AP-1 and SP1 trans-activate the expression of hepatic CYP1A1 and CYP2A6 in the bioactivation of AFB1 in chicken

Dietary exposure to aflatoxin B1 (AFB1) is harmful to the health and performance of domestic animals. The hepatic cytochrome P450s (CYPs), CYP1A1 and CYP2A6, are the primary enzymes responsible for the bioactivation of AFB1 to the highly toxic exo-AFB1-8,9-epoxide (AFBO) in chicks. However, the transcriptional regulation mechanism of these CYP genes in the liver of chicks in AFB1 metabolism remains unknown. Dual-luciferase reporter assay, bioinformatics and site-directed mutation results indicated that specificity protein 1 (SP1) and activator protein-1 (AP-1) motifs were located in the core region -1,063/-948, -606/-541 of the CYP1A1 promoter as well as -636/-595, -503/-462, -147/-1 of the CYP2A6 promoter. Furthermore, overexpression and decoy oligodeoxynucleotide technologies demonstrated that SP1 and AP-1 were pivotal transcriptional activators regulating the promoter activity of CYP1A1 and CYP2A6. Moreover, bioactivation of AFB1 to AFBO could be increased by upregulation of CYP1A1 and CYP2A6 expression, which was trans-activated owing to the upregulalion of AP-1, rather than SP1, stimulated by AFB1-induced reactive oxygen species. Additionally, nano-selenium could reduce ROS, downregulate AP-1 expression and then decrease the expression of CYP1A1 and CYP2A6, thus alleviating the toxicity of AFB1. In conclusion, AP-1 and SP1 played important roles in the transactivation of CYP1A1 and CYP2A6 expression and further bioactivated AFB1 to AFBO in chicken liver, which could provide novel targets for the remediation of aflatoxicosis in chicks.

Cytochromes P450: Role in Carcinogenesis and Relevance to Cancers

Abstracts:

Cancer is a leading factor of mortality globally. Cytochrome P450 (CYP) enzymes play a pivotal role in the biotransformation of both endogenous and exogenous compounds. Evidence from numerous epidemiological, animal, and clinical studies points to instrumental role of CYPs in cancer initiation, metastasis, and prevention. Substantial research has found that CYPs are involved in activating different carcinogenic chemicals in the environment, such as polycyclic aromatic hydrocarbons and tobacco-related nitrosamines. Electrophilic intermediates produced from these chemicals can covalently bind to DNA, inducing mutation and cellular transformation that collectively result in cancer development. While bioactivation of procarcinogens and promutagens by CYPs has long been established, the role of CYP-derived endobiotics in carcinogenesis has emerged in recent years. Eicosanoids derived from arachidonic acid via CYP oxidative pathways have been implicated in tumorigenesis, cancer progression and metastasis. The purpose of this review is to update on the current state of knowledge about the cancer molecular mechanism involving CYPs with focus on the biochemical and biotransformation mechanisms in the various CYP-mediated carcinogenesis, and the role of CYP-derived reactive metabolites, from both external and endogenous sources, on cancer growth and tumour formation.

Genetic and Enzymatic Characteristics of CYP2A13 in Relation to Lung Damage

Cytochrome P450 2A13 is an omitted brother of CYP2A6 that has an important role in the drug metabolism of liver. Due to extrahepatic expression, it has gained less attention than CYP2A6, despite the fact that it plays a significant role in toxicant-induced pulmonary lesions and, therefore, lung cancer. The purpose of this mini-review is to summarize the basic knowledge about this enzyme in relation to the substrates, inhibitors, genetic polymorphisms, and transcriptional regulation that are known so far (September 2021).

Immunohistochemical Detection of Aflatoxin in Lesions of Aflatoxin-producing Aspergillus flavus Infection

Aflatoxin produced by Aspergillus flavus is known to be strongly related to liver injury (hepatocellular carcinoma) and immune system damage involving leukocytes. This toxin suppresses both the cell-mediated immune system and macrophage function, and decreases the production of complement and interferon molecules.

PURPOSE

To evaluate the presence of aflatoxin in infectious lesions as well as how the toxin is taken up by leukocytes.

METHOD

Pathological specimens from a patient who died from aspergillosis caused by aflatoxin-producing A. flavus were used. Anti-aflatoxin B₁ antibody was reacted with paraffin-embedded lesion specimens from the heart, kidney, and thyroid gland of the patient and observed microscopically.

RESULT

Positive reactions were detected in fungal elements and leukocytes (neutrophils and macrophages) in inflammatory lesions.

