Apoptosis in C3H/10T1/2 mouse embryonic cells: evidence for internucleosomal DNA modification in the absence of double-strand cleavage

REVIEW ■ : Keeping Neurons Alive: The Molecular Control of Apoptosis (Part I

Apoptosis is a form of cellular suicide in which the cell activates an intrinsic program to bring about its own demise. Recognized for years as the mechanism by which developing cells are lost naturally, it has become apparent recently that this same process may play an important role in many acute and chronic diseases in which neural cell death occurs, such as stroke and Alzheimer's disease. This growing recognition suggests that a knowledge of the gene products controlling this process may lead to improved treatments for some disease states, as well as to improved understanding of neuronal development, physiology, and pathophysiology. Some controls with important roles in neural apoptosis have been identified, and these controls, as well as their putative mechanisms of action, are described in this article. NEUROSCIENTIST 2:181-190, 1996

Cell Cycle Arrest and Apoptosis Induction via Modulation of Mitochondrial Integrity by Bcl-2 Family Members and Caspase Dependence in Dracaena cinnabari-Treated H400 Human Oral Squamous Cell Carcinoma

Dracaena cinnabari Balf.f. is a red resin endemic to Socotra Island, Yemen. Although there have been several reports on its therapeutic properties, information on its cytotoxicity and anticancer effects is very limited. This study utilized a bioassay-guided fractionation approach to determine the cytotoxic and apoptosis-inducing effects of D. cinnabari on human oral squamous cell carcinoma (OSCC). The cytotoxic effects of D. cinnabari crude extract were observed in a panel of OSCC cell lines and were most pronounced in H400. Only fractions DCc and DCd were active on H400 cells; subfractions DCc15 and DCd16 exhibited the greatest cytotoxicity against H400 cells and D. cinnabari inhibited cells proliferation in a time-dependent manner. This was achieved primarily via apoptosis where externalization of phospholipid phosphatidylserine was observed using DAPI/Annexin V fluorescence double staining mechanism studied through mitochondrial membrane potential assay cytochrome c enzyme-linked immunosorbent and caspases activities revealed depolarization of mitochondrial membrane potential (MMP) and significant activation of caspases 9 and 3/7, concomitant with S phase arrest. Apoptotic proteins array suggested that MMP was regulated by Bcl-2 proteins family as results demonstrated an upregulation of Bax, Bad, and Bid as well as downregulation of Bcl-2. Hence, D. cinnabari has the potential to be developed as an anticancer agent.

Effect of metformin and adriamycin on transplantable tumor model

Adriamycin is a cytotoxic anthracycline antibiotic used in treatment of many types of cancer. Metformin is antidiabetic drug and is under investigation for treatment of cancer. The aim of this work was to study the effect of each of adriamycin and metformin alone and in combination on solid Ehrlich carcinoma (SEC) in mice. Eighty BALB/C mice were divided into four equal groups: SEC group, SEC+adriamycin, SEC+metformin, SEC+adriamycin+metformin. Tumor volume, survival rate, tissue catalase, tissue reduced glutathione, tissue malondialdehyde, tissue sphingosine kinase 1 activity, tissue caspase 3 activity and tissue tumor necrosis factor alpha were determined. A part of the tumor was examined for histopathological and immunohistochemical study. Adriamycin or metformin alone or in combination induced significant increase in the survival rate, tissue catalase, reduced glutathione and tissue caspase 3 activity with significant decrease in tumor volume, tissue malondialdehyde, tissue sphingosine kinase 1 activity and tumor necrosis factor alpha and alleviated the histopathological changes with significant increase in Trp53 expression and apoptotic index compared to SEC group. In conclusion, the combination of adriamycin and metformin had a better effect than each of these drugs alone against transplantable tumor model in mice.

The untranslated regions of classic swine fever virus RNA trigger apoptosis

Classical swine fever virus (CSFV) causes a broad range of disease in pigs, from acute symptoms including high fever and hemorrhages, to chronic disease or unapparent infection, depending on the virus strain. CSFV belongs to the genus Pestivirus of the family Flaviviridae. It carries a single-stranded positive-sense RNA genome. An internal ribosomal entry site (IRES) in the 5' untranslated region (UTR) drives the translation of a single open reading frame encoding a 3898 amino acid long polypeptide chain. The open reading frame is followed by a 3' UTR comprising four highly structured stem-loops. In the present study, a synthetic RNA composed of the 5' and 3' UTRs of the CSFV genome devoid of any viral coding sequence and separated by a luciferase gene cassette (designated 5'UTR-Luc-3'UTR) triggered apoptotic cell death as early as 4 h post-transfection. The apoptosis was measured by DNA laddering analysis, TUNEL assay, annexin-V binding determined by flow cytometry, and by analysis of caspase activation. Contrasting with this, only trace DNA laddering was observed in cells transfected with the individual 5' or 3' UTR RNA; even when the 5' UTR and 3' UTR were co-transfected as separate RNA molecules, DNA laddering did not reach the level induced by the chimeric 5'UTR-Luc-3'UTR RNA. Interestingly, RNA composed of the 5'UTR and of stem-loop I of the 3'UTR triggered much stronger apoptosis than the 5' or 3'UTR alone. These results indicate that the 5' and 3' UTRs act together in cis induce apoptosis. We furthered obtained evidence that the UTR-mediated apoptosis required double-stranded RNA and involved translation shutoff possibly through activation of PKR.

Effect of atorvastatin and methotrexate on solid Ehrlich tumor

Hydroxymethyl glutaryl CoA reductase is the key enzyme in cholesterol synthesis. A relationship was found between cholesterol and the development of many types of cancer. Atorvastatin is a hypolipidemic drug that may have a role in treatment of cancer. Moreover, atorvastatin was reported to decrease the resistance of cancer cells to many chemotherapeutic agents. The aim of this work was to study the effect of each of methotrexate (MTX) and atorvastatin alone and in combination on solid Ehrlich carcinoma (SEC) in mice. Fifty BALB/c mice were divided into five equal groups: control untreated group, SEC, SEC+MTX, SEC+atorvastatin, SEC+MTX+atorvastatin. Tumor volume, tissue glutathione reductase (GR), catalase, malondialdehyde (MDA), cholesterol and tumor necrosis factor alpha (TNF-α) were determined. A part of the tumor was examined for histopathological and immunohistochemical study. MTX or atorvastatin alone or in combination induced significant increase in tissue catalase and GR with significant decrease in tumor volume, tissue MDA, cholesterol and TNF-α and alleviated the histopathological changes with significant increase in p53 expression and apoptotic index compared to SEC group. In conclusion, the combination of MTX and atorvastatin had a better effect than each of MTX or atorvastatin alone against solid Ehrlich tumor in mice.

