Acquisition of apoptotic resistance in cadmium-transformed human prostate epithelial cells: Bcl-2 overexpression blocks the activation of JNK signal transduction pathway

The promotion of non-small cell lung cancer progression by collagen and calcium binding EGF domain 1 is mediated through the regulation of ERK/JNK/P38 phosphorylation by reactive oxygen species

Reactive oxygen species (ROS) are metabolic by-products of cells, and abnormal changes in their levels are often associated with tumor development. Our aim was to determine the role of collagen and calcium binding EGF domain 1 (CCBE1) in oxidative stress and tumorigenesis in non-small cell lung cancer cells (NSCLC). We investigated the tumorigenic potential of CCBE1 in NSCLC using in vitro and in vivo models of CCBE1 overexpression and knockdown. Immunohistochemical staining results showed that the expression of CCBE1 in cancer tissues was significantly higher than that in adjacent tissues. Cell counting Kit 8, clonal formation, wound healing, and transwell experiments showed that CCBE1 gene knockdown significantly inhibited the migration, invasion, and proliferation of NSCLC cell lines. In terms of mechanism, the silencing of CCBE1 can significantly promote the morphological abnormalities of mitochondria, significantly increase the intracellular ROS level, and promote cell apoptosis. This change of oxidative stress can affect cell proliferation, migration, and invasion by regulating the phosphorylation level of ERK/JNK/P38 MAPK. Specifically, the downregulation of CCBE1 inhibits the phosphorylation of ERK/P38 and promotes the phosphorylation of JNK in NSCLC, and this regulation can be reversed by the antioxidant NAC. In vivo experiments confirmed that downregulating CCBE1 gene could inhibit the growth of NSCLC in BALB/c nude mice. Taken together, our results confirm the tumorigenic role of CCBE1 in promoting tumor invasion and migration in NSCLC, and reveal the molecular mechanism by which CCBE1 regulates oxidative stress and the ERK/JNK/P38 MAPK pathway.

Mechanisms of Heavy Metal Cadmium (Cd)-Induced Malignancy

The environmental pollution of cadmium is worsening, and its significant carcinogenic effects on humans have been confirmed. Cadmium can induce cancer through various signaling pathways, including the ERK/JNK/p38MAPK, PI3K/AKT/mTOR, NF-κB, and Wnt. It can also cause cancer by directly damaging DNA and inhibiting DNA repair systems, or through epigenetic mechanisms such as abnormal DNA methylation, LncRNA, and microRNA. However, the detailed mechanisms of Cd-induced cancer are still not fully understood and require further investigation.

The dynamic face of cadmium-induced Carcinogenesis: Mechanisms, emerging trends, and future directions

Cadmium (Cd) is a malleable element with odorless, tasteless characteristics that occurs naturally in the earth's crust, underground water, and soil. The most common reasons for the anthropological release of Cd to the environment include industrial metal mining, smelting, battery manufacturing, fertilizer production, and cigarette smoking. Cadmium-containing products may enter the environment as soluble salts, vapor, or particle forms that accumulate in food, soil, water, and air. Several epidemiological studies have highlighted the association between Cd exposure and adverse health outcomes, especially renal toxicity, and the impact of Cd exposure on the development and progression of carcinogenesis. Also highlighted is the evidence for early-life and even maternal exposure to Cd leading to devastating health outcomes, especially the risk of cancer development in adulthood. Several mechanisms have been proposed to explain how Cd mediates carcinogenic transformation, including epigenetic alteration, DNA methylation, histone posttranslational modification, dysregulated non-coding RNA, DNA damage in the form of DNA mutation, strand breaks, and chromosomal abnormalities with double-strand break representing the most common DNA form of damage. Cd induces an indirect genotoxic effect by reducing p53's DNA binding activity, eventually impairing DNA repair, inducing downregulation in the expression of DNA repair genes, which might result in carcinogenic transformation, enhancing lipid peroxidation or evasion of antioxidant interference such as catalase, superoxide dismutase, and glutathione. Moreover, Cd mediates apoptosis evasion, autophagy activation, and survival mechanisms. In this review, we decipher the role of Cd mediating carcinogenic transformation in different models and highlight the interaction between various mechanisms. We also discuss diagnostic markers, therapeutic interventions, and future perspectives.

Comparative Effects of Brominated Flame Retardants BDE-209, TBBPA, and HBCD on Neurotoxicity in Mice

Brominated flame retardants (BFRs) are ubiquitous industrial chemicals. In China, BFRs that are applied in large quantities include decabromodiphenyl ether (BDE-209), tetrabromobisphenol A (TBBPA), and hexabromocyclododecane (HBCD). Although findings are not always unequivocal, mounting evidence in vivo suggests that the BFRs have potential neurotoxicity. The present study aimed to assess and compare the neurotoxic effects of these three BFRs' exposure. Male mice were orally exposed to BDE-209, TBBPA, or HBCD at 50 and 100 mg/kg bw/day for 28 days. The cognitive behavior, oxidative stress (ROS, MDA, and GSH), apoptosis-related genes (caspase-3, bax, and bcl-2), memory-related proteins (BDNF and PSD-95), and neurotransmitters (AChE and ChAT) were detected comparatively. Results showed that high doses of BDE-209, TBBPA, and HBCD exposure impaired spatial memory of mice, elevated ROS and MDA and reduced GSH levels of hippocampus, upregulated caspase-3 and bax expressions, decreased BDNF and PSD-95 levels, and disordered AChE and ChAT levels. Notably, BDE-209 caused greater adverse effects > HBCD > TBBPA. This study confirms and extends that these three BFRs had similar neurotoxic effects at current concentrations, although they may be more or less toxic.

