Intracellular Cadmium Concentrations Research Articles

Cadmium detoxification induced by salt stress improves cadmium tolerance of multi-stress-tolerant Pichia kudriavzevii

Heavy metal tolerance of microorganisms is the basis of heavy metal removal by growing cells. In this study, a cross-protection effect generated by salt stress significantly enhanced the cadmium tolerance of multi-stress-tolerant Pichia kudriavzevii. Comparative transcriptome analysis using RNA-Seq linked with physiological and biochemical observation was used to elucidate the underlying mechanisms of the improved cadmium tolerance. The expression of cadmium transport related genes (GSTY2, GLR1, GLO2, YCF1 and YOR1), GSH content and GST activity were elevated by salt stress, suggesting enhanced cadmium conjugation and detoxification in yeast cells. The inhibited cadmium uptake by ZRT1 and enhanced cadmium efflux by YOR1 contributed to the decrease in the intracellular cadmium concentration. The improved expression of antioxidant enzyme genes (SOD1, SOD2, SOD6, CAT1 and PRXIID), along with the enhanced activities of antioxidant enzymes (SOD, CAT and POD) resulted in a decrease in cadmium-induced ROS production, protein carbonylation, lipid peroxidation and cell death. The abundant expression of heat shock protein genes (HSP12, HSP10 and SSC1) and genes related to trehalose synthesis (TPS1 and TSL1) induced by salt stress protected yeast cells against complex stress conditions, contributing to the improved cadmium tolerance. These findings will be useful to develop cadmium-tolerant yeasts for cadmium removal by growing cells.

Induction of cytotoxic and genotoxic damage following exposure of V79 cells to cadmium chloride

Cadmium is a toxic heavy metal with many industrial and commercial uses resulting in widespread environmental pollution. Exposure to cadmium occurs occupationally, through tainted food, tobacco leaves, and the environment. Cadmium exposure has been linked to neurological and respiratory problems and cancer. Past studies have examined cytotoxicity, DNA damage, micronuclei formation, or mutagenesis individually, but no study has examined these endpoints together and correlated them with intracellular cadmium concentrations. This study examines the cytotoxic, genotoxic, and mutagenic effects of cadmium exposure in V79 cells providing a correlation between the induction of DNA damage, the generation of mutations, and intracellular cadmium concentration. Cells exposed to 2.5–40μM cadmium exhibited a concentration-dependent decrease in survival which correlated with increases in PARP cleavage and caspase activity. Cytotoxicity was detected at intracellular cadmium concentrations of 12.9ppb. Exposure to cadmium also resulted in the production of single and double strand breaks and the induction micronuclei and mutations in the Hprt gene. Collectively, this study demonstrates that exposure of V79 cells to cadmium results in the induction of apoptosis which is related to the formation of DNA strand breaks and genotoxic damage.

A blood pressure-associated variant of theSLC39A8gene influences cellular cadmium accumulation and toxicity

Genome-wide association studies have revealed a relationship between inter-individual variation in blood pressure and the single nucleotide polymorphism rs13107325 in the SLC39A8 gene. This gene encodes the ZIP8 protein which co-transports divalent metal cations, including heavy metal cadmium, the accumulation of which has been associated with increased blood pressure. The polymorphism results in two variants of ZIP8 with either an alanine (Ala) or a threonine (Thr) at residue 391. We investigated the functional impact of this variant on protein conformation, cadmium transport, activation of signalling pathways and cell viability in relation to blood pressure regulation. Following incubation with cadmium, higher intracellular cadmium was detected in cultured human embryonic kidney cells (HEK293) expressing heterologous ZIP8-Ala391, compared with HEK293 cells expressing heterologous ZIP8-Thr391. This Ala391-associated cadmium accumulation also increased the phosphorylation of the signal transduction molecule ERK2, activation of the transcription factor NFκB, and reduced cell viability. Similarly, vascular endothelial cells with the Ala/Ala genotype had higher intracellular cadmium concentration and lower cell viability than their Ala/Thr counterpart following cadmium exposure. These results indicate that the ZIP8 Ala391-to-Thr391 substitution has an effect on intracellular cadmium accumulation and cell toxicity, providing a potential mechanistic explanation for the association of this genetic variant with blood pressure.

