Pancreas Oxygenation Is Limited During Preservation With the Two-Layer Method

New methods for improving pancreas preservation

PURPOSE OF REVIEW

Pancreas and islet transplantation face critical organ shortage challenges, with many potential grafts discarded due to concerns about consequences of ischemia-reperfusion injury, particularly from donation after circulatory death (DCD) donors. Static cold storage remains standard practice but has significant limitations. Novel preservation technologies may improve transplant outcomes, donor selection and even expand the donor pool.

RECENT FINDINGS

Normothermic regional perfusion in DCD donors has increased pancreas utilization with promising one-year graft survival comparable to donation after brain-death (DBD) donors. Hypothermic machine perfusion maintains tissue integrity and shows promising preclinical results. Oxygenated hypothermic machine perfusion successfully restores tissue adenosine triphosphate (ATP) levels without notable tissue injury. Normothermic machine perfusion, despite challenges, offers potential for viability assessment and resuscitation.

SUMMARY

Advanced preservation technologies provide platforms for assessment, reconditioning, and therapeutic interventions for pancreas grafts. Clinical translation requires consensus on perfusion parameters and perfusate composition optimized for pancreatic preservation. Future developments should focus on implementing sensitive and specific assessment methods, including beta-cell specific biomarkers, to confidently select and utilize marginal pancreas grafts for transplantation.

Pancreas Preservation: Hypothermic Oxygenated Perfusion to Improve Graft Reperfusion

BACKGROUND

The clinical standard for pancreas preservation for transplantation is static cold storage (SCS). Oxygenation during preservation has been shown to be advantageous in clinical studies. This study evaluates the efficiency of different oxygenation modalities during hypothermic pancreas preservation.

METHODS

Thirty-two porcine pancreases were procured in a controlled donation after circulatory death model and were divided to be preserved in 8 groups: (1) SCS, (2) hypothermic machine perfusion (HMP), (3) hypothermic oxygenated machine perfusion (HOPE) with 21% oxygen, (4) HOPE and 100%, (5) SCS and oxygen carrier, M101, (6) HMP and M101, (7) HOPE 21% and M101, and (8) HOPE 100% and M101. All the groups underwent 24 h of hypothermic preservation, followed by 2 h of normothermic reperfusion. Oxygen partial pressures were assessed using parenchymal probes. Perfusion parameters, perfusate samples, and tissue biopsies were analyzed.

RESULTS

This study showed that HMP was linked to higher tissue oxygen partial pressures, lower succinate levels, and better reperfusion parameters. Furthermore, the addition of M101 to either SCS or HMP was associated with lower succinate and creatinine phosphokinase accumulation, suggesting a protective effect against ischemia.

CONCLUSIONS

Our research has demonstrated the efficacy of machine perfusion in hypothermic conditions in providing oxygen to the pancreas during preservation and conditioning the pancreatic microvasculature for reperfusion during transplantation. Furthermore, the addition of M101 suggests a protective effect on the graft from ischemia.

Exploring Preservation Modalities in a Split Human Pancreas Model to Investigate the Effect on the Islet Isolation Outcomes

BACKGROUND

In islet transplantation, the use of dynamic hypothermic preservation techniques is a current challenge. This study compares the efficacy of 3 pancreas preservation methods: static cold storage, hypothermic machine perfusion (HMP), and oxygenated HMP.

METHODS

A standardized human pancreas split model was employed using discarded organs from both donation after brain death (n = 15) and donation after circulatory death (DCD) (n = 9) donors. The pancreas head was preserved using static cold storage (control group), whereas the tail was preserved using the 3 different methods (study group). Data on donor characteristics, pancreas histology, isolation outcomes, and functional tests of isolated islets were collected.

RESULTS

Insulin secretory function evaluated by calculating stimulation indices and total amount of secreted insulin during high glucose stimulation (area under the curve) through dynamic perifusion experiments was similar across all paired groups from both DCD and donation after brain death donors. In our hands, islet yield (IEQ/g) from the pancreas tails used as study groups was higher than that of the pancreas heads as expected although this difference did not always reach statistical significance because of great variability probably due to suboptimal quality of organs released for research purposes. Moreover, islets from DCD organs had greater purity than controls (P ≤ 0.01) in the HMP study group. Furthermore, our investigation revealed no significant differences in pancreas histology, oxidative stress markers, and apoptosis indicators.

CONCLUSIONS

For the first time, a comparative analysis was conducted, using a split model, to assess the effects of various preservation methods on islets derived from pancreas donors. Nevertheless, no discernible variances were observed in terms of islet functionality, histological attributes, or isolation efficacy. Further investigations are needed to validate these findings for clinical application.

Pancreas preservation: clinical practice and future developments

PURPOSE OF REVIEW

To summarize recently published studies of preservation strategies including machine perfusion in pancreas transplantation.

RECENT FINDINGS

The shortage of conventional donors is leading units to use extended criteria donors (ECDs) and donors after cardiac death (DCD). Static cold storage (SCS) is still the standard method of preservation for pancreases and University of Wisconsin remains the gold standard preservation solution. In experimental studies, oxygen delivered during preservation reduced tissue injury and improved islet cell yield and function. Hypothermic machine perfusion of discarded human pancreases has been shown to improve adenosine triphosphate levels without adversely effect histology and oedema compared with SCS. Normothermic machine perfusion of discarded human organs has so far been challenging and led to increasing injury, rather than preservation. There are currently no clinical studies in pancreas transplant with the exception of a small number of pancreases being transplanted following normothermic regional perfusion.

SUMMARY

The storm of new organ preservation methods is now being more widely studied in the pancreas, with some promising results. These new strategies have the potential to allow expansion of the donor pool and greater utilization of ECD and DCD organs.

Development of a Bioartificial Vascular Pancreas

Transplantation of pancreatic islets has been shown to be effective, in some patients, for the long-term treatment of type 1 diabetes. However, transplantation of islets into either the portal vein or the subcutaneous space can be limited by insufficient oxygen transfer, leading to islet loss. Furthermore, oxygen diffusion limitations can be magnified when islet numbers are increased dramatically, as in translating from rodent studies to human-scale treatments. To address these limitations, an islet transplantation approach using an acellular vascular graft as a vascular scaffold has been developed, termed the BioVascular Pancreas (BVP). To create the BVP, islets are seeded as an outer coating on the surface of an acellular vascular graft, using fibrin as a hydrogel carrier. The BVP can then be anastomosed as an arterial (or arteriovenous) graft, which allows fully oxygenated arterial blood with a pO2 of roughly 100 mmHg to flow through the graft lumen and thereby supply oxygen to the islets. In silico simulations and in vitro bioreactor experiments show that the BVP design provides adequate survivability for islets and helps avoid islet hypoxia. When implanted as end-to-end abdominal aorta grafts in nude rats, BVPs were able to restore near-normoglycemia durably for 90 days and developed robust microvascular infiltration from the host. Furthermore, pilot implantations in pigs were performed, which demonstrated the scalability of the technology. Given the potential benefits provided by the BVP, this tissue design may eventually serve as a solution for transplantation of pancreatic islets to treat or cure type 1 diabetes.

