to a reference scenario, the most polar extracts yielded highest cytotoxicity while higher genotoxicity (including oxidative damage) was elicited by non-polar solvents. While the former caused effects similar to those expected from biocides, the latter triggered effects compatible with known pro-mutagens like PAHs, even though the overall levels of toxicants were considered of low risk. The results indicate that the approach may constitute an effective line-of-evidence to infer on the predominant set of hazardous contaminants present in complex environmental mixtures.

Protective role of cytochrome P450 1A1 (CYP1A1) against benzo[a]pyrene-induced toxicity in mouse aorta

Benzo[a]pyrene (BaP) is an environmental pollutant produced by combustive processes, such as cigarette smoke and coke ovens, and is implicated in the pathogenesis of atherosclerosis. Cytochrome P450 1A1 (CYP1A1) plays a role in both metabolic activation and detoxication of BaP in a context-dependent manner. The role of CYP1A1 in BaP-induced toxicity in aorta remains unknown. First, we fed Apoe⁻/⁻ mice an atherogenic diet plus BaP and found that oral BaP-enhanced atherosclerosis is associated with increased reactive oxygen species (ROS) and inflammatory markers, such as plasma tumor necrosis factor levels and aortic mRNA expression of vascular endothelial growth factor A (Vegfa). We next examined the effect of an atherogenic diet plus BaP on ROS and inflammatory markers in Cyp1a1⁻/⁻ mice. Although this treatment was not sufficient to induce atherosclerotic lesions in Cyp1a1⁻/⁻ mice, plasma antioxidant levels were decreased in Cyp1a1⁻/⁻ mice even in the absence of BaP treatment. The atherogenic diet plus BaP effectively elevated plasma ROS levels and expression of atherosclerosis-related genes, specifically Vegfa, in Cyp1a1⁻/⁻ mice compared with wild-type mice. BaP treatment increased Vegfa mRNA levels in mouse embryonic fibroblasts from Cyp1a1⁻/⁻ mice but not from wild-type mice. BaP-induced DNA adduct formation was increased in the aorta of Cyp1a1⁻/⁻ mice, but not wild-type or Apoe⁻/⁻ mice, and the atherogenic diet decreased BaP-induced DNA adducts in Cyp1a1⁻/⁻ mice compared with mice on a control diet. These data suggest that ROS production contributes to BaP-exacerbated atherosclerosis and that CYP1A1 plays a protective role against oral BaP toxicity in aorta.

Tissue-specific metabolism of benzo[a]pyrene in rainbow trout (Oncorhynchus mykiss): a comparison between the liver and immune organs

Polycyclic aromatic hydrocarbons (PAHs) are immunotoxicants in fish. In mammals, phase I metabolites are believed to be critically involved in the immunotoxicity of PAHs. This mechanism has been suggested for fish as well. The present study investigates the capacity of immune organs (head kidney, spleen) of rainbow trout, Oncorhynchus mykiss, to metabolize the prototypic PAH, benzo[a]pyrene (BaP). To this end, we analyzed 1) the induction of enzymatic capacity measured as 7-ethoxyresorufin-O-deethylase (EROD) activity in immune organs compared with liver, 2) the organ profiles of BaP metabolites generated in vivo, and 3) rates of microsomal BaP metabolite production in vitro. All measurements were done for control fish and for fish treated with an intraperitoneal injection of 15 mg BaP/kg body weight. In exposed trout, the liver, head kidney, and spleen contained similar levels of BaP, whereas EROD induction differed significantly between the organs, with liver showing the highest induction factor (132.8×), followed by head kidney (38.4×) and spleen (1.4×). Likewise, rates of microsomal metabolite formation experienced the highest induction in the liver of BaP-exposed trout, followed by the head kidney and spleen. Microsomes from control fish displayed tissue-specific differences in metabolite production. In contrast, in BaP-exposed trout, microsomes of all organs produced the potentially immunotoxic BaP-7,8-dihydrodiol as the main metabolite. The findings from this study show that PAHs, like BaP, are distributed into immune organs of fish and provide the first evidence that immune organs possess inducible PAH metabolism leading to in situ production of potentially immunotoxic PAH metabolites.

