A simple method for accurate estimation of apoptotic cells

The fast-halo assay for the assessment of DNA damage at the single-cell level

The detection of breaks in mammalian cell DNA and the measurement of their repair represent primary endpoints for genotoxicity testing. Over the past three decades many techniques sensitive to the presence of DNA breaks have been developed: their availability significantly increased the knowledge in the area of genetic toxicology. In general, these techniques have evolved to become more sensitive and flexible as well as less complicated. The fast-halo assay (FHA) is a very recent method to detect DNA-strand breakage induced either by various genotoxic agents or secondary to apoptotic DNA cleavage, and to study the repair of primary DNA breaks at the single-cell level. In FHA, damaged DNA is separated from intact one by means of solvent gradient, stained with ethidium bromide and visualized under a fluorescence microscope. The level of DNA breaks is then determined with an image analysis software. FHA is as sensitive, reliable, and flexible as the well-established comet assay, but it has the advantage of being, as compared to any other existing method, the most rapid and less expensive one. Taken collectively, these unique features render FHA the ideal method to perform a large number of genotoxicity tests on mammalian cells in a particularly cost-effective and time-saving manner.

Estimation of Apoptosis and Necrosis Caused by PesticidesIn Vitroon Human Lymphocytes Using DNA Diffusion Assay

Organophosphorus pesticides like monocrotophos, profenofos, chlorpyrifos, and acephate are most commonly used in India for agriculture and public health programs. Previous studies have revealed that at low doses, organophosphorus pesticides not only act as genotoxic agents but also affect several other biochemical pathways. The aim of the current investigation was to assess apoptosis and necrosis caused by these pesticides on human peripheral blood lymphocytes under in vitro conditions using the DNA diffusion assay. Our studies have revealed that all the above pesticides induced apoptosis and necrosis in cultured human peripheral blood lymphocytes in in vitro conditions. The results are statistically significant (p < 0.001). Data on these alterations of immune cells are required for understanding the subchronic effects mediated by pesticides on nontarget organisms.

DNA fragmentation in microorganisms assessed in situ

Chromosomal DNA fragmentation may be a direct or indirect outcome of cell death. Unlike DNA fragmentation in higher eukaryotic cells, DNA fragmentation in microorganisms is rarely studied. We report an adaptation of a diffusion-based assay, developed as a kit, which allows for simple and rapid discrimination of bacteria with fragmented DNA. Intact cells were embedded in an agarose microgel on a slide, incubated in a lysis buffer to partially remove the cell walls, membranes, and proteins, and then stained with a DNA fluorochrome, SYBR Gold. Identifying cells with fragmented DNA uses peripheral diffusion of DNA fragments. Cells without DNA fragmentation show only limited spreading of DNA fiber loops. These results have been seen in several gram-negative and gram-positive bacteria, as well as in yeasts. Detection of DNA fragmentation was confirmed by fluoroquinolone treatment and by DNA breakage detection-fluorescence in situ hybridization. Proteus mirabilis with spontaneously fragmented DNA during exponential and stationary growth or Escherichia coli with DNA damaged after exposure to hydrogen peroxide or antibiotics, such as ciprofloxacin or ampicillin, was clearly detected. Similarly, fragmented DNA was detected in Saccharomyces cerevisiae after amphotericin B treatment. Our assay may be useful for the simple and rapid evaluation of DNA damage and repair as well as cell death, either spontaneous or induced by exogenous stimuli, including antimicrobial agents or environmental conditions.

Use of the comet assay in environmental toxicology

The comet assay, also known as the single-cell gel electrophoresis assay, is a method of detecting DNA damage in virtually any nucleated cell. The comet assay has significant advantages over other genotoxicity tests, but it is very sensitive to subtle changes that can yield appreciable variability in results. The purpose of our chapter is to present background information and detailed standard operating procedures for the use of the alkaline comet assay in environmental genotoxicity assessment. We address pitfalls and concerns associated with conducting the comet assay, and briefly discuss modifications of the general alkaline procedure that can be used to address different issues relevant to environmental toxicology.

Application of DNA diffusion assay in earthworm coelomocytes

We have applied the DNA diffusion assay proposed by Singh (2000) Exp Cell Res 256:328-337, for quantitative estimation of apoptosis in earthworm coelomocytes, exposed to Chromium (VI) and cypermethrin as model toxicants in vitro. The DNA diffusion assay was originally described for mammalian cells. H2O2, Sodium ascorbate, and hyperthermia were used as positive controls in present study. Apoptosis such as DNA diffusion occurred in dose-dependent manner for Chromium (VI) and cypermethrin at very low concentration (1, 3, and 10 ppm for Chromium (VI) and 4, 8, and 16 ppm for cypermethrin). Three distinct patterns (apoptosis like DNA diffusion, necrosis, and normal) were observed in exposed and nonexposed cells. Present study is probably the first report of application of the DNA diffusion technique in earthworm coelomocytes. Findings of this study indicate that this assay has potential for use in invertebrate cells to differentiate between apoptosis and necrosis.

