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Platkov M, Tirosh R, Kaufman M, Zurgil N, Deutsch M. Photobleaching of fluorescein as a probe for oxidative stress in single cells. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2014; 140:306-14. [PMID: 25218588 DOI: 10.1016/j.jphotobiol.2014.08.016] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2014] [Revised: 08/18/2014] [Accepted: 08/24/2014] [Indexed: 11/26/2022]
Abstract
BACKGROUND ROS are involved in the regulation of many physiological and pathological processes. Apoptosis and necrosis are processes that are induced by changes in concentrations of Reactive Oxygen Species (ROS). This study aims to detect and quantify the cellular response to changing ROS concentrations in the scope of apoptosis and necrosis. METHODS Photobleaching of the fluorescent substrate fluorescein is used as a probe to detect the response of individual Jurkat-T-lymphocytes and Prostate-Cancer-3(PC-3) cells to oxidative stress, induced by hydrogen peroxide (H₂O₂). A kinetic model is proposed to describe changes in intracellular dye quantities due to photobleaching, dye hydrolysis, influx and leakage, yielding a single time-dependent decaying exponent+constant. RESULTS Fluorescein photobleaching is controlled and used to detect intracellular ROS. An increase in the decay time of fluorescence of intracellular fluorescein (slow photobleaching) was measured from cells incubated with H₂O₂ at 50 μM. At higher H₂O₂ concentrations a decrease in the decay time was measured (fast photobleaching), in contrast to in vitro results with fluorescein and H₂O₂ in phosphate buffer saline (PBS), where the addition of H₂O₂ decreases the decay time, regardless of the irradiation dose used. CONCLUSIONS The anomalous, ROS-concentration dependent reduction of the photobleaching rate in cells, as opposed to solutions, might indicate on the regulation of the activity of intracellular oxidative-stress protective mechanisms, as seen earlier with other methods. SIGNIFICANCE Assessing photobleaching via the time decay of the fluorescence intensity of an ROS-sensitive fluorophore may be adapted to monitor oxidative stress or ROS-related processes in cells.
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Affiliation(s)
- Max Platkov
- The Biophysical Interdisciplinary Jerome Schottenstein Center for the Research and the Technology of the Cellome, Physics Department, Bar-Ilan University, Ramat-Gan 52900, Israel.
| | - Reuven Tirosh
- The Biophysical Interdisciplinary Jerome Schottenstein Center for the Research and the Technology of the Cellome, Physics Department, Bar-Ilan University, Ramat-Gan 52900, Israel
| | - Menahem Kaufman
- The Biophysical Interdisciplinary Jerome Schottenstein Center for the Research and the Technology of the Cellome, Physics Department, Bar-Ilan University, Ramat-Gan 52900, Israel
| | - Naomi Zurgil
- The Biophysical Interdisciplinary Jerome Schottenstein Center for the Research and the Technology of the Cellome, Physics Department, Bar-Ilan University, Ramat-Gan 52900, Israel
| | - Mordechai Deutsch
- The Biophysical Interdisciplinary Jerome Schottenstein Center for the Research and the Technology of the Cellome, Physics Department, Bar-Ilan University, Ramat-Gan 52900, Israel
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Herman S, Zurgil N, Langevitz P, Ehrenfeld M, Deutsch M. The Immunosuppressive Effect of Methotrexate in Active Rheumatoid Arthritis Patients vs. its Stimulatory Effect in Nonactive Patients, as Indicated by Cytometric Measurements of CD4 + T Cell Subpopulations. Immunol Invest 2009; 33:351-62. [PMID: 15495793 DOI: 10.1081/imm-120039865] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
This cytometric study assesses the effects of methotrexate (MTX) on the expanded CD4+ lymphocyte population in active and nonactive rheumatoid arthritis (RA) patients. In the active patients, MTX was found to reduce the predominant CD4+ CD28+ subpopulation (by 30%), and the minor subpopulation of CD4+ CD28- (by 34%). The incidence of CD25 phenotype was downregulated by 15%. These reductions can be attributed to immunosuppression through apoptosis, which was demonstrated by MTX-induced fluorescein diacetate (FDA) hyperpolarization (an established indicator of early apoptosis). In contrast, in nonactive RA patients, the major CD4+ CD28+ subpopulation of small lymphocytes appeared to be activated by MTX, subsequently transforming into a major hyperblast population, whereas the minor CD4+ CD28- subpopulation was not affected by MTX treatment. The activation by MTX in this group of patients is evidenced by MTX-induced FDA depolarization (an indicator of early activation). Thus, MTX immunosuppressive effect on CD4+ subsets was found in active patients, whereas immunostimulation by MTX was shown in nonactive patients. The found discriminative effect of MTX may suggest a higher effectiveness of low-dose MTX therapy in active RA patients.
