Changes in spermatozoal chromatin packaging and susceptibility to oxidative challenge during aging

Application of Flow Cytometry Using Advanced Chromatin Analyses for Assessing Changes in Sperm Structure and DNA Integrity in a Porcine Model

Chromatin status is critical for sperm fertility and reflects spermatogenic success. We tested a multivariate approach for studying pig sperm chromatin structure to capture its complexity with a set of quick and simple techniques, going beyond the usual assessment of DNA damage. Sperm doses from 36 boars (3 ejaculates/boar) were stored at 17 °C and analyzed on days 0 and 11. Analyses were: CASA (motility) and flow cytometry to assess sperm functionality and chromatin structure by SCSA (%DFI, DNA fragmentation; %HDS, chromatin maturity), monobromobimane (mBBr, tiol status/disulfide bridges between protamines), chromomycin A3 (CMA3, protamination), and 8-hydroxy-2'-deoxyguanosine (8-oxo-dG, DNA oxidative damage). Data were analyzed using linear models for the effects of boar and storage, correlations, and multivariate analysis as hierarchical clustering and principal component analysis (PCA). Storage reduced sperm quality parameters, mainly motility, with no critical oxidative stress increases, while chromatin status worsened slightly (%DFI and 8-oxo-dG increased while mBBr MFI-median fluorescence intensity-and disulfide bridge levels decreased). Boar significantly affected most chromatin variables except CMA3; storage also affected most variables except %HDS. At day 0, sperm chromatin variables clustered closely, except for CMA3, and %HDS and 8-oxo-dG correlated with many variables (notably, mBBr). After storage, the relation between %HDS and 8-oxo-dG remained, but correlations among other variables disappeared, and mBBr variables clustered separately. The PCA suggested a considerable influence of mBBr on sample variance, especially regarding storage, with SCSA and 8-oxo-dG affecting between-sample variability. Overall, CMA3 was the least informative, in contrast with results in other species. The combination of DNA fragmentation, DNA oxidation, chromatin compaction, and tiol status seems a good candidate for obtaining a complete picture of pig sperm nucleus status. It raises many questions for future molecular studies and deserves further research to establish its usefulness as a fertility predictor in multivariate models. The usefulness of CMA3 should be clarified.

Epidemiology of sperm DNA fragmentation in a retrospective cohort of 1191 men

BACKGROUND

The scientific and clinical communities now recognize that sperm DNA integrity is crucial for successful fertilization, good embryo development, and offspring quality of life. Despite the apparent unanimity, this criterion is rarely evaluated in clinical practice. We evaluated the sperm DNA fragmentation index of nearly 1200 sperm samples and its connections based on the patient's age, body mass index, the season of sperm collection, geographical location, medical history, and addictive behaviors.

METHODS

A cohort of 1503 patients who were referred to the Royan Institute between July 2018 and March 2020 was examined. Only 1191 patient records with demographic data, complete semen analysis, and DNA fragmentation index measurements were included in the final cohort. Documents were classified, incorporated into statistical models, and analyzed.

RESULTS

The results confirmed previous findings that the sperm DNA fragmentation index was significantly higher in aging men. The sperm DNA fragmentation index and high DNA stainability levels were significantly higher in spring and summer samples than in those of other seasons. No correlation was found between semen DNA fragmentation index and patient body mass index, although the study cohort was significantly overweight. Contrary to what might be expected, we observed that the sperm DNA fragmentation index was higher in rural than in urban patients. Intriguingly, epileptic patients exhibited significantly higher sperm DNA fragmentation index levels.

DISCUSSION AND CONCLUSION

Age is the factor that is most strongly associated with sperm DNA fragmentation index levels. Our analysis of 1191 samples indicates that between the ages of 19 and 59, the sperm DNA fragmentation index increases by an average of 2% each year. Intriguingly, from an epidemiological perspective, the warm season (spring/summer) is associated with a higher sperm DNA fragmentation index in the study population, possibly due to the deleterious effect of temperature on sperm quality. Some neurological diseases, such as epilepsy, are associated with decreased sperm DNA integrity. This observation could be related to the iatrogenic effects of associated therapies. In the study cohort, body mass index did not appear to be correlated with the DNA fragmentation index.

Pre-freezing selection of Holstein bull semen with the BoviPure colloid as double- or single-layer centrifugation improves the post-thawing quality

Artificial insemination (AI) is critical for breeding in the dairy industry. High-merit bulls can present low freezability, hampering genetic dissemination. Thawed semen can be improved using density gradient centrifugation (DGC) with colloids, but little information deals with the pre-freezing application. Thus, the BoviPure colloid (optimized for bull spermatozoa) was tested for pre-freezing application as the usual double-layer (DLC) versus single-layer (SLC, quick and economical). Semen from twelve Holstein-Friesian bulls was extended with OPTIXcell extender, frozen (Control), or processed by SLC or DLC and frozen. Sperm were assessed pre-freezing for motility and viability and post-thawing (directly and after 4 h 38 °C) for apoptosis, capacitation status, acrosomal damage, mitochondrial activity, cytoplasmic and mitochondrial reactive oxygen species (ROS), and chromatin status (SCSA for DNA fragmentation and chromatin compaction and monobromobimane, mBBr, for disulfide bridges evaluation). The DGC improved parameters post-thawing (e.g., 57.5%±10.1 motility vs. control 53.3% ± 11.2) at the cost of sperm loss (sperm recovery of DGC 14.4% ± 2.5 and SLC 17.4% ± 2.5). DNA fragmentation (%DFI) decreased (0.21% ± 0.53 vs. control 1.30% ± 0.10), and SLC reduced chromatin compaction. A clustering procedure separated lesser (LF) and greater freezability (GF) bulls. LF samples were especially benefited by DGC, with SLC providing better post-thawing results for this group. In conclusion, pre-freezing DGC improved sperm parameters post-thawing, potentially improving the cryopreservation of low-freezability semen from high-merit bulls. SLC, quicker and economical, would be preferable since it showed similar or higher performance than DLC.

Single layer centrifugation (SLC) for bacterial removal with Porcicoll positively modifies chromatin structure in boar spermatozoa

The storage of boar semen samples at 17 °C for artificial insemination (AI) doses enables the proliferation of the bacteria, making antibiotics necessary. This can contribute to the development of antimicrobial resistance (AMR). This study tested bacterial presence and sperm chromatin structure after using a low-density colloid (Porcicoll) as an antibiotic alternative to eliminate bacteria. Ejaculates (8 boars, 3 ejaculates each) were split as control and low-density colloid centrifugation (single layer centrifugation, SLC, 20%, and 30% Porcicoll) into 500 ml tubes. Analyses were carried out at days 0, 3, and 7 (17 °C) for microbial presence and sperm chromatin structure analysis: %DFI (DNA fragmentation) and %HDS (chromatin immaturity), monobromobimane (mBBr; free thiols and disulfide bridges), and chromomycin A3 (CMA3; chromatin compaction). Besides comparing bacterial presence (7 species identified) and chromatin variables between treatments, the associations between these sets of variables were described by canonical correlation analysis (CCA). Results showed a significant decrease of some bacteria or a complete removal after SLC (especially for P30). SLC also caused a decrease of %HDS and an increase of disulfide bridges and low and medium mBBr populations, suggesting the removal of immature sperm (poor chromatin compaction). CCA showed an association pattern compatible with the degradation of sperm chromatin parameters with bacterial contamination, especially Enterobacteria, P. aeuriginosa, and K. variicola. In conclusion, bacterial contamination affects sperm chromatin beyond DNA fragmentation; SLC with low-density colloid not only removes bacteria from boar semen, but also chromatin structure is enhanced after selection.