Phototoxicity and cytotoxicity of fullerol in human lens epithelial cells

The water-soluble, hydroxylated fullerene [fullerol, nano-C60(OH)22-26] has several clinical applications including use as a drug carrier to bypass the blood ocular barriers. We have assessed fullerol's potential ocular toxicity by measuring its cytotoxicity and phototoxicity induced by UVA and visible light in vitro with human lens epithelial cells (HLE B-3). Accumulation of nano-C60(OH)22-26 in the cells was confirmed spectrophotometrically at 405 nm and cell viability estimated using MTS and LDH assays. Fullerol was cytotoxic to HLE B-3 cells maintained in the dark at concentrations higher than 20 microM. Exposure to either UVA or visible light in the presence of >5 microM fullerol-induced phototoxic damage. When cells were pretreated with non-toxic antioxidants: 20 microM lutein, 1 mM N-acetyl cysteine, or 1 mM l-ascorbic acid prior to irradiation, only the singlet oxygen quencher-lutein significantly protected against fullerol photodamage. Apoptosis was observed in lens cells treated with fullerol whether or not the cells were irradiated, in the order UVA>visible light>dark. Dynamic light scattering (DLS) showed that in the presence of the endogenous lens protein alpha-crystallin, large aggregates of fullerol were reduced. In conclusion, fullerol is both cytotoxic and phototoxic to human lens epithelial cells. Although the acute toxicity of water-soluble nano-C60(OH)22-26 is low, these compounds are retained in the body for long periods, raising concern for their chronic toxic effect. Before fullerols are used to deliver drugs to the eye, they should be tested for photo- and cytotoxicity in vivo.

Spermatozoal sensitive biomarkers to defective protaminosis and fragmented DNA

Human sperm DNA damage may have adverse effects on reproductive outcome. Infertile men possess substantially more spermatozoa with damaged DNA compared to fertile donors. Although the extent of this abnormality is closely related to sperm function, the underlying etiology of ensuing male infertility is still largely controversial. Both intra-testicular and post-testicular events have been postulated and different mechanisms have been proposed to explain the presence of damaged DNA in human spermatozoa. Three among them, i.e. abnormal chromatin packaging, oxidative stress and apoptosis, are the most studied and discussed in the present review. Furthermore, results from numerous investigations are presented, including our own findings on these pathological conditions, as well as the techniques applied for their evaluation. The crucial points of each methodology on the successful detection of DNA damage and their validity on the appraisal of infertile patients are also discussed. Along with the conventional parameters examined in the standard semen analysis, evaluation of damaged sperm DNA seems to complement the investigation of factors affecting male fertility and may prove an efficient diagnostic tool in the prediction of pregnancy outcome.

Methods and goals for the use of in vitro and in vivo chemosensitivity testing

Sensitive, specific, and accurate methods to assay chemosensitivity are needed to (1) screen new therapeutic agents, (2) identify patterns of chemosensitivity for different tumor types, (3) establish patterns of cross-resistance and sensitivity in treatment of naïve and relapsing tumors, (4) identify genomic and proteomic profiles associated with sensitivity, (5) correlate in vitro response with preclinical in vivo effects and clinical outcomes for a particular therapeutic agent, and (6) tailor chemotherapy regimens to individual patients. Various methods are available to achieve these end points, including several in vitro clonogenic and proliferation assays, cell metabolic activity assays, molecular assays to monitor expression of markers for responsiveness, drug resistance, and for induction of apoptosis, in vivo tumor growth and survival assays in metastatic and orthotopic models, and in vivo imaging assays. The advantages and disadvantages of the specific assays are discussed. A summary of research questions related to chemosensitivity testing is also included.

T cell targeting and phagocytosis of apoptotic biliary epithelial cells in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is characterized by loss of tolerance against ubiquitously expressed mitochondrial autoantigens followed by biliary and salivary gland epithelial cell (BEC and SGEC) destruction by autoreactive T cells. It is unclear why BECs and SGECs are targeted. Previous work demonstrated that the reduced form of the major PBC autoantigen predominated in apoptotic BECs and SGECs as opposed to an oxidized form in other apoptotic cells. This led to the hypothesis that presentation of novel self-peptides from phagocytosed apoptotic BECs might contribute to BEC targeting by autoreactive T cells. The effect of autoantigen redox status on self-peptide formation was examined along with the phagocytic ability of BECs. Oxidation of PBC autoantigens first was shown to be due to protein S-glutathionylation of lipoyllysine residues. Absence of protein S-glutathionylation generated novel self-peptides and affected T cell recognition of a lipoyllysine containing peptide. Liver biopsy staining revealed BEC phagocytosis of apoptotic BECs (3.74+/-2.90% of BEC) was present in PBC (7 of 7 cases) but not in normal livers (0 of 3). BECs have the ability to present novel mitochondrial self-peptides derived from phagocytosed apoptotic BECs. Apoptotic cell phagocytosis by non-professional phagocytes may influence the tissue specificity of autoimmune diseases.

The comet assay as a method of assessment of neurotoxicity: usefulness for drugs of abuse

Comet assay is a quick and versatile method for assessing DNA damage in individual cells. It allows the detection of single and double DNA strand breaks, as well as the presence of alkali labile sites. DNA breaks may represent the direct effect of some damaging agent, or they may be intermediates in cellular repair. DNA strand breaks may also come from the action of free radicals generated by oxidative stress processes. The present article summarizes some data from our and other groups underlining the suitability of the Comet assay in assessing neurotoxicity and its potential in evaluating drugs of abuse-related genotoxicity.

Evidence of modified nuclear protein matrix in human spermatozoa with fragmented deoxyribonucleic acid

Human spermatozoa were processed for determination of DNA fragmentation with use of an in situ diffusion assay, so that those cells containing DNA fragmentation produce extensive peripheral dissemination of DNA fragments after lysis in an agarose microgel. Quantification of specific protein staining confirmed that sperm cells without DNA fragmentation had almost complete removal of nuclear matrix proteins, whereas spermatozoa with DNA fragmentation tended to retain residual nucleoskeletal protein in a collapsed and condensed state. This result suggests that a modified nuclear protein matrix associates with fragmented sperm DNA.

