Mechanisms of peroxisome proliferator-induced DNA hypomethylation in rat liver

Assessment of the mode of action of perchloroethylene-induced mouse liver tumors

Perchloroethylene (PCE) is used as a solvent and chemical intermediate. Following chronic inhalation exposure, PCE selectively induced liver tumors in mice. Understanding the mode of action (MOA) for PCE carcinogenesis in mice is important in defining its possible human cancer risk. The proposed MOA is based on the extensive examination of the peer-reviewed studies that have assessed the mouse liver effects of PCE and its major oxidative metabolite trichloroacetic acid (TCA). Similar to PCE, TCA has also been demonstrated to liver tumors selectively in mice following chronic exposure. The Key Events (KE) of the proposed PCE MOA involve oxidative metabolism of PCE to TCA [KE 1]; activation of the peroxisome proliferator-activated receptor alpha (PPARα) [KE 2]; alteration in hepatic gene expression including cell growth pathways [KE 3]; increase in cell proliferation [KE 4]; selective clonal expansion of hepatic preneoplastic foci [KE 5]; and formation of hepatic neoplasms [KE 6]. The scientific evidence supporting the PPARα MOA for PCE is strong and satisfies the requirements for a MOA analysis. The PPARα liver tumor MOA in rodents has been demonstrated not to occur in humans; thus, human liver cancer risk to PCE is not likely.

Endogenous phthalates as a prospective regulator of interspecific relations in a biocoenosis

It is widely believed that phthalates are xenobiotic pollutants whose prevalence in the environment is associated with their facilitated diffusion from plastic materials. Studies into the effect of synthetic phthalates on living organisms revealed their extremely negative action on the metabolism of animals and humans. The acting mechanism of these compounds is realised through a ligand-receptor pathway. Along with dioxins, polychlorinated biphenyls and similar compounds, phthalates are classified as endocrine disrupters. However, at present, sufficient evidence has been accumulated confirming the natural origin of phthalates. Thus, phthalates were de novo biosynthesised from labelled precursors in an algae culture. These compounds were detected in closed experimental systems, including cell cultures of highest plants, as well as those isolated from a number of bacterial, fungi, lowest and highest plant forms located far from the sources of technogenic pollution. The concept of phthalate biogenesis assumes the action of these compounds on living systems. Phthalates exhibit bactericidal and fungicidal action and compose allelopathic exudates, suppressing the growth of competing plant forms. Phthalates possess insecticidal and repellent properties. An analogy can be traced between the action of phthalates and endocrine disrupters of another chemical category, namely phytoestrogens, which regulate herbivorous mammal populations. A hypothesis is proposed about the biological role of endogenous plant phthalates representing secondary metabolic compounds. Exhibiting predominantly a shielding function, these compounds participate in the network of interactions between plants, animals, fungi and microorganisms. It should be noted that synthetic and endogenous phthalates are characterised by essential stereochemical differences, which can explain their different action on living organisms.

The selected epigenetic effects of phthalates: DBP, BBP and their metabolites: MBP, MBzP on human peripheral blood mononuclear cells (In Vitro)

Phthalates are classified as non-genotoxic carcinogens. These compounds do not cause direct DNA damage but may induce indirect DNA lesions leading to cancer development. In the presented paper we have studied the effect of di-n-butyl phthalate (DBP), butylbenzyl phthalate (BBP), and their metabolites, such as mono-n-butyl phthalate (MBP) and monobenzyl phthalate (MBzP) on selected epigenetic parameters in human peripheral blood mononuclear cells (PBMCs). The cells were incubated with tested phthalates at 0.001, 0.01 and 0.1 μg/mL for 24 h. Next, global DNA methylation, methylation in the promoter regions of tumor suppressor genes (P16, TP53) and proto-oncogenes (BCL2, CCND1) were assessed as well as the expression profile of the indicated genes was analysed. The obtained results have revealed significant reduction of global DNA methylation level in PBMCs exposed to BBP, MBP and MBzP. Phthalates changed methylation pattern of the tested genes, decreased expression of P16 and TP53 genes and increased the expression of BCL2 and CCND1. In conclusion, our results have shown that the examined phthalates disturbed the processes of methylation and expression of tumor suppressor genes (P16, TP53) and protooncogenes (BCL2, CCND1) in human PBMCs.

Phthalate esters in surface sediments from fishing ports in Circum-Bohai-Sea region, China

The concentration, composition, distribution, and possible sources of phthalate esters (PAEs) in surface sediments from fishing ports in the Circum-Bohai-Sea region were investigated. The potential ecological risks of PAEs on three sensitive aquatic organisms (algae, crustacean, and fish) were assessed based on the risk quotient. The concentrations of 16 PAEs were in the range of 8.53-86.13 μg/g. Six PAEs, which were considered as priority pollutants by the United States Environmental Protection Agency, were main congeners. Fishing ports with high PAE concentration were located near the eastern area of the Shandong Peninsula, the southern area of the Liaodong Peninsula, and the estuary of the Yellow River. Wastewater, atmospheric deposition, plastic, and rubber products were possible sources of PAEs. The PAEs showed medium to high ecological risks on the three aquatic organisms, and the ecological risks were attributed to four PAEs, including dimethyl phthalate, diethyl phthalate, dibutyl phthalate, and benzylbutyl phthalate.

Prenatal Exposure to Per- and Polyfluoroalkyl Substances, Umbilical Cord Blood DNA Methylation, and Cardio-Metabolic Indicators in Newborns: The Healthy Start Study

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are environmentally persistent chemicals widely detected in women of reproductive age. Prenatal PFAS exposure is associated with adverse health outcomes in children. We hypothesized that DNA methylation changes may result from prenatal PFAS exposure and may be linked to offspring cardio-metabolic phenotype.

OBJECTIVES

We estimated associations of prenatal PFAS with DNA methylation in umbilical cord blood. We evaluated associations of methylation at selected sites with neonatal cardio-metabolic indicators.

