Quantification Of Apoptotic Cells Research Articles

Cell death in the development of the posterior cortex in male and female rats

Work from our laboratory has shown that adult male rats have 19% more neurons than female rats in the binocular region and 18% more in the monocular region of the primary visual cortex (Reid and Juraska [1992] J Comp Neurol 321:448-455; Nuñez et al., [1999] Soc Neurosci Abstr 25:229). In the current experiment, we investigated whether cell death in male and female rats (postnatal days 2-35) contributes to the formation of these differences. Using stereological techniques, we investigated neuron density along with pyknotic and apoptotic (TdT-mediated deoxyuridine triphosphate nick end-labeled) cell density in the developing posterior cortex (future primary visual cortex). Although no sex differences in neuronal density were found in early development, we observed a differential time course of cell death between the sexes. Consistent with earlier reports, males displayed a rapid rise in cell death, with a peak on day 7 followed by a sharp decline to negligible levels by day 15. Females, however, displayed moderate peaks of cell death on days 7 and 11, with the persistence of low-to-modest levels until day 25. Similar patterns were obtained from both pyknotic and apoptotic cell quantification. Also, a formula was developed to estimate the percentage of cells that die during development and the amount of time a dying cell is visible. This study demonstrates that there is a prolonged period of cell death in the posterior cortex of developing female rats that appears to result in more cell death in females than males. This may be an important mechanism by which the sex difference in adult neuron number is created.

Detection of Apoptosis by a Modified Trichrome Technique

This report describes a cytological method that allows the easy detection and quantification of apoptotic cells and bodies. By simple and inexpensive modifications of Crossmon's trichrome method, that consist of omitting the stain in Mayer acid hemalum, reduction of the staining time and concentration of fuchsin and orange G, and increasing the stain of light green to 30 min, differential staining of apoptotic and normal nuclei in paraffin sections was obtained. The procedure was applied to the study of the apoptotic process evoked by cyclophosphamide in the thymus of mice, Peyer's patches, and crypts of the small intestine. Quantitative comparison of this method with H&E demonstrated statistically no significant differences. The assay is easy and reliable, and its application to cell biology and experimental pathology offers many possibilities. (The J Histotechnol 22:301, 1999)

Detection of Apoptosis by a Modified Trichrome Technique

This report describes a cytological method that allows the easy detection and quantification of apoptotic cells and bodies. By simple and inexpensive modifications of Crossmon's trichrome method, that consist of omitting the stain in Mayer acid hemalum, reduction of the staining time and concentration of fuchsin and orange G, and increasing the stain of light green to 30 min, differential staining of apoptotic and normal nuclei in paraffin sections was obtained. The procedure was applied to the study of the apoptotic process evoked by cyclophosphamide in the thymus of mice, Peyer's patches, and crypts of the small intestine. Quantitative comparison of this method with H&E demonstrated statistically no significant differences. The assay is easy and reliable, and its application to cell biology and experimental pathology offers many possibilities. (The J Histotechnol 22:301, 1999)

Technetium-99m HYNIC-annexin V: a potential radiopharmaceutical for the in-vivo detection of apoptosis.

