Zinc suppresses apoptosis of U937 cells induced by hydrogen peroxide through an increase of the Bcl-2/Bax ratio

External zinc stimulates proliferation of tumor Hep-2 cells by active modulation of key signaling pathways

The effect of external zinc supplementation (10 and 35 micromol) on cell proliferation and mitogenic signaling of Hep-2 tumor cells was examined during 72 h of treatment. Zinc levels were manipulated by using zinc-free cultivation medium with or without addition of zinc ions. Proliferation of Hep-2 cells exposed to zinc-free medium decreased in a time-dependent manner and corresponded to decreasing intracellular zinc content. Hep-2 cells accumulated in G(0)/G(1) phase, showed reduced abundance of AKT and NF-kappaB as well as of anti-apoptotic Bcl-2 and Bcl-XL proteins. Zinc supplied to Hep-2 cells maintained in the presence of zinc-free medium stimulated their proliferation as well as mitogenic signaling which paralleled increasing intracellular zinc content. In zinc-exposed Hep-2 cells, several changes in various mitogenic signaling pathways were noted such as enhanced expression of p53, AKT and MAP kinases, NF-kappaB and increased DNA binding of AP-1 family. Also, supplementation with zinc of Hep-2 cells resulted in the suppression of key apoptotic molecules such as Bax protein and increased expression of anti-apoptotic Bcl-2 and Bcl-XL proteins. Since only the highest supplied zinc concentration (35 micromol) induced oxidative stress, it is reasoned that the observed activation of pro-survival signaling occurs both directly and indirectly. These data show that zinc may stimulate growth and proliferation of some tumor cells by a combination of internal mechanisms with a varying contribution of external signaling pathways too.

Ginsenoside Rd from Panax notoginseng is cytotoxic towards HeLa cancer cells and induces apoptosis

The saponin ginsenoside Rd (1), isolated from Panax notoginseng, is used for the treatment of cardiovascular diseases, inflammation, different body pains, trauma, and internal and external bleeding due to injury. In this study, we report that 1 inhibits the cell growth of human cervical cancer (HeLa) cells in a concentration- and time-dependent manner, with an IC(50) value of 150.5+/-0.8 mcirog/ml after 48 h of incubation. The drug-treated cells displayed features of apoptosis, including typical morphological characteristics and formation of DNA ladders, as evident from agarose-gel electrophoresis. Flow-cytometric analysis showed that the cell-cycle distribution of HeLa cells exposed to 1 is characterized by a decrease of the G(0)/G(1)-phase and an increase of the S-phase cells, respectively, in a dose-dependent manner. The apoptotic rate of HeLa cells treated for 48 h with 210 microg/ml of 1 was 35.8%. Further, 1 was found to increase the expression of Bax and to decrease the expression of Bcl-2 proteins, respectively, and to lower the mitochondrial transmembrane potential of HeLa cells. The caspase-3 inhibitor DEVD-CHO (at 2 microM) increased the viability of HeLa cells treated with 1. Taken together, our study suggests that ginsenoside Rd (1) significantly inhibits HeLa cell proliferation, and induces cell apoptosis through down-regulating Bcl-2 expression, up-regulating Bax expression, lowering the mitochondrial transmembrane potential, and activating the caspase-3 pathway. Thus, 1 could serve as a lead to develop novel chemotherapeutic or chemopreventive agents against human cervical cancer.

Cytotoxic effects of intra and extracellular zinc chelation on human breast cancer cells

Zinc is an essential trace element with cofactor functions in a large number of proteins of intermediary metabolism, hormone secretion pathways, immune defence mechanisms, and as a cofactor of transcription factors it is also involved in the control of gene expression. Our study demonstrates that the modulation of intra and extracellular zinc alone is sufficient to induce metabolic changes or even apoptosis in two model human breast cancer cell lines MCF-7 and MDA-MB468. Treatment of breast cancer cells with different concentrations of a cell membrane permeable zinc chelator, N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) and the membrane impermeable zinc chelator, diethylenetriaminepentacetic acid, (DTPA) resulted in a significant increase of cell death. Features of apoptosis, such as chromatin condensation and nuclear fragmentation accompanied the DTPA and TPEN-induced cell death. A significant increase in the activity of caspase-9 was observed in both cell lines; whereas, caspase-3 activity was only increased in MDA-MB468 cells since caspase-3 is not expressed in MCF-7 cells. Caspase-8 activation was negligible in both cell lines. Addition of Zn(2+) or Cu(2+) prevented DTPA and TPEN-induced cytotoxicity, indicating that both bivalent cations can be replaced functionally to a certain extent in our experimental system. Interestingly, addition of Ca(2+), or Mg(2+) had no effect. The antioxidant N-Acetyl-L-Cysteine inhibited the cytotoxic effect of DTPA and TPEN, indicating that oxidative stress is the likely mediator of Zn-deficiency-related cell death.

Induction of cell apoptosis in 3T3-L1 pre-adipocytes by flavonoids is associated with their antioxidant activity

Obesity is biologically characterized at the cellular level by an increase in the number and size of adipocytes differentiated from fibroblastic pre-adipocytes in adipose tissue. In this study, we focused on the relationship between the influence of flavonoids on cell population growth and their antioxidant activity. The results showed that the inhibition of flavonoids (naringenin, rutin, hesperidin, resveratrol, naringin and quercetin) on 3T3-L1 pre-adipocytes was 28.3, 8.1, 11.1, 33.2, 5.6 and 71.5%, respectively. In oxygen radical absorbance capacity (ORAC) assay, quercetin had the highest ORAC(ROO) value among the six flavonoids tested. Apoptosis assays showed that quercetin increased apoptotic cells in time- and dose-dependent manner. Treatment of cells with quercetin decreased the mitochondrial membrane potential in the courses of time and dose. The cell apoptosis/necrosis assay showed that quercetin increased the number of apoptotic cells, but not necrotic cells. Quercetin treatment of cells caused a significant time- and dose-dependent increase in the caspase-3 activity. Western analysis indicated that treatment of quercetin markedly down-regulated PARP and Bcl-2 proteins, and activated caspase-3, Bax, and Bak proteins. These results indicate that quercetin efficiently inhibits cell population growth and induction of apoptosis in 3T3-L1 pre-adipocytes.

The cDNA cloning and mRNA expression of heat shock protein 70 gene in the haemocytes of bay scallop (Argopecten irradians, Lamarck 1819) responding to bacteria challenge and naphthalin stress

Heat shock protein 70 (HSP70) is an important member of the heat shock protein superfamily, and it plays a key role in the process of protecting cells, facilitating the folding of nascent peptides and responding to stress. The cDNA of bay scallop Argopecten irradians HSP70 (designated AIHSP70) was cloned by the techniques of homological cloning and rapid amplification of cDNA end (RACE). The full length of AIHSP70 cDNA was 2651bp in length, having a 5' untranslated region (UTR) of 96bp, a 3' UTR of 575bp, and an open reading frame (ORF) of 1980bp encoding a polypeptide of 659 amino acids with an estimated molecular mass of 71.80kDa and an estimated isoelectric point of 5.26. BLAST analysis revealed that the AIHSP70 gene shared high identity with other known HSP70 genes. Three classical HSP signature motifs were detected in AIHSP70 by InterPro analysis. 3-D structural prediction of AIHSP70 showed that its N terminal ATPase activity domain and C terminal substrate-binding domain shared high similarity with that in human heat shock protein 70. The results indicated that the AIHSP70 was a member of the heat shock protein 70 family. A semi-quantitive RT-PCR method was used to analyse the expression of AIHSP70 gene after the treatment of naphthalin which is one kind of polycyclic aromatic hydrocarbon (PAH) and the challenge of bacteria. mRNA expression of AIHSP70 in scallop was up-regulated significantly after the stimulation of naphthalin and increased with increasing naphthalin concentration. A clearly time-dependent expression pattern of AIHSP70 was observed after the scallops were infected by Vibrio anguillarum, and the mRNA expression reached a maximum level at 8h and lasted to 16h, and then dropped progressively. The results indicated that AIHSP70 could play an important role in mediating the environmental stress and immune response in scallop.

