Cadmium sensitivity, uptake, subcellular distribution and thiol induction in a marine diatom: Recovery from cadmium exposure

Studies in the recovery from metal stress and the tolerance development to metal exposure of aquatic organisms are important for the understanding of epidemic pollution. In this study, the responses of a marine diatom, Thalassiosira nordenskioeldii, following recovery from environmental cadmium (Cd) stress were investigated. The diatoms were exposed to different concentrations of Cd for 7 days, and were then allowed different periods of time to recover. The Cd sensitivity increased after recovery from Cd stress, followed by a gradual restoration. The extent of restoration depended on both the recovery time and the environmental Cd stress during the exposure period. A complete restoration of Cd tolerance proved to be impossible for cells pre-exposed to High-Cd. The Cd cellular burden and subcellular Cd concentration decreased to the control level within the first day of recovery, indicating that the elevated sensitivity may have been due to the accumulation of functional damage caused by Cd exposure instead of a result of physical Cd accumulation. The rapid change in phytochelatins (PC) to both the increase in and the withdrawal of environmental Cd stress made it a good quantitative bioindicator of environmental Cd contamination. However, the relationships between Cd distribution in the metal sensitive fraction (MSF-Cd) or intracellular Cd to thiol ratio (intra-Cd/PC-SH) and the relative change in the median inhibition [Cd²⁺] ([Cd²⁺]-based-IC₅₀, i.e., Cd sensitivity) differed for the various exposure and recovery periods tested. Our study suggests that more attention should be given to the recovery of aquatic organisms from episodic metal exposure.     

Relationships between subcellular distributions of cadmium and perturbations in reproduction in the polychaete Neanthes arenaceodentata

The accumulation and subcellular distribution of Cd in the polychaete worm, Neanthes arenaceodentata, were examined following an eleven-week period of exposure to a range of free cadmium ion activities, [Cd²⁺]. The accumulation of Cd in N. arenaceodentata was directly proportional to [Cd²⁺] in seawater at lower concentrations (10⁻¹² M to 10⁻¹⁰ M) but deviated from proportionality at higher concentrations (10⁻⁹ M and 10⁻⁸ M). This deviation in proportionality at higher [Cd²⁺] was attributable to a relative increase in the concentration of metal associated with the metallothionein and the very low molecular weight metal-ligand pools of the cytosol.Reproductive potential was also monitored in these organisms to examine the ecological significance of Cd accumulation and shifts in its subcellular distribution. Perturbations in reproduction were observed at 10⁻⁸ M [Cd²⁺] which coincided with the deviation in proportionality of Cd accumulation and increased accumulation of Cd in the cytosol.     

Identification of subcellular organelles involved in Ba2+- and Cd2+-induced adrenomedullary secretion

To determine which subcellular organelles of bovine adrenal medulla are mainly involved in catecholamine secretion evoked by Ba²⁺ or Cd²⁺, glands were stimulated with these trace metals and subsequently subcellular fractions were assayed for Ba or Cd. Media of varying pH were used since low H+ concentrations are thought to promote Ba²⁺ and Cd²⁺ penetration into adrenal medulla. Of all the adrenomedullary fractions isolated, only the microsomes contained significantly more Cd when exposure to Cd²⁺ was accomplished at the high pH, and only mitochondrial Ba was enhanced after exposure to Ba²⁺ at the high pH. Furthermore, a significant correlation was found between adrenal catecholamine release and residual microsomal Cd. Similary, adrenal catecholamine release by Ba²⁺ was proportional to the Ba content of mitochondria. Since Cd and Ba levels in tissue fractions were determined only after a 15-min washout of the adrenals with trace metal-free Locke's solution, residual Cd and Ba in microsomes and mitochondria, respectively, probably represent metallic cations removed from the cytoplasm during termination of the secretory response. It is therefore proposed that microsomal structures remove Cd²⁺ from the cytoplasm to limit Cd²⁺-induced adrenal catecholamine release and that mitochondria remove Ba²⁺ from adrenomedullary cytoplasm to terminate Ba²⁺-induced catecholamine release.     

