Calcium chelators induce apoptosis--evidence that raised intracellular ionised calcium is not essential for apoptosis

Trichlorfon inhibits proliferation and promotes apoptosis of porcine trophectoderm and uterine luminal epithelial cells

Trichlorfon is an organophosphate insecticide widely used in agriculture. Additionally, it is applied to pigs for control of endo- and ectoparasites. Previous studies have shown the effects of trichlorfon in pigs during late stages of gestation; however, little is known about its effects during early pregnancy, including implantation and placentation. We investigated whether trichlorfon affects proliferation and apoptosis of porcine trophectoderm (pTr) and uterine luminal epithelial (pLE) cells. Trichlorfon inhibited the proliferation of pTr and pLE cells, as evidenced by cell cycle arrest, and altered the expression of proliferation-related proteins. In addition, trichlorfon induced cell death and apoptotic features, such as loss of mitochondrial membrane potential and DNA fragmentation, in pTr and pLE cells. Moreover, trichlorfon treatment decreased concentrations of Ca²⁺ in the cytoplasm in both cell lines and increased concentrations of Ca²⁺ in mitochondria of pTr cells. Trichlorfon inhibited the activation of phosphoinositide 3-kinase/AKT and mitogen-activated protein kinase signaling pathways in pTr and pLE cells. Therefore, we suggest that trichlorfon-treated pTr and pLE cells exhibited abnormal cell physiology which might lead to early pregnancy failure.

Use of Calcium Channel Blockers and Risk of Breast Cancer: A Population-based Cohort Study

BACKGROUND

Several observational studies have associated use of calcium channel blockers with an increased risk of breast cancer, but this association remains controversial. The objective of this study was to determine whether these drugs are associated with an increased risk of breast cancer overall, and to assess whether this risk varies with cumulative duration of use.

METHODS

We identified a cohort of 273,152 women newly treated with antihypertensive drugs between 1 January 1995 and 31 December 2009, followed until 31 December 2010, using the UK Clinical Practice Research Datalink. We treated calcium channel blocker use as a time-varying variable, and lagged exposure by 1 year for latency considerations and to minimize reverse causality. We used time-dependent Cox proportional hazards models to estimate adjusted hazard ratios with 95% confidence intervals of incident breast cancer associated with use of calcium channel blockers overall and by cumulative duration of use (<5, 5-10, and ≥10 years).

RESULTS

During 1,567,104 person-years of follow-up, 4,520 women were newly diagnosed with breast cancer (incidence rate: 2.9 per 1,000 per year). Compared with use of other antihypertensive drugs, use of calcium channel blockers was not associated with increased risk of breast cancer overall (hazard ratio: 0.97, 95% confidence interval: 0.91, 1.03). Similarly, there was no evidence of a duration-response relationship in terms of cumulative duration of use (P trend = 0.26).

CONCLUSIONS

The results of this large population-based study indicate that long-term use of calcium channel blockers is not associated with an increased risk of breast cancer.

Ursolic acid induces autophagy in U87MG cells via ROS-dependent endoplasmic reticulum stress

Malignant gliomas are the most common primary brain tumors, and novel ways of treating gliomas are urgently needed. Ursolic acid (UA), a pentacyclic triterpenoid, has been reported to exhibit promising antitumor activity. Here, we evaluated the effects of UA on U87MG cells and explored the underlying molecular mechanisms. The results demonstrated that both G1-phase arrest and autophagy were induced by UA in U87MG cells. Evidence of UA-induced autophagy included the formation of acidic vesicular organelles, increase of autophagolysosomes and LC3-II accumulation. UA was also found to induce ER stress and an increase in intracellular calcium accompanied by ROS production. The increase in free cytosolic calcium induced by UA activated the CaMKK-AMPK-mTOR kinase signaling cascade, which ultimately triggered autophagy. Western blot analysis showed that UA promoted the phosphorylation of PERK and eIF2α; this was followed by the upregulation of the downstream protein CHOP, implying the involvement of the ER stress-mediated PERK/eIF2α/CHOP pathway in glioma cells. Meanwhile, UA activated IRE1α and subsequently increased the levels of phosphorylated JNK and Bcl-2, resulting in the dissociation of Beclin1 from Bcl-2. Furthermore, TUDCA and the silencing of either PERK or IRE1α partially blocked the UA-induced accumulation of LC3-II, suggesting that ER stress precedes the process of autophagy. Additionally, NAC attenuated the UA-induced elevation in cytosolic calcium, ER stress markers and autophagy-related proteins, indicating that UA triggered ER stress and autophagy via a ROS-dependent pathway. Collectively, our findings revealed a novel cellular mechanism triggered by UA and provide a molecular basis for developing UA into a drug candidate.

Reduced cellular Ca(2+) availability enhances TDP-43 cleavage by apoptotic caspases

Accumulation of transactive response DNA binding protein (TDP-43) fragments in motor neurons is a post mortem hallmark of different neurodegenerative diseases. TDP-43 fragments are the products of the apoptotic caspases-3 and -7. Either excessive or insufficient cellular Ca(2+) availability is associated with activation of apoptotic caspases. However, as far as we know, it is not described whether activation of caspases, due to restricted intracellular Ca(2+), affects TDP-43 cleavage. Here we show that in various cell lineages with restricted Ca(2+) availability, TDP-43 is initially cleaved by caspases-3 and -7 and then, also by caspases-6 and -8 once activated by caspase-3. Furthermore, we disclose the existence of a TDP-43 caspase-mediated fragment of 15kDa, in addition to the well-known fragments of 35 and 25kDa. Interestingly, with respect to the other two fragments this novel fragment is the major product of caspase activity on murine TDP-43 whereas in human cell lines the opposite occurs. This outcome should be considered when murine models are used to investigate TDP-43 proteinopathies.

Pro-apoptotic activity of new analog of anthracyclines--WP 631 in advanced ovarian cancer cell line

In this work we investigated the mode of cell death induced by WP 631, a novel anthracycline antibiotic, in the ovarian cancer cell line (OV-90) derived from the malignant ascites of a patient diagnosed with advanced disease. The effects were compared with those of doxorubicin (DOX), a first generation anthracycline. The ability of WP 631 to induce apoptosis and necrosis was examined by double staining with Annexin V and propidium iodide, measurements of the level of intracellular calcium ions and cytochrome c, PARP cleavage. We also investigated the possible involvement of the caspases activation, DNA degradation (comet assay) and intracellular reactive oxygen species (ROS) production in the development of the apoptotic events and their significance for drug efficiency. The results obtained clearly demonstrate that antiproliferative capacity of WP 631 in tested cell line was a few times greater than that of DOX. Furthermore, ovarian cancer cells treated with WP 631 showed a higher mean level of basal DNA damage in comparison to DOX. In conclusion, WP 631 is able to induce caspase - dependent apoptosis in human ovarian cancer cells. Obtained results suggested that WP 631 may be a candidate for further evaluation as chemotherapeutic agents for human cancers.

Activation of apoptotic pathway in normal, cancer ovarian cells by epothilone B

The epothilones, a new class of microtubule-targeting agents, seem to be a very promising alternative to the current strategy of cancer treatment. We have analyzed the aspects of epothilone B (Epo B) on cellular metabolism of tumor (OV-90) and normal (MM 14) ovarian cells. The observed effects were compared with those of paclitaxel (PTX), which is now a standard for the treatment of ovarian cancer. The results provide direct evidence that Epo B is considerably more cytotoxic to human OV-90 ovarian cancer cells than PTX. We have found, that antitumor efficacy of this new drug is related to its apoptosis-inducing ability, which was confirmed during measurements typical markers of the process. Epo B induced changes in morphology of cells, mitochondrial membrane potential and cytochrome c release. Also a slight increase of the intracellular calcium level was observed. Moreover, we have found that ROS production, stimulated by Epo B, is directly involved in the induction of apoptosis via mitochondrial pathway.

