The role of endoplasmic reticulum in cadmium-induced mesangial cell apoptosis

Cadmium stress alleviates lipid accumulation caused by chiral penthiopyrad through regulating endoplasmic reticulum stress and mitochondrial dysfunction in zebrafish liver

The coexistence of cadmium (Cd) can potentiate (synergism) or reduce (antagonism) the pesticide effects on organisms, which may change with chiral pesticide enantiomers. Previous studies have reported the toxic effects of chiral penthiopyrad on lipid metabolism in zebrafish (Danio rerio) liver. The Cd effects and toxic mechanism on lipid accumulation were investigated from the perspective of endoplasmic reticulum (ER) stress and mitochondrial dysfunction. The coexistence of Cd increased the concentrations of penthiopyrad and its metabolites in zebrafish. Penthiopyrad exposure exhibited significant effects on lipid metabolism and mitochondrial function-related indicators, which were verified by lipid droplets and mitochondrial damage in subcellular structures. Moreover, penthiopyrad activated the genes of ER unfolded protein reaction (UPR) and Ca2+ permeable channels, and S-penthiopyrad exhibited more serious effects on ER stress with ER hyperplasia than R-penthiopyrad. As a mitochondrial uncoupler, the coexistence of Cd could decrease lipid accumulation by alleviating ER stress and mitochondrial dysfunction, and these effects were the most significant for R-penthiopyrad. There were antagonistic effects between Cd and penthiopyrad, which could reduce the damage caused by penthiopyrad in zebrafish, thus increasing the bioaccumulation of penthiopyrad in zebrafish. These findings highlighted the importance and necessity of evaluating the ecological risks of metal-chiral pesticide mixtures.

The role of calcium, Akt and ERK signaling in cadmium-induced hair cell death

Exposure to heavy metals has been shown to cause damage to a variety of different tissues and cell types including hair cells, the sensory cells of our inner ears responsible for hearing and balance. Elevated levels of one such metal, cadmium, have been associated with hearing loss and shown to cause hair cell death in multiple experimental models. While the mechanisms of cadmium-induced cell death have been extensively studied in other cell types they remain relatively unknown in hair cells. We have found that calcium signaling, which is known to play a role in cadmium-induced cell death in other cell types through calmodulin and CaMKII activation as well as IP3 receptor and mitochondrial calcium uniporter mediated calcium flow, does not appear to play a significant role in cadmium-induced hair cell death. While calmodulin inhibition can partially protect hair cells this may be due to impacts on mechanotransduction activity. Removal of extracellular calcium, and inhibiting CaMKII, the IP3 receptor and the mitochondrial calcium uniporter all failed to protect against cadmium-induced hair cell death. We also found cadmium treatment increased pAkt levels in hair cells and pERK levels in supporting cells. This activation may be protective as inhibiting these pathways enhances cadmium-induced hair cell death rather than protecting cells. Thus cadmium-induced hair cell death appears distinct from cadmium-induced cell death in other cell types where calcium, Akt and ERK signaling all promote cell death.

The ameliorative effect of kaempferol against CdCl2- mediated renal damage entails activation of Nrf2 and inhibition of NF-kB

This study evaluated the nephroprotective effect of kaempferol against cadmium chloride (CdCl₂) -induced nephropathy in rats. It also investigated if activation of Nrf2 is a common mechanism of action. Adult male rats ((150 ± 15 g) were divided into 4 groups (n = 8/each) as a control (1% DMSO, orally), control + kaempferol (200 mg/kg, orally), CdCl₂ (50 mg/l in drinking water), and CdCl₂ + kaempferol (200 mg/kg)-treated rats. All treatments were conducted for 8 weeks. Kaempferol significantly attenuated CdCl₂-induced weight loss, reduction in kidney weights, and the injury in the glomeruli, proximal tubules, and distal tubules in the treated rats. It also significantly lowered serum levels of urea and creatinine, increased urine output and urinary creatinine levels and clearance but reduced urinary levels of albumin urinary albumin exertion (UAER), and urinary albumin/creatinine ratio (UACR) in these rats. In parallel, kaempferol downregulated renal levels of cleaved caspase-3 and Bax and unregulated those of Bcl2. In the kidney tissues of the control animals and CdCl₂ rats, kaempferol significantly attenuated oxidative stress, inflammation and significantly boosted levels of manganese superoxide dismutase and glutathione. Also, and in both groups, kaempferol suppressed the nuclear levels of NF-κB p65, downregulated Keap1, and stimulated the nuclear activation and protein levels of Nrf2. In conclusion, kaempferol is a potential therapeutic drug to prevent CdCl₂-induced nephropathy due to its anti-inflammatory and anti-oxidant effects mediated by suppressing NF- NF-κB p65 and transactivating Nrf2.

Involvement of caspase-3 in apoptosis of human lymphocytes exposed to cadmium chloride

BACKGROUND

Lymphocytes are a group of white blood cells with a variety of roles their integrity is crucial for the body's immune responses. Cadmium, a heavy metal and environmental pollutant, is known as a toxicant to exert its adverse effects on some sort of cells including blood cells.

RESEARCH DESIGN

In this study, human lymphocytes were divided into 3 groups: (1) lymphocytes at 0-h, (2) lymphocytes at 24 h (control), (3) lymphocytes treated with cadmium chloride (15 μM). Lymphocyte viability and plasma membrane integrity were assessed in these groups. In addition, the occurrence of apoptosis was investigated by assessment of nucleus diameter and flow cytometry. Activation of caspase-3 was also detected by immunocytochemistry.

RESULTS

Result showed that lymphocyte's viability and plasma membrane integrity decreased in lymphocytes treated with cadmium as compared with the control group. Decreased nucleus diameter and result of flow cytometry demonstrated cadmium-induced apoptosis in human lymphocytes. Furthermore, lymphocytes treated with cadmium displayed intensely activated caspase-3 immunoreactivity in their cytoplasm.

CONCLUSION

In conclusion, cadmium not only negatively effect on viability and plasma membrane, but also induces caspase-dependent apoptosis in human lymphocytes.

