Cryopreservation of rat islets of Langerhans by vitrification

Cryopreservation of organoids: Strategies, innovation, and future prospects

Organoid technology has demonstrated unique advantages in multidisciplinary fields such as disease research, tumor drug sensitivity, clinical immunity, drug toxicology, and regenerative medicine. It will become the most promising research tool in translational research. However, the long preparation time of organoids and the lack of high-quality cryopreservation methods limit the further application of organoids. Although the high-quality cryopreservation of small-volume biological samples such as cells and embryos has been successfully achieved, the existing cryopreservation methods for organoids still face many bottlenecks. In recent years, with the development of materials science, cryobiology, and interdisciplinary research, many new materials and methods have been applied to cryopreservation. Several new cryopreservation methods have emerged, such as cryoprotectants (CPAs) of natural origin, ice-controlled biomaterials, and rapid rewarming methods. The introduction of these technologies has expanded the research scope of cryopreservation of organoids, provided new approaches and methods for cryopreservation of organoids, and is expected to break through the current technical bottleneck of cryopreservation of organoids. This paper reviews the progress of cryopreservation of organoids in recent years from three aspects: damage factors of cryopreservation of organoids, new protective agents and loading methods, and new technologies of cryopreservation and rewarming.

Pancreatic islet cryopreservation by vitrification achieves high viability, function, recovery and clinical scalability for transplantation

Pancreatic islet transplantation can cure diabetes but requires accessible, high-quality islets in sufficient quantities. Cryopreservation could solve islet supply chain challenges by enabling quality-controlled banking and pooling of donor islets. Unfortunately, cryopreservation has not succeeded in this objective, as it must simultaneously provide high recovery, viability, function and scalability. Here, we achieve this goal in mouse, porcine, human and human stem cell (SC)-derived beta cell (SC-beta) islets by comprehensive optimization of cryoprotectant agent (CPA) composition, CPA loading and unloading conditions and methods for vitrification and rewarming (VR). Post-VR islet viability, relative to control, was 90.5% for mouse, 92.1% for SC-beta, 87.2% for porcine and 87.4% for human islets, and it remained unchanged for at least 9 months of cryogenic storage. VR islets had normal macroscopic, microscopic, and ultrastructural morphology. Mitochondrial membrane potential and adenosine triphosphate (ATP) levels were slightly reduced, but all other measures of cellular respiration, including oxygen consumption rate (OCR) to produce ATP, were unchanged. VR islets had normal glucose-stimulated insulin secretion (GSIS) function in vitro and in vivo. Porcine and SC-beta islets made insulin in xenotransplant models, and mouse islets tested in a marginal mass syngeneic transplant model cured diabetes in 92% of recipients within 24–48 h after transplant. Excellent glycemic control was seen for 150 days. Finally, our approach processed 2,500 islets with >95% islets recovery at >89% post-thaw viability and can readily be scaled up for higher throughput. These results suggest that cryopreservation can now be used to supply needed islets for improved transplantation outcomes that cure diabetes.

Optimization of vitrification approaches substantially improves pancreatic islet cryopreservation for banking and boosts transplantation outcomes in diabetes.

Fabrication of functional rat pseudo-islets after cryopreservation of pancreatic islets or dispersed islet cells

