A comparison of the concentration-effect relationships of PAHs on CYP1A induction in HepG2 and Mcf7 cells

A novel approach to assess the health risk of aryl hydrocarbon receptor-bound contaminants via inhalation exposure using CYP1A1 expression as a biomarker

Polycyclic aromatic hydrocarbons (PAHs) and dioxins are potential causes of multiple diseases by activating the aryl hydrocarbon receptor (AhR) pathway. Health risk assessment of chemicals primarily relies on the relative potency factor (RPF), although its accuracy may be limited when solely using EC50 values. The induction of cytochrome P4501A1 (CYP1A1) serves as a biomarker for AhR activation and is an integrator of dioxin-like toxicity. Here, we present a method for evaluating the risks associated with AhR activation using mathematical models of dose-CYP1A1 induction. The dose-effect curves for certain PAHs and dioxins, including Ant, BghiP, 1,2,3,4,7,8-HxCDD, and others, exhibited a non-classical S-shaped form. The toxic equivalent factor (TEF) profiles revealed a broad range of toxic equivalent factor values. The TEFs for PAHs ranged from approximately 0.01 to 6, with higher values being observed when the concentration was less than 10-10 M, with the exceptions of Ace, Phe, and BghiP. Most congeners of dioxins got the lowest TEF value at around 10-10 M, ranging from 0.04 to 1.00. The binding affinity of AhR to ligands did not display a strong correlation with the EC50 of CYP1A1 expression, suggesting that the AhR-mediated effects of PAHs and dioxins are not fixed but instead fluctuate with the dose. Air samples acquired from a parking area were used to compare the proficiency of RPF and our current approach. In the current method, naphthalene and chrysene were the primary contributors of PAHs to AhR-mediated risks in parking lots air samples, respectively. However, the contributions of naphthalene and chrysene could be disregarded in the RPF approach.

Toxicity and oxidative stress of HepG2 and HL-7702 cells induced by PAH4 using oil as a carrier

Polycyclic aromatic hydrocarbons (PAHs), a widespread class of food pollutants, are commonly exposed to humans along with edible oil. The dietary exposure pattern of PAH4 was simulated to study the toxicity and oxidative stress of oil-based PAH4 on hepatocytes. The findings demonstrated that oil-based PAH4 induced cell viability and mitochondrial membrane potential decreased and promoted apoptosis and oxidative stress in a concentration-dependent manner. Benzo[a]pyrene had the strongest toxicity and HL-7702 cells were more sensitive to toxicity than HepG2 cells, due to differences in induced CYP1A enzyme activity. Oil-based PAH4 had greater cytotoxicity than PAH4, attributed to the synergistic effect of oil and PAH4. Furthermore, oil-based PAH4 induced oxidative stress in HepG2 and HL-7702 cells through the same AHR-Nrf2-KEAP1 pathway, which was elucidated by detecting genes and proteins expression. This study lays the foundation for elucidating the harm of dietary exposure to PAHs and reminds us that food composition may increase the harm of PAHs.

CYP1A inhibitors: Recent progress, current challenges, and future perspectives

Mammalian cytochrome P450 1A (CYP1A) are key phase I xenobiotic-metabolizing enzymes that play a distinctive role in metabolic activation or metabolic clearance of a variety of procarcinogens, drugs, and endogenous substances. Human CYP1A subfamily contains two members (hCYP1A1 and hCYP1A2), which are known to catalyze the oxidative activation of some environmental procarcinogens into carcinogenic species. Increasing evidence has demonstrated that CYP1A inhibitor therapies are promising strategies for cancer chemoprevention or overcoming CYP1A-associated drug toxicity and resistance. Herein, we reviewed recent advances in the discovery and characterization of hCYP1A inhibitors, from the discovery approaches to structural features and biomedical applications of hCYP1A inhibitors. The inhibition potentials, inhibition modes, and inhibition constants of all reported hCYP1A inhibitors are comprehensively summarized. Meanwhile, the structural features and structure-activity relationships of different classes of hCYP1A1 and hCYP1A2 inhibitors are analyzed and discussed in depth. Furthermore, the major challenges and future directions for this field are presented and highlighted. Collectively, the information and knowledge presented here will strongly facilitate the researchers to discover and develop more efficacious CYP1A inhibitors for specific purposes, such as chemo-preventive agents or as tool molecules in hCYP1A-related fundamental studies.