Cell death and thymic export during fetal life

In the fetus the peripheral T cell pool expands as the fetus grows, but the mechanisms that regulate T cell homeostasis during fetal life are unknown. Here, we show that the peripheral T cell pool in the sheep fetus is established by the export from the fetal thymus of twice as many CD8+ as CD4+ thymic emigrants every day. Clonal deletion of CD4+ thymocytes in the fetal thymus appeared to be more stringent than was the case for CD8+ thymocytes because only 1 in 35 single-positive CD4 (SPCD4) thymocytes was exported from the thymus whereas the majority (2/3) of the single-positive CD8 (SPCD8) thymocytes were exported from the fetal thymus each day. Furthermore, within the thymus, the number of apoptotic SPCD4 thymocytes was 40 times greater than the number of apoptotic SPCD8 thymocytes. A tissue-specific migration of CD8+ emigrants localizing in the spleen was also established in the fetus in contrast to CD4+ emigrants, which migrated randomly to spleen and LN.

Influence of the SCGE protocol on the amount of basal DNA damage detected in the Mediterranean mussel, Mytilus galloprovincialis

Genotoxicity studies using the single cell gel electrophoresis (SCGE) assay indicate that basal levels of DNA strand breaks (SBs) in marine invertebrates are higher and more variable than those in marine vertebrates. This elevated level of DNA damage was attributed to a large number of alkali-labile sites, which are characteristic of the tightly-packaged DNA in invertebrate cells. To investigate if altering the SCGE protocol can artificially modulate high levels of SBs, SCGE experiments were performed on haemocytes from the Mediterranean mussel (Mytilus galloprovincialis) using proteinase K (PK) digestion in combination with assay buffers containing various concentrations of EDTA. In addition, the effects of Trolox (soluble antioxidant) and aurintricarboxylic acid (ATA; inhibitor of Ca(2+)/Mg(2+)-dependent nucleases) also were tested. The levels of SBs in M. galloprovincialis cells were compared with SBs in cells from a terrestrial mollusk (the snail Helix aspersa), and a teleost fish (the seabass Dicentrarchus labrax). The integrity of M. galloprovincialis DNA isolated with phenol extractions using EDTA, Trolox, and ATA was further assayed by gel electrophoresis. High SBs in mussel cells were reduced by combining EDTA with PK digestion, or using Trolox or ATA during cell processing for the SCGE assay. Snails and seabass had lower levels of SBs in the SCGE assay, and the levels were not affected by the protocol modifications. Adding EDTA, Trolox, or ATA to phenol extractions of M. galloprovincialis genomic DNA also reduced the extent of DNA fragmentation. These results suggest that the internal fluids of M. galloprovincialis may increase the basal levels of DNA SBs through oxidative and/or enzyme-mediated pathways. M. galloprovincialis is used extensively as a sentinel species for assessing the genotoxic hazard of marine pollutants. Our data suggest that the SCGE protocol should be carefully considered when assessing DNA damage in these species.

Subcellular compartmentalization of glutathione: correlations with parameters of oxidative stress related to genotoxicity

Glutathione (GSH) is a major component of the antioxidant defence system of mammalian cells and is found in subcellular pools within the cytoplasm, nucleus and mitochondria. To evaluate the relationships between these pools and parameters of oxidative stress related to genotoxicity, wild type (WT) and 8-oxo-2'-deoxyguanosine glycosylase 1 (OGG1)-null (mOGG1(-/-)) mouse embryonic fibroblasts (MEF) were treated with buthionine sulphoximine (BSO; 0-1000 microM, 24 h), an inhibitor of GSH biosynthesis. BSO treatment resulted in a concentration-dependent depletion of GSH from the cytoplasm, but depletion of mitochondrial and nuclear GSH occurred only at concentrations > or =100 microM. GSH levels were correlated with reactive oxygen species (ROS), lipid peroxidation (measured as the increase in the genotoxic end-product malondialdehyde (MDA)) and oxidative DNA modifications, measured as both frank DNA strand-breaks (FSB) and oxidized purine lesions (OxP) using the alkaline comet assay with formamidopyrimidine DNA glycosylase (FPG) modification; this system allowed for the identification of BSO-induced DNA modifications as primarily mutagenic 8-oxo-2'-deoxyguanosine lesions. A number of significant correlations were observed. First, negative linear correlations were observed between mitochondrial GSH and ROS (r = -0.985 and r = -0.961 for WT and mOGG1(-/-) MEF, respectively), and mitochondrial GSH and MDA (r = -0.967 and r = -0.963 for WT and mOGG1(-/-) MEF, respectively). Second, positive linear correlations were observed between ROS and MDA (r = 0.996 and r = 0.935 for WT and mOGG1(-/-) MEF, respectively), and ROS and OxP (r = 0.938 and r = 0.981 for WT and mOGG1(-/-) MEF, respectively). Finally, oxidative DNA modifications displayed a negative linear correlation with nuclear GSH (r = -0.963 and -0.951 between nuclear GSH and FSB and OxP, respectively, for WT MEF and r = -0.960 between nuclear GSH and OxP in mOGG1(-/-) MEF), thus, demonstrating the genotoxic potential of compounds that deplete GSH. The findings highlight the critical roles of the mitochondrial and nuclear GSH pools in protecting cellular components, particularly DNA, from oxidative modification.