Dispersed single cells from pancreatic islets can configure the three-dimensional islet-like architecture (pseudo-islets) with insulin secretion potential and controllable size through their aggregation property. The present study was designed to investigate whether cryopreservation of islets or islet cells can contribute to the efficient pseudo-islet fabrication in the rat model. In control group (CT), islet single cells were prepared by trypsin digestion of 50-400-µm ø fresh control islets, and then cultured for 3 days in the U-bottom microwell to fabricate pseudo-islets. In vitrification-warming group (VW), islet single cells were prepared from postwarm islets cryopreserved by vitrification on nylon mesh device, and then cultured for 3 days. In freezing group (FR), islet single cells originated from fresh islets were subjected to a conventional Bicell® freezing, and postthaw cells were cultured for 3 days. To generate 1 islet equivalent pseudo-islets (150 µm ø) by the sphere culture, 1250 CT cells, 1250 VW cells, and 1500 FR cells were seeded to each microwell. The viability of the pseudo-islets was comparable among the three groups (93.9%-96.9%). Furthermore, the insulin secretion assay showed that those pseudo-islets responded sufficiently to the high glucose stimulation. Immunostaining for insulin and glucagon showed that the endocrine cell arrangement of those pseudo-islets is similar to that of native and isolated islets. These islets/pseudo-islets had the β-cells in core and the α-cells in mantle, which was typical characteristic of the rodent islets. However, some clusters of α-cells were observed inside the FR pseudo-islets. Interestingly, the VW pseudo-islets had significantly fewer α-cells than the CT or FR pseudo-islets. These results suggest that the sphere culture of islet cells is useful tool to generate the pseudo-islets with the customized size and normal functionality, even after islet cryopreservation.

The Fragility of Cryopreserved Insulin-producing Cells Differentiated from Adipose-tissue-derived Stem Cells

The aim of our study is to determine whether insulin-producing cells (IPCs) differentiated from adipose-tissue-derived stem cells (ADSCs) can be cryopreserved. Human ADSCs were differentiated into IPCs using our two-step protocol encompassing a three-dimensional culture and xenoantigen-free method. Thereafter, IPCs were frozen using three different methods. First, IPCs were immediately frozen at -80°C (-80°C group). Second, IPCs were initially placed into a Bicell freezing container before freezing at -80°C (BICELL group). Third, a vitrification method for oocytes and embryos was used (CRYOTOP group). Cell counting kit-8 (CCK-8) assay showed that cell viability was decreased in all groups after cryopreservation (P < 0.01). Corroboratively, the amount of adenosine triphosphate was markedly decreased after cryopreservation in all groups (P < 0.01). Immunofluorescence staining showed a reduced positive staining area for insulin in all cryopreservation groups. Furthermore, 4',6-diamidino-2-phenylindole and merged immunofluorescence images showed that cryopreserved cells appeared to be randomly reduced in the -80°C group and CRYOTOP group, while only the central region was visibly reduced in the BICELL group. Using immunohistochemical staining, IPCs after cryopreservation were shown to be positive for cleaved caspase-3 antibody in all groups. Finally, insulin secretion following glucose stimulation was significantly reduced in IPCs from all groups after cryopreservation (P < 0.01). In conclusion, IPCs may be too fragile for cryopreservation with accomplished methods and further investigations for a suitable preservation method are required.

Acellular matrix derived from rat liver improves the functionality of rat pancreatic islets before or after vitrification

Cryopreservation of pancreatic islets can overcome the severe shortage of islet donors in clinical islet transplantation, but the impaired quality of post-warm islets need improvement. This present study was conducted to investigate whether the pre- or post-treatment of rat islets with liver decellularized matrix (LDM) for vitrification can improve the viability (FDA/PI double staining) and the functionality (glucose-stimulated insulin secretion [GSIS] assay). Rat LDM was prepared by high-hydrostatic pressure, lyophilization, and re-suspension in saline. Co-culturing of isolated islets with 0 (control), 30, 60, or 90 μg/ml LDM for 24 h resulted in the comparable viability among the 4 groups (98.7-99.6%) and the higher insulin secretion potential in 30 and 60 μg/ml LDM treatment groups than the control group (stimulation index [SI]: 12.1 and 12.7, respectively, vs. 6.5 in the control group, P < 0.05). When the islets co-cultured with 60 μg/ml LDM were vitrified-warmed on a nylon mesh cryodevice, the viability and the GSIS of the post-warm islets were not improved. Post-treatment of vitrified-warmed islets with 60 μg/ml LDM during the recovery culture for 12 h resulted in the comparable clearance of degenerating cell debris from the post-warm islets, while their insulin secretion potential was improved (SI: 5.0 vs. 3.5 in the control group, P < 0.05). These findings indicate that the components in LDM can enhance the insulin secretion potential of rat islets suffering damage by enzymatic stress during the islet isolation process or by cryoinjuries during the vitrification-warming process.

