Benzo(a)pyrene-induced alterations in growth-related gene expression and signaling in precision-cut adult rat liver and kidney slices

Role of RAS signaling in ovarian cancer

The RAS family of proteins is among the most frequently mutated genes in human malignancies. In ovarian cancer (OC), the most lethal gynecological malignancy, RAS, especially KRAS mutational status at codons 12, 13, and 61, ranges from 6-65% spanning different histo-types. Normally RAS regulates several signaling pathways involved in a myriad of cellular signaling cascades mediating numerous cellular processes like cell proliferation, differentiation, invasion, and death. Aberrant activation of RAS leads to uncontrolled induction of several downstream signaling pathways such as RAF-1/MAPK (mitogen-activated protein kinase), PI3K phosphoinositide-3 kinase (PI3K)/AKT, RalGEFs, Rac/Rho, BRAF (v-Raf murine sarcoma viral oncogene homolog B), MEK1 (mitogen-activated protein kinase kinase 1), ERK (extracellular signal-regulated kinase), PKB (protein kinase B) and PKC (protein kinase C) involved in cell proliferation as well as maintenance pathways thereby driving tumorigenesis and cancer cell propagation. KRAS mutation is also known to be a biomarker for poor outcome and chemoresistance in OC. As a malignancy with several histotypes showing varying histopathological characteristics, we focus on reviewing recent literature showcasing the involvement of oncogenic RAS in mediating carcinogenesis and chemoresistance in OC and its subtypes.

Fenthion and terbufos induce DNA damage, the expression of tumor-related genes, and apoptosis in HEPG2 cells

This study investigates the effects of fenthion and terbufos, two organophosphorous pesticides, on DNA damage, tumor-related gene expression, and apoptosis in HepG2 cells. We found that exposure to concentrations ranging from 50 to 200 μM of fenthion and terbufos for 2 hr caused significant death in HepG2 cells. Both compounds induced DNA damage in a concentration-dependent manner as measured using the alkaline comet assay. Tumor-related genes (jun, myc, and fos) and apoptosis-related genes (socs3, tnfaip3, ppp1r15a, and nr4a1) were up-regulated by both compounds. Finally, both compounds induced apoptosis. The results demonstrate that both terbufos and fenthion induce DNA damage and should be considered potentially hazardous to humans.

Sulfur dioxide and benzo(a)pyrene modulates CYP1A and tumor-related gene expression in rat liver

Sulfur dioxide (SO(2)) and benzo(a)pyrene (B(a)P) are common industrial and environmental contaminants. However, few data are available on the effects of SO(2) on proto-oncogenes and tumor suppressor genes, as well as the interactions between SO(2) and other xenobiotics regulating proto-oncogenes or tumor suppressor genes expression. To investigate the interactions between SO(2) and B(a)P, male Wistar rats were exposed to intratracheally instilled with B(a)P or SO(2) inhalation alone or together. We detected mRNA expression of CYP1A1 and 1A2, 7-ethoxyresorufin O-deethylase (EROD), and methoxyresorufin O-demethylase (MROD) activities in livers. The mRNA and protein levels of several cancer-related genes were analyzed in livers by real-time RT-PCR and Western blot, respectively. The EROD/MROD activities and CYP1A1/2 expression were down-regulated by SO(2) but up-regulated by B(a)P alone. Exposure of SO(2) alone induced c-fos, c-jun, c-myc, H-ras, and p53 expression, and depressed p16 and Rb expression in livers. The effects of B(a)P on the above gene were similar to SO(2) except c-fos expression. Furthermore, SO(2) + B(a)P exposure increased the expression of c-fos, c-jun, c-myc, and p53, and decreased p16 and Rb expression in livers compared with exposed to SO(2) or B(a)P alone. However, no synergistic effects were observed on H-ras and CYP1A1/2 after SO(2) + B(a)P exposure. Our findings indicate that multiple cell cycle regulatory proteins play key roles in the toxicity of SO(2) and B(a)P in livers. It might involve the activation of c-fos, c-jun, c-myc, and p53. And p16-Rb pathway might also participate in the progress. Although the gene products we studied are classed as oncogenes and tumor suppressor genes, their functions actually relate to more general processes of control of cell proliferation, survival, and/or apoptosis.

