The nuclear DNA longevity in cryopreserved boar spermatozoa assessed using the Sperm-Sus-Halomax

Insights into crucial molecules and protein channels involved in pig sperm cryopreservation

Cryopreservation is the most efficient procedure for long-term preservation of mammalian sperm; however, its use is not currently dominant for boar sperm before its use for artificial insemination. In fact, freezing and thawing have an extensive detrimental effect on sperm function and lead to impaired fertility. The present work summarises the basis of the structural and functional impact of cryopreservation on pig sperm that have been extensively studied in recent decades, as well as the molecular alterations in sperm that are related to this damage. The wide variety of mechanisms underlying the consequences of alterations in expression levels and structural modifications of sperm proteins with diverse functions is detailed. Moreover, the use of cryotolerance biomarkers as predictors of the potential resilience of a sperm sample to the cryopreservation process is also discussed. Regarding the proteins that have been identified to be relevant during the cryopreservation process, they are classified according to the functions they carry out in sperm, including antioxidant function, plasma membrane protection, sperm motility regulation, chromatin structure, metabolism and mitochondrial function, heat-shock response, premature capacitation and sperm-oocyte binding and fusion. Special reference is made to the relevance of sperm membrane channels, as their function is crucial for boar sperm to withstand osmotic shock during cryopreservation. Finally, potential aims for future research on cryodamage and cryotolerance are proposed, which might be crucial to minimise the side-effects of cryopreservation and to make it a more advantageous strategy for boar sperm preservation.

Improved fertility of frozen-thawed porcine spermatozoa with 3,3-dimethylglutaric anhydride poly-L-lysine as a novel cryoprotectant

In this study, we determined the efficacy of 3,3-dimethylglutaric anhydride poly-L-lysine (DMGA-PLL) as a cryoprotectant for porcine spermatozoa. Porcine spermatozoa were cryopreserved in a freezing extender containing 3% (v/v) glycerol and various concentrations of DMGA-PLL. At 12 h after thawing, the motility index of spermatozoa cryopreserved with 0.25% (v/v) DMGA-PLL (25.9) was significantly (P < 0.01) higher than that of spermatozoa cryopreserved with 0%, 0.125%, or 0.5% DMGA-PLL (10.0-16.3). In addition, the blastocyst formation rate of embryos derived from spermatozoa cryopreserved with 0.25% DMGA-PLL (22.8%) was significantly (P < 0.01) higher than that of embryos derived from spermatozoa cryopreserved with 0%, 0.125%, or 0.5% DMGA-PLL (7.9%-10.9%). The mean number of total piglets born to sows inseminated with spermatozoa cryopreserved without DMGA-PLL (9.0) was significantly (P < 0.05) lower than that of total piglets born to sows inseminated with spermatozoa stored at 17°C (13.8). However, when spermatozoa cryopreserved with 0.25% DMGA-PLL were used for artificial insemination, the mean number of total piglets (11.7) was not significantly different from that obtained following artificial insemination using spermatozoa stored at 17°C. The results showed the usefulness of DMGA-PLL as a cryoprotectant in the cryopreservation of porcine spermatozoa.

Nuclear DNA Fragmentation in Boar Spermatozoa: Measurement Methods and Reproductive Performance Implications

The aim of this research was to compare the different techniques to measure sperm nuclear DNA fragmentation (sDF) and to check its relations to boar reproductive value, classical spermiogram parameters, and reproductive results of the doses in sows. Sperm chromatin stability assay (SCSA), terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, and sperm chromatin dispersion test (SCD, Halomax^®) results were compared, finding a statistically significant correlation only between SCSA and TUNEL results. The fertility direct boar effect (DBE) index, calculated from the whole productive life of the boar, was not correlated (p > 0.05) with sDF (measured by any technique). Total or progressive sperm motility was not correlated with sDF, while it found a positive correlation between TUNEL measure and abnormal acrosomes (%) and between SCD measure and total sperm morphological abnormalities (%). No significant correlations were obtained between fertility or prolificacy results and sDF results with the different techniques. However, in the case of total born and SCSA measure, the correlation was close to significance (r partial = −0.095; p = 0.066), appointing to a tendency; as SCSA increases, the number of total piglets born decreases. In conclusion, although the different techniques for the sDF seem not to target exactly the same DNA events and the relationship between their values and the reproductive results and the classical spermiogram results is still to be elucidated, the studied sDF techniques may offer extra information that could be useful for the management of AI studs.