Transplantation of rat pancreatic islets vitrified-warmed on the nylon mesh device and the silk fibroin sponge disc

We report the adaptability of rat islets vitrified-warmed on nylon mesh (NM) device or silk fibroin (SF) sponge disc for the normalization of the blood glucose level in rat models of diabetes. One-hundred rat islets were cryopreserved according to a minimum volume cooling protocol on an NM device or a solid surface vitrification protocol on an SF sponge disc. The recovery rate (97.1% vs. 93.8%), the viability (77.9% vs. 74.4%), and the stimulation index (4.7 vs. 4.2) in glucose-stimulated insulin secretion (GSIS) assay of the post-warm islets were comparable between the NM vitrification and the SF vitrification groups. The viability and the stimulation index of the fresh control islets were identified to be 97.5% and 6.5, respectively. Eight hundred islets from the NM or the SF vitrification group or the fresh control group were transplanted beneath the kidney capsule of a streptozotocin-induced diabetic rat (blood glucose level > 350 mg/dl). Within 3 weeks after transplantation, the acquisition of euglycemia (< 200 mg/dl) was observed in recipient rats (80.0-83.3%). An intraperitoneal glucose tolerance test on Day-30 and Day-60 showed similar 2-h responses to the glucose uptake of cured rats among the compared groups. Moreover, the successful engraftment of transplants was confirmed by the Day-70 nephrectomy through the subsequent diabetes reversal and histological evaluation. Thus, large quantities of rat islets vitrified-warmed on an NM device or an SF sponge disc were proven to be fully functional both in vitro and in vivo, due to the GSIS and syngeneic transplantation, respectively.

Engineering Strategies to Improve Islet Transplantation for Type 1 Diabetes Therapy

Type 1 diabetes is an autoimmune disease in which the immune system attacks insulin-producing beta cells of pancreatic islets. Type 1 diabetes can be treated with islet transplantation; however, patients must be administered immunosuppressants to prevent immune rejection of the transplanted islets if they are not autologous or not engineered with immune protection/isolation. To overcome biological barriers of islet transplantation, encapsulation strategies have been developed and robustly investigated. While islet encapsulation can prevent the need for immunosuppressants, these approaches have not shown much success in clinical trials due to a lack of long-term insulin production. Multiple engineering strategies have been used to improve encapsulation and post-transplantation islet survival. In addition, more efficient islet cryopreservation methods have been designed to facilitate the scaling-up of islet transplantation. Other islet sources have been identified including porcine islets and stem cell-derived islet-like aggregates. Overall, islet-laden capsule transplantation has greatly improved over the past 30 years and is moving towards becoming a clinically feasible treatment for type 1 diabetes.

Supplementary cryoprotective effect of carboxylated ε-poly-l-lysine during vitrification of rat pancreatic islets

This study was designed to investigate whether cryosurvival of rat pancreatic islets can be improved by carboxylated ε-poly-l-lysine (CPLL). Islets isolated from Wistar × Brown-Norway F1 rats (101-200 μm in diameter) were cryopreserved in three vitrification solutions containing ethylene glycol (EG; 30%, v/v) and CPLL (0%, 10%, or 20%, v/v) by Cryotop^® protocol (10 islets per device). The post-warm survival rate of the islets vitrified in the presence of 20% CPLL (74%), assessed by FDA/PI double staining, was higher than those in 0% and 10% CPLL (65% and 66%, respectively). Decreased EG concentrations (10% and 20%) in the presence of 20% CPLL resulted in impaired post-warm islet survival rates (50% and 64%, respectively). Value of stimulus index (SI) for 20 mM/3 mM glucose-stimulated insulin secretion was 4.1 in islets vitrified-warmed in the presence of 30% EG and 20% CPLL, which was comparable with those in fresh control islets and vitrified islets in 30% EG alone (4.1 and 4.4, respectively). A large number of islets (50 islets per device) could be cryopreserved in the presence of 30% EG and 20% CPLL by using nylon mesh as the device, without considerable loss of post-warm survival (68%) and SI value (3.7). In conclusion, supplementation of antifreeze 20% CPLL was effective in improving the post-warm survival of isolated rat pancreatic islets when vitrification solution containing 30% EG was used.

