Vitrification of mature mouse oocytes in a 6 M Me2SO solution supplemented with antifreeze glycoproteins: the effect of temperature

Exopolysaccharide ID1 Improves Post-Warming Outcomes after Vitrification of In Vitro-Produced Bovine Embryos

This study aimed to assess the cryoprotectant role of exopolysaccharide (EPS) ID1, produced by Antarctic Pseudomonas sp., in the vitrification of in vitro-produced (IVP) bovine embryos. IVP day 7 (D7) and day 8 (D8) expanded blastocysts derived from cow or calf oocytes were vitrified without supplementation (EPS0) or supplemented with 10 µg/mL (EPS10) or 100 µg/mL (EPS100) EPS ID1. The effect of EPS ID1 was assessed in post-warming re-expansion and hatching rates, differential cell count, apoptosis rate, and gene expression. EPS100 re-expansion rates were significantly higher than those observed for the EPS0 and EPS10 treatments, regardless of culture length or oocyte source. EPS100 hatching rate was similar to the one of the fresh blastocysts except for those D7 blastocysts derived from calf oocytes. No differences were observed among EPS ID1 treatments when the inner cell mass, trophectoderm, and total cell number were assessed. Although apoptosis rates were higher (p ≤ 0.05) in vitrified groups compared to fresh embryos, EPS100 blastocysts had a lower number (p ≤ 0.05) of apoptotic nuclei than the EPS0 or EPS10 groups. No differences in the expression of BCL2, AQP3, CX43, and SOD1 genes between treatments were observed. Vitrification without EPS ID1 supplementation produced blastocysts with significantly higher BAX gene expression, whereas treatment with 100 µg/mL EPS ID1 returned BAX levels to those observed in non-vitrified blastocysts. Our results suggest that 100 µg/mL EPS ID1 added to the vitrification media is beneficial for embryo cryopreservation because it results in higher re-expansion and hatching ability and it positively modulates apoptosis.

Small-molecule fulvic acid with strong hydration ability for non-vitreous cellular cryopreservation

The exploitation of biocompatible ice-control materials especially the small molecules for non-vitreous cryopreservation remains challenging. Here, we report a small molecule of fulvic acid (FA) with strong hydration ability, which enables non-vitreous cellular cryopreservation by reducing ice growth during freezing and reducing ice recrystallization/promoting ice melting during thawing. Without adding any other cryoprotectants, FA can enhance the recovery of sheep red blood cells (RBCs) by three times as compared with a commercial cryoprotectant (hydroxyethyl starch) under a stringent test condition. Investigation of water mobility reveals that the ice-control properties of FA can be ascribed to its strong bondage to water molecules. Furthermore, we found that FA can be absorbed by RBCs and mainly locates on membranes, suggesting the possible contribution of FA to cell protection through stabilizing membranes. This work bespeaks a bright future for small-molecule cryoprotectants in non-vitreous cryopreservation application.

•

FA shows strong hydration ability

•

FA reduces ice growth/recrystallization and promotes ice melting

•

FA can be absorbed by RBCs and mainly locates on membranes

•

FA enables non-vitreous cellular cryopreservation

Anti freeze proteins (Afp): Properties, sources and applications - A review

Extreme cold marine and freshwater temperatures (below 4 °C) induce massive deterioration to the cell membranes of organisms resulting in the formation of ice crystals, consequently causing organelle damage or cell death. One of the adaptive mechanisms organisms have evolved to thrive in cold environments is the production of antifreeze proteins with the functional capabilities to withstand frigid temperatures. Antifreeze proteins are extensively identified in different cold-tolerant species and they facilitate the persistence of cold-adapted organisms by decreasing the freezing point of their body fluids. Various structurally diverse types of antifreeze proteins detected possess the ability to modify ice crystal growth by thermal hysteresis and ice recrystallization inhibition. The unique properties of antifreeze proteins have made them a promising resource in industry, biomedicine, food storage and cryobiology. This review collates the findings of the various studies carried out in the past and the recent developments observed in the properties, functional mechanisms, classification, distinct sources and the ever-increasing applications of antifreeze proteins. This review also summarizes the possibilities of the way forward to identify new avenues of research on anti-freeze proteins.

Antifreeze proteins for low-temperature preservation in reproductive medicine: A systematic review over the last three decades

Antifreeze proteins (AFPs) are synthesized by diverse non-mammalian species, allowing them to survive in severely cold environments. Since the 1990s, the scientific literature reports their use for low-temperature preservation of germplasm. The aim of this systematic review was to compile available scientific evidence regarding the use of AFP for low-temperature preservation of several reproductive specimens. Internet databases were consulted using the terms: "antifreeze protein" OR "AFP" OR "antifreeze glycoprotein" OR "AFGP" OR "ice-binding protein" OR "IBP" OR "thermal hysteresis protein" AND "cryopreservation". From 56 articles, 87 experiments testing AFPs in low-temperature preservation of gametes, embryos or reproductive tissues/cells were fully analyzed and outcomes were annotated. A positive outcome was considered as a statistically significant improvement on any parameter evaluated after low-temperature preservation with AFP, whereas a negative outcome included worsening of any evaluated parameter, in comparison to untreated groups or groups treated with a lower concentration of AFP. The findings indicated that research on the use of AFP as a cryoprotectant for reproductive specimens has increased markedly over the past decade. Some experiments reported both positive and negative results, which depended, on AFP concentration in the preservation media. Variation in the outcomes associated with species was also observed. Among the 66 experiments conducted in mammals, 77.3% resulted in positive, and 28.8% in negative outcomes after the use of AFP. In fishes, positive and negative outcomes were observed in 71.4% and 33.3% of 21 experiments, respectively. Most positive outcomes included preserving cell post-warming survival. The beneficial effect of AFP supports its use in cryobiological approaches used in human and veterinary medicines and animal protein industry. Moreover, combination of different AFP types, or AFP with antioxidants, or even the use of AFP-biosimilar, comprise some promising approaches to be further explored in cryopreservation.

