Sole use of sucrose in human sperm cryopreservation

Sperm Cryopreservation Today: Approaches, Efficiency, and Pitfalls

The cryopreservation of human spermatozoa has been an option for patients undergoing chemo or radiotherapies since the late 1950s. Presently, there are different techniques for the cryopreservation of spermatozoa. The most commonly used techniques are programmable slow freezing and freezing on liquid nitrogen vapors, while the use of vitrification is still not accepted as clinically relevant. Although there have been many improvements, the ideal technique for achieving better post-thaw sperm quality continues to be a mystery. A major obstacle during cryopreservation is the formation of intracellular ice crystals. Cryodamage generated by cryopreservation causes structural and molecular alterations in spermatozoa. Injuries can happen because of oxidative stress, temperature stress, and osmotic stress, which then result in changes in the plasma membrane fluidity, motility, viability, and DNA integrity of the spermatozoa. To prevent cryodamage as much as possible, cryoprotectants are added, and in some clinical trial cases, even antioxidants that may improve post-thaw sperm quality are added. This review discusses cryopreservation techniques, cryodamage on molecular and structural levels, and cryoprotectants. It provides a comparison of cryopreservation techniques and describes recent advances in those techniques.

Cryopreservation of NK and T Cells Without DMSO for Adoptive Cell-Based Immunotherapy

Dimethylsufoxide (DMSO) being universally used as a cryoprotectant in clinical adoptive cell-therapy settings to treat hematological malignancies and solid tumors is a growing concern, largely due to its broad toxicities. Its use has been associated with significant clinical side effects-cardiovascular, neurological, gastrointestinal, and allergic-in patients receiving infusions of cell-therapy products. DMSO has also been associated with altered expression of natural killer (NK) and T-cell markers and their in vivo function, not to mention difficulties in scaling up DMSO-based cryoprotectants, which introduce manufacturing challenges for autologous and allogeneic cellular therapies, including chimeric antigen receptor (CAR)-T and CAR-NK cell therapies. Interest in developing alternatives to DMSO has resulted in the evaluation of a variety of sugars, proteins, polymers, amino acids, and other small molecules and osmolytes as well as modalities to efficiently enable cellular uptake of these cryoprotectants. However, the DMSO-free cryopreservation of NK and T cells remains difficult. They represent heterogeneous cell populations that are sensitive to freezing and thawing. As a result, clinical use of cryopreserved cell-therapy products has not moved past the use of DMSO. Here, we present the state of the art in the development and use of cryopreservation options that do not contain DMSO toward clinical solutions to enable the global deployment of safer adoptively transferred cell-based therapies.

Osmotic tolerance of rabbit spermatozoa is affected by extender composition and temperature

Sperm osmotic adaptability to anisosmotic conditions is important for sperm epididymal maturation, motility activation at ejaculation, and female tract colonization, or for conducting technological procedures such as cryopreservation. Several factors affect this adaptability, including the fluid composition that contributes to water flow dynamics, and the temperature at which osmotic stress is initiated. This study was designed to investigate the effect of medium composition (electrolyte- or sugar-based extender) and temperature (25 and 5 °C) on rabbit sperm adaptability to anisosmotic conditions. Rabbit spermatozoa, therefore, were diluted at both temperatures (25 and 5 °C) in electrolyte- or sugar-based media at increasing osmotic conditions (100 to 1,000 mOsm/kg), and values for sperm variables (sperm kinetics, membrane integrity, mitochondrial membrane potential) were estimated as endpoints. Sperm kinetics seemed to be more sensitive to osmotic stress than membrane integrity or mitochondrial function. The effect of moderate hypoosmotic stress did not differ when there was use of sugar- and electrolyte-based extenders at 25 °C (P > 0.05). In hyper-tonic conditions at 25 °C, the sugar-based extender was more effective in protecting sperm membrane integrity and mitochondrial function (P < 0.05). The lesser temperature made the differences more relevant because of the detrimental effect of hyperosmotic stress was more evident in the electrolyte-based extender at 5 °C (P < 0.05). The results from this study indicated rabbit spermatozoa have different adaptability to anisosmotic conditions induced by sugar- and electrolyte-based media and that the temperature at which the osmotic stress is initiated affects the cellular response.