Confocal microscopy as a tool to examine DNA fragmentation, chromatin condensation and other apoptotic changes in Parkinson's disease

There is considerable controversy regarding the possibility that nigral dopaminergic neurons may die via apoptosis in Parkinson's disease. It is now clear that both single- and/or double-stranded DNA breaks can be generated in the apoptotic degradative process. Since these breaks may also be present in necrotic cell death, in situ end labeling cannot be used in isolation to identify apoptotic neurons. We have developed a fluorescent double-labeling method that combines in situ end labeling with the simultaneous visualization of chromatin condensation. When viewed with laser confocal scanning microscopy, the structural detail of the nucleus is provided to unequivocally identify apoptotic nuclei.

Apoptosis: Molecular mechanisms, regulation and role in pathogenesis

OBJECTIVE

To review the current state of knowledge of apoptosis, with an emphasis on identifying potential and established roles for apoptosis in the pathogenesis of infectious diseases.

DATA SOURCES

MEDLINE and the University of British Columbia library system were searched using the search subject, "apoptosis", for the years 1992 to 1996. Further search terms (eg, "pathogenesis") were used to narrow the results. These review articles and reference books were used as the basis for locating original articles on particular studies.

DATA SELECTION

Approximately 40 studies were reviewed, with the criterion for selection being the relevance to either the molecular mechanisms behind apoptosis or roles for apoptosis in the pathogenesis of infectious diseases.

DATA EXTRACTION

Relevant information from each study was collated into categories specific to morphological and biochemical characterization, and the regulation and molecular mechanisms of apoptosis and its role in the pathogenesis of infectious diseases.

DATA SYNTHESIS AND CONCLUSIONS

Apoptosis is characterized by distinct morphological and biochemical changes that distinguish it from cell necrosis. Different signal transduction events and transcription factors can promote or inhibit apoptosis, although where and how these tie into the cell death pathway is still poorly understood. Apoptosis has been implicated in the pathogenesis of infectious diseases in two distinct ways: first, multicellular organisms use apoptosis to combat viral infections; and second, pathogens can alter the normal process of apoptosis in host cells by abnormal upregulation or downregulation. Many diseases have been shown to implicate apoptosis in their pathogenesis, raising the possibility of novel treatments for some disorders by therapeutically altering the occurrence and course of apoptosis. Therefore, further study of apoptosis in both health and disease needs to be rigorously pursued.

Amifostine protective effect on cisplatin-treated rat testis

Cisplatin is a potent drug used in clinical oncology but causes spermatogenesis damage. Amifostine is a drug used against toxicity caused by ionizing irradiation and chemotherapeutic drugs. Since cisplatin provokes fertility and induces germ cell apoptosis and necrosis, we proposed to evaluate the amifostine cytoprotective action on testes of cisplatin-treated rats. Thirty-day-old prepubertal Wistar rats received a single cisplatin dose of 5 mg/kg and were killed after 3, 6, and 12 hr. The hematoxylin-eosin stained testicular sections were submitted to histological, morphometric, and stereological analysis. The terminal deoxynucleotidyl transferase-mediated deoxyuridinetriphosphate nick end-labeling (TUNEL) method was used to label apoptotic cells. TUNEL-positive and TUNEL-negative germ cells with abnormal nuclear morphology (ANM) were scored. Significant alterations of greater part of the parameters occurred in the cisplatin-treated group (CE) compared to the group that received amifostine before the cisplatin-treatment (ACE); however, testicular weight and volume did not vary between these groups. Tubular diameter was reduced in CE in comparison to ACE rats, while interstitial tissue and lymphatic space volume and volume density were significantly higher in CE rats; interstitial testicular edema probably occurred in cisplatin-treated rats. CE rats showed important histological alterations, which were more accentuated than in ACE rats. The numerical densities of apoptotic germ cells and TUNEL-negative cells with ANM were lower in ACE than in CE rats. In conclusion, the amifostine previously administered to prepubertal rats reduced the testicular damage caused by cisplatin. We conclude that amifostine partially protected the rat seminiferous epithelium against cisplatin toxicity.

Programmed cell death in Entamoeba histolytica induced by the aminoglycoside G418

This study presents morphological and biochemical evidence of programmed cell death (PCD) in Entamoeba histolytica induced by exposure of trophozoites to the aminoglycoside antibiotic G418. Morphological characteristics of PCD, including cell shrinkage, reduced cellular volume, nuclear condensation, DNA fragmentation and vacuolization were observed, with preservation of trophozoite membrane integrity. PCD is orchestrated biochemically by alterations in intracellular ion fluxes. In G418-treated trophozoites, overproduction of reactive oxygen species (ROS), decreased intracellular K+, increased cytosolic calcium, and decreased intracellular pH levels were observed. However, externalization of phosphatidylserine was not detected. These results suggest that amoebae can undergo PCD under stress conditions, and that this PCD shares several properties with PCD reported in mammals and in a variety of unicellular organisms.

Cloning and characterization of a caspase gene from black tiger shrimp (Penaeus monodon)-infected with white spot syndrome virus (WSSV)

A black tiger shrimp (Penaeus monodon) caspase cDNA homologue (PmCasp) has been identified from a hemocyte library using a previously identified caspase homologue from the banana shrimp (Penaeus merguiensis) as a probe. The full-length PmCasp was 1202bp with a 954bp open reading frame, encoding 317 amino acids. The deduced protein contained a potential active site (QACRG pentapeptide) conserved in most caspases. It had 83% identity with caspase of P. merguiensis and 30% identity with drICE protein of Drosophila melanogaster, and it exhibited caspase-3 activity in vitro. PmCasp was cloned and expressed in Escherichia coli and a rabbit polyclonal antiserum was produced. In Western blots, the antiserum reacted with purified recombinant PmCasp and with lysates of E. coli containing the expressed plasmid. In crude protein extracts from normal shrimp, the antiserum reacted with 36 and 26kDa bands likely to correspond to inactive pro-caspase and its proteolytic intermediate form, respectively. PmCasp expression was measured in normal shrimp and in white spot syndrome virus (WSSV)-infected shrimp at 24 and 48h post-injection (p.i.) by semi-quantitative RT-PCR, Western blot analysis, and immunohistochemistry. Semi-quantitative RT-PCR analysis revealed up-regulation of PmCasp at 48h p.i. and expression remained high up to the moribund state. These results were supported by Western blot analysis showing increased PmCasp protein levels at 24 and 48h p.i. when compared to normal control shrimp. Immunohistochemical analysis of gills from the WSSV-infected shrimp revealed immunoreactivity localized in the cytoplasm of both normal and apparently apoptotic cells. In summary, a caspase-3 like gene is conserved in P. monodon and is up-regulated after WSSV infection.

