Reduction in Red Blood Cell Lysis by Polymer Intervention During Rodent Liver Normothermic Machine Perfusion

This study addresses a practical problem in liver transplantation and normothermic machine perfusion: red blood cell damage during ex vivo perfusion. Normothermic machine perfusion has become an important organ preservation strategy because it keeps donor livers functioning in near-physiologic conditions before transplant, allowing teams to assess viability and potentially rescue higher-risk grafts. But RBC-based perfusates can undergo shear-related hemolysis inside pumps and tubing, releasing free hemoglobin that may worsen oxidative stress, endothelial dysfunction, and inflammatory injury. The authors tested whether two membrane-stabilizing polymers, Poloxamer 188 (P188) and Ficoll PM70, could reduce this damage during rodent liver normothermic machine perfusion. 

The paper used two rat liver models to make the findings more clinically relevant. The first was a donation after brain death model, which served as a nonischemic baseline. The second was a warm ischemia model, in which livers were exposed to 1 hour of warm ischemic injury before perfusion, simulating a more stressed graft. As shown in the study diagram on page 3, each liver then underwent 3 hours of normothermic machine perfusion in a closed-loop system with a reservoir, pump, oxygenator, and organ chamber. The perfusate included packed rat RBCs, and the authors added P188, Ficoll PM70, or no additive depending on group. Sample sizes were small, with 3 to 4 livers per group. 

The main endpoint was hemolysis, measured as cell-free hemoglobin in perfusate samples using NanoDrop spectrophotometry at 414 nm. The study also tracked vascular resistance, oxygen uptake, venous lactate, AST, ALT, bile production, cytokines, and histology. This broader design matters because it lets the reader judge whether lower hemolysis actually translates into better liver function or only improves one isolated biomarker. The investigators also included blinded histologic assessment with H&E and TUNEL staining, which strengthens the tissue-level interpretation even in a small exploratory study. 

The clearest result was that both polymers reduced hemolysis. In the donation after brain death model, P188 and Ficoll PM70 significantly lowered circulating free hemoglobin compared with untreated controls. The graphs on page 5 show the untreated livers accumulating much more cell-free hemoglobin across the 3-hour perfusion period, while the polymer-treated groups remained substantially lower. That finding supports the core hypothesis that membrane-stabilizing or rheology-modifying perfusate additives can protect RBCs from mechanical injury during liver machine perfusion. 

The warm ischemia arm produced a similar message. When the authors used the combination of P188 and Ficoll PM70 in ischemically injured livers, free hemoglobin again rose far less than in untreated controls. The graph on page 8 shows a clear separation between the groups over time, suggesting that polymer treatment may be especially useful in higher-risk grafts that are already vulnerable to ischemia-reperfusion stress. Histology also favored treatment. In untreated warm ischemic livers, the sinusoids appeared more dilated and congested, while polymer-treated livers showed less congestion and better preservation of liver sinusoidal endothelial cells. 

The histology findings are one of the most interesting parts of the paper. In the nonischemic donation after brain death model, untreated controls showed more vascular congestion, while polymer-treated livers showed clearer sinusoids and better-preserved endothelial architecture on page 5. TUNEL staining suggested that hepatocyte viability was largely maintained across groups. In the warm ischemia model, both treated and untreated livers showed some focal disruption in lobular structure, which is expected after ischemic injury, but the treated group still appeared less congested and more structurally preserved. That makes the study relevant not just for hemolysis reduction but also for microcirculatory protection during liver perfusion. 

Where the paper becomes more cautious is in the functional liver data. Despite lower hemolysis, the additives did not significantly improve vascular resistance, oxygen uptake, AST, ALT, lactate, or bile production during the 3-hour ex vivo perfusion window. In the donation after brain death groups, oxygen uptake and resistance were similar across groups, transaminases rose over time regardless of treatment, and bile production was not significantly different. In the warm ischemia arm, neither group produced bile, and the other metabolic and injury markers again did not differ significantly. So the polymers improved RBC stability and some histologic features, but not the short-term functional metrics most transplant teams would ultimately want to optimize. 

The inflammatory results added another layer of complexity. In donation after brain death livers, P188 was associated with higher IL-6 and TNF-α levels than both control and Ficoll PM70 groups, as shown in the cytokine plots on page 6. ICAM-1 also trended higher with P188, while IL-10 did not significantly differ. The authors appropriately interpret this as a possible proinflammatory signal linked to P188, even though they also note that cytokines like IL-6 can sometimes participate in repair and regeneration rather than pure injury. Ficoll PM70 looked cleaner from an inflammatory standpoint in this model, which may matter for future perfusate design. 

From an SEO and translational standpoint, this is best viewed as an early preclinical proof-of-concept study in liver transplantation, organ preservation, and normothermic machine perfusion. Its strengths are a relevant biologic question, objective hemolysis measurements, complementary histology, and use of both nonischemic and warm ischemic rodent liver models. Its limitations are equally important: very small sample sizes, short perfusion duration, limited cytokine detectability, no transplantation endpoint, and no demonstration that lower hemolysis improved downstream graft performance. The authors themselves conclude that P188 and Ficoll PM70 are promising for reducing RBC lysis and preserving sinusoidal endothelial cells, but that more work is needed before clinical translation. For researchers following liver machine perfusion, hemolysis mitigation, and donor organ optimization, this paper offers a useful and promising step rather than a definitive solution.