The role of intracellular zinc in chromium(VI)-induced oxidative stress, DNA damage and apoptosis

Several studies have demonstrated that zinc is required for the optimal functioning of the skin. Changes in intracellular zinc concentrations have been associated with both improved protection of skin cells against various noxious factors as well as with increased susceptibility to external stress. Still, little is known about the role of intracellular zinc in hexavalent chromium (Cr(VI))-induced skin injury. To address this question, the effects of zinc deficiency or supplementation on Cr(VI)-induced cytotoxicity, oxidative stress, DNA injury and cell death were investigated in human diploid dermal fibroblasts during 48 h. Zinc levels in fibroblasts were manipulated by pretreatment of cells with 100 microM ZnSO4 and 4 or 25 microM zinc chelator TPEN. Cr(VI) (50, 10 and 1 microM) was found to produce time- and dose-dependent cytotoxicity resulting in oxidative stress, suppression of antioxidant systems and activation of p53-dependent apoptosis which is reported for the first time in this model in relation to environmental Cr(VI). Increased intracellular zinc partially attenuated Cr(VI)-induced cytotoxicity, oxidative stress and apoptosis by enhancing cellular antioxidant systems while inhibiting Cr(VI)-dependent apoptosis by preventing the activation of caspase-3. Decreased intracellular zinc enhanced cytotoxic effects of all the tested Cr(VI) concentrations, leading to rapid loss of cell membrane integrity and nuclear dispersion--hallmarks of necrosis. These new findings suggest that Cr(VI) as a model environmental toxin may damage in deeper regions residing skin fibroblasts whose susceptibility to such toxin depends among others on their intracellular Zn levels. Further investigation of the impact of Zn status on skin cells as well as any other cell populations exposed to Cr(VI) or other heavy metals is warranted.

Effect of Zn treatment on wild type and MT-null cell lines in relation to apoptotic and/or necrotic processes and on MT isoform gene expression

It has been shown in various systems that zinc is able to antagonize the catalytic properties of the redox-active transition metals iron and copper, although the process is still unclear. Probably, the protective effect of Zn against oxidative stress is mainly due to the induction of a scavenger metal binding protein such as metallothionein (MT), rather than a direct action. To support this hypothesis, in this study, the effects of Zn, Cu, Fe, Zn + Cu and Zn + Fe treatments were investigated in a fibroblast cell line corresponding to an SV40-transformed MT-1/-2 mutant (MT-/-), and in wild type (MT+/+), by valuing metal concentrations and apoptotic and/or necrotic processes. We also investigated the synthesis of MT and the levels of both MT-1 and MT-2 mRNAs. In MT+/+ cells, co-treatment with Zn + Fe caused a decrease in Fe content compared to treatment with Fe alone. After Zn and Zn + Cu exposure the expression of MT-1 and MT-2 isoforms increased with a concomitant increase in MT synthesis. Annexin V-FITC and propidium iodide staining revealed necrotic or apoptotic cells in terminal stages, especially after Fe treatments. Immunofluorescent staining with an anti-ssDNA Mab and annexin detected a lower signal in co-treated cells compared to the single treatments in both cell lines. The intensity and quantity of fluorescence resulting from anti-ssDNA and Annexin V staining of MT null cells was higher compared to wild type cells. These results suggest that Zn alone does not completely exert an anti-oxidant effect against Cu and Fe toxicity, but that induction of MT is necessary.

Zinc as an insulin replacement in hybridoma cultures

There are many advantages to the use of protein-free media for biologics production, including a reduced risk of viral contamination from animal-derived proteins and simplification of downstream purification. In the course of developing protein-free media for hybridoma and myeloma cells, zinc was found to be an effective replacement for insulin, with no negative impact on viable cell density and antibody production. Transcript profiling using DNA microarrays indicated no major change in the global expression profile between the insulin and zinc-supplemented cultures, which is consistent with their similar growth and metabolic characteristics. Both DNA microarray and quantitative RT-PCR analysis showed increase in insulin receptor substrate 1 (Irs1) expression in zinc-supplemented cultures, while several key genes downstream of Irs1 in the insulin-signaling pathway, such as protein kinase B (PKB/Akt) and 3-phosphoinositide dependent protein kinase 1 (Pdpk1) did not show significant differences at the transcript level. Comparison of transcript profiles from cultures with low versus optimal zinc supplementation implicated the involvement of the insulin-related genes Pax6 and Phas1. Subtle differences were also observed between insulin and zinc in the serine-473 phosphorylation of Akt. Zinc increased serine-473 phosphorylation of Akt, but to a lesser extent than insulin. The phosphoinositide 3-kinase (PI3K) inhibitor, wortmannin, totally blocked the effect of both zinc and insulin on Akt activation, indicating the involvement of PI3K in the activation of Akt by zinc, rather than zinc acting on Akt directly. Our results highlight the impact of trace metal supplementation as protein-free media formulations move towards greater chemical definition.

Growth inhibitory effect of quercetin on SW 872 human liposarcoma cells

Adipocytic tumors represent the largest single group of soft tissue tumors. In the present study, we investigated the antiproliferative potential of quercetin in SW 872 human liposarcoma cells. Cell viability was significantly influenced by quercetin treatment in a time- and dose-dependent manner. Flow cytometric analyses of SW 872 human liposarcoma cells exposed to quercetin showed that the increase of apoptotic cells was time- and dose-dependent. The percentages of normal cells were decreased and apoptotic cells (including early apoptotic and late apoptotic) were increased with increasing concentrations of quercetin. Quercetin-induced apoptosis in SW 872 human liposarcoma cells was associated with the loss of mitochondrial membrane potential (DeltaPsi(m)). The apoptosis in SW 872 human liposarcoma cells induced by quercetin was mediated through the activation of caspase-3, Bax, and Bak and then cleavage of PARP and downregulation of Bcl-2. These results demonstrate that quercetin may prevent atypical lipomatous tumors/well-differentiated liposarcomas from mature adipocytic proliferation, which may contribute to its antiproliferative function.

Changes in expression of bcl-2 and bax in Syrian hamster embryo (SHE) cells exposed to ZnCl2

Zinc is involved in many physiological processes and plays a critical role in functional and structural cells. Zinc at concentrations ranging from 100 to 150 micromol L(-1) has been shown to induce morphological transformation of Syrian hamster embryo (SHE) cells. At these concentrations, zinc inhibited apoptosis in SHE cells. The objective of this study was to elucidate the mechanisms of action of zinc on the apoptotic pathway. Effects of 100 and 150 micromol L(-1) ZnCl(2) on the expression of two members of the Bcl-2 family of proteins and on the transcription factor c-Myc in SHE cells was investigated using RT-PCR. No effect on the proto-oncogene c-myc was observed. Up-regulation of bcl-2 expression was found and bax expression was reduced. These changes have been corroborated by immunoblotting. Effects of Zn(2+) on bcl-2/bax ratio were confirmed in apoptotic camptothecin-treated SHE cells. Cloned and sequenced cDNAs obtained from RT-PCR amplifications allowed us to check the RT-PCR products encoded the expected proteins. This study demonstrated that zinc acts in the early phases of the apoptotic process by modification of the bcl-2/bax ratio in normal and apoptotic SHE cells.

Growth arrest and apoptosis of human hepatocellular carcinoma cells induced by hexamethylene bisacetamide

AIM: To investigate the cellular effects of hybrid polar compound hexamethylene bisacetamide (HMBA) on the growth and apoptosis of human hepatocellular carcinoma cells and to provide the molecular mechanism for potential application of HMBA in the treatment of liver cancer.

