Cadmium induces apoptotic cell death in WI 38 cells via caspase-dependent Bid cleavage and calpain-mediated mitochondrial Bax cleavage by Bcl-2-independent pathway

Previous reports have demonstrated that cadmium (Cd) may induce cell death via apoptosis, but the mechanism responsible for cellular death is not clear. In this study, we investigated the signaling pathways implicated in Cd-induced apoptosis in lung epithelial fibroblast (WI 38) cells. Apoptotic features were observed using terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay, propidium iodide staining and DNA laddering. A treatment of cadmium caused the caspase-8-dependent Bid cleavage, the release of cytochrome c (Cyt c), activation of caspase-9 and -3, and PARP cleavage. A caspase-8 specific inhibitor prevented the Bid cleavage, caspase-3 activation and cell death. Alternatively, we observed that full-length Bax was cleaved into 18-kDa fragment (p18/Bax); this was initiated after 12 h and by 36 h the full-length Bax protein was totally cleaved to the p18/Bax, which caused a drastic release of Cyt c from mitochondria. The p18/Bax was detected exclusively in the mitochondrial fraction, and it originated from mitochondrial full-length Bax, but not from the cytosol full-length Bax. Cd also induced the activation of the mitochondrial 30-kDa small subunit of calpain that was preceded by Bax cleavage. Cd induced the upregulation of Bcl-2 and the degradation of p53 protein. N-acetyl cysteine effectively inhibited the Cd-induced DeltaPsim reduction, indicating ROS acts upstream of mitochondrial membrane depolarization. Taken together, our results suggest that Cd-induced apoptosis was thought to be mediated at least two pathways; caspase-dependent Bid cleavage, and the other is calpain-mediated mitochondrial Bax cleavage. Moreover, we found that the function of Bid and Bax was not dependent of Bcl-2, and that ROS can also contribute in the Cd-induced cell death.     

Cadmium induces Ca2+-dependent necrotic cell death through calpain-triggered mitochondrial depolarization and reactive oxygen species-mediated inhibition of nuclear factor-kappaB activity

This study investigates the mechanism of cell death induced by cadmium (Cd) in Chinese hamster ovary (CHO) cells. Cells exposed to 4 microM Cd for 24 h did not show signs of apoptosis, such as DNA fragmentation and caspase-3 activation. The pro-apoptotic (Bax) or anti-apoptotic (Bcl-2 and Bcl-xL) protein levels in the Bcl-2 family were not altered. However, an increase in propidium iodide uptake and depletion of ATP, characteristics of necrotic cell death, were observed. Cd treatment increased the intracellular calcium (Ca2+) level. Removal of the Ca2+ by a chelator, BAPTA-AM, efficiently inhibited Cd-induced necrosis. The increased Ca2+ subsequently mediated calpain activation and intracellular ROS production. Calpains then triggered mitochondrial depolarization resulting in cell necrosis. Cyclosporin A, an inhibitor of mitochondrial permeability transition, recovered the membrane potential and reduced the necrotic effect. The generated ROS reduced basal NF-kappaB activity and led cells to necrosis. An increase of NF-kappaB activity by its activator, PMA, attenuated Cd-induced necrosis. Calpains and ROS act cooperatively in this process. The calpain inhibitor and the ROS scavenger synergistically inhibited Cd-induced necrosis. Results in this study suggest that Cd stimulates Ca2+-dependent necrosis in CHO cells through two separate pathways. It reduces mitochondrial membrane potential by activating calpain and inhibits NF-kappaB activity by increasing the ROS level.     

Cadmium induces apoptosis partly via caspase-9 activation in HL-60 cells.

