Enzyme kinetic studies in cell populations using fluorogenic substrates and flow cytometric techniques

Colcemid inhibits growth during early G1 in normal but not in tumorigenic lymphocytes

Mitogenically stimulated human and mouse lymphocytes enter the cell cycle (G0, G1A, G1B, S, G2+M) via a newly recognized subphase, G1'. This subphase precedes G1A and is distinct from G0. The G1' subphase is absent in immortalized and tumorigenic lymphoblastoid cell lines (LCLs) by cytofluorimetric criteria. Furthermore, colcemid inhibits transition through the G0/G1' as well as G2 phases in mitogen-stimulated lymphocytes and in LCLs. Tumorigenic LCLs are not sensitive to growth inhibition by colcemid during early G1. These observations suggest that a progressive series of changes have occurred during G0/G1' which lead to deregulation of growth control.

The application of flow cytophotometry in measurements of cell adhesion

A common approach to the study of cell substrate interactions is the measurement of the attachment of cells to different substrates or to cultured cell layers. The evaluation of attachment is made either by scintillation counting of previously labelled adhering cells, or by light microscopy using the criterion of cell shape, sometimes refined by automatic image analysis. These methods have many drawbacks. This paper suggests the use of fluorescence-activated flow cytophotometry, (FC) which yields direct counts of the non-adhering cells. These "free" cells are removed after completion of the adhesion experiment from the microtitre plate wells. An internal standard, in the form of fluorescent polystyrene beads is added, allowing evaluation of the percentage of cells adhering to the well walls. Flow cytophotometry then produces data based on the analysis of large populations of cells. Unequivocal discrimination is obtained between the counted cells and counted fluorescent beads eliminating counting errors. The results can be processed on line by computer. A suspension of mouse splenocytes was used for the evaluation of the overall error of the method arising from inaccuracies in pipetting, interference of glutaraldehyde with ethidium bromide (EB) staining and instrumental error. Each adhesion experiment was terminated by staining and post-fixation and it was established that this introduces no change in cell counting, in comparison with the original unfixed cells. Prefixation, however, quenches the EB staining and would interfere with the counting procedure. The overall standard error of the technique was found to be 5%-10%.(ABSTRACT TRUNCATED AT 250 WORDS)

Flow cytometry: methodology and applications in pathology

Flow cytometry offers pathologists a powerful new method which can be applied especially for diagnosis, prediction of prognosis and measurement of response to therapy of tumours. It also has a wide variety of other applications in research and its use for investigation of non-neoplastic disease has only just begun. The object of this brief review is to stimulate interest in this technique and to outline some of the most interesting applications that may be of use to pathologists in the near future.

Cervical brush biopsy specimens suitable for DNA and oncoprotein analysis using flow cytometry

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Flow cytometry analysis of recombinant Saccharomyces cerevisiae populations

A new fluorescent stain has been developed for detecting cloned beta-galactosidase activity in individual cells of Saccharomyces cerevisiae by flow cytometry. The staining reaction is based on enzymatic cleavage of alpha-naphthol-beta-D-galactopyranoside by intracellular beta-galactosidase and trapping of the liberated naphthol by hexazoniumpararosaniline yielding a fluorescent, insoluble end product. This stain, in connection with an appropriate host strain, has been applied for detecting plasmids encoding inducible beta-galactosidase in unstable recombinant cell populations carrying plasmids with different origins of replication. The method enables rapid determination of the fraction of plasmid-containing cells as well as quantitation of intracellular beta-galactosidase content by kinetic enzyme assay. Inducibility of the marker enzyme is important for maintaining correlation between enzyme and gene content.

The clinical significance of flow cytometric c-myc oncoprotein quantitation in testicular cancer

A sensitive flow cytometric assay has been developed using a monoclonal antibody, Myc 1-6E10, to quantitate c-myc oncoprotein levels in nuclei isolated from wax embedded testicular tumours. The oncoprotein (p62c-myc) level increased significantly with increasing teratoma differentiation. Patients with intermediate and undifferentiated tumours who developed recurrence had lower p62c-myc levels than those who were disease free since their initial treatment. Such quantitative biochemical methods may provide new prognostic indices for cancer patients.

