Lipopolysaccharide induces double-stranded DNA fragmentation in mouse thymus: protective effect of zinc pretreatment

Protective Effects of Zinc on 2.45 GHz Electromagnetic Radiation-Induced Oxidative Stress and Apoptosis in HEK293 Cells

Several epidemiological studies have shown that exposure to electromagnetic radiation (EMR) can be harmful to human health. The purpose of this study was to examine oxidative parameters and apoptosis induced by EMR in human kidney embryonic cells (HEK293) and to investigate whether zinc (Zn) has protective effect on EMR-induced apoptosis in HEK293 cells. For our experiment, HEK293 cells were divided into four main groups, control, EMR, 50 μM Zn + EMR, and 100 μM Zn + EMR. HEK293 cells of EMR groups were exposed to 2.45 GHz EMR for 1 h. In Zn groups, HEK293 cells were incubated with different concentrations of Zn for 48 h before EMR exposure. Oxidative stress parameters were determined by spectrophotometric method; bcl-2 and caspase-3 were assessed immunohistochemically and TUNEL method was performed for apoptotic activity. EMR group had higher malondialdehyde (MDA) level and lower superoxide dismutase (SOD) activity compared with control group. In Zn-applied groups, MDA was decreased and SOD activity was increased compared with EMR group. The number of the apoptotic cells and caspase-3 immunopositive cells at EMR group was increased significantly compared with the control group, whereas bcl-2 was decreased. Besides, Zn-treated groups showed a significant reduction in the number of apoptotic cells and caspase-3 from that of EMR group, whereas there was an increase in bcl-2 immunopositivity. Our findings show that EMR caused oxidative stress and apoptotic activation in HEK293 cells. Zn seems to have protective effects on the EMR by increasing SOD activity and bcl-2 immunopositivity, decreasing lipid peroxidation and caspas-3 immunopositivity.

Effects of commercially produced almond by-products on chemotherapy-induced mucositis in rats

AIM

To determine if almond extracts reduce the severity of chemotherapy-induced mucositis as determined through biochemical, histological and behavioural markers.

METHODS

Intestinal mucositis is a debilitating condition characterized by inflammation and ulceration of the gastrointestinal mucosa experienced by cancer patients undergoing chemotherapy. Certain bioactive plant products have shown promise in accelerating mucosal repair and alleviating clinical symptoms. This study evaluated almond extracts for their potential to reduce the severity of chemotherapy-induced mucositis in Dark Agouti rats. Female Dark Agouti rats were gavaged (days 3-11) with either PBS, almond hull or almond blanched water extract at two doses, and were injected intraperitoneally with 5-fluorouracil (5-FU-150 mg/kg) or saline on day 9 to induce mucositis. Burrowing behavior, histological parameters and myeloperoxidase activity were assessed.

RESULTS

Bodyweight was significantly reduced in rats that received 5-FU compared to saline-treated controls (P < 0.05). Rats administered 5-FU significantly increased jejunal and ileal MPO levels (1048%; P < 0.001 and 409%; P < 0.001), compared to healthy controls. Almond hull extract caused a pro-inflammatory response in rats with mucositis as evidenced by increased myeloperoxidase activity in the jejunum when compared to 5-FU alone (rise 50%, 1088 ± 96 U/g vs 723 ± 135 U/g, P = 0.02). Other extract-related effects on inflammatory activity were minimal. 5-FU significantly increased histological severity score compared to healthy controls confirming the presence of mucositis (median of 9.75 vs 0; P < 0.001). The extracts had no ameliorating effect on histological severity score in the jejunum or ileum. Burrowing behavior was significantly reduced in all chemotherapy-treated groups (P = 0.001). The extracts failed to normalize burrowing activity to baseline levels.

CONCLUSION

Almond extracts at these dosages offer little beneficial effect on mucositis severity. Burrowing provides a novel measure of affective state in studies of chemotherapy-induced mucositis.

Differential Effectiveness of Clinically-Relevant Analgesics in a Rat Model of Chemotherapy-Induced Mucositis

Chemotherapy-induced intestinal mucositis is characterized by pain and a pro-inflammatory tissue response. Rat models are frequently used in mucositis disease investigations yet little is known about the presence of pain in these animals, the ability of analgesics to ameliorate the condition, or the effect that analgesic administration may have on study outcomes. This study investigated different classes of analgesics with the aim of determining their analgesic effects and impact on research outcomes of interest in a rat model of mucositis. Female DA rats were allocated to 8 groups to include saline and chemotherapy controls (n = 8). Analgesics included opioid derivatives (buprenorphine; 0.05mg/kg and tramadol 12.5mg/kg) and NSAID (carprofen; 15mg/kg) in combination with either saline or 5-Fluorouracil (5-FU; 150mg/kg). Research outcome measures included daily clinical parameters, pain score and gut histology. Myeloperoxidase assay was performed to determine gut inflammation. At the dosages employed, all agents had an analgesic effect based on behavioural pain scores. Jejunal myeloperoxidase activity was significantly reduced by buprenorphine and tramadol in comparison to 5-FU control animals (53%, p = 0.0004 and 58%, p = 0.0001). Carprofen had no ameliorating effect on myeloperoxidase levels. None of the agents reduced the histological damage caused by 5-FU administration although tramadol tended to increase villus length even when administered to healthy animals. These data provide evidence that carprofen offers potential as an analgesic in this animal model due to its pain-relieving efficacy and minimal effect on measured parameters. This study also supports further investigation into the mechanism and utility of opioid agents in the treatment of chemotherapy-induced mucositis.

Effects of Metabolic Cage Housing on Rat Behavior and Performance in the Social Interaction Test

Although the metabolic cage is commonly used for housing nonhuman animals in the laboratory, it has been recognized as constituting a unique stressor. Such an environment would be expected to affect behavioral change in animals housed therein. However, few studies have specifically addressed the nature or magnitude of this change. The current study sought to characterize the behavioral time budget of rats in metabolic cage housing in comparison to that of individually housed animals in standard open-top cages. Rats in metabolic cages spent less time moving, manipulating enrichment, and carrying out rearing behaviors, and there was a corresponding shift toward inactivity. In an applied Social Interaction Test, behavioral scoring implied that metabolic cage housing had an anxiogenic effect. In conclusion, metabolic cage housing produces measurable effects on spontaneous and evoked behavior in rats in the laboratory. These behavioral changes may lead to a negative emotional state in these animals, which could have negative welfare consequences. Further research is needed to quantify the existence and magnitude of such an effect on rat well being.