Cadmium (Cd), a potent immunotoxic metal, induces apoptosis both in vitro and in vivo. However, the mode of action remains unclear. We previously reported that Cd-induced apoptosis was partly dependent on mitochondria. In the present study, we investigated the involvement of caspase-9, which is the apex caspase in the mitochondoria-dependent apoptosis pathway, in Cd-induced apoptosis in human promyelocytic leukemia HL-60 cells. A specific inhibitor of caspase-9, Z-LEHD-FMK, partly inhibited DNA fragmentation induced by Cd treatment in HL-60 cells. Moreover, treatment of HL-60 cells with Cd resulted in the appearance of Cytochrome c (Cyt c), a potent activator of caspase-9, in the cytosol at 3 h, which closely paralleled the activation of caspase-9. Caspase-9 is an initiator caspase that is a potent activator of downstream effector caspases such as caspase-3. Caspase-3 activation was subsequent to the Cyt c release at 6 h. DNA fragmentation, an index of induction of apoptosis, also appeared 6 h after Cd treatment. The effects were more pronounced at 9 h after Cd addition. A broad-specificity inhibitor of caspases, Z-Asp-CH(2)-DCB, inhibited caspase-3 activation and DNA fragmentation induced by Cd in a dose-dependent fashion. The results suggest that Cd-induced apoptosis is partly caused by caspase-9 activation triggered by Cyt c.     

A rapid and transient ROS generation by cadmium triggers apoptosis via caspase-dependent pathway in HepG2 cells and this is inhibited through N-acetylcysteine-mediated catalase upregulation

Although reactive oxygen species (ROS) have been implicated in cadmium (Cd)-induced hepatotoxicity, the role of ROS in this pathway remains unclear. Therefore, we attempted to determine the molecular mechanisms relevant to Cd-induced cell death in HepG2 cells. Cd was found to induce apoptosis in the HepG2 cells in a time- and dose-dependent fashion, as confirmed by DNA fragmentation analysis and TUNEL staining. In the early stages, both rapid and transient ROS generation triggered apoptosis via Fas activation and subsequent caspase-8-dependent Bid cleavage, as well as by calpain-mediated mitochondrial Bax cleavage. The timing of Bid activation was coincided with the timing at which the mitochondrial transmembrane potential (MMP) collapsed as well as the cytochrome c (Cyt c) released into the cytosol. Furthermore, mitochondrial permeability transition (MPT) pore inhibitors, such as cyclosporin A (CsA) and bongkrekic acid (BA), did not block Cd-induced ROS generation, MMP collapse and Cyt c release. N-acetylcysteine (NAC) pretreatment resulted in the complete inhibition of the Cd-induced apoptosis via catalase upregulation and subsequent Fas downregulation. NAC treatment also completely blocked the Cd-induced intracellular ROS generation, MMP collapse and Cyt c release, indicating that Cd-induced mitochondrial dysfunction may be regulated indirectly by ROS-mediated signaling pathway. Taken together, a rapid and transient ROS generation by Cd triggers apoptosis via caspase-dependent pathway and subsequent mitochondrial pathway. NAC inhibits Cd-induced apoptosis through the blocking of ROS generation as well as the catalase upregulation.     

Berberine-induced apoptosis in human glioblastoma T98G cells is mediated by endoplasmic reticulum stress accompanying reactive oxygen species and mitochondrial dysfunction

