Atypical cytochrome P450 induction profiles in glomerular mesangial cells at the mRNA and enzyme level. Evidence for CYP1A1 and CYP1B1 expression and their involvement in benzo[a]pyrene metabolism

Cytochrome P450 1B1: role in health and disease and effect of nutrition on its expression

This review summarizes the available literature stating CYP1B1 to provide the readers with a comprehensive understanding of its role in different diseases, as well as the importance of nutrition in their control in terms of the influence of different nutrients on its expression. CYP1B1, a member of the cytochrome P450 enzyme family is expressed in different human tissues and is known to contribute to different life alarming pathologies. Particularly, till now much attention has been paid to its involvement in the development of primary congenital glaucoma (PCG) and cancer. However, recently there are some reports highlighting CYP1B1 as a potential regulator in energy homeostasis and adipogenesis thus promoting obesity and hypertension as well. Therefore, seeking out effective strategies to modulate the expression of CYP1B1 is a challenging task. In this context, nutrients based strategies will be the best choice as they are mostly harmless and are easily available in one's diet. In conclusion, this article will be helpful in providing a base for further research that is needed to identify the role of CYP1B1 in progression of different diseases, hypertension and obesity in particular, and then to present the effectiveness, mechanisms, and biologic plausibility of nutrients against its expression.

Progressive Glomerulonephritis and Histiocytic Sarcoma Associated with Macrophage Functional Defects in CYP1B1-Deficient Mice

The cytochrome P450 CYP1B1 enzyme metabolically activates polycyclic aromatic hydrocarbons and is a major P450 isoenzyme in human monocytes and macrophages. We have shown previously that mice deficient in CYP1B1 were resistant to induced tumors after 7,12-dimethylbenz[a]anthracene exposure. The pathology of aging CYP1B1 null mice on a B6; 129 background was studied in groups of 29 males and 30 females. By 12 months, 50% of the female mice had developed a unusual progressive glomerulonephritis while males had similar renal lesions later in life. This disease followed a sequence of proliferative, membranoproliferative and sclerotic glomerulonephritis. Anti-DNA antibodies were found in the blood of the mice along with immune deposits containing immunoglobulins in subepithelial locations of the glomerular basement membrane. The lesions were unlike those found in aging wild-type B6;129 mice or mice of other strains. We found that macrophages from CYP1B1-null mice were impaired in the phagocytosis of apoptotic, necrotic, and opsonized cells. This suggests a generalized defect in the phagocytic activity of CYP1B1-null mouse macrophages. Male mice also developed a high incidence (62—64%) of histiocytic sarcomas. Our study provides evidence that deficiency of CYP1B1 can play a role in the development of glomerular disease, normal processing of catabolic DNA and tumors of the mononuclear phagocyte system. The function of CYP1B1 in histiocytes and macrophages may involve both self-tolerance and tumor suppression.

Polycyclic aromatic hydrocarbons: from metabolism to lung cancer

Excessive exposure to polycyclic aromatic hydrocarbons (PAHs) often results in lung cancer, a disease with the highest cancer mortality in the United States. After entry into the lung, PAHs induce phase I metabolic enzymes such as cytochrome P450 (CYP) monooxygenases, i.e. CYP1A1/2 and 1B1, and phase II enzymes such as glutathione S-transferases, UDP glucuronyl transferases, NADPH quinone oxidoreductases (NQOs), aldo-keto reductases (AKRs), and epoxide hydrolases (EHs), via the aryl hydrocarbon receptor (AhR)-dependent and independent pathways. Humans can also be exposed to PAHs through diet, via consumption of charcoal broiled foods. Metabolism of PAHs through the CYP1A1/1B1/EH pathway, CYP peroxidase pathway, and AKR pathway leads to the formation of the active carcinogens diol-epoxides, radical cations, and o-quinones. These reactive metabolites produce DNA adducts, resulting in DNA mutations, alteration of gene expression profiles, and tumorigenesis. Mutations in xenobiotic metabolic enzymes, as well as polymorphisms of tumor suppressor genes (e.g. p53) and/or genes involved in gene expression (e.g. X-ray repair cross-complementing proteins), are associated with lung cancer susceptibility in human populations from different ethnicities, gender, and age groups. Although various metabolic activation/inactivation pathways, AhR signaling, and genetic susceptibilities contribute to lung cancer, the precise points at which PAHs induce tumor initiation remain unknown. The goal of this review is to provide a current state-of-the-science of the mechanisms of human lung carcinogenesis mediated by PAHs, the experimental approaches used to study this complex class of compounds, and future directions for research of these compounds.

Effects on specific promoter DNA methylation in zebrafish embryos and larvae following benzo[a]pyrene exposure

Benzo[a]pyrene (BaP) is an established carcinogen and reproductive and developmental toxicant. BaP exposure in humans and animals has been linked to infertility and multigenerational health consequences. DNA methylation is the most studied epigenetic mechanism that regulates gene expression, and mapping of methylation patterns has become an important tool for understanding pathologic gene expression events. The goal of this study was to investigate aberrant changes in promoter DNA methylation in zebrafish embryos and larvae following a parental and continued embryonic waterborne BaP exposure. A total of 21 genes known for their role in human diseases were selected to measure percent methylation by multiplex deep sequencing. At 96hpf (hours post fertilization) compared to 3.3hpf, dazl, nqo1, sox3, cyp1b1, and gstp1 had higher methylation percentages while c-fos and cdkn1a had decreased CG methylation. BaP exposure significantly reduced egg production and offspring survival. Moreover, BaP decreased global methylation and altered CG, CHH, and CHG methylation both at 3.3 and 96hpf. CG methylation changed by 10% or more due to BaP in six genes (c-fos, cdkn1a, dazl, nqo1, nrf2, and sox3) at 3.3hpf and in ten genes (c-fos, cyp1b1, dazl, gstp1, mlh1, nqo1, pten, p53, sox2, and sox3) at 96hpf. BaP also induced gene expression of cyp1b1 and gstp1 at 96hpf which were found to be hypermethylated. Further studies are needed to link aberrant CG, CHH, and CHG methylation to heritable epigenetic consequences associated with disease in later life.