The Use of Antifreeze Proteins in the Cryopreservation of Gametes and Embryos

The cryopreservation of gametes and embryos is a technique widely used in reproductive biology. This technology helps in the reproductive management of domesticated animals, and it is an important tool for gene banking and for human-assisted reproductive technologies. Antifreeze proteins are naturally present in several organisms exposed to subzero temperatures. The ability for these proteins to inhibit ice recrystallization together with their ability to interact with biological membranes makes them interesting molecules to be used in cryopreservation protocols. This mini-review provides a general overview about the use of antifreeze proteins to improve the short and long term storage of gametes and embryos.

Polymer mimics of biomacromolecular antifreezes

Antifreeze proteins from polar fish species are remarkable biomacromolecules which prevent the growth of ice crystals. Ice crystal growth is a major problem in cell/tissue cryopreservation for transplantation, transfusion and basic biomedical research, as well as technological applications such as icing of aircraft wings. This review will introduce the rapidly emerging field of synthetic macromolecular (polymer) mimics of antifreeze proteins. Particular focus is placed on designing polymers which have no structural similarities to antifreeze proteins but reproduce the same macroscopic properties, potentially by different molecular-level mechanisms. The application of these polymers to the cryopreservation of donor cells is also introduced.

Marine Antifreeze Proteins: Structure, Function, and Application to Cryopreservation as a Potential Cryoprotectant

Antifreeze proteins (AFPs) are biological antifreezes with unique properties, including thermal hysteresis(TH),ice recrystallization inhibition(IRI),and interaction with membranes and/or membrane proteins. These properties have been utilized in the preservation of biological samples at low temperatures. Here, we review the structure and function of marine-derived AFPs, including moderately active fish AFPs and hyperactive polar AFPs. We also survey previous and current reports of cryopreservation using AFPs. Cryopreserved biological samples are relatively diverse ranging from diatoms and reproductive cells to embryos and organs. Cryopreserved biological samples mainly originate from mammals. Most cryopreservation trials using marine-derived AFPs have demonstrated that addition of AFPs can improve post-thaw viability regardless of freezing method (slow-freezing or vitrification), storage temperature, and types of biological sample type.

Gold Nanoparticle Aggregation as a Probe of Antifreeze (Glyco) Protein-Inspired Ice Recrystallization Inhibition and Identification of New IRI Active Macromolecules

Antifreeze (glyco)proteins are found in polar fish species and act to slow the rate of growth of ice crystals; a property known as ice recrystallization inhibition. The ability to slow ice growth is of huge technological importance especially in the cryopreservation of donor cells and tissue, but native antifreeze proteins are often not suitable, nor easily available. Therefore, the search for new materials that mimic this function is important, but currently limited by the low-throughout assays associated with the antifreeze properties. Here 30 nm gold nanoparticles are demonstrated to be useful colorimetric probes for ice recrystallization inhibition, giving a visible optical response and is compatible with 96 well plates for high-throughout studies. This method is faster, requires less infrastructure, and has easier interpretation than the currently used 'splat' methods. Using this method, a series of serum proteins were identified to have weak, but specific ice recrystallization inhibition activity, which was removed upon denaturation. It is hoped that high-throughput tools such as this will accelerate the discovery of new antifreeze mimics.

Rational, yet simple, design and synthesis of an antifreeze-protein inspired polymer for cellular cryopreservation

Antifreeze (glyco) proteins AF(G)Ps are potent ice recrystallization inhibitors, which is a desirable property to enhance cryopreservation of donor tissue/cells. Here we present the rational synthesis of a new, biomimetic, ice-recrystallization inhibiting polymer derived from a cheap commodity polymer, based on an ampholyte structure. The polymer is used to enhance the cryopreservation of red blood cells, demonstrating a macromolecular solution to tissue storage.

Development of Cryopreservation Techniques for Gorgonian (Junceella juncea) Oocytes through Vitrification

Gorgonian corals are slowly declining due to human interaction and environmental impacts. Cryopreservation of gorgonian corals is an ex-situ method of conservation, ensuring future reproduction. The present study assessed the vitrification properties of cryoprotectant (CPT) mixtures using the cryotop, cryoloop and open pulled straw (OPS) cryopereservation methods prior to experimentation on gorgonian (Junceella juncea) oocytes. Investigations of the equilibration and vitrification solutions’ (ES and VS) effect on oocytes throughout different incubation periods were conducted. The cryotop method was found to be the most successful in ensuring vitrification. The most favourable VS was composed of propylene glycol (PG), ethylene glycol (EG) and methanol with concentrations of 3.5M, 1.5M and 2M respectively. Experiments were performed using the cryotop method to cryopreserve Junceella juncea oocytes using VS2, the solution had the least impact on oocytes at 5°C rather than at 26°C. The success of the vitrification procedures was determined by adenosine triphosphate (ATP) levels in cooled-thaw oocytes and the highest viability obtained from the present study was 76.6 ± 6.2%. This study provides information regarding gorgonian corals’ tolerance and viability throughout vitrification to further advance the vitrification protocol on whip corals.

Effect of antifreeze protein on mouse ovarian tissue cryopreservation and transplantation

PURPOSE

To investigate the effect of antifreeze protein (AFP) supplementation on ovarian vitrification and transplantation.

