Normothermic machine perfusion versus static cold storage in donation after circulatory death kidney transplantation: a randomized controlled trial

[Machine perfusion in transplantation surgery]

The use of machine perfusion in solid organ transplantation has developed tremendously worldwide in recent years. Although the number of randomized controlled trials in the field of organ preservation is still limited, machine perfusion has been shown to be superior to static cold storage of donor organs. Various devices for clinical use with hypothermia or normothermia are already available for most organs. Whether and which perfusion strategy is superior to the others is the subject of current clinical research. This also applies to the further evaluation of possible synergistic effects in the sequential use of the various protocols. The common goal of all dynamic perfusion technologies is to optimize organ preservation between removal and transplantation. By testing the quality of marginal donor organs prior to transplantation, it should also be possible to use these organs without exposing the patient to increased risk. This can lead to a significant expansion of the donor pool. This is particularly important in Germany, where there is an ongoing shortage of organs and restrictive legislation regarding the expansion of the donor pool. Furthermore, the perfusion technology offers the possibility to serve as a platform for other ex situ and in situ therapies on isolated organs. In addition to the conditioning of pre-damaged organs for transplantation, this could lead to further applications in the context of targeted organ therapies and also to improved transplant logistics in the future.

The association between hemoglobin levels and renal function parameters during normothermic machine perfusion: A retrospective cohort study using porcine kidneys

BACKGROUND

Ex vivo normothermic machine perfusion (NMP) is a promising tool for assessing an isolated kidney prior to transplantation. However, there is no consensus on the perfusate's optimal oxygen-carrying capacity to support renal function. To investigate the association of hemoglobin levels with renal function parameters, a retrospective analysis of isolated, normothermically, perfused porcine kidneys was performed.

METHODS

Between 2015 and 2021, a total of 228 kidneys underwent 4 h of NMP with perfusates that varied in hemoglobin levels. A generalized linear model was used to determine the association of hemoglobin levels with time-weighted means of renal function markers, such as fractional sodium excretion (FENa) and creatinine clearance (CrCl). Stratified by baseline hemoglobin level (<4.5, 4.5-6, or >6 mmol/L), these markers were modeled over time using a generalized linear mixed-effects model. All models were adjusted for potential confounders.

RESULTS

Until a hemoglobin level of around 5 mmol/L was reached, increasing hemoglobin levels were associated with superior FENa and CrCl. Thereafter, this association plateaued. When hemoglobin levels were categorized, hemoglobin <4.5 mmol/L was associated with worse renal function. Hemoglobin levels were neither significantly associated with proteinuria during NMP nor with ATP levels at the end of NMP. Hemoglobin levels >6 mmol/L showed no additional benefits in renal function.

CONCLUSION

In conclusion, we found an association between baseline hemoglobin levels and superior renal function parameters, but not injury, during NMP of porcine kidneys. Furthermore, we show that performing a retrospective cohort study of preclinical data is feasible and able to answer additional questions, reducing the potential use of laboratory animals.

Impact of machine perfusion on transplant infectious diseases: New challenges and opportunities

Preservation techniques that maintain the viability of an organ graft between retrieval from the donor and implantation into the recipient remain a critical aspect of solid organ transplantation. While traditionally preservation is accomplished with static cold storage, advances in ex vivo dynamic machine perfusion, both hypothermic and normothermic, have allowed for prolongation of organ viability and recovery of marginal organs effectively increasing the usable donor pool. However, the use of these novel machine perfusion technologies likely exposes the recipient to additional infectious risk either through clonal expansion of pathogens derived during organ recovery or de novo exogenous acquisition of pathogens while the organ remains on the machine perfusion circuit. There is a paucity of high-quality studies that have attempted to quantify infection risk, although it appears that prolonging the time on the machine perfusion circuit and normothermic parameters increases the risk of infection. Conversely, the use of ex vivo machine perfusion unlocks new opportunities to detect and treat donor-derived infections before implantation into the recipient. This review seeks to reveal how the use of ex vivo machine perfusion strategies may augment the risk of infection in the organ recipient as well as outline ways that this technology could be leveraged to enhance our ability to manage donor-derived infections.

Diagnostic and Prognostic Value of Machine Perfusion Biomarkers in Kidney Graft Evaluation

BACKGROUND

With the rising prevalence of end-stage kidney disease, the use of expanded criteria donor allografts, seen as essential for meeting organ demand, still proves challenging due to their higher risk of graft loss, delayed function, and rejection. Machine perfusion, a technique in preserving allografts, offers improved allograft outcomes compared to static cold storage while allowing for the noninvasive measurement of kidney injury biomarkers in the perfusate solution. This offers an objective method to assess graft function at various preservation stages.