Targeting cytochrome P450 CYP1B1 with a therapeutic cancer vaccine

The role that the immune system plays in limiting tumor formation and growth is becoming increasingly clear and passive immunotherapeutic approaches, such as the use of monoclonal antibodies, are now being successfully applied in clinical practice. Active immunization against tumors, however, has not yet been shown to have the same level of clinical efficacy. Two important reasons for this lack of efficacy have to do with the antigens being targeted, as well as the immunization approaches that have been tested. This review will highlight some of the requirements thought to be important for the successful development of an active immunization approach, with a focus on the ongoing development efforts for a novel agent targeting the cytochrome P450 family member, CYP1B1.

Bioactivation of Polycyclic Aromatic Hydrocarbon Carcinogens within the vascular Wall: Implications for Human Atherogenesis

Atherogenesis is a complex pathogenetic process involving a variety of structural and functional deficits within the arterial wall that culminate in the formation of fibrous atherosclerotic plaques. Cigarette smoking is potentially the most remediable contributor to cardiovascular mortality and morbidity. Among the 4000 plus chemicals present in tobacco and tobacco smoke, polycyclic aromatic hydrocarbons (PAHs) have been firmly implicated in the etiology of atherosclerosis in experimental model systems. However, the molecular mechanisms responsible for PAH-induced vascular injury are not well understood. In this review, we have focused on the mechanisms of bioactivation of PAHs in the vas-culature, and the possible role(s) of cytochrome P4501A and 1B enzymes in the formation of PAH-DNA adducts within the vessel wall, a phenomenon that may contribute to the development of atherosclerotic plaques in humans.

Influence of TCDD on zebrafish CYP1B1 transcription during development

Cytochrome P450 1B1 (CYP1B1) is a heme-containing monooxygenase that metabolizes various polycyclic aromatic hydrocarbons and aryl amines, as well as retinoic acid and steroid hormones. Here we report the cloning of an ortholog of CYP1B1 from zebrafish and the demonstration that transcription of zebrafish CYP1B1 was modulated by two types of mechanisms during different developmental stage. First in late pharyngula stage before hatching, CYP1B1 was constitutively transcribed in retina, midbrain-hindbrain boundary and diencephalon regions through a close coordination between aryl hydrocarbon receptor 2 (AHR2)-dependent and AHR2-independent pathways. After hatching, the basal transcription was attenuated and it could not be elicited upon 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure. In contrast, TCDD exposure induced de novo CYP1B1 transcription in larval branchial arches and heart tissues via an AHR2-dependent pathway. Blocking AHR2 translation completely eliminated the TCDD-mediated CYP1B1 transcription. However, we did not detect any types of CYP1B1 transcription in liver and kidney tissues through the developmental stage. It suggests that the constitutive and TCDD-inducible types of CYP1B1 transcriptions are modulated by distinct pathways with different tissue specificities. Finally, we investigated the role of CYP1B1 in TCDD-mediated embryonic toxicity. Because knockdown of CYP1B1 did not prevent TCDD-induced pericardial edema and cranial defects, it suggests that CYP1B1 is not involved in the developmental toxicity of dioxin.

Activation profiles of HSPA5 during the glomerular mesangial cell stress response to chemical injury

Environmental injury has been associated with endoplasmic reticulum (ER) stress, a response characterized by activation of the unfolded protein response, proteasomal degradation of proteins, and induction of HSPA5, also known as GRP78 or BiP. Although HSPA5 has been implicated in the stress response to environmental injury in several cell types, its role in the glomerular ER stress response is unknown. In this study, we evaluated HSPA5 activation profiles in rat glomerular mesangial cells (rGMCs) challenged with heavy metals (HgCl2 or Pb2+ acetate) or polycyclic aromatic hydrocarbons (PAHs, ie, benzo(a)pyrene [BaP]). Challenge of rGMCs with 1 or 10 microM HgCl2 or Pb2+ acetate increased HSPA5 mRNA and protein levels. The induction response was sensitive to transcriptional and translational inhibition by actinomycin D (AD) and cyclohexamide, respectively. HSPA5 mRNA was induced by 3 microM BaP in an AD-sensitive manner, but this response was unaffected by the presence of heavy metals. A promoter construct containing sequences that mediate thapsigargin (TH) inducibility of the HSPA5 promoter was refractory to both heavy metals and BaP. The HSPA5 induction response in rGMCs is conserved because it was reproduced with fidelity in immunolocalization experiments of HSPA5 protein in M15 and HEK293 cells in embryonic lines of murine and human origin, respectively. Collectively, these findings identify HSPA5 in the stress response of rGMCs and implicate regulatory mechanisms that are distinct from those involved in TH inducibility.

Competing roles of aldo-keto reductase 1A1 and cytochrome P4501B1 in benzo[a]pyrene-7,8-diol activation in human bronchoalveolar H358 cells: role of AKRs in P4501B1 induction

