Catalase improves motility,vitality and DNA integrity of cryopreserved human spermatozoa

Cryopreservation of human spermatozoa offers a pre‐therapeutic possibility of preserving progenity in patients with testicular tumours. We aimed to investigate effects of cryopreservation and addition of catalase on sperm motility, vitality and DNA integrity in fresh and swim‐up spermatozoa. Semen samples were collected from 50 fertile men. Each sample was divided into two parts. First part was subdivided into two equal aliquots: both cryopreserved with and without catalase. The second part was subdivided into two equal aliquots: both processed by swim up and then cryopreserved with or without catalase. Semen analyses, sperm vitality and sperm DNA integrity were performed. Sperm concentration showed significant decrease while percentage of progressive motility, sperm vitality and % of DNA damage showed significant increase in processed and cryopreserved processed samples when compared with fresh and cryopreserved fresh samples. There was no significant difference in sperm concentration while there was significant increase in % of progressive motility and sperm vitality and % of DNA damage showed significant decrease in samples with catalase when compared with samples without catalase (either fresh or processed). Catalase supplementation (fresh and processed) during cryopreservation results in better post‐thawing percentage of progressive motility and percentage of sperm vitality and improved DNA integrity.     

冷冻复苏对精子结构及表观遗传学影响

精子的冷冻保存已广泛用于男性生育力保存和辅助生殖技术。然而,精子冷冻、保存与复苏过程可能造成结构和功能的损伤,包括精子活力、存活率、形态学及受精能力等方面的损伤;存在较大争议的是,精子冷冻复苏是否引起DNA完整性改变及表观遗传损伤。至今,有很多文章报道辅助生殖技术可能导致早期胚胎发育异常,甚至子代表观遗传缺陷,但是有关冷冻是否导致表观遗传缺陷的文章很少。本文系统介绍冷冻复苏对精子细胞膜、线粒体膜、DNA完整性的影响,重点介绍其对表观遗传学中DNA甲基化、组蛋白乙酰化和非编码RNA调控的影响,简要介绍了引起争论的原因和修复机制,并探索最佳冷冻方法及建立实验室规范与标准。     

Canthaxanthin protects human sperm parameters during cryopreservation

Different antioxidants have been introduced to reduce oxidative stress during the cryopreservation. The main goal of this study was to evaluate the effects of canthaxanthin on human sperm parameters during the freeze‐thaw process. This study was performed on 25 normozoospermic semen samples dividing into five groups including 0, 0.1, 1, 10, and 25 µM of canthaxanthin. The prepared spermatozoa were cryopreserved by rapid freezing technique. Sperm motility, viability (eosin‐nigrosin), morphology (Papanicolaou), acrosome reaction (double staining), DNA denaturation (acridine orange), chromatin packaging (aniline blue and toluidine blue), and DNA fragmentation (sperm chromatin dispersion test) were evaluated before freezing and after thawing. All sperm parameters after thawing significantly were decreased compared to before freezing. Twenty‐five micromolar canthaxanthin could significantly improve the progressive and total motility, viability, normal morphology, chromatin packaging, acrosome integrity and DNA denaturation and fragmentation. Ten micromolar canthaxanthin significantly improved total motility, viability, normal morphology, chromatin packaging, acrosome integrity and DNA denaturation and fragmentation. Whereas, in 1 µM group, there were significant differences only in improvement of acrosome integrity, chromatin packaging (toluidine blue) and DNA denaturation and fragmentation. But, in 0.1 µM group, there were no significant differences in any of measured parameters. It seems that canthaxanthin ameliorates detrimental effects of cryopreservation on human sperm parameters.     

不采用冷冻保护剂的玻璃化法与常规冷冻法对人精子冷冻复苏效果的比较

目的比较不采用冷冻保护剂的玻璃化法与常规冷冻法对人精子冷冻复苏的效果。方法将15份上游后的精液标本分别采用常规精子冷冻和不使用冷冻保护剂的冷冻环玻璃化法冷冻,比较精子复苏后的活力、形态及精子膜的完整性三项指标。结果冷冻前、前向活动精子百分率、正常精子形态百分率及精子膜完整率分别为(79±6.42)%、(34±9.36)%和(91±5.18)%;不采用冷冻保护剂的玻璃化法冷冻复苏后,三者分别为(42.20±8.35)%、(31.00±7.63)%和(50.00±9.34)%。常规冷冻法冷冻复苏后,三者分别为(38.00±15.80)%、(30.00±5.24)%和(47.00±13.67)%。冷冻前后前向活动精子百分率和精子膜完整率的差别有统计学意义,但两种冷冻方法相比差异无统计学意义。结论使用不加入冷冻保护剂的玻璃化方法冷冻人的精子是可行的,可取得与常规冷冻相同的效果。     