The fast halo assay: an improved method to quantify genomic DNA strand breakage at the single-cell level

The present study describes the improvement of a technique, the alkaline-halo assay (AHA), for the assessment of DNA single-strand breakage at the single-cell level. AHA involves a series of sequential steps in which cells are embedded in melted agarose and spread onto microscope slides, incubated in a high-salt alkaline lysis solution, then in a hypotonic alkaline solution and, finally, stained with ethidium bromide (EB). Under these conditions, single-stranded DNA fragments diffuse radially from the nuclear cage and generate a fluorescent image that resembles a halo concentric to the nuclear remnants: the area of the halo is a direct function of the extent of DNA strand scission. These phenomena can be conveniently monitored with a fluorescence microscope and quantified by image-processing analysis. The behaviour of single-stranded DNA fragments under the conditions of the modified assay, called fast halo assay (FHA), is essentially the same as in AHA. The modifications consist in the simplification of the lysis, denaturation and staining procedures, and allow, as compared with AHA, the preparation of samples within 15 min, with a two-third reduction in total processing time, using only two reagents to promote DNA extraction and staining: NaOH and EB. A variation of the FHA operating at non-denaturing conditions to discriminate apoptotic cells from non-apoptotic cells bearing DNA single-strand breaks is also illustrated. To benchmark FHA sensitivity and reliability, the DNA single-strand breaks (SSBs) resulting either from exposure of cultured mammalian cells to different DNA-damaging agents or from secondary apoptotic DNA cleavage, have been quantified and results compared with the outcomes of reference techniques run in parallel, namely AHA, comet assay and Hoechst 33342 staining. The results indicate that FHA has the same reliability and sensitivity of the reference assays, but presents the additional advantages of being inexpensive, more rapid and strikingly simple.

Evaluation of DNA damage induced by atrazine and atrazine-based herbicide in human lymphocytes in vitro using a comet and DNA diffusion assay

Atrazine is one of the most widely used herbicides in the world. When applied, it is not used as a pure active ingredient but in the form of commercial formulations. Besides atrazine, these formulations contain other substances that might represent a risk to human health due to their mutual interactions. We evaluated the genotoxicity, apoptosis and necrosis induction of atrazine as an active ingredient, the commercial formulation Gesaprim, and a Gesaprim adjuvant mixture without atrazine by comet and DNA diffusion assay, respectively. Human lymphocytes were treated for 0.5, 1, 3, 5, and 8 h with 0.047 microg/ml, 0.47 microg/ml, 4.7 microg/ml of substances tested both in the presence and in the absence of an exogenous metabolic activator. Atrazine did not appear to be genotoxic or to be capable of inducing apoptosis or necrosis. Unlike atrazine, Gesaprime and the adjuvant mixture increased DNA damage in lymphocytes. After 5 h of treatment, it also increased the number of apoptotic cells. Metabolic activation additionally enhanced the DNA-damaging potential of Gesaprim and the adjuvant mixture but did not affect atrazine genotoxicity. Thus, both assay endpoints differed significantly for the active ingredient and formulation. To evaluate the potential health risk of simultaneous exposure to adjuvants and an active ingredient, further efforts using a biomonitoring approach should be made.

DNA staining with the fluorochromes EtBr, DAPI and YOYO-1 in the comet assay with tobacco plants after treatment with ethyl methanesulphonate, hyperthermia and DNase-I

We applied the alkaline version of the single-cell gel electrophoresis (comet) assay to roots and leaves of tobacco (Nicotiana tabacum var. xanthi) seedlings or isolated leaf nuclei treated with: (1) the alkylating agent ethyl methanesulphonate, (2) necrotic heat treatments at 50 degrees C, and (3) DNase-I. All three treatments induced a dose-dependent increase in DNA migration, expressed as percentage of tail DNA. A comparison of the fluorochrome DNA dyes ethidium bromide, DAPI and YOYO-1 demonstrated that for the alkaline version of the comet assay in plants, the commonly used fluorescent dye ethidium bromide can be used with the same efficiency as DAPI or YOYO-1.

Recombinant hybrid protein, Shiga toxin and granulocyte macrophage colony stimulating factor effectively induce apoptosis of colon cancer cells

AIM: To investigate the selective cytotoxic effect of constructed hybrid protein on cells expressing granulocyte macrophage colony stimulating factor (GM-CSF) receptor.

METHODS: HepG2 (human hepatoma) and LS174T (colon carcinoma) were used in this study. The fused gene was induced with 0.02 % of arabinose for 4 h and the expressed protein was detected by Western blotting. The chimeric protein expressed in E.coli was checked for its cytotoxic activity on these cells and apoptosis was measured by comet assay and nuclear staining.

RESULTS: The chimeric protein was found to be cytotoxic to the colon cancer cell line expressing GM-CSFRs, but not to HepG2 lacking these receptors. Maximum activity was observed at the concentration of 40 ng/mL after 24 h incubation. The IC₅₀ was 20  ±  3.5 ng/mL.

CONCLUSION: Selective cytotoxic effect of the hybrid protein on the colon cancer cell line expressing GM-CSF receptors (GM-CSFRs) receptor and apoptosis can be observed in this cell line. The hybrid protein can be considered as a therapeutic agent.