Fluorometric determination of polystyrene latex: application to the measurement of phagosomes and phagocytosis

Intrinsic fluorescence of polystyrene dissolved in organic solvents such as 1,2-dimethoxyethane was used to develop a sensitive method for the quantification of polystyrene latex beads. This method allows the assay of latex in the microgram range and is one order of magnitude more sensitive than the conventional spectrophotometric method. The fluorometric technique was used in the quantification of phagocytic latex particle uptake by macrophages and in the quantification of isolated phagosomal fractions.

Cell-cell contact affects cellular sensitivity to hyperthermia

The influence on heat sensitivity of interactions between HT29 human colon adenocarcinoma cells grown in two- or three-dimensional contact was investigated. No evidence for intercellular cooperation affecting cellular sensitivity to hyperthermia was found. Cells grown in monolayer were found to be more heat sensitive than those in aggregates, probably due to the different physical properties of the membrane of flat cells attached to the substratum. Cell-cell contact appears to affect the heat sensitivity of HT29 cells possibly by means of inducing arrest in a heat resistant phase of the cell cycle.

A simultaneous flow cytometric assay for c-myc oncoprotein and DNA in nuclei from paraffin embedded material

A simultaneous flow cytometric assay for the c-myc oncoprotein and DNA in nuclei extracted from archival paraffin wax embedded clinical biopsies is presented. The nuclei were extracted by pepsin digestion after dewaxing 20 micron sections. The c-myc oncoprotein was probed with a mouse monoclonal antibody. This was raised against a synthetic peptide corresponding to a hydrophilic region of the protein predicted from the amino acid sequence. The technique is illustrated with biopsies from patients with testicular cancer and with benign and malignant neoplasms of the colon.

Establishment and characterisation of cell lines from patients with lung cancer (predominantly small cell carcinoma)

Tissue samples from 59 patients with lung cancer have been used to establish cell lines in culture. The primary diagnosis was small cell carcinoma in all except four. Most of the samples were of bone marrow but pleural effusions, lymph node biopsies and skin metastases were also included. The samples were usually split between HITES serum-free medium and HITES plus 2.5% foetal calf serum. A total of 19 cell lines were established and characterised. One line is large cell anaplastic lung carcinoma, four are B-lymphoblastoid and fourteen are small cell lung cancer. Considerable heterogeneity in gross morphology, neuroendocrine differentiation (by electron microscopy) and content of the enzyme L-dopa decarboxylase was seen. The use of HITES plus 2.5% foetal calf serum resulted in better establishment of cultures than did serum-free HITES.

Metabolism of c-myc gene products: c-myc mRNA and protein expression in the cell cycle

The presence and synthesis of c-myc protein and mRNA in the cell cycle has been studied. We find that c-myc mRNA is present, at equivalent levels, at all times in the cell cycle with the possible exception of mitosis. Furthermore, we demonstrate that this mRNA is transcribed in both G1 and G2 phases. An analysis of the c-myc protein in vivo shows that de novo synthesis occurs in G1 and G2 and the protein turns over with a half-life of approximately 20-30 min in both phases. Furthermore, the level of c-myc protein rapidly increases in cell populations when they re-initiate the cell cycle, thereafter decreasing as the culture reaches quiescence. The results therefore suggest that expression of c-myc can be rapidly modulated and that it is activated during the G0 to G1 transition, but is expressed thereafter in the cell cycle.

Flow cytometric fluorescence emission spectrum analysis of Hoechst-33342-stained DNA in chicken thymocytes

Hoechst-33342-stained chicken thymocytes were analysed simultaneously on two fluorescence wavelength bands (green and violet) in our custom-built flow cytometer, and two major subsets were identified. In one subset (33% of the total) the emission spectrum remained constant with time, with little change in the respective green and violet fluorescence intensities. In the other subset (42% of the total) the green fluorescence increased during staining, resulting in a considerable change in the green-to-violet ratio, due to a change in the "shape" of the fluorescence emission with time. The data indicate that two binding sites, or two types of binding at the same site, exist in DNA for this dye and that these have different binding energies and, consequently, different fluorescence emission properties.

