Oxidative stress alters global histone modification and DNA methylation

Association between ambient air pollution and proliferation of umbilical cord blood cells

It has been established as a common knowledge that ambient air pollution (AAP) has an adverse effect on human health. The pathophysiological mechanism of this impact is likely to be related to the oxidative stress. In the current study we estimate the association between AAP and cell proliferation (CP) of umbilical cord blood cells, representing maternal organism most proximal to the fetal body. Blood samples were tested for proliferation in 292 enrolled Arab-Bedouin women at delivery (July 2012-March 2013). The estimates of AAP were defined by a hybrid satellite based model predicting both PM_2.5 (particles<2.5µm in diameter) and PM₁₀ (particles<10µm in diameter) as well as monitoring stations for gaseous air pollutants. Risk estimates of pollution exposure were adjusted to medical history, household risk factors and meteorological factors on the day of delivery or one week prior. Ambient ozone (O₃) levels on 1, 2, 3and 4 days prior to delivery were associated with lower CP (Prevalence ratio (PR)=0.92, 0.92, 0.93, 0.93, respectively). Increase in inter-quartile range (IOR) of PM_2.5 one day before delivery was associated with 9% increase in CP levels (PR=1.09). The positive direction in association was changed to negative association with CP for PM_2.5 levels measured at more distant time periods (PR=0.90 and 0.93 for lags 5 and 6 days, respectively). Investigation of PM₁₀ levels indicated a similar pattern (PR=1.05 for pollution values recorded one day before delivery and 0.93 and 0.95 for lags of 5 and 6 days, respectively). Carbon monoxide (CO) levels were associated with lower CP on the day of delivery and 1day prior (PR=0.92 and PR=0.94). To conclude, the levels of cell proliferation of umbilical cord blood cells appear to be associated with the AAP. More studies are needed to support our findings.

Perspectives on the interactions between metabolism, redox, and epigenetics in plants

Epigenetic modifications of chromatin usually involve consumption of key metabolites and redox-active molecules. Primary metabolic flux and cellular redox states control the activity of enzymes involved in chromatin modifications, such as DNA methylation, histone acetylation, and histone methylation, which in turn regulate gene expression and/or enzymatic activity of specific metabolic and redox pathways. Thus, coordination of metabolism and epigenetic regulation of gene expression is critical to control growth and development in response to the cellular environment. Much has been learned from animal and yeast cells with regard to the interplay between metabolism and epigenetic regulation, and now the metabolic control of epigenetic pathways in plants is an increasing area of study. Epigenetic mechanisms are largely similar between plant and mammalian cells, but plants display very important differences in both metabolism and metabolic/redox signaling pathways. In this review, we summarize recent developments in the field and discuss perspectives of studying interactions between plant epigenetic and metabolism/redox systems, which are essential for plant adaptation to environmental conditions.

Time in Redox Adaptation Processes: From Evolution to Hormesis

Life on Earth has to adapt to the ever changing environment. For example, due to introduction of oxygen in the atmosphere, an antioxidant network evolved to cope with the exposure to oxygen. The adaptive mechanisms of the antioxidant network, specifically the glutathione (GSH) system, are reviewed with a special focus on the time. The quickest adaptive response to oxidative stress is direct enzyme modification, increasing the GSH levels or activating the GSH-dependent protective enzymes. After several hours, a hormetic response is seen at the transcriptional level by up-regulating Nrf2-mediated expression of enzymes involved in GSH synthesis. In the long run, adaptations occur at the epigenetic and genomic level; for example, the ability to synthesize GSH by phototrophic bacteria. Apparently, in an adaptive hormetic response not only the dose or the compound, but also time, should be considered. This is essential for targeted interventions aimed to prevent diseases by successfully coping with changes in the environment e.g., oxidative stress.

