Enhanced cadmium cytotoxicity in A549 cells with reduced glutathione levels is due to neither enhanced cadmium accumulation nor reduced metallothionein synthesis

Zinc intoxication induces ferroptosis in A549 human lung cells

Zinc (Zn) is an essential trace metal required for all forms of life, but is toxic at high concentrations. While the toxic effects of high levels of Zn are well documented, the mechanism of cell death appears to vary based on the study and concentration of Zn. Zn has been proposed as an anti-cancer treatment against non-small cell lung cancer (NSCLC). The goal of this analysis was to determine the effects of Zn on metabolism and cell death in A549 cells. Here, high throughput multi-omics analysis identified the molecular effects of Zn intoxication on the proteome, metabolome, and transcriptome of A549 human NSCLC cells after 5 min to 24 h of Zn exposure. Multi-omics analysis combined with additional experimental evidence suggests Zn intoxication induces ferroptosis, an iron and lipid peroxidation-dependent programmed cell death, demonstrating the utility of multi-omics analysis to identify cellular response to intoxicants.

Can thiol compounds be used as biomarkers of aquatic ecosystem contamination by cadmium?

Due to anthropogenic activities, heavy metals still represent a threat for various trophic levels. If aquatic animals are exposed to heavy metals we can obviously observe considerable toxicity. It is well known that an organism affected by cadmium (Cd) synthesize low molecular mass thiol compounds rich in cysteine (Cys), such as metallothioneins (MT) and glutathione (GSH/GSSG). The aim of this study was to summarize the effect of Cd on level of thiol compounds in aquatic organisms, and evaluate that the concentrations of thiol compounds are effective indicators of Cd water pollution and explain their potential use in biomonitoring applications.

Glutathione levels and enzyme activity in the tissues of bank vole Clethrionomys glareolus chronically exposed to a mixture of metal contaminants

The biochemical response to chronic heavy metal exposure was studied in tissues of bank voles Clethrionomys glareolus. Animals were collected from three sites located 4, 8 and 30km from a zinc-lead smelter, the area's main source of metal contamination. Concentrations of Cd, Pb, Zn and Fe were measured in the liver, kidneys and gonads to assess the level of metal intoxication. In response to intoxication, organisms activate detoxification mechanisms which can protect animals from metals' toxicity. Glutathione plays an important role in toxic substance detoxification. Total glutathione (tGSH) and glutathione disulfide (GSSG) were measured in the tissues. Also, the activity of glutathione reductase (GR), glutathione peroxidase (GPX), and glutathione-S-transferase (GST) was measured in the studied tissues. Results indicate that levels of all studied parameters were tissue and site-dependent. Evidence indicates that the most sensitive parameter of metal toxicity for animals living in a chronically contaminated environment is the GSH/GSSG ratio. In our study, the GSH/GSSG ratio was decreased in the liver of animals with high Cd levels. However, the relationship between Pb and the GSH/GSSG ratio was positive in the gonads. Cadmium and lead negatively influenced GPX activity in the liver; this was probably connected with inhibition of the Se-dependent fraction. The relationship between iron and GR activity in the kidney was also negative, but other correlations for iron both in liver and kidney were not significant. Positive correlations between Zn levels and GST and GR activity were found in the gonads of bank voles.

Effect of cadmium on free amino acid, glutathione and ascorbic acid concentrations in two barley genotypes (Hordeum vulgare L.) differing in cadmium tolerance

Hydroponic experiment was carried out to study the effect of three Cd levels on glutathione (GSH), free amino acids (FAA), and ascorbic acid (ASA) concentration in the different tissues of 2 barley cultivars with different Cd tolerance. Cadmium concentration in both roots and shoots increased with external Cd level, while biomass and ASA concentration declined, and Wumaoliuling, a Cd-sensitive genotype was more affected than ZAU 3, a Cd-tolerant genotype. The effect of Cd on GSH concentration was dose- and time-dependent. In the 5 d exposure, root GSH concentration increased in 0.5 microM Cd treatment compared with control, but decreased significantly in 5 microM Cd treatment, irrespective of genotypes. However, in the 10 d exposure, GSH concentration in all plant tissues decreased with increasing Cd levels in the culture medium, and Wumaoliuling was much more affected than ZAU 3. Cadmium treatment greatly altered FAA concentration and composition in plants. The effect of Cd on glutathione (Glu) concentration in roots varied with genotypes. ZAU 3 showed a steady increase in root Glu concentration in both 0.5 and 5 microM Cd treatments, while Wumaoliuling was decreased by 38.0% in 5 microM Cd treatment, compared with the control. The results indicate that GSH and ASA are attributed to Cd tolerance in barley plants, and the relative less reduction in GSH concentration in ZAU 3 under Cd stress relative to the control may account for its higher Cd tolerance.