The electrophysiological effects of cadmium on Retzius nerve cells of the leech Haemopis sanguisuga

Cadmium is considered one of the most toxic heavy metals which can cause cytotoxicity in multiple organs including the brain. Despite many studies over the past decades, the cellular and molecular mechanisms underlying its neurotoxicity remain unclear. The present study was designed to examine the acute effects of cadmium chloride (CdCl₂) on the electrical activity of the Retzius nerve cells of leech Haemopis sanguisuga using electrophysiological techniques. CdCl₂, in concentrations of 10-100 μM, produced a dose- and time-dependent depolarization of Retzius neurons, paralleled by an increase in firing frequency and action potential duration. To examine potential mechanisms, we studied the effects of cadmium on the outward potassium current upon depolarization using a point microelectrode voltage-clamp technique. Reduction of the fast, and partial inhibition of the slow outward current were observed after adding 50 and 100 μM CdCl₂ in the external fluid. The present results support the view that the effect of cadmium on the outward potassium channel may be a potential contributing mechanism for cadmium-induced neurotoxic damage. The proposed mechanism of cadmium action on the electrical properties of leech Retzius neurons might have broader significance concerning not only the leeches but vertebrate brains as well.

Mechanistic analysis of cadmium toxicity in Saccharomyces cerevisiae

As a potentially toxic heavy metal, Cadmium (Cd) can cause endoplasmic reticulum and oxidative stress, and thus lead to cell death. To explore the mechanisms of Cd toxicity, we investigated the UPRE-lacZ expression, the intracellular reactive oxygen species (ROS) and cell death in the 151 Cd-sensitive mutants of Saccharomyces cerevisiae in response to Cd stress. We identified 101 genes regulating UPRE-lacZ expression were involved in preventing ROS production and/or cell death from increasing to high levels, while mutants for 72 genes caused both elevated ROS production and cell death, indicating the Cd-induced ROS production and cell death are mediated by UPR. Genes involved in cell wall integrity (CWI) pathway, vacuolar protein sorting (VPS) and vacuolar transport, calcium/calcineurin pathway and PHO pathways were all required for the Cd-induced UPR, intracellular ROS and cell death. To conclude, this study highlights the importance of Cd-induced UPR, intracellular ROS levels and cell death that may play crucial roles in Cd-induced toxicity.

Quercetin alleviates cadmium chloride-induced renal damage in rats by suppressing endoplasmic reticulum stress through SIRT1-dependent deacetylation of Xbp-1s and eIF2α

Endoplasmic reticulum (ER) stress plays a key role in cadmium chloride (CdCl2)-induced nephrotoxicity. Sirtuin-1 (SIRT1) is a potent inhibitor of ER stress. In this study, we examined whether the protective effect of quercetin (QUR) against CdCl₂-induced nephrotoxicity in rats involved modulation of SIRT1 and/or ER stress. Adult male rats were divided into five groups (n = 8, each) and treated for eight weeks as follows: control, control + QUR, CdCl₂, CdCl₂ + QUR, and CdCl₂ + QUR + EX-527 (a SIRT1 inhibitor). Treatment of rats with QUR preserved the glomerulus and tubule structure, attenuated interstitial fibrosis, increased creatinine excretion, and reduced urinary levels of albumin, N-acetyl-β-D-glucosaminidase, and β2-microglobulin in CdCl₂-treated rats. Concomitantly, QUR increased renal levels of Bcl-2, reduced mRNA levels of CHOP, and protein levels of Bax, caspase-3, and cleaved caspase-3, but failed to reduce the mRNA levels of GRP78, PERK, eIf2α, ATF-6, and xbp-1. QUR also reduced the renal levels of reactive oxygen species, tumour necrosis factor, and interleukin-6 and the nuclear activity of NF-κB in the control and CdCl₂-treated rats but increased the nuclear activity of Nrf2 and levels of glutathione and manganese superoxide dismutase. Additionally, QUR increased the total levels and nuclear activity of SIRT1 and reduced the acetylation of eIf2α and xbp-1. The nephroprotective effects of QUR were abrogated by treatment with EX-527. Thus, QUR ameliorated CdCl₂-induced nephrotoxicity through antioxidant and anti-inflammatory effects and suppressed ER stress mediated by the upregulation or activation of SIRT1-induced deacetylation of Nrf2, NF-κB p65, eIF2α, and xbp-1.

Analysis of Cadmium, Epigallocatechin Gallate, and Vitamin C Co-exposure on PC12 Cellular Mechanisms

Exposure to cadmium (Cd) is a risk factor to health impairments, wherein its cytotoxicity is attributed to induction of oxidative stress. Usage of anti-oxidants, however, can help lessen the damaging effects of Cd. The effect of Cd interaction with low concentration of dietary anti-oxidants, L-ascorbic acid and (-)-epigallocatechin gallate (EGCG), to PC12 cellular mechanisms was examined. The expected toxicity of Cd was observed on PC12 cells but addition of L-ascorbic acid ameliorated this effect. On the other hand, addition of EGCG was able to increase the cytotoxicity of Cd and to decrease the protective effect of L-ascorbic acid against Cd. Increase in LDH activity and decrease in free sulfhydryl levels indicated cell membrane damage and oxidative stress, respectively, in Cd- and EGCG-Cd-treated cells. Downregulation of pro-apoptotic proteins (pro-caspase-9, p53, and ERK1) was observed in cells treated with Cd alone and EGCG-Cd, while upregulation of autophagy-linked proteins (p62 and pBeclin1) was found on L-ascorbic acid-Cd combination treatments. These findings indicate that Cd causes cells to undergo an autophagy-enhanced cell death; low-concentration EGCG and L-ascorbic acid promotes cell survival individually; however, interaction of EGCG with Cd showed enhancement of Cd toxicity and antagonism of L-ascorbic acid efficiency.

