Longitudinal Blood Epigenetic Aging, DNA Methylation-Predicted Protein, and Estimated Leukocyte Proportion Trends in Two Astronauts from the Axiom Space Mission 1: An Exploratory Analysis.

<b>Background/Objectives:</b> Spaceflight presents a combination of physical and psychosocial stressors that may impact biological aging and health. Understanding how spaceflight influences molecular aging processes is essential as commercial and professional space travel continue to expand. <b>Methods:</b> We analyzed publicly available DNA methylation data to evaluate longitudinal changes in 10 epigenetic aging biomarkers, 6 leukocyte proportion estimates, and 109 DNA methylation-derived protein scores in two astronauts participating in Axiom Space's AX1 17-day low Earth orbit mission. We calculated mean values for all biomarkers across three timepoints: two weeks before spaceflight (T0), 24 h after spaceflight (T1), and three months after spaceflight (T2). Using the mean values, we next calculated the fold change from baseline for all biomarkers. Because the sample size precluded statistical testing, we identified the top 5% of absolute fold changes to highlight the largest shifts across candidate biomarkers. <b>Results:</b> Across epigenetic clocks, MiAge showed the greatest T0-T1 decrease (-4.26-fold), and DNAmFitAge showed the greatest T0-T2 increase (2.47-fold). NK cells exhibited the largest T0-T1 change, decreasing by 49% (-0.49-fold). B cells exhibited the largest T0-T2 change, decreasing by 11% (-0.11-fold). Proteins meeting a predefined top 5% fold change from baseline criterion at both T1 and T2, included BMP1, CLEC11A, CXCL11, FAP, and LTF. Enrichment analysis indicated involvement of serine-type endopeptidase activity, molecular function activator activity, and cell aggregation pathways. <b>Conclusions:</b> These findings suggest that spaceflight influences methylation-derived biomarkers of aging and immunity even in short-duration missions. These results, though exploratory, contribute to emerging efforts to characterize molecular resilience and vulnerability in human spaceflight.