Development of vitrification solutions. In: Tucker MJ, Liebermann J, editors. Vitrification in Assisted Reproduction. Informa Healthcare; 2007. pp. 45-64. [DOI: 10.3109/9780203090022.004]

Epididymal tail solid-surface vitrification as an effective method for domestic cat sperm cryobanking

This study aimed to describe the viability of domestic feline spermatozoa after epididymal tail vitrification. For this, 10 pairs of testis-epididymis complexes were used. The epididymal tails were vitrified using the solid-surface vitrification (SSV) method, in which two vitrification media containing ethylene glycol (EG) 40% or glycerol (GLY) 40% were tested. Vitrification with the presence of EG resulted in better results for all sperm motility parameters (motility, vigour and CASA) compared with GLY (P < 0.05). There were no statistical differences for sperm viability and acrosome integrity, plasma membrane integrity, or overall health of morphologically normal sperm before or after vitrification among experimental groups. In conclusion, epididymal tail vitrification appears to be a suitable method for long-term storage of cat sperm, especially if the procedure is performed with EG as the cryoprotectant.

Development of sperm vitrification protocols for two endangered salmonid species: the Adriatic grayling, Thymallus thymallus, and the marble trout, Salmo marmoratus

Vitrification was applied to the sperm of two endangered fish species of Soča River basin in Slovenia, the Adriatic grayling (Thymallus thymallus) and marble trout (Salmo marmoratus) following testing different cooling devices and vitrifying media. Sperm was collected, diluted in species-specific non-activating media containing cryoprotectants, and vitrified by plunging directly into liquid nitrogen without pre-cooling. Progressive motility, curvilinear velocity, and straightness of fresh and vitrified-warmed sperm were evaluated with computer-assisted sperm analysis (CASA). Fertilization trials were carried out to test the effectiveness of vitrification in the case of grayling. A protocol utilizing a glucose-based extender, 30% cryoprotectants (15% methanol + 15% propylene glycol), 1:1 dilution ratio, and droplets of 2 μl on a Cryotop as cooling device yielded the highest post-thaw motility values for both Adriatic grayling (7.5 ± 6.5%) and marble trout (26.6 ± 15.8%). Viable embryos were produced by fertilizing eggs with vitrified grayling sperm (hatching 13.1 ± 11.7%, control hatching 73.9 ± 10.4%). The vitrification protocol developed in this study can be utilized in the conservation efforts for the two species as an alternative to slow-rate freezing when working in field conditions or when specific equipment necessary for slow-rate freezing is not available.

Development of sperm vitrification protocols for freshwater fish (Eurasian perch, Perca fluviatilis) and marine fish (European eel, Anguilla anguilla)

Vitrification was successfully applied to the sperm of two fish species, the freshwater Eurasian perch (Perca fluviatilis) and marine European eel (Anguilla anguilla). Sperm was collected, diluted in species-specific non-activating media and cryoprotectants and vitrified by plunging directly into liquid nitrogen without pre-cooling in its vapor. Progressive motility of fresh and vitrified-thawed sperm was evaluated with computer-assisted sperm analysis (CASA). Additional sperm quality parameters such as sperm head morphometry parameters (in case of European eel) and fertilizing capacity (in case of Eurasian perch) were carried out to test the effectiveness of vitrification. The vitrification method for Eurasian perch sperm resulting the highest post-thaw motility (14±1.6%) was as follows: 1:5 dilution ratio, Tanaka extender, 30% cryoprotectant (15% methanol+15% propylene-glycol), cooling device: Cryotop, 2μl droplets, and for European eel sperm: dilution ratio 1:1, with 40% cryoprotectant (20% MeOH and 20% PG), and 10% FBS, cooling device: Cryotop, with 2μl of sperm suspension. Viable embryos were produced by fertilization with vitrified Eurasian perch sperm (neurulation: 2.54±1.67%). According to the ASMA analysis, no significant decrease in head area and perimeter of vitrified European eel spermatozoa were found when compared to fresh spermatozoa.

Vitrification of Sperm from Marine Fishes: Effect on Motility and Membrane Integrity

Our goal was to develop a standardized approach for sperm vitrification of marine fishes that can be applied generally in aquatic species. The objectives were to: 1) estimate acute toxicity of cryoprotectants over a range of concentrations; 2) evaluate the properties of vitrification solutions (VS); 3) evaluate different thawing solutions, and 4) evaluate sperm quality after thawing by examination of motility and membrane integrity. Sperm were collected from red snapper (Lutjanus campechanus), spotted seatrout (Cynoscion nebulosus), and red drum (Sciaenops ocellatus). A total of 29 combinations of cryoprotectants were evaluated for toxicity and glass formation. Samples were loaded onto 10-µL polystyrene loops and plunged into liquid nitrogen. There was a significant difference (P < 0.05) in post-thaw motility among VS and among species when using the same VS. The sperm in VS of 15% DMSO + 15% ethylene glycol + 10% glycerol + 1% X-1000™ + 1% Z-1000™ had an average post-thaw motility of 58% and membrane integrity of 19% for spotted seatrout, 38% and 9% for red snapper, and 30% and 19% for red drum. Adaptations by marine fish to high osmotic pressures could explain the survival in the high cryoprotectant concentrations. Vitrification offers an alternative to conventional cryopreservation.

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.