MicroRNAs serve as a bridge between oxidative stress and gastric cancer (Review)

Gastric cancer (GC) remains one of the most prevalent tumors worldwide and affects human health due to its high morbidity and mortality. Mechanisms underlying occurrence and development of GC have been widely studied. Studies have revealed reactive oxygen species (ROS) generated by cells under oxidative stress (OS) are involved in gastric tumorigenesis, and modulate expression of microRNAs (miRs). As such, miRs have been shown to be associated with OS-related GC. Given the association of OS and miRs in development of GC, this review aims to summarize the relationship between miRs and OS and their role in GC development. Serving as a link between OS and GC, miRs may offer new approaches for gaining a more in-depth understanding of mechanisms of GC and may lead to the identification of new therapeutic approaches against GC.

Remodelling of the hepatic epigenetic landscape of glucose-intolerant rainbow trout (Oncorhynchus mykiss) by nutritional status and dietary carbohydrates

The rainbow trout, a carnivorous fish, displays a 'glucose-intolerant' phenotype revealed by persistent hyperglycaemia when fed a high carbohydrate diet (HighCHO). Epigenetics refers to heritable changes in gene activity and is closely related to environmental changes and thus to metabolism adjustments governed by nutrition. In this study we first assessed in the trout liver whether and how nutritional status affects global epigenome modifications by targeting DNA methylation and histone marks previously reported to be affected in metabolic diseases. We then examined whether dietary carbohydrates could affect the epigenetic landscape of duplicated gluconeogenic genes previously reported to display changes in mRNA levels in trout fed a high carbohydrate diet. We specifically highlighted global hypomethylation of DNA and hypoacetylation of H3K9 in trout fed a HighCHO diet, a well-described phenotype in diabetes. g6pcb2 ohnologs were also hypomethylated at specific CpG sites in these animals according to their up-regulation. Our findings demonstrated that the hepatic epigenetic landscape can be affected by both nutritional status and dietary carbohydrates in trout. The mechanism underlying the setting up of these epigenetic modifications has now to be explored in order to improve understanding of its impact on the glucose intolerant phenotype in carnivorous teleosts.

Oxidative stress signaling to chromatin in health and disease

Oxidative stress has a significant impact on the development and progression of common human pathologies, including cancer, diabetes, hypertension and neurodegenerative diseases. Increasing evidence suggests that oxidative stress globally influences chromatin structure, DNA methylation, enzymatic and non-enzymatic post-translational modifications of histones and DNA-binding proteins. The effects of oxidative stress on these chromatin alterations mediate a number of cellular changes, including modulation of gene expression, cell death, cell survival and mutagenesis, which are disease-driving mechanisms in human pathologies. Targeting oxidative stress-dependent pathways is thus a promising strategy for the prevention and treatment of these diseases. We summarize recent research developments connecting oxidative stress and chromatin regulation.

Oxidative products from alcohol metabolism differentially modulate pro-inflammatory cytokine expression in Kupffer cells and hepatocytes

Pro-inflammatory cytokines play a vital role in the pathogenesis of alcoholic steatohepatitis. The present study was to determine the role of alcohol-induced oxidative stress in modulating cytokine production. A rat model of alcohol consumption was used to determine alcohol-induced hepatic cytokine expression. Chronic alcohol exposure caused lipid accumulation, oxidative stress, and inflammation in the livers of Wistar rats. The role of oxidative stress in regulating cell type-specific cytokine production was further dissected in vitro. Lipopolysaccharide (LPS) dose-dependently upregulated TNF-α, MIP-1α, MCP-1, and CINC-1 in Kupffer cells-SV40, whereas TNF-α dose-dependently induced CINC-1, IP-10, and MIP-2 expression in H4IIEC3 hepatoma cells. An additive effect on cytokine production was observed in both Kupffer cells-SV40 and hepatocytes when combined hydrogen peroxide with LPS or TNF-α, respectively, which was associated with NF-κB activation and histone H3 hyper-acetylation. Unexpectedly, an inhibitory effect of 4-hydroxynonenal on cytokine production was revealed in LPS-treated Kupffer cells-SV40. Mechanistic study showed that 4-hydroxynonenal significantly enhanced mRNA degradation of TNF-α, MCP-1, and MIP-1α, and decreased the protein levels of MCP-1 in LPS-stimulated Kupffer cells-SV40 through reducing the phosphorylation of mRNA binding proteins. This study suggests that Kupffer cells and hepatocytes express distinct pro-inflammatory cytokines/chemokines in response to alcohol intoxication, and oxidative products (4-hydroxynonenal) differentially modulate pro-inflammatory cytokine/chemokine production via NF-κB signaling, histone acetylation, and mRNA stability.