The effect of combined exposure of 900 MHz radiofrequency fields and doxorubicin in HL-60 cells

Human promyelocytic leukemia HL-60 cells were pre-exposed to non-ionizing 900 MHz radiofrequency fields (RF) at 12 µW/cm² power density for 1 hour/day for 3 days and then treated with a chemotherapeutic drug, doxorubicin (DOX, 0.125 mg/L). Several end-points related to toxicity, viz., viability, apoptosis, mitochondrial membrane potential (MMP), intracellular free calcium (Ca²⁺) and Ca²⁺-Mg²⁺ -ATPase activity were measured. The results obtained in un-exposed and sham-exposed control cells were compared with those exposed to RF alone, DOX alone and RF+DOX. The results indicated no significant differences between un-exposed, sham-exposed control cells and those exposed to RF alone while treatment with DOX alone showed a significant decrease in viability, increased apoptosis, decreased MMP, increased Ca²⁺ and decreased Ca²⁺-Mg^2+-ATPase activity. When the latter results were compared with cells exposed RF+DOX, the data showed increased cell proliferation, decreased apoptosis, increased MMP, decreased Ca²⁺ and increased Ca²⁺-Mg²⁺-ATPase activity. Thus, RF pre-exposure appear to protect the HL-60 cells from the toxic effects of subsequent treatment with DOX. These observations were similar to our earlier data which suggested that pre-exposure of mice to 900 MHz RF at 120 µW/cm² power density for 1 hours/day for 14 days had a protective effect in hematopoietic tissue damage induced by subsequent gamma-irradiation.

Nifetepimine, a dihydropyrimidone, ensures CD4+ T cell survival in a tumor microenvironment by maneuvering sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA)

Multiple mechanisms have been proposed by which tumors induce T cell apoptosis to circumvent tumor immune-surveillance. Although sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) have long been known to regulate intracellular Ca(2+) homeostasis, few studies have examined the role of SERCA in processes of T lymphocyte survival and activation. In this context it remains largely unexplored as to how tumors jeopardize SERCA function to disable T cell-mediated anti-tumor immunity. Here, we show that human CD4(+) T cells in the presence of tumor conditions manifested an up-regulation of SERCA3 expression that resulted in development of endoplasmic reticulum stress leading to CD4(+) T cell apoptosis. Prostaglandin E(2) produced by the tumor cell plays a critical role in up-regulating SERCA3 by enhancing the binding of its transcription factor Sp1. Gene manipulation and pharmacological approaches further established that an increase in SERCA expression also resulted in subsequent inhibition of PKCα and -θ and retention of NFκB in the cytosol; however, down-modulation of SERCA3 expression by a dihydropyrimidone derivative, ethyl-4-(3-nitro)-phenyl-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5 carboxylate (nifetepimine), protected the CD4(+) T cells from tumor-induced apoptosis. In fact, nifetepimine-mediated restoration of PKC activity resulted in nuclear translocation of p65NFκB, thereby ensuring its survival. Studies further undertaken in a tumor-bearing mice model revalidated the immunoprotective role of nifetepimine. Our present study thus strongly suggests that imbalance in cellular calcium homeostasis is an important factor leading to CD4(+) T cell death during cancer and holds promise that nifetepimine may have the potential to be used as an immunorestoring agent in cancer bearers.

Deficiency of calcium and magnesium induces apoptosis via scavenger receptor BI

AIMS

Cells undergo apoptosis in stressed status such as in intracellular calcium overload or extracellular calcium/magnesium deficiency. The mechanisms of how deficiency of the divalent metal ions induces apoptosis remain to be defined. Scavenger receptor BI (SR-BI) is a high density lipoprotein (HDL) receptor. Recent studies demonstrated that SR-BI is a stress response molecule which induces apoptosis upon serum deprivation. In this study, we assessed our hypothesis that the deficiency of calcium/magnesium induces apoptosis via SR-BI apoptotic pathway.

MAIN METHODS

We employed CHO cell lines expressing vector and SR-BI to test the effect of SR-BI on apoptosis induced by deficiency of calcium, magnesium and zinc in culture medium. The regain of different metal ions in deficient medium was also performed, respectively. Cell death was detected by morphological changes and quantified by LDH cytotoxicity assay. Apoptosis was also assessed by DNA ladder assay and DNA condensation assay. The SR-BIC323G mutant cells which lack the apoptotic activity of SR-BI were employed to verify the SR-BI-dependent effect on calcium/magnesium induced apoptosis.

KEY FINDINGS

The deficiency of calcium/magnesium induced cell apoptosis in CHO-SR-BI cells, but not in CHO-vector cells. Moreover, no apoptotic cell death was observed in SR-BIC323G mutant cells, indicating that the deficiency of divalent metal ions induces apoptosis in a SR-BI-dependent manner. Furthermore, the restoration of calcium or magnesium, but not zinc, protected CHO-SR-BI cells from apoptotic cell death, in a dose-dependent fashion.

SIGNIFICANCE

These findings extend our understanding about how calcium and magnesium deficiency induces apoptosis.

Role of intracellular calcium and S-glutathionylation in cell death induced by a mixture of isothiazolinones in HL60 cells

Previously we reported that brief exposure of HL60 cells to a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one (CMI) and 2-methyl-4-isothiazolin-3-one (MI) shifts the cells into a state of oxidative stress that induces apoptosis and necrosis. In this study, flow cytometric analysis showed that CMI/MI induces early perturbation of calcium homeostasis, increasing cytosolic and mitochondrial calcium and depleting the intracellular endoplasmic reticulum (ER) stores. The calcium chelator BAPTA-AM reduced necrosis and secondary necrosis, the loss of DeltaPsim and S-glutathionylation induced by necrotic doses of CMI/MI, but did not protect against CMI/MI-induced apoptosis, mitochondrial calcium uptake and mitochondrial hyperpolarization. This indicates that increased cytoplasmic calcium does not have a causal role in the induction of apoptosis, while cross-talk between the ER and mitochondria could be responsible for the induction of apoptosis. GSH-OEt pretreatment, which enhances cellular GSH content, reduced S-glutathionylation and cytosolic and mitochondrial calcium levels, thus protecting against both apoptosis and necrosis shifting to apoptosis. Therefore, the degree of GSH depletion, paralleled by the levels of protein S-glutathionylation, may have a causal role in increasing calcium levels. The mitochondrial calcium increase could be responsible for apoptosis, while necrosis is associated with cytoplasmic calcium overload. These findings suggest that S-glutathionylation of specific proteins acts as a molecular linker between calcium and redox signalling.

