Re-evaluating acridine orange for rapid flow cytometric enumeration of parasitemia in malaria-infected rodents.

Methods facilitating research in malaria are of pivotal relevance. Flow cytometry offers the possibility of rapid enumeration of parasitemia. It relies on staining the parasite DNA to distinguish between infected and non-infected red blood cell (RBC) populations. Unfortunately, in rodents abundant reticulocyte RNA interferes with the application of the method. This results in time-consuming sample preparation protocols that offer no clear advantage over microscopic counting. We re-evaluated the use of the DNA/RNA discriminating vital fluorochrome acridine orange (AO) for rapid flow cytometric enumeration of parasitemia in rodents. Whole blood from rodents infected with Plasmodium berghei and Plasmodium yoelii was stained with AO and analyzed by flow cytometer. A newly developed two-channel (FL1/FL3) detection method was compared with conventional one-channel (FL1) detection and microscopic counting. The new AO two-channel detection method clearly discriminated between infected and non-infected RBC populations. It showed to be linear above parasitemias of 0.3%. Sample processing time amounted to approximately 5 min. It is shown that AO can be used for rapid, precise, and accurate enumeration of parasitemia in rodents. Due to its ease of handling the method might find widespread application in malaria research.     

Flow Cytometry Pulse Width Data Enables Rapid and Sensitive Estimation of Biomass Dry Weight in the Microalgae Chlamydomonas reinhardtii and Chlorella vulgaris

Dry weight biomass is an important parameter in algaculture. Direct measurement requires weighing milligram quantities of dried biomass, which is problematic for small volume systems containing few cells, such as laboratory studies and high throughput assays in microwell plates. In these cases indirect methods must be used, inducing measurement artefacts which vary in severity with the cell type and conditions employed. Here, we utilise flow cytometry pulse width data for the estimation of cell density and biomass, using Chlorella vulgaris and Chlamydomonas reinhardtii as model algae and compare it to optical density methods. Measurement of cell concentration by flow cytometry was shown to be more sensitive than optical density at 750 nm (OD₇₅₀) for monitoring culture growth. However, neither cell concentration nor optical density correlates well to biomass when growth conditions vary. Compared to the growth of C. vulgaris in TAP (tris-acetate-phosphate) medium, cells grown in TAP + glucose displayed a slowed cell division rate and a 2-fold increased dry biomass accumulation compared to growth without glucose. This was accompanied by increased cellular volume. Laser scattering characteristics during flow cytometry were used to estimate cell diameters and it was shown that an empirical but nonlinear relationship could be shown between flow cytometric pulse width and dry weight biomass per cell. This relationship could be linearised by the use of hypertonic conditions (1 M NaCl) to dehydrate the cells, as shown by density gradient centrifugation. Flow cytometry for biomass estimation is easy to perform, sensitive and offers more comprehensive information than optical density measurements. In addition, periodic flow cytometry measurements can be used to calibrate OD₇₅₀ measurements for both convenience and accuracy. This approach is particularly useful for small samples and where cellular characteristics, especially cell size, are expected to vary during growth.     

Discrimination of cycling and non-cycling lymphocytes by BUdR-suppressed acridine orange fluorescence in a flow cytometric system.

Stimulated lymphocytes which pass through the cell cycle may be distinguished from dormant G0 lymphocytes rapidly by flow cytometry. The method is based on cell incubation with 5-bromodeoxyuridine (BUdR) and their subsequent staining with acridine orange under conditions in which cellular DNA and RNA stain differentially. The DNA-specific green fluorescence of stimulated, cycling cells is suppressed while RNA-specific red fluorescence is affected only minimally. It is possible, therefore, to distinguish cycling vs non-cycling cells based on two entirely different parameters, i.e. BUdR incorporation and RNA content.     

Rapid identification and detection of parasitized human red cells by automated flow cytometry

Rapid and reliable identification of various human red cells parasites is important in many chemotherapeutic and immunologic studies. Because manual microscopic counting is tedious and imprecise, we have developed a simple diagnostic procedure for the automated flow cytometric detection of in vitro infected red cells, using a nucleic acid-binding fluorescent dye, acridine orange. Human malaria (Plasmodium falciparum)-infected red cells from continuous human erythrocyte culture were incubated at room temperature in acridine orange stain for 5 min after which the samples were analyzed by flow cytometry. Since mature red cells contain no DNA, infected red cells were identified with a distinct fluorescent signal. A total of 200,000 cells per sample were counted and analyzed in less than 2 min. Rings, trophozoites, and schizonts were assessed and identified in synchronized infected red cell cultures by flow cytometry. In addition, various stages of infected red cells were isolated with a cell sorter. This rapid method permits accurate and reliable assessment of data with the exclusion of anomalous data such as damaged cells, extraneous material, and contaminating particles.     

