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

Metabolic Derangement by Arsenic: a Review of the Mechanisms

Studies have implicated arsenic exposure in various pathological conditions, including metabolic disorders, which have become a global phenomenon, affecting developed, developing, and under-developed nations. Despite the huge risks associated with arsenic exposure, humans remain constantly exposed to it, especially through the consumption of contaminated water and food. This present study provides an in-depth insight into the mechanistic pathways involved in the metabolic derangement by arsenic. Compelling pieces of evidence demonstrate that arsenic induces metabolic disorders via multiple pathways. Apart from the initiation of oxidative stress and inflammation, arsenic prevents the phosphorylation of Akt at Ser473 and Thr308, leading to the inhibition of PDK-1/Akt insulin signaling, thereby reducing GLUT4 translocation through the activation of Nrf2. Also, arsenic downregulates mitochondrial deacetylase Sirt3, decreasing the ability of its associated transcription factor, FOXO3a, to bind to the agents that support the genes for manganese superoxide dismutase and PPARg co-activator (PGC)-1a. In addition, arsenic activates MAPKs, modulates p53/ Bcl-2 signaling, suppresses Mdm-2 and PARP, activates NLRP3 inflammasome and caspase-mediated apoptosis, and induces ER stress, and ox-mtDNA-dependent mitophagy and autophagy. More so, arsenic alters lipid metabolism by decreasing the presence of 3-hydroxy-e-methylglutaryl-CoA synthase 1 and carnitine O-octanoyl transferase (Crot) and increasing the presence of fatty acid-binding protein-3 mRNA. Furthermore, arsenic promotes atherosclerosis by inducing endothelial damage. This cascade of pathophysiological events promotes metabolic derangement. Although the pieces of evidence provided by this study are convincing, future studies evaluating the involvement of other likely mechanisms are important. Also, epidemiological studies might be necessary for the translation of most of the findings in animal models to humans.

Pathological angiogenesis: mechanisms and therapeutic strategies

In multicellular organisms, angiogenesis, the formation of new blood vessels from pre-existing ones, is an essential process for growth and development. Different mechanisms such as vasculogenesis, sprouting, intussusceptive, and coalescent angiogenesis, as well as vessel co-option, vasculogenic mimicry and lymphangiogenesis, underlie the formation of new vasculature. In many pathological conditions, such as cancer, atherosclerosis, arthritis, psoriasis, endometriosis, obesity and SARS-CoV-2(COVID-19), developmental angiogenic processes are recapitulated, but are often done so without the normal feedback mechanisms that regulate the ordinary spatial and temporal patterns of blood vessel formation. Thus, pathological angiogenesis presents new challenges yet new opportunities for the design of vascular-directed therapies. Here, we provide an overview of recent insights into blood vessel development and highlight novel therapeutic strategies that promote or inhibit the process of angiogenesis to stabilize, reverse, or even halt disease progression. In our review, we will also explore several additional aspects (the angiogenic switch, hypoxia, angiocrine signals, endothelial plasticity, vessel normalization, and endothelial cell anergy) that operate in parallel to canonical angiogenesis mechanisms and speculate how these processes may also be targeted with anti-angiogenic or vascular-directed therapies.

Misuse of Cardiac Lipid upon Exposure to Toxic Trace Elements-A Focused Review

Heavy metals and metalloids like cadmium, arsenic, mercury, and lead are frequently found in the soil, water, food, and atmosphere; trace amounts can cause serious health issues to the human organism. These toxic trace elements (TTE) affect almost all the organs, mainly the heart, kidney, liver, lungs, and the nervous system, through increased free radical formation, DNA damage, lipid peroxidation, and protein sulfhydryl depletion. This work aims to advance our understanding of the mechanisms behind lipid accumulation via increased free fatty acid levels in circulation due to TTEs. The increased lipid level in the myocardium worsens the heart function. This dysregulation of the lipid metabolism leads to damage in the structure of the myocardium, inclusive fibrosis in cardiac tissue, myocyte apoptosis, and decreased contractility due to mitochondrial dysfunction. Additionally, it is discussed herein how exposure to cadmium decreases the heart rate, contractile tension, the conductivity of the atrioventricular node, and coronary flow rate. Arsenic may induce atherosclerosis by increasing platelet aggregation and reducing fibrinolysis, as exposure interferes with apolipoprotein (Apo) levels, resulting in the rise of the Apo-B/Apo-A1 ratio and an elevated risk of acute cardiovascular events. Concerning mercury and lead, these toxicants can cause hypertension, myocardial infarction, and carotid atherosclerosis, in association with the generation of free radicals and oxidative stress. This review offers a complete overview of the critical factors and biomarkers of lipid and TTE-induced cardiotoxicity useful for developing future protective interventions.

Key Characteristics of Cardiovascular Toxicants

BACKGROUND

The concept of chemical agents having properties that confer potential hazard called key characteristics (KCs) was first developed to identify carcinogenic hazards. Identification of KCs of cardiovascular (CV) toxicants could facilitate the systematic assessment of CV hazards and understanding of assay and data gaps associated with current approaches.

OBJECTIVES

We sought to develop a consensus-based synthesis of scientific evidence on the KCs of chemical and nonchemical agents known to cause CV toxicity along with methods to measure them.

METHODS

An expert working group was convened to discuss mechanisms associated with CV toxicity.

RESULTS

The group identified 12 KCs of CV toxicants, defined as exogenous agents that adversely interfere with function of the CV system. The KCs were organized into those primarily affecting cardiac tissue (numbers 1-4 below), the vascular system (5-7), or both (8-12), as follows: 1) impairs regulation of cardiac excitability, 2) impairs cardiac contractility and relaxation, 3) induces cardiomyocyte injury and death, 4) induces proliferation of valve stroma, 5) impacts endothelial and vascular function, 6) alters hemostasis, 7) causes dyslipidemia, 8) impairs mitochondrial function, 9) modifies autonomic nervous system activity, 10) induces oxidative stress, 11) causes inflammation, and 12) alters hormone signaling.

DISCUSSION

These 12 KCs can be used to help identify pharmaceuticals and environmental pollutants as CV toxicants, as well as to better understand the mechanistic underpinnings of their toxicity. For example, evidence exists that fine particulate matter [PM ≤2.5μm in aerodynamic diameter (PM2.5)] air pollution, arsenic, anthracycline drugs, and other exogenous chemicals possess one or more of the described KCs. In conclusion, the KCs could be used to identify potential CV toxicants and to define a set of test methods to evaluate CV toxicity in a more comprehensive and standardized manner than current approaches. https://doi.org/10.1289/EHP9321.

