Cdc42 Regulates Arsenic-induced NADPH Oxidase Activation and Cell Migration through Actin Filament Reorganization

Mechanisms of genotoxicity and proteotoxicity induced by the metalloids arsenic and antimony

Arsenic and antimony are metalloids with profound effects on biological systems and human health. Both elements are toxic to cells and organisms, and exposure is associated with several pathological conditions including cancer and neurodegenerative disorders. At the same time, arsenic- and antimony-containing compounds are used in the treatment of multiple diseases. Although these metalloids can both cause and cure disease, their modes of molecular action are incompletely understood. The past decades have seen major advances in our understanding of arsenic and antimony toxicity, emphasizing genotoxicity and proteotoxicity as key contributors to pathogenesis. In this review, we highlight mechanisms by which arsenic and antimony cause toxicity, focusing on their genotoxic and proteotoxic effects. The mechanisms used by cells to maintain proteostasis during metalloid exposure are also described. Furthermore, we address how metalloid-induced proteotoxicity may promote neurodegenerative disease and how genotoxicity and proteotoxicity may be interrelated and together contribute to proteinopathies. A deeper understanding of cellular toxicity and response mechanisms and their links to pathogenesis may promote the development of strategies for both disease prevention and treatment.

Expression-Based Diagnosis, Treatment Selection, and Drug Development for Breast Cancer

There is currently no gene expression assay that can assess if premalignant lesions will develop into invasive breast cancer. This study sought to identify biomarkers for selecting patients with a high potential for developing invasive carcinoma in the breast with normal histology, benign lesions, or premalignant lesions. A set of 26-gene mRNA expression profiles were used to identify invasive ductal carcinomas from histologically normal tissue and benign lesions and to select those with a higher potential for future cancer development (ADHC) in the breast associated with atypical ductal hyperplasia (ADH). The expression-defined model achieved an overall accuracy of 94.05% (AUC = 0.96) in classifying invasive ductal carcinomas from histologically normal tissue and benign lesions (n = 185). This gene signature classified cancer development in ADH tissues with an overall accuracy of 100% (n = 8). The mRNA expression patterns of these 26 genes were validated using RT-PCR analyses of independent tissue samples (n = 77) and blood samples (n = 48). The protein expression of PBX2 and RAD52 assessed with immunohistochemistry were prognostic of breast cancer survival outcomes. This signature provided significant prognostic stratification in The Cancer Genome Atlas breast cancer patients (n = 1100), as well as basal-like and luminal A subtypes, and was associated with distinct immune infiltration and activities. The mRNA and protein expression of the 26 genes was associated with sensitivity or resistance to 18 NCCN-recommended drugs for treating breast cancer. Eleven genes had significant proliferative potential in CRISPR-Cas9/RNAi screening. Based on this gene expression signature, the VEGFR inhibitor ZM-306416 was discovered as a new drug for treating breast cancer.

Role of a small GTPase Cdc42 in aging and age-related diseases

A small GTPase, Cdc42 is evolutionarily one of the most ancient members of the Rho family, which is ubiquitously expressed and involved in a wide range of fundamental cellular functions. The crucial role of Cdc42 includes regulation of the actin cytoskeleton, cell polarity, morphology and migration, endocytosis and exocytosis, cell cycle, and proliferation in many different cell types. Many studies have provided compelling yet contradicting evidence that Cdc42 dysregulation plays an important role in cellular and tissue aging. Furthermore, Cdc42 is a critical factor in the development and progression of aging-related pathologies, such as neurodegenerative and cardiovascular disorders, diabetes type 2, and aging-related disorders of the joints and bones, and the inhibition of the Cdc42 demonstrates potentially significant therapeutic and anti-aging effects in animal models of aging and disease. However, regulation of Cdc42 expression and activity is very complex and depends on many factors, such as the origin and complexity of the tissues, hormonal status, etc. Therefore, this review is focused on current advances in understanding the underlying cellular and molecular mechanisms associated with Cdc42 activity and regulation of senescence in different cell types since they may provide a foundation for novel therapeutic strategies and targeted drugs to reverse the aging process and treat aging-associated disorders.

Functional interactions between NADPH oxidase 5 and actin

NADPH oxidase 5 (NOX5) is a transmembrane oxidative signaling enzyme which produces superoxide in response to intracellular calcium flux. Increasing evidence indicates that NOX5 is involved in a variety of physiological processes as well as human disease, however, details of NOX5 signaling pathways and targets of NOX5 mediated oxidative modifications remain poorly resolved. Actin dynamics have previously been shown to be modulated by oxidative modification, however, a direct connection to NOX5 expression and activity has not been fully explored. Here we show that NOX5 and actin interact in the cell, and each modulate the activity of the other. Using actin effector molecules jasplakinolide, cytochalasin D and latrunculin A, we show that changes in actin dynamics affect NOX5 superoxide production. In tandem, NOX5 oxidatively modifies actin, and shifts the ratio of filamentous to monomeric actin. Finally, we show that knockdown of NOX5 in the pancreatic cancer cell line PSN-1 impairs cell migration. Together our findings indicate an important link between actin dynamics and oxidative signaling through NOX5.

Contribution of NADPH oxidase to the retention of UVR-induced DNA damage by arsenic

Arsenic is a naturally occurring element present in food, soil and water and human exposure is associated with increased cancer risk. Arsenic inhibits DNA repair at low, non-cytotoxic concentrations and amplifies the mutagenic and carcinogenic impact of other DNA-damaging agents, such as ultraviolet radiation (UVR). Arsenic exposure leads to oxidation of zinc coordinating cysteine residues, zinc loss and decreased activity of the DNA repair protein poly(ADP)ribose polymerase (PARP)-1. Because arsenic stimulates NADPH oxidase (NOX) activity leading to generation of reactive oxygen species (ROS), the goal of this study was to investigate the role of NOX in arsenic-induced inhibition of PARP activity and retention of DNA damage. NOX involvement in the arsenic response was assessed in vitro and in vivo. Keratinocytes were treated with or without arsenite, solar-simulated UVR, NOX inhibitors and/or isoform specific NOX siRNA. Knockdown or inhibition of NOX decreased arsenite-induced ROS, PARP-1 oxidation and DNA damage retention, while restoring arsenite inhibition of PARP-1 activity. The NOX2 isoform was determined to be the major contributor to arsenite-induced ROS generation and DNA damage retention. In vivo DNA damage was measured by immunohistochemical staining and analysis of dorsal epidermis sections from C57BI/6 and p91phox knockout (NOX2^-/-) mice. There was no significant difference in solar-simulated UVR DNA damage as detected by percent PH2AX positive cells within NOX2^-/- mice versus control. In contrast, arsenite-dependent retention of UVR-induced DNA damage was markedly reduced. Altogether, the in vitro and in vivo findings indicate that NOX is involved in arsenic enhancement of UVR-induced DNA damage.

Arsenic co-carcinogenesis: Inhibition of DNA repair and interaction with zinc finger proteins

Arsenic is widely present in the environment and is associated with various population health risks including cancers. Arsenic exposure at environmentally relevant levels enhances the mutagenic effect of other carcinogens such as ultraviolet radiation. Investigation on the molecular mechanisms could inform the prevention and intervention strategies of arsenic carcinogenesis and co-carcinogenesis. Arsenic inhibition of DNA repair has been demonstrated to be an important mechanism, and certain DNA repair proteins have been identified to be extremely sensitive to arsenic exposure. This review will summarize the recent advances in understanding the mechanisms of arsenic carcinogenesis and co-carcinogenesis, including DNA damage induction and ROS generation, particularly how arsenic inhibits DNA repair through an integrated molecular mechanism which includes its interactions with sensitive zinc finger DNA repair proteins.

p62 functions as a signal hub in metal carcinogenesis

A number of metals are toxic and carcinogenic to humans. Reactive oxygen species (ROS) play an important role in metal carcinogenesis. Oxidative stress acts as the converging point among various stressors with ROS being the main intracellular signal transducer. In metal-transformed cells, persistent expression of p62 and erythroid 2-related factor 2 (Nrf2) result in apoptosis resistance, angiogenesis, inflammatory microenvironment, and metabolic reprogramming, contributing to overall mechanism of metal carcinogenesis. Autophagy, a conserved intracellular process, maintains cellular homeostasis by facilitating the turnover of protein aggregates, cellular debris, and damaged organelles. In addition to being a substrate of autophagy, p62 is also a crucial molecule in a myriad of cellular functions and in molecular events, which include oxidative stress, inflammation, apoptosis, cell proliferation, metabolic reprogramming, that modulate cell survival and tumor growth. The multiple functions of p62 are appreciated by its ability to interact with several key components involved in various oncogenic pathways. This review summarizes the current knowledge and progress in studies of p62 and metal carcinogenesis with emphasis on oncogenic pathways related to oxidative stress, inflammation, apoptosis, and metabolic reprogramming.

