Benzo(a)pyrene induces oxidative stress,pro-inflammatory cytokines,expression of nuclear factor-kappa B and deregulation of wnt/beta-catenin signaling in colons of BALB/c mice

The incidence of colonic toxicity has been epidemiologically linked to the consumption of foods contaminated with benzo(a)pyrene (B[a]P). The present study investigated the effects of B[a]P on biomarkers of oxidative stress, inflammation and wnt-signaling in colon of BALB/c mice following exposure to 62.5, 125 and 250 mg/kg of B[a]P for 7 days by oral gavage. Exposure to B[a]P significantly decreased the colonic antioxidant enzymes activities and glutathione level with concomitant significant increase in myeloperoxidase activity, nitric oxide and lipid peroxidation levels. Colon histopathology results showed treatment-related lesions characterized by atrophy, mucosal ulceration and gland erosion in the B[a]P-treated mice. Immunohistochemistry analysis showed that B[a]P treatment increased the protein expression of nuclear factor kappa B, pro-inflammatory cytokines namely tumor necrosis factor alpha and interleukin-1β, as well as cyclooxygenase-2 and inducible nitric oxide synthase in the mice colon. Altered canonical wnt-signaling was confirmed by strong diaminobenzidine staining for p38 mitogen activated protein kinase, β-catenin expression and absence of adenomatous polyposis coli following B[a]P administration. The present data highlight that exposure to B[a]P induces colon injury via induction of oxidative and nitrosative stress, inflammatory biomarkers and dsyregulation wnt/β-catenin signaling, thus confirming the role of B[a]P in the pathogenesis of colonic toxicity.     

In vitro exposure to cigarette smoke induces oxidative stress in follicular cells of F1 hybrid mice

This study assessed the influence of cigarette smoke condensate (CSC) and benzo(a)pyrene [B(a)P] on the levels of two oxidative stress biomarkers [8‐isoprostane (8‐IsoP) and 8‐hydroxy‐2‐deoxy Guanosine (8‐OH‐dG)], in in‐vitro spent media of follicle cells. Follicles (100–130 µm) isolated from ovaries of F₁ hybrid (C57Bl/6j × CBA/Ca) mice were cultured for 13 days in media exposed to B(a)P [0 ng ml^–1 (control) to 45 ng ml^–1] or CSC [0 µg ml^–1 (control) to 130 µg ml^–1]. The concentrations of oxidative stress biomarkers in spent media were quantified by enzyme‐linked immune sorbent assays (ELISA). CSC and B(a)P treatment induced a significant, dose‐dependent increase in the concentrations of 8‐IsoP and 8‐OH‐dG in the spent media. We conclude that CSC and B(a)P exposure can induce oxidative stress in ovarian follicles, an effect that may contribute to the previously documented decline in follicle development and premature ovarian failure in women who smoke. © Her Majesty the Queen in Right of Canada 2013.     

Di (2-ethylhexyl) phthalate inhibits growth of mouse ovarian antral follicles through an oxidative stress pathway

Di (2-ethylhexyl) phthalate (DEHP) is a plasticizer that has been shown to inhibit growth of mouse antral follicles, however, little is known about the mechanisms by which DEHP does so. Oxidative stress has been linked to follicle growth inhibition as well as phthalate-induced toxicity in non-ovarian tissues. Thus, we hypothesized that DEHP causes oxidative stress and that this leads to inhibition of the growth of antral follicles. To test this hypothesis, antral follicles isolated from CD-1 mice (age 31-35 days) were cultured with vehicle control (dimethylsulfoxide [DMSO]) or DEHP (1-100 μg/ml) ± N-acetyl cysteine (NAC, an antioxidant at 0.25-1 mM). During culture, follicles were measured daily. At the end of culture, follicles were collected and processed for in vitro reactive oxygen species (ROS) assays to measure the presence of free radicals or for measurement of the expression and activity of various key antioxidant enzymes: Cu/Zn superoxide dismutase (SOD1), glutathione peroxidase (GPX) and catalase (CAT). The results indicate that DEHP inhibits the growth of follicles compared to DMSO control and that NAC (0.25-1 mM) blocks the ability of DEHP to inhibit follicle growth. Furthermore, DEHP (10 μg/ml) significantly increases ROS levels and reduces the expression and activity of SOD1 compared to DMSO controls, whereas NAC (0.5 mM) rescues the effects of DEHP on ROS levels and SOD1. However, the expression and activity of GPX and CAT were not affected by DEHP treatment. Collectively, these data suggest that DEHP inhibits follicle growth by inducing production of ROS and by decreasing the expression and activity of SOD1.     

