Effect of oxygenated perfluorocarbons on isolated rat pancreatic islets in culture

Type 1 diabetes and engineering enhanced islet transplantation

The development of new therapeutic approaches to treat type 1 diabetes mellitus (T1D) relies on the precise understanding and deciphering of insulin-secreting β-cell biology, as well as the mechanisms responsible for their autoimmune destruction. β-cell or islet transplantation is viewed as a potential long-term therapy for the millions of patients with diabetes. To advance the field of insulin-secreting cell transplantation, two main research areas are currently investigated by the scientific community: (1) the identification of the developmental pathways that drive the differentiation of stem cells into insulin-producing cells, providing an inexhaustible source of cells; and (2) transplantation strategies and engineered transplants to provide protection and enhance the functionality of transplanted cells. In this review, we discuss the biology of pancreatic β-cells, pathology of T1D and current state of β-cell differentiation. We give a comprehensive view and discuss the different possibilities to engineer enhanced insulin-secreting cell/islet transplantation from a translational perspective.

Design Considerations for Macroencapsulation Devices for Stem Cell Derived Islets for the Treatment of Type 1 Diabetes

Stem cell derived insulin producing cells or islets have shown promise in reversing Type 1 Diabetes (T1D), yet successful transplantation currently necessitates long-term modulation with immunosuppressant drugs. An alternative approach to avoiding this immune response is to utilize an islet macroencapsulation device, where islets are incorporated into a selectively permeable membrane that can protect the transplanted cells from acute host response, whilst enabling delivery of insulin. These macroencapsulation systems have to meet a number of stringent and challenging design criteria in order to achieve the ultimate goal of reversing T1D. In this progress report, the design considerations and functional requirements of macroencapsulation systems are reviewed, specifically for stem-cell derived islets (SC-islets), highlighting distinct design parameters. Additionally, a perspective on the future for macroencapsulation systems is given, and how incorporating continuous sensing and closed-loop feedback can be transformative in advancing toward an autonomous biohybrid artificial pancreas.

Generation of Human Stem Cell-Derived Pancreatic Organoids (POs) for Regenerative Medicine

Insulin-dependent diabetes mellitus or type 1 diabetes mellitus (T1DM) is an auto-immune condition characterized by the loss of pancreatic β-cells. The curative approach for highly selected patients is the pancreas or the pancreatic islet transplantation. Nevertheless, these options are limited by a growing shortage of donor organs and by the requirement of immunosuppression.Xenotransplantation of porcine islets has been extensively investigated. Nevertheless, the strong xenoimmunity and the risk of transmission of porcine endogenous retroviruses, have limited their application in clinic. Generation of β-like cells from stem cells is one of the most promising strategies in regenerative medicine. Embryonic, and more recently, adult stem cells are currently the most promising cell sources exploited to generate functional β-cells in vitro. A number of studies demonstrated that stem cells could generate functional pancreatic organoids (POs), able to restore normoglycemia when implanted in different preclinical diabetic models. Nevertheless, a gradual loss of function and cell dead are commonly detected when POs are transplanted in immunocompetent animals. So far, the main issue to be solved is the post-transplanted islet loss, due to the host immune attack. To avoid this hurdle, nanotechnology has provided a number of polymers currently under investigation for islet micro and macro-encapsulation. These new approaches, besides conferring PO immune protection, are able to supply oxygen and nutrients and to preserve PO morphology and long-term viability.Herein, we summarize the current knowledge on bioengineered POs and the stem cell differentiation platforms. We also discuss the in vitro strategies used to generate functional POs, and the protocols currently used to confer immune-protection against the host immune attack (micro- and macro-encapsulation). In addition, the most relevant ongoing clinical trials, and the most relevant hurdles met to move towards clinical application are revised.