Therapeutic potential of diosmin, a citrus flavonoid against arsenic-induced neurotoxicity via suppression of NOX 4 and its subunits

OBJECTIVES:

Water contaminated with arsenic affected millions of people worldwide and arsenic exposure is related to various neurological disorders. Hence, the current study was planned to investigate the neuroprotective activity of diosmin (DSN) against arsenic induced neurotoxicity as an attempt to identify therapeutic intervention to combat arsenicism.

MATERIALS AND METHODS:

Sodium arsenite an inducer of neurotoxicity was administered orally (13 mg/kg) and DSN treatment at two selected doses (50 and 100 mg/kg) was done for 21 days. Behavioral and biochemical variations were examined by various parameters. Furthermore, histopathological and immunohistochemistry studies were done with the brain sections.

RESULTS:

The behavioral studies evidenced that arsenic has suppressed the exploratory behavior and motor coordination in rats and DSN treatment has recovered the behavioral changes to normal. Arsenic administration has also found to induce oxidative stress and DSN co-treatment has ameliorated the oxidative stress markers. Interestingly, depleted levels of neurotransmitters were observed with the arsenic and it was restored back by the DSN treatment. Histopathological alterations like pyknosis of the neuronal cells were identified with arsenic exposure and subsided upon DSN co administration. Immunohistochemical studies have revealed the expression of NOX4 and its gp91^phox and P47^phox subunits and its suppression by DSN treatment may be the key therapeutic factor of it.

CONCLUSIONS:

Treatment with DSN showed a beneficial effect in protecting against arsenic-induced neurotoxicity by suppressing the toxicity changes and the antioxidant effect of DSN might be attributed to its ability of suppressing NOX4 and its subunits.

Metals and molecular carcinogenesis

Many metals are essential for living organisms, but at higher doses they may be toxic and carcinogenic. Metal exposure occurs mainly in occupational settings and environmental contaminations in drinking water, air pollution and foods, which can result in serious health problems such as cancer. Arsenic (As), beryllium (Be), cadmium (Cd), chromium (Cr) and nickel (Ni) are classified as Group 1 carcinogens by the International Agency for Research on Cancer. This review provides a comprehensive summary of current concepts of the molecular mechanisms of metal-induced carcinogenesis and focusing on a variety of pathways, including genotoxicity, mutagenesis, oxidative stress, epigenetic modifications such as DNA methylation, histone post-translational modification and alteration in microRNA regulation, competition with essential metal ions and cancer-related signaling pathways. This review takes a broader perspective and aims to assist in guiding future research with respect to the prevention and therapy of metal exposure in human diseases including cancer.

Zinc exerts its renal protection effect on arsenic-exposed common carp: A signaling network comprising Nrf2, NF-κB and MAPK pathways

Epidemiological and laboratory investigations have extensively indicated that arsenic exposure accounts for several kidney diseases. Zinc has been suggested as a possible natural preventive and therapeutic agent. This study is designed to explore the beneficial effect of zinc supplementation against arsenic-induced renal toxicity in common carp, and the results point to signaling pathway possibly compromised. In the present study, renal injury was induced in common carp by waterborne exposure to arsenic (2.83 mg/L) for 30 days, and zinc (1 mg/L) was simultaneously supplemented. First, the arsenic-exposed fish showed histological and functional renal alterations (indicated by hematoxylin-eosin staining, biochemical indexes and a TUNEL assay). Moreover, as a reactive oxygen species (ROS) stimulant, arsenic was found to induce oxidative toxicity as determined by increased renal ROS, malondialdehyde, protein carbonyl and 8-hydroxydeoxyguanosine levels. When antioxidant-mediation attempts (through superoxide dismutase and glutathione)-mediated to restore homeostasis failed and ROS increased to extreme levels, inflammation (indicated by elevated inducible nitric oxide synthetase, tumor necrosis factor-alpha and interleukins levels) and apoptosis (through both mitochondrial- and death receptor-dependent pathways) were triggered. However, abnormalities in the upstream mediators Nrf2, NF-κB and MAPK were significantly ameliorated and blocked by treatment with zinc. In conclusion, zinc exerts a substantial protective effect against arsenic-triggered subchronic renal injury in common carp via the amelioration of oxidative stress, suppression of apoptosis and reduced inflammation through Nrf2, NF-κB and MAPK signaling.

Arsenite and its trivalent methylated metabolites inhibit glucose-stimulated calcium influx and insulin secretion in murine pancreatic islets

Chronic exposure to inorganic arsenic (iAs), a common drinking water and food contaminant, has been associated with an increased risk of type 2 diabetes in population studies worldwide. Several mechanisms underlying the diabetogenic effects of iAs have been proposed through laboratory investigations. We have previously shown that exposure to arsenite (iAs(III)) or its methylated trivalent metabolites, methylarsonite (MAs(III)) and dimethylarsinite (DMAs(III)), inhibits glucose-stimulated insulin secretion (GSIS) in pancreatic islets, without significant effects on insulin expression or insulin content. The goal of the present study was to determine if iAs(III) and/or its metabolites inhibit Ca²⁺ influx, an essential mechanism that regulates the release of insulin from β cells in response to glucose. We found that in vitro exposures for 48 h to non-cytotoxic concentrations of iAs(III), MAs(III), and DMAs(III) impaired Ca²⁺ influx in isolated murine pancreatic islets stimulated with glucose. MAs(III) and DMAs(III) were more potent inhibitors of Ca²⁺ influx than iAs(III). These arsenicals also inhibited Ca²⁺ influx and GSIS in islets treated with depolarizing levels of potassium chloride in the absence of glucose. Treatment with Bay K8644, a Ca_v1.2 channel agonist, did not restore insulin secretion in arsenical-exposed islets. Tolbutamide, a K_ATP channel blocker, prevented inhibition of insulin secretion in MAs(III)- and DMAs(III)-exposed islets, but only marginally in islets exposed to iAs(III). Our findings suggest that iAs(III), MAs(III), and DMAs(III) inhibit glucose-stimulated Ca²⁺ influx in pancreatic islets, possibly by interfering with K_ATP and/or Ca_v1.2 channel function. Notably, the mechanisms underlying inhibition of GSIS by iAs(III) may differ from those of its trivalent methylated metabolites.

2,3,7,8-Tetrachlorodibenzo-p-dioxin promotes migration ability of primary cultured rat astrocytes via aryl hydrocarbon receptor

Emerging evidence showed that 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) could induce expression of certain reactivation-associated genes in astrocytes, however, the consequent cellular effects and molecular mechanisms are still unclear. During the process of astrocyte reactivation, migration is a critical cellular event. In the present study, we employed wound-healing assay and Transwell® motility assay to explore the effects of TCDD on cell migration in primary cultured rat cortical astrocytes. We found that upon TCDD treatments at relative low concentrations (10^-10 and/or 10^-9 mol/L), the ability of primary astrocytes to migrate horizontally and vertically was promoted. In line with this cellular effect, the mRNA expression of two pro-migratory genes, including cell division cycle 42 (CDC42) and matrix metalloproteinase 2 (MMP2) was induced by TCDD treatment. Dioxin exerts its toxic effects mainly through aryl hydrocarbon receptor (AhR) pathway. So the role of AhR pathway in the pro-migratory effects of TCDD was examined using an AhR antagonist, CH223191. We found that application of CH223191 significantly reversed the pro-migratory effects of TCDD. Interestingly, the basal ability of horizontal migration as well as basal levels of CDC42 and MMP2 expression were dramatically reduced suggesting a possible physiological role of AhR in maintaining the endogenous migration ability of the primary astrocytes. These findings support the notion that dioxin promotes astrocyte reactivation at molecular and cellular levels.