MATERIALS AND METHODS

In this experimental study, we researched a total of 182 ovaries from 4-week-old ICR mice. The equilibration solution included 20% ethylene glycol (EG), and the vitrification solution included 40% EG, 18% Ficoll, and 0.3 M sucrose. Intact ovaries were first suspended in 1 mL of equilibration solution for 10 min, and then mixed with 0.5 mL of vitrification solution for 5 min. Ovaries were randomly assigned to 3 groups and 0, 5, or 20 mg/mL of type III AFP was added into the vitrification solution (control, AFP5, and AFP20 groups, respectively). The vitrified ovaries were evaluated after warming and 2 weeks after autotransplantation. The main outcome measurements are follicular morphology and apoptosis assessed by histology and the TUNEL assay.

RESULTS

A significantly higher intact follicle ratio was shown in the AFP treated groups (control, 28.9%; AFP5, 42.3%; and AFP20, 44.7%). The rate of apoptotic follicles was significantly lower in the AFP treated groups (control, 26.6%; AFP5, 18.7%; and AFP20, 12.6%). After transplantation of the vitrified-warmed ovaries, a significantly higher intact follicle ratio was shown in the AFP20 group. The rate of apoptotic follicles was similar among the groups.

CONCLUSION

The results of the present study suggest that supplementing AFP in the vitrification solution has beneficial effects on the survival of ovarian tissue during cryopreservation and transplantation.

Efficiency of antifreeze glycoproteins for cryopreservation of Nili-Ravi (Bubalus bubalis) buffalo bull sperm

Experiments were conducted to evaluate the effect of Antarctic fish antifreeze glycoproteins, (AFGP) size 1-5 (34-10.5 kDa) and 7-8 (3.2 and 2.4 kDa) in extender on buffalo bull sperm at cooling (4 °C) and at post thawing. Semen was collected from three Nili-Ravi buffalo bulls with artificial vagina for 3 weeks. Qualifying ejaculates from each buffalo bull were diluted (at 37 °C having 50×10(6) sperm/mL) in tris-citric acid extender containing AFGP at 0 (control), 0.1, 1 and 10 μg/mL. An aliquot of diluted semen was evaluated for sperm progressive motility and plasma membrane integrity, while the remaining fraction was cooled to 4 °C in 2 h. Further, an aliquot of cooled semen was evaluated for the previously described variables and the remaining fraction was cryopreserved (-196 °C). After 24 h of storage, straws were thawed at 37 °C for 30 s to assess post-thaw sperm quality. Inclusion of AFGP in the extender did not affect (P>0.05) sperm progressive motility and plasma membrane integrity of buffalo bull sperm at cooling stage (4 °C). However, at post thawing, improvement (P<0.05) in sperm progressive motility and plasma membrane integrity was recorded in extender containing AFGP 1-5 and AFGP 7-8 at 1 μg/mL compared to the control. Percentage of live sperm with an intact acrosome remained similar (P>0.05) in extenders containing different amounts of AFGP and control. In conclusion, supplementation of 1 μg/ml of AFGP in extender improved the motility and plasma membrane integrity of Nili-Ravi buffalo sperm after thawing.

Prolonging hypothermic storage (4 C) of bovine embryos with fish antifreeze protein

Embryos obtained via superovulation are necessary for mammalian artificial reproduction, and viability is a key determinant of success. Nonfreezing storage at 4 C is possible, but currently used storage solutions can maintain embryo viability for only 24-48 h. Here we found that 10 mg/ml antifreeze protein (AFP) dissolved in culture medium 199 with 20% (v/v) fetal bovine serum and 25 mM HEPES could keep bovine embryos alive for 10 days at 4 C. We used a recombinant AFP isolated from the notched-fin eelpout (Zoarces elongatus Kner). Photomicroscopy indicated that the AFP-embryo interaction was enhanced at 37 C. Embryos pre-warmed with the AFP solution at 37 C for 60 min maintained high viability, whereas those that were not pre-warmed could live no longer than 7 days. Thus, short-term storage of bovine embryos was achieved by a combination of AFP-containing medium and controlled pre-warming.

Quantitative study on the antifreeze protein mimetic ice growth inhibition properties of poly(ampholytes) derived from vinyl-based polymers

Antifreeze (glyco) proteins (AF(G)Ps) from the blood of polar fish species are extremely potent ice recrystallization inhibitors (IRI), but are difficult to synthesise or extract from natural sources. Despite this challenge, materials which display IRI are appealing due to their ability to enhance cellular cryopreservation, for applications including regenerative and transplantation medicine. Here, poly(ampholytes), which contain a mixture of cationic and anionic side chains are quantitatively evaluated for their IRI activity. Poly(aminoethyl methacrylate), obtained by RAFT polymerization, is functionalised with succinic anhydride to generate the poly(ampholytes). The charge balance of the side chains is shown to be crucial, with only 50 : 50 mixtures having strong IRI activity, which also scales with molecular weight. This is the first example of a non-hydroxylated synthetic polymer with quantifiable IRI activity and raises questions about the mechanism of IRI, as the polymers have no obvious ice-binding motif. The ampholytic structure is shown to be transferable to carbohydrate-centred polymers with activity retained, but poly(betaines) are shown to be inactive.

Determination of the ice quantity by quantitative microscopic imaging of vitrification solutions

Based on Boutron's semi-empirical crystallization theory, a quantitative microscopic imaging method was developed to determine the quantity of ice in thin films of vitrification solutions. A universal equation was obtained for various vitrification solutions. The new method was applied to determine the ice quantity and critical cooling rates (Vcc) for two new vitrification solutions. Results reveal that the new quantitative imaging method is reliable. This new method has several advantages including the fact that it is cheaper than differential scanning calorimetry (DSC) and that it can be used to study vitrification solutions with Vcc values extending beyond the maximum cooling rate of a typical DSC system. Also, this method should permit quantitative imaging of the volume fraction of ice in space and time in microscope samples.

