Cadmium induces apoptosis in a human T cell line

Dermal bioaccessibility and cytotoxicity of heavy metals in urban soils from a typical plateau city: Implication for human health

The dermal exposure of heavy metals in contaminated urban soils poses huge environmental health risks globally. However, their dermal bioaccessibility and adverse effects on human skin cells were not fully understood. In this study, we measured the total and dermal bioaccessibility of Cr, As, Cd, Pb, and Cu in four selected urban soil samples from Kunming, Yunnan, China, and evaluated the cellular responses of these bioaccessible extracts on human keratinocytes (HaCaT). Among all the metals, only As in Soil-3 (S3) exceeded Chinese risk screening and Yunnan background values at 38.2 mg/kg. The average concentrations of Cr, As, Cd, Pb, and Cu in all soil samples were 47.79, 15.50, 3.11, 104.27, and 180.29 mg/kg respectively. Although relatively high concentrations of heavy metals were detected in soil samples, the highest dermal bioaccessibility of Cd was 3.57% with others' being lower than 1%. The bioaccessible dermal-absorbed doses (DADs) of Cr, As, Cd, Pb, and Cu from soils reflected acceptable health risks since all DADs were below the corresponding derived dermal reference values. However, the toxic data showed the extracts of S3 and S4 presented certain cytotoxicity in HaCaT cells, indicating the existing models based on dermal bioaccessibility and DADs may be not accurate enough to assess their human health risk. Taken together, the human health risk assessment should be modified by taking their skin cytotoxicity into account.

In vitro cytotoxic assessment of e-waste-related chemical pollution in impacted soil matrix

The environmental quality and toxicity of soil from some selected informal e-waste sites in West Africa was assessed on PLHC-1 liver cells. In addition, toxicity mechanisms such as apoptosis, necrosis and necroptosis were analysed in order to determine the effect of the actual chemical mixture present in the e-waste soil matrix. The investigation revealed that although e-waste soil extracts (polar and non-polar) and elutriates were significantly cytotoxic at the tested concentration (16 mg soil EQ/ml), PLHC-1 cell viability was not reduced below 50%. The non-polar extracts were more toxic compared to polar extracts and elutriates. The cytotoxic potency of soil from the informal e-waste-recycling sites ranged in this order: Alaba > Godome-Kouhounou > Agbogblosie. The study revealed that all e-waste soil extracts and elutriates induced significant (P < 0.01) PLHC-1 cell death by apoptosis and necrosis; however, cell death by apoptosis was higher compared to that by necrosis. The results indicated that except for non-polar extracts (N4, B4 and G4) from open burning areas that induced significant (P < 0.01) PLHC-1 cell death by necroptosis, other extracts and elutriates could not cause cell death by necroptosis. The study has demonstrated that soils from the Alaba e-waste site in Lagos could be more toxic than soils from Godome-Kouhounou (Cotonou) and Agbogblosie (Accra) e-waste sites and further highlighted open burning as an informal e-waste-handling method with greater negative impact on soil quality in the e-waste sites. The study emphasizes the urgent need for regulatory agencies to introduce regular residue-monitoring programmes in order to forestall the adverse effects of soil pollution episodes in the e-waste sites.

Involvement of caspase-3 in apoptosis of human lymphocytes exposed to cadmium chloride

BACKGROUND

Lymphocytes are a group of white blood cells with a variety of roles their integrity is crucial for the body's immune responses. Cadmium, a heavy metal and environmental pollutant, is known as a toxicant to exert its adverse effects on some sort of cells including blood cells.

RESEARCH DESIGN

In this study, human lymphocytes were divided into 3 groups: (1) lymphocytes at 0-h, (2) lymphocytes at 24 h (control), (3) lymphocytes treated with cadmium chloride (15 μM). Lymphocyte viability and plasma membrane integrity were assessed in these groups. In addition, the occurrence of apoptosis was investigated by assessment of nucleus diameter and flow cytometry. Activation of caspase-3 was also detected by immunocytochemistry.

RESULTS

Result showed that lymphocyte's viability and plasma membrane integrity decreased in lymphocytes treated with cadmium as compared with the control group. Decreased nucleus diameter and result of flow cytometry demonstrated cadmium-induced apoptosis in human lymphocytes. Furthermore, lymphocytes treated with cadmium displayed intensely activated caspase-3 immunoreactivity in their cytoplasm.

CONCLUSION

In conclusion, cadmium not only negatively effect on viability and plasma membrane, but also induces caspase-dependent apoptosis in human lymphocytes.

Potential mechanisms of some selected heavy metals in the induction of inflammation and autoimmunity

Inflammation is a physiological event that protects tissues from infection and injury. Chronic inflammation causes immune cell over activation and sustained release of inflammatory cytokines and chemokines cause pathologic conditions including autoimmune diseases. Heavy metals exposure affects innate and adaptive immune systems through triggering inflammatory responses. It seems that extended inflammatory responses could accelerate heavy metal-induced autoimmunity. In the present review we discuss the exposure route and toxicity of Cadmium (Cd), Lead (Pb), Mercury (Hg), Vanadium (V) and Platinum (Pt) and their effects on inflammatory responses by innate and adaptive immune system and autoimmunity.

Concentration/activity of superoxide dismutase isozymes and the pro-/antioxidative status, in context of type 2 diabetes and selected single nucleotide polymorphisms (genes: INS, SOD1, SOD2, SOD3) - Preliminary findings

The alterations in concentration/activity of superoxide dismutase isozymes in the context of type 2 diabetes or obesity are well-described. Moreover, many hereditary factors, including single-nucleotide polymorphisms (SNPs) of genes for coding insulin, insulin receptors, or insulin receptor substrates (INS, INSR, IRS1, IRS2) or superoxide dismutase isozymes (SOD1, SOD2, SOD3), have been linked with the incidence of obesity and diabetes. However, the underlying changes in the plasma concentration/activity of superoxide dismutase isozymes and their potential connection with the said hereditary factors remain unexplored. Previously, we have observed that the plasma concentration/activity of superoxide dismutase isozymes differs in the context of obesity and/or rs2234694 (SOD1) and rs4880 (SOD2) and that the concentrations of SOD1, SOD2, SOD3 are correlated with each other. Intersexual variability of SOD1 concentration was detected regardless of obesity. In this study, the variability of concentration/activity of superoxide dismutase isozymes in plasma is considered in the context of type 2 diabetes and/or SNPs: rs2234694 (SOD1), rs5746105 (SOD2), rs4880 (SOD2), rs927450 (SOD2), rs8192287 (SOD3). Genotypic variability of SNP rs3842729 (INS), previously studied in the context of insulin-dependent diabetes, is investigated in terms of selected clinical parameters associated with type 2 diabetes. This study revealed higher SOD1 concentration in diabetic men compared to women, and extremely high SOD1 concentration, higher total superoxide dismutase, and copper-zinc superoxide dismutase activity, and lower superoxide dismutase and copper-zinc superoxide dismutase activity (when adjusted for the concentration of SODs) in the diabetic group regardless of sex. Multiple logistic regression, applied to explore possible links between the studied SNPs and other factors with the odds of type 2 diabetes or obesity, revealed that the genotypic variability of rs4880 (SOD2) could affect these odds, supporting the findings of several other studies.