Berberine has a wide range of biochemical and pharmacologic effects, including antitumor activity, but the mechanisms involved in berberine-induced apoptosis remain unclear. The purpose of the present study was to investigate the changes in oxidative stress and endoplasmic reticulum (ER)-related molecules, which are closely associated with cell death-signaling transduction pathways, in human glioblastoma T98G cells treated with berberine. Berberine significantly decreased the cell viability of T98G cells in a dose-dependent manner. Berberine increased the production of reactive oxygen species (ROS) and level of intracellular Ca(2+). Berberine induced ER stress as evidenced by the detection of ER stress-associated molecules such as phosphorylated protein kinase-like ER kinase, eukaryotic translation initiation factor-2α, glucose-regulated protein 78/immunoglobulin heavy chain-binding protein, and CCAAT/enhancer-binding protein (C/EBP)-homologous protein/growth arrest and DNA damage-inducible gene 153, which was associated with the activation of caspase-3. Furthermore, the administration of the antioxidants, N-acetylcysteine and glutathione, reversed berberine-induced apoptosis. Berberine also markedly enhanced apoptosis in T98G cells through the induction of a higher ratio of Bax/Bcl-2 proteins, disruption of the mitochondrial membrane potential, activation of caspase-9 and -3, and cleavage of the poly(ADP-ribose) polymerase (PARP). The inhibition of ER stress using salubrinal led to an increased the level of Bcl-2, whereas the level of Bax, cleavage of procaspase-9 and -3, and PARP were decreased when compared with cells treated with berberine alone, indicating that berberine-induced apoptosis is associated with mitochondrial dysfunction. These results demonstrate that berberine induces apoptosis via ER stress through the elevation of ROS and mitochondrial-dependent pathway in human glioblastoma T98G cells.     

4-hydroxynonenal induces apoptosis via caspase-3 activation and cytochrome c release

We investigated the mechanism by which 4-hydroxynonenal (HNE), a major aldehydic product of lipid peroxidation, induces apoptosis in tumor cells. Treatment of human colorectal carcinoma (RKO) cells with HNE-induced poly-ADP-ribose-polymerase (PARP) cleavage and DNA fragmentation in a dose- and time-dependent manner. The induction of PARP cleavage and DNA fragmentation paralleled caspase-2, -3, -8, and -9 activation. Pretreatment of cells with an inhibitor of caspase-3, z-DEVD-fmk, or a broad spectrum caspase inhibitor, z-VAD-fmk, abolished caspase activation and subsequent PARP cleavage. Constitutive expression of high levels of Bcl-2 protected cells from HNE-mediated apoptosis. In addition, Bcl-2 overexpression inhibited cytochrome c release from mitochondria and subsequent caspase-2, -3, and -9 activation. These findings demonstrate that HNE triggers apoptotic cell death through a mitochondrion-dependent pathway involving cytochrome c release and caspase activation. Bcl-2 overexpression protected cells from HNE-induced apoptosis through inhibition of cytochrome c release.     

Cadmium-induced non-apoptotic cell death mediated by oxidative stress under the condition of sulfhydryl deficiency

Cadmium (Cd), which accumulates primarily in the liver and the kidney, induces apoptosis and also causes necrotic cell death in certain pathophysiologic situations. Previously, we have shown that Cd activated mitogen-activated protein kinases and that sulfur amino acid deficiency potentiated Cd-induced cytotoxicity via activation of mitogen-activated protein kinases. In the present study, we established the mechanistic basis of apoptotic and non-apoptotic cell death induced by Cd in H4IIE cells a rat-derived hepatocyte cell line. Cd at 0.3-10 microM decreased viability of cells in a concentration-dependent manner. Cd-induced cytotoxicity was enhanced by pretreatment with buthionine sulfoximine (BSO). Cd at 0.3 microM induced translocation of Bad to mitochondria, decreased the level of mitochondrial BcL(XL) with the release of cytochrome c, and induced procaspase-9 activation and poly(ADP-ribose) polymerase (PARP) cleavage. Sulfhydryl deficiency by BSO, however, blocked PARP cleavage in spite of the decrease in procaspase-9. Cytochrome c release, procaspase-9 activation and PARP cleavage were all increased by 1 microM Cd irrespective of BSO pretreatment. We also used H(2)O(2) (10-100 microM) as a source of oxidative stress. Cd (0.3-1 microM) + H(2)O(2) (70 microM) resulted in greater extents of cytochrome c release, procaspase-9 activation and PARP cleavage in H4IIE cells than Cd alone. Flow cytometric analysis confirmed apoptotic and non-apoptotic cell death by Cd depending on cellular glutathione (GSH) content. These results provide evidence that Cd at the physiologically obtainable concentration causes non-apoptotic cell death under the condition of sufhydryl deficiency, whereas Cd at the micromolar level induces apoptosis. The cell death mechanism involves cytochrome c release from mitochondria and decrease in the level of procaspase-9, but not PARP cleavage, implying that alterations in cellular sulfhydryls may be the major determining factor for the path of cell death in response to low level of Cd.     

