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Human Flight to Mars: Challenges for Integrative Human Physiology. R. Gerzer, M. Heer, K. Ivanova. DLR Institute of Aerospace Medicine, Cologne, Germany

   The effects of microgravity and of radiation in space on the human body are still incompletely understood. Being exposed to these conditions and being isolated during flights to Mars for over a year makes it necessary to understand these influences and to prepare countermeasures. A holistic approach including molecular analyses and systems interplay is mandatory.

   Results from the recent years, e.g., suggest that sodium homeostasis is altered in microgravity. Sodium exchange with hydrogen on glycosaminoglycans appears to be important and may also have important roles in physiology and pathophysiology on earth. This newly discovered mechanism not only influences our understanding on fluid and electrolyte balance in space, but also on acid balance and bone and muscle turnover and on immune function, to name just a few of the systems involved. This indicates that countermeasure development is a multidisciplinary task that has to involve knowledge on the interplay and relative importances of a multitude of body systems.

   Since gravity affects all cells, some general mechanisms of cell functions appear also altered in microgravity. Thus, in melanocytes hypergravity alters the expression of MRP4 and 5 (“drug resistance proteins”), enzymes involved in the functions of malignant tumors. If also microgravity alters the expression profiles of these enzymes, then it can be expected that astronauts may have altered sensitivity to carcinogenic effects, e.g., to space radiation.

   A concerted “digital human” approach in which the interplay of body systems is studied based on molecular analyses may be more important for the future of (space) physiology and for countermeasure development than the reductionistic approach of only studying isolated molecular or functional systems.