A novel approach to predict the comprehensive EROD potency: Mechanism-based curve fitting of CYP1A1 activity by PAHs

Cytochrome P450 1A1 (CYP1A1) plays critical roles in polycyclic aromatic hydrocarbon (PAH) toxicity, including DNA adduction and ROS generation. Therefore, CYP1A1 activity quantified by the 7-ethoxyresorufin-O-deethylase (EROD) assay (named EROD potency) has been considered a typical biomarker of PAH exposure and toxicity. The EROD dose-response curve always presents a biphasic style, increasing at low concentrations and decreasing at high concentrations of PAHs, but relative effect potency (REP) commonly used in PAH risk assessment is only involved in the increasing phase. In this study, a full bell-shaped EROD curve fitting formula Eq. (1) was obtained by considering both CYP1A1 mRNA induction and enzyme inhibition to completely assess the EROD potency of PAHs. Correspondingly, in silico models of QSAR and docking methods successfully predicted the full EROD curves of PAHs, and the structure-activity relationship indicated that PAHs with heavy molecular weight and large diameter showed stronger EROD potency. Further EROD potency with predicted curve parameters (EC_50,ind and area index) was confirmed by the reported REP (R² = 0.697-0.977) and experimental data from human and mouse cells (R² = 0.700-0.804). This study provides a novel curve fitting for the EROD dose-response relationship and a prediction model for PAH EROD potency.

Integrative analysis to explore the biological association between environmental skin diseases and ambient particulate matter

Although numerous experimental studies have suggested a significant association between ambient particulate matter (PM) and respiratory damage, the etiological relationship between ambient PM and environmental skin diseases is not clearly understood. Here, we aimed to explore the association between PM and skin diseases through biological big data analysis. Differential gene expression profiles associated with PM and environmental skin diseases were retrieved from public genome databases. The co-expression among them was analyzed using a text-mining-based network analysis software. Activation/inhibition patterns from RNA-sequencing data performed with PM_2.5-treated normal human epidermal keratinocytes (NHEK) were overlapped to select key regulators of the analyzed pathways. We explored the adverse effects of PM on the skin and attempted to elucidate their relationships using public genome data. We found that changes in upstream regulators and inflammatory signaling networks mediated by MMP-1, MMP-9, PLAU, S100A9, IL-6, and S100A8 were predicted as the key pathways underlying PM-induced skin diseases. Our integrative approach using a literature-based co-expression analysis and experimental validation not only improves the reliability of prediction but also provides assistance to clarify underlying mechanisms of ambient PM-induced dermal toxicity that can be applied to screen the relationship between other chemicals and adverse effects.

Benzo[a]pyrene-Induced Genotoxicity in Rats Is Affected by Co-Exposure to Sudan I by Altering the Expression of Biotransformation Enzymes

The environmental pollutant benzo[a]pyrene (BaP) is a human carcinogen that reacts with DNA after metabolic activation catalysed by cytochromes P450 (CYP) 1A1 and 1B1 together with microsomal epoxide hydrolase. The azo dye Sudan I is a potent inducer of CYP1A1/2. Here, Wistar rats were either treated with single doses of BaP (150 mg/kg bw) or Sudan I (50 mg/kg bw) alone or with both compounds in combination to explore BaP-derived DNA adduct formation in vivo. Using 32P-postlabelling, DNA adducts generated by BaP-7,8-dihydrodiol-9,10-epoxide were found in livers of rats treated with BaP alone or co-exposed to Sudan I. During co-exposure to Sudan I prior to BaP treatment, BaP-DNA adduct levels increased 2.1-fold in comparison to BaP treatment alone. Similarly, hepatic microsomes isolated from rats exposed to Sudan I prior to BaP treatment were also the most effective in generating DNA adducts in vitro with the activated metabolites BaP-7,8-dihydrodiol or BaP-9-ol as intermediates. DNA adduct formation correlated with changes in the expression and/or enzyme activities of CYP1A1, 1A2 and 1B1 in hepatic microsomes. Thus, BaP genotoxicity in rats in vivo appears to be related to the enhanced expression and/or activity of hepatic CYP1A1/2 and 1B1 caused by exposure of rats to the studied compounds. Our results indicate that the industrially employed azo dye Sudan I potentiates the genotoxicity of the human carcinogen BaP, and exposure to both substances at the same time seems to be hazardous to humans.