A Model of Cadmium Uptake and Transport in Caco-2 Cells.

We created a physiologically substantiated kinetic model of cadmium transport and toxicity in intestinal cell model (Caco-2 cells). Transcriptome profiling of Caco-2 cells revealed high content of transporter DMT1 and ZIP14 and intensive expression of some calcium channels of the CACN family. The mathematical model describing three types of transporters, as well as intracellular cadmium binding with metallothionein and excretion through the basolateral membrane allowed us to construct cadmium uptake and transport curves that approximated the previously obtained experimental data. Using the proposed model, we determined toxic intracellular cadmium concentration leading to cell death and impairing the integrity of cell monolayer and described cadmium transport in this case.

Cadmium-induced activation of high osmolarity glycerol pathway through its Sln1 branch is dependent on the MAP kinase kinase kinase Ssk2, but not its paralog Ssk22, in budding yeast.

Cadmium ions disrupt reactive oxygen species/Ca(2+) homeostasis and subsequently elicit cell death and adaptive signaling cascades in eukaryotic cells. Through a functional genomics approach, we have identified deletion mutants of 106 yeast genes, including three MAP kinase genes (HOG1, SLT2, and KSS1), are sensitive to a sublethal concentration of cadmium, and 64 mutants show elevated intracellular cadmium concentrations upon exposure to cadmium. Hog1 is phosphorylated, reaching a peak 30min after the cadmium treatment. Both Sln1 and Sho1 upstream branches are involved in the cadmium-induced activation of high osmolarity glycerol (HOG) pathway. Cadmium-induced HOG activation is dependent on the MAP kinase kinase kinase Ssk2, but not its paralog Ssk22, in the Sln1 branch.

Study the cytotoxicity of different kinds of water-soluble nanoparticles in human osteoblast-like MG-63 cells

Quantum nanoparticles have been applied extensively in biological and medical fields, the cytotoxicity of nanoparticles becomes the key point we should concern. In this paper, the cytotoxicity of three kinds of water-soluble nanoparticles: CdTe, CdTe@SiO2 and Mn:ZnSe was studied. We evaluated the nanoparticles toxicity qualitatively by observing the morphological changes of human osteoblast-like MG-63 cells at different incubation times and colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assays were carried out to detect the cell viability quantitatively. The results showed that CdTe nanoparticles with high concentrations caused cells to die largely while CdTe@SiO2 and Mn:ZnSe nanoparticles had no obvious effect. For further study, we studied the relation between the cell viability and the total cadmium concentration in cells and found that the viability of cells treated with CdTe@SiO2 nanoparticles was higher than that treated with CdTe nanoparticles. We also discovered that the death rate of cells co-incubated with CdTe nanoparticles was proportional to the total intracellular cadmium concentrations.

Enhancement of cadmium bioremediation by endophytic bacterium Bacillus sp. L14 using industrially used metabolic inhibitors (DCC or DNP)

Bioremediations of cadmium by endophytic bacterium (EB) L14 ( Bacillus sp.) in the presence of industrially used metabolic inhibitors (DCC or DNP) were investigated. In the presence of DCC or DNP, the biomass population of EB L14 was greatly inhibited. However, the cadmium removal of EB L14 increased from 73.6% (in the absence of DCC or DNP) to 93.7% and 80.8%, respectively. The analysis of total and intracellular cadmium concentrations during 24 h of incubation indicated that this enhanced cadmium removal was the inhibition effect of DCC or DNP on the cations export resistance system of EB L14. This unique property strongly indicated the superiority of this endophyte for practical application in cadmium bioremediation in the presence of industrially used metabolic inhibitors.

