The 2022 world health organization reevaluation of human and mammalian toxic equivalency factors for polychlorinated dioxins, dibenzofurans and biphenyls.

In October 2022, the World Health Organization (WHO) convened an expert panel in Lisbon, Portugal in which the 2005 WHO TEFs for chlorinated dioxin-like compounds were reevaluated. In contrast to earlier panels that employed expert judgement and consensus-based assignment of TEF values, the present effort employed an update to the 2006 REP database, a consensus-based weighting scheme, a Bayesian dose response modeling and meta-analysis to derive "Best-Estimate" TEFs. The updated database contains almost double the number of datasets from the earlier version and includes metadata that informs the weighting scheme. The Bayesian analysis of this dataset results in an unbiased quantitative assessment of the congener-specific potencies with uncertainty estimates. The "Best-Estimate" TEF derived from the model was used to assign 2022 WHO-TEFs for almost all congeners and these values were not rounded to half-logs as was done previously. The exception was for the mono-ortho PCBs, for which the panel agreed to retain their 2005 WHO-TEFs due to limited and heterogenous data available for these compounds. Applying these new TEFs to a limited set of dioxin-like chemical concentrations measured in human milk and seafood indicates that the total toxic equivalents will tend to be lower than when using the 2005 TEFs.

Gestational arsenic exposure induces anxiety-like behaviors in F1 female mice by dysregulation of neurological and immunological markers.

BACKGROUND: Arsenic is a harmful heavy metal and a well-known developmental neurotoxicant. Previously, we have reported that gestational arsenic exposure resulted in impaired social behaviors in F1 and F2 male mice. However, little is known about the developmental arsenic exposure on anxiety-like behavior. This study aimed to detect the effect of gestational arsenic exposure on anxiety-like behavior and related gene expressions in 74-week-old F1 female mice. METHOD: Pregnant C3H/HeN mice (F0) were given drinking water containing 85 ppm sodium arsenite (NaAsO2) from gestational day 8 to 18. The control mice were given tap water only. At 74-week-old, open field test was performed, then anxiety and apoptosis-related factors were determined by real_time RT_PCR and immunohistochemical analyses. RESULTS: The arsenite-exposed F1 female mice showed decreased center entry and center time in open field test. In addition, the number of grooming and fecal pallet was significantly increased in the arsenite-exposed F1 female mice compared to the control. Downregulation of brain-derived neurotrophic factor (BDNF), serotonin receptor (5HT1A) and upregulation of nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB), interleukin 1 ß (IL-1ß), cyclooxygenase 2 (COX2), caspase-3, Bcl2-associated X protein (Bax) were detected in the prefrontal cortex in the arsenite-exposed F1 female mice. Microglial marker ionized calcium-binding adapter molecule 1 (Iba1)-positive cells were increased in the arsenite-exposed F1 female mice. Moreover, a significantly increased plasma corticosterone level was observed in the arsenic-exposed F1 female mice. CONCLUSIONS: This study suggested that gestational arsenic exposure induced anxiety-like behavior accompanied with dysregulation of neurological and immunological markers, neuroinflammatory responses, neuronal apoptosis, and decreased neurogenesis in the prefrontal cortex of F1 female mice.

Inorganic arsenic exposure-induced premature senescence and senescence-associated secretory phenotype (SASP) in human hepatic stellate cells.