Ca2+-Dependent caspase activation by gallic acid derivatives.

Gallic acid (GA) derivatives, 3,4-methylenedioxyphenyl 3,4,5-trihydroxybenzoate (GD-1) and S-(3,4-methylenedioxyphenyl)3,4,5-trihydroxythiobenzoate (GD-3), were previously reported to induce apoptosis in tumor cells with IC50s of 14.5 microm and 3.9 microm, respectively. To elucidate the mechanism by which these gallic acid derivatives (GDs) induce apoptosis, we studied whether GD-1 and GD-3 can activate caspases. When promyelocytic leukemia HL-60RG cells were treated with GD-1 and GD-3, poly(ADP-ribose)polymerase (PARP), a substrate of caspase-3, was cleaved into 85 kDa of degradative product with increasing incubation time. GA also activated PARP cleavage, which was inhibited by catalase, N-acetyl-L-cysteine (NAC), and intracellular Ca2+ chelator 1,2-bis(2-aminophenoxyethane)-N,N,N,N'-tetraacetic acid tetrakis (acetoxymethyl ester) (BAPTA-AM), in addition to a caspase inhibitor, Z-VAD-FMK. Its inhibitory pattern was identical with that of hypoxanthine/xanthine oxidase. On the other hand, GD-1- and GD3-induced PARP cleavage was not suppressed by catalase or NAC, but by BAPTA-AM. This suggested that the GD-elicited signaling pathway is different from GA's. Taken together, GDs activated caspase-3 following intracellular Ca2+ elevation independent of reactive oxygen species. Thus, it became evident that the signaling pathway leading to apoptosis was regulated by GDs in a different manner from GA.     

Mechanism of ricin-induced apoptosis in human cervical cancer cells

The mechanism of ricin-induced apoptosis in human cervical cancer cell line HeLa was studied. The present study demonstrated that ricin induces apoptosis of human cervical cancer cells (HeLa) in a time dependent manner with an IC(50) for cell viability of 1 microg/ml. Ricin treatment resulted in a time dependent increase in LDH leakage, DNA fragmentation, percent apoptotic cells, generation of reactive oxygen species and depletion of intracellular glutathione levels. DNA agarose gel electrophoresis showed typical oligonucleosomal length DNA fragmentation. Additionally, DNA diffusion assay was performed to confirm DNA damage and apoptosis. Ricin activated caspase-3 as evidenced by both proteolytic cleavage of procaspase-3 into 20 and 18 kDa subunits, and increased protease activity. Caspase activity was maximum at 4h and led to the cleavage of 116 kDa poly(ADP-ribose) polymerase (PARP), resulting in the 85 kDa cleavage product. Ricin-induced caspase-3 activation also resulted in cleavage of DNA fragmentation factor-45 (DFF45/ICAD) and DFF40 or caspase-activated DNase in HeLa cells. Activation of caspase-3, cleavage of PARP and DNA fragmentation was blocked by pre-treatment with caspase-3 specific inhibitor Ac-DEVD-CHO (100 microM) and broad-spectrum caspase inhibitor Z-VAD-FMK (40 microM). Ricin-induced DNA fragmentation was inhibited by pre-treatment with PARP inhibitors 3-aminobenzamide (100 microM) and DPQ (10 microM). Our results indicate that ricin-induced cell death was mediated by generation of reactive oxygen species and subsequent activation of caspase-3 cascade followed by down stream events leading to apoptotic mode of cell death.     

Induction of apoptosis by diallyl disulfide through activation of caspase-3 in human leukemia HL-60 cells.