Cardioprotection via Metabolism for Rat Heart Preservation Using the High-Pressure Gaseous Mixture of Carbon Monoxide and Oxygen

The high-pressure gas (HPG) method with carbon monoxide (CO) and oxygen (O₂) mixture maintains the preserved rat heart function. The metabolites of rat hearts preserved using the HPG method (HPG group) and cold storage (CS) method (CS group) by immersion in a stock solution for 24 h were assessed to confirm CO and O₂ effects. Lactic acid was significantly lower and citric acid was significantly higher in the HPG group than in the CS group. Moreover, adenosine triphosphate (ATP) levels as well as some pentose phosphate pathway (PPP) metabolites and reduced nicotinamide adenine dinucleotide phosphate (NADPH) were significantly higher in the HPG group than in the CS group. Additionally, reduced glutathione (GSH), which protects cells from oxidative stress, was also significantly higher in the HPG group than in the CS group. These results indicated that each gas, CO and O₂, induced the shift from anaerobic to aerobic metabolism, maintaining the energy of ischemic preserved organs, shifting the glucose utilization from glycolysis toward PPP, and reducing oxidative stress. Both CO and O₂ in the HPG method have important effects on the ATP supply and decrease oxidative stress for preventing ischemic injury. The HPG method may be useful for clinical application.

Composite Tissue Preservation

Composite tissue (CT) preservation is important to outcomes after replant or transplant. Since the first limb replant, the mainstay of preservation has been static cold storage with the amputated part being placed in moistened gauze over ice. Historically, the gold-standard in solid organ preservation has been static cold storage with specialized solution, but this has recently evolved in the last few decades to develop technologies such as machine perfusion and even persufflation. This review explores the impact of cooling and oxygenation on CT, summarizes the work done in the area of CT preservation, discusses lessons learned from our experience in solid organ preservation, and proposes future directions.

Oxygenation strategies for encapsulated islet and beta cell transplants

Human allogeneic islet transplantation (ITx) is emerging as a promising treatment option for qualified patients with type 1 diabetes. However, widespread clinical application of allogeneic ITx is hindered by two critical barriers: the need for systemic immunosuppression and the limited supply of human islet tissue. Biocompatible, retrievable immunoisolation devices containing glucose-responsive insulin-secreting tissue may address both critical barriers by enabling the more effective and efficient use of allogeneic islets without immunosuppression in the near-term, and ultimately the use of a cell source with a virtually unlimited supply, such as human stem cell-derived β-cells or xenogeneic (porcine) islets with minimal or no immunosuppression. However, even though encapsulation methods have been developed and immunoprotection has been successfully tested in small and large animal models and to a limited extent in proof-of-concept clinical studies, the effective use of encapsulation approaches to convincingly and consistently treat diabetes in humans has yet to be demonstrated. There is increasing consensus that inadequate oxygen supply is a major factor limiting their clinical translation and routine implementation. Poor oxygenation negatively affects cell viability and β-cell function, and the problem is exacerbated with the high-density seeding required for reasonably-sized clinical encapsulation devices. Approaches for enhanced oxygen delivery to encapsulated tissues in implantable devices are therefore being actively developed and tested. This review summarizes fundamental aspects of islet microarchitecture and β-cell physiology as well as encapsulation approaches highlighting the need for adequate oxygenation; it also evaluates existing and emerging approaches for enhanced oxygen delivery to encapsulation devices, particularly with the advent of β-cell sources from stem cells that may enable the large-scale application of this approach.

Oxygen Perfusion (Persufflation) of Human Pancreata Enhances Insulin Secretion and Attenuates Islet Proinflammatory Signaling

BACKGROUND

All human islets used in research and for the clinical treatment of diabetes are subject to ischemic damage during pancreas procurement, preservation, and islet isolation. A major factor influencing islet function is exposure of pancreata to cold ischemia during unavoidable windows of preservation by static cold storage (SCS). Improved preservation methods may prevent this functional deterioration. In the present study, we investigated whether pancreas preservation by gaseous oxygen perfusion (persufflation) better preserved islet function versus SCS.

METHODS

Human pancreata were preserved by SCS or by persufflation in combination with SCS. Islets were subsequently isolated, and preparations in each group matched for SCS or total preservation time were compared using dynamic glucose-stimulated insulin secretion as a measure of β-cell function and RNA sequencing to elucidate transcriptomic changes.

RESULTS

Persufflated pancreata had reduced SCS time, which resulted in islets with higher glucose-stimulated insulin secretion compared to islets from SCS only pancreata. RNA sequencing of islets from persufflated pancreata identified reduced inflammatory and greater metabolic gene expression, consistent with expectations of reducing cold ischemic exposure. Portions of these transcriptional responses were not associated with time spent in SCS and were attributable to pancreatic reoxygenation. Furthermore, persufflation extended the total preservation time by 50% without any detectable decline in islet function or viability.

CONCLUSIONS

These data demonstrate that pancreas preservation by persufflation rather than SCS before islet isolation reduces inflammatory responses and promotes metabolic pathways in human islets, which results in improved β cell function.

Applications of particulate oxygen-generating substances (POGS) in the bioartificial pancreas

Type-1 Diabetes (T1D) is a devastating autoimmune disorder which results in the destruction of beta cells within the pancreas. A promising treatment strategy for T1D is the replacement of the lost beta cell mass through implantation of immune-isolated microencapsulated islets referred to as the bioartificial pancreas. The goal of this approach is to restore blood glucose regulation and prevent the long-term comorbidities of T1D without the need for immunosuppressants. A major requirement in the quest to achieve this goal is to address the oxygen needs of islet cells. Islets are highly metabolically active and require a significant amount of oxygen for normal function. During the process of isolation, microencapsulation, and processing prior to transplantation, the islets' oxygen supply is disrupted, and a large amount of islet cells are therefore lost due to extended hypoxia, thus creating a major barrier to clinical success with this treatment. In this work, we have investigated the oxygen generating compounds, sodium percarbonate (SPO) and calcium peroxide (CPO) as potential supplemental oxygen sources for islets during isolation and encapsulation before and immediately after transplantation. First, SPO particles were used as an oxygen source for islets during isolation. Secondly, silicone films containing SPO were used to provide supplemental oxygen to islets for up to 4 days in culture. Finally, CPO was used as an oxygen source for encapsulated cells by co-encapsulating CPO particles with islets in permselective alginate microspheres. These studies provide an important proof of concept for the utilization of these oxygen generating materials to prevent beta cell death caused by hypoxia.

Evaluation of Perfluorohexyloctane/Polydimethylsiloxane for Pancreas Preservation for Clinical Islet Isolation and Transplantation

This study aimed to evaluate a 50:50 mix of perfluorohexyloctane/polydimethylsiloxane 5 (F6H8S5) preservation of pancreases in a clinical setting compared with standard solutions for 1) cold ischemia time (CIT) <10 h and 2) an extended CIT >20 h. Procured clinical-grade pancreases were shipped in either F6H8S5 or in standard preservation solutions, that is, University of Wisconsin (UW) or Custodiol. F6H5S5 was preoxygenated for at least 15 min. Included clinical-grade pancreases were procured in UW or Custodiol. Upon arrival at the islet isolation laboratory, the duodenum was removed followed by rough trimming while F6H8S5 was oxygenated for 15-20 min. Trimmed pancreases were immersed into oxygenated F6H8S5 and stored at 4°C overnight followed by subsequent islet isolation. Pancreas preservation using F6H8S5 proved as effective as UW and Custadiol when used within CIT up to 10 h, in terms of both isolation outcome and islet functionality. Preservation in F6H8S5 of pancreases with extended CIT gave results similar to controls with CIT <10 h for both isolated islet functionality and isolation outcome. This study of clinically obtained pancreases indicates a clear benefit of using F6H8S5 on pancreases with extended CIT as it seems to allow extended cold ischemic time without affecting islet function and islet numbers.