Comparing the genotoxicity of a potentially carcinogenic and a noncarcinogenic PAH, singly, and in binary combination, on peripheral blood cells of the European sea bass

Research on the toxicological mechanisms of polycyclic aromatic hydrocarbons (PAHs) deemed carcinogenic and noncarcinogenic has mostly been developed for individual compounds even though, in the environment, PAHs invariably occur in mixtures. The present work aimed at understanding the interaction effects of two model PAHs, the potentially carcinogenic benzo[b]fluoranthene (B[b]F) and the noncarcinogenic phenanthrene (Phe) to a marine fish (the sea bass Dicentrarchus labrax). The study endeavoured an ecologically-relevant scenario with respect to concentrations and contaminant matrix, sediments, which are the main reservoirs of these substances in the environment, due to their hydrophobic nature. For the purpose, 28-day laboratorial bioassays with spiked sediments (with individual and combined PAHs at equitoxic concentrations) were conducted. Genotoxicity was determined in peripheral blood through the "Comet" assay and by scoring erythrocytic nuclear abnormalities (ENA). The results showed that exposure to either PAHs induced similar levels of DNA strand breaks, although without a clear dose- or time-response, likely due to the low concentrations of exposure and potential shits in PAH bioavailability during the assays. However, clastogenic/aneugenic lesions were only observed in fish exposed to B[b]F-spiked sediments. Conversely, the combination assays revealed a supra-additive effect especially at chromosome level, linked to concentrations of PAHs in water. A decrease in DNA-strand breakage was observed over time during all assays, revealing some ability of fish to cope with this DNA lesion. Overall, the findings show that low-moderate concentrations of sediment-bound mixed PAHs may significantly increase the hazard of mutagenesis even when the individual concentrations indicate low risk, especially considering that chromosome-level damage is unlikely to be repaired, leading to the fixation of DNA lesions upon prolonged exposures. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1307-1318, 2016.

Inhibition of the formation of benzo[a]pyrene adducts to DNA in A549 lung cells exposed to mixtures of polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous pollutants, which exhibit carcinogenic properties especially in lungs. In the present work, we studied the effect of mixtures of 12 PAHs on the A549 alveolar cells. We first assess the ability of each PAH at inducing gene expression of phase I metabolization enzymes and at generating DNA adducts. A good correlation was found between these two endpoints. We then exposed cells to either binary mixtures of the highly genotoxic benzo[a]pyrene (B[a]P) with each PAH or complex mixtures of all studied PAHs mimicking by real emissions including combustion of wood, cigarette smoke, and atmospheres of garage, silicon factory and urban environments. Compared to pure B[a]P, both types of mixtures led to reduced CYP450 activity measured by the EROD test. A similar trend was observed for the formation of DNA adducts. Surprisingly, the complex mixtures were more potent than B[a]P used at the same concentration for the induction of genes coding for CYP. Our results stress the lack of additivity of the genotoxic properties of PAH in mixtures. Interestingly, an opposite synergy in the formation of B[a]P adducts were observed previously in hepatocytes. Our data also show that measurement of the metabolic activity rather than quantification of gene expression reflects the actual bioactivation of PAHs into DNA damaging species.