Low-density colloid centrifugation removes bacteria from boar semen doses after spiking with selected species

Single-layer centrifugation (SLC) with a low-density colloid is an efficient method for removing contaminating microorganisms from boar semen while recovering most spermatozoa from the original sample. This study tested the performance of this technique, using 50-ml tubes, by spiking commercial semen doses prepared without antibiotics with selected bacterial species followed by storage at 17 °C. The doses were spiked up to 10²/ml CFU (colony forming units) of the bacteria Burkholderia ambifaria, Pseudomonas aeruginosa, and Staphylococcus simulans. The semen was processed by SLC (15 ml of sample and 15 ml of colloid) with the colloid Porcicoll at 20% (P20) and 30% (P30), with a spiked control (CTL) and an unspiked control (CTL0), analyzing microbiology and sperm quality on days 0, 3 and 7. SLC completely removed B. ambifaria and S. simulans, considerably reducing P. aeruginosa and overall contamination (especially P30, ∼10⁴ CFU/ml of total contamination on day 7, median). Sperm viability was lower in P20 and P30 samples at day 0, with higher cytoplasmic ROS. Still, results were similar in all groups on day 3 and reversed on day 7, indicating a protective effect of SLC (possibly directly by removal of damaged sperm and indirectly because of lower bacterial contamination). Sperm chromatin was affected by the treatment (lower DNA fragmentation and chromatin decondensation) and storage (higher overall condensation on day 7 as per chromomycin A3 and monobromobimane staining). In conclusion, SLC with low-density colloids can remove most bacteria in a controlled contamination design while potentially improving sperm quality and long-term storage at practical temperatures.

Advanced Paternal Age Affects the Sperm DNA Fragmentation Index and May Lead to Lower Good-quality Blastocysts

Several studies show reductions in some seminal parameters in aged men and describe them as a consequence of many age-dependent changes in male organisms. This study aims to evaluate the impact of age on seminal parameters, particularly the DNA fragmentation index (DFI), and outcomes after in vitro fertilization (IVF) cycles. This is a retrospective study that includes 367 patients who underwent sperm chromatin structure assay testing between 2016 and 2021. The participants were split into three groups according to age: < 35 years (younger group, n = 63), 35-45 years (intermediate group, n = 227), and ≥ 45 years (older group, n = 77). The mean DFI (%) was compared. Among all patients, 255 received IVF cycles after DFI evaluation. For these patients, the sperm concentration, motility, and volume, as well as the fertilization rate, mean oocyte age, and good-quality blastocyst formation rate, were analyzed. One-way ANOVA was applied. The older group showed a significantly higher sperm than did the younger group (28.6% vs. 20.8% p = 0.0135). Despite not presenting a significant difference, the DFI level tends to be inversely related to good-quality blastocyst formation since the oocyte age was similar between the groups (32.0 v.s 33.6 vs. 32.3 years, respectively, p = 0.1183). Among aged men, the sperm DFI level is increased but other seminal parameters are not modified. Considering that men with a high sperm DFI can present some degree of infertility due to high sperm chromatin damage, male age should also be considered a limiting factor of IVF.

Extension of the equilibration period up to 24 h maintains the post-thawing quality of Holstein bull semen frozen with OPTIXcell®

Semen cryopreservation in bovine livestock is well established, but logistics often require deviations from standard protocols. Extending the equilibration time to the following day is convenient in many situations. To improve our knowledge of the effects of this modification, we studied the post-thawing and post-incubation (4 h, 38 °C) sperm quality after freezing with 4 or 24-h extension in the OPTIXcell extender by using an ample panel of analyses: CASA for motility; flow cytometry for viability, physiology, oxidative stress, and chromatin parameters (DNA fragmentation, chromatin compaction, and thiol groups status); and spectrometry for malondialdehyde production. Semen was obtained from 12 Holstein bulls. The 24-h equilibration time showed few significant effects, with only a tiny decrease in progressive motility and a positive impact on chromatin structure. The incubation removed some of these effects, with the pattern for chromatin compaction remaining the same. No detrimental oxidative stress or increase in apoptotic or capacitation markers was detected. Additionally, the individual bull interacted with the effects of the incubation and the equilibration, especially regarding the chromatin status. Whereas this interaction did not critically affect sperm quality, it could be relevant in practice. Bull fertility as non-return rates (NRR56) was associated with some sperm parameters (especially with an improved chromatin structure) but not in the 4-h post-thawing analysis. Our study supports that extending the equilibration time by at least 24-h is feasible for bull semen freezing with the OPTIXcell extender.

Deciphering sperm chromatin properties to predict stallion sperm fertility

Although previous studies have examined the relationship between the sperm DNA fragmentation index and fertility in stallions, other aspects of chromatin structure or packaging and fertility have not been explored. In the present study, relationships between fertility and DNA fragmentation index, protamine deficiency, total thiols, free thiols and disulfide bonds in stallion spermatozoa were investigated. Ejaculates (n = 36) were collected from 12 stallions and extended to prepare semen doses for insemination. One dose from each ejaculate was sent to the Swedish University of Agricultural Sciences. Aliquots of semen were stained for flow cytometry with acridine orange for the Sperm Chromatin Structure Assay (DNA fragmentation Index, %DFI), with chromomycin A3 (CMA) for protamine deficiency, and with monobromobimane (mBBr) for detection of total and free thiols and disulfide bonds. Per season pregnancy rates after insemination were obtained. Mixed linear models were used to analyze data. Negative correlations were found between pregnancy rate and %DFI (r = -0.35, P < 0.03) and pregnancy rate and free thiols (r = -0.60, P < 0.0001). Furthermore, there were positive correlations between total thiols and disulfide bonds (r = 0.95, P < 0.0001), and protamine and disulfide bonds (r = 0.4100, P < 0.01986). Since chromatin integrity, protamine deficiency and packaging were all associated with fertility, a combination of these factors could be used as a biomarker of fertility when assessing ejaculates.

Increased sperm DNA damage leads to poor embryo quality and subfertility of male rats treated with methylphenidate hydrochloride in adolescence

BACKGROUND

Methylphenidate hydrochloride (MPH) is a psychostimulant widely used in the treatment of attention deficit hyperactive disorder (ADHD), as well as a performance enhancer, for at least 60 years. Despite the notable effectiveness as a psychostimulant, ADHD is a chronic disorder and has a two-third chance of accompanying the individual throughout life. Long-term use of MPH has been associated not only with an increase in the development of neurodegenerative diseases, but it also has side effects on male fertility in experimental animals.

OBJECTIVES

To investigate whether methylphenidate poses a risk to sperm DNA structure and to the quality of embryos conceived after treatment during adolescence in rats.

MATERIALS AND METHODS

Wistar rats at 38 days of age were treated either with 5 mg/kg body weight of MPH, in a single daily dose for 30 days, via gavage or with distilled water-only protocol. Levels of oxidative stress in testicular and epididymal tissues were evaluated. Sperm chromatin quality and acrosome integrity was assessed under flow cytometry. From 107 days of age, animals were mated with untreated females. The effects of the paternal contribution at two different embryo development moments - cleavage stage (2.5 days post coitum) and late gestation (20 days post coitum) - were analyzed.

