Successful cryopreservation of mouse oocytes by using low concentrations of trehalose and dimethylsulfoxide

Impact of Electroporation-Delivered Intracellular Trehalose on the Characteristics of Intracellular Ice in Oocytes

Intracellular ice formation (IIF) is the primary cause of cell death during cryopreservation. IIF prevention strategies typically optimize the cooling and warming rates using cryoprotectants. The introduction of trehalose into cells has been shown to significantly enhance cryosurvival rates; however, how intracellular trehalose influences the dynamics of ice formation remains unclear. To address this knowledge gap, this study used an innovative electroporation-based method to efficiently deliver trehalose directly into oocytes and systematically explored its intracellular effect on ice formation in oocytes. Although the trehalose solution exhibited a strong ice-regulating capacity, its efficacy in controlling the intracellular ice dynamics was significantly limited in the extracellular environment. However, intracellular delivery of trehalose significantly inhibited intracellular ice nucleation and growth. Specifically, oocytes treated with 0.15-0.3 M intracellular trehalose exhibited a delayed initial IIF temperature (-55.9 °C) and reduced cumulative probability of cells with IIF (0.52) during cooling to -120 °C. After thawing, the proportion of oocytes with no significant volume change increased to 33.3%, and the extent of cellular damage was significantly alleviated. Collectively, our findings provide theoretical support for the application of intracellular trehalose for cryopreservation and highlight its efficiency in enhancing oocyte cryopreservation, thereby extending its practical applications to reproductive medicine, biobanking, and other fields relying on high-quality cryopreservation.

Reducing dimethyl sulfoxide content in Jurkat cell formulations suitable for cryopreservation

Cell-based medicinal products (CBMPs) are usually cryopreserved in formulations containing up to 10 % dimethyl sulfoxide (Me2SO) at temperatures below -145 °C. Although Me2SO effectively protects cells during the freezing process, it can be damaging to cells at ambient temperatures and lead to side effects in patients. The aim of this study was to reduce the amount of Me2SO in cryopreservation formulations for an immortalized T cell line (Jurkat cells). A design of experiment (DoE) approach was applied for formulation development using seven different excipients, i.e., Me2SO, trehalose, sorbitol, proline, ectoine, poloxamer 188 (P188) and poly vinyl pyrrolidone 40 (PVP). A DoE model was generated to predict optimal formulations resulting in a high post-thaw viability and a high glass transition temperature of the formulation to allow for frozen storage without the use of liquid nitrogen. Subsequently a stability study was performed with promising lead candidates over three months at storage temperatures of -145 °C, -80 °C, -40 °C. Three benchmark solutions were used, i.e., Cryostor CS10, CryoSOfree as well as 10 % Me2SO in Roswell Park Memorial Institute Medium (RPMI). The excipient affecting the post-thaw viability of Jurkat cells the most was, as expected, Me2SO, which led to increased viabilities at higher concentrations. Most formulations resulted in similar viabilities for cells stored at -145 °C and -80 °C, whereas samples stored at -40 °C did not survive. In general, benchmark formulations resulted in slightly higher viabilities than the tested formulations. Furthermore, cell samples stored at -80 °C were recultivated in cell culture and the viability was assessed after 24h. The cell viability after 24h was much lower compared to the cells analyzed directly post-thaw, indicating that freeze-thaw damages continue to unfold after thawing. In summary, several promising excipients and combinations thereof, e.g., trehalose and PVP, were identified for the cryopreservation of Jurkat cells with reduced concentrations of Me2SO or Me2SO-free cryopreservation. Additionally, storage at -80 °C is possible for the developed formulations.

Trehalose in cryopreservation. Applications, mechanisms and intracellular delivery opportunities

Cryopreservation is crucial to fields including immune and stem cell therapies, reproductive technology, blood banking, regenerative medicine and across all biotechnology. During cryopreservation, cryoprotectants are essential to protect cells from the damage caused by exposure to freezing temperatures. The most common penetrating cryoprotectants, such as DMSO and glycerol do not give full recovery and have a cytotoxicity limit on the concentration which can be applied. The non-reducing disaccharide trehalose has been widely explored and used to supplement these, inspired by its use in nature to aid survival at extreme temperatures and/or desiccation. However, trehalose has challenges to its use, particular its low membrane permeability, and how its protective role compares to other sugars. Here we review the application of trehalose and its reported benefit and seek to show where chemical tools can improve its function. In particular, we highlight emerging chemical methods to deliver (as cargo, or via selective permeation) into the intracellular space. This includes encapsulation, cell penetrating peptides or (selective) modification of hydroxyls on trehalose.

Slow Cooling and Controlled Ice Nucleation Enabling the Cryopreservation of Human T Lymphocytes with Low-Concentration Extracellular Trehalose

Cryopreservation of human T lymphocytes has become a key strategy for supporting cell-based immunotherapy. However, the effects of ice seeding on the cryopreservation of cells under relatively slow cooling have not been well researched. The cryopreservation strategy with a nontoxic, single-ingredient, and injectable cryoprotective solution remains to be developed. We conducted ice seeding for the cells in a solution of normal saline with 1% (v/v) dimethyl sulfoxide (Me2SO), 0.1 M trehalose, and 4% (w/v) human serum albumin (HSA) under different slow cooling rates. With the positive results, we further applied seeding in the solution of 0.2 M trehalose and 4% (w/v) HSA under the same cooling rates. The optimal concentration of trehalose in the Me2SO-free solutions was then investigated under the optimized cooling rate with seeding, with control groups without seeding, and in a freezing container. In vitro toxicity of the cryoprotective solutions to the cells was also tested. We found that the relative viability of cells (1% [v/v] Me2SO, 0.1 M trehalose and 4% [w/v] HSA) was improved significantly from 88.6% to 94.1% with ice seeding, compared with that without seeding (p < 0.05). The relative viability of cells (0.2 M trehalose and 4% [w/v] HSA) with seeding was significantly higher than that without seeding, 96.3% and 92.0%, respectively (p < 0.05). With no significant difference in relative viability between the solutions of 0.2 M trehalose or 0.3 M trehalose with 4% (w/v) HSA (92.4% and 94.6%, respectively, p > 0.05), the solution of 0.2 M trehalose and 4% (w/v) HSA was selected as the optimized Me2SO-free solution. This strategy could cryopreserve human T lymphocytes without any toxic cryoprotectant and boost the application of cell products in humans by intravenous injection, with the osmolality of the low-concentration cryoprotective solution close to that of human plasma.

Dimethyl Sulfoxide: A Bio-Friendly or Bio-Hazard Chemical? The Effect of DMSO in Human Fibroblast-like Synoviocytes

The effect of dimethyl sulfoxide (DMSO) in rheumatoid arthritis (RA) human fibroblast-like synoviocytes (FLSs) has been studied on five different samples harvested from the joints (fingers, hands and pelvis) of five women with RA. At high concentrations (>5%), the presence of DMSO induces the cleavage of caspase-3 and PARP-1, two phenomena associated with the cell death mechanism. Even at a 0.5% concentration of DMSO, MTT assays show a strong toxicity after 24 h exposure (≈25% cell death). Therefore, to ensure a minimum impact of DMSO on RA FLSs, our study shows that the concentration of DMSO has to be below 0.05% to be considered safe.

Optimized Protocol for Proportionate CNS Cell Retrieval as a Versatile Platform for Cellular and Molecular Phenomapping in Aging and Neurodegeneration

Efficient purification of viable neural cells from the mature CNS has been historically challenging due to the heterogeneity of the inherent cell populations. Moreover, changes in cellular interconnections, membrane lipid and cholesterol compositions, compartment-specific biophysical properties, and intercellular space constituents demand technical adjustments for cell isolation at different stages of maturation and aging. Though such obstacles are addressed and partially overcome for embryonic premature and mature CNS tissues, procedural adaptations to an aged, progeroid, and degenerative CNS environment are underrepresented. Here, we describe a practical workflow for the acquisition and phenomapping of CNS neural cells at states of health, physiological and precocious aging, and genetically provoked neurodegeneration. Following recent, unprecedented evidence of post-mitotic cellular senescence (PoMiCS), the protocol appears suitable for such de novo characterization and phenotypic opposition to classical senescence. Technically, the protocol is rapid, efficient as for cellular yield and well preserves physiological cell proportions. It is suitable for a variety of downstream applications aiming at cell type-specific interrogations, including cell culture systems, Flow-FISH, flow cytometry/FACS, senescence studies, and retrieval of omic-scale DNA, RNA, and protein profiles. We expect suitability for transfer to other CNS targets and to a broad spectrum of engineered systems addressing aging, neurodegeneration, progeria, and senescence.

