Pretransplant assessment of renal viability by phosphorus-31 magnetic resonance spectroscopy. Clinical experience in 40 recipient patients

Two point Dixon-based chemical exchange saturation transfer (CEST) MRI in renal transplant patients on 3 T

PURPOSE

To assess the performance of two point (2-pt) Dixon-based chemical exchange saturation transfer (CEST) imaging for fat suppression in renal transplant patients.

METHODS

The 2-pt Dixon-based CEST MRI was validated in an egg-phantom and in fourteen renal transplant recipients (5 females and 9 males; age range: 23-78 years; mean age: 51 ± 16.8). All CEST experiments were performed on a 3 T clinical MRI scanner using a dual-echo CEST sequence. The 2-pt Dixon technique was applied to generate water-only CEST images at different frequency offsets, which were further used to calculate the z-spectra. The magnetization transfer ratio asymmetry (MTR_asym) values in the frequency ranges of hydroxyl, amine and amide protons were estimated in the renal cortex and medulla.

RESULTS

Results of the in vitro experiments suggest that the 2-pt Dixon technique enables effective fat peak removal and does not introduce additional asymmetries to the z-spectrum. Accordingly, our results in vivo show that the fat-corrected amide proton transfer (APT) effect in the kidney is significantly higher compared to that obtained from the CEST data acquired close to the in-phase condition both in the renal cortex (-0.1 [0.7] vs. -0.7 [1.2], P = 0.029) and medulla (0.3 [0.8] vs. 0.01 [1.3], P = 0.049), indicating that the 2-pt Dixon-based CEST method increases the specificity of the APT contrast by correcting the fat-induced artifacts.

CONCLUSION

Combination of the dual-echo CEST acquisition with Dixon post-processing provides effective water-fat separation, allowing more accurate quantification of the APT CEST effect in the transplanted kidney.

Organ-specific metabolic profiles of the liver and kidney during brain death and afterwards during normothermic machine perfusion of the kidney

We investigated metabolic changes during brain death (BD) using hyperpolarized magnetic resonance (MR) spectroscopy and ex vivo graft glucose metabolism during normothermic isolated perfused kidney (IPK) machine perfusion. BD was induced in mechanically ventilated rats by inflation of an epidurally placed catheter; sham-operated rats served as controls. Hyperpolarized [1-¹³ C]pyruvate MR spectroscopy was performed to quantify pyruvate metabolism in the liver and kidneys at 3 time points during BD, preceded by injecting hyperpolarized[1-¹³ C]pyruvate. Following BD, glucose oxidation was measured using tritium-labeled glucose (d-6-3H-glucose) during IPK reperfusion. Quantitative polymerase chain reaction and biochemistry were performed on tissue/plasma. Immediately following BD induction, lactate increased in both organs (liver: eµ_d 0.21, 95% confidence interval [CI] [-0.27, -0.15]; kidney: eµ_d 0.26, 95% CI [-0.40, -0.12]. After 4 hours of BD, alanine production decreased in the kidney (eµ_d 0.14, 95% CI [0.03, 0.25], P < .05). Hepatic lactate and alanine profiles were significantly different throughout the experiment between groups (P < .01). During IPK perfusion, renal glucose oxidation was reduced following BD vs sham animals (eµ_d 0.012, 95% CI [0.004, 0.03], P < .001). No differences in enzyme activities were found. Renal gene expression of lactate-transporter MCT4 increased following BD (P < .01). In conclusion, metabolic processes during BD can be visualized in vivo using hyperpolarized magnetic resonance imaging and with glucose oxidation during ex vivo renal machine perfusion. These techniques can detect differences in the metabolic profiles of the liver and kidney following BD.

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.

Organ-specific responses during brain death: increased aerobic metabolism in the liver and anaerobic metabolism with decreased perfusion in the kidneys

Hepatic and renal energy status prior to transplantation correlates with graft survival. However, effects of brain death (BD) on organ-specific energy status are largely unknown. We studied metabolism, perfusion, oxygen consumption, and mitochondrial function in the liver and kidneys following BD. BD was induced in mechanically-ventilated rats, inflating an epidurally-placed Fogarty-catheter, with sham-operated rats as controls. A 9.4T-preclinical MRI system measured hourly oxygen availability (BOLD-related R2*) and perfusion (T1-weighted). After 4 hrs, tissue was collected, mitochondria isolated and assessed with high-resolution respirometry. Quantitative proteomics, qPCR, and biochemistry was performed on stored tissue/plasma. Following BD, the liver increased glycolytic gene expression (Pfk-1) with decreased glycogen stores, while the kidneys increased anaerobic- (Ldha) and decreased gluconeogenic-related gene expression (Pck-1). Hepatic oxygen consumption increased, while renal perfusion decreased. ATP levels dropped in both organs while mitochondrial respiration and complex I/ATP synthase activity were unaffected. In conclusion, the liver responds to increased metabolic demands during BD, enhancing aerobic metabolism with functional mitochondria. The kidneys shift towards anaerobic energy production while renal perfusion decreases. Our findings highlight the need for an organ-specific approach to assess and optimise graft quality prior to transplantation, to optimise hepatic metabolic conditions and improve renal perfusion while supporting cellular detoxification.

