Studies on the mechanisms of Ni2(+)-induced cell injury: I. Effects of Ni2+ on microtubules

Effect of Sublethal Nickel Chloride Exposure on Crayfish, Astacus leptodactylus Ovary: An Ultrastructural, Autometallographic, and Electrophoretic Analyses

Cytological responses in different organs of sentinel organisms have proven to be useful tools for characterizing the health status of those organisms and assessing the impact of environmental contaminants. Our study shows that nickel (II) accumulated in both germ cells (oogonia and developing oocytes) and somatic cells (muscle cells, follicle cells) in the Astacus leptodactylus ovary. Muscle cells from ovarian wall show disorganization and the disruption of cytoplasmic microtubules and pyknosis of the cell nucleus. Follicle cells, both those that surround the developing oocytes and also those that are not associated with the oocytes contained within the cytoplasm vacuoles of different sizes, degenerated mitochondria, myelin bodies, disorganized microtubules, and pyknotic nuclei. The most evident pathological phenomenon was the alteration and disorganization of the basal matrix, which separates the ovarian interstitium from ovarian follicles compartment. Exposure to nickel induces cytoplasmic vacuolation in oogonia and developing oocytes, structural alteration of the developing yolk granules and condensation of the nucleoli. Ultrastructural autometallography has shown grains of silver-enhanced nickel inside the cytoplasm of the muscle cells with altered morphology, including the cytoplasm, nucleus, and basal matrix of the follicle cells, and in intracisternal granules and developing yolk granules of the oocytes.

Nickel-induced structural and functional alterations in porcine granulosa cells in vitro

The present study was aimed at investigating the effect of nickel chloride (NiCl2) on secretion of progesterone (P), ultrastructure and apoptosis in porcine granulosa cells. NiCl2 was added to the cells to achieve a Ni(2+) concentration of 62.5, 125, 250, 500 and 1,000 μmol/L. A control group contained no NiCl2 addition. Quantification of P was performed directly from aliquots of the media from control and treated porcine granulosa cells after 48 h of culture using radioimmunoassay. Quantification of apoptotic cells was performed using terminal deoxynucleotidyl transferase dUTP nick end labelling assay, and ultrastructural changes were analyzed using transmission electron microscopy. A concentration-dependent depletion of P production was observed significantly for 1,000 μmol/L NiCl2. The percentage of apoptotic cells was increased in all experimental groups significantly only after addition of 1,000 μmol/L NiCl2. After addition of ≥250 μmol/L NiCl2, a higher incidence of euchromatin was observed. Also, lipid droplets and vacuoles in the cytoplasm increased after addition of ≥250 μmol/L NiCl2. NiCl2 induced the decrease in numbers of mitochondria and smooth endoplasmic reticulum after treatment with ≥500 μmol/L NiCl2. Our findings suggest a negative effect of NiCl2 on steroidogenesis and apoptosis as well as ultrastructure of porcine granulosa cells.

Differential gene expression profile of the calanoid copepod, Pseudodiaptomus annandalei, in response to nickel exposure

To better understand the underlying mechanisms of reactions of copepods exposed to elevated level of nickel, the suppression subtractive hybridization (SSH) was used to elucidate the response of the copepod Pseudodiaptomus annandalei to nickel exposure at the gene level. P. annandale is one of a few copepod species that can be cultured relatively easy under laboratory condition, and it is considered to be a potential model species for toxicity study. In the present study, P. annandalei were exposed to nickel at a concentration of 8.86 mgL(-1) for 24h, after which the RNA was prepared for SSH using unexposed P. annandalei as drivers. A total of 474 clones on the middle scale in the SSH library were sequenced. Among these genes, 129 potential functional genes were recognized based on the BLAST searches in NCBI and Uniprot databases. These genes were then categorized into nine groups in association with different biological processes using AmiGO against the Gene Ontology database. Of the 129 genes, 127 translatable DNA sequences were predicted to be proteins, and the putative amino acid sequences were searched for conserved domains (CD) and proteins using the CD-Search service and BLASTp. Among 129 genes, 119 (92.2%) were annotated to be involved in different biological processes, while 10 genes (7.8%) were classified as an unknown-function gene group. To further confirm the up-regulation of differentially expressed genes, the quantitative real time PCR were performed to test eight randomly selected genes, in which five of them, i.e. α-tubulin, ribosomal protein L13, ferritin, separase and Myohemerythrin-1, exhibited clear up-regulation after nickel exposure. In addition, MnSOD was further studied for the differential expression pattern after nickel exposure and the results showed that MnSOD had a time- and dose-dependent expression pattern in the copepod after nickel exposure. To the best of our knowledge, this is the first attempt to investigate the toxicity effects of nickel on a copepod at molecular level.