RESULTS

MPH caused high levels of sperm DNA damage, which was reflected in 40% of decrease in early embryo quality and a lower number of live pups at 20 dpc.

DISCUSSION

The high level of fragmentation seen in the embryos sired from the MPH group is consistent with the poor chromatin structure of the sperm, and does not seem to be a result of oxidative stress in the reproductive tissues.

CONCLUSIONS

The results presented here suggest that the subchronic use of MPH during male prepubertal phase may cause long term subfertility and compromise embryo survival. This article is protected by copyright. All rights reserved.

Sperm chromatin integrity and DNA methylation in Norwegian Red bulls of contrasting fertility

In this study, the complexity of chromatin integrity was investigated in frozen-thawed semen samples from 37 sires with contrasting fertility, expressed as 56-day non-return rates (NR56). Protamine deficiency, thiols, and disulfide bonds were assessed and compared with previously published data for DNA fragmentation index (DFI) and high DNA stainability (HDS). In addition, in vitro embryo development and sperm DNA methylation were assessed using semen samples from 16 of these bulls. The percentages of DFI and HDS were negatively associated with NR56 and cleavage rate and positively associated with sperm protamine deficiency (p < 0.05). Significant differences in cleavage and blastocyst rates were observed between bulls of high and low NR56. However, once fertilization occurred, further development into blastocysts was not associated with NR56. The differential methylation analysis showed that spermatozoa from bulls of low NR56 were hypermethylated compared to bulls of high NR56. Pathway analysis showed that genes annotated to differentially methylated cytosines could participate in different biological pathways and have important biological roles related to bull fertility. In conclusion, sperm cells from Norwegian Red bulls of inferior fertility have less compact chromatin structure, higher levels of DNA damage, and are hypermethylated compared with bulls of superior fertility.

Antioxidant Enzymes and Male Fertility: Lessons from Knockout Models

Significance: Spermatozoa are very sensitive to high levels of reactive oxygen species (ROS) due to the limited antioxidant systems present in these terminal cells. However, tight regulation of ROS levels must be ensured to accomplish the unique goal of the spermatozoon, that is, the transfer of the paternal genome into the mature oocyte during the fertilization process. Thus, it is essential that the restricted antioxidant enzymatic systems are active for sperm function. Recent Advances: Oxidative stress is associated with low sperm quality. High levels of ROS in spermatozoa produce oxidation of lipids, proteins, and DNA that lead to lipid peroxidation, oxidation of essential structural proteins and enzymes, and mutations due to oxidation of DNA. Critical Issues: In this study, we described the available knockout mouse models that helped to better understand the role of different antioxidant enzymes in male fertility. We focused mainly on those studies that directly explore the effects of the lack of these enzymes in male fertility and included information when existing knockout mouse models produced for other purposes were used. Special attention was given in this review to the consequences of the absence of antioxidant enzymes on sperm quality and fertility of aging males from the knockout models. Future Directions: Further studies using novel mouse models lacking different antioxidants and their combinations are essential to understand the consequences of high levels of ROS in aging testes, epididymes, spermatozoa, and embryo development to produce a healthy baby.

DNA methylation patterns vary in boar sperm cells with different levels of DNA fragmentation

BACKGROUND

Sperm DNA integrity is considered essential for successful transmission of the paternal genome, fertilization and normal embryo development. DNA fragmentation index (DFI, %) has become a key parameter in the swine artificial insemination industry to assess sperm DNA integrity. Recently, in some elite Norwegian Landrace boars (boars with excellent field fertility records), a higher level of sperm DFI has been observed. In order to obtain a better understanding of this, and to study the complexity of sperm DNA integrity, liquid preserved semen samples from elite boars with contrasting DFI levels were examined for protamine deficiency, thiol profile and disulphide bonds. Additionally, the DNA methylation profiles of the samples were determined by reduced representation bisulphite sequencing (RRBS).

RESULTS

In this study, different traits related to sperm DNA integrity were investigated (n = 18 ejaculates). Upon liquid storage, the levels of total thiols and disulphide bonds decreased significantly, while the DFI and protamine deficiency level increased significantly. The RRBS results revealed similar global patterns of low methylation from semen samples with different levels of DFI (low, medium and high). Differential methylation analyses indicated that the number of differentially methylated cytosines (DMCs) increased in the low-high compared to the low-medium and the medium-high DFI groups. Annotating the DMCs with gene and CpG features revealed clear differences between DFI groups. In addition, the number of annotated transcription starting sites (TSS) and associated pathways in the low-high comparison was greater than the other two groups. Pathway analysis showed that genes (based on the closest TSS to DMCs) corresponding to low-high DFI comparison were associated with important processes such as membrane function, metabolic cascade and antioxidant defence system.

CONCLUSION

To our knowledge, this is the first study evaluating DNA methylation in boar sperm cells with different levels of DFI. The present study shows that sperm cells with varying levels of DNA fragmentation exhibit similar global methylation, but different site-specific DNA methylation signatures. Moreover, with increasing DNA fragmentation in spermatozoa, there is an increase in the number of potentially affected downstream genes and their respective regulatory pathways.

Sperm DNA fragmentation: causes and identification

Sperm DNA fragmentation is referred to as one of the main causes of male infertility. Failures in the protamination process, apoptosis and action of reactive oxygen species (ROS) are considered the most important causes of DNA fragmentation. Action of ROS or changes in sperm protamination would increase the susceptibility of sperm DNA to fragmentation. Routine semen analysis is unable to estimate sperm chromatin damage. Sperm DNA integrity influences sperm functional capability, therefore tests that measure sperm DNA fragmentation are important to assess fertility disorders. Actually, there is a considerable number of methods for assessing sperm DNA fragmentation and chromatin integrity, sperm chromatin stability assay (SCSA modified), sperm chromatin dispersion (SCD), comet assay, transferase dUTP nick end labelling (TUNEL); and protamine evaluation in sperm chromatin assay, such as toluidine blue, CMA3, protamine expression and evaluation of cysteine radicals. This review aims to describe the main causes of sperm DNA fragmentation and the tests commonly used to evaluate sperm DNA fragmentation.

Individual male dependent improvement in post-thaw dromedary camel sperm quality after addition of catalase

Cryopreservation is stressful to sperm cells inducing an increase in the production of reactive oxygen species and subsequently reducing post-thaw sperm quality. With the present study, there was evaluation of the protective effects of two antioxidants, epigallocatechin (1 mM) and catalase (500 IU/ml), added at thawing, as well as inter-individual variation on quality of cryopreserved dromedary camel spermatozoa. Semen was collected from six males and sperm, selected using single layer centrifugation, were cryopreserved. Post-thaw sperm quality was evaluated by assessing motility variables, viability and acrosome integrity then sperm were co-incubated with or without antioxidant (control) and further assessed at 1.5 and 3 h of the incubation period. Oxidative damage was measured colorimetrically for malondialdehyde production at 3 h of the incubation period. With the use of epigallocatechin there were not promising results, however, with use of catalase there were greater total and progressive motility, and values for some kinematic variables (P<0.05) at both incubation time points, although there were some differences among males. There was no overall effect of antioxidant based on production of malonaldehyde. The capacity of thawed sperm to fertilize, with and without addition of catalase at thawing, was studied using artificial insemination (n = 10 per treatment) with no differences between treatments (10% for both). It is concluded that catalase supplementations to semen extender prolong sperm survival, however, there is no improvement of in vivo fertilization as a result of this supplementation. There was an obvious male effect, necessitating further studies to understand the mechanisms of action of catalase.

