Improving post-thaw survival of cryopreserved mouse blastocysts by hydrostatic pressure challenge

Cellular transfection using rapid decrease in hydrostatic pressure

Of all methods exercised in modern molecular biology, modification of cellular properties through the introduction or removal of nucleic acids is one of the most fundamental. As such, several methods have arisen to promote this process; these include the condensation of nucleic acids with calcium, polyethylenimine or modified lipids, electroporation, viral production, biolistics, and microinjection. An ideal transfection method would be (1) low cost, (2) exhibit high levels of biological safety, (3) offer improved efficacy over existing methods, (4) lack requirements for ongoing consumables, (5) work efficiently at any scale, (6) work efficiently on cells that are difficult to transfect by other methods, and (7) be capable of utilizing the widest array of existing genetic resources to facilitate its utility in research, biotechnical and clinical settings. To address such issues, we describe here Pressure-jump-poration (PJP), a method using rapid depressurization to transfect even difficult to modify primary cell types such as embryonic stem cells. The results demonstrate that PJP can be used to introduce an array of genetic modifiers in a safe, sterile manner. Finally, PJP-induced transfection in primary versus transformed cells reveals a surprising dichotomy between these classes which may provide further insight into the process of cellular transformation.

Nitric oxide and hormesis

This present paper provides an assessment of the occurrence of nitric oxide (NO)-induced hormetic-biphasic dose/concentration relationships in biomedical research. A substantial reporting of such NO-induced hormetic effects was identified with particular focus on wound healing, tumor promotion, and sperm biology, including mechanistic assessment and potential for translational applications. Numerous other NO-induced hormetic effects have been reported, but require more development prior to translational applications. The extensive documentation of NO-induced biphasic responses, across numerous organs (e.g., bone, cardiovascular, immune, intestine, and neuronal) and cell types, suggests that NO-induced biological activities are substantially mediated via hormetic processes. These observations are particularly important because broad areas of NO biology are constrained by the quantitative features of the hormetic response. This determines the amplitude and width of the low dose stimulation, affecting numerous biomedical implications, study design features (e.g., number of doses, dose spacing, sample sizes, statistical power), and the potential success of clinical trials.

Application of High Hydrostatic Pressure (HHP) to Improve Cryopreservation of Young Bull Semen

The objective of the study was to determine the effect of high hydrostatic pressure (HHP) on quality of cryopreserved semen of young bulls. Semen for this study was collected from 8 bulls aged between 13 and 18 months at monthly intervals, from June to September. After collection, semen was diluted in a commercial Bioxcell® extender (one part at 1:1 and a second part to give a sperm concentration of 20 million/0.2 mL), filled into straws and treated with HHP at 30 MPa for 90 min. After HHP treatment, pre-diluted semen (1:1) was diluted to a sperm concentration 20 million/0.2 mL and filled into straws. In addition, part of the semen diluted to a concentration of 20 million/0.2 mL was not treated with HHP (control). All of it was held at +4°C and frozen in a freezer after 2.5-h equilibration. Semen was thawed in a water bath at 38°C and subjected to estimation of the percentage of motile sperm both subjectively and using a computer-assisted semen analyzer and cytometric assessment of sperm cell membrane integrity. Subjective motility and fast progressive motility were significantly higher with pre-diluted (1:1) and HHP treated semen compared to control (P<0.05). No significant differences were observed in percentage of membraneintact spermatozoa between control and experimental groups. Additionally, the influence of HHP on the sperm of individual bulls was assessed. In bull number 2, the HHP treatment after semen pre-dilution significantly improved progressive motility from 54.1 to 63.4 percent (P<0.05). In bull number 4, the HHP treatment after semen pre-dilution significantly improved subjective motility, rapid motility and progressive motility by 12.5, 16.8 and 16.3 percent, respectively (P<0.05). No effect was seen for 6 bulls. It is concluded that for some bulls, the application of HHP before semen freezing may improve the cryopreservation outcome. However, this requires further research in this area, also to determine the fertilizing capacity of bull semen exposed to high hydrostatic pressure.

