Cryoprotectant-free ultra-rapid freezing of human spermatozoa in cryogenic vials

Effects of Slow Freezing and Vitrification of Human Semen on Post-Thaw Semen Quality and miRNA Expression

Semen cryopreservation has played an important role in medically assisted reproduction for decades. In addition to preserving male fertility, it is sometimes used for overcoming logistical issues. Despite its proven clinical usability and safety, there is a lack of knowledge of how it affects spermatozoa at the molecular level, especially in terms of non-coding RNAs. Therefore, we conducted this study, where we compared slow freezing and vitrification of good- and poor-quality human semen samples by analyzing conventional sperm quality parameters, performing functional tests and analyzing the expression of miRNAs. The results revealed that cryopreservation of normozoospermic samples does not alter the maturity of spermatozoa (protamine staining, hyaluronan binding), although cryopreservation can increase sperm DNA fragmentation and lower motility. On a molecular level, we revealed that in both types of cryopreservation, miRNAs from spermatozoa are significantly overexpressed compared to those in the native semen of normozoospermic patients, but in oligozoospermic samples, this effect is observed only after vitrification. Moreover, we show that expression of selected miRNAs is mostly overexpressed in native oligozoospermic samples compared to normozoospermic samples. Conversely, when vitrified normozoospermic and oligozoospermic samples were compared, we determined that only miR-99b-5p was significantly overexpressed in oligozoospermic sperm samples, and when comparing slow freezing, only miR-15b-5p and miR-34b-3p were significantly under-expressed in oligozoospermic sperm samples. Therefore, our results imply that cryopreservation of normozoospermic sperm samples can modulate miRNA expression profiles in spermatozoa to become comparable to those in oligozoospermic samples.

Vapour fast freezing with low semen volumes can highly improve motility and viability or DNA quality of cryopreserved human spermatozoa

Objectives

To challenge a vapour fast freezing (VFF) cryopreservation procedure (conventional VFF) with several vitrification protocols and VFF conducted with small semen volumes (10 μl, microVFF), in order to implement a procedure for sperm banking in subjects with small sperm number.

Materials and methods

Conventional VFF was conducted with test yolk buffer (TYB) as freezing medium and 500 μl straws as carriers. MicroVFF was conducted with TYB and using tips or cell sleepers as carriers. Vitrification was performed with TYB or SpermFreeze as freezing medium and with microspheres and tips as carriers. The effect of different procedures on progressive and total motility, viability, oxidative stress and DNA fragmentation of spermatozoa (sDF) was determined. Fresh and thawed samples, the latter after adequate washing/centrifuging, were evaluated. In some experiments, motility and viability recovery was determined in thawed samples, omitting the washing/centrifuging step.

Results

All the cryopreservation procedures blunted sperm motility and viability and induced increase of oxidative stress and sDF. However, VFF better preserved sperm motility and viability and less induced oxidative stress and sDF than vitrification, independently from the freezing medium and the carriers used in the latter. MicroVFF with cell sleepers resulted in a percentage increase of 57.58 ± 63.63%, 48.82 ± 74.96% and 24.55 ± 39.20% of, respectively, progressive and total motility and viability compared to the conventional VFF. Further, when tips were used, microVFF resulted in a percentage decrease of 15.77 ± 20.77% of sDF with respect to conventional VFF. Finally, omission of washing/centrifuging in post thawed samples, resulted in a much lower negative effect on motility and viability.

Discussion and conclusion

VFF, and in particular microVFF, better prevents sperm cryodamage than vitrification. Washing/centrifuging step after sample thawing seems to be responsible for a relevant fraction of damage to sperm motility and viability. Overall, our results are promising for developing a novel strategy of sperm banking in subjects with small sperm number, where low semen volumes are mandatory.