Oxygenated Static Preservation of Donation after Cardiac Death Liver Grafts Improves Hepatocyte Viability and Function

BACKGROUND

Cell therapy, such as hepatocyte transplantation (HTx), is promising for the treatment of metabolic liver diseases or as a bridge to orthotopic liver transplantation in patients with fulminant liver failure. However, one of the limitations of this therapy is the shortage of donors. The present study aims to investigate whether the two-layer method (TLM) of cold preservation with oxygenation improves the viability and activity of hepatocytes from rat donation after cardiac death (DCD) donors compared with results obtained with the University of Wisconsin (UW) solution. Moreover, we evaluated the hepatocyte function after culture or transplantation into the spleen.

MATERIALS AND METHODS

We used male Sprague-Dawley rats for this study. The DCD model was induced by phrenotomy after injecting heparin. We assigned rats based on warm ischemia times of 15 and 30 min to groups S and L, respectively. Each group (n = 5) was then subdivided as follows: (1) group S: not preserved (S/N), preserved by TLM for 3 h (S/TLM3) and 12 h (S/TLM12), and in the UW solution for 3 h (S/UW3) and 12 h (S/UW12), and (2) group L: not preserved (L/N), preserved by TLM for 3 h (L/TLM3) and 12 h (L/TLM12), and in the UW solution for 3 h (L/UW3) and 12 h (L/UW12). The cell viability and function of isolated DCD hepatocytes were analyzed for culture or HTx into the spleen.

RESULTS

The viability and ATP levels of DCD hepatocytes significantly improved after TLM compared with the values after preservation in cold UW solution in group S/N (p < 0.059). The levels of albumin production and urea synthesis by hepatocytes after culture were significantly higher in groups S/TLM3 and S/TLM12 than in groups S/UW3 and S/UW12 (p < 0.05), respectively. Further, serum albumin levels after HTx were also markedly higher in groups S/TLM3 and S/TLM12 than in groups S/UW3 and S/UW12. The morphological features revealed that cultured and transplanted hepatocytes remained clearly viable and maintained an expression for specific hepatic function, such as the production of albumin and glycogen.

CONCLUSION

This novel method of oxygenated cold preservation of DCD livers can expand the hepatocyte donor pool for HTx and establish a wider application of this developing technique.

Utilization of organs from donors after circulatory death for vascularized pancreas and islet of Langerhans transplantation: recommendations from an expert group

Donation after circulatory death (DCD) donors are increasingly being used as a source of pancreas allografts for vascularized organ and islet transplantation. We provide practice guidelines aiming to increase DCD pancreas utilization. We review risk assessment and donor selection criteria. We report suggested factors in donor and recipient clinical management and provide an overview of the activities and outcomes of vascularized pancreas and islet transplantation.

Portal Venous Oxygen Persufflation of the Donation after Cardiac Death pancreas in a rat model is superior to static cold storage and hypothermic machine perfusion

Success of clinical pancreatic islet transplantation depends on the mass of viable islets transplanted and the proportion of transplanted islets that survive early ischaemia reperfusion injury. Novel pancreas preservation techniques to improve islet preservation and viability can increase the utilization of donation after cardiac death donor pancreases for islet transplantation. Rat pancreases were retrieved after 30 min of warm ischaemia and preserved by static cold storage, hypothermic machine perfusion or retrograde portal venous oxygen persufflation for 6 h. They underwent collagenase digestion and density gradient separation to isolate islets. The yield, viability, morphology were compared. In vitro function of isolated islets was compared using glucose stimulated insulin secretion test. Portal venous oxygen persufflation improved the islet yield, viability and morphology as compared to static cold storage. The percentage of pancreases with good in vitro function (stimulation index > 1.0) was also higher after oxygen persufflation as compared to static cold storage. Retrograde portal venous oxygen persufflation of donation after cardiac death donor rat pancreases has the potential to improve islet yield.

Histologic effects of University of Wisconsin two-layer method preservation of rat pancreas

Marginal donors represent a poorly utilized source of organs for transplantation despite their availability. The key is to reduce the ischemic damage in the effort to improve organ quality. This study investigated the histologic effects after in situ perfusion of preservation with a two-layer method compared with the classic University of Wisconsin preservation in term of tissue integrity and number of viable exocrine cells in the rat pancreas both after exsanguination and at 8 weeks of cryopreservation. Pancreata harvested from 60 rats were collected using 3 methods: two-layer method following University of Wisconsin perfusion; exsanguination; and classic University of Wisconsin perfusion/storage. In addition to histologic analysis of collected pancreata, we analyzed the number of CK19(+) cells and their viability using chi-square tests with values P < .05 considered to be significant. Rat pancreas histology showed as University of Wisconsin in situ perfusion and preservation by the two-layer method to be more effective to maintain the morphologic integrity of both exocrine and endocrine tissues. There were a larger number of CK19(+) cells with good viability. Moreover, the effects of oxygenation were visible in pancreas biopsies preserved after exsanguination. In situ University of Wisconsin perfusion and preservation for 240 minutes with the two-layer method yielded greater numbers and viability of CK19(+) cells even after 8 weeks of cryopreservation.

Persufflation (gaseous oxygen perfusion) as a method of heart preservation

Persufflation (PSF; gaseous oxygen perfusion) is an organ preservation technique with a potential for use in donor heart preservation. Improved heart preservation with PSF may improve outcomes by maintaining cardiac tissue quality in the setting of longer cold ischemia times and possibly increasing the number of donor hearts available for allotransplant. Published data suggests that PSF is able to extend the cold storage times for porcine hearts up to 14 hours without compromising viability and function, and has been shown to resuscitate porcine hearts following donation after cardiac death. This review summarizes key published work on heart PSF, including prospective implications and future directions for PSF in heart transplantation. We emphasize the potential impact of extending preservation times and expanding donor selection criteria in heart allotransplant. Additionally, the key issues that need to be addressed before PSF were to become a widely utilized preservation strategy prior to clinical heart transplantation are summarized and discussed.

International workshop: islet transplantation without borders enabling islet transplantation in Greece with international collaboration and innovative technology

Recently, initiatives have been undertaken to establish an islet transplantation program in Athens, Greece. A major hurdle is the high cost associated with the establishment and maintenance of a clinical-grade islet manufacturing center. A collaboration was established with the University Hospitals of Geneva, Switzerland, to enable remote islet cell manufacturing with an established and validated fully operational team. However, remote islet manufacturing requires shipment of the pancreas from the procurement to the islet manufacturing site (in this case from anywhere in Greece to Geneva) and then shipment of the islets from the manufacturing site to the transplant site (from Geneva to Athens). To address challenges related to cold ischemia time of the pancreas and shipment time of islets, a collaboration was initiated with the University of Arizona, Tucson, USA. An international workshop was held in Athens, December 2011, to mark the start of this collaborative project. Experts in the field presented in three main sessions: (i) islet transplantation: state-of-the-art and the "network approach"; (ii) technical aspects of clinical islet transplantation and outcomes; and (iii) islet manufacturing - from the donated pancreas to the islet product. This manuscript presents a summary of the workshop.