Zinc pyrithione inhibits caspase-3 activity, promotes ErbB1-ErbB2 heterodimerization and suppresses ErbB2 downregulation in cardiomyocytes subjected to ischemia/reperfusion

Heart tissue becomes zinc-depleted and the capacity to mobilize labile zinc is diminished, indicating zinc dyshomeostasis during ischemia/reperfusion (I/R). Apparently, zinc pyrithione restores the basal zinc levels during I/R and prevents apoptosis by activating phosphatidyl inositol-3-kinase/Akt and targeting mitochondrial permeability transition. Receptor tyrosine kinases of the ErbB family (ErbB1 to ErbB4) are cell surface proteins that can regulate cell growth, proliferation and survival. Previous studies have shown that zinc pyrithione-induced activation of PI3kinase/Akt requires ErbB2 expression. On the other hand, while I/R decreases ErbB2 levels causing cardiomyocyte dysfunction and cell death, zinc pyrithione restores ErbB2 levels and maintains cardiomyocyte function. H9c2 cells expressed all the four ErbBs, although the expression of ErbB1 and ErbB2 were higher compared to ErbB3 and ErbB4. Hypoxia/Reoxygenation (H/R) had opposing effects on the mRNA expression of ErbB1 and ErbB2. ErbB2 mRNA levels were enhanced, but corresponding ErbB2 protein levels decreased after reoxygenation. H/R induced the degradation of ErbB2 in caspase-3 dependent manner, with the formation of a 25kDa fragment. This fragment could be detected after H/R only upon treatment of the cells with a proteasomal inhibitor, ALLN, suggesting that caspase-mediated cleavage of 185kDa ErbB2 results in C-terminal cleavage and formation of 25kDa fragment, which is further degraded by proteasome. Heterodimerization and phosphorylation of ErbB2/ErbB1 which decreased upon reoxygenation, was promoted by zinc pyrithione. Zinc pyrithione effectively suppressed the caspase activation, decreased the proteolytic cleavage of ErbB2, enhanced the phosphorylation and activation of ErbB1-ErbB2 complexes and improved the cell survival after hypoxia/reoxygenation.

Effects of acute chemotherapy-induced mucositis on spontaneous behaviour and the grimace scale in laboratory rats

Intestinal mucositis is a frequent side-effect of chemotherapy treatment. Many oncological research programs aim to identify novel treatments for this distressing condition, and these programs frequently use rat models. Little is known about the presence and progression of pain in these models and how this can best be treated by analgesic therapy. We used a number of behaviour-based methods of pain assessment to determine which tools were best suited for pain identification. Baseline measures for behavioural assessment, rat grimace score and sociability were determined through analysis of continuously recorded video data and an applied social interaction test ( n = 16). Mucositis was then induced by intraperitoneal injection of 5-fluorouracil (150 mg/kg) and further behavioural analyses undertaken. An assessment of enrichment interaction was also made by determining the mass of a plastic chew toy gnawed both pre- and post-chemotherapy injection. Behavioural scoring was performed 1, 6, 12, 24 and 48 h after injection, with facial expression being scored at the 12, 24 and 48 h time-points. Sociability testing was performed once during the post-injection period. No significant differences were found in grimace scores between baseline and later daily measures. Behaviours similar to those previously reported post-laparotomy were observed. Writhing, twitching and back-arching behaviours were most evident in rats affected by mucositis and were increased in frequency (respective P values: 0.002, 0.004 and 0.008) 48 h after chemotherapy injection compared with baseline, implying that pain onset occurred around this time-point. Social investigatory behaviour was also increased ( P = 0.002) following disease onset. Each day, rats post-5FU injection gnawed a greater percentage of their nylabone enrichment by weight than the saline-injected control rats ( P = 0.046). These data suggest that, of the tools tested, behavioural assessment scoring may find greatest utility in rodent models of intestinal mucositis and should be investigated further.

Expression of executioner procaspases and their activation by a procaspase-activating compound in chronic lymphocytic leukemia cells

Intrinsic and extrinsic apoptotic pathways converge to activate common downstream executioner caspases (caspase-3, -6, and -7), resulting in cell death. In chronic lymphocytic leukemia (CLL), neoplastic B cells evade apoptosis owing to the overexpression of survival proteins. We hypothesized that direct activation of procaspases could bypass the apoptosis resistance induced by the upstream prosurvival proteins. The procaspase-activating compounds (PAC-1), including B-PAC-1 (L14R8), convert inactive executioner procaspases to their active cleaved forms by chelation of labile zinc ions. Both at transcript and protein levels, primary CLL cells express high levels of latent procaspases (3, -7, and -9). B-PAC-1 treatment induced CLL lymphocyte death which was higher than that in normal peripheral blood mononuclear cells or B cells, and was independent of prognostic markers and microenvironmental factors. Mechanistically, B-PAC-1 treatment activated executioner procaspases and not other Zn-dependent enzymes. Exogenous zinc completely, and pancaspase inhibitors partially, reversed B-PAC-1-induced apoptosis, elucidating the zinc-mediated mechanism of action. The cell demise relied on the presence of caspase-3/7 but not caspase-8 or Bax/Bak proteins. B-PAC-1 in combination with an inhibitor of apoptosis protein antagonist (Smac066) synergistically induced apoptosis in CLL samples. Our investigations demonstrated that direct activation of executioner procaspases via B-PAC-1 treatment bypasses apoptosis resistance and is a novel approach for CLL therapeutics.

The assessment of general well-being using spontaneous burrowing behaviour in a short-term model of chemotherapy-induced mucositis in the rat

Mucositis is a common and serious side-effect experienced by cancer patients during treatment with chemotherapeutic agents. Consequently, programmes of research focus on the elucidation of novel therapeutics for alleviation of mucositis symptoms, and these frequently use animal models. However, although these models are assumed to be painful and distressing to the animal, endpoints are difficult to determine. The aim of this study was to evaluate whether a change in burrowing behaviour could provide an indication of disease onset and potentially be applied as a humane endpoint. Baseline burrowing behaviour was measured in healthy animals on three occasions by determining the weight of gravel displaced from a hollow tube. Mucositis was then induced in the same animals by intraperitoneal injection of 5-fluorouracil (150 mg/kg) and burrowing behaviour recorded over three consecutive days. Standard measures of disease progression, including body weight loss and clinical score, were also made. The presence of mucositis was confirmed at necropsy by findings of decreased duodenal and colon lengths, and reduced liver, spleen and thymus weights in comparison with non-treated control animals. Histological score of the jejunum and ileum was also significantly increased. Mucositis onset coincided with a decrease in mean burrowing behaviour which was progressive, however this result did not achieve statistical significance (P = 0.66).We conclude that burrowing may be a useful indicator of inflammation in the mucositis model, although this requires further characterization. Pre-selection of animals into treatment groups based on their prior burrowing performance should be pursued in further studies.