Pre-transplantation 31P-magnetic resonance spectroscopy for quality assessment of human pancreatic grafts - A feasibility study

OBJECTIVE

To investigate the feasibility of using ³¹P-MRS for objective non-invasive quality assessment of human pancreas grafts prior to transplantation or islet isolation.

MATERIALS AND METHODS

Pancreata from 5 human donors, 3 males and 2 females, aged 49-78years, with body mass index (BMI) 22-31kg/m², were included. Pancreata were perfused with histidine-tryptophan-ketoglutarate solution during procurement and stored in hypothermic condition (4°C) for 21-44h. During the period of hypothermic storage repeated spectra were obtained for each graft by ³¹P-MRS (1.5Tesla) to measure the cold ischemia time (CIT) dependent changes of the phosphorous metabolites adenosine triphosphate (ATP), phosphomonoesters (PME), phosphodiesters (PDE) and inorganic phosphate (Pi), in the grafts. Graft temperature was measured immediately before and after MR-examination. Reference spectrum for non-viable tissue was obtained after graft exposure to room temperature.

RESULTS

PME/Pi, PDE/Pi and ATP/Pi spectral intensities ratios decreased with increasing CIT, reflecting the decreased viability of the grafts. PME/Pi ratio was the most discriminatory variable at prolonged CIT. ³¹P-MRS could be performed without significantly increasing graft temperature.

CONCLUSIONS

³¹P-MRS may provide quantitative parameters for evaluating graft viability ex vivo, and is a promising tool for objective non-invasive assessment of the quality of human pancreas grafts prior to transplantation or islet isolation.

Detection of alterations in membrane metabolism during neoadjuvant chemotherapy in patients with breast cancer using phosphorus magnetic resonance spectroscopy at 7 Tesla

Here we investigate the feasibility of tumor metabolism monitoring in T1c to T3 breast cancer during neoadjuvant chemotherapy by means of phosphorus (³¹P) magnetic resonance spectroscopy at 7 tesla (T). Five breast cancer patients were examined using a ³¹P MRSI sequence, prior to-, halfway-, and after neoadjuvant chemotherapy. The ³¹P MRSI data were analyzed on group and individual level and compared to a spectrum of a group of healthy volunteers. Ratios of phosphomonoesters (PME) to phosphodiesters (PDE) and phosphomonoesters to inorganic phosphate (Pi) were determined. Histopathologic assessment showed four partial responders and one complete responder to chemotherapy. The ³¹P spectrum of the patient group was distinctly different from the ³¹P spectrum of healthy volunteers and transformed its shape during the course of chemotherapy towards the shape of the spectrum of the healthy volunteers. Prior to chemotherapy the PME to PDE signal ratio and the PME to Pi signal ratio were high, and during the course of the chemotherapy these ratios normalized to the value of the healthy volunteers. Metabolite T₂ values in tumor tissue tended to be lower than those for healthy glandular tissue. Assessment of individual patients showed that four out of five had a significant drop of the PME to Pi ratio by a factor of 2 or more. On average, the pH of the tumor, calculated from chemical shift variation of Pi, was 0.19 units lower before chemotherapy. We have demonstrated that the sensitivity of ³¹P MRSI in breast cancer at 7 T is sufficient to detect alterations in membrane metabolism during neoadjuvant chemotherapy, which may be used for early assessment of treatment efficacy.

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.

Machine perfusion viability testing

PURPOSE OF REVIEW

Pretransplant assessment of kidney graft viability may help clinicians to decide whether to accept or discard a kidney for transplantation. With the increasing demand for donor kidneys and the increased use of marginal kidneys, the need of viability markers has increased to pursue superior transplant outcomes. Hypothermic machine perfusion (HMP) provides the theoretical opportunity to assess the viability of donor kidneys. We discuss the novel developments in viability testing during HMP and address the future prospects.

RECENT FINDINGS

HMP viability testing has focused on the analysis of machine perfusion parameters and perfusate biomarkers. Renal resistance and the biomarkers lactate dehydrogenase, aspartate transaminase, glutathione-S-transferase, N-acetyl-β-D-glucosaminidase, heart-type fatty acid binding protein, lipid peroxidation products, redox-active iron and IL-18 are correlated with transplant outcome in terms of development of delayed graft function or graft survival. However, they all lack adequate predictive value for transplant outcome. New techniques including contrast-enhanced ultrasound, three-dimensional ultrasound and magnetic resonance spectrometry are promising methods to test kidney viability during HMP, but their value has to be established. The introduction of normothermic machine perfusion offers other promising opportunities for viability testing.

SUMMARY

Machine perfusion characteristics and perfusate biomarkers have been extensively studied. They often correlate with the transplant outcome, but the present viability tests are not reliable predictors of transplant outcome. New developments in kidney graft viability assessment are necessary to have a chance of being clinically useful in the future.

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.