In vitrometabolism of [14C]methoxychlor in rat, mouse, Japanese quail and rainbow trout in precision-cut liver slices

1. The in vitro metabolism of [14C]methoxychlor (MXC) has been studied using precision-cut liver slices from the Sprague-Dawley male rat, CD-1 male mouse, WE strain male Japanese quail and juvenile rainbow trout (Oncorhynchus mykiss). The results demonstrated integrated phase I and II metabolism of MXC and species differences in the metabolic profiles were observed. 2. In rat liver slice preparations, MXC was rapidly metabolized to bis-OH-MXC by sequential O-demethylation followed by subsequent O-glucuronidation forming bis-OH-MXC glucuronide. No mono-OH-MXC glucuronide was detected. The doubly conjugated metabolite, bis-OH-MXC 4-O-sulphate 4'-O-glucuronide, was also detected as a rat-specific metabolite. 3. Formation of mono-OH-MXC and its glucuronide was the main metabolic pathway in the mouse and Japanese quail. In contrast to the rat, only minor amounts of bis-OH-MXC glucuronide were detected. A reductively dehalogenated metabolite, dechlorinated mono-OH-MXC glucuronide, was observed only in mouse preparations. 4. In rainbow trout, comparative amounts of both mono- and bis-OH-MXC glucuronide were formed as the major metabolites. Unconjugated forms of these metabolites were detected only as minor products. 5. The different metabolic profiles of MXC observed in the four animal species are possibly due to substrate specificity of contributing CYP450 monooxgenase enzyme(s) in different animal species.

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.

Ras gene in marine mussels: a molecular level response to petrochemical exposure

Mussels are susceptible to numerous toxicants and are often employed as bioindicators. This study investigated the status of the ras proto-oncogene in Mytilus galloprovincialis following petrochemical exposure. A M. galloprovincialis homologue of the vertebrate ras gene was isolated, showing conserved sequence in regions of functional importance and a high incidence of polymorphic variation. Mutational damage was investigated in mussels chronically exposed to the water-accommodated fraction of #4 fuel-oil (WAF), and in mussels collected along the NW coast of Portugal in sites with different levels of petrochemical contamination. A ras gene point mutation was identified in the codon 35 of one individual exposed to 12.5% WAF. No mutations were detected in mussels from the WAF control or environmental samples. This represents the first report of a ras gene mutation, experimentally-induced by petrochemical exposure, in an invertebrate species.

Benzo[a]pyrene-dependent activation of transcription factors NF-κB and AP-1 related to tumor promotion in hepatoma cell cultures

The activation by the carcinogenic polycyclic aromatic hydrocarbon (PAH) benzo[a]pyrene (BP) of transcription factors NF-kappaB and AP-1 in hepatoma 27 and HepG2 cell cultures was studied. In contrast to the hepatoma HepG2 cells, cytochrome P450 isoforms and Ah-receptor are not expressed in the hepatoma 27 cells. The transcription factor NF-kappaB was activated only in the hepatoma 27 cells by BP treatment but not by its noncarcinogenic isomer benzo[e]pyrene (BeP). Conversely to NF-kappaB activation the transcription factor AP-1 was activated in the hepatoma HepG2 cells by cell treatment with BP but not in the hepatoma 27 cells. It is concluded that the NF-kappaB activation is caused by nonmetabolized BP molecule and not related to activation of the Ah-receptor. The transcription factor AP-1 seems to be activated as a result of the interaction of BP with the Ah-receptor. The realization of tumor promotion stage by carcinogenic PAHs treatment in dependence on the cytochrome P450 and Ah-receptor levels in the initiated cells is discussed.

Modulation of gene expression and DNA-adduct formation in precision-cut liver slices exposed to polycyclic aromatic hydrocarbons of different carcinogenic potency

Polycyclic aromatic hydrocarbons (PAHs) differ markedly in their carcinogenic potencies. Differences in transcriptomic responses upon PAH exposures might improve our current understanding of the differences in carcinogenicity, and therefore gene expression modulation by six PAHs in precision-cut rat liver slices was investigated. Gene expression modulation by benzo[a]pyrene (B[a]P), dibenzo[a,l]pyrene (DB[a,l]P), benzo[b]fluoranthene (B[b]F), fluoranthene (FA), dibenzo[a,h]anthracene (DB[a,h]A) and 1-methylphenanthrene (1-MPA) was assessed after 6- (B[a]P, DB[a,l]P) and 24-h (all compounds) exposure, using oligonucleotide arrays. DNA-adduct formation was determined using (32)P-post-labelling. The effects of PAHs on gene expression and on DNA-adduct formation were much more pronounced after 24-h exposure than after a 6-h exposure. Each compound induced gene expression changes dose-dependently and gene expression profiles were generally compound-specific. B[a]P, B[b]F and DB[a,h]A displayed comparable gene expression profiles, and so did DB[a,l]P, FA and 1-MPA. Only the carcinogenic PAHs (B[a]P, B[b]F, DB[a,l]P and DB[a,h]A) induced the oxidative stress pathway. DNA-adduct levels were: DB[a,l]P >> B[a]P > B[b]F > or = DB[a,h]A > FA > or = 1-MPA. The expression of only a few genes was found to correlate significantly with DNA-adduct formation, carcinogenic potency or Ah-receptor binding capacity (the last two taken from literature). These genes differed between the parameters. Our results indicate that PAHs generally induce a compound-specific response on gene expression and that discrimination of carcinogenic from non-carcinogenic compounds is partly feasible using this approach. Only at a specific pathway level, namely oxidative stress response, PAHs with high and low carcinogenic potency could be discriminated.