MATERIALS AND METHODS

We conducted a narrative review of the databases PubMed and Scopus, including studies written in the English language and published after 2010.

RESULTS

In this narrative review, we identified biomarkers, like 4-hydroxyproline, taurine, and glutathione transferase, as predictive markers of delayed graft function. Additionally, biomarkers, like extracellular histone h3, vascular cell adhesion protein, and matrix metalloprotease protein, have shown correlation with decreased graft function, although their predictive ability remains inconclusive.

DISCUSSION

The review outlines various suggestions for potential areas of research focus to enhance future expanded criteria donor allograft utilization. However, limitations exist, including the absence of a singular reliable biomarker and the challenges of validating biomarker effectiveness across diverse outcomes.

Combined Organ Transplantation in Patients with Advanced Liver Disease

Transplantation of the liver in combination with other organs is an increasingly performed procedure. Over the years, continuous improvement in survival could be realized through careful patient selection and refined organ preservation techniques, in spite of the challenges posed by aging recipients and donors, as well as the increased use of steatotic liver grafts. Herein, we revisit the epidemiology, allocation policies in different transplant zones, indications, and outcomes with regard to simultaneous organ transplants involving the liver, that is combined heart-liver, liver-lung, liver-kidney, and multivisceral transplantation. We address challenges surrounding combined organ transplantation such as equity, utility, and logistics of dual organ implantation, but also advantages that come along with combined transplantation, thereby focusing on molecular mechanisms underlying immunoprotection provided by the liver to the other allografts. In addition, the current standing and knowledge of machine perfusion in combined organ transplantation, mostly based on center experience, will be reviewed. Notwithstanding all the technical advances, shortage of organs, and the lack of universal eligibility criteria for certain multi-organ combinations are hurdles that need to be tackled in the future.

Normothermic Machine Perfusion and Normothermic Regional Perfusion of DCD Kidneys Before Transplantation: A Systematic Review

BACKGROUND

To overcome organ shortages, donation after circulatory death (DCD) kidneys are being increasingly used for transplantation. Prior research suggests that DCD kidneys have inferior outcomes compared with kidneys donated after brain death. Normothermic machine perfusion (NMP) and normothermic regional perfusion (NRP) may enhance the preservation of DCD kidneys and improve transplant outcomes. This study aimed to review the evidence surrounding NMP and NRP in DCD kidney transplantation.

METHODS

Two independent reviewers conducted searches for all publications reporting outcomes for NMP and NRP-controlled DCD kidneys, focusing on delayed graft function, primary nonfunction, graft function, graft survival, and graft utilization. Weighted means were calculated for all relevant outcomes and controls. Formal meta-analyses could not be conducted because of significant heterogeneity.

RESULTS

Twenty studies were included for review (6 NMP studies and 14 NRP studies). Delayed graft function rates seemed to be lower for NRP kidneys (24.6%) compared with NMP kidneys (54.3%). Both modalities yielded similar outcomes with respect to primary nonfunction (NMP 3.3% and NRP 5.6%), graft function (12-mo creatinine 149.3 μmol/L for NMP and 129.9 μmol/L for NRP), and graft utilization (NMP 83.3% and NRP 89%). Although no direct comparisons exist, our evidence suggests that both modalities have good short- and medium-term graft outcomes and high graft survival rates.

CONCLUSIONS

Current literature demonstrates that both NMP and NRP are feasible strategies that may increase donor organ utilization while maintaining acceptable transplant outcomes and likely improved outcomes compared with cold-stored DCD kidneys. Further research is needed to directly compare NRP and NMP outcomes.

Normothermic and hypothermic machine perfusion preservation versus static cold storage for deceased donor kidney transplantation

BACKGROUND

Kidney transplantation is the optimal treatment for kidney failure. Donation, transport and transplant of kidney grafts leads to significant ischaemia reperfusion injury. Static cold storage (SCS), whereby the kidney is stored on ice after removal from the donor until the time of implantation, represents the simplest preservation method. However, technology is now available to perfuse or "pump" the kidney during the transport phase ("continuous") or at the recipient centre ("end-ischaemic"). This can be done at a variety of temperatures and using different perfusates. The effectiveness of these treatments manifests as improved kidney function post-transplant.

OBJECTIVES

To compare machine perfusion (MP) technologies (hypothermic machine perfusion (HMP) and (sub) normothermic machine perfusion (NMP)) with each other and with standard SCS.

