Defective postreperfusion metabolic recovery directly associates with incident delayed graft function

Development and Validation of Ultrasound Hemodynamic-based Prediction Models for Acute Kidney Injury After Renal Transplantation

RATIONALE AND OBJECTIVES

Acute kidney injury (AKI) post-renal transplantation often has a poor prognosis. This study aimed to identify patients with elevated risks of AKI after kidney transplantation.

MATERIALS AND METHODS

A retrospective analysis was conducted on 422 patients who underwent kidney transplants from January 2020 to April 2023. Participants from 2020 to 2022 were randomized to training group (n=261) and validation group 1 (n=113), and those in 2023, as validation group 2 (n=48). Risk factors were determined by employing logistic regression analysis alongside the least absolute shrinkage and selection operator, making use of ultrasound hemodynamic, clinical, and laboratory information. Models for prediction were developed using logistic regression analysis and six machine-learning techniques. The evaluation of the logistic regression model encompassed its discrimination, calibration, and applicability in clinical settings, and a nomogram was created to illustrate the model. SHapley Additive exPlanations were used to explain and visualize the best of the six machine learning models.

RESULTS

The least absolute shrinkage and selection operator combined with logistic regression identified and incorporated five risk factors into the predictive model. The logistic regression model (AUC=0.927 in the validation set 1; AUC=0.968 in the validation set 2) and the random forest model (AUC=0.946 in the validation set 1;AUC=0.996 in the validation set 2) showed good performance post-validation, with no significant difference in their predictive accuracy.

CONCLUSION

These findings can assist clinicians in the early identification of patients at high risk for AKI, allowing for timely interventions and potentially enhancing the prognosis following kidney transplantation.

Clinical ischemia-reperfusion injury: Driven by reductive rather than oxidative stress? A narrative review

Ischemia-reperfusion (IR) injury remains a major contributor to organ dysfunction following transient ischemic insults. Although numerous interventions have been found effective to reduce IR injury in preclinical models, none of these therapies have been successfully translated to the clinical setting. In the context of the persistent translational gap, we systematically investigated the mechanisms implicated in IR injury using kidney donation and transplantation as a clinical model of IR. Whilst our results do not implicate traditional culprits such as reactive oxygen species, complement activation or inflammation as triggers of IR injury, they reveal a clear metabolic signature for renal IR injury. This discriminatory signature of IR injury is consistent with a post-reperfusion metabolic paralysis and involves high-energy phosphate depletion, tricarboxylic acid cycle defects, and a compensatory activation of catabolic routes. Against this background, the picture emerges that clinical IR injury is driven by reductive stress. In this article, we therefore wish to elaborate on the processes contributing to reductive stress in the context of clinical IR injury and provide a better insight in potential clinical therapeutic strategies that might be helpful in restoring the redox balance.

Assessment of metabolites in urine in post-kidney transplant patients: insights into allograft function and creatinine clearance

INTRODUCTION

The suboptimal function of transplanted kidney can lead to imbalances in processes controlled by the kidneys, necessitating long-term monitoring of the graft's function and viability. Given the kidneys' high metabolic activity, a metabolomics approach is well-suited for tracking changes in post-transplant patients and holds significant potential for monitoring graft function.

OBJECTIVES

Examination of the response of urinary creatinine levels to (i) serum creatinine levels and (ii) allograft function during periods of impaired kidney function in post-transplant patients.

METHODS

We analyzed morning and 24-h urine samples from 55 patients who underwent primary kidney transplantation and were uniformly treated with immunosuppressants, with an average follow-up of 50 months post-surgery. We assessed the relative levels of urinary metabolites detectable by NMR spectroscopy and investigated correlations between these metabolite levels and renal function.

RESULTS

We observed rather unexpected independence of urinary creatinine levels on levels of serum creatinine as well as on allograft function expressed by eGFR (estimated glomerular filtration rate). This observation allowed a very good agreement of outcomes from raw and creatinine-normalized data, consistent for both morning urine samples and 24-h urine collections. The urinary levels of citrate and acetone were detected to be sensitive to allograft function, and the urinary levels of metabolites in combination showed promising prediction for kidney function, on the level of p-value: for 24 h pooled urine: 4.6 × 10-12 and morning urine: 5.36 × 10-9. We discussed the data also in the light of metabolic changes in blood plasma.

CONCLUSION

We support the opinion of critical assessment of renal creatinine clearance when judging the filtration function of the allograft. As the next, urinary metabolomics can serve as an easily available supplement to prediction for allograft function in patients after kidney transplantation.

Red blood cells as oxygen carrier during normothermic machine perfusion of kidney grafts: Friend or foe?

