Intracellular ATP is required for actinomycin D-induced apoptotic cell death in HeLa cells

Influence of Ce3+ Substitution on Antimicrobial and Antibiofilm Properties of ZnCexFe2-xO4 Nanoparticles (X = 0.0, 0.02, 0.04, 0.06, and 0.08) Conjugated with Ebselen and Its Role Subsidised with γ-Radiation in Mitigating Human TNBC and Colorectal Adenocarcinoma Proliferation In Vitro

Cancers are a major challenge to health worldwide. Spinel ferrites have attracted attention due to their broad theranostic applications. This study aimed at investigating the antimicrobial, antibiofilm, and anticancer activities of ebselen (Eb) and cerium-nanoparticles (Ce-NPs) in the form of ZnCexFe2-XO4 on human breast and colon cancer cell lines. Bioassays of the cytotoxic concentrations of Eb and ZnCexFe2-XO4, oxidative stress and inflammatory milieu, autophagy, apoptosis, related signalling effectors, the distribution of cells through the cell-cycle phases, and the percentage of cells with apoptosis were evaluated in cancer cell lines. Additionally, the antimicrobial and antibiofilm potential have been investigated against different pathogenic microbes. The ZOI, and MIC results indicated that ZnCexFe2-XO4; X = 0.06 specimen reduced the activity of a wide range of bacteria and unicellular fungi at low concentration including P. aeruginosa (9.5 mm; 6.250 µg/mL), S. aureus (13.2 mm; 0.390 µg/mL), and Candida albicans (13.5 mm; 0.195 µg/mL). Reaction mechanism determination indicated that after ZnCexFe2-xO4; X = 0.06 treatment, morphological differences in S.aureus were apparent with complete lysis of bacterial cells, a concomitant decrease in the viable number, and the growth of biofilm was inhibited. The combination of Eb with ZFO or ZnCexFe2-XO4 with γ-radiation exposure showed marked anti-proliferative efficacy in both cell lines, through modulating the oxidant/antioxidant machinery imbalance, restoring the fine-tuning of redox status, and promoting an anti-inflammatory milieu to prevent cancer progression, which may be a valuable therapeutic approach to cancer therapy and as a promising antimicrobial agent to reduce the pathogenic potential of the invading microbes.

Neutral metalloaminopeptidases APN and MetAP2 as newly discovered anticancer molecular targets of actinomycin D and its simple analogs

The potent transcription inhibitor Actinomycin D is used with several cancers. Here, we report the discovery that this naturally occurring antibiotic inhibits two human neutral aminopeptidases, the cell-surface alanine aminopeptidase and intracellular methionine aminopeptidase type 2. These metallo-containing exopeptidases participate in tumor cell expansion and motility and are targets for anticancer therapies. We show that the peptide portions of Actinomycin D and Actinomycin X₂ are not required for effective inhibition, but the loss of these regions changes the mechanism of interaction. Two structurally less complex Actinomycin D analogs containing the phenoxazone chromophores, Questiomycin A and Actinocin, appear to be competitive inhibitors of both aminopeptidases, with potencies similar to the non-competitive macrocyclic parent compound (K_i in the micromolar range). The mode of action for all four compounds and both enzymes was demonstrated by molecular modeling and docking in the corresponding active sites. This knowledge gives new perspectives to Actinomycin D's action on tumors and suggests new avenues and molecules for medical applications.

Live fluorescence and transmission-through-dye microscopic study of actinomycin D-induced apoptosis and apoptotic volume decrease

The effect of actinomycin D on HeLa cells was studied by live fluorescence and transmission-through-dye microscopy-a recently developed technique that permits volume measurements in live cells. In particular, it is well suited for the observation and quantification of the apoptotic volume decrease (AVD), which is widely viewed as an essential feature of apoptosis. The main results from our study are as follows. (1) Apoptosis caused in HeLa cells by actinomycin D proceeds in two morphologically distinct stages: the early stage is characterized by extensive blebbing, and the late stage by a more compact shape. The loss of mitochondrial membrane potential occurs at about the same time as blebbing, and chromatin condensation follows 30-90 min later. Caspase-3 and 7 become activated during the late stage. (2) Because blebbing occurs before activation of caspase-3, it has to be initiated by a different mechanism. Although blebbing is one of the earliest observable changes, it can be selectively inhibited without affecting other apoptotic reactions. (3) The majority of cells experience a temporary volume increase after the appearance of blebs. Eventually, AVD takes over and the cells shrink by approximately 40 % of their initial volume; the volume loss becomes noticeable at the end of the blebbing phase and continues through the late stage. Sometimes, at the end of long incubations, shrinkage gives way to swelling, possibly indicating secondary necrosis. (4) Both early and late apoptosis are accompanied by intracellular accumulation of Na(+), while low-sodium medium prevents apoptosis. Except for a partial protective effect of quinine, all of the tested blockers of Na(+), K(+) and Cl(-) channels failed to prevent apoptosis or AVD.