31-Phosphorus magnetic resonance spectroscopy for dynamic assessment of adenosine triphosphate levels in pancreas preserved by the two-layer method

Cold preservation injury influences islet graft function. Reliable tools for real-time assessment of pancreas viability before islet isolation are lacking. Phosphorus magnetic resonance spectroscopy ((31)P-MRS) was used immediately after organ harvest to study rat pancreases at 4 °C to 6 °C in five randomized preservation groups: Marshall's solution, static two-layer method (TLM), continuous TLM with oxygen perfused at 0.5 L/min, and static TLM or continuous TLM both the latter following 30 minutes of warm ischemia (WI). (31)P spectra were analyzed for phosphomonoesters, inorganic phosphate (Pi) and α-, β-and γ-nucleotide triphosphate. Intergroup rates of change of [γ-adenosine triphosphate (ATP)]/[Pi] and [β-ATP]/[Pi] throughout preservation period were significantly different. For continuous TLM there was an increase relative to baseline (0.043 (SD0.033) h(-1) and 0.029 (0.029) h(-1), respectively) but a decrease for both static TLM (-0.023 (0.016) h(-1) and 0.015 (0.026), P < .001 and < .05, respectively) and Marshall's (-0.049 (0.025) h(-1) and -0.036 (0.019) h(-1), respectively, both P < .001) with respect to continuous TLM. Rate of decrease was similar for the Marshall's and static TLM groups. [γ-ATP]/[Pi] and [β-ATP]/[Pi] increased with WI continuous TLM (0.008 [0.009] h(-1) and 0.007 [0.008] hr(-1), respectively) but decreased for WI static TLM (-0.018 (0.008) h(-1) and -0.014 (0.004) hr(-1), respectively, P < .001). (31)P-MRS is an effective tool for noninvasive assessment of pancreas bioenergetics. Continuous TLM preserves cellular bioenergetics and is superior to current non-perfluorocar bone based solutions for pancreas preservation.

Oxygenated hypothermic pulsatile perfusion versus cold static storage for kidneys from non heart-beating donors tested by in-line ATP resynthesis to establish a strategy of preservation

AIM

The scarcity of kidneys for transplantation impels an expansion of the donor source to include the use of organs from Maastricht II and Maastricht I non heart-beating donors. The aim of this study was to establish the best method to preserve kidneys from non heart-beating donors (NHBD): cold static storage (CSS) or perfusion. ATP production during kidney preservation has been retained as a measure of their energetic levels and, consequently, their viability. The presence of warm ischemia with both types of preservation was studied.

METHODS

Porcine kidneys presenting no warm ischemia or 30 minutes of warm ischemia were submitted to immediate oxygenated hypothermic pulsatile perfusion or immediate cold static storage. The study was divided into four groups. ATP resynthesis was measured after 8 h. of perfusion. ATP was assessed by in-line (31)P nuclear magnetic resonance spectroscopy (NMRS) during the preservations.

RESULTS

Only oxygenated perfusion could restore ATP in organs with warm ischemia. Initial cold static storage seems deleterious on organs having suffered from warm ischemia.

DISCUSSION

Only oxygenated perfusion could restore ATP in organs with warm ischemia. Initial cold static storage seems deleterious to organs having suffered from warm ischemia. Oxygenated perfusion must be introduced immediately after kidney removal from non heart-beating donors. In organs without warm ischemia, any kind of preservation is equivalent.

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.

Hypothermic perfusion preservation: the future of organ preservation revisited?

Hypothermic perfusion preservation (HPP) was an integral step in the development of early clinical transplantation programmes, and considerable progress was made in understanding the basic principles underlying the technique. In subsequent years, the development of better preservation solutions for cold hypoxic storage, along with pragmatic choices made on grounds of costs and logistics, saw a fall in the application of HPP. More recently, the acute shortage of suitable organ donors and the inevitable pressure to use organs from sub-optimal (or expanded criteria) donors, has forced a re-evaluation of HPP, and the development of a new generation of HPP machines and associated perfusion solutions. This review sets out the historical development of HPP across the range of organs in which the method was originally investigated, describes the biological benefits and drawbacks associated with HPP, and sets out the most recent literature on the topic (including comments on the interest in use of higher temperatures in organ perfusion).

IMPROVED PRETRANSPLANT ASSESSMENT OF RENAL QUALITY BY MEANS OF PHOSPHORUS-31 MAGNETIC RESONANCE SPECTROSCOPY USING CHEMICAL SHIFT IMAGING

BACKGROUND

Phosphorus-31 (P) magnetic resonance spectroscopy (MRS) has been evaluated in several studies for pretransplant assessment of renal viability. As an indicator of graft quality, the ratio of phosphomonoesters (PME) to an organ's inorganic phosphate (Pio) is the parameter of choice. However, exact calculation of the PME/Pio ratio is disturbed by interference from the signal of phosphorus contained in the preservation solution (Pip). In this article, the authors present an improvement attained by using volume selective P-MRS using chemical shift imaging (CSI) enabling reduction in the disturbing influence of Pip.

METHODS

Sixteen renal grafts were investigated using a 2.0-T whole-body scanner and a cross-coil setting with an active decoupled receiver coil. P-CSI was used to measure two-dimensional spectra of a 4-cm slice of the graft in a 12 x 12 matrix. Peaks of each spectrum were fitted with magnetic resonance user interface-MatLab software using VarPro and the mean PME/Pio ratio was calculated.