METHODS

Among 583 mother-infant pairs in a prospective cohort, five PFAS were quantified in maternal serum (median 27 wk of gestation). Umbilical cord blood DNA methylation was evaluated using the Illumina HumanMethylation450 array. Differentially methylated positions (DMPs) were evaluated at a false discovery rate ( FDR ) < 0.05 and differentially methylated regions (DMRs) were identified using comb-p (Šidák-adjusted p < 0.05 ). We estimated associations between methylation at candidate DMPs and DMR sites and the following outcomes: newborn weight, adiposity, and cord blood glucose, insulin, lipids, and leptin.

RESULTS

Maternal serum PFAS concentrations were below the median for females in the U.S. general population. Moderate to high pairwise correlations were observed between PFAS concentrations (ρ = 0.28 - 0.76 ). Methylation at one DMP (cg18587484), annotated to the gene TJAP1, was associated with perfluorooctanoate (PFOA) at FDR <   0.05 . Comb-p detected between 4 and 15 DMRs for each PFAS. Associated genes, some common across multiple PFAS, were implicated in growth (RPTOR), lipid homeostasis (PON1, PON3, CIDEB, NR1H2), inflammation and immune activity (RASL11B, RNF39), among other functions. There was suggestive evidence that two PFAS-associated loci (cg09093485, cg09637273) were associated with cord blood triglycerides and birth weight, respectively (FDR <   0.1 ).

DISCUSSION

DNA methylation in umbilical cord blood was associated with maternal serum PFAS concentrations during pregnancy, suggesting potential associations with offspring growth, metabolism, and immune function. Future research should explore whether DNA methylation changes mediate associations between prenatal PFAS exposures and child health outcomes. https://doi.org/10.1289/EHP6888.

Multi and transgenerational epigenetic effects of di-(2-ethylhexyl) phthalate (DEHP) in liver

Di-(2-ethylhexyl) phthalate (DEHP), a ubiquitous industrial pollutant, is a known endocrine disrupter implicated in metabolic diseases. Prenatal DEHP exposure promotes epigenetic multi- and transgenerational inheritance of adult onset disease in subsequent generations (F1-F3). However, the epigenetic toxicity is less understood in the liver. In this study, CD-1 mice were prenatally exposed to 20 μg/kg/day, 200 μg/kg/day, 500 mg/kg/day, or 750 mg/kg/day DEHP from gestational day (GD) 10.5 until birth of pups. Following prenatal exposure, the multigenerational and transgenerational effects of mRNA expression of epigenetic regulators were evaluated in F1, F2, and F3 generation mouse livers at postnatal days (PNDs) 8 and 60. Results showed that DEHP exposed mice livers exhibited significant changes in global DNA methylation levels in all three generations, with the effect being different in F2 after high dosage exposure. Histopathology indicated that DEHP exposure could induce mild damage in F1 livers. The expression levels of DNA methyltransferase 1 (Dnmt1) were significantly changed in both the F1 and F2 generations at PND 8, suggesting that maintenance Dnmt1 plays a major role in the multigenerational effect that occur in the early developmental stages. Additionally, DEHP exposure caused significant changes in ten-eleven translocation methylcytosine (Tet) dioxygenases encoding Tet1 expression in all three generations and Tet2 expression in F3 at PND 60, implicating their contributions in inducing both multi- and transgenerational effects after DEHP exposure in mouse liver. Overall, our results establish that prenatal and ancestral DEHP exposure are critical for epigenetic regulation of DNA methylation in female mouse livers.

Efficacy coefficient method assisted quadruple-activities 3D-QSAR pharmacophore model for application in environmentally friendly PAE molecular modification

Phthalate acid esters (PAEs) are among the most widely used plasticizers in plastic products. They are easily diffused from plastic during use and seriously affect the environment and human health. Therefore, designing environmentally friendly PAE derivatives has important practical applications. In this paper, the environmentally friendly molecular modification of PAEs was carried out according to a comprehensive structural evaluation based on a three-dimensional quantitative structure-activity relationship (3D-QSAR) pharmacophore model of four activity modes. First, the efficacy coefficient method was used to process the mobility, toxicity, degradation and bioconcentration data of the PAEs to calculate comprehensive evaluation values. The PAE 3D-QSAR pharmacophore complex model was constructed based on the PAE four-activity comprehensive evaluation value (a comprehensive value representing the mobility, toxicity, degradation and bioconcentration of the PAEs), and a total of 4 PAE derivatives with reduced comprehensive evaluation values were obtained. Functional evaluation of the derivatives showed that the five PAEs with lower comprehensive evaluation values were stable in the environment, while the insulating properties of the derivative molecules were less affected. Following the four-activity pharmacophore model (Hypo 1) of the target molecules, dimethyl phthalate (DMP) and di-n-octyl phthalate (DNOP), comprehensive evaluation models and their mobility, toxicity, degradation and bioconcentration single-activity models, the substitution sites selected by the comprehensive evaluation model were demonstrated to be highly representative. By constructing a two-dimensional quantitative structure-activity relationship (2D-QSAR) model of the comprehensive evaluation values of the PAEs and the four single-effect 2D-QSAR models of their derivatives, the different effects of the five key parameters on the comprehensive evaluation values, toxicity, degradation, mobility and bioconcentration of molecules were analysed.

Environmental neglect: endocrine disruptors as underappreciated but potentially modifiable diabetes risk factors

Type 2 diabetes prevalence is increasing dramatically across the globe, imposing a tremendous toll on individuals and healthcare systems. Reversing these trends requires comprehensive approaches to address both classical and emerging diabetes risk factors. Recently, environmental toxicants acting as endocrine-disrupting chemicals (EDCs) have emerged as novel metabolic disease risk factors. EDCs implicated in diabetes pathogenesis include various inorganic and organic molecules of both natural and synthetic origin, including arsenic, bisphenol A, phthalates, polychlorinated biphenyls and organochlorine pesticides. Indeed, evidence implicates EDC exposures across the lifespan in metabolic dysfunction; moreover, specific developmental windows exhibit enhanced sensitivity to EDC-induced metabolic disruption, with potential impacts across generations. Importantly, differential exposures to diabetogenic EDCs likely also contribute to racial/ethnic and economic disparities. Despite these emerging links, clinical practice guidelines fail to address this underappreciated diabetes risk factor. Comprehensive approaches to stem the tide of diabetes must include efforts to address its environmental drivers.