Cadmium sulfate induces apoptosis in planarians

With rapid socio-economic development, heavy metal pollution in water has become common and affects both environment and human health. Cadmium (Cd) has been recognized as one of the heavy metals which cause acute or chronic toxic effects if ingested. Although its toxicity is undisputed, the underlying molecular mechanisms in vivo are not fully understood. Planarians, a model organism famous for their regenerative prowess, have long been utilized to study the effects of chemical exposure. In this study, we observed apoptosis with TUNEL assay in planarians induced by cadmium sulfate (CdSO₄) in a dose-dependent manner. The apoptosis-related genes were detected with quantitative RT-PCR. Significant changes in c-Myc, P53, and BcL-2 were indicated, which may play a partial role in the regulation of the process of apoptosis in the planarians. H&E staining showed that Cd had obvious biological toxicity in the planarians. Here, new insights on metal toxicity mechanisms are provided, contributing to understand how CdSO₄ induces the pathological and physiological processes of apoptosis in the living bodies. Meanwhile, planarians are proved to be a freshwater pollution indicator and toxicological research model.

The effects of cadmium exposure in the induction of inflammation

Inflammation is a physiological process essential for maintaining homeostatic mechanisms in human, but however, exaggerated inflammatory responses are closely related to many chronic diseases. Cadmium (Cd) is a heavy metal with high toxicity when present in food, water and air has the potential of eliciting inflammatory reactions, with a major health risk to human. This review aimed to elucidate on the major routes of Cd exposure, the main organs affected by the exposure, the degree of toxicity as well as the roles of the toxic effects on the immune system which results to inflammatory responses. Immune modulation by Cd may cause serious adverse health effects in humans. Various studies have highlighted the ability of Cd as an environmental pollutant involved in the modulation of the innate, adaptive and mucosal immune responses in relations to the release of chemokine, gene expression, and susceptibility to microbial infections.

In vitro cyto-toxic assessment of heavy metals and their binary mixtures on mast cell-like, rat basophilic leukemia (RBL-2H3) cells

We investigated the cytotoxicity and mechanisms of cell death induced by salts of Cadmium (Cd²⁺), Lead (Pb²⁺), Arsenic (AsO₄^3-) and Chromium (Cr⁺⁶) on RBL-2H3 cells (a model mast cell line). In addition, cyto-toxic effect on cell viability was assessed to reveal their nature of interaction in binary mixture. The individual cytotoxic characteristics of these metals on RBL-2H3 cell viability showed a concentration-dependent reduction of cell viability. We observed that concentration-dependent cytotoxic potency on RBL-2H3 cells of these metals range in the following order Cd²⁺>Cr⁺⁶>As O₄^3-> Pb²⁺ with LC₅₀ values of 0.11 μM, 93.58 μM, 397.9 μM and 485.3 μM respectively. Additive effects were observed with Pb²⁺ + Cd²⁺, Pb²⁺ + AsO₄^3-, Pb²⁺ + Cr⁺⁶ and AsO₄^3- + Cr⁺⁶. The study revealed that Pb²⁺, Cd²⁺, AsO₄^3- and Cr⁺⁶ could induce significant (P < 0.01) cell death by apoptosis in RBL-2H3. Highly significant necrotic cell death was observed with Pb²⁺ and Cr⁺⁶ (P < 0.01) than Cd²⁺ and AsO₄^3- (P < 0.05). Overall, it can be deduced that several cell death executing pathways may be concomitantly activated on exposure to heavy metals and the predominance of one over others might depend on the type of heavy metal, concentration and the metabolic state of the cell. Eventually, binary mixtures of some of these metals showed less cytotoxicity than would be expected from their individual actions and may depend on the co-exposure of the metal ions and their modes of action.

Potential ability for metallothionein and vitamin E protection against cadmium immunotoxicity in head kidney and spleen of grass carp (Ctenopharyngodon idellus)

Cadmium (Cd) pollution is an important issue affecting the food safety of aquatic products. Cd can impair the immune system and cause irreversible damage to fish and other aquatic organisms. The immunoprotection activities of exogenous metallothionein (MT) and vitamin E (VE) were investigated in Cd poisoned grass carp, Ctenopharyngodon idellus, in the present study. C. idellus were divided into three groups: Cd+phosphate-buffered saline (PBS) group; Cd+MT; and Cd+VE. All fish were injected with cadmium chloride (CdCl₂) on the first day and then treated with PBS, MT or VE four days post-injection. Fish not injected with Cd were used as a negative control. Cd exposure caused severe head-kidney and splenic injury in C. idellus, mainly expressed as an increase in Cd content, histological damage, percentage of head-kidney and splenic cells apoptosis and decreases in immune-related gene mRNA transcript expression. However, MT and VE treatments protected against Cd-induced immunotoxicity in C. idellus by decreasing Cd contents, lessening histological damage, reducing the percentage of apoptosis and recovering immune-related mRNA transcript expression. Our results demonstrate that MT and VE can alleviate Cd-induced immunotoxicity and that MT has a more powerful effect than VE, indicating that MT could be a potential antidote in cases of Cd poisoning.

Overexpression of OLE1 Enhances Cytoplasmic Membrane Stability and Confers Resistance to Cadmium in Saccharomyces cerevisiae

The heavy metal cadmium is widely used and released into the environment, posing a severe threat to crops and humans. Saccharomyces cerevisiae is one of the most commonly used organisms in the investigation of environmental metal toxicity. We investigated cadmium stress and the adaptive mechanisms of yeast by screening a genome-wide essential gene overexpression library. A candidate gene, OLE1, encodes a delta-9 desaturase and was associated with high anti-cadmium-stress activity. The results demonstrated that the expression of OLE1 was positively correlated with cadmium stress tolerance and induction was independent of Mga2p and Spt23p (important regulatory factors for OLE1). Moreover, in response to cadmium stress, cellular levels of monounsaturated fatty acids were increased. The addition of exogenous unsaturated fatty acids simulated overexpression of OLE1, leading to cadmium resistance. Such regulation of OLE1 in the synthesis of unsaturated fatty acids may serve as a positive feedback mechanism to help cells counter the lipid peroxidation and cytoplasmic membrane damage caused by cadmium.

IMPORTANCE

A S. cerevisiae gene encoding a delta-9 desaturase, OLE1, was associated with high anti-cadmium-stress activity. The data suggest that the regulation of OLE1 in the synthesis of unsaturated fatty acids may serve as a positive feedback mechanism to help yeast cells counter the lipid peroxidation and cytoplasmic membrane damage caused by cadmium. The discovery of OLE1 involvement in membrane stability may indicate a novel defense strategy against cadmium stress.

