Effects of the cryopreservation process on dog sperm integrity

Optimization of canine sperm cryopreservation by focusing on glycerol concentration and freezing rate

The purpose of this study was to improve the quality of frozen-thawed canine spermatozoa through the optimization of glycerol concentration (GC) and freezing rate in the semen freezing protocol. Ejaculates from nine dogs were diluted with an extender containing 0%, 1.5%, 3%, 6%, or 9% glycerol. The suspensions were loaded into 0.25 ml straws, frozen in nitrogen vapor in a closed box, and immersed in liquid nitrogen (LN2). The freezing rate was controlled by setting the distance from the LN2 surface to the straws as 1, 4, 7, or 10 cm. Firstly, freezing curves for each GC and freezing rate were analyzed. The analysis showed that the temperature of ice nucleation, freezing point, and immersion were changed with a certain trend depending on the GCs and freezing rates. Secondly, the sperm motility index (MI), viability and mitochondrial (MT) activity were evaluated. At 0 h after thawing, the MI was higher in the 3% and 6% GCs than the 0% GCs (P < 0.05). At 24 h, the 3% GC with 1 cm LN2 distance (1 cm-3%) and the 7 cm-6% showed higher viability than the other conditions (P < 0.05), and the highest MT activity was obtained in the 1 cm-3%, which was higher than the other conditions (P < 0.05). The present findings indicate that the rapid freezing rate at 1 cm (average - 31 °C/min) with 3% GC provided the optimal condition in this study; use of this condition should reduce the detrimental damage to dog spermatozoa caused by ice crystal formation during freezing.

Flavone and 3-hydroxyflavone supplementation in cryopreservation medium protects canine sperm against apoptosis and lipid peroxidation

Cryopreservation is a pivotal technique in safeguarding genetic material across diverse species, despite its inherent challenges linked to induced spermatozoa damage, notably apoptosis and lipid peroxidation (LPO). Given the insufficient antioxidant defense of spermatozoa against LPO, there is a rising interest in integrating additional additives into extenders to ameliorate mammalian semen quality. Among these additives, flavonoids have garnered considerable attention due to their potent antioxidative properties. Hence, our study aimed to assess the efficacy of flavone (FL) and 3-hydroxyflavone (3-OH = ) supplementation in the cryopreservation medium to protect canine sperm against the damaging impacts of freezing and ensure the preservation of their reproductive potential. Semen was collected from five Beagle stud dogs and then pooled. Then, the sample was divided into 7 groups, each treated with 1) 0 mM, 2) 0.1 mM FL, 3) 0.2 mM FL, 4) 0.4 mM FL, 5) 0.1 mM 3-OH = , 6) 0.2 mM 3-OH = , 7) 0.4 mM 3-OH = . Semen samples were subjected to cryopreservation in French straws and glycerol as a cryoprotectant. In the frozen thawed semen, sperm motility parameters by CASA system and sperm membrane integrity, acrosome status, mitochondrial activity, DNA fragmentation, early apoptosis with capacitation, and LPO were assessed using flow cytometry just after thawing (0 h) and 4 h post thaw. Results reveal significant increase in the proportion of live spermatozoa with undamaged acrosomes in the FL 0.1 and 3-OH = 0.2 groups at 0 h post thaw. At this time point, 3-OH = 0.1 significantly reduced the DNA fragmentation index (DFI) compared to the FL 0.1 and 0.2 groups. However, after the next 4 h, 3-OH = 0.4 exhibited the lowest (P < 0.05) DFI compared to FL 0.2 and 3-OH = 0.1. Additionally, 3-OH = 0.4 showed the highest (P < 0.05) proportion of non apoptotic and non capacitated spermatozoa compared to FL 0.1 0 h post-thaw. Simultaneously, the same group demonstrated significant reduction in apoptotic and capacitated sperm cells, at 0 h and 4 h post-thaw. Moreover, 3-OH = at 0.1 (0 h and 4 h) and 0.2 mM (4 h) significantly enhances the proportion of live sperm without LPO post thaw. Whitin the FL groups, only 0.4 FL significantly increased the percentage of live sperm without LPO. No significant effect of the tested substances was observed on sperm motility, cell membrane integrity, or mitochondrial activity. These findings highlight the promising role of flavone and 3-hydroxyflavone in enhancing sperm resilience during cryopreservation, suggesting their protective function against acrosome damages, capacitation, apoptosis and lipid peroxidation.