SEARCH METHODS

We contacted the information specialist and searched the Cochrane Kidney and Transplant Register of Studies until 15 June 2024 using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Registry Platform (ICTRP) Search Portal, and ClinicalTrials.gov.

SELECTION CRITERIA

All randomised controlled trials (RCTs) and quasi-RCTs comparing machine perfusion techniques with each other or versus SCS for deceased donor kidney transplantation were eligible for inclusion. All donor types were included (donor after circulatory death (DCD) and brainstem death (DBD), standard and extended/expanded criteria donors). Both paired and unpaired studies were eligible for inclusion.

DATA COLLECTION AND ANALYSIS

The results of the literature search were screened, and a standard data extraction form was used to collect data. Both of these steps were performed by two independent authors. Dichotomous outcome results were expressed as risk ratios (RR) with 95% confidence intervals (CI). Survival analyses (time-to-event) were performed with the generic inverse variance meta-analysis of hazard ratios (HR). Continuous scales of measurement were expressed as a mean difference (MD). Random effects models were used for data analysis. The primary outcome was the incidence of delayed graft function (DGF). Secondary outcomes included graft survival, incidence of primary non-function (PNF), DGF duration, economic implications, graft function, patient survival and incidence of acute rejection. Confidence in the evidence was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach.

MAIN RESULTS

Twenty-two studies (4007 participants) were included. The risk of bias was generally low across all studies and bias domains. The majority of the evidence compared non-oxygenated HMP with standard SCS (19 studies). The use of non-oxygenated HMP reduces the rate of DGF compared to SCS (16 studies, 3078 participants: RR 0.78, 95% CI 0.69 to 0.88; P < 0.0001; I2 = 31%; high certainty evidence). Subgroup analysis revealed that continuous (from donor hospital to implanting centre) HMP reduces DGF (high certainty evidence). In contrast, this benefit over SCS was not seen when non-oxygenated HMP was not performed continuously (low certainty evidence). Non-oxygenated HMP reduces DGF in both DCD and DBD settings in studies performed in the 'modern era' and when cold ischaemia times (CIT) were short. The number of perfusions required to prevent one episode of DGF was 7.69 and 12.5 in DCD and DBD grafts, respectively. Continuous non-oxygenated HMP versus SCS also improves one-year graft survival (3 studies, 1056 participants: HR 0.46, 0.29 to 0.75; P = 0.002; I2 = 0%; high certainty evidence). Assessing graft survival at maximal follow-up confirmed a benefit of continuous non-oxygenated HMP over SCS (4 studies, 1124 participants (follow-up 1 to 10 years): HR 0.55, 95% CI 0.40 to 0.77; P = 0.0005; I2 = 0%; high certainty evidence). This effect was not seen in studies where HMP was not continuous. The effect of non-oxygenated HMP on our other outcomes (PNF, incidence of acute rejection, patient survival, hospital stay, long-term graft function, duration of DGF) remains uncertain. Studies performing economic analyses suggest that HMP is either cost-saving (USA and European settings) or cost-effective (Brazil). One study investigated continuous oxygenated HMP versus non-oxygenated HMP (low risk of bias in all domains); the simple addition of oxygen during continuous HMP leads to additional benefits over non-oxygenated HMP in DCD donors (> 50 years), including further improvements in graft survival, improved one-year kidney function, and reduced acute rejection. One large, high-quality study investigated end-ischaemic oxygenated HMP versus SCS and found end-ischaemic oxygenated HMP (median machine perfusion time 4.6 hours) demonstrated no benefit compared to SCS. The impact of longer periods of end-ischaemic HMP is unknown. One study investigated NMP versus SCS (low risk of bias in all domains). One hour of end ischaemic NMP did not improve DGF compared with SCS alone. An indirect comparison revealed that continuous non-oxygenated HMP (the most studied intervention) was associated with improved graft survival compared with end-ischaemic NMP (indirect HR 0.31, 95% CI 0.11 to 0.92; P = 0.03). No studies investigated normothermic regional perfusion (NRP) or included any donors undergoing NRP.

AUTHORS' CONCLUSIONS

Continuous non-oxygenated HMP is superior to SCS in deceased donor kidney transplantation, reducing DGF, improving graft survival and proving cost-effective. This is true for both DBD and DCD kidneys, both short and long CITs, and remains true in the modern era (studies performed after 2008). In DCD donors (> 50 years), the simple addition of oxygen to continuous HMP further improves graft survival, kidney function and acute rejection rate compared to non-oxygenated HMP. Timing of HMP is important, and benefits have not been demonstrated with short periods (median 4.6 hours) of end-ischaemic HMP. End-ischaemic NMP (one hour) does not confer meaningful benefits over SCS alone and is inferior to continuous HMP in an indirect comparison of graft survival. Further studies assessing NMP for viability assessment and therapeutic delivery are warranted and in progress.