Diallyl disulfide (DADS), a component of garlic (Allium sativum), has been known to exert potent chemopreventative activity against colon, lung, and skin cancers. However, its molecular mechanism of action is still obscure. The present study demonstrated that DADS induces apoptosis of human leukemia HL-60 cells in a concentration- and time-dependent manner with an IC50 for cell viability of less than 25 microM. DADS activated caspase-3 as evidenced by both the proteolytic cleavage of the proenzyme and increased protease activity. Activation of caspase-3 was maximal at 3 hr and led to the cleavage of 116 kDa poly(ADP-ribose) polymerase (PARP), resulting in the accumulation of an 85 kDa cleavage product. Both activation of caspase-3 and cleavage of PARP were blocked by pretreatment with either antioxidants or a caspase-3 inhibitor, but not a caspase-1 inhibitor. DADS increased the production of intracellular hydrogen peroxide, which was blocked by preincubation with catalase. These results indicate that DADS-induced apoptosis is triggered by the generation of hydrogen peroxide, activation of caspase-3, degradation of PARP, and fragmentation of DNA. The induction of apoptosis by DADS may be the pivotal mechanism by which its chemopreventative action against cancer is based.     

Protection of betulin against cadmium-induced apoptosis in hepatoma cells

The protective effects of betulin (BT) against cadmium (Cd)-induced cytotoxicity have been previously reported. However, the mechanisms responsible for these protective effects are unclear. Therefore, this study investigated the mechanisms responsible for the protection of BT against Cd-induced cytotoxicity in human hepatoma cell lines. The protection of BT against Cd cytotoxicity was more effective in the HepG2 than in the Hep3B cells. The protection of BT on Cd-induced cytotoxicity in the HepG2 cells appeared to be related to the inhibition of apoptosis, as determined by PI staining and DNA fragmentation analysis. The anti-apoptosis exerted by BT involved the blocking of Cd-induced reactive oxygen species (ROS) generation, the abrogation of the Cd-induced Fas upregulation, the blocking of caspase-8-dependent Bid activation, and subsequent inhibition of mitochondrial pathway. The BT pretreatment did not affect the p21 and p53 expression levels, when compared with those of the treated cells with Cd alone. BT induced the transient S phase arrest at an early stage and the G₀/G₁ arrest at a relatively late stage, but it did not observe the sub-G1 apoptotic peak. In the Hep3B cells, Cd did not induce ROS generation. The BT pretreatment partially inhibited the Cd-induced apoptosis, which was related with the incomplete blockage in caspase-9 or -3 activation, as well as in Bax activation.     

Involvement of both intrinsic and extrinsic pathways in hepatoprotection of arjunolic acid against cadmium induced acute damage in vitro

Cadmium (Cd) is one of the ubiquitous environmental pollutants and is responsible for various organ pathophysiology including hepatic disorders. It is extremely toxic even in low concentrations and bioaccumulate in organisms. The present study has been carried out to investigate the cytoprotective role of arjunolic acid (AA), a tri terpenoid saponin, against Cd induced oxidative impairment and cell death in murine hepatocytes. Administration of cadmium (30 μM), in the form of chloride (CdCl(2)) for 2h, significantly enhanced the ALT, ALP and LDH leakage, increased reactive oxygen species (ROS) production, reduced hepatocytes viability and altered the antioxidant status of hepatocytes by reducing intracellular GSH level, anti-oxidant enzymes activity and increasing intracellular GSSG and lipid peroxidation. Evidence for Cd-induced nature of cell death was sought by flow cytometric analysis. Signal transduction studies revealed that Cd markedly increased the levels of caspase-9, -8, -3, Fas and Bid, decreased mitochondrial membrane potential, enhanced cytochrome c release in the cytosol, disturbed the Bcl-2 family protein balance, cleaved PARP protein and ultimately led to apoptotic cell death. Results showed that Cd could trigger both intrinsic and extrinsic apoptotic pathways. In addition, Cd markedly increased NF-κB nuclear translocation in association with IKKα/β phosphorylation and IκBα degradation. Simultaneous treatment with AA (200 μM), however, reduced Cd-induced oxidative stress, attenuated the nuclear translocation of NF-κB and protects the hepatocytes from Cd-induced apoptotic death. Combining, data suggest that Cd-induced hepatic dysfunction and apoptosis might be supported by the ROS formation and mediated via the activation of NF-κB. AA treatment, on the other hand, reduced Cd-induced oxidative stress, attenuated the activation of NF-κB and mitochondrion-dependent and independent apoptotic signaling pathways.     

