Can amides be alternative cryoprotectors for the preservation of feline semen?

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.

Insights into alternative cryoprotectants to freeze sperm of domestic cats

Globalization and habitat destruction pose a significant threat to wildlife felids. Even though conservation banks for genetic materials have been created, the sperm cryopreservation with minimal cell damage is still a great challenge. Thus, this study aimed to compare the effects of two commercial extenders with different concentrations of alternative cryoprotectants on thawed sperm quality of domestic cats. Five adult cats were anaesthetized (using a combination of 40 μg/kg medetomidine associated to 5 mg/kg ketamine), and the semen was collected by electroejaculation (electrical stimulation of 2-3 V). Semen samples were evaluated for sperm characteristics (kinetics, morphology, membrane integrity and morphometry). Subsequently, they were sorted into two aliquots and centrifuged. The aliquots were added to a commercial extender containing 3% glycerol and 2% methylformamide (extender I) or 2% glycerol and 3% methylformamide (extender II), frozen, thawed (37°C/30 s) and reevaluated. Comparatively, the sperm kinetics and membrane integrity of fresh semen were higher (p < .002) than frozen samples in extender I and II. Total and progressive motility were lowest in the thawed samples. However, the subjective analysis indicated high sperm motility, since the kinetics evaluation was impaired by the low cell number in the thawed samples. There were no differences in sperm morphology between the groups. In the sperm morphometric analysis, a significant difference (p = .04) was identified in the length of the intermediate piece in extender II samples compared with fresh and extender I. Thus, it can be concluded that although the concentrations tested did not maintain the kinetic parameters and membrane integrity of spermatozoa after thawing, the extender with a lower concentration of glycerol was less toxic for maintaining the midpiece length.

Transcriptome Analysis Reveals Key Gene Expression Changes in Blue Catfish Sperm in Response to Cryopreservation

The hybrids of female channel catfish (Ictalurus punctatus) and male blue catfish (I. furcatus) account for >50% of US catfish production due to superior growth, feed conversion, and disease resistance compared to both parental species. However, these hybrids can rarely be naturally spawned. Sperm collection is a lethal procedure, and sperm samples are now cryopreserved for fertilization needs. Previous studies showed that variation in sperm quality causes variable embryo hatch rates, which is the limiting factor in hybrid catfish breeding. Biomarkers as indicators for sperm quality and reproductive success are currently lacking. To address this, we investigated expression changes caused by cryopreservation using transcriptome profiles of fresh and cryopreserved sperm. Sperm quality measurements revealed that cryopreservation significantly increased oxidative stress levels and DNA fragmentation, and reduced sperm kinematic parameters. The present RNA-seq study identified 849 upregulated genes after cryopreservation, including members of all five complexes in the mitochondrial electron transport chain, suggesting a boost in oxidative phosphorylation activities, which often lead to excessive production of reactive oxygen species (ROS) associated with cell death. Interestingly, functional enrichment analyses revealed compensatory changes in gene expression after cryopreservation to offset detrimental effects of ultra-cold storage: MnSOD was induced to control ROS production; chaperones and ubiquitin ligases were upregulated to correct misfolded proteins or direct them to degradation; negative regulators of apoptosis, amide biosynthesis, and cilium-related functions were also enriched. Our study provides insight into underlying molecular mechanisms of sperm cryoinjury and lays a foundation to further explore molecular biomarkers on cryo-survival and gamete quality.

Establishment of semen collection technique using electroejaculator and semen cryopreservation of Javan leopard (Panthera pardus melas Cuvier, 1809)

Background and Aim:

The Javan leopard (Panthera pardus melas Cuvier, 1809) is a subspecies of Panthera pardus spp., spread across the African and Asian regions. Information on reproductive aspects is crucial for wild animals, including the Javan leopard. In this study, we aimed to developelectroejaculator (EE) techniques and evaluate cryopreservation success in Javan leopard semen.

Materials and Methods:

The semen of four adult Javan leopards was collected once a week using EE. Placement of the EE probe in the rectum was performed after ultrasound imaging (ultrasonography) to determine the prostate body location. The semen obtained was then evaluated macroscopically and microscopically. Three Javan leopards were used for cryopreservation. The ejaculate was divided into two parts [i.e., one part diluted with AndroMed^® (Minitüb, Tiefenbach, Germany) and the other part with Steridyl^®(Minitüb, Tiefenbach, Germany)] at a 1:1 ratio immediately after collection and evaluation. The semen was then packed in a 0.25 mL MiniStraw^® (Minitüb, Tiefenbach, Germany) then equilibrated at 4°C for 2 h. After equilibration, the straw was then frozen in liquid nitrogen vapor. Frozen semen was then stored in containers until further evaluation.

Results:

The results showed that ejaculation response occurred at all levels of stimulation, while erections did not always occur. The fastest ejaculation and erection occurred at the fourth voltage. The macroscopic evaluation showed that the semen volume was 0.80±0.26 mL, cloudy white, pH 7.44±0.14, and with watery semen consistency. The microscopic evaluation showed that the sperm motility was 66.98±0.39%, with sperm viability of 75.6±1.79%. Sperm concentration was 62.17±46.95×10⁶ mL⁻¹ with a total concentration of 42.14±23.51×10⁶ cells. Normal sperm morphology is only 40.72±6.26%.

Conclusion:

This study concluded that the development of a semen collection technique using an EE preceded by imaging of the EE probe location using ultrasound was effective for the ejaculation of Javan leopards. The characteristics of the semen of the Javan leopard showed moderate semen volume, sperm motility, and viability. Javan leopard showed low sperm concentration and normal sperm morphology.

In vitro effects of two different commercial freezing and thawing extenders on boar sperm quality

This study was conducted to evaluate whether there were differences in viability of cryopreserved semen when using two different freezing (Minitube Cryoguard - F1 or Androstar® CryoPlus - F2) and thawing (Minitube Cryoguard Thawing solution - T1 or Androstar® Plus - T2) extenders. Ejaculates were collected, diluted (1:1), and cooled before shipping at 17 °C overnight. Samples were aliquoted in cryopreservation extender F1 or F2. Four straws from each treatment sample were thawed and diluted in T1 or T2, resulting in four treatments (F1-T1, F1-T2, F2-T1, and F2-T2). The sperm in diluted semen were evaluated for motility kinetics at 30, 180, and 360 min after thawing. The integrity assessments of the plasma and acrosomal membranes were performed at 30 and 360 min after thawing. There was no interaction between F × T × Time (P > 0.05), and no interaction between F × T (P > 0.05). The sperm progressive motility (PMOT) as time post-thawing increased was greater (P = 0.015) when dilutions occurred using F1 compared with F2 extender. Sperm thawed in T1 had a greater TMOT (P = 0.008) and PMOT (P = 0.033) at all times evaluated. The sperm plasma and acrosomal membrane integrity (AIMI) were greater (P = 0.009) when samples were preserved in F1 compared to F2 extender. The use of T2, as compared with T1 thawing extender, resulted in an enhanced integrity of the plasma and acrosomal membranes (P = 0.008). It is concluded different combinations of commercial freezing extenders and thawing solutions have effects on the quality of cryopreserved boar semen in vitro.