Direct but Not Indirect Methods Correlate the Percentages of Sperm With Altered Chromatin to the Intensity of Chromatin Damage

Although sperm chromatin damage, understood as damage to DNA or affectations in sperm protamination, has been proposed as a biomarker for sperm quality in both humans and livestock, the low incidence found in some animals raises concerns about its potential value. In this context, as separate methods measure different facets of chromatin damage, their comparison is of vital importance. This work aims at analyzing eight techniques assessing chromatin damage in pig sperm. With this purpose, cryopreserved sperm samples from 16 boars were evaluated through the following assays: TUNEL, TUNEL with decondensation, SCSA, alkaline and neutral sperm chromatin dispersion (SCD) tests, alkaline and neutral Comet assays, and chromomycin A3 test (CMA3). In all cases, the extent of chromatin damage and the percentage of sperm with fragmented DNA were determined. The degree of chromatin damage and the percentage of sperm with fragmented DNA were significantly correlated (p < 0.05) in direct methods (TUNEL, TUNEL with decondensation, and alkaline and neutral Comet) and CMA3, but not in the indirect ones (SCD and SCSA). Percentages of sperm with fragmented DNA determined by alkaline Comet were significantly (p < 0.05) correlated with TUNEL following decondensation and CMA3; those determined by neutral Comet were correlated with the percentage of High DNA Stainability (SCSA); those determined by SCSA were correlated with neutral and alkaline SCD; and those determined by neutral SCD were correlated with alkaline SCD. While, in pigs, percentages of sperm with fragmented DNA are directly related to the extent of chromatin damage when direct methods are used, this is not the case for indirect techniques. Thus, the results obtained herein differ from those reported for humans in which TUNEL, SCSA, alkaline SCD, and alkaline Comet were found to be correlated. These findings may shed some light on the interpretation of these tests and provide some clues for the standardization of chromatin damage methods.

Species-Specific Differences in Sperm Chromatin Decondensation Between Eutherian Mammals Underlie Distinct Lysis Requirements

Sperm present a highly particular DNA condensation that is acquired during their differentiation. Protamines are key elements for DNA condensation. However, whereas the presence of protamine 1 (P1) is conserved across mammalian species, that of protamine 2 (P2) has evolved differentially, existing only few species that use both protamines for sperm DNA condensation. In addition, altered P1/P2 ratios and alterations in the expression of P1 have previously been associated to infertility and DNA damage disorders. On the other hand, different methods evaluating DNA integrity, such as Sperm Chromatin Dispersion (SCD) and Comet tests, need a previous complete DNA decondensation to properly assess DNA breaks. Related with this, the present study aims to analyze the resilience of sperm DNA to decodensation in different eutherian mammals. Sperm samples from humans, horses, cattle, pigs and donkeys were used. Samples were embedded in low melting point agarose and treated with lysis solutions to induce DNA decondensation and formation of sperm haloes. The treatment consisted of three steps: (1) incubation in SDS + DTT for 30 min; (2) incubation in DTT + NaCl for 30 min; and (3) incubation in DTT + NaCl with or without proteinase K for a variable time of 0, 30, or 180 min. How incubation with the third lysis solution (with or without proteinase K) for 0, 30, and 180 min affected DNA decondensation was tested through analyzing core and halo diameters in 50 sperm per sample. Halo/core length ratio was used as an indicator of complete chromatin decondensation. While incubation time with the third lysis solution had no impact on halo/core length ratios in species having P1 and P2 (human, equine and donkey), DNA decondensation of pig and cattle sperm, which only present P1, significantly (P < 0.05) increased following incubation with the third lysis solution for 180 min. In addition, the inclusion of proteinase K was found to accelerate DNA decondensation. In conclusion, longer incubations in lysis solution including proteinase K lead to higher DNA decondensation in porcine and bovine sperm. This suggests that tests intended to analyze DNA damage, such as halo or Comet assays, require complete chromatin deprotamination to achieve high sensitivity in the detection of DNA breaks.