Efficiency of cadmium chelation by phytochelatins in Nitzschia palea (Kützing) W. Smith

Phytochelatins (PCs) are thiol-rich peptides, enzymatically synthesized by plants and algae under exposure to certain metals (Cd, Pb, Zn, Ag, As, Cu). Due to their ability to bind metal ions, they play an important role in the cellular detoxification, forming stable metal–PC complexes that minimize the intracellular deleterious effects of metals. The aim of the present work was to evaluate the efficiency of PC–Cd chelation in the freshwater diatom Nitzschia palea under 0, 0.1 and 0.2 mg Cd L^?1, which induced different levels of oxidative stress. This objective was accomplished by the isolation of PC–Cd complexes through size exclusion chromatography. Two peaks were identified, corresponding to high molecular weight (HMW) and low molecular weight (LMW) complexes. In each of the complexes, Cd was quantified by inductively coupled plasma-mass spectrometry, thiol composition was determined by HPLC analysis and the efficiency of Cd chelation calculated by –SH/Cd ratios in HMW and LMW complexes at both Cd concentrations. Results showed that the majority of intracellular Cd was complexed with PCs (75.2–91.2 %). PCs-binding efficiency in this diatom species was higher at HMW than at LMW complexes and enhanced with the increase of Cd concentration exposure. Our work evidenced the important role of PCs as the main intracellular tolerance mechanism in this species. The efficiency increase of Cd–PC binding is related to the increment of PCs synthesis and to the number of Cd ions coordinately bonded to –SH groups in LMW and HMW complexes.     

Metallothionein accumulation in response to cadmium in a clonal rat liver cell line

RLC cells, a clonal line of cells derived from rat liver, accumulate ¹⁰⁹Cd in a unique bound form in response to exposure to Cd²⁺. Cadmium administration also causes increased incorporation of [³⁵S]cystine into a chromatographically distinct macromolecule. The ¹⁰⁹Cd-binding activity and the macromolecule preferentially labeled by [³⁵S]cystine cochromatograph both on gel filtration and ion exchange columns. In addition, the Cd²⁺ responsive [³H]cystine-labeled moiety of RLC cells cochromatographs in both systems with rat liver [³⁵S]cystine metallothionein labeled in response to Cd²⁺ challenge in vivo. These data suggest that RLC cells are able to accumulate authentic metallothionein in culture in response to Cd²⁺ challenge. Time course and concentration data for metallothionein accumulation and labeling with ¹⁰⁹Cd and [³⁵S]cystine are presented. RLC cells in culture appear to be able to accumulate Cd²⁺ into metallothionein at a rate comparable to rat liver tissue in vivo when both systems are maximally activated.     

Cadmium-induced inflammatory responses in cells relevant for lung toxicity: Expression and release of cytokines in fibroblasts,epithelial cells and macrophages

Inhalation is an important route of cadmium (Cd) exposure, and the lung is considered to be one of the main target organs of Cd toxicity. Pulmonary inflammation seems to be involved in development of many lung diseases. In the present study we show that Cd²⁺ at fairly low concentrations affects gene expression of several different cytokines/chemokines in human M1 fibroblasts. The chemokines CXCL2, CXCL3, IL-8/CXCL8 and CCL26, the pro-inflammatory cytokine IL-6 and the receptor IL-1RL1 were expressed at high levels after exposure to 7 μM Cd²⁺ for 7 h. The expression of some important cytokines was further studied in two different primary cell cultures from rat lungs. Cd²⁺ induced cytokine responses at low concentrations (3–6 μM) and early time-points both in type 2 epithelial cell-enriched cultures and alveolar macrophages. However, the two primary lung cells displayed different patterns of cytokine release. Cd²⁺ induced an increased release of IL-6 and MIP-2/CXCL2 from the epithelial cells and MIP-2, IL-1β and TNF-α from alveolar macrophages. In conclusion, the marked up-regulation of different cytokines in these cell types, that are important in development of lung injury and disease, suggests that inflammation may contribute in Cd-induced lung damage.     