Tissue-specific changes in Srebf1 and Srebf2 expression and DNA methylation with perinatal phthalate exposure

Perinatal exposure to endocrine disrupting chemicals negatively impacts health, but the mechanism by which such toxicants damage long-term reproductive and metabolic function is unknown. Lipid metabolism plays a pivotal role in steroid hormone synthesis as well as energy utilization and storage; thus, aberrant lipid regulation may contribute to phthalate-driven health impairments. In order to test this hypothesis, we specifically examined epigenetic disruptions in lipid metabolism pathways after perinatal phthalate exposure. During gestation and lactation, pregnant Long-Evans rat dams were fed environmentally relevant doses of phthalate mixture: 0 (CON), 200 (LO), or 1000 (HI) µg/kg body weight/day. On PND90, male offspring in the LO and HI groups had higher body weights than CON rats. Gene expression of lipid metabolism pathways was altered in testis and adipose tissue of males exposed to the HI phthalate dosage. Specifically, Srebf1 was downregulated in testis and Srebf2 was upregulated in adipose tissue. In testis of HI rats, DNA methylation was increased at two loci and reduced at one other site surrounding Srebf1 transcription start site. In adipose tissue of HI rats, we observed increased DNA methylation at one region within the first intron of Srebf2. Computational analysis revealed several potential transcriptional regulator binding sites, suggesting functional relevance of the identified differentially methylated CpGs. Overall, we show that perinatal phthalate exposure affects lipid metabolism gene expression in a tissue-specific manner possibly through altering DNA methylation of Srebf1 and Srebf2.

Chromatin dynamics underlying latent responses to xenobiotics

Pleiotropic xenobiotics can trigger dynamic alterations in mammalian chromatin structure and function but many of these are likely non-adverse and simply reflect short-term changes in DNA transactions underlying normal homeostatic, adaptive and protective cellular responses. However, it is plausible that a subset of xenobiotic-induced perturbations of somatic tissue or germline epigenomes result in delayed-onset and long-lasting adverse effects, in particular if they occur during critical stages of growth and development. These could include reprogramming, dedifferentiation, uncontrolled growth, and cumulative toxicity effects through molecular memory of prior xenobiotic exposures or altered susceptibility to subsequent xenobiotic exposures. Here we discuss the current evidence for epigenetic mechanisms underlying latent responses to xenobiotics, and the potential for identifying molecular epigenetic changes that are prodromal to overt morphologic or functional toxicity phenotypes.

DNA methylation of imprinted genes in Mexican-American newborn children with prenatal phthalate exposure

AIM

Imprinted genes exhibit expression in a parent-of-origin-dependent manner and are critical for child development. Recent limited evidence suggests that prenatal exposure to phthalates, ubiquitous endocrine disruptors, can affect their epigenetic dysregulation.

MATERIALS & METHODS

We quantified DNA methylation of nine imprinted gene differentially methylated regions by pyrosequencing in 296 cord blood DNA samples in a Mexican-American cohort. Fetal exposure was estimated by phthalate metabolite concentrations in maternal urine samples during pregnancy.

RESULTS

Several differentially methylated regions of imprinted genes were associated with high molecular weight phthalates. The most consistent, positive, and false discovery rate significant associations were observed for MEG3.

CONCLUSION

Phthalate exposure in utero may affect methylation status of imprinted genes in newborn children.

Urinary 1-hydroxypyrene and smoking are determinants of LINE-1 and AhRR promoter methylation in coke oven workers

Coke oven emissions (COE) containing polycyclic aromatic hydrocarbons (PAHs) are predominant toxic constituents of particulate air pollution that have been linked to increased risk of lung cancer. Aberrant DNA methylation is one of the best known epigenetic changes in human cancers and healthy subjects exposed to carcinogens. The purpose of this study is to explore the factors influencing the methylation of long interspersed nuclear element-1 (LINE-1) and aryl-hydrocarbon receptor repressor (AhRR) in coke oven workers. The study population is composed by coke oven workers (348) and water treatment workers (131). And their urinary PAH metabolites were analyzed by high performance liquid chromatography; DNA methylation were measured by pyrosequencing. The urinary PAHs metabolites were significantly elevated in coke oven workers (P < 0.01). The results from multivariate logistic regression analysis showed that a high level of urinary 1-hydroxypyrene was associated with a significantly increased risk of hypomethylation of LINE-1 (OR: 1.80; 95% CI: 1.25, 2.60), and heavy smoking was associated with a significantly increased risk of hypomethylation of AhRR (OR: 1.44; 95% CI: 1.04, 2.00). Our findings demonstrate that urinary 1-hydroxypyrene may be a useful biomarker for evaluating the role of PAHs exposure on hypomethylation of LINE-1 among coke oven workers and that smoking may be an important factor affecting hypomethylation of AhRR.

Defining baseline epigenetic landscapes in the rat liver

Aim

Characterization of the hepatic epigenome following exposure to chemicals and therapeutic drugs provides novel insights into toxicological and pharmacological mechanisms, however appreciation of genome-wide inter- and intra-strain baseline epigenetic variation, particularly in under-characterized species such as the rat is limited.

Material & methods

To enhance the utility of epigenomic endpoints safety assessment, we map both DNA modifications (5-methyl-cytosine and 5-hydroxymethyl-cytosine) and enhancer related chromatin marks (H3K4me1 and H3K27ac) across multiple male and female rat livers for two important outbred laboratory rat strains (Sprague–Dawley and Wistar).

Results & conclusion

Integration of DNA modification, enhancer chromatin marks and gene expression profiles reveals clear gender-specific chromatin states at genes which exhibit gender-specific transcription. Taken together this work provides a valuable baseline liver epigenome resource for rat strains that are commonly used in chemical and pharmaceutical safety assessment.