Single sperm vitrification with permeable cryoprotectant-free medium is more effective in patients with severe oligozoospermia and azoospermia

Testicular sperm extraction (TESE) is an invasive surgery for achieving the spermatozoa in cases with azoospermia. In these patients, the number of retrieved spermatozoa is limited and the optimal cryo-storage is very critical for their fertility preservation. Therefore, single sperm vitrification has been introduced for preservation of low number of spermatozoa. The goal was to assess the efficacy of sperm freezing medium (SFM) and sucrose medium as cryoprotectants for single sperm vitrification in cases with severe oligozoospermia and azoospermia. A total of 20 ejaculates from severe oligozoospermia and 20 testicular samples from azoospermia were processed. Twenty-five sperm cells were collected using ICSI injection pipette and transferred to a cryoprotectant droplet placed on the Cryotech, then vitrified by plunging in liquid nitrogen. Sperm motility, viability, fine-morphology, mitochondrial activity and DNA fragmentation index (DFI) were assessed before and after vitrification. Sperm motility, viability and the percentage of cells with mitochondrial activity were significantly decreased after vitrification in both severe oligozoospermic and testicular samples in either cryoprotectants. However, the rates of post-warm sperm motility and the cells with mitochondrial activity increased significantly in sucrose medium in both severe oligozoospermic and testicular samples compared to SFM. In testicular samples, the DFI of spermatozoa vitrified in SFM was significantly higher than those vitrified with sucrose medium. Sperm motility, viability, mitochondrial activity, and DNA integrity were better preserved in sucrose medium than SFM after single cell vitrification. The presented method may be a useful candidate for successful freezing of individual sperm cells in clinical setting.

A review of methods for preserving male fertility

Male infertility is responsible for 50% of men's health problems and has always been a concern for personal and social issues. A survey of global statistics suggests an increase in infertility rate as one of the critical issues documented in studies. There are different ways of maintaining fertility in men, depending on their age. In this paper, we review the preservation methods used for fertility treatment in Iran and other countries. Available data were reviewed from Google Scholar, PubMed, Scopus, Web of Science, IranMedex, MEDLIB, IranDoc and Scientific Information Database and searched for articles published up to 2018, using the medical subject heading (MeSH) terms for cryopreservation, sperm, testicular, spermatogonia stem cell, male infertility and/or Iranian and in the world, to provide evidence from evaluation of fertility preservation the methods. Based the search strategy, 274 manuscripts were found. After reviewing the titles, abstracts and manuscripts in their entirety, 119 articles were obtained and selected according to the eligibility criteria. The 85 studies mentioned above were divided into three categories (sperm, testis, and spermatogonia stem cells (SSCs)), and methods of fertility preservation were investigated. Ways to maintain male fertility were different depending on age, and included sperm, testicular, and SSC freezing. The number of studies on testicular tissue and SSCs was low for human samples, and more studies are still needed. Sperm freezing at infertility centres is the top for male fertility preservation.

Sperm Selection Procedures for Optimizing the Outcome of ICSI in Patients with NOA

Retrieving spermatozoa from the testicles has been a great hope for patients with non-obstructive azoospermia (NOA), but relevant methods have not yet been developed to the level necessary to provide resolutions for all cases of NOA. Although performing testicular sperm extraction under microscopic magnification has increased sperm retrieval rates, in vitro selection and processing of quality sperm plays an essential role in the success of in vitro fertilization. Moreover, sperm cryopreservation is widely used in assisted reproductive technologies, whether for therapeutic purposes or for future fertility preservation. In recent years, there have been new developments using advanced technologies to freeze and preserve even very small numbers of sperm for which conventional techniques are inadequate. The present review provides an up-to-date summary of current strategies for maximizing sperm recovery from surgically obtained testicular samples and, as an extension, optimization of in vitro sperm processing techniques in the management of NOA.

Cryo-banking of human spermatozoa by aseptic cryoprotectants-free vitrification in liquid air: Positive effect of elevated warming temperature