Resveratrol protects against cadmium chloride-induced hippocampal neurotoxicity by inhibiting ER stress and GAAD 153 and activating sirtuin 1/AMPK/Akt

This study investigated whether the apoptotic effect induced by cadmium chloride (CdCl₂ ) in rat's hippocampi and neuroprotection afforded by resveratrol (RES) are mediated by modulation of ER stress and involve sirtuin 1 (SIRT1)/AMPK/Akt axis. Adult male Wistar rats were divided into four groups (n = 24/group) as control, control + RES (300 mg/kg), CdCl₂ (5 mg/kg), and CdCl₂  + RES. All treatments were conducted orally for 45 days. Also, cultured hippocampal cells were treated with CdCl₂ in the presence or absence of RES and with or without preincubation with SIRT1, AMPK, or PI3K inhibitors. CdCl₂ impaired retention and spatial memories of rats and reduced levels and activities of SIRT1 and inhibited AMPK/Akt axis in their hippocamapi where SIRT1 was the upstream regulator. It also enahnced hippocampal levels of reactive oxygen species (ROS) and expression of caspase-12 and caspase-3, depleted glutathione (GSH) levels, and activated GRP78, activating transcription factor-6, GAAD 153, X-box binding protein-1 arms of ER stress. On the contrary, RES coadminsitration completley abolished all these events. Interstingly and in control rats, RES not only increased levels of GSH, but also enhenced protein levels of B-cell lymphoma 2 (Bcl-2) and dwonregulated GAAD 153. In both control and CdCl₂ -treated rats, pharmacological inhibtion of SIRT1, AMPK, and Akt compleltely abolished all effects afforded by RES. In conclusion, CdCl₂ -induced hippocampal apopotis is associated with reduction of SIRT1/AMPK/Akt activity levels, ROS generation, downregulation of Bcl-2, and activities, activation of ER stress, and GAAD 153, whereas RES is able to reverse these effects through activation of SIRT1/AMPK/Akt.

CaMKⅡ mediates cadmium induced apoptosis in rat primary osteoblasts through MAPK activation and endoplasmic reticulum stress

Ca²⁺ is an important ion in various intracellular metabolic pathways. Endoplasmic reticulum (ER) is a major intracellular calcium store and ER calcium homeostasis plays a key part in the regulation of apoptosis. We have previously shown that Cadmium (Cd) induces apoptosis in osteoblasts (OBs), accompany by increased cytoplasmic calcium. As the role of calcium in OBs apoptosis induced by Cd has not been clarified we investigated the effects of Cd exposure in rat OBs on intracellular Ca²⁺, CaMKII phosphorylation, and the pathways implicated in inducing apoptosis. The results showed that cadmium(Cd) induced elevation of intracellular Ca²⁺ ([Ca²⁺]_i) in OBs by the release of Ca²⁺ from ER and the inflow of Ca²⁺ from the extracellular matrix. Cd induced [Ca²⁺]_i elevation and phosphorylation of CaMKII which might be involved in activation of MAPKs and participated in Cd-induced mitochondrial apoptosis through the alteration of the ratio of Bax/Bcl-2 expression. Meanwhile, CaMKII phosphorylation activated unfolded protein response (UPR) during cadmium treatment and could enable the ER apoptosis pathway through the activation of caspase-12. These results indicated that CaMKII plays an important role in Cd induced ER apoptosis and MAPK activation. Our data provide new insights into the mechanisms underlying apoptosis in OBs following Cd exposure. This provides a theoretical basis for future investigations into the clinical therapeutic application of CaMKⅡ inhibitors in osteoporosis induced by Cd exposure.

Selenium protects against cadmium-induced kidney apoptosis in chickens by activating the PI3K/AKT/Bcl-2 signaling pathway

Cadmium (Cd) is a toxic heavy metal that can induce apoptosis. Selenium (Se) is a necessary trace element and can antagonize the toxicity of many heavy metals, including Cd. PI3K/AKT/Bcl-2 is a key survival signaling pathway that regulates cellular defense system against oxidative injury as well as cell proliferation, survival, and apoptosis. The antagonistic effects of Se on Cd-induced toxicity have been reported. However, little is known about the effect of Se on Cd-induced apoptosis in chicken kidneys via the PI3K/AKT/Bcl-2 signaling pathway. In the present study, we fed chickens with Se, Cd, or both Se and Cd supplements, and after 90 days of treatment, we detected the related index. The results showed that the activity of inducible nitric oxide synthase (iNOS) and concentration of nitric oxide (NO) were increased; activities of the mitochondrial respiratory chain complexes (complexes I, II, and V) and ATPases (the Na⁺-K⁺-ATPase, the Mg²⁺-ATPase, and the Ca²⁺-ATPase) were decreased; expression of PI3K, AKT, and Bcl-2 were decreased; and expression of Bax, Bak, P53, Caspase-3, Caspase-9, and cytochrome c (Cyt c) were increased. Additionally, the results of the TUNEL assay showed that the number of apoptotic cells was increased in the Cd group. By contrast, there was a significant improvement of the correlation indicators and occurrence of apoptosis in the Se + Cd group compared to the Cd group. In conclusion, our results confirmed that Se had a positive effect on ameliorating Cd-induced apoptosis in chicken kidney tissue by activating the PI3K/AKT/Bcl-2 signaling pathway.

Increased Intracellular Reactive Oxygen Species Mediates the Anti-Cancer Effects of WZ35 via Activating Mitochondrial Apoptosis Pathway in Prostate Cancer Cells

BACKGROUND

The limited treatment option for recurrent prostate cancer and eventual resistant to conventional chemotherapy drugs has fueled continued interest in finding new anti-neoplastic agents. WZ35, a chemical analog of curcumin, had been demonstrated to have high chemical stability and potential anticancer effects in gastric cancer cells. The present study aimed to investigate the anti-prostate cancer effects of WZ35 in vitro and in vivo as well as the underlying mechanism.

METHODS

Two prostate cancer cell lines RM-1 and DU145 were utilized to test the anti-cancer effects of WZ35 and the underlying mechanism. MTT assay was used to assess the cytotoxic effect of WZ35. Cell cycle distribution, apoptosis, alteration of ROS, and [Ca²⁺ ]_i level were evaluated using flow cytometry. Western blotting assay was applied to measure the levels of proteins associated with apoptosis and cell cycle. Immunofluorescence staining and Electron micrographs were used to evaluate activation of mitochondrial apoptosis pathway. Tumor models in nude mice were induced by injection of RM-1 prostate cancer cells to test the in vivo anticancer action of WZ35.

RESULTS

Our results showed that WZ35 treatment induced loss of cell viability, cell apoptosis, and G2/M cycle arrest in both RM-1 and DU145 cells, coupled with ROS overproduction, intracellular calcium surge, and activation of mitochondrial apoptosis pathway in RM-1 cells. Interestingly, all above changes induced by WZ35 were completely reversed by ROS blockage. In addition, prevention of [Ca²⁺ ]_i elevation by BAPTA/AM also inhibited activation of mitochondrial apoptosis pathway induced by WZ35. In vivo studies, WZ35 treatment significantly inhibited RM-1 homograft tumor growth along with increased ROS accumulation, mitochondrial disruption, and cell apoptosis in tumor tissues.

