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Spaceflight presents a unique environment that can significantly impact liver function, potentially leading to liver injury, metabolic dysfunction, and an increased risk of liver-related diseases like NAFLD .
Research also suggests that microgravity can impact liver regeneration and potentially affect how the liver processes medications
Space medicine is fundamental to the human exploration of space. It supports survival, function and performance in this challenging and potentially lethal environment. It is international, intercultural and interdisciplinary, operating at the boundaries of exploration, science, technology and medicine.This website introduces the field of space medicine and describes the different types of spaceflight, environmental challenges, associated medical and physiological effects, and operational medical considerations. It will describe the varied roles of the space medicine doctor, including the conduct of surgery and anaesthesia, and concludes with a vision of the future for space medicine.
Space medicine doctors have a responsibility to space workers and spaceflight participants. These flight surgeons are key in developing mitigation strategies to ensure the safety, health and performance of space travellers in what is an extreme and hazardous environment. This includes all phases from selection, training and spaceflight itself to post-flight rehabilitation and long-term health.
Space medicine is a key component of the spacecraft design process that extends throughout the entirety of the spacecraft’s functional life. Proper consideration of space medicine is integral to the success of an exploration-class mission because space medicine has the potential to largely reduces the risk of death or debilitation from an otherwise preventable onboard medical event. Proper consideration of space medicine requirements for spaceflight will also benefit medical research because it will provide an opportunity for more data to be recorded, which will allow subsequent missions to better implement countermeasures in light of the research gained.
1.Liver Injury and Inflammation:
Microgravity exposure can induce liver injury and inflammation, potentially linked to apoptosis (programmed cell death) and oxidative stress.
Studies have shown increased levels of inflammatory markers and signs of liver damage in animals after spaceflight.
2. Metabolic Dysregulation:
Carbohydrate Metabolism:
Spaceflight can lead to changes in carbohydrate metabolism, potentially contributing to a "diabetogenic phenotype" (an increased risk of diabetes).
Lipid Metabolism:
Alterations in lipid metabolism can result in the deposition of lipids in the liver, which may contribute to non-alcoholic fatty liver disease (NAFLD)-like conditions.
Xenobiotic Biotransformation:
The liver's ability to process drugs and other foreign substances can be compromised during spaceflight.
3. Oxidative Stress:
Spaceflight can downregulate antioxidant defense systems in the liver, leading to oxidative stress.
This oxidative stress can contribute to liver damage and inflammation.
4. Transcriptional Changes:
Spaceflight induces broad alterations in the liver's transcriptome (the set of all RNA transcripts), affecting genes involved in metabolism, cellular processes, and oxidative stress.
Some genes related to autophagy, a cellular process that removes damaged components, are also altered.
5. Liver Tissue Changes:
Studies have shown that spaceflight can affect the index of reflectivity (IR) of the liver, suggesting changes in tissue properties or structure.
These changes may be related to alterations in liver position or tissue compression due to pressure changes in the body during spaceflight.
6. Potential for NAFLD:
The observed changes in lipid metabolism, retinol loss, and activation of PPAR pathways suggest a potential for the development of NAFLD with longer spaceflights.
< liver organoid developed-in-tissue-orbital-bioreactor (ISS National Lab)
< liver organoid developed-in-tissue-orbital-bioreactor (ISS National Lab)
Research also suggests that microgravity can impact liver regeneration and potentially affect how the liver processes medications.
Liver tissue changes during and post 6-month spaceflight as measured by ultrasound radio frequency signal processing.
Analysis of ultrasound radio frequency (RF) signals allows for the determination of the index of reflectivity (IR), which is a new measure that is dependent on tissue properties. Previous work has shown differences in the IR of the carotid artery wall with long-duration spaceflight; therefore, it was hypothesized that liver tissue would also show differences in this measure with spaceflight.
Previous studies have shown a connection between insulin resistance and liver steatosis (Genazzani et al., 2024; Anousin et al., 2024). Elevation of an insulin resistance index has also been found after 6 months of spaceflight (Hughson et al., 2016). This suggests that liver structure may also be altered with long-duration spaceflight on the International Space Station (ISS).
Measurement of the index of reflectivity (IR), determined from analysis of the ultrasound radio frequency (RF) signal, has shown changes in the carotid artery wall with long-duration spaceflight (Arbeille et al., 2021). As this new ultrasound measurement was able to detect changes in tissue properties of the arterial wall, it is possible that similar measures of liver tissue will also identify changes in liver tissue properties with long-duration spaceflight on the ISS. Therefore, the objective of the present research was to determine whether the IR, determined by ultrasound RF signal processing, was altered for liver tissue during long-duration spaceflight and postflight recovery.
The RF signal is the native ultrasound signal that is processed by the ultrasound system manufacturer’s software (i.e., filtered, smoothed, and amplified) to construct B-mode (black and white) ultrasound images. During operation, ultrasound probes emit hundreds of ultrasound beams in the plane below the probe head. As the beams reflect off successive interfaces along linear paths, changes in the reflected waves are captured by the probe as the radio frequency signal (RF).
Changes in liver position or morphology may also contribute to the altered liver IR with spaceflight. Microgravity may result in changes in liver position, or liver tissue may be compressed with increased thoracic or abdominal pressure with spaceflight. However, the hypothesis of possible liver compression by surrounding organs or in relation to fluid shifts does not look likely as there was no difference in the density of the hepatic vein (subjectively evaluated) between pre and inflight ultrasound images. Increased portal vein size with spaceflight does indicate fluid retention and blood pooling at the level of the liver, but it is unknown if this has a compression effect on liver tissue.
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