Pathological apoptosis in the developing brain

More than half of the initially-formed neurons are deleted in certain brain regions during normal development. This process, whereby cells are discretely removed without interfering with the further development of remaining cells, is called programmed cell death (PCD). The term apoptosis is used to describe certain morphological manifestations of PCD. Many of the effectors of this developmental cell death program are highly expressed in the developing brain, making it more susceptible to accidental activation of the death machinery, e.g. following hypoxia-ischemia or irradiation. Recent evidence suggests, however, that activation and regulation of cell death mechanisms under pathological conditions do not exactly mirror physiological, developmentally regulated PCD. It may be argued that the conditions after e.g. ischemia are not even compatible with the execution of PCD as we know it. Under pathological conditions cells are exposed to various stressors, including energy failure, oxidative stress and unbalanced ion fluxes. This results in parallel triggering and potential overshooting of several different cell death pathways, which then interact with one another and result in complex patterns of biochemical manifestations and cellular morphological features. These types of cell death are here called "pathological apoptosis," where classical hallmarks of PCD, like pyknosis, nuclear condensation and caspase-3 activation, are combined with non-PCD features of cell death. Here we review our current knowledge of the mechanisms involved, with special focus on the potential for therapeutic intervention tailored to the needs of the developing brain.

Anti-recoverin antibodies induce an increase in intracellular calcium, leading to apoptosis in retinal cells

Autoantibodies against recoverin, a Ca2+-binding protein found in patients with cancer-associated retinopathy (CAR syndrome), penetrate retinal cells and induce their apoptosis via a mitochondrial pathway. The goal of this study was to investigate whether the entry of anti-recoverin antibody into E1A.NR3 retinal cells causes a change in intracellular Ca2+. Intracellular Ca2+ was measured using the Ca2+-sensitive fluorescent dye Fura-2 AM in living E1A.NR3 retinal cells treated with anti-recoverin antibody Rec-1, patients' autoantibodies, and control rat and human IgG. The exposure of retinal cells to Rec-1 antibody and to the CAR patients' autoantibodies in vitro caused a significant increase in intracellular Ca2+, while non-specific antibodies did not induce such an effect. Co-treatment of the E1A.NR3 cells with Rec-1 in the presence of nifedipine, a L-type Ca2+ channel blocker, significantly suppressed the increase of Ca2+. Treatment with nifedipine also blocked changes in the anti-apoptotic protein bcl-xL and in expressions of the pro-apoptotic protein bax. Nifedipine-treated cells also showed a decrease in cytosolic cytochrome c release and a decrease in caspase 3 activation, compared to cells treated only with Rec-1 antibody. The increase in the antibody-induced Ca2+ is at least in part dependent on extracellular Ca2+. Nifedipine was found to inhibit the entry of Ca2+ into the cells and to protect them from Rec-1-induced apoptosis. Increased levels of intracellular Ca2+ may lead to retinal dysfunction and degeneration in the CAR syndrome. Our results provide a molecular basis for the use of Ca2+ blockers in the treatment of the CAR syndrome.

Alkaline stress-induced apoptosis in human pulmonary artery endothelial cells

The effect of alkaline stress, or an increase in extracellular pH (pHext), on cell viability is poorly defined. Human pulmonary artery endothelial cells (HPAEC) were subjected to alkaline stress using different methods of increasing pHext. Viability and mode of cell death following alkaline stress were determined by assessing nuclear morphology, ultrastructural features, and caspase-3 activity. Incubation of monolayers in media set to different pHext values (7.4-8.4) for 24-h induced morphological changes suggesting apoptosis (35-45% apoptotic cells) following severe alkaline stress. The magnitude of apoptosis was related to the severity of alkaline stress. These findings were confirmed with an assessment of ultrastructural changes and caspase-3 activation. While there was no difference in the intracellular calcium level ([Ca(2+)](i)) in monolayers set to pHext 7.4 versus 8.4 following the first hour of alkaline stress, blockade of calcium uptake with the chelator, EGTA, potentiated the magnitude of apoptosis under these conditions. Potentiation of apoptosis was reduced by calcium supplementation of the media. Finally, alkaline stress was associated with an increase in intracellular pH. This is the first report of apoptosis following alkaline stress in endothelial cells in the absence of other cell death stimuli.

Anticancer activity of sodium caffeate and its mechanism

AIM

To study the anticancer activity of sodium caffeate (SC).

METHODS

A nucleoside transport assay was used to analyze the inhibitory effects of SC on nucleoside rescue. The MTT assay was used to measure cell proliferation. Flow cytometry was used to measure the apoptosis of BEC-7402 induced by SC and the cell cycle distribution change. Western blotting analysis was employed to investigate Bcl-2, caspase and Bax expression. Intracellular Ca2+ and mitochondrial membrane potential were determined by flow cytometry. In vivo anti-tumor activity was measured using a tumor transplantation model in mice.

RESULTS

SC inhibited the nucleoside transport of BEL-7402 cells with an IC(50) of 1.02 microg/mL. SC inhibited tumor cell proliferation with an IC50 between 100 microg/mL and 200 microg/mL. SC induced BEL-7402 cell apoptosis in a time- and dose-dependent manner, which was induced by arresting cells in S phase. The in vivo study showed that tumor growth was inhibited in a dose-dependent manner. Activated caspase-3 and Bax expression were up-regulated after treatment with SC, while Bcl-2 expression was down-regulated. Intracellular Ca2+ was increased while mitochondrial membrane potential was decreased by SC.

CONCLUSION

SC is a new anticancer agent with promising potential.

Role of store-dependent influx of Ca2+ and efflux of K+ in apoptosis of CHO cells

Agents mobilising Ca(2+) from the endoplasmic reticulum are known to activate apoptosis. Whatever means are used, the release of Ca(2+) is often followed by a store-dependent entry of Ca(2+). Whether apoptosis is triggered by the depletion of the stores or by the subsequent store-dependent entry of Ca(2+) is still a matter of controversy. Here we studied apoptosis in CHO cells transfected with the rat neurotensin (NT) receptor, in which the store-dependent entry of Ca(2+) is abolished by repressing the transient receptor potential channel 2 (TRPC2) by an antisense oligonucleotide strategy (TRPC2(-) cells) [Cell Calcium 30 (2001) 157]. When stimulated with thapsigargin (TG), apoptosis occurred in both TRPC2(+) and TRPC2(-) cells but 12h earlier in TRPC2(+) cells, suggesting that store-dependent entry of Ca(2+) can accelerate the process. The expression and localisation of caspase-12, an enzyme that has been involved in the apoptosis triggered by a stress on the endoplasmic reticulum, was not different in TRPC2(+) and TRPC2(-) cells. On the contrary, the expression of GADD153 (Growth Arrest and DNA Damage inducible gene 153) triggered by TG treatment depended on external Ca(2+) and occurred earlier in TRPC2(+) than in TRPC2(-) cells. In these cells, we also noted the presence of K(+) channels activated by Ca(2+) (K(Ca) channels). Stimulation of TRPC2(+) cells with TG or with NT triggered a long sustained K(+) current, parallel to [Ca(2+)](i) transients, and resulting in a sustained hyperpolarisation of the cell membrane. K(+) current and hyperpolarisation were transient and not sustained in TRPC2(-) cells. Inhibition of K(Ca) channels with charybdotoxin dramatically reduced the K(+) current and also significantly brought down the level of apoptosis, suggesting that a prolonged efflux of K(+) could be involved in the apoptosis process. We conclude that in CHO cells, store-dependent entry of Ca(2+) can accelerate apoptosis by accelerating the expression of GADD153 and by inducing a prolonged efflux of K(+) out of the cell.

Constitutive opsin signaling: night blindness or retinal degeneration?

