Associations of Perfusate Biomarkers and Pump Parameters With Delayed Graft Function and Deceased Donor Kidney Allograft Function

Tissue-resident Lymphocytes Are Released During Hypothermic and Normothermic Machine Perfusion of Human Donor Kidneys

BACKGROUND

Machine perfusion is the preferred preservation method for deceased donor kidneys. Perfusate fluid, which contains a complex mixture of components, offers potential insight into the organ's viability and function. This study explored immune cell release, particularly tissue-resident lymphocytes (TRLs), during donor kidney machine perfusion and its correlation with injury markers.

METHODS

Perfusate samples from hypothermic machine perfusion (HMP; n = 26) and normothermic machine perfusion (NMP; n = 16) of human donor kidneys were analyzed for TRLs using flow cytometry. Residency was defined by expressions of CD69, CD103, and CD49as. TRL release was quantified exclusively in NMP. Additionally, levels of cell-free DNA, neutrophil gelatinase-associated lipocalin, and soluble E-cadherin (sE-cadherin) were measured in NMP supernatants with quantitative polymerase chain reaction and enzyme-linked immunosorbent assay.

RESULTS

Both HMP and NMP samples contained a heterogeneous population of TRLs, including CD4 + tissue-resident memory T cells, CD8 + tissue-resident memory T cells, tissue-resident natural killer cells, tissue-resident natural killer T cells, and helper-like innate lymphoid cells. Median TRL proportions among total CD45 + lymphocytes were 0.89% (NMP) and 0.84% (HMP). TRL quantities in NMP did not correlate with donor characteristics, perfusion parameters, posttransplant outcomes, or cell-free DNA and neutrophil gelatinase-associated lipocalin concentrations. However, CD103 + TRL release positively correlated with the release of sE-cadherin, the ligand for the CD103 integrin.

CONCLUSIONS

Human donor kidneys release TRLs during both HMP and NMP. The release of CD103 + TRLs was associated with the loss of their ligand sE-cadherin but not with general transplant injury biomarkers.

Impact of Deceased-donor Acute Kidney Injury on Kidney Transplantation

Even as record numbers of deceased donors are undergoing organ recovery, the global transplant community continues to struggle with a shortage of donor organs and a high organ discard rate. Acute kidney injury (AKI) occurs in many hospitalized patients, including up to 25% of patients in critical condition. Registry studies have shown a significant increase in nonrecovery or organ discard rates in AKI donors, despite most studies reporting similar clinical outcomes compared with non-AKI donors. This review aims to capture the salient information learned from these studies and to summarize the efforts that have been made to gain a more granular understanding of how kidneys from donors with AKI behave posttransplant. In particular, we reviewed the studies that analyzed the clinical outcomes in different stages of AKI and AKI in marginal donors, such as kidney donor profile index of >85%, older donors, and donation after circulatory death donors. We summarized studies investigating molecular biomarkers, transcriptomics, and possible future therapeutic targets for postdonation AKI.

Noninvasive measurement of 13Carbon turnover for evaluation of porcine renal grafts during ex vivo machine perfusion

BACKGROUND

Kidney transplantation suffers from a shortage of donor organs. Despite this, a lot of grafts are discarded due to inadequate quality. As many kidneys are afflicted by transient filtration failure early after preservation, classical renal function tests are not applicable to differentiate between prospective recovery or continuing deficit of renal function.

METHODS

Using normothermic machine perfusion as a platform for pre-implantation evaluation of the graft, we present a novel evaluative approach based on the metabolic turnover of 13C-acetate during isolated perfusion. After injection of the tracer, 13CO2 as a metabolic end-product can be quantified by high-precision laser-based spectroscopy in the gas outflow of the oxygenator. Three groups of porcine kidneys with graduated ischemic injury were investigated.

RESULTS

This quantitative approach is able to discriminate acceptable quality kidneys, most likely to recover within days from poor kidney grafts that are unlikely to regain notable glomerular function with high discriminatory power (area under the ROC curve 0.91; P < 0.001 By contrast, conventional renal function tests are rather ineffective under these circumstances.

CONCLUSIONS

This assessment method offers the potential to quantitatively assess donor kidney quality using a measurable output, salvaging donors that would otherwise have been discarded.

Outcomes of Kidney Perfusion Techniques in Transplantation from Deceased Donors: A Systematic Review and Meta-Analysis

The high demand for organs in kidney transplantation and the expansion of the donor pool have led to the widespread implementation of machine perfusion technologies. In this study, we aim to provide an up-to-date systematic review of the developments in this expanding field over the past 10 years, with the aim of answering the question: "which perfusion technique is the most promising technique in kidney transplantation?" A systematic review of the literature related to machine perfusion in kidney transplantation was performed. The primary outcome measure was delayed graft function (DGF), and secondary outcomes included rates of rejection, graft survival, and patient survival rates after 1 year. Based on the available data, a meta-analysis was performed. The results were compared with data from static cold storage, which is still the standard of care in many centers worldwide. A total of 56 studies conducted in humans were included, and 43 studies reported outcomes of hypothermic machine perfusion (HMP), with a DGF rate of 26.4%. A meta-analysis of 16 studies showed significantly lower DGF rates in the HMP group compared to those of static cold storage (SCS). Five studies reported outcomes of hypothermic machine perfusion + O₂, with an overall DGF rate of 29.7%. Two studies explored normothermic machine perfusion (NMP). These were pilot studies, designed to assess the feasibility of this perfusion approach in the clinical setting. Six studies reported outcomes of normothermic regional perfusion (NRP). The overall incidence of DGF was 71.5%, as it was primarily used in uncontrolled DCD (Maastricht category I-II). Three studies comparing NRP to in situ cold perfusion showed a significantly lower rate of DGF with NRP. The systematic review and meta-analysis provide evidence that dynamic preservation strategies can improve outcomes following kidney transplantation. More recent approaches such as normothermic machine perfusion and hypothermic machine perfusion + O₂ do show promising results but need further results from the clinical setting. This study shows that the implementation of perfusion strategies could play an important role in safely expanding the donor pool.

First Multicenter Clinical Trial on Machine Perfusion Preservation for Marginal Donor Kidney Transplantation in Japan

BACKGROUND

Machine perfusion has not been widely used because of its low demand in Japan; however, we believe its advantages may increase the number of organ transplants.

METHODS

Here, we report the first clinical trial of machine perfusion for kidney transplantation in Japan. We used the CMP-X08 perfusion device (Chuo-Seiko Co, Ltd, Asahikawa, Hokkaido, Japan) to preserve the donated organs. The flow rate, perfusion pressure, renal resistance, and temperature were monitored during continuous hypothermic perfusion.

RESULTS

From August 2020 to the present, 13 cases of perfusion-preserved kidney transplantation have been performed. Of these, ten and 3 cases were performed using organs donated after brain death (DBD) and cardiac death (DCD), respectively. The average age of the recipients was 55.9 ± 7.3 (45-66) years. The average dialysis period was 14.8 ± 8.4 (0-26) years. The donor's final creatinine level before organ retrieval was 1.58 ± 1.0 (0.46-3.07) mg/dL. The warm ischemic times of the 3 DCD donors were 3, 12, and 18 minutes. The average total ischemic time was 12.0 ± 3.7 (7.17-19.88) hours. The average MP time was 140 (60-240) minutes. A total of 7 cases had delayed graft function. The best creatinine level during hospitalization was 1.17 ± 0.43 (0.71-1.85) mg/dL. There were no primary non-functional cases, and perfusion preservation was safely performed in all cases.

CONCLUSIONS

Therefore, we present this report as the first clinical trial on machine perfusion for kidney transplantation from marginal donors with DBD and DCD in Japan.

Knowing When to Ignore the Numbers: Single-Center Experience Transplanting Deceased Donor Kidneys with Poor Perfusion Parameters

BACKGROUND

Hypothermic machine perfusion is frequently used in evaluating marginal kidneys with poor perfusion parameters (PPP) contributing to delays in kidney placement or discard. We examined outcomes in deceased donor kidney transplants with PPP compared with those with optimal perfusion parameters (OPP).

STUDY DESIGN

We conducted a retrospective single-center cohort study from 2001 to 2021 comparing PPP (n = 91) with OPP (n = 598) deceased donor kidney transplants. PPP was defined as terminal flow ≤80 mL/min and terminal resistance ≥0.40 mmHg/mL/min. OPP was defined as terminal flow ≥120 mL/min and terminal resistance ≤0.20 mmHg/mL/min.

