Induction of c-fos proto-oncogene in mesangial cells by cadmium

Ameliorative effects of morel mushroom (Morchella esculenta) against Cadmium-induced reproductive toxicity in adult male rats

Cadmium (Cd) is one of the major toxicants, which affects human health through occupational and environmental exposure. In the current study, we evaluated the protective effects of morel mushrooms against Cd-induced reproductive damages in rats. For this purpose, 30 male rats were divided into 6 groups (n=5/group), the first group served as the control group, second group was treated with an intraperitoneal (i.p) injection of 1 mg/kg/day of Cd. Third and fourth groups were co-treated with 1 mg/kg/day of Cd (i.p) and 10 and 20 mg/kg/day of morel mushroom extract (orally) respectively. The final 2 groups received oral gavage of 10 and 20 mg/kg/day of morel mushroom extract alone. After treatment for 17 days, the animals were euthanized, and testes and epididymis were dissected out. One testis and epididymis of each animal were processed for histology, while the other testis and epididymis were used for daily sperm production (DSP) and comet assay. Our results showed that Cd and morel mushrooms have no effect on animal weight, but Cd significantly decreases the DSP count and damages the heritable DNA which is reversed in co-treatment groups. Similarly, the histopathological results of testes and epididymis show that morel mushrooms control the damage to these tissues. Whereas the morel mushroom extract alone could enhance the production of testosterone. These results conclude that morel mushrooms not only control the damage done by Cd, but it could also be used as a protection mechanism for heritable DNA damage.

Protective role of Roflumilast against cadmium-induced cardiotoxicity through inhibition of oxidative stress and NF-κB signaling in rats

Cadmium (Cd), a potent cardiotoxic environmental heavy metal, induces oxidative stress and membrane disturbances in cardiac myocytes. Phosphodiesterase (PDEs) retards the positive inotropic effects of β-adrenoceptor activation by decreasing levels of cAMP via degradation. Hence, PDE inhibitors sensitize the heart to catecholamine and are therefore, used as positive inotropic agents. The present study was designed to probe the potential attenuating effects of the selective PDE4 inhibitor (Roflumilast, ROF), on cardiac biomarkers, lipid profile, lipid peroxidation products, antioxidant status and histology of cardiac tissues against Cd-induced cardiotoxicity in rats. Rats were randomly distributed into four different groups: group 1, served as the normal control group. Group 2, served as the toxic control group and were administered Cd (3 mg/kg, i.p.) for next 7 days. Groups 3 and 4, served as treatment groups that received Cd with concomitant oral administration of ROF doses (0.5 and 1.5 mg/kg), respectively for 7 days. Serum samples of toxic control group rats resulted in significant (P < 0.001) increase in lactate dehydrogenase (LDH), creatine phosphokinase (CPK), total cholesterol (TC), triglycerides (TG) and low density lipoproteins (LDL) levels with concomitant decrease in high density lipoproteins (HDL) levels in serum which were found reversed with both of ROF treatment groups. Cd also causes significant increased (P < 0.001) in myocardial malondialdehyde (MDA) contents while cardiac glutathione (GSH) level, superoxide dismutase (SOD) and catalase (CAT) enzyme activities were found decreased whereas both doses of ROF, significantly reversed these oxidative stress markers and antioxidant enzymes. Cardiotoxicity induced by Cd also resulted in enhanced expression of non-phosphorylated and phosphorylated form of NF-κB p65 and decreased expression of glutathione-S-transferase (GST) and NQO1 which were found reversed with ROF treatments, comparable to normal control group. Histopathological changes were also improved by ROF administration as compared to Cd treated rats alone. In conclusion, Roflumilast exhibited attenuating effect against Cd-induced cardiac toxicity.

GSK-3β-mediated regulation of cadmium-induced cell death and survival

Background

Previous studies indicated that cadmium (Cd) increases PI3-kinase/Akt phosphorylation, resulting in an alteration in GSK-3β activity. However, the mechanism of Cd-induced endoplasmic reticulum (ER) stress in neuronal cells has yet to be studied in needs further elucidation. We examined the role of GSK-3β in Cd-induced neuronal cell death and the related downstream signaling pathways.

Methods

SH-SY5Y human neuroblastoma cells were treated with 10 or 20 μM BAPTA-AM and 1 μM wortmannin for 30 min and then incubated with 25 μM Cd for 12 h. Apoptotic cells were visualized via DAPI and PI staining. Data were evaluated with one-way analysis of variance (ANOVA) followed by Student’s t-test. Data are expressed as the means ± SD of experiments performed at least three times.

Results

Treatment of human neuronal SH-SY5Y cells with Cd induced ER, stress as evidenced by the increased expression of GRP78, which is a marker of ER stress. Cd exposure significantly increased the phosphorylation of Akt at thr308 and ser473 and that of GSK-3β at ser9 in a time-dependent manner, while the total protein levels of GSK-3β and Akt did not change. Cd-induced apoptosis was higher in GSK-3β-knockdown cells than in normal cells.

Conclusions

Our data suggest that Akt/GSK-3β signaling activated by Cd is involved in neuronal cell survival.

Cadmium favors F-actin depolymerization in rat renal mesangial cells by site-specific, disulfide-based dimerization of the CAP1 protein

Cadmium is a toxic metal that produces oxidative stress and has been shown to disrupt the actin cytoskeleton in rat renal mesangial cells (RMC). In a survey of proteins that might undergo Cd2+-dependent disulfide crosslinking, we identified the adenylyl cyclase-associated protein, CAP1, as undergoing a dimerization in response to Cd2+ (5-40 µM) that was sensitive to disulfide reducing agents, was reproduced by the disulfide crosslinking agent diamide, and was shown by site-directed mutagenesis to involve the Cys29 residue of the protein. Reactive oxygen species are not involved in the thiol oxidation, and glutathione modulates background levels of dimer. CAP1 is known to enhance cofilin's F-actin severing activity through binding to F-actin and cofilin. F-actin sedimentation and GST-cofilin pulldown studies of CAP1 demonstrated enrichment of the CAP1 dimer's association with cofilin, and in the cofilin-F-actin pellet, suggesting that Cd2+-induced dimer increases the formation of a CAP1-cofilin-F-actin complex. Both siRNA-based silencing of CAP1 and overexpression of a CAP1 mutant lacking Cys29 (and therefore, incapable of dimerization in response to Cd2+) increased RMC viability and provided some protection of F-actin structures against Cd2+. It is concluded that Cd2+ brings about disruption of the RMC cytoskeleton in part through formation of a CAP1 dimer that increases recruitment of cofilin to F-actin filaments.

Protective effect of cadmium-induced autophagy in rat renal mesangial cells

Cadmium damages renal cells, and in particular may cause mesangial cell death by necrosis or apoptosis, depending on exposure conditions in cultured cells. However, there is an uncertainty as to whether Cd²⁺-induced autophagy can protect mesangial cells against these other mechanisms of cell death. We have used autophagy-incompetent mouse embryonic fibroblast (MEF) cells lacking the Atg16 gene, as well as cultured rat mesangial cells (RMC) in which Atg16 has been silenced, to examine this issue. Measuring the processing of LC3-I to LC3-II and expression of sequestosome-1 (p62), we define conditions under which RMC can be induced to undergo autophagy in response to 0-20 µM CdCl₂. Similarly, Cd²⁺ can initiate autophagy in MEF cells. However, when autophagy is compromised, either by gene knockout in MEF cells or by RNA silencing in RMC, cell viability is decreased, and concomitantly a Cd²⁺ dose-dependent increase in pro-caspase-3 cleavage indicates the initiation of apoptotic cell death. In contrast to some previous reports, Cd²⁺-induced autophagy is not correlated with increased levels of cellular reactive oxygen species but, among a panel of kinases investigated, is suppressed by inhibition of the Jun kinase. We conclude that concentrations of Cd²⁺ that initiate autophagy may afford renal mesangial cells some degree of protection against other modes (apoptosis, necrosis) of cell death.

