Desiccation tolerance of spermatozoa dried at ambient temperature: production of fetal mice

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.

Production of offspring from vacuum-dried mouse spermatozoa and assessing the effect of drying conditions on sperm DNA and embryo development

Freeze-dried sperm (FD sperm) are of great value because they can be stored at room temperature for long periods of time, However, the birth rate of offspring derived from FD sperm is low and the step in the freeze-drying process particularly responsible for low offspring production remains unknown. In this study, we determined whether the drying process was responsible for the low success rate of offspring by producing vacuum-dried sperm (VD sperm), using mouse spermatozoa dried in a vacuum without being frozen. Transfer of embryos fertilized with VD sperm to recipients resulted in the production of several successful offspring. However, the success rate was slightly lower than that of FD sperm. The volume, temperature, and viscosity of the medium were optimized to improve the birth rate. The results obtained from a comet assay indicated that decreasing the drying rate reduced the extent of DNA damage in VD sperm. Furthermore, even though the rate of blastocyst formation increased upon fertilization with VD sperm, full-term development was not improved. Analysis of chromosomal damage at the two-cell stage through an abnormal chromosome segregation (ACS) assay revealed that reduction in the drying rate failed to prevent chromosomal damage. These results indicate that the lower birth rate of offspring from FD sperm may result from the drying process rather than the freezing process.

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.

Drying and temperature induced conformational changes of nucleic acids and stallion sperm chromatin in trehalose preservation formulations

Even though dried sperm is not viable, it can be used for fertilization as long as its chromatin remains intact. In this study, we investigated drying- and temperature-induced conformational changes of nucleic acids and stallion sperm chromatin. Sperm was diluted in preservation formulations with and without sugar/albumin and subjected to convective drying at elevated temperatures on glass substrates. Accumulation of reactive oxygen species was studied during storage at different temperatures, and the sperm chromatin structure assay was used to assess DNA damage. Fourier transform infrared spectroscopy was used to identify dehydration and storage induced conformational changes in isolated DNA and sperm chromatin. Furthermore, hydrogen bonding in the preservation solutions associated with storage stability were investigated. Reactive oxygen species and DNA damage in dried sperm samples were found to accumulate with increasing storage temperature and storage duration. Non-reducing disaccharides (i.e., trehalose, sucrose) and albumin counteracted oxidative stress and preserved sperm chromatin during dried storage, whereas glucose increased DNA damage during storage. When sperm was dried in the presence of trehalose and albumin, no spectral changes were detected during storage at refrigeration temperatures, whereas under accelerated aging conditions, i.e., storage at 37 °C, spectral changes were detected indicating alterations in sperm chromatin structure.

Whole genome integrity and enhanced developmental potential in ram freeze-dried spermatozoa at mild sub-zero temperature

Freeze-dried spermatozoa typically shows a reduction in fertility primarily due to the DNA damage resulting from the sublimation process. In order to minimize the physical/mechanical damage resulting from lyophilization, here we focused on the freezing phase, comparing two cooling protocols: (i) rapid-freezing, where ram sperm sample is directly plunged into liquid nitrogen (LN-group), as currently done; (ii) slow-freezing, where the sample is progressively cooled to − 50 °C (SF-group). The spermatozoa dried in both conditions were analysed to assess residual water content by Thermal Gravimetric Analysis (TGA) and DNA integrity using Sperm Chromatin Structure Assay (SCSA). TGA revealed more than 90% of water subtraction in both groups. A minor DNA damage, Double-Strand Break (DSB) in particular, characterized by a lower degree of abnormal chromatin structure (Alpha-T), was detected in the SF-group, comparing to the LN-one. In accordance with the structural and DNA integrity data, spermatozoa from SF-group had the best embryonic development rates, comparing to LN-group: cleaved embryos [42/100 (42%) versus 19/75 (25.3%), P < 0.05, SL and LN respectively] and blastocyst formation [7/100 (7%) versus 2/75 (2.7%), P < 0.05, SF and LN respectively]. This data represents a significant technological advancement for the development of lyophilization as a valuable and cheaper alternative to deep-freezing in LN for ram semen.

Effect of chelating and antioxidant agents on morphology and DNA methylation in freeze-drying rabbit (Oryctolagus cuniculus) spermatozoa

Freeze-drying (FD) has been exhaustively tried in several mammalian species as an alternative technique to sperm cryopreservation, but few studies have been done in rabbits (Oryctolagus cuniculus). The main objective of this study was to compare the protective effect of various antioxidants added to EDTA medium on structural and functional components of FD rabbit spermatozoa and on their status of global DNA methylation. FD media used were composed of basic FD medium (10 mM Tris-HCl buffer and 50 mM NaCl) supplemented with either 50 mM EDTA alone (EDTA) or added with 105 µM of rosmarinic acid (RA, EDTA-RA) or 10 µM of melatonin (MLT, EDTA-MLT). The effect of each medium on the preservation of FD spermatozoon structure was evaluated with light and scanning electron microscopy (SEM). Global DNA methylation was quantified in all FD sperm samples as well as in fresh spermatozoa. Morphologically, fracture points were evidenced in the neck, mid and principal piece of the spermatozoon tail. No differences in spermatozoon fracture points were evidenced among FD treatments: intact spermatozoa were the largest (p < .01) category, whereas the most frequent (p < .01) injury was the neck fracture, resulting in tailless heads. At SEM, the head of spermatozoa showed a well-conserved shape and intact membrane in all treatments. DNA methylation status was the same in all FD treatments. In conclusion, supplementation of EDTA, EDTA-RA and EDTA-MLT during FD preserved rabbit sperm morphological integrity and methylation status as well. Therefore, the difficulty of getting viable offspring using FD semen is likely unrelated to the impact of the lyophilization process on DNA methylation and morphology of lyophilized spermatozoa.

