Cadmium induces cell cycle arrest in rat kidney epithelial cells in G2/M phase

Cadmium disrupts spermatogenic cell cycle via piRNA-DQ717867/p53 pathway

Cadmium (Cd) is a harmful environmental pollutant that disrupts public health, including respiratory, digestive, and reproductive systems. In this study, male rats were exposed to CdCl2 at a dose of 3 mg/kg by oral for 28 days to investigate the impact on spermatogenesis. Testis tissue samples were collected after sacrifice, and piRNA expression levels were measured using piRNA microarray and qPCR. PiRNAs, specialized molecules involved in spermatogenesis, were examined. CdCl2 exposure led to disrupted piRNA expression, particularly in piRNA-DQ759395 in rats. This piRNA was found to have a binding site with p53, and a similar piRNA-DQ717867 was discovered in mice. In GC-2spd cells, CdCl2 exposure increased piRNA-DQ717867 expression, which resulted in cell cycle arrest and abnormal expression of cell cycle-related proteins. The activation of p53-related pathways and disruptions in cell cycle regulation were also observed. Antagomir-717867 transfections and PFT-a pretreatment in GC-2spd cells supported the involvement of piRNA-DQ717867 in regulating cell cycle-related proteins. This study suggests that Cd exposure induces abnormal expression of piRNA-DQ759395 in rat testis and that piRNA-DQ717867 may regulate p53, causing cell cycle abnormalities in GC-2spd cells. These findings help understand the mechanisms of male reproductive toxicity caused by Cd exposure and emphasize the role of piRNAs in cell cycle regulation and male reproductive health.

Malvidin-3-O-Glucoside Ameliorates Cadmium-Mediated Cell Dysfunction in the Estradiol Generation of Human Granulosa Cells

Cadmium (Cd) is a frequent environmental pollutant associated with biological toxicity that can harm female reproduction. Anthocyanins have been reported to reduce the toxicity of Cd. In the present study, the protective effects and underlying mechanisms of malvidin-3-O-glucoside (M3G) against the toxicity of Cd on female reproduction in KGN cells (human ovarian granulosa-like tumor cells) were investigated. After treating cells with 10 µmol/L cadmium chloride, the results showed that M3G lessened Cd-induced KGN cell cytotoxicity better than malvidin and malvidin-3,5-O-diglucoside. Additionally, M3G significantly decreased the Cd-induced generation of reactive oxygen species, inhibited the Cd-induced arrest of the G2/M phase of the cell cycle, and increased estradiol (E2) production. According to transcriptomic results, M3G reduced the abnormal expression of genes that responded to estrogen. Additionally, M3G promoted the endogenous synthesis and secretion of E2 by controlling the expression of CYP17A1 and HSD17B7. The current findings indicated that M3G is of great potential to prevent Cd-induced female reproductive impairment as a dietary supplement.

The protective mechanism of a novel polysaccharide from Lactobacillus-fermented Nostoc commune Vauch. on attenuating cadmium-induced kidney injury in mice

A novel polysaccharide (NCVP-F) from Lactobacillus-fermented Nostoc commune Vauch. was obtained to investigate its underlying mechanism in cadmium-induced kidney injury. Results indicated that in comparison with NCVP, NCVP-F with lower molecular weight of 365.369 kDa, exhibited higher mole percentage of Man and Glc-UA, whereas slightly lower mole percentage of other monosaccharides. NCVP-F is a α-pyran polysaccharide similar to NCVP. Meanwhile, NCVP-F can more effectively alleviate hepatorenal injury (ALT, AST, TG, BUN and SCr) and kidney tissue lesions in Cd-injured mice model by increasing antioxidant enzyme activity (SOD, GSH and GSH-Px), inhibiting cytokines levels (IL-6, IL-1β, TNF-α and IL-18). In addition, NCVP-F effectively inhibited apoptosis proteins (Bax, cytochrome c, a-caspase-9 and a-caspase-3) and enhanced anti-apoptotic protein (Bcl-2) probably via activating PI3K/AKT/mTOR pathway in the Cd-injury kidney. Furthermore, 16S rRNA sequencing results indicated that NCVP-F better enriched Lachnospiraceae, reduced Muribaculaceae, Alloprevotella and Blautia to regulate Cd-induced gut microbiota disorders, which was probably down-regulated 7 pathways including apoptosis and lipopolysaccharide biosynthesis, and up-regulated 63 pathways, such as carbohydrate metabolism and lipid metabolism. This study suggested that applying functional NCVP-F prepared by biotransformation with low molecular weight might be more beneficial.

Regulatory actions of rare earth elements (La and Gd) on the cell cycle of root tips in rice seedlings (Oryza sativa L.)

The continuous expansion of the application of rare earth elements (REEs) in various fields has attracted attention to their biosafety. At present, the molecular mechanisms underlying the biological effects of REEs are unclear. In this study, the effects of lanthanum (La) and gadolinium (Gd) on cell cycle progression in the root tips of rice seedlings were investigated. Low concentrations of REEs (0.1 mg L^-1) induced an increase in the number of cells in the prophase and metaphase, while high concentrations of REEs (10 mg L^-1) induced an increase in the number of cells in the late and terminal stages of the cell cycle, and apoptosis or necrosis. Additionally, low concentrations of REEs induced a significant increase in the expression of the cell cycle factors WEE1, CDKA;1, and CYCB1;1, and promoted the G2/M phase and accelerated root tip growth. However, at high REEs concentrations, the DNA damage response sensitized by BRCA1, MRE11, and TP53 could that prevent root tip growth by inhibiting the transcription factor E2F, resulting in obvious G1/S phase transition block and delayed G2/M phase conversion. Furthermore, by comparing the biological effect mechanisms of La and Gd, we found that these two REEs share regulatory actions on the cell cycle of root tips in rice seedlings.

Mechanisms of Cd-induced Cytotoxicity in Normal Human Skin Keratinocytes: Implication for Human Health

Cadmium (Cd) is one of the toxic heavy metals found widely in the environment. Skin is an important target organ of Cd exposure. However, the adverse effects of Cd on human skin are still not well known. In this study, normal human skin keratinocytes (HaCaT cells) were studied for changes in cell viability, morphology, DNA damage, cycle, apoptosis, and the expression of endoplasmic reticulum (ER) stress-related genes (XBP-1, BiP, ATF-4, and CHOP) after exposure to Cd for 24 h. We found that Cd decreased cell viability in a concentration-dependent manner, with a median lethal concentration (LC₅₀) of 11 µM. DNA damage induction was evidenced by upregulation of the level of γ-H2AX. Furthermore, Cd induced G0/G1 phase cell cycle arrest and apoptosis in a dose-dependent manner and upregulated the mRNA levels of ER stress biomarker genes (XBP-1, BiP, ATF4, and CHOP). Taken together, our results showed that Cd induced cytotoxicity and DNA damage in HaCaT cells, eventually resulting in cell cycle arrest in the G0/G1 phase and apoptosis. In addition, ER stress may be involved in Cd-induced HaCaT apoptosis. Our data imply the importance of reducing Cd pollution in the environment to reduce its adverse impacts on human skin.