Proteome profiling of cadmium-induced apoptosis by antibody array analyses in human bronchial epithelial cells

Protein array technology is a powerful platform for the simultaneous determination of the expression levels of a number of proteins as well as post-translational modifications such as phosphorylation. Here, we screen and report for the first time, the dominant signaling cascades and apoptotic mediators during the course of cadmium (Cd)-induced cytotoxicity in human bronchial epithelial cells (BEAS-2B) by antibody array analyses. Proteins from control and Cd-treated cells were captured on Proteome Profiler™ Arrays for the parallel determination of the relative levels of protein phosphorylation and proteins associated with apoptosis. Our results indicated that the p38 MAPK- and JNK-related signal transduction pathways were dramatically activated by Cd treatment. Cd potently stimulates the phosphorylations of p38α (MAPK14), JNK1/2 (MAPK8/9), and JUN; while the phosphorylations of Akt1, ERK1/2 (MAPK3/1), GSK3β, and mTOR were suppressed. Moreover, there was an induction of proapoptotic protein BAX, release of cytochrome c (CYCS) from mitochondria, activation of caspase-3/9 (CASP3/9); as well as decreased expression of cell cycle checkpoint proteins (TP53, p21, and p27) and several inhibitors of apoptosis proteins (IAPs) [including cIAP-1/2 (BIRC2/3), XIAP (BIRC4), and survivin (BIRC5)]. Pretreatment of cells with the thiol antioxidant glutathione or p38 MAPK/JNK inhibitors before Cd treatment effectively abrogated ROS activation of p38 MAPK/JNK pathways and apoptosis-related proteins. Taken together, our results demonstrate that Cd causes oxidative stress-induced apoptosis; and the p38 MAPK/JNK and mitochondrial pathways are more importantly participated for signal transduction and the induction of apoptosis in Cd-exposed human lung cells.

Proteomic analysis of secreted proteins by human bronchial epithelial cells in response to cadmium toxicity

For years, many studies have been conducted to investigate the intracellular response of cells challenged with toxic metal(s), yet, the corresponding secretome responses, especially in human lung cells, are largely unexplored. Here, we provide a secretome analysis of human bronchial epithelial cells (BEAS-2B) treated with cadmium chloride (CdCl2 ), with the aim of identifying secreted proteins in response to Cd toxicity. Proteins from control and spent media were separated by two-dimensional electrophoresis and visualized by silver staining. Differentially-secreted proteins were identified by MALDI-TOF-MS analysis and database searching. We characterized, for the first time, the extracellular proteome changes of BEAS-2B dosed with Cd. Our results unveiled that Cd treatment led to the marked upregulation of molecular chaperones, antioxidant enzymes, enzymes associated with glutathione metabolic process, proteins involved in cellular energy metabolism, as well as tumor-suppressors. Pretreatment of cells with the thiol antioxidant glutathione before Cd treatment effectively abrogated the secretion of these proteins and prevented cell death. Taken together, our results demonstrate that Cd causes oxidative stress-induced cytotoxicity; and the differentially-secreted protein signatures could be considered as targets for potential use as extracellular biomarkers upon Cd exposure.

Molecular mechanisms of cadmium-induced fibroblast growth factor 23 upregulation in osteoblast-like cells

Itai-itai disease is thought to be the result of chronic cadmium (Cd) intoxication. Renal proximal tubules are a major target of Cd toxicity. The whole mechanism of the adverse effects of Cd remains unresolved, especially how renal damage is related to the development of bone lesions. Fibroblast growth factor 23 (FGF23) is a bone-derived phosphaturic factor that regulates vitamin D and inorganic phosphate metabolism in the kidney. To clarify the role of FGF23 on Cd toxicity, we investigated the mechanisms of Cd-induced FGF23 production in the bone. Cd injection into mice significantly increased plasma FGF23 concentrations, but did not change FGF23 mRNA expression in bone. GalNAc-T3 is involved in secreting intact FGF23. To determine potential roles of GalNAc-T3 in Cd-induced FGF23 production, we examined the effect of Cd on GalNAc-T3 mRNA expression in vivo and in vitro. GalNAc-T3 gene expression was significantly increased in the bones of Cd-injected mice. Cd also enhanced the expression of GalNAc-T3 in cultured osteosarcoma UMR106 cells and primary osteocytes. Cd activated aryl hydrocarbon receptors (AhR) and AhR were required for GalNAc-T3 gene expression induced by Cd. In addition, Cd-dependent FGF23 production was completely inhibited by an AhR antagonist. AhR siRNA markedly suppressed the stimulation of transcriptional activity by Cd. Furthermore, Cd induced AhR activation via phosphorylation of Ser-68 by p38 kinase in the nuclear export signal of AhR. Thus, Cd stimulated GalNAc-T3 gene transcription via enhanced AhR binding to the GalNAc-T3 promoter. These findings suggest that the Cd-induced increase in GalNAc-T3 suppresses proteolytic processing of FGF23 and increases serum FGF23 concentrations.

An update on oxidative stress-mediated organ pathophysiology

Exposure to environmental pollutants and drugs can result in pathophysiological situations in the body. Research in this area is essential as the knowledge on cellular survival and death would help in designing effective therapeutic strategies that are needed for the maintenance of the normal physiological functions of the body. In this regard, naturally occurring bio-molecules can be considered as potential therapeutic targets as they are normally available in commonly consumed foodstuffs and are thought to have minimum side effects. This review article describes the detailed mechanisms of oxidative stress-mediated organ pathophysiology and the ultimate fate of the cells either to survive or to undergo necrotic or apoptotic death. The mechanisms underlying the beneficial role of a number of naturally occurring bioactive molecules in oxidative stress-mediated organ pathophysiology have also been included in the review. The review provides useful information about the recent progress in understanding the mechanism(s) of various types of organ pathophysiology, the complex cross-talk between these pathways, as well as their modulation in stressed conditions. Additionally, it suggests possible therapeutic applications of a number of naturally occurring bioactive molecules in conditions involving oxidative stress.

Serine 9 and tyrosine 216 phosphorylation of GSK-3β differentially regulates autophagy in acquired cadmium resistance

Glycogen synthase kinase-3β (GSK-3β) plays an important role in the regulation of apoptosis. To investigate its involvement in acquired cadmium (Cd) resistance, Cd-resistant cells (RH460) were established from H460 lung carcinoma cells. Cd resistance led to interruption of apoptosis and autophagy, as determined by an apoptotic sub-G1 population, procaspase-3 clevage, and LC3-II induction. Cd-induced autophagy preceded apoptosis as determined by 3-methyladenine or zVAD and time-course experiments after Cd treatment. Despite β-catenin accumulation, phospho(p)-Ser/Tyr GSK-3α/β increased in the nucleus until 12h after treatment and then p-Ser partly translocated to the cytoplasm. The GSK-3 inhibitor lithium augmented Cd-induced p-Ser GSK-3α/β, which accumulated in the nucleus and cytoplasm, and increased autophagy. SB216763 inhibited p-Ser/p-Tyr GSK-3α/β and subsequent autophagy. GSK-3β knockdown decreased Cd-induced autophagy. Cd exposure to RH460 cells overexpressed with pcDNA-GSK-3β-HA strongly phosphorylated Ser(9)/Tyr(216) residues and decreased LC3-II. Constitutively active pcDNA-GSK-3β(S9A)-HA overexpression phosphorylated Tyr(216) and decreased LC3-II, suggesting that p-Tyr inhibits autophagy. PI3K inhibitors decreased Cd-induced p-Ser GSK-3αβ and LC3-II, whereas a Ser/Thr phosphatase inhibitor, okadaic acid, hyperphosphorylated Ser residues, which accumulated in the nucleus and cytosol, and enhanced LC3-II. The general tyrosine kinase inhibitor genistein suppressed Cd-induced p-Tyr/p-Ser GSK-3α/β and LC3-II. Mouse lung tissues respond to long-term Cd exposure increased p-Tyr, downregulated LC3-II, and accumulated full-length Bax and procaspase-3. Taken together, this study shows that acquired Cd resistance is regulated by GSK-3β phosphorylation state, but not activation state, and intracellular localization of p-Ser GSK-3 regulates Cd-induced autophagy and apoptosis.

