Anti-apoptotic treatment of warm ischemic male rat livers in machine perfusion improves symptoms of ischemia-reperfusion injury

Background

Liver donation after cardiac death (DCD) makes up a small percentage of the organs used in transplantation and poses a higher risk of graft loss compared to donation after brain death (DBD); this is a result of ischemia reperfusion for which the exact injury mechanisms are currently not fully understood. However, reperfusion injury has been shown to lead to necrosis as well as apoptosis through oxidative stress and mitochondrial dysfunction. In this work, we propose that use of the pro-survival, anti-apoptotic CEPT cocktail in post-ischemia normothermic machine perfusion (NMP) may improve recovery in rat livers subjected to extended durations of warm ischemia.

Materials and Methods

Livers procured from male Lewis rats were subjected to 90 min of warm ischemia, followed by 6 h of NMP where they were treated either with the survival-enhancing anti-apoptotic cocktail (CEPT), the vehicle (DMSO) or the base media with no additives.

Results

The CEPT-treated group exhibited lower expression of hepatic injury biomarkers, and improvement in a range of hepatocellular symptoms associated with the hepatic parenchyma, biliary epithelium and the sinusoidal endothelium, including recovery of bile secretion and lowered vascular resistance.

Conclusions

This study's findings suggest apoptosis plays a more significant role in ischemia-reperfusion injury than previously understood, and provide useful insight for further investigation of the specific underlying mechanisms and development of novel treatment methods.

Acellular Perfusate is an Adequate Alternative to Packed Red Blood Cells During Normothermic Human Kidney Perfusion

Background

Brief normothermic machine perfusion is increasingly used to assess and recondition grafts before transplant. During normothermic machine perfusion, metabolic activity is typically maintained using red blood cell (RBC)-based solutions. However, the utilization of RBCs creates important logistical constraints. This study explored the feasibility of human kidney normothermic perfusion using William's E-based perfusate with no additional oxygen carrier.

Methods

Sixteen human kidneys declined for transplant were perfused with a perfusion solution containing packed RBCs or William's E medium only for 6 h using a pressure-controlled system. The temperature was set at 37 °C. Renal artery resistance, oxygen extraction, metabolic activity, energy metabolism, and histological features were evaluated.

Results

Baseline donor demographics were similar in both groups. Throughout perfusion, kidneys perfused with William's E exhibited improved renal flow (P = 0.041) but similar arterial resistance. Lactic acid levels remained higher in kidneys perfused with RBCs during the first 3 h of perfusion but were similar thereafter (P = 0.95 at 6 h). Throughout perfusion, kidneys from both groups exhibited comparable behavior regarding oxygen consumption (P = 0.41) and reconstitution of ATP tissue concentration (P = 0.55). Similarly, nicotinamide adenine dinucleotide levels were preserved during perfusion. There was no evidence of histological damage caused by either perfusate.

Conclusions

In human kidneys, William's E medium provides a logistically convenient, off-the-shelf alternative to packed RBCs for up to 6 h of normothermic machine perfusion.

A Swine Burn Model for Investigating the Healing Process in Multiple Depth Burn Wounds

Burn wound healing is a complex and long process. Despite extensive experience, plastic surgeons and specialized teams in burn centers still face significant challenges. Among these challenges, the extent of the burned soft tissue can evolve in the early phase, creating a delicate balance between conservative treatments and necrosing tissue removal. Thermal burns are the most common type, and burn depth varies depending on multiple parameters, such as temperature and exposure time. Burn depth also varies in time, and the secondary aggravation of the "shadow zone" remains a poorly understood phenomenon. In response to these challenges, several innovative treatments have been studied, and more are in the early development phase. Nanoparticles in modern wound dressings and artificial skin are examples of these modern therapies still under evaluation. Taken together, both burn diagnosis and burn treatments need substantial advancements, and research teams need a reliable and relevant model to test new tools and therapies. Among animal models, swine are the most relevant because of their strong similarities in skin structure with humans. More specifically, Yucatan minipigs show interesting features such as melanin pigmentation and slow growth, allowing for studying high phototypes and long-term healing. This article aims to describe a reliable and reproducible protocol to study multi-depth burn wounds in Yucatan minipigs, enabling long-term follow-up and providing a relevant model for diagnosis and therapeutic studies.

Short-term hypercaloric carbohydrate loading increases surgical stress resilience by inducing FGF21

Dietary restriction promotes resistance to surgical stress in multiple organisms. Counterintuitively, current medical protocols recommend short-term carbohydrate-rich drinks (carbohydrate loading) prior to surgery, part of a multimodal perioperative care pathway designed to enhance surgical recovery. Despite widespread clinical use, preclinical and mechanistic studies on carbohydrate loading in surgical contexts are lacking. Here we demonstrate in ad libitum-fed mice that liquid carbohydrate loading for one week drives reductions in solid food intake, while nearly doubling total caloric intake. Similarly, in humans, simple carbohydrate intake is inversely correlated with dietary protein intake. Carbohydrate loading-induced protein dilution increases expression of hepatic fibroblast growth factor 21 (FGF21) independent of caloric intake, resulting in protection in two models of surgical stress: renal and hepatic ischemia-reperfusion injury. The protection is consistent across male, female, and aged mice. In vivo, amino acid add-back or genetic FGF21 deletion blocks carbohydrate loading-mediated protection from ischemia-reperfusion injury. Finally, carbohydrate loading induction of FGF21 is associated with the induction of the canonical integrated stress response (ATF3/4, NF-kB), and oxidative metabolism (PPARγ). Together, these data support carbohydrate loading drinks prior to surgery and reveal an essential role of protein dilution via FGF21.

Role of Machine Perfusion in Liver Transplantation

Given the current severe shortage of available livers for transplantation, there is an urgent need to maximize the utilization of donor organs. One of the strategies to increase the number of available livers for transplantation is to improve organ utilization through the use of elderly, overweight, or organs donated after circulatory death. However, the utilization of these "marginal" organs was associated with an increased risk of early allograft dysfunction, primary nonfunction, ischemic biliary complications, or even re-transplantation. Ischemia-reperfusion injury is a key mechanism in the pathogenesis of these complications.

Sub-Zero Non-Freezing of Vascularized Composite Allografts Preservation in Rodents

Ischemia is a major limiting factor in Vascularized Composite Allotransplantation (VCA) as irreversible muscular injury can occur after as early as 4-6 hours of static cold storage (SCS). Organ preservation technologies have led to the development of storage protocols extending rat liver ex vivo preservation up to 4 days. Development of such a protocol for VCAs has the added challenge of inherent ice nucleating factors of the graft, therefore this study focused on developing a robust protocol for VCA supercooling. Rodent partial hindlimbs underwent subnormothermic machine perfusion (SNMP) with several loading solutions, followed by cryoprotective agent (CPA) cocktail developed for VCAs. Storage occurred in suspended animation for 24h and VCAs were recovered using SNMP with modified Steen. This study shows a robust VCA supercooling preservation protocol in a rodent model. Further optimization is expected to allow for its application in a transplantation model, which would be a breakthrough in the field of VCA preservation.