Fertility preservation in Hodgkin's lymphoma patients that undergo targeted molecular therapies: an important step forward from the chemotherapy era

In total, 80%-90% of Hodgkin's lymphoma (HL) patients are curable with combination chemoradiotherapy. Due to improvements in therapeutic strategies, 50% of all relapsed/refractory patients may undergo complete clinical responses and have long-term survival. Treatment options for HL are effective, but may have a negative impact on post-chemotherapy fertility. Thus, cryopreservation of semen prior to treatment is recommended for male patients. For female patients, assisted reproductive techniques (ART) consult and fertility preservation should be offered as a therapeutical option. In the last years, new targeted molecules have been available for HL treatment. These new drugs showed a high rate of overall responses in the setting of heavily pretreated patients, most of them in relapse after autologous stem cell transplantation, a group previously considered very poor risk. Up to 50% of patients have a complete response and an improved overall survival. Future studies will address the usefulness of novel molecules as a frontline therapy. Considering the high response and survival rates with monoclonal antibody-based therapeutics, fertility has become a concerning issue for long-term HL survivors. As progress has been made regarding ART, with the rigorous steps planned for HL patients, more survivors will become parents.

Effect of cholesterol loaded cyclodextrin on semen cryopreservation of Aksaray Malakli shepherd dogs of different ages

The objective of the study was to determine the effect of cholesterol-loaded cyclodextrin (CLC) on the quality parameters of semen from Aksaray Malakli Shepherd dogs of different age groups. Forty-eight male dogs were divided into 3 groupings according to their ages (young age (Y): ≤3 years, n: 20; middle age (M): 4-6 years, n: 20; old age (O): ≥7 years; n: 8). The sperm-rich portion of the ejaculate from each dog was divided into four aliquots and extended with either tris as a control (C) or tris loaded with 0.5, 1.0, and 1.5 mg/120 × 10⁶ CLC as low (L), intermediate (I), and high (H) doses, respectively. Following equilibration for at least half an hour, the straws were frozen in nitrogen vapor and then stored in liquid nitrogen at least for 48 h. Later, the frozen straws were thawed in a water bath for spermatological evaluation. Significant differences were observed between different age groups in terms of the spermatological parameters (p < 0.05). The evidence suggests that increasing age is associated with poor in-vitro spermatological parameters and CLC was able to protect the acrosome integrity from cryo-damage during the freeze-thawing process. Better semen freezability characteristics were obtained at young ages, considering the overall parameters.

Does lipid peroxidation and oxidative DNA damage differ in cryopreserved semen samples from young, adult and aged Nellore bulls?

The aims of this study were to evaluate cryopreserved semen of Nellore bulls of different ages and verify whether sperm quality declines with advancing age and whether lipid peroxidation and DNA damage are involved in this process. For this purpose, 40 Nellore bulls were divided into three age groups: Young, aged 1.8-2 years (n = 9); Adult, aged 3.5-7.0 years (n = 19); and Seniors, aged 8.0-14.3 years (n = 12). Three ejaculates were collected from each bull, cryopreserved and evaluated for various parameters including membrane integrity, mitochondrial potential (FITC-PSA and JC1), lipid peroxidation (C-11BODIPY 581 / 591) and oxidative DNA damage (8OHdG) using flow cytometry. The thawed semen of senior bulls was characterized by a low percentage of motile sperm (33.7 ± 6.1%), higher damage to the plasma and acrosomal membrane (37.5 ± 9.8%), and low mitochondrial potential (29.1 ± 13.8%), as well as higher percentages of peroxidated cells (53.6 ± 12.2%) and DNA damage (44.1 ± 11.0%; P < 0.05). Lipid peroxidation was negatively correlated with motility (r = -0.35, P < 0.0002), average mitochondrial potential (r = -0.42; P < 0.0001) and showed a positive correlation with membrane injury and oxidative DNA damage (r = 039; P = 0.0003). Young bulls presented superior thawed sperm quality, possibly due to greater resistance to oxidative stress and, consequently, to cryopreservation. In conclusion, the sperm quality of bull semen declines with advancing age and is strongly associated with increased oxidative damage to both the plasma membrane and DNA.

Does sperm quality and DNA integrity differ in cryopreserved semen samples from young, adult, and aged Nellore bulls?

Background

In humans, it is now well documented that rising paternal age is correlated with decreased sperm DNA integrity and embryonic developmental failures. On the other side of the coin, it is also reported that very young fathers such as teenagers carry an increased risk of adverse birth outcomes. These observations suggest that, at least in humans, there is an age window for optimal sperm DNA integrity. In bovine, little is known about sperm DNA quality in young bulls and how it evolves with age. This study aimed to fill in this gap as it may be of importance for the bovine industry to know when exactly a bull is an optimal performer for reproductive programs.

Methods

Forty Nellore bulls were divided into three age groups: 1.8 to 2 years – young bulls; 3.5 to 7 years – adult bulls; and 8 to 14.3 years – aged bulls. Three ejaculates were collected from each bull, cryopreserved and evaluated for various parameters including: computer-assisted sperm analysis (CASA), plasma membrane and acrosome integrity, mitochondrial potential, sperm nuclear protamination, DNA oxidative damage, and Sperm Chromatin Structure Assay (SCSA).

Results

We report here that young bulls presented superior values for motility, plasma and acrosomal membrane integrity, and high mitochondrial potential. However, they also presented higher values for sperm morphological abnormalities compared to adult and aged animal groups (p < 0.05). In addition, young bulls exhibited more defective protamination than older animals did. The oldest bulls showed more nuclear oxidative damage than the younger groups of bulls while both the young and aged groups were found more susceptible to DNA denaturation as revealed with the SCSA test (p < 0.05).

Conclusion

These results indicate that young bulls spermatozoa best survived the freezing procedure, followed by adult and aged bulls. However, young and aged bulls were found to be more susceptible to DNA damage, respectively caused by protamine deficiency and oxidation. Therefore, although young bulls have correct semen parameters according to classical evaluation, our results indicate that they may show some structural nuclear immaturity.

Free-radical production after post-thaw incubation of ram spermatozoa is related to decreased in vivo fertility

The aim of the present study was to evaluate the effect of sperm reactive oxygen species (ROS) production and DNA changes on male fertility. For that purpose, six rams with significantly different pregnancy rates were used; these were classified as having high fertility, i.e. 59.4% average pregnancy rate, or low fertility, i.e. 23.1% average pregnancy rate. Sperm quality was assessed after a two-step process of sample thawing followed by an incubation of 2h, either in the freezing extender (37°C) or after dilution in synthetic oviductal fluid (SOF; 38°C, 5%CO2). Sperm viability (YO-PRO-1), ROS production (5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein acetyl ester (CM-H2DCFDA)) and undamaged chromatin (sperm chromatin structure assay, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling, chromomycin A3) were evaluated by flow cytometry. Although no significant differences in sperm viability were observed, our results showed increased ROS production during incubation in the freezing extender as well as in SOF medium. Comparison between fertility groups showed significant differences in ROS production after 2h of incubation for the two treatments. Regarding DNA integrity, our results showed no significant differences either between treatments and incubation times or fertility groups. Linear regression analysis showed that ROS production determined by CM-H2DCFDA was a good indicator parameter for in vivo male fertility of SOF-incubated samples, yielding a fair correlation between both parameters (r=-0.92). These results indicate that detection of ROS production by CM-H2DCFDA and flow cytometry after 2h of incubation in SOF could be a useful procedure for predicting fertility of ram spermatozoa.