Chemical-based risk assessment and in vitro models of human health effects induced by organic pollutants in soils from the Olona Valley

Risk assessment of soils is usually based on chemical measurements and assuming accidental soil ingestion and evaluating induced toxic and carcinogenic effects. Recently biological tools have been coupled to chemical-based risk assessment since they integrate the biological effects of all xenobiotics in soils. We employed integrated monitoring of soils based on chemical analyses, risk assessment and in vitro models in the highly urbanized semirural area of the Olona Valley in northern Italy. Chemical characterization of the soils indicated low levels of toxic and carcinogenic pollutants such as PAHs, PCDD/Fs, PCBs and HCB and human risk assessment did not give any significant alerts. HepG2 and BALB/c 3T3 cells were used as a model for the human liver and as a tool for the evaluation of carcinogenic potential. Cells were treated with soil extractable organic matters (EOMs) and the MTS assay, LDH release and morphological transformation were selected as endpoints for toxicity and carcinogenicity. Soil EOMs induced dose-dependent inhibition of cell growth at low doses and cytotoxicity after exposure to higher doses. This might be the result of block of cell cycle progression to repair DNA damage caused by oxidative stress; if this DNA damage cannot be repaired, cells die. No significant inductions of foci were recorded after exposure to EOMs. These results indicate that, although the extracts contain compounds with proven carcinogenic potential, the levels of these pollutants in the analyzed soils were too low to induce carcinogenesis in our experimental conditions. In this proposed case study, HepG2 cells were found an appropriate tool to assess the potential harm caused by the ingestion of contaminated soil as they were able to detect differences in the toxicity of soil EOMs. Moreover, the cell transformation assay strengthened the combined approach giving useful information on carcinogenic potential of mixtures.

Complex metabolic interactions between benzo(a)pyrene and tributyltin in presence of dichlorodiphenyltrichloroethane in South American catfish Rhamdia quelen

In an attempt to explore complex metabolic interactions between toxicants present in polluted freshwater, hepatic metabolism of benzo(a)pyrene (BaP) and tributyltin (TBT) in fish was investigated when these compounds were administrated alone, mixed together and along with dichlorodiphenyltrichloroethane (DDT). Ten Rhamdia quelen per group were treated with a single intra-peritoneal (IP) dose (5-day experiment) or three successive doses (15-day experiment) either containing BaP (0.3; 3 or 30mgkg(-1)) or TBT (0.03; 0.3 or 3mgkg(-1)) or a combination of BaP+TBT, BaP+DDT, TBT+DDT and BaP+TBT+DDT under their respective lower doses, with DDT dose kept at 0.03mgkg(-1). Tetrahydroxy-benzo(a)pyrene (BaP-tetrol-I), and dibutyltin (DBT) and monobutyltin (MBT) were analyzed to assess BaP and TBT hepatic metabolism, respectively. A significant difference in BaP-tetrol-I concentration was observed in liver and bile between the lowest and the highest doses of BaP in both 5 and 15-day experiments. In the 15-day experiment, the presence of TBT with BaP reduced the amount of BaP-tetrol-I in bile compared to the BaP alone. The time of exposure and the number of doses affected BaP-tetrol-I concentration in the bile of fish exposed to BaP 0.3mgkg(-1) and BaP+DDT. TBT and its metabolites concentrations showed a dose-dependent increase in the liver in both experiments and in the bile in the 5-day experiment. TBT at its lowest dose was completely metabolized into DBT and MBT in the liver in the 15-day experiment. No TBT metabolites were detected in the bile of fish exposed to the mixtures in the 5-day experiment, except for a small MBT amount found in BaP+TBT+DDT. This study strengthens the hypothesis of a metabolic interaction between BaP and TBT in fish and suggests DDT as an important third player when present in the mixture.