The effects of alpha and gamma interferons on human lung cancer cells grown in vitro or as xenografts in nude mice

We have compared the effects of alpha and recombinant gamma interferons (IFNs) on the growth of human lung cancer cell lines in vitro. There was a diversity of response amongst the lines studied, the most sensitive being COR-L23 (a large cell anaplastic carcinoma line) and POC (a small cell line). In these two lines, IFN-gamma was found to be more potent than IFN-alpha. During cell growth of line POC in the presence of IFN-gamma no significant shift in cell cycle distribution occurred. When lines COR-L23 and POC were grown as xenograft tumours in nude mice, daily injection of 4 X 10(5) units per mouse per day of IFN-gamma produced no discernible retardation of tumour growth.

How does flow cytometry express Gaussian distributed biological information?

The analogue-to-digital conversion step in flow cytometric analysis introduces a positive skew into the distribution of any measured parameter. In this communication we describe a semi-analytical method to determine if a distribution skewed by the analogue-to-digital conversion step is compatible with a Gaussian origin. The procedure involves determining the errors associated with calculating the coefficient of variation from the skewed distribution and applying systematic corrections. The method was tested with a number of experimental data sets and is illustrated with 3 distributions. One of these was not compatible with a Gaussian origin, but the other 2 were, in spite of considerable positive skewness in the data.

Direct measurement of phagolysosomal esterase activity

A new method of directly measuring esterase activity within phagolysosomes has been developed. Decanoyl fluorescein- binding microspheres were prepared and phagocytosed by human peripheral neutrophils. Within phagolysosomes lysosomal esterase hydrolyzed decanoyl fluorescein on the microspheres, causing the conversion of decanoyl fluorescein- binding microspheres (non-fluorescent) into fluorescein- binding microspheres (fluorescent). The activity of phagolysosomal esterase in intact neutrophils was assayed by the measurement of the fluorescence intensity without rupturing cells. By use of a flow cytometer, esterase activity within phagolysosomes in single cells was measured.

Cyclosporin-A binds lymphocyte surface receptors induced by activation

Cyclosporin A (CyA) is a new immunosuppressive drug of very considerable and widespread interest not only for clinicians and transplant immunologists but also for cell biologists concerned with activation mechanisms, as it causes a selective blockade of lymphocyte proliferation. Clearly, the molecular biology of CyA action is of fundamental importance, and in attempting to understand this we have looked for a cell surface receptor. We used indirect staining with antibody (at 4 degrees C and in azide) to ensure that only those CyA molecules held at the cell surface would be seen. The drug molecules which partition into the cell membrane, due to the extreme lipophilicity of CyA, are not detected by extracellular antibody. This technique differs from other methods using a directly labelled drug, where it is not possible to discriminate between specific and non-specific binding. Using high sensitivity flow cytometric analysis we were unable to find CyA on resting lymphocytes, whereas lymphocytes activated by concanavalin A (Con A) or mixed lymphocyte reaction (MLR) showed a CyA-dependent increase in fluorescence.

An easy-to-build-timer for kinetic measurements in flow cytometry

Measuring kinetics of any time-dependent intracellular process on a cell-to-cell basis is a powerful extension of flow cytometry (FCM) possibilities. A digital timer is described that is easy to build and that fits with all commercial or custom made multiparameter equipment. Of all possible applications of this timer (phagocytosis kinetics, staining of cell components, enzyme reactions, etc.), one example is given: enzymatic intracellular precipitation owing to myeloperoxidase in human peripheral blood cells.

A new method for fast blood cell counting and partial differentiation by flow cytometry

A new blood counting method by flow cytometry is described which determines absolute counts and relative proportions of erythrocytes, reticulocytes, thrombocytes, lymphocytes and granulocytes from one sample of saline diluted human or animal blood. Staining time is 2 to 5 min and measuring time between 1 and 2 additional minutes. Measured simultaneously are the electrical cell volume, the green and optionally also the red fluorescence of the transmembrane potential sensitive dye 3,3-dihexyloxacarbocyanine DiOC6(3) and the RNA/DNA stain acridine orange (AO). Work is under way to fully automate staining, measurement and data evaluation. The use of stains by which blood cell counting and biochemical analysis can be combined offers new possibilities for routine blood cell counting without requirement for additional time. The potential of such stains is that pathologic cell conditions which are not, or not yet reflected in the cell count may be earlier detectable by biochemical stains.