Effects of temperature and storage time on the motility, viability, DNA integrity and apoptosis of processed human spermatozoa

The aim of this study was to evaluate motility, viability, DNA integrity and apoptosis of spermatozoa when washed semen samples were kept for up to 12 days at 4-6°C and 25°C. In this experimental study, 26 normozoospermic semen samples were washed twice in Modified Ham's F10 and resuspended in IVF fertilisation medium. Half of the specimens were stored at 4-6°C, and the other half was kept at 25°C for 12 days. The proportions of viable, motile, spermatozoa with double-stranded DNA and apoptotic spermatozoa were examined during storage time. Apoptosis was measured using annexin V-PI staining followed by flow cytometry. Results showed that sperm motility and viability decreased during 12 days of sample storage (p < .001). There was no significant difference between the two temperatures in terms of motility and viability for up to 2 days (p < .05). The percentage of spermatozoa with double-stranded DNA remained unchanged during the 12 days of storage at both temperatures (p > .05). Although there was no difference between the two temperatures in terms of motility, viability and apoptosis during the first two days of storage, storage of spermatozoa at 4-6°C is better than storage for a longer period than storage at 25°C. Sperm DNA resisted against denaturation during storage.

Effect of preservation of human semen sample at 4-6 and 25 °C on sperm motility

Sperm motility is the result of transverse movements that exist along its tail. It plays an important role in male fertility. The aim of this study was to evaluate the influence of keeping washed normozoospermic semen samples at 4-6 and 25 °C on the motility of spermatozoa. 26 semen samples of normozoospermic were washed twice in modified Ham's F10 medium. Then, thirteen of the semen samples were kept in refrigerator (4-6 °C) and the remaining samples were stored in incubator (25 °C) for 12 days. On the 0 (immediately after sampling as control group), 1st, 2nd, 5th, 7th and the 12th days, the percentage of fast progressive (grade a), slow progressive (grade b), non-progressive (grade c) and immotile (grade d) sperm cells were calculated for each temperature. The data obtained from this study showed that the percentages of a, b and c grades of motile spermatozoa were significantly decreased (p < 0.001) during 12 days at the both temperatures but reduction of these percentages has a gentle slope at 4-6 °C. There was no motile sperm after 12 days of storage. This study suggests that motile spermatozoa could be retrieved up to 7 days after the storage of washed normozoospermic men semen samples at 4-6 and 25 °C. Also, there were no motile sperm cells 12 days after sampling.

Assessing the tolerance to room temperature and viability of freeze-dried mice spermatozoa over long-term storage at room temperature under vacuum

Freeze-drying has been frequently used to preserve food and microorganisms at room temperature (RT) for extended periods of time; however, its application to mammalian species is difficult. Here, we developed a method to prolong the stability of freeze-dried (FD) mice spermatozoa at RT for more than one year without using any cryoprotectant agents. Our data showed that maintaining a vacuum in ampoules is critical to ensuring the viability of FD spermatozoa, as the stability of spermatozoa DNA increased when imperfectly vacuumed ampoules were detected using a non-destructive test and eliminated. Finally a large number of healthy offspring were obtained from mice oocytes fertilized with FD spermatozoa stored at RT for more than one year. Although the birth rate from three-month stored spermatozoa was lower than that from one-day stored spermatozoa, no further reduction was observed even in one-year stored spermatozoa. Therefore, FD spermatozoa preserved in this study were highly tolerant to warm temperatures. This method of storage shows a great potential for the preservation of genetic resources of mammalian species, such as genetically-modified mouse strains, without the use of electric power.

Dry Preservation of Spermatozoa: Considerations for Different Species

The current gold standard for sperm preservation is storage at cryogenic temperatures. Dry preservation is an attractive alternative, eliminating the need for ultralow temperatures, reducing storage maintenance costs, and providing logistical flexibility for shipping. Many seeds and anhydrobiotic organisms are able to survive extended periods in a dry state through the accumulation of intracellular sugars and other osmolytes and are capable of returning to normal physiology postrehydration. Using techniques inspired by nature's adaptations, attempts have been made to dehydrate and dry preserve spermatozoa from a variety of species. Most of the anhydrous preservation research performed to date has focused on mouse spermatozoa, with only a small number of studies in nonrodent mammalian species. There is a significant difference between sperm function in rodent and nonrodent mammalian species with respect to centrosomal inheritance. Studies focused on reproductive technologies have demonstrated that in nonrodent species, the centrosome must be preserved to maintain sperm function as the spermatozoon centrosome contributes the dominant nucleating seed, consisting of the proximal centriole surrounded by pericentriolar components, onto which the oocyte's centrosomal material is assembled. Preservation techniques used for mouse sperm may therefore not necessarily be applicable to nonrodent spermatozoa. The range of technologies used to dehydrate sperm and the effect of processing and storage conditions on fertilization and embryogenesis using dried sperm are reviewed in the context of reproductive physiology and cellular morphology in different species.

Sperm freeze-drying and micro-insemination for biobanking and maintenance of genetic diversity in mammals

Breeding by natural mating is ideal for maintaining animal populations. However, the lack of breeding space resulting from an increased number of strains and the decline in fertility caused by inbreeding inhibits the reproduction of subsequent generations. Reproductive technologies, such as gamete preservation and artificial fertilisation, have been developed to overcome these problems. These approaches efficiently produce offspring of laboratory, domestic and wild animals, and can also be used to treat human infertility. Gamete preservation using sperm contributes to improvements in reproductive systems and enables the use of smaller breeding spaces. Although cryopreservation with liquid nitrogen has been used to preserve spermatozoa, freeze-drying without liquid nitrogen, a novel method, facilitates long-term storage of spermatozoa. This method has recently been applied to maintain animal strains. Micro-insemination techniques, such as intracytoplasmic sperm injection (ICSI), are exceptional for improving assisted reproduction. ICSI can be used to fertilise oocytes, even with immotile and immature spermatozoa that are unsuitable for AI and IVF. Reproductive technologies provide a substantial advantage for biobanking and maintaining the genetic diversity of laboratory, domestic and wild animals. This review covers the latest method of sperm freeze-drying and micro-insemination, and future possibilities for maintaining animal strains and populations.

