Preclinical models versus clinical renal ischemia reperfusion injury: A systematic review based on metabolic signatures

Role of Renal Venous Oxygen Pressure for Renal Function Monitoring After Related Living-Donor Kidney Transplantation: Cohort Study

BACKGROUND

Monitoring of renal function after kidney transplantation (KT) is performed by measuring serum creatinine (SCr), urine volumes (UV), and glomerular filtration rate (GFR). Other methods based on oxygen metabolism, such as the renal venous oxygen pressure (PrvO2), may be useful. The aim of this study was to explore the correlation between PrvO2 and SCr, UV, and GFR 5 days after KT (SCr5, UV5, and GFR5, respectively).

METHODS

We conducted a prospective cohort study in adults scheduled for living donor KT. A venous blood sample was taken from the renal vein after declamping the renal artery, and blood gas determinations were made. Correlation analyses between PrvO2 and SCr5, UV5, and GFR5 were done by calculating Spearman's correlation coefficient with generalized linear models (GLM). A Spearman's correlation analysis was performed between the percentage decrease in SCr (%ΔSCr) and PrvO2. A GLM was also performed to determine the association of PrvO2 with slow graft function (SGF).

RESULTS

The study included 42 patients, of whom 67% were men. The median age was 31 years (IQR, 27-43.5). PrvO2 was negatively correlated with SCr5 (ρ = -0.53, P = .003), and positively correlated with GFR5 (ρ = 0.49, P = .001) and %ΔSCr (ρ = 0.47, P = .002). A higher PrvO2 was associated with an increase in GFR in univariable (β = 1.24, 95% CI, 0.56-1.93, P = .001) and multivariable (β = 1.24, 95% CI, 0.53-1.94, P = .001) analyses. No association was found between PrvO2 and SGF.

CONCLUSION

PrvO2 could be used to monitor renal function in the first 5 days after related living-donor KT, given its good correlation with SCr and GFR.

Free heme and hemopexin in acute kidney injury after cardiopulmonary bypass and transient renal ischemia

Free heme is released from hemoproteins during hemolysis or ischemia reperfusion injury and can be pro-inflammatory. Most studies on nephrotoxicity of hemolysis-derived proteins focus on free hemoglobin (fHb) with heme as a prosthetic group. Measurement of heme in its free, non-protein bound, form is challenging and not commonly used in clinical routine diagnostics. In contrast to fHb, the role of free heme in acute kidney injury (AKI) after cardiopulmonary bypass (CPB) surgery is unknown. Using an apo-horseradish peroxidase-based assay, we identified free heme during CPB surgery as predictor of AKI in patients undergoing cardiac valve replacement (n = 37). Free heme levels during CPB surgery correlated with depletion of hemopexin (Hx), a heme scavenger-protein. In mice, the impact of high levels of circulating free heme on the development of AKI following transient renal ischemia and the therapeutic potential of Hx were investigated. C57BL/6 mice were subjected to bilateral renal ischemia/reperfusion injury for 15 min which did not cause AKI. However, additional administration of free heme in this model promoted overt AKI with reduced renal function, increased renal inflammation, and reduced renal perfusion on functional magnetic resonance imaging. Hx treatment attenuated AKI. Free heme administration to sham operated control mice did not cause AKI. In conclusion, free heme is a predictor of AKI in CPB surgery patients and promotes AKI in transient renal ischemia. Depletion of Hx in CPB surgery patients and attenuation of AKI by Hx in the in vivo model encourage further research on Hx therapy in patients with increased free heme levels during CPB surgery.

Perfusate Proteomes Provide Biological Insight Into Oxygenated Versus Standard Hypothermic Machine Perfusion in Kidney Transplantation

OBJECTIVE

To provide mechanistic insight into key biological alterations in donation after circulatory death kidneys during continuous pefusion we performed mass spectrometry profiling of perfusate samples collected during a phase 3 randomized double-blind paired clinical trial of hypothermic machine perfusion with and without oxygen (COMPARE).

BACKGROUND

Despite the clinical benefits of novel perfusion technologies aiming to better preserve donor organs, biological processes that may be altered during perfusion have remained largely unexplored. The collection of serial perfusate samples during the COMPARE clinical trial provided a unique resource to study perfusate proteomic profiles, with the hypothesis that in-depth profiling may reveal biologically meaningful information on how donor kidneys benefit from this intervention.

METHODS

Multiplexed liquid chromatography-tandem mass spectrometry was used to obtain a proteome profile of 210 perfusate samples. Partial least squares discriminant analysis and multivariate analysis involving clinical and perfusion parameters were used to identify associations between profiles and clinical outcomes.

RESULTS

Identification and quantitation of 1716 proteins indicated that proteins released during perfusion originate from the kidney tissue and blood, with blood-based proteins being the majority. Data show that the overall hypothermic machine perfusion duration is associated with increasing levels of a subgroup of proteins. Notably, high-density lipoprotein and complement cascade proteins are associated with 12-month outcomes, and blood-derived proteins are enriched in the perfusate of kidneys that developed acute rejection.

