DNA hypomethylation induced by drinking water disinfection by-products in mouse and rat kidney

Dichloroacetic acid and trichloroacetic acid as disinfection by-products in drinking water are endocrine-disrupting chemicals

Dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) are two typical non-volatile disinfection by-products (DBPs) found in drinking water. Increasing evidence has demonstrated that they show reproductive toxicity. However, whether they might have endocrine disrupting properties remains largely unknown. To discover this, we treated male mice or pregnant mice with 0, 1-, 102-, 103-, 104-, or 5 × 104-fold maximal concentration level (MCL) of DCAA or TCAA in drinking water. In male mice, the levels of testosterone in serum and androgen receptor (AR) in testis were declined with ≥ 103-fold MCL of DCAA (26.4 mg/kg/d) or TCAA (52.7 mg/kg/d). In pregnant mice, miscarriage rates were increased with ≥ 104-fold MCL of DCAA (264 mg/kg/d) or ≥ 103-fold MCL of TCAA. The levels of FSH in serum were increased and those of estradiol and progesterone were reduced with ≥ 103-fold MCL of DCAA or TCAA. The protein levels of estrogen receptors (ERα and ERβ) in ovary were reduced with ≥ 102-fold MCL of DCAA (2.64 mg/kg/d) or TCAA (5.27 mg/kg/d). Exposure to some certain fold MCL of DCAA or TCAA also altered the protein levels of ERα and ERβ in uterus and placenta. Exposure to 5 × 104-fold MCL of both DCAA and TCAA showed the combined effects. Therefore, both DCAA and TCAA could be considered as novel reproductive endocrine disrupting chemicals, which might be helpful for further assessment of the toxicological effects of DCAA and TCAA and the awareness of reproductive endocrine disrupting properties caused by DCAA and TCAA in drinking water.

Exposures to drinking water disinfection byproducts and kidney function in Chinese women

BACKGROUND

Disinfection byproducts (DBPs), the ubiquitous contaminants in drinking water, have been shown to impair renal function in experimental studies. However, epidemiological evidence is sparse.

OBJECTIVE

To investigate exposures to DBPs in associations with renal function among women.

METHODS

A total of 920 women from December 2018 to January 2020 were abstracted from the Tongji Reproductive and Environmental (TREE) Study, an ongoing cohort study in Wuhan, China. Urine samples were gathered at baseline recruitment and analyzed for dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) as biomarkers of DBP exposures. Serum uric acid (UA), creatinine, and estimated glomerular filtration rate (eGFR) were measured as indicators of renal function. Multivariate linear regression and restricted cubic spline (RCS) models were conducted to assess urinary DCAA and TCAA concentrations in associations with renal function indicators. Stratified analyses by age and body mass index (BMI) were also performed.

RESULTS

We found null evidence of urinary TCAA in associations with renal function indicators. However, elevated urinary DCAA tertiles were related to decreased eGFR (β = -1.78%, 95% CI: 3.21%, -0.36%, comparing the upper vs. lower tertile; P for trend = 0.01). This inverse association still existed when urinary DCAA concentration was treated as a continuous variable, and the dose-response relationship was linear based on the RCS model (P for overall association = 0.002 and P for non-linear associations = 0.44). In the stratified analyses, we found an association of urinary DCAA concentration with decreased UA level among women <30 years but an association with increased UA level among women ≥30 years (P for interaction = 0.04).

CONCLUSION

Urinary DCAA but not TCAA was associated with impaired renal function among women undergoing assisted reproductive technology.

Impacts of disinfection byproduct exposures on male reproductive health: Current evidence, possible mechanisms and future needs

Disinfection byproducts (DBPs) are a class of ubiquitous chemicals in drinking water and inevitably result in widespread human exposures. Potentially adverse health effects of DBP exposures, including reproductive and developmental outcomes, have been increasing public concerns. Several reviews have focused on the adverse pregnancy outcomes of DBPs. This review summarized current evidence on male reproduction health upon exposure to DBPs from toxicological and epidemiological literature. Based on existing experimental studies, there are sufficient evidence showing that haloacetic acids (HAAs) are male reproductive toxicants, including reduced epididymal weight, decreased semen parameters and sperm protein 22, and declined testosterone levels. However, epidemiological evidence remains insufficient to support a link of DBP exposures with adverse male reproductive outcomes, despite that blood and urinary DBP biomarkers are associated with decreased semen quality. Eight potential mechanisms, including germ/somatic cell dysfunction, oxidative stress, genotoxicity, inflammation, endocrine hormones, folate metabolism, epigenetic alterations, and gut microbiota, are likely involved in male reproductive toxicity of DBPs. We also identified knowledge gaps in toxicological and epidemiological studies to enhance future needs.