Utilizing pathophysiological concepts of ischemia-reperfusion injury to design renoprotective strategies and therapeutic interventions for normothermic ex vivo kidney perfusion

Normothermic machine perfusion (NMP) has emerged as a promising tool for the preservation, viability assessment, and repair of deceased-donor kidneys prior to transplantation. These kidneys inevitably experience a period of ischemia during donation, which leads to ischemia-reperfusion injury when NMP is subsequently commenced. Ischemia-reperfusion injury has a major impact on the renal vasculature, metabolism, oxygenation, electrolyte balance, and acid-base homeostasis. With an increased understanding of the underlying pathophysiological mechanisms, renoprotective strategies and therapeutic interventions can be devised to minimize additional injury during normothermic reperfusion, ensure the safe implementation of NMP, and improve kidney quality. This review discusses the pathophysiological alterations in the vasculature, metabolism, oxygenation, electrolyte balance, and acid-base homeostasis of deceased-donor kidneys and delineates renoprotective strategies and therapeutic interventions to mitigate renal injury and improve kidney quality during NMP.

Unlocking Transplant Tolerance with Biomaterials

For patients suffering from organ failure due to injury or autoimmune disease, allogeneic organ transplantation with chronic immunosuppression is considered the god standard in terms of clinical treatment. However, the true "holy grail" of transplant immunology is operational tolerance, in which the recipient exhibits a sustained lack of alloreactivity toward unencountered antigen presented by the donor graft. This outcome is resultant from critical changes to the phenotype and genotype of the immune repertoire predicated by the activation of specific signaling pathways responsive to soluble and mechanosensitive cues. Biomaterials have emerged as a medium for interfacing with and reprogramming these endogenous pathways toward tolerance in precise, minimally invasive, and spatiotemporally defined manners. By viewing seminal and contemporary breakthroughs in transplant tolerance induction through the lens of biomaterials-mediated immunomodulation strategies-which include intrinsic material immunogenicity, the depot effect, graft coatings, induction and delivery of tolerogenic immune cells, biomimicry of tolerogenic immune cells, and in situ reprogramming-this review emphasizes the stunning diversity of approaches in the field and spotlights exciting future directions for research to come.

Delayed Graft Function and the Renin-angiotensin System

Delayed graft function (DGF) is a form of acute kidney injury (AKI) and a common complication following kidney transplantation. It adversely influences patient outcomes increases the financial burden of transplantation, and currently, no specific treatments are available. In developing this form of AKI, activation of the renin-angiotensin system (RAS) has been proposed to play an important role. In this review, we discuss the role of RAS activation and its contribution to the pathophysiology of DGF following the different stages of the transplantation process, from procurement and ischemia to transplantation into the recipient and including data from experimental animal models. Deceased kidney donors, whether during cardiac or brain death, may experience activation of the RAS. That may be continued or further potentiated during procurement and organ preservation. Additional evidence suggests that during implantation of the kidney graft and reperfusion in the recipient, the RAS is activated and may likely remain activated, extrapolating from other forms of AKI where RAS overactivity is well documented. Of particular interest in this setting is the status of angiotensin-converting enzyme 2, a key RAS enzyme essential for the metabolism of angiotensin II and abundantly present in the apical border of the proximal tubules, which is the site of predominant injury in AKI and DGF. Interventions aimed at safely downregulating the RAS using suitable shorter forms of angiotensin-converting enzyme 2 could be a way to offer protection against DGF.

Normothermic Preservation of the Intestinal Allograft

Intestinal allotransplantation was first described in the 1960s and successfully performed in the 1980s. Since that time, less progress has been made in the preservation of the allograft before transplantation and static cold storage remains the current standard. Normothermic machine perfusion represents an opportunity to simultaneously preserve, assess, and recondition the organ for transplantation and improve the procurement radius for allografts. The substantial progress made in the field during the last 60 years, coupled with the success of the preclinical animal model of machine perfusion-preserved intestinal transplantation, suggest we are approaching the point of clinical application.