Behaviour and biomarkers as tools to assess the acute toxicity of benzo(a)pyrene in the common prawn Palaemon serratus

Benzo(a)pyrene (BaP) is considered an important marine environmental contaminant, given its recognised environmental persistence and toxicity. However, its effects in marine crustaceans are poorly studied, namely the accumulation and sub-cellular effects that might be linked to behavioural alterations and may lead to ecologically relevant consequences. This study aims to investigate behavioural and physiological responses of the common prawn (Palaemon serratus) after acute exposure to BaP and infer the potential effects for the population in the wild. The applied approach included the evaluation of swimming performance after exposure, and several biochemical biomarkers involved in biotransformation, oxidative damage, energy production and levels of BaP-type compounds in tissues (eye, digestive gland and muscle) in a 96 h acute bioassay with exposure to BaP (16-4096 μg/L). The objective was to establish a link between behaviour (swimming velocity) and biochemical responses in order to assess the ecological relevance of the effects induced by BaP in P. serratus and to select useful tools for environmental risk assessment. Results showed swimming velocity impairment (LOEC = 128 μg/L), lipid peroxidation (LPO) induction (LOEC = 4096 μg/L) and BaP-type compounds increase in eye (LOEC = 32 μg/L), digestive gland and muscle (LOEC = 512 μg/L) of prawn after exposure to BaP. This oxidative damage in lipids seems to be caused by the incapacity to activate detoxification and anti-oxidant enzymes, once glutathione-S-transferase (GST), catalase (CAT) and glutathione peroxidase (GPx) were not affected by the exposure. This could be also an explanation to the increased levels of BaP-type compounds observed in tissues. An inability to increase the activities of enzymes involved in the production of energy was also observed, which may help to explain the detoxification failure and consequent increased levels of lipid peroxidation. The inhibition of swimming velocity was negatively correlated with biochemical parameters, including the presence of BaP-type compounds in different tissues and LPO, and thus, these parameters might be used as ecologically relevant and early-warning tools to assess the effects of PAHs. This study also highlights the usefulness of the fixed wavelength fluorescence (FF) technique to quantify PAHs-type compounds in tissues as indicative of exposure of P. serratus to PAHs, namely the sensitivity of eyes, which might be used for monitoring purposes and in marine ecological risk assessment studies.

Organ-specific distribution of 7-chlorinated benz[a]anthracene and regulation of selected cytochrome P450 genes in rats

We previously reported that 14-day exposure to 7-chlorinated benz[a]anthracene (7-Cl-BaA), a new environmental pollutant, selectively induced hepatic cytochrome P450 (CYP)1A2 in rats, although treatment with its parent, benz[a]anthracene (BaA), induced CYP1A1, CYP1A2, and CYP1B1. In this study, to better understand the relative contribution of chlorination to the toxicity of polycyclic aromatic hydrocarbons (PAHs), we investigated the organ-specific distributions of 7-Cl-BaA and BaA in F334 rats. After 14 days of oral administration of 7-Cl-BaA or BaA at a concentration of 1 or 10 mg/kg body weight/day, both chemicals were detected in their plasma, which was collected 24 hr after the last administration, even at the lower dosage. Dose-dependent accumulation patterns were observed in the liver, muscle, kidney, spleen, heart, and lung. The 7-Cl-BaA concentrations in the organs were higher than those of the BaA. Furthermore, at the end of the exposure, 7-Cl-BaA specifically regulated several CYP genes in the heart more so than in other organs, although these inductions were not significant in the BaA treatment. 7-Cl-BaA might also stimulate the metabolic pathways of chemicals other than AhR-mediated metabolism, which is specific to normal PAHs, because of the alterations of CYP2J4, CYP4B1, and CYP17A1 expression in rats. In conclusion, our results imply that the chlorination of PAHs may change their organ-specific distribution and consequently alter their toxicological impacts compared to their parent PAHs.

