Assessing Kidney Graft Viability and Its Cells Metabolism during Machine Perfusion

Dynamic conditioning of porcine kidney grafts with extracellular vesicles derived from urine progenitor cells: A proof-of-concept study

 : Among strategies to limit ischemia/reperfusion (IR) injuries in transplantation, cell therapy using stem cells to condition/repair transplanted organs appears promising. We hypothesized that using a cell therapy based on extracellular vesicles (EVs) derived from urine progenitor cells (UPCs) during hypothermic and normothermic machine perfusion can prevent IR-related kidney damage. We isolated and characterized porcine UPCs and their extracellular vesicles (EVs). Then these were used in an ex vivo porcine kidney preservation model. Kidneys were subjected to warm ischemia (32 min) and then preserved by hypothermic machine perfusion (HMP) for 24 h before 5 h of normothermic machine perfusion (NMP). Three groups were performed (n = 5-6): Group 1 (G1): HMP/vehicle + NMP/vehicle, Group 2 (G2): HMP/EVs + NMP/vehicle, Group 3 (G3): HMP/EVs + NMP/EVs. Porcine UPCs were successfully isolated from urine and fully characterized as well as their EVs which were found of expected size/phenotype. EVs injection during HMP alone, NMP alone, or both was feasible and safe and did not impact perfusion parameters. However, cell damage markers (LDH, ASAT) were decreased in G3 compared with G1, and G3 kidneys displayed a preserved tissue integrity with reduced tubular dilatation and inflammation notably. However, renal function indicators such as creatinine clearance measured for 5 h of normothermic perfusion or NGAL perfusate's level were not modified by EVs injection. Regarding perfusate analysis, metabolomic analyses and cytokine quantification showed an immunomodulation signature in G3 compared with G1 and highlighted potential metabolic targets. In vitro, EVs as well as perfusates from G3 partially recovered endothelial cell metabolic activity after hypoxia. Finally, RNA-seq performed on kidney biopsies showed different profiles between G1 and G3 with regulation of potential IR targets of EVs therapy. We showed the feasibility/efficacy of UPC-EVs for hypothermic/normothermic kidney conditioning before transplantation, paving the way for combining machine perfusion with EVs-based cell therapy for organ conditioning. HIGHLIGHTS: ·UPCs from porcine urine can be used to generate a cell therapy product based on extracellular vesicles (pUPC-EVs). ·pUPC-EVs injection during HMP and NMP decreases cell damage markers and has an immunomodulatory effect. ·pUPC-EVs-treated kidneys have distinct biochemical, metabolic, and transcriptomic profiles highlighting targets of interest. ·Our results pave the way for combining machine perfusion with EV-based cell therapy for kidney conditioning.

Normothermic Machine Perfusion Reconstitutes Porcine Kidney Tissue Metabolism But Induces an Inflammatory Response, Which Is Reduced by Complement C5 Inhibition

Normothermic machine perfusion (NMP) is a clinical strategy to reduce renal ischemia-reperfusion injury (IRI). Optimal NMP should restore metabolism and minimize IRI induced inflammatory responses. Microdialysis was used to evaluate renal metabolism. This study aimed to assess the effect of complement inhibition on NMP induced inflammatory responses. Twenty-two pig kidneys underwent 18 h of static cold storage (SCS) followed by 4 h of NMP using a closed-circuit system. Kidneys were randomized to receive a C5-inhibitor or placebo during SCS and NMP. Perfusion resulted in rapidly stabilized renal flow, low renal resistance, and urine production. During SCS, tissue microdialysate levels of glucose and pyruvate decreased significantly, whereas glycerol increased (p < 0.001). In the first hour of NMP, glucose and pyruvate increased while glycerol decreased (p < 0.001). After 4 h, all metabolites had returned to baseline. Inflammatory markers C3a, soluble C5b-9, TNF, IL-6, IL-1β, IL-8, and IL-10 increased significantly during NMP in perfusate and kidney tissue. C5-inhibition significantly decreased perfusate and urine soluble C5b-9 (p < 0.001; p = 0.002, respectively), and tissue IL-1β (p = 0.049), but did not alter other inflammatory markers. Microdialysis can accurately monitor the effect of NMP on renal metabolism. Closed-circuit NMP induces inflammation, which appeared partly complement-mediated. Targeting additional immune inhibitors should be the next step.