Renal ex vivo normothermic machine perfusion (NMP) is under development as an assessment tool for high-risk kidney grafts and as a means of achieving more physiologically accurate organ preservation. On-going hemolysis has been reported during NMP, as this technique relies on red blood cells for oxygen delivery. In this study, we confirm the occurrence of progressive hemolysis during 6-hour kidney NMP. NMP-associated erythrostasis in the glomeruli and in peri-glomerular vascular networks points to an interaction between the red blood cells and the graft. Continuous hemolysis resulted in prooxidative changes in the perfusate, which could be quenched by addition of fresh frozen plasma. In a cell-based system, this hemolysis induced redox stress and exhibited toxic effects at high concentrations. These findings highlight the need for a more refined oxygen carrier in the context of renal NMP.

Metabolomic and lipidomic landscape of porcine kidney associated with kidney perfusion in heart beating donors and donors after cardiac death

Transplant centers are currently facing a lack of tools to ensure adequate evaluation of the quality of the available organs, as well as a significant shortage of kidney donors. Therefore, efforts are being made to facilitate the effective use of available organs and expand the donor pool, particularly with expanded criteria donors. Fulfilling a need, we aim to present an innovative analytical method based on solid-phase microextraction (SPME) - chemical biopsy. In order to track changes affecting the organ throughout the entire transplant procedure, porcine kidneys were subjected to multiple samplings at various time points. The application of small-diameter SPME probes assured the minimal invasiveness of the procedure. Porcine model kidney autotransplantation was executed for the purpose of simulating two types of donor scenarios: donors with a beating heart (HBD) and donors after cardiac death (DCD). All renal grafts were exposed to continuous normothermic ex vivo perfusion. Following metabolomic and lipidomic profiling using high-performance liquid chromatography coupled to a mass spectrometer, we observed differences in the profiles of HBD and DCD kidneys. The alterations were predominantly related to energy and glucose metabolism, and differences in the levels of essential amino acids, purine nucleosides, lysophosphocholines, phosphoethanolamines, and triacylglycerols were noticed. Our results indicate the potential of implementing chemical biopsy in the evaluation of graft quality and monitoring of renal function during perfusion.

Kidney Tissue Proteome Profiles in Short Versus Long Duration of Delayed Graft Function - A Pilot Study in Donation After Circulatory Death Donors

Introduction

Delayed graft function (DGF) is often defined as the need for dialysis treatment in the first week after a kidney transplantation. This definition, though readily applicable, is generic and unable to distinguish between "types" of DGF or time needed to recover function that may also significantly affect longer-term outcomes. We aimed to profile biological pathways in donation after circulatory death (DCD) kidney donors that correlate with DGF and different DGF durations.

Methods

A total of N = 30 DCD kidney biopsies were selected from the UK Quality in Organ Donation (QUOD) biobank and stratified according to DGF duration (immediate function, IF n = 10; "short-DGF" (1-6 days), SDGF n = 10; "long-DGF" (7-22 days), LDGF n = 10). Samples were matched for donor and recipient demographics and analyzed by label-free quantitative (LFQ) proteomics, yielding identification of N = 3378 proteins.

Results

Ingenuity pathway analysis (IPA) on differentially abundant proteins showed that SDGF kidneys presented upregulation of stress response pathways, whereas LDGF presented impaired response to stress, compared to IF. LDGF showed extensive metabolic deficits compared to IF and SDGF.

Conclusion

DCD kidneys requiring dialysis only in the first week posttransplant present acute cellular injury at donation, alongside repair pathways upregulation. In contrast, DCD kidneys requiring prolonged dialysis beyond 7 days present minimal metabolic and antioxidant responses, suggesting that current DGF definitions might not be adequate in distinguishing different patterns of injury in donor kidneys contributing to DGF.

How to Best Protect Kidneys for Transplantation-Mechanistic Target

The increasing number of patients on the kidney transplant waiting list underlines the need to expand the donor pool and improve kidney graft utilization. By protecting kidney grafts adequately from the initial ischemic and subsequent reperfusion injury occurring during transplantation, both the number and quality of kidney grafts could be improved. The last few years have seen the emergence of many new technologies to abrogate ischemia-reperfusion (I/R) injury, including dynamic organ preservation through machine perfusion and organ reconditioning therapies. Although machine perfusion is gradually making the transition to clinical practice, reconditioning therapies have not yet progressed from the experimental setting, pointing towards a translational gap. In this review, we discuss the current knowledge on the biological processes implicated in I/R injury and explore the strategies and interventions that are being proposed to either prevent I/R injury, treat its deleterious consequences, or support the reparative response of the kidney. Prospects to improve the clinical translation of these therapies are discussed with a particular focus on the need to address multiple aspects of I/R injury to achieve robust and long-lasting protective effects on the kidney graft.