Identification of two isoforms of CYP4 in Marsupenaeus japonicus and their mRNA expression profile response to benzo[a]pyrene

CYP4 enzymes are essential components of cellular detoxification systems and play important roles in monitoring persistent organic pollutants in marine environments. However, there are few studies on CYP4 in shrimp. In this study, two CYP4 isoforms, CYP4V28 and CYP4V29, were cloned from Marsupenaeus japonicus for the first time, and the tissue distributions and mRNA expression profile in response to benzo[a]pyrene (B[a]P) were analyzed by quantitative real-time PCR (QRT-PCR). The full lengths of CYP4V28 and CYP4V29 were 1771 bp and 1647 bp respectively, with deduced amino acid sequences of 511 and 515 amino acids. The two CYP4s were predominantly expressed in the hepatopancreas and weakly expressed in other six tested tissues. As demonstrated by QRT-PCR, the mRNA levels of the two CYP4s show both a time- and dose-dependent response to B[a]P. The mRNA expression levels of CYP4V28 and CYP4V29 peaked at 12 h and 6 h respectively, and the peak level exhibited a tendency of positive correlation with the concentration of B[a]P. This study provides clues for further elucidating the function and regulation mechanisms of the two CYP4s in M. japonicas and evaluating of the biomarker potential of the two CYP4 isoforms.

Aryl hydrocarbon receptor activation and developmental toxicity in zebrafish in response to soil extracts containing unsubstituted and oxygenated PAHs

Many industrial sites are polluted by complex mixtures of polycyclic aromatic compounds (PACs). Besides polycyclic aromatic hydrocarbons (PAHs), these mixtures often contain significant amounts of more polar PACs including oxygenated PAHs (oxy-PAHs). The effects of oxy-PAHs are, however, poorly known. Here we used zebrafish embryos to examine toxicities and transcriptional changes induced by PAC containing soil extracts from three different industrial sites: a gasworks (GAS), a former wood preservation site (WOOD), and a coke oven (COKE), and to PAH and oxy-PAH containing fractions of these. All extracts induced aryl hydrocarbon receptor (Ahr)-regulated mRNAs, malformations, and mortality. The WOOD extract was most toxic and the GAS extract least toxic. The extracts induced glutathione transferases and heat shock protein 70, suggesting that the toxicity also involved oxidative stress. With all extracts, Ahr2-knock-down reduced the toxicity, indicating a significant Ahr2-dependence on the effects. Ahr2-knock-down was most effective with the PAH fraction of the WOOD extract and with the oxy-PAH fraction of the COKE extract. Our results indicate that oxy-PAH containing mixtures can be as potent Ahr activators and developmental toxicants as PAHs. In addition to Ahr activating potency, the profile of cytochrome P4501 inhibitors may also determine the toxic potency of the extracts.

Three novel cytochrome P450 genes identified in the marine polychaete Perinereis nuntia and their transcriptional response to xenobiotics

Polychaetes have previously been used as bioindicators of environmental pollution. Their ability to eliminate organic pollutants such as polycyclic aromatic hydrocarbons (PAH) has been extensively analyzed. However, the cytochrome P450 monooxygenases (CYP) genes in polychaetes, which catalyze the first step of oxidative degradation of PAHs, have received little attention. Based on the partial sequences of three CYP genes that were enriched by subtractive cDNA libraries of the polychaete Perinereis nuntia, we amplified and sequenced the full-length cDNA of these novel CYP genes. These genes were named CYP4BB2, CYP423A1 and CYP424A1 by the Cytochrome P450 Nomenclature Committee. The deduced amino acid sequence of CYP4BB2 in P. nuntia showed 68% sequence identity to CYP4BB1 in Nereis virens, and was listed as a new member of the CYP4BB subfamily. The sequence of CYP423A1 and CYP424A1 both share less than 40% sequence identity to all known CYP enzymes and were classed into new CYP families. CYP family members are composite parts of a larger group called a clan. CYP4BB2 and CYP424A1 are listed as CYP4 clan members, while CYP423A1 is of the CYP2 clan. The 3D structures of these P. nuntia CYPs were successfully predicted by homology-modeling using the SWISS-MODEL workspace. The models of CYP424A1 and CYP4BB2 were created using 1jpzB (CYP102A) as a template, while CYP423A1 utilized 3czhB (CYP2R1) as its template. The presence of characteristic CYP superfamily motifs, such as the F-G⋯C-G amino acid sequence, and the conservation of the three-dimensional CYP structure shown by the modeling, suggested that these novel P. nuntia CYP genes may contain conserved functional domains of CYP monooxygenases. To examine the effect of xenobiotics on living organisms, we analyzed the transcriptional levels of these three new CYP genes in sandworms (P. nuntia) exposed to seawater artificially contaminated with benzo[a]pyrene (BaP). We also exposed individuals to industrial wastewater collected from Quanzhou Bay, Fujian, China, which was known to be contaminated with PAHs. Worms exposed to BaP had significantly higher levels of CYP4BB2, CYP423A1 and CYP424A1 mRNA. Transcription was up-regulated 5.9-, 5.3- and 12.3-folds respectively compared with the control worms living in clean seawater. The transcriptional levels of CYPs in worms cultured in the diluted wastewater collected from Quanzhou Bay, all positively correlated with the levels of PAHs detected in the water. The transcriptional up-regulation of the three CYP genes observed in this study, suggest the monooxygenases encoded by these CYP genes may play an important role in the detoxification of PAHs in this polychaete worm. These CYPs maybe essential for the adaptation of worms to contaminated environments and may be useful in the assessment of xenobiotic exposure.