The Autonomization Principle in Vascularized Flaps: An Alternative Strategy for Composite Tissue Scaffold In Vivo Revascularization

Autonomization is a physiological process allowing a flap to develop neo-vascularization from the reconstructed wound bed. This phenomenon has been used since the early application of flap surgeries but still remains poorly understood. Reconstructive strategies have greatly evolved since, and fasciocutaneous flaps have progressively replaced muscle-based reconstructions, ensuring better functional outcomes with great reliability. However, plastic surgeons still encounter challenges in complex cases where conventional flap reconstruction reaches its limitations. Furthermore, emerging bioengineering applications, such as decellularized scaffolds allowing a complex extracellular matrix to be repopulated with autologous cells, also face the complexity of revascularization. The objective of this article is to gather evidence of autonomization phenomena. A systematic review of flap autonomization is then performed to document the minimum delay allowing this process. Finally, past and potential applications in bio- and tissue-engineering approaches are discussed, highlighting the potential for in vivo revascularization of acellular scaffolds.

Towards Optimizing Sub-Normothermic Machine Perfusion in Fasciocutaneous Flaps: A Large Animal Study

Machine perfusion has developed rapidly since its first use in solid organ transplantation. Likewise, reconstructive surgery has kept pace, and ex vivo perfusion appears as a new trend in vascularized composite allotransplants preservation. In autologous reconstruction, fasciocutaneous flaps are now the gold standard due to their low morbidity (muscle sparing) and favorable functional and cosmetic results. However, failures still occasionally arise due to difficulties encountered with the vessels during free flap transfer. The development of machine perfusion procedures would make it possible to temporarily substitute or even avoid microsurgical anastomoses in certain complex cases. We performed oxygenated acellular sub-normothermic perfusions of fasciocutaneous flaps for 24 and 48 h in a porcine model and compared continuous and intermittent perfusion regimens. The monitored metrics included vascular resistance, edema, arteriovenous oxygen gas differentials, and metabolic parameters. A final histological assessment was performed. Porcine flaps which underwent successful oxygenated perfusion showed minimal or no signs of cell necrosis at the end of the perfusion. Intermittent perfusion allowed overall better results to be obtained at 24 h and extended perfusion duration. This work provides a strong foundation for further research and could lead to new and reliable reconstructive techniques.

Polyethylene Glycol and Caspase Inhibitor Emricasan Alleviates Cold Injury in Primary Rat Hepatocytes

Current methods of storing explanted donor livers at 4°C in University of Wisconsin (UW) solution result in loss of graft function and ultimately leads to less-than-ideal outcomes post transplantation. Our lab has previously shown that supplementing UW solution with 35-kilodalton polyethylene glycol (PEG) has membrane stabilizing effects for cold stored primary rat hepatocytes in suspension. Expanding on past studies, we here investigate if PEG has the same beneficial effects in an adherent primary rat hepatocyte cold storage model. In addition, we investigated the extent of cold-induced apoptosis through treating cold-stored hepatocytes with pan caspase inhibitor emricasan. In parallel to storage at the current cold storage standard of 4°C, we investigated the effects of lowering the storage temperature to -4°C, at which the storage solution remains ice-free due to the supercooling phenomenon. We show the addition of 5% PEG to the storage medium significantly reduced the release of lactate dehydrogenase (LDH) in plated rat hepatocytes and a combinatorial treatment with emricasan maintains hepatocyte viability and morphology following recovery from cold storage. These results show that cold-stored hepatocytes undergo multiple mechanisms of cold-induced injury and that PEG and emricasan treatment in combination with supercooling may improve cell and organ preservation.

Sodium Hydrosulfide Treatment During Porcine Kidney Ex Vivo Perfusion and Transplantation

Background

In rodents, hydrogen sulfide (H2S) reduces ischemia-reperfusion injury and improves renal graft function after transplantation. Here, we hypothesized that the benefits of H2S are conserved in pigs, a more clinically relevant model.

Methods

Adult porcine kidneys retrieved immediately or after 60 min of warm ischemia (WI) were exposed to 100 µM sodium hydrosulfide (NaHS) (1) during the hypothermic ex vivo perfusion only, (2) during WI only, and (3) during both WI and ex vivo perfusion. Kidney perfusion was evaluated with dynamic contrast-enhanced MRI. MRI spectroscopy was further employed to assess energy metabolites including ATP. Renal biopsies were collected at various time points for histopathological analysis.

Results

Perfusion for 4 h pig kidneys with Belzer MPS UW + NaHS resulted in similar renal perfusion and ATP levels than perfusion with UW alone. Similarly, no difference was observed when NaHS was administered in the renal artery before ischemia. After autotransplantation, no improvement in histologic lesions or cortical/medullary kidney perfusion was observed upon H2S administration. In addition, AMP and ATP levels were identical in both groups.

Conclusions

In conclusion, treatment of porcine kidney grafts using NaHS did not result in a significant reduction of ischemia-reperfusion injury or improvement of kidney metabolism. Future studies will need to define the benefits of H2S in human, possibly using other molecules as H2S donors.

Supercooling: A Promising Technique for Prolonged Organ Preservation in Solid Organ Transplantation, and Early Perspectives in Vascularized Composite Allografts

Ex-vivo preservation of transplanted organs is undergoing spectacular advances. Machine perfusion is now used in common practice for abdominal and thoracic organ transportation and preservation, and early results are in favor of substantially improved outcomes. It is based on decreasing ischemia-reperfusion phenomena by providing physiological or sub-physiological conditions until transplantation. Alternatively, supercooling techniques involving static preservation at negative temperatures while avoiding ice formation have shown encouraging results in solid organs. Here, the rationale is to decrease the organ's metabolism and need for oxygen and nutrients, allowing for extended preservation durations. The aim of this work is to review all advances of supercooling in transplantation, browsing the literature for each organ. A specific objective was also to study the initial evidence, the prospects, and potential applications of supercooling preservation in Vascularized Composite Allotransplantation (VCA). This complex entity needs a substantial effort to improve long-term outcomes, marked by chronic rejection. Improving preservation techniques is critical to ensure the favorable evolution of VCAs, and supercooling techniques could greatly participate in these advances.

