Cadmium is a ubiquitous toxic metal and environmental pollutant. More and more studies have shown that cadmium exposure can damage lung function. Alveolar epithelial cells (AECs) are structural cells that maintain the stability of lung function. The injury of AECs is an essential determinant of many lung diseases. In the lung, cadmium accumulation can cause damage to AECs. However, the specific mechanism is still unclear. This study aimed to explore the key mechanism underlying the injury of AECs caused by cadmium exposure.

The main modes of death of AECs induced by cadmium exposure were evaluated in vivo and in vitro. Transcriptomic changes of AECs induced by cadmium exposure were analyzed using RNA-sequence. Mitochondrial ROS scavengers (mitoQ), voltage-dependent anion channel 1 (VDAC1) oligomer inhibitor (VBIT4), and cyclic GMP-AMP synthase (cGAS) inhibitor (RU.521) were used to assess whether cadmium exposure triggered pyroptosis of AECs by inducing mitochondrial stress to activate the cGAS-STING-NLRP3 axis.

In this study, the expression of pyroptosis-related proteins was significantly up-regulated in the cadmium-exposed AECs, while the expression of apoptosis, necroptosis, and ferroptosis-related proteins had no significant up-regulated. The pan-caspase inhibitor ZVAD-FMK significantly reduced cell death. Thus, our research indicates that pyroptosis is the primary type of AEC death exported to cadmium. Mechanistically, RNA-seq and Western Blot results showed that cadmium exposure activated the cGAS-STING pathway in AECs and promoted pyroptosis by activating the NLRP3 inflammasome. Further investigation of the mechanism found that cadmium exposure caused mitochondrial oxidative stress, which led to mtDNA leakage into the cytoplasm and activated the cGAS-STING pathway. In addition, inhibition of the cGAS-STING pathway significantly alleviated lung injury induced by cadmium exposure in mice.

Our study confirmed that pyroptosis of AECs was a vital mechanism of lung injury after cadmium exposure in a cGAS-STING-dependent manner, which may provide a new target for the treatment of lung diseases induced by cadmium exposure.

Recent advances have uncovered the non-random distribution of 7, 8-dihydro-8-oxoguanine (8-oxoGua) induced by reactive oxygen species, which is believed to have epigenetic effects. Its cognate repair protein, 8-oxoguanine DNA glycosylase 1 (OGG1), reads oxidative substrates and participates in transcriptional initiation. When redox signaling is activated in small airway epithelial cells, the DNA repair function of OGG1 is repurposed to transmit acute inflammatory signals accompanied by cell state transitions and modification of the extracellular matrix. Epithelial-mesenchymal and epithelial-immune interactions act cooperatively to establish a local niche that instructs the mucosal immune landscape. If the transitional cell state governed by OGG1 remains responsive to inflammatory mediators instead of differentiation, the collateral damage provides positive feedback to inflammation, ascribing inflammatory remodeling to one of the drivers in chronic pathologies. In this review, we discuss the substrate-specific read through OGG1 has evolved in regulating the innate immune response, controlling adaptations of the airway to environmental and inflammatory injury, with a focus on the reader function of OGG1 in initiation and progression of epithelial to mesenchymal transitions in chronic pulmonary disease.

Cadmium (Cd) is a widespread environmental pollutant and carcinogen. Although the exact mechanisms of Cd-induced carcinogenesis remain unclear, previous acute/chronic Cd exposure studies have shown that Cd exerts its cytotoxic and carcinogenic effects through multiple mechanisms, including interference with the DNA repair system. However, the effects of post-chronic Cd exposure remain unknown. Here, we establish a unique post-chronic Cd-exposed human lung cell model (the "CR0" cells) and investigate the effects of post-chronic Cd exposure on the DNA repair system. We found that the CR0 cells retained Cd-resistant property even though it was grown in Cd-free culture medium for over a year. The CR0 cells had lasting DNA damage due to reduced DNA repair capacity and an aberrant DNA repair gene expression profile. A total of 12 DNA repair genes associated with post-chronic Cd exposure were identified, and they could be potential biomarkers for identifying post-chronic Cd exposure. Clinical database analysis suggests that some of the DNA repair genes play a role in lung cancer patients with different smoking histories. Generally, CR0 cells were more sensitive to chemotherapeutic (cisplatin, gemcitabine, and vinorelbine tartrate) and DNA damaging (H₂O₂) agents, which may represent a double-edged sword for cancer prevention and treatment. Overall, we demonstrated for the first time that the effects of post-chronic Cd exposure on human lung cells are long-lasting and different from that of acute and chronic exposures. Findings from our study unveiled a new perspective on Cd-induced carcinogenesis-the post-chronic exposure of Cd. This study encourages the field of post-exposure research which is crucial but has long been ignored.

