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

Semifluorinated Alkanes as New Drug Carriers-An Overview of Potential Medical and Clinical Applications

Fluorinated compounds have been used in clinical and biomedical applications for years. The newer class of semifluorinated alkanes (SFAs) has very interesting physicochemical properties including high gas solubility (e.g., for oxygen) and low surface tensions, such as the well-known perfluorocarbons (PFC). Due to their high propensity to assemble to interfaces, they can be used to formulate a variety of multiphase colloidal systems, including direct and reverse fluorocarbon emulsions, microbubbles and nanoemulsions, gels, dispersions, suspensions and aerosols. In addition, SFAs can dissolve lipophilic drugs and thus be used as new drug carriers or in new formulations. In vitreoretinal surgery and as eye drops, SFAs have become part of daily clinical practice. This review provides brief background information on the fluorinated compounds used in medicine and discusses the physicochemical properties and biocompatibility of SFAs. The clinically established use in vitreoretinal surgery and new developments in drug delivery as eye drops are described. The potential clinical applications for oxygen transport by SFAs as pure fluids into the lungs or as intravenous applications of SFA emulsions are presented. Finally, aspects of drug delivery with SFAs as topical, oral, intravenous (systemic) and pulmonary applications as well as protein delivery are covered. This manuscript provides an overview of the (potential) medical applications of semifluorinated alkanes. The databases of PubMed and Medline were searched until January 2023.

The Influence of Microenvironment on Survival of Intraportal Transplanted Islets

Clinical islet transplantation has the potential to cure type 1 diabetes. Despite recent therapeutic success, it is still uncommon because transplanted islets are damaged by multiple challenges, including instant blood mediated inflammatory reaction (IBMIR), inflammatory cytokines, hypoxia/reperfusion injury, and immune rejection. The transplantation microenvironment plays a vital role especially in intraportal islet transplantation. The identification and targeting of pathways that function as “master regulators” during deleterious inflammatory events after transplantation, and the induction of immune tolerance, are necessary to improve the survival of transplanted islets. In this article, we attempt to provide an overview of the influence of microenvironment on the survival of transplanted islets, as well as possible therapeutic targets.

Diazoxide Preconditioning of Nonhuman Primate Pancreas Improves Islet Isolation Outcomes by Mitochondrial Protection

OBJECTIVES

Previously, we showed that diazoxide (DZ), an effective ischemic preconditioning agent, protected rodent pancreas against ischemia-reperfusion injury. Here, we further investigate whether DZ supplementation to University of Wisconsin (UW) solution during pancreas procurement and islet isolation has similar cytoprotection in a preclinical nonhuman primate model.

METHODS

Cynomolgus monkey pancreata were flushed with UW or UW + 150 μM DZ during procurement and preserved for 8 hours before islet isolation.

RESULTS

First, a significantly higher islet yield was observed in UW + DZ than in UW (57,887 vs 23,574 IEq/pancreas and 5396 vs 1646 IEq/g). Second, the DZ treated islets had significantly lower apoptotic cells per islet (1.64% vs 9.85%). Third, DZ significantly inhibited ROS surge during reperfusion with a dose-response manner. Fourth, DZ improved in vitro function of isolated islets determined by mitochondrial potentials and calcium influx in responses to glucose and KCI. Fifth, the DZ treated islets had much higher cure rate and better glycemia control in diabetic mice transplant model.

CONCLUSIONS

This study showed a strong mitochondrial protection of DZ on nonhuman primate islets against ischemia-reperfusion injury that provides strong evidence for its clinical application in islet and pancreas transplantation.

Potential Benefits of Nrf2/Keap1 Targeting in Pancreatic Islet Cell Transplantation

Permanent pancreatic islet cell destruction occurs in type 1 diabetes mellitus (T1DM) through the infiltration of inflammatory cells and cytokines. Loss of β-cell integrity secondary to oxidation leads to an inability to appropriately synthesize and secrete insulin. Allogenic islet cell transplantation (ICT) has risen as a therapeutic option to mitigate problematic hypoglycemia. Nevertheless, during the process of transplantation, islet cells are exposed to oxidatively caustic conditions that severely decrease the islet cell yield. Islet cells are at a baseline disadvantage to sustain themselves during times of metabolic stress as they lack a robust anti-oxidant defense system, glycogen stores, and vascularity. The Nrf2/Keap1 system is a master regulator of antioxidant genes that has garnered attention as pharmacologic activators have shown a protective response and a low side effect profile. Herein, we present the most recently studied Nrf2/Keap1 activators in pancreas for application in ICT: Dh404, dimethyl fumarate (DMF), and epigallocatechin gallate (EGCG). Furthermore, we discuss that Nrf2/Keap1 is a potential target to ameliorate oxidative stress at every step of the Edmonton Protocol.

