Objective and rapid assessment of pancreas graft viability using 31P-nuclear magnetic resonance spectroscopy combined with two- layer cold storage method

Ischemia-Reperfusion Injuries Assessment during Pancreas Preservation

Maintaining organ viability between donation and transplantation is of critical importance for optimal graft function and survival. To date in pancreas transplantation, static cold storage (SCS) is the most widely practiced method of organ preservation. The first experiments in ex vivo perfusion of the pancreas were performed at the beginning of the 20th century. These perfusions led to organ oedema, hemorrhage, and venous congestion after revascularization. Despite these early hurdles, a number of factors now favor the use of perfusion during preservation: the encouraging results of HMP in kidney transplantation, the development of new perfusion solutions, and the development of organ perfusion machines for the lung, heart, kidneys and liver. This has led to a resurgence of research in machine perfusion for whole organ pancreas preservation. This review highlights the ischemia-reperfusion injuries assessment during ex vivo pancreas perfusion, both for assessment in pre-clinical experimental models as well for future use in the clinic. We evaluated perfusion dynamics, oedema assessment, especially by impedance analysis and MRI, whole organ oxygen consumption, tissue oxygen tension, metabolite concentrations in tissue and perfusate, mitochondrial respiration, cell death, especially by histology, total cell free DNA, caspase activation, and exocrine and endocrine assessment.

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.

Use of Ex Vivo Normothermic Perfusion for Quality Assessment of Discarded Human Donor Pancreases

A significant number of pancreases procured for transplantation are deemed unsuitable due to concerns about graft quality and the associated risk of complications. However, this decision is subjective and some declined grafts may be suitable for transplantation. Ex vivo normothermic perfusion (EVNP) prior to transplantation may allow a more objective assessment of graft quality and reduce discard rates. We report ex vivo normothermic perfusion of human pancreases procured but declined for transplantation, with ABO-compatible warm oxygenated packed red blood cells for 1-2 h. Five declined human pancreases were assessed using this technique after a median cold ischemia time of 13 h 19 min. One pancreas, with cold ischemia over 30 h, did not appear viable and was excluded. In the remaining pancreases, blood flow and pH were maintained throughout perfusion. Insulin secretion was observed in all four pancreases, but was lowest in an older donation after cardiac death pancreas. Amylase levels were highest in a gland with significant fat infiltration. This is the first study to assess the perfusion, injury, as measured by amylase, and exocrine function of human pancreases using EVNP and demonstrates the feasibility of the approach, although further refinements are required.

Pattern recognition and biomarker validation using quantitative1H-NMR-based metabolomics

The collection of global metabolic data and their interpretation (both spectral and biochemical) using modern spectroscopic techniques and appropriate statistical approaches, are known as 'metabolic profiling', 'metabonomics' or 'metabolomics'. This review addresses 1H-nuclear magnetic resonance (NMR)-based metabolomic principles and their application in biomedical science, with special emphasis on their potential in translational research in transplantation, oncology, and drug toxicity or discovery. Various steps in metabolomics analysis are described in order to illustrate the types of biological samples, their respective handling and preparation for 1H-NMR analysis; provide a rationale for using pattern-recognition techniques (spectral database concept) versus quantitative 1H-NMR-based metabolomics (metabolite database concept); and identify necessary technological and logistical future developments that will allow 1H-NMR-based metabolomics to become an established tool in biomedical research and patient care.

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.

Pancreas oxygen persufflation increases ATP levels as shown by nuclear magnetic resonance

BACKGROUND

Islet transplantation is a promising treatment for type 1 diabetes. Due to a shortage of suitable human pancreata, high cost, and the large dose of islets presently required for long-term diabetes reversal; it is important to maximize viable islet yield. Traditional methods of pancreas preservation have been identified as suboptimal due to insufficient oxygenation. Enhanced oxygen delivery is a key area of improvement. In this paper, we explored improved oxygen delivery by persufflation (PSF), ie, vascular gas perfusion.

METHODS

Human pancreata were obtained from brain-dead donors. Porcine pancreata were procured by en bloc viscerectomy from heparinized donation after cardiac death donors and were either preserved by either two-layer method (TLM) or PSF. Following procurement, organs were transported to a 1.5-T magnetic resonance (MR) system for (31)P nuclear magnetic resonance spectroscopy to investigate their bioenergetic status by measuring the ratio of adenosine triphosphate to inorganic phosphate (ATP:P(i)) and for assessing PSF homogeneity by MRI.

RESULTS

Human and porcine pancreata can be effectively preserved by PSF. MRI showed that pancreatic tissue was homogeneously filled with gas. TLM can effectively raise ATP:P(i) levels in rat pancreata but not in larger porcine pancreata. ATP:P(i) levels were almost undetectable in porcine organs preserved with TLM. When human or porcine organs were preserved by PSF, ATP:P(i) was elevated to levels similar to those observed in rat pancreata.

CONCLUSION

The methods developed for human and porcine pancreas PSF homogeneously deliver oxygen throughout the organ. This elevates ATP levels during preservation and may improve islet isolation outcomes while enabling the use of marginal donors, thus expanding the usable donor pool.

Imaging Molecular and Cellular Events in Transplantation

Imaging methods such as nuclear medicine (including positron emission tomography), magnetic resonance imaging, ultrasound, and optical imaging can be used to provide information about the expression of genes, and the location of molecules and cells in intact animals or patients. In the setting of transplantation, this will allow monitoring of inflammatory responses, as well as the state of the graft. In this review, the advantages and disadvantages of different approaches to imaging will be discussed, as well as their potential application to transplantation.

Molecular imaging in transplantation: basic concepts and strategies for potential application

BACKGROUND

The potential applications of molecular imaging in the clinical arena are diverse and expanding rapidly. One such area of application is transplantation. Currently, biopsy is the gold standard for monitoring allograft well-being after transplantation of organs or tissues. However, biopsies are invasive, associated with morbidity if performed on a routine basis and can potentially miss focal rejection.

AIM

It is notable that none of the existing studies in the literature have examined the possible role of molecular imaging in transplantation-related indications. In this direction, this paper aims to discuss imaging strategies that could be of pertinence in monitoring immune events and improving long-term outcomes after solid organ or tissue transplantation.

METHODS

This paper discusses the currently available direct/surrogate imaging techniques/agents that can be used to detect chemokine receptors/ligands, leucocyte endothelial events and ischaemia-reperfusion injury in transplantation.

CONCLUSION

Molecular imaging methods can non-invasively detect, quantify and monitor immune phenomena, such as rejection or graft-versus-host disease, after transplantation. Molecular imaging could help in targeted biopsy and could improve graft survival by allowing for early intervention with tailored immunosuppressive regimens. Given the unprecedented progress in the field, the potential benefits of molecular imaging to the speciality of organ and tissue transplantation cannot be underestimated.