Occupational and environmental exposure to cadmium is associated with the development of urothelial cancer. The metallothionein (MT) family of genes encodes proteins that sequester metal ions and modulate physiological processes, including zinc homeostasis. Little is known about the selectivity of expression of the different MT isoforms. Here, we examined the effect of cadmium exposure on MT gene and isoform expression by normal human urothelial (NHU) cell cultures. Baseline and cadmium-induced MT gene expression was characterized by next-generation sequencing and RT-PCR; protein expression was assessed by Western blotting using isoform-specific antibodies. Expression of the zinc transporter-1 (SLC30A1) gene was also assessed. NHU cells displayed transcription of MT-2A, but neither MT-3 nor MT-4 genes. Most striking was a highly inducer-specific expression of MT-1 genes, with cadmium inducing transcription of MT-1A, MT-1G, MT-1H, and MT-1M. Whereas MT-1G was also induced by zinc and nickel ions and MT-1H by iron, both MT-1A and MT-1M were highly cadmium-specific, which was confirmed for protein using isoform-specific antibodies. Protein but not transcript endured post-exposure, probably reflecting sequestration. SLC30A1 transcription was also affected by cadmium ion exposure, potentially reflecting perturbation of intracellular zinc homeostasis. We conclude that human urothelium displays a highly inductive profile of MT-1 gene expression, with two isoforms identified as highly specific to cadmium, providing candidate transcript and long-lived protein biomarkers of cadmium exposure.

Reactive oxygen species (ROS)-induced DNA damage occurs in heavy metal exposure, but the simultaneous effect on DNA repair is unknown. We investigated the influence of co-exposure of lead (Pb), cadmium (Cd), and mercury (Hg) on 8-hydroxydeoxyguanosine (8-OHdG) and human repair enzyme 8-oxoguanine DNA glycosylase (hOGG1) mRNA levels in exposed children to evaluate the imbalance of DNA damage and repair. Children within the age range of 3-6 years from a primitive electronic waste (e-waste) recycling town were chosen as participants to represent a heavy metal-exposed population. 8-OHdG in the children's urine was assessed for heavy metal-induced oxidative effects, and the hOGG1 mRNA level in their blood represented the DNA repair ability of the children. Among the children surveyed, 88.14% (104/118) had a blood Pb level >5 μg/dL, 22.03% (26/118) had a blood Cd level >1 μg/dL, and 62.11% (59/95) had a blood Hg level >10 μg/dL. Having an e-waste workshop near the house was a risk factor contributing to high blood Pb (r _s  = 0.273, p < 0.01), while Cd and Hg exposure could have come from other contaminant sources. Preschool children of fathers who had a college or university education had significantly lower 8-OHdG levels (median 242.76 ng/g creatinine, range 154.62-407.79 ng/g creatinine) than did children of fathers who had less education (p = 0.035). However, we did not observe a significant difference in the mRNA expression levels of hOGG1 between the different variables. Compared with children having low lead exposure (quartile 1), the children with high Pb exposure (quartiles 2, 3, and 4) had significantly higher 8-OHdG levels (β _Q2 = 0.362, 95% CI 0.111-0.542; β _Q3 = 0.347, 95% CI 0.103-0.531; β _Q4 = 0.314, 95% CI 0.087-0.557). Associations between blood Hg levels and 8-OHdG were less apparent. Compared with low levels of blood Hg (quartile 1), elevated blood Hg levels (quartile 2) were associated with higher 8-OHdG levels (β _Q2 = 0.236, 95% CI 0.039-0.406). Compared with children having low lead exposure (quartile 1), the children with high Pb exposure (quartiles 2, 3, and 4) had significantly higher 8-OHdG levels.

Cadmium (Cd) is a highly toxic heavy metal and has spread widely in the environment in recent decades. This review summarizes current knowledge about Cd contamination of leafy vegetables, its toxicity, exposure, health risks, and approaches to reducing its toxicity in humans. Leafy vegetable consumption has been identified as a dominant exposure pathway of Cd in the human body. An overview of Cd pollution in leafy vegetables as well as the main sources of Cd is given. Notable estimated daily intakes and health risks of Cd exposure through vegetable consumption for humans are revealed in occupational exposure areas and even in some reference areas. Vegetable consumption is one of the most significant sources of exposure to Cd, particularly in occupational exposure regions. Therefore, numerous approaches have been developed to minimize the accumulation of Cd in leafy vegetables, among which the breeding of Cd pollution-safe cultivars is one of the most effective tools. Furthermore, dietary supplements from leafy vegetables perform positive roles in alleviating Cd toxicity in humans with regard to the effects of essential mineral elements, vitamins and phytochemicals taken into the human body via leafy vegetable consumption.

Gene-environment interactions have long been known to play an important role in complex disease aetiology, such as nasal polyposis (NP). The present study supports the concept that DNA repair gene polymorphisms play critical roles in modifying individual susceptibility to environmental diseases. In fact, we investigated the role of polymorphisms in DNA repair genes and cadmium as risk factors for Tunisian patients with NP. To the best of our knowledge, this is the first report on the impact of combined effects of cadmium and ERCC3 7122 A>G (rs4150407), ERCC2 Lys751Gln (rs13181) and XRCC1 Arg399Gln (rs25487) genes in the susceptibility to NP disease. Significant associations between the risk of developing NP disease and ERCC2 [odds ratio (OR) = 2.0, 95 % confidence interval (CI) = 1.1-3.7, p = 0.023] and ERCC3 (OR = 2.2, 95 % CI = 1.2-4.1, p = 0.013) genotypes polymorphisms were observed. Blood concentrations of Cd in NP patients (2.2 μg/L) were significantly higher than those of controls (0.5 μg/L). A significant interaction between ERCC3 (7122 A>G) polymorphism and blood-Cd levels (for the median of blood-Cd levels: OR = 3.8, 95 % CI = 1.3-10.8, p = 0.014 and for the 75th percentiles of blood-Cd levels: OR = 2.7, 95 % CI = 1.1-7.2, p = 0.041) was found in association with the risk of NP disease. In addition, when we stratified ERCC2, ERCC3 and XRCC1 polymorphism genotypes by the median and 75th percentiles of blood-Cd levels, we found also significant interactions between ERCC2 (Lys751Gln) and ERCC3 (7122 A>G) genotypes polymorphism and this metal in association with NP disease. However, no interaction was found between XRCC1 (Arg399Gln) polymorphism genotypes and Cd in association with NP disease.

