Is CYP1A1 induction always related to AHR signaling pathway?

Differential effects of oxytetracycline on detoxification and antioxidant defense in the hepatopancreas and intestine of Chinese mitten crab under cadmium stress

This study aims to evaluate the effects of oxytetracycline (OTC) on detoxification and oxidative defense in the hepatopancreas and intestine of Chinese mitten crab (Eriocheir sinensis) under cadmium (Cd) stress. The crab was exposed to 0.6 μM Cd, 0.6 μM OTC, and 0.6 μM Cd plus 0.6 μM OTC for 42 days. Our results showed that in the intestine, OTC alone enhanced protein carboxylation (PC) and malondialdehyde (MDA) contents, which was associated with the increased OTC accumulation. Compared to Cd alone, Cd plus OTC increased Cd and OTC contents, and reduced detoxification (i.e., glutathione (GSH) content, gene expressions of cytochrome P450 (CYP) isoforms, 7-ethoxyresorufin O-deethylase (EROD) activity, mRNA levels and activities of glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione-S-transferase (GST)), and antioxidant defense (i.e., gene expressions and activities of catalase (CAT) and superoxide dismutase (SOD)) in the intestine, leading to the increased in PC and MDA contents, suggesting that OTC had a synergistic effect on Cd-induced oxidative damage. In the hepatopancreas, although OTC alone increased OTC accumulation, it did not affect PC and MDA contents. Compared to Cd alone, Cd plus OTC reduced MDA content, which was closely related to the improvement of detoxification (i.e., GSH content, mRNA levels of CYP isoforms, EROD activity, gene expressions and activities of GPx, GR and GST), and antioxidant defense (gene expressions and activities of CAT and SOD, metallothionein content). Aryl hydrocarbon receptor (AhR) and nuclear factor E2-related factor 2 (Nrf2) transcriptional expressions were positively correlated with most detoxification- and antioxidant-related gene expressions, respectively, indicating that AhR and Nrf2 were involved in the regulation of these gene expressions. Our results unambiguously demonstrated that OTC had tissue-specific effects on Cd-induced toxicological effect in E. sinensis, which contributed to accurately evaluating Cd toxicity modulated by TCs in crab.

On the Possible Effect of Phytic Acid (Myo-Inositol Hexaphosphoric Acid, IP6) on Cytochromes P450 and Systems of Xenobiotic Metabolism in Different Hepatic Models

As compounds of natural origin enter human body, it is necessary to investigate their possible interactions with the metabolism of drugs and xenobiotics in general, namely with the cytochrome P450 (CYP) system. Phytic acid (myo-inositol hexaphosphoric acid, IP6) is mainly present in plants but is also an endogenous compound present in mammalian cells and tissues. It has been shown to exhibit protective effect in many pathological conditions. For this paper, its interaction with CYPs was studied using human liver microsomes, primary human hepatocytes, the HepG2 cell line, and molecular docking. Docking experiments and absorption spectra demonstrated the weak ability of IP6 to interact in the heme active site of CYP1A. Molecular docking suggested that IP6 preferentially binds to the protein surface, whereas binding to the active site of CYP1A2 was found to be less probable. Subsequently, we investigated the ability of IP6 to modulate the metabolism of xenobiotics for both the mRNA expression and enzymatic activity of CYP1A enzymes. Our findings revealed that IP6 can slightly modulate the mRNA levels and enzyme activity of CYP1A. However, thanks to the relatively weak interactions of IP6 with CYPs, the chances of the mechanisms of clinically important drug-drug interactions involving IP6 are low.

Zhizhu decoction alleviates slow transit constipation by regulating aryl hydrocarbon receptor through gut microbiota

CONTEXT

Slow transit constipation (STC), the most common type of constipation, seriously affects the life of patients. Zhizhu decoction (ZZD), a traditional Chinese medicine compound, has is effective against functional constipation, but the mechanism is still unclear.

OBJECTIVE

This research explores the mechanism of ZZD on STC from the perspective of metabolomics and gut microbiota.

MATERIALS AND METHODS

Fifty-four C57BL/6 mice were randomly divided into six groups (n = 9): control (control); STC (model); positive control (positive); low-dose (5 g/kg; L-ZZD), medium-dose (10 g/kg; M-ZZD), and high-dose (20 g/kg; H-ZZD) ZZD treatment. Following treatment of mice with ZZD for two weeks, the changes in intestinal motility, colon histology, intestinal neurotransmitters, and aryl hydrocarbon receptor (AHR) pathway determined the effects of ZZD on the pathophysiology of STC. LC-MS targeting serum metabolomics was used to analyze the regulation of ZZD on neurotransmitters, and 16S rRNA high-throughput sequencing was used to detect the regulation of the gut microbiome.

RESULTS

ZZD had the highest content of naringin (6348.1 mg/L), and could significantly increase the 24 h defecations (1.10- to 1.42-fold), fecal moisture (1.14-fold) and intestinal transport rate (1.28-fold) of STC mice, increased the thickness of the mucosal and muscular tissue (1.18- to 2.16-fold) and regulated the neurotransmitters in the colon of STC mice. Moreover, ZZD significantly activated the AHR signaling pathway, and also affected the composition of gut microbiota in STC mice.

DISCUSSION AND CONCLUSIONS

The beneficial effect and the possible mechanism of ZZD on STC could provide a theoretical basis for the broader clinical application of ZZD.

The complex biology of aryl hydrocarbon receptor activation in cancer and beyond

The aryl hydrocarbon receptor (AHR) signaling pathway is a complex regulatory network that plays a critical role in various biological processes, including cellular metabolism, development, and immune responses. The complexity of AHR signaling arises from multiple factors, including the diverse ligands that activate the receptor, the expression level of AHR itself, and its interaction with the AHR nuclear translocator (ARNT). Additionally, the AHR crosstalks with the AHR repressor (AHRR) or other transcription factors and signaling pathways and it can also mediate non-genomic effects. Finally, posttranslational modifications of the AHR and its interaction partners, epigenetic regulation of AHR and its target genes, as well as AHR-mediated induction of enzymes that degrade AHR-activating ligands may contribute to the context-specificity of AHR activation. Understanding the complexity of AHR signaling is crucial for deciphering its physiological and pathological roles and developing therapeutic strategies targeting this pathway. Ongoing research continues to unravel the intricacies of AHR signaling, shedding light on the regulatory mechanisms controlling its diverse functions.

Interactions between Benzo(a)pyrene exposure and genetic polymorphisms of AhR signaling pathway on missed abortion

Benzo(a)pyrene (BaP) is an environmental pollutant widely exposed to human beings. While the relationship between BaP and missed abortion is few understood. To explore the association between missed abortion and BaP, genetic polymorphisms of AhR pathway, we recruited 112 cases women with missed abortion and 137 controls women with normal pregnancy from Shanxi, China. The BPDE-DNA adducts level in the case group was higher than that in the control group (P < 0.001). The subjects were categorized according to the tertiles of BPDE-DNA adduct concentrations: T1 ( Collapse

Key Words

• AhR signaling pathway
• BaP
• genetic polymorphisms
• missed abortion

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MESH Headings

• Pregnancy
• Humans
• Female
• DNA Adducts
• Benzo(a)pyrene/toxicity
• 7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide/metabolism
• Abortion, Missed
• Signal Transduction
• Polymorphism, Genetic

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Affiliation(s)

Sha Liu Department of Epidemiology, School of Public Health, Shanxi Medical University, Taiyuan, Shanxi, China
Mei Han Department of Epidemiology, School of Public Health, Shanxi Medical University, Taiyuan, Shanxi, China
Jiayu Zhang Department of Epidemiology, School of Public Health, Shanxi Medical University, Taiyuan, Shanxi, China
Jingru Ji Department of Obstetrics, The First Affiliated Hospital, Shanxi Medical University, Taiyuan, Shanxi, China
Yanfei Wu Department of Obstetrics, The First Affiliated Hospital, Shanxi Medical University, Taiyuan, Shanxi, China Department of Chinese Medicine, The First Affiliated Hospital, Shanxi Medical University, Taiyuan, Shanxi, China
Junni Wei Department of Epidemiology, School of Public Health, Shanxi Medical University, Taiyuan, Shanxi, China

