Cadmium induces reactive oxygen species generation and lipid peroxidation in cortical neurons in culture

Environmental cadmium and breast cancer risk

Breast cancer is the most prevalent women's cancer, with an age-adjusted incidence of 122.9 per 100,000 US women. Cadmium, a ubiquitous carcinogenic pollutant with multiple biological effects, has been reported to be associated with breast cancer in one US regional case-control study. We examined the association of breast cancer with urinary cadmium (UCd), in a case-control sample of women living on Long Island (LI), NY (100 with breast cancer and 98 without), a region with an especially high rate of breast cancer (142.7 per 100,000 in Suffolk County) and in a representative sample of US women (NHANES 1999-2008, 92 with breast cancer and 2,884 without). In a multivariable logistic model, both samples showed a significant trend for increased odds of breast cancer across increasing UCd quartiles (NHANES, p=0.039 and LI, p=0.023). Compared to those in the lowest quartile, LI women in the highest quartile had increased risk for breast cancer (OR=2.69; 95% CI=1.07, 6.78) and US women in the two highest quartiles had increased risk (OR=2.50; 95% CI=1.11, 5.63 and OR=2.22; 95% CI=.89, 5.52, respectively). Further research is warranted on the impact of environmental cadmium on breast cancer risk in specific populations and on identifying the underlying molecular mechanisms.

The role of active site residues in the oxidant specificity of the Orp1 thiol peroxidase

In this study we investigated the role of active site residues in the peroxidase activity of Orp1 (GPx3) using three different peroxide substrates. Using a structural homology model of the reduced form of Orp1, we identified Asn126 and Phe127 as evolutionarily conserved residues that line the back of the Orp1 active site and which are likely to affect the peroxidase activity of Orp1. Additionally, we identified Phe38 as a surface residue that could influence substrate specificity as it is located adjacent to Cys36, in the same position occupied by similar hydrophobic amino acids in many Orp1 homologs. We individually mutated these residues to alanine and examined the effect of each mutation in vitro and in vivo. Chloro-4-nitrobenzo-2-oxa-1,3-diazole was used to identify Cys-SOH modification of Cys36 in response to H(2)O(2), tert-butyl-hydroperoxide (tert-BHP), and cumene hydroperoxide (CHP) in Orp1(WT). Mutation of Asn126 and Phe127 eliminate Cys-SOH formation and peroxidase activity in response to H(2)O(2), tert-BHP and CHP. Furthermore, the pK(a) of Cys36 is elevated closer to that of free cysteine compared to Orp1(WT). Mutation of Phe38 does not affect the peroxidase activity of Orp1 upon exposure to H(2)O(2). The Phe38 mutation decreases Orp1 peroxidase activities in response to either tert-BHP or CHP. The in vivo sensitivity of the Phe38 mutant to both tert-BHP and CHP is increased, while the H(2)O(2) sensitivity is unchanged. The pK(a) of Cys36 in the Phe38 mutant is 5.0, which is the same as Orp1(WT). Taken together, these results suggest that Phe38 does not play a role in the reactivity of Cys36, but does modulate the affinity of Orp1 for alkyl hydroperoxides.

Cadmium directly induced mitochondrial dysfunction of human embryonic kidney cells

Cadmium (Cd) is the major component of polluted environment, which has numerous undesirable effects on health. Cd could induce apoptosis of HEK293 cells, and the mitochondria may play a key role. However, the mode of action is unclear. In the present study, we aimed to evaluate the ability of the Cd to induce dysfunction of mitochondria. We examined the effect of cadmium chloride (1, 5 and 10 μM) on mitochondrial membrane permeability and potential as well as oxidative stress markers in mitochondria isolated from HEK293 cells. We found that Cd could directly increase in permeability and decrease in membrane potential of mitochondria, even resulted in mitochondrial swelling, and that Cd could inhibit the activities of ATPase, lactate dehydrogenase (LDH), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), enhanced the levels of reactive oxygen species (ROS) and lipid peroxidation (LPO). On the whole, the results show that Cd can directly lead to mitochondrial dysfunction of HEK293 cells, including increased permeability, inhibiting respiration and evoking oxidative stress. Thus, for the first time, this paper makes an overall analysis of Cd-induced changes of structure and function of isolated mitochondria. Our findings may also have general implications in Cd-induced apoptosis by mitochondria pathway.

Effect of Ni2+ and Cd2+ ions on thermally induced conformational transitions in poly(dA)-poly(dT) system

Effects of Ni(2+) and Cd(2+) ions on thermally induced conformational transitions in the poly(dA)·poly(dT) polynucleotide duplex and poly(dA)·2poly(dT) triplex under near physiological ionic conditions were studied by measurement of UV absorption melting curves and static light scattering intensity. The diagrams of conformational transitions in poly(dA)-poly(dT)-Me(2+) systems were plotted. An aggregation in these polynucleotide systems arises at certain values of the metal ions concentration and the temperature after the polymer dissociation into single strands. The phenomenon is conditioned by the aggregation of poly(dA) via the interstrand cross-linking by the dication bridges. Unlike Ni(2+), Cd(2+) induces formation of very stable aggregates which did not disintegrate even upon cooling up to room temperature.

