Long-distance trail running induces inflammation-associated protein, lipid, and purine oxidation in red blood cells

• In vivo RBC damage resulting from ultra-running mirrors molecular damage accrued by RBC during ex vivo storage under blood bank conditions • Ultra-running accelerates RBC aging via inflammation, IL-6, kynurenine, oxidation, copper Ultra-endurance running imposes extreme demands on oxygen transport, yet how red blood cells (RBCs) respond at the molecular level remains poorly defined. We integrated plasma and RBC multi-omics with hematology and hemorheology in athletes sampled before and after two trail races of distinct duration: a 40-km marathon (MCC) and a 171-km ultramarathon (UTMB). Both races elicited systemic inflammation, but UTMB was distinguished by marked IL-6 and kynurenine increases, acute-phase protein induction, and profound lipid remodeling. In RBCs, acylcarnitine accumulation, pantothenate depletion, and oxidized lipid species indicated Lands cycle activation, while purine salvage and carboxylate metabolism reflected redox-sensitive rerouting of energy pathways. Proteomics revealed non-random oxidation, particularly methionine oxidation of antioxidant enzymes, metabolic proteins, and proteasome components, correlating with impaired deformability as gleaned by testing of rheological properties. Elevated copper provided an additional correlate of reduced RBC mechanics. Despite minimal signatures of intravascular hemolysis, plasma bilirubin and hypoxanthine rose, consistent with extravascular clearance of damaged RBCs. Collectively, these results demonstrate that ultra-running accelerates RBC aging through inflammatory and oxidative pathways beyond mechanical trauma, linking systemic cytokine responses to molecular lesions, biomechanical dysfunction, and splenic sequestration. These findings not only identify actionable biomarkers of exercise-induced hemolysis but also provide translational insight into oxidative lesions that similarly limit RBC survival in transfusion and inflammatory disease settings.