METHODS: Effects of HMBA on the growth of human hepatocellular carcinoma SMMC-7721 cells were assayed by MTT chronometry. Apoptosis induced by HMBA was detected by phase-contrast microscopy, flow cytometry, propidium iodide staining and immunocytochemical analysis.

RESULTS: The growth of SMMC-7721 cells was significantly inhibited by HMBA, and the growth inhibitory rate was 51.1%, 62.6%, 68.7% and 73.9% respectively after treatment with 5.0, 7.5, 10.0 and 12.5 mmol/L of HMBA. In the cells treated with 10 mmol/L of HMBA for 72 h, the population of cells at sub-G₁ phase significantly increased, and the apoptotic bodies and condensed nuclei were detected. Moreover, treatment of SMMC-7721 cells with 10 mmol/L of HMBA down-regulated the expression of Bcl-2 anti-apoptotic protein, while slightly up-regulated the level of pro-apoptotic protein Bax.

CONCLUSION: Treatment with 10.0 mmol/L of HMBA can significantly inhibit the growth and induce apoptosis of human hepatocellular carcinoma SMMC-7721 cells by decreasing the ratio of Bcl-2 to Bax.

Foetal rat lung epithelial (FRLE) cells: alterations in cellular homeostasis and gene expression in response to etoposide, hydrogen peroxide and sodium butyrate

Genomics technology offers a way of detecting the effects of a toxin on the expression of many genes in a single experiment. We have previously partially characterised a foetal rat lung epithelial (FRLE) cell line and shown that it is suitable for use in a pneumocytotoxicity screen. In this study, we wanted to ascertain whether we could use alterations in FRLE cell gene expression as a sensitive marker of cell stress. Sodium butyrate and etoposide were shown to arrest FRLE cell cycle at G0/G1 and G2/M phase of the cell cycle, respectively and this was associated with a decrease in the number of cells in culture. Following 24 h of culture both compounds caused a statistically significant increase in the mRNA levels of the cell cycle inhibitory protein, gadd153, whereas p21 was statistically altered by etoposide only. Hydrogen peroxide induced growth arrest at low concentrations (< or =250 microM) following 24 h of culture. We could not detect an increase in apoptosis or in the mRNA levels of the pro-apoptotic protein bax in FRLE cells following culture with hydrogen peroxide or etoposide. Thus, it was possible to correlate cellular perturbations in FRLE cells with alterations in gene expression, demonstrating that these cells are suitable for use in a toxicity screen.

Trace elements in human physiology and pathology: zinc and metallothioneins

Zinc is one of the most abundant nutritionally essential elements in the human body. It is found in all body tissues with 85% of the whole body zinc in muscle and bone, 11% in the skin and the liver and the remaining in all the other tissues. In multicellular organisms, virtually all zinc is intracellular, 30-40% is located in the nucleus, 50% in the cytoplasm, organelles and specialized vesicles (for digestive enzymes or hormone storage) and the remainder in the cell membrane. Zinc intake ranges from 107 to 231 micromol/d depending on the source, and human zinc requirement is estimated at 15 mg/d. Zinc has been shown to be essential to the structure and function of a large number of macromolecules and for over 300 enzymic reactions. It has both catalytic and structural roles in enzymes, while in zinc finger motifs, it provides a scaffold that organizes protein sub-domains for the interaction with either DNA or other proteins. It is critical for the function of a number of metalloproteins, inducing members of oxido-reductase, hydrolase ligase, lyase family and has co-activating functions with copper in superoxide dismutase or phospholipase C. The zinc ion (Zn(++)) does not participate in redox reactions, which makes it a stable ion in a biological medium whose potential is in constant flux. Zinc ions are hydrophilic and do not cross cell membranes by passive diffusion. In general, transport has been described as having both saturable and non-saturable components, depending on the Zn(II) concentrations involved. Zinc ions exist primarily in the form of complexes with proteins and nucleic acids and participate in all aspects of intermediary metabolism, transmission and regulation of the expression of genetic information, storage, synthesis and action of peptide hormones and structural maintenance of chromatin and biomembranes.

Structure determination, apoptosis induction, and telomerase inhibition of CFP-2, a novel lichenin from Cladonia furcata

A great deal of experimental evidence has accumulated in the past several decades, suggesting that polysaccharides have wide bioactivities. Cladonia furcata polysaccharide, CFP-2, a water-soluble lichenin with a mean Mr 7.6 x 10(4), was first obtained by 0.25 M NaOH solution extraction, ethanol precipitation, DEAE-cellulose, and Sephadex G-200 column chromatography. Gas chromatography of acid hydrolyzate of CFP-2 suggested that it was composed of D-glucose, D-galactose, and D-mannose in the molar ratios of 8:1:1. Periodate oxidation, Smith degradation, IR, and NMR spectroscopy analysis revealed that CFP-2 had a backbone consisting of alpha-(1-->3) and alpha-(1-->4)-linked D-glucopyranosyl residues substituted at O-6 with beta-(1-->6)-linked D-galactopyranosyl residue and alpha-(1-->6)-linked D-mannopyranosyl residue. CFP-2 was able to reduce viability of cultured HL-60 and K562 cells. The antiproliferative properties of CFP-2 appeared to be attributable to its induction of apoptotic cell death as determined by ultrastructural change, internucleosomal DNA fragmentation, and increased proportion of the subdiploid cell population. To elucidate molecular events in the apoptosis, protein expressions of Bcl-2, Bax, Fas, and FasL were measured by Western blotting using specific antibodies in HL-60 cells. The level of Bcl-2 remained largely unchanged, but the Bax, Fas, and FasL expression showed up-regulation. Moreover, the telomerase activity analyzed by TRAP-ELISA assay in HL-60 cells treated with CFP-2 decreased as compared with the untreated control cells. These results suggest that CFP-2 could have a possible cancer therapeutic potential.

ZnCl2 induces Syrian hamster embryo (SHE) cell transformation

In order to test the hypothesis of a relationship between apoptosis and neoplastic transformation, we studied the transforming potency of zinc, known for its antiapoptotic effects. In this study, zinc chloride (100 microM) was shown to induce morphological transformation (MT) in Syrian hamster embryo (SHE) cells. It was also tested in combination with benzo(a)pyrene (BaP), a positive control for carcinogenicity, or fomesafen, a carcinogenic pesticide with hepatic peroxisomal proliferation properties. A co-exposure of the two carcinogens with 100 microM zinc increased cell transformation in SHE cells. These results were in agreement with the theory of a relationship between the inhibition of apoptosis and induction of cell transformation. The cloning efficiency (CE) of SHE cells seeded at clonal density was raised by zinc, fomesafen and furthermore by the mixture of the two chemicals, which could be explained by the antiapoptotic action of zinc and fomesafen on SHE cells. No change in myc and bax expressions was observed in zinc-treated SHE cells.

Sauchinone, a Lignan from Saururus chinensis, Inhibits Staurosporine-Induced Apoptosis in C6 Rat Glioma Cells

Neuronal apoptosis may contribute to pathologic neuronal loss in certain disease states such as neurodegenerative diseases. Staurosporine (ST), a nonselective protein kinase inhibitor, has been shown to induce apoptosis in a variety of cells including nerve cell lines. In this study, we investigated the neuroprotective effect of sauchinone, which is a unique lignan from Saururus chinensis, on ST-induced apoptosis in C6 rat glioma cells. Sauchinone attenuated ST-induced apoptosis of C6 glioma cells as evidenced by DNA fragmentation. We also provide evidence that the inhibitory effect of sauchinone on ST-induced apoptosis involves a dose-dependent upregulation of an antiapoptotic protein, Bcl-2. Mounting evidence shows that the activation of caspases, especially caspase-3, triggers the apoptotic process. The activity of caspase-3 of ST-pretreated cells was significantly decreased upon sauchinone treatment in a dose-dependent manner. Taken together, the data demonstrate that sauchinone protects C6 glioma cells from ST-induced apoptosis in a caspase-3 dependent manner. Our findings may be critical for developing a strategy to protect nerve cells from apoptosis, suggesting the potential development of sauchinone as a neuroprotective agent.