Benzo[a]pyrene (BP) requires metabolic activation to electrophiles to exert its deleterious effects. We compared the respective roles of aldo-keto reductase 1A1 (AKR1A1, aldehyde reductase) and P4501B1 in the formation of BP-7,8-dione and BP-tetrols, respectively, in intact bronchoalveolar cells manipulated to express either enzyme. Metabolite formation was confirmed by HPLC/MS and quantitatively measured by HPLC/UV/beta-RAM. In TCDD-treated H358 cells (P4501B1 expression), the anti-BPDE hydrolysis product BP-tetrol-1 increased over 3-12 h to a constant level. In H358 AKR1A1 transfectants, formation of BP-7,8-dione was elevated for 3-12 h but significantly decreased after 24 h. Interestingly, BP-tetrols were also detected in AKR1A1 transfectants even though they do not constitutively express P4501A1/P4501B1 enzymes. Northern and Western blotting confirmed the induction of P4501B1 by BP-7,8-dione in parental cells and the induction of P4501B1 by BP-7,8-diol in AKR1A1-transfected cells. P4501B1 induction was blocked in AKR1A1 transfectants by the AKR1A1 inhibitor (sulfonylnitromethane), the o-quinone scavenger (N-acetyl-l-cysteine), or the cytosolic AhR antagonist (diflubenzuron). Attenuation of P4501B1 induction in these cells was verified by measuring a decrease in BP-tetrol formation. Our studies show that the formation of BP-7,8-dione by AKR1A1 in human bronchoalveolar cells leads to an induction of P4501B1 and that a functional consequence of this induction is elevated anti-BPDE production as detected by increased BP-tetrol formation. Therefore, the role of AKR1A1 in the activation of BP-7,8-diol is bifunctional; that is, it directly activates BP-7,8-diol to the reactive and redox-active PAH o-quinone (BP-7,8-dione) and it indirectly trans-activates the P4501B1 gene by generating the aryl hydrocarbon receptor (AhR) ligand BP-7,8-dione.

Streptozotocin (STZ) diabetes enhances benzo(alpha)pyrene induced renal injury in Sprague Dawley rats

Information is lacking regarding the biological response to environmental chemicals in the context of pre-existing disease. Benzo(alpha)pyrene (BaP), a polycyclic aromatic hydrocarbon, is a byproduct of combustion that causes renal injury and elicits a nephropathic response. This study evaluated the nephrotoxicity of BaP in normoglycemic and diabetic rats. Female Sprague Dawley rats were divided into four groups: normoglycemic-vehicle (NV), normoglycemic-BaP (N-BaP), diabetic-vehicle (DV) and diabetic-BaP (D-BaP). Diabetes was induced by intraperitoneal (ip) injection of streptozotocin (60 mg/kg, 1 ml/kg). Rats were injected (ip) with vehicle or 10 mg/kg BaP (1 ml/kg) once per week for 5 weeks. Urinary protein and albumin, plasma creatinine and light microscopy were performed to assess the effects of BaP on kidney function. Diabetes was confirmed by plasma glucose levels >400 mg/dl in the DV and D-BaP groups. BaP increased kidney weight and blood urea nitrogen (BUN) levels in the D-BaP relative to the DV group. No change in BUN was observed following 5 weeks of BaP treatment in the normoglycemic animals, however, kidney weight was increased (p=0.013) in the N-BaP relative to the NV animals. STZ diabetes increased susceptibility to BaP mediated renal damage following repeated treatment for 5 weeks when compared to age matched normoglycemic rats.

Effects of 3-methylcholanthrene on gene expression profiling in the rat using cDNA microarray analyses

There is significant human exposure to polycyclic aromatic hydrocarbons (PAHs), many of which are bioactivated by the cytochrome P450 (P450) 1A family of enzymes to metabolites that are capable of covalently binding to DNA, a critical step in the initiation of carcinogenesis. We reported earlier that exposure of rats to 3-methylcholanthrene (MC) causes sustained induction of hepatic cytochrome P4501A expression for up to 45 days. Here, we tested the hypothesis that MC elicits persistent induction of other genes that are regulated by the Ah receptor (AHR). Female Sprague-Dawley rats were treated with MC (100 micromol/kg) ip once daily for 4 days, and gene expression patterns were investigated using total liver RNA isolated from animals at 1, 15, and 28 days after MC withdrawal. Gene expression was studied by cDNA microarray analyses using 4608 unique clones from liver-derived expressed sequence tag (EST) libraries fortified with clones of known liver genes representing approximately 4000 genes. Several phase I (P4501A1, -1A2) and phase II [e.g., glutathione-S-transferase (GST)-M1, UDP-glucuronosyl transferases (UGT)] genes were persistently induced (3-10-fold) by MC for 15-28 days. The persistent induction of P4501A1 gene expression was confirmed by real time reverse transcriptase polymerase chain reaction (RT-PCR) experiments. MC also elicited a 5-fold persistent augmentation of acute phase genes such as orosomucoid 1 and alpha-1-acid glycoprotein (AGP), and this was accompanied by sustained liver damage and inflammation in the MC-exposed rats. In conclusion, our results strongly suggest that sustained induction of P4501A1 by MC is accompanied by persistent expression of other genes belonging to the Ah gene battery, as well as certain other genes involved in toxic responses. Elucidating the mechanisms of persistent induction of P4501A1 and other genes by MC might lead to a better understanding of the mechanisms of toxicity mediated by PAHs.

Cytochrome P4501A induction and DNA adduct formation in glaucous gulls (Larus hyperboreus), fed with environmentally contaminated gull eggs

This study indicates that complex mixtures of pollutants found in the Arctic marine environment have genotoxic effects in glaucous gulls (Larus hyperboreus). DNA adducts were quantified, by the (32)P-postlabeling technique, in liver samples from gulls fed with hen eggs (controls) and from gulls fed with environmentally contaminated gull eggs (exposed). All birds were grown and fed under laboratory conditions. Hepatic homologues to mammalian cytochrome P4501A (CYP1A) proteins were also determined by Western blotting. DNA adducts were detected in all but one liver sample, but the exposed birds had a significantly increased level of DNA adducts relative to that of the controls. There was no clear significant correlation between the DNA adduct level and the level of organochlorine compounds (OCs) in blood. The level of CYP1A protein was significantly higher in the liver of exposed male gulls than in the liver of control males and positively correlated, with significance, to the level of OC compounds measured in blood. There was no significant correlation between the level of DNA adducts and the CYP1A protein content.