RESULTS

Mean terminal flow was PPP 66 ± 16 vs OPP 149 ± 21 mL/min and resistance was PPP 0.47 ± 0.10 vs OPP 0.15 ± 0.04 mmHg/mL/min (both p < 0.001). Donor age, donation after cardiac death, and terminal serum creatinine levels were similar between groups. Mean Kidney Donor Profile Index was higher among PPP donors (PPP 65 ± 23% vs OPP 52 ± 27%, p < 0.001). The PPP transplant group had more females and lower weight and BMI. Delayed graft function was comparable (PPP 32% vs OPP 27%, p = 0.33) even though cold ischemia times trended toward longer in PPP kidneys (PPP 28 ± 10 vs OPP 26 ± 9 hours, p = 0.09). One-year patient survival (PPP 98% vs OPP 97%, p = 0.84) and graft survival (PPP 91% vs OPP 92%, p = 0.23) were equivalent. PPP did predict inferior overall and death-censored graft survival long-term (overall hazard ratio 1.63, 95% CI 1.19 to 2.23 and death-censored hazard ratio 1.77, 95% CI 1.15 to 2.74). At 1 year, the estimated glomerular filtration rate was higher with OPP kidneys (PPP 40 ± 17 vs OPP 52 ± 19 mL/min/1.73 m 2 , p < 0.001).

CONCLUSIONS

Short-term outcomes in PPP kidneys were comparable to OPP kidneys despite higher Kidney Donor Profile Index and longer cold ischemia times, suggesting a role for increased utilization of these organs with careful recipient selection.

Kidney-specific metabolomic profiling in machine perfusate

Given their accessibility and relevance to established clinical workflows, blood and urine have been the major focus of investigation in metabolomics studies of human kidney disease. In this issue, Liu et al. describe the application of metabolomics to perfusate from donor kidneys subjected to hypothermic machine perfusion. In addition to providing an elegant model for investigating kidney metabolism, this study highlights the limitations of allograft quality assessment and identifies metabolites of interest in kidney ischemia.

Untargeted metabolomics of perfusate and their association with hypothermic machine perfusion and allograft failure

Although hypothermic machine perfusion (HMP) is associated with improved kidney graft viability and function, the underlying biological mechanisms are unknown. Untargeted metabolomic profiling may identify potential metabolites and pathways that can help assess allograft viability and contribute to organ preservation. Therefore, in this multicenter study, we measured all detectable metabolites in perfusate collected at the beginning and end of deceased-donor kidney perfusion and evaluated their associations with graft failure. In our cohort of 190 kidney transplants, 33 (17%) had death-censored graft failure over a median follow-up of 5.0 years (IQR 3.0-6.1 years). We identified 553 known metabolites in perfusate and characterized their experimental and biological consistency through duplicate samples and unsupervised clustering. After perfusion-time adjustment and false discovery correction, six metabolites in post-HMP perfusate were significantly associated with death-censored graft failure, including alpha-ketoglutarate, 3-carboxy-4-methyl-5-propyl-2-furanpropanoate, 1-carboxyethylphenylalanine, and three glycerol-phosphatidylcholines. All six metabolites were associated with an increased risk of graft failure (Hazard Ratio per median absolute deviation range 1.04-1.45). Four of six metabolites also demonstrated significant interaction with donation after cardiac death with notably greater risk in the donation after cardiac death group (Hazard Ratios up to 1.69). Discarded kidneys did not have significantly different levels of any death-censored graft failure-associated metabolites. On interrogation of pathway analysis, production of reactive oxygen species and increased metabolism of fatty acids were upregulated in kidneys that subsequently developed death-censored graft failure. Thus, further understanding the role of these metabolites may inform the HMP process and help improve the objective evaluation of allograft offers, thereby reducing the discard of potentially viable organs.

Perfusate Neutrophil Gelatinase-Associated Lipocalin, Kidney Injury Molecular-1, Liver-Type Fatty Acid Binding Protein, and Interleukin-18 as Potential Biomarkers to Predict Delayed Graft Function and Long-Term Prognosis in Kidney Transplant Recipients: A Single-Center Retrospective Study

BACKGROUND Delayed graft function (DGF) caused by ischemia-reperfusion injury is a common pathophysiological process that should be monitored by specific biomarkers in addition to serum creatinine. Thus, this single-center retrospective study aimed to investigate the association between levels of neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecular-1 (KIM-1), liver-type fatty acid binding protein (L-FABP), and interleukin-18 (IL-18) in DGF associated with acute kidney injury in kidney transplant recipients (KTRs) and estimated glomerular filtration rate (eGFR) at 3 years post-transplant. MATERIAL AND METHODS A total of 102 KTRs [14(13.7%) of DGF and 88(86.3%) of NON-DGF] were enrolled. DGF was defined as "dialysis is needed within 1 week after kidney transplantation". NGAL, KIM-1, L-FABP, and IL-18 were obtained from perfusate samples of donation-after-cardiac-death (DCD) kidneys, and measured by ELISA. RESULTS Compared to the NON-DGF group, KTRs in the DGF group had a statistically significant increase in levels of NGAL (P<0.001) and KIM-1 (P<0.001). Multiple logistic regression analyses showed that NGAL (OR=1.204, 95% CI 1.057-1.372, P=0.005) and KIM-1 (OR=1.248, CI=1.065-1.463, P=0.006) could be regarded as independent risk factors. The accuracy of NGAL and KIM-1 was 83.3% and 82.1%, respectively, calculated using the area under the receiver operating characteristic curve. Furthermore, the eGFR at 3 years post-transplant had a moderate negative correlation with NGAL (r=-0.208, P=0.036) and KIM-1 (r=-0.260, P=0.008). CONCLUSIONS Our results support those from previous studies showing that perfusate levels of NGAL and KIM-1 are associated with DGF in KTRs and also with reduced eGFR at 3 years post-transplant.

Deceased-Donor Acute Kidney Injury and Acute Rejection in Kidney Transplant Recipients: A Multicenter Cohort

RATIONALE & OBJECTIVE

Donor acute kidney injury (AKI) activates innate immunity, enhances HLA expression in the kidney allograft, and provokes recipient alloimmune responses. We hypothesized that injury and inflammation that manifested in deceased-donor urine biomarkers would be associated with higher rates of biopsy-proven acute rejection (BPAR) and allograft failure after transplantation.

STUDY DESIGN

Prospective cohort.

SETTING & PARTICIPANTS

862 deceased donors for 1,137 kidney recipients at 13 centers.

EXPOSURES

We measured concentrations of interleukin 18 (IL-18), kidney injury molecule 1 (KIM-1), and neutrophil gelatinase-associated lipocalin (NGAL) in deceased donor urine. We also used the Acute Kidney Injury Network (AKIN) criteria to assess donor clinical AKI.

OUTCOMES

The primary outcome was a composite of BPAR and graft failure (not from death). A secondary outcome was the composite of BPAR, graft failure, and/or de novo donor-specific antibody (DSA). Outcomes were ascertained in the first posttransplant year.

ANALYTICAL APPROACH

Multivariable Fine-Gray models with death as a competing risk.

RESULTS

Mean recipient age was 54 ± 13 (SD) years, and 82% received antithymocyte globulin. We found no significant associations between donor urinary IL-18, KIM-1, and NGAL and the primary outcome (subdistribution hazard ratio [HR] for highest vs lowest tertile of 0.76 [95% CI, 0.45-1.28], 1.20 [95% CI, 0.69-2.07], and 1.14 [95% CI, 0.71-1.84], respectively). In secondary analyses, we detected no significant associations between clinically defined AKI and the primary outcome or between donor biomarkers and the composite outcome of BPAR, graft failure, and/or de novo DSA.

LIMITATIONS

BPAR was ascertained through for-cause biopsies, not surveillance biopsies.

CONCLUSIONS

In a large cohort of kidney recipients who almost all received induction with thymoglobulin, donor injury biomarkers were associated with neither graft failure and rejection nor a secondary outcome that included de novo DSA. These findings provide some reassurance that centers can successfully manage immunological complications using deceased-donor kidneys with AKI.

Unraveling metabolism during kidney perfusion using tracer studies, a systematic review

BACKGROUND

Understanding kidney metabolism during perfusion is vital to further develop the technology as a preservation, viability assessment, and resuscitation platform. We reviewed the evidence on the use of labeled metabolites (tracers) to understand "on-pump" kidney behavior.

METHODS

PubMed, Embase, Web of Science, and Cochrane databases were systematically searched for studies evaluating metabolism of (non)radioactively labeled endogenous compounds during kidney perfusion.

RESULTS

Of 5899 articles, 30 were included. All were animal studies [rat (70%), dog (13%), pig (10%), rabbit (7%)] perfusing but not transplanting kidneys. Perfusion took place at hypothermic (4-12°C) (20%), normothermic (35-40°C) (77%), or undefined temperatures (3%). Hypothermic perfusion used albumin or a clinical kidney preservation solution, mostly in the presence of oxygen. Normothermic perfusion was mostly performed with oxygenated crystalloids often containing glucose and amino acids with unclear partial oxygen tensions. Active metabolism of carbohydrate, amino acid, lipids, and large molecules was shown in hypothermic and normothermic perfusion. Production of macromolecules, such as prostaglandin, thromboxane, and vitamin D, takes place during normothermic perfusion. No experiments compared differences in metabolic activity between hypothermic and normothermic perfusion. One conference abstract showed increased anaerobic metabolism in kidneys donated after circulatory death by adding labeled glucose to hypothermically perfused human kidneys.