Quality of isolated pig islets is improved using perfluorohexyloctane for pancreas storage in a split lobe model

Pancreas transportation between donor center and islet production facility is frequently associated with prolonged ischemia impairing islet isolation and transplantation outcomes. It is foreseeable that shipment of pig pancreases from distant centralized biosecure breeding facilities to institutes that have a long-term experience in porcine islet isolation is essentially required in future clinical islet xenotransplantation. Previously, we demonstrated that perfluorohexyloctan (F6H8) is significantly more efficient to protect rat and human pancreata from ischemically induced damage compared to perfluorodecalin (PFD). To evaluate the effect of F6H8 on long-term stored pig pancreases in a prospective study, we utilized the split lobe model to minimize donor variability. Retrieved pancreases were dissected into the connecting and splenic lobe, intraductally flushed with UW solution and immersed alternately in either preoxygenated F6H8 or PFD for 8-10 h. Prior to pancreas digestion, the intrapancreatic pO2 and the ratio of ATP-to-inorganic phosphate was compared utilizing 31P-NMR spectroscopy. Isolated islets were cultured for 2-3 days at 37°C and subjected to quality assessment. Pancreatic lobes stored in preoxygenated F6H8 had a significantly higher intrapancreatic pO2 compared to pancreata in oxygen-precharged PFD (10.11 ± 3.87 vs. 1.64 ± 1.13 mmHg, p < 0.05). This correlated with a higher ATP-to-inorganic phosphate ratio (0.30 ± 0.04 vs. 0.14 ± 0.01). No effect was observed concerning yield and purity of freshly isolated islets. Nevertheless, a significantly improved glucose-stimulated insulin response, increased viability and postculture survival (57.2 ± 5.7 vs. 39.3 ± 6.4%, p < 0.01) was measured in islets isolated from F6H8-preserved pancreata. The present data suggest that F6H8 does not increase islet yield but improves quality of pig islets isolated after prolonged cold ischemia.

Supplements in human islet culture: human serum albumin is inferior to fetal bovine serum

Culture of human islets before clinical transplantation or distribution for research purposes is standard practice. At the time the Edmonton protocol was introduced, clinical islet manufacturing did not include culture, and human serum albumin (HSA), instead of fetal bovine serum (FBS), was used during other steps of the process to avoid the introduction of xenogeneic material. When culture was subsequently introduced, HSA was also used for medium supplementation instead of FBS, which was typically used for research islet culture. The use of HSA as culture supplement was not evaluated before this implementation. We performed a retrospective analysis of 103 high-purity islet preparations (76 research preparations, all with FBS culture supplementation, and 27 clinical preparations, all with HSA supplementation) for oxygen consumption rate per DNA content (OCR/DNA; a measure of viability) and diabetes reversal rate in diabetic nude mice (a measure of potency). After 2-day culture, research preparations exhibited an average OCR/DNA 51% higher (p < 0.001) and an average diabetes reversal rate 54% higher (p < 0.05) than clinical preparations, despite 87% of the research islet preparations having been derived from research-grade pancreata that are considered of lower quality. In a prospective paired study on islets from eight research preparations, OCR/DNA was, on average, 27% higher with FBS supplementation than that with HSA supplementation (p < 0.05). We conclude that the quality of clinical islet preparations can be improved when culture is performed in media supplemented with serum instead of albumin.

Oxygen-charged HTK-F6H8 emulsion reduces ischemia-reperfusion injury in kidneys from brain-dead pigs

BACKGROUND

Prolonged cold ischemia is frequently associated with a greater risk of delayed graft function and enhanced graft failure. We hypothesized that media, combining a high oxygen-dissolving capacity with specific qualities of organ preservation solutions, would be more efficient in reducing immediate ischemia-reperfusion injury from organs stored long term compared with standard preservation media.

METHODS

Kidneys retrieved from brain-dead pigs were flushed using either cold histidine-tryptophan-ketoglutarate (HTK) or oxygen-precharged emulsion composed of 75% HTK and 25% perfluorohexyloctane. After 18 h of cold ischemia the kidneys were transplanted into allogeneic recipients and assessed for adenosine triphosphate content, morphology, and expression of genes related to hypoxia, environmental stress, inflammation, and apoptosis.

RESULTS

Compared with HTK-flushed kidneys, organs preserved using oxygen-precharged HTK-perfluorohexyloctane emulsion had increased elevated adenosine triphosphate content and a significantly lower gene expression of hypoxia inducible factor-1α, vascular endothelial growth factor, interleukin-1α, tumor necrosis factor-α, interferon-α, JNK-1, p38, cytochrome-c, Bax, caspase-8, and caspase-3 at all time points assessed. In contrast, the mRNA expression of Bcl-2 was significantly increased.

CONCLUSIONS

The present study has demonstrated that in brain-dead pigs the perfusion of kidneys with oxygen-precharged HTK-perfluorohexyloctane emulsion results in significantly reduced inflammation, hypoxic injury, and apoptosis and cellular integrity and energy content are well maintained. Histologic examination revealed less tubular, vascular, and glomerular changes in the emulsion-perfused tissue compared with the HTK-perfused counterparts. The concept of perfusing organs with oxygen-precharged emulsion based on organ preservation media represents an efficient alternative for improved organ preservation.

Persufflation (or gaseous oxygen perfusion) as a method of organ preservation

Improved preservation techniques have the potential to improve transplant outcomes by better maintaining donor organ quality and by making more organs available for allotransplantation. Persufflation, (PSF, gaseous oxygen perfusion) is potentially one such technique that has been studied for over a century in a variety of tissues, but has yet to gain wide acceptance for a number of reasons. A principal barrier is the perception that ex vivo PSF will cause in vivo embolization post-transplant. This review summarizes the extensive published work on heart, liver, kidney, small intestine and pancreas PSF, discusses the differences between anterograde and retrograde PSF, and between PSF and other conventional methods of organ preservation (static cold storage, hypothermic machine perfusion). Prospective implications of PSF within the broader field of organ transplantation, and in the specific application with pancreatic islet isolation and transplant are also discussed. Finally, key issues that need to be addressed before PSF becomes a more widely utilized preservation strategy are summarized and discussed.

Implication of mitochondrial cytoprotection in human islet isolation and transplantation

Islet transplantation is a promising therapy for type 1 diabetes mellitus; however, success rates in achieving both short- and long-term insulin independence are not consistent, due in part to inconsistent islet quality and quantity caused by the complex nature and multistep process of islet isolation and transplantation. Since the introduction of the Edmonton Protocol in 2000, more attention has been placed on preserving mitochondrial function as increasing evidences suggest that impaired mitochondrial integrity can adversely affect clinical outcomes. Some recent studies have demonstrated that it is possible to achieve islet cytoprotection by maintaining mitochondrial function and subsequently to improve islet transplantation outcomes. However, the benefits of mitoprotection in many cases are controversial and the underlying mechanisms are unclear. This article summarizes the recent progress associated with mitochondrial cytoprotection in each step of the islet isolation and transplantation process, as well as islet potency and viability assays based on the measurement of mitochondrial integrity. In addition, we briefly discuss immunosuppression side effects on islet graft function and how transplant site selection affects islet engraftment and clinical outcomes.