Membrane-permeable trehalose improves the freezing ability and developmental competence of in-vitro matured feline oocytes

Oocytes are highly sensitive to cryopreservation, which frequently results in an irreversible loss of developmental competence. We examined the effect of membrane-permeable trehalose on the freezing ability of feline oocytes matured in vitro. In Experiment 1, intracellular trehalose (trehalose hexaacetate; Tre-(OAc)₆) was synthesized from trehalose precursor and subjected to spectroscopic characterization. The membrane permeability of the Tre-(OAc)₆ was investigated by incubating oocytes with different concentrations of Tre-(OAc)₆ (3, 15, and 30 mM). Optimum concentration and the toxicity of Tre-(OAc)₆ were assessed in Experiment 2. The effects of Tre-(OAc)₆ on freezing ability in terms of apoptotic gene expression and developmental competence of in-vitro matured oocytes were examined in Experiments 3 and 4, respectively. The Tre-(OAc)₆ permeated into the ooplasm of cat oocytes in a dose- and time-dependent manner. The highest concentration of intracellular trehalose was detected when the oocytes were incubated for 24 h with 30 mM Tre-(OAc)₆. For the toxicity test, incubation of oocytes with 3 mM Tre-(OAc)₆ for 24 h did not affect maturation rate and embryo development. However, high doses of Tre-(OAc)₆ (15 and 30 mM) significantly reduced maturation and fertilization rates (p < 0.05). In addition, frozen-thawed oocytes treated with 3 mM Tre-(OAc)₆ significantly upregulated anti-apoptotic (BCL-2) gene expression compared with the control (0 mM) and other Tre-(OAc)₆ concentrations (15 and 30 mM). Oocyte maturation in the presence of 3 mM Tre-(OAc)₆ prior to cryopreservation significantly improved oocyte developmental competence in terms of cleavage and blastocyst rates when compared with the control group (p < 0.05). Our results lead us to infer that increasing the levels of intracellular trehalose by Tre-(OAc)₆ during oocyte maturation improves the freezing ability of feline oocytes, albeit at specific concentrations.

Co-supplementation of freezing media with trehalose and vitamin C on cell viability and apoptotic gene expression in ovine spermatogonial stem cells

The purpose of this research was to investigate the trehalose and vitamin C (Vit C) co-supplementation of freezing media to create a successful cryopreservation protocol for conservation of ovine spermatogonial stem cells (SSCs). SSCs were cryopreserved and cultured with an essential freezing medium containing 200 mM trehalose, 40 µg/mL Vit C, and a combination of both for 3 weeks. Cell viability, colony number and diameter and mRNA levels of Bax, and Bcl-2 genes were evaluated before and after cryopreservation with quantitative real-time PCR. The results showed that cells cryopreserved in freezing medium containing 200 mM of trehalose plus 40 µg/mL Vit C had considerably greater cell viability than the control group (P<0.0001). Up to the 3rd week of cell culture, supplementation of freezing medium with 200 mM trehalose resulted in significantly lower colonies diameters than in the control group. No significant differences were observed during the 1st to 2nd weeks in colony diameter and number of colonies between cells cryopreserved in the freezing medium containing either Vit C or trehalose compared with the control groups. Following thawing, the mRNA level of Bax in the Vit C + trehalose group was drastically lower than in those treated with trehalose or Vit C only (P<0.0001). High expression of Bcl-2 in the 40 µg/mL Vit C group was recorded in the thawed cells compared to the control group (P<0.0001). These findings indicate that the concomitant use of antioxidants and sugar in the freezing medium can improve the quality and viabi­lity of SSCs after freezing via different mechanisms. Further studies are needed to clarify apoptosis and cell biomarkers in SSCs during freezing and thawing.

Effects of the donor factors and freezing protocols on the bovine embryonic lipid profile

Embryo lipid profile is affected by in vitro culture conditions, that lead to an increase in lipids. Efforts have been made to optimize embryo lipid composition as it is associated with their quality. The objective of this study was to evaluate whether the diet supplementation of donor cows (n-3 or n-6 PUFA), or the slow freezing protocols (ethylene glycol sucrose EG-S vs. glycerol trehalose GLY-TRE), or the physiological stage of the donor (nulliparous heifers vs. primiparous lactating cows) may impact the bovine embryo lipid profile. Lipid extracts of 97 embryos were individually analysed by liquid chromatography-high resolution mass spectrometry, highlighting 246 lipids including 85% being overabundant in cow embryos compared to heifer embryos. Among 105 differential lipids, 72 were overabundant after EG-S protocol, including a single glycerophosphate PA(32:1) representing 27.3% of the significantly modulated lipids, suggesting that it is degraded when GLY-TRE is used. No lipids were different according to the n-3 or n-6 supplementation of the donor cows. In conclusion, the embryonic lipid profile was mainly affected by the physiological stage of the donors and the slow freezing protocols. The overabundance of lipids in lactating cow embryos and the resulting lower quality of these embryos is consistent with the lower pregnancy rate observed in cows compared to heifers. Unlike GLY-TRE protocol, EG-S freezing allowed to preserve glycerophospholipids potentially improving the slow freezing of in vitro-produced embryos. Further studies are required to modulate embryo quality and freezability by modulating the lipidome and integrating all stages of embryonic production.

Advanced biomaterials in cell preservation: Hypothermic preservation and cryopreservation

Cell-based medicine has made great advances in clinical diagnosis and therapy for various refractory diseases, inducing a growing demand for cell preservation as support technology. However, the bottleneck problems in cell preservation include low efficiency and poor biocompatibility of traditional protectants. In this review, cell preservation technologies are categorized according to storage conditions: hypothermic preservation at 1 °C~35 °C to maintain short-term cell viability that is useful in cell diagnosis and transport, while cryopreservation at -196 °C~-80 °C to maintain long-term cell viability that provides opportunities for therapeutic cell product storage. Firstly, the background and developmental history of the protectants used in the two preservation technologies are briefly introduced. Secondly, the progress in different cellular protection mechanisms for advanced biomaterials are discussed in two preservation technologies. In hypothermic preservation, the hypothermia-induced and extracellular matrix-loss injuries to cells are comprehensively summarized, as well as the recent biomaterials dependent on regulation of cellular ATP level, stabilization of cellular membrane, balance of antioxidant defense system, and supply of mimetic ECM to prolong cell longevity are provided. In cryopreservation, cellular injuries and advanced biomaterials that can protect cells from osmotic or ice injury, and alleviate oxidative stress to allow cell survival are concluded. Last, an insight into the perspectives and challenges of this technology is provided. We envision advanced biocompatible materials for highly efficient cell preservation as critical in future developments and trends to support cell-based medicine. STATEMENT OF SIGNIFICANCE: Cell preservation technologies present a critical role in cell-based applications, and more efficient biocompatible protectants are highly required. This review categorizes cell preservation technologies into hypothermic preservation and cryopreservation according to their storage conditions, and comprehensively reviews the recently advanced biomaterials related. The background, development, and cellular protective mechanisms of these two preservation technologies are respectively introduced and summarized. Moreover, the differences, connections, individual demands of these two technologies are also provided and discussed.

Intracellular delivery of trehalose renders mesenchymal stromal cells viable and immunomodulatory competent after cryopreservation

Trehalose is a nontoxic disaccharide and a promising cryoprotection agent for medically applicable cells. In this study, the efficiency of combining trehalose with reversible electroporation for cryopreservation of two types of human mesenchymal stromal cells was investigated: adipose-derived stromal cells, and umbilical-cord-derived stromal cells. Comparable results to standard dimethyl sulfoxide cryopreservation protocols were achieved, even without extensive electroporation parameters and protocol optimization. The presence of high extracellular trehalose resulted in comparable cell viabilities without and with electroporation. According to the determination of trehalose concentrations, 250 mM extracellular trehalose resulting in, 20 mM to 50 mM intracellular trehalose were sufficient for successful cryopreservation of cells. With electroporation, higher (i.e. 50 mM to 90 mM) intracellular trehalose was achieved after cryopreservation, although cell survival was not improved significantly. To evaluate the impact of electroporation and cryopreservation on cells, stress and immune-activation-related gene expression were analyzed. Electroporation and/or cryopreservation resulted in increased SOD2 and HSPA1A expression. Despite the increased stress response, the high up-regulation by mesenchymal stromal cells of immunomodulatory genes in the inflammatory environment was not affected. Highest expression was seen for the IDO1 and TSG6 genes. In conclusion, cryopreservation of mesenchymal stromal cells in trehalose results in comparable characteristics to their cryopreservation using dimethyl sulfoxide.

Oocyte vitrification induces loss of DNA methylation and histone acetylation in the resulting embryos derived using ICSI in dromedary camel

Oocyte cryopreservation has become an important component of assisted reproductive technology with increasing implication in female fertility preservation and animal reproduction. However, the possible adverse effects of oocyte cryopreservation on epigenetic status of the resulting embryos is still an open question. This study evaluated the effects of MII-oocyte vitrification on gene transcripts linked to epigenetic reprogramming in association with the developmental competence and epigenetic status of the resulting embryos at 2-cell and blastocyst stages in dromedary camel. The cleavage rate of vitrified oocytes following intracytoplasmic sperm injection was significantly increased compared with the control (98.2 ± 2 vs. 72.7 ± 4.1%, respectively), possibly due to the higher susceptibility of vitrified oocytes to spontaneous activation. Nonetheless, the competence of cleaved embryos derived from vitrified oocytes for development to the blastocyst and hatched blastocyst was significantly reduced compared with the control (7.7 ± 1.2 and 11.1 ± 11.1 compared with 28.1 ± 2.6 and 52.4 ± 9.9%, respectively). The relative transcript abundances of epigenetic reprogramming genes DNMT1, DNMT3B, HDAC1, and SUV39H1 were all significantly reduced in vitrified oocytes relative to the control. Evaluation of the epigenetic marks showed significant reductions in the levels of DNA methylation (6.1 ± 0.3 vs. 9.9 ± 0.5, respectively) and H3K9 acetylation (7.8 ± 0.2 vs. 10.7 ± 0.3, respectively) in 2-cell embryos in the vitrification group relative to the control. Development to the blastocyst stage partially adjusted the effects that oocyte vitrification had on the epigenetic status of embryos (DNA methylation: 4.9 ± 0.4 vs. 6.2 ± 0.6; H3K9 acetylation: 5.8 ± 0.3 vs. 8 ± 0.9, respectively). To conclude, oocyte vitrification may interfere with the critical stages of epigenetic reprogramming during preimplantation embryo development.