Structural and functional preservation of specific sequences of DNA and mRNA in apoptotic bodies from ES cells

Retinoic acid-induced apoptosis of embryonic stem (ES) cells is an experimental system which resembles the physiological programmed cell death that occurs during differentiation in embryonic development. Our aim was to analyze the involvement of epigenetic modifications such as DNA methylation and chromatin structure in the apoptotic process and to investigate the metabolic activity of apoptotic bodies. We found a relationship between DNA methylation and apoptosis, shown by a dose-dependent induction of apoptosis after treatment with the inhibitor of DNA methylation 5-aza-2'-deoxycytidine. Interestingly, we found a slight demethylation of specific sequences of the U2afl-rs1 imprinted gene in those RA treated cells which were specifically undergoing apoptosis. In addition, apoptotic bodies exhibited an unexpected open chromatin conformation accessible to the endonuclease DNase-I. Furthermore, we observed a structural and functional preservation of specific DNA sequences and mRNA. These results suggest that biological activities, such as transcription or protein synthesis, could be maintained even towards the end of the apoptotic process.

Immunohistochemical Detection of Human Telomerase Reverse Transcriptase (hTERT), Topoisomerase II?? Expression, and Apoptosis in Endometrial Adenocarcinoma and Atypical Hyperplasia

This study evaluated the immunohistochemical expression of human telomerase reverse transcriptase (hTERT) in endometrial carcinoma and atypical endometrial hyperplasia, and related it to the expression of topoisomerase (TP)IIalpha (a proliferation associated enzyme); apoptosis as determined by the frequency of apoptotic bodies (ABI); mitotic counts; and other clinicopathologic variables. Immunoreactivity for hTERT and TPIIalpha as well as ABI were assessed in 57 endometrial samples (12 atypical hyperplasias, 33 endometrioid carcinomas, 12 serous/clear cell carcinomas). hTERT immunoreactivity, TPIIalpha labeling indices (LI), ABI, and ratios of the indices (ABI/TPIIalpha LI) increased from atypical hyperplasias to endometrioid carcinomas to serous/clear cell carcinomas (p < 0.0001 for each variable). hTERT expression increased with ABI (p < 0.0001), TPIIalpha LI (p = 0.0019), ABI/TPIIalpha ratios (p < 0.0001), and grade (p = 0.0005), but not with FIGO stage (p = 0.2775). TPIIalpha LI, ABI, and ratios were related to high grade (p = 0.0001 for each variable), but not with FIGO stage (p = 0.7362, p = 0.7554, and p = 0.7405, respectively). TPIIalpha LI and ABI were significantly correlated in atypical hyperplasias (p = 0.0004), endometrioid carcinomas (p < 0.0001), and serous/clear cell carcinomas (p = 0.024). Immunostaining levels for hTERT were similar in atypical hyperplasias and grade 1 endometrioid carcinomas (p = 0.1956). These results suggest that hTERT expression is closely related to proliferation, apoptosis, and high grade in endometrial carcinomas, reflecting cell cycle deregulation in endometrial carcinogenesis.

Endonuclease genes up-regulated in tissues undergoing programmed cell death are expressed during male gametogenesis in barley

In the process of programmed cell death (PCD), a key role has been attributed to endonucleases capable to cleave nuclear DNA at internucleosomal sites. In barley (Hordeum vulgare L.), two such nucleases (Bnuc1 and BEN1) were individually identified in unrelated tissues. In the present work, we demonstrate that their genes are also expressed in immature anthers at different stages of pollen development. Further experiments carried out on RNA extracted from immature barley anthers led to discover a novel endonuclease gene, namely Bnuc2 (AJ311603 in the EMBL/GenBank/DDBJ databases), eventually found up-regulated at the tetrad stage. The protein encoded was found to conserve large sequence portions of Bnuc1 and BEN1 endonucleases, including the domain regions involved in secretion and DNA/RNA binding. A survey conducted on barley EST libraries showed that Bnuc2 and BEN1 mRNAs are jointly present also in the transcriptome of 20 DAP spike and that other endonuclease ESTs are co-expressed with Bnuc1 or BEN1 in tissues where PCD has been recorded. Therefore, it can be concluded that during the PCD process, a set of S1-type endonucleases is synthesised regardless of the tissue considered.

Mapping the initial DNA breaks in apoptotic Jurkat cells using ligation-mediated PCR

Apoptotic DNA degradation could be initiated by the accumulation of single-strand (ss) breaks in vulnerable chromatin regions, such as base unpairing regions (BURs), which might be preferentially targeted for degradation by both proteases and nucleases. We tested this hypothesis in anti-Fas-treated apoptotic Jurkat cells. Several nuclear proteins known for their association with both MARs and the nuclear matrix, that is, PARP, NuMA, lamin B and SATB1, were degraded, but the morphological rearrangement of the BUR-binding SATB1 protein was one of the earliest detected changes. Subsequently, we have identified several genes containing sequences homologous to the 25 bp BUR element of the IgH gene, a known SATB1-binding site, and examined the integrity of genomic DNA in their vicinity. Multiple ss breaks were found in close proximity to these sites relative to adjacent regions of DNA. Consistent with our prediction, the results indicated that the initiation of DNA cleavage in anti-Fas-treated Jurkat cells occurred within the BUR sites, which likely became accessible to endonucleases due to the degradation of BUR-binding proteins.

Apoptosis in the myocardium: much is still expected

Apoptosis continues to be a controversial concept and subject of debate among scientists regarding its value as the basis for new therapeutic strategies. Today, it is widely accepted that the death of cardiac myocytes under a variety of conditions appears to be apoptotic based on a variety of criteria. However, the significance of these observations and how the insights into apoptotic molecular pathways may provide novel therapeutic targets remains to be determined. It is important to reconsider the pertinent underlying mechanisms of apoptosis regulation, and how these molecular pathways may be viewed in the functioning, intact heart. This knowledge can be applied in pursuit of practical goals in a search for new ways to prevent myocardial damage following such injuries as ischaemia/reperfusion or exposure to cardiotoxic drugs. Although recent literature contains reports of positive findings, there has not yet been a rigorous application of the model of apoptosis in the myocardium, and the potential for development of new therapeutic strategies is not yet understood.

Studies on neuronal apoptosis in primary forebrain cultures: neuroprotective/anti-apoptotic action of NR2B NMDA antagonists

While the role of apoptosis in neuronal injury is continually being re-defined, approaches to intervene in the progression of apoptotic injury have been documented to provide neuroprotection against a variety of insults. The present studies were undertaken to systematically study the effects of certain neuroprotective agents against neuronal apoptosis mediated by staurosporine (ST). ST (0.01-5 micro M) produced a dose-related apoptotic injury (as characterized by cellular morphology, 'Comet' assay analysis [single cell gel electrophoresis] and caspase-3 activation) in primary cultures of forebrain neurons. ST significantly increased caspase-3 activity. The NMDA receptor subtype non-selective antagonist dizocilpine [(+) MK-801; 0.1-50 micro M] and a novel sodium channel blocker RS100642 (1.0-250 micro M) had no significant effects against ST-induced neurotoxicity. Conversely, NR2B-selective NMDA receptor antagonists CGX-1007 (0.01-50 micro M) and ifenprodil (0.01-50 micro M) provided dose-dependent neuroprotection against ST-induced neurotoxicity (as measured by neuronal viability and comet assay analysis). CGX-1007 had no significant effect on ST-induced caspase-3 activity; however, ifenprodil did block activation of caspase-3. These studies demonstrate that NR2B NMDA receptor antagonists are anti-apoptotic and may mediate their action via mechanism(s) that are dependent or independent of caspase-3 activation.