Effects of Ba2+ and Cd2+ on convulsive electroshock sensitivity and 45Ca distribution in brain subcellular fractions in mice

Barium increases the convulsive corneal electroshock sensitivity of mice tested 0.5 hr after Ba²⁺ administration (6.6 and 20 mg/kg, ip) but decreases sensitivity of mice tested 24 hr after Ba²⁺ (2, 6.6, and 20 mg/kg, ip). Twenty-four hours after Cd²⁺ injection (0.34, 1.1, and 3.4 mg/kg, ip) the percentage of mice convulsing after electroshock was decreased, but 0.5 hr after Cd²⁺ was given no alteration of electroshock sensitivity was seen. Doses of Ba²⁺ and Cd²⁺ which alter electroshock threshold were used to determine effects of these ions on ⁴⁵Ca distribution in subcellular fractions of whole mouse brain. Distribution of Ba and Cd in brain subcellular fractions was also determined. Elevated ⁴⁵Ca in synaptosomes 0.5 hr after Ba²⁺ injection may reflect the ability of Ba²⁺ to cause membrane depolarization and influx of calcium, and these effects may be associated with increased electroshock sensitivity. Increased ⁴⁵Ca in brain synaptosomes was correlated with elevated electroconvulsive shock threshold 24 hr after Cd²⁺ administration. Excess Ca²⁺ in cortical neurons may explain the decreased responsiveness of mice to electroconvulsive shock 24 hr after Cd²⁺ treatment. Accumulation of Ba²⁺ in neurons in the CNS also appears to increase electroconvulsive shock threshold.     

Effects of cadmium alone and in combination with low molecular weight chitosan on metallothionein,glutathione‐S‐transferase,acid phosphatase,and ATPase of freshwater crab Sinopotamon yangtsekiense

Cadmium (Cd) is an environmental contaminant showing a variety of deleterious effects, including the potential threat for the ecological environment and human health via food chains. Low molecular weight chitosan (LMWC) has been demonstrated to be an effective antioxidant. Metallothionein (MT) mRNA levels and activities of glutathione‐S‐transferase (GST), superoxide dismutase (SOD), acid phosphatase (ACP), Na⁺,K⁺‐ATPase, and Ca²⁺‐ATPase as well as malondialdehyde (MDA) contents in the gills of the freshwater crab Sinopotamon yangtsekiense were analyzed in vivo in order to determine the injury of Cd exposure on the gill tissues as well as the protective effect of LMWC against this injury. The results showed that there was an apparent accumulation of Cd in the gills, which was lessened by the presence of LMWC. Moreover, Cd²⁺ significantly increased the gill MT mRNA levels, ACP activity and MDA content while decreasing the activities of SOD, GST, Na⁺,K⁺‐ATPase, and Ca²⁺‐ATPase in the crabs relative to the control. Cotreatment with LMWC reduced the levels of MT mRNA and ACP but raised the activities of GST, Na⁺,K⁺‐ATPase, and Ca²⁺‐ATPase in gill tissues compared with the crabs exposed to Cd²⁺ alone. These results suggest that LMWC may exert its protective effect through chelating Cd²⁺ to form LMWC‐Cd²⁺ complex, elevating the antioxidative activities of GST, Na⁺,K⁺‐ATPase, and Ca²⁺‐ATPase as well as alleviating the stress pressure on MT and ACP, consequently protecting the cell from the adverse effects of Cd. © 2012 Wiley Periodicals, Inc. Environ Toxicol 29: 298–309, 2014.     

Cadmium induced oxidative damage and apoptosis in the hepatopancreas of <Emphasis Type="Italic">Meretrix meretrix</Emphasis>