Simultaneous Heart and Kidney Transplantation: A Systematic Review and Proportional Meta-Analysis of Its Characteristics and Long-Term Variables

Patients with end-stage heart disease who undergo a heart transplant frequently have simultaneous kidney insufficiency, therefore simultaneous heart and kidney transplantation is an option and it is necessary to understand its characteristics and long-term variables. The recipient characteristics and operative and long-term variables were assessed in a meta-analysis. A total of 781 studies were screened, and 33 were thoroughly reviewed. 15 retrospective cohort studies and 376 patients were included. The recipient's mean age was 51.1 years (95% CI 48.52-53.67) and 84% (95% CI 80-87) were male. 71% (95% CI 59-83) of the recipients were dialysis dependent. The most common indication was ischemic cardiomyopathy [47% (95% CI 41-53)] and cardiorenal syndrome [22% (95% CI 9-35)]. Also, 33% (95% CI 20-46) of the patients presented with delayed graft function. During the mean follow-up period of 67.49 months (95% CI 45.64-89.33), simultaneous rejection episodes of both organ allografts were described in 5 cases only. Overall survival was 95% (95% CI 88-100) at 30 days, 81% (95% CI 76-86) at 1 year, 79% (95% CI 71-87) at 3, and 71% (95% CI 59-83) at 5 years. Simultaneous heart and kidney transplantation is an important option for concurrent cardiac and renal dysfunction and has acceptable rejection and survival rates.

Perfusion Techniques in Kidney Allograft Preservation to Reduce Ischemic Reperfusion Injury: A Systematic Review and Meta-Analysis

The limited supply and rising demand for kidney transplantation has led to the use of allografts more susceptible to ischemic reperfusion injury (IRI) and oxidative stress to expand the donor pool. Organ preservation and procurement techniques, such as machine perfusion (MP) and normothermic regional perfusion (NRP), have been developed to preserve allograft function, though their long-term outcomes have been more challenging to investigate. We performed a systematic review and meta-analysis to examine the benefits of MP and NRP compared to traditional preservation techniques. PubMed (MEDLINE), Embase, Cochrane, and Scopus databases were queried, and of 13,794 articles identified, 54 manuscripts were included (n = 41 MP; n = 13 NRP). MP decreased the rates of 12-month graft failure (OR 0.67; 95%CI 0.55, 0.80) and other perioperative outcomes such as delayed graft function (OR 0.65; 95%CI 0.54, 0.79), primary nonfunction (OR 0.63; 95%CI 0.44, 0.90), and hospital length of stay (15.5 days vs. 18.4 days) compared to static cold storage. NRP reduced the rates of acute rejection (OR 0.48; 95%CI 0.35, 0.67) compared to in situ perfusion. Overall, MP and NRP are effective techniques to mitigate IRI and play an important role in safely expanding the donor pool to satisfy the increasing demands of kidney transplantation.

A cell-free nutrient-supplemented perfusate allows four-day ex vivo metabolic preservation of human kidneys

The growing disparity between the demand for transplants and the available donor supply, coupled with an aging donor population and increasing prevalence of chronic diseases, highlights the urgent need for the development of platforms enabling reconditioning, repair, and regeneration of deceased donor organs. This necessitates the ability to preserve metabolically active kidneys ex vivo for days. However, current kidney normothermic machine perfusion (NMP) approaches allow metabolic preservation only for hours. Here we show that human kidneys discarded for transplantation can be preserved in a metabolically active state up to 4 days when perfused with a cell-free perfusate supplemented with TCA cycle intermediates at subnormothermia (25 °C). Using spatially resolved isotope tracing we demonstrate preserved metabolic fluxes in the kidney microenvironment up to Day 4 of perfusion. Beyond Day 4, significant changes were observed in renal cell populations through spatial lipidomics, and increases in injury markers such as LDH, NGAL and oxidized lipids. Finally, we demonstrate that perfused kidneys maintain functional parameters up to Day 4. Collectively, these findings provide evidence that this approach enables metabolic and functional preservation of human kidneys over multiple days, establishing a solid foundation for future clinical investigations.

Ex vivo kidney machine perfusion: meta-analysis of randomized clinical trials

BACKGROUND

Machine perfusion is an organ preservation strategy used to improve function over simple storage in a cold environment. This article presents an updated systematic review and meta-analysis of machine perfusion in deceased donor kidneys.

METHODS

RCTs from November 2018 to July 2023 comparing machine perfusion versus static cold storage in kidney transplantation were evaluated for systematic review. The primary outcome in meta-analysis was delayed graft function.

RESULTS

A total 19 studies were included, and 16 comparing hypothermic machine perfusion with static cold storage were analysed. The risk of delayed graft function was lower with hypothermic machine perfusion (risk ratio (RR) 0.77, 95% c.i. 0.69 to 0.86), even in kidneys after circulatory death (RR 0.78, 0.68 to 0.90) or brain death (RR 0.73, 0.63 to 0.84). Full hypothermic machine perfusion decreased the risk of delayed graft function (RR 0.69, 0.60 to 0.79), whereas partial hypothermic machine perfusion did not (RR 0.92, 0.69 to 1.22). Normothermic machine perfusion or short-term oxygenated hypothermic machine perfusion preservation after static cold storage was equivalent to static cold storage in terms of delayed graft function and 1-year graft survival.