Effects of Streptococcus thermophilus TH-4 in a rat model of doxorubicin-induced mucositis

BACKGROUND

Mucositis is a debilitating intestinal side effect of chemotherapeutic regimens. Probiotics have been considered a possible preventative treatment for mucositis. Streptococcus thermophilus TH-4 (TH-4), a newly identified probiotic, has been shown to partially alleviate mucositis induced by administration of the antimetabolite chemotherapy drug, methotrexate in rats; likely mediated through a mechanism of folate production. However, its effects against other classes of chemotherapy drug have yet to be determined.

AIMS

The authors investigated the effects of TH-4 in a rat model of mucositis induced by the anthracycline chemotherapy drug, doxorubicin.

METHODS

Gastrointestinal damage was induced in female Dark Agouti rats (148.3 ± 1.5 g) by intraperitoneal injection of doxorubicin (20 mg/kg). Animals recieved a daily oral gavage of TH-4 at 10(9) cfu/ml or skim milk (vehicle) from days 0 to 8. At day 6, rats were injected with either saline or doxorubicin. At kill, small intestinal tissues were collected for determination of sucrase and myeloperoxidase (MPO) activities and histological assessment.

RESULTS

Body weight was significantly decreased by doxorubicin compared with normal controls (p < 0.05). Histological parameters, such as crypt depth and villus height, were also significantly decreased by doxorubicin. TH-4 partially prevented the loss of body weight induced by doxorubicin (2.3% compared with 4%), but provided no further therapeutic benefit.

CONCLUSIONS

The minimal amelioration of doxorubicin-induced mucositis by TH-4 further supports folate production as a likely mechanism of TH-4 action against methotrexate-induced mucositis. Further studies into TH-4 are required to confirm its applicability to other conventional chemotherapy regimens.

The effect of zinc and the role of p53 in copper-induced cellular stress responses

Metals can directly or indirectly cause an increase in reactive oxygen species (ROS) accumulation in cells, and this may result in programmed cell death. A number of previous studies have shown that zinc (Zn) modulates mitogenic activity via several signalling pathways, such as AKT, mitogen-activated protein kinase (MAPK), nuclear factor-kappa B (NF -κB), AP-1 and p53. The exact role that Zn plays in the regulation of apoptosis remains ambiguous. Intracellular free Zn modulates p53 activity and stability, and excess Zn alters the p53 protein structure and down-regulates p53's binding to DNA. Copper (Cu) accumulation causes apoptosis that seems to be mediated by DNA damage and subsequent p53 activation. Cu can also displace Zn from its normal binding site on p53, resulting in abnormal protein folding and disruption of p53 function. In spite of the induction of the tumour suppressor p53, hepatic Cu accumulation significantly increases the risk of cancerous neoplasm both in humans and rats, suggesting that p53 function may be impaired in these cells. It is generally understood that imbalances in Cu and Zn levels may lead to a higher prevalence of p53 mutations. An increased number of p53 mutations have been found in liver samples from Wilson's disease (WD) patients. High levels of the p53 mutation most probably contribute to the pathogenesis of cancer in individuals with WD, but the cause and effect are not clear. The protein p53 also plays a crucial role in the transcriptional regulation of metallothionein, which indicates a novel regulatory role for p53. This review discusses the central role of p53 and the redox-inert metal Zn in the cellular stress responses induced by the redox active biometal Cu.

Morphine prevents the mitochondrial permeability transition pore opening through NO/cGMP/PKG/Zn2+/GSK-3beta signal pathway in cardiomyocytes

The aim of this study was to test whether morphine prevents the mitochondrial permeability transition pore (mPTP) opening through Zn(2+) and glycogen synthase kinase 3beta (GSK-3beta). Fluorescence dyes including Newport Green Dichlorofluorescein (DCF), 4-amino-5-methylamino-2',7'-difluorofluorescein (DAF-FM), and tetramethylrhodamine ethyl ester (TMRE) were used to image free Zn(2+), nitric oxide (NO), and mitochondrial membrane potential (DeltaPsi(m)), respectively. Fluorescence images were obtained with confocal microscopy. Cardiomyocytes treated with morphine for 10 min showed a significant increase in Newport Green DCF fluorescence intensity, an effect that was reversed by the NO synthase inhibitor N (G)-nitro-L-arginine methyl ester (L-NAME), indicating that morphine mobilizes Zn(2+) via NO. Morphine rapidly produced NO. ODQ and NS2028, the inhibitors of guanylyl cyclase, prevented Zn(2+) release by morphine, implying that cGMP is involved in the action of morphine. The effect of morphine on Zn(2+) release was also abolished by KT5823, a specific inhibitor of protein kinase G (PKG). Morphine prevented oxidant-induced loss of DeltaPsi(m), indicating that morphine can modulate the mPTP opening. The effect of morphine on the mPTP was reversed by KT5823 and the Zn(2+) chelator N,N,N',N'-tetrakis-(2-pyridylmethyl)ethylenediamine (TPEN). The action of morphine on the mPTP was lost in cells transfected with the constitutively active GSK-3beta mutant, suggesting that morphine may prevent the mPTP opening by inactivating GSK-3beta. In support, morphine significantly enhanced phosphorylation of GSK-3beta at Ser(9), and this was blocked by TPEN. GSK-3beta small interfering RNA prevented the pore opening in the control cardiomyocytes but failed to enhance the effect of morphine on the mPTP opening. In conclusion, morphine mobilizes intracellular Zn(2+) through the NO/cGMP/PKG signaling pathway and prevents the mPTP opening by inactivating GSK-3beta through Zn(2+).

