ESA VIVALDI Dry Immersion Microgravity Simulations Induce Increases in Immune Biomarkers Associated With Physical and Psychological Stress, and Sex-Specific Factors

Abstract

With future manned space projects involving missions of unprecedented duration, multisystem deconditioning induced by spaceflight could seriously affect the well-being and health of astronauts. Safe and easily determined in-flight biomarkers are therefore needed to monitor health status. In this study, we simulated space deconditioning with a 5-day dry immersion (DI) of 18 healthy women and 19 healthy men and evaluated the effects of this protocol on three biomarkers: the neutrophil-to-lymphocyte ratio (NLR), the granulocyte-to-lymphocyte ratio (GLR) and the platelet-to-lymphocyte ratio (PLR). Increases in all three ratios were observed in both men and women, as also observed at the end of a space mission or after exposure to simulated microgravity. These increases were associated with physical and psychological stress in both sexes. Furthermore, our work suggested a positive link between NLR increase and cardiovascular system alteration in women, whereas in men, there would be a positive relationship between NLR, GLR, PLR, and inflammation. Thus, in addition to physical and psychological stress, sex-specific factors could contribute to increases in NLR, GLR, and PLR ratios during DI. As for the increase in PLR, it did not predict the development of long-lasting immune diseases during DI, in contrast to 2 months of head-down tilt bed rest (HDBR), another spaceflight analog. These data show that the NLR, GLR, and PLR ratios are promising biomarkers that deserve further study to determine the relationships between their increase and microgravity-induced deconditioning. These dry immersion investigations are registered at clinicaltrials.gov as NCT05043974 for women and NCT05493176 for men.

Keywords: astronaut health; biomarker; deep‐space missions; ground‐based model; monitoring; peripheral blood cells; physical stress; vascular system.

FIGURE 1

Evolution of the NLR (A), GLR (B) and PLR (C) ratios before, during and after five days of dry immersion in women (n = 18) and men (n = 19). The data are shown as mean ± SEM. Statistically significant differences were revealed via repeated‐measures one‐way ANOVA or linear mixed effects model analysis when some data were missing, both of which were followed by a Tukey post hoc test. *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001. BDC, baseline data collection (pink); DI, dry immersion (blue); R, recovery (green).

FIGURE 2

Evolution of neutrophil (A), granulocyte (B), lymphocyte (C) and platelet (D) counts before, during and after five days of dry immersion in women (n = 18) and men (n = 19). The data are shown as mean ± SEM. Statistically significant differences were revealed via repeated‐measures one‐way ANOVA or linear mixed effects model analysis when some data were missing, both of which were followed by a Tukey's post hoc test. *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001. BDC, baseline data collection (pink); DI, dry immersion (blue); R, recovery (green).

FIGURE 3

Evolution of the night sleep quality score (A), back pain mean score (B), general discomfort mean score (C) and GHQ‐28 score (D), used to estimate psychological state, in women (n = 18) and men (n = 19) exposed to 5 days of dry immersion. The morning and evening back pain and discomfort scores were averaged to obtain a daily score. The data are shown as mean ± SEM. Statistically significant differences were revealed via repeated‐measures one‐way ANOVA or linear mixed effects model analysis when some data were missing, followed by a Tukey or Boneferroni post hoc test. *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001. BDC, baseline data collection (pink); DI, dry immersion (blue); R, recovery (green).

FIGURE 4

Evolution of VEGF (A), VEGFR‐1 (B), E‐selectin (C), AIP (D), UFC (E) and hsCRP (F) in women (n = 18) and men (n = 19) exposed to five days of dry immersion. Note that we could not quantify VEGF, VEGFR‐1, E‐selectin, AIP and hsCRP at BDC‐4, DI1 and R+1, and UFC at BDC‐4. The data are shown as mean ± SEM. Statistically significant differences were revealed via repeated‐measures one‐way ANOVA or linear mixed effects model analysis when some data were missing, both of which were followed by a Tukey's post hoc test. *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001. BDC, baseline data collection (pink); DI, dry immersion (blue); R, recovery (green).