Major determinants of primary non function from kidney donation after Maastricht II circulatory death: A single center experience

PURPOSE

Organ shortage greatly limits treatment of patients with end-stage chronic kidney. Maastricht type 2 donation after circulatory death (DCD) has been shown to have similar results in long term outcomes in kidney transplantation, when compared with brain dead donation. Our main goal was to assess Maastricht type 2 DCD and evaluate factors that impact on early graft function.

METHODS

A retrospective study was conducted in an ECMO Referral Centre. All patients who received a kidney transplant from Maastricht type 2 DCD were included in study. Early graft function and short term outcomes were assessed.

RESULTS

From October 2017 to December 2022, 47 renal grafts were collected from 24 uDCD donors. Median warm ischemia time was 106 min (94-115), cannulation time was 10 min (8; 20) and duration of extracorporeal reperfusion (ANOR) was 180 min (126-214). Regarding early graft function, 25% had immediate graft function, 63.6% had delayed graft function and 11.4% had primary non-function (PNF). There was a correlation between cannulation time (p = 0.006) and ANOR with PNF (p = 0.016).

CONCLUSIONS

Cannulation time and ANOR were the main factors that correlated with PNF. Better understanding of underlying mechanisms should be sought in future studies to reduce the incidence of PNF.

Energy Metabolism and Metformin: Effects on Ischemia-Reperfusion Injury in Kidney Transplantation

Metformin (MTF) is the only biguanide included in the World Health Organization's list of essential medicines; representing a widespread drug in the management of diabetes mellitus. With its accessibility and affordability being one of its biggest assets, it has become the target of interest for many trying to find alternative treatments for varied pathologies. Over time, an increasing body of evidence has shown additional roles of MTF, with unexpected interactions of benefit in other diseases. Metformin (MTF) holds significant promise in mitigating ischemia-reperfusion injury (IRI), particularly in the realm of organ transplantation. As acceptance criteria for organ transplants expand, IRI during the preservation phase remain a major concern within the transplant community, prompting a keen interest in MTF's effects. Emerging evidence suggests that administering MTF during reperfusion may activate the reperfusion injury salvage kinase (RISK) pathway. This pathway is pivotal in alleviating IRI in transplant recipients, potentially leading to improved outcomes such as reduced rates of organ rejection. This review aims to contextualize MTF historically, explore its current uses, pharmacokinetics, and pharmacodynamics, and link these aspects to the pathophysiology of IRI to illuminate its potential future role in transplantation. A comprehensive survey of the current literature highlights MTF's potential to recondition and protect against IRI by attenuating free radical damage, activating AMP-activated protein kinase to preserve cellular energy and promote repair, as well as directly reducing inflammation and enhancing microcirculation.

Necroptosis-related genes allow novel insights into predicting graft loss and diagnosing delayed graft function in renal transplantation

Ischemia-reperfusion injury (IRI) is an inevitable pathophysiological phenomenon in kidney transplantation. Necroptosis is an undoubtedly important contributing mechanism in renal IRI. We first screened differentially expressed necroptosis-related genes (DENRGs) from public databases. Eight DENRGs were validated by independent datasets and verified by qRT-PCR in a rat IRI model. We used univariate and multivariate Cox regression analyses to establish a prognostic signature, and graft survival analysis was performed. Immune infiltrating landscape analysis and gene set enrichment analysis (GSEA) were performed to understand the underlying mechanisms of graft loss, which suggested that necroptosis may aggravate the immune response, resulting in graft loss. Subsequently, a delayed graft function (DGF) diagnostic signature was constructed using the Least Absolute Shrinkage and Selection Operator (LASSO) and exhibited robust efficacy in validation datasets. After comprehensively analyzing DENRGs during IRI, we successfully constructed a prognostic signature and DGF predictive signature, which may provide clinical insights for kidney transplant.

Progress in preservation of intestinal grafts by oxygenated hypothermic machine perfusion

Intestine transplantation (IT) is a critical treatment strategy for irreversible intestinal failure. Among all abdominal solid organ transplants, the intestine was the most vulnerable to ischemia and reperfusion injury (IRI). The static cold storage (SCS) technique is currently the most commonly used graft preservation method, but its hypoxia condition causes metabolic disorders, resulting in the occurrence of IRI, limiting its application in marginal organs. It is especially important to improve preservation techniques in order to minimize damage to marginal donor organs, which draws more attention to machine perfusion (MP). There has been much debate about whether it is necessary to increase oxygen in these conditions to support low levels of metabolism since the use of machine perfusion to preserve organs. There is evidence that oxygenation helps to restore intracellular ATP levels in the intestine after thermal or cold ischemia damage. The goal of this review is to provide an overview of the role of oxygen in maintaining environmental stability in the gut under hypoxic conditions, as well as to investigate the possibilities and mechanisms of oxygen delivery during preservation in intestine transplantation studies and clinical models.

