New methods for cooling and storing oocytes and embryos in a clean environment of -196°C

Three live births after human embryo vitrification with the use of aluminum oxide as an intermediate cooling agent: a case report

Objective

To study the possibility of increasing the cooling rates of the vitrification procedure in a closed system with the use of aluminum oxide as an intermediate coolant.

Design

Case report.

Subjects

Six patients undergoing procedures for assisted reproduction.

Intervention

Comparative studies of cryopreservation of donor embryos with aluminum oxide as an intermediate cooling agent (experimental group) and without it (control group) have been performed. After thawing, the embryo morphology and its potential to develop to the blastocyst stage have been assessed. The methodology was then applied to clinical practice.

Main Outcome Measures

Twenty embryos of 6 patients have been vitrified on day 4 after fertilization with the use of aluminum oxide as an intermediate coolant. Fourteen of them have been thawed. All have displayed normal morphology and 10 have formed blastocysts after 24 hours of culture. Four of the patients received embryo transfer with 2 embryos and the other 2 with single embryos.

Results

After preliminary comparative studies of embryos frozen with aluminum oxide and a control group, the results showed no statistically significant difference between their quality and potential to reach to blastocyst stage. That gave us ground to apply the methodology in clinical practice. After the embryo transfer, 3 clinical pregnancies with successful live births have been obtained.

Conclusions

Our experience shows that preimplantation embryos can be cryopreserved aseptically, in closed systems, with the help of aluminum oxide as an intermediate coolant.

The Effect of Cryoprotectants Concentration on Ice Crystal Propagation Velocity

Background: Two physicochemical effects occur during vitrification: nucleation and crystallization. Nucleation is a statistical occurrence by its nature. Thus, the more water molecules that are present the higher are the chances for nucleation to occur. Crystallization is a first-order transition where a water molecule is incorporated into ice crystal. Intracellular viscosity, which is the combination of water, salts, and cryoprotectants (CPs), affects both the nucleation and crystal growth rates. Ice velocity is inversely correlated with the viscosity and directly proportional to the function of the system's supercooling. However, little is known about the speed of ice crystal propagation in vitrification solutions containing different concentrations of CPs. Methods: This article describes the ice crystal propagation velocity while referring to vitrification. Ice crystal propagation velocity was measured in solutions containing different CP (dimethyl sulfoxide [DMSO], propylene glycol [PG], ethylene glycol [EG], and glycerol) concentrations at a supercooled temperature. The different CPs solutions were inserted into 0.25 mL straws and placed in different temperatures of an alcohol bath (Tc) at supercooling temperatures of -8°C to -10°C. Results: We found that ice crystal propagation is inversely correlated to CP concentrations. Interestingly, PG showed, with statistically significant results, lower ice crystal growth velocities up to concentrations of 30% (v/v), compared with DMSO, and EG at the same concentrations. The combination of EG with PG showed better results (0.25 mm/s) than EG with DMSO (0.39 mm/s) in terms of decreasing the ice crystal growth velocity. When the concentration was increased to 40% (v/v), EG showed the lowest ice crystal propagation velocity (0.09 mm/s), although not significantly different than PG and glycerol but significantly lower than DMSO (0.13 mm/s). Conclusion: These results suggest that current vitrification solutions are not optimized. Based on our results, we suggest that combining PG with EG has advantages over the combination of DMSO and EG, which might promote successful cell and tissue vitrification.

Cryostorage management of reproductive cells and tissues in ART: status, needs, opportunities and potential new challenges

Among the wide range of procedures performed by clinical embryologists, the cryopreservation of reproductive cells and tissues represents a fundamental task in the daily routine. Indeed, cryopreservation procedures can be considered a subspecialty of medically assisted reproductive technology (ART), having the same relevance as sperm injection or embryo biopsy for preimplantation genetic testing. However, although a great deal of care has been devoted to optimizing cryopreservation protocols, the same energy has only recently been spent on developing and implementing strategies for the safe and reliable storage and transport of reproductive specimens. Herein, we have summarized the content of the available guidelines, the risks, the needs and the future perspectives regarding the management of cryopreservation biorepositories used in ART.