Systematic review of islet cryopreservation

Pancreatic islet transplantation is being extensively researched as an alternative treatment for type 1 diabetic patients. This treatment is currently limited by temporal mismatch, between the availability of pancreas and isolated islets from deceased organ donor, and the recipient's need for freshly isolated islets. To solve this issue, cryopreservation of islets may offer the potential to bank islets for transplant on demand. Cryopreservation, however, introduces an overwhelmingly harsh environment to the ever-so-fragile islets. After exposure to the freezing and thawing, islets are usually either apoptotic, non-functional, or non-viable. Several studies have proposed various techniques that could lead to increased cell survival and function following a deep freeze. The purpose of this article is to critically review the techniques of islet cryopreservation, with the goal of highlighting optimization parameters that can lead to the most viable and functional islet upon recovery and/or transplant.

Nylon Mesh Device for Vitrification of Large Quantities of Rat Pancreatic Islets

The practical requirements of islet transplantation necessitate that a large quantity of pancreatic islets be cryopreserved for a long period of time in a simple and convenient manner. We cryopreserved rat islets (size range 101-150 μm in mean diameter) by vitrification with either a Cryotop^® device or a ø = 57-μm nylon mesh device in units of 10 islets, or by conventional freezing with a Bicell^® vessel in units of 50 islets. Postwarm/thaw survival rates of the islets were 68.1% ± 5.9%, 64.1% ± 3.5%, and 47.7 ± 1.2% following Cryotop vitrification, nylon mesh vitrification, and Bicell freezing, respectively (p < 0.05). Glucose-stimulated insulin secretion in the two vitrification groups (stimulus index [SI] = 3.1-3.9) was superior to that in the freezing group (SI = 0.8). Additional experiments involved scaling-up the cryopreservation process using the nylon mesh device in units of 10, 50, or 100 islets. Increased numbers of islets per device had no adverse effects on cryosurvival (58.6%-68.5%) or insulin secretion potential (SI = 2.8-4.2). As the nylon mesh device does not require the handling of individual islets with glass pipettes, pre- and postvitrification islet treatment is less complicated. Therefore, nylon mesh can serve as a simple cryodevice for the vitrification of large quantities of rat pancreatic islets.

Long-term cryopreservation of reaggregated pancreatic islets resulting in successful transplantation in rats

Preservation of pancreatic islets for long-term storage of islets used for transplantation or research has long been a goal. Unfortunately, few studies on long-term islet cryopreservation (1 month and longer) have reported positive outcomes in terms of islet yield, survival and function. In general, single cells have been shown to tolerate the cryopreservation procedure better than tissues/multicellular structures like islets. Thus, we optimized a method to cryopreserve single islet cells and, after thawing, reaggregated them into islet spheroids. Cryopreserved (CP) single human islet cells formed spheroids efficiently within 3-5 days after thawing. Approximately 79% of islet cells were recovered following the single-cell cryopreservation protocol. Viability after long-term cryopreservation (4 weeks or more) was significantly higher in the CP islet cell spheroids (97.4 ± 0.4%) compared to CP native islets (14.6 ± 0.4%). Moreover, CP islet cell spheroids had excellent viability even after weeks in culture (88.5 ± 1.6%). Metabolic activity was 4-5 times higher in CP islet cell spheroids than CP native islets at 24 and 48 h after thawing. Diabetic rats transplanted with CP islet cell spheroids were normoglycemic for 10 months, identical to diabetic rats transplanted with fresh islets. However, the animals receiving fresh islets required a higher volume of transplanted tissue to achieve normoglycemia compared to those transplanted with CP islet cell spheroids. By cryopreserving single cells instead of intact islets, we achieved highly viable and functional islets after thawing that required lower tissue volumes to reverse diabetes in rats.