CONCLUSIONS

Perfusate profiling by mass spectrometry was informative and revealed proteomic changes that are biologically meaningful and, in part, explain the clinical observations of the COMPARE trial.

Calcineurin Inhibition in Deceased Organ Donors: A Systematic Review and Meta-analysis of Preclinical Studies

Background

Preconditioning deceased organ donors with calcineurin inhibitors (CNIs) may reduce ischemia-reperfusion injury to improve transplant outcomes.

Methods

We searched MEDLINE, EMBASE, Cochrane Library, and conference proceedings for animal models of organ donation and transplantation, comparing donor treatment with CNIs with either placebo or no intervention, and evaluating outcomes for organ transplantation. Reviewers independently screened and selected studies, abstracted data, and assessed the risk of bias and clinical relevance of included studies. Where possible, we pooled results using meta-analysis; otherwise, we summarized findings descriptively.

Results

Eighteen studies used various animals and a range of CNI agents and doses and evaluated their effects on a variety of transplant outcomes. The risk of bias and clinical applicability were poorly reported. Pooled analyses suggested benefit of CNI treatment on early graft function in renal transplants (3 studies; serum creatinine: ratio of means [RoM] 0.54; 95% confidence interval [CI], 0.34-0.86) but not for liver transplants (2 studies; serum alanine transaminase: RoM 0.61; 95% CI, 0.30-1.26; and serum aspartate aminotransferase: RoM 0.58; 95% CI, 0.26-1.31). We found no reduction in graft loss at 7 d (2 studies; risk ratio 0.54; 95% CI, 0.08-3.42). CNI treatment was associated with reduced transplant recipient levels of interleukin-6 (4 studies; RoM 0.36; 95% CI, 0.19-0.70), tumor necrosis factor-alpha (5 studies; RoM 0.36; 95% CI, 0.12-1.03), and cellular apoptosis (4 studies; RoM 0.30; 95% CI, 0.19-0.47).

Conclusions

Although this compendium of animal experiments suggests that donor preconditioning with CNIs may improve early kidney graft function, the limited ability to reproduce a true clinical environment in animal experiments and to assess for risk of bias in these experiments is a serious weakness that precludes current clinical application.

New therapeutic concepts against ischemia-reperfusion injury in organ transplantation

INTRODUCTION

Ischemia-reperfusion injury (IRI) involves a positive amplification feedback loop that stimulates innate immune-driven tissue damage associated with organ procurement from deceased donors and during transplantation surgery. As our appreciation of its basic immune mechanisms has improved in recent years, translating putative biomarkers into therapeutic interventions in clinical transplantation remains challenging.

AREAS COVERED

This review presents advances in translational/clinical studies targeting immune responses to reactive oxygen species in IRI-stressed solid organ transplants, especially livers. Here we focus on novel concepts to rejuvenate suboptimal donor organs and improve transplant function using pharmacologic and machine perfusion (MP) strategies. Cellular damage induced by cold ischemia/warm reperfusion and the latest mechanistic insights into the microenvironment's role that leads to reperfusion-induced sterile inflammation is critically discussed.

EXPERT OPINION

Efforts to improve clinical outcomes and increase the donor organ pool will depend on improving donor management and our better appreciation of the complex mechanisms encompassing organ IRI that govern the innate-adaptive immune interface triggered in the peritransplant period and subsequent allo-Ag challenge. Computational techniques and deep machine learning incorporating the vast cellular and molecular mechanisms will predict which peri-transplant signals and immune interactions are essential for improving access to the long-term function of life-saving transplants.

Effect of hydrogen sulfide on ischemia-reperfusion injury of kidney: A systematic review and meta-analysis of in vivo animal studies

Hydrogen sulfide (H₂S) has been shown to be effective against kidney ischemia-reperfusion injury (IRI) in animal studies. We aimed to evaluate the current evidence from in vivo animal studies for the protective effects of H₂S against kidney IRI by systematically reviewing the literature and performing a meta-analysis. Based on the preregistered protocol (PROSPERO: CRD42021295469); PubMed, Medline, Embase, Web of Science, and Scopus were searched to identify in vivo animal studies evaluating the effect of H₂S against kidney IRI. Standardized mean difference (SMD) with 95% confidence interval (CI) was calculated and pooled using random-effects meta-analysis. Twenty-two articles complied with eligibility criteria, from which the creatinine levels of 152 control animals and 182 animals treated with H₂S from 27 individual experiments were pooled. H₂S treatment significantly decreased serum creatinine (SMD = -1.82 [95% CI -1.12, -2.51], p < 0.0001), blood urea nitrogen (-2.50 [-1.46, -3.54], p < 0.0001), tissue malondialdehyde (-2.59 [-3.30, -1.88], p < 0.0001), tunel positive cells (-3.16 [-4.38, -1.94], p < 0.0001), and tubular damage score (-2.01 [-3.03, -0.99], p < 0.0001). There was a high heterogeneity across studies (I² = 83.5% for serum creatinine level). In meta-regression analysis, the type of H₂S donor and its application time accounted for 11.3% (p = 0.025) and 16.6% (p = 0.039) of heterogeneity, respectively. Accordingly, H₂S protects the kidney against IRI only if it is given as GYY4137 before or during ischemia. Although H₂S is a potential candidate against kidney IRI, further well-designed preclinical studies focusing on GYY4137 are warranted before clinical implication.

