Rate of DNA synthesis determined by flow cytometry using the BrdUrd/Hoechst technique in combination with propidium-iodide staining

Distraction frequency and the gastrocnemius muscle in tibial lengthening. Studies in rabbits

We compared the effect of various distraction frequencies on the gastrocnemius muscle by evaluating the histological findings, intramuscular enzyme contents, and DNA contents. In 15 rabbits, both tibiae were distracted 1 mm per day. The distraction frequency was 2 steps (0.5 mm/12 hour) by hand on the right side and 120 steps (0.0083 mm/12 minutes) by an auto-distractor on the left. The rabbits were divided into 3 subgroups based on length gain: 10%, 20%, and 30%. Histologically, there were no signs of fibrosis or edema and no differences in the number of necrotic cells, and intramuscular enzyme contents between the 2- and 120-step groups. The DNA content, however, was higher in the 120-step group at 30% lengthening in the middle of the muscle belly, and at 20% and 30% lengthening in the musculotendinous junction. Our findings suggest that an increase in the distraction frequency may promote DNA synthesis in the muscle, thus providing better muscle accommodation during bone lengthening.

Detection of bromodeoxyuridine incorporation by alteration of the fluorescence emission from nucleic acid binding dyes using only an argon ion laser

A method was developed that uses paired DNA dyes to detect the incorporation of bromodeoxyuridine (BrdUrd) into cellular DNA and requires only 488 nm excitation. The fluorescence of thiazole blue, TO-PRO-3, and LDS-751 was found to be enhanced by the presence of BrdUrd in DNA. Pairing LDS-751, thiazole blue, or TO-PRO-3 with propidium iodide (PI) for flow cytometry allowed the differentiation of cells containing BrdUrd from BrdUrd unlabeled cells. LDS-751 can be excited directly at 488 nm, and TO-PRO-3 or thiazole blue can be excited indirectly by resonance energy transfer from PI. The enhancement of fluorescence from these dyes is correlated with a decrease in PI fluorescence, suggesting an increased energy transfer from PI to the red emitting dye. Fluorescence from other dyes, including thiazole orange, TO-PRO-1, rhodamine 800, oxazine 750, and 7-aminoactinomycin D, was not altered by the presence of BrdUrd in DNA. Results also were obtained showing that BrdUrd detection using PI and TO-PRO-3 is compatible with immunofluorescence staining with FITC-labeled antibodies.

Measurement of efflux from G1-phase in a growth factor dependent cell line

In order to test a mathematical model of G1/S-phase transition, the proliferative response of the murine myeloid interleukin 3 (IL-3) dependent cell line NFS-78 to graded reduction of IL-3 levels was measured. Exponentially growing cells were exposed to bromodeoxyuridine (BUdR), which replaces thymidine (TdR) in the DNA double strands during DNA synthesis. After incubation periods ranging from 3 to 36 h the cells were fixed and stained with a fluorescence dye mixture of Hoechst 33258 and ethidium bromide (EB) and subsequently analyzed in a two-parametrical flow cytometer. The BUdR-quenched TdR-specific Hoechst 33258 fluorescence of each cell provides information on the cell cycle location at the start of incubation and on whether or not a cell has divided. The DNA-specific EB fluorescence provides information on the actual cell cycle location at the end of the incubation period. From the 2-dimensional fluorescence distributions the efflux from G1-phase was calculated. Upon IL-3 reduction the cells showed accumulation in the G1-phase along with a reduction in the progression rate through the other phases of the cell cycle. By staining with the vital dye Hoechst 33342 as well as with propidium iodide (PI) it was further possible to show that cell death after IL-3 withdrawal occurred in all phases of the cell cycle.

Improved BrdUrd-Hoechst bivariate cell kinetic analysis by helium-cadmium single laser excitation

In laser based flow cytometers, UV excitation of Hoechst 33258 and propidium iodide (PI) or ethidium bromide (EB) is performed with 351/364 nm high power lines of UV-capable argon ion lasers, which are expensive and short-lived. In this paper we note for the first time that helium-cadmium lasers emitting 10 to 30 mW at 325 nm are even more superior for cell kinetic bivariate bromodeoxyuridine (BrdUrd)/Hoechst PI or EB cell cycle analysis. HeCd single laser UV excitation gives comparable CVs for cell cycle distributions, and almost normal G2M/G1 ratios of 1.9 to 2.0 for all cell cycles. This is shown for synchronous and asynchronous cell populations on a FACStar+ and an Ortho Cytofluorograf. Therefore we recommend helium-cadmium lasers as low-power, cheap, and long-lived UV excitation sources for the cytochemically simple but high resolution multiparameter BrdUrd-Hoechst cell kinetic analysis.