PM2.5 collected in China causes inflammatory and oxidative stress responses in macrophages through the multiple pathways

Air pollution continues to increase in East Asia, particularly in China, and is considered to cause serious health problems. In this study, we investigated the toxicological properties of particulate matter ≤2.5 mm (PM_2.5) collected in an urban area in China (Shenyang), focusing on inflammation and oxidative stress tightly linked to respiratory diseases. Exposure to PM_2.5 significantly increased the expression levels of inflammatory (interleukin-1β and cyclooxygenase-2) and oxidative stress (heme oxygenase1) genes in the mouse macrophages. PM_2.5-caused inflammatory response was strongly suppressed by endotoxin neutralizer (polymyxin B) and knock-out of toll-like receptor 4, while oxidative stress was not. On the other hand, an antioxidant (N-acetylcystein) suppressed oxidative stress, but not inflammatory response. These results suggest that PM_2.5 in the atmospheric environment of China causes inflammation and oxidative stress in macrophages via separate pathways.     

PCB126 enhanced the genotoxicity of BaP in HepG2 cells by modulating metabolic enzyme and DNA repair activities

Both of benzo(a)pyrene (BaP) and 3,3′,4,4′,5-pentachlorobiphenyl (PCB126) are ubiquitous and persistent environmental pollutants. These two chemicals coexist in various environmental media and human samples and thus may have combined effects on human health. However, the toxic effects and related mechanism of co-exposure to BaP and PCB126 remain unknown. In a series of experiments using the HepG2 cells exposed to BaP (50 μM) or/and PCB126 (0.01, 0.1, 1 and 10 nM), we measured the rate of micronucleus (MN) formation, CYP1A1 activity and expression of nucleotide excision repair (NER) proteins (XPA and XPC). We found that the exposure to BaP or PCB126 alone could effectively increase the CYP1A1 activity and the XPA expression. BaP alone had a profound enhancement of MN formation. Compared with BaP alone, co-exposure to both BaP and PCB126 significantly enhanced the CYP1A1 activity and the formation of MN but reduced the expression of both XPA and XPC. The synergistic effect of PCB126 on BaP-induced MN formation was inhibited by alpha-naphthoflavone (ANF), an inhibitor of CYP1A1. Our findings suggest that PCB126 may enhance BaP-induced DNA damage and genotoxicity by increasing cytochrome P450 1A activity and decreasing the NER capacity.     

Exposure of mice to benzo(a)pyrene impairs endometrial receptivity and reduces the number of implantation sites during early pregnancy

Benzo(a)pyrene (BaP) is a ubiquitous environmental pollutant. Studies have demonstrated it to be an endocrine-disrupting chemical that can cause adverse effects on the female reproductive system. However, the effect of BaP on early pregnancy has not been reported. We investigated the effect of BaP on endometrial receptivity and embryo implantation. Pregnant mice were dosed with BaP at 0.2, 2 and 20 mg/kg/day from day 1 (D1) to day 5 (D5) of gestation. Exposure to BaP impaired the morphology of the endometrium and decreased the number of implantation sites (p_0.2 = 0.006, p₂ = 0.167, p₂₀ = 0.003). Levels of estrodiol (p < 0.001, for three treatment group compare with control group) and progesterone-4 in plasma were elevated in BaP-treatment groups (p_0.2 < 0.001, p₂ < 0.001, p₂₀ = 0.032). Expression of estrogen receptor-α was up-regulated (p_0.2 = 0.002, p₂ = 0.131, p₂₀ = 0.024) whereas expression of the progesterone receptor was down-regulated (p_0.2 < 0.001, p₂ = 0.064, p₂₀ = 0.021). Levels of receptivity-related genes HoxA10 (p_0.2 < 0.001, p₂ = 0.135, p₂₀ < 0.001) and E-cadherin (p_0.2 = 0.002, p₂ = 0.624, p₂₀ = 0.137) were changed by BaP. These results revealed that BaP can disrupt the balance of estrogen and progesterone, influence expression of their receptors and downstream related genes, lead to changes in endometrium receptivity, and reduce of the number of implantation sites.     