Metabolic flux between organs measured by arteriovenous metabolite gradients

Mammalian organs convert dietary nutrients into circulating metabolites and share them to maintain whole-body metabolic homeostasis. While the concentrations of circulating metabolites have been frequently measured in a variety of pathophysiological conditions, the exchange flux of circulating metabolites between organs is not easily measurable due to technical difficulties. Isotope tracing is useful for measuring such fluxes for a metabolite of interest, but the shuffling of isotopic atoms between metabolites requires mathematical modeling. Arteriovenous metabolite gradient measurements can complement isotope tracing to infer organ-specific net fluxes of many metabolites simultaneously. Here, we review the historical development of arteriovenous measurements and discuss their advantages and limitations with key example studies that have revealed metabolite exchange flux between organs in diverse pathophysiological contexts.

Circulating Metabolites in Relation to the Kidney Allograft Function in Posttransplant Patients

End-stage kidney disease is preferably treated by kidney transplantation. The suboptimal function of the allograft often results in misbalances in kidney-controlled processes and requires long-term monitoring of allograft function and viability. As the kidneys are organs with a very high metabolomic rate, a metabolomics approach is suitable to describe systematic changes in post-transplant patients and has great potential for monitoring allograft function, which has not been described yet. In this study, we used blood plasma samples from 55 patients after primary kidney transplantation identically treated with immunosuppressants with follow-up 50 months in the mean after surgery and evaluated relative levels of basal plasma metabolites detectable by NMR spectroscopy. We were looking for the correlations between circulating metabolites levels and allograft performance and allograft rejection features. Our results imply a quantitative relationship between restricted renal function, insufficient hydroxylation of phenylalanine to tyrosine, lowered renal glutamine utilization, shifted nitrogen balance, and other alterations that are not related exclusively to the metabolism of the kidney. No link between allograft function and energy metabolism can be concluded, as no changes were found for glucose, glycolytic intermediates, and 3-hydroxybutyrate as a ketone body representative. The observed changes are to be seen as a superposition of changes in the comprehensive inter-organ metabolic exchange, when the restricted function of one organ may induce compensatory effects or cause secondary alterations. Particular differences in plasma metabolite levels in patients with acute cellular and antibody-mediated allograft rejection were considered rather to be related to the loss of kidney function than to the molecular mechanism of graft rejection since they largely follow the alterations observed by restricted allograft function. In the end, we showed using a simple mathematical model, multilinear regression, that the basal plasmatic metabolites correlated with allograft function expressed by the level of glomerular filtration rate (with creatinine: p-value = 4.0 × 10⁻²⁶ and r = 0.94, without creatinine: p-value = 3.2 × 10⁻²² and r = 0.91) make the noninvasive estimation of the allograft function feasible.

Estimated Renal Metabolomics at Reperfusion Predicts One-Year Kidney Graft Function

Renal transplantation is the gold-standard procedure for end-stage renal disease patients, improving quality of life and life expectancy. Despite continuous advancement in the management of post-transplant complications, progress is still needed to increase the graft lifespan. Early identification of patients at risk of rapid graft failure is critical to optimize their management and slow the progression of the disease. In 42 kidney grafts undergoing protocol biopsies at reperfusion, we estimated the renal metabolome from RNAseq data. The estimated metabolites' abundance was further used to predict the renal function within the first year of transplantation through a random forest machine learning algorithm. Using repeated K-fold cross-validation we first built and then tuned our model on a training dataset. The optimal model accurately predicted the one-year eGFR, with an out-of-bag root mean square root error (RMSE) that was 11.8 ± 7.2 mL/min/1.73 m2. The performance was similar in the test dataset, with a RMSE of 12.2 ± 3.2 mL/min/1.73 m2. This model outperformed classic statistical models. Reperfusion renal metabolome may be used to predict renal function one year after allograft kidney recipients.

Assessing Kidney Graft Viability and Its Cells Metabolism during Machine Perfusion

Kidney transplantation is the golden treatment for end-stage renal disease. Static cold storage is currently considered the standard method of preservation, but dynamic techniques, such as machine perfusion (MP), have been shown to improve graft function, especially in kidneys donated by extended criteria donors and donation after circulatory death. With poor organ quality being a major reason for kidneys not being transplanted, an accurate, objective and reliable quality assessment during preservation could add value and support to clinicians' decisions. MPs are emerging technologies with the potential to assess kidney graft viability and quality, both in the hypothermic and normothermic scenarios. The aim of this review is to summarize current tools for graft viability assessment using MP prior to implantation in relation to the ischemic damage.

Current progress in the therapeutic options for mitochondrial disorders

Mitochondrial disorders manifest enormous genetic and clinical heterogeneity - they can appear at any age, present with various phenotypes affecting any organ, and display any mode of inheritance. What mitochondrial diseases do have in common, is impairment of respiratory chain activity, which is responsible for more than 90% of energy production within cells. While diagnostics of mitochondrial disorders has been accelerated by introducing Next-Generation Sequencing techniques in recent years, the treatment options are still very limited. For many patients only a supportive or symptomatic therapy is available at the moment. However, decades of basic and preclinical research have uncovered potential target points and numerous compounds or interventions are now subjects of clinical trials. In this review, we focus on current and emerging therapeutic approaches towards the treatment of mitochondrial disorders. We focus on small compounds, metabolic interference, such as endurance training or ketogenic diet and also on genomic approaches.