Addition of a liver to the normothermic perfusion circuit reduces renal pro-inflammatory factors

BACKGROUND

Normothermic machine perfusion (NMP) provides a novel platform to preserve isolated organs in an artificial condition. Our study aimed to explore the interaction between the liver and kidney at an ex vivo organ level by adding a liver to the kidney NMP circuit.

METHODS

Porcine kidney and liver obtained from abattoir were subjected to 9 h NMP after suffering 30-min warm ischemia time and 90-min cold ischemia time. The liver-kidney NMP group (n = 5) and the single-kidney NMP group (n = 5) were designed. During the NMP, perfusion parameters, blood gas analysis, and tissue samples were compared.

RESULTS

The perfusate of both groups remained stable, and continuous urine production was observed during NMP. In the liver-kidney NMP group, the lactate level was low, while blood urea nitrogen increased and glucose levels decreased. After the NMP, the renal tissue in the liver-kidney group exhibited fewer histological changes such as tubular epithelium vacuolization, along with reduced expression of IL-6, IL-8, IL-1β, NLRP3, and GSDMD.

CONCLUSIONS

Our results indicated that the expression of renal pro-inflammatory factors was reduced in the liver-kidney NMP system.

Intermittent Surface Oxygenation Results in Similar Mitochondrial Protection and Maintenance of Aerobic Metabolism as Compared to Continuous Oxygenation during Hypothermic Machine Kidney Machine Perfusion

Short bubble and subsequent surface oxygenation is an innovative oxygenation technique and alternative for membrane oxygenation during hypothermic machine perfusion (HMP). The metabolic effect of the interruption of surface oxygenation for 4 h (mimicking organ transport) during HMP was compared to continuous surface and membrane oxygenation in a pig kidney ex situ preservation model. After 30 min of warm ischemia by vascular clamping, a kidney of a ±40 kg pig was procured and subsequently preserved according to one of the following groups: (1) 22-h HMP + intermittent surface oxygenation (n = 12); (2) 22-h HMP + continuous membrane oxygenation (n = 6); and (3) 22-h HMP + continuous surface oxygenation (n = 7). Brief perfusate O2 uploading before kidney perfusion was either obtained by direct bubble (groups 1, 3) or by membrane (group 2) oxygenation. Bubble oxygenation during minimum 15 min was as efficient as membrane oxygenation in achieving supraphysiological perfusate pO2 levels before kidney perfusion. Metabolic tissue analysis (i.e., lactate, succinate, ATP, NADH, and FMN) during and at the end of the preservation period demonstrated similar mitochondrial protection between all study groups. Short bubble and subsequent intermittent surface oxygenation of the perfusate of an HMP-kidney might be an effective and cheap preservation strategy to protect mitochondria, eliminating the need/costs of a membrane oxygenator and oxygen source during transport.

Whole-Organ Pancreas and Islets Transplantations in UK: An Overview and Future Directions

Whole-organ pancreas and islets transplantations are two therapeutic options to treat type 1 diabetic patients resistant to optimised medical treatment in whom severe complications develop. Selection of the best option for β-cell replacement depends on several factors such as kidney function, patient comorbidities, and treatment goals. For a patient with end-stage kidney disease, the treatment of choice is often a simultaneous transplant of the pancreas and kidney (SPK). However, it remains a major surgical procedure in patients with multiple comorbidities and therefore it is important to select those who will benefit from it. Additionally, in view of the organ shortage, new strategies to improve outcomes and reduce immune reactions have been developed, including dynamic organ perfusion technologies, pancreas bioengineering, and stem cell therapies. The purpose of this article is to review the indications, surgical techniques, outcomes, and future directions of whole-organ pancreas and islets transplantations.