Advancing microwave technology for dehydration processing of biologics

Our prior work has shown that microwave processing can be effective as a method for dehydrating cell-based suspensions in preparation for anhydrous storage, yielding homogenous samples with predictable and reproducible drying times. In the current work an optimized microwave-based drying process was developed that expands upon this previous proof-of-concept. Utilization of a commercial microwave (CEM SAM 255, Matthews, NC) enabled continuous drying at variable low power settings. A new turntable was manufactured from Ultra High Molecular Weight Polyethylene (UHMW-PE; Grainger, Lake Forest, IL) to provide for drying of up to 12 samples at a time. The new process enabled rapid and simultaneous drying of multiple samples in containment devices suitable for long-term storage and aseptic rehydration of the sample. To determine sample repeatability and consistency of drying within the microwave cavity, a concentration series of aqueous trehalose solutions were dried for specific intervals and water content assessed using Karl Fischer Titration at the end of each processing period. Samples were dried on Whatman S-14 conjugate release filters (Whatman, Maidestone, UK), a glass fiber membrane used currently in clinical laboratories. The filters were cut to size for use in a 13 mm Swinnex(®) syringe filter holder (Millipore(™), Billerica, MA). Samples of 40 μL volume could be dehydrated to the equilibrium moisture content by continuous processing at 20% with excellent sample-to-sample repeatability. The microwave-assisted procedure enabled high throughput, repeatable drying of multiple samples, in a manner easily adaptable for drying a wide array of biological samples. Depending on the tolerance for sample heating, the drying time can be altered by changing the power level of the microwave unit.

Simple gamete preservation and artificial reproduction of mammals using micro-insemination techniques

Assisted reproductive technology (ART) has been applied in various procedures as an effective breeding method in experimental, domestic, and wild animals, and for the treatment of human infertility. Micro-insemination techniques such as intracytoplasmic injection of spermatozoa and spermatids are now routinely used ART tools. With these techniques, even immotile and immature sperm cells can be employed as donors for producing the next generation. Gamete preservation, another ART tool, has contributed to reproductive regulation, worldwide transportation, and disease protection of animal strains, and the preserved gametes have been effectively used for the production of offspring. ART is now an indispensable tool in mammalian reproduction. This review covers the latest ART tools, with a particular emphasis on micro-insemination and gamete preservation, and discusses the future direction of mammalian artificial reproductive technology.

Live pups from evaporatively dried mouse sperm stored at ambient temperature for up to 2 years

The purpose of this study is to develop a mouse sperm preservation method based on evaporative drying. Mouse sperm were evaporatively dried and stored at 4°C and ambient temperature for 3 months to 2 years. Upon rehydration, a single sperm was injected into a mature oocyte to develop into a blastocyst after culture or a live birth after embryo transfer to a recipient female. For the samples stored at 4°C for 3, 6, 12, 18, and 24 months, the blastocyst formation rate was 61.5%, 49.1%, 31.5%, 32.2%, and 41.4%, respectively. The blastocyst rate for those stored at ambient temperature (∼22°C) for 3, 6, 12, and 18 months was 57.8%, 36.2%, 33.6%, and 34.4%, respectively. Fifteen, eight and three live pups were produced from sperm stored at room temperature for 12, 18, and 24 months, respectively. This is the first report of live offspring produced from dried mouse sperm stored at ambient temperature for up to 2 years. Based on these results, we suggest that evaporative drying is a potentially useful method for the routine preservation of mouse sperm.

In vitro equine embryo production using air-dried spermatozoa, with different activation protocols and culture systems

The aim of this work was to evaluate the use of air-dried spermatozoa for in vitro production of equine embryos and verify if sperm extract activation and in vivo culture improve in vitro embryo production. Cooled spermatozoa (control) and air-dried spermatozoa stored for 2, 14 or 28 days were used for ICSI sperm extract, or ionomycin was used for oocyte activation, and embryos were in vitro or in vivo (in mare's oviduct) cultured for 7 days. With in vitro culture, cleavage rate was higher when activating with sperm extract (P < 0.05). No differences in embryo development were seen between the two activation treatments nor between storage periods (P > 0.05). Blastocysts were obtained with cooled spermatozoa, and morulae were achieved using in vivo culture with 28-day storage spermatozoa and ionomycin-activated oocytes. When in vivo culture was performed, sperm DNA fragmentation was assessed using the sperm chromatin dispersion test and did not show statistical correlation with cleavage nor embryo recovery rates. In conclusion, equine embryos can be produced using air-dried spermatozoa stored for several weeks. Sperm extract activation increased cleavage rates but did not improve embryo development. In vivo culture allowed intrauterine stage embryos to be achieved.

Develop to term rat oocytes injected with heat-dried sperm heads

This study investigated the development of rat oocytes in vitro and in vivo following intracytoplasmic injection of heads from spermatozoa heat-dried at 50°C for 8 h and stored at 4°C in different gas phases. Sperm membrane and chromosome are damaged by the process of heat-drying. Oocyte activation and cleavage of oocytes were worse in oocytes injected with spermatozoa heat-dried and stored for 1 week than unheated, fresh spermatozoa, but in heat-dried spermatozoa, there were no differences in these abilities of oocytes between the samples stored in nitrogen gas and in air. The oocytes injected with heat-dried spermatozoa stored for 1 week could develop to the morula and blastocyst stages without difference between the samples stored in nitrogen gas and in air after artificial stimulation. Cleavage of oocytes and development of cleaved embryos were higher when heat-dried spermatozoa were stored for 3 and 6 months in nitrogen gas than in air. However, the ability of injected oocytes to develop to the morula and blastocyst stages was not inhibited even when heat-dried spermatozoa stored in both atmosphere conditions for as long as 6 months were used. When 2-cell embryos derived from oocytes injected with heads from spermatozoa heat-dried and stored for 1 week and 1 month were transferred, each 1 of 4 recipients was conceived, and the conceived recipients delivered 1 live young each. These results demonstrate that rat oocytes can be fertilized with heat-dried spermatozoa and that the fertilized oocytes can develop to term.