Exogenous zinc protects cardiac cells from reperfusion injury by targeting mitochondrial permeability transition pore through inactivation of glycogen synthase kinase-3beta

The purpose of this study was to determine whether exogenous zinc prevents cardiac reperfusion injury by targeting the mitochondrial permeability transition pore (mPTP) via glycogen synthase kinase-3beta (GSK-3beta). The treatment of cardiac H9c2 cells with ZnCl2 (10 microM) in the presence of zinc ionophore pyrithione for 20 min significantly enhanced GSK-3beta phosphorylation at Ser9, indicating that exogenous zinc can inactivate GSK-3beta in H9c2 cells. The effect of zinc on GSK-3beta activity was blocked by the phosphatidylinositol 3-kinase (PI3K) inhibitor LY-294002 but not by the mammalian target of rapamycin (mTOR) inhibitor rapamycin or the PKC inhibitor chelerythrine, implying that PI3K but not mTOR or PKC accounts for the action of zinc. In support of this interpretation, zinc induced a significant increase in Akt but not mTOR phosphorylation. Further experiments found that zinc also increased mitochondrial GSK-3beta phosphorylation. This may indicate an involvement of the mitochondria in the action of zinc. The effect of zinc on mitochondrial GSK-3beta phosphorylation was not altered by the mitochondrial ATP-sensitive K+ channel blocker 5-hydroxydecanoic acid. Zinc applied at reperfusion reduced cell death in cells subjected to simulated ischemia/reperfusion, indicating that zinc can prevent reperfusion injury. However, zinc was not able to exert protection in cells transfected with the constitutively active GSK-3beta (GSK-3beta-S9A-HA) mutant, suggesting that zinc prevents reperfusion injury by inactivating GSK-3beta. Cells transfected with the catalytically inactive GSK-3beta (GSK-3beta-KM-HA) also revealed a significant decrease in cell death, strongly supporting the essential role of GSK-3beta inactivation in cardioprotection. Moreover, zinc prevented oxidant-induced mPTP opening through the inhibition of GSK-3beta. Taken together, these data suggest that zinc prevents reperfusion injury by modulating the mPTP opening through the inactivation of GSK-3beta. The PI3K/Akt signaling pathway is responsible for the inactivation of GSK-3beta by zinc.

Zinc, antioxidant systems and metallothionein in metal mediated-apoptosis: biochemical and cytochemical aspects

Copper, zinc and iron are essential metals for different physiological functions, even though their excess can lead to biological damage. This review provides a background of toxicity related to copper, iron and zinc excess, biological mechanisms of their homeostasis and their respective roles in the apoptotic process. The antioxidant action of metallothionein has been highlighted by summarizing the most important findings that confirm the role of zinc in cellular protection in relation to metallothionein expression and apoptotic processes. In particular, we show that a complex and efficient antioxidant system, the induction of metallothionein and the direct action of zinc have protective roles against oxidative damage and the resulting apoptosis induced by metals with redox proprieties. In addition, to emphasize the protective effects of Zn and Zn-MT in Cu and Fe-mediated oxidative stress-dependent apoptosis, some aspects of apoptotic cell death are shown. The most widely used cytochemical techniques also have been examined in order to critically evaluate the available data from a methodological point of view. The observations on the role of Zn and MT could potentially develop new applications for this metal and MT in biomedical research.

NO mobilizes intracellular Zn2+ via cGMP/PKG signaling pathway and prevents mitochondrial oxidant damage in cardiomyocytes

OBJECTIVE

Our aim was to determine if NO prevents mitochondrial oxidant damage by mobilizing intracellular free zinc (Zn(2+)).

METHODS

Zn(2+) levels were determined by imaging enzymatically isolated adult rat cardiomyocytes loaded with Newport Green DCF. Mitochondrial membrane potential (DeltaPsi(m)) was assessed by imaging cardiomyocytes loaded with tetramethylrhodamine ethyl ester (TMRE).

RESULTS

S-nitroso-N-acetylpenicillamine (SNAP) dramatically increased Zn(2+), which was blocked by both ODQ and NS2028, two specific inhibitors of guanylyl cyclase. The protein kinase G (PKG) inhibitor KT5823 blocked the effect of SNAP while the PKG activator 8-Br-cGMP mimicked the action of SNAP, indicating that the cGMP/PKG pathway is responsible for the effect of SNAP. The increased Zn(2+) was prevented by 5-hydroxydecanoate (5HD) but was mimicked by diazoxide, implying that mitochondrial K(ATP) channel opening may account for this effect. Since chelation of Zn(2+) blocked the preventive effect of SNAP on H(2)O(2)-induced loss of DeltaPsi(m) and exogenous zinc (1 microM ZnCl(2)) prevented dissipation of DeltaPsi(m), Zn(2+) may play a critical role in the protective effect of NO. The MEK (mitogen-activated protein kinase or extracellular signal-regulated kinase) inhibitor PD98059 blocked the preventive effects of SNAP and zinc on DeltaPsi(m), indicating that extracellular signal-regulated kinase (ERK) mediates the protective effect of both these compounds on mitochondrial oxidant damage. A Western blot analysis further showed that ZnCl(2) significantly enhances phosphorylation of ERK, confirming the involvement of ERK in the action of Zn(2+).

CONCLUSIONS

In isolated cardiomyocytes, NO mobilizes endogenous zinc by opening mitochondrial K(ATP) channels through the cGMP/PKG pathway. In these cells, Zn(2+) may be an important mediator of the action of NO on the mitochondrial death pathway.

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.

Evaluation of MT expression and detection of apoptotic cells in LEC rat kidneys

To confirm our previous observations on the effectiveness of long term treatment with Zn on Long-Evans Cinnamon (LEC) rats, we extended these studies determining the effects of Zn on trace elements, metallothionein (MT) concentrations and immunolocalization, and on the levels of both MT-1 and MT-2 mRNAs in the LEC rat kidneys. We also localized the renal cells that had chromatin condensation and nuclear fragmentation typical of apoptosis. The results demonstrate that the amount of Zn increased in the treated rats with respect to both untreated and basal rats. In the treated rats the amount of Cu and Fe was similar to that of the basal rats. MT concentrations did not change either with or without Zn treatment, but were higher than the basal group. However, if we consider the percentage of oxidized MT (MTox), we note that Zn treatment is very effective in reducing this value. MTox is not able to bind metals, so it does not perform a "scavenger" function. Moreover, quantification of mRNA indicates that the MT-1 isoform was significantly higher than the MT-2 isoform following Zn treatment. Untreated group sections showed a confocal fluorescent signal that highlighted the irregular nuclei and small apoptotic bodies. The intensity and quantity of fluorescence decreased in the treated group sections. These findings suggest that, in LEC rats, Zn may contribute to cytoprotection through the regulation of MT expression which may provide a cellular defence strategy in response to DNA damage.

