Effect of different cryoprotectants and vitrificant solutions on the hatching rate of turbot embryos (Scophthalmus maximus)

Effect of non-permeable cryoprotectant sucrose on the development of spotted knifejaw (Oplegnathus punctatus) embryos

In this study, the toxicity of sucrose to Oplegnathus punctatus embryos was evaluated. Embryos at the 4-6 somite, tail-bud, heart formation, and heart-beating stages were exposed to 0, 0.5, 1,1.5, 2, 2.5, or 3 M sucrose for 1 h. Survival rates of embryos at the tail-bud, heart formation, and heart-beating stages after rehydration for 1 h were not affected by treatment with 2 M sucrose (the maximum concentration). Embryos at the tail-bud, heart formation, and heart-beating stages were exposed to 2 M sucrose for 0, 30, 60, 90, 120, 150, or 180 min. Long-term developmental indicators, including rates of survival, hatching, swimming, and malformation, were evaluated for 4 days after rehydration. Based on the survival rates 10 min after rehydration, the longest tolerance time for embryos at the three stages was 120 min. Based on long-term developmental indicators, the longest tolerance times were 60 min at the tail-bud, 60 min at the heart formation stage and 30 min at the heart beating stage. The malformation rates increased as the treatment time increased. The malformation rates were 100% when embryos were exposed to sucrose for ≥120 min. Malformation was divided into larval and embryonic abnormality. As the exposure time increased for tail-bud stage embryos, the rate of larval malformation increased. Treatment at heart formation and heart-beating stages resulted in higher rates of failure to hatch at exposure time. Based on these results, toxicity tests of non-permeable cryoprotectant in embryos requires the observation of development for at least 2 days after rehydration. Based on long-term observation, it was concluded that dehydration before freezing was not the direct cause of larvae deformity that hatched from frozen-thawing embryo. These results provide a reference for the singly use of representative non-permeable cryoprotectant sucrose.

Advanced cryopreservation engineering strategies: the critical step to utilize stem cell products

With the rapid development of stem cell-related therapies and regenerative medicine, the clinical application of stem cell products is on the rise. However, ensuring the effectiveness of these products after storage and transportation remains a challenge in the transformation to clinical trials. Cryopreservation technology allows for the long-term storage of cells while ensuring viability, making it a top priority for stem cell preservation. The field of cryopreservation-related engineering technologies is thriving, and this review provides an overview of the background and basic principles of cryopreservation. It then delves into the main bioengineering technologies and strategies used in cryopreservation, including photothermal and electromagnetic rewarming, microencapsulation, and synergetic ice inhibition. Finally, the current challenges and future prospects in the field of efficient cryopreservation of stem cells are summarized and discussed.

Cryopreservation of sperm in Grey mullet Mugil cephalus (Linnaeus, 1758)

The aim of this study was to document the effects of cryopreservation on sperm motility and viability in Grey mullet Mugil cephalus. Cryopreservation of sperm was attempted by using two extenders ringer solution for marine fish (RSMF) and V2 extender (V2E) and cryoprotectants dimethylacetamide (DMA), dimethylsulfoxide (DMSO), ethylene glycol (EG), glycerol (GLY), propylene glycol (PG) and methanol (MeOH). Cryoprotectants were assessed at different concentrations individually as well as in combination with varying equilibration times (10 and 30min). For optimization of freezing rate, four freezing protocols (-5, -10, -20 and -30°C/min) were evaluated. After achieving final temperature, samples were plunged in liquid nitrogen (-196°C) and stored for a week. Samples were subsequently thawed in a water bath at 30°C for assessment of sperm motility and viability. Results indicated that cryomedium constituting of V2E extender+10% glycerol with a dilution ratio of 1:1 (sperm: cryomedium) at an equilibration time of 5 to- 10min and freezing rate of -20°C/min was more desirable compared with other factors that were assessed. Use of this protocol resulted in retaining the greatest sperm motility grade 3.0±0.0 (50%-80% sperm movement, fast swimming) and 48.19±3.12% of sperm viability. The results of the present study, therefore, provide base-line data for establishing a protocol for sperm cryopreservation in M.cephalus. Further studies are, however, required for optimization of most suitable sperm cryopreservation protocol.