RESULTS

Significant correlation between the PME/ Pio ratio and clinical kidney function was found. In comparison to former trials using PME/Pio ratios calculated from non-volume-selective spectra, the correlation outcome improved significantly. Furthermore, overlay of CSI-spectra matrix and corresponding slice image of the kidney illustrates the origin of different signals in the spectra.

CONCLUSIONS

The authors' work demonstrates that the PME/Pio ratio calculated from CSI spectra is a reliable indicator of viability of renal grafts. Early knowledge of graft quality may allow therapy to be adapted to the conditions of the organ, for example, by initial withholding of nephrotoxic calcineurin-inhibitors in kidneys with high risk of delayed graft function.

Biphasic behavior of the kinetics of 31P-containing metabolites in ischemic porcine kidneys

The assessment of kidney viability before transplantation (with a view of discarding nonviable organs) remains an obstacle to confidently extending organ harvesting to marginal donors. In the present study phosphorus magnetic resonance spectroscopy was used to monitor metabolic changes in (31)P-containing metabolites in isolated porcine kidneys. After various warm ischemia times, the organs were stored at 0 degrees C. Time-dependent changes in the phosphomonoester/inorganic-phosphate ratio were recorded at 0 degrees C were shown to follow a biexponential decay. The first-order kinetic rate constant of the short-time decay was strongly dependent on the warm ischemia time, a result that was discreted in terms of the underlying biochemistry. The metabolic events responsible for the dramatic decrease in phosphomonoester/inorganic phosphate ratio that occur immediately after organ perfusion and storage, suggest that any procedure to minimize organ damage must occur immediately after harvesting.

Long-term assessment of posttransplant renal prognosis with 31 P magnetic resonance spectroscopy

BACKGROUND

31P-magnetic resonance spectroscopy (MRS) has been widely used to study pretransplantation renal viability, and although some had discussed posttransplant renal viability, no one has examined long-term posttransplant renal prognosis. We discuss the use of 31P-MRS to assess the long-term prognosis from the time when MRS was performed.

METHODS

We studied 20 patients with renal allografts. 1.5 Tesla clinical magnetic resonance imaging (MRI) and 15 cm surface coil was used for 31P-MRS. Localized 31P-MRS was done using image selected in vivo spectroscopy (ISIS) method. Individual peaks were fitted by Lorenzian line-shapes with a least square method and peak area ratios were calculated.

RESULTS

A beta-adenosine triphosphate/inorganic phosphate (beta-ATP/Pi) ratio >1.2 had sensitivity of 92.8%, specificity of 100%, and accuracy of 95% for predicting 3-year renal survival; a beta-ATP/Pi ratio >1.2 had sensitivity of 90.9%, specificity of 66.7%, and accuracy of 76.9% for predicting 5-year renal survival. We compared 31P-MRS spectra data between the survived group and failed group. The survived group had significantly higher beta-ATP/Pi, alpha-ATP/Pi, and phosphodiester (PDE)/Pi ratios than the failed group.

CONCLUSIONS

We discussed the beta-ATP/Pi value as a parameter for predicting long-term survival of a transplanted kidney from the time when MRS was performed. A value above 1.2 suggests a high probability of 3-year renal survival, whereas a value over 2.5 indicates that the transplanted kidney could survive over 5 years. 31P-MRS may be useful for predicting long-term survival of transplanted kidneys, but additional studies are needed.

Deuterium nuclear magnetic resonance for evaluating the metabolic status of livers subjected to warm ischemia

BACKGROUND

The development of reliable methods for assessing the viability of currently available livers is expected to increase the number of successful transplantations.

METHODS

2 H nuclear magnetic resonance (NMR) was used to search for metabolic markers of ischemia in explanted rat livers. Deuterium oxide (2 H2O) was used as a source of 2 H. A total of 10-80% v/v 2 H2O was added to homogenates obtained from a liver biopsy and the formation of 2 H-labeled metabolites was monitored.

RESULTS

Some well-resolved 2 H resonances were found in the homogenates from biopsies of warm ischemic liver. Two of these were identified as [3-2 H] lactate and [2-2 H] lactate, and a linear relationship was found between the ratio of [[2-2 H] lactate] to [[3-2 H] lactate] and the warm ischemia time. The deuterium incorporation into lactate was explained on the basis of the metabolic events occurring under hypoxic conditions.

CONCLUSIONS

The experimental results support the application of 2 H NMR for a reliable evaluation of the metabolic status of a liver harvested from non-heart-beating donors.