Exposure to inorganic arsenic has been known to induce cancers in various organs, however, the underlying mechanisms remain unclear. Premature senescence refers to the irreversible growth arrest induced by stress stimuli. The senescence-associated secretory phenotype (SASP), particularly in fibroblasts, has been shown to promote cancer development. In this study, we examined whether arsenite exposure causes premature senescence and induction of SASP in liver fibroblasts using the human hepatic stellate cell line, LX-2. Exposure of LX-2 cells to 5 or 7.5 µM of sodium arsenite for 144 h induced the features of senescence in the cells, including morphological changes, growth inhibition, increased senescence-associated ß-galactosidase activity, increased P21 gene expression, and decreased LAMINB1 gene expression. The mRNA expressions of SASP factors, such as MMP1, MMP3, IL-8, IL-1ß, and CXCL1, were also highly upregulated. The wound healing assay revealed that the conditioned medium from LX-2 cells with arsenite-induced senescence increased the migration activity of cells of the human hepatoma cell line, Huh-7. Gene expression data of liver cancer samples from the Human Protein Atlas showed that high expression levels of the SASP factors that were upregulated in the cells with arsenite-induced senescence were strongly associated with a poor prognosis. In addition, the cellular levels of γ-H2AX, a DNA double-strand break marker, were increased by arsenite exposure, suggesting that DNA damage could contribute to premature senescence induction. These results show that arsenite exposure induces premature senescence in hepatic stellate cells and suggest that the SASP factors from the senescent cells promote hepatic carcinogenesis.

Effects of maternal exposure to arsenic on social behavior and related gene expression in F2 male mice.

BACKGROUND: Arsenic is a developmental neurotoxicant. It means that its neurotoxic effect could occur in offspring by maternal arsenic exposure. Our previous study showed that developmental arsenic exposure impaired social behavior and serotonergic system in C3H adult male mice. These effects might affect the next generation with no direct exposure to arsenic. This study aimed to detect the social behavior and related gene expression changes in F2 male mice born to gestationally arsenite-exposed F1 mice. METHODS: Pregnant C3H/HeN mice (F0) were given free access to tap water (control mice) or tap water containing 85 ppm sodium arsenite from days 8 to 18 of gestation. Arsenite was not given to F1 or F2 mice. The F2 mice were generated by mating among control F1 males and females, and arsenite-F1 males and females at the age of 10 weeks. At 41 weeks and 74 weeks of age respectively, F2 males were used for the assessment of social behavior by a three-chamber social behavior apparatus. Histological features of the prefrontal cortex were studied by ordinary light microscope. Social behavior-related gene expressions were determined in the prefrontal cortex by real time RT-PCR method. RESULTS: The arsenite-F2 male mice showed significantly poor sociability and social novelty preference in both 41-week-old group and 74-week-old group. There was no significant histological difference between the control mice and the arsenite-F2 mice. Regarding gene expression, serotonin receptor 5B (5-HT 5B) mRNA expression was significantly decreased (p < 0.05) in the arsenite-F2 male mice compared to the control F2 male mice in both groups. Brain-derived neurotrophic factor (BDNF) and dopamine receptor D1a (Drd1a) gene expressions were significantly decreased (p < 0.05) only in the arsenite-F2 male mice of the 74-week-old group. Heme oxygenase-1 (HO-1) gene expression was significantly increased (p < 0.001) in the arsenite-F2 male mice of both groups, but plasma 8-hydroxy-2'-deoxyguanosine (8-OHdG) and cyclooxygenase-2 (COX-2) gene expression were not significantly different. Interleukin-1ß (IL-1ß) mRNA expression was significantly increased only in 41-week-old arsenite-F2 mice. CONCLUSIONS: These findings suggest that maternal arsenic exposure affects social behavior in F2 male mice via serotonergic system in the prefrontal cortex. In this study, COX-2 were not increased although oxidative stress marker (HO-1) was increased significantly in arsnite-F2 male mice.

Gestational arsenite exposure augments hepatic tumors of C3H mice by promoting senescence in F1 and F2 offspring via different pathways.