Apoptotic bodies as a morphological feature in serous ovarian carcinoma: correlation with nuclear grade, Ki-67 and mitotic indices

This study evaluated the relation of apoptosis with mitotic activity, Ki-67 indices, and nuclear and architectural grades in serous ovarian carcinoma. Apoptotic body (ABI) and mitotic indices (MI) were obtained by examining hematoxylin and eosin-stained sections from 35 serous ovarian carcinomas for apoptotic bodies and mitotic figures. ABI and MI were reported as the number of apoptotic bodies, and mitotic figures and immunostaining for Ki-67, respectively, as positive cells in 1000 cells. Nuclear grade was determined as grade 1 [n = 11], grade 2 [n = 13], and grade 3 [n = 11] according to recently defined criteria. There was a significant correlation between Ki-67 indices and ABI (p < 0.0001), Ki-67 and MI (p < 0.0001), as well as between MI and ABI (p < 0.0001). ABI increased with nuclear grade (p < 0.0001) and the type of the histological differentiation pattern (from glandular to papillary and solid architectural patterns) (p < 0.0001). Apoptosis, quantitated by ABI, is positively correlated with proliferation, thereby constituting a factor in the regulation of tumor growth of serous ovarian carcinomas. The positive correlation between ABI and increasing nuclear grade, mitotic activity, and architectural growth pattern may indicate that apoptotic bodies are another variable for grading serous ovarian carcinomas.

Immature and mature cortical neurons engage different apoptotic mechanisms involving caspase-3 and the mitogen-activated protein kinase pathway

The authors used cultured mouse cortical neurons to study mechanisms of DNA damage-induced apoptosis in immature and mature neurons. Neurons were maintained viably for 60 days in vitro (DIV60). The increased levels of glutamate receptors, synaptic proteins, and glycolytic enzyme were used to track maturation. Exposure of neurons to the DNA-damaging agent camptothecin induced apoptosis in immature (DIV5) and mature (DIV25-30) neurons. Internucleosomal fragmentation of DNA emerged more rapidly in mature neurons than in immature neurons. Immunoblotting revealed that cleaved caspase-3 increased in apoptotic DIV5 neurons but not in DIV30 neurons, but immunolocalization showed accumulation of cleaved caspase-3 in DIV5 and DIV30 neurons. A reversible caspase-3 inhibitor blocked apoptosis in DIV5 neurons but not in DIV30 neurons. Phosphorylation of extracellular signal-regulated kinase/mitogen-activated protein kinase (Erk/MAP kinase)-42/44 occurred preapoptotically in mature but not immature neurons, while Erk54 nuclear translocation and MAP kinase kinase kinase-1 cleavage into putative caspase-3-generated proapoptotic fragments occurred in DIV5 but not DIV30 neurons. Inhibition of Erk activation with MAP kinase kinase inhibitor blocked apoptosis at both ages. The results show that immature and mature cortical neurons engage different signaling mechanisms in MAP kinase and caspase pathways during apoptosis; thus, neuron age influences the mechanisms and progression of apoptosis.

Differential modulation of signaling pathways and apoptosis of ras-transformed 10T1/2 cells by the depsipeptide FR901228

(E)-(1S,4S,10S,21R)-7-[(Z)-ethylidene]-4,21-diisopropyl-2-oxa-12,13-dithia-5,8,20,23-tetraazabicyclo[8,7,6]-tricos-16-ene-3,6,9,19,22-pentanone (FR901228), a natural anticancer depsipeptide, induces apoptosis of ras-transformed 10T1/2 cells whereas it induces growth arrest of nontransformed counterpart cells in G0/G1 phase of the cell cycle. Our study of the effect of FR901228 treatment on intracellular signaling pathways reveals a discriminating activity of FR901228 to regulate signaling cascades differently in ras-transformed 10T1/2 cells and nontransformed counterpart cells. Induction of apoptosis of ras-transformed cells by FR901228 correlates with suppression of the extracellular signal-regulated kinase (ERK) signaling pathway through reduction of Raf expression and deactivation of Mek and Erk, inhibition of the phosphoinositide-3 kinase (PI3-K) pathway indexed by suppression of Akt activity, suppression of p38 activity, and activation of caspase-3. Expression of p21(Cip1) is not induced in ras-transformed cultures undergoing apoptosis induced by FR901228. In contrast, FR901228 induces p21(Cip1) expression in nontransformed counterpart cultures growth-arrested in G0/G1 that is also accompanied by moderate induction of the kinase activities of Raf, Mek, Erk, and Akt, but not accompanied by activation of caspase-3 or changes in p38 activity. Our study indicates a potential value of FR901228 in the treatment of cancer cells involving aberrant regulation of Ras through preferential induction of the caspase cascade and suppression of the ERK, PI3-K, and p38 pathways.

Induction of apoptosis in the blue mussel Mytilus galloprovincialis by tri-n-butyltin chloride

Induction of apoptosis by tri-n-butyltin (TBT) in gill tissue of the mussel Mytilus galloprovincialis was investigated. The terminal dUTP nick-end labeling technique (TUNEL) was used to detect cells displaying DNA fragmentation within gill structures. Genomic DNA fragmentation was detected as characteristically ladder-like pattern of DNA fragments induced by single injection of different doses of TBT (1-5 microg/g) below the mantle, directly into the pallial fluid, after 24 h of incubation. DNA degradation of higher order DNA structure, as well as reduced G(0)/G(1) cell cycle region (the sub-G(1) region) was detectable after 1.5 h of TBT incubation. Presence of apoptotic cells in mussels' gills was indicated by the selective loss of G(2)/M cells concomitant with the appearance of cells with decreased DNA content in S and G(0)/G(1) cell cycle regions. The effect of the TBT on cell cycle in a mussel gill was a dose related and exposure time depending. The possible mechanism of induction of apoptosis in vivo in gill tissue of mussel treated with TBT is discussed.