Cryoprotective effect of l‐carnitine on motility,vitality and DNA oxidation of human spermatozoa

Successful cryopreservation for human spermatozoa markedly influences the reproductive outcomes of assisted reproductive technologies. But in spite of its usefulness, cryopreservation significantly decreases sperm quality. l ‐carnitine has been found to improve the quality of spermatozoa in selected cases with male infertility. Here, we examined the efficacy of l ‐carnitine in improving sperm motility and vitality and reducing sperm DNA oxidation during cryopreservation. Semen samples from infertile patients (n = 22) were collected and analysed. Cryopreservation medium supplemented with l ‐carnitine was mixed with the semen at a ratio of 1 : 1 (v/v). The final l ‐carnitine concentration in each cryovial was 0.5 mg ml^?1 per 5 × 10⁶ cell ml^?1. Controls were cryopreserved without addition of l ‐carnitine. After 24 h of cryopreservation, thawed sperm samples were analysed for motility, vitality and DNA oxidation. Sperm vitality was assessed by the eosin–nigrosin test, while sperm DNA oxidation was measured by flow cytometry. Addition of l ‐carnitine significantly improved sperm motility and vitality (P < 0.05) compared with the control. The flow cytometry experiment showed no statistical difference (P > 0.05) in the levels of DNA oxidation between samples and controls. In conclusion, l ‐carnitine improves human sperm motility and vitality, but has no effect on sperm DNA oxidation after cryopreservation.     

Sperm characteristics and DNA integrity of Iberian red deer (Cervus elaphus hispanicus) epididymal spermatozoa frozen in the presence of enzymatic and nonenzymatic antioxidants

The main goal of this study was to investigate the potential protective effects of enzymatic and nonenzymatic antioxidants on cryopreservation injuries to red deer epididymal spermatozoa. In Experiment 1, the effects on sperm freezability of the enzymatic antioxidants catalase, superoxide dismutase, and a combination thereof were studied. In Experiment 2, sperm cryoresistance was evaluated when different nonenzymatic antioxidants, such as vitamin E, vitamin C, and butylated hydroxytoluene (BHT), were added to the freezing extender. Sperm quality was judged in vitro by microscopic assessments of individual sperm motility (SMI), viability, and acrosome (ie, spermatozoa with normal apical ridges; % NAR) and membrane (by means of the HOS test) integrity. To address fully these topics, we incorporated a new set of functional sperm tests for mitochondrial function, membrane phospholipid disorder, and sperm chromatin stability. Samples were evaluated after freezing and thawing, and after a 2-hour period of incubation at 37 degrees C. The present study demonstrates that the addition of enzymatic antioxidants to freezing extenders improves sperm viability after cooling, and improves sperm motility, acrosome integrity, and mitochondrial status (P<.05) after thawing. After a 2-hour incubation period at 37 degrees C in the presence of enzymatic antioxidants, an improvement in membrane integrity (P<.05) was observed. However, when nonenzymatic antioxidants were present in the freezing diluents, no positive effects on thawed sperm parameters were noted. The chromatin stability test did not show significant differences between the treatments. We conclude that enzymatic antioxidants should be present in the early steps of cryopreservation of epididymal spermatozoa from red deer, so as to improve motility and acrosome integrity.     

Cryopreservation of human sperm: efficacy and use of a new nitrogen-free controlled rate freezer versus liquid nitrogen vapour freezing

Preservation of spermatozoa is an important aspect of assisted reproductive medicine. The aim of this study was to investigate the efficacy and use of a recently developed liquid nitrogen and cryogen-free controlled rate freezer and this compared with the classical liquid nitrogen vapour freezing method for the cryopreservation of human spermatozoa. Ten patients entering the IVF programme donated semen samples for the study. Samples were analysed according to the World Health Organization guidelines. No significant difference in total sperm motility after freeze-thawing between the new technique and classical technique was demonstrated. The advantage of the new freezing technique is that it uses no liquid nitrogen during the freezing process, hence being safer to use and clean room compatible. Investment costs are higher for the apparatus but running costs are only 1% in comparison with classical liquid nitrogen freezing. In conclusion, post-thaw motility of samples frozen with the classical liquid nitrogen vapour technique was comparable with samples frozen with the new nitrogen-free freezing technique. This latter technique can thus be a very useful asset to the sperm cryopreservation laboratory.     