DNA damage in leukocytes of workers occupationally exposed to 1-bromopropane

1-bromopropane (1-BP; n-propyl bromide) (CAS No. 106-94-5) is an alternative to ozone-depleting chlorofluorocarbons that has a variety of potential applications as a degreasing agent for metals and electronics, and as a solvent vehicle for spray adhesives. Its isomer, 2-brompropane (2-BP; isopropyl bromide) (CAS No. 75-26-3) impairs antioxidant cellular defenses, enhances lipid peroxidation, and causes DNA damage in vitro. The present study had two aims. The first was to assess DNA damage in human leukocytes exposed in vitro to 1- or 2-BP. DNA damage was also assessed in peripheral leukocytes from workers with occupational exposure to 1-BP. In the latter assessment, start-of- and end-of-work week blood and urine samples were collected from 41 and 22 workers at two facilities where 1-BP was used as a solvent for spray adhesives in foam cushion fabrication. Exposure to 1-BP was assessed from personal-breathing zone samples collected for 1-3 days up to 8h per day for calculation of 8h time weighted average (TWA) 1-BP concentrations. Bromide (Br) was measured in blood and urine as a biomarker of exposure. Overall, 1-BP TWA concentrations ranged from 0.2 to 271 parts per million (ppm) at facility A, and from 4 to 27 ppm at facility B. The highest exposures were to workers classified as sprayers. 1-BP TWA concentrations were statistically significantly correlated with blood and urine Br concentrations. The comet assay was used to estimate DNA damage. In vitro, 1- or 2-BP induced a statistically significant increase in DNA damage at 1mM. In 1-BP exposed workers, start-of- and end-of-workweek comet endpoints were stratified based on job classification. There were no significant differences in DNA damage in leukocytes between workers classified as sprayers (high 1-BP exposure) and those classified as non-sprayers (low 1-BP exposure). At the facility with the high exposures, comparison of end-of-week values with start-of-week values using paired analysis revealed non-sprayers had significantly increased comet tail moments, and sprayers had significantly increased comet tail moment dispersion coefficients. A multivariate analysis included combining the data sets from both facilities, log transformation of 1-BP exposure indices, and the use of multiple linear regression models for each combination of DNA damage and exposure indices including exposure quartiles. The covariates were gender, age, smoking status, facility, and glutathione S-transferase M1 and T1 (GSTM1, GSTT1) polymorphisms. In the regression models, start-of-week comet tail moment in leukocytes was significantly associated with serum Br quartiles. End-of-week comet tail moment was significantly associated with 1-BP TWA quartiles, and serum Br quartiles. Gender, facility, and GSTM1 had a significant effect in one or more models. Additional associations were not identified from assessment of dispersion coefficients. In vitro and in vivo results provide limited evidence that 1-BP exposure may pose a small risk for increasing DNA damage.

Induction of Apoptosis by Disturbing Mitochondrial-Membrane Potential and Cleaving PARP in Jurkat T Cells through Treatment with Acetoxyscirpenol Mycotoxins

Paecilomyces tenuipes is a famous Chinese medicinal entomopathogenic fungus that grows within the larvae of silkworms. 4beta-acetoxyscirpendiol (4-MAS), a cytotoxic compound belonging to the scirpenol subfamily of trichothecene mycotoxin, was isolated from Paecilomyces tenuipes. To further elucidate the cytotoxic mechanism of 4-MAS, evidences of its induction of apoptosis, together with the structurally related acetoxyscirpenol moiety mycotoxins (ASMs) such as, 15-acetoxyscirpenol (15-MAS), 4,15-diacetoxyscirpenol (4,15-DAS), and 3alpha-acetyldiacetoxyscirpenol (TAS), in the human Jurkat T cell line were reported herein. In the MTT reduction and time-course cytotoxicity assays for monitoring cell viability, all the four ASMs that were tested exhibited cytotoxicity; single acetoxylation at C-4 of the scirpenol family resulted in relatively weak cytotoxicity, while acetoxylation at C-15 resulted in strong cytotoxicity regardless of the other acetoxylations at the C-3 and/or C-4 positions. Phosphatidylserine externalization was induced by all the ASMs that were treated at an early phase in a time-dependent manner, showing a typical apoptotic phenomenon, not a necrotic one. The ASMs also reduced the mitochondria's inner-membrane potential (deltaPsim) through flow cytometry analysis after staining these with DiOC6, a mitochondria-specific and voltage-dependent dye. Acetoxylation of ASM at C-15 increased deltaPsim disruption, but that at C-3 reduced the deltaPsim. The ASMs that were tested also cleaved 113 kDa PARP to an 89-kDa fragment through Western blot assay, suggesting the activation of caspase-3 and/or caspase-7 in the Jurkat T cell. DNA fragmentation was also observed to have been increased in a time-dependent manner by the ASMs that were tested in Jurkat T cells, resulting in the DNA fragmentation intensity order of 4,15-DAS>15-MAS>TAS>4-MAS. These data indicate that the Jurkat T cells that were treated with ASMs underwent typical cascades of apoptotic cell death.

Fibered confocal fluorescence microscopy for imaging apoptotic DNA fragmentation at the single-cell level in vivo

The major characteristic of cell death by apoptosis is the loss of nuclear DNA integrity by endonucleases, resulting in the formation of small DNA fragments. The application of confocal imaging to in vivo monitoring of dynamic cellular events, like apoptosis, within internal organs and tissues has been limited by the accessibility to these sites. Therefore, the aim of the present study was to test the feasibility of fibered confocal fluorescence microscopy (FCFM) to image in situ apoptotic DNA fragmentation in surgically exteriorized sheep corpus luteum in the living animal. Following intra-luteal administration of a fluorescent DNA-staining dye, YO-PRO-1, DNA cleavage within nuclei of apoptotic cells was serially imaged at the single-cell level by FCFM. This imaging technology is sufficiently simple and rapid to allow time series in situ detection and visualization of cells undergoing apoptosis in the intact animal. Combined with endoscope, this approach can be used for minimally invasive detection of fluorescent signals and visualization of cellular events within internal organs and tissues and thereby provides the opportunity to study biological processes in the natural physiological environment of the cell in living animals.