Relationship of DNA integrity to HRG C633T SNP and ART outcome in infertile couples

The status of sperm DNA fragmentation, protamine deficiency, free thiols and disulphide bonds in colloid-selected samples and its relationship to ART outcome or HRG C633T SNP is not known. The objective of this study was to determine these relationships in spermatozoa from men with male factor or unknown factor infertility (n = 118) undergoing in vitro fertilisation (IVF) or intracytoplasmic sperm injection (ICSI). Sperm DNA integrity was analysed by flow cytometry using three fluorescent probes (acridine orange, monobromobimane and chromomycin A3). Principal component analysis (PCA) was used to identify the parameters that most influenced fertility. The relationships of sperm DNA integrity with seminal parameters, HRG C633T SNP and ART outcome were established using ANOVA and t-test. Sperm concentration and yield after preparation accounted for 27% of the total variance; sperm DNA integrity (%DFI and disulphide bonds) accounted for 16% of the variance in men from infertile couples. Sperm %DFI was significantly higher (P < 0.05) in older men than in younger men. A significant difference (P < 0.01) was observed in %DFI between smokers and non-smokers. Sperm %DFI was significantly higher (P < 0.01) in male factor infertility compared to either female factor or unknown factor infertility while free thiols were significantly higher (P < 0.01) in unknown infertility factor. No significant difference was observed between IVF success/failure in any of the seminal parameters studied. There was a tendency for protamine deficiency to be higher and disulphide concentration to be lower in men with HRG 633T. Such assessments may provide additional useful information about the prognosis for ART outcome, although more research is needed before clinical guidelines can be provided.

A cost for high levels of sperm competition in rodents: increased sperm DNA fragmentation

Sperm competition, a prevalent evolutionary process in which the spermatozoa of two or more males compete for the fertilization of the same ovum, leads to morphological and physiological adaptations, including increases in energetic metabolism that may serve to propel sperm faster but that may have negative effects on DNA integrity. Sperm DNA damage is associated with reduced rates of fertilization, embryo and fetal loss, offspring mortality, and mutations leading to genetic disease. We tested whether high levels of sperm competition affect sperm DNA integrity. We evaluated sperm DNA integrity in 18 species of rodents that differ in their levels of sperm competition using the sperm chromatin structure assay. DNA integrity was assessed upon sperm collection, in response to incubation under capacitating or non-capacitating conditions, and after exposure to physical and chemical stressors. Sperm DNA was very resistant to physical and chemical stressors, whereas incubation in non-capacitating and capacitating conditions resulted in only a small increase in sperm DNA damage. Importantly, levels of sperm competition were positively associated with sperm DNA fragmentation across rodent species. This is the first evidence showing that high levels of sperm competition lead to an important cost in the form of increased sperm DNA damage.

Sperm morphometry and chromatin condensation in Nelore bulls of different ages and their effects on IVF

The aim of this study was to evaluate the chromatin packing and sperm head morphometry of cryopreserved semen of Nelore bulls (Bos taurus indicus) of different ages. Furthermore, the influence of the degree of chromatin compaction on in vitro embryo production (IVP) was investigated. Forty bulls were divided into three groups: young (1.8-2 years), adult (3.5-7 years), and senile (8-14.3 years). The ejaculates were frozen according to standards established by the Artificial Insemination Center located in the Southeast of Brazil. Toluidine blue staining was used for simultaneous evaluation of the sperm chromatin and sperm head morphometry. Chromomycin A3 (CMA3) was applied to analyze sperm protamination and IVP for embryonic development. Spermatozoa of young bulls presented higher values for area (A, pixels), perimeter (P, pixels), and width (W, pixels) compared to adults and senile (young: A = 1848.5 ± 119.79, P = 10.23 ± 0.29, and W = 1.95 ± 0.1; adults: A = 1672.9 ± 104.46, P = 9.86 ± 0.33, and W = 1.81 ± 0.06; senile: A = 1723.1 ± 124.41, P = 9.97 ± 0.33, and W = 1.83 ± 0.09; P < 0.0001) and showed higher protamination deficiency when analyzed by CMA3 (young: 1.57 ± 0.76; adults: 1.09 ± 0.63, and senile: 0.90 ± 0.59; P < 0.05). Likewise, variables of sperm head size (A, P, and W) and protamination assessed by CMA3 showed negative correlation with age and positive correlation with ellipticity, evaluated by toluidine blue method (P < 0.05). Sperm head area was larger in spermatozoa presenting chromatin instabilities than spermatozoa without chromatin alteration (P < 0.0001). There was no difference in IVP when using semen with larger or smaller portions of spermatozoa with chromatin instabilities, indicating that the proportion of sperm with abnormal chromatin compaction (4%-16.15%) did not interfere with early embryonic development. From our results, it can be concluded that sperm of young Nelore bulls have larger heads compared to adults and senile due to reduced protamine content when evaluated by CMA3 and higher proportion of major sperm defects assessed by differential interference contrast microscopy.

Viable offspring obtained from Prm1-deficient sperm in mice

Protamines are expressed in the spermatid nucleus and allow denser packaging of DNA compared with histones. Disruption of the coding sequence of one allele of either protamine 1 (Prm1) or Prm2 results in failure to produce offspring, although sperm with disrupted Prm1 or Prm2 alleles are produced. Here, we produced Prm1-deficient female chimeric mice carrying Prm1-deficient oocytes. These mice successfully produced Prm1(+/-) male mice. Healthy Prm1(+/-) offspring were then produced by transferring blastocysts obtained via in vitro fertilization using zona-free oocytes and sperm from Prm1(+/-) mice. This result suggests that sperm lacking Prm1 can generate offspring despite being abnormally shaped and having destabilised DNA, decondensed chromatin and a reduction in mitochondrial membrane potential. Nevertheless, these mice showed little derangement of expression profiles.

Advancing age increases sperm chromatin damage and impairs fertility in peroxiredoxin 6 null mice

Due to socioeconomic factors, more couples are choosing to delay conception than ever. Increasing average maternal and paternal age in developed countries over the past 40 years has raised the question of how aging affects reproductive success of males and females. Since oxidative stress in the male reproductive tract increases with age, we investigated the impact of advanced paternal age on the integrity of sperm nucleus and reproductive success of males by using a Prdx6(-/-) mouse model. We compared sperm motility, cytoplasmic droplet retention sperm chromatin quality and reproductive outcomes of young (2-month-old), adult (8-month-old), and old (20-month-old) Prdx6(-/-) males with their age-matched wild type (WT) controls. Absence of PRDX6 caused age-dependent impairment of sperm motility and sperm maturation and increased sperm DNA fragmentation and oxidation as well as decreased sperm DNA compaction and protamination. Litter size, total number of litters and total number of pups per male were significantly lower in Prdx6(-/-) males compared to WT controls. These abnormal reproductive outcomes were severely affected by age in Prdx6(-/-) males. In conclusion, the advanced paternal age affects sperm chromatin integrity and fertility more severely in the absence of PRDX6, suggesting a protective role of PRDX6 in age-associated decline in the sperm quality and fertility in mice.

