Cell Population Kinetics Research Articles

Cell Population Kinetics in Atherogenesis Cell Births and Losses in Intimal Cell Mass‐Derived Lesions in the Abdominal Aorta of Swinea

Atherosclerotic lesions may arise in a number of different ways. The two most notable, perhaps, are by monocyte infiltration of the intima and by hyperplasia of normally occurring intimal cell masses. This report is limited to the ICM-derived lesion type induced by a hyperlipidemic diet in the abdominal aorta of swine. The HL diet results, by 49 days, in accumulation of lipid in about 50% of the ICM cells and increases in cell division activity, as indicated by tritiated thymidine LI fourfold greater than in ICM of control swine. Cell numbers are not significantly increased over controls at 49 days, but by 90 HL diet days, they have increased to eightfold over control values. Throughout the 90 days, about 95% of the cells in the ICM or ICM-lesions are smooth muscle cells. Monocytes appear to constitute no more than 5% of the cells. Calculated lesion cell deaths are small during the 90 days, and foci of necrosis are rarely found. By scanning electron microscopy, the endothelial cell integrity appears to be maintained even over the ICM-lesions at 90 days. Calculations from tritiated thymidine LI indicate endothelial cell losses equivalent to 50% of the LI, but they are not significantly greater for the HL swine than for controls. We suggest, then, that the lipid in the ICM (or something associated with it) is the most likely candidate for the SMC growth stimulatory agent accounting for the increased tritiated thymidine LI and the great increase in ICM-lesion cell numbers between HL diet days 49 and 90. Platelet- and/or monocyte-derived growth factors may also be involved in some subtle fashion, but this study provides no positive evidence to support this hypothesis. Progression of the ICM-derived lesions to the advanced atheromatous phase by 300 days on HL diet appears to be a much more complex process. By 300 days in the specific experiment cited, approximately 65% of the atherosclerotic lesion volume consisted of lipid-rich calcific necrotic debris; calculated death rates of lesion cells were very high compared to that at 90 days; calculated endothelial cell loss rates were considerably higher than in controls; and, large numbers of monocyte-macrophages were present in many areas generally associated with necrotic foci. These changes in the aggregate suggest a much more complex mode of pathogenesis for progression to advanced stages than for initiation and early development.

Cell Population Kinetics and Dna Content During Thyroid Carcinogenesis

The proliferation kinetics and DNA content of thyroid follicular cells in rats were studied by autoradiography and cytophotometry. Continuous treatment of animals with methylthiouracil (MTU) results in hyperplasia followed by tumour growth in the thyroid gland. The mitotic index (MI) increases from 0.006 +/- 0.002% in controls to 0.13 +/- 0.06% in hyperplasia and to 0.09 +/- 0.03% in malignant cells. The same is true for the labelling index (LI) which rises from 0.08 +/- 0.003% in controls to 1.4 +/- 1.1% in hyperplasia and to 1.0 +/- 0.6% in follicular adenomas. The S-phase duration (TS) is shortened from 8.0 +/- 1.2 hr in controls to 6.0 +/- 1.4 hr in animals treated for 9 months with MTU and prolonged to 15.4 +/- 2.1 hr in papillary carcinomas. In all MTU-treated animals a decrease in the value of the potential population doubling time (TPD) and thyroid weight doubling time (TD) was observed. The cell loss factor (phi) decreases in animals treated for 3 months with MTU and increases during the stage of tumour growth in the gland (animals treated 12-15 months with MTU). DNA measurements in the nuclei of hyperplastic and neoplastic thyroid tissues reveal cells with values exceeding that in control animals. However, no difference was found in the DNA content between thyroid adenomas and carcinomas, nor between thyroid hyperplasia and neoplasia.

Options for bone aging with the microscope

The skeletons of all large living verebrates undergo bone-specific ontogenetic changes in the numbers and distributions of cells which secrete new calcifiable collagen matrices (osteoblasts) and which resorb preexisting bone matrix (osteoclasts). The numbers and activities of these cells, which function via tissue remodeling to maintain the external and internal morphology of bones, are also constrained by nutritional and endocrinological influences. Investigators concerned with the practical problem of aging intact and fragmentary archaeological bone specimens, and possibly identifying frank evidence of metabolic bone disease, are denied direct access to information about cell population kinetics. The cells are not preserved. Nonetheless, age-related changes in the microscopic structure and organization of bone in contemporary populations present some useful endpoints which can be applied to this problem. In this paper, microscopic techniques which have been applied to this problem are reviewed, and the range and utility of structures in bone which form as a consequence of bone remodeling activity are examined. The major problems in microscopic bone aging studies relate to sampling site speciticity since normative values for each parameter in every human and primate skeletal element throughout the life span are not available. Secular changes should also be considered.