Low level of mono(2-ethylhexyl) phthalate reduces oocyte developmental competence in association with impaired gene expression

Di-(2-ethylhexyl) phthalate (DEHP) and its metabolite, mono-(2-ethylhexyl) phthalate (MEHP), are reproductive toxicants. However, disruptive effects of MEHP at low concentrations on the oocyte and developing blastocyst are unknown. Previously, we detected low levels of MEHP in follicular fluid aspirated from DEHP-treated cows associated with reduced estradiol levels. Moreover, the MEHP concentrations found were similar to those reported for follicular fluid aspirated from women who have undergone IVF cycles. In the current study, we used an in vitro embryo production model to examine the effect of MEHP at low levels on oocyte developmental competence. We set up several experiments to mimic the follicular fluid content, i.e., low MEHP level and low estradiol. For all experiments, cumulus oocyte complexes (COCs) were aspirated from bovine ovaries, then matured in vitro in standard oocyte maturation medium (OMM) supplemented with: MEHP at a range levels (20-1000nM) or with estradiol at a range levels (0-2000ng/ml). Then, oocytes were fertilized and cultured for an additional 7days to allow blastocyst development. Findings revealed that MEHP at low levels impairs oocyte developmental competence in a dose-dependent manner (P<0.05) and that estradiol by itself does not impair it. Accordingly, in another set of experiments, COCs were matured in vitro with MEHP at two choosen concentrations (20 or 1000nM) with or without estradiol, fertilized and cultured for 7days. Samples of mature oocytes and their derived blastocysts were subjected to quantitative real-time PCR to examine the profiles of selected genes (CYC1, MT-CO1, ATP5B, POU5F1, SOX2 and DNMT3b). Maturation of COCs with MEHP (20 or 1000nM) affected gene expression in the mature oocyte. Maturation of COCs with MEHP (20 or 1000nM) in the absence of estradiol reduced oocyte developmental competence (P<0.05). A differential carryover effect on transcript abundance was recorded in blastocysts developed from MEHP-treated oocytes. In the presence of estradiol, increased expression was recorded for CYC1, ATP5B, SOX2 and DNMT3b. In the absence of estradiol, decreased expression was recorded, with a significant effect for 1000nM MEHP (P<0.05). Taken together, the findings suggest that low levels of phthalate must be taken into consideration in risk assessments.

Maternal phthalate exposure during pregnancy is associated with DNA methylation of LINE-1 and Alu repetitive elements in Mexican-American children

Phthalates are frequently used in personal care products and plasticizers and phthalate exposure is ubiquitous in the US population. Exposure to phthalates during critical periods in utero has been associated with a variety of adverse health outcomes but the biological mechanisms linking these exposures with disease are not well characterized. In this study, we examined the relationship of in utero phthalate exposure with repetitive element DNA methylation, an epigenetic marker of genome instability, in children from the longitudinal birth cohort CHAMACOS. Methylation of Alu and long interspersed nucleotide elements (LINE-1) was determined using pyrosequencing of bisulfite-treated DNA isolated from whole blood samples collected from newborns and 9 year old children (n=355). Concentrations of eleven phthalate metabolites were measured in urine collected from pregnant mothers at 13 and 26 weeks gestation. We found a consistent inverse association between prenatal concentrations of monoethyl phthalate, the most frequently detected urinary metabolite, with cord blood methylation of Alu repeats (β(95%CI): -0.14 (-0.28,0.00) and -0.16 (-0.31, -0.02)) for early and late pregnancy, respectively, and a similar but weaker association with LINE-1 methylation. Additionally, increases in urinary concentrations of di-(2-ethylhexyl) phthalate metabolites during late pregnancy were associated with lower levels of methylation of Alu repeats in 9 year old blood (significant p-values ranged from 0.003 to 0.03). Our findings suggest that prenatal exposure to some phthalates may influence differences in repetitive element methylation, highlighting epigenetics as a plausible biological mechanism through which phthalates may affect health.

Role of fumonisin B1 on DNA methylation changes in rat kidney and liver cells

CONTEXT

Fumonisin B1 (FB1) is a mycotoxin produced by Fusarium verticillioides (Sacc.) Nirenberg (Nectriaceae) mold that contaminates maize and other agricultural products. Although the effects of FB1 on sphingolipid metabolism are clear, little is known about early molecular changes associated with FB1 carcinogenicity.

OBJECTIVE

Alteration on DNA methylation, as an early event in non-genotoxic carcinogenesis, may play an important role in the mechanism of FB1 toxiciy.

MATERIALS AND METHODS

Dose-related effects of FB1 (1-50 µM for 24 h) on global DNA methylation by using high-performance liquid chromatography with UV-diode array detection (HPLC-UV/DAD) and CpG promoter methylation by methylation-specific PCR (MSP) were performed in rat liver (Clone 9) and rat kidney (NRK-52E) epithelial cells.

RESULTS

Cell viability reduction is 39% and 34% by the XTT test and LDH release in the growth medium is 32% and 26% at 200 µM of FB1 treatment in Clone 9 and NRK-52E cells, respectively. No significant dose-related effects of FB1 on global DNA methylation which ranged from 4 to 5% were observed in both cells compared with controls. Promoter regions of c-myc gene were methylated (>33%) at 10 and 50 µM of FB1 treatment in Clone 9 cells while it was unmethylated in NRK-52E cells. Promoter regions of p15 gene were unmethylated while VHL gene were found to be methylated (>33%) at 10, 25, and 50 µM and 10 and 50 µM of FB1 treatment in Clone 9 and NRK-52E cells, respectively.

DISCUSSION AND CONCLUSION

Alteration in DNA methylation might play an important role in the toxicity of FB1 in risk assessment process.

