Changes in gene expression and assessment of DNA methylation in primary human hepatocytes and HepG2 cells exposed to the environmental contaminants-Hexabromocyclododecane and 17-beta oestradiol

In Vivo and In Vitro Models of Hepatocellular Carcinoma: Current Strategies for Translational Modeling

Hepatocellular carcinoma (HCC) is the sixth most common cancer worldwide and the third leading cause of cancer-related death globally. HCC is a complex multistep disease and usually emerges in the setting of chronic liver diseases. The molecular pathogenesis of HCC varies according to the etiology, mainly caused by chronic hepatitis B and C virus infections, chronic alcohol consumption, aflatoxin-contaminated food, and non-alcoholic fatty liver disease associated with metabolic syndrome or diabetes mellitus. The establishment of HCC models has become essential for both basic and translational research to improve our understanding of the pathophysiology and unravel new molecular drivers of this disease. The ideal model should recapitulate key events observed during hepatocarcinogenesis and HCC progression in view of establishing effective diagnostic and therapeutic strategies to be translated into clinical practice. Despite considerable efforts currently devoted to liver cancer research, only a few anti-HCC drugs are available, and patient prognosis and survival are still poor. The present paper provides a state-of-the-art overview of in vivo and in vitro models used for translational modeling of HCC with a specific focus on their key molecular hallmarks.

Avermectin induced global DNA hypomethylation and over-expression of heat shock proteins in cardiac tissues of pigeon

Despite increasing evidences pointing to residues of avermectin (AVM) pose toxic effects on non-target organisms in environment, but the data in pigeon is insufficient. The alteration of global DNA methylation and response of heat shock proteins (Hsps) are important for assessing the AVM toxicity in cardiac tissues of pigeon (Columba livia). To investigate the effects of AVM exposure in cardiac tissues of pigeon, we detected the expression levels of DNA methyltransferases (Dnmts), methylated DNA-binding domain protein 2 (MBD2), and Hsp 60, 70 and 90. Pigeons were exposed to feed containing AVM (0, 20, 40 and 60mg/kg diet) for 30, 60, 90days respectively, and cardiac tissues were collected and analyzed. We found the transcriptional levels of Dnmt1, Dnmt3_a and Dnmt3_b mRNA were down-regulated, but the transcriptional levels of MBD2 mRNA were up-regulated by AVM exposure in cardiac tissues of pigeon. Necrocytosis, hemorrhage, infiltration of inflammatory cells and abundant vacuoles appeared in cardiac tissues after AVM exposure. Accompanying this phenotype, the mRNA transcriptional and/or protein levels of Hsp30, Hsp60, Hsp70 and Hsp90 increased. In conclusion, these results underscored AVM exposure caused DNA methylation machinery malfunctions, and induced over-expression of Hsps to improve the protective function against cardiac injury.

The "adaptive responses" of low concentrations of HBCD in L02 cells and the underlying molecular mechanisms

This study aimed to investigate the "adaptive responses" of hexabromocyclododecanes (HBCD) at environmentally relevant concentrations in human hepatocytes L02. L02 cells were pre-treated with low concentrations of HBCD (10(-13)-10(-11) M), followed by treatment with high concentrations of HBCD, α-hexachlorocyclohexane (α-HCH), polychlorinated biphenyls (PCBs), or polybrominated diphenyl ether-47 (BDE47). The results showed that the pre-treatment with low concentrations of HBCD induced "adaptive responses" to high concentrations of HBCD/α-HCH exposure (but not to PCBs and BDE47), as evidenced by attenuation of survival inhibition, reactive oxygen species (ROS) over-production, and deoxyribonucleic acid (DNA) damage induction. The "adaptive responses" induced by low concentrations of HBCD, which depended on the activation of the phosphatidylinositide 3-kinase/protein kinase B (PI3K/Akt) pathway, reduced the phosphorylation of adenosine monophosphate-activated kinase (AMPK) and enhanced the phosphorylation of p38 mitogen-activated protein kinases (p38 MAPK). The observations were further confirmed by the experiments with inhibitors. Moreover, the evaluation on the changes of metabolic enzymes revealed that HBCD and α-HCH shared a similar pattern of cytochrome P450 induction (CYP2B6), which was different from those of PCBs and BDE47 (CYP1A1 and CYP2B6). These results indicated that low concentrations of HBCD could induce "adaptive responses" to the subsequent treatment with high concentrations of HBCD/α-HCH in L02 cells, which was associated with the PI3K/Akt pathway, and AMPK and p38 MAPK signaling. The "adaptive responses" seemed to be dependent on the types of chemicals in terms of the metabolic patterns and chemical structures.