CONCLUSIONS

Tracer studies during kidney perfusion contribute to unraveling kidney metabolic behavior in pre-clinical models. Whether findings are truly translational needs further investigation in large animal models of human kidneys. Furthermore, it is essential to better understand how ischemia changes this metabolic behavior.

Cold but not too cold: advances in hypothermic and normothermic organ perfusion

Transplantation is the method of choice and, in many cases, the only method of treatment for patients with end-stage organ disease. Excellent results have been achieved, and the main focus today is to extend the number of available donors. The use of extended-criteria donors or donors after circulatory death is standard, but is accompanied by an increased risk of ischemia reperfusion injury. This review presents newly developed machine perfusion techniques using hypothermic, subnormothermic, or normothermic conditions, with or without oxygenation. Possibilities for treatment and quality assessment in decision-making about organ acceptability are also discussed.

Sense and Sensibilities of Organ Perfusion as a Kidney and Liver Viability Assessment Platform

Predicting organ viability before transplantation remains one of the most challenging and ambitious objectives in transplant surgery. Waitlist mortality is high while transplantable organs are discarded. Currently, around 20% of deceased donor kidneys and livers are discarded because of “poor organ quality”, Decisions to discard are still mainly a subjective judgement since there are only limited reliable tools predictive of outcome available. Organ perfusion technology has been posed as a platform for pre-transplant organ viability assessment. Markers of graft injury and function as well as perfusion parameters have been investigated as possible viability markers during ex-situ hypothermic and normothermic perfusion. We provide an overview of the available evidence for the use of kidney and liver perfusion as a tool to predict posttransplant outcomes. Although evidence shows post-transplant outcomes can be predicted by both injury markers and perfusion parameters during hypothermic kidney perfusion, the predictive accuracy is too low to warrant clinical decision making based upon these parameters alone. In liver, further evidence on the usefulness of hypothermic perfusion as a predictive tool is needed. Normothermic perfusion, during which the organ remains fully metabolically active, seems a more promising platform for true viability assessment. Although we do not yet fully understand “on-pump” organ behaviour at normothermia, initial data in kidney and liver are promising. Besides the need for well-designed (registry) studies to advance the field, the catch-22 of selection bias in clinical studies needs addressing.

Renal Normothermic Machine Perfusion: The Road Toward Clinical Implementation of a Promising Pretransplant Organ Assessment Tool

The increased utilization of high-risk renal grafts for transplantation requires optimization of pretransplant organ assessment strategies. Current decision-making methods to accept an organ for transplantation lack overall predictive power and always contain an element of subjectivity. Normothermic machine perfusion (NMP) creates near-physiological conditions, which might facilitate a more objective assessment of organ quality before transplantation. NMP is rapidly gaining popularity, with various transplant centers developing their own NMP protocols and renal viability criteria. However, to date, no validated sets of on-pump viability markers exist nor are there unified NMP protocols. This review provides a critical overview of the fundamentals of current renal NMP protocols and proposes a framework to approach further development of ex vivo organ evaluation. We also comment on the potential logistical implications of routine clinical use of NMP, which is a more complex procedure compared with static cold storage or even hypothermic machine perfusion.

Hemodynamics and Metabolic Parameters in Normothermic Kidney Preservation Are Linked With Donor Factors, Perfusate Cells, and Cytokines

Kidney transplantation is the best renal-replacement option for most patients with end-stage renal disease. Normothermic machine preservation (NMP) of the kidney has been studied extensively during the last two decades and implemented in clinical trials. Biomarker research led to success in identifying molecules with diagnostic, predictive and therapeutic properties in chronic kidney disease. However, perfusate biomarkers and potential predictive mechanisms in NMP have not been identified yet. Twelve discarded human kidneys (n = 7 DBD, n = 5 DCD) underwent NMP for up to 24 h. Eight were perfused applying urine recirculation (URC), four with replacement of urine (UR) using Ringer's lactate. The aim of our study was to investigate biomarkers (NGAL, KIM-1, and L-FABP), cells and cytokines in the perfusate in context with donor characteristics, perfusate hemodynamics and metabolic parameters. Cold ischemia time did not correlate with any of the markers. Perfusates of DBD kidneys had a significantly lower number of leukocytes after 6 h of NMP compared to DCD. Arterial flow, pH, NGAL and L-FABP correlated with donor creatinine and eGFR. Arterial flow was higher in kidneys with lower perfusate lactate. Perfusate TNF-α was higher in kidneys with lower arterial flow. The cytokines IL-1β and GM-CSF decreased during 6 h of NMP. Kidneys with more urine output had lower perfusate KIM-1 levels. Median and 6-h values of lactate, arterial flow, pH, NGAL, KIM-1, and L-FABP correlated with each other indicating a 6-h period being applicable for kidney viability assessment. The study results demonstrate a comparable cytokine and cell profile in perfusates with URC and UR. In conclusion, clinically available perfusate and hemodynamic parameters correlate well with donor characteristics and measured biomarkers in a discarded human NMP model.

Doxycycline Alters the Porcine Renal Proteome and Degradome during Hypothermic Machine Perfusion

Ischemia-reperfusion injury (IRI) is a hallmark for tissue injury in donation after circulatory death (DCD) kidneys. The implementation of hypothermic machine perfusion (HMP) provides a platform for improved preservation of DCD kidneys. Doxycycline administration has shown protective effects during IRI. Therefore, we explored the impact of doxycycline on proteolytic degradation mechanisms and the urinary proteome of perfused kidney grafts. Porcine kidneys underwent 30 min of warm ischemia, 24 h of oxygenated HMP (control/doxycycline) and 240 min of ex vivo reperfusion. A proteomic analysis revealed distinctive clustering profiles between urine samples collected at T15 min and T240 min. High-efficiency undecanal-based N-termini (HUNTER) kidney tissue degradomics revealed significantly more proteolytic activity in the control group at T-10. At T240, significantly more proteolytic activity was observed in the doxycycline group, indicating that doxycycline alters protein degradation during HMP. In conclusion, doxycycline administration during HMP led to significant proteomic and proteolytic differences and protective effects by attenuating urinary NGAL levels. Ultimately, we unraveled metabolic, and complement and coagulation pathways that undergo alterations during machine perfusion and that could be targeted to attenuate IRI induced injury.

Advances in Hypothermic and Normothermic Perfusion in Kidney Transplantation

Hypothermic and normothermic machine perfusion in kidney transplantation are purported to exert a beneficial effect on post-transplant outcomes compared to the traditionally used method of static cold storage. Kidney perfusion techniques provide a window for organ reconditioning and quality assessment. However, how best to deliver these preservation methods or improve organ quality has not yet been conclusively defined. This review summarises the promising advances in machine perfusion science in recent years, which have the potential to further improve early graft function and prolong graft survival.

Hypothermic Machine Perfusion of Kidney Transplant: A Mini-Review

Most kidney grafts are marginal and from deceased donors, which yield worse clinical outcomes. Hypothermic machine perfusion has created a paradigm shift in kidney preservation. This mini-review summarizes the main points of hypothermic machine perfusion of kidney transplants that should be known by any physician and surgeon involved with kidney transplantation. Specifically, this review explains a proposed mechanism of action of hypothermic machine perfusion of kidney transplants. This review also describes the clinical effectiveness of hypothermic machine perfusion and explains how to evaluate and predict graft functionality according to machine parameters and perfusate biomarkers. Finally, treatment options and the most recent studies on oxygenated hypothermic machine perfusion are mentioned.

Proteomic analysis of machine perfusion solution from brain dead donor kidneys reveals that elevated complement, cytoskeleton and lipid metabolism proteins are associated with 1-year outcome

Assessment of donor kidney quality is based on clinical scores or requires biopsies for histological assessment. Noninvasive strategies to identify and predict graft outcome at an early stage are, therefore, needed. We evaluated the perfusate of donation after brain death (DBD) kidneys during nonoxygenated hypothermic machine perfusion (HMP). In particular, we compared perfusate protein profiles of good outcome (GO) and suboptimal outcome (SO) 1‐year post‐transplantation. Samples taken 15 min after the start HMP (T1) and before the termination of HMP (T2) were analysed using quantitative liquid chromatography–tandem mass spectrometry (LC‐MS/MS). Hierarchical clustering of the 100 most abundant proteins showed discrimination between grafts with a GO and SO at T1. Elevated levels of proteins involved in classical complement cascades at both T1 and T2 and a reduced abundance of lipid metabolism at T1 and of cytoskeletal proteins at T2 in GO versus SO was observed. ATP‐citrate synthase and fatty acid‐binding protein 5 (T1) and immunoglobulin heavy variable 2‐26 and desmoplakin (T2) showed 91% and 86% predictive values, respectively, for transplant outcome. Taken together, DBD kidney HMP perfusate profiles can distinguish between outcome 1‐year post‐transplantation. Furthermore, it provides insights into mechanisms that could play a role in post‐transplant outcomes.