Zebrafish as a high throughput model for organ preservation and transplantation research

Despite decades of effort, the preservation of complex organs for transplantation remains a significant barrier that exacerbates the organ shortage crisis. Progress in organ preservation research is significantly hindered by suboptimal research tools that force investigators to sacrifice translatability over throughput. For instance, simple model systems, such as single cell monolayers or co-cultures, lack native tissue structure and functional assessment, while mammalian whole organs are complex systems with confounding variables not compatible with high-throughput experimentation. In response, diverse fields and industries have bridged this experimental gap through the development of rich and robust resources for the use of zebrafish as a model organism. Through this study, we aim to demonstrate the value zebrafish pose for the fields of solid organ preservation and transplantation, especially with respect to experimental transplantation efforts. A wide array of methods were customized and validated for preservation-specific experimentation utilizing zebrafish, including the development of assays at multiple developmental stages (larvae and adult), methods for loading and unloading preservation agents, and the development of viability scores to quantify functional outcomes. Using this platform, the largest and most comprehensive screen of cryoprotectant agents (CPAs) was performed to determine their toxicity and efficiency at preserving complex organ systems using a high subzero approach called partial freezing (i.e., storage in the frozen state at -10°C). As a result, adult zebrafish cardiac function was successfully preserved after 5 days of partial freezing storage. In combination, the methods and techniques developed have the potential to drive and accelerate research in the fields of solid organ preservation and transplantation.

Anti-apoptotic treatment of warm ischemic male rat livers in machine perfusion improves symptoms of ischemia-reperfusion injury

Liver donation after cardiac death (DCD) makes up a small percentage of the donor pool and poses a higher risk of graft loss compared to donation after brain death (DBD); this is a result of ischemia reperfusion for which the exact injury mechanisms are currently not fully understood. However, reperfusion injury has been shown to lead to necrosis as well as apoptosis at the cellular level. In this work, we propose that use of the pro-survival, anti-apoptotic CEPT cocktail in post-ischemia normothermic machine perfusion (NMP) may improve recovery in rat livers subjected to extended durations of warm ischemia. Livers procured from male lewis rats were subjected to 90 minutes of warm ischemia, followed by 6 hours of NMP where they were treated with the survival-enhancing anti-apoptotic cocktail (CEPT), the vehicle (DMSO) or the base media with no additives. The CEPT-treated group exhibited lower expression of hepatic injury biomarkers, and improvement in a range of hepatocellular functions associated with the hepatic parenchyma, biliary epithelium and especially the sinusoidal endothelium. This study's findings provide useful insight for further investigation of the extent of apoptotic contribution to ischemia reperfusion injury (IRI).

Modified Tail Vein and Penile Vein Puncture for Blood Sampling in the Rat Model

Blood samples are required in most experimental animal designs to assess various hematological parameters. This paper presents two procedures for blood collection in rats: the lateral tail vein puncture and the dorsal penile vein puncture, which offer significant advantages over other previously described techniques. This study shows that these two procedures allow for fast sampling (under 10 min) and yield sufficient blood volumes for most assays (202 μL ± 67.7 μL). The dorsal penile vein puncture must be done under anesthesia, whereas the lateral tail vein puncture can be done on a conscious, restrained animal. Alternating these two techniques, therefore, enables blood draw in any situation. While it is always recommended for an operator to be assisted during a procedure to ensure animal welfare, these techniques require only a single operator, unlike most blood sampling methods that require two. Moreover, whereas these previously described methods (e.g., jugular stick, subclavian vein blood draw) require extensive prior training to avoid harm to or death of the animal, tail vein and dorsal penile vein puncture are rarely fatal. For all these reasons, and according to the context (e.g., for studies including male rats, during the perioperative or immediate postoperative period, for animals with thin tail veins), both techniques can be used alternately to enable repeated blood draws.

Gluteal Propeller Perforator Flaps: A Paradigm Shift in Abdominoperineal Amputation Reconstruction

Abdominoperineal amputation (AAP) is a gold standard procedure treating advanced abdominal and pelvic cancers. The defect resulting from this extensive surgery must be reconstructed to avoid complications, such as infection, dehiscence, delayed healing, or even death. Several approaches can be chosen depending on the patient. Muscle-based reconstructions are a reliable solution but are responsible for additional morbidity for these fragile patients. We present and discuss our experience in AAP reconstruction using gluteal-artery-based propeller perforator flaps (G-PPF) in a case series. Between January 2017 and March 2021, 20 patients received G-PPF reconstruction in two centers. Either superior gluteal artery (SGAP)- or inferior artery (IGAP)-based perforator flaps were performed depending on the best configuration. Preoperative, intraoperative, and postoperative data were collected. A total of 23 G-PPF were performed-12 SGAP and 11 IGAP flaps. Final defect coverage was achieved in 100% of cases. Eleven patients experienced at least one complication (55%), amongst whom six patients (30%) had delayed healing, and three patients (15%) had at least one flap complication. One patient underwent a new surgery at 4 months for a perineal abscess under the flap, and three patients died from disease recurrence. Gluteal-artery-based propeller perforator flaps are an effective and modern surgical procedure for AAP reconstruction. Their mechanic properties, in addition to their low morbidity, make them an optimal technique for this purpose; however, technical skills are needed, and closer surveillance with patient compliance is critical to ensure success. G-PPF should be widely used in specialized centers and considered a modern alternative to muscle-based reconstructions.

Exceeding the Limits of Static Cold Storage in Limb Transplantation Using Subnormothermic Machine Perfusion

BACKGROUND

 For 50 years, static cold storage (SCS) has been the gold standard for solid organ preservation in transplantation. Although logistically convenient, this preservation method presents important constraints in terms of duration and cold ischemia-induced lesions. We aimed to develop a machine perfusion (MP) protocol for recovery of vascularized composite allografts (VCA) after static cold preservation and determine its effects in a rat limb transplantation model.

METHODS

 Partial hindlimbs were procured from Lewis rats and subjected to SCS in Histidine-Tryptophan-Ketoglutarate solution for 0, 12, 18, 24, and 48 hours. They were then either transplanted (Txp), subjected to subnormothermic machine perfusion (SNMP) for 3 hours with a modified Steen solution, or to SNMP + Txp. Perfusion parameters were assessed for blood gas and electrolytes measurement, and flow rate and arterial pressures were monitored continuously. Histology was assessed at the end of perfusion. For select SCS durations, graft survival and clinical outcomes after transplantation were compared between groups at 21 days.

RESULTS

 Transplantation of limbs preserved for 0, 12, 18, and 24-hour SCS resulted in similar survival rates at postoperative day 21. Grafts cold-stored for 48 hours presented delayed graft failure (p = 0.0032). SNMP of limbs after 12-hour SCS recovered the vascular resistance, potassium, and lactate levels to values similar to limbs that were not subjected to SCS. However, 18-hour SCS grafts developed significant edema during SNMP recovery. Transplantation of grafts that had undergone a mixed preservation method (12-hour SCS + SNMP + Txp) resulted in better clinical outcomes based on skin clinical scores at day 21 post-transplantation when compared to the SCS + Txp group (p = 0.01613).

CONCLUSION

 To date, VCA MP is still limited to animal models and no protocols are yet developed for graft recovery. Our study suggests that ex vivo SNMP could help increase the preservation duration and limit cold ischemia-induced injury in VCA transplantation.

Continuous versus Pulsatile Flow in 24-Hour Vascularized Composite Allograft Machine Perfusion in Swine: A Pilot Study

INTRODUCTION

Multiple perfusion systems have been investigated on vascularized composite allografts, with various temperatures and different preservation solutions, most using continuous flow (CF). However, physiological flow is pulsatile and provides better outcomes in kidney and lung ex vivo perfusions. The objective of this pilot study is to compare pulsatile flow (PF) with CF in our 24-h subnormothermic machine perfusion protocol for swine hindlimbs.