Cryoprotectant-free vitrification is a common method for spermatozoa cryopreservation by direct plunging into liquid nitrogen. However, the commercial liquid nitrogen could be potentially contaminated by microorganisms. Warming temperature plays an essential role for quality of human spermatozoa after vitrification. This study aimed to evaluate comparatively a quality spermatozoa after vitrification in liquid nitrogen and clean liquid air as well as with two warming rates: at 42 °C and 45 °C. After performing of routine swim-up of normozoospermia samples, spermatozoa from the same ejaculate were divided into two groups: vitrified in liquid nitrogen (LN) and sterile liquid air (LA). Spermatozoa of LN group were warmed at 42 °C, and spermatozoa of LA groups were divided and warmed at 42 °C (LA42) and 45 °C (LA45). Then spermatozoa motility, reactive oxygen species (ROS), mitochondrial membrane potential (MMP), reactive nitrogen species (RNS), and viability were assessed. It was no found significant differences in quality of spermatozoa from LN and LA groups in the motility, ROS, MMP, RNS rates after warming at 42 °C. A tendency to obtain better spermatozoa quality was found with using of warming by 42 °C in comparison with 45 °C. It was concluded that cryoprotectant-free vitrification by direct dropping of human spermatozoa into clean liquid air can be used as an alternative to cooling in liquid nitrogen. Warming of spermatozoa at 42 °C allows to preserve the spermatozoa physiological parameters.

Aseptic capillary vitrification of human spermatozoa: Cryoprotectant-free vs. cryoprotectant-included technologies

The protocol of aseptic cryoprotectant-free vitrification on human spermatozoa is well documented. However, data about the effect of permeable cryoprotectants at this procedure is limited. Presented study aimed to test the aseptic capillary vitrification technologies using permeable cryoprotectant-included or cryoprotectant-free media. Thirty-two normal samples were included and analyzed after vitrification in three different media and thawing. Three treatment groups were formed: Group 1, basic medium; Group 2, basic medium with 0.25 M sucrose; Group 3, basic medium with glycerol. Before plunging into liquid nitrogen, capillaries were filled by 10 μl of spermatozoa suspension and isolated from liquid nitrogen by location in hermetically closed 0.25 ml straws. Progressive motility, plasma membrane integrity, total motility/viability after 24, 48 and 72 h in vitro culture, apoptosis and mitochondrial membrane potential (ΔΨm) were determined after thawing at 42 °C. Progressive motility of spermatozoa in groups 1, 2, 3 was 24.9 ± 1.7%, 34.5 ± 2.8% and 34.0 ± 1.4%, respectively (P_1-2,3<0.05). The plasma membrane integrity of spermatozoa in groups 2 and 3 (48.4 ± 2.9% and 45.5 ± 3.9%, respectively) was higher than in Group 1 (33.3 ± 2.1%, P < 0.05). After 24 h, 48 h and 72 h in vitro culture, the total motility and viability of spermatozoa in Group 1 was significantly lower than Group 2 and Group 3. The apoptosis rate in Group 3 (44.5 ± 3.0%) and Group 2 (47.7 ± 4.1%) were lower than in Group 1 (52.5 ± 4.4%; P < 0.05). ΔΨm rates in Group 3 and Group 2 were higher than in Group 1 (P < 0.05) with no statistical differences between this parameter in Group 2 and Group 3 (P > 0.1). In conclusion, supplementation of medium for aseptic capillary technology for cryoprotectant-free vitrification of human spermatozoa by permeable cryoprotectant does not improve the quality of spermatozoa after warming.

Vitrification of Donkey Sperm: Is It Better Using Permeable Cryoprotectants?

Simple Summary

Conventional donkey sperm-freezing using permeable cryoprotectants has been successfully performed, and good sperm parameters have been obtained after thawing. Unfortunately, artificial insemination of jennies with cryopreserved semen has given unsatisfactory results. Vitrification by directly dropping the sperm into the liquid nitrogen following the spheres methodology has been developed in human beings as an alternative to conventional freezing. This technique has shown to be a species-specific methodology and the concentration of cryoprotectants should be optimized in donkeys. Additionally, in this study, a permeable cryoprotectant (glycerol) has been tested for the first time for donkey sperm vitrification. According to our findings, vitrification of donkey sperm was effectively carried out using an extender supplemented with sucrose or bovine serum albumin (BSA) as non-permeable agent. When glycerol, a permeable agent, was compared to sucrose 0.1 M and BSA 5%, sperm quality significantly decreased. Therefore, donkey sperm vitrification in the absence of permeable agents obtained better results and gives a new approach to create a pattern for future studies of fertility trials.