Cryopreservation of equine oocytes: looking into the crystal ball

Invitro embryo production has evolved rapidly in the horse over the past decade, but blastocyst rates from vitrified equine oocytes remain quite poor and further research is needed to warrant application. Oocyte vitrification is affected by several technical and biological factors. In the horse, short exposure of immature oocytes to the combination of permeating and non-permeating cryoprotective agents has been associated with the best results so far. High cooling and warming rates are also crucial and can be obtained by using minimal volumes and open cryodevices. Vitrification of invivo-matured oocytes has yielded better results, but is less practical. The presence of the corona radiata seems to partially protect those factors that are necessary for the construction of the normal spindle and for chromosome alignment, but multiple layers of cumulus cells may impair permeation of cryoprotective agents. In addition to the spindle, the oolemma and mitochondria are also particularly sensitive to vitrification damage, which should be minimised in future vitrification procedures. This review presents promising protocols and novel strategies in equine oocyte vitrification, with a focus on blastocyst development and foal production as most reliable outcome parameters.

Cryoprotectant toxicity and hypothermic sensitivity among Anopheles larvae

Laboratory rearing of mosquitoes is commonly practiced by researchers studying mosquito-borne infectious diseases and vector control methods. In the absence of cryopreservation methods to stabilize unique or genetically modified strains, mosquito lines must be continuously maintained, a laborious process that risks selection effects, contamination, and genetic drift. Towards the development of a cryopreservation protocol, several commonly used cryoprotectants were systematically characterized here both individually and as cocktails. Among first instar, feeding-stage An. gambiae and An. stephensi larvae, cryoprotectant toxicity followed the order of dimethyl sulfoxide > ethylene glycol > methanol. The resulting LD₅₀ values were used as the basis for the development of cryoprotectant cocktail solutions, where formulation optimization was streamlined using Taguchi methods of experimental design. Sensitivity to hypothermia was further evaluated to determine the feasibility of cryoprotectant loading at reduced temperatures and slow cooling approaches to cryopreservation. The information described here contributes to the knowledge base necessary to inform the development of a cryopreservation protocol for Anopheles larvae.

Probing lasting cryoinjuries to oocyte-embryo transcriptome

Clinical applications of oocytes cryopreservation include preservation of future fertility of young cancer patients, substitution of embryo freezing to avoid associated legal and ethical issues, and delaying childbearing years. While the outcome of oocyte cryopreservation has recently been improved, currently used vitrification method still suffer from increased biosafety risk and handling issues while slow freezing techniques yield overall low success. Understanding better the mechanism of cryopreservation-induced injuries may lead to development of more reliable and safe methods for oocyte cryopreservation. Using the mouse model, a microarray study was conducted on oocyte cryopreservation to identify cryoinjuries to transcriptionally active genome. To this end, metaphase II (MII) oocytes were subjected to standard slow freezing, and then analyzed at the four-cell stage after embryonic genome activation. Non-frozen four-cell embryos served as controls. Differentially expressed genes were identified and validated using RT-PCR. Embryos produced from the cryopreserved oocytes displayed 200 upregulated and 105 downregulated genes, associated with the regulation of mitochondrial function, protein ubiquitination and maintenance, cellular response to stress and oxidative states, fatty acid and lipid regulation/metabolism, and cell cycle maintenance. These findings reveal previously unrecognized effects of standard slow oocyte freezing on embryonic gene expression, which can be used to guide improvement of oocyte cryopreservation methods.

Effect of Equilibration Time and Temperature on Murine Spermatogonial Stem Cell Cryopreservation

Cryopreservation of spermatogonial stem cells (SSCs) is essential for preservation of valuable livestock and clinical applications. Although optimal equilibration of cryoprotectants has emerged as a promising approach to improve the cryopreservation efficiency, standard equilibration protocols have not yet been considered in cryopreservation of SSCs. This study aimed to establish a standard equilibration protocol to improve the cryopreservation efficiency of murine germ cells enriched for SSCs. After time- and temperature-dependent equilibration, the germ cells were cryopreserved with 10% dimethyl sulfoxide (DMSO) and 200 mM trehalose. To investigate cryopreservation efficiency at different equilibration conditions, the survival and proliferation rates were assessed after thawing, and then, cytotoxicity and intracellular trehalose quantification were analyzed. Protein (PLZF, GFRα1, VASA, and c-Kit) and gene (Bcl6b, Erm, Dazl, and Sycp1) expression was determined using immunofluorescence and real-time quantitative polymerase chain reaction (RT-qPCR), respectively. The proliferation rate increased significantly following equilibration for 20 minutes at room temperature (RT; 163.7% ± 24.6%) or 4°C (269.0% ± 18.2%). Cytotoxicity was reduced in 10% DMSO with 200 mM trehalose compared with that of 10% DMSO alone. Also, intracellular trehalose was observed after equilibration. The immunofluorescence and RT-qPCR data revealed that the murine germ cells enriched for SSCs retained their self-renewal ability after cryopreservation following equilibration. The most effective protocol was equilibration with 10% DMSO and 200 mM trehalose for 20 minutes at RT or 4°C, which is due to synergistic effects of intracellular and extracellular trehalose. This improved methodology will contribute toward the development of a standardized freezing protocol for murine germ cells enriched for SSCs and thereby expand their application in various fields.

Freeze-Dried Extracellular Vesicles From Adipose-Derived Stem Cells Prevent Hypoxia-Induced Muscle Cell Injury

Cellular therapies have tremendous potential for the successful treatment of major extremity wounds in the combat setting, however, the challenges associated with transplanting stem cells in the prolonged field care (PFC) environment are a critical barrier to progress in treating such injuries. These challenges include not only production and storage but also transport and handling issues. Our goal is to develop a new strategy utilizing extracellular vesicles (EVs) secreted by stem cells that can resolve many of these issues and prevent ischemic tissue injury. While EVs can be preserved by freezing or lyophilization, both processes result in decrease in their bioactivity. Here, we describe optimized procedures for EVs production, isolation, and lyophilization from primary human adipose-derived stem cells (hADSCs). We compared two isolation approaches that were ultrafiltration (UF) using a tangential fluid filtration (TFF) system and differential ultracentrifugation (UC). We also optimized EVs lyophilization in conjunction with trehalose and polyvinylpyrrolidone 40 (PVP40) as lyoprotectants. Bioactivity of EVs was assessed based on reversal of hypoxia-induced muscle cell injury. To this end, primary human myoblasts were subjected to hypoxic conditions for 6 h, and then treated with hADSC-derived EVs at a concentration of 50 μg/mL. Subsequently, muscle cell viability and toxicity were evaluated using MTS and LDH assays, respectively. Overall, nanoparticle tracking data indicated that UF/TFF yields threefold more particles than UC. Lyophilization of EVs resulted in a significantly reduced number of particles, which could be attenuated by adding lyoprotections to the freeze-drying solution. Furthermore, EVs isolated by UF/TFF and freeze-dried in the presence of trehalose significantly increased viability (P < 0.0193). Taken together, our findings suggest that the isolation and preservation methods presented in this study may enhance therapeutic applications of EVs.

Effects of Me2SO and Trehalose on the Cell Viability, Proliferation, and Bcl-2 Family Gene (BCL-2, BAX, and BAD) Expression in Cryopreserved Human Breast Cancer Cells

Long-term cryopreservation of the viability and metabolic state of cells in cancer cell/tissue specimens has significant implications for diagnostic verification of disease progression in cancer patients and selection of effective treatment options via development of the patient-derived xenograft (PDX) models for drug screening. The purpose of this study is to investigate the effects of cryoprotectant agents (CPAs) on the expression of BCL-2 family genes (BCL-2, BAX, and BAD) that are involved in the growth and development of breast cancers. MCF-7 cells were cryopreserved in Dulbecco's modified Eagle's medium (DMEM) with 20% (v/v) fetal bovine serum, using 10% (v/v) Me₂SO (dimethyl sulfoxide, DMSO) or 7.5% (v/v) Me₂SO with 100is-300 mM trehalose as cryoprotectant solutions. After storage at -80°C for 7 days, the cells were thawed for evaluation. The use of Me₂SO and trehalose has affected cell survival, proliferation, apoptotic state, as well as BCL-2 family gene expression. The conventional 10% (v/v) Me₂SO method yields ∼80% post-thaw cell survival and good cell proliferation, but it drastically alters the pattern of the BCL-2 family gene expression. The antiapoptotic gene BCL-2 is downregulated, whereas two proapoptotic genes BAX and BAD are upregulated. The partial substitution of Me₂SO with 200 or 300 mM trehalose enhances cell proliferation of survived cells after cryopreservation. The presence of trehalose upregulates the expression of both the antiapoptotic gene BCL-2 and proapoptotic genes BAX and BAD. Cryopreservation could tip off the checkpoint of the apoptotic pathway regulated by the BCL-2 family members, and the effect may be protectant dependent. The findings of this study demonstrate the importance of paying attention to the potential change of gene expression and metabolic state of cancer cells after cryopreservation in an attempt to development of the PDX models from cryopreserved cancer cells or tissue specimens.