Tissue specific induction of cytochrome P450 (CYP) 1A1 and 1B1 in rat liver and lung following in vitro (tissue slice) and in vivo exposure to benzo(a)pyrene

Cytochrome P-450s (CYPs) detoxify a wide variety of xenobiotics and environmental contaminants, but can also bioactivate carcinogenic polycyclic aromatic hydrocarbons, such as benzo(a)pyrene (BaP), to DNA-reactive species. The primary CYPs involved in the metabolism and bioactivation of BaP are CYP1A1 and CYP1B1. Furthermore, BaP can induce expression of CYP1A1 and CYP1B1 via the aryl hydrocarbon receptor. Induction of CYP1A1 and CYP1B1 by BaP in target (lung) and non-target (liver) tissues was investigated utilizing precision-cut rat liver and lung slices exposed to BaP in vitro. Tissue slices were also prepared from rats pretreated in vivo with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to induce expression of CYP1A1 and CYP1B1. In addition, in vivo exposure studies were performed with BaP to characterize and validate the use of the in vitro tissue slice model. In vitro exposure of liver and lung slices to BaP resulted in a concentration-dependent increase in CYP1A1 and CYP1B1 mRNA and protein levels, which correlated directly with the exposure-related increase in BaP-DNA adduct levels observed previously in the tissue slices [Harrigan, J.A., Vezina, C.M., McGarrigle, B.P., Ersing, N., Box, H.C., Maccubbin, A.E., Olson, J.R., 2004. DNA adduct formation in precision-cut rat liver and lung slices exposed to benzo(a)pyrene. Toxicological Sciences 77, 307-314]. Pretreatment of animals in vivo with TCDD produced a marked induction of CYP1A1 and CYP1B1 expression in the tissue slices, which was similar to the levels of CYP1A1 and CYP1B1 mRNA achieved in liver and lung following in vivo treatment with BaP. Following in vitro exposure to BaP, the levels of CYP1A1 were greater in the lung than the liver, while following all exposures (in vitro and in vivo), the levels of CYP1B1 mRNA were greater in lung tissue compared to liver. The higher expression of CYP1A1 and CYP1B1 in the lung was associated with higher levels of BaP-DNA adducts in the lung slices (Harrigan et al.'s work) and together, these results may contribute to the tissue specificity of BaP-mediated carcinogenesis.

Profiling the hepatic effects of flutamide in rats: a microarray comparison with classical aryl hydrocarbon receptor ligands and atypical CYP1A inducers

The antiandrogen flutamide (FLU) is used primarily for prostate cancer and is an idiosyncratic hepatotoxicant that sometimes causes severe liver problems. To investigate FLU's overt hepatic effects, especially on inducible drug clearance-related gene networks, FLU's hepatic gene expression profile was examined in female Sprague-Dawley rats using approximately 22,500 oligonucleotide microarrays. Rats were dosed daily for 3 days with FLU at 500, 250, 62.5, 31.3, and 15.6 mg/kg/day, and hepatic RNA was isolated. FLU resulted in the dose-dependent regulation of approximately 350 genes. Employing a gene-response compendium, FLU was compared with three classical aryl hydrocarbon receptor (AhR) ligands, 3-methylcholanthrene, benzo[a]pyrene, and beta-naphthoflavone, and four atypical CYP1A inducers, indole-3-carbinol (I3C), omeprazole (OME), chlorpromazine (CPZ), and clotrimazole (CLO). The FLU gene response was comparable with classical AhR ligands across a signature AhR ligand gene set that included CYP1A1 and other members of the AhR gene battery. Dose-related responses of CYP1 genes established a maximum response ceiling and discerned potency differences in atypical inducers. FLU had a sharp down-regulation of c-fos that was comparable with all the compounds except CPZ and CLO. FLU absorption, distribution, metabolism, and excretion (ADME) gene expression analysis revealed that FLU, as well as I3C and OME, induced CYP2B and CYP3A, distinguishing them from the classical AhR ligands. By using a compendium of gene expression profiles, FLU was shown to signal in rats similar to an AhR activator with additional CYP2B and CYP3A effects that most resembled the ADME gene expression pattern of the atypical CYP1A inducers I3C and OME.