Effects of polycyclic aromatic hydrocarbons (PAHs) on an aquatic ecosystem: acute toxicity and community-level toxic impact tests of benzo[a]pyrene using lake zooplankton community

We estimated acute toxicity of benzo[a]pyrene (B[a]P) using two cladoceran species, Ceriodaphnia reticulata and Daphnia magna, and also analyzed its impact on zooplankton community throughout an exposure experiment using small-scale mesocosms. LC(50) of B[a]P for C. reticulata and D. magna was 4.3 and 4.7 µg/l, respectively. However, individuals fed with Chlorella showed higher LC(50), 6.1 µg/l for C. reticulata and 8.0 µg/l for D. magna. In the exposure experiment, we examined the impact of B[a]P on zooplankton community using conceivable concentrations in the environment (5 and 10 µg/l) using typical zooplankton community in eutrophicated systems. Despite the residence time of B[a]P in the water column was short as < 4 days, application of B[a]P induced decrease of zooplankton abundance. However, the recovery pattern was different among cladocerans and rotifers. Consequently, B[a]P showed insecticide-like impacts, suppressing cladoceran populations and inducing the dominance of rotifers particularly under high concentration (10 µg/l). Results have suggested that, even such short duration of B[a]P in the water body can have impact on zooplankton abundance and community structure. Since B[a]P easily precipitate to the bottom and rapidly disappears from the water body, careful monitoring and further assessment of the potential toxicity of polycyclic aromatic hydrocarbons are necessary.

MicroRNA changes associated with atypical CYP1A1 inducer BMS-764459

The corticotrophin releasing factor (CRF) receptor I antagonist, BMS-764459 (evaluated as a potential treatment of affective disorders), was orally dosed to female Sprague-Dawley rats once daily for 2 weeks (vehicle control or 175mg/kg/day). To investigate the mechanism of BMS-764459-related liver weight increases, total liver RNA was isolated and evaluated for mRNA gene expression by microarray analysis (assessing the expression of approximately 24,000 genes) from snap-frozen tissue. Subsequently, mRNA and miRNA (microRNA) were also analyzed 5 years later from FFPE (Formalin Fixed Paraffin Embedded) samples via RT-PCR (about 800 miRNA evaluated). Genomic analyses showed that BMS-764459 induces AhR target genes with additional inductions of CYP2B, CYP3A, and Abcc3 consistent with the gene expression pattern of atypical CYP1A1 inducers. Analysis of miRNA expression identified a number of significantly affected miRNAs. To further evaluate their role in atypical CYP1A1 induction, an in silico evaluation of differentially expressed miRNA was performed and their putative mRNA 3'-UTR (untranslated region) binding sequences were evaluated. MiR-680 and miR-29a were identified as potential regulators and biomarkers of atypical CYP1A1 induction by regulating Abcc3, CYP3A and CYP2B as well as a number of AhR targeted genes.

Oral benzo[a]pyrene: understanding pharmacokinetics, detoxication, and consequences--Cyp1 knockout mouse lines as a paradigm