Presenilin mediates neuroprotective functions of ephrinB and brain-derived neurotrophic factor and regulates ligand-induced internalization and metabolism of EphB2 and TrkB receptors

Activation of EphB receptors by ephrinB (efnB) ligands on neuronal cell surface regulates important functions, including neurite outgrowth, axonal guidance, and synaptic plasticity. Here, we show that efnB rescues primary cortical neuronal cultures from necrotic cell death induced by glutamate excitotoxicity and that this function depends on EphB receptors. Importantly, the neuroprotective function of the efnB/EphB system depends on presenilin 1 (PS1), a protein that plays crucial roles in Alzheimer's disease (AD) neurodegeneration. Furthermore, absence of one PS1 allele results in significantly decreased neuroprotection, indicating that both PS1 alleles are necessary for full expression of the neuroprotective activity of the efnB/EphB system. We also show that the ability of brain-derived neurotrophic factor (BDNF) to protect neuronal cultures from glutamate-induced cell death depends on PS1. Neuroprotective functions of both efnB and BDNF, however, were independent of γ-secretase activity. Absence of PS1 decreases cell surface expression of neuronal TrkB and EphB2 without affecting total cellular levels of the receptors. Furthermore, PS1-knockout neurons show defective ligand-dependent internalization and decreased ligand-induced degradation of TrkB and Eph receptors. Our data show that PS1 mediates the neuroprotective activities of efnB and BDNF against excitotoxicity and regulates surface expression and ligand-induced metabolism of their cognate receptors. Together, our observations indicate that PS1 promotes neuronal survival by regulating neuroprotective functions of ligand-receptor systems.

Influence of glucose starvation on the pathway of death in insect cell line Sl: apoptosis follows autophagy

The relation between autophagy and apoptosis has not been clearly elucidated. Here, we reported that apoptosis followed autophagy in insect Spodoptera litura cells (Sl) undergoing glucose starvation. Sl cells have been adapted to Leibovitz-15 medium supplemented with glucose (1.0 g/l) and 5% fetal bovine serum (FBS), used for mammalian cell cultures. If glucose (1 g/l) or glutamine (1.6 g/l) had not been supplemented in L-15 medium with 5% FBS, Sl cells began to form many vacuoles and these vacuoles gradually enlarged in the cytoplasm, which were autophagic vacuoles. However, these large vacuoles began to disappear gradually after 48 h of glucose starvation, accompanied with remarkable apoptosis without apoptotic bodies, which was demonstrated by DNA fragmentation and activation of caspase-3-like. During glucose starvation, Sl cell ATP concentrations gradually decreased. Interestingly, if the conditioned L-15 medium without glucose was replaced with fresh L-15 medium supplemented with glucose or glutamine after the cultures had been starved seriously for 48 h or longer, the formation of apoptotic bodies was initiated. These data suggested that the partial depletion of cell ATP triggered apoptosis following autophagy in glucose-starved Sl cells and the formation of apoptotic bodies required higher level of ATP than DNA fragmentation and activation of caspase-3-like activity. Additionally, the disappearance of autophagic vacuoles, negative staining of neutral red, green staining of acridine orange and diffusion of acid phosphatase activity in Sl cells at the late stage of starvation (over 48 h) suggested that the dysfunction of lysosome was more likely to involve in apoptosis. The facts that Actinomycin D-induced apoptosis was partially inhibited and cyclosporin A, blocking the opening of mitochondrial permeability transition (MPT) pores, inhibited partially apoptosis in glucose-starved Sl cells, suggested the pathway of glucose starvation-induced apoptosis seemed to be different from that induced by actinomycin D and the opening of MPT pores on mitochondria probably involved in apoptosis triggered by glucose starvation, respectively.