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Affiliation(s)
- Shoshy Herman
- Physics Department, The Biophysical Interdisciplinary Jerome Schottenstein Center for the Research and the Technology of the Cellome, Bar-Ilan University, Ramat-Gan, Israel
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3
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Kaufman M, Bloch D, Zurgil N, Shafran Y, Deutsch M. A cluster pattern algorithm for the analysis of multiparametric cell assays. J Comput Biol 2008; 12:1014-28. [PMID: 16201919 DOI: 10.1089/cmb.2005.12.1014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The issue of multiparametric analysis of complex single cell assays of both static and flow cytometry (SC and FC, respectively) has become common in recent years. In such assays, the analysis of changes, applying common statistical parameters and tests, often fails to detect significant differences between the investigated samples. The cluster pattern similarity (CPS) measure between two sets of gated clusters is based on computing the difference between their density distribution functions' set points. The CPS was applied for the discrimination between two observations in a four-dimensional parameter space. The similarity coefficient (r) ranges between 0 (perfect similarity) to 1 (dissimilar). Three CPS validation tests were carried out: on the same stock samples of fluorescent beads, yielding very low r's (0, 0.066); and on two cell models: mitogenic stimulation of peripheral blood mononuclear cells (PBMC), and apoptosis induction in Jurkat T cell line by H2O2. In both latter cases, r indicated similarity (r < 0.23) within the same group, and dissimilarity (r > 0.48) otherwise. This classification and algorithm approach offers a measure of similarity between samples. It relies on the multidimensional pattern of the sample parameters. The algorithm compensates for environmental drifts in this apparatus and assay; it also may be applied to more than four dimensions.
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Affiliation(s)
- Menachem Kaufman
- The Biophysical Interdisciplinary Schottenstein Center for the Research and Technology of the Cellome, Physics Department, Bar-Ilan University, Ramat-Gan, Israel
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Harel M, Gilburd B, Schiffenbauer YS, Shoenfeld Y. Application of a static fluorescence-based cytometer (the CellScan) in basic cytometric studies, clinical pharmacology, oncology and clinical immunology. Clin Dev Immunol 2005; 12:187-95. [PMID: 16295524 PMCID: PMC2275416 DOI: 10.1080/17402520500160895] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
The CellScan apparatus is a laser scanning cytometer enabling repetitive
fluorescence intensity (FI) and polarization (FP) measurements in living cells, as
a means of monitoring lymphocyte activation. The CellScan may serve as a tool for
diagnosis of rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) as
well as other autoimmune diseases by monitoring FP changes in peripheral blood
lymphocytes (PBLs) following exposure to autoantigenic stimuli. Changes in FI and
FP in atherosclerotic patients' PBLs following exposure to various stimuli have
established the role of the immune system in atherosclerotic disease. The CellScan
has been evaluated as a diagnostic tool for drug-allergy, based on FP reduction in
PBLs following incubation with allergenic drugs. FI and FP changes in cancer cells
have been found to be well correlated with the cytotoxic effect of anti-neoplastic
drugs. In conclusion, the CellScan has a variety of
applications in cell biology, immunology, cancer research and clinical pharmacology.
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Affiliation(s)
- Michal Harel
- Center for Autoimmune Diseases, Department of Medicine B, Chaim Sheba Medical Center, Israel
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5
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Afek A, Zurgil N, Bar-Dayan Y, Polak-Charcon S, Goldberg I, Deutsch M, Kopolovich J, Keren G, Harats D, George J. Overexpression of 15-lipoxygenase in the vascular endothelium is associated with increased thymic apoptosis in LDL receptor-deficient mice. Pathobiology 2005; 71:261-6. [PMID: 15459485 DOI: 10.1159/000080060] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2003] [Accepted: 04/08/2004] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND 15-Lipoxygenase (15-LO) is a nonheme iron-containing enzyme that catalyzes the peroxidation of fatty acids. Herein, we studied the effect of 15-LO overexpression in the vascular endothelium on thymocyte apoptosis by evaluating thymuses from low-density lipoprotein receptor-deficient (LDL-RD) mice and LDL-RD/15-LO mice. Thymuses were evaluated by immunohistochemistry and by TUNEL whereas in vitro studies were carried out by employing freshly isolated thymocytes from the respective mice and evaluation of apoptosis by propidium iodide and annexin V cytometry. METHODS AND RESULTS The apoptotic index in LDL-RD/15-LO mice was significantly higher than in the LDL-RD mice. In the thymic medulla the difference was smaller, although still significant. Freshly isolated thymus cells from LDL-RD/15-LO mice exhibited a higher rate of spontaneous cell death than controls. Incubation of thymus cells in the presence of the cell-permeable caspase-3 inhibitor DEVD-CMK resulted in a decrease in the frequency of apoptotic cells in LDL-RD/15-LO thymocytes, whereas no effect was evident in control thymocytes. The antioxidant N-acetylcysteine causes the increase in apoptosis in both groups. CONCLUSION LDL-RD/15-LO mice exhibit increased thymocyte apoptosis both in vivo and in vitro. These findings may suggest a role for 15-LO in the natural selection of thymocytes.