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Crosstalk between the aryl hydrocarbon receptor (AhR) and the peroxisome proliferator-activated receptor gamma (PPARγ) as a key factor in the metabolism of silver nanoparticles in neuroblastoma (SH-SY5Y) cells in vitro

The potential usefulness of silver nanoparticles (AgNPs) in anticancer therapy has been postulated for many years. However, little is known to date about the exact impact of such NPs on intracellular detoxication pathways. Therefore, the aim of this study was to determine the impact of AgNPs on the AhR-PPARγ-CYP1A1 pathway in neuroblastoma (SH-SY5Y) cells. The obtained results showed a decrease in the metabolic activity of the SH-SY5Y cells at the 50 and 100 μg/mL concentrations with an increase in caspase-3 activity. An increase in the intercellular ROS production was observed at the 1 and 10 μg/mL concentrations. The co-treatment of the AgNP-treated cells with the AhR and PPARγ inhibitors abolished the effect of the tested AgNPs in the SH-SY5Y cells. In turn, the CYP1A1 activity assay showed a decrease in this parameter in the AgNP-treated cells. Moreover, the gene expression analysis demonstrated that AgNPs were able to increase the AhR and CYP1A1 mRNA expression and decrease the PPARγ gene expression after the 6-h treatment. In turn, an increase in the AhR and PPARγ protein expression was observed after 24 h. Summarizing, the study shows for the first time that AgNPs with a 5-nm diameter size are able to exert a cytotoxic effect on SH-SH5Y cells in a ROS-dependent manner affect the AhR-PPARγ-CYP1A1 pathway inter alia by inhibiting the activity of CYP1A1. This is important due to given present research approaches using such NPs as enhancer agents in the modern PPARγ inhibitor-based anticancer therapy.

Indole-3-Carbinol, a Phytochemical Aryl Hydrocarbon Receptor-Ligand, Induces the mRNA Overexpression of UBE2L3 and Cell Proliferation Arrest

Cervical cancer (CC) is one of the most common cancers in women, and is linked to human papillomavirus (HPV) infection. The virus oncoprotein E6 binds to p53, resulting in its degradation and allowing uncontrolled cell proliferation. Meanwhile, the HPV E7 protein maintains host cell differentiation by targeting retinoblastoma tumor suppressor. The host cell can ubiquitinate E6 and E7 through UBE2L3, whose expression depends on the interaction between the aryl hydrocarbon receptor (AhR) with Xenobiotic Responsive Elements (XREs) located in the UBE2L3 gene promoter. In this study, we used cell culture to determine the effect of indole-3-carbinol (I3C) over cellular viability, apoptosis, cell proliferation, and mRNA levels of UBE2L3 and CYP1A1. In addition, patients’ samples were used to determine the mRNA levels of UBE2L3 and CYP1A1 genes. We found that I3C promotes the activation of AhR and decreases cell proliferation, possibly through UBE2L3 mRNA induction, which would result in the ubiquitination of HPV E7. Since there is a strong requirement for selective and cost-effective cancer treatments, natural AhR ligands such as I3C could represent a novel strategy for cancer treatment.

Unraveling the Genetic Architecture of Hepatoblastoma Risk: Birth Defects and Increased Burden of Germline Damaging Variants in Gastrointestinal/Renal Cancer Predisposition and DNA Repair Genes

The ultrarare hepatoblastoma (HB) is the most common pediatric liver cancer. HB risk is related to a few rare syndromes, and the molecular bases remain elusive for most cases. We investigated the burden of rare damaging germline variants in 30 Brazilian patients with HB and the presence of additional clinical signs. A high frequency of prematurity (20%) and birth defects (37%), especially craniofacial (17%, including craniosynostosis) and kidney (7%) anomalies, was observed. Putative pathogenic or likely pathogenic monoallelic germline variants mapped to 10 cancer predisposition genes (CPGs: APC, CHEK2, DROSHA, ERCC5, FAH, MSH2, MUTYH, RPS19, TGFBR2 and VHL) were detected in 33% of the patients, only 40% of them with a family history of cancer. These findings showed a predominance of CPGs with a known link to gastrointestinal/colorectal and renal cancer risk. A remarkable feature was an enrichment of rare damaging variants affecting different classes of DNA repair genes, particularly those known as Fanconi anemia genes. Moreover, several potentially deleterious variants mapped to genes impacting liver functions were disclosed. To our knowledge, this is the largest assessment of rare germline variants in HB patients to date, contributing to elucidate the genetic architecture of HB risk.

Branched alkyl of phenyl 4-(2-oxo-3-alkylimidazolidin-1-yl)benzenesulfonates as unique cytochrome P450 1A1-activated antimitotic prodrugs: Biological evaluation and mechanism of bioactivation

We recently discovered a new family of prodrugs deriving from phenyl 4-(2-oxo-3-imidazolidin-1-yl)benzenesulfonates (PIB-SOs) bioactivatable by cytochrome P450 1A1 (CYP1A1) into potent antimitotics referred to as phenyl 4-(2-oxo-3-alkylimidazolidin-1-yl)benzenesulfonates (PAIB-SOs). PAIB-SOs display significant selectivity toward human breast cancer cells based on the N-dealkylation of PAIB-SOs into their corresponding PIB-SOs by CYP1A1. In this study, we have evaluated the molecular mechanism of the bioactivation of PAIB-SOs into PIB-SOs by branching the linear alkyl chain on the imidazolidin-2-one (IMZ) moiety of PAIB-SOs by branched alkyl groups such as isopropyl, isobutyl and sec-butyl. Our results show that PAIB-SOs bearing an isobutyl group on the IMZ moiety and either a methoxy, a chloro or a bromo group at positions 3, 3,5 or 3,4,5 on the aromatic ring B exhibit antiproliferative activity ranging from 0.13 to 6.9 μM and selectivity toward MCF7 and MDA-MB-468 mammary cancer cells comparatively to other cell lines tested. Moreover, the most potent and selective PAIB-SOs bearing an isobutyl group and either a 3,5-Cl (44), 3,5-Br (45) or a 3,4,5-OMe (46) on the IMZ moiety exhibit antiproliferative activity in the sub-micromolar range and high selectivity ratios toward mammary cancer cells. They stop the cell cycle of MCF7 cells in the G2/M phase and disrupt their cytoskeleton. Furthermore, our studies evidenced that PAIB-SOs bearing either an isopropyl, a sec-butyl or an isobutyl group are hydroxylated on the carbon atom adjacent to the IMZ (Cα-OH) but only PAIB-SOs bearing an isobutyl group are bioactivated into PIB-SOs. Finally, PAIB-SOs 45 and 46 exhibit low toxicity toward normal cells and chick embryos and are thus promising antimitotic prodrugs highly selective toward CYP1A1-expressing breast cancer cells.

Aromatic hydrocarbon receptors in mitochondrial biogenesis and function

Mitochondria are ubiquitous membrane-bound organelles that not only play a key role in maintaining cellular energy homeostasis and metabolism but also in signaling and apoptosis. Aryl hydrocarbons receptors (AhRs) are ligand-activated transcription factors that recognize a wide variety of xenobiotics, including polyaromatic hydrocarbons and dioxins, and activate diverse detoxification pathways. These receptors are also activated by natural dietary compounds and endogenous metabolites. In addition, AhRs can modulate the expression of a diverse array of genes related to mitochondrial biogenesis and function. The aim of the present review is to analyze scientific data available on the AhR signaling pathway and its interaction with the intracellular signaling pathways involved in mitochondrial functions, especially those related to cell cycle progression and apoptosis. Various evidence have reported the crosstalk between the AhR signaling pathway and the nuclear factor κB (NF-κB), tyrosine kinase receptor signaling and mitogen-activated protein kinases (MAPKs). The AhR signaling pathway seems to promote cell cycle progression in the absence of exogenous ligands, whereas the presence of exogenous ligands induces cell cycle arrest. However, its effects on apoptosis are controversial since activation or overexpression of AhR has been observed to induce or inhibit apoptosis depending on the cell type. Regarding the mitochondria, although activation by endogenous ligands is related to mitochondrial dysfunction, the effects of endogenous ligands are not well understood but point towards antiapoptotic effects and inducers of mitochondrial biogenesis.