Cadmium-induced glutathionylation of actin occurs through a ROS-independent mechanism: implications for cytoskeletal integrity

Cadmium disrupts the actin cytoskeleton in rat mesangial cells, and we have previously shown that this involves a complex interplay involving activation of kinase signaling, protein translocation, and disruption of focal adhesions. Here we investigate the role that glutathionylation of actin plays in Cd(2+)-associated cytoskeletal reorganization. Low concentrations of Cd(2+) (0.5-2 μM) caused an increase in actin glutathionylation by 6h, whereas at higher concentrations glutathionylation remained at basal levels. Although oxidation with diamide increased glutathionylation, reactive oxygen species (ROS) were not involved in the Cd(2+)-dependent effect, as only Cd(2+) concentrations above 2 μM were sufficient to increase ROS. However, low [Cd(2+)] increased total glutathione levels without affecting the ratio of reduced/oxidized glutathione, and inhibition of glutathione synthesis suppressed actin glutathionylation. Cadmium increased the activity of the enzyme glutaredoxin, which influences the equilibrium between glutathionylated and deglutathionylated proteins and thus may influence levels of glutathionylated actin. Together these observations show that cadmium-dependent effects on actin glutathionylation are affected by glutathione metabolism and not by direct effects of ROS on thiol chemistry. In vitro polymerization assays with glutathionylated actin show a decreased rate of polymerization. In contrast, immunofluorescence of cytoskeletal structure in intact cells suggests that increases in actin glutathionylation accompanying increased glutathione levels occurring under low Cd(2+) exposure are protective in vivo, with cytoskeletal disruption ensuing only when higher Cd(2+) concentrations increase ROS levels and prevent an increase in actin-glutathione conjugates.

Mechanism of the protective action of taurine in toxin and drug induced organ pathophysiology and diabetic complications: a review

Taurine (2-aminoethanesulfonic acid), a conditionally essential amino acid, is found in large concentrations in all mammalian tissues and is particularly abundant in aquatic foods. Taurine exhibits membrane stabilizing, osmoregulatory and cytoprotective effects, antioxidative properties, regulates intracellular Ca(2+) concentration, modulates ion movement and neurotransmitters, reduce the levels of pro-inflammatory cytokines in various organs and controls blood pressure. Recently, emerging evidence from the literature shows the effectiveness of taurine as a protective agent against several environmental toxins and drug-induced multiple organ injuries as the outcome of hepatotoxicity, nephrotoxicity, neurotoxicity, testicular toxicity and cardiotoxicity in several animal models. Besides, taurine is also effective in combating diabetes and its associated complications, including cardiomyopathy, nephropathy, neuropathy, retinopathy and atherosclerosis. These beneficial effects appear to be due to the multiple actions of taurine on cellular functions. This review summarizes the mechanism of the prophylactic role of taurine against several environmental toxins and drug-induced organ pathophysiology and diabetes.

Taurine attenuates apoptosis in primary liver cells isolated from Atlantic salmon (Salmo salar)

One of the many functions of taurine is to protect cells against oxidation, by protecting mitochondrial integrity and respiration. Taurine metabolism has attracted much attention in fish nutrition due to the fact that as plant ingredients replace fishmeal, dietary taurine has declined. As the endogenous synthesis of taurine might be too low to protect cells against oxidative stress and apoptosis, the present study aimed to test whether taurine may protect liver cells from apoptosis. Liver cells isolated from Atlantic salmon (Salmo salar) were grown in media supplemented with a physiological concentration of taurine (25 (se0·5) mm) or without any taurine supplementation (14 (se3) μm) for 3 d. To increase oxidation in the mitochondria and maximise any cellular response of taurine supplementation, 100 μm-CdCl2was added or not added to the cells at day 3. At day 4, cells were harvested and assessed for viability. As expected, the addition of CdCl2decreased cell viability without showing any interaction with taurine supplementation. Cells grown in the taurine-supplemented media had lower protein abundance of active caspase-3. In addition, the protein abundance of phosphorylated mitogen-activating phosphokinase (P-p63, P-p42/44 and P-p38) as well as cytochrome P450 were reduced when taurine was added to the media. Cells grown without taurine supplementation had a more condensed chromatin and more smeared DNA, also pointing to a higher apoptosis in these cells. In conclusion, taurine attenuated apoptosis in primary liver cells isolated from Atlantic salmon, and as such, taurine may be conditionally indispensable in Atlantic salmon.

Effects of heavy metals on mitogen-activated protein kinase pathways

The signaling pathways leading to cellular protection or cell death following exposure to heavy metals have not been fully clarified. Mitogen-activated protein kinases (MAPKs), i.e., extracellular signal-regulated protein kinase (ERK), c-Jun NH(2)-terminal kinase (JNK) and p38 MAPK transmit extracellular signals into the nucleus, and have been shown to participate in a diverse array of cellular functions such as cell growth, differentiation and apoptosis. Treatment with cadmium, inorganic mercury or tributyltin can activate ERK, JNK and p38 MAPK, and induces the expression of c-fos and c-jun genes prior to the development of apoptosis. However, the members of the MAPK family appear to be differentially activated depending on the heavy metal and the cell type exposed. Consequently, various cellular responses may be caused by the distinct pattern of MAPKs activation. MAPKs may be one of the important cellular signal transduction pathways affected by various environmental pollutants, including heavy metals.

Prenatal cadmium exposure dysregulates sonic hedgehog and Wnt/beta-catenin signaling in the thymus resulting in altered thymocyte development

Cadmium (Cd) is both an environmental pollutant and a component of cigarette smoke. Although evidence demonstrates that adult exposure to Cd causes changes in the immune system, there are limited reports in the literature of immunomodulatory effects of prenatal exposure to Cd. The sonic hedgehog (Shh) and Wnt/beta-catenin pathways are required for thymocyte maturation. Several studies have demonstrated that Cd exposure affects these pathways in different organ systems. This study was designed to investigate the effect of prenatal Cd exposure on thymocyte development, and to determine if these effects were linked to dysregulation of Shh and Wnt/beta-catenin pathways. Pregnant C57Bl/6 mice were exposed to an environmentally relevant dose (10 ppm) of Cd throughout pregnancy and effects on the thymus were assessed on the day of birth. Thymocyte phenotype was determined by flow cytometry. A Gli:luciferase reporter cell line was used to measure Shh signaling. Transcription of target genes and translation of key components of both signaling pathways were assessed using real-time RT-PCR and western blot, respectively. Prenatal Cd exposure increased the number of CD4(+) cells and a subpopulation of double-negative cells (DN; CD4(-)CD8(-)), DN4 (CD44(-)CD25(-)). Shh and Wnt/beta-catenin signaling were both decreased in the thymus. Target genes of Shh (Patched1 and Gli1) and Wnt/beta-catenin (c-fos, and c-myc) were affected differentially among thymocyte subpopulations. These findings suggest that prenatal exposure to Cd dysregulates two signaling pathways in the thymus, resulting in altered thymocyte development.

Cadmium-induced alterations of gene expression in human cells

We have reported the changes in gene expression in human HeLa cells exposed to a low concentration (5μM) of Cd. In the present study, cells exposed to a higher concentration of Cd were analyzed using a DNA microarray with 9182 human cDNA probes, in an attempt to obtain a comprehensive view on the biological effects of Cd. After a 6h exposure to 50μM Cd, 48 genes were up-regulated 2.5-fold or greater and 14 genes were down-regulated to 40% or less. Marked up-regulation of genes coding for metallothioneins, anti-oxidant proteins, and heat shock proteins was observed. Cd appeared to repress cell proliferation by modulating genes involved in multiple pathways. Cd also affected a number of genes related to apoptosis. Interestingly, it appeared that a series of genes were regulated to accelerate the intrinsic pathway of apoptosis, while others were directed to suppress the extrinsic pathway. Of these, rapid and transient induction of the TR3 gene was noted as a possible key process in Cd-induced apoptosis. Effects on several genes that may reflect mechanistic backgrounds of Cd toxicity were also observed. The present study disclosed a complex pleiotypic response of human cells to Cd, which was composed of a variety of changes in gene expression directed to defense, growth arrest, recovery from damage, apoptosis and so on.

Induction of necrosis in cadmium-induced hepatic oxidative stress and its prevention by the prophylactic properties of taurine

The present study has been carried out to investigate the protective role of taurine against cadmium (Cd)-induced oxidative impairment in murine liver. Oral administration of cadmium chloride (CdCl(2)) at a dose of 4mg/kg body weight for 6 days increased the accumulation of the Cd in the liver and diminished the liver weight to body weight ratio. The CdCl(2) altered the levels of intracellular trace elements, cofactors of various metalloenzymes and increased the activities of serum marker enzymes related to liver dysfunction. In addition, Cd intoxication also attenuated intracellular antioxidant power, the activities of antioxidant enzymes as well as the levels of cellular metabolites. Moreover, level of hepatic metallothionein, lipid peroxidation, protein carbonylation, DNA fragmentation, concentration of intracellular reactive oxygen species (ROS) and the activities of cytochrome P450s have been increased due to Cd toxicity. In addition to the oxidative impairments, Cd exposure caused hepatic cell death mainly via the necrotic pathway. Oral administration of taurine at a dose of 100mg/kg body weight for 5 days prior to CdCl(2) intoxication prevented the alterations of all the toxic-induced hepatic damages. Histological studies also supported the beneficial role of taurine against Cd-induced hepatic damages. Combining all, results suggest that taurine could protect hepatic tissues against Cd-induced oxidative stress probably through its antioxidant activity.