Apoptosis in cultured hNT neurons

Programmed cell death (apoptosis) is an important mechanism shaping the size of different cell populations within the developing nervous system. In our study we used the NT2/D1 clone originally established from the Ntera 2 cell line to investigate the baseline levels of apoptosis in cultured postmitotic hNT (NT2-N) neurons previously treated for 3, 4 or 5 weeks with retinoic acid (RA) and compared it with apoptosis in NT2 precursors unexposed to RA. First, we examined whether different lengths of exposure to RA might affect baseline apoptotic rate in differentiating hNT neurons. Second, we investigated whether cultured hNT neurons, previously shown to possess dopaminergic characteristics, would be preferentially affected by apoptosis. Using the terminal deoxynucleotidyl transferase (tdt)-labeling technique we found that the postmitotic hNT neuronal cells exposed to RA demonstrated significantly higher numbers of apoptotic cells (12.5-15.8%) in comparison to rapidly dividing NT2 precursor cell line (3.6-4.4%) at both studied (1 and 5 days in vitro, DIV) time points. Similar apoptotic nuclear morphology, including a variable extent of nuclear fragmentation was observed in all examined hNT cultures. On the other hand, the incidence of apoptotic nuclei was rare in cultures of NT2 precursors not subjected to RA treatment. Combined immunocytochemistry for tyrosine hydroxylase (TH) and Hoechst staining revealed dopaminergic hNT neurons destined to die. Our double-labeling studies have demonstrated that only a subset of TH-positive hNT cells had condensed chromatin after 1 (approx. 15%) and 5 (approx. 20%) DIV. NT2 precursors were not TH-positive. Collectively, our results demonstrated that exposure to differentiating agent RA triggers an apoptotic commitment in a subset of postmitotic hNT neurons. These results suggest that this cell line may serve as a model of neuronal development to test various pathogenic factors implicated in the etiology of Parkinson's disease (PD), as well as to screen numerous pharmacological treatments that may slow or prevent dopaminergic deterioration.

In Vitro Investigations on the Toxicity and Cell Death Induced by Tamoxifen on Two Non-Breast Cancer Cell Types

Tamoxifen, a potent anticancer agent known to interrupt the enhanced estrogen activity of malignant mammary gland cells, was recently approved by the Food and Drug Administration (FDA)for the treatment of breast cancer. In this investigation, the toxic effects of tamoxifen were evaluated through cell multiplication, and cytological, surface ultrastructural, and biochemical studies on human cervical carcinoma cells (HeLa)and/or murine erythroleukemic (MEL) cells (BB-88). Tamoxifen treatment demonstrated an inhibitory effect on HeLa cell multiplication at lower concentrations and toxicity at higher concentrations and longer treatment durations. The drug also triggered morphological and biochemical changes as revealed by light microscopy, scanning electron microscopy (SEM), fluorescence microscopy, Nucleosome ELISA, and the DNA smear pattern. Cytological observations showed nuclear condensation, cell shrinkage, multinucleation, and apoptotic bodies. Surface ultrastructure of tamoxifen treated cells examined under the SEM revealed abnormalities such as membrane blebbing, holes, and cytoplasmic extrusions, all of which are characteristics of programmed cell death (apoptosis). Redistribution of the membrane phospholipid phosphatidylserine (PS) from the protoplasmic surface of the plasma membrane to the cell surface was identified using annexin V-enhanced green fluorescent protein (EGFP) in tamoxifen treated MEL BB-88 cells, a general feature of cells undergoing apoptosis. Tamoxifen treated cells demonstrated internucleosomal damages of the genomic DNA and DNA fragmentations, evidenced by an increase in free nucleosomes, and distinctive DNA smear patterns on the agarose gel.

Factors controlling ovarian apoptosis

Apoptosis is a form of programmed cell death that is essential for the development of the embryo and adult tissue plasticity. In adults, it is observed mainly in those tissues undergoing active differentiation such as the hematopoietic system, testis, ovary, and intestinal epithelium. Apoptosis can be triggered by many factors, such as hormones, cytokines, and drugs, depending on the type of the cell. While the intracellular signaling mechanisms may vary in different cells, they all display similar morphological and biochemical features at the later stages of the apoptotic process. This review focuses on the factors controlling ovarian apoptosis, emphasizing observations made on GnRH-induced apoptotic process in goldfish follicles.Key words: apoptosis, ovary, GnRH.

Fas-mediated apoptosis of proliferating, transiently growth-arrested, and senescent normal human fibroblasts

Previous studies suggest that apoptotic signaling may require proteins that are critical to cellular proliferation and cell cycle regulation. To further examine this question, proliferating, transiently growth-arrested, and senescent normal human fibroblasts were induced to undergo apoptosis in response to two distinct mediators of apoptosis-Fas (APO-1/CD95) death receptor and staurosporine. Ligation of the Fas receptor in the presence of cycloheximide or actinomycin D resulted in apoptosis of proliferating cells, cells transiently growth arrested by gamma-irradiation or serum starvation (i.e., G(0) arrest), and permanently growth-arrested senescent fibroblasts. Proliferating and G(0)-arrested cells were also susceptible to staurosporine-mediated apoptosis. Surprisingly, gamma-irradiated cells did not undergo staurosporine-mediated apoptosis, and remained viable for a prolonged time. Fas-mediated apoptosis of senescent fibroblasts was evidenced by chromosome condensation and by activation of caspase-8 and -3, proteases crucial for the execution of the Fas apoptosis pathway. In addition, ligation of the Fas receptor in G(0)-arrested cells did not result in the activation of p34(cdc2) kinase, arguing that activation of this kinase is not essential in this apoptotic process. From these studies we conclude that proliferating, transiently growth-arrested, and senescent normal human fibroblasts are susceptible to apoptotic signals and that apoptosis is not necessarily dependent upon cell cycle or proliferative state of the cell.

Ultrastructural identification of dentate granule cell death from pilocarpine-induced seizures

Cell loss in the hippocampal formation is a common event in patients with temporal lobe epilepsy. The belief that dentate granule neurons are relatively resistant to excitotoxic injury has recently been challenged both, in epileptic patients and in animal models of temporal lobe epilepsy. The nature of dentate granule cell damage in epilepsy has been reported as either apoptotic, necrotic or both. The lack of a consensus on this topic stems from use of different animal models and different experimental techniques for characterizing the apoptotic/necrotic process. Using electron microscopy for defining the, nature of cell loss and one of the main animal models of status epilepticus (SE) we have focussed on the nature of the degenerative process in dentate granule cells. Ultrastructural morphological changes of these cells were evaluated 2.5-48 h after pilocarpine-induced status epilepticus. A variety of morphologies ranging from apoptosis to necrosis, could be seen at 2.5 h after SE onset and continued at least over the following 48 h. Some cells displayed coalescence of chromatin against nuclear membranes. In such cases however, chromatin did not have well-defined edges (as it should, if it were apoptosis). Condensation of cytoplasm. present in both processes was also frequently found. Neither obvious apoptotic budding-off of cytoplasm nor typical membrane-bound apoptotic bodies were found. Our results indicate that in the dentate granule cell layer pilocarpine-induced SE promotes a degenerative process in which apoptotic and necrotic features overlap.