The genetic toxicology of 5-bromodeoxyuridine in mammalian cells

The thymidine analog, BrdUrd, induces many biological responses which are of importance to the field of genetic toxicology and related disciplines. These include the induction of SCE, specific-locus mutations, and toxicity, inhibition of cell proliferation, and the expression of fragile sites in the human genome. In early models which addressed the mechanisms of the biological effects of BrdUrd exposure, two pathways were proposed to account for the induction of the biological responses. Incorporation of the enol form of BrdUrd into the nascent DNA strand after pairing with deoxyguanosine was proposed as one pathway, whereas the incorporation of BrdUrd opposite adenosine in place of thymidine was proposed as the second pathway. Many novel and sophisticated techniques have been applied to the study of the mechanism of the induction of biological effects by BrdUrd leading to a substantial increase in our understanding of these mechanisms. However, the experimental evidence clearly supports the contention that BrdUrd exerts its effects on eukaryotic cells through mechanisms similar to those originally proposed to explain the genotoxicity of BrdUrd.

Lactate production and amino acid incorporation in interleukin 3-dependent, factor-deprived hemopoietic murine cell lines

Interleukin 3 (IL-3) stimulates the growth of various types of hemopoietic progenitors. In vitro, survival of a series of murine cell lines derived from either neoplastic or nonneoplastic hemopoietic tissue shows a strict IL-3 dependence. In order to test the implication of energy metabolism in this dependence as claimed in several studies, intracellular ATP levels as well as accumulative lactate release were measured in the murine hemopoietic lines FDC-P1, 32Dcl.23, DA-1, DA-3, NFS-60, and NFS-78. ATP levels showed little or no changes within 4-6 h of IL-3 starvation. In the absence of IL-3 the accumulative lactate release ranged from 1.4 to 2.6 mM, and in its presence values between 1.5 and 3.4 mM were recorded within 7 h. Only 32Dcl.23 showed an almost complete suppression of lactate release upon IL-3 withdrawal. The cell cycle times of these cell lines determined by flow cytometry ranged between 9 (DA-3) and 24 h (NFS-78). In the presence of IL-3 there was a significant inverse relationship between cell cycle times and lactate production. It is concluded that neither ATP generation nor the metabolic pathway of lactate production, although the latter correlated with proliferative activity in the studied cell lines, is controlled by IL-3. Furthermore, no control by IL-3 of essential amino acid incorporation into proteins was detected in cell lines 32Dcl.23 and NFS-60.

Flow cytometric evaluation of cell cycle characteristics during in vitro differentiation of chick embryo chondrocytes

The cell cycle kinetic characteristics of chick endochondral chondrocytes differentiating in vitro were studied by flow cytometry. In addition, the synthesis of type I and type X collagens of the same cells was evaluated by immunoprecipitation. Dedifferentiated cells, derived from chick embryo tibiae and grown attached to a substratum, were characterized by type I collagen synthesis, a high growth fraction (GF = 0.94), minimal cell loss factor (phi = 0.02), and a total cell cycle time of the proliferating cells of about 17 h (tG1 = 8 h, tS = 5 h, and tG2 + M = 4 h). Transfer of dedifferentiated cells to suspension culture on agarose-coated dishes induced differentiation to hypertrophic chondrocytes. These were characterized by type X collagen synthesis, a low growth fraction (GF = 0.52), maximal cell loss factor (phi = 1.0), and a total cell cycle time of the proliferating cells of about 73 h (tG1 = 53 h, tS = 12 h, and tG2 + M = 8 h). The transition from dedifferentiated chondrocytes to hypertrophic chondrocytes was accompanied by large increases of the duration of all the cell cycle phases and of the number of quiescent and degenerating cells. Associated with these alterations in cell cycle kinetics was a switch from type I to type X collagen synthesis. Further preliminary data suggest that the population of differentiating chondrocytes (a state between dedifferentiated and hypertrophic chondrocytes) comprises a heterogeneous population of fast and slow growing cells.