CONCLUSIONS

In conclusion, this work provides a novel anticancer candidate for the treatment of prostate cancer and demonstrated that increased ROS mediate the anti-cancer effects of WZ35 via activating mitochondrial apoptosis pathway. Importantly, this work also reveals that targeting ROS generation might be an effective strategy in human androgen-resistant prostate cancer treatment. Prostate 77:489-504, 2017. © 2016 Wiley Periodicals, Inc.

Celastrol Attenuates Cadmium-Induced Neuronal Apoptosis via Inhibiting Ca2+ -CaMKII-Dependent Akt/mTOR Pathway

Cadmium (Cd), an environmental and industrial pollutant, affects the nervous system and consequential neurodegenerative disorders. Recently, we have shown that celastrol prevents Cd-induced neuronal cell death partially by suppressing Akt/mTOR pathway. However, the underlying mechanism remains to be elucidated. Here, we show that celastrol attenuated Cd-elevated intracellular-free calcium ([Ca²⁺ ]_i ) level and apoptosis in neuronal cells. Celastrol prevented Cd-induced neuronal apoptosis by inhibiting Akt-mediated mTOR pathway, as inhibition of Akt with Akt inhibitor X or ectopic expression of dominant negative Akt reinforced celastrol's prevention of Cd-induced phosphorylation of S6K1/4E-BP1 and cell apoptosis. Furthermore, chelating intracellular Ca²⁺ with BAPTA/AM or preventing [Ca²⁺ ]_i elevation using EGTA potentiated celastrol's repression of Cd-induced [Ca²⁺ ]_i elevation and consequential activation of Akt/mTOR pathway and cell apoptosis. Moreover, celastrol blocked Cd-elicited phosphorylation of CaMKII, and pretreatment with BAPTA/AM or EGTA enhanced celastrol's suppression of Cd-increased phosphorylation of CaMKII in neuronal cells, implying that celastrol hinders [Ca²⁺ ]_i -mediated CaMKII phosphorylation. Inhibiting CaMKII with KN93 or silencing CaMKII attenuated Cd activation of Akt/mTOR pathway and cell apoptosis, and this was strengthened by celastrol. Taken together, these data demonstrate that celastrol attenuates Cd-induced neuronal apoptosis via inhibiting Ca²⁺ -CaMKII-dependent Akt/mTOR pathway. Our findings underscore that celastrol may act as a neuroprotective agent for the prevention of Cd-induced neurodegenerative disorders. J. Cell. Physiol. 232: 2145-2157, 2017. © 2016 Wiley Periodicals, Inc.

Treatment of cadmium-induced renal oxidative damage in rats by administration of alpha-lipoic acid

Cadmium (Cd) is a toxic heavy metal that is widespread and nephrotoxic, but the mechanism of its toxicity is not well understood. Alpha-lipoic acid (α-LA) has a protective effect on Cd-induced oxidative stress, but the underlying mechanism is also not clear. This study aimed to confirm that Cd causes renal damage and to explore the potential underlying mechanism of α-LA to the kidney. Rats were randomly divided into four groups: control group, Cd group (50 mg/L CdAc₂), Cd+α-LA group (50 mg/L CdAc₂ + 50 mg/kg body wt/day α-LA), and α-LA group (50 mg/kg body wt/day). The rats were exposed to Cd via drinking water and α-LA in the form of gavage at the same time every day. After 12 weeks, the activity of antioxidant enzymes and the level of Cd in the kidney were analyzed. Renal damage was evaluated based on histopathological and ultrastructure examinations. The apoptosis index was determined based on the results of western blotting and qRT-PCR. Our results indicate that accumulation of Cd causes serious kidney damage and α-LA has a protective effect against Cd-induced oxidative stress and apoptosis. Further, the findings indicate that the antioxidant, Cd chelation, and antiapoptotic activities of α-LA are the key factors that alleviate nephrotoxicity.

Low Dose Cadmium Inhibits Proliferation of Human Renal Mesangial Cells via Activation of the JNK Pathway

Cadmium (Cd) is a heavy metal and environmental pollutant. The kidney is the principal target organ of Cd exposure. Previously, we found that low concentration of Cd damages the integrity of the glomerular filtration barrier. However, little is known about the effects of Cd on renal mesangial cells, which provide structural support for the glomerular capillary loops and regulate intraglomerular blood flow. In this study, human renal mesangial cells (HRMCs) were cultured in the presence of serum and treated with 4 μM Cd. We found that Cd activates the c-Jun N-terminal kinase (JNK) pathway, and increases the protein levels of c-Jun and c-Fos. Cd treatment also induces a decrease in proliferation and an increase in apoptosis of HRMCs, but only the decrease in HRMC proliferation was reversed by pretreatment with SP600125, an inhibitor of the JNK pathway. In addition, Cd does not change the expression of α-smooth muscle actin and platelet-derived growth factor receptor-β, the markers of mesangial cells, or the alignment of the filamentous actin (F-actin) cytoskeleton of HRMCs. Our data indicate that the JNK pathway mediates the inhibitory effects of Cd on HRMC proliferation.

Asymmetric dimethylarginine (ADMA) treatment induces apoptosis in cultured rat mesangial cells via endoplasmic reticulum stress activation

Asymmetric dimethylarginine (ADMA), a high risk factor for endothelial dysfunction and cardiovascular disease (CVD), has been reported to promote cellular dysfunction via endoplasmic reticulum (ER) stress activation in various cells. Additionally, increased serum ADMA levels have been observed in incipient kidney diseases. Previously, we reported that activated ER stress is associated with mesangial cell apoptosis, observed mainly in overt nephropathy or chronic kidney disease (CKD). However, the effect of ADMA on mesangial cell apoptosis is unknown. Thus, we investigated the effects of ADMA on mesangial cell apoptosis and ER stress signaling. ADMA treatment increased caspase-3 activity and activated three branches of ER stress signaling (PERK, IRE1, and ATF6) that induce mesangial cell apoptosis. Pharmacological inhibitors of ER stress (inhibitors of PERK, IRE1, and S1P) attenuated ADMA-induced cleavage of caspase-3 and induced a decrease in the mitochondrial membrane potential. Furthermore, these inhibitors diminished the number of apoptotic cells induced by ADMA treatment. Taken together, our results indicated that ADMA treatment induces mesangial cell apoptosis via ER stress signaling. These results suggest that ADMA-induced mesangial cell apoptosis could contribute to the progression of overt nephropathy and CKD.