The combined effects of DEHP and PCBs on phospholipase in the livers of mice

Di(2-ethylhexyl) phthalate (DEHP) and polychlorinated biphenyls (PCBs) are two widely distributed pollutants that are of great concern due to their adverse health effects. However, few studies have investigated the combined effects of DEHP and PCBs. In this study, adult mice were continuously exposed to mixtures of DEHP (15 mg/kg bodyweight/day) and Aroclor 1254 (7.5 mg/kg bodyweight/day) for 12 days to investigate the combined effects of these compounds. The results showed that the ratio of the liver weight to the body weight was higher in the treated group than that in the control group. The effects of combined exposure on three important receptors, the proliferator-activated receptor (PPAR), estrogen receptor (ER), and aryl hydrocarbon receptor (AHR), were investigated. The mRNA level of PPARγ was significantly up-regulated after exposure. The expression level of ERα was decreased in the male treated group. In contrast, the expression levels of AHR and related genes (cyp1a1 and cyp1b1) were not markedly affected. The expression level of phospholipase A (PLA) was significantly down-regulated at both the mRNA and protein levels in male mice after combined treatment. In all, our study demonstrated the combined effects of DEHP and PCBs on the expression levels of key receptors in mice. The combined exposure led to a decrease in phospholipase in male mice.

Aging and DNA methylation

In this Opinion article, we summarize how changes in DNA methylation occur during aging in mammals and discuss examples of how such events may contribute to the aging process. We explore mechanisms that could facilitate DNA methylation changes in a site-specific manner and highlight a model in which region-specific DNA hypermethylation during aging is facilitated in a competitive manner by destabilization of the Polycomb repressive complex.

Changes of c-Myc and DNMT1 mRNA and protein levels in the rat livers induced by dibutyl phthalate treatment

We investigated the relationship between dibutyl phthalate (DBP)-induced hypomethylation of the c-Myc promoter region (as evident in our early study) and the expression of c-Myc and DNMT1 genes (at messenger RNA (mRNA) and protein level) in the rat liver. Male Wistar rats received DBP in 1, 3, or 14 daily doses of 1800 mg kg−1 body weight. Levels of DNMT1, c-Myc mRNA, and proteins were detected using real-time polymerase chain reaction and Western blot analysis, respectively. Our findings indicate that DBP caused an increase in mRNA levels of c-Myc at all time points. The results showed that protein levels of c-Myc in rat liver also increased significantly by DBP treatment, which were more pronounced at last time point (after 14 doses). Furthermore, overexpression of DNMT1gene have been found after one dose of DBP, which was confirmed at the protein level by Western blot analysis. Reduced levels of DNMT1mRNA and proteins (3 and 14 doses) were coordinated with depletion DNA synthesis (reported previously). Based on our previous results and those presented here, the following conclusion could be drawn: (1) DBP exerted biological activity through epigenetic modulation of c-Myc gene expression; (2) it seems possible that DBP-induced active demethylation of c-Myc gene through mechanism(s) linked to generation of reactive oxygen species by activated c-Myc; and (3) control of DNA replication was not directly dependent on c-Myc transcriptional activity and we attribute this finding to DNMT1gene expression which was tightly coordinated with DNA synthesis.

Global and MGMT promoter hypomethylation independently associated with genomic instability of lymphocytes in subjects exposed to high-dose polycyclic aromatic hydrocarbon

Global hypomethylation, gene-specific methylation, and genome instability are common events in tumorigenesis. To date, few studies have examined the aberrant DNA methylation patterns in coke oven workers, who are highly at risk of lung cancer by occupational exposure to polycyclic aromatic hydrocarbons (PAHs). We recruited 82 PAH-exposed workers and 62 unexposed controls, assessed exposure levels by urinary 1-hydroxypyrene, and measured genetic damages by comet assay, bleomycin sensitivity, and micronucleus assay. The PAHs in coke oven emissions (COE) were estimated based on toxic equivalency factors. We used bisulfite-PCR pyrosequencing to quantitate DNA methylation in long interspersed nuclear element-1 (LINE-1) and O(6)-methylguanine-DNA methyltransferase (MGMT). Further, the methylation alteration was also investigated in COE-treated human bronchial epithelial (16HBE) cells. We found there are higher levels of PAHs in COE. Among PAH-exposed workers, LINE-1 and MGMT methylation levels (with CpG site specificity) were significantly lowered. LINE-1, MGMT, and its hot CpG site-specific methylation were negatively correlated with urinary 1-hydroxypyrene levels (r = -0.329, p < 0.001; r = -0.164, p = 0.049 and r = -0.176, p = 0.034, respectively). In addition, LINE-1 methylation was inversely associated with comet tail moment and micronucleus frequency, and a significant increase of micronucleus in low MGMT methylation group. In vitro study revealed that treatment of COE in 16HBE cells resulted in higher production of BPDE-DNA adducts, LINE-1 hypomethylation, hypomethylation, and suppression of MGMT expression. These findings suggest hypomethylation of LINE-1 and MGMT promoter could be used as markers for PAHs exposure and merit further investigation.

DNA methylome alterations in chemical carcinogenesis

Carcinogenesis, a complex multifactorial process of the transformation of normal cells into malignant cells, is characterized by many biologically significant and interdependent alterations triggered by the mutational and/or non-mutational (i.e., epigenetic) events. One of these events, specific to all types of cancer, is alterations in DNA methylation. This review summarizes the current knowledge of the role of DNA methylation changes induced by various genotoxic chemicals (carcinogenic agents that interact with DNA) and non-genotoxic carcinogens (chemicals causing tumor by mechanisms other than directly damaging DNA) in the lung, colorectal, liver, and hematologic carcinogenesis. It also emphasizes the potential role for epigenetic changes to serve as markers for carcinogen exposure and carcinogen risk assessment.

Applications of metabolomics for understanding the action of peroxisome proliferator-activated receptors (PPARs) in diabetes, obesity and cancer

The peroxisome proliferator-activated receptors (PPARs) are a set of three nuclear hormone receptors that together play a key role in regulating metabolism, particularly the switch between the fed and fasted state and the metabolic pathways involving fatty-acid oxidation and lipid metabolism. In addition, they have a number of important developmental and regulatory roles outside metabolism. The PPARs are also potent targets for treating type II diabetes, dyslipidemia and obesity, although a number of individual agonists have also been linked to unwanted side effects, and there is a complex relationship between the PPARs and the development of cancer. This review examines the part that metabolomics, including lipidomics, has played in elucidating the roles PPARs have in regulating systemic metabolism, as well as their role in aspects of drug-induced cancer and xenobiotic metabolism. These studies have defined the role PPARδ plays in regulating fatty-acid oxidation in adipose tissue and the interaction between aging and PPARα in the liver. The potential translational benefits of these approaches include widening the role of PPAR agonists and improved monitoring of drug efficacy.