Intracellular Delivery of Trehalose for Cell Banking

Advances in stem cell technology and regenerative medicine have underscored the need for effective banking of living cells. Cryopreservation, using very low temperatures to achieve suspended animation, is widely used to store or bank cells for later use. This process requires the use of cryoprotective agents (CPAs) to protect cells against damage caused by the cooling and warming process. However, current popular CPAs like DMSO can be toxic to cells and must be thoroughly removed from cells before they can be used for research or clinical applications. Trehalose, a nontoxic sugar found in organisms capable of withstanding extreme cold or desiccation, has been explored as an alternative CPA. The disaccharide must be present on both sides of the cellular membrane to provide cryo-protection. However, trehalose is not synthesized by mammalian cells nor has the capability to diffuse through their plasma membranes. Therefore, it is crucial to achieve intracellular delivery of trehalose for utilizing the full potential of the sugar for cell banking. In this review, various methods that have been explored to deliver trehalose into mammalian cells for their banking at both cryogenic and ambient temperatures are surveyed. Among them, the nanoparticle-mediated approach is particularly exciting. Collectively, studies in the literature demonstrate the great potential of using trehalose as the sole CPA for cell banking, to facilitate the widespread use of living cells in modern medicine.

Amphibian Assisted Reproductive Technologies: Moving from Technology to Application

Amphibians have experienced a catastrophic decline since the 1980s driven by disease, habitat loss, and impacts of invasive species and face ongoing threats from climate change. About 40% of extant amphibians are under threat of extinction and about 200 species have disappeared completely. Reproductive technologies and biobanking of cryopreserved materials offer technologies that could increase the efficiency and effectiveness of conservation programs involving management of captive breeding and wild populations through reduced costs, better genetic management and reduced risk of species extinctions. However, there are relatively few examples of applications of these technologies in practice in on-the-ground conservation programs, and no example that we know of where genetic diversity has been restored to a threatened amphibian species in captive breeding or in wild populations using cryopreserved genetic material. This gap in the application of technology to conservation programs needs to be addressed if assisted reproductive technologies (ARTs) and biobanking are to realise their potential in amphibian conservation. We review successful technologies including non-invasive gamete collection, IVF and sperm cryopreservation that work well enough to be applied to many current conservation programs. We consider new advances in technology (vitrification and laser warming) of cryopreservation of aquatic embryos of fish and some marine invertebrates that may help us to overcome factors limiting amphibian oocyte and embryo cryopreservation. Finally, we address two case studies that illustrate the urgent need and the opportunity to implement immediately ARTs, cryopreservation and biobanking to amphibian conservation. These are (1) managing the biosecurity (disease risk) of the frogs of New Guinea which are currently free of chytridiomycosis, but are at high risk (2) the Sehuencas water frog of Bolivia, which until recently had only one known surviving male.

Effect of different penetrating and non-penetrating cryoprotectants and media temperature on the cryosurvival of vitrified in vitro produced porcine blastocysts

The aim of this study was to determine the most efficient vitrification protocol for the cryopreservation of day 7 in vitro produced (IVP) porcine blastocysts. The post-warm survival rate of blastocysts vitrified in control (17% dimethyl sulfoxide + 17% ethylene glycol [EG] + 0.4 mol/L sucrose) and commercial media did not differ, nor did the post-warm survival rate of blastocysts vitrified in medium containing 1,2-propandiol in place of EG. However, vitrifying embryos in EG alone decreased the cryosurvival rate (55.6% and 33.6%, respectively, p < .05). Furthermore, the post-warm survival rates of blastocysts vitrified with either trehalose or sucrose as the non-penetrating cryoprotectant did not differ. There was also no significant difference in post-warm survival of blastocysts vitrified in control (38°C) media and room temperature (22°C) media with extended equilibration times, although when blastocysts were vitrified using control media at room temperature, the post-warm survival rate increased (56.8%, 57.3%, 72.5%, respectively, p < .05). The findings show that most cryoprotectant combinations examined proved equally effective at supporting the post-warm survival of IVP porcine blastocysts. The improved post-warm survival rate of blastocysts vitrified using media held at room temperature suggests that the cryoprotectant toxicity exerted in 22°C media was reduced.

Developmental competence of in vitro matured ovine oocytes vitrified in solutions with different concentrations of trehalose

This study aimed to determine the optimum concentration of trehalose in solutions used for vitrification of in vitro matured (IVM) ovine oocytes. IVM oocytes were randomly divided into four experimental (vitrified) and one control (fresh) groups. Experimental groups were treated with different concentrations (0.0, 0.25, 0.5 and 1.0 M) of trehalose. After warming, some viable oocytes were exposed to 0.25% pronase to test zona pellucida hardening, whereas the others were fertilized and cultured in vitro for 8 days to evaluate their developmental competence. Blastocysts quality was assessed by differential staining and TUNEL test. Survival and developmental rates of oocytes vitrified in the presence of 0.5 M trehalose were significantly higher than those of the other vitrified groups. Furthermore, there was a significant difference between fresh and vitrified groups in total blastocyst rate. Analysis of blastocysts quality also revealed a significant difference between the group treated with 0.5 M trehalose and other groups in terms of apoptotic index. Furthermore,zona pellucida digestion time period was longer in trehalose-free (0.0 M) group compared to other groups. In conclusion, we found that IVM ovine oocytes vitrified in solutions containing 0.5 M trehalose are fertilization-competent and are able to produce good-quality blastocysts with an apoptotic index comparable to that of the fresh oocytes. Therefore, 0.5 M may be considered the optimum concentration of trehalose to be used in solutions prepared for vitrification of oocytes.

A study of cryogenic tissue-engineered liver slices in calcium alginate gel for drug testing

To address issues such as transportation and the time-consuming nature of tissue-engineered liver for use as an effective drug metabolism and toxicity testing model, "ready-to-use" cryogenic tissue-engineered liver needs to be studied. The research developed a cryogenic tissue-engineered liver slice (TELS), which comprised of HepG2 cells and calcium alginate gel. Cell viability and liver-specific functions were examined after different cryopreservation and recovery culture times. Then, cryogenic TELSs were used as a drug-testing model and treated with Gefitinib. Cryogenic TELSs were stored at -80 °C to ensure high cell viability. During recovery in culture, the cells in the cryogenic TELS were evenly distributed, massively proliferated, and then formed spheroid-like aggregates from day 1 to day 13. The liver-specific functions in the cryogenic TELS were closely related to cryopreservation time and cell proliferation. As a reproducible drug-testing model, the cryogenic TELS showed an obvious drug reaction after treatment with the Gefitinib. The present study shows that the cryopreservation techniques can be used in drug-testing models.

Effect of water content on the glass transition temperature of mixtures of sugars, polymers, and penetrating cryoprotectants in physiological buffer

Long-term storage of viable mammalian cells is important for applications ranging from in vitro fertilization to cell therapy. Cryopreservation is currently the most common approach, but storage in liquid nitrogen is relatively costly and the requirement for low temperatures during shipping is inconvenient. Desiccation is an alternative strategy with the potential to enable viable cell preservation at more convenient storage temperatures without the need for liquid nitrogen. To achieve stability during storage in the dried state it is necessary to remove enough water that the remaining matrix forms a non-crystalline glassy solid. Thus, the glass transition temperature is a key parameter for design of cell desiccation procedures. In this study, we have investigated the effects of moisture content on the glass transition temperature (T_g) of mixtures of sugars (trehalose or raffinose), polymers (polyvinylpyrrolidone or Ficoll), penetrating cryoprotectants (ethylene glycol, propylene glycol, or dimethyl sulfoxide), and phosphate buffered saline (PBS) solutes. Aqueous solutions were dried to different moisture contents by equilibration with saturated salt solutions, or by baking at 95°C. The glass transition temperatures of the dehydrated samples were then measured by differential scanning calorimetry. As expected, T_g increased with decreasing moisture content. For example, in a desiccation medium containing 0.1 M trehalose in PBS, T_g ranged from about 360 K for a completely dry sample to about 220 K at a water mass fraction of 0.4. Addition of polymers to the solutions increased T_g, while addition of penetrating cryoprotectants decreased T_g. Our results provide insight into the relationship between relative humidity, moisture content and glass transition temperature for cell desiccation solutions containing sugars, polymers and penetrating cryoprotectants.