Cadmium (Cd), a potent toxic heavy metal, is a widespread environmental contaminant. Its cellular traffic via pathways dedicated to transition metals contributes to the toxicity mechanisms. Zinc (Zn) homeostasis is complex, involving both zinc importers (Zip) and zinc exporters (ZnT). Cellular signal transduction pathways are influenced by Zn and redox status of the cell. The aim of the present study is to examine if the accumulation of Cd in the human lymphocyte B cell line BJAB and its capacity to promote oxidative stress and adverse effects could result from changes in the mRNA expression pattern of Zn transporters and metallothioneins. Cells were exposed to 5, 10, 20 and 40μM of CdCl₂ equivalent to 0.91, 1.83, 3.66 and 7.33μg/ml respectively, for 24h. Cd significantly reduced the viability of BJAB cells and induced a dose-dependent increase in DNA damage. Cd also induced the formation of 8-hydroxy-2'-deoxyguanosine adducts and augmented MTF1 expression in BJAB cells. We observed interesting responses in relative gene expression to Cd exposure among the seven transporters we analyzed. Cd exposure increased the expression of DMT1 and caused an up-regulation of ZnT1. However, the T calcium channel alpha1G subunit could not be detected. A change in expression of ZnTs and Zips in response to Cd exposure emphasizes the involvement of Zn transporters in Cd cellular metabolism and induced oxidative stress.

We investigated the effects of cadmium on lung cell DNA in immature mice. The mice were randomly divided into four groups: control group, low-dose group (1/100 LD(50)), middle-dose group (1/50 LD(50)), and high-dose group (1/25 LD(50)); they were supplied with cadmium chloride or control water for 40 days. Lung cells collected from sacrificed mice were used to evaluate the extent of DNA damage by comet assay. The ratio of tailing cells, DNA tail length, DNA comet length, DNA tail moment, DNA olive tail moment, and percentage of DNA in the comet tail were measured. The rate of tailing lung cells exposed to cadmium increased significantly; the low-concentration group had significantly (P < 0.05) higher rates, and the middle- and high-concentration groups had higher (P < 0.01) rates compared to the control. DNA tail length, DNA comet length, DNA tail moment, and DNA olive tail moment all increased with the increase in cadmium doses, but compared with those of the control group, no significant differences in low-dose group were found (P > 0.05), and the differences in middle- and high-dose groups were all highly significant (P < 0.01). The degree of DNA damage also increased with the increase of the cadmium concentrations. We conclude that cadmium significantly increases DNA damage in lung cells of immature mice in a dose-dependent manner.

Silica/cadmium containing nanomaterials are now produced on industrial scale due to their potential for a variety of technological applications. Nevertheless, information on toxicity, exposure and health impact of these nanomaterials is still limited. In this study, in vivo effects of silica nanoparticles (SiNPs) doped with Cd (SiNPs-Cd, 1mg/rat), soluble CdCl(2) (400 μg/rat), or SiNPs (600 μg/rat) have been investigated by evaluating F(2)-isoprostanes (F(2)-IsoPs), superoxide dismutase (SOD1), inducible nitric oxide synthase (iNOS) and cyclooxygenase type 2 (COX-2) enzymes, as markers of oxidative stress, 24h, 7 and 30 days after intra-tracheal (i.t.) instillation to rats. Free and esterified F(2)-IsoPs were evaluated in lung and plasma samples by GC/NICI-MS/MS analysis, and SOD1, iNOS and COX-2 expression in pulmonary tissue by immunocytochemistry. Thirty days after exposure, pulmonary total F(2)-IsoPs were increased by 56% and 43% in CdCl(2) and SiNPs-Cd groups, respectively, compared to controls (32.8 ± 7.8 ng/g). Parallel elevation of free F(2)-IsoPs was observed in plasma samples (by 113% and 95% in CdCl(2) and SiNPs-Cd groups, respectively), compared to controls (28 ± 8 pg/ml). These effects were already detectable at day 7 and lasted until day 30 post-exposure. Pulmonary SOD1-, iNOS-, and COX-2-immunoreactivity was significantly enhanced in a time-dependent manner (7 days <30 days) after both CdCl(2) and SiNPs-Cd treatments. SiNPs did not influence any of the evaluated endpoints. The results indicate the capacity of engineered SiNPs-Cd to cause long-lasting oxidative tissue injury following pulmonary exposure in rat.

