Effects of arsenic, cadmium, chromium, and lead on gene expression regulated by a battery of 13 different promoters in recombinant HepG2 cells

Unboxing the molecular modalities of mutagens in cancer

The etiology of the majority of human cancers is associated with a myriad of environmental causes, including physical, chemical, and biological factors. DNA damage induced by such mutagens is the initial step in the process of carcinogenesis resulting in the accumulation of mutations. Mutational events are considered the major triggers for introducing genetic and epigenetic insults such as DNA crosslinks, single- and double-strand DNA breaks, formation of DNA adducts, mismatched bases, modification in histones, DNA methylation, and microRNA alterations. However, DNA repair mechanisms are devoted to protect the DNA to ensure genetic stability, any aberrations in these calibrated mechanisms provoke cancer occurrence. Comprehensive knowledge of the type of mutagens and carcinogens and the influence of these agents in DNA damage and cancer induction is crucial to develop rational anticancer strategies. This review delineated the molecular mechanism of DNA damage and the repair pathways to provide a deep understanding of the molecular basis of mutagenicity and carcinogenicity. A relationship between DNA adduct formation and cancer incidence has also been summarized. The mechanistic basis of inflammatory response and oxidative damage triggered by mutagens in tumorigenesis has also been highlighted. We elucidated the interesting interplay between DNA damage response and immune system mechanisms. We addressed the current understanding of DNA repair targeted therapies and DNA damaging chemotherapeutic agents for cancer treatment and discussed how antiviral agents, anti-inflammatory drugs, and immunotherapeutic agents combined with traditional approaches lay the foundations for future cancer therapies.

Metals and Metallothionein Expression in Relation to Progression of Chronic Kidney Disease of Unknown Etiology (CKDu) in Sri Lanka

Chronic kidney disease of unknown etiology was investigated for metal relations in an endemic area by a cross-sectional study with CKD stages G1, G2, G3a, G3b, G4, G5 (ESRD), and endemic and nonendemic controls (EC and NEC) as groups. Subjects with the medical diagnosis were classified into groups by eGFR (SCr, CKD-EPI) and UACR of the study. It determined 24 metals/metalloids in plasma (ICPMS) and metallothionein (MT) mRNA in blood (RT-PCR). MT1A at G3b and MT2A throughout G2−G5 showed increased transcription compared to NEC (ANOVA, p < 0.01). Both MT1A and MT2A remained metal-responsive as associations emerged between MT2A and human MT inducer Cr (in EC: r = 0.54, p < 0.05, n = 14), and between MT1A and MT2A (in EC pooled with G1−G5: r = 0.58, p < 0.001, n = 110). Human MT (hMT)-inducers, namely Zn, Cu, As, Pb, and Ni; Σ hMT-inducers; 14 more non-inducer metals; and Σ MT-binding metals remained higher (p < 0.05) in EC as compared to NEC. Declining eGFR or CKD progression increased the burden of Be, Mg, Al, V, Co, Ni, Rb, Cs, Ba, Mn, Zn, Sr, Σ hMT-inducers, and Σ MT-binding metals in plasma, suggesting an MT role in the disease. MT1A/2A mRNA followed UACR (PCA, Dendrogram: similarity, 57.7%). The study provides evidence that proteinuric chronic renal failure may increase plasma metal levels where blood MT2A could be a marker.

Environmentally induced ribosomal DNA (rDNA) instability in human cells and populations exposed to hexavalent chromium [Cr (VI)]

Hexavalent Chromium [Cr (VI)] is an established toxicant, carcinogen, and a significant source of public health concern. The multicopy ribosomal DNA (rDNA) array is mechanistically linked to aging and cancer, is the most evolutionarily conserved segment of the human genome, and gives origin to nucleolus, a nuclear organelle where ribosomes are assembled. Here we show that exposure to Cr (VI) induces instability in the rDNA, triggering cycles of rapid, specific, and transient amplification and contraction of the array in human cells. The dynamic of environmentally responsive rDNA copy number (CN) amplification and contraction occurs at doses to which millions of individuals are regularly exposed. Finally, analyses of human populations occupationally exposed to Cr (VI) indicate that environmental exposure history and drinking habits but not age shape extensive naturally occurring rDNA copy number variation. Our observations identify a novel pathway of response to hexavalent chromium exposure and raise the prospect that a suite of environmental determinants of rDNA copy number remain to be discovered.

Arsenic: Various species with different effects on cytochrome P450 regulation in humans

Arsenic is well-recognized as one of the most hazardous elements which is characterized by its omnipresence throughout the environment in various chemical forms. From the simple inorganic arsenite (iAsIII) and arsenate (iAsV) molecules, a multitude of more complex organic species are biologically produced through a process of metabolic transformation with biomethylation being the core of this process. Because of their differential toxicity, speciation of arsenic-based compounds is necessary for assessing health risks posed by exposure to individual species or co-exposure to several species. In this regard, exposure assessment is another pivotal factor that includes identification of the potential sources as well as routes of exposure. Identification of arsenic impact on different physiological organ systems, through understanding its behavior in the human body that leads to homeostatic derangements, is the key for developing strategies to mitigate its toxicity. Metabolic machinery is one of the sophisticated body systems targeted by arsenic. The prominent role of cytochrome P450 enzymes (CYPs) in the metabolism of both endobiotics and xenobiotics necessitates paying a great deal of attention to the possible effects of arsenic compounds on this superfamily of enzymes. Here we highlight the toxicologically relevant arsenic species with a detailed description of the different environmental sources as well as the possible routes of human exposure to these species. We also summarize the reported findings of experimental investigations evaluating the influence of various arsenicals on different members of CYP superfamily using human-based models.

Anticancer Potential of Mefenamic Acid Derivatives with Platelet-Derived Growth Factor Inhibitory Property

Background:

Numerous studies suggest that non-steroidal anti-inflammatory drugs reduce cancer cell proliferation, progression, angiogenesis, apoptosis, and invasiveness.

Objective:

The current study focuses on the evaluation of novel mefenamic acid derivatives for the treatment of hepatocellular carcinoma.

Methods:

Derivatives were subjected to molecular modeling for prediction of pharmacological activity using software, followed by synthesis and in vitro assay. In in vivo study, disease was induced with N-Nitrosodiethylamine followed by 2-acetylaminofluorene orally for 2 weeks. After 12 weeks of induction, treatment was given for a period of one week. At the end of the treatment, determination of liver weight, a number of nodules, biochemical parameters, immunohistochemistry, histopathology, and gene expression studies, were carried out.

Results:

Based on molecular docking score for PDGF-α (Platelet-Derived Growth Factor) and IC50 values in HepG2 cell line study, JS-PFA was selected for the in vivo study where JS-PFA showed a statistically significant reduction in a number of nodules and liver weight. Protective role of JS-PFA has been observed in tumorspecific markers like α-fetoprotein, carcinoembryonic antigen, and lactate dehydrogenase levels. The JS-PFA has shown a significant reduction in PDGF-α levels as well as liver markers and total bilirubin levels. Histopathological analysis also showed a protective effect. The results of immunohistochemical analysis of P53 and down-regulation of vascular endothelial growth factor and matrix metalloproteinases-9 genes suggest that derivative inhibits PDGF mediated tumor growth and leads to apoptosis, inhibition of angiogenesis, and metastasis.

Conclusion:

The effectiveness of JS-PFA in our studies suggests targeting PDGF by COX 2 inhibitor can serve as a novel treatment strategy for the treatment of HCC.