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Affiliation(s)
- A Afek
- Institute of Pathology, Sheba Medical Center, Tel Hashomer, Israel
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Yishai Y, Fixler D, Cohen-Kashi M, Zurgil N, Deutsch M. Ratiometric fluorescence polarization as a cytometric functional parameter: theory and practice. Phys Med Biol 2003; 48:2255-68. [PMID: 12953896 DOI: 10.1088/0031-9155/48/15/301] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The use of ratiometric fluorescence polarization (RFP) as a functional parameter in monitoring cellular activation is suggested, based on the physical phenomenon of fluorescence polarization dependency on emission wavelengths in multiple (at least binary) solutions. The theoretical basis of this dependency is thoroughly discussed and examined via simulation. For simulation, aimed to imitate a fluorophore-stained cell, real values of the fluorescence spectrum and polarization of different single fluorophore solutions were used. The simulation as well as the experimentally obtained values of RFP indicated the high sensitivity of this measure. Finally, the RFP parameter was utilized as a cytometric measure in three exemplary cellular bioassays. In the first, the apoptotic effect of oxLDL in a human Jurkat FDA-stained T cell line was monitored by RFP. In the second, the interaction between cell surface membrane receptors of human T lymphocyte cells was monitored by RFP measurements as a complementary means to the fluorescence resonance energy transfer (FRET) technique. In the third bioassay, cellular thiol level of FDA- and CMFDA-labelled Jurkat T cells was monitored via RFP.
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Affiliation(s)
- Yitzhak Yishai
- The Biophysical Interdisciplinary Jerome Schottenstein Center for the Research and the Technology of the Cellome, Department of Physics, Bar-Ilan University, Ramat-Gan 52900, Israel.
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7
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Herman S, Zurgil N, Langevitz P, Ehrenfeld M, Deutsch M. The induction of apoptosis by methotrexate in activated lymphocytes as indicated by fluorescence hyperpolarization: a possible model for predicting methotrexate therapy for rheumatoid arthritis patients. Cell Struct Funct 2003; 28:113-22. [PMID: 12808231 DOI: 10.1247/csf.28.113] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The objectives of this study were to test the in vitro response of healthy non-activated, activated, and rheumatoid arthritis (RA) lymphocytes to methotrexate (MTX), and design an in vitro model for predicting the efficiency of MTX treatment for RA patients. Considering the RA profile of clonal-expanded CD4(+) T cells, phytohemagglutinin-activated mononuclear cells taken from healthy donors were incubated with different concentrations of MTX. The MTX-immunosuppressive effect was tested by fluorescence intensity measurements, including PI assay and annexin V assay. For simple detection, we used the Individual Cell Scanner (IC-S), which enables the measurement of early events in individual cells. Healthy mononuclear cells (MNC), and MNC derived from RA patients, were tested by the IC-S while utilizing fluorescence polarization (FP) measurements of fluorescein diacetate (FDA) as an established marker of activation or suppression. In healthy activated MNC, we found that MTX, through its early incubation period, interferes with the activation signal obtained by PHA and exerts an apoptotic signal, which is noted by increases in the FP. Comparing our model to six long-standing RA patients and five newly-diagnosed patients revealed significant differences in the FP measurements, including fluorescence depolarization as an early established measurement of lymphocyte activation, and hyperpolarization as a measurement of an early immunosuppressive effect. We conclude that MTX, an effective therapy for RA patients, could easily be tested by fluorescence polarization measurements of FDA before (or during) clinical use in order to predict its efficiency on a specific RA patient. Moreover, the FP measurements can be used for the diagnosis, and making timing and dosage decisions.