Exposures to volatile organic compounds, serum vitamin D, and kidney function: association and interaction assessment in the US adult population

The relationships of exposures to volatile organic compounds (VOCs) with vitamin D and kidney function remain unclear. Our analyses included 6070 adults from 2003 to 2010 survey cycles of the National Health and Nutrition Examination Survey to explore associations of six VOCs with serum vitamin D, albumin-to-creatinine ratio (ACR), and estimated glomerular filtration rate (eGFR). The results suggested that dibromochloromethane was positively associated with ACR, and chloroform was inversely associated with ACR. U-shaped associations of toluene, m-/p-xylene, bromodichloromethane, and 1,4-dichlorobenzene with ACR were observed. Toluene, m-/p-xylene, and 1,4-dichlorobenzene were associated with eGFR in U-shaped manners, while bromodichloromethane and chloroform were inversely associated with eGFR. Elevation in 1,4-dichlorobenzene was associated with decrease in vitamin D, while chloroform and m-/p-xylene were in U-shaped associations with vitamin D. VOCs mixture was U-shaped associated with ACR, inversely associated with eGFR, and inversely associated with vitamin D. Vitamin D was in a U-shaped association with ACR. Vitamin D significantly interacted with VOCs on the two kidney parameters. In the US adult population, exposures to VOCs were associated with kidney function and serum vitamin D level decline, and the serum vitamin D may have interaction effects with VOCs exposures on kidney function.

The involvement of branched-chain amino acids (BCAAs) in aromatic trihalogenated DBP exposure-induced kidney damage in mice

Disinfection by-products (DBPs) are inevitably generated in the process of disinfection. Among them, aromatic halogenated DBPs, such as 2,4,6-trichlorophenol (TCP), 2,4,6-tribromophenol (TBP) and 2,4,6-triiodophenol (TIP), have attracted considerable interest for their high toxicity. A systematic nephrotoxicity evaluation of 2,4,6-trihalophenols is still lacking. In this study, mice were exposed to TCP, TBP and TIP ranging from environmental-related low concentration to high concentration that commonly used in animal study (0.5-200 μg/L). Kidney histopathology, urine protein detection and urine metabolomics were performed. Remarkable changes including kidney damage, proteinuria and glomerular mesangial cell proliferation were observed after three 2,4,6-trihalophenol exposure, even at low concentration of 0.5 μg/L. The nephrotoxicity rank order was TIP > TBP > TCP. Additionally, in vivo exposure to 2,4,6-trihalophenols also led to apparent changes in urinary metabolic profiles. Biosynthesis pathways of branched-chain amino acids (BCAAs, containing valine, leucine and isoleucine) were disturbed even at the early stage of exposure (4 weeks). Intriguingly, it has been reported that BCAAs could promote the proliferation of glomerular mesangial cells. Thus, in vitro cell experiments were further performed on mouse glomerular mesangial cell line MES-13. Consistently with in vivo results, cell proliferation was observed in MES-13 cells after exposure to 2,4,6-trihalophenols, especially to TBP and TIP. Meanwhile, TCP at high concentration, TBP and TIP at not only high concentration but also low concentration, induced BCAAs accumulation in glomerular mesangial cells, which was completely commensurate to that observed in cell proliferation assay. Then the proliferation of MES-13 cells induced by 2,4,6-trihalophenols was remarkably inhibited after BCAAs interference. Here we provide direct link between disturbed BCAAs and the nephrotoxicity of 2,4,6-trihalophenols. 2,4,6-trihalophenols could induce excess BCAAs, which further led to proliferation of glomerular mesangial cells and renal injury. This study revealed the nephrotoxicity of aromatic trihalogenated DBPs and provided new insights into the potential toxic mechanisms.

Precursor characteristics of mono-HAAs during chlorination and cytotoxicity of mono-HAAs on HEK-293T cells