In vivo monitoring of the transfer kinetics of trace elements in animal brains with hyphenated inductively coupled plasma mass spectrometry techniques

The roles of metal ions to sustain normal function and to cause dysfunction of neurological systems have been confirmed by various studies. However, because of the lack of adequate analytical method to monitor the transfer kinetics of metal ions in the brain of a living animal, research on the physiopathological roles of metal ions in the CNS remains in its early stages and more analytical efforts are still needed. To explicitly model the possible links between metal ions and physiopathological alterations, it is essential to develop in vivo monitoring techniques that can bridge the gap between metalloneurochemistry and neurophysiopathology. Although inductively coupled plasma mass spectrometry (ICP-MS) is a very powerful technique for multiple trace element analyses, when dealing with chemically complex microdialysis samples, the detection capability is largely limited by instrumental sensitivity, selectivity, and contamination that arise from the experimental procedure. As a result, in recent years several high efficient and clean on-line sample pretreatment systems have been developed and combined with microdialysis and ICP-MS for the continuous and in vivo determination of the concentration-time profiles of metal ions in the extracellular space of rat brain. This article reviews the research relevant to the development of analytical techniques for the in vivo determination of dynamic variation in the concentration levels of metal ions in a living animal.

N-acetylcysteine prevents memory deficits, the decrease in acetylcholinesterase activity and oxidative stress in rats exposed to cadmium

The present study investigated the effect of the administration of N-acetylcysteine (NAC), on memory, on acetylcholinesterase (AChE) activity and on lipid peroxidation in different brain structures in cadmium (Cd)-exposed rats. The rats received Cd (2 mg/kg) and NAC (150 mg/kg) by gavage every other day for 30 days. The animals were divided into four groups (n=12-13): control/saline, NAC, Cd, and Cd/NAC. The results showed a decrease in step-down latency in the Cd-group, but NAC reversed the impairment of memory induced by Cd intoxication. Rats exposed to Cd and/or treated with NAC did not demonstrate altered shock sensitivity. Decreased AChE activity was found in hippocampus, cerebellum and hypothalamus in the Cd-group but NAC reversed this effect totally or partially while in cortex synaptosomes and striatum there was no alteration in AChE activity. An increase in TBARS levels was found in hippocampus, cerebellum and hypothalamus in the Cd-group and NAC abolished this effect while in striatum there was no alteration in TBARS levels. Urea and creatinine levels were increased in serum of Cd-intoxicated rats, but NAC was able to abolish these undesirable effects. The present findings show that treatment with NAC prevented the Cd-mediated decrease in AChE activity, as well as oxidative stress and consequent memory impairment in Cd-exposed rats, demonstrating that this compound may modulate cholinergic neurotransmission and consequently improve cognition. However, it is necessary to note that the mild renal failure may be a contributor to the behavioral impairment found in this investigation.

Endoplasmic reticulum is a major target of cadmium toxicity in yeast

Cadmium (Cd(2+)) is a very toxic metal that causes DNA damage, oxidative stress and apoptosis. Despite many studies, the cellular and molecular mechanisms underlying its high toxicity are not clearly understood. We show here that very low doses of Cd(2+) cause ER stress in Saccharomyces cerevisiae as evidenced by the induction of the unfolded protein response (UPR) and the splicing of HAC1 mRNA. Furthermore, mutant strains (Delta ire1 and Delta hac1) unable to induce the UPR are hypersensitive to Cd(2+), but not to arsenite and mercury. The full functionality of the pathways involved in ER stress response is required for Cd(2+) tolerance. The data also suggest that Cd(2+)-induced ER stress and Cd(2+) toxicity are a direct consequence of Cd(2+) accumulation in the ER. Cd(2+) does not inhibit disulfide bond formation but perturbs calcium metabolism. In particular, Cd(2+) activates the calcium channel Cch1/Mid1, which also contributes to Cd(2+) entry into the cell. The results reinforce the interest of using yeast as a cellular model to study toxicity mechanisms in eukaryotic cells.