Nicotine stimulates CYP1A1 expression in human hepatocellular carcinoma cells via AP-1, NF-κB, and AhR

Cytochrome P450 1A1 (CYP1A1) is a member of a subfamily of enzymes involved in the metabolism of both endogenous and exogenous substrates and the chemical activation of xenobiotics to carcinogenic derivatives. Here, the effects of nicotine, a major psychoactive compound present in cigarette smoke, on CYP1A1 expression and human hepatocellular carcinoma (HepG2) cell proliferation were investigated. Nicotine stimulated CYP1A1 expression via the transcription factors, activator protein 1, nuclear factor-kappa B, and the aryl hydrocarbon receptor (AhR) signaling pathway. Pharmacological inhibition and mutagenesis studies indicated that p38 mitogen-activated protein kinase, as well as RelA (or p65), mediated the upregulation of CYP1A1 of nicotine in HepG2 cells. The antioxidant compound, N-acetyl-cysteine, abrogated nicotine-activated production of reactive oxygen species and inhibited CYP1A1 expression by nicotine. Furthermore, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity was inhibited by diphenyleneiodonium (an NADPH oxidase inhibitor). Thus, these results demonstrated that AhR played an important role in nicotine-induced CYP1A1 expression. Additionally, liver hepatocellular carcinoma HepG2 cells treated with nicotine exhibited markedly enhanced proliferation via CYP1A1 expression and Akt activation.

Normothermic Ex-vivo Kidney Perfusion in a Porcine Auto-Transplantation Model Preserves the Expression of Key Mitochondrial Proteins: An Unbiased Proteomics Analysis

Normothermic ex-vivo kidney perfusion (NEVKP) results in significantly improved graft function in porcine auto-transplant models of donation after circulatory death injury compared with static cold storage (SCS); however, the molecular mechanisms underlying these beneficial effects remain unclear. We performed an unbiased proteomics analysis of 28 kidney biopsies obtained at three time points from pig kidneys subjected to 30 min of warm ischemia, followed by 8 h of NEVKP or SCS, and auto-transplantation. 70/6593 proteins quantified were differentially expressed between NEVKP and SCS groups (false discovery rate < 0.05). Proteins increased in NEVKP mediated key metabolic processes including fatty acid ß-oxidation, the tricarboxylic acid cycle, and oxidative phosphorylation. Comparison of our findings with external datasets of ischemia-reperfusion and other models of kidney injury confirmed that 47 of our proteins represent a common signature of kidney injury reversed or attenuated by NEVKP. We validated key metabolic proteins (electron transfer flavoprotein subunit beta and carnitine O-palmitoyltransferase 2, mitochondrial) by immunoblotting. Transcription factor databases identified members of the peroxisome proliferator-activated receptors (PPAR) family of transcription factors as the upstream regulators of our dataset, and we confirmed increased expression of PPARA, PPARD, and RXRA in NEVKP with reverse transcription polymerase chain reaction. The proteome-level changes observed in NEVKP mediate critical metabolic pathways. These effects may be coordinated by PPAR-family transcription factors and may represent novel therapeutic targets in ischemia-reperfusion injury.

The UVR Filter Octinoxate Modulates Aryl Hydrocarbon Receptor Signaling in Keratinocytes via Inhibition of CYP1A1 and CYP1B1

Ultraviolet radiation (UVR) is a consistent part of the environment that has both beneficial and harmful effects on human health. UVR filters in the form of commercial sunscreens have been widely used to reduce the negative health effects of UVR exposure. Despite their benefit, literature suggests that some filters can penetrate skin and have off-target biological effects. We noted that many organic filters are hydrophobic and contain aromatic rings, making them potential modulators of Aryl hydrocarbon Receptor (AhR) signaling. We hypothesized that some filters may be able to act as agonists or antagonists on the AhR. Using a luciferase reporter cell line, we observed that the UVR filter octinoxate potentiated the ability of the known AhR ligand, 6-formylindolo[3,2-b]carbazole (FICZ), to activate the AhR. Cotreatments of keratinocytes with octinoxate and FICZ lead to increased levels of cytochrome P4501A1 (CYP1A1) and P4501B1 (CYP1B1) mRNA transcripts, in an AhR-dependent fashion. Mechanistic studies revealed that octinoxate is an inhibitor of CYP1A1 and CYP1B1, with IC50 values at approximately 1 µM and 586 nM, respectively. In vivo topical application of octinoxate and FICZ also elevated CYP1A1 and CYP1B1 mRNA levels in mouse skin. Our results show that octinoxate is able to indirectly modulate AhR signaling by inhibiting CYP1A1 and CYP1B1 enzyme function, which may have important downstream consequences for the metabolism of various compounds and skin integrity. It is important to continue studying the off-target effects of octinoxate and other UVR filters, because they are used on skin on a daily basis world-wide.

Angelicin-A Furocoumarin Compound With Vast Biological Potential

Angelicin, a member of the furocoumarin group, is related to psoralen which is well known for its effectiveness in phototherapy. The furocoumarins as a group have been studied since the 1950s but only recently has angelicin begun to come into its own as the subject of several biological studies. Angelicin has demonstrated anti-cancer properties against multiple cell lines, exerting effects via both the intrinsic and extrinsic apoptotic pathways, and also demonstrated an ability to inhibit tubulin polymerization to a higher degree than psoralen. Besides that, angelicin too demonstrated anti-inflammatory activity in inflammatory-related respiratory and neurodegenerative ailments via the activation of NF-κB pathway. Angelicin also showed pro-osteogenesis and pro-chondrogenic effects on osteoblasts and pre-chondrocytes respectively. The elevated expression of pro-osteogenic and chondrogenic markers and activation of TGF-β/BMP, Wnt/β-catenin pathway confirms the positive effect of angelicin bone remodeling. Angelicin also increased the expression of estrogen receptor alpha (ERα) in osteogenesis. Other bioactivities, such as anti-viral and erythroid differentiating properties of angelicin, were also reported by several researchers with the latter even displaying an even greater aptitude as compared to the commonly prescribed drug, hydroxyurea, which is currently on the market. Apart from that, recently, a new application for angelicin against periodontitis had been studied, where reduction of bone loss was indirectly caused by its anti-microbial properties. All in all, angelicin appears to be a promising compound for further studies especially on its mechanism and application in therapies for a multitude of common and debilitating ailments such as sickle cell anaemia, osteoporosis, cancer, and neurodegeneration. Future research on the drug delivery of angelicin in cancer, inflammation and erythroid differentiation models would aid in improving the bioproperties of angelicin and efficacy of delivery to the targeted site. More in-depth studies of angelicin on bone remodeling, the pro-osteogenic effect of angelicin in various bone disease models and the anti-viral implications of angelicin in periodontitis should be researched. Finally, studies on the binding of angelicin toward regulatory genes, transcription factors, and receptors can be done through experimental research supplemented with molecular docking and molecular dynamics simulation.

Artificial turf infill associated with systematic toxicity in an amniote vertebrate

Artificial athletic turf containing crumb rubber (CR) from shredded tires is a growing environmental and public health concern. However, the associated health risk is unknown due to the lack of toxicity data for higher vertebrates. We evaluated the toxic effects of CR in a developing amniote vertebrate embryo. CR water leachate was administered to fertilized chicken eggs via different exposure routes, i.e., coating by dropping CR leachate on the eggshell; dipping the eggs into CR leachate; microinjecting CR leachate into the air cell or yolk. After 3 or 7 d of incubation, embryonic morphology, organ development, physiology, and molecular pathways were measured. The results showed that CR leachate injected into the yolk caused mild to severe developmental malformations, reduced growth, and specifically impaired the development of the brain and cardiovascular system, which were associated with gene dysregulation in aryl hydrocarbon receptor, stress-response, and thyroid hormone pathways. The observed systematic effects were probably due to a complex mixture of toxic chemicals leaching from CR, such as metals (e.g., Zn, Cr, Pb) and amines (e.g., benzothiazole). This study points to a need to closely examine the potential regulation of the use of CR on playgrounds and artificial fields.