Cadmium is a toxic metal, and the mechanism of cadmium toxicity in living organisms has been well studied. Here, we used Saccharomyces cerevisiae as a model system to examine the detailed molecular mechanism of cell growth defects caused by cadmium. Using a plate assay of a yeast deletion mutant collection, we found that deletion of SML1, which encodes an inhibitor of Rnr1, resulted in cadmium resistance. Sml1 protein levels increased when cells were treated with cadmium, even though the mRNA levels of SML1 remained unchanged. Using northern and western blot analyses, we found that cadmium inhibited Sml1 degradation by inhibiting Sml1 phosphorylation. Sml1 protein levels increased when cells were treated with cadmium due to disruption of the dependent protein degradation pathway. Furthermore, cadmium promoted cell cycle progression into the G2 phase. The same result was obtained using cells in which SML1 was overexpressed. Deletion of SML1 delayed cell cycle progression. These results are consistent with Sml1 accumulation and with growth defects caused by cadmium stress. Interestingly, although cadmium treatment led to increase Sml1 levels, intracellular dNTP levels also increased because of Rnr3 upregulation due to cadmium stress. Taken together, these results suggest that cadmium specifically affects the phosphorylation of Sml1 and that Sml1 accumulates in cells.

Cadmium is an ubiquitous environmental contaminant that represents hazard to humans and wildlife. It is found in the air, soil and water and, due to its extremely long half-life, accumulates in plants and animals. The main source of cadmium exposure for non-smoking human population is food. Cadmium is primarily toxic to the kidney, but has been also classified as carcinogenic to humans by several regulatory agencies. Current evidence suggests that exposure to cadmium induces genomic instability through complex and multifactorial mechanisms. Cadmium dose not induce direct DNA damage, however it induces increase in reactive oxygen species (ROS) formation, which in turn induce DNA damage and can also interfere with cell signalling. More important seems to be cadmium interaction with DNA repair mechanisms, cell cycle checkpoints and apoptosis as well as with epigenetic mechanisms of gene expression control. Cadmium mediated inhibition of DNA repair mechanisms and apoptosis leads to accumulation of cells with unrepaired DNA damage, which in turn increases the mutation rate and thus genomic instability. This increases the probability of developing not only cancer but also other diseases associated with genomic instability. In the in vitro experiments cadmium induced effects leading to genomic instability have been observed at low concentrations that were comparable to those observed in target organs and tissues of humans that were non-occupationally exposed to cadmium. Therefore, further studies aiming to clarify the relevance of these observations for human health risks due to cadmium exposure are needed.

8-Oxoguanine DNA glycosylase 1 (EC 3.2.2.23) is encoded by OGG1 gene and plays a key role in removing 8-oxo-7,8-dihydroguanine (8-oxoG) base in DNA lesion by reactive oxygen species (ROS). To identify and characterize OGG1 gene (TJ-OGG1) in the copepod Tigriopus japonicus, the full-length cDNA sequence, genomic structure, and promoter region was analyzed. In addition, to investigate transcriptional change of TJ-OGG1 mRNA under oxidative stress conditions, T. japonicus were exposed to environmental oxidative inducers, H(2)O(2), UV-B, and heavy metals (Cd, Cu, and Zn), respectively. The full-length cDNA of TJ-OGG1 gene was 1708 bp in length, encoding 343 amino acid residues. The deduced amino acid sequences of TJ-OGG1 showed a 56% similarity with human. Two conserved motifs (HhH and PVD loop) and two conserved residues (lysine and aspartic acid) in active sites were also observed. TJ-OGG1 genome structure contained six exons and five introns and putative transcription factor binding sites such as Nrf-2, p53, ERE-half sites, and XRE were detected on the promoter region. TJ-OGG1 mRNA level was increased at approximately three-fold (P<0.05) at 1mM and approximately 4-fold (P<0.01) at 10mM of H(2)O(2), respectively. UV-B enhanced the expression of TJ-OGG1 mRNA at 15kJ/m(2) (P<0.05) and more (P<0.001). In a time-course experiment, TJ-OGG1 gene was highly transcribed within 12h after exposure of 10 kJ/m(2) (P<0.01) and 20 kJ/m(2) (P<0.001). The expression of TJ-OGG1 mRNA after exposure to Cu and Cd for 96 h was significantly up-regulated at 0.1 μg/L and then remarkably reduced in a dose-dependent manner. Their transcript levels did not change at low dose (0.1 and 1 μg/L) but were dose-dependently down-regulated at high dose (10 and 100 μg/L). These findings suggest that H(2)O(2), UV-B, and heavy metals induce oxidative stress and generate oxidatively damaged DNA. Consequently, the enhanced TJ-OGG1 gene expression would be associated with active involvement of TJ-OGG1 gene in DNA repair process as a cellular protection mechanism. This is the first report on the cloning and characterization of OGG1 gene in aquatic animals. This study is helpful for a better understanding of the molecular mechanisms of cellular protection against various environmental oxidative stress inducers such as UV-B and heavy metals in aquatic invertebrates.

Cadmium (Cd) is a carcinogenic heavy metal of environmental concern. Exposure to both Cd and carcinogenic organic compounds, such as polycyclic aromatic hydrocarbons or aromatic amines (AAs), is a common environmental problem. Human arylamine N-acetyltransferases (NATs) are xenobiotic-metabolizing enzymes that play a key role in the biotransformation of AA carcinogens. Changes in NAT activity have long been associated with variations in susceptibility to different cancers in relation with exposure to certain AAs.

We explored the possible interactions between Cd and the NAT-dependent biotransformation of carcinogenic AAs.

We exposed purified enzymes, lung epithelial cells, and mouse models to Cd and subsequently analyzed NAT-dependent metabolism of AAs.