Luteolin from Purple Perilla mitigates ROS insult particularly in primary neurons

Increased attention has been paid to the role of oxidant/antioxidant imbalance in neurodegenerative process and pharmaceutical neuroprotective interventions. Food-derived compound luteolin possesses multitarget actions including reactive oxygen species (ROS)-scavenging activity in cultured human endothelial cells or permanent immature rat oligodendrocytes. This study aims to elucidate whether luteolin has a neuroprotective tendency toward ROS-insulted neural cells. The present results showed that luteolin, isolated from the ripe seed of Perilla frutescens (L.) Britt., markedly reversed hydrogen peroxide-induced cytotoxicity in primary culture cortical neurons but not in cultured human neuroblastoma cells. Upon the ROS-insulted primary neurons, luteolin concentration-dependently enhanced neuronal cell survival with efficacy higher than and potency similar to vitamin E. Additionally, luteolin significantly attenuated the increase in ROS production and prevented the decreases in activities of mitochondria, catalase, and glutathione in ROS-insulted primary neurons. Thus, luteolin functions by neuroprotection possibly through a rebalancing of pro-oxidant-antioxidant status. This agent points to possible interventions for preventing neurodegenerative diseases such as cerebral ischemia, Parkinson's disease, and Alzheimer's disease, as well as for improving brain aging.

Cadmium stress: an oxidative challenge

At the cellular level, cadmium (Cd) induces both damaging and repair processes in which the cellular redox status plays a crucial role. Being not redox-active, Cd is unable to generate reactive oxygen species (ROS) directly, but Cd-induced oxidative stress is a common phenomenon observed in multiple studies. The current review gives an overview on Cd-induced ROS production and anti-oxidative defense in organisms under different Cd regimes. Moreover, the Cd-induced oxidative challenge is discussed with a focus on damage and signaling as downstream responses. Gathering these data, it was clear that oxidative stress related responses are affected during Cd stress, but the apparent discrepancies observed in between the different studies points towards the necessity to increase our knowledge on the spatial and temporal ROS signature under Cd stress. This information is essential in order to reveal the exact role of Cd-induced oxidative stress in the modulation of downstream responses under a diverse array of conditions.

Accumulation and oxidative stress biomarkers in Japanese flounder larvae and juveniles under chronic cadmium exposure

This study investigated how Cd exposure affected oxidative biomarkers in Japanese flounder, Paralichthys olivaceus, at early life stages (ELS). Fish were exposed to waterborne Cd (0-48microg L(-1)) from embryonic to juvenile stages for 80days. Growth, Cd accumulation, activities of superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), glutathione S-transferase (GST, EC 2.5.1.18), and levels of glutathione (GSH) and lipid peroxidation (LPO) were investigated at three developmental stages. Flounder growth decreased and Cd accumulation increased with increasing Cd concentration. In metamorphosing larvae, CAT and SOD activities were inhibited and GSH level was elevated, while LPO was enhanced by increasing Cd concentrations. CAT and GST activities of settling larvae were inhibited but GSH level was elevated at high Cd concentrations. In juveniles, SOD activity and LPO level were increased but GST activity was inhibited as Cd concentration increased. Antioxidants in flounder at ELS were able to develop ductile responses to defend against oxidative stress, but LPO fatally occurred due to Cd exposure. These biochemical parameters could be used as effective oxidative biomarkers for evaluating Cd contamination and toxicity in marine environments: CAT, SOD, GSH, and LPO for metamorphosing stage; CAT, GSH, and GST for settling stage; and SOD, GST, and LPO for juvenile stage.

Disease-toxicant screen reveals a neuroprotective interaction between Huntington's disease and manganese exposure

Recognizing the similarities between Huntington's disease (HD) pathophysiology and the neurotoxicology of various metals, we hypothesized that they may exhibit disease-toxicant interactions revealing cellular pathways underlying neurodegeneration. Here, we utilize metals and the STHdh mouse striatal cell line model of HD to perform a gene-environment interaction screen. We report that striatal cells expressing mutant Huntingtin exhibit elevated sensitivity to cadmium toxicity and resistance to manganese toxicity. This neuroprotective gene-environment interaction with manganese is highly specific, as it does not occur with iron, copper, zinc, cobalt, cadmium, lead, or nickel ions. Analysis of the Akt cell stress signaling pathway showed diminished activation with manganese exposure and elevated activation after cadmium exposure in the mutant cells. Direct examination of intracellular manganese levels found that mutant cells have a significant impairment in manganese accumulation. Furthermore, YAC128Q mice, a HD model, showed decreased total striatal manganese levels following manganese exposure relative to wild-type mice. Thus, this disease-toxicant interaction screen has revealed that expression of mutant Huntingtin results in heightened sensitivity to cadmium neurotoxicity and a selective impairment of manganese accumulation.