Tissue pH in human kidney transplants during hypothermic ischemia

Ex vivo NMR spectroscopy was used to investigate pH in 67 human kidney transplants. (1)H and (31)P spectra were recorded at 1.5 T during regular hypothermic storage in histidine-tryptophane-alpha-ketoglutarate (HTK) solution. Estimations of cytosolic pH from chemical shift differences between inorganic phosphate and phosphodiesters and of extracellular pH from the varepsilon1 and delta2 protons of histidine were based upon systematic titration studies. The possibility to predict acute tubular necrosis (ATN) by measuring pH was compared to results obtained with peak area ratios of phosphomonoesters (PME) and Pi and of the gamma-phosphorus of nucleoside 5'-triphosphate (gamma-NTP) and Pi. Cytosolic pH was 6.86+/-0.10 in kidneys showing immediate post-transplant function and 6.84+/-0.10 in those with ATN. Time-dependent studies demonstrated a monoexponential pH decay (velocity constant: 0.14+/-0.07 h(-1)). Extracellular pH varied between 7.40 and 7.15. Grafts with immediate function showed higher PME/Pi (2.24+/-0.57 vs. 1.77+/-0.50, p<0.05) and gamma-NTP/Pi (0.33+/-0.16 vs. 0.16+/-0.08, p<0.001). Intra- and extracellular pH can be monitored non-invasively during hypothermic transplant storage. The pH gradient between both compartments provides quantitative information about the buffer capacity of the preservation medium. Acidification is not a primary cause of ATN during regular HTK storage. The total nucleotide pool is a determinant of the reversibility of ischemic injury.

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.

Localized 31P MR spectroscopy of the transplanted human kidney in situ shows altered metabolism in rejection and acute tubular necrosis

The purpose of this study was to investigate the function of transplant kidneys in situ, and to detect pathologic changes, using volume-selective phosphorous NMR spectroscopy (31P MRS). Localized 31P MR spectra were obtained from 37 patients using a whole-body MR scanner with a combination of surface coils, adiabatic excitation pulses, and a modified image-selected in vivo spectroscopy (ISIS) sequence. Seventeen patients with pathologic changes after renal transplant were compared with a control group of 20 patients with no evidence of transplant dysfunction. The transplant kidneys with rejection reaction showed higher ratios of inorganic phosphate (P2i) to adenosine triphosphate-alpha (ATP-alpha) than the normal control group (.4 +/- .16 compared with .22 +/- .11, P = .01) and reduced pH. The spectra of transplant kidneys with tubular necrosis had lower phosphomonoester (PME)/phosphodiester (PDE) ratios than the control group (.65 +/- .35 compared with .96 +/- .5, P = .04). The pathologies of rejection and tubular necrosis could be differentiated from each other by pH (6.93 +/- .1 in rejection versus 7.14 +/- .19 in tubular necrosis, P = .04). Preliminary results indicate that localized image-guided 31P MR spectroscopy of transplant kidneys in situ can detect rejection reactions and acute tubular necrosis noninvasively, providing an incentive for further research.

Noninvasive metabolic assessment of human donor livers: prognostic value of 31P-magnetic resonance spectroscopy for early graft function

BACKGROUND

The purpose of this study was to investigate whether phosphorus-31 magnetic resonance spectroscopy (31P-MRS) of the isolated donor liver can serve as a viability indicator with prognostic value for transplantation outcome.

METHODS

Forty human donor livers preserved with University of Wisconsin solution were studied shortly before transplantation. The respective spectral peak areas of the isolated donor liver were correlated with the amount of hepatocellular graft damage and liver metabolic function shortly after implantation.

RESULTS

The individual phosphomonoesters, inorganic phosphate, phosphodiesters, and nicotine adenine dinucleotide peaks were not prognostic for postoperative hepatocellular damage or liver metabolic capacity. The presence of adenosine triphosphate, however, predicts a significantly better metabolic capacity to eliminate bilirubin, to synthesize fibrinogen and antithrombin III, and to maintain a better prothrombin time after transplantation. Furthermore, this study is probably the first 31P-MRS demonstration in the human liver of phosphocreatine.

CONCLUSIONS

In the clinical setting described, metabolic assessment using 31P-MRS did not result in a reliable noninvasive test to predict primary graft dysfunction. Study of the role of phosphocreatine in liver metabolism during cold storage is needed.

Evaluation of normothermic ischemia and simple cold preservation injury in pig kidney by proton nuclear magnetic resonance spectroscopy

The isolated perfused pig kidney (IPK) model was used to mimic the non-heart-beating donor situation. This model was performed to assess initial renal functions after normothermic ischemia, cold flush, and 24 hr cold-storage preservation (CSP) with Euro-Collins and to determine normothermic ischemia and reperfusion impairment by biochemical, histological, and proton nuclear magnetic resonance (NMR) spectroscopy analysis. Twenty-four pig kidneys were used. There were three experimental groups: Group 1 (G1), control kidneys flushed with cold heparinized saline and immediately perfused; Group 2 (G2), cold flush followed by 24 hr CSP and reperfusion; and Group 3 (G3), 30 min of normothermic ischemia followed by cold flush and 24 hr CSP and reperfusion. Kidneys were perfused for 2 hr at 37.5 degrees C for functional evaluation. Perfusate flow rate is significantly different for G3 (P < 0.01). Glomerular filtration rate is less in G3 (P < 0.05). Fractional reabsorptions of sodium (FRNa+) and glucose (Glc) excretion in urine are different in G3 (P < 0.01 and P < 0.05, respectively). Amino acid excretion in NMR spectroscopy was higher in G3 (P < 0.05). Elevated levels of trimethylamine-N-oxide (TMAO) and lactate (Lac) were detected by proton NMR spectroscopy in G2 and particularly G3. A peak is present in G3 and related with poor glomerular and tubular functions and worse histological data. Malondialdehyde tissue level was higher in G3. This study shows that the IPK with proton NMR spectroscopy may be a useful method in the evaluation of kidneys after cold ischemia and transplantation. This model might be suitable for a variety of experimental protocols, particularly to improve functional performance after ischemia and reperfusion.