Periodic optimization of a class of bilinear systems with application to control of cell proliferation and cancer therapy

The authors are concerned with the optimization of a class of bilinear systems under an exponential stability constraint by periodic control functions. Such problems arise in many practical applications, a typical one being the design of optimal strategies for cancer chemotherapy by a suitable control of the proliferation kinetics of cell populations. To provide a focus to the approach used for optimization and the utility of periodic controls, this particular application is discussed in detail. An integration of a pharmacokinetic model with a multicompartmental model for cell proliferation is made. This is done in order to obtain a mathematical formulation of the problem of designing treatment strategies as a parameter optimization problem of determining the optimal dose and the optimal period for minimizing the total quantity of drug administered (and hence the host toxicity) under a specified rate of cure constraint. A procedure for solving this problem is developed, and an illustration is made by designing strategies for administering the phase-specific drug ara-c on L1210 leukemia.

Perturbations in the erythroid marrow progenitor cell pools may play a role in the augmentation of HbF by 5-azacytidine

In vivo observations on the kinetics of F cells and of fetal hemoglobin (HbF) synthesis and in vitro studies of erythroid progenitors, their number, and the gamma-gene expression in their progeny were carried out in baboons (Papio cynocephalus) treated with 5-azacytidine. Maximum effect on the increase of HbF production in vivo was observed only when an expanded erythroid marrow population was present. In these animals, as well as in normal animals, treatment resulted in a significant reduction of the late erythroid progenitor cell pools (erythroid clusters and erythroid colony-forming units, CFU-E) in the marrow. This reduction was more pronounced among those progenitors grown in the absence of added erythropoietin, and it was followed by a rebound a few days after treatment cessation, reflecting the accumulation of regenerating progenitors. An early increase in the in vitro synthesis of HbF in erythroid clusters and CFU-E colonies was observed. This increase was further documented at the cellular level, with immunofluorescent labeling of colonies with monoclonal anti-gamma-globin chain antibodies. In contrast to the findings in late progenitors, the number of erythroid burst-forming unit (BFU-E) colonies and the synthesis of HbF in these colonies was not influenced significantly by 5-azacytidine treatment. It is proposed that the toxic effects of 5-azacytidine on late progenitors, leading to faster mobilization of earlier progenitors to the next more mature compartment, play a role in the in vivo augmentation of HbF synthesis by this drug. This perturbation in the progenitor cell population kinetics and the presumed hypomethylation of the surviving differentiating cells may act synergistically to produce a maximum HbF response after 5-azacytidine treatment.

Perturbations in the Erythroid Marrow Progenitor Cell Pools May Play a Role in the Augmentation of HbF by 5-Azacytidine

Abstract In vivo observations on the kinetics of F cells and of fetal hemoglobin (HbF) synthesis and in vitro studies of erythroid progenitors, their number, and the gamma-gene expression in their progeny were carried out in baboons (Papio cynocephalus) treated with 5-azacytidine. Maximum effect on the increase of HbF production in vivo was observed only when an expanded erythroid marrow population was present. In these animals, as well as in normal animals, treatment resulted in a significant reduction of the late erythroid progenitor cell pools (erythroid clusters and erythroid colony-forming units, CFU-E) in the marrow. This reduction was more pronounced among those progenitors grown in the absence of added erythropoietin, and it was followed by a rebound a few days after treatment cessation, reflecting the accumulation of regenerating progenitors. An early increase in the in vitro synthesis of HbF in erythroid clusters and CFU-E colonies was observed. This increase was further documented at the cellular level, with immunofluorescent labeling of colonies with monoclonal anti-gamma- globin chain antibodies. In contrast to the findings in late progenitors, the number of erythroid burst-forming unit (BFU-E) colonies and the synthesis of HbF in these colonies was not influenced significantly by 5-azacytidine treatment. It is proposed that the toxic effects of 5-azacytidine on late progenitors, leading to faster mobilization of earlier progenitors to the next more mature compartment, play a role in the in vivo augmentation of HbF synthesis by this drug. This perturbation in the progenitor cell population kinetics and the presumed hypomethylation of the surviving differentiating cells may act synergistically to produce a maximum HbF response after 5-azacytidine treatment.