Mechanisms of JP-8 jet fuel toxicity. I. Induction of apoptosis in rat lung epithelial cells

JP-8 is a kerosene-based fuel widely used by the U.S. military. Various models of human occupational and animal exposure to JP-8 have demonstrated the potential for local and systemic toxicity but the mechanisms involved are unknown. The purpose of our investigation was to study the molecular mechanisms of JP-8 toxicity by using an in vitro model. JP-8 exposure in a rat lung alveolar type II epithelial cell line (RLE-6TN) induces biochemical and morphological markers of apoptotic cell death: caspase-3 activation, poly(ADP-ribose) polymerase (PARP) cleavage, chromatin condensation, membrane blebbing, cytochrome c release from mitochondria, and genomic DNA cleavage into both oligonucleosomal (DNA ladder) and high-molecular-weight (HMW) fragments. The human histiocytic lymphoma cell line (U937) also responds to JP-8 with caspase-3 activation, cleavage of caspase substrates, including PARP, DNA-PK, and lamin B1, and degradation of genomic DNA with the production of HMW fragments. Caspase-3 activation and PARP cleavage also occur in the acute T-cell leukemia cell line (Jurkat) following treatment with JP-8. Furthermore, Jurkat cells stably transfected with a plasmid encoding the antiapoptotic protein Bcl-x(L) or pretreated with the pan-caspase inhibitor Boc-d-fmk, are relatively resistant to the cytotoxic effects of JP-8 compared to control cells. Finally, we demonstrate that PARP cleavage occurs in primary mouse thymocytes exposed to JP-8. In conclusion, our data support the hypothesis that apoptotic cell death is responsible at least partially for the cytotoxic effects of JP-8 and suggest that inhibition of the apoptotic cascade might reduce JP-8 toxicity.     

Mechanisms of cell death induced by 2-chloroadenosine in leukemic B-cells

2-chloroadenosine (2-CAdo) is an adenosine deaminase-resistant analogue of adenosine, widely used as an adenosine receptor agonist. This compound has been shown to induce apoptosis in several cell types either via activation of adenosine receptors or via intracellular metabolism. However, the molecular mechanisms of 2-CAdo-induced apoptosis are unclear. Here, we analyzed the effects of 2-CAdo in the leukemia cell line EHEB. 2-CAdo was found to induce apoptosis in EHEB cells, as shown by caspase-3 activation, DNA fragmentation, poly(ADP-ribose) polymerase (PARP) cleavage and phosphatidylserine exposure. Cytotoxicity of 2-CAdo was completely suppressed by 5-iodotubercidin, an adenosine kinase inhibitor, indicating that apoptosis induced by 2-CAdo was the result of its intracellular metabolism. Accordingly, we found that 2-CAdo was efficiently converted into 2-chloroATP. In parallel, a decrease of intracellular ATP concentration as well as a general inhibition of macromolecular synthesis, involving DNA, RNA and protein synthesis, was observed. Moreover, 2-CAdo induced cytochrome c release into the cytosol, indicating activation of the intrinsic pathway of apoptosis. This was found associated with a decline in Mcl-1 protein level and p53-independent. Inhibition of AMP deaminase by coformycin markedly prevented ATP depletion, and also significantly reduced 2-CAdo cytotoxicity and caspase-3 activation. In conclusion, our data show that intracellular metabolism of 2-CAdo can lead to activation of the intrinsic pathway of apoptosis and that ATP depletion, in addition to the accumulation of the triphosphate analogue, contributes to 2-CAdo-induced apoptosis.     