Cadmium overkill: autophagy, apoptosis and necrosis signalling in endothelial cells exposed to cadmium

Apoptosis, necrosis, or autophagy-it is the mode of cell demise that defines the response of surrounding cells and organs. In case of one of the most toxic substances known to date, cadmium (Cd), and despite a large number of studies, the mode of cell death induced is still unclear. As there exists conflicting data as to which cell death mode is induced by Cd both across various cell types and within a single one, we chose to analyse Cd-induced cell death in primary human endothelial cells by investigating all possibilities that a cell faces in undergoing cell death. Our results indicate that Cd-induced death signalling starts with the causation of DNA damage and a cytosolic calcium flux. These two events lead to an apoptosis signalling-related mitochondrial membrane depolarisation and a classical DNA damage response. Simultaneously, autophagy signalling such as ER stress and phagosome formation is initiated. Importantly, we also observed lysosomal membrane permeabilization. It is the integration of all signals that results in DNA degradation and a disruption of the plasma membrane. Our data thus suggest that Cd causes the activation of multiple death signals in parallel. The genotype (for example, p53 positive or negative) as well as other factors may determine the initiation and rate of individual death signals. Differences in the signal mix and speed may explain the differing results recorded as to the Cd-induced mode of cell death thus far. In human endothelial cells it is the sum of most if not all of these signals that determine the mode of Cd-induced cell death: programmed necrosis.

Cadmium Induces Apoptosis in Freshwater Crab Sinopotamon henanense through Activating Calcium Signal Transduction Pathway

Calcium ion (Ca²⁺) is one of the key intracellular signals, which is implicated in the regulation of cell functions such as impregnation, cell proliferation, differentiation and death. Cadmium (Cd) is a toxic environmental pollutant that can disturb cell functions and even lead to cell death. Recently, we have found that Cd induced apoptosis in gill cells of the freshwater crab Sinopotamon henanense via caspase activation. In the present study, we further investigated the role of calcium signaling in the Cd-induced apoptosis in the animals. Our data showed that Cd triggered gill cell apoptosis which is evidenced by apoptotic DNA fragmentation, activations of caspases-3, -8 and -9 and the presence of apoptotic morphological features. Moreover, Cd elevated the intracellular concentration of Ca²⁺, the protein concentration of calmodulin (CaM) and the activity of Ca²⁺-ATPase in the gill cells of the crabs. Pretreatment of the animals with ethylene glycol-bis-(b-aminoethyl ether)-N,N,N’,N’-tetraacetic acid (EGTA), Ca²⁺ chelator, inhibited Cd-induced activation of caspases-3, -8 and -9 as well as blocked the Cd-triggered apoptotic DNA fragmentation. The apoptotic morphological features were no longer observed in gill cells pretreated with the Ca²⁺ signaling inhibitors before Cd treatment. Our results indicate that Cd evokes gill cell apoptosis through activating Ca²⁺-CaM signaling transduction pathway.

LcBiP, a endoplasmic reticulum chaperone binding protein gene from Lycium chinense, confers cadmium tolerance in transgenic tobacco

Cadmium (Cd) accumulation is very toxic to plants. The presence of Cd may lead to excessive production of reactive oxygen species (ROS), and then cause inhibition of plant growth. The endoplasmic reticulum chaperone binding protein (BiP) is an important functional protein, which has been shown to function as a sensor of alterations in the ER environment. BiP overexpression in plants was shown to increase drought tolerance through inhibition of ROS accumulation. Due to the above relationships, it is likely that there may be a link between Cd stress tolerance, ROS accumulation and the BiP transcript expression in plants. In this study, a BiP gene, LcBiP, from L. chinense was isolated and characterized. Overexpression of LcBiP in tobacco conferred Cd tolerance. Under Cd stress conditions, the transgenic tobacco lines exhibited better chlorophyll retention, less accumulation of ROS, longer root length, more glutathione (GSH) content, and less antioxidant enzyme activity than the wild type. These data demonstrated that LcBiP act as a positive regulator in Cd stress tolerance. It is hypothesized that the improved Cd tolerance of the transgenic tobacco plants may be due to the enhanced ROS scavenging capacity. The enhancement of GSH content might contribute to this ROS scavenging capacity in the transgenic plants. However, the underlying mechanism for BiP-mediated increase in Cd stress tolerance need to be further clarified.

Aldose reductase inhibition alleviates hyperglycemic effects on human retinal pigment epithelial cells

Chronic hyperglycemia is an important risk factor involved in the onset and progression of diabetic retinopathy (DR). Among other effectors, aldose reductase (AR) has been linked to the pathogenesis of this degenerative disease. The purpose of this study was to investigate whether the novel AR inhibitor, beta-glucogallin (BGG), can offer protection against various hyperglycemia-induced abnormalities in human adult retinal pigment epithelial (ARPE-19) cells. AR is an enzyme that contributes to cellular stress by production of reactive oxygen species (ROS) under high glucose conditions. A marked decrease in cell viability (from 100% to 78%) following long-term exposure (4 days) of RPE cells to high glucose (HG) was largely prevented by siRNA-mediated knockdown of AR gene expression (from 79% to 97%) or inhibition using sorbinil (from 66% to 86%). In HG, BGG decreased sorbitol accumulation (44%), ROS production (27%) as well as ER stress (22%). Additionally, we demonstrated that BGG prevented loss of mitochondrial membrane potential (MMP) under HG exposure. We also showed that AR inhibitor pretreatment reduced retinal microglia-induced apoptosis in APRE-19 cells. These results suggest that BGG may be useful as a therapeutic agent against retinal degeneration in the diabetic eye by preventing RPE cell death.

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.

