Neutrophil gelatinase-associated lipocalin, a new biomarker candidate in perfusate of machine-perfused kidneys: a porcine pilot experiment

Toxicologic Pathology Forum Opinion Paper*: Recommendations for a Tiered Approach to Nonclinical Mechanistic Nephrotoxicity Evaluation

Nephrotoxicity is one of the more common causes of attrition in nonclinical drug development. Like most tissues, the kidney has a limited number of ways of responding to toxicological insults from diverse mechanistic pathways, which can limit the ability to determine mechanisms of renal injury using the assays routinely performed in preclinical toxicologic studies. In situations where the renal injury is unusual in morphology or if a therapeutic margin is low, additional investigative techniques may be needed to identify a potential mechanism of toxicity in order to inform clinical risk assessment or establish human relevance and translatability of the toxicity. While routine microscopic evaluation can suggest a specific pathogenesis, understanding the mechanism of renal injury often requires additional hypothesis-driven investigations and specialized techniques to obtain the data necessary to identify a nephrotoxic mechanism. Nonclinical mechanistic investigations can be resource-intensive and often yield limited new information. Although there are multiple avenues to investigate renal toxicity, no single mechanistic study or prescriptive battery of tests will identify the pathophysiologic basis for every potential mechanism of renal injury. To aid the nonclinical investigator, we outline a tiered approach for prioritizing investigations to provide a rational and linear road map for the exploration of mechanisms of drug-induced kidney injury.

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Neutrophil Gelatinase-Associated Lipocalin as a Biomarker of Allograft Function After Renal Transplantation: Evaluation of the Current Status and Future Insights

Neutrophil gelatinase‐associated lipocalin (NGAL), a protein belonging to the lipocalin superfamily initially found in activated neutrophils, is expressed by several cell types, including kidney tubule. The increase in NGAL production and release from tubular cells in response to various insults has been proven to predict acute kidney injury (AKI). For this reason, it has emerged as a valuable noninvasive biomarker of AKI in clinical nephrology. Also in the renal transplant setting, different studies have indicated NGAL as a valuable tool, especially in the early postoperative period, since the currently available clinical and laboratory parameters remain poorly sensitive to monitor immediate posttransplant graft function. This is an analysis of the recent literature to assess the utility of plasma and urinary NGAL, exosomal mRNA for NGAL, and NGAL levels in the perfusate of machine‐perfused kidneys for the prediction of graft function recovery in the early postsurgery phase after renal transplantation. We found that NGAL appears as a promising troponin‐like biomarker to detect short‐term impairment of graft function after renal transplant, but there are still some limitations in its clinical application, essentially related to its low specificity. Moreover, comparing NGAL assayed in serum, urine, machine‐perfusate, or as exosomal mRNA, each one has shown limitations and benefits in terms of predictive performance for DGF, according to various existing studies, feasibly due to different cut‐off levels, designs and patient sample sizes.

Neutrophil Gelatinase-Associated Lipocalin, but Not Kidney Injury Marker 1, Correlates with Duration of Delayed Graft Function

BACKGROUND

No specific early biomarker is available to measure kidney injury after kidney transplantation (KT). Both neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury marker 1 (KIM-1) increase after oxidative injury. Their potential as early biomarkers was evaluated in this one-arm pilot study.

MATERIALS AND METHODS

Twenty consecutive KT patients receiving a kidney from a donation after circulatory death donor were included. Graft perfusate was collected, as well as serum samples before transplantation, at the end of surgery, and 1, 4, and 7 days after transplantation. NGAL and KIM-1 were measured using ELISA. Kidney function and delayed graft function (DGF) were monitored.

RESULTS

In this cohort, 85% of the KT patients developed DGF. Perfusate NGAL correlated with donor age (r2 = 0.094, p = 0.01) and serum creatinine (r2 = 0.243, p = 0.05). A cardiac cause of death was associated with higher NGAL in the perfusate (p = 0.03). Serum NGAL at day 1 was significantly higher in patients with DGF (730 ng/ml, range 490-1,655, vs. 417 ng/ml, range 232-481; p = 0.01). Serum NGAL levels at day 1, 4, and 7 correlated with the duration of DGF. KIM-1 was not detectable in the perfusate or in the serum until postoperative day 4 in 80% of patients.

CONCLUSIONS

NGAL in the perfusate correlates with known donor risk factors for DGF. For the first time, we describe that serum NGAL at day 1 can discriminate between DGF and immediate graft function. Also, serum NGAL levels at day 1, 4, and 7 correlate with the duration of DGF. No association with KIM-1 was found. These data suggest that NGAL may be used as an early biomarker to detect DGF and warrants further study.

Determination of the Preferred Conditions for the Isolated Perfusion of Porcine Kidneys

Background: The isolated perfused porcine kidney (IPPK) model has been the method of choice for the early preclinical evaluation of kidney graft preservation techniques. The preferred reperfusion conditions have not yet been determined. Here, we examined the effects of pressure- or flow-controlled perfusion and oxygenation by pure oxygen or carbogen (95% O2/5% CO2) on normothermic reperfusion in the IPPK model. Methods: Porcine kidneys were cold-stored for 24 h in histidine-tryptophan-ketoglutarate solution and reperfused for 1 h with normothermic whole blood/Krebs-Henseleit buffer medium (20/80%). Kidneys (n = 5/group) were flow-controlled reperfused with pure oxygen (1 ml/min/g; Flow-O2) or pressure-controlled reperfused (85 mm Hg mean arterial pressure) and oxygenated with either pure oxygen (Pressure-O2) or carbogen (Pressure-O2/CO2). Renal function and damage were assessed during reperfusion and NGAL and HIF-1α levels were analyzed using an ELISA. Results: Pressure-O2 and Pressure-O2/CO2 were associated with significantly better renal hemodynamics and acid-base homeostasis compared to Flow-O2. Urine protein concentrations and the fractional excretion of sodium were lower with both Pressure-O2 and Pressure-O2/CO2 than with Flow-O2. NGAL and HIF-1α levels were also lower with Pressure-O2 and Pressure-O2/CO2 than with Flow-O2. Only Pressure-O2/CO2 could demonstrate a significantly increased urine production compared to Flow-O2. The structural integrity was well preserved in the Pressure-O2 and Pressure-O2/CO2 groups, whereas diffuse and global glomerular destruction was observed in the Flow-O2 group. Conclusion: In the IPPK model, the application of pressure-controlled reperfusion with carbogen oxygenation, and to a lesser extent with pure oxygen, maintained physiological renal function for 1 h, thus providing a reliable and reproducible ex vivo evaluation of kidney preservation quality.