Toxic Mechanisms of Five Heavy Metals: Mercury, Lead, Chromium, Cadmium, and Arsenic

The industrial activities of the last century have caused massive increases in human exposure to heavy metals. Mercury, lead, chromium, cadmium, and arsenic have been the most common heavy metals that induced human poisonings. Here, we reviewed the mechanistic action of these heavy metals according to the available animal and human studies. Acute or chronic poisonings may occur following exposure through water, air, and food. Bioaccumulation of these heavy metals leads to a diversity of toxic effects on a variety of body tissues and organs. Heavy metals disrupt cellular events including growth, proliferation, differentiation, damage-repairing processes, and apoptosis. Comparison of the mechanisms of action reveals similar pathways for these metals to induce toxicity including ROS generation, weakening of the antioxidant defense, enzyme inactivation, and oxidative stress. On the other hand, some of them have selective binding to specific macromolecules. The interaction of lead with aminolevulinic acid dehydratase and ferrochelatase is within this context. Reactions of other heavy metals with certain proteins were discussed as well. Some toxic metals including chromium, cadmium, and arsenic cause genomic instability. Defects in DNA repair following the induction of oxidative stress and DNA damage by the three metals have been considered as the cause of their carcinogenicity. Even with the current knowledge of hazards of heavy metals, the incidence of poisoning remains considerable and requires preventive and effective treatment. The application of chelation therapy for the management of metal poisoning could be another aspect of heavy metals to be reviewed in the future.

Ins and outs of cadmium-induced carcinogenesis: Mechanism and prevention

Cadmium (Cd) is a heavy metal and a highly toxic pollutant that is released into the environment as a byproduct of most modern factories and industries. Cd enters our body in significant quantities from contaminated water, cigarette smoke, or food product to many detrimental health hazards. Based on causal association all the Cd-related or derived compounds have been classified as carcinogens. In this study, we present an overview of the published literature to understand the molecular mechanisms for Cd-induced carcinogenesis and its prevention. In acute Cd poisoning production of reactive oxygen species is a key factor. However, chronic Cd exposure can transform cells to become more resistant to oxidative stress. Also, as an epigenetic mechanism Cd acts indirectly on DNA repair mechanisms via alteration of reactions upstream. Those transformed cells acquire resistance to apoptosis and deregulation of calcium homeostasis. Leading to uncontrolled carcinogenic cell proliferation and inherent DNA lesions. Flavonoids commonly found in plant foods have been shown to have a protective effect against Cd-induced carcinogenicity. A wide variety of tumorigenic mechanisms involved in chronic Cd exposure and the beneficial effects of flavonoids against Cd-induced carcinogenicity necessitate further investigations.

Mode of action-based risk assessment of genotoxic carcinogens

The risk assessment of chemical carcinogens is one major task in toxicology. Even though exposure has been mitigated effectively during the last decades, low levels of carcinogenic substances in food and at the workplace are still present and often not completely avoidable. The distinction between genotoxic and non-genotoxic carcinogens has traditionally been regarded as particularly relevant for risk assessment, with the assumption of the existence of no-effect concentrations (threshold levels) in case of the latter group. In contrast, genotoxic carcinogens, their metabolic precursors and DNA reactive metabolites are considered to represent risk factors at all concentrations since even one or a few DNA lesions may in principle result in mutations and, thus, increase tumour risk. Within the current document, an updated risk evaluation for genotoxic carcinogens is proposed, based on mechanistic knowledge regarding the substance (group) under investigation, and taking into account recent improvements in analytical techniques used to quantify DNA lesions and mutations as well as "omics" approaches. Furthermore, wherever possible and appropriate, special attention is given to the integration of background levels of the same or comparable DNA lesions. Within part A, fundamental considerations highlight the terms hazard and risk with respect to DNA reactivity of genotoxic agents, as compared to non-genotoxic agents. Also, current methodologies used in genetic toxicology as well as in dosimetry of exposure are described. Special focus is given on the elucidation of modes of action (MOA) and on the relation between DNA damage and cancer risk. Part B addresses specific examples of genotoxic carcinogens, including those humans are exposed to exogenously and endogenously, such as formaldehyde, acetaldehyde and the corresponding alcohols as well as some alkylating agents, ethylene oxide, and acrylamide, but also examples resulting from exogenous sources like aflatoxin B1, allylalkoxybenzenes, 2-amino-3,8-dimethylimidazo[4,5-f] quinoxaline (MeIQx), benzo[a]pyrene and pyrrolizidine alkaloids. Additionally, special attention is given to some carcinogenic metal compounds, which are considered indirect genotoxins, by accelerating mutagenicity via interactions with the cellular response to DNA damage even at low exposure conditions. Part C finally encompasses conclusions and perspectives, suggesting a refined strategy for the assessment of the carcinogenic risk associated with an exposure to genotoxic compounds and addressing research needs.