Benzo[a]pyrene (BaP) is a prototypical polycyclic aromatic hydrocarbon (PAH); this ubiquitous environmental carcinogenic agent is found in tobacco smoke, charcoal-grilled foods, and PAH-contaminated surfaces of roofs, playgrounds, and highways. Cytochrome P450 1 wild-type, Cyp1a2(-/-), Cyp1b1(-/-), or Cyp1a2/1b1(-/-) knockouts, and mice with Cyp1a1 expression deleted in hepatocytes can ingest large oral BaP doses (125 mg/kg/d) without apparent toxicity. Cyp1a1(-/-) and Cyp1a1/1a2(-/-) knockouts and mice with Cyp1a1 expression deleted in gastrointestinal (GI) tract epithelial cells develop immunotoxicity and die within 32 days, indicating that GI tract inducible CYP1A1 is absolutely required for detoxication of oral BaP. Cyp1a1/1b1(-/-) and Cyp1a1/1a2/1b1(-/-) mice are rescued from immunosuppression and early death due to absent metabolic activation of BaP by CYP1B1 in immune cells. Ten-fold lower oral BaP doses result in adenocarcinoma of the proximal small intestine (PSI) in Cyp1a1(-/-) mice; Cyp1a1/1b1(-/-) double-knockout mice show no PSI cancer but develop squamous cell carcinoma of the preputial gland duct (PGD). BaP-metabolizing CYP1B1 in the PSI and CYP3A59 in the PGD are the most likely candidates to participate in tumor initiation in the epithelial cells of these two tissues; oncogenes and tumor-suppressor genes upregulated and downregulated during tumorigenesis are completely different between these tissues. This "oral BaP Cyp1" mouse paradigm represents a powerful teaching tool, showing that gene-environment interactions depend on route-of-administration: the same oral, but not intraperitoneal, BaP exposure leads to dramatic differences in target-organ toxicity and tumor type as a function of dose and Cyp1 genotype.

Genome-Wide Functional and Stress Response Profiling Reveals Toxic Mechanism and Genes Required for Tolerance to Benzo[a]pyrene in S. cerevisiae

Benzo[a]pyrene (BaP) is a ubiquitous, potent, and complete carcinogen resulting from incomplete organic combustion. BaP can form DNA adducts but other mechanisms may play a role in toxicity. We used a functional toxicology approach in S. cerevisiae to assess the genetic requirements for cellular resistance to BaP. In addition, we examined translational activities of key genes involved in various stress response pathways. We identified multiple genes and processes involved in modulating BaP toxicity in yeast which support DNA damage as a primary mechanism of toxicity, but also identify other potential toxicity pathways. Gene ontology enrichment analysis indicated that DNA damage and repair as well as redox homeostasis and oxidative stress are key processes in cellular response to BaP suggesting a similar mode of action of BaP in yeast and mammals. Interestingly, toxicant export is also implicated as a potential novel modulator of cellular susceptibility. In particular, we identified several transporters with human orthologs (solute carrier family 22) which may play a role in mammalian systems.

Oral benzo[a]pyrene in Cyp1a1/1b1(-/-) double-knockout mice: Microarray analysis during squamous cell carcinoma formation in preputial gland duct

Benzo[a]pyrene (BaP) is a prototypical polycyclic aromatic hydrocarbon (PAH) found in combustion processes. Cytochrome P450 1A1 and 1B1 enzymes (CYP1A1, CYP1B1) and other enzymes can activate PAHs to reactive oxygenated intermediates involved in mutagenesis and tumor initiation; also, CYP1 enzymes can detoxify PAHs. Cyp1(+/+) wild-type (WT) and Cyp1b1(-/-) knockout mice receiving oral BaP (12.5 mg/kg/day) remain healthy for >12 months. In contrast, we found that global knockout of the Cyp1a1 gene (1a1KO) results in proximal small intestine (PSI) adenocarcinoma within 8-12 weeks on this BaP regimen; striking compensatory increases in PSI CYP1B1 likely participate in initiation of adenocarcinoma in 1a1KO mice. Cyp1a1/1b1(-/-) double-knockout (DKO) mice on this BaP regimen show no PSI adenocarcinoma, but instead preputial gland duct (PGD) squamous cell carcinoma (SCC) occurs by 12 weeks. Herein, we compare microarray expression of PGD genes in WT, 1a1KO and DKO mice at 0, 4, 8, 12 and 16 weeks of oral BaP; about four dozen genes up- or down-regulated during most critical time-points were further verified by qRT-PCR. In DKO mice, CYP3A59 was unequivocally identified as the BaP-inducible and BaP-metabolizing best candidate responsible for initiation of BaP-induced SCC. Striking increases or decreases were found in 26 cancer-related genes plus eight Serpin genes in DKO, but not in 1a1KO or WT, mice on this BaP regimen; of the 26, 8 were RAS-related oncogenes. The mechanism by which cancer-related genes are responsible for SCC tumor progression in the PGD remains to be elucidated.