Education, fish consumption, well water, chicken coops, and cooking fires: Using biogeochemistry and ethnography to study exposure of children from Yucatan, Mexico to metals and arsenic

Around the world, the nocuous health effects of exposure to environmental contaminants, especially metals and Arsenic, are a growing health concern. This is especially the case in Mexico, where corruption and ineffective political administration are contributing to increasing deterioration in the environment. Importantly, shallow soils and the karstic nature of bedrock in Yucatan, Mexico make the subterranean aquifer especially susceptible to contamination because contaminates are carried to it with little resistance. Given these environmental conditions, we developed a multi/interdisciplinary project to evaluate the impact of metal and Arsenic pollution on a sample of 107 children, ages 6 to 9years, living in the urban areas of Progreso, Merida, and Ticul, in the State of Yucatan using urine and blood samples. In addition, ethnographic research was carried out in the homes of the children that participated in the study to identify potential exposure pathways. This research proved invaluable because the complexity of human social organization, lifestyles, and geographical patterning create an intricate array of exposure pathways that vary across social sectors and geographic space. In the following article, we use nonparametric univariate statistical analysis to reveal potential exposure pathways among sub-populations included in our sample. These analyses show that children from poor/marginal families tend to be exposed to Copper, Lead, and Nickel; whereas, children, from wealthier families, tend to be exposed to Cadmium, Arsenic, and inorganic Copper (Copper Sulfate).

Comparison of antioxidant enzyme activities and DNA damage in chickpea (Cicer arietinum L.) genotypes exposed to vanadium

The present study was done to elucidate the effects of vanadium (V) on photosynthetic pigments, membrane damage, antioxidant enzymes, protein, and deoxyribonucleic acid (DNA) integrity in the following chickpea genotypes: C-44 (tolerant) and Balkasar (sensitive). Changes in these parameters were strikingly dependent on levels of V, at 60 and 120 mg V L(-1) induced DNA damage in Balkasar only, while photosynthetic pigments and protein were decreased from 15 to 120 mg V L(-1) and membrane was also damaged. It was shown that photosynthetic pigments and protein production declined from 15 to 120 mg V L(-1) and the membrane was also damaged, while DNA damage was not observed at any level of V stress in C-44. Moreover, the antioxidant enzyme activities such as superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) were increased in both genotypes of chickpea against V stress; however, more activities were observed in C-44 than Balkasar. The results suggest that DNA damage in sensitive genotypes can be triggered due to exposure of higher vanadium.

Role of autophagy in cadmium-induced apoptosis of primary rat osteoblasts

Cadmium (Cd) is a common environmental pollutant that can damage many organs and the fetus. We previously reported that Cd induced apoptosis in primary rat osteoblasts (OBs). OB apoptosis induced by Cd will eventually lead to osteoporosis. In this study, a novel pharmacotherapeutic approach was investigated involving the regulation of autophagy to prevent Cd osteoporosis. The results showed that Cd treatment induced apoptosis in OBs, as demonstrated by the ratio of Bax/Bcl-2, activation of poly (ADP-ribose) polymerase (PARP) and nuclear condensation. In addition, cells treated with Cd were observed to undergo autophagic cell death by monitoring the induction of the beclin 1, autophagy gene 5 (Atg5) and the expression of microtubule-associated protein 1 light chain 3 (LC3). The results indicated that promotion of apoptotic cell death by Cd is accompanied by induction of autophagy in OBs. Interestingly, Cd-mediated apoptotic cell death was suppressed by pretreatment with the autophagy activator rapamycin (RAP) and potentiated by the autophagy inhibitor chloroquine (CQ) or small interfering RNA against beclin 1. These findings suggest that the autophagic response plays a protective role that impedes eventual cell death. Activation of autophagy could therefore be an adjunctive strategy for treatment of Cd-induced osteoporosis.

Aluminum Chloride Induces Osteoblasts Apoptosis via Disrupting Calcium Homeostasis and Activating Ca(2+)/CaMKII Signal Pathway

Aluminum promotes osteoblast (OB) apoptosis. Apoptosis is induced by the disordered calcium homeostasis. Therefore, to investigate the relationship between Al-induced OB apoptosis and calcium homeostasis, calvarium OBs from neonatal rats (3-4 days) were cultured and exposed to 0.048-mg/mL Al(3+) or 0.048-mg/mL Al(3+) combined with 5 μM BAPTA-AM (OBs were pretreated with 5 μM BAPTA-AM for 1 h, then added 0.048 mg/mL Al(3+)), respectively. Then OB apoptosis rate, intracellular calcium ions concentration ([Ca(2+)]i), mRNA expression level of calmodulin (CaM), and protein expression levels of CaM and p-CaMKII in OBs were examined. The result showed that AlCl3 increased OB apoptosis rate, and [Ca(2+)]i and p-CaMKII expression levels and decreased CaM expression levels, whereas BAPTA-AM relieved the effects. These results proved that AlCl3 induced OB apoptosis by disrupting the intracellular Ca(2+) homeostasis and activating the Ca(2+)/CaMKII signal pathway. Our findings can provide new insights for revealing the apoptosis mechanism of OBs exposed to AlCl3.

Delineating the anti-cytotoxic and anti-genotoxic potentials of catechin hydrate against cadmium toxicity in human peripheral blood lymphocytes

Catechins (flavan-3-ol) are a type of natural phenol and well-studied antioxidants. Catechin hydrate, also known as taxifolin; is non-mutagenic, low in toxicity compared to other immunomodulator antioxidants. We aimed to determine the potential of catechin hydrate to prevent the cyto-genotoxic effects of cadmium in lymphocytes; demonstrate the immuno-protective activity of catechin hydrate. Our previous study indicated that cadmium is apoptogenic. Lymphocytes were treated with catechin hydrate or cadmium and catechine hydrate combinations (range 0.1-100μM) to determine their effects on cell viability. Lymphocytes treated with 100μM catechin hydrate and 100μM cadmium showed cell viability 70.65±6.92% and 5.69±2.27%, respectively. In our previous study cadmium (10 and 20μM) induced apoptosis in 31.8% and 44.4% of lymphocytes, respectively. However, the percentage of apoptotic cells after treatment with the combination of cadmium and catechin hydrate was not significantly different from that of catechin hydrate (P>0.05). Only 7.3% and 10.5% of the lymphocytes were apoptotic after treatment with 10μM cadmium+10μM catechin hydrate and 20μM cadmium+20μM catechin hydrate, respectively. The anti-geno-cytotoxic and immuno-protective potential of catechin hydrate was also demonstrated by the non-significant expression of apoptosis-related genes after treatment with catechin hydrate.