Duplicated CCAAT/enhancer-binding protein β (C/EBPβ) gene: transcription and methylation changes in response to dietary betaine in Landes goose liver

The CCAAT/enhancer-binding protein β gene (C/EBPβ) is one of the key regulating factors of lipid metabolic balance in the liver. To better understand how C/EBPβ affects lipid accumulation in the Landes goose liver, its DNA was cloned. The goose C/EBPβ DNA sequence (2,075 bp) contains a 984-bp open reading frame and part of the 5'-flanking region, and shares 96.66 and 62.07% similarity with the chicken and human sequences at the amino acid level, respectively. Tissue expression profiling showed that the relative expression level was high in the liver and adipose tissue. To understand the effect of betaine on C/EBPβ in goose liver, the relative expression levels of C/EBPβ were detected under different treatments. Compared with the control group, C/EBPβ expression increased in the high-carbohydrate group (P < 0.01) and decreased in the betaine treatment group (P > 0.05). Using bisulfite sequencing PCR, the gene methylation status was analyzed among the different treatment groups. None of the 54 CpG sites in the promoter region or the 28 CpG sites in the structural domain of the coding region showed any significantly different methylation patterns among the groups. Taken together, the results showed that betaine decreased the goose C/EBPβ gene expression, but did not directly regulate its methylation. The data may form the basis for further investigation of the mechanisms of the effect of C/EBPβ on the regulation of lipometabolism in the goose liver and the effect of betaine on lipid metabolic genes at the molecular level.

Triclosan reduces the levels of global DNA methylation in HepG2 cells

Triclosan (TCS), an antibacterial agent, is widely used in a variety of personal care and industrial products. TCS is associated with the development of liver tumors in rodents and has become a concern to environmental and human health. This study is aimed at investigating whether TCS could modulate the levels of global DNA methylation (GDM) in human hepatocytes. We found that treatment with different doses (1.25-10 μM) of TCS did not affect HepG2 cell viability, but significantly reduced the levels of GDM in HepG2 cells, and inhibited DNMT1 activity. Furthermore, treatment with TCS significantly inhibited the methylated DNA-binding domain 2 (MBD2), MBD3, and MeCP2 mRNA transcription. In addition, treatment with TCS promoted the accumulation of 8-hydroxy-2-deoxyguanosine (8-OHdG) in a dose-dependent manner, which was abrogated by treatment with an antioxidant, N-acetylcysteine (NAC). Collectively, our data indicated that TCS reduced the levels of GDM and down-regulated the MBD2, MBD3, and MeCP2 gene expression by increasing 8-OHdG levels and inhibiting the DNMT1 activity in HepG2 cells.

The cytological effects of HBCDs on human hepatocyte L02 and the potential molecular mechanism

The concentration of hexabromocyclododecanes (HBCDs) in the environment media and organism samples are gradually rising with the increase of HBCDs usage. This study is designed to investigate the cytological effects of HBCDs on human hepatocyte L02 and explore the potential molecular mechanism. The results of CCK-8 assay showed that high concentration of HBCDs (>20 μM) significantly suppressed cell survival, while comparatively lower dose of HBCDs (10(-13)-10(-7)M) slightly stimulated cell proliferation (P < 0.05). In the mean time, high concentration HBCDs markedly induced cell apoptosis and DNA damage, accompanying with increase of intracellular Ca(2+)level and decrease of mitochondrial membrane potential (P < 0.05). ROS level induced by low concentration of HBCDs was comparatively lower than that by high concentration of HBCDs. In addition, low concentration HBCDs exposure (10(-13)-10(-7)M) resulted in up-regulation of PCNA protein expression level in a time-dependent manner. However, high concentration HBCDs exposure led to increase of Apaf-1 expression level. In conclusion, loss of mitochondrial membrane potential and activation of Apaf-1 mediated pathway involve the L02 cell apoptosis induced by high concentration HBCDs exposure. However, low concentration HBCDs exposure could stimulate cell proliferation of L02 cells, which might be associated with enhancement of PCNA expression.

Increased risk of stroke in oral contraceptive users carried replicated genetic variants: a population-based case-control study in China

Combined oral contraceptives (COC) use is a unique risk factor for stroke in women, and may modify the associations between genetic polymorphisms and stroke. To investigate whether the genetic variants identified in a recent genome-wide association study (GWAS) could be replicated in Chinese women, as well as, whether related risk was different in COC users, 451 stroke cases and 831 age- and region-matched controls were recruited from our cohort. Genotyping of 3 SNPs (rs700651, rs10958409, and rs1333040) was performed by the polymerase chain reaction assay with TaqMan probes. The history of contraceptive use and relevant information were obtained from a face-to-face interview. Odds ratios (OR) with 95 % confidence interval (CI) were estimated under conditional logistic regression model after adjustment for cardiovascular covariates. Our study replicated the associations of rs10958409 and rs1333040, with the risk of stroke, especially hemorrhagic subtype, but failed to confirm association of rs700651. COC use was associated with a 1.56-fold (OR 1.56, 95 % CI 1.21-2.01) increased risk of stroke. COC users with rs10958409 GA/AA or rs1333040 CT/TT genotypes had an increased risk of overall stroke by 1.59-fold (OR 2.59, 95 % CI 1.59-4.19) and 3.24-fold (OR 4.24, 95 % CI 1.71-10.49), respectively, compared with the non-users with wild-type genotypes. Moreover, the risk of hemorrhagic stroke increased by 4.81- and 15.06-fold when risk allele carriers of rs10958409 or rs1333040 who took COC. Our results confirmed the associations of two GWAS SNPs, also suggested combination effects of these genetic variants and COC use on stroke risk.