Evaluation of flow cytometry as a method for quantification of circulating blood cell populations in salmonid fish

Flow cytometry was used to estimate the proportions of different blood cell types in brown and rainbow trout. On the basis of forward light scatter and 90° side scatter three populations were differentiated. The relative abundance of these cells correlated with that of erythrocytc (r²= 0.994), lymphocyte plus thrombocyte(r²= 0.676) and neutrophil populations (r²= 0.571) enumerated by direct microscopy. By density gradient separation of cells, cell sorting and acridine orange staining it was confirmed that these cell types could be assigned to the populations detected. Changes in blood cell populations were monitored by flow cytometry in a group of experimental fish placed under confinement stress. Flow cytometry proved to be a rapid and reliable method for monitoring cell population dynamics in fish blood.     

In-depth validation of acridine orange staining for flow cytometric parasite and reticulocyte enumeration in an experimental model using Plasmodium berghei

Flow cytometry is potentially an effective method for counting malaria parasites, but inconsistent results have hampered its routine use in rodent models. A published two-channel method using acridine orange offers clear discrimination between the infected and uninfected erythrocytes. However, preliminary studies showed concerns when dealing with Plasmodium berghei-infected blood samples with high numbers of reticulocytes.In hyperparasitemic or chronic P. berghei infection, enhanced erythropoietic activity results in high numbers of circulating immature reticulocytes. We show that even though the protocol offered good discrimination in newly infected animals, discrimination between infected erythrocytes and uninfected reticulocytes became difficult in animals with hyperparasitemia or chronic infections maintained with subcurative treatment. Discrimination was especially hampered by increased nucleic acid content in immature uninfected reticulocytes. Our data confirms that though flow cytometry is a promising analytical tool in malaria research, care should still be taken when analysing samples from anemic or chronically infected animals.     

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.     

Decreased nucleic acid synthesis in low-dose-irradiated lymphocytes--effect of TCGF addition

Flow cytometry was used to evaluate nucleic acid synthesis in irradiated mixed lymphocyte cultures (MLC) compared to nonirradiated control cultures. Two staining methods were used (propidium iodide and acridine orange). We showed that RNA and DNA synthesis are retarded in MLC receiving 0.2 Gy. This effect was reversed by lymphocyte growth factor.     

Single-cell analysis demonstrates how nutrient deprivation creates apoptotic and quiescent cell populations in tumor cylindroids

Understanding how quiescent and apoptotic populations form in tumors is necessary because these cell types can considerably diminish therapeutic efficacy. Most cancer therapeutics are ineffective against quiescent cells because they target rapidly proliferating cells. Distinguishing apoptosis is important because apoptotic cells are committed to death and do not require treatment. Regrowth of quiescent cell can lead to tumor re-occurrence and metastasis, which are the leading causes of cancer mortality. We hypothesized that cylindroid cultures and acridine orange staining could be used to determine how nutrient diffusion creates apoptotic and quiescent regions in tumors. To test this hypothesis we developed a microscopy technique to measure cellular DNA and RNA content in single cells using thin cylindroids and acridine orange staining. Cell classification was compared to flow cytometry of cells grown in defined monolayer cultures. The presence of apoptosis was confirmed by morphological nuclear analysis. The effect of diffusion was determined by varying incubation time, cylindroid size, and exposing cylindroids to nutrient-deficient media. Four overlapping regions were identified as a function of cylindroid radius: an outer viable/quiescent region; a second quiescent/apoptotic region; a third late-stage apoptotic region; and an inner dead region. In monolayer cultures the absence of glutamine and growth factors induced apoptosis and hypoxia induced quiescence. Treating with nutrient-deficient media suggested that cells became quiescent near the periphery because of glucose and oxygen limitations, and became apoptotic and died further from the edge because of glutamine and growth factor limitations. These results show that cellular microenvironments can be identified in cylindroids using simple acridine orange staining and that single cell fluorescence can be measured in three-dimensional culture. The developed techniques will be useful for developing cancer therapies and determining how cell death and apoptosis are induced in three-dimensional tumor tissue.     