Cadmium-induced apoptosis of hepatocytes is not associated with death receptor-related caspase-dependent pathways in the rat

Cadmium (Cd) is a heavy metal of considerable environmental and occupational concern. The liver is the major target organ of Cd toxicity that follows from repeated exposure to Cd. The aim of this study was to investigate the mechanism of cell death of Cd-induced hepatotoxicity in a rat model. Eighteen adult male Sprague–Dawley (SD) rats were injected daily with a dose of Cd acetate (30 μM/kg body weight, subcutaneously). After 1, 2 and 7 days rats were euthanized and blood and liver tissues were sampled for analysis. Biochemical analyses of the level of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were undertaken. Histopathological and Western blot analyses for liver cellular damage and cell death were also performed. The results for the Cd-treated group of animals were compared to those from 12 control rats. The serum AST/ALT levels increased significantly 24 h after CD exposure. From the Western blot analyses, activation of Bid, independent of caspase-8 was seen and Bax induced the release of cytochrome c into the cytosol from mitochondria in a dose-dependent manner. The level of Bcl-2 was decreased. Eventually, caspase-9 and caspase-3 were activated, and poly(ADP-ribose) polymerase (PARP) was cleaved in a dose-dependent manner. A histopathological analysis and DNA fragmentation test showed apoptotic cell death of the hepatocytes increased over time. These results suggest that Cd-induced liver cell apoptosis in the rat, over a period of 7 days, may not be related to the death-receptor pathway. Moreover, apoptosis is dose-dependent and associated with the decrement of Bcl-2.     

Calcium–calmodulin signaling elicits mitochondrial dysfunction and the release of cytochrome c during cadmium-induced apoptosis in primary osteoblasts

Cadmium (Cd) is a toxic heavy metal used in industry and is associated with adverse effects on human health following long- or short-term environmental exposure. Although Cd is known to induce apoptosis in many human organ systems, the mechanism that underlies its toxicity in primary osteoblasts (OBs) is not yet established. In the present study, we confirmed that Cd induced apoptosis in OBs isolated from the craniums of fetal Sprague-Dawley rats. We then showed that exposure to Cd transiently increased intracellular calcium ([Ca²⁺]i) levels for up to 1.5 h, after which the levels returned to normal. Pretreatment with the calcium chelator BAPTA-AM was able to prevent Cd-induced apoptosis by reversing Cd-induced changes in the mitochondrial transmembrane potential (ΔΨm). In addition, we found that the antagonist of calcium-dependent calmodulin (CaM), W-7, inhibited the conformational change of calmodulin induced by Cd. Furthermore, Cd-induced apoptosis could be inhibited by W-7 through the suppression of the mitochondrial release of cytochrome c to the cytosol and the reversal of Cd-activation of caspase-3. These data indicate that activated Ca²⁺/CaM might transmit apoptotic signals to the mitochondria during Cd-induced apoptosis. Our findings provide new insights into the mechanisms underlying apoptosis in OBs following exposure to Cd.     

Apoptosis induced in neuronal cells by oxidative stress: role played by caspases and intracellular calcium ions

Reactive oxygen species (ROS) have been implicated in the pathophysiology of many neurologic disorders and brain dysfunction. In the same pathological settings evidence has been provided in favour of a participation of intracellular Ca(2+) concentration altered homeostasis in the chain of events leading to neuronal apoptosis. In the present review literature reports and experimental data on the relationship between caspase activation and alteration of intracellular calcium concentrations in the mechanisms triggering neuronal apoptosis are discussed. The data gathered support the conclusion that during oxidative stress in neuronal cells the production of ROS triggers a mechanism that, through the release of cytochrome c from mitochondria and caspase-3 activation, leads to apoptosis; the concomitant ROS-mediated elevation of intracellular Ca(2+) concentration triggers caspase-2 activation but both events do not seem to be involved in cell death.     