Perfluorooctane Sulfonate (PFOS) and Perfluorohexane Sulfonate (PFHxS) Alters Protein Phosphorylation, Increase ROS Levels and DNA Fragmentation during In Vitro Capacitation of Boar Spermatozoa

Simple Summary

Perfluorinated compounds are synthetic chemicals, with a wide variety of applications like firefighting foams, food packaging, additives in paper and fabrics to avoid dyes. Perfluorooctane sulfonate and perfluorohexane sulfonate are globally distributed, and contaminates air, water, food, and dust, have toxic effects and bioaccumulate. Significant levels of these compounds have found in blood serum, breast milk, and semen of occupationally exposed and unexposed people, as well as in blood serum and organs of the domestic, farm, and wild animals. The present study seeks to analyze the toxic effects and possible alterations caused by the presence of these compounds in boar sperm during the in vitro capacitation, due to their toxicity, worldwide distribution, and lack of information in spermatozoa physiology during pre-fertilization processes.

Abstract

Perfluorooctane sulfonate (PFOS) and perfluorohexane sulfonate (PFHxS) are toxic and bioaccumulative, included in the Stockholm Convention’s list as persistent organic pollutants. Due to their toxicity, worldwide distribution, and lack of information in spermatozoa physiology during pre-fertilization processes, the present study seeks to analyze the toxic effects and possible alterations caused by the presence of these compounds in boar sperm during the in vitro capacitation. The spermatozoa capacitation was performed in supplemented TALP-Hepes media and mean lethal concentration values of 460.55 μM for PFOS, and 1930.60 μM for PFHxS were obtained. Results by chlortetracycline staining showed that intracellular Ca²⁺ patterns bound to membrane proteins were scarcely affected by PFOS. The spontaneous acrosome reaction determined by FITC-PNA was significantly reduced by PFOS and slightly increased by PFHxS. Both toxic compounds significantly alter the normal capacitation process from 30 min of exposure. An increase in ROS production was observed by flow cytometry and considerable DNA fragmentation by the comet assay. The immunocytochemistry showed a decrease of tyrosine phosphorylation in proteins of the equatorial and acrosomal zone of the spermatozoa head. In conclusion, PFOS and PFHxS have toxic effects on the sperm, causing mortality and altering vital parameters for proper sperm capacitation.

Effect of epigallocatechin-3-gallate (EGCG) on embryos inseminated with oxidative stress-induced DNA damage sperm

Cryopreservation can induce damage in human spermatozoa through reactive oxygen species (ROS) generation. To reduce the potential risk of oxidative stress-induced sperm DNA damage, addition of different epigallocatechin-3-gallate (EGCG) concentrations were performed to determine the optimum concentration which was beneficial for IVF outcome for both fresh and frozen-thawed sperm. Next, the mouse sperm model exhibiting oxidative stress-induced DNA damage by exogenously treating with H₂O₂ but overcoming the low fertilization rate of frozen-thawed sperm was used to investigate the effect of EGCG on the embryonic development and the potential EGCG-mediated effects on ataxia telangiectasia mutated (ATM) pSer-1981 in zygotes, the latter was known for leading to the activation of major kinases involved in the DNA repair pathway and the cell cycle checkpoint pathway. We found the fertilization and embryonic development of embryos inseminated with frozen-thawed sperm was impaired compared to fresh sperm. EGCG promoted the development of embryos inseminated with both types of sperm at optimum concentration. In embryos inseminated with the H₂O₂ sperm, fertilization, embryonic development, and the time at which the cleavage rate of one-cell embryos reached ≥95% were not affected by EGCG treatment. However, the EGCG-treated group required less time to achieve 50% cleavage rate of one-cell embryos, and the EGCG-treated zygotes showed enhanced expression of ATM (pSer-1981) than the untreated group. EGCG at optimum concentrations may exert beneficial effects by modulating the ATM activation and moving up the time to enter into mitotic (M) phase.