Tolerance to environmental desiccation in moss sperm

• Sexual reproduction in mosses requires that sperm be released freely into the environment before finding and fertilizing a receptive female. After release from the male plant, moss sperm may experience a range of abiotic stresses; however, few data are available examining stress tolerance of moss sperm and whether there is genetic variation for stress tolerance in this important life stage. • Here, we investigated the effects of environmental desiccation and recovery on the sperm cells of three moss species (Bryum argenteum, Campylopus introflexus, and Ceratodon purpureus). • We found that a fraction of sperm cells were tolerant to environmental desiccation for extended periods (d) and that tolerance did not vary among species. We found that this tolerance occurs irrespective of ambient dehydration conditions, and that the addition of sucrose during dry-down improved cell recovery. Although we observed no interspecific variation, significant variation among individuals within species in sperm cell tolerance to environmental desiccation was observed, suggesting selection could potentially act on this basic reproductive trait. • The observation of desiccation-tolerant sperm in multiple moss species has important implications for understanding bryophyte reproduction, suggesting the presence of a significant, uncharacterized complexity in the ecology of moss mating systems.

Preservation of mouse sperm by convective drying and storing in 3-O-methyl-D-glucose

With the fast advancement in the genetics and bio-medical fields, the vast number of valuable transgenic and rare genetic mouse models need to be preserved. Preservation of mouse sperm by convective drying and subsequent storing at above freezing temperatures could dramatically reduce the cost and facilitate shipping. Mouse sperm were convectively dried under nitrogen gas in the Na-EGTA solution containing 100 mmol/L 3-O-methyl-D-glucose and stored in LiCl sorption jars (Relative Humidity, RH, 12%) at 4°C and 22°C for up to one year. The functionality of these sperm samples after storage was tested by intracytoplasmic injection into mouse oocytes. The percentages of blastocysts produced from sperm stored at 4°C for 1, 2, 3, 6, and 12 months were 62.6%, 53.4%, 39.6%, 33.3%, and 30.4%, respectively, while those stored at 22°C for 1, 2, and 3 months were 28.8%, 26.6%, and 12.2%, respectively. Transfer of 38 two- to four-cell embryos from sperm stored at 4°C for 1 year produced two live pups while 59 two- to four-cell embryos from sperm stored at 22°C for 3 months also produced two live pups. Although all the pups looked healthy at 3 weeks of age, normality of offspring produced using convectively dried sperm needs further investigation. The percentages of blastocyst from sperm stored in the higher relative humidity conditions of NaBr and MgCl(2) jars and driest condition of P(2)O(5) jars at 4°C and 22°C were all lower. A simple method of mouse sperm preservation is demonstrated. Three-O-methyl-D-glucose, a metabolically inactive derivative of glucose, offers significant protection for dried mouse sperm at above freezing temperatures without the need for poration of cell membrane.

Novel Approaches to the Cryopreservation of Human Spermatozoa: History and Development of the Spermatozoa Vitrification Technology

Cryobiology is very intensively applied in reproductive and veterinary medicine for preservation of gametes, embryos and reproductive tissues. Sub-zero temperatures combined with appropriate cryoprotective agents preserve the physiological and reproductive functions of the cells making long-term storage possible without loss of viability. With the use of cryoprotective agents it has become possible to develop cryopreservation techniques, such as the slow conventional freezing and vitrification that are in use in the present times. In slow controlled-rate conventional freezing extracellular ice crystals are formed whereas in vitrification no ice crystals are formed. Glass formation is compatible with the survival of the cell and the preservation of its intracellular structures provided the type(s) and concentrations of cryoprotectant used are not chemo- or osmotoxic. However, irrespective of the type of cooling method employed the cryosurvival of cells and tissues is influenced by the size and maturity of cells, amounts of intracellular water, quality and quantity of intracellular lipids, type of cells, their function and morphology. The intracellular milieu of cryopreserved cells and tissues remain less understood. The application of nanotechnology may help reveal and help advance our knowledge of the cryobiological principles involved in cryosurvival. At this moment the methods of cryopreservation that merit further investigation are vitrification and lyophilization. Vitrification is cheap if reagents are prepared in-house and the procedure can be performed rapidly. It has been successfully applied for gametes and embryos (of different stages of development), and reproductive cells/tissues, somatic cells and stem cells. However, vitrification is more demanding technically and requires operation and storage at sub-zero temperatures. On the other hand lyophilization deserves further investigation because it is a cheaper form of cryopreservation that may enable cryostorage at less demanding temperatures of 4°C and may even allow transport at ambient temperature. These possibilities are explored in this review.

Chromosomal integrity and DNA damage in freeze-dried spermatozoa

Freeze-drying technology may one day be used to preserve mammalian spermatozoa indefinitely without cryopreservation. Freeze-dried mouse spermatozoa stored below 4°C for up to 1 year have maintained the ability to fertilize oocytes and support normal development. The maximum storage period for spermatozoa increases at lower storage temperatures. Freeze-drying, per se, may reduce the integrity of chromosomes in freeze-dried mouse spermatozoa, but induction of chromosomal damage is suppressed if spermatozoa are incubated with divalent cation chelating agents prior to freeze-drying. Nevertheless, chromosomal damage does accumulate in spermatozoa stored at temperatures above 4°C. Currently, no established methods or strategies can prevent or reduce damage accumulation, and damage accumulation during storage is a serious obstacle to advances in freeze-drying technology. Chromosomal integrity of freeze-dried human spermatozoa have roughly background levels of chromosomal damage after storage at 4°C for 1 month, but whether these spermatozoa can produce healthy newborns is unknown. The safety of using freeze-dried human spermatozoa must be evaluated based on the risks of heritable chromosome and DNA damage that accumulates during storage.