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Affiliation(s)
- Shoshy Herman
- The Biophysical Interdisciplinary Schottenstein Center for the Research and the Technology of the Cellome, Physics Department, Bar-Ilan University, Ramat-Gan 52900, Israel
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8
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Fixler D, Tirosh R, Zinman T, Shainberg A, Deutsch M. Fluorescence polarization: a novel indicator of cardiomyocyte contraction. Biochem Biophys Res Commun 2003; 300:23-8. [PMID: 12480515 DOI: 10.1016/s0006-291x(02)02768-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The changes measured in intracellular fluorescein fluorescence polarization (IFFP) are used as a new tool for tracing cytoplasmic effects during contractile cycles of cardiac myocytes (1-2-day-old rat hearts), in addition to the established Ca(2+) monitoring and/or videometric methods of tracking cell-shortening. This novel method was found to be non-intrusive to the contraction cycles. The decay of the transient IFFP signal (from 0.220+/-0.01 to 0.170+/-0.013) seems to be closely related to the extended phase of contractile activation. This fact was further supported when Ca(2+) exchanger inhibitor was introduced and significantly decreased (90%) the rate of beats of contraction and IFFP, but not the Ca(2+) beat rate changes. This result suggests that the IFFP indicator is probably associated with the physiological activation, rather than with Ca(2+) alterations. The IFFP measure monitors the average of effective changes in the micro-viscosity of the cytoplasm protein matrix, associated with cellular activation.
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Affiliation(s)
- Dror Fixler
- The Biophysical Interdisciplinary Schottenstein Center for the Research and the Technology of the Cellome, Physics Department, Bar-Ilan University, Ramat-Gan 52900, Israel.
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9
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Cohen-Kashi M, Moshkov S, Zurgil N, Deutsch M. Fluorescence resonance energy transfers measurements on cell surfaces via fluorescence polarization. Biophys J 2002; 83:1395-402. [PMID: 12202365 PMCID: PMC1302238 DOI: 10.1016/s0006-3495(02)73910-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
A method has been developed for the determination of the efficiency of fluorescence resonance energy transfer efficiency between moieties located on cell surfaces by performing individual cell fluorescence polarization (FP) measurements. The absolute value of energy transfer efficiency (E) is calculated on an individual cell basis. The examination of this methodology was carried out using model experiments on human T lymphocyte cells. The cells were labeled with fluorescein-conjugated Concanavalin A (ConA) as donor, or rhodamine-conjugated ConA as acceptor. The experiments and results clearly indicate that determination of E via FP measurements is possible, efficient, and more convenient than other methods.
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Affiliation(s)
- Meir Cohen-Kashi
- The Biophysical Interdisciplinary Jerome Schottenstein Center for the Research and Technology of the Cellome Physics Department, Bar-Ilan University, Ramat-Gan 52900, Israel
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10
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Zurgil N, Shafran Y, Fixler D, Deutsch M. Analysis of early apoptotic events in individual cells by fluorescence intensity and polarization measurements. Biochem Biophys Res Commun 2002; 290:1573-82. [PMID: 11820802 DOI: 10.1006/bbrc.2002.6382] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Apoptosis is a dynamic process of variable duration. The ability to continuously detect the death process occurring in single or subgroups of cells is therefore very important in identifying apoptotic cells within a complex population. The Individual Cell Scanner (ICS), a multiparametric, multilaser-based scanning static cytometer, was used in the present report for the continuous monitoring of the apoptosis process. Fluorescence intensity (FI), polarization (FP), kinetic measurements, and cluster analysis of subpopulations were carried out utilizing various fluorescent probes. Hydrogen peroxide-induced apoptosis was monitored online in intact live lymphocytes by continuous sequential measurements of intracellular hyperpolarization. Plasma membrane asymmetry, mitochondrial membrane potential, and lysosomal rupture were monitored in individual cells. Cytoplasmic condensations, due to cell shrinkage and early lysosomal rupture, were found to be very early events of apoptosis. The new analytical capabilities suggested here may provide simple and convenient methods for detecting apoptosis from its earlier stages.
