Cell Generation Cycle Research Articles

Thermo-environ analyses of a novel trigeneration cycle based on clean technologies of molten carbonate fuel cell, stirling engine and Kalina cycle

In the present paper, a novel combined cooling, heating and power cycle is studied. In the cycle, three technologies of molten carbonate fuel cell, Stirling engine (Alpha type) and Kalina power generation cycle are combined. The Stirling engine and Kalina cycle are used to recover heat from the stack gases of the molten carbonate fuel cell. Also, the condenser of the Kalina cycle is used to supply heating, while the cooling load is produced by an absorption chiller. In analyzing this cycle, a parametric study and a sensitivity analysis are presented to investigate the cycle from thermodynamic and environmental points of views. The analyses are carried out by selecting 7 design parameters, which four-most important parameters include current density, air to fuel ratio at the fuel cell input, fuel cell input pressure and the temperature ratio at the Stirling engine. The results showed that the combined cycle saves up to 45% fuel in comparison to the conventional systems. The overall and electrical efficiencies of the cycle can reach more than 70% and 50%, respectively. Furthermore, carbon monoxide and carbon dioxide yearly reduction for 6000 h of operation is 15 tons and 225 tons, respectively.

X-Ray Sensitivity during the Cell Generation Cycle of Cultured Chinese Hamster Cells1

Our earlier reports (1–3) have provided a general, qualitative description of the X-ray sensitivity of Chinese hamster cells as a function of their age within the generation cycle. With a partially synchronized cell population and colony survival used as an assay, it was established that cells were least sensitive to X-rays in the latter part of the DNA synthetic period (S period) and appeared to be about equally sensitive in the pre-DNA synthetic period (G1) and post-DNA synthetic period (G2). The variations in sensitivity throughout the cycle seemed mainly but not exclusively due to variations in the threshold or shoulder of the survival curve. We were, however, aware of the fact that even a few resistant S cells present during stages we had designated as G1 or G2 could significantly alter the survival curve for G1 and G2 cells. Such S cells may be present not only because of inadequacies in the synchronization procedure but also because of differences in the rate of progression of cells through the cycle which tends to desynchronize the population. Even if the number of S cells present were known, their exact contribution to the survival curve would be difficult to estimate, especially if the sensitivity of S cells varied throughout the S period. To determine X-ray sensitivity more accurately at all stages, we have used lethal amounts of tritiated thymidine (HTdR) to inactivate the S cells. Furthermore, since the previous technique could not be used to obtain the sensitivity of mitotic (M) cells, we have modified our procedure so that this may be accomplished. Finally, in view of the possible association between X-ray resistance and DNA synthesis, it was important to find out whether cells in S had a constant or variable sensitivity throughout the synthetic period. MATERIALS AND METHODS

Effect of Valproic Acid on the Expression of P27Kip1 and Multidrug Resistance in HL60 Cells.