Renal gluconeogenesis: an underestimated role of the kidney in systemic glucose metabolism

Glucose levels are tightly regulated at all times. Gluconeogenesis is the metabolic pathway dedicated to glucose synthesis from non-hexose precursors. Gluconeogenesis is critical for glucose homoeostasis, particularly during fasting or stress conditions. The renal contribution to systemic gluconeogenesis is increasingly recognized. During the post-absorptive phase, the kidney accounts for ∼40% of endogenous gluconeogenesis, occurring mainly in the kidney proximal tubule. The main substrate for renal gluconeogenesis is lactate and the process is regulated by insulin and cellular glucose levels, but also by acidosis and stress hormones. The kidney thus plays an important role in the maintenance of glucose and lactate homoeostasis during stress conditions. The impact of acute and chronic kidney disease and proximal tubular injury on gluconeogenesis is not well studied. Recent evidence shows that in both experimental and clinical acute kidney injury, impaired renal gluconeogenesis could significantly participate in systemic metabolic disturbance and thus alter the prognosis. This review summarizes the biochemistry of gluconeogenesis, the current knowledge of kidney gluconeogenesis, its modifications in kidney disease and the clinical relevance of this fundamental biological process in human biology.

Spatiotemporal ATP Dynamics during AKI Predict Renal Prognosis

BACKGROUND

Depletion of ATP in renal tubular cells plays the central role in the pathogenesis of kidney diseases. Nevertheless, inability to visualize spatiotemporal in vivo ATP distribution and dynamics has hindered further analysis.

METHODS

A novel mouse line systemically expressing an ATP biosensor (an ATP synthase subunit and two fluorophores) revealed spatiotemporal ATP dynamics at single-cell resolution during warm and cold ischemic reperfusion (IR) with two-photon microscopy. This experimental system enabled quantification of fibrosis 2 weeks after IR and assessment of the relationship between the ATP recovery in acute phase and fibrosis in chronic phase.

RESULTS

Upon ischemia induction, the ATP levels of proximal tubule (PT) cells decreased to the nadir within a few minutes, whereas those of distal tubule (DT) cells decreased gradually up to 1 hour. Upon reperfusion, the recovery rate of ATP in PTs was slower with longer ischemia. In stark contrast, ATP in DTs was quickly rebounded irrespective of ischemia duration. Morphologic changes of mitochondria in the acute phase support the observation of different ATP dynamics in the two segments. Furthermore, slow and incomplete ATP recovery of PTs in the acute phase inversely correlated with fibrosis in the chronic phase. Ischemia under conditions of hypothermia resulted in more rapid and complete ATP recovery with less fibrosis, providing a proof of concept for use of hypothermia to protect kidney tissues.

CONCLUSIONS

Visualizing spatiotemporal ATP dynamics during IR injury revealed higher sensitivity of PT cells to ischemia compared with DT cells in terms of energy metabolism. The ATP dynamics of PTs in AKI might provide prognostic information.

Organ-specific metabolic profiles of the liver and kidney during brain death and afterwards during normothermic machine perfusion of the kidney

We investigated metabolic changes during brain death (BD) using hyperpolarized magnetic resonance (MR) spectroscopy and ex vivo graft glucose metabolism during normothermic isolated perfused kidney (IPK) machine perfusion. BD was induced in mechanically ventilated rats by inflation of an epidurally placed catheter; sham-operated rats served as controls. Hyperpolarized [1-¹³ C]pyruvate MR spectroscopy was performed to quantify pyruvate metabolism in the liver and kidneys at 3 time points during BD, preceded by injecting hyperpolarized[1-¹³ C]pyruvate. Following BD, glucose oxidation was measured using tritium-labeled glucose (d-6-3H-glucose) during IPK reperfusion. Quantitative polymerase chain reaction and biochemistry were performed on tissue/plasma. Immediately following BD induction, lactate increased in both organs (liver: eµ_d 0.21, 95% confidence interval [CI] [-0.27, -0.15]; kidney: eµ_d 0.26, 95% CI [-0.40, -0.12]. After 4 hours of BD, alanine production decreased in the kidney (eµ_d 0.14, 95% CI [0.03, 0.25], P < .05). Hepatic lactate and alanine profiles were significantly different throughout the experiment between groups (P < .01). During IPK perfusion, renal glucose oxidation was reduced following BD vs sham animals (eµ_d 0.012, 95% CI [0.004, 0.03], P < .001). No differences in enzyme activities were found. Renal gene expression of lactate-transporter MCT4 increased following BD (P < .01). In conclusion, metabolic processes during BD can be visualized in vivo using hyperpolarized magnetic resonance imaging and with glucose oxidation during ex vivo renal machine perfusion. These techniques can detect differences in the metabolic profiles of the liver and kidney following BD.