The role of autophagy in cadmium-induced acute toxicity in glomerular mesangial cells and tracking polyubiquitination of cytoplasmic p53 as a biomarker

Cadmium (Cd) is a highly toxic environmental pollutant that can severely damage the kidneys. Here, we show that Cd-induced apoptosis is promoted by the cytoplasmic polyubiquitination of p53 (polyUb-p53), which is regulated by the polyubiquitination of SQSTM1/p62 (polyUb-p62) and autophagy in mouse kidney mesangial cells (MES13E cells). p53 was detected in monomeric and different high-molecular-weight (HMW) forms after Cd exposure. Monomeric p53 levels decreased in a concentration- and time-dependent manner. HMW-p53 transiently accumulated in the cytoplasm independent of proteasome inhibition. The expression patterns of p53 were similar to those of p62 upon Cd exposure, and the interactions between polyUb-p53 and polyUb-p62 were observed using immunoprecipitation. P62 knockdown reduced polyUb-p53 and upregulated nuclear monomeric p53, whereas p53 knockdown reduced polyUb-p62. Autophagy inhibition induced by ATG5 knockdown reduced Cd-induced polyUb-p62 and polyUb-p53 but upregulated the levels of nuclear p53. Pharmacological inhibition of autophagy by bafilomycin A1 increased polyUb-p62 and polyUb-p53 in the cytoplasm, indicating that p53 protein levels and subcellular localization were regulated by polyUb-p62 and autophagy. Immunoprecipitation and immunofluorescence revealed an interaction between p53 and LC3B, indicating that p53 was taken up by autophagosomes. Cd-resistant RMES13E cells and kidney tissues from mice continuously injected with Cd had reduced polyUb-p53, polyUb-p62, and autophagy levels. Similar results were observed in renal cell carcinoma cell lines. These results indicate that cytoplasmic polyUb-p53 is a potential biomarker for Cd-induced acute toxicity in mesangial cells. In addition, upregulation of nuclear p53 may protect cells against Cd cytotoxicity, but abnormal p53 accumulation may contribute to tumor development.

The cellular localization and chemical modification of a protein that acts as a critical safeguard against cellular damage may directly contribute to the toxic effects of cadmium. P53 is an essential tumor suppressor that is also involved in numerous other important biological functions. Ki-Tae Jung and Seon-Hee Oh of Chosun University, Gwangju, South Korea have now demonstrated that this protein also undergoes rapid changes in response to the environmental pollutant cadmium. P53 normally manages gene expression in the nucleus, but the authors found that it is rapidly shuttled to the cytoplasm and subjected to extensive chemical modification in cadmium-treated cultured kidney cells. This relocation appears to contribute directly to subsequent cell death, and the authors suggest that this P53 response could be an important biomarker for diagnosing human cadmium exposure.

Giant Toads (Rhinella marina) From the Industrial Zones of Low Basin of the Coatzacoalcos River (Veracruz, MX) Presents Genotoxicity in Erythrocytes

The lower basin of Coatzacoalcos River is one of the most polluted regions of the southern Gulf of Mexico. Organochlorine compounds, polybrominated diphenyl ethers, polycyclic aromatic hydrocarbons, and heavy metals have been registered in this region. In the present study, genotoxicity was evaluated in the blood of giant toads (Rhinella marina) from Coatzacoalcos' rural and industrial zones, and compared with laboratory toads. Determination of the frequency of micronucleus and erythrocyte nuclear abnormalities by the light microscope and cell cycle and apoptosis by flow cytometry were used as biomarkers of genotoxicity. We found more variability in micronucleus and more nuclear buds in toads from industrial zones. Also, cell cycle alterations and an increase of apoptosis in erythrocytes were found in toads from rural and industrial zones. Multivariate statistics show that the toads from the industrial zone were more affected than toads from laboratory and rural zones.

MAPK, AKT/FoxO3a and mTOR pathways are involved in cadmium regulating the cell cycle, proliferation and apoptosis of chicken follicular granulosa cells

The occurrence of cadmium (Cd) in feed is a major problem in animal health and production. Studies have confirmed that Cd depresses egg production of laying hens, which is closely related to follicular atresia. This study aimed to assess the toxic impacts of Cd on the ovarian tissue, and to examine the mechanism of Cd-induced granulosa cell proliferation and apoptosis. Results from the nitric oxide (NO) and malondialdehyde (MDA) content, total superoxide dismutase (T-SOD), glutathione peroxide (GSH-Px), total nitric oxide synthase (T-NOS) and adenosine triphosphatase (ATPase) activities, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay, and hematoxylin-eosin (H & E) staining indicated that excess Cd induced oxidative stress, granulosa cell apoptosis and follicular atresia in the layer ovary. Low-dose Cd exposure (1 μM) induced the granulosa cell proliferation, upregulated the mRNA levels of RSK1 and RHEB, activated FoxO3a, AKT, ERK1/2, mTOR and p70S6K1 phosphorylation, and promoted cell cycle progression from phase G1 to S. However, high-dose Cd exposure (15 μM) induced reactive oxygen species (ROS) generation and cell apoptosis, upregulated the mRNA levels of the inflammatory factors, ASK1, JNK, p38 and TAK1, downregulated the expressions of RSK1 and RHEB genes, and inhibited the phosphorylation of ERK1/2, mTOR and p70S6K1 proteins, and the cell cycle progression. Rapamycin pre-treatment completely blocked the phosphorylation of mTOR and p70S6K1 proteins, and the cell cycle progression induced by 1 μM Cd, and accelerated 15 μM Cd-induced cell apoptosis and cell cycle arrest. The microRNA sequencing result showed that 15 μM Cd induced differential expression of microRNA genes, which may regulate AKT, ERK1/2 and mTOR signaling and cell cycle progression by regulating the activity of G proteins and cell cycle-related proteins. Conclusively, these results indicated that Cd can cause the ovarian damage and follicular atresia, and regulate cell cycle, cell proliferation or apoptosis of granulosa cells through MAPK, AKT/FoxO3a and mTOR pathways in laying hens.

Cadmium triggers oxidative stress and mitochondrial injury mediated apoptosis in human extravillous trophoblast HTR-8/SVneo cells

Cadmium (Cd) is a bioaccumulative heavy metal element with potential placental toxicity during pregnancy. Up to now, however, the precise toxic effects of Cd on human placentae, particularly as they pertain to trophoblast cells remain obscure. We therefore sought to investigate the cytotoxic effects of Cd on human extravillous trophoblast HTR-8/SVneo cells and the mechanisms involved in the processes. Results in this present study showed that CdCl2 treatment significantly suppressed cell viability and induced noticeable oxidative stress in HTR-8/SVneo cells. Further studies showed that CdCl2 treatment caused distortion of mitochondrial structure, reduction of mitochondrial membrane potential (Δψm), DNA damage and G0/G1 phase arrest. Under the same condition, CdCl2 treatment increased Bax/Bcl-2 ratios by up-regulating Bax expression and down-regulating Bcl-2 expression, and activated apoptotic executive molecule caspase-3, which irreversibly induced HTR-8/SVneo cell apoptosis. N-acetyl-l-cysteine (NAC), ROS scavenger, significantly attenuated CdCl2-caused mitochondrial injury, DNA damage, G0/G1 phase arrest and apoptosis. In addition, in vivo assay suggested that CdCl2 induced trophoblast cells apoptosis but not other cells in mice placental tissue. Taken together, these data suggest that Cd selectively triggers oxidative stress and mitochondrial injury mediated apoptosis in trophoblast cells, which might contribute to placentae impairment and placental-related disorders after Cd exposure. These findings may provide new insights to understand adverse effects of Cd on placentae during pregnancy.

Transcriptome analysis of cadmium exposure in kidney fibroblast cells of the North Atlantic Right Whale (Eubalaena glacialis)

An 8X15k oligonucleotide microarray was developed consisting of 2334 Eubalaena glacialis probes and 2166 Tursiops truncatus probes and used to measure the effects, at transcriptomic level, of cadmium exposure in right whale kidney fibroblast cells. Cells were exposed to three concentrations (1 μM, 0.1 μM, and 0.01 μM) of cadmium chloride (CdCl₂) for three exposure times (1, 4, and 24 h). Cells exposed to 1 μM CdCl₂ for 4 h and 24 h showed upregulated genes involved in protection from metal toxicity and oxidative stress, protein renaturation, apoptosis inhibition, as well as several regulators of cellular processes. Downregulated genes represented a suite of functions including cell proliferation, transcription regulation, actin polymerization, and stress fiber synthesis. The collection of differentially expressed genes in this study support proposed mechanisms of cadmium-induced apoptosis such as ubiquitin proteasome system disruption, Ca²⁺ homeostasis interference, mitochondrial membrane potential collapse, reactive oxygen species (ROS) production, and cell cycle arrest. The results also have confirmed the right whale microarray as a reproducible tool in measuring differentiated gene expression that could be a valuable asset for transcriptome analysis of other baleen whales and potential health assessment protocols.