Vitamin D receptor activation enhances benzo[a]pyrene metabolism via CYP1A1 expression in macrophages

Benzo[a]pyrene (BaP) activates the aryl hydrocarbon (AHR) and induces the expression of genes involved in xenobiotic metabolism, including CYP1A1. CYP1A1 is involved not only in BaP detoxification but also in metabolic activation, which results in DNA adduct formation. Vitamin D receptor (VDR) belongs to the NR1I subfamily of the nuclear receptor superfamily, which also regulates expression of xenobiotic metabolism genes. We investigated the cross-talk between AHR and VDR signaling pathways and found that 1α,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], a potent physiological VDR agonist, enhanced BaP-induced transcription of CYP1A1 in human monocytic U937 cells and THP-1 cells, breast cancer cells, and kidney epithelium-derived cells. 1,25(OH)(2)D(3) alone did not induce CYP1A1, and 1,25(OH)(2)D(3) plus BaP did not increase CYP1A2 or CYP1B1 mRNA expression in U937 cells. The combination of 1,25(OH)(2)D(3) and BaP increased CYP1A1 protein levels, BaP hydroxylation activity, and BaP-DNA adduct formation in U937 cells and THP-1 cells more effectively than BaP alone. The combined effect of 1,25(OH)(2)D(3) and BaP on CYP1A1 mRNA expression in U937 cells and/or THP-1 cells was inhibited by VDR knockdown, VDR antagonists, and α-naphthoflavone, an AHR antagonist. Electrophoretic mobility shift assays and chromatin immunoprecipitation assays showed that VDR directly bound to an everted repeat (ER) 8 motif in the human CYP1A1 promoter. Thus, CYP1A1 is a novel VDR target gene involved in xenobiotic metabolism. Induction of CYP1A1 by the activation of VDR and AHR may contribute to BaP-mediated toxicity and the physiological function of this enzyme.

Exposure of primary porcine urothelial cells to benzo(a)pyrene: in vitro uptake, intracellular concentration, and biological response

More than 90 % of all bladder cancers are transitional cell carcinomas arising from the cells lining the inside of the hollow organ (uroepithelium). Cell cultures from primary urinary bladder epithelial cells (PUBEC) of pigs were established to assess the uptake, intracellular concentration, and subcellular distribution of the environmental pollutant benzo(a)pyrene (BaP). During treatment of the cells with 0.5 μM BaP for up to 24 h, intracellular concentration of BaP increased without saturation but with marked differences between various PUBEC pools. Analysis of BaP uptake by laser scanning microscopy indicated that BaP is rapidly partitioned into the cell membrane, while only a slight but significant increase in BaP fluorescence intensity was observed in the cytosol and nucleus. Spectrofluorometric quantification of BaP in PUBEC using ex situ calibration revealed a strong accumulation of BaP, leading to intracellular concentrations ranging from 7.28 to 35.70 μM in cells exposed to 0.5 μM BaP and from 29.9 to 406.64 μM in cells exposed to 10 μM BaP. These results were confirmed by gas chromatographic mass spectrometric analysis. Apoptotic cell nuclei were assessed by TUNEL analysis to see whether BaP exposure at the given concentrations results in a toxic effect. While apoptotic cells were barely detectable in control epithelial cells, there was a marked elevation in apoptosis in the BaP-exposed cells. In conclusion, a comprehensive study on uptake and quantification of BaP in epithelial cells from pig bladder is reported for the first time. The study may be helpful in understanding the pattern of BaP uptake and distribution in bladder and its possible implication in bladder cancer development.

