Background. The lack of organs for kidney transplantation is a growing concern. Expansion in organ supply has been proposed through the use of organs after circulatory death (donation after circulatory death [DCD]). However, many DCD grafts are discarded because of long warm ischemia times, and the absence of reliable measure of kidney viability. 31P magnetic resonance imaging (pMRI) spectroscopy is a noninvasive method to detect high-energy phosphate metabolites, such as ATP. Thus, pMRI could predict kidney energy state, and its viability before transplantation. Methods. To mimic DCD, pig kidneys underwent 0, 30, or 60 min of warm ischemia, before hypothermic machine perfusion. During the ex vivo perfusion, we assessed energy metabolites using pMRI. In addition, we performed Gadolinium perfusion sequences. Each sample underwent histopathological analyzing and scoring. Energy status and kidney perfusion were correlated with kidney injury. Results. Using pMRI, we found that in pig kidney, ATP was rapidly generated in presence of oxygen (100 kPa), which remained stable up to 22 h. Warm ischemia (30 and 60 min) induced significant histological damages, delayed cortical and medullary Gadolinium elimination (perfusion), and reduced ATP levels, but not its precursors (AMP). Finally, ATP levels and kidney perfusion both inversely correlated with the severity of kidney histological injury. Conclusions. ATP levels, and kidney perfusion measurements using pMRI, are biomarkers of kidney injury after warm ischemia. Future work will define the role of pMRI in predicting kidney graft and patient’s survival.

Background. The ideal preservation temperature for donation after circulatory death kidney grafts is unknown. We investigated whether subnormothermic (22 °C) ex vivo kidney machine perfusion could improve kidney metabolism and reduce ischemia-reperfusion injury. Methods. To mimic donation after circulatory death procurement, kidneys from 45-kg pigs underwent 60 min of warm ischemia. Kidneys were then perfused ex vivo for 4 h with Belzer machine perfusion solution UW at 22 °C or at 4 °C before transplantation. Magnetic resonance spectroscopic imaging coupled with LCModel fitting was used to assess energy metabolites. Kidney perfusion was evaluated with dynamic-contrast enhanced MRI. Renal biopsies were collected at various time points for histopathologic analysis. Results. Total adenosine triphosphate content was 4 times higher during ex vivo perfusion at 22 °C than at 4 °C perfusion. At 22 °C, adenosine triphosphate levels increased during the first hours of perfusion but declined afterward. Similarly, phosphomonoesters, containing adenosine monophosphate, were increased at 22 °C and then slowly consumed over time. Compared with 4 °C, ex vivo perfusion at 22 °C improved cortical and medullary perfusion. Finally, kidney perfusion at 22 °C reduced histological lesions after transplantation (injury score: 22 °C: 10.5 ± 3.5; 4 °C: 18 ± 2.25 over 30). Conclusions. Ex vivo kidney perfusion at 22°C improved graft metabolism and protected from ischemia-reperfusion injuries upon transplantation. Future clinical studies will need to define the benefits of subnormothermic perfusion in improving kidney graft function and patient’s survival.

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31P-SPAWNN, in order to fully analyze phosphorus-31 ( 31 P) magnetic resonance spectra. The flexibility and speed of the technique rival traditional least-square fitting methods, with the performance of the two approaches, are compared in this work.Theory and Methods: Convolutional neural network architectures have been proposed for the analysis and quantification of 31 P-spectroscopy. The generation of training and test data using a fully parameterized model is presented herein.In vivo unlocalized free induction decay and three-dimensional 31 P-magnetic resonance spectroscopy imaging data were acquired from healthy volunteers before being quantified using either 31P-SPAWNN or traditional least-square fitting techniques. Results:The presented experiment has demonstrated both the reliability and accuracy of 31P-SPAWNN for estimating metabolite concentrations and spectral parameters. Simulated test data showed improved quantification using 31P-SPAWNN compared with LCModel. In vivo data analysis revealed higher accuracy at low signal-to-noise ratio using 31P-SPAWNN, yet with equivalent precision. Processing time using 31P-SPAWNN can be further shortened up to two orders of magnitude. Conclusion:The accuracy, reliability, and computational speed of the method open new perspectives for integrating these applications in a clinical setting.