Antifreeze peptides and glycopeptides, and their derivatives: potential uses in biotechnology

Antifreeze proteins (AFPs) and glycoproteins (AFGPs), collectively called AF(G)Ps, constitute a diverse class of proteins found in various Arctic and Antarctic fish, as well as in amphibians, plants, and insects. These compounds possess the ability to inhibit the formation of ice and are therefore essential to the survival of many marine teleost fishes that routinely encounter sub-zero temperatures. Owing to this property, AF(G)Ps have potential applications in many areas such as storage of cells or tissues at low temperature, ice slurries for refrigeration systems, and food storage. In contrast to AFGPs, which are composed of repeated tripeptide units (Ala-Ala-Thr)_n with minor sequence variations, AFPs possess very different primary, secondary, and tertiary structures. The isolation and purification of AFGPs is laborious, costly, and often results in mixtures, making characterization difficult. Recent structural investigations into the mechanism by which linear and cyclic AFGPs inhibit ice crystallization have led to significant progress toward the synthesis and assessment of several synthetic mimics of AFGPs. This review article will summarize synthetic AFGP mimics as well as current challenges in designing compounds capable of mimicking AFGPs. It will also cover our recent efforts in exploring whether peptoid mimics can serve as structural and functional mimics of native AFGPs.

Antifreeze (glyco)protein mimetic behavior of poly(vinyl alcohol): detailed structure ice recrystallization inhibition activity study

This manuscript reports a detailed study on the ability of poly(vinyl alcohol) to act as a biomimetic surrogate for antifreeze(glyco)proteins, with a focus on the specific property of ice-recrystallization inhibition (IRI). Despite over 40 years of study, the underlying mechanisms that govern the action of biological antifreezes are still poorly understood, which is in part due to their limited availability and challenging synthesis. Poly(vinyl alcohol) (PVA) has been shown to display remarkable ice recrystallization inhibition activity despite its major structural differences to native antifreeze proteins. Here, controlled radical polymerization is used to synthesize well-defined PVA, which has enabled us to obtain the first quantitative structure-activity relationships, to probe the role of molecular weight and comonomers on IRI activity. Crucially, it was found that IRI activity is "switched on" when the polymer chain length increases from 10 and 20 repeat units. Substitution of the polymer side chains with hydrophilic or hydrophobic units was found to diminish activity. Hydrophobic modifications to the backbone were slightly more tolerated than side chain modifications, which implies an unbroken sequence of hydroxyl units is necessary for activity. These results highlight that, although hydrophobic domains are key components of IRI activity, the random inclusion of addition hydrophobic units does not guarantee an increase in activity and that the actual polymer conformation is important.

Supplementation of maturation medium with L-carnitine improves cryo-tolerance of bovine in vitro matured oocytes

The objective was to determine the effects of adding L-carnitine (an enhancer of lipid metabolism) during IVM, on cryotolerance and developmental competence of bovine oocytes. Oocytes matured in the absence (control) or presence (0.6 mg/mL) of L-carnitine were subjected to IVF and embryo culture after Cryotop vitrification or nonvitrification at the metaphase stage of the second meiotic cell division. Cleavage and blastocyst formation rates, and inner cell mass and trophectoderm cell numbers were determined. Also, ATP content in IVM oocytes was measured and intracellular lipid droplets were observed (Nile red staining and confocal microscopy). L-carnitine had no significant effect on the rate of matured oocytes. Vitrification reduced (P < 0.05) mean (±SEM) rates of live oocytes both in control (80.6 ± 1.9%) and L-carnitine groups (82.7 ± 5.1%) compared with nonvitrified oocytes (100%). After IVF, cleavage rates of vitrified control and L-carnitine groups (56.5 ± 3.9% and 62.8 ± 5.1%, respectively) were significantly lower than those in nonvitrified control and L-carnitine groups (83.9 ± 4.2% and 84.3 ± 1.3%). After vitrification, blastocyst formation rate in the L-carnitine group (54.4 ± 5.2%) was significantly higher compared with the control (34.9 ± 4.4%), and did not significantly differ from those in nonvitrified control and L-carnitine groups (52.1 ± 4.2% and 52.8 ± 3.0%). The numbers and ratio of inner cell mass and trophectoderm cells in blastocysts did not differ significantly among groups. The ATP content in L-carnitine-treated oocytes tended to be higher compared with the control. Vitrification did not reduce ATP content in oocytes, irrespective of L-carnitine treatment. Treatment with L-carnitine dislocated lipid droplets from the peripheral area to the inner cytoplasm. In conclusion, L-carnitine supplementation during IVM redistributed lipid droplets in oocytes; if they survived vitrification, their developmental competence was similar to that of nonvitrified oocytes.

Analytical optimal controls for the state constrained addition and removal of cryoprotective agents

Cryobiology is a field with enormous scientific, financial, and even cultural impact. Successful cryopreservation of cells and tissues depends on the equilibration of these materials with high concentrations of permeating chemicals (CPAs) such as glycerol or 1,2 propylene glycol. Because cells and tissues are exposed to highly anisosmotic conditions, the resulting gradients cause large volume fluctuations that have been shown to damage cells and tissues. On the other hand, there is evidence that toxicity to these high levels of chemicals is time dependent, and therefore it is ideal to minimize exposure time as well. Because solute and solvent flux is governed by a system of ordinary differential equations, CPA addition and removal from cells is an ideal context for the application of optimal control theory. Recently, we presented a mathematical synthesis of the optimal controls for the ODE system commonly used in cryobiology in the absence of state constraints and showed that controls defined by this synthesis were optimal. Here we define the appropriate model, analytically extend the previous theory to one encompassing state constraints, and as an example apply this to the critical and clinically important cell type of human oocytes, where current methodologies are either difficult to implement or have very limited success rates. We show that an enormous increase in equilibration efficiency can be achieved under the new protocols when compared to classic protocols, potentially allowing a greatly increased survival rate for human oocytes and pointing to a direction for the cryopreservation of many other cell types.

