Improved sperm cryopreservation using cold cryoprotectant

A Pilot Analysis of Whole Transcriptome of Human Cryopreserved Sperm

Sperm cryopreservation is a procedure widely used to store gametes for later use, to preserve fertility in patients prior to gonadotoxic treatments or surgery, and for sperm donation programs. The purpose of the study was to assess the impact of cryopreservation on human sperm transcriptome. Semen samples were collected from 13 normospermic men. Each sample was divided into two aliquots. The total RNA was immediately extracted from one aliquot. The second aliquot was frozen and total RNA was extracted after a week of storage in liquid nitrogen. The RNA samples were randomized in four pools, each of six donors, and analyzed by microarrays. The paired Significance Analysis of Microarray was performed. We found 219 lower abundant transcripts and 28 higher abundant transcripts in cryopreserved sperm than fresh sperm. The gene ontology analysis disclosed that cryopreservation alters transcripts of pathways important for fertility (i.e., spermatogenesis, sperm motility, mitochondria function, fertilization, calcium homeostasis, cell differentiation, and early embryo development), although the increase of some transcripts involved in immune response can compensate for the harmful effects of freezing.

Toxicity of cryoprotective agents to semen from two closely related snake species: The endangered Louisiana pinesnake (Pituophis ruthveni) and bullsnake (Pituophis cantenifer)

Cryopreservation of sperm is an important tool for the conservation of threatened species. Many species of reptile are under considerable threat of extinction and there has been limited investigation of sperm cryopreservation in this taxonomic group. We performed a comparative test of toxicity to sperm of six commonly used cryoprotective agents (CPAs) at three concentrations (5%, 10%, 20%) from the Louisiana pinesnake, Pituophis ruthveni (n = 11), and the closely related bullsnake, Pituophis cantenifer (n = 8). Our objective was to determine the general toxicity of CPAs for cryopreservation in snakes and the cryoprotective ability of CPAs for sperm from the endangered Louisiana pinesnake. We conducted three experiments to: 1) evaluate the short-term in vitro toxicity of common CPAs in two closely related snake species, 2) determine the effectiveness of cryoprotectants for freezing and thawing semen in the Louisiana pinesnake, and 3) test the possible reduction in toxic effects of individual CPAs on semen of the Louisiana pinesnake by combining two of them. We used measures of motility including total motility, forward motility, and forward progressive motility index to characterize toxic effects and cryoprotective ability of each CPA. The results of our three experiments provide several important findings: 1) sperm of the bullsnake and Louisiana pinesnake responded differently to CPAs, 2) few CPAs provided any cryoprotection, as measured by percent recovered motility, in Louisiana pinesnakes, and 3) using mixtures of CPAs did not reduce toxicity relative to the best performing CPA on its own. Motility was best maintained at a concentration of 5% for CPAs tested; however, cryoprotection was best achieved with glycerol at 20% followed by DMA and DMF at 10%. These results provide further insight into the challenges faced by researchers attempting to cryopreserve sperm from snakes. Further comparative studies are required to determine the generality of cryopreservation methods in reptiles and suggest caution should be taken when developing cryopreservation protocols across species, particularly in snakes. All CPAs tested in this study were permeating CPAs and showed a significant acute toxic effect on motility at concentrations that provided cryoprotection. Future work in snakes might consider additional avenues of cryoprotection and combinations of multiple approaches.

Cryopreservation of Sperm: Effects on Chromatin and Strategies to Prevent Them

Cryopreservation is a technique that can keep sperm alive indefinitely, enabling the conservation of male fertility. It involves the cooling of semen samples and their storage at -196 °C in liquid nitrogen. At this temperature all metabolic processes are arrested. Sperm cryopreservation is of fundamental importance for patients undergoing medical or surgical treatments that could induce sterility, such as cancer patients about to undergo genotoxic chemotherapy or radiotherapy, as it offers these patients not only the hope of future fertility but also psychological support in dealing with the various stages of the treatment protocols.Despite its importance for assisted reproduction technology (ART) and its success in terms of babies born, this procedure can cause cell damage and impaired sperm function. Various studies have evaluated the impact of cryopreservation on chromatin structure, albeit with contradictory results. Some, but not all, authors found significant sperm DNA damage after cryopreservation. However, studies attempting to explain the mechanisms involved in the aetiology of cryopreservation-induced DNA damage are still limited. Some reported an increase in sperm with activated caspases after cryopreservation, while others found an increase in the percentage of oxidative DNA damage. There is still little and contradictory information on the mechanism of the generation of DNA fragmentation after cryopreservation. A number of defensive strategies against cryoinjuries have been proposed in the last decade. Most studies focused on supplementing cryoprotectant medium with various antioxidant molecules, all aimed at minimising oxidative damage and thus improving sperm recovery. Despite the promising results, identification of the ideal antioxidant treatment method is still hampered by the heterogeneity of the studies, which describe the use of different antioxidant regimens at different concentrations or in different combinations. For this reason, additional studies are needed to further investigate the use of antioxidants, individually and in combination, in the cryopreservation of human sperm, to determine the most beneficial conditions for optimal sperm recovery and preservation of fertility.

