Detection of ghost cells in the standard alkaline comet assay is not a good measure of apoptosis

The single cell gel electrophoresis assay, or Comet assay, is a powerful tool for measurement of DNA strands breaks, oxidative damage, and alkali labile sites, and the assay was recently modified to detect DNA cross-links. It has also been proposed as a measure of apoptosis since apoptotic cells are suspected to result in total migration of the DNA from the nucleus into the tail. Cells with this appearance are called ghost cells, clouds, hedgehogs, or NDCN (nondetectable cell nuclei). The aim of this study was to determine if ghost cells can be used to measure apoptosis in the standard alkaline comet assay. To answer this question, we made use of two cell lines: CTLL-2 cells that can enter apoptosis upon addition of apoptosis stimuli or IL-2 deprivation, and CTLL-2 bcl2 cells that are protected from apoptosis due to the overexpression of the apoptosis inhibitor gene bcl2. The two cell lines were treated with cytotoxins (nongenotoxic apoptosis inducers, nongenotoxic necrotic agents) or genotoxins. They were also subjected to growth factor withdrawal, which induced apoptosis in the CTLL-2 cell line. The level of apoptosis was measured by the Annexin V-FITC method in parallel with performing the Comet assay. The results obtained in the two cell lines suggest that apoptotic or necrotic death does not correlate well with the detection of ghost cells, presumably because these cells are lost upon electrophoresis. A variant of the alkaline Comet assay that was performed without electrophoresis (halo method) was able to efficiently detect cells undergoing apoptosis, but it was unable to clearly distinguish between apoptosis and genotoxic damage.     

The comet assay: Genotoxic damage or nuclear fragmentation?

The single cell gel electrophoresis (SCGE) or comet assay is based on the assumption that comet images result from genotoxic damage that ultimately generate DNA single- or double-strand breaks. A criticism of the assay is that some or all of the comet images may be the result of apoptosis-mediated nuclear fragmentation. The objective of this study was to determine if mutagen-induced DNA damage leading to strand breakage observed in the SCGE assay was repairable or was due to nonrepairable nuclear fragmentation. Chinese hamster ovary cells were treated with ethylmethanesulfonate, 2-acetoxyacetylaminofluorene, or H(2)O(2). These mutagens induce genetic damage by different molecular mechanisms. One group of SCGE slides was prepared immediately after treatment, while parallel treated cultures were repeatedly washed and allowed to undergo liquid holding recovery for DNA repair. It was hypothesized that cells with genotoxic damage can repair their genomic DNA, while apoptotic cells cannot reverse nuclear fragmentation. We found a significant decrease in the tail moments of nuclei from mutagen-treated cells after 4 hr of liquid holding. However, this measurement may represent only those cells capable of repair. Apoptotic cells may continue DNA fragmentation during the recovery time and this DNA may become so diffuse that the nuclei disappear after electrophoresis. To overcome this possible artifact, images of nuclei were captured before and after alkaline electrophoresis. Constellations of nuclei were located on SCGE slides by their coordinates on the microscope stage. We found that no nuclei were lost due to apoptotic nuclear fragmentation and DNA migration. Even the so-called "hedgehog" comet images with extreme DNA damage were not lost during liquid holding. These data support the conclusion that mutagen-induced DNA damage is the principal cause of the damage measured in the comet assay.     

阿糖胞苷对肺腺癌细胞凋亡的诱导作用及其机制

目的探讨阿糖胞苷（Ara-C）对人肺腺癌细胞株A549的凋亡诱导作用及其机制。方法Ara—C体外作用于／t549细胞,噻唑蓝还原法（MTT法）检测Ara—C对A549细胞增殖的抑制作用;Hoechst33258荧光染色观察细胞核形态学的变化;单细胞凝胶电泳技术（comet assay）测定A549细胞DNA的损伤程度;以Western blotting进一步证明A549细胞发生凋亡。结果Ara-C对A549细胞的增殖有明显抑制作用;观察到特异性的凋亡小体;Ara—C导致A549细胞发生DNA链断裂,并呈明显剂量依赖性增强：Western blotting显示caspase8,9,3都不同程度被激活,多聚ADP核糖聚合酶（PARP）被剪切降解。结论揭示了Ara—C明显诱导A549细胞凋亡;细胞凋亡通路不仅通过线粒体途径,还通过膜受体途径,两条通路协同作用使凋亡信号增强;提示Ara-C对A549细胞有明显的化疗作用。     