Dermatotoxicity of oral cadmium is strain-dependent and related to differences in skin stress response and inflammatory/immune activity

Adverse effects of non-occupational exposure to cadmium (Cd) are increasingly acknowledged. Since our previous study has showed that orally acquired Cd affects skin, the contribution of genetic background to dermatotoxicity of oral cadmium was examined in two rat strains, Albino Oxford (AO) and Dark Agouti (DA), which differed in response to chemicals. While similar accumulation of Cd in the skin of both strains was noted, the skin response to the metal differed. DA rat individuals mounted antioxidant enzyme defense in the skin already at lower Cd dose, in contrast to AO rats which reacted to higher metal dose solely (and less pronounced), implying higher susceptibility of DA strain to Cd dermatotoxicity. Epidermal cells from both strains developed stress response, but higher intensity of antioxidant response in AO rats implied this strain`s better ability to defend against Cd insult. Cd induced epidermal cells' proinflammatory cytokine response only in DA rats. Increased IL-10 seems responsible for the lack of response in AO rats. Differences in the pattern of skin/epidermal cell responsiveness to cadmium give a new insight into repercussion of genetic variability to dermatotoxicity of orally acquired cadmium, bearing relevance for variations in the link between dietary cadmium and inflammation-based skin pathologies.

Biological and molecular modifications induced by cadmium and arsenic during breast and prostate cancer development

Breast and prostate cancer are two of the most common malignancies worldwide. Both cancers can develop into hormone -dependent or -independent subtypes and are associated to environmental exposure in the context of an inherited predisposition. As and Cd have been linked to the onset of both cancers, with the exception of As, which lacks a definitive association with breast carcinogenesis. The two elements exert an opposite effect dependent on acute versus chronic exposure. High doses of As or Cd were shown to induce cell death in acute experimental exposure, while chronic exposure triggers cell proliferation and viability, which is no longer limited by telomere shortening and apoptosis. The chronically exposed cells also increase their invasion capacity and tumorigenic potential. At molecular level, malignant transformation is evidenced mainly by up-regulation of BCL-2, MMP-2, MMP-9, VIM, Snail, Twist, MT, MLH and down-regulation of Casp-3, PTEN, E-CAD, and BAX. The signaling pathways most commonly activated are KRAS, p53, TGF-β, TNF-α, WNT, NRF2 and AKT. This knowledge could potentially raise public awareness over the health risks faced by the human population living or working in a polluted environment and smokers. Human exposure to As and Cd should be minimize as much as possible. Healthcare policies targeting people belonging to these risk categories should include analysis of: DNA damage, oxidative stress, molecular alterations, and systemic level of heavy metals and of essential minerals. In this review, we present the literature regarding cellular and molecular alterations caused by exposure to As or Cd, focusing on the malignant transformation of normal epithelial cells after long-term intoxication with these two carcinogens.

Effect of both selenium and biosynthesized nanoselenium particles on cadmium-induced neurotoxicity in albino rats

Because cadmium (Cd) is not naturally degradable by ecosystems, it interferes with many types of food chains. Cd accumulates in the kidney, liver and in the nervous tissues, especially the brain. The neurotoxicity of Cd is very high, as it alters the integrity, and increases the permeability, of the blood–brain barrier. Cd penetrates and accumulates in neurons in the brains of rats. This study reveals that Cd decreases antioxidant enzymes and increases oxidative stress in the brain. In addition, Cd increases lipid peroxidation of brain tissues. Cd increases the expression of the Cu/Zn superoxide dismutase gene. It also affects cholinergic, glutamatergic, gamma-Aminobutyric acid (GABAergic), dopamine, serotonin and acetylcholine neurotransmitters in brain tissue. Consequently, Cd increases the formation of amyloid β, a neurotoxic index, and induces apoptosis by changing the quality and the quantity of Bcl-2, Bax and p53 proteins. In conclusion, both selenium and nanoselenium show potential antioxidant activity and promote recovery from the neurotoxic action of Cd.

Neuroprotective Effects of Polydeoxyribonucleotide in a Murine Model of Cadmium Toxicity