A subset of genetic mutations in photoreceptor-specific genes results in abnormally prolonged activation of transducin-mediated photosignaling in rod cells. In humans and animal models, these mutations cause visual dysfunctions ranging from a mild stationary night blindness to severe, early-onset retinal degeneration. There are mechanistic differences between mutations causing night blindness and those causing retinal degeneration. Here, we hypothesize that mutations causing continuous activation of the visual cascade as the result, for example, of the inability of the photoreceptor to regenerate rhodopsin, lead to retinal degeneration; those mutations that can terminate signaling, even if only partially and intermittently, slow the rate of degeneration sufficiently to give rise to stationary night blindness. Furthermore, we hypothesize that a prolonged decrease in intracellular calcium concentration resulting from persistent activation is responsible for triggering apoptotic rod-cell death.

Inhibition of apoptosis in pulmonary endothelial cells by altered pH, mitochondrial function, and ATP supply

We investigated the effect of altered extracellular pH, mitochondrial function, and ATP content on development of apoptosis in human pulmonary artery endothelial cells after treatment with staurosporine (STS). STS produced a concentration- and time-dependent increase in caspase-3 activity in pH 7.4 medium that reached a peak at 6 h. The increase in caspase activity was associated with significant DNA fragmentation. Fluorescent imaging of treated monolayers in pH 7.4 medium with Hoechst-33342-propidium iodide demonstrated a large percentage of apoptotic cells ( approximately 40%) with no evidence of necrosis. Caspase activity, DNA fragmentation, and percentage of apoptotic cells were reduced after STS treatment in acidic media (pH 7.0 and 6.6). The Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM inhibited STS-induced apoptosis, whereas the rise in intracellular Ca2+concentration in STS-treated cells in pH 7.4 medium was reduced in pH 7.0 medium. These results suggest that one mechanism for inhibitory effects of acidosis may be a pH-induced alteration in Ca2+ signaling. Treatment with STS in the presence of oligomycin (10 microM), an inhibitor of the mitochondrial F(0)F(1)-ATPase, in glucose-free media abolished caspase activation and DNA fragmentation in association with severe ATP depletion ( approximately 2% of control cells). Imaging demonstrated a change in the mode of cell death from apoptosis to necrosis under these conditions. This change was linked to the level of ATP depletion, because STS treatment in the absence of glucose or the presence of oligomycin in media with glucose still leads to apoptosis in the presence of only moderate ATP depletion. These results demonstrate that pH, mitochondrial function, and ATP supply are important variables that regulate STS-induced apoptosis in human pulmonary artery endothelial cells.

Increased cytosol Ca(2+) and type 1 programmed cell death in Bcl-2-positive U937 but not in Bcl-2-negative PC-3 and Panc-1 cells induced by the 5-lipoxygenase inhibitor MK 886

MK 886, an arachidonic acid-related analog which inhibits the enzyme, 5-lipoxygenase by an indirect mechanism involving the 5-lipoxygenase activating protein, rapidly increased U937 cytosol Ca(2+), much of which localized around the cell nuclei. Five-lipoxygenase activity was not directly involved since the direct redox-dependent 5-LPOx inhibitor, SC-41661A did not increase Ca(2+). U937 cells subsequently undergo classic type 1 programmed cell death. At least initially the ionized calcium originates from internal stores. Coincident with the rise in U937 ionized calcium, MK 886 rapidly increased reactive oxygen species and reduced mitochondrial membrane potential, as judged by several fluorescent probes. The Ca(2+) response of myeloid leukemia-derived HL-60 cells to MK 886 was similar and both cell lines express Bcl-2 protein. Bcl-2-negative Panc-1 and PC-3 cells did not respond to MK 886 with a Ca(2+) signal but did develop oxidative stress and a decline in mitochondrial membrane potential; these events are thought to contribute to the inhibition of cell proliferation and induction of a type 2 PCD. In addition to its marked inhibition of Bcl-2 mRNA synthesis, an interesting hypothesis is that MK 886, serving as a low molecular weight ligand, either by direct or indirect inhibition of U937 Bcl-2 protein function, possibly related to an ion channel activity, alters the distribution of intracellular, possibly nuclear Ca(2+), thereby promoting the development of type 1 programmed cell death.

Papaverine induces apoptosis in vascular endothelial and smooth muscle cells

Papaverine is a vasodilator commonly used in the treatment of vasospasmic diseases such as cerebral spasm associated with subarachnoid hemorrhage, and in the prevention of spasm of coronary artery bypass graft by intraluminal and/or extraluminal administration. In this study, we examined whether papaverine in the range of concentrations used clinically causes apoptosis of vascular endothelial and smooth muscle cells. Apoptotic cells were identified by morphological changes and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay. In porcine coronary endothelial cells (EC) and rat aortic smooth muscle cells (SMC), papaverine at the concentration of 10(-3) M induced membrane blebbing within 1 hour of incubation. Nuclear condensation and fragmentation were found after 24 hours of treatment. The number of apoptotic cells stained with the TUNEL method was significantly higher in the EC and the SMC after 24 hours of incubation with papaverine at the concentrations of 10(-4) and 10(-3) M than their respective controls. Acidified saline solution (pH 4.8, as control for 10(-3) M papaverine hydrochloride) did not cause apoptosis in these cells. These results showed that papaverine could damage endothelial and smooth muscle cells by inducing changes which are associated with events leading to apoptosis. Since integrity of endothelial cells is critical for normal vascular function, vascular administration of papaverine for clinical use, especially at high concentrations (> or = 10(-4) M), should be re-considered.

Calretinin and calbindin D-28k delay the onset of cell death after excitotoxic stimulation in transfected P19 cells

In some neurological diseases, injury to neurones reflects an over-stimulation of their receptors for excitatory amino acids. This response may disturb the Ca(2+)-homeostasis and lead to a pronounced and sustained increase in the intracellular concentration of this ion. On the basis of data derived from correlative studies, calcium-binding proteins have been postulated to play a protective role in these pathologies. We tested, directly, the capacity of the three calcium-binding proteins calretinin (CR), calbindin D-28k (CB) and parvalbumin (PV) to buffer [Ca(2+)], and to protect cells against excitotoxic death. We used P19 murine embryonic carcinoma cells, which can be specifically induced (by retinoic acid) to transform into nerve-like ones. The differentiated cells express functional glutamate-receptors and are susceptible to excitotoxic shock. Undifferentiated P19-cells were stably transfected with the cDNA for CR, CB or PV, induced to differentiate, and then exposed to NMDA, a glutamate-receptor agonist. The survival rates of clones expressing CR, CB or PV were compared with those of untransfected P19-cells using the lactate-dehydrogenase assay. CR- and CB-expressing cells were protected from death during the first 2 h of exposure to NMDA. This protection was, however, transient, and did not suffice to rescue P19-cells after prolonged stimulation. Two of the three PV-transfected clones raised were vulnerable to NMDA-induced excitotoxicity; the third, which expressed the lowest level of PV, was protected to a similar degree as that found for the CR- and CB-transfected clones. Our results indicate that in the P19-cell model, CR and CB can help to delay the onset of cell death after excitotoxic stimulation.