METHODS

Partial hindlimbs were harvested from Yorkshire pigs and perfused with a modified Steen solution at 21°C for 24 h either with CF (n = 3) or with pulsatile flow (PF) at 60 beats/min (n = 3). Perfusion parameters, endothelial markers, and muscle biopsies were assessed at different timepoints.

RESULTS

Overall, lactate levels were significantly lower in the PF group (P = 0.001). Glucose uptake and potassium concentration were similar in both groups throughout perfusion. Total nitric oxide levels were significantly higher in the PF group throughout perfusion (P = 0.032). Nitric oxide/endothelin-1 ratio also tends to be higher in the PF group, reflecting a potentially better vasoconductivity with PF, although not reaching statistical significance (P = 0.095). Arterial resistances were higher in the PF group (P < 0.001). Histological assessment did not show significant difference in muscular injury between the two groups. Weight increased quicker in the CF group but reached similar values with the PF after 24 h.

CONCLUSIONS

This pilot study suggests that PF may provide superior preservation of vascularized composite allografts when perfused for 24 h at subnormothermic temperatures, with potential improvement in endothelial function and decreased ischemic injury.

Optimal Temperature Protocols for Liver Machine Perfusion Using a Monte Carlo Method

Monte Carlo simulation with a novel acceptance procedure is used to find optimal temperature profiles for liver machine perfusion. Numerical results for MC simulation are compared to a greedy approach and to current practice in machine perfusion research. Results show that the proposed Monte Carlo simulation approach finds optimal temperature profiles that agree with current clinical research practice.

The Superficial Inferior Epigastric Artery Axial Flap to Study Ischemic Preconditioning Effects in a Rat Model

Fasciocutaneous flaps (FCF) have become the gold standard for complex defect reconstruction in plastic and reconstructive surgery. This muscle-sparing technique allows transferring vascularized tissues to cover any large defect. FCF can be used as pedicled flaps or as free flaps; however, in the literature, failure rates for pedicled FCF and free FCF are above 5%, leaving room for improvement for these techniques and further knowledge expansion in this area. Ischemic preconditioning (I.P.) has been widely studied, but the mechanisms and the optimization of the I.P. regimen are yet to be determined. This phenomenon is indeed poorly explored in plastic and reconstructive surgery. Here, a surgical model is presented to study the I.P. regimen in a rat axial fasciocutaneous flap model, describing how to safely and reliably assess the effects of I.P. on flap survival. This article describes the complete surgical procedure, including suggestions to improve the reliability of this model. The objective is to provide researchers with a reproducible and reliable model to test various ischemic preconditioning regimens and assess their effects on flap survivability.

Development of a rat forelimb vascularized composite allograft (VCA) perfusion protocol

Vascularized composite allografts (VCAs) refer to en bloc heterogenous tissue that is transplanted to restore form and function after amputation or tissue loss. Rat limb VCA has emerged as a robust translational model to study the pathophysiology of these transplants. However, these models have predominately focused on hindlimb VCAs which does not translate anatomically to upper extremity transplantation, whereas the majority of clinical VCAs are upper extremity and hand transplants. This work details our optimization of rat forelimb VCA procurement and sub-normothermic machine perfusion (SNMP) protocols, with results in comparison to hindlimb perfusion with the same perfusion modality. Results indicate that compared to hindlimbs, rat forelimbs on machine perfusion mandate lower flow rates and higher acceptable maximum pressures. Additionally, low-flow forelimbs have less cellular damage than high-flow forelimbs based on oxygen uptake, edema, potassium levels, and histology through 2 hours of machine perfusion. These results are expected to inform future upper extremity VCA preservation studies.

Microvascular assessment of fascio-cutaneous flaps by ultrasound: A large animal study

Objectives: Blood perfusion quality of a flap is the main prognostic factor for success. Microvascular evaluation remains mostly inaccessible. We aimed to evaluate the microflow imaging mode, MV-Flow, in assessing flap microvascularization in a pig model of the fascio-cutaneous flap. Methods: On five pigs, bilateral saphenous fascio-cutaneous flaps were procured on the superficial femoral vessels. A conventional ultrasound evaluation in pulsed Doppler and color Doppler was conducted on the ten flaps allowing for the calculation of the saphenous artery flow rate. The MV-Flow mode was then applied: for qualitative analysis, with identification of saphenous artery collaterals; then quantitative, with repeated measurements of the Vascularity Index (VI), percentage of pixels where flow is detected relative to the total ultrasound view area. The measurements were then repeated after increasing arterial flow by clamping the distal femoral artery. Results: The MV-Flow mode allowed a better follow-up of the saphenous artery's collaterals and detected microflows not seen with the color Doppler. The VI was correlated to the saphenous artery flow rate (Spearman rho of 0.64; p = 0.002) and allowed to monitor the flap perfusion variations. Conclusion: Ultrasound imaging of microvascularization by MV-Flow mode and its quantification by VI provides valuable information in evaluating the microvascularization of flaps.

Pan-caspase inhibition during normothermic machine perfusion of discarded livers mitigates ex situ innate immune responses

Access to liver transplantation is limited by a significant organ shortage. The recent introduction of machine perfusion technology allows surgeons to monitor and assess ex situ liver function prior to transplantation. However, many donated organs are of inadequate quality for transplant, though opportunities exist to rehabilitate organ function with adjunct therapeutics during normothermic machine perfusion. In this preclinical study, we targeted the apoptosis pathway as a potential method of improving hepatocellular function. Treatment of discarded human livers during normothermic perfusion with an irreversible pan-caspase inhibitor, emricasan, resulted in significant mitigation of innate immune and pro-inflammatory responses at both the transcriptional and protein level. This was evidenced by significantly decreased circulating levels of the pro-inflammatory cytokines, interleukin-6, interleukin-8, and interferon-gamma, compared to control livers. Compared to emricasan-treated livers, untreated livers demonstrated transcriptional changes notable for enrichment in pathways involved in innate immunity, leukocyte migration, and cytokine-mediated signaling. Targeting of unregulated apoptosis may represent a viable therapeutic intervention for immunomodulation during machine perfusion.

Partial freezing of rat livers extends preservation time by 5-fold

The limited preservation duration of organs has contributed to the shortage of organs for transplantation. Recently, a tripling of the storage duration was achieved with supercooling, which relies on temperatures between -4 and -6 °C. However, to achieve deeper metabolic stasis, lower temperatures are required. Inspired by freeze-tolerant animals, we entered high-subzero temperatures (-10 to -15 °C) using ice nucleators to control ice and cryoprotective agents (CPAs) to maintain an unfrozen liquid fraction. We present this approach, termed partial freezing, by testing gradual (un)loading and different CPAs, holding temperatures, and storage durations. Results indicate that propylene glycol outperforms glycerol and injury is largely influenced by storage temperatures. Subsequently, we demonstrate that machine perfusion enhancements improve the recovery of livers after freezing. Ultimately, livers that were partially frozen for 5-fold longer showed favorable outcomes as compared to viable controls, although frozen livers had lower cumulative bile and higher liver enzymes.