We found that Cd, at biologically relevant concentrations, impairs the NAT-dependent acetylation of carcinogenic AAs such as 2-aminofluorene (2-AF) in lung epithelial cells. NAT activity was strongly impaired in the tissues of mice exposed to Cd. Accordingly, mice exposed to Cd and 2-AF displayed altered in vivo toxicokinetics with a significant decrease (~ 50%) in acetylated 2-AF in plasma. We found that human NAT1 was rapidly and irreversibly inhibited by Cd [median inhibitory concentration (IC₅₀) ≈ 55 nM; rate inhibition constant (k(inact)) = 5 × 10⁴ M⁻¹ • sec⁻¹], with results of acetyl coenzyme A (acetyl-CoA) protection assays indicating that Cd-mediated inhibition was due to the reaction of metal with the active-site cysteine residue of the enzyme. We found similar results for human NAT2, although this isoform was less sensitive to inactivation (IC₅₀ ≈ 1 μM; k(inact) = 1 × 10⁴ M⁻¹ • sec⁻¹).

Our data suggest that Cd can alter the metabolism of carcinogenic AAs through the impairment of the NAT-dependent pathway, which may have important toxicological consequences.

MutS homolog 6 (MSH6) is the major mismatch contacting component of the MSH2-MSH6 heterodimeric complex (MutSα) that mediates DNA mismatch repair (MMR) of simple mispairs and small insertion-deletion loops in eukaryotes. This study examined the potential of cadmium (Cd) to disturb the gene expression of MSH6 in vertebrates using zebrafish (Danio rerio) embryo as a model organism. Semiquantitative RT-PCR indicated that msh2 and msh6 expressions were suppressed in embryos at 1h post fertilization (hpf), then drastically up-regulated in 2 hpf embryos and actively expressed in 3-25 hpf embryos. In the presence of a constitutive β-actin expression, exposure of 1 hpf embryos to sublethal concentrations of CdCl(2) at 0.5-3 μM for 4 or 9h caused a time and concentration-dependent down-regulation of msh6 transcription. Cd failed to inhibit msh2 transcription except at 3 μM, reflecting the higher sensitivity of msh6 than msh2 transcription to Cd. Whole mount in situ hybridization showed a wide distribution of msh6 transcripts in the front body portions of 10 hpf embryos and Cd-induced a general suppression of msh6 expression in zebrafish tissues. Cd-induced down-regulation of msh6 transcription paralleled with reduced levels of MSH6 protein synthesis and MSH6-mediated G-T mismatch binding activities identified by band shift assay using recombinant zebrafish MSH6 and an anti-human MSH6 antibody. Our results revealed the inhibition of Cd on MSH6 expression at both mRNA and protein levels and this mechanism may play a role in Cd genotoxicity.

Human exposure to heavy metals is of increasing concern due to their well-documented toxicological and carcinogenic effects and rising environmental levels through industrial processes and pollution. It has been widely reported that such metals can be genotoxic by several modes of action including generation of reactive oxygen species and inhibition of DNA repair. However, although it has been observed that certain heavy metals can inhibit single strand break (SSB) rejoining, the effects of these metals on SSB end-processing enzymes has not previously been investigated. Accordingly, we have investigated the potential inhibition of polynucleotide kinase (PNK)-dependent single strand break repair by six metals: cadmium, cobalt, copper, nickel, lead and zinc. It was found that micromolar concentrations of cadmium and copper are able to inhibit the phosphatase and kinase activities of PNK in both human cell extracts and purified recombinant protein, while the other metals had no effect at the concentrations tested. The inhibition of PNK by environmentally and physiologically relevant concentrations of cadmium and copper suggests a novel means by which these toxic heavy metals may exert their carcinogenic and neurotoxic effects.

Ionizing radiation-induced formation of genomic DNA damage can be modulated by nearby chemical species such as heavy metal ions, which can lead to non-linear dose response. To investigate this phenomenon, we studied cell survival and formation of 8-hydroxyguanine (8-OHG) base modifications and double strand breaks (DSB) caused by combined action of cadmium (Cd) and gamma radiation in cultured medaka fish (Oryzias latipes) fibroblast cells. Our data show that the introduction of Cd leads to a significant decrease in the fraction of surviving cells and to increased sensitivity of cells to ionizing radiation (IR). Cd also appears to cause non-linear increases in radiation-induced yields of 8-OHG and DSB as dose-yield plots of these lesions exhibit non-linear S-shaped curves with a sharp increase in the yields of lesions in the 10-20 microM range of Cd concentrations. The combined action of ionizing radiation and Cd leads to increased DNA damage formation compared to the effects of the individual stressors. These results are consistent with a hypothesis that the presence of Cd modulates the efficiency of DNA repair systems thus causing increases in radiation-induced DNA damage formation and decreases in cell survival.

This article introduces an approach to estimating the uncertain potential effects on lung cancer risk of removing a particular constituent, cadmium (Cd), from cigarette smoke, given the useful but incomplete scientific information available about its modes of action. The approach considers normal cell proliferation; DNA repair inhibition in normal cells affected by initiating events; proliferation, promotion, and progression of initiated cells; and death or sparing of initiated and malignant cells as they are further transformed to become fully tumorigenic. Rather than estimating unmeasured model parameters by curve fitting to epidemiological or animal experimental tumor data, we attempt rough estimates of parameters based on their biological interpretations and comparison to corresponding genetic polymorphism data. The resulting parameter estimates are admittedly uncertain and approximate, but they suggest a portfolio approach to estimating impacts of removing Cd that gives usefully robust conclusions. This approach views Cd as creating a portfolio of uncertain health impacts that can be expressed as biologically independent relative risk factors having clear mechanistic interpretations. Because Cd can act through many distinct biological mechanisms, it appears likely (subjective probability greater than 40%) that removing Cd from cigarette smoke would reduce smoker risks of lung cancer by at least 10%, although it is possible (consistent with what is known) that the true effect could be much larger or smaller. Conservative estimates and assumptions made in this calculation suggest that the true impact could be greater for some smokers. This conclusion appears to be robust to many scientific uncertainties about Cd and smoking effects.