ABBREVIATIONS

ROS: reactive oxygen species; EGCG: epigallocatechin-3-gallate; ATM: ataxia telangiectasia mutated; M: mitotic.

Different approaches for assessing sperm function

Different approaches can be used to assess sperm function in different conditions, i.e. sperm storage, freezing-thawing or activation by induction of capacitation and acrosome reaction. In this review we will focus on the assays routinely performed in our laboratories, giving a literature support to critically analyse different approaches. In fact, researchers usually tend to look for the "one shot" parameter that could explain itself a specific process; it is our conviction that a multiparametric approach is still more valid, as some changes in sperm function are very complex and could be explained only by operating in different ways. Sperm motility, the most evident sperm characteristic, should be assessed by computer-aided sperm analysers that permit an objective evaluation of the motility and its kinematic parameters. Commercial and open source instruments are available and could be profitably used together with specific statistical approaches. The use of microscopy, and particularly fluorescent microscopy, could be a very useful tool to assess different parameters in sperm cells both by fluorophores that give indication of a determined function, and by immunolocalization of proteins, that permits the discover of new features or to explain particular sperm functions. The same substrates could be used also in flow cytometry: the difference is that it permits to study wider sperm populations (and their sub-population distribution). Flow cytometry is undergoing a very wide use in spermatology and technical and experimental rigor is needed to obtain reliable results. Metabolic assessment of sperm features, particularly energetic supply, ATP formation and other enzyme activities, could represent a very important challenge to acquire new information and complete/integrate those derived from other techniques. Finally, functional assays such as oocyte binding and in vitro fertilization, represent a very strong tool to assess sperm function in vitro, as they could evidence the functional intactness of some pathways.

Tropical summer induces DNA fragmentation in boar spermatozoa: implications for evaluating seasonal infertility

Summer infertility continues to undermine pig productivity, costing the pig industry millions in annual losses. The boar's inefficient capacity to sweat, non-pendulous scrotum and the extensive use of European breeds in tropical conditions, can make the boar particularly vulnerable to the effects of heat stress; however, the link between summer heat stress and boar sperm DNA damage has not yet been demonstrated. Semen from five Large White boars was collected and evaluated during the early dry, late dry and peak wet seasons to determine the effect of seasonal heat stress on the quality and DNA integrity of boar spermatozoa. DNA damage in spermatozoa during the peak wet was 16-fold greater than during the early dry and nearly 9-fold greater than during the late dry season. Sperm concentration was 1.6-fold lower in the peak wet than early dry whereas no difference was found across several motility parameters as determined by computer-assisted sperm analysis. These results demonstrate that tropical summer (peak wet season) induces DNA damage and reduces concentration without depressing motility in boar spermatozoa, suggesting that traditional methods of evaluating sperm motility may not detect inherently compromised spermatozoa. Boar management strategies (such as antioxidant supplementation) need to be developed to specifically mitigate this problem.

The proteome of frozen-thawed pig spermatozoa is dependent on the ejaculate fraction source

The preservation of sperm functional parameters and fertility post-cryopreservation largely varies in the porcine, a species with a fractionated ejaculate. Although intrinsic individual differences have primarily been linked to this variation, differences in protein abundance among frozen-thawed (FT)-spermatozoa are far more relevant. This study, performed in two experiments, looked for proteomic quantitative differences between FT-sperm samples differing in post-thaw viability, motility, apoptosis, membrane lipid peroxidation and nuclear DNA fragmentation. The spermatozoa were either derived from the sperm-rich ejaculate fraction (SRF) or the entire ejaculate (Experiment 1) or from the first 10 mL of the SRF, the remaining SRF and the post-SRF (Experiment 2). Quantitative sperm proteomic differences were analysed using a LC-ESI-MS/MS-based SWATH approach. In Experiment 1, FT-spermatozoa from the SRF showed better preservation parameters than those from the entire ejaculate, with 26 Sus scrofa proteins with functional sperm relevance showing relative quantitative differences (FC ≥ 1.5) between sperm sources. In Experiment 2, FT-spermatozoa from the first 10 mL of the SRF and the remaining SRF were qualitatively better than those from the post-SRF, and 187 proteins showed relative quantitative differences among the three ejaculate sources. The results indicate that quantitative proteome differences are linked to sperm cryosurvival.