Calprotectin (S100A8/S100A9), an inflammatory protein complex from neutrophils with a broad apoptosis-inducing activity

Calprotectin, a complex of two calcium-binding proteins that belong to the S100 protein family, is abundant in the cytosolic fraction of neutrophils. A high level of calprotectin reportedly exists in extracellular fluid during various inflammatory conditions, such as rheumatoid arthritis, cystic fibrosis and abscesses. However, the exact biological role(s) of the factor is now under investigation. We recently observed that neutrophils contain a factor that shows growth-inhibitory and apoptosis-inducing activities against various cell types including tumor cells and normal fibroblasts, and we identified that factor as calprotectin. The findings suggest that calprotectin exerts a regulatory activity in inflammatory processes through its effect on the survival or growth states of cells participating in the inflammatory reaction. It is also possible that calprotectin, at a high concentration, might have a deleterious effect on fibroblasts and influence the recovery of inflammatory tissue. Therefore, the protein factor may be a new drug target to control inflammatory reactions. We found that a few of the Amaryllidaceae alkaloids effectively inhibited the growth-inhibitory and apoptosis-inducing activities of calprotectin. In this article, we focus on the biological functions of calprotectin in extracellular fluids, focusing on its apoptosis-inducing activity.

Metallothionein-1 and metallothionein-2 gene expression and localisation of apoptotic cells in Zn-treated LEC rat liver

The aims of the present work were to determine the effect of long-term treatment with zinc (Zn) on metallothionein (MT) concentrations and to study the levels of both MT-1 and MT-2 mRNAs in Long-Evans Cinnamon (LEC) rat liver. We also identified apoptotic cells comparing two cytochemical techniques. Thirteen rats received 50 mg zinc acetate daily by gavage, 13 rats received no treatment, and both groups were killed after 60 days. Finally four rats were killed 35 days after birth (T(0)). The results demonstrate that the Zn-treated group had higher levels of MT than both the untreated and basal ones. Quantification of mRNA indicates that the level of the Zn-treated group was significantly higher than the untreated group. Confocal fluorescent staining with monoclonal antibody (Mab) against single-strand DNA localised the hepatic cells that had chromatin condensation and nuclear fragmentation typical of apoptosis, especially in the untreated group sections. The intensity and quantity of fluorescence decreased in both the treated and basal groups. The higher sensitivity of Mab staining compared to TUNEL, which revealed both apoptotic and necrotic cells, reflects the different action mechanism of the two techniques. These findings confirm, in LEC rats, the important role of Zn in cellular protection in relation to MT expression and apoptotic processes as cellular responses to DNA damage by free radicals.

Role of the maternal acute phase response and tumor necrosis factor alpha in the developmental toxicity of lipopolysaccharide in the CD-1 mouse

The acute phase response (APR) functions to reset metabolic homeostasis following infectious, toxic, or traumatic insult. TNF-alpha, a putative mediator of the APR, has been associated with fetal death in rodents and preterm labor and delivery in humans. We hypothesized that physiologic changes associated with the maternal APR may play a role in adverse embryo/fetal outcome. Pregnant CD-1 mice injected i.p. with lipopolysaccharide (LPS), a model inducer of the APR, on gestation day (gd) 9 showed a dose-related increase in embryo death on gd 10. Histology indicated placental infarct and necrosis. Maternal serum TNF-alpha levels, measured by ELISA following administration of 0.05 mg/kg LPS on gd 9, were found to increase significantly and peak within 1 to 1.5 h. Pretreatment with 0.01 mg/kg LPS on gd 8 ameliorated embryotoxicity of the 0.05 mg/kg LPS treatment on gd 9 and also eliminated the increase in serum TNF-alpha. Direct LPS exposure in whole embryo culture was nontoxic. These data support a maternally mediated mechanism of LPS embryolethality, and suggest that TNF-alpha may be an important mediator of this developmental toxicity.

Zinc inhibition of caspase-3 activation does not protect HeLa cells from apoptotic cell death

Zinc is proposed to be antiapoptotic for it has been shown to inhibit late events of apoptotic pathways such as Ca(2+)/Mg(2+)-dependent endonuclease cleavage of chromatin DNA, poly-ADP ribose polymerase cleavage, and caspase-3 activity. Because caspase-3 is a critical executioner caspase in apoptosis, this study was undertaken to examine specifically a correlation between zinc inhibition of caspase-3 activation and apoptosis in HeLa cells. Cultured HeLa cells were exposed to 100 microM ZnCl(2) for 1 h prior to 12 h treatment with 1.0 microM doxorubicin (DOX), an important anticancer agent that causes apoptosis in a wide variety of tumor cells. Western blot analysis of HeLa cells treated with DOX for 12 h revealed that DOX caused proteolytic activation of caspase-3 and zinc inhibited this activation. Interestingly, zinc did not inhibit DOX-induced apoptosis as measured by a terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay. Furthermore, a microculture tetrazolium assay confirmed that cell death occurred in the presence of zinc. These results demonstrate that zinc specifically inhibits DOX-induced activation of caspase-3 in HeLa cells, but does not suppress DOX-induced apoptosis or otherwise cell death, thus suggesting DOX-induced caspase-3 activation may not play a major role in overall cell death and/or non-caspase-3 pathways are involved in DOX-induced apoptosis in HeLa cells.

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.

Apoptosis induced by chelation of intracellular zinc is associated with depletion of cellular reduced glutathione level in rat hepatocytes

Zn(2+) has multiple implications in cellular metabolism, including free radicals metabolism and cell death by apoptosis. In the present study, we examined the role of Zn(2+) in the regulation of apoptosis in cultured rat hepatocytes. The chelation of Zn(2+) by a membrane permeable metal ion chelator, N, N, N', N'-tetrakis(2-pyridylmethyl) ethylenediamine (TPEN), induced apoptosis. Addition of ZnSO(4) prevented TPEN-induced apoptosis. Unlike the effect of TPEN, a membrane impermeable metal ion chelator, diethylenetriamine pentaacetic acid (DTPA), did not induce apoptosis, indicating that chelation of intracellular Zn(2+) was required to trigger apoptosis. Caspase-3-like proteolytic activity, a general biochemical mediator of apoptosis in a variety of cells and tissues, was also activated with the treatment of TPEN but not DTPA. TPEN treatment, but not DTPA, also resulted in the depletion of intracellular reduced glutathione (GSH) but addition of Zn(2+) recovered the GSH level. N-acetyl-L-cysteine (NAC), a thiol antioxidant, prevented TPEN-induced apoptosis. These results taken together suggest that intracellular Zn(2+) interfere with the apoptosis process, possibly through the regulation of cellular redox potential involving GSH.