Consensus statement on normothermic regional perfusion in donation after circulatory death: report from the European Society for Organ Transplantation's Transplant Learning Journey

Normothermic regional perfusion (NRP) in donation after circulatory death (DCD) is a safe alternative to in situ cooling and rapid procurement. An increasing number of countries and centres are performing NRP, a technically and logistically challenging procedure. This consensus document provides evidence-based recommendations on the use of NRP in uncontrolled and controlled DCDs. It also offers minimal ethical, logistical and technical requirements that form the foundation of a safe and effective NRP programme. The present article is based on evidence and opinions formulated by a panel of European experts of Workstream 04 of the Transplantation Learning Journey project, which is part of the European Society for Organ Transplantation.

Deceased-Donor Acute Kidney Injury and BK Polyomavirus in Kidney Transplant Recipients

BACKGROUND AND OBJECTIVES

BK polyomavirus (BKV) infection commonly complicates kidney transplantation, contributing to morbidity and allograft failure. The virus is often donor-derived and influenced by ischemia-reperfusion processes and disruption of structural allograft integrity. We hypothesized that deceased-donor AKI associates with BKV infection in recipients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We studied 1025 kidney recipients from 801 deceased donors transplanted between 2010 and 2013, at 13 academic centers. We fitted Cox proportional-hazards models for BKV DNAemia (detectable in recipient blood by clinical PCR testing) within 1 year post-transplantation, adjusting for donor AKI and other donor- and recipient-related factors. We validated findings from this prospective cohort with analyses for graft failure attributed to BKV within the Organ Procurement and Transplantation Network (OPTN) database.

RESULTS

The multicenter cohort mean kidney donor profile index was 49±27%, and 26% of donors had AKI. Mean recipient age was 54±13 years, and 25% developed BKV DNAemia. Donor AKI was associated with lower risk for BKV DNAemia (adjusted hazard ratio, 0.53; 95% confidence interval, 0.36 to 0.79). In the OPTN database, 22,537 (25%) patients received donor AKI kidneys, and 272 (0.3%) developed graft failure from BKV. The adjusted hazard ratio for the outcome with donor AKI was 0.7 (95% confidence interval, 0.52 to 0.95).

CONCLUSIONS

In a well-characterized, multicenter cohort, contrary to our hypothesis, deceased-donor AKI independently associated with lower risk for BKV DNAemia. Within the OPTN database, donor AKI was also associated with lower risk for graft failure attributed to BKV.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2021_03_10_CJN18101120_final.mp3.

Perioperative risk factors associated with delayed graft function following deceased donor kidney transplantation: A retrospective, single center study

BACKGROUND

There is an abundant need to increase the availability of deceased donor kidney transplantation (DDKT) to address the high incidence of kidney failure. Challenges exist in the utilization of higher risk donor organs into what appears to be increasingly complex recipients; thus the identification of modifiable risk factors associated with poor outcomes is paramount.

AIM

To identify risk factors associated with delayed graft function (DGF).

METHODS

Consecutive adults undergoing DDKT between January 2016 and July 2017 were identified with a study population of 294 patients. The primary outcome was the occurrence of DGF.

RESULTS

The incidence of DGF was 27%. Under logistic regression, eight independent risk factors for DGF were identified including recipient body mass index ≥ 30 kg/m², baseline mean arterial pressure < 110 mmHg, intraoperative phenylephrine administration, cold storage time ≥ 16 h, donation after cardiac death, donor history of coronary artery disease, donor terminal creatinine ≥ 1.9 mg/dL, and a hypothermic machine perfusion (HMP) pump resistance ≥ 0.23 mmHg/mL/min.

CONCLUSION

We delineate the association between DGF and recipient characteristics of pre-induction mean arterial pressure below 110 mmHg, metabolic syndrome, donor-specific risk factors, HMP pump parameters, and intraoperative use of phenylephrine.

Urinary liver-type fatty acid-binding protein is independently associated with graft failure in outpatient kidney transplant recipients

Urinary liver-type fatty acid-binding protein (uL-FABP) is a biomarker of kidney hypoxia and ischemia, and thus offers a novel approach to identify early kidney insults associated with increased risk of graft failure in outpatient kidney transplant recipients (KTR). We investigated whether uL-FABP is associated with graft failure and whether it improves risk prediction. We studied a cohort of 638 outpatient KTR with a functional graft ≥1-year. During a median follow-up of 5.3 years, 80 KTR developed graft failure. uL-FABP (median 2.11, interquartile range 0.93-7.37 µg/24"/>h) was prospectively associated with the risk of graft failure (hazard ratio 1.75; 95% confidence interval 1.27-2.41 per 1-SD increment; P = .001), independent of potential confounders including estimated glomerular filtration rate and proteinuria. uL-FABP showed excellent discrimination ability for graft failure (c-statistic of 0.83) and its addition to a prediction model composed by established clinical predictors of graft failure significantly improved the c-statistic to 0.89 (P for F-test <.001). These results were robust to several sensitivity analyses. Further validation studies are warranted to evaluate the potential use of a risk-prediction model including uL-FABP to improve identification of outpatient KTR at high risk of graft failure in clinical care.

Donor-Recipient Matching to Optimize the Utility of High Kidney Donor Profile Index Kidneys

BACKGROUND

In December 2014, the Kidney Donor Profile Index (KDPI) was developed to give more precise information on donor kidney quality. Kidneys with KDPI scores ≥ 85 (K ≥ 85) have been reported to have inferior outcomes to kidneys with KDPI scores < 85.

METHODS

After the implementation of the new Kidney Allocation System, we developed a protocol to evaluate K ≥ 85 use. We analyzed the safety and efficacy of our institutional criteria and evaluated post-transplant outcomes. K ≥ 85 recipients were stratified based on their 1-year creatinine and estimated glomerular filtration rates to elucidate characteristics associated with serum creatinine < 1.7 mg/dL or estimated glomerular filtration rates ≤ 45 mL/min/1.73 m².

RESULTS

From December 2014 to December 2019, 304 deceased donor kidney transplants were performed at Hartford Hospital; 58 (19%) were K ≥ 85 with an average KDPI of 91%. There were 4 graft losses; 2 were death censored. Prolonged cold ischemia time and black recipient race were associated with inferior recipient graft function at 1 year.

CONCLUSIONS

High KDPI kidney use requires a multifaceted evaluation that takes into account donor and recipient characteristics for an ideal match. We have identified several characteristics that may predict optimal post-transplant kidney function.

[Machine perfusion for conditioning liver and kidneys before transplantation]

Machine perfusion will become established as the standard of care for solid organ transplantation in the near future. Ongoing studies are investigating the appropriate perfusion algorithms for each specific organ. Although it is neither proven which perfusion principle nor type of device is superior, it has already been sufficiently shown that the increasing number of marginal organs that are currently transplanted in Germany would benefit from machine perfusion for conditioning before transplantation. The addition of hypothermic and normothermic perfusion sequences opens up the possibility of conditioning of previously damaged organs as well as viability testing. Overall, machine perfusion increases the safety for the recipient and can counteract the increasingly more difficult scenario of working hour restrictions because solid organ transplantations in the future will be plannable and carried out during the day.

Perfusate Analysis During Dual Hypothermic Oxygenated Machine Perfusion of Liver Grafts: Correlations With Donor Factors and Early Outcomes

BACKGROUND

Liver graft viability assessment has long been considered a limit of hypothermic oxygenated machine perfusion (HOPE). Aim of this study was assessing correlations of easily available perfusate parameters (PP) (aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, glucose, lactate, and pH) with graft features and outcome.

METHODS

In the period October 2018-February 2020, perfusate samples were obtained every 30 minutes during 50 dual-HOPE (D-HOPE) procedures. Correlations of PP with graft factors, 90-day graft loss, early allograft dysfunction (EAD), L-GrAFT score, acute kidney injury, and comprehensive complication index were analyzed using Pearson coefficient, receiver-operating characteristics analysis and by univariable and multivariable regression.

RESULTS

Median D-HOPE time was 122 minutes. All parameters were normalized to liver weight. Only macrovesicular steatosis (MaS) significantly impacted PP levels and slope. Grafts with ≥30% MaS exhibited significantly different PP values and slope. Graft loss and EAD rate were 2% (n = 1) and 26% (n = 13). All PP except lactate correlated with EAD, 90-minute alanine aminotransferase showing the highest area under the receiver-operating characteristics curve (0.84). However, at multivariable analysis, the only factor independently associated with EAD was MaS (odds ratio, 5.44; confidence interval, 1.05-28.21; P = 0.04). Ninety minutes lactate dehydrogenase had the strongest correlation with L-GrAFT (R = 0.70; P < 0.001). PP correlated poorly with comprehensive complication index and grades 2-3 acute kidney injury rate.