Bilirubin selectively inhibits cytochrome c oxidase activity and induces apoptosis in immature cortical neurons: assessment of the protective effects of glycoursodeoxycholic acid

High levels of unconjugated bilirubin (UCB) may initiate encephalopathy in neonatal life, mainly in pre-mature infants. The molecular mechanisms of this bilirubin-induced neurologic dysfunction (BIND) are not yet clarified and no neuroprotective strategy is currently worldwide accepted. Here, we show that UCB, at conditions mimicking those of hyperbilirubinemic newborns (50 microM UCB in the presence of 100 muM human serum albumin), rapidly (within 1 h) inhibited cytochrome c oxidase activity and ascorbate-driven oxygen consumption in 3 days in vitro rat cortical neurons. This was accompanied by a bioenergetic and oxidative crisis, and apoptotic cell death, as judged by the collapse of the inner-mitochondrial membrane potential, increased glycolytic activity, superoxide anion radical production, and ATP release, as well as disruption of glutathione redox status. Furthermore, the antioxidant compound glycoursodeoxycholic acid (GUDCA) fully abrogated UCB-induced cytochrome c oxidase inhibition and significantly prevented oxidative stress, metabolic alterations, and cell demise. These results suggest that the neurotoxicity associated with neonatal bilirubin-induced encephalopathy occur through a dysregulation of energy metabolism, and supports the notion that GUDCA may be useful in the treatment of BIND.

Cadmium increases ferroportin-1 gene expression in J774 macrophage cells via the production of reactive oxygen species

Cadmium intoxication has been associated with the dysregulation of iron homeostasis. In the present study, we investigated the effect of cadmium on the expression of ferroportin 1 (FPN1), an important iron transporter protein that is involved in iron release from macrophages. When we incubated cadmium with J774 mouse macrophage cells, FPN1 mRNA levels were significantly increased in a dose- and time-dependent manner. Furthermore, the cadmium-induced FPN1 mRNA expression was associated with increased levels of FPN1 protein. On the other hand, cadmium-mediated FPN1 mRNA induction in J774 cells was completely blocked when cells were co-treated with a transcription inhibitor, acitomycin D. Also, cadmium directly stimulated the activity of the FPN1-promoter driven luciferase reporter, suggesting that the cadmium up-regulates FPN1 gene expression in a transcription-dependent manner. Finally, cadmium exposure to J774 macrophages increased intracellular reactive oxygen species (ROS) levels by ~ 2-fold, compared to untreated controls. When J774 cells were co-treated with antioxidant N-acetylcystein, the cadmium-induced FPN1 mRNA induction was significantly attenuated. In summary, the results of this study clearly demonstrated that cadmium increased FPN1 expression in macrophages through a mechanism that involves ROS production, and suggests another important interaction between iron and cadmium metabolism.

Effect of Chlorella vulgaris intake on cadmium detoxification in rats fed cadmium

The aim of this study was to investigate if dietary Chlorella vulgaris (chlorella) intake would be effective on cadmium (Cd) detoxification in rats fed dietary Cd. Fourteen-week old male Sprague-Dawley (SD) rats weighing 415.0 +/- 1.6 g were randomly divided into two groups and fed slightly modified American Institute of Nutrition-93 Growing (AIN-93G) diet without (n=10) or with (n=40) dietary Cd (200 ppm) for 8 weeks. To confirm alteration by dietary Cd intake, twenty rats fed AIN-93G diet without (n=10) and with (n=10) dietary Cd were sacrificed and compared. Other thirty rats were randomly blocked into three groups and fed slightly modified AIN-93G diets replacing 0 (n=10), 5 (n=10) or 10% (n=10) chlorella of total kg diet for 4 weeks. Daily food intake, body weight change, body weight gain/calorie intake, organ weight (liver, spleen, and kidney), perirenal fat pad and epididymal fat pad weights were measured. To examine Cd detoxification, urinary Cd excretion and metallothonein (MT) concentrations in kidney and intestine were measured. Food intake, calorie intake, body weight change, body weight gain/calorie intake, organ weight and fat pad weights were decreased by dietary Cd intake. Urinary Cd excretion and MT concentrations in kidney and small intestine were increased by dietary Cd. After given Cd containing diet, food intake, calorie intake, body weight change, body weight gain/calorie intake, organ weights and fat pad weights were not influenced by dietary chlorella intake. Renal MT synthesis tended to be higher in a dose-dependent manner, but not significantly. And chlorella intake did not significantly facilitate renal and intestinal MT synthesis and urinary Cd excretion. These findings suggest that, after stopping cadmium supply, chlorella supplementation, regardless of its percentage, might not improve cadmium detoxification from the body in growing rats.