Benzo(a)pyrene-induced acute neurotoxicity in the F-344 rat: role of oxidative stress

Given the link between neurotoxicity and exposure to pollutants, the potential behavioral neurotoxicity of benzo(a)pyrene [B(a)P] was investigated. Studies have established that B(a)P requires metabolic activation to highly reactive species to elicit many of its adverse effects. This study investigated the perturbation of nervous system function by correlating behavioral changes with the metabolism of B(a)P, antioxidant enzyme levels and lipid peroxidation in selected brain regions. The neurobehavioral effects of single oral doses of B(a)P (25-200 mg kg(-1) body weight) on motor activity were examined in male F-344 rats at 2, 4, 6, 12, 24, 48, 72 and 96 h post treatment. Parent B(a)P and metabolites were measured at the above mentioned time points by reverse phase HPLC. The activity of several antioxidant enzymes (superoxide dismutase, catalase and glutathione peroxidase) and levels of malondialdehyde were determined at 6 and 96 h in both the striatum and hippocampus of B(a)P exposed rats. Suppression of motor activity (up to 70%) reached a maximum at 6 h, but was reversible at 96 h in all dose groups. The kinetics of disposition data show a strong link between B(a)P metabolism and the onset and duration of behavioral effects. Benzo(a)pyrene caused a 15-70% inhibition in the activity of superoxide dismutase and glutathione peroxidase and an enhancement in catalase and lipid peroxidation (up to 68%) in the striatum and hippocampus at 6 and 96 h post treatment, respectively. These findings suggest that B(a)P-induced acute neurobehavioral toxicity may occur through oxidative stress due to inhibition of the brain antioxidant scavenging system.     

2-Methoxyestradiol induces endoreduplication through the induction of mitochondrial oxidative stress and the activation of MAPK signaling pathways

2-Methoxyestradiol (2ME2) is a normal physiological metabolite of 17β-estradiol with anti-proliferative and anti-angiogenic activities. The purpose of this study is to elucidate the mechanism whereby 2ME2 induces endoreduplication of the well-differentiated nasopharyngeal carcinoma (NPC) cells. We report here that 2ME2 induces G2/M phase cell cycle arrest followed by endoreduplication of the well-differentiated HK-1 cells. The increase in chromosome number was confirmed by cytogenetic study. Analysis of stress signaling pathways revealed the phosphorylation activation of ERK, JNK and p38 MAPKs at various times after 2ME2 treatment. Pre-treatment of 2ME2-treated HK-1 cells with JNK inhibitor (SP600125), ERK inhibitor (PD98059) and p38 MAPK inhibitor (SB203580) resulted in the reduction of endoreduplicating cells. Furthermore, the increase in the phosphorylation of JNK was accompanied by an increase in the reactive oxygen species. In addition, endoreduplication was observed in cells after treatment with superoxide donor, 2,3-dimethoxy-1,4-naphoquinone (DMNQ). Confocal microscopic analysis also revealed the increase in mitochondrial superoxide anion in 2ME2-treated HK-1 cells. Pre-treatment of HK-1 cells with superoxide dismutase mimetic 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) or overexpressing the mitochondrial enzyme MnSOD resulted in the reduction of phosphorylation of JNK and the formation of endoreduplicating cells. Furthermore, the tubulin filaments in cytoplasm remain intact in 2ME2-treated HK-1 cells after pre-treatment of TEMPO. Our results suggest that 2ME2 induces endoreduplication through the induction of oxidative stress and the activation of MAPK signal pathways. The biological significance of drug-induced endoreduplication will also be discussed.     