Cryopreservation of Gametes and Embryos and Their Molecular Changes

The process of freezing cells or tissues and depositing them in liquid nitrogen at -196 °C is called cryopreservation. Sub-zero temperature is not a physiological condition for cells and water ice crystals represent the main problem since they induce cell death, principally in large cells like oocytes, which have a meiotic spindle that degenerates during this process. Significantly, cryopreservation represents an option for fertility preservation in patients who develop gonadal failure for any condition and those who want to freeze their germ cells for later use. The possibility of freezing sperm, oocytes, and embryos has been available for a long time, and in 1983 the first birth with thawed oocytes was achieved. From the mid-2000s forward, the use of egg vitrification through intracytoplasmic sperm injection has improved pregnancy rates. Births using assisted reproductive technologies (ART) have some adverse conditions and events. These risks could be associated with ART procedures or related to infertility. Cryopreservation generates changes in the epigenome of gametes and embryos, given that ART occurs when the epigenome is most vulnerable. Furthermore, cryoprotective agents induce alterations in the integrity of germ cells and embryos. Notably, cryopreservation extensively affects cell viability, generates proteomic profile changes, compromises crucial cellular functions, and alters sperm motility. This technique has been widely employed since the 1980s and there is a lack of knowledge about molecular changes. The emerging view is that molecular changes are associated with cryopreservation, affecting metabolism, cytoarchitecture, calcium homeostasis, epigenetic state, and cell survival, which compromise the fertilization in ART.

Effect of high hydrostatic pressure on mitochondrial activity, reactive oxygen species level and developmental competence of cultured pig embryos

High hydrostatic pressure (HHP) has been previously used to increase mammalian oocyte and embryo tolerance on subsequent stresses related with different assisted reproductive technologies. Nevertheless, the mechanisms for HHP-induced stress responses in early embryos have not been yet well understood. Previous studies focused mainly on HHP-modified gene expression while possible changes in cellular functions, including modification of energy metabolism and oxidative stress were neglected. Therefore, we aimed to analyze the effect of HHP treatment on the efficiency of subsequent in vitro pig embryos culture in NCSU-23 medium, on mitochondrial membrane potential (ΔΨm) and reactive oxygen species (ROS) level during their pre-implantation development. Porcine embryos were exposed to the hydrostatic pressure of 20 MPa and their quick response to such stress was analyzed 1 h later. In comparison with control embryos, we detected lower ΔΨm by ∼13% only in expanded blastocysts as well as decreased ROS level by ∼30% and ∼42% at the morula and expanded blastocyst stages, respectively. After HHP-treatment at transcriptionally inactive zygote stage and subsequent embryo culture, long-time responses were found: (1) at expanded blastocyst stage manifesting by ΔΨm decrease by ∼16%, (2) at the morula and expanded blastocyst stages in the form of ROS level reduction by ∼38% and ∼33% respectively. Following HHP stress applied at the transcriptionally active morula stage the long-time response in the expanded blastocysts as a decrease of ΔΨm by ∼19% and ROS level by ∼37% was observed. The percentage of obtained expanded blastocysts was higher after culture of HHP-treated zygotes in comparison to the control. Moreover, expanded blastocysts developed in vitro from both HHP-treated zygotes or morulae, exhibited higher total number of cells per blastocyst, higher number of cells in the inner cell mass as well as lower number of TUNEL-positive nuclei per blastocyst and lower TUNEL index, when compared to untreated embryos. Therefore, the HHP stress applied at the zygote stage, enhances developmental potential and quality of in vitro obtained porcine blastocysts due to the both decreased ΔΨm and ROS level. Our findings may contribute to better understanding of the mechanism of HHP-mediated modifications of energy metabolism and oxidative stress during in vitro development of pig embryos.

Induction of Sublethal Oxidative Stress on Human Sperm before Cryopreservation: A Time-Dependent Response in Post-Thawed Sperm Parameters

Objective

A recent innovative approach, based on induction of sublethal oxidative stress to enhance sperm cryosurvival, has been applied before sperm cryopreservation. The purpose of this study was to investigate the effects of different induction times of sublethal oxidative stress before cryopreservation on human post-thawed sperm quality.