Over-expression of the MxIRT1 gene increases iron and zinc content in rice seeds

Iron and zinc are essential in plant and human nutrition. Iron deficiency has been one of the causes of human mortality, especially in developing countries with high rice consumption. MxIRT1 is a ferrous transporter that has been screened from an iron-efficient genotype of the apple tree, Malus xiaojinensis Cheng et Jiang. In order to produce Fe-biofortified rice with MxIRT1 to solve the Fe-deficiency problem, plant expression vectors of pCAMBIA1302-MxIRT1:GFP and pCAMBIA1302-anti MxIRT1:GFP were constructed that led to successful production of transgenic rice. The transgenic plant phenotypes showed that the expression of endogenous OsIRT1 was suppressed by anti-MxIRT1 in antisense lines that acted as an opposing control, while sense lines had a higher tolerance under Zn- and Fe-deficient conditions. The iron and zinc concentration in T3 seeds increased by three times in sense lines when compared to the wild type. To understand the MxIRT1 cadmium uptake, the MxIRT1 cadmium absorption trait was compared with AtIRT1 and OsIRT1 in transgenic rice protoplasts, and it was found that MxIRT1 had the lowest Cd uptake capacity. MxIRT1 transgenic tobacco-cultured bright yellow-2 (BY-2) cells and rice lines were subjected to different Fe conditions and the results from the non-invasive micro-test technique showed that iron was actively transported compared to cadmium as long as iron was readily available in the environment. This suggests that MxIRT1 is a good candidate gene for plant Fe and Zn biofortification.

Molecular functions of metallothionein and its role in hematological malignancies

Metallothionein (MT) was reported to be a potential negative regulator of apoptosis, and various reports have suggested that it may play roles in carcinogenesis and drug resistance, in at least a portion of cancer cells. The author summarizes the current understanding of the molecular functions of MT for tumor cell growth and drug resistance. These activities are regulated through intracellular metal ion modulation and free radical scavenging. Compared with analyses of solid tumors, few studies have analyzed the roles of MT in hematological malignancies. This review mainly describes the functions of MT in hematopoietic cells. Furthermore, through expression analyses of leukemias and lymphomas, the roles of MT in the biology of these diseases are particularly focused upon.

Cadmium-induced changes in genomic DNA-methylation status increase aneuploidy events in a pig Robertsonian translocation model

Although cadmium is a well-established human carcinogen, the mechanisms by which it induces cancer are poorly understood. It is suggested that cadmium-mediated carcinogenesis may include the modulation of gene expression and signal-transduction pathways, interference with antioxidant enzymes, inhibition of DNA repair and DNA methylation, and induction of apoptosis. Nevertheless, no predominant mechanism playing a role in metal-induced carcinogenesis has been reported. In the present study, we used a pig Robertsonian translocation model, which is a cross between a wild boar and domestic pig resulting in Robertsonian translocation (37,XX,der15;17 or 37,XY,der15;17), to determine the role of cadmium sulfate in the modulation of genomic DNA-methylation status and the induction of aneuploidy. We found a cadmium-mediated increase in aneuploidy within chromosome group A and C, but not within chromosome group D containing the translocated chromosome der15,17 which indicates that translocated chromosome is not more prone to chromosomal aberrations than are other chromosomes. We suggest that cadmium-induced aneuploidy (up to 5-μM concentration) may be mediated by global DNA hypermethylation as monitored with HPLC and 5-mdC immunostaining. In addition, the cyto- and genotoxic potential of cadmium was evaluated. Cadmium sulfate was able to induce apoptosis, inhibit cell-proliferative status and expression of nucleolar organizer regions (NORs), and increase oxidative DNA damage (8-oxoG content).

Cadmium-induced apoptosis and necrosis in human osteoblasts: role of caspases and mitogen-activated protein kinases pathways

Cadmium is a widespread environmental pollutant which induces severe toxic alterations, including osteomalacia and osteoporosis, likely by estrogen receptor-dependent mechanisms. Indeed, cadmium has been described to act as an endocrine disruptor and its toxicity is exerted both in vivo and in vitro through induction of apoptosis and/or necrosis by not fully clarified intracellular mechanism(s) of action. Aim of the present study was to further investigate the molecular mechanism by which cadmium might alter homeostasis of estrogen target cells, such as osteoblast homeostasis, inducing cell apoptosis and/or necrosis. Human osteoblastic cells (hFOB 1.19) in culture were used as an in vitro model to characterize the intracellular mechanisms induced by this heavy metal. Cells were incubated in the presence/ absence of 10-50 μM cadmium chloride at different times and DNA fragmentation and activation of procaspases- 8 and -3 were induced upon CdCl(2) treatment triggering apoptotic and necrotic pathways. Addition of caspase-8 and -3 inhibitors (Z-IETD-FMK and Z-DQMD-FMK) partially blocked these effects. No activation of procaspase-9 was observed. To determine the role of mitogen-activated protein kinases (MAPK) in these events, we investigated c-jun N-terminal kinase (JNK), p38 and extracellular signal-regulated protein kinase (ERK1/2) phosphorylation which were activated by 10 μM CdCl(2). Chemical inhibitors of JNK, p38, and ERK1/2, SP600125, SB202190, and PD98059, significantly reduced the phosphorylation of the kinases and blunted apoptosis. In contrast, caspase inhibitors did not reduce the cadmium-induced MAPK phosphorylation, suggesting an independent activation of these pathways. In conclusion, at least 2 pathways appear activated by cadmium in osteoblasts: a direct induction of caspase-8 followed by activation of caspase-3 and an indirect induction by phosphorylation of ERK1/2, p38, and JNK MAPK triggering activation of caspase-8 and -3.

Role of the cytoskeleton in Cd2+-induced death of mouse mesangial cells

Cadmium induces apoptotic cell death in mouse mesangial cells that is in part dependent on reactive oxygen species (ROS). Cadmium also activates multiple kinases in these cells, including the Ca2+/calmodulin-dependent protein kinase II (CaMK-II) and p38 kinase, and also leads to disruption of the filamentous actin cytoskeleton. We investigated the role of the cytoskeleton in Cd2+-induced cell death. Cell viability was decreased by Cd2+ and two types of apoptotic death, defined by flow cytometry, were increased. Disruption of actin filaments with cytochalasin D was partially protective, whereas stabilization of the cytoskeleton with jasplakinolide was without effect, indicating that cytoskeletal disruption contributes to, but is not necessary for, induction of apoptosis. Inhibition of CaMK-II and p38 kinase, mitochondrial stabilization with cyclosporine A, and the antioxidant N-acetyl cysteine all protected against apoptosis and prevented disruption of the cytoskeleton. Cytochalasin D decreased Cd2+-dependent ROS production, reduced the decline in mitochondrial membrane potential, and decreased phosphorylation of p38 kinase. We conclude that Cd2+-dependent actin disruption is a downstream event facilitating apoptotic death. Cadmium-dependent cell death involves actin-dependent mitochondrial changes, ROS production, and p38 activation.