Ice nucleation in emulsified aqueous solutions of antifreeze protein type III and poly(vinyl alcohol)

Antifreeze protein (AFP) III and poly(vinyl alcohol) (PVA) are known as anti-ice nucleating agents (anti-INAs), which inhibit heterogeneous ice nucleation. However, the effectiveness of these anti-INAs in inhibiting ice nucleation in water-in-oil (W/O) emulsions, in which homogeneous ice nucleation can be experimentally simulated, is unclear. In this study, the ice nucleation temperature in emulsified solutions of AFP III, PVA, and other nonanti-INA polymers was measured, and then the nucleation rate was analyzed based on classical nucleation theory. Results showed that ice nucleation was surface-initiated and, except for PVA solutions, probably caused heterogeneously by the emulsifier, SPAN 65, at the droplet surfaces. In this nucleation mode, AFP III had no significant effect on the ice nucleation rate. In contrast, PVA exhibited ice-nucleating activity only at the droplet surfaces, suggesting that the nucleation is due to the interaction between PVA and SPAN 65.

Cryoprotective effects of antifreeze proteins delivered into zebrafish embryos

Fish embryo cryopreservation, which is useful in aquaculture or biodiversity conservation, is still far from being achieved. Structural barriers reduce the entrance of cryoprotectants into embryo compartments. Previous studies demonstrated a better ability for freezing in Arctic species which naturally express antifreeze proteins (AFPs). In this study, AFPs were delivered in early zebrafish embryos by incubation in media containing protein. Their cryoprotective effects were then analyzed. Chilling sensitivity was evaluated at 4 degrees C and -10 degrees C. Survival rates significantly increased in embryos incorporating AFPI and kept at -10 degrees C. To analyze their effects on cryopreservation, 5-somite embryos were vitrified. Incorporation of AFPI reduced the percentage of embryos that collapsed at thawing (14.2% of AFPI-treated embryos and 48.9% of controls). Cellular damage caused by vitrification was assessed after thawing by cell dissociation and further analysis of cell survival in culture (SYBR-14/IP labeling). The percentage of viable cells at thawing ranged from 25 to 50%, considered incompatible with embryo development. Cells recovered from frozen-control embryos did not survive in culture. However, the incorporation of AFPs allowed survival similar to that of cells recovered from non-frozen embryos. Blastomere cryopreservation trials incorporating AFPI in the extender also demonstrated a significant increase in viability after freezing. Our findings demonstrated that delivery of AFPs into zebrafish embryos by incubation in media containing protein at early stages is a simple and harmless method that increases cryoprotection of the cellular compartment. This beneficial effect is also noticed in blastomeres, encouraging their use in further protocols for embryo cryopreservation.

Effect of sugars on maturation rate of vitrified-thawed immature porcine oocytes

This study examined the effects of monosaccharide (glucose), disaccharide (sucrose) and polysaccharides (Ficoll and Lycium barbarum polysaccharide (LBP)) at different concentrations, using ethylene glycol (EG) as membrane-permeating cryoprotectant, on in vitro maturation of vitrified-thawed immature (GV) porcine oocytes. A total of 1145 oocytes were obtained by follicle aspiration from 496 ovaries of pigs slaughtered at a local abattoir and vitrified using a five-step method. After thawing and removal of cryoprotectant, oocytes were cultured for 44 h at 39 degrees C in a humidified atmosphere of 5% CO(2) in air. Oocytes were stained with DAPI and nuclear maturation was examined. The highest maturation rates were obtained in 1.5M glucose (8.62%), 0.75 M sucrose (20.0%), 3.0 g/ml Ficoll (13.79%) and 0.10 g/ml LBP (20.69%), respectively. The maturation rate using 0.75 M sucrose or 0.10 g/ml LBP was significantly higher compared to 1.5M glucose (P<0.05), but there was no significant difference from using 3.0 g/ml Ficoll (P>0.05). The percentage of oocytes reaching metaphase II (MII) stage in the cryopreserved groups was significantly lower than control (P<0.05). These results suggest that LBP is an effective non-permeating membrane cryoprotectant and 0.75 M sucrose or 0.10 g/ml LBP can be used as the vitrification solution for immature porcine oocytes.

Incorporation of antifreeze proteins into zebrafish embryos by a non-invasive method

The cryopreservation of fish embryos is a challenge because of their structure, with multiple compartments and permeability barriers, and their high chilling sensitivity. Vitrification at advanced developmental stages is considered to be the more promising option. Nevertheless, all reported attempts have failed. Previous studies demonstrated a better ability for freezing in species that naturally express antifreeze proteins (AFPs). These proteins have been delivered into other fish embryos using time-consuming techniques like microinjection. In the present study, the introduction of FITC labelled AFPs was assayed in zebrafish embryos at early developmental stages (from 2-cell to high blastula stage), before the formation of the yolk syncytial layer, by an easy and non-invasive method and evaluated by fluorescence and confocal microscopy. Incubation with AFPs at 128-cell or high blastula stage provides incorporation of the protein in 50-90% of embryos without affecting hatching. Incubation in media containing protein is a simple, harmless and effective method which makes it possible to treat several embryos at the same time. AFPs remain located in derivatives from marginal blastomeres: the yolk syncytial layer, the most cryosensitive and impermeable barrier, and different digestive organs. Our findings demonstrate that delivery of AFP type I and AFP type III into zebrafish embryos by incubation in media containing protein is a simple and harmless method that may improve cryoprotection of the cellular compartment.