Comparison of rapid freezing versus vitrification for human sperm cryopreservation using sucrose in closed straw systems

Rapid freezing and vitrification using sucrose are two simple and cost-effective sperm cryopreservation methods. However, it is still unclear which method is better and what the optimal concentration of sucrose is. This study aimed to determine the optimal sucrose concentration for human sperm cryopreservation and compare the cryoprotective effects of rapid freezing versus vitrification using different closed straw systems in terms of sperm motility and DNA integrity. Our data showed that: (1) The optimal sucrose concentration for vitrification was 0.25 mol/l among the tested 0, 0.125, 0.25 and 0.5 mol/l concentrations; (2) Sperm total motility and progressive motility were cryopreserved significantly better by rapid freezing than vitrification in standard 0.5 ml cryostraws (P < 0.05); and (3) Sperm total motility and progressive motility were cryopreserved significantly better by vitrification in the straw-in-straw system than rapid freezing in the standard 0.5 cryostraw (P < 0.05), but no difference was found in sperm nuclear DNA fragmentation level between the two cryopreservation methods (P > 0.05). It was concluded that sucrose at 0.25 mol/l concentration is suitable for human sperm rapid freezing and vitrification, and sperm cryopreservation can be achieved by rapid freezing using closed standard 0.5 ml straws or by vitrification using the novel straw-in-straw system made of standard 0.25 and 0.5 ml straws.

Cryopreservation of human spermatozoa with minimal non-permeable cryoprotectant

Cryopreservation of human spermatozoa is a commonly used technique in assisted reproduction, however freezing low concentrations of sperm while maintaining adequate post-thaw motility remains a challenge. In an effort to optimize post-thaw motility yields, low volumes of human sperm were frozen in polyimide-coated fused silica micro-capillaries using 0.065 M, 0.125 M, 0.25 M, or 0.5 M trehalose as the only cryoprotectant. Micro-capillaries were either initially incubated in liquid nitrogen vapor before plunging into liquid nitrogen, or directly plunged into liquid nitrogen. Post thaw sperm counts and motility were estimated. Spermatozoa that were initially incubated in liquid nitrogen vapor had greater post thaw motility than those plunged immediately into liquid nitrogen independent of trehalose concentration. The protective effect of 0.125 M d-glucose, 3-O-methyl-d-glucopyranose, trehalose, sucrose, raffinose, or stachyose were evaluated individually. Trehalose and sucrose were the most effective cryoprotectants, recovering 69.0% and 68.9% of initial sperm motility, respectively.

Cryopreservation of a small number of human sperm using enzymatically fabricated, hollow hyaluronan microcapsules handled by conventional ICSI procedures

PURPOSE

We investigated whether enzymatically fabricated hyaluronan (HA) microcapsules were feasible for use in the cryopreservation of a small number of sperm.

METHODS

HA microcapsules were fabricated using a system of water-immiscible fluid under laminar flow. Three sperm were injected into a hollow HA microcapsule using a micromanipulator. Capsules containing injected sperm were incubated in a freezing medium composed of sucrose as the cryoprotectant and then placed in a Cryotop® device and plunged into liquid nitrogen. After thawing, the capsule was degraded by hyaluronidase, and the recovery rate of sperm and their motility were investigated.

RESULTS

The HA microcapsule measuring 200 μm in diameter and with a 30-μm thick membrane was handled using a conventional intracytoplasmic sperm injection (ICSI) system, and the procedure involved the injection of sperm into the capsule. The HA microcapsules containing sperm were cryopreserved in a Cryotop® device and decomposed by the addition of hyaluronidase. The recovery rate of sperm after cryopreservation and degradation of HA microcapsules was sufficient for use in clinical practice (90 %).

CONCLUSIONS

Hollow HA microcapsules can be used for the cryopreservation of a small number of sperm without producing adverse effects on sperm quality.