Phytochelatin induction, cadmium accumulation, and algal sensitivity to free cadmium ion in Scenedesmus vacuolatus

Phytochelatins are small, intracellular, metal-binding polypeptides produced by algae on exposure to increased metal concentration in their environment. The aim of the present study was to examine the relationship between phytochelatin concentration, bioaccumulated metal, and sensitivity of algal growth on cadmium exposure. For that purpose, intracellular cadmium concentration and thiol (glutathione, gamma-glutamylcysteine [gammaGluCys], and phytochelatins [PCn]) content were determined in the freshwater green alga Scenedesmus vacuolatus exposed to growth-inhibitory and noninhibitory concentrations of free Cd2+ in the range from 10(-14) to 10(-7) M. The algal growth rate was optimal up to a free Cd2+ concentration of 10(-9) M and then decreased by 40% at higher concentrations. The intracellular cadmium content increased sharply from 0.22 to 746 amol/cell over this free Cd2+ range. At the lowest Cd2+ concentration (control), glutathione was the only detectable thiol (127 amol/cell). With increasing Cd2+, formation of gammaGluCys and phytochelatins from PC2 to PC6 were observed. The predominant oligomer was PC3, with 42 amol/cell at the highest Cd2+ concentration (10(-7) M). The ratio of the concentration of total thiol groups to intracellular cadmium was important for maintaining optimal growth. In contrast, thiol groups from phytochelatins were never measured in excess to intracellular cadmium content.

Heterologously Expressed Bacterial and Human Multidrug Resistance Proteins Confer Cadmium Resistance to Escherichia coli

The human MDR1 gene is induced by cadmium exposure although no resistance to this metal is observed in human cells overexpressing hMDR1. To access the role of MDR proteins in cadmium resistance, human MDR1, Lactococcus lactis lmrA, and Oenococcus oeni omrA were expressed in an Escherichia coli tolC mutant strain which proved to be hypersensitive to cadmium. Both the human and bacterial MDR genes conferred cadmium resistance to E. coli up to 0.4 mM concentration. Protection was abolished by 100 microM verapamil. Quantification of intracellular cadmium concentration by atomic absorption spectrometry showed a reduced cadmium accumulation in cells expressing the MDR genes. Inside-out membrane vesicles of L. lactis overexpressing lmrA displayed an ATP-dependent (109)Cd(2+) uptake that was stimulated by glutathione. An evolutionary model is discussed in which MDR proteins have evolved independently from an ancestor protein displaying both organic xenobiotic- and divalent metal-extrusion abilities.

Investigation of cadmium toxicity on renal epithelial cells using nuclear microprobe analysis

Cadmium is a highly toxic metal that causes well-known severe renal damages. Its toxicity is frequently investigated in vitro using numerous epithelial models. The accumulation and transport of cadmium in cultured renal epithelial cells has been studied by means of nuclear microscopy (micro-PIXE coupled with micro-RBS) for cell monolayer analyses, and by ICP-MS for culture medium analyses. Cell viability, measured by biochemical tests, was used as toxicity indicator. Dependence on cadmium concentration (1–100 μM) and exposure time (1–24 h) was found. Micro-PIXE reveals a strong anti-correlation of intra-cellular cadmium concentration with zinc concentration, a biological metal, suggesting substitution mechanism of both metals.

Toxicity of metal mixtures to a tropical freshwater alga (Chlorella sp.): The effect of interactions between copper, cadmium, and zinc on metal cell binding and uptake

