The interphase death of dividing cells. The relation of interphase death to cell energy requirements

In experiments with irradiated cells of Chinese hamster and Ehrlich ascites tumor a study was made of the influence of energy provision on their interphase death rate. The presence of the uncoupler of respiration and oxidative phosphorylation--carbonyl cyanide-3-chlorophenylhydrazone--in a medium without glucose was shown to drastically increase the interphase death rate of cells of both types, whereas this effect was not observed in a medium with glucose.     

The mechanism of radiation-induced interphase death of lymphoid cells: a new hypothesis

The interphase death of irradiated rat thymocytes depends on their concentration during postirradiation incubation. The kinetics of pycnosis and cell death determined with the trypan blue exclusion test in the samples with the highest cell concentration (1-2 x 10(7) cells/ml) is consistent with the data available in the literature, whereas the samples with the lowest concentration (2 x 10(5) cells/ml) undergo almost no pycnosis and death after irradiation with doses up to 50 Gy. On the basis of these results, we suggest a new mechanism of interphase death involving an interaction between irradiated thymocytes and the fraction of thymus cells possessing cytocidal activity. The observed correlation between the cytocidal activity and interphase death of thymocytes from animals of different ages favors our mechanism. It was found that the inhibitors which prevent the conjugation of killer cells and their targets do not influence interphase death, while the substances which block the secretion of cytotoxic factors or their action on the target membrane do protect from interphase death. Thus we suggest that the irradiation activates the killer cells to secrete some cytotoxic factors which induce pycnosis and interphase death of thymocytes.     

The interphase death of dividing cells. The kinetics of the death of cultured Chinese hamster fibroblasts after irradiation at various doses

In studying the kinetics of interphase death (ID) of cultured Chinese hamster cells after irradiation with doses of 100 to 800 Gy the authors showed an increase in the ID rate with increasing radiation dose; the presence of serum in the medium both during and after irradiation prevents the cell death.     

The role of glutathione in the interphase death of dividing cells

A study was made of a change in the content of reduced glutathione (GSH) in Ehrlich ascites tumor (EAT) cells after irradiation with doses evoking their interphase death (ID). GSH content was determined in a suspension of EAT cells fixed by hot ethanol. The postirradiation decrease in the GSH content of the suspension was due to its oxidation by hydrogen peroxide resulting from radiochemical reactions after releasing thereof from cells upon fixation. In the absence of an irradiated medium no changes occurred in the GSH content of EAT cells. It is concluded that ID of EAT cells is not associated with the radiation-induced decrease in the content of GSH, an endogenous antioxidant.     

Prostaglandins and interphase death of irradiated cells

The contribution of the post-irradiation changes in prostaglandin transformation to the biochemical mechanism of interphase death of irradiated cells is estimated. It is supposed that prostaglandins are secondary trigger-effectors which initiate the development of primary biochemical reactions giving rise to radiation sickness. It is suggested that the biochemical mechanism of interphase death is complex and involves several concurrent trigger mechanisms including prostaglandin regulation system.     

The role of adenine nucleotide catabolism in the interphase death of thymocytes, caused by papaverine and dipyridamole

Papaverine and dipyridamole induce the interphase death of thymocytes rapidly growing four hours later and reaching its maximum by the seventh-eighth hour of the cell incubation. To induce death of thymocytes no constant presence of these preparations in the incubation medium is needed, a definite (for each of preparations) time of the contact with cells being enough. The interphase death of thymocytes induced by papaverine and dipyridamole is preceded by acceleration of the release of adenine nucleotide catabolism products from cells mainly as hypoxanthine and inosine, respectively. These both processes are induced by papaverine for a shorter period of its incubation with cells than by dipyridamole and the joined use of these substances intensifies the above processes. The analysis of the data obtained indicates that thymocytes under the effect of papaverine die rather from the exhaustion of the adenine nucleotide pool, than from a decrease in the adenylate charge of cells. Exogenous adenosine essentially removes the toxic effect of papaverine but not of dipyridamole. Addition of adenine and inosine to thymocytes does not affect their survival rate in the presence of the preparations under study.     

Radiation disturbance of RNA metabolism during interphase death of lymphoid cells

The data are reviewed concerning the radiation--induced disturbances of RNA metabolism in lymphoid cells. The role of the observed disorders in activation and realization of the interphase cell death program is discussed.     

Thymocyte membrane changes and modifications of interphase death

A reduction in the rate of interphase death of X-irradiated thymocytes is observed when they are previously treated with triton X-100 or trypsin at low concentrations. The data obtained demonstrate the importance of the structural integrity of the cell surface in the initiation of processes leading to interphase death of lymphoid cells.     

Modification of the interphase death of thymocytes by using colcemid

The pretreatment of thymocytes by colcemid (0.02 to 0.5 mu g/ml) induces a change in the plasma membrane state, registered by a pyrene fluorescent probe, and a decrease in the interphase cell death after 4 Gy X-irradiation. The authors discuss the role of the cell surface as a trigger initiating death program in irradiated lymphoid cells.     

Lipid metabolism in rat tissues after irradiation at doses causing interphase cell death

Irradiation of animals with doses eliciting interphase death of 50-80% of cells activates lipogenesis and decreases the cholesterol content of cells. Cholesterol synthesis is activated after irradiation with doses causing death of 50% of cells: a further increase in radiation dose decreases the cholesterol synthesis. It is assumed that as membranes are destructed by radiation the adaptive lipogenesis activated to restore them.     