The citrus flavonone hesperetin attenuates the nuclear translocation of aryl hydrocarbon receptor

The environmental polycyclic aromatic hydrocarbons (PAH) and dioxins are carcinogens and their adverse effects have been largely attributed to the activation of AhR. Hesperetin is a flavonone found abundantly in citrus fruits and has been shown to be a biologically active agent. In the present study, the effect of hesperetin on the nuclear translocation of AhR and the downstream gene expression was investigated in MCF-7 cells. Confocal microscopy indicated that 7, 12-dimethylbenz[α]anthracene (DMBA) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) -induced nuclear translocation of AhR was deterred by hesperetin treatment. The reduced nuclear translocation could also be observed in Western analysis. Reporter-gene assay further illustrated that the induced XRE transactivation was weakened by the treatment of hesperetin. Quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) assay demonstrated that the gene expressions of CYP1A1, 1A2, and 1B1 followed the same pattern of AhR translocation. These results suggested that hesperetin counteracted AhR transactivation and suppressed the downstream gene expression.

From the Cover: Development and Application of a Dual Rat and Human AHR Activation Assay

Significant prolonged aryl hydrocarbon receptor (AHR) activation, classically exhibited following exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin, can cause a variety of undesirable toxicological effects. Novel pharmaceutical chemistries also have the potential to cause activation of AHR and consequent toxicities in pre-clinical species and man. Previous methods either employed relatively expensive and low-throughput primary hepatocyte dosing with PCR endpoint, or low resolution overexpressing reporter gene assays. We have developed, validated and applied an in vitro microtitre plate imaging-based medium throughput screening assay for the assessment of endogenous species-specific AHR activation potential via detection of induction of the surrogate transcriptional target Cytochrome P450 CYP1A1. Routine testing of pharmaceutical drug development candidate chemistries using this assay can influence the chemical design process and highlight AHR liabilities. This assay should be introduced such that human AHR activation liability is flagged early for confirmatory testing.

Modulation of CYP1A1 metabolism: From adverse health effects to chemoprevention and therapeutic options

The human cytochrome P450 (CYP) 1A1 gene encodes a monooxygenase that metabolizes multiple exogenous and endogenous substrates. CYP1A1 has become infamous for its oxidative metabolism of benzo[a]pyrene and related polycyclic aromatic hydrocarbons, converting these chemicals into very potent human carcinogens. CYP1A1 expression is mainly controlled by the aryl hydrocarbon receptor (AHR), a transcription factor whose activation is induced by binding of persistent organic pollutants, including polycyclic aromatic hydrocarbons and dioxins. Accordingly, induction of CYP1A1 expression and activity serves as a biomarker of AHR activation and associated xenobiotic metabolism as well as toxicity in diverse animal species and humans. Determination of CYP1A1 activity is integrated into modern toxicological concepts and testing guidelines, emphasizing the tremendous importance of this enzyme for risk assessment and regulation of chemicals. Further, CYP1A1 serves as a molecular target for chemoprevention of chemical carcinogenesis, although present literature is controversial on whether its inhibition or induction exerts beneficial effects. Regarding therapeutic applications, first anti-cancer prodrugs are available, which require a metabolic activation by CYP1A1, and thus enable a specific elimination of CYP1A1-positive tumors. However, the application range of these drugs may be limited due to the frequently observed downregulation of CYP1A1 in various human cancers, probably leading to a reduced metabolism of endogenous AHR ligands and a sustained activation of AHR and associated tumor-promoting responses. We here summarize the current knowledge on CYP1A1 as a key player in the metabolism of exogenous and endogenous substrates and as a promising target molecule for prevention and treatment of human malignancies.

Taxifolin Inhibits 7,12-Dimethylbenz(a)anthracene-induced Breast Carcinogenesis by Regulating AhR/CYP1A1 Signaling Pathway

Background:

Breast cancer (BC), because of its invasive characteristics, is one of the most common and deadliest cancers among the female population around the world. Research has demonstrated that AhR signaling also plays a vital role in BC initiation and development as well. Therefore, blocking this pathway to natural interferences paves a new channel for the prevention of BC. Several natural compounds such as flavonoids possess the anticancer activities against different cancers.

Objective:

The present study has been designed to estimate the chemotherapeutic potential of taxifolin (TAX) against 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary carcinoma in Sprague-Dawley rats.

Materials and Methods:

Initially, the molecular docking analysis of AhR and cytochrome P450s (CYPs) (CYP1A1 and CYP1B1) was performed using MAESTRO tool, in an attempt to rationalize the activity of TAX, based on their CYP1-binding potential. The in vitro CYP1A1 activity was determined by luciferase assay with CYP1A1 substrate luciferin CEE. The in vivo analysis was performed by administrating TAX at 10, 20, 40 mg/kg BW for 28 days intragastrically in DMBA induced (25 mg/animal dose) at 55 days of age Sprague-Dawley (SD) rats. BC initiates after 90 days of tumor induction phase. The molecular mechanism of TAX on Ahr and CYPs was also examined through the mRNA and protein expressions using reverse transcription-quantitative polymerase chain reaction and Western blotting analysis.

Results:

Furthermore, TAX altered the energy regulation on DMBA-induced BC in SD rats by considerably restoring the cancer-induced modulations in tumor growth. Our results showed that TAX reduced the expressions of CYP1A1 and CYP1B1 in DMBA-induced mammary carcinoma by downregulating the AhR signaling pathway.

Conclusion:

This study revealed that TAX might be able to act as a chemotherapeutic agent against CYP1A1- and CYP1B1-mediated cancer and the inhibition of the DMBA-induced mammary carcinogenesis in a rat model.

Abbreviations used: CYPs: Cytochrome P450s; PAH: polycyclic aromatic hydrocarbons; HRP- Horseradish peroxidase; BSA: Bovine serum albumin; DTTP: Deoxythymidine Triphosphate (nucleotide); RT-qPCR: Real Time quantitative polymerase chain reaction; CADD: Computer Aided Drug Drafting.

Aryl hydrocarbon receptor activation maintained the intestinal epithelial barrier function through Notch1 dependent signaling pathway

Intestinal ischemia/reperfusion (I/R) induces disruption of the intestinal barrier function. Aryl hydrocarbon receptor (AhR) has a vital role in maintaining the intestinal barrier function. However, the precise mechanism by which AhR maintains intestinal barrier function remains unclear. Notch1 signaling is downstream of AhR, and has also been reported to have a role in the development of tight junctions (TJs) and maintenance of intestinal homeostasis. Therefore, we hypothesized that AhR activation may attenuate the intestinal barrier dysfunction through increased activation of Notch1 signaling. Adult C57BL/6J mice were divided into three groups: Sham, I/R and I/R + 6-formylindolo(3,2-b)carbazole (Ficz) groups. Mice were sacrificed after I/R for 6 h and the intestine was harvested for histological examination, mRNA and protein content analysis, and mucosal permeability investigation. Additionally, a hypoxic Caco‑2 cell culture model was used to evaluate the role of AhR‑Notch1 signaling in the development of TJs and epithelial permeability in vitro. The AhR‑Notch1 signaling components and TJ proteins were assessed by reverse transcription‑quantitative polymerase chain reaction, western blotting, immunohistochemistry or immunofluorescence staining. Epithelial permeability was detected by transepithelium electrical resistance. The data demonstrated that Ficz significantly attenuated the intestinal tissue damage and the disrupted distribution of TJs, increased the expression of TJ proteins, reversed the decrease in TER and upregulated epithelial Notch1 signaling following intestinal I/R in vivo and hypoxia in vitro. Furthermore, inhibition of Notch1 signaling by N‑[N‑(3,5‑difluorophenacetyl)‑L‑alanyl]‑S‑phenylglycine t‑butyl ester (inhibitor of Notch signaling) counteracted the effects of Ficz on the development of TJs in hypoxic Caco‑2 cells. In conclusion, AhR activation ameliorated epithelial barrier dysfunction following intestinal I/R and hypoxia through upregulation of Notch1 signaling, which suggests that AhR may be a potential pharmaceutical agent to combat this condition.