CONCLUSION

Hypothermic machine perfusion reduces delayed graft function risks and normothermic approaches show promise.

Pre-transplant kidney quality evaluation using photoacoustic imaging during normothermic machine perfusion

Due to the shortage of kidneys donated for transplantation, surgeons are forced to use the organs with an elevated risk of poor function or even failure. Although the existing methods for pre-transplant quality evaluation have been validated over decades in population cohort studies across the world, new methods are needed as long as delayed graft function or failure in a kidney transplant occurs. In this study, we explored the potential of utilizing photoacoustic (PA) imaging during normothermic machine perfusion (NMP) as a means of evaluating kidney quality. We closely monitored twenty-two porcine kidneys using 3D PA imaging during a two-hour NMP session. Based on biochemical analyses of perfusate and produced urine, the kidneys were categorized into 'non-functional' and 'functional' groups. Our primary focus was to quantify oxygenation (sO2) within the kidney cortical layer of depths 2 mm, 4 mm, and 6 mm using two-wavelength PA imaging. Next, receiver operating characteristic (ROC) analysis was performed to determine an optimal cortical layer depth and time point for the quantification of sO2 to discriminate between functional and non-functional organs. Finally, for each depth, we assessed the correlation between sO2 and creatinine clearance (CrCl), oxygen consumption (VO2), and renal blood flow (RBF). We found that hypoxia of the renal cortex is associated with poor renal function. In addition, the determination of sO2 within the 2 mm depth of the renal cortex after 30 min of NMP effectively distinguishes between functional and non-functional kidneys. The non-functional kidneys can be detected with the sensitivity and specificity of 80% and 85% respectively, using the cut-off point of sO2 < 39%. Oxygenation significantly correlates with RBF and VO2 in all kidneys. In functional kidneys, sO2 correlated with CrCl, which is not the case for non-functional kidneys. We conclude that the presented technique has a high potential for supporting organ selection for kidney transplantation.

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.

Enzymatic conversion of human blood group A kidneys to universal blood group O

ABO blood group compatibility restrictions present the first barrier to donor-recipient matching in kidney transplantation. Here, we present the use of two enzymes, FpGalNAc deacetylase and FpGalactosaminidase, from the bacterium Flavonifractor plautii to enzymatically convert blood group A antigens from the renal vasculature of human kidneys to 'universal' O-type. Using normothermic machine perfusion (NMP) and hypothermic machine perfusion (HMP) strategies, we demonstrate blood group A antigen loss of approximately 80% in as little as 2 h NMP and HMP. Furthermore, we show that treated kidneys do not bind circulating anti-A antibodies in an ex vivo model of ABO-incompatible transplantation and do not activate the classical complement pathway. This strategy presents a solution to the donor organ shortage crisis with the potential for direct clinical translation to reduce waiting times for patients with end stage renal disease.

Association of procurement technique with organ yield and cost following donation after circulatory death

Donation after circulatory death (DCD) could account for the largest expansion of the donor allograft pool in the contemporary era. However, the organ yield and associated costs of normothermic regional perfusion (NRP) compared to super-rapid recovery (SRR) with ex-situ normothermic machine perfusion, remain unreported. The Organ Procurement and Transplantation Network (December 2019 to June 2023) was analyzed to determine the number of organs recovered per donor. A cost analysis was performed based on our institution's experience since 2022. Of 43 502 donors, 30 646 (70%) were donors after brain death (DBD), 12 536 (29%) DCD-SRR and 320 (0.7%) DCD-NRP. The mean number of organs recovered was 3.70 for DBD, 3.71 for DCD-NRP (P < .001), and 2.45 for DCD-SRR (P < .001). Following risk adjustment, DCD-NRP (adjusted odds ratio 1.34, confidence interval 1.04-1.75) and DCD-SRR (adjusted odds ratio 2.11, confidence interval 2.01-2.21; reference: DBD) remained associated with greater odds of allograft nonuse. Including incomplete and completed procurement runs, the total average cost of DCD-NRP was $9463.22 per donor. By conservative estimates, we found that approximately 31 donor allografts could be procured using DCD-NRP for the cost equivalent of 1 allograft procured via DCD-SRR with ex-situ normothermic machine perfusion. In conclusion, DCD-SRR procurements were associated with the lowest organ yield compared to other procurement methods. To facilitate broader adoption of DCD procurement, a comprehensive understanding of the trade-offs inherent in each technique is imperative.