The clinical and biochemical effects of propofol infusion with and without EDTA for maintenance anesthesia in healthy children undergoing ambulatory surgery

We conducted this randomized, double-blinded, comparative, parallel-group study to determine whether adding EDTA to propofol would affect the clinical profile, calcium and magnesium homeostasis, or renal function in healthy children. After the induction of anesthesia with halothane, 69 ambulatory surgical patients (1 mo to <17 yr old), received propofol without EDTA (n = 33) or propofol with EDTA (n = 36). Blood samples were obtained for the measurement of ionized calcium, ionized magnesium, and laboratory indicators of renal function. Hemodynamic measurements, recovery, and adverse events were recorded. Propofol with EDTA produced no significant effects on clinical efficacy or renal function. Propofol and propofol EDTA produced a statistically significant decrease from baseline in serum concentrations of ionized calcium and magnesium during infusion (P<0.05), but with no apparent clinical effect. Hemodynamic measurements generally remained stable and were similar for both groups. Statistically significant changes in systolic blood pressure, mean arterial pressure, and heart rate were not considered clinically significant. Adverse events were mild or moderate. The addition of EDTA does not alter the clinical profile of propofol in pediatric ambulatory surgical patients. With or without EDTA, propofol is associated with a decrease in ionized calcium with no apparent clinical effect.

IMPLICATIONS

The addition of EDTA does not alter the clinical profile of propofol in pediatric ambulatory surgical patients. With or without EDTA, propofol is associated with a decrease in ionized calcium with no apparent clinical effect.

Involvement of L-DNase II in nuclear degeneration during chick retina development

During the development of the neural retina, 50% of the neurons die physiologically by apoptosis. In the chick embryo, the apoptotic wave starts at E8 and ends at E18, with a peak at E11. The onset of apoptosis is accompanied by the activation of several degradative enzymes. Among these, the activation of the endonucleases leads to the degradation of the genomic DNA of the cell which is thought to be the final event in apoptosis. Here, we have investigated the endonucleases activated during apoptosis associated with retinal development. We have found that Ca2+-Mg2+-dependent endonucleases, as well as acid endonucleases are activated. The results obtained in vitro using purified nuclei from chicken retina indicate that the endonuclease activity resulting from the activation of L-DNase II, an acid DNase is responsible for most of the DNA degradation observed in these cells.

First and second messenger role of calcium. Survival versus apoptosis in serum-free cultured granulosa explants

In order to elucidate the causal relationship between increased intracellular free calcium ([Ca2+]i) and induction of apoptosis, serum-free cultured granulosa cell (GC) explants were subjected to various experimental protocols interfering with normal Ca2+ homeostasis. Modulation of apoptotic indices was calculated on DAPI-stained GC explants. In some experiments [Ca2+]i was measured with the Ca2+ probe fura-2 in combination with epifluorescence microscopy. Buffering of [Ca2+]i with BAPTA-AM resulted in inhibition of apoptosis, while increasing extracellular Ca2+ (otherwise called [Ca2+]e load) resulted in a biphasic response characterized by an initial inhibitory effect on apoptosis followed by a delayed phase of increased apoptosis that became apparent at 4 h after withdrawal of the [Ca2+]e load. The initial inhibitory effect of the [Ca2+]e load on apoptosis was dependent on the concentration of the load (range 2-50 mM), was augmented when the [Ca2+]e load was applied in the presence of the Ca2+ channel blocker methoxyverapamil, and was mimicked by applying Mg2+ and Gd3+, two Ca(2+)-receptor agonists. These observations point towards the involvement of an extracellular Ca(2+)-sensing receptor (CaR). Measurements of [Ca2+]i showed that the ion was increased just after [Ca2+]e load, followed by recovery that was complete at 2 h after the load. Collectively these data suggest that a [Ca2+]e load initiates apoptosis, becoming manifest 4 h later, by the provoked [Ca2+]i increase, and this effect is preceded by an apoptosis-inhibiting phase presumably involving CaR activation. We conclude that Ca2+ may act as a first (extracellular) messenger promoting cell survival and as a second (intracellular) messenger activating the cell death pathway.

Mitochondrial Ca(2+)homeostasis in the regulation of apoptotic and necrotic cell deaths

Using distinct models of apoptosis and necrosis, we have investigated the effect of mitochondrial Ca(2+)(Ca(m)) homeostasis in the regulation of cell death in neuroblastoma cells as well as cardiac myocytes. The steady state level of Ca(m)was determined as the FCCP-releasable Ca(2+). Culturing cells with low concentration of extracellular Ca(2+)(Ca(o)) or with EGTA triggered an early reduction in both the Ca(m)store and the membrane potential (DeltaPsi(m)). This was followed by the detection of cytochrome c release, caspase activation, and apoptosis. Inhibitors of the mitochondrial permeability transition pore such as cyclosporin A and Bcl-2 blocked the release of Ca(m)and inhibited apoptosis. In contrast, mitochondrial Ca(2+)overload resulted in necrotic cell death. Culturing cells in the presence of excess Ca(o)led to increased Ca(m)load together with a decrease of DeltaPsi(m)that reached maximum at 1 h, with necrosis occurring at 2 h. While the decline of Ca(m)and DeltaPsi(m)was a coupled reaction for apoptosis, this relationship was uncoupled during necrosis. Clonazepam, a relatively specific inhibitor of the mitochondrial Na/Ca exchanger, was able to protect the cells from necrosis by reducing Ca(m)overload. Importantly, combination of clonazepam and cyclosporin showed a cooperative effect in further reducing the Ca(m)overload and abolished cell death. The data imply the participation of Ca(m)homeostasis in the regulation of apoptosis and necrosis.

DNases and apoptosis

Here we review the different apoptotic DNases. From a functional point of view, DNases implicated in apoptosis may be classified into three groups: the Ca2+/Mg2+endonucleases, the Mg2+-endonucleases, and the cation-independent endonucleases. The first group includes DNase I which has no specificity for the linker region, DNase gamma which has some homology with DNase I, and other DNases which cleave DNA in the linker region. Both DNase I and DNase gamma have been cloned. The other nucleases of this category have dispersed molecular weights. Their sequences are unknown and it is difficult to determine their role(s) in apoptosis. It seems that different pathways are present and that these nucleases may be activated either by caspases or serine proteases. The caspase 3 activated DNase (CAD, CPAN, or DFF40) belongs to the Mg2+-dependent endonucleases. DNase II belongs to the third group of acid endonucleases or cation-independent DNases. We have shown the involvement of DNase II in lens cell differentiation. Recently, the molecular structure of two different enzymes has been elucidated, one of which has a signal peptide and appears to be secreted. The other, called L-DNase II, is an intracellular protein having two enzymatic activities; in its native form, it is an anti-protease, and after posttranslational modification, it becomes a nuclease.Key words: endonucleases, apoptosis, caspases, serine proteases.

Nifedipine does not induce but rather prevents apoptosis in cardiomyocytes

The potential of Ca(2+) channel antagonists, particularly nifedipine, to cause apoptotic cell death has been controversial and is of considerable importance for cardiomyocytes as loss of these cells is an important component of the pathophysiology leading to heart failure. To examine the hypothesis that nifedipine induces cell death and modulates calcium-induced apoptosis, cardiomyocytes in culture from embryonic chick hearts, that readily manifest apoptosis, were studied. Apoptosis was evaluated by fluorescent activated cell sorting (FACS) analysis and by quantitative analysis of DNA fragmentation by an enzyme-linked immunosorbent assay (ELISA) specific for histone-associated DNA fragments of mono- and oligonucleosome size. Cell death was evaluated by using the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assay. Cardiomyocytes were treated with various concentrations of nifedipine over a concentration range relevant to serum concentrations in man. Nifedipine, 1 to 100 microM, did not produce cell death in cardiomyocytes. There was no evidence of apoptosis on FACS analysis of cardiomyocytes stained with fluoresceine diacetate or propidum iodide (PI). Neither was there any evidence of apoptotic nuclei on PI staining of permeabilized cardiomyocytes treated with nifedipine. In contrast, DNA fragmentation consistent with apoptosis was induced in a significant (P<0.05) concentration-dependent manner, by increases in extracellular Ca(2+) concentration ([Ca(2+)](o)). Importantly, nifedipine reduced DNA fragmentation produced by increased [Ca(2+)](o). Furthermore, nifedipine blocked calcium-induced cell death as high [Ca(2+)](o) significantly (P<0. 05) reduced cell viability. These data indicate that nifedipine does not induce apoptosis in cardiomyocytes rather apoptosis in cardiomyocytes is under regulatory control by Ca(2+) and nifedipine can antagonize Ca(2+)-mediated apoptotic cell death.