CONCLUSION

Within the patient's body, A. flavus likely produced aflatoxin, which then was taken up by neutrophils and macrophages.These results suggest that leukocyte function and the immune mechanism are locally suppressed by aflatoxin.

AHR mediates the aflatoxin B1 toxicity associated with hepatocellular carcinoma

Aflatoxin exposure is a crucial factor in promoting the development of primary hepatocellular carcinoma (HCC) in individuals infected with the hepatitis virus. However, the molecular pathways leading to its bioactivation and subsequent toxicity in hepatocytes have not been well-defined. Here, we carried out a genome-wide CRISPR-Cas9 genetic screen to identify aflatoxin B1 (AFB1) targets. Among the most significant hits was the aryl hydrocarbon receptor (AHR), a ligand-binding transcription factor regulating cell metabolism, differentiation, and immunity. AHR-deficient cells tolerated high concentrations of AFB1, in which AFB1 adduct formation was significantly decreased. AFB1 triggered AHR nuclear translocation by directly binding to its N-terminus. Furthermore, AHR mediated the expression of P450 induced by AFB1. AHR expression was also elevated in primary tumor sections obtained from AFB1-HCC patients, which paralleled the upregulation of PD-L1, a clinically relevant immune regulator. Finally, anti-PD-L1 therapy exhibited greater efficacy in HCC xenografts derived from cells with ectopic expression of AHR. These results demonstrated that AHR was required for the AFB1 toxicity associated with HCC, and implicate the immunosuppressive regimen of anti-PD-L1 as a therapeutic option for the treatment of AFB1-associated HCCs.

Hydroxytyrosol and Oleuropein Inhibit Migration and Invasion of MDA-MB-231 Triple-Negative Breast Cancer Cell via Induction of Autophagy

BACKGROUND

Breast Cancer (BC) is the leading cause of cancer-related deaths among women. As such, novel chemotherapeutic agents are urgently needed, especially for Triple-Negative Breast Cancer (TNBC). Hydroxytyrosol (HT) and Oleuropein (OL) are rich in olive oil, which is associated with a low occurrence of BC. However, the effects and mechanisms of action of HT and OL in BC cells are still unclear. This study aimed to explore the molecular mechanisms underlying the antitumor effect of HT and OL in TNBC.

METHODS

TNBC MDA-MB-231 cells were treated with HT and OL in combination with Hepatocyte Growth Factor (HGF), rapamycin (Rapa, an inducer of autophagy) or 3-methyladenine (3-MA, an inhibitor of autophagy). Cell viability, migration, invasion, and autophagy signaling were analyzed by scratch assays, transwell migration assays, and Western blot analysis.

RESULTS

Treatment with HT or OL reduced MDA-MB-231 cell viability in a dose-dependent manner. MDAMB- 231 cells were more sensitive to HT treatment than OL treatment. Rapa treatment could significantly block HGF-induced MDA-MB-231 cell migration and invasion, suggesting that inhibition of autophagy could promote migration and invasion. Moreover, HT or OL treatment significantly suppressed HGF or 3-MA induced cell migration and invasion by reversing LC3-II/LC3-I and Beclin-1 downregulation and reversing p62 upregulation.

CONCLUSION

These data indicated that HT and OL may inhibit migration and invasion of TNBC cells by activating autophagy. These findings provide potential therapeutic strategies that target autophagy to limit the pathogenesis and progression of BC.

Annexin A3 may play an important role in ochratoxin-induced malignant transformation of human gastric epithelium cells

Ochratoxin A (OTA), one of the most abundant food-contaminating mycotoxins, is a possible carcinogen to humans. We previously demonstrated that long-term (40 weeks) OTA exposure induces the malignant transformation of human gastric epithelium cells (GES-1) in vitro. However, the specific mechanism underlying OTA-induced gastric carcinogenesis is complex. In the present study, we used 2-DE and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI/TOF MS) combined with bioinformatics and immunoblotting to investigate the differentially expressed proteins between GES-1 and OTA-malignant transformed GES-1 cells (OTA-GES-1_T cells) in vitro. We found that four differentially expressed proteins were identified after malignant transformation, including actin, cytoplasmic 1 (ACTB), F-actin-capping protein subunit alpha-1 (CAPZA1), Annexin A3 (ANXA3), thioredoxin peroxidase B from red blood cells (TPx-B) and Fibrinogen beta B (Fibrinogen β). Among the differentially expressed proteins, the effect of Annexin A3 was analyzed by MTT assay, western blot, cell cycle analysis, wound healing assay, Transwell assay, and colony formation assay in OTA-GES-1_T cells. The results showed that inhibition of Annexin A3 by siRNA effectively prevented the proliferation, migration, and invasion abilities of OTA-GES-1_T cells. Collectively, the results of this study will guide future research on OTA carcinogenicity.