Chromene induces apoptosis via caspase-3 activation in human leukemia HL-60 cells

In this study, the potent anti-tumor effects of brown algae on human leukemia HL-60 cells were investigated. The Sargassum siliquastrum extract among the 14 species of brown algae exhibited profound growth inhibitory effect on HL-60 cells in the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, therefore, S. siliquastrum was selected for use in further experiments. The highest inhibitory activity of S. siliquastrum on HL-60 cells was detected in the chloroform fraction, and the active compound was identified as a kind of chromene, sargachromanol E (SE). SE treatment showed significant growth inhibitory effects on HL-60 cells in a dose-dependent manner by inducing apoptosis, as evidenced by the formation of apoptotic bodies, fragmented DNA ladder, and the accumulation of DNA in the sub-G₁ phase of cell cycle. SE induced apoptosis was accompanied by downregulation of Bcl-xL, upregulation of Bax, activation of caspase-3, and cleavage of poly (ADP-ribose) polymerase (PARP). Moreover, z-DEVD-fmk, a caspase-3 inhibitor, significantly inhibited cell cytotoxicity, apoptotic characteristics such as apoptotic bodies, sub-G₁ DNA content, and cleavage of PARP induced by SE. These results suggest that SE exerts its growth inhibitory effects on HL-60 cells through caspase-3-mediated induction of apoptosis. Therefore, SE offers promising chemotherapeuric potential to prevent cancers such as human leukemia.     

Induction of apoptosis in HT-29 colon cancer cells by crude saponin from Platycodi Radix

This study examined the apoptotic effects of crude saponins acquired from the roots of Platycodon grandiflorum (SPR) in HT-29 human colon cancer cells.SPR decreased HT-29 cell proliferation in dose- and time-dependent manners by inducing apoptosis via DNA fragmentation and poly (ADP-ribose) polymerase (PARP) cleavage. The apoptosis induced by SPR was associated with the activation of initiator caspases-8 and -9, as well as the effector caspase-3. SPR stimulated Bid cleavage, indicating that the apoptotic action of caspase-8-mediated Bid cleavage leads to the activation of caspase-9. SPR increased the expression of the pro-apoptotic protein, Bax, and decreased the expression of the anti-apoptotic protein, Bcl-2. SPR also increased the expression of the caspase-independent mitochondrial apoptosis factor, AIF, in HT-29 cells. These results indicate that SPR inhibits HT-29 cell proliferation by inducing apoptosis, which may be mediated via both caspase-dependent and -independent pathways.     

Activation of caspase-3 in HL-60 cells treated with pyrithione and zinc

The transition metal zinc (Zn) is an endogenous regulator of apoptosis. The ability of Zn to modulate apoptosis is believed to be mediated by the regulation of caspase activity. Previously, we reported that an acute influx of labile Zn induced apoptosis via activation of caspase in human leukemia HL-60 cells treated with a Zn ionophore (Py, pyrithione) and Zn at 1 and 25 microM, respectively. In the present study, we investigated the involvement of caspase-3 in Py (1 microM)/Zn (25 microM)-induced apoptosis in HL-60 cells. Pro-caspase-3 is an inactive form of caspase-3. The processing of pro-caspase-3, a sign of caspase-3 activation, occurred 6 h after treatment with Py/Zn. Proteolysis of poly (ADP-ribose) polymerase (PARP), a substrate of caspase-3, was also observed 6 h after treatment with Py/Zn. We also confirmed the elevation of caspase-3 activity as an index of the cleavage of amino acid sequences recognized by activated caspase-3. An inhibitor of caspase-3 attenuated the appearance of the DNA ladder. Taken together, these results indicate that the activation of caspase-3 is partly responsible for the induction of apoptosis in Py/Zn-treated HL-60 cells.