Prevention of high-temperature-induced chromosome damage in mouse spermatozoa freeze-dried using Ca2+ chelator-containing buffer alkalinized with NaOH or KOH

Damages and stress responses in sperm cells and other germplasms during dehydration and storage at nonfreezing temperatures for fertility preservation

Long-term preservation of sperm, oocytes, and gonadal tissues at ambient temperatures has the potential to lower the costs and simplify biobanking in human reproductive medicine, as well as for the management of animal populations. Over the past decades, different dehydration protocols and long-term storage solutions at nonfreezing temperatures have been explored, mainly for mammalian sperm cells. Oocytes and gonadal tissues are more challenging to dehydrate so little to no progress have been made. Currently, the detrimental effects of the drying process itself are better characterized than the impact of long-term storage at nonfreezing temperatures. While structural and functional properties of germ cells can be preserved after dehydration, a long list of damages and stresses in nuclei, organelles, and cytoplasmic membranes have been reported and sometimes mitigated. Characterizing those damages and better understanding the response of germ cells and tissues to the stress of dehydration is fundamental. It will contribute to the development of optimal protocols while proving the safety of alternative storage options for fertility preservation. The objective of this review is to (1) document the types of damages and stress responses, as well as their mitigation in cells dried with different techniques, and (2) propose new research directions.

Freeze Drying as a Method of Long-Term Conservation of Mammalian Semen – A Review

With the development of biotechnological methods that allow the manipulation and free exchange of genetic material, the methods for collecting and storing such material need to be improved. To date, freezing in liquid nitrogen has allowed the storage of cells and entire plant and animal tissues for practically unlimited times. However, alternatives are still being sought to eliminate the constant need to maintain samples at a low temperature. Lyophilization or freeze drying is an alternative to standard freezing procedures. The storage of samples (lyophilisates) does not require specialised equipment but only refines the preservation method itself. In the case of cells capable of movement e.g., sperm, they lose the ability to reach the oocyte in vivo and for in vitro fertilization (IVF) because of the lyophilization process. However, freeze-dried sperm may be used for in vitro fertilization by intracytoplasmic sperm injection (ICSI), based on the results obtained in cleavage, embryo development and the production of live born offspring after embryo transfer. Studies on the lyophilization of sperm have been performed on many animal species, both in the laboratory and in livestock. This conservation method is considered to create biobanks for genetically valuable and endangered species with the simultaneous application of ICSI. This review article aimed to present the issues of the freeze-drying process of mammalian semen and help find solutions that will improve this technique of the long-term preservation of biological material.

Preservation of Mammalian Sperm by Freeze-Drying

Long-term preservation of mammalian sperm at suprazero temperatures is desired to save storage and space costs, as well as to facilitate transport of preserved samples. This can be accomplished by the freeze-drying of sperm samples. Although freeze-drying results in immotile and membrane-compromised sperm, intracytoplasmic sperm injection (ICSI) can be used to introduce such an immotile sperm into an oocyte and thus start the fertilization process. So far, it has been shown that improved freeze-drying protocols preserve chromosomal integrity and oocyte-activating factor(s) in rodent and mammalian species at 4 °C for several years and at ambient temperature for up to 1 year depending on species, which permits shipping freeze-dried samples at ambient temperature. This chapter concisely reviews freeze-drying of mammalian sperm first and then presents a simple freeze-drying protocol.

Dehydration of llama sperm using different osmolarity media and temperatures for preservation