Results of an explorative clinical evaluation suggest immediate and persistent post-reperfusion metabolic paralysis drives kidney ischemia reperfusion injury

Delayed graft function is the manifestation of ischemia reperfusion injury in the context of kidney transplantation. While hundreds of interventions successfully reduce ischemia reperfusion injury in experimental models, all clinical interventions have failed. This explorative clinical evaluation examined possible metabolic origins of clinical ischemia reperfusion injury combining data from 18 pre- and post-reperfusion tissue biopsies with 36 sequential arteriovenous blood samplings over the graft in three study groups. These groups included living and deceased donor grafts with and without delayed graft function. Group allocation was based on clinical outcome. Magic angle NMR was used for tissue analysis and mass spectrometry-based platforms were used for plasma analysis. All kidneys were functional at one-year. Integration of metabolomic data identified a discriminatory profile to recognize future delayed graft function. This profile was characterized by post-reperfusion ATP/GTP catabolism (significantly impaired phosphocreatine recovery and significant persistent (hypo)xanthine production) and significant ongoing tissue damage. Failing high-energy phosphate recovery occurred despite activated glycolysis, fatty-acid oxidation, glutaminolysis and autophagia, and related to a defect at the level of the oxoglutarate dehydrogenase complex in the Krebs cycle. Clinical delayed graft function due to ischemia reperfusion injury associated with a post-reperfusion metabolic collapse. Thus, efforts to quench delayed graft function due to ischemia reperfusion injury should focus on conserving metabolic competence, either by preserving the integrity of the Krebs cycle and/or by recruiting metabolic salvage pathways.

Brain Death Enhances Activation of the Innate Immune System and Leads to Reduced Renal Metabolic Gene Expression

BACKGROUND

Brain death (BD)-associated inflammation has been implicated in decreased kidney allograft function and survival, but the underlying mechanisms have not been well distinguished from the conditions of critical care itself. We have developed a clinically translatable model to separate and investigate strategies to improve donor management and critical care.

METHODS

Brain-dead (n = 12) and sham (n = 5) rhesus macaques were maintained for 20 hours under intensive care unit-level conditions. Samples were collected for immunophenotyping, analysis of plasma proteins, coagulation studies, and gene analysis for changes in immune and metabolic profile with comparison to naive samples (n = 10).

RESULTS

We observed an increase in circulating leukocytes and cytokines, activation of complement and coagulation pathways, and upregulation of genes associated with inflammation in both brain-dead and sham subjects relative to naïve controls. Sham demonstrated an intermediate phenotype of inflammation compared to BD. Analysis of gene expression in kidneys from BD kidneys revealed a similar upregulation of inflammatory profile in both BD and sham subjects, but BD presented a distinct reduction in metabolic and respiratory processes compared to sham and naïve kidneys.

CONCLUSION

BD is associated with activation of specific pathways of the innate immune system and changes to metabolic gene expression in renal tissue itself; however, sham donors presented an intermediate inflammatory response attributable to the critical care environment. The early onset and penetrating impact of this inflammatory response underscores the need for early intervention to prevent perioperative tissue injury to transplantable organs.

The Effect of Preservation Temperature on Liver, Kidney, and Pancreas Tissue ATP in Animal and Preclinical Human Models

The recent advances in machine perfusion (MP) technology involve settings ranging between hypothermic, subnormothermic, and normothermic temperatures. Tissue level adenosine triphosphate (ATP) is a long-established marker of viability and functionality and is universal for all organs. In the midst of a growing number of complex clinical parameters for the quality assessment of graft prior to transplantation, a revisit of ATP may shed light on the underlying reconditioning mechanisms of different perfusion temperatures in the form of restoration of metabolic and energy status. This article aims to review and critically analyse animal and preclinical human studies (discarded grafts) during MP of three abdominal organs (liver, kidney, and pancreas) in which ATP was a primary endpoint. A selective review of recent novel reconditioning approaches relevant to mitigation of graft ischaemia-reperfusion injury via MP and for different perfusion temperatures was also conducted. With a current reiterated interest for oxygenation during MP, a re-introduction of tissue ATP levels may be valuable for graft viability assessment prior to transplantation. Further studies may help delineate the benefits of selective perfusion temperatures on organs viability.

Mitochondria in Sepsis-Induced AKI

AKI is a common clinical condition associated with the risk of developing CKD and ESKD. Sepsis is the leading cause of AKI in the intensive care unit (ICU) and accounts for nearly half of all AKI events. Patients with AKI who require dialysis have an unacceptably high mortality rate of 60%-80%. During sepsis, endothelial activation, increased microvascular permeability, changes in regional blood flow distribution with resulting areas of hypoperfusion, and hypoxemia can lead to AKI. No effective drugs to prevent or treat human sepsis-induced AKI are currently available. Recent research has identified dysfunction in energy metabolism as a critical contributor to the pathogenesis of AKI. Mitochondria, the center of energy metabolism, are increasingly recognized to be involved in the pathophysiology of sepsis-induced AKI and mitochondria could serve as a potential therapeutic target. In this review, we summarize the potential role of mitochondria in sepsis-induced AKI and identify future therapeutic approaches that target mitochondrial function in an effort to treat sepsis-induced AKI.

