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

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

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.

Comparison of 2 Immunosuppression Minimization Strategies in Kidney Transplantation: The ALLEGRO Trial.

BACKGROUND: Evidence on the optimal maintenance of immunosuppressive regimen in kidney transplantation recipients is limited. METHODS: The Amsterdam, LEiden, GROningen trial is a randomized, multicenter, investigator-driven, noninferiority, open-label trial in de novo kidney transplant recipients, in which 2 immunosuppression minimization strategies were compared with standard immunosuppression with basiliximab, corticosteroids, tacrolimus, and mycophenolic acid. In the minimization groups, either steroids were withdrawn from day 3, or tacrolimus exposure was reduced from 6 mo after transplantation. The primary endpoint was kidney transplant function at 24 mo. RESULTS: A total of 295 participants were included in the intention-to-treat analysis. Noninferiority was shown for the primary endpoint; estimated glomerular filtration rate at 24 mo was 45.3 mL/min/1.73 m 2 in the early steroid withdrawal group, 49.0 mL/min/1.73 m 2 in the standard immunosuppression group, and 44.7 mL/min/1.73 m 2 in the tacrolimus minimization group. Participants in the early steroid withdrawal group were significantly more often treated for rejection ( P = 0.04). However, in this group, the number of participants with diabetes mellitus during follow-up and total cholesterol at 24 mo were significantly lower. CONCLUSIONS: Tacrolimus minimization can be considered in kidney transplant recipients who do not have an increased immunological risk. Before withdrawing steroids the risk of rejection should be weighed against the potential metabolic advantages.

Endothelial to mesenchymal transition in kidney fibrosis.

Fibrotic disease are characterized by the uncontrolled accumulation of extracellular matrix (ECM) components leading to disruption of tissue homeostasis. Myofibroblasts as main ECM-producing cells can originate from various differentiated cell types after injury. Particularly, the process of endothelial-to-mesenchymal transition (endMT), describing phenotypic shifts of endothelial cells (ECs) to adopt a fully mesenchymal identity, may contribute to the pool of myofibroblasts in fibrosis, while leading to capillary rarefaction and exacerbation of tissue hypoxia. In renal disease, incomplete recovery from acute kidney injury (AKI) and the ensuing fibrotic reaction stand out as major contributors to chronic kidney disease (CKD) development. While the focus has largely been on impaired tubular epithelial repair as a potential fibrosis-driving mechanism, alterations in the renal microcirculation post-AKI, and in particular endMT as a maladaptive response, could hold equal significance. Dysfunctional interplays among various cell types in the kidney microenvironment can instigate endMT. Transforming growth factor beta (TGF-ß) signaling, with its downstream activation of canonical/Smad-mediated and non-canonical pathways, has been identified as primary driver of this process. However, non-TGF-ß-mediated pathways involving inflammatory agents and metabolic shifts in intercellular communication within the tissue microenvironment can also trigger endMT. These harmful, maladaptive cell-cell interactions and signaling pathways offer potential targets for therapeutic intervention to impede endMT and decelerate fibrogenesis such as in AKI-CKD progression. Presently, partial reduction of TGF-ß signaling using anti-diabetic drugs or statins may hold therapeutic potential in renal context. Nevertheless, further investigation is warranted to validate underlying mechanisms and assess positive effects within a clinical framework.

Metabolic needs of the kidney graft undergoing normothermic machine perfusion.

Normothermic machine perfusion (NMP) is emerging as a novel preservation strategy. During NMP, the organ is maintained in a metabolically active state that may not only provide superior organ preservation, but that also facilitates viability testing before transplantation, and ex situ resuscitation of marginal kidney grafts. Although the prevailing perfusion protocols for renal NMP are refined from initial pioneering studies concerning short periods of NMP, it could be argued that these protocols are not optimally tailored to address the putatively compromised metabolic plasticity of marginal donor grafts (i.e., in the context of viability testing and/or preservation), or to meet the metabolic prerequisites associated with prolonged perfusions and the required anabolic state in the context of organ regeneration. Herein, we provide a theoretical framework for the metabolic requirements for renal NMP. Aspects are discussed along the lines of carbohydrates, fatty acids, amino acids, and micronutrients required for optimal NMP of an isolated kidney. In addition, considerations for monitoring aspects of metabolic status during NMP are discussed.