Previous studies showed that gestational arsenite exposure increases incidence of hepatic tumors in the F1 and F2 male offspring in C3H mice. However, the mechanisms are largely unknown. In this study, we focused on whether cellular senescence and the senescence-associated secretory phenotype (SASP) contribute to tumor formation in C3H mice, and whether gestational arsenite exposure augments hepatic tumors through enhancement of cellular senescence. Three senescence markers (p16, p21 and p15) and two SASP factors (Cxcl1 and Mmp14) were increased in hepatic tumor tissues of 74- or 100-weeks-old C3H mice without arsenite exposure, and treatment with a senolytic drug (ABT-263) diminished hepatic tumor formation. Gestational arsenite exposure enhanced the expression of p16, p21 and Mmp14 in F1 and p15 and Cxcl1 in F2, respectively. Exploring the mechanisms by which arsenite exposure promotes cellular senescence, we found that the expression of antioxidant enzymes (Sod1 and Cat) were reduced in the tumors of F1 in the arsenite group, and Tgf-ß and the receptors of Tgf-ß were increased in the tumors of F2 in the arsenite group. Furthermore, the analysis of the Cancer Genome Atlas database showed that gene expression levels of the senescence markers and SASP factors were increased and associated with poor prognosis in human hepatocellular carcinoma (HCC). These results suggest that cellular senescence and SASP have important roles in hepatic tumorigenesis in C3H mice as well as HCC in humans, and gestational arsenite exposure of C3H mice enhances senescence in F1 and F2 via oxidative stress and Tgf-ß activation, respectively.

Gestational arsenic exposure and paternal intergenerational epigenetic inheritance.

A growing body of evidence has shown that gestational exposure to environmental factors such as imbalanced diet, environmental chemicals, and stress can lead to late-onset health effects in offspring and that some of these effects are heritable by the next generation and subsequent generations. Furthermore, altered epigenetic modifications in DNA methylation, histone modifications and small RNAs in a single sperm genome have been shown to transmit disease phenotypes acquired from the environment to later generations. Recently, our group found that gestational exposure of F0 pregnant dams to an inorganic arsenic, sodium arsenite, increases the incidence of hepatic tumors in male F2 mice, and the effects are paternally transmitted to the F2. Here, we first overview the epigenetic changes involved in paternal intergenerational and transgenerational inheritance caused by exposure to environmental factors. Then, we discuss our recent studies regarding paternal inheritance of the tumor-augmenting effects in F2 mice by gestational arsenite exposure, in which we investigated alterations of DNA methylation status in F2 tumors and causative F1 sperm. We also discuss the possible targets of the F2 effects. Finally, we discuss future perspectives on the studies that are needed to fully understand the health effects of arsenic exposure.

Identification by TCGA database search of five genes that are aberrantly expressed and involved in hepatocellular carcinoma potentially via DNA methylation changes.

BACKGROUND: Various treatments for hepatocellular carcinoma (HCC) are utilized in clinical practice; however, the prognosis is still poor on account of high recurrence rates. DNA methylation levels of CpG islands around promoters (promoter CpGis) inversely regulate gene expression and closely involved in carcinogenesis. As a new strategy, several chemicals globally inhibiting DNA methylation have been developed aiming at reducing DNA methylation levels and maintaining the expression of tumor suppressor genes. On the other hand, since these drugs nonspecifically modify DNA methylation, they can cause serious adverse effects. In order to ameliorate the methods by targeting specific CpGs, information of cancer-related genes that are regulated by DNA methylation is required. METHODS: We searched candidate genes whose expressions were regulated by DNA methylation of promoter CpGi and which are involved in HCC cases. To do so, we first identified genes whose expression were changed in HCC by comparing gene expressions of 371 HCC tissues and 41 non-tumor tissues using the Cancer Genome Atlas (TCGA) database. The genes were further selected for poor prognosis by log-rank test of Kaplan-Meier plot and for cancer relevance by Pubmed search. Expression profiles of upregulated genes in HCC tissues were assessed by Gene Ontology (GO) analysis. Finally, using DNA methylation data of TCGA database, we selected genes whose promoter DNA methylation levels were inversely correlated with gene expression. RESULTS: We found 115 genes which were significantly up- or downregulated in HCC tissues and were associated with poor prognosis and cancer relevance. The upregulated genes were significantly enriched in cell division, cell cycle, and cell proliferation. Among the upregulated genes in HCC, we identified hypomethylation of CpGis around promoters of FANCB, KIF15, KIF4A, ERCC6L, and UBE2C. In addition, TCGA data showed that the tumor suppressor gene P16 is unexpectedly overexpressed in many types of cancers. CONCLUSIONS: We identified five candidate genes whose expressions were regulated by DNA methylation of promoter CpGi and associate with cancer cases and poor prognosis in HCC. Modification of site-specific DNA methylation of these genes enables a different approach for HCC treatment with higher selectivity and lower adverse effects.