Stimulus-triggered enhancement of chilling tolerance in zebrafish embryos

Background

Cryopreservation of zebrafish embryos is still an unsolved problem despite market demand and massive efforts to preserve genetic variation among numerous existing lines. Chilled storage of embryos might be a step towards developing successful cryopreservation, but no methods to date have worked.

Methods

In the present study, we applied a novel strategy to improve the chilling tolerance of zebrafish embryos by introducing a preconditioning hydrostatic pressure treatment to the embryos. In our experiments, 26-somites and Prim-5 stage zebrafish embryos were chilled at 0°C for 24 hours after preconditioning. Embryo survival rate, ability to reach maturation and fertilizing capacity were tested.

Results

Our results indicate that applied preconditioning technology made it possible for the chilled embryos to develop normally until maturity, and to produce healthy offspring as normal, thus passing on their genetic material successfully. Treated embryos had a significantly higher survival and better developmental rate, moreover the treated group had a higher ratio of normal morphology during continued development. While all controls from chilled embryos died by 30 day-post-fertilization, the treated group reached maturity (~90–120 days) and were able to reproduce, resulting in offspring in expected quantity and quality.

Conclusions

Based on our results, we conclude that the preconditioning technology represents a significant improvement in zebrafish embryo chilling tolerance, thus enabling a long-time survival. Furthermore, as embryonic development is arrested during chilled storage this technology also provides a solution to synchronize or delay the development.

Cultivation and phenotypic characterization of rabbit epithelial cells expanded ex vivo from fresh and cryopreserved limbal and oral mucosal explants

PURPOSE

To compare the morphology of cultured rabbit epithelial sheets and the expression of stem cells with differentiated cell markers of cultivated epithelial cells from fresh and cryopreserved limbal and oral mucosal biopsies.

MATERIALS AND METHODS

Six New Zealand white rabbits were divided into two groups of three, from which limbal and oral mucosal biopsies were taken. Harvested tissues from each rabbit were brought to immediate cultivation, while another set of tissues was cryopreserved. Cultivation was performed by the explant culture technique using human amniotic membrane as a culture substrate, co-culturing with 3T3 fibroblasts and using the air-lifting method. Cells were cultured for three weeks; then cultured epithelial sheets were stained with hematoxylin-eosin and examined for expression patterns of p63, keratin 3 (K3) and connexin 43 (Cx43). Cryopreservation was carried out using the vitrification method. Tissues were preserved in liquid nitrogen using 25% dimethyl sulfoxide combined with 25% propylene glycol in Dulbecco's Modified Eagle's Medium containing 20% fetal bovine serum. After two months, the tissues were warmed, cultured and stained using the same processes as for fresh tissue cultures.

RESULTS

Cultivation of fresh limbal and fresh oral mucosal tissues showed epithelial stratification, with two to five cell layers. Immunohistochemical staining showed p63-positive cells in basal and intermediate cell layers. K3 staining was observed in cells in the suprabasal layer, while expression of Cx43 was scattered throughout all layers of the epithelia. All culture sheets expressed p63, K3 and Cx43 with the exception of one sheet from the oral mucosal culture that was p63-negative. Cultured epithelial sheets from cryopreserved tissues showed results similar to those from fresh tissue culture.

CONCLUSIONS

This study found that cells in cultivated fresh limbal and oral mucosal tissues had similar morphology to cells in cultivated cryopreserved limbal and oral mucosal tissues, both containing a heterogeneous population of cells including stem cells and differentiated cells.