Multidrug resistance (MDR) was the main cause of treatment failure in leukemic chemotherapy. P170, the protein expressed from MDR-1 gene, play an important role in MDR. P27Kip1 was a member of cyclin dependent kinase inhibitor family. It was also a negative regulator in cell generation cycle. It also promoted cells apoptosis. Valproic acid (VPA) was a kind of histone deacetylace inhibitor which could inhibit cell cycle and induce apoptosis. In the current study, we investigated the effects of VPA on the expression of P27Kip1 and P170 of HL60 cells in vitro. HL60/HT cells were induced from HL60 cells by harringtonine (HT) in gradient concentrations. The P27Kip1 expression and P170 expression were tested in flow cytometry. We tested the expression of P27Kip1 and P170 in normal mononuclear cells, HL60 cells and HL60/HT cells, also the effects of VPA on P27Kip1 expression and P170 expression in HL60 cells and HL60/HT cells. The 50% inhibiting concentration (IC50) of vincristine for HL60/HT cells was 5.2 times higher than that for HL60 cells (0.078ug/ml vs. 0.015ug/ml). The IC50 of HT for HL-60/HT cells was 9.3 times higher than that for HL-60 cells (0.14μg/ml vs. 0.015μg/ml). The IC50 of Cytarabine for HL60/HT cells was 3.65 times higher than that for HL60 cells (0.73ug/ml vs. 0.20ug/ml). The expression of P27Kip1 in normal mononuclear cells was the highest, while that in HL60 cells was higher than HL60/HT cells (96.18±3.13% vs. 85.83±4.65% vs. 35.91±3.13%, one way ANOVA, P<0.05). The expression of P170 in normal mononuclear cells and HL60 cells had no significant difference (0.54±0.32% vs. 0.62±0.31%, P>0.05). But the P170 expression of HL60/HT cells was 6.71±1.61%, which was much higher than that of normal mononuclear cells or HL60 cells (P<0.05). In HL60 cells, the expression of P27Kip1 increased after cultured with 1mmol/L VPA (92.21±3.43% vs. 85.83±4.65%, P<0.05), but the expression of P170 didn't change significantly (0.65±0.18% vs. 0.62±0.31%, P>0.05). In HL60/HT cells, the expression of P27Kip1 increased after cultured with VPA (66.20±5.07% vs. 35.91±3.13%, P<0.05), and the expression of P170 didn't change significantly either (6.40±1.59% vs. 6.71±1.61%, P>0.05). These results indicate that the P27Kip1 expression in normal mononuclear cells were higher than that in leukemia cells (HL60 cells), and the P27Kip1 expression in common HL60 cells were higher than that in MDR HL60/HT cells. VPA could increase the expression of P27Kip1 in HL60 cells and HL60/HT cells. VPA had no effect on the expression of P170 in HL60 cells or HL60/HT cells. That means, The MDR-reverse effect of VPA may not come from the P170 descent mechanism.

Flow cytometric analysis of fluorescence in situ hybridization with dye dilution and DNA staining (flow‐FISH‐DDD) to determine telomere length dynamics in proliferating cells

Telomeres shorten during DNA replication; extensive erosion of telomeres likely promotes replicative senescence and chromosomal instability. Telomere length in individual cells has been quantified by flow cytometric analysis of fluorescence in situ hybridization (flow-FISH). To determine the rate of telomere attrition (telomere erosion per cell division), we combined flow-FISH with dye dilution and DNA staining (flow-FISH-DDD) and measured telomere-specific fluorescence in proliferating cells identified by cell generation and cell cycle phase. Peripheral blood mononuclear cells (PBMC) were stained with the cell division tracking dye carboxyfluorescein diacetate succinimidyl ester (CFSE), stimulated with phytohemagglutinin (PHA), grown for 5-6 days, hybridized with a telomere sequence-specific peptide nucleic acid fluorescent probe (PNA-Cy5), counterstained with DAPI, and analyzed by flow cytometry. The cell cycle distribution and cell division generations were respectively identified by analysis of DAPI emission and deconvolution of CFSE emission, and Cy5 emission was used to determine telomere-specific fluorescence, an indicator of telomere length, in each cell. In stimulated PBMC, in each cell cycle phase, the telomere-specific fluorescence diminished with increasing cell generation. The rate of decline of the telomere-specific fluorescence per cell generation did not significantly differ between cell cycle phases. Application of flow-FISH-DDD to measure mean telomere length and the rate of telomere attrition in proliferating cells may find use in studies of ageing and disease, the effects of telomere-modifying agents, and variability between individuals.

Radiotherapeutic enhancement by razoxane

Razoxane blocks cell division in the G 2/M phase of the cell generation cycle and appears to normalize tumour neovasculature development. These were the principal reasons for the examination and probably for the demonstration of the radiosensitizing activity of Rz. Specially intriguing has been the finding that radiation of primary tumour implants in animals treated with Rz has a powerful potentiating effect on the antimetastatic activity of the combination. This concept has not yet received any clinical examination. Clinical trials with radiotherapy and Rz have demonstrated the clearest beneficial effects in terms of response rates and maintained local control in soft tissue sarcomas and possibly in recurrent rectal and in bladder carcinomas. Interesting heightened activity has also been found in hepatic metastases from gastrointestinal tumours. Carcinomas of the cervix, bronchus and head and neck, however, have not shown any benefit from the combination compared with radiotherapy alone.