Calcium channel blockers, apoptosis and cancer: is there a biologic relationship?

Calcium channel blockers (CCBs) represent a chemically and pharmacologically diverse group of agents that are widely used for the treatment of hypertension and angina. A small number of retrospective, observational analyses have raised concern about a potential causal link between CCB use and an increased risk for cancer development. Despite the absence of cancer findings in extensive preclinical studies, it has been proposed that CCBs may work differently in humans by interfering with apoptosis, leading to an increased potential for abnormal cell proliferation and tumor growth. This biologic hypothesis has attracted considerable attention in the medical community but has not been critically evaluated. An analysis of the basic and clinical literature was conducted to examine biologic relationships among cell Ca2+ modulation, apoptosis, and cancer. In addition to a comprehensive review of the cellular and animal data, the results of large observational studies were included in this analysis. Results of this review demonstrated that the effects of CCBs on apoptosis are complex as both increases and decreases in intracellular Ca2+ have been linked to this form of programmed cell death. Most studies show that an effect (either positive or negative) of CCBs on apoptosis requires doses in the supra-pharmacologic range, and are therefore not clinically relevant. Results of large and methodologically robust observational studies fail to provide support for the hypothesis that CCB use is associated with an increased susceptibility for cancer incidence. A comprehensive analysis of the basic and clinical evidence does not support a causal relationship between the therapeutic use of CCBs and an increased incidence of cancer development as a result of interfering with apoptosis.

Effects of calcium channel blockers on cellular apoptosis: implications for carcinogenic potential

BACKGROUND

A small number of well-publicized, retrospective epidemiologic reports have suggested a causal relation between the use of calcium channel blockers (CCBs) for the treatment of hypertension and an increased risk for cancer. The biologic mechanism proposed to explain this possible relation is that CCBs interfere with apoptosis, an active cell death process required for the regulation of normal cell populations in the body. Because an elevation in cellular calcium (Ca2+) is thought to be involved in apoptosis, it has been argued that CCBs could inhibit apoptosis, leading directly to tumor promotion.

METHODS

A comprehensive and critical review of the scientific literature was conducted specifically to evaluate the effects of pharmacologic CCBs on apoptosis and tumor development in various experimental models.

RESULTS

A review of the scientific literature revealed that CCBs have complex and often contradictory effects on cellular apoptosis. In various experimental models of cancer, CCBs did not promote neoplastic growth. By contrast, CCB treatment was associated with an inhibition of tumor growth in certain models of neoplasia and was also an effective adjuvant therapy in the treatment of certain drug-resistant tumors. Additional large epidemiologic studies have failed to support the hypothesis that CCB use is associated with an increased susceptibility for cancer.

CONCLUSIONS

A biologic link between the use of CCBs and increased human risk for cancer development as a result of modulating cellular apoptosis is not supported by the scientific literature.

The effects of nitrogen-containing bisphosphonates on human epithelial (Caco-2) cells, an in vitro model for intestinal epithelium

Nitrogen-containing bisphosphonates (N-PCP) are bisphosphonates with an increased antiresorptive potency. Aminobisphosphonates, N-PCPs with an amino group, can cause nonspecific gastrointestinal complaints. It is not known whether these side effects are specific for these bisphosphonates or for the whole class of N-PCPs. In this study, we investigated the effects of two aminobisphosphonates (pamidronate and alendronate) and a structurally similar N-PCP (olpadronate) and their three respective calcium complexes on the viability and the intracellular calcium concentration ([Ca2+]i) of cultured Caco-2 cells a model for intestinal epithelium. These cells were also examined for apoptosis or necrosis. In the presence of calcium, pamidronate and alendronate were toxic to the cells, with pamidronate being more toxic than alendronate. Olpadronate induced toxicity only at concentrations more than ten times higher than the toxic concentrations of pamidronate. In the absence of calcium definite signs of toxicity were observed only with pamidronate at clinically relevant concentrations. The complexes of pamidronate and alendronate with calcium were considerably less soluble than the olpadronate calcium complex. There were no signs of apoptosis. [Ca2+]i was transiently raised after treatment with the N-PCPs. Doses at which responses were seen were, respectively, 0.02 mM (pamidronate), 0.3 mM (alendronate), and 2 mM (olpadronate). The peak of response was slightly greater after pamidronate treatment than after alendronate or olpadronate, respectively. In conclusion pamidronate, either as an ion or as a calcium complex, is the most toxic of the bisphosphonates tested for Caco-2 cells. Alendronate was less toxic while olpadronate was the least toxic in presence of calcium. The solubility of the bisphosphonate complexes with calcium may account for these differences in toxicity.

A relationship between 5-lipoxygenase-activating protein and bcl-xL expression in murine pro-B lymphocytic FL5.12 cells

Inhibitors of 5-lipoxygenase-activating protein (FLAP) have been found to induce apoptosis. The current study examined the expression of FLAP and bcl family proteins and the induction of apoptosis in interleukin-3-dependent control and bcl-xL-overexpressing FL5.12 cell lines after treatment with MK886, a specific FLAP inhibitor. FL5.12 cells contained a substantial amount of FLAP protein and mRNA but surprisingly had no measurable 5-lipoxygenase protein or 5-, 12-, or 15-lipoxygenase activity. The basal level of FLAP protein in cells overexpressing bcl-xL was 70% less than in controls. FLAP disappeared 4 h after withdrawal of interleukin-3 in bcl-xL cells but not in control cells, which underwent apoptosis. A dose- and time-response study revealed that 5 nmol of MK886/10(6) cells was sufficient to induce apoptosis both in control and bcl-xL cells, respectively, but to different degrees. bcl-xL and bcl-2 proteins, but not bax or FLAP, were decreased by 4 h after 5 nmol of MK886/10(6) cells in both cell lines, although the higher levels of bcl-xL in overexpressors took longer to disappear. This early loss of bcl-xL and bcl-2 was not attributable to generalized proteolysis, as shown by Coomassie Blue staining and by the maintenance of bax. Caspase-3 was activated 2 h after MK886 treatment in control cells but not in bcl-xL cells. Inhibition of caspase-3 decreased MK886-induced apoptosis by 50% in control cells. Inhibition of this caspase after MK886 treatment was unable to prevent the loss of bcl-xL in control cells but did provide partial protection for the loss of the transfected form, but not the endogenous form, in overexpressing cells. These data indicate that MK886 induces extensive apoptosis that is partially caspase-3 dependent and may be related to a rapid loss of bcl-xL. Although caspase-3 inhibitors had no effect on the loss of bcl-xL, other caspases or protease systems may still be involved. The absence of 5-lipoxygenase in cells containing FLAP, the lower level of FLAP in bcl-xL cells, the apoptosis-inducing activity of MK886, and the rapid loss of bcl-xL and bcl-2 proteins after treatment with MK886 strongly indicate that FLAP has activities unrelated to lipoxygenase and suggest a possible functional or regulatory link between these proteins, which share similar subcellular localizations.