Monohaloacetic acids (mono-HAAs), a class of disinfection by-products widely occurred in drinking water, receives significant attention due to their extremely high toxicity. Many studies on the biological toxicity of mono-HAAs have been reported, yet the toxic effects of mono-HAAs on human renal cells (kidney is one of the target organs for disinfection by-products) has not been involved. Studies on organic precursors for mono-HAAs formation were also very limited due to their lower levels as compared to di-HAAs and tri-HAAs. Based on this, the formation of mono-HAAs after chlorination of some typical source water samples and their relationship with water quality parameters were investigated. Meanwhile, the cytotoxicity of monochloroacetic acid (MCAA), monobromoacetic acid (MBAA), and monoiodoacetic acid (MIAA) were tested using human embryonic kidney cells (HEK-293 T cells). The results showed that the levels of mono-HAAs formed during chlorination of source water samples were between 0.44 and 0.87 μg/L. Formation of MBAA positively (p < 0.05) correlated with bromide ion and dissolved organic carbon, but negatively (p < 0.01) correlated with SUVA₂₅₄ (specific UV absorbance at 254 nm), while formation of MCAA was only positively (p < 0.05) related with SUVA₂₅₄. These results suggested that although MCAA and MBAA both belong to the mono-HAAs, the characteristics of their organic precursors differ significantly. MCAA precursors have high aromaticity and are more hydrophobic, yet MBAA precursors have low aromaticity and are more hydrophilic. The half-lethal concentrations (LC₅₀) of MCAA, MBAA, and MIAA on HEK293T cells were 1196-1211 μM, 16.07-18.96 μM, and 6.08-6.17 μM, respectively. An in-depth analysis showed that the cytotoxicity of mono-HAAs on HEK 293 T cells could not be explained by the parameters concerning cellular uptake (e.g., logP and pKa), but the S_N2 reaction of C-X bond with cellular molecules (e.g., glyceraldehyde-3-phosphate dehydrogenase, etc) may be the relevant cause for the cytotoxicity of mono-HAAs on HEK 293 T cells.

The Co-occurrence of Chronic Hepatitis B and Fibrosis Is Associated With a Decrease in Hepatic Global DNA Methylation Levels in Patients With Non-alcoholic Fatty Liver Disease

Global DNA hypomethylation has been reported in patients with chronic hepatitis B (CHB) and non-alcoholic fatty-liver disease (NAFLD). However, the global DNA methylation profile of patients with concurrent NAFLD and CHB (NAFLD + CHB) is still unclear. We aimed to detect the hepatic global DNA methylation levels of NAFLD + CHB patients and assess the associated risk factors. Liver biopsies were collected from 55 NAFLD patients with or without CHB. The histological characteristics of the biopsy were then assessed. Hepatic global DNA methylation levels were quantified by fluorometric method. The hepatic global DNA methylation levels in NAFLD + CHB group were significantly lower than that in NAFLD group. Participants with fibrosis showed lower levels of hepatic global DNA methylation than those without fibrosis. Participants with both CHB and fibrosis had lower levels of hepatic global DNA methylation than those without either CHB or fibrosis. The co-occurrence of CHB and fibrosis was significantly associated with a reduction in global DNA methylation levels compared to the absence of both CHB and fibrosis. Our study suggests that patients with NAFLD + CHB exhibited lower levels of global DNA methylation than patients who had NAFLD alone. The co-occurrence of CHB and liver fibrosis in NAFLD patients was associated with a decrease in global DNA methylation levels.

A Luciferase-EGFP Reporter System for the Evaluation of DNA Methylation in Mammalian Cells

DNA methylation is an essential epigenetic modification involved in numerous biological processes. Here, we present a cell-based system pLTR-Luc2P-EGFP for evaluation of DNA methylation in mammalian cells. In this system, the expression of reporter gene luciferase2P (Luc2P)-EGFP is under the control of HIV-1 promoter 5' long terminal repeat (LTR), which contains multiple CpG sites. Once these sites are methylated, the expression of Luc2P-EGFP is turned off, which may be visualized under fluorescence microscopy, with quantification performed in luciferase activity assay. As a proof of principle, pLTR-Luc2P-EGFP was methylated in vitro, and transfected into 293T cells, where the reduction of Luc2P-EGFP expression was confirmed. Premixed reporter DNA samples with the methylation levels varying from 0 to 100% were used for quantitative measurements of DNA methylation. The resulting standard curves indicated the accuracy of luciferase activity exceeding that of the Western blotting against EGFP. The Bland–Altman analysis showed that data from luciferase activity assay were in good agreement with the actual DNA methylation levels. In summary, we have established a reporter system coupled with reliable detection technique capable of efficient quantifying the changes in methylation in mammalian cells. This system may be utilized as a high throughput screening tool for identifying molecules that modulate DNA methylation.

Global DNA Hypomethylation and Rassf1a and c-myc Promoter Hypermethylation in Rat Kidney Cells after Bisphenol A Exposure

OBJECTIVES

Bisphenol A (BPA) is a synthetic monomer used in the production of polycarbonate and an environmental contaminant with endocrine disrupting properties. BPA release from plastic carriers is thought to cause high amounts of exposure, which result in high risk to human and environment health.