Moderate zinc deficiency increases cell death after brain injury in the rat

Zinc supplementation has been used clinically to reduce Zn losses and protein turnover in patients suffering from traumatic brain injury. Despite the known role of zinc in cell survival and integrity, the influence of zinc status on central nervous system wound healing in the weeks and months after brain injury has not been addressed. In this investigation, we examined cell death after unilateral cortical stab wounds in adult rats (n = 5 per group) that were provided diets containing adequate zinc (30 mg Zn/kg diet), supplemental zinc (180 mg/kg), or moderately deficient zinc (5 mg/kg). Four weeks following the brain injury there was a 1.82-2.65-fold increase in terminal deoxynucleotidyl transferase-mediated biotinylated dUTP nick-end labeling (TUNEL)-positive cells with DNA fragmentation at the site of injury in animals receiving a moderately zinc deficient diet compared to animals receiving a zinc-adequate or supplemented diet (p0.05). Examination of the nuclear morphology of these cells suggested the presence of both apoptosis and necrosis. Immunohistochemistry showed that the TUNEL-positive cells expressed both ED-1 and OX-42, identifying them as microglia/macrophages. Thus it appears that adequate zinc status may be necessary to minimize the amount of neuroimmune cell death after brain injury.

Inhibition of proteasome activity is involved in cobalt-induced apoptosis of human alveolar macrophages

Inhalation of particulate cobalt has been known to induce interstitial lung disease. There is growing evidence that apoptosis plays a crucial role in physiological and pathological settings and that the ubiquitin-proteasome system is involved in the regulation of apoptosis. Cadmium, the same transitional heavy metal as cobalt, has been reported to accumulate ubiquitinated proteins in neuronal cells. On the basis of these findings, we hypothesized that cobalt would induce apoptosis in the lung by disturbance of the ubiquitin-proteasome pathway. To evaluate this, we exposed U-937 cells and human alveolar macrophages (AMs) to cobalt chloride (CoCl(2)) and examined their apoptosis by DNA fragmentation assay, 4',6-diamidino-2'-phenylindol dihydrochloride staining, and Western blot analysis. CoCl(2) induced apoptosis and accumulated ubiquitinated proteins. Exposure to CoCl(2) inhibited proteasome activity in U-937 cells. Cobalt-induced apoptosis was mediated via mitochondrial pathway because CoCl(2) released cytochrome c from mitochondria. These results suggest that cobalt-induced apoptosis of AMs may be one of the mechanisms for cobalt-induced lung injury and that the accumulation of ubiquitinated proteins might be involved in this apoptotic process.

Involvement of lysosomal cysteine proteases in hydrogen peroxide-induced apoptosis in HL-60 cells

Hydrogen peroxide is a well-known mediator of apoptosis. As a mechanism for H202-induced apoptosis, both a mitochondrial Cyt.c-dependent pathway and a lysosome-mediated pathway have been suggested. However, the relative roles of and the relation between these two pathways in H2O2-induced apoptosis remain to be discovered. In this study, to find the relative roles of the lysosomal and mitochondrial pathways, the effects of E-64-d, a cell-permeable inhibitor of lysosomal cysteine proteases, on apoptosis caused by H2O2 in HL-60 cells were investigated. It was found that the concentration of H2O2 strongly affected the inhibitory effect of E-64-d on the apoptosis in HL-60 cells: dose-dependent inhibition (up to 40%) of both DNA fragmentation and caspase-3 activation was observed when a high concentration of H2O2 (50 microM) was used to induce apoptosis, but no inhibitory effect was detected when a low concentration (10 microM) was used. Consistent with these observations, apparent lysosomal destabilization was observed only with 50 microM H2O2. The release of mitochondrial Cyt.c, in contrast, was observed at both 10 microM and 50 microM. These results indicated that the mitochondrial Cyt.c-mediated pathway predominates in the H202-induced apoptosis in HL-60 cells and the lysosomal mediated pathway is partially involved when high concentrations of H2O2 are used to induce apoptosis.

p53 protein and p21 mRNA levels and caspase-3 activity are altered by zinc status in aortic endothelial cells

The influence of zinc status on the levels of p53, as well as downstream targets of p53 in cell repair and survival, was examined in human aortic endothelial cells (HAECs). A serum-reduced low-zinc medium (ZD) was used to deplete zinc over one passage. Other treatments included zinc-normal control (ZN), zinc-adequate (ZA), and zinc-supplemented (ZS) treatment with 3.0, 16.0, and 32.0 microM zinc, respectively. Cellular zinc levels in the ZD cells were 64% of ZN controls; levels in the ZA cells were not different, but levels in ZS cells were significantly higher (40%) than in ZN cells. No difference in p53 mRNA abundance was detected among all treatments; however, p53 nuclear protein levels were >100% higher in the ZD and ZS cells and almost 200% higher in the ZA cells than in ZN controls. In addition, p21 mRNA abundance, a downstream target of p53 protein, was increased in the ZS cells compared with both the ZN control and ZD cells. In the ZS cells, bax and mcl-1 were also approximately 50% higher compared with ZN controls, whereas bcl-2 mRNA was increased compared with ZA cells. Moreover, caspase-3 activity of ZD cells was not different from that of ZN controls but was reduced to 83 and 69% of ZN controls in ZA and ZS cells, respectively. Thus p53 protein and p53 downstream target genes appeared to be modulated by intracellular zinc status in HAECs.

ZnCl(2) prevents c-myc repression and apoptosis in serum-deprived Syrian hamster embryo cells

In order to understand the c-myc implication in the apoptotic process better, we investigated the influence of ZnCl(2) on its expression in normal and transformed Syrian hamster embryo (SHE) cells in relation to apoptosis induced by serum withdrawal. Normal primary SHE cells exposed to a serum-free medium undergo rapid apoptosis characterised by a dramatic down-regulation of c-myc transcription. In these normal cells treated with ZnCl(2), c-myc expression is maintained in serum-starved conditions while apoptosis is inhibited. The results shed light on the involvement of c-myc expression in the survival of normal cells in the absence of growth factors. The regulation of c-myc expression appears to be influenced by zinc treatment as an inhibitor of apoptosis, but mechanisms sustaining the level of c-myc transcription remain to be demonstrated. The hypothesis that maintenance of c-myc expression allows cells to escape apoptosis is in accordance with results in transformed SHE cells that underwent low apoptosis and poor down-regulation of c-myc in serum-deprived conditions.

Role of zinc ions in ricin-induced apoptosis in U937 cells

We found that treatment of U937 cells with ZnCl(2) resulted in marked inhibition of ricin-induced DNA fragmentation and nuclear morphological change. Zn(2+) also completely inhibited the activation of caspase-3-, caspase-6-, and caspase-9-like proteases in ricin-treated cells, while no significant effect of Zn(2+) on these protease activities was observed when added directly to the lysate of ricin-treated cells, suggesting that Zn(2+) blocks the process of the activation of these caspases rather than the direct inhibition of the already activated enzymes. Fluorescence microscopic observation with Zn(2+) specific fluorescent probe dansylaminoethyl-cyclen suggested that there was a substantial increase in probe-detectable Zn(2+) in ricin-treated cells. Since the differences in the total Zn(2+) contents between ricin-treated and -untreated cells as measured with an atomic absorption spectrophotometer were too small to explain the increase in probe fluorescence in ricin-treated cells, it was suggested that release of Zn(2+) from intracellular stores or metalloproteins may occur rather than enhanced uptake from the medium. The Zn(2+) probe fluorescence change was observed prior to the depletion of intracellular glutathione. Carbobenzoxy-Asp-1-yl-[(2,6-dichlorobenzoyl)oxy]methane (Z-Asp-CH(2)-DCB), a caspase family protease inhibitor, prevented ricin-induced increase in Zn(2+) probe fluorescence. These results suggest that redistribution of intracellular Zn(2+) occurs during ricin-induced apoptosis as early apoptotic event, and exogenously added Zn(2+) may prevent such intracellular Zn(2+) redistribution resulting in the inhibition of apoptosis.