Cadmium toxicity at low concentration on rabbit spermatozoa motility, morphology and membrane integrity in vitro

In this study the effect of cadmium on various parameters of spermatozoa motility, morphology as well as on the spermatozoa membrane integrity in rabbits was analyzed in vitro, experimental concentrations ranging from 0.62 to 0.98 micro g CdCl(2)/mL. Pooled rabbit (n = 5) semen was cultured in vitro with cadmium and subsequently diluted to various experimental concentrations apart from control which received no cadmium exposure. Using computer assisted semen analysis method (CASA) we detected decrease of total motility with in the higher concentration range at Time 0. However, with increasing time (after 1 and 2 h of culture), cadmium exerted deleterious effect leading to significant motility reduction in comparison to control. A similar trend was exhibited in case of progressive motility, too. Most of the spermatozoa distance and velocity parameters detected no significant change in comparison to control at the beginning of culture (Time 0), although the toxic effect became significant (P < 0.05) with the passage of culture time (Times 1 and 2 h) in all concentrations. Analysis of spermatozoa morphology detected significant (P < 0.05) alterations at higher concentrations. At higher concentrations acrosomal changes, head without flagellum/separated flagellum, broken flagellum and other abnormalities were significantly higher (P < 0.05), while knob-twisted flagellum and small heads differed significantly (P < 0.05) in comparison to control at all concentrations. In regards to flagellum torso, flagellum ball and retention of cytoplasmic drop statistically higher values (P < 0.05) were noted at the maxium experimental concentration only. Annexin analysis for detection of spermatozoa with disordered membranes revealed higher occurrence of positive spermatozoa in cadmium exposed groups. Annexin-positive reactions suggested alterations in anterior part of head (acrosome) and in flagellum (mitochondrial segment) of spermatozoa. This paper underlines that cadmium is highly toxic for rabbit spermatozoa, as visualized by the toxic effects on parameters of spermatozoa motility, morphology and membrane integrity. The toxic effect is more drastic at higher concentrations. This study also indicates that cadmium requires a minimum one hour incubation time to exert its deletorious effects on various parameters of spermatozoa, particularly at low concentrations.

Effects of cadmium on osteoblasts and osteoclasts in vitro

Cadmium (Cd) may have direct effects on bone metabolism and the mechanism is not fully understood. To investigate the effects of Cd on bone metabolism, effects of Cd on osteoblasts and osteoclasts in vitro were observed at cellular and molecular levels. Osteoblasts were cultured by sequential enzyme digestion from Sprague-Dawley rats calvarial bone and osteoclasts were isolated from long bones of new-born male and female Sprague-Dawley rats, and then cells were exposed to different concentrations of Cd (0-2.0 μ mol/L for osteoblasts; 0.03 μmol/L for osteoclasts). As for osteoblasts, cell viability, alkaline phosphatase (ALP) activity, and mineralization were determined. Osteoprotegerin (OPG) and receptor activator of NF-kB ligand (RANKL) were studied via reverse transcription-polymerase chain reaction (RT-PCR). For osteoclasts, after exposure to Cd (0.03 μmol/L) for 72 h and 120 h, number of osteoclasts and pits formation was observed. Cd inhibited the viability, ALP activity, mineralization and up-regulated RANKL mRNA expression in osteoblasts. But Cd had no obvious effect on OPG mRNA expression. For osteoclasts, cadmium (0.03 μmol/L) could increase the numbers of osteoclasts (p<0.05) and enhance pits formation (p<0.05). These results suggested that Cd could inhibit bone formation at high concentrations and enhance bone resorption at low level. OPG/RANKL may constitute an important pathway of Cd effects on bone.

Cytotoxic effects of CdSe quantum dots on maturation of mouse oocytes, fertilization, and fetal development

Quantum dots (QDs) are useful novel luminescent markers, but their embryonic toxicity is yet to be fully established, particularly in oocyte maturation and sperm fertilization. Earlier experiments by our group show that CdSe-core QDs have cytotoxic effects on mouse blastocysts and are associated with defects in subsequent development. Here, we further investigate the influence of CdSe-core QDs on oocyte maturation, fertilization, and subsequent pre- and postimplantation development. CdSe-core QDs induced a significant reduction in the rates of oocyte maturation, fertilization, and in vitro embryo development, but not ZnS-coated CdSe QDs. Treatment of oocytes with 500 nM CdSe-core QDs during in vitro maturation (IVM) led to increased resorption of postimplantation embryos and decreased placental and fetal weights. To our knowledge, this is the first study to report the negative impact of CdSe-core QDs on mouse oocyte development. Moreover, surface modification of CdSe-core QDs with ZnS effectively prevented this cytotoxicity.

Inhibition of benzopyrene-diol-epoxide (BPDE)-induced bax and caspase-9 by cadmium: role of mitogen activated protein kinase

Cadmium, a major metal constituent of tobacco smoke, elicits synergistic enhancement of cell transformation when combined with benzo[a]pyrene (BP) or other polynuclear aromatic hydrocarbons (PAHs). The mechanism underlying this synergism is not clearly understood. Present study demonstrates that (+/-)-anti-benzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE), an ultimate carcinogen of BP, induces apoptosis in human leukemic HL-60 cells and others, and cadmium at non-cytotoxic concentration inhibits BPDE-induced apoptosis. We observed that BPDE treatment also activates all three MAP kinases e.g. ERK1/2, p38 and JNK in HL-60 cells, and inhibition of BPDE-induced apoptosis by cadmium is associated with down-regulation of pro-apoptotic bax induction/caspase-9 activation and up-regulation of ERK phosphorylation, whereas p38 MAP kinase and c-Jun phosphorylation (indicative of JNK activation) remain unaffected. Inhibition of ERKs by prior treatment of cells with 10muM U0126 relieves cadmium-mediated inhibition of apoptosis/bax induction/caspase-9 activation. Our results suggest that cadmium inhibits BPDE-induced apoptosis by modulating apoptotic signaling through up-regulation of ERK, which is known to promote cell survival.

Cadmium- and lead-induced apoptosis in mallard erythrocytes (Anas platyrhynchos)

Cadmium, lead and cadmium-lead (1:10) induced apoptosis were studied using mallard blood cells. The allowable range in concentrations were: 0.01-0.5, 0.1-5.0, and 0.01:0.10-0.50:5.00 mM, for cadmium, lead and cadmium-lead, respectively. The lowest EC(50) achieved was for cadmium (0.22+/-0.04 mM). Two doses from each treatment group were chosen to study apoptosis and the presence of metals in cells. The percentage of apoptotic cells increased as the concentration of metals increased. The percentage of cells with intracellular metals was high for both exposure levels and the quantity of intracellular metal was greater for exposure to high concentrations. Morphological alterations for all types of exposure were related to the diverse range of effects that these metals have on membranes. We suggest that the decrease in the number of erythrocytes observed in specimens suffering from lead and cadmium poisoning is related to the induction of apoptosis.

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.

Cytotoxic effect of CdSe quantum dots on mouse embryonic development

AIM

The aim of this study was to examine the cytotoxic effect of quantum dots (QD), a novel luminescent material, on early post-implantation embryonic development.

METHODS

Mouse blastocysts were incubated in medium with or without CdSe-core QD (250 or 500 nmol/L) for 24 h. Cell apoptosis was analyzed by terminal deoxynucleotidyl transferase-mediated digoxigenin-dUTP nick-end labeling assay and Annexin V/propidium iodide staining, and proliferation was investigated by dual differential staining. Pre-implantation and post-implantation development was assessed by in vitro and in vivo analyses, respectively.