Successful vitrification of pronuclear-stage pig embryos with a novel cryoprotective agent, carboxylated ε-poly-L-lysine

Vitrification is a powerful tool for the efficient production of offspring derived from cryopreserved oocytes or embryos in mammalian species including domestic animals. Genome editing technologies such as transcription activator-like effector nucleases (TALENs) and clustered regularly interspaced short palindromic repeats (CRISPR)/ CRISPR-associated (Cas)9 are now available even for domestic species, suggesting that the vitrification of embryos at the pronuclear stage (PN) will be more important because they could provide genomic host cells to be targeted by TALENs or CRISPR/Cas9. Although we reported the successful production of piglets derived from vitrified PN embryos by a solid-surface vitrification method with glutathione supplementation, further improvements are required. The cryoprotective agent (CPA) carboxylated ε-poly-L-lysine (COOH-PLL) was introduced in 2009. COOH-PLL reduces the physical and physiological damage caused by cryopreservation in mammalian stem cells and the vitrification of mouse oocytes and embryos. Those results suggested that vitrification of COOH-PLL may help improve the developmental ability of pig embryos vitrified at the PN stage. However, it remains unclear whether COOH-PLL is available as a CPA for the vitrification of embryos in domestic species. In this study, we evaluated COOH-PLL as a CPA with ethylene glycol (EG) and Cryotop as a device for the vitrification of PN pig embryos. Exposure to vitrification solution supplemented with COOH-PLL up to 30% did not decrease developmental ability to the 2-cell stage and the blastocyst stage. After warming, most of the vitrified embryos survived regardless of the concentration of COOH-PLL (76.0 ± 11.8% to 91.8 ± 4.6%). However, the vitrified embryos without COOH-PLL showed a lower development rate up to the blastocyst stage (1.3 ± 1.0%) compared to the fresh embryos (28.4 ± 5.0%) (p<0.05). In contrast, supplementation of 20% (w/v) COOH-PLL in the vitrification solution dramatically improved the developmental ability to blastocysts of the vitrified embryos (19.4 ± 4.6%) compared to those without COOH-PLL (p<0.05). After the transfer of embryos vitrified with 30% (v/v) EG and 20% (w/v) COOH-PLL, we successfully obtained 15 piglets from 8 recipients. Taken together, our present findings demonstrate for the first time that COOH-PLL is an effective CPA for embryo vitrification in the pig. COOH-PLL is a promising CPA for further improvements in the vitrification of oocytes and embryos in mammalian species.

Impact of alginate concentration on the viability, cryostorage, and angiogenic activity of encapsulated fibroblasts

Cryopreservation or cryostorage of tissue engineered constructs can enhance the off-the shelf availability of these products and thus can potentially facilitate the commercialization or clinical translation of tissue engineered products. Encapsulation of cells within hydrogel matrices, in particular alginate, is widely used for fabrication of tissue engineered constructs. While previous studies have explored the cryopreservation response of cells encapsulated within alginate matrices, systematic investigation of the impact of alginate concentration on the metabolic activity and functionality of cryopreserved cells is lacking. The objective of the present work is to determine the metabolic and angiogenic activity of cryopreserved human dermal fibroblasts encapsulated within 1.0%, 1.5% and 2.0% (w/v) alginate matrices. In addition, the goal is to compare the efficacy of dimethyl sulfoxide (DMSO) and trehalose as cryoprotectant. Our study revealed that the concentration of alginate plays a significant role in the cryopreservation response of encapsulated cells. The lowest metabolic activity of the cryopreserved cells was observed in 1% alginate microspheres. When higher concentration of alginate was utilized for cell encapsulation, the metabolic and angiogenic activity of the cells frozen in the absence of cryoprotectants was comparable to that observed in the presence of DMSO or trehalose.

Chemically Defined and Xeno-Free Cryopreservation of Human Adipose-Derived Stem Cells

The stromal compartment of adipose tissue harbors multipotent cells known as adipose-derived stem cells (ASCs). These cells can differentiate into various lineages including osteogenic, chrondrogenic, adipogenic, and neurogenic; this cellular fraction may be easily obtained in large quantities through a clinically safe liposuction procedure. Therefore, ASCs offer exceptional opportunities for tissue engineering and regenerative medicine. However, current practices involving ASCs typically use fetal bovine serum (FBS)-based cryopreservation solutions that are associated with risks of immunological reactions and of transmitting infectious diseases and prions. To realize clinical applications of ASCs, serum- and xeno-free defined cryopreservation methods are needed. To this end, an animal product-free chemically defined cryopreservation medium was formulated by adding two antioxidants (reduced glutathione and ascorbic acid 2-phosphate), two polymers (PVA and ficoll), two permeating cryoprotectants (ethylene glycol and dimethylsulfoxide), a disaccharide (trehalose), and a calcium chelator (EGTA) to HEPES-buffered DMEM/F12. To limit the number of experimental groups, the concentration of trehalose, both polymers, and EGTA was fixed while the presence of the permeating CPAs and antioxidants was varied. ASCs suspended either in different versions of the defined medium or in the conventional undefined cryopreservation medium (10% dimethylsulfoxide+10% DMEM/F12+80% serum) were cooled to -70°C at 1°C/min before being plunged into liquid nitrogen. Samples were thawed either in air or in a water bath at 37°C. The presence of antioxidants along with 3.5% concentration of each penetrating cryoprotectant improved the freezing outcome to the level of the undefined cryopreservation medium, but the plating efficiency was still lower than that of unfrozen controls. Subsequently, increasing the concentration of both permeating cryoprotectants to 5% further improved the plating efficiency to the level of unfrozen controls. Moreover, ASCs cryopreserved in this defined medium retained their multipotency and chromosomal normality. These results are of significance for tissue engineering and clinical applications of stem cells.

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.

A combination of hydroxypropyl cellulose and trehalose as supplementation for vitrification of human oocytes: a retrospective cohort study

PURPOSE

This study aimed to determine whether the new formulation of vitrification solutions containing a combination of hydroxypropyl cellulose (HPC) and trehalose does not affect outcomes in comparison with using conventional solutions made of serum substitute supplement (SSS) and sucrose.

METHODS

Ovum donation cycles were retrospectively compared regarding the solution used for vitrification and warming of human oocytes. The analysis included 218 cycles (N = 2532 oocytes) in the study group (HPC + trehalose) and 214 cycles (N = 2353 oocytes) in the control group (SSS + sucrose).

RESULTS

No statistical differences were found in ovarian stimulation parameters and baseline characteristics of donors and recipients. The survival rate was 91.3% (95% confidence interval (CI) = 89.8-92.9) in the HPC + trehalose group vs. 92.1% (95% CI = 90.4-93.7) in the SSS + sucrose group (NS). The implantation rate (42.8%, 95% CI = 37.7-47.9 vs. 41.2%, 95% CI = 36.0-46.4), clinical pregnancy rate (CPR) per transfer (60.7%, 95% CI = 53.9-67.5 vs. 56.4%, 95% CI = 49.3-63.5), and ongoing pregnancy rate (OPR) per transfer (48.5%, 95% CI = 41.5-55.5 vs. 46.3%, 95% CI = 39.2-53.4) were similar for patients who received either HPC + trehalose-vitrified oocytes or SSS + sucrose-vitrified oocytes. Statistical differences were found when analyzing blastocyst rate both per injected oocyte (30.2%, 95% CI = 28.3-32.1 vs. 24.1%, 95% CI = 22.3-25.9) and per fertilized oocyte (40.8%, 95%CI = 38.5-43.1 vs. 33.2%, 95% CI = 30.8-35.5) (P < 0.0001). Delivery rate was comparable between groups (37.2%, 95% CI = 30.8-46.6 vs. 36.9%, 95% CI = 30.4-43.4; NS).

CONCLUSIONS

Our data demonstrate that HPC and trehalose are suitable and safe substitutes for serum and sucrose. Therefore, the new commercial media can be used efficiently in the vitrification of human oocytes avoiding viral and endotoxin contamination risk.

Cryoprotectant Toxicity: Facts, Issues, and Questions

High levels of penetrating cryoprotectants (CPAs) can eliminate ice formation during cryopreservation of cells, tissues, and organs to cryogenic temperatures. But CPAs become increasingly toxic as concentration increases. Many strategies have been attempted to overcome the problem of eliminating ice while minimizing toxicity, such as attempting to optimize cooling and warming rates, or attempting to optimize time of adding individual CPAs during cooling. Because strategies currently used are not adequate, CPA toxicity remains the greatest obstacle to cryopreservation. CPA toxicity stands in the way of cryogenic cryopreservation of human organs, a procedure that has the potential to save many lives. This review attempts to describe what is known about CPA toxicity, theories of CPA toxicity, and strategies to reduce CPA toxicity. Critical analysis and suggestions are also included.

Successful cryopreservation of whole sheep ovary by using DMSO-free cryoprotectant

PURPOSE

The study aims to assess the protective effects of dimethyl sulfoxide (DMSO)-free solution based on trehalose on the cryopreservation of a whole sheep ovary and evaluate its use as an efficient cryoprotectant.