Preliminary studies on the vitrification of red sea bream (Pagrus major) embryos

The objective was to identify an appropriate cryoprotectant and protocol for vitrification of red sea bream (Pagrus major) embryos. The toxicity of five single-agent cryoprotectants, dimethyl sulfoxide (DMSO), propylene glycol (PG), ethylene glycol (EG), glycerol (GLY), and methyl alcohol (MeOH), as well as nine cryoprotectant mixtures, were investigated by comparing post-thaw hatching rates. Two vitrifying protocols, a straw method and a solid surface vitrification method (copper floating over liquid nitrogen), were evaluated on the basis of post-thaw embryo morphology. Exposure to single-agent cryoprotectants (10% concentration for 15 min) was not toxic to embryos, whereas for higher concentrations (20 and 30%) and a longer duration of exposure (30 min), DMSO and PG were better tolerated than the other cryoprotectants. Among nine cryoprotectant mixtures, the combination of 20% DMSO+10% PG+10% MeOH had the lowest toxicity after exposure for 10 min or 15 min. High percentages of morphologically intact embryos, 50.6+/-16.7% (mean+/-S.D.) and 77.8+/-15.5%, were achieved by the straw vitrifying method (20.5% DMSO+15.5% acetamide+10% PG, thawing at 43 degrees C and washing in 0.5M sucrose solution for 5 min) and by the solid surface vitrification method (40% GLY, thawing at 22 degrees C and washing in 0.5M sucrose solution for 5 min). After thawing, morphological changes in the degenerated embryos included shrunken yolks and ruptured chorions. Furthermore, thawed embryos that were morphologically intact did not consistently survive incubation.

Ice formation of vitrification solutions for cryopreservation of tissues

Based on Boutron's semi-empirical crystallization theory, a quantitative microscopic imaging method was developed to determine the quantity of ice in thin films of vitrification solutions. A universal equation was obtained for various vitrification solutions. The new method was applied to determine the ice quantity and critical cooling rates for two new vitrification solutions. This new method has several advantages including the fact that it is cheaper than differential scanning calorimetry (DSC) and that it can be used to study vitrification solutions with critical cooling rates extending beyond the maximum cooling rate of a typical DSC system.

Stable transmission and transcription of newfoundland ocean pout type III fish antifreeze protein (AFP) gene in transgenic mice and hypothermic storage of transgenic ovary and testis

Here we describe the generation of transgenic mice carrying type III fish antifreeze protein (AFP) gene and evaluate whether AFP type III protects transgenic mouse ovaries and testes from hypothermic storage. AFPs exist in many different organisms. In fish, AFPs protect the host from freezing at temperatures below the colligative freezing point by adsorbing to the surface of nucleating ice crystals and inhibiting their growth. The transgenic expression of AFP holds great promise for conferring freeze-resistant plant and animal species. AFP also exhibits a potential for the cryopreservation of tissues and cells. In this study, we have generated 42 founder mice harboring the Newfoundland ocean pout (OP5A) type III AFP transgene and established one transgenic line (the line #6). This study demonstrated that AFP gene construct has been stably transmitted to the mouse progeny in the F3 generations in the line #6. Furthermore, the presence of AFP transcripts was confirmed by RT-PCR analysis on cDNAs from liver, kidney, ovarian, and testis tissues of the mouse from F3 generation in this line. These results indicate that ocean pout type III AFP gene could be integrated and transmitted to the next generation and stably transcribed in transgenic mice. In histological analysis of testis and ovarian tissues of nontransgenic control and AFP transgenic mice it has been shown that both tissues of AFP transgenic mice were protected from hypothermic storage (+4 degrees C). The AFP III transgenic mice obtained for the first time in this study would be useful for investigating the biological functions of AFP in mammalian systems and also its potential role in cryopreservation.

Simplified EM grid vitrification is a convenient and efficient method for mouse mature oocyte cryopreservation

This study was performed to evaluate the efficiency of simplified EM grid vitrification, skipping the step of removing the cryoprotectant (5.5M EG + 1.0M sucrose) droplet on the grid after loading oocytes, compared to conventional cryopreservation protocols for mouse mature oocytes. Firstly, the recovery, survival, fertilization and hatching rates of simplified EM grid vitrification were compared with those of the slow freezing method using 1.5M DMSO. Then, conventional EM grid vitrification was compared with simplified EM grid vitrification. Simplified EM grid vitrification showed higher survival, fertilization and hatching rates than those of the slow freezing method (85.6% vs. 63.2%; 51.0% vs. 22.3%; 38.7% vs. 12.5%, p < 0.01, respectively). Moreover, simplified EM grid vitrification showed higher recovery, survival and fertilization rates than those of conventional EM grid vitrification (100% vs. 95.0%, p=0.024; 90.0% vs. 78.9%, p=0.033; 56.7% vs. 38.7%, p=0.021, respectively). Hatching rate tended to be higher for simplified EM grid vitrification compared to conventional EM grid vitrification (41.1% vs. 24.1%). In conclusion, simplified EM grid vitrification is a convenient and efficient method for cryopreservation of mouse mature oocytes, compared to conventional EM grid vitrification and slow freezing methods.