Effects of TCDD and estradiol-17beta on the proliferation and Na+/glucose cotransporter in renal proximal tubule cells

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) is a highly toxic environmental toxicant that alters cell proliferation and function. Estrogens are noted for their ability to stimulate cell proliferation in various tissues. However, little is known about any interaction between TCDD and estradiol-17beta (E(2)) that affects renal proximal tubule cell proliferation and Na(+)/glucose cotransporters' activity. Thus, the effects of TCDD and E(2) on [(3)H]-thymidine incorporation and on alpha-methyl-d-glucopyranoside (alpha-MG) uptake were investigated in the primary rabbit kidney proximal tubule cells (PTCs). TCDD (>10(-10) M >1 h) inhibited [(3)H]-thymidine incorporation and c-fos transcripts in real-time RT-PCR, whereas E(2) (>10(-9) M, 24 h) stimulated them. Aryl hydrocarbon receptor (AhR) agonists, beta-naphthoflavone (beta-NF) and polychlorinated biphenyls (PCBs) (10(-6) M) synergistically increased the TCDD-induced inhibition of [(3)H]-thymidine incorporation. However, the AhR antagonist, alpha-naphthoflavone (alpha-NF) as well as E(2) blocked TCDD-induced inhibition of [(3)H]-thymidine incorporation. TCDD (10(-8) M, 48 h) specifically inhibited alpha-MG uptake and its effect was due to V(max) value but not K(m) value. Indeed, TCDD decreased Na(+)/glucose cotransporter 1, 2 (SGLT1, 2) protein level compared with control. In addition, TCDD-induced inhibition of alpha-MG uptake was blocked by alpha-NF or E(2). In conclusion, TCDD inhibited [(3)H]-thymidine incorporation and alpha-MG uptake, and E(2) blocked TCDDs effects in primary cultured renal proximal tubule cells.

Chemopreventive effects of Cuminum cyminum in chemically induced forestomach and uterine cervix tumors in murine model systems

Lately, a strong correlation has been established between diet and cancer. For ages, cumin has been a part of the diet. It is a popular spice regularly used as a flavoring agent in a number of ethnic cousins. In the present study, cancer chemopreventive potentials of different doses of a cumin seed-mixed diet were evaluated against benzo(a)pyrene [B(a)P]-induced forestomach tumorigenesis and 3-methylcholanthrene (MCA)-induced uterine cervix tumorigenesis. Results showed a significant inhibition of stomach tumor burden (tumors per mouse) by cumin. Tumor burden was 7.33 +/- 2.10 in the B(a)P-treated control group, whereas it reduced to 3.10 +/- 0.57 (P < 0.001) by a 2.5% dose and 3.11 +/- 0.60 (P <0.001) by a 5% dose of cumin seeds. Cervical carcinoma incidence, compared with the MCA-treated control group (66.67%), reduced to 27.27% (P < 0.05) by a diet of 5% cumin seeds and to 12.50% (P < 0.05) by a diet of 7.5% cumin seeds. The effect of 2.5 and 5% cumin seed-mixed diets was also examined on carcinogen/xenobiotic metabolizing phase I and phase II enzymes, antioxidant enzymes, glutathione content, lactate dehydrogenase (LDH), and lipid peroxidation in the liver of Swiss albino mice. Levels of cytochrome P-450 (cyt P-450) and cytochrome b5 (cyt b(5)) were significantly augmented (P < 0.05) by the 2.5% dose of cumin seed diet. The levels of cyt P-450 reductase and cyt b(5) reductase were increased (significance level being from P < 0.05 to P < 0.01) by both doses of cumin. Among the phase II enzymes, glutathione S-transferase specific activity increased (P < 0.005) by the 5% dose, whereas that of DT-diaphorase increased significantly (P < 0.05) by both doses used (2.5 and 5%). In the antioxidant system, significant elevation of the specific activities of superoxide dismutase (P < 0.01) and catalase (P < 0.05) was observed with the 5% dose of cumin. The activities of glutathione peroxidase and glutathione reductase remained unaltered by both doses of cumin. The level of reduced glutathione measured as nonprotein sulfhydryl content was elevated (significance level being from P < 0.05 to P < 0.01) by both doses of cumin. Lipid peroxidation measured as formation of MDA production showed significant inhibition (P < 0.05 to P < 0.01) by both doses of cumin. LDH activity remained unaltered by both doses of cumin. The results strongly suggest the cancer chemopreventive potentials of cumin seed and could be attributed to its ability to modulate carcinogen metabolism.

Evaluation of a real-time polymerase chain reaction method for the quantification of CYP1B1 gene expression in MCF-7 human breast carcinoma cells

INTRODUCTION

Cytochrome P450 1B1 (CYP1B1) catalyzes the bioactivation of numerous procarcinogens and it is expressed in tumor cells, including human breast cancer cells. To study CYP1B1 gene expression, it is important to have an accurate, precise, reproducible, specific, and quantitative method.

METHODS

MCF-7 human breast carcinoma cells were treated with beta-naphthoflavone (BNF; 50 microM), emodin (0.1-3 microM), trans-resveratrol (2.5-20 microM), or 0.1% dimethylsulfoxide (DMSO; vehicle control). Total cellular RNA was isolated and reverse transcribed. cDNA samples were quantified by a fluorescence assay and a constant amount (1 ng) was amplified in a real-time DNA thermal cycler (LightCycler).

RESULTS

Melting curve analysis and agarose gel electrophoresis of the amplicons resulted in a single peak and a single band, respectively. The identity of the amplicon was confirmed to be CYP1B1 by sequencing analysis. The standard curve for the real-time PCR amplification of CYP1B1 cDNA was log-linear for at least four orders of magnitude. The limit of quantitation (LOQ) of the assay was 100 copies. At the LOQ, the assay had an accuracy of 8% and a precision of 10%. The intraday (n=4) variability (expressed as percent coefficient of variation) was 9% for a sample with low CYP1B1 mRNA expression (cells treated with 0.1% DMSO; i.e., Sample A) and 3% for a sample with elevated CYP1B1 mRNA expression (cells treated with BNF; i.e., Sample B). The interday (n=4) variability was 16% for Sample A and 15% for Sample B. Emodin increased CYP1B1 mRNA expression in cultured MCF-7 cells (maximal effect of ninefold induction achieved at 1 microM), whereas trans-resveratrol suppressed it (IC(50)=6.6+/-1.0 microM, mean+/-S.E.M., n=3).