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.

Human DU145 prostate cancer cells overexpressing mitogen-activated protein kinase phosphatase-1 are resistant to Fas ligand-induced mitochondrial perturbations and cellular apoptosis

Recent studies have suggested that MAP kinase phosphatase 1 (MKP-1) is overexpressed in prostate cancer. To evaluate the role of MKP-1 in regulating cell death and tumor growth in prostate cancer, MKP-1 was conditionally overexpressed in the human prostate cancer cell line DU145. Overexpression of MKP-1 in DU145 cells blocked activation of stress-activated protein kinase (SAPK/JNK). MKP-1 overexpression in DU-145 cells was also found to inhibit Fas ligand (FasL)-induced apoptosis, as well as block the activation of caspases by Fas engagement. In addition, MKP-1 blocked the activation of apoptosis by transfected MEKK-1 and ASK-1, presumably through its inhibition of the SAPK/JNK family of enzymes. MKP-1 blocked the ability of FasL to induce loss of mitochondrial transmembrane potential (delta Psi(m)), suggesting that MKP-1 acts upstream of mitochondrial pro-apoptotic events induced by FasL and that the SAPK/JNK pathway may form the signaling link between Fas receptor and mitochondrial dysfunction. Thus, MKP-1 overexpression in prostate cancer may play a role in promoting prostate carcinogenesis by inhibiting FasL-induced cell death.

Induction of apoptosis in mouse thymocytes by microcolin A and its synthetic analog

Microcolin A (Mic-1), a marine-derived compound, has been shown to be a novel antiproliferative and immunosuppressive agent. We investigated the ability of Mic-1 and its chemosynthetic analog, microcolin A3 (Mic-3), to induce apoptosis in murine thymocytes. Following incubation of the cells with Mic-1 (10-100 nM) or Mic-3 (10-100 nM), internucleosomal DNA fragmentation in apoptotic cells was detected by agarose gel electrophoresis and the diphenylamine (DPA) assay; the presence of hypodiploid nuclei assessed by propidium iodide (PI) staining; and the percentages of apoptotic and necrotic cells quantified by morphological observation and fluorescein labeled annexin-V binding. Our results show that both Mic-1 and Mic-3 are potent inducers of apoptosis in thymocytes depending on drug concentration and time of exposure, with Mic-3 being more potent than Mic-1 in the induction of apoptosis. Furthermore, flow cytometric analysis using monoclonal antibodies specific to thymocyte subpopulations showed that the proportion of the early immature CD4+ CD8+ T-cell subpopulation in thymocytes was selectively decreased by both agents with a corresponding increase of other subpopulations, indicating that CD4+ CD8+ T cells are the most likely targets of Mic-1 and Mic-3. These in vitro results suggest that the antiproliferative and immunosuppressive properties of both compounds are possibly associated with apoptosis-inducing events and imply that they may have additional potential value as antineoplastic agents.

Nitric oxide induction of neuronal endonuclease activity in programmed cell death

Neuronal survival is intricately linked to the maintenance of intact DNA. In contrast, neuronal degeneration following nitric oxide (NO) exposure is dependent, in part, on the degradation of DNA through programmed cell death (PCD). We therefore investigated in primary rat hippocampal neurons the role of endogenous deoxyribonucleases, enzymes responsible for metabolically derived DNA cleavage, during NO-induced neurodegeneration. Twenty-four hours following exposure to the NO generators sodium nitroprusside (300 microM) and SIN-1 (300 microM), neuronal survival was reduced from approximately 88 to 23%. Treatment with aurintricarboxylic acid (1-100 microM), an endonuclease inhibitor, during NO exposure increased neuronal survival from 23 to 80% and decreased DNA fragmentation from 70 to 30% over a 24-h period. Enhancement of endonuclease activity alone with zinc chelation actively decreased neuronal survival from approximately 80% to approximately 34%. DNA digestion assays identified not only two constitutively active endonucleases, an acidic endonuclease (pH 4.0-7.0) and a calcium/magnesium-dependent endonuclease (pH 7.2-8.0), but also a NO-inducible magnesium-dependent endonuclease (pH 8.0). In the absence of endonuclease activity, DNA degradation did not occur during NO application, suggesting that endonuclease activity was a requisite pathway for NO-induced PCD. In addition, NO independently altered intracellular pH in ranges that were physiologically relevant for the activity of the endonucleases responsible for DNA degradation. Our identification and characterization of specific neuronal endonucleases suggest that the constitutive endonucleases may play a role in the initial stages of NO-induced PCD, but the subsequent "downstream" degradation of DNA may ultimately be dependent upon the NO-inducible endonuclease.

Trace elements and apoptosis

It is known that apoptosis is considered to be responsible for selective deletion of cells during embryogenesis, the homeostasis of cell populations in continuously renewing tissues (i.e., serving as a counterbalance to mitosis), and tissue involution in response to chemical or physical stimuli. There are many publications on these questions. On the other hand, the intracellular processes that contribute to apoptosis are incompletely understood. Therefore, the role of apoptosis in the intracellular accumulation and outflow of minerals is of considerable importance in light of both their essential functions and toxic effects.