N,N-dimethyltryptamine Prevents Renal Ischemia-Reperfusion Injury in a Rat Model

BACKGROUND

Ischemia reperfusion (I/R) injury remains one of the most challenging fields of organ transplantation. It is highly associated with the use of expanded criteria donors that might conclude to delayed graft function or early or late graft failure.

OBJECTIVE

To investigate the metabolic, microcirculatory parameters, and histologic changes under the effect of N,N-dimethyltryptamine (DMT) in a renal I/R model in rats.

METHOD

In 26 anesthetized rats both kidneys were exposed. In the control group (n = 6) no other intervention happened. In 20 other animals, the right renal vessels were ligated, and after 60 minutes the right kidney was removed. The left renal vessels were clamped for 60 minutes then released, followed by 120 minutes of reperfusion. In the I/R group (n = 10), there was no additive treatment, while in I/R + DMT group (n = 10) DMT was administered 15 minutes before ischemia. Blood samples were taken, laser Doppler measurement was performed, and both kidneys were evaluated histologically.

RESULTS

Microcirculation (blood flux units [BFU]) diminished in all groups, but remarkably so in the I/R + DMT group. This group compensated better after the 30th minute of reperfusion. The control and I/R + DMT groups had similar BFUs after 120 minutes of reperfusion, but in the I/R group BFU was higher. Tubular necrosis developed in the I/R and I/R + DMT groups too; it was moderated under DMT effect, and severe without. Histologic injuries were less in I/R + DMT Group compared to non-treated animals.

CONCLUSION

Histologic changes characteristic to I/R injuries were reversible and microcirculation recovered at the end of 120 minutes reperfusion under the administration of DMT. DMT can be used for renoprotection in kidney transplantation.

Elamipretide Improves Mitochondrial Function in the Failing Human Heart

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Mitochondrial function is impaired in explanted failing pediatric and adult human hearts.

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Elamipretide is a novel mitochondria-targeted drug that is targeted to cardiolipin on the inner mitochondrial membrane and improves coupling of the electron transport chain.

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Treatment of explanted human hearts with elamipretide improves human cardiac mitochondrial function.

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The study provides novel methods to evaluate the influence of compounds on mitochondria in the human heart and provides proof of principle for the use of elamipretide to improve mitochondrial energetics in failing myocardium due to multiple etiologies and irrespective of age.

Negative alterations of mitochondria are known to occur in heart failure (HF). This study investigated the novel mitochondrial-targeted therapeutic agent elamipretide on mitochondrial and supercomplex function in failing human hearts ex vivo. Freshly explanted failing and nonfailing ventricular tissue from children and adults was treated with elamipretide. Mitochondrial oxygen flux, complex (C) I and CIV activities, and in-gel activity of supercomplex assembly were measured. Mitochondrial function was impaired in the failing human heart, and mitochondrial oxygen flux, CI and CIV activities, and supercomplex-associated CIV activity significantly improved in response to elamipretide treatment. Elamipretide significantly improved failing human mitochondrial function.

Association of Impaired Reactive Aldehyde Metabolism with Delayed Graft Function in Human Kidney Transplantation

Delayed graft function is an early complication following kidney transplantation with an unclear molecular mechanism. Here we determined whether impaired reactive aldehyde metabolism is associated with delayed graft function. Human kidney biopsies from grafts with delayed graft function were compared with grafts that did not develop delayed graft function by Ingenuity gene pathway analysis. A second series of grafts with delayed graft function (n = 10) were compared to grafts that did not develop delayed graft function (n = 10) by measuring reactive aldehyde metabolism, reactive aldehyde-induced protein adduct formation, and aldehyde dehydrogenase (ALDH) gene and protein expression. In the first series of kidney biopsies, several gene families known for metabolizing reactive aldehydes, such as aldehyde dehydrogenase (ALDH), aldo-keto reductase (AKR), and glutathione-S transferase (GSTA), were upregulated in kidneys that did not develop delayed graft function versus those that did. In the second series of kidney grafts, we focused on measuring aldehyde-induced protein adducts and ALDH enzymatic activity. The reactive aldehyde metabolism by ALDH enzymes was reduced in kidneys with delayed graft function compared to those that did not (37 ± 12^∗ vs. 79 ± 5 μg/min/mg tissue, ^∗P < 0.005, respectively). ALDH enzymatic activity was also negatively correlated with length of hospital stay after a kidney transplant. Together, our study identifies a reduced ALDH enzymatic activity with kidneys developing delayed graft function compared to those that did not. Measuring ALDH enzymatic activity and reactive aldehyde-induced protein adducts can potentially be further developed as a biomarker to assess for delayed graft function and recovery from a kidney transplant.