Cooling of pirapitinga (Piaractus brachypomus) embryos stored at -10ºC

Cryopreservation has not been used successfully to preserve fish embryos, although chilling techniques have been used with good results. The aim of this study was to chill Piaractus brachypomus embryos at - 10°C for various storage times. Embryos at the following ontogenetic stages were used: blastoderm - 1.2 hours post-fertilization (hpf); epiboly - 5 hpf; blastopore closure - 8 hpf; and appearance of the optic vesicle - 13 hpf. One hundred embryos were selected from each ontogenetic stage and chilled at - 10°C for 6 or 10 h. The results were analysed using analysis of variance (ANOVA) and Tukey's test at a 5% significance level. A significantly greater number of completely developed live larvae were observed following embryonic treatment with a cryoprotectant solution that contained 17.5% sucrose and 10% methanol. There was no survival for embryos cooled at - 10°C in initial developmental stages (1, 2 and 5 h hpf). Furthermore, higher survival rates were observed when embryos were treated at more advanced developmental stages (8 and 13 hpf). Therefore, P. brachypomus embryos at the blastopore-closure (8 hpf) or appearance-of-optic-vesicle (13 hpf) stages should be used for embryo chilling protocols and chilling should be performed using a 17.5% sucrose with a 10% methanol solution at - 10°C for up to 6 h. The best results were obtained with 13-hpf and 8-hpf embryos and cooling at 6 h of storage.

DMSO modifies the permeability of the zebrafish (Danio rerio) chorion-implications for the fish embryo test (FET)

Since 2007, when REACH came into force, the fish embryo test has received increasing attention as a potential alternative for the acute fish test. Due to its low toxicity and the ability to permeate biological membranes without significant damage to their structural integrity, dimethyl sulfoxide (DMSO) is a commonly used solvent in the fish embryo test. Little is known, however, about the membrane penetration properties of DMSO, the impact of different concentrations of DMSO on the potential barrier function of the zebrafish chorion and on changes in the uptake of chemicals into the embryo. Therefore, in the present study, the fluorescent dyes fluorescein (mol wt 332; Pow 3.4) and 2,7-dichlorofluorescein (mol wt 401; Pow 4.7), both substances with limited water solubility, were used to visualize the uptake into the egg as well as the accumulation in the embryo of the zebrafish depending on different concentrations of DMSO. The distribution of fluorescein within the egg compartments varied with DMSO concentration: When dissolved in 0.01% DMSO, fluorescein did not pass the chorion. In contrast, concentrations ≥ 0.1% DMSO increasingly facilitated the uptake into the perivitelline space. In contrast, the uptake of 2,7-dichlorofluorescein was not substantially increased with rising DMSO concentrations, indicating the importance of factors other than the solvent (e.g. mol wt). With respect to the fish embryo test, results indicate that DMSO may be used without complications as a solvent, however, only at a maximum concentration of 0.01% (0.1 mL/L) as already indicated in the OECD difficult substances paper (OECD, 2000).

Effect of cryoprotectants on the survival of cascudo preto (Rhinelepis aspera) embryos stored at -8 °C

Cryopreservation of germplasm provides a promising method to preserve fish genetic material, which is of great importance in preservation of species diversity, aquaculture, and management of fish models used in biomedical research. In the present study, cryopreservation of Rhinelepis aspera embryos, a Brazilian endangered species, was studied for the first time using a short-term cooling protocol. Embryos at blastoporous closing stage were selected, placed in 6-ml glass vials and stored at -8 °C for 6 h in 10 different cryoprotectant solutions: S1 (17.1% sucrose + 9% methanol); S2 (17.1% sucrose + 9% DMSO); S3 (8.5% sucrose + 8.5% glucose + 9% methanol); S4 (8.5% sucrose + 8.5% glucose + 9% DMSO); S5 (17.1% sucrose + 9% ethylene glycol); S6 (8.5% sucrose + 8.5% glucose + 9% ethylene glycol); S7 (17.1% sucrose + 4.5% methanol + 4.5% DMSO); S8 (17.1% sucrose + 4.5% methanol + 4.5% ethylene glycol); S9 (17.1% sucrose + 4.5% DMSO + 4.5% ethylene glycol); and S10 (100% water). Embryo viability was assessed by hatching rate, counting live larvae and number of failed eggs under a stereomicroscope. The results showed that only the cryoprotectant solutions that contained methanol associated to sucrose (S1, S7 and S8) provided partial protection of Rhinelepis aspera embryos from cold damage (over 50% hatching rate in S1), while the use of DMSO and ethylene glycol, isolated or in combination, resulted in no hatching rate. Further studies are needed in order to extend the storage time and to improve the hatching rate for the species.