Cryopreservation of immature bovine oocytes by vitrification in straws

The aim of this study was to cryopreserve by vitrification by ethylene glycol (EG) and dimethyl sulfoxide (DMSO) immature bovine oocytes in straws and to investigate the effects of vitrification on post-thaw oocyte maturation. A total of 575 cumulus oocyte complexes were obtained by follicle aspiration from 238 ovaries of cows slaughtered at a local abattoir. Following selection, oocytes with compacted cumulus cells and evenly granulated ooplasm were vitrified using one of the three different solutions with a non-vitrified group served as control. The first step vitrification solution contained 20% EG while the second step solution contained 40% EG+1M sucrose in a basic media used in group EG. Oocytes were matured in N-2-hidroxyethyl piperazine-N-2-ethanosulfonic acid (HEPES) buffered tissue culture medium (TCM) 199 for 24h at 39 degrees C in a humidified atmosphere of 5% CO2 in air. Oocytes were fixed following evaluation for polar body formation, stained with Giemsa solution and nuclear maturation was examined. The numbers of oocytes which were observed at Metaphase II (MII) stage were 41 (34.1%), 17 (14.9%), 29 (20.7%) and 78 (79.6%) in groups EG, DMSO, Mix and Control, respectively. Maturation rate distribution in group Mix was not statistically different when compared to maturation rate distributions in groups EG and DMSO (p>0.05). Differences between other groups were significant (p<0.001). However, better results were obtained in EG group compared to DMSO and mix groups. Maturation rates were lower in all treatment groups than the control group. The lowest maturation result was obtained in DMSO group. Maturation rate in group Mix was between maturation rates of EG and DMSO groups. Immature bovine oocytes can be vitrified in straws, but maturation success differs with the cryoprotectant and it seems that to obtain better maturation rates, new cryopreservation techniques specific for immature bovine oocytes are needed.

Vitrification assays with embryos from a cold tolerant sub-arctic fish species

Pseudopleuronectes americanus is a Northern teleost species that produces antifreeze proteins (AFPs) to protect them from freezing during the winter. These AFPs bind to ice crystals to inhibit their growth, and they also protect cell membranes at low temperatures. In this study, vitrification trials were done with fish embryos at three different developmental stages, using two different protocols for incorporating the vitrifying solutions. Toxicity of the cryoprotectants and permeability to dimethyl sulfoxide were analyzed. Embryos were vitrified in 0.5 ml straws by direct immersion in liquid nitrogen, and their morphology and development analyzed following thaw. The embryos responded well to vitrification as evidenced by the high percentage that exhibited good morphology following thaw. Although none of the embryos hatched, a small percentage (0.92%) of them showed active movements within the chorion and continued to develop for a number of days following thaw. This is the first record of post-thaw development of vitrified fish embryos.

An efficient cryopreservation procedure for potato (Solanum tuberosum L.) utilizing the new ice blocking agent, Supercool X1000

Cryopreservation has been recognized as a practical and efficient tool for long-term storage of vegetatively propagated plants. This study was conducted to investigate effects of modified vitrification techniques on cryopreservation of potato. In vitro plants of potato cultivars "Superior" and "Atlantic" were cold acclimated, and axillary buds were precultured, osmoprotected, exposed to PVS-2 solution, plunged into liquid nitrogen, thawed, and finally planted in the regeneration medium. In the modified vitrification technique an ice-blocking agent, Supercool X1000, was added with PVS-2 solution. Cold acclimation affected survival of cryopreserved shoot tips, and the highest survival (46.7%) was obtained after 3 weeks of acclimation at 10 degrees C. Shoot tips exposed to 2M glycerol plus 0.6M sucrose for 40 min gave 51.5% and 11.7% survival in "Atlantic" and "Superior" at 10 degrees C, respectively. Cold acclimated and osmoprotected shoot tips were dehydrated with PVS-2 containing different concentrations of Supercool X1000 prior to a plunge into liquid nitrogen. Treatments with 0.1% and 1% of Supercool X1000 significantly improved survival by 55% in "Superior" and 71.3% in "Atlantic", respectively. After cryopreservation, vitrified shoot tips resumed growth within a week in a medium (1 mg l(-1) GA(3), 0.5 mg l(-1) zeatin, and 0.1 mg l(-1) IAA) with a low level of Pluronic F-68 (0.005%) and survival was 33.7% higher in "Atlantic" and 14.7% higher in "Superior" than the control (without Pluronic F-68).

Biopreservation of cells and engineered tissues

The development of effective preservation and long-term storage techniques is a critical requirement for the successful clinical and commercial application of emerging cell-based technologies. Biopreservation is the process of preserving the integrity and functionality of cells, tissues and organs held outside the native environment for extended storage times. Biopreservation can be categorized into four different areas on the basis of the techniques used to achieve biological stability and to ensure a viable state following long-term storage. These include in vitro culture, hypothermic storage, cryopreservation and desiccation. In this chapter, an overview of these four techniques is presented with an emphasis on the recent developments that have been made using these technologies for the biopreservation of cells and engineered tissues.