Oocyte and embryo cryopreservation in assisted reproductive technology: past achievements and current challenges

Cryopreservation has revolutionized the treatment of infertility and fertility preservation. This review summarizes the milestones that paved the way to the current routinary clinical implementation of this game-changing practice in assisted reproductive technology. Still, evidence to support "the best practice" in cryopreservation is controversial and several protocol adaptations exist that were described and compared here, such as cumulus-intact vs. cumulus-free oocyte cryopreservation, artificial collapse, assisted hatching, closed vs. open carriers, and others. A last matter of concern is whether cryostorage duration may impact oocyte/embryo competence, but the current body of evidence in this regard is reassuring. From social and clinical perspectives, oocyte and embryo cryopreservation has evolved from an afterthought when assisted reproduction was intended for immediate pregnancy with supernumerary embryos of secondary interest to its current purpose, which primarily is to preserve fertility long-term and more comprehensively allow for family planning. However, the initial consenting process, which still is geared to short-term fertility care, may no longer be relevant when the individuals that initially preserved the tissues have completed their reproductive journey. A more encompassing counseling model is required to address changing patient values over time.

Cryopreservation by Directional Freezing and Vitrification Focusing on Large Tissues and Organs

The cryopreservation of cells has been in routine use for decades. However, despite the extensive research in the field, cryopreservation of large tissues and organs is still experimental. The present review highlights the major studies of directional freezing and vitrification of large tissues and whole organs and describes the different parameters that impact the success rate of large tissue and organ cryopreservation. Key factors, such as mass and heat transfer, cryoprotectant toxicity, nucleation, crystal growth, and chilling injury, which all have a significant influence on whole-organ cryopreservation outcomes, are reviewed. In addition, an overview of the principles of directional freezing and vitrification is given and the manners in which cryopreservation impacts large tissues and organs are described in detail.

Cryopreservation of Porcine Embryos: Recent Updates and Progress

Cryopreservation of embryos is important for long-distance embryo transfer and conservation of genetic resources. Porcine research is important for animal husbandry and biomedical research. However, porcine embryos are difficult to cryopreserve because of their high cytoplasmic lipid content and sensitivity to chilling stress. Vitrification is more efficient than slow freezing, and vitrification is mostly used in embryo cryopreservation. So far, the vitrification process of porcine embryos has been continuously improved, resulting in improved survival rates of warmed embryos and farrowing rates after the transplant procedure. It is worth noting that automatic vitrification has made great progress, which is expected to promote the standardization and application of vitrification. In this article, the vitrification process of porcine embryos at the blastula stage and early development stages is reviewed in detail. In addition, the efficiency of different vitrification systems was compared. In addition, we summarize technology that can improve the survival rate of cryopreserved porcine embryos, such as delipidation methods (including physical delipidation and chemical delipidation) and medium improvements (including chemically defined media and adding antioxidants). Meanwhile, gene expression changes during cryopreservation are also elaborated.

Cryo-banking of human spermatozoa by aseptic cryoprotectants-free vitrification in liquid air: Positive effect of elevated warming temperature

Cryoprotectant-free vitrification is a common method for spermatozoa cryopreservation by direct plunging into liquid nitrogen. However, the commercial liquid nitrogen could be potentially contaminated by microorganisms. Warming temperature plays an essential role for quality of human spermatozoa after vitrification. This study aimed to evaluate comparatively a quality spermatozoa after vitrification in liquid nitrogen and clean liquid air as well as with two warming rates: at 42 °C and 45 °C. After performing of routine swim-up of normozoospermia samples, spermatozoa from the same ejaculate were divided into two groups: vitrified in liquid nitrogen (LN) and sterile liquid air (LA). Spermatozoa of LN group were warmed at 42 °C, and spermatozoa of LA groups were divided and warmed at 42 °C (LA42) and 45 °C (LA45). Then spermatozoa motility, reactive oxygen species (ROS), mitochondrial membrane potential (MMP), reactive nitrogen species (RNS), and viability were assessed. It was no found significant differences in quality of spermatozoa from LN and LA groups in the motility, ROS, MMP, RNS rates after warming at 42 °C. A tendency to obtain better spermatozoa quality was found with using of warming by 42 °C in comparison with 45 °C. It was concluded that cryoprotectant-free vitrification by direct dropping of human spermatozoa into clean liquid air can be used as an alternative to cooling in liquid nitrogen. Warming of spermatozoa at 42 °C allows to preserve the spermatozoa physiological parameters.