Materials and Methods

In this experimental study, we selected semen samples (n=20) from normozoospermic men according to 2010 World Health Organization (WHO) guidelines. After processing the samples by the density gradient method, we divided each sample into 5 experimental groups: fresh, control freezing, and 3 groups exposed to 0.01 μM sodium nitroprusside (SNP) [nitric oxide (NO) donor] for 30 (T30), 60 (T60), or 90 minutes (T90) at 37˚C and 5% CO₂ before cryopreservation. Motion characteristics [computer-assisted sperm analyser], viability, apoptosis [annexin V/propidium iodide (PI) assay], DNA fragmentation [sperm chromatin structure assay (SCSA)], and caspase 3 activity (FLICA Caspase Detection Kit) were assessed after thawing. The results were analysed by using one-way ANOVA and Tukey's test. The means were significantly different at P<0.05.

Results

Cryopreservation significantly decreased sperm viability and motility parameters, and increased the percentage of apoptosis, caspase 3 activity, and DNA fragmentation (P<0.01) compared to the fresh group. The T60 group had a higher significant percentage of total motility (TM) and progressive motility compared with other cryopreserved groups (P<0.05). We observed a significantly lower percentage of apoptotic rate and caspase 3 activity in the T60 group compared to the other cryopreserved groups (P<0.05). DNA integrity was not significantly affected by this time of sublethal stress induction (P>0.05).

Conclusion

Our results have demonstrated that the application of sublethal oxidative stress by using 0.01 μM NO for 60 minutes before the freezing process can be a beneficial approach to improve post-thawed human sperm quality.

Blocking connexin channels improves embryo development of vitrified bovine blastocysts

Connexins (Cxs) are required for normal embryo development and implantation. They form gap junctions (GJs) connecting the cytoplasm of adjacent cells and hemichannels (HCs), which are normally closed but open in response to stress conditions. Excessive HC opening is detrimental for cell function and may lead to cell death. We found that hatching of in vitro-produced bovine embryos, matured in serum-containing conditions, was significantly improved when vitrification/warming was done in the presence of Gap26 that targets GJA1 (Cx43) and GJA4 (Cx37). Further work showed that HCs from blastocysts produced after oocyte maturation in the presence of serum were open shortly after vitrification/warming, and this was prevented by Gap26. Gap26, applied for the exposure times used, inhibited Cx43 and Cx37 HCs while it did not have an effect on GJs. Interestingly, Gap26 had no effect on blastocyst degeneration or cell death. We conclude that blocking HCs protects embryos during vitrification and warming by a functional effect not linked to cell death.

Effect of High Hydrostatic Pressure Applied Before Cryopreservation on the Survival Rate and Quality of Porcine Mesenchymal Stem Cells After Thawing

The aim of the present study was to examine the effects of varied high hydrostatic pressure (HHP) values on survival rate, proliferation rate, cell multipotency (transcript expression of SOX2, C-MYC, and REX1) and apoptosis (expression of phosphatidylserine (PS), SURVIVIN at the RNA level and BAX at the protein level) of porcine mesenchymal stem cells (MSCs). MSCs were isolated from porcine bone marrow and cultured in vitro. Before cryopreservation and storage in liquid nitrogen, MSCs were subjected to HHP at the varied pressures of 20, 30, 40, 50, or 60 MPa for 1 h at 24°C. Immediately after thawing and after 8 days of in vitro culture, cells were subjected to trypan blue staining, cell counting, real-time Polymerase Chain Reaction (PCR), western blotting, and fluorescence microscopy. BAX protein expression was only estimated immediately after HHP to exclusively examine the impact of HHP on apoptosis of MSCs. The viability of MSC subjected to 40, 50, and 60 MPa and estimated immediately after thawing increased significantly (P < 0.001 for 60 MPa and P < 0.05 for 40 and 50 MPa) in comparison to control. The proliferation rate of MSCs subjected to 40 MPa HHP was significantly higher than in the control group (P < 0.02) after 8 days of in vitro culture. After 8 days of in vitro culture, no significant differences were noted in the survival rates, PS exposure, or levels of SOX2, C-MYC, REX1, and SURVIVIN gene expression in all analyzed groups compared to control.