[Role of intracellular zinc in programmed cell death]

Apoptosis is a type of cell death involved in several biological events during tissue development, remodelling or involution. It could be induced by several extracellular or intracellular stimuli with an important role for metals like zinc or calcium. Cellular zinc is described as an inhibitor of apoptosis, while its depletion induces death in many cell lines. Using different chemical tools like specific zinc-chelators or ionophores, it is possible to study and understand the mechanisms of programmed cell death induction. The decrease in intracellular zinc concentration induces a characteristic apoptosis with apoptotic bodies formation and nuclear DNA condensation and fragmentation. This zinc depletion activates the caspases-3, -8 and -9, responsible for the proteolysis of several target proteins like poly(ADP-ribose) polymerase or transcription factors. Zinc addition in cell culture medium prevents the apparition of morphological and biochemical signs induced by intracellular zinc chelation, but also by other apoptosis inducers like etoposide or tumour necrosis factor alpha (TNF alpha). However, excess of zinc can also be cytotoxic. The balance between life and cell death is maintained by several zinc channels, controlling the intracellular zinc movements and the free amount of the metal.

Cellular zinc content is a major determinant of iron chelator-induced apoptosis of thymocytes

Desferrioxamine (DFO) and the hydroxypiridinone (HPO) deferiprone (CP20) chelate iron as well as other metals. These chelators are used clinically to treat iron overload, but they induce apoptosis in thymocytes. Thymocyte apoptosis is potentiated by zinc deficiency, suggesting that these iron chelators may induce apoptosis by depleting stores of zinc. Exposure of murine thymocytes to either DFO or deferiprone resulted in significant reductions in the labile intracellular zinc pool. Moreover, increasing intracellular zinc levels, by chronic zinc dietary supplementation to mice or in vitro loading with zinc, abrogated deferiprone-induced murine thymocyte apoptosis. Bidentate hydroxypyridinones such as deferiprone interact with intracellular zinc pools in a manner distinct from that of DFO, which is a hexadentate iron chelator. Whereas deferiprone acts synergistically with the zinc chelator NNNN-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) to induce apoptosis, DFO does not. This difference is most likely due to the ability of HPOs but not DFO to "shuttle" zinc onto acceptors such as metallothioneins. By nature of its structure, DFO is larger than deferiprone and is thus less able to access some intracellular zinc pools. Additionally, metal complexes of DFO are more stable than those of HPOs and thus are less likely to donate zinc to other acceptors. The ability of deferiprone to preferentially access zinc pools was also demonstrated by inhibition of a zinc-containing enzyme phospholipase C, particularly when combined with TPEN. These findings suggest that bidentate iron chelators access intracellular zinc pools not available to DFO and that zinc chelation is a mechanism of apoptotic induction by such chelators in thymocytes.

Zinc resistance impairs sensitivity to oxidative stress in HeLa cells: protection through metallothioneins expression

To analyze the effects of high concentrations of zinc ions on oxidative stress protection, we developed an original model of zinc-resistant HeLa cells (HZR), by using a 200 microM zinc sulfate-supplemented medium. Resistant cells specifically accumulate high zinc levels in intracellular vesicles. These resistant cells also exhibit high expression of metallothioneins (MT), mainly located in the cytoplasm. Exposure of HZR to Zn-depleted medium for 3 or 7 d decreases the intracellular zinc content, but only slightly reduces MT levels of resistant cells. No changes of the intracellular redox status were detected, but zinc resistance enhanced H2O2-mediated cytotoxicity. Conversely, zinc-depleted resistant cells were protected against H2O2-induced cell death. Basal- and oxidant-induced DNA damage was increased in zinc resistant cells. Moreover, measurement of DNA damage on zinc-depleted resistant cells suggests that cytoplasmic metal-free MT ensures an efficient protection against oxidative DNA damage, while Zn-MT does not. This newly developed Zn-resistant HeLa model demonstrates that high intracellular concentrations of zinc enhance oxidative DNA damage and subsequent cell death. Effective protection against oxidative damage is provided by metallothionein under nonsaturating zinc conditions. Thus, induction of MT by zinc may mediate the main cellular protective effect of zinc against oxidative injury.

Chemopreventive allylthiopyridazine derivatives induce apoptosis in SK-Hep-1 hepatocarcinoma cells through a caspase-3-dependent mechanism

Dietary organosulphur compounds including diallylsulphide, a component of garlic oil, were shown to inhibit the proliferation of tumour cells. Since hepatocellular carcinoma is one of the most lethal malignancies and there is no effective preventive measure to date, we wished to pursue the chemopreventive potential of the synthetic allylthiopyridazine derivatives (K compounds) on hepatocarcinoma cells. Here, we report that the K compounds efficiently inhibited SK-Hep-1 cell proliferation through induction of apoptosis. Increased chain length at the 3-position of allylthiopyridazine ring improved the potency of growth inhibition. K compounds downregulated Bcl-2, while Bax remained unchanged, reducing the ratio of Bcl-2 to Bax. We also provide evidence that the K compound-induced apoptosis involves cytochrome c release and caspase-3 activation. These results suggest that the allythiopyridazine derivatives, especially 3-propoxy-6-allylthiopyridazine, induce apoptosis in SK-Hep-1 cells through a caspase-3-dependent mechanism, which may contribute to the chemopreventive function for hepatocellular carcinoma.

Impaired accumulation of granulocytes in the lung during ozone adaptation

Respiratory alterations induced by an acute exposure to ozone (O(3)) paradoxically resolve during multiday exposure. This adaptation is characteristically accompanied by a gradual attenuation of lung neutrophilia. As maintenance of neutrophilia at the site of inflammation is due to cytokine-mediated delayed neutrophil apoptosis, which is associated with reduced levels of Bax, a proapoptotic protein, we sought to determine whether defects in these mechanisms could account for O(3) adaptation. Lung granulocytes obtained at different time points from calves exposed to 0.75 ppm O(3) for 12 h/d for 7 consecutive days neither showed enhancement of survival nor Bax deficiency, when compared to blood granulocytes. To further investigate the effects of an exogenous oxidative stress on neutrophil survival, human granulocytes were treated with hydrogen peroxide alone, or in combination with granulocyte/macrophage colony-stimulating factor, an antiapoptotic cytokine. Both treatments led to rapid apoptosis associated with downregulation of Bcl-x(L) and Bcl-2, two antiapoptotic proteins. This study shows that O(3) adaptation is associated with a failure in the mechanisms leading to accumulation of neutrophils at the site of inflammation, and suggests that this defect is due to direct proapoptotic effects of exogenous oxidative stress on granulocytes.