Effect of pre-freezing conditions on the progressive motility recovery rate of human frozen spermatozoa

We evaluated the effects of sperm concentration, progressive motility, sperm morphology, duration of abstinence and collection season on the progressive motility recovery rate of human frozen spermatozoa to identify characteristics that predict the progressive motility recovery rate of human frozen spermatozoa and improve the protocol for sperm collecting in sperm banks. A total of 14 190 semen samples donated at Zhejiang human sperm bank of China between September 2006 and June 2011 were collected from 1624 donors. Semen was evaluated according to WHO standard procedures for sperm concentration. Progressive motility, sperm morphology, ejaculate collection season and abstinence time were recorded. After freezing and thawing, the progressive motility was assessed. Results showed that sperm concentration, progressive motility and normal morphology were significantly associated with the progressive motility recovery rate of human frozen spermatozoa. In addition, the abstinence time and collection season also significantly affected progressive motility recovery rate. Our results indicated that sperm concentration, progressive motility and normal morphology could be valuable in predicting the progressive motility recovery rate of human frozen spermatozoa. As such, progressive motility recovery may be improved by donating semen when abstinent for 3–5 days and during seasons other than summer.     

The response of bovine spermatozoa to bicarbonate and its use to assess the influence of added oviductal epithelial proteins on cryopreservation

The oviduct is a crucial organ for fertilization and has been demonstrated to perform a variety of interactions with spermatozoa ranging from sperm storage, to stabilizing sperm membranes and reducing free radicals. The oviduct is separated into 2 anatomically and physiologically distinct regions: the isthmus, in which sperm are stored, and the ampulla where fertilization occurs. We aimed to investigate whether proteins derived from different regions of the bovine oviduct had beneficial effects on bovine sperm membrane integrity, osmotic resistance, and motility following cryopreservation. The extent to which sperm motility could be activated by bicarbonate was demonstrated and used as a novel approach to postthaw sperm assessment. While oviductal proteins did not increase the degree of postthaw sperm viability, spermatozoa exposed to the isthmic proteins before freezing showed higher osmotic resistance after thawing. The presence of bicarbonate increased the proportion of spermatozoa with high curvilinear (VCL) and straight line velocity (VSL) in all treatment groups. After thawing, spermatozoa exposed to isthmic proteins had higher VCL and VSL than spermatozoa exposed to the ampullar proteins. We conclude that proteins derived from the isthmus can stabilize and protect spermatozoa during cryopreservation.     

不同浓度的蔗糖溶液快速冻存人类精子的实验研究

目的:探讨使用非渗透性冷冻保护剂蔗糖快速冻存人类精子的可行性。方法:收集正常精液标本40份,经上游法处理后,收集上游精子悬液,分成6份,1份作为对照,其余5份分别用常规精子冷冻法,0.15、0.20、0.25、0.30 mol/L蔗糖溶液冷冻精子,复苏后比较6组精子活动率、前向运动精子活动率及精子质膜完整性。结果:所有冷冻组复苏后精子活动率、前向运动精子活动率及膜完整率与冷冻前上游组(96.2±1.8)%,(93.8±2.8)%,(99.0±0.8)%比较均显著下降,差异有显著性(P<0.05)。精子活动率结果:蔗糖冷冻组之间比较,0.20 mol/L组解冻后精子活动率高于0.15、0.25、0.30 mol/L组,分别为(55.5±6.3)%、(45.9±6.6)%、(50.4±9.4)%、(45.5±11.2)%,差异有显著性(P<0.05)。0.20、0.25 mol/L蔗糖冷冻组与常规慢速冷冻组(53.6±5.0)%比较,差异均无显著性(P>0.05);0.15、0.30 mol/L蔗糖组均低于常规慢速冷冻组(P<0.05)。前向运动精子活动率结果:0.20 mol/L蔗糖冷冻组与常规冷冻组比较差异无显著性[(44.4±7.4)%vs(42.3±8.1)%,P>0.05];以上两组均高于0.15、0.25、0.30 mol/L蔗糖冷冻组,分别为(37.1±8.3)%、(33.1±9.2)%、(22.0±9.1)%,差异有显著性(P<0.05)。精子膜完整率结果:0.20 mol/L蔗糖冷冻组(70.1±6.9)%高于常规冷冻组、0.15、0.25、0.30 mol/L蔗糖冷冻组,分别为(63.1±6.8)%、(57.7±8.3)%、(63.5±10.7)%、(57.8±12.9)%,差异有显著性(P<0.05);常规冷冻组与0.15、0.25、0.30 mol/L蔗糖冷冻组比较差异无显著性(P>0.05)。结论:终浓度为0.20 mol/L的蔗糖溶液作为人类精子冷冻保护剂是可行的,快速冷冻方法简便、快速、经济、安全有效。     