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Objective Lifelong low-protein, high-carbohydrate diets extend lifespan in rodent. Consistently in human, the administration of oral carbohydrate drinks the day before surgery might improve clinical outcome. However, the fundamental questions of what represents a macronutritionally balanced diet, and how this impact surgical stress remain unanswered. Methods Here, we induced dietary protein dilution by giving mice ad libitum access to 50% sucrose water, without any food restriction. Mice were randomized into four regimens: regular diet (17,6 % protein, Ctrl), and a low protein diet (5.6% protein, LP), with or without high sucrose water (50% sucrose) for 7 days. At the end of the preconditioning, calorimetric data, fasting blood glucose, IGF1, glucose tolerance, and finally resistance to renal failure following a bilateral renal ischemia-reperfusion was evaluated. Results We demonstrate that access to carbohydrate drinks promotes dietary protein restriction despite a total caloric intake that was twice higher. This short-term self-restriction in daily protein, independent of caloric intake, improved insulin sensitivity, reduced serum triglyceride, and enhanced mitochondrial respiration as well as energy expenditure. Importantly, a 7-day pre-conditioning protein dilution regimen promotes recovery following kidney ischemia and reperfusion (IRI), a model of surgical stress. This protection from kidney IRI inversely correlated with pre-operative protein intake, but not carbohydrate or fat. The benefit of a low protein, high-carbohydrate regimen was independent of the protein sensing pathway eIF2α/ATF4, NRF2 and hydrogen sulfide, but instead required Insulin-like growth factor 1 (IGF1) downregulation. Conclusion These results support further clinical studies of a low protein diet combined with carbohydrate drinks prior to surgery.

Objective Better preservation strategies for the storage of donation after circulatory death grafts could increase the number of kidneys available and improve patient survival. Warm (22°C and 37°C) ex-vivo perfusion has emerged as an alternative to hypothermia and a feasible strategy to recover/repair organs, but the underlying mechanism remains elusive. Here, using magnetic resonance imaging spectroscopy (MRIs), we evaluated kidney viability, and adenosine triphosphate (ATP) production during sub-normothermic ex-vivo kidney perfusion (22°C + O2) versus hypothermic machine perfusion (4°C and 4°C + O2) in a porcine kidney autotransplantation model. Methods To mimic donation after circulatory death (DCD), kidneys from 8-month-old pigs underwent 60 minutes of warm ischemia, prior to procurement. Kidneys were then perfused ex-vivo at 4°C with (4°C + O2), and without oxygen (4°C) or at 22°C (22°C + O2) before autotransplantation. During the ex-vivo perfusion, and after transplantation we assessed energy metabolites using MRIs. In addition, we performed Gadolinum (Gd) perfusion sequences. Each sample underwent histopathological analyzing and scoring. mRNA expression was analyzed on renal biopsies at various time points. Results Using MRI, we found that in pig kidney, total ATP content was 4 times higher during ex-vivo perfusion at sub-normothermic temperature compared to cold perfusion, with or without oxygen. At 22°C, ATP levels gradually increased up to 10 hrs of perfusion, then progressively declined. Similarly, AMP content was increased in SNOP perfused organs, then slowly consumed. over time. In addition, 22°C + O2 improved cortical and medullary perfusion (Gd elimination). Finally, sub-normothermic ex-vivo perfused graft had lower grade of histological damages 1 hour after transplantation compared to cold perfused organs (injury score 22°C + O2 : 8.8–12.2, 4°C : 13.5–18.8, 4°C + O2 : 17.5–18.5). Conclusion In kidneys, sub-normothermic perfusion improved graft viability when compared with hypothermic perfusions. These results suggest that sub-normothermic ex-vivo kidney perfusion might dampen the negative effect of warm ischemia and promote kidney metabolism such as ATP production. Future clinical studies will define the benefits of sub-normothermic ex-vivo kidney perfusion in improving kidney graft function, and patient's survival.