Direct comparison of Cryotop® vitrification and Bicell® freezing on recovery of functional rat pancreatic islets

Two protocols, Bicell^® freeze-thawing and Cryotop^® vitrification-warming, were compared for suitability in cryopreserving rat pancreatic islets (101-150 μm in mean diameter). Immediate survival rates of post-thaw and post-warm islets (50 and 57%, respectively), assessed by FDA/PI double staining, were lower than that of fresh control islets (90%). Most of the PI-positive dead cells were detected in peripheral area of post-warm islets, and were removed after subsequent 24 h culture (survival rate; 85% vs 59% in post-thaw islets). Quantitative PCR analysis showed that Bicell^® freeze-thawing compromised expression of genes relating to β-cell function (Pdx1 and Glut2), but not to one of apoptotic pathways (Bax/Bcl2 ratio). Expression of these genes was maintained in islets before and after the Cryotop^® vitrification-warming. Values of stimulus index (SI) for 20 mM/3 mM glucose-stimulated insulin secretion were 6.7, 1.9 and 3.9 in fresh control, post-thaw and post-warm islets, respectively. The SI values after 24 h culture were 4.1, 1.9 and 3.1, respectively. Larger islets (>150 μm in diameter) had comparable survival rates, but lower SI values after Cryotop^® vitrification-warming when compared to smaller counterparts. These results suggest that rat pancreatic islets can be cryopreserved by Cryotop^® vitrification-warming rather than Bicell^® freeze-thawing, without considerable loss of in vitro β-cell function.

Sensing and Sensibility: Single-Islet-based Quality Control Assay of Cryopreserved Pancreatic Islets with Functionalized Hydrogel Microcapsules

Despite decades of research and clinical studies of islet transplantations, finding simple yet reliable islet quality assays that correlate accurately with in vivo potency is still a major challenge, especially for real-time and single-islet-based quality assessment. Herein, proof-of-concept studies of a cryopreserved microcapsule-based quality control assays are presented for single islets. Individual rat pancreatic islets and fluorescent oxygen-sensitive dye (FOSD) are encapsulated in alginate hydrogel microcapsules via a microfluidic device. To test the susceptibility of the microcapsules and the FOSD to cryopreservation, the islet microcapsules containing FOSD are cryopreserved and the islet functionalities (adenosine triphosphate, static insulin release measurement, and oxygen consumption rate) are assessed after freezing and thawing steps. The cryopreserved islet capsules with FOSD remain functional after encapsulation and freezing/thawing procedures, validating a simple yet reliable individual-islet-based quality control method for the entire islet processing procedure prior to transplantation. This work also demonstrates that the functionality of cryopreserved islets can be improved by introducing trehalose into the routinely used cryoprotectant dimethyl sulfoxide. The functionalized alginate hydrogel microcapsules with embedded FOSD and optimized cryopreservation protocol presented in this work serve as a versatile islet quality assay and offer tremendous promise for tackling existing challenges in islet transplantation procedures.

The preservation of islet with alginate encapsulation in the process of transportation

Restoration of insulin secretion by transplantation of isolated islets is a treatment for type Ι diabetes mellitus. One of the major issues with clinical treatment of islet transplantation is how to maintain islet viability during transportation from the donor to the patient. We developed a method that uses alginate encapsulation to protect islets from mechanical damage during shipment. We tested several variables for their impact on islet viability during transportation and used the significant variable to build a response surface methodology (RSM) model by the Box-Behnken design method. This type of model is a mathematical and statistical technique that we used to optimize the conditions for islet viability during shipment. In this study, the factors that significantly affected islet survival rate were incubation time, serum concentration, and preservation time. Then, an empirical model was built to optimize conditions of the islets for shipping according to the responses of the effect factors with RSM. This model can be used to predict the islet survival rate and can serve as a guide for optimizing the transportation method of islets and increasing the success rate of the transplant procedure.