Microgravity effects on frozen human sperm samples

Abstract

Purpose: Microgravity has severe effects on cellular and molecular structures as well as on metabolic interactions. The aim of this study is to investigate the effects of microgravity (μg) exposure on human frozen sperm samples.

Methods: Sibling samples from 15 normozoospermic healthy donors were frozen using glycerol as cryoprotectant and analyzed under microgravity and ground conditions. Microgravity was obtained by parabolic flights using a CAP10B plane. The plane executed 20 parabolic maneuvers with a mean of 8.5 s of microgravity for each parabola.

Results: Frozen sperm samples preserved in cryostraws and stored in a secure and specific nitrogen vapor cryoshipper do not suffer significant alterations after μg exposure. Comparing the study group (μg) and the control group (1 g), similar results were obtained in the main parameters studied: sperm motility (M/ml) 13.72 ± 12.57 vs 13.03 ± 12.13 (- 0.69 95% CI [- 2.9; 1.52]), progressive a + b sperm motility (%) 21.83 ± 11.69 vs 22.54 ± 12.83 (0.03 95% CI [- 0.08; 0.15]), sperm vitality (%) 46.42 ± 10.81 vs 44.62 ± 9.34 (- 0.04 95% CI [- 0.13; 0.05]), morphologically normal spermatozoa (%) 7.03 ± 2.61 vs 8.09 ± 3.61 (0.12 95% CI [0.01; 0.24]), DNA sperm fragmentation by SCD (%) 13.33 ± 5.12 vs 13.88 ± 6.14 (0.03 95% CI [- 0.09; 0.16]), and apoptotic spermatozoa by MACS (%) 15.47 ± 15.04 vs 23.80 ± 23.63 (- 0.20 95% CI [- 0.66; 1.05]).

Conclusion: The lack of differences obtained between frozen samples exposed to μg and those maintained in ground conditions provides the possibility of considering the safe transport of human male gametes to space. Nevertheless, further research is needed to validate the results and to consider the possibility of creating a human sperm bank outside the Earth.

Trial registration number: ClinicalTrials.gov: NCT03760783.

Keywords: Apoptosis; DNA fragmentation; Microgravity; Motility; Sperm; Vitality.