Effect of cell density on intracellular adriamycin concentration and cytotoxicity in exponential and plateau phase EMT6 cells

The relationship between cell number and available Adriamycin (ADM) has been investigated in EMT6 cells. Results have shown that the ratio between cell number and total available ADM is important in determining in vitro ADM uptake and surviving fraction. Having established this effect, the sensitivity of exponentially growing and plateau phase EMT6 cells to ADM was investigated. ADM was assayed by extraction followed by spectrofluorimetry and also by flow cytometry (FCM); both methods were found to give the same ratio of intracellular ADM between exponentially growing and plateau phase cells. We found that for a given exposure dose plateau phase cells were more sensitive than exponentially growing cells. For the same dose per cell, plateau cells take up more ADM than exponentially growing cells. But for a given intracellular ADM concentration exponentially growing cells have a lower surviving fraction than plateau phase cells. We conclude that the surviving fraction is dependent on the proliferative state of the cells and in order to draw that conclusion it is important to relate the ADM effect on cells in vitro to the total ADM available to each cell.

Continuous measurement and analysis of staining kinetics by flow cytometry

The measurement of color development with time in cells following the start of a staining reaction is of interest in a number of biological systems. These include the subsets of peripheral white blood cells after acridine orange staining, the uptake by cells and nuclei of fluorescent agents, especially antitumor drugs, and measurement of intracellular enzyme kinetics using fluorogenic or absorbing substrates. The present work describes a simple computer program for analyzing flow cytometric (FCM) data versus time, including both the population kinetics of color development and the variability of staining speed within one population of cells. A single-channel absorption measurement in flow (Technicon Hemalog D) was used to record peroxidase kinetics in peripheral blood cells. Every 5 s, a 64-channel absorption histogram was recorded, up to a maximum of 64 histograms. The data were then analyzed by a computer program which searched for the peak channel of each histogram. A least-squares fit was computed for these maxima. The asymmetries of the 64 absorption histograms were compared to see if there was more than one population present with different time constants. Although developed for enzyme kinetic measurements, this program may have wider usefulness in any measurements of time-dependent phenomena by FCM.

Complement-mediated lysis of pigeon erythrocyte ghosts analysed by flow cytometry. Evidence for the involvement of a 'threshold' phenomenon

Flow-cytometric analysis of complement-mediated lysis of antibody-coated pigeon erythrocyte ghosts containing fluorescein was carried out to determine whether lysis involved a gradual release of fluorescein or a 'threshold' release from individual cells. Antibody-coated ghosts were comprised of three subpopulations identified by fluorescence and scatter (size). These were: (a) highly fluorescent, medium scatter, (b) medium fluorescence, high scatter, and (c) low (or zero) fluorescence, low scatter. Lysed ghosts and isolated nuclei were identified by fluorescence microscopy and scanning electron microscopy. Fluorescence distributions analysed by flow cytometry indicated that, after complement attack, those ghosts remaining intact retained all their fluorescent label. A time course of changes in ratios of the three subpopulations indicated that once lysis of an individual ghost was initiated, release of label was complete within 1 min; no stages of intermediary fluorescence appeared, and those ghosts remaining at the end of the experiment retained the same fluorescence intensity as control ghosts. The results supported the hypothesis that complement-mediated cell lysis is a 'threshold' phenomenon; a submaximal response by a cell population representing a complete response by only some of the cells rather than a partial response by all of the cells.

Application of the CYTOMIC 12 flow cytometric compact analyzer for automatic kinetic measurements

Flow cytometry, usually applied to cells which have time independent features, can also be used for kinetic experiments where the change of cell populations with time is investigated. Dedicated time sequencing programs written in Assembler and incorporated in the CYTOMIC 12 analyzer (4) are described. A sequence of 64 one parameter histograms can be automatically acquired and immediately displayed as a pseudo-two-parameter histogram. The acquisition time for each of the subsequent histograms can be selected between 1 and 32 seconds. Kinetics lasting up to 34 minutes are resolved into 64 time intervals. Two parameter kinetics can be resolved into 12 32 X 32 channel, two parameter histograms which are displayed and evaluated immediately on the analyzer screen in groups of 4 without using complicated list mode procedures. The standard CYTOMIC 12 software can be applied for processing and printing of the sequence distribution curves.