Either inadequate or excessive apoptosis (programmed cell death) is associated with many diseases. A method to image apoptosis in vivo, rather than requiring histologic evaluation of tissue, could assist with therapeutic decision making in these disorders. Programmed cell death is associated with a well-choreographed series of events resulting in the cessation of normal cell function, and the ultimate disappearance of the cell. One component of apoptosis is signaling adjacent cells that this cell is committing suicide by externalizing phosphatidylserine to the outer leaflet of the cell membrane. Annexin V, a 32-kDa endogenous human protein, has a high affinity for membrane-bound phosphatidylserine. We have coupled annexin V with the bifunctional hydrazinonicotinamide reagent (HYNIC) to prepare technetium-99m HYNIC-annexin V and demonstrated localization of radioactivity in tissues undergoing apoptosis in vivo. In this report we describe the results of a series of experiments in mice and rats to characterize the biologic behavior of (99m)Tc-HYNIC- annexin V. Biodistribution studies were performed in groups of rats at 10-180 min after intravenous injection of (99m)Tc-HYNIC-annexin V. In order to estimate the degree of apoptosis required for localization of (99m)Tc-annexin V in vivo, mice were treated with dexamethasone at doses ranging from 1 to 20 mg/kg, 5 h prior to (99m)Tc-HYNIC-annexin V administration, to induce thymic apoptosis. Thymus was excised 1 h after radiolabeled HYNIC-annexin V injection; thymocytes were isolated, incubated with Hoechst 33342 followed by propidium iodide, and analyzed on a fluorescence-activated cell sorter. Each sorted cell population was counted in a scintillation counter. To test (99m)Tc-HYNIC-annexin V as a tracer for external radionuclide imaging of apoptotic cell death, radionuclide imaging of Fas-defective mice (lpr/lpr mice) and wild-type mice treated with the antibody to Fas (anti-Fas) was carried out 1 h post injection. Rat biodistribution studies demonstrated a blood clearance half-time of less than 10 min for (99m)Tc-HYNIC-annexin V. The kidneys had the highest concentration of radioactivity at all time points. Studies in the mouse thymus demonstrated a 40-fold increase in (99m)Tc-HYNIC-annexin V concentration in apoptotic thymocytes compared with the viable cell population. A correlation of r=0.78 was found between radioactivity and flow cytometric and histologic evidence of apoptosis. Imaging studies in the lpr/lpr and wild-type mice showed a substantial increase of activity in the liver of wild-type mice treated with anti-Fas, while there was no significant change, irrespective of anti-Fas administration, in lpr/lpr mice. Excellent images of hepatic apoptosis were obtained in wild-type mice 30 min after injection of (99m)Tc-HYNIC-annexin V. The imaging results were consistent with histologic analysis in these animals. In conlusion, these studies confirm the value of (99m)Tc-HYNIC-annexin V uptake as a marker for the detection and quantification of apoptotic cells in vivo.

Role of radical oxygen species in rat testicular germ cell apoptosis induced by heat stress.

The present study was designed to clarify the role of radical oxygen species in testicular germ cell apoptosis induced by heat stress. Testicular cells isolated from immature rats were cultured with or without elevated temperature, and occurrence of apoptosis in these cells was defined by the appearance of DNA fragmentation following agarose gel electrophoresis and by flow cytometric quantification of apoptotic cells. At 32.5 degrees C, < 1% of cells showed signs of apoptosis throughout the culture period, whereas under heat stress, the proportion of apoptotic cells increased to 5% at 37 degrees C after 24 h of culture, or to 14% after 1-h exposure at 43 degrees C followed by 23-h culture at 32.5 degrees C. Similar to the effect of heat stress, exogenously supplied oxygen free radicals also induced apoptosis. In contrast, treatment with catalase significantly attenuated heat stress-induced apoptosis. Furthermore, heat stress of testicular cells was associated with an increased intracellular peroxide level as measured by a fluorescent probe, 2', 7'-dichlorofluorescin diacetate. In conclusion, our data indicate the involvement of radical oxygen species during testicular germ cell apoptosis induced by heat stress. This study provides a useful in vitro model for the study of testicular germ cell apoptosis.

Morphologic criteria and detection of apoptosis.