Cadmium (Cd) is a harmful heavy metal, which causes severe brain damage and neurotoxic effects. Polydeoxyribonucleotide (PDRN) stimulates adenosine A_2A receptor, thus contrasting several deleterious mechanisms in course of tissue damages. We aimed to investigate the possible neuroprotective effect of PDRN in a murine model of Cd-induced brain toxicity. Male C57 BL/6J mice were treated as follows: vehicle (0.9% NaCl, 1 ml/kg/day), PDRN (8 mg/kg/day), CdCl₂ (2 mg/kg/day), and CdCl₂ + PDRN. Animals were tested with the Morris water maze test to assess spatial memory and learning. After 14 days of treatment, brains were processed to evaluate the presence of edema in the cerebral tissue, the expression of mammalian target of rapamycin kinase (mTOR) and brain-derived neurotrophic factor (BDNF), and the morphological behavior of the hippocampal structures. After CdCl₂ administration, the escape latency was high, protein expression of BDNF was significantly decreased if compared to controls, mTOR levels were higher than normal controls, and brain edema and neuronal damages were evident. The coadministration of CdCl₂ and PDRN significantly diminished the escape latency, increased BDNF levels, and decreased protein expression of mTOR. Furthermore, brain edema was reduced and the structural organization and the number of neurons, particularly in the CA1 and CA3 hippocampal areas, were improved. In conclusion, a functional, biochemical, and morphological protective effect of PDRN against Cd induced toxicity was demonstrated in mouse brain.

Recent views of heavy metals as possible risk factors and potential preventive and therapeutic agents in prostate cancer

Prostate cancer is the most common cancer in men in many industrialized countries. A role for androgens in prostate tumor progression is well recognized, while estrogens may cooperate with androgens in prostate carcinogenesis. The incidence of prostate cancer is highly variable in the different countries, suggesting an important role of environmental factors. Heavy metals are common environmental contaminants and some of them are confirmed or suspected human carcinogens. Some metals are endowed with estrogenic and/or androgenic activities and may play a role as cancer risk factors through this mechanism. Moreover, prostate cancer may present alterations in the intracellular balance of trace metals, such as zinc and copper, which are involved in several regulatory proteins. Herein, we review the possible role of environmental heavy metals and of metal-dyshomeostasis in prostate cancer development and promotion as well as the potential use of some metals in the prevention and therapy of prostate cancer.

Induction of Plac8 promotes pro-survival function of autophagy in cadmium-induced prostate carcinogenesis

Chronic exposure to cadmium is known to be a risk factor for human prostate cancer. Despite over-whelming evidence of cadmium causing carcinogenicity in humans, the specific underlying molecular mechanisms that govern metal-induced cellular transformation remain unclear. Acute exposure (up to 72 h) to cadmium induces apoptosis in normal prostate epithelial cells (RWPE-1), while chronic exposure (>1 year) transforms these cells to a malignant phenotype (cadmium-transformed prostate epithelial cells; CTPE). Increased expression of autophagy-regulated genes; Plac8, LC3B and Lamp-1; in CTPE cells was associated with cadmium-induced transformation. Increased expression of Plac8, a regulator of autophagosome/autolysosome fusion, facilitates the pro-survival function of autophagy and upregulation of pAKT^(ser473) and NF-κβ, to allow CTPE to proliferate. Likewise, inhibition of Plac8 suppresses CTPE cell growth. Additionally, overexpression of Plac8 in RWPE-1 cells induces resistance to cadmium toxicity. Pharmacological inhibitors and an inducer of autophagy failed to affect Plac8 expression and CTPE cell viability, suggesting a unique role for Plac8 in cadmium-induced prostate epithelial cell transformation. These results support a role for Plac8 as an essential component in the cadmium-induced transformation of normal prostate epithelial cells to a cancerous state.

Progressive silencing of the zinc transporter Zip8 (Slc39a8) in chronic cadmium-exposed lung epithelial cells

Cadmium (Cd), a non-essential metal, stealthily enters the cells by utilizing the essential metal importing pathways. The zinc transporters Zip8, Zip14, and divalent metal transporter 1 (Dmt1) are now emerging as several important metal transporters involved in cellular Cd incorporation and their expressions have been shown to be down-regulated in several Cd-resistant (CdR) cell lines, however, the involvement of these transporters during the development of Cd-resistance in lung cells is unclear. In this study, we therefore check the expression of these metal transporters in our previously established rat lung epithelial cells (LECs) and show that the level of Zip8 is progressively silenced when LECs are adapted to increasing concentrations of CdCl2 (from 1 to 20 μM). Subsequent measurement of the cellular Cd content indicated that CdR LECs exhibit a marked decrease of Cd accumulation, possibly due to the loss of Zip8 expression. We investigate the possibility that epigenetic silencing of the Zip8 gene by DNA hypermethylation is involved in the down-regulation of Zip8 expression. CdR LECs show a higher mRNA level of DNA methyltransferase 3b (Dnmt3b) than parental cells. Treatment of CdR LECs with 5-aza-2'-deoxycytidine, an inhibitor of DNA methyltransferases, reverted the expression of Zip8 and sensitivity to Cd in these cells, indicating the critical role of Zip8 for Cd import. Taken together, our results demonstrate that the progressive silencing of Zip8 expression is involved in the acquisition of resistance against Cd in lung cells, representing an adaptive survival mechanism that resists Cd-induced cytotoxicity.