Enhanced Cytotoxicity of Cadmium by a Sulfated Polysaccharide from Abalone

Consumption of seafood is a common route of cadmium ion (Cd²⁺) exposure to consumers. The seafood matrices may alter the toxicity profile of Cd²⁺ due to the interaction between Cd²⁺ and biomacromolecules in seafood. In this study, enhanced cytotoxicity of Cd²⁺ was found in the presence of an abalone gonad sulfated polysaccharide (AGSP) and the mechanism was investigated at a metabolic level. The formation of the AGSP-Cd²⁺ complex was demonstrated by isothermal titration calorimetry. The level of reactive oxygen species (ROS) increased and mitochondrial membrane potential reduced upon exposure to the AGSP-Cd²⁺ complex as compared with those of Cd²⁺ exposure. The decreased cell viability after incubation with the AGSP-Cd²⁺ complex also suggested enhanced Cd²⁺ toxicity induced by AGSP. The metabolomics and lipidomics analysis revealed that, compared with the Cd²⁺ group, the AGSP-Cd²⁺ downregulated the phospholipid metabolism and resulted in more serious damage in the cellular membrane. The lipid metabolism disorder, in turn, amplified the generation of ROS, leading to a decrease in cell viability. These results provided new evidence of the enhanced Cd²⁺ toxicity upon interaction with seafood polysaccharides, and much attention should be paid to the effect of food ingredients on heavy metal ion toxicity.

Oncogenic transformation of human benign prostate hyperplasia with chronic cadmium exposure

Experimentally, it has been proved that cadmium served as an effective carcinogen and able to induce tumors in rodents in a dose-specific manner. However, systemic evaluation of cadmium exposure for the transformation of prostatic hyperplasia into prostate cancer (PCa) is still unclear. In the present study, an attempt has been made to establish cadmium-induced human prostate carcinogenesis using an in vitro model of BPH cells. Wide range of cadmium concentrations, i.e., 1 nM, 10 nM, 100 nM and 1μM, were chronically exposed to the human BPH cells for transformation into PCa and monitored using cell and molecular biology approaches. After eight weeks of exposure, the cells showed subtle morphological changes and shifts of cell cycle in the G2M phase. Significant increase in expression of prostatic genes AR, PSA, ER-β, and 5αR with increased nuclear localization of AR and pluripotency markers Cmyc, Klf4 indicated the carcinogenic effect of Cd. Further, the BPH cells exposed to Cd showed a substantial increase in the secretion of MMP-2 and MMP-9, influencing migratory potential of the cells along with decreased expression of the p63 protein which further strengthen the progression towards carcinogenesis and aggressive tumor studies. Data from the present study state that Cd exhibited marked invasiveness in BPH cells. These observations established a connecting link of BPH towards PCa pathogenesis. Further, the study will also help in investigating the intricate pathways involved in cancer progression.

Effect of cell cycle synchronization on cadmium-induced apoptosis and necrosis in NRK-52E cells

Heavy metal pollution is a problem that cannot be ignored. Due to the prevalence of cadmium in the environment and its harmful effects on humans, cadmium pollution has become a research hotspot recently. The mechanism of cadmium-induced toxicity has also drawn much attention and most studies have been conducted using whole cells, but the toxicological mechanism of cadmium remains unclear. In this study, we aimed to obtain NRK-52E cells at different growth stages by various methods and analyze the differences in cadmium toxicity. The results show that the cadmium sensitivity of cells in each phase was different and the late apoptotic rate was increased significantly after 5 µM Cd treatment. In addition, cadmium easily induces apoptosis of G0- and S-phase cells, as well as necrosis of S- and M-phase cells, but has no significant effect on G1-phase cells. Overall, we first explored the differences in the effects of cadmium on NRK-52E cells at various growth phases. Besides, the findings of this study might provide a theoretical basis for further exploration of the toxicological mechanism of cadmium.Abbreviations Cd: cadmium; CDK: cyclin-dependent kinases; DAPI 2-(4-amidinophenyl)-1H-indole-6-carboxamidine; TBST: Tris-buffered saline with Tween-20; PI: propidium iodide; DMEM: Dulbecco's Modified Eagle Medium; BCA: bicinchoninic acid.

Role of poly (ADP-ribose) polymerase-1 in cadmium-induced cellular DNA damage and cell cycle arrest in rat renal tubular epithelial cell line NRK-52E

With the development of modern industry, the problem of cadmium (Cd) pollution cannot be ignored and its toxicity has caused great personal injury to humans. Poly (ADP-ribose) polymerase 1 (PARP-1) protein is a research hotspot in recent years, the research we have published shows that 5 μM of Cd-treated NRK-52E cells activated PARP-1, but the specific effects of PARP-1 on DNA damage and cell cycle is unclear. Therefore, the purpose of this study is to reveal the effect of Cd on DNA damage and cell cycle arrest in NRK-52E cells, in addition, to investigate the role of PARP-1 in mediating this effect. Western blotting, comet assay, QRT-PCR, immunofluorescence, and co-immunoprecipitation were used to detect DNA damage and cell cycle-associated protein expression. Flow cytometry was used to assess cell cycle distribution and the apoptosis rates. Results showed that after the increase in treatment time and Cd concentration, the degree of DNA damage was significantly increased, and a transition from G0/G1 to S phase arrest was observed. In addition, inhibition of PARP-1 expression exacerbated cell damage and cell cycle arrest when DNA damage was low, but attenuated cell damage and even cell cycle arrest when DNA damage was severe. These findings in this study indicate that Cd causes DNA damage in NRK-52E cells, leading to cell cycle arrest at different phases depending on the degree of DNA damage. Moreover, PARP-1 plays an important role in mediating this effect, when DNA damage is low, it functions in DNA repair, however, when DNA damage is severe, it aggravates cell damage and induces cell death.

Mechanisms used by DNA MMR system to cope with Cadmium-induced DNA damage in plants

Cadmium (Cd) is found widely in soil and is severely toxic for plants, causing oxidative damage in plant cells because of its heavy metal characteristics. The DNA damage response (DDR) is triggered in plants to cope with the Cd stress. The DNA mismatch repair (MMR) system known for its mismatch repair function determines DDR, as mispairs are easily generated by a translesional synthesis under Cd-induced genomic instability. Cd-induced mismatches are recognized by three heterodimeric complexes including MutSα (MSH2/MSH6), MutSβ (MSH2/MSH3), and MutSγ (MSH2/MSH7). MutLα (MLH1/PMS1), PCNA/RFC, EXO1, DNA polymerase δ and DNA ligase participate in mismatch repair in turn. Meanwhile, ATR is preferentially activated by MSH2 to trigger DDR including the regulation of the cell cycle, endoreduplication, cell death, and recruitment of other DNA repair, which enhances plant tolerance to Cd. However, plants with deficient MutS will bypass MMR-mediated DDR and release the multiple-effect MLH1 from requisition of the MMR system, which leads to weak tolerance to Cd in plants. In this review, we systematically illustrate how the plant DNA MMR system works in a Cd-induced DDR, and how MMR genes regulate plant tolerance to Cd. Additionally, we also reviewed multiple epigenetic regulation systems acting on MMR genes under stress.

Isoorientin plays an important role in alleviating Cadmium-induced DNA damage and G0/G1 cell cycle arrest

Cadmium is a heavy metal pollutant that has been reported to cause oxidative stress, apoptosis, and autophagy in cells, while the flavone isoorientin is a traditional Chinese medicine extract that has proven antioxidant and anti-inflammatory properties. Accordingly, in this study we used the rat proximal tubular cell line NRK-52E and primary rat proximal tubular (rPT) cells as models to investigate the effects of isoorientin against Cadmium-induced cell injury and the mechanism of these effects. Comet assay, Western blot, flow cytometry, immunofluorescence, and transmission electron microscopy were used to evaluate cell damage and cell-cycle-related protein expression. Furthermore, real-time cell analysis, cell-counting kit-8, and ELISA were used to investigate the role of isoorientin in Cadmium-induced cell injury. The results revealed that treatment of rat renal tubular epithelial cells with 2.5 μM Cd for 12 h resulted in DNA damage and G0/G1 cell cycle arrest, while isoorientin attenuated this Cd-induced damage.