The effect of benzo(a)pyrene on porcine urinary bladder epithelial cells analyzed for the expression of selected genes and cellular toxicological endpoints

Consumption of tobacco products is the most relevant risk factor for the development of bladder cancer beside occupational contributions. In order to investigate mechanisms of tobacco smoke components in bladder carcinogenesis we have introduced a primary epithelial cell culture system derived from porcine urinary bladder as a suitable representative for the corresponding human tissue under physiological conditions. Two independent readouts were selected as markers for genotoxic events. Changes in the expression level of several toxicologically relevant genes should serve as indicators for early response, while classical genotoxic endpoints monitored manifested damages. Here, we present the first results of our study with benzo(a)pyrene (BaP) as a member of polycyclic aromatic hydrocarbons (PAHs) found in tobacco smoke. Cells treated with BaP show a dramatic increase in the expression of CYP1A1 that appears to be both indicator of and contributor for BaP toxicity. Genes coding for other proteins relevant in xenobiotic metabolism, signal transduction or tumor suppression show moderate effects or no enhancement of their expression levels. Comet assay and micronucleus test did show a significant, dose-dependent increase in DNA damages or aberrations after cell division. While these effects are conforming to the response at the mRNA expression level, they are less pronounced and require rather higher dosages of the chemical.

Aryl hydrocarbon receptor, cell cycle regulation, toxicity, and tumorigenesis

Most effects of exposure to halogenated and polycyclic aromatic hydrocarbons are mediated by the aryl hydrocarbon receptor (AHR). It has long been recognized that the AHR is a ligand-activated transcription factor that plays a central role in the induction of drug-metabolizing enzymes and hence in xenobiotic detoxification. Of late, it has become evident that outside this well-characterized role, the AHR also functions as a modulator of cellular signaling pathways. In this Prospect, we discuss the involvement of the AHR in pathways critical to cell cycle regulation, mitogen-activated protein kinase cascades, immediate-early gene induction, and the functions of the RB protein. Ultimately, the toxicity of AHR xenobiotic ligands may be intrinsically connected with the perturbation of these pathways and depend on the many critical signaling pathways and effectors with which the AHR itself interacts.

A critical role of PI-3K/Akt/JNKs pathway in benzo[a]pyrene diol-epoxide (B[a]PDE)-induced AP-1 transactivation in mouse epidermal Cl41 cells

Mouse skin tumorigenicity studies indicate that benzo[a]pyrene-7,8-diol-9,10-epoxide (B[a]PDE) contributes to carcinogenesis as both a tumor initiator and promoter. However, the mechanisms that mediate B[a]PDE tumor promotion effects remain unclear. Our results demonstrated that in mouse epidermal Cl41 cells, B[a]PDE treatment resulted in marked activation of AP-1 and its upstream MAPKs, including ERKs, JNKs and p38K. B[a]PDE exposure also led to activation of phosphotidylinositol 3-kinase (PI-3K), Akt and p70 S6 kinase (p70S6k). B[a]PDE-induced AP-1 transactivation was inhibited by pretreatment of cells with PI-3K inhibitors, wortmannin or Ly294002. In contrast, inhibition of p70S6k with rapamycin did not show any inhibitory effects. An overexpression of dominant-negative mutant of PI-3K, Deltap85, impaired B[a]PDE-induced activation of PI-3K, Akt and AP-1 transactivation. Furthermore, an overexpression of dominant-negative Akt mutant, Akt-T308A/S473A, blocked B[a]PDE-induced activation of Akt, AP-1 and JNKs, while it did not affect the activation of p70S6k, ERKs and p38 kinase. These results demonstrated that B[a]PDE was able to induce AP-1 transactivation and this AP-1 induction was specific through PI-3K/Akt/JNKs-dependent and p70S6k-independent pathways. This study also indicated that Akt-T308A/S473A blocks B[a]PDE-induced AP-1 activation specific through impairing JNK pathway. These findings will help us to understand the signal transduction pathways involved in the carcinogenic effects of B[a]PDE.