Mimicking oxygen delivery and waste removal functions of blood

In addition to immunological and wound healing cell and platelet delivery, ion stasis and nutrient supply, blood delivers oxygen to cells and tissues and removes metabolic wastes. For decades researchers have been trying to develop approaches that mimic these two immediately vital functions of blood. Oxygen is crucial for the long-term survival of tissues and cells in vertebrates. Hypoxia (oxygen deficiency) and even at times anoxia (absence of oxygen) can occur during organ preservation, organ and cell transplantation, wound healing, in tumors and engineering of tissues. Different approaches have been developed to deliver oxygen to tissues and cells, including hyperbaric oxygen therapy (HBOT), normobaric hyperoxia therapy (NBOT), using biochemical reactions and electrolysis, employing liquids with high oxygen solubility, administering hemoglobin, myoglobin and red blood cells (RBCs), introducing oxygen-generating agents, using oxygen-carrying microparticles, persufflation, and peritoneal oxygenation. Metabolic waste accumulation is another issue in biological systems when blood flow is insufficient. Metabolic wastes change the microenvironment of cells and tissues, influence the metabolic activities of cells, and ultimately cause cell death. This review examines advances in blood mimicking systems in the field of biomedical engineering in terms of oxygen delivery and metabolic waste removal.

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.

Impact of Pancreatic Rat Islet Density on Cell Survival during Hypoxia

In bioartificial pancreases (BP), the number of islets needed to restore normoglycaemia in the diabetic patient is critical. However, the confinement of a high quantity of islets in a limited space may impact islet survival, particularly in regard to the low oxygen partial pressure (PO2) in such environments. The aim of the present study was to evaluate the impact of islet number in a confined space under hypoxia on cell survival. Rat islets were seeded at three different concentrations (150, 300, and 600 Islet Equivalents (IEQ)/cm(2)) and cultured in normal atmospheric pressure (160 mmHg) as well as hypoxic conditions (15 mmHg) for 24 hours. Cell viability, function, hypoxia-induced changes in gene expression, and cytokine secretion were then assessed. Notably, hypoxia appeared to induce a decrease in viability and increasing islet density exacerbated the observed increase in cellular apoptosis as well as the loss of function. These changes were also associated with an increase in inflammatory gene transcription. Taken together, these data indicate that when a high number of islets are confined to a small space under hypoxia, cell viability and function are significantly impacted. Thus, in order to improve islet survival in this environment during transplantation, oxygenation is of critical importance.

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.

Use of perfluorocarbon nanoparticles for non-invasive multimodal cell tracking of human pancreatic islets

In vivo imaging of engraftment and immunorejection of transplanted islets is critical for further clinical development, with (1)H MR imaging of superparamagnetic iron oxide-labeled cells being the current premier modality. Using perfluorocarbon nanoparticles, we present here a strategy for non-invasive imaging of cells using other modalities. To this end, human cadaveric islets were labeled with rhodamine-perfluorooctylbromide (PFOB) nanoparticles, rhodamine-perfluoropolyether (PFPE) nanoparticles or Feridex as control and tested in vitro for cell viability and c-peptide secretion for 1 week. (19)F MRI, computed tomography (CT) and ultrasound (US) imaging was performed on labeled cell phantoms and on cells following transplantation beneath the kidney capsule of mice and rabbits. PFOB and PFPE-labeling did not reduce human islet viability or glucose responsiveness as compared with unlabeled cells or SPIO-labeled cells. PFOB- and PFPE-labeled islets were effectively fluorinated for visualization by (19)F MRI. PFOB-labeled islets were acoustically reflective for detection by US imaging and became sufficiently brominated to become radiopaque allowing visualization with CT. Thus, perfluorocarbon nanoparticles are multimodal cellular contrast agents that may find applications in real-time targeted delivery and imaging of transplanted human islets or other cells in a clinically applicable manner using MRI, US or CT imaging.

Fluorocapsules for improved function, immunoprotection, and visualization of cellular therapeutics with MR, US, and CT imaging

PURPOSE

To develop novel immunoprotective alginate microcapsule formulations containing perfluorocarbons (PFCs) that may increase cell function, provide immunoprotection for xenografted cells, and simultaneously enable multimodality imaging.