UVA-induced apoptosis studied by the new apo/necro-Comet-assay which distinguishes viable, apoptotic and necrotic cells

An adaptation of the Comet-assay was developed which enables the discrimination of viable, apoptotic and necrotic single cells by use of the common Annexin-V staining and a dye exclusion test on the cells already embedded in agarose gel on glass slides. Membrane integrity (Ethidium-Homodimer exclusion), cellular esterase activity (Calcein blue-AM) as well as translocation of phosphadidyl-serine (Annexin-V) were analysed using these stains. The advantage of the 'apo/necro-Comet-assay' is that the viability status of individual cells can be determined and correlated with the DNA fragmentation pattern (comet) formed by the same cells. Hence, DNA damage can be assessed and correlated with viable cells or cells undergoing early, mid- or late stage apoptosis or necrosis as identified by the staining pattern. The staining was verified using heat and etoposide-induced apoptosis. This technique, among others, was used to study whether apoptotic fragmentation interferes with repair kinetics measured with the comet assay following UVA exposure (doses up to 1,280 kJ/m(2)) in the cultured human keratinocytes (HaCaT). Therefore, a time course of apoptotic events (phosphatidyl translocation and TUNEL fragmentation) was established and correlated to the DNA fragmentation in the comet-assay. Apoptotic cells were detected more than 8 h later. The combined three-colour staining method with the comet assay showed that there was no significant interference of DNA repair by apoptotic fragmentation processes since DNA repair was almost completed before the onset of apoptotic fragmentation. The apo/necro-Comet-assay reduces the general problem of false-positive results in genotoxicity tests using the Comet-assay.     

Oridonin-induced apoptosis of Jurkat cells and its mechanism

Jurkat cells in culture medium in vitro were exposed to different concentrations of oridonin. The proliferation rate of the cells was measured by MTT assay, cell apoptotic rate was detected by flow cytometry, morphology of cell apoptosis was observed by Hoechst 33258 fluorescence staining, DNA fragmentation was assayed by agarose gel electrophoresis, caspase-3 and poly(ADP-ribose) polymerase (PARP) expressions were detected by Western blotting using polyclonal anti-caspase-3 antibody and mouse anti-human PARP monoclonal antibodies, and caspase-3 activity was assayed with a colorimetric assay kit before and after apoptosis had occurred. Oridonin (over 32 mol/l) inhibited the growth of Jurkat cells and caused significant apoptosis. The suppression was both time-dependent and dose-dependent. Marked morphological changes of cell apoptosis, including condensation of chromatin and nuclear fragmentation, were clearly observed by Hoechst 33258 fluorescence staining, as well as by agarose gel electrophoresis. Western blotting showed cleavage of the caspase-3 zymogen protein (32 kDa), with the appearance of its 17 kDa subunit, and a cleaved 89-kDa fragment of 116 kDa PARP was also found, together with a concurrent increase in caspase-3 apoptotic activity. Oridonin can induce apoptosis in Jurkat cells via activation of caspase-3; the results indicate that oridonin might be an important potential anti-leukaemia reagent.     

Apoptosis of primary-culture rat microglial cells induced by pathogenic Acanthamoeba spp

To determine whether trophozoites and lysates of pathogenic Acanthamoeba spp. induce apoptosis in primary-culture microglial cells, transmission electron microscopic (TEM) examinations, assessment of DNA fragmentation by agarose gel electrophoresis, and the TdT-mediated dUTP nick-end labeling assay were performed. When a trophozoite of pathogenic Acanthamoeba culbertsoni came in contact with a microglial cell, the digipodium was observed by TEM. Nuclear chromatin condensation was observed in 10% of microglial cells, while it was not revealed when they were cocultured with weakly pathogenic Acanthamoeba royreba trophozoites. DNA fragmentation in microglial cells cocultured with the A. culbertsoni lysate was detected by electrophoresis, showing DNA ladder formation, whereas it was hardly observed in microglial cells cocultured with A. royreba. DNA fragmentation of microglial cells was also confirmed by flow cytometry analysis. The fluorescence of TdT-stained apoptotic bodies became intensely visible with microglial cells cocultured with the A. culbertsoni lysate. In contrast, with microglial cells cocultured with the A. royreba lysate, only a background level of fluorescence of TdT-stained apoptotic bodies was detected. These results suggest that some rat microglial cells cocultured with pathogenic A. culbertsoni undergo cytopathic changes which show the characteristics of the apoptotic process, such as nuclear condensation and DNA fragmentation.     