Current Evidence and Future Perspectives to Implement Continuous and End-Ischemic Use of Normothermic and Oxygenated Hypothermic Machine Perfusion in Clinical Practice

The use of high-risk renal grafts for transplantation requires the optimization of pretransplant assessment and preservation reconditioning strategies to decrease the organ discard rate and to improve short- and long-term clinical outcomes. Active oxygenation is increasingly recognized to play a central role in dynamic preservation strategies, independent of preservation temperature, to recondition mitochondria and to restore the cellular energy profile. The oxygen-related decrease in mitochondrial succinate accumulation ameliorates the harmful effects of ischemia-reperfusion injury. The differences between normothermic and hypothermic machine perfusion with regard to organ assessment, preservation, and reconditioning, as well as the logistic and economic implications, are factors to take into consideration for implementation at a local level. Therefore, these different techniques should be considered complementary to the perfusion strategy selected depending on functional intention and resource availability. This review provides an overview of the current clinical evidence of normothermic and oxygenated hypothermic machine perfusion, either as a continuous or end-ischemic preservation strategy, and future perspectives.

Protective effects of mefunidone on ischemia-reperfusion injury/Folic acid-induced acute kidney injury

Renal ischemia-reperfusion injury (IRI) is one of the most common causes of acute kidney injury (AKI). It poses a significant threat to public health, and effective therapeutic drugs are lacking. Mefunidone (MFD) is a new pyridinone drug that exerts a significant protective effect on diabetic nephropathy and the unilateral ureteral obstruction (UUO) model in our previous study. However, the effects of mefunidone on ischemia-reperfusion injury-induced acute kidney injury remain unknown. In this study, we investigated the protective effect of mefunidone against ischemia-reperfusion injury-induced acute kidney injury and explored the underlying mechanism. These results revealed that mefunidone exerted a protective effect against ischemia-reperfusion injury-induced acute kidney injury. In an ischemia-reperfusion injury-induced acute kidney injury model, treatment with mefunidone significantly protected the kidney by relieving kidney tubular injury, suppressing oxidative stress, and inhibiting kidney tubular epithelial cell apoptosis. Furthermore, we found that mefunidone reduced mitochondrial damage, regulated mitochondrial-related Bax/bcl2/cleaved-caspase3 apoptotic protein expression, and protected mitochondrial electron transport chain complexes III and V levels both in vivo and in vitro, along with a protective effect on mitochondrial membrane potential in vitro. Given that folic acid (FA)-induced acute kidney injury is a classic model, we used this model to further validate the efficacy of mefunidone in acute kidney injury and obtained the same conclusion. Based on the above results, we conclude that mefunidone has potential protective and therapeutic effects in both ischemia-reperfusion injury- and folic acid-induced acute kidney injury.

Kidney utilization in the Netherlands - do we optimally use our donor organs?

BACKGROUND

To ensure optimal utilization of deceased donor kidneys, it is important to understand the precise reasons why kidneys are discarded. In this study we aimed to obtain a comprehensive overview of kidney utilization and discard during the entire donation process in the Netherlands.

METHODS

In this retrospective cohort study we analysed kidney utilization of 3856 kidneys in the Netherlands between 1 January 2015 and 31 December 2020. For every kidney that was not transplanted, we determined the moment of and reason for discard through a unique case-by-case assessment.

RESULTS

Kidney discard according to the traditional definition (procured but not transplanted) was 7.8%. However, when kidneys that seemed medically suitable at the beginning of the donation process were also included, many more potential donor kidneys were lost and the total non-utilization was 24.4%. Subjectively presumed impaired organ quality was responsible for 34.2% of all discarded kidneys. Two-thirds of kidneys discarded due to acute kidney injury (AKI) had only AKI stage 1 or 2.

CONCLUSION

The classical definition of organ discard underestimates the non-utilization of deceased donor kidneys. Strategies to improve kidney utilization could be a revision of the maximum allowed agonal time in donation after circulatory death, careful consideration in reporting and accepting kidneys from donors with AKI and a prospectively filled registry of detailed organ discard reasons, including the 'silent' non-utilization before procurement.