The effect of microwave radiation on the cell genome

Cultured V79 Chinese hamster cells were exposed to continuous radiation, frequency 7.7 GHz, power density 30 mW/cm 2 for 15, 30, and 60 min. The parameters investigated were the incorporation of [ 3H]thymidine and the frequency of chromosome aberrations. Data obtained by 2 methods (the incorporation of [ 3H]thymidine into DNA and autoradiography) showed that the inhibition of [ 3H]thymidine incorporation took place by complete prevention of DNA from entering into the S phase. The normal rate of incorporation of [ 3H]thymidine was recovered within 1 generation cycle of V79 cells. Mutagenic tests performed concurrently showed that even DNA macromolecules were involved in the process. In comparison with the control samples there was a higher frequency of specific chromosome lesions in cells that had been irradiated. Results discussed in this study suggest that microwave radiation causes changes in the synthesis as well as in the structure of DNA molecules.

Cytofluorometric determination of protein‐bound thiols and DNA in cell nuclei

The aim of the present study was to establish a cytofluorometric method for the simultaneous determination of protein-bound sulfhydryl-groups (PSH) and DNA in isolated cell nuclei. DNA was stained with ethidiumbromide and PSH with N-iodoacetyl-N(5-sulfo-1-naphthyl) ethylendiamine (AEDANS). Disulfide groups of nuclear proteins were determined by the same method after reduction with sodium borohydride or thioglycollic acid. The method was established by using nuclei of human lymphocytes, which then served as a biological standard for further investigations of the nuclei of different mammalian cell types: nuclei from mouse liver cells and nuclei from the cells of two human melanoma cell lines. For non-proliferating lymphocytes distinct DNA- and PSH-values could be measured. The PSH-values detected in the nuclei of the other cell types were higher by comparison and varied within the cell cycle; i.e., PSH increased during the S-phase and was almost doubled during the cell generation cycle from G1- to G2-phase. Cell line and cell cycle-dependent variations of nuclear disulfides could also be detected. These results are discussed with respect to their radiobiological implications. In conclusion, thiol groups may represent one factor determining the radiosensitivity of cells, but they are not the only decisive one.

Autoradiographic analysis of effects of 5-bromodeoxyuridine on neurogenesis in the chick embryo spinal cord

Bromodeoxyuridine (BUdR) can reversibly inhibit the terminal differentiation of embryonic cell types when they are grown in culture. The goal of these experiments was to see if BUdR could interfere with the terminal differentiation of neurones in the intact chick embryo, a possibility disputed in different reports. Therefore, 0.02 mg BUdR plus 15 μCi[ 3H]BUdR was injected into the albumen of incubating eggs at stage 14–16 of development. Controls received an equimolar amount of [ 3H]thymidine ([ 3H]TdR). The doses and mode of administration are known to result in availability times for the nucleosides that are longer than one cell generation cycle and therefore similar to the pharmacokinetic conditions possible in vitro. The time of treatment is known to correspond to the period of most rapid neurone production in the chick spinal cord. By autoradiography of semithin sections the fates of the cells that had incorporated the nucleosides could be followed. BUdR was taken up by the S phase population of the spinal cord neuroepithelium (NE). In the first 10 h after treatment the BUdR treated NE behaved the same as the control. From then until 24 h after treatment, NE cells underwent necrosis as a result of BUdR and neurone production was almost completely suppressed. Between 24 and 48 h after treatment the BUdR-treated NE produced neurones at a faster rate than the TdR-treated controls. However, this effort at compensation was not entirely effective and by 6 days after treatment the BUdR-treated embryos had an absolute reduction in motor neurone number. Motor neurones with BUdR incorporated in their DNA that survived until after neurogenesis was completed were strikingly more lightly labelled than those in controls treated with [ 3H]TdR. This suggests that the survivors had incorporated less BUdR than those that had died. It was concluded that the neuronal deficit resulting from BUdR treatment was not the result of an inhibition of terminal differentiation, but rather of cytotoxicity.

Regulatory mechanisms affecting the blast stem cells of acute myeloblastic leukemia.