Cells die with increased cytosolic ATP during apoptosis: a bioluminescence study with intracellular luciferase

Apoptosis is a distinct form of cell death, which requires energy. Here, we made real-time continuous measurements of the cytosolic ATP level throughout the apoptotic process in intact HeLa, PC12 and U937 cells transfected with the firefly luciferase gene. Apoptotic stimuli (staurosporine (STS), tumor necrosis factor alpha (TNFalpha), etoposide) induced significant elevation of the cytosolic ATP level. The cytosolic ATP level remained at a higher level than in the control for up to 6 h during which activation of caspase-3 and internucleosomal DNA fragmentation took place. When the STS-induced ATP response was abolished by glucose deprivation-induced inhibition of glycolysis, both caspase activation and DNA laddering were completely inhibited. Annexin V-binding induced by STS or TNFalpha was largely suppressed by glycolysis inhibition. Thus, it is suggested that the cells die with increased cytosolic ATP, and elevation of cytosolic ATP level is a requisite to the apoptotic cell death process.

Critical role of mitochondrial damage in determining outcome of macrophage infection with Mycobacterium tuberculosis

Human macrophages (Mphi) respond to Mycobacterium tuberculosis (Mtb) infection by undergoing apoptosis, a cornerstone of effective antimycobacterial host defense. Virulent mycobacteria override this reaction by inducing necrosis leading to uncontrolled Mtb replication. Accordingly, Mphi death induced by inoculation with Mtb had the characteristics of apoptosis and necrosis and correlated with moderate increase of mitochondrial permeability transition (MPT), mitochondrial cytochrome c release, and caspase-9 and -3 activation. We hypothesized that changes in intramitochondrial Ca(2+) concentration ([Ca(2+)](m)) determine whether Mphi undergo either apoptosis or necrosis. Therefore, we induced mechanism(s) leading to predominant apoptosis or necrosis by modulating [Ca(2+)](m) and examined their physiological consequences. Adding calcium ionophore A23187 to Mphi inoculated with Mtb further increased calcium flux into the cells which is thought to lead to increased [Ca(2+)](m), blocked necrosis, stabilized MPT, decreased mitochondrial cytochrome c release, lowered caspase activation, and accompanied effective antimycobacterial activity. In contrast, Mphi infected with Mtb in presence of the mitochondrial calcium uniporter inhibitor ruthenium red showed increased mitochondrial swelling and cytochrome c release and decreased MPT and antimycobacterial activity. Thus, in Mtb-infected Mphi, high levels of mitochondrial membrane integrity, low levels of caspase activation, and diminished mitochondrial cytochrome c release are hallmarks of apoptosis and effective antimycobacterial activity. In contrast, breakdown of mitochondrial membrane integrity and increased caspase activation are characteristic of necrosis and uncontrolled Mtb replication.

The mitochondrial apoptotic pathway is activated by serum and glucose deprivation in cardiac myocytes

Many cell types undergo apoptosis under conditions of ischemia. Little is known, however, about the molecular pathways that mediate this response. A cellular and biochemical approach to elucidate such signaling pathways was undertaken in primary cultures of cardiac myocytes, a cell type that is especially sensitive to ischemia-induced apoptosis. Deprivation of serum and glucose, components of ischemia in vivo, resulted in myocyte apoptosis, as determined by nuclear fragmentation, internucleosomal cleavage of DNA, and processing of caspase substrates. These manifestations of apoptosis were blocked by zVAD-fmk, a peptide caspase inhibitor, indicating that caspase activity is necessary for the progression of apoptosis in this model. In contrast to control cells, apoptotic myocytes exhibited cytoplasmic accumulation of cytochrome c, indicating release from the mitochondria. Furthermore, both caspase-9 and caspase-3 were processed to their active forms in serum-/glucose-deprived myocytes. Caspase processing, but not cytochrome c release, was inhibited by zVAD-fmk, placing the latter event upstream of caspase activation. This evidence demonstrates that components of ischemia activate the mitochondrial death pathway in cardiac myocytes.

Inhibition of PARP prevents oxidant-induced necrosis but not apoptosis in LLC-PK1 cells

Oxidant-induced cell injury has been implicated in the pathogenesis of several forms of acute renal failure. The present studies examined whether activation of poly(ADP-ribose)polymerase (PARP) by oxidant-induced DNA damage contributes to oxidant injury of renal epithelial cells. H2O2 exposure resulted in an increase in PARP activity and decreases in cell ATP and NAD content. These changes were significantly inhibited by 10 mM 3-aminobenzamide (3-ABA), a PARP inhibitor. In contrast, H2O2-induced DNA damage was not prevented by 3-ABA. Exposure of LLC-PK(1) cells to 1 mM H2O2 for 2 h induced necrotic cell death as measured by increased lactate dehydrogenase (LDH) release. 3-ABA completely prevented the H2O2-induced LDH release. Live/dead fluorescent staining confirmed the protection by 3-ABA. These results are consistent with the view that oxidant-induced DNA damage activates PARP and that the subsequent ATP and NAD depletion contribute to necrotic cell death. Of note, although protected from necrosis, cells treated with H2O2 and 3-ABA underwent apoptosis as evidenced by DNA fragmentation and bis-benzimide staining. In conclusion, activation of PARP contributes to oxidant-induced ATP depletion and necrosis in LLC-PK1 cells. However, PARP inhibition may target cells toward an apoptotic form of cell death.