Evaluation of EROD and CYP3A4 activities in earthworm Eisenia fetida as biomarkers for soil heavy metal contamination

In this study, the effects of heavy metals (Cd, Cu, Pb, Zn) on EROD and CYP3A4 activities in the earthworm Eisenia fetida were evaluated to find out their possible induction and potential as biomarkers for soil heavy metal contamination. The earthworms were exposed to increasing concentrations of Cd (0.1-8 mg L(-1)), Cu (10-200 mg L(-1)), Pb (20-400 mg L(-1)) or Zn (50-400 mg L(-1)) in filter papers for 48 h. EROD activity was significantly changed in dose-dependent manners after exposure to each of the four metals. CYP3A4 activity was significantly induced by Cd and Pb, rather by Cu and Zn. This is the first report on heavy metal-induced changes of CYP3A4 activity in earthworms. Among the four heavy metals, Cd was the most potent inducing EROD and CYP3A4. While EROD and CYP3A4 activities showed a similar trend, EROD is more sensitive than CYP3A4 activity in E. fetida as a biomarker for heavy metals pollution.

Benzo(a)pyrene-induced mitochondrial dysfunction and cell death in p53-null Hep3B cells

Benzo(a)pyrene (BaP) has been shown to induce apoptosis and necrosis in various cell types. However, the effect of BaP on mitochondria function and p73, and their possible roles in BaP-induced cell death have not been well studied. This study focused on mitochondria-mediated cell death and the occurrence of p73 protein accumulation in BaP-treated human hepatoma Hep3B (p53-null) cells. We found that BaP (8, 16, 32 and 64μM) induced early necrosis at 12h and delayed apoptosis at 24h. BaP dramatically induced ethoxyresorufin-O-deethylase activity and led to significant increase in oxidative stress at early time points (6 and 12h). Necrotic cell death was concurrent with loss of mitochondrial membrane potential, decrease in the ATP level and activities of Na(+)/K(+)-ATPase and Ca(2+)/Mg(2+)-ATPase. However, these changes were reversed in the process of apoptosis. In addition, after BaP treatment, c-Jun N-terminal kinase (JNK) and Bax were activated during apoptosis and no change in p73 protein level was observed. These results revealed that the cells with mitochondria dysfunction and ATP depletion underwent necrosis at early time point and apoptosis afterward when they recovered from mitochondrial dysfunction and ATP depletion. Activation of JNK and Bax possibly contributed to BaP-induced apoptosis.