A Systematic Review on the Investigation of SARS-CoV-2 in Semen

Background

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is a virus that is present in most bodily fluids. However, whether SARS-CoV-2 is present in the semen remains underexplored. Thus, we systematically reviewed the existing studies on the presence of SARS-CoV-2 in semen.

Methods

A literature search of the PubMed, Embase, Cochrane, Web of Science, Google Scholar, and Ovid databases was performed for articles from the dates of their inception to August 2020 using the following keywords: COVID-19, SARS-CoV2, seminal, semen, and sperm. After excluding non-human studies and articles that were not in the English language, we identified 19 relevant studies. The full text of the articles were reviewed and a total of eight articles remained after applying our selection criteria.

Results

After reviewing the presence of SARS-CoV-2 in the eight different studies using semen samples, only one reported the presence of the virus. Six out of 160 total semen samples with SARS-CoV-2 positive demonstrated the presence of viral RNA, of which 2 were from males in the recovery phase and 4 from the acute phase of the infection.

Conclusion

The novel nature of SARS-CoV-2 has limited the number and size of studies on semen. Nevertheless, the current literature, while limited, has confirmed the presence of SARS-CoV-2 in semen in one out of the eight reported studies and totaling 4.3% of the population screened. Taken together, the risk of the presence of SARS-CoV-2 in semen appears to be extremely low and likely negligible in recovered men. Future studies need to focus on whether complete viral particles can be seen in semen and the possibility of sexual transmission.

Fertility preservation during the COVID-19 pandemic: mitigating the viral contamination risk to reproductive cells in cryostorage

Reopening fertility care services across the world in the midst of a pandemic brings with it numerous concerns that need immediate addressing, such as the impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on the male and female reproductive cells and the plausible risk of cross-contamination and transmission. Due to the novelty of the disease the literature contains few reports confirming an association of SARS-CoV-2 with reproductive tissues, gametes and embryos. Cryobanking, an essential service in fertility preservation, carries the risk of cross-contamination through cryogenic medium and thus calls for risk-mitigation strategies. This review aims to address the available literature on the presence of SARS-CoV-2 on tissues, gametes and embryos, with special reference to the possible sources of cross-contamination through liquid nitrogen. Strategies for risk mitigation have been extrapolated from reports dealing with other viruses to the current global crisis, for safety in fertility treatment services in general, and specifically for oncofertility.

Aseptic Cryoprotectant-Free Vitrification of Human Spermatozoa by Direct Dropping into a Cooling Agent

Spermatozoa cryopreservation is used for the management of infertility and some other medical conditions. Routinely applied cryopreservation techniques depend on permeating cryoprotectants and relatively slow freezing rates. Cryoprotectant-free vitrification is an alternative and cost-effective method that is based on rapid cooling of spermatozoa by direct plunging into a cooling agent to prevent lethal intracellular ice crystallization and the detrimental effects of high salt concentrations. One of the problems with this technique is that full sterilization of commercially produced liquid nitrogen, which could be contaminated with different pathogens, is not possible. Here we use a benchtop device for the production of sterile liquid air with the same temperature as liquid nitrogen (-195.7 °C). This has been used to develop aseptic technology for cryoprotectant-free vitrification of human spermatozoa.

Human sperm vitrification: the state of the art

Sperm cryopreservation has been widely used in assisted reproductive technology (ART) and has resulted in millions of live births. Two principal approaches have been adopted: conventional (slow) freezing and vitrification. As a traditional technique, slow freezing has been successfully employed and widely used at ART clinics whereas the latter, a process to solidify liquid into an amorphous or glassy state, may become a faster alternative method of sperm cryopreservation with significant benefits in regard to simple equipment and applicability to fertility centers. Sperm vitrification has its own limitations. Firstly, small volume of load is usually plunged to liquid nitrogen to achieve high cooling rate, which makes large volume sample cryopreservation less feasible. Secondly, direct contact with liquid nitrogen increases the potential risk of contamination. Recently, new carriers have been developed to facilitate improved control over the volume and speed, and new strategies have been implemented to minimize the contamination risk. In summary, although sperm vitrification has not yet been applied in routine sperm cryopreservation, its potential as a standard procedure is growing.