Oxidative stress and apoptotic changes in primary cultures of rat proximal tubular cells exposed to lead

Lead is a known nephrotoxic element. In this study, primary cultures of rat proximal tubular (rPT) cells were treated with different concentrations of lead acetate (0.25, 0.5 and 1 microM) to investigate its cytotoxic mechanism. A progressive loss in cell viability together with a significant increase in the number of apoptotic and necrotic cells and lactate dehydrogenase release were seen in the experiment. Simultaneously, elevation of reactive oxygen species levels and intracellular [Ca(2+)]i, depletion of mitochondrial membrane potential and intracellular glutathione were revealed during the lead exposure. In addition, apoptotic morphological changes induced by lead exposure in rPT cells were demonstrated by Hoechst 33258 staining. The apoptosis was markedly prevented by N-acetyl-L-cysteine, while the necrosis was not affected. Moreover, catalase and superoxide dismutase activities in the living cells rose significantly. In conclusion, exposure of rPT cells to low-concentration lead led to cell death, mediated by an apoptotic and a necrotic mechanism. The apoptotic death induced by oxidative stress was the chief mechanism. Meanwhile, a group of cells survived lead action, mediated by their ability to activate antioxidant defense systems.

Cadmium-induced decrease in RUNX2 mRNA expression and recovery by the antioxidant N-acetylcysteine (NAC) in the human osteoblast-like cell line, Saos-2

Exposure to cadmium poses a threat to human health, including increased susceptibility to developing the bone disease osteoporosis. Despite its recognized importance as an environmental toxin, little is known about how cadmium directly impacts bone-forming osteoblasts. We previously reported that cadmium induces apoptosis in human osteoblast-like Saos-2 cells. In this work, we hypothesize that cadmium exposure induces oxidative stress which leads to decreased RUNX2 mRNA expression and increased apoptotic death, and predict that the antioxidant NAC mitigates the damaging effects of cadmium. Oxidative stress is implicated in osteoporosis; furthermore the osteoblast transcriptional factor RUNX2 is reported to play a protective role against osteoporosis in postmenopausal women. Cells treated with 10 microM CdCl2 exhibited signs of oxidative damage including depletion in glutathione, increased reactive oxygen species formation, and enhanced lipid peroxidation. RUNX2 mRNA expression, by RT-PCR, was significantly reduced after exposure to 10 microM CdCl2. Pretreatment with the antioxidant NAC (1mM) prevented cadmium-induced decrease in RUNX2 mRNA and protected cells from apoptotic death. This study provides insight into the mechanisms underlying cadmium-induced osteotoxicity. In addition, this study distinguishes itself by identifying RUNX2 as a target for heavy metal-induced osteotoxicity.

Suppressive effects of cadmium on neurons and affected proteins in cultured developing cortical cells

The purpose of the present study was to examine the in vitro effects of low-dose cadmium (Cd) on developing cortical cells. The cortical cells removed from fetuses (embryonic day 15) were treated with 10nM of Cd for 24h. The effects of Cd on dendritic and synaptic development were immunocytochemically observed with anti-microtubule associated protein-2 (MAP2) and anti-synapsin I antibodies, respectively. Administration of Cd suppressed dendritic as well as synaptic development at 10nM. By two-dimensional gel electrophoresis and liquid chromatography-tandem mass spectrometric (LC/MS/MS) analysis, we identified three proteins with different expression after Cd-treatment; dihydropyrimidinase-related protein 2 (DRP-2/CRMP-2), 14-3-3-epsillon and calmodulin (CaM). Though the number of identified proteins was small, these proteins are known to be involved in neuronal development. The present study demonstrated the morphological effects as well as affected proteins in Cd-treated cortical cells, providing tools and insights in elucidating mechanisms how low-dose Cd distorts brain development.

Hispolon induces apoptosis in human gastric cancer cells through a ROS-mediated mitochondrial pathway

Severe side effects and complications such as gastrointestinal and hematological toxicities because of current anticancer drugs are major problems in the clinical management of gastric cancer, which highlights the urgent need for novel effective and less toxic therapeutic approaches. Hispolon, an active polyphenol compound, is known to possess potent antineoplastic and antiviral properties. In this study, we investigated the efficacy of hispolon in human gastric cancer cells and explored the cell death mechanism. Hispolon induced ROS-mediated apoptosis in gastric cancer cells and was more toxic toward gastric cancer cells than toward normal gastric cells, suggesting greater susceptibility of the malignant cells. The mechanism of hispolon-induced apoptosis was that hispolon abrogated the glutathione antioxidant system and caused massive ROS accumulation in gastric cancer cells. Excessive ROS caused oxidative damage to the mitochondrial membranes and impaired the membrane integrity, leading to cytochrome c release, caspase activation, and apoptosis. Furthermore, hispolon potentiated the cytotoxicity of chemotherapeutic agents used in the clinical management of gastric cancer. These results suggest that hispolon could be useful for the treatment of gastric cancer either as a single agent or in combination with other anticancer agents.