HapMap-based study: CYP2A13 may be a potential key metabolic enzyme gene in the carcinogenesis of lung cancer in non-smokers

Background

The aim of this study was to evaluate the association between CYP2A13 polymorphisms and lung cancer susceptibility using the HapMap database.

Methods

A case‐control analysis of 532 subjects with lung cancer and 614 controls with no personal history of the disease was performed. The tag SNPs rs1645690 and rs8192789 for CYP2A13 were selected, and the genetic polymorphisms were confirmed experimentally through real‐time PCR, cloning, and sequencing assay.

Results

SNP frequency in this study was consistent with the HapMap Project database of Han‐Chinese and lung cancer risk was associated with CYP2A13 polymorphisms in non‐smokers. CYP2A13 shares a 93.5% identity with CYP2A6 in the amino acid sequence and the homologous sequences may interfere with the study of SNPs of CYP2A13.

Conclusions

CYP2A13 may be a potential key metabolic enzyme gene in the carcinogenesis of lung cancer in non‐smokers. The common polymorphisms of CYP2A13 may be candidate biomarkers for lung cancer susceptibility in Han‐Chinese.

DNA damage checkpoint response to aflatoxin B1

Although most countries regulate the aflatoxin levels in food by legislations, high amounts of aflatoxin B1 (AFB1)-DNA adducts can still be detected in normal and tumorous tissue obtained from cancer patients. AFB1 cannot directly interact with DNA unless it is biotransformed to AFB1-8, 9-epoxide via cytochrome p450 enzymes. This metabolite spontaneously and irreversibly attaches to guanine residues to generate highly mutagenic DNA adducts. AFB1-induced mutation of ATM kinase results in the deterioration of the cell cycle checkpoint activation at the G2/M checkpoint site. Genomic instability and increased cancer risk due to A-T mutation is the result of diminished repair of DNA double strand breaks. The major point mutation caused by AFB1 is G-to-T transversion that is related with the high frequency of p53 mutation. Majority of AFB1 associated hepatocellular cancer cases carry TP53 mutant DNA, which is an indicator of AFB1 exposure, as well as hepatocellular cancer risk.

Identification of 5-hydroxymethylfurfural in cigarette smoke extract as a new substrate metabolically activated by human cytochrome P450 2A13

Cytochrome P450 2A13 (CYP2A13) is an extrahepatic enzyme mainly expressed in the human respiratory system and is reported to mediate tobacco-specific N-nitrosamines (TSNA) metabolism in cigarette smoke. This study aimed to identify other new substrates of CYP2A13 in cigarette smoke and their corresponding respiratory toxicity. Following separation by HPLC, GC-MS/MS, NMR and cytotoxicity assays in BEAS-2B cells stably expressing CYP2A13 (B-2A13), 5-Hydroxymethylfurfural (5-HMF) was screened and identified in the 4-5 min section of cigarette smoke extract (CSE). In vitro metabolism results showed that CYP2A13 mediated the fast clearance of 5-HMF and formed the metabolite 5-HMF acid (5-HMFA). CSE 5-HMF (CSE-5-HMF) showed cytotoxicity similar to that of standard 5-HMF in B-2A13 and B-2A5 cells, which was inhibited by 8-methoxypsoralen (8-MOP), a CYP enzyme inhibitor. Mouse CYP2A5, a homologous CYP enzyme to CYP2A13, shares many substrates with CYP2A13 in cigarette smoke. Thus, CYP2A5^-/- mice were generated to explore the role of CYP2A5 in 5-HMF bioactivation. Compared with CYP2A5^-/- mice, WT mice showed serious histological lung and nasal olfactory mucosa damage, as well as increased inflammatory cells and elevated TNF-α and IL-6 levels in bronchoalveolar lavage fluid. Besides, nasal microsomes undertook fast 5-HMFA formation in WT mice than that in CYP2A5^-/- mice, which could be inhibited by 8-MOP. This study is the first to identify 5-HMF as a new toxic substrate of human CYP2A13 in cigarette smoke, it may play a potential role in cigarette smoke-induced respiratory injuries.