Recent studies have indicated the existence of a novel regulatory system governing cell growth and differentiation. The system is based on the cellular homologues of the transforming genes (oncogenes) of retroviruses. Cellular oncogene products include regulators of the cell generation cycle, cell-surface receptors, and growth factors. Preliminary evidence is available that this regulatory system is important in hemopoiesis. In this paper, the biology of the blast cells of acute myeloblastic leukemia is reviewed. Data is presented indicating that genetic control may be exercised in the nucleus to affect self-renewal, at the cell surface, to mediate cell-to-cell interactions and through the environment by the production of growth factors. These findings support the suggestion that the blast population is a suitable model for studying oncogene-based regulation. Blasts have the further advantage that laboratory observations made with their use can be correlated with the clinical course of the disease.

Testicular morphology and cell proliferation kinetics of immature germ cells and Sertoli cells in suckling undernourished rats.

Undernutrition during suckling was induced in newborn rats by increasing the litter size to sixteen pups to be fed by one mother. Animals reared in litters of eight served as controls. Undernourished animals showed retarded body and testicular growth during a suckling period of 22 days. Sequential morphogenesis of the testis was not altered up to 15 days of age. However, certain morphological alterations in Sertoli cells and Leydig cells were observed from 15 days onwards. Cell generation cycle of spermatogonial germ cells and supporting cells (future Sertoli cells) on day 9 showed marked prolongation of DNA synthetic phase (S), unaltered post-DNA synthetic phase (G2) and total cycle (Tc) and shortening of the pre-DNA synthetic phase (G1) indicating a depression in DNA synthesis in undernutrition.

A Model of the Cell Cycle and Cell Division Phasing in a Marine Diatom

A model of the cell generation cycle of Thalassiosira pseudonana Hasle and Heimdal (Clone 3H) has been produced in which the cell cycle is visualized as being composed of two successive timed periods. The first period is temperature compensated but inversely proportional in duration to the rate of supply of energy (light intensity) whilst the second, culminating in division, has a high Q 10 but proceeds independently of illumination. Numerical simulations based upon this model and incorporating a feature to encompass variability in individual cell generation times have successfully generated many of the population growth features exhibited by cultures of this species grown under a variety of experimental conditions.

Proliferation and migration of rat incisor mesenchymal cells

Sixty female Wistar rats were injected with tritiated thymidine and killed at intervals between 1 hr and 72 hr after injection. Autoradiographs of paraffin and Vestopal W embedded sagittal sections of the maxillary incisors were prepared. The distribution of labeled cells after 1 hr revealed the basal pulp cells and the preodontoblasts as proliferative cells. The growth rate of the incisor and the migration of the basal pulp cells were established from the position of labeled cells at 72 hr observation time. The number and localization of labeled and unlabeled mitoses were registered in order to determine the duration of the generation cycle of the proliferative cells. The identical cell generation time of preodontoblasts and basal pulp cells and the migration pattern of the latter indicate that the preodontoblasts are renewed by preodontoblast multiplication and not by migration of basal pulp cells.

DNA synthesis and cell generation cycle during determination and differentiation of the metanephric mesenchyme

Isolated metanephrogenic mesenchyme can be induced for epithelial differentiation and tubule formation by an embryonic spinal cord that is cultivated in a transfilter position to the target cells. Under such conditions, determination of the cells starts at 12 hr and is completed around 24 hr. To correlate this event to DNA synthesis, thymidine incorporation was followed in such cultures from 2 to 96 hr after setting up the transfilter explants. Controls were cultured under conditions which did not result in induction. Incorporation into both induced and noninduced mesenchymes dropped rapidly during the first 12 hr when the tissues were transferred to the in vitro conditions. During the subsequent critical 12- to 24-hr period, mesenchymes continuously exposed to an inductor showed a marked increase in their incorporation of thymidine. If induction was interrupted during the first 10 hr there was no stimulation of incorporation when measured at 24 hr. Similarly, isolated mesenchymes and those exposed to a tissue devoid of inducing capacity did not show stimulation, and their incorporation remained at a low level when measured at 24 hr. Parallel DNA measurements were made by flow cytometry of individual nuclei from mesenchymes exposed to the inductor from 0 to 46 hr. No major changes in the distribution of the various phases of the cell generation cycle were detected nor could any synchronization be shown. Hence the changes in the incorporation rate of thymidine seem to be due to variations in the total length of the cell cycle. We conclude that induction of differentiation of the metanephric mesenchyme is accompanied by a contact-mediated stimulation of DNA synthesis. The stimulation may represent a permissive effect on a predetermined cell population in the metanephrogenic mesenchyme.