The secondary Fusarium metabolite aurofusarin induces oxidative stress, cytotoxicity and genotoxicity in human colon cells

Aurofusarin (AURO), a dimeric naphthoquinone, is produced by Fusarium fungi. Although frequently found in food and feed, toxicological studies are limited. Hence, the in vitro toxicity of AURO was investigated in the colon adenocarcinoma cell line HT29 and the non-tumorigenic colon cells HCEC-1CT. Cytotoxic effects were found at concentrations ≥1 μM by evaluating mitochondrial activity (WST-1) and cellular proliferation (sulforhodamine B assay). 10 μM of AURO induced a decrease of cells in the S-phase, measured by flow cytometry. Confocal microscopy revealed AURO-mediated increase of intracellular p53 protein. In accordance, DNA-damage was seen in the comet assay (≥1 μM) together with enhanced levels of formamidopyrimidine-DNA-glycosylase (fpg)-sensitive sites, indicative for oxidative stress. An increase of intracellular reactive oxygen species was observed in the dichlorofluorescein (DCF) assay (≥5 μM). The GSSG/GSH ratio was elevated, but no impact on redox-sensitive Nrf2-dependent genes (Nrf2, γ-GCL, NQO1) was found at the gene expression level. However, induction of cytochrome P450 monooxygenase (CYP) 1A1 was measured at the gene expression and protein level. In conclusion, these in vitro data suggest that, when co-occurring, AURO might be considered as a potential contributor to the overall toxicity of respective Fusarium mycotoxin mixtures.

Effects of the soya isoflavone genistein in early life stages of the Senegalese sole, Solea senegalensis: Thyroid, estrogenic and metabolic biomarkers

This study examines the effects induced by environmentally relevant concentrations of the isoflavone genistein (3mg/L and 10mg/L) during early life stages of the Senegalese sole. Throughout the hypothalamus-pituitary-thyroid (HPT) axis, several neurohormonal regulatory thyroid signalling patterns (thyroglobulin/Tg, thyroid peroxidase/TPO, transthyretin/TTR, thyroid receptors/TRβ, and iodothrynonine deiodinases, Dio2 and Dio3) were analysed. Furthermore, the expression patterns of estrogen receptor ERβ and haemoprotein Cyp1a were also evaluated. In the control larvae, progressive increases of constitutive hormonal signalling pathways have been evidenced from the pre-metamorphosis phase onwards, reaching the highest expression basal levels at the metamorphosis (Tg, TPO, Dio2) and/or during post-metamorphosis (TTR, TRβ, ERβ). When the early larvae were exposed to both genistein concentrations (3mg/L and 10mg/L), a statistically significant down-regulation of TPO, TTR and Tg mRNA levels was clearly detected at the metamorphic stages. In addition, the Dio2 and Dio3 transcript expression levels were also down and up-regulated when exposed to both genistein concentrations. In the larvae exposed to genistein, no statistically significant responses were recorded for the TRβ expression patterns. Nevertheless, the ERβ and Cyp1a transcript levels were up-regulated at the middle metamorphic stage (S2, at 16 dph) in the larvae exposed to high genistein concentrations and, only the ERβ was down-regulated (S1, at 12dph) at the lower doses. Finally, all these pointed out imbalances were only temporarily disrupted by exposure to genistein, since most of the modulated transcriptional signals (i.e. up or down-regulation) were quickly restored to the baseline levels. Additionally, the control and genistein-exposed Senegalese sole specimens showed characteristic ontogenetic patterns and completely suitable for an optimal development, metamorphosis, and growth.

Reduction of dioxin-like toxicity in effluents by additional wastewater treatment and related effects in fish

Efficiency of advanced wastewater treatment technologies to reduce micropollutants which mediate dioxin-like toxicity was investigated. Technologies compared included ozonation, powdered activated carbon and granular activated carbon. In addition to chemical analyses in samples of effluents, surface waters, sediments, and fish, (1) dioxin-like potentials were measured in paired samples of effluents, surface waters, and sediments by use of an in vitro biotest (reporter gene assay) and (2) dioxin-like effects were investigated in exposed fish by use of in vivo activity of the mixed-function, monooxygenase enzyme, ethoxyresorufin O-deethylase (EROD) in liver. All advanced technologies studied, based on degradation or adsorption, significantly reduced dioxin-like potentials in samples and resulted in lesser EROD activity in livers of fish. Results of in vitro and in vivo biological responses were not clearly related to quantification of targeted analytes by use of instrumental analyses.

Mutagenicity and antimutagenicity of hydrophilic and lipophilic extracts of Thai northern purple rice

Purple rice (Oryza sativa L. var. indica) cv. Kum Doisaket is cultivated in northern Thailand. This study evaluated the mutagenic and antimutagenic properties of hydrophilic and lipophilic components of purple rice using the Ames test. The seed and hull of purple rice were extracted with hexane, methanol, ethanol, and water. The methanol extracts had the highest amounts of phenolic acids and flavonoids, while the hexane extracts contained large amount of tocols and γ-oryzanol. None of the extracts were mutagenic in Salmonella typhimurium strains TA98 and TA100. The hexane extract of rice hull and the methanol extract of rice seed were strongly effective against aflatoxin B1- and 2-amino-3, 4 dimethylimidazo (4, 5-f) quinoline-induced mutagenesis, while aqueous extracts showed weakly antimutagenic properties. All extracts with the exception of aqueous extracts enhanced the number of revertant colonies from benzo (a) pyrene induced-mutagenesis. None of the extracts inhibited mutagenesis induced by the direct mutagens 2-(2-furyl)-3-(5-nitro-2-furyl)-acrylamide and sodium azide. The hull extracts showed more potent antimutagenicity than the seed extracts. Based on a chemical analysis, γ-oryzanol and γ-tocotrienol in the hull and cyanidin-3-glucoside and peonidin-3-glucoside in the seed are candidate antimutagens in purple rice. The antimutagenic mechanisms of purple rice might be related to either modulation of mutagen metabolizing enzymes or direct attack on electrophiles. These findings supported the use of Thai purple rice as a cancer chemopreventive agent.

Cadmium interference with ERK1/2 and AhR signaling without evidence for cross-talk

The possibility that Cd may activate AhR indirectlyviaERK1/2 phosphorylation was tested as a function of enterocytic differentiation status in the human Caco-2 cells.

Aryl hydrocarbon receptor protein and Cyp1A1 gene induction by LPS and phenanthrene in Atlantic cod (Gadus morhua) head kidney cells

The objective of this study was to evaluate interactions between environmental toxicants and cod immune cells during inflammation. Phenanthrene is abundant in plant oils (rapeseed, palm, and soya oil) as compared to fish oils, and consequently constitute an undesirable element in plant replacement diets in aquaculture. Phenanthrene was added to head kidney cell cultures, alone or together with LPS (lipopolysaccharide) or poly I: C (polyinosinic acid: polycytidylic acid), and the responses were evaluated in terms of protein and gene expression. The results showed that LPS, poly I: C or phenanthrene, added to the cultures separately, induced aryl hydrocarbon receptor (AhR) protein expression. Phenanthrene treatment in combination with LPS induced AhR protein expression and Cyp1A1 gene transcription, which not was observed combining poly I: C and phenanthrene. Phenanthrene exposure up regulated the transcription of common stress and detoxification enzymes like catalase, caspase 3 and glutathione S-transferase alfa 3 subunit B (GSTAB3), while LPS exposure alone or combined with phenanthrene down regulated GSTAB3 and catalase in cod leukocytes. It seems clear that immune regulation and phenanthrene induced signaling pathways interact; transcriptional down regulation of detoxification and antioxidant enzymes by LPS could indicate that combating bacterial infections is the number one priority in these cells, and that AhR and Cyp1A1 is somehow involved in this signaling cascade. LPS seems to affect the mitogen activated protein kinases (MAPKs) pathways (P-p38 and ERK1/2) thus modulating the AhR protein and Cyp1A1 gene transcription, while phenanthrene possibly activates AhR by ligand binding.