Short-term storage of human spermatozoa in electrolyte-free medium without freezing maintains sperm chromatin integrity better than cryopreservation

Previous attempts to maintain human spermatozoa without freezing were based on short-term storage in component-rich medium and led to fast decline in motility and increased incidence of chromosome breaks. Here we report a new method in which sperm are maintained without freezing in an electrolyte-free medium (EFM) composed of glucose and bovine serum albumin. Human sperm were stored in EFM or human tubal fluid medium (HTFM) or were cryopreserved, and their motility, viability, and DNA integrity were examined at different intervals. Cryopreservation led to significant decline in sperm motility and viability and induced DNA fragmentation. Sperm stored in EFM maintained motility and viability for up to 4 and 7 wk, respectively, much longer than sperm stored in HTFM (<2 and <4 wk, respectively). DNA integrity, assessed with comet assay, was also maintained significantly better in EFM than in HTFM. One-week storage in EFM yielded motility and viability similar to that of cryopreserved sperm, but DNA integrity was significantly higher, resembling that of fresh sperm. After several weeks of storage in EFM, sperm were able to activate oocytes, undergo chromatin remodeling, and form normal zygotic chromosomes after intracytoplasmic sperm injection. This study demonstrated that human spermatozoa can be stored in EFM without freezing for several weeks while maintaining motility, viability, and chromatin integrity and that 1-wk storage in EFM offers better protection of sperm DNA integrity than cryopreservation. Sperm storage in EFM may become a viable option for the physicians working in assisted reproduction technology clinics, which would avoid cryodamage.

Nanoscale Measurements of Water Loss during Desiccation of Biological Cell Suspensions

There is an urgent need to protect and conserve the endangered species of the world. Desiccation, or the phenomenon of anhydrobiosis, offers the attractive possibility of low cost, long term storage of reproductive tissues and cells from endangered species at ambient temperatures. Biophysical optimization of anhydrobiosis procedures requires dynamic and accurate quantification of the rate of moisture loss during a prescribed desiccation protocol. Engineered microstructures can serve as a multifunctional and highly sensitive method to measure the rate of moisture loss. This study presents a novel ultrasound based (resonant) mass sensor to quantify water loss during a drying process by measuring the corresponding shift in the resonant frequency of a micromachined vibrating structure. To model the proposed ultrasound based sensor, we performed a static (stress) and dynamic (frequency change with change in imposed mass) analysis. The results suggest that by tailoring the dimension of the vibrating element appropriate sensitivity can be achieved.

Preservation protocols for human adipose tissue-derived adult stem cells

The development of simple but effective storage protocols for adult stem cells will greatly enhance their use and utility in tissue-engineering applications. There are three primary storage techniques, freezing (cryopreservation), drying (anhydrobiosis), and freeze drying (lyophilization), each with its own advantages and disadvantages. Cryopreservation has shown the most promise but is a fairly complex process, necessitating the use of chemicals called cryoprotective agents (CPAs), freezing equipment, and obviously, storage in liquid nitrogen. Preservation by desiccation is an alternative that attempts to reproduce a naturally occurring preservative technique, namely, the phenomenon of anhydrobiosis and requires the use of high (and possibly, toxic) concentration of CPAs as well as disaccharides (sugars). Lyophilization works by first cryopreserving (freezing) the material and then desiccating (drying) it by the process of sublimation or the conversion of ice (solid) to water vapor (gas phase). The purpose of this chapter is to present a general overview of these storage techniques and the optimal protocols/results obtained in our laboratory for long-term storage of adult stem cells using freezing storage and drying storage.

Assessment of three generations of mice derived by ICSI using freeze-dried sperm

Although the derivation of mice by intracytoplasmic sperm injection (ICSI) using freeze-dried sperm has been demonstrated previously, a comprehensive analysis of their viability, health, and fertility has not. The purpose of the present study was to determine the extent to which ICSI using freeze-dried sperm stored at 4 degrees C for 1-2 months from mice on either an inbred (C57BL/6J) or hybrid (B6D2F1/J) genetic background results in genomic instability and/or phenotypic abnormality in mice and two generations of their progeny. Fertilization rates (number of 2-cells per injected oocytes) using ICSI of fresh and freeze-dried sperm were similar within and between mouse strains, although fewer freeze-dried sperm-derived embryos than fresh sperm-derived embryos developed to blastocysts in vitro (C57BL/6J and B6D2F1/J) and liveborn pups in vivo (B6D2F1/J only). Nevertheless, once born, mice derived by ICSI using freeze-dried sperm in both mouse strains were healthy and reproductively sound. No major differences in litter size, weaning rate, and sex ratio were noted in the two generations of progeny (F2 and F3) of ICSI-derived offspring using freeze-dried sperm compared with that in the natural mating (control) group. Further, there was no evidence that either ICSI or freeze drying induced genomic instability, as determined by microsatellite analysis of the derived mice and subsequent generations when compared with both parental genotypes, nor were there differences in the number or types of pathological changes in any of the three generations of progeny. We conclude that viable, healthy and genomically stable mice can be derived by ICSI using freeze-dried mouse sperm stored in the refrigerator for at least 2 months. Further, because freeze drying is a simpler and more economical technique compared with embryo and sperm cryopreservation, the results of this study justify additional research to continue to develop and enhance the technique for the preservation, storage, and sharing of genetically altered mice.

Further optimization of mouse spermatozoa evaporative drying techniques

It has been shown in the past that mouse spermatozoa could be dried under a stream of nitrogen gas at ambient temperature and stored at 4 degrees C or 22 degrees C for up to 3 months and was capable of generating live-born offspring. In previous desiccation work, dried sperm were stored in a vacuum-sealed plastic bag placed in a vacuum-packed Mylar bag. However, dried specimens stored in this way often lost moisture, particularly in samples stored at higher temperatures (22 degrees C) compared to lower temperatures (4 degrees C). The present report describes a method which minimizes this water loss from the dried sperm samples. Its use is described in a preliminary study on the effect of supplementing the trehalose with glycerol. The results have demonstrated that mouse sperm can be stored at 4 degrees C over saturated NaBr without the uptake of water which occurs when they are stored in Mylar packages. In addition, we were able to get some survival of sperm (9-15%) at room temperature storage after 3 months. The addition of glycerol to trehalose had little effect on the survival of dried mouse sperm stored over NaBr for 1 and 3 months.

Rhesus macaque blastocysts resulting from intracytoplasmic sperm injection of vacuum-dried spermatozoa

BACKGROUND

Sperm desiccation is an attractive approach for sperm preservation. In this study, we examined the feasibility and efficiency of intracytoplasmic sperm injection using vacuum-dried rhesus macaque sperm in CZB medium supplemented with 10% fetal bovine serum.