Apoptosis Versus Cytotoxicity in HeLa Cells Exposed to Paracetamol

Apoptosis is a programmed form of cell death which occurs in response to specific stimuli. It is distinguished from necrotic or accidental cell death by unique events, including the degradation of chromatin and a loss of cellular volume. In contrast to necrotic cell death, cell membrane integrity and mitochondrial function are thought to be maintained until the apoptotic process is well advanced. One of the novel assays for detecting apoptosis is flow cytometry. In our experiments, we used a flow cytometric assay to detect DNA changes in a human cell line (HeLa) exposed to paracetamol, by measuring propidium iodide binding. We were able to detect the apoptotic process in cells exposed to paracetamol. Apoptosis did not correlate with cytotoxicity, and was only found in samples exposed to 4-5mg/ml paracetamol for 8 hours in minimum essential medium and incubated in fresh medium without paracetamol for 14-19 hours. The greatest effect was noted 18 hours after paracetamol exposure. These results were confirmed by studying cell morphology and chromatin condensation by fluorescent microscopy with the fluorochromes acridine orange and ethidium bromide. Our results support the hypothesis that, in cultured cells, apoptosis is induced by a relatively narrow range of chemical concentrations which are known to inhibit the cell cycle, and that apoptosis and inhibition of cell proliferation coincide to some degree.

Tobacco smoke induces both apoptosis and necrosis in mammalian cells: differential effects of HSP70

Tobacco smoke (TS) has been implicated as a major risk factor in human pulmonary diseases including cancer. In this study, we used TS as a model of oxidative stress. TS-mediated oxidative stress has been shown to induce protein oxidation, DNA damage, and cell death. Here we investigated, in human and rodent cell lines, whether TS induces cell death by apoptosis or by necrosis. As described for classic oxidants, TS induced apoptosis at low concentrations and necrosis at higher concentrations. We have previously described the induction of heat shock (HS) protein (HSP) (in particular, HSP70) in human monocytes exposed to TS. HSP70 is implicated in the regulation of cell injury and cell death and, in particular, modulates apoptosis, as does the antiapoptotic oncoprotein Bcl-2. At both apoptotic and necrotic concentrations, TS induced a dose-dependent HSP70 expression, whereas Bcl-2 was induced only at necrotic concentrations. TS- or HS-induced HSP had no protective effects either on apoptosis or on necrosis, but HSP70 overexpression prevented TS-induced necrosis and consequently led to increased apoptosis. These results might reconcile the apparently contradictory data previously reported on the effects of HSP on apoptosis.

Pyruvate prevents hydrogen peroxide-induced apoptosis

Studies were carried out to investigate the protective effects of pyruvate, a key glycolytic intermediate and alpha-keto-monocarboxylate, against oxidative stress-induced apoptosis. Oxidative stress was induced by treating mouse thymocytes with 25 microM hydrogen peroxide for 15 min at 37 degrees C under 5% CO2 in air. Pre- and post-treatment of cells with 10 mM pyruvate inhibited morphological changes, internucleosomal DNA fragmentation, and translocation of phosphatidylserine to the plasma membrane surface, which are characteristic features of apoptosis. L-lactate (10 mM) and acetate (10 mM) were ineffective in inhibiting apoptosis and appeared to be toxic to the cells under similar conditions. The results suggest that pyruvate has therapeutic potential for use in the treatment of oxidative stress-induced disorders associated with increased apoptosis.

Energy metabolism of rat colonocytes changes during the tumorigenic process and is dependent on diet and carcinogen