MATERIALS AND METHODS

The study examined the possible changes in global DNA methylation, CpG promoter DNA methylation, and gene expressions of Rassf1a and c-myc after BPA exposure in rat kidney epithelial cells (NRK-52E).

RESULTS

The IC50 values of BPA in NRK-52E cells were 133.42 and 101.74 μM in the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and neutral red uptake tests, respectively. The cells were treated with BPA at 1 nM, 10 nM, 100 nM, 1 μM, and 10 μM concentrations for 24 h and at 100 nM concentration for 24, 48, 72, 96 h, and 6 days. Decreased global 5-methylcytosine levels were observed after 48, 72, 96 h, and 6 days at the concentration of 100 nM BPA. Changes in CpG promoter DNA methylation were detected in the genes of Rassf1a and c-myc in BPA-treated NRK-52E cells. Expression levels of Rassf1a and c-myc changed in response to BPA at the high concentrations after 24 h treatment, whereas 100 nM exposure to BPA altered gene expression after 48, 72, and 96 h.

CONCLUSION

These results indicate that changes in global and gene-specific DNA methylation may play an important role in the mechanism of BPA toxicity in kidney cells.

Essential oil-incorporated carbon nanotubes filters for bacterial removal and inactivation

In this study, essential oils (EO)-incorporated multi-walled carbon nanotubes (MWCNTs) filters were developed for achieving dual functions in effective removing bacteria from aqueous solutions and inactivating bacteria cells captured on the filters. Tea tree essential oil (TTO), lemon essential oil (LEO), and TTO-LEO-mixture were coated on MWCNTs filters with different MWCNTs loadings ranging from 3 mg to 6 mg. MWCNTs filters with 6.0 mg MWCNTs showed complete removal (100%) of E. coli cells from PBS buffer with 6.35 log10 decrease of cell numbers. TTO, LEO, and TTO/LEO Mix (1:1) coatings at the volume of 50 μL on MWCNTs filters achieved bacterial removal rates of >98%, and highly effective inactivation efficiency. TTO coatings had the highest antimicrobial efficacies than LEO and Mix coatings, MWCNTs filters with 50 μL TTO coating showed 100% inhibitory rate of the captured bacteria on the filter surfaces. Those captured but survived cells on filters with less TTO coating (20μL) significantly reduced their salt tolerances to 30 and 40 g/L NaCl in LB agar, and became less salt tolerance with longer incubation time on the filters. The developed TTO-MWCNTs filters had much higher antimicrobial efficacies than the filters with dual functions developed previously.

Prenatal exposure to drinking water disinfection by-products and DNA methylation in cord blood

Maternal exposure to drinking water disinfection by-products (DBPs) during pregnancy has been related to adverse birth outcomes. While experimental studies have shown that exposure to DBPs induce DNA hypomethylation, evidence from humans is limited. This study aimed to examine whether prenatal exposure to drinking water DBPs was associated with DNA methylation in cord blood. Maternal biomarkers of exposure to drinking water DBPs including blood trihalomethanes [THMs, including chloroform (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), and bromoform (TBM)] and urinary trichloroacetic acid (TCAA) were measured during late pregnancy. DNA methylation in Alu and long interspersed nucleotide element-1 (LINE-1) repetitive elements from cord blood samples (n=115) was measured by pyrosequencing. We used multivariable linear regression to estimate the associations of DNA methylation in cord blood with maternal blood THMs and urinary TCAA. We found no statistically significant association between urinary TCAA and DNA methylation. However, we found that blood TBM was associated with decreased Alu methylation (-0.39%; 95% CI: -0.83%, 0.05% for the highest versus lowest exposure group; p for trend=0.08) and decreased LINE-1 methylation (-1.27%; 95% CI: -2.91%, 0.36% for the highest versus lowest exposure group; p for trend=0.06). Our results suggest that prenatal exposure to drinking water TBM is associated with DNA hypomethylation in cord blood. However, further studies are needed to confirm our findings.