710 Specific Patterns of Vital Sign Fluctuations Predict Bloodstream Infection in Pediatric Burn Patients

Introduction

Early recognition of the clinical signs of bloodstream infection in pediatric burn patients is key to improving survival rates in the burn unit. The objective of this study was to propose a simple scoring criteria that used readily available temperature, heart rate (HR) and mean arterial pressure (MAP) data to accurately predict bloodstream infection in pediatric burn patients.

Methods

A retrospective chart review included 100 patients admitted to the pediatric burn unit for &gt;20% total body surface area (TBSA) burn injuries. Each patient had multiple blood culture tests, and each test was treated as a separate and independent “infection event” for analysis. The time at each blood culture draw was time 0 for that event, and temperature, HR and MAP data was collected for 24 hours after the blood culture was drawn. “Infection events” included in this study had at least six complete sets of temperature, HR and MAP data entries. Median temperature, HR and MAP, as well as mean fever spikes, HR spikes and MAP dips, were compared between infection group (positive blood cultures) and control group (negative blood cultures). These vital sign fluctuations were evaluated individually and as a combination of all three as timely predictors of bloodstream infection. In addition, we tested the prediction of Gram-negative bacteria versus Gram-positive or fungi present in blood cultures.

Results

Patients in the infection group had significantly higher median temperatures (p&lt; 0.001), mean fever spikes (p&lt; 0.001) and mean HR spikes (p&lt; 0.001), compared to the control group. Using the combination scoring criteria to predict bloodstream infection, the strongest predictive values in the 24-hour timeframe had high sensitivity (93%) and specificity (81%). The predictive test metric based on vital sign spikes predicted Gram-negative bacteria, but with limited sensitivity (57%) and specificity (44%).

Conclusions

This study found that using a combination scoring criteria of fever spikes, HR spikes and MAP dips predicted bloodstream infection in pediatric patients with burn injuries with 87% accuracy, which may justify its use in resource-poor environments, or in cases where practical supporting evidence is needed for preemptive antibiotic treatment before culture results are available.

Modeling energy depletion in rat livers using Nash equilibrium metabolic pathway analysis

The current gold standard of Static Cold Storage (SCS), which is static cold storage on ice (about + 4 °C) in a specialized media such as the University of Wisconsin solution (UW), limits storage to few hours for vascular and metabolically active tissues such as the liver and the heart. The liver is arguably the pinnacle of metabolism in human body and therefore metabolic pathway analysis immediately becomes very relevant. In this article, a Nash Equilibrium (NE) approach, which is a first principles approach, is used to model and simulate the static cold storage and warm ischemia of a proposed model of liver cells. Simulations of energy depletion in the liver in static cold storage measured by ATP content and energy charge are presented along with comparisons to experimental data. In addition, conversion of Nash Equilibrium iterations to time are described along with an uncertainty analysis for the parameters in the model. Results in this work show that the Nash Equilibrium approach provides a good match to experimental data for energy depletion and that the uncertainty in model parameters is very small with percent variances less than 0.1%.

Optimization of Ex Vivo Machine Perfusion and Transplantation of Vascularized Composite Allografts

BACKGROUND

Machine perfusion is gaining interest as an efficient method of tissue preservation of Vascularized Composite Allografts (VCA). The aim of this study was to develop a protocol for ex vivo subnormothermic oxygenated machine perfusion (SNMP) on rodent hindlimbs and to validate our protocol in a heterotopic hindlimb transplant model.

METHODS

In this optimization study we compared three different solutions during 6 h of SNMP (n = 4 per group). Ten control limbs were stored in a preservation solution on Static Cold Storage [SCS]). During SNMP we monitored arterial flowrate, lactate levels, and edema. After SNMP, muscle biopsies were taken for histology examination, and energy charge analysis. We validated the best perfusion protocol in a heterotopic limb transplantation model with 30-d follow up (n = 13). As controls, we transplanted untreated limbs (n = 5) and hindlimbs preserved with either 6 or 24 h of SCS (n = 4 and n = 5).

RESULTS

During SNMP, arterial outflow increased, and lactate clearance decreased in all groups. Total edema was significantly lower in the HBOC-201 group compared to the BSA group (P = 0.005), 4.9 (4.3-6.1) versus 48.8 (39.1-53.2) percentage, but not to the BSA + PEG group (P = 0.19). Energy charge levels of SCS controls decreased 4-fold compared to limbs perfused with acellular oxygen carrier HBOC-201, 0.10 (0.07-0.17) versus 0.46 (0.42-0.49) respectively (P = 0.002).

CONCLUSIONS

Six hours ex vivo SNMP of rodent hindlimbs using an acellular oxygen carrier HBOC-201 results in superior tissue preservation compared to conventional SCS.

The role of antifreeze glycoprotein (AFGP) and polyvinyl alcohol/polyglycerol (X/Z-1000) as ice modulators during partial freezing of rat livers

Introduction

The current liver organ shortage has pushed the field of transplantation to develop new methods to prolong the preservation time of livers from the current clinical standard of static cold storage. Our approach, termed partial freezing, aims to induce a thermodynamically stable frozen state at high subzero storage temperatures (-10°C to -15°C), while simultaneously maintaining a sufficient unfrozen fraction to limit ice-mediated injury.

Methods and results

Using glycerol as the main permeating cryoprotectant agent, this research first demonstrated that partially frozen rat livers showed similar outcomes after thawing from either -10°C or -15°C with respect to subnormothermic machine perfusion metrics. Next, we assessed the effect of adding ice modulators, including antifreeze glycoprotein (AFGP) or a polyvinyl alcohol/polyglycerol combination (X/Z-1000), on the viability and structural integrity of partially frozen rat livers compared to glycerol-only control livers. Results showed that AFGP livers had high levels of ATP and the least edema but suffered from significant endothelial cell damage. X/Z-1000 livers had the highest levels of ATP and energy charge (EC) but also demonstrated endothelial damage and post-thaw edema. Glycerol-only control livers exhibited the least DNA damage on Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining but also had the lowest levels of ATP and EC.

Discussion

Further research is necessary to optimize the ideal ice modulator cocktail for our partial-freezing protocol. Modifications to cryoprotective agent (CPA) combinations, including testing additional ice modulators, can help improve the viability of these partially frozen organs.