Biomarkers for renal transplantation: where are we?

Although surgical techniques, post-transplant care medicine, and immunosuppressants have been greatly improved, permanent acceptance of renal allograft remains a clinical challenge owing to the appearance of various influencing factors. To predict graft dysfunction, development of noninvasive biomarkers is becoming a highlighted research topic in the field of renal transplantation, which provides a possibility for physicians to give preemptive rescue treatment. From the viewpoint of diagnostic techniques, repetitive sampling is prerequisite to identify applicable biomarkers in the clinic. Early biomarkers can be used to dynamically monitor renal graft status and accurately predict transplant outcome independent of various confounders. This review highlights recent studies on the predictive value of biomarkers and methods to quantify biomarkers for monitoring kidney transplant. It is important to analyze and compare different biomarkers for living, and nonliving donors. Analysis of identified clinically relevant biomarkers will advance our understanding of distinct molecular and cellular mechanisms of transplantation and provide insight into developing novel potential approaches to induce transplant tolerance.

Machine perfusion viability testing

PURPOSE OF REVIEW

Pretransplant assessment of kidney graft viability may help clinicians to decide whether to accept or discard a kidney for transplantation. With the increasing demand for donor kidneys and the increased use of marginal kidneys, the need of viability markers has increased to pursue superior transplant outcomes. Hypothermic machine perfusion (HMP) provides the theoretical opportunity to assess the viability of donor kidneys. We discuss the novel developments in viability testing during HMP and address the future prospects.

RECENT FINDINGS

HMP viability testing has focused on the analysis of machine perfusion parameters and perfusate biomarkers. Renal resistance and the biomarkers lactate dehydrogenase, aspartate transaminase, glutathione-S-transferase, N-acetyl-β-D-glucosaminidase, heart-type fatty acid binding protein, lipid peroxidation products, redox-active iron and IL-18 are correlated with transplant outcome in terms of development of delayed graft function or graft survival. However, they all lack adequate predictive value for transplant outcome. New techniques including contrast-enhanced ultrasound, three-dimensional ultrasound and magnetic resonance spectrometry are promising methods to test kidney viability during HMP, but their value has to be established. The introduction of normothermic machine perfusion offers other promising opportunities for viability testing.

SUMMARY

Machine perfusion characteristics and perfusate biomarkers have been extensively studied. They often correlate with the transplant outcome, but the present viability tests are not reliable predictors of transplant outcome. New developments in kidney graft viability assessment are necessary to have a chance of being clinically useful in the future.

Neutrophil gelatinase-associated lipocalin (NGAL) levels in response to unilateral renal ischaemia in a novel pilot two-kidney porcine model

OBJECTIVES

To test a novel porcine two-kidney model for evaluating the effect of controlled acute kidney injury (AKI) related to induced unilateral ischaemia on both renal units (RUs) To use neutrophil gelatinase-associated lipocalin (NGAL) and physiological serum and urinary markers to assess AKI and renal function.

METHODS

Twelve female Yorkshire pigs had bilateral cutaneous ureterostomies placed laparoscopically with identical duration of pneumoperitoneum for all cases. An experimental group (n = 9) underwent induced unilateral renal ischaemia with left hilar clamping of timed duration (15, 30, 60 min) and a control group (n = 3) had no induced renal ischaemia. Urine was collected and analysed from each RU to assess creatinine and NGAL concentration preoperatively and at multiple postoperative time points. Serum was collected and analysed daily for creatinine and NGAL levels. Statistical comparisons were made using the rank-sum and sign-rank tests.

RESULTS

Three pigs were excluded because of intra-operative and postoperative complications. In the RUs that experienced renal ischaemia (n = 7),the median urine volume was lower (P = 0.04) at 6, 12, 24 and 48 h and the median NGAL concentration was higher (P = 0.04) at 12 and 48 h compared with the RUs of control pigs that experienced no renal ischaemia (n = 2). When comparing the ischaemic (left) RU of the pigs in the experimental group with their contralateral non-ischaemic (right) RU, ischaemic RUs had a lower median cumulative urine volume at 6, 12, 24 and 48 h (P = 0.05) and a higher median NGAL concentration at 12, 24 and 48 h (P < 0.05). At 48 h, no significant increase was found in serum NGAL in pigs in the experimental group compared with controls (P = 0.2). Creatinine clearance (CC) was lower in ischaemic RUs compared with non-ischaemic RUs 1 day after surgery (P = 0.04) with decreasing CC as the duration of ischaemia increased.

CONCLUSIONS

We have developed a promising novel small-scale pilot surgical model that allowed the evaluation of bilateral RU function separately during and after unilateral renal ischaemia. The induction of unilateral renal ischaemia corresponds with physiological changes in both the ischaemic and contralateral RU. AKI as measured by increases in NGAL and decreased renal function as measured by decreases in CC, are specific to the RU exposed to ischaemia.