The effect of technical conditions and storage medium composition on the phosphomonoesters to inorganic phosphate ratio determined by 31P nuclear magnetic resonance spectroscopy in rabbit kidney

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.

Kinetics of PME/Pi in pig kidneys during cold ischemia

Quality assessment of renal grafts via (31)P magnetic resonance spectroscopy (MRS) has been investigated since 1986. As ATP concentrations decay rapidly during cold ischemia, the ratio of phosphomonoesters (PME) to inorganic phosphate (Pi(O)) within the organ (PME/Pi(O)) is commonly used as a quality marker and is considered to be the most reliable parameter. MRS did not lead to any delay in the transplantation procedure since it was performed during the time necessary for immunological matching (cross-match). Differences in the time period until transplantation call for extrapolation of the measured ratio to the end of cold ischemia before correlating with graft performance after transplantation. Therefore, quantitative determination of PME/Pi(O) kinetics is essential. As a model for metabolite decay in human renal grafts, pig kidneys obtained from a slaughterhouse were monitored for up to 80 h via (31)P MRS at 2 T. By employing chemical shift imaging (CSI) with a spatial resolution of approximately 1 x 1 x 4 cm(3), it was possible to reduce partial volume effects significantly. The improved spectral resolution gained through CSI enabled reliable PME/Pi(O) ratios to be determined only from those voxels containing renal tissue. Spectra were fitted automatically using the magnetic resonance user interface (MRUI), with prior knowledge obtained from unlocalized spectra when necessary. A monoexponential time dependence of PME/Pi(O) for histidine-tryptophane-alpha-ketoglutarate (HTK)-perfused kidneys during cold ischemia was observed, and the determined value of the decay constant alpha was 0.0099 +/- 0.0012 h(-1). In University of Wisconsin solution (UW)-perfused kidneys, an alpha of 0.0183 +/- 0.0053 h(-1) was determined. Determination of the decay constant enables a usable extrapolation of PME/Pi(O) for quality assessment of UW perfusion and a reliable extrapolation for HTK-perfused human renal grafts.

In vivo 31P NMR OSIRIS of bioenergetic changes in rabbit kidneys during and after ischaemia: effect of pretreatment with an indeno-indole compound

Changes in energy phosphates of rabbit kidneys subjected to ischaemia-reperfusion have been measured in vivo with volume selective 31P NMR spectroscopy. The effects of pretreatment with a new lipid peroxidation inhibitor (indeno-indol derivate--code name H290/51) on the bioenergetic changes were analysed. The left kidney was moved to a subcutaneous pocket to facilitate exact positioning over the surface coil. A 1H NMR image was acquired and a 3.5-mL cube selected for 31P NMR spectra. 31P NMR spectra were recorded before occlusion of the left renal artery, during 1 h of ischaemia and 2 hours of reperfusion. Ischaemia induced drastic changes in the levels of inorganic phosphates and ATP as well as intracellular acidosis. A normalization was observed during reperfusion. Two hours after reperfusion significantly higher values for beta-ATP/Pi and intracellular pH were recorded in the animals pretreated with H290/51. The present technique allows quantitative analyses of changes in kidney bioenergetics in vivo during different experimental conditions. The importance of ischaemia-reperfusion induced lipid peroxidation for mitochondrial function is emphasized.

The role of magnetic resonance spectroscopy in the assessment of kidney viability

Renal transplant programmes are seriously limited by the continuing shortage of donor organs. Kidneys from marginal and non-heart-beating donors are increasingly being used, but their viability may be compromised. There is currently no rapid yet accurate method for assessing donor organ viability which can be applied within the window of opportunity between harvesting and implantation. Magnetic resonance spectroscopy (MRS) is a non-invasive technique which is being increasingly applied to delineate biochemical changes in vivo. Studies in animal models and humans now suggest that phosphorus-31 MRS may be useful in the non-invasive assessment of isolated donor kidney viability.

Pre-transplantation assessment of renal viability with 31P magnetic resonance spectroscopy

As acute tubular necrosis (ATN) is still an important cause for postoperative malfunction of renal grafts, it would be useful to have a method predicting such a complication. We investigated the possibility to predict ATN by measuring the ratio of phosphomonoesters (PME, largely consisting of adenosine monophosphate) and inorganic phosphate (Pi) in the renal tissue, using 31P magnetic resonance spectroscopy (MRS) during the cold ischemia period. Assuming that this ratio reflects the tissue high-energy phosphate status, we studied five kidneys from living related donors (LRD), 28 kidneys from heart beating donors (HBD) and nine kidneys from non-heart beating donors (non-HBD). All kidneys were preserved with a phosphate free solution. We found an inverse relation between the time of 31P MRS and the PME/Pi ratio, suggesting a graded decay of tissue high energy phosphates during cold ischemia. The PME/Pi ratio was highest in grafts from LRD (2.65 +/- 0.50, no ATN), intermediate in grafts from HBD (1.65 +/- 0.41, 21% ATN) and lowest in those derived from non-HBD (1.05 +/- 0.47, 56% ATN). The differences in PME/Pi ratio between the groups was statistically significant (P < 0.01). Moreover, the ratio was significantly lower in grafts developing ATN (1.73 +/- 0.41 vs. 1.35 +/- 0.29 in the HBD group, 1.41 +/- 0.24 vs. 0.76 +/- 0.36 in the non-HBD group, P < 0.05). These observations point to a general relation between the pre-transplant kidney PME/Pi ratio and the development of ATN. However, the predictive value of a low PME/Pi ratio was too low (36%) to reliably predict development of ATN in individual cases.(ABSTRACT TRUNCATED AT 250 WORDS)