DNA methylation levels and long-term trihalomethane exposure in drinking water: an epigenome-wide association study

Trihalomethanes (THM) are undesired disinfection byproducts (DBPs) formed during water treatment. Mice exposed to DBPs showed global DNA hypomethylation and c-myc and c-jun gene-specific hypomethylation, while evidence of epigenetic effects in humans is scarce. We explored the association between lifetime THM exposure and DNA methylation through an epigenome-wide association study. We selected 138 population-based controls from a case-control study of colorectal cancer conducted in Barcelona, Spain, exposed to average lifetime THM levels ≤85 μg/L vs. >85 μg/L (N = 68 and N = 70, respectively). Mean age of participants was 70 years, and 54% were male. Average lifetime THM level in the exposure groups was 64 and 130 µg/L, respectively. DNA was extracted from whole blood and was bisulphite converted to measure DNA methylation levels using the Illumina HumanMethylation450 BeadChip. Data preprocessing was performed using RnBeads. Methylation was compared between exposure groups using empirical Bayes moderated linear regression for CpG sites and Gaussian kernel for CpG regions. ConsensusPathDB was used for gene set enrichment. Statistically significant differences in methylation between exposure groups was found in 140 CpG sites and 30 gene-related regions, after false discovery rate <0.05 and adjustment for age, sex, methylation first principal component, and blood cell proportion. The annotated genes were localized to several cancer pathways. Among them, 29 CpGs had methylation levels associated with THM levels (|Δβ|≥0.05) located in 11 genes associated with cancer in other studies. Our results suggest that THM exposure may affect DNA methylation in genes related to tumors, including colorectal and bladder cancers. Future confirmation studies are required.

Epigenetic Regulation in Environmental Chemical Carcinogenesis and its Applicability in Human Health Risk Assessment

Although several studies have shown that chemically mediated epigenetic changes are an etiological factor in several human disease conditions, the utility of epigenetic data, such as DNA methylation, in the current human health risk assessment paradigm is unclear. The objective of this study is to investigate the relationship between the points of departure (PODs) for cancer incidence and DNA methylation changes in laboratory animals exposed to the following environmental toxicants: bromodichloromethane, dibromochloromethane, chloroform, hydrazine, trichloroethylene, benzidine, trichloroacetic acid, and di(2-ethylhexyl) phthalate (DEHP; a known reproductive toxicant). The results demonstrate that the PODs for cancer incidence and altered DNA methylation are similar. Furthermore, based on the available data, the POD for DNA methylation appeared more sensitive compared to that for cancer incidence following the administration of DEHP to rats during different life stages. The high degree of correlation between PODs for cancer incidence and DNA methylation (for both total DNA and individual genes) suggests that DNA methylation end points could potentially be used as a screening tool in predicting the potential toxicity/carcinogenicity and in prioritizing large numbers of chemicals with sparse toxicity databases. The life stage during which treatment occurs is also an important consideration when assessing the potential application of epigenetic end points as a screening tool.

LINE-1 methylation in granulocyte DNA and trihalomethane exposure is associated with bladder cancer risk

DNA methylation changes contribute to bladder carcinogenesis. Trihalomethanes (THM), a class of disinfection by-products, are associated with increased urothelial bladder cancer (UBC) risk. THM exposure in animal models produces DNA hypomethylation. We evaluated the relationship of LINE-1 5-methylcytosine levels (LINE-1%5mC) as outcome of long-term THM exposure among controls and as an effect modifier in the association between THM exposure and UBC risk. We used a case-control study of UBC conducted in Spain. We obtained personal lifetime residential THM levels and measured LINE-1%5mC by pyrosequencing in granulocyte DNA from blood samples in 548 incident cases and 559 hospital controls. Two LINE-1%5mC clusters (above and below 64%) were identified through unsupervised hierarchical cluster analysis. The association between THM levels and LINE-1%5mC was evaluated with β regression analyses and logistic regression was used to estimate odds ratios (OR) adjusting for covariables. LINE-1%5mC change between percentiles 75(th) and 25(th) of THM levels was 1.8% (95% confidence interval (CI): 0.1, 3.4%) among controls. THM levels above vs. below the median (26 μg/L) were associated with increased UBC risk, OR = 1.86 (95% CI: 1.25, 2.75), overall and among subjects with low levels of LINE-1%5mC (n = 975), OR = 2.14 (95% CI: 1.39, 3.30), but not associated with UBC risk among subjects' high levels of LINE-1%5mC (n = 162), interaction P = 0.03. Results suggest a positive association between LINE-1%5mC and THM levels among controls, and LINE-1%5mC status may modify the association between UBC risk and THM exposure. Because reverse causation and chance cannot be ruled out, confirmation studies are warranted.

The prognostic value of global DNA hypomethylation in cancer: a meta-analysis

BACKGROUND

Aberrant methylation of the global genome has been investigated as a prognostic indicator in various cancers, but the results are controversial and ambiguous.