Even trace amounts of cadmium (Cd), a non-essential metal, are known to be toxic to aquatic organisms. Here we investigated the relationship between cadmium ion (Cd²⁺) exposure and oxidative damage and apoptosis in the hepatopancreas of the clam Meretrix meretrix. Clams were exposed to different concentrations of Cd²⁺ (0, 1.5, 3, 6 and 12 mg L^?1) for 5 days. We monitored both antioxidant enzyme activity, including that of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidases (GPx), and levels of malondialdehyde (MDA), glutathione (GSH) and glutathione disulfide (GSSG). Apoptosis of hepatopancreatic cells was detected by DNA laddering and AO/EB double fluorescent staining. The results show that the rate of apoptotis, MDA levels, and caspase-3 activity, increased with Cd²⁺ concentration, whereas GPx activity and the ratio of GSH/GSSG, decreased. SOD and CAT enzyme activity first increased, then decreased, with increasing Cd²⁺ concentration; peak activity of these enzymes was recorded in the 3 mg L^?1 Cd²⁺-treatment group. These results show that Cd-induced oxidative damage can both induce, and aggravate, apoptosis in the hepatopancreatic cells of clams, even at Cd²⁺ concentrations far below the semi-lethal dose for adult clams. The observed changes in caspase-3 activity enhanced significantly at lower Cd²⁺ concentrations, indicating that caspase-3 is a suitable biomarker for heavy metal pollution, especially cadmium pollution, in marine organisms.     

Cd2+ responses of cultured human blood cells

Cd²⁺ cytotoxicity, uptake, and partitioning, and Cd²⁺-induced metallothioneine synthesis were studied in cultured peripheral human blood cells. Mononuclear cells were found to resist relatively high levels of Cd²⁺. Few cells were killed below 50 μm Cd²⁺. Above this value, survival decreased exponentially with dose. The mean LD50 for mononuclear cells cultured in Cd²⁺ for 40 hr was 100 μm. Polymorphonuclear cells (granulocytes) were found to be more resistant, with a significantly higher threshold and LD50, and a more complex dose response.Most of the Cd²⁺ incorporated by blood cells was taken up by nucleated cells. Despite their greater resistance, polymorphonuclear cells incorporated more Cd²⁺ at higher doses (50 to 150 μm) than did mononuclear cells. No Cd²⁺ was bound to metallothioneine in polymorphonuclear cells following exposure to Cd²⁺ for even extended periods of time (18 hr) at high doses of ¹⁰⁹Cd²⁺ (25 μm). Instead Cd²⁺ appeared in a Sephadex G-75 peak of approximately 60,000 Da, as well as in the void peak.No significant amount of preexisting metallothioneine (MT) or metallothioneine mRNA was found in the mononuclear cells. However, MT synthesis was induced rapidly following exposure to Cd²⁺. [¹⁰⁹Cd²⁺]MT appeared within 1 hr following exposure to 50 μm¹⁰⁹Cd²⁺, and MT synthesis rates measured from [³⁵S]cysteine incorporation were found to be maximal within 4 hr.     

Cadmium resistance and content of cadmium-binding protein in two enzyme-deficient mutants of mouse fibroblasts (L-cells)

The toxic Cd²⁺ ion accumulates in mammalian organisms, the main storage organs are apparently the liver and the kidney. In these organs Cd²⁺ is bound to low molecular weight proteins (thioneins) as metallothionein. We describe here the development of resistance to otherwise lethal concentrations of Cd²⁺ by two non-epithelial cell lines, both derived from mouse fibroblasts (L-cells). One of the cell lines (clone ID) is deficient in thymidine kinase and resistant to 5-bromodeoxyuridine, the other (A9) deficient in hypoxanthine-guanine phosphoribosyl transferase and resistant to 8-azaguanine. After stepwise increase in Cd²⁺ concentration, clone 1D cells had apparently normal growth rate in the presence of 100 micromolar Cd²⁺ after 6 months of Cd treatment. The A9 cells were apparently more sensitive to Cd²⁺, after about one year's Cd treatment they had apparently normal growth in the presence of 100 micromolar Cd²⁺. This concentration of Cd²⁺ would kill cells of both cell lines not previously exposed to Cd. In the resistant A9 cells about 40 per cent of the cadmium were bound to a cadmiumbinding protein (Cd-BP) of molecular weight of about 12,000, most probably metallothionein, in the resistant clone 1D cells the corresponding figure was 60 per cent. The non-resistant cell lines had apparently no metallothionein. We have thus found that also non-epithelial cells can synthesize low molecular weight Cd-BP and that there apparently is a good correlation between cadmium resistance and content of Cd-BP.     

