Using egg yolk in a TRIS-Equex STM paste extender for freezing of dog semen is superior to egg yolk plasma, also after addition of lecithin and catalase

Comprehensive overview of the toxicities of small-molecule cryoprotectants for carnivorous spermatozoa: foundation for computational cryobiotechnology

Background

The specific and non-specific toxicities of cryoprotective agents (CPAs) for semen or spermatozoa cryopreservation/vitrification (SC/SV) remain challenges to the success of assisted reproductive technologies.

Objective

We searched for and integrated the physicochemical and toxicological characteristics of small-molecule CPAs as well as curated the information of all extenders reported for carnivores to provide a foundation for new research avenues and computational cryobiology.

Methods

The PubMed database was systematically searched for CPAs reported in SC/SV of carnivores from 1964 to 2024. The physicochemical features, ADMET parameters, toxicity classes, optimized structures, biological activities, thermodynamic equilibrium constants, and kinetic parameters were curated and assessed computationally.

Results

Sixty-two relevant papers pertaining to CPAs used in SC/SV were found, and 11 CPAs were selected. Among the properties of CPAs, the molecular weight range (59-758 g/mol), melting point (-60°C to 236°C), XlogP3 (-4.5 to 12.9), topological polar surface area (TPSA; 20-160 Å2), Caco2 permeability (-0.62 to 1.55 log(Papp) in 10-6 cm/s), volume of distribution (-1.04 to 0.19 log L/kg), unbound fraction of a CPA in plasma (0.198-0.895), and Tetrahymena pyriformis toxicity (log µg/L; -2.230 to 0.285) are reported here. Glutathione, dimethyl formamide, methyl formamide, and dimethyl sulfoxide were used as the P-glycoprotein substrates. Ethylene glycol, dimethyl sulfoxide, dimethyl formamide, methyl formamide, glycerol, and soybean lecithin showed Caco2 permeabilities in this order, whereas fructose, glutathione, glutamine, glucose, and citric acid were not Caco2-permeable. The CPAs were distributed in various compartments and could alter the physiological properties of both seminal plasma and spermatozoa. Low volume distributions of all CPAs except glucose indicate high water solubility or high protein binding because higher amounts of the CPAs remain in the seminal plasma.

Conclusion

ADMET information of the CPAs and extenders in the bipartite compartments of seminal plasma and intracellular spaces of spermatozoa are very important for systematic definition and integration because the nature of the extenders and seminal plasma could alter the physiology of cryopreserved spermatozoa.

Effect of Centrifuged Chicken Egg Yolk on the Cryopreservation of Boar Semen

Egg yolk, commonly employed as a cryoprotectant in semen cryopreservation, contains large particle matter that can diminish semen quality post thaw and complicate its quality assessment. For this reason, we designed a centrifugal treatment of chicken egg yolk to evaluate its effect on the cryopreservation of porcine semen. The control group (CG) was prepared with a dilution of chicken egg yolk by conventional mixing treatment, and the experimental group (EG) used a dilution of centrifugally treated chicken egg yolk for the ultra-low-temperature cryopreservation of porcine semen. The freezing process was carried out by conventional freezing methods. The spermatozoa were subsequently assessed for various parameters, including motility, acrosome integrity rate, plasma membrane integrity rate, antioxidant indexes, apoptosis rate, and the expression of apoptosis-related genes. The results showed that, post freeze-thawing, the motility, viability, VSL, and VCL of the spermatozoa in the EG were significantly higher than those observed in the CG (p < 0.05). Additionally, the acrosome integrity and plasma membrane integrity of the spermatozoa in the EG were significantly enhanced compared to the CG (p < 0.05). Furthermore, the EG exhibited significantly lower MDA content and sperm apoptosis rate (p < 0.05), while demonstrating significantly higher T-AOC and CAT levels (p < 0.05) relative to the CG. In comparison to the CG, the EG exhibited a significant reduction in the gene expression of TNF-a and Bax in the spermatozoa (p < 0.05), whereas the expression levels of CAT and Bcl-2 were significantly elevated (p < 0.05). In conclusion, the dilution solution formulated through the centrifugal processing of chicken egg yolk demonstrated efficacy in enhancing the quality of porcine spermatozoa following cryopreservation and subsequent thawing.

Effect of Detergents Based on Sodium Dodecyl Sulfate on Functional Metrics of Frozen-Thawed Collared Peccary (Pecari tajacu) Semen

We evaluated the effects of detergents based on sodium dodecyl sulfoxide (SDS) on the functional parameters of collared peccary frozen-thawed sperm. Semen aliquots from ten individuals were diluted in a Tris-egg yolk-glycerol extender alone or with 0.5% Equex STM^® paste or SDS (at 0.1%, 0.3% or 0.5% (v/v) concentration). Samples were fast frozen in liquid nitrogen with a post-thaw evaluation of motility, membrane functionality and integrity, mitochondrial activity, sperm binding ability and thermal resistance. The treatments without SDS (41.8 ± 3.5%) and those containing Equex (41.8 ± 4.4%) or 0.1% SDS (41.2 ± 5.5%) provided greater sperm motility (p < 0.05) than those containing SDS 0.3% (30.5 ± 4.7%) and 0.5% (31.2 ± 6.3%). Immediately after thawing, only treatments containing 0.1% SDS effectively preserved sperm straightness (STR) when compared to the negative control. All treatments preserved the amplitude of lateral head (ALH) and straightness (STR) during a thermal resistance test (p > 0.05), but SDS 0.5% impaired the membrane functionality and mitochondrial activity after thawing (p < 0.05). All treatments provided a similar recovery of sperm binding ability after thawing (p < 0.05). Our results showed that the addition of 0.1% SDS to the Tris-yolk-glycerol extender optimized the freeze-thaw recovery of peccary semen.

Assisted reproductive techniques for canines: preservation of genetic material in domestic dogs

Assisted reproductive techniques (ARTs), such as artificial insemination, in vitro fertilization, and cryopreservation of gametes/zygotes, have been developed to improve breeding and reproduction of livestock and for the treatment of human infertility. Their widespread use has contributed to improvements in human health and welfare. However, in dogs, only artificial insemination using frozen semen is readily available as an ART to improve breeding and control genetic diversity. A recent priority in sperm cryopreservation is the development of alternatives to egg yolk, which is widely used as a component of the sperm extender. Egg yolk can vary in composition among batches and is prone to contamination by animal pathogens. The latter can be a problem for international exchange of cryopreserved semen. Low-density lipoprotein and skim milk are promising candidates for use as extenders, to ensure fertility after artificial insemination. Although not tested for its effects on fertility following artificial insemination, polyvinyl alcohol may also be a useful alternative to egg yolk as an extender. The development of cryopreservation techniques for canine embryos lags behind that for other mammals, including humans. However, given the success of non-surgical embryo transfer in 2011, studies have sought to refine this approach for practical use. Research on sperm cryopreservation has yielded satisfactory results. However, investigation of other approaches, such as cryopreservation of oocytes and gonadal tissues, remains insufficient. Techniques for the efficient induction of estrus may aid in the development of successful canine ARTs.