Mode of action of cryoprotectants for sperm preservation

Sperm cryopreservation facilitates storage and transport for use in artificial reproduction technologies. Cryopreservation processing, however, exposes cells to stress resulting in cellular damage compromising sperm function. Cryoprotective agents are needed to minimize cryopreservation injury, but at higher concentration they are toxic to cells. In this review, we describe cryoinjury mechanisms, and modes of action of different types of cryoprotective agents. Furthermore, measures are discussed how to minimize toxic effects caused by adding and removing cryoprotective agents. Cryoprotective agents can be divided into permeating and non-permeating agents. Permeating agents such as glycerol can move across cellular membranes and modulate the rate and extent of cellular dehydration during freezing-induced membrane phase transitions. Permeating protectants provide intracellular protection because they are preferentially excluded from the surface of biomolecules thereby stabilizing the native state. Non-permeating agents can be divided into osmotically active smaller molecules and osmotically inactive macromolecules. Both, permeating and non-permeating protectants form a protective glassy state during freezing preserving biomolecular and cellular structures. Freezing extenders for sperm contain salts, buffer compounds, sugars, proteins and lipids, and typically contain glycerol as the main permeating cryoprotective agent providing intracellular protection. Non-permeating protectants including sugars and proteins are used as bulking agents and to increase the glass transition temperature of the freezing extender. Ultra-heat-treated milk and egg yolk are frequently added as membrane modifying agents to enhance the inherent sperm cryostability. The protocol how to use and add cryoprotectants is a compromise between their beneficial and potentially detrimental effects.

Production of F₁ offspring with vitrified sperm from a live-bearing fish, the green swordtail Xiphophorus hellerii

This study reports the first production of offspring with vitrified sperm from a live-bearing fish Xiphophorus hellerii. The overall goal of this study was to develop streamlined protocols for integration into a standardized approach for vitrification of aquatic species germplasm. The objectives were to (1) estimate acute toxicity of cryoprotectants, (2) evaluate vitrification solutions, (3) compare different thawing methods, (4) evaluate membrane integrity of post-thaw sperm vitrified in different cryoprotectants, and (5) evaluate the fertility of vitrified sperm. Nine cryoprotectants and two commercial vitrification additives were tested for acute toxicity and glass forming ability, alone and in combination. Two vitrification solutions, 40% glycerol (Gly) and 20% Gly+20% ethylene glycol (EG) in 500 mOsmol/kg Hanks' balanced salt solution (HBSS), were selected for vitrification of 10 μL sperm samples using inoculating loops plunged into liquid nitrogen. Samples were thawed at 24°C (one loop in 5 μL of HBSS or three loops in 500 μL of HBSS). Samples thawed in 500 μL were concentrated by centrifugation (1000 g for 5 min at 4°C) into 5 μL for artificial insemination. Offspring were produced from virgin females inseminated with sperm vitrified with 20% Gly+20% EG and concentrated by centrifugation.

Comparison of different osmolalities and egg-yolk composition in processing media for the cryopreservation of red wolf (Canis rufus) sperm

Successful cryopreservation of sperm and the maintenance of a sperm-based genome resource bank have been identified as priorities for the recovery of the endangered red wolf (Canis rufus). The objectives were to improve sperm processing and to determine the relative timing of damage to red wolf sperm during freezing and thawing. Fresh ejaculates (n=37) from adult red wolves (n=15, aged 2-13 y) were collected via electroejaculation and subjected to cooling, freezing and thawing in four TRIS-egg-yolk extender treatments varying in osmolality ( approximately 305 mOsm versus approximately 350 mOsm) and egg-yolk composition (0.8 microm-filtered versus unfiltered). Ejaculates were evaluated for sperm percentage motility, forward progressive motion, and morphological characteristics immediately upon collection and following extension, cooling (prior to freezing) and thawing. Although no single treatment consistently produced superior results, sperm suspended in approximately 305 mOsm extenders exhibited slight losses in motility post-thawing (13 and 7%). Also, sperm suspended in approximately 350 mOsm extenders tended to have slower rates of decline in motility in vitro post-thawing than those stored in approximately 305 mOsm extenders (P=0.55). Finally, extenders incorporating unfiltered egg yolk exhibited a slightly larger ratio of absent to partial acrosomes than did sperm frozen in extenders prepared with clarified egg yolk. For approximately 350 mOsm extenders, most motility loss occurred during the cooling rather than freezing and thawing. In conclusion, these data contribute to knowledge regarding cryopreservation of red wolf sperm.