Abstract

Vitrification by direct exposure of sperm to liquid nitrogen is increasing in popularity as an alternative to conventional freezing. In this study, the effect of permeable cryoprotectant agents for donkey sperm vitrification was compared to an extender containing non-permeable cryoprotectants. First, three different concentrations of sucrose (0.1, 0.2, and 0.3 molar, M) and bovine serum albumin, BSA (1, 5, and 10%) were compared. Secondly, the concentration of non-permeable agents producing the most desirable results was compared to an extender containing glycerol as permeable agent. Vitrification was performed by dropping 30 μL of sperm suspension directly into LN2 and warming at 42 °C. Sperm motility (total, TM; and progressive, PM) and plasma membrane integrity, PMI (mean ± SEM) were statistically compared between treatments. Sucrose 0.1 M showed a significantly higher percentage of total sperm motility (21.67 ± 9.22%) than sucrose 0.2 M (14.16 ± 4.50%) and 0.3 M (8.58 ± 6.22%); and no differences were found in comparison to the control (19.71 ± 10.16%). Vitrification with sucrose 0.1 M or BSA 5% obtained similar results for TM (21.67 ± 9.22% vs. 19.93 ± 9.93%), PM (13.42 ± 6.85% vs. 12.54 ± 6.37%) and PMI (40.90 ± 13.51% vs. 37.09 ± 14.28); but both showed higher percentages than glycerol (TM = 9.71 ± 4.19%; PM = 5.47 ± 3.17%; PMI = 28.48 ± 15.55%). In conclusion, donkey sperm vitrification in spheres using non-permeable cryoprotectants exhibited better sperm motility and viability parameters after warming than sperm vitrification using extenders containing permeable cryoprotectants.

Aseptic Cryoprotectant-Free Vitrification of Human Spermatozoa by Direct Dropping into a Cooling Agent

Spermatozoa cryopreservation is used for the management of infertility and some other medical conditions. Routinely applied cryopreservation techniques depend on permeating cryoprotectants and relatively slow freezing rates. Cryoprotectant-free vitrification is an alternative and cost-effective method that is based on rapid cooling of spermatozoa by direct plunging into a cooling agent to prevent lethal intracellular ice crystallization and the detrimental effects of high salt concentrations. One of the problems with this technique is that full sterilization of commercially produced liquid nitrogen, which could be contaminated with different pathogens, is not possible. Here we use a benchtop device for the production of sterile liquid air with the same temperature as liquid nitrogen (-195.7 °C). This has been used to develop aseptic technology for cryoprotectant-free vitrification of human spermatozoa.

Human sperm vitrification: the state of the art

Sperm cryopreservation has been widely used in assisted reproductive technology (ART) and has resulted in millions of live births. Two principal approaches have been adopted: conventional (slow) freezing and vitrification. As a traditional technique, slow freezing has been successfully employed and widely used at ART clinics whereas the latter, a process to solidify liquid into an amorphous or glassy state, may become a faster alternative method of sperm cryopreservation with significant benefits in regard to simple equipment and applicability to fertility centers. Sperm vitrification has its own limitations. Firstly, small volume of load is usually plunged to liquid nitrogen to achieve high cooling rate, which makes large volume sample cryopreservation less feasible. Secondly, direct contact with liquid nitrogen increases the potential risk of contamination. Recently, new carriers have been developed to facilitate improved control over the volume and speed, and new strategies have been implemented to minimize the contamination risk. In summary, although sperm vitrification has not yet been applied in routine sperm cryopreservation, its potential as a standard procedure is growing.

Aseptic Technology for Cryoprotectant-Free Vitrification of Human Spermatozoa by Direct Dropping into Clean Liquid Air: Apoptosis, Necrosis, Motility, and Viability