CONCLUSIONS

PP were predictive of graft function after transplant, but their association with graft survival and clinical outcomes requires further evaluation. MaS influenced levels of PP and was the only independent predictor of EAD.

Role of novel biomarkers in kidney transplantation

Clinical application of biomarkers is an integral component of transplant care. Clinicians and scientists alike are in search of better biomarkers than the current serologic (serum creatinine, donor-specific antibodies), urine-derived (urinalysis, urine protein), and histologic ones we now use. The science behind recent biomarker discovery spans across multiple molecular biologic disciplines, including transcriptomics, proteomics, and metabolomics. Innovative methodology and integration of basic and clinical approaches have allowed researchers to unearth molecular phenomena preceding clinical disease. Biomarkers can be classified in several ways. In this review, we have classified them via their origin and outcome: Primarily immunologic, i.e., representative of immune regulation and dysfunction and non-immunologic, pertaining to delayed graft function, cardiovascular events/mortality, infection, malignancy, post-transplant diabetes, graft, and patient survival. Novel biomarker uses to guide the diagnosis and management of transplant-related outcomes is a promising area of research. However, the use of biomarkers to predict outcomes after kidney transplantation is not well studied. In this review, we summarize the recent studies illustrating biomarker use and transplant outcomes.

Delayed graft function and perfusion parameters of kidneys from uncontrolled donors after circulatory death

Better preservation and evaluation of kidneys from donors after circulatory death serve to increase the number of kidneys available for transplantation and hypothermic machine perfusion has been shown to decrease ischemia reperfusion injury and delayed graft function. Data on relation between hemodynamic parameters during hypothermic machine perfusion and delayed graft function in kidneys from donors after circulatory death are so far scarce and not univocal. We aimed at assessing whether hemodynamic parameters measured during hypothermic machine perfusion (flow, mean perfusion pressure, and renal resistance) are associated with delayed graft function in 26 kidneys retrieved from uncontrolled donors after circulatory death. In our series, the incidence of delayed graft function was 57.7% (15/26). Recipients who developed delayed graft function had a longer warm ischemic time (p = 0.04). All hemodynamic parameters measured during hypothermic machine perfusion were comparable between recipients with delayed graft function and those without. According to our data, in kidneys from uncontrolled donors after circulatory death, a longer warm ischemic time (that is the overall time of no flow, as the sum of the no-flow and the no-touch period) is associated with delayed graft function. This finding underscores the pivotal role of ischemic injury in terms of absence of flow in affecting graft function. No association was detectable between hemodynamic parameters during hypothermic machine perfusion and the development of delayed graft function in our series.

Assessment of Organ Quality in Kidney Transplantation by Molecular Analysis and Why It May Not Have Been Achieved, Yet

Donor organ shortage, growing waiting lists and substantial organ discard rates are key problems in transplantation. The critical importance of organ quality in determining long-term function is becoming increasingly clear. However, organ quality is difficult to predict. The lack of good measures of organ quality is a serious challenge in terms of acceptance and allocation of an organ. The underlying review summarizes currently available methods used to assess donor organ quality such as histopathology, clinical scores and machine perfusion characteristics with special focus on molecular analyses of kidney quality. The majority of studies testing molecular markers of organ quality focused on identifying organs at risk for delayed graft function, yet without prediction of long-term graft outcome. Recently, interest has emerged in looking for molecular markers associated with biological age to predict organ quality. However, molecular gene sets have not entered the clinical routine or impacted discard rates so far. The current review critically discusses the potential reasons why clinically applicable molecular quality assessment using early kidney biopsies might not have been achieved yet. Besides a critical analysis of the inherent limitations of surrogate markers used for organ quality, i.e., delayed graft function, the intrinsic methodological limitations of studies assessing organ quality will be discussed. These comprise the multitude of unpredictable hits as well as lack of markers of nephron mass, functional reserve and regenerative capacity.

Machine perfusion in kidney transplantation

PURPOSE OF REVIEW

The shortage of kidneys for transplantation has led to an urgent need to efficiently utilize the available cadaveric kidneys. Efficient use of machine perfusion may potentially lead to increased use of marginal kidneys by lowering the incidence of delayed graft function (DGF) and improving graft outcomes.

RECENT FINDINGS

Machine perfusion has had a resurgence in the last 10-15 years over static cold storage (SCS). Hypothermic machine perfusion (HMP), the most commonly utilized type of machine perfusion reduces the rates of DGF when compared with SCS with a trend towards improving the overall graft survival.

SUMMARY

Despite reduction in the rates of DGF by HMP, its effect on long-term renal and patient outcomes is not clearly known. There is limited clinical literature in the use of normothermic machine perfusion (NMP) but a few pilot studies have shown its potential to resuscitate commonly discarded kidneys. In addition to preservation, machine perfusion also allows for various diagnostic and therapeutic interventions during the preservation period to assess and optimize the viability of the procured kidney.

Kidney Perfusion as an Organ Quality Assessment Tool-Are We Counting Our Chickens Before They Have Hatched?

The final decision to accept an organ for transplantation remains a subjective one. With “poor organ quality” commonly cited as a major reason for kidney discard, accurate, objective, and reliable quality assessment is essential. In an era of increasingly higher-risk deceased donor kidneys, the catch is to accept those where the risk–benefit scale will tip in the right direction. Currently available assessment tools, such as risk-scores predicting outcome and zero-time biopsy, perform unsatisfactory, and assessment options during static cold storage are limited. Kidney perfusion technologies are finding their way into clinical practice, and they bring a new opportunity to assess kidney graft viability and quality, both in hypothermic and normothermic conditions. We give an overview of the current understanding of kidney viability assessment during ex situ kidney perfusion. A pragmatic framework to approach viability assessment is proposed as an interplay of three different compartments: the nephron, the vascular compartment, and the immune compartment. Although many interesting ways to assess kidney injury and function during perfusion have been proposed, none have reached the stage where they can reliably predict posttransplant outcome. Larger well-designed studies and validation cohorts are needed to provide better guidance.

A systematic review to identify whether perfusate biomarkers produced during hypothermic machine perfusion can predict graft outcomes in kidney transplantation

There is good evidence to support the use of hypothermic machine perfusion (HMP) over static cold storage as the favoured preservation method for deceased donor kidneys. However, the utility of HMP as a tool to assess the viability of kidneys for transplant is unclear. There is a need to determine whether perfusate biomarkers produced during HMP can predict post-transplant outcomes and assess the suitability of organs for transplantation. Three different databases (MEDLINE, Embase, Transplant Library) were screened to 31 May 2019. Articles were included if a relationship was reported between one or more perfusate biomarkers and post-transplant outcomes. Studies were assessed and graded for methodological quality and strength of evidence. Glutathione S-transferase was the most promising biomarker for predicting delayed graft function, but its predictive ability was at best moderate. Analysis of primary nonfunction rates was challenging due to low occurrence rates and small sample sizes. Existing studies are limited in quality and have not yielded biomarkers for kidneys undergoing HMP that are able to predict post-transplant outcomes with sufficient accuracy to support routine clinical use. Further studies with larger samples and more robust methodology are needed. (PROSPERO registration: CRD42019121161).

A Novel Method to Improve Perfusion of Ex Vivo Pumped Human Kidneys

OBJECTIVE

To determine if addition of the S-nitrosylating agent ethyl nitrite (ENO) to the preservation solution can improve perfusion parameters in pumped human kidneys.

BACKGROUND

A significant percentage of actively stored kidneys experience elevations in resistance and decreases in flow rate during the ex vivo storage period. Preclinical work indicates that renal status after brain death is negatively impacted by inflammation and reduced perfusion-processes regulated by protein S-nitrosylation. To translate these findings, we added ENO to the preservation solution in an attempt to reverse the perfusion deficits observed in nontransplanted pumped human kidneys.

METHODS

After obtaining positive proof-of-concept results with swine kidneys, we studied donated human kidneys undergoing hypothermic pulsatile perfusion deemed unsuitable for transplantation. Control kidneys continued to be pumped a 4°C (ie, standard of care). In the experimental group, the preservation solution was aerated with 50 ppm ENO in nitrogen. Flow rate and perfusion were recorded for 10 hours followed by biochemical analysis of the kidney tissue.

RESULTS

In controls, perfusion was constant during the monitoring period (ie, flow rate remained low and resistance stayed high). In contrast, the addition of ENO produced significant and sustained reductions in resistance and increases in flow rate. ENO-treated kidneys had higher levels of cyclic guanosine monophosphate, potentially explaining the perfusion benefits, and increased levels of interleukin-10, suggestive of an anti-inflammatory effect.

CONCLUSIONS

S-Nitrosylation therapy restored the microcirculation and thus improved overall organ perfusion. Inclusion of ENO in the renal preservation solution holds promise to increase the number and quality of kidneys available for transplant.