Cell population kinetics of 12-O-tetradecanoylphorbol-13-acetate (TPA) induced hyperplasia : Erle Grieg Astrup and Olav Hilmar Iversen, Institute of Pathology, University of Oslo, The Natioal Hospital, Oslo 1, Norway

Cell population kinetics of 12-O-tetradecanoylphorbol-13-acetate (TPA) induced hyperplasia : Erle Grieg Astrup and Olav Hilmar Iversen, Institute of Pathology, University of Oslo, The Natioal Hospital, Oslo 1, Norway

Cellular heterogeneity in tumours.

Malignant tumours contain normal cells, descendants of transformed cells, and conceivably also initiated cells which have taken some but not all of the steps toward malignancy, and hybrid cells. Tumours are propagated by multiplication of clonogenic cells, which are a subclass of the descendants of transformed cells. The clonogenic cells of a tumour may differ in respect of morphology, karyotype, metastatic capacity, sensitivity to cytotoxic drugs, expression of cell surface antigens and hormone receptors, immunogenicity, sensitivity to the immune reaction of the host, and other properties. Evidence (disputed by some) suggests that selection of particular subpopulations plays a role in tumour metastasis and recurrence. Heterogeneity may be due to pleoclonal origin, generation of phenotypic diversity within a clone, or spontaneous hybridization and chromosome loss. The possibility of interaction between different subpopulations must be taken into account in discussing tumour cell population kinetics. Heterogeneity also has important therapeutic implications and may help to explain the failure of some therapeutic regimes and the success of others.

Cell population kinetics in hairless mouse epidermis following a single topical application of 12-O-tetradecanoylphorbol-13-acetate II

It is known that a single application of 17 nmol 12-O-tetradecanoylphorbol-13-acetate (TPA) to hairless mouse skin first induces (from 0-12 h) a short block in mitotic activity followed by a transient stimulation of proliferation (from 12-96 h) characterized by multiple waves of rapid proliferation in partly synchronized basal cells, leading to hyperplasia. The replication rate of basal cells, the number of basal and suprabasal (maturing) cells per unit of interfollicular epidermis and the number of squamous layers in the stratum corneum were recorded. Changes in the nuclear area of living cells were monitored by morphometry. The changes in the rate of basal cell proliferation are accompanied by concomitant waves of increased rates of cell maturation and cell loss, with a considerable reduction in epidermal cell transit time. When 14-15 squamous layers were observed, this resulted in an increased cell loss, which was visible as scaling from 24 h onwards. The total cell mass lost from 16 to 72 h after TPA application amounted to about 67% of the newborn cell mass. Thus the hyperplasia occurring after a single TPA treatment results from a considerably enhanced cell proliferation that exceeds concomitant increases in the rates of cell maturation and loss. There is no delayed maturation. The results are also consistent with the chalone theory of epidermal growth regulation, assuming that the G1 chalone is produced during cell maturation.

The kinetics of villus cell populations in the mouse small intestine

Cytosine arabinoside was used to kill large numbers of proliferating crypt cells in the mouse small intestine, and the recovery sequence was analysed in terms of the villus population size, the crypt population size, the crypt: villus and the net villus cell influx: because the crypt: villus ratio changed considerably, it was found appropriate to express the crypt population in terms of the crypt cell mass per villus in order to relate it to the villus cell population. All parameters measured showed a series of damped oscillations over the experimental period, and analysis of the relationship between the several population changes strongly suggest that negative feedback control mechanisms are responsible for the response pattern. The importance of measuring the correct kinetic parameters in growth control studies on renewing epithelia is stressed.

The kinetics of villus cell populations in the mouse small intestine. I. Normal villi: the steady state requirement.

Abstract. The cell population kinetics of the villus epithelium of the mouse have been analysed with respect to the size, flux and time. Microdissection methods were employed to measure the villus cell population size and yielded reproducible, precise results. There was a proximodistal negative size gradient in villus cell population and, in those villi of normal morphology, there was a good correlation with the usual morphometric estimators such as height and row count, although correlation was improved by a product variable consisting of a height multiplied by a width parameter.Flux onto the villus is the product of the crypt cell production rate, which was measured by a metaphase arrest method using vincristine and crypt microdissection, and the crypt:villus ratio; net villus influx was maximum proximally in the bowel, where the largest villi were found, and decreased distally. The distribution of transit times of labelled cells to the crypt: villus junction and to the villus tip was measured, allowing the measurement of the median villus transit time.Comparison of the measured villus transit time with the theoretical transit time calculated from the villus influx and population size gave results consistent with a steady state hypothesis. It was found, at each level of the small intestine studied, that the number of epithelial cells on the villus was equivalent to the total number of crypt cells associated with the villus.