Urinary metabolites predict prolonged duration of delayed graft function in DCD kidney transplant recipients

Extending kidney donor criteria, including donation after circulatory death (DCD), has resulted in increased rates of delayed graft function (DGF) and primary nonfunction. Here, we used Nuclear Magnetic Resonance (NMR) spectroscopy to analyze the urinary metabolome of DCD transplant recipients at multiple time points (days 10, 42, 180, and 360 after transplantation). The aim was to identify markers that predict prolonged duration of functional DGF (fDGF). Forty-seven metabolites were quantified and their levels were evaluated in relation to fDGF. Samples obtained at day 10 had a different profile than samples obtained at the other time points. Furthermore, at day 10 there was a statistically significant increase in eight metabolites and a decrease in six metabolites in the group with fDGF (N = 53) vis-à-vis the group without fDGF (N = 22). In those with prolonged fDGF (≥21 days) (N = 17) urine lactate was significantly higher and pyroglutamate lower than in those with limited fDGF (<21 days) (N = 36). In order to further distinguish prolonged fDGF from limited fDGF, the ratios of all metabolites were analyzed. In a logistic regression analysis, the sum of branched-chain amino acids (BCAAs) over pyroglutamate and lactate over fumarate, predicted prolonged fDGF with an AUC of 0.85. In conclusion, kidney transplant recipients with fDGF can be identified based on their altered urinary metabolome. Furthermore, two ratios of urinary metabolites, lactate/fumarate and BCAAs/pyroglutamate, adequately predict prolonged duration of fDGF.

Postoperative Care in Kidney Transplantation: A Comparison Between Controlled and Uncontrolled Donation After Circulatory Death

Recent research in kidney transplantation has revealed differences in the evolution of renal function among patients transplanted from 2 alternative programs for donation after circulatory death (DCD). A retrospective, observational, single-center study was carried out from 2013 to 2016 at a level III hospital intensive care unit (ICU) to assess the progression of kidney recipients after transplants from uncontrolled DCD (uDCD) or controlled DCD (cDCD). The following variables were collected for data analysis: demographics, comorbidities, type of donation, lactate, hemoglobin and glucose levels at ICU admission, creatinine concentration at ICU admission, at-hospital ward transfer, at-hospital discharge, radioisotope imaging results, ICU and in-hospital length of stay, and mortality. There were 87 patients eligible for analysis, 42.5% of which were uDCD recipients. Improvement in kidney function was significantly delayed after uDCD compared with cDCD. A multivariate analysis showed that both uDCD and lactate levels at ICU admission increase the risk of poor outcome after renal transplantation. No deaths were registered in either patient group. Our results suggest that kidney transplantation recipients from uDCD recover renal function at a slower rate than patients transplanted from cDCD, a factor that does not affect mortality.

Organ-specific responses during brain death: increased aerobic metabolism in the liver and anaerobic metabolism with decreased perfusion in the kidneys

Hepatic and renal energy status prior to transplantation correlates with graft survival. However, effects of brain death (BD) on organ-specific energy status are largely unknown. We studied metabolism, perfusion, oxygen consumption, and mitochondrial function in the liver and kidneys following BD. BD was induced in mechanically-ventilated rats, inflating an epidurally-placed Fogarty-catheter, with sham-operated rats as controls. A 9.4T-preclinical MRI system measured hourly oxygen availability (BOLD-related R2*) and perfusion (T1-weighted). After 4 hrs, tissue was collected, mitochondria isolated and assessed with high-resolution respirometry. Quantitative proteomics, qPCR, and biochemistry was performed on stored tissue/plasma. Following BD, the liver increased glycolytic gene expression (Pfk-1) with decreased glycogen stores, while the kidneys increased anaerobic- (Ldha) and decreased gluconeogenic-related gene expression (Pck-1). Hepatic oxygen consumption increased, while renal perfusion decreased. ATP levels dropped in both organs while mitochondrial respiration and complex I/ATP synthase activity were unaffected. In conclusion, the liver responds to increased metabolic demands during BD, enhancing aerobic metabolism with functional mitochondria. The kidneys shift towards anaerobic energy production while renal perfusion decreases. Our findings highlight the need for an organ-specific approach to assess and optimise graft quality prior to transplantation, to optimise hepatic metabolic conditions and improve renal perfusion while supporting cellular detoxification.

Strategies to Restore Adenosine Triphosphate (ATP) Level After More than 20 Hours of Cold Ischemia Time in Human Marginal Kidney Grafts

Background

The persisting organ shortage in the field of transplantation recommends the use of marginal kidneys which poorly tolerate ischemic damage. Adenosine triphosphate (ATP) depletion during cold ischemia time (CIT) is considered crucial for graft function. We tested different strategies of kidney perfusion before transplantation in the attempt to improve the technique.