Copper induces apoptosis in BA/F3beta cells: Bax, reactive oxygen species, and NFkappaB are involved

Copper, an essential trace element, can be toxic to some cells when present in excess. But thorough investigations into the cytotoxicity of copper and subsequent molecular mechanisms are rare, although the cytotoxicity of copper has been applied to cancer chemotherapy. The present study demonstrates that Cu(2+) inhibits [(3)H] thymidine incorporation in mouse pro-B cell line BA/F3beta and induces apoptosis. Apoptosis was mainly judged by morphology of cells, quantification of subdiploid DNA contents by flow cytometry, and detection of DNA fragmentation by gel electrophoresis. The apoptotic effect is dose and time dependent. Western blotting shows Bax is upregulated by Cu(2+). Bcl-2 overexpression can partially inhibit this apoptosis. Moreover, Cu(2+) increases the production of reactive oxygen species (ROS) in a dose-dependent manner. The antioxidant N-acetylcysteine (NAC) not only significantly inhibited copper-induced apoptosis but also totally blocked generation of ROS, while Bcl-2 overexpression has no effect on the generation of ROS. Furthermore, our results show that NFkappaB is downregulated by Cu(2+). Bcl-2 overexpression or NAC can sustain the activity of NFkappaB. These data indicate that Cu(2+) might induce apoptosis in BA/F3beta cells via upregulation of Bax and ROS and subsequent inactivation of NFkappaB.

Polyamine depletion delays apoptosis of rat intestinal epithelial cells

The polyamines spermidine, spermine, and their precursor putrescine are essential for cell growth and the regulation of the cell cycle. Recent studies suggest that excessive accumulation of polyamines favors either malignant transformation or apoptosis, depending on the cell type and the stimulus. This study examines the involvement of polyamines in the induction of apoptosis by the DNA topoisomerase I inhibitor, camptothecin. In IEC-6 cells, camptothecin induced apoptosis within 6 h, accompanied by detachment of cells. Detached cells showed DNA laddering and caspase 3 induction, characteristic features of apoptosis. Depletion of putrescine, spermidine, and spermine by DL-alpha-difluoromethylornithine (DFMO), a specific inhibitor of ornithine decarboxylase (ODC) that is the first rate-limiting enzyme for polyamine biosynthesis, decreased the apoptotic index. Delayed apoptosis was accompanied by a decrease in caspase 3 activity in polyamine-depleted cells. Addition of putrescine restored the induction of apoptosis as indicated by an increase in the number of detached cells and caspase 3 activity. Polyamine depletion did not change the level of caspase 3 protein. Inhibition of S-adenosylmethionine decarboxylase by a specific inhibitor [diethylglyoxal bis-(guanylhydrazone); DEGBG] led to depletion of spermidine and spermine with a significant accumulation of putrescine and induction of ODC. The DEGBG-treated cells showed an increase in apoptosis, suggesting the importance of putrescine in the apoptotic process. Addition of putrescine to DFMO-treated cell extracts did not increase caspase 3 activity. The above results indicate that polyamine depletion delays the onset of apoptosis in IEC-6 cells and confers protection against DNA damaging agents, suggesting that polyamines might be involved in the caspase activating signal cascade.

Cell death in denervated skeletal muscle is distinct from classical apoptosis

Denervation of skeletal muscle is followed by the progressive loss of tissue mass and impairment of its functional properties. The purpose of the present study was to investigate the occurrence of cell death and its mechanism in rat skeletal muscle undergoing post-denervation atrophy. We studied the expression of specific markers of apoptosis and necrosis in experimentally denervated tibialis anterior, extensor digitorum longus and soleus muscles of adult rats. Fluorescent staining of nuclear DNA with propidium iodide revealed the presence of nuclei with hypercondensed chromatin and fragmented nuclei typical of apoptotic cells in the muscle tissue 2, 4 and to a lesser extent 7 months after denervation. This finding was supported by electron microscopy of the denervated muscle. We found clear morphological manifestations of muscle cell death, with ultrastructural characteristics very similar if not identical to those considered as nuclear and cytoplasmic markers of apoptosis. With increasing time of denervation, progressive destabilization of the differentiated phenotype of muscle cells was observed. It included disalignment and spatial disorganization of myofibrils as well as their resorption and formation of myofibril-free zones. These changes initially appeared in subsarcolemmal areas around myonuclei, and by 4 months following nerve transection they were spread throughout the sarcoplasm. Despite an increased number of residual bodies and secondary lysosomes in denervated muscle, we did not find any evidence of involvement of autophagocytosis in the resorption of the contractile system. Dead muscle fibers were usually surrounded by a folded intact basal lamina; they had an intact sarcolemma and highly condensed chromatin and sarcoplasm. Folds of the basal lamina around the dead cells resulted from significant shrinkage of cell volume. Macrophages were occasionally found in close proximity to dead myocytes. We detected no manifestations of inflammation in the denervated tissue. Single myocytes expressing traits of the necrotic phenotype were very rare. A search for another marker of apoptosis, nuclear DNA fragmentation, using terminal deoxyribonucleotidyl transferase mediated dUTP nick end labeling (the TUNEL method) in situ, revealed the presence of multiple DNA fragments in cell nuclei in only a very small number of cell nuclei in 2 and 4 month denervated muscle and to less extent in 7 month denervated muscle. Virtually no TUNEL reactivity was found in normal muscle. Double labeling of tissue denervated for 2 and 4 months for genome fragmentation with the TUNEL method and for total nuclear DNA with propidium iodide demonstrated co-localization of the TUNEL-positive fragmented DNA in some of the nuclei containing condensed chromatin and in fragmented nuclei. However, the numbers of nuclei of abnormal morphology containing condensed and/or irregular patterns of chromatin distribution, as revealed by DNA staining and electron microscopy, exceeded by 33-38 times the numbers of nuclei positive for the TUNEL reaction. Thus, we found a discrepancy between the frequences of expression of morphological markers of apoptosis and DNA fragmentation in denervated muscle. This provides evidence that fragmentation of the genomic DNA is not an obligatory event during atrophy and death of muscle cells, or, alternatively, it may occur only for a short period of time during this process. Unlike classical apoptosis described in mammalian thymocytes and lymphoid cells, non-inflammatory death of muscle fibers in denervated muscle occurs a long time after the removal of myotrophic influence of the nerve and is preceded by the progressive imbalance of the state of terminal differentiation. Our results indicate that apoptosis appears to be represented by a number of distinct isotypes in animals belonging to different taxonomic groups and in different cell lineages of the same organism.