METHOD

Twenty-one ovaries collected from 6- to 8-month-old non-pregnant female sheep were randomly distributed into three groups, namely, a fresh group, a DMSO-free group, and a DMSO group. The morphology, cell apoptosis (by hematoxylin and eosin (HE) staining and terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling (TUNEL) assay), and mRNA transcript of Bcl-2-associated X protein (BAX) and cold inducible RNA-binding protein (CIRP) (by real-time PCR) of the thawed sheep ovaries and fresh controls were tested to establish a criterion for appraising the results of the cryopreservation.

RESULTS

(i) The histological assessment indicated that the structure of the DMSO-free ovaries remained largely intact and comparable to those of the fresh control groups; whereas, significant damage was observed in the ovaries of the DMSO group (P < 0.05). (ii) The TUNEL assay and mRNA transcript of the BAX assessment showed that the apoptosis parameter in the fresh group was the lowest among all the groups (P < 0.05), and the parameter in the DMSO-free group was significantly lower than that in the DMSO group (P < 0.05). (iii) The level of the CIRP transcripts increased the most in the DMSO-free group followed by the DMSO group and the fresh control group (P < 0.05).

CONCLUSIONS

These results indicate that a DMSO-free cryoprotectant solution, especially a trehalose cryoprotectant, is an efficient cryoprotectant and has a beneficial effect on the cryopreservation of whole sheep ovaries.

Freezing tolerance of sea urchin embryonic cells: Differentiation commitment and cytoskeletal disturbances in culture

This study focuses on the freezing tolerance of sea urchin embryonic cells. To significantly reduce the loss of physiological activity of these cells that occurs after cryopreservation and to study the effects of ultra-low temperatures on sea urchin embryonic cells, we tested the ability of the cells to differentiate into spiculogenic or pigment directions in culture, including an evaluation of the expression of some genes involved in pigment differentiation. A morphological analysis of cytoskeletal disturbances after freezing in a combination of penetrating (dimethyl sulfoxide and ethylene glycol) and non-penetrating (trehalose and polyvinylpyrrolidone) cryoprotectants revealed that the distribution pattern of filamentous actin and tubulin was similar to that in the control cultures. In contrast, very rare spreading cells and a small number of cells with filamentous actin and tubulin were detected after freezing in the presence of only non-penetrating cryoprotectants. The largest number of pigment cells was found in cultures frozen with trehalose or trehalose and dimethyl sulfoxide. The ability to induce the spicule formation was lost in the cells frozen only with non-penetrating cryoprotectants, while it was maximal in cultures frozen in a cryoprotective mixture containing both non-penetrating and penetrating cryoprotectants (particularly, when ethylene glycol was present). Using different markers for cell state assessment, an effective cryopreservation protocol for sea urchin cells was developed: three-step freezing with a low cooling rate (1-2°C/min) and a combination of non-penetrating and penetrating cryoprotectants made it possible to obtain a high level of cell viability (up to 65-80%).

An essential role for heat shock transcription factor binding protein 1 (HSBP1) during early embryonic development

Heat shock factor binding protein 1 (HSBP1) is a 76 amino acid polypeptide that contains two arrays of hydrophobic heptad repeats and was originally identified through its interaction with the oligomerization domain of heat shock factor 1 (Hsf1), suppressing Hsf1's transcriptional activity following stress. To examine the function of HSBP1 in vivo, we generated mice with targeted disruption of the hsbp1 gene and examined zebrafish embryos treated with HSBP1-specific morpholino oligonucleotides. Our results show that hsbp1 is critical for preimplantation embryonic development. Embryonic stem (ES) cells deficient in hsbp1 survive and proliferate normally into the neural lineage in vitro; however, lack of hsbp1 in embryoid bodies (EBs) leads to disorganization of the germ layers and a reduction in the endoderm-specific markers (such as α-fetoprotein). We further show that hsbp1-deficient mouse EBs and knockdown of HSBP1 in zebrafish leads to an increase in the expression of the neural crest inducers Snail2, Tfap2α and Foxd3, suggesting a potential role for HSBP1 in the Wnt pathway. The hsbp1-deficient ES cells, EBs and zebrafish embryos with reduced HSBP1 levels exhibit elevated levels of Hsf1 activity and expression of heat shock proteins (Hsps). We conclude that HSBP1 plays an essential role during early mouse and zebrafish embryonic development.

Optimization of cryoprotectant loading into murine and human oocytes

Loading of cryoprotectants into oocytes is an important step of the cryopreservation process, in which the cells are exposed to potentially damaging osmotic stresses and chemical toxicity. Thus, we investigated the use of physics-based mathematical optimization to guide design of cryoprotectant loading methods for mouse and human oocytes. We first examined loading of 1.5 M dimethyl sulfoxide (Me(2)SO) into mouse oocytes at 23°C. Conventional one-step loading resulted in rates of fertilization (34%) and embryonic development (60%) that were significantly lower than those of untreated controls (95% and 94%, respectively). In contrast, the mathematically optimized two-step method yielded much higher rates of fertilization (85%) and development (87%). To examine the causes for oocyte damage, we performed experiments to separate the effects of cell shrinkage and Me(2)SO exposure time, revealing that neither shrinkage nor Me(2)SO exposure single-handedly impairs the fertilization and development rates. Thus, damage during one-step Me(2)SO addition appears to result from interactions between the effects of Me(2)SO toxicity and osmotic stress. We also investigated Me(2)SO loading into mouse oocytes at 30°C. At this temperature, fertilization rates were again lower after one-step loading (8%) in comparison to mathematically optimized two-step loading (86%) and untreated controls (96%). Furthermore, our computer algorithm generated an effective strategy for reducing Me(2)SO exposure time, using hypotonic diluents for cryoprotectant solutions. With this technique, 1.5 M Me(2)SO was successfully loaded in only 2.5 min, with 92% fertilizability. Based on these promising results, we propose new methods to load cryoprotectants into human oocytes, designed using our mathematical optimization approach.

Oocyte cryopreservation: searching for novel improvement strategies

PURPOSE

To highlight emerging techniques aimed at improving oocyte cryopreservation.

METHODS

Review of available and relevant literature through Pubmed and Medline searches.

RESULTS

Oocyte cryopreservation is an increasingly common procedure utilized for assisted reproduction and may benefit several patient populations. Therefore, improving efficiency is paramount in realizing the tremendous promise of this approach. However, in addition to numerous studies looking to improve oocyte cryopreservation efficacy via examination of variables involved with protocol methodology, such as type/concentration of cryoprotectant (CPA), type of storage device, or cooling/warming rates, there are more novel approaches for improvement. These alternate approaches include utilizing different the stages of oocytes, examining alteration of basal media and buffer composition, optimizing CPA exchange protocols and device loading through use of automated technology, as well as examination/manipulation of oocyte cellular composition to improve cryotolerance. Finally, elucidating more accurate or insightful indicators of "success" is crucial for continued improvement of oocyte cryopreservation.

CONCLUSION

Oocyte cryopreservation has improved dramatically in recent years and is receiving widespread clinical use. Novel approaches to further improve success, as well as improved methods to assess this success will aid in continued improvement.

Retention of structure and function of the cat germinal vesicle after air-drying and storage at suprazero temperature

The study explored a novel approach for preserving the maternal genome without the entire oocyte by air-drying the cat germinal vesicle (GV) in the presence of the disaccharide trehalose. Specifically, we examined GV structure and function after desiccation, storage at 4 °C (up to 32 wk), and rehydration including the ability to resume meiosis after injection into a fresh, conspecific cytoplast. In experiment 1, DNA integrity was similar to fresh controls after 1 and 4 wk storage in the presence of trehalose, but was more fragmented at later time points (especially after 32 wk). Nuclear envelope integrity was sustained in >90% of oocytes stored for 0, 4, or 16 wk regardless of protective treatment. In experiment 2, compacted, air-dried GVs were stored for 2 or 4 wk, rehydrated, and injected into fresh cytoplasts. After culture for 24 h in vitro, up to 73% of oocytes reconstructed with desiccated GVs preserved in trehalose resumed meiosis compared to 30% of those dried in the absence of the disaccharide. At each storage time point, trehalose presence during air-drying was advantageous for resumption of meiosis, with >20% of oocytes completing nuclear maturation to metaphase II. This demonstrates a potential for preserving the female genome using the GV alone and for multiple weeks after desiccation. Trehalose enhanced the process by retaining the ability of a dried and rehydrated GV to resume communication with the surrounding cytoplasm of the recipient oocyte to permit reaching metaphase II and likely sustain subsequent embryo development.

Mouse Oocytes and Embryos Cryotop-vitrification Using Low Concentrated Solutions: Effects on Meiotic Spindle, Genetic Material Array and Developmental Ability

OBJECTIVE(S)

The examination of the possibility of applying lower CPA- concentrations and obtaining the similar results to those using higher concentrations; as it is shown, the toxicity of the CPAs used in vitrification approach will diminish.

MATERIALS AND METHODS

Following vitrification/warming, oocytes were subjected to PZD/ICSI. SRs, FRs, and DRs were recorded. SRs and DRs of the embryos were monitored after vitrification/warming. IHC studies were done. Data were analyzed in comparison to the data of Exp. (experimental groups) applying 1.5 M CPA- concentrations (largely-used concentration).