Male Rat Germ Cells Display Age-Dependent and Cell-Specific Susceptibility in Response to Oxidative Stress Challenges

For decades male germ cells were considered unaffected by aging, due to the fact that males continue to generate sperm into old age; however, evidence indicates that germ cells from aged males are of lower quality than those of young males. The current study examines the effects of aging on pachytene spermatocytes and round spermatids, and is the first study to culture these cells in isolation for an extended period. Our objective is to determine the cell-specific responses germ cells have to aging and oxidative insult. Culturing isolated germ cells from young and aged Brown Norway rats revealed that germ cells from aged males displayed an earlier decline in viability, elevated levels of reactive oxygen species (ROS), and increased spermatocyte DNA damage, compared to young males. Furthermore, oxidative insult by prooxidant 3-morpholinosydnonimine provides insight into how spermatocytes and spermatids manage excess ROS. Genome-wide microarray analyses revealed that several transcripts for antioxidants, Sod1, Cat, and Prdxs, were up-regulated in response to ROS in germ cells from young males while being expressed at lower levels in the aged. In contrast, the expression of DNA damage repair genes Rad50 and Atm were increased in the germ cells from aged animals. Our data indicate that as germ cells undergo spermatogenesis, they adapt and respond to oxidative stress differently, depending on their phase of development, and the process of aging results in redox dysfunction. Thus, even at early stages of spermatogenesis, germ cells from aged males are unable to mount an appropriate response to manage oxidative stress.

The use of complimentary assays to evaluate the enrichment of human sperm quality in asthenoteratozoospermic and teratozoospermic samples processed with Annexin-V magnetic activated cell sorting

Sperm chromatin integrity may affect the outcomes of assisted reproductive technology (ART). Developing a clinically reliable strategy to enrich sperm samples with high chromatin quality spermatozoa prior to sperm banking or use in ART would thus be advantageous. The objectives of this study were to: (i) assess the sperm chromatin quality in men with different categories of semen parameters; and (ii) evaluate the extents of Annexin-V magnetic-activated cell sorting (MACS) technology coupled with differential density gradient centrifugation (DGC) in improving sperm chromatin quality. Three categories of men from couples attending a university-based fertility clinic were recruited based on their semen parameters: normozoospermic (n = 13), asthenoteratozoospermic (n = 17) and teratozoospermic (n = 12). For each patient, spermatozoa in semen samples were processed first by DGC to enrich the motility and further by MACS to remove spermatozoa showing apoptotic features. The yield and enrichment of sperm quality was evaluated at each step with conventional semen parameters in conjunction with a combination of five complementary assays, to assess sperm maturity, chromatin structure, compaction and DNA integrity (Hyaluronic Binding Assay, SCSA, chromomycine A3 staining and TUNEL and COMET assays). Our results demonstrated that, compared with normozoospermic samples, raw asthenoteratozoospermic and teratozoospermic samples had a higher proportion of spermatozoa containing DNA breaks, but only asthenoteratozoospermic exhibited altered chromatin structure and decreased binding to hyaluronic acid. Interestingly, the DGC appeared to select for more mature spermatozoa with high DNA compaction. More importantly, in all categories of semen samples, Annexin-V MACS allows enrichment of spermatozoa with good chromatin quality as measured by the TUNEL and SCSA. Because effective treatment modalities to improve sperm DNA damage are limited, our results suggest a potential clinical value of MACS as a mean to enhance sperm quality that may improve assisted reproductive outcomes.

The three-dimensional image analysis of the chromocenter in motile and immotile human sperm

Chromosomes in human spermatozoa are arranged non-randomly with the centromeres of non-homologous chromosomes forming a chromocenter. We have compared motile and immotile sperm populations in normozoospermic patients to determine if there is any dissimilarity in the formation of the chromocenter and the nuclear position of chromosome 17. Based on the differences between motile and immotile populations, we propose for the 'optimal' nuclear organization to be defined as containing 1 to 3 chromocenter(s) with central radial and median longitudinal position for the centromere of chromosome 17. By this definition, 42% of motile spermatozoa had 'optima' nuclei, in comparison to 25% of immotile spermatozoa (P < 0.05). Immotile spermatozoa exhibited a greater disruption in the formation of the chromocenter, altered position of the centromere of chromosome 17, and were more prone to chemical decondensation, resulting in higher nuclear and chromocenter volumes. The altered topology of the chromosomes might lead to the disruption of the sequence of events involved in fertilization and early embryonic development.

Exposure to bleomycin, etoposide, and cis-platinum alters rat sperm chromatin integrity and sperm head protein profile

Testicular cancer, currently the most common cancer affecting men of reproductive age, is one of the most curable malignancies due to the progress made in the early diagnosis and effective treatment of this disease. The coadministration of bleomycin, etoposide, and cis-platinum (BEP) has brought the 5-yr survival rate of testis cancer patients to over 90%. However, this treatment results in reproductive chemotoxic effects. We assessed the effect of BEP treatment on sperm chromatin integrity and sperm head protein profiles of adult male Brown Norway rats following 9 wk of treatment with BEP and in animals treated for 9 wk and then subjected to a 9-wk recovery period. Both the susceptibility of DNA to denaturation and the number of strand breaks were significantly increased in mature sperm following 9 wk of treatment with BEP; proteomic analysis revealed that the expression of several proteins, including HSP90AA1 and HSP90B1, was markedly affected. Following a 9-wk recovery period, mature sperm did not show significant DNA damage, indicating that repair had potentially occurred. Interestingly, the protamination level of the sperm of these animals was significantly decreased, while histones HIST1H1D (H1.2), HIST1H4B (H4), HIST2H2AA3 (H2A1), and HIST1H2BA (H2B1A) were concomitantly up-regulated; this was not observed in the sperm immediately following 9 wk of treatment. Thus, there are persistent effects on proteins in sperm heads from the cauda epididymidis 9 wk posttreatment, in the absence of DNA strand breaks. We suggest that these effects on the sperm head proteome may contribute to long-lasting adverse effects in the progeny of BEP-exposed males.

Age-related instability in spermatogenic cell nuclear and mitochondrial DNA obtained from Apex1 heterozygous mice

The prevalence of spontaneous mutations increases with age in the male germline; consequently, older men have an increased risk of siring children with genetic disease due to de novo mutations. The lacI transgenic mouse can be used to study paternal age effects, and in this system, the prevalence of de novo mutations increases in the male germline at old ages. Mutagenesis is linked with DNA repair capacity, and base excision repair (BER), which can ameliorate spontaneous DNA damage, decreases in nuclear extracts of spermatogenic cells from old mice. Mice heterozygous for a null allele of the Apex1 gene, which encodes apurinic/apyrimidinic endonuclease I (APEN), an essential BER enzyme, display an accelerated increase in spontaneous germline mutagenesis early in life. Here, the consequences of lifelong reduction of APEN on genetic instability in the male germline were examined, for the first time, at middle and old ages. Mutant frequency increased earlier in spermatogenic cells from Apex1(+/-) mice (by 6 months of age). Nuclear DNA damage increased with age in the spermatogenic lineage for both wild-type and Apex1(+/-) mice. By old age, mutant frequencies were similar for wild-type and APEN-deficient mice. Mitochondrial genome repair also depends on APEN, and novel analysis of mitochondrial DNA (mtDNA) damage revealed an increase in the Apex1(+/-) spermatogenic cells by middle age. Thus, Apex1 heterozygosity results in accelerated damage to mtDNA and spontaneous mutagenesis, consistent with an essential role for APEN in maintaining nuclear and mtDNA integrity in spermatogenic cells throughout life.