Optimization of perfluoro nano-scale emulsions: the importance of particle size for enhanced oxygen transfer in biomedical applications

Nano-scale emulsification has long been utilized by the food and cosmetics industry to maximize material delivery through increased surface area to volume ratios. More recently, these methods have been employed in the area of biomedical research to enhance and control the delivery of desired agents, as in perfluorocarbon emulsions for oxygen delivery. In this work, we evaluate critical factors for the optimization of PFC emulsions for use in cell-based applications. Cytotoxicity screening revealed minimal cytotoxicity of components, with the exception of one perfluorocarbon utilized for emulsion manufacture, perfluorooctylbromide (PFOB), and specific w% limitations of PEG-based surfactants utilized. We optimized the manufacture of stable nano-scale emulsions via evaluation of: component materials, emulsification time and pressure, and resulting particle size and temporal stability. The initial emulsion size was greatly dependent upon the emulsion surfactant tested, with pluronics providing the smallest size. Temporal stability of the nano-scale emulsions was directly related to the perfluorocarbon utilized, with perfluorotributylamine, FC-43, providing a highly stable emulsion, while perfluorodecalin, PFD, coalesced over time. The oxygen mass transfer, or diffusive permeability, of the resulting emulsions was also characterized. Our studies found particle size to be the critical factor affecting oxygen mass transfer, as increased micelle size resulted in reduced oxygen diffusion. Overall, this work demonstrates the importance of accurate characterization of emulsification parameters in order to generate stable, reproducible emulsions with the desired bio-delivery properties.

Organ preservation using a photosynthetic solution

BACKGROUND

Organs harvested from a body lapsing into circulatory deficit are exposed to low O2/high CO2, and reach a critical point where original functionality after transplantation is unlikely. The present study evaluates the effect of respiratory assistance using Chlorella photosynthesis on preservation of the rat pancreas from the viewpoint of donation after cardiac death (DCD).

METHODS

Gas was exchanged through the peritoneum of rats under controlled ventilation with or without Chlorella photosynthetic respiratory assistance. A gas permeable pouch containing Chlorella in solution was placed in the peritoneum and then the space between the pouch and the peritoneum was filled with an emulsified perfluorocarbon gas carrier. Rat DCD pancreases procured 3 h after cardiac arrest were preserved for 30 min in a cold or mildly hypothermic environment or in a mildly hypothermic environment with photosynthetic respiratory support. The pancreases were then heterotopically transplanted into rats with STZ-induced diabetes.

RESULTS

Levels of blood oxygen (PaO2) and carbon dioxide (PaCO2) increased and significantly decreased, respectively, in rats with mechanically reduced ventilation and rats given intraperitoneal photosynthetic respiratory support when compared with those without such support. Transplantation with DCD pancreases that had been stored under photosynthetic respiratory support resulted in the survival of all rats, which is impossible to achieve using pancreases that have been maintained statically in cold storage.

CONCLUSION

Respiratory assistance using photosynthesis helps to improve not only blood gas status in the event of respiratory insufficiency, but also graft recovery after pancreas transplantation with a DCD pancreas that has been damaged by prolonged warm ischemia.

Perfluorocarbon Emulsions Prevent Hypoxia of Pancreatic β-Cells

As oxygen carriers, perfluorocarbon emulsions might be useful to decrease hypoxia of pancreatic islets before transplantation. However, their hydrophobicity prevents their homogenisation in culture medium. To increase the surface of contact between islets and Perfluorooctyl bromide (PFOB), and consequently oxygen delivery, we tested effect of a PFOB emulsion in culture medium on β-cell lines and rat pancreatic islets. RINm5F β-cell line or pancreatic rat islets were incubated for 3 days in the presence of PFOB emulsion in media (3.5% w/v). Preoxygenation of the medium was performed before culture. Cell viability was assessed by apoptotic markers (Bax and Bcl-2) and by staining (fluoresceine diacetate and propidium iodide). β-Cell functionality was determined by insulin release during a glucose stimulation test and. Hypoxia markers, HIF-1α and VEGF, were studied at days 1 and 3 using RT-PCR, Western blotting, and ELISA. PFOB emulsions preserved viability and functionality of RINm5F cells with a decrease of HIF-1α and VEGF expression. Islets viability was preserved during 3 days of culture. Secretion of VEGF was higher in untreated control (0.09 ± 0.041 μg VEGF/mg total protein) than in PFOB emulsion incubated islets (0.02 ± 0.19 μg VEGF/mg total protein, n = 4, p < 0.05) at day 1. At day 3, VEGF secretion was increased as compared to day 1 in control (0.23 ± 0.04 μg VEGF/mg total protein) but it was imbalance by the presence of PFOB emulsion (0.09 ± 0.03 μg VEGF/mg total protein, n = 5, p < 0.05). While insulin secretion was maintained in response to a glucose stimulation test until day 3 when islets were incubated in the presence of PFOB emulsion preoxygenated (0.81 ± 0.16 at day 1 vs. 0.75 ± 0.24 at day 3), the ability to secrete insulin in the presence of high glucose concentration was lost in islets controls (0.51 ± 0.18 at day 1 vs. 0.21 ± 0.13 at day 3). Atmospheric oxygen delivery by PFOB emulsion might be sufficient to decrease islets hypoxia. However, to improve islets functionality, overoxygenation is needed. Finally, maintenance of islet viability and functionality for several days after isolation could improve the outcome of islets transplantation.

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 procurement and preservation for islet transplantation: personal considerations

Pancreatic islet transplantation is a promising option for the treatment of type 1 diabetic patients. After the successful demonstration of the Edmonton protocol, islet transplantation has advanced significantly on several fronts, including improved pancreas procurement and preservation systems. Since we frequently use pancreata from donors after cardiac death in Japan,we have applied the in situ regional organ cooling system for pancreas procurement to reduce the warm ischemic time. To reduce the apoptosis of pancreatic tissue during cold preservation, we have applied the ductal injection of preservation solution. For pancreas preservation, we use modified Kyoto solution, which is advantageous at trypsin inhibition and less collagenase inhibition. In this paper, we show pancreas procurement and preservation in our group for islet transplantation.

The two layer method does not improve the preservation of porcine kidneys

BACKGROUND

The Two layer method (TLM) has been extremely successful in the preservation of the pancreas. However, this has not been thoroughly investigated in other organs or in clinically relevant large animal models. The aim of this study was to assess the effects of TLM in a large animal model of kidney preservation.

MATERIAL/METHODS

Porcine kidneys were retrieved after 10 minutes of warm ischaemic injury and flushed with 300 ml UW solution at 4°C. Kidneys were then either placed in University of Wisconsin solution (UW) or TLM using pre-oxygenated perfluorodecalin and UW. Kidneys were stored for 18 hours at 4°C then reperfused with oxygenated autologous blood to assess renal function.

RESULTS

Renal blood flow (RBF) was significantly lower and intra-renal resistance (IRR) higher in TLM compared to UW group [Area under the curve (AUC) RBF, UW; 427±168 vs TLM; 247±55 ml/min/100g.h; P=0.041, AUC IRR, UW; 7.7±2.2 vs TLM; 10.5±1.9 ml/min/mmHg; P=0.041]. Levels of creatinine clearance (CrCl) were significantly lower in TLM group [AUC CrCl, UW; 1.8±1.0 vs TLM; 0.6±0.4 ml/min/100 g.h; P=0.034]. Levels of lipid peroxidation were significantly lower in TLM group [8-isoprostane/Cr ratio 3h; UW 3338±896 vs TLM 2072±886 pg/ml/mmol/L; P=0.04]. Levels of total nitric oxide were significantly higher in TLM group (P=0.009).

CONCLUSIONS

TLM did not improve the preservation condition of porcine kidneys. Furthermore, there appeared to be increased inflammation, endothelial injury and reduced renal function compared to preservation with UW. Further experimental work is needed to determine the role of PFC in kidney preservation.