Effect of progesterone on acrosome reaction, hypoosmotic swelling test, and DNA stability in human spermatozoa

The association between different sperm parameters, an in vitro effect of progesterone, has not been studied satisfactorily. In this article, the effect of progesterone on acrosome reaction (AR), plasma membrane integrity, and chromatin stability has been assessed in human spermatozoa with normal morphology and motility. Semen samples were obtained by masturbation from 25 patients. Two criteria of classification were utilized in this study: high motility group and normal morphology group incubated with progesterone. The effect of progesterone on AR, plasma membrane integrity, and chromatin stability in human spermatozoa with normal morphology and motility was realized. The results suggest that only the subpopulation of spermatozoa with normal morphology is able to undergo the progesterone-induced AR. It is possible that in the reproductive female tract it takes place a high selection of sperm with chromatin stability determined and optimal plasma membrane to undergo the AR prerequisite for the fecundation.     

The association of seminal leucocytes,interleukin‐6 and interleukin‐8 with sperm DNA fragmentation: A prospective study

The effect of seminal leucocytes on sperm DNA integrity has been discussed controversially in literatures. Moreover, the studies investigating the in vivo effect of pro‐inflammatory cytokines interleukin‐6 and interleukin‐8 on sperm DNA fragmentation are scarce and inconsistent. The association of standard sperm parameters with sperm DNA fragmentation is also a matter of ongoing discussion. Hence, the aims of this study were, first, to evaluate the effect of seminal leucocytes, interleukin‐6 and interleukin‐8 on sperm DNA integrity and, second, to examine whether standard semen parameters are associated with sperm DNA fragmentation. Seminal leucocytes, interleukin‐6, interleukin‐8 and standard semen parameters, including total sperm number, sperm concentration, progressive motility, nonprogressive motility, immotility and normal morphology, were determined in 134 consecutive men. The concentrations of seminal leucocytes, interleukin‐6 and interleukin‐8, did not correlate with sperm DNA fragmentation. In contrast, total sperm number, sperm concentration, progressive motility, nonprogressive motility and normal morphology exhibited significant inverse correlations with sperm DNA fragmentation. Immotile spermatozoa were directly correlated with sperm DNA fragmentation. In conclusion, seminal leucocytes, interleukin‐6 and interleukin‐8, are not associated with sperm DNA fragmentation. Poor standard semen parameters are significantly related to the high levels of sperm DNA fragmentation.     

Evaluation of zeta and HA-binding methods for selection of spermatozoa with normal morphology, protamine content and DNA integrity

Sperm selection parameters based on morphology and motility for ICSI might not be relevant to chromatin integrity. Thus sperm selection based on sperm characteristics has been suggested. Therefore, the aim of this study was to evaluate the efficiency of the zeta and hyaluronic acid (HA) sperm selection procedures with neat semen, for recovering spermatozoa with normal morphology, protamine content and DNA integrity in infertile men. Semen samples from 77 infertile couples were assessed during this study. Semen analysis was carried out according to World Health Organization criteria. Protamine content, DNA integrity and sperm morphology were assessed by chromomycin A3, sperm chromatin dispersion and Papanicolaou staining respectively. The results show that both HA and zeta methods were efficient to recover spermatozoa with normal morphology and protamine content. In terms of the latter parameters, there was no superiority between the two procedures. However, in terms of DNA integrity, the zeta method was more efficient compared with the control and HA procedure and no significant difference was observed between HA and the controls. Therefore, the zeta method appears to be a suitable procedure to recover spermatozoa with normal DNA integrity.     