Protective effects of lemongrass essential oil against benzo(a)pyrene-induced oxidative stress and DNA damage in human embryonic lung fibroblast cells

Benzo(a)pyrene (BaP) was a well-known environmental pollutant, numerous studies had implicated BaP as a causative agent in human cancer, particularly lung cancer. The lemongrass essential oil (LEO) possessed various pharmacological activities, especially the anti-oxidative stress and cancer prevention. In the current study, human embryonic lung fibroblast (HELF) cells were treated with 25?mM BaP in the absence or presence of 0.5%, 1% or 2.5% LEO and the cell viability and levels of oxidative stress (OS) and DNA damage in the cells were then measured. Nineteen chemical constituents were identified in LEO, with citral being the main component, representing about 68.78%. LEO was able to protect the HELF cells against BaP-induced loss in cell viability, achieving a maximum of 95.58% cell viability at the 0.5% concentration. Treatment of HELF cells with BaP alone significantly increased the level of Malondialdehyde (MDA) and decreased superoxide dismutase (SOD) and catalase (CAT). However, these effects were suppressed when the cells were also treated with LEO, leading to enhanced levels of SOD and CAT activities (2.9- and 2-fold, respectively, compared with BaP treatment only) and reduced the level of MDA in the cells (43% reduction in malondialdehyde level). At the same time, LEO also reduced the level of DNA damage, as shown by a reduced level of 8-hydroxy-deoxyguanosine (8-OHdG). Taken together, the results showed that LEO offered protection against BaP-induced OS and DNA damage, suggesting that LEO could be a promising agent for lung cancer chemoprevention.     

Effects of repeated Cr(VI) intratracheal instillation on club (Clara) cells and activation of nuclear factor-kappa B pathway via oxidative stress

Hexavalent chromium [Cr(VI)] exposure is known to induce respiratory inflammation and contribute to lung cancer development, but little is known about its target cell type in lung. In the current study, we investigated the effects of repeated Cr(VI) intratracheal instillation on club (Clara) cells and club (Clara) cell secretory protein (CC16) in rats and explored whether the nuclear factor-kappa B (NF-κB) related pathway was involved. We also studied the role of orally delivered Zn against Cr-induced adverse health effects. For four weeks, sixty Sprague-Dawley male rats received weekly intratracheal instillation of potassium dichromate (K₂Cr₂O₇) at 0, 0.063 and 0.630 mg Cr/kg with or without daily intragastric administration of zinc sulfate (ZnSO₄) at 10 mg Zn/kg. Results showed that exposure to Cr(VI) significantly increased the organ coefficient of lung (organ weight as a percentage of body weight), albumin and total protein level in bronchoalveolar lavage fluid (BALF), indicating lung injury and compromised bronchoalveolar/blood barrier (BA/BB) integrity. With increasing Cr(VI) dose, the secretion of CC16 decreased in a dose-dependent manner, suggesting that CC16 can serve as a peripheral biomarker for club cell damage during early lung injury induced by Cr(VI). Increased expression of NF-κB were observed in club cells in both Cr-exposed groups, indicating upregulation of NF-κB, which can be induced by reactive oxygen species (ROS) generated by club cells during Cr reduction with repetitive Cr(VI) exposure. Cr-induced DNA damage was also observed, as significant increase of 8-OHdG was found with Cr exposure at 0.630 mg/kg week. Oral Zn supplementation did not alleviate changes in serum CC16 level under Cr(VI) exposure, indicating its failure in protecting against Cr(VI)-induced club cell damage.     