Lack of cross-tolerance following heat and cadmium exposure in functional MDCK monolayers

Exposure of monolayers of Madin-Darby canine kidney epithelial (MDCK) cells to a mild heat stimulus induces a state of physiological thermotolerance in which epithelial barrier function is maintained following a second more severe heat stress. We have previously shown that expression of exogenous HSP70 fully mimics the effects of the conditioning heat stress. Exposure of MDCK cells to elevated temperatures or medium containing CdCl2 caused a robust increase in cellular levels of HSP70. Pretreatment of MDCK monolayers with cadmium but not heat caused a small protection of epithelial barrier function against a second challenge with cadmium. In addition, a prior exposure of monolayers to cadmium at levels sufficient to induce HSP70 expression and increased cellular chaperone activity did not afford protection against a subsequent thermal challenge. Therefore multiple stress-specific cellular pathways impinge on the ability of heat shock proteins to induce physiological thermotolerance. Occludin, a component of tight junctions, is induced in MDCK cells engineered to express high levels of exogenous HSP70, potentially accounting for an elevation in baseline resistance. However neither basal levels of occludin, nor alterations in occludin expression, were correlated with epithelial barrier function in MDCK cells either exposed to elevated temperatures or challenged with cadmium.

Initiation of caspase-independent death in mouse mesangial cells by Cd2+: involvement of p38 kinase and CaMK-II

Cadmium (Cd) is a toxic metal with multiple effects on cell signaling and cell death. We studied the effects of Cd(2+) on quiescent mouse mesangial cells in serum-free conditions. Cadmium induces cell death over 6 h through annexin V+ states without or with causing uptake of propidium iodide, termed apoptotic and apoptosis-like death, respectively. Little or no necrosis is observed, and cell death is caspase-independent and associated with nuclear translocation of the apoptosis-inducing factor, AIF. We previously showed that Cd(2+) increased phosphorylation of Erk and CaMK-II, and CaMK-II activation increased cell death in an Erk-independent manner. Here we demonstrate that Cd(2+) increases Jnk and p38 kinase phosphorylation, and inhibition of p38-but not of Jnk-increases cell viability by suppressing apoptosis in preference to apoptosis-like death. Neither p38 kinase nor CaMK-II inhibition protects against a decrease in mitochondrial membrane potential, psi, indicating that kinase-mediated death is either independent of, or involves events downstream of a mitochondrial pathway. However, both the antioxidant N-acetyl cysteine (NAC) and the mitochondrial membrane-stabilizing agent cyclosporine A (CsA) partially preserve psi, suppress activation of p38 kinase, and partially protect the cells from Cd(2+)-induced death. Whereas the effect of CsA is on apoptosis, NAC acts on apoptosis-like death. Inhibition of glutathione synthesis exacerbates a Cd(2+)-dependent increase in cellular peroxides and favors apoptosis-like death over apoptosis. The caspase-independence of these modes of cell death is not due to an absence of this machinery in the mesangial cells: when they are exposed to Cd(2+) for longer periods in the presence of serum, procaspase-3 and PARP are cleaved and caspase inhibition is protective. We conclude that Cd(2+) can kill mesangial cells by multiple pathways, including caspase-dependent and -independent apoptotic and apoptosis-like death. Necrosis is not prominent. Activation of p38 kinase and of CaMK-II by Cd(2+) are associated with caspase-independent apoptosis that is not dependent on mitochondrial destabilization.

Rapid activation of ERK1/2 and AKT in human breast cancer cells by cadmium

Cadmium (Cd), an endocrine disruptor, can induce a variety of signaling events including the activation of ERK1/2 and AKT. In this study, the involvement of estrogen receptors (ER) in these events was evaluated in three human breast cancer cell lines, MCF-7, MDA-MB-231, and SK-BR-3. The Cd-induced signal activation patterns in the three cell lines mimicked those exhibited in response to 17 beta-estradiol. Specifically, treatment of MCF-7 cells, that express ER alpha, ER beta and GPR30, to 0.5-10 microM Cd for only 2.5 min resulted in transient phosphorylation of ERK1/2. Cd also triggered a gradual increase and sustained activation of AKT during the 60 min treatment period. In SK-BR-3 cells, that express only GPR30, Cd also caused a transient activation of ERK1/2, but not of AKT. In contrast, in MDA-MB-231 cells, that express only ER beta, Cd was unable to cause rapid activation of either ERK1/2 or AKT. A transient phosphorylation of ER alpha was also observed within 2.5 min of Cd exposure in the MCF-7 cells. While the estrogen receptor antagonist, ICI 182,780, did not prevent the effect of Cd on these signals, specific siRNA against hER alpha significantly reduced Cd-induced activation of ERK1/2 and completely blocked the activation of AKT. It is concluded that Cd, like estradiol, can cause rapid activation of ERK1/2 and AKT and that these signaling events are mediated by possible interaction with membrane ER alpha and GPR30, but not ER beta.

Cadmium exposure induces expression of the HOXB8 gene in COS-7 cells

Cadmium (Cd) is a serious toxic metal, which is classified as a possible human carcinogen. We assessed the effects of Cd on the expression levels of homeobox genes, which are associated with carcinogenesis. Among 6 homeobox genes examined in this study, only HOXB8 exhibited increased mRNA expression in COS-7 cells treated with 10 microM CdCl(2). Semiquantitative reverse transcription-polymerase chain reaction analysis revealed that the HOXB8 mRNA level was increased by a maximum of 5.4-fold after 6h of Cd exposure. The levels of HOXA7, A9, C4, C9 and C10 mRNAs decreased from 0.1 to 0.3-fold. Silencing of HOXB8 mRNA expression using a siRNA increased HOXC9 and C10 mRNA expression levels by 6.6- and 1.9-fold, respectively. These results suggest that HOXB8 upregulation is associated with suppression of HOXC9 and C10, and that decreased expression of HOXC9 and C10 after Cd exposure is partly due to HOXB8 induction. In conclusion, Cd disrupts the HOX network. Comprehensive analyses of all the HOX gene expression levels in the presence of Cd may afford clues toward understanding Cd-induced carcinogenesis and teratogenesis.

Global DNA hypomethylation, rather than reactive oxygen species (ROS), a potential facilitator of cadmium-stimulated K562 cell proliferation

Cell proliferation plays a critical role in the process of cadmium (Cd) carcinogenesis. Although both induction of reactive oxygen species (ROS) and alteration of DNA methylation are involved in Cd-stimulated cell proliferation, the detailed mechanism of Cd-stimulated cell proliferation remains poorly understood. In this study, K562 cells pre-treated with N-acetylcysteine (NAC) or methionine (Meth) were exposed to Cd to investigate the potential contribution of ROS and global DNA methylation pathways in Cd-induced cell proliferation. The results showed that Cd-stimulated cell proliferation, increased ROS and DNA damage levels, and induced global DNA hypomethylation. The increases of ROS and DNA damage levels were attenuated by pre-treatment with NAC. Cd-stimulated cell proliferation did not appear to be suppressed through eliminating ROS by NAC. However, methionine was shown to prevent Cd-induced global DNA hypomethylation and Cd-stimulated cell proliferation. Our results suggest that global DNA hypomethylation, rather than ROS, is a potential facilitator of Cd-stimulated K562 cell proliferation.

Hepatic c-fos expression is independent of oxidative stress and inflammation induced by acute cadmium exposure in rats

AIM

To investigate the relationships between c-fos expression and oxidative stress or inflammation in the liver induced by acute cadmium (Cd) exposure.