Effect of different oxidative stress degrees generated by hydrogen peroxide on motility and DNA fragmentation of zebrafish (Danio rerio) spermatozoa

An increase in reactive oxygen species (ROS) or decrease in antioxidant barriers can provoke lipid peroxidation of the membranes or DNA damage of the spermatozoa. The aim of this work is to study the effect of the different degrees of oxidative stress generated by H₂ O₂ incubation on total motility, kinetics, and DNA fragmentation of zebrafish (Danio rerio) spermatozoa. For this process, experimental groups were incubated in 50 µM (Low; L) and 200 µM (High; H) H₂ O₂ , respectively, for 20 min at 4ºC. Sperm motility parameters were obtained with a computer-assisted sperm analysis (CASA) system. Sperm DNA fragmentation (SDF) was assessed using the sperm chromatin dispersion test. Both low and high H₂ O₂ concentration groups showed lower motility than control groups. Progressive motility of spermatozoa incubated in the H group dropped rapidly in comparison with other groups. Regarding SDF, the control and L groups had significantly lower values than the H group (25.0% and 31.6% vs. 48.1% fragmented sperm for C, L, and H groups, respectively; p < 0.05). Sperm motility, mostly progressive motility, decreased as H₂ O₂ concentration increased, mainly when time after sperm activation increased. SDF increased as the H₂ O₂ concentration increased. However, measurements of the halo area did not agree with the subjective SDF rate.

Effects of boar variability on comet-detected sperm-DNA damage following cryopreservation

Assessment of sperm-DNA integrity is a crucial issue in male fertility. In the present study, parameters derived from the image analysis of comets after single-cell gel electrophoresis were used to analyse the types of DNA damage of frozen–thawed boar spermatozoa. Semen, frozen in a cryoprotectant-free extender or in cryoprotectant-based extenders, was analysed for DNA fragmentation and with the following comet tail measures: percentage DNA in comet tail, comet tail length and olive tail moment. The percentages of sperm DNA damage in the comet tails were classified as Type 0 (no DNA damage), Type I (very low DNA damage), Type II (light DNA damage), Type III (medium DNA damage) and Type IV (heavy DNA damage). Sperm motility characteristics and membrane integrity were assessed in the pre-freeze and frozen–thawed semen samples. Assessment of sperm DNA fragmentation and comet tail measures showed marked inter-boar variability following cryopreservation. However, consistent differences among the boars, with respect to cryo-induced sperm DNA damage, were detected by the comet tail length and olive tail moment. Besides Type IV, all types of DNA damage were detected in the cryoprotectant-based extenders. It was found that the frequency of Type II and Type III of DNA damage of frozen–thawed spermatozoa was significantly greater in the cryoprotectant-based and cryoprotectant-free extenders respectively. Deterioration in the quality of the sperm DNA integrity was concomitant with a marked decline in sperm motility characteristics, reduced plasma membrane integrity and higher lipid peroxidation and aspartate aminotransferase activity after cryopreservation. It can be suggested that the comet-assay parameters, coupled with routine laboratory tests, are useful to improve the sperm evaluations of post-thaw quality of semen from individual boars and would offer more comprehensive information for a better understanding of the degree of cryo-induced sperm-DNA damage.