DISCUSSION

An accurate, precise, reproducible, and specific method is described for the real-time PCR quantification of CYP1B1 gene expression in MCF-7 human breast carcinoma cells.

Tobacco smoke-dependent changes in cytochrome P450 1A1, 1A2, and 2E1 protein expressions in fetuses, newborns, pregnant rats, and human placenta

Tobacco smoke (TS) was described as a mixture of numerous cytochrome P450 (P450) substrates, inducers, and inhibitors. These inducers and inhibitors may modify drug clearance and xenobiotic or endogenous metabolism affecting P450s expression. In the present study, the effect of gestation and TS on: (1) cytochrome P450 CYP1A1, CYP1A2, and CYP2E1 protein expressions, and (2) cytochrome P450-linked microsomal enzyme activities, were studied in fetal rat liver, rat, and human placenta and in newborn and adult rat hepatic and extrahepatic tissues. Non-pregnant and pregnant 4-month-old female Wistar rats were exposed to TS (500, 1,000, or 1,500 mg carbon monoxide per m(3) air) in a toxicological chamber for 3 weeks (6 h daily, 5 days weekly). Human placentas were sampled from non-smoking, passive smoking, or active smoking primiparas. The efficacy of exposure was assessed by measuring urine cotinine levels. The TS-dependent inductory effect on the expression of CYP1A1 and 1A2 and related monooxygenase activities, and the inhibitory/inductory effect on CYP2E1 expression in rat tissues were observed. Pregnancy was associated with decreased levels of constitutive CYP1A1 and 2E1 in hepatic and extrahepatic tissues, TS-inducible CYP1A2 expression in the liver, and CYP1A1 expression in lungs and heart, but had no inhibitory effect on TS-inducible CYP1A1 and 2E1 expression, EROD, and P450-cooperated enzyme activities in the liver, kidney, and, in the latter case, in the heart. The presence of TS-induced CYP1A1 protein was confirmed in rat and human placenta and showed in newborn liver and lungs. CYP1A2 and 2E1 proteins were detectable in fetal rat liver. It was concluded that the expression of CYP1A1, 1A2, and 2E1, which metabolize some drugs and activate carcinogens, is controlled by age-, pregnancy-, and tissue-specific regulatory mechanisms in rats. Gestational differences in the regulation of expression of CYP1A subfamily members are not excluded. CYP1A1 and 2E1, but not CYP1A2 inductory mechanisms seem to be functional in fetal liver at day 21 of pregnancy but they appeared to be uninducible under a TS exposure. In TS-exposed pregnant females and fetuses the effects of metabolic activation of CYP1A1 and 1A2 substrates might be reduced because of lower CYP expressions or poor induction, respectively.

Inducible cytochrome P450 activities in renal glomerular mesangial cells: biochemical basis for antagonistic interactions among nephrocarcinogenic polycyclic aromatic hydrocarbons

Background

Benzo(a)pyrene (BaP), anthracene (ANTH) and chrysene (CHRY) are polynuclear aromatic hydrocarbons (PAHs) implicated in renal toxicity and carcinogenesis. These PAHs elicit cell type-specific effects that help predict toxicity outcomes in vitro and in vivo. While BaP and ANTH selectively injure glomerular mesangial cells, and CHRY targets cortico-tubular epithelial cells, binary or ternary mixtures of these hydrocarbons markedly reduce the overall cytotoxic potential of individual hydrocarbons.

Methods

To study the biochemical basis of these antagonistic interactions, renal glomerular mesangial cells were challenged with BaP alone (0.03 – 30 μM) or in the presence of ANTH (3 μM) or CHRY (3 μM) for 24 hr. Total RNA and protein will be harvested for Northern analysis and measurements of aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin-O-deethylase (EROD) activity, respectively, to evaluate cytochrome P450 mRNA and protein inducibility. Cellular hydrocarbon uptake and metabolic profiles of PAHs were analyzed by high performance liquid chromatography (HPLC).

Results

Combined hydrocarbon treatments did not influence the cellular uptake of individual hydrocarbons. ANTH or CHRY strongly repressed BaP-inducible cytochrome P450 mRNA and protein expression, and markedly inhibited oxidative BaP metabolism.

Conclusion

These findings indicate that antagonistic interactions among nephrocarcinogenic PAHs involve altered expression of cytochrome P450s that modulate bioactivation profiles and nephrotoxic/ nephrocarcinogenic potential.

Ligand-activated Ahr signaling leads to disruption of nephrogenesis and altered Wilms' tumor suppressor mRNA splicing

The aryl hydrocarbon receptor (Ahr), a member of the large basic helix-loop-helix (bHLH) and PAS homology domain superfamily, is a highly conserved transcriptional regulator involved in mammalian development. In the present study, a murine metanephros organ culture system was employed to evaluate the role of the Ahr signaling in nephrogenesis in vitro. Ahr and Wilms' tumor suppressor (wt1) mRNAs were detected by in situ hybridization and RT-PCR during the course of renal development. Treatment with 3 microM BaP, a hydrocarbon ligand of Ahr, inhibited glomerulogenesis and branching morphogenesis of metanephric kidneys. Deficits in the epithelialization of mesenchymal cells were evidenced by inhibition of the formation of podocyte foot processes and glomerular basement membranes. Hydrocarbon treatment markedly induced -KTS wt1 splice variants, although total wt1 mRNA levels remained unchanged. A significant decrease in total WT1 protein was observed by both immunocytochemistry and Western analysis in cultures challenged with BaP compared to controls. Comparison of metanephric cultures from Ahr+/+ and Ahr-/- mice showed that Ahr is involved in kidney development, and required for BaP-induced deficits in nephrogenesis. These results indicate that ligand activation of Ahr signaling disrupts nephrogenesis in vitro, and that this response involves modulation of wt1 alternative splicing and post-transcriptional control.