Addition of low concentration of cholesterol-loaded cyclodextrin (CLC) has a positive effect on cryopreserved canine spermatozoa evaluated by andrological and biophysical methods

BACKGROUND

This study was conducted to find the best concentration of cholesterol-loaded cyclodextrin (CLC) which has a positive impact on canine post thaw semen quality. Three different concentrations of CLC (0.83 mg/ml; 1.66 mg/ml; 3.32 mg/ml) and 2-hydroxylpropyl-beta-cyclodextrin (HBCD) (1.66 mg/ml) were used in addition to cryopreservation extender and compared with the control after thawing. Samples were assessed using computer-assisted semen analyzer (CASA), flow cytometry, fluorimeter by measuring the fluorescence anisotropy (ANISO) and determining the generalized membrane polarization (GP).

RESULTS

An addition of 0.83 mg/ml CLC significantly increased the percentage of progressive motile (PROG) and rapid spermatozoa (RAP) (P < 0.05). 1.66 mg/ml HBCD decreased progressive motility of spermatozoa and population with rapid movement relative to the control (P < 0.05). Furthermore, the groups with an addition of 1.66 mg/ml and 3.32 mg/ml of CLC, as well as the group with only cyclodextrin, increased percentage of dead spermatozoa without lipid peroxidation and decreased percentage of viable spermatozoa without LPO which was lower in these groups than in the control (P < 0.05). Other sperm parameters assessed on flow cytometer were not significantly different. The addition of CLC at 0.83 mg/ml and 3.32 mg/ml concentrations and 1.66 mg/ml of HBCD caused an increase in ANISO measured at 23 ºC (P < 0.05).

CONCLUSIONS

In conclusion, the results suggest that increasing cholesterol in the plasma membrane of canine spermatozoa can improve their freezability. However, only low concentrations of CLC may improve semen quality after thawing without adversely affecting other parameters.

Effects of extender filtration and egg yolk concentration on canine semen cryopreservation

The semen cooling and freezing extenders commonly contain the chicken egg yolk (EY) as the main sperm cryoprotectant. Besides its advantages, the EY has large lipoprotein granules that cause several physical and biological interferences. The previous studies have proposed several methods to resolve the problems with the EY-based semen extenders, including mechanical agitation, EY fractionation, replacing the EY with purified EY LDL, and ultrasonication. In the current research, we aimed to evaluate the syringe filtration (220 nm) of an EY-based canine semen freezing extender as a simple and cheap method to remove the EY granules. We also studied the possibility of re-aggregation of EY granules after cooling, freeze/thawing, and lyophilization/rehydration of the filtered extenders. Additionally, we compared the effects of the filtration on lipid profile, turbidity, EY particle size distribution, and osmolality of the EY-based extenders. Next, we examined the effects of filtered extenders containing different levels of EY (5%, 10%, 15%, 20%, and 25%) versus the control extender (20% EY, unfiltered) on post-thaw sperm quality traits. We collected the semen samples from seven clinically healthy mixed-breed adult dogs and pooled them for sperm freezing procedures. Samplings were repeated at least five times, independently. Our results indicated that the syringe filtration could remove the large EY particles and reduce the extender turbidity without affecting the lipid profile of the whole extender solution. The filtered extender supplemented with 25% (v/v) EY led to the best post-thaw canine spermatozoa quality markers. The frozen-thawed spermatozoa evaluations included motility parameters (computer-assisted semen analysis system), membrane and acrosome integrity (hypo-osmotic swelling test, chlortetracycline binding assay), DNA fragmentation (sperm chromatin dispersion assay), membrane lipid peroxidation (MDA levels), apoptosis (Annexin V/propidium iodide assay), and fertility-associated sperm mRNA transcript abundance (protamine 2 and 3). In conclusion, the syringe filtration of the EY-based semen extenders was a simple and cheap method that could effectively remove large EY lipoprotein granules and possibly prevent EY-origin bacterial contamination of the final extender solution. The EY at 25% (v/v) concentration in the filtered extenders resulted in the highest canine spermatozoa cryo-tolerance.