Cancer Metabolism and Ischemia-Reperfusion Injury: Two Sides of the Same Coin

Cancer cells are characterized by the reprogramming of certain cell metabolisms via activation of definite pathways and regulation of gene signaling. Ischemia-reperfusion injury (IRI) is characterized by tissue damage and death following a lack of perfusion and oxygenation. It is most commonly seen in the setting of organ transplantation. Interestingly, the microenvironments seen in cancer and ischemic tissues are quite similar, especially due to the hypoxic state that occurs in both. As a consequence, there is genetic signaling involved in response to IRI that has common pathways with cancer. Some of these changes are seen across the board with many cancer cells and are known as Hallmarks of Cancer, among which are aerobic glycolysis and the induction of angiogenesis. This literature review aims to compare the metabolic pathways that are altered in cancer tissues and in normal tissues subjected to IRI in order to find common adaptive processes and to identify key pathways that could represent a therapeutic target in both pathologies. By increasing our understanding of this relationship, clinical correlations can be made and applied practically to improve outcomes of transplanted organs, given the known association with acute rejection, delayed graft function, and poor graft survival. The following metabolic pathways are discussed in our review, both in the setting of cancer and IRI: apoptosis, glycolysis, and angiogenesis. The role of the immune system in both pathologies as well as mitochondrial function and the production of reactive oxygen species (ROS) are reviewed.

Contrast Enhanced Ultrasound Compared with MRI and CT in the Evaluation of Post-Renal Transplant Complications

Renal transplantation (RT) is the treatment of choice for end-stage renal disease, significantly improving patients’ survival and quality of life. However, approximately 3–23% of patients encounter post-operative complications, and radiology plays a major role for their early detection and treatment or follow-up planning. CT and MRI are excellent imaging modalities to evaluate renal transplant post-operative course; nevertheless, they are both associated with a high cost and low accessibility, as well as some contraindications, making them not feasible for all patients. In particular, gadolinium-based contrast can lead to the rare condition of nephrogenic systemic fibrosis, and iodine-based contrast can lead to contrast-induced nephropathy (CIN). CT also exposes the patients who may require multiple examinations to ionizing radiation. Therefore, considering the overall advantages and disadvantages, contrast-enhanced ultrasound (CEUS) is presently considered an effective first-line imaging modality for post-operative early and long-term follow-up in RT, reducing the need for biopsies and providing adequate guidance for drainage procedures. Hence, this paper aims to review the updated knowledge on CEUS compared with CT and MRI for the evaluation of RT renal transplant complications; advantages, limitations, and possible recommendations are provided.

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.

Simply Adding Oxygen during Hypothermic Machine Perfusion to Combat the Negative Effects of Ischemia-Reperfusion Injury: Fundamentals and Current Evidence for Kidneys

The use of high-risk renal grafts for transplantation requires optimization of pretransplant preservation and assessment strategies to improve clinical outcomes as well as to decrease organ discard rate. With oxygenation proposed as a resuscitative measure during hypothermic machine preservation, this review provides a critical overview of the fundamentals of active oxygenation during hypothermic machine perfusion, as well as the current preclinical and clinical evidence and suggests different strategies for clinical implementation.

A Role for Human Renal Tubular Epithelial Cells in Direct Allo-Recognition by CD4+ T-Cells and the Effect of Ischemia-Reperfusion

Direct allorecognition is the earliest and most potent immune response against a kidney allograft. Currently, it is thought that passenger donor professional antigen-presenting cells (APCs) are responsible. Further, many studies support that graft ischemia-reperfusion injury increases the probability of acute rejection. We evaluated the possible role of primary human proximal renal tubular epithelial cells (RPTECs) in direct allorecognition by CD4+ T-cells and the effect of anoxia-reoxygenation. In cell culture, we detected that RPTECs express all the required molecules for CD4+ T-cell activation (HLA-DR, CD80, and ICAM-1). Anoxia-reoxygenation decreased HLA-DR and CD80 but increased ICAM-1. Following this, RPTECs were co-cultured with alloreactive CD4+ T-cells. In T-cells, zeta chain phosphorylation and c-Myc increased, indicating activation of T-cell receptor and co-stimulation signal transduction pathways, respectively. T-cell proliferation assessed with bromodeoxyuridine assay and with the marker Ki-67 increased. Previous culture of RPTECs under anoxia raised all the above parameters in T-cells. FOXP3 remained unaffected in all cases, signifying that proliferating T-cells were not differentiated towards a regulatory phenotype. Our results support that direct allorecognition may be mediated by RPTECs even in the absence of donor-derived professional APCs. Also, ischemia-reperfusion injury of the graft may enhance the above capacity of RPTECs, increasing the possibility of acute rejection.