Inhibition of cadmium-induced oxidative injury in rat primary astrocytes by the addition of antioxidants and the reduction of intracellular calcium

Exposure of the brain to cadmium ions (Cd(2+)) is believed to lead to neurological disorders of the central nervous system (CNS). In this study, we tested the hypothesis that astrocytes, the major CNS-supporting cells, are resistant to Cd(2+)-induced injury compared with cortical neurons and microglia (CNS macrophages). However, treatment with CdCl(2) for 24 h at concentrations higher than 20 microM substantially induced astrocytic cytotoxicity, which also resulted from long-term exposure to 5 microM of CdCl(2). Intracellular calcium levels were found to rapidly increase after the addition of CdCl(2) into astrocytes, which led to a rise in reactive oxygen species (ROS) and to mitochondrial impairment. In accordance, preexposure to the extracellular calcium chelator EGTA effectively reduced ROS production and increased survival of Cd(2+)-treated astrocytes. Adenovirus-mediated transfer of superoxide dismutase (SOD) or glutathione peroxidase (GPx) genes increased survival of Cd(2+)-exposed astrocytes. In addition, increased ROS generation and astrocytic cell death due to Cd(2+) exposure was inhibited when astrocytes were treated with the polyphenolic compound ellagic acid (EA). Taken together, Cd(2+)-induced astrocytic cell death resulted from disrupted calcium homeostasis and an increase in ROS. Moreover, our findings demonstrate that enhancement of the activity of intracellular antioxidant enzymes and supplementation with a phenolic compound, a natural antioxidant, improves survival of Cd(2+)-primed astrocytes. This information provides a useful approach for treating Cd(2+)-induced CNS neurological disorders.

Antioxidants and phase 2 enzymes in macrophages: regulation by Nrf2 signaling and protection against oxidative and electrophilic stress

Macrophages play important roles in immunity and other physiological processes. They are also target cells of various toxic agents, including oxidants and electrophiles. However, little is known regarding the molecular regulation and chemical inducibility of a spectrum of endogenous antioxidants and phase 2 enzymes in normal macrophages. Understanding the molecular pathway(s) controlling the coordinated expression of various macrophage antioxidants and phase 2 defenses is of importance for developing strategies to protect against macrophage injury induced by oxidants and electrophiles. Accordingly, this study was undertaken to determine the role of the nuclear factor E2-related factor 2 (Nrf2) in regulating both constitutive and chemoprotectant-inducible expression of various antioxidants and phase 2 enzymes in mouse macrophages. The constitutive expression of a series of antioxidants and phase 2 enzymes was significantly lower in macrophages derived from Nrf2-null (Nrf2(-/-)) mice than those from wild-type (Nrf2(+/+)) littermates. Incubation of wild-type macrophages with 3H-1,2-dithiole-3-thione (D3T) led to significant induction of various antioxidants and phase 2 enzymes, including catalase, glutathione, glutathione peroxidase (GPx), glutathione reductase, glutathione S-transferase, and NAD(P)H:quinone oxidoreductase 1. The inducibility of the above cellular defenses except for GPx by D3T was completely abolished in Nrf2(-/-) macrophages. As compared with wild-type cells, Nrf2(- /-) macrophages were much more susceptible to cell injury induced by reactive oxygen/nitrogen species, as well as two known macrophage toxins, acrolein and cadmium. Up-regulation of the antioxidants and phase 2 enzymes by D3T in wild-type macrophages resulted in increased resistance to the above oxidant-and electrophile-induced cell injury, whereas D3T treatment of Nrf2(- /-) macrophages provided only marginal or no cytoprotec-tion. This study demonstrates that Nrf2 is an indispensable factor in controlling both constitutive and inducible expression of a wide spectrum of antioxidants and phase 2 enzymes in macrophages as well as the susceptibility of these cells to oxidative and electrophilic stress.

Cadmium accumulation in the human retina: effects of age, gender, and cellular toxicity

Tobacco smoking and aging are among the few factors linked to age-related macular degeneration (AMD), a major cause of blindness in the elderly. Recent studies indicate that cadmium (Cd), an environmental toxic trace metal, is approximately four-fold higher in the retinas of smokers compared to non-smokers. In this study, we determined the effects of age and gender on Cd accumulation in human retinal tissues, specifically the neural retina, retinal pigment epithelium (RPE), and choroid. Cadmium levels in cultured RPE cells or retinal tissues isolated from frozen donor eyes were measured using inductively coupled plasma mass spectrometry (ICP-MS) and graphite furnace atomic absorption spectrophotometry (GF-AAS). Cadmium uptake in cultured human RPE cells (ARPE-19) was also assessed using GF-AAS. Toxic effects of cadmium were determined from cell loss (measured as a decrease in cell density) and lactate dehydrogenase release (an indicator of membrane disruption). In "young" eyes (< 55 years) Cd was highest in the retinal pigment epithelium and lowest in the neural retina. Cd was higher in all tissues in aged eyes (>or=55 years) and was significantly higher in the neural retina and RPE in older females. Cultured RPE cells exposed to Cd showed altered cell morphology, decreased cell survival, elevated ROS levels and concentration-dependent disruption of membrane integrity. We conclude that cadmium is accumulated differently in the neural retinal and RPE of older men and women. The deleterious effects of Cd on RPE cells indicate that this environmental toxin is a potentially important factor in age-related retinal disease.