Overlapping Mechanisms of Peripheral Nerve Regeneration and Angiogenesis Following Sciatic Nerve Transection

Peripheral nervous system owns the ability of self-regeneration, mainly in its regenerative microenvironment including vascular network reconstruction. More recently, more attentions have been given to the close relationship between tissue regeneration and angiogenesis. To explore the overlap of molecular mechanisms and key regulation molecules between peripheral nerve regeneration and angiogenesis post peripheral nerve injury, integrative and bioinformatic analysis was carried out for microarray data of proximal stumps after sciatic nerve transection in SD rats. Nerve regeneration and angiogenesis were activated at 1 day immediately after sciatic nerve transection simultaneously. The more obvious changes of transcription regulators and canonical pathways suggested a phase transition between 1 and 4 days of both nerve regeneration and angiogenesis after sciatic nerve transection. Furthermore, 16 differentially expressed genes participated in significant biological processes of both nerve regeneration and angiogenesis, a few of which were validated by qPCR and immunofluorescent staining. It was demonstrated that STAT3, EPHB3, and Cdc42 co-expressed in Schwann cells and vascular endothelial cells to play a key role in regulation of nerve regeneration and angiogenesis simultaneously response to sciatic nerve transection. We provide a framework for understanding biological processes and precise molecular correlations between peripheral nerve regeneration and angiogenesis after peripheral nerve transection. Our work serves as an experimental basis and a valuable resource to further understand molecular mechanisms that define nerve injury-induced micro-environmental variation for achieving desired peripheral nerve regeneration.

Unexpected cross-reactivity of anti-cathepsin B antibodies leads to uncertainties regarding the mechanism of action of anti-CD20 monoclonal antibody GA101

GA101, also known as obinutuzumab or Gazyva (Gazyvaro), is a glycoengineered type II humanized antibody that targets the CD20 antigen expressed at the surface of B-cells. This novel anti-CD20 antibody is currently assessed in clinical trials with promising results as a single agent or as part of therapeutic combinations for the treatment of B-cell malignancies. Detailed understanding of the mechanisms of GA101-induced cell death is needed to get insight into possible resistance mechanisms occurring in patients. Although multiple in vitro and in vivo mechanisms have been suggested to describe the effects of GA101 on B-cells, currently available data are ambiguous. The aim of our study was to clarify the cellular mechanisms involved in GA101-induced cell death in vitro, and more particularly the respective roles played by lysosomal and mitochondrial membrane permeabilization. Our results confirm previous reports suggesting that GA101 triggers homotypic adhesion and caspase-independent cell death, two processes that are dependent on actin remodeling and involve the production of reactive oxygen species. With respect to lysosomal membrane permeabilization (LMP), our data suggest that lack of specificity of available antibodies directed against cathepsin B may have confounded previously published results, possibly challenging current LMP-driven model of GA101 action mode.

Cdc42 Promotes Schwann Cell Proliferation and Migration Through Wnt/β-Catenin and p38 MAPK Signaling Pathway After Sciatic Nerve Injury

Schwann cells (SCs) are unique glial cells in the peripheral nerve and may secrete multiple neurotrophic factors, adhesion molecules, extracellular matrix molecules to form the microenvironment of peripheral nerve regeneration, guiding and supporting nerve proliferation and migration. Cdc42 plays an important regulatory role in dynamic changes of the cytoskeleton. However, there is a little study referred to regulation and mechanism of Cdc42 on glial cells after peripheral nerve injury. The present study investigated the role of Cdc42 in the proliferation and migration of SCs after sciatic nerve injury. Cdc42 expression was tested, showing that the mRNA and protein expression levels of Cdc42 were significantly up-regulated after sciatic nerve injury. Then, we isolated and purified SCs from injuried sciatic nerve at day 7. The purified SCs were transfected with Cdc42 siRNA and pcDNA3.1-Cdc42, and the cell proliferation, cell cycle and migration were assessed. The results implied that Cdc42 siRNA remarkably inhibited Schwann cell proliferation and migration, and resulted in S phase arrest. While pcDNA3.1-Cdc42 showed a contrary effect. Besides, we also observed that Cdc42 siRNA down-regulated the protein expression of β-catenin, Cyclin D1, c-myc and p-p38, which were up-regulated by pcDNA3.1-Cdc42. Meanwhile, the inhibitor of Wnt/β-catenin and p38 MAPK signaling pathway IWP-2 and SB203580 significantly inhibited the effect of pcDNA3.1-Cdc42 on cell proliferation and migration. Overall, our data indicate that Cdc42 regulates Schwann cell proliferation and migration through Wnt/β-catenin and p38 MAPK signaling pathway after sciatic nerve injury, which provides further insights into the therapy of the sciatic nerve injury.

NOX2 amplifies acetaldehyde-mediated cardiomyocyte mitochondrial dysfunction in alcoholic cardiomyopathy

Alcoholic cardiomyopathy (ACM) resulting from excess alcohol consumption is an important cause of heart failure (HF). Although it is assumed that the cardiotoxicity of the ethanol (EtOH)-metabolite acetaldehyde (ACA) is central for its development and progression, the exact mechanisms remain obscure. Murine cardiomyocytes (CMs) exposed to ACA or EtOH showed increased superoxide (O₂^•−) levels and decreased mitochondrial polarization, both being normalized by NADPH oxidase (NOX) inhibition. C57BL/6 mice and mice deficient for the ACA-degrading enzyme mitochondrial aldehyde dehydrogenase (ALDH-2^−/−) were fed a 2% EtOH diet for 5 weeks creating an ACA-overload. 2% EtOH-fed ALDH-2^−/− mice exhibited a decreased cardiac function, increased heart-to-body and lung-to-body weight ratios, increased cardiac levels of the lipid peroxidation product malondialdehyde (MDA) as well as increased NOX activity and NOX2/glycoprotein 91^phox (NOX2/gp91^phox) subunit expression compared to 2% EtOH-fed C57BL/6 mice. Echocardiography revealed that ALDH-2^−/−/gp91^phox−/− mice were protected from ACA-overload-induced HF after 5 weeks of 2% EtOH-diet, demonstrating that NOX2-derived O₂^•− contributes to the development of ACM. Translated to human pathophysiology, we found increased gp91^phox expression in endomyocardial biopsies of ACM patients. In conclusion, ACM is promoted by ACA-driven mitochondrial dysfunction and can be improved by ablation of NOX2/gp91^phox. NOX2/gp91^phox therefore might be a potential pharmacological target to treat ACM.

Gene-arsenic interaction in longitudinal changes of blood pressure: Findings from the Health Effects of Arsenic Longitudinal Study (HEALS) in Bangladesh

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality worldwide and mounting evidence indicates that toxicant exposures can profoundly impact on CVD risk. Epidemiologic studies have suggested that arsenic (As) exposure is positively related to increases in blood pressure (BP), a primary CVD risk factor. However, evidence of whether genetic susceptibility can modify the association between As and BP is lacking. In this study, we used mixed effect models adjusted for potential confounders to examine the interaction between As exposure from well water and potential genetic modifiers on longitudinal change in BP over approximately 7years of follow-up in 1137 subjects selected from the Health Effects of Arsenic Longitudinal Study (HEALS) cohort in Bangladesh. Genotyping was conducted for 235 SNPs in 18 genes related to As metabolism, oxidative stress and endothelial function. We observed interactions between 44 SNPs with well water As for one or more BP outcome measures (systolic, diastolic, or pulse pressure (PP)) over the course of follow-up. The interaction between CYBA rs3794624 and well water As on annual PP remained statistically significant after correction for multiple comparisons (FDR-adjusted p for interaction=0.05). Among individuals with the rs3794624 variant genotype, well water As was associated with a 2.23mmHg (95% CI: 1.14-3.32) greater annual increase in PP, while among those with the wild type, well water As was associated with a 0.13mmHg (95% CI: 0.02-0.23) greater annual increase in PP. Our results suggest that genetic variability may contribute to As-associated increases in BP over time.

Arsenic causes aortic dysfunction and systemic hypertension in rats: Augmentation of angiotensin II signaling

The groundwater pollutant arsenic can cause various cardiovascular disorders. Angiotensin II, a potent vasoconstrictor, plays an important role in vascular dysfunction by promoting changes in endothelial function, vascular reactivity, tissue remodeling and oxidative stress. We investigated whether modulation of angiotensin II signaling and redox homeostasis could be a mechanism contributing to arsenic-induced vascular disorder. Rats were exposed to arsenic at 25, 50 and 100ppm of sodium arsenite through drinking water consecutively for 90 days. Blood pressure was recorded weekly. On the 91st day, the rats were sacrificed for blood collection and isolation of thoracic aorta. Angiotensin converting enzyme and angiotensin II levels were assessed in plasma. Aortic reactivity to angiotensin II was assessed in organ-bath system. Western blot of AT1 receptors and G protein (Gαq/11), ELISA of signal transducers of MAP kinase pathway and reactive oxygen species (ROS) generation were assessed in aorta. Arsenic caused concentration-dependent increase in systolic, diastolic and mean arterial blood pressure from the 10th, 8th and 7th week onwards, respectively. Arsenic caused concentration-dependent enhancement of the angiotensin II-induced aortic contractile response. Arsenic also caused concentration-dependent increase in the plasma levels of angiotensin II and angiotensin converting enzyme and the expression of aortic AT1 receptor and Gαq/11 proteins. Arsenic increased aortic protein kinase C activity and the concentrations of protein tyrosine kinase, extracellular signal-regulated kinase-1/2 and vascular endothelial growth factor. Further, arsenic increased aortic mRNA expression of Nox2, Nox4 and p22phox, NADPH oxidase activity and ROS generation. The results suggest that arsenic-mediated enhancement of angiotensin II signaling could be an important mechanism in the arsenic-induced vascular disorder, where ROS could augment the angiotensin II signaling through activation of MAP kinase pathway.