OGG1 is essential in oxidative stress induced DNA demethylation

DNA demethylation is an essential cellular activity to regulate gene expression; however, the mechanism that triggers DNA demethylation remains unknown. Furthermore, DNA demethylation was recently demonstrated to be induced by oxidative stress without a clear molecular mechanism. In this manuscript, we demonstrated that 8-oxoguanine DNA glycosylase-1 (OGG1) is the essential protein involved in oxidative stress-induced DNA demethylation. Oxidative stress induced the formation of 8-oxoguanine (8-oxoG). We found that OGG1, the 8-oxoG binding protein, promotes DNA demethylation by interacting and recruiting TET1 to the 8-oxoG lesion. Downregulation of OGG1 makes cells resistant to oxidative stress-induced DNA demethylation, while over-expression of OGG1 renders cells susceptible to DNA demethylation by oxidative stress. These data not only illustrate the importance of base excision repair (BER) in DNA demethylation but also reveal how the DNA demethylation signal is transferred to downstream DNA demethylation enzymes.

Epigenetic Regulation of Oxidative Stress in Ischemic Stroke

The prevalence and incidence of stroke rises with life expectancy. However, except for the use of recombinant tissue-type plasminogen activator, the translation of new therapies for acute stroke from animal models into humans has been relatively unsuccessful. Oxidative DNA and protein damage following stroke is typically associated with cell death. Cause-effect relationships between reactive oxygen species and epigenetic modifications have been established in aging, cancer, acute pancreatitis, and fatty liver disease. In addition, epigenetic regulatory mechanisms during stroke recovery have been reviewed, with focuses mainly on neural apoptosis, necrosis, and neuroplasticity. However, oxidative stress-induced epigenetic regulation in vascular neural networks following stroke has not been sufficiently explored. Improved understanding of the epigenetic regulatory network upon oxidative stress may provide effective antioxidant approaches for treating stroke. In this review, we summarize the epigenetic events, including DNA methylation, histone modification, and microRNAs, that result from oxidative stress following experimental stroke in animal and cell models, and the ways in which epigenetic changes and their crosstalk influence the redox state in neurons, glia, and vascular endothelial cells, helping us to understand the foregone and vicious epigenetic regulation of oxidative stress in the vascular neural network following stroke.

Potential Role of Epigenetic Mechanism in Manganese Induced Neurotoxicity

Manganese is a vital nutrient and is maintained at an optimal level (2.5–5 mg/day) in human body. Chronic exposure to manganese is associated with neurotoxicity and correlated with the development of various neurological disorders such as Parkinson's disease. Oxidative stress mediated apoptotic cell death has been well established mechanism in manganese induced toxicity. Oxidative stress has a potential to alter the epigenetic mechanism of gene regulation. Epigenetic insight of manganese neurotoxicity in context of its correlation with the development of parkinsonism is poorly understood. Parkinson's disease is characterized by the α-synuclein aggregation in the form of Lewy bodies in neuronal cells. Recent findings illustrate that manganese can cause overexpression of α-synuclein. α-Synuclein acts epigenetically via interaction with histone proteins in regulating apoptosis. α-Synuclein also causes global DNA hypomethylation through sequestration of DNA methyltransferase in cytoplasm. An individual genetic difference may also have an influence on epigenetic susceptibility to manganese neurotoxicity and the development of Parkinson's disease. This review presents the current state of findings in relation to role of epigenetic mechanism in manganese induced neurotoxicity, with a special emphasis on the development of Parkinson's disease.