Endonuclease VIII (Nei) excises oxidatively damaged pyrimidines from DNA and shares structural and functional homology with formamidopyrimidine-DNA glycosylase. Although the structure of Escherichia coli Nei is solved [Zharkov et al. (2002) EMBO J. 21, 789-800], the functions of many of its amino acid residues involved in catalysis and substrate specificity are not known. We constructed a series of Nei mutants that interfere with eversion of the damaged base from the helix (QLY69-71AAA, DeltaQLY69-71) or perturb the conserved zinc finger (R171A, Q261A). Steady-state kinetics were measured with these mutant enzymes using substrates containing 5,6-dihydrouracil, two enantiomers of thymine glycol, 8-oxo-7,8-dihydroguanine, and an abasic site positioned opposite each of the four canonical DNA bases. To some extent, all Nei mutants were deficient in processing damaged DNA, with mutations in the zinc finger generally having a more profound effect. Wild-type Nei showed prominent opposite-base specificity (G > C approximately = T > A) when the lesion was 5,6-dihydrouracil or cis-(5S,6R)-thymine glycol but not for other lesions tested. Mutations in the Q69-Y71 loop eliminated this effect. Only wild-type Nei and Nei-Q261A mutants could be reductively cross-linked to damaged base-containing DNA. Experiments involving trapping with NaBH4 and the kinetics of DNA cleavage catalyzed by Nei-Q261A suggested that this mutant was deficient in regenerating free enzyme from the Nei-DNA covalent complex formed during the reaction. We conclude that the opposite-base specificity of Nei is primarily governed by residues in the Q69-Y71 loop and that both this loop and the zinc finger contribute significantly to the substrate specificity of Nei.

8-Oxoguanine (8-oxoG), a common and mutagenic form of oxidized guanine in DNA, is eliminated mainly through base excision repair. In human cells its repair is initiated by human OGG1 (hOGG1), an 8-oxoG DNA glycosylase. We investigated the effects of an acute cadmium exposure of human lymphoblastoid cells on the activity of hOGG1. We show that coinciding with alteration of the redox cellular status, the 8-oxoG DNA glycosylase activity of hOGG1 was nearly completely inhibited. However, the hOGG1 activity returned to normal levels once the redox cellular status was normalized. In vitro, the activity of purified hOGG1 was abolished by cadmium and could not be recovered by EDTA. In cells, however, the reversible inactivation of OGG1 activity by cadmium was strictly associated with reversible oxidation of the protein. Moreover, the 8-oxoG DNA glycosylase activity of purified OGG1 and that from crude extracts were modulated by cysteine-modifying agents. Oxidation of OGG1 by the thiol oxidant diamide led to inhibition of the activity and a protein migration pattern similar to that seen in cadmium-treated cells. These results suggest that cadmium inhibits hOGG1 activity mainly by indirect oxidation of critical cysteine residues and that excretion of the metal from the cells leads to normalization of the redox cell status and restoration of an active hOGG1. The results presented here unveil a novel redox-dependent mechanism for the regulation of OGG1 activity.

Cadmium (Cd2+), nickel (Ni2+) and cobalt (Co2+) are human and/or animal carcinogens. Zinc (Zn2+) is not categorized as a carcinogen, and rather an essential element to humans. Metals were recently shown to inhibit DNA repair proteins that use metals for their function and/or structure. Here we report that the divalent ions Cd2+, Ni2+, and Zn2+ can inhibit the activity of a recombinant human N-methylpurine-DNA glycosylase (MPG) toward a deoxyoligonucleotide with ethenoadenine (varepsilonA). MPG removes a variety of toxic/mutagenic alkylated bases and does not require metal for its catalytic activity or structural integrity. At concentrations starting from 50 to 1,000 microM, both Cd2+ and Zn2+ showed metal-dependent inhibition of the MPG catalytic activity. Ni2+ also inhibited MPG, but to a lesser extent. Such an effect can be reversed with EDTA addition. In contrast, Co2+ and Mg2+ did not inhibit the MPG activity in the same dose range. Experiments using HeLa cell-free extracts demonstrated similar patterns of inactivation of the varepsilonA excision activity by the same metals. Binding of MPG to the substrate was not significantly affected by Cd2+, Zn2+, and Ni2+ at concentrations that show strong inhibition of the catalytic function, suggesting that the reduced catalytic activity is not due to altered MPG binding affinity to the substrate. Molecular dynamics (MD) simulations with Zn2+ showed that the MPG active site has a potential binding site for Zn2+, formed by several catalytically important and conserved residues. Metal binding to such a site is expected to interfere with the catalytic mechanism of this protein. These data suggest that inhibition of MPG activity may contribute to metal genotoxicity and depressed repair of alkylation damage by metals in vivo.