IN CONCLUSION

40-60 MPa HHP has a positive impact by improving cell viability in short term. 20-60 MPa HHP does not induce nor decrease apoptosis in MSCs. Fortunately, HHP does not induce differentiation of MSC. Our results calls for further analysis using HHP values higher than 60 MPa.

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.

Improved cryotolerance and developmental competence of human oocytes matured in vitro by transient hydrostatic pressure treatment prior to vitrification

BACKGROUND

At present, the metaphase II (MII) oocytes have a very special structure that leads to complex difficulties associated with its vitrification, and their efficacy still needs a large amount of study to observe. The present study was to investigate whether transient hydrostatic pressure (THP), which was utilized for oocytes before vitrification, had positive effect on the oocytes' developmental ability and reactive oxygen species, and had no damage on meiotic spindle, zona pellucida, and DNA copy number.

METHODS

All the immature oocytes used in this research were collected between February 2015 and December 2015 in Shanghai Ji Ai Genetics & IVF Institute. The MII oocytes, which were originated from metaphase I (MI) oocytes, were randomly distributed into three groups: A) fresh oocytes; B) vitrification; and C) vitrification after THP treatment. The embryo developmental outcome was evaluated after intracytoplasmic sperm injection and embryo culture. Furthermore, the meiotic spindle behavior, reactive oxygen species (ROS), zona pellucida (ZP), and DNA copy number variation were evaluated and compared among the three groups.

RESULTS

A total of 568 MII oocytes were included in the study. Embryos from group B had fewer cells on day 3 compared with group A and C (5.01 ± 2.11 for group A, 3.89 ± 2.21 for group B, and 4.69 ± 2.05 for group C). The developmental feature of blastocyst in groups A and C were superior to those of group B. The MII oocytes were manipulated with THP before vitrification, and the equilibration time was significantly shorter in the vitrification procedure (244.9 ± 30.1 vs. 181.5 ± 10.1). The ROS, ZP of vitrified/warmed oocytes in group C were improved with THP before vitrification. THP had no influence on the meiotic spindle and DNA copy number variation of vitrified/warmed oocytes.

CONCLUSIONS

The results of the study indicated that sublethal THP treatment before vitrification increased the developmental competence of human in vitro matured oocytes, reduced vitrification-related changes in the ROS, which occurred during oocyte vitrification, and did not damage the meiotic spindle, ZP and DNA copy number variation.

Effects of High Hydrostatic Pressure on Expression Profiles of In Vitro Produced Vitrified Bovine Blastocysts

High hydrostatic pressure (HHP) has been used to pre-condition embryos before essential, yet potentially detrimental procedures such as cryopreservation. However, the mechanisms for HHP are poorly understood. We treated bovine blastocysts with three different HHP (40, 60 and 80 MPa) in combination with three recovery periods (0, 1 h, 2 h post HHP). Re-expansion rates were significantly higher at 40 and 60 but lower at 80 MPa after vitrification-warming in the treated groups than controls. Microarray analysis revealed 399 differentially expressed transcripts, representing 254 unique genes, among different groups. Gene ontology analysis indicated that HHP at 40 and 60 MPa promoted embryo competence through down-regulation of genes in cell death and apoptosis, and up-regulation of genes in RNA processing, cellular growth and proliferation. In contrast, 80 MPa up-regulated genes in apoptosis, and down-regulated protein folding and cell cycle-related genes. Moreover, gene expression was also influenced by the length of the recovery time after HHP. The significantly over-represented categories were apoptosis and cell death in the 1 h group, and protein folding, response to unfolded protein and cell cycle in the 2 h group compared to 0 h. Taken together, HHP promotes competence of vitrified bovine blastocysts through modest transcriptional changes.