RESULTS

The data of oocytes exposed to 1.25 M concentrated CPAs were in consistency with those exposed to 1.5 M and fresh oocytes in terms of SRs, FRs and DRs. Normal spindle and chromatin configuration is in consistence between the two experimental groups, but lower in comparison with control group. The lower the concentrations were, the less SRs, FRs, DRs were. Also, spindle organizations were more normal in comparison with the experimental groups as the concentrations decreased. The results of DRs for embryos which were exposed to 1.25 and 1.0 M concentrated CPAs were close to those vitrified with 1.5 M and fresh embryos but IHC observations in the three Exp. were significantly lower than those of fresh embryos. The results of 7.5 M concentrated CPAs solutions were significantly lower than those of the control group 1.5, 1.25 and 1.0 M treated.

CONCLUSIONS

Vitrification by cryotop technology using minimal volume approach increases both cooling and warming rates, therefore, the CPAs limited reduction to 1.25 and 1.0 M instead of using 1.5 M for oocytes and embryos cryotop-vitrification procedure, may be a slight adjustment.

Mouse Oocytes and Embryos Cryotop-vitrification Using Low Concentrated Solutions: Effects on Meiotic Spindle, Genetic Material Array and Developmental Ability

OBJECTIVE(S)

The examination of the possibility of applying lower CPA- concentrations and obtaining the similar results to those using higher concentrations; as it is shown, the toxicity of the CPAs used in vitrification approach will diminish.

MATERIALS AND METHODS

Following vitrification/warming, oocytes were subjected to PZD/ICSI. SRs, FRs, and DRs were recorded. SRs and DRs of the embryos were monitored after vitrification/warming. IHC studies were done. Data were analyzed in comparison to the data of Exp. (experimental groups) applying 1.5 M CPA- concentrations (largely-used concentration).

RESULTS

The data of oocytes exposed to 1.25 M concentrated CPAs were in consistency with those exposed to 1.5 M and fresh oocytes in terms of SRs, FRs and DRs. Normal spindle and chromatin configuration is in consistence between the two experimental groups, but lower in comparison with control group. The lower the concentrations were, the less SRs, FRs, DRs were. Also, spindle organizations were more normal in comparison with the experimental groups as the concentrations decreased. The results of DRs for embryos which were exposed to 1.25 and 1.0 M concentrated CPAs were close to those vitrified with 1.5 M and fresh embryos but IHC observations in the three Exp. were significantly lower than those of fresh embryos. The results of 7.5 M concentrated CPAs solutions were significantly lower than those of the control group 1.5, 1.25 and 1.0 M treated.

CONCLUSIONS

Vitrification by cryotop technology using minimal volume approach increases both cooling and warming rates, therefore, the CPAs limited reduction to 1.25 and 1.0 M instead of using 1.5 M for oocytes and embryos cryotop-vitrification procedure, may be a slight adjustment.

Generation of live offspring from vitrified mouse oocytes of C57BL/6J strain

In mammals, unfertilized oocytes are one of the most available stages for cryopreservation because the cryopreserved oocytes can be used for assisted reproductive technologies, including in vitro fertilization (IVF) and intracytoplasmic sperm injection. However, it has generally been reported that the fertility and developmental ability of the oocytes are reduced by cryopreservation. C57BL/6J mice, an inbred strain, are used extensively for the production of transgenic and knockout mice. If the oocytes from C57BL/6J mice can be successfully cryopreserved, the cryopreservation protocol used will contribute to the high-speed production of not only gene-modified mice but also hybrid mice. Very recently, we succeeded in the vitrification of mouse oocytes derived from ICR (outbred) mice. However, our protocol can be applied to the vitrification of oocytes from an inbred strain. The aim of the present study was to establish the vitrification of oocytes from C57BL/6J mice. First, the effect of cumulus cells on the ability of C57BL/6J mouse oocytes to fertilize and develop in vitro was examined. The fertility and developmental ability of oocyte-removed cumulus cells (i.e., denuded oocytes, or DOs) after IVF were reduced compared to cumulus oocyte complexes (COCs) in both fresh and cryopreserved groups. Vitrified COCs showed significantly (P<0.05) higher fertility and ability to develop into the 2-cell and blastocyst stages compared to the vitrified DOs with cumulus cells and vitrified DOs alone. The vitrified COCs developed to term at a high success rate, equivalent to the rate obtained with IVF using fresh COCs. Taken together, our results demonstrate that we succeeded for the first time in the vitrification of mouse oocytes from C57BL/6J mice. Our findings will also contribute to the improvement of oocyte vitrification not only in animals but also in clinical applications for human infertility.

Advancing the preservation of cellular therapy products

Cell therapies are typically collected in one location, processed in a second location, and then administered in a third location. The ability to preserve the cells is critical to their clinical application. It improves patient access to therapies by increasing the genetic diversity of cells available. In addition, the ability to preserve cells improves the "manufacturability" of a cell therapy product by permitting the cells to be stored until the patient is ready for administration of the therapy, permitting inventory control of products, and improving management of staffing at cell therapy facilities. Finally, the ability to preserve cell therapies improves the safety of cell therapy products by extending the shelf life of a product and permitting completion of safety and quality control testing before release of the product for use. The support of the National Blood Foundation has been critical to our work on improving the quality of frozen and thawed cell therapy products through the development of a microfluidic device to remove dimethlysulfoxide (DMSO). We are also involved in research to replace DMSO with other agents that are less toxic to cells and patients. Finally, the need to advance the preservation of cell therapies was a driving force behind the development of the Biopreservation Core Resource (http://www.biocor.net), a national resource in biopreservation. New interest in translation of cell therapies from the bench to the patient's bedside has the potential to drive the transformation of preservation science, technology, and practice.

Comparison and avoidance of toxicity of penetrating cryoprotectants

The objective of this study was to elucidate the toxicity of widely used penetrating cryoprotective agents (CPAs) to mammalian oocytes. To this end, mouse metaphase II (M II) oocytes were exposed to 1.5 M solutions of dimethylsulfoxide (DMSO), ethylene glycol (EG), or propanediol (PROH) prepared in phosphate buffered saline (PBS) containing 10% fetal bovine serum. To address the time- and temperature-dependence of the CPA toxicity, M II oocytes were exposed to the aforementioned CPAs at room temperature (RT, ∼23°C) and 37°C for 15 or 30 minutes. Subsequently, the toxicity of each CPA was evaluated by examining post-exposure survival, fertilization, embryonic development, chromosomal abnormalities, and parthenogenetic activation of treated oocytes. Untreated oocytes served as controls. Exposure of MII oocytes to 1.5 M DMSO or 1.5 M EG at RT for 15 min did not adversely affect any of the evaluated criteria. In contrast, 1.5 M PROH induced a significant increase in oocyte degeneration (54.2%) and parthenogenetic activation (16%) under same conditions. When the CPA exposure was performed at 37°C, the toxic effect of PROH further increased, resulting in lower survival (15%) and no fertilization while the toxicity of DMSO and EG was still insignificant. Nevertheless, it was possible to completely avoid the toxicity of PROH by decreasing its concentration to 0.75 M and combining it with 0.75 M DMSO to bring the total CPA concentration to a cryoprotective level. Moreover, combining lower concentrations (i.e., 0.75 M) of PROH and DMSO significantly improved the cryosurvival of MII oocytes compared to the equivalent concentration of DMSO alone. Taken together, our results suggest that from the perspective of CPA toxicity, DMSO and EG are safer to use in slow cooling protocols while a lower concentration of PROH can be combined with another CPA to avoid its toxicity and to improve the cryosurvival as well.

Three-dimensional culture of mouse bone marrow cells on stroma formed within a porous scaffold: influence of scaffold shape and cryopreservation of the stromal layer on expansion of haematopoietic progenitor cells

This study's primary goal was to develop an effective ex vivo expansion method for haematopoietic cells. 3D culture of mouse bone marrow cells was performed in porous scaffolds using a sheet or cube shape. Bone marrow cells were cultured on bone marrow-derived stromal layers formed within the scaffolds and the effect of scaffold shape on the expansion of haematopoietic cells was examined. In some experiments, stromal layers within cubic scaffolds were frozen and then used to culture bone marrow cells after thawing. Results show that after comparison, total cell density and expansion of haematopoietic cells were greater in cultures using the cubic scaffold, suggesting that it was superior to the sheet-like scaffold for expanding haematopoietic cells. When cryopreserved stroma was used, it effectively supported the expansion of haematopoietic cells, and a greater expansion of haematopoietic cells [(erythroid and haematopoietic progenitor cells (HPCs)] was achieved than in cultures with stromal cells that had not been cryopreserved. Expansion of cells using cryopreserved stroma had several other advantages such as a shorter culture period than the conventional method, a stable supply of stromal cells, and ease of handling and scaling up. As a result, this is an attractive method for ex vivo expansion of haematopoietic stem cells (HSCs) and HPCs for clinical use.