The individual and combined effects of copper, cadmium, and zinc on the cell division rate of the tropical freshwater alga Chlorella sp. were determined over 48 to 72 h. Metal mixtures were prepared based on multiples of their single-metal median effective concentration (EC50) values, i.e., toxic units (TU) using a triangular mixture design with five toxicant levels (0, 0.75, 1.0, 1.25, and 1.5 TU). Single-metal EC50 values after a 72-h exposure were 0.11, 0.85, and 1.4 microM for copper, cadmium, and zinc, respectively. Significant interactions were observed for all metal combinations after 48 and 72 h. An equitoxic mixture of Cu + Cd was more than concentration additive (synergistic) to the growth of Chlorella sp., while combinations of Cu + Zn, Cd + Zn, and Cu + Cd + Zn were all less than concentration additive or were antagonistic. To determine the effect of each metal on the uptake of the other, extracellular (membrane-bound) and intracellular metal concentrations, both alone and in mixtures, were compared. The increased growth inhibition observed for mixtures of Cu + Cd was due to higher concentrations of cell-bound and intracellular copper in the presence of cadmium compared with copper alone (i.e., cadmium-enhanced copper uptake). In contrast, both extra- and intracellular cadmium concentrations were reduced in the presence of copper. In mixtures of Cu + Zn, copper also inhibited the binding and cellular uptake of zinc, which resulted in decreased toxicity. Zinc had no appreciable effect on the uptake of copper by Chlorella sp. Our results suggest that all three metals share some common uptake and transport sites on Chlorella cells and that copper out competes both cadmium and zinc for cell binding. Determination of metal cell distribution coefficients (K(d)) confirmed that K(d) values for cadmium and zinc in single-metal exposures decreased in the presence of copper.

Effect of fetal calf serum on the cadmium clastogenicity

Inconsistent results among reports on cadmium genotoxicity revealed that certain confounding factors might significantly influence the outcomes of assessment. In Chinese hamster ovary (CHO-W8) cells, chromosome aberration induced by six different cadmium compounds was found positively associated with intracellular cadmium concentration. A parallel association was also observed among different CHO strains treated with same cadmium compound, the cadmium acetate. Both the cadmium-induced chromosome aberration and cadmium uptake were influenced by the presence of fetal calf serum (FCS). The presence of 10% FCS during the 2 h treatment period greatly retarded the cellular cadmium uptake, and concurrently reduced the chromosome aberration induction. Other factors such as specific cadmium anion involved and the duration of cadmium treatment period in the investigation also influenced the assessment results of cadmium-induced chromosome aberration. In the protocol with a 2 h pulse treatment, cadmium acetate, chloride and sulfate induced more chromosome aberration than cadmium nitrate, carbonate and oxide. When cadmium was present in the culture of the entire treatment period for 18 h, the results went the opposite way. Cadmium nitrate, carbonate and oxide induced significant chromosome aberration, while other three cadmium compounds gave negative results. Cadmium compounds did not induce significant SCE at the same dose level that yielded significant chromosome aberration induction, either in the protocol with the short pulse or long treatment period.

Cell culture studies of menkes kinky hair disease

The dose response as well as kinetics of uptake and retention of copper and cadmium of normal and Menkes kinky hair disease (MKHD) cultured fibroblasts are described. In basal culture medium, intracellular copper concentration in MKHD fibroblasts was approximately 3 times that of control cultures. The intracellular copper concentration of MKHD cells was significantly higher than that of normal fibroblasts at medium copper concentrations below 20 μg/ ml. Death of MKHD cells occurred at medium copper concentrations between 15 and 20 μg/ml with an intracellular copper level 3 times that at basal medium. Normal cells died at medium copper concentration above 30 μg/ml with an intracellular copper concentration 19 times that at basal medium. These observations suggested the existence of a regulatory mechanism for maintenance and control of intracellular copper in normal fibroblasts which is effective at medium copper concentrations below 30 μg/ml. This system is defective in MKHD fibroblasts. In basal medium MKHD and normal fibroblasts had similar intracellular cadmium concentrations; however, at higher medium cadmium concentrations MKHD cells had increased intracellular cadmium levels. The uptake of both 64Cu and 109Cd was significantly higher in MKHD cells than in normal cells, indicating that the uptake of 64Cu and 109Cd is not impaired in MKHD cells. A higher retention of 64Cu was observed in MKHD cells at both 37°C and 4°C. No obvious trend, however, was observed in the difference of retention of 109Cd between MKHD and normal cells. An impairment of egress of copper in MKHD cells is implicated by these results.