肝细胞生长因子基因转染对人淋巴瘤细胞凋亡的影响

探讨肝细胞生长因子（HGF）基因转染人淋巴瘤细胞系Raji细胞后,拮抗足叶乙甙（VP－16）诱导细胞凋亡的研究。将三种细胞：未转染Raji细胞、空载体pVITR02－mcs转染细胞和HGF基因转染细胞,分成正常对照组和经vP－16处理的药物组。采用Westernblot法验证HGF蛋白的表达：CCK－8法检测诱导Raji细胞凋亡的药物浓度;通过透射电镜、流式细胞术、吖啶橙（A0）染色、苏木精咿红（HE）染色等方法观察Raji细胞的凋亡情况,并进行相关分析。结果显示：Westernblot法验证了HGF蛋白质的表达;CCK．8法显示100μg／mL足叶乙甙可明显抑制Raii细胞增殖;透射电镜下可发现典型的凋亡细胞;流式检测结果表明：给药组与正常组相比,三组细胞的凋亡率明显升高（P〈0．01）,提示VP－16具有诱导细胞凋亡的作用：但给药组间：HGF基因转染组凋亡率明显低于未转染组（P＜0．05）和空载体pVITR02．mcs转染组（P〈0．05）,提示嬲F基因转染可明显抑制VP-16诱导的Raji细胞的凋亡,AO染色和HE染色结果也同样提示HGF具有拮抗VP－16诱导的细胞凋亡效应。     

Determination of in situ bacterial growth rates in aquifers and aquifer sediments

Laboratory and field-scale studies with stained cells were performed to monitor cell growth in groundwater systems. During cell division, the fluorescence intensity of the protein stain 5-(and 6-)-carboxyfluorescein diacetate succinimidyl ester (CFDA/SE) for each cell is halved, and the intensity can be tracked with a flow cytometer. Two strains of bacteria, Comamonas sp. strain DA001 and Acidovorax sp. strain OY-107, both isolated from a shallow aquifer, were utilized in this study. The change in the average generation or the average fluorescence intensity of the CFDA/SE-stained cells could be used to obtain estimates of doubling times. In microcosm experiments, the CFDA/SE-based doubling times were similar to the values calculated by total cell counting and were independent of cell concentration. Intact and repacked sediment core experiments with the same bacteria indicated that changes in groundwater chemistry were just as important as growth rates in determining planktonic cell concentrations. The growth rates within the sediment cores were similar to those calculated in microcosm experiments, and preferential transport of the daughter cells was not observed. The experiments indicated that the growth rates could be determined in systems with cell losses due to other phenomena, such as attachment to sediment or predation. Application of this growth rate estimation method to data from a field-scale bacterial transport experiment indicated that the doubling time was approximately 15 days, which is the first known direct determination of an in situ growth rate for bacteria in an aquifer.     

Determination of In Situ Bacterial Growth Rates in Aquifers and Aquifer Sediments

Laboratory and field-scale studies with stained cells were performed to monitor cell growth in groundwater systems. During cell division, the fluorescence intensity of the protein stain 5-(and 6-)-carboxyfluorescein diacetate succinimidyl ester (CFDA/SE) for each cell is halved, and the intensity can be tracked with a flow cytometer. Two strains of bacteria, Comamonas sp. strain DA001 and Acidovorax sp. strain OY-107, both isolated from a shallow aquifer, were utilized in this study. The change in the average generation or the average fluorescence intensity of the CFDA/SE-stained cells could be used to obtain estimates of doubling times. In microcosm experiments, the CFDA/SE-based doubling times were similar to the values calculated by total cell counting and were independent of cell concentration. Intact and repacked sediment core experiments with the same bacteria indicated that changes in groundwater chemistry were just as important as growth rates in determining planktonic cell concentrations. The growth rates within the sediment cores were similar to those calculated in microcosm experiments, and preferential transport of the daughter cells was not observed. The experiments indicated that the growth rates could be determined in systems with cell losses due to other phenomena, such as attachment to sediment or predation. Application of this growth rate estimation method to data from a field-scale bacterial transport experiment indicated that the doubling time was approximately 15 days, which is the first known direct determination of an in situ growth rate for bacteria in an aquifer.     