A morphological study of uterine alterations in mice due to exposure to cadmium

We investigated the morphologic and molecular effects of exposure to cadmium (Cd) for 30 and 60 days on the uteri of mice. We assessed uterine morphometric measurements, eosinophilia, mast cell numbers, endometrial apoptosis, proliferation and estrogen receptor alpha (ERα) immunoreactivity. We examined vaginal smears that reflected the hormonal alterations in the female reproductive tract. Because the female reproductive tract exhibits different morphology at each stage of the estrous cycle, we sacrificed all animals at estrus to make appropriate comparisons. Female BALB/c mice were exposed to 200 ppm Cd in their drinking water for either 30 or 60 days. Cd exposure caused significant decreases in endometrial thickness and number of glands in estrus phase uteri. The endometrial eosinophilia in the groups exposed to Cd also decreased compared to controls. Cd exposure increased the number of mast cells. Luminal and glandular epithelia were examined using the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and by immunostaining proliferating cell nuclear antigen (PCNA) and estrogen receptor α (ERα). Compared to controls, the apoptotic index increased with time in both Cd exposed groups, while the proliferation index decreased. ERα immunoreactivity was decreased in both Cd exposed groups compared to controls; the decrease was most apparent in the 30 day Cd group. We found that 60 day Cd exposure increased apoptosis in the endometrium, which may affect the receptivity of the uterus for implantation.

Role of connexin 43 in cadmium-induced proliferation of human prostate epithelial cells

Connexins (Cxs), the subunits of gap junction channels, are involved in many physiological processes. Aberrant control of Cxs and gap junction intercellular communication may contribute to many diseases, including the promotion of cancer. Cd exposure is associated with increased risk of human prostate cancer and benign prostatic hyperplasia. The roles of Cxs in the effects of Cd on the prostate have, however, not been reported previously. In this study, the human prostate epithelial cell line RWPE-1 was exposed to Cd. A low dose of Cd stimulated cell proliferation along with a lower degree of gap junction intercellular communication and an elevated level of the protein Cx43. Cd exposure increased the levels of intracellular Ca²⁺ and phosphorylated Cx43 at the Ser368 site. Knockdown of Cx43 using siRNA blocked Cd-induced proliferation and interfered with the Cd-induced changes in the protein levels of cyclin D1, cyclin B1, p27^Kip1 (p27) and p21^Waf1/Cip1 (p21). The increase in Cx43 expression induced by Cd was presumably mediated by the androgen receptor, because it was abolished upon treatment with the androgen receptor antagonist, flutamide. Thus, a low dose of Cd promotes cell proliferation in RWPE-1, possibly mediated by Cx43 expression through an effect on cell cycle-associated proteins. Cx43 might be a target for prostatic diseases associated with Cd exposure. Copyright © 2017 John Wiley & Sons, Ltd.

Silencing KRAS Overexpression in Cadmium-Transformed Prostate Epithelial Cells Mitigates Malignant Phenotype

Cadmium (Cd) is a potential human prostate carcinogen. Chronic Cd exposure malignantly transforms RWPE-1 human prostate epithelial cells into CTPE cells by an unclear mechanism. Previous studies show that RWPE-1 can also be malignantly transformed by arsenic, and KRAS activation is key to causation and maintenance of this phenotype. Although Cd and arsenic can both transform prostate epithelial cells, it is uncertain whether their mechanisms are similar. Thus, here we determined whether KRAS activation is critical in causing and maintaining Cd-induced malignant transformation in CTPE cells. Expression of KRAS, miRNAs, and other genes of interest was analyzed by Western blot and RT-PCR. Following stable KRAS knockdown (KD) by RNA interference using shRNAmir, the malignant phenotype was assessed by various physical and genetic parameters. CTPE cells greatly overexpressed KRAS by 20-fold, indicating a likely role in Cd transformation. Thus, we attempted to reverse the malignant phenotype via KRAS KD. Two weeks after shRNAmir transduction, KRAS protein was undetectable in CTPE KD cells, confirming stable KD. KRAS KD reduced stimulated RAS/ERK and PI3K/AKT signaling pathways and markedly mitigated multiple physical and molecular malignant cell characteristics including: hypersecretion of MMP-2, colony formation, cell survival, and expression of cancer-relevant genes (reduced proliferation and cell cycle-related genes; activated tumor suppressor PTEN). However, KRAS KD did not reverse miRNA expression originally down-regulated by Cd transformation. These data strongly suggest KRAS is a key gene in development and maintenance of the Cd-induced malignant phenotype, at least in the prostate. It is not, however, the only genetic factor sustaining this phenotype.

BH4 domain of Bcl-2 as a novel target for cancer therapy

Overexpression of B cell lymphoma 2 (Bcl-2) proteins is associated with therapy resistance in various human cancers. Traditional approaches target the Bcl-2 homology (BH)3 domain of Bcl-2; however, the BH4 domain represents a superior therapeutic target in light of its unique structure and crucial involvement in many cellular functions. In this critical review, we focus on the structural and functional basis of targeting the BH4 domain of Bcl-2, and highlight the recent advances in drug discovery efforts toward small-molecule BH4 domain inhibitors (e.g. BDA-366). The proof-of-concept studies support the hypothesis that targeting the BH4 domain of Bcl-2 holds promise to offer a novel anticancer therapy through the induction of apoptosis and an increased potential to overcome therapeutic resistance.