Cytotoxin-induced NADPH oxides activation: roles in regulation of cell death

Numerous studies have shown that a variety of cytotoxic agents can activate the NADPH oxidase system and induce redox-dependent regulation of cellular functions. Cytotoxin-induced NADPH oxidase activation may either exert cytoprotective actions (e.g., survival, proliferation, and stress tolerance) or cause cell death. Here we summarize the experimental evidence showing the context-dependent dichotomous effects of NADPH oxidase on cell fate under cytotoxic stress conditions and the potential redox signaling mechanisms underlying this phenomenon. Clearly, it is difficult to create a unified paradigm on the toxicological implications of NADPH oxidase activation in response to cytotoxic stimuli. We suggest that interventional strategies targeting the NADPH oxidase system to prevent the adverse impacts of cytotoxins need to be contemplated in a stimuli- and cell type-specific manner.

Role of reactive oxygen species in arsenic-induced transformation of human lung bronchial epithelial (BEAS-2B) cells

Arsenic is an environmental carcinogen, its mechanisms of carcinogenesis remain to be investigated. Reactive oxygen species (ROS) are considered to be important. A previous study (Carpenter et al., 2011) has measured ROS level in human lung bronchial epithelial (BEAS-2B) cells and arsenic-transformed BEAS-2B cells and found that ROS levels were higher in transformed cells than that in parent normal cells. Based on these observations, the authors concluded that cell transformation induced by arsenic is mediated by increased cellular levels of ROS. This conclusion is problematic because this study only measured the basal ROS levels in transformed and parent cells and did not investigate the role of ROS in the process of arsenic-induced cell transformation. The levels of ROS in arsenic-transformed cells represent the result and not the cause of cell transformation. Thus question concerning whether ROS are important in arsenic-induced cell transformation remains to be answered. In the present study, we used expressions of catalase (antioxidant against H2O2) and superoxide dismutase 2 (SOD2, antioxidant against O2(-)) to decrease ROS level and investigated their role in the process of arsenic-induced cell transformation. Our results show that inhibition of ROS by antioxidant enzymes decreased arsenic-induced cell transformation, demonstrating that ROS are important in this process. We have also shown that in arsenic-transformed cells, ROS generation was lower and levels of antioxidants are higher than those in parent cells, in a disagreement with the previous report. The present study has also shown that the arsenic-transformed cells acquired apoptosis resistance. The inhibition of catalase to increase ROS level restored apoptosis capability of arsenic-transformed BEAS-2B cells, further showing that ROS levels are low in these cells. The apoptosis resistance due to the low ROS levels may increase cells proliferation, providing a favorable environment for tumorigenesis of arsenic-transformed cells.

Regulation of p53 and Rb links the alternative NF-κB pathway to EZH2 expression and cell senescence

There are two major pathways leading to induction of NF-κB subunits. The classical (or canonical) pathway typically leads to the induction of RelA or c-Rel containing complexes, and involves the degradation of IκBα in a manner dependent on IκB kinase (IKK) β and the IKK regulatory subunit NEMO. The alternative (or non-canonical) pathway, involves the inducible processing of p100 to p52, leading to the induction of NF-κB2(p52)/RelB containing complexes, and is dependent on IKKα and NF-κB inducing kinase (NIK). Here we demonstrate that in primary human fibroblasts, the alternative NF-κB pathway subunits NF-κB2 and RelB have multiple, but distinct, effects on the expression of key regulators of the cell cycle, reactive oxygen species (ROS) generation and protein stability. Specifically, following siRNA knockdown, quantitative PCR, western blot analyses and chromatin immunoprecipitation (ChIP) show that NF-κB2 regulates the expression of CDK4 and CDK6, while RelB, through the regulation of genes such as PSMA5 and ANAPC1, regulates the stability of p21WAF1 and the tumour suppressor p53. These combine to regulate the activity of the retinoblastoma protein, Rb, leading to induction of polycomb protein EZH2 expression. Moreover, our ChIP analysis demonstrates that EZH2 is also a direct NF-κB target gene. Microarray analysis revealed that in fibroblasts, EZH2 antagonizes a subset of p53 target genes previously associated with the senescent cell phenotype, including DEK and RacGAP1. We show that this pathway provides the major route of crosstalk between the alternative NF-κB pathway and p53, a consequence of which is to suppress cell senescence. Importantly, we find that activation of NF-κB also induces EZH2 expression in CD40L stimulated cells from Chronic Lymphocytic Leukemia patients. We therefore propose that this pathway provides a mechanism through which microenvironment induced NF-κB can inhibit tumor suppressor function and promote tumorigenesis.

Although the classical NF-κB pathway is frequently associated with the induction of cellular senescence and the senescence associated secretory phenotype (SASP), the role of the alternative NF-κB pathway, which is frequently activated in hematological malignancies as well as some solid tumors, has not been defined. We therefore investigated the role of the alternative NF-κB pathway in this process. Here we report that NF-κB2 and RelB, the effectors of the alternative NF-κB pathway, suppress senescence through inhibition of p53 activity. Using primary human fibroblasts, we demonstrate that this is accomplished through NF-κB2/RelB dependent control of a previously unknown pathway, incorporating regulation of CDK4 and 6 expression as well as regulators of p21WAF1 and p53 protein stability. Loss of NF-κB2/RelB results in suppression of retinoblastoma (Rb) tumour suppressor phosphorylation, which in turn leads to inhibition of EZH2 expression and de-repression of p53 activity. Interestingly, we find that CD40 ligand stimulation of cells from Chronic Lymphocytic Leukemia patients, which strongly induces the alternative NF-κB pathway, also induces EZH2 expression. We propose that the alternative NF-κB pathway can promote tumorigenesis through suppression of p53 dependent senescence, a process that may have relevance to cancer cells retaining wild type p53.

Endothelial actin depolymerization mediates NADPH oxidase-superoxide production during flow reversal

Slow moving blood flow and changes in flow direction, e.g., negative wall shear stress, can cause increased superoxide (O2(·-)) production in vascular endothelial cells. The mechanism by which shear stress increases O2(·-) production, however, is not well established. We tested the hypothesis that actin depolymerization, which occurs during flow reversal, mediates O2(·-) production in vascular endothelial cells via NADPH oxidase, and more specifically, the subunit p47(phox). Using a swine model, we created complete blood flow reversal in one carotid artery, while the contralateral vessel maintained forward blood flow as control. We measured actin depolymerization, NADPH oxidase activity, and reactive oxygen species (ROS) production in the presence of various inhibitors. Flow reversal was found to induce actin depolymerization and a 3.9 ± 1.0-fold increase in ROS production as compared with forward flow. NADPH oxidase activity was 1.4 ± 0.2 times higher in vessel segments subjected to reversed blood flow when measured by a direct enzyme assay. The NADPH oxidase subunits gp91(phox) (Nox2) and p47(phox) content in the vessels remained unchanged after 4 h of flow reversal. In contrast, p47(phox) phosphorylation was increased in vessels with reversed flow. The response caused by reversed flow was reduced by in vivo treatment with jasplakinolide, an actin stabilizer (only a 1.7 ± 0.3-fold increase). Apocynin (an antioxidant) prevented reversed flow-induced ROS production when the animals were treated in vivo. Cytochalasin D mimicked actin depolymerization in vitro and caused a 5.2 ± 3.0-fold increase in ROS production. These findings suggest that actin filaments play an important role in negative shear stress-induced ROS production by potentiating NADPH oxidase activity, and more specifically, the p47(phox) subunit in vascular endothelium.

Multi-walled carbon nanotubes induce human microvascular endothelial cellular effects in an alveolar-capillary co-culture with small airway epithelial cells

BACKGROUND

Nanotechnology, particularly the use of multi-walled carbon nanotubes (MWCNT), is a rapidly growing discipline with implications for advancement in a variety of fields. A major route of exposure to MWCNT during both occupational and environmental contact is inhalation. While many studies showed adverse effects to the vascular endothelium upon MWCNT exposure, in vitro results often do not correlate with in vivo effects. This study aimed to determine if an alveolar-capillary co-culture model could determine changes in the vascular endothelium after epithelial exposure to MWCNT.