Photoperiod and Melatonin Supplementation: Variable Effects on the Quality of Chilled Dog Semen

The addition of melatonin in seminal extenders due to its antioxidant properties and its beneficial role in sperm preservation has been previously described, especially in seasonal species. The aim of this study was to study a potential seasonal effect based on photoperiod duration when adding a physiological concentration of melatonin in the canine ejaculate. A total of 24 ejaculates were obtained from 10 healthy dogs during the increasing photoperiod (from December 21 to June 21), whereas 12 ejaculates were collected from five healthy individuals during the decreasing photoperiod (from June 22 to December 20). Each ejaculate was separated into two aliquots, and one of them remained as a control, whereas melatonin (100 pM) was added to the other one (C and M treatment groups, respectively). Diluted semen was refrigerated at 5°C. On days 0, 1, 2, 3, and 6, sperm motility analyses were performed using a CASA system and hypoosmotic swelling test (HOST), osmotic resistance test (ORT), and flow cytometry analysis. No effect of melatonin on motility was detected in either photoperiod. Negative effects of melatonin were found for acrosomal defects, apoptosis, and viability in the decreasing photoperiod. The addition of melatonin to sperm in the decreasing photoperiod could create such a high level that it would cause the described negative effects. We found a beneficial effect of melatonin in the increasing photoperiod on acrosomal defects and apoptosis during 0–6 days. Melatonin treatment also increased viability in the short term (days 1 and 2) for both photoperiods. Also, melatonin can provide certain beneficial effects on mitochondrial activity in the medium term (days 2 and 3) in the decreasing photoperiod.

Supplementation of melatonin to cooling and freezing extenders improves canine spermatozoa quality measures

Background

Sperm freezing and cold storage are the two most common assisted reproductive technologies in the canine breeding industry. The freeze-thawing process causes significant detrimental changes in both sperm cell structure and function. Previous research has confirmed that excessive accumulation of un-scavenged free radicals (oxidative stress) plays an important role in the cryopreservation-induced damage to sperm cells. Also, the gradual accumulation of the free radicals during cold storage leads to a decline in the sperm quality markers. Melatonin is an endogenous neurohormone synthesized from tryptophan amino acid by pineal glands. Besides its several well-known physiologic roles, melatonin has a significant antioxidant potential through direct free radical scavenging properties. Therefore, the current study was designed to evaluate the potential in vitro protective properties of melatonin (0.5, 1, and 2 mM) on canine sperm cells after freezing or during long-term cold storage (9 days, 5 °C) on most important sperm in vitro fertility markers.

Results

Melatonin at 0.5, 1- or 2-mM concentrations could preserve significantly higher sperm total motility after 4 days of cold storage. However, only the 1- and 2 mM melatonin concentrations could result in better TM and PM values after 7 days of cold storage. Furthermore, melatonin supplementation could preserve higher sperm viability and acrosome integrity after 7 days of storage. Also, it could have significant protective effects on the cooled sperm DNA integrity. In the freezing section of the current research, melatonin at either 1- or 2-mM concentrations could not improve the sperm post-thaw TM and PM, whereas they improved sperm DNA integrity. Also, the post-thaw plasma membrane functional integrity and sperm velocity parameters were not affected by the treatment. Although DMSO (Dimethyl Sulfoxide) as the melatonin solvent could reduce the level of sperm lipid peroxidation and even improve the post-thaw sperm DNA integrity compared to the negative control, it reduced the post-thaw sperm progressive motility. However, the negative effects were reversed by concurrent melatonin supplementation at 1- and 2-mM concentrations.

Conclusion

The addition of 1- or 2-mM melatonin to the canine sperm freezing and cooling media could improve sperm motility, viability, acrosome, and DNA integrity.

A triple stain method in conjunction with an in-depth screening of cryopreservation effects on post-thaw sperm in dogs

In order to accurately analyze the possible side effects of sperm cryopreservation, an in-depth screening of post-thaw sperm status is necessary. Thus, this study aimed to identify thorough effects of sperm cryopreservation, by evaluating the integrity of all specific structures of the canine spermatozoa. Thirteen (n = 13) mature dogs of different breeds were selected. Six dogs (n = 6) were subjected to sperm cryopreservation, whereas seven dogs (n = 7) were used as semen donors to validate a simultaneous assessment of sperm plasmatic, acrosomal, and mitochondrial membranes (triple stain) by fluorescent probes. Fresh and post-thaw semen samples were evaluated through a computer-assisted analysis of sperm motility, sperm morpho-functional evaluation, triple stain and sperm DNA integrity. Post-thaw semen samples had lower total and progressive motility, as well as higher percentage of minor and major defects. Moreover, post-thaw samples had higher percentage of sperm with plasma membrane and mitochondrial damage but intact acrosome, and also sperm with simultaneous damaged plasma, acrosomal and mitochondrial membranes. Furthermore, post-thaw sperm had higher protamination deficiency and DNA fragmentation. In conclusion, cryopreservation has a broad impact in sperm morphology and function, altering motility patterns, plasma, acrosome and mitochondrial membranes integrity, as well as sperm DNA.