DNA methylation changes involved in the tumor increase in F2 males born to gestationally arsenite-exposed F1 male mice.

Multigenerational adverse effects from the environment such as nutrition and chemicals are among important concerns in environmental health issues. Previously, we have found that arsenite exposure of only F0 females during their pregnancy increases hepatic tumors in the F2 males in C3H mice. In the current study, we investigated the association of DNA methylation with the hepatic tumor increase in the F2 males of the arsenite group. Reduced-representation bisulfite sequencing analysis newly identified that DNA methylation levels of regions around the transcriptional start sites of Tmem54 and Cd74 were decreased and the expression of these genes were significantly increased in the hepatic tumors of F2 males of the arsenite group. The associations between DNA methylation in these regions and gene expression changes were confirmed by treatment of murine hepatoma cell lines and hepatic stellate cell line with 5-aza-2'-deoxycytidine. Overexpression of Cd74 in Hepa1c1c7 cells increased Trib3 expression and suppressed the expression of tumor suppressor genes Id3 and Atoh8. Human database analysis using the Cancer Genome Atlas indicated that TMEM54, CD74, and TRIB3 were significantly increased and that ATOH8 was decreased in hepatocellular carcinoma. The data also showed that high expression of TMEM54 and TRIB3 and low expression of ATOH8 were associated with poor survival. These results suggested that an increase in Tmem54 and Cd74 expression via DNA methylation reduction was involved in the tumor increase in the F2 male offspring by gestational arsenite exposure of F0 females. This study also suggested that genes downstream of Cd74 were involved in tumorigenesis.

Oral exposure to lead for Japanese children and pregnant women, estimated using duplicate food portions and house dust analyses.

BACKGROUND: Lead is a toxic metal abundant in the environment. Consumption of food contaminated at low levels of lead, especially by small children and pregnant women, raises a health concern. METHODS: Duplicated food portions and drinking water were collected over 3 days from 88 children and 87 pregnant women in Shimotsuke, Tochigi, Japan. Participants were recruited in this study between January 2014 and October 2015. Dust was also collected from their homes. Lead concentrations were measured and consequent oral lead exposure levels were estimated for this population at high risk to environmental toxicants. Lead concentrations of peripheral and cord blood, taken from children and pregnant women, and were also analyzed. RESULTS: Lead concentrations in food, drinking water, and house dust were low in general. Oral lead exposure to lead was higher for children (Mean ± SEM; 5.21 ± 0.30 µg/kg BW/week) than in pregnant women (1.47 ± 0.13 µg/kg BW/week). Food and house dust were main sources of lead contamination, but the contribution of house dust widely varied. Means ± SEM of peripheral and cord blood lead concentrations were 0.69 ± 0.04 µg/dL and 0.54 ± 0.05 µg/dL, respectively for pregnant women and 1.30 ± 0.07 µg/dL (peripheral only) in children. We detect no correlation between smoking situations and blood lead concentration in pregnant women. CONCLUSION: We conclude that oral lead exposure levels for Japanese children and pregnant women were generally low, with higher concentrations and exposure for children than for pregnant women. More efforts are necessary to clarify the sources of lead contamination and reduce lead exposure of the population at high risk even in Japan.

The DNA methylation profile of liver tumors in C3H mice and identification of differentially methylated regions involved in the regulation of tumorigenic genes.