Stress preconditioning of semen before cryopreservation improves fertility and increases the number of offspring born: a prospective randomised study using a porcine model

The aim of the present study was to investigate the effect of applying sublethal stress treatment at room temperature, before cryopreservation (hydrostatic pressure (HP): 40 MPa, 80 min) of 34 boar ejaculate samples, on post-thawed motility and sow fertility. Sows (n = 102) were randomly allocated into equal groups inseminated with HP-treated or untreated frozen–thawed semen. Sows were inseminated twice, 10 h apart, with 6 × 109 spermatozoa per dose without oestrus synchronisation. Rates of non-return of oestrus and pregnancy, and total numbers of piglets and live piglets were significantly higher (P < 0.05) in the HP-treated group. There was also a numerical, albeit non-significant (P > 0.05), improvement in the farrowing rate in the HP-treated group. Although the number of live piglets per litter decreased approximately 15% in both groups by 42 days after farrowing, but this remained significantly higher in the HP-treated group. Although total and progressive sperm motility were significantly (P < 0.001) higher in the HP-treated group, there were no significant differences (P > 0.05) in these parameters between pregnant and non-pregnant sows in either group; thus motility can indicate, but not predict, improved fertility. In conclusion, HP treatment, with sperm cryopreservation, increases in vitro sperm motility and improves reproductive performance without adversely affecting the health of the piglets.

Controlled hydrostatic pressure stress downregulates the expression of ribosomal genes in preimplantation embryos: a possible protection mechanism?

The efficiency of various assisted reproductive techniques can be improved by preconditioning the gametes and embryos with sublethal hydrostatic pressure treatment. However, the underlying molecular mechanism responsible for this protective effect remains unknown and requires further investigation. Here, we studied the effect of optimised hydrostatic pressure treatment on the global gene expression of mouse oocytes after embryonic genome activation. Based on a gene expression microarray analysis, a significant effect of treatment was observed in 4-cell embryos derived from treated oocytes, revealing a transcriptional footprint of hydrostatic pressure-affected genes. Functional analysis identified numerous genes involved in protein synthesis that were downregulated in 4-cell embryos in response to hydrostatic pressure treatment, suggesting that regulation of translation has a major role in optimised hydrostatic pressure-induced stress tolerance. We present a comprehensive microarray analysis and further delineate a potential mechanism responsible for the protective effect of hydrostatic pressure treatment.

Effects of high hydrostatic pressure on genomic expression profiling of porcine parthenogenetic activated and cloned embryos

Handmade cloning (HMC) has been used to generate transgenic pigs for biomedical research. Recently, we found that parthenogenetic activation (PA) of porcine oocytes and improved HMC efficiency could be achieved by treatment with sublethal high hydrostatic pressure (HHP). However, the molecular mechanism underlying the effects of HHP treatment on embryonic development is poorly understood and so was investigated in the present study. Thus, in the present study, we undertook genome-wide gene expression analysis in HHP-treated and untreated oocytes, as well as in 4-cell and blastocyst stage embryos derived by PA or HMC. Hierarchical clustering depicted stage-specific genomic expression profiling. At the 4-cell and blastocyst stages, 103 and 163 transcripts were differentially expressed between the HMC and PA embryos, respectively (P<0.05). These transcripts are predominantly involved in regulating cellular differentiation, gene expression and cell-to-cell signalling. We found that 44 transcripts were altered by HHP treatment, with most exhibiting lower expression in HHP-treated oocytes. Genes involved in embryonic development were prominent among the transcripts affected by HHP. Two of these genes (INHBB and ME3) were further validated by quantitative reverse transcription-polymerase chain reaction. We also observed that HHP treatment activated expression of the imprinting gene DLX5 in 4-cell PA embryos. In conclusion, our genomic expression profiling data suggest that HHP alters the RNA constitution in porcine oocytes and affects the expression of imprinting genes during embryonic development.