METHODS

A total of 109 MII oocytes were injected with 69 fresh ejaculated sperm and 40 vacuum-dried sperm.

RESULTS

Cleavage occurred in 97% of oocytes injected with fresh, motile sperm and in 88% of oocytes injected with vacuum-dried sperm. Of the cleaved oocytes, 68% fresh sperm-injected oocytes and 74% of dried sperm-injected oocytes developed to the compact morula stage. Blastocyst development was comparable between fresh-injected (16%) and vacuum-dried-injected (17%) oocytes. Differences between treatment groups were not significant. Transmission electron microscopic observation of the blastocysts indicated no detectable differences between fresh sperm and dried sperm-derived embryos.

CONCLUSIONS

We conclude that vacuum-dried rhesus macaque sperm are capable of inducing fertilization and development of pre-implantation embryos when sperm were dried under vacuum and microinjected into normal viable oocytes.

Heterogeneity in desiccated solutions: implications for biostabilization

Biopreservation processes such as freezing and drying inherently introduce heterogeneity. We focused on exploring the mechanisms responsible for heterogeneity in isothermal, diffusively dried biopreservation solutions that contain a model protein. The biopreservation solutions used contained trehalose (a sugar known for its stabilization effect) and salts (LiCl, NaCl, MgCl2, and CaCl2). Performing Fourier transform infrared spectroscopy analysis on the desiccated droplets, spatial distributions of the components within the dried droplet, as well as their specific interactions, were investigated. It was established that the formation of multiple thermodynamic states was induced by the spatial variations in the cosolute concentration gradients, directly affecting the final structure of the preserved protein. The spatial distribution gradients were formed by two competing flows that formed within the drying droplet: a dominant peripheral flow, induced by contact line pinning, and the Marangoni flow, induced by surface tension gradients. It was found that the changes in cosolute concentrations and drying conditions affected the spatial heterogeneity and stability of the product. It was also found that trehalose and salts had a synergistic stabilizing effect on the protein structure, which originated from destructuring of the vicinal water, which in turn mediated the interactions of trehalose with the protein. This interaction was observed by the change in the glycosidic CO, and the CH stretch vibrations of the trehalose molecule.

Ejaculated and epididymal mouse spermatozoa are different in their susceptibility to nuclease-dependent DNA damage and in their nuclease activity

Ejaculated mouse sperm retrieved from the uteri are more susceptible to DNA damage during freeze-drying and freezing without cryoprotection than epididymal sperm. This prompted us to speculate that a factor present in the uterus after mating, either male or female derived, was responsible for increased susceptibility of ejaculated sperm to DNA damage during preservation and that the differences between epididymal and ejaculated mouse sperm in response to stress originated from varying nuclease activity. We first exposed epididymal sperm to the uterine content from females mated to vasectomized males (UCSP), to the uterine content from unmated females in estrus (UC), and to the seminal vesicle fluid (SVF) and examined sperm chromosomes after intracytoplasmic sperm injection (ICSI). We found an increased incidence of chromosome breaks and extremely severe DNA breakage after exposure to UCSP and SVF, respectively, but the chromosomes were normal in sperm exposed to UC. Comet assay results verified that DNA damage after exposure to SVF was present in sperm before fertilization. Next, we examined nuclease activity in sperm and their associated components with a plasmid digestion assay. Nuclease activity was detected in isolated epididymal and ejaculated sperm, as well as in epididymal fluid and seminal plasma, and was much more pronounced in all samples originating from ejaculate. The combined results from the present study imply that there are intrinsic differences between the epididymal and ejaculated mouse sperm preparations in their susceptibility to nuclease-dependent DNA damage that originates from their nuclease activity. This nuclease activity was detected both in the sperm-free fraction of preparations and isolated sperm.

Long-term storage of mouse spermatozoa after evaporative drying

To determine if mouse spermatozoa could be preserved long-term without using liquid nitrogen, mouse spermatozoa in trehalose–EGTA solution were partially evaporatively dried under nitrogen gas (5 min at flow rate10 l/min) and stored for 1 week and 5 months at 4, −20, and −80 °C before intracytoplasmic sperm injection. Fertilization rates were neither different with spermatozoa stored at 4, −20, or −80 °C for 1 week or 1, 3, and 5 months respectively, nor blastocyst formation rates with spermatozoa stored for 1 week and 1 month. However, spermatozoa stored at 4 and −20 °C for 3 months resulted in fewer blastocysts (35.1 and 54.3% respectively) when compared with spermatozoa stored at −80 °C (74.4%). Blastocyst formation rates using spermatozoa stored for 5 months at −20 °C (57.4%) or −80 °C (74.5%) were not significantly different from those stored for 3 months at the same temperatures respectively, but were significantly better than those stored for 5 months at 4 °C (10.2%). Blastocysts derived from spermatozoa stored for 3 and 5 months at −20 and −80 °C respectively, were then transferred to pseudopregnant mothers to develop into healthy liveborn offspring. No significant differences were found in embryo transfer rates (number of pups born/number of embryos transferred), weaning rates, or sex ratios of resultant pups, which were healthy and reproductively sound. These results demonstrate for the first time that partially evaporatively dried mouse spermatozoa in trehalose–EGTA solution can be preserved for long term at −20 and −80 °C. The possibility that the storage temperature must be less than the glass transition temperature is discussed.