The Neglectable Impact of Delayed Graft Function on Long-term Graft Survival in Kidneys Donated After Circulatory Death Associates With Superior Organ Resilience.

OBJECTIVE: To explore putative different impacts of delayed graft function (DGF) on long-term graft survival in kidneys donated after brain death (DBD) and circulatory death (DCD). BACKGROUND: Despite a 3-fold higher incidence of DGF in DCD grafts, large studies show equivalent long-term graft survival for DBD and DCD grafts. This observation implies a differential impact of DGF on DBD and DCD graft survival. The contrasting impact is remarkable and yet unexplained. METHODS: The impact of DGF on DBD and DCD graft survival was evaluated in 6635 kidney transplants performed in The Netherlands. DGF severity and functional recovery dynamics were assessed for 599 kidney transplants performed at the Leiden Transplant Center. Immunohistochemical staining, gene expression profiling, and Ingenuity Pathway Analysis were used to identify differentially activated pathways in DBD and DCD grafts. RESULTS: While DGF severely impacted 10-year graft survival in DBD grafts (HR 1.67; P < 0.001), DGF did not impact graft survival in DCD grafts (HR 1.08; P = 0.63). Shorter dialysis periods and superior posttransplant eGFRs in DBD grafts show that the differential impact was not caused by a more severe DGF phenotype in DBD grafts. Immunohistochemical evaluation indicates that pathways associated with tissue resilience are present in kidney grafts. Molecular evaluation showed selective activation of resilience-associated pathways in DCD grafts. CONCLUSIONS: This study shows an absent impact of DGF on long-term graft survival in DCD kidneys. Molecular evaluation suggests that the differential impact of DGF between DBD and DCD grafts relates to donor-type specific activation of resilience pathways in DCD grafts.

No indications for platelet activation in acute clinical myocardial or renal ischemia/reperfusion injury.

The pathophysiology of ischemia/reperfusion (I/R) injury is complex and poorly understood. Animal studies imply platelet activation as an initiator of the inflammatory response upon reperfusion. However, it remains unclear whether and how these results translate to clinical I/R. This study evaluates putative platelet activation in the context of two forms of clinical I/R (heart valve surgery with aortic-cross clamping, n = 39 and kidney transplantation, n = 34). The technique of sequential selective arteriovenous (AV) measurements over the reperfused organs was applied to exclude the influence of systemic changes occurring during surgery while simultaneously maximizing sensitivity. Platelet activation and degranulation was evaluated by assessing the expression levels of established markers, i.e. RANTES (Regulated on Activation, Normal T Cell Expressed and Secreted), ß-thromboglobulin (ß-TG), platelet-derived growth factor (PDGF)-BB and CXCL8 (known as interleukin-8), and by employing an in-vitro assay that specifically tests for platelet excitability. Moreover, a histological analysis was performed by means of CD41 staining. Results show stable RANTES, ß-TG, PDGF-BB and CXCL8 AV-concentrations within the first half hour over the reperfused organs, suggesting that myocardial and renal I/R are not associated with platelet activation. Results from the platelet excitability assay were in line with these findings and indicated reduced and stable platelet excitability following renal and myocardial reperfusion, respectively. Histological analysis yield evidence of platelet marginalization in the reperfused organs. In conclusion, results from this study do not support a role for platelet activation in early phases of clinical I/R injury.

Equivalent Long-term Transplantation Outcomes for Kidneys Donated After Brain Death and Cardiac Death: Conclusions From a Nationwide Evaluation.

BACKGROUND: Despite growing waiting lists for renal transplants, hesitations persist with regard to the use of deceased after cardiac death (DCD) renal grafts. We evaluated the outcomes of DCD donations in The Netherlands, the country with the highest proportion of DCD procedures (42.9%) to test whether these hesitations are justified. METHODS: This study included all procedures with grafts donated after brain death (DBD) (n = 3611) and cardiac death (n = 2711) performed between 2000 and 2017. Transplant outcomes were compared by Kaplan Meier and Cox regression analysis, and factors associated with short (within 90 days of transplantation) and long-term graft loss evaluated in multi-variable analyses. FINDINGS: Despite higher incidences of early graft loss (+ 50%) and delayed graft function (+ 250%) in DCD grafts, 10-year graft and recipient survival were similar for the two graft types (Combined 10-year graft survival: 73.9% (95% CI: 72.5-75.2), combined recipient survival: 64.5% (95 CI: 63.0-66.0%)). Long-term outcome equivalence was explained by a reduced impact of delayed graft function on DCD graft survival (RR: 0.69 (95% CI: 0.55-0.87), p < 0.001). Mid and long-term graft function (eGFR), and the impact of incident delayed graft function on eGFR were similar for DBD and DCD grafts. INTERPRETATION: Mid and long term outcomes for DCD grafts are equivalent to DBD kidneys. Poorer short term outcomes are offset by a lesser impact of delayed graft function on DCD graft survival. This nation-wide evaluation does not justify the reluctance to use of DCD renal grafts. A strong focus on short-term outcome neglects the superior recovery potential of DCD grafts.

