A Simulated Microgravity Environment Causes a Sustained Defect in Epithelial Barrier Function

Potential Biomarkers of Resilience to Microgravity Hazards in Astronauts

Space exploration exposes astronauts to the unique environment of microgravity, which poses significant health challenges. Identifying biomarkers that can predict an individual's resilience to the stressors of microgravity holds great promise for optimizing astronaut selection and developing personalized countermeasures. This narrative review examines the principal health risks associated with microgravity and explores potential biomarkers indicative of resilience. The biomarkers being evaluated represent a broad spectrum of physiological domains, including musculoskeletal, neurological, immunological, gastrointestinal, cardiovascular, and cutaneous systems. Earth-based microgravity analogs, such as dry immersion and head-down tilt bed rest, may provide valuable platforms to validate candidate biomarkers. However, biomarker sensitivity and specificity must be further evaluated to ensure efficacy and reliability. Establishing a panel of biomarkers predictive of resilience to microgravity-induced health risks would significantly enhance astronaut health and mission success, especially for long-duration exploration missions. Insights gained may also translate to health conditions on Earth characterized by reduced physical activity and mechanical loading.

Simulated Microgravity Alters P-Glycoprotein Efflux Function and Expression via the Wnt/β-Catenin Signaling Pathway in Rat Intestine and Brain

The drug efflux transporter permeability glycoprotein (P-gp) plays an important role in oral drug absorption and distribution. Under microgravity (MG), the changes in P-gp efflux function may alter the efficacy of oral drugs or lead to unexpected effects. Oral drugs are currently used to protect and treat multisystem physiological damage caused by MG; whether P-gp efflux function changes under MG remains unclear. This study aimed to investigate the alteration of P-gp efflux function, expression, and potential signaling pathway in rats and cells under different simulated MG (SMG) duration. The altered P-gp efflux function was verified by the in vivo intestinal perfusion and the brain distribution of P-gp substrate drugs. Results showed that the efflux function of P-gp was inhibited in the 7 and 21 day SMG-treated rat intestine and brain and 72 h SMG-treated human colon adenocarcinoma cells and human cerebral microvascular endothelial cells. P-gp protein and gene expression levels were continually down-regulated in rat intestine and up-regulated in rat brain by SMG. P-gp expression was regulated by the Wnt/β-catenin signaling pathway under SMG, verified by a pathway-specific agonist and inhibitor. The elevated intestinal absorption and brain distribution of acetaminophen levels also confirmed the inhibited P-gp efflux function in rat intestine and brain under SMG. This study revealed that SMG alters the efflux function of P-gp and regulates the Wnt/β-catenin signaling pathway in the intestine and the brain. These findings may be helpful in guiding the use of P-gp substrate drugs during spaceflight.

Prospective Use of Probiotics to Maintain Astronaut Health during Spaceflight

Maintaining an astronaut's health during space travel is crucial. Multiple studies have observed various changes in the gut microbiome and physiological health. Astronauts on board the International Space Station (ISS) had changes in the microbial communities in their gut, nose, and skin. Additionally, immune system cell alterations have been observed in astronauts with changes in neutrophils, monocytes, and T-cells. Probiotics help tackle these health issues caused during spaceflight by inhibiting pathogen adherence, enhancing epithelial barrier function by reducing permeability, and producing an anti-inflammatory effect. When exposed to microgravity, probiotics demonstrated a shorter lag phase, faster growth, improved acid tolerance, and bile resistance. A freeze-dried Lactobacillus casei strain Shirota capsule was tested for its stability on ISS for a month and has been shown to enhance innate immunity and balance intestinal microbiota. The usage of freeze-dried spores of B. subtilis proves to be advantageous to long-term spaceflight because it qualifies for all the aspects tested for commercial probiotics under simulated conditions. These results demonstrate a need to further study the effect of probiotics in simulated microgravity and spaceflight conditions and to apply them to overcome the effects caused by gut microbiome dysbiosis and issues that might occur during spaceflight.