Effect of 5-fluoro-2'-deoxyuridine (FdUrd) on 5-bromo-2'-deoxyuridine (BrdUrd) incorporation into DNA measured with a monoclonal BrdUrd antibody and by the BrdUrd/Hoechst quenching effect

The purpose of this study was to improve the application of bromodeoxyuridine (BrdUrd) for the flow cytometric analysis of cell kinetics. In order to obtain a quantitative measure of the DNA synthesis rate (or the number of divided cells), BrdUrd should replace thymidine (dThd) completely in the newly synthesized DNA strands. The de novo synthesis of dThd monophosphate competing with BrdUrd incorporation was stopped by fluorodeoxyuridine (FdUrd). Cells of a human leukemic cell line (REH) were exposed to BrdUrd for either 20 min, 8 h, or 24 h. Bromodeoxyuridine incorporation was determined by a monoclonal antibody as well as by the BrdUrd/Hoechst (H) technique. Counterstaining of the DNA was performed with propidium iodide or ethidium bromide. DNA fluorescence was measured in both techniques with a two-parameter flow cytometer, the histograms being analyzed by computer. It was found that FdUrd is required in the BrdUrd/H technique for replacement of dThd at low BrdUrd concentrations and long incubation times. With short incubation periods, as used for detection by the monoclonal anti-BrdUrd antibody, FdUrd increases the incorporated BrdUrd amount when BrdUrd concentrations of 10 microM or less are applied.

The use of flow cytometry and cell sorting in a human colon carcinoma model

We investigated the growth characteristics of a human colon carcinoma cell line, WiDr, grown in culture flasks and on chick embryonic skin (CES). WiDr cells labeled in vitro with bromodeoxyuridine (BrdU) and analyzed by combined propidium iodide/Hoechst 33258 fluorescence showed evidence of more BrdU incorporation in early S phase as compared to late S phase. When inoculated on the CES, WiDr cells multiplied and invaded the underlying skin. Morphologic examination showed that with extended culture WiDr cells on the CES undergo progressive structural organization with the development of acini and basal lamina, structures similar to those in in vivo tumors. WiDr cells were labeled with monoclonal antibody to carcinoembryonic antigen (CEA) and the brightest 2% of the population was sorted. When subsequently grown on the CES, the sorted cells formed significantly more acinar structures at 3 and 6 days of culture than an unsorted population grown for a comparable time.

Modification of the BrdU/H33258 technique for flow cytometry based on the pH-dependence of the fluorescence of H33258 stained DNA

A simple analytical method is described for the evaluation of cell cycle progression data by modification of the BrdU/H33258 technique for flow cytometry. This procedure allows to obtain quenched and unquenched DNA-histograms of cells containing BrdU-substituted DNA by staining with one dye only, namely H33258. Quenched histograms are obtained at pH = 7 and give information about how far cells have passed the cell cycle since the beginning of the incubation. The unquenched ones obtained at pH less than or equal to 4 of the staining solution give information about the actual position of the cells in the cell cycle.

Flow cytometry and cell proliferation kinetics

Flow cytometric techniques are presented which allow to determine parameters of cell proliferation kinetics by means of histogram sequences after special manipulations of the cell culture under investigation: (a) In the stathmokinetic method metaphase blocking agents are applied which allow the cells of the population to continue progression through interphase and accumulate at 4C DNA content. The development of DNA specific histograms during this process is analysed as to the G1 phase duration and the fraction of nonproliferating cells. (b) In the BUdR/Hoechst method the suppression of Hoechst fluorescence after BUdR incorporation during S phase is taken as a means for inducing a temporal change of histogram shapes without perturbing the cell cycle progression of the population. This temporal development of histogram shapes is analysed as to phase duration, whole cycle time and fraction of nonproliferating cells. (c) By combining the BUdR/Hoechst technique with a simultanous DNA specific stain and analysing with a two-parametrical flow cytometer, more information is obtained from each histogram after BUdR incorporation: The location of cells in the cycle at the beginning of the experiment, the cycle stage at cell harvest, and from this the distance and velocity of progression through the cycle during drug incubation. By introduction of these dynamic methods flow cytometry has become a powerful tool for the study of cell proliferation kinetics in culture.