Monoamine and iron-related toxicity: from "serotonin-binding proteins" to lipid peroxidation and apoptosis in PC12 cells

1. Monoamines do not form coordination bonds with a preformed iron-serotonin-binding protein (SBP) complex, as initially believed. Instead, metals oxidize the monoamines either directly (manganese, copper) or by oxygen free radical formation (iron), the oxidation products bind covalently to SBP and the conjugates are able to undergo redox cycling. These interactions are denoted as a "molecular oxidative mechanism." 2. Dopamine in combination with iron induces lipid peroxidation and apoptosis in PC12 cells by a stress oxidative-Ca2+ independent mechanism. 3. Dopamine-iron cytotoxicity may have relevance to an understanding of the mechanism by which dopaminergic neurons are eroded in some neurodegenerative disorders.

Non-small-cell lung carcinoma cells invade human bronchial mucosa in vitro

To study invasion of lung cancer in vitro a novel three-dimensional coculture assay consisting of living human tissues has been developed. Multicellular spheroids initiated from a new large-cell lung carcinoma cell line (GaL23), found to be invasive in immunodeficient mice, were confronted with precultured bronchial fragments derived from mucosal biopsies obtained during routine fiberoptic bronchoscopy. The bronchial fragments consist of a stromal core with scattered fibroblasts covered by a continuous surface epithelium resting on a basal lamina. During the first 2 wk of confrontation, a gradual retraction of the bronchial epithelium with subsequent adhesion of the tumor cells to the underlying basal lamina occurred. The following week, a limited invasion of tumor cells into the bronchial stroma was seen. To facilitate the entrance of tumor cells through the mucosal surface, the surface epithelium was removed prior to coculture by ethylenediaminetetraacetic acid (EDTA) buffer treatment. Upon confrontation, GaL23 cells then rapidly attached to and migrated on the exposed basal lamina and an increasing number of tumor cells was seen in the stroma during the first week of culture. This model offers opportunities for studying mechanisms of lung cancer adhesion, migration, and invasion using human bronchial mucosa as the natural target tissue.

Altered [Ca2+] homeostasis in PC12 cells after nerve growth factor deprivation

[Ca2+]i homeostasis in individual PC12 cells after elevated [K+]o was studied by ratiometric microscopy, during nerve growth factor (NGF) deprivation. A significantly lower number of cells responded with an increased [Ca2+]i in the NGF deprived condition. Moreover, the responding cells were more deficient in regulating their [Ca2+]i back to control levels, after the transient peak. This suggests that differentiated neurons do not traverse the apoptotic program homogeneously with regard to their [Ca2+]i regulation and that NGF deprived PC12 cells have more difficulties to reduce their [Ca2+]i after influx of [Ca2+]o.

Effects of integrins on proliferation and apoptosis of renal epithelial cells after acute injury

We sought to determine the importance of integrins for recovery after acute tubular injury and to investigate the signal transduction pathways for integrin effects on cell cycle regulation involving proliferation and apoptosis. Primary cultures of rat renal proximal tubule epithelial cells were exposed to a superoxide-generating system to induce injury in the absence of overt necrosis. Integrin function was antagonized by the integrin recognition sequence tetrapeptide Gly-Arg-Gly-Asp (GRGD) or monoclonal antibody to beta 1-integrin. Injured cells had reduced thymidine uptake compared with normal cells. The presence of GRGD during recovery from injury caused a further 44% reduction in DNA synthesis but did not affect DNA synthesis in normal cells. Injured cells had an increased proportion of apoptosis that was further accentuated by exposed to GRGD during recovery. Integrin antagonism also stimulated apoptosis in uninjured cells. To investigate signal transduction mechanisms for this effect of integrins, inhibitors and activators of protein tyrosine kinase (PTK) and protein kinase C (PKC) were evaluated. Activation of PKC stimulated cellular proliferation, whereas inhibitors of PKC and PTK had no significant effect. Genistein, a PTK inhibitor, induced apoptosis in normal cells, mimicking the effect of integrin inhibition. On the other hand, PMA, an activator of PKC, prevented cells from becoming apoptotic when exposed to injury plus GRGD. The phosphorylation status of intracellular proteins was evaluated by immunoblotting with antiphosphotyrosine antibody. A similar pattern of decreased phosphorylation was observed after either integrin inhibition, injury, both, or PTK inhibition. These findings suggest that kinase cascades are involved in the effects of integrins on renal epithelial cell proliferation and apoptosis. After injury, an interaction between cells and the extracellular matrix is required for cells to proliferate and contribute to repair rather than to enter an apoptotic pathway.

Involvement of extracellular calcium in phosphatidylserine exposure during apoptosis

The appearance of phosphatidylserine (PS) on the outer surface of apoptotic cells is an important signal for their ingestion. In platelets, elevation of intracellular Ca2+ with thapsigargin can trigger large amounts of PS exposure within minutes. We detected PS exposure in U937 promonocytes and Jurkat T-cells after incubation with thapsigargin, but in only 10% of the cells, and it took up to 6 h to occur. Tumor necrosis factor and anti-Fas antibody rapidly trigger apoptosis in these cells, and chelation of extracellular Ca2+ with 5 mM EGTA inhibited PS exposure by 65% and 50%, respectively. Chelation of intracellular Ca2+ with BAPTA-AM had no effect. Other parameters of apoptosis, including cell blebbing, shrinkage, nuclear fragmentation, activation of the ICE-like proteases, and fodrin cleavage, were not inhibited by extracellular EGTA. We conclude that while an elevation of intracellular Ca2+ is an ineffective trigger of apoptosis in the cells investigated, extracellular Ca2+ is required for efficient PS exposure during apoptosis.

Intracellular calcium stores are not required for Bcl-2-mediated protection from apoptosis

The ability of Bcl-2 to inhibit cell death is well documented but its mechanism of action remains elusive. Recent reports have suggested that Bcl-2 prevents apoptosis by inhibiting the release of Ca2+ from the thapsigargin-sensitive Ca2+ store. The mobilization of Ca2+ from this store has been implicated as a signal regulating apoptotic cell death induced by glucocorticoids and by interleukin-3 withdrawal. The present study was designed to determine if Bcl-2 would still inhibit apoptosis after depletion of intracellular Ca2+ stores. We compared the response of two Chinese hamster ovary cell lines (5AHSmyc and 5A300bcl-2.2) following incubation with the calcium ionophore ionomycin to deplete intracellular Ca2+ stores. Continued incubation of 5AHSmyc cells in calcium-free media induced substantial apoptotic DNA fragmentation within 4 h and >95% loss of viability within 48 h. However, 5A300bcl-2.2 cells showed no evidence of DNA fragmentation or loss of viability over the same time period. Intracellular Ca2+ was analyzed with the Ca2+-sensitive fluorescent dye INDO-1 and confirmed that ionomycin was capable of releasing Ca2+ from intracellular stores in both cell lines. These results show that depletion of intracellular Ca2+ stores induces apoptosis and that these Ca2+ stores are not required for the protection afforded by Bcl-2.