Activation of autophagy during normothermic machine perfusion of discarded livers is associated with improved hepatocellular function

Liver transplantation is hampered by a severe shortage of donor organs. Normothermic machine perfusion (NMP) of donor livers allows dynamic preservation in addition to viability assessment before transplantation. Little is known about the injury and repair mechanisms induced during NMP. To investigate these mechanisms, we examined gene and protein expression changes in a cohort of discarded human livers, stratified by hepatocellular function, during NMP. Six human livers acquired through donation after circulatory death (DCD) underwent 12 h of NMP. Of the six livers, three met predefined criteria for adequate hepatocellular function. We applied transcriptomic profiling and protein analysis to evaluate temporal changes in gene expression during NMP between functional and nonfunctional livers. Principal component analysis segregated the two groups and distinguished the various perfusion time points. Transcriptomic analysis of biopsies from functional livers indicated robust activation of innate immunity after 3 h of NMP followed by enrichment of prorepair and prosurvival mechanisms. Nonfunctional livers demonstrated delayed and persistent enrichment of markers of innate immunity. Functional livers demonstrated effective induction of autophagy, a cellular repair and homeostasis pathway, in contrast to nonfunctional livers. In conclusion, NMP of discarded DCD human livers results in innate immune-mediated injury, while also activating autophagy, a presumed mechanism for support of cellular repair. More pronounced activation of autophagy was seen in livers that demonstrated adequate hepatocellular function.NEW & NOTEWORTHY We demonstrate that ischemia-reperfusion injury occurs in all livers during NMP, though there are notable differences in gene expression between functional and nonfunctional livers. We further demonstrate that activation of the liver's repair and homeostasis mechanisms through autophagy plays a vital role in the graft's response to injury and may impact liver function. These findings indicate that liver autophagy might be a key therapeutic target for rehabilitating the function of severely injured or untransplantable livers.

The effect of blood cells retained in rat livers during static cold storage on viability outcomes during normothermic machine perfusion

In transplantation, livers are transported to recipients using static cold storage (SCS), whereby livers are exposed to cold ischemic injury that contribute to post-transplant risk factors. We hypothesized that flushing organs during procurement with cold preservation solutions could influence the number of donor blood cells retained in the allograft thereby exacerbating cold ischemic injury. We present the results of rat livers that underwent 24 h SCS after being flushed with a cold University of Wisconsin (UW) solution versus room temperature (RT) lactated ringers (LR) solution. These results were compared to livers that were not flushed prior to SCS and thoroughly flushed livers without SCS. We used viability and injury metrics collected during normothermic machine perfusion (NMP) and the number of retained peripheral cells (RPCs) measured by histology to compare outcomes. Compared to the cold UW flush group, livers flushed with RT LR had lower resistance, lactate, AST, and ALT at 6 h of NMP. The number of RPCs also had significant positive correlations with resistance, lactate, and potassium levels and a negative correlation with energy charge. In conclusion, livers exposed to cold UW flush prior to SCS appear to perform worse during NMP, compared to RT LR flush.

Non-invasive quantification of the mitochondrial redox state in livers during machine perfusion

Ischemia reperfusion injury (IRI) is a critical problem in liver transplantation that can lead to life-threatening complications and substantially limit the utilization of livers for transplantation. However, because there are no early diagnostics available, fulminant injury may only become evident post-transplant. Mitochondria play a central role in IRI and are an ideal diagnostic target. During ischemia, changes in the mitochondrial redox state form the first link in the chain of events that lead to IRI. In this study we used resonance Raman spectroscopy to provide a rapid, non-invasive, and label-free diagnostic for quantification of the hepatic mitochondrial redox status. We show this diagnostic can be used to significantly distinguish transplantable versus non-transplantable ischemically injured rat livers during oxygenated machine perfusion and demonstrate spatial differences in the response of mitochondrial redox to ischemia reperfusion. This novel diagnostic may be used in the future to predict the viability of human livers for transplantation and as a tool to better understand the mechanisms of hepatic IRI.

Thrombolytic Therapy During ex-vivo Normothermic Machine Perfusion of Human Livers Reduces Peribiliary Vascular Plexus Injury

Background: A major limitation in expanding the use of donation after circulatory death (DCD) livers in transplantation is the increased risk of graft failure secondary to ischemic cholangiopathy. Warm ischemia causes thrombosis and injury to the peribiliary vascular plexus (PVP), which is supplied by branches of the hepatic artery, causing higher rates of biliary complications in DCD allografts.

Aims/Objectives: We aimed to recondition discarded DCD livers with tissue plasminogen activator (tPA) while on normothermic machine perfusion (NMP) to improve PVP blood flow and reduce biliary injury.

Methods: Five discarded DCD human livers underwent 12 h of NMP. Plasminogen was circulated in the base perfusate prior to initiation of perfusion and 1 mg/kg of tPA was administered through the hepatic artery at T = 0.5 h. Two livers were split prior to perfusion (S1, S2), with tPA administered in one lobe, while the other served as a control. The remaining three whole livers (W1-W3) were compared to seven DCD control liver perfusions (C1-C7) with similar hepatocellular and biliary viability criteria. D-dimer levels were measured at T = 1 h to verify efficacy of tPA. Lactate, total bile production, bile pH, and difference in biliary injury scores before and after perfusion were compared between tPA and non-tPA groups using unpaired, Mann-Whitney tests.

Results: Average weight-adjusted D-dimer levels were higher in tPA livers in the split and whole-liver model, verifying drug function. There were no differences in perfusion hepatic artery resistance, portal vein resistance, and arterial lactate between tPA livers and non-tPA livers in both the split and whole-liver model. However, when comparing biliary injury between hepatocellular and biliary non-viable whole livers, tPA livers had significantly lower PVP injury scores (0.67 vs. 2.0) and mural stroma (MS) injury scores (1.3 vs. 2.7).

Conclusion: This study demonstrates that administration of tPA into DCD livers during NMP can reduce PVP and MS injury. Further studies are necessary to assess the effect of tPA administration on long term biliary complications.

Partial Heterotopic Hindlimb Transplantation Model in Rats

Vascularized composite allotransplantations (VCA) represent the most advanced reconstruction option for patients without autologous surgical possibilities after a complex tissue defect. Face and hand transplantations have changed disfigured patients' lives, giving them a new aesthetic and functional social organ. Despite promising outcomes, VCA is still underperformed due to life-long immunosuppression comorbidities and infectious complications. The rat is an ideal animal model for in vivo studies investigating immunological pathways and graft rejection mechanisms. Rats are also widely used in novel composite tissue graft preservation techniques, including perfusion and cryopreservation studies. Models used for VCA in rats must be reproducible, reliable, and efficient with low postoperative morbidity and mortality. Heterotopic limb transplantation procedures fulfill these criteria and are easier to perform than orthotopic limb transplants. Mastering rodent microsurgical models requires solid experience in microsurgery and animal care. Herein is reported a reliable and reproducible model of partial heterotopic osteomyocutaneous flap transplantation in rats, the postoperative outcomes, and the means of prevention of potential complications.