METHODS

A co-culture system in which both human small airway epithelial cells and human microvascular endothelial cells were separated by a Transwell membrane so as to resemble an alveolar-capillary interaction was used. Following exposure of the epithelial layer to MWCNT, the effects to the endothelial barrier were determined.

RESULTS

Exposure of the epithelial layer to MWCNT induced multiple changes in the endothelial cell barrier, including an increase in reactive oxygen species, actin rearrangement, loss of VE-cadherin at the cell surface, and an increase in endothelial angiogenic ability. Overall increases in secreted VEGFA, sICAM-1, and sVCAM-1 protein levels, as well as increases in intracellular phospho-NF-κB, phospho-Stat3, and phospho-p38 MAPK, were also noted in HMVEC after epithelial exposure.

CONCLUSION

The co-culture system identified that alveolar-capillary exposure to MWCNT induced multiple changes to the underlying endothelium, potentially through cell signaling mediators derived from MWCNT-exposed epithelial cells. Therefore, the co-culture system appears to be a relevant in vitro method to study the pulmonary toxicity of MWCNT.

Morpho-mechanical intestinal remodeling in type 2 diabetic GK rats--is it related to advanced glycation end product formation?

Little is known about the mechanisms for the biomechanical remodeling in diabetes. The histomorphology, passive biomechanical properties and expression of advanced glycation end product (N epsilon-(carboxymethyl) lysine, AGE) and its receptor (RAGE) were studied in jejunal segments from 8 GK diabetic rats (GK group) and 10 age-matched normal rats (Normal group). The mechanical test was done by using a ramp distension of fluid into the jejunal segments in vitro. Circumferential stress and strain were computed from the length, diameter and pressure data and from the zero-stress state geometry. AGE and RAGE were detected by immunohistochemistry staining. Linear regression analysis was done to study association between the glucose level and AGE/RAGE expression with the histomorphometric and biomechanical parameters. The blood glucose level, the jejunal weight per length, wall thickness, wall area and layer thickness significantly increased in the GK group compared with the Normal group (P<0.05, P<0.01 and P<0.001). The opening angle and absolute values of residual strain decreased whereas the circumferential stiffness of the jejunal wall increased in the GK group (P<0.05 and P<0.01). Furthermore, stronger AGE expression in the villi and crypt and RAGE expression in the villi were found in the GK group (P<0.05 and P<0.01). Most histomorphometric and biomechanical changes were associated with blood glucose level and AGE/RAGE expression. In conclusion, histomorphometric and biomechanical remodeling occurred in type 2 diabetic GK rats. The increasing blood glucose level and the increased AGE/RAGE expression were associated with the remodeling, indicating a causal relationship.

The effect of inorganic arsenic on endothelium-dependent relaxation: role of NADPH oxidase and hydrogen peroxide

Chronic arsenic ingestion predisposes to vascular disease, but underlying mechanisms are poorly understood. In the present study we have analyzed the effects of short-term arsenite exposure on vascular function and endothelium-dependent relaxation. Endothelium-dependent relaxations, nitric oxide (NO) and endothelium derived hyperpolarizing factor (EDHF)-type, were studied in rabbit iliac artery and aortic rings using the G protein-coupled receptor agonist acetylcholine (ACh) and by cyclopiazonic acid (CPA), which promotes store-operated Ca(2+) entry by inhibiting the endothelial SERCA pump. Production of reactive oxygen species (ROS) in the endothelium of rabbit aortic valve leaflets and endothelium-denuded RIA and aortic rings was assessed by imaging of dihydroethidium. In the iliac artery, exposure to 100 μM arsenite for 30 min potentiated EDHF-type relaxations evoked by both CPA and ACh. Potentiation was prevented by catalase, the catalase/superoxide dismutase mimetic manganese porphyrin and the NADPH oxidase inhibitor apocynin. By contrast in aortic rings, that exhibited negligible EDHF-type responses, endothelium-dependent NO-mediated relaxations evoked by CPA and ACh were unaffected by arsenite. Arsenite induced apocynin-sensitive increases in ROS production in the aortic valve endothelium, but not in the media and adventitia of the iliac artery and aorta. Our results suggest that arsenite can potentiate EDHF-type relaxations via a mechanism that is dependent on hydrogen peroxide, thus demonstrating that dismutation of the superoxide anion generated by NADPH oxidase can potentially offset loss of NO bioavailability under conditions of reduced eNOS activity. By contrast, selective increases in endothelial ROS production following exposure to arsenite failed to modify relaxations mediated by endogenous NO.

Systematic analysis of multiwalled carbon nanotube-induced cellular signaling and gene expression in human small airway epithelial cells

Multiwalled carbon nanotubes (MWCNT) are one of the most commonly produced nanomaterials, and pulmonary exposure during production, use, and disposal is a concern for the developing nanotechnology field. The airway epithelium is the first line of defense against inhaled particles. In a mouse model, MWCNT were reported to reach the alveolar space of the lung after in vivo exposure, penetrate the epithelial lining, and result in inflammation and progressive fibrosis. This study sought to determine the cellular and gene expression changes in small airway epithelial cells (SAEC) after in vitro exposure to MWCNT in an effort to elucidate potential toxicity mechanisms and signaling pathways. A direct interaction between SAEC and MWCNT was confirmed by both internalization of MWCNT and interaction at the cell periphery. Following exposure, SAEC showed time-dependent increases in reactive oxygen species production, total protein phosphotyrosine and phosphothreonine levels, and migratory behavior. Analysis of gene and protein expression suggested altered regulation of multiple biomarkers of lung damage, carcinogenesis, and tumor progression, as well as genes involved in related signaling pathways. These results demonstrate that MWCNT exposure resulted in the activation of SAEC. Gene expression data derived from MWCNT exposure provide information that may be used to elucidate the underlying mode of action of MWCNT in the small airway and suggest potential prognostic gene signatures for risk assessment.

Wogonin inhibits H2O2-induced vascular permeability through suppressing the phosphorylation of caveolin-1

Wogonin, a naturally occurring monoflavonoid extracted from the root of Scutellaria baicalensis Georgi, has been reported for its anti-oxidant activity. However, it is still unclear whether wogonin can inhibit oxidant-induced vascular permeability. In this study, we evaluated the effects of wogonin on H2O2-induced vascular permeability in human umbilical vein endothelial cells (HUVECs). We found that wogonin can suppress the H2O2-stimulated actin remodeling and albumin uptake of HUVECs, as well as transendothelial cell migration of the human breast carcinoma cell MDA-MB-231. The mechanism revealed that wogonin inhibited H2O2-induced phosphorylation of caveolin-1 (cav-1) associating with the suppression of stabilization of VE-cadherin and β-catenin. Moreover, wogonin repressed anisomycin-induced phosphorylation of p38, cav-1 and vascular permeability. These results suggested that wogonin could inhibit H2O2-induced vascular permeability by downregulating the phosphorylation of cav-1, and that it might have a therapeutic potential for the diseases associated with the development of both oxidant and vascular permeability.

Cdc42-dependent activation of NADPH oxidase is involved in ethanol-induced neuronal oxidative stress

It has been suggested that excessive reactive oxygen species (ROS) and oxidative stress play an important role in ethanol-induced damage to both the developing and mature central nervous system (CNS). The mechanisms underlying ethanol-induced neuronal ROS, however, remain unclear. In this study, we investigated the role of NADPH oxidase (NOX) in ethanol-induced ROS generation. We demonstrated that ethanol activated NOX and inhibition of NOX reduced ethanol-promoted ROS generation. Ethanol significantly increased the expression of p47^phox and p67^phox, the essential subunits for NOX activation in cultured neuronal cells and the cerebral cortex of infant mice. Ethanol caused serine phosphorylation and membrane translocation of p47^phox and p67^phox, which were prerequisites for NOX assembly and activation. Knocking down p47^phox with the small interfering RNA was sufficient to attenuate ethanol-induced ROS production and ameliorate ethanol-mediated oxidative damage, which is indicated by a decrease in protein oxidation and lipid peroxidation. Ethanol activated cell division cycle 42 (Cdc42) and overexpression of a dominant negative (DN) Cdc42 abrogate ethanol-induced NOX activation and ROS generation. These results suggest that Cdc42-dependent NOX activation mediates ethanol-induced oxidative damages to neurons.