Arsenic Stimulates Myoblast Mitochondrial Epidermal Growth Factor Receptor to Impair Myogenesis

Arsenic exposure impairs muscle metabolism, maintenance, progenitor cell differentiation, and regeneration following acute injury. Low to moderate arsenic exposures target muscle fiber and progenitor cell mitochondria to epigenetically decrease muscle quality and regeneration. However, the mechanisms for how low levels of arsenic signal for prolonged mitochondrial dysfunction are not known. In this study, arsenic attenuated murine C2C12 myoblasts differentiation and resulted in abnormal undifferentiated myoblast proliferation. Arsenic prolonged ligand-independent phosphorylation of mitochondrially localized epidermal growth factor receptor (EGFR), a major driver of proliferation. Treating cells with a selective EGFR kinase inhibitor, AG-1478, prevented arsenic inhibition of myoblast differentiation. AG-1478 decreased arsenic-induced colocalization of pY845EGFR with mitochondrial cytochrome C oxidase subunit II, as well as arsenic-enhanced mitochondrial membrane potential, reactive oxygen species generation, and cell cycling. All of the arsenic effects on mitochondrial signaling and cell fate were mitigated or reversed by addition of mitochondrially targeted agents that restored mitochondrial integrity and function. Thus, arsenic-driven pathogenesis in skeletal muscle requires sustained mitochondrial EGFR activation that promotes progenitor cell cycling and proliferation at the detriment of proper differentiation. Collectively, these findings suggest that the arsenic-activated mitochondrial EGFR pathway drives pathogenic signaling for impaired myoblast metabolism and function.

Potential molecular mechanisms underlying the effect of arsenic on angiogenesis

Arsenic is a potent chemotherapeutic drug that is applied as a treatment for cancer; it exerts its functions through multiple pathways, including angiogenesis inhibition. As angiogenesis is a critical component of the progression of many diseases, arsenic is a feasible treatment option for patients with other angiogenic diseases, including rheumatoid arthritis and psoriasis, among others. However, arsenic is also a well-known carcinogen, demonstrating a pro-angiogenesis effect. This review will focus on the dual effects of arsenic on neovascularization and the relevant mechanisms underlying these effects, aiming to provide a rational understanding of arsenic treatment. In particular, we expect to provide a comprehensive overview of the current knowledge of the mechanisms by which arsenic influences angiogenesis.

Mitochondria are a substrate of cellular memory

Cellular memory underlies cellular identity, and thus constitutes a unifying mechanism of genetic disposition, environmental influences, and cellular adaptation. Here, we demonstrate that enduring physicochemical changes of mitochondrial networks invoked by transient stress, a phenomenon we term 'mitoengrams', underlie the transgenerational persistence of epigenetically scripted cellular behavior. Using C2C12 myogenic stem-like cells, we show that stress memory elicited by transient, low-level arsenite exposure is stored within a self-renewing subpopulation of progeny cells in a mitochondrial-dependent fashion. Importantly, we demonstrate that erasure of mitoengrams by administration of mitochondria-targeted electron scavenger was sufficient to reset key epigenetic marks of cellular memory and redirect the identity of the mitoengram-harboring progeny cells to a non-stress-like state. Together, our findings indicate that mnemonic information emanating from mitochondria support the balance between the persistence and transience of cellular memory.

Proteomic Analysis Reveals Dab2 Mediated Receptor Endocytosis Promotes Liver Sinusoidal Endothelial Cell Dedifferentiation

Sinusoidal dedifferentiation is a complicated process induced by several factors, and exists in early stage of diverse liver diseases. The mechanism of sinusoidal dedifferentiation is poorly unknown. In this study, we established a NaAsO₂-induced sinusoidal dedifferentiation mice model. Liver sinusoidal endothelial cells were isolated and isobaric tag for relative and absolute quantitation (iTRAQ) based proteomic approach was adopted to globally examine the effects of arsenic on liver sinusoidal endothelial cells (LSECs) during the progression of sinusoidal dedifferentiation. In all, 4205 proteins were identified and quantified by iTRAQ combined with LC-MS/MS analysis, of which 310 proteins were significantly changed in NaAsO₂ group, compared with the normal control. Validation by western blot showed increased level of clathrin-associated sorting protein Disabled 2 (Dab2) in NaAsO₂ group, indicating that it may regulate receptor endocytosis, which served as a mechanism to augment intracellular VEGF signaling. Moreover, we found that knockdown of Dab2 reduced the uptake of VEGF in LSECs, furthermore blocking VEGF-mediated LSEC dedifferentiation and angiogenesis.

Effects of Inorganic Arsenic, Methylated Arsenicals, and Arsenobetaine on Atherosclerosis in the Mouse Model and the Role of As3mt-Mediated Methylation

BACKGROUND

Arsenic is metabolized through a series of oxidative methylation reactions by arsenic (3) methyltransferase (As3MT) to yield methylated intermediates. Although arsenic exposure is known to increase the risk of atherosclerosis, the contribution of arsenic methylation and As3MT remains undefined.

OBJECTIVES

Our objective was to define whether methylated arsenic intermediates were proatherogenic and whether arsenic biotransformation by As3MT was required for arsenic-enhanced atherosclerosis.

METHODS

We utilized the apoE^−/− mouse model to compare atherosclerotic plaque size and composition after inorganic arsenic, methylated arsenical, or arsenobetaine exposure in drinking water. We also generated apoE^−/−/As3mt^−/− double knockout mice to test whether As3MT-mediated biotransformation was required for the proatherogenic effects of inorganic arsenite. Furthermore, As3MT expression and function were assessed in in vitro cultures of plaque-resident cells. Finally, bone marrow transplantation studies were performed to define the contribution of As3MT-mediated methylation in different cell types to the development of atherosclerosis after inorganic arsenic exposure.

RESULTS

We found that methylated arsenicals, but not arsenobetaine, are proatherogenic and that As3MT is required for arsenic to induce reactive oxygen species and promote atherosclerosis. Importantly, As3MT was expressed and functional in multiple plaque-resident cell types, and transplant studies indicated that As3MT is required in extrahepatic tissues to promote atherosclerosis.