BACKGROUND: C3H mice have been frequently used in cancer studies as animal models of spontaneous liver tumors and chemically induced hepatocellular carcinoma (HCC). Epigenetic modifications, including DNA methylation, are among pivotal control mechanisms of gene expression leading to carcinogenesis. Although information on somatic mutations in liver tumors of C3H mice is available, epigenetic aspects are yet to be clarified. METHODS: We performed next generation sequencing-based analysis of DNA methylation and microarray analysis of gene expression to explore genes regulated by DNA methylation in spontaneous liver tumors of C3H mice. Overlaying these data, we selected cancer-related genes whose expressions are inversely correlated with DNA methylation levels in the associated differentially methylated regions (DMRs) located around transcription start sites (TSSs) (promoter DMRs). We further assessed mutuality of the selected genes for expression and DNA methylation in human HCC using the Cancer Genome Atlas (TCGA) database. RESULTS: We obtained data on genome-wide DNA methylation profiles in the normal and tumor livers of C3H mice. We identified promoter DMRs of genes which are reported to be related to cancer and whose expressions are inversely correlated with the DNA methylation, including Mst1r, Slpi and Extl1. The association between DNA methylation and gene expression was confirmed using a DNA methylation inhibitor 5-aza-2'-deoxycytidine (5-aza-dC) in Hepa1c1c7 cells and Hepa1-6 cells. Overexpression of Mst1r in Hepa1c1c7 cells illuminated a novel downstream pathway via IL-33 upregulation. Database search indicated that gene expressions of Mst1r and Slpi are upregulated and the TSS upstream regions are hypomethylated also in human HCC. These results suggest that DMRs, including those of Mst1r and Slpi, are involved in liver tumorigenesis in C3H mice, and also possibly in human HCC. CONCLUSIONS: Our study clarified genome wide DNA methylation landscape of C3H mice. The data provide useful information for further epigenetic studies of mice models of HCC. The present study particularly proposed novel DNA methylation-regulated pathways for Mst1r and Slpi, which may be applied not only to mouse HCC but also to human HCC.

Chronic exposure to arsenic, LINE-1 hypomethylation, and blood pressure: a cross-sectional study in Bangladesh.

BACKGROUND: Chronic exposure to arsenic is associated with cancer and hypertension. Growing evidence suggests that altered methylation in long interspersed nuclear element-1 (LINE-1) is involved in many types of disorders, including cardiovascular disease. Here we evaluated the association between arsenic exposure and LINE-1 methylation levels, especially in relation to blood pressure (BP). METHODS: A total of 236 subjects (175 from arsenic-endemic areas and 61 from a non-endemic area) in rural Bangladesh were recruited. The subjects' arsenic exposure levels (i.e., drinking water, hair and nail arsenic concentrations) were measured by inductively coupled plasma mass spectroscopy. The subjects' LINE-1 methylation levels were determined by pyrosequencing. RESULTS: The average LINE-1 methylation levels of the subjects living in the arsenic-endemic areas were significantly (p < 0.01) lower than those of the subjects living in the non-endemic area. In a sex-stratified analysis, the arsenic exposure levels in female but not male subjects showed a significant inverse association with LINE-1 methylation levels before (water arsenic: p < 0.01, hair arsenic: p < 0.05, nail arsenic: p < 0.001) and after (water arsenic: p < 0.01, hair arsenic: p < 0.05, nail arsenic: p < 0.001) adjustment for age, body mass index and smoking. Analyses examining interactions among arsenic levels, BP and LINE-1 methylation showed that arsenic-related elevated levels of BP were associated with LINE-1 hypomethylation. CONCLUSIONS: Our findings demonstrated that chronic exposure to arsenic was inversely associated with LINE-1 methylation levels in blood leukocyte DNA and this was more pronounced in females than males; in addition, the decreased levels of LINE-1 methylation might be involved in the arsenic-induced elevation of BP.