Selenitetriglicerydes affect CYP1A1 and QR activity by involvement of reactive oxygen species and Nrf2 transcription factor

Selenitetriglycerides are a group of compounds that contain selenium (Se) (IV). In this paper, we present the results of examinations of three structurally-related selenitetriglicerydes that contain various Se concentrations: 2%, 5% and 7% Selol. The present study concentrates on the effect of Selol on phase 1 and 2 enzyme activity and the implications of free radicals and the nuclear erythroid 2-related factor 2 (Nrf2)-antioxidant response element (ARE) pathway in the activity of this compound. The cytotoxic and cytostatic activities of the three kinds of Selol were evaluated; however, the cytotoxic effect was observed only for 7% Selol. Our results show that 2% Selol acts as a monofunctional inducer of phase 2 enzyme activity, and the induction is mediated by the Nrf2 transcription factor. Selol 7% acts in an opposite manner and induces phase 1 with simultaneous inhibition of phase 2 enzyme activity. The differential effect can be associated with the increase in Se content, leading to a change in the structure of the compound.

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.

Construction of a system that simultaneously evaluates CYP1A1 and CYP1A2 induction in a stable human-derived cell line using a dual reporter plasmid

Human CYP1A1 and CYP1A2 genes are in a head-to-head orientation on chromosome 15 and are separated by a 23-kb intergenic space. To our knowledge, this is the first report on a stable cell line that contains the 23-kb full-length regulatory region and is able to simultaneously assess the transcriptional activation of CYP1A1 and CYP1A2 genes. The stable cell line that constitutively expresses the reporter activities was constructed by inserting the dual reporter plasmid containing the 23-kb region between the CYP1A1 and CYP1A2 genes into the chromosome. Transcriptional activation of the CYP1A1 and CYP1A2 genes was measured simultaneously using luciferase (Luc) and secreted alkaline phosphatase (SEAP) activities, respectively. To demonstrate the utility of the stable cell line, CYP1A1/1A2 induction by the majority of compounds previously identified as CYP1A1/1A2 inducers was measured. The results clearly show that all compounds caused induction of reporter activities. In addition to assessing transcriptional activation of the CYP1A1 and CYP1A2 genes by measuring reporter activities, we determined the intrinsic CYP1A1 and CYP1A2 mRNA levels by treating them with the same compounds. The results suggest that this stable cell line may be used to rapidly and accurately predict CYP1A1/1A2 induction.

Influence of aroclor 1254 on benzo(a)pyrene-induced DNA breakage, oxidative DNA damage, and cytochrome P4501A activity in human hepatoma cell line

Both polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) are important environmental pollutants. They coexist widely in the environment at very low levels. Numerous studies indicated that aroclor1254 (one of PCBs mixture) is the inducer of cytochrome P450 1A enzyme acitivity. Benzo(a)pyrene (BaP) can cause a variety of toxicities in vitro, such as oxidative DNA damage and genotoxicity. In the present study, HepG2 cells were treated with either BaP (50 microM) or aroclor1254 at concentrations of 11.5 (low), 23.0 (medium), and 46.0 microM (high) alone, or pretreated the cells with aroclor1254 (11.5, 23.0, and 46.0 microM), followed by BaP (50 microM). It was found that 7-ethoxyresorufin-O-deetylase (EROD) activities of HepG2 cells exposed to either BaP or aroclor 1254 increased. DNA damage measured by DNA migration and the formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) also increased in cells exposed to BaP, but not in cells exposed to aroclor1254. Under the Aroclor 1254 pretreatment condition, BaP-induced EROD activities was enhanced in cells exposed to the medium and high concentrations of aroclor1254 (P < 0.01 for both), whereas in all pretreatment groups aroclor1254 significantly increased BaP-induced DNA migration (P < 0.01 for all) and the 8-OHdG formation (P < 0.05 for all). In addition, there was positive correlation between the EROD induction activity and Olive tail moment (r(2) = 0.958, P < 0.01) or the levels of 8-OHdG (r(2) = 0.992, P < 0.01). The findings suggest that under the experimental conditions aroclor1254 may enhance BaP-induced DNA migration and oxidative DNA damage in HepG2, due to inducing CYP1A enzyme activity.