Impact of Carcinogenic Chromium on the Cellular Response to Proteotoxic Stress

Worldwide, several million workers are employed in the various chromium (Cr) industries. These workers may suffer from a variety of adverse health effects produced by dusts, mists and fumes containing Cr in the hexavalent oxidation state, Cr(VI). Of major importance, occupational exposure to Cr(VI) compounds has been firmly associated with the development of lung cancer. Counterintuitively, Cr(VI) is mostly unreactive towards most biomolecules, including nucleic acids. However, its intracellular reduction produces several species that react extensively with biomolecules. The diversity and chemical versatility of these species add great complexity to the study of the molecular mechanisms underlying Cr(VI) toxicity and carcinogenicity. As a consequence, these mechanisms are still poorly understood, in spite of intensive research efforts. Here, we discuss the impact of Cr(VI) on the stress response—an intricate cellular system against proteotoxic stress which is increasingly viewed as playing a critical role in carcinogenesis. This discussion is preceded by information regarding applications, chemical properties and adverse health effects of Cr(VI). A summary of our current understanding of cancer initiation, promotion and progression is also provided, followed by a brief description of the stress response and its links to cancer and by an overview of potential molecular mechanisms of Cr(VI) carcinogenicity.

PFOS Modulates Interactive Epigenetic Regulation in First-Trimester Human Trophoblast Cell Line HTR-8/SVneo

Organic compounds have been linked to adverse pregnancy complications. Perfluorooctanesulfonic acid (PFOS), a man-made fluorosurfactant and global pollutant, has been shown to induce oxidative stress in various cell types. Oxidative stress plays a key role in leading several placental diseases including preeclampsia (PE), gestational diabetes, spontaneous abortion, preterm labor, and intrauterine growth restriction. Recently, epigenetic regulation such as histone modifications, DNA methylation, and microRNAs (miRNAs), are shown to be associated with oxidative stress as well as pregnancy complications such as PE. However, whether PFOS exerts its detrimental effects in the placenta through epigenetics remains to be unveiled. Therefore, we aimed to investigate the effect of PFOS-induced reactive oxygen species (ROS) generation in first trimester human trophoblast cell line (HTR-8/SV_neo) and whether epigenetic regulation is involved in this process. When treated with a range of PFOS doses at 24 and 48 h, even at 10 μM, it significantly increased the ROS production and decreased gene and protein expression, respectively, of the DNA methyltransferases DNMT1 (p < 0.001; p < 0.05), DNMT3A (p < 0.001; p < 0.05), and DNMT3B (p < 0.01; p < 0.01) and the sirtuins, for example, SIRT1 (p < 0.001; p < 0.001) and SIRT3 (p < 0.001; p < 0.05), while reducing global DNA methylation (p < 0.01) and increasing protein lysine acetylation (p < 0.001) as compared to vehicle controls. Interestingly, PFOS (10 μM) significantly increased miR29-b (p < 0.01), which has been previously reported to be associated with PE. The observed epigenetic effects were shown to be dependent on the expression of miR-29b, as knockdown of miR-29b significantly alters the gene and protein expression of DNMT1, DNMT3A, DNMT3B, SIRT1, and SIRT3 and ROS production as well as global DNA methylation and protein acetylation. This study provides for the first time a novel insight into PFOS-induced ROS generation via regulation of sets of the interactive epigenetic circuit in the placenta, which may lead to pregnancy complications.

Ecogenetics of lead toxicity and its influence on risk assessment

Lead (Pb) toxicity is a public health problem affecting millions worldwide. Advances in 'omic' technology have paved the way to toxico-genomics which is currently revolutionizing the understanding of interindividual variations in susceptibility to Pb toxicity and its functional consequences to exposure. Our objective was to identify, comprehensively analyze, and curate all the potential genetic and epigenetic biomarkers studied to date in relation to Pb toxicity and its association with diseases. We screened a volume of research articles that focused on Pb toxicity and its association with genetic and epigenetic signatures in the perspective of occupational and environmental Pb exposure. Due to wide variations in population size, ethnicity, age-groups, and source of exposure in different studies, researchers continue to be skeptical on the topic of the influence of genetic variations in Pb toxicity. However, surface knowledge of the underlying genetic factors will aid in elucidating the mechanism of action of Pb. Moreover, in recent years, the application of epigenetics in Pb toxicity has become a promising area in toxicology to understand the influence of epigenetic mechanisms such as DNA methylation, chromatin remodeling, and small RNAs for the regulation of genes in response to Pb exposure during early life. Growing evidences of ecogenetic understanding (both genetic and epigenetic processes) in a dose-dependent manner may help uncover the mechanism of action of Pb and in the identification of susceptible groups. Such studies will further help in refining uncertainty factors and in addressing risk assessment of Pb poisoning.

HSF1 mediated stress response of heavy metals

The heat shock response (HSR) pathway is a highly conserved cellular stress response and mediated by its master regulator HSF1. Activation of the pathway results in the expression of chaperone proteins (heat shock proteins; HSP) to maintain protein homeostasis. One of the genes strongest upregulated upon stress is HSPA1A (HSP72). Heavy metals are highly toxic to living organisms and known as environmental contaminants, due to industrialisation. Furthermore, many of them are well-described inducers of the HSR pathway. Here we compare the effect of different heavy metals, concerning their potential to activate HSF1 with a sensitive artificial heat shock reporter cell line, consisting of heat shock elements (HSE). In general the responses of the artificial promoter to heavy metal stress were in good agreement with those of well-established HSF1 target genes, like HSPA1A. Nevertheless, differences were observable when effects of heat and heavy metal stress were compared. Whereas heat stress preferentially activated the HSE promoter, heavy metals more strongly induced the HSPA1A promoter. We therefore analysed the HSPA1A promoter in more detail, by isolating and mutating the HSEs. The results indicate that the importance of the individual binding sites for HSF1 is determined by their sequence similarity to the consensus sequence and their position relative to the transcription start site, but they were not differentially affected by heat or heavy metal stress. In contrast, we found that other parts of the HSPA1A promoter have different impact on the response under different stress conditions. In this work we provide deeper insights into the regulation of HSP72 expression as a well as a method to quantitatively and sensitively evaluate different stressor on their potential to activate HSF1.

Modulations of TCDD-mediated induction of zebrafish cyp1a1 and the AHR pathway by administering Cd2+in vivo

Trace metal ions such as cadmium (Cd²⁺) and trace organics typified by 2,3,7,8- tetrachlorodibenzo-p-dioxin (TCDD) are common co-contaminants in the environment and cause toxic effects in aquatic organisms that pose serious health risks. We studied the effects of Cd²⁺ on the regulation of cytochrome P450 1A1 (cyp1a1) gene-induction by TCDD using zebrafish embryos and larvae and adult zebrafish tissues. Our results showed that TCDD induced the cyp1a1 gene in all developmental stages and tissues of zebrafish, and the induction was higher in females than males. However, for the upstream genes (ahr2 and arnt2b) that mediate cyp1a1 gene induction in the zebrafish liver cell line was not induced by TCDD similar to the pattern of cyp1a1 in all investigated groups. After co-treatment with Cd²⁺, induction of the aryl hydrocarbon receptor pathway by TCDD was inhibited in the zebrafish larvae and the livers, intestines, kidneys and gills of adult zebrafish, but not in the embryos or brains of adult zebrafish, indicating that the toxicological effects of Cd²⁺ on TCDD are dependent on the developmental stages and tissue types. The present study confirms that Cd²⁺ blocks the TCDD-induced cyp1a1 gene in vivo but emphasizes that the effects are specific to the developmental stage, type of tissue and sex. The combined effects of Cd²⁺ and TCDD must be taken into consideration together with these parameters to accurately predict and assess cadmium and TCDD-induced toxicity in fish and carcinogenesis in animals in general.