This study aimed to compare the quality of human spermatozoa vitrified by direct plunging into liquid nitrogen vs. liquid air. Spermatozoa were divided into three groups: fresh spermatozoa (Group F) were used as a control. Spermatozoa suspension (20 μl) was vitrified in open granules by direct dropping into liquid nitrogen (Group LN) or clean liquid air (Group LA). After warming at 37°C, the progressive motility rate of Group F was reduced from 65.9 ± 2.5% to 34.0 ± 1.9% (Group LN) and 38.1 ± 2.3% (Group LA), respectively (P_1-2,3 < 0.05). The reductions in viability were 65.6 ± 2.2%, 29.0 ± 1.8%, and 36.6 ± 2.6% for Groups F, LN, and LA, respectively (P_1-2,3 < 0.05). Comparing spermatozoa vitrified in liquid nitrogen vs. liquid air, no significant differences were detected in motility (34.0 ± 1.9% vs. 38.1 ± 2.3%), viability (29.0 ± 1.8% vs. 36.6 ± 2.6%), early apoptosis (13.8 ± 1.5% vs. 14.3 ± 1.8%), late apoptosis (45.5 ± 1.8% vs. 43.7 ± 2.2%), and necrosis (19.5 ± 2.0% vs. 15.0 ± 1.8%; p > 0.01 for all respective differences). There was a statistical tendency for increasing rates of “progressive motility” and “viability” and decreasing rates of “apoptosis” and “necrosis” when comparing spermatozoa vitrified in liquid air vs. liquid nitrogen. It is concluded that cryoprotectant-free vitrification by the direct dropping of human spermatozoa in a clean cooling agent (liquid air) is a good alternative to the use of nonsterile liquid nitrogen and can be used to cool cells while minimising the risk of microbial contamination.

The anti-oxidant roles of Taurine and Hypotaurine on acrosome integrity, HBA and HSPA2 of the human sperm during vitrification and post warming in two different temperature

Despite advances in vitrification techniques for sperm cryopreservation, cryo-damages of sperm caused by generation of reactive oxygen species (ROS) continue to impede implementation of this technique. This study analyses the effects of taurine and hypotaurine as anti-oxidants during vitrification of human sperms. The study was performed in two steps. In the first step, 20 normospermic semen samples were vitrified in the presence of varying concentrations of taurine and hypotaurine, and their effects as anti-oxidant agents on classical sperm parameters, hyaluronan-binding assay (HBA), lipid peroxidation (LPO) and acrosome reaction (AR) were studied. Statistical analyses showed that the sperm parameters in all vitrified groups decreased significantly (P < 0.05) compared to the fresh group. However, HBA and acrosome integrity in vitrified groups containing taurine and 50 mM of hypotaurine were better than in the control group (P < 0.05). The morphology of the vitrified group was good only in the group that contained 50 mM of hypotaurine (P < 0.05). Based on the results from the first step, 50 mM of hypotaurine was considered the ideal anti-oxidant formulation and further tests were carried out on 10 normospermic semen samples with this protecting agent. In addition to the mentioned parameters, the expression of heat shock proteinA2 (HSPA2) was studied in the vitrified group with 50 mM hypotaurine, warmed under two different warming temperatures 37 and 42 °C. 50 mM Hypotaurine was found to equally improve motility, morphology, HBA, and AR after warming at 37 °C and 42 °C (P < 0.05). However, at both warming temperatures, the expression of HSPA2 was reduced in all vitrified groups comparing to the fresh group (P < 0.05). In conclusion, taurine and hypotaurine antioxidants, especially 50 mM hypotaurine, are able to reduce deleterious cryo-injuries on morphology, acrosome and HBA and improve sperm recovery at both warming temperatures (37 and 42 °C). However, they do not have any protective action on expression of HSPA2.

A new system of sperm cryopreservation: evaluation of survival, motility, DNA oxidation, and mitochondrial activity

BACKGROUND

Sperm vitrification (V) is a method for cryopreservation, without the use of conventional cryoprotectants, by plunging the sperm suspension directly into liquid nitrogen (LN25).

OBJECTIVE

This study aimed to compare the new system of V with conventional freezing (CF) protocol using fresh spermatozoa as reference (C).

MATERIAL AND METHODS

Prospective cohort study. A total of 47 sperm samples from men attending the infertility clinic at Instituto Valenciano de Infertilidad Valencia. The sperm V solution was 0.3 M trehalose-sucrose and plunged directly in liquid nitrogen in microdroplets of 5-10 lL, using a new system collector of V. Sperm viability indicators such as sperm motility, vitality rates, mitochondrial function, and sperm DNA oxidation were assessed before and after cryopreservation. Sperm motility and vitality analysis were performed according to published guidelines of the World Health Organization (WHO, 2010). Mitochondrial function was evaluated using JC-1 (fluorescent cationic dye, 5,50,6,60-tetrachloro-1-10,3,30-tetraethyl-benzamidazolocarbocyanin iodide). Sperm DNA oxidation was determined using a fluorescent assay (Oxy-DNA test) for the detection of 8-oxoguanine. The evaluation was carried out before and after cryopreservation using flow cytometry. Statistical analysis was performed using ANOVA and chi-square test, and p < 0.05 was considered statistically significant.