Changes in the oxidative stress/anti-oxidant system after exposure to sulfur mustard and antioxidant strategies in the therapy,a review

Sulfur mustard, in a chemical name bis(2-chloroethyl) sulfide, is a chemical warfare agent. It is cytotoxic and blister forming once spread over the skin. Though exact molecular mechanism of sulfur mustard toxic action remains unknown, inflammation and oxidative stress development are considered as the most relevant pathological consequences. Applications of either low-molecular weight antioxidants or cofactors for enzymatic antioxidants are considered as suitable ways how to ameliorate the poisoning. In this article, survey of literature on countermeasures against sulfur mustard poisoning are given and evidence of oxidative stress role during sulfur mustard poisoning and availability of antioxidants for the therapy are discussed.     

Tadalafil alleviates cisplatin-induced reproductive toxicity through the activation of the Nrf2/HO-1 pathway and the inhibition of oxidative stress and apoptosis in male rats

Male reproductive toxicity is a well-known adverse effect of cisplatin (CIS), an important antineoplastic agent used to control several types of cancers. Tadalafil (TDF), is a long-acting phosphodiesterase-5 (PDE5) inhibitor commonly used as treatment for erectile dysfunction. The aim of this work was to study the possible protective effect of TDF against CIS-induced testicular toxicity in rats and the possible involvement of Nrf2/HO-1 pathway, which demonstrates antioxidant and inflammatory activities utilizing zinc protoporphyrin-IX (ZnPP) as HO-1 inhibitor. Results revealed that TDF attenuated the CIS-induced disturbances in sperm count and activities, normalized the serum testosterone level, improved the CIS-induced changes in epididymal and testicular weights and restored the normal structure of testicular tissues. In addition, TDF upregulated the gene expression levels of Nrf2 and HO-1 and the activity of HO-1 whereas, it reduced the CIS-induced changes in testicular oxidative stress markers and the levels of inflammatory mediators (TNF-α and iNOS). Furthermore, TDF antagonized the CIS-induced increase in testicular gene expression of apoptotic markers caspase-3 and Bax, and the decrease in Bcl-2. However, ZnPP co-administration significantly attenuated all TDF-mediated improvements in CIS-induced testicular toxicity, biochemical changes, and apoptosis. In conclusion, TDF exerts a protective effect against CIS-induced reproductive toxicity in males, through different mechanisms, besides its inhibitory action to PDE5, possibly mediated by the upregulation of Nrf2/HO-1, along with its antioxidant, anti-inflammatory, and anti-apoptotic effects. Hence, the use of TDF represents a promising therapeutic approach to protect the male reproductive system from the harmful toxic effects of CIS.     

Oxidative stress and NFkappaB activation in the lungs of rats: a synergistic interaction between soot and iron particles

Particulate matter (PM) has been associated with a variety of adverse health effects primarily involving the cardiopulmonary system. However, the precise biological mechanisms to explain how exposure to PM exacerbates or directly causes adverse effects are unknown. Particles of varying composition may play a critical role in these effects. To study such a phenomenon, a simple, laminar diffusion flame was used to generate aerosols of soot and iron particles in the ultrafine size range. Exposures of healthy adult rats were for 6 h/day for 3 days. Conditions used included exposure to soot only, iron only, or a combination of soot and iron. We found animals exposed to soot particles at 250 microg/m3 had no adverse respiratory effects. Exposure to iron alone at a concentration of 57 microg/m3 also had no respiratory effects. However, the addition of 45 microg/m3 of iron to soot with a combined total mass concentration of 250 microg/m3 demonstrated significant pulmonary ferritin induction, oxidative stress, elevation of IL-1beta, and cytochrome P450s, as well as activation of NFkappaB. These findings suggest that a synergistic interaction between soot and iron particles account for biological responses not found with exposure to iron alone or to soot alone.     