CONCLUSION

Taken together, our findings indicate that As3MT acts to promote cardiovascular toxicity of arsenic and suggest that human AS3MT SNPs that correlate with enzyme function could predict those most at risk to develop atherosclerosis among the millions that are exposed to arsenic. https://doi.org/10.1289/EHP806.

Citron Rho-interacting kinase mediates arsenite-induced decrease in endothelial nitric oxide synthase activity by increasing phosphorylation at threonine 497: Mechanism underlying arsenite-induced vascular dysfunction

We reported that arsenite causes an acute decrease in nitric oxide (NO) production by increasing phosphorylation of endothelial NO synthase at threonine 497 (eNOS-Thr(497)); however, the detailed mechanism has not yet been clarified. Here, we investigated the kinase involving in arsenite-stimulated eNOS-Thr(497) phosphorylation. Although treatment with H-89, a known protein kinase A (PKA) inhibitor, inhibited arsenite-stimulated eNOS-Thr(497) phosphorylation, no inhibition was found in cells treated with other PKA inhibitors, including Rp-8-Br-cAMPS or PKI. Based on previous reports, we also tested whether RhoA mediates arsenite-stimulated eNOS-Thr(497) phosphorylation and found that arsenite causes an acute increase in RhoA activity. Ectopic expression of dominant negative (DN)-RhoA significantly reversed arsenite-stimulated eNOS-Thr(497) phosphorylation. An in vitro phosphorylation assay also revealed that the well-known Rho effectors, Rho-associated protein kinase 1/2 (ROCK1/2), directly phosphorylate eNOS-Thr(497). Y27632, a selective ROCK inhibitor, reversed arsenite-stimulated eNOS-Thr(497) phosphorylation. However, overexpression of a small interfering RNA (siRNA) against ROCK1/2 or DN-ROCK did not reverse arsenite-stimulated eNOS-Thr(497) phosphorylation, thereby providing no conclusive evidence of a role for ROCK1/2. Knockdown of PKC-related protein kinase 1/2, another Rho effector, also did not reverse arsenite-stimulated eNOS-Thr(497) phosphorylation. In contrast, we found that transfection with an siRNA against citron Rho-interacting kinase (CRIK), the other downstream effector of Rho, significantly reversed the arsenite-induced eNOS-Thr(497) phosphorylation that was accompanied by restoration of eNOS enzymatic activity repressed by arsenite. Moreover, CRIK directly phosphorylated eNOS-Thr(497)in vitro. Finally, we also found that arsenite increased eNOS-Thr(497) phosphorylation and decreased acetylcholine-induced vessel relaxation in rat aortas. In conclusion, we demonstrate that arsenite acutely inhibits eNOS enzymatic activity and vessel relaxation in part by increasing the RhoA/CRIK/eNOS-Thr(497) phosphorylation signaling axis, which provides a molecular mechanism underlying arsenite-induced impaired vascular diseases.

Functional role of inorganic trace elements in angiogenesis part III: (Ti, Li, Ce, As, Hg, Va, Nb and Pb)

Many essential elements exist in nature with significant influence on human health. Angiogenesis is vital in developmental, repair, and regenerative processes, and its aberrant regulation contributes to pathogenesis of many diseases including cancer. Thus, it is of great importance to explore the role of these elements in such a vital process. This is third in a series of reviews that serve as an overview of the role of inorganic elements in regulation of angiogenesis and vascular function. Here we will review the roles of titanium, lithium, cerium, arsenic, mercury, vanadium, niobium, and lead in these processes. The roles of other inorganic elements in angiogenesis were discussed in part I (N, Fe, Se, P, Au, and Ca) and part II (Cr, Si, Zn, Cu, and S) of these series. The methods of exposure, structure, mechanisms, and potential activities of these elements are briefly discussed. An electronic search was performed on the role of these elements in angiogenesis from January 2005 to April 2014. These elements can promote and/or inhibit angiogenesis through different mechanisms. The anti-angiogenic effect of titanium dioxide nanoparticles comes from the inhibition of angiogenic processes, and not from its toxicity. Lithium affects vasculogenesis but not angiogenesis. Nanoceria treatment inhibited tumor growth by inhibiting angiogenesis. Vanadium treatment inhibited cell proliferation and induced cytotoxic effects through interactions with DNA. The negative impact of mercury on endothelial cell migration and tube formation activities was dose and time dependent. Lead induced IL-8 production, which is known to promote tumor angiogenesis. Thus, understanding the impact of these elements on angiogenesis will help in development of new modalities to modulate angiogenesis under various conditions.

Assessing the carcinogenic potential of low-dose exposures to chemical mixtures in the environment: focus on the cancer hallmark of tumor angiogenesis

One of the important 'hallmarks' of cancer is angiogenesis, which is the process of formation of new blood vessels that are necessary for tumor expansion, invasion and metastasis. Under normal physiological conditions, angiogenesis is well balanced and controlled by endogenous proangiogenic factors and antiangiogenic factors. However, factors produced by cancer cells, cancer stem cells and other cell types in the tumor stroma can disrupt the balance so that the tumor microenvironment favors tumor angiogenesis. These factors include vascular endothelial growth factor, endothelial tissue factor and other membrane bound receptors that mediate multiple intracellular signaling pathways that contribute to tumor angiogenesis. Though environmental exposures to certain chemicals have been found to initiate and promote tumor development, the role of these exposures (particularly to low doses of multiple substances), is largely unknown in relation to tumor angiogenesis. This review summarizes the evidence of the role of environmental chemical bioactivity and exposure in tumor angiogenesis and carcinogenesis. We identify a number of ubiquitous (prototypical) chemicals with disruptive potential that may warrant further investigation given their selectivity for high-throughput screening assay targets associated with proangiogenic pathways. We also consider the cross-hallmark relationships of a number of important angiogenic pathway targets with other cancer hallmarks and we make recommendations for future research. Understanding of the role of low-dose exposure of chemicals with disruptive potential could help us refine our approach to cancer risk assessment, and may ultimately aid in preventing cancer by reducing or eliminating exposures to synergistic mixtures of chemicals with carcinogenic potential.

