Urine Recirculation During Normothermic Kidney Preservation Improves Energy Balance Involving the Urea and TCA Cycles

BackgroundDeceased donor kidneys experience cellular stress before undergoing transplantation. To alleviate this, preservation techniques were developed including normothermic machine perfusion (NMP). MethodsHere, we performed kidney NMP on discarded human kidneys for up to 24 hours. Volume management was regulated either by urine recirculation (UR) or urine replacement (NUR) with Ringers lactate. Notably, UR led to longer perfusion times compared to NUR. To investigate kidney NMP metabolic traits with or without UR over time, we performed longitudinal metabolomics analyses of perfusates of eight NMP kidneys by 2D-gas chromatography mass spectrometry (GCxGC-MS). ResultsOver 600 metabolic features were profiled, from which 74 were identified and 54 consistently quantified across 26 perfusate samples. Most notably, elevated levels of disaccharides (different isomers), hydroxy-purines, urea, glutamate and amino acids associated with the perfusion factor UR. Moreover, donor estimated glomerular filtration rate (eGFR) correlated significantly with the accumulation of lactate and gluconate. Most strikingly, lactate levels seemed to be more balanced in UR NMP perfusate, which otherwise accumulated rapidly within the first six hours. ConclusionsKidney preservation by NMP was previously limited to hours. UR-NMP affected kidney energy homeostasis, carbohydrate & purine metabolism and the Urea and TCA cycles. These insights add value to explain how urine-driven adaptations contribute to prolonged kidney function under NMP. Research in contextO_ST_ABSEvidence before this studyC_ST_ABSDeceased donors provide kidneys that experience cellular stress during retrieval and during transplantation. To attenuate tissue damage, preservation techniques were optimised to offer the most optimal environment for kidney organs retrieved from donation after circulatory death and brain death patients. Normothermic machine perfusion (NMP) of donor kidneys has been considered feasible, safe, offers viability assessment and contributes to favourable outcomes. However, there has been a limit in the length of time that this preservation method could be applied to kidney organs, thereby potentially restricting functional recovery of the kidney before organ transplantation. Added value of this studyBefore urine recirculation (UR) was introduced, NMP time was limited to a few hours. Remarkably, NMP with UR led to longer perfusion times and more stable kidney organ function as compared to no urine recirculation (NUR). In order to find out why, we compared urine recirculation with Ringers lactate solution for volume management during NMP on discarded human kidneys for up to 24 hours. Kidney NMP metabolic traits with or without UR over time were measured. More than 600 metabolic features were profiled, Most strikingly, lactate levels seemed to be more balanced in UR NMP perfusate of the course of 24 hours, which otherwise accumulated rapidly within the first six hours. Taken together, UR-NMP affected kidney energy metabolic pathways and rendering these more balanced. Ultimately, these urine-driven adaptations contribute to prolonged kidney function under NMP. Implications of all the available evidenceNMP as a procedure to preserve kidney organs including urine recirculation is now becoming standard in many transplantation units around the world. Our study provided a molecular snapshot of why kidney organs preserved in this way are maintained longer with a functionally active metabolism. This provides the basis for additional improvements leading to better kidney organ preservation, ultimately resulting in benefits for kidney transplant recipients.