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.

Defective postreperfusion metabolic recovery directly associates with incident delayed graft function.

Delayed graft function (DGF) following kidney transplantation affects long-term graft function and survival and is considered a manifestation of ischemia reperfusion injury. Preclinical studies characterize metabolic defects resulting from mitochondrial damage as primary driver of ischemia reperfusion injury. In a comprehensive approach that included sequential establishment of postreperfusion arteriovenous concentration differences over the human graft, metabolomic and genomic analysis in tissue biopsies taken before and after reperfusion, we tested whether the preclinical observations translate to the context of clinical DGF. This report is based on sequential studies of 66 eligible patients of which 22 experienced DGF. Grafts with no DGF immediately recovered aerobic respiration as indicated by prompt cessation of lactate release following reperfusion. In contrast, grafts with DGF failed to recover aerobic respiration and showed persistent adenosine triphosphate catabolism indicated by a significant persistently low post reperfusion tissue glucose-lactate ratio and continued significant post-reperfusion lactate and hypoxanthine release (net arteriovenous difference for lactate and hypoxanthine at 30 minutes). The metabolic data for the group with DGF point to a persistent post reperfusion mitochondrial defect, confirmed by functional (respirometry) and morphological analyses. The archetypical mitochondrial stabilizing peptide SS-31 significantly preserved mitochondrial function in human kidney biopsies following simulated ischemia reperfusion. Thus, development of DGF is preceded by a profound post-reperfusion metabolic deficit resulting from severe mitochondrial damage. Strategies aimed at preventing DGF should be focused on safeguarding a minimally required post-reperfusion metabolic competence.

Silencing of miRNA-126 in kidney ischemia reperfusion is associated with elevated SDF-1 levels and mobilization of Sca-1+/Lin- progenitor cells.

Integrity of the capillary network in the kidney is essential in the recovery from ischemia/ reperfusion injury (IRI), a phenomenon central to kidney transplantation and acute kidney injury. MicroRNA- 126 (miR-126) is known to be important in maintaining vascular homeostasis by facilitating vascular regeneration and modulating the mobilization of vascular progenitor cells. Stromal cell-derived factor 1 (SDF-1), important in the mobilization of vascular progenitor cells, is a direct target of miR-126 and modulation of miR-126 was previously shown to affect the number of circulating Sca-1(+)/Lin(-) vascular progenitor cells in a mouse model for hind limb ischemia. Here, we assessed the in vivo contribution of miR-126 to progenitor cell mobilization and kidney function following IRI in mice. A three day follow up of blood urea levels following kidney IRI demonstrated that systemic antagomir silencing of miR-126 did not impact the loss or subsequent restoration of kidney function. However, whole kidney lysates displayed elevated gene expression levels of Sdf-1, Vegf-A and eNOS after IRI as a result of systemic silencing of miR-126. Furthermore, FACS-analysis on whole blood three days after surgery revealed a marked up regulation of the number of circulating Sca-1(+)/Lin(-) progenitor cells in the antagomir-126 treated mice, in an ischemia dependent manner. Our data indicate that silencing of miR-126 can enhance renal expression of Sdf-1 after IRI, leading to the mobilization of vascular progenitor cells into the circulation.

Donor pre-treatment in clinical kidney transplantation: a critical appraisal.