Cd-induced apoptosis through the mitochondrial pathway in the hepatopancreas of the freshwater crab Sinopotamon henanense

Cd is one of the most common pollutants in the environment that also induces the apoptosis. To explore the mechanism of apoptosis in the hepatopancreas, freshwater crab S. henanense were treated with 0, 3.56, 7.12, 14.25, 28.49 and 56.98 mg/L Cd for 72 h. Apoptosis was noticeable in every treatment group and necrosis was observed clearly in the high concentration Cd groups. Classical apoptotic bodies were found by transmission electronic microscopy, which revealed chromatin condensation under nuclear membrane and mitochondrial membrane rupture. An increasing number of autolysosomes, damaged rough endoplamic reticulum and Golgi complex were observed as the Cd concentration increase. Brown colored apoptotic cells were detected by the TUNEL test in all Cd-treatment groups. The apoptosis index increased following the elevation of Cd concentration and got 32.9% in the highest Cd group. Caspase-9 and caspase-3 activities increased in the lower Cd treatment groups but no changes in the higher Cd concentration groups (comparing to the control group). The activity of caspase-8 did not change significantly. No significant change in the content of mitochondrial cytochrome c (cyt c) in Cd exposed groups except the decrease in the 56.98 mg/L group. In crabs treated with 3.56, 7.12 and 14.25 mg/L Cd, hyperpolarization of mitochondrial membrane potential (Δψ_m) significantly increased. These results implied that apoptosis in the hepatopancreas induced by Cd occurrs through the mitochondrial caspase-dependent pathway. However, whether there are other apoptotic pathways needs to be studied further.

Cadmium-induced apoptosis in primary rat cerebral cortical neurons culture is mediated by a calcium signaling pathway

Cadmium (Cd) is an extremely toxic metal, capable of severely damaging several organs, including the brain. Studies have shown that Cd disrupts intracellular free calcium ([Ca²⁺]_i) homeostasis, leading to apoptosis in a variety of cells including primary murine neurons. Calcium is a ubiquitous intracellular ion which acts as a signaling mediator in numerous cellular processes including cell proliferation, differentiation, and survival/death. However, little is known about the role of calcium signaling in Cd-induced apoptosis in neuronal cells. Thus we investigated the role of calcium signaling in Cd-induced apoptosis in primary rat cerebral cortical neurons. Consistent with known toxic properties of Cd, exposure of cerebral cortical neurons to Cd caused morphological changes indicative of apoptosis and cell death. It also induced elevation of [Ca²⁺]_i and inhibition of Na⁺/K⁺-ATPase and Ca²⁺/Mg²⁺-ATPase activities. This Cd-induced elevation of [Ca²⁺]_i was suppressed by an IP₃R inhibitor, 2-APB, suggesting that ER-regulated Ca²⁺ is involved. In addition, we observed elevation of reactive oxygen species (ROS) levels, dysfunction of cytochrome oxidase subunits (COX-I/II/III), depletion of mitochondrial membrane potential (ΔΨm), and cleavage of caspase-9, caspase-3 and poly (ADP-ribose) polymerase (PARP) during Cd exposure. Z-VAD-fmk, a pan caspase inhibitor, partially prevented Cd-induced apoptosis and cell death. Interestingly, apoptosis, cell death and these cellular events induced by Cd were blocked by BAPTA-AM, a specific intracellular Ca²⁺ chelator. Furthermore, western blot analysis revealed an up-regulated expression of Bcl-2 and down-regulated expression of Bax. However, these were not blocked by BAPTA-AM. Thus Cd toxicity is in part due to its disruption of intracellular Ca²⁺ homeostasis, by compromising ATPases activities and ER-regulated Ca²⁺, and this elevation in Ca²⁺ triggers the activation of the Ca²⁺-mitochondria apoptotic signaling pathway. This study clarifies the signaling events underlying Cd neurotoxicity, and suggests that regulation of Cd-disrupted [Ca²⁺]_i homeostasis may be a new strategy for prevention of Cd-induced neurodegenerative diseases.

Cadmium induces neuronal cell death through reactive oxygen species activated by GADD153

Background

Cadmium(Cd), a heavy metal, which has a potent harmful effects, is a highly stress-inducible material that is robustly expressed following disruption of homeostasis in the endoplasmic reticulum (ER) (so-called ER stress). The mechanism Cd induced cell death of neuroblastoma cells complex, involving cellular signaling pathways as yet incompletely defined but, in part, involving the generation of reactive oxygen species (ROS). Several studies have correlated GADD153 expression with cell death, but a mechanistic link between GADD153 and apoptosis has never been demonstrated.

Results

SH-SY5Y cells were treated Cd led to increase in intracellular ROS levels. ROS generation is not consistent with intracellular [Ca²⁺]. The exposure of neuroblastoma cells to Cd led to increase in intracellular GADD153 and Bak levels in a doses and time dependent manner. The induction of these genes by Cd was attenuated by NAC. Cd-induced apoptosis is decreased in GADD153 knockdown cells compared with normal cells. The effect of GADD153 on the binding of C/EBP to the Bak promoters were analyzed ChIP assay. Basal constitutive GADD153 recruitment to the –3,398/–3,380 region of the Bak promoter is observed in SH-SY5Y cells.

Conclusions

The exposure of SH-SY5Y cells to Cd led to increase in intracellular ROS levels in a doses and time dependent manner. The generation of ROS result in the induction of GADD153 is causative of cadmium-induced apoptosis. GADD153 regulates Bak expression by its binding to promoter region (between −3,398 and −3,380). Therefore, we conclude that GADD153 sensitizes cells to ROS through mechanisms that involve up-regulation of BAK and enhanced oxidant injury.

C/EBP homologous protein induces mesangial cell apoptosis under hyperglycemia

Diabetes mellitus is known to cause kidney impairment; however, the mechanism remains elusive. The aim of this study was to investigate the role of C/EBP homologous protein (CHOP), an important protein in endoplasmic reticulum stress‑mediated mesangial cell apoptosis in hyperglycemia. Mesangial cells were cultured in normal (control group) and high glucose medium (high glucose group). TUNEL staining was performed to assess apoptotic cells in the groups. The expression of CHOP and caspase‑3 was also assayed by immunohistochemistry and western blot analysis. Following 24 h culture in high glucose medium, TUNEL‑positive cells were observed to be significantly increased (P<0.01). The expression of CHOP and caspase‑3 in mesangial cells was also found to be significantly enhanced under high glucose conditions compared with the normal group (P<0.01). The results indicate that CHOP mediates apoptosis in mesangial cells under hyperglycemia and may play a role in the development of diabetic nephropathy.

