The brain-eye-liver axis during spaceflight: implications of hepatic dysfunction in spaceflight associated neuro-ocular syndrome

Spaceflight presents unique physiological challenges, with prolonged exposure to microgravity, cosmic radiation, and psychological stress impacting astronaut health. Hepatic dysfunction may contribute to the pathogenesis of astronaut diseases, including spaceflight-associated neuro-ocular syndrome (SANS), one of the largest physiologic barriers to future spaceflight. This paper explores the interconnected effects of spaceflight on the liver, particularly focusing on alterations in carbohydrate and lipid metabolism, liver injury, inflammation, and compromised biotransformation processes. The liver responds to the extreme conditions of spaceflight, including microgravity and chronic ionizing radiation. These responses include specific changes in gene expression and cytochrome activity, suggesting a complex interplay between the liver, brain, and eyes. This brain-eye-liver axis may be a crucial study area in understanding and mitigating SANS, for long-duration spaceflight (LDSF) missions, emphasizing the need for further research to unravel these complex interdisciplinary connections in the context of LDSF missions.