Programmed cell death in the interdigital tissue of the fetal mouse limb is apoptosis with DNA fragmentation

Background: Programmed cell death is an essential event during mammalian morphogenesis which eliminates unnecessary cells to accomplish histogenesis and organogenesis. Cell death in interdigital spaces of the developing limb is a classical example of morphogenetic cell death. We investigated whether classical programmed cell death in the interdigital tissue of the developing limb in mice is apoptosis with fragmentation of nuclear DNA and also examined sequentially the occurrence of programmed cell death and cell proliferation in the developing limb of mouse fetuses to analyze their interrelation. Methods: We examined the occurrence of apoptotic cell death in the developing limbs of mouse fetuses by using Nile blue sulphate staining, agarose gel electrophoresis for detecting DNA laddering, and a cytochemical labeling of DNA fragmentation. We also labeled proliferating cells using BrdU/anti-BrdU immunohistochemistry and examined the interrelation between apoptotic programmed cell death and cell proliferation. Results: DNA ladders, a biochemical evidence of apoptosis, were detected in DNA extracts from the interdigital tissue of day 13 mouse fetuses by agarose gel electrophoresis. Programmed cell death and DNA fragmentation were detected by Nile blue staining and cytochemical labeling of DNA fragmentation, respectively, in the interdigital mesoderm and in the regions of presumptive joints of the digit. BrdU/anti-BrdU immunohistochemistry for identifying proliferating S-phase cells revealed that interdigital mesenchymal cells cease DNA synthesis before programmed cell death and DNA fragmentation begin. Conclusions: We confirmed that both cytological apoptotic alterations and fragmentation of nuclear DNA occur in the interdigital tissue and presumptive joint areas of fetal mouse limbs, and they appear to play a significant role in the separation of digits as well as the formation of joint cavities. © 1995 Wiley-Liss, Inc.     

兔抗人DR5抗血清诱导Jurkat细胞凋亡

制备兔抗人sDR5抗血清,检测它对Jurkat细胞的生长抑制和凋亡诱导作用。采用本室制备的sDR5免疫新西兰白兔,制备兔抗人sDR5抗血清,用ELISA法测定抗sDR5抗血清效价及抗血清的特异性。MTT试验分析它对Jurkat细胞生长抑制影响,倒置光显微镜和荧光显微镜观察抗sDR5抗血清对Jurkat细胞形态的影响,用AnnexinV/PI双染试剂盒检测Jurkat细胞凋亡率,琼脂糖凝胶电泳检测Jurkat细胞中DNA的片断化。结果:获得了高效价特异性兔抗人sDR5抗血清。兔抗人sDR5抗血清对Jurkat细胞具有显著的细胞生长抑制作用,并呈剂量依赖性。兔抗人sDR5抗血清处理后,Jurkat细胞可出现典型的细胞凋亡的形态特征:细胞膜皱缩,出泡,染色质浓缩,形成凋亡小体等。流式细胞术结果显示:兔抗人sDR5血清1/80、1/160作用Jurkat细胞2 h,细胞凋亡率分别为54.98%和34.13%。兔抗人sDR5抗血清可导致Jurkat细胞中的DNA片段化。本室制备的兔抗人sDR5抗血清能抑制Jurkat细胞生长和诱导Jurkat细胞凋亡。     

Detection of Alu sequences and mtDNA in comets using padlock probes

Single cell gel electrophoresis, or the comet assay, is widely used to measure DNA damage and repair. However, the behaviour of the DNA under the conditions used for the comet assay is not fully understood. In developing a method for studying specific gene sequences within comets, using 'padlock probes' (circularizable oligonucleotide probes), we have first applied probes that hybridize to Alu repetitive elements and to mitochondrial DNA (mtDNA). During the sequence of stages in the comet assay, mtDNA progressively disperses into the surrounding agarose gel, showing no tendency to remain with nuclear DNA in the comets. In contrast, Alu probes remain associated with both tail and head DNA.     