The effect of environmental stress stimuli on cell division in rat palatal epithelium.

The effect on cell proliferation of procedures commonly used in studies in laboratory animals was examined in the palatal epithelium of rats. Groups of rats were exposed to ether anaesthesia, immobilization in the supine position or to cage change. Animals left undisturbed in the cages during the experiment were used as controls. At intervals of 30 min, four animals of each group were killed and histological sections of the palatal mucosa were prepared. The number of prophases, metaphases and ana/telophases in the epithelium was counted and related to 1 mm2 of the surface. Thirty minutes after the various procedures the number of metaphases and ana/telophases were extremely low. After a further 30 min a high number of prophases was observed. The number of metaphases rose within the following 30 min, during which time the number of ana/telophases also reached a maximum. These observations indicate that the environmental stimuli have blocked the entrance of cells into mitosis and have resulted in an accumulation of cells, which, following the raising of the blockade, pass through the various stages of the mitotic phase. In studies of cell population kinetics the blockade of cell division as a result of environmental stress stimuli may lead to misleading results.

A mathematical model for cell population kinetics in the intestine

A compartmental model for the cell populations in the intestine is set up. The results obtained are compared with experimental data in the mouse. It is shown that chemical feedback from the villus cells to the crypt together with a self-regulatory mechanism for the stem cells is sufficient to explain the reaction of the villus cell population which is observed after a cytotoxic insult to the crypt cells.

Comparative study of the cellular replication kinetics of rat mammary epithelial cells in vivo and in vitro

Differential staining techniques based on the incorporation of 5-bromo-2′-deoxyuridine (BrdU) into DNA permit the unequivocal identification of metaphrase cells which have replicated once, twice and three or more times. This technique is used to analyze the cell replication kinetics of mammary epithelial cells from young virgin rats in culture. Comparison is made between these in vitro observations and expected results derived from in vivo determination of labelling index, growth fraction, cell cycle length and distribution for the different structures and cell types of the rat mammary gland. The correlation coefficient for the comparison between in vivo and in vitro results is 0.84 suggesting that the heterogeneity of cell population and replication kinetics of the rat mammary gland is preserved when cells are placed in culture. Furthermore, the BrdU incorporation system for the analysis of cell replication kinetics is accurate and acceptable for the study of rat mammary epithelial cell kinetics.

CHANGES IN CELL POPULATION KINETICS IN AN OPEN MERISTEM DURING ROOT GROWTH

SummaryThe problem of root meristems, previously considered to exchange cells between the stele and the cap as well as between cortex and cap, has been solved by using DNA‐labelling and stathmokinetic methods to observe the change in behaviour of the meristem as the primary root ages in Cucurbita pepo L.The stelar pole is quiescent and can contribute few, if any, cells to the cap. During early growth the tiers of cells of the columella meristem are intermittently quiescent and active. This causes the highest average rate of mitosis in the cap to occur in a tier of the columella that is not adjacent to the stelar pole. It also interrupts the patterns of cells in the columella to form up to four complexes of cells along its length. As the root ages, rates of mitosis become generally lower, except in the quiescent stelar pole, and fewer tiers of the columella stay meristematic. The proximal tier of the columella, adjacent to the stelar pole, now acquires the highest rate of mitosis in the meristem. This simplifies the columella pattern, but the meristem never becomes closed because no quiescent buffer establishes itself between the stele and the central cap meristem and so a boundary between the cortex and peripheral cap meristems never becomes stabilized.

Cell population kinetics of thyroid follicular cells in infant rats.

T cell population kinetics of thyroid follicular cells in rats were studied by means of autoradiography and a statmokinetic technique. During the first fortnight after birth no significant changes in the mitotic index (MI) and labelling index (LI) were found. In the next 2 weeks a constant decrease in the number of proliferating cells occurs. In 10-day old animals 40% of the follicular cells were in the cell cycle (GF); 3.25 +/- 0.77 (SEM) % in the S phase and 0.18 +/- 0.04% in mitoses (MI). Day-night changes in the LI and mitotic rate (MR) indicated a peak value at 13.30 hours with a lowest value at 22.30 hours. The mean LI and MR averaged over the whole 24 hr were 3.1 +/- 0.1% and 122.2 +/- 18.1%, respectively. In 10-day old animals, using the fraction of labelled mitoses (FLM) method the median cell cycle time (TC) was 79 hr and the phase durations were TG1--64.6 hr, TS--8.2 hr and TG2--5.1 hr. The decrease in the number of proliferating cells with the age of the animals is considered to be a result of both cell cycle prolongation and in growth fraction reduction.

