Life sciences: radiobiological advanced biostack experiment.

The radiobiological properties of the heavy ions of cosmic radiation were investigated on Spacelab 1 by use of biostacks, monolayers of biological test organisms sandwiched between thin foils of different types of nuclear track detectors. Biostacks were exposed to cosmic radiation at several locations with different shielding environments in the module and on the pallet. Evaluations of the physical and biological components of the experiment to date indicate that in general they survived the spaceflight in good condition. Dosimetric data are presented for the different shielding environments.

[Study of the intra- and extracellular electrolyte content in Paramecia cultures carried out during a space flight (author's transl)]. / Etude de la teneur intra et extracellulaire des electrolytes dans les cultures de Paramecies réalisées pendant un vol spatial.

In the results of previous investigations we have already reported that cultures of Paramecium tetraurelia submitted to a space flight present a stimulation of their proliferative ability, an increase in cell volume and a decrease in dry weight and in total protein content. These results suggest changes of cell metabolism induced by the space environment. In order to confirm this hypothesis we have studied the concentration of extracellular electrolytes in the control and the in-flight culture media with respect to the intracellular content of the same electrolytes. These measures concern Na, Cl, K, P, Mg, Ca. In this paper we report the results of these analyses and note that if no differences are noted for Na and Cl between control and in-flight cultures, modifications in P, K, Ca and Mg levels are observed. Generally there is a higher concentration of these elements in the in-flight medium but, in contrast, a lower intracellular content is noted for in-flight Paramecia. We have established a double comparison: on the one hand between control and in-flight media and between control and in flight cells, on the other hand between media and cells. All these data suggest possible changes in the membrane permeability, or of the binding proteins in Paramecia cultivated in hypogravity.

Radiation-induced changes in late effects and in developmental capacities of exposed artemia cysts.

Artemia dry cysts from a Californian bisexual strain used in several space experiments were irradiated with 60Co gamma rays. The three cyst populations experimented could be differentiated according to their development and survival rates. The variations observed for both of these criteria were related to the age of the cysts and the selection technique. The study of radiosensitivity based on LD50 value showed that the highest radiosensitivity differences were related to the cyst selection technique and not to the age. Furthermore, the three cyst populations showed that radio-induced lethal effects were enhanced, or appeared with time, namely following the delay between irradiation and the cyst development study. The observation of late effects after irradiations or after space flights show the difficulties encountered in assessing radiative risks during long duration space flights.

Effects of a very low dose rate of chronic ionizing radiation on the division potential of human embryonic lung fibroblasts in vitro.

Among the various parameters that are supposed to play a role in aging at the cellular level, the "free radical theory" involves biochemical modifications that can be induced by radiation. Human embryonic lung fibroblasts were serially subcultivated at low density under chronic low dose rate irradiation (40 mrad/day) and in a normal environment. Irradiation increases cell attachment and the population doubling/day throughout their entire in vitro lifespan. Consequently, the doubling potential reached by irradiated cells was higher than that of control cultures. Finally, the total number of cells produced under chronic irradiation was 8-14 times higher than in a normal environment. These results are discussed with respect to the increased enzymatic activities (superoxidismutase, catalase, glutathion-reductase, G6PD) found in some irradiated organisms.

Effects of gravity and cosmic rays on cell proliferation kinetics in Paramecium tetraurelia.

Space flights resulted in a stimulating effect on kinetics of proliferation in Paramecium tetraurelia. Additional experiments were performed in order to determine the origin of this phenomena. Paramecia were cultivated in balloon flights or in a slow clinostat, or were exposed to different levels of hypergravity. The results suggest that changes in cell proliferation rate are related to cosmic rays and to a direct effect of microgravity.

Space environmental factors affecting responses to radiation at the cellular level.

Previous space experiments suggest a high value for the RBE of cosmic radiation. A possible explanation could be a change in cell radiosensitivity due to a combined effect of radiation and other factors related to the space environment and to the space flight. Results of the EXOBLOC II experiment support this assumption. On earth, vibrations or accelerations applied before or after irradiation can change the responses to radiation. Microgravity could be the main factor affecting the radiosensitivity and DNA repair but this hypothesis must be confirmed by additional experiments.

Results on Artemia cysts, lettuce and tobacco seeds in the Biobloc 4 experiment flown aboard the Soviet Biosatellite Cosmos 1129.