Diepoxybutane activates the mitochondrial apoptotic pathway and mediates apoptosis in human lymphoblasts through oxidative stress

Diepoxybutane (DEB) is the most potent metabolite of the environmental chemical 1,3-butadiene (BD), which is prevalent in petrochemical industrial areas. BD is a known mutagen and human carcinogen, and possesses multi-systems organ toxicity. We recently reported that DEB-induced cell death in TK6 lymphoblasts was due to the occurrence of apoptosis, and not necrosis. In this study, we investigated the molecular mechanisms responsible for DEB-induced apoptosis in these cells. Bax and Bak were found to be over-expressed and activated, and the mitochondrial trans-membrane potential was attenuated in cells undergoing DEB-induced apoptosis. Cytochrome c was depleted from the mitochondria of TK6 cells undergoing apoptosis, and was released into the cytosol in Jurkat T-lymphoblasts exposed to the same concentrations of DEB. Executioner caspase 3 was deduced to be activated by initiator caspase 9. DEB-induced reactive oxygen species (ROS) formation, and the ROS scavenger N-acetyl-L-cysteine effectively blocked DEB-induced apoptosis in TK6 cells. Collectively, these results demonstrate that the mitochondrial apoptotic pathway is activated to mediate DEB-induced apoptosis in human TK6 lymphoblasts. These results further demonstrate that DEB-induced apoptosis is also mediated by the DEB-induced generation of ROS. This is the first report to examine the mechanism of DEB-induced apoptosis in human lymphoblasts.     

Comparison of 2,2-bis(bromomethyl)-1,3-propanediol induced genotoxicity in UROtsa cells and primary rat hepatocytes: Relevance of metabolism and oxidative stress

2,2-Bis(bromomethyl)-1,3-propanediol (BMP) is a brominated flame retardant used in urethane foams and polyester resins. In a two year dietary study, BMP caused neoplastic lesions at multiple sites including the urinary bladder of both rats and mice. However, liver was not a target tissue. We previously reported that BMP elicited oxidative DNA damage in a human uroepithelial cell line (UROtsa). The present in vitro study investigated the susceptibility of target (UROtsa cells) and non-target cells (primary rat hepatocytes) to BMP-induced genotoxicity. In contrast to hepatocytes, BMP exhibited greater genotoxic potential in UROtsa cells as evidenced by the concentration dependent increase in DNA strand breaks and DNA binding. Total content of intracellular GSH quantified in UROtsa cells (2.7 ± 1.0 nmol/mg protein) was 4 fold lower than that in hepatocytes (10.7 ± 0.3 nmol/mg protein). HPLC analysis indicated BMP was not metabolized and/or consumed in UROtsa cells at any of the concentrations tested (10–250 μM) but was extensively converted to a mono-glucuronide in hepatocytes. These results demonstrate that a target cell line such as UROtsa cells are more susceptible to BMP-induced DNA damage when compared to non-target cells. This increased susceptibility may relate to the deficiency of antioxidant and/or metabolic capabilities in UROtsa cells.     

Exposure to Pb, Cd, and As mixtures potentiates the production of oxidative stress precursors: 30-day, 90-day, and 180-day drinking water studies in rats

Exposure to chemical mixtures is a common and important determinant of toxicity and is of particular concern due to their appearance in sources of drinking water. Despite this, few in vivo mixture studies have been conducted to date to understand the health impact of chemical mixtures compared to single chemicals. Interactive effects of lead (Pb), cadmium (Cd) and arsenic (As) were evaluated in 30-, 90-, and 180-day factorial design drinking water studies in rats designed to test the hypothesis that ingestion of such mixtures at individual component Lowest-Observed-Effect-Levels (LOELs) results in increased levels of the pro-oxidant delta aminolevulinic acid (ALA), iron, and copper. LOEL levels of Pb, Cd, and As mixtures resulted in the increased presence of mediators of oxidative stress such as ALA, copper, and iron. ALA increases were followed by statistically significant increases in kidney copper in the 90- and 180-day studies. Statistical evidence of interaction was identified for six biologically relevant variables: blood delta aminolevulinic acid dehydratase (ALAD), kidney ALAD, urinary ALA, urinary iron, kidney iron, and kidney copper. The current investigations underscore the importance of considering interactive effects that common toxic agents such as Pb, Cd, and As may have upon one another at low-dose levels. The interactions between known toxic trace elements at biologically relevant concentrations shown here demonstrate a clear need to rigorously review methods by which national/international agencies assess health risks of chemicals, since exposures may commonly occur as complex mixtures.     