Studies on the role of polyamines associated with the ribosomes from Bacillus stearothermophilus

1. Spermine and spermidine were the main polyamines detectable in Bacillus stearothermophilus. 2. When grown at 65 degrees B. stearothermophilus contained lower concentrations of polyamines per mg. of RNA than when grown at 45 degrees or at 55 degrees . 3. Ribosomes isolated from B. stearothermophilus in 0.01m-tris-hydrochloric acid buffer (pH7.4)-0.01m-magnesium chloride contained sufficient polyamines to neutralize between 4% and 9% of their RNA phosphorus. 4. Removal of polyamines from the ribosomes by dialysis against m-potassium chloride did not appreciably alter the hypochromicity or thermal denaturation profiles of the ribosomes when measured in 0.01m-tris-hydrochloric acid buffer (pH7.4)-0.01m-magnesium chloride, though it did cause a loss of ribosome particles sedimenting at greater than 78s. 5. When ribosomes were dialysed against acridine orange solutions acridine orange bound to the ribosomes and did not displace spermine, but when a mixture of ribosomal RNA and spermine was dialysed against acridine orange the acridine orange displaced the spermine. It is concluded that polyamines in the ribosomes are less accessible for displacement by acridine orange than when polyamines are bound to ribosomal RNA.     

Encephalitozoon cuniculi: quantitation of parasites and evaluation of viability

Two methods (manual and automated) for quantitation of viable versus dead Encephalitozoon cuniculi are reported. The manual method uses ethidium bromide and acridine orange to stain dead and viable organisms, respectively. The stained organisms are visually differentiated with the aid of a fluorescence microscope. The automated method uses propidium iodide to stain dead parasites, which are differentiated from viable unstained parasites with the aid of a flow cytometer. An automated cell counter (Coulter Counter) was used to count rapidly large numbers of samples and to improve the sensitivity of counting low concentrations of parasites. These methods will enhance investigators' abilities to conduct quantitative experiments on host defense mechanisms against E. cuniculi.     

Survival of Aeromonas salmonicida in lake water.

The survival of Aeromonas salmonicida subsp. salmonicida in lake water was investigated by using a variety of techniques. They included acridine orange epifluorescence, respiration, cell culture, cell revival, flow cytometry, plasmid maintenance, and membrane fatty acid analysis. During a 21-day study, A. salmonicida became nonculturable in sterile lake water samples. Flow cytometry and direct microscopy indicated that cells were present. Although the nonculturable cells could not be revived, the recovery method did indicate that the presence of low numbers of culturable cells within samples could produce misleading results. Plasmid DNA, genomic DNA, and RNA were maintained in the nonculturable cells; in addition, changes in the fatty acid profiles were also detected. Although viability could not be proven, it was shown that the morphological integrity of nonculturable cells was maintained.     

Survival of Aeromonas salmonicida in lake water

The survival of Aeromonas salmonicida subsp. salmonicida in lake water was investigated by using a variety of techniques. They included acridine orange epifluorescence, respiration, cell culture, cell revival, flow cytometry, plasmid maintenance, and membrane fatty acid analysis. During a 21-day study, A. salmonicida became nonculturable in sterile lake water samples. Flow cytometry and direct microscopy indicated that cells were present. Although the nonculturable cells could not be revived, the recovery method did indicate that the presence of low numbers of culturable cells within samples could produce misleading results. Plasmid DNA, genomic DNA, and RNA were maintained in the nonculturable cells; in addition, changes in the fatty acid profiles were also detected. Although viability could not be proven, it was shown that the morphological integrity of nonculturable cells was maintained.     

The ratio of RNA to total nucleic acid content as a quantitative measure of unbalanced cell growth

Use of the metachromatic dye, acridine orange, to stain cells in suspension for flow cytometry allows for the simultaneous measurement of DNA and RNA content in individual cells. The relative RNA content as a function of total cellular nucleic acid content [alpha r = RNA/(RNA + DNA)] is a constant value, characteristic for particular cell lines during their exponential growth under optimal conditions. This ratio can be estimated for the G1A, G1B, S, and G2 + M cell cycle compartments. Changes in growth rate or the addition of antitumor drugs induces characteristic changes in the ratio either evenly throughout or at a particular phase of the cell cycle. Under such conditions, measurement of cellular DNA and RNA content provides a sensitive assay of any deviation from balanced cell growth. Unbalanced growth caused by suboptimal culture conditions or as a result of incubation with various antitumor agents is illustrated. Examples of unbalanced growth which are not correlated with cell viability as measured by cell clonogenicity are discussed.     