Role of cytochrome P4501B1 in benzo[a]pyrene bioactivation to DNA-binding metabolites in mouse vascular smooth muscle cells: evidence from 32P-postlabeling for formation of 3-hydroxybenzo[a]pyrene and benzo[a]pyrene-3,6-quinone as major proximate genotoxic intermediates

Benzo[a]pyrene (BP), a polycylic aromatic hydrocarbon (PAH), is a potent atherogen and carcinogen in laboratory animals. Since genotoxic mechanisms may contribute to the development of atherosclerosis by PAHs, we have tested the hypotheses that: 1) BP induces DNA adducts in mouse aortic smooth muscle cells (SMCs); 2) 3-hydroxybenzo[a]pyrene (3-OH-BP) and benzo[a]pyrene-3,6-quinone (BPQ) are proximate genotoxic metabolites; and 3) cytochrome P4501B1 (CYP1B1) mediates the activation of BP and its metabolites to ultimate genotoxic intermediates. Cultured mouse aortic SMCs were treated with BP, 3-OH-BP, or BPQ for 24 h, and DNA adduct formation was analyzed by (32)P-postlabeling. In some experiments, cells were pretreated with the CYP1B1 inhibitor 1-ethynylpyrene (EP) prior to exposure to BP or its metabolites. BP, 3-OH-BP, and BPQ induced formation of several DNA adducts that were not observed in dimethylsulfoxide-treated cells. Re- and cochromatography experiments indicated that 3-OH-BP and BPQ were proximate genotoxic metabolites of BP. DNA adduct formation was strongly inhibited by EP, a specific inhibitor of CYP1B1. BP treatment of SMCs resulted in induction of aryl hydrocarbon hydroxylase (AHH) activity and CYP1B1, but not CYP1A1, apoprotein. EP also blocked AHH induction by BP. In conclusion, the results of this study support the hypothesis that in SMCs, which are target sites for the development of atherosclerosis, the major bioactivation pathway of BP entails CYP1B1-mediated formation of the 3-OH-BP and BPQ, which are proximate genotoxic metabolites that may in turn get transformed to ultimate DNA-binding metabolites, which may contribute to atherogenesis by PAHs.

Polycyclic aromatic hydrocarbon-inducible DNA adducts: evidence by 32P-postlabeling and use of knockout mice for Ah receptor-independent mechanisms of metabolic activation in vivo

There is significant human exposure to polycyclic aromatic hydrocarbons (PAHs), many of which are potent carcinogens in laboratory animals and are suspected human carcinogens. The PAHs are bioactivated by cytochrome P450 (CYP)1A1/1B1 enzymes to reactive intermediates that bind to DNA, a critical step in the initiation of carcinogenesis. The Ah receptor (AHR) plays a critical role in the induction of CYP1 enzymes (i.e., CYP1A1, 1A2 and 1B1) by PAHs such as benzo[a]pyrene (BP) and 3-methylcholanthrene (MC). In our investigation, we tested the hypothesis that AHR-null animals are less susceptible to PAH-induced DNA adduct formation than wild-type animals. Wild-type [AHR (+/+)] mice or mice lacking the gene for the AHR were treated with a single dose (100 micromol/kg) of BP or MC, and hepatic DNA adducts were analyzed by (32)P-postlabeling. BP induced multiple hepatic DNA adducts in wild-type as well as AHR-null animals, suggesting the existence of AHR-independent mechanisms for BP metabolic activation. On the other hand, DNA adduct formation was markedly suppressed in AHR-null animals exposed to MC, although the major MC-DNA adduct was produced in these animals. Hepatic activities and apoprotein contents of 7-ethoxyresorufin O-deethylase (EROD) (CYP1A1) and 7-methoxyresorufin O-demethylase (MROD) (CYP1A2) activities were markedly induced by BP and MC in the wild-type, but not, in AHR-null animals. CYP1B1 expression was also induced, albeit to a lesser extent by the PAH MC, but not BP, in the wild-type animals. In conclusion, these results demonstrate the existence of AHR- and CYP1A1-independent mechanisms of PAH metabolic activation in mouse liver, a phenomenon that may have important implications for PAH-mediated carcinogenesis.

Differential regulation of expression of hepatic and pulmonary cytochrome P4501A enzymes by 3-methylcholanthrene in mice lacking the CYP1A2 gene

The cytochrome P4501A enzymes play important roles in carcinogen metabolism. We reported previously that 3-methylcholanthrene (MC) elicits a persistent induction of hepatic, pulmonary, and mammary microsomal cytochrome P450 (P450) 1A enzymes for several weeks after MC withdrawal. In this study, we tested the hypothesis that CYP1A2, a liver-specific P450 isozyme, plays an important role in the mechanisms governing persistent CYP1A1 induction by MC in liver but not in extra-hepatic tissues such as lung, which is devoid of endogenous CYP1A2. Administration of wild-type (WT) or CYP1A2-null mice with MC (100 micromol/kg i.p.) once daily for 4 days caused significant increases in hepatic CYP1A1/1A2 activities, apoprotein contents, and mRNA levels 1 day after carcinogen withdrawal compared with vehicle-treated controls. The induction persisted in the WT, but not CYP1A2-null animals, for up to 15 days. In the lung, MC caused persistent CYP1A1 induction for 15 days in both the genotypes. Since MC is almost completely eliminated by day 15, we hypothesize that CYP1A2 contributes to the up-regulation of CYP1A1 in liver, but not lung, by a novel mechanism, presumably involving a CYP1A2-dependent persistent metabolite. The studies demonstrate tissue-specific differences in the regulation of CYP1A by MC, a phenomenon that may have implications for human carcinogenesis caused by environmental chemicals.