Seminal plasma antioxidants are directly involved in boar sperm cryotolerance

Boar ejaculates are ejected in fractions with a specific composition in terms of sperm numbers and seminal plasma (SP), which is reflected in the varying sperm cryotolerance observed among different fractions. As boar sperm are particularly sensitive to oxidative stress, this study evaluated the role of SP antioxidants in the observed differences in sperm cryotolerance among ejaculate fractions. Ten ejaculates from five boars were manually collected in fractions: the first 10 mL of the sperm-rich fraction (SRF), the rest of the SRF and the post-SRF. Semen samples comprising the entire ejaculate (EE) were created by proportionally mixing the three fractions described above. Each of the 40 resulting semen samples was split into two aliquots: one was used for sperm cryopreservation following a standard protocol utilizing 0.5-mL straws, and the other was used to collect SP for antioxidant assessment. Frozen-thawed (FT) sperm from the SRF (the first 10 mL of the SRF and the rest of the SRF) and those from post-SRF were of the highest and worst quality, respectively, which was measured in terms of total and objective progressive motility and viability (P < 0.01). Viable FT sperm from the post-SRF generated more reactive oxygen species and experienced more lipid peroxidation than those from the SRF (both the first 10 mL and the rest of the SRF) (P < 0.01). The percentage of FT sperm exhibiting fragmented nuclear DNA did not differ among ejaculate fractions and the EE. Catalase, glutathione peroxidase and glutathione peroxidase 5 (GPx-5) were lowest in SP from the first 10 mL of the SRF (P < 0.001), whereas superoxide dismutase (SOD) and paraoxonase 1 (PON-1) were highest in SP of the SRF (both the first 10 mL and the rest of the SRF) (P < 0.01). Trolox-equivalent antioxidant capacity (TEAC) and the ferric-reducing ability of plasma (FRAP) were highest in SP from the first 10 mL of the SRF and lowest in the post-SRF (P < 0.001), whereas cupric-reducing antioxidant capacity was lowest (P < 0.05) in SP from the first 10 mL of the SRF. Regression analyses indicated that certain SP antioxidants had good predictive value for post-thaw recovery rates of total motility (R² = 54.8%, P < 0.001; including SOD, TEAC and FRAP) and viability (R² = 56.1%, P < 0.001; including SOD, PON-1, GPx-5 and TEAC). These results demonstrated that certain SP antioxidants are positively involved in boar sperm cryotolerance, minimizing the oxidative stress imposed by cryogenic handling.

Artificial insemination with frozen-thawed boar sperm

Artificial insemination with frozen-thawed semen in pigs is not a routine technique; its use is restricted to specific cases, such as preservation of valuable genetic material (germplasm banks), safety strategies in case of natural disasters, long-distance transport of sperm, and in combination with sex-sorting. Cryoinjuries resulting from freeze-thawing protocols are a major concern with regard to the fertilization capacity of the treated sperm, which is lower than that of liquid-stored semen. Here, we provide an overview of artificial insemination using cryopreserved sperm, and summarize the factors that influence cryopreservation success before, during, and after freeze-thaw (i.e., sperm selection before starting the cryopreservation process, holding time, use of cryoprotectants, and rates of freezing and thawing) and that are driving the identification of biomarkers to predict sensitivity to cryodamage. Three different artificial insemination techniques (conventional or intracervical; intrauterine; and deep intrauterine) are also discussed with regards to their relevance when using frozen-thawed semen. Finally, we review the use of additives to freezing and thawing media, given reports that they may maintain and improve the quality and fertilizing capacity of frozen-thawed sperm. In sum, artificial insemination with frozen-thawed boar sperm can provide reasonable fertility outcomes, if freezable ejaculates, specific additives, and appropriate insemination techniques are used.