Distributions of endocrine cell clusters during porcine pancreatic development

Background

Pancreatic islet xenotransplantation is a potential treatment for diabetes mellitus, and porcine pancreas may provide a readily available source of islets. Islets in juvenile pigs are smaller than those in young adult pigs, but the insulin content is very similar. In addition, as juvenile pigs are more easily reared in uncontaminated conditions, many researchers have conducted studies using pancreatic islets from juvenile pigs. We aimed to analyze the distributions of endocrine cell clusters by comprehensively evaluating juvenile porcine pancreatic development and to propose an appropriate age at which islets could be isolated from the juvenile porcine pancreas.

Methods

Splenic (SL) and duodenal lobe (DL) samples were collected from the pancreases of pigs aged 0–180 days (n = 3/day after birth). The chronological changes in endocrine cell clustering were analyzed in relation to morphological changes, cell characterization, numbers, islet areas, and gene expression.

Results

In juvenile pigs aged 0–21 days, the pancreas contained numerous endocrine cells, and compact islets appeared from 21 days of age. Well-defined small islets were seen at 28 days of age, and the clusters were denser in the SL than in the DL. At 35 days of age, the islets were morphologically similar to those observed at 180 days of age, and the greater number of islets was similar to that seen at 90 days of age. The differences in the islets’ cytoarchitecture between the lobes were negligible. The expression of β-cell-related genes was higher in the juvenile pancreas than in the adult pancreas, and the expression of neurogenin-3 decreased dramatically over time.

Conclusions

These findings may have implications for attempts to refine the most appropriate age for islet isolation from porcine donors. Focusing on porcine pancreatic islets isolated at around 35 days after birth may offer benefits regarding their xenotransplantation potential.

Impact of Oxygen on Pancreatic Islet Survival

Pancreatic islet transplantation is a promising treatment option for individuals with type 1 diabetes; however, maintaining islet function after transplantation remains a large challenge. Multiple factors, including hypoxia associated events, trigger pretransplant and posttransplant loss of islet function. In fact, islets are easily damaged in hypoxic conditions before transplantation including the preparation steps of pancreas procurement, islet isolation, and culture. Furthermore, after transplantation, islets are also exposed to the hypoxic environment of the transplant site until they are vascularized and engrafted. Because islets are exposed to such drastic environmental changes, protective measures are important to maintain islet viability and function. Many studies have demonstrated that the prevention of hypoxia contributes to maintaining islet quality. In this review, we summarize the latest oxygen-related islet physiology, including computational simulation. Furthermore, we review recent advances in oxygen-associated treatment options used as part of the transplant process, including up-to-date oxygen generating biomaterials as well as a classical oxygen inhalation therapy.

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.

Production of high-quality islets from goettingen minipigs: Choice of organ preservation solution, donor pool, and optimal cold ischemia time

BACKGROUND

The transplantation of porcine islets into man might soon become reality for patients with type 1 diabetes mellitus. Therefore, porcine islets of high quality and quantity, and a scalable isolation process with strict quality control will be an unconditional prerequisite to enable the best possible transplantation graft. In this study, we provide a comparative study evaluating islet isolation outcome and in vitro survival based upon donor age, organ preservation solution (OPS), and cold ischemia time (CIT).

METHODS

Goettingen minipigs of younger age (1 year) and retired breeder animals (3.5 years) were studied. Pancreata were harvested according to the standards of human organ retrieval including in situ cold perfusion with either Custodiol^® -HTK or Belzer^® UW solution. Pancreatic tissue was characterized by quantification of apoptotic cells. Islet isolations were performed according to a modified Ricordi method, and isolation outcome was assessed by determining islet particle numbers (IP), islet equivalents (IEQ), and isolation factor (IF). Isolated islets were cultured for 24 and 48 h for the assessment of in vitro survival.