Non-invasive assessment of ATP regeneration potential of the preserved donor liver. A 31P MRS study in pig liver

We have developed a quick, non-invasive method for measuring the ability of an isolated preserved liver to regenerate high energy phosphate nucleotides without the need for biopsy. Using 31P MRS we have monitored the hepatic energetics of intact cold preserved pig liver using standard clinical harvesting and storage techniques. Following cold storage for 2 h the livers were hypothermically reperfused with oxygenated modified University of Wisconsin preservation fluid. Prior to reperfusion MRS detectable adenosine diphosphate plus adenosine triphosphate was negligible; however, the spectrum showed intense resonances from phosphomonoesters and inorganic phosphate, as a consequence of adenosine triphosphate hydrolysis during cold preservation. Following a 10-min period of hypothermic reperfusion, regeneration of adenosine triphosphate occurred with a concurrent decline in inorganic phosphate and phosphomonoester, both of which are associated with adenosine triphosphate synthesis. The capacity of the liver to regenerate adenosine triphosphate following a 24-h period of cold storage was reduced by approximately 40% (p < 0.01) of the total amount achieved following the shorter cold storage time. Adenosine triphosphate regeneration rates were biphasic and were decreased upon prolonged storage, with the initial rate being reduced from 40.6 x 10(-2).min-1 (standard deviation (sd) 2.70 x 10(-2).min-1) to 14.8 x 10(-2).min-1 (sd; 2.4 x 10(-2).min-1) and the secondary rate from 1.77 x 10(-2).min-1 (sd; 0.18 x 10(-2).min-1) to 0.84 x 10(-2).min-1 (sd; 0.45 x 10(-2).min-1). MR images of the liver during the period of hypothermic reperfusion were also performed providing an assessment for the degree of hepatic vascular perfusion. This non-invasive, 31P MRS assessment of hepatic energetics in a clinically relevant animal model has great potential for the understanding of graft preservation injury.

Glutathione S-transferase as predictor of functional outcome in transplantation of machine-preserved non-heart-beating donor kidneys

Non-heart-beating (NHB) donors are a valuable source of kidneys for transplantation. The organs, however, sustain substantial warm ischemic damage that may jeopardize the transplantability and result in nonfunction of the grafts. Quantification of warm ischemic time (WIT) and prediction of transplant outcome are essential for the use of NHB donor organs. During machine preservation (MP) the viability of NHB donor kidneys was evaluated through calculating intrarenal vascular resistance and determining lactate dehydrogenase and alpha-glutathione S-transferase (alphaGST) in the perfusate. Thirty-seven functioning (F) and nine nonfunctioning kidneys (NF) were compared. WIT was longer in NF; serum creatinine, donor age, and preservation time were not different. WIT correlated well with alphaGST after 4 and 8 hr of MP (r=0.353, P=0.009, and r=0.346, P=0.011, respectively). When compared with F, intrarenal vascular resistance was increased in NF after 4 and 8 hr of perfusion (P<0.05); at all time points, alphaGST levels were elevated in NF (P<0.05). Lactate dehydrogenase activity was not different between the groups, but could identify immediate functioning grafts within the F group. In conclusion, alphaGST levels correlated strongly with WIT and were also able to distinguish NF from F grafts. alphaGST can adequately predict the functional outcome of NHB donor grafts before transplantation; levels of alphaGST can be used to define reliable safety margins for viability. Therefore, MP is useful in evaluating the viability of NHB donor kidneys, and the parameters discussed will help to select nonviable grafts from this valuable pool of kidneys for transplantation.

Changes in 31P-relaxation times during organ preservation: observations on cold stored human donor livers

During cold preservation for transplantation the tissue hydration state changes. It is not known whether such changes lead to altered relaxation times of 31P nuclei with potential consequences for the quantification of tissue metabolites. Therefore, 31P spectroscopic and proton T1 relaxometric measurements were performed on 42 isolated human donor livers shortly before implantation. The results demonstrate that 31P T1 relaxation times change during preservation for clinical transplantation, thus quantification of tissue metabolites in cold stored donor livers may be in part dependent on the tissue hydration state. Furthermore, it appeared that changes in tissue hydration state especially affect the physico-chemical characteristics of the intracellular fluid compartment. This study indicates that reliable spectroscopic quantification of tissue metabolites, particularly during sequential spectroscopic measurements in cold stored donor organs is best warranted under fully relaxed conditions.

Proton-decoupled phosphorus-31 magnetic resonance spectroscopy in the evaluation of native and well-functioning transplanted kidneys

RATIONALE AND OBJECTIVES

To evaluate whether decoupling improves signal-to-noise ratio and frequency resolution of in vivo kidney spectra, and to compare native and well-functioning transplant kidneys.