Protein degradation during the interphase death of thymocytes induced by radiation and dexamethasone

A study was made of protein degradation in rat thymocytes after exposure to ionizing radiation and dexamethasone. The pattern of degradation of 35S-methionine labelled proteins in gamma-irradiated cells and in those incubated in the presence of dexamethasone did not vary from that in control cells. No essential increase was noted in the intracellular protein degradation during interphase death of thymocytes.     

Interphase death of dividing cells. Relation of the death of cultured Chinese hamster fibroblasts to the inter- and extracellular pH

In studying interphase death (ID) of dividing cells from Chinese hamster fibroblast culture a differently directed relationship between ID rate and pH has been shown: the ID rate increases with pH increasing from 6.6 to 8.1 and decreases with pH from 5.0 to 6.6. The dependence is the same as that observed with lymphoid cells. With radiation doses increasing from 100 to 600 Gy and pH defined, the ID rate increases.     

Radiation-induced interphase death of rat thymocytes is internally programmed (apoptosis)

Thymocytes are highly radiosensitive and show 'interphase death' within a few hours after low doses of irradiation. However, the mechanisms responsible for this type of death remain ill-defined. Separation of the dead thymocyte fraction from irradiated thymocyte suspensions by centrifugation on Percoll gradients provided homogeneous populations of dead cells suitable for detailed study. Using this method, radiation-induced interphase death of thymocytes was found to involve a sharp but transient increase in buoyant density, concomitant with the appearance of distinctive morphologic changes which included disappearance of microvilli and blistering of the cell surface. The chromatin in the dead cells had a molecular weight sufficiently low to resist sedimentation, and consisted of short oligonucleosome chains. We were unable to detect populations of cells intermediate between the dead and normal in the above characteristics. Interphase death thus involves a discrete, abrupt transition from the normal state and is not merely the consequence of progressive and degenerative changes. Furthermore, immediate cessation of development of interphase death by cycloheximide suggested a possible involvement of protein synthesis on this transition step.     

Mathematical model of interphase cell death. Biophysical justification and generalization

The authors propose a biophysical justification of a radiation-induced injury and interphase death of cells. The injury to certain units of the microtrabecular network and cytoskeleton is considered to be a primary biological effect of radiation on cells. The role of these structural changes in the development of the specific radiation response is discussed. It is found possible to describe formally, by the defined parameters of the proposed model, the survival curves for not only interphase but also reproductive cell death.     

Prevention of interphase death in rat thymocytes by bisulfite

The effect of sodium bisulfite, a specific inhibitor of chromatin proteolysis, on radiation damage in rat thymocytes in vitro was examined. Rat thymocytes irradiated with 1 kR X rays in vitro were incubated at 37 degrees C with 10 mM glucose for 4 to 6 hr. During that time development of interphase death as judged by erythrosin B uptake, release of low molecular weight DNA (free DNA), and reduction in cell size was measured. Sodium bisulfite added to the cells at the beginning of incubation exerted a marked preventive effect on radiation damage. The effect was enhanced with increasing concentration of bisulfite from 0.25 to 2 mM. The effect of bisulfite was reversible; i.e., removal of bisulfite from the cells resulted in the reappearance of the radiation damage.     

Modification of the interphase death of thymocytes: the effect of agents inhibiting the killing process

The influence of different killing inhibiting agents on the interphase death of irradiated rat thymocytes has been investigated. The results confirm the previously proposed hypothesis of the interphase death mechanism involving activation of killing potency in the irradiated population of thymus cells.     

Cell-cycle dependence of heat-induced interphase death in mouse L5178Y cells.

Cell lysis and eosin staining were observed in L5178Y cells within the first 3 h of post-hyperthermia incubation at 37 degrees C, after which both leveled to a plateau. Lysis and eosin staining were proportional to the severity of heat in asynchronous cells, whereas it was maximum in the most heat-sensitive M phase, intermediate in S, and least in heat-resistant G1 for the same heat treatment. Further, leakage of labeled [3H]thymidine and a decrease in radioactivity retained within heated cells coincided with an increase in eosin staining, indicating that the dye uptake was due to membrane damage. It was presumed that the eosin-stained fraction represented dead cells. The percentage eosin-stained cells reached a plateau, and this level was used to determine survival; when the results were compared with those obtained by the colony formation method, they were identical. By comparing the two survival assay methods we concluded that cell death after hyperthermia in L5178Y cells is mainly by interphase death in all phases of the cell cycle. The reasons for this conclusion are that a reduction in survival could be detected within one generation of L5178Y cells by the eosin staining method, and the survival values obtained by this method were identical to those obtained by the colony formation method.     

A model of the stochastic dynamics of interphase lymphocyte death

Dynamics of interphase peripheral blood lymphocyte death is studied in terms of a general model based on a random damage distribution among cells and stochastic time of their death. Some particular cases of this model are analysed. Possible causes of shaping "biphase" dose-dependence curves for lymphoid cell survival after irradiation are discussed.     

Abscopal action of gamma radiation in the death of lymphoid cells

In the in vitro experiments with lymphoid cells Raji and X63-Ag8.653 gamma-irradiated in a synthetic medium, it was shown that a cessation of division (reproductive death) and lysis (interphase death) of cells were evoked by the abscopal effect of long-lived quinoid radiotoxins enhancing the direct effect of radiation to make it not additive but synergistic: a synergism coefficient was 1.3.     

Accounting for recovery processes in the description of interphase cell death

A phenomenological scheme is proposed to describe dose- and time-dependences of the interphase cell death in terms of a continual model of radiation injury. Different regularities of the postirradiation recovery of cells are discussed. The results obtained are in agreement with the experimental data.