Preservation of ejaculated mouse spermatozoa from fertile C57BL/6 and infertile Hook1/Hook1 mice collected from the uteri of mated females

Methods routinely used to preserve mouse spermatozoa require that the male be killed to recover spermatozoa from the epididymides. Here we obtained multiple samples of ejaculated spermatozoa from normal fertile C57BL/6 and infertile Hook1/Hook1 (formerly known as azh/azh) mutant males from uteri after mating, thus avoiding termination of the males. Ejaculated sperm were preserved by conventional cryopreservation or by rapid freezing without cryoprotection, and were injected into the oocytes by intracytoplasmic sperm injection (ICSI). The proportions of oocytes that survived, became activated, and developed into two-cell embryos were similar when comparing the two preservation methods in wild-type versus Hook1/Hook1 mice and tested mice versus controls (fresh and rapid-frozen epididymal and fresh ejaculated sperm). Two-cell embryos were transferred into the oviducts of pseudopregnant females, and fetal development was examined at Day 15 of gestation. A total of 39%-54% of transferred embryos produced with preserved ejaculated sperm implanted. Live, normal fetuses (11%-17%) were obtained in all examined groups and from all males included in the study. More implants (71%-82%) and fetuses (28%-31%) were noted in controls. Lower developmental potentials of embryos produced with preserved ejaculated sperm might be due to their capacitation status; the majority of sperm retrieved from the uterus were capacitated. This study bears significance for the maintenance and distribution of novel mouse strains. The method is applicable for all types of mice, including those with male infertility syndromes. The sole requirement is that the male of interest is able to copulate and its ejaculate contains spermatozoa.

Engineering complex tissues

This article summarizes the views expressed at the third session of the workshop "Tissue Engineering--The Next Generation," which was devoted to the engineering of complex tissue structures. Antonios Mikos described the engineering of complex oral and craniofacial tissues as a "guided interplay" between biomaterial scaffolds, growth factors, and local cell populations toward the restoration of the original architecture and function of complex tissues. Susan Herring, reviewing osteogenesis and vasculogenesis, explained that the vascular arrangement precedes and dictates the architecture of the new bone, and proposed that engineering of osseous tissues might benefit from preconstruction of an appropriate vasculature. Jennifer Elisseeff explored the formation of complex tissue structures based on the example of stratified cartilage engineered using stem cells and hydrogels. Helen Lu discussed engineering of tissue interfaces, a problem critical for biological fixation of tendons and ligaments, and the development of a new generation of fixation devices. Rita Kandel discussed the challenges related to the re-creation of the cartilage-bone interface, in the context of tissue engineered joint repair. Frederick Schoen emphasized, in the context of heart valve engineering, the need for including the requirements derived from "adult biology" of tissue remodeling and establishing reliable early predictors of success or failure of tissue engineered implants. Mehmet Toner presented a review of biopreservation techniques and stressed that a new breakthrough in this field may be necessary to meet all the needs of tissue engineering. David Mooney described systems providing temporal and spatial regulation of growth factor availability, which may find utility in virtually all tissue engineering and regeneration applications, including directed in vitro and in vivo vascularization of tissues. Anthony Atala offered a clinician's perspective for functional tissue regeneration, and discussed new biomaterials that can be used to develop new regenerative technologies.

Cryo-injury and biopreservation

Mammalian cells appear to be naturally tolerant to cold temperatures, but the formation of ice when cells are cooled leads to a variety of damaging effects. The study of cryo-injury, therefore, becomes the study of when and how ice is formed both inside and outside the cell during cooling. Protectant chemicals are used to control or prevent ice formation in many preservation protocols, but these chemical themselves tend to be damaging. Cooling and warming rates also strongly affect the amount and location of ice that is formed. Through careful modification of these parameters successful cold preservation techniques for many cell types have been developed, but there are many more cell types that have defied preservation techniques, and the extension of cell-based techniques to tissues and whole organs has been very limited. There are many aspects to the damaging effects of ice in cells that are still poorly understood. In this brief article we review our current understanding of cellular injury and highlight the aspects of cellular injury during cryopreservation that are still poorly understood.

Forced and natural convective drying of trehalose/water thin films: implication in the desiccation preservation of Mammalian cells

Trehalose is believed to offer desiccation protection to mammalian cells by forming stable glassy matrices. The goal of the current study was to explore the desiccation kinetics of thin films of trehalose-water solution under forced and natural convective conditions and to investigate the thermophysical state of mammalian cells at the bottom of the thin film. We developed a finite difference model based on the mass and energy conservation equations coupled to the water transport model from the cells. The boundary conditions were obtained from correlations or experimental measurements and the Gordon-Taylor equation was used to predict the glass transition temperature at every location. Results indicated that there are three distinct regimes for drying for both forced and natural convection, characterized by the slope of the moisture content plot as a function of time. Our results also indicate that the surface of the solution reached the glassy state in less than 10 min for the Reynolds (forced) numbers explored and approximately 30 min for some Rayleigh (natural convective) numbers; however, significant water was trapped at this instant. Larger drying force hastened quicker glass formation but trapped more water. The numerical model was capable of predicting the drying kinetics for the dilute region accurately, but deviated while predicting the other regimes. Based on these experimental validations of the model, the osmotic response of different cells located at the bottom of the solution with orders of magnitude difference in their membrane permeability (Lp) was predicted. The results suggested that extracellular glass formed around cells at the bottom of a trehalose-water solution by the propagation of glass into the solution; however it takes more than an order of magnitude time (approximately 7 min to >100 min for forced convective drying) to remove sufficient water to form glass around cells from the time when the first surface glass is formed. This is attributed to low diffusivity of water through the glass. In addition, the water transport from the glassy matrix could be either diffusion or Lp limited. For diffusion-limited transport, lowering the film thickness at the beginning of drying by half almost lowers the drying time by an order of magnitude. In summary, the optimal design of convective desiccation protocols requires accounting for the size of the cell, their membrane permeability (Lp) and the starting thickness of the solution.

Dry storage of sperm: applications in primates and domestic animals

Cryopreservation of spermatozoa, oocytes and embryos, as well as somatic cells or cell lines for cloning from cells, are all options for the long-term storage of unique genotypes and endangered species. Spermatozoal cryopreservation and storage currently require liquid nitrogen or ultralow refrigeration-based methods for long- or short-term storage, which requires routine maintenance and extensive space requirements. The preservation of stem cells also has strict requirements for long-term storage to maintain genetic integrity. Dessicated (lyopreserved) sperm and stem cells will provide an unprecedented type of long-term storage without the need for expensive and burdensome cryogenic conditions. Experiments were conducted to determine an effective intracellular concentration of the lyoprotectant trehalose. High-pressure liquid chromatography studies revealed that trehalose can be incorporated into mature sperm cells as well as spermatogonial stem cells from rhesus monkeys. In addition, using fourier transform infrared spectroscopy, we determined that thermotropic phase transitions for fresh ejaculates from rhesus monkey and stallion sperm occurred at 10-15, 33-37 and 55-59 degrees C. Preliminary studies in our laboratory have indicated that spermatogonial stem cells can be dried to <3 g g(-1) water and maintain viability following rehydration. Studies in our laboratory have provided preliminary results suggesting that the desiccated storage of sperm and spermatogonial stem cells may be a viable alternative to conventional cryopreservation.