METHODS

Sixty male Sprague-Dawley rats were randomly assigned to 1 of 6 groups, 10 rats in each group. They were intragastrically pretreated with distilled water, distilled water, vitamin E (50 mg/100 g body weight), 25, 50 and 75% Sagittaria sagittifolia (SS) extract (2 ml/100 g weight) once a day for 10 consecutive days. Twenty-four hours after the last feeding, all animals were intraperitoneally administered CdCl(2) (20 micromol/kg body weight) except for the control group which was given distilled water. Twenty-four hours after intoxication, the glutathione (GSH) and malondialdehyde (MDA) contents and gene expression of tumor necrosis factor-alpha (TNF-alpha) and c-fos were measured in the livers.

RESULTS

Acute Cd exposure significantly increased MDA levels, decreased GSH levels and upregulated the gene expression of TNF-alpha and c-fos in the liver. Vitamin E and middle and high doses of SS were able to inhibit the MDA level, but only middle and high doses of SS enhanced the GSH level and inhibited the upregulation of TNF-alpha gene expression. However, neither vitamin E nor SSwas able to inhibit the upregulation of c-fos gene expression in the liver.

CONCLUSION

Our data suggested that c-fos induction is independent of oxidative stress or inflammation in the liver during the process of acute Cd exposure in rats.

[Visualization and evaluation of the promoter activities of genes for stress-inducible proteins in response to environmental pollutants]

We examined the systematic assay of the reporter gene for the assessment of heavy metals and organic chemical pollutants using the reporter plasmids carrying stress-responsive elements fused to the green fluorescence protein (GFP) gene as follows: metallothionein (MTIIA), heme oxigenase-1 (HO-1), quinone reductase (ARE), and c-fos genes. The treatment of COS7 cells in which the c-fos gene promoter-, ARE-, or HO-1 enhancer-fused GFP with a low concentration of NaAsO(2) was introduced led to the detection of the fluorescent cells, and an agrichemical paraquat enhanced the fluorescence of ARE or HO-1 enhancer-transfected cells. The cells in which the plasmid carrying the MT-IIA gene promoter (the -765 bp upstream from the transcription initiation site) was introduced highly expressed GFP on treatment with CdCl(2), ZnSO(4), or CuCl(2). The plasmid carrying seven metal-responsive elements of the MT-IIA gene increased the response of the fluorescence intensity to these heavy metals. These results indicated that the use of the gene promoters and enhancers of the stress-responsive genes fused to GFP contributes to the visualization of pollutant-responsive mammalian cells and can be applied to biomonitoring of environmental pollution.

Comparative cytotoxicity of cadmium and mercury in a human bronchial epithelial cell line (BEAS-2B) and its role in oxidative stress and induction of heat shock protein 70

A number of toxic heavy metals, such as cadmium (Cd) and mercury (Hg), are widely used in occupational settings, and exposure to these metals is associated with the development of pulmonary diseases. Cytotoxicity, apoptosis, and reactive oxygen species (ROS) generation were tested to compare the biological reactivity of these two heavy metals using a human bronchial epithelial cell line, BEAS-2B. Further, heat-shock protein 70 (Hsp70) expression was observed as a sensitive indicator of cellular stress. Exposure to metals (0-50 microM) for 72 h showed more significant cytotoxicity in Cd-treated than Hg-treated cells. Apoptosis was significantly increased in the cells exposed to 50 microM of Cd (3.5-fold) and Hg (3.6-fold). Cd and Hg produced an induction of Hsp70 protein as assayed by Western blotting and enzyme-linked immunosorbent assay (ELISA). Induction of Hsp70 protein by these metals was inhibited by addition of N-acetylcysteine. However, addition of catalase blocked the synthesis of Hsp70 only in Hg-treated cells. Hsp70B and Hsp70C mRNA expression was induced by both metals, while Hsp70A mRNA expression showed no change. Electron spin resonance (ESR) tests showed that hydroxyl radical generation was greater in the reaction of cells with Hg compared to Cd. Intracellular generation of ROS was detected in the cells exposed to both Cd and Hg. These results suggest that both cytotoxicity and apoptosis were significantly elevated with all metals tested; however, Cd was relatively more toxic. Hsp70 protein and mRNA were sensitive to exposure to these metals. Depletion of sulfhydryl groups of cellular proteins and generation of ROS may be involved in metal-induced lung cell damage.

Cadmium activates CaMK-II and initiates CaMK-II-dependent apoptosis in mesangial cells

Cadmium is a toxic metal that initiates both mitogenic responses and cell death. We show that Cd(2+) increases phosphorylation and activity of Ca(2+)/calmodulin-dependent protein kinase II (CaMK-II) in mesangial cells, in a concentration-dependent manner. Activation is biphasic with peaks at 1-5 min and 4-6 h. Cadmium also activates Erk, but this appears to be independent of CaMK-II. At 10-20 microM, Cd(2+) initiates apoptosis in 25-55% of mesangial cells by 6h. Inhibition of CaMK-II, but not of Erk, suppresses Cd(2+)-induced apoptosis. We conclude that activation of CaMK-II by Cd(2+) contributes to apoptotic cell death, independent of Erk activation.

The Possible Role of Cytokeratin 8 in Cadmium-Induced Adaptation and Carcinogenesis

Chronic exposures to cadmium compounds are carcinogenic. It was hypothesized that the development of resistance to cadmium may drive carcinogenesis. This is achieved by selection of resistant cells in which the apoptotic response is significantly attenuated. The induction of cadmium resistance in rat lung epithelial cells (LEC) was used to explore the mechanisms of cadmium-induced adaptation and carcinogenesis. Our previous results showed that LECs developed resistance to apoptosis during cadmium adaptation possibly due to perturbation of the c-Jun NH(2)-terminal kinase pathway. Here, we further study these cells by comparative proteomics. Interestingly, we showed that two intermediate filament proteins, cytokeratin 8 (CK8) and cytokeratin 14 (CK14), were increased significantly and stably maintained only in the adapted cells but not in cadmium-treated parental cells. It has been documented that CK8/cytokeratin 18 provided resistance to tumor necrosis factor (TNF)-induced apoptosis and CK14 may function as an inhibitor of TNF-TNF receptor 1 (TNFR1) signaling through an association with TNFR1-associated death domain protein, suggesting that up-regulation of CK8 and CK14 may be responsible for apoptotic resistance. Finally, we showed that small interfering RNA-specific knockdown of CK8 in cadmium-adapted cells attenuated the cadmium resistance, indicating the potential role of CK8 in cadmium resistance. This acquired self-resistance to apoptosis could account for cadmium-induced carcinogenesis, as this promotes neoplastic cell survival as well as subsequent clonal expansion and then progression of tumor development. Thus, increased expression of these cytokeratins represents an adaptive survival mechanism that resists cadmium-induced apoptosis and it is unprecedented that cells respond to long-term cadmium exposure by modulating keratin dynamics.

Cadmium restores in vitro splicing activity inhibited by zinc-depletion

Zinc (Zn)-depletion inhibits the second step of RNA splicing, namely exon-ligation. To investigate the effects of cadmium (Cd) and other metal ions on RNA splicing inhibited by Zn-depletion, we measured in vitro splicing activities in the presence of these metals. Zn-depletion in the splicing reaction mixture was achieved by addition of a Zn-chelator, 1,10-phenanthroline. Cd(II) at 1, 5 and 10 microM restored the splicing activity to 2, 24 and 72% of that in the control reaction mixture, while higher concentrations of Cd(II) decreased the splicing activity, and more than 50 microM Cd(II) showed a complete absence of spliced products. Hg(II) also restored the splicing activity, albeit to a lesser extent, since 5 and 10 microM Hg(II) restored the splicing activity to 3 and 4% of the control value. The other metal ions examined in this study, Co(II), Cu(II), Mg(II) and Mn(II), did not show any restoration of the splicing activity. We concluded that Cd(II) could restore the in vitro splicing activity inhibited by Zn-depletion, although higher concentrations of Cd(II) prevented progress of the RNA splicing reaction. These results suggest that Cd(II) has a bifunctional property regarding RNA splicing, and is stimulatory at low concentrations and inhibitory at high concentrations.

Interactive effects of cadmium and all-trans-retinoic acid on the induction of forelimb ectrodactyly in C57BL/6 mice

BACKGROUND

Most toxicological studies have tested single chemical agents at relatively high doses, and fewer studies have addressed the toxic effects of chemical interactions. It is important to understand the toxicity of chemical mixtures in order to assess the more realistic risks of environmental and occupational exposures. A number of chemicals are known to induce a predominantly postaxial forelimb ectrodactyly in C57BL/6 mice, including acetazolamide, ethanol, cadmium, valproic acid, carbon dioxide, dimethadione, phenytoin, and 13-cis-retinoic acid and all-trans-retinoic acid (RA). In the present study, the interactive effects of coadministration of cadmium and RA on developing limbs were investigated.