METHODS AND FINDINGS

This meta-analysis presents pooled estimates of the evidence to elucidate this issue. We searched the electronic databases: PubMed, Embase, ISI Web of Science and the Cochrane library (up to August 2013) to identify all of the relevant studies. The association between the level of surrogates' indexes of genome-wide hypomethylation (LINE-1, Alu and Sat-α) and the overall survival (OS) of cancer patients was examined. In addition, the pooled hazard ratios (HRs) with their 95% confidence interval (95%CI) were calculated to estimate the influences through fixed-effects and random-effects model. Finally, twenty studies with total population of 5447 met the inclusion criteria. The results indicate that the summary HRs for the studies employing LINE-1, Alu, and Sat-α repetitive elements also show that the global DNA hypomethylation have significant desirable effects on the tumour prognostic value. The pooled HRs (and CIs) of LINE-1, Alu and Sat-α were 1.83 (1.38-2.44), 2.00 (1.16-3.45), and 2.92 (1.04-8.25), with a heterogeneity measure index of I2 (and p-value) shows of 66.6% (p = 0.001), 57.1% (p = 0.053) and 68.2% (p = 0.076) respectively. The meta-regression and subgroup analysis indicated that the percentage of hypomethylated sample of cancer patients is one source of heterogeneity.

CONCLUSION

Our meta-analysis findings support the hypothesis that the global DNA hypomethylation is associated with a detrimental prognosis in tumour patients.

Epigenetic changes in p21 expression in renal cells after exposure to bromate

This study tested the hypothesis that bromate (KBrO3)-induced renal cell death is mediated by epigenetic mechanisms. Global DNA methylation, as assessed by 5-methylcytosine staining, was not changed in normal rat kidney cells treated with acute cytotoxic doses of KBrO3 (100 and 200 ppm), as compared with controls. However, KBrO3 treatment did increase p38, p53 and histone 2AX (H2AX) phosphorylation, and p21 expression. Treatment of cells with inhibitors of DNA methyltransferase (5-azacytidine or 5-Aza) and histone deacetylase (trichostatin A or TSA) in addition to KBrO3 increased cytotoxicity, as compared with cells exposed to KBrO3 alone. 5-Aza and TSA co-treatment did not alter p38 or p53 phosphorylation, but slightly decreased H2AX phosphorylation and significantly decreased p21 expression. We also assessed epigenetic changes in cells treated under sub-chronic conditions with environmentally relevant concentrations of KBrO3. Under these conditions (0-10ppm KBrO3 for up to 18 days), we detected no increases in cell death or DNA damage. In contrast, slight alterations were detected in the phosphorylation of H2AX, p38, and p53. Sub-chronic low-dose KBrO3 treatment also induced a biphasic response in p21 expression, with lower concentrations increasing expression, but higher concentrations decreasing expression. Methylation-specific PCR demonstrated that sub-chronic KBrO3 treatment altered the methylation of cytosine bases in the p21 gene, as compared with controls, correlating to alterations in p21 protein expression. Collectively, these data show the novel finding that KBrO3-induced renal cell death is altered by inhibitors of epigenetic modifying enzymes and that KBrO3 itself induces epigenetic changes in the p21 gene.

[Advances of DNA methylation in early diagnosis of lung cancer]

Lung cancer is the leading cause of cancer-related death and thus a major health problem nowadays. No early diagnostic method is ideal up to now. Changes in DNA methylation occur on early stage of lung cancer. Detection of DNA methylation is expected to be an important method in early diagosis of lung cancer.

Epigenetics in women's health care

Epigenetics refers to structural modifications to genes that do not change the nucleotide sequence itself but instead control and regulate gene expression. DNA methylation, histone modification, and RNA regulation are some of the mechanisms involved in epigenetic modification. Epigenetic changes are believed to be a result of changes in an organism's environment that result in fixed and permanent changes in most differentiated cells. Some environmental changes that have been linked to epigenetic changes include starvation, folic acid, and various chemical exposures. There are periods in an organism's life cycle in which the organism is particularly susceptible to epigenetic influences; these include fertilization, gametogenesis, and early embryo development. These are also windows of opportunity for interventions during the reproductive life cycle of women to improve maternal-child health. New data suggest that epigenetic influences might be involved in the regulation of fetal development and the pathophysiology of adult diseases such as cancer, diabetes, obesity, and neurodevelopmental disorders. Various epigenetic mechanisms may also be involved in the pathogenesis of preeclampsia and intrauterine growth restriction. Additionally, environmental exposures are being held responsible for causing epigenetic changes that lead to a disease process. Exposure to heavy metals, bioflavonoids, and endocrine disruptors, such as bisphenol A and phthalates, has been shown to affect the epigenetic memory of an organism. Their long-term effects are unclear at this point, but many ongoing studies are attempting to elucidate the pathophysiological effects of such gene-environment interactions.