Cryopreservation of dog epididymal spermatozoa by conventional freezing or ultra-rapid freezing with nonpermeable cryoprotectant

This study was aimed to assess the effectiveness of two methods for cryopreservation of dog epididymal spermatozoa, one by conventional freezing (CF) with shortening both equilibration and cooling times, and the other by ultra-rapid freezing (URF) with nonpermeable cryoprotectant. Sixty epididymides were recovered from thirty orchiectomized adult dogs and the sperm samples were retrieved by retrograde flushing using TCG-EY (tris, citric acid, glucose + 20% egg yolk) extender and then 20 pools were conformed. Each pool was divided into 2 aliquots and then cryopreserved by CF and URF methods respectively. The CF method maintained the cooled-pool samples for 2h (1h without and 1h with 5% glycerol) and then were frozen by liquid nitrogen (LN₂) vapors for 2 min. The URF method cryopreserved the cooled-pool samples using TCG-EY+250 mM sucrose, equilibrating during 30 min (5 °C) and submerging 30-μL drops directly in LN₂. The results showed that the URF method produced a lower percentage of total and progressive motilities and acrosome integrity (P < 0.05) than the CF method. However, the kinetic variables (curvilinear and straight-line velocities, straightness, linearity, wobble, amplitude of lateral head displacement, and beat-cross frequency) and plasma membrane integrity did not differ (P > 0.05) between both cryopreservation methods. Unlike the URF method, the width, area and perimeter of sperm head were reduced after the CF method (P < 0.05). In conclusion, despite the low motility achieved after the ultra-rapid freezing method, the similar values of kinetic, viability and head morphometric dimensions to those obtained after conventional freezing, suggest that ultra-rapid freezing with sucrose may be a useful alternative for the cryopreservation of canine epididymal sperm.

First successful frozen semen of the maned wolf (Chrysocyon brachyurus)

This study aimed to describe successful cryopreservation of sperm from maned wolves (Chrysocyon brachyurus). Three ejaculates from 2 maned wolves were collected by digital manipulation of the penis and evaluated subjectively, centrifuged and frozen in BotuCrio^® (Botupharma, Botucatu, Brazil) or Tris-yolk egg extender. Spermatozoa were thawed at 37ºC/30s or 70ºC/4s and evaluated for kinetics, morphology, plasma and acrosome membrane integrity, mitochondrial potential, hydrogen peroxide, superoxide anion and lipid peroxidation. From 5 thawed samples, two had sperm total motility >55% (56.0% and 64.0%) and progressive motility ~35% (35% and 40%), both frozen with Tris-yolk egg. Plasma and acrosome membrane integrity decreased and percentage of sperm defects increased post-thawing. We concluded that is possible to freeze spermatozoa from maned wolves using semen collection and processing methods applied for domestic dogs.

Overview on the Antioxidants, Egg Yolk Alternatives, and Mesenchymal Stem Cells and Derivatives Used in Canine Sperm Cryopreservation

Sperm cryopreservation is a widely used assisted reproductive technology for canine species. The long-term storage of dog sperm is effective for the breeding of dogs living far apart, scheduling the time of artificial insemination that suits the female, and preventing diseases of the reproductive tract. However, spermatozoa functions are impaired during the freeze-thaw processes, which may decrease reproductive performance. Numerous attempts have been made to restore such impairments, including the use of cryoprotectants to prevent the damage caused by ice crystal formation, and supplementation of antioxidants to reduce reactive oxygen species generation due to osmotic stress during the procedure. Egg yolk derivatives, antioxidants, and, more recently, mesenchymal stem cells (MSCs) and their derivatives have been proposed in this research field. This review article will summarize the current literature available on the topic.