Aflatoxin B1 induced multiple epigenetic modulators in human epithelial cell lines

The compulsive and insidious secondary metabolite aflatoxin B₁, produced by the opportunistic fungi Aspergillus flavus, upholds a distinguished place in midst of the toxicants causing fatal hazards to humans. Aflatoxins alter the function of host cells by inducing multiple effects through genetic and non-genetic pathways. Epigenetic mechanisms drag major attention towards finding novel and new mechanisms involved in this process. Our present work intends to study the functional expression profile of multiple epigenetic regulators. AFB₁ modulates multiple epigenetic regulators like DNA methyltransferases (DMNTs), histones modifying enzymes and polycomb proteins. AFB₁ upregulates the expression of DNMTs at gene and protein level in a dose dependent manner. It reduced the histone acetyl transferase (HAT) activity significantly with a remarkable increase in histone deacetylase (HDAC) activity along with an induction in expression of HDACs gene and protein in a dose dependent manner. The gene and protein expression of polycomb repressor proteins B cell specific moloney murine leukemia virus integration site 1 (BMI-1) and enhancer of zeste homolog 2 (EZH2) was significantly over expressed with enhanced trimethylation of H3K27 and ubiquitination of H2AK119. In summary, our results show impact of aflatoxin B₁ on multiple epigenetic modulations known to be pivotal in oncogenic processes.

Metabolomics profiles delineate uridine deficiency contributes to mitochondria-mediated apoptosis induced by celastrol in human acute promyelocytic leukemia cells

Celastrol, extracted from “Thunder of God Vine”, is a promising anti-cancer natural product. However, its effect on acute promyelocytic leukemia (APL) and underlying molecular mechanism are poorly understood. The purpose of this study was to explore its effect on APL and underlying mechanism based on metabolomics. Firstly, multiple assays indicated that celastrol could induce apoptosis of APL cells via p53-activated mitochondrial pathway. Secondly, unbiased metabolomics revealed that uridine was the most notable changed metabolite. Further study verified that uridine could reverse the apoptosis induced by celastrol. The decreased uridine was caused by suppressing the expression of gene encoding Dihydroorotate dehydrogenase, whose inhibitor could also induce apoptosis of APL cells. At last, mouse model confirmed that celastrol inhibited tumor growth through enhanced apoptosis. Celastrol could also decrease uridine and DHODH protein level in tumor tissues. Our in vivo study also indicated that celastrol had no systemic toxicity at pharmacological dose (2 mg/kg, i.p., 21 days). Altogether, our metabolomics study firstly reveals that uridine deficiency contributes to mitochondrial apoptosis induced by celastrol in APL cells. Celastrol shows great potential for the treatment of APL.

Caffeic acid ameliorates colitis in association with increased Akkermansia population in the gut microbiota of mice

Emerging evidence shows that dietary agents and phytochemicals contribute to the prevention and treatment of ulcerative colitis (UC). We first reported the effects of dietary caffeic acid (CaA) on murine experimental colitis and on fecal microbiota. Colitis was induced in C57BL/6 mice by administration of 2.5% dextran sulfate sodium (DSS). Mice were fed a control diet or diet with CaA (1 mM). Our results showed that dietary CaA exerted anti-inflammatory effects in DSS colitis mice. Moreover, CaA could significantly suppress the secretion of IL-6, TNFα, and IFNγ and the colonic infiltration of CD3⁺ T cells, CD177⁺ neutrophils and F4/80⁺ macrophages via inhibition of the activation of NF-κB signaling pathway. Analysis of fecal microbiota showed that CaA could restore the reduction of richness and inhibit the increase of the ratio of Firmicute to Bacteroidetes in DSS colitis mice. And CaA could dramatically increase the proportion of the mucin-degrading bacterium Akkermansia in DSS colitis mice. Thus, CaA could ameliorate colonic pathology and inflammation in DSS colitis mice, and it might be associated with a proportional increase in Akkermansia.

Chlorogenic Acid Ameliorates Experimental Colitis by Promoting Growth of Akkermansia in Mice

Chlorogenic acid (ChA)—one of the most abundant polyphenol compounds in the human diet—exerts anti-inflammatory activities. The aim of this study was to investigate the effect of ChA on gut microbiota in ulcerative colitis (UC). Colitis was induced by 2.5% dextran sulfate sodium (DSS) in C57BL/6 mice, which were on a control diet or diet with ChA (1 mM). The histopathological changes and inflammation were evaluated. Fecal samples were analyzed by 16S rRNA gene sequencing. ChA attenuated several effects of DSS-induced colitis, including weight loss, increased disease activity index, and improved mucosal damage. Moreover, ChA could significantly suppress the secretion of IFNγ, TNFα, and IL-6 and the colonic infiltration of F4/80⁺ macrophages, CD3⁺ T cells, and CD177⁺ neutrophils via inhibition of the active NF-κB signaling pathway. In addition, ChA decreased the proportion of Firmicutes and Bacteroidetes. ChA also enhanced a reduction in fecal microbiota diversity in DSS treated mice. Interestingly, ChA treatment markedly increased the proportion of the mucin-degrading bacterium Akkermansia in colitis mice. ChA acted as the intestine-modifying gut microbial community structure, resulting in a lower intestinal and systemic inflammation and also improving the course of the DSS-induced colitis, which is associated with a proportional increase in Akkermansia.