NADPH oxidase-produced superoxide mediates EGFR transactivation by c-Src in arsenic trioxide-stimulated human keratinocytes

Arsenic is a well-known poison and carcinogen in humans. However, it also has been used to effectively treat some human cancers and non-carcinogenic ailments. Previously, we demonstrated in keratinocytes that arsenic trioxide (ATO)-induced p21(WAF1/CIP1) (p21) expression leading to cellular cytotoxicity through the c-Src/EGFR/ERK pathway and generation of reactive oxygen species (ROS). In this study, we found that EGFR-Y845 and EGFR-Y1173 could be phosphorylated by ATO. Using confocal microscopy and flow cytometry, we found that pretreatment with apocynin, DPI, and tiron could remove ATO-induced ROS production. Furthermore, to increase NADPH oxidase activity, ATO could induce cytosolic p67(phox) expression and translocation to membrane. In addition, knockdown of p67(phox) could abolish ATO-induced ROS production. Therefore, we suggest that NADPH oxidase-produced superoxide was a major source of ATO-induced ROS production. Conversely, ATO-induced NADPH oxidase activation and superoxide generation could be inhibited by the c-Src inhibitor PP1, but not by the EGFR inhibitor PD153035. In addition, overexpression of c-Src as well as treatment with ATO could stimulate EGFR-Y845/ERK phosphorylation, p21 expression, and cellular arrest/apoptosis, which could be attenuated by pretreatment with apocynin or knockdown of p67(phox). Collectively, we suggest that NADPH oxidase was involved in the ATO-induced arrest/apoptosis of keratinocytes, which was regulated by c-Src activation.

Arsenic and chromium in drinking water promote tumorigenesis in a mouse colitis-associated colorectal cancer model and the potential mechanism is ROS-mediated Wnt/β-catenin signaling pathway

Exposure to carcinogenic metals, such as trivalent arsenic [As(III)] and hexavalent chromium [Cr(VI)], through drinking water is a major global public health problem and is associated with various cancers. However, the mechanism of their carcinogenicity remains unclear. In this study, we used azoxymethane/dextran sodium sulfate (AOM/DSS)-induced mouse colitis-associated colorectal cancer model to investigate their tumorigenesis. Our results demonstrate that exposure to As(III) or Cr(VI), alone or in combination, together with AOM/DSS pretreatment has a promotion effect, increasing the colorectal tumor incidence, multiplicity, size, and grade, as well as cell inflammatory response. Two-dimensional differential gel electrophoresis coupled with mass spectrometry revealed that As(III) or Cr(VI) treatment alone significantly changed the density of proteins. The expression of β-catenin and phospho-GSK was increased by treatment of carcinogenic metals alone. Concomitantly, the expression of NADPH oxidase1 (NOX1) and the level of 8-OHdG were also increased by treatment of carcinogenic metals alone. Antioxidant enzymes, such as superoxide dismutase (SOD) and catalase, were decreased. Similarly, in an in vitro system, exposure of CRL-1807 to carcinogenic metals increased reactive oxygen species (ROS) generation, the expression of β-catenin, phospho-GSK, and NOX1. Inhibition of ROS generation by addition of SOD or catalase inhibited β-catenin expression and activity. Our study provides a new animal model to study the carcinogenicity of As(III) and Cr(VI) and suggests that As(III) and Cr(VI) promote colorectal cancer tumorigenesis, at least partly, through ROS-mediated Wnt/β-catenin signaling pathway.

Arsenic trioxide induces abnormal mitotic spindles through a PIP4KIIγ/Rho pathway

Arsenite-induced spindle abnormalities result in mitotic cell apoptosis in several cancer cell lines, but how arsenite induces these effects is not known. Evidence to date has revealed that arsenite activates Rho guanosine triphosphatases (GTPases). Because Rho GTPases regulate spindle orientation, chromosome congression, and cytokinesis, we therefore examined the involvement of Rho GTPases and their modulators in arsenite-induced mitotic abnormalities. We demonstrated that arsenic trioxide (ATO) disrupted the positioning of bipolar mitotic spindles and induced centrosome and spindle abnormalities. ATO increased the level of the active guanosine triphosphate-bound form of Rho. Inhibition of Rho-associated protein kinases (ROCKs) by Y-27632 ameliorated ATO-induced spindle defects, mitotic arrest, and cell death. These results indicate that ATO may induce spindle abnormalities and mitotic cell death through a Rho/ROCK pathway. In addition, screening of a human kinase and phosphatase shRNA library to select genes that mediate ATO induction of spindle abnormalities resulted in the identification of phosphatidylinositol-5-phosphate 4-kinase type-2 gamma (PIP4KIIγ), a phosphatidylinositol 4,5-biphosphate (PIP2) synthesis enzyme that belongs to the phosphatidylinositol phosphate kinase (PIPK) family. Sequestration of PIP2 by ectopic overexpression of the pleckstrin homology domain of phospholipase C-δ1 protected cells from ATO-induced cell death. Furthermore, depletion of PIP4KIIγ, but not other isoforms of the PIPK family, not only reduced Rho GTPase activation in ATO-treated cells but also alleviated ATO-induced spindle defects, mitotic arrest, and mitotic cell apoptosis. Thus, our results imply that ATO induces abnormalities in mitotic spindles through a PIP4KIIγ/Rho pathway, leading to apoptosis of mitotic cells.

Cell permeability, migration, and reactive oxygen species induced by multiwalled carbon nanotubes in human microvascular endothelial cells

Multiwalled carbon nanotubes (MWCNT) have elicited great interest in biomedical applications due to their extraordinary physical, chemical, and optical properties. Intravenous administration of MWCNT-based medical imaging agents and drugs in animal models was utilized. However, the potential harmful health effects of MWCNT administration in humans have not yet been elucidated. Furthermore, to date, there are no apparent reports regarding the precise mechanisms of translocation of MWCNT into target tissues and organs from blood circulation. This study demonstrates that exposure to MWCNT leads to an increase in cell permeability in human microvascular endothelial cells (HMVEC). The results obtained from this study also showed that the MWCNT-induced rise in endothelial permeability is mediated by reactive oxygen species (ROS) production and actin filament remodeling. In addition, it was found that MWCNT promoted cell migration in HMVEC. Mechanistically, MWCNT exposure elevated the levels of monocyte chemoattractant protein-1 (MCP-1) and intercellular adhesion molecule 1 (ICAM-1) in HMVEC. Taken together, these results provide new insights into the bioreactivity of MWCNT, which may have implications in the biomedical application of MWCNT in vascular targeting, imaging, and drug delivery. The results generated from this study also elucidate the potential adverse effects of MWCNT exposure on humans at the cellular level.

Cell permeability, migration, and reactive oxygen species induced by multiwalled carbon nanotubes in human microvascular endothelial cells

Multiwalled carbon nanotubes (MWCNT) have elicited great interest in biomedical applications due to their extraordinary physical, chemical, and optical properties. Intravenous administration of MWCNT-based medical imaging agents and drugs in animal models was utilized. However, the potential harmful health effects of MWCNT administration in humans have not yet been elucidated. Furthermore, to date, there are no apparent reports regarding the precise mechanisms of translocation of MWCNT into target tissues and organs from blood circulation. This study demonstrates that exposure to MWCNT leads to an increase in cell permeability in human microvascular endothelial cells (HMVEC). The results obtained from this study also showed that the MWCNT-induced rise in endothelial permeability is mediated by reactive oxygen species (ROS) production and actin filament remodeling. In addition, it was found that MWCNT promoted cell migration in HMVEC. Mechanistically, MWCNT exposure elevated the levels of monocyte chemoattractant protein-1 (MCP-1) and intercellular adhesion molecule 1 (ICAM-1) in HMVEC. Taken together, these results provide new insights into the bioreactivity of MWCNT, which may have implications in the biomedical application of MWCNT in vascular targeting, imaging, and drug delivery. The results generated from this study also elucidate the potential adverse effects of MWCNT exposure on humans at the cellular level.

Arsenic toxicology: translating between experimental models and human pathology

BACKGROUND

Chronic arsenic exposure is a worldwide health problem. How arsenic exposure promotes a variety of diseases is poorly understood, and specific relationships between experimental and human exposures are not established. We propose phenotypic anchoring as a means to unify experimental observations and disease outcomes.

OBJECTIVES

We examined the use of phenotypic anchors to translate experimental data to human pathology and investigated research needs for which phenotypic anchors need to be developed.

METHODS

During a workshop, we discussed experimental systems investigating arsenic dose/exposure and phenotypic expression relationships and human disease responses to chronic arsenic exposure and identified knowledge gaps. In a literature review, we identified areas where data exist to support phenotypic anchoring of experimental results to pathologies from specific human exposures.