Comparative profiling of genes and miRNAs expressed in the newborn, young adult, and aged human epididymides

To understand roles of transcriptional factors and miRNAs in regulating gene expression in the epididymis from postnatal development through aging, systematic profiling of genes and miRNAs expressed in the newborn, young adult, and aged human epididymides was performed by cDNA array and miRNA array analysis, respectively. The newborn human epididymis expressed the fewest mRNAs but the largest number of miRNAs, whereas the adult and aged epididymides expressed the most mRNAs but the fewest miRNAs, a negative correlation between mRNAs and miRNA during aging. By integrative analysis, a set of miRNA targets were predicted based on the miRNA and cDNA arrays. In the newborn epididymis, 127 miRNAs were exclusively or preferentially expressed but only 3 and 2 miRNAs showed an age-enriched expression pattern in the adult and aged epididymides, respectively. This study provides a basic database as well as new insights and foundations for further studies on the complex regulation of gene expression in the epididymis.

Memoirs of an insult: sperm as a possible source of transgenerational epimutations and genetic instability

Male transgenerational epigenetic effects have been discovered in the discipline of mouse radiation genetics, using genetic and non-genetic readouts. The mechanism to explain the origin of the transmission of epigenetic and genetic instability is still unknown. In a search for a hypothesis that could satisfy the data, we propose that regulation of chromosome structure in the germline, by the occupancy of matrix/scaffold associated regions, contains molecular memory function. The male germline is strikingly dynamic as to chromatin organization. This could explain why experience of irradiation stress leaves a persistent mark in the male germline only. To be installed, such memory requires both S-phase and chromatin reorganization during spermatogenesis and in the zygote, that likely also involves reorganization of loop domains. By this reorganization, another layer of information is added, needed to accommodate early embryonic development. Observations point at the involvement of DNA repair as inducer of transgenerational epigenetic modulation. Nuclear structure, chromatin composition and loop domain organization are aspects of human sperm variability that in many cases of assisted reproduction is increased due to inclusion of more incompletely differentiated/maturated sperm nuclei. Adjustment of loop domains in early embryo development can be anticipated and zygotic and cleavage stage S-phase repair activity will have to deal with potential paternal DNA lesions. Therefore, by changing male nucleus structure due to reproduction from impaired spermatogenesis, the transgenerational information content could be changed as well. We discuss aspects of male reproductive performance in the context of this hypothesis.

Characterization of sperm chromatin quality in testicular cancer and Hodgkin's lymphoma patients prior to chemotherapy

BACKGROUND

Although the incidences of testicular cancer and Hodgkin's lymphoma have increased in young men over the past decade, combination chemotherapy has improved survival. As fertility is of importance to these patients, characterization of sperm chromatin structure is needed. We assessed sperm chromatin in testicular cancer and Hodgkin's lymphoma patients prior to chemotherapy, in comparison with control community and idiopathic infertile volunteers.

METHODS

DNA damage was assessed with the sperm chromatin structure assay (SCSA), terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) and comet assays; reactive thiols (SH) and DNA compaction were determined with the monobromobimane (mBBr) and chromomycin A3 (CMA3) assays, respectively.

RESULTS

Both testicular cancer (37%) and Hodgkin's lymphoma (81%) patients had normospermic samples with increased DNA damage, compared with controls. Cancer patients also had higher reactive thiols and CMA3 staining, indicating low DNA compaction.

CONCLUSIONS

Sperm DNA integrity and compaction were affected in testicular cancer and Hodgkin's lymphoma patients prior to chemotherapy. Although SCSA, TUNEL and comet assays all detected DNA damage, the latter was optimal for use in cancer patients. A combination of the comet assay with tests that evaluate sperm DNA compaction, such as flow cytometry-based CMA3 and mBBr assays, is a reliable strategy to characterize sperm chromatin quality in cancer patients at the time of sperm banking.

Oxidative stress and male infertility--a clinical perspective

Oxidative stress occurs when the production of potentially destructive reactive oxygen species (ROS) exceeds the bodies own natural antioxidant defenses, resulting in cellular damage. Oxidative stress is a common pathology seen in approximately half of all infertile men. ROS, defined as including oxygen ions, free radicals and peroxides are generated by sperm and seminal leukocytes within semen and produce infertility by two key mechanisms. First, they damage the sperm membrane, decreasing sperm motility and its ability to fuse with the oocyte. Second, ROS can alter the sperm DNA, resulting in the passage of defective paternal DNA on to the conceptus. This review will provide an overview of oxidative biochemistry related to sperm health and will identify which men are most at risk of oxidative infertility. Finally, the review will outline methods available for diagnosing oxidative stress and the various treatments available.

The effects of age on DNA fragmentation, chromatin packaging and conventional semen parameters in spermatozoa of oligoasthenoteratozoospermic patients

PURPOSE

To investigate the effects of male ageing on DNA fragmentation and chromatin packaging in the spermatozoa of oligoasthenoteratozoospermic (OAT) patients.

METHODS

Sixty-one OAT patients and 49 men with proven fertility (controls) were included in the present study. DNA fragmentation was detected by terminal deoxynucleotidyl transferase-mediated dUTP-nick end labelling (TUNEL) assay, while chromatin packaging was assessed by chromomycin A3 (CMA3) staining.

RESULTS

In the patient group, semen volume, percentage of normally shaped spermatozoa and sperm motility decreased significantly (P<0.05) with age, while sperm concentration and the percentage of TUNEL and CMA3 positive spermatozoa showed a statistically significant increase with age (P<0.05). In the control group, conventional semen parameters as well as DNA fragmentation and chromatin packaging did not show a statistically significant change with age (P>0.05).

CONCLUSION

Increased age in OAT patients is associated with an increase in sperm concentration, DNA fragmentation and poor chromatin packaging, as well as a decline in semen volume, sperm morphology and motility.

Spermatozoal sensitive biomarkers to defective protaminosis and fragmented DNA

Human sperm DNA damage may have adverse effects on reproductive outcome. Infertile men possess substantially more spermatozoa with damaged DNA compared to fertile donors. Although the extent of this abnormality is closely related to sperm function, the underlying etiology of ensuing male infertility is still largely controversial. Both intra-testicular and post-testicular events have been postulated and different mechanisms have been proposed to explain the presence of damaged DNA in human spermatozoa. Three among them, i.e. abnormal chromatin packaging, oxidative stress and apoptosis, are the most studied and discussed in the present review. Furthermore, results from numerous investigations are presented, including our own findings on these pathological conditions, as well as the techniques applied for their evaluation. The crucial points of each methodology on the successful detection of DNA damage and their validity on the appraisal of infertile patients are also discussed. Along with the conventional parameters examined in the standard semen analysis, evaluation of damaged sperm DNA seems to complement the investigation of factors affecting male fertility and may prove an efficient diagnostic tool in the prediction of pregnancy outcome.

