Activation of the Complement System and Changes in the Content of Modified Lipoproteins in Antiorthostatic Hypokinesia in Humans and Mice.

The correlation between the total activity of the complement system (TACS) and the content of modified LDL (mLDL) in blood serum when modeling microgravity in Earth conditions was evaluated. Healthy volunteers were placed in a state of antiorthostatic hypokinesia for 21 days. Microgravity in ICR mice was modeled by tail suspension for 14 days. TACS, activity of the alternative pathway (in humans), and the content of mLDL in serum from volunteers and mice were measured by turbidimetry. On day 7 of antiorthostatic hypokinesia, volunteers had a significant increase in TACS, which persisted until day 21. The content of mLDL in blood serum increased significantly on day 7. In experiments with mice, TACS increased significantly on day 14, and mLDL content decreased significantly. The limitation of mobility, which is an integral part of microgravity modeling, causes an increase in the overall hemolytic activity of the complement system in both humans and laboratory animals, indicating a response to significant physiological stress.