Tissue-specific molecular and cellular toxicity of Pb in the oyster (Crassostrea gigas): mRNA expression and physiological studies

Lead (Pb) is one of the ubiquitous and toxic elements in aquatic environment. In oysters, gills and digestive glands are the main target organs for Pb-induced toxicity, but there is limited information on the molecular mechanisms underlying its toxicity. The present study investigated the Pb-induced toxicity mechanisms in the Pacific oyster (Crassostrea gigas) based on transcriptome, phenotypic anchoring, and validation of targeted gene expression. Gene ontology and pathway enrichment analyses revealed the differential Pb toxicity mechanisms in the tissues. In the gills, Pb disturbed the protein metabolism, with the most significant enrichment of the "protein processing in endoplasmic reticulum" pathway. The main mechanism comprised of a Pb-stimulated calcium (Ca²⁺) increase by the up-regulation of transporter-Ca-ATPase expression. The disturbed Ca²⁺ homeostasis then further induced high expressions of endoplasmic reticulum (ER) chaperones, leading to ER stress in the oysters. Unfolded proteins induced ER associated degradation (ERAD), thereby preventing the accumulation of folding-incompetent glycoproteins. However, Pb mainly induced oxidative reduction reactions in the digestive gland with high accumulation of lipid peroxidation products and high expression of antioxidant enzymes. Further, Pb induced fatty acid β-oxidation and CYP450 catalyzed ω-oxidation due to increased metabolic expenditure for detoxification. The increased content of arachidonic acid indicated that Pb exposure might alter unsaturated fatty acid composition and disturb cellular membrane functions. Taken together, our results provided a new insight into the molecular mechanisms underlying Pb toxicity in oysters.

Embryonic exposure to an aqueous coal dust extract results in gene expression alterations associated with the development and function of connective tissue and the hematological system, immunological and inflammatory disease, and cancer in zebrafish

Coal mining is one of the economic activities with the greatest impact on environmental quality. At all stages contaminants are released as particulates such as coal dust. The first aim of this study was to obtain an aqueous coal dust extract and characterize its composition in terms of trace elements by ICP-MS. In addition, the developmental toxicity of the aqueous coal extract was evaluated using zebrafish (Danio rerio) after exposure to different concentrations (0-1000 ppm; μg mL^-1) to establish acute toxicity, morphology and transcriptome changes. Trace elements within the aqueous coal dust extract present at the highest concentrations (>10 ppb) included Sr, Zn, Ba, As, Cu and Se. In addition, Cd and Pb were found in lower concentrations. No significant difference in mortality was observed (p > 0.05), but a delay in hatching was found at 0.1 and 1000 ppm (p < 0.05). No significant differences in morphological characteristics were observed in any of the treatment groups (p > 0.05). Transcriptomic results of zebrafish larvae revealed alterations in 77, 61 and 1376 genes in the 1, 10, and 100 ppm groups, respectively. Gene ontology analysis identified gene alterations associated with the development and function of connective tissue and the hematological system, as well as pathways associated with apoptosis, the cell cycle, transcription, and oxidative stress including the MAPK signaling pathway. In addition, altered genes were associated with cancer; connective tissue, muscular, and skeletal disorders; and immunological and inflammatory diseases. Overall, this is the first study to characterize gene expression alterations in response to developmental exposure to aqueous coal dust residue from coal mining with transcriptome results signifying functions and systems to target in future studies.

Effect of biochar and Fe-biochar on Cd and As mobility and transfer in soil-rice system

In this study, the effects of biochar derived from rice-straw (biochar) and iron-impregnated biochar (Fe-biochar) on Cd and As mobility in rice rhizosphere and transfer from soil to rice were investigated with different application rates. 1-3% biochar reduced porewater Cd in rhizosphere but elevated soluble As, resulting in 49-68% and 26-49% reduction in the root and grain Cd, with a simultaneous increase in root As. Unlike biochar, 0.5% Fe-biochar decreased porewater As throughout rice growth, resulting in reduced root As, which, however, increased Cd uptake by root. Biochar-induced soil As mobilization was probably through competitive desorption and Fe-biochar-induced soil Cd mobilization was probably via soil acidification. The results suggested that biochar and Fe-biochar was effective in reducing Cd and As uptake by rice, respectively, so they may be used as emergency measures to cope with single Cd or As contamination in paddy soils.

Transcriptional inhibition of TCDD-mediated induction of cytochrome P450 1A1 and alteration of protein expression in a zebrafish hepatic cell line following the administration of TCDD and Cd2

We studied the effects of Cd²⁺ on TCDD-mediated induction of the cytochrome P450 1A1 (cyp1a1) gene using a zebrafish liver cell line (ZFL). Our results showed that Cd²⁺ inhibited the TCDD-mediated induction of the cyp1a1 protein, enzyme activity, and mRNA expression level. Cd²⁺ also down-regulated levels of the aryl hydrocarbon receptor (ahr2) and the aryl hydrocarbon receptor nuclear translocator 2b (arnt2b) mRNAs. Compared with TCDD (3nM) treatment alone, co-treatment with Cd²⁺ (0-30μM) and TCDD (3nM) significantly inhibited the activity of the luciferase reporter gene constructs harboring the distal promoter region (P-2626/-2009) of CYP1A1 and the synthetic 3XRE gene promoter. This indicates that Cd²⁺ decreased the level of TCDD-induced cyp1a1 through transcriptional inhibition. Proteomic analysis was also used to evaluate the effect of Cd²⁺ on TCDD-altered protein expression in ZFL cells. The identified proteins are mainly enzymes of the glycolysis pathway and proteasomes, and have anti-oxidative and anti-stress effects.

Endoplasmic Reticulum Stress and Apoptosis Triggered by Sub-Chronic Lead Exposure in Mice Spleen: a Histopathological Study

Lead (Pb) is an environmental oncogenic metal that induces immunotoxicity and anaemia. Emerging evidence has linked Pb toxicity with endoplasmic reticulum-driven apoptosis and autophagy. Glucose-regulated protein of 78 kDa (Grp78 or binding immunoglobulin protein (BiP)), a master endoplasmic reticulum chaperone, drives macrophage activation and regulates protein folding and calcium flux in response to heavy metals. The spleen may be involved in Pb poisoning due to its crucial role in erythrocatheresis and immune response, although there are no data to support this theory. Here, we found haematic and histopathological changes in the spleen of mice exposed to medium doses of Pb acetate (200 ppm-1 mM) in drinking water for 45 days. Pb deposition was also detected in organs such as the liver, kidney, brain, bone, blood and faeces, indicating an accumulation of this metal despite relatively short exposure time. Blood Pb content (BBL) reached 21.6 μg/dL; echinocytes and poikilocytes were found in Pb smears of treated group. Inside the spleen, higher Fe(II) and Fe(III) deposits inside macrophages were observed. Grp78 immunostaining, weakly expressed in spleen cells of control mice, after Pb exposure was specifically restricted to macrophages and megakaryocytes of the marginal zone of red pulp. Furthermore, Pb exposure induced superoxide dismutase 1 (SOD1) expression, cleaved caspase-3 and p62/SQSTM1, consistent with oxidative stress, apoptosis and dysregulated autophagy in spleen compartments. We suggest that even at a middle dose, oral Pb intake induces oxidant iron deposition in the spleen and that this may trigger sustained Grp78 redistribution to cells, thus leading to oxidative and autophagy dysfunction as early local reactions to this dangerous metal.