Histological and clinical evaluation of marginal donor kidneys before transplantation: Which is best?

Organ shortage represents one of the major limitations to the development of kidney transplantation. To increase the donor pool and to answer the ever increasing kidney request, physicians are recurring to marginal kidneys as kidneys from older donors, from hypertensive or diabetic donors and from non-heart beating donors. These kidneys are known to have frequently a worse outcome in the recipients. To date major problem is to evaluate such kidneys in order to use or to discard them before transplantation. The use of such kidneys create other relevant question as whether to use them as single or dual transplant and to allocate them fairly according transplant programs. The pre-transplant histological evaluation, the clinical evaluation of the donor or both the criteria joined has been used and according the time each criterion prevailed over the others. Aim of this review has been to examine the advantages and the drawbacks of any criterion and how they have changed with time. To date any criterion has several limitations and several authors have argued for the development of new guidelines in the field of the kidney evaluation for transplantation. Several authors argue that the use of omic technologies should improve the organ evaluation and studies are ongoing to evaluate these technologies either in the donor urine or in the biopsies taken before transplantation.

Cell-free MicroRNA miR-505-3p in Graft Preservation Fluid Is an Independent Predictor of Delayed Graft Function After Kidney Transplantation

BACKGROUND

Delayed graft function (DGF), a common complication after transplantation of deceased donor kidneys, affects both short- and long-term outcomes. Currently available biomarkers during graft preservation lack sensitivity in predicting risk for DGF. The aim of this study is to identify cell-free micro ribonucleic acid (miRNA) biomarkers in graft preservation fluid predictive of DGF after kidney transplantation.

METHODS

Vascular bed preservation fluid was collected from 48 kidney grafts from donation after circulatory death (DCD) or donation after brain death (DBD) donors. miRNA profiles were determined by polymerase chain reaction (PCR) array (n = 8) and validated by reverse transcription and quantitative PCR (n = 40). Graft function posttransplantation was defined as immediate good function (IF) or DGF.

RESULTS

A total of 223 miRNAs fulfilled the preset parameters (Ct < 40 in 3 or more samples) and were included in the analysis. Thirty-two miRNAs were significantly different between DGF and IF kidney grafts (P < 0.05) but, after correction for multiple testing, only miR-505-3p remained significant. The significant association of high miR-505-3p levels with DGF was confirmed in an independent validation cohort using conventional reverse transcription and quantitative PCR detection. Multivariate analyses showed miR-505-3p as an independent predictor for DGF (odds ratio, 1.12; P = 0.028). If stratified for donor type, miR-505-3p levels remained significantly different between IF and DGF in DCD grafts (P < 0.01), but not in DBD grafts. Receiver operating characteristic curve analysis showed a high sensitivity and specificity (area under the curve, 0.833).

CONCLUSIONS

In DCD grafts, high levels of miR-505-3p in preservation fluid are associated with increased risk of DGF after kidney transplantation. Further study is required to confirm the utility of cell-free miR-505-3p as prognostic biomarker for DGF.

To discard or not to discard: transplantation and the art of scoring

The growing gap between inadequate supply and constantly high demand for kidney transplantation observed in the last two decades led to exploring the possibility of using organs from older donors with an increasing number of comorbidities. The main issue in this scenario is to identify transplantable organs and to allocate them to the most suitable recipients. A great number of clinical investigations proposed several acceptance/allocation criteria to reduce the discard rate of these kidneys and to improve their outcome, including histological features at the time of transplant. Despite the widespread use of several histological scoring systems, there is no consensus on their value in predicting allograft survival and there is established evidence that histological analysis is the most common reason to discard expanded criteria donor kidneys. To overcome this issue, a clinical scoring system, the Kidney Donor Profile Index (KDPI), was developed on the basis of easily accessible donor features. The KDPI score, adopted in the new US allocation procedure, has good reproducibility but presents several limitations, as suggested also in this issue of Clinical Kidney Journal. This observation should stimulate the search for novel scores combining clinical, histological and molecular features in an attempt to improve the decision process.

Outcomes of Deceased Donor Kidney Transplantation Using Expanded Criteria Donor Kidneys Following Pulsatile Preservation

Aim

We compared the outcomes of transplanting expanded criteria donor (ECD) kidneys undergoing machine perfusion (MP) versus cold storage (CS).

Material and methods

Data on all expanded criteria deceased donor kidney transplants performed at the University of Pittsburgh Medical Center from January 2003 through December 2012 were collected from an in-house electronic repository. There were 78 patients in the MP group and 101 patients in the CS group. The majority of the ECD kidneys were imported from other organ procurement organizations: 69 of 73 in the MP group (94.5%, 5 from unknown sources); and 90 of 99 in the CS group (91%), 2 from an unknown source). Most of the patients in the MP group (77 of 78) received a combination of MP and static CS. MP was performed just prior to transplantation in all MP patients. We used descriptive statistics to characterize our sample. We used logistic regression analysis to model the binary outcome of delayed graft function (DGF; i.e., “yes/no”) and Cox (proportional hazard) regression to model time until graft failure. The Kaplan-Meier product-limit method was used to estimate survival curves for graft and patient survival.

Results

A total of 179 transplants were done from ECD donors (MP, 78; CS, 101). The mean static cold storage time was 14 ± 4.1 hours and the mean machine perfusion time was 11.2 ± 6.3 hours in the MP group. The donor creatinine was higher (1.3 ± 0.6 mg/dl vs. 1.2 ± 0.4 mg/dl, p = 0.01) and the cold ischemia time was longer (28.9 ± 10 hours vs. 24 ± 7.9 hours, p = 0.0003) in the MP patients. There were no differences between the two groups in DGF rate (20.8% [MP] vs. 25.8% [CS], p = 0.46), six-year patient survival (74% [MP] vs. 63.2% [CS], p = 0.11), graft survival (64.3% [MP] vs. 51.5% [CS], p = 0.22), and serum creatinine levels (1.5 mg/dl vs. 1.5 mg/dl) on univariate analysis. On unadjusted analysis, MP subjects without DGF had longer graft survival compared to CS subjects with DGF (p < 0.0032) and MP subjects with DGF (p < 0.0005). MP subjects without DGF had longer death-censored graft survival compared to CS subjects with DGF (p < 0.0077) and MP subjects with DGF (p < 0.0016). However, on regression analysis, MP subjects had longer graft survival than CS subjects when DGF was not present. MP subjects without DGF had longer patient survival compared to CS subjects with DGF (p < 0.0289), on unadjusted analysis. MP subjects had a reduced risk of graft failure (hazard ratio [HR], 0.34; 95% confidence interval [CI], 0.17, 0.68) and death-censored graft failure (HR, 0.44; 95% CI, 0.19, 1.00), compared to CS subjects when DGF was not present.

Conclusions

Reduction of DGF rates for imported ECD kidneys is vital to optimize outcomes and increase their utilization. One strategy to decrease DGF rates may be to reduce static CS time during transportation, by utilizing a portable kidney perfusion machine.

Evaluation of donor kidneys prior to transplantation: an update of current and emerging methods

The lack of suitable kidney donor organs has led to rising numbers of patients with end stage renal disease waiting for kidney transplantation. Despite decades of clinical experience and research, no evaluation process that can reliably predict the outcome of an organ has yet been established. This review is an overview of current methods and emerging techniques in the field of donor kidney evaluation prior to transplantation. Established techniques like histological evaluation, clinical scores, and machine perfusion systems offer relatively reliable predictions of delayed graft function but are unable to consistently predict graft survival. Emerging techniques including molecular biomarkers, new imaging technologies, and normothermic machine perfusion offer innovative approaches toward a more global evaluation of an organ with better outcome prediction and possibly even identification of targets for therapeutic interventions prior to transplantation. These techniques should be studied in randomized controlled trials to determine whether they can be safely used in routine clinical practice to ultimately reduce the discard rate and improve graft outcomes.

Rapid Identification of Ischemic Injury in Renal Tissue by Mass-Spectrometry Imaging

The increasing analytical speed of mass-spectrometry imaging (MSI) has led to growing interest in the medical field. Acute kidney injury is a severe disease with high morbidity and mortality. No reliable cut-offs are known to estimate the severity of acute kidney injury. Thus, there is a need for new tools to rapidly and accurately assess acute ischemia, which is of clinical importance in intensive care and in kidney transplantation. We investigated the value of MSI to assess acute ischemic kidney tissue in a porcine model. A perfusion model was developed where paired kidneys received warm (severe) or cold (minor) ischemia ( n = 8 per group). First, ischemic tissue damage was systematically assessed by two blinded pathologists. Second, MALDI-MSI of kidney tissues was performed to study the spatial distributions and compositions of lipids in the tissues. Histopathological examination revealed no significant difference between kidneys, whereas MALDI-MSI was capable of a detailed discrimination of severe and mild ischemia by differential expression of characteristic lipid-degradation products throughout the tissue within 2 h. In particular, lysolipids, including lysocardiolipins, lysophosphatidylcholines, and lysophosphatidylinositol, were dramatically elevated after severe ischemia. This study demonstrates the significant potential of MSI to differentiate and identify molecular patterns of early ischemic injury in a clinically acceptable time frame. The observed changes highlight the underlying biochemical processes of acute ischemic kidney injury and provide a molecular classification tool that can be deployed in assessment of acute ischemic kidney injury.