Perfluorooctanoic acid induces gene promoter hypermethylation of glutathione-S-transferase Pi in human liver L02 cells

Perfluorooctanoic acid (PFOA) is one of the most commonly used perfluorinated compounds. Being a persistent environmental pollutant, it can accumulate in human tissues via various exposure routes. PFOA may interfere in a toxic fashion on the immune system, liver, development, and endocrine systems. In utero human exposure had been associated with cord serum global DNA hypomethylation. In light of this, we investigated possible PFOA-induced DNA methylation alterations in L02 cells in order to shed light into its epigenetic-mediated mechanisms of toxicity in human liver. L02 cells were exposed to 5, 10, 25, 50 or 100 mg/L PFOA for 72h. Global DNA methylation levels were determined by LC/ESI-MS, glutathione-S-transferase Pi (GSTP) gene promoter DNA methylation was investigated by methylation-specific polymerase chain reaction (PCR) with bisulfite sequencing, and consequent mRNA expression levels were measured with quantitative real-time reverse transcriptase PCR. A dose-related increase of GSTP promoter methylation at the transcription factor specificity protein 1 (SP1) binding site was observed. However, PFOA did not significantly influence global DNA methylation; nor did it markedly alter the promoter gene methylation of p16 (cyclin-dependent kinase inhibitor 2A), ERα (estrogen receptor α) or PRB (progesterone receptor B). In addition, PFOA significantly elevated mRNA transcript levels of DNMT3A (which mediates de novo DNA methylation), Acox (lipid metabolism) and p16 (cell apoptosis). Considering the role of GSTP in detoxification, aberrant methylation may be pivotal in PFOA-mediated toxicity response via the inhibition of SP1 binding to GSTP promoter.

Hexabromocyclododecane: current understanding of chemistry, environmental fate and toxicology and implications for global management

Hexabromocyclododecane (HBCD) is a globally produced brominated flame retardant (BFR) used primarily as an additive FR in polystyrene and textile products and has been the subject of intensified research, monitoring and regulatory interest over the past decade. HBCD is currently being evaluated under the Stockholm Convention on Persistent Organic Pollutants. HBCD is hydrophobic (i.e., has low water solubility) and thus partitions to organic phases in the aquatic environment (e.g., lipids, suspended solids). It is ubiquitous in the global environment with monitoring data generally exhibiting the expected relationship between proximity to known sources and levels; however, temporal trends are not consistent. Estimated degradation half-lives, together with data in abiotic compartments and long-range transport potential indicate HBCD may be sufficiently persistent and distributed to be of global concern. The detection of HBCD in biota in the Arctic and in source regions and available bioaccumulation data also support the case for regulatory scrutiny. Toxicity testing has detected reproductive, developmental and behavioral effects in animals where exposures are sufficient. Recent toxicological advances include a better mechanistic understanding of how HBCD can interfere with the hypothalamic-pituitary-thyroid axis, affect normal development, and impact the central nervous system; however, levels in biota in remote locations are below known effects thresholds. For many regulatory criteria, there are substantial uncertainties that reduce confidence in evaluations and thereby confound management decision-making based on currently available information.

Methylation at global LINE-1 repeats in human blood are affected by gender but not by age or natural hormone cycles

Previously, we reported on inter-individual and gender specific variations of LINE-1 methylation in healthy individuals. In this study, we investigated whether this variability could be influenced by age or sex hormones in humans. To this end, we studied LINE-1 methylation in vivo in blood-derived DNA from individuals aged 18 to 64 years and from young healthy females at various hormone levels during the menstrual cycle. Our results show that no significant association with age was observed. However, the previously reported increase of LINE-1 methylation in males was reconfirmed. In females, although no correlation between LINE-1 or Alu methylation and hormone levels was observed, a significant stable individual specific level of methylation was noted. In vitro results largely confirmed these findings, as neither estrogen nor dihydrotestosterone affected LINE-1 or Alu methylation in Hek293T, HUVEC, or MDA-kb2 cell lines. In contrast, a decrease in methylation was observed in estrogen-treated T47-Kbluc cell lines strongly expressing estrogen receptor. The very low expression of estrogen receptor in blood cells could explain the observed insensitivity of methylation at LINE-1 to natural hormonal variations in females. In conclusion, neither natural cycle of hormones nor age has a detectable effect on the LINE-1 methylation in peripheral blood cells, while gender remains an important factor.