METHODS

Proton decoupling in conjunction with three-dimensional chemical shift imaging (3D-CSI) in phosphorus-31 magnetic resonance (MR) spectroscopy was used with a spatial resolution of 64 cm3 and 17-minute acquisition time to compare native (n = 10) and well-functioning transplant (n = 9) kidneys.

RESULTS

Proton decoupling improved peak amplitudes by almost 30%, as well as chemical shift resolution of in vivo kidney spectra. No statistically significant differences in phosphometabolite ratios and renal spectra were observed between healthy volunteers and patients with nonrejecting transplants. The phosphodiester-phosphomonoester ratio was 3.02 +/- 0.88, phosphomonoester-inorganic phosphate ratio was 1.07 +/- 0.44, and inorganic phosphate-adenosine triphosphate ratio was 0.58 +/- 0.22 after correction for saturation effects.

CONCLUSION

Improved spectra of native and transplant kidneys can be obtained in vivo with MR spectroscopy by using a short acquisition time.

Tissue pH in cold-stored human donor livers preserved in University of Wisconsin solution. A noninavasive clinical study with 31P-magnetic resonance spectroscopy

It is not known whether the tissue acidosis that accompanies cold storage is the beginning of irreversible cell injury, ultimately leading to cell death, or whether it is a natural "protective" mechanism for cells to survive hypoxic periods. To answer this question, the tissue pH of 45 cold-stored human donor livers preserved in University of Wisconsin solution (UW) was assessed shortly before implantation using noninvasive 31P magnetic resonance spectroscopy. We conclude that tissue pH during cold storage may be partly dependent upon hepatic glycogen stores and donor age. The wide range of tissue pH values that was observed at the time of implantation does not result in significant effects on cellular damage after transplantation. This indicates that tissue pH is not a major determinant for the viability of UW solution-preserved human donor livers, as indicated by postoperative hepatocellular damage and liver synthesis function. The membrane stabilizing and buffering capacity of UW solution appears to protect liver viability against tissue acidosis. Our results also indicate that liver tissue pH can be lower than has been previously assumed in the literature without significant adverse effects on liver viability.

Development and applications of in vivo clinical magnetic resonance spectroscopy

4.1 CURRENT STATUS. While an extensive clinical literature of MRS of muscle, brain, heart and liver has been achieved, the MRS technique is not considered essential for routine diagnosis because it is inherently insensitive and metabolic changes tend to be small. However, MRS techniques have proven to be of considerable value for prognosis in some circumstances, notably for predicting outcome following hypoxic-ischaemic injury in the newborn and also in predicting graft viability following organ transplantation. The chemical specificity of MRS has been illustrated, and exploiting the non-invasive nature of the technique, metabolic fingerprinting of pathophysiological processes throughout the natural history of a wide variety of diseases is now being accomplished. Particularly exciting are the applications of 13C MRS for measuring hepatic and muscle glycogen levels, for example in diabetics, and the use of hepatic 31P MRS for assessing liver function in cirrhosis. Other areas of excitement are the applications of 1H MRS in assessing neuronal function in epilepsy and stroke, and for measuring the evolution of lactate in stroke and hypoxic-ischaemic encephalopathy. Emphasis on technique development continues, and applications still tend to be technology-led. The availability of routine clinical MRI systems with spectroscopy capabilities has given MRS studies wider applicability. The recent improvements in spatial resolution have been impressive and the technique is slowly becoming more quantitative. 4.2. FUTURE PERSPECTIVES. Given the flexibility of clinical magnetic resonance techniques, particularly magnetic resonance imaging, it is likely that MRI will be the diagnostic tool of choice in a wider range of diseases, such as multiple sclerosis, stroke, neurodegenerative conditions, sports injuries and in staging malignancies. Since proton magnetic resonance spectroscopy packages have become a routine addition to many MRI systems, it is feasible to select the MRI sequences of most value in highlighting anatomical and pathological abnormalities and to incorporate specifically selected MRS sequences to emphasize biochemical differences. Improvements in technical methodologies are central to further developments. For example, use of internal coils, such as implantable or endoscopic coils, will enable small regions of tissue to be studied in considerable detail, which may otherwise be inaccessible to measurement. Chemical MRS studies have benefited from the use of higher magnetic fields, and the same may be expected for clinical MRS studies. Whole-body magnets up to 4 T have been used in a few centres, and certainly 3 T systems are becoming more widely available with the recent tremendous interest in functional imaging. Certainly, better control of artefacts can be expected; for example, improved definition of spectral changes due to voluntary or involuntary movements. Wider use of proton decoupling methods will improve the specificity of the spectra, by allowing definitive assignments of overlapping resonances, as well as the sensitivity. Comparing PET and MRS studies, it is becoming increasingly obvious that both will be required in parallel to explore parameters of brain metabolism and function. The ability to measure 13C MR signals in the brain has been demonstrated, which allows measurements of glutamate and glucose turnover. MRS measurements have the advantage of not requiring a radioactive isotope, as well as being insensitive to activity-related changes in regional cerebral blood flow. Also the study of cerebral glucose metabolism by MRS is very promising, allowing a resolution and sensitivity comparable to PET. A combination of MRS and PET studies will allow the pathogenesis of neuropsychiatric disorders to be better understood. (ABSTRACT TRUNCATED)

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)

Selection criteria for liver donation: a review

An overview of the criteria that are currently being used for the selection of liver donors is presented. The validity of the different criteria is discussed. The potential benefits of introducing other modalities is dealt with.

