Urine Recirculation During Normothermic Kidney Preservation Improves Energy Balance Involving the Urea and Citric Acid Cycles.

Background: Deceased-donor kidneys experience cellular stress before undergoing transplantation. To alleviate this, preservation techniques were developed, including normothermic machine perfusion (NMP). Methods: Here, we performed kidney NMP on discarded human kidneys for up to 24 h. Volume management was regulated either by urine recirculation (UR) or urine replacement (NUR) with Ringer's lactate. Notably, UR led to longer perfusion times compared with NUR. To investigate kidney NMP metabolic traits with or without UR over time, we performed longitudinal metabolomics analyses of perfusates of 8 NMP kidneys by 2-dimensional gas chromatography mass spectrometry (GCxGC-MS). Results: Over 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 are associated with the perfusion factor UR. Moreover, donor estimated glomerular filtration rate 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 6 h. Conclusions: Kidney preservation by NMP was previously limited to hours. UR-NMP affected kidney energy homeostasis, carbohydrate and purine metabolism, and the urea and citric acid cycles. These insights add value to explain how urine-driven adaptations contribute to prolonged kidney function under NMP.