Persufflation improves pancreas preservation when compared with the two-layer method

Islet transplantation is emerging as a promising treatment for patients with type 1 diabetes. It is important to maximize viable islet yield for each organ due to scarcity of suitable human donor pancreata, high cost, and the large dose of islets required for insulin independence. However, organ transport for 8 hours using the two-layer method (TLM) frequently results in low islet yields. Since efficient oxygenation of the core of larger organs (eg, pig, human) in TLM has recently come under question, we investigated oxygen persufflation as an alternative way to supply the pancreas with oxygen during preservation. Porcine pancreata were procured from donors after cardiac death and preserved by either TLM or persufflation for 24 hours and subsequently fixed. Biopsies collected from several regions of the pancreas were sectioned, stained with hematoxylin and eosin, and evaluated by a histologist. Persufflated tissues exhibited distended capillaries and significantly less autolysis/cell death relative to regions not exposed to persufflation or to tissues preserved with TLM. The histology presented here suggests that after 24 hours of preservation, persufflation dramatically improves tissue health when compared with TLM. These results indicate the potential for persufflation to improve viable islet yields and extend the duration of preservation, allowing more donor organs to be utilized.

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.

Continuous real-time viability assessment of kidneys based on oxygen consumption

BACKGROUND

Current ex vivo quality assessment of donor kidneys is limited to vascular resistance measurements and histological analysis. New techniques for the assessment of organ quality before transplantation may further improve clinical outcomes while expanding the depleted deceased-donor pool. We propose the measurement of whole organ oxygen consumption rate (WOOCR) as a method to assess the quality of kidneys in real time before transplantation.

METHODS

Five porcine kidneys were procured using a donation after cardiac death (DCD) model. The renal artery and renal vein were cannulated and the kidney connected to a custom-made hypothermic machine perfusion (HMP) system equipped with an inline oxygenator and fiber-optic oxygen sensors. Kidneys were perfused at 8 degrees C, and the perfusion parameters and partial oxygen pressures (pO(2)) were measured to calculate WOOCR.

RESULTS

Without an inline oxygenator, the pO(2) of the perfusion solution at the arterial inlet and venous outlet diminished to near 0 within minutes. However, once adequate oxygenation was provided, a significant pO(2) difference was observed and used to calculate the WOOCR. The WOOCR was consistently measured from presumably healthy kidneys, and results suggest that it can be used to differentiate between healthy and purposely damaged organs.

CONCLUSIONS

Custom-made HMP systems equipped with an oxygenator and inline oxygen sensors can be applied for WOOCR measurements. We suggest that WOOCR is a promising approach for the real-time quality assessment of kidneys and other organs during preservation before transplantation.

Preoxygenation of different preservation solutions for porcine pancreas preservation

INTRODUCTION

Organ preservation quality impacts porcine islet cell isolation and transplantation success. Among several preservation methods, the two-layer method is promising, but technically demanding and fails to deliver sufficient oxygen. The use of hyperbaric oxygenation may be an easier, more effective method to supply high partial pressure of oxygen (pO(2)) for organ storage. Therefore, the aim of this study was to test the capability of preoxygenation of various preservation solutions with HBO to maintain high pO(2) levels.

METHODS

University of Wisconsin (UW), Custodiol, Perfadex, or Celsior solutions were preoxygenated in a pressure chamber. NaCl served as the control. pO(2) levels were measured at defined times. The oxygen storage capability was evaluated by leaving the storage bottles open for 2 minutes.

RESULTS

It was feasible to preoxygenate preservation solutions. The best solution to maintain high pO(2) tensions was Perfadex, followed by Celsior, and UW.

DISCUSSION

The greater the amount of oxygen in the preservation solution, the more oxygen can be delivered to the preserved pancreas. Further studies on the influence of preoxygenated preservation solutions on the porcine pancreas are warranted to improve organ quality, porcine islet cell isolation, and transplantation success.

Limited beneficial effects of perfluorocarbon emulsions on encapsulated cells in culture: experimental and modeling studies

Due to the high solubility of oxygen in perfluorocarbons (PFCs), these compounds have been explored for improved cell and tissue oxygenation. The goal of this study is to investigate the effects of a PFC emulsion on cellular growth and function in a tissue engineered construct. A perfluorotributylamine (PFTBA) emulsion was co-encapsulated at 10 vol% with mouse βTC-tet insulinoma cells in calcium alginate beads and cultured under normoxic and severely hypoxic conditions. The number of metabolically active cells and the induced insulin secretion rate were measured over time for up to 16 days. Results showed no significant effect of PFTBA relative to the PFTBA-free control. The alginate-PFC-cell system was also modeled mathematically, and simulations tracked the number of viable cells over time under the same conditions used experimentally. Simulations revealed only a small, likely experimentally undetectable difference in cell density between the PFC-containing and PFC-free control beads. It is concluded that PFTBA up to 10 vol% has no significant effect on the growth and function of encapsulated βTC-tet cells under normoxic and hypoxic conditions.

Use of perfluorodecalin for pancreatic islet culture prior to transplantation: a liquid-liquid interface culture system--preliminary report

Although the issue remains controversial, short-term culture is probably beneficial for islet graft quality. However, significant islet loss is invariably observed. This is related to reduced survival of large islets, which is compromised by hypoxia under standard culture conditions. We aimed to develop a method of culture, which would avoid exposure to relative hypoxia and hence maintain the quality of islets. Isolated rat islets cultured for 48 h in a liquid-liquid interface culture system (LICS) with a perfluorocarbon were compared to islets cultured under standard (C1) and suboptimal conditions (C2). Islets were tested for viability and response to a glucose challenge, and a marginal mass was transplanted into syngeneic diabetic recipients. The viability of islets after 24-h culture in LICS was higher than in C1 and C2 groups (89.0% vs. 77.5% and 64.6%, respectively) and decreased with time to reach 79.0%, 62.9%, and 53.4% after 72-h culture. The stimulation index in LICS-cultured islets was also significantly higher than in C1 and C2 groups (12.3 ± 0.4 vs. 5.8 ± 0.5 and 4.1 ± 0.2, respectively). Following transplantation of LICS-cultured islets 50% of recipients were rendered normoglycemic compared with 14.3% and 31.3% for C2 and fresh islets, respectively. Our liquid-liquid interface culture system using perfluorodecalin provides optimized culture conditions, which preserve both islet viability and their ability to engraft successfully after intraportal transplantation and could be used for islet transportation.

Limited Penetration of Perfluorocarbon in Porcine Pancreas Preserved by Two-Layer Method with 19Fluorine Magnetic Resonance Spectroscopy and Headspace Gas Chromatography

The mechanism of the two-layer method (TLM) of pancreas preservation is unclear. Facilitating oxygen diffusion into preserved pancreas has been suggested, but direct measurements of tissue pO2 have yielded conflicting results. The degree of penetration of perfluorocarbon (PFC) into the pancreas during TLM storage is unknown. Segments of porcine pancreas (7.5 cm in length) were preserved either in University of Wisconsin solution (UW) alone ( n = 6) or in TLM for 24 h ( n = 6). Pancreatic samples were analyzed using Varian INOVA 9.4T MR scanner. External PFC standard was introduced for quantification. Four consecutive transverse images of 4 mm thickness were obtained using a spin-echo sequence. 19Fluorine magnetic resonance spectroscopy (19F MRS) was performed with the same parameters except with more averages. MR data were confirmed by headspace chromatography. PFC standard was readily detected in 19F MR images. There was no signal from pancreas in 19F MR images following either UW or TLM storage. 19F MR spectra typical of PFC were not obtained from either UW- or TLM-preserved pancreas with nonlocalized 19F MRS. Mean concentration of PFC in TLM pancreas measured by head space chromatography was 0.011 nl/g (SD ±0.006), not significantly different from background concentration (0.012 nl/g, SD ±0.006) in UW pancreas ( p = 0.42). There was no evidence of penetration of PFC into pancreas tissues investigated either by MR or chromatography in organs preserved at hypothermia by TLM, and mechanisms of TLM remain speculative.