Mechanisms of hexabromocyclododecanes induced developmental toxicity in marine medaka (Oryzias melastigma) embryos

Hexabromocyclododecanes (HBCDs) are widely used as additive brominated flame retardants, and are now ubiquitous contaminants in the environmental media and biota, including the marine environment and marine organisms. However, the impacts of HBCDs on marine fish are not well known. In this study the embryos of marine medaka (Oryzias melastigma) were used to assess the developmental toxicity of HBCDs. Freshly fertilized marine medaka embryos were exposed to various concentrations of technical HBCD (tHBCD, 0, 5, 20 and 50μg/L) until the first fry stage, and hatch success, morphology and cardiac function were examined. In all the exposure groups (5, 20 and 50μg/L) tHBCD significantly increased the embryo heart beats. The measurement of sinus venosus-bulbus arteriosus (SV-BA) distance indicated that tHBCD significantly enlarged the SV-BA distance at exposure concentrations of 20 and 50μg/L. The malformation rate at the first fry stage was also induced by tHBCD in a dose dependent manner, with the formation of pericardial edema and yolk sac edema as the most frequently observed malformation. In addition, the concentrations of total HBCD isomers (ΣHBCDs) in embryos in the current study were comparative with environmental levels and increased with increasing exposure duration. Furthermore, exposure to tHBCD also induced the level of 8-oxodG, a representative oxidative DNA damage. The mechanisms of HBCD-induced developmental toxicity were further explored by TUNEL assay, gel-based quantitative proteomic approach and measurement of the expression of several stress responsive genes, such as p53, TNF-α, IL-1β, CYP1A, COX-1 and COX-2, together with the activities of caspases. The results suggested that HBCDs exposure at environmentally realistic concentrations induced oxidative stress and apoptosis, and suppressed nucleotide and protein synthesis, which all together resulted in developmental toxicity, particularly in the cardiovascular system, in the embryos of O. melastigma.

Genetic polymorphisms in the CYP1A1 and CYP1B1 genes and susceptibility to bladder cancer: a meta-analysis

The current meta-analysis of case-control studies was conducted to evaluated the relationships of genetic polymorphisms in the CYP1A1 and CYP1B1 genes with the susceptibility to bladder cancer, aiming at determine whether these polymorphisms may contribute to the pathogenesis of bladder cancer. Related articles were determined via searching the following electronic databases without any language restrictions: PubMed, CISCOM, CINAHL, Web of Science, Google Scholar, EBSCO, Cochrane Library, and CBM databases for relevant articles published before November 1st, 2013. STATA 12.0 software was also selected to deal with statistical data. The relationships were evaluated using the pooled odds ratios (ORs) and their 95% confidence intervals (CI). Eleven case-control studies with a total of 2,609 bladder cancer patients and 2,634 healthy subjects met the inclusion criteria. The results of our meta-analysis demonstrated that CYP1A1 genetic polymorphisms were associated with increased risks of bladder cancer (allele model: RR = 1.18, 95% CI 1.07-1.30, P = 0.001; dominant model: RR = 1.15, 95% CI 1.05-1.27, P = 0.003; respectively), especially among 11599G>C, 2455A>G, 3810T>C, and 113T>C polymorphisms. A subgroup analysis by ethnicity was conducted to investigate its effect on susceptibility to bladder cancer. The subgroup analysis results revealed positive significant correlations between CYP1A1 genetic polymorphisms and bladder cancer risk among Asians (allele model: RR = 1.26, 95% CI 1.10-1.44, P = 0.001; dominant model: RR = 1.22, 95% CI 1.08-1.38, P = 0.001), but not among Caucasians (all P < 0.05). Nevertheless, we observed no significant correlations between CYP1B1 genetic polymorphisms and bladder cancer risk (all P > 0.05). Our meta-analysis indicates that CYP1A1 genetic polymorphisms may be involved in the pathogenesis of bladder cancer, especially among 11599G>C, 2455A>G, 3810T>C, and 113T>C polymorphisms. However, CYP1B1 genetic polymorphisms may not be important determinants of bladder cancer susceptibility.

Relationships between CYP1A1 genetic polymorphisms and bladder cancer risk: a meta-analysis

This meta-analysis aims at evaluating the relationships between CYP1A1 genetic polymorphisms and bladder cancer risk. The PubMed, CISCOM, CINAHL, Web of Science, Google Scholar, EBSCO, Cochrane Library, and CBM databases were searched from inception through November 1st, 2013 without language restrictions. Meta-analysis was conducted with the use of the STATA 12.0 software. The relationships were evaluated by calculating the pooled odds ratios (ORs) and their 95% confidence intervals (CIs). Eight case-control studies with a total of 2120 bladder cancer patients and 2061 healthy subjects met the inclusion criteria. Ten common polymorphisms in the CYP1A1 gene were assessed. The results of our meta-analysis suggested that CYP1A1 genetic polymorphisms might be strongly correlated with an increased risk of bladder cancer (allele model: OR=1.23, 95%CI=1.08-1.39, p=0.001; dominant model: OR=1.25, 95%CI=1.07-1.46, p=0.005; respectively), especially for 11599G>C, 2455A>G, 3810T>C, and 113T>C polymorphisms. A subgroup analysis was done to investigate the effect of ethnicity on an individual's risk of bladder cancer. Our results revealed positive significant correlations between CYP1A1 genetic polymorphisms and an increased risk of bladder cancer among Asians (allele model: OR=1.33, 95%CI=1.08-1.65, p=0.009; dominant model: OR=1.37, 95%CI=1.02-1.85, p=0.034; respectively), but not among Caucasians (all p<0.05). Our findings provide convincing evidence that CYP1A1 genetic polymorphisms may contribute to susceptibility to bladder cancer, especially for 11599G>C, 2455A>G, 3810T>C, and 113T>C polymorphisms among Asians.

CYP1A1 gene polymorphisms and polycystic ovary syndrome risk: a meta-analysis and meta-regression

AIMS

Emerging evidence suggests that common functional polymorphisms in the CYP1A1 gene are involved in the regulation of the activities of cytochrome P450 enzymes, thereby increasing an individual's susceptibility to polycystic ovary syndrome (PCOS), but individually published results are inconclusive. This meta-analysis aimed to derive a more precise estimation of the relationship between CYP1A1 gene polymorphisms and PCOS risk.

METHODS

A literature search of PubMed, Embase, Web of Science, the Cochrane Library, Chinese National Knowledge Infrastructure, Chinese Bio-medicine Database, and Chinese Sci-tech Journals Database (VIP) databases was conducted from inception to March 1, 2013. The crude odds ratio (OR) with 95% confidence interval (CI) were calculated.

RESULTS

Five case-control studies were included with a total of 1,036 subjects, including 521 PCOS cases and 515 healthy controls. Our meta-analysis results indicated that the C variant of the CYP1A1 rs4646903 (T>C) polymorphism was associated with an increased risk of PCOS (allele model: OR=1.62, 95% CI: 1.06-2.48, P=0.025; dominant model: OR=2.37, 95% CI: 1.25-4.48, P=0.008; homozygous model: OR=2.52, 95% CI: 1.17-5.44, P=0.019), especially among the general female population in Turkey and India. However, there was no statistically significant association between the CYP1A1 rs1048943 (A>G) polymorphism and PCOS risk (all P>0.05). No publication bias was detected in this meta-analysis.

CONCLUSION

The current meta-analysis indicates that the CYP1A1 rs4646903 (T>C) polymorphism may contribute to increasing susceptibility to PCOS, especially among the general female population in Turkey and India. However, further studies are still needed to accurately determine whether the CYP1A1 rs1048943 (A>G) polymorphism is associated with PCOS risk.