Association of downregulated HDAC 2 with the impaired mitochondrial function and cytokine secretion in the monocytes/macrophages from gestational diabetes mellitus patients

Gestational diabetes mellitus (GDM) is associated with an increased risk of type 2 diabetes (T2DM) and cardiovascular diseases in later life, yet with underlying mechanisms unclear. The present study was to explore the association of upregulated histone deacetylase 2 (HDAC 2) with the impaired mitochondrial function and the cytokine secretion in the monocytes/macrophages from GDM patients. In this study, we examined the mitochondrial function, proinflamatory cytokine secretion and the HDAC 2 level in the serum or in the monocytes/macrophages from GDM patients, investigated the influence by HDAC 2 inhibitor, AR-42 (N-hydroxy-4-[[(2S)-3-methyl-2-phenylbutanoyl]amino]benzamide), on the mitochondrial function and cytokine secretion in the isolated GDM monocytes/macrophages. Results demonstrated an increased mitochondria size, mitochondrial superoxide and reactive oxygen species (ROS) production, and an undermined mitochondria membrane potential (MMP) in the GDM monocytes/macrophages. And the serum levels of interleukin (IL)-1β, tumor necrosis factor (TNF)-α and IL-6 were also markedly higher in the GDM pregnancies, while the expression and activity of HDAC 2 was downregulated. Moreover, AR-42-mediated HDAC 2 inhibition in vitro contributed to the impaired mitochondrial function and the proinflamatory cytokine secretion. In conclusion, this study suggests an association of the impaired mitochondrial function and the promoted proinflamatory cytokine secretion with the reduced HDAC 2 activity in GDM. These findings may present HDAC 2 as a target for GDM treatment.

The Emerging Role of DNA Methylation in Kidney Transplantation: A Perspective

Allograft outcome depends on a range of factors, including donor age, the allo-immune response, ischemia-reperfusion injury, and interstitial fibrosis of the allograft. Changes in the epigenome, and in DNA methylation in particular, have been implicated in each of these processes, in either the kidney or other organ systems. This review provides a primer for DNA methylation analyses and a discussion of the strengths and weaknesses of current studies, but it is also a perspective for future DNA methylation research in kidney transplantation. We present exciting prospects for leveraging DNA methylation analyses as a tool in kidney biology research, and as a diagnostic or prognostic marker for predicting allograft quality and success. Topics discussed include DNA methylation changes in aging and in response to hypoxia and oxidative stress upon ischemia-reperfusion injury. Moreover, emerging evidence suggests that DNA methylation contributes to organ fibrosis and that systemic DNA methylation alterations correlate with the rate of kidney function decline in patients with chronic kidney disease and end-stage renal failure. Monitoring or targeting the epigenome could therefore reveal novel therapeutic approaches in transplantation and open up paths to biomarker discovery and targeted therapy.

Demethylation drug 5-Aza-2'-deoxycytidine-induced upregulation of miR-200c inhibits the migration, invasion and epithelial-mesenchymal transition of clear cell renal cell carcinoma in vitro