In Vivo Activity of Genetically Modified Cells Preseeded in Rat Vascularized Composite Allografts

OBJECTIVE

Transplantation of the hand or face, known as vascularized composite allotransplantation (VCA), has revolutionized reconstructive surgery. Notwithstanding, there are still several areas of improvement to mitigate immune rejection while sparing systemic adverse effects. The goal of this study was to evaluate the engraftment and viability of a genetically modified cell population pre-engrafted into a VCA transplant, to potentially act as a local biosensor to report and modify the graft in vivo. A rat fibroblast cell line genetically modified to secrete Gaussia-Luciferase (gLuc), which served as a constitutive biomarker of cells, was incorporated into a VCA to study the viability of biosensor cells in a syngeneic rat heterotopic partial hindlimb transplantation model.

RESULTS

Five perfusions were first performed as engineering runs to have a stable limb perfusion protocol, followed by 3 perfusions to analyze the cell engraftment during machine perfusion, and finally 4 perfusions to study in vivo persistence of the cell biosensors. Blood samples were collected to monitor gLuc secretion during perfusion and postoperatively. A time-dependent increase in gLuc secretion in the limb perfusion outflow during machine perfusion indirectly verified the presence of biosensors within the graft. After the ex vivo perfusion, VCA hindlimbs were analyzed for near infrared fluorescence emission that showed a presence of dyed engineered cells in all areas of the limbs. Postoperatively, gLuc was detectable 4 to 5 days after transplantation (W = 16, P = .02857). This study demonstrated that engineered cells could be successfully preimplanted into VCAs-an important step toward development of an in vivo biosensor platform to use in modulating acute VCA outcomes.

Evolving utilization of donation after circulatory death livers in liver transplantation: The day of DCD has come

Compared to donation after brain death (DBD), livers procured for transplantation from donation after circulatory death (DCD) donors experience more ischemia-reperfusion injury and higher rates of ischemic cholangiopathy due to the period of warm ischemic time (WIT) following withdrawal of life support. As a result, utilization of DCD livers for liver transplant (LT) has generally been limited to short WITs and younger aged donor grafts, causing many recovered DCD organs to be discarded without consideration for transplant. This study assesses how DCD liver utilization and outcomes have changed over time, using OPTN data from adult, first-time, deceased donor, whole-organ LTs between January 1995 and December 2019. Results show that increased clinical experience with DCD LT has translated into increased use of livers from DCD donors, shorter ischemic times, shorter lengths of hospitalization after transplant, and lower rates of retransplantation. The data also reveal that over the past decade, the rate of increase in DCD LTs conducted in the United States has outpaced that of DBD. Together, these trends signal an opportunity for the field of liver transplantation to mitigate the organ shortage by capitalizing on DCD liver allografts that are currently not being utilized.

Liver donor age affects hepatocyte function through age-dependent changes in decellularized liver matrix

The only treatment available for end stage liver diseases is orthotopic liver transplantation. Although there is a big donor scarcity, many donor livers are discarded as they do not qualify for transplantation. Alternatively, decellularization of discarded livers can potentially render them transplantable upon recellularization and functional testing. The success of this approach will heavily depend on the quality of decellularized scaffolds which might show variability due to factors including age. Here we assessed the age-dependent differences in liver extracellular matrix (ECM) using rat and human livers. We show that the liver matrix has higher collagen and glycosaminoglycan content and a lower growth factor content with age. Importantly, these changes lead to deterioration in primary hepatocyte function potentially due to ECM stiffening and integrin-dependent signal transduction. Overall, we show that ECM changes with age and these changes significantly affect cell function thus donor age should be considered as an important factor for bioengineering liver substitutes.

A portable single-sided magnetic-resonance sensor for the grading of liver steatosis and fibrosis

Low-cost non-invasive diagnostic tools for staging the progression of non-alcoholic chronic liver failure from fatty liver disease to steatohepatitis are unavailable. Here, we describe the development and performance of a portable single-sided magnetic-resonance sensor for grading liver steatosis and fibrosis using diffusion-weighted multicomponent T2 relaxometry. In a diet-induced mouse model of non-alcoholic fatty liver disease, the sensor achieved overall accuracies of 92% (Cohen's kappa, κ = 0.89) and 86% (κ = 0.78) in the ex vivo grading of steatosis and fibrosis, respectively. Localization of the measurements in living mice through frequency-dependent spatial encoding led to an overall accuracy of 87% (κ = 0.81) for the grading of steatosis. In human liver samples, the sensor graded steatosis with an overall accuracy of 93% (κ = 0.88). The use of T2 relaxometry as a sensitive measure in fully automated low-cost magnetic-resonance devices at the point of care would alleviate the accessibility and cost limits of magnetic-resonance imaging for diagnosing liver disease and assessing liver health before liver transplantation.

Viability testing of discarded livers with normothermic machine perfusion: Alleviating the organ shortage outweighs the cost

BACKGROUND

Over 700 donor livers are discarded annually in the United States due to high risk of poor graft function. The objective of this study was to determine the impact of using normothermic machine perfusion to identify transplantable livers among those currently discarded.

STUDY DESIGN

A series of 21 discarded human livers underwent viability assessment during normothermic machine perfusion. Cross-sectional analysis of the Scientific Registry of Transplant Recipients database and cost analysis was performed to extrapolate the case series to national experience.

RESULTS

21 discarded human livers were included in the perfusion cohort. 11 of 20 (55%) eligible grafts met viability criteria for transplantation. Grafts in the perfusion cohort had a similar donor risk index compared with discarded grafts (n = 1402) outside of New England in 2017 and 2018 (median [IQR]: 2.0 [1.5, 2.4] vs. 2.0 [1.7, 2.3], P = .40). 705 (IQR 677-741) livers were discarded annually in the United States since 2005, translating to the potential for 398 additional transplants nationally. The median cost to identify a transplantable graft with machine perfusion was $28,099 USD.

CONCLUSIONS

Normothermic machine perfusion of discarded livers could identify a significant number of transplantable grafts, significantly improving access to liver transplantation.

Multiorgan Metabolomics and Lipidomics Provide New Insights Into Fat Infiltration in the Liver, Muscle Wasting, and Liver-Muscle Crosstalk Following Burn Injury

Burn injury mediated hypermetabolic syndrome leads to increased mortality among severe burn victims, due to liver failure and muscle wasting. Metabolic changes may persist up to 2 years following the injury. Thus, understanding the underlying mechanisms of the pathology is crucially important to develop appropriate therapeutic approaches. We present detailed metabolomic and lipidomic analyses of the liver and muscle tissues in a rat model with a 30% body surface area burn injury located at the dorsal skin. Three hundred and thirty-eight of 1587 detected metabolites and lipids in the liver and 119 of 1504 in the muscle tissue exhibited statistically significant alterations. We observed excessive accumulation of triacylglycerols, decreased levels of S-adenosylmethionine, increased levels of glutamine and xenobiotics in the liver tissue. Additionally, the levels of gluconeogenesis, glycolysis, and tricarboxylic acid cycle metabolites are generally decreased in the liver. On the other hand, burn injury muscle tissue exhibits increased levels of acyl-carnitines, alpha-hydroxyisovalerate, ophthalmate, alpha-hydroxybutyrate, and decreased levels of reduced glutathione. The results of this preliminary study provide compelling observations that liver and muscle tissues undergo distinctly different changes during hypermetabolism, possibly reflecting liver-muscle crosstalk. The liver and muscle tissues might be exacerbating each other's metabolic pathologies, via excessive utilization of certain metabolites produced by each other.