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

We compared the results of using egg yolk plasma (EYP) instead of egg yolk (EY) in a TRIS-based Equex STM Paste freezing extender system for dog semen [25]. We also tested whether the addition of lecithin and catalase to the EYP extenders would improve results. Fractionated semen collection was done in 17 stud dogs and the sperm rich fraction diluted with different extenders in 2 steps: (I) TRIS-fructose-citric acid extender (TRIS) containing 20% egg yolk (EY) and 3% glycerol [25], (II) TRIS containing 20% egg yolk plasma (EYP) and 3% glycerol, and (III) TRIS containing 20% EYP and 0.8% lecithin (EYP-L) and 3% glycerol. After equilibration the second dilution step was done: samples with (I) were diluted with TRIS-EY with 7% glycerol and 1% Equex STM paste [25]; samples with (II) and (III) were divided in 2 aliquots each, and one part diluted with TRIS-EYP or TRIS-EYP-L, both containing 7% glycerol and 1% Equex STM paste, and the other one part with the same extenders containing additionally 300 I.U./mL catalase. After freezing and thawing, samples were analyzed by CASA and sperm chromatin structure assay (SCSA); reactive oxygen species (ROS), degree of apoptosis and zona binding ability were determined. Semen samples with TRIS-EY with a final concentration of 5% glycerol and 0.5% Equex STM paste [25] showed best post thaw progressive motility (P), most intact cells, lowest percentage of ROS, acrosome damages, dead and apoptotic cells. Curvilinear velocity (VCL), DNA fragmentation, morphological abnormalities and zona binding ability did not differ between groups. Replacement of egg yolk by EYP increased the ROS and late apoptotic cells. Addition of lecithin and catalase to EYP containing extenders decreased motility and increased complete apoptosis. We conclude that egg yolk is superior to EYP in the here investigated extenders. The TRIS-based extender [25] with EYP could not be improved by addition of lecithin and catalase; however, in-vivo fertilization capacity of the here examined extenders remains to be investigated.

Conditioned Medium from Canine Amniotic Membrane-Derived Mesenchymal Stem Cells Improved Dog Sperm Post-Thaw Quality-Related Parameters

Simple Summary

Mesenchymal stem cells and their derivatives are used in clinical studies for their anti-apoptotic, anti-oxidant, immunomodulatory, and regenerative properties. Their use in reproductive medicine is increasing as they have been proved to be beneficial for infertility treatment. Mesenchymal stem cells can secrete factors that influence biological processes in target tissues or cells; these factors are either directly secreted by the cells or mediated through their derivatives. Although the amniotic membrane is easy to obtain and is a good source of stem cells, clinical trials using amniotic membrane-derived mesenchymal stem cells are still uncommon, especially in reproductive medicine or artificial reproductive technologies. The objective of the present study was to demonstrate the effects of conditioned medium prepared from amniotic membrane-derived stem cells on dog sperm cryopreservation. Our results showed that 10% of the conditioned medium enhanced the quality-related parameters of frozen–thawed sperm cells because of the presence of antioxidants and growth factors in the medium, which probably protected spermatozoa during the freeze–thaw process. These results suggest that conditioned media prepared from amniotic membrane-derived mesenchymal stem cells might have clinical applications in assisted reproductive technologies.

Abstract

This study investigated the effects of conditioned medium (CM) from canine amniotic membrane-derived MSCs (cAMSCs) on dog sperm cryopreservation. For this purpose, flow cytometry analysis was performed to characterize cAMSCs. The CM prepared from cAMSCs was subjected to proteomic analysis for the identification of proteins present in the medium. Sperm samples were treated with freezing medium supplemented with 0%, 5%, 10%, and 15% of the CM, and kinetic parameters were evaluated after 4–6 h of chilling at 4 °C to select the best concentration before proceeding to cryopreservation. Quality-related parameters of frozen–thawed sperm were investigated, including motility; kinetic parameters; viability; integrity of the plasma membrane, chromatin, and acrosome; and mitochondrial activity. The results showed that 10% of the CM significantly enhanced motility, viability, mitochondrial activity, and membrane integrity (p < 0.05); however, the analysis of chromatin and acrosome integrity showed no significant differences between the treatment and control groups. Therefore, we concluded that the addition of 10% CM derived from cAMSC in the freezing medium protected dog sperm during the cryopreservation process.