Evaluation of the nuclear DNA Diffusion Assay to detect apoptosis and necrosis

We applied the nuclear DNA Diffusion Assay, described as an accurate tool to estimate apoptotic and necrotic cells [N.P. Singh, A simple method for accurate estimation of apoptotic cells, Exp. Cell Res. 256 (2000) 328-337] to tobacco root and leaf cells. In this assay, isolated nuclei are embedded in an agarose microgel on a microscope slide and low molecular-weight DNA fragments diffuse into the microgel. Exposure of the roots to hydrogen peroxide significantly increased the average nuclear area of isolated nuclei. After 4 and 24 h of recovery, all DNA damage was repaired. The data clearly demonstrate that the manifestation of diffused nuclei upon exposure to hydrogen peroxide is not the result of non-repairable apoptotic or necrotic DNA fragmentation, but represents repairable genotoxin-induced DNA damage. In contrast, treatment with the alkylating agent ethyl methanesulphonate (EMS) followed by 24 h of recovery produced a significant increase in the average nuclear area. The contribution of apoptosis to this increase cannot be excluded. Heat treatment of leaves at 50 degrees C for 1-15 min leading to necrosis, and treatment of isolated nuclei with DNase-I, which digests DNA to nucleosome-sized fragments as during apoptosis, also led to a dose-dependent increase in the nuclear area. The use of different fluorochromes (ethidium bromide, DAPI or YOYO-1) for DNA staining yielded similar results in the DNA Diffusion Assay. As all types and sizes of diffused nuclei were observed after EMS and hydrogen peroxide treatments, we were unable to differentiate, on the basis of the structure of the nuclei, between apoptotic or necrotic DNA fragmentation and other types of genotoxin-induced DNA damage in plants.

Mechanism of ricin-induced apoptosis in human cervical cancer cells

The mechanism of ricin-induced apoptosis in human cervical cancer cell line HeLa was studied. The present study demonstrated that ricin induces apoptosis of human cervical cancer cells (HeLa) in a time dependent manner with an IC(50) for cell viability of 1 microg/ml. Ricin treatment resulted in a time dependent increase in LDH leakage, DNA fragmentation, percent apoptotic cells, generation of reactive oxygen species and depletion of intracellular glutathione levels. DNA agarose gel electrophoresis showed typical oligonucleosomal length DNA fragmentation. Additionally, DNA diffusion assay was performed to confirm DNA damage and apoptosis. Ricin activated caspase-3 as evidenced by both proteolytic cleavage of procaspase-3 into 20 and 18 kDa subunits, and increased protease activity. Caspase activity was maximum at 4h and led to the cleavage of 116 kDa poly(ADP-ribose) polymerase (PARP), resulting in the 85 kDa cleavage product. Ricin-induced caspase-3 activation also resulted in cleavage of DNA fragmentation factor-45 (DFF45/ICAD) and DFF40 or caspase-activated DNase in HeLa cells. Activation of caspase-3, cleavage of PARP and DNA fragmentation was blocked by pre-treatment with caspase-3 specific inhibitor Ac-DEVD-CHO (100 microM) and broad-spectrum caspase inhibitor Z-VAD-FMK (40 microM). Ricin-induced DNA fragmentation was inhibited by pre-treatment with PARP inhibitors 3-aminobenzamide (100 microM) and DPQ (10 microM). Our results indicate that ricin-induced cell death was mediated by generation of reactive oxygen species and subsequent activation of caspase-3 cascade followed by down stream events leading to apoptotic mode of cell death.

DNA damage in eelpout (Zoarces viviparus) from Göteborg harbour

The relationship between DNA damage and the exposure of marine organisms to environmental contaminants was examined in the Göteborg harbour area. This research is part of a wider ecotoxicological study planned to evaluate the biological impact of chemical contamination in the River Göta estuary, following a bunker oil (10-100 tonnes) spill occurred in June 2003. Here we present data on the DNA strand breaks derived using the comet assay and the presence of apoptotic cells using the diffusion assay in nucleated erythrocytes of the eelpout (Zoarces viviparus) from the study area and at a clean reference site. Polycyclic aromatic hydrocarbon metabolites were also analyzed in the bile of exposed fish. The results showed a high level of damaged DNA, paralleled by a peak in bile PAH metabolites, in fish from the most impacted site, 3 weeks after the oil spill. A significant recovery was observed in specimens from the spill site, 5 months later, but not in fish caught in the middle part of Göteborg harbour, which is chronically subjected to heavy chemical pollution. The levels of apoptic cells did not show any marked variations, but a significant recovery was observed in fish from the oil impacted site 5 months after the spill.