Anticancer drug-induced apoptosis in human monocytic leukemic cell line U937 requires activation of endonuclease(s)

Anticancer agents effect tumor cell killing both in vivo and in vitro through the induction of apoptosis. Endonuclease-mediated internucleosomal DNA fragmentation, the most widely used biochemical marker of apoptosis, has been shown to play a central role in apoptosis in many experimental systems. In the present investigation, we report that activation of endonuclease(s) leading to oligonucleosomal DNA fragmentation is common and an essential event in apoptosis, induced by different anticancer drugs, adriamycin, etoposide and cisplatin. The endonuclease inhibitors aurintricarboxylic acid and zinc ion prevented apoptotic cell death in human monocytic leukemic cell line U937, as documented by DNA fragmentation, morphological and nuclear alterations, and cell viability assay. Additional studies suggest endonuclease(s)-mediated DNA fragmentation may not play a central role in apoptosis in the same cell line in response to other inducers such as heat shock and cells may undergo cell death showing all morphological features of apoptosis even in the absence of DNA fragmentation.

Antiapoptotic activity of the Bowman-Birk inhibitor can be attributed to copurified phospholipids

Previous studies have shown that extracts from soy possess potent antiapoptotic activity in in vitro and in vivo models. We recently reported that this antiapoptotic activity can be attributed to the presence of specific phospholipids. In this study, a conventional preparation of the soy-derived Bowman-Birk inhibitor (BBI) was tested for antiapoptotic activity in a C3H/10T1/2 cell serum deprivation assay. The BBI preparation was separated into lipid- or protein-containing fractions by organic extraction. The lipid fraction contained only antiapoptotic activity; the protein fraction contained only enzyme inhibition activity. We therefore conclude that the antiapoptotic activity of the BBI preparation is due to specific phospholipids that copurify with BBI. These phospholipids retain their antiapoptotic activity after autoclave treatment, whereas autoclave treatment of the protein fraction results in a loss of its enzyme inhibition activity.

Strain-specific differences in formation of apoptotic DNA ladders in MCF-7 breast cancer cells

We tested the ability of seven MCF-7 strains to undergo DNA fragmentation, as measured by DNA laddering, following doxorubicin-induced apoptosis. Four strains were found to undergo DNA laddering while three were not. All strains were inhibited by doxorubicin, although sensitivity differed. Finally, we show by detection of sub-G1 DNA that doxorubicin induced the same fold increase in apoptosis in MCF-7-ATCC, which did not ladder, and MCF-7-MG, which did ladder. Therefore, detection of DNA ladders is not an accurate indicator of apoptosis in MCF-7 cells as fragmentation of DNA appears to vary between strains.

Poly(ADP-ribosylation) and apoptosis

Poly(ADP-ribosylation) is a post-translational modification playing a relevant role in DNA damage recovery, DNA replication and viral integration. Several reports also suggest a modulation of this process during cell death by apoptosis. The aim of this review is to discuss the possible involvement of poly(ADP-ribosylation) during apoptosis, by dealing with general considerations on apoptosis, and further examining the correlation between NAD consumption and cell death, the regulation of poly(ADP-ribose) metabolism in apoptotic cells, the effect of poly(ADP-ribose) polymerase inhibition on cell death occurrence and the use of enzyme cleavage as a marker of apoptosis. Finally, the future prospects of the research in this area will be addressed.

Quantitative assessment of apoptosis in oral lichen planus

OBJECTIVE

The aims of this study were to examine the frequency of apoptoses in oral lichen planus by in situ end labeling, to ascertain whether this technique is as sensitive as conventional histologic analysis, and to examine the effect of lymphocytic infiltration.

STUDY DESIGN

Numbers of apoptoses in hematoxylin-eosin stained sections were compared with numbers of apoptotic nuclei identified by in situ end labeling in oral lichen planus (n = 26) and normal buccal epithelium (n = 8). Immunohistochemical staining with MIB-1 and for Bcl-2 and Bax enabled possible regulatory pathways to be investigated.

RESULTS

In oral lichen planus, approximately 1 apoptotic cell was detected per millimeter of basal layer, cell death increasing with lymphocytic infiltration. Epithelial cell proliferation did not correlate with apoptosis. Bcl-2 expression was weak or absent in basal cells, and Bax was localized to upper prickle cells.

CONCLUSIONS

Increased numbers of apoptoses were detected in oral lichen planus, especially in association with lymphocytic infiltration, higher numbers being seen with hematoxylin-eosin staining than with in situ end labeling.

Do nuclear condensation or fragmentation and DNA fragmentation reflect the mode of neuronal death?

It is generally believed that nuclear condensation and fragmentation as well as DNA fragmentation reflect the events related to the neuronal apoptosis. Our report demonstrates that severe oxygen-glucose deprivation (OGD) induced condensation and fragmentation of nuclear chromatin of neurones in primary cultures of cerebellar granule cells without intemucleosomal DNA fragmentation. DNA fragmentation detected by TUNEL assay was seen only after mild OGD or after addition of colchicine but not after severe OGD. Thus, at least in primary cerebellar granule cell cultures, the chromatin condensation and fragmentation cannot be considered as a hallmark of apoptosis but rather reflect the neuronal death despite of its form.

Chicken thrombocytes in culture: lymphocyte-conditioned medium delays apoptosis

Chicken thrombocytes are nucleated cells, analogs to mammalian platelets. These cells are involved in hemostasis, phagocytosis and secretion of specific products. Most of the properties of avian thrombocytes have been established in experiments that employed recently isolated blood cells. Attempts to cultivate these cells for a long period of time under optimal culture conditions for peripheral blood cells were unsuccessful; thrombocytes died after 24 h of cultivation unlike macrophages cocultured with them. Here we investigate the reasons and type of thrombocyte death in culture. Thrombocytes were separated from peripheral blood of roosters and cultured for 48 h. The influence of different culture conditions on thrombocyte viability was studied. Cells were cultured as adherent cell monolayers or under agitation (preventing adherence), in the presence or lack of lymphocytes or their soluble factors, and various concentrations of fetal bovine serum. After 24 h in standard culture thrombocytes displayed cytoplasm and chromatin condensation, DNA cleaved into oligonucleosomal fragments and unaltered mitochondria. These results strongly suggest that thrombocytes suffer an apoptotic cell death in culture. Apoptosis could be delayed by culturing thrombocytes in the presence of lymphocytes or their soluble factors.

Soy-derived antiapoptotic fractions protect gastrointestinal epithelium from damage caused by methotrexate treatment in the rat

The ability of a previously described soy-derived antiapoptotic fraction (SDAAF), a soy water extract (Lexirin), and raw soy flour to inhibit methotrexate (MTX)-induced gastrointestinal damage was evaluated by histological examination of duodenal/jejunal sections from MTX-treated rats. Male Sprague-Dawley rats were fed diets containing casein as a sole protein source or diets supplemented with fractions isolated from soy (SDAAF or Lexirin) before and after MTX treatment. The soy fractions were also shown to inhibit serum deprivation-induced programmed cell death (apoptosis) in mouse embryonic C3H10T1/2 cells. Protein sequence (Lexirin) and enzyme activity (Lexirin and SDAAF) were also analyzed. Rats that received SDAAF- and Lexirin-supplemented diets had significantly reduced necrotic and apoptotic damage in the duodenal mucosa, as demonstrated by difference in villi height, mitotic activity, epithelial cell height, and inflammatory response.