MATERIALS AND METHODS

All animal experiments were approved by an Institutional Animal Care and Use Committee. Cadaveric human islet cells were encapsulated with alginate, poly-l-lysine, and perfluorooctyl bromide (PFOB) or perfluoropolyether (PFPE). In vitro viability and the glucose-stimulation index for insulin were determined over the course of 2 weeks and analyzed by using a cross-sectional time series regression model. The sensitivity of multimodality (computed tomography [CT], ultrasonography [US], and fluorine 19 [(19)F] magnetic resonance [MR] imaging) detection was determined for fluorocapsules embedded in gel phantoms. C57BL/6 mice intraperitoneally receiving 6000 PFOB-labeled (n = 6) or 6000 PFPE-labeled (n = 6) islet-containing fluorocapsules and control mice intraperitoneally receiving 6000 PFOB-labeled (n = 6) or 6000 PFPE-labeled (n = 6) fluorocapsules without islets were monitored for human C-peptide (insulin) secretion during a period of 55 days. Mice underwent (19)F MR imaging at 9.4 T and micro-CT. Swine (n = 2) receiving 9000 PFOB capsules through renal artery catheterization were imaged with a clinical multidetector CT scanner. Signal intensity was evaluated by using a paired t test.

RESULTS

Compared with nonfluorinated alginate microcapsules, PFOB fluorocapsules increased insulin secretion of encapsulated human islets, with values up to 18.5% (3.78 vs 3.19) at 8-mmol/L glucose concentration after 7 days in culture (P < .001). After placement of the immunoprotected encapsulated cells into mice, a sustained insulin release was achieved with human C-peptide levels of 19.1 pmol/L ± 0.9 (standard deviation) and 33.0 pmol/L ± 1.0 for PFPE and PFOB capsules, respectively. Fluorocapsules were readily visualized with (19)F MR imaging, US imaging, and CT with research- and clinical-grade imagers for all modalities.

CONCLUSION

Fluorocapsules enhance glucose responsiveness and insulin secretion in vitro, enable long-term insulin secretion by xenografted islet cells in vivo, and represent a novel contrast agent platform for multimodality imaging.

β2-Syntrophin is a Cdk5 substrate that restrains the motility of insulin secretory granules

The molecular basis for the interaction of insulin granules with the cortical cytoskeleton of pancreatic β-cells remains unknown. We have proposed that binding of the granule protein ICA512 to the PDZ domain of β2-syntrophin anchors granules to actin filaments and that the phosphorylation/dephosphorylation of β2-syntrophin regulates this association. Here we tested this hypothesis by analyzing INS-1 cells expressing GFP-β2-syntrophin through the combined use of biochemical approaches, imaging studies by confocal and total internal reflection fluorescence microscopy as well as electron microscopy. Our results support the notion that β2-syntrophin restrains the mobility of cortical granules in insulinoma INS-1 cells, thereby reducing insulin secretion and increasing insulin stores in resting cells, while increasing insulin release upon stimulation. Using mass spectrometry, in vitro phosphorylation assays and β2-syntrophin phosphomutants we found that phosphorylation of β2-syntrophin on S75 near the PDZ domain decreases its binding to ICA512 and correlates with increased granule motility, while phosphorylation of S90 has opposite effects. We further show that Cdk5, which regulates insulin secretion, phosphorylates S75. These findings provide mechanistic insight into how stimulation displaces insulin granules from cortical actin, thus promoting their motility and exocytosis.

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.

Effect of oxygenated perfluorocarbon on isolated islets during transportation

BACKGROUND

Previous studies demonstrated the efficacy of the two-layer method (TLM) using oxygenated perfluorochemicals (PFC) for pancreas preservation. The current study investigated the effect of oxygenated PFC on isolated islets during transportation.