Alterations in ATP production, intracellular energy levels and mitochondrial function have been shown to trigger cytokinetic events in vitro, including inhibition of cell division, abnormal or blocked differentiation and inhibition of apoptosis. Changes in colonic cytokinetics are directly related to colon tumorigenesis but alterations in energy metabolism during the tumorigenic process have never been reported. We conducted a 2 x 2 x 3 factorial design study in 120 male Sprague-Dawley rats with two diets (pectin or cellulose-supplemented), two injected subgroups (with or without the carcinogen azoxymethane, AOM) and three termination time points (6, 16 and 36 wk post-second injection). Colonocytes were isolated and incubated with their primary energy substrates (radiolabeled butyrate, glucose, glutamine and beta-hydroxybutyrate) for 60 min. Production of lactate, ketone bodies and CO2 were determined. At 6 wk, there were no significant differences in metabolism among treatments. In contrast, at 16 wk, AOM-injected rats had dramatically lower rates of CO2 production (P < 0.001) from both glucose and butyrate and lower rates of lactate and ketone body production than their saline counterparts. At 36 wk, when tumors developed, the depressed production of lactate and ketone bodies seen in AOM-injected rats at 16 wk returned to control values. However, in AOM-injected rats, CO2 production from glucose and butyrate remained depressed. Cellulose feeding resulted in decreased oxidation of glucose, butyrate and glutamine and an increased production of ketone bodies from butyrate by colonocytes compared with pectin feeding at 36 wk. We conclude that colonocyte energy metabolism differs in AOM-injected rats vs. saline controls and changes during tumorigenesis, and suggest a relationship between intracellular energy status and changes in cell kinetics. This is the first report that such a relationship may exist in vivo.

The role of calcium in apoptosis

One general signalling mechanism used to transfer the information delivered by agonists into appropriate intracellular compartments involves the rapid redistribution of ionised calcium throughout the cell, which results in transient elevations of the cytosolic free Ca2+ concentration. Various physiological stimuli increase [Ca2+]i transiently and, thereby, induce cellular responses. However, under pathological conditions, changes of [Ca2+]i are generally more pronounced and sustained. Marked elevations of [Ca2+]i activate hydrolytic enzymes, lead to exaggerated energy expenditure, impair energy production, initiate cytoskeletal degradation, and ultimately result in cell death. Such Ca(2+)-induced cytotoxicity may play a major role in several diseases, including neuropathological conditions such as chronic neurodegenerative diseases and acute neuronal losses (e.g. in stroke).

Tumor necrosis factor-alpha increases ATP content in metabolically inhibited L929 cells preceding cell death

The effects of tumor necrosis factor-alpha (TNF) on ATP levels were studied in metabolically inhibited L929 cells. Treatment of these cells with TNF in the presence of actinomycin D or cycloheximide induces cyclic changes in the intracellular ATP content preceding cell death. After 3 h of incubation, the intracellular ATP content increased by 48 +/- 6% (p < 0.001), but at 4 h, it decreased to the control level. Two hours later, it increased again by 23 +/- 5% over the control level (p < 0.001). Coinciding with cell death, ATP content decreased progressively until almost complete depletion. These changes in ATP content were associated with parallel alterations in the respiratory coupling and with increased generation of reactive oxygen species. The mechanism by which TNF/actinomycin D or TNF/cycloheximide increased cellular ATP seemed to be dependent on the mitochondrial ATP synthesis and related to the cytotoxic effect of TNF, since blockade of mitochondrial electron transport prevented the increase in cellular ATP, the formation of reactive oxygen species, and the apoptotic cell death caused by TNF. We suggest that the TNF/actinomycin D- or TNF/cycloheximide-induced changes in intracellular ATP levels may be involved in the cytotoxic effect of TNF in metabolically inhibited L929 cells.

Oxygen-dependent fragmentation of cellular DNA by nitric oxide

Although active oxygen species and related metabolites, such as nitric oxide (NO), have been postulated to play important roles in the apoptosis of various cells, a precise mechanism leading to cell death remains to be elucidated. Recently we found that the lifetime of NO depends greatly on the concentration of environmental oxygen and that NO reversibly inhibits mitochondrial respiration and ATP synthesis; the inhibitory effect is stronger at physiologically low oxygen tension than under atmospheric conditions (Arch. Biochem. Biophys. 323, 27-32, 1995). The present work describes the effects of the NO-generating agent, 1-hydroxy-2-oxo-3,3-bis(2-aminoethyl)-1-triazene (NOC 18) and oxygen tension on the respiration, ATP synthesis and apoptosis of HL-60 cells. When respiration was inhibited by NOC 18, cellular ATP levels decreased significantly and DNA fragmentation was elicited. Both events were enhanced by decreasing oxygen tension and suppressed by adding NO-trapping agents, such as 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO) and oxyhemoglobin. The fragmentation of cellular DNA was inhibited in a dose dependent manner by herbimycin A, a tyrosine kinase inhibitor. Fragmentation of the DNA of HL-60 cells was also induced either by peroxynitrite, superoxide or hydroxyl radical by some mechanism which was diminished by lowering the oxygen tension. These results indicated that the decrease in cellular ATP and activation of tyrosine kinase might play important roles in NO-induced apoptosis particularly under physiologically low oxygen tensions.