(368br) Polymerized Human Hemoglobin-Based Oxygen Carrier Preserves Lung Allograft Function during Normothermic Ex Vivo Lung Perfusion (Meet the Industry)

There is a significant disparity between the number of patients on the organ transplant list and available organs due to geography, number of donors, and organ health. Machine perfusion (MP) is a clinically implemented strategy designed to preserve organs ex vivo while limiting ischemia reperfusion injury that is commonly associated with the traditional static cold storage technique for organ preservation. MP circulates a nutrient-rich perfusate solution through the organ to maintain native metabolism while also clearing metabolic waste products to sustain organ function ex vivo for an extended period. In addition to maintaining organ metabolism, MP has demonstrated a capacity to monitor and rehabilitate organs that have initially been deemed non-viable for transplantation upon initial inspection; overall, improving the number of organs available for transplant.

The clinical standard for MP is a red blood cell (RBC) supplemented solution for O₂ delivery. The major shortcoming of this approach is 1) donated RBCs are a scarce resource, and 2) RBCs are prone to lysis on the MP circuit, releasing cell-free hemoglobin (Hb) that extravasates into the tissue space where it scavenges nitric oxide and leads to vasoconstriction and systemic hypertension. An established RBC substitute is polymerized hemoglobin (PolyHb), which retains Hb’s native O₂ delivery properties with improved mechanical stability compared to RBCs. The application of PolyHb in MP has shown success in liver perfusions with commercial PolyHb candidates. Unfortunately, these commercial candidates failed phase III clinical trials for use in transfusion medicine due to their small size. This work explores the application of a next generation PolyhHb, optimized to not contain low MW protein species (< 500 kDa), to a perfusate solution for an ex vivo lung perfusion (EVLP) rat model. The goal of this work was to create a viable alternative to RBCs to extend the preservation timeline for lungs ex vivo.

MATERIALS AND METHODS

PolyHb was synthesized via a crosslinking reaction of glutaraldehyde and Hb. The material was purified using tangential flow filtration and bracketed between 500 kDa and 0.2 µm. For the perfusate, PolyHb or rat RBCs (3.5 wt%) were added to a solution of 4 wt% human serum albumin, 1 mL heparin, and balanced with William’s E. Media to yield a 165 mL solution. Following IACUC guidelines, a rat heart-lung bloc was attached to a MP circuit by the pulmonary vein and left atrium. The perfusate was cycled through the circuit while the lung was ventilated for 2 hours at normothermia. Perfusate samples were collected throughout EVLP for full biophysical characterizations, and lung tissue was analyzed for stress responses following EVLP.

RESULTS AND DISCUSSION

Throughout EVLP, the pulmonary arterial pressure and pulmonary vascular resistance were significantly higher in lungs perfused with RBCs. This is consistent with hemolysis and the extravasation of Hb from the pulmonary vasculature into the tissue space. Lungs perfused with PolyHb had improved tissue oxygenation compared to RBCs. Post-EVLP analysis revealed that the PolyHb-based perfusate elicited less cellular damage, tissue extravasation, iron tissue deposition, and edema formation than either RBCs or colloid perfusates. These results are promising for future application of a next-generation PolyHb to maintain lung function and overall graft health throughout EVLP.

IMPLICATIONS

The integration of a next generation PolyHb-based perfusate into EVLP would ensure allocation of donated blood units to emergency transfusions and surgeries, where there is a continuous shortage. In addition, by applying PolyHb for EVLP, we can ultimately increase the number of organs available for transplantation. Organs that were initially discarded due to nonviability can be rehabilitated and reassessed on the MP circuit and potentially transplanted. With methods to increase the number of donated organs available for transplant, there can be a reduction in the inequity associated with access to transplantations.

DISCLAIMER

A.F.P., A.G. and C.C. are inventors on US patent application PCT/US2022/041743. A.F.P., C.C, B.A.W, and S.M.B. are inventors on US patent application PCT/US2023/017765.

Research Interests

I am interested in pursuing a career in industry focusing on the clinical translation of biotechnologies, biotherapeutics, and pharmaceutics with the intention of making medicine more accessible. My current research focuses on artificial blood substitutes for transfusion medicine and organ preservation technologies, but I am excited to explore any research topic that prioritizes human health.

RELATED ORAL AND/OR POSTER PRESENTATION

Title: Polymerized Human Hemoglobin-Based Oxygen Carrier Preserves Lung Allograft Function during Normothermic Ex Vivo Lung Perfusion
ID: 686172