Fungal Aflatoxins Reduce Respiratory Mucosal Ciliary Function

Aflatoxins are mycotoxins secreted by Aspergillus flavus, which can colonize the respiratory tract and cause fungal rhinosinusitis or bronchopulmonary aspergillosis. A. flavus is the second leading cause of invasive aspergillosis worldwide. Because many respiratory pathogens secrete toxins to impair mucociliary immunity, we examined the effects of acute exposure to aflatoxins on airway cell physiology. Using air-liquid interface cultures of primary human sinonasal and bronchial cells, we imaged ciliary beat frequency (CBF), intracellular calcium, and nitric oxide (NO). Exposure to aflatoxins (0.1 to 10 μM; 5 to 10 minutes) reduced baseline (~6-12%) and agonist-stimulated CBF. Conditioned media (CM) from A. fumigatus, A. niger, and A. flavus cultures also reduced CBF by ~10% after 60 min exposure, but effects were blocked by an anti-aflatoxin antibody only with A. flavus CM. CBF reduction required protein kinase C but was not associated with changes in calcium or NO. However, AFB2 reduced NO production by ~50% during stimulation of the ciliary-localized T2R38 receptor. Using a fluorescent reporter construct expressed in A549 cells, we directly observed activation of PKC activity by AFB2. Aflatoxins secreted by respiratory A. flavus may impair motile and chemosensory functions of airway cilia, contributing to pathogenesis of fungal airway diseases.

Bioactivation and Regioselectivity of Pig Cytochrome P450 3A29 towards Aflatoxin B₁

Due to unavoidable contaminations in feedstuff, pigs are easily exposed to aflatoxin B₁ (AFB₁) and suffer from poisoning, thus the poisoned products potentially affect human health. Heretofore, the metabolic process of AFB₁ in pigs remains to be clarified, especially the principal cytochrome P450 oxidases responsible for its activation. In this study, we cloned CYP3A29 from pig liver and expressed it in Escherichia coli, and its activity has been confirmed with the typical P450 CO-reduced spectral characteristic and nifedipine-oxidizing activity. The reconstituted membrane incubation proved that the recombinant CYP3A29 was able to oxidize AFB₁ to form AFB₁-exo-8,9-epoxide in vitro. The structural basis for the regioselective epoxidation of AFB₁ by CYP3A29 was further addressed. The T309A mutation significantly decreased the production of AFBO, whereas F304A exhibited an enhanced activation towards AFB₁. In agreement with the mutagenesis study, the molecular docking simulation suggested that Thr309 played a significant role in stabilization of AFB₁ binding in the active center through a hydrogen bond. In addition, the bulk phenyl group of Phe304 potentially imposed steric hindrance on the binding of AFB₁. Our study demonstrates the bioactivation of pig CYP3A29 towards AFB₁ in vitro, and provides the insight for understanding regioselectivity of CYP3A29 to AFB₁.

Malignant transformation of human gastric epithelium cells via reactive oxygen species production and Wnt/β-catenin pathway activation following 40-week exposure to ochratoxin A

Ochratoxin A (OTA), one of the most abundant food-contaminating mycotoxins, is a possible carcinogenic to humans. We previously demonstrated that OTA treatment induced oxidative damage in human gastric epithelium cells (GES-1) in vitro. In this study, we found that long-term OTA treatment could result in increased proliferation, migration, and invasion abilities of GES-1 cells and induce anchorage-independent growth of cells in soft agar. Inoculation of OTA-treated GES-1 cells resulted in the formation of tumor xenografts in Balb/c nude mice in vivo, confirming that long-term OTA treatment can induce the malignant transformation of GES-1 cells. In addition, we found that long-term OTA treatment induced oxidative stress and activated the Wnt/β-catenin pathway, including the nuclear transition of β-catenin and the upregulation of the downstream molecules of the pathway. Finally, pretreatment with the antioxidant N-acetyl-L-cysteine (NAC) inhibited ROS formation and activation of the Wnt pathway in OTA-transformed GES-1 cells, which decreased the tumor formation abilities of these cells after inoculation in nude mice. These findings suggest that long-term OTA exposure induces the malignant transformation of GES-1 cells via intracellular ROS production and activation of the Wnt/β-catenin signaling pathway.