Flow cytometric analysis of cellular changes in mice after intradermal inoculation with a liposome-iscom adjuvanted vaccine

As it is not known what changes to leucocyte homeostasis are mandatory for effective adjuvant action, the biological relevance of systemic changes elicited by different vaccine formulations can only be interpreted in the context of the immunological outcomes. We used flow cytometry to quantify the changes in leucocyte subsets induced in mice intradermally immunized with SAMA4 (adjuvant group), outer membrane proteins (OMP) purified from Actinobacillus pleuropneumoniae (OMP antigen group), SAMA4 adjuvanted OMP (OMP vaccine group), or phosphate-buffered saline (PBS: control group). This approach allowed direct comparisons to be made between the effects of antigen, adjuvant or antigen-adjuvant complexes on immune effector cell populations. Antigens complexed with the liposome-iscom hybrid adjuvant, SAMA4, generated strong antibody responses and cytotoxic T-cell activity in animals immunized intradermally, reflecting remobilization and recruitment of specific cell populations. Splenomegaly, due to granulocytosis, monocytosis and megakaryocytosis, was most prominent in the OMP vaccine group. Histological examination of spleen sections confirmed that these changes were due primarily to splenic haematopoiesis. Circulating numbers of granulocytes and monocytes increased significantly (P < 0.05) in the blood of the OMP vaccine group, as did granulocyte numbers in the lungs (P < 0.05). No changes in T- and B-cell numbers were detected by flow cytometry in the spleens, lungs or blood over the 28-day period in any treatment group. Thymocyte numbers (predominantly CD4+CD8+ cells) in the OMP vaccine group fell by 95% within 3 days of immunization. Identical cellular responses were obtained when an innocuous antigen, ovalbumin, was complexed with SAMA4 instead of OMP, thus demonstrating that the adjuvant effects of SAMA4 were due to synergistic interaction between antigen and adjuvant and not due to the presence of toxic components. The association of strong adaptive immune responses with such complex changes in leucocyte homeostasis induced by complexing adjuvant and antigen suggested that the changes were important for effective vaccination and were not purely circumstantial.

Zinc is a potent inhibitor of the apoptotic protease, caspase-3. A novel target for zinc in the inhibition of apoptosis

The prevention of apoptosis by Zn2+ has generally been attributed to its inhibition of an endonuclease acting in the late phase of apoptosis. In this study we investigated the effect of Zn2+ on an earlier event in the apoptotic process, the proteolysis of the "death substrate" poly(ADP-ribose) polymerase (PARP). Pretreatment of intact Molt4 leukemia cells with micromolar concentrations of Zn2+ caused an inhibition of PARP proteolysis induced by the chemotherapeutic agent etoposide. Using a cell-free system consisting of purified bovine PARP as a substrate and an apoptotic extract or recombinant caspase-3 as the PARP protease, Zn2+ inhibited PARP proteolysis in the low micromolar range. To rule out an effect of Zn2+ on PARP, a protein with two zinc finger domains, we used recombinant caspase-3 and a chromogenic tetrapeptide substrate containing the caspase-3 cleavage site. In this system, Zn2+ inhibited caspase-3 with an IC50 of 0.1 microM. These results identify caspase-3 as a novel target of Zn2+ inhibition in apoptosis and suggest a regulatory role for Zn2+ in modulating the upstream apoptotic machinery.

Adding Zn2+ induces DNA fragmentation and cell condensation in cultured human Chang liver cells

Zinc (Zn) is a trace element in human cells and regarded as an essential nutrient with established deficiency states affecting multiple organs in the body. However, it has been reported that Zn uptake is associated with some serious harmful effects, such as inhibition of DNA synthesis and enhanced toxicity from reactive oxygen species. We have previously shown that in vivo administration of Zn2+ in C57/6J mice induces weight loss and massive hair loss where the normal course hair becomes replaced by fine vello hair, simulating the side effects from cancer chemotherapy where oxidative free radical damage is implicated in association with DNA fragmentation and programmed cell death (PCD). Here, in vitro flow cytometric studies on human Chang liver showed Zn2+ causing cell condensation with DNA fragmentation that occurred in a dose-dependent manner, an effect replicated by micrococcal nuclease digestion. Specific terminal deoxynucleotidyl transferase-(TdT) mediated labeling of 3'-OH ends of DNA nicks corroborated the flow cytometric profiles of propidium iodide-DNA binding where degradation of both 2 and 4 N genomic DNA resulted in a solitary 1N peak presentation. DNA degradation concomitant with cell condensation is seen as an established hallmark of PCD. We further showed that Zn2+ could enhance the generation of hydroxyl free radicals (OH.) by the transition metal vanadium. Glutathione, the cell's main reducing agent, underwent corresponding reduction. The results suggested that Zn supplementation could induce features resembling PCD.

Effect of systemic zinc administration on delayed neuronal death in the gerbil hippocampus

The divalent cation zinc has been reported to possess several physiological properties such as blocking apoptotic cell death through an inhibitory effect on Ca(2+)-Mg2+ endonuclease activity, or modulating the neurotoxicity via glutamate receptor subtypes. In the present study, we investigated the effect of peripherally injected zinc on delayed neuronal death seen in the hippocampus after transient global ischemia, in order to elucidate a possible beneficial role on zinc in ischemic neuronal cell death. Forty-five adult Mongolian gerbils of both sexes underwent transient bilateral clipping of the common carotid arteries for 3 min. In the pretreated animals, ZnCl2 (20 mg/kg) was injected subcutaneously once, 1 h before ischemia (superacute group; n = 6) or twice at 24 and 48 h before ischemia (subacute group; n = 14). Histological survey was carried out 3 days later by in situ DNA fragmentation method and 4 days later by hematoxylin-eosin staining by semiquantatively counting dead neurons in the CA1 sector. Subacute zinc pre-administration significantly reduced the nuclear damage and subsequent neuronal death; however, superacutely pre-administered zinc did not protect hippocampal neurons against ischemia but it did not aggravate the effect of ischemia, either. The present study suggested that transfer of exogenous zinc into the intracellular space is required for neuroprotection, presumably via the anti-endonuclease activity.

1,10-Phenanthroline stimulates internucleosomal DNA fragmentation in isolated rat-liver nuclei by promoting the redox activity of endogenous copper ions

Isolated rat-liver nuclei were incubated with a series of membrane-permeable metal-ion-complexing agents and examined for DNA damage. Of the reagents tested, only 1,10-phenanthroline (OP) and neocuproine (NC) were found to induce DNA fragmentation. Agarose-gel electrophoresis of the DNA fragments generated in the presence of OP revealed internucleosomal cleavage, which is widely considered to be a hallmark for the enzymic DNA digestion that occurs during apoptosis. Ascorbate, particularly in the presence of hydrogen peroxide, increased the levels of fragmentation induced by OP. As well as undergoing fragmentation, the DNA from nuclei was also found to contain 8-hydroxydeoxyguanosine, which indicates attack (oxidation) by the hydroxyl radical. Complementary experiments in vitro involving ESR determinations of hydroxyl radical formation and measurements of DNA oxidation under biomimetic conditions demonstrated that Cu2+, but not Fe3+, forms a complex with either OP or NC (but not the other complexing agents tested) that stimulates hydroxyl radical formation and DNA damage in the presence of hydrogen peroxide and ascorbate. It is therefore proposed that OP in the nuclei incubations binds to Cu2+, which exists naturally in chromosomes, forming a complex that promotes hydroxyl-radical-dependent DNA fragmentation. These findings demonstrate the promotion of hydroxyl-radical-mediated DNA damage by endogenous Cu2+ and, perhaps more significantly, demonstrate that the internucleosomal DNA 'laddering' that is often used as an indicator of apoptosis may also result from DNA fragmentation by non-enzymic processes.