New Approaches to Boar Semen Evaluation, Processing and Improvement

The improvement of boar reproductive performance may be the next frontier in reproductive management of swine herd in Unites States, facilitated by better understanding of boar sperm function and by the introduction of new advanced instrumentation in the andrology field. Objective single ejaculate evaluation and individual boar fertility prediction may be possible by introducing automated flow cytometric semen analysis with vital stains (e.g. acrosomal integrity and mito-potential), DNA fragmentation analysis and biomarkers (ubiquitin, PAWP, ALOX15, aggresome) associated with normal or defective sperm phenotypes. Measurement of sperm-produced reactive oxygen species (ROS) is a helpful indicator of normal semen sample. Semen ROS levels could be managed by the addition of ROS-scavenging antioxidants. Alternative energy regeneration substrates and sperm stimulants such as inorganic pyrophosphate and caffeine could increase sperm lifespan in extended semen and within the female reproductive system. Such technology could be combined with timed sperm release in the female reproductive system after artificial insemination. Sperm phenotype analysis by the image-based flow cytometry will go hand in hand with the advancement of swine genomics, linking aberrant sperm phenotype to the fertility influencing gene polymorphisms. Finally, poor-quality ejaculates could be rescued and acceptable ejaculates improved by semen purification methods such as the nanoparticle-based semen purification and magnetic-activated sperm sorting. Altogether, these scientific and technological advances could benefit swine industry, provided that the challenges of new technology adoption, dissemination and cost reduction are met.

Recent Advances in Boar Sperm Cryopreservation: State of the Art and Current Perspectives

While sperm cryopreservation is the best technology to store boar semen for long-term periods, only 1% of all artificial inseminations (AI) conducted worldwide are made using frozen-thawed boar sperm. With the emergence of long-term extenders for liquid storage, the use of cryopreserved sperm in routine AI is less required. However, banks of boar semen contain cryopreserved sperm and planning inseminations in AI centres may benefit from the use of frozen-thawed semen. Therefore, there is an interest in the use of this technology to preserve boar sperm. In this regard, although the first attempts to cryopreserve boar semen date back to the seventies and this technology is still considered as optimal, some relevant improvements have been made in the last decade. After giving a general picture about boar sperm cryodamage, the present review seeks to shed light on these recent cryopreservation advances. These contributions regard to protein markers for predicting ejaculate freezability, sperm selection prior to start cryopreservation procedures, additives to freezing and thawing extenders, relevance of the AI-technique and insemination-to-ovulation interval. In conclusion, most of these progresses have allowed counteracting better boar sperm cryodamage and are thus considered as forward steps for this storage method. It is also worth noting that, despite being lower than fresh/extended semen, reproductive performance outcomes following AI with frozen-thawed boar sperm are currently acceptable.

Sperm cryopreservation update: Cryodamage, markers, and factors affecting the sperm freezability in pigs

Cryopreservation is the most efficient method for long-term preservation of mammalian sperm. However, freeze-thawing procedures may strongly impair the sperm function and survival and thus decrease the reproductive performance. In addition, the sperm resilience to withstand cryopreservation, also known as freezability, presents a high individual variability. The present work summarizes the principles of cryoinjury and the relevance of permeating and nonpermeating cryoprotective agents. Descriptions about sperm cryodamage are mainly focused on boar sperm, but reference to other mammalian species is also made when relevant. Main cryoinjuries not only regard to sperm motility and membrane integrity, but also to the degradation effect exerted by freeze-thawing on other important components for sperm fertilizing ability, such as mRNAs. After delving into the main differences between good and poor freezability boar ejaculates, those protein markers predicting the sperm ability to sustain cryopreservation are also mentioned. Moreover, factors that may influence sperm freezability, such as season, diet, breed, or ejaculate fractions are discussed, together with the effects of different additives, like seminal plasma and antioxidants. After briefly referring to the effects of long-term sperm preservation in frozen state and the reproductive performance of frozen-thawed boar sperm, this work speculates with new research horizons on the preservation of boar sperm, such as vitrification and freeze-drying.