Long-term arsenite exposure induces premature senescence in B cell lymphoma A20 cells.

Chronic arsenite exposure induces immunosuppression, but the precise mechanisms remain elusive. Our previous studies demonstrated that arsenite exposure for 24 h induces G0/G1 arrest in mouse B lymphoma A20 cells and the arrest is caused through induction of cyclin-dependent kinase inhibitor p16(INK4a) followed by accumulation of an Rb family protein, p130. In this study, we further investigated the consequences of long-term arsenite exposure of A20 cells. The results demonstrated that exposure to 10 µM sodium arsenite up to 14 days induces a great increase in G0/G1 arrest, irreversible cell growth suppression, cellular morphological changes and positive staining for senescence-associated ß-galactosidase. The long-term arsenite exposure also induced up-regulation of p16(INK4a) followed by robust accumulation of p130 and activation of the p53 pathway. Knockdown experiments with siRNA showed that p130 accumulation is essential for cell cycle arrest by long-term arsenite exposure. Since p16(INK4a) and the p53 pathway are known to be activated by DNA damage, we investigated the involvement of DNA damage formation by long-term arsenite exposure. We found that a variety of DNA repair-related genes were significantly down-regulated from 24 h of arsenite exposure and activation-induced cytidine deaminase was greatly up-regulated after long-term arsenite exposure. Consistent with these findings, long-term arsenite exposure increased a DNA double-strand break marker, γ-H2AX and increased mutation frequency in a Bcl6 gene region. These results revealed that long-term arsenite exposure induces premature senescence through DNA damage increase and p130 accumulation in lymphoid cells.

Augmenting effects of gestational arsenite exposure of C3H mice on the hepatic tumors of the F2 male offspring via the F1 male offspring.

Gestational exposure can affect the F2 generation through exposure of F1 germline cells. Previous studies reported that arsenite exposure of only F0 females during their pregnancy increases hepatic tumors in the F1 males in C3H mice, whose males are predisposed spontaneously to develop hepatic tumors later in life. The present study addressed the effects of gestational arsenite exposure on tumorigenesis of the F2 males in C3H mice. Expression analysis of several genes in the normal livers at 53 and 80 weeks of age clearly showed significant changes in the F2 males obtained by crossing gestational arsenite-exposed F1 (arsenite-F1) males and females compared to the control F2 males. Some of the changes were shown to occur in a late-onset manner. Then the tumor incidence was assessed at 75-82 weeks of age in the F2 males obtained by reciprocal crossing between the control and arsenite-F1 males and females. The results demonstrated that the F2 males born to arsenite-F1 males developed tumors at a significantly higher rate than the F2 males born to the control F1 males, irrespective of exposure of F1 females. Gene expressions of hepatocellular carcinoma markers ß-catenin (CTNNB1) and interleukin-1 receptor antagonist in the tumors were significantly upregulated in the F2 males born to arsenite-F1 males compared to those born to the control F1 males. These results show that arsenite exposure of only F0 pregnant mice causes late-onset changes and augments tumors in the livers of the F2 males by affecting the F1 male offspring.

[Biological effects of arsenic and diseases: The mechanisms involved in arsenic-induced carcinogenesis].

Chronic arsenic exposure is associated with many diseases, including cancers. Our study using in vivo assay in gpt-delta transgenic mice showed that arsenic particularly induces G : C to T : A transversions, a mutation type induced through oxidative-stress-induced 8-OHdG formation. Gestational arsenic exposure of C3H mice was reported to increase hepatic tumor incidence. We showed that gestational arsenic exposure increased hepatic tumors having activated oncogene Ha-ras by C to A mutation. We also showed that DNA methylation status of Fosb region is implicated in tumor augmentation by gestational arsenic exposure. We further showed that long-term arsenic exposure induces premature senescence. Recent studies reported that senescence is involved in not only tumor suppression, but also tumorgenesis. All these effects of arsenic might be involved in arsenic-induced carcinogenesis.