Apoptosis is an organized, energy dependent process, which leads to cell death. Its definition is based on distinct morphological features [10] and demonstration of internucleosomal DNA degradation [27], executed by selectively activated DNAses [4, 22]. The morphologic hallmarks of apoptosis include chromatic margination, nuclear condensation and fragmentation, and condensation of the cell with preservation of organelles. The process is followed by fragmentation of the cell into membrane-bound apoptotic bodies, which undergo phagocytosis by nearby cells without associated inflammation [10, 11]. Apoptosis characteristically occurs in insolated single cells. The duration of apoptosis is estimated to be from 12 to 24 hours, but in cell culture visible morphologic changes are accomplished in less than two hours [10, 16]. Non-apoptotic cell death, a prototype of which is cell death due to ischemia (oncosis), is characterized by depletion of intracellular ATP stores, swelling of the cell with disruption of organelles and rupture of the plasma membrane [15]. Groups of necrotic cells and inflammation are found in tissues [10, 15]. The significance of apoptosis has mostly been studied using the TUNEL assay that detects DNA strand breaks in tissue sections and allows quantification of apoptotic cells by light microscopy [6]. Common experience seems to be that the TUNEL assay is prone to false positive or negative findings. This has been explained by the dependence of the staining kinetics on the reagent concentration [17], fixation of the tissue [2] and the extent of proteolysis [17]. Active RNA synthesis [12] and DNA damage in necrotic cells [17, 19] may cause non-specific staining. To obtain reliable and reproducible results, TUNEL assay should be carefully standardized by using tissue sections treated with DNAse (positive control of apoptosis). Quantification of apoptosis should include enough microscopic fields and identification of the cell type undergoing apoptosis. The specificity of the results can be substantiated by combining other methods with TUNEL, such as assessment of the pattern of DNA fragmentation or evaluation of the morphological features. Even though there is high variation in the results obtained in consecutive studies under the same circumstances, increasing evidence shows that TUNEL-positive cardiomyocytes and internucleosomal DNA fragmentation are associated with various cardiac diseases, including acute myocardial infarction and heart failure [reviewed in 5, 9]. Some morphological features of apoptosis have been observed in TUNEL-positive cardiomyocytes using light microscopy (Figure 1) or confocal microscopy [20]. Electron microscopic evidence of apoptosis has been found in the degenerating conduction system [7], in experimental heart failure [23], and in human hibernating myocardium [3]. In acutely ischemic myocardium the interpretation of the findings remains controversial, since only non-apoptotic cell morphology has been found in electron microscopy [8, 19]. One explanation might be abortion of the apoptotic program due to the lack of ATP before the morphologic features are fully evident [14]. Another explanation is the possibility that non-apoptotic cell death and apoptosis share common mechanisms in the early phases of the processes [14, 19]. The exact mechanisms of ischemic cell death remain to be clarified and the classification between apoptosis and non-apoptosis cell death to be specified. Recently, caspase activation has emerged as the central molecular event leading to apoptosis, preceding DNA degradation and the development of apoptotic morphology [22, 25]. New methods have been developed to demonstrate caspase activation [1, 13]. Inhibition of caspase may be an efficient way to prevent apoptotic cardiomyocyte death as well as to define and specifically probe the significance of apoptotic cell death in cardiac diseases.

Cardiomyocyte apoptosis in acute and chronic conditions.

Myocytes can die by necrosis or by apoptosis and the characteristics of both kinds of cell death are so typical that a differentiation can be made by histological and molecular-biological methods using electron microscopy, dUTP labeling with fluorescence or peroxidase staining (TUNEL) and the DNA laddering method. However, the problem of quantification of apoptotic cells has not been completely solved because of lack of standardization as well as uncritical use and interpretation of the TUNEL method. Equally, quantification of apoptotic cells is not optimal until now because of three reasons: methodological (overinterpretation of results, no differentiation between myocytes and non-myocytes), experimental (global or regional acute ischemia, chronic conditions such as heart failure or hibernating myocardium), and interpretation (unknown time period for the completion of apoptosis). This problem is reflected in the large differences in incidence of apoptosis reported. Our own data show that in dog myocardium made globally ischemic for 90 min, 8% of the myocytes showed a positive staining for apoptosis (TUNEL method) after 6 h of reperfusion. Despite these results the question of reperfusion injury and the influence of apoptosis still remains open, because it can not be excluded until now that the apoptotic process is initiated during the ischemic period. Studies in hibernating myocardium and chronic heart failure show a similar situation, because of a wide variation of numbers of apoptotic cells and the limited possibility to investigate human tissue. There is no doubt that apoptosis plays an important role in chronic pathophysiological situations such as heart failure and hibernating myocardium but the importance of apoptosis in the acute situation of ischemia/reperfusion still has to be clarified.

Quantification of apoptotic cells using isolated glomeruli.

In order to detect apoptotic cells in the kidney, the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) method is used in tissue sections. But the number of apoptotic cells per glomerulus in several experimental models of nephritides is about 1 per single tissue section even at peak levels. In this study, we have reported that the TUNEL method and immunostaining of cell-specific markers to a whole isolated glomerulus in combination with laser scan microscopy are potentially useful methods for the analysis of cell turnover within glomeruli.