Development of a cryopreservation protocol for long-term storage of black tiger shrimp (Penaeus monodon) spermatophores

The objectives of this study were to determine the effect of cryoprotectants on sperm viability and develop a freezing protocol for long-term storage of P. monodon spermatophores. Spermatophores suspended for 30 min in calcium-free saline (Ca-F saline) containing the cryoprotectants dimethyl sulfoxide (DMSO), ethylene glycol (EG), 1,2-propylene glycol (PG), formamide, and methanol at concentrations of 5, 10, 15, or 20% were studied using a modified eosin-nigrosin staining technique. The smallest reductions in apparent sperm viability occurred with DMSO; therefore, a freezing protocol was developed using Ca-F saline containing 5% DMSO. Spermatophores were cryopreserved using three protocols; cooling to a final temperature of -30, -80 or -80 degrees C and immediately stored in liquid nitrogen (cooling rates of -2, -4, -6, -8, -10, -12, -14 or -16 degrees C/min). Frozen spermatophores were thawed (2 min) at 30, 60, 70, or 90 degrees C. Successful cryopreservation of spermatophores in liquid nitrogen was achieved by a one-step cooling rate of -2 degrees C/min between 25 and -80 degrees C before storing in liquid nitrogen. Optimal thawing was in a 30 degrees C water bath for 2 min; this yielded live sperm after storage in liquid nitrogen for 210 days. Average sperm viability for fresh (97.8+/-2.9%) and cryopreserved spermatophores held for less than 60 days (87.3+/-4.1%) did not differ (P>0.05); however, that for spermatophores stored in liquid nitrogen between 90 and 210 days were lower (P<0.05) and varied from 27.3+/-3.4 to 53.3+/-4.3%. Thawed spermatophores previously held in liquid nitrogen for less than 62 days fertilized eggs (fertilization and hatching rates of 71.6-72.2% and 63.6-64.1%, respectively) at rates comparable to fresh spermatophores (70.8-78.2% and 66.3-67.8%, respectively). In conclusion, sperm within cryopreserved spermatophores stored in liquid nitrogen retained their viability for up to 210 days.

Osmotic tolerance and membrane permeability characteristics of rhesus monkey (Macaca mulatta) spermatozoa

Biophysical characteristics of the plasma membrane, such as osmotic sensitivity and water and cryoprotectant permeability are important determinants of the function of spermatozoa after cryopreservation. A series of experiments was conducted with rhesus macaque spermatozoa at 23 degrees C to determine their: (1) cell volume and osmotically inactive fraction of the cell volume; (2) permeability coefficients for water and the cryoprotectants dimethyl sulfoxide, glycerol, propylene glycol, and ethylene glycol; (3) tolerance to anisosmotic conditions; and (4) motility after a one step addition and removal of the four cryoprotectants. An electronic particle counter and computer aided semen analysis were used to determine the cell volume and permeability coefficients, and motility, respectively. Rhesus spermatozoa isosmotic cell volume was 27.7+/-3.0 microm3 (mean+/-SEM) with an osmotically inactive cell fraction of 51%. Hydraulic conductivity in the presence of dimethyl sulfoxide, glycerol, propylene glycol, and ethylene glycol was 1.09+/-0.30, 0.912+/-0.27, 1.53+/-0.53, and 1.94+/-0.47 microm/min/atm, respectively. Cryoprotectant permeability was 1.39+/-0.31, 2.21+/-0.32, 3.38+/-0.63, and 6.07+/-1.1 (x10(-3)cm/min), respectively. Rhesus sperm tolerated all hyposmotic exposures. However, greater than 70% motility loss was observed after exposure to solutions of 600 mOsm and higher. A one step addition and removal of all four cryoprotectants did not cause significant motility loss. These data suggest that rhesus sperm are tolerant to hyposmotic conditions, and ethylene glycol may be the most appropriate cryoprotectant for rhesus sperm cryopreservation, as it has the highest permeability coefficient of the tested cryoprotectants.