PI-3K and Akt are mediators of AP-1 induction by 5-MCDE in mouse epidermal Cl41 cells

5-Methylchrysene has been found to be a complete carcinogen in laboratory animals. However, the tumor promotion effects of (+/-)-anti-5-methylchrysene-1,2-diol-3,4-epoxide (5-MCDE) remain unclear. In the present work, we found that 5-MCDE induced marked activator protein-1 (AP-1) activation in Cl41 cells. 5-MCDE also induced a marked activation of phosphatidylinositol 3-kinase (PI-3K). Inhibition of PI-3K impaired 5-MCDE-induced AP-1 transactivation, suggesting that PI-3K is an upstream kinase involved in AP-1 activation by 5-MCDE. Furthermore, we found that Akt is a PI-3K downstream mediator for 5-MCDE-induced AP-1 transactivation, whereas another PI-3K downstream kinase, p70(S6K), was not involved in AP-1 activation by 5-MCDE. Moreover, inhibition of Akt activation blocked 5-MCDE-induced activation of extracellular signal-regulated protein kinases (ERKs) and c-Jun NH(2)-terminal kinases (JNKs), whereas it did not affect p38K activation. Consistently, overexpression of a dominant-negative mutant of ERK2 or JNK1 blocked the AP-1 activation by 5-MCDE. These results demonstrate that 5-MCDE is able to induce AP-1 activation, and the AP-1 induction is specifically through a PI-3K/Akt-dependent and p70(S6K)-independent pathway.

Differential effects of polycyclic aromatic hydrocarbons on transactivation of AP-1 and NF-?B in mouse epidermal cl41 cells

Polycyclic aromatic hydrocarbons (PAHs) and their derivatives, such as benzo[a]pyrene (B[a]P), (+/-)-anti-benzo[a]pyrene-7,8-diol-9,10-epoxide (B[a]PDE), and 5-methylchrysene-1,2-diol-3,4-epoxide (5-MCDE), are complete carcinogens. However, the tumor promotion effects of PAHs remain unclear. We therefore investigated the possible activation of activator protein-1 (AP-1) and nuclear factor-kappaB (NFkappaB) in mouse epidermal Cl41 cells after different PAHs treatments, including B[a]P, B[a]PDE, chrysene-1,2-diol-3,4-epoxid (CDE), and 5-MCDE. The results showed that B[a]PDE and 5-MCDE were able to activate AP-1 and NF-kappaB, whereas B[a]P showed only marginal effect on AP-1 activation, and B[a]P and CDE had no effect on NF-kappaB activation. Treatment with either B[a]PDE or 5-MCDE also resulted in mitogen-activated protein kinases (MAPKs) activation as well as inhibitory subunit kappa-B (IkappaBalpha) phosphorylation and degradation, whereas B[a]P and CDE had no effect. Pretreatment with PD98059, a specific inhibitor for extracellular signal-regulated protein kinases (ERKs) upstream kinase MEK1/2, or SB202190, a p38 kinase inhibitor, resulted in a dramatic inhibition of B[a]PDE-induced AP-1 transactivation. In addition, B[a]PDE-induced AP-1 activation was also inhibited by overexpressing a dominant negative mutant of JNK1 in the cells. All these suggest ERKs, c-jun N-terminal kinases (JNKs), and p38 kinase signal transduction pathways are required for AP-1 induction by B[a]PDE. Taken together, B[a]PDE and 5-MCDE are the active compounds of PAHs to initiate signaling pathways. Considering the important roles of AP-1 and NF-kappaB in tumor promotion, we speculated the activation of AP-1 and NF-kappaB by B[a]PDE and 5-MCDE may involve in their or their parent compounds' tumor promotion effects. This study may help in better understanding the tumor promotion effects of PAHs.

Cryopreserved precision-cut rat liver slices: morphology and cytochrome P450 isoforms expression after prolonged incubation

Precision-cut liver slices are an accepted in vitro system for toxicological investigations. However, cryopreservation of slices would make a more efficient utilisation, particularly of human liver tissue possible. In the present study sections of cryopreserved male rat liver slices were examined immunohistochemically for cytochrome P450 (CYP) isoforms expression after prolonged incubation and after exposure to typical inducers. Morphologically, with just thawed slices no major alterations were seen, but remarkable cell damage was observed even after 2 h of incubation mainly in the middle of the slices and in the periportal and intermediate regions of the lobules. After 24 h of incubation, viable cells were only observed at the edges of the slices or around bigger vessels. In the viable cells of the cryopreserved liver slices after 2 h of incubation CYP expression pattern was similar to that in normal liver specimens: a low CYP1A1, but a strong CYP2B1 and 3A2 expression predominantly in the central and intermediate lobular zones. After 24 h, the immunostaining for CYP2B1 and 3A2 in the viable cells was reduced, but that for CYP1A1 was increased. Incubation with beta-naphthoflavone further elevated CYP1A1 and 2B1 expression. Phenobarbital caused an enhanced CYP2B1 and 3A2 and dexamethasone and pregnenolone 16 alpha-carbonitrile an increased CYP3A2 immunostaining. These results show that also in cryopreserved liver slices and after a prolonged incubation, a distinct expression pattern and an in vitro induction of phase I enzymes can be demonstrated immunohistochemically.