Exploring the effects of epigallocatechin gallate on lipid metabolism in the rat steatotic liver during normothermic machine perfusion: Insights from lipidomics and RNA sequencing

BACKGROUND

Hepatic steatosis is the leading cause of discarded liver grafts. Defatting steatotic liver grafts using drug combinations during ex vivo normothermic machine perfusion (NMP) has been reported. However, the effectiveness of NMP in reducing fat content using epigallocatechin gallate (EGCG) as a single defatting agent and its effect on lipid metabolism are poorly investigated.

METHODS

In this study, an NMP system was set up to perfuse a steatotic liver from a rat model with 10 mM EGCG. Livers without EGCG served as NMP controls, whereas static cold-preserved livers in the University of Wisconsin medium were used as static cold storage controls. Liver enzyme, reactive oxygen species (ROS), histology, and lipid content assessments were conducted post-perfusion, complemented by lipidomics, RNA sequencing, and western blotting to determine the lipid metabolism changes.

RESULTS

EGCG during NMP reduced hepatocellular injury markers and defatted steatotic liver grafts. Additionally, we observed a significant increase in triglyceride (TG) content in the perfusate post-NMP in the NMP + EGCG group, suggesting TG output from the liver. Furthermore, lipidomics analysis revealed that EGCG primarily affected metabolites involved in glycerophospholipid (GP) and glycerolipid (GL) metabolism. Further, the RNA sequencing indicated the modulation of these metabolic pathways via ECGC, which was associated with the downregulated Lpin1 and Gpat3 expression.

CONCLUSIONS

EGCG defats steatotic livers as a single defatting agent during NMP by promoting GL and GP metabolism via decreasing Lpin1 and Agpat9 levels.

Ex vivo normothermic preservation of a kidney graft from uncontrolled donation after circulatory death over 73 hours

The transplant community is focused on prolonging the ex vivo preservation time of kidney grafts to allow for long-distance kidney graft transportation, assess the viability of marginal grafts, and optimize a platform for the translation of innovative therapeutics to clinical practice, especially those focused on cell and vector delivery to organ conditioning and reprogramming. We describe the first case of feasible preservation of a kidney from a donor after uncontrolled circulatory death over a 73-h period using normothermic perfusion and analyze hemodynamic, biochemical, histological, and transcriptomic parameters for inflammation and kidney injury. The mean pressure and flow values were 71.24 ± 9.62 mmHg and 99.65 ± 18.54 mL/min, respectively. The temperature range was 36.7°C-37.2°C. The renal resistance index was 0.75 ± 0.15 mmHg/mL/min. The mean pH was 7.29 ± 0.15. The lactate concentration peak increased until 213 mg/dL at 6 h, reaching normal values after 34 h of perfusion (8.92 mg/dL). The total urine output at the end of perfusion was 1.185 mL. Histological analysis revealed no significant increase in acute tubular necrosis (ATN) severity as perfusion progressed. The expression of KIM-1, VEGF, and TGFβ decreased after 6-18 h of perfusion until 60 h in which the expression of these genes increased again together with the expression of β-catenin, Ki67, and TIMP1. We show that normothermic perfusion can maintain a kidney graft viable ex vivo for 3 days, thus allowing a rapid translation of pre-clinical therapeutics to clinical practice.

Organ storage in renal transplantation

PURPOSE OF REVIEW

Kidney transplantation is vital for those with end-stage renal disease, enhancing quality of life and longevity. It is the preferred treatment but is hindered by a global disparity between donor kidney availability and demand. Therefore, optimizing organ storage techniques is crucial to mitigate the effects of ischemia reperfusion injury in available organs. Recent interest has centered on innovative methods like oxygenated normothermic perfusion and abdominal regional perfusion.

RECENT FINDINGS

Multiple recent metanalyses, including a Cochrane review, confirm the benefits of hypothermic machine perfusion (HMP) for deceased donor kidneys, demonstrating its utility and cost effectiveness. The benefits of oxygenated normothermic perfusion have been seen in retrospective data sets but not in prospective trials. Abdominal regional perfusion (aNRP) is gaining interest, especially for liver transplantation, but kidney specific data are scant.

SUMMARY

High-quality evidence backs the use of HMP for deceased donor kidneys. Despite interest in other techniques, clinical evidence for their benefits in kidney transplantation is lacking. The gap between innovation and verified success emphasizes the need for continued research and collaboration between medical professionals, researchers, and ethical committees. This review aims to further illuminate the complexities and advancements in the field, bridging the knowledge gap and aiding in the continual pursuit of excellence in transplantation.