Mechanisms of cadmium- and barium-induced adrenal catecholamine release

Different patterns of catecholamine release are produced by perfusion of isolated bovine adrenals with Cd²⁺, Ba²⁺, and Zn²⁺ (5 mm). The action of Zn²⁺ is weak but prolonged. The effect of Cd²⁺ is slow in onset and prolonged in duration compared to that of Ba²⁺. Neither Cd²⁺ nor Ba²⁺ increased release of the cytoplasmic enzyme, lactate dehydrogenase. These ions, therefore, do not disrupt adrenomedullary cells to cause catecholamine release. Neither Ba²⁺ nor Zn²⁺ affected ⁴⁵Ca distribution in subcellular fractions of adrenal medulla. Cadmium ion, however, decreased mitochondrial and increased microsomal and supernatant ⁴⁵Ca²⁺ contents. Mitochondria accumulated relatively large quantities of both cadmium and barium, but chromaffin granules contained twice as much cadmium as barium. Zinc contents were relatively low in all subcellular fractions. It is concluded that Cd²⁺ probably releases adrenal amines by mobilizing mitochondrial Ca and possibly by a direct effect on chromaffin granules. Barium ion does not affect the distribution of adrenomedullary cell Ca, but it probably mimics the action of Ca²⁺ in evoking catecholamine release. The weak effect of Zn²⁺ may be related to limited penetration of cells of adrenal medulla.     

Calmodulin-mediated cadmium inhibition of phosphodiesterase activity,in vitro

Ion-stripped bovine brain calmodulin (CaM) binds 4 moles Cd²⁺ as well as 4 moles Ca²⁺ per mole protein, with similar affinity; in the presence of 1 mM Mg²⁺ the molar binding ratio of CaM for Ca²⁺ decreased to 3, the apparent K_0.5 for Ca²⁺ nearly doubled, but the binding characteristics of CaM for Cd²⁺ were not changed. Saturating concentrations Ca²⁺ did not affect the molar binding ratio of CaM for Cd²⁺, but increased the apparent K_0.5 for Cd²⁺; vice versa, saturating concentrations Cd²⁺ decreased the molar binding ratio for Ca²⁺ to 2 without affecting the apparent K_0.5 for Ca²⁺.CaM-independent phosphodiesterase (PDE) activity was inhibited at [Cd²⁺]>10^–5 M. Cd²⁺-CaM as well as Ca²⁺-CaM activated PDE. However, the Cd²⁺-CaM complex is less effective than the Ca²⁺-CaM complex in stimulating CaM-dependent enzyme activities. Cd²⁺ inhibits Ca²⁺- and CaM-dependent PDE in a competitive way. Introduction of Cd²⁺ in a medium containing Ca²⁺ and CaM may, therefore, result in a reduction of CaM-dependent enzyme stimulation.By its interference with Ca²⁺- and CaM- dependent PDE activity, Cd²⁺ could upset the catabolic pathway of cellular cyclic nucleotide metabolism.     

Cadmium toxicity in tadpoles of <Emphasis Type="Italic">Rhinella arenarum</Emphasis> in relation to calcium and humic acids

Bioassays were carried out to study the differences in cadmium (Cd) toxicity to premetamorphic tadpoles of Rhinella arenarum, in aqueous solutions with variable contents of calcium in the presence and absence of humic acids, and to analyze the relationship between the free Cd²⁺ ion concentrations calculated by chemical modeling and the biological results. The correlation analysis of the free Cd²⁺ concentration calculated by chemical speciation and the analytical Cd yielded a direct relationship between the degree of toxicity and the slope value. The lowest slope was obtained from the treatments with lowest free Cd²⁺ ion concentration and lowest toxicity, whereas the highest slope was obtained from the most toxic treatment. At comparable concentrations of free Cd²⁺, intralarval Cd increased as the Ca in the solution decreased. At equal contents of Ca, in the presence of humic acids, the content of Cd in larvae was higher and the toxicity values lower. The results obtained in this study show that waterborne Ca could offer some protection from metal uptake and accumulation by competitive inhibition in the uptake mechanism that involves active transport via cell membrane. In the systems with humic materials, a certain proportion of the Cd present in the solution was associated to them and thus became less bioavailable.     