Aseptic Technology for Cryoprotectant-Free Vitrification of Human Spermatozoa by Direct Dropping into Clean Liquid Air: Apoptosis, Necrosis, Motility, and Viability

This study aimed to compare the quality of human spermatozoa vitrified by direct plunging into liquid nitrogen vs. liquid air. Spermatozoa were divided into three groups: fresh spermatozoa (Group F) were used as a control. Spermatozoa suspension (20 μl) was vitrified in open granules by direct dropping into liquid nitrogen (Group LN) or clean liquid air (Group LA). After warming at 37°C, the progressive motility rate of Group F was reduced from 65.9 ± 2.5% to 34.0 ± 1.9% (Group LN) and 38.1 ± 2.3% (Group LA), respectively (P_1-2,3 < 0.05). The reductions in viability were 65.6 ± 2.2%, 29.0 ± 1.8%, and 36.6 ± 2.6% for Groups F, LN, and LA, respectively (P_1-2,3 < 0.05). Comparing spermatozoa vitrified in liquid nitrogen vs. liquid air, no significant differences were detected in motility (34.0 ± 1.9% vs. 38.1 ± 2.3%), viability (29.0 ± 1.8% vs. 36.6 ± 2.6%), early apoptosis (13.8 ± 1.5% vs. 14.3 ± 1.8%), late apoptosis (45.5 ± 1.8% vs. 43.7 ± 2.2%), and necrosis (19.5 ± 2.0% vs. 15.0 ± 1.8%; p > 0.01 for all respective differences). There was a statistical tendency for increasing rates of “progressive motility” and “viability” and decreasing rates of “apoptosis” and “necrosis” when comparing spermatozoa vitrified in liquid air vs. liquid nitrogen. It is concluded that cryoprotectant-free vitrification by the direct dropping of human spermatozoa in a clean cooling agent (liquid air) is a good alternative to the use of nonsterile liquid nitrogen and can be used to cool cells while minimising the risk of microbial contamination.

Importance of messenger RNA stability of toxin synthetase genes for monitoring toxic cyanobacterial bloom

Toxic cyanobacterial blooms, occurring frequently worldwide, have posed serious threats to human health and aquatic ecosystem. RNA-based quantitative PCR, which could detect potential toxin-producing cyanobacteria that are actively transcribing toxin genes, is a more reliable method, compared to DNA-based qPCR. However, single-stranded mRNA is labile, and their degradation may lead to an underestimate of gene expression level, even misleading toxic risk management, and thus impeding its application. Here, the mRNA stability of microcystin synthetase genes (mcyA-J) was systematically evaluated in unicellular and colonial Microcystis with various treatments (-80 ℃, -196 ℃, 4 °C or 25 °C with RNases inhibitors). Results revealed the highly instability of toxin gene transcripts, affected by transcript structures and cell aggregation. The -196 ℃ treatment was the most effective for stabilizing these transcripts. RNAstore^® (4 °C) could stabilize these transcripts effectively for a short time (less than 7 d), but their stability was strikingly reduced in colonial Microcystis. Furthermore, decay kinetics of mcyA-J transcripts in various treatments was developed, and showed that their decay rates were varied (0.0018-3.014 d^-1), due to different molecular structures. The mcyH transcripts had the lowest decay rate (0.0018 d^-1 at -196 ℃), attributed to the fewest AU sites and stem-loops involved in its secondary structure. Thus, mcyH was the most proper target gene for monitoring toxic cyanobacterial bloom. These findings provided new insight into mRNA stability of toxin genes, and contributed to monitoring toxic cyanobacterial blooms and water managements using RNA-based molecular techniques.