Differential effects of p38 and JNK activation by GSK3 on cadmium-induced autophagy and apoptosis

A proposed schematic model of the roles of p38 and JNK MAPK activation in the regulation of Cd-induced autophagy through site-specific phosphorylation in serine and tyrosine residues of GSK3αβ.

A review of molecular events of cadmium-induced carcinogenesis

Cadmium (Cd) is a toxic, heavy industrial metal that poses serious environmental health hazards to both humans and wildlife. Recently, Cd and Cd-containing compounds have been classified as known human carcinogens, and epidemiological data show causal associations with prostate, breast, and lung cancer. The molecular mechanisms involved in Cd-induced carcinogenesis are poorly understood and are only now beginning to be elucidated. The effects of chronic exposure to Cd have recently attracted great interest due to the development of malignancies in Cd-induced tumorigenesis in animals models. Briefly, various in vitro studies demonstrate that Cd can act as a mitogen, can stimulate cell proliferation and inhibit apoptosis and DNA repair, and can induce carcinogenesis in several mammalian tissues and organs. Thus, the various mechanisms involved in chronic Cd exposure and malignant transformations warrant further investigation. In this review, we focus on recent evidence of various leading general and tissue-specific molecular mechanisms that follow chronic exposure to Cd in prostate-, breast-, and lung-transformed malignancies. In addition, in this review, we consider less defined mechanisms such as epigenetic modification and autophagy, which are thought to play a role in the development of Cd-induced malignant transformation.

Cellular mechanisms of cadmium-induced toxicity: a review

Cadmium is a widespread toxic pollutant of occupational and environmental concern because of its diverse toxic effects: extremely protracted biological half-life (approximately 20-30 years in humans), low rate of excretion from the body and storage predominantly in soft tissues (primarily, liver and kidneys). It is an extremely toxic element of continuing concern because environmental levels have risen steadily due to continued worldwide anthropogenic mobilization. Cadmium is absorbed in significant quantities from cigarette smoke, food, water and air contamination and is known to have numerous undesirable effects in both humans and animals. Cadmium has a diversity of toxic effects including nephrotoxicity, carcinogenicity, teratogenicity and endocrine and reproductive toxicities. At the cellular level, cadmium affects cell proliferation, differentiation, apoptosis and other cellular activities. Current evidence suggests that exposure to cadmium induces genomic instability through complex and multifactorial mechanisms. Most important seems to be cadmium interaction with DNA repair mechanism, generation of reactive oxygen species and induction of apoptosis. In this article, we have reviewed recent developments and findings on cadmium toxicology.

Protective effects of Lactobacillus plantarum CCFM8610 against chronic cadmium toxicity in mice indicate routes of protection besides intestinal sequestration

Our previous study confirmed the ability of Lactobacillus plantarum CCFM8610 to protect against acute cadmium (Cd) toxicity in mice. This study was designed to evaluate the protective effects of CCFM8610 against chronic Cd toxicity in mice and to gain insights into the protection mode of this strain. Experimental mice were divided into two groups and exposed to Cd for 8 weeks via drinking water or intraperitoneal injection. Both groups were further divided into four subgroups, control, Cd only, CCFM8610 only, and Cd plus CCFM8610. Levels of Cd were measured in the feces, liver, and kidneys, and alterations of several biomarkers of Cd toxicity were noted. The results showed that when Cd was introduced orally, cotreatment with Cd and CCFM8610 effectively decreased intestinal Cd absorption, reduced Cd accumulation in tissue, alleviated tissue oxidative stress, reversed hepatic and renal damage, and ameliorated the corresponding histopathological changes. When Cd was introduced intraperitoneally, administration of CCFM8610 did not have an impact on tissue Cd accumulation or reverse the activities of antioxidant enzymes. However, CCFM8610 still offered protection against oxidative stress and reversed the alterations of Cd toxicity biomarkers and tissue histopathology. These results suggest that CCFM8610 is effective against chronic cadmium toxicity in mice. Besides intestinal Cd sequestration, CCFM8610 treatment offers direct protection against Cd-induced oxidative stress. We also provide evidence that the latter is unlikely to be mediated via protection against Cd-induced alteration of antioxidant enzyme activities.

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.

The effects of cadmium on VEGF-mediated angiogenesis in HUVECs

Cadmium (Cd) is a highly toxic element that causes morphologic alterations and dysfunction in blood vessels. The altered vascular function caused by cadmium has been implicated in a range of chronic diseases, including hypertension. The effects of cadmium are a multisystem phenomenon involving inflammation, hypertrophy, apoptosis, angiogenesis and important processes involved in vascular remodeling systems. Vascular endothelial growth factor (VEGF) plays a major role in cell growth and angiogenesis under pathologic conditions. VEGF secretion is related to anti-apoptosis protein expression and attenuates apoptosis in endothelial cells. This study examined the VEGF-dependent mechanisms of angiogenesis and apoptosis in cadmium-treated endothelial cells (HUVECs). The effects and mechanisms of cadmium in endothelial cells (HUVECs) were examined by exposing the cells to different doses of cadmium chloride (2.5-40 μ m). After the cadmium treatment, the angiogenesis and apoptosis mechanisms related to VEGF in cadmium-treated HUVECs were examined. As a result, the low concentration of cadmium increased the tube formation in HUVECs. In addition, cadmium at concentrations of 5 and 10 μ m increased VEGF secretion and VEGFR2 activity, which suggest that cadmium affects the growth of blood vessels. All three MAPK pathways, namely ERK, JNK and p38, were activated by cadmium in HUVECs. However, high concentrations of cadmium caused cell damage, disrupted tube formation and inhibited VEGF expression and the activities of VEGFR2 and MAPK in HUVECs. Cadmium has dual functions through VEGF-dependent mechanisms in a dose-dependent manner. In this study, the dual effects of cadmium might alter angiogenesis and induce apoptosis through VEGF pathways in HUVECs.