Prediction of marginal mass required for successful islet transplantation

Islet quality assessment methods for predicting diabetes reversal (DR) following transplantation are needed. We investigated two islet parameters, oxygen consumption rate (OCR) and OCR per DNA content, to predict transplantation outcome and explored the impact of islet quality on marginal islet mass for DR. Outcomes in immunosuppressed diabetic mice were evaluated by transplanting mixtures of healthy and purposely damaged rat islets for systematic variation of OCR/DNA over a wide range. The probability of DR increased with increasing transplanted OCR and OCR/DNA. On coordinates of OCR versus OCR/DNA, data fell into regions in which DR occurred in all, some, or none of the animals with a sharp threshold of around 150-nmol/min mg DNA. A model incorporating both parameters predicted transplantation outcome with sensitivity and specificity of 93% and 94%, respectively. Marginal mass was not constant, depended on OCR/DNA, and increased from 2,800 to over 100,000 islet equivalents/kg body weight as OCR/DNA decreased. We conclude that measurements of OCR and OCR/DNA are useful for predicting transplantation outcome in this model system, and OCR/DNA can be used to estimate the marginal mass required for reversing diabetes. Because human clinical islet preparations in a previous study had OCR/DNA.

Pancreas preservation by the two-layer method: does it have a beneficial effect compared with simple preservation in University of Wisconsin solution?

A large number of reports have shown that the two-layer method (TLM), which employs oxygenated perfluorochemical (PFC) and University of Wisconsin (UW) solution, is superior to simple cold storage in UW in islet transplantation. However, two recent large-scale studies showed no beneficial effect of TLM compared with UW storage in human islet transplantation. We reevaluated the effect of TLM by following three groups: group 1: UW simple storage; group 2: TLM performed by multiorgan procurement teams (not specialists of islet isolation); and group 3: TLM performed by specialists of islet isolation (Noguchi and Matsumoto). There were no significant differences between groups 1 and 2, whereas islet yields were significantly higher in group 3 compared with either group 1 or 2. Our data suggest that exact, complete performance of TLM could improve the outcome of islet isolation and transplantation. In this review, we describe the mechanisms of the TLM, the procedure of preoxygenated TLM, and the several possibilities for the reasons of the discrepancy.

Pancreatic duct: A suitable route to oxygenate tissue during pancreas hypothermic preservation?

The effectiveness of Two-Layer Method has been questioned recently. In this study we hypothesized that pancreatic duct might be an appropriate route to oxygenate the organ and prevent cold ischemic injury. Male Sprague-Dawley rats were employed for the pancreas procurement. Pancreata were removed after 20ml ductal injection of cold Hank's Balanced Salt Solution (HBSS), or pre-oxygenated solutions of HBSS (O-HBSS), perfluorocarbon (O-PFC), and emulsified PFC (O-ePFC) and then preserved in HBSS for 24h. Spectrophotometric analysis was performed to measure ATP, adenosine diphosphate (ADP), and adenosine monophosphate (AMP). To standardize metabolite data, values were reported in terms of 'per gram protein of pancreatic tissue'. Protein was measured according to Lowry et al. ADP/ATP ratio, total adenylates and energy charge (EC) were calculated. There was a significant decrease in tissue ATP after hypothermic preservation. Pancreatic tissues lost 47.8% of their ATP values just in the first hour of preservation and 98.5% of their ATP values within 12h of preservation and ductal oxygenation could not prevent the ischemia. Unlike the other groups, ductal injection of oxygenated PFC could slow the total adenylates reduction rate that no significant difference was detected (9.6+/-2.9 vs. 14.8+/-2.1mol/g protein, NS) after 12h of preservation. Ductal injection of oxygenated PFC significantly reduced ADP/ATP ratio (8.57+/-0.6 vs. 14.2+/-2.4, p<0.03) and improved intracellular energy charge (0.36+/-0.05 vs. 0.22+/-0.03, p<0.001) as compared to HBSS group. The findings indicate that the pancreatic duct might be a suitable route for pancreatic oxygenation.

Pig pancreas oxygenation at 20 degrees C increases islet ATP generation but deteriorates islet function

Successful pancreas preservation during storage in oxygenated perfluorodecalin (PFD) is mainly related to oxidative ATP generation during storage. Increasing the storage temperature would accelerate this process essential for resuscitation of ischemically damaged pancreatic tissue. The present study aimed at comparing islet isolation outcome from adult pig pancreata preserved in oxygenated PFD by means of a one-layer method during storage on ice or at 20 degrees C. Resected pancreata were intraductally flushed with cold UW solution and promptly processed (n = 6) or stored for 3 h in continuously oxygenated PFD at 4 degrees C (n = 5) or 20 degrees C (n = 7). Prior to digestion-filtration pancreata were intraductally injected with UW supplemented with Serva collagenase NB8 and neutral protease. Islet quality assessment determined viability, glucose stimulation index, mitochondrial activity, intracellular ATP content, and transplant function in diabetic nude mice. Pancreata oxygenated for 3 h at 20 degrees C yielded islet numbers similar to organs oxygenated at 4 degrees C. Compared to a storage temperature of 20 degrees C, preservation at 4 degrees C reduced islet ATP content (p < 0.05) as well as islet viability (p < 0.05). Nevertheless, PFD storage at 20 degrees C decreased insulin response to glucose compared to unstored pancreata (p < 0.05). In contrast to unstored pancreata or cold-stored organs, transplantation of islets isolated after oxygenation at 20 degrees C was characterized by an early loss of transplant function in 50% of recipients (p < 0.05). The present study demonstrates that PFD storage at 20 degrees C enhances islet ATP synthesis within a short period of oxygenation but deteriorates islet function. We conclude that the present data reflect an equilibration between reduced depression of metabolic activity resulting in damage of islets and temperature-stimulated acceleration of ATP synthesis. Future studies are required to adjust the optimum storage temperature for pancreas oxygenation in different species.

FEM-based oxygen consumption and cell viability models for avascular pancreatic islets

BACKGROUND

The function and viability of cultured, transplanted, or encapsulated pancreatic islets is often limited by hypoxia because these islets have lost their vasculature during the isolation process and have to rely on gradient-driven passive diffusion, which cannot provide adequate oxygen transport. Pancreatic islets (islets of Langerhans) are particularly susceptible due to their relatively large size, large metabolic demand, and increased sensitivity to hypoxia. Here, finite element method (FEM) based multiphysics models are explored to describe oxygen transport and cell viability in avascular islets both in static and in moving culture media.

METHODS

Two- and three-dimensional models were built in COMSOL Multiphysics using the convection and diffusion as well as the incompressible Navier-Stokes fluid dynamics application modes. Oxygen consumption was assumed to follow Michaelis-Menten-type kinetics and to cease when local concentrations fell below a critical threshold; in a dynamic model, it was also allowed to increase with increasing glucose concentration.