Predictive Score Model for Delayed Graft Function Based on Hypothermic Machine Perfusion Variables in Kidney Transplantation

Background:

Hypothermic machine perfusion (HMP) is being used more often in cardiac death kidney transplantation; however, the significance of assessing organ quality and predicting delayed graft function (DGF) by HMP parameters is still controversial. Therefore, we used a readily available HMP variable to design a scoring model that can identify the highest risk of DGF and provide the guidance and advice for organ allocation and DCD kidney assessment.

Methods:

From September 1, 2012 to August 31, 2016, 366 qualified kidneys were randomly assigned to the development and validation cohorts in a 2:1 distribution. The HMP variables of the development cohort served as candidate univariate predictors for DGF. The independent predictors of DGF were identified by multivariate logistic regression analysis with a P < 0.05. According to the odds ratios (ORs) value, each HMP variable was assigned a weighted integer, and the sum of the integers indicated the total risk score for each kidney. The validation cohort was used to verify the accuracy and reliability of the scoring model.

Results:

HMP duration (OR = 1.165, 95% confidence interval [CI ]: 1.008–1.360, P = 0.043), resistance (OR = 2.190, 95% CI: 1.032–10.20, P < 0.001), and flow rate (OR = 0.931, 95% CI: 0.894–0.967, P = 0.011) were the independent predictors of identified DGF. The HMP predictive score ranged from 0 to 14, and there was a clear increase in the incidence of DGF, from the low predictive score group to the very high predictive score group. We formed four increasingly serious risk categories (scores 0–3, 4–7, 8–11, and 12–14) according to the frequency associated with the different risk scores of DGF. The HMP predictive score indicates good discriminative power with a c-statistic of 0.706 in the validation cohort, and it had significantly better prediction value for DGF compared to both terminal flow (P = 0.012) and resistance (P = 0.006).

Conclusion:

The HMP predictive score is a good noninvasive tool for assessing the quality of DCD kidneys, and it is potentially useful for physicians in making optimal decisions about the organs donated.

Twenty-four-hour normothermic perfusion of discarded human kidneys with urine recirculation

Transportable normothermic kidney perfusion for 24 hours or longer could enable viability assessment of marginal grafts, increased organ use, and improved transplant logistics. Eleven clinically declined kidneys were perfused normothermically, with 6 being from donors after brain death (median cold ischemia time 33 ± 36.9 hours) and 5 being from donors after circulatory death (36.2 ± 38.3 hours). Three kidneys were perfused using Ringer's lactate to replace excreted urine volume, and 8 kidneys were perfused using urine recirculation to maintain perfusate volume without fluid replenishment. In all cases, normothermic perfusion either maintained or slightly improved the histopathologically assessed tubular condition, and there was effective urine production in kidneys from both donors after brain death and donors after circulatory death (2367 ± 1798 mL vs 744.4 ± 198.4 mL, respectively; P = .44). Biomarkers, neutrophil gelatinase-associated lipocalin, and kidney injury molecule-1 were successfully detected and quantified in the perfusate. All kidneys with urine recirculation were readily perfused for 24 hours (n = 8) and exhibited physiological perfusate sodium levels (140.7 ± 1.2 mmol/L), while kidneys without urine recirculation (n = 3) achieved a reduced normothermic perfusion time of 7.7 ± 1.5 hours and significantly higher perfusate sodium levels (159.6 ± 4.63 mmol/:, P < .01). Normothermic machine perfusion of human kidneys for 24 hours appears to be feasible, and urine recirculation was found to facilitate the maintenance of perfusate volume and homeostasis.

Propofol-based anaesthesia versus sevoflurane-based anaesthesia for living donor kidney transplantation: results of the VAPOR-1 randomized controlled trial

Background

Kidney transplantation is associated with harmful processes affecting the viability of the graft. One of these processes is associated with the phenomenon of ischaemia-reperfusion injury. Anaesthetic conditioning is a widely described strategy to attenuate ischaemia-reperfusion injury. We therefore conducted the Volatile Anaesthetic Protection of Renal Transplants-1 trial, a pilot project evaluating the influence of two anaesthetic regimens, propofol- vs sevoflurane-based anaesthesia, on biochemical and clinical outcomes in living donor kidney transplantation.

Methods

Sixty couples were randomly assigned to the following three groups: PROP (donor and recipient propofol), SEVO (donor and recipient sevoflurane), and PROSE (donor propofol and recipient sevoflurane). The primary outcome was renal injury reflected by urinary biomarkers. The follow-up period was 2 yr.

Results

Three couples were excluded, leaving 57 couples for analysis. Concentrations of kidney injury molecule-1 (KIM-1), N -acetyl-β- d -glucosaminidase (NAG), and heart-type fatty acid binding protein (H-FABP) in the first urine upon reperfusion showed no differences. On day 2, KIM-1 concentrations were higher in SEVO [952.8 (interquartile range 311.8-1893.0) pg mmol -1 ] compared with PROP [301.2 (202.0-504.7) pg mmol -1 ]. This was the same for NAG: SEVO, 1.835 (1.162-2.457) IU mmol -1 vs PROP, 1.078 (0.819-1.713) IU mmol -1 . Concentrations of H-FABP showed no differences. Measured glomerular filtration rate at 3, 6, and 12 months showed no difference. After 2 yr, there was a difference in the acute rejection rate ( P =0.039). Post hoc testing revealed a difference between PROP (35%) and PROSE (5%; P =0.020). The difference between PROP and SEVO (11%) was not significant ( P =0.110).

Conclusions

The SEVO group showed higher urinary KIM-1 and NAG concentrations in living donor kidney transplantation on the second day after transplantation. This was not reflected in inferior graft outcome.

Clinical trial registration

NCT01248871.

Deceased-donor acute kidney injury is not associated with kidney allograft failure

Deceased-donor acute kidney injury (AKI) is associated with organ discard and delayed graft function, but data on longer-term allograft survival are limited. We performed a multicenter study to determine associations between donor AKI (from none to severe based on AKI Network stages) and all-cause graft failure, adjusting for donor, transplant, and recipient factors. We examined whether any of the following factors modified the relationship between donor AKI and graft survival: kidney donor profile index, cold ischemia time, donation after cardiac death, expanded-criteria donation, kidney machine perfusion, donor-recipient gender combinations, or delayed graft function. We also evaluated the association between donor AKI and a 3-year composite outcome of all-cause graft failure or estimated glomerular filtration rate ≤ 20 mL/min/1.73 m² in a subcohort of 30% of recipients. Among 2,430 kidneys transplanted from 1,298 deceased donors, 585 (24%) were from donors with AKI. Over a median follow-up of 4.0 years, there were no significant differences in graft survival by donor AKI stage. We found no evidence that pre-specified variables modified the effect of donor AKI on graft survival. In the subcohort, donor AKI was not associated with the 3-year composite outcome. Donor AKI was not associated with graft failure in this well-phenotyped cohort. Given the organ shortage, the transplant community should consider measures to increase utilization of kidneys from deceased donors with AKI.

Recent advances in kidney transplantation: a viewpoint from the Descartes advisory board

Transplantation medicine is a rapidly evolving field. Keeping afloat of the published literature to offer the best clinical care to our patients is a daunting task. As part of its educational mission, the Descartes advisory board identified seven topics in kidney transplantation where there has been substantial progresses over the last years: kidney allocation within Eurotransplant; kidney exchange strategies; kidney machine perfusion strategies; the changing landscape of anti-human leukocyte antigen (HLA) antibodies; the new immunosuppressive drugs in the pipeline; strategies for immunosuppression minimization; and the continuous enigma of focal segmental glomerular sclerosis recurrence after transplantation. Here, we have summarized the main knowledge and the main challenges of these seven topics with the aim to provide transplant professionals at large with key bullet points to successfully understand these new concepts.

Procurement Biopsy Findings Versus Kidney Donor Risk Index for Predicting Renal Allograft Survival

BACKGROUND

Efforts to maximize transplantation by matching organ quality to recipient longevity require reliable tools. The US kidney allocation system uses the Kidney Donor Risk Index (KDRI) for this purpose, and many centers additionally rely on donor biopsies. The Leuven score combines donor age with procurement histology (glomerulosclerosis and interstitial fibrosis/tubular atrophy) to predict allograft survival.

METHODS

We compared KDRI with Leuven scores for associations with kidney discard, delayed graft function, and allograft function and survival. We used Cox, modified Poisson, and linear regression to calculate risks based on KDRI and (separately) Leuven scores, adjusting for important transplant and recipient variables.