How does airway exposure of aflatoxin B1 affect serum albumin adduct concentrations? Evidence based on epidemiological study and animal experimentation

Aflatoxin B1 (AFB1) airway inhalation represents an additional route of exposure to this toxin. However, the association between AFB1 inhalation and serum AFB1 albumin adducts remains unclear. The aim of this study was to explore the association between airway exposure to AFB1 and serum AFB1 albumin adduct concentrations via an epidemiological study, as well as in an AFB1 airway exposure animal model. Our epidemiological study was conducted in a sugar factory in the Guangxi Autonomous Region of China. In order to examine fungal contamination, air samples were obtained in the workshop and areas outside the workshop, such as the office and nearby store. Dust samples were also collected from the bagasse warehouse and presser workshop, and were analyzed using an indirect competitive enzyme-linked immunosorbent assay (ELISA). Additionally, blood samples were collected from a total of 121 workshop workers, and a control group (n = 80) was comprised of workers who undertook administrative tasks or other work outside the workshop. The animal experiment was conducted in the laboratory animal center of Guangxi Medical University, where a total of 60 adult male rabbits were involved in this study. By intubation, AFB1 was administered in three groups of rabbits daily, at dose rates of 0.075, 0.05 and 0.025 mg/kg/day for a period of 7 days. Blood samples were collected on day 1, day 3, day 7 and day 21, and the measurements of the AFB1 albumin adducts in the serum were performed by a double antibody sandwich ELISA. The epidemiological study showed that serum albumin adducts were detected in 67 workshop workers (55.37%), and the values ranged 6.4 pg/mg albumin to 212 pg/mg albumin (mean value: 51 ± 4.62 pg/mg albumin). In contrast, serum albumin adducts were detected in only 7 control group participants, with the values ranging from 9 pg AFB1/mg albumin to 59 pg/mg albumin (mean value: 20 ± 13.72 pg/mg albumin). The animal experiment revealed that the rabbits had detectable levels of AFB1 in their serum with a minimum effective dose of 0.05 mg/kg/day; while 11 of 17 (64.71%) rabbits had detectable levels of AFB1 albumin adducts in the high exposure group (0.075 mg/kg/day), and only 5 rabbits (26.32%) had detectable levels of AFB1 albumin adducts in the moderate exposure group (0.05 mg/kg/day). No rabbits had detectable levels of AFB1 albumin adducts in the low exposure group (0.025 mg/kg/day). Our results demonstrated that only exposure to a certain level of AFB1 would result in detectable levels of serum AFB1 albumin adducts. Interventional programs aimed at reducing exposure to AFB1 by inhalation are urgently needed in high-risk populations. Additional large-sample, well-designed randomized controlled trials are needed to further confirm our results.

Role of Cytochrome P450 Monooxygenase in Carcinogen and Chemotherapeutic Drug Metabolism

The purpose of this chapter is to provide insight into which human cytochromes P450 (CYPs) may be involved in metabolism of chemical carcinogens and anticancer drugs. A historical overview of this field and the development of literature using relevant animal models and expressed human CYPs have provided information about which specific CYPs may be involved in carcinogen metabolism. Definition of the biochemical properties of CYP activity came from several groups who studied the reaction stoichiometry of butter yellow and benzo[α]pyrene, including their role in induction of these enzyme systems. This chapter will list as much as is known about the human CYPs involved in carcinogen and anticancer drug metabolism, as well as summarize studies with rodent CYPs. A review of three major classes of anticancer drugs and their metabolism in humans is covered for cyclophosphamide, procarbazine, and anthracycline antibiotics, cancer chemotherapeutic compounds extensively metabolized by CYPs. The emerging information about human CYP gene polymorphisms as well as other enzymes involved in foreign compound metabolism provides considerable information about how these genetic variants affect carcinogen and anticancer drug metabolism. With information available from individual's genomic sequences, consideration of populations who may be at risk due to environmental exposure to carcinogens or how to optimize their cancer therapy regimens to enhance efficacy of the anticancer drugs appears to be an important field of study to benefit individuals in the future.