Material/Methods

Twenty human discarded kidneys from donors after brain death and with at least 20 hours of CIT were randomized to the following experimental groups (treatment time three-hours at 4°C): a) static cold storage (CS); b) static cold hyperbaric oxygenation (Hyp); c) hypothermic perfusion (PE); d) hypothermic perfusion in hyperbaric oxygenation (PE-Hyp); and e) hypothermic oxygenated perfusion (PE-O₂).

Results

Histological results showed that perfusion with or without oxygen did not produce any endothelial damage. A depletion of ATP content following the preservation procedure was observed in CS, PE, and Hyp, while PE-Hyp and PE-O₂ were associated with a net increase of ATP content with respect to baseline level. In addition, PE-Hyp was associated with a significant downregulation of endothelial isoform of nitric oxide synthase (eNOS) gene expression and of hypoxia inducible factor-1α (HIF-1α).

Conclusions

Hyperbaric or normobaric oxygenation with perfusion improves organ metabolic preservation compared to other methods. This approach may prevent the onset of delayed graft function, but clinical trials are needed to confirm this.

Pharmacologic Approaches to Improve Mitochondrial Function in AKI and CKD

AKI is associated with high morbidity and mortality, and it predisposes to the development and progression of CKD. Novel strategies that minimize AKI and halt the progression of CKD are urgently needed. Normal kidney function involves numerous different cell types, such as tubular epithelial cells, endothelial cells, and podocytes, working in concert. This delicate balance involves many energy-intensive processes. Fatty acids are the preferred energy substrates for the kidney, and defects in fatty acid oxidation and mitochondrial dysfunction are universally involved in diverse causes of AKI and CKD. This review provides an overview of ATP production and energy demands in the kidney and summarizes preclinical and clinical evidence of mitochondrial dysfunction in AKI and CKD. New therapeutic strategies targeting mitochondria protection and cellular bioenergetics are presented, with emphasis on those that have been evaluated in animal models of AKI and CKD. Targeting mitochondrial function and cellular bioenergetics upstream of cellular damage may offer advantages compared with targeting downstream inflammatory and fibrosis processes.

Peptide SS-31 upregulates frataxin expression and improves the quality of mitochondria: implications in the treatment of Friedreich ataxia

Friedreich ataxia is a progressive neurodegenerative disease caused by the expansion of GAA trinucleotide repeats within the first intron of the FXN gene, which encodes frataxin. The pathophysiology of the disease is thought to be derived from the decrease of Fe-S cluster biogenesis due to frataxin deficiency. There is currently no effective treatment for the disease. In our study, we demonstrated that treatment with the mitochondrion-targeted peptide SS-31 reduced frataxin deficiency-induced oxidative stress in lymphoblasts and fibroblasts derived from patients. Interestingly, SS-31 treatment translationally upregulated the protein level of frataxin in a dose-dependent manner. Furthermore, SS-31 treatment increased the enzymatic activities of the iron-sulphur enzymes, including aconitase and complex II and III of the respiratory chain. Further evaluation of the quality of mitochondria showed that mitochondrial membrane potential, ATP content, NAD+/NADH, and the morphology of mitochondria all improved. Our results suggest that SS-31 might potentially be a new drug for the early treatment of Friedreich ataxia.

The hypoxanthine-xanthine oxidase axis is not involved in the initial phase of clinical transplantation-related ischemia-reperfusion injury

The hypoxanthine-xanthine oxidase (XO) axis is considered to be a key driver of transplantation-related ischemia-reperfusion (I/R) injury. Whereas interference with this axis effectively quenches I/R injury in preclinical models, there is limited efficacy of XO inhibitors in clinical trials. In this context, we considered clinical evaluation of a role for the hypoxanthine-XO axis in human I/R to be relevant. Patients undergoing renal allograft transplantation were included (n = 40) and classified based on duration of ischemia (short, intermediate, and prolonged). Purine metabolites excreted by the reperfused kidney (arteriovenous differences) were analyzed by the ultra performance liquid chromatography-tandem mass spectrometer (UPLCMS/MS) method and tissue XO activity was assessed by in situ enzymography. We confirmed progressive hypoxanthine accumulation (P < 0.006) during ischemia, using kidney transplantation as a clinical model of I/R. Yet, arteriovenous concentration differences of uric acid and in situ enzymography of XO did not indicate significant XO activity in ischemic and reperfused kidney grafts. Furthermore, we tested a putative association between hypoxanthine accumulation and renal oxidative stress by assessing renal malondialdehyde and isoprostane levels and allantoin formation during the reperfusion period. Absent release of these markers is not consistent with an association between ischemic hypoxanthine accumulation and postreperfusion oxidative stress. On basis of these data for the human kidney we hypothesize that the role for the hypoxanthine-XO axis in clinical I/R injury is less than commonly thought, and as such the data provide an explanation for the apparent limited clinical efficacy of XO inhibitors.