MATERIALS AND METHODS

Purified rat islets were stored in an airtight conical tube for 24h in RPMI culture medium at 22 degrees C or University of Wisconsin solution (UW) at 4 degrees C, either with or without oxygenated PFC. After storage, the islets were assessed for in vitro viability by static incubation (SI), FDA/PI staining, and energy status (ATP, energy charge, and ADP/ATP ratio) and for in vivo viability by a transplantation study.

RESULTS

UW at 4 degrees C and RPMI medium at 22 degrees C maintained islet quality almost equally in both in vitro and in vivo assessments. The ATP levels and energy status in the groups with PFC were significantly lower than those without PFC. The groups with PFC showed a significantly higher ADP/ATP ratio than those without PFC. In the transplantation study, blood glucose levels and AUC in the UW+PFC group were significantly higher than those in UW group.

CONCLUSIONS

UW at 4 degrees C and RPMI medium at 22 degrees C maintained islet quality equally under the conditions for islet transportation. The addition of oxygenated PFC, while advantageous for pancreas preservation, is not useful for islet transportation.

Beta cell chromogranin B is partially segregated in distinct granules and can be released separately from insulin in response to stimulation

AIMS/HYPOTHESIS

We investigated, in three beta cell lines (INS-1E, RIN-5AH, betaTC3) and in human and rodent primary beta cells, the storage and release of chromogranin B, a secretory protein expressed in beta cells and postulated to play an autocrine role. We asked whether chromogranin B is stored together with and discharged in constant ratio to insulin upon various stimuli.

METHODS

The intracellular distribution of insulin and chromogranin B was revealed by immunofluorescence followed by three-dimensional image reconstruction and by immunoelectron microscopy; their stimulated discharge was measured by ELISA and immunoblot analysis of homogenates and incubation media.

RESULTS

Insulin and chromogranin B, co-localised in the Golgi complex/trans-Golgi network, appeared largely segregated from each other in the secretory granule compartment. In INS-1E cells, the percentage of granules positive only for insulin or chromogranin B and of those positive for both was 66, 7 and 27%, respectively. In resting cells, both insulin and chromogranin B were concentrated in the granule cores; upon stimulation, chromogranin B (but not insulin) was largely redistributed to the core periphery and the surrounding halo. Strong stimulation with a secretagogue mixture induced parallel release of insulin and chromogranin B, whereas with 3-isobutyl-1-methylxantine and forskolin +/- high glucose release of chromogranin B predominated. Weak, Ca(2+)-dependent stimulation with ionomycin or carbachol induced exclusive release of chromogranin B, suggesting a higher Ca(2+) sensitivity of the specific granules.

CONCLUSIONS/INTERPRETATION

The unexpected complexity of the beta cell granule population in terms of heterogeneity, molecular plasticity and the differential discharge, could play an important role in physiological control of insulin release and possibly also in beta cell pathology.

Resolution of severe atopic dermatitis after tacrolimus withdrawal

Tacrolimus is an immunosuppressive agent used in solid organ and islet transplantation. Its topical form has shown benefit in the treatment of inflammatory skin conditions. Although tacrolimus has a wide spectrum of side effects, dermatological complications related to systemic tacrolimus therapy are limited in the literature. Atopic dermatitis (AD) is a chronic pruritic cutaneous condition that usually begins in infancy and is characterized by an increased Th2 response. We report the case of a patient with type 1 diabetes mellitus (T1DM) and history of AD latent for 10 years who developed severe dermatitis and alopecia 5 months after undergoing allogeneic islet transplantation and initiating a steroid-free immunosuppressive regimen with sirolimus and tacrolimus maintenance. After exclusion of other possible causes for the progression and exacerbation of the clinical presentation of AD, discontinuation of tacrolimus and introduction of mycophenolate mofetil resulted in full remission of the symptoms. The beneficial effects of tacrolimus withdrawal suggest a cause-effect relationship between this adverse event and the utilization of the drug. Islet graft function remained stable after modification of the therapeutic regimen (stable glycemic control and unchanged C-peptide).