RESULTS

The apoptotic staining analysis showed that CdSe-core QD induced apoptosis in mouse blastocysts in a dose-dependent manner. Pretreatment of blastocysts with CdSe-core QD inhibited cell proliferation, primarily in the inner cell mass. CdSe-core QD also inhibited post-implantation embryonic development; fewer CdSe-core QD-pretreated blastocysts reached the later stages of development compared to the controls. The pre-implantation development of morulas into blastocysts was also inhibited by CdSe-core QD. Furthermore, CdSe-core QD at 500 nmol/L were associated with resorption of post-implantation blastocysts and a decrease in fetal weight. The cytotoxicity of CdSe QD in embryonic development was significantly reduced by the addition of a ZnS coating.

CONCLUSION

Our results show that CdSe-core QD induce apoptosis in mouse blastocysts, inhibit cell proliferation, retard early post-implantation blastocyst development, and increase early-stage blastocyst death in vitro and in vivo.

Metals and apoptosis: recent developments

Apoptosis, also known as programmed cell death is a highly regulated and crucial process found in all multicellular organisms. It is not only implicated in regulatory mechanisms of cells, but has been attributed to a number of diseases, i.e. inflammation, malignancy, autoimmunity and neurodegeneration. A variety of toxins can induce apoptosis. Carcinogenic transition metals, viz. cadmium, chromium and nickel promote apoptosis along with DNA base modifications, strand breaks and rearrangements. Generation of reactive oxygen species, accumulation of Ca(2+), upregulation of caspase-3, down regulation of bcl-2, and deficiency of p-53 lead to arsenic-induced apoptosis. In the case of cadmium, metallothionein expression determines the choice between apoptosis and necrosis. Reactive oxygen species (ROS) and p53 contribute in apoptosis caused by chromium. Immuno suppressive mechanisms contribute in lead-induced apoptosis whereas in the case of mercury, p38 mediated caspase activation regulate apoptosis. Nickel kills the cells by apoptotic pathways. Copper induces apoptosis by p53 dependent and independent pathways. Beryllium stimulates the formation of ROS that play a role in Be-induced macrophage apoptosis. Selenium induces apoptosis by producing superoxide that activates p53. Thus, disorders of apoptosis may play a critical role in some of the most debilitating metal-induced afflictions including hepatotoxicity, renal toxicity, neurotoxicity, autoimmunity and carcinogenesis. An understanding of metal-induced apoptosis will be helpful in the development of preventive molecular strategies.

JWA gene is involved in cadmium-induced growth inhibition and apoptosis in HEK-293T cells

Cadmium (Cd) is widely dispersed in the environment due to occupational and personal (cigarette) emissions. Exposure of human embryonic kidney 293T (HEK-293T) cells to CdCl2 resulted in growth inhibition and apoptosis. Our previous studies demonstrated that JWA, a novel retinoic acid-inducible and cytoskeleton-associated gene, is a potential environmental-responsive gene with increased expression attributed to oxidative and heat-shock stresses. In the present study, JWA was also found to be responsive to Cd exposure. After treatment with 20 microM CdCl2 for 12 h, the expression level of JWA was increased with accompanied growth inhibition and apoptosis. In addition, knock-down JWA protein expression by using transient transfecting of HEK-293T cells with antisense JWA express vector showed a protective effect against Cd-induced apoptosis. To determine whether the upregulation of JWA by Cd involved regulation by transcriptional mechanisms, further reporter gene assays were employed, which demonstrated a marked increase in JWA promoter activity. In addition, elevated intracellular levels of ROS components (O2-* and H2O2) and activation of JNK, ERK, and MAPK were found with corresponding upregulation of JWA protein expression. These results suggest that Cd-induced growth inhibition and apoptosis may involve ROS generation and subsequent affect on MAPK signal pathway. JWA responsiveness to CdCl2 might be through both transcriptional and posttranslational mechanisms.

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.

Clotrimazole, an antifungal drug possessing diverse actions, increases the vulnerability to cadmium in lymphocytes dissociated from rat thymus

Since clotrimazole, known as an antifungal drug, exerts diverse actions on cellular functions, it is expected that clotrimazole can be used for other purposes. This antifungal drug protects the cells overloaded with Ca(2+) by A23187, a calcium ionophore. Therefore, the agent may prevent the cells from death induced by heavy metals such as CdCl(2), PbCl(2), or HgCl(2) that are respectively proposed to increase intracellular Ca(2+) concentration. To test this possibility, we have examined the effect of clotrimazole on the cells simultaneously treated with CdCl(2), PbCl(2), or HgCl(2) using rat thymocytes and a flow cytometer with fluorescent probes. The simultaneous application of clotrimazole and CdCl(2) significantly decreased cell viability, even though the concentrations of both were ineffective at affecting the viability. The significant decrease in cell viability was not due to the inhibition of Ca(2+)-ATPase and Ca(2+)-dependent K(+) channels that were induced by clotrimazole. The simultaneous application increased the population of cells with phosphatidylserine exposed on membrane surface, indicating the change in asymmetrical distribution of membrane phospholipids. Furthermore, the cytotoxicity induced by the combination of clotrimazole and CdCl(2) under nominally Ca(2+)-free condition was more profound than that under normal Ca(2+) condition. Therefore, the membrane may be a target for the cytotoxic action of clotrimazole and CdCl(2) that were simultaneously applied. It is also the case for PbCl(2), but not the case for HgCl(2). It is concluded that clotrimazole can modulate the cytotoxicity of some heavy metals.

Activation of c-Jun N-terminal kinase by cadmium in mouse embryo neural cells in vitro

Members of the c-Jun NH(2)-terminal kinase (JNK) signalling pathway have been found to be stimulated by a variety of stresses, including heavy metals, hyperthermia, and UV-irradiation. In the present study, we examined whether exposure of micromass cultures of mouse embryonic midbrain cells to a known teratogen, cadmium, leads to the phosphorylation and activation of JNK. Midbrain cells exposed to 0.5, 1, 2, or 4μM cadmium chloride (CdCl(2)) showed a dose-dependent decline in cell numbers, cell viability and differentiation after 5 days. In cells exposed to 4μM CdCl(2) for up to 1h, the level of phosphorylated JNK increased by 15min and peaked at 30min exposure time, as determined by a phospho-specific anti-JNK antibody, while the total amount of JNK protein did not change. This phosphorylated JNK was active, as shown by a corresponding increase in the level of c-Jun phosphorylated on Ser63 in a kinase assay. These results demonstrate that CdCl(2) induces a rapid and transient activation of the JNK pathway in primary embryonic neuron cell cultures.