DISCUSSION

Disease outcome is likely dependent on cell-type-specific responses and interaction with individual genetics, other toxicants, and infectious agents. Potential phenotypic anchors include target tissue dosimetry, gene expression and epigenetic profiles, and tissue biomarkers.

CONCLUSIONS

Translation to human populations requires more extensive profiling of human samples along with high-quality dosimetry. Anchoring results by gene expression and epigenetic profiling has great promise for data unification. Genetic predisposition of individuals affects disease outcome. Interactions with infectious agents, particularly viruses, may explain some species-specific differences between human pathologies and experimental animal pathologies. Invertebrate systems amenable to genetic manipulation offer potential for elaborating impacts of specific biochemical pathways. Anchoring experimental results to specific human exposures will accelerate understanding of mechanisms of arsenic-induced human disease.

Reactive oxygen species mediate arsenic induced cell transformation and tumorigenesis through Wnt/β-catenin pathway in human colorectal adenocarcinoma DLD1 cells

Long term exposure to arsenic can increase incidence of human cancers, such as skin, lung, and colon rectum. The mechanism of arsenic induced carcinogenesis is still unclear. It is generally believed that reactive oxygen species (ROS) may play an important role in this process. In the present study, we investigate the possible linkage between ROS, β-catenin and arsenic induced transformation and tumorigenesis in human colorectal adenocarcinoma cell line, DLD1 cells. Our results show that arsenic was able to activate p47(phox) and p67(phox), two key proteins for activation of NADPH oxidase. Arsenic was also able to generate ROS in DLD1 cells. Arsenic increased β-catenin expression level and its promoter activity. ROS played a major role in arsenic-induced β-catenin activation. Treatment of DLD1 cells by arsenic enhanced both transformation and tumorigenesis of these cells. The tumor volumes of arsenic treated group were much larger than those without arsenic treatment. Addition of either superoxide dismutase (SOD) or catalase reduced arsenic induced cell transformation and tumor formation. The results indicate that ROS are involved in arsenic induced cell transformation and tumor formation possible through Wnt/β-catenin pathway in human colorectal adenocarcinoma cell line DLD1 cells.

Arsenic-induced oxidative stress and its reversibility

This review summarizes the literature describing the molecular mechanisms of arsenic-induced oxidative stress, its relevant biomarkers, and its relation to various diseases, including preventive and therapeutic strategies. Arsenic alters multiple cellular pathways including expression of growth factors, suppression of cell cycle checkpoint proteins, promotion of and resistance to apoptosis, inhibition of DNA repair, alterations in DNA methylation, decreased immunosurveillance, and increased oxidative stress, by disturbing the pro/antioxidant balance. These alterations play prominent roles in disease manifestation, such as carcinogenicity, genotoxicity, diabetes, cardiovascular and nervous systems disorders. The exact molecular and cellular mechanisms involved in arsenic toxicity are rather unrevealed. Arsenic alters cellular glutathione levels either by utilizing this electron donor for the conversion of pentavalent to trivalent arsenicals or directly binding with it or by oxidizing glutathione via arsenic-induced free radical generation. Arsenic forms oxygen-based radicals (OH(•), O(2)(•-)) under physiological conditions by directly binding with critical thiols. As a carcinogen, it acts through epigenetic mechanisms rather than as a classical mutagen. The carcinogenic potential of arsenic may be attributed to activation of redox-sensitive transcription factors and other signaling pathways involving nuclear factor κB, activator protein-1, and p53. Modulation of cellular thiols for protection against reactive oxygen species has been used as a therapeutic strategy against arsenic. N-acetylcysteine, α-lipoic acid, vitamin E, quercetin, and a few herbal extracts show prophylactic activity against the majority of arsenic-mediated injuries in both in vitro and in vivo models. This review also updates the reader on recent advances in chelation therapy and newer therapeutic strategies suggested to treat arsenic-induced oxidative damage.

Modulation of early stress-related biomarkers in cytoplasm by the antioxidants silymarin and quercetin using a cellular model of acute arsenic poisoning

Several pathologies (e.g. cancer and diabetes) are increased in arsenic-exposed populations, with oxidative stress being a major toxicological mechanism. Since the flavonoids silymarin (S) and quercetin (Q) are antioxidants and may protect cells, it would be valuable to develop a model which allows assessing the potential of xenobiotic against arsenic cytotoxicity in an efficient and rapid way. Thus, the oxidant production [e.g. reactive oxygen species and reactive nitrogen species (RNS)], the molecular parameters of biological response [e.g. plasma membrane composition, actin microfilaments and activated diphosphorilated c-Jun N-terminal kinase (JNK)] and cellular viability were determined in CHO-K1 cells treated with arsenite (As), S and Q. Arsenic caused loss of the cellular viability in a time-dependent manner. This effect was accompanied by a lipid hydroperoxide (LHP) formation, with no RNS induction or ganglioside content changes being found. Both flavonoids counteracted oxidative damage. Despite all treatments had unspecific responses on nitrite cellular release along the time, there was no relation between them and the cellular viability. Arsenic induced cytoplasmic microfilament rearrangement (tight perinuclear distribution with projections, stress fibres and pseudopodia) which was reversed by S. Also, activated JNK showed a similar distribution to actin. Contrarily, Q caused a dysmorphic granular pattern, thus behaving as a toxic agent. Summing up, toxic levels of arsenic disturb the redox homeostasis with LHP induction and early triggering of stress responses in cytoskeleton and cell signalling. Using the proposed model, only S showed to protect cells from arsenical cytotoxicity without own toxic properties. Thus, S might be considered for modulation of the human arsenic susceptibility.

NADPH oxidase-mediated redox signaling: roles in cellular stress response, stress tolerance, and tissue repair

NADPH oxidase (Nox) has a dedicated function of generating reactive oxygen species (ROS). Accumulating evidence suggests that Nox has an important role in signal transduction in cellular stress responses. We have reviewed the current evidence showing that the Nox system can be activated by a collection of chemical, physical, and biological cellular stresses. In many circumstances, Nox activation fits to the cellular stress response paradigm, in that (1) the response can be initiated by various forms of cellular stresses; (2) Nox-derived ROS may activate mitogen-activated protein kinases (extracellular signal-regulated kinase, p38) and c-Jun NH(2)-terminal kinase, which are the core of the cell stress-response signaling network; and (3) Nox is involved in the development of stress cross-tolerance. Activation of the cell survival pathway by Nox may promote cell adaptation to stresses, whereas Nox may also convey signals toward apoptosis in irreversibly injured cells. At later stage after injury, Nox is involved in tissue repair by modulating cell proliferation, angiogenesis, and fibrosis. We suggest that Nox may have an integral role in cell stress responses and the subsequent tissue repair process. Understanding Nox-mediated redox signaling mechanisms may be of prominent significance at the crossroads of directing cellular responses to stress, aiming at either enhancing the stress resistance (in such situations as preventing ischemia-reperfusion injuries and accelerating wound healing) or sensitizing the stress-induced cytotoxicity for proliferative diseases such as cancer. Therefore, an optimal outcome of interventions on Nox will only be achieved when this is dealt with in a timely and disease-and stage-specific manner.

Perfluorooctane sulfonate (PFOS) induces reactive oxygen species (ROS) production in human microvascular endothelial cells: role in endothelial permeability

Perfluorooctane sulfonate (PFOS) is a member of the perfluoroalkyl acids (PFAA) containing an eight-carbon backbone. PFOS is a man-made chemical with carbon-fluorine bonds that are among the strongest in organic chemistry, and PFOS is widely used in industry. Human occupational and environmental exposure to PFOS occurs globally. PFOS is non-biodegradable and is persistent in the human body and environment. In this study, data demonstrated that exposure of human microvascular endothelial cells (HMVEC) to PFOS induced the production of reactive oxygen species (ROS) at both high and low concentrations. Morphologically, it was found that exposure to PFOS induced actin filament remodeling and endothelial permeability changes in HMVEC. Furthermore, data demonstrated that the production of ROS plays a regulatory role in PFOS-induced actin filament remodeling and the increase in endothelial permeability. Our results indicate that the generation of ROS may play a role in PFOS-induced aberrations of the endothelial permeability barrier. The results generated from this study may provide a new insight into the potential adverse effects of PFOS exposure on humans at the cellular level.