In vivo NMR imaging and spectroscopic investigation of renal pathology in lean and obese rat kidneys

Diabetic nephropathy is a major cause of end-stage renal failure. While our understanding of the pathogenesis of nephropathy is incomplete, progressive glomerular injury appears to play a significant role in the decline of renal function. Proton NMR spectroscopy and imaging techniques were used to address changes in renal pathology associated with glomerular mesangial expansion in vivo in kidneys from spontaneously obese and lean (control) littermate Zucker rats. Fully functioning rat kidneys were surgically exposed and externalized for direct NMR signal detection via a coil placed around the organ. High-resolution (78 microns in plane) proton images were obtained at 4.7 T magnetic field strength revealing fine structure within the well-defined cortical and medullary regions. The obese rat kidney images were distinct in appearance from the lean kidney images and exhibited marked cortical expansion as well as increased overall kidney size. Enlargement of mean glomerular diameter was verified histologically in the obese kidneys as compared with the lean kidneys. Proton T1 and T2 relaxation times were determined from the entire kidney using standard spectroscopic techniques, and from specific regions within the kidney from multiple T1- and T-2 weighted images. Additionally, image contrast enhancement resulting from saturation transfer between protons in restricted-mobility environments and mobile water protons within the kidney was investigated in the lean and obese rat kidneys using magnetization-transfer imaging techniques. At the early stage of renal injury examined in this study, diseased and healthy kidneys could not be differentiated on the basis of relaxation times alone. The magnitude of saturation transfer obtained in cortical tissue in the lean and obese kidneys was also not statistically significantly different. However, the magnitude of saturation transfer achieved in the medullary tissue of obese kidneys was statistically significantly less than that achieved in lean kidneys.

Study of kidney and liver viability in the rat after exclusive aortic perfusion using intracellular ATP measurement

To find whether the liver can be procured after exclusive aortic perfusion, three organ perfusion models were used in three groups of donor rats. Group 1 underwent liver wash-out via the portal vein; in group 2, the kidneys alone were perfused via the aorta; and group 3 underwent simultaneous aortic perfusion of liver and kidneys. All perfusion flow rates in the three groups were adjusted to physiological values. Harvested organs were transplanted and recipient animals were killed 4 h after transplantation to study liver and kidney viability by using intracellular ATP measurement. Liver ATP was lower (P < 0.005) in the portal perfusion group (group 1: 1.396 +/- 0.412) than in the aortic perfusion group (group 3: 2.181 +/- 0.061). Kidney ATP was comparable in groups 2 and 3:1.066 +/- 0.09 vs 1.059 +/- 0.273 (mumol/g) tissue). Liver cooling was quicker with portal perfusion than with the aortic flush (20 degrees C in 20 s vs 15 degrees C in 60 s). Aortic perfusion at a physiologic flow rate has no detrimental effect on renal viability studied by intracellular ATP measurement. We conclude that liver cooling via the aortic route only is a good alternative to portal perfusion and seems to give good preservation. Application of this observation to emergency procurement in humans is still the subject of controversy.

Improved renal transplant preservation using a modified intracellular flush solution (PB-2). Characterization of mechanisms by renal clearance, high performance liquid chromatography, phosphorus-31 magnetic resonance spectroscopy, and electron microscopy studies

A number of new intracellular renal flush solutions have been found to be more efficacious than Collins-2 (C-2) solution in extending organ viability during simple cold storage. However, the mechanism of action of these solutions remains poorly understood. To delineate better underlying intracellular mechanisms, we studied a modified, simple, hypothermic, intracellular (340 mOsm/kg) flush solution (PB-2). The development of PB-2 solution is based on the ability of some of its individual components to minimize ischemic adenine nucleotide (AN) catabolism and endothelial post "reperfusion injury." Preliminary results in 10 canine autorenal transplants show a significant (P less than 0.02) improvement in renal recovery and viability (recipient posttransplant inulin clearance and survival) after 50 h of cold storage compared with 10 canine kidneys similarly preserved using conventional C-2 flush solution. High performance liquid chromotography (HPLC) studies show a significant (P less than 0.01) loss of AN using C-2, while PB-2 was associated with regeneration of AN within 45 min of reperfusion. Magnetic resonance spectroscopy using phosphorus 31 (31P-MRS) showed more high energy phosphorus metabolites (phosphomonoester and nicotinamide-adenine-dinucleotide phosphate: P less than 0.001) at 50 h cold storage using PB-2 compared with C-2. Electron micrographs (EM) revealed normal microcapillary morphology for the PB-2 group; however, moderate vascular red and white blood cell clumping was observed in the C-2 group. Characterization of the basic preservation mechanisms by HPLC, 31P-MRS, and EM studies indicates that PB-2 solution enhances renal preservation by diminution of both reperfusion injury and the loss of intracellular high energy metabolites that are necessary for viability.