Cells can be irradiated under conditions that approximate those in living tissues.
The cell radiation experiment system (CRES) is a perfused-cell culture apparatus, within which cells from humans or other animals can (1) be maintained in homeostasis while (2) being exposed to ionizing radiation during controlled intervals and (3) being monitored to determine the effects of radiation and the repair of radiation damage. The CRES can be used, for example, to determine effects of drug, radiation, and combined drug and radiation treatments on both normal and tumor cells. The CRES can also be used to analyze the effects of radiosensitive or radioprotectant drugs on cells subjected to radiation. The knowledge gained by use of the CRES is expected to contribute to the development of better cancer treatments and of better protection for astronauts, medical-equipment operators, and nuclear-power-plant workers, and others exposed frequently to ionizing radiation.
Traditionally, experiments to determine the effects of ionizing radiation on cells involved (1) culturing the cells in test tubes, Petri dishes, or culture flasks; (2) removing the cells from the cultures and exposing them to radiation; and (3) reculturing the cells to enable the cells to attempt to repair the radiation damage and continue to grow. The great disadvantage of the traditional approach is that cells are subjected to a succession of environments that differ radically from the precisely controlled natural environment in a human or other animal body; the effects of the succession of nonlifelike environments can alter the subtle effects of radiation damage mechanisms and intracellular repair processes, thereby introducing uncertainty into interpretation of experimental observations. By maintaining more nearly lifelike conditions, the CRES can increase the accuracy of, and confidence in, experimental observations.
The CRES (see figure) includes one or more cell-culture chambers equipped with a very thin, impermeable Mylar (or equivalent polyethylene terephthalate) membrane at one end, described in more detail below. At the opposite end of each culture chamber there is a perfusion chamber separated from a culture chamber by a permeable membrane. Through this membrane, waste and nutrients are exchanged between the culture and perfusion chambers. A circulation subsystem that includes fluid reservoirs, conduits, valves, pumps, and automated process controls provides for the slow perfusion of the nutrient medium used to culture the cells.
The system includes a source of ionizing radiation in a shielded enclosure with motor-driven shutters that are used to effect timed, selective irradiation of the cell-culture chamber(s). A process-control module exerts overall control over the circulation subsystem and other subsystems to regulate such parameters as the temperature, the rate of circulation of fresh nutrient medium, the pH of the medium, and radiation doses via the shutters. Another subsystem monitors the metabolic rates of cells by measuring ultraviolet fluorescence from the cells, the pH of the medium, and/or the concentrations of O2 and CO2. Still another subsystem under control by the process-control module can be made to introduce a fixative substance to preserve the cell cultures for subsequent analysis. The impermeable front membrane is thin enough to allow the ionizing radiation to pass through. Before installation, the inner face of this membrane is subjected to a special oxygen etch to enable epithelial or other anchor-dependent cells to attach themselves. As a result, a monolayer of cells grows on this membrane and, by virtue of the precision with which their location is thus known, radiation dosimetry can be quite accurate.
This work was done by Dennis R. Morrison of Johnson Space Center. For more information, download the Technical Support Package (free white paper) at www.medicaldesignbriefs.com. MSC-23060-1