DNA Damage, Cell Cycle Arrest, and Apoptosis Induction Caused by Lead in Human Leukemia Cells

In recent years, the industrial use of lead has been significantly reduced from paints and ceramic products, caulking, and pipe solder. Despite this progress, lead exposure continues to be a significant public health concern. The main goal of this research was to determine the in vitro mechanisms of lead nitrate [Pb(NO₃)₂] to induce DNA damage, apoptosis, and cell cycle arrest in human leukemia (HL-60) cells. To reach our goal, HL-60 cells were treated with different concentrations of Pb(NO₃)₂ for 24 h. Live cells and necrotic death cells were measured by the propidium idiode (PI) assay using the cellometer vision. Cell apoptosis was measured by the flow cytometry and DNA laddering. Cell cycle analysis was evaluated by the flow cytometry. The result of the PI demonstrated a significant (p < 0.05) increase of necrotic cell death in Pb(NO₃)₂-treated cells, indicative of membrane rupture by Pb(NO₃)₂ compared to the control. Data generated from the comet assay indicated a concentration-dependent increase in DNA damage, showing a significant increase (p < 0.05) in comet tail-length and percentages of DNA cleavage. Data generated from the flow cytometry assessment indicated that Pb(NO₃)₂ exposure significantly (p < 0.05) increased the proportion of caspase-3 positive cells (apoptotic cells) compared to the control. The flow cytometry assessment also indicated Pb(NO₃)₂ exposure caused cell cycle arrest at the G₀/G₁ checkpoint. The result of DNA laddering assay showed presence of DNA smear in the agarose gel with little presence of DNA fragments in the treated cells compared to the control. In summary, Pb(NO₃)₂ inhibits HL-60 cells proliferation by not only inducing DNA damage and cell cycle arrest at the G₀/G₁ checkpoint but also triggering the apoptosis through caspase-3 activation and nucleosomal DNA fragmentation accompanied by secondary necrosis. We believe that our study provides a new insight into the mechanisms of Pb(NO₃)₂ exposure and its associated adverse health effects.

Cytotoxic, genotoxic, and neurotoxic effects of Mg, Pb, and Fe on pheochromocytoma (PC-12) cells

Metals such as lead (Pb), magnesium (Mg), and iron (Fe) are ubiquitous in the environment as a result of natural occurrence and anthropogenic activities. Although Mg, Fe, and others are considered essential elements, high level of exposure has been associated with severe adverse health effects including cardiovascular, hematological, nephrotoxic, hepatotoxic, and neurologic abnormalities in humans. In the present study we hypothesized that Mg, Pb, and Fe are cytotoxic, genotoxic and neurotoxic, and their toxicity is mediated through oxidative stress and alteration in protein expression. To test the hypothesis, we used the pheochromocytoma (PC-12) cell line as a neuro cell model and performed the LDH assay for cell viability, Comet assay for DNA damage, Western blot for oxidative stress, and HPLC-MS to assess the concentration levels of neurological biomarkers such as glutamate, dopamine (DA), and 3-methoxytyramine (3-MT). The results of this study clearly show that Mg, Pb, and Fe, respectively in the form of MgSO4 , Pb(NO3 )2 , FeCl2 , and FeCl3 induce cytotoxicity, oxidative stress, and genotoxicity in PC-12 cells. In addition, exposure to these metallic compounds caused significant changes in the concentration levels of glutamate, dopamine, and 3-MT in PC-12 cells. Taken together the findings suggest that MgSO4 , Pb(NO3 )2 , FeCl2 , and FeCl3 have the potential to induce substantial toxicity to PC-12 cells.

Effects of mining chemicals on fish: exposure to tailings containing Lilaflot D817M induces CYP1A transcription in Atlantic salmon smolt

Background

Mine tailings, containing metals and production chemicals such as flotation chemicals and flocculants, may pose an environmental threat to aquatic organisms living in downstream ecosystems. The aim of this work was to study to which degree Lilaflot D817M, a flotation chemical extensively used by the mining industry, represents a hazard for migrating salmon in rivers affected by mining activity. Smoltifying Atlantic salmon were exposed to four concentrations of iron-ore mine tailings containing residual Lilaflot D817M [water versus tailing volumes of 0.002 (Low), 0.004 (Medium), 0.013 (High) and 0.04 (Max)]. After 96 h of exposure, gill and liver tissues were harvested for transcriptional responses. Target genes included markers for oxidative stress, detoxification, apoptosis and DNA repair, cell signaling and growth.

Results

Of the 16 evaluated markers, significant transcriptional responses of exposure to tailings enriched with Lilaflot D817M were observed for CYP1A, HSP70 and HMOX1 in liver tissue and CYP1A in gill tissue. The significant induction of CYP1A in both liver and gills suggest that the flotation chemical is taken up by the fish and activates cytochrome P450 detoxification via phase I biotransformation in the cells.

Conclusions

The overall weak transcriptional responses to short-term exposure to Lilaflot D817M-containing iron-ore tailings suggest that the mining chemical has relatively low toxic effect on fish. The underlying mechanisms behind the observed CYP1A induction should be studied further.

Functional role of inorganic trace elements in angiogenesis-Part II: Cr, Si, Zn, Cu, and S

Trace elements play critical roles in angiogenesis events. The effects of nitrogen, iron, selenium, phosphorus, gold, and calcium were discussed in part I. In part II, we evaluated the effect of chromium, silicon, zinc, copper, and sulfur on different aspects of angiogenesis, with critical roles in healing and regeneration processes, and undeniable roles in tumor growth and cancer therapy. This review is the second of series that serves as an overview of the role of inorganic elements in regulation of angiogenesis and vascular function. The methods of exposure, structure, mechanism, and potential activity of these trace elements are briefly discussed. An electronic search was performed on the role of these trace elements in angiogenesis from January 2005 to April 2014. The recent aspects of the relationship between five different trace elements and their role in regulation of angiogenesis, and homeostasis of pro- and anti-angiogenic factors were assessed. Many studies have investigated the effects and importance of these elements in angiogenesis events. Both stimulatory and inhibitory effects on angiogenesis are observed for the evaluated elements. Chromium can promote angiogenesis in pathological manners. Silicon as silica nanoparticles is anti-angiogenic, while in calcium silicate extracts and bioactive silicate glasses promote angiogenesis. Zinc is an anti-angiogenic agent acting on important genes and growth factors. Copper and sulfur compositions have pro-angiogenic functions by activating pro-angiogenic growth factors and promoting endothelial cells migration, growth, and tube formation. Thus, utilization of these elements may provide a unique opportunity to modulate angiogenesis under various setting.

Heavy metal toxicity and the environment

Heavy metals are naturally occurring elements that have a high atomic weight and a density at least five times greater than that of water. Their multiple industrial, domestic, agricultural, medical, and technological applications have led to their wide distribution in the environment, raising concerns over their potential effects on human health and the environment. Their toxicity depends on several factors including the dose, route of exposure, and chemical species, as well as the age, gender, genetics, and nutritional status of exposed individuals. Because of their high degree of toxicity, arsenic, cadmium, chromium, lead, and mercury rank among the priority metals that are of public health significance. These metallic elements are considered systemic toxicants that are known to induce multiple organ damage, even at lower levels of exposure. They are also classified as human carcinogens (known or probable) according to the US Environmental Protection Agency and the International Agency for Research on Cancer. This review provides an analysis of their environmental occurrence, production and use, potential for human exposure, and molecular mechanisms of toxicity, genotoxicity, and carcinogenicity.