Genetic deletion of LXRα prevents arsenic-enhanced atherosclerosis, but not arsenic-altered plaque composition

Arsenic exposure has been linked to an increased incidence of atherosclerosis. Previously, we have shown in vitro and in vivo that arsenic inhibits transcriptional activation of the liver X receptors (LXRs), key regulators of lipid homeostasis. Therefore, we evaluated the role of LXRα in arsenic-induced atherosclerosis using the apoE(-/-) mouse model. Indeed, deletion of LXRα protected apoE(-/-) mice against the proatherogenic effects of arsenic. We have previously shown that arsenic changes the plaque composition in apoE(-/-) mice. Arsenic decreased collagen content in the apoE(-/-) model, and we have observed the same diminution in LXRα(-/-)apoE(-/-) mice. However, the collagen-producing smooth muscle cells (SMCs) were decreased in apoE(-/-), but increased in LXRα(-/-)apoE(-/-). Although transcriptional activation of collagen remained the same in SMC from both genotypes, arsenic-exposed LXRα(-/-)apoE(-/-) plaques had increased matrix metalloproteinase activity compared with both control LXRα(-/-)apoE(-/-) and apoE(-/-), which could be responsible for both the decrease in plaque collagen and the SMC invasion. In addition, arsenic increased plaque lipid accumulation in both genotypes. However, macrophages, the cells known to retain lipid within the plaque, were unchanged in arsenic-exposed apoE(-/-) mice, but decreased in LXRα(-/-)apoE(-/-). We confirmed in vitro that these cells retained more lipid following arsenic exposure and are more sensitive to apoptosis than apoE(-/-). Mice lacking LXRα are resistant to arsenic-enhanced atherosclerosis, but arsenic-exposed LXRα(-/-)apoE(-/-) mice still present a different plaque composition pattern than the arsenic-exposed apoE(-/-) mice.

MicroRNA-200b suppresses arsenic-transformed cell migration by targeting protein kinase Cα and Wnt5b-protein kinase Cα positive feedback loop and inhibiting Rac1 activation

MicroRNA-200b (miR-200b) is a member of miR-200 family that has been found to inhibit cell migration and cancer metastasis; however, the underlying mechanism is not well understood. We previously reported that miR-200 expression is depleted in arsenic-transformed human bronchial epithelial cells with highly migratory and invasive characteristics, whereas stably re-expressing miR-200b strongly suppresses arsenic-transformed cell migration. This study was performed to investigate how miR-200b inhibits arsenic-transformed cell migration. We found that protein kinase Cα (PKCα) is significantly up-regulated in arsenic-transformed cells. Combining bioinformatics analysis with PKCα 3'-untranslated region vector luciferase reporter assays, we showed that PKCα is a direct target of miR-200b. Inhibiting PKCα activity or knocking down PKCα expression drastically reduced cell migration, phenocoping the inhibitory effect of overexpressing miR-200b. In contrast, forced expression of PKCα in miR-200b overexpressing cells impaired the inhibitory effect of miR-200b on cell migration. In addition, we also found a positive feedback loop between Wnt5b and PKCα in arsenic-transformed cells. Knocking down Wnt5b expression reduced phospho-PKC levels and cell migration; and knocking down PKCα expression decreased Wnt5b level and cell migration. Moreover, forced expression of PKCα increased Wnt5b and phospho-PKC levels and cell migration. Further mechanistic studies revealed that Rac1 is highly activated in arsenic-transformed cells and stably expressing miR-200b abolishes Rac1 activation changing actin cytoskeleton organization. Manipulating PKCα or Wnt5b expression levels significantly altered the level of active Rac1. Together, these findings indicate that miR-200b suppresses arsenic-transformed cell migration by targeting PKCα and Wnt5b-PKCα positive feedback loop and subsequently inhibiting Rac1 activation.

Interaction between arsenic exposure from drinking water and genetic susceptibility in carotid intima-media thickness in Bangladesh

Epidemiologic studies that evaluated genetic susceptibility for the effects of arsenic exposure from drinking water on subclinical atherosclerosis are limited. We conducted a cross-sectional study of 1078 participants randomly selected from the Health Effects of Arsenic Longitudinal Study in Bangladesh to evaluate whether the association between arsenic exposure and carotid artery intima-media thickness (cIMT) differs by 207 single-nucleotide polymorphisms (SNPs) in 18 genes related to arsenic metabolism, oxidative stress, inflammation, and endothelial dysfunction. Although not statistically significant after correcting for multiple testing, nine SNPs in APOE, AS3MT, PNP, and TNF genes had a nominally statistically significant interaction with well-water arsenic in cIMT. For instance, the joint presence of a higher level of well-water arsenic (≥ 40.4 μg/L) and the GG genotype of AS3MT rs3740392 was associated with a difference of 40.9 μm (95% CI = 14.4, 67.5) in cIMT, much greater than the difference of cIMT associated with the genotype alone (β = -5.1 μm, 95% CI = -31.6, 21.3) or arsenic exposure alone (β = 7.2 μm, 95% CI = -3.1, 17.5). The pattern and magnitude of the interactions were similar when urinary arsenic was used as the exposure variable. Additionally, the at-risk genotypes of the AS3MT SNPs were positively related to the proportion of monomethylarsonic acid (MMA) in urine, which is indicative of arsenic methylation capacity. The findings provide novel evidence that genetic variants related to arsenic metabolism may play an important role in arsenic-induced subclinical atherosclerosis. Future replication studies in diverse populations are needed to confirm the findings.

Curcumin ameliorates intrahepatic angiogenesis and capillarization of the sinusoids in carbon tetrachloride-induced rat liver fibrosis

Neoangiogenesis and the development of an abnormal angio-architecture in the liver are strongly linked with progressive fibrogenesis. This study aimed to evaluate the ability of curcumin to protect liver fibrosis-associated angiogenesis and capillarization of the sinusoids in experimental rats. Liver fibrosis was induced by intraperitoneal injection of carbon tetrachloride (CCl₄) with or without curcumin for 6 weeks. The results suggest that curcumin treatment markedly attenuated CCl₄-induced liver fibrosis, as assessed by histology and hydroxyproline content, and inhibited hepatic stellate cell activation. Curcumin ameliorated hepatic angiogenesis, as assessed by measuring microvessel density using Von Willebrand factor staining and by examining the expression of the endothelial cell markers CD31 and vascular endothelial growth factor receptor (VEGFR)-2 in the livers. Pathologic remodeling of liver sinusoidal capillarization, as assessed by electron-microscopic analysis of Disse's space and by evaluation of the levels of basement membrane protein expression, was also attenuated by curcumin administration. The intrahepatic gene or protein expression of hypoxia-inducible factor-1α, VEGFR-1, placental growth factor, and cyclooxygenase-2 decreased with treatment with curcumin in fibrotic rats. In conclusion, curcumin ameliorates hepatic angiogenesis and sinusoidal capillarization in CCl₄-induced rat liver fibrosis through suppressing multiple proangiogenic factors.

