Impact of device variability and protocol differences on kidney function during normothermic machine perfusion: A comparative study using porcine and human kidneys.

INTRODUCTION: A growing interest in renal normothermic machine perfusion (NMP) has resulted in more clinically available perfusion devices. While all perfusion systems have the same aim, there are significant differences in their circuits, pumps, sensors, and software. Therefore, our objective was to assess the impact of different perfusion protocols and devices on kidney function and perfusion parameters during NMP. METHODS: Porcine kidneys were subjected to 30 min of warm ischemia, 24 h of static cold storage, and subsequently perfused for 6 h using (1) the Kidney Assist (KA) machine with a pressure of 75 mm Hg, (2) the KA device incorporating several adjustments and a pressure of 85 mm Hg (modified KA), or (3) the Perlife (PL) perfusion device (n = 4). Consecutively, discarded human kidneys were perfused using the KA or modified KA (n = 3) protocol. RESULTS: The PL group quickly reached the device's upper flow limit and consequently received a significantly lower pressure compared to the KA groups. The arterial pO2 was significantly lower in the PL group. Yet, hemoglobin concentration increased over time, and oxygen consumption was significantly higher compared to the KA groups. Fractional sodium excretion was significantly lower in the PL group. Tissue ATP levels, urine production, and creatinine clearance rates did not differ between groups. In human kidneys, the modified KA group showed significantly lower vascular resistance, higher oxygen delivery, and lower levels of lactate in the perfusate compared to the KA group. CONCLUSIONS: This study shows that perfusion characteristics and kidney function are significantly influenced by the perfusion protocol and the device and its settings during normothermic machine perfusion and therefore should be interpreted with caution.

Peri-Operative Kinetics of Plasma Mitochondrial DNA Levels during Living Donor Kidney Transplantation.

During ischemia and reperfusion injury (IRI), mitochondria may release mitochondrial DNA (mtDNA). mtDNA can serve as a propagator of further injury but in specific settings has anti-inflammatory capacities as well. Therefore, the aim of this study was to study the perioperative dynamics of plasma mtDNA during living donor kidney transplantation (LDKT) and its potential as a marker of graft outcome. Fifty-six donor-recipient couples from the Volatile Anesthetic Protection of Renal Transplants-1 (VAPOR-1) trial were included. Systemic venous, systemic arterial, and renal venous samples were taken at multiple timepoints during and after LDKT. Levels of mtDNA genes changed over time and between vascular compartments. Several donor, recipient, and transplantation-related variables significantly explained the course of mtDNA genes over time. mtDNA genes predicted 1-month and 24-month estimated glomerular filtration rate (eGFR) and acute rejection episodes in the two-year follow-up period. To conclude, mtDNA is released in plasma during the process of LDKT, either from the kidney or from the whole body in response to transplantation. While circulating mtDNA levels positively and negatively predict post-transplantation outcomes, the exact mechanisms and difference between mtDNA genes are not yet understood and need further exploration.

Urinary Biomarkers in a Living Donor Kidney Transplantation Cohort-Predictive Value on Graft Function.

Early non-invasive detection and prediction of graft function after kidney transplantation is essential since interventions might prevent further deterioration. The aim of this study was to analyze the dynamics and predictive value of four urinary biomarkers: kidney injury molecule-1 (KIM-1), heart-type fatty acid binding protein (H-FABP), N-acetyl-ß-D-glucosaminidase (NAG), and neutrophil gelatinase-associated lipocalin (NGAL) in a living donor kidney transplantation (LDKT) cohort. Biomarkers were measured up to 9 days after the transplantation of 57 recipients participating in the VAPOR-1 trial. Dynamics of KIM-1, NAG, NGAL, and H-FABP significantly changed over the course of 9 days after transplantation. KIM-1 at day 1 and NAG at day 2 after transplantation were significant predictors for the estimated glomerular filtration rate (eGFR) at various timepoints after transplantation with a positive estimate (p < 0.05), whereas NGAL and NAG at day 1 after transplantation were negative significant predictors (p < 0.05). Multivariable analysis models for eGFR outcome improved after the addition of these biomarker levels. Several donor, recipient and transplantation factors significantly affected the baseline of urinary biomarkers. In conclusion, urinary biomarkers are of added value for the prediction of graft outcome, but influencing factors such as the timing of measurement and transplantation factors need to be considered.

Systemic and Renal Dynamics of Free Sulfhydryl Groups during Living Donor Kidney Transplantation.

During ischemia−reperfusion injury (IRI), reactive oxygen species are produced that can be scavenged by free sulfhydryl groups (R-SH, free thiols). In this study, we hypothesized that R-SH levels decrease as a consequence of renal IRI and that R-SH levels reflect post-transplant graft function. Systemic venous, arterial, renal venous, and urinary samples were collected in donors and recipients before, during, and after transplantation. R-SH was measured colorimetrically. Systemic arterial R-SH levels in recipients increased significantly up to 30 sec after reperfusion (p < 0.001). In contrast, renal venous R-SH levels significantly decreased at 5 and 10 min compared to 30 sec after reperfusion (both p < 0.001). This resulted in a significant decrease in delta R-SH (defined as the difference between renal venous and systemic arterial R-SH levels) till 30 sec after reperfusion (p < 0.001), indicating a net decrease in R-SH levels across the transplanted kidney. Overall, these results suggest trans-renal oxidative stress as a consequence of IRI during kidney transplantation, reflected by systemic and renal changes in R-SH levels in transplant recipients.

Proteomic analysis of machine perfusion solution from brain dead donor kidneys reveals that elevated complement, cytoskeleton and lipid metabolism proteins are associated with 1-year outcome.

Assessment of donor kidney quality is based on clinical scores or requires biopsies for histological assessment. Noninvasive strategies to identify and predict graft outcome at an early stage are, therefore, needed. We evaluated the perfusate of donation after brain death (DBD) kidneys during nonoxygenated hypothermic machine perfusion (HMP). In particular, we compared perfusate protein profiles of good outcome (GO) and suboptimal outcome (SO) 1-year post-transplantation. Samples taken 15 min after the start HMP (T1) and before the termination of HMP (T2) were analysed using quantitative liquid chromatography-tandem mass spectrometry (LC-MS/MS). Hierarchical clustering of the 100 most abundant proteins showed discrimination between grafts with a GO and SO at T1. Elevated levels of proteins involved in classical complement cascades at both T1 and T2 and a reduced abundance of lipid metabolism at T1 and of cytoskeletal proteins at T2 in GO versus SO was observed. ATP-citrate synthase and fatty acid-binding protein 5 (T1) and immunoglobulin heavy variable 2-26 and desmoplakin (T2) showed 91% and 86% predictive values, respectively, for transplant outcome. Taken together, DBD kidney HMP perfusate profiles can distinguish between outcome 1-year post-transplantation. Furthermore, it provides insights into mechanisms that could play a role in post-transplant outcomes.