Cadmium-induced apoptosis in h9c2, a7r5, and c6-glial cell

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.

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.

Effects of cadmium on the glial architecture in lizard brain

The glial cells are positioned to be the first cells of the brain parenchyma to face molecules crossing the blood-brain barrier with a relevant neuroprotective role from cytotoxic action of heavy metals on the nervous system. Cadmium is a highly toxic metal and its levels in the environment are increasing due to industrial activities. This element can pass the blood-brain barrier and have neurotoxic activity. For this reason we have studied the effects of cadmium on the glial architecture in the lizard Podarcis siculus, a significant bioindicator of chemical exposure due to its persistence in a variety of habitats. The study was performed on two groups of lizards. The first group of P. siculus was exposed to an acute treatment by a single i.p. injection (2 mg/kg-BW) of CdCl2 and sacrificed after 2, 7 and 16 days. The second one was used as control. The histology of the brain was studied by Hematoxylin/Eosin and Cresyl/Violet stains while the glial structures were analyzed by immunodetection of the glial fibrillary acidic protein (GFAP), the most widely accepted marker for astroglial cells. Evident morphological alterations of the brain were observed at 7 and 16 days from the injection, when we revealed also a decrease of the GFAP-immunopositive structures in particular in the rhombencephalic ventricle, telencephalon and optic tectum. These results show that in the lizards an acute exposure to cadmium provokes morphological cellular alterations in the brain but also a decrement of the expression of GFAP marker with possible consequent damage of glial cells functions.

In vitro evaluation of cell death induced by cadmium, lead and their binary mixtures on erythrocytes of Common buzzard (Buteo buteo)

Cadmium and lead are persistent and ubiquitous metals that can cause several deleterious effects in living beings. Apoptosis and necrosis are two types of cell death that can be found after in vivo and in vitro exposure to these metals. In this study, isolated red blood cells from living captive Common buzzard (Buteo buteo) were exposed in vitro to different concentrations of lead, cadmium, and the mixture lead-cadmium in a proportion of 1:10 (similar to that found in previous field studies). Data obtained from dose-response curves were used to evaluate the interactive effects of metal mixtures on cell viability. In general, except for the exposure to NOEC, additivity was the most frequently observed response. As described in human, after in vitro exposure, lead was highly accumulated in buzzard erythrocytes, while cadmium accumulation was scarce. Finally, the type of cell death (apoptosis or necrosis) induced by the exposure to different concentrations of these heavy metals and their mixtures was evaluated in the red blood cells. Apoptosis was found to be the main type of cell death observed after cadmium and/or lead exposure. However, this exposure caused an increase in lysis or necrosis, especially if red blood cells were exposed to high doses.

Combined effects of γ-irradiation and cadmium exposures on osteoblasts in vitro

The combined effects of γ-irradiation and cadmium (Cd) exposures on osteoblasts were observed in the present study. Osteoblasts were exposed to γ-irradiation (0.5 Gy) and Cd (0-0.5 μmol/L). Cell viability, alkaline phosphatase (ALP) activity, mineralization ability, cell apoptosis and genes expression of ALP, osteocalcin (OC) and caspase 3 were observed. Low concentrations of Cd exposure had no obvious influence on cell viability, ALP activity and apoptosis. However, low levels of Cd exposure combined with γ-irradiation induced more toxic effects on osteoblasts than those treated with Cd or irradiation alone. High concentrations of Cd combined with irradiation exposure induced more significant inhibition in cell viability, ALP activity and mineralization ability than those exposed to Cd or irradiation alone. Meanwhile, OC and ALP mRNA expression of cells treated with Cd combined with irradiation were down-regulated more significantly than those treated with Cd or irradiation alone. Cd combined with γ-irradiation could obviously enhance osteoblast apoptosis and up-regulated caspase 3 mRNA expression compared with those treated with Cd or irradiation alone. This study indicated that ionizing irradiation can enhance Cd toxic effects on osteoblast viability and differentiation and apoptosis may play an important role in this progress.

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.