IGF—IR反义硫代磷酸型寡核苷酸诱导胶质瘤细胞凋亡的病理学研究

目的：探讨IGF-IR基因的反义硫代磷酸型寡核苷酸对胶质瘤细胞的形态学影响。方法：根据IGF-IRcDNA序列设计正义,反义寡核苷酸片段,并对其部分碱基进行硫代磷酸修饰。体外培养的胶质瘤细胞分别经正义寡核苷酸和反义寡核苷酸处理,应用倒置显微镜活细胞观察,HE染色光镜观察,透射电镜及DNA琼脂糖凝胶电泳等方法研究IGF-IR反义硫代磷酸型寡核苷酸诱导胶质瘤细胞凋亡作用。结果：经反义寡核苷酸转染的胶质瘤细胞中,呈现典型的凋亡形态学改变,凋亡细胞最早期表现为细胞体积,容量减少,染色质凝聚,继之染色质集聚于核膜下成7新月状或块状;细胞核内染色质可完全固缩成团呈“黑洞”样或萎缩的核破裂形成一些较小的膜包绕的球体位于胞质内,最后出泡形成凋亡小体,DNA琼脂糖凝胶电泳分析经反义寡核苷酸处理的胶质瘤细胞DNA降解片段,可见有明显的小分子量DNA梯状条带,而野生型和正义寡核苷酸处理的胶质瘤细胞未见DNA梯状条带。结论：IGF-IR所介导失发泌环路IGF-I/IGF-IR。在胶质瘤细胞增殖和维持恶性表型中起重要作用。IGF-IR反义硫代磷酸型寡核苷酸能诱导胶质瘤细胞凋亡。     

Induction of apoptosis in a carp leucocyte cell line infected with turbot (Scophthalmus maximus L.) rhabdovirus

A rhabdovirus was observed from the diseased turbot (Scophthalmus maximus L.) with lethal syndrome. In this study, a carp leucocyte (CLC) cell line was used to investigate the infection process and cell death mechanism occurring during the virus infection. Strong cytopathogenic effect (CPE) and the morphological changes, such as extreme chromatin condensation, nucleus fragmentation, and apoptotic body formation, were observed under fluorescence microscopy after DAPI staining in the infected CLC cells. Transmission electron microscopy analysis showed cell shrinkage, plasma membrane blebbing, cytoplasm vacuolization, chromatin condensation, nuclear breakdown and formation of discrete apoptotic bodies. The bullet-shaped nucleocapsids were measured and ranged in size from 110 to 150 nm in length and 40 to 60 nm in diameter. And therefore the virus is called Scophthalmus maximus rhabdovirus (SMRV). Agarose gel electrophoresis analysis of the DNA extracted from infected cells showed typical DNA ladder in the course of SMRV infection. Flow cytometry analysis of SMRV infected CLC cells detected apoptotic peak in the virus infected CLC cells. Virus titre analysis and electron microscopic observation revealed that the virus replication fastigium was earlier than that of the apoptosis occurrence. No apoptosis was observed in the CLC infected with UV-inactivated SMRV. All these supported that SMRV infected CLC cells undergo apoptosis and the virus replication is necessary for apoptosis induction of CLC cells.     

用反义寡核苷酸阻断热休克蛋白70表达诱导卵巢癌细胞凋亡

目的 观察特异性热体克蛋白７０（ｈｅａｔ－ｓｈｏｃｋ ｐｒｏｔｅｉｎ,ＨＳＰ）反义寡核苷酸阻断卵巢癌细胞的ＨＳＰ７０表达,及其对卵巢癌细胞生长和增殖的影响。方法 用胎盘蓝拒染法计算卵巢癌细胞的生长抑制率。Ｇｉｅｎｓａ染色法从形态上了解凋亡的发生,用琼脂糖凝胶电脉进一步检测发生凋亡的特征性ＤＮＡ降解,流式细胞仪定量分析凋亡发生率及周期性异性。结果 用ＨＳＰ７０反义寡核苷酸处理的卵巢细胞表现有显的生长     