METHODS

Pregnant C57BL/6 mice were treated with different intraperitoneal (IP) doses of cadmium chloride (CdCl2) and/or RA on gestational day (GD) 9.5, and fetuses were collected on GD 18 and double stained for examination of skeletal defects.

RESULTS

When RA was given simultaneously with cadmium, a significant increase in the incidence and severity of forelimb ectrodactyly (predominantly postaxial) was observed compared to the results with corresponding doses of cadmium or RA alone. When mice were exposed to subthreshold doses of both cadmium (0.5 mg/kg) and RA (1 mg/kg), the combined treatment exceeded the threshold, resulting in forelimb ectrodactyly in 19% of the fetuses. Moreover, coadministration of cadmium and RA at doses exceeding the respective thresholds showed a synergistic effect, that is, 92% of fetuses were found with the forelimb defect as opposed to 10% if the response were additive.

CONCLUSIONS

The findings demonstrate that concurrent exposure to these teratogens can have a synergistic effect and that subteratogenic doses may combine to exceed a threshold.

Cadmium inhibits both intrinsic and extrinsic apoptotic pathways in renal mesangial cells

Cadmium is a potent nephrotoxin that has been shown to induce apoptosis in some cells but also to prevent it under certain circumstances. In several clinical situations and experimental models of injury to the renal glomerulus, pathological proliferation of mesangial cells is followed by resolution involving mesangial cell apoptosis. We investigated the effects of Cd(2+) on rat mesangial cells induced to undergo apoptosis through either the extrinsic receptor-mediated pathway or the intrinsic mitochondrial-dependent pathway. Camptothecin initiated the intrinsic pathway with activation of caspase-9 and caspase-dependent cleavage of procaspase-3. Tumor necrosis factor-alpha (TNF-alpha) initiated caspase-8 activity and cleavage of pro-caspase-3 at the convergence point of the two pathways. However, pro-caspase-8 levels were low, and caspase-9 was also activated in response to TNF-alpha, characteristic of what have been termed type II cells. With both TNF-alpha and camptothecin, concurrent exposure to 10 microM CdCl(2) suppressed DNA laddering, nuclear condensation, and pro-caspase-3 cleavage. It also decreased activity of both caspase-8 and caspase-9, prevented caspase-8-dependent cleavage of the proapoptotic factor Bid, and suppressed release of cytochrome c from mitochondria. At this 10-microM concentration, Cd(2+) was unique among a number of metal ions in preventing DNA fragmentation. We conclude that Cd(2+) is anti-apoptotic in rat mesangial cells, acting by a mechanism that may involve general caspase inhibition. This may have consequences for the resolution of nephritis in situations of mesangial cell hyperproliferation.

p38 MAPK/HSP25 signaling mediates cadmium-induced contraction of mesangial cells and renal glomeruli

The environmental pollutant cadmium affects human health, with the kidney being a primary target. In addition to proximal tubules, glomeruli and their contractile mesangial cells have also been identified as targets of cadmium nephrotoxicity. Glomerular contraction is thought to contribute to reduced glomerular filtration, a characteristic of cadmium nephrotoxicity. Because p38 MAPK/HSP25 signaling has been implicated in smooth muscle contraction, we examined its role in cadmium-induced contraction of mesangial cells. We report that exposure of mesangial cells to cadmium resulted in 1) cell contraction, 2) activation of MAP kinases, 3) increased HSP25 phosphorylation coincident with p38 MAP kinase activation, 4) sequential phosphorylation of the two phosphorylation sites of mouse HSP25 with Ser15 being phosphorylated before Ser86, 5) reduction of oligomeric size of HSP25, and 6) association of HSP25 with microfilaments. Exposure of isolated rat glomeruli to cadmium also resulted in contraction and increased HSP25 phosphorylation. The cadmium-induced responses were inhibited by the specific p38 MAP kinase inhibitor SB-203580, and cadmium-induced phosphorylation of HSP25 was inhibited by expression of a dominant-negative p38 MAP kinase mutant. These findings tentatively suggest that cadmium-induced nephrotoxicity results, in part, from glomerular contraction due to p38 MAP kinase/HSP25 signaling-dependent contraction of mesangial cells. With regard to the cellular action of HSP25, these data support a change in paradigm: in addition to its well-established cytoprotective function, HSP25 may also be involved in processes that ultimately lead to adverse effects, as is observed in the response of mesangial cells to cadmium.

Regulation of cadmium-induced apoptosis by PKCδ in U937 human promonocytic cells

Pulse treatment with cadmium chloride followed by recovery caused apoptosis in U937 human promonocytic cells. In addition, the treatment-induced PKCdelta translocation from cytosol to membrane fraction, which was already detected at 30 min of treatment; and also caused PKCdelta cleavage to give a 41-kDa fragment, which was detected at 3-6 h of recovery, concomitantly with the execution of apoptosis. All these effects were reduced by the PKCdelta-specific inhibitor rottlerin. By contrast, rottlerin did not prevent the cadmium-provoked stimulation of the stress response (as measured by HSP70 expression), nor inhibited the generation of apoptosis by heat-shock, which failed to cause PKCdelta translocation. Cadmium chloride rapidly induced p38(MAPK) activation, which was not affected by rottlerin. By contrast, the p38(MAPK) inhibitor SB203580 reduced PKCdelta translocation and cleavage, indicating that p38(MAPK) activation precedes and regulates PKCdelta activation. It is concluded that PKCdelta mediates apoptosis induction by cadmium ions via early membrane translocation, and also possibly through late kinase proteolytic cleavage and phosphorylation on tyrosine residues.

Identification of ASK1, MKK4, JNK, c-Jun, and caspase-3 as a signaling cascade involved in cadmium-induced neuronal cell apoptosis

Cd induces oxidative stress and apoptosis in various cells by activating mitogen-activated protein kinases (MAPKs), but the precise signaling components of the MAPK cascade and their role in neuronal apoptosis are still unclear. Here, we report that Cd treatment of SH-SY5Y cells caused apoptosis through sequential phosphorylation of the apoptosis signal regulating kinase 1, MAPK kinase 4, c-Jun N-terminal kinase (JNK), and c-Jun as determined by overexpression of dominant negative (DN) constructs of these genes or using a specific JNK inhibitor SP600125. Both Cd-induced JNK and c-Jun phosphorylation and apoptosis were inhibited dramatically by N-acetyl-L-cysteine, a free radical scavenger. In addition, caspase inhibitors, zDEVD and zVAD, reduced apoptosis but not JNK and c-Jun phosphorylation induced by Cd, while overexpression of DN JNK1 inhibited caspase-3 activity. Taken together, our data suggested that the JNK/c-Jun signaling cascade plays a crucial role in Cd-induced neuronal cell apoptosis and provides a molecular linkage between oxidative stress and neuronal apoptosis.

Pentachlorophenol-Induced Cytotoxic, Mitogenic, and Endocrine-Disrupting Activities in Channel Catfish, Ictalurus punctatus

Pentachlorophenol (PCP) is an organochlorine compound that has been widely used as a biocide in several industrial, agricultural, and domestic applications. Although it has been shown to induce systemic toxicity and carcinogenesis in several experimental studies, the literature is scarce regarding its toxic mechanisms of action at the cellular and molecular levels. Recent investigations in our laboratory have shown that PCP induces cytotoxicity and transcriptionally activates stress genes in human liver carcinoma (HepG2) cells [1]. In this research, we hypothesize that environmental exposure to PCP may trigger cytotoxic, mitogenic, and endocrine-disrupting activities in aquatic organisms including fish. To test this hypothesis, we carried out in vitro cultures of male channel catfish hepatocytes, and performed the fluorescein diacetate assay (FDA) to assess for cell viability, and the Western Blot analysis to assess for vitellogenin expression following exposure to PCP. Data obtained from FDA experiments indicated a strong dose-response relationship with respect to PCP cytotoxicity. Upon 48 hrs of exposure, the chemical dose required to cause 50% reduction in cell viability (LD50) was computed to be 1,987.0 +/- 9.6 microg PCP/mL. The NOAEL and LOAEL were 62.5 +/- 10.3 microg PCP/mL and 125.0+/-15.2 microg PCP/mL, respectively. At lower levels of exposure, PCP was found to be mitogenic, showing a strong dose- and time-dependent response with regard to cell proliferation. Western Blot analysis demonstrated the potential of PCP to cause endocrine-disrupting activity, as evidenced by the up regulation of the 125-kDa vitellogenin protein the hepatocytes of male channel catfish.

