Preliminary Biological Examination for the Space Experiment „Cellular Responses to Radiation in Space“

The German experiment “Cellular Responses to Radiation in Space (CERASP)”, to be performed on the International Space Station (ISS) will supply basic information on the cellular response to radiation applied in microgravity. The biological endpoints under investigation will be gene activation, apoptosis and DNA damage induction by space flight conditions in mammalian cells. Gene expression and cytotoxic effects will be monitored using a promoter reporter system with Enhanced Green Fluorescent Protein (EGFP). In the current thesis preliminary experiments were performed, including a biocompatibility test of the experimental hardware components, first radiation biological experiments with the radiation source developed for space experiments, measurement of the fluorescence yield and biological half life time of different EGFP variants in stably transfected HEK/293 clones and determination of the growth parameters of HEK cell clones. Untransfected and stably transfected HEK cells had a doubling time between 20.2 and 25.4 h. The half-life of EGFP was 95.5 hours in HEK cells, and the half-lives of d2EGFP ranged between 21.9 and 4.7 h in three clones, suggesting the use of EGFP for cytoxicity monitoring and of d2EGFP for monitoring of gene expression. The biocompatibility tests revealed very slight reductions in viability for some tube materials and superglue, which can be replaced by other materials included in the batch of test materials. The comparison of several cytotoxicity tests revealed a high performance for the EGFP expression test and a good performance for the determination of DNA content, the MTT test and the CellTiterBlue™ Assay, while protein content and neutral red uptake had the lowest performance. The survival curve clearly shows that the radiation source is well suited to deliver a sufficiently high dose during a short time