Induction of cytochromes P-450 1A1 and 1B1 by motorcycle exhaust particulate in human breast cancer MCF-7 cells

The effects of motorcycle exhaust particulate (MEP) on cytochrome P-450-dependent monooxygenases were determined using MCF-7 human breast cancer cells treated with organic extracts of MEP. Treatment with MEP extract produced concentration- and time-dependent increases of monooxygenase activity in S9 fractions. Treatment with 50 microg/ml MEP extract for 24 h increased benzo[a]pyrene hydroxylase and 7-ethoxycoumarin, 7-ethoxyresorufin, and methoxyresorufin O-dealkylases activities in S9. Treatments with 1 and 10 microg/ml MEP extract for 24 h markedly enhanced catabolism of 17beta-estradiol in MCF-7 cells. Cotreatment of the cells with 2 microM alpha-naphthoflavone, a cytochrome P-450 inhibitor and arylhydrocarbon receptor antagonist, blocked the increase of benzo[a]pyrene hydroxylase activity induced by treatment with MEP extract alone. Immunoblot analyses of S9 proteins using a mouse monoclonal antibody 1-12-3 against rat cytochrome P-450 1A1 and a rabbit polyclonal antibody against human cytochrome P-450 1B1 revealed that MEP extract induced proteins immunorelated to cytochromes P-450 1A1 and 1B1. RNA blot analysis of total RNA using human cytochrome P-450 (CYP)1A1 3'-end and human CYP1B1 RT-PCR product cDNA probes showed that MEP extract increased the levels of cytochromes P-450 1A1 and 1B1 mRNA hybridizable to the respective cDNA probes. Treatment with 10 micro M benzo[a]pyrene, a component of MEP extract, for 24 h induced catalytic activity, protein, and mRNA of cytochromes P-450 1A1 and 1B1 in MCF-7 cells. Treatment with MEP extract increased cytochromes P-450 1A1 and 1B1 proteins and mRNA levels in NCI-H322 human lung carcinoma and CL5 human lung adenocarcinoma cells. The extract also increased cytochrome P-450 1A1, but not cytochrome P-450 1B1, protein, and mRNA, in HepG2 human hepatoma cells. The present findings demonstrate that MEP extract has the ability to induce cytochromes P-450 1A1 and 1B1 in the estrogen-responsive MCF-7 cells. Induction of the carcinogen- and estrogen-metabolizing cytochromes P-450 1A1 and 1B1 may be an important factor to consider in assessing the potential health effects associated with human exposure to MEP.

Cytochrome P450 (CYP1A) induction and DNA adducts in a rat hepatoma cell line (Fao), exposed to environmentally relevant concentrations of organic compounds, singly and in combinations

Cytochrome P4501A (CYP1A) induction and DNA adduct formation were evaluated in the rat hepatoma cell line Fao, as biomarkers of exposure to organic compounds. Cells were exposed to environmentally relevant concentrations of benzo[a]pyrene (B[a]P) or 3,3',4,4'-tetrachlorobiphenyl (TCB), and to combinations of B[a]P and TCB. Both B[a]P and TCB induced CYP1A proteins in a concentration-dependent relationship, up to concentrations of 10 and 1 μM, respectively, detected by Western blotting. DNA adducts, analyzed by (32)P-postlabeling, were found at the highest concentrations of B[a]P (1 and 10 μM). No adducts were found in cells exposed to 0.1 μM TCB alone. The cotreatment of TCB and B[a]P indicated an increase in DNA adduct formation, compared with B[a]P, but no further induction of CYP1A protein compared with TCB alone. This study suggests that Western blotting and (32)P-postlabeling might be suitable methods for detecting CYP1A protein induction and DNA adducts, respectively, after exposure to environmentally relevant concentrations of organic compounds.

Characterization of glomerular cell phenotypes following repeated cycles of benzo[a]pyrene injury in vitro

Exposure of cultured glomeruli to benzo[a]pyrene (BaP), a carcinogenic hydrocarbon, modulates mesangial and visceral epithelial cell proliferation in vivo and in vitro. The present studies were conducted to characterize mitogenic signaling profiles of cultured glomeruli following repeated cycles of BaP challenge. Enhanced rates of DNA synthesis were observed by the third passage in randomly cycling cultures after single or repeated carcinogen exposure. This response was characterized by upregulation of mitogenic sensitivity during early cell cycle transit, and increased cell numbers under restrictive growth conditions. The mitogenic response to platelet-derived growth factor (0.5 to 25 ng/mL), acidic fibroblast growth factor (2.5 to 10 ng/mL), basic fibroblast growth factor (0.05 to 5 ng/mL), epidermal growth factor (0.5 to 5 ng/mL), or conditioned medium was not enhanced by hydrocarbon challenge. BaP-treated cultures exhibited anchorage-independent growth and increased expression of hepatocyte growth factor mRNA and E-cadherin protein. Binding of activator protein-1 to DNA was enhanced in BaP-treated cells, but this change did not involve truncation or mutation of the c-jun delta region. Collectively, the data demonstrate that repeated cycles of BaP injury alter mitogenic signaling profiles in cultured glomerular cells. These alterations may contribute to deregulation of proliferative control following carcinogen exposure in vivo.

Role of methoxyestradiols in the growth inhibitory effects of estradiol on human glomerular mesangial cells