RESULTS

Partial differential equation (PDE) based exploratory cellular-level oxygen consumption and cell viability models incorporating physiologically realistic assumptions have been implemented for fully scaled cell culture geometries with 100, 150, and 200 microm diameter islets as representative. Calculated oxygen concentrations and intra-islet regions likely to suffer from hypoxia-related necrosis obtained for traditional flask-type cultures, oxygen-permeable silicone-rubber membrane bottom cultures, and perifusion chambers with flowing media and varying incoming glucose levels are presented in detail illustrated with corresponding colour-coded figures and animations.

CONCLUSION

Results of the computational models are, as a first estimate, in good quantitative agreement with existing experimental evidence, and they confirm that during culture, hypoxia is often a problem for non-vascularised islet and can lead to considerable cell death (necrosis), especially in the core region of larger islets. Such models are of considerable interest to improve the function and viability of cultured, transplanted, or encapsulated islets. The present implementation allows convenient extension to true multiphysics applications that solve coupled physics phenomena such as diffusion and consumption with convection due to flowing or moving media.

Islet specific Wnt activation in human type II diabetes

The Wnt pathway effector gene TCF7L2 has been linked to type II diabetes, making it important to study the role of Wnt signaling in diabetes pathogenesis. We examined the expression of multiple Wnt pathway components in pancreases from normal individuals and type II diabetic individuals. Multiple members of the Wnt signaling pathway, including TCF7L2, Wnt2b, beta-catenin, pGSK3beta, TCF3, cyclinD1, and c-myc, were undetectable or expressed at low levels in islets from nondiabetic individuals, but were also upregulated specifically in islets of type II diabetic patients. Culture of pancreatic tissue and islet isolation led to Wnt activation that was reversed by the Wnt antagonist sFRP, demonstrating that Wnt activation in that setting was due to soluble Wnt factors. These data support a model in which the Wnt pathway plays a dynamic role in the pathogenesis of type II diabetes and suggest manipulation of Wnt signaling as a new approach to beta-cell-directed diabetes therapy.

A Meta-Analysis of the Impact of the Two-Layer Method of Preservation on Human Pancreatic Islet Transplantation

There are conflicting reports about the effectiveness of perfluorocarbons used in the two-layer method (TLM) of pancreas preservation for human islet transplantation. The mechanism of action is unclear and the optimal role of this method uncertain. The study design was a meta-analysis of the evidence that TLM improves islet isolation outcomes. Pubmed, CENTRAL, EMBASE, Science Citation Index, and BIOSIS were searched electronically in January 2008. After selecting the relevant human trials for meta-analysis data relating to donor variables, study design, primary and secondary islet isolation outcomes were extracted. Electronic searches identified eight unique citations, describing 11 human studies that were eligible for the meta-analysis. When comparing TLM with preservation in University of Wisconsin (UW) solution, there was a statistically significant higher islet yield [WMD 711.55, 95% confidence interval (CI) 140.03–1283.07] in the TLM group. The proportion of transplantable preparations obtained was not significantly different (OR 1.30, 95% CI 0.89–1.88) between the two groups. The rate of successful islet isolations for marginal organs was higher in the TLM group (OR 6.69, 95% CI 1.80–24.87). Improved oxygenation and preservation of cellular bioengertics is thought to be the main underlying mechanism, although no single mechanism has yet been confirmed. There is currently no clear evidence that the TLM is beneficial in human islet transplantation. It may improve the preservation of marginal organs.

Organ preservation in pancreas and islet transplantation

PURPOSE OF REVIEW

Organ preservation aims at reducing ischemia-reperfusion injury and maintains or even improves its function, and, therefore, increases transplant safety and efficiency. With the chronic lack of organs for transplantation, marginal donors are more and more frequently used in Western countries. New challenges, therefore, have to be met in organ preservation.

RECENT FINDINGS

We summarize the effects of cold preservation on various organ grafts, with particular emphasis on the pancreas. We review the different preservation solutions currently available in the clinic, and we present the current knowledge and clinical experience in pancreas and islet transplantation.

SUMMARY

Overall, in whole pancreas and islet transplantation, current cold preservation solutions (University of Wisconsin solution, Celsior, histidine-tryptophan-ketoglutarate) seem to be equivalent, with only few studies showing better results with University of Wisconsin solution. Regarding preservation with the two-layer method, conflicting results have been reported, and proper prospective controlled studies have yet to be performed to gather evidence on its impact on islet yield and function. Some recent developments and future strategies in general organ preservation not yet applied to pancreas preservation are reviewed at the end of the article.

Pancreas preservation for pancreas and islet transplantation

PURPOSE OF REVIEW

To summarize advances and limitations in pancreas procurement and preservation for pancreas and islet transplantation, and review advances in islet protection and preservation.

RECENT FINDINGS

Pancreases procured after cardiac death, with in-situ regional organ cooling, have been successfully used for islet transplantation. Colloid-free Celsior and histidine-tryptophan-ketoglutarate preservation solutions are comparable to University of Wisconsin solution when used for cold storage before pancreas transplantation. Colloid-free preservation solutions are inferior to University of Wisconsin solution for pancreas preservation prior to islet isolation and transplantation. Clinical reports on pancreas transplants suggest that the two-layer method may not offer significant benefits over cold storage with the University of Wisconsin solution: improved oxygenation may depend on the graft size; benefits in experimental models may not translate to human organs. Improvements in islet yield and quality occurred from pancreases treated with inhibitors of stress-induced apoptosis during procurement, storage, isolation or culture desirable before islet isolation and transplantation and may improve islet yield and quality. Methods for real-time, noninvasive assessment of pancreas quality during preservation have been implemented and objective islet-potency assays have been developed and validated. These innovations should contribute to objective evaluation and establishment of improved pancreas-preservation and islet-isolation strategies.

SUMMARY

Cold storage may be adequate for preservation before pancreas transplants, but insufficient when pancreases are processed for islets or when expanded donors are used. Supplementation of cold-storage solutions with cytoprotective agents and perfusion may improve pancreas and islet transplant outcomes.

Pancreas preservation for pancreas and islet transplantation

PURPOSE OF REVIEW

To summarize advances and limitations in pancreas procurement and preservation for pancreas and islet transplantation, and review advances in islet protection and preservation.

RECENT FINDINGS

Pancreases procured after cardiac death, with in-situ regional organ cooling, have been successfully used for islet transplantation. Colloid-free Celsior and histidine-tryptophan-ketoglutarate preservation solutions are comparable to University of Wisconsin solution when used for cold storage before pancreas transplantation. Colloid-free preservation solutions are inferior to University of Wisconsin solution for pancreas preservation prior to islet isolation and transplantation. Clinical reports on pancreas and islet transplants suggest that the two-layer method may not offer significant benefits over cold storage with the University of Wisconsin solution: improved oxygenation may depend on the graft size; benefits in experimental models may not translate to human organs. Improvements in islet yield and quality occurred from pancreases treated with inhibitors of stress-induced apoptosis during procurement, storage, isolation or culture. Pancreas perfusion may be desirable before islet isolation and transplantation and may improve islet yields and quality. Methods for real-time, noninvasive assessment of pancreas quality during preservation have been implemented and objective islet potency assays have been developed and validated. These innovations should contribute to objective evaluation and establishment of improved pancreas preservation and islet isolation strategies.

SUMMARY

Cold storage may be adequate for preservation before pancreas transplants, but insufficient when pancreases are processed for islets or when expanded donors are used. Supplementation of cold storage solutions with cytoprotective agents and perfusion may improve pancreas and islet transplant outcomes.