Comparative investigations of sodium arsenite, arsenic trioxide and cadmium sulphate in combination with gamma-radiation on apoptosis, micronuclei induction and DNA damage in a human lymphoblastoid cell line

In the field of radiation protection the combined exposure to radiation and other toxic agents is recognised as an important research area. To elucidate the basic mechanisms of simultaneous exposure, the interaction of the carcinogens and environmental toxicants cadmium and two arsenic compounds, arsenite and arsenic trioxide, in combination with gamma-radiation in human lymphoblastoid cells (TK6) were investigated. Gamma-radiation induced significant genotoxic effects such as micronuclei formation, DNA damage and apoptosis, whereas arsenic and cadmium had no significant effect on these indicators of cellular damage at non-toxic concentrations. However, in combination with gamma-radiation arsenic trioxide induced a more than additive apoptotic rate compared to the sum of the single effects. Here, the level of apoptotic cells was increased, in a dose-dependent way, up to two-fold compared to the irradiated control cells. Arsenite did not induce a significant additive effect at any of the concentrations or radiation doses tested. On the other hand, arsenic trioxide was less effective than arsenite in the induction of DNA protein cross-links. These data indicate that the two arsenic compounds interact through different pathways in the cell. Cadmium sulphate, like arsenite, had no significant effect on apoptosis in combination with gamma-radiation at low concentrations and, at high concentrations, even reduced the radiation-induced apoptosis. An additive effect on micronuclei induction was observed with 1muM cadmium sulphate with an increase of up to 80% compared to the irradiated control cells. Toxic concentrations of cadmium and arsenic trioxide seemed to reduce micronuclei induction. The results presented here indicate that relatively low concentrations of arsenic and cadmium, close to those occuring in nature, may interfere with radiation effects. Differences in action of the two arsenic compounds were identified.

Influence of cadmium on murine thymocytes: potentiation of apoptosis and oxidative stress

Cadmium (Cd) is a well-known environmental carcinogen and a potent immunotoxicant. It induces thymocyte apoptosis in vitro. However, the mode of action is unclear. In this study, we examined the effect of Cd (10, 25 and 50microM) on mitochondrial membrane potential and caspase-3 as well as oxidative stress markers in murine thymocytes. The cadmium induced apoptosis occurred in a concentration and time dependent manner. The early markers of apoptosis-loss in mitochondrial membrane potential and caspase-3 activation were evident as early as 1.5h by 50microM Cd. Enhanced reactive oxygen species (ROS) generation and glutathione (GSH) depletion were observed at 60min, prior to the lowering of mitochondrial membrane potential. The Cd induced DNA damage as depicted by internucleosomal fragmentation on agarose and histone associated mono- and oligonucleosomes detection by ELISA, corrobated with the apoptotic DNA (sub-G(1) population) and total apoptotic cells by Annexin V binding assay. The number of cells in sub-G(1) population increased to 66% at 50microM Cd concentration and the distribution of early and late apoptotic cells was 47% and 15%, respectively. Addition of N-acetylcysteine and pyrrolidine dithiocarbamate (thiol antioxidants) to the Cd treated cells, lowered the sub-G(1) population, inhibited the ROS generation and raised the GSH levels. Buthionine sulfoximine (GSH depletor) on the other hand, enhanced both the ROS production and the sub-G(1) fraction. These results clearly demonstrate the apoptogenic potential of Cd in murine thymocytes, following mitochondrial membrane depolarization, caspase activation and ROS and GSH acting as critical mediators.

Oxidative stress and apoptotic changes in murine splenocytes exposed to cadmium

Cadmium being a potent immunotoxicant, affects both humoral and cell mediated immunity. However, its effect on spleen is not clearly understood. Hence, to delineate the action of Cd, mouse splenic lymphocytes were exposed to Cd (10, 25 and 50 microM) for 60 min, 1.5, 3, 6 and 18 h. At 6 h, apoptosis was reflected by DNA fragmentation, increased sub-G1 population (apoptotic DNA) and apoptotic cells (Annexin V binding assay). The early stage markers of apoptosis, i.e. decreased mitochondrial membrane potential and caspase-3 activation were observed as early as 1.5 h by the highest dose of Cd (50 microM). Significant ROS production by 25 and 50 microM Cd at 60 min occurred prior to the lowering of mitochondrial membrane potential, suggesting involvement of ROS in causing mitochondrial membrane damage. N-acetylcysteine and pyrrolidine dithiocarbamate (thiol antioxidants) lowered the sub-G(1) population, inhibited the ROS generation and raised the GSH levels induced by Cd. Buthionine sulfoximine (GSH depletor) on the other hand, enhanced the ROS production as well as the sub-G1 fraction. These results imply that ROS is a critical mediator of Cd-induced apoptosis and that cadmium may compromise splenic immune function by accelerating apoptosis.

Effects of cadmium on cell death and cell proliferation in chick embryos

The aim of this study was to examine cell death and cell proliferation in chick embryos destined to have ventral body wall defects as a result of cadmium (Cd) treatment. Embryos in shell-less culture were treated with 50 microL Cd acetate (8.9x10(-5)M Cd2+) at Hamilton-Hamburger (H.-H.) stage 16-17, or with equimolar sodium acetate. TdT-Mediated dUTP nick end labelling (TUNEL) showed the mode of cell death to be apoptosis commencing 4 h after treatment in somites and neural tube. Desquamation also occurred in the peridermal layer of the ectoderm. Cd caused no changes in the S-phase population of any tissue except ectoderm. The peridermal layer of the latter had a 40% reduction in labeling index (LI) 5.25 h after treatment but increased thereafter, being 30% greater than control values at 25.25 h. The occurrence of gross malformation was strongly correlated with the degree of apoptosis and in turn with the extent of peridermal desquamation. Pre-treatment with zinc acetate (10x the dose of Cd) prevented gross malformation, apoptosis and the effect of Cd on peridermal proliferation. We hypothesize that the ventral body wall defect resulting from Cd treatment in chick embryos is the result of changes in the somites perhaps following interruption of a signalling pathway originating in ectoderm.

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.

Sex-specific effects of neonatal exposures to low levels of cadmium through maternal milk on development and immune functions of juvenile and adult rats

Cadmium (Cd) is a major environmental contaminant. Although immunotoxic effects have been associated with Cd exposure, the inconsistency of experimental results underlines the need of an experimental approach more closely related to environmental conditions. We investigated the effects of exposing neonatal Sprague-Dawley rats to environmentally relevant doses of Cd through maternal milk. Dams received 10 parts per billion (ppb) or 5 parts per million (ppm) Cd chloride (CdCl2) in drinking water from parturition until the weaning of the pups. Half of the offspring was sampled at weaning time. The remaining juvenile rats received water without addition of Cd until adulthood. Cd accumulation in kidneys of juvenile rats fed from dams exposed to Cd indicated the transfer of the metal from mother to pups through maternal milk. This neonatal exposure resulted in decreased body, kidney and spleen weights of just weaned females but not of males. This effect was more pronounced in the less exposed females fed from dams exposed to 10 ppb Cd, which also displayed lower hepatic metallothionein-1 (MT-1) mRNA levels. The effect of Cd exposure on body and organ weights did not persist to adulthood. In contrast, we observed gender-specific effects of neonatal Cd exposure on the cytotoxic activity of splenic NK-cells of both juvenile and adult rats. Cd also strongly inhibited the proliferative response of Con A-stimulated thymocytes in both male and female adult rats 5 weeks after the cessation of Cd exposure. These immunotoxic effects were observed at doses much lower than those reported to produce similar effects when exposure occurred during adulthood. In conclusion, neonatal exposures to environmentally relevant levels of Cd through maternal milk represent a critical hazard liable to lead to both transitory and persistent immunotoxic effects.