Pulmonary expression of CYP2A13 and ABCB1 is regulated by FOXA2, and their genetic interaction is associated with lung cancer

Inhaled xenobiotics such as tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone are mainly metabolized by phase I oxidase cytochrome P450, family 2, subfamily A, polypeptide 13 (CYP2A13), phase II conjugate UDP glucuronosyltransferase 2 family, polypeptide B17 (UGT2B17), and phase III transporter ATP-binding cassette, subfamily B (MDR/TAP), member 1 (ABCB1), with genetic polymorphisms implicated in lung cancer. Their genetic interaction and pulmonary expression regulation are largely unknown. We analyzed joint association for CYP2A13 and ABCB1 polymorphisms in 2 independent lung cancer case populations (669 and 566 patients) and 1 common control population (749 subjects), and characterized the trans-acting function of the lung development-related transcription factor forkhead box A2 (FOXA2). We undertook FOXA2 overexpression and down-regulation in lung epithelial cell lines, analyzed functional impact on the transactivation of CYP2A13, UGT2B17, and ABCB1, and measured correlation for their expressions in lung tissues. We found a substantial reduction in cancer risk (OR 0.39; 95% CI 0.25-0.61; Pinteraction = 0.029) associated with combined genotypes for CYP2A13 R257C and a functionary regulatory variant in the cis element of ABCB1 synergistically targeted by GATA binding protein 6 and FOXA2. Genetic manipulation of FOXA2 consistently influenced its binding to and transactivation of the promoters of CYP2A13, UGT2B17, and ABCB1, whose mRNA and protein expressions were all consistently correlated with those of FOXA2 in both tumorous and normal lung tissues. We therefore establish FOXA2 as a core transcriptional modulator for pulmonary xenobiotic metabolic pathways and uncover an etiologically relevant interaction between CYP2A13 and ABCB1, furthering our understanding of expression and function of the xenobiotic metabolism system.

Culture conditions profoundly impact phenotype in BEAS-2B, a human pulmonary epithelial model

BEAS-2B, an immortalized, human lung epithelial cell line, has been used to model pulmonary epithelial function for over 30 years. The BEAS-2B phenotype can be modulated by culture conditions that include the presence or absence of fetal bovine serum (FBS). The popularity of BEAS-2B as a model of arsenic toxicology, and the common use of BEAS-2B cultured both with and without FBS, led us to investigate the impact of FBS on BEAS-2B in the context of arsenic toxicology. Comparison of genome-wide gene expression in BEAS-2B cultured with or without FBS revealed altered expression in several biological pathways, including those related to carcinogenesis and energy metabolism. Real-time measurements of oxygen consumption and glycolysis in BEAS-2B demonstrated that FBS culture conditions were associated with a 1.4-fold increase in total glycolytic capacity, a 1.9-fold increase in basal respiration, a 2.0-fold increase in oxygen consumed for ATP production and a 2.8-fold increase in maximal respiration, compared with BEAS-2B cultured without FBS. Comparisons of the transcriptome changes in BEAS-2B resulting from FBS exposure to the transcriptome changes resulting from exposure to 1 μM sodium arsenite revealed that mRNA levels of 43% of the arsenite-modulated genes were also modulated by FBS. Cytotoxicity studies revealed that BEAS-2B cells exposed to 5% FBS for 8 weeks were almost 5 times more sensitive to arsenite cytotoxicity than non-FBS-exposed BEAS-2B cells. Phenotype changes induced in BEAS-2B by FBS suggest that culture conditions should be carefully considered when using BEAS-2B as an experimental model of arsenic toxicity.

Assessment of workers' exposure to aflatoxin B1 in a Portuguese waste industry

Aflatoxin B1 (AFB1) is considered by different International Agencies as a genotoxic and potent hepatocarcinogen. However, despite the fact that the fungi producing this compound are detected in some work environments, AFB1 is rarely monitored in occupational settings. The aim of the present investigation was to assess exposure to AFB1 of workers from one Portuguese waste company located in the outskirt of Lisbon. Occupational exposure assessment to AFB1 was done with a biomarker of internal dose that measures AFB1 in the serum by enzyme-linked immunosorbent assay. Forty-one workers from the waste company were enrolled in this study (26 from sorting; 9 from composting; 6 from incineration). A control group (n = 30) was also considered in order to know the AFB1 background levels for the Portuguese population. All the workers showed detectable levels of AFB1 with values ranging from 2.5ng ml(-1) to 25.9ng ml(-1) with a median value of 9.9±5.4ng ml(-1). All of the controls showed values below the method's detection limit. Results obtained showed much higher (8-fold higher) values when compared with other Portuguese settings already studied, such as poultry and swine production. Besides this mycotoxin, other mycotoxins are probably present in this occupational setting and this aspect should be taken into consideration for the risk assessment process due to possible synergistic reactions. The data obtained suggests that exposure to AFB1 occurs in a waste management setting and claims attention for the need of appliance of preventive and protective safety measures.