Zinc status affects p53, gadd45, and c-fos expression and caspase-3 activity in human bronchial epithelial cells

This study was designed to examine the influence of zinc depletion and supplementation on the expression of p53 gene, target genes of p53, and caspase-3 activity in normal human bronchial epithelial (NHBE) cells. A serum-free, low-zinc medium containing 0.4 micromol/l of zinc [zinc deficient (ZD)] was used to deplete cellular zinc over one passage. In addition, cells were cultured for one passage in media containing 4.0 micromol/l of zinc [zinc normal (ZN)], which represents normal culture concentrations (Clonetics); 16 micromol/l of zinc [zinc adequate (ZA)], which represents normal human plasma zinc levels; or 32 micromol/l of zinc [zinc supplemented (ZS)], which represents the high end of plasma zinc levels attainable by oral supplementation in humans. Compared with ZN cells, cellular zinc levels were 76% lower in ZD cells but 3.5-fold and 6-fold higher in ZA and ZS cells, respectively. Abundances of p53 mRNA and nuclear p53 protein were elevated in treatment groups compared with controls (ZN). For p53 mRNA abundance, the highest increase (3-fold) was observed in ZD cells. In contrast, the highest increase (17-fold) in p53 nuclear protein levels was detected in ZS cells. Moreover, gadd45 mRNA abundance was moderately elevated in ZD and ZA cells and was not altered in ZS cells compared with ZN cells. Furthermore, the only alteration in c-fos mRNA and caspase-3 activity was the twofold increase and the 25% reduction, respectively, detected in ZS compared with ZN cells. Thus p53, gadd45, and c-fos and caspase-3 activity appeared to be modulated by cellular zinc status in NHBE cells.

Inhibition of invasion and induction of apoptosis by curcumin in H-ras-transformed MCF10A human breast epithelial cells

Curcumin, a dietary pigment in turmeric, posseses anti-carcinogenic and anti-metastatic properties. The present study was conducted to study in vitro chemopreventive effects of curcumin in transformed breast cells. Here, we show that curcumin inhibits H-ras-induced invasive phenotype in MCF10A human breast epithelial cells (H-ras MCF10A) and downregulates matrix metalloproteinase (MMP)-2 dose-dependently. Curcumin exerted cytotoxic effect on H-ras MCF10A cells in a concentration-dependent manner. Curcumin-induced cell death was mainly due to apoptosis in which a prominent downregulation of Bcl-2 and upregulation of Bax were involved. We also suggest a possible involvement of caspase-3 in curcumin-induced apoptosis. Curcumin treatment resulted in the production of reactive oxygen species (ROS) in H-ras MCF10A cells. Apoptotic event by curcumin was significantly inhibited by pretreatment of an antioxidant N-acetyl-L-cysteine (NAC), suggesting redox signaling as a mechanism responsible for curcumin-induced apoptosis in H-ras MCF10A cells. Taken together, our results demonstrate that curcumin inhibits invasion and induces apoptosis, proving the chemopreventive potential of curcumin.

Role of zinc in pulmonary endothelial cell response to oxidative stress

Although zinc is a well-known inhibitor of apoptosis, it may contribute to oxidative stress-induced necrosis. We noted that N,N,N',N'- tetrakis(2-pyridylmethyl)ethylenediamine (TPEN; >10 microM), a zinc chelator, quenched fluorescence of the zinc-specific fluorophore Zinquin and resulted in an increase in spontaneous apoptosis in cultured sheep pulmonary artery endothelial cells (SPAECs). Addition of exogenous zinc (in the presence of pyrithione, a zinc ionophore) to the medium of SPAECs caused an increase in Zinquin fluorescence and was associated with a concentration-dependent increase in necrotic cell death. Exposure of SPAECs to TPEN (10 microM) resulted in enhanced apoptosis after lipopolysaccharide or complete inhibition of t-butyl hydroperoxide (tBH)-induced necrosis. We further investigated the role of two zinc-dependent enzymes, poly(ADP-ribose) polymerase (PARP) and protein kinase (PK) C, in tBH toxicity. tBH toxicity was only affected by the PARP inhibitors 4-amino-1,8-naphthalimide or 3-aminobenzamide over a narrow range, whereas the PKC inhibitors bisindolylmaleimide and staurosporine significantly reduced tBH toxicity. tBH caused translocation of PKC to the plasma membrane of SPAECs that was partially inhibited by TPEN. Thus pulmonary endothelial cell zinc inhibits spontaneous and lipopolysaccharide-dependent apoptosis but contributes to tBH-induced necrosis, in part, via a PKC-dependent pathway.

Zinc has an insulin-like effect on glucose transport mediated by phosphoinositol-3-kinase and Akt in 3T3-L1 fibroblasts and adipocytes

Zinc has insulin-like effects on cells, including promotion of both lipogenesis and glucose transport. The relationship between zinc and the stimulation of glucose transport is unclear. We hypothesize that zinc affects the insulin-signaling pathway. In this study, the effect of zinc on glucose transport and insulin signaling was examined in 3T3-L1-preadipocytes and -adipocytes. Treatment of cells with up to 200 micromol/L zinc significantly increased glucose transport (P < 0.05). The effect of zinc on adipocytes was greater than on preadipocytes, and the effect of zinc plus insulin was greater than that of either insulin or zinc alone. Cytochalasin D, which disrupts actin filaments, attenuated the increase of glucose transport induced by zinc or insulin (P < 0.05). At 100 nmol/L, wortmannin, the phosphoinositide (PI) 3-kinase inhibitor, decreased basal glucose transport and blocked zinc-stimulated glucose transport in both cell types (P < 0.05). H7, an inhibitor of protein kinase C, did not reduce basal glucose transport but decreased zinc-induced glucose transport (P < 0.05). Zinc increased tyrosine phosphorylation of the insulin receptor beta subunit of both preadipocytes and adipocytes after 5-10 min of treatment (P < 0.05). Zinc at 200 micromol/L did not affect tyrosine phosphorylation of insulin receptor substrate (IRS)-1 or -2; further, there was no effect of zinc on the association of the p85 subunit of PI 3-kinase and IRS-1. Zinc significantly increased serine-473 phosphorylation of Akt in both preadipocytes and adipocytes (P < 0.05). The PI 3-kinase inhibitor, wortmannin, totally blocked the effect of zinc on Akt activation. Hence, it appears that zinc can induce an increase in glucose transport into cells and potentiate insulin-induced glucose transport, likely acting through the insulin-signaling pathway.

Capsaicin-induced apoptosis in SK-Hep-1 hepatocarcinoma cells involves Bcl-2 downregulation and caspase-3 activation

Hepatocellular carcinoma is one of the most lethal malignancies and there is no effective preventive measure in this highly malignant disease to date. In the present study, we investigated the chemopreventive potential of capsaicin (8-methyl-N- vanillyl-6-nonenamide), the principal pungent ingredient found in hot red pepper, in SK-Hep-1 hepatocellular carcinoma cells. Treatment of capsaicin inhibited growth of SK-Hep-1 cells in a concentration-dependent manner while 4-methoxy capsaicin (Met-capsaicin) was less potent. This inhibitory effect of capsaicin on SK-Hep-1 cell growth was mainly due to the induction of apoptosis as evidenced by DNA fragmentation and nuclear condensation. Furthermore, capsaicin prominently reduced the ratio of anti-apoptotic Bcl-2 to pro-apoptotic Bax and consequently increased caspase-3 activity. These results demonstrate that capsaicin efficiently induced apoptosis in SK-Hep-1 cells through a caspase-3-dependent mechanism, which may contribute to its chemopreventive function.

New insights into the role of zinc in the respiratory epithelium

Over the past 30 years, many researchers have demonstrated the critical role of zinc (Zn), a group IIb metal, in diverse physiological processes, such as growth and development, maintenance and priming of the immune system, and tissue repair. This review will discuss aspects of Zn physiology and its possible beneficial role in the respiratory epithelium. Here we have detailed the mechanisms by which Zn diversely acts as: (i) an anti-oxidant; (ii) an organelle stabilizer; (iii) an anti-apopototic agent; (iv) an important cofactor for DNA synthesis; (v) a vital component for wound healing; and (vi) an anti-inflammatory agent. This paper will also review studies from the authors' laboratory concerning the first attempts to map Zn in the respiratory epithelium and to elucidate its role in regulating caspase-3 activated apoptosis. We propose that Zn, being a major dietary anti-oxidant has a protective role for the airway epithelium against oxyradicals and other noxious agents. Zn may therefore have important implications for asthma and other inflammatory diseases where the physical barrier is vulnerable and compromised.