Transcriptional response of Saccharomyces cerevisiae to desiccation and rehydration

A transcriptional analysis of the response of Saccharomyces cerevisiae strain BY4743 to controlled air-drying (desiccation) and subsequent rehydration under minimal glucose conditions was performed. Expression of genes involved in fatty acid oxidation and the glyoxylate cycle was observed to increase during drying and remained in this state during the rehydration phase. When the BY4743 expression profile for the dried sample was compared to that of a commercially prepared dry active yeast, strikingly similar expression changes were observed. The fact that these two samples, dried by different means, possessed very similar transcriptional profiles supports the hypothesis that the response to desiccation is a coordinated event independent of the particular conditions involved in water removal. Similarities between "stationary-phase-essential genes" and those upregulated during desiccation were also noted, suggesting commonalities in different routes to reduced metabolic states. Trends in extracellular and intracellular glucose and trehalose levels suggested that the cells were in a "holding pattern" during the rehydration phase, a concept that was reinforced by cell cycle analyses. Application of a "redescription mining" algorithm suggested that sulfur metabolism is important for cell survival during desiccation and rehydration.

Thermal characterization of Nakagata's mouse sperm freezing protocol

This paper reports the results of an experimental study of the warming and cooling rates achieved using the popular Nakagata Protocol for murine sperm cryopreservation. Problems with the storage and maintenance of the huge number of genetically engineered mouse strains have led to an increased need for murine sperm preservation. Recent studies have begun to focus on optimizing the cryopreservation of murine sperm by carefully studying the effects of cooling and warming rates on sperm survival. In current practice, however, the Nakagata protocol is widely used. The actual cooling and warming rates achieved using the Nakagata protocol have not previously been determined; and the Nakagata protocol has a number of unspecified parameters which we have found can significantly affect cooling rates, warming rates and sperm survival. A detailed study of the thermal response of samples frozen and thawed using the Nakagata protocol reveals that the cooling rates range from 30 to almost 300 degrees C per minute depending on the exact manner in which the Nakagata protocol is implemented. Warming rates range from 160 degrees C/min to about 1000 degrees C/min. Sperm survival depended significantly on the particular cooling rate achieved, and less strongly on the warming rates. Overall, it was found that the particular manner in which the Nakagata protocol was implemented could strongly affect cooling rates and sperm survival; and, consistent with the findings of Mazur and Koshimoto, an optimal cooling rate appears to exist in the range of cooling rates that can be achieved using the Nakagata protocol.

Fertilization and development in vitro of bovine oocytes following intracytoplasmic injection of heat-dried sperm heads

This study investigated the development of bovine oocytes following intracytoplasmic injection of sperm heads from spermatozoa dried by heating. When sperm suspension was heated in a dry oven at 50, 56, 90, and 120 degrees C, the mean amounts of residual water were about 0.3 g water/g dry weight within 8 h, 6 h, 1.5 h, and 20 min of heating, respectively. Oocyte activation, cleavage of oocytes, and development of cleaved embryos to the morula stage were better in oocytes injected with spermatozoa stored at 25 degrees C for 7-10 days following drying at 50 and 56 degrees C than at 90 and 120 degrees C; however, only a small proportion of oocytes developed to the blastocyst stage. When spermatozoa were dried at 50 degrees C for 16 h, activation, male pronucleus (MPN) formation, cleavage, and development to the morula stage were less good than when spermatozoa were dried for 8 and 10 h and no blastocysts were obtained. The development of oocytes was significantly better when spermatozoa were stored for 7-10 days at 4 degrees C than 25 degrees C after drying at 50 degrees C for 8 h. Longer storage (7 days-12 mo) of heat-dried spermatozoa at 4 degrees C did not affect MPN formation in activated oocytes, but blastocyst development was significantly lower when spermatozoa were stored for 3 mo or more. These results demonstrate that bovine oocytes can be fertilized with heat-dried spermatozoa and that the fertilized oocytes can develop at least to the blastocyst stage.

Mouse sperm desiccated and stored in trehalose medium without freezing

Mouse sperm with and without trehalose were desiccated under nitrogen gas and stored at 4 degrees C and 22 degrees C. After rehydration, sperm were injected into oocytes using intracytoplasmic sperm injection and embryonic development was followed. Sperm were dried for 5.0, 6.25, or 7.5 min, stored at 22 degrees C for 1 wk with and without trehalose. The percentages of blastocysts that developed from sperm with trehalose were 51%, 31%, and 20%, respectively, which was significantly higher than sperm without trehalose (10%, 3%, and 5%, respectively). Desiccation and storage in medium with trehalose significantly increased sperm developmental potential compared to medium without trehalose. Sperm dried for 5 min produced more blastocysts than sperm dried for 6.25 or 7.5 min. When sperm were dried in trehalose for 5 min and stored for 1 wk, 2 wk, 1 mo, or 3 mo at 4 degrees C, the percentages of blastocysts were 73%, 84%, 63%, and 39%; whereas those stored at 22 degrees C for 1 wk, 2 wk, or 1 mo were significantly lower (53%, 17%, and 6%, respectively). Embryos from sperm partially desiccated in trehalose for 5 min and stored at 4 degrees C for 1 or 3 mo were transferred to 10 pseudopregnant recipients. Implantation rates were 81% and 48%; live fetuses were 26% and 5%, respectively. One of the recipients delivered three live fetuses. The results show that trehalose has a significant beneficial effect in preserving the developmental potential of mouse sperm following partial desiccation and storage at temperatures above freezing.