La viabilité des reins marginaux testée par perfusion de gadolinium sous IRM pendant leur réanimation

Subnormothermic Ex Vivo Porcine Kidney Perfusion Improves Energy Metabolism: Analysis Using 31P Magnetic Resonance Spectroscopic Imaging

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.

Ex Vivo Analysis of Kidney Graft Viability Using 31P Magnetic Resonance Imaging Spectroscopy

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. P 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.

Evaluation of donor kidneys prior to transplantation: an update of current and emerging methods

The lack of suitable kidney donor organs has led to rising numbers of patients with end stage renal disease waiting for kidney transplantation. Despite decades of clinical experience and research, no evaluation process that can reliably predict the outcome of an organ has yet been established. This review is an overview of current methods and emerging techniques in the field of donor kidney evaluation prior to transplantation. Established techniques like histological evaluation, clinical scores, and machine perfusion systems offer relatively reliable predictions of delayed graft function but are unable to consistently predict graft survival. Emerging techniques including molecular biomarkers, new imaging technologies, and normothermic machine perfusion offer innovative approaches toward a more global evaluation of an organ with better outcome prediction and possibly even identification of targets for therapeutic interventions prior to transplantation. These techniques should be studied in randomized controlled trials to determine whether they can be safely used in routine clinical practice to ultimately reduce the discard rate and improve graft outcomes.

DCD pigs' kidneys analyzed by MRI to assess ex vivo their viability

BACKGROUND

Magnetic resonance imaging (MRI) gadolinium-perfusion was applied in simulated Donation after Cardiac Death (DCD) in porcine kidneys to measure intrarenal perfusion. Adenosine triphosphate (ATP) resynthesis during oxygenated hypothermic perfusion was compared to evaluate the "ex vivo organ viability". Adenine nucleotide (AN) was measured by P nuclear magnetic resonance (NMR) spectroscopy. Whereas this latter technique requires sophisticated hardware, gadolinium-perfusion can be realized using any standard proton-MRI scanner. The aim of this work was to establish a correlation between the two methods.

METHODS

Twenty-two porcine kidneys presenting up to 90 min warm ischemia were perfused with oxygenation at 4 °C using our magnetic resonance-compatible machine. During the perfusion, P NMR spectroscopy and gadolinium-perfusion sequences were performed. Measures obtained from the gadolinium-perfusion were the speed of elimination of the cortical gadolinium and the presence or absence of a corticomedullar shunt. For ATP resynthesis analysis, P chemical shift imaging was acquired and analyzed. All the kidneys have been submitted to histologic examination.

RESULTS

ATP resynthesis was observed in all organs presenting a cortical gadolinium elimination slope of (-) 23° or greater. In organs with lower gadolinium elimination, no AN or only precursors were detected. This study reveals a link between the two methods and demonstrates ex vivo viability in 93% of the analyzed kidneys. Benefits and side effects of both methods are discussed.

CONCLUSION

Oxygenated hypothermic perfusion enables the evaluation of kidneys in DCD simulated situation; gadolinium-perfusion can be introduced into any center equipped with a proton-MRI scanner allowing results superposable with ATP measurement.

Detection of ATP by "in line" 31P magnetic resonance spectroscopy during oxygenated hypothermic pulsatile perfusion of pigs' kidneys

OBJECT

To demonstrate that adenosine triphosphate (ATP), which provides a valuable biomarker for kidney viability in the context of donation after cardiac death (DCD) transplantation, can be detected by means of (31)P magnetic resonance spectroscopy (MRS) if kidneys are perfused with oxygenated hypothermic pulsatile perfusion (O(2)+HPP).

MATERIALS AND METHODS

Porcine kidney perfusion was carried out using a home made, MR-compatible HPP-machine. Consequently, kidney perfusion could be performed continuously during magnetic resonance imaging and magnetic resonance spectroscopy recording. (31)P MR spectroscopy consisted of 3-dimensional chemical shift imaging (CSI), which allowed for the detection of ATP level in line. (31)P CSI was performed at 3 tesla in 44 min with a nominal voxel size of 6.1 cc.

RESULTS

(31)P CSI enabled the detection of renal ATP when pO(2) was equal to 100 kPa. With pO(2) of 20 kPa, only phosphomonoester, inorganic phosphate and nicotinamide adenine dinucleotide could be found. Semi-quantitative analysis showed that ATP level was 1.3 mM in normal kidney perfused with pO(2) of 100 kPa.

CONCLUSIONS

This combined technology may constitute a new advance in DCD organ diagnostics prior to transplantation, as it allows direct assessment of ATP concentration, which provides a reliable indicator for organ bioenergetics and viability. In this study, kidneys presenting no warm ischemia were tested in order to establish values in normal organs. The test could be easily integrated into the clinical environment and would not generate any additional delay into the transplantation clinical workflow.