Mode of action of ethyl tertiary-butyl ether hepatotumorigenicity in the rat: Evidence for a role of oxidative stress via activation of CAR,PXR and PPAR signaling pathways

To elucidate possible mode of action (MOA) and human relevance of hepatotumorigenicity in rats for ethyl tertiary-butyl ether (ETBE), male F344 rats were administered ETBE at doses of 0, 150 and 1000 mg/kg body weight twice a day by gavage for 1 and 2 weeks. For comparison, non-genotoxic carcinogen phenobarbital (PB) was applied at a dose of 500 ppm in diet. Significant increase of P450 total content and hydroxyl radical levels by low, high doses of ETBE and PB treatments at weeks 1 and 2, and 8-OHdG formation at week 2, accompanied accumulation of CYP2B1/2B2, CYP3A1/3A2 and CYP2C6, and downregulation of DNA oxoguanine glycosylase 1, induction of apoptosis and cell cycle arrest in hepatocytes, respectively. Up-regulation of CYP2E1 and CYP1A1 at weeks 1 and 2, and peroxisome proliferation at week 2 were found in high dose ETBE group. Results of proteome analysis predicted activation of upstream regulators of gene expression altered by ETBE including constitutive androstane receptor (CAR), pregnane-X-receptor (PXR) and peroxisome proliferator-activated receptors (PPARs). These results indicate that the MOA of ETBE hepatotumorigenicity in rats may be related to induction of oxidative stress, 8-OHdG formation, subsequent cell cycle arrest, and apoptosis, suggesting regenerative cell proliferation after week 2, predominantly via activation of CAR and PXR nuclear receptors by a mechanism similar to that of PB, and differentially by activation of PPARs. The MOA for ETBE hepatotumorigenicity in rats is unlikely to be relevant to humans.     

Exposure of human skin to benzo[a]pyrene: Role of CYP1A1 and aryl hydrocarbon receptor in oxidative stress generation

Exposure to benzo[a]pyrene (BaP) can induce inflammatory skin diseases and skin cancer, which are both associated to oxidative stress. BaP is known to bind with high specificity to the aryl hydrocarbon receptor (AhR), modifying the expression of CYP1A1, involved both in cancer and inflammation.     

Oxidative biotransformation in primary cultures of chick embryo hepatocytes: induction of cytochrome P-450 and the metabolism of benzo(a)pyrene

Primary cultures of chick embryo hepatocytes are known to maintain their initial level of cytochrome P-450 for a number of days. To explore the possibilities of chick embryo hepatocyte cultures as a tool in drug metabolism, induction profiles of cytochrome P-450 were determined and the metabolism of benzo(a)pyrene as a model substrate was studied.Maximum induction by phenobarbitone and Aroclor 1254 is reached after 21 h and 18 h, respectively, both in the presence and absence of serum. For -naphthoflavone induction is maximal after 31 h in the presence and 43 h in the absence of serum. The levels of P-450 after induction are comparable to those found in vivo in rats: increases of 200% for phenobarbitone, 200% for -naphthoflavone and 210% for Aroclor 1254. Ethoxyresorufin-0-deethylase activities are induced by -naphthoflavone and Aroclor 1254, but as expected only slightly by phenobarbitone. In the absence of serum in the culture medium, for the control as well as the induced cells a plateau of activity is maintained for at least 24 h. In the presence of serum a decline in P-450 levels is observed. Especially in the case of Aroclor, an increase in porphyrin content of 320% of control values is seen at the same time.A number of representative metabolites of benzo(a)pyrene were quantitated during a 4-h incubation. Relative amounts are comparable to those observed with rat liver microsomes. As expected, -naphthoflavone and Aroclor induce the rate of metabolism (by 500% and 400%, respectively, in the absence of serum), but phenobarbitone has no or very little effect.Interestingly, when benzo(a)pyrene is incubated with control or phenobarbitone-induced cells an increase in rate of metabolite formation with time is observed: benzo (a)pyrene seems to induce its own metabolism. The chick embryo hepatocytes thus offer the possibility of studying induction and biotransformation in the same system at the same time, in vitro.