Cadmium induces apoptotic program imbalance and cell cycle inhibitor expression in cultured human astrocytes

Cadmium is a highly neurotoxic heavy metal impairing neurogenesis and induces neurodegenerative disorders. Toxic concentrations of cadmium induce astrocytic apoptosis by depleting intracellular glutathione levels, elevating intracellular calcium levels, altering mitochondria membrane potentials, and activating JNK and PI3K/Akt signaling pathways. Cadmium suppresses cell proliferation in kidney epithelial cells, lung fibroblasts, and primary myelocytes; however, cadmium's effects on proteins regulating oxidative stress, apoptosis, and cell proliferation in astrocytes are less known. The present study hypothesized that cadmium alters levels of antioxidant enzymes, apoptotic regulator proteins, and cell cycle inhibitor proteins, resulting in apoptosis and cell cycle arrest. Concentrations ≥20 μM cadmium induced apoptosis and led to intracellular changes including DNA fragmentation, reduced mRNA expression of antioxidant enzymes (i.e., catalase and glutathione S transferase-A4), downregulation of B-cell lymphoma 2 (Bcl-2), and upregulation of Bcl-2-associated X protein (Bax). Moreover, cadmium suppressed astrocytic proliferation by inducing S and G2/M phase cell cycle arrest and promoting p53, p21, and p27 expression. In conclusion, this study provides mechanistic insight into cadmium-induced cytotoxicity of astrocytes and highlights potential targets for prevention of cadmium-induced apoptosis and cell cycle arrest.

Silica - A trace geogenic element with emerging nephrotoxic potential

Silica is a trace-geogenic compound with limited-bioavailability. It inflicts health-perils like pulmonary-silicosis and chronic kidney disease (CKD), when available via anthropogenic-disturbances. Amidst silica-imposed pathologies, pulmonary toxicological-mechanisms are well-described, ignoring the renal-pathophysiological mechanisms. Hence, the present-study aimed to elucidate cellular-cum-molecular toxicological-mechanisms underlying silica-induced renal-pathology in-vitro. Various toxicity-assessments were used to study effects of silica on the physiological-functions of HK-cells (human-kidney proximal-tubular cells - the toxin's prime target) on chronic (1-7 days) sub-toxic (80 mg/L) and toxic (100-120 mg/L) dosing. Results depicted that silica triggered dose-cum-time dependent cytotoxicity/cell-death (MTT-assay) that significantly increased on long-term dosing with ≥100 mg/L silica; establishing the nephrotoxic-potential of this dose. Contrarily, insignificant cell-death on sub-toxic (80 mg/L) dosing was attributed to rapid intracellular toxin-clearance at lower-doses preventing toxic-effects. The proximal-tubular (HK-cells) cytotoxicity was found to be primarily mediated by silica-triggered incessant oxidative-stress (elevated ROS).·This enhanced ROS inflicted severe inflammation and subsequent fibrosis, evident from increased pro-inflammatory-cum-fibrogenic cytokines generation (IL-1β, IL-2, IL-6, TNF-α and TGF-β). Simultaneously, ROS induced persistent DNA-damage (Comet-assay) that stimulated G2/M arrest for p53-mediated damage-repair, aided by checkpoint-promoter (Chk1) activation and mitotic-inducers (i.e. Cdc-25, Cdk1, cyclinB1) inhibition. However, DNA-injuries surpassed the cellular-repair, which provoked the p53-gene to induce mitochondrial-mediated apoptotic cell-death via activation of Bax, cytochrome-c and caspase-cascade (9/3). This persistent apoptotic cell-death and simultaneous incessant inflammation culminated in the development of tubular-atrophy and fibrosis, the major pathological-manifestations of CKD. These findings provided novel-insights into the pathological-mechanisms (cellular and molecular) of silica-induced CKD, inflicted on chronic toxic-dosing (≥100 mg/L).Thereby, encouraging the development of therapeutic-strategies (e.g. anti-oxidant treatment) for specific molecular-targets (e.g. ROS) to retard silica-induced CKD-progression, for reduction in the global-CKD burden.

Oxidative stress and cell cycle arrest induced by short-term exposure to dustfall PM2.5 in A549 cells

It was reported that in vitro short-term exposure to PM_2.5 caused different lung diseases through inflammatory response, immune toxicity, oxidative stress, and genetic mutations. However, the complex molecular biological mechanism for its toxicity had not been fully elucidated. Therefore, the present study investigated the cytotoxicity, oxidative damage, mitochondria damage, apoptosis, and cell cycle arrest of NX and QH PM_2.5 in A549 cells. Further, cell cycle arrest-related gene levels in PM_2.5-induced A549 cells were also detected. Our results suggested that PM_2.5 reduced the cell viability in A549 cells. Simultaneously, excessive ROS decreased MMP levels and damaged mitochondrial membrane integrity and induced mitochondrial oxidative damage through the oxygen-dependent killer route, resulting in mitochondrial damage and cell apoptosis. Besides, the results also showed that PM_2.5 induced A549 cell cycle alteration in G2/M phase after co-culture for 24 h. G2/M phase arrest was induced by upregulation of p53 and p21 and downregulation of CDK1 mRNA expression. In addition, lncRNA Sox2ot might play an important role as the specific oncogenes and it participated in G2/M phase arrest by regulating the expression of EZH₂.

Retracted Article: Cd induces G2/M cell cycle arrest by up-regulating miR-133b via directly targeting PPP2R2D in L02 hepatocytes

This study could provide a novel epigenetic mechanism for Cd-induced acute hepatotoxicity and it would offer new targets for its intervention.

Cell cycle arrest mediated by Cd-induced DNA damage in Arabidopsis root tips

Accumulating evidence demonstrates that the aberrant expression of cell cycle regulation and DNA repair genes can result in abnormal cell proliferation and genomic instability in eukaryotic cells under different stresses. Herein, Arabidopsis thaliana (Arabidopsis) seedlings were grown hydroponically on 0.5 × MS media containing cadmium (Cd) at 0-2.5mgL^-1 for 5d of treatment. Real time quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis revealed that expression of DNA damage repair and cell cycle regulation genes, including BRCA1, MRE11, WEE1, CDKA;1 and PCNA1, showed an inverted U-shaped dose-response. In contrast, notably reduced expression was observed for G1-to-S transition-related genes, Histone H4, E2Fa and PCNA2; DSB end processing, GR1; G2-to-M transition-related gene, CYCB1;1; and DNA mismatch repair, MSH2, MSH6 and MLH1 genes in root tips exposed to 0.125-2.5mg/L Cd for 5d. Flow cytometry (FCM) analysis revealed significant increases of cells with a ²C nuclear content and with a ⁴C and ⁸C nuclear content under Cd stresses of 0.125 and 1-2.5mgL^-1, respectively. Our results suggest that 0.125mgL^-1 Cd-induced DNA damage induced the marked G1/S arrest, leading to accelerated growth in root tips, while 1.0-2.5mgL^-1 Cd-induced DNA damage caused a notable G2/M arrest in root tips, leading to reduced growth in root tips. This may be a protective mechanism that prevents cells with damaged DNA from dividing under Cd stress.