Nickel induced structural and functional alterations in mouse Leydig cells in vitro

The present study was aimed at investigating effects of nickel (NiCl(2)) on secretion of testosterone (T), cell viability, ultrastructure and apoptosis in mouse Leydig cells. Testosterone release was measured after 48h of culture with 15.67, 31.25, 62.5, 125, 250, 500 and 1000μmol/L NiCl(2) or without NiCl(2) using radioimmunoassay. Cell viability was assessed by a MTT (metabolic activity assay). Quantification of apoptotic cells was performed using TUNEL assay and the ultrastructural changes were analyzed using transmission electron microscopy. The viability was decreased after addition of ≥250μmol/L NiCl(2). A concentration-dependent depression of T production was observed. The percentage of apoptotic cells was significantly increased only after addition of 125, 250 and 1000μmol/L NiCl(2). After addition of ≥250μmol/L NiCl(2) higher incidence of euchromatin was observed. Lipid droplets and vacuoles in cytoplasm were increased after addition of ≥125μmol/L NiCl(2). NiCl(2) induced decrease in numbers of mitochondria and smooth endoplasmic reticulum after treatment with ≥500μmol/L NiCl(2). Our findings suggest a negative effect of NiCl(2) on steroidogenesis, viability, apoptosis and ultrastructure of mouse Leydig cells.

Adsorption of nickel on husk of Lathyrus sativus: Behavior and binding mechanism

Husk of Lathyrus sativus (HLS) has been found to be a good sorbent for the removal of nickel(II) from its aqueous solution. The adsorption process depends on pH of the solution with an optimum at 5.0, and follows Langmuir isotherm model (correlation coefficient 0.998). Initial adsorption rate is very fast and reaches equilibrium following pseudo-second order kinetics within 60 min. Amino, carboxyl, hydroxyl and phosphate groups of the biomass are involved in chemical interaction with nickel ions as revealed from SEM-EDX and FTIR studies. Chemical modifications of the functional groups of the biosorbent show that amino groups contribute largely (approximately 57%) for the binding of nickel ions and probably undergo chelation through dative bond formation. HLS biomass has been found to adsorb both nickel and cadmium equally from their mixed solution to the extent of approximately 70% indicating the importance of this sorbent in industrial effluent treatment.

Amplification of the Ect2 proto-oncogene and over-expression of Ect2 mRNA and protein in nickel compound and methylcholanthrene-transformed 10T1/2 mouse fibroblast cell lines

Occupational exposure of humans to mixtures of insoluble and soluble nickel (Ni) compounds correlates with increased incidences of lung, sinus, and pharyngeal tumors. Specific insoluble Ni compounds are carcinogenic to animals by inhalation and induce morphological and neoplastic transformation of cultured rodent cells. Our objectives were to (1) understand mechanisms of nickel ion-induced cell transformation, hence carcinogenesis and (2) develop biomarkers of nickel ion exposure and nickel ion-induced cell transformation. We isolated mRNAs from green nickel oxide (NiO), crystalline nickel monosulfide (NiS), and 3-methylcholanthrene (MCA) transformed C3H/10T1/2 Cl 8 cell lines, and determined by mRNA differential display that nine mRNA fragments were differentially expressed between Ni transformed and non-transformed 10T1/2 cell lines. Fragment R2-5 was expressed at higher steady-state levels in the transformed cell lines. R2-5 had 100% sequence identity to part of the coding region of Ect2, a mouse proto-oncogene encoding a GDP-GTP exchange factor. The 3.9-kb Ect2 transcript was expressed at 1.6- to 3.6-fold higher steady-state levels in four Ni transformed, and in two MCA-transformed, cell lines. Ect2 protein was expressed at 3.0- to 4.5-fold higher steady-state levels in Ni-transformed and in MCA-transformed cell lines. The Ect2 gene was amplified by 3.5- to 10-fold in Ni transformed, and by 2.5- to 3-fold in MCA transformed cell lines. Binding of nickel ions to enzymes of DNA synthesis likely caused amplification of the Ect2 gene. Ect2 gene amplification and over-expression of Ect2 mRNA and protein can cause microtubule disassembly and cytokinesis, contributing to induction and maintenance of morphological, anchorage-independent, and neoplastic transformation of these cell lines. Over-expression of Ect2 protein is a useful biomarker to detect exposure to nickel compounds and nickel ion-induced morphological and neoplastic cell transformation.

Nickel (Ni2+) enhancement of microtubule assembly in vitro is dependent on GTP function

Microtubule (MT) assembly in vitro is accompanied by hydrolysis of tubulin-bound GTP at E-site. Ni2+, a human carcinogen, has been shown to markedly perturb the MT system in cultured cells and enhance MT assembly in vitro. To further probe the mechanisms of such multiple Ni2+ damaging actions on MT, we have focused on dissecting the role of the Ni2+/GTP interaction in influencing MT assembly in vitro as monitored by a turbidity assay at A350 at 27 degrees C using purified bovine brain MT proteins containing 162 microM each of Mg2+ and EGTA. MT assembly was initiated by addition of GTP and progressed in a GTP dose-dependent manner. The minimal and optimal exogenous [GTP] required for MT assembly were 15.6 and 500 microM, respectively. Replacement of GTP (25-87%) with increasing [NiCl2] while keeping the sum of [GTP] and [Ni2+] constant at 500 microM enabled MT assembly to proceed with shortened "lags" but reaching the same maximum plateau levels or elongation rates as with 500 microM GTP only. However, in reactions with Ni2+ replacing >94% of GTP, marked inhibition of MT assembly (lower plateaus) occurred. Electron microscopic (EM) examinations showed that MT formed with high Ni2+ substitutions for GTP appeared shorter, more numerous, and resistant to Ca2+ disruption than those assembled with 500 microM GTP only. Notably, in the presence of 500 microM Ni2+ with no GTP added, no typical MT were observed under EM, despite increases in turbidity of the reaction. In addition, the critical concentration of MT proteins required for assembly was also considerably decreased under conditions of Ni2+ replacements of GTP. These results point to an important role of GTP/Ni2+ interaction in modulating the Ni2+ enhancement of MT assembly in vitro.