Involvement of mitogen-activated protein kinases and protein kinase C in cadmium-induced prostaglandin E2 production in primary mouse osteoblastic cells

We previously reported that cadmium (Cd) induced prostaglandin E2 (PGE2) biosynthesis through the activation of cytosolic phospholipase A2 (cPLA2) and induction of cyclooxygenase 2 (COX-2) in primary mouse osteoblastic cells. In the present study, we further investigated the mechanism of PGE2 production by Cd focusing on the main mitogen-activated protein kinase (MAPK) subfamilies that mediate prostaglandin synthesis, extracellular signal-regulated kinase (ERK1/2 MAPK), c-jun-amino-terminal kinase (JNK MAPK) and p38 MAPK, and protein kinase C (PKC) which is activated by Cd in several kinds of cells. Cd at 2 microM and above stimulated PGE2 production in osteoblastic cells and its production was inhibited by the kinase-specific inhibitors PD98059, SB203580, curcumin, and calphostin C. Calphostin C also inhibited the production of PGE2 by phorbol 12-myristate 13-acetate (PMA), which is a potent activator of PKC. PD98059 inhibited PGE2 production stimulated by PMA as well as Cd, indicating that activation of PKC by ERK1/2 MAPK was necessary for Cd-stimulated PGE2 production. Moreover, Cd stimulated the phosphorylation of these three MAPKs, and inhibition of the phosphorylation of ERK1/2 MAPK by calphostin C was also observed. On the other hand, Cd was found to phosphorylate cPLA2 and the phosphorylation was inhibited by PD98059, indicating that cPLA2 was activated by Cd through ERK1/2 MAPK and released arachidonic acid (AA), a substrate of COX-2, from membranous phospholipids. From these results, it was suggested that activation of each of the ERK1/2, p38, and JNK MAPK cascades in addition to that of PKC and cPLA2 played an important role in the Cd-stimulated biosynthesis of PGE2 in mouse osteoblastic cells.

Differential effects of mercury, lead, and cadmium on IL-2 production by Jurkat T cells

Mercury, lead, and cadmium are widespread and highly toxic pollutants. The aim of this study was to determine the effects of sublethal doses of CH(3)HgCl, CdCl(2), and PbCl(2) on IL-2 production by T lymphocytes. Jurkat T cells were stimulated by triggering CD3 and CD28 molecules before, in conjunction with, or following heavy metal exposure. Heavy metals, individually or mixed together at equimolar concentrations, were used. Results demonstrated that low, noncytotoxic doses of metals induce tyrosine phosphorylation. Mercury and lead (1 microM) inhibit IL-2 production regardless of the state of T cell activation. Cadmium stimulated IL-2 production only in preactivated T cells. Surprisingly, a mixture of these three metals had no effect. We subsequently determined the effects of heavy metals on NFAT (nuclear factors of activated T cells) activity. When cells were stimulated by potent stimulation involving the CD3 and CD28 molecules, an increased NFAT activation was noted when the cells were exposed to mercury and to the metal mixture. Activation with PMA/calcium ionophores indicated that the target of heavy metals is located downstream from PKC and calcium mobilization. These results suggest that the state and mode of T cell activation are important parameters to consider in heavy metal toxicity.

Induction of mitogenic signalling in the 1LN prostate cell line on exposure to submicromolar concentrations of cadmium+

Cadmium exposure increases the risk of prostate cancer. We now describe the effects of Cd2+ on signalling and proliferation in 1LN prostate cells. Cd2+ increased [3H]thymidine uptake and cell number twofold. Cd2+ elevated intracellular IP3, cytosolic-free Ca2+, phosphorylated MEK1/2, ERK1/2, p38 MAPK and JNK two- to threefold. Increased PDK1 and phosphorylation of the 85-kDa regulatory subunit of PI 3-kinase, Akt and p70s6k were also observed. Cd2+ treatment increased transcription factors NFkappaB and CREB, and the expression of c-fos and c-myc. Cd2+-induced increased uptake of [3H]thymidine was abolished by translational and transcriptional inhibitors, and Ca2+ channel blockers. Inhibition of phospholipase C and of Ca2+ binding to IP3 receptors inhibited Cd2+-induced DNA synthesis as did inhibition of tyrosine kinases, protein kinase C, PI 3-kinase, farnesyl transferase, MEK1/2, ERK1/2 and p38MAPK. Thus signalling events, which are triggered on exposure of 1LN cells to submicromolar concentrations of Cd2+, induce increased proliferation of these cells.

Differential effect of cadmium on cholinephosphotransferase activity in normal and cancerous human mammary epithelial cell lines

Cadmium (Cd) is an ubiquitous environmental carcinogen. Membrane phospholipids as well as fatty acid profile of membrane phospholipids are known to be altered in tumorigenicity and malignancy. Synthesis of cellular phosphatidylcholine (PC) has been used as a marker for membrane proliferation in the neoplastic mammary gland tissue. Cholinephosphotransferase (CPT), the terminal enzyme in de novo synthesis of PC, has an important role in regulating the acyl group of PC in mammalian cells. Our previous studies have shown that CPT is expressed differentially in the normal and cancerous mammary epithelial cell lines. In this study, we examined the effect of cadmium on CPT activity using normal (MCF-12A and MCF-12F) and cancerous (MCF-7, BT-549, and 11-9-1-4) human mammary epithelial cell lines. There was no consistent pattern of CPT activity in response to different doses of cadmium. The activity did not show a time-dependent variation at 5 μm concentration, except in MCF-7 and 11-9-1-4. CPT gene expression increased with cadmium as evident from slot blots. Mutation in the nucleotide sequence was also observed as the result of cadmium but this did not result into amino acid sequence changes.

Mediation of cadmium-induced oxidative damage and glucose-6-phosphate dehydrogenase expression through glutathione depletion

The effect of cadmium (Cd), a significant environmental contaminant, on the expression of glucose-6-phosphate dehydrogenase (G6PDH), has been investigated. G6PDH is the key rate-limiting enzyme in the pentose pathway and the expression of its gene has been shown to be redox-sensitive. We show that incubation of primary rat hepatocytes with Cd induces oxidative stress in a time- and concentration-dependent manner as measured by increases in the cytotoxic parameters, lactate dehydrogenase (LDH) and lipid peroxidation (LPO). Significant increases in LDH leakage and LPO can be measured after 12 and 24 h, respectively, in the presence of 4 microM cadmium chloride. However, prior to significant increases in cytotoxic parameters, and within only 6 h of Cd treatment, significant decreases in reduced glutathione and increases in the expression of G6PDH as measured by mRNA levels and enzyme activity are observed. The signal protein MAP kinase (MAPK) is also induced by Cd within 6 h. Blocking the Cd induction of MAPK using the antioxidant N-acetyl cysteine (10 mM) or Trolox (0.5 mM) or the MEK specific inhibitor PD098059 (20 microM) also blocks the Cd induction of G6PDH suggesting that MAPK is a signal protein involved in the redox regulation of this gene.

Molecular and cellular mechanisms of cadmium carcinogenesis

Cadmium is a heavy metal, which is widely used in industry, affecting human health through occupational and environmental exposure. In mammals, it exerts multiple toxic effects and has been classified as a human carcinogen by the International Agency for Research on Cancer. Cadmium affects cell proliferation, differentiation, apoptosis and other cellular activities. Cd2+ does not catalyze Fenton-type reactions because it does not accept or donate electrons under physiological conditions, and it is only weakly genotoxic. Hence, indirect mechanisms are implicated in the carcinogenicity of cadmium. In this review multiple mechanisms are discussed, such as modulation of gene expression and signal transduction, interference with enzymes of the cellular antioxidant system and generation of reactive oxygen species (ROS), inhibition of DNA repair and DNA methylation, role in apoptosis and disruption of E-cadherin-mediated cell-cell adhesion. Cadmium affects both gene transcription and translation. The major mechanisms of gene induction by cadmium known so far are modulation of cellular signal transduction pathways by enhancement of protein phosphorylation and activation of transcription and translation factors. Cadmium interferes with antioxidant defense mechanisms and stimulates the production of reactive oxygen species, which may act as signaling molecules in the induction of gene expression and apoptosis. The inhibition of DNA repair processes by cadmium represents a mechanism by which cadmium enhances the genotoxicity of other agents and may contribute to the tumor initiation by this metal. The disruption of E-cadherin-mediated cell-cell adhesion by cadmium probably further stimulates the development of tumors. It becomes clear that there exist multiple mechanisms which contribute to the carcinogenicity of cadmium, although the relative weights of these contributions are difficult to estimate.