Fundamentals of cryobiology in reproductive medicine

The aim of this review will be to provide a basic understanding of the biophysical processes that accompany the application of cryopreservation in reproductive medicine. The ability to store cells in 'suspended animation' outside the body has become a keystone practice in the development of many modern clinical therapies, and, in fact, the sciences of cryobiology and IVF have developed in parallel over the past 50 years. During this time, some of the underlying principles of the quantitative biophysical aspects of cryobiology have been clarified. Water is the universal biocompatible solvent, but also possesses unique properties for stability of living cells. Whilst low temperatures themselves have defined effects on cell structure and function, it is the phase transition of water to ice that is the most profound challenge for survival. The thermodynamics of dilute aqueous solutions dictate how cells and tissues respond to the freezing process. Current concepts of nucleation, ice crystal growth and solute exclusion from the ice lattice will be discussed to illustrate what cells must negotiate to avoid lethal damage, and the role of cryoprotectants in enhancing recovery. Quantitative formalisms now exist to model and predict how water and solutes move across cell membranes before and during freezing, or how nucleation events will proceed, and these will be outlined. Cryoprotectants have both positive and negative effects on cell function depending on the kinetics of exposure. The concept of tolerable osmotic excursion of cell volume will be discussed, along with the evidence for a 'pseudo-glassy' state for cells during traditional cryopreservation. This will be compared with the recent interest in promoting glassy states in the whole sample using vitrification protocols, outlining the advantages and drawbacks of each approach. Additional methods for controlling ice nucleation have a role to play here, and a brief outline of current technologies will be given. Finally, issues of safety and stability of cryopreserved samples will be set out.

Biotechnological applications of plant freezing associated proteins

Plants use a wide array of proteins to protect themselves against low temperature and freezing conditions. The identification of these freezing tolerance associated proteins and the elucidation of their cryoprotective functions will have important applications in several fields. Genes encoding structural proteins, osmolyte producing enzymes, oxidative stress scavenging enzymes, lipid desaturases and gene regulators have been used to produce transgenic plants. These studies have revealed the potential capacity of different genes to protect against temperature related stresses. In some cases, transgenic plants with significant cold tolerance have been produced. Furthermore, the biochemical characterization of the cold induced antifreeze proteins and dehydrins reveals many applications in the food and the medical industries. These proteins are being considered as food additives to improve the quality and shelf-life of frozen foods, as cryoprotective agents for organ and cell cryopreservation, and as chemical adjuvant in cancer cryosurgery.

A comprehensive evaluation of the effects and mechanisms of antifreeze proteins during low-temperature preservation

During the past 10 years, it has become clear that the effects of antifreeze proteins (AFPs) on cell viability and on thermodynamic properties during low-temperature preservation are complex, even controversial. In this paper, these studies are reviewed systematically and some conclusions are drawn. It is shown that AFPs can display both protective and cytotoxic actions and both nucleation of ice and inhibition of ice crystal growth, depending on several factors; these include the specific storage protocol, the dose and type of AFP, the composition and concentration of cryoprotectant, and the features of the biological material. A novel model, incorporating some recent findings concerning these proteins, is proposed to explain this dual effect of AFPs during cryopreservation. AFP-ice complexes have some affinity interactions with cell membranes and with many other molecules present in cryopreservation solutions. When the intensity of these interactions reaches a certain level, the AFP-ice complexes may be induced to aggregate, thereby inducing ice nucleation and loss of the ability to inhibit recrystallization.

Vitrification enhancement by synthetic ice blocking agents

Small concentrations of the synthetic polymer polyvinyl alcohol (PVA) were found to inhibit formation of ice in water/cryoprotectant solutions. Ice inhibition improved with decreasing molecular weight. A PVA copolymer of molecular weight 2 kDa consisting of 20% vinyl acetate was found to be particularly effective. PVA copolymer concentrations of 0.001, 0.01, 0.1, and 1% w/w decreased the concentration of glycerol required to vitrify in a 10-ml volume by 1, 3, 4, and 5% w/w, respectively. Dimethyl sulfoxide concentrations required for vitrification were also reduced by 1, 2, 2, and 3% w/w, respectively. Crystallization of ice on borosilicate glass in contact with cryoprotectant solutions was inhibited by only 1 ppm of PVA copolymer. Devitrification of ethylene glycol solutions was also strongly inhibited by PVA copolymer. Visual observation and differential scanning calorimeter data suggest that PVA blocks ice primarily by inhibition of heterogeneous nucleation. PVA thus appears to preferentially bind and inactivate heterogeneous nucleators and/or nascent ice crystals in a manner similar to that of natural antifreeze proteins found in cold-hardy fish and insects. Synthetic PVA-derived ice blocking agents can be produced much less expensively than antifreeze proteins, offering new opportunities for improving cryopreservation by vitrification.

Kinetic and temporal factors influence chilling injury to germinal vesicle and mature bovine oocytes

In this study we examined the effects of low, above freezing temperatures on the viability and functionality of bovine oocytes. Germinal vesicle (GV) stage and in vitro matured oocytes (MII) were exposed to various combinations of time (15 and 60 min) and temperature (4, 16, 23, and 39 degrees C). After being treated, the ability of oocytes to undergo maturation and fertilization in vitro was examined, as well as their viability assayed by two fluorescent probes, fluorescein diacetate (FDA) and 5-carboxyfluorescein diacetate (cFDA). Cooling GV oocytes to 16 degrees C for 15 min reduced the fertilization rate by more than 40%, compared with those left at 39 degrees C. Surprisingly, cooling oocytes to 4 degrees C reduced the fertilization rate by only 10% compared with control. Exposing GV oocytes to temperatures below 23 degrees C reduced their viability. Similar to the reduction in fertilization, the viability of GV oocytes after exposure to 16 degrees C was reduced by more than 50%, whereas exposure to 4 degrees C reduced it by only 9%. Viability measurements using FDA and cFDA gave comparable results and showed a similar trend. The viability of MII oocytes and of GV oocytes pretreated with butylated hydroxytoluene, following exposure to low temperatures, was higher compared with that of GV controls. We interpret these results as indicating chilling effects on membrane integrity. Improving the chilling resistance of bovine oocytes may facilitate their short- and long-term preservation.