Mechanisms in cadmium-induced carcinogenicity: recent insights

Cadmium is an environmental pollutant,with relevant exposures at workplaces and in the general population. The carcinogenicity has been long established, most evident for tumors in the lung and kidney, but with increasing evidence also for other tumor locations. While direct interactions with DNA appear to be of minor importance, the interference with the cellular response to DNA damage, the deregulation of cell growth as well as resistance to apoptosis have been demonstrated in diverse experimental systems. With respect to DNA repair processes,cadmium has been shown to disturb nucleotide excision repair, base excision repair and mismatch repair; consequences are increased susceptibility towards other DNA damaging agents and endogenous mutagens. Furthermore, cadmium induces cell proliferation, inactivates negative growth stimuli, such as the tumor suppressor protein p53, and provokes resistance towards apoptosis. Particularly the combination of these multiple mechanisms may give rise to a high degree of genomic instability in cadmium-adapted cells, relevant not only for tumor initiation, but also for later steps in tumor development. Future research needs to clarify the relevance of these interactions for low exposure conditions in humans.

The role of Fas ligand protein in the oxidative stress induced by azoxymethane on crypt colon of rats

PURPOSE: To study the protein Fas ligand (FasL) on the expression of apoptosis, using a model of oxidative stress induced by azoxymethane (AOM), in the crypt of colon in rats. METHODS: Wistar rats (n=14) were assigned into two groups: control (n=7) and AOM (n=7). A single subcutaneous administration of AOM (5mg/kg) or saline solution was performed at the beginning of third week and after three hours samples of proximal colon were collected. The expression of FasL was quantified (Software ImageLab) in percentage of areas in the top, base and all crypt. Results were expressed as mean ± sd (Shapiro-Wilks test and t Student test) (p < 0.05). RESULTS: In the animals of CG there was no significant difference between the FasL expression of the top (10.75±3.33) and basal (11.14±3.53) colon crypt (p=0.34293740). In the animals of AOM there was no significant difference between the FasL expression of the top (8.86±4.19) and basal (8.99±4.08) colon crypt (p=0.78486003). In the animals of CG (10.95±3.43) and AOM (8.92±4.13) there was a significant difference of the FasL expression (p=0.026466821). A significantly decrease on the FasL expression was observed in the animals of CG (10.75±3.33) and AOM (8.86±4.19) in the top crypt (p=0.00003755*). A significant decrease was also observed in the animals of CG (11.14±3.53) and AOM (8.99±4.08) in the basal colon crypt (p=0.00000381**). CONCLUSION: Azoxymethane induce the oxidative stress and the significantly decrease of FasL expression, although there is no significant difference between basal and top of colon crypt linked to consumption-activation of Fas ligand.

The role of oxidative stress in carcinogenesis induced by metals and xenobiotics

In addition to a wide range of adverse effects on human health, toxic metals such as cadmium, arsenic and nickel can also promote carcinogenesis. The toxicological properties of these metals are partly related to generation of reactive oxygen species (ROS) that can induce DNA damage and trigger redox-dependent transcription factors. The precise mechanisms that induce oxidative stress are not fully understood. Further, it is not yet known whether chronic exposures to low doses of arsenic, cadmium or other metals are sufficient to induce mutations in vivo, leading to DNA repair responses and/or tumorigenesis. Oxidative stress can also be induced by environmental xenobiotics, when certain metabolites are generated that lead to the continuous release of superoxide, as long as the capacity to reduce the resulting dions (quinones) into hydroquinones is maintained. However, the specific significance of superoxide-dependent pathways to carcinogenesis is often difficult to address, because formation of DNA adducts by mutagenic metabolites can occur in parallel. Here, we will review both mechanisms and toxicological consequences of oxidative stress triggered by metals and dietary or environmental pollutants in general. Besides causing DNA damage, ROS may further induce multiple intracellular signaling pathways, notably NF-kB, JNK/SAPK/p38, as well as Erk/MAPK. These signaling routes can lead to transcriptional induction of target genes that could promote proliferation or confer apoptosis resistance to exposed cells. The significance of these additional modes depends on tissue, cell-type and is often masked by alternate oncogenic mechanisms being activated in parallel.