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.

A Single Oral Dose of Diclofenac Causes Transition of Experimental Subclinical Acute Kidney Injury to Chronic Kidney Disease

Nephrotoxic drugs can cause acute kidney injury (AKI) and analgesic nephropathy. Diclofenac is potentially nephrotoxic and frequently prescribed for pain control. In this study, we investigated the effects of single and repetitive oral doses of diclofenac in the setting of pre-existing subclinical AKI on the further course of AKI and on long-term renal consequences. Unilateral renal ischemia–reperfusion injury (IRI) for 15 min was performed in male CD1 mice to induce subclinical AKI. Immediately after surgery, single oral doses (100 mg or 200 mg) of diclofenac were administered. In a separate experimental series, repetitive treatment with 100 mg diclofenac over three days was performed after IRI and sham surgery. Renal morphology and pro-fibrotic markers were investigated 24 h and two weeks after the single dose and three days after the repetitive dose of diclofenac treatment using histology, immunofluorescence, and qPCR. Renal function was studied in a bilateral renal IRI model. A single oral dose of 200 mg, but not 100 mg, of diclofenac after IRI aggravated acute tubular injury after 24 h and caused interstitial fibrosis and tubular atrophy two weeks later. Repetitive treatment with 100 mg diclofenac over three days aggravated renal injury and caused upregulation of the pro-fibrotic marker fibronectin in the setting of subclinical AKI, but not in sham control kidneys. In conclusion, diclofenac aggravated renal injury in pre-existing subclinical AKI in a dose and time-dependent manner and already a single dose can cause progression to chronic kidney disease (CKD) in this model.

Metabolomic profiling demonstrates evidence for kidney and urine metabolic dysregulation in a piglet model of cardiac surgery-induced acute kidney injury

Acute kidney injury (AKI) is a common cause of morbidity after congenital heart disease surgery. Progress on diagnosis and therapy remains limited, however, in part due to poor mechanistic understanding and a lack of relevant translational models. Metabolomic approaches could help identify novel mechanisms of injury and potential therapeutic targets. In the present study, we used a piglet model of cardiopulmonary bypass with deep hypothermic circulatory arrest (CPB/DHCA) and targeted metabolic profiling of kidney tissue, urine, and serum to evaluate metabolic changes specific to animals with histological acute kidney injury. CPB/DHCA animals with acute kidney injury were compared with those without acute kidney injury and mechanically ventilated controls. Acute kidney injury occurred in 10 of 20 CPB/DHCA animals 4 h after CPB/DHCA and 0 of 7 control animals. Injured kidneys showed a distinct tissue metabolic profile compared with uninjured kidneys (R² = 0.93, Q² = 0.53), with evidence of dysregulated tryptophan and purine metabolism. Nine urine metabolites differed significantly in animals with acute kidney injury with a pattern suggestive of increased aerobic glycolysis. Dysregulated metabolites in kidney tissue and urine did not overlap. CPB/DHCA strongly affected the serum metabolic profile, with only one metabolite that differed significantly with acute kidney injury (pyroglutamic acid, a marker of oxidative stress). In conclusion, based on these findings, kidney tryptophan and purine metabolism are candidates for further mechanistic and therapeutic investigation. Urine biomarkers of aerobic glycolysis could help diagnose early acute kidney injury after CPB/DHCA and warrant further evaluation. The serum metabolites measured at this early time point did not strongly differentiate based on acute kidney injury.

NEW & NOTEWORTHY This project explored the metabolic underpinnings of postoperative acute kidney injury (AKI) following pediatric cardiac surgery in a translationally relevant large animal model of cardiopulmonary bypass with deep hypothermic circulatory arrest. Here, we present novel evidence for dysregulated tryptophan catabolism and purine catabolism in kidney tissue and increased urinary glycolysis intermediates in animals who developed histological AKI. These pathways represent potential diagnostic and therapeutic targets for postoperative AKI in this high-risk population.

The Effect of Hypothermic Machine Perfusion to Ameliorate Ischemia-Reperfusion Injury in Donor Organs

Hypothermic machine perfusion (HMP) has become the new gold standard in clinical donor kidney preservation and a promising novel strategy in higher risk donor livers in several countries. As shown by meta-analysis for the kidney, HMP decreases the risk of delayed graft function (DGF) and improves graft survival. For the liver, HMP immediately prior to transplantation may reduce the chance of early allograft dysfunction (EAD) and reduce ischemic sequelae in the biliary tract. Ischemia-reperfusion injury (IRI), unavoidable during transplantation, can lead to massive cell death and is one of the main causes for DGF, EAD or longer term impact. Molecular mechanisms that are affected in IRI include levels of hypoxia inducible factor (HIF), induction of cell death, endothelial dysfunction and immune responses. In this review we have summarized and discussed mechanisms on how HMP can ameliorate IRI. Better insight into how HMP influences IRI in kidney and liver transplantation may lead to new therapies and improved transplant outcomes.