Assessing human variability in kinetics for exposures to multiple environmental chemicals: a physiologically based pharmacokinetic modeling case study with dichloromethane, benzene, toluene, ethylbenzene, and m-xylene

The objective of this study was to compare the magnitude of interindividual variability in internal dose for inhalation exposure to single versus multiple chemicals. Physiologically based pharmacokinetic models for adults (AD), neonates (NEO), toddlers (TODD), and pregnant women (PW) were used to simulate inhalation exposure to "low" (RfC-like) or "high" (AEGL-like) air concentrations of benzene (Bz) or dichloromethane (DCM), along with various levels of toluene alone or toluene with ethylbenzene and xylene. Monte Carlo simulations were performed and distributions of relevant internal dose metrics of either Bz or DCM were computed. Area under the blood concentration of parent compound versus time curve (AUC)-based variability in AD, TODD, and PW rose for Bz when concomitant "low" exposure to mixtures of increasing complexities occurred (coefficient of variation (CV) = 16-24%, vs. 12-15% for Bz alone), but remained unchanged considering DCM. Conversely, AUC-based CV in NEO fell (15 to 5% for Bz; 12 to 6% for DCM). Comparable trends were observed considering production of metabolites (AMET), except for NEO's CYP2E1-mediated metabolites of Bz, where an increased CV was observed (20 to 71%). For "high" exposure scenarios, Cmax-based variability of Bz and DCM remained unchanged in AD and PW, but decreased in NEO (CV= 11-16% to 2-6%) and TODD (CV= 12-13% to 7-9%). Conversely, AMET-based variability for both substrates rose in every subpopulation. This study analyzed for the first time the impact of multiple exposures on interindividual variability in toxicokinetics. Evidence indicates that this impact depends upon chemical concentrations and biochemical properties, as well as the subpopulation and internal dose metrics considered.

Cadmium supplement triggers endoplasmic reticulum stress response and cytotoxicity in primary chicken hepatocytes

Cadmium (Cd), a potent hepatotoxin, has been reported to induce endoplasmic reticulum (ER) stress in various cell types. However, whether such effect exists in bird is still unclear. To delineate the effects of Cd exposure on ER stress response, we examined the expression of 78-kDa glucose-regulated protein (GRP78) and alteration in calcium homeostasis in primary chicken hepatocytes treated with 2-22 µM Cd for 24 h. A significant decrease of cell viability was observed in chicken hepatocytes following Cd administration. In cells treated with Cd, GRP78 protein levels increased in a dose-dependent manner. In addition, GRP78 and GRP94mRNA levels were elevated in response to Cd exposure. The increase of the intracellular Ca(2+) concentration in chicken hepatocytes was found during Cd exposure. Cd significantly decreased the CaM mRNA levels in hepatocytes. These results show that Cd regulates the expression of GRP78 and calcium homeostasis in chicken hepatocytes, suggesting that ER stress induced by Cd plays an important role in the mechanisms of Cd cytotoxicity to the bird hepatocytes.

Using expression profiling to understand the effects of chronic cadmium exposure on MCF-7 breast cancer cells

Cadmium is a metalloestrogen known to activate the estrogen receptor and promote breast cancer cell growth. Previous studies have implicated cadmium in the development of more malignant tumors; however the molecular mechanisms behind this cadmium-induced malignancy remain elusive. Using clonal cell lines derived from exposing breast cancer cells to cadmium for over 6 months (MCF-7-Cd4, -Cd6, -Cd7, -Cd8 and -Cd12), this study aims to identify gene expression signatures associated with chronic cadmium exposure. Our results demonstrate that prolonged cadmium exposure does not merely result in the deregulation of genes but actually leads to a distinctive expression profile. The genes deregulated in cadmium-exposed cells are involved in multiple biological processes (i.e. cell growth, apoptosis, etc.) and molecular functions (i.e. cadmium/metal ion binding, transcription factor activity, etc.). Hierarchical clustering demonstrates that the five clonal cadmium cell lines share a common gene expression signature of breast cancer associated genes, clearly differentiating control cells from cadmium exposed cells. The results presented in this study offer insights into the cellular and molecular impacts of cadmium on breast cancer and emphasize the importance of studying chronic cadmium exposure as one possible mechanism of promoting breast cancer progression.

Evaluation of the toxic potential of graphene copper nanocomposite (GCNC) in the third instar larvae of transgenic Drosophila melanogaster (hsp70-lacZ)Bg(9.)

Graphene, a two-dimensional carbon sheet with single-atom thickness, have attracted the scientific world for its potential applications in various field including the biomedical areas. In the present study the graphene copper nanocomposite (GCNC) was synthesized, characterized and evaluated for its toxic potential on third instar larvae of transgenic Drosophila melanogaster (hsp70-lacZ)Bg(9) . The synthesized GCNC was analyzed by X-ray diffraction (XRD), scanning/transmission electron microscopy (SEM/TEM), atomic force microscopy (AFM), and fourier transform infrared spectroscopy (FTIR). The GCNC in 0.1% DMSO was sonicated for 10 min and the final concentration of 0.033, 0.099, 0.199 and 3.996 µg/µl of diet were established. The third instar larvae were allowed to feed on it separately for 24 and 48 hrs. The hsp70 expression was measured by O-nitrophenyl-β-D-galactopyranoside assay, tissue damage by trypan blue exclusion test and β-galactosidase activity was monitored by in situ histochemical β-galactosidase staining. Oxidative stress was monitored by performing lipid peroxidation assay and total protein estimation. Ethidium bromide/acridine orange staining was performed on midgut cells for apoptotic index and the comet assay was performed for the DNA damage. The results of the present study showed that the exposure of 0.199 and 3.996 µg/µl of GCNC were toxic for 24 hr of exposure and for 48 hr of exposure: 0.099, 0.199 and 3.996 µg/µl of GCNC was toxic. The dose of 0.033 µg/µl of GCNC showed no toxic effects on its exposure to the third instar larvae for 24 hr as well as 48 hrs. This dose can be considered as No Observed Adverse Effect Level (NOAEL).

Genome-wide identification of molecular pathways and biomarkers in response to arsenic exposure in zebrafish liver

Inorganic arsenic is a worldwide metalloid pollutant in environment. Although extensive studies on arsenic-induced toxicity have been conducted using in vivo and in vitro models, the exact molecular mechanism of arsenate toxicity remains elusive. Here, the RNA-SAGE (serial analysis of gene expression) sequencing technology was used to analyse hepatic response to arsenic exposure at the transcriptome level. Based on more than 12 million SAGE tags mapped to zebrafish genes, 1,444 differentially expressed genes (750 up-regulated and 694 down-regulated) were identified from a relatively abundant transcripts (>10 TPM [transcripts per million]) based on minimal two-fold change. By gene ontology analyses, these differentially expressed genes were significantly enriched in several major biological processes including oxidation reduction, translation, iron ion transport, cell redox, homeostasis, etc. Accordingly, the main pathways disturbed include metabolic pathways, proteasome, oxidative phosphorylation, cancer, etc. Ingenity Pathway Analysis further revealed a network with four important upstream factors or hub genes, including Jun, Kras, APoE and Nr2f2. The network indicated apparent molecular events involved in oxidative stress, carcinogenesis, and metabolism. In order to identify potential biomarker genes for arsenic exposure, 27 out of 29 up-regulated transcripts were validated by RT-qPCR analysis in pooled RNA samples. Among these, 14 transcripts were further confirmed for up-regulation by a lower dosage of arsenic in majority of individual zebrafish. Finally, at least four of these genes, frh3 (ferrintin H3), mgst1 (microsomal glutathione S-transferase-like), cmbl (carboxymethylenebutenolidase homolog) and slc40a1 (solute carrier family 40 [iron-regulated transporter], member 1) could be confirmed in individual medaka fish similarly treated by arsenic; thus, these four genes might be robust arsenic biomarkers across species. Thus, our work represents the first comprehensive investigation of molecular mechanism of asenic toxicity and genome-wide search for potential biomarkers for arsenic exposure.

