Spermine: A Hemoglobin Modifier That Reduces Autoxidation and Regulates Oxygen Delivery

One of the major factors currently hindering the development of hemoglobin-based oxygen carriers (HBOCs) is the autoxidation of hemoglobin to inactive methemoglobin (MetHb). The effects of spermine on the stability, aggregation, structure, and function of adult hemoglobin (HbA) were studied. The interaction of spermine with HbA was elucidated by dynamic light scattering, colloid osmotic pressure measurements, thermal denaturation analysis, static light scattering, and oxygen dissociation assay. The antioxidant capacity of spermine was confirmed through UV-vis spectroscopic recordings, calculations of MetHb formation, and hydroxyl radical scavenging. The P50 value was determined by the oxygen dissociation curve to investigate the roles of spermine in increasing HbA's oxygen affinity. The pH-dependent affinity between spermine and HbA was validated through surface plasmon resonance experiments. The transformation of HbA's partial α-helix to a β-sheet structure induced by spermine was clarified using a microfluidic modulation spectrometer. The binding of spermine to βASP99, βGLU101, αTHR38, and αASN97 on HbA and the conformational shift in HbA towards the 'R' state were investigated via molecular docking and molecular dynamics simulations. In a word, spermine can enhance the oxygen affinity of HbA, effectively reduce autoxidation, and hold promise for applications in the research of HBOCs or hemoglobin modification.