Gravity and the Gut: A Hypothesis of Irritable Bowel Syndrome

The pathogenesis of irritable bowel syndrome (IBS)-a disorder of gut-brain interaction that affects up to 10% of the world's population-remains uncertain. It is puzzling that a disorder so prevalent and archetypal among humans can be explained by disparate theories, respond to treatments with vastly different mechanisms of action, and present with a dazzling array of comorbidities. It is reasonable to question whether there is a unifying factor that binds these divergent theories and observations, and if so, what that factor might be. This article offers a testable hypothesis that seeks to accommodate the manifold theories, clinical symptoms, somatic comorbidities, neuropsychological features, and treatment outcomes of IBS by describing the syndrome in relation to a principal force of human evolution: gravity. In short, the hypothesis proposed here is that IBS may result from ineffective anatomical, physiological, and neuropsychological gravity management systems designed to optimize gastrointestinal form and function, protect somatic and visceral integrity, and maximize survival in a gravity-bound world. To explain this unconventional hypothesis of IBS pathogenesis, referred to herein as the gravity hypothesis, this article reviews the influence of gravity on human evolution; discusses how Homo sapiens imperfectly evolved to manage this universal force of attraction; and explores the mechanical, microbial, and neuropsychological consequences of gravity intolerance with a focus on explaining IBS. This article concludes by considering the diagnostic and therapeutic implications of this new hypothesis and proposes experiments to support or reject this line of inquiry. It is hoped that the ideas in this thought experiment may also help encourage new or different ways of thinking about this common disorder.

Periodontal connection with intestinal inflammation: Microbiological and immunological mechanisms

Humans have coevolved with the trillions of resident microbes that populate every nook and cranny of the body. At each site, the resident microbiota creates a unique ecosystem specialized to its environment, benefiting the development and maintenance of human physiology through harmonious symbiotic relationships with the host. However, when the resident microbiota is perturbed, significant complications may arise with disastrous consequences that affect the local and distant ecosystems. In this context, periodontal disease results in inflammation beyond the oral cavity, such as in the gastrointestinal tract. Accumulating evidence indicates that potentially harmful oral resident bacteria (referred to as pathobionts) and pathogenic immune cells in the oral mucosa can migrate to the lower gastrointestinal tract and contribute to intestinal inflammation. We will review the most recent advances concerning the periodontal connection with intestinal inflammation from microbiological and immunological perspectives. Potential therapeutic approaches that target the connection between the mouth and the gut to treat gastrointestinal diseases, such as inflammatory bowel disease, will be examined. Deciphering the complex interplay between microbes and immunity along the mouth-gut axis will provide a better understanding of the pathogenesis of both oral and gut pathologies and present therapeutic opportunities.

Spaceflight Virology: What Do We Know about Viral Threats in the Spaceflight Environment?

Viruses constitute a significant part of the human microbiome, so wherever humans go, viruses are brought with them, even on space missions. In this mini review, we focus on the International Space Station (ISS) as the only current human habitat in space that has a diverse range of viral genera that infect microorganisms from bacteria to eukaryotes. Thus, we have reviewed the literature on the physical conditions of space habitats that have an impact on both virus transmissibility and interaction with their host, which include UV radiation, ionizing radiation, humidity, and microgravity. Also, we briefly comment on the practices used on space missions that reduce virus spread, that is, use of antimicrobial surfaces, spacecraft sterilization practices, and air filtration. Finally, we turn our attention to the health threats that viruses pose to space travel. Overall, even though efforts are taken to ensure safe conditions during human space travel, for example, preflight quarantines of astronauts, we reflect on the potential risks humans might be exposed to and how those risks might be aggravated in extraterrestrial habitats.

What can biofabrication do for space and what can space do for biofabrication?

Biofabrication in space is one of the novel promising and prospective research directions in the rapidly emerging field of space STEM. There are several advantages of biofabrication in space. Under microgravity, it is possible to engineer constructs using more fluidic channels and thus more biocompatible bioinks. Microgravity enables biofabrication of tissue and organ constructs of more complex geometries, thus facilitating novel scaffold-, label-, and nozzle-free technologies based on multi-levitation principles. However, when exposed to microgravity and cosmic radiation, biofabricated tissues could be used to study pathophysiological phenomena that will be useful on Earth and for deep space manned missions. Here, we provide leading concepts about the potential mutual benefits of the application of biofabrication technologies in space.