Cell population kinetics in the small intestine of the Mongolian gerbil.

The cell population kinetics studies reveal differences when compared to other rodents. Proliferative activity is slower in the gerbil than the mouse and the rat. Further study is indicated since the use of the gerbil for research is expanding.

Serum enhances the cycling and survival of HeLa cells treated with 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole.

We have defined the growth kinetics of HeLa cell populations by determining the frequencies of mitoses and deaths and the lengths of intermitotic intervals. This was done by time-lapse cinemicrography. Untreated control cells proliferated at closely similar rates in medium enriched with 5% or 15% fetal calf serum, with an average of 4% dividing and less than 0.1% dying per hr. The mean intermitotic interval was 16 hr during exponential growth of the control populations. In contrast, in cultures treated with 40 or 60 microM 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB), a selective inhibitor of heterogeneous nuclear RNA synthesis, the frequency of mitoses was markedly and directly dependent on serum concentration, whereas the frequency of deaths was inversely dependent. DRB prolonged the intermitotic interval in cells cycling in the presence of the drug, but the effect was less in 15% than in 5% serum. After prolonged treatment of HeLa cells with DRB, the inhibition of heterogeneous nuclear RNA synthesis by DRB appeared to be reduced, which was not due to inactivation of DRB in the culture medium.

Effect of retinoic acid pretreatment on 12-O-tetradecanoylphorbol-13-acetate-induced cell population kinetics and polyamine biosynthesis in hairless mouse epidermis.

A single topical application of 17 nmol 12-O-tetradecanoyl-phorbol-13-acetate (TPA) to the skin of hairless mice induces characteristic transient alterations in the epidermal cells turnover and maturation (0.96 h), associated in time with characteristic changes in the activities of L-ornithine carboxy-lyase (E.C. 4.1.1.17) (ODC) and S-adenosyl-L-methionine carboxy-lyase (E.C.4.1.1.50) (SAM-D) and in the accumulation of polyamines. The effects on these responses of local pretreatment of the skin with retinoic acid 1 h prior to TPA were investigated at selected time points. Retinoic acid inhibited the TPA-induced ODC activity and the ensuing accumulation of putrescine, but did not alter the TPA-induced SAM-D activity or the molar ratio of spermidine/spermine. This pretreatment also decreased in number of dividing basal cells in the first TPA-induced synchronized wave of proliferating cells. However, during the subsequent period of proliferation, the number of dividing cells in the retinoic acid pretreated group was comparatively increased. Hence, at four levels of retinoic acid (0.17, 1.70, 17.0 and 170 nmol), which all inhibited the TPA-induced ODC effectively, there was no change in the total number of basal cells that divided during 16-48 h after TPA-application. Theory is put forward the retinoic acid might exert its antitumorigenic effect during tumor promotion with TPA by interfering with the rate and/or quality of epidermal cell maturation, rather than by inhibiting cell proliferation.

Study of kinetics of epithelial cell populations in normal tissues of the rat's intestines and in carcinogenesis: III. Changes in kinetics of enterocyte populations in the course of experimental intestinal tumour induction in rats

A stage-by-stage study of disturbances in enterocyte proliferation in the ileum and descending colon in the course of tumour induction by treatment with 1,2-dimethylhydrazine was performed. Even at early stages, an expansion of the zone of epithelial cell proliferation in the crypts and migration of dividing cells as far as to the crypt mouth, which is a manifestation of enterocyte differentiation disturbances, were observed. Enterocytes of the crypts chiefly proliferated through a short cycle, the mean duration of which was slightly greater than in normal intestinal tissue. The reduced cell loss in the epithelium and resultant disturbances of its steady state led to the accumulation of great numbers of atypical cells in the superficial layers of the crypts and formation of carcinomas in situ in the descending colon. The microscopically unaltered sections of the mucosa, prior to development of overt neoplastic changes carcinomas in situ, superficial cancers and small-size adenocarcinomas revealed a simplified structure of enterocyte population, as compared with normal epithelium. As tumours progressed, the heterogeneity of its component cell subpopulations increased, and several subpopulations, differing in mean duration of the mitotic cycle, were formed. Pathologic mitoses made up a greater portion (50-60 per cent) of the dividing cells of the descending colon, as compared with ordinary 4 per cent at all stages of experimental tumour induction.