Zinc deficiency causes apoptosis but not cell cycle alterations in organogenesis-stage rat embryos: effect of varying duration of deficiency

Zinc deficiency is teratogenic in all species in which it has been examined. Zinc is an essential component of enzymes involved in DNA synthesis and cell proliferation, and may play an as yet undetermined role in apoptosis. To further our understanding of the role of zinc in normal development, we examined cell death and cell cycle parameters in embryos of pregnant rats fed a zinc-deficient diet for 2 to 10 days (0.5 microgram zinc/g diet; zinc-adequate diet was 25 micrograms zinc/g). To elucidate sensitive periods of development and susceptible cell populations, dams were fed the zinc-deficient diet from gestation day 1, 3, 7, or 9 and killed on day 11. Embryos were examined for morphology and developmental stage. From each litter, 2-3 embryos were stained with Nile blue sulfate (NBS) to visualize cell death, 3 embryos were frozen for flow cytometric cell cycle analysis and cell counts, and selected embryos were preserved for histological examination. Dams fed the zinc-deficient diet for more than 3 days reduced their food intake through gestation day 8 but increased food intake on day 9. Maternal plasma zinc dropped to 10-25% of control levels in the zinc-deficient groups. Zinc deficiency from gestation day 1 or 3 resulted in two categories of affected litters on day 11. One category had embryos which were morphologically normal but displayed extensive NBS staining in the visceral arches, neural tube, and somites. The second category had developmentally retarded or maldeveloped embryos which showed little NBS staining. Zinc deficiency from gestation day 7 produced cell death in the posterior dorsal midline in the area of premigratory neural crest cells, which was confirmed by histological examination. Zinc deficiency from gestation day 9 did not affect morphology or NBS staining. Percentages of cells in the G0/G1, S, and G2M phases of the cell cycle on gestation day 11, determined by flow cytometry, were similar to controls in all groups. This study shows that as few as 4 days of maternal zinc deficiency can produce excess embryonal cell death, and that neural crest cells may be particularly sensitive.

Role of intracellular free Ca(II) and Zn(II) in dexamethasone-induced apoptosis and dexamethasone resistance in human leukemic CEM cell lines

The levels of intracellular free Ca(II) and Zn(II) during dexamethasone (dex)-induced apoptosis in CEM cell lines were determined by 19F nuclear magnetic resonance (NMR), using the fluorinated intracellular chelator 1,2-bis-(2- amino-5-fluorophenoxy)ethane-N,N,N',N'-tetraacetic acid (5-FBAPTA). The effects of these divalent metal ions on growth rate and DNA degradation were evaluated. Measurements were done on one dex-sensitive (CEM-C7) and three different dex-resistant variants (CEM-C1, CEM-4R4, and CEM-ICR27). Dex caused a continuous increase in the Ca(II) level in dex-sensitive CEM-C7 cells, while in CEM-C1 cells dex caused an initial increase in the Ca(II) level which in approximately 36 h was restored to its normal value. The intracellular Ca(II) level in CEM-4R4 cells was not significantly affected by dex, while that of CEM-ICR27 cells decreased after dex incubation. Only the dex-sensitive CEM-C7 cells showed dex-induced DNA degradation. An intracellular free Zn(II) level of approximately 1 nM was measured for the dex-resistant CEM-C1 cells. No detectable level of intracellular Zn(II) was found in the other cell lines. Incubation with < 100 microM Zn(II) did not inhibit dex-induced apoptosis in CEM-C7 cells (e.g., DNA degradation). Treatment with approximately 250 microM Zn(II) caused significant decrease in growth rate in all cell lines and prevented dex-induced DNA degradation in CEM-C7 cells. A calibrated amount of Ca(II) ionophore (A23187), used to increase Ca(II) concentrations up to the dex-induced levels, did not induce DNA degradation in CEM-C7 or CEM-C1 cells. While elevation of intracellular Ca(II) by itself is not sufficient to initiate apoptosis in CEM-C7 cells, the results reported here suggest that Ca(II) is involved in the killing mechanism as a secondary factor. The combination of dex and ionophore caused significant DNA degradation in CEM-C1 cells, which normally showed resistance to each compound individually. The combination of dex and the Zn(II) chelator phenanthroline also caused extensive DNA degradation in the normally dex-resistant CEM-C1 cells, suggesting that Zn(II) plays a role in the dex resistance of these cells.

Programmed cell death of the normal human neutrophil: an in vitro model of senescence

The present study provides experimental data which indicate that the neutrophil is ideal for studying programmed cell death or apoptosis in vitro. Neutrophils can be obtained from human peripheral blood in large numbers with minimal experimental manipulation and are easily separated from other leukocytes, providing nearly pure cell suspensions. The neutrophil life span in vitro is sufficiently short to allow observations to be made within eight hours after experimental manipulation. Neutrophils can also be easily maintained in serum-free, chemically defined media which can be systematically altered, thereby defining specific variables that influence the apoptotic process. Since the neutrophils do not need an exogenous trigger to undergo programmed cell death, it is also an excellent model to study senescence. It was determined from this study that neutrophils undergo apoptosis most efficiently at 37 degrees C, a temperature requirement for physiologic cell death. Neutrophils undergo apoptosis at a slightly faster rate and maintain membrane integrity better when incubated in a tissue culture medium (e.g., RPMI 1640) compared with a balanced salt solution (e.g., HBBB). Cycloheximide, an inhibitor of protein synthesis, was shown to accelerate apoptosis in a dose-dependent manner. The presence of Zn++ significantly decreased the rate of apoptosis, whereas the presence of Ca++ and Mg++ had no apparent effect. These studies indicate that the process of senescence, culminating in cell death, is subject to modulation by a variety of agents and experimental conditions. In addition, the ultrastructural features of neutrophils undergoing programmed cell death in vitro were compared in detail to those occurring in vivo and were found to be comparable.