Kidney transplantation represents one of the medical achievements of the 20th century. However, its continued success is limited by the increasing shortage of donor grafts. As a result, more kidney grafts from marginal donors are being considered for transplantation, with concomitantly more initial graft injury and limited organ and patient survival. This has led to an increased need for interventions aiming to optimize and preserve graft quality. Interventions within the donor may protect against ischemia/reperfusion injury, and therefore, donor pre-treatment is a promising strategy to increase graft function and survival. During the last decade, diverse donor pre-treatment interventions have been explored in animal studies. Moreover, the first human trials concerning donor pre-treatment in kidney transplantation have provided encouraging results. Unfortunately, it remains difficult to determine how and where to intervene in the multifactorial and complex processes that affect the donor kidney. Moreover, ethical matters play a critical role in donor interventions, and pre-treatment should principally not have any potentially unfavorable effects on other organs to be transplanted or on the living donor. This review provides an overview of promising therapeutical strategies for donor pre-treatment in kidney transplantation and discusses the clinical trials that have been conducted thus far.

Renal ischemia-reperfusion induces a dysbalance of angiopoietins, accompanied by proliferation of pericytes and fibrosis.

Endothelial cells (ECs) are highly susceptible to hypoxia and easily affected upon ischemia-reperfusion (I/R) during renal transplantation. Pericytes and angiopoeitins play important role in modulating EC function. In the present study, we investigate the effect of renal I/R on the dynamics of angiopoietin expression and its association with pericytes and fibrosis development. Male Lewis rats were subjected to unilateral renal ischemia for 45 min followed by removal of the contralateral kidney. Rats were killed at different time points after reperfusion. Endothelial integrity (RECA-1), pericytes [platelet-derived growth factor receptor-ß (PDGFR-ß)], angiopoietin-2 (Ang-2)/angiopoietin-1 (Ang-1) expression, and interstitial collagen deposition (Sirius red and α-smooth muscle actin) were assessed using immunohistochemistry and RT-PCR. Our study shows an increase in protein expression of Ang-2 starting at 5 h and remaining elevated up to 72 h, with a consequently higher Ang-2/Ang-1 ratio after renal I/R (P < 0.05 at 48 h). This was accompanied by an increase in protein expression of the pericytic marker PDGFR-ß and a loss of ECs (both at 72 h after I/R, P < 0.05). Nine weeks after I/R, when renal function was restored, we observed normalization of the Ang-2/Ang-1 ratio and PDGFR-ß expression and increase in cortical ECs, which was accompanied by fibrosis. Renal I/R induces a dysbalance of Ang-2/Ang-1 accompanied by proliferation of pericytes, EC loss, and development of fibrosis. The Ang-2/Ang-1 balance was reversed to baseline at 9 wk after renal I/R, which coincided with restoration of cortical ECs and pericytes. Our findings suggest that angiopoietins and pericytes play an important role in renal microvascular remodeling and development of fibrosis.

Renal ischemia-reperfusion induces release of angiopoietin-2 from human grafts of living and deceased donors.

BACKGROUND: Recent insights suggest that endothelial cell (EC) activation plays a major role in renal ischemia-reperfusion (I/R) injury. Interactions between ECs and pericytes via signaling molecules, including angiopoietins, are involved in maintenance of the vascular integrity. Experimental data have shown that enhancement of Angiopoietin (Ang)-1 signaling might be beneficial in renal I/R injury. However, little is known about the role of angiopoietins in human renal I/R injury. METHODS: In this study, EC activation and changes in angiopoeitins are assessed in human living-donor (LD) and deceased-donor (DD) kidney transplantation. Local release of angiopoietins was measured by unique, dynamic arteriovenous measurements over the reperfused kidney. RESULTS: Renal I/R is associated with acute EC activation shown by a vast Ang-2 release from both LD and DD shortly after reperfusion. Its counterpart Ang-1 was not released. Histologic analysis of kidney biopsies showed EC loss after reperfusion. Baseline protein and mRNA Ang-1 expression was significantly reduced in DD compared with LD and declined further after reperfusion. CONCLUSIONS: Human renal I/R injury induces EC activation after reperfusion reflected by Ang-2 release from the kidney. Interventions aimed at maintenance of vascular integrity by modulating angiopoietin signaling may be promising in human clinical kidney transplantation.

Bone marrow-derived mesenchymal stromal cells from patients with end-stage renal disease are suitable for autologous therapy.