The microRNA (miR)-200 family has been found to be involved in the process of mesenchymal-epithelial transition during renal development. Deregulation of miR-200c has been suggested to be involved in clear cell renal cell carcinoma (ccRCC). However, the precise role of miR-200c in the regulation of ccRCC metastasis has not been previously reported. In the present study, it was observed that miR-200c was frequently downregulated in ccRCC tissue compared with matched adjacent normal tissue. The expression of miR-200c was additionally reduced in ccRCC cell lines when compared with levels in normal renal cells. The DNA demethylation drug 5-Aza-2'-deoxycytidine (Aza) was used to treat several ccRCC cell lines, and it was observed that the expression of miR-200c was significantly increased following Aza treatment. Furthermore, treatment with Aza markedly inhibited ccRCC cell invasion and migration, while treatment with miR-200c inhibitor significantly enhanced invasion and migration of ccRCC cells. In addition, Aza treatment significantly promoted expression of E-cadherin and inhibited the expression of N-cadherin, while the inhibition of miR-200c downregulated E-cadherin and upregulated the expression of N-cadherin, suggesting that miR-200c has a suppressive role in epithelial-mesenchymal transition (EMT) of ccRCC cells. In conclusion, it was suggested that demethylation drug Aza-induced upregulation of miR-200c may inhibit migration, invasion and EMT in ccRCC cells.

The Simultaneous Elevation of Oxidative Stress Markers and Wilms' Tumor 1 Gene during the Progression of Myelodysplastic Syndrome

Oxidative stress is closely related to iron overload in myelodysplastic syndrome (MDS) and induces DNA damage. We evaluated the oxidative stress markers derivatives of reactive oxidative metabolites (dROM) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) during azacitidine treatment in an MDS patient. Simultaneous with an increase in the expression of Wilms' Tumor 1 (WT1) gene in the peripheral blood, the serum dROM level was elevated, and this increase was observed earlier than the increases in ferritin and 8-OHdG. Throughout the clinical course, dROM and 8-OHdG correlated significantly with WT1 and with ferritin, suggesting that changes in the oxidative stress marker levels reflect not only iron overload but also disease progression of MDS.

Role of Chlorogenic Acids in Controlling Oxidative and Inflammatory Stress Conditions

Chlorogenic acids (CGAs) are esters formed between caffeic and quinic acids, and represent an abundant group of plant polyphenols present in the human diet. CGAs have different subgroups that include caffeoylquinic, p-coumaroylquinic, and feruloyquinic acids. Results of epidemiological studies suggest that the consumption of beverages such as coffee, tea, wine, different herbal infusions, and also some fruit juices are linked to reduced risks of developing different chronic diseases. These beverages contain CGAs present in different concentrations and isomeric mixtures. The underlying mechanism(s) for specific health benefits attributed to CGAs involves mitigating oxidative stress, and hence the related adverse effects associated with an unbalanced intracellular redox state. There is also evidence to show that CGAs exhibit anti-inflammatory activities by modulating a number of important metabolic pathways. This review will focus on three specific aspects of the relevance of CGAs in coffee beverages; namely: (1) the relative composition of different CGA isomers present in coffee beverages; (2) analysis of in vitro and in vivo evidence that CGAs and individual isomers can mitigate oxidative and inflammatory stresses; and (3) description of the molecular mechanisms that have a key role in the cell signaling activity that underlines important functions.

Effects of Phenobarbital on Expression of UDP-Glucuronosyltransferase 1a6 and 1a7 in Rat Brain

UDP-glucuronosyltransferase (UGT), a phase II drug-metabolizing enzyme, is expressed in the brain and can catalyze glucuronidation of endogenous and exogenous substrates in the brain. Thus, changes in UGT1A expression could affect homeostasis and drug efficacy. Phenobarbital (PB), a typical inducer of drug-metabolizing enzymes, has been reported to induce oxidative stress and epigenetic changes, which could alter UGT expression in the brain. Here, we aimed to clarify the effects of PB on Ugt1a6 and Ugt1a7 gene expression in rat brains. Sprague-Dawley rats were treated intraperitoneally with PB (80 mg/kg), once daily for 7 days. Ugt1a6 and Ugt1a7 mRNA expression levels were increased in the striatum and thalamus (Ugt1a6, 3.0- and 2.9-fold, respectively; Ugt1a7, 2.6- and 2.6-fold, respectively). Acetaminophen glucuronidation was also increased in the medulla oblongata and thalamus by 1.8- and 1.2-fold, respectively. The induction rates within different brain regions were correlated with Ugt1a6 and Ugt1a7 mRNA expression, and the degree of induction also correlated with that of NF-E2-related factor-2 mRNA. Measurement of oxidative stress markers suggested that PB induced oxidative stress in brain regions in which Ugt1a6 and Ugt1a7 mRNAs were increased. Moreover, histone modifications were altered by PB treatment, resulting in increased histone H3 lysine 4 trimethylation in the striatum and thalamus and decreased histone H3 lysine 9 trimethylation in the thalamus. These results suggested that oxidative stress and histone modifications may promote transcriptional activation of Ugt1a6 and Ugt1a7 genes. In summary, Ugt1a6 and Ugt1a7 mRNA levels were increased by PB treatment, which may alter pharmacokinetics in the brain.