Arsenic-stimulated lipolysis and adipose remodeling is mediated by G-protein-coupled receptors

Arsenic in drinking water promotes a number of diseases that may stem from dysfunctional adipose lipid and glucose metabolism. Arsenic inhibits adipocyte differentiation and promotes insulin resistance; however, little is known of the impacts of and mechanisms for arsenic effects on adipose lipid storage and lipolysis. Based on our earlier studies of arsenic-signaling mechanisms for vascular remodeling and inhibition of adipogenesis, we investigated the hypothesis that arsenic acts through specific adipocyte G-protein-coupled receptors (GPCRs) to promote lipolysis and decrease lipid storage. We first demonstrated that 5-week exposure of mice to 100 μg/l of arsenic in drinking water stimulated epididymal adipocyte hypertrophy, reduced the adipose tissue expression of perilipin (PLIN1, a lipid droplet coat protein), and increased perivascular ectopic fat deposition in skeletal muscle. Incubating adipocytes, differentiated from adipose-derived human mesenchymal stem cell, with arsenic stimulated lipolysis and decreased both Nile Red positive lipid droplets and PLIN1 expression. Arsenic-stimulated lipolysis was not associated with increased cAMP levels. However, preincubation of adipocytes with the Gi inhibitor, Pertussis toxin, attenuated As(III)-stimulated lipolysis and lipid droplet loss. Antagonizing Gi-coupled endothelin-1 type A and B receptors (EDNRA/EDNRB) also attenuated arsenic effects, but antagonizing other adipose Gi-coupled receptors that regulate fat metabolism was ineffective. The endothelin receptors have different roles in arsenic responses because only EDNRA inhibition prevented arsenic-stimulated lipolysis, but antagonists to either receptor protected lipid droplets and PLIN1 expression. These data support a role for specific GPCRs in arsenic signaling for aberrant lipid storage and metabolism that may contribute to the pathogenesis of metabolic disease caused by environmental arsenic exposures.

Chronic arsenic exposure in nanomolar concentrations compromises wound response and intercellular signaling in airway epithelial cells

Paracrine ATP signaling in the lung epithelium participates in a variety of innate immune functions, including mucociliary clearance, bactericide production, and as an initiating signal in wound repair. We evaluated the effects of chronic low-dose arsenic relevant to U.S. drinking water standards (i.e., 10 ppb [130nM]) on airway epithelial cells. Immortalized human bronchial epithelial cells (16HBE14o-) were exposed to 0, 130, or 330nM arsenic (as Na-arsenite) for 4-5 weeks and examined for wound repair efficiency and ATP-mediated Ca(2+) signaling. We found that chronic arsenic exposure at these low doses slows wound repair and reduces ATP-mediated Ca(2+) signaling. We further show that arsenic compromises ATP-mediated Ca(2+) signaling by altering both Ca(2+) release from intracellular stores (via metabotropic P2Y receptors) and Ca(2+) influx mechanisms (via ionotropic P2X receptors). To better model the effects of arsenic on ATP-mediated Ca(2+) signaling under conditions of natural exposure, we cultured tracheal epithelial cells obtained from mice exposed to control or 50 ppb Na-arsenite supplemented drinking water for 4 weeks. Tracheal epithelial cells from arsenic-exposed mice displayed reduced ATP-mediated Ca(2+) signaling dynamics similar to our in vitro chronic exposure. Our findings demonstrate that chronic arsenic exposure at levels that are commonly found in drinking water (i.e., 10-50 ppb) alters cellular mechanisms critical to airway innate immunity.

Arsenic activates endothelin-1 Gi protein-coupled receptor signaling to inhibit stem cell differentiation in adipogenesis

Dysfunctional lipid and glucose metabolism contribute to metabolic syndrome-a major public health concern that enhances cardiovascular disease risk. Arsenic (As(III)) exposure may increase metabolic syndrome and cardiovascular disease risk by impairing adipose tissue differentiation, function, and insulin sensitivity through pathogenic mechanisms that remain unclear. We hypothesized that As(III) signals through the Pertussis toxin (Ptx) sensitive, Gi protein-coupled receptor (GPCR) to impair adipogenesis, as previously demonstrated for its stimulation of vascular oxidant generation, angiogenesis, and remodeling. Because both As(III) and GPCR ligands inhibit progenitor cell differentiation into adipocytes, we investigated the hypothesis in a model of low-passage human mesenchymal stem cells (hMSC). As(III) (0.1-1.0 µM) suppressed dexamethasone/insulin-induced hMSC adipogenesis, as indicated by decreased transcriptional promoters of differentiation, decreased fat droplet formation, and decreased expression of differentiated adipocyte markers, such as adiponectin and perilipin. Preincubating hMSC with Ptx prevented 90% of the suppressive effect of As(III). Selective competitive antagonists of Gi-coupled endothelin-1 type A and B receptors were ~60% effective in blocking As(III) inhibition and combination of antagonists to both receptors were 85% effective. In contrast, antagonists to the sphingosine-1-phosphate type 1 receptor (previously shown to mediate As(III) vascular effects) or the angiotensin II type 1 receptor were ineffective in blocking As(III) effects. These studies suggest a majority of arsenic-inhibited adipocyte differentiation, and metabolism requires endothelin-1 GPCRs and that As(III) effects on GPCR signaling are tissue and context specific. This may represent a significant mechanism for the contribution of arsenic exposure to increased metabolic and cardiovascular diseases.