Role of Environmental Chemical Insult in Neuronal Cell Death and Cytoskeleton Damage.

Environmental influences, such as chemical exposure, have long been considered potential risk factors for neurodegenerative disorders, including neuromuscular diseases. However, no definitive links between environmental chemical exposure and a pathogenic mechanism of neurodegenerative disease has yet been established. In this study, we describe that exposure to arsenic, an environmental pollutant naturally found in drinking water, induces neuronal cell death and alteration of morphology, particularly neurite outgrowth and in the cytoskeleton of neurons. Since progressive cell loss accompanied by the alteration of neuronal structures and cytoskeleton is considered the major pathologic feature of neurodegenerative disorders, arsenic-induced neurotoxicity might contribute to an etiologic mechanism of some neurodegenerative diseases. Further, we discuss the importance of in vitro assay, particularly an embryonic toxicity test, for assessing the neurotoxicity of chemicals, because most of chemicals found in our environment remain to be evaluated regarding their neurotoxicity risk for neurodegenerative diseases.

The effect of a methyl-deficient diet on the global DNA methylation and the DNA methylation regulatory pathways.

Methyl-deficient diets are known to induce various liver disorders, in which DNA methylation changes are implicated. Recent studies have clarified the existence of the active DNA demethylation pathways that start with oxidization of 5-methylcytosine (5meC) to 5-hydroxymethylcytosine by ten-eleven translocation (Tet) enzymes, followed by the action of base-excision-repair pathways. Here, we investigated the effects of a methionine-choline-deficient (MCD) diet on the hepatic DNA methylation of mice by precisely quantifying 5meC using a liquid chromatography-electrospray ionization-mass spectrometry and by investigating the regulatory pathways, including DNA demethylation. Although feeding the MCD diet for 1 week induced hepatic steatosis and lower level of the methyl donor S-adenosylmethionine, it did not cause a significant reduction in the 5meC content. On the other hand, the MCD diet significantly upregulated the gene expression of the Tet enzymes, Tet2 and Tet3, and the base-excision-repair enzymes, thymine DNA glycosylase and apurinic/apyrimidinic-endonuclease 1. At the same time, the gene expression of DNA methyltransferase 1 and a, was also significantly increased by the MCD diet. These results suggest that the DNA methylation level is precisely regulated even when dietary methyl donors are restricted. Methyl-deficient diets are well known to induce oxidative stress and the oxidative-stress-induced DNA damage, 8-hydroxy-2'-deoxyguanosine (8OHdG), is reported to inhibit DNA methylation. In this study, we also clarified that the increase in 8OHdG number per DNA by the MCD diet is approximately 10 000 times smaller than the reduction in 5meC number, suggesting the contribution of 8OHdG formation to DNA methylation would not be significant.

Inorganic arsenic exposure induces E2F-dependent G0/G1 arrest via an increase in retinoblastoma family protein p130 in B-cell lymphoma A20 cells.

Inorganic arsenic exerts toxic effect on multiple systems including the immune system. We previously showed in a study on mouse thymocytes and B-cell lymphoma A20 cells that arsenite induces cell cycle arrest at G0/G1 by suppressing expression of E2F-target genes. In this study, we furthermore investigated the involvement of retinoblastoma (RB) family proteins in E2F-dependent cell cycle arrest by arsenite. Arsenite exposure of A20 cells was showed to increase the protein level of p130, a RB family member, without changing the mRNA level. Suppression of arsenite-induced p130 by siRNA reduced the G0/G1 phase, indicating that p130 accumulation is responsible for arsenite-induced G0/G1 arrest. The accumulated p130 was shown to increase the p130 complex with E2F4, a transcription-suppressing E2F. Comparison by Western blotting of arsenite-induced p130 and p130 accumulated by a proteasome inhibitor suggested that arsenite-induced p130 is hypophosphorylated and hypoubiquitinated and refractory to proteasome-dependent degradation. We also showed that arsenite increases mRNA and protein of p16(INK4a), an inhibitor of CDK4/6 that phosphorylates p130. Down-regulation of arsenite-induced p16(INK4a) by siRNA suppressed the p130 accumulation. We propose a novel mechanism in which arsenite inhibits phosphorylation/ubiquitin-dependent proteasome degradation of p130 by inducing p16(INK4a) and the accumulated p130 causes cell cycle arrest with E2F4.