BACKGROUND AIMS: Mesenchymal stromal cells (MSCs) are pluripotent cells that have immunosuppressive and reparative properties in vitro and in vivo. Although autologous bone marrow (BM)-derived MSCs are already clinically tested in transplant recipients, it is unclear whether these BM cells are affected by renal disease. We assessed whether renal failure affected the function and therapeutic potential of BM-MSCs. METHODS: MSCs from 10 adults with end-stage renal disease (ESRD) and 10 age-matched healthy controls were expanded from BM aspirates and tested for phenotype and functionality in vitro. RESULTS: MSCs from ESRD patients were >90% positive for CD73, CD90 and CD105 and negative for CD34 and CD45 and showed a similar morphology and differentiation capacity as MSCs from healthy controls. Of importance for their clinical utility, growth characteristics were similar in both groups, and sufficient numbers of MSCs were obtained within 4 weeks. Messenger RNA expression levels of self-renewal genes and factors involved in repair and inflammation were also comparable between both groups. Likewise, microRNA expression profiling showed a broad overlap between ESRD and healthy donor MSCs. ESRD MSCs displayed the same immunosuppressive capacities as healthy control MSCs, demonstrated by a similar dose-dependent inhibition of peripheral blood mononuclear cell proliferation, similar inhibition of proinflammatory cytokines tumor necrosis factor-α and interferon-γ production and a concomitant increase in the production of interleukin-10. CONCLUSIONS: Expanded BM-MSCs procured from ESRD patients and healthy controls are both phenotypically and functionally similar. These findings are important for the potential autologous clinical application of BM-MSCs in transplant recipients.

Autologous bone marrow-derived mesenchymal stromal cells for the treatment of allograft rejection after renal transplantation: results of a phase I study.

Despite excellent short-term results, long-term survival of transplanted kidneys has not improved accordingly. Although alloimmune responses and calcineurin inhibitor-related nephrotoxicity have been identified as main drivers of fibrosis, no effective treatment options have emerged. In this perspective, mesenchymal stromal cells (MSCs) are an interesting candidate because of their immunosuppressive and regenerative properties. Of importance, no other clinical studies have investigated their effects in allograft rejection and fibrosis. We performed a safety and feasibility study in kidney allograft recipients to whom two intravenous infusions (1 million cells per kilogram) of autologous bone marrow (BM) MSCs were given, when a protocol renal biopsy at 4 weeks or 6 months showed signs of rejection and/or an increase in interstitial fibrosis/tubular atrophy (IF/TA). Six patients received MSC infusions. Clinical and immune monitoring was performed up to 24 weeks after MSC infusions. MSCs fulfilled the release criteria, infusions were well-tolerated, and no treatment-related serious adverse events were reported. In two recipients with allograft rejection, we had a clinical indication to perform surveillance biopsies and are able to report on the potential effects of MSCs in rejection. Although maintenance immunosuppression remained unaltered, there was a resolution of tubulitis without IF/TA in both patients. Additionally, three patients developed an opportunistic viral infection, and five of the six patients displayed a donor-specific downregulation of the peripheral blood mononuclear cell proliferation assay, not reported in patients without MSC treatment. Autologous BM MSC treatment in transplant recipients with subclinical rejection and IF/TA is clinically feasible and safe, and the findings are suggestive of systemic immunosuppression.

Oxidative damage in clinical ischemia/reperfusion injury: a reappraisal.

AIMS: Ischemia/reperfusion (I/R) injury is a common clinical problem. Although the pathophysiological mechanisms underlying I/R injury are unclear, oxidative damage is considered a key factor in the initiation of I/R injury. Findings from preclinical studies consistently show that quenching reactive oxygen and nitrogen species (RONS), thus limiting oxidative damage, alleviates I/R injury. Results from clinical intervention studies on the other hand are largely inconclusive. In this study, we systematically evaluated the release of established biomarkers of oxidative and nitrosative damage during planned I/R of the kidney and heart in a wide range of clinical conditions. RESULTS: Sequential arteriovenous concentration differences allowed specific measurements over the reperfused organ in time. None of the biomarkers of oxidative and nitrosative damage (i.e., malondialdehyde, 15(S)-8-iso-prostaglandin F2α, nitrite, nitrate, and nitrotyrosine) were released upon reperfusion. Cumulative urinary measurements confirmed plasma findings. As of these negative findings, we tested for oxidative stress during I/R and found activation of the nuclear factor erythroid 2-related factor 2 (Nrf2), the master regulator of oxidative stress signaling. INNOVATION: This comprehensive, clinical study evaluates the role of RONS in I/R injury in two different human organs (kidney and heart). Results show oxidative stress, but do not provide evidence for oxidative damage during early reperfusion, thereby challenging the prevailing paradigm on RONS-mediated I/R injury. CONCLUSION: Findings from this study suggest that the contribution of oxidative damage to human I/R may be less than commonly thought and propose a re-evaluation of the mechanism of I/R.