MicroRNA-181b and microRNA-9 mediate arsenic-induced angiogenesis via NRP1

Environmental exposure to inorganic arsenic compounds has been reported to have serious health effects on humans. Recent studies reported that arsenic targets endothelial cells lining blood vessels, and endothelial cell activation or dysfunction, may underlie the pathogenesis of arsenic-induced diseases and developmental toxicity. It has been reported that microRNAs (miRNAs) may act as an angiogenic switch by regulating related genes. The present study was designed to test the hypothesis that arsenite-regulated miRNAs play pivotal roles in arsenic-induced toxicity. Fertilized eggs were injected via the yolk sac with 100  nM sodium arsenite at Hamburger-Hamilton (HH) stages 6, 9, and 12, and harvested at HH stage 18. To identify the individual miRNAs and mRNAs that may regulate the genetic network, the expression profiles of chick embryos were analyzed by microarray analysis. Microarray analyses revealed that the expression of a set of miRNAs changed after arsenite administration, especially miRNA-9, 181b, 124, 10b, and 125b, which exhibited a massive decrease in expression. Integrative analyses of the microarray data revealed that several miRNAs, including miR-9 and miR-181b, might target several key genes involved in arsenic-induced developmental toxicity. A luciferase reporter assay confirmed neuropilin-1 (Nrp1) as a target of mir-9 and mir-181b. Data from the transwell migration assay and the tube-formation assay indicated that miR-9 and mir-181b inhibited the arsenic-induced EA.hy926 cell migration and tube formation by targeting NRP1. Our study demonstrates that the environmental toxin, sodium arsenite, induced angiogenesis by altering the expression of miRNAs and their cognate mRNA targets.

LPS and TNF-α induce expression of sphingosine-1-phosphate receptor-2 in human microvascular endothelial cells

Sphingosine-1-phosphate (S1P) is a bioactive sophospholipid with various S1P receptor (S1PR) expression profiles in cells of different origin. S1PR1, R3 and - to a lesser extent - R2 were the main receptors expressed in most of endothelial cells (ECs). The balances in the expression and activation of S1PR1, R2 and R3 help to maintain the physiological functions of ECs. Reverse transcription-PCR and Western blotting were used to detect the mRNA transcript level and protein expression of S1PR. Endothelial barrier function was measured by transflux of tracer protein through endothelial monolayer. Human dermal microvascular ECs predominantly expressed S1PR1 and S1PR3. Lipopolysaccharide (LPS) or tumor necrosis factor-α (TNF-α) significantly upregulated S1PR2 mRNA and protein levels. The application of S1PR2 antagonist JTE-013 decreased the endothelial monolayer hyper-permeability response induced by LPS and TNF-α. Inflammatory mediators LPS and TNF-α induce S1PR2 expression in endothelium, suggesting that S1PR2 up-regulation may be involved in LPS and TNF-α elicited endothelial barrier dysfunction.

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.

Oxidases and peroxidases in cardiovascular and lung disease: new concepts in reactive oxygen species signaling

Reactive oxygen species (ROS) are involved in numerous physiological and pathophysiological responses. Increasing evidence implicates ROS as signaling molecules involved in the propagation of cellular pathways. The NADPH oxidase (Nox) family of enzymes is a major source of ROS in the cell and has been related to the progression of many diseases and even environmental toxicity. The complexity of this family's effects on cellular processes stems from the fact that there are seven members, each with unique tissue distribution, cellular localization, and expression. Nox proteins also differ in activation mechanisms and the major ROS detected as their product. To add to this complexity, mounting evidence suggests that other cellular oxidases or their products may be involved in Nox regulation. The overall redox and metabolic status of the cell, specifically the mitochondria, also has implications on ROS signaling. Signaling of such molecules as electrophilic fatty acids has an impact on many redox-sensitive pathologies and thus, as anti-inflammatory molecules, contributes to the complexity of ROS regulation. This review is based on the proceedings of a recent international Oxidase Signaling Symposium at the University of Pittsburgh's Vascular Medicine Institute and Department of Pharmacology and Chemical Biology and encompasses further interaction and discussion among the presenters.

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.

R-Ras and Rac GTPase cross-talk regulates hematopoietic progenitor cell migration, homing, and mobilization

Adult hematopoietic progenitor cells (HPCs) are maintained by highly coordinated signals in the bone marrow. The molecular mechanisms linking intracellular signaling network of HPCs with their microenvironment remain poorly defined. The Rho family GTPase Rac1/Rac2 has previously been implicated in cell functions involved in HPC maintenance, including adhesion, migration, homing, and mobilization. In the present studies we have identified R-Ras, a member of the Ras family, as a key signal mediator required for Rac1/Rac2 activation. We found that whereas Rac1 activity is up-regulated upon stem cell factor, integrin, or CXCL12 stimulation, R-Ras activity is inversely up-regulated. Expression of a constitutively active R-Ras mutant resulted in down-regulation of Rac1-activity whereas deletion of R-Ras led to an increase in Rac1/Rac2 activity and signaling. R-Ras(-/-) HPCs displayed a constitutively assembled cortical actin structure and showed increased directional migration. Rac1/Rac2 inhibition reversed the migration phenotype of R-Ras(-/-) HPCs, similar to that by expressing an R-Ras active mutant. Furthermore, R-Ras(-/-) mice showed enhanced responsiveness to G-CSF for HPC mobilization and exhibited decreased bone marrow homing. Transplantation experiments indicate that the R-Ras deficiency-induced HPC mobilization is a HPC intrinsic property. These results indicate that R-Ras is a critical regulator of Rac signaling required for HPC migration, homing, and mobilization.

Role and mechanism of arsenic in regulating angiogenesis

Arsenic is a wide spread carcinogen associated with several kinds of cancers including skin, lung, bladder, and liver cancers. Lung is one of the major targets of arsenic exposure. Angiogenesis is the pivotal process during carcinogenesis and chronic pulmonary diseases, but the role and mechanism of arsenic in regulating angiogenesis remain to be elucidated. In this study we show that short time exposure of arsenic induces angiogenesis in both human immortalized lung epithelial cells BEAS-2B and adenocarcinoma cells A549. To study the molecular mechanism of arsenic-inducing angiogenesis, we find that arsenic induces reactive oxygen species (ROS) generation, which activates AKT and ERK1/2 signaling pathways and increases the expression of hypoxia-inducible factor 1 (HIF-1) and vascular endothelial growth factor (VEGF). Inhibition of ROS production suppresses angiogenesis by decreasing AKT and ERK activation and HIF-1 expression. Inhibition of ROS, AKT and ERK1/2 signaling pathways is sufficient to attenuate arsenic-inducing angiogenesis. HIF-1 and VEGF are downstream effectors of AKT and ERK1/2 that are required for arsenic-inducing angiogenesis. These results shed light on the mechanism of arsenic in regulating angiogenesis, and are helpful to develop mechanism-based intervention to prevent arsenic-induced carcinogenesis and angiogenesis in the future.