Role of oxidative stress in cadmium toxicity and carcinogenesis

Cadmium (Cd) is a toxic metal, targeting the lung, liver, kidney, and testes following acute intoxication, and causing nephrotoxicity, immunotoxicity, osteotoxicity and tumors after prolonged exposures. Reactive oxygen species (ROS) are often implicated in Cd toxicology. This minireview focused on direct evidence for the generation of free radicals in intact animals following acute Cd overload and discussed the association of ROS in chronic Cd toxicity and carcinogenesis. Cd-generated superoxide anion, hydrogen peroxide, and hydroxyl radicals in vivo have been detected by the electron spin resonance spectra, which are often accompanied by activation of redox sensitive transcription factors (e.g., NF-kappaB, AP-1 and Nrf2) and alteration of ROS-related gene expression. It is generally agreed upon that oxidative stress plays important roles in acute Cd poisoning. However, following long-term Cd exposure at environmentally-relevant low levels, direct evidence for oxidative stress is often obscure. Alterations in ROS-related gene expression during chronic exposures are also less significant compared to acute Cd poisoning. This is probably due to induced adaptation mechanisms (e.g., metallothionein and glutathione) following chronic Cd exposures, which in turn diminish Cd-induced oxidative stress. In chronic Cd-transformed cells, less ROS signals are detected with fluorescence probes. Acquired apoptotic tolerance renders damaged cells to proliferate with inherent oxidative DNA lesions, potentially leading to tumorigenesis. Thus, ROS are generated following acute Cd overload and play important roles in tissue damage. Adaptation to chronic Cd exposure reduces ROS production, but acquired Cd tolerance with aberrant gene expression plays important roles in chronic Cd toxicity and carcinogenesis.

Long duration exposure to cadmium leads to increased cell survival, decreased DNA repair capacity, and genomic instability in mouse testicular Leydig cells

Epidemiological and experimental studies have shown that cadmium is carcinogenic to human and experimental animals, however, the mechanism of cadmium-induced carcinogenesis is not clear. The aberrant expression of cell cycle and DNA repair genes resulting in increased cell proliferation and genomic instability are the characteristic features of cancer cells. The purpose of this study was to determine if exposure to cadmium can perturb cell proliferation/survival and causes genomic instability in TM3 cells, a mouse testicular Leydig cell line. The results of this study revealed that short-duration exposure to lower doses of cadmium significantly increase the growth of TM3 cells, whereas, higher doses are toxic and cause cell death. The long duration exposure to higher doses of cadmium, however, results in increased cell survival and acquisition of apoptotic resistance. Gene expression analysis by real-time PCR revealed increased expression of the anti-apoptotic gene Bcl-2, whereas decreased expression of pro-apoptotic gene Bax. Decreased expression of genes for maintenance of DNA methylation, DNMT1, and DNA repair, OGG1 and MYH, was also observed in cells exposed to cadmium for 24h. The random amplified polymorphic DNA (RAPD) assay revealed genomic instability in cells with chronic exposure to cadmium. The findings of this study indicate that mouse testicular Leydig cells adapt to chronic cadmium exposure by increasing cell survival through increased expression of Bcl-2, and decreased expression of Bax. The increased proliferation of cells with genomic instability may result in malignant transformation, and therefore, could be a viable mechanism for cadmium-induced cancers.

Transcriptome analyses in normal prostate epithelial cells exposed to low-dose cadmium: oncogenic and immunomodulations involving the action of tumor necrosis factor

BACKGROUND

Cadmium is implicated in prostate carcinogenesis, but its oncogenic action remains unclear.

OBJECTIVES

In this study we aimed to decipher changes in cell growth and the transcriptome in an immortalized human normal prostate epithelial cell line (NPrEC) following exposure to low-dose Cd.

METHODS

Synchronized NPrEC cells were exposed to different doses of Cd and assayed for cell viability and cell-cycle progression. We investigated changes in transcriptome by global profiling and used Ingenuity Pathways Analysis software to develop propositions about functional connections among differentially expressed genes. A neutralizing antibody was used to negate the effect of Cd-induced up-regulation of tumor necrosis factor (TNF) in NPrEC cells.

RESULTS

Exposure of NPrEC to 2.5 microM Cd enhanced cell viability and accelerated cell-cycle progression. Global expression profiling identified 48 genes that exhibited >or= 1.5-fold changes in expression after 4, 8, 16, and 32 hr of Cd treatment. Pathway analyses inferred a functional connection among 35 of these genes in one major network, with TNF as the most prominent node. Fourteen of the 35 genes are related to TNF, and 11 exhibited an average of >2-fold changes in gene expression. Real-time reverse transcriptase-polymerase chain reaction confirmed the up-regulation of 7 of the 11 genes (ADAM8, EDN1, IL8, IL24, IL13RA2, COX2/PTGS2, and SERPINB2) and uncovered a 28-fold transient increase in TNF expression in Cd-treated NPrEC cells. A TNF-neutralizing antibody effectively blocked Cd-induced elevations in the expression of these genes.

CONCLUSIONS

Noncytotoxic, low-dose Cd has growth-promoting effects on NPrEC cells and induces transient overexpression of TNF, leading to up-regulation of genes with oncogenic and immunomodulation functions.