Ginsenosides are novel naturally-occurring aryl hydrocarbon receptor ligands

The aryl hydrocarbon receptor (AHR) is a ligand-dependent transcription factor that mediates many of the biological and toxicological actions of structurally diverse chemicals. In this study, we examined the ability of a series of ginsenosides extracted from ginseng, a traditional Chinese medicine, to bind to and activate/inhibit the AHR and AHR signal transduction. Utilizing a combination of ligand and DNA binding assays, molecular docking and reporter gene analysis, we demonstrated the ability of selected ginsenosides to directly bind to and activate the guinea pig cytosolic AHR, and to stimulate/inhibit AHR-dependent luciferase gene expression in a recombinant guinea pig cell line. Comparative studies revealed significant species differences in the ability of ginsenosides to stimulate AHR-dependent gene expression in guinea pig, rat, mouse and human cell lines. Not only did selected ginsenosides preferentially activate the AHR from one species and not others, mouse cell line was also significantly less responsive to these chemicals than rat and guinea pig cell lines, but the endogenous gene CYP1A1 could still be inducted in mouse cell line. Overall, the ability of these compounds to stimulate AHR signal transduction demonstrated that these ginsenosides are a new class of naturally occurring AHR agonists.

Tristetraprolin suppresses AHRR expression through mRNA destabilization

The aryl hydrocarbon receptor repressor (AHRR) inhibits the transcription of the aryl hydrocarbon receptor (AHR) by binding to XRE. We report that AHRR expression is inhibited by tristetraprolin (TTP), an AU-rich element (ARE)-binding protein. Overexpression of TTP decreased the mRNA stability and protein expression of AHRR, and TTP-overexpressing cells made smaller colonies than the control. Contrarily, inhibition of TTP by siRNA increased AHRR expression. Analyses of point mutants of the AREs demonstrated that AREs were responsible for the TTP-mediated destabilization of AHRR mRNA. RNA EMSA revealed that TTP directly binds to the AHRR 3'UTR. Taken together, we demonstrate that TTP acts as a negative regulator of AHRR and may affect tumor development through induction of tumor suppressor genes as observed in MDA-MB435.

The citrus flavanone naringenin suppresses CYP1B1 transactivation through antagonising xenobiotic-responsive element binding

Exposure to environmental toxicants or exogenous oestrogen increases the risk of cancer. Some toxicants such as polycyclic aromatic hydrocarbons (PAH) undergo biotransformation to become genotoxic agents. Cytochrome p450 (CYP) 1B1 is an enzyme catalysing this transformation. Consumption of fruit and vegetables is considered to be protective against carcinogenesis, and naringenin can be found abundantly in citrus fruits. In the present study, the effect of naringenin on the regulation of CYP1B1 was investigated in MCF-7 cells. Enzyme inhibition assays revealed that naringenin inhibited CYP1B1 at or above 5 μm but not CYP1A1 activity. Quantitative PCR analysis also demonstrated that 1 μm-naringenin reduced CYP1B1 mRNA expression induced by 7,12-dimethylbenz(α)anthracene (DMBA). Further study illustrated that the suppression was at the transcriptional level. Since previous studies have shown that oestrogen response element (ERE) and xenobiotic-responsive element (XRE) are functional binding sequences in the promoter region of CYP1B1, interference of DNA binding on these two elements was pursued. Employing reporter gene assays as well as the electromobility shift assay, we verified that naringenin counteracted DMBA-induced XRE binding at − 1675. These results supported the notion that fruit consumption could be a protective measure against PAH biotransformation.

Cytochrome P450 1A1-mediated anticancer drug discovery: in silico findings

INTRODUCTION

Target-specific drugs may offer fewer side/adverse effects in comparison with other anticancer agents and thus save normal healthy cells to a greater extent. The selective overexpression of cytochrome P450 1A1 (CYP1A1) in tumor cells induces the metabolism of benzothiazole and aminoflavone compounds to their reactive species, which are responsible for DNA adduct formation and cell death. This review encompasses the novelty of CYP1A1 as an anticancer drug target and explores the possible in silico strategies that would be applicable in the discovery and development of future antitumor compounds.

AREAS COVERED

This review highlights the various ligand-based and target-based in silico methodologies that were efficiently used in exploration of CYP1A1 as a novel antitumor target. These methodologies include electronic structure analysis, CoMFA studies, homology modeling, molecular docking, molecular dynamics analysis, pharmacophore mapping and quantitative structure activity relationship (QSAR) studies. It also focuses on the various approaches used in the development of the lysyl amide prodrug of 5F-203 (NSC710305) and dimethanesulfonate salt of 5-aminoflavone (NSC710464) as clinical candidates from their less potent analogues.

EXPERT OPINION

Selective overexpression of CYP1A1 in cancer cells offers tumor-specific drug design to ameliorate the current adverse effects associated with existing antitumor agents. Medicinal chemistry and in vitro driven approaches, in combination with knowledge-based drug design and by using the currently available tools of in silico methodologies, would certainly make it possible to design and develop novel anticancer compounds targeting CYP1A1.

Impact of six fruits--banana, guava, mangosteen, pineapple, ripe mango and ripe papaya--on murine hepatic cytochrome P450 activities

The effects of six Thai fruits, namely banana, guava, mangosteen, pineapple, ripe mango and ripe papaya, on cytochrome P450 (P450) activities were investigated. The median inhibitory concentrations (IC(50) ) of each of the fruit juices on CYP1A1, CYP1A2, CYP2E1 and CYP3A11 activities were determined. Pineapple juice showed the strongest inhibitory effect against all the evaluated P450 isozyme activities in mouse hepatic microsomes, followed by mangosteen, guava, ripe mango, ripe papaya and banana. The study was further performed in male ICR mice given pineapple juice intragastrically at doses of 10, 20 and 40 mg kg(-1) per day for 7 or 28 days. In a concentration-dependent fashion, the pineapple juice raised ethoxyresorufin O-deethylase, aniline hydroxylase and erythromycin N-demethylase activities, which are marker enzymatic reactions responsible for CYP1A1, CYP2E1 and CYP3A11, respectively. The effect of pineapple juice on the expression of CYP1A1, CYP2E1 and CYP3A11 mRNAs corresponded to their enzymatic activities. However, the pineapple juice significantly decreased methoxyresorufin O-demethylase activity. These observations supported that the six Thai fruits were a feasible cause of food-drug interaction or adverse drug effects owing to their potential to modify several essential P450 activities. Individuals consuming large quantities of pineapple for long periods of time should be cautioned of these potential adverse effects.

Quercetin, quercetin glycosides and taxifolin differ in their ability to induce AhR activation and CYP1A1 expression in HepG2 cells

The natural flavonoid quercetin is a low affinity ligand of the aryl hydrocarbon receptor (AhR), a transcription factor regulating the expression of cytochrome P450 (CYP) 1A enzymes. This study examined the ability of quercetin, isoquercitrin (quercetin-3-O-glucoside), rutin (quercetin-3-O-rutinoside) and taxifolin (dihydroquercetin) to activate AhR and to induce CYP1A1 expression in human hepatoma HepG2 cells. Gene reporter assays showed that quercetin significantly activated AhR and triggered CYP1A1 transcription after 24 h exposure. These effects were, however, much lower than those of 2,3,7,8-tetrachlorodibenzo-p-dioxin, a prototypical AhR ligand. Quercetin also induced a significant increase in CYP1A1 mRNA levels together with a moderate increase in the level of CYP1A1 activity. In contrast, isoquercitrin and rutin had negligible effects on AhR activity and CYP1A1 expression. Taxifolin at the highest concentration tested (50 µm) produced a mild non-significant increase in AhR activity and CYP1A1 transcription. Taxifolin also significantly increased CYP1A1 mRNA expression, but this effect was approximately 15 times weaker than that of quercetin and was not accompanied by induction of CYP1A1 activity. It is concluded that quercetin, but not its 3-O-glycosides isoquercitrin and rutin, induces AhR activation and CYP1A1 expression in HepG2 cells and that the CYP1A1-inducing activity of taxifolin has a low toxicological potential.