Cadmium removal from water by green synthesized nanobioadsorbent [SiO2@DOPP]: Mechanism,isotherms, kinetics and regeneration studies

In this study, dried orange peel powder [DOPP] is chemically modified with nanosilica (SiO₂) employing sonication technique to produce nanobioadsorbent [SiO₂@DOPP]. [SiO₂@DOPP] This nanoadsorbent was evaluated for Cd²⁺ removal from aqueous systems. Successful functionalization of [DOPP] into nanosilica was confirmed by various analytical techniques like XRD, FTIR, SEM, EDX, TEM, DLS, pH_zpc and TGA. XRD, FTIR and EDX confirmed the emergence of new peaks after modification of [DOPP] by nanosilica and adsorption of Cd²⁺ onto [SiO₂@DOPP]. Further, TGA spectrum suggested that [SiO₂@DOPP] nanoadsorbent is thermally more stable than [DOPP]. pH plays a major role to Cd²⁺ adsorption onto [SiO₂@DOPP]. The optimum conditions for Cd²⁺ removal include pH = 6.5 and 0.03g adsorbent dose with 100 min contact time. Different adsorption isotherms models [best fitted-(Langmuir adsorption model)], adsorption kinetics [best fitted–(Pseudo second order and Intraparticle diffusion)] were examined for the removal of Cd²⁺. The maximum monolayer adsorption capacity [q_max] was 142 mg/g. Thermodynamic evaluation indicates the endothermic and spontaneous nature of Cd²⁺ adsorption onto [SiO₂@DOPP]. Furthermore complexation mechanism of Cd²⁺ onto [SiO₂@DOPP] is discussed in detail. The results indicate involvement of functional group interactions, π–metal interactions, proton exchange, chelate complexes and electrostatic interactions during adsorption of Cd²⁺ onto [SiO₂@DOPP]. Based on the results it has been inferred that [SiO₂@DOPP] is a promising nanobioadsorbent to manage environment burden of Cd²⁺ from aqueous systems.     

Metabolism of cadmium in the neonate: Effect of hepatic zinc,copper and metallothionein concentrations on the uptake of cadmium in the rat liver

The accumulation and subcellular distribution of Cd²⁺ (1 mg/kg body wt, i.p.) in the liver of the neonatal rat is age-dependent. At 4 hr after treatment the liver Cd²⁺ contents in the 12-day-old, 20-day-old and adult rat are similar and greater than in the 2-day-old animal. The differences in hepatic Cd²⁺ concentration in the older age groups are consistent with the nonlinear weight gain of the liver in the developing animal. In the hepatic cytosol Cd²⁺ is incorporated into a high molecular weight and metallothionein fractions and transferred from the former to the latter. This process occurs less rapidly with increasing age. The uptake of Cd²⁺ by the whole liver and the hepatic metallothionein is not related to the total liver concentration of Zn²⁺ or copper and is not significantly influenced by the concentration of pre-existing metallothionein or the concentration of thionein-bound Zn²⁺ or copper. The results are discussed in relation to the possible effects of Cd²⁺ on the liver metabolism and tissue distribution of Zn²⁺ and copper in the developing animal.     

Cadmium (Cd2+) exposure differentially elicits both cell proliferation and cell death related responses in SK-RC-45