RESULT(S)

Sperm parameters, including progressive motility, total motility, and viability, observed after cryopreservation were as follows: C = 74.9% [1] 12.3, CF = 27.2% [1] 8.4, V = 42.3% [1] 9.3, p < 0.001; C = 90.1 [1] 6.8, CF = 42.0 [1] 12.9, V = 61.4 [1] 11.8, p < 0.001; C = 90.0% [1] 7.4, CF = 42.5% [1] 14.6, V = 70.9% [1] 6.5, p < 0.001, respectively. Regarding Oxy-DNA and mitochondrial activity, they were significantly affected in both groups (V and CF) when compared to the control group.

DISCUSSION

The sperm V and CF have negative impact on sperm parameters as well as DNA integrity and mitochondrial activity. However, sperm V presented improved sperm motility recovery, similar levels of DNA oxidation, and, moreover, a slightly increase in mitochondrial activity when compared to the conventional method.

CONCLUSION(S)

V as an optimal protocol for sperm cryopreservation.

Vitrification and conventional freezing methods in sperm cryopreservation: A systematic review and meta-analysis

OBJECTIVE

The objective is to systematically review and synthesize the literature on the efficacy with two different cryopreservation methods used for human spermatozoa and evaluate whether vitrification protocol and quality of sperm influence effect estimates.

DESIGN

The following electronic databases were searched up to September 2017: Pubmed, Embase and Web of Science. The search strategy used the following the relevant medical subject heading (MeSH) terms, keywords, and word variants for: sperm parameters, conventional freezing, and vitrification. Queries were limited to those involving humans. Randomized controlled trials (RCTs) that published in English languages were considered eligible. Studies and references were included if they reported total motility, progressive motility, morphology, or DNA fragmentation index (DFI) for vitrified or conventional cryopreserved human spermatozoa. Patients recruited in RCTs considering sperm vitrification as one of the experimental arms and conventional freezing (including slow freezing or vapor fast freezing) sperm control as the other. Studies that had high risks of allocation concealment were excluded when performing sensitivity analysis. We specified 2 subgroup variables, including vitrification protocol and quality of spermatozoa cryopreserved, to investigate sources of heterogeneity. A meta-analysis was performed using a random effects (I² > 50%) or fixed effects (I² < 50%) model to calculate weighted mean differences (MD) and 95% CI.

RESULT(S)

The search yielded a total of 2428 articles and 13 RCTs were included for analysis. They involved 486 vitrified and 486 conventional cryopreserved sperm samples. Four sperm parameters were reported as mean differences and based on adjusted estimates in all included studies. Meta-analysis of these studies showed significantly higher total motility [weighted mean differences (WMD) 6.98; 95% confidence interval (CI) 2.94; 11.02; P < 0.0001] and progressive motility [WMD 4.59; 95% CI 0.78; 8.39; P = 0.02] of past-thawed sperm following vitrification compared with conventional freezing methods. However, DNA fragmentation index (DFI) [WMD -1.18; 95% CI -2.81; 0.45; P = 0.16] and morphology [WMD 0.11; 95% CI -0.42; 0.63; P = 0.69] of past-thawed sperm are similar between two freezing groups. Subgroup analysis shown that the vitrification protocol and quality of spermatozoa are potential risk factors for the efficacy of vitrification. Higher past-thawed sperm parameters following the cryoprotectants-free (CPAs-free) vitrification were observed, as well as a lower past-thawed sperm parameters with the cryoprotectants-presence (CPAs-presence) vitrification, which could reflect the CPAs related cytotoxicity. Meanwhile, vitrification had higher ability in preservation of high quality of spermatozoa compared with vitrification of low quality spermatozoa.