Epigenetic regulation of Keap1-Nrf2 signaling

The kelch-like ECH-associated protein 1 (Keap1)-nuclear factor erythroid 2-related factor 2 (Nrf2) signaling axis serves as a "master regulator" in response to oxidative/electrophilic stresses and chemical insults through the coordinated induction of a wide array of cytoprotective genes. Therefore, activation of Nrf2 is considered to be an important approach for preventing chronic diseases triggered by stresses and toxins, including cancer. Despite extensive studies suggested that the Keap1-Nrf2 signaling pathway is subject to multiple layers of regulation at the transcriptional, translational, and post-translational levels, the potential epigenetic regulation of Nrf2 and Keap1 has begun to be recognized only in recent years. Epigenetic modifications, heritable alterations in gene expression that occur without changes in the primary DNA sequence, have been reported to be profoundly involved in oxidative stress responses. In this review, we discuss the latest findings regarding the epigenetic regulation of Keap1-Nrf2 signaling by DNA methylation, histone modification, and microRNAs. The crosstalk among these epigenetic modifications in the regulation of Keap1-Nrf2 signaling pathways is also discussed. Studies of the epigenetic modification of Nrf2 and Keap1 have not only enhanced our understanding of this complex cellular defense system but have also provided potential new therapeutic targets for the prevention of certain diseases.

LINE-1 hypomethylation induced by reactive oxygen species is mediated via depletion of S-adenosylmethionine

Whether long interspersed nuclear element-1 (LINE-1) hypomethylation induced by reactive oxygen species (ROS) was mediated through the depletion of S-adenosylmethionine (SAM) was investigated. Bladder cancer (UM-UC-3 and TCCSUP) and human kidney (HK-2) cell lines were exposed to 20 μM H2O2 for 72 h to induce oxidative stress. Level of LINE-1 methylation, SAM and homocysteine (Hcy) was measured in the H2O2 -exposed cells. Effects of α-tocopheryl acetate (TA), N-acetylcysteine (NAC), methionine, SAM and folic acid on oxidative stress and LINE-1 methylation in the H2O2 -treated cells were explored. Viabilities of cells treated with H2O2 were not significantly changed. Intracellular ROS production and protein carbonyl content were significantly increased, but LINE-1 methylation was significantly decreased in the H2O2 -treated cells. LINE-1 methylation was restored by TA, NAC, methionine, SAM and folic acid. SAM level in H2O2 -treated cells was significantly decreased, while total glutathione was significantly increased. SAM level in H2O2 -treated cells was restored by NAC, methionine, SAM and folic acid; while, total glutathione level was normalized by TA and NAC. Hcy was significantly decreased in the H2O2 -treated cells and subsequently restored by NAC. In conclusion, in bladder cancer and normal kidney cells exposed to H2O2 , SAM and Hcy were decreased, but total glutathione was increased. Treatments with antioxidants (TA and NAC) and one-carbon metabolites (SAM, methionine and folic acid) restored these changes. This pioneer finding suggests that exposure of cells to ROS activates glutathione synthesis via the transsulfuration pathway leading to deficiency of Hcy, which consequently causes SAM depletion and eventual hypomethylation of LINE-1.