Freeze-dried dog sperm: Dynamics of DNA integrity

Freeze-drying (FD) has been proposed as an alternative method to preserve spermatozoa. During the FD procedure, sperm DNA might become damaged by both freezing and drying stresses caused by the endonucleases, the oxidative stress and the storage conditions. We examined the DNA integrity of dog sperm freeze-dried with two kinds of chelating agents in FD buffers and storage at two different temperatures. Ejaculated sperm from four dogs were suspended in basic medium (10 mM Tris-HCl buffer+50 mM NaCl) supplemented with 50 mM EGTA or with 50 mM EDTA and then freeze-dried. Sperm samples were stored at 4°C as room temperature, and the analysis of DNA damage was performed after a month and 5 months of storage using a Sperm Chromatin Dispersion test. We found four different sperm populations according to the size of the halos around the sperm head: (1) absent halo, (2) <6 μm, (3) 6-10 μm, (4) >10 μm. All of them coexisted in each freeze-dried dog semen samples and differed significantly among different treatments. The highest percentage of spermatozoa with halo >10 μm was obtained when the semen samples were freeze-dried in EDTA medium and stored at room temperature for five months. Results suggested that both, the kind of chelating agent as well as storage temperature and period, influenced DNA integrity of freeze-dried dog sperm.

Effect of cryopreservation on the sperm DNA fragmentation dynamics of the bottlenose dolphin (Tursiops truncatus)

Sperm DNA fragmentation is one of the major causes of infertility; the sperm chromatin dispersion test (SCDt) evaluates this parameter and offers the advantage of species-specific validated protocol and ease of use under field conditions. The main purpose of this study was to evaluate sperm DNA fragmentation dynamics in both fresh and post-thaw bottlenose dolphin sperm using the SCDt following different cryopreservation protocols to gain new information about the post-thaw differential sperm DNA longevity in this species. Fresh and cryopreserved semen samples from five bottlenose dolphins were examined for sperm DNA fragmentation dynamics using the SCDt (Halomax(®)). Sperm DNA fragmentation was assessed immediately at collection and following cryopreservation (T0) and then after 0.5, 1, 4, 8, 24, 48 and 72 h incubation at 37°C. Serially collected ejaculates from four dolphins were frozen using different cryopreservation protocols in a TES-TRIS-fructose buffer (TTF), an egg-yolk-free vegetable lipid LP1 buffer (LP1) and human sperm preservation medium (HSPM). Fresh ejaculated spermatozoa initially showed low levels of DNA fragmentation for up to 48 h. Lower Sperm DNA fragmentation (SDF) was found in the second fresh ejaculate compared to the first when more than one sample was collected on the same day (p < 0.05); this difference was not apparent in any other seminal characteristic. While there was no difference observed in SDF between fresh and frozen-thawed sperm using the different cryopreservation protocols immediately after thawing (T0), frozen-thawed spermatozoa incubated at 37°C showed an increase in the rate of SDF after 24 h. Sperm frozen in the LP1(℗) buffer had higher levels (p < 0.05) of DNA fragmentation after 24- and 48-h incubation than those frozen in TTF or HSPM. No correlation was found between any seminal characteristic and DNA fragmentation in either fresh and/or frozen-thawed samples.

Effect of cryopreservation and single layer centrifugation on canine sperm DNA fragmentation assessed by the sperm chromatin dispersion test

The aims of this study were: 1) to assess the effect of freezing and thawing on dog sperm DNA fragmentation index (sDFI) using the sperm chromatin dispersion test (SCDt); and 2) to determine whether or not the sperm selection by single layer centrifugation (SLC) using Androcoll-C improves sperm DNA longevity in SLC-selected frozen-thawed dog semen samples. Semen samples were collected from 4 dogs using digital manipulation. After collection, ejaculates were pooled and cryopreserved following a standard protocol. Sperm motility and morphology were assessed before freezing and after thawing as a control for the cryopreservation method used. In experiment 1, sDFI was analyzed immediately before freezing and after thawing (baseline values), showing no significant differences between fresh and frozen-thawed semen samples. In experiment 2, frozen-thawed semen samples were processed or not by SLC using Androcoll-C and longevity of DNA were assessed in terms of sDFI after 24h of in vitro incubation at physiological temperature (38°C). The results showed low values of sDFI in SLC-selected semen in comparison to unselected samples. In conclusion, no effect of cryopreservation was observed on baseline values of dog sperm DNA fragmentation. Additionally, SLC-selection using Androcoll-C improved longevity of frozen-thawed sperm DNA assessed by the SCDt.