Initial autophagic protection switches to disruption of autophagic flux by lysosomal instability during cadmium stress accrual in renal NRK-52E cells

The renal proximal tubule (PT) is the major target of cadmium (Cd2+) toxicity where Cd2+ causes stress and apoptosis. Autophagy is induced by cell stress, e.g., endoplasmic reticulum (ER) stress, and may contribute to cell survival or death. The role of autophagy in Cd2+-induced nephrotoxicity remains unsettled due to contradictory results and lack of evidence for autophagic machinery damage by Cd2+. Cd2+-induced autophagy in rat kidney PT cell line NRK-52E and its role in cell death was investigated. Increased LC3-II and decreased p62 as autophagy markers indicate rapid induction of autophagic flux by Cd2+ (5-10 µM) after 1 h, accompanied by ER stress (increased p-PERK, p-eIF2α, CHOP). Cd2+ exposure exceeding 3 h results in p62/LC3-II accumulation, but diminished effect of lysosomal inhibitors (bafilomycin A1, pepstatin A +E-64d) on p62/LC3-II levels, indicating decreased autophagic flux and cargo degradation. At 24 h exposure, Cd2+ (5-25 µM) activates intrinsic apoptotic pathways (Bax/Bcl-2, PARP-1), which is not evident earlier (≤6 h) although cell viability by MTT assay is decreased. Autophagy inducer rapamycin (100 nM) does not overcome autophagy inhibition or Cd2+-induced cell viability loss. The autophagosome-lysosome fusion inhibitor liensinine (5 μM) increases CHOP and Bax/Bcl-2-dependent apoptosis by low Cd2+ stress, but not by high Cd2+. Lysosomal instability by Cd2+ (5 μM; 6 h) is indicated by increases in cellular sphingomyelin and membrane fluidity and decreases in cathepsins and LAMP1. The data suggest dual and temporal impact of Cd2+ on autophagy: Low Cd2+ stress rapidly activates autophagy counteracting damage but Cd2+ stress accrual disrupts autophagic flux and lysosomal stability, possibly resulting in lysosomal cell death.

Cadmium and α-lipoic acid activate similar de novo synthesis and recycling pathways for glutathione balance

Glutathione (GSH) protects cells against oxidative stress. Redox modifiers induce GSH biosynthesis and recycling to maintain reduced environment inside cells. Cadmium (Cd²⁺) is a heavy metal that activates redox-sensitive transcriptional factors. The antioxidant α-lipoic acid (ALA) has shown to modulate GSH pathways. This study aimed to investigate de novo synthesis and recycling pathways for GSH balance by different Cd²⁺ concentrations and ALA in HepG2 cells. ALA activates Nrf2 pathway leading to GSH increment. Pre-treatment with 1μM Cd²⁺ or ALA produces tolerance to 5μM Cd²⁺ toxic effects. 5μM Cd²⁺ exposure significantly augmented nuclear Nrf2, GSH and GCLC, GCLM, HMOX1, TNFα and IL-6 mRNA expression but not GSR, however these upsurges were significantly abrogated by ALA or 1μM Cd²⁺ pre-treatments. Exposure to low Cd²⁺ concentration generate timely protective responses, similar to that elicited by ALA, maintaining a normal redox balance inside the cell due to GSH replenishment.

Accumulation of p53 via down-regulation of UBE2D family genes is a critical pathway for cadmium-induced renal toxicity

Chronic cadmium (Cd) exposure can induce renal toxicity. In Cd renal toxicity, p53 is thought to be involved. Our previous studies showed that Cd down-regulated gene expression of the UBE2D (ubiquitin-conjugating enzyme E2D) family members. Here, we aimed to define the association between UBE2D family members and p53-dependent apoptosis in human proximal tubular cells (HK-2 cells) treated with Cd. Cd increased intracellular p53 protein levels and decreased UBE2D2 and UBE2D4 gene expression via inhibition of YY1 and FOXF1 transcription factor activities. Double knockdown of UBE2D2 and UBE2D4 caused an increase in p53 protein levels, and knockdown of p53 attenuated not only Cd-induced apoptosis, but also Cd-induced apoptosis-related gene expression (BAX and PUMA). Additionally, the mice exposed to Cd for 6 months resulted in increased levels of p53 and induction of apoptosis in proximal tubular cells. These findings suggest that down-regulation of UBE2D family genes followed by accumulation of p53 in proximal tubular cells is an important mechanism for Cd-induced renal toxicity.

Dietary NiCl₂ causes G₂/M cell cycle arrest in the broiler's kidney

Here we showed that dietary NiCl2 in excess of 300 mg/kg caused the G2/M cell cycle arrest and the reduction of cell proportion at S phase. The G2/M cell cycle arrest was accompanied by up-regulation of phosphorylated ataxia telangiectasia mutated (p-ATM), p53, p-Chk1, p-Chk2, p21 protein expression and ATM, p53, p21, Chk1, Chk2 mRNA expression, and down-regulation of p-cdc25C, cdc2, cyclinB and proliferating cell nuclear antigen (PCNA) protein expression and the cdc25, cdc2, cyclinB, PCNA mRNA expression.

Cadmium promotes the proliferation of triple-negative breast cancer cells through EGFR-mediated cell cycle regulation

Cadmium (Cd) is a carcinogenic metal which is implicated in breast cancer by epidemiological studies. It is reported to promote breast cancer cell growth in vitro through membrane receptors. The study described here examined Cd-mediated growth of non-metastatic human breast cancer derived cells that lack receptors for estrogen, progesterone, and HER2. Treatment of triple-negative HCC 1937 cells with 0.1-0.5 μM Cd increased cell growth by activation of AKT and ERK. Accelerated cell cycle progression was achieved by increasing the levels of cyclins A, B, and E, as well as those of CDKs 1 and 2. Although triple negative cells lack estrogen receptor, they express high levels of EGFR. Therefore, further studies on HCC 1937 and another triple-negative cell line, HCC 38, were conducted using specific siRNA and an inhibitor of EGFR to determine whether EGFR was responsible for mediating the effect of Cd. The results revealed that in both cell types EGFR was not only activated upon Cd treatment, but was also essential for the downstream activation of AKT and ERK. Based on these observations, it is concluded that, in breast cancer cells lacking estrogen receptor, sub-micromolar concentration of Cd can promote cell proliferation. Furthermore, that EGFR plays a critical role in this process.

Temporal changes in rat liver gene expression after acute cadmium and chromium exposure

U.S. Service Members and civilians are at risk of exposure to a variety of environmental health hazards throughout their normal duty activities and in industrial occupations. Metals are widely used in large quantities in a number of industrial processes and are a common environmental toxicant, which increases the possibility of being exposed at toxic levels. While metal toxicity has been widely studied, the exact mechanisms of toxicity remain unclear. In order to further elucidate these mechanisms and identify candidate biomarkers, rats were exposed via a single intraperitoneal injection to three concentrations of CdCl₂ and Na₂Cr₂O₇, with livers harvested at 1, 3, or 7 days after exposure. Cd and Cr accumulated in the liver at 1 day post exposure. Cd levels remained elevated over the length of the experiment, while Cr levels declined. Metal exposures induced ROS, including hydroxyl radical (•OH), resulting in DNA strand breaks and lipid peroxidation. Interestingly, ROS and cellular damage appeared to increase with time post-exposure in both metals, despite declines in Cr levels. Differentially expressed genes were identified via microarray analysis. Both metals perturbed gene expression in pathways related to oxidative stress, metabolism, DNA damage, cell cycle, and inflammatory response. This work provides insight into the temporal effects and mechanistic pathways involved in acute metal intoxication, leading to the identification of candidate biomarkers.

Differences of cytotoxicity of orthodontic bands assessed by survival tests in Saccharomyces cerevisiae

The aim of this study was to evaluate the cytotoxicity induced by orthodontic bands through survival tests on Saccharomyces cerevisiae, a microorganism that presents several genetic and biochemical characteristics similar to human cells. Three groups of bands were evaluated: silver soldered (SSB), laser soldered (LSB), and bands without any solder (WSB). Yeast cells were directly exposed to the bands and indirectly, when a previous elution of the metals in artificial saliva was performed. The negative control was composed of yeast cells or artificial saliva not exposed to any kind of metal. In the direct exposure experiments, all tested groups of bands induced a slight reduction in yeast viability compared to the control. This effect was more intense for the SSB, although not statistically significant. For the indirect exposure experiments, the SSB induced a statistically significant decrease in cell viability compared to the LSB. There were no significant differences between the survival rates of the negative control and the LSB group in both direct and saliva tests. SSBs were cytotoxic, whilst LSBs were not, confirming that laser soldering may be a more biocompatible alternative for use in connecting wires to orthodontic appliances.