Cadmium induced apoptotic changes in chromatin structure and subphases of nuclear growth during the cell cycle in CHO cells

CHO cells were grown in the presence of 1 mu M CdCl(2) and subjected to ATP-dependent replicative DNA synthesis after permeabilization. By decreasing the density of the cell culture replicative DNA synthesis was diminishing. At higher than 2 x 10(6) cell/ml concentration Cd had virtually no effect on the rate of DNA replication. Growth at higher cell concentrations could be suppressed by increasing Cd concentration. After Cd treatment cells were synchronized by counterflow centrifugal elutriation. Cadmium toxicity on cell growth in early and mid S phase led to the accumulation of enlarged cells in late S phase. Flow cytometry showed increased cellular and nuclear sizes after Cd treatment. As the cells progressed through the S phase, 11 subpopulations of nuclear sizes were distinguished. Apoptotic chromatin changes were visualized by fluorescent microscopy in a cell cycle dependent manner. In the control untreated cells the main transitory forms of chromatin corresponded to those we have published earlier (veil-like, supercoiled chromatin, fibrous, ribboned structures, chromatin strings, elongated prechromosomes, precondensed chromosomes). Cadmium treatment caused: (a) the absence of decondensed veil-like structures and premature chromatin condensation in the form of apoptotic bodies in early S phase (2.2-2.4 average C-value), (b) the absence of fibrous structures, the lack of supercoiled chromatin, the appearance of uncoiled ribboned chromatin and perichromatin semicircles, in early mid S phase (2.5-2.9 C), (c) the presence of perichromatin fibrils and chromatin bodies in mid S phase (2.9-3.2 C), (d) early intra-nuclear inclusions, elongated forms of premature chromosomes, the extrusion and rupture of nuclear membrane later in mid S phase (3.3-3.4 C), (e) the exclusion of chromatin bodies and the formation of clusters of large-sized perichromatin granules in late S phase (3.5-3.8 C) and (f) large extensive disruptions and holes in the nuclear membrane and the clumping of incompletely folded chromosomes (3.8-4. C).

Mercury impairment of mouse thymocyte survival in vitro: involvement of cellular thiols

Heavy metals are well known to be able to induce immunotoxicity, but comparative metal studies related to apoptosis have not been conducted. In the present study, the effects of arsenic, cadmium, gold, lead, manganese, and mercury on thymocytes from BALB/c mice were analyzed. Thymic cells were cultured for 3-24 h in vitro in the absence or presence of metal, and markers of apoptosis or cell death, including annexin V binding, DNA loss/oligonucleosomal fragmentation, 7-amino-actinomycin D uptake (loss of impermeance), changes of the mitochondrial membrane potential (JC-1 fluorescence), and Western analysis of cellular thiols, were assayed. Mercury (Hg) was the only metal shown to be consistently toxic with the dose and times utilized. Cadmium (Cd) was the only other metal tested that also produced some significant level of DNA loss; however, the induction of apoptosis by Cd was not as consistent as that observed with Hg. When Hg was added with 2-mercaptoethanol (2-ME), Hg produced greater toxicity. Endogenous DNA synthesis by thymocytes was immediately inhibited by Hg and Hg + 2-ME. The Hg + 2-ME-induced apoptosis appeared to be associated with altered levels of cellular thiols, in that glutathione (GSH) depletion was significant in comparison to the non-metal control and Hg alone. The increased Hg-induced toxicity in the presence of 2-ME likely was due to the ability of 2-ME to enhance (10- to 20-fold) the cellular uptake of Hg. Western analysis with biotin maleimide demonstrated that Hg + 2-ME and to a lesser extent the positive control dexamethasone eliminated many reactive thiols; the major thiol-reactive protein still reactive with the maleimide probe had an approximate Molecular Mass of 45 kD. Surprisingly, Hg alone enhanced the expression of this thiol-expressing protein, which by Mass Spectrometry (MS)/MS analysis was shown to be beta-actin. Hg also produced the appearance of yet to be identified new proteins. Based on the results with Hg + 2-ME, it is suggested that numerous protein thiols participate in maintenance of cell survival and their loss is associated with apoptosis. The increased expression of new thiol-reactive proteins or thiol-reactive proteins with altered electrophoretic profiles needs to be further investigated. However, the enhanced toxicity attributed to Hg + 2-ME suggests that increased intracellular oxidative stress, observed as increased depletion of GSH, is responsible for the accelerated cell death.

Heme oxygenase-1-mediated partial cytoprotective effect by NO on cadmium-induced cytotoxicity in C6 rat glioma cells

Heme oxygenase-1 (HO-1) is a 32-kDa stress induced enzyme that degrades heme to carbon monoxide (CO) and biliverdin. By employing RT-PCR and Western blotting techniques, we have examined the HO-1 induction in C6 glioma cells that were treated with cadmium chloride (CdCl(2)) or spermine NONOate (SPER/NO). By employing a cell viability assay, we have also examined the cytoprotective effect of HO-1 induction against the cytotoxicity caused by toxic dose of CdCl(2). In C6 glioma cells exposed to CdCl(2), expression of HO-1 (mRNA and protein) was increased in a dose- and time-dependent manner. Nitric oxide (NO) generated from SPER/NO very rapidly increased HO-1 mRNA expression in the C6 glioma cells. The induction of HO-1 by SPER/NO protected the cells from toxic dose of CdCl(2). The up-regulation of HO-1 mRNA expression by CdCl(2) was inhibited by a pre-incubation of the cells with actinomycin D, a potent inhibitor of mRNA transcription. Upon the inhibition of elevated HO-1 mRNA expression by the use of zinc protoporphyrin IX (ZnPP), an inhibitor of HO activity, the change of HO-1 mRNA expression by ZnPP was not observed. Thus, the glial cell may respond to CdCl(2) toxicity by enhancing the HO-1 expression in its effort to minimize the CdCl(2)-derived oxidative damage, and to survive. In the glioma cells, when the HO-1 expression was elevated by a prior incubation with SPER/NO, the cell viability against the cytotoxicity of CdCl(2) was significantly increased. When the results of our experiment are taken together, we discovered that NO provided a rapid enhancement of HO-1 expression, and it provided a protective effect against CdCl(2)-derived oxidative injury in the C6 rat glioma cells.

Oxidative stress and apoptosis in metal ion-induced carcinogenesis

Epidemiological evidence suggests that exposure to certain metals causes carcinogenesis. The mechanisms of metal-induced carcinogenesis have been pursued in chemical, biochemical, cellular, and animal models. Significant evidence has accumulated that oxidative stress may be a common pathway in cellular responses to exposure to different metals. For example, in the last few years evidence in support of a correlation between the generation of reactive oxygen species, DNA damage, tumor promotion, and arsenic exposure has strengthened. This article summarizes the current literature on metal-mediated oxidative stress, apoptosis, and their relation to metal-mediated carcinogenesis, concentrating on arsenic and chromium.