Ca(2+)/calmodulin-dependent and cAMP-dependent kinases in induction of c-fos in human mesangial cells

Mesangial cell proliferation is an early event in several progressive renal diseases. When mesangial cells in culture are rendered quiescent by serum starvation and subsequently stimulated to proliferate, induction of c-fos is an early indicator of entry into the cell cycle. Several heparin-sensitive signals transduce these events. We have examined the potential roles of CaMK and PKA. Selective stimulation of CaMK with Ca(2+) ionophores and of PKA with forskolin or dibutyryl cAMP both result in induction of c-fos mRNA. CaMK but not PKA signaling is suppressed by low concentrations of heparin. Cross talk between the pathways has been demonstrated in some cells, with evidence of CaMK phosphorylating cAMP response element binding protein (CREB) at an inhibitory site and PKA suppressing CaMK-dependent signaling. However, in the present study, both pathways phosphorylated CREB on Ser(133) and induced c-fos in an additive manner. Serum, ionomycin, and forskolin all caused a rapid decline in cyclin D1 levels, but only serum effected a subsequent increase, indicative of cell cycle progression. We conclude that, in human mesangial cells, CaMK and PKA can both contribute to cell cycle entry, and, although induction of c-fos by CaMK requires active PKA, neither pathway antagonizes or synergizes c-fos induction by the other.

Molecular inhibitory mechanisms of antioxidant enzymes in rat liver and kidney by cadmium

Catalase, Mn-superoxide dismutase (MnSOD) and Cu,Zn-superoxide dismutase (CuZnSOD) activities were studied in rat liver and kidney 6-48 h after CdCl(2) intraperitoneal administration or 10-30 days daily oral CdCl(2) intake in drinking water. This approach provided some indications as to the sensitivity of each enzyme to cadmium toxicity. These experiments showed that the formation of thiobarbituric acid reactive substance (TBARS) did not strictly depend on how well the antioxidant enzyme worked. From in vitro experiments it appeared that TBARS removal by vitamin E did not restore the three enzyme activities at all. As for cadmium's inhibitory mechanism on catalase activity, our data, obtained in the pH range 6.0-8.0, are a preliminary indication that the negative effect of this metal is probably due to imidazole residue binding of His-74 which is essential in the decomposition of hydrogen peroxide. Cadmium inhibition of liver mitochondrial MnSOD activity was completely removed by Mn(2+) ions, suggesting that the reducing effect on this enzyme is probably due to the substitution of cadmium for manganese. We also observed the antioxidant capacity of Mn(2+) ions, since they were able to normalize the increased TBARS levels occurring when liver mitochondria were exposed to cadmium. The reduced activity of CuZnSOD does not seem to be due to the replacement of Zn by Cd, nor to the peroxides formed. As this enzyme activity was almost completely recovered after 48 h, we hypothesize that the momentary inhibition is imputable to a cadmium/enzyme interaction. This causes some perturbation in the enzyme topography which is critical for its catalytic activity. The pathological implications linked to antioxidant enzyme disorders induced by cadmium toxicity are discussed.

Evaluation of cadmium-induced transcriptome alterations by three color cDNA labeling microarray analysis on a T-cell line

Beside heavy metals, cadmium (Cd(2+)) is a ubiquitous toxic metal with a well established apoptotic and genotoxic effect, chronic exposure of which has been involved in a variety of pathological conditions. In the present study, we investigated by 1455 genes cDNA microarrays the toxic and apoptotic effect of Cd(2+), on the T-cell line CCRF-CEM, applying a three laser differential analysis, on the same microarray slide. The cells were cultured for 6 and 24 h in the absence (control) or presence of Cd(2+) (10 or 20 microM), RNAs were extracted and the produced cDNAs were labeled with rhodamine derivatives fluorescent dyes. A microarray slide was simultaneously hybridized by the labeled cDNAs and analyzed. We found that, in relation to control, treatment of the cells for 6 h with 10 and 20 microM Cd(2+), induces up-regulation in 20 and 34 genes, respectively. Treatment for 24 h with 10 and 20 microM Cd(2+) induces up-regulation in 22 and 84 genes, respectively. Twenty-eight genes were found down-regulated only after treatment for 24 h with Cd(2+) 10 microM. These data suggest that Cd(2+) produces a time- and dose-dependent molecular cascade, induces disturbances in different subcellular compartments, influencing thereafter the normal cellular functions, the differentiation process, the malignant transformation and the cell death.

Cadmium affects genes involved in growth regulation during two-stage transformation of Balb/3T3 cells

Cadmium (Cd), a carcinogenic metal in human and rodents, has been shown to transform cells in vitro. However, the carcinogenic mechanisms of Cd as a mutagen and/or promoter are not well clarified. We already reported that CdCl2 in a range of 1.5 approximately 360 ng/ml enhanced transformation of Balb/3T3 A31 cells induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG, 0.1 microg/ml) in a dose-dependent manner (Fang et al., Toxicol. In Vitro 15(3) (2001a) 51-7). In previous study, we observed that Cd stimulated cell proliferation on MNNG-initiated cells through inactivation of p53 and p27 and increase of proliferating cell nuclear antigen (PCNA) expression after 24 h treatment (Fang et al., Toxicology 163 (2001b) 175-84). The aim of this study is to further elucidate the long-term effect of Cd in terms of cell cycle control gene expressions during the promotion stage of in vitro two-stage transformation. For the purpose, we determined the expression levels of the genes involved in growth regulation, such as p53, p27, c-myc, mdm2, cyclins D1 and B1, CDK4, and PCNA in the cells treated with Cd for 14 days after MNNG-initiation. In MNNG+CdCl2 group, cells apparently expressed cellular tumor antigen p53 mRNA, but did not express the wild-type p53 protein; the protein and mRNA levels of p27 were reduced apparently in the cells of MNNG+CdCl2 group compared to the cells of control and MNNG group. In addition, the protein levels of cyclin D1, CDK4, PCNA, c-myc, and mdm2, and cyclin B1 mRNA level were higher in MNNG+CdCl2 group than control and MNNG group. Together with previous data (Fang et al., Toxicology 163 (2001b) 175-84), our results indicated that during the transformation process of MNNG-treated cells, Cd may activate oncogenes such as c-myc, mdm2, and cellular tumor antigen p53, inhibit the tumor suppressor genes such as wild-type p53 and p27, and consequently accelerate the proliferation of initiated cells. This work firstly demonstrates that Cd affects the genes involved in growth regulation on initiated cells during the promotion stage of in vitro cell transformation.

Upregulation of stress response mRNAs in COS-7 cells exposed to cadmium

Exposure of cells to cadmium (Cd) is known to stimulate the expression of various types of genes. These changes in gene expression are presumed to be related to the cellular response to Cd toxicity. To better understand the mechanisms related to Cd toxicity, suppression subtractive hybridization was carried out on COS-7 cells (African green monkey kidney cells) and the gene expression induced by Cd exposure was investigated. Heat shock protein (hsp) 10, 40, 60, 70, 89alpha and metallothionein II (MTII) mRNAs were found to be induced by Cd. This is the first report to describe the Cd-inducibility of hsp10, 40 and 89alpha mRNAs. Semi-quantitative reverse-transcription polymerase chain reaction showed the diverse expression patterns of these genes, depending on Cd concentration and exposure time. A marked elevation of hsp70 mRNA and induction of mRNA for the co-chaperone, hsp40, were detected. A relatively low level of hsp10 and hsp60 mRNAs was induced, with only a 2-fold increase within 24 h. Hsp89alpha mRNA was induced shortly after Cd exposure. These various induction patterns suggest that hsps play different roles in the cell against Cd toxicity.