The effects of cadmium exposure on the oxidative state and cell death in the gill of freshwater crab Sinopotamon henanense

We studied here the short-term toxicity effects of Cd on the oxidative state and cell death in the gill of freshwater crab Sinopotamon henanense. Crabs were exposed to Cd that resulted in Cd accumulation and a significant increase in the metallothionein (MT) level in the gill, but MT level increased disproportionally compared to the Cd accumulation with an extension of exposure time. Significant changes in the activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) were observed. An increase in the levels of reactive oxygen species (ROS) and lipid peroxidation (LPO) was detected that will cause oxidative stress. Histological abnormalities of the gills were discovered, including the expansion of gill cavity, a decrease in the numbers of connection of the upper and the lower of the gill lamellae and epithelial cells, and an increase in the number of hemocytes. The results of a TUNEL test and transmission electron microscope (TEM) showed that more gill cells had apoptotic characteristics after 48 h of Cd treatment compared to the control, but epithelial cell necrosis and inflammatory response appeared only after 72 h. It was concluded that (1) Cd induced the ROS production and accumulation through inhibiting antioxidant enzyme activities and exceeding the saturation values of MT binging; (2) Cd led to lipid peroxidation and histopathological alternations; and (3) Cd induced apoptotic response at short time exposure, followed by necrotic features and inflammatory reaction after longer time exposure.

The fate of arsenic, cadmium and lead in Typha latifolia: a case study on the applicability of micro-PIXE in plant ionomics

Understanding the uptake, accumulation and distribution of toxic elements in plants is crucial to the design of effective phytoremediation strategies, especially in the case of complex multi-element pollution. Using micro-proton induced X-ray emission, the spatial distribution of Na, Mg, Al, Si, P, S, Cl, K, Ca, Mn, Fe, Zn, As, Br, Rb, Sr, Cd and Pb have been quantitatively resolved in roots and rhizomes of an obligate wetland plant species, Typha latifolia, treated with a mixture of 100 μM each of As, Cd and Pb, together. The highest concentrations of As, Cd and Pb were found in the roots of the T. latifolia, with tissue-specific distributions. The As was detected in the root rhizodermis, and in the rhizome the majority of the As was within the vascular tissues, which indicates the high mobility of As within T. latifolia. The Cd was detected in the root exodermis, and in the vascular bundle and epidermis of the rhizome. The highest Pb concentrations were detected in the root rhizodermis and exodermis, and in the epidermis of the rhizome. These data represent an essential step in the resolution of fundamental questions in plant ionomics.

Characterization of the interaction between cadmium and chlorpyrifos with integrative techniques in incurring synergistic hepatoxicity

Mixture toxicity is an important issue for the risk assessment of environmental pollutants, for which an extensive amount of data are necessary in evaluating their potential adverse health effects. However, it is very hard to decipher the interaction between compounds due to limited techniques. Contamination of heavy metals and organophosphoric insecticides under the environmental and biological settings poses substantial health risk to humans. Although previous studies demonstrated the co-occurrence of cadmium (Cd) and chlorpyrifos (CPF) in environmental medium and food chains, their interaction and potentially synergistic toxicity remain elusive thus far. Here we integrated the approaches of thin-layer chromatography and (1)H NMR to study the interaction between Cd(2+) and CPF in inducing hepatoxicity. A novel interaction was identified between Cd(2+) and CPF, which might be the bonding between Cd(2+) and nitrogen atom in the pyridine ring of CPF, or the chelation formation between one Cd(2+) and two CPF molecules. The Cd-CPF complex was conferred with distinct biological fate and toxicological performances from its parental components. We further demonstrated that the joint hepatoxicity of Cd ion and CPF was chiefly due to the Cd-CPF complex-facilitated intracellular transport associated with oxidative stress.

Protective effect of quercetin on lead-induced oxidative stress and endoplasmic reticulum stress in rat liver via the IRE1/JNK and PI3K/Akt pathway

Lead (Pb), a well-known environmental toxin, is one of the major hazards for human health. Quercetin (QE), a natural flavonoid, has been reported to have many benefits and medicinal properties. However, its protective effects against Pb-induced endoplasmic reticulum (ER) stress in liver have not been clarified. The aim of the present study was to investigate the effects of quercetin on hepatic ER stress in rats exposed to Pb. Wistar rats were exposed to lead acetate in the drinking water with or without quercetin co-administration for 75 days. Our data showed that quercetin significantly prevented Pb-induced hepatotoxicity in a dose-dependent manner, indicated by both diagnostic indicators of liver damage and histopathological analysis. Quercetin markedly decreased Pb contents in blood and liver. Western blot analysis showed that Pb-induced ER stress in rat liver was significantly inhibited by quercetin. In exploring the underlying mechanisms of quercetin action, we found quercetin markedly suppressed Pb-induced oxidative stress. Quercetin decreased reactive oxygen species (ROS) production and increased the total antioxidant capacity in rat livers. Additionally, quercetin dramatically increased Phosphoinositide-3-kinase (PI3K) and phosphorylated protein kinase B (PKB/Akt) levels in liver rats. In the examined unfolded protein response (UPR) pathways, quercetin markedly inhibited the Pb-induced increase of the phosphorylated inositol-requiring enzyme 1 (IRE1) and c-jun N-terminal kinase (JNK) in rat liver. Taken together, these results suggested that the inhibition of Pb-induced ER stress by quercetin is due at least in part to its anti-oxidant stress activity and its ability to modulate the PI3K/Akt and IRE1/JNK signaling pathway.

Cytotoxic and Genotoxic effects of Arsenic and Lead on Human Adipose Derived Mesenchymal Stem Cells (AMSCs)

Arsenic and lead, known to have genotoxic and mutagenic effects, are ubiquitously distributed in the environment. The presence of arsenic in drinking water has been a serious health problem in many countries. Human exposure to these metals has also increased due to rapid industrialization and their use in formulation of many products. Liposuction material is a rich source of stem cells. In the present study cytotoxic and genotoxic effects of these metals were tested on adipose derived mesenchymal stem cells (AMSCs). Cells were exposed to 1-10 μg/ml and 10-100 μg/ml concentration of arsenic and lead, respectively, for 6, 12, 24 and 48 h. The cytotoxic effects were measured by neutral red uptake assay, while the genotoxic effects were tested by comet assay. The growth of cells decreased with increasing concentration and the duration of exposure to arsenic. Even the morphology of cells was changed; they became round at 10 μg /ml of arsenic. The cell growth was also decreased after exposure to lead, though it proved to be less toxic when cells were exposed for longer duration. The cell morphology remained unchanged. DNA damage was observed in the metal treated cells. Different parameters of comet assay were investigated for control and treated cells which indicated more DNA damage in arsenic treated cells compared to that of lead. Intact nuclei were observed in control cells. Present study clearly demonstrates that both arsenic and lead have cytotoxic and genotoxic effects on AMSCs, though arsenic compared to lead has more deleterious effects on AMSCs.