Role of the aryl hydrocarbon receptor in cell cycle regulation

Traditionally, the aryl hydrocarbon receptor (AHR) is considered to be a ligand-activated receptor and transcription factor responsible for the induction of drug-metabolizing enzymes. Its role in the combinatorial matrix of cell functions was neatly established long before the first report of an AHR cDNA sequence was published. Only recently, other functions of this protein have begun to be recognized. This review addresses novel findings relating to AHR functions that have resulted from experimental approaches markedly outside traditional receptor analyses. Here we examine the aspects of AHR biology relevant to its role in cell cycle regulation, from the activation of mitogen-activated protein kinases to the cross-talk between AHR and the RAS pathway and the functional significance of the interaction between AHR and the retinoblastoma protein. We have attempted to provide the reader with a balanced interpretation of the evidence, highlighting areas of consensus as well as areas still being contested.

Benzo(a)pyrene activates extracellular signal-related and p38 mitogen-activated protein kinases in HT29 colon adenocarcinoma cells: involvement in NAD(P)H:quinone reductase activity and cell proliferation

Benzo(a)pyrene (BP) is a polyaromatic hydrocarbon generated from the combustion of fossil fuel. Human exposure results primarily through dietary sources and smoking. Little is known about the effect of BP on mitogen-activated protein (MAP) kinases, which include extracellular signal-related kinase (ERK), Jun N-terminal kinase (JNK), and p38. We investigated the participation of BP-induced MAP kinase activation in cell growth and increases in activity of the detoxification enzyme NAD(P)H:quinone reductase (QR). In HT29 human colon carcinoma cells, 10 nM BP activated ERK and p38 but not JNK after 24 h. Treatment with 10 nM BP increased QR activity within 24 h and tritiated thymidine ([(3)H]thyd) incorporation after 48 h and reduced cell viability after 72 h. Using the MAP kinase inhibitors PD98059 and SB203580, we investigated the relative contributions of ERK and p38 to QR activity and [(3)H]thyd cell incorporation. Inhibition of ERK eliminated BP-induced QR activity, whereas inhibition of p38 had no effect on QR activity. Treatment of cells with 10 nM BP increased [(3)H]thyd incorporation by 50% after 48 h. This increase was eliminated by ERK but not p38 inhibition. In conclusion, 10 nM BP activates ERK and p38, but only ERK contributes to BP-induced QR activity. ERK, but not p38 activation participated in [(3)H]thyd incorporation. In summary, BP influences cellular signaling pathways at concentrations present in routine human exposures.

Morphology and cytochrome P450 isoforms expression in precision-cut rat liver slices

Precision-cut liver slices are a widely accepted in vitro system for the examination of drug metabolism, enzyme induction, or hepatotoxic effects of xenobiotics. The maintenance of the distinct lobular expression and induction pattern of phase I biotransformation enzymes, however, has not been examined systematically so far. Thus, in the present study, both longitudinal and transversal sections of male rat liver slices were investigated morphologically, as well as immunohistochemically for the expression of different cytochrome P450 (CYP) isoforms after prolonged incubation or after exposure to typical inducers. Histopathological examinations revealed an increasing vacuolization of the periportal hepatocytes mainly in the middle of the slices from 6 h of incubation on, paralleled by a loss of glycogen in the respective cells. After 24 h, mainly in the center of the slices, necroses of cells occurred. After 48 h of incubation, typically a central band of coagulative necrosis flanked by superficial layers of viable cells was observed. Freshly prepared slices displayed a CYP subtypes expression as normal liver specimen, a very low centrilobular CYP 1A1 immunostaining, but a strong CYP 2B1 and 3A2 expression predominantly in the central and intermediate lobular zones. From 2 h on, the immunostaining for CYP 2B1 and 3A2 was to some extent reduced. After 24 h of incubation with beta-naphthoflavone, the CYP 1A1 and 2B1 expression was induced mainly in the viable cells around central veins, around some portal fields with bigger vessels and in the cell layers close to the slice surface. At the same sites, phenobarbital led to an increased CYP 2B1 and 3A2 expression and dexamethasone to an elevated CYP 3A2 immunostaining. These results show, that an in vitro induction of phase I enzymes in precision-cut liver slices can be demonstrated also immunohistochemically.