Arsenic and its combinations in cancer therapeutics

Arsenic is a metalloid that is considered to be a paradox in terms of its role both as a carcinogen and as a therapeutic agent. Chronic exposure to arsenic in drinking water has been linked with the development of various pathological conditions including cancer. Nevertheless, the therapeutic potential of arsenic and its derivatives in a variety of diseases have been exploited in the past. However, its role and mechanism of action as a therapeutic agent still remain an active area of research and investigation. Our ongoing work also suggests varied responses in cancer cells exposed to lower versus higher concentrations of arsenic. Furthermore, the arsenic combinations with chemopreventive or anticancer agents have been observed to sensitize the cell for cell-cycle arrest and cell death. Here, we have provided the account of recent updates on the mechanism of action of arsenic and its derivatives that lead to various disorders, and its role as a therapeutic agent both as a single agent as well as in combination chemotherapy.

Arsenic exposure from drinking water and mortality from cardiovascular disease in Bangladesh: prospective cohort study

OBJECTIVE

To evaluate the association between arsenic exposure and mortality from cardiovascular disease and to assess whether cigarette smoking influences the association.

DESIGN

Prospective cohort study with arsenic exposure measured in drinking water from wells and urine.

SETTING

General population in Araihazar, Bangladesh.

PARTICIPANTS

11,746 men and women who provided urine samples in 2000 and were followed up for an average of 6.6 years.

MAIN OUTCOME MEASURE

Death from cardiovascular disease.

RESULTS

198 people died from diseases of circulatory system, accounting for 43% of total mortality in the population. The mortality rate for cardiovascular disease was 214.3 per 100,000 person years in people drinking water containing <12.0 µg/L arsenic, compared with 271.1 per 100,000 person years in people drinking water with ≥ 12.0 µg/L arsenic. There was a dose-response relation between exposure to arsenic in well water assessed at baseline and mortality from ischaemic heart disease and other heart disease; the hazard ratios in increasing quarters of arsenic concentration in well water (0.1-12.0, 12.1-62.0, 62.1-148.0, and 148.1-864.0 µg/L) were 1.00 (reference), 1.22 (0.65 to 2.32), 1.35 (0.71 to 2.57), and 1.92 (1.07 to 3.43) (P = 0.0019 for trend), respectively, after adjustment for potential confounders including age, sex, smoking status, educational attainment, body mass index (BMI), and changes in urinary arsenic concentration since baseline. Similar associations were observed when baseline total urinary arsenic was used as the exposure variable and for mortality from ischaemic heart disease specifically. The data indicate a significant synergistic interaction between arsenic exposure and cigarette smoking in mortality from ischaemic heart disease and other heart disease. In particular, the hazard ratio for the joint effect of a moderate level of arsenic exposure (middle third of well arsenic concentration 25.3-114.0 µg/L, mean 63.5 µg/L) and cigarette smoking on mortality from heart disease was greater than the sum of the hazard ratios associated with their individual effect (relative excess risk for interaction 1.56, 0.05 to 3.14; P = 0.010).

CONCLUSIONS

Exposure to arsenic in drinking water is adversely associated with mortality from heart disease, especially among smokers.

Exposure to moderate arsenic concentrations increases atherosclerosis in ApoE-/- mouse model

Arsenic is a widespread environmental contaminant to which millions of people are exposed worldwide. Exposure to arsenic is epidemiologically linked to increased cardiovascular disease, such as atherosclerosis. However, the effects of moderate concentrations of arsenic on atherosclerosis formation are unknown. Therefore, we utilized an in vivo ApoE(-/-) mouse model to assess the effects of chronic moderate exposure to arsenic on plaque formation and composition in order to facilitate mechanistic investigations. Mice exposed to 200 ppb arsenic developed atherosclerotic lesions, a lower exposure than previously reported. In addition, arsenic modified the plaque content, rendering them potentially less stable and consequently, potentially more dangerous. Moreover, we observed that the lower exposure concentration was more atherogenic than the higher concentration. Arsenic-enhanced lesions correlated with several proatherogenic molecular changes, including decreased liver X receptor (LXR) target gene expression and increased proinflammatory cytokines. Significantly, our observations suggest that chronic moderate arsenic exposure may be a greater cardiovascular health risk than previously anticipated.

Role for peroxynitrite in sphingosine-1-phosphate-induced hyperalgesia in rats

Sphingosine-1-phosphate (S1P) is an important mediator of inflammation recently shown in in vitro studies to increase the excitability of small-diameter sensory neurons, at least in part, via activation of the S1P(1) receptor subtype. Activation of S1PR(1) has been reported to increase the formation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-derived superoxide (O(2)(·-)) and nitric oxide synthase (NOS)-derived nitric oxide (NO). This process favors the formation of peroxynitrite (ONOO(-) [PN]), a potent mediator of hyperalgesia associated with peripheral and central sensitization. The aims of our study were to determine whether S1P causes peripheral sensitization and thermal hyperalgesia via S1PR(1) activation and PN formation. Intraplantar injection of S1P in rats led to a time-dependent development of thermal hyperalgesia that was blocked by the S1PR(1) antagonist W146, but not its inactive enantiomer W140. The hyperalgesic effects of S1P were mimicked by intraplantar injection of the well-characterized S1PR(1) agonist SEW2871. The development of S1P-induced hyperalgesia was blocked by apocynin, a NADPH oxidase inhibitor; N(G)-nitro-l-arginine methyl ester, a nonselective NOS inhibitor; and by the potent PN decomposition catalysts (FeTM-4-PyP(5+) and MnTE-2-PyP(5+)). Our findings provide mechanistic insight into the signaling pathways engaged by S1P in the development of hyperalgesia and highlight the contribution of the S1P(1) receptor-to-PN signaling in this process. Sphingosine-1-phosphate (S1P)-induced hyperalgesia is mediated by S1P1 receptor activation and mitigated by inhibition or decomposition of peroxynitrite, providing a target pathway for novel pain management strategies.