In vivo mutagenicity of arsenite in the livers of gpt delta transgenic mice.

While arsenic has been classified as a Group 1 human carcinogen by the International Agency for Research on Cancer (IARC), its mutagenicity has not been fully characterized in experimental animals. The aim of this study was to assess the in vivo mutagenicity of arsenite in C57BL/6J gpt delta mice. Male gpt delta mice were given drinking water containing sodium arsenite for 3 weeks, and the hepatic genome was assayed for mutations 2 weeks later. The gpt mutation assays showed a significant increase in mutation frequency in the liver following arsenite exposure. Sequence analysis revealed that 67% of mutations detected are G:C to A:T transitions and 5% are G:C to T:A transversions in the control group, and arsenite exposure resulted in a markedly higher rate of G:C to T:A transversions (46% of mutations detected). G:C to T:A transversions have been reported to be induced following formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a representative product that results from oxidative DNA damage. We also detected a significant increase in 8-OHdG in the livers of the mice exposed to arsenite. These results demonstrate that arsenite has mutagenicity in vivo and suggest that arsenite induces G:C to T:A transversions through oxidative-stress-induced 8-OHdG formation.

Aryl hydrocarbon receptor deficiency in T cells suppresses the development of collagen-induced arthritis.

The contributions of aryl hydrocarbon receptor (Ahr) to the pathogenesis of rheumatoid arthritis have not been elucidated. Here, we show that Ahr deficiency ameliorated collagen-induced arthritis, a mouse model of RA. Collagen-immunized Ahr KO mice showed decreased serum levels of such proinflammatory cytokines as IL-1ß and IL-6. The Th17 and Th1 cell populations in lymph nodes from these mice decreased and increased, respectively, whereas the percentage of regulatory T cells was unchanged. Interestingly, a lack of Ahr specifically in T cells significantly suppressed collagen-induced arthritis development, whereas Ahr deficiency in macrophages had no effect. These finding indicate that the development of experimental autoimmune arthritis depends on the presence of Ahr in T cells, and that Th1/Th17 balance may be particularly important for this process.

Genome-wide analysis of DNA methylation changes induced by gestational arsenic exposure in liver tumors.

Inorganic arsenic is known to be a human carcinogen. Previous studies have reported that DNA methylation changes are involved in arsenic-induced carcinogenesis, therefore, DNA methylation changes that are specific to arsenic-induced tumors would be useful to distinguish tumors induced by arsenic from tumors caused by other factors and to dissect arsenic carcinogenesis. Previous studies have shown that gestational arsenic exposure of C3H mice, which tend to spontaneously develop liver tumors, increases the incidence of tumors in male offspring. In this study we used the same experimental protocol as in those previous studies and searched for DNA regions where methylation status was specifically altered in the liver tumors of arsenic-exposed offspring by using methylated DNA immunoprecipitation-CpG island microarrays. The methylation levels of the DNA regions selected were measured by quantitative methylation-specific PCR and bisulfite sequencing. The results of this study clarified a number of regions where DNA methylation status was altered in the liver tumors in the C3H mice compared to normal liver tissues. Among such regions, we showed that a gene body region of the oncogene Fosb underwent alteration in DNA methylation by gestational arsenic exposure. We also showed that Fosb expression significantly increased corresponding to the DNA methylation level of the gene body in the arsenic-exposed group. These findings suggest that the DNA methylation status can be used to identify tumors increased by gestational arsenic exposure.