Immunotoxicity of dibromoacetic acid administered via drinking water to female B₆C₃F₁ mice

Dibromoacetic acid (DBA) is a disinfection by-product commonly found in drinking water as a result of chlorination/ ozonation processes. The Environmental Protection Agency estimates that more than 200 million people consume disinfected water in the United States. This study was conducted to evaluate the potential immunotoxicological effects of DBA exposure when administered for 28 days via drinking water to B₆C₃F₁ mice, at concentrations of 125, 500, and 1000 mg/L. Multiple endpoints were evaluated to assess innate, humoral, and cell-mediated immune components, as well as host resistance. Standard toxicological parameters were unaffected, with the exception of a dose-responsive increase in liver weight and a decrease in thymus weight at the two highest exposure levels. Splenocyte differentials were affected, although the effects were not dose-responsive. Exposure to DBA did not significantly affect humoral immunity (immunoglobulin M [IgM] plaque assay and serum IgM anti-sheep erythrocyte titers) or cell-mediated immunity (mixed-leukocyte response). No effects were observed on innate immune function in either interferon-γ-induced in vitro macrophage cytotoxic activity or basal natural killer (NK)-cell activity. Augmented NK-cell activity (following exposure to polyinosinic-polycytidylic acid) was decreased at the low dose, however the effect was not dose-responsive. Finally, DBA exposure had no effect on resistance to infection with either Streptococcus pneumoniae or Plasmodium yoelii, or challenge with B16F10 melanoma cells. With the exception of changes in thymus weight, these results indicate that DBA exposure resulted in no immunotoxic effects at concentrations much larger than those considered acceptable in human drinking water.

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.

Effects of mixtures of polychlorinated biphenyls, methylmercury, and organochlorine pesticides on hepatic DNA methylation in prepubertal female Sprague-Dawley rats

DNA methylation is one of the epigenetic mechanisms that regulates gene expression, chromosome structure, and stability. Our objective was to determine whether the DNA methylation system could be a target following in utero and postnatal exposure to human blood contaminants. Pregnant rats were dosed daily from gestation day 1 until postnatal day 21 with 2 dose levels of either organochlorine pesticides (OCP; 0.019 or 1.9 mg/kg/day), methylmercury chloride (MeHg; 0.02 or 2 mg/kg/day), polychlorinated biphenyls (PCBs; 0.011 or 1.1 mg/kg/day), or a mixture (Mix; 0.05, or 5 mg/kg/day) including all 3 groups of chemicals. Livers from 1 female offspring per litter were collected at postnatal day 29. Hepatic analysis revealed that the mRNA abundance for DNA methyltransferase (DNMT)-1, -3a, and -3b were significantly reduced by the high dose of PCB, that the high dose of MeHg also reduced mRNA levels for DNMT-1, and -3b, but that OCP had no significant effects compared with control. The high dose of PCB and Mix reduced the abundance of the universal methyl donor S-adenosylmethionine, and Mix also reduced global genome DNA methylation (5-methyl-deoxycytidine/5-methyl-deoxycytidine + deoxycytidine). The latter is consistent with pyrosequencing methylation analysis, revealing that the high-dose groups (except OCP) generally decreased the methylation of CpG sites (position -63 to -29) in the promoter of the tumor suppressor gene p16(INK4a). Overall, these hepatic results suggest that the DNA methylation system can be affected by exposure to high doses of blood contaminants, and that OCP is the least potent chemical group from the investigated mixtures.

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.

Mechanisms of peroxisome proliferator-induced DNA hypomethylation in rat liver

Genomic hypomethylation is a consistent finding in both human and animal tumors and mounting experimental evidence suggests a key role for epigenetic events in tumorigenesis. Furthermore, it has been suggested that early changes in DNA methylation and histone modifications may serve as sensitive predictive markers in animal testing for carcinogenic potency of environmental agents. Alterations in metabolism of methyl donors, disturbances in activity and/or expression of DNA methyltransferases, and presence of DNA single-strand breaks could contribute to the loss of cytosine methylation during carcinogenesis; however, the precise mechanisms of genomic hypomethylation induced by chemical carcinogens remain largely unknown. This study examined the mechanism of DNA hypomethylation during hepatocarcinogenesis induced by peroxisome proliferators WY-14,643 (4-chloro-6-(2,3-xylidino)-pyrimidynylthioacetic acid) and DEHP (di-(2-ethylhexyl)phthalate), agents acting through non-genotoxic mode of action. In the liver of male Fisher 344 rats exposed to WY-14,643 (0.1% (w/w), 5 months), the level of genomic hypomethylation increased by approximately 2-fold, as compared to age-matched controls, while in the DEHP group (1.2% (w/w), 5 months) DNA methylation did not change. Global DNA hypomethylation in livers from WY-14,643 group was accompanied by the accumulation of DNA single-strand breaks, increased cell proliferation, and diminished expression of DNA methyltransferase 1, while the metabolism of methyl donors was not affected. In contrast, none of these parameters changed significantly in rats fed DEHP. Since WY-14,643 is much more potent carcinogen than DEHP, we conclude that the extent of loss of DNA methylation may be related to the carcinogenic potential of the chemical agent, and that accumulation of DNA single-strand breaks coupled to the increase in cell proliferation and altered DNA methyltransferase expression may explain genomic hypomethylation during peroxisome proliferator-induced carcinogenesis.