Artemia cysts, lettuce and tobacco seeds were flown aboard the Cosmos 1129 for 19 days. A correlative method was used in order to determine the passage of cosmic heavy ions (HZE particles) through the biological test objects. This space flight resulted in a decrease on hatchability, nucleic acid and protein synthesis in hydrated Artemia cysts. HZE particle effects on plant cellular chromosomes are confirmed. In tobacco seeds, a stimulating effect on germination rate and a higher frequency of abnormalities were observed. Dormant biological objects are a very suitable material to study cosmic ray effects: these objects can be arranged in monolayers and sandwiched between visual track detectors in order to determine the passage of the cosmic heavy ions (HZE particles). On the other hand this method allows us to study effects of microgravity and those of the protonic component of cosmic rays in the objects not hit by the HZE articles.

Changes in developmental capacity of artemia cyst and chromosomal aberrations in lettuce seeds flown aboard Salyut-7 (Biobloc III experiment).

This paper gives the results of investigations performed on the first container (A) of the Biobloc III experiment, flown aboard the orbital station Salyut 7 for 40 days. The space flight resulted in a decreased developmental capacity of Arterlia cysts, hit or not hit by the HZE particles. No effect was observed in cysts in bulk. A synergetic effect of microgravity and gamma pre irradiation is described. The germination of in-flight lettuce seeds was decreased. The space flight resulted also in a higher percentage of cells with chromosomal aberrations. Relations between biological response, TEL and location of HZE particles are discussed.

Influence of a long duration exposure, 69 months, to the space flight factors in Artemia cysts, tobacco and rice seeds.

Three french laboratories have participated in the Free Flyer Biostack experiment. Artemia cysts, tobacco seeds and rice caryopsis and embryos were used. Biological objects in monolayers were dead. In opposite, a large fraction of samples used in bulk survived. A stimulatory effect occurred in the first steps of development in Artemia cysts. In fact, the larval survival was unchanged or slightly reduced. In tobacco a drastic decrease in germination and survival rate was observed. Space flight did not induce genetic changes. In rice, results depend on the variety which was investigated; the growth rate stimulation in flight samples is discussed with respect to controls.

Radiation stimulation during the early stationary growth phase in Synechococcus lividus and its correlation with photooxidative stress occurring before the stationary phase.

The effects of chronic gamma radiation at dose rates ranging from 0.058 mGy d-1 on growth rate calculated during the early stationary phase were studied. A stimulatory effect occurred for all doses and for all phases of the cells selected for use in the inoculation of the medium. During the same period, the rate of nucleic acid synthesis was increased in irradiated cultures compared to control cultures. The stimulating effect always occurred in cultures irradiated from the inoculation to the eighteenth day only. This result led us to conclude that the stimulation mechanism depended upon the events occurring at the end of the exponential phase in the deceleration period. Studies on cell metabolism showed that cells presented features of photooxidative stress in this period. Increases in superoxide dismutase, glutathione reductase and glucose-6-phosphate dehydrogenase were observed in irradiated cultures. It was assumed that irradiation at very low doses could help cells to better defend against photooxidative stress by increasing oxidants that activate the glucose metabolism and C5-sugars production and nucleic acid synthesis.

Influence on cell proliferation of background radiation or exposure to very low, chronic gamma radiation.

Investigations carried out on the protozoan Paramecium tetraurelia and the cyanobacteria Synechococcus lividus, which were shielded against background radiation or exposed to very low doses of gamma radiation, demonstrated that radiation can stimulate the proliferation of these two single-cell organisms. Radiation hormesis depends on internal factors (age of starting cells) and external factors (lighting conditions). The stimulatory effect occurred only in a limited range of doses and disappeared for dose rates higher than 50 mGy/y.

Effects of space flight factors at the cellular level: results of the Cytos experiment.

Paramecium tetraurelia was cultivated aboard the Soviet orbital station Salyut 6. Each culture included one cell, bacterized culture medium, and two small glass tubes filled with a fixative. Cultures were kept at a low temperature before Soyouz-Salyut docking. Cultures were maintained at 25 degrees +/- 0.1 degree C in orbit and were fixed every 12 h. The space flight resulted in an increase in cell growth rate and in cell volume. Measurements of cell dry weight and total protein content favour a higher cell water content. Respective roles of cosmic rays and microgravity are discussed. Cytos results are compared to those of previous space experiments.

Proliferation kinetics of paramecium tetraurelia in balloon-borne experiments.