British Transplantation Society guidelines on abdominal organ transplantation from deceased donors after circulatory death

The British Transplantation Society (BTS) 'Guideline on transplantation from deceased donors after circulatory death' has recently been updated and this manuscript summarises the relevant recommendations in abdominal organ transplantation from Donation after Circulatory Death (DCD) donors, encompassing the chapters on liver, kidney, pancreas and islet cell transplantation.

Normothermic ex vivo perfusion of deceased donor kidneys and its clinical potential in kidney transplantation outcomes

In recent years, normothermic machine perfusion (NMP) has emerged in conversation surrounding organ preservation and transplantation techniques with the goal of improving patient and clinical outcomes. This is in great attempt to address the rate of non-utilization and the shortage of available organs in kidney transplantation. This focus in mind, normothermic perfusion presents itself as a potential tool to mimic physiological conditions and improve current preservation methods, such as static cold storage. This review serves to improve understanding of the observed connection between the consequences of ischemia and reperfusion injury and traditional preservation techniques as well as how renal NMP may mitigate these issues. Previous studies suggest that reducing time in static cold storage methods by promoting the normothermic perfusion model results in decreased delayed graft function and post-transplant complications. This review also aims to present the immense clinical potential NMP has on future kidney transplantation success and what this means for the fields of nephrology and transplantation. While great strides have been made to evaluate normothermic perfusion's impact on kidney graft viability and transplant success, future research into unified protocol, clinically relevant biomarkers, cost-utility analysis, and use with associated therapeutic and imaging modalities is paramount.

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.

48 h Normothermic Machine Perfusion With Urine Recirculation for Discarded Human Kidney Grafts

Normothermic machine perfusion (NMP) has reshaped organ preservation in recent years. In this preclinical study, prolonged normothermic perfusions of discarded human kidney grafts were performed in order to investigate perfusion dynamics and identify potential quality and assessment indicators. Five human discarded kidney grafts were perfused normothermically (37°C) for 48 h using the Kidney Assist device with a red-blood-cell based perfusate with urine recirculation. Perfusion dynamics, perfusate and urine composition as well as injury markers were measured and analyzed. Donor age ranged from 41 to 68 years. All but one kidney were from brain dead donors. Perfusions were performed successfully for 48 h with all discarded kidneys. Median arterial flow ranged from 405 to 841 mL/min. All kidneys excreted urine until the end of perfusion (median 0.43 mL/min at the end of perfusion). While sodium levels were consistently lower in urine compared to perfusate samples, this was only seen for chloride and potassium in kidney KTX 2. Lactate, AST, LDH as well as pro-inflammatory cytokines increased over time, especially in kidneys KTX 3 and 4. Ex vivo normothermic perfusion is able to identify patterns of perfusion, biological function, and changes in inflammatory markers in heterogenous discarded kidney grafts.

Long and Short-Term Effects of Hypothermic Machine Perfusion vs. Cold Storage on Transplanted Kidneys from Expanded Criteria Donors-A Matched Comparison Study

Hypothermic machine perfusion (HMP) has been shown to reduce delayed graft function (DGF)-rates in kidneys from expanded criteria donors (ECD) and may increase graft survival compared with static cold storage (SCS). This single-center, retrospective observational study aimed to evaluate this effect. The primary endpoint was the DGF-rate, defined as the use of dialysis in the first postoperative week, excluding the first 24 h. The main secondary endpoint was graft survival at 5 years. Recipients of ECD-kidneys between 2013 and 2021 with ≤2 grafts were included (n = 438). The SCS-kidneys were marginal-matched by propensity score to the HMP-group for donor age, cold ischemia time, and graft number. Multivariable adjusted analysis for confounders in the unmatched cohort and caliper-based ID-matching constituted sensitivity analyses. HMP showed a trend to lower DGF-rate in the marginal-matched comparison (9.2% vs. 16.1%, p = 0.063). This was strengthened by a significant benefit observed for HMP in both the sensitivity analyses: an adjusted OR of 0.45 (95% CI: 0.24; 0.84; p = 0.012) in the multivariable analysis and DGF-rate of 8.7% vs. 17.4% (p = 0.024) after ID-matching. The 5-year graft survival rate was >90% in both groups, with no benefit using HMP (HR = 0.79; 95% CI:0.39-1.16; p = 0.52). Our results suggest that HMP may be effective in decreasing DGF-rates, however, without any significant benefit in graft survival.