Cadmium (Cd(2+)) exposure differentially elicits both cell proliferation and cell death related responses in SK-RC-45

Cadmium (Cd(2+)) is a major nephrotoxic environmental pollutant, affecting mostly proximal convoluted tubule (PCT) cells of the mammalian kidney, while conditionally Cd(2+) could also elicit protective responses with great variety and variability in different systems. The present study was designed to evaluate the molecular mechanism of Cd(2+) toxicity on human PCT derived Renal Cell Carcinoma (RCC), SK-RC-45 and compare its responses with normal human PCT derived cell line, NKE. Exposure of SK-RC-45 cells with different concentrations of CdCl2 (e.g. 0, 10 and 20μM) in serum free medium for 24h generate considerable amount of ROS, accompanied with decreased cell viability and alternations in the cellular and nuclear morphologies, heat shock responses and GCLC mediated protective responses. Also phosphatidylserine externalization, augmentation in the level of caspase-3, PARP, BAD, Apaf1 and cleaved caspase-9 along with decreased expression of Bcl2 and release of cytochrome c confirmed that, Cd(2+) dose dependently induces solely intrinsic pathway of apoptosis in SK-RC-45, independent of JNK. Furthermore, the non-toxic concentration (10μM) of Cd(2+) induced nuclear translocation of Nrf2 and increased expression in the level of HO-1 enzyme suggesting that at the milder concentration, Cd(2+) induces protective signaling pathways. On the other hand, exposure of NKE to different concentrations of CdCl2 (e.g. 0, 10, 20, 30 and 50μM) under the same conditions elevate stronger heat shock and SOD2 mediated protective responses. In contrary to the RCC PCT, the normal PCT derived cell follows JNK dependent and extrinsic pathways of apoptosis. Cumulatively, these results suggest that Cd(2+) exposure dose dependently elicit both cell proliferative and cell death related responses in SK-RC-45 cells and is differentially regulated with respect to normal kidney epithelia derived NKE cells.

Cadmium impairment of reproduction in the female wall lizard Podarcis sicula

The exposure to environmental toxicants such cadmium (Cd) is an important research area in wildlife protection. In this study, the effect of Cd oral administration on the ovarian structure and function and on reproductive performance of the Italian wall lizard Podarcis sicula was studied. In vivo, adult female lizards were randomly assigned to three groups. Cd was given with food in single dose and in multiple doses 3 days/week for 4 weeks at dose of 1.0 μg/g body weight. Following euthanasia, the ovaries were removed and analyzed for morpho-functional changes. Results demonstrated that Cd increases prefollicular germ cells number; the evaluation of the number of follicles detects significantly higher number of atretic growing follicles, whereas primary follicles remain unchanged with respect to controls. After Cd treatments, follicles are deformed by the presence of large protrusions and a general dysregulation in the follicle organization is observed. The zona pellucida is also affected. Cd causes alteration in sugar metabolism and in metallothionein gene expression. Finally, Cd administration significantly reduces clutch size and dramatically increases embryo mortality. In conclusion, data here described show that Cd induces morpho-functional alterations in lizard follicles and indicates that these are responsible for a significant impairment of oogenesis. The effects of the dose are time independent, persisting essentially unchanged regardless of single or multiple administration, so it can be concluded that even occasional, sublethal Cd contamination may significantly impair reproductive performance in these animals.

Cadmium and cellular signaling cascades: interactions between cell death and survival pathways

Cellular stress elicited by the toxic metal Cd(2+) does not coerce the cell into committing to die from the onset. Rather, detoxification and adaptive processes are triggered concurrently, allowing survival until normal function is restored. With high Cd(2+), death pathways predominate. However, if sublethal stress levels affect cells for prolonged periods, as in chronic low Cd(2+) exposure, adaptive and survival mechanisms may deregulate, such that tumorigenesis ensues. Hence, death and malignancy are the two ends of a continuum of cellular responses to Cd(2+), determined by magnitude and duration of Cd(2+) stress. Signaling cascades are the key factors affecting cellular reactions to Cd(2+). This review critically surveys recent literature to outline major features of death and survival signaling pathways as well as their activation, interactions and cross talk in cells exposed to Cd(2+). Under physiological conditions, receptor activation generates 2nd messengers, which are short-lived and act specifically on effectors through their spatial and temporal dynamics to transiently alter effector activity. Cd(2+) recruits physiological 2nd messenger systems, in particular Ca(2+) and reactive oxygen species (ROS), which control key Ca(2+)- and redox-sensitive molecular switches dictating cell function and fate. Severe ROS/Ca(2+) signals activate cell death effectors (ceramides, ASK1-JNK/p38, calpains, caspases) and/or cause irreversible damage to vital organelles, such as mitochondria and endoplasmic reticulum (ER), whereas low localized ROS/Ca(2+) levels act as 2nd messengers promoting cellular adaptation and survival through signal transduction (ERK1/2, PI3K/Akt-PKB) and transcriptional regulators (Ref1-Nrf2, NF-κB, Wnt, AP-1, bestrophin-3). Other cellular proteins and processes targeted by ROS/Ca(2+) (metallothioneins, Bcl-2 proteins, ubiquitin-proteasome system, ER stress-associated unfolded protein response, autophagy, cell cycle) can evoke death or survival. Hence, temporary or permanent disruptions of ROS/Ca(2+) induced by Cd(2+) play a crucial role in eliciting, modulating and linking downstream cell death and adaptive and survival signaling cascades.

Acute enhancement of non-rapid eye movement sleep in rats after drinking water contaminated with cadmium chloride

Cadmium (Cd) is a heavy metal widely used or effused by industries. Serious environmental Cd pollution has been reported over the past two centuries, whereas the mechanisms underlying Cd-mediated diseases are not fully understood. Interestingly, an increase in reactive oxygen species (ROS) after Cd exposure has been shown. Our group has demonstrated that sleep is triggered via accumulation of ROS during neuronal activities, and we thus hypothesize the involvement of Cd poisoning in sleep-wake irregularities. In the present study, we analyzed the effects of Cd intake (1-100 ppm CdCl₂ in drinking water) on rats by monitoring sleep encephalograms and locomotor activities. The results demonstrated that 100 ppm CdCl₂ administration for 28 h was sufficient to increase non-rapid-eye-movement (non-REM) sleep and reduce locomotor activities during the night (the rat active phase). In contrast, free-running locomotor rhythms under constant dim red light and their re-entrainment to 12:12-h light/dark cycles were intact under chronic (1 month) 100 ppm CdCl₂ administrations, suggesting a limited influence on circadian clock movements at this dosage. The relative amount of oxidized glutathione increased in the brain after the 28-h 100 ppm CdCl₂ administrations similar to the levels in cultured astrocytes receiving H₂O₂ or CdCl₂ in culture medium. Therefore, we propose Cd-induced sleep as a consequence of oxidative stress. As oxidized glutathione is an endogenous sleep substance, we suggest that Cd rapidly induces sleepiness and influences activity performance by occupying intrinsic sleep-inducing mechanisms. In conclusion, we propose increased non-REM sleep during the active phase as an index of acute Cd exposure.