Construction and characterization of an Escherichia coli strain genetically engineered for Ni(II) bioaccumulation

An Escherichia coli strain that accumulated Ni(II) was constructed by introducing the nixA gene (coding for a nickel transport system) from Helicobacter pylori into JM109 cells that expressed a glutathione S-transferase-pea metallothionein fusion protein. The resulting strain accumulated 15 micromol of Ni(II) per g (dry weight) from a 10 microM Ni(II) solution, four times the level taken up by JM109 cells. Ni(II) accumulation did not require an energy source, was inhibited by only 50% by 0.1 M NaCl, and occurred over the pH range from 3 to 9.

The assembly of Ni2+-actin: some peculiarities

Nickel alters the organisation of highly dynamic cytoskeletal elements. In cultured cells Ni2+ causes microtubule aggregation and bundling as well as microfilament aggregation and redistribution. Here, we have analysed the effect(s) of Ni2+ on in vitro actin polymerisation. Using limited proteolysis by trypsin we have suggested that the regions around Arg-62 and Lys-68 change their conformation following Ni2+ binding to the single high-affinity site for divalent cations in the G-actin molecule. We have found that Ni2+ shortens the lag phase of actin polymerisation and increases the rate of assembly mainly because of an increased elongation rate. Ni2+ has no significant effect on the final plateau of actin polymerisation nor on the actin critical concentration. Electron microscopy revealed that actin filaments polymerised by 2 mM Ni2+ showed some tendency to lateral aggregation, being frequently formed by the cohesion of two or three filaments. Furthermore, they often appeared shorter than those of control as also confirmed by the larger amount of free filament ends as well as the faster depolymerisation rate than control.

Alterations in cytoskeletal protein sulfhydryls and cellular glutathione in cultured cells exposed to cadmium and nickel ions

To understand the mechanisms of Cd2+ and Ni2+ cytotoxicity, we have studied the effects of these two metal ions on the organization of cytoskeletal elements, microtubules (MT) and microfilaments (MF), cytoskeletal protein sulfhydryls and cellular glutathione (GSH) in cultured 3T3 cells. At a metal ion dose that caused 95% inhibition of DNA synthesis, Cd2+ (10 microM, 16 h exposure) induced MT depolymerization whereas Ni2+ (2 mM, 20 h exposure) elicited MT aggregation and bundling. Under these conditions, Cd2+ and Ni2+ also caused MF aggregation and redistribution. Furthermore, exposure of cells to Cd2+ resulted in a dose-dependent increase in cytoskeletal protein sulfhydryls and cellular GSH levels. In contrast, treatment of cells with Ni2+ resulted in a dose-dependent decrease in cytoskeletal protein sulfhydryls as well as cellular GSH content. Time course studies showed that cells exposed to 10 microM Cd2+ exhibited a biphasic response in regulating their cytoskeletal protein sulfhydryls and cellular GSH, e.g. an initial decrease followed by a steady recovery and overshooting upon prolonged incubation. However, restoration of cytoskeletal protein sulfhydryls occurred approximately 2 h after commencement of cellular GSH recovery in Cd(2+)-treated cells. These results suggest that cellular GSH may play an important role in regulating cytoskeletal protein sulfhydryls. On the other hand, decrease of cellular GSH induced by Ni2+ might facilitate oxidation of cytoskeletal protein sulfhydryls and formation of disulfide bonds between individual MT polymers which would favor MT aggregation in Ni(2+)-exposed cells. In addition, we also demonstrated that elevation of cellular GSH in Cd(2+)-treated cells probably resulted from new GSH synthesis.

Metal carcinogenesis: mechanistic implications

Cancer epidemiology has identified several metal compounds as human carcinogens. Recent evidence suggests that carcinogenic metals induce genotoxicity in a multiplicity of ways, either alone or by enhancing the effects of other agents. This review summarizes current information on the genotoxicity of arsenic, chromium, nickel, beryllium and cadmium compounds and their possible roles in carcinogenesis. Each of these metals is distinct in its primary modes of action; yet there are several mechanisms induced by more than one metal, including: the induction of cellular immunity and oxidative stress, the inhibition of DNA metabolism and repair and the formation of DNA- and/or protein-crosslinks.