Metabolism of aflatoxins: key enzymes and interindividual as well as interspecies differences

Aflatoxins are potent hepatocarcinogen in animal models and suspected carcinogen in humans. The most important aflatoxin in terms of toxic potency and occurrence is aflatoxin B1 (AFB1). In this review, we mainly summarized the key metabolizing enzymes of AFB1 in animals and humans. Moreover, the interindividual and the interspecies differences in AFB1 metabolism are highly concerned. In human liver, CYP3A4 plays an important role in biotransforming AFB1 to the toxic product AFB1-8,9-epoxide. In human lung, CYP2A13 has a significant activity in metabolizing AFB1 to AFB1-8,9-epoxide and AFM1-8,9-epoxide. The epoxide of AFB1-8,9-epoxide could conjugate with glutathione to reduce the toxicity by glutathione-S-transferase (GST). In poultry species, CYP2A6, CYP3A37, CYP1A5, and CYP1A1 are responsible for bioactivation of AFB1. There are interindividual variations in the rate of activation of aflatoxins in various species, and there are also differences between children and adults. The age and living regions are important factors affecting resistance of species to AFB1. The rate of AFB1-8,9-epoxide formation and its conjugation with glutathione are key parameters in interspecies and interindividual differences in sensitivity to the toxic effect of AFB1. This review provides an important information for key metabolizing enzymes and the global metabolism of aflatoxins in different species.

Association between aflatoxin B1 occupational airway exposure and risk of hepatocellular carcinoma: a case-control study

The aim of this study was to determine the airway exposure of sugar and papermaking factory workers to aflatoxin B1 (AFB1) and to explore the potential association between AFB1 airway exposure and the risk of hepatocellular carcinoma (HCC) in a case-control study. Dust samples were collected from the sugarcane bagasse warehouse, and presser and paper production workshops. Blood samples were collected from 181 workshop employees and 203 controls who worked outside the workshop. AFB1 albumin adducts were detected using a double antibody sandwich enzyme-linked immunosorbent assay (ELISA). To explore the association between AFB1 airway exposure and the risk of HCC, the medical records of 68 HCC patients who worked in a sugar and papermaking factory between January 1994 and December 2013 were analyzed. A questionnaire was used to collect information from 150 healthy controls who worked for the same company and lived near the factory. AFB1 was detected in the dust samples, but could not be detected in any of the rice samples. An analysis of serum samples revealed serum AFB1 albumin adducts in 102 (56.35 %) of the study participants. However, in the control group, only 12 (5.9 %) individuals had detectable levels of AFB1 albumin adducts. Those with airway exposure to Aspergillus flavus-contaminated dust had an elevated risk of HCC compared to those without exposure (odds ratio, 5.24; 95 % confidence interval, 2.77-9.88; P = 0.00). The findings of this study indicate that occupational AFB1 airway exposure might be associated with the risk of AFB1-related HCC among the population that was used in this study. Intervention programs aimed at reducing exposure to inhalational AFB1 are needed urgently. Additional suitably designed, multicenter, prospective studies using large samples are needed to further confirm the results.

Association between aflatoxin B1 occupational airway exposure and risk of hepatocellular carcinoma: a case-control study

The aim of this study was to determine the airway exposure of sugar and papermaking factory workers to aflatoxin B1 (AFB1) and to explore the potential association between AFB1 airway exposure and the risk of hepatocellular carcinoma (HCC) in a case-control study. Dust samples were collected from the sugarcane bagasse warehouse, and presser and paper production workshops. Blood samples were collected from 181 workshop employees and 203 controls who worked outside the workshop. AFB1 albumin adducts were detected using a double antibody sandwich enzyme-linked immunosorbent assay (ELISA). To explore the association between AFB1 airway exposure and the risk of HCC, the medical records of 68 HCC patients who worked in a sugar and papermaking factory between January 1994 and December 2013 were analyzed. A questionnaire was used to collect information from 150 healthy controls who worked for the same company and lived near the factory. AFB1 was detected in the dust samples, but could not be detected in any of the rice samples. An analysis of serum samples revealed serum AFB1 albumin adducts in 102 (56.35 %) of the study participants. However, in the control group, only 12 (5.9 %) individuals had detectable levels of AFB1 albumin adducts. Those with airway exposure to Aspergillus flavus-contaminated dust had an elevated risk of HCC compared to those without exposure (odds ratio, 5.24; 95 % confidence interval, 2.77–9.88; P = 0.00). The findings of this study indicate that occupational AFB1 airway exposure might be associated with the risk of AFB1-related HCC among the population that was used in this study. Intervention programs aimed at reducing exposure to inhalational AFB1 are needed urgently. Additional suitably designed, multicenter, prospective studies using large samples are needed to further confirm the results.