Study of cadmium-induced cytotoxicity using two-photon excitation endogenous fluorescence microscopy

We demonstrate that using time-resolved two-photon excitation endogenous fluorescence microscopy, the cadmium (Cd)-induced cellular toxic level can be assessed by the free-to protein-bound reduced nicotinamide adenine dinucleotide (free/bound NADH) ratio in a living cell. NADH fluorescence excited at 730 nm is captured at different times following exposure to cadmium at a variety of concentrations. The temporal characteristics of NADH fluorescence from mitochondrial and nuclear compartments are analyzed, respectively. The results show that cadmium induces a significant increase of the free/bound NADH ratio in mitochondria and nucleus, caused by the inhibition effect on the electron transport chain (ETC) and the stimulating effect on the glycolysis pathway, respectively. It is found that induction of metallothionein (MT) in cells occurs after 4 h of exposure to a sublethal concentration of Cd and reaches a peak at 6 h. More importantly, the increase in MT level can effectively suppress the elevation of the free/bound NADH ratio caused by a subsequent exposure to a higher concentration of Cd, indicating that MT plays a key role in protecting cells from Cd-induced toxicity. Our findings show that the free/bound NADH ratio can potentially be used as a sensitive indicator of toxic and carcinogenic actions induced by Cd.

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.

Manganese-induced apoptosis in rat myocytes

Manganese can be toxic to the heart, causing dysfunction following long exposure. In our experiments, we examined the cytotoxicity of manganese in neonatal rat ventricular myocytes (NRVM) by MTT assays in vitro. Results showed that after incubation in the different concentrations of manganese for 24 h, apparent cytotoxicity was observed. At 500, 1000, and 1500 2 microM of manganese, the percentage of cell viability dropped to 82% +/- 6.13, 78% +/- 5.28, and 66% +/- 4.22, respectively. When cells were treated for 48 h, all concentrations tested exerted toxic effect; especially from 500 to 1500 microM the cell viability dropped from 67% +/- 4.84 to 37% +/- 3.25. Apoptosis in NRVM was then examined by flow cytometry. Results showed that the percentage of apoptotic cells treated with 500 microM of manganese for 24 h increased from 4% +/- 0.84 to 7% +/- 1.16. After 48 h of incubation, this percentage increased to 11% +/- 0.91. There was no significant difference between control groups (0 microM manganese) after 24 and 48 h incubation. The morphological changes of NRVM nuclei were visualized with the fluorescent DNA-binding dye Hoechst33342 after incubation in 500 microM of manganese for 48 h. Compared with normal nuclei, apoptotic nuclei showed the typical features of fragmentation and condensation. To investigate whether there are any apoptotic gene expression changes during apoptosis, we examined the expression level of Bcl-2, Bax, and P53 mRNAs after treatment with 500 microM of manganese for 48 h. The Bcl-2 mRNA expression decreased while the expression of Bax as well as P53 mRNAs increased. These results suggested that manganese cytotoxicity on NRVM could induce apoptosis in NRVM cells. The apoptosis process might involve, and be promoted by, the changes of the expression levels of P53, Bcl-2, and Bax proteins.

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 induced mitochondrial injury and apoptosis in vero cells: Protective effect of diallyl tetrasufide from garlic

Oxidative stress and mitochondrial injury has been implicated in cadmium-induced apoptosis. In this study, we examined the protective effect of diallyl tetrasulfide from garlic on cadmium induced oxidative stress and apoptosis in vero cells. Exposure of vero cells to cadmium (10 microM) for 18 h showed the apoptotic events such as loss of cell viability, alterations in nuclear morphology and decreased mitochondrial membrane potential with significantly increased levels of reactive oxygen species (super oxide anion and hydrogen peroxide). Treatment of vero cells with cadmium (10 microM) and diallyl tetrasulfide (5-50 microg/ml) showed that diallyl tetrasulfide attenuated the cadmium-induced suppression of cell viability in a dose dependent manner and highly significant effect was observed at 40 microg/ml. The nuclei morphological analysis with 4',6-diamidino-2-phenylindole staining confirmed that diallyl tetrasulfide at 40 microg/ml prevented the Cd (10 microM) induced apoptosis. Flow cytometric analysis with 2',7'-dichlorofluorencein diacetate showed that the inhibitory effect of diallyl tetrasulfide (10-40 microg/ml) on reactive oxygen species generation parallel with its effect on cell viability. In addition, diallyl tetrasulfide (40 microg/ml) remarkably reduced the cadmium-induced accumulation of superoxide radical and hydrogen peroxide with in cells. Further, diallyl tetrasulfide significantly protected the cadmium-induced decrease in mitochondrial membrane potential, an indicator of mitochondrial function. Our study suggest that diallyl tetrasulfide affect the reactive oxygen species generation induced by cadmium, and possesses a novel protective effect on the cytolethality associated with mitochondrial injury, which contributes to the antiapoptotic effect of diallyl tetrasulfide against cadmium.