A brief history of oocyte cryopreservation: Arguments and facts

The term "cryopreservation" refers to the process of cooling cells and tissues and storing them at subzero temperatures in order to stop all biological activity and preserve their viability and physiological competences for future use. Cooling to subzero temperatures is not a physiological condition for human cells; this is probably due to the high content of water in the living matter, whose conversion to ice crystals may be associated with severe and irreversible damage. Among reproductive cells and tissues, metaphase II oocytes are notably vulnerable to cryopreservation, mainly because of their large size, low surface area to volume ratio, relatively high water content and presence of the meiotic spindle. As human biological systems lack efficient internal defense mechanisms against chilling injuries, it is of the utmost importance to supply adequate external support, in terms of cryoprotectant additives, appropriate cooling/warming rates, and suitable long-term storage. Over the years, scientists have proposed different cryopreservation strategies in the effort to achieve an optimized recipe ensuring cell survival and, at the same time, maintenance of the physiological functions and abilities necessary to continue life. However, despite the first success obtained in the 1980s with frozen oocytes, it was not until recently that notable improvements in the cryopreservation technique, thanks to the advent of vitrification, allowed a breakthrough of this fine procedure.

The Near Future of Vitrification of Oocytes and Embryos: Looking into Past Experience and Planning into the Future

Currently vitrification is the method of choice for low-temperature preservation of oocytes and embryos. However, that was not the case until about 10 years ago when freezing methods were used relatively successfully for embryos and investigated (unsuccessfully) for oocyte preservation. In this paper we will review the history of oocyte and embryo cryopreservation and look into ways and methods for overcoming and improving the vitrification method since it suffers from inherent disadvantages since it is a cumbersome, time-consuming and costly procedure.

A new, simple, automatic vitrification device: preliminary results with murine and bovine oocytes and embryos

PURPOSE

This paper reports the use of a novel automatic vitrification device (Sarah, Fertilesafe, Israel) for cryopreservation of oocytes and embryos.

METHODS

Mice oocytes (n = 40) and embryos (8 cells, n = 35 and blastocysts, n = 165), bovine embryos (2PN, n = 35), and MII oocytes (n = 84) were vitrified using this automated device. A total of 42 (2 cells) mice embryos, 20 (2PN) bovine embryos, and 150 MII bovine oocytes were used as fresh controls and grown to blastocysts. Upon rewarming, all were assessed for viability, cleavage, blastocyst, and hatching rates.

RESULTS

Ninety-five % (38/40) of the mice MII oocytes regained isotonic volumes and all (100%) the surviving were viable. Rewarmed 8-cell mice embryos had 95% (33/35) blastulation rate and 80% (28/35) hatched. Rewarmed mice blastocysts had 97% survival rate (160/165) and 81% (135/165) hatched. Fresh control mice embryos had 100% (42/42) blastulation and 73% (21/42) hatching rates. Bovine embryos' survival was 100% with 54% (19/35) cleavage and 9% (3/35) blastulation rate. Fresh control bovine embryos had 65% (13/20) cleavage and 20% (4/20) blastulation rate. Vitrified bovine oocytes had 100% survival (84/84), 73% (61/84) cleavage, and 7% (6/84) blastocysts' rates; fresh control had 83% (125/150) cleavage and 11% (17/150) blastocysts' rates.

CONCLUSION

This novel automatic vitrification device is capable to produce high survival rates of oocytes and embryos. We anticipate that as the demand for vitrification of gametes, embryos, and reproductive tissues increases worldwide, the availability of an automated vitrification device will become indispensable for standardization, simplification, and reproducibility of the entire process.

Risk of Contamination of Gametes and Embryos during Cryopreservation and Measures to Prevent Cross-Contamination

The introduction and widespread application of vitrification are one of the most important achievements in human assisted reproduction techniques (ART) of the past decade despite controversy and unclarified issues, mostly related to concerns about disease transmission. Guidance documents published by US Food and Drug Administration, which focused on the safety of tissue/organ donations during Zika virus spread in 2016, as well as some reports of virus, bacteria, and fungi survival to cryogenic temperatures, highlighted the need for a review of the way how potentially infectious material is handled and stored in ART-related procedures. It was experimentally demonstrated that cross-contamination between liquid nitrogen (LN₂) and embryos may occur when infectious agents are present in LN₂ and oocytes/embryos are not protected by a hermetically sealed device. Thus, this review summarizes pertinent data and opinions regarding the potential hazard of infectious transmission through cryopreserved and banked reproductive cells and tissues in LN₂. Special attention is given to the survival of pathogens in LN₂, the risk of cross-contamination, vitrification methods, sterility of LN₂, and the risks associated with the use of straws, cryovials, and storage dewars.