Sulforaphane and its analogues inhibit CYP1A1 and CYP1A2 activity induced by benzo[a]pyrene

CYP1A1 and CYP1A2 enzymes metabolize polycyclic aromatic hydrocarbons (PAHs) to the reactive oxyderivatives. PAHs can induce the activity of both enzymes, which increases its conversion and enhances risk of carcinogenesis. Thus, the inhibition of CYP enzymes is recognized as a cancer chemoprevention strategy. A well-known group of chemopreventive agents is isothiocyanates, which occur naturally in Brassica vegetables. In this paper, a naturally occurring sulforaphane and its two synthetic analogues isothiocyanate-2-oxohexyl and alyssin were investigated. The aim of the study was to determine whether the differences in the isothiocyanate structure change its ability to inhibit CYP1A1 and CYP1A2 activity induced by benzo[a]pyrene in HepG2 and Mcf7 cells. Also a mechanistic study was performed including isothiocyanates' influence on CYP1A1 and CYP1A2 catalytic activity, enzymatic protein level, and AhR translocation. It was shown that both enzymes were significantly induced by benzo[a]pyrene, and isothiocyanates were capable of decreasing the induced activity. The inhibitory properties depend on the types of isothiocyanate and enzyme. In general, CYP1A2 was altered in the more meaningful way than CYP1A1 by isothiocyanates. Sulforaphane exhibited weak inhibitory properties, whereas both analogues were capable of inhibiting BaP-induced activity with the similar efficacy. The mechanistic study revealed that analogues decreased the CYP1A2 activity via the protein-level reduction and CYP1A1 directly. The results indicate that isothiocyanates can be considered as potent chemopreventive substances and the change in the sulforaphane structure increases its chemopreventive potency.

The effect of isothiocyanates on CYP1A1 and CYP1A2 activities induced by polycyclic aromatic hydrocarbons in Mcf7 cells

Polycyclic aromatic hydrocarbons (PAHs)--environmental carcinogens--are metabolized by CYP1A1 and CYP1A2 enzymes to oxy-derivatives, which are able to bind to DNA and initiate carcinogenesis. PAHs induce CYP1A1 and CYP1A2 activity, which increases the risk of development of carcinogenesis. Isothiocyanates (ITCs), naturally occurring in Brassica vegetables, possess chemopreventive properties and are able to reduce the CYP1A enzyme activity. In this paper we report our study of the ability of ITCs: sulforaphane and its analogues: isothiocyanate-2-oxohexyl and alyssin, to inhibit CYP1A1 and CYP1A2 enzyme activity induced by the PAHs, anthracene (ANT) and dibenzo[a,h]anthracene (DBA) in human breast cancer cell line Mcf7. The aim was to determine whether the differences in structure of ITCs change their inhibitory properties, and whether these properties depend on the type of inducer. The results indicate that the properties of ITCs depend on the type of PAH: ITCs are more potent in inhibiting activity induced by the weaker inducer. It was also found that the change in ITCs' structure influences their activities. ITC 2-oxohexyl was the weakest inhibitor, whereas sulforaphane and alyssin exhibited similar potency. The study revealed that inhibition of CYP1A1 activity is direct whereas inhibition of CYP1A2 activity is not only direct but is also caused by the level of protein disturbance.

Interactions between polycyclic aromatic hydrocarbons in binary mixtures: effects on gene expression and DNA adduct formation in precision-cut rat liver slices

Although exposure to polycyclic aromatic hydrocarbons (PAHs) occurs mostly through mixtures, hazard and risk assessment are mostly based on the effects caused by individual compounds. The objective of the current study was to investigate whether interactions between PAHs occur, focusing on gene expression (as measured by cDNA microarrays) and DNA adduct formation. The effects of benzo[a]pyrene or dibenzo[a,h]anthracene (DB[a,h]A) alone and in binary mixtures with another PAH (DB[a,h]A, benzo[b]fluoranthene, fluoranthene or dibenzo[a,l]pyrene) were investigated using precision-cut rat liver slices. All compounds significantly modulated the expression of several genes, but overlap between genes affected by the mixture and by the individual compounds was relatively small. All mixtures showed an antagonistic response on total gene expression profiles. Moreover, at the level of individual genes, mostly antagonism was evident, with additivity and synergism observed for only a few genes. As far as DNA adduct formation is concerned, the binary mixtures generally caused antagonism. The effects in liver slices suggest a lower carcinogenic potency of PAH mixtures than estimated based on additivity of individual compounds.