RESULTS

From 890 donors, 1729 kidneys were procured and biopsied. Five hundred eighty-five (34%) kidneys were discarded. Median donor age was 53 years (interquartile range [IQR], 44-61 years). Median KDRI and Leuven scores were 1.56 (IQR, 1.28-1.90) and 59 (IQR, 49-69). Relative risk for discard was 1.21 (95% confidence interval [CI], 1.17-1.24) per 0.2-unit increase in KDRI and 1.38 (1.31-1.46) per 10-unit increase in Leuven score. Adjusted relative risks for delayed graft function were 0.98 (95% CI, 0.94-1.02) and 0.94 (95% CI, 0.90-0.99), adjusted hazard ratios for graft failure were 1.10 (95% CI, 1.04-1.16) and 1.11 (95% CI, 1.02-1.21), and adjusted linear regression coefficients for 3-year estimated glomerular filtration rate were -3.88 (-4.63 to -3.13) and -5.18 (-6.19 to -4.18).

CONCLUSIONS

In kidneys clinically selected for procurement biopsy, the Leuven score was more strongly associated with discard but performed similarly to KDRI for predicting transplant outcomes, suggesting the need to reevaluate current procurement biopsy practices. Given modest associations for both tools; however, neither KDRI nor the Leuven score should be used in isolation for individual organ acceptance decisions.

Observations on the ex situ perfusion of livers for transplantation

Normothermic ex situ liver perfusion might allow viability assessment of livers before transplantation. Perfusion characteristics were studied in 47 liver perfusions, of which 22 resulted in transplants. Hepatocellular damage was reflected in the perfusate transaminase concentrations, which correlated with posttransplant peak transaminase levels. Lactate clearance occurred within 3 hours in 46 of 47 perfusions, and glucose rose initially during perfusion in 44. Three livers required higher levels of bicarbonate support to maintain physiological pH, including one developing primary nonfunction. Bile production did not correlate with viability or cholangiopathy, but bile pH, measured in 16 of the 22 transplanted livers, identified three livers that developed cholangiopathy (peak pH < 7.4) from those that did not (pH > 7.5). In the 11 research livers where it could be studied, bile pH > 7.5 discriminated between the 6 livers exhibiting >50% circumferential stromal necrosis of septal bile ducts and 4 without necrosis; one liver with 25-50% necrosis had a maximum pH 7.46. Liver viability during normothermic perfusion can be assessed using a combination of transaminase release, glucose metabolism, lactate clearance, and maintenance of acid-base balance. Evaluation of bile pH may offer a valuable insight into bile duct integrity and risk of posttransplant ischemic cholangiopathy.

Does Rabbit Antithymocyte Globulin (Thymoglobuline®) Have a Role in Avoiding Delayed Graft Function in the Modern Era of Kidney Transplantation?

Delayed graft function (DGF) increases the risk of graft loss by up to 40%, and recent developments in kidney donation have increased the risk of its occurrence. Lowering the risk of DGF, however, is challenging due to a complicated etiology in which ischemia-reperfusion injury (IRI) leads to acute tubular necrosis. Among various strategies explored, the choice of induction therapy is one consideration. Rabbit antithymocyte globulin (rATG [Thymoglobuline]) has complex immunomodulatory effects that are relevant to DGF. In addition to a rapid and profound T-cell depletion, rATG inhibits leukocyte migration and adhesion. Experimental studies of rATG have demonstrated attenuated IRI-related tissue damage in reperfused tissues, consistent with histological evidence from transplant recipients. Starting rATG intraoperatively instead of postoperatively can improve kidney graft function and reduce the incidence of DGF. rATG is effective in preventing acute rejection in kidney transplant recipients at high immunological risk, supporting delayed calcineurin inhibitor (CNI) introduction which protects the graft from early insults. A reduced rate of DGF has been reported with rATG (started intraoperatively) and delayed CNI therapy compared to IL-2RA induction with immediate CNI in patients at high immunological risk, but not in lower-risk patients. Overall, induction with rATG induction is the preferred choice for supporting delayed introduction of CNI therapy to avoid DGF in high-risk patients but shows no benefit versus IL-2RA in lower-risk individuals. Evidence is growing that intraoperative rATG ameliorates IRI, and it seems reasonable to routinely start rATG before reperfusion.

Improved approach for normothermic machine perfusion of cold stored kidney grafts

Normothermic machine perfusion can decrease reperfusion injury in renal transplantation. Clinical procurement logistics include retrieval and initial transport of the graft using static cold storage. Therefore, use and benefits of brief normothermic reconditioning by machine perfusion should be investigated in the initially cold preserved graft. Porcine kidneys (6 per group) were retrieved 20 min after cardiac standstill. After 20 h of static cold preservation some grafts were put on a machine perfusion circuit and normothermically perfused for 2 h at 35°C (NMP). Another group was subjected to controlled oxygenated rewarming (COR), starting perfusion at 8°C and elevating temperature and pressure slowly up to 35°C and 75 mmHg during the first 90 min of 2 h perfusion. Control kidneys were only cold stored (CS). Post implant graft function was evaluated afterwards in an established in vitro reperfusion model. During graft reconditioning, COR reduced oxygen free radical production and formation of 4-hydroxy-2-nonenal (HNE), an activator of mitochondrial uncoupling proteins, in comparison to NMP. Upon reperfusion, NMP only led to a slight improvement of renal function (clearance of creatinine, fractional excretion of Na and glucose) compared to controls. But 2-3 fold improvements of renal function were seen after COR, which also significantly improved aerobic efficiency (total Na absorption/VO₂) upon reperfusion. A slow and controlled increase in temperature up to normothermia improves mitochondrial recovery and oxygen utilization efficiency, resulting in better functional recovery, possibly through a more mild and adapted increase of cellular metabolism.

Systematic review of kidney transplantation functional predictors

CONTEXT

Kidney transplantation from donors with expanded criteria has increased the pool of kidneys at the cost of a higher risk of short and long-term graft dysfunction. The main issue lies in determining which kidneys will offer acceptable function and survival compared with the risk represented by surgery and subsequent immunosuppression.

OBJECTIVE

The objective of our article is to review the current evidence on the tools for predicting the functionality of kidney transplantation from cadaveric donors with expanded criteria and determining the validity for their use in standard practice.

ACQUISITION OF EVIDENCE

We conducted a systematic literature review according to the PRISM criteria, through Medline (http://www.ncbi.nlm.nih.gov) and using the keywords (in isolation or in conjunction) "cadaveric renal transplantation; kidney graft function appraisal, graft function predictors". We selected prospective and retrospective series and review articles. A total of 375 articles were analysed, 39 of which were ultimately selected for review.

SUMMARY OF THE EVIDENCE

The predictors of functionality include the following: The donor risk indices; the calculation of the renal functional weight or the assessment of the nephronic mass; the measurement of vascular resistances during perfusion in hypothermia; the measurement of the donor's biomarkers in urine and in the perfusion liquid; the measurement of functional and reperfusion parameters in normothermia; and the measurement of morphological parameters (microscopic and macroscopic) of the target organ. In this article, we present an explanatory summary of each of these parameters, as well as their most recent evidence on this issue.

DISCUSSION

None of the reviewed parameters in isolation could reliably predict renal function and graft survival. There is a significant void in terms of the macroscopic assessment of kidney transplantation.

CONCLUSIONS

We need to continue developing predictors of renal functionality to accurately define the distribution of each currently available donor kidney.

Renal resistance thresholds during hypothermic machine perfusion and transplantation outcomes - a retrospective cohort study

Renal resistance (RR), of allografts undergoing hypothermic machine perfusion (HMP), is considered a measure of organ quality. We conducted a retrospective cohort study of adult deceased donor kidney transplant (KT) recipients whose grafts underwent HMP. Our aim was to evaluate whether RR is predictive of death-censored graft failure (DCGF). Of 274 KT eligible for analysis, 59% were from expanded criteria donor. RR was modeled as a categorical variable, using a previously identified terminal threshold of 0.4, and 0.2 mmHg/ml/min (median in our cohort). Hazard ratios (HR) of DCGF were 3.23 [95% confidence interval (CI): 1.12-9.34, P = 0.03] and 2.67 [95% CI: 1.14-6.31, P = 0.02] in univariable models, and 2.67 [95% CI: 0.91-7.86, P = 0.07] and 2.42 [95% CI: 1.02-5.72, P = 0.04] in multivariable models, when RR threshold was 0.4 and 0.2, respectively. Increasing risk of DCGF was observed when RR over the course of HMP was modeled using mixed linear regression models: HR of 1.31 [95% CI: 1.07-1.59, P < 0.01] and 1.25 [95% CI: 1.00-1.55, P = 0.05], in univariable and multivariable models, respectively. This suggests that RR during HMP is a predictor of long-term KT outcomes. Prospective studies are needed to assess the survival benefit of patients receiving KT with higher RR in comparison with staying wait-listed.