Successful use of the Cryolock device for cryopreservation of scarce human ejaculate and testicular spermatozoa

The existing methods for cryopreservation of very low count sperm samples are complex and sub-optimal for individual spermatozoa. Our purpose is to establish an effective simple method for cryoprotecting individual spermatozoa. Samples from patients with OTA were mixed with TYB or HEPES-buffered salt solution with glycerol + glucose and placed on a Cryolock that was plunged directly into liquid nitrogen or exposed to its vapors. Thawing was performed by direct immersion into a drop of warmed medium. The favorable method was tested on diluted samples (10-50 cells) and leftover TESE specimens from patients with azoospermia. Cryopreservation was considered successful if >30 spermatozoa, (>3 motile), or >5 spermatozoa (>1 motile) in diluted and TESE samples, were detected post-thawing. A significantly higher survival rate of seminal spermatozoa was obtained when using the Cryolock with TYB and freezing with liquid nitrogen vapor, compared to HEPES glycerol-glucose (95 vs. 35% respectively). Plunging the Cryolock into liquid nitrogen was detrimental. Cryolock combined with TYB cryoprotection and liquid nitrogen vapor freezing was highly effective for cryopreservation of individual spermatozoa in diluted and TESE samples. The Cryolock may serve for freezing very low-count sperm samples and individual spermatozoa. This method offers simplicity, efficacy, use of available materials, without requiring micromanipulation equipment or skills.

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.

Inhibiting ice recrystallization and optimization of cell viability after cryopreservation

The ice recrystallization inhibition activity of various mono- and disaccharides has been correlated with their ability to cryopreserve human cell lines at various concentrations. Cell viabilities after cryopreservation were compared with control experiments where cells were cryopreserved with dimethylsulfoxide (DMSO). The most potent inhibitors of ice recrystallization were 220 mM solutions of disaccharides; however, the best cell viability was obtained when a 200 mM d-galactose solution was utilized. This solution was minimally cytotoxic at physiological temperature and effectively preserved cells during freeze-thaw. In fact, this carbohydrate was just as effective as a 5% DMSO solution. Further studies indicated that the cryoprotective benefit of d-galactose was a result of its internalization and its ability to mitigate osmotic stress, prevent intracellular ice formation and/or inhibit ice recrystallization. This study supports the hypothesis that the ability of a cryoprotectant to inhibit ice recrystallization is an important property to enhance cell viability post-freeze-thaw. This cryoprotective benefit is observed in three different human cell lines. Furthermore, we demonstrated that the ability of a potential cryoprotectant to inhibit ice recrystallation may be used as a predictor of its ability to preserve cells at subzero temperatures.

Rhesus monkey sperm cryopreservation with TEST-yolk extender in the absence of permeable cryoprotectant

Recently, there has been increased interest in ultra-rapid freezing with mammalian spermatozoa, especially for vitrification in the absence of cryoprotectants. Sperm cryopreservation in non-human primates has been successful, but the use of frozen-thawed sperm in standard artificial insemination (AI) remains difficult, and removal of permeable cryoprotectant may offer opportunities for increased AI success. The present study intended to explore the possibility of freezing rhesus monkey sperm in the absence of permeable cryoprotectants. Specifically, we evaluated various factors such as presence or absence of egg yolk, the percentage of egg yolk in the extenders, and the effect of cooling and thawing rate on the success of freezing without permeable cryoprotectants. Findings revealed that freezing with TEST in the absence of egg yolk offers little protection (<15% post-thaw motility). Egg yolk of 40% or more in TEST resulted in decreased motility, while egg yolk in the range of 20-30% yielded the most motile sperm. Cooling at a slow rate (29 degrees C/min) reduced post-thaw motility significantly for samples frozen with TEST-yolk alone, but had no effect for controls in the presence of glycerol. Similarly, slow thawing in room temperature air is detrimental for freezing without permeable cryoprotectant (<2% motility). In addition to motility, the ability of sperm to capacitate based on an increase in intracellular calcium levels upon activation with cAMP and caffeine suggested no difference between fresh and frozen-thawed motile sperm, regardless of treatment. In summary, the present study demonstrates that ejaculated and epididymal sperm from rhesus monkeys can be cryopreserved with TEST-yolk (20%) in the absence of permeable cryoprotectant when samples were loaded in a standard 0.25-mL straw, cooled rapidly in liquid nitrogen vapor at 220 degrees C/min, and thawed rapidly in a 37 degrees C water bath. This study also represents the first success of freezing without permeable cryoprotectant in non-human primates.