Cadmium (Cd) is a heavy metal and a potent carcinogen implicated in tumor development through occupational and environmental exposure. Recent evidence suggests that proteins participating in the DNA repair systems, especially in excision and mismatch repair, are sensitive targets of Cd toxicity. Cd by interfering and inhibiting these DNA repair processes might contribute to increased risk for tumor formation in humans. In the present review, the information available on the interference of Cd with DNA repair systems and their inhibition is summarized. These actions could possibly explain the indirect contribution of Cd to mutagenic effects and/or carcinogenicity.

Cadmium is a human carcinogen of worldwide concern because it accumulates in the environment due to its extremely long half-life. Its compounds are classified as human carcinogens by several regulatory agencies. Cadmium affects cell proliferation, differentiation, apoptosis and other cellular activities and can cause numerous molecular lesions that would be relevant to carcinogenesis. For a long time cadmium has been considered as a non-genotoxic carcinogen, as it is only weakly mutagenic in bacterial and mammalian cell test systems. Recently, we presented evidence that when assayed in a test system, in which both intragenic and multilocus mutations can be detected, cadmium acts as a strong mutagen which induces predominantly multilocus deletions. In this review, we discuss two mechanisms that play an important role in cadmium mutagenicity: (i) induction of reactive oxygen species (ROS); and (ii) inhibition of DNA repair. Experimental evidence suggests that cadmium at low, for environmental exposure relevant concentrations, induces mutations by inducing oxidative DNA damage and that it decreases genetic stability by inhibiting the repair of endogenous and exogenous DNA lesions, which in turn increase the probability of mutations and consequently cancer initiation by this metal.

Cadmium is a well known human and animal carcinogen and is a ubiquitous contaminant in the environment. Although the carcinogenic mechanism of cadmium is a multifactorial process, oxidative DNA damage is believed to be of prime importance. In particular, cadmium suppresses the capacity of cells to repair oxidative DNA damage. In this study, cadmium treatment led to a significant increase in gamma-ray-induced 8-oxoguanine (8-oxoG) formation. Western blotting and semiquantitative reverse transcription-PCR revealed that cadmium treatment caused a decrease in the expression level of human OGG1 (8-oxoguanine-DNA glycosylase-1; hOGG1) in human fibroblast GM00637 and HeLa S3 cells. In addition, the cadmium-mediated decrease in hOGG1 transcription was the result of decreased binding of the transcription factor Sp1 to the hOGG1 promoter. Finally, we show that an increase in the functional hOGG1 expression level could inhibit the cadmium-mediated increase in gamma-ray-induced 8-oxoG accumulation as well as in gamma-radiation-induced mutation frequency at the HPRT (hypoxanthine-guanine phosphoribosyltransferase) gene locus. These results suggest that cadmium attenuates removal of gamma-ray-induced 8-oxoG adducts, which in turn increases the mutation frequency, and that this effect might, at least in part, result from suppression of hOGG1 transcription via inactivation of Sp1 as a result of cadmium treatment.

Cadmium is a heavy metal, which is widely used in industry, affecting human health through occupational and environmental exposure. In mammals, it exerts multiple toxic effects and has been classified as a human carcinogen by the International Agency for Research on Cancer. Cadmium affects cell proliferation, differentiation, apoptosis and other cellular activities. Cd2+ does not catalyze Fenton-type reactions because it does not accept or donate electrons under physiological conditions, and it is only weakly genotoxic. Hence, indirect mechanisms are implicated in the carcinogenicity of cadmium. In this review multiple mechanisms are discussed, such as modulation of gene expression and signal transduction, interference with enzymes of the cellular antioxidant system and generation of reactive oxygen species (ROS), inhibition of DNA repair and DNA methylation, role in apoptosis and disruption of E-cadherin-mediated cell-cell adhesion. Cadmium affects both gene transcription and translation. The major mechanisms of gene induction by cadmium known so far are modulation of cellular signal transduction pathways by enhancement of protein phosphorylation and activation of transcription and translation factors. Cadmium interferes with antioxidant defense mechanisms and stimulates the production of reactive oxygen species, which may act as signaling molecules in the induction of gene expression and apoptosis. The inhibition of DNA repair processes by cadmium represents a mechanism by which cadmium enhances the genotoxicity of other agents and may contribute to the tumor initiation by this metal. The disruption of E-cadherin-mediated cell-cell adhesion by cadmium probably further stimulates the development of tumors. It becomes clear that there exist multiple mechanisms which contribute to the carcinogenicity of cadmium, although the relative weights of these contributions are difficult to estimate.

The current study tested the hypothesis that the pulmonary carcinogenic potential of cadmium (Cd) is related to its ability to inhibit the expression (mRNA and protein) and activity of 8-oxoguanine-DNA glycosylase (OGG1), a base excision repair (BER) enzyme that functions to preferentially excise pre-mutagenic 7,8-dihydro-8-oxoguanine (8-oxoG) from DNA. We demonstrate that a single Cd aerosol exposure of adult male Lewis rats causes time- and dose-dependent down-regulation in the pulmonary levels of rOGG1 mRNA and OGG1 protein, quantified by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) assays and western analyses, respectively. Immunohistochemical studies confirmed that Cd inhalation reduces the relative amount of OGG1 in lungs of exposed animals without altering its over-all distribution within the lung, which appears to be more prominent within the alveolar epithelium. In agreement with our in vivo studies, we show that OGG1 expression is also attenuated in alveolar epithelial cell cultures exposed to CdCl(2) either acutely or by repeated passaging in Cd-containing medium. The effects caused by Cd were observed in cells that show no loss in viability, as assessed by colony forming ability, the MTT assay, and propidium iodide membrane permeability studies. Nuclear extracts prepared from Cd-treated cells also exhibit a reduction in the ability to nick a synthetic oligonucleotide containing 8-oxoG. We conclude from these studies that Cd causes suppression of OGG1 in the lung and that this mechanism may, in part, play a role in the Cd carcinogenic process.