Retinol binding protein expression is induced in HepG2 cells by zinc deficiency

Zinc (Zn) deficiency is often associated with low plasma vitamin A (retinol) concentrations. It has been suggested that the reduction in plasma retinol is secondary to reduced liver retinol binding protein (RBP) synthesis. In the present study, RBP expression was determined in HepG2 cells cultured in either Zn adequate media or chelated media containing varying concentrations of Zn. Levels of RBP mRNA increased in a time- and Zn concentration-dependent manner such that 0.5 microM Zn-treated cells exhibited a >7.5-fold increase while cells treated with 15 microM Zn were increased 2.9-fold at 72 h compared to controls. RBP protein also progressively increased by 72 h to levels >8-fold and 3-fold higher than controls, in 0.5 microM and 15 microM Zn-treated cells, respectively. The increase in RBP occurred without any change in DNA concentration between groups through 72 h. The Zn deficiency-induced elevations in RBP transcript levels could be reversed within 24-48 h of repletion in Zn adequate media. Thus, the reductions in plasma retinol observed in Zn deficiency are in part a direct consequence of the deficiency.

Effects of zinc acetate on splenocytes of endotoxemic mice: enhanced immune response, reduced apoptosis, and increased expression of heat shock protein 70

Immune function is markedly attenuated in endotoxemia. Zinc is involved in the regulation of cellular functions and maintenance of immune function, and its level in the serum is low in endotoxemia. We mainly investigated the effects of zinc acetate (ZA) on splenocytes in mice with endotoxemia. After we confirmed increased plasma zinc level by ZA treatment, C57BL/6 mice were randomly divided into four groups: 10 control mice received 500 microL saline solution as vehicle; 10 control mice received ZA at 3 mg/kg body weight; 20 endotoxemic mice received a 40 mg/kg lethal dose of lipopolysaccharide (LPS); 20 mice received ZA followed by LPS as the above dose. In vivo, we confirmed that ZA pretreatment did not significantly affect the plasma cytokine level in endotoxemic mice. In vitro, splenocytes from ZA-plus-LPS mice showed drastic effects, in that ZA abrogated LPS-induced suppression of cellular proliferation and production of interleukin-2 and interferon-gamma. The percentage of apoptotic splenocytes was significantly reduced in ZA-plus-LPS mice (23.4%) as compared with LPS mice (41.6%). Furthermore, the expression of HSP-70 mRNA in splenocytes was strongly enhanced in both ZA and ZA-plus-LPS mice, especially in the latter group. Finally, studies monitoring survival rates for 6 days showed that LPS caused 100% mortality while ZA-plus-LPS mice showed 75% survival. Our results suggest that zinc normalized the immune response and reduced apoptosis of splenocytes. These changes were probably caused by increased synthesis of HSP-70 by splenocytes, which might enhance survival of mice with LPS-induced endotoxemia.

Zinc and the immune system

Zn is an essential trace element for all organisms. In human subjects body growth and development is strictly dependent on Zn. The nervous, reproductive and immune systems are particularly influenced by Zn deficiency, as well as by increased levels of Zn. The relationship between Zn and the immune system is complex, since there are four different types of influence associated with Zn. (1) The dietary intake and the resorption of Zn depends on the composition of the diet and also on age and disease status. (2) Zn is a cofactor in more than 300 enzymes influencing various organ functions having a secondary effect on the immune system. (3) Direct effects of Zn on the production, maturation and function of leucocytes. (4) Zn influences the function of immunostimulants used in the experimental systems. Here we summarize all four types of influence on the immune function. Nutritional aspects of Zn, the physiology of Zn, the influence of Zn on enzymes and cellular functions, direct effects of Zn on leucocytes at the cellular and molecular level, Zn-altered function of immunostimulants and the therapeutic use of Zn will be discussed in detail.

Intracellular zinc depletion induces caspase activation and p21 Waf1/Cip1 cleavage in human epithelial cell lines

To better understand the mechanisms by which zinc deficiency induces epithelial cell death, studies were done of the effects of intracellular zinc depletion induced by the zinc chelator TPEN on apoptosis-related events in human malignant epithelial cell lines LIM1215 (colonic), NCI-H292 (bronchial), and A549 (alveolar type II). In TPEN-treated cells, depletion of zinc was followed by activation of caspase-3 (as demonstrated by enzymatic assay and Western blotting), DNA fragmentation, and morphologic changes. Increase in caspase-3 activity began 12 h after addition of TPEN, suggesting that zinc may suppress a step just before the activation of this caspase. Caspase-6, a mediator of caspase-3 processing, also increased, but later than caspase-3. Effects of TPEN on apoptosis were completely prevented by exogenous ZnSO4 and partially prevented by peptide caspase inhibitors. A critical substrate of caspase-3 may be the cell cycle regulator p21Waf1/Cip1, which was rapidly cleaved in TPEN-treated cells to a 15-kDa fragment before further degradation.

Protection by polaprezinc, an anti-ulcer drug, against indomethacin-induced apoptosis in rat gastric mucosal cells

Polaprezinc [N-(3-aminopropionyl)-L-histidinato zinc] (PZ), an anti-ulcer drug, is a chelate compound consisting of zinc and L-carnosine. PZ has been shown to prevent gastric mucosal injury. In the present study, we investigated the inhibitory effect of PZ on indomethacin (IND)-induced apoptosis in a rat gastric mucosal cell line, RGM1. Pretreatment with PZ suppressed caspase-3 activation and subsequent apoptosis in the cells exposed to 500 microM IND in a dose-dependent manner, and 50 microM PZ exhibited the maximum inhibitory effect. Among PZ subcomponents, zinc but not L-carnosine played a pivotal role in this antiapoptotic function. PZ did not affect mitochondrial cytochrome c release upstream of caspase-3 activation in the IND-induced apoptotic signal pathway. Treatment with 500 microM IND evidently produced reactive oxygen species (ROS) in RGM1 cells. However, PZ did not scavenge ROS in IND-treated cells. Moreover, N-acetylL-cysteine, a potent antioxidant, inhibited ROS generation but did not suppress apoptosis in RGM1 cells exposed to IND. These observations demonstrate a novel pharmacological action of PZ; i.e., that PZ, and in particular its zinc subcomponent, inhibits apoptosis via inhibition of caspase-3 activation but not antioxidant activity.

Mitochondrial cytochrome c release and caspase-3-like protease activation during indomethacin-induced apoptosis in rat gastric mucosal cells

Indomethacin (IND), a nonsteroidal anti-inflammatory drug, has been known to cause gastric mucosal injury as a side effect. Using a rat gastric mucosal cell line, RGM1, we determined whether apoptosis is involved in IND-mediated gastropathy, and whether caspase activation and mitochondrial cytochrome c release play an important role in producing apoptosis of IND-treated RGM1 cells in the presence of serum. IND caused caspase-3-like protease activation followed by apoptosis in a dose- and time-dependent manner. Caspase-1-like protease activity did not change during IND-induced apoptosis. IND also increased mitochondrial cytochrome c release in a time-dependent fashion. Mitochondrial cytochrome c efflux occurred just before or at the same time as caspase-3-like protease activation, and preceded the increase in apoptotic cell numbers. Z-VAD-FMK, a caspase inhibitor, inhibited both the increase in caspase-3-like protease activity and apoptosis in IND-treated RGM1 cells but did not affect caspase-1-like protease activity or mitochondrial cytochrome c release. These observations suggest that the apoptosis of gastric mucosal cells could be involved in IND-induced gastropathy, that cytochrome c is released from mitochondria into the cytosol during the early phase of IND-mediated apoptosis, and that subsequent activation of caspase-3-like protease, but not caspase-1-like protease, is required for the execution of apoptosis.