14-3-3 Proteins are Regulators of Autophagy

14-3-3 proteins are implicated in the regulation of proteins involved in a variety of signaling pathways. 14-3-3-dependent protein regulation occurs through phosphorylation-dependent binding that results, in many cases, in the release of survival signals in cells. Autophagy is a cell digestion process that contributes to overcoming nutrient deprivation and is initiated under stress conditions. However, whether autophagy is a cell survival or cell death mechanism remains under discussion and may depend on context. Nevertheless, autophagy is a cellular process that determines cell fate and is tightly regulated by different signaling pathways, some of which, for example MAPK, PI3K and mTOR, are tightly regulated by 14-3-3 proteins. It is therefore important to understand the role of 14-3-3 protein in modulating the autophagic process. Within this context, direct binding of 14-3-3 to mTOR regulatory proteins, such as TSC2 and PRAS40, connects 14-3-3 with autophagy regulatory processes. In addition, 14-3-3 binding to human vacuolar protein sorting 34 (hVps34), a class III phosphatidylinositol-3-kinase (PI3KC3), indicates the involvement of 14-3-3 proteins in regulating autophagosome formation. hVps34 is involved in vesicle trafficking processes such as autophagy, and its activation is needed for initiation of autophagy. Chromatography and overlay techniques suggest that hVps34 directly interacts with 14-3-3 proteins under physiological conditions, thereby maintaining hVps34 in an inactive state. In contrast, nutrient starvation promotes dissociation of the 14-3-3–hVps34 complex, thereby enhancing hVps34 lipid kinase activity. Thus, 14-3-3 proteins are regulators of autophagy through regulating key components of the autophagic machinery. This review summarizes the role of 14-3-3 protein in the control of target proteins involved in regulating the master switches of autophagy.

Inhibition of mitochondria- and endoplasmic reticulum stress-mediated autophagy augments temozolomide-induced apoptosis in glioma cells

Autophagy is a crucial process for cells to maintain homeostasis and survival through degradation of cellular proteins and organelles, including mitochondria and endoplasmic reticula (ER). We previously demonstrated that temozolomide (TMZ), an alkylating agent for brain tumor chemotherapy, induced reactive oxygen species (ROS)/extracellular signal-regulated kinase (ERK)-mediated autophagy to protect glioma cells from apoptosis. In this study, we investigated the role of mitochondrial damage and ER stress in TMZ-induced cytotoxicity. Mitochondrial depolarization and mitochondrial permeability transition pore (MPTP) opening were observed as a prelude to TMZ-induced autophagy, and these were followed by the loss of mitochondrial mass. Electron transport chain (ETC) inhibitors, such as rotenone (a complex I inhibitor), sodium azide (a complex IV inhibitor), and oligomycin (a complex V inhibitor), or the MPTP inhibitor, cyclosporine A, decreased mitochondrial damage-mediated autophagy, and therefore increased TMZ-induced apoptosis. TMZ treatment triggered ER stress with increased expression of GADD153 and GRP78 proteins, and deceased pro-caspase 12 protein. ER stress consequently induced autophagy through c-Jun N-terminal kinases (JNK) and Ca²⁺ signaling pathways. Combination of TMZ with 4-phenylbutyrate (4-PBA), an ER stress inhibitor, augmented TMZ-induced cytotoxicity by inhibiting autophagy. Taken together, our data indicate that TMZ induced autophagy through mitochondrial damage- and ER stress-dependent mechanisms to protect glioma cells. This study provides evidence that agents targeting mitochondria or ER may be potential anticancer strategies.

Mitochondrial pathway of apoptosis in the hepatopancreas of the freshwater crab Sinopotamon yangtsekiense exposed to cadmium

Cadmium (Cd) is one of the most common toxic metals in water. To investigate the mechanism of Cd-induced apoptosis in the hepatopancreas, freshwater crabs Sinopotamon yangtsekiense were exposed to 0, 3.56, 7.12, 14.25, 28.49 and 56.98 mg/L Cd for 48 h. After a 48 h exposure, apoptosis and necroptosis were apparent in the group exposed to 28.49 mg/L Cd and only one case of necrosis was observed in the highest concentration of Cd. Electronic microscopy revealed chromatin condensation under nuclear membrane and mitochondrial membrane rupture in 14.25 and 28.49 mg/L Cd treatment groups. Brown colored apoptotic cells were detected with the TUNEL test in all Cd-treatment groups. The AI in 56.98 mg/L group was 1.4-fold greater than that in crabs exposed to 14.25mg/L Cd. Caspase-9, caspase-3, SDH and Ca(2+)-ATPase activities increased with increasing Cd concentration. However, the activities of caspase-8 and LDH did not change significantly compared with control group. These results implied that Cd induced apoptosis in the hepatopancreas occurs through a mitochondrial pathway.

Effects of salubrinal on cadmium-induced apoptosis in HK-2 human renal proximal tubular cells

Cadmium exposure is known to cause endoplasmic reticulum (ER) stress. In our current study, we examined the effects of salubrinal, a selective inhibitor of eukaryotic translation initiation factor 2 subunit α (eIF2α) dephosphorylation, on apoptotic cell death and ER stress-signaling events in HK-2 human renal proximal tubular cells exposed to cadmium chloride (CdCl(2)). Using phase-contrast microscopy and a cell viability assay, we observed that salubrinal suppressed CdCl(2)-induced cellular damage and cell death. Treatment with salubrinal reduced the number of TUNEL-positive cells and the cleavages of caspase-3 and poly(ADP-ribose) polymerase, but not the cleavage of light chain 3B, indicating protection from CdCl(2)-induced apoptosis but not autophagy. Although eIF2α remained phosphorylated after CdCl(2) exposure to salubrinal-treated HK-2 cells, the expression of activating transcription factor 4 (ATF4) and the 78 kDa glucose-regulated protein (GRP78) was not increased. On the other hand, CdCl(2)-induced expression of C/EBP homologous protein (CHOP) was reduced by salubrinal treatment. Expression of ATF4, an upstream regulator of GRP78 and CHOP, appeared to be a prerequisite for full protection by salubrinal against cadmium cytotoxicity, because CdCl(2)-induced cellular damage was not fully suppressed in ATF4-deficient cells. Phosphorylated forms of mitogen-activated protein kinases (MAPKs), including c-Jun NH(2)-terminal kinase (JNK), p38, and extracellular signal-regulated protein kinase (ERK), increased after CdCl(2) exposure, whereas salubrinal suppressed the phosphorylation of JNK and p38 but not ERK. These results suggest that salubrinal protects CdCl(2)-exposed HK-2 cells from apoptosis by suppressing cell death signal transduction pathways.