This study demonstrates that in vitro exposure of adult rat alveolar epithelial cells to CdCl(2) decreases DNA binding activity of specificity protein 1 (Sp1), a zinc-finger transcription factor known to play a key role in eukaryotic gene expression, maintenance of homeostasis, cell cycle control, terminal differentiation, and apoptosis. Suppression of Sp1 function, as assessed by electrophoretic mobility shift assays (EMSAs), is dependent upon cadmium (Cd) dose and duration of exposure. A 45% decrease of Sp1 activity occurs as early as 30 min after Cd addition. By 2 h, Sp1 activity is reduced even further with no loss of cell viability, suggesting that Sp1 inactivation precedes cell death. If Cd is removed from cultures during these early periods of exposure, inhibition of Sp1 binding activity is reversed. Sp1 inactivation does not appear to be a generalized, non-selective response to Cd as other transcription factors are up-regulated under the same conditions. Phosphorylation is involved in Sp1 down-regulation, as evidenced by the finding that alkaline phosphatase treatment of nuclear extracts from cells exposed to Cd for 2 h helps restore Sp1 binding activity. A broad spectrum Protein Kinase C (PKC) inhibitor, GF109203X, substantially reduces the Cd-mediated effect on Sp1 suggesting that a member of the PKC family is required for Sp1 phosphorylation. More prolonged Cd exposure promotes Sp1 degradation with the appearance of cleavage products (40 and 50 kDa), as detected by Western blotting. Changes in the integrity of the Sp1 protein are accompanied by a corresponding decline in cell survival. Cd-induced cell death is substantially attenuated if cells are pretreated with antagonists of PKC activity which implies that a PKC isoform is also a participant in this process.

Cadmium(II) is a toxic, mutagenic and carcinogenic metal (IARC Class 1 human carcinogen). It causes damage to eukaryotic cells both in acute and chronic modes of exposure via multiple biochemical mechanisms. In particular, Cd diminishes the capacity of cells to repair oxidative DNA damage. Oxidative DNA lesions are important precursors to mutations and ultimately may lead to neoplastic transformation of human cells. We investigated interactions of Cd with murine Ogg1 (mOgg1), an enzyme that removes 8-oxoguanine (8-oxoG), an abundant oxidative lesion, from DNA. Cd(2+) and Zn(2+), but not other divalent cations tested, suppressed mOgg1-catalyzed reactions. The apparent inhibition by Cd consisted of at least two independent processes: irreversible, DNA-independent first-order inactivation of mOgg1 and DNA-dependent inhibition. Irreversibly inactivated mOgg1 has nearly normal affinity for damaged DNA and a normal catalytic rate constant but is defective in formation of the covalent reaction intermediate. When both modes of inhibition are in effect, the catalytic rate constant is dramatically lowered, while affinity to damaged DNA is decreased moderately. Potential sites for Cd binding in mOgg1 and mOgg1-DNA complex are identified. Inactivation of Ogg1 may play a role in the mutagenic and carcinogenic action of Cd.

This review article discusses the major cellular and molecular responses characterizing pulmonary adaptation to cadmium (Cd) that may ultimately contribute to Cd carcinogenesis. Hallmarks of Cd adaptation include hyperplasia and hypertrophy of type II alveolar epithelial stem cells, an inflammatory response involving polymorphonuclear leukocytes, and the increased gene and protein expression of several resistance factors. The most prominent biochemical change is associated with Cd-induced up-regulation of metallothionein, a cysteine-rich, metal-binding protein that sequesters Cd and also possesses considerable free radical scavenging ability. Increased levels of glutathione (GSH) and induction of enzymes involved with both the synthesis of GSH (gamma-glutamylcysteine synthetase regulatory and catalytic subunits) and its metabolism (GSH S-transferases) also constitute important components of the pulmonary adaptive response. Enhancement of several important cellular defense systems in response to Cd exposure may, at first, appear to be beneficial. However, recent evidence suggests that the Cd-adaptive phenotype could have deleterious consequences and may represent a double-edged sword. It has been discovered that Cd-adapted alveolar epithelial cells have a reduced ability to repair DNA damage due, in part, to the inhibition of two base excision repair enzymes (8-oxoguanine-DNA glycosylase and endonuclease III). Cells with genetic aberrations resulting from unrepaired DNA lesions would normally be removed from the lung by apoptosis. However, another study has demonstrated that apoptotic cell death, following an oxidant challenge, is significantly attenuated in Cd-adapted cells compared to non-adapted counterparts. Suppressed apoptosis could leave pre-neoplastic or neoplastic cells alive, favor their clonal expansion, and ultimately promote tumor development. The presence of superior antioxidant defenses would also be expected to increase the resistance of these tumors to chemotherapeutic agents.