The effects of tobacco smoke and nicotine on cognition and the brain

Tobacco smoke consists of thousands of compounds including nicotine. Many constituents have known toxicity to the brain, cardiovascular, and pulmonary systems. Nicotine, on the other hand, by virtue of its short-term actions on the cholinergic system, has positive effects on certain cognitive domains including working memory and executive function and may be, under certain conditions, neuroprotective. In this paper, we review recent literature, laboratory and epidemiologic, that describes the components of mainstream and sidestream tobacco smoke, including heavy metals and their toxicity, the effect of medicinal nicotine on the brain, and studies of the relationship between smoking and (1) preclinical brain changes including silent brain infarcts; white matter hyperintensities, and atrophy; (2) single measures of cognition; (3) cognitive decline over repeated measures; and (4) dementia. In most studies, exposure to smoke is associated with increased risk for negative preclinical and cognitive outcomes in younger people as well as in older adults. Potential mechanisms for smoke's harmful effects include oxidative stress, inflammation, and atherosclerotic processes. Recent evidence implicates medicinal nicotine as potentially harmful to both neurodevelopment in children and to catalyzing processes underlying neuropathology in Alzheimer's Disease. The reviewed evidence suggests caution with the use of medicinal nicotine in pregnant mothers and older adults at risk for certain neurological disease. Directions for future research in this area include the assessment of comorbidities (alcohol consumption, depression) that could confound the association between smoking and neurocognitive outcomes, the use of more specific measures of smoking behavior and cognition, the use of biomarkers to index exposure to smoke, and the assessment of cognition-related genotypes to better understand the role of interactions between smoking/nicotine and variation in genotype in determining susceptibility to the neurotoxic effects of smoking and the putative beneficial effects of medicinal nicotine.

Cytoprotective effects of selenium on cadmium-induced LLC-PK1 cells apoptosis by activating JNK pathway

Extensive studies have indicated that the apoptosis pathway appears to be associated with intracellular reactive oxygen species (ROS) production in cadmium-induced nephrotoxicity, however, the precise cellular mechanism remains unclear. The purpose of this study was to determine the relationships between the activation of phosphorylated c-jun N-terminal kinase (JNK) and cadmium-induced apoptosis, and assess the possible cytoprotective mechanism of selenium. Our study clearly revealed cadmium treatment caused apoptosis in LLC-PK1 cells, which was partially suppressed by pretreatment with selenium, an antioxidant nutrient. Further studies found the phosphorylation of JNK kinase increased with exposure to cadmium for 3 h, even remained elevated at 9 h in the time course study, and the activation of phosphorylated JNK was detected in a dose-dependent manner. In addition, a concomitant time-dependent increase in caspase-3 activities was observed by cadmium treatment. During the process, selenium played the same role as N-acetyl-L-cysteine (NAC), a free radical scavenger. Pretreatment of cells with selenium partially suppressed of the phosphorylation of JNK, coupled with caspase-3 activation involved in cadmium-induced apoptosis. In conclusion, our studies provided a molecular linkage between the phosphorylation of JNK and cadmium-induced LLC-PK1 cells apoptosis, and demonstrated selenium also contributed a potentially protection to prevent cadmium-cytotoxicity.

Cadmium neurotoxicity

The Cd has been recognized as one of the most toxic environmental and industrial pollutants due to its ability to induce disturbances in several organs and tissues following either acute or chronic exposure. This review accounts for the recent evidence on its mechanisms to induce neurotoxicity, the role of the blood-brain barrier, oxidative stress, interference with calcium, and zinc-dependent processes and apoptosis induction as well as the modulatory effect of metallothionein. Discussion about cadmium neurotoxicity is centered on mechanisms of induction of cellular disfunctions. Future investigations must address those neuronal mechanisms in detail in order to understand cadmium-induced neurotoxicity.

Quantum dot-induced cell death involves Fas upregulation and lipid peroxidation in human neuroblastoma cells

Background

Neuroblastoma, a frequently occurring solid tumour in children, remains a therapeutic challenge as existing imaging tools are inadequate for proper and accurate diagnosis, resulting in treatment failures. Nanoparticles have recently been introduced to the field of cancer research and promise remarkable improvements in diagnostics, targeting and drug delivery. Among these nanoparticles, quantum dots (QDs) are highly appealing due to their manipulatable surfaces, yielding multifunctional QDs applicable in different biological models. The biocompatibility of these QDs, however, remains questionable.