Heavy metal toxicity and the environment

Heavy metals are naturally occurring elements that have a high atomic weight and a density at least five times greater than that of water. Their multiple industrial, domestic, agricultural, medical, and technological applications have led to their wide distribution in the environment, raising concerns over their potential effects on human health and the environment. Their toxicity depends on several factors including the dose, route of exposure, and chemical species, as well as the age, gender, genetics, and nutritional status of exposed individuals. Because of their high degree of toxicity, arsenic, cadmium, chromium, lead, and mercury rank among the priority metals that are of public health significance. These metallic elements are considered systemic toxicants that are known to induce multiple organ damage, even at lower levels of exposure. They are also classified as human carcinogens (known or probable) according to the US Environmental Protection Agency and the International Agency for Research on Cancer. This review provides an analysis of their environmental occurrence, production and use, potential for human exposure, and molecular mechanisms of toxicity, genotoxicity, and carcinogenicity.

HDAC inhibitor modulation of proteotoxicity as a therapeutic approach in cancer

The strong clinical activity of the proteasome inhibitor bortezomib (Velcade) in multiple myeloma and other hematological malignancies has focused considerable attention on its mechanisms of action. Although NFκB inhibition was initially the mechanism in focus, accumulating evidence indicates that misfolded protein accumulation leading to proteotoxicity plays an even more important role in cell killing. Proteotoxicity that occurs as a consequence of protein aggregate accumulation has long been associated with the development of neurodegenerative diseases, and a large and growing body of literature has documented how protein aggregates are handled and disposed of via evolutionarily conserved mechanisms involving cross talk between the proteasome and autophagy in normal cells. The type II histone deacetylase HDAC6 plays important roles in these processes and HDAC6 inhibition enhances proteotoxicity. These observations served as the basis for the development of HDAC6-specific chemical inhibitors that are now being evaluated in combination with proteasome inhibitors in preclinical models. Nonetheless, there is also strong evidence that the more classical, chromatin-associated (type I) HDACs are also involved in the regulation of proteotoxicity, although the biochemical mechanisms underlying their effects are not well defined. Importantly, emerging evidence indicates that subsets of tumor cells contain defects in these protein quality control pathways, which may underlie their vulnerability to proteasome inhibitor-induced death. In addition, our clearer understanding of cytoprotective protein quality control responses is identifying novel candidate targets for therapeutic intervention. In this chapter, we present an overview of protein quality control mechanisms in normal tissues and describe how this information is informing our development of proteasome inhibitors and other agents that impact upon these pathways for cancer therapy.

Selection of scFv phages specific for chloramphenicol acetyl transferase (CAT), as alternatives for antibodies in CAT detection assays

Reporter gene assays are commonly used in applied toxicology to measure the transcription of genes involved in toxic responses. In these reporter gene assays, transgenic cells are used, which contain a promoter-operator region of a gene of interest fused to a reporter gene. The transcription of the gene of interest can be measured by the detection of the reporter protein. Chloramphenicol acetyl transferase (CAT) is frequently used as a reporter protein in mammalian reporter gene assays. Although CAT can be measured by different detection systems, like enzymatic and immune assays, most of these tests are expensive, time-consuming and labor-intensive. The excellent characteristics of phages, like their high affinity and specificity, their fast, cheap and animal-friendly manufacturing process with low batch-to-batch variations and their stability, make them appropriate as alternatives for antibodies in detection assays. Therefore, in this study single-chain variable fragment (scFv) phages were selected with affinity for CAT. Several scFv phages were selected that showed affinity towards CAT in a screening ELISA. Surface plasmon resonance analyses showed that the tested scFv phages have an affinity for CAT with a dissociation constant (K(d)) around 1 µM. The selected scFv phages in this study could be used as capture elements in a highly sensitive sandwich ELISA to detect CAT concentration as low as 0.1 ng ml⁻¹ or 4 pM. This low detection limit demonstrates the potential of the scFv phages as an alternative for capturing antibodies in a highly sensitive detection test to measure CAT concentrations in reporter gene assays.

Basic apoptotic mechanisms of lead toxicity in human leukemia (HL-60) cells

Lead exposure represents a medical and public health emergency, especially in children consuming high amounts of lead-contaminated flake paints. It may also cause hematological effects to people of all ages. Recent studies in our laboratory have indicated that apoptosis may be associated with the lead-induced oxidative stress and DNA damage. However, the mechanisms underlying its effect on lymphocytes are still largely unknown. Therefore, the aim of the present study was to investigate the apoptotic mechanisms of lead nitrate [Pb(NO(3))(2)] using HL-60 cells as a test model. HL-60 cells were treated with different concentrations of Pb(NO(3))(2) for 24 h prior to cell viability assay and flow cytometry assessment. The results obtained from the trypan blue exclusion test indicated that at very low concentration, Pb(NO(3))(2) has no effect on the viability of HL-60 cells. A significant (p < 0.05) decrease in cell viability was observed when exposed to high level of Pb(NO(3))(2). Data generated from the flow cytometric assessment indicated that Pb(NO(3))(2) exposure significantly (p < 0.05) increased the proportion of annexin V positive cells (apoptotic cells) compared to the control. Pb(NO(3))(2) induced apoptosis of HL-60 cells was associated with the activation of caspase-3. In summary, these studies demonstrated that Pb(NO(3))(2) represents an apoptosis-inducing agent in HL-60 promyelocytic leukemia cells and its apoptotic mechanism functions, at least in part via, induction of phosphatidylserine externalization and caspase-3 activation.

Humic acid enhances the cytotoxic effects of arsenic trioxide on human cervical cancer cells

Cervical cancer is the second leading cancer affecting women, and recent studies have demonstrated arsenic trioxide (As(2)O(3)) has therapeutic effects on cervical cancer by promoting apoptosis and inhibiting metastasis in vitro and in vivo. Humic acid (HA) possesses various pharmacologic properties, including anti-inflammatory, anti-neoplastic, and anti-proliferative effects by inducing apoptosis. We examined the growth inhibition properties and the combined effects of HA and As(2)O(3) in human cervical adenocarcinoma cell lines. Our results shown both As(2)O(3) and HA-induced inhibition of cell growth, most likely by ROS-mediated cell damage and activation of the apoptosis pathway, and HA enhanced the anti-proliferative action of As(2)O(3) in HeLa and SiHa cells, which reduced the LC(50) about 57.62 or 73.52% (300μg HA/mL) to 83.67 or 79.03% (500μg HA/mL), respectively. This study is relevant to the development of chemotherapeutic approaches using As(2)O(3) in treating human cervical cancer.

Endoplasmic reticulum may not be involved in the lead-induced apoptosis in PC 12 cells in vitro

Recent researches indicated that mitochondrial pathway might play an important role in lead-induced apoptosis. Our previous study also found that lead could induce apoptosis in PC 12 cells, and mitochondrial pathway events were involved in this process. As lead can disturb Ca(2+) homeostasis, the present study was undertaken to determine whether lead can activate key cellular events in the endoplasmic reticulum (ER) pathway, including the expressions of C/EBP homology protein (CHOP) and glucose-regulated protein 78 (GRP78), and the activation of caspase-12 and calpain. The results showed that lead could increase the expression of GRP78, while the expressions of CHOP and procaspase-12 remained unchanged. Moreover, the caspase-12 and calpain were not activated, and the ultrastructure of endoplasmic reticulum was not altered. Therefore, it suggests that lead may induce apoptosis in PC 12 cells through mitochondrial pathway, but not through the endoplasmic reticulum pathway.