Cryopreservation and quality control of mouse embryonic feeder cells

Stem cell research is a highly promising and rapidly progressing field inside regenerative medicine. Embryonic stem cells (ESCs), reprogrammed "induced pluripotent" cells (iPS), or lately protein induced pluripotent cells (piPS) share one inevitable factor: mouse embryonic feeder cells (MEFs), which are commonly used for ESC long term culture procedures and colony regeneration. These MEFs originate from different mouse strains, are inactivated by different methods and are differently cryopreserved. Incomprehensibly, there are to date no established quality control parameters for MEFs to insure consistency of ESC experiments and culture. Hence, in this work, we developed a bench-top quality control for embryonic feeder cells. According to our findings, MEFs should be inactivated by irradiation (30Gy) and cryopreserved with optimal 10% DMSO at 1K/min freezing velocity. Thawed cells should be free of mycoplasma and should have above 85 ± 13.1% viability. Values for the metabolic activity should be above 150 ± 10.5% and for the combined gene expression of selected marker genes above 225 ± 43.8% compared to non-irradiated, cryopreserved controls. Cells matching these criteria can be utilized for at least 12 days for ESC culture without detaching from the culture dish or disruption of the cell layer.

Sperm cryopreservation of the critically endangered olive barb (Sarpunti) Puntiussarana (Hamilton, 1822)

The present study focused on development of a sperm cryopreservation protocol for the critically endangered olive barb Puntiussarana (Hamilton, 1822) collected from two stocks within Bangladesh and reared in the Fisheries Field Laboratory, Bangladesh Agricultural University (BAU). The sperm were collected in Alsever's solution prepared at 296mOsmol kg(-1). Sperm were activated with distilled water (24mOsmol kg(-1)) to characterize motility. Maximum motility (90%) was observed within 15s after activation, and sperm remained motile for 35s. Sperm activation was evaluated in different osmolalities and motility was completely inhibited when osmolality of the extender was ≥287mOsmol kg(-1). To evaluate cryoprotectant toxicity, sperm were equilibrated with 5%, 10% and 15% each of dimethyl sulfoxide (DMSO) and methanol. Sperm motility was noticeably reduced within 10min, when sperm were equilibrated with 15% DMSO, indicating acute toxicity to spermatozoa and therefore this concentration was excluded in further trials. Sperm were cryopreserved using DMSO at concentrations of 5% and 10% and methanol at 5%, 10% and 15%. The one-step freezing protocol (from 5°C to -80°C at 10°C/min) was carried out in a computer-controlled freezer (FREEZE CONTROL® CL-3300; Australia) and 0.25-ml straws containing spermatozoa were stored in liquid nitrogen for 7-15days at -196°C. The highest motility in thawed sperm 61±8% (mean±SD) was obtained with 10% DMSO. The fertilization and hatching rates were 70% and 37% for cryopreserved sperm, and 72% and 62% for fresh sperm. The protocol reported here can be useful for hatchery-scale production of olive barb. The use of cryopreserved sperm can facilitate hatchery operations, and can provide for long-term conservation of genetic resources to contribute in the recovery of critically endangered fish such as the olive barb.

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.

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.