CONCLUSION(S)

According to the results of present meta-analysis, vitrification is superior to conventional freezing methods in preservation of spermatozoa, regarding total and progressive motility. However, the efficacy of vitrification is influence by using different vitrification protocol and cryopreservation of different quality spermatozoa. It is must emphasized that the results of present meta-analysis is limited by the small number of studies of variable vitrification protocol. Further well conducted studies are required to confirm the efficacy of vitrification in cryopreservation of spermatozoa, in addition, allow the examination of the two cryopreservation methods in terms of pregnancy achievement and determination of the role of clinical variable on efficacy of vitrification.

Putative role of an SLC45 H+/sugar cotransporter in mammalian spermatozoa

In the present study, we describe the detection and analysis of a novel type of sugar transporter in mammalian spermatozoa. This transporter belongs to the SLC45 family for which two features are remarkable and distinguish it from other known families of sugar transporters. Firstly, SLC45 transporters recognise not only the monosaccharides glucose or fructose but also the disaccharide sucrose as a substrate. Secondly, the uptake of sugars is coupled to a proton gradient. Uptake experiments using radioactively labelled sucrose indicated a functional transporter of the SLC45 family in bull spermatozoa. Real-time PCR as well as Western blots demonstrated the occurrence of the SLC45 member A4 in mouse testis and sperms. Furthermore, immunocytochemical analysis of mouse tissues revealed that the signal of SLC45A4 was mainly located in the principle piece of spermatozoa. We postulate that the SLC45A4 transporter plays an important role in nutrition of spermatozoa during their maturation in the epididymis. Moreover, we suggest that knowledge about the presence of the SLC45A4 may be useful also for the methodical improvement of cryopreservation of mammalian spermatozoa.

Cryopreservation of human spermatozoa with minimal non-permeable cryoprotectant

Cryopreservation of human spermatozoa is a commonly used technique in assisted reproduction, however freezing low concentrations of sperm while maintaining adequate post-thaw motility remains a challenge. In an effort to optimize post-thaw motility yields, low volumes of human sperm were frozen in polyimide-coated fused silica micro-capillaries using 0.065 M, 0.125 M, 0.25 M, or 0.5 M trehalose as the only cryoprotectant. Micro-capillaries were either initially incubated in liquid nitrogen vapor before plunging into liquid nitrogen, or directly plunged into liquid nitrogen. Post thaw sperm counts and motility were estimated. Spermatozoa that were initially incubated in liquid nitrogen vapor had greater post thaw motility than those plunged immediately into liquid nitrogen independent of trehalose concentration. The protective effect of 0.125 M d-glucose, 3-O-methyl-d-glucopyranose, trehalose, sucrose, raffinose, or stachyose were evaluated individually. Trehalose and sucrose were the most effective cryoprotectants, recovering 69.0% and 68.9% of initial sperm motility, respectively.

Cryopreservation of a small number of human sperm using enzymatically fabricated, hollow hyaluronan microcapsules handled by conventional ICSI procedures

PURPOSE

We investigated whether enzymatically fabricated hyaluronan (HA) microcapsules were feasible for use in the cryopreservation of a small number of sperm.

METHODS

HA microcapsules were fabricated using a system of water-immiscible fluid under laminar flow. Three sperm were injected into a hollow HA microcapsule using a micromanipulator. Capsules containing injected sperm were incubated in a freezing medium composed of sucrose as the cryoprotectant and then placed in a Cryotop® device and plunged into liquid nitrogen. After thawing, the capsule was degraded by hyaluronidase, and the recovery rate of sperm and their motility were investigated.

RESULTS

The HA microcapsule measuring 200 μm in diameter and with a 30-μm thick membrane was handled using a conventional intracytoplasmic sperm injection (ICSI) system, and the procedure involved the injection of sperm into the capsule. The HA microcapsules containing sperm were cryopreserved in a Cryotop® device and decomposed by the addition of hyaluronidase. The recovery rate of sperm after cryopreservation and degradation of HA microcapsules was sufficient for use in clinical practice (90 %).

CONCLUSIONS

Hollow HA microcapsules can be used for the cryopreservation of a small number of sperm without producing adverse effects on sperm quality.