Abstract 403: Leveraging the Zebrafish to Overcome Barriers in Heart Transplantation

Cardiac transplantation is the only curative therapy for patients with end-stage heart disease; however, there is a severe shortage of viable donor organs. Heart transplantation faces many interwoven challenges, including both biological factors and research limitations. For example, ischemia-reperfusion injury plays a role in early graft dysfunction and is associated with rejection episodes in heart transplantation. Moreover, experimental transplantation relies heavily on animal studies that are laborious and expensive, prohibiting the discovery of novel, bold solutions. We propose that the zebrafish, Danio rerio , would be a valuable tool for the field since it’s amenable to high-throughput screens, captures the complex structure of organs, and offers a suite of tools to monitor the biology of cardiac injury. Here, we develop a new subzero heart preservation method by strategically leveraging animal models from zebrafish to mammalian hearts. Using zebrafish larvae, we screened for agents which preserve hearts at -10°C. As a result of these screens, we identified promising preservative cocktails which restored heartbeat in 82% of larvae immediately post-recovery. Next, we excised adult zebrafish hearts and developed methods to mimic the ex vivo handling practices of hearts destined for transplant using a heart-on-a-plate assay. Using this assay, we carried forward promising agents identified in our initial zebrafish larvae screen to isolated adult zebrafish hearts that were cooled to -10°C and held for up to 24 hours. After rewarming, heart rate was restored and metabolic rate of zebrafish hearts was like time-matched controls (0.213 ± 0.047 and 0.275 ± 0.060, respectively, p = 0.200). Finally, we report our preliminary scale-up efforts whereby rodent hearts are stored for up to 24 hours at -10°C and viability were assessed by the TUNEL assay. The data shows high viability of cardiomyocytes post-preservation, as compared to controls. In summary, we present data to illustrate our efforts in leveraging the zebrafish to aid new discoveries in subzero heart preservation. Similar efforts to model heart transplantation in zebrafish may provide a different vantage point and enable us to make advances faster.

Tryptophan Metabolism via the Kynurenine Pathway: Implications for Graft Optimization during Machine Perfusion

Access to liver transplantation continues to be hindered by the severe organ shortage. Extended-criteria donor livers could be used to expand the donor pool but are prone to ischemia-reperfusion injury (IRI) and post-transplant graft dysfunction. Ex situ machine perfusion may be used as a platform to rehabilitate discarded or extended-criteria livers prior to transplantation, though there is a lack of data guiding the utilization of different perfusion modalities and therapeutics. Since amino acid derivatives involved in inflammatory and antioxidant pathways are critical in IRI, we analyzed differences in amino acid metabolism in seven discarded non-steatotic human livers during normothermic- (NMP) and subnormothermic-machine perfusion (SNMP) using data from untargeted metabolomic profiling. We found notable differences in tryptophan, histamine, and glutathione metabolism. Greater tryptophan metabolism via the kynurenine pathway during NMP was indicated by significantly higher kynurenine and kynurenate tissue concentrations compared to pre-perfusion levels. Livers undergoing SNMP demonstrated impaired glutathione synthesis indicated by depletion of reduced and oxidized glutathione tissue concentrations. Notably, ATP and energy charge ratios were greater in livers during SNMP compared to NMP. Given these findings, several targeted therapeutic interventions are proposed to mitigate IRI during liver machine perfusion and optimize marginal liver grafts during SNMP and NMP.

Specific Patterns of Postoperative Temperature Elevations Predict Blood Infection in Pediatric Burn Patients

Using readily available temperature data, we seek to propose a scoring criteria that can facilitate accurate and immediate prediction of blood infection. The standard in diagnosing blood infection is a positive blood culture result that may take up to 3 days to process, requiring providers to make a prediction about which febrile patient is actually bacteremic. This prediction is difficult in burned children as systemic inflammation can cause fever in the absence of infection. An ability to make this prediction more accurate using readily available information would be useful. A retrospective chart review was performed for 28 pediatric patients, with a burn size 20% or greater, admitted to the burn unit between 2010 and 2014. All children had blood cultures drawn. They were divided into either infection (positive blood cultures) or control (negative blood cultures) groups. Median temperature and mean number of temperature elevations were compared between the two groups. We evaluated the predictive accuracy of using temperature elevation, pattern, and timing to predict blood infection. A significant difference was seen in the mean number of temperature elevations above 39°C. This was significant for each time stage, especially in the 0- to 24-hour post-surgery period. We found the most predictive accuracy in the 0- to 12-, 12- to 38-, and 12- to 48-hour time periods. We found a strong association between mean number of fever spikes above 39°C and blood infection, especially 12 to 24 hours after surgery. This readily available data can be useful to clinicians as they access children with burns.

Subzero non-frozen preservation of human livers in the supercooled state

Preservation of human organs at subzero temperatures has been an elusive goal for decades. The major complication hindering successful subzero preservation is the formation of ice at temperatures below freezing. Supercooling, or subzero non-freezing, preservation completely avoids ice formation at subzero temperatures. We previously showed that rat livers can be viably preserved three times longer by supercooling as compared to hypothermic preservation at +4 °C. Scalability of supercooling preservation to human organs was intrinsically limited because of volume-dependent stochastic ice formation at subzero temperatures. However, we recently adapted the rat preservation approach so it could be applied to larger organs. Here, we describe a supercooling protocol that averts freezing of human livers by minimizing air-liquid interfaces as favorable sites of ice nucleation and uses preconditioning with cryoprotective agents to depress the freezing point of the liver tissue. Human livers are homogeneously preconditioned during multiple machine perfusion stages at different temperatures. Including preparation, the protocol takes 31 h to complete. Using this protocol, human livers can be stored free of ice at -4 °C, which substantially extends the ex vivo life of the organ. To our knowledge, this is the first detailed protocol describing how to perform subzero preservation of human organs.

Improvement of steatotic rat liver function with a defatting cocktail during ex situ normothermic machine perfusion is not directly related to liver fat content

There is a significant organ shortage in the field of liver transplantation, partly due to a high discard rate of steatotic livers from donors. These organs are known to function poorly if transplanted but make up a significant portion of the available pool of donated livers. This study demonstrates the ability to improve the function of steatotic rat livers using a combination of ex situ machine perfusion and a "defatting" drug cocktail. After 6 hours of perfusion, defatted livers demonstrated lower perfusate lactate levels and improved bile quality as demonstrated by higher bile bicarbonate and lower bile lactate. Furthermore, defatting was associated with decreased gene expression of pro-inflammatory cytokines and increased expression of enzymes involved in mitochondrial fatty acid oxidation. Rehabilitation of marginal or discarded steatotic livers using machine perfusion and tailored drug therapy can significantly increase the supply of donor livers for transplantation.