Effect of Molecular Size on the Systemic and Microcirculatory Response to Polymerized Based Hemoglobin-Based Oxygen Carriers

Hemoglobin-based oxygen carriers (HBOCs) provide a promising alternative to traditional resuscitative solutions for hemorrhagic shock, especially in scenarios where blood is unavailable. The key advantages of HBOCs include reduced storage requirements, no need for blood type matching, and no risk of disease transmission. However, many HBOC formulations have encountered limitations due to adverse effects associated with the molecular size of the hemoglobin solution. Smaller hemoglobin molecules in the solution may contribute to systemic toxicities, which necessitate improvements in the formulation of these carriers. This study investigates the effects of polymerization and filtration in modifying the size distribution of hemoglobin molecules, thereby improving the systemic and microcirculatory performance of polymerized human hemoglobin (PolyHb) solutions compared to unmodified human hemoglobin (hHb). The unmodified hemoglobin solution had an average molecular weight of 64 kDa and an average molecular diameter of 6 nm. The first polymerized hemoglobin solution had an average molecular weight of 1,078 kDa, an average molecular diameter of 28 nm, and a polydispersity index (PDI) of 0.412. Furthermore, this solution contained 13% of hemoglobin molecules with a molecular weight <500 kDa. The final polymerized solution had an average molecular weight of 1,200 kDa, an average molecular diameter of 33 nm, a PDI of 0.384, and only 3% of hemoglobin molecules <500 kDa. The experiments were conducted in fully conscious Golden Syrian hamsters, each implanted with a catheter in the carotid artery for controlled infusion. The animals were infused with the three hemoglobin solutions at a volume equivalent to 10% of the animal's blood volume (top load). Baseline measurements of mean arterial pressure (MAP), heart rate (HR), and microhemodynamics were recorded before infusion, with follow-up measurements taken at 30 minutes post-infusion. Results revealed that the unmodified hHb solution resulted in the greatest deviations from baseline MAP and HR. In contrast, the polymerized and filtered PolyHb solutions displayed significantly reduced deviations from baseline values. Microhemodynamic analyses showed that the polymerized and highly filtered PolyHb solutions better preserved baseline function in both arterioles and venules compared to hHb. These findings highlight the importance of increasing the average molecular size via polymerization and reducing the fraction of smaller hemoglobin molecules via filtration, leading to enhanced safety and efficacy of HBOC solutions in vivo. This study was supported by National Institutes of Health grants R01HL162120, R01HL159862 and the Department of Defense under grants HT9425-24-1-0238. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.