Artificial tissue creation under microgravity conditions: Considerations and future applications

Traditional tissue engineering methods often fail to promote robust cell growth and differentiation, limiting the development of functioning tissues. However, the microgravity conditions created by rotating wall vessel bioreactors minimize shear stress and unload the gravitational force usually placed on cells. In a microgravity environment, cell proliferation, cell differentiation, and the 3D organization of cells are altered, potentially encouraging the formation of more biosimilar artificial tissues for certain cell types. Additionally, cells in these engineered tissues display lowered immunogenicity, pointing to the transplantation potential of tissues engineered in microgravity conditions. However, these benefits are not consistent across all cell types, and the long-term impact of microgravity on tissue development and stability remains an unanswered question. Even so, there is potential that with further research, microgravity tissue engineering will have productive clinical applications for medical and pharmaceutical purposes.

The effects of combined environmental factors on the intestinal flora of mice based on ground simulation experiments

The composition and function of intestinal microbial communities are important for human health. However, these intestinal floras are sensitive to changes in the environment. Adverse changes to intestinal flora can affect the health of astronauts, resulting in difficulties in implementing space missions. We randomly divided mice into three groups and placed each group in either a normal environment, simulated microgravity environment or a combined effects environment, which included simulated microgravity, low pressure and noise. Fecal samples of the mice were collected for follow-up analysis based on metagenomics technology. With the influence of different space environmental factors, the species composition at the phylum and genus levels were significantly affected by the combined effects environment, especially the abundance of the Firmicutes and Bacteroidetes. Furthermore, screening was conducted to identify biomarkers that could be regarded as environmental markers. And there have also been some noticeable changes in the function of intestinal floras. Moreover, the abundance of antibiotic resistance genes (ARGs) was also found to be changed under different environmental conditions, such as bacitracin and vancomycin. The combined effects environment could significantly affect the species composition, function, and the expression of ARGs of intestinal flora of mice which may provide a theoretical basis for space medical supervision and healthcare.

The effect of hypergravity in intestinal permeability of nanoformulations and molecules

The oral administration of drugs remains a challenge due to rapid enzymatic degradation and minimal absorption in the gastrointestinal tract. Mechanical forces, namely hypergravity, can interfere with cellular integrity and drug absorption, and there is no study describing its influence in the intestinal permeability. In this work, it was studied the effect of hypergravity on intestinal Caco-2 cells and its influence in the intestinal permeability of different nanoformulations and molecules. It was shown that the cellular metabolic activity and integrity were maintained after exposure to different gravity-levels (g-levels). Expression of important drug transporters and tight junctions' proteins was evaluated and, most proteins demonstrated a switch of behavior in their expression. Furthermore, paracellular transport of FITC-Dextran showed to significantly increase with hypergravity, which agrees with the decrease of transepithelial electrical resistance and the increase of claudin-2 at higher g-levels. The diffusion of camptothecin released from polymeric micelles revealed a significant decrease, which agrees with the increased expression of the P-gp observed with the increase in g-levels, responsible for pumping this drug out. The neonatal Fc receptor-mediated transport of albumin-functionalized nanoparticles loaded with insulin showed no significant changes when increasing the g-levels. Thus, this study supports the effect of hypergravity on intestinal permeability is dependent on the molecule studied and the mechanism by which it is absorbed in the intestine.

