A Prebiotic Diet Increases Cardiovascular Adaptability Under Hypergravity-Induced Stress

Abstract

Life in space presents significant challenges to mammalian physiology and the longer one is in space, the greater the impact. Three major stressors are present in space: 1) changes in gravitational environment, 2) psychological/physiological stress, and 3) constant low dose radiation. It is critical, therefore, to discover interventions that promote stress resilience. Dietary prebiotics selectively increase the relative abundances of probiotic bacterial species in the gut. We have previously reported that a diet enriched in galactooligosaccharide (GOS) and polydextrose (PDX) compared to control diet robustly elevates parabacteroides distasonis, clostridium leptum, and reduces the negative impact of acute and chronic stress. Interoceptors (e.g., baroreceptors) sense gravity-induced changes in blood pressure and cardiac function/structure. There is evidence that hypergravity disrupts autonomic and cardiovascular homeostasis and function. Cardiovascular homeostasis depends on a sympathetic and parasympathetic balance reflected in heart rate variability (HRV), a measure of cardiovascular stress. The following study was designed to test the hypothesis that GOS+PDX reduces the cardiovascular impacts of living in an altered gravitational environment. Adult female mice were housed in 1G or 3G and were fed GOS+PDX or a matched control diet for 4 weeks on the NASA Ames 1.22-meter radius centrifuge. We recorded electrocardiograms (ECG) in animals from all four groups immediately before, halfway through, and immediately after centrifugation. We analyzed HRV data using a Python-based Jupyter notebook and R. R was used to perform a 1F-LD-1F ANOVA with pair-wise comparisons to quantify changes in HRV longitudinally. Classic time domain based HRV metrics, standard deviation of the successive differences between adjacent R-R intervals and standard deviation of NN intervals, showed little change over time. Instead, frequency domain measures showed results were housing in 3G compared to 1G reliably changed Shannon entropy, Sample entropy, and low to high frequency ratio at each time-point. The changes across time reflected adaptation to hypergravity and a consequent reduction in HRV. Poincare plot analysis and low to high frequency ratio metrics showed divergent compensatory reactions between diets at 3G. Overall, 3G impacted HRV less in mice that were fed the prebiotic diet compared to the control diet. Further longitudinal studies with greater temporal resolution are needed to assess changes in HRV caused by gravitational changes. However, our data suggests the prebiotic diet significantly reduces 3G activation of sympathetic drive and increases parasympathetic drive, potentially reducing cardiovascular stress in animals exposed to high gravity. NASA grant 80NSSC19K1038 funded this project. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.