Cryobanking of embryoid bodies to facilitate basic research and cell-based therapies

Pluripotent stem cells offer unique opportunities for curing debilitating diseases. However, further comprehensive research is needed to better understand cell signaling during the differentiation of pluripotent cells into different cell lineages and accordingly to develop clinically applicable protocols. One of the limiting steps for differentiation studies is proper culture and expansion of pluripotent stem cells, which is labor intensive, expensive, and requires a great deal of expertise. This limiting step can be overcome by successful banking and distribution of embryoid bodies (EBs), which are aggregates of pluripotent stem cells and typically the starting point of differentiation protocols. The objective of this study was to investigate the feasibility of EB banking by studying survival and functionality of cryopreserved EBs. To this end, EBs were formed by culturing mouse 129 embryonic stem (ES) cells in the absence of leukemia inhibitory factor (LIF) in hanging drops and then subjected to different cryopreservation protocols. In a series of experiments, we first tested the postthaw survival of EBs as a function of dimethylsulfoxide (DMSO) and extracellular trehalose concentrations and cooling rates. Next, we studied the functionality of cryopreserved EBs by assessing their postthaw attachment, growth, and differentiation into various cell types. Higher (≥5%) DMSO concentrations alone or in combination with trehalose (0.1 M and 0.2 M) yielded good postthaw survival rates of >80%, whereas cooling of EBs at 1°C/min in the presence of 5% DMSO +0.1 M trehalose gave the best attachment and growth rates, with differentiation into cell lineages of three germ layers. Taken together, our results suggest that EBs are tolerant to cryopreservation-associated stresses and retain their differentiation potential after freezing and thawing. Furthermore, our experiments with dissociated EB cells and nondissociated EBs suggest that the extracellular matrix may play a beneficial role in the cryotolerance of EBs. Overall, our data support the feasibility of EB banking, which would facilitate advancement of cell-based therapies.

Inhibiting ice recrystallization and optimization of cell viability after cryopreservation

The ice recrystallization inhibition activity of various mono- and disaccharides has been correlated with their ability to cryopreserve human cell lines at various concentrations. Cell viabilities after cryopreservation were compared with control experiments where cells were cryopreserved with dimethylsulfoxide (DMSO). The most potent inhibitors of ice recrystallization were 220 mM solutions of disaccharides; however, the best cell viability was obtained when a 200 mM d-galactose solution was utilized. This solution was minimally cytotoxic at physiological temperature and effectively preserved cells during freeze-thaw. In fact, this carbohydrate was just as effective as a 5% DMSO solution. Further studies indicated that the cryoprotective benefit of d-galactose was a result of its internalization and its ability to mitigate osmotic stress, prevent intracellular ice formation and/or inhibit ice recrystallization. This study supports the hypothesis that the ability of a cryoprotectant to inhibit ice recrystallization is an important property to enhance cell viability post-freeze-thaw. This cryoprotective benefit is observed in three different human cell lines. Furthermore, we demonstrated that the ability of a potential cryoprotectant to inhibit ice recrystallation may be used as a predictor of its ability to preserve cells at subzero temperatures.

On-chip characterization of cryoprotective agent mixtures using an EWOD-based digital microfluidic device

For tissue engineering and regenerative medicine, cryopreservation, a technique for preserving biomaterials in the frozen state with cryoprotective agents (CPAs), is critically important for preserving engineered tissues (ETs) as well as cells necessary to create ETs. As more diverse ETs are produced using various cell types, CPAs and corresponding freeze/thaw (F/T) protocols need to be developed cell/tissue-type specifically. This is because CPAs and F/T protocols that have been successful for one cell/tissue type have proven to be difficult to adapt to other cell/tissue types. The most critical barrier to address this challenge is the inability to screen and identify CPA or CPA mixtures efficiently. In this paper, we developed an "electro-wetting-on-dielectic" (EWOD) based digital microfluidic platform to characterize and screen CPA mixtures cell-type specifically. The feasibility of the EWOD platform was demonstrated by characterizing and optimizing a mixture of dimethlysulfoxide (DMSO) and PBS for human breast cancer cell line as model CPA mixture and cell line. The developed platform multiplexed droplets of DMSO and PBS to create an array of DMSO-PBS mixtures, and mapped the phase change diagram of the mixture. After loading cell suspensions on the platform, the mixture was further screened on-chip for toxicity and cryoprotection. The results were discussed to illustrate the capabilities and limitations of the EWOD platform for cell and tissue-type specific optimization of CPA mixtures and F/T protocols.

John JC. The generation of live offspring from vitrified oocytes

Oocyte cryopreservation is extremely beneficial for assisted reproductive technologies, the treatment of infertility and biotechnology and offers a viable alternative to embryo freezing and ovarian grafting approaches for the generation of embryonic stem cells and live offspring. It also offers the potential to store oocytes to rescue endangered species by somatic cell nuclear transfer and for the generation of embryonic stem cells to study development in these species. We vitrified mouse oocytes using a range of concentrations of trehalose (0 to 0.3 M) and demonstrated that 0.1 and 0.3 M trehalose had similar developmental rates, which were significantly different to the 0.2 M cohort (P<0.05). As mitochondria are important for fertilisation outcome, we observed that the clustering and distribution of mitochondria of the 0.2 M cohort were more affected by vitifrication than the other groups. Nevertheless, all 3 cohorts were able to develop to blastocyst, following in vitro fertilisation, although developmental rates were better for the 0.1 and 0.3 M cohorts than the 0.2 M cohort (P<0.05). Whilst blastocysts gave rise to embryonic stem-like cells, it was apparent from immunocytochemistry and RT-PCR that these cells did not demonstrate true pluripotency and exhibited abnormal karyotypes. However, they gave rise to teratomas following injection into SCID mice and differentiated into cells of each of the germinal layers following in vitro differentiation. The transfer of 2-cell embryos from the 0.1 and 0.3 M cohorts resulted in the birth of live offspring that had normal karyotypes (9/10). When 2-cell embryos from vitrified oocytes underwent vitrification, and were thawed and transferred, live offspring were obtained that exhibited normal karyotypes, with the exception of one offspring who was larger and died at 7 months. We conclude that these studies highlight the importance of the endometrial environment for the maintenance of genetic stability and thus the propagation of specific genetic traits.

Cryopreservation of amniotic fluid-derived stem cells using natural cryoprotectants and low concentrations of dimethylsulfoxide

Amniotic fluid-derived stem cells (AFSCs) are a potential cell source for therapeutic applications. They can be easily mass produced, cryopreserved and shipped to clinics for immediate use. However, one major obstacle to the manufacturing of clinical grade stem cells is the need for current good manufacturing practices for cryopreservation, storage, and distribution of these cells. Most current cryopreservation methods used for stem cells include the potentially toxic cryoprotectant (CPA) dimethylsulfoxide (Me(2)SO) in the presence of animal serum proteins that prevent direct use of these cells in human therapeutic applications. To avoid any potential cryoprotectant related complications, it will be essential to develop non-toxic CPAs or reduce CPA concentration in the freezing media used. In this study, we assessed the use of disaccharides, antioxidants and caspase inhibitors for cryopreservation of AFSCs in combination with a reduced concentration of Me(2)SO. The thawed cells were tested for viability with MTT assays and a growth curve was created to measure population doubling time. In addition, we performed flow cytometry analysis for cell surface antigens, RT-PCR for mRNA expression of stem cell markers, and assays to determine the myogenic differentiation potential of the cells. A statistically significant (p<0.05) increase in post-thawed cell viability in solutions containing trehalose, catalase and (Z)VAD-fmk with 5% Me(2)SO was observed. The solutions containing trehalose and catalase with 5% or 2.5% (v/v) Me(2)SO produced results similar to those for the control (10% (v/v) Me(2)SO and 30% FBS) in terms of culture growth, expression of cell surface antigens and mRNA expression of stem cell markers in AFSCs cryopreserved for a minimum of 3 weeks. Thus, AFSCs can be cryopreserved with 1/4 the standard Me(2)SO concentration with the addition of disaccharides, antioxidants and caspase inhibitors. The use of Me(2)SO at low concentrations in cell freezing solutions may support the development of clinical trials of AFSCs.

Cryopreservation of oocytes in experimental models

Until recently, success in oocyte cryopreservation has been very limited mainly due to poor understanding of the complex physiological processes that lead to cell damage during cryopreservation. In the past three decades, however, a wealth of information has been collected using various different animal models, which has led to development of new technologies and optimization of existing ones. The use of these models has provided the opportunity for research that may not have been possible with human material. Today, results of these studies still continue to form the basis of oocyte cryobiology. This review discusses these studies, especially the physiological impacts of cryopreservation on oocyte biology. It will also focus on the role that animal models have played in improvement strategies, validation before translating new techniques into the human model and the advances made in the human in IVF because of these animal models. Finally, existing investigations and their potential impact in other areas of research will be discussed. Until recently, success in oocyte cryopreservation has been very limited mainly due to poor understanding of the complex physiological processes that lead to cell damage during cryopreservation. In the past three decades, however, a wealth of information has been collected using various different animal models, which has led to development of new technologies and optimization of existing ones. The use of these models provided the opportunity for research that may not have been possible with human material. Today, animal models still continuously provide imperative data that facilitate further advancements in oocyte cryobiology. This review will focus on the physiological impacts, current improvement strategies and future applications of oocyte cryopreservation using animal models as they benefit not only human oocyte cryopreservation procedures, but also the human species through their usefulness in agriculture, medicine and conservation.