Adaptive response, evidence of cross-resistance and its potential clinical use

Organisms and their cells are constantly exposed to environmental fluctuations. Among them are stressors, which can induce macromolecular damage that exceeds a set threshold, independent of the underlying cause. Stress responses are mechanisms used by organisms to adapt to and overcome stress stimuli. Different stressors or different intensities of stress trigger different cellular responses, namely induce cell repair mechanisms, induce cell responses that result in temporary adaptation to some stressors, induce autophagy or trigger cell death. Studies have reported life-prolonging effects of a wide variety of so-called stressors, such as oxidants, heat shock, some phytochemicals, ischemia, exercise and dietary energy restriction, hypergravity, etc. These stress responses, which result in enhanced defense and repair and even cross-resistance against multiple stressors, may have clinical use and will be discussed, while the emphasis will be on the effects/cross-effects of oxidants.

Vitrification of bovine blastocysts pretreated with sublethal hydrostatic pressure stress: evaluation of post-thaw in vitro development and gene expression

Sublethal stress treatment has been reported to enhance gametes' performance in subsequent procedures, such as cryopreservation. The aim of the present study was to evaluate the effect of different equilibration times between the termination of a sublethal hydrostatic pressure (HP) stress treatment and the initiation of vitrification on the post-thaw survival, continued in vitro development, hatching rate and gene expression of selected candidate genes of in vitro-produced (IVP) expanded bovine blastocysts. Day 7 IVP blastocysts were subjected to 600 bar pressure for 60 min at 32°C. Immediately after pressure treatment (HP0h) or after 1 or 2h incubation (HP1h and HP2h groups, respectively), embryos were either vitrified and warmed using the open pulled straw method, followed by 72 h in vitro culture or were stored at -80°C until gene expression analysis. Re-expansion and hatching rates after vitrification-warming were significantly (P<0.05) higher in the HP0h (88 and 76%, respectively) and HP1h (90 and 75%, respectively) groups than in the untreated (82 and 63%, respectively) and HP2h groups (79 and 70%, respectively). Moreover, the HP1h group showed further improvement in the speed of re-expansion and resumption of normal in vitro development. Cumulative analysis of all genes (SC4MOL, HSP1A1A, SOD2 and GPX4) revealed a similar pattern of expression, with a tendency for peak transcript abundance 1h after HP treatment. Application of HP stress treatment was found to be efficient in increasing the in vitro developmental competence of vitrified bovine embryos.

Cells under pressure: how sublethal hydrostatic pressure stress treatment increases gametes' and embryos' performance

The principal approach in in vitro embryo culture and manipulation has been a defensive one: procedures aim to satisfy passively the supposed or real physiological needs of gametes and embryos. Similarly, during cryopreservation the aim is to cause minimal damage to cells whilst attempting to obtain the highest achievable cell survival. However, carefully chosen and precisely controlled sublethal stress treatment of cells has been described to improve embryos’ and gametes’ performance, and, as a consequence, subsequent morphological survival, fertilisation, in vitro development, pregnancy and farrowing rates improved considerably compared with untreated controls. This review summarises studies that open up a new approach: instead of – and besides – trying to passively reduce the harm to cells during in vitro manipulations and culture, procedures may also prepare the cells themselves to ward off or reduce the damage by turning up the cells’ own, inner capacities.

Current progress in oocyte and embryo cryopreservation by slow freezing and vitrification

Preservation of female genetics is currently done primarily by means of oocyte and embryo cryopreservation. The field has seen much progress during its four-decade history, progress driven predominantly by research in humans, cows, and mice. Two basic cryopreservation techniques rule the field – controlled-rate freezing, the first to be developed, and vitrification, which, in recent years, has gained a foothold. While much progress has been achieved in human medicine, the cattle industry, and in laboratory animals, this is far from being the case for most other mammals and even less so for other vertebrates. The major strides and obstacles in human and other vertebrate oocyte and embryo cryopreservation will be reviewed here.