已烯雌酚诱导T细胞肿瘤Jurkat细胞系凋亡中转录因子Oct-1的表达

研究己烯雌酚对Ｔ细胞肿瘤的细胞凋亡诱导作用,以及凋亡过程中转录因子Ｏｃｔ－１的表达,方法采用ＤＮＡ梯形片段化,荧光染色流式细胞技术分析细胞凋亡,以电泳泳 动度迁移率法检测Ｏｃｔ－１的表达。结果己烯雌酚可诱导Ｔ细胞出现细菌凋亡,并有典型的ＤＮＡ梯形片段化,１０μｇ己烯雌酚诱导１２ｈ后,凋亡过程中细胞数达３０％以上。己烯雌酚诱导Ｔ细胞凋亡过程与Ｏｃｔ－１转录因子的表达有关。结论己烯雌酚可诱导Ｔ细胞肿瘤     

Apoptosis of Primary-Culture Rat Microglial Cells Induced by Pathogenic Acanthamoeba spp.

To determine whether trophozoites and lysates of pathogenic Acanthamoeba spp. induce apoptosis in primary-culture microglial cells, transmission electron microscopic (TEM) examinations, assessment of DNA fragmentation by agarose gel electrophoresis, and the TdT-mediated dUTP nick-end labeling assay were performed. When a trophozoite of pathogenic Acanthamoeba culbertsoni came in contact with a microglial cell, the digipodium was observed by TEM. Nuclear chromatin condensation was observed in 10% of microglial cells, while it was not revealed when they were cocultured with weakly pathogenic Acanthamoeba royreba trophozoites. DNA fragmentation in microglial cells cocultured with the A. culbertsoni lysate was detected by electrophoresis, showing DNA ladder formation, whereas it was hardly observed in microglial cells cocultured with A. royreba. DNA fragmentation of microglial cells was also confirmed by flow cytometry analysis. The fluorescence of TdT-stained apoptotic bodies became intensely visible with microglial cells cocultured with the A. culbertsoni lysate. In contrast, with microglial cells cocultured with the A. royreba lysate, only a background level of fluorescence of TdT-stained apoptotic bodies was detected. These results suggest that some rat microglial cells cocultured with pathogenic A. culbertsoni undergo cytopathic changes which show the characteristics of the apoptotic process, such as nuclear condensation and DNA fragmentation.     

浅蓝菌素诱发人结肠癌细胞凋亡的实验研究

目的　探讨脂肪酸合酶抑制剂———浅蓝菌素能否阻遏人结肠癌细胞增殖与诱发凋亡。方法　采用人结肠癌细胞系LoVo ,应用细胞形态学观察 ,噻唑蓝法 (MTT法 ) ,片断DNA琼脂糖凝胶电泳及流式细胞仪等方法进行检测和观察。结果　LoVo细胞在浅蓝菌素作用下 ,细胞增殖被阻遏 ,并呈现剂量效应关系 ,浅蓝菌素浓度 10 -9～ 10 -5mol/L增殖抑制率由 ( 2 1.0± 15 .9) %到 ( 96 .3± 2 7) %(P <0 .0 5或 0 .0 1)。同时诱发细胞发生凋亡。凋亡细胞表现为细胞固缩 ,核染色质凝聚、边集或断裂。细胞DNA裂解片段呈典型的“阶梯状”排列的条带 ,流式细胞仪显示“凋亡”峰 ,细胞周期分析浅蓝菌素能阻滞肿瘤细胞从S期进入G2 M期 ,并诱导其细胞凋亡。浅蓝菌素对人成纤维细胞增殖无明显影响。结论　脂肪酸合酶抑制剂可能通过抑制LoVo细胞内源性脂肪酸合成 ,诱发细胞凋亡来阻遏LoVo细胞的增殖     

Apoptosis induced by peste des petits ruminants virus in goat peripheral blood mononuclear cells

The ability of peste des petits ruminants virus (PPRV) to induce apoptosis in goat peripheral blood mononuclear cell (PBMC) culture was investigated. Goat PBMC were infected with PPRV and the infectivity was confirmed by cytopathic effect, demonstration of presence of infectious viral progeny and expression of viral antigens in the lymphocytes, cultured in vitro. Infected PBMC showed morphological features of apoptosis. DNA extracted from PPRV-infected cells displayed laddering pattern in agarose gel electrophoresis. Infected cells also showed significantly higher apoptotic indices measured by bisbenzimide staining than control cells. Electronmicrographs of PPRV-infected PBMC revealed features typical of apoptosis such as peripheral condensation of chromatin, blebbing of plasma membrane, fragmentation of nucleus and cell leading to formation of apoptotic bodies. Our results suggest that PPRV can induce apoptosis, in vitro, in goat lymphocytes.     