Enhanced ROS production and redox signaling with combined arsenite and UVA exposure: contribution of NADPH oxidase

Solar ultraviolet radiation (UVR) is the major etiological factor in skin carcinogenesis. However, in vivo studies demonstrate that mice exposed to arsenic and UVR exhibit significantly more tumors and oxidative DNA damage than animals treated with either agent alone. Interactions between arsenite and UVR in the production of reactive oxygen species (ROS) and stress-associated signaling may provide a basis for the enhanced carcinogenicity. In this study keratinocytes were pretreated with arsenite (3 microM) and then exposed to UVA (10 kJ/m(2)). We report that exposure to UVA after arsenite pretreatment enhanced ROS production, p38 MAP kinase activation, and induction of a redox-sensitive gene product, heme oxygenase-1, compared to either stimulus alone. UVR exposure resulted in rapid and transient NADPH oxidase activation, whereas the response to arsenite was more pronounced and persistent. Inhibition of NADPH oxidase decreased ROS production in arsenite-treated cells but had little impact on UVA-exposed cells. Furthermore, arsenite-induced, but not UVA-induced, p38 activation and HO-1 expression were dependent upon NADPH oxidase activity. These findings indicate differences in the mechanisms of ROS production by arsenite and UVA that may provide an underlying basis for the observed enhancement of redox-related cellular responses upon combined UVA and arsenite exposure.

Arsenic requires sphingosine-1-phosphate type 1 receptors to induce angiogenic genes and endothelial cell remodeling

Arsenic in drinking water is a major public health concern as it increases risk and incidence of cardiovascular disease and cancer. Arsenic exposure affects multiple vascular beds, promoting liver sinusoidal capillarization and portal hypertension, ischemic heart disease, peripheral vascular disease, and tumor angiogenesis. While Rac1-GTPase and NADPH oxidase activities are essential for arsenic-stimulated endothelial cell signaling for angiogenesis or liver sinusoid capillarization, the mechanism for initiating these effects is unknown. We found that arsenic-stimulated cell signaling and angiogenic gene expression in human microvascular endothelial cells were Pertussis toxin sensitive, indicating a G-protein coupled signaling pathway. Incubating human microvascular endothelial cells with the sphingosine-1-phosphate type 1 receptor (S1P(1)) inhibitor VPC23019 or performing small interfering RNA knockdown of S1P(1) blocked arsenic-stimulated HMVEC angiogenic gene expression and tube formation, but did not affect induction of either HMOX1 or IL8. Liver sinusoidal endothelial cells (LSECs) defenestrate and capillarize in response to aging and environmental oxidant stresses. We found that S1P(1) was enriched on LSECs in vivo and in primary cell culture and that VPC23019 inhibited both sphingosine-1-phosphate-stimulated and arsenic-stimulated LSEC oxidant generation and defenestration. These studies identified novel roles for S1P(1) in mediating arsenic stimulation of both angiogenesis and pathogenic LSEC capillarization, as well as demonstrating a role for S1P(1) in mediating environmental responses in the liver vasculature, providing possible mechanistic insight into arsenic-induced vascular pathogenesis and disease.

Genetic basis of arsenite and cadmium tolerance in Saccharomyces cerevisiae

Background

Arsenic and cadmium are widely distributed in nature and pose serious threats to the environment and human health. Exposure to these nonessential toxic metals may result in a variety of human diseases including cancer. However, arsenic and cadmium toxicity targets and the cellular systems contributing to tolerance acquisition are not fully known.

Results

To gain insight into metal action and cellular tolerance mechanisms, we carried out genome-wide screening of the Saccharomyces cerevisiae haploid and homozygous diploid deletion mutant collections and scored for reduced growth in the presence of arsenite or cadmium. Processes found to be required for tolerance to both metals included sulphur and glutathione biosynthesis, environmental sensing, mRNA synthesis and transcription, and vacuolar/endosomal transport and sorting. We also identified metal-specific defence processes. Arsenite-specific defence functions were related to cell cycle regulation, lipid and fatty acid metabolism, mitochondrial biogenesis, and the cytoskeleton whereas cadmium-specific defence functions were mainly related to sugar/carbohydrate metabolism, and metal-ion homeostasis and transport. Molecular evidence indicated that the cytoskeleton is targeted by arsenite and that phosphorylation of the Snf1p kinase is required for cadmium tolerance.

Conclusion

This study has pin-pointed core functions that protect cells from arsenite and cadmium toxicity. It also emphasizes the existence of both common and specific defence systems. Since many of the yeast genes that confer tolerance to these agents have homologues in humans, similar biological processes may act in yeast and humans to prevent metal toxicity and carcinogenesis.

Trans-10, cis-12 conjugated linoleic acid modulates phagocytic responses of canine peripheral blood polymorphonuclear neutrophilic leukocytes exposed to Clostridium difficile toxin B

Trans-10, cis-12 conjugated linoleic acid (t10c12-CLA) has been reported to enhance phagocyte function. Clostridium difficile toxin B (TcdB) has been known to inhibit Ras-homologous (Rho) guanosine triphosphatases (GTPases) which play essential roles in neutrophil immune functions. Here, we examined whether in vitro treatment with t10c12-CLA modulates the filamentous actin (F-actin) polymerization, phagocytic capacity, and oxidative burst activity (OBA) of canine peripheral blood polymorphonuclear neutrophilic leukocytes (PMNs) exposed to TcdB. Treatment with t10c12-CLA, but not linoleic acid, enhanced PMN F-actin polymerization, phagocytic capacity, and OBA, while TcdB suppressed these functions. t10c12-CLA reversed the suppressive effects of TcdB on these PMN functions. t10c12-CLA stimulated F-actin polymerization regardless of whether phagocytosis was stimulated by microspheres but only elevated OBA when microspheres were added. We asked whether the effects of t10c12-CLA were associated with changes in the activation of the Rho GTPase Cdc42. Treatment with t10c12-CLA augmented Cdc42 activity in both TcdB-treated and TcdB-naive PMNs during phagocytosis. Thus, t10c12-CLA up-regulates PMN phagocytic responses attenuated by TcdB. This effect is associated with an increase in actin polymerization and may involve the activation of Cdc42.

Iron oxide nanoparticles induce human microvascular endothelial cell permeability through reactive oxygen species production and microtubule remodeling

Background

Engineered iron nanoparticles are being explored for the development of biomedical applications and many other industry purposes. However, to date little is known concerning the precise mechanisms of translocation of iron nanoparticles into targeted tissues and organs from blood circulation, as well as the underlying implications of potential harmful health effects in human.

Results

The confocal microscopy imaging analysis demonstrates that exposure to engineered iron nanoparticles induces an increase in cell permeability in human microvascular endothelial cells. Our studies further reveal iron nanoparticles enhance the permeability through the production of reactive oxygen species (ROS) and the stabilization of microtubules. We also showed Akt/GSK-3β signaling pathways are involved in iron nanoparticle-induced cell permeability. The inhibition of ROS demonstrate ROS play a major role in regulating Akt/GSK-3β – mediated cell permeability upon iron nanoparticle exposure. These results provide new insights into the bioreactivity of engineered iron nanoparticles which can inform potential applications in medical imaging or drug delivery.

Conclusion

Our results indicate that exposure to iron nanoparticles induces an increase in endothelial cell permeability through ROS oxidative stress-modulated microtubule remodeling. The findings from this study provide new understandings on the effects of nanoparticles on vascular transport of macromolecules and drugs.

Confirmation of gene expression-based prediction of survival in non-small cell lung cancer

PURPOSE

It is a critical challenge to determine the risk of recurrence in early stage non-small cell lung cancer (NSCLC) patients. Accurate gene expression signatures are needed to classify patients into high- and low-risk groups to improve the selection of patients for adjuvant therapy.

EXPERIMENTAL DESIGN

Multiple published microarray data sets were used to evaluate our previously identified lung cancer prognostic gene signature. Expression of the signature genes was further validated with real-time reverse transcription-PCR and Western blot assays of snap-frozen lung cancer tumor tissues.

RESULTS

Our previously identified 35-gene signature stratified 264 patients with NSCLC into high- and low-risk groups with distinct overall survival rates (P < 0.05, Kaplan-Meier analysis, log-rank tests). The 35-gene signature further stratified patients with clinical stage 1A diseases into poor prognostic and good prognostic subgroups (P = 0.0007, Kaplan-Meier analysis, log-rank tests). This signature is independent of other prognostic factors for NSCLC, including age, sex, tumor differentiation, tumor grade, and tumor stage. The expression of the signature genes was validated with real-time reverse transcription-PCR analysis of lung cancer tumor specimens. Protein expression of two signature genes, TAL2 and ILF3, was confirmed in lung adenocarcinoma tumors by using Western blot analysis. These two biomarkers showed correlated mRNA and protein overexpression in lung cancer development and progression.

CONCLUSIONS

The results indicate that the identified 35-gene signature is an accurate predictor of survival in NSCLC. It provides independent prognostic information in addition to traditional clinicopathologic criteria.