Quantification of apoptotic cells with fluorescein isothiocyanate-labeled annexin V in chinese hamster ovary cell cultures treated with cisplatin

Plasma membrane binding of annexin V was used to detect and quantitate apoptotic cells induced by cytotoxic drug treatment in epithelial cell cultures. Chinese hamster ovary (CHO) cells were incubated for 2 h with the ID90 concentration of Cisplatin (20 microM), and 24, 48, 72, and 96 h later the unfixed cells were stained with fluorescein isothiocyanate (FITC)-conjugated annexin V. The fluorescence signal was quantitated by flow cytometry (FCM). During the early phase of the apoptotic response, the annexin V-binding frequency histograms showed two separate cell populations, a dimly and a brightly fluorescent one. At t = 96 h after drug incubation, when the process of apoptosis was completed, only the brightly fluorescent population was present. A dose-effect relationship could be established between the Cisplatin concentration used in the 2 h incubation and the binding of annexin V on the cell membrane, as estimated by FITC fluorescence. The dimly and brightly fluorescent populations were sorted on the basis of annexin V binding, and assayed for 1) DNA breaks by in situ nick translation assay and DNA content by DNA-propidium iodine fluorescence in a bivariate analysis, 2) membrane integrity by dye exclusion, and 3) morphological characteristics of apoptosis. The dimly fluorescent cell population appeared to represent apoptotic cells in the early phase of the death process, as demonstrated by intact cell membranes, normal DNA content, few DNA breaks, and chromatin condensation. The brightly fluorescent cells predominantly had sub-G1 DNA content, nuclear fragmentation, leaky cell membranes, and probably represent late apoptotic cells. These results demonstrate that cytotoxic drug-induced apoptosis can be quantitated by annexin V binding and that by using this assay early and late apoptotic cells can be identified.

Silica induces apoptosis in macrophages and the release of interleukin-1 α and interleukin-1β

Resident adherent peritoneal cells selectively released high amounts of interleukin-1 (IL-1) activity when treated with silica. The use of anti-IL-1 antisera showed that both IL-1 alpha and IL-1 beta were present in supernatants of silica-treated macrophages. In contrast, intracellular IL-1 activity was totally neutralized by anti-IL-1 alpha antibodies and was easily converted into the mature IL-1 alpha form by autolysis in cytoplasmic extracts. Anion exchange chromatography clearly separated the two IL-1 species present in supernatants of silica-stimulated macrophages. Natural IL-1 beta was further characterized by chromatofocalization; it had an apparent isoelectric point, pI, in the range 8.3-8.6. In agreement with previous findings showing that IL-1 beta was released only by apoptotic cells, we have found that silica-treated macrophages underwent apoptosis. This was demonstrated by the characteristic laddering electrophoretic pattern of DNA extracted from silica-treated cells and by the morphology of macrophage nuclei stained with the DNA-specific dye DAPI. In addition, quantification of apoptotic cells was performed by a flow cytometric analysis based on the reduction of cellular DNA content exhibited by apoptotic cells. Treatment of macrophages with silica, therefore, results in an active process that promotes the processing and liberation of IL-1 beta.

A new method to detect apoptosis in paraffin sections: in situ end-labeling of fragmented DNA.

Apoptosis (programmed cell death) can be difficult to detect in routine histological sections. Since extensive DNA fragmentation is an important characteristic of this process, visualization of DNA breaks could greatly facilitate the identification of apoptotic cells. We describe a new staining method for formalin-fixed, paraffin-embedded tissue sections that involves an in situ end-labeling (ISEL) procedure. After protease treatment to permeate the tissue sections, biotinylated nucleotides are in situ incorporated into DNA breaks by polymerase and subsequently stained with DAB via peroxidase-conjugated avidin. Staining of cells with the morphological characteristics of apoptosis was demonstrated in tissues known to exhibit programmed cell death, i.e., prostate and uterus after castration, tumors, lymph node follicles, and embryos. Apoptotic cells could be discriminated morphologically from areas of labeled necrotic cells, in which DNA degradation also occurs. Because apoptosis is relatively easily recognized in H&E-stained sections of involuting prostates of castrated rats, we used this model system to validate the ISEL method for the quantification of apoptotic cells. A high correlation was found between the fractions of ISEL-labeled cells and the fractions of apoptotic cells that were morphologically determined in adjacent sections. We conclude that ISEL is a useful technique for quantification of apoptosis in paraffin sections, especially for those tissues in which morphological determination is difficult. Furthermore, this new staining method enables the use of automated image cytometry for evaluating apoptosis.