Review of oil and HNS accidental spills in Europe: identifying major environmental monitoring gaps and drawing priorities

The European Atlantic area has been the scene of a number of extensive shipping incidents with immediate and potential long-term impacts to marine ecosystems. The occurrence of accidental spills at sea requires an effective response that must include a well executed monitoring programme to assess the environmental contamination and damage of the affected marine habitats. Despite a number of conventions and protocols developed by international and national authorities that focused on the preparedness and response to oil and HNS spills, much remains to be done, particularly in relation to the effectiveness of the environmental monitoring programmes implemented after oil and HNS spills. Hence, the present study reviews the status of the environmental monitoring programmes established following the major spill incidents over the last years in European waters, aiming at identifying the key monitoring gaps and drawing priorities for an effective environmental monitoring of accidental spills.

In utero exposure to benzo(a)pyrene predisposes offspring to cardiovascular dysfunction in later-life

In utero exposure of the fetus to benzo(a)pyrene [B(a)P], a polycyclic aromatic hydrocarbon, is thought to dysregulate cardiovascular development. To investigate the effects of in utero B(a)P exposure on cardiovascular development, timed-pregnant Long Evans Hooded (LEH) rats were exposed to diluent or B(a)P (150, 300, 600 and 1200 μg/kg/BW) by oral gavage on embryonic (E) days E14 (the metamorphosing embryo stage) through E17 (the 1st fetal stage). There were no significant effects of in utero exposure to B(a)P on the number of pups born per litter or in pre-weaning growth curves. Pre-weaning profiles for B(a)P metabolite generation from cardiovascular tissue were shown to be dose-dependent and elimination of these metabolites was shown to be time-dependent in exposed offspring. Systolic blood pressure on postnatal day P53 in the middle and high exposure groups of offspring were significantly elevated as compared to controls. Microarray and quantitative real-time PCR results were directly relevant to a biological process pathway in animal models for "regulation of blood pressure". Microarray and quantitative real-time PCR analysis revealed upregulation of mRNA expression for angiotensin (AngII), angiotensinogen (AGT) and endothelial nitric oxide synthase (eNOS) in exposed offspring. Biological network analysis and gene set enrichment analysis subsequently identified potential signaling mechanisms and molecular pathways that might explain the elevated systolic blood pressures observed in B(a)P-exposed offspring. Our findings suggest that in utero exposure to B(a)P predispose offspring to functional deficits in cardiovascular development that may contribute to cardiovascular dysfunction in later life.

Carnosol, a constituent of Zyflamend, inhibits aryl hydrocarbon receptor-mediated activation of CYP1A1 and CYP1B1 transcription and mutagenesis

The aryl hydrocarbon receptor (AhR), a ligand-activated member of the basic helix-loop-helix family of transcription factors, plays a significant role in polycyclic aromatic hydrocarbon (PAH)-induced carcinogenesis. In the upper aerodigestive tract of humans, tobacco smoke, a source of PAHs, activates the AhR leading to increased expression of CYP1A1 and CYP1B1, which encode proteins that convert PAHs to genotoxic metabolites. Inhibitors of Hsp90 ATPase cause a rapid decrease in levels of AhR, an Hsp90 client protein, and thereby block PAH-mediated induction of CYP1A1 and CYP1B1. The main objective of this study was to determine whether Zyflamend, a polyherbal preparation, suppressed PAH-mediated induction of CYP1A1 and CYP1B1 and inhibited DNA adduct formation and mutagenesis. We also investigated whether carnosol, one of multiple phenolic antioxidants in Zyflamend, had similar inhibitory effects. Treatment of cell lines derived from oral leukoplakia (MSK-Leuk1) and skin (HaCaT) with benzo[a]pyrene (B[a]P), a prototypic PAH, induced CYP1A1 and CYP1B1 transcription, resulting in enhanced levels of message and protein. Both Zyflamend and carnosol suppressed these effects of B[a]P. Notably, both Zyflamend and carnosol inhibited Hsp90 ATPase activity and caused a rapid reduction in AhR levels. The formation of B[a]P-induced DNA adducts and mutagenesis was also inhibited by Zyflamend and carnosol. Collectively, these results show that Zyflamend and carnosol inhibit Hsp90 ATPase leading to reduced levels of AhR, suppression of B[a]P-mediated induction of CYP1A1 and CYP1B1, and inhibition of mutagenesis. Carnosol-mediated inhibition of Hsp90 ATPase activity can help explain the chemopreventive activity of herbs such as Rosemary, which contain this phenolic antioxidant.