Commitment to apoptosis by ceramides depends on mitochondrial respiratory function, cytochrome c release and caspase-3 activation in Hep-G2 cells

Apoptosis and necrosis are distinct forms of cell death that occur in response to various agents. We studied the action of N-Acetyl-D-sphingosine (C2-ceramide) or N-hexanoyl-D-sphingosine (C6-ceramide) in human hepatoma HepG2 cell line. The cells were treated in vitro for 1-24 h. Cell toxicity was evaluated by MTT assay. DNA content was estimated by gel electrophoresis and flow cytometry. Measurement of mitochondrial respiration, analysis of cytochrome c release and caspase-3 activation were assessed in order to determine if either of these events in the induction of apoptosis and/or necrosis was predominant. We have demonstrated that C2 and C6-ceramide were cytotoxic in a time and dose-dependent manner. After 24 h of treatment with 100 microM of C2 and C6 the morphology (May-Giemsa staining) of treated cells displayed an apoptotic phenotype in C6-treated cells, confirmed by a high (sub-G1 peak > 20%) proportion by flow cytometry while a necrotic morphology was observed after C2-ceramide treatment, confirmed by DNA smearing in DNA electrophoresis. After C6-ceramide incubation, the respiratory chain was functional only slightly inhibited (20%), there was production of ATP, cytochrome c release without ROS production, activation of caspase-3 and induction of apoptosis. On the contrary, C2-ceramide inhibited the respiratory chain more intensely (80%) increased significantly ROS production, which resulted in an arrest of ATP production, no cytochrome c release and absence of caspase-3 activation. Finally after complete exhaustion of intracellular ATP, mitochondrial explosion induced necrotic cell death. In conclusion, evidence suggest that mitochondrial respiratory chain function is essential for controlling the decision of the cell to enter a apoptotic or necrosis process.

Comparison in vivo Study of Genotoxic Action of High- Versus Very Low Dose-Rate gamma-Irradiation

The aim of the present study was to compare genotoxicity induced by high- versus very low dose-rate exposure of mice to gamma-radiation within a dose range of 5 to 61 cGy using the single-cell gel electrophoresis (comet) assay and the micronucleus test. CBA/lac male mice were irradiated at a dose rate of 28.2 Gy/h (high dose rate) or 0.07 mGy/h (very low dose rate). The comet assay study on spleen lymphocytes showed that very low dose-rate irradiation resulted in a statistically significant increase in nucleoid relaxation (DNA breaks), starting from a dose of 20 cGy. Further prolongation of exposure time and, hence, increase of a total dose did not, however, lead to further increase in the extent of nucleoid relaxation. Doses of 20 and 61 cGy were equal in inducing DNA breaks in mouse spleen lymphocytes as assayed by the comet assay. Of note, the level of DNA damage by 20-61 cGy doses of chronic irradiation (0.07 mGy/h) was similar to that an induced by an acute (28.2 Gy/h) dose of 14 cGy. The bone marrow micronucleus test revealed that an increase in polychromatic erythrocytes with micronuclei over a background level was induced by very low-level gamma-irradiation with a dose of 61 cGy only, with the extent of the cytogenetic effect being similar to that of 10 cGy high-dose-rate exposure. In summary, presented results support the hypothesis of the nonlinear threshold nature of mutagenic action of chronic low dose-rate irradiation.

Detection of radiation-induced apoptosis using the comet assay

The electrophoresis pattern of apoptotic cells detected by the comet assay has a characteristic small head and spread tail. This image has been referred to as an apoptotic comet, but it has not been previously proven to be apoptotic cells by any direct method. In order to identify this image obtained by the comet assay as corresponding to an apoptotic cell, the frequency of appearance of apoptosis was examined using CHO-K1 and L5178Y cells which were exposed to gamma irradiation. As a method for detecting apoptosis, the terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) assay was used. When the frequency of appearance of apoptotic cells following gamma irradiation was observed over a period of time, there was a significant increase in appearance of apoptosis when using the TUNEL assay. However, there was only a slight increase when using the comet assay. In order to verify the low frequency of appearance of apoptosis when using the comet assay, we attempted to use the TUNEL assay to stain the apoptotic comets detected in the comet assay. The apoptotic comets were TUNEL positive and the normal comets were TUNEL negative. This indicates that the apoptotic comets were formed from DNA fragments with 3'-hydroxy ends that are generated as cells undergo apoptosis. Therefore, it was understood that the characteristic pattern of apoptotic comets detected by the comet assay corresponds to cells undergoing apoptosis.

Effects of age on DNA double-strand breaks and apoptosis in human sperm

OBJECTIVE

This study was designed to explore the relationship between men's age and DNA damage and apoptosis in human spermatozoa.

DESIGN

Semen samples were collected from men between the ages of 20 and 57 years. Sperm DNA double-strand breaks were assessed using the neutral microgel electrophoresis (comet) assay, and apoptosis was estimated using the DNA diffusion assay.

SETTING

Academic medical center.

PATIENT(S)

Sixty-six men aged 20 to 57 years were recruited from infertility laboratory and general populations and consented to donate a semen sample. Recruitment was determined by time and day of analysis; the only exclusions were for azoospermia, prostatitis, or prior cancer therapy.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

DNA damage and apoptosis in human sperm.

RESULT(S)

Age correlated with an increasing percentage of sperm with highly damaged DNA (range: 0-83%) and tended to inversely correlate with percentage of apoptotic sperm (range: 0.3%-23%). For example, percentage of sperm with highly damaged DNA, comet extent, DNA break number, and other comet measures was statistically significantly higher in men aged 36-57 years than in those aged 20-35 years, but percentage apoptosis was statistically significantly lower in the older group. Semen analysis showed percentage motility to be significantly higher in younger age groups.

CONCLUSION(S)

This study clearly demonstrates an increase in sperm double-stranded DNA breaks with age. Our findings also suggest for the first time an age-related decrease in human sperm apoptosis. These novel findings may indicate deterioration of healthy sperm cell selection process with age.