Nicotine switches the form of H(2)O(2)-induced cell death from apoptosis to necrosis in U937 cells

Cigarette smoking is a major risk factor for lung diseases and oral diseases. The present study examined the effect of nicotine on H(2)O(2)-induced apoptosis in U937 cells. In the presence of 1 microg/ml nicotine, cell viability was not affected, but the cells were unable to undergo H(2)O(2)-induced apoptosis and instead died as a result of necrosis. Nicotine reduced the intracellular level of ATP, which is an important determinant of the form of cell death. These results suggest that nicotine can alter the cell death pathway by reducing the level of intracellular ATP, and that this effect may contribute to cigarette smoke-induced tissue destruction.

Cellular zinc fluxes and the regulation of apoptosis/gene-directed cell death

The maintenance of discrete subcellular pools of zinc (Zn) is critical for the functional and structural integrity of cells. Among the important biological processes influenced by Zn is apoptosis, a process that is important in cellular homeostasis (an important cellular homeostatic process). It has also been identified as a major mechanism contributing to cell death in response to toxins and in disease, offering hope that novel therapies that target apoptotic pathways may be developed. Because Zn levels in the body can be increased in a relatively nontoxic manner, it may be possible to prevent or ameliorate degenerative disorders that are associated with high rates of apoptotic cell death. This review begins with brief introductions that address, first, the cellular biology of Zn, especially the critical labile Zn pools, and, second, the phenomenon of apoptosis. We then review the evidence relating Zn to apoptosis and address three major hypotheses: (1) that a specific pool or pools of intracellular labile Zn regulates apoptosis; (2) that systemic changes in Zn levels in the body, due to dietary factors, altered physiological states or disease, can influence cell susceptibility to apoptosis, and (3) that this altered susceptibility to apoptosis contributes to pathophysiological changes in the body. Other key issues are the identity of the molecular targets of Zn in the apoptotic cascade, the types of cells and tissues most susceptible to Zn-regulated apoptosis, the role of Zn as a coordinate regulator of mitosis and apoptosis and the apparent release of tightly bound intracellular pools of Zn during the later stages of apoptosis. This review concludes with a section highlighting areas of priority for future studies.

Zinc-deficient rat embryos have increased caspase 3-like activity and apoptosis

Caspase activity is a hallmark of apoptosis. Given that maternal zinc (Zn) deficiency results in apoptosis in the rat embryo, we assessed caspase activity in Zn-deficient embryos. Mid-gestation rat embryos were collected from dams fed either a Zn-deficient (0.5 Zn/g) diet ad libitum, or a Zn-adequate (25 microg Zn/g) diet ad libitum or pair fed to dams fed the Zn-deficient diet. Embryos from dams fed the Zn-adequate diet had a normal level of cell death, while embryos from the dams fed the Zn-deficient diet had either increased or normal levels of cell death. Zn-deficient embryos displaying increased cell death had increased caspase activity. Embryos with normal levels of cell death, regardless of maternal diet, had similar caspase activities. Thus, Zn-deficiency-induced apoptosis in vivo is associated with increased caspase activity.

Zinc has no effect on IL-3-mediated apoptosis of BAF-3 cells but enhances CD95-mediated apoptosis of jurkat cells

The feasibility of using a zinc-inducible gene expression system for the study of apoptosis-controlling genes in BAF-3 murine B cells and Jurkat human T cells was evaluated. Initially, cell sensitivity to a range of zinc concentrations was examined. It was found that zinc concentrations above 60 microM were toxic to BAF-3 cells and those above 50 microM were toxic to Jurkat cells. Secondly, the zinc concentration required to achieve maximal gene expression was examined. BAF-3 cells transiently transfected with the pMTCB6+/luciferase vector were exposed to zinc concentrations ranging from 0-120 microM, whilst stably transfected Jurkat cells were exposed to 0-70 microM zinc. At zinc concentrations nontoxic to each cell type, the maximum induction achieved was 20-fold (at 60 microM) in BAF-3 cells, and 7.5-fold (at 50 microM) in Jurkat cells. Thirdly, the effect of zinc on apoptosis was examined. It was shown that exposure to nontoxic zinc concentrations had no effect on IL-3 withdrawal-mediated apoptosis of BAF-3 cells. However, in the case of Jurkat cells, pre-exposure to zinc augmented CD95-mediated apoptosis. These results illustrate the importance of characterizing individual cell lines when using zinc-inducible gene expression systems.

Blunt cell growth potential in carcinogen resistant inbred DRH rats

A carcinogen-resistant inbred strain DRH/Sea has been developed from the Crj:Donryu strain. The rats had a very low incidence of liver tumors when they were fed diets containing a hepatocarcinogen such as 3'-methyl-4-dimethylamino-azobenzene (3'-Me-DAB). Despite using 3'-Me-DAB during the stage of selection, the DRH/Sea rats developed normally, reproduced and did not have any spontaneous tumor in the lung, liver or uterus at over 1 year of age. Although their growth curves were similar to the Crj:Donryu rats, the progression of polyploidization in the liver was significantly delayed when compared with Crj:Donryu rats. Mitogenic changes that occurred in the liver caused by either 3'-Me-DAB or lead nitrate were less significant in the DRH rats than in Crj:Donryu rats. Furthermore, the growth rate of cultured fibroblasts derived from the DRH rats was slower than that of Crj:Donryu rats. These results, together with our previous results, suggest that slow growth potential is present under certain conditions in DRH rats. These findings may explain partly the meaning of the different susceptibility to hepatocarcinogens.

Resveratrol, an antioxidant present in red wine, induces apoptosis in human promyelocytic leukemia (HL-60) cells

Resveratrol, a triphenolic stilbene present in grapes and other plants, has striking antioxidant and anti-inflammatory activities which have been considered to be responsible for the beneficial effects of red wine consumption on coronary heart disease. Recent studies reveal that resveratrol can inhibit each step of multistage carcinogenesis. However, the molecular mechanisms underlying anti-tumorigenic or chemopreventive activities of this phytochemical remain largely unknown. In the present work, we have found that resveratrol reduces viability and DNA synthesis capability of cultured human promyelocytic leukemia (HL-60) cells. The growth inhibitory and antiproliferative properties of resveratrol appear to be attributable to its induction of apoptotic cell death as determined by morphological and ultrastructural changes, internucleosomal DNA fragmentation, and increased proportion of the subdiploid cell population. Resveratrol treatment resulted in a gradual decrease in the expression of anti-apoptotic Bcl-2. These results, together with previous findings, suggest the cancer therapeutic as well as chemopreventive potential of resveratrol.

Regulation of caspase activation and apoptosis by cellular zinc fluxes and zinc deprivation: A review

Non-toxic agents that target intracellular signalling pathways in apoptosis may have potential therapeutic use in many diseases. One such agent is the transition metal Zn, a dietary cytoprotectant and anti-oxidant, which stimulates cell proliferation and suppresses apoptosis. Zn is maintained in discrete subcellular pools that are critical for the functional and structural integrity of cells. The present review initially describes the current state of knowledge on the cellular biology of Zn, especially the critical free or loosely bound (labile) pools of Zn, which are thought to regulate apoptosis. We then review the evidence relating Zn to apoptosis, including studies from our laboratory showing potent synergy between intracellular Zn deficiency and the short chain fatty acid butyrate in induction of caspase activation and the downstream events of apoptosis. Our studies have also reported the suppressive effects of micromolar concentrations of Zn on caspase-3 activation in cell-free models. Other key issues that will be discussed include the identification of the putative molecular targets of Zn and the evidence that systemic changes in labile Zn levels are sufficient to alter susceptibility to apoptosis and lead to physiopathological changes in the human body. Finally, we propose that labile Zn may serve as a coordinate regulator of mitosis and apoptosis to regulate tissue growth.