Dragon's Blood Regulates Rac1-WAVE2-Arp2/3 Signaling Pathway to Protect Rat Intestinal Epithelial Barrier Dysfunction Induced by Simulated Microgravity

Dragon’s Blood is a red resin from Dracaena cochinchinensis (Lour.) S.C. Chen (Yunnan, China). As a traditional Chinese medicinal herb, it has shown protective effects on intestinal disorders. Microgravity could alter intestinal homeostasis. However, the potential herbal drugs for preventing intestine epithelial barrier (IEB) dysfunction under microgravity are not available. This study aimed to investigate the effects of Dragon’s Blood (DB) on microgravity-induced IEB injury and explore its underlying mechanism. A rat tail-suspension model was used to simulate microgravity (SMG). Histomorphology, ultrastructure, permeability, and expression of junction proteins in jejunum, ileum, and colon of SMG rats were determined. Proteomic analysis was used to identify differentially expressed proteins (DEPs) in rat ileum mucosa altered by DB. The potential mechanism of DB to protect IEB dysfunction was validated by western blotting. The effects of several components in DB were evaluated in SMG-treated Caco-2 cells. DB protected against IEB disruption by repairing microvilli and crypts, inhibiting inflammatory factors, lowering the permeability and upregulating the expression of tight and adherens junction proteins in the ileum of SMG rats. Proteomic analysis showed that DB regulated 1080 DEPs in rat ileum mucosa. DEPs were significantly annotated in cell–cell adhesion, focal adhesion, and cytoskeleton regulation. DB increased the expression of Rac1-WAVE2-Arp2/3 pathway proteins and F-actin to G-actin ratio, which promoted the formation of focal adhesions. Loureirin C in DB showed a protective effect on epithelial barrier injury in SMG-treated Caco-2 cells. DB could protect against IEB dysfunction induced by SMG, and its mechanism is associated with the formation of focal adhesions mediated by the Rac1-WAVE2-Arp2/3 pathway, which benefits intestinal epithelial cell migration and barrier repair.

Nutritional Orthopedics and Space Nutrition as Two Sides of the Same Coin: A Scoping Review

Since the Moon landing, nutritional research has been charged with the task of guaranteeing human health in space. In addition, nutrition applied to Orthopedics has developed in recent years, driven by the need to improve the efficiency of the treatment path by enhancing the recovery after surgery. As a result, nutritional sciences have specialized into two distinct fields of research: Nutritional Orthopedics and Space Nutrition. The former primarily deals with the nutritional requirements of old patients in hospitals, whereas the latter focuses on the varied food challenges of space travelers heading to deep space. Although they may seem disconnected, they both investigate similar nutritional issues. This scoping review shows what these two disciplines have in common, highlighting the mutual features between (1) pre-operative vs. pre-launch nutritional programs, (2) hospital-based vs. space station nutritional issues, and (3) post-discharge vs. deep space nutritional resilience. PubMed and Google Scholar were used to collect documents published from 1950 to 2020, from which 44 references were selected on Nutritional Orthopedics and 44 on Space Nutrition. Both the orthopedic patient and the astronaut were found to suffer from food insecurity, malnutrition, musculoskeletal involution, flavor/pleasure issues, fluid shifts, metabolic stresses, and isolation/confinement. Both fields of research aid the planning of demand-driven food systems and advanced nutritional approaches, like tailored diets with nutrients of interest (e.g., vitamin D and calcium). The nutritional features of orthopedic patients on Earth and of astronauts in space are undeniably related. Consequently, it is important to initiate close collaborations between orthopedic nutritionists and space experts, with the musculoskeletal-related dedications playing as common fuel.

Cell-free DNA (cfDNA) and Exosome Profiling from a Year-Long Human Spaceflight Reveals Circulating Biomarkers

Liquid biopsies based on cell-free DNA (cfDNA) or exosomes provide a noninvasive approach to monitor human health and disease but have not been utilized for astronauts. Here, we profile cfDNA characteristics, including fragment size, cellular deconvolution, and nucleosome positioning, in an astronaut during a year-long mission on the International Space Station, compared to his identical twin on Earth and healthy donors. We observed a significant increase in the proportion of cell-free mitochondrial DNA (cf-mtDNA) inflight, and analysis of post-flight exosomes in plasma revealed a 30-fold increase in circulating exosomes and patient-specific protein cargo (including brain-derived peptides) after the year-long mission. This longitudinal analysis of astronaut cfDNA during spaceflight and the exosome profiles highlights their utility for astronaut health monitoring, as well as cf-mtDNA levels as a potential biomarker for physiological stress or immune system responses related to microgravity, radiation exposure, and the other unique environmental conditions of spaceflight.