Epigenetic reprogramming and imprinting in origins of disease

The traditional view that gene and environment interactions control disease susceptibility can now be expanded to include epigenetic reprogramming as a key determinant of origins of human disease. Currently, epigenetics is defined as heritable changes in gene expression that do not alter DNA sequence but are mitotically and transgenerationally inheritable. Epigenetic reprogramming is the process by which an organism's genotype interacts with the environment to produce its phenotype and provides a framework for explaining individual variations and the uniqueness of cells, tissues, or organs despite identical genetic information. The main epigenetic mediators are histone modification, DNA methylation, and non-coding RNAs. They regulate crucial cellular functions such as genome stability, X-chromosome inactivation, gene imprinting, and reprogramming of non-imprinting genes, and work on developmental plasticity such that exposures to endogenous or exogenous factors during critical periods permanently alter the structure or function of specific organ systems. Developmental epigenetics is believed to establish "adaptive" phenotypes to meet the demands of the later-life environment. Resulting phenotypes that match predicted later-life demands will promote health, while a high degree of mismatch will impede adaptability to later-life challenges and elevate disease risk. The rapid introduction of synthetic chemicals, medical interventions, environmental pollutants, and lifestyle choices, may result in conflict with the programmed adaptive changes made during early development, and explain the alarming increases in some diseases. The recent identification of a significant number of epigenetically regulated genes in various model systems has prepared the field to take on the challenge of characterizing distinct epigenomes related to various diseases. Improvements in human health could then be redirected from curative care to personalized, preventive medicine based, in part, on epigenetic markings etched in the "margins" of one's genetic make-up.

Epigenetic effects of the continuous exposure to peroxisome proliferator WY-14,643 in mouse liver are dependent upon peroxisome proliferator activated receptor alpha

Peroxisome proliferators are potent rodent liver carcinogens that act via a non-genotoxic mechanism. The mode of action of these agents in rodent liver includes increased cell proliferation, decreased apoptosis, secondary oxidative stress and other events; however, it is not well understood how peroxisome proliferators are triggering the plethora of the molecular signals leading to cancer. Epigenetic changes have been implicated in the mechanism of liver carcinogenesis by a number of environmental agents. Short-term treatment with peroxisome proliferators and other non-genotoxic carcinogens leads to global and locus-specific DNA hypomethylation in mouse liver, events that were suggested to correlate with a burst of cell proliferation. In the current study, we investigated the effects of long-term exposure to a model peroxisome proliferator WY-14,643 on DNA and histone methylation. Male SV129mice were fed a control or WY-14,643-containing (1000ppm) diet for one week, five weeks or five months. Treatment with WY-14,643 led to progressive global hypomethylation of liver DNA as determined by an HpaII-based cytosine extension assay with the maximum effect reaching over 200% at five months. Likewise, trimethylation of histone H4 lysine 20 and H3 lysine 9 was significantly decreased at all time points. The majority of cytosine methylation in mammals resides in repetitive DNA sequences. In view of this, we measured the effect of WY-14,643 on the methylation status of major and minor satellites, as well as in IAP, LINE1 and LINE2 elements in liver DNA. Exposure to WY-14,643 resulted in a gradual loss of cytosine methylation in major and minor satellites, IAP, LINE1 and LINE2 elements. The epigenetic changes correlated with the temporal effects of WY-14,643 on cell proliferation rates in liver, but no sustained effect on c-Myc promoter methylation was observed. Finally, WY-14,643 had no effect on DNA and histone methylation status in Pparalpha-null mice at any of the time points considered in this study. These data indicate the importance of epigenetic alterations in the mechanism of action of peroxisome proliferators and the key role of Pparalpha.