Experiments were carried out to demonstrate the effect of cosmic radiation, at a balloon-flight ceiling of about 36,500 m (120,000 ft) on single-cell organism proliferation. Paramecium tetraurelia were placed in air-tight containers and maintained at 25 degrees +/- 0.1 degrees C. Cellular growth was determined by cell count, either after recovery or during the flight, by means of an automatic fixation device. Dosimetry was performed by a tissue equivalent proportional counter and was of about 0.5 mrad/h. Flight ceiling duration ranged from 48 min - 22 h. A secondary stimulating effect of growth rate, preceded by a temporary decrease, was observed after recovery. Because of the high bacterial concentration in the trans-Mediterranean flight culture medium, the temporary drop of the growth rate, due to the radiolysis products, disappears. We consider that the stimulating effect can be the result of enzymatic intracellular scavenging of radiolysis products generated in the cell.

Development capacity of artemia cysts and lettuce seeds flown in Cosmos 936 and directly exposed to cosmic rays.

Developmental capacity of Artemia cysts and chromosomal aberration frequency in lettuce seeds, flown aboard Cosmos 936 have been investigated. Biological objects were located inside or outside the spacecraft. Lettuce seeds were stuck on plastic plates and sandwiched in cellulose sheets in order to discriminate the objects hit by the cosmic heavy ions from the ones not hit. The absorbed dose inside the spacecraft was about 650 mrad. Biological objects were located at different levels in the "outside" container; absorbed doses were 1.5 rad for lettuce seeds and 30 rad for Artemia cysts. There was no change in hatch-ability of Artemia cysts located inside or outside the spacecraft when eggs were tested 2-4 months after recovery, but a marked decrease was observed in eggs 9 months after the space flight. Survival of larvae and adults was normal in "inside" eggs, but decreased in "outside" eggs. Space flight also resulted in a higher frequency of single chromosomal aberrations in cells developed from "inside and outside", hit and non-hit seeds. This highest percentage of multiple chromosomal aberrations occurred in seeds hit by the heavy ions.

Respective role of microgravity and cosmic rays on Paramecium tetraurelia cultured aboard Salyut 6.

Paramecium tetraurelia cultured aboard Salyut 6 have shown in increase in cell growth rate, cell volume, water content and changes in electrolyte content. Additional experiments, carried out in balloon flight and on earth, showed that the stimulating effect observed on cell proliferation is related to exposure to cosmic rays. Other changes seem to be due to a direct effect of microgravity on cell. Mechanism of gravity action on cell is discussed.

Effects of microgravity and hypergravity on the cell: investigations on Paramecium tetraurelia.

Previous space CYTOS experiments have shown that space flights resulted in an increase in growth of Paramecia cultures. Microgravity is the major factor responsible of this response: indeed the stimulatory effect disappeared in inflight cultures placed on a 1 g centrifuge aboard the Spacelab. On the other hand, exposure to different levels of hypergravity on Earth resulted in an opposite response, i.e. to a reduced cell growth rate. A possible mechanism of microgravity on paramecia is discussed.

Preliminary results of Cytos 2 experiment.

Cytos 2 experiment, carried out during the French-Soviet manned flight (July 1982), has studied the antibiotics sensitivity of bacteria cultivated in vitro during the orbital flight. The results show an increase of the antibiotics resistance and a larger thickness of the cellular envelope for the inflight cells. The increase of antibiotics resistance can be related to a stimulating effect of space on the cell growth rate or to changes of the cellular envelope structure.

Theoretical and experimental investigations on the fast rotating clinostat.

We have investigated both theoretically and experimentally the validity of the fast rotating clinostat to simulate microgravity for a free swimming single-cell organism such as the paramecium. Computer simulations show that cells on suspension move as cells cultivated in space. However, rotated paramecia are still affected by gravity, as shown by the variations in the rate of paramecium rotation on their axis. Using a fast clinostat, which allows to investigate simultaneously twenty cultures, we have observed a stimulating effect on cell growth rate similar to that previously reported in space. All these results point towards the fact that the fast clinostat can reproduce some of the effects of microgravity on paramecia.

Effects of angular speed in responses of Paramecium tetraurelia to hypergravity.

The paper shows the results of investigations carried out in a single cell organism. Paramecium tetraurelia exposed to different gravitational levels. Hypergravity resulted in a decrease in cell growth rate. The responses depend on g level and angular speed of the centrifuge; furthermore they depend also on small short fluctuations in g levels, delta g, due to the swimming of the cells inside the culture tubes. Delta g depends on angular speed and size of the holding device. The inhibitory effect of hypergravity, for the same angular speed, increases with respect of the diameter of the culture tubes.