Development of high hydrostatic pressure in biosciences: pressure effect on biological structures and potential applications in biotechnologies

Compared to temperature, the development of pressure as a tool in the research field has emerged only recently (at the end of the XIXth century). Following several developments in Physics and Chemistry during the first half of the XXth century (in particular the synthesis of diamond in 1953-1954), high pressures were applied in Food Science, especially in Japan. The main objective was then to achieve the decontamination of foods while preserving their organoleptic properties. Now, a new step is engaged: the biological applications of high pressures, from food to pharmaceuticals and biomedical applications. This paper will focus on three main points: (i) a brief presentation of the pressure parameter and its characteristics, (ii) a description of the pressure effects on biological constituents from simple to more complex structures and (iii) a review of the different domains for which the application of high pressures is able to initiate potential developments in Biotechnologies.

Challenge testing of gametes to enhance their viability

Embryos, oocytes and spermatozoa undergo several manipulations during the in vitro procedures that are an integral part of assisted reproductive technologies (ART) in mammals. Consequently, some of the gametes are damaged irreparably, whereas others react to these challenges with some sort of survival mechanism that enables them to come through the process. The details of the mechanism remain unknown but, if identified, it could have immense potential as a new way to improve the viability of embryos produced by ART. However, few publications describe systematic ways to challenge test gametes and then to use the results as a basis for improving gamete viability. Furthermore, new methods to monitor the reactions of gametes to such challenge tests are needed. In the present review, these two issues are discussed, as are some of the conditions necessary before a challenge test protocol can be part of future work with ART.

Embryo culture: can we perform better than nature?

Culture of preimplantation-stage embryos has always been a key element of laboratory embryology and has contributed substantially to the success of many assisted reproduction procedures. During the past decade, its importance has increased as extended in-vitro embryo culture and single blastocyst transfer have become indispensable parts of the approach to decreasing the chance of multiple pregnancy while preserving the overall efficiency of the treatment. However, in spite of the scientific and commercial challenge stimulating research worldwide to optimize embryo culture conditions, a consensus is missing even in the basic principles, including composition and exchange of media, the required physical and biological environment and even the temperature of incubation. This review attempts to summarize the controversies, demonstrate the fragility of some widely accepted dogmas and generate an open-minded debate towards rapid and efficient optimization. New approaches expanding the traditional frames of mammalian embryo culture are also discussed. Although some researchers suppose that the efficiency of the presently applied in-vitro culture systems have already approached the biological limits, authors are confident that substantial improvement may be achieved that may expand considerably the possibilities of future assisted reproduction in humans.

Short-term exposure to hydrogen peroxide during oocyte maturation improves bovine embryo development

Recent studies have shown that short-term exposure of oocytes to a stressor such as hydrostatic pressure or osmotic stress might induce stress tolerance in embryos. The aim of the present study was to investigate the consequences of short-term hydrogen peroxide (H(2)O(2)) exposure to bovine in vitro matured cumulus-oocyte complexes (COCs) on subsequent preimplantation embryo development and apoptosis. In the first experiment, mature COCs were incubated in H(2)O(2) at concentrations ranging between 0.01 and 100 micromol/l, and subsequently fertilized and cultured. Oocyte incubation with 50-100 micromol/l of H(2)O(2) resulted in a significantly higher blastocyst yield (47.3%) in comparison with control medium (31.8%), while apoptotic cell ratio was inversely related with H(2)O(2) concentration. In the second experiment, we showed that the stress tolerance after H(2)O(2) exposure was not mediated by increased glutathione content in treated oocytes nor by enhanced fertilization or penetration. Further research should concentrate on the potential role of players that have been associated with stress tolerance in somatic cell lines.

Factors affecting the outcome of human blastocyst vitrification

With single blastocyst transfer practice becoming more common in ART, there is a greater demand for a convenient and reliable cryostorage of surplus blastocysts. Vitrification has emerged in the last decade as an alternative promising substitute for slow freezing. Blastocysts represent a unique challenge in cryostorage due to their size, multicellular structure and presence of blastocoele. The continuous acquisition of experience and introduction of many different technological developments has led to the improvement of vitrification as a technology and improved the results of its application in blastocyst cryostorage. The current information concerning safety and efficacy of the vitrification of blastocysts will be reviewed along with the variables that can impact the outcome of the procedure.