Acute but transient release of terminal complement complex after reperfusion in clinical kidney transplantation.

BACKGROUND: Ischemia/reperfusion (I/R) injury has a major impact on kidney graft function and survival. Animal studies have suggested a role for complement activation in mediating I/R injury; however, results are not unambiguous. Whether complement activation is involved in clinical I/R injury in humans is still unclear. METHODS: In the present study, we assessed the formation and release of C5b-9 during early reperfusion in clinical kidney transplantation in living donor, brain-dead donor, and cardiac dead donor kidney transplantation. By arteriovenous measurements and histologic studies, local terminal complement activation in the reperfused kidney was assessed. RESULTS: There was no release of soluble C5b-9 (sC5b-9) from living donor kidneys, nor was there a release of C5a. In contrast, instantly after reperfusion, there was a significant but transient venous release of sC5b-9 from the reperfused kidney graft in brain-dead donor and cardiac dead donor kidney transplantation. This short-term activation of the terminal complement cascade in deceased-donor kidney transplantation was not reflected by renal tissue deposition of C5b-9 in biopsies taken 45 min after reperfusion. CONCLUSIONS: This systematic study in human kidney transplantation shows an acute but nonsustained sC5b-9 release on reperfusion in deceased-donor kidney transplantation. This instantaneous, intravascular terminal complement activation may be induced by intravascular cellular debris and hypoxic or injured endothelium.

Interleukin-9 release from human kidney grafts and its potential protective role in renal ischemia/reperfusion injury.

OBJECTIVE AND DESIGN: The pathophysiology of ischemia/reperfusion (I/R) injury is dominated by an inflammatory response. In the identification of new therapeutic agents, the role of individual cytokines may be essential. Interleukin (IL)-9 is a pleiotropic cytokine recently identified to be involved in various immune responses. In this study, the role of IL-9 in renal I/R injury was assessed. METHODS: We performed repeated direct measurements of arteriovenous IL-9 concentration differences over the reperfused graft in human kidney transplantation. RESULTS: Substantial renal IL-9 release was observed from deceased donor kidneys (P = 0.006). In contrast, living donor kidneys, which have a more favourable clinical outcome, did not release IL-9 during early reperfusion (P = 0.78). Tissue expression of IL-9 did not change upon reperfusion in both living and deceased human donor kidneys. To assess the role of IL-9 in I/R injury, an experimental study comprising IL-9 inhibition in mice undergoing renal I/R was performed. Although there was no difference in kidney function, structural damage was significantly aggravated in anti-IL-9 treated mice. CONCLUSIONS: Deceased donor grafts show a substantial IL-9 release upon reperfusion in clinical kidney transplantation. However, inhibition of IL-9 aggravated kidney damage, suggesting a regulating or minor role of IL-9 in clinical I/R injury.

Mesenchymal stromal cells in renal ischemia/reperfusion injury.

Ischemia/reperfusion (I/R) injury is an inevitable consequence of organ transplantation and a major determinant of patient and graft survival in kidney transplantation. Renal I/R injury can lead to fibrosis and graft failure. Although the exact sequence of events in the pathophysiology of I/R injury remains unknown, the role of inflammation has become increasingly clear. In this perspective, mesenchymal stromal cells (MSCs) are under extensive investigation as potential therapy for I/R injury, since MSCs are able to exert immune regulatory and reparative effects. Various preclinical studies indicate the beneficial effects of MSCs in ameliorating renal injury and accelerating tissue repair. These versatile cells have been shown to migrate to sites of injury and to enhance repair by paracrine mechanisms instead of by differentiating and replacing the injured cells. The first phase I studies of MSCs in human renal I/R injury and kidney transplantation have been started, and results are awaited soon. In this review, preliminary results and opportunities of MSCs in human renal I/R injury are summarized. We might be heading towards a cell-based paradigm shift in the treatment of renal I/R injury.