Transforming growth factor β-1 stimulates profibrotic epithelial signaling to activate pericyte-myofibroblast transition in obstructive kidney fibrosis

Pericytes have been identified as the major source of precursors of scar-producing myofibroblasts during kidney fibrosis. The underlying mechanisms triggering pericyte-myofibroblast transition are poorly understood. Transforming growth factor β-1 (TGF-β1) is well recognized as a pluripotent cytokine that drives organ fibrosis. We investigated the role of TGF-β1 in inducing profibrotic signaling from epithelial cells to activate pericyte-myofibroblast transition. Increased expression of TGF-β1 was detected predominantly in injured epithelium after unilateral ureteral obstruction, whereas downstream signaling from the TGF-β1 receptor increased in both injured epithelium and pericytes. In mice with ureteral obstruction that were treated with the pan anti-TGF-β antibody (1D11) or TGF-β receptor type I inhibitor (SB431542), kidney pericyte-myofibroblast transition was blunted. The consequence was marked attenuation of fibrosis. In addition, epithelial cell cycle G2/M arrest and production of profibrotic cytokines were both attenuated. Although TGF-β1 alone did not trigger pericyte proliferation in vitro, it robustly induced α smooth muscle actin (α-SMA). In cultured kidney epithelial cells, TGF-β1 stimulated G2/M arrest and production of profibrotic cytokines that had the capacity to stimulate proliferation and transition of pericytes to myofibroblasts. In conclusion, this study identified a novel link between injured epithelium and pericyte-myofibroblast transition through TGF-β1 during kidney fibrosis.

Diurnal variation of cadmium-induced mortality in mice

Circadian timing largely modifies efficacy of many medicinal drugs. This viewpoint has been applied in the clinical medicine, known as chronotherapy. We think this viewpoint should also be introduced into toxicology as "chronotoxicology", however, information about the diurnal variation in toxicant sensitivity is still very scarce. We present here a clear and reproducible diurnal variation of cadmium (Cd)-induced mortality in mice. Male ICR mice kept under standard condition (12 hr light/dark cycle, lights on at 08:00) were injected with CdCl(2) (7.2 mg/kg, one shot) intraperitoneally at different time points in the day (zeitgeber time (ZT) 0, 4, 8, 12, 16 or 20). Survival number was determined at 14 days after injection. Interestingly, mice were sensitive to Cd acute toxicity at ZT8, while tolerant at mid-dark to early-light phase (ZT16, ZT20 and ZT0). Hepatic GSH level showed small daily fluctuation, lowest at ZT8 and highest at ZT20, and this fluctuation was similar to the diurnal variation of Cd sensitivity. In contrast, hepatic metallothionein (MT) level was not significant in these time points, although their level also showed small daily fluctuation. Our results indicated that Cd-induced mortality had clear diurnal variation, and suggested that the hepatic GSH level was one of the important factors for determination of this Cd-induced diurnal mortality.

Mechanisms of cadmium induced genomic instability

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.

Involvement of E2F1 transcriptional activity in cadmium-induced cell-cycle arrest at G1 in human lung fibroblasts

Human cadmium (Cd) exposure is associated with cancers of the lung and kidney. Using cDNA microarray analysis, we have recently reported that the expression of E2F1 is reduced by Cd in human lung fibroblasts, indicating the possibility of G1-phase arrest. To test this hypothesis, we investigated the effects of Cd on the cyclin-dependent kinase (CDK2) and retinoblastoma protein (Rb) regulatory pathways in WI38 human lung fibroblasts. We demonstrate here that G1-phase accumulation was induced by Cd in WI38 (wild-type for p53 and Rb), but not in the SV40 large T antigen-transformed variant WI38-VA13 (p53- and Rb-defective). Cd-induced cell-cycle arrest was associated with a decrease in CDK2 protein and with increase in p21 expression and p53 phosphorylation. Cd treatment caused a distinct increase in the formation of p21-cyclin E-CDK2 complex, as revealed by immunoprecipitation. The level of Rb-E2F1 complexes was increased, and the translocation of E2F1 to the nucleus was decreased by Cd treatment. Consequently, the transcriptional activity of E2F1 and the expression of the E2F1 target genes were also decreased by Cd. These results clearly demonstrate that Cd-mediated G1 arrest in WI38 cells is associated with the suppression of Rb phosphorylation and with the inhibition of E2F1 transcriptional activity.

Adaptation to alkalosis induces cell cycle delay and apoptosis in cortical collecting duct cells: role of Aquaporin-2

Collecting ducts (CD) not only constitute the final site for regulating urine concentration by increasing apical membrane Aquaporin-2 (AQP2) expression, but are also essential for the control of acid-base status. The aim of this work was to examine, in renal cells, the effects of chronic alkalosis on cell growth/death as well as to define whether AQP2 expression plays any role during this adaptation. Two CD cell lines were used: WT- (not expressing AQPs) and AQP2-RCCD(1) (expressing apical AQP2). Our results showed that AQP2 expression per se accelerates cell proliferation by an increase in cell cycle progression. Chronic alkalosis induced, in both cells lines, a time-dependent reduction in cell growth. Even more, cell cycle movement, assessed by 5-bromodeoxyuridine pulse-chase and propidium iodide analyses, revealed a G2/M phase cell accumulation associated with longer S- and G2/M-transit times. This G2/M arrest is paralleled with changes consistent with apoptosis. All these effects appeared 24 h before and were always more pronounced in cells expressing AQP2. Moreover, in AQP2-expressing cells, part of the observed alkalosis cell growth decrease is explained by AQP2 protein down-regulation. We conclude that in CD cells alkalosis causes a reduction in cell growth by cell cycle delay that triggers apoptosis as an adaptive reaction to this environment stress. Since cell volume changes are prerequisite for the initiation of cell proliferation or apoptosis, we propose that AQP2 expression facilitates cell swelling or shrinkage leading to the activation of channels necessary to the control of these processes.

Indoxyl sulfate inhibits proliferation of human proximal tubular cells via endoplasmic reticulum stress

Uremic toxins can deteriorate renal function, but little is known about its mechanism. Because tubular injury is central to progression of chronic kidney disease (CKD), we investigated the effects of a representative uremic toxin indoxyl sulfate (IS) on tubular cells. IS induced endoplasmic reticulum (ER) stress in cultured human proximal tubular cells, demonstrated by the increase in C/EBP homologous protein (CHOP) in the immunoblots. Moreover, administration of an oral adsorbent AST-120 reduced serum IS concentration and decreased tubular expression of CHOP in immunohistochemistry in 5/6-nephretomized, CKD model, rats. Furthermore, we disclosed that IS inhibited proliferation of tubular cells in 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium and 5-bromo-2'-deoxyuridine assay, whereas the results of trypan blue exclusion and lactate dehydrogenase assay showed that IS did not promote cell death. This inhibition was mitigated by small interfering (si) RNA against CHOP. Furthermore, IS increased the cyclin-dependent kinase inhibitor p21(WAF1/CIP1) (p21). Surprisingly, this was mediated by the inflammatory cytokine interleukin (IL)-6, the expression of which was decreased by siRNA against activating transcription factor 4, another ER stress marker; however, the induction of IL-6 and p21 by IS was not suppressed by siRNA targeted to CHOP, suggesting that they were downstream of ER stress, but independent of CHOP. Moreover, we found that their upregulation was dependent on ERK, using the ERK pathway inhibitor U-0126. Collectively, we demonstrated that IS induced ER stress in tubular cells and inhibited cell proliferation via two pathways downstream of ER stress, namely CHOP and ERK-IL-6-p21. These are possible targets for suppressing progression of CKD.