Osmotic stress induced by sodium chloride, sucrose or trehalose improves cryotolerance and developmental competence of porcine oocytes

Exposure of porcine oocytes to increased concentrations of NaCl prior to manipulation has been reported not only to increase cryotolerance after vitrification, but also to improve developmental competence after somatic cell nuclear transfer (SCNT). In the present study we compared the effects of NaCl with those of concentrated solutions of two non-permeable osmotic agents, namely sucrose and trehalose, on the cryotolerance and developmental competence of porcine oocytes. In Experiment 1, porcine in vitro-matured cumulus–oocyte complexes (COCs; n = 1200) were exposed to 588 mOsmol NaCl, sucrose or trehalose solutions for 1 h, allowed to recover for a further 1 h, vitrified, warmed and subjected to parthenogenetic activation. Both Day 2 (where Day 0 is the day of activation) cleavage and Day 7 blastocyst rates were significantly increased after NaCl, sucrose and trehalose osmotic treatments compared with untreated controls (cleavage: 46 ± 5%, 44 ± 7%, 45 ± 4% and 26 ± 6%, respectively; expanded blastocyst rate: 6 ± 1%, 6 ± 2%, 7 ± 2% and 1 ± 1%, respectively). In Experiment 2, COCs (n = 2000) were treated with 588 mOsmol NaCl, sucrose or trehalose, then used as recipients for SCNT (Day 0). Cleavage rates on Day 1 did not differ between the NaCl-, sucrose-, trehalose-treated and the untreated control groups (92 ± 3%, 95 ± 3%, 92 ± 2% and 94 ± 2%, respectively), but blastocyst rates on Day 6 were higher in all treated groups compared with control (64 ± 2%, 69 ± 5%, 65 ± 3% and 47 ± 4%, respectively). Cell numbers of Day 6 blastocysts were higher in the control and NaCl-treated groups compared with the sucrose- and trehalose-treated groups. In conclusion, treatment of porcine oocytes with osmotic stress improved developmental competence after vitrification combined with parthenogenetic activation, as well as after SCNT.

High hydrostatic pressure treatment of porcine oocytes before handmade cloning improves developmental competence and cryosurvival

An innovative technique, called the high hydrostatic pressure (HHP) treatment, has been recently reported to improve the cryosurvival of gametes or embryos in certain mammalian species. The aim of the present study was to investigate the in vitro and in vivo developmental competence and cryotolerance of embryos produced by handmade cloning (HMC) after pressure treatment of recipient oocytes. In vitro-matured porcine oocytes were treated with a sublethal hydrostatic pressure of 20 MPa (200 times greater than atmospheric pressure) and recovered for either 1 or 2 h (HHP1 and HHP2 groups, respectively) before they were used for HMC. After 7 days of in vitro culture, blastocyst rates and mean cell numbers were determined. Randomly selected blastocysts were vitrified with the Cryotop method based on minimum volume cooling procedure. The blastocyst rate was higher in the HHP2 group than in the control group (68.2 +/- 4.1% vs. 46.4 +/- 4.2%; p < 0.01), while there was no difference between HHP1 and control group (52.1 +/- 1.2% vs. 49.0 +/- 2.7%; p > 0.05). Similar mean cell numbers of produced blastocysts were obtained in HHP2 and control groups (56 +/- 4 vs. 49 +/- 5; p > 0.05). Subsequent blastocyst vitrification with the Cryotop method resulted in significantly higher survival rate after thawing in the HHP2 group than in the control group (61.6 +/- 4.0% vs. 30.2 +/- 30.9%; p < 0.01). Fifty-six and 57 day 5 to day 7 fresh blastocysts in HHP1 group were transferred into two recipient sows on day 5 of the estrous cycle. One recipient was diagnosed pregnant and gave birth to two healthy piglets by naturally delivery on day 122 of gestation. This pilot study proved that the sublethal HHP treatment of porcine oocytes before HMC results in improved in vitro developmental competence and cryotolerance, and supports embryonic and fetal development as well as pregnancy establishment and maintenance up to the birth of healthy piglets.