RESULTS

Islet viability was significantly higher in Custodiol^® -HTK preserved pancreas organs compared to Belzer^® UW. Furthermore, organs harvested from retired breeder preserved in Custodiol^® -HTK resulted in stable islet isolation yields even after prolonged CIT and showed superior survival rates of islets in vitro compared to the Belzer^® UW group. Younger porcine donor organs resulted generally in lower islet yield and survival rates.

CONCLUSIONS

In summary, Custodiol^® -HTK solution should be preferred over Belzer^® UW solution for the preservation of pancreata from porcine origin. Custodiol^® -HTK allows for maintaining islet viability and promotes reproducible isolation outcome and survival even after longer CIT. The usage of retired breeder animals over young animals for islet isolation is highly advisable to yield high quality and quantity.

Comparison of Perfluorodecalin and HEMOXCell as Oxygen Carriers for Islet Oxygenation in an In Vitro Model of Encapsulation

Transplantation of encapsulated islets in a bioartificial pancreas is a promising alternative to free islet cell therapy to avoid immunosuppressive regimens. However, hypoxia, which can induce a rapid loss of islets, is a major limiting factor. The efficiency of oxygen delivery in an in vitro model of bioartificial pancreas involving hypoxia and confined conditions has never been investigated. Oxygen carriers such as perfluorocarbons and hemoglobin might improve oxygenation. To verify this hypothesis, this study aimed to identify the best candidate of perfluorodecalin (PFD) or HEMOXCell^® to reduce cellular hypoxia in a bioartificial pancreas in an in vitro model of encapsulation ex vivo. The survival, hypoxia, and inflammation markers and function of rat islets seeded at 600 islet equivalents (IEQ)/cm² and under 2% pO₂ were assessed in the presence of 50 μg/mL of HEMOXCell or 10% PFD with or without adenosine. Both PFD and HEMOXCell increased the cell viability and decreased markers of hypoxia (hypoxia-inducible factor mRNA and protein). In these culture conditions, adenosine had deleterious effects, including an increase in cyclooxygenase-2 and interleukin-6, in correlation with unregulated proinsulin release. Despite the effectiveness of PFD in decreasing hypoxia, no restoration of function was observed and only HEMOXCell had the capacity to restore insulin secretion to a normal level. Thus, it appeared that the decrease in cell hypoxia as well as the intrinsic superoxide dismutase activity of HEMOXCell were both mandatory to maintain islet function under hypoxia and confinement. In the context of islet encapsulation in a bioartificial pancreas, HEMOXCell is the candidate of choice for application in vivo.

Pancreatic Islets: Methods for Isolation and Purification of Juvenile and Adult Pig Islets

The current situation of organ transplantation is mainly determined by the disbalance between the number of available organs and the number of patients on the waiting list. This obvious dilemma might be solved by the transplantation of porcine organs into human patients. The metabolic similarities which exist between both species made pancreatic islets of Langerhans to that donor tissue which will be most likely transplanted in human recipients. Nevertheless, the successful isolation of significant yields of viable porcine islets is extremely difficult and requires extensive experiences in the field. This review is focussing on the technical challenges, pitfalls and particularities that are associated with the isolation of islets from juvenile and adult pigs considering donor variables that can affect porcine islet isolation outcome.

Pancreatic L-Glutamine Administration Protects Pig Islets From Cold Ischemic Injury and Increases Resistance Toward Inflammatory Mediators