己烯雌酚诱导T细胞肿瘤Jurkat细胞系凋亡中转录因子Oct-1的表达(英文)

目的研究己烯雌酚对 T细胞肿瘤的细胞凋亡诱导作用 ,以及调亡过程中转录因子 Oct- 1的表达。方法采用DNA梯形片段化 ,荧光染色流式细胞技术分析细胞凋亡 ,以电泳泳动度迁移率法 (EMSA)检测 Oct- 1的表达。结果己烯雌酚 (5 .0 mg/L )可诱导 T细胞出现细胞凋亡 ,并有典型的 DNA梯形片段化 ,10μg己烯雌酚诱导 12 h后 ,凋亡过程中细胞数达 30 %以上。己烯雌酚诱导 T细胞凋亡过程与 Oct- 1转录因子的表达有关。结论己烯雌酚可诱导 T细胞肿瘤凋亡 ,并与转录因子 Oct- 1的表达有关。     

Neuroprotection by (-)-deprenyl and related compounds

There is an increasing number of data by in vitro and in vivo experiments, indicating that (-)-deprenyl is neuroprotective to dopamine neurons, even though detailed mechanism remains to be clarified. In this paper neuroprotection by (-)-deprenyl and structurally related compounds was examined in concern with the suppression of apoptosis induced by a reactive oxygen species, peroxynitrite generated from SIN-1. The apoptotic DNA damage was quantitatively determined using dopaminergic SH-SYSY cells and by a single cell gel electrophoresis (comet) assay. DNA damage induced by peroxynitrite was proved to be apoptotic by prevention of the damage by cycloheximide or actinomycin-D. (-)-Deprenyl and other propargylamines protected the cells from apoptosis in a dose-dependent way. (-)-Deprenyl protected the cells even after it was washed out, suggesting that it may initiate the intracellular process to repress the apoptotic death program. The study on the structure-activity relationship of (-)-deprenyl analogues revealed that a N-propargyl residue with adequate size of hydrophobic structure is essentially required for the anti-apoptotic activity. These results suggest that (-)-deprenyl and related compounds may protect neurons from apoptosis and be applicable to delay the deterioration of neurons during advancing ageing and in neurodegenerative disorders.     

γ-terpineol inhibits cell growth and induces apoptosis in human liver cancer BEL-7402 cells in vitro

To investigate the effect of γ-terpineol on cell proliferation and apoptosis of human hepatoma BEL-7402 cells to elucidate its molecular mechanism. Here, BEL-7402 cells were treated with various concentrations (40, 80, 160, 320 and 640 μg/ml) of γ-terpineol for 48 h, cell proliferation was determined by 3-(4,5-dimethyl-thiazolyl-2)-2,5-diphenyl tetrazolium bromides (MTT) assay. Cell colony inhibition was determined by soft agar assay. Apoptosis and possible molecular mechanisms were evaluated by morphological observation, flow cytometry analysis, and DNA fragmentation assay. The γ-terpineol significantly suppressed BEL-7402 cell proliferation in a dose-dependent manner. Characteristic morphological and biochemical changes associated with apoptosis such as cells shrinkage, deformation and vacuolization of mitochondria, nuclear chromatin condensation and fragmentation, formation of apoptotic bodies were observed after BEL-7402 cells treated with γ-terpineol for 24 h and 48 h. Cell cycle were displayed by flow cytometry analysis, the γ-terpineol treatment resulted in accumulation of cells at G₁ or S phase and a blockade of cell proliferation compared to control group. Treating BEL-7402 cells with 320 μg/ml of γ-terpineol for 36 h and 48 h, a typical apoptotic “DNA ladder” was observed using DNA fragmentation assay. The present study demonstrated that possible anti-cancer mechanism of γ-terpineol on human hematomas cells is through inducing cell apoptosis to suppress tumor cell growth.