Regulating cytoplasmic calcium homeostasis can reduce aluminum toxicity in yeast

Our previous study suggested that increased cytoplasmic calcium (Ca) signals may mediate aluminum (Al) toxicity in yeast (Saccharomyces cerevisiae). In this report, we found that a yeast mutant, pmc1, lacking the vacuolar calcium ion (Ca²⁺) pump Ca²⁺-ATPase (Pmc1p), was more sensitive to Al treatment than the wild-type strain. Overexpression of either PMC1 or an anti-apoptotic factor, such as Bcl-2, Ced-9 or PpBI-1, decreased cytoplasmic Ca²⁺ levels and rescued yeast from Al sensitivity in both the wild-type and pmc1 mutant. Moreover, pretreatment with the Ca²⁺ chelator BAPTA-AM sustained cytoplasmic Ca²⁺ at low levels in the presence of Al, effectively making the cells more tolerant to Al exposure. Quantitative RT-PCR revealed that the expression of calmodulin (CaM) and phospholipase C (PLC), which are in the Ca²⁺ signaling pathway, was down-regulated under Al stress. This effect was largely counteracted when cells overexpressed anti-apoptotic Ced-9 or were pretreated with BAPTA-AM. Taken together, our results suggest that the negative regulation of Al-induced cytoplasmic Ca signaling is a novel mechanism underlying internal resistance to Al toxicity.

Regulation of autophagy by kinases

Autophagy is a process of self-degradation that maintains cellular viability during periods of metabolic stress. Although autophagy is considered a survival mechanism when faced with cellular stress, extensive autophagy can also lead to cell death. Aberrations in autophagy are associated with several diseases, including cancer. Therapeutic exploitation of this process requires a clear understanding of its regulation. Although the core molecular components involved in the execution of autophagy are well studied there is limited information on how cellular signaling pathways, particularly kinases, regulate this complex process. Protein kinases are integral to the autophagy process. Atg1, the first autophagy-related protein identified, is a serine/threonine kinase and it is regulated by another serine/threonine kinase mTOR. Emerging studies suggest the participation of many different kinases in regulating various components/steps of this catabolic process. This review focuses on the regulation of autophagy by several kinases with particular emphasis on serine/threonine protein kinases such as mTOR, AMP-activated protein kinase, Akt, mitogen-activated protein kinase (ERK, p38 and JNK) and protein kinase C that are often deregulated in cancer and are important therapeutic targets.

Autophagy involvement in cadmium resistance through induction of multidrug resistance-associated protein and counterbalance of endoplasmic reticulum stress WI38 lung epithelial fibroblast cells

Human multidrug-resistance associated protein (MRP1) is known as a cellular efflux pump of heavy metals and anticancer drugs. In our previous study, MRP was found to have involvement in cell protection against cadmium (Cd) toxicity through apoptosis interruption. The purpose of the present study was to investigate the molecular mechanism of MRP1 in Cd resistance. For this purpose, we developed Cd-resistant cells (RWI38) from WI38 human lung epithelial fibroblast cells, which showed a 4-fold resistance to Cd when compared to WI38 cells. WI38 cells elicited endoplasmic reticulum (ER) stress through RNA-dependent protein kinase-like ER kinase (PERK) and the eukaryotic translation initiation factor 2 alpha (eIF2alpha), Chop, and glucose-regulated protein (Grp78). RWI38 cells responding to Cd did not elicit ER stress or mitochondrial apoptosis, but induced autophagy, as demonstrated by Atg5 induction, LC3 conversion, and formation of GFP-LC3 dots. A pharmacological inhibitor of p38 downregulated Cd-induced Atg5 and LC3II. A pharmacological inhibitor of autophagy or silencing of atg5 dephosphorylated p38 and Akt, and downregulated MRP1 and procaspase-3. However, pharmacological inhibition or silencing of mrp-1 had no affect on Cd-induced phosphorylated p38 and LC3II. These data indicate that Cd induces autophagy in RWI38 cells through a mechanism that involves p38 activation, which is involved in cell protection through counterbalance of ER stress and MRP1 induction.

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.

Cadmium and cardiovascular diseases: cell biology, pathophysiology, and epidemiological relevance

Today cardiovascular diseases (CVDs) are the killer number one world wide. In 2004 an estimated 17.1 million people died due to CVDs and this number will further increase to an estimated 23.6 million by 2030. Importantly, currently known risk factors, like hypertension, and hypercholesterolemia, can only be made responsible for about 50-75% of all CVDs, highlighting the urgent need to search for and define new CVD risk factors. Cadmium (Cd) was shown to have the potential to serve as one such novel risk factor, as it was demonstrated-in vitro, in animal studies, and in human studies-that Cd causes atherosclerosis (the basis of most CVDs). Herein, we discuss the molecular and cellular biological effects of Cd in the cardiovascular system; we present concepts on the pathophysiology of Cd-caused atherosclerosis, and provide data that indicate an epidemiological relevance of Cd as a risk factor for CVDs.

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 induces intracellular Ca2+- and H2O2-dependent apoptosis through JNK- and p53-mediated pathways in skin epidermal cell line

Cadmium is a toxic heavy metal and has been widely used in industry. The skin is an important target for this metal. The mechanisms by which cadmium leads to damage to the skin are unclear at present. The aims of this study were to examine whether cadmium induces apoptosis in mouse skin epidermal cell line, JB6 Cl41 cells, and to investigate the cellular mechanisms by which cadmium causes cytotoxicity in the cells. The present study showed that cadmium induced cell death by apoptosis in a dose-dependent manner, as proven by the appearance of cell shrinkage, the increase of Annexin V positively stained cells, and the formation of nuclear DNA ladders. Cadmium-induced apoptosis involved a mitochondria-mediated mechanism but not caspase-dependent pathway in that the critical apoptotic events induced by cadmium, such as the decrease of Bcl-2/Bcl-xL, the increase of GADD45alpha, and the nuclear translocation of apoptosis inducing factor, were not affected by the inhibition of executive caspases. In contrast, blockage of p53 and JNK by pharmacological inhibitors or small interference RNA transfection suppressed the cadmium-induced apoptosis with the concomitant inhibition of antiapoptotic Bcl-2 family proteins and GADD45alpha, respectively. Furthermore, the activation of p53 and JNK and their downstream proteins in cadmium-exposed cells were inhibited by individual treatment with catalase and Bapta-acetoxymethyl. These results suggest that cadmium induces apoptosis via the activation of JNK- and p53-mediated signaling, where calcium ion and hydrogen peroxide act as the pivotal mediators of the apoptotic signaling.