Crypt cell renewal and chemical sympathectomy in the pre-closure ileum of the neonatal rat.

The present study was designed to analyze the effect of guanethidine-induced sympathectomy on ileal crypt cell proliferation before neonatal closure to macromolecular absorption (pre-closure ileum). The present experiments demonstrated an alteration of the crypt cell generation cycle (T&lt;sub&gt;C&lt;/sub&gt;) in the pre-closure ileum (15 days after birth) with guanethidine treatment. Percent labeled mitoses measurements for 15-day-old rats indicated a lengthening of T&lt;sub&gt;C&lt;/sub&gt; from 18.1 to 23.0 h with the elongation primarily due to alteration of T&lt;sub&gt;G1&lt;/sub&gt; (pre-DNA-synthetic gap period) and T&lt;sub&gt;S&lt;/sub&gt; (DNA-synthetic period). Mitotic and labeling indices and the amplitude of the circadian rhythm in mitotic activity were significantly depressed in guanethidine-treated rats.

The Action of Caffeine on X-Irradiated HeLa Cells. IV. Progression Delays and Enhanced Cell Killing at High Caffeine Concentrations

The response of x-irradiated and unirradiated HeLa S3 cells to treatment with caffeine at concentrations between 1 and 10 nM has been examined with respect to both delay in progression through the cell generation cycle and enhancement of the expression of potentially lethal x-ray damage. Progression is delayed in a concentration-dependent fashion: the generation time is doubled at about 4 mM. The duration of G/sub 1/ is lengthened, and the rate of DNA synthesis is reduced, although the kinetics are different in the two phases; the rate of DNA synthesis is usually unaffected at 1 or 2 mM, while there is no concentration threshold for the slowing of progression through G/sub 1/. Progression through G/sub 2/ appears to be unaffected by concentrations up to at least 10 mM. Killing of irradiated cells in G/sub 2/ is somewhat greater after treatment with the higher caffeine concentrations than reported previously for 1 mM. Moreover, an additional mode of killing is observed in irradiated G/sub 1/ cells which had been found previously to be only slightly affected by 1 mM caffeine; they suffer extensive killing at concentrations above 5 mM. The time-survival curves for irradiated, caffeine-treated G/sub 1/ and G/sub 2/ cells havemore » characteristically different shapes. The dose-survival curves for cells treated with the higher caffeine concentrations display steeper terminal slopes and narrower shoulders.« less

Kinetics of cell proliferation in the pre-implanted mouse embryo in vivo and in vitro.

The cell proliferation of pre-implanted mouse embryos was investigated after development in vivo and in vitro. The studies were started at the pronuclear stage, 2 h post conception (p.c.) and continued until the hatching of blastocysts, 120-144 h p.c. The number of cell nuclei, the DNA content of each nucleus, the mitotic index and the labelling index were determined. From these data it was possible to calculate the length of the cell generation cycle and its various phases. With the exception of the first cell cycle the S-phase was constant. The G1- as well as the G2-phase varied in length during the different cell cycles. From 31-72 h p.c. the increase in cell number was exponential. After cultivation in vitro this increase was smaller than in vivo. At later periods the proliferation rate decreased with proceeding development. In late blastocysts most of the cells were in the G1-phase. The development of the embryos was somewhat faster in vivo than in vitro. But in principle conditions were comparable.