Lead induces the expression of endoplasmic reticulum chaperones GRP78 and GRP94 in vascular endothelial cells via the JNK-AP-1 pathway

Lead, a ubiquitous heavy metal, is an important industrial and environmental pollutant that can target the vascular endothelium. To clarify the effects of lead on the unfolded protein response (UPR) and their significance in cytotoxicity, we examined the expression and function of endoplasmic reticulum (ER) chaperones glucose-regulated protein 78 (GRP78) and glucose-regulated protein 94 (GRP94) in vascular endothelial cells. We used bovine aortic endothelial cells as an in vitro model of the vascular endothelium. Exposure of vascular endothelial cells to lead nitrate resulted in a marked induction of GRP78 and GRP94 messenger RNA levels. In response to lead, the expression of GRP78 and GRP94 proteins also significantly increased in a dose- and time-dependent manner. In addition, small interfering RNA (siRNA)-mediated knockdown of GRP78 significantly enhanced lead-induced cytotoxicity. Compared with other metal(loid)s, including cadmium chloride, zinc sulfate, copper sulfate, and sodium arsenite, lead nitrate was found to be the most potent metal to induce these chaperones in endothelial cells. In the examined UPR pathways, lead increased the phosphorylation of inositol-requiring enzyme 1 (IRE1) and c-jun N-terminal kinase (JNK). Interestingly, the lead-induced upregulation of GRP78 and GRP94 was almost completely blocked by the JNK inhibitor SP600125 or activator protein-1 (AP-1) inhibitor curcumin. Taken together, these results suggest that lead induces ER stress, but the induction of GRP78 and GRP94 expression via the JNK-AP-1 pathway functions as a defense mechanism against lead-induced cytotoxicity in vascular endothelial cells.

Do heavy metals and metalloids influence the detoxification of organic xenobiotics in plants?

BACKGROUND, AIM AND SCOPE

Mixed pollution with trace elements and organic industrial compounds is characteristic for many spill areas and dumping sites. The danger for the environment and human health from such sites is large, and sustainable remediation strategies are urgently needed. Phytoremediation seems to be a cheap and environmentally sound option for the removal of unwanted compounds, and the hyperaccumulation of trace elements and toxic metals is seemingly independent from the metabolism of organic xenobiotics. However, stress reactions, ROS formation and depletion of antioxidants will also cause alterations in xenobiotic detoxification. Here, we investigate the capability of plants to detoxify chlorophenols via glutathione conjugation in a mixed pollution situation.

MATERIALS AND METHODS

Typha latifolia and Phragmites australis plants for the present study were grown under greenhouse conditions in experimental ponds. A Picea abies L. suspension culture was grown in a growth chamber. Cadmium sulphate, sodium arsenate and lead chloride in concentrations from 10 to 500 microM were administered to plants. Enzymes of interest for the present study were: glutathione transferase (GST), glutathione reductase, ascorbate peroxidase and peroxidase. Measurements were performed according to published methods. GST spectrophotometric assays included the model substrates CDNB, DCNB, NBC, NBoC and the herbicide Fluorodifen.

RESULTS

Heavy metals lead to visible stress symptoms in higher plants. Besides one long-term experiment of 72 days duration, the present study shows time and concentration-dependent plant alterations already after 24 and 72 h Cd incubation. P. abies spruce cell cultures react to CdSO(4) and Na(2)HAsO(4) with an oxidative burst, similar to that observed after pathogen attack or elicitor treatment. Cd application resulted in a reduction in GSH and GSSG contents. When a heavy metal mixture containing Na(2)HAsO(4), CdSO(4) and PbCl(2) was applied to cultures, both GSH and GSSG levels declined. Incubation with 80 microM arsenic alone doubled GSSG values. Based on these results, further experiments were performed in whole plants of cattail and reed, using cadmium in Phragmites and cadmium and arsenic in Typha as inducers of stress. In Phragmites australis, GST activities for CDNB and DCNB were significantly reduced after short-term Cd exposure (24 h). In the same samples, all antioxidant enzymes increased with rising heavy metal concentrations. Typha latifolia rhizome incubation with Cd and As leads to an increase in glutathione reductase and total peroxidase activity and to a decrease in ascorbate peroxidase activity. Measurements of the same enzymes in leaves of the same plants show increased GR activities, but no change in peroxidases. GST conjugation for CDNB was depressed in both cattail rhizomes and leaves treated with Cd. After As application increased, DCNB enzyme activities were detected.

DISCUSSION

T. latifolia and P. australis are powerful species for phytoremediation because they penetrate a large volume of soil with their extensive root and rhizome systems. However, an effective remediation process will depend on active detoxifying enzymes, and also on the availability of conjugation partners, e.g. glutathione and its analogues. Species-specific differences seem to exist between the regulations of primary defence enzymes like SOD, catalase, peroxidases, whereas others prefer to induce the glutathione-dependent enzymes. As long as the pollutant mix encountered is simple and dominated by heavy metals, plant defence might be sufficient. When pollution plumes contain heavy metals and organic xenobiotics at the same time, this means that part of the detoxification capacity, at least of glutathione-conjugating reactions, is withdrawn from the heavy metal front to serve other purposes. In fact, glutathione S-transferases show strong reactions in stressed plants or in the presence of heavy metals. The spruce cell culture was a perfect model system to study short-term responses on heavy metal impact. Overall, and on the canopy level, this inhibitory effect might result in a lower detoxification capacity for organic pollutants and thus interfere with phytoremediation.

CONCLUSIONS

We present evidence that pollution with heavy metals will interfere with both the oxidative stress defence in plants, and with their ability to conjugate organic xenobiotics. Despite plant-species-dependent differences, the general reactions seem to include oxidative stress and an induction of antioxidative enzymes. Several processes seem to depend on direct binding of heavy metals to enzyme proteins, but effects on transcription are also observed. Induction of xenobiotic metabolism will be obtained at high heavy metal concentrations, when plant stress is elevated.

RECOMMENDATIONS AND PERSPECTIVES

Plants for phytoremediation of complex pollution mixtures have to be selected according to three major issues: uptake/accumulation capacity, antioxidative stress management, and detoxification/binding properties for both the trace elements and the organic xenobiotics. By way of this, it might be possible to speed up the desired remediation process and/or to obtain the desired end products. And, amongst the end products, emphasis should be laid on industrial building materials, biomass for insulation or biogas production, but not for feed and fodder. Each of these attempts would increase the chances for publicly accepted use of phytoremediation and help to cure the environment.

Acetaminophen induces xenobiotic-metabolizing enzymes in rat: Impact of a uranium chronic exposure

The extensive use of uranium in civilian and military applications increases the risk of human chronic exposure. Uranium is a slightly radioactive heavy metal with a predominantly chemical toxicity, especially in kidney but also in liver. Few studies have previously shown some effects of uranium on xenobiotic-metabolizing enzymes (XME) that might disturb drug pharmacokinetic. The aim of this study was to determine whether a chronic (9 months) non-nephrotoxic low dose exposure to depleted uranium (DU, 1mg/rat/day) could modify the liver XME, using a single non-hepatotoxic acetaminophen (APAP) treatment (50mg/kg). Most of XME analysed were induced by APAP treatment at the gene expression level but at the protein level only CYP3A2 was significantly increased 3h after APAP treatment in DU-exposed rats whereas it remained at a basal level in unexposed rats. In conclusion, these results showed that a chronic non-nephrotoxic DU exposure specially modify CYP3A2 after a single therapeutic APAP treatment.