Results

We show here that QD surface modifications with N-acetylcysteine (NAC) alter QD physical and biological properties. In human neuroblastoma (SH-SY5Y) cells, NAC modified QDs were internalized to a lesser extent and were less cytotoxic than unmodified QDs. Cytotoxicity was correlated with Fas upregulation on the surface of treated cells. Alongside the increased expression of Fas, QD treated cells had increased membrane lipid peroxidation, as measured by the fluorescent BODIPY-C₁₁ dye. Moreover, peroxidized lipids were detected at the mitochondrial level, contributing to the impairment of mitochondrial functions as shown by the MTT reduction assay and imaged with confocal microscopy using the fluorescent JC-1 dye.

Conclusion

QD core and surface compositions, as well as QD stability, all influence nanoparticle internalization and the consequent cytotoxicity. Cadmium telluride QD-induced toxicity involves the upregulation of the Fas receptor and lipid peroxidation, leading to impaired neuroblastoma cell functions. Further improvements of nanoparticles and our understanding of the underlying mechanisms of QD-toxicity are critical for the development of new nanotherapeutics or diagnostics in nano-oncology.

Oxidative stress and DNA damages induced by cadmium accumulation

Experimental evidence shows that cadmium (Cd) could induce oxidative stress and then causes DNA damage in animal cells, however, whether such effect exists in plants is still unclear. In the present study, Vicia faba plants was exposed to 5 and 10 mg/L Cd for 4 d to investigate the distribution of Cd in plant, the metal effects on the cell lipids, antioxidative enzymes and DNA damages in leaves. Cd induced an increase in Cd concentrations in plants. An enhanced level of lipid peroxidation in leaves and an enhanced concentration of H2O2 in root tissues suggested that Cd caused oxidative stress in Vicia faba. Compared with control, Cd-induced enhancement in superoxide dismutase activity was more significant at 5 mg/L than at 10 mg/L in leaves, by contrast, catalase and peroxidase activities were significantly suppressed by Cd addition. DNA damage was detected by neutral/neutral, alkaline/neutral and alkaline/alkaline Comet assay. Increased levels of DNA damages induced by Cd occurred with reference to oxidative stress in leaves, therefore, oxidative stress induced by Cd accumulation in plants contributed to DNA damages and was likely an important mechanism of Cd-phytotoxicity in Vicia faba plants.

Reactive oxygen species produced by the mitochondrial respiratory chain are involved in Cd2+-induced injury of rat ascites hepatoma AS-30D cells

Using AS-30D rat ascites hepatoma cells, we studied the modulating action of various antioxidants, inhibitors of mitochondrial permeability transition pore and inhibitors of the respiratory chain on Cd(2+)-produced cytotoxicity. It was found that Cd(2+) induced both necrosis and apoptosis in a time- and dose-dependent way. This cell injury involved dissipation of the mitochondrial transmembrane potential, respiratory dysfunction and initial increase of the generation of reactive oxygen species (ROS), followed by its decrease after prolonged incubation. Inhibitors of the mitochondrial permeability transition pore, cyclosporin A and bongkrekic acid, and inhibitors of respiratory complex III, stigmatellin and antimycin A, but not inhibitor of complex I, rotenone, partly prevented necrosis evoked by exposure of the cells to Cd(2+). Apoptosis of the cells was partly prevented by free radical scavengers and by preincubation with N-acetylcysteine. Stigmatellin, antimycin A and cyclosporin A also abolished Cd(2+)-induced increase in ROS generation. It is concluded that Cd(2+) toxicity in AS-30D rat ascites hepatoma, manifested by cell necrosis and/or apoptosis, involves ROS generation, most likely at the level of respiratory complex III, and is related to opening of the mitochondrial permeability transition pore.

Cadmium distribution and metallothionein expression in lizard tissues following acute and chronic cadmium intoxication

The present report is an attempt to investigate the influence of intraperitoneal and dietary cadmium exposure on the distribution of cadmium accumulation and induction of metallothionein gene expression in different tissues of the lizard Podarcis sicula. Cadmium accumulation in liver, kidney, ovary, brain and intestine was measured by atomic absorption spectrometry. Metallothionein gene induction was determined by dot blot analyses on the total RNA extracted from the same organs. Our data indicate that cadmium exposure results in significant cadmium uptake, but the patterns of this uptake varies with organ and exposure route. After a single intraperitoneal treatment, concentrations of cadmium and metallothionein transcript are positively correlated in kidney, liver and ovary. Following a dietary cadmium treatment, a positive correlation between the increase of metallothionein mRNA and cadmium accumulation is found in intestine, ovary and kidney, while no correlation is present in liver and brain.