Cell size and RNA content correlate with cell differentiation and proliferative capacity of rat keratinocytes.

Keratinocytes from rat skin were separated according to their size in a specially designed unit-gravity sedimentation chamber. The fractions obtained with this technique showed clear morphological differences, and analysis of size distribution confirmed that size was the criterion for separation. Simultaneous DNA and RNA staining of the fractions with acridine orange and subsequent flow cytometric analysis enabled one to classify cells into resting, proliferating, and differentiating stages. Cell size was not directly correlated with proliferation in situ as determined with acridine orange flow cytometry, nor with proliferative capacity in culture as assayed by BrdU/Hoechst flow cytometry. The smallest cells, exhibiting low DNA and RNA content, which do not proliferate in vivo, required a prolonged period of serum stimulation in vitro to initiate RNA and DNA synthesis. Cells of intermediate size exhibited early RNA synthesis and maximal proliferative capacity, whereas the largest cell population displayed no RNA synthesis in culture and the least proliferative capacity. In conclusion, these results suggest that RNA synthesis early after serum stimulation, in addition to a specific, optimal cell size, correlates with the proliferative capacity of keratinocytes in cell culture.     

bFGF对乳腺癌细胞系MCF-7细胞增殖与凋亡的影响

目的观察碱性成纤维细胞生长因子（bFGF）对体外培养人乳腺癌MCF-7细胞增殖和凋亡的影响,初步探讨bFGF作用机制。方法在饥饿培养的MCF-7细胞中加入bFGF和PD98059处理,以MTT法、吖啶橙染色及流式细胞术观察细胞生长与凋亡情况;并用Western blot检测caspase-3蛋白含量。结果对照组细胞形态发生改变：核质固缩、有凋亡小体形成;细胞凋亡率较高;Western blot分析表明,caspase-3蛋白明显表达。bFGF处理后,细胞变饱满,凋亡现象减少;细胞增殖比明显增加;与对照组相比凋亡细胞比例下降,并诱导细胞进入S期;随着bFGF浓度增加,caspase-3蛋白表达水平降低,在一定范围内呈剂量依赖性。加入PD98059可抑制bFGF的这些作用。结论bFGF可以促进细胞增殖,加速人乳腺癌细胞系MCF-7细胞的细胞周期进程,抵抗无血清饥饿诱导的凋亡,其作用部分可能是通过Ras-Raf-ERK1/2途径介导的。     

An easy-to-use simulation program demonstrates variations in bacterial cell cycle parameters depending on medium and temperature

Many studies are performed on chromosome replication and segregation in Escherichia coli and other bacteria capable of complex replication with C phases spanning several generations. For such investigations an understanding of the replication patterns, including copy numbers of origins and replication forks, is crucial for correct interpretation of the results.Flow cytometry is an important tool for generation of experimental DNA distributions of cell populations. Here, a Visual Basic based simulation program was written for the computation of theoretical DNA distributions for different choices of cell cycle parameters (C and D phase durations, doubling time etc). These cell cycle parameters can be iterated until the best fit between the experimental and theoretical DNA histograms is obtained. The Excel file containing the simulation software is attached as supporting information.Cultures of Escherichia coli were grown at twelve different media and temperature conditions, with following measurements by flow cytometry and simulation of the DNA distributions. A good fit was found for each growth condition by use of our simulation program. The resulting cell cycle parameters displayed clear inter-media differences in replication patterns, but indicated a high degree of temperature independence for each medium. The exception was the poorest medium (acetate), where the cells grew with overlapping replication cycles at 42 °C, but without at the lower temperatures.We have developed an easy-to-use tool for determination of bacteria's cell cycle parameters, and consequently the cells' chromosome configurations. The procedure only requires DNA distribution measurements by flow cytometry. Use of this simulation program for E. coli cultures shows that even cells growing quite slowly can have overlapping replication cycles. It is therefore always important not only to assume cells' replication patterns, but to actually determine the cell cycle parameters when changing growth conditions.