ANALYSIS OF INTESTINAL CELL PROLIFERATION AFTER GUANETHIDINE‐INDUCED SYMPATHECTOMY

ABSTRACTRats were treated with guanethidine‐sulphate every 48 hr from birth until 15 days and then maintained until young adulthood. Sympathectomy was verified by dissection and light microscopic preparation of the superior cervical and coeliac ganglia which showed at least a 78% reduction in the number of perikarya. The effect of the chemical sympathectomy was a decrease in the amplitude of the circadian mitotic rhythm from 44·7 to 27·1%, 67·0 to 25·3% and 54·9 to 24·7%, in the duodenum, jejunum, and ileum, respectively. The shape of the mitotic index curve was altered and the mean mitotic index was significantly decreased (P &lt; 0·01) in all three segments of the small intestine. The mean mitotic index of control intestinal epithelium was 3·2 ± 0·1%, 3·6 ± 0·1% and 4·0 ± 0·1% in the duodenum, jejunum, and ileum, respectively, and 2·3 ± 0·1%, 2·4 ± 0·1%, and 2·5 ± 0·1% in guanethidine‐treated rats. Stathmokinetic estimates of cycle time were obtained by use of the metaphase arrest agent, colchicine. The longest cell generation cycle time (Tc) and lowest mitotic index occurred between 12.00 and 16.00 hours and the shortest Tc and highest mitotic index occurred between 00.00 and 04.00 hours, in all three segments of the small intestine. Guanethidine‐treatment lengthens Tc throughout the small intestinal epithelium and reduces the range of variation in Tc over a 24‐hr period. It is suggested that norepinephrine depletion induced by guanethidine may be the cause of the inhibition in circadian periodicity and that norepinephrine and the sympathetic nervous system may be essential for the maintenance of circadian rhythms in mitotic activity.

Alteration of neonatal rat parotid gland acinar cell proliferation by guandethidine-induced sympathectomy.

Newborn rats were injected with guanethidine-sulfate (20 micrograms/g body weight) every 48 hr from 12 hr after birth until day 14 (eight injections per animal). The guanethidine treatment resulted in an 86% absolute reduction in cell number in the superior cervical ganglia of 15 day old rats. The cells which remained after guanethidine treatment showed destruction of mitochondria and an extensive decrease in endoplasmic reticulum. Chemical sympathectomy with guanethidine induced a 3.1 hr lengthening of the acinar cell generation cycle time (17.4 hr to 20.5 hr), resulting from a longer G1 period (6.9 hr in the control group as compared to 10.5 hr in the guanethidine-treated group), as well as a cecrease in the mean percentage of [3H]thymidine-labeled acinar cells (22.3 +/- 0.5% to 19.3 +/- 0.5%) and mean acinar cell mitotic index (2.6 +/- 0.2% to 2.1 +/- 0.1%). A circadian rhythm was found to exist in parotid gland acinar cell mitotic activity of 15 day old rats and the amplitude of the rhythm was reduced from 26.5% to 14.9% in guanethidine-treated rats. This study indicates that the diminution of sympathetic influence on the developing parotid gland results in a slight, but significant alteration in acnar cell proliferation.

Effects of malnutrition on cell genesis and migration in developing brain in rats

Rats were fed a diet containing either 5% (LP) or 25% (HP) casein throughout gestation. The animals, delivered by a cesarean section on the 21st day of gestation, were given a pulse of [ 3H]thymidine and killed 2 h later. No differences were observed in the mitotic index, but the labeling index of the ventricular zone cells of the lateral ventricle was higher in the case of litters of the LP dams. This we atribute to a disproportionate increase of the S phase in relation to the cell cycle in malnutrition. To study the effects of malnutrition on the programming of cell genesis, the dams were given [ 3H]thymidine on the 20th day of gestation, and the litters were killed on the 21st postnatal day. The labeled neurons reached the second layer of the cerebral cortex in both groups, indicating that the programming was not affected by gestational malnutrition. Postnatal undernutrition was induced by doubling the litter size. The cell generation cycle was prolonged in the undernourished animals. Not all phases, however, were evenly affected: S was prolonged, G 2 was not affected, but G 1 was shortened. The external granular layer maintained its proliferative activity in the undernourished animals beyond the stage it had ceased in the controls. The migration of the cerebellar granule neurons was slow. It is proposed that tardiness in the migration of the neurons may interfere with synaptogenesis.

Generation cycle of mesenchymal cells of palatal shelves of rat foetuses

The generation cycle of the mesenchymal cells of the palatal shelves of rat foetuses was determined using tritiated thymidine during the 24-h prior to their fusion. The S-phase was 4 to 5 h and the total generation cycle approximately 18 h. The G 1 was determined as 11 h.