Inherent and benzo[a]pyrene-induced differential aryl hydrocarbon receptor signaling greatly affects life span, atherosclerosis, cardiac gene expression, and body and heart growth in mice

Little is known of the environmental factors that initiate and promote disease. The aryl hydrocarbon receptor (AHR) is a key regulator of xenobiotic metabolism and plays a major role in gene/environment interactions. The AHR has also been demonstrated to carry out critical functions in development and disease. A qualitative investigation into the contribution by the AHR when stimulated to different levels of activity was undertaken to determine whether AHR-regulated gene/environment interactions are an underlying cause of cardiovascular disease. We used two congenic mouse models differing at the Ahr gene, which encodes AHRs with a 10-fold difference in signaling potencies. Benzo[a]pyrene (BaP), a pervasive environmental toxicant, atherogen, and potent agonist for the AHR, was used as the environmental agent for AHR activation. We tested the hypothesis that activation of the AHR of different signaling potencies by BaP would have differential effects on the physiology and pathology of the mouse cardiovascular system. We found that differential AHR signaling from an exposure to BaP caused lethality in mice with the low-affinity AHR, altered the growth rates of the body and several organs, induced atherosclerosis to a greater extent in mice with the high-affinity AHR, and had a huge impact on gene expression of the aorta. Our studies also demonstrated an endogenous role for AHR signaling in regulating heart size. We report a gene/environment interaction linking differential AHR signaling in the mouse to altered aorta gene expression profiles, changes in body and organ growth rates, and atherosclerosis.

Secondhand tobacco smoke, arterial stiffness, and altered circadian blood pressure patterns are associated with lung inflammation and oxidative stress in rats

Chronic smoking and secondhand tobacco smoke exposure are major risk factors for cardiovascular disease that are known to adversely alter the structural and mechanical properties of arteries. The objective of this study was to determine the effects of subchronic secondhand tobacco smoke exposure on circadian blood pressure patterns, arterial stiffness, and possible sources of oxidative stress in conscious, unsedated radiotelemetry-implanted rats. Pulse wave change in pressure over time (dP/dt) was used an indicator of arterial stiffness and was compared with both structural (wall thickness) and functional (nitric oxide production and bioactivity and endothelin-1 levels) features of the arterial wall. In addition, histology of lung, heart, and liver was examined as well as pulmonary and hepatic detoxifying enzyme activity (cytochrome P450, specifically CYP1A1). Subchronic secondhand tobacco smoke exposure altered the circadian pattern of heart rate and blood pressure, with a loss in the normal dipping pattern of blood pressure during sleep. Secondhand tobacco smoke exposure also increased pulse wave dP/dt in the absence of any structural modifications in the arterial wall. Furthermore, although nitric oxide production and endothelin-1 levels were not altered by secondhand tobacco smoke, there was increased inactivation of nitric oxide as indicated by peroxynitrite production. Increased lung neutrophils or pulmonary CYP1A1 may be responsible for the increase in oxidative stress in rats exposed to secondhand tobacco smoke. In turn, this may be related to the observed failure of blood pressure to dip during periods of sleep and a possible increase in arterial stiffness.