Effect of pentoxifylline on motility and membrane integrity of cryopreserved human spermatozoa

The purpose of this study was to examine the effects of pentoxifylline used before and after semen cryopreservation-thawing on sperm motility and membrane integrity. Twenty-four semen samples were split into four equal aliquots. Aliquots were incubated at 37 degrees C for 30 min, followed by cryopreservation with TEST-yolk freezing medium using slow programmable freezing protocol. After 2 weeks the sperm samples were thawed, washed twice in Quinn's Sperm Washing Medium (modified HTF with 5.0 mg/mL Human Albumin) and incubated at 37 degrees C for 30 min. Aliquots were treated by adding 3 mmol/L pentoxifylline to: (1) fresh sperm samples during incubation period prior to cryopreservation, (2) sperm samples as a supplement to the cryoprotectant prior to cryopreservation, and (3) thawed sperm samples during incubation period. One aliquot received no treatment (control group). The addition of 3 mmol/L pentoxifylline to fresh semen during incubation period prior to cryopreservation significantly decreased progressive and total motility compared with controls. However, the addition of 3 mmol/L pentoxifylline to cryopreserved semen after thawing significantly increased progressive and total motility compared with controls. After post-thaw, no differences in motion characteristics between sperm samples treated by adding 3 mmol/L pentoxifylline as a supplement to the cryoprotectant and control groups were observed. Post-thaw hypoosmotic swelling (HOS) test scores did not improve with the addition of pentoxifylline compared with the control group. It is concluded that pentoxifylline enhanced post-thaw motility of cryopreserved human spermatozoa when added after thawing. No improvement was found by freezing sperm with pentoxifylline.     

Effect of freeze–thawing procedure on chromatin stability, morphological alteration and membrane integrity of human spermatozoa in fertile and subfertile men

Cryopreservation is known to impair sperm motility and decrease the fertilization rate by detrimental effects on acrosomal structure and acrosin activity. However, the consequences of cryopreservation on the integrity of the sperm nucleus, chromatin stability and centrosome are less clear. The present study was designed to determine the effect of the freeze-thawing procedure on chromatin condensation (aniline blue staining) and the morphology (strict criteria) and membrane integrity of human spermatozoa. The structural and functional characteristics of the sperm plasma membrane were measured by the eosin-test and hypo-osmotic swelling test which were done separately. Sperm cryopreservation was performed on semen samples from two groups of men classified as fertile (n = 20) and subfertile (n = 72), based on their reproductive history and semen analysis according to WHO guidelines. The mean percentage of condensed chromatin, morphologically normal spermatozoa and membrane integrity in all semen samples investigated (n = 92) decreased significantly (p = 0.0001) after freeze-thawing, in comparison to the value observed prior to freezing. By comparing the semen samples between fertile and subfertile patients, significantly (p = 0.0009) greater damage was demonstrated in the subfertile than in the fertile group. Furthermore, no significant difference was observed between the two groups with regard to the morphological alteration and structural as well as functional damage of the sperm membrane. In conclusion, the freeze-thawing procedure significantly affects chromatin structure and sperm morphology, especially in the head and the tail regions, and this may explain the lower fertilization rate and IVF/ICSI outcome when frozen-thawed spermatozoa are used. In addition, this study demonstrates that chromatin condensation is a sensitive parameter for the evaluation of cryodamage of semen samples from fertile and subfertile patients, though subfertile patients with very poor semen characteristics have yet to be studied. It is therefore recommended that chromatin condensation be used as an additional parameter for the assessment of sperm quality after freeze-thawing.     

Osmotic tolerance of equine spermatozoa and the effects of soluble cryoprotectants on equine sperm motility, viability, and mitochondrial membrane potential.