Tyrphostin [correction of Tryphostin] AG879, a tyrosine kinase inhibitor: prevention of transcriptional activation of the electrophile and the aromatic hydrocarbon response elements

To investigate a possible role of phosphorylation in the signal transduction pathways responsible for transcriptional regulation of drug-metabolizing enzymes, we tested seven specific tyrosine kinase inhibitors (tyrphostins) for their effects on NAD(P)H:quinone oxidoreductase-1 (NQO1) mRNA levels in mouse hepatoma Hepa-1c1c7 (Hepa-1) cells and chose to study AG879 further. The potent electrophile tert-butylhydroquinone (tBHQ) is known to activate NQO1 gene transcription via the electrophile response element (EPRE). Among the tyrphostins tested, tyrphostin AG879 was unique in preventing the accumulation of tBHQ-induced NQO1 mRNA; this effect was dependent on the AG879 dose and was also sensitive to the time when AG879 was added relative to the beginning of tBHQ treatment. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (dioxin; TCDD) is known to activate Cyp1a1 gene transcription by way of aromatic hydrocarbon response elements (AHREs). We found that AG879 also prevents, to a lesser extent, the AHRE-mediated induction of CYP1A1 and NQO1 mRNA by dioxin. Zinc or cadmium is known to activate metallothionein (Mt1) gene transcription via the metal response element (MRE). AG879 induced MT1 mRNA, and AG879 did not block zinc- or cadmium-induced MT1 mRNA, indicating that the effects of AG879 on NQO1 or CYP1A1 mRNA levels cannot be generalized to all transcripts. Using transient transfection of EPRE-, AHRE-, or MRE-driven luciferase reporter gene constructs in Hepa-1 cells, we showed that the inhibitory effects of AG879 occurred at the level of EPRE- and AHRE-mediated transcription, but that AG879 did not affect the MRE-driven transcriptional response. These data suggest that AG879 might inhibit an unknown tyrosine kinase(s) whose activity is essential for EPRE- and AHRE-mediated trans-activation of certain mammalian genes. These results also indicate that some sharing of common signal transduction pathways might exist in the regulation of genes involved in drug metabolism that also respond to oxidative stress.

Effects of carcinogen-induced transcription factors on the activation of hepatitis B virus expression in human hepatoblastoma HepG2 cells and its implication on hepatocellular carcinomas

To elucidate the molecular mechanisms involved in the action of common carcinogens, which can act as important cofactors in modulating hepatitis B virus-mediated hepatocellular carcinogenesis, we have investigated the influence of aflatoxin B(1) (AFB), a potent liver carcinogen, as well as benzo[a]pyrene (BP) and 4-aminobiphenyl (4-ABP), carcinogens in cigarette smoke, on the induction of various transcription factors in human hepatoblastoma HepG2 cells. DNA electrophoretic mobility shift assays were performed with nuclear extracts from HepG2 cells treated with 10 micromol/L AFB, 40 micromol/L BP, or 300 micromol/L 4-ABP for 6 and 24 hours. Eight- and 6-fold increases in nuclear transcription factor kappaB (NF-kappaB), and 5- and 10-fold increases in activated protein (AP-1) transcription factor were observed with 24 hours AFB and BP treatments, respectively, whereas 4-ABP treatment resulted in an approximately 4-fold induction of both NF-kappaB and AP-1. Moreover, 4-ABP gave the strongest NF-kappaB activation in 6 hours of treatment. Four- and 10-fold activation of stress protein was detected by a consensus heat shock factor (HSF) sequence binding probe, with AFB and BP treatments, respectively. DNA adducts were observed by immunoassays in HepG2 cells treated with AFB and BP but not with 4-ABP. Increased human hepatitis B virus (HBV) surface antigen (HBsAg) synthesis was detected in AFB- and BP-treated HepG2 cells following transfection with recircularized HBV DNA. These data suggest that certain carcinogen-induced transcription factors may influence viral carcinogenesis and initiate hepatocellular carcinomas (HCC).

Use of precision-cut tissue slices in organ culture to study metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) by hamster lung, liver and kidney