Modulations of cytochrome P450 expression in diabetic mice by berberine

Berberine, an isoquinoline alkaloid isolated from medicinal plants such as Berberis aristata, Coptis chinesis, Coptis japonica, Coscinium fenestatun, and Hydrastis Canadensis, is widely used in Asian countries for the treatment of diabetes, hypertension, and hypercholesterolemia. Interaction between berberine and the cytochrome P450 enzymes (CYPs) has been extensively reported, but there are only a few reports of this interaction in the diabetic state. In this study, the effect of berberine on the mRNA of the CYPs in primary mouse hepatocytes and in streptozotocin (STZ)-induced diabetic mice was investigated. In primary mouse hepatocytes, berberine suppressed the induction of Cyp1a1, Cyp1a2, Cyp2e1, Cyp3a11, Cyp4a10, and Cyp4a14 mRNA expression by their prototypical inducers in a concentration-dependent fashion. However, berberine treatment alone increased the expression of Cyp2b9 and Cyp2b10 mRNA. In vivo, berberine showed the same hypoglycemic activity as metformin, an established hypoglycemic drug. The hepatic mRNA levels of Cyp1a1, Cyp2b9, Cyp2b10, Cyp3a11, Cyp4a10, and Cyp4a14 were increased in STZ-induced diabetic mice. Interestingly, berberine itself suppressed the expression of Cyp2e1, an adverse hepatic event-associated enzyme, while the expression of Cyp3a11, Cyp4a10, and Cyp4a14 were restored to normal levels by berberine. In conclusion, berberine has the potential to modify the expression of CYPs by either suppression or enhancement of CYPs' levels. Consumption of berberine as an anti-hyperglycemic compound by diabetic patients might provide an extra benefit due to its potential to restore the expression of Cyp2e1, Cyp3a, and Cyp4a to normal levels. However, an herb-drug interaction might be of concern since any berberine-containing product would definitely cause pronounced interactions based on CYP3A4 inhibition.

Methysticin and 7,8-dihydromethysticin are two major kavalactones in kava extract to induce CYP1A1

Kava is a plant traditionally used for making beverages in Pacific Basin countries and has been used for the treatment of nervous disorders in the United States. The pharmacological activity of kava is achieved through kavalactones in kava extract, which include kawain, 7,8-dihydrokawain, yangonin, 5,6-dehydrokawain, methysticin, and 7,8-dihydromethysticin. Recent studies have shown that kava extract induces hepatic CYP1A1 enzyme; however, the mechanisms of CYP1A1 induction have not been elucidated, and the kavalactones responsible for CYP1A1 induction have not yet been identified. Using a combination of biochemical assays and molecular docking tools, we determined the functions of kava extract and kavalactones and delineated the underlying mechanisms involved in CYP1A1 induction. The results showed that kava extract displayed a concentration-dependent effect on CYP1A1 induction. Among the six major kavalactones, methysticin triggered the most profound inducing effect on CYP1A1 followed by 7,8-dihydromethysticin. The other four kavalactones (yangonin, 5,6-dehydrokawain, kawain, and 7,8-dihydrokawain) did not show significant effects on CYP1A1. Consistent with the experimental results, in silico molecular docking studies based on the aryl hydrocarbon receptor (AhR)-ligand binding domain homology model also revealed favorable binding to AhR for methysticin and 7,8-dihydromethysticin compared with the remaining kavalactones. Additionally, results from a luciferase gene reporter assay suggested that kava extract, methysticin, and 7,8-dihydromethysticin were able to activate the AhR signaling pathway. Moreover, kava extract-, methysticin-, and 7,8-dihydromethysticin-mediated CYP1A1 induction was blocked by an AhR antagonist and abolished in AhR-deficient cells. These findings suggest that kava extract induces the expression of CYP1A1 via an AhR-dependent mechanism and that methysticin and 7,8-dihydromethysticin contribute to CYP1A1 induction. The induction of CYP1A1 indicates a potential interaction between kava or kavalactones and CYP1A1-mediated chemical carcinogenesis.

Harmaline and harmalol inhibit the carcinogen-activating enzyme CYP1A1 via transcriptional and posttranslational mechanisms

Dioxins are known to cause several human cancers through activation of the aryl hydrocarbon receptor (AhR). Harmaline and harmalol are dihydro-β-carboline compounds present in several medicinal plants such as Peganum harmala. We have previously demonstrated the ability of P. harmala extract to inhibit TCDD-mediated induction of Cyp1a1 in murine hepatoma Hepa 1c1c7 cells. Therefore, the aim of this study is to examine the effect of harmaline and its main metabolite, harmalol, on dioxin-mediated induction of CYP1A1 in human hepatoma HepG2 cells. Our results showed that harmaline and harmalol at concentrations of (0.5-12.5μM) significantly inhibited the dioxin-induced CYP1A1 at mRNA, protein and activity levels in a concentration-dependent manner. The role of AhR was determined by the inhibition of the TCDD-mediated induction of AhR-dependent luciferase activity and the AhR/ARNT/XRE formation by both harmaline and harmalol. In addition, harmaline significantly displaced [(3)H]TCDD in the competitive ligand binding assay. At posttranslational level, both harmaline and harmalol decreased the protein stability of CYP1A1, suggesting that posttranslational modifications are involved. Moreover, the posttranslational modifications of harmaline and harmalol involve ubiquitin-proteasomal pathway and direct inhibitory effects of both compounds on CYP1A1 enzyme. These data suggest that harmaline and harmalol are promising agents for preventing dioxin-mediated effects.

Polycyclic aromatic hydrocarbons and digestive tract cancers: a perspective

Cancers of the colon are most common in the Western world. In majority of these cases, there is no familial history and sporadic gene damage seems to play an important role in the development of tumors in the colon. Studies have shown that environmental factors, especially diet, play an important role in susceptibility to gastrointestinal (GI) tract cancers. Consequently, environmental chemicals that contaminate food or diet during preparation become important in the development of GI cancers. Polycyclic aromatic hydrocarbons (PAHs) are one such family of ubiquitous environmental toxicants. These pollutants enter the human body through consumption of contaminated food, drinking water, inhalation of cigarette smoke, automobile exhausts, and contaminated air from occupational settings. Among these pathways, dietary intake of PAHs constitutes a major source of exposure in humans. Although many reviews and books on PAHs and their ability to cause toxicity and breast or lung cancer have been published, aspects on contribution of diet, smoking and other factors toward development of digestive tract cancers, and strategies to assess risk from exposure to PAHs have received much less attention. This review, therefore, focuses on dietary intake of PAHs in humans, animal models, and cell cultures used for GI cancer studies along with epidemiological findings. Bioavailability and biotransformation processes, which influence the disposition of PAHs in body and the underlying causative mechanisms of GI cancers, are also discussed. The existing data gaps and scope for future studies is also emphasized. This information is expected to stimulate research on mechanisms of sporadic GI cancers caused by exposure to environmental carcinogens.

Different AhR binding sites of diterpenoid ligands from Andrographis paniculata caused differential CYP1A1 induction in primary culture in mouse hepatocytes

Andrographis paniculata has been employed as a folklore remedy. Andrographolide (Andro), 14-deoxy-11,12-didehydroandrographolide (DHA), andrographiside (AS), and neoandrographolide (Neo), are major diterpenoids isolated from this plant. In the present study, influence of the four diterpenoids on CYP1A1 mRNA expression was investigated in primary cultured mouse hepatocytes. Additionally, binding of these compounds to aryl hydrocarbon receptor (AhR) was examined using molecular docking analysis to clarify mechanism of CYP1A1 induction. Andro and DHA induced CYP1A1 expression by itself, and co-treatment with a CYP1A1 inducer (BNF, beta-naphthoflavone) showed a synergistic increase of CYP1A1 expression. Andro demonstrated higher enhancing activity than DHA at every similar concentration. On the other hand, Neo suppressed BNF-induced CYP1A1 expression, but AS did not modify the induction. Results from molecular docking analysis of BNF and four diterpenoids on ligand binding domain of AhR were consistent with levels of CYP1A1 mRNA expressions. Furthermore, difference of binding sites of BNF in the presence of diterpenoids might affect the synergism or inhibition of CYP1A1 expression. These results suggest that use of A. paniculata as a health supplement should be concerned in term of herb-drugs interactions or risk of carcinogenesis, according to its ability to influence CYP1A1 expression.