The objective of this study was to evaluate effects of dehydration on sperm DNA with the aim of eventually using this method for preserving llama spermatozoa. Two experiments were conducted: 1) sperm preservation at 5 °C for 60 days in different hyperosmotic solutions (500, 800, 1000 and 1200 mOsmol/l) (n = 6, replications = 2) and 2) sperm preservation at 5 and -20 °C for 60 days in the same hyperosmotic solutions, with supplementary antibiotics (n = 6, replications = 2). Sperm motility, membrane functional integrity, viability and morphology were evaluated at 0 and 48 h of the preservation period (Experiment 1) and at 30 min and 24 h (Experiment 2). Sperm DNA was evaluated at 0 or 30 min (Experiment 1 and 2, respectively) and on days 7, 14, 21, 30 and 60 of the preservation periods. Motility, membrane functional integrity and viability were less when sperm were dehydrated, while sperm cell morphology was not affected. There was a smaller percentage of sperm with condensed chromatin as duration of the preservation period increased when stored in the different hyperosmotic solutions. There was a markedly smaller (P < 0.05) percentage of sperm with intact DNA in all solutions as the duration of preservation increased, with there being greater values for intact DNA at -20 °C than sperm preserved at 5 °C. Llama sperm chromatin condensation was slightly affected by the process of dehydration. There was a markedly smaller percentage of sperm with intact DNA in the dehydrated semen samples.

Tolerance of the freeze-dried mouse sperm nucleus to temperatures ranging from -196 °C to 150 °C

It has long been believed that tolerance against extreme environments is possible only for ‘lower’ groups, such as archaea, bacteria or tardigrades, and not for more ‘advanced’ species. Here, we demonstrated that the mammalian sperm nucleus also exhibited strong tolerance to cold and hot temperatures. When mouse spermatozoa were freeze-dried (FD), similar to the anhydrobiosis of Tardigrades, all spermatozoa were ostensibly dead after rehydration. However, offspring were obtained from recovered FD sperm nuclei, even after repeated treatment with conditions from liquid nitrogen to room temperature. Conversely, when FD spermatozoa were heated at 95 °C, although the birth rate was decreased with increasing duration of the treatment, offspring were obtained even for FD spermatozoa that had been heat-treated for 2 h. This period was improved up to 6 h when glucose was replaced with trehalose in the freeze-drying medium, and the resistance temperature was extended up to 150 °C for short periods of treatment. Randomly selected offspring grew into healthy adults. Our results suggest that, when considering the sperm nucleus/DNA as the material that is used as a blueprint of life, rather than cell viability, a significant tolerance to extreme temperatures is present even in ‘higher’ species, such as mammals.

Production of mouse fetuses using spermatozoa exposed temporarily to high temperature or continuously to room temperature after freeze-drying in Na+-free/K+-rich EGTA buffer

Present study aimed to determine to what extent freeze-dried spermatozoa were able to withstand high-temperature conditions: transient increase in storage temperature and long-term exposure to room temperature. Mouse spermatozoa were freeze-dried in EGTA/Tris-HCl buffered solution alkalinized using KOH (K-ETBS, pH 7.7), and then stored for up to 7 months at 4 °C or 25 °C. After 2 months' storage, some of the 4°C-stored spermatozoa were exposed to 40 °C for 1 week or 1 month, then again stored at 4 °C for the remaining storage period. Following storage, rehydrated spermatozoa were injected into mouse oocytes. The resulting zygotes were assessed for chromosome damage, in vitro development up to the blastocyst stage, and post-implantation development to normal fetuses on day 18 of gestation. In storage at 4 °C, one-week exposure to 40 °C had no adverse effect on the chromosome integrity and developmental competence compared to non-exposure to 40 °C (continuous storage at 4 °C). In contrast, one-month exposure to 40 °C caused an increasing level of chromosome damage (36%, P < 0.05) and reduced frequencies of blastocysts (54%, P < 0.05) and normal fetuses (36%, P < 0.05) compared to the frequencies obtained by continuous storage at 4 °C (15%, 82% and 52%, respectively). Storage at 25 °C resulted in accumulation of chromosome damage (27%, P < 0.05), leading to decreased blastocyst formation (63%, P < 0.05). But, the frequency of normal fetus (44%) was not significantly different from that obtained by continuous storage at 4 °C. Consequently, mouse spermatozoa freeze-dried in K-ETBS withstood temporary exposure to 40 °C for 1 week. Chromosome damage accumulated in spermatozoa during storage at 25 °C.