The pharmacokinetics of in vitro metabolism of the tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK; concentration range 0.03-250 microM) and its proximal metabolite, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL; 0.04-250 microM), were determined in Syrian golden hamster liver, lung, and kidney tissue slices in organ culture under identical experimental conditions. In the lung, a target organ for NNK animal carcinogenesis, total NNK metabolism was relatively low (maximum 23%) and oxidative metabolism by alpha-hydroxylation to DNA-reactive intermediates accounted for 13-31% of metabolism. The liver, a non-target organ for NNK carcinogenesis, showed the highest capacity to metabolise NNK (total metabolism 80%), and alpha-hydroxylation accounted for 12-25% of metabolism. The kidney, another non-target organ, also showed a low capacity for NNK metabolism (maximum 32%) and alpha-hydroxylation accounted for <3% of metabolism. Detoxification of NNK by pyridyl N-oxidation was similar in lung (5-22%) and liver (5-23%), and negligible in kidney (<2%), while carbonyl reduction of NNK to NNAL was greatest in the kidney (95-100%), followed by liver (59-79%) and lung (47-81%). NNAL is devoid of biological activity in the hamster and total metabolism was about tenfold lower than that of NNK in all tissues (<13% liver; <4% lung and kidney). In the liver, alpha-hydroxylation was the predominant pathway of NNAL metabolism at almost all concentrations (31-68% of total metabolism), whereas N-oxidation prevailed in the kidney (47-68%). In the lung, a concentration dependent decrease in the relative amount of alpha-hydroxylation (23-72%) with increasing NNAL concentrations occurred at the expense of N-oxidation (25-72%). Little or no metabolism of NNAL back to NNK was evident in any tissue.

Aryl hydrocarbon hydroxylase activity in F-344 rats subchronically exposed to benzo(a)pyrene and fluoranthene through diet

In order to investigate the relationship between aryl hydrocarbon hydroxylase (AHH) activity and exposure to benzo[a]pyrene [B(a)p] and fluoranthene (FLA), AHH activities in liver tissues of male and female F-344 rats were determined. Based on a range-finding study, doses of 0, 5, 50, and 100 mg/kg B(a)p or 0, 150, 750, and 1500 mg/kg FLA were administered in the animal diet over a 90-day period. After dosing, animals were sacrificed, liver tissues were removed, and microsomes were isolated. AHH activities were determined by reverse-phase HPLC coupled with fluorescence detection using 3-hydroxy B(a)p, and trans-2,3-dihydroxy-1,10-epoxy-1,2,3,10b tetrahydrofluoranthene as the standards. A dose-dependent increase in enzyme activity was observed with increased B(a)p or FLA exposure in both males and females. Our results also demonstrate that B(a)p-exposed females possess a higher AHH activity than males, but there is no significant sex difference with regard to enzyme activity in the case of FLA at higher doses. Overall, our findings suggest that long-term exposure to the parent compound results in elevated levels of AHH activity, which may contribute to the formation of toxic reactive metabolites and subsequent symptoms in target organs.

Comparison of oxidative stress response parameters in newborn mouse liver versus simian virus 40 (SV40)-transformed hepatocyte cell lines

Induction of approximately one dozen genes and/or enzyme activities in liver of the untreated newborn c(14CoS)/c(14CoS) mouse-when compared with the c(ch)/c(14CoS) heterozygote or the c(ch)/c(ch) wild-type-is the result of enhanced levels of reactive oxygenated metabolites originating from a block in the tyrosine degradation pathway. Oxidative stress activates genes via the electrophile response element, whereas dioxin activates genes via the receptor-mediated aromatic hydrocarbon response element. Here, we compared several parameters in 14CoS/14CoS versus ch/ch newborn mouse liver with that in simian virus 40 (SV40)-transformed hepatocyte lines that had been derived from newborn liver. We showed in this study that: (a) NADP(H):quinone oxidoreductase and UDP glucuronosyltransferase 1A6 mRNA levels were increased in both the (untreated) 14CoS/14CoS newborn liver and cell line; (b) aldehyde dehydrogenase 3A1 mRNA was increased by both oxidative stress and dioxin in hepatocyte cultures, but was not detectable in liver of the intact mouse; (c) the glutathione S-transferase GSTA1, GSTP1, GSTA3, and GSTM1 mRNA levels were increased by oxidative stress in 14CoS/14CoS newborn liver, but these transcripts were either low or undetectable in the cell lines; (d) GSTA1 mRNA was up-regulated by the absence of cytochrome P450 1A1 (CYP1A1) activity (i.e. the Gsta1 gene is a member of the aromatic hydrocarbon [Ah] battery); and (e) GSTP1 mRNA was not up-regulated by the absence of CYP1A1 activity (i. e. Gstp1 is not a member of the [Ah] battery). The 14CoS/14CoS and ch/ch hepatocyte established cell lines were transformed with SV40, which expresses large T antigen; this gene product is known to bind to, and interact with, several cell cycle regulatory proteins such as p53 and the retinoblastoma protein-E2F complex. It is therefore likely that differences in the oxidative stress responses between the 14CoS/14CoS newborn liver and the immortalized hepatocyte cell line might be explained by the presence of large T antigen in the established cell line.