Cadmium transport through type II alveolar cell monolayers: contribution of transcellular and paracellular pathways in the rat ATII and the human A549 cells

Cadmium (CD) transport in alveolar type II (ATII) cells has been studied using two in vitro models widely used to investigate lung function: primary cultures of rat ATII cells and the human cell line A549. Nonlinear regression analyses of the uptake time-course of (109)Cd revealed: a zero-time accumulation, a fast process of accumulation which proceeds within minutes, and a much slower process which takes hours. This three-step mechanism was characterized by different parameter values under dishes-or filter-growth conditions. A higher initial uptake rate (v(i)) and equilibrium accumulation (A(max)) of (109)Cd were found in the rat ATII cells; these differences were not related to a higher level of adsorption onto the external surface of the cell membrane. Specific transport systems of similar capacity but different affinity (threefold higher in rat cells) were characterized. A significant transepithelial transport of (109)Cd, with similar P(coeff) in both cell models, could not be exclusively related to cellular metal release. Results on 3H-mannitol permeability together with (109)Cd efflux data strongly suggest a greater contribution of the paracellular pathways in Cd transport through A549 cell monolayers. These differences in transport properties between the two lung cell models may modify the dose-response curve for Cd toxicity.

Alterations of tissue glutathione levels and metallothionein mRNA in rainbow trout during single and combined exposure to cadmium and zinc

The objective of this study was to assess the effects of Cd and Zn exposure of rainbow trout (Oncorhynchus mykiss) on (a) hepatic glutathione (GSH) levels; and (b) hepatic and branchial metallothionein (MT) mRNA expression. Juvenile rainbow trout were exposed to waterborne Cd (nominal concentrations: 1.5 or 10 microg Cd l(-1)), Zn (150 or 1000 microg Zn l(-1)) or Cd/Zn mixtures (1.5 microg Cd l(-1) with 200 microg Zn l(-1) or 10 microg Cd l(-1) with 1000 microg Zn l(-1)). After 14 and 28 days of treatment, hepatic concentrations of total glutathione, oxidized glutathione (GSSG) and cysteine were determined by means of fluorometric high performance liquid chromatography (HPLC). Branchial and hepatic expression of MT mRNA was measured by means of semi-quantitative RT-PCR. Exposure of trout to Zn did not result in significantly elevated tissue levels of Zn, whereas Cd accumulation factors changed significantly with time and concentration. Despite of the absence of Zn accumulation, hepatic GSH but not MT mRNA levels were significantly altered in Zn-exposed fish. Cd, on the contrary, affected mainly the MT response but not GSH. Also tissue specific differences in the regulation of the two thiol pools were expressed. The thiol response after exposure to metal mixtures could not be explained by simple addition of the effects of the individual metals. The results indicate that cellular thiol pools show different reaction patterns with respect to specific metals and metal mixtures. Under conditions of long-term, low dose metal exposure, the function of GSH appears to go beyond that of a transitory, first line defense.

Biochemical studies on the toxicity of 1, 1'-dimethyl-4, 4'-bipyridylium dichloride in the rat

The effect of intraperitoneal administration of lethal dose (50 mg/kg) of paraquat on the microsomal cysteine levels in the plasma, liver and lung of adult male Wistar rats has been investigated using Rank Chromaspek amino acid analyzer. The microsomal alanine levels were also determined to help in assessing the extent of paraquat interference with cellular protein. DL-Buthionine-[S,R]-Sulfoximine (BSO) and Diethyl maleate (DEM) were used to potentiate the toxic effect of the bipyridyl. The microsomal cysteine levels were significantly (P < or = 0.05) depressed in the plasma, liver and lung of the paraquat-treated rats compared with the saline-injected group but the alanine levels were not similarly affected. Probably, paraquat poisoning interferes specifically with the cellular cysteine content in the rat. These findings could provide a valuable information on the biochemical mechanism of paraquat intoxication.