MicroRNA dysregulation during chemical carcinogenesis

MicroRNAs, potent negative modulators of gene expression, are involved in the regulation of fundamental cellular processes, including cell differentiation, metabolic regulation, signal transduction, cell proliferation and apoptosis. Aberrant levels of miRNAs have been documented in all major human cancers, leading to the suggestion that deregulation of miRNA expression might be significant in tumorigenesis. This review presents the current evidence that demonstrates the involvement of miRNA deregulation in the early stages of lung, liver and breast carcinogenesis induced by chemical carcinogens, suggesting their major role as contributors to the pathogenesis of cancer.

Perfluorooctanoic acid (PFOA) acts as a tumor promoter on Syrian hamster embryo (SHE) cells

Perfluorooctane sulfonate (PFOS) (C(8)F(17)SO(3)) and perfluorooctanoic acid (PFOA) (C(8)HF(15)O(2)) are synthetic chemicals widely used in industrial applications for their hydrophobic and oleophobic properties. They are persistent, bioaccumulative, and toxic to mammalian species. Their widespread distribution on earth and contamination of human serum raised concerns about long-term side effects. They are suspected to be carcinogenic through a nongenotoxic mode of action, a mechanism supported by recent findings that PFOS induced cell transformation but no genotoxicity in Syrian hamster embryo (SHE) cells. In the present study, we evaluated carcinogenic potential of PFOA using the cell transformation assay on SHE cells. The chemical was applied alone or in combination with a nontransformant concentration of benzo[a]pyrene (BaP, 0.4 μM) in order to detect PFOA ability to act as tumor initiator or tumor promoter. The results showed that PFOA tested alone in the range 3.7 × 10(-5) to 300 μM did not induce SHE cell transformation frequency in a 7-day treatment. On the other side, the combination BaP/PFOA induced cell transformation at all PFOA concentrations tested, which revealed synergistic effects. No genotoxicity of PFOA on SHE cells was detected using the comet assay after 5 and 24 h of exposure. No significant increase in DNA breakage was found in BaP-initiated cells exposed to PFOA in a 7-day treatment. The whole results showed that PFOA acts as a tumor promoter and a nongenotoxic carcinogen. Cell transformation in initiated cells was observed at concentrations equivalent to the ones found in human serum of nonoccupationally and occupationally exposed populations. An involvement of PFOA in increased incidence of cancer recorded in occupationally exposed population cannot be ruled out.

Interstrain differences in the liver effects of trichloroethylene in a multistrain panel of inbred mice

Trichloroethylene (TCE) is a widely used industrial chemical and a common environmental contaminant. It is a well-known carcinogen in rodents and a probable carcinogen in humans. Studies utilizing panels of mouse inbred strains afford a unique opportunity to understand both metabolic and genetic basis for differences in responses to TCE. We tested the hypothesis that strain- and liver-specific toxic effects of TCE are genetically controlled and that the mechanisms of toxicity and susceptibility can be uncovered by exploring responses to TCE using a diverse panel of inbred mouse strains. TCE (2100 mg/kg) or corn oil vehicle was administered by gavage to 6- to 8-week-old male mice of 15 mouse strains. Serum and liver were collected at 2, 8, and 24 h postdosing and were analyzed for TCE metabolites, hepatocellular injury, and gene expression of liver. TCE metabolism, as evident from the levels of individual oxidative and conjugative metabolites, varied considerably between strains. TCE treatment-specific effect on the liver transcriptome was strongly dependent on genetic background. Peroxisome proliferator-activated receptor-mediated molecular networks, consisting of the metabolism genes known to be induced by TCE, represent some of the most pronounced molecular effects of TCE treatment in mouse liver that are dependent on genetic background. Conversely, cell death, liver necrosis, and immune-mediated response pathways, which are altered by TCE treatment in liver, are largely genetic background independent. These studies provide better understanding of the mechanisms of TCE-induced toxicity anchored on metabolism and genotype-phenotype correlations that may define susceptibility or resistance.

Global DNA hypomethylation is associated with in utero exposure to cotinine and perfluorinated alkyl compounds

Environmental exposures in-utero may alter the epigenome, thus impacting chromosomal stability and gene expression. We hypothesized that in utero exposures to maternal smoking and perfluoroalkyl compounds (PFCs) are associated with global DNA hypomethylation in umbilical cord serum. Our objective was to determine if global DNA methylation could be used as a biomarker of in utero exposures to maternal smoking and PFCs. Using an ELISA-based method, global DNA methylation was quantified in umbilical cord serum from 30 newborns with high (> 10 ng/ml, mean 123.8 ng/ml), low (range 1-10 ng/ml, mean 1.6 ng/ml) and very low (< 1 ng/ml, mean 0.06 ng/ml) cord serum cotinine levels. Y chromosome analysis was performed to rule out maternal DNA cross-contamination. Cord serum global DNA methylation showed an inverse dose response to serum cotinine levels (p< 0.001). Global DNA methylation levels in cord blood were the lowest among newborns with smoking mothers (mean=15.04%; 95% CI, 8.4, 21.7) when compared to babies of mothers who were second-hand smokers (21.1%; 95% CI, 16.6, 25.5) and non-smokers (mean=29.2%; 95% CI, 20.1, 38.1). Global DNA methylation was inversely correlated with serum PFOA (r= -0.72, p < 0.01) but not PFOS levels. Serum Y chromosome analyses did not detect maternal DNA cross-contamination. This study supports the use of global DNA methylation status as a biomarker of in utero exposure to cigarette smoke and PFCs.