Osmotic stress attributed to differences in the relative permeability of cryoprotectants, such as glycerol and water, appears to be an important factor in cryodamage. The objective of this study was to characterize the osmotic tolerance of equine spermatozoa, and to evaluate the effects of addition and removal of cryoprotectants from equine spermatozoa on their motility, and membrane and acrosomal integrity, as well as their mitochondrial membrane potential. Equine spermatozoa had a limited osmotic tolerance to anisosmotic conditions. Although the addition of increasing concentrations of glycerol decreased the motility and viability of equine spermatozoa, the rapid removal of glycerol by dilution in isosmotic media resulted in an even greater decline in motility and viability compared with spermatozoa maintained under anisosmotic conditions. Likewise, the addition and rapid removal of 1.0 M glycerol, ethylene glycol, dimethylsulfoxide, or propylene glycol resulted in a significant decline in sperm motility and viability. Among these cryoprotectants, ethylene glycol had the least detrimental effect on either viability or motility of spermatozoa following the rapid addition and removal of these cryoprotectants. These data demonstrate that equine spermatozoa have a limited osmotic tolerance compared with published reports for mouse or human spermatozoa, and appear to be more similar to boar spermatozoa in their osmotic tolerance. Of the 4 cryoprotectants evaluated in equine spermatozoa, the addition and removal of glycerol resulted in a more marked osmotic stress as indicated by alterations in motility, viability, and acrosomal integrity. These data suggest that alternative cryoprotectants should be considered for cryopreservation of equine spermatozoa in order to reduce osmotic stress associated with the addition of these agents during semen freezing.     

Comparison and evaluation of capacitation and acrosomal reaction in freeze‐thawed human ejaculated spermatozoa treated with L‐carnitine and pentoxifylline

Cryopreservation is used to preserve the spermatozoa; however, it leads to a reduction in sperm quality. L‐carnitine (LC) influences sperm motility and preserves the sperm membrane and DNA integrity. The objectives of this study were to evaluate the protective effects of LC on the membrane integrity of normal human spermatozoa and compare it with pentoxifylline (PT) during cryopreservation. Thirty normal semen samples, prepared by swim‐up procedure, were divided into three aliquots: a control without any treatment and two experimental aliquots that were incubated in PT or LC for 30 min. All aliquots were cryopreserved and thawed after 48 hr. To evaluate the percentages of intact, acrosomal‐reacted and capacitated spermatozoa, lectin histochemistry and flow cytometry were performed by wheat germ agglutinin, peanut agglutinin and Con A. Statistical analyses were performed using ANOVA. LC supplementation elevated the percentage of noncapacitated spermatozoa compared with control and PT‐treated samples and the percentages of acrosomal intact spermatozoa compared with PT‐treated samples. PT pre‐treatment improved the motility but not membrane integrity. LC supplementation reduced the percentages of acrosomal‐reacted spermatozoa compared with the control and PT‐treated samples. Although LC did not improve motility, it protected the plasma membrane and acrosomal integrity. Therefore, LC may be the superior choice compared to PT for maintaining the sperm integrity.     

Freezing-free preservation of human spermatozoa--a pilot study

This study tested a method for maintaining human spermatozoa without freezing for subsequent use in intracytoplasmic sperm injection (ICSI). We demonstrated that human sperm stored in electrolyte-free solution maintain their motility and viability for at least 4 and 6 weeks, respectively. We also have shown that preserved spermatozoa are fully functional in ICSI. Sperm chromosome analysis after injection of human sperm into mouse oocytes revealed that two weeks of storage does not negatively affect sperm DNA integrity. A mouse model was used to analyze the ability of preserved sperm to participate in normal embryogenesis. Mouse sperm preserved in electrolyte-free solution in a similar manner as human sperm maintained motility for up to 3 weeks. When mouse spermatozoa stored for 1 week were injected into the oocytes by ICSI, they yielded normal blastoctysts and normal viable fetuses. The results of the study bear significance for human assisted reproduction technologies (ART) and provide clinicians and infertile patients with a new method that can simplify sperm preparation for ICSI, assisting men who are unable to provide semen on the day of assisted fertilization.     

Small‐volume vitrification for human spermatozoa in the absence of cryoprotectants by using Cryotop

Cryotop is a carrier that has been used successfully in the cryopreservation of human spermatozoa. Here, we explored a novel method to vitrify human spermatozoa without cryoprotective agents (CPAs) using Cryotop. Spermatozoa from 21 Normozoospermic patients were collected and vitrified without CPAs or with sucrose in small volume using Cryotop. The sperm recovery rate, motility, viability, chromatin damage and DNA fragmentation were assessed. No significant difference was observed in the sperm recovery rate and motility rate between the spermatozoa cryopreserved without CPAs and with sucrose. The post‐thawed spermatozoa cryopreserved without CPAs had a higher viability and lower damage to sperm chromatin and DNA than those cryopreserved with sucrose. These results suggest that small numbers of human spermatozoa can be successfully vitrified without CPAs using Cryotop.