Metallothionein and anticancer agents: the role of metallothionein in cancer chemotherapy

Metallothioneins (MTs) are intracellular proteins containing the highest amount of thiol groups within the cytoplasm. These thiol groups are able to bind several cytotoxic agents, such as platinum compounds and alkylating agents. Increased levels of MT are one mechanism of resistance to these anticancer drugs, as intracytoplasmic binding of MT prevents the active molecules from reaching their target, the intranuclear DNA of tumor cells. MT synthesis can easily be induced by physiologic heavy metals such as zinc and copper. Pharmacological modulation of MT levels has been used to increase the MT pool in normal tissues and decrease their susceptibility to the toxicity of anticancer drugs. In the case of tumors arising in the brain, where the inducibility of MT synthesis is low, this approach would allow protection of normal tissues without decreasing the antitumor activity of the cytotoxic agents. The interaction of MT with cytotoxic agents is not limited to covalent binding. A correlation between MT synthesis and amplification of oncogenes such as ras has been reported. Furthermore, the cytotoxic drugs are bound by MT after competition with zinc and copper; these metals are cofactors of numerous metalloenzymes, some of which are involved in the metabolism of nucleic acids. Competitive displacement of these metals might modify nucleic acid metabolism and influence cellular proliferation. On the other hand, increased MT levels could provide a zinc cofactor reserve that increases the cell's reparative potential when faced by DNA damage by cytotoxic agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Buthionine sulfoximine induced growth inhibition in human lung carcinoma cells does not correlate with glutathione depletion

Treatment of A549 human lung carcinoma cells with L-buthionine-[S,R]-sulfoximine (BSO) results concomitantly in cellular glutathione (GSH) depletion and growth inhibition. The nature of BSO effects on cell growth and the relationships between BSO inhibition of cell growth and BSO effects on cellular GSH levels were determined in this study. A dose dependent effect of BSO on cell growth was observed, but this effect was found not to correlate with BSO effects on cellular GSH levels. Treatment with BSO for 60 h at concentrations of 5 and 10 mM was found to deplete cellular GSH at similar rates and to an undetectable level (below 0.5 nmol/mg protein). However, cessation of growth occurred in 10 mM BSO whereas growth continued at better than one half the control rate in 5 mM BSO. The results suggest there may be a distinct threshold level of intracellular GSH (on the order of or less than 0.5 nmol/mg protein) required for cell growth and for cells to protect themselves from the antiproliferative effects of BSO. At a concentration of 10 mM, BSO inhibited both DNA and protein synthesis and arrested growth of A549 cells throughout rather than at a specific phase of the cell cycle. BSO inhibition of growth was not, as indicated by colony-forming efficiency (CFE) and electron microscopy studies, accompanied by indications of cytotoxic effects. A stimulatory effect of 0.1 mM BSO on the growth of A549 cells was found also.

Cellular cadmium responses in subpopulations T20 and T27 of human lung carcinoma A549 cells

Subpopulations T20 and T27, cloned from the human lung carcinoma line A549, differ significantly in their Cd2+ cytotoxic response. T27 has an LC50 of 31 microM Cd2+ and a cytotoxic response threshold of 5 microM Cd2+, whereas the T20s LC50 is 15 microM Cd2+ and there is no observed threshold for cytotoxicity. Cadmium-induced metallothionein (MT) synthesis, cadmium accumulation, glutathione (GSH) content, and Cd2(+)-induced changes in GSH content were studied in T20 and T27 in an attempt to determine the mechanism(s) causing differential cytotoxic response. MT synthesis measured by following Cd2(+)-induced [35S] incorporation into MT was found not to differ between T20 and T27. There is, however, a difference in Cd2+ accumulation between the two subclones. T20 and T27 cells were exposed to 5 microM Cd2+ for different times or to different concentrations of Cd2+ for 8 h. The T27 subline, which is the more Cd2+ resistant, was found to accumulate significantly more Cd2(+)-both as a function of time exposed to Cd2+ and as a function of Cd2+ concentration. The two subpopulations were found to have comparable initial GSH contents, but showed different Cd2(+)-induced changes in [GSH] when the cells were exposed to 5 microM Cd2+. T27 cells maintained their GSH content following Cd2+ exposure but T20 cells showed a Cd2(+)-induced decrease in GSH content. The results indicate that the difference in Cd2+ cytotoxic response between A549--T20 and A549--T27 cells is not attributable to alterations in MT synthesis nor to a difference in initial GSH content. Relative Cd2+ cytotoxicity also does not in these cells correlate with relative Cd2+ accumulation. The fact that T27 cells accumulate more Cd2+ and yet are more Cd2+ resistant than T20 cells suggests that T27 cells have a much more effective non-MT mechanism to handle intracellular Cd2+. This may involve different GSH metabolism and/or yet undefined molecular factors.