Pasteurella haemolytica leukotoxin induces bovine leukocytes to undergo morphologic changes consistent with apoptosis in vitro

Infection of the bovine lung with Pasteurella haemolytica results in an acute respiratory disorder known as pneumonic pasteurellosis. One of the key virulence determinants used by this bacterium is secretion of an exotoxin that is specific for ruminant leukocytes (leukotoxin). At low concentrations, the leukotoxin can activate ruminant leukocytes, whereas at higher concentrations, it inhibits leukocyte functions and is cytolytic, presumably as a result of pore formation and subsequent membrane permeabilization. We have investigated the possibility that the activation-inhibition paradox is explained in part by leukotoxin-mediated apoptosis (i.e., activation-induced cell death) of bovine leukocytes. Incubation of bovine leukocytes with P. haemolytica leukotoxin caused marked cytoplasmic membrane blebbing (zeiosis) and chromatin condensation and margination, both of which are hallmarks of apoptosis. The observed morphologic changes in bovine leukocytes were leukotoxin dependent, because they were significantly diminished in the presence of an anti-leukotoxin monoclonal antibody. In addition, bovine leukocytes incubated with culture supernatant from a mutant strain of P. haemolytica that does not produce any detectable leukotoxin failed to exhibit the morphologic changes characteristic of cells undergoing apoptosis. These observations may represent an important mechanism by which P. haemolytica overwhelms host defenses, contributing to the fibrinous pleuropneumonia characteristic of bovine pasteurellosis.

Differential effects of phorbol ester on apoptosis in HL-60 promyelocytic leukemia cells

The role of the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) in apoptosis of HL-60 cells was investigated. PMA inhibited DNA fragmentation induced by thapsigargin (TG) and 4-bromo-calcium ionophore (Br-A23187). The inhibitory effect of PMA was concentration-related and was abolished by a specific PKC inhibitor, bisindolylmaleimide (GF109203X. In addition TG-induced apoptosis was decreased in cells in which PKC activity was down-regulated by long-term pretreatment with PMA. These results indicate that PKC activation by PMA inhibits HL-60 cell apoptosis induced by TG and Br-A23187, and that this inhibition is not influenced by the down-regulation of PKC. However, PMA did not inhibit DNA fragmentation induced by 1-beta-D-arabinofuranosylcytosine (Ara-C) and cycloheximide. PMA suppressed TG- or Br-A23187. Our results indicate that PKC participates in the regulation of apoptosis only by some pathways. Down-regulation of PKC is not responsible for the diverse effects of PKC activators on apoptosis. The effect of a PKC modulator on apoptosis is dependent upon interaction with individual apoptotic stimulus.

In vivo studies of cadmium-induced apoptosis in testicular tissue of the rat and its modulation by a chelating agent

In vivo CdCl2-induced apoptotic DNA fragmentation in the testes of the male Wistar rat has been demonstrated on agarose gel. Characteristic DNA migration patterns (laddering) provide evidence of apoptosis (programmed cell death) in testicular tissue of rats administered CdCl2 at a level of 0.03 mmol/kg 48 h previously. Evidence that administration of an appropriate cadmium chelating agent within the first 24 h can suppress some or all of the apoptotic changes in testicular DNA has also been obtained for the first time. A greater reduction in apoptosis is observed as the interval between the administration of the cadmium and that of the chelating agent is shortened. Administration of monoisoamyl meso-2,3-dimercaptosuccinate (Mi-ADMS) to male Wistar rats given CdCl2 is effective in the modulation of the typically apoptotic DNA fragmentation and associated histopathologic injury when the antagonist is given within approximately 1 h after the CdCl2 exposure. When the antagonist is given at later times there is a progressively more pronounced degradation of the DNA into oligonucleotides as seen in the typical electrophoretic DNA ladder pattern found with apoptosis. There is also a progressive increase in histopathological tissue changes as the antagonist is administered at progressively greater intervals after the cadmium.

Ionic regulation of endonuclease activity in PC12 cells

We have investigated the Ca2+ dependency of DNA degradation into nucleosome-sized fragments in intact chromaffin-like PC12 cells and PC12 nuclear fractions. In intact cells we were unable to trigger DNA fragmentation by inducing either transient or sustained elevations of cytoplasmic Ca2+ ([Ca2+]i) with the Ca2+ ionophore ionomycin. On the contrary, DNA fragmentation was induced in intact cells by the intracellular Zn2+ chelator NNN'N'-tetrakis-(2-pyridylmethyl)ethylenediamine (TPEN). To characterize further PC12 cell endonuclease activity, we then investigated digestion by purified PC12 cell fractions of exogenously added plasmids. In nuclear fractions two endonuclease activities were identified: an acidic (pH 5.0) endonuclease activity that was fully Ca2+- and Mg(2+)-independent; and a neutral (pH 7.6) endonuclease activity that was Ca(2+)-independent but Mg(2+)-dependent. Both endonuclease activities were inhibited by Zn2+. Nuclear membrane permeabilization greatly enhanced plasmid digestion at pH 7.6, but not at pH 5.0. This suggests that neutral endonuclease was located in a membrane-bound compartment, whereas acidic endonuclease was freely accessible to the substrate even in the presence of an intact nuclear membrane. In intact nuclei, digestion of genomic DNA could not be triggered by increasing the bivalent cation composition of the medium. On the contrary, in hypotonic medium we observed a large spontaneous nucleolytic DNA degradation that was increased by Zn2+ chelation. However, an acidic pH shift was a potent stimulus for DNA fragmentation in isotonic as well as hypotonic medium.

Roles of calcium in the regulation of apoptosis in HL-60 promyelocytic leukemia cells

Increase in intracellular calcium concentrations ([Ca2+]i) is critical for the initiation of apoptosis in cells such as thymocytes and in other cells, calcium chelators may promote apoptosis. However, calcium modulators, such as calcium ionophore 4-bromo-calcium ionophore (Br-A23187) and thapsigargin (TG), induce apoptosis in different cells, including HL-60 cells in which the induction of apoptosis seems a calcium-independent process. These observations imply that the disturbance of calcium homeostasis is probably the most important factor in the regulation of apoptosis. In this article, reagents with different potencies of modulating calcium homeostasis were used to study the possible role of [Ca2+]i and the status of intracellular calcium stores in the causation of HL-60 cell apoptosis. We found that an increase in [Ca2+]i alone did not result in apoptosis, while the depletion of TG-sensitive calcium stores in the endoplasmic reticulum was closely related with the induction of apoptosis. In HL-60 cells, extracellular and intracellular calcium chelators promoted apoptosis. Calmodulin antagonist did not attenuate apoptosis induced by other reagents. Our results suggest that the depletion of Ca2+ stores is an important mean to modulate calcium homeostasis and that the mobilization of calcium (Ca2+) from intracellular stores, rather than an increase in [Ca2+]i, provides the signal for the induction of apoptosis in HL-60 cells.

Programmed cell death in development

Although cell death has long been recognized to be a significant element in the process of embryonic morphogenesis, its relationships to differentiation and its mechanisms are only now becoming apparent. This new appreciation has come about not only through advances in the understanding of cell death in parallel immunological and pathological situations, but also through progress in developmental genetics which has revealed the roles played by death in the cell lineages of invertebrate embryos. In this review, we discuss programmed cell death as it is understood in developmental situations, and its relationship to apoptosis. We describe the morphological and biochemical features of apoptosis, and some methods for its detection in tissues. The occurrence of programmed cell death during invertebrate development is reviewed, as well as selected examples in vertebrate development. In particular, we discuss cell death in the early vertebrate embryo, in limb development, and in the nervous system.