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Affiliation(s)
- N Zurgil
- Biophysical Interdisciplinary Center for the Research and the Technology of the Cellome and Jerome Schottenstein Center for Early Detection of Cancer, Bar Ilan University, Ramat Gan 52900, Israel
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11
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Sunray M, Zurgil N, Shafran Y, Deutsch M. Determination of individual cell Michaelis-Menten constants. CYTOMETRY 2002; 47:8-16. [PMID: 11774344 DOI: 10.1002/cyto.10029] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
BACKGROUND A novel methodology for the measurement and analysis of apparent K(M) (Michaelis-Menten constant) and V(MAX) values of individual cells is suggested. It is based on a mathematical model that considers substrate influx into the cell, its intracellular enzymatic hydrolysis, and the product efflux. The mathematical formulation was approximated linearly in order to analyze intracellular substrate conversion characteristics via Michaelis-Menten theory. METHODS Utilizing static cytometry, the time dependence of the fluorescence intensity [FI(t)] emitted from prelocalized and defined FDA stained cells was recorded. This required frequent periodical measurements of the same cells, which are sequentially exposed to various fluorogenic substrate concentrations. RESULTS Model simulations correlated with experimental results. Differences in distributions of individual K(M) and V(MAX) values of cells incubated with and without PHA were evident. Average K(M) and V(MAX) values of PHA-stimulated cells increased by 99% and 540%, respectively. CONCLUSIONS This study may provide a tool for assessing intracellular enzymatic activity in individual intact cells under defined physiologic conditions. This may open new vistas in various areas, giving answers to critical questions arising in the field of cell and developmental biology, immunology, oncology, and pharmacology.
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Affiliation(s)
- Merav Sunray
- The Jerome Schottenstein Center for Early Detection of Cancer, Department of Physics, Bar-Ilan University, Ramat-Gan, Israel
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12
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Zurgil N, Schiffer Z, Shafran Y, Kaufman M, Deutsch M. Fluorescein fluorescence hyperpolarization as an early kinetic measure of the apoptotic process. Biochem Biophys Res Commun 2000; 268:155-63. [PMID: 10652230 DOI: 10.1006/bbrc.1999.1934] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The ability to identify apoptotic cells within a complex population is crucial in the research and diagnosis of normal physiology and disease states. The Cellscan mark S (CS-S) cytometer was used in this study to detect intracellular fluorescence intensity and polarization (FI and FP) in several well-established models of apoptosis: Following spontaneous apoptosis, as well as glucocorticoid or anti Fas-induced apoptosis, CS-S individual cell-based analysis revealed the appearance of a cell cluster characterized by low FI and high FP. Temporal analysis of annexine V binding and FP measurements following DXM treatment showed that hyperpolarization preceded phosphatidylserine appearance on the outer plasma membrane. The early increase in FP was found to be dose dependent and inversely related to cell diameter. Cell dehydration and alteration of plasma membrane transport properties, both occurring during early stages of apoptosis, may be involved in the phenomena of intracellular fluorescein hyper-polarization in apoptosis.
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Affiliation(s)
- N Zurgil
- The Jerome Schottenstein Cellscan Center for Early Detection of Cancer, Bar-Ilan University, Ramat-Gan, 52900, Israel
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Deutsch M, Kaufman M, Shapiro H, Zurgil N. Analysis of enzyme kinetics in individual living cells utilizing fluorescence intensity and polarization measurements. CYTOMETRY 2000; 39:36-44. [PMID: 10655561 DOI: 10.1002/(sici)1097-0320(20000101)39:1<36::aid-cyto6>3.0.co;2-6] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
BACKGROUND The Cellscan mark-S (CS-S) scanning cytometer was used for tracing enzymatic reactions in the same individual cells under various physiological conditions over periods of minutes. On-line reagent addition and changes in the experimental conditions (buffers, ions, substrates and inhibitors) were performed. METHODS Kinetic events were monitored by fluorescence intensity (FI) and fluorescence polarization (FP) measurements of fluorescein diacetate (FDA) and chloromethyl fluorescein diacetate (CMFDA) intracellular hydrolysis. FP measurements have been used to assess the intracellular marker's mobility restrictions. RESULTS Kinetic measurement along 1000 s of FDA labeled individual Jurkat T cells, indicated variation of 65% for FI(t) and approximately 10% for FP(t). While FI increased linearly with time, FP(t) decreased nonlinearly and asymptotically, reaching a constant value. The FP(t) of CMFDA-labeled cells was different from that of FDA-labeled cells. Average cellular Km of 3.9 microM was calculated from individual cell FDA hydrolysis curves. CONCLUSIONS (1) Analysis of the reaction kinetics of intracellular enzymes can be refined by using FP measurements of the products of fluorogenic substrates in addition to the FI measurements. (2) Subpopulations or individual cells could be classified according to their reaction rates. (3) A specific dependence of FP(t) on type of enzyme substrate is suggested.
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Affiliation(s)
- M Deutsch
- The Jerome Schottenstein Cellscan Center for Early Detection of Cancer, Physics Department, Bar-Ilan University, Ramat-Gan 52900 Israel.
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