Multistation multiparameter flow cytometry: a critical review and rationale

The capacity for fluorescence excitation by beams of different wavelengths at separate points along the sample stream, and the capacity for computer analysis of multiparameter data thus obtained, are now available in flow cytometer/sorter systems from commercial producers. It is now readily apparent to most experienced users of flow cytometers that such multiparameter analysis offers the most convenient solution to the problem of characterizing subpopulations of cells within a mixed population. The use of multiple beams facilitates resolution of fluorescence signals from several probes within or upon a single cell and widens the range of analytical alternatives available to experimenters. This critical review discusses the history of the instrumentation, the parameters now measurable and the probes used for their measurement, and the methods for data analysis. Required sensitivity and precision are discussed, leading to the conclusion that many of the advantages of multistation, multiparameter flow cytometry can be made available in less complex and less costly instruments using less powerful sources and less elaborate computer hardware than are presently incorporated in commercial apparatus.

Sensitive three-parameter flow-cytometric detection of abnormal cells in human cervical cancers: a pilot study

The cell volume, the DNA, and the carcino-embryonic (CEA) or epithelial-membrane (EMA) antigen of formaldehyde-fixed human cervical cells from 21 malignant cervix tumors and 11 normal patients were measured simultaneously with a Fluvo-Metricell flow cytometer. The simultaneous cell volume and DNA measurement provided the distinction of morphologically intact cells from cell debris, the determination of the cell cycle phase combined with the detection of aneuploid cells, and the distinct of inflammatory cells from parenchymal and tumor cells. Malignant samples were recognized because they contained more than 0.5% CEA positive cells which were of intermediate size. CEA and EMA expression in the malignant samples was not linked. The false positive rate in a total of 32 samples was 6.3% when the sum of CEA and EMA positive cells of each cell sample was calculated. No false negative malignant sample was observed.

Dual laser beam focussing for flow cytometry through a single crossed cylindrical lens pair

Two laser beans (argon 488 nm blue, and krypton UV lines) have been focussed either to the same point or to two different points in a vertical plane in a multiparameter flow cytometer. The technique exploits the focal length shortening of the longer wavelength beam that occurs with spherical and astigmatic lens aberrations. Ethidium bromide-stained DNA is excited by both the argon 488 nm and krypton UV lines and the excitation intensities of both beams were set to give the same red fluorescence pulse height from ethidium bromide-stained nuclei. DNA histograms were obtained for sequential focussing of the two beams and these were virtually identical irrespective of which beam was the first excitor and irrespective of which beam the histogram was recorded from. Coincident focussing of the two exciting beams resulted in a histogram of double the emission intensity.

Flow cytometric determination of esterase and phosphatase activities and kinetics in hematopoietic cells with fluorogenic substrates

Viable and formaldehyde fixed rat bone marrow or spleen cells and rat or human blood leukocytes were incubated with fluorescein (fluorescein-diacetate, -dibutyrate and -laurate) or umbelliferone (4-methyl umbelliferyl acetate and -phosphate) fluorogenic substrates for subsequent flow cytometric determination of cell fluorescence and cell volume. Formaldehyde-fixed cells preserved between 14 and 20% of the enzyme activity of the unfixed cells and the number of cell clusters for fixed and unfixed cells was the same. The esterase substrates revealed one cell cluster for spleen cells, two for bone marrow cells and four for peripheral blood leukocytes. Phosphatase activity was only associated with a cell cluster of large cells. The time course of substrate cleavage was linear during the first 10 min of incubation. Later on a plateau was reached. Specific enzyme activities were calculated on a single cell level from the simultaneous cell volume and cell fluorescence measurement. Two enzyme activities could be measured simultaneously by using a substrate mixture of umbelliferone acetate and fluorescein acetate.