The isolation and transplantation of porcine islets represent a future option for the treatment of type 1 diabetic patients. Stringent product release criteria and limited availability of transgenic and specific pathogen-free pigs will essentially require processing of explanted pig pancreata in specialized, possibly remote isolation facilities, whereby pancreata are exposed to cold ischemia due to prolonged tissue transit time. In the present study we investigated whether pancreas oxygenation can be efficiently combined with an antioxidant strategy utilizing intraductal L-glutamine administration. Pig pancreata were intraductally perfused after retrieval and after cold storage in oxygen-precharged perfluorohexyloctane utilizing University of Wisconsin solution supplemented with (n = 16) or without (n = 14) 5 mmol/L L-glutamine. After isolation purified islets were subjected to extensive quality assessment. Islet recovery postpurification was significantly higher in glutamine-treated pancreata (77.0 ± 3.3% vs. 60.3 ± 6.0%, p < 0.05). Glutamine administration increased intraislet content of reduced glutathione (117.8 ± 16.5 vs. 15.9 ± 2.8 ng/ng protein, p < 0.001) associated with increased islet recovery after culture (65.8 ± 12.1% vs. 40.3 ± 11.7%, p < 0.05), enhanced glucose stimulation index (1.82 ± 0.16 vs. 1.38 ± 0.10, p < 0.05), and improved posttransplant function in diabetic nude mice (p < 0.05). Furthermore, intraductally administered glutamine increased pig islet resistance toward reactive oxygen species, nitric oxide, and high-dose proinflammatory cytokines. The present study demonstrates that quality and function of pig islets exposed to warm and cold ischemia can significantly be improved using intraductal l-glutamine administration. As the efficiency of the intraductal route may be inferior compared to intravascular administration further studies should aim on assessment of l-glutamine as supplement for pancreas perfusion during organ procurement.

Islet xenotransplantation from genetically engineered pigs

PURPOSE OF REVIEW

Pigs have emerged as potential sources of islets for clinical transplantation. Wild-type porcine islets (adult and neonatal) transplanted into the portal vein have successfully reversed diabetes in nonhuman primates. However, there is a rapid loss of the transplanted islets on exposure to blood, known as the instant blood-mediated inflammatory reaction (IBMIR), as well as a T-cell response that leads to rejection of the graft.

RECENT FINDINGS

Genetically modified pig islets offer a number of potential advantages, particularly with regard to reducing the IBMIR-related graft loss and protecting the islets from the primate immune response. Emerging data indicate that transgenes specifically targeted to pig β cells using an insulin promoter (in order to maximize target tissue expression while limiting host effects) can be achieved without significant effects on the pig's glucose metabolism.

SUMMARY

Experience with the transplantation of islets from genetically engineered pigs into nonhuman primates is steadily increasing, and has involved the deletion of pig antigenic targets to reduce the primate humoral response, the expression of transgenes for human complement-regulatory and coagulation-regulatory proteins, and manipulations to reduce the effect of the T-cell response. There is increasing evidence of the advantages of using genetically engineered pigs as sources of islets for future clinical trials.

Gene expression changes in rat pancreas transplant model after long-term cold storage of the graft in perfluorohexyloctane

BACKGROUND

Perfluorohexyloctane (PFH) is a promising storage solution that has been successfully used for pancreas preservation before islet isolation. This hyperoxygen carrier has been designed to prevent ischemic injury to the pancreas graft during cold storage. In our storage, we aimed to evaluate the impact of this solution on long-term cold storage in a rat whole pancreas transplantation model.

METHOD

Brown-Norway rats were used for syngeneic heterotopic pancreas transplantation. The procured organs were cold-stored for 18 hours in preoxygenated PFH (PFH group; n = 8) or in the University of Wisconsin solution (UW group; n = 8), or were transplanted immediately in the control group (n = 8). Two hours after reperfusion, we obtained blood and pancreas tissue samples for biochemistry and gene analyses (real-time polymerase chain reaction).

RESULTS

A significant difference between the UW and PFH group was observed in the tumor necrosis factor (TNF)β and endothelin 1 genes, which was overexpressed more than twofold in the UW group. In the blood samples, the UW group compared with the PFH group showed significantly higher levels of pancreatic amylase and lipase (94.2 ± 25.2 vs 67.7 ± 13.4 μkat/L and 5.5 ± 2.8 vs 3 ± 0.7 μkat/L, respectively; P < .05).

CONCLUSION

We found significantly lower expression levels of the endothelin 1 and TNFβ genes and lower concentrations of pancreatic amylase and lipase in the PFH group. All these findings suggest lower rate of ischemic reperfusion injury in the PFH group. These findings may result in better post-transplant outcomes after long-term cold storage in PFH compared with the UW solution. Further research in this area is required.