Metabolism of locally applied 17beta-estradiol (estradiol) to methoxyestradiols contributes to the growth inhibiting effects of estradiol on vascular smooth muscle cells via an estrogen receptor (ER)-independent mechanism. Because vascular smooth muscle cells are phenotypically similar to glomerular mesangial cells, it is feasible that estradiol inhibits glomerular mesangial cell growth via a similar mechanism, and this possibility was investigated. In human glomerular mesangail cells, estradiol concentration dependently (1 to 100 nmol/L) inhibited serum-induced proliferation (cell number) and DNA ((3)[H]-thymidine incorporation) and collagen ((3)[H]-proline incorporation) synthesis. The inhibitory effects of estradiol were mimicked by 2-hydroxyestradiol and 2-methoxyestradiol, metabolites of estradiol with little affinity for ERs. 2-Hydroxyestradiol and 2-methoxyestradiol were more potent growth inhibitors than estradiol. The inhibitory effects of estradiol were enhanced by CYP450 inducers 3-methylcholanthrene (10 micromol/L) and phenobarbital (10 micromol/L) and blocked by the CYP450 inhibitor 1-aminobenzotriazole (10 micromol/L). The growth inhibitory effects of estradiol were also blocked by quercetin (10 micromol/L) and OR 486 (10 micromol/L) inhibitors of catechol-O-methyltransferase (converts catecholestradiols to methoxyestradiols). ICI182780 (ER antagonist with ER binding affinity similar to estradiol) blocked the growth inhibitory effects of estradiol (1 to 100 nmol/L) only at concentrations (>50 micromol/L) that inhibited estradiol metabolism to catecholestradiols. The growth inhibitory effects of 2-hydroxyestradiol were abrogated by quercetin and OR486 (two structurally dissimilar catechol-O-methyltransferase inhibitors), but not by ICI182780. However, the growth inhibitory effects of 2-methoxyestradiol were unaltered by catechol-O-methyltransferase inhibitors and ICI182780. In conclusion, our findings provide the first evidence that methoxyestradiols mediate the growth inhibitory effects of locally applied estradiol on glomerular mesangial cell growth via an ER-independent mechanism.

Phenotypic profiles of cultured glomerular cells following repeated cycles of hydrocarbon injury

BACKGROUND

The glomerulus has been implicated as a target of hydrocarbon injury in vitro and in vivo. In the present studies, the phenotypic profiles of cultured rat glomerular cells (GCs) following repeated cycles of hydrocarbon injury were evaluated. Cultured GCs were incubated for 24 hours with benzo[a]pyrene (BaP; 3 micromol/L), a prototypical polycyclic aromatic hydrocarbon, and were allowed to recover overnight before two additional cycles of chemical challenge during serial propagation in vitro. At the end of this regimen, control cultures were characterized by predominance of fusiform cells that grew in "hills and valleys," while GCs subjected to hydrocarbon injury displayed an epithelial morphology characterized by a rounded, polygonal shape clearly distinct from that normally exhibited by glomerular mesangial cells (GMCs) in culture.

METHODS

Indirect immunofluorescent detection of cell markers was conducted to identify cells of mesenchymal or epithelial origin. Measurements of DNA synthesis and cell number were performed to determine proliferative capacities of the different cell types in response to hydrocarbon challenge.

RESULTS

Immunofluorescence studies revealed that control GC cultures contained mostly alpha-smooth muscle (SM) actin-positive cells, with a few (5.1% +/- 2.6) E-cadherin-positive cells occasionally identified. In contrast, BaP-treated cultures exhibited a mixed cell population in which E-cadherin-positive cells were predominant (66.6% +/- 4.1). Single-cell cloning of naive cultures of GCs yielded four clones, three of which exhibited a fusiform morphology and were alpha-SM actin positive (SCC 1 through SCC 3) and one (SCC 4E) that exhibited epithelial characteristics similar to those found in hydrocarbon-treated cultures. Immunofluorescence studies showed that epithelial cells in hydrocarbon-treated cultures, as well as SCC 4E-derived clones, were vimentin positive and cytokeratin negative, characteristics similar to glomerular visceral epithelial cells (GVECs). DNA synthesis and cell proliferation in clone SCC 1 were decreased following acute BaP challenge, while growth rates in SCC 4E-derived clones were unaffected by hydrocarbon injury. Repeated cycles of hydrocarbon challenge in clonal populations yielded different profiles of DNA synthesis, with significant decreases in SCC 1 and no changes in SCC 4E.

CONCLUSIONS

These observations suggest that hydrocarbon injury induces differential responses in cells of the glomerulus, resulting in inhibition of GMCs and selective growth advantage of GVECs. These alterations are reminiscent of critical events described in the pathogenesis of focal segmental glomerulosclerosis and raise important questions about the pathogenesis of hydrocarbon-induced nephropathies.

Regulation of cytochrome P450 enzymes by aryl hydrocarbon receptor in human cells: CYP1A2 expression in the LS180 colon carcinoma cell line after treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin or 3-methylcholanthrene

It has been difficult to study the regulation of cytochrome P4501A2 (CYP1A2) because expression of this enzyme is reported to be limited or absent in cell culture. We found that CYP1A2 can be induced significantly by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 3-methylcholanthrene (MC), or benz[a]anthracene in the human colon carcinoma cell line LS180. TCDD and MC each caused a dramatic elevation of CYP1A2 mRNA, as assessed by reverse transcription-polymerase chain reaction or by northern blot analysis. TCDD also increased immunoreactive CYP1A2 protein and the activity of phenacetin-O-deethylase, a diagnostic catalytic marker for CYP1A2. The induction of CYP1A2 at all levels (mRNA, protein, catalytic activity) was concentration- and time-dependent: the EC50 for mRNA induction by TCDD = 0.5 nM, and by MC = 1.4 microM. Inducible CYP1A2 mRNA also was detected at lower levels in two other human cell lines, the hepatoma cell line HepG2 and the breast carcinoma cell line MCF-7. CYP1A1 and CYP1B1, additional CYP1 enzymes regulated by the aryl hydrocarbon receptor (AHR), also were inducible by TCDD and MC in LS180 cells; their concentration-dependent induction was highly correlated with induction of CYP1A2 at mRNA, protein, and catalytic levels. CYP1B1 was constitutively expressed and inducible in the LS180, MCF-7, and HepG2 cell lines as well as in the human choriocarcinoma cell line JEG-3 and the squamous cell carcinoma line A431. CYP1A2 was neither constitutively expressed nor inducible in A431 or JEG-3 cells. The expression of mRNAs encoding the regulators of CYP1 enzymes-the AHR and its heterodimerization partner, the ARNT (AH receptor nuclear translocator) protein-was not altered by treatment with TCDD or MC. However, the cytosolic content of AHR protein and ARNT protein was depleted substantially following treatment with TCDD. The LS180 cell line should constitute a good model for further mechanistic studies on AHR-regulated CYP1A2 expression.