Apoptosis in neuronal development and transplantation: role of caspases and trophic factors

Fetal ventral mesencephalic (VM) transplants have been studied in the context of dopaminergic (DA) replacement therapy for Parkinson's disease (PD). DA neurons from VM transplants will grow axons and form functional synapses in the adult host central nervous system (CNS). Recently, studies have demonstrated that most of the transplanted DA neurons die in grafts within the first week after implantation. An important feature of neural development, also in transplanted developing fetal neural tissue, is cell death. However, while about 50% of cells born in the CNS will die naturally, up to 99% of fetal cells die after neural transplantation. It has been shown that VM grafts contain many apoptotic cells even at 14 days after transplantation. The interleukin-1beta converting enzyme (ICE) cysteine protease and 11 other ICE-like-related proteases have been identified, now named caspases. Activation of caspases is one of the final steps before a neuron is committed to die by apoptosis. Here we review this cell death process in detail: Since the growth of fetal neural grafts placed in the adult brain in many ways mimics normal development, it is likely that the caspases also play a functional role in transplants. Pharmacological inhibitors of caspases and genetically modified mice are now available for the study of neuronal death in fetal neuronal transplants. Understanding cell death mechanisms involved in acute cellular injury, necrosis, and programmed cell death (PCD) is useful in improving future neuronal transplantation methodology, as well as in neuroprotection, for patients with neurodegenerative diseases.

Contribution of phosphatidylinositol 3-kinase to radiation resistance in human melanoma cells

The activity of phosphatidylinositol 3-kinase (PI3K), a key component of multiple signal transduction pathways, was investigated in early- and late-stage melanoma cells that have varying degrees of radiation resistance. Analysis of PI3K biproducts (PI-3,4-P2 and PI-3,4,5-triphosphate) revealed a direct correlation between radiation resistance and levels of PI3K activity. Treating melanoma cells with wortmanin or LY294002, two different PI3K inhibitors, decreased PI3K activity and caused a dose-dependent decrease in resistance to ultraviolet radiation. Lower resistance to radiation elicited by LY294002 coincided with increased apoptosis. To further establish the role of PI3K in radiation resistance, we transfected early-stage melanoma cells with the cDNA of p85, the regulatory subunit of PI3K. Clones that constitutively overexpressed p85 exhibited a higher degree of PI-3,4-P2 synthesis and a corresponding increase in their resistance to ultraviolet radiation. The results of this study point to the role of PI3K and its biproducts in radiation resistance of human melanoma cells.

The pharmacology of apoptosis

Apoptosis is an area of intense scientific interest, which encompasses the study of and triggers mechanisms involved in mediating the cell biology of programmed cell death. A number of low molecular weight compounds have been used to inhibit or enhance this fundamental cellular process and so apoptosis has now become amenable to pharmacological manipulation. In this review Ross Kinloch, Mark Treherne, Mike Furness and Iradj Hajimohamadreza will focus on the current literature describing the pharmacology of apoptosis, with particular reference to the therapeutic potential that could arise from the development of pro- and anti-apoptotic drugs. The pivotal role of apoptosis in such diverse pathological processes as tumour growth, the immune response and neurodegeneration suggests that an understanding of how apoptosis can be regulated by drugs will become increasingly important to the pharmaceutical industry.

Cell death induced by topoisomerase-targeted drugs: more questions than answers

Chemotherapeutic agents that target topoisomerase I and II set into motion a series of biochemical changes that culminate in cell death, but only under some conditions. The realization that stabilization of covalent topoisomerase-DNA complexes is not sufficient to insure cell death has prompted investigators to examine various aspects of the drug-induced death process itself. Several discrete steps along this pathway have been identified, including (a) the processing of stabilized cleavage complexes into frank DNA strand breaks; (b) sensing of the DNA damage, leading to activation of stress-associated signaling pathways and cell cycle arrest; and (c) activation of a preexisting group of enzymes and enzyme precursors, typified by the cysteine-dependent aspartate-directed proteases (caspases), that catalyze the relatively orderly biochemical cascade of terminal events known as apoptosis. The present review discusses the evidence that these steps occur after treatment with etoposide or camptothecin, the two prototypic topoisomerase poisons that are commonly studied. As in any emerging area, a large number of questions remain to be answered about the process of cell death induced by topoisomerase-directed drugs.

Use of the Microculture Kinetic Assay of Apoptosis to Determine Chemosensitivities of Leukemias

Chemotherapeutic agents exert their antitumor effects by inducing apoptosis. The microculture kinetic (MiCK) assay provides an automated, continuous means of monitoring apoptosis in a cell population. We used the MiCK assay to determine the chemosensitivities of the human promyelocytic HL-60 and lymphoblastic CEM cell lines and leukemia cells freshly isolated from patients with acute nonlymphocytic (ANLL) or acute lymphocytic (ALL) leukemias. Continuous monitoring of apoptosis in the MiCK assay permits determination of the time to the maximum apoptosis (Tm) and its two components which are initiation time (Ti) and development time (Td). Duration of the three timing components of apoptosis varies from hours to days depending on the drug, drug concentration, and type of target cells. In the MiCK assay, the extent of apoptosis is reported in kinetic units of apoptosis. Kinetic units are determined by the slope of the curve created when optical density caused by cell blebbing is plotted as a function of time. Using the leukemia cell lines, we define the relationship between kinetic units determined by the MiCK assay and the percentage of morphologically apoptotic cells in the culture. Flow cytometry analysis of apoptosis in Annexin-V-fluorescein isothiocyanate–labeled preparations of HL-60 and CEM cells was also used to compare with data obtained by the MiCK assay. The feasibility of the MiCK assay of apoptosis as a chemosensitivity test was confirmed by its comparison with a 3H-thymidine incorporation assay. We show that samples from 10 ANLL and ALL patients patients tested for sensitivity to various doses of idarubicin (IDR), daunorubicin (DNR), or mitoxantrone (MTA) gave the same percentages of apoptotic cells when calculated by the MiCK assay as when determined by morphological analysis. The MiCK assay was used for dose-response analyses of the sensitivities to IDR, DNR, and MTA of leukemia cells from 4 other patients (2 ANLL and 2 ALL). The results from both cell lines and patient samples indicate that ANLL cells are more sensitive than ALL cells to all three of these chemotherapeutic agents. However, for individual patients the chemosensitivities varied significantly among the three chemotherapeutic agents. These varying responses to IDR, DNR, and MTA indicate that the MiCK assay results can be of potential use in designing a treatment regimen for a specific patient with acute leukemia. Among several drugs of presumed similar efficacy, the MiCK assay can permit the selection of the specific chemotherapeutic agent that causes the most apoptosis in the patient's leukemic cells.

© 1998 by The American Society of Hematology.