Cadmium (Cd²⁺) is a major nephrotoxic environmental pollutant, affecting mostly proximal convoluted tubule (PCT) cells of the mammalian kidney, while conditionally Cd²⁺ could also elicit protective responses with great variety and variability in different systems. The present study was designed to evaluate the molecular mechanism of Cd²⁺ toxicity on human PCT derived Renal Cell Carcinoma (RCC), SK-RC-45 and compare its responses with normal human PCT derived cell line, NKE. Exposure of SK-RC-45 cells with different concentrations of CdCl₂ (e.g. 0, 10 and 20 μM) in serum free medium for 24 h generate considerable amount of ROS, accompanied with decreased cell viability and alternations in the cellular and nuclear morphologies, heat shock responses and GCLC mediated protective responses. Also phosphatidylserine externalization, augmentation in the level of caspase-3, PARP, BAD, Apaf1 and cleaved caspase-9 along with decreased expression of Bcl2 and release of cytochrome c confirmed that, Cd²⁺ dose dependently induces solely intrinsic pathway of apoptosis in SK-RC-45, independent of JNK. Furthermore, the non-toxic concentration (10 μM) of Cd²⁺ induced nuclear translocation of Nrf2 and increased expression in the level of HO-1 enzyme suggesting that at the milder concentration, Cd²⁺ induces protective signaling pathways. On the other hand, exposure of NKE to different concentrations of CdCl₂ (e.g. 0, 10, 20, 30 and 50 μM) under the same conditions elevate stronger heat shock and SOD2 mediated protective responses. In contrary to the RCC PCT, the normal PCT derived cell follows JNK dependent and extrinsic pathways of apoptosis. Cumulatively, these results suggest that Cd²⁺ exposure dose dependently elicit both cell proliferative and cell death related responses in SK-RC-45 cells and is differentially regulated with respect to normal kidney epithelia derived NKE cells.     

New insights into the Ca2+-ATPases that contribute to cadmium tolerance in yeast

Cadmium (Cd²⁺) is a toxic heavy metal which triggers several toxic effects in eukaryotes, including neurotoxicity and impaired calcium metabolism. In the model organism Saccharomyces cerevisiae, the best characterized pathway for Cd²⁺ detoxification involves conjugation with glutathione (GSH) and subsequent transport to vacuoles by Ycf1p, an ATPase homologous to human MRP1 (Multidrug resistance associated protein 1). However, Cd²⁺ tolerance also can be mediated by Pmr1p, a Ca²⁺ pump located in the Golgi membrane, possibly through to the secretory pathway. Herein, we showed that inactivation of the PMR1 gene, alone or simultaneously with YCF1, delayed initial Cd²⁺ capture compared to wild-type (WT) cells. In addition, Cd²⁺ treatment altered the expression profile of yeast internal Ca²⁺ transporters; specifically, PMC1 gene expression is induced substantially by the metal in WT cells, and this induction is stronger in mutants lacking YCF1. Taken together, these results indicate that, in addition to Pmr1p, the vacuolar Ca²⁺-ATPase Pmc1p also helps yeast cells cope with Cd²⁺ toxicity. We propose a model where Pmc1p and Pmr1p Ca²⁺-ATPase function in cooperation with Ycf1p to promote Cd²⁺ detoxification.     

Inhibition of the liberation of arachidonic acid by cadmium ions in rabbit alveolar macrophages

The effects of CdCl₂ on the liberation of arachidonic acid (20∶4) from membrane phospholipids of A23187-stimulated rabbit alveolar macrophages and on the activity of phospholipase A₂ (PLA₂) in a cytosolic fraction were studied. Alveolar macrophages were prelabeled with [³H]arachidonic acid (20∶4) and then treated with A23187. This treatment resulted in a remarkable increase in the liberation of [³H]20∶4 from their phospholipids. Exposure of cells to Cd²⁺ inhibited the liberation of [³H]20∶4 in a dose-dependent manner. Liberation of [³H]20∶4 from cell lipids was calcium dependent and the inhibitory effect of Cd²⁺ competed with the stimulatory effect of Ca²⁺. When Ca²⁺ was removed from the incubation medium, Cd²⁺ did not influence the liberation of [³H]20∶4. Entry of⁴⁵Ca²⁺ into cells was enhanced by treatment of A23187. However, Cd²⁺ did not influence the cellular uptake of⁴⁵Ca²⁺. Treatment with A23187 markedly enhanced entry of¹⁰⁹Cd²⁺ into cells. The effect of Cd²⁺ on the activity of phospholipase A₂ was determined with 1-palmitoyl-2-[¹⁴C]arachidonoyl-sn-glycero-3-phosphocholine as substrate. Calcium-dependent activation of PLA₂ was observed and Cd²⁺ inhibited activation in a dose-dependent manner. These results suggest that exposure of alveolar macrophages to Cd²⁺ causes a reduction in the rate of liberation of 20∶4 from cell lipids, as a possible result of the inhibition of PLA₂ activity by Cd²⁺.