Influence of arsenate and arsenite on signal transduction pathways: an update

Arsenic has been a recognized contaminant and toxicant, as well as a medicinal compound throughout human history. Populations throughout the world are exposed to arsenic and these exposures have been associated with a number of human cancers. Not much is known about the role of arsenic as a human carcinogen and more recently its role in non-cancerous diseases, such as cardiovascular disease, hypertension and diabetes mellitus have been uncovered. The health effects associated with arsenic are numerous and the association between arsenic exposure and human disease has intensified the search for molecular mechanisms that describe the biological activity of arsenic in humans and leads to the aforementioned disease states. Arsenic poses a human health risk due in part to the regulation of cellular signal transduction pathways and over the last few decades, some cellular mechanisms that account for arsenic toxicity, as well as, signal transduction pathways have been discovered. However, given the ubiquitous nature of arsenic in the environment, making sense of all the data remains a challenge. This review will focus on our knowledge of signal transduction pathways that are regulated by arsenic.

Arsenic exposure perturbs epithelial-mesenchymal cell transition and gene expression in a collagen gel assay

Arsenic is a naturally occurring metalloid and environmental contaminant. Arsenic exposure in drinking water is reported to cause cancer of the liver, kidneys, lung, bladder, and skin as well as birth defects, including neural tube, facial, and vasculogenic defects. The early embryonic period most sensitive to arsenic includes a variety of cellular processes. One key cellular process is epithelial-mesenchymal transition (EMT) where epithelial sheets develop into three-dimensional structures. An embryonic prototype of EMT is found in the atrioventricular (AV) canal of the developing heart, where endothelia differentiate to form heart valves. Effects of arsenic on this cellular process were examined by collagen gel invasion assay (EMT assay) using explanted AV canals from chicken embryo hearts. AV canals treated with 12.5-500 ppb arsenic showed a loss of mesenchyme at 12.5 ppb, and mesenchyme formation was completely inhibited at 500 ppb. Altered gene expression in arsenic-treated explants was investigated by microarray analysis. Genes whose expression was altered consistently at exposure levels of 10, 25, and 100 ppb were identified, and results showed that 25 ppb in vitro was particularly effective. Three hundred and eighty two genes were significantly altered at this exposure level. Cytoscape analysis of the microarray data using the chicken interactome identified four clusters of altered genes based on published relationships and pathways. This analysis identified cytoskeleton and cell adhesion-related genes whose disruption is consistent with an altered ability to undergo EMT. These studies show that EMT is sensitive to arsenic and that an interactome-based approach can be useful in identifying targets.

Expression of sphingosine-1-phosphate receptor 1 in mantle cell lymphoma

The distribution and pathological significance of sphingosine-1-phosphate receptor 1 expression are still unclear. In this study, we evaluated sphingosine-1-phosphate receptor 1's suitability as a diagnostic marker for malignant lymphoma by immunostaining formalin-fixed paraffin-embedded sections using a well-defined commercial anti-sphingosine-1-phosphate receptor 1 antibody. Sphingosine-1-phosphate receptor 1 was strongly expressed on the surface of small lymphocytes forming primary lymphoid follicles and in the mantle zone of secondary lymphoid follicles. Microarray-based immunohistochemistry with tissue samples from 85 lymphoid malignancy cases demonstrated that sphingosine-1-phosphate receptor 1 was expressed on the surface of mantle cell lymphoma cells. Strong expression was observed in all classical mantle cell lymphoma cases involving the lymph node (19 out of 19), gastrointestinal tract (10 out of 10), bone marrow (9 out of 9), and orbita (1 out of 1). Good results were obtained even in sections where cyclin D1 signals were lost because of over-fixation and/or decalcification. One aggressive variant of mantle cell lymphoma displayed a weaker membranous staining than classical mantle cell lymphoma in the lymph node and bone marrow. In a cyclin D1-negative mantle cell lymphoma of the orbita, no conclusive result was obtained. No cases of follicular lymphoma, marginal zone lymphoma, B lymphoblastic leukemia/lymphoma, or Burkitt's lymphoma showed any significant expression, whereas 2 out of 6 chronic lymphocytic leukemia/small lymphocytic lymphomas in bone marrow, 1 out of 3 lymphoplasmacytic lymphomas in the lymph node, and 2 out of 37 diffuse large B-cell lymphomas exhibited staining. A quantitative reverse transcription polymerase chain reaction-based analysis of mantle cell lymphoma lines revealed the sphingosine-1-phosphate receptor 1 mRNA expression level to be well correlated with the results of immunocytochemistry, flow cytometry, and western blotting. Thus, sphingosine-1-phosphate receptor 1 immunohistochemistry may be useful in the histological diagnosis of mantle cell lymphoma with formalin-fixed and paraffin-embedded sections. The antigen may be particularly valuable in cases where cyclin D1 immunostaining is not successful.

Arsenic promotes angiogenesis in vitro via a heme oxygenase-1-dependent mechanism

Angiogenesis and vessel remodeling are fundamental to the pathogenesis of a number of diseases caused by environmental arsenic exposure, including tumorigenesis and cardiovascular diseases. Arsenic (AsIII) has been shown to stimulate angiogenesis and vascular remodeling in vivo. However, the exact molecular mechanisms accounting for arsenic-induced angiogenesis are not clear. The present study investigates the role of heme oxygenase-1 (HO-1) in sodium arsenite-mediated angiogenesis in vitro. Transwell assay, three-dimensional Matrigel assay, RT-PCR, ELISA and immunoblotting were used to determine cell migration, vascular tube formation, mRNA and protein expression. Chromatin immunoprecipitation and luciferase assay were applied to examine the DNA binding with protein and HO-1 transcriptional activity. Here, we report that low concentrations of arsenite (0.1-1 muM) stimulated cell migration and vascular tube formation in human microvascular endothelial cells (HMVEC). Arsenite induced HO-1 mRNA and protein expression. Knock down of HO-1 expression decreased arsenite-induced VEGF expression, cell migration, and tube formation. We showed that arsenite promoted dissociation of Bach1 (a transcriptional repressor) from the HO-1 enhancers and increased Nrf2 binding to these elements. Site directed mutagenesis assay identified that Bach1 cysteine residues 557 and 574 were essential for the induction of HO-1 gene in response to arsenite. These findings demonstrate a role for HO-1 in arsenite-mediated angiogenesis in vitro.