Cdc20 proteolysis requires p38 MAPK signaling and Cdh1-independent APC/C ubiquitination during spindle assembly checkpoint activation by cadmium

Cdc20, an activator of the anaphase promoting complex/cyclosome (APC/C) ubiquitin ligase, initiates the destruction of key mitotic regulators to facilitate mitosis, while it is negatively regulated by the spindle assembly checkpoint (SAC) to prevent premature anaphase entry. Activation of the p38 mitogen-activated protein kinase could contribute to mitotic arrest, but the underlying mechanism is unknown. Here we report a novel pathway in which the p38 signaling triggers Cdc20 destruction under SAC elicited by cadmium, a human carcinogen. We found that the cadmium-induced prometaphase arrest was linked to decreased Cdc20 and accumulated cyclin A protein levels in human cells, whereas the activity of cyclin B1-Cdk1 was unaffected. The Cdc20 half-life was markedly shortened along with its ubiquitination and degradation via 26S proteasome in cadmium-treated asynchronous or G(2)-enriched cells. Depletion of APC3 markedly suppressed the cadmium-induced Cdc20 ubiquitination and proteolysis, while depletion of Cdh1, another activator of APC/C, did not. Intriguingly, blockage of p38 activity restored the Cdc20 levels for continuing mitosis under cadmium, while inhibition of JNK activity had no effect. The cadmium-induced Cdc20 proteolysis was also suppressed during transient depletion of p38alpha or stable expression a dominant negative form of p38. Inhibition of p38 abolished the induction of Mad2-Cdc20-APC3 complex by cadmium. Moreover, forced expression of MKK6-p38 signaling could promote Cdc20 degradation in a Cdh1-independent APC/C pathway. In summary, accelerated ubiquitination and proteolysis of Cdc20 is essential for prometaphase arrest that is mediated via the p38 signaling during SAC activation.

The oxidative stress: endoplasmic reticulum stress axis in cadmium toxicity

Cadmium preferentially accumulates in the kidney, the major target for cadmium-related toxicity. Several underlying mechanisms are postulated, and reactive oxygen species (ROS) have been considered as crucial mediators for tissue injuries. In addition to oxidative stress, we recently disclosed that endoplasmic reticulum (ER) stress also plays a critical role. Cadmium causes ER stress in vitro and in vivo and mediates induction of apoptosis in target tissues. In this article, we describe a role for ER stress and involvement of particular branches of the unfolded protein response (UPR) in cadmium-triggered tissue injury, especially nephrotoxicity. We also discuss relationship between oxidative stress and ER stress, and involvement of selective ROS in the induction of pro-apoptotic branches of the UPR.

Cadmium-induced DNA damage triggers G(2)/M arrest via chk1/2 and cdc2 in p53-deficient kidney proximal tubule cells

Carcinogenesis is a multistep process that is frequently associated with p53 inactivation. The class 1 carcinogen cadmium (Cd(2+)) causes renal cancer and is known to inactivate p53. G(2)/mitosis (M) arrest contributes to stabilization of p53-deficient mutated cells, but its role and regulation in Cd(2+)-exposed p53-deficient renal cells are unknown. In p53-inactivated kidney proximal tubule (PT) cells, comet assay experiments showed that Cd(2+) (50-100 microM) induced DNA damage within 1-6 h. This was associated with peak formation of reactive oxygen species (ROS) at 1-3 h, measured with dihydrorhodamine 123, and G(2)/M cell cycle arrest at 6 h, which were abolished by the antioxidant alpha-tocopherol (100 microM). Cd(2+)-induced G(2)/M arrest was enhanced approximately twofold on release from cell synchronization (double thymidine block or nocodazole) and resulted in approximately twofold increase of apoptosis, indicating that G(2)/M arrest mirrors DNA damage and toxicity. The Chk1/2 kinase inhibitor UCN-01 (0.3 microM), which relieves G(2)/M transition block, abolished Cd(2+)-induced G(2) arrest and increased apoptosis. This was accompanied by prevention of Cd(2+)-induced cyclin-dependent kinase cdc2 phosphorylation at tyrosine 15, as shown by immunofluorescence microscopy and immunoblotting. The data indicate that in p53-inactivated PT cells Cd(2+)-induced ROS formation and DNA damage trigger signaling of checkpoint activating kinases ataxia telangiectasia-mutated kinase (ATM) and ataxia telangiectasia and Rad3-related kinase (ATR) to cause G(2)/M arrest. This may promote survival of premalignant PT cells and Cd(2+) carcinogenesis.

Divergence to apoptosis from ROS induced cell cycle arrest: effect of cadmium

Recently, the role of cadmium (Cd) in immunosupression has gained importance. Nevertheless, the signaling pathways underlying cadmium-induced immune cell death remains largely unclear. In accordance to our previous in vivo report, and to evaluate the further details of the mechanism, we have investigated the effects of cadmium (CdCl(2), H(2)O) on cell cycle regulation and apoptosis in splenocytes in vitro. Our results have revealed that reactive oxygen species (ROS) and p21 are involved in cell cycle arrest in a p53 independent manner but late hour apoptotic response was accompanied by the p53 up-regulation, loss of mitochondrial transmembrane potential (MTP), down-regulation of Bcl-xl, activation of caspase-3 and release of cytochrome c (Cyt c). However, pifithrin alfa (PFT-alpha), an inhibitor of p53, fails to rescue the cells from the cadmium-induced cell cycle arrest but prevents Bcl-xl down-regulation and loss of Deltapsi(m), which indicates that there is an involvement of p53 in apoptosis. In contrast, treatment with N-acetyl cysteine (NAC) can prevent cell cycle arrest and p21 up-regulation at early hours. Although it is clear that, NAC has no effect on apoptosis, p53 expression and MPT changes at late stage events. Taken together, we have demonstrated that cadmium promotes ROS generation, which potently initiates the cell cycle arrest at early hours and finally induces p53-dependent apoptosis at later part of the event.

Lack of cross-tolerance following heat and cadmium exposure in functional MDCK monolayers

Exposure of monolayers of Madin-Darby canine kidney epithelial (MDCK) cells to a mild heat stimulus induces a state of physiological thermotolerance in which epithelial barrier function is maintained following a second more severe heat stress. We have previously shown that expression of exogenous HSP70 fully mimics the effects of the conditioning heat stress. Exposure of MDCK cells to elevated temperatures or medium containing CdCl2 caused a robust increase in cellular levels of HSP70. Pretreatment of MDCK monolayers with cadmium but not heat caused a small protection of epithelial barrier function against a second challenge with cadmium. In addition, a prior exposure of monolayers to cadmium at levels sufficient to induce HSP70 expression and increased cellular chaperone activity did not afford protection against a subsequent thermal challenge. Therefore multiple stress-specific cellular pathways impinge on the ability of heat shock proteins to induce physiological thermotolerance. Occludin, a component of tight junctions, is induced in MDCK cells engineered to express high levels of exogenous HSP70, potentially accounting for an elevation in baseline resistance. However neither basal levels of occludin, nor alterations in occludin expression, were correlated with epithelial barrier function in MDCK cells either exposed to elevated temperatures or challenged with cadmium.

Impact of overexpression of metallothionein-1 on cell cycle progression and zinc toxicity

Metallothioneins (MTs) have an important role in zinc homeostasis and may counteract the impact of oversupply. Both intracellular zinc and MT expression have been implicated in proliferation control and resistance to cellular stress, although the interdependency is unclear. The study addresses the consequences of a steady-state overexpression of MT-1 for intracellular zinc levels, cell cycle progression, and protection from zinc toxicity using a panel of cell lines with differential expression of MT-1. The panel comprised parental Chinese hamster ovary-K1 cells with low endogenous expression of MT and transfectants with enhanced expression of mouse MT-1 on an autonomously replicating expression vector with a noninducible promoter. Cell cycle progression, determined by flow cytometry and time-lapse microscopy, revealed that enhanced cytoplasmic expression of MT-1 does not impact on normal cell cycle operation, suggesting that basal levels of MT-1 expression are not limiting for background levels of oxidative stress. MT-1 overexpression correlated with a steady-state increase in cytoplasmic free Zn(2+), assessed using the fluorescent zinc-sensor Zinquin, particularly at high levels of overexpression, further suggesting that zinc availability is normally not limiting for cell cycle progression. Enhanced MT-1 expression, over a 10-fold range, had a clear impact on resistance to Cd(2+) and Zn(2+) toxicity. In the case of Zn(2+), the degree of protection afforded was less, indicating that MT-1 has a limited range and saturable capacity for effecting resistance. The results have implications for the use of cellular stress responses to exogenously supplied zinc and zinc-based systemic therapies.