Relationship between age and semen parameters in men with normal sperm concentration: analysis of 6022 semen samples

This study evaluates retrospectively the relationship between age and semen parameters among men with normal sperm concentration. It was based on computerized data and performed in an Academic Fertility and IVF Unit. Six thousand and twenty-two semen samples with sperm concentrations of >or=20 x 10(6) ml(-1) were examined according to WHO criteria and analysed in relation to patients' age. For each age group, mean values +/- SD of semen volume, sperm concentration, percentage of motile spermatozoa, normal morphology, acrosome index, total sperm count/ejaculate, total motile sperm count/ejaculate and sexual abstinence duration were examined. A peak semen volume of 3.51 +/- 1.76 ml(-1) was observed at age >or=30 to <35 years and a lowest volume of 2.21 +/- 1.23 ml(-1) was observed at age >or=55 years (P<0.05). Sperm motility was found to be inversely related to age with peak motility of 44.39 +/- 20.69% at age <25 years and lowest motility of 24.76 +/- 18.27% at age >or=55 years (P<0.05). A reduction of 54% was observed for total motile sperm, between values of 103.34 +/- 107 x 10(6) at age >or=30 to <35 years and 46.68 +/- 53.73 x 10(6) (P<0.05) at age >55 years. A statistically significant and inverse relationship was observed between semen volume, sperm quality and patient age, in spite of prolonged sexual abstinence duration. Top sperm parameters were observed at age >or=30 to <35 years, while the most significant reduction in sperm parameters occurred after the age of 55 years.

Impact of cryopreservation and reactive oxygen species on DNA integrity, lipid peroxidation, and functional parameters in ram sperm

Assisted reproduction using frozen-thawed semen has practical advantages, although cryopreservation is detrimental to sperm fertility in most mammals. We examined the influence of cryopreservation and reactive oxygen species (ROS) on ram sperm DNA stability (using SCSA), lipid peroxidation (LPO), chlortetracycline fluorescence (CTC) patterns, motility and viability. In Experiment 1, DNA integrity, LPO, CTC, motility and viability tests were performed on fresh and cryopreserved sperm after 0, 6, and 24 hr in synthetic oviductal fluid (SOF). In Experiment 2, fresh sperm were incubated in serum-free SOF (SOF-S; 1, 4, and 24 hr) with 0, 50, 150, or 300 microM H2O2 then assayed. Cryopreservation increased the percentage of sperm with a high DNA fragmentation index (%DFI), decreased the percentages of motile and viable sperm at thawing (0 hr), but did not affect LPO. H2O2 (150 or 300 microM) increased %DFI after 24 hr. LPO or sperm viability were not affected by H2O2, although most motility parameters decreased. H2O2 decreased the percentage of chlortetracycline pattern F sperm at 4 hr and increased the percentage of acrosome-reacted sperm (pattern AR) after 1 hr. Pooled data of Experiment 2 showed LPO was positively correlated with SCSA (r = 0.29 to r = 0.59; P < 0.05 to P < 0.01), while most motility parameters and the percentage of viable sperm were negatively correlated with LPO (r = -0.30 to r = -0.38; P < 0.05 to P < 0.01). LPO was positively correlated with the percentage of pattern AR sperm (r = 0.33; P < 0.01). Cryopreservation and H2O2 promote DNA instability in ram sperm, though motility is a more sensitive indicator of oxidative stress than the other parameters investigated.

Effects of ageing on spermatozoal chromatin and its sensitivity to in vivo and in vitro oxidative challenge in the Brown Norway rat

BACKGROUND

The goals of our study were to examine chromatin packaging and integrity in spermatozoa taken from the caput and cauda epididymides of young (4-month-old) and old (21-month-old) Brown Norway rats and to assess whether spermatozoal sensitivity to oxidative treatments is altered with age.

METHODS

Oxidative treatments consisted of (i) in vivo oxidative challenge by systemic administration of the glutathione-depleting drug l-buthionine-[S,R]-sulphoximine (BSO) and (ii) in vitro oxidative challenge by incubating collected spermatozoa with hydrogen peroxide (H(2)O(2)). Chromatin parameters assessed included quantification of thiols, nuclear chromomycin A3 (CMA3) penetration, DNA breaks by TdT (terminal deoxynucleotidyl transferase)-mediated dUDP nick-end labelling (TUNEL) and ease of DNA dissociation by acridine orange (AO) staining.

RESULTS

In spermatozoa from older rats, we found decreases in thiols, CMA3 penetration and the percentage of cells that undergo DNA dissociation. Administration of BSO had oxidizing effects on the thiol groups. It also decreased CMA3 penetration and DNA dissociation and increased TUNEL staining. Furthermore, BSO treatment sensitized cauda epididymidis spermatozoa, from older animals, to H(2)O(2).

CONCLUSIONS

Overall, we show that spermatozoa from older rats have altered chromatin packaging and integrity and that spermatozoa from the cauda epididymidis are more responsive to combined in vivo and in vitro oxidative challenge than spermatozoa from young rats.

Sperm DNA fragmentation

Several techniques have been developed to measure the amount of sperm DNA damage in an effort to identify more objective parameters for evaluation of infertile men. The integrity of sperm DNA influences a couple's fertility and helps predict the chances of pregnancy and its successful outcome. The available tests of sperm DNA damage require additional large-scale clinical trails before their integration into routine clinical practice. The physiological/molecular integrity of sperm DNA is a novel parameter of semen quality and a potential fertility predictor. Although DNA integrity assessment appears to be a logical biomarker of sperm quality, it is not being assessed as a routine part of semen analysis by clinical andrologists. Extensive investigation has been conducted for the comparative evolution of these techniques. However, some of these techniques require expensive instrumentation for optimal and unbiased analysis, are labor intensive, or require the use of enzymes whose activity and accessibility to DNA breaks may be irregular. Thus, these techniques are recommended for basic research rather than for routine andrology laboratories. Sperm chromatin structure evaluation is applied to detect male factors that may affect the chance of success with IVF as well as natural fertility. Further research is needed to define the optimal test of sperm chromatin structure. The clinical application of this test will evolve as well.

Protamines and male infertility

Protamines are the major nuclear sperm proteins. The human sperm nucleus contains two types of protamine: protamine 1 (P1) encoded by a single-copy gene and the family of protamine 2 (P2) proteins (P2, P3 and P4), all also encoded by a single gene that is transcribed and translated into a precursor protein. The protamines were discovered more than a century ago, but their function is not yet fully understood. In fact, different hypotheses have been proposed: condensation of the sperm nucleus into a compact hydrodynamic shape, protection of the genetic message delivered by the spermatozoa, involvement in the processes maintaining the integrity and repair of DNA during or after the nucleohistone-nucleoprotamine transition and involvement in the epigenetic imprinting of the spermatozoa. Protamines are also one of the most variable proteins found in nature, with data supporting a positive Darwinian selection. Changes in the expression of P1 and P2 protamines have been found to be associated with infertility in man. Mutations in the protamine genes have also been found in some infertile patients. Transgenic mice defective in the expression of protamines also present several structural defects in the sperm nucleus and have variable degrees of infertility. There is also evidence that altered levels of protamines may result in an increased susceptibility to injury in the spermatozoan DNA causing infertility or poor outcomes in assisted reproduction. The present work reviews the articles published to date on the relationship between protamines and infertility.