Apoptosis: biochemical aspects and clinical implications

Apoptosis and necrosis represent two distinct types of cell death. Apoptosis possesses unique morphologic and biochemical features which distinguish this mechanism of programmed cell death from necrosis. Extrinsic apoptotic cell death is receptor-linked and initiates apoptosis by activating caspase 8. Intrinsic apoptotic cell death is mediated by the release of cytochrome c from mitochondrial and initiates apoptosis by activating caspase 3. Cancer chemotherapy utilizes apoptosis to eliminate tumor cells. Agents which bind to the minor groove of DNA, like camptothecin and Hoechst 33342, inhibit topoisomerase I, RNA polymerase II, DNA polymerase and initiate intrinsic apoptotic cell death. Hoechst 33342-induced apoptosis is associated with disruption of TATA box binding protein/TATA box complexes, replication protein A/single-stranded DNA complexes, topoisomerase I/DNA cleavable complexes and with an increased intracellular concentration of E2F-1 transcription factor and nitric oxide concentration. Nitric oxide and transcription factor activation or respression also regulate the two apoptotic pathways. Some human diseases are associated with excess or deficient rates of apoptosis, and therapeutic strategies to regulate the rate of apoptosis include inhibition or activation of caspases, mRNA antisense to reduce anti-apoptotic factors like Bcl-2 and survivin and recombinant TRAIL to activate pro-apoptotic receptors, DR4 and DR5.

The postgenomic era: implications for the clinical laboratory

OBJECTIVES

To review the advances in clinically useful molecular biological techniques and to identify their applications in clinical practice, as presented at the Tenth Annual William Beaumont Hospital DNA Symposium.

DATA SOURCES

The 11 manuscripts submitted were reviewed and their major findings were compared with literature on the same topic.

STUDY SELECTION

Manuscripts address creative thinking techniques applied to DNA discovery, extraction of DNA from clotted blood, the relationship of mitochondrial dysfunction in neurodegenerative disorders, and molecular methods to identify human lymphocyte antigen class I and class II loci. Two other manuscripts review current issues in molecular microbiology, including detection of hepatitis C virus and biological warfare. The last 5 manuscripts describe current issues in molecular cardiovascular disease, including assessing thrombotic risk, genomic analysis, gene therapy, and a device for aiding in cardiac angiogenesis.

DATA SYNTHESIS

Novel problem-solving techniques have been used in the past and will be required in the future in DNA discovery. The extraction of DNA from clotted blood demonstrates a potential cost-effective strategy. Cybrids created from mitochondrial DNA-depleted cells and mitochondrial DNA from a platelet donor have been useful in defining the role mitochondria play in neurodegeneration. Mitochondrial depletion has been reported as a genetically inherited disorder or after human immunodeficiency virus therapy. Hepatitis C viral detection by qualitative, quantitative, or genotyping techniques is useful clinically. Preparedness for potential biological warfare is a responsibility of all clinical laboratorians. Thrombotic risk in cardiovascular disorders may be assessed by coagulation screening assays and further defined by mutation analysis for specific genes for prothrombin and factor V Leiden. Gene therapy for reducing arteriosclerotic risk has been hindered primarily by complications introduced by the vectors used to introduce the therapeutic genes. Neovascularization in cardiac muscle with occluded vessels represents a promising method for recovery of viable tissue following ischemia.

CONCLUSIONS

The sequence of the human genome was reported by 2 groups in February 2001. The postgenomic era will emphasize the use of microarrays and database software for genomic and proteomic screening in the search for useful clinical assays. The number of molecular pathologic techniques and assays will expand as additional disease-associated mutations are defined. Gene therapy and tissue engineering will represent successful therapeutic adjuncts.

Measurement of DNA damage associated with apoptosis by laser scanning cytometry

BACKGROUND

Phosphatidylserine (PS) binding by annexin V (AV) is an early membrane marker of apoptosis. Using laser scanning cytometry (LSC) and the comet assay, we showed that the DNA of AV(+) cells is so highly fragmented that it cannot be quantified by the comet assay (Bacso et al.: Cancer Res 60:4623-8, 2000).

METHODS

The "halo" assay was used instead of the comet assay to quantify DNA damage associated with apoptosis. The LSC was used to measure both AV fluorescence and DNA damage on the same Jurkat cells following treatment with anti-Fas. The data from both sets of measurements were merged, allowing direct correlation of membrane and nuclear markers of cell death.

RESULTS

AV(+) cells had significant DNA damage determined by the ratio between nuclear DNA and peripheral (migrated) DNA. Cells in the early and late stages of apoptosis could be discriminated on the basis of DNA content. In addition, it was possible to distinguish between apoptotic and necrotic cells in the AV(+) propidium iodide-positive population based on DNA content and DNA damage. The addition of specific inhibitors for caspases-8, 9, and 3 blocked both PS externalization and DNA fragmentation, indicating these events are downstream from caspase activation.

CONCLUSIONS

This technique allows accurate distinction between apoptotic and necrotic cells and cytometric grading of apoptosis.

Microgels for estimation of DNA strand breaks, DNA protein crosslinks and apoptosis

This report describes a part of the evolution of microgel electrophoresis in the author's laboratory for the last 15 years. It also describes the importance of estimation of DNA single and double strand breaks, DNA crosslinks and apoptosis. Some experiments based on each methodology are included here. A new protocol for rapid and efficient precipitation of DNA in microgel is included. A step by step description of laboratory protocol is also included.