Dynamic effect of di-2-(ethylhexyl) phthalate on testicular toxicity: epigenetic changes and their impact on gene expression

This study investigated epigenetic (specifically, DNA methylation) changes and their impact on gene expression in testes induced by maternal exposure to Di-2-(ethylhexyl) phthalate (DEHP) in mice. Testicular dysgenesis syndrome was induced in fetuses and pups by maternal exposure to DEHP at 500 mg/kg/d, and testes were excised for analysis on gestation day (GD) 19 and postnatal days (PNDs) 3, 21, 56, and 90. High-performance liquid chromatography (HPLC) was performed to analyze DNA methylation status, and expression levels of the DNA methyltransferases were examined by quantitative real-time polymerase chain reaction (qPCR). Testis-specific gene, insulin-like hormone 3 (Insl3), and testosterone production were also detected. DEHP significantly increased DNA methylation levels on GD 19 and PND 3 (P < .05 and P < .05) but not on PNDs 21, 56, and 90. DEHP also significantly increased the expression of DNA methyltransferases. For DNA methyltransferase 1, the difference was not significant on PND 21, and DNA methyltransferase 3a and 3b returned to normal levels on PND 56. Fetal testes were a main target for DEHP as evidenced by a reduction in Insl3 expression and testosterone production. Effects of DEHP on Insl3 expression continued until PND 21. The DEHP-induced suppression of testosterone had not recovered on PND 56. Changes in DNA methylation may play an important role in abnormal testicular function caused by environmental factors such as maternal exposure to DEHP, which may be a mechanism of DEHP-mediated testicular toxicity.

Alterations in tumor biomarker GSTP gene methylation patterns induced by prenatal exposure to PFOS

The adverse environmental exposure in early life may have adverse effects on animals through epigenetic aspects. The current study examined the possibility of early epigenetic alteration in PFOS-exposed rat liver. Pregnant Sprague-Dawley (SD) rats were exposed to perfluorooctane sulfonate (PFOS) at doses of 0.1, 0.6 and 2.0 mg/kg/d and 0.05% Tween 80 as control by gavage from gestation days 2 to 21. The dams were allowed to give birth and liver samples from weaned (postnatal day 21) offspring rats were analyzed for PFOS content, relative liver weight, global DNA methylation, methylation of LINE-1 regulatory region, tumor suppressor gene glutathione S-transferase pi (GSTP) and p16 promoter methylation level, as well as related genes expression level. In PFOS-exposed weaned rats, compared to the control, global DNA methylation and methylation of LINE-1 regulatory region decreased significantly only in the 2.0 mg/kg/d group. Up to 30% of critical CpG sites (+79, 81 and 84) in GSTP promoter region were methylated in the livers of PFOS-treated rats, while p16 promoter methylation was not affected. In addition, the up-regulated expression of GSTP was observed and this increase was associated with its main pathway of transcription regulation: Keap1-Nrf2/MafK. Thus, early-induced changes in critical cytosines within the GSTP gene promoter region may be a biomarker of hepatic PFOS burden, though their direct role in PFOS-induced hepatotoxicity, including its potential carcinogenic action, needs further research.

Di-butyl phthalate-induced hypomethylation of the c-myc gene in rat liver

Peroxisome proliferators (PPs)-induced DNA hypomethylation has been proposed as a mechanism of their toxicity, including carcinogenic action. The effect of di-butyl phthalate (DBP), a known peroxisome proliferators, on the methylation level of the c-myc promoter region in rat liver was studied. Changes in the methylation status of the c-myc gene were correlated with changes in DNA synthesis, DNA methyltransferase (DNMTs) activity and liver weight. Male Wistar rats received DBP in one, three or fourteen daily oral doses of 1800 mg/kg body weight (b.w.) x day(-1) (this dose is close to the dose that increases the numbers of peroxisomes in male Wistar rats). We have demonstrated that DBP decreased the methylation of the c-myc gene. Cytosine hypomethylation in the analyzed CpG sites of the c-myc gene promoter occurred during the whole period of study, although after 14 doses of DBP the difference from control was only on the borderline of significance (p = 0.066). An increase in DNA synthesis was only observed after 24 hours of treatment with DBP, and it preceded liver growth. We hypothesize that DBP-induced demethylation of the c-myc gene was an active mechanism, not associated with DNMTs activity and DNA replication.

A comparison of the cytogenetic alterations and global DNA hypomethylation induced by the benzene metabolite, hydroquinone, with those induced by melphalan and etoposide

Specific cytogenetic alterations and changes in DNA methylation are involved in leukemogenesis. Benzene, an established human leukemogen, is known to induce cytogenetic changes through its active metabolites including hydroquinone (HQ), but the specific alterations have not been fully characterized. Global DNA hypomethylation was reported in a population exposed to benzene, but has not been confirmed in vitro. In this study, we examined cytogenetic changes in chromosomes 5, 7, 8, 11 and 21, and global DNA methylation in human TK6 lymphoblastoid cells treated with HQ for 48 h, and compared the HQ-induced alterations with those induced by two well-known leukemogens, melphalan, an alkylating agent, and etoposide, a DNA topoisomerase II inhibitor. We found that rather than inducing cytogenetic alterations distinct from those induced by melphalan and etoposide, HQ induced alterations characteristic of each agent. HQ induced global DNA hypomethylation at a level intermediate to melphalan (no effect) and etoposide (potent effect). These results suggest that HQ may act similar to an alkylating agent and also similar to a DNA topoisomerase II inhibitor in living cells, both of which may be potential mechanisms of benzene toxicity. In addition to cytogenetic changes, global DNA hypomethylation may be another mechanism underlying the leukemogenicity of benzene.

Functional role of phospholipase D (PLD) in di(2-ethylhexyl) phthalate-induced hepatotoxicity in Sprague-Dawley rats

Phospholipase D (PLD) is an enzyme that catalyzes the hydrolysis of phosphatidyl choline (PC) to generate phosphatidic acid (PA) and choline. PLD is believed to play an important role in cell proliferation, survival signaling, cell transformation, and tumor progression. However, it remains to be determined whether enhanced expression of PLD in liver is sufficient to induce hepatotoxicity. The aim of this study was to investigate the possible role of PLD in di(2-ethylhexyl) phthalate (DEHP)-induced hepatotoxicity in Sprague-Dawley rats. The phthalate, DEHP (500 mg/kg/d), was administered orally, daily to prepubertal rats (4 wk of age, weighing approximately 70-90 g) for 1, 7, or 28 d. In this study, protein expression levels of PLD1/2, peroxisome proliferator-activated receptor (PPAR), and cytochrome P-450 (CYP) were determined by Western blot analysis using specific antibodies. Liver weight was significantly increased in the DEHP treatment groups. Immunohistochemical analysis demonstrated that DEHP produced strong staining of proliferating cell nuclear antigen (PCNA) at 28 d of exposure, suggestive of hepatocyte proliferation. A significant rise in PLD1/2 expression was observed in liver of DEHP-exposed rats after 7 d. Further, PPARα, constitutive androstane receptor (CAR), pregnane X receptor (PXR), and CYP2B1 protein expression levels were markedly elevated in DEHP-treated groups. Our results suggest that DEHP significantly enhanced the expression of PLD, which may be correlated with PPARα-induced hepatotoxicity through a complex interaction with nuclear receptors including CAR and PXR.

DNA hypomethylation induced by tributyltin, triphenyltin, and a mixture of these in Sebastiscus marmoratus liver

Tributyltin (TBT) and triphenyltin (TPT) coexist in freshwater and marine environments. However, the effects of TBT, TPT, and a mixture of the two on DNA methylation in marine fish livers and the mechanism involved remain to be elucidated. Previous study have proved that abnormal methylation patterns are induced by the balance of transmethylation reaction including the tissue level of S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH) or the activity of DNA (cytosine-5) methyltransferase 1 (DNMT1). Therefore, in the present study, we assessed their ability to cause hepatic DNA hypomethylation in Sebastiscus marmoratus liver and the related mechanism. The results showed that TBT, TPT, and a mixture of the two significantly induced DNA hypomethylation in the fish livers in a dose-dependent manner. Using Pearson correlation coefficient analysis, we identified strong linear correlations between S-adenosylhomocysteine, S-adenosylmethionine, or the SAM to SAH ratio and the hepatic genome-wide 5-methylcytosine content of the DNA, but no correlation between the latter and the DNMT1 expression level. It is therefore proposed that the organotins hypomethylation induced in the marine fish livers was due to altering the balance of the substrate and the product in transmethylation reactions.

Vitamin C and resveratrol supplementation to rat dams treated with di(2-ethylhexyl)phthalate: impact on reproductive and oxidative stress end points in male offspring

This study was carried out to assess the influence of di(2-ethylhexyl)phthalate (DEHP) alone or associated with antioxidants on the male reproductive system in newborn rats, emphasizing the implications of oxidative stress and hormonal balance during prenatal and early postnatal periods. Wistar females were exposed by oral route to DEHP alone or associated with antioxidants from gestational day 7 to lactational day 2 according to the following treatment regimens: (C) vehicle control (canola oil + 1% Tween-80); (V) vitamin C (200 mg/kg) + canola oil; (R) resveratrol (10 mg/kg) + canola oil; (D) DEHP (500 mg/kg) + 1% Tween-80; (DV) DEHP (500 mg/kg) + vitamin C (200 mg/kg); and (DR) DEHP (500 mg/kg) + resveratrol (10 mg/kg). Two male pups per litter were randomly selected and necropsied on postnatal day 2. The brain and liver were removed and weighed and anogenital distance (AGD) was measured. Additionally, the testes were removed for assessment of intratesticular testosterone levels and histopathology; the liver was used to measure biomarkers of oxidative stress. Vitamin C and resveratrol alone did not affect the reproductive end points and did not induce oxidative stress. Exposure of dams to DEHP alone and associated with antioxidants resulted in hepatomegaly in offspring and significantly increased the incidence of multinucleated gonocytes in seminiferous cords. Testosterone and AGD presented a trend to decrease in DEHP-exposed groups. Catalase activity increased only in groups exposed to DEHP associated with antioxidants, although GST (gluthatione-S-transferase) activity decreased in all DEHP-exposed groups. The levels of hydroperoxides increased only in group exposed to DEHP associated with vitamin C. These results indicate that the association of DEHP with antioxidants was unable to ameliorate DEHP-induced reproductive changes, and the coadministration of DEHP and these antioxidants might even contribute to an overall increase in oxidative stress.

Role of DNA damage and alterations in cytosine DNA methylation in rat liver carcinogenesis induced by a methyl-deficient diet

Currently, cancer is recognized as a disease provoked by both genetic and epigenetic events. However, the significance of early genetic and epigenetic alterations with respect to carcinogenic process in general and to liver carcinogenesis in particular remains unexplored. A lack of knowledge regarding how specific alterations during early preneoplasia may be mechanistically related to tumor formation creates a major gap in understanding the role of these genetic and epigenetic abnormalities in carcinogenesis. In the present study we investigated the contribution of DNA damage and epigenetic alterations to liver carcinogenesis induced by a methyl-deficient diet. Feeding Fisher 344 rats a methyl-deficient diet for 9 weeks resulted in DNA damage and aberrant DNA methylation. This was evidenced by an early up-regulation of the base excision DNA repair genes, accumulation of 8-oxodeoxyguanosine and 3'OH-end strand breaks in DNA, pronounced global loss of DNA methylation, and hypermethylation of CpG islands in the livers of methyl-deficient rats. These abnormalities were completely restored in the livers of rats exposed to methyl-deficiency for 9 weeks after removal of the methyl-deficient diet and re-feeding a methyl-sufficient diet. However, when rats were fed a methyl-deficient diet for 18 week and then given a methyl-sufficient diet, only DNA lesions were repaired. The methyl-sufficient diet failed to restore completely the altered DNA methylation status and prevent the progression of liver carcinogenesis. These results suggest